text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
One of the theories on the specific formation mechanism for bainite is that it occurs by a shear transformation, as in martensite. The crystal structure change is achieved by a deformation rather than by diffusion. The shape change associated with bainite is an invariant—plane strain with a large shear component. This kind of deformation implies a disciplined motion of atoms (rather than a chaotic transfer associated with diffusion), and is typical of all displacive transformations in steels, for example, martensite, bainite and Widmanstaetten ferrite. There is a strain energy associated with such relief, that leads to the plate shape of the transformation product Any diffusion is subsequent to the diffusionless transformation of austenite, for example the partitioning of carbon from supersaturated bainitic ferrite, or the precipitation of carbides; this is analogous to the tempering of martensite.
There are many features of bainite that are correctly predicted by this theory, including:
* the plate shape, which is a consequence of the minimisation of strain energy due to the shape deformation accompanying transformation.
* The fact that excess carbon is retained inside the even defect-free regions of bainitic ferrite.
* The fact that the unit cell of bainitic ferrite can be tetragonal rather than cubic.
* The fact that the bainite transformation can be dramatically retarded when the austenite is first plastically deformed, a phenomenon known as mechanical stabilisation, which is unique to displacive transformations.
* The obvious fact that displacements occur when bainite grows. The transformation is a combination of deformation and crystal structure change, just like martensite. | 8 | Metallurgy |
In molecular biology, gel extraction or gel isolation is a technique used to isolate a desired fragment of intact DNA from an agarose gel following agarose gel electrophoresis. After extraction, fragments of interest can be mixed, precipitated, and enzymatically ligated together in several simple steps. This process, usually performed on plasmids, is the basis for rudimentary genetic engineering.
After DNA samples are run on an agarose gel, extraction involves four basic steps: identifying the fragments of interest, isolating the corresponding bands, isolating the DNA from those bands, and removing the accompanying salts and stain.
To begin, UV light is shone on the gel in order to illuminate all the ethidium bromide-stained DNA. Care must be taken to avoid exposing the DNA to mutagenic radiation for longer than absolutely necessary. The desired band is identified and physically removed with a cover slip or razor blade. The removed slice of gel should contain the desired DNA inside. An alternative method, utilizing SYBR Safe DNA gel stain and blue-light illumination, avoids the DNA damage associated with ethidium bromide and UV light.
Several strategies for isolating and cleaning the DNA fragment of interest exist. | 1 | Biochemistry |
The stereochemical term diastereotopic refers to the relationship between two groups in a molecule which, if replaced, would generate compounds that are diastereomers. Diastereotopic groups are often, but not always, identical groups attached to the same atom in a molecule containing at least one chiral center.
For example, the two hydrogen atoms of the CH moiety in (S)-2-bromobutane are diastereotopic. Replacement of one hydrogen atom (colored blue) with a bromine atom will produce (2S,3R)-2,3-dibromobutane. Replacement of the other hydrogen atom (colored red) with a bromine atom will produce the diastereomer (2S,3S)-2,3-dibromobutane.
In chiral molecules containing diastereotopic groups, such as in 2-bromobutane, there is no requirement for enantiomeric or optical purity; no matter its proportion, each enantiomer will generate enantiomeric sets of diastereomers upon substitution of diastereotopic groups (though, as in the case of substitution by bromine in 2-bromobutane, meso isomers have, strictly speaking, no enantiomer).
Diastereotopic groups are not mirror images of one another about any plane. They are always different, in any environment, but may not be distinguishable. For instance, both pairs of CH hydrogens in ethyl phenylalaninate hydrochloride (PhCHCH(NH)COOCHCH Cl) are diastereotopic and both give pairs of distinct H-NMR signals in DMSO-d at 300 MHz, but in the similar ethyl 2-nitrobutanoate (CHCHCH(NO)COOCHCH), only the CH group next to the chiral center gives distinct signals from its two hydrogens with the same instrument in CDCl. Such signals are often complex because of small differences in chemical shift, overlap and an additional strong coupling between geminal hydrogens. On the other hand, the two CH groups of ipsenol, which are three bonds away from the chiral center, give separate H doublets at 300 MHz and separate C-NMR signals in CDCl, but the diastereotopic hydrogens in ethyl alaninate hydrochloride (CHCH(NH)COOCHCH Cl), also three bonds away from the chiral center, show barely distinguishable H-NMR signals in DMSO-d.
Diastereotopic groups also arise in achiral molecules. For instance, any one pair of CH hydrogens in 3-pentanol (Figure 1) are diastereotopic, as the two CH carbons are enantiotopic. Substitution of any one of the four CH hydrogens creates two chiral centers at once, and the two possible hydrogen substitution products at any one CH carbon will be diastereomers. This kind of relationship is often easier to detect in cyclic molecules. For instance, any pair of CH hydrogens in cyclopentanol (Figure 2) are similarly diastereotopic, and this is easily discerned as one of the hydrogens in the pair will be cis to the OH group (on the same side of the ring face) while the other will be trans to it (on the opposite side).
The term diastereotopic is also applied to identical groups attached to the same end of an alkene moiety which, if replaced, would generate geometric isomers (also falling in the category of diastereomers). Thus, the CH hydrogens of propene are diastereotopic, one being cis to the CH group, and the other being trans to it, and replacement of one or the other with CH would generate cis- or trans--2-butene.
Diastereotopicity is not limited to organic molecules, nor to groups attached to carbon, nor to molecules with chiral tetrahedral (sp-hybridized) centers: for instance, the pair of hydrogens in any CH or NH group in tris(ethylenediamine)chromium(III) ion (Cr(en)), where the metal center is chiral, are diastereotopic (Figure 2).
The terms enantiotopic and diastereotopic can also be applied to the faces of planar groups (especially carbonyl groups and alkene moieties). See Cahn-Ingold-Prelog priority rule. | 4 | Stereochemistry |
Two-dimensional diffraction images of a fine synchrotron beam interacting with the specimen are recorded in time frames, such that reflections stemming from individual crystallites of the polycrystalline material can be distinguished. Data treatment is undertaken in a way that diffraction rings are straightened and presented line by line streaked in time. The traces, so-called timelines in azimuthal-angle/time plots resemble to traces of an oscilloscope, giving insight on the processes happening in the material, while undergoing plastic deformation, or heating, or both, These timelines allow to distinguish grain growth or refinement, subgrain formation, slip deformation systems, crystallographic twinning, dynamic recovery, dynamic recrystallization, simultaneously in multiple phases. | 7 | Physical Chemistry |
Total ionic strength adjustment buffer (TISAB) is a buffer solution which increases the ionic strength of a solution to a relatively high level. This is important for potentiometric measurements, including ion selective electrodes, because they measure the activity of the analyte rather than its concentration. TISAB essentially masks minor changes made in the ionic strength of the solution and hence increases the accuracy of the reading. | 3 | Analytical Chemistry |
Source:
*1997 Ahmed Zewail
*1998 Robin M. Hochstrasser
*1999 Richard N. Zare
*2000 Ad Bax
*2001 William A. Klemperer
*2002 Takeshi Oka
*2003 Marilyn E. Jacox
*2004 James K.G. Watson
*2005 Eizi Hirota
*2006 Donald H. Levy
*2007 Michael D. Fayer
*2008 Jack H. Freed
*2009 Paul F. Barbara
*2010 George W. Flynn
*2011 Veronica Vaida
*2012 Robert W. Field
*2013 Steven G. Boxer
*2014 Richard P. Van Duyne
*2015 R. J. Dwayne Miller
*2016 Robert G. Griffin
*2017 David J. Nesbitt
*2018 Richard J. Saykally
*2019 Martin Moskovits
*2020 Angela M. Gronenborn | 7 | Physical Chemistry |
The commercial manufacture of wood pulp grade chemical cellulose using the kraft chemical pulping processes releases resin acids. The Kraft process is conducted under strongly basic conditions of sodium hydroxide, sodium sulfide and sodium hydrosulfide, which neutralizes these resin acids, converting them to their respective sodium salts, sodium abietate, ((CH)CHCOONa) sodium pimarate ((CH)(CH)CHCOONa) and so on. In this form, the sodium salts are insoluble and, being of lower density than the spent pulping process liquor, float to the surface of storage vessels during the process of concentration, as a somewhat gelatinous pasty fluid called kraft soap, or resin soap.
Kraft soap can be reneutralized with sulfuric acid to restore the acidic forms abietic acid, palmitic acid, and related resin acid components. This refined mixture is called tall oil. Other major components include fatty acids and unsaponifiable sterols.
Resin acids, because of the same protectant nature they provide in the trees where they originate, also impose toxic implications on the effluent treatment facilities in pulp manufacturing plants. Furthermore, any residual resin acids that pass the treatment facilities add toxicity to the stream discharged to the receiving waters. | 1 | Biochemistry |
The structure of DNA shows a variety of forms, both double-stranded and single-stranded. The mechanical properties of DNA, which are directly related to its structure, are a significant problem for cells. Every process which binds or reads DNA is able to use or modify the mechanical properties of DNA for purposes of recognition, packaging and modification. The extreme length (a chromosome may contain a 10 cm long DNA strand), relative rigidity and helical structure of DNA has led to the evolution of histones and of enzymes such as topoisomerases and helicases to manage a cell's DNA. The properties of DNA are closely related to its molecular structure and sequence, particularly the weakness of the hydrogen bonds and electronic interactions that hold strands of DNA together compared to the strength of the bonds within each strand.
Experimental methods which can directly measure the mechanical properties of DNA are relatively new, and high-resolution visualization in solution is often difficult. Nevertheless, scientists have uncovered large amount of data on the mechanical properties of this polymer, and the implications of DNA's mechanical properties on cellular processes is a topic of active current research.
The DNA found in many cells can be macroscopic in length: a few centimetres long for each human chromosome. Consequently, cells must compact or package DNA to carry it within them. In eukaryotes this is carried by spool-like proteins named histones, around which DNA winds. It is the further compaction of this DNA-protein complex which produces the well known mitotic eukaryotic chromosomes.
In the late 1970s, alternate non-helical models of DNA structure were briefly considered as a potential solution to problems in DNA replication in plasmids and chromatin. However, the models were set aside in favor of the double-helical model due to subsequent experimental advances such as X-ray crystallography of DNA duplexes, and later the nucleosome core particle, and the discovery of topoisomerases. Such non-double-helical models are not currently accepted by the mainstream scientific community. | 4 | Stereochemistry |
There is significant overlap in function with regards to some of these proteins. In particular, the Rho-related genes are important in nuclear trafficking (i.e.: mitosis) as well as with mobility along the cytoskeleton in general. These genes of particular interest in cancer research.
*ARHGAP35
*ARHGAP5
*ARHGDIA
*ARHGEF10L Rho guanine nucleotide exchange factor 10L
*ARHGEF11 Rho guanine nucleotide exchange factor 11
*ARHGEF40 Rho guanine nucleotide exchange factor 40
*ARHGEF7 Rho guanine nucleotide exchange factor 7
*RAB10 NM_016131 The small GTPases Rab are key regulators of intracellular membrane trafficking, from the formation of transport vesicles to their fusion with membranes
*RAB11A NM_004663
*RAB11B NM_004218
*RAB14 NM_016322
*RAB18 NM_021252
*RAB1A NM_004161 Homo sapiens RAB1A, member RAS oncogene family (RAB1A), mRNA
*RAB1B NM_030981
*RAB21 NM_014999
*RAB22A NM_020673
*RAB2A NM_002858
*RAB2B NM_001163380
*RAB3GAP1 NM_012233
*RAB3GAP2 NM_012414
*RAB40C NM_021168
*RAB4A NM_004578
*RAB5A NM_004162
*RAB5B NM_002865
*RAB5C NM_004583
*RAB6A NM_002868
*RAB7A NM_004637
*RAB9A NM_004251
*RABEP1 NM_004703
*RABEPK NM_005833
*RABGEF1 NM_014504
*RABGGTA NM_004581
*RABGGTB NM_004582
*CENPB Centromere protein B
*CTBP1 Centromere protein T
*CCNB1IP1 NM_021178 E3 ubiquitin-protein ligase. Modulates cyclin B levels and participates in the regulation of cell cycle progression through the G2 phase
*CCNDBP1 NM_012142 May negatively regulate cell cycle progression
*CCNG1 NM_004060 May play a role in growth regulation
*CCNH NM_001239 Involved in cell cycle control and in RNA transcription by RNA polymerase II. Its expression and activity are constant throughout the cell cycle
*CCNK NM_001099402 Regulatory subunit of cyclin-dependent kinases that mediates phosphorylation of the large subunit of RNA polymerase II
*CCNL1 NM_020307 Transcriptional regulator which participates in regulating the pre-mRNA splicing process
*CCNL2 NM_030937 Transcriptional regulator which participates in regulating the pre-mRNA splicing process. Also modulates the expression of critical apoptotic factor, leading to cell apoptosis.
*CCNY NM_145012 Positive regulatory subunit of the cyclin-dependent kinases CDK14/PFTK1 and CDK16. Acts as a cell-cycle regulator of Wnt signaling pathway during G2/M phase
*PPP1CA NM_002708 Protein phosphatase that associates with over 200 regulatory proteins to form highly specific holoenzymes which dephosphorylate hundreds of biological targets
*PPP1CC NM_002710
*PPP1R10 NM_002714
*PPP1R11 NM_021959 Homo sapiens protein phosphatase 1, regulatory (inhibitor) subunit 11 (PPP1R11),
*PPP1R15B NM_032833
*PPP1R37 NM_019121
*PPP1R7 NM_002712
*PPP1R8 NM_002713
*PPP2CA NM_002715
*PPP2CB NM_001009552
*PPP2R1A NM_014225 Negative regulator of growth and cell divisionHomo sapiens protein phosphatase 2 (formerly 2A), regulatory subunit A (PR 65),
*PPP2R2A NM_002717
*PPP2R2D NM_018461
*PPP2R3C NM_017917
*PPP2R4 NM_021131
*PPP2R5A NM_006243
*PPP2R5B NM_006244
*PPP2R5C NM_002719
*PPP2R5D NM_006245
*PPP2R5E NM_006246
*PPP4C NM_002720
*PPP4R1 NM_005134
*PPP4R2 NM_174907
*PPP5C NM_006247
*PPP6C NM_002721
*PPP6R2 NM_014678
*PPP6R3 NM_018312
*RAD1Homo sapiens ribonuclease/angiogenin inhibitor (RNH), mRNA
*RAD17 NM_002869 Essential for sustained cell growth, maintenance of chromosomal stability, and ATR-dependent checkpoint activation upon DNA damage
*RAD23B NM_002873
*RAD50 NM_005732
*RAD51C NM_002874
*IST1 (locates to central dividing line of dividing cells) | 1 | Biochemistry |
Elevated blood ketone levels are most often caused by accelerated ketone production but may also be caused by consumption of exogenous ketones or precursors.
When glycogen and blood glucose reserves are low, a metabolic shift occurs in order to save glucose for the brain which is unable to use fatty acids for energy. This shift involves increasing fatty acid oxidation and production of ketones in the liver as an alternate energy source for the brain as well as the skeletal muscles, heart, and kidney. Low levels of ketones are always present in the blood and increase under circumstances of low glucose availability. For example, after an overnight fast, 2–6% of energy comes from ketones and this increases to 30–40% after a 3-day fast.
The amount of carbohydrate restriction required to induce a state of ketosis is variable and depends on activity level, insulin sensitivity, genetics, age and other factors, but ketosis will usually occur when consuming less than 50 grams of carbohydrates per day for at least three days.
Neonates, pregnant women and lactating women are populations that develop physiological ketosis especially rapidly in response to energetic challenges such as fasting or illness. This can progress to ketoacidosis in the setting of illness, although it occurs rarely. Propensity for ketone production in neonates is caused by their high-fat breast milk diet, disproportionately large central nervous system and limited liver glycogen. | 1 | Biochemistry |
The phosphate/oxygen ratio, or P/O ratio, refers to the amount of ATP produced from the movement of two electrons through a defined electron transport chain, terminated by reduction of an oxygen atom.
The P/O ratio is dependent on the number of hydrogen ions transported outward across an electrochemical gradient, and the number of protons which return inward through the membrane via an enzyme such as ATP synthase. The ATP synthase works by a rotary mechanism. The ATP generated will be dependent on the amount of ATP produced per rotation of the ATP synthase rotor, and the number of protons necessary to complete a rotation. Every full rotation produces 3 ATPs. According to current understanding of the mechanism of the F part, the number of protons translocated per rotation is exactly equal to the number of subunits in the c ring. Recent structural studies show that this is not the same for all organisms. For vertebrate mitochondrial ATP synthase, the number of c subunits is 8
. The synthase thus requires 8 protons to synthesize three ATP, or 8/3 protons/ATP.
Inward moving protons must not only power rotation of ATP synthase, but may also be used in the transport of products and precursors. Given the net charge differences between ATP and ADP, the enzyme ATP–ADP translocase dissipates the charge equivalent of one hydrogen ion from the gradient when moving ATP (outward) and ADP (inward) across the inner mitochondrial membrane. The electroneutral symport of phosphate ion and H+ results in importing one proton, without its charge, per phosphate. Taken together, import of ADP and Pi and export of the resulting ATP results in one proton imported, subtracting from the number available for use by the ATP synthase directly. Taking this into account, it takes 8/3 +1 or 3.67 protons for vertebrate mitochondria to synthesize one ATP in the cytoplasm from ADP and Pi in the cytoplasm.
Within aerobic respiration, the P/O ratio continues to be debated; however, current figures place it at 2.5 ATP per 1/2(O) reduced to water, though some claim the ratio is 3. This figure arises from accepting that 10 H are transported out of the matrix per 2 e, and 4 H are required to move inward to synthesize a molecule of ATP.
The H+/2e ratios of the three major respiratory complexes are generally agreed to be 4, 4, and 2 for Complexes I, III, and IV respectively. The H/O ratio thus depends whether the substrate electrons enter at the level of NADH (passing through all three for 10 H/2e) or ubiquinol (passing through only complexes III and IV for 6H/2e). The latter is the case when the substrate is succinate or extramitochondrial NADH being oxidized via the glycerol phosphate shuttle; or other UQH2-linked dehydrogenase. During normal aerobic respiration the ratio would be somewhere between these values, as the TCA cycle produces both NADH and ubiquinol.
The resulting P/O ratio would be the ratio of H/O and H/P; which is 10/3.67 or 2.73 for NADH-linked respiration, and 6/3.67 or 1.64 for UQH2-linked respiration, with actual values being somewhere between. | 1 | Biochemistry |
There are many biologically active chemicals which elicit an effect on the nervous system. Neurotransmitters and similarly functioning biochemical messengers elicit effects on postsynaptic neurons at neuronal synapses. Excitatory Amino Acids include Glutamate, whereas inhibitory Amino Acids include GABA and Glycine. Additionally, catecholamines, serotonin, acetylcholine, histamine, and orexins have widely-projecting effects and are often referred to as neuromodulators. Neuropeptides include bradykinin, cholecystokinin, corticotropin-releasing factor (CRF), galanin, MCH, MSH, Neuropeptide Y (NPY), Neurotensin, Opioids, orexin, oxytocin, somatostatin, tachykinins, TRH, CUP, and vasopressin. Purines, endogenous cannabinoids, gasses, neurotrophic factors, chemokines, and VEGF are all classified as atypical neurotransmitters. Major receptors of neurotransmitters include AMPA receptors, NMDA receptors, and Kainate Receptors. | 1 | Biochemistry |
The formal naming of haloalkanes should follow IUPAC nomenclature, which put the halogen as a prefix to the alkane. For example, ethane with bromine becomes bromoethane, methane with four chlorine groups becomes tetrachloromethane. However, many of these compounds have already an established trivial name, which is endorsed by the IUPAC nomenclature, for example chloroform (trichloromethane) and methylene chloride (dichloromethane). But nowadays, IUPAC nomenclature is used. To reduce confusion this article follows the systematic naming scheme throughout. | 0 | Organic Chemistry |
OCP was first described in 1981 by Holt and Krogmann who isolated it from the unicellular cyanobacterium Arthrospira maxima, although its function would remain obscure until 2006. The crystal structure of the OCP was reported in 2003. At the same time the protein was shown to be an effective quencher of singlet oxygen and was suggested to be involved in photoprotection, or carotenoid transport. In 2000, it was demonstrated that cyanobacteria could perform photoprotective fluorescence quenching independent of lipid phase transitions, differential transmembrane pH, and inhibitors. The action spectrum for this quenching process suggested the involvement of carotenoids, and the specific involvement of the OCP was later demonstrated by Kirilovsky and coworkers in 2006. In 2008, OCP was shown to require photoactivation by strong blue-green light for its photoprotective quenching function. Photoactivation is accompanied by a pronounced color change, from orange to red, which had been previously observed by Kerfeld et al in the initial structural studies. In 2015 a combination of biophysical methods by researchers in Berkeley showed that the visible color change is the consequence of a 12Å translocation of the [https://today.lbl.gov/2015/07/01/protein-shifts-more-than-just-color-for-cyanobacterial-photoprotection/ carotenoid]. | 5 | Photochemistry |
In evolutionary developmental biology, homeosis is the transformation of one organ into another, arising from mutation in or misexpression of certain developmentally critical genes, specifically homeotic genes. In animals, these developmental genes specifically control the development of organs on their anteroposterior axis. In plants, however, the developmental genes affected by homeosis may control anything from the development of a stamen or petals to the development of chlorophyll. Homeosis may be caused by mutations in Hox genes, found in animals, or others such as the MADS-box family in plants. Homeosis is a characteristic that has helped insects become as successful and diverse as they are.
Homeotic mutations work by changing segment identity during development. For example, the Ultrabithorax genotype gives a phenotype wherein metathoracic and first abdominal segments become mesothoracic segments. Another well-known example is Antennapedia: a gain-of-function allele causes legs to develop in the place of antennae.
In botany, Rolf Sattler has revised the concept of homeosis (replacement) by his emphasis on partial homeosis in addition to complete homeosis; this revision is now widely accepted.
Homeotic mutants in angiosperms are thought to be rare in the wild: in the annual plant Clarkia (Onagraceae), homeotic mutants are known where the petals are replaced by a second whorl of sepal-like organs, originating in a mutation of a single gene. The absence of lethal or deleterious consequences in floral mutants resulting in distinct morphological expressions has been a factor in the evolution of Clarkia, and perhaps also in many other plant groups. | 1 | Biochemistry |
Iron-sulfur proteins are involved in various biological electron transport processes, such as photosynthesis and cellular respiration, which require rapid electron transfer to sustain the energy or biochemical needs of the organism. To serve their various biological roles, iron-sulfur proteins effect rapid electron transfers and span the whole range of physiological redox potentials from -600 mV to +460 mV.
Fe-SR bonds have unusually high covalency which is expected. When comparing the covalency of Fe with the covalency of Fe, Fe has almost double the covalency of Fe (20% to 38.4%). Fe is also much more stabilized than Fe. Hard ions like Fe normally have low covalency because of the energy mismatch of the metal lowest unoccupied molecular orbital with the ligand highest occupied molecular orbital.
External water molecules positioned close to the iron-sulfur active site reduces covalency; this can be shown by lyophilization experiments where water is removed from the protein. This reduction is because external water hydrogen bonds with cysteine S, decreasing the latter's lone pair electron donation to the Fe by pulling away S electrons. Since covalency stabilizes Fe more than Fe, Fe is more destabilized by the HOH-S hydrogen-bonding.
The Fe 3d orbital energies follow the "inverted" bonding scheme which fortuitously has the Fe d-orbitals closely matched in energy with the sulfur 3p orbitals, giving high covalency in the resulting bonding molecular orbital. This high covalency lowers the inner sphere reorganization energy and ultimately contributes to a rapid electron transfer. | 7 | Physical Chemistry |
Methyl fluoroacetate is a methyl ester of fluoroacetic acid.
MFA is a liquid, which is odorless or can have a faint, fruity smell. The boiling point of MFA is 104.5 °C and the melting point is −35.0 °C. It is soluble in water (117 g/L at 25 °C) and slightly soluble in petroleum ether.
MFA is resistant to the displacement of fluorine by nucleophiles, so there is higher stability of the bond compared to the other halogens (, , ). The other haloacetates are more powerful alkylating agents that react with group of proteins. This, however, does not happen for MFA and gives it a unique toxic action. Moreover, MFA is a derivative of fluoroacetate (FA) compound which is as toxic and has similar biotransformation to MFA. | 1 | Biochemistry |
GenePattern is available:
# As a free public web application, hosted on Amazon Web Services. Users can create accounts, perform analyses, and create pipelines on the server.
# As open-source software that can be downloaded and installed locally.
# Public web servers hosted by other organizations. | 1 | Biochemistry |
Ethane-1,2-dithiol is made commercially by the reaction of 1,2-dichloroethane with aqueous sodium bisulfide. In the laboratory, it can also be prepared by the action of 1,2-dibromoethane on thiourea followed by hydrolysis. | 0 | Organic Chemistry |
The patio process is a process for extracting silver from ore. Smelting, or refining, is most often necessary because silver is only infrequently found as a native element like some metals nobler than the redox couple 2 + 2 ⇌ (gold, mercury, ...). Instead, it is made up of a larger ore body. Thus, smelting, or refining, is necessary to reduce the compound containing the cation into metallic Ag and to remove other byproducts to get at pure silver. The process, which uses mercury amalgamation to recover silver from ore, was first used at scale by Bartolomé de Medina in Pachuca, Mexico, in 1554. It replaced smelting as the primary method of extracting silver from ore at Spanish colonies in the Americas. Although some knowledge of amalgamation techniques were likely known since the classical era, it was in the New World that it was first used on a large industrial scale. Other amalgamation processes were later developed, importantly the pan amalgamation process, and its variant, the Washoe process. The silver separation process generally differed from gold parting and gold extraction, although amalgamation with mercury is also sometimes used to extract gold. While gold was often found in the Americas as a native metal or alloy, silver was often found as a compound such as silver chloride and silver sulfide, and therefore required mercury amalgamation for refinement. | 8 | Metallurgy |
Until recently, there were only two known pathways to process Okazaki fragments. However, current investigations have concluded that a new pathway for Okazaki fragmentation and DNA replication exists. This alternate pathway involves the enzymes Pol δ with Pif1 which perform the same flap removal process as Pol δ and FEN1. | 1 | Biochemistry |
The Sonogashira reaction is typically run under mild conditions. The cross-coupling is carried out at room temperature with a base, typically an amine, such as diethylamine, that also acts as the solvent. The reaction medium must be basic to neutralize the hydrogen halide produced as the byproduct of this coupling reaction, so alkylamine compounds such as triethylamine and diethylamine are sometimes used as solvents, but also DMF or ether can be used as solvent. Other bases such as potassium carbonate or cesium carbonate are occasionally used. In addition, deaerated conditions are formally needed for Sonogashira coupling reactions because the palladium(0) complexes are unstable in the air, and oxygen promotes the formation of homocoupled acetylenes. Recently, development of air-stable organopalladium catalysts enable this reaction to be conducted in the ambient atmosphere. In addition, R.M Al-Zoubi and co-workers successfully developed a method with high regioselectivity for 1,2,3-trihaloarene derivatives in good to high yields under ambient conditions. | 0 | Organic Chemistry |
Because water molecules absorb microwaves and other radio wave frequencies, water in the atmosphere attenuates radar signals. In addition, atmospheric water will reflect and refract signals to an extent that depends on whether it is vapor, liquid or solid.
Generally, radar signals lose strength progressively the farther they travel through the troposphere. Different frequencies attenuate at different rates, such that some components of air are opaque to some frequencies and transparent to others. Radio waves used for broadcasting and other communication experience the same effect.
Water vapor reflects radar to a lesser extent than do water's other two phases. In the form of drops and ice crystals, water acts as a prism, which it does not do as an individual molecule; however, the existence of water vapor in the atmosphere causes the atmosphere to act as a giant prism.
A comparison of GOES-12 satellite images shows the distribution of atmospheric water vapor relative to the oceans, clouds and continents of the Earth. Vapor surrounds the planet but is unevenly distributed. The image loop on the right shows monthly average of water vapor content with the units are given in centimeters, which is the precipitable water or equivalent amount of water that could be produced if all the water vapor in the column were to condense. The lowest amounts of water vapor (0 centimeters) appear in yellow, and the highest amounts (6 centimeters) appear in dark blue. Areas of missing data appear in shades of gray. The maps are based on data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on NASA's Aqua satellite. The most noticeable pattern in the time series is the influence of seasonal temperature changes and incoming sunlight on water vapor. In the tropics, a band of extremely humid air wobbles north and south of the equator as the seasons change. This band of humidity is part of the Intertropical Convergence Zone, where the easterly trade winds from each hemisphere converge and produce near-daily thunderstorms and clouds. Farther from the equator, water vapor concentrations are high in the hemisphere experiencing summer and low in the one experiencing winter. Another pattern that shows up in the time series is that water vapor amounts over land areas decrease more in winter months than adjacent ocean areas do. This is largely because air temperatures over land drop more in the winter than temperatures over the ocean. Water vapor condenses more rapidly in colder air.
As water vapor absorbs light in the visible spectral range, its absorption can be used in spectroscopic applications (such as DOAS) to determine the amount of water vapor in the atmosphere. This is done operationally, e.g. from the Global Ozone Monitoring Experiment (GOME) spectrometers on ERS (GOME) and MetOp (GOME-2). The weaker water vapor absorption lines in the blue spectral range and further into the UV up to its dissociation limit around 243 nm are mostly based on quantum mechanical calculations and are only partly confirmed by experiments. | 2 | Environmental Chemistry |
Adsorbable organic halides (AOX) is a measure of the organic halogen load at a sampling site such as soil from a land fill, water, or sewage waste. The procedure measures chlorine, bromine, and iodine as equivalent halogens, but does not measure fluorine levels in the sample. | 2 | Environmental Chemistry |
Daily intakes of fluoride can vary significantly according to the various sources of exposure. Values ranging from 0.46 to 3.6–5.4 mg/day have been reported in several studies (IPCS, 1984). In areas where water is fluoridated this can be expected to be a significant source of fluoride, however fluoride is also naturally present in virtually all foods and beverages at a wide range of concentrations. The maximum safe daily consumption of fluoride is 10 mg/day for an adult (U.S.) or 7 mg/day (European Union).
The upper limit of fluoride intake from all sources (fluoridated water, food, beverages, fluoride dental products and dietary fluoride supplements) is set at 0.10 mg/kg/day for infants, toddlers, and children through to 8 years old. For older children and adults, who are no longer at risk for dental fluorosis, the upper limit of fluoride is set at 10 mg/day regardless of weight. | 1 | Biochemistry |
Two adjacent structural units in a polymer molecule constitute a diad. Diads overlap: each structural unit is considered part of two diads, one diad with each neighbor. If a diad consists of two identically oriented units, the diad is called a meso diad (abbreviated m) as in a meso compound. If a diad consists of units oriented in opposition, the diad is called a racemo diad (r) as in a racemic compound. In the case of vinyl polymer molecules, a meso diad is one in which the substituents are oriented on the same side of the polymer backbone: in the Natta projection they both point into the plane, or both point out of the plane. | 4 | Stereochemistry |
Cytoplasmic abundant heat soluble (CAHS) proteins are highly expressed in response to desiccation. There are two hypotheses for their function in tardigrades. The vitrification hypothesis is the idea that, when a tardigrade becomes desiccated, the viscosity within its cells increases to the point that denaturation and membrane fusion in proteins would stop. A second hypothesis, the water replacement hypothesis, posits that CAHS proteins replace water in other desiccation-sensitive proteins, protecting the hydrogen bonds normally reliant on water. CAHS proteins are dispersed throughout the cell in normal conditions, but form a network of filaments during environmentally stressful conditions. This network transforms the cytoplasm into a gel-like matrix and prevents the cell from collapsing as water leaches out. This state is reversible and the proteins disaggregate when exposed to less stressful conditions.
When forming the filament network, CAHS proteins have long helical domains that interact in a coiled manner with each other. These interactions are possible due to the proteins' partial disorder, with two flexible tails surrounding the helical domains.
CAHS proteins have been studied to observe their interactions with trehalose, a sugar used by other species to prevent desiccation. Trehalose was found to interact at higher levels with CAHS proteins than other sugars such as sucrose. However, the exact functions of trehalose inside tardigrade cells are still unknown. | 1 | Biochemistry |
In chemistry and crystallography, crystal structures that have the same set of interatomic distances are called homometric structures. Homometric structures need not be congruent (that is, related by a rigid motion or reflection). Homometric crystal structures produce identical diffraction patterns; therefore, they cannot be distinguished by a diffraction experiment.
Recently, a Monte Carlo algorithm was proposed to calculate the number of homometric structures corresponding to any given set of interatomic distances. | 4 | Stereochemistry |
In mathematics, a symmetry operation is a geometric transformation of an object that leaves the object looking the same after it has been carried out. For example, a turn rotation of a regular triangle about its center, a reflection of a square across its diagonal, a translation of the Euclidean plane, or a point reflection of a sphere through its center are all symmetry operations. Each symmetry operation is performed with respect to some symmetry element (a point, line or plane). Symmetry operations can be classified either as point symmetry operations or as travel symmetry operations.
In the context of molecular symmetry, a symmetry operation is a permutation of atoms such that the molecule or crystal is transformed into a state indistinguishable from the starting state.
Two basic facts follow from this definition, which emphasizes its usefulness.
# Physical properties must be invariant with respect to symmetry operations.
# Symmetry operations can be collected together in groups which are isomorphic to permutation groups.
In the context of molecular symmetry, quantum wavefunctions need not be invariant, because the operation can multiply them by a phase or mix states within a degenerate representation, without affecting any physical property. | 7 | Physical Chemistry |
Once the C-H bond of methane is activated by bonding to a transition metal complex, the net functionalization of the alkyl metal complex into another hydrocarbon containing a functional group is actually much harder to achieve. In general, alkanes of various lengths have typically been functionalized by a number of more commonly known reactions: electrophilic activation (Shilov system, see above), dehydrogenation, borylation, hydrogen-deuterium exchange, and carbene/nitrene/oxo insertion. The functionalization of methane in particular has been reported in four different methods that use homogeneous catalysts rather than heterogeneous catalysts. Heterogeneous systems, using copper- and iron exchanged Zeolite, are also investigated. In these systems, reactive oxygen species such as Alpha-Oxygen are generated which can perform a hydrogen atom abstraction. | 0 | Organic Chemistry |
*Thermal wheel, or rotary heat exchanger (including enthalpy wheel and desiccant wheel)
*Recuperator, or cross plate heat exchanger
*Heat pipe | 7 | Physical Chemistry |
The mineralization of copper is restricted to a few areas in western, central and southern Africa, and some have the richest deposits of copper in the world. In the west, copper has only been found in the arid regions of the Sahel and southern Sahara. The main sources of copper are:
# Akjoujt in Mauritania
# Nioro du Sahel to Sirakoro in Northern Mali
# The Aïr Massif near Azelik and Agadez in Niger
There are not any known mines in tropical West Africa, however copper and lead workings have been in the Benue Trough in southeastern Nigeria. With the exception of a few areas near Kilembe in Uganda and Rwanda, there are no sources of copper in East Africa. The largest concentration of copper found in Africa is the Lufilian Arc. It is an eight hundred kilometer crescent shaped belt, which extends from the Copperbelt in Zambia to the southern Shaba Province in Congo. | 8 | Metallurgy |
For the case of counterpropagating waves with orthogonal circular polarizations the resulting polarization is linear everywhere, but rotates about at an angle . As a result, there is no Sisyphus effect. The rotating polarization instead leads to motion-induced population imbalances in the Zeeman levels that cause imbalances in radiation pressure leading to a damping of the atomic motion. These population imbalances are only present for states with or higher.
Consider two EM waves detuned from an atomic transition with equal amplitudes: and . The superposition of these two waves is:
As previously stated, the polarization of the total field is linear, but rotated around by an angle with respect to .
Consider an atom moving along z with some velocity v. The atom sees the polarization rotating with a frequency of . In the rotating frame, the polarization is fixed, however, there is an inertial field due to the frame rotating. This inertial term appears in the Hamiltonian as follows.
Here we see the inertial term looks like a magnetic field along with an amplitude such that the Larmor precession frequency is equal to rotation frequency in the lab frame. For small v, this term in Hamiltonian can be treated using perturbation theory.
Choosing the polarization in the rotating frame to be fixed along , the unperturbed atomic eigenstates are the eigenstates of . The rotating term in the Hamiltonian causes perturbations in the atomic eigenstates such that the Zeeman sublevels become contaminated by each other. For the is light shifted more than the states. Thus the steady state population of the is higher than that of the other states. The populations are equal for the states. Thus states are balanced with . However, when we change basis we see that populations are not balanced in the z-basis and there is a non-zero value of proportional to the atom's velocity:
Where is the light shift for the state. There is a motion induced population imbalance in the Zeeman sublevels in the z basis. For red detuned light, is negative, and thus there will be a higher population in the state when the atom is moving to the right (positive velocity) and a higher population in the state when the atom is moving to the left (negative velocity). From the Clebsch-Gordan coefficients, we see that the state has a six times greater probability of absorbing a photon moving to the left than a photon moving to the right. The opposite is true for the state. When the atom moves to the right it is more likely to absorb a photon moving to the left and likewise when the atom moves to the left it is more likely to absorb a photon moving to the right. Thus there is an unbalanced radiation pressure when the atom moves which dampens the motion of the atom, lowering its velocity and therefore its temperature.
Note the similarity to Doppler cooling in the unbalanced radiation pressures due to the atomic motion. The unbalanced pressure in PG cooling is not due to a Doppler shift but an induced population imbalance. Doppler cooling depends on the parameter where is the scattering rate, whereas PG cooling depends on . At low intensity and thus PG cooling works at lower atomic velocities (temperatures) than Doppler Cooling. | 7 | Physical Chemistry |
Biochemists are scientists who are trained in biochemistry. They study chemical processes and chemical transformations in living organisms. Biochemists study DNA, proteins and cell parts. The word "biochemist" is a portmanteau of "biological chemist."
Biochemists also research how certain chemical reactions happen in cells and tissues and observe and record the effects of products in food additives and medicines.
Biochemist researchers focus on playing and constructing research experiments, mainly for developing new products, updating existing products and analyzing said products. It is also the responsibility of a biochemist to present their research findings and create grant proposals to obtain funds for future research.
Biochemists study aspects of the immune system, the expressions of genes, isolating, analyzing, and synthesizing different products, mutations that lead to cancers, and manage laboratory teams and monitor laboratory work. Biochemists also have to have the capabilities of designing and building laboratory equipment and devise new methods of producing correct results for products.
The most common industry role is the development of biochemical products and processes. Identifying substances' chemical and physical properties in biological systems is of great importance, and can be carried out by doing various types of analysis. Biochemists must also prepare technical reports after collecting, analyzing and summarizing the information and trends found.
In biochemistry, researchers often break down complicated biological systems into their component parts. They study the effects of foods, drugs, allergens and other substances on living tissues; they research molecular biology, the study of life at the molecular level and the study of genes and gene expression; and they study chemical reactions in metabolism, growth, reproduction, and heredity, and apply techniques drawn from biotechnology and genetic engineering to help them in their research. About 75% work in either basic or applied research; those in applied research take basic research and employ it for the benefit of medicine, agriculture, veterinary science, environmental science, and manufacturing. Each of these fields allows specialization; for example, clinical biochemists can work in hospital laboratories to understand and treat diseases, and industrial biochemists can be involved in analytical research work, such as checking the purity of food and beverages.
Biochemists in the field of agriculture research the interactions between herbicides with plants. They examine the relationships of compounds, determining their ability to inhibit growth, and evaluate the toxicological effects surrounding life.
Biochemists also prepare pharmaceutical compounds for commercial distribution.
Modern biochemistry is considered a sub-discipline of the biological sciences, due to its increased reliance on, and training, in accord with modern molecular biology. Historically, even before the term biochemist was formally recognized, initial studies were performed by those trained in basic chemistry, but also by those trained as physicians. | 1 | Biochemistry |
Cytochrome b559 is an important component of Photosystem II (PSII) is a multisubunit protein-pigment complex containing polypeptides both intrinsic and extrinsic to the photosynthetic membrane. Within the core of the complex, the chlorophyll and beta-carotene pigments are mainly bound to the antenna proteins CP43 (PsbC) and CP47 (PsbB), which pass the excitation energy on to chlorophylls in the reaction centre proteins D1 (Qb, PsbA) and D2 (Qa, PsbD) that bind all the redox-active cofactors involved in the energy conversion process. The PSII oxygen-evolving complex (OEC) provides electrons to re-reduce the PSII reaction center, and oxidizes 2 water molecules to recover its reduced initial state. It consists of OEE1 (PsbO), OEE2 (PsbP) and OEE3 (PsbQ). The remaining subunits in PSII are of low molecular weight (less than 10 kDa), and are involved in PSII assembly, stabilisation, dimerization, and photoprotection.
Cytochrome b559, which forms part of the reaction centre core of PSII, is a heterodimer composed of one alpha subunit (PsbE), one beta (PsbF) subunit, and a heme cofactor. Two histidine residues from each subunit coordinate the heme. Although cytochrome b559 is a redox-active protein, it is unlikely to be involved in the primary electron transport in PSII due to its very slow photo-oxidation and photo-reduction kinetics. Instead, cytochrome b559 could participate in a secondary electron transport pathway that helps protect PSII from photo-damage. Cytochrome b559 is essential for PSII assembly.
This domain occurs in both the alpha and beta subunits of cytochrome B559. In the alpha subunit, it occurs together with a lumenal domain (), while in the beta subunit it occurs on its own.
Cytochrome b559 can exist in three forms, each with a characteristic redox potential. These forms are very low potential (VLP), ≤ zero mV; low potential (LP) at 60 mV; and high potential (HP) at 370 mV. There is also an intermediate potential (IP) form that has a redox potential at pH 6.5-7.0 that ranges from 170 to 240 mV. In oxygen-evolving reaction centers, more than half of the cyt b559 is in the HP form. In manganese-depleted non-oxygen evolving photosystem II reaction centers, cyt b559 is usually in the LP form. | 5 | Photochemistry |
Clinical trials of vitamin D supplementation for depressive symptoms have generally been of low quality and show no overall effect, although subgroup analysis showed supplementation for participants with clinically significant depressive symptoms or depressive disorder had a moderate effect. | 1 | Biochemistry |
The first researcher to suggest the existence of a molecular knot in a protein was Jane Richardson in 1977, who reported that carbonic anhydrase B (CAB) exhibited apparent knotting during her survey of various proteins' topological behavior. However, the researcher generally attributed with the discovery of the first knotted protein is Marc. L. Mansfield in 1994, as he was the first to specifically investigate the occurrence of knots in proteins and confirm the existence of the trefoil knot in CAB. Knotted DNA was found first by Liu et al. in 1981, in single-stranded, circular, bacterial DNA, though double-stranded circular DNA has been found to also form knots.
In 1989, Sauvage and coworkers reported the first synthetic knotted molecule: a trefoil synthesized via a double-helix complex with the aid of Cu+ ions.
Vogtle et al. was the first to describe molecular knots as knotanes in 2000. Also in 2000 was William Taylor's creation of an alternative computational method to analyze protein knotting that set the termini at a fixed point far enough away from the knotted component of the molecule that the knot type could be well-defined. In this study, Taylor discovered a deep knot in a protein. With this study, Taylor confirmed the existence of deeply knotted proteins.
In 2007, Eric Yeates reported the identification of a molecular slipknot, which is when the molecule contains knotted subchains even though their backbone chain as a whole is unknotted and does not contain completely knotted structures that are easily detectable by computational models. Mathematically, slipknots are difficult to analyze because they are not recognized in the examination of the complete structure.
A pentafoil knot prepared using dynamic covalent chemistry was synthesized by Ayme et al. in 2012, which at the time was the most complex non-DNA molecular knot prepared to date. Later in 2016, a fully organic pentafoil knot was also reported, including the very first use of a molecular knot to allosterically regulate catalysis. In January 2017, an 8 knot was synthesized by David Leigh's group, making the 8 knot the most complex molecular knot synthesized.
An important development in knot theory is allowing for intra-chain contacts within an entangled molecular chain. Circuit topology has emerged as a topology framework that formalises the arrangement of contacts as well as chain crossings in a folded linear chain. As a complementary approach, Colin Adams. et al., developed a singular knot theory that is applicable to folded linear chains with intramolecular interactions. | 6 | Supramolecular Chemistry |
Pasteur observed that fermentation does not require oxygen, but needs yeast, which is alive. Fermentation is a biological process, not a reduction and oxygen chemical process. He used two slender bottles. One of the bottles had a curved neck; this is called a swan neck. Pasteur poured liquid broth into the two bottles, and heated in the bottom of the bottles. When the liquid boiled, he let them cool. Pasteur observed that the broth in the curved bottle stayed clear, except when the bottle was shaken.
Pasteur explained that the two bottles were filled with air, but the curved bottle could stop most of the particles in the air, and it kept its nature. However, the liquid in the other bottle degenerated. Therefore, he concluded that fermentation does not require oxygen, but needs the yeast. When yeast is allowed to grow over time, the substance will spoil or rot.
Pasteur's viewed fermentation as a type of vitalism. He observed that living organisms were responsible for the process of fermentation. | 1 | Biochemistry |
Below are useful results from the Maxwell–Boltzmann distribution for an ideal gas, and the implications of the Entropy quantity. The distribution is valid for atoms or molecules constituting ideal gases.
Corollaries of the non-relativistic Maxwell–Boltzmann distribution are below. | 7 | Physical Chemistry |
The 2006 Nobel Prize in Chemistry was awarded to Roger D. Kornberg for creating detailed molecular images of RNA polymerase during various stages of the transcription process.
In most prokaryotes, a single RNA polymerase species transcribes all types of RNA. RNA polymerase "core" from E. coli consists of five subunits: two alpha (α) subunits of 36 kDa, a beta (β) subunit of 150 kDa, a beta prime subunit (β′) of 155 kDa, and a small omega (ω) subunit. A sigma (σ) factor binds to the core, forming the holoenzyme. After transcription starts, the factor can unbind and let the core enzyme proceed with its work. The core RNA polymerase complex forms a "crab claw" or "clamp-jaw" structure with an internal channel running along the full length. Eukaryotic and archaeal RNA polymerases have a similar core structure and work in a similar manner, although they have many extra subunits.
All RNAPs contain metal cofactors, in particular zinc and magnesium cations which aid in the transcription process. | 1 | Biochemistry |
In Alabama, industrialization was generating a ravenous appetite for the states coal and iron ore. Production was booming, and unions were attempting to organize unincarcerated miners. Convicts provided an ideal captive work force: cheap, usually docile, unable to organize and available when unincarcerated laborers went on strike." The Southern agrarian economy did not accommodate convict leasing as well as the industrial economy did, whose jobs were often unappealing or dangerous, offering hard-labor and low pay. The competition, expansion, and growth of mining and steel companies also created a high demand for labor, but union labor posed a threat to expanding companies. As unions bargained for higher wages and better conditions, often organizing strikes in order to achieve their goals, the growing companies would be forced to agree to union demands or face abrupt halts in production. The rate companies paid for convict leases, which paid the laborer nothing, was regulated by government and state officials who entered the labor contracts with companies. "The companies built their own prisons, fed and clothed the convicts, and supplied guards as they saw fit." (Blackmon 2001) Alabamas use of convict leasing was commanding; 51 of its 67 counties regularly leased convicts serving for misdemeanors at a rate of about $5–20 per month, equal to about $160–500 in 2015. Although the influence of labor unions forced some states to move away from the profitable convict lease agreements and run traditional prisons, plenty of companies began substituting convict labor in their operations in the twentieth century. "The biggest user of forced labor in Alabama at the turn of the century was Tennessee Coal, Iron & Railroad Co., [of] U.S. Steel" | 8 | Metallurgy |
The term excimer (excited state dimer) is, strictly speaking, limited to cases in which a true dimer is formed; that is, both components of the dimer are the same molecule or atom. The term exciplex refers to the heterodimeric case; however, common usage expands excimer to cover this situation. | 5 | Photochemistry |
The term "paucimannose" (occasionally spelled as "pauci-mannose") was coined in the early 1990s glycobiology literature Paucimannose utilises the prefix "pauci" meaning few or small in Latin and the suffix "mannose" indicating glycans involving mannose-terminating glycans.
The phrases protein paucimannosylation and paucimannosidic proteins are commonly used in the literature to describe paucimannose-modified glycoproteins displaying intact structural and functional integrity. In contrast, the oligosaccharides themselves are often referred to as paucimannosidic, low mannose, and truncated glycans or other less conventional nomenclature.
A simple shorthand nomenclature has been proposed as a convenient way to name the individual paucimannosidic glycan structures, e.g. M3F denotes ManGlcNAcFuc. | 1 | Biochemistry |
This metabolic pathway leading to the alternative oxidase diverges from the cytochrome-linked electron transport chain at the ubiquinone pool. Alternative pathway respiration only produces proton translocation at Complex 1 (NADH dehydrogenase) and so has a lower ATP yield than the full pathway. The expression of the alternative oxidase gene AOX is influenced by stresses such as cold, reactive oxygen species and infection by pathogens, as well as other factors that reduce electron flow through the cytochrome pathway of respiration. Although the benefit conferred by this activity remains uncertain, it may enhance an organism's ability to resist these stresses by maintaining the oxidized state of the upstream electron-transport components, thereby reducing the level of oxidative stress induced by overreduced electron carriers.
Unusually, the bloodstream form of the protozoan parasite Trypanosoma brucei, which is the cause of sleeping sickness, depends entirely on the alternative oxidase pathway for cellular respiration through its electron transport chain. This major metabolic difference between the parasite and its human host has made the T. brucei alternative oxidase an attractive target for drug design. Of the known inhibitors of alternative oxidases, the antibiotic ascofuranone inhibits the T. brucei enzyme and cures infection in mice.
In fungi, the ability of the alternative oxidase to bypass inhibition of parts of the electron transport chain can contribute to fungicide resistance. This is seen in the strobilurin fungicides that target complex III, such as azoxystrobin, picoxystrobin and fluoxastrobin. However, even though the alternative pathway generates less ATP, these fungicides are still effective in preventing spore germination, as this is an energy-intensive process. | 1 | Biochemistry |
Unsaturated compounds, especially alkenes and alkynes, add halogens:
In oxychlorination, the combination of hydrogen chloride and oxygen serves as the equivalent of chlorine, as illustrated by this route to 1,2-dichloroethane:
The addition of halogens to alkenes proceeds via intermediate halonium ions. In special cases, such intermediates have been isolated.
Bromination is more selective than chlorination because the reaction is less exothermic. Illustrative of the bromination of an alkene is the route to the anesthetic halothane from trichloroethylene:
Iodination and bromination can be effected by the addition of iodine and bromine to alkenes. The reaction, which conveniently proceeds with the discharge of the color of , is the basis of the analytical method. The iodine number and bromine number are measures of the degree of unsaturation for fats and other organic compounds. | 0 | Organic Chemistry |
Lithium–sulfur system arranged in a network of nanoparticles eliminates the requirement that charge moves in and out of particles that are in direct contact with a conducting plate. Instead, the nanoparticle network allows electricity to flow throughout the liquid. This allows more energy to be extracted.
In a Semi-solid flow battery, the positive and negative electrodes are composed of particles suspended in a carrier liquid. The positive and negative suspensions are stored in separate tanks and pumped through separate pipes into a stack of adjacent reaction chambers, where they are separated by a barrier such as a thin, porous membrane. The approach combines the basic structure of aqueous-flow batteries, which use electrode material suspended in a liquid electrolyte, with the chemistry of lithium-ion batteries in both carbon-free suspensions and slurries with conductive carbon network. The carbon free semi-solid redox flow battery is also sometimes referred to as Solid Dispersion Redox Flow Battery. Dissolving a material changes its chemical behavior significantly. However, suspending bits of solid material preserves the solid's characteristics. The result is a viscous suspension that flows like molasses.
In 2022, Influit Energy announced a flow battery electrolyte consisting of a metal oxide suspended in an aqueous solution.
Flow batteries with redox-targeted solids (ROTS), also known as solid energy boosters (SEBs), is another recent development. In these batteries either posolyte or negolyte or both (a.k.a. redox fluids), come in contact with a one or more solid electroactive materials, stored in tanks outside the power stack. The redox fluids comprise one or more redox couples, with redox potentials flanking the redox potential of the solid electroactive material. Such RFBs with Solid Energy Boosters (SEBs) combine the high specific energy advantage of conventional batteries (such as lithium-ion) with the decoupled energy-power advantage of flow batteries. SEB(ROTS) RFBs have several advantages compared to semi-solid RFBs, such as no need to pump viscous slurries, no precipitation /clogging, higher area-specific power, longer durability, wider chemical design space. However, because of double energy losses (one in the stack and another in the tank between the SEB(ROTS) and a mediator), such batteries suffer from a poor energy efficiency. On a system-level, the practical specific energy of traditional lithium-ion batteries is larger than that of SEB(ROTS)-flow versions of lithium-ion batteries. | 7 | Physical Chemistry |
Spathulenol is a tricyclic sesquiterpene alcohol which has a basic skeleton similar to the azulenes. It occurs in oregano among other plants. | 1 | Biochemistry |
Also well studied is the sea pansy, Renilla reniformis. In this organism, the luciferase (Renilla-luciferin 2-monooxygenase) is closely associated with a luciferin-binding protein as well as a green fluorescent protein (GFP). Calcium triggers release of the luciferin (coelenterazine) from the luciferin binding protein. The substrate is then available for oxidation by the luciferase, where it is degraded to coelenteramide with a resultant release of energy. In the absence of GFP, this energy would be released as a photon of blue light (peak emission wavelength 482 nm). However, due to the closely associated GFP, the energy released by the luciferase is instead coupled through resonance energy transfer to the fluorophore of the GFP, and is subsequently released as a photon of green light (peak emission wavelength 510 nm). The catalyzed reaction is:
* coelenterazine + O → coelenteramide + CO + photon of light | 1 | Biochemistry |
The Sanford–Wang parameterisation is an empirical formula used to model the production of pions in nuclear interaction of the form p+A → +X where a beam of high-energy protons hit a material.
Its formula for the double-differential cross section with respect to momentum (p) and solid angle () is as follows.
Where p and are the momentum of the outgoing pion and its angle from the direction of the incident proton. The numbers are the Sanford-Wang parameters and are typically varied to give a good fit with experimental data. | 7 | Physical Chemistry |
* Димитров П. 1988. [https://www.researchgate.net/publication/312155281_Dalec_ot_bregove_i_farvateri_Far_from_the_coasts_and_waterways Далеч от брегове и фарватери]. Варна. Изд. „Галактика“. Библиотека „Нептун“, 161 с., doi:[https://doi.org/10.13140/RG.2.2.19449.36965/1 10.13140/RG.2.2.19449.36965/1]
* Димитров П., Д. Димитров. 2003. [https://www.researchgate.net/publication/290946364_Cerno_more_Potopt_i_drevnite_mitove Черно море, Потопът и древните митове]. „Славена“, Варна, ISBN 954-579-278-7, 91 с., doi:[https://doi.org/10.13140/RG.2.2.27133.05609 10.13140/RG.2.2.27133.05609]
** ((en)) Dimitrov P., D. Dimitrov. 2004. [https://www.researchgate.net/publication/290938137_The_Black_Sea_The_Flood_and_the_ancient_myths The Black Sea The Flood and the ancient myths]. „Slavena“, Varna, ISBN 954-579-335-X, 91 p., doi:[https://doi.org/10.13140/RG.2.2.18954.16327 10.13140/RG.2.2.18954.16327]
** ((ru)) Димитров П., Д. Димитров. 2008. [https://www.researchgate.net/publication/290946378_Cernoe_more_Potop_i_drevnie_mify Черное море, Потоп и древние мифы]. „Славена“, Варна, ISBN 954-579-278-7, 89 с., doi:[https://doi.org/10.13140/RG.2.2.23148.46729 10.13140/RG.2.2.23148.46729] | 9 | Geochemistry |
Non-B DNA can be classified into several types, including A-DNA, Z-DNA, H-DNA, G-quadruplexes, and Triplexes (Triple-stranded DNA).
A-DNA is a right-handed double helix structure for RNA-DNA duplexes and RNA-RNA duplexes that is less common than the more well-known B-DNA structure. A-DNA is a form of DNA that occurs when the DNA is in a dehydrated state or is bound to certain proteins, and it has a shorter and wider helix than B-DNA. The helix of A-DNA is also tilted and compressed compared to B-DNA. A-DNA is believed to play a role in certain biological processes, such as DNA replication and gene expression.
Z-DNA is a left-handed helix with a zigzag backbone, in contrast to the right-handed B-DNA helix. It is stabilized by the alternating purine-pyrimidine sequence and can form in regions of DNA with high GC-content, supercoiling, or negative superhelicity. Z-DNA has been implicated in gene regulation and immunity, but it can also induce DNA damage and inflammation.
H-DNA is a triple-stranded DNA structure that forms when two homologous DNA strands come together and one strand displaces the other. H-DNA is stabilized by Hoogsteen base pairing and can cause mutations, rearrangements, and genome instability. H-DNA is thought to be involved in DNA replication, recombination, and repair, but its precise biological functions remain unclear.
G-quadruplexes are four-stranded DNA structures formed by guanine-rich sequences. G-quadruplexes can form in telomeres, oncogene promoters, and other genomic regions and can affect gene expression, DNA replication, and telomere maintenance. G-quadruplexes are also potential targets for cancer therapy.
Triplexes are three-stranded DNA structures formed by the binding of a third strand to a DNA duplex. Triplexes can be formed by pyrimidine-rich or purine-rich third strands, and they can occur in genomic regions with inverted repeats, mirror repeats, or other special sequences. Triplexes can affect DNA replication, transcription, and recombination, but they can also cause DNA damage and mutagenesis. | 1 | Biochemistry |
Some researchers prefer to define the term “photoinhibition” so that it contains all reactions that lower the quantum yield of photosynthesis when a plant is exposed to light. In this case, the term "dynamic photoinhibition" comprises phenomena that reversibly down-regulate photosynthesis in the light and the term "photodamage" or "irreversible photoinhibition" covers the concept of photoinhibition used by other researchers. The main mechanism of dynamic photoinhibition is non-photochemical quenching of excitation energy absorbed by PSII. Dynamic photoinhibition is acclimation to strong light rather than light-induced damage, and therefore "dynamic photoinhibition" may actually protect the plant against "photoinhibition". | 5 | Photochemistry |
Heparin cofactor II (HCII), a protein encoded by the SERPIND1 gene, is a coagulation factor that inhibits IIa, and is a cofactor for heparin and dermatan sulfate ("minor antithrombin").
The product encoded by this gene is a serine protease inhibitor which rapidly inhibits thrombin in the presence of dermatan sulfate or heparin. The gene contains five exons and four introns. This protein shares homology with antithrombin III and other members of the alpha-1 antitrypsin superfamily. Mutations in this gene are associated with heparin cofactor II deficiency. Heparin cofactor II deficiency can lead to increased thrombin generation and a hypercoagulable state.
A purification experiment of heparin cofactor II was performed in 1981, in which it was discovered that the purified version of the protein consists of a single polypeptide chain. Further experimentation demonstrated that whether β-Mercaptoethanol is present does not affect HCII's activity in gel electrophoresis. β-Mercaptoethanol is typically used for the reduction of disulfide bonds within a molecule, but the gel electrophoresis revealed that HCII does not have any of these bonds. The structure is similar to antithrombin III (ATIII), which was known to effectively inhibit thrombin as well as coagulation factor X. This experiment suggested that HCII has strong thrombin inhibition, yet weak inhibition of coagulation factor X.
Heparin cofactor II may play a role in the immune response, as it has been associated with leukocyte-mediated protein degradation, which releases cytokines in the inflammatory response with neutrophils and monocytes. Its role has been questioned because although it is a thrombin inhibitor, an absence of HCII does not result in significantly higher levels of thrombosis. This does not negate the results of the 1981 study, but novel discoveries create more questions of the biological mechanism and function of the protein. However, this cofactor shows stronger capability in inhibiting thrombin in pregnant women, protecting them from thrombosis. Pregnant women have shown increased levels of heparin cofactor II as well as dermatan sulfate, which is a polysaccharide that is expected to be involved in wound repair, coagulation, and overall maintenance throughout the body. Pregnant women who had thrombosis are likely to also have low levels of heparin cofactor II, but whether this is a causation is still unknown. | 1 | Biochemistry |
BSi preservation is measured by:
* Sedimentation rates, mainly sediment traps (Honjo);
* Benthic remineralization rates ("recycling"), benthic flux chamber (Berelson);
* BSi concentration in sediments, chemical leaching in alkaline solution, site specific, need to differentiate lithogenic vs. biogenic Si, X-ray diffraction.
BSi preservation is controlled by:
* Sedimentation rate;
* Porewater dissolved silica concentration: saturation at 1.100 μmol/L;
* Surface coatings: dissolved Al modifies solubility of deposited biogenic silica particles, dissolved silica can also precipitate with Al as clay or Al-Si coatings. | 1 | Biochemistry |
;Wins
* North American Bridge Championships (12)
** Master Mixed Teams (1) 1990
** Open Swiss Teams (1) 1991
** North American Swiss Teams (1) 1990
** Grand National Open Teams (1) 1981
** Men's Board-a-Match Teams (2) 1984, 1987
** Reisinger Board-a-Match Teams (1) 1985
** Spingold Knockout Teams (2) 1976, 1984
** Vanderbilt Knockout Teams (3) 1975, 1976, 1982
;Runners-up
* North American Bridge Championships (15)
** Blue Ribbon Pairs (1) 1974
** Silver Ribbon Pairs (1) 1992
** Master Mixed Teams (3) 1967, 1984, 1994
** Open Swiss Teams (2) 1998, 2003
** Men's Board-a-Match Teams (1) 1975
** Open Board-a-Match Teams (2) 1990, 2000
** Spingold Knockout Teams (1) 1967
** Vanderbilt Knockout Teams (2) 1978, 2001
** Reisinger Board-a-Match Teams (2) 1980, 1997
* Other notable 2nd places:
** United States Bridge Federation Bermuda Bowl qualifiers (1) 1982 | 0 | Organic Chemistry |
A deuterated drug is a small molecule medicinal product in which one or more of the hydrogen atoms contained in the drug molecule have been replaced by deuterium. Because of the kinetic isotope effect, deuterium-containing drugs may have significantly lower rates of metabolism, and hence a longer half-life. In 2017, deutetrabenazine became the first deuterated drug to receive FDA approval. | 9 | Geochemistry |
Phase inversion is a common method to form filtration membranes, which are typically formed using artificial polymers. The method of phase inversion is highly dependent on the type of polymer used and the solvent used to dissolve the polymer.
Phase inversion can be carried out through one of four typical methods:
*Reducing the temperature of the solution
*Immersing the polymer solution into anti-solvent
*Exposing the polymer solution to a vapor of anti-solvent
*Evaporating the solvent in atmospheric air or at high temperature
The rate at which phase inversion occurs and the characteristics of the resulting membrane are dependent on several factors, including:
*Solubility of solvent in the anti-solvent
*Insolubility of the polymer in the anti-solvent
*Temperature of the anti-solvent | 7 | Physical Chemistry |
# Wash pipe ends to create clean surfaces for joining
# Square pipe ends to facilitate optimal fit-up
# Clean area where coupler will be placed with isopropyl alcohol
# Mark the pipes slightly beyond half the length of the coupler, to indicate where scraping will take place in later steps
# Mark the area to be scraped
# Scrape pipe in marked areas to remove surface layer, allowing clean pipe material to contact the coupler
# Examine scraped area thoroughly, making sure that fresh pipe material is exposed throughout area
# Insert pipe ends into coupling to appropriate depth
# Secure coupler using clamp
# Connect fitting to control box using electrical leads
# Apply fusion cycle
# Allow joint to be undisturbed for the entire prescribed cooling time
# Pressure test pipe
# Back fill pipe with appropriate contents
# Begin service | 7 | Physical Chemistry |
Most cell types take up iron primarily through receptor-mediated endocytosis via transferrin receptor 1 (TFR1), transferrin receptor 2 (TFR2) and GAPDH. TFR1 has a 30-fold higher affinity for transferrin-bound iron than TFR2 and thus is the main player in this process. The higher order multifunctional glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) also acts as a transferrin receptor. Transferrin-bound ferric iron is recognized by these transferrin receptors, triggering a conformational change that causes endocytosis. Iron then enters the cytoplasm from the endosome via importer DMT1 after being reduced to its ferrous state by a STEAP family reductase.
Alternatively, iron can enter the cell directly via plasma membrane divalent cation importers such as DMT1 and ZIP14 (Zrt-Irt-like protein 14). Again, iron enters the cytoplasm in the ferrous state after being reduced in the extracellular space by a reductase such as STEAP2, STEAP3 (in red blood cells), Dcytb (in enterocytes) and SDR2. | 1 | Biochemistry |
Hellmut Fischmeister was elected as a foreign member of the Royal Swedish Academy of Engineering Sciences in 1975. In 1981, he was elected as a corresponding member of the Austrian Academy of Sciences and was a member of the Academia Europaea since 1989. In 1995, he became a full member of the mathematical-natural sciences class of the Austrian Academy of Sciences.
* 1969: Knight of the Royal Order of the North Star
* 1991: Honorary doctorate from the Royal Institute of Technology in Stockholm
* 1992: Honorary doctorate from Graz University of Technology
* 1997: Order of Merit of the Federal Republic of Germany, Cross of Merit 1st Class
* 2007: Honorary doctorate from the University of Leoben
* 2010: Austrian Cross of Honour for Science and Art, 1st class
* 2010: Honorary member of the German Materials Society (Deutsche Gesellschaft für Materialkunde) | 8 | Metallurgy |
The TFQI can be calculated with
from quantiles of FT4 and TSH concentration (as determined based on cumulative distribution functions). Per definition the TFQI has a mean of 0 and a standard deviation of 0.37 in a reference population. This explains the reference range of –0.74 to + 0.74. | 1 | Biochemistry |
In hydrothermal liquefaction processes, long carbon chain molecules in biomass are thermally cracked and oxygen is removed in the form of HO (dehydration) and CO (decarboxylation). These reactions result in the production of high H/C ratio bio-oil. Simplified descriptions of dehydration and decarboxylation reactions can be found in the literature (e.g. Asghari and Yoshida (2006) and Snåre et al. (2007). | 0 | Organic Chemistry |
In organometallic chemistry, a metallacycle is a derivative of a carbocyclic compound wherein a metal has replaced at least one carbon center; this is to some extent similar to heterocycles. Metallacycles appear frequently as reactive intermediates in catalysis, e.g. olefin metathesis and alkyne trimerization. In organic synthesis, directed ortho metalation is widely used for the functionalization of arene rings via C-H activation. One main effect that metallic atom substitution on a cyclic carbon compound is distorting the geometry due to the large size of typical metals. | 0 | Organic Chemistry |
The arrangement of the continents has changed over time due to plate tectonics, resulting in the bathymetry of ocean basins also changing over time. The shape and size of the basins influences the circulation patterns and concentration of nutrients within them. Numerical models simulating past arrangements of continents have shown that nutrient traps can form in certain scenarios, increasing local concentrations of phosphate and setting up potential euxinic conditions. On a smaller scale, silled basins often act as nutrient traps due to their estuarine circulation. Estuarine circulation occurs where surface water is replenished from river input and precipitation, causing an outflow of surface waters from the basin, while deep water flows into the basin over the sill. This type of circulation allows for anoxic, high nutrient bottom water to develop within the basin. | 9 | Geochemistry |
Carbon-14 is produced in coolant at boiling water reactors (BWRs) and pressurized water reactors (PWRs). It is typically released to the atmosphere in the form of carbon dioxide at BWRs, and methane at PWRs. Best practice for nuclear power plant operator management of carbon-14 includes releasing it at night, when plants are not photosynthesizing. Carbon-14 is also generated inside nuclear fuels (some due to transmutation of oxygen in the uranium oxide, but most significantly from transmutation of nitrogen-14 impurities), and if the spent fuel is sent to nuclear reprocessing then the carbon-14 is released, for example as during PUREX. | 9 | Geochemistry |
Freiherr Christian Johann Dietrich Theodor von Grotthuss (20 January 1785 – 26 March 1822) was a Baltic German scientist known for establishing the first theory of electrolysis in 1806 and formulating the first law of photochemistry in 1817. His theory of electrolysis is considered the first description of the so-called Grotthuss mechanism. | 5 | Photochemistry |
The HiFIT hammer operates with a hardened pin with a ball resting on the workpiece with a diameter D of 3 mm.
This pin is hammered with an adjustable intensity at around 180–300 Hz at the weld toe. Local mechanical deformations occur in the form of a treatment track. The weld toe is deformed plastically. The induced compressive residual stress prevents the track cracking and the crack propagation on the surface. | 8 | Metallurgy |
The concept of potential energy surface was very important in the development of TST. The foundation of this concept was laid by René Marcelin in 1913. He theorized that the progress of a chemical reaction could be described as a point in a potential energy surface with coordinates in atomic momenta and distances.
In 1931, Henry Eyring and Michael Polanyi constructed a potential energy surface for the reaction below. This surface is a three-dimensional diagram based on quantum-mechanical principles as well as experimental data on vibrational frequencies and energies of dissociation.
H + H → H + H
A year after the Eyring and Polanyi construction, Hans Pelzer and Eugene Wigner made an important contribution by following the progress of a reaction on a potential energy surface. The importance of this work was that it was the first time that the concept of col or saddle point in the potential energy surface was discussed. They concluded that the rate of a reaction is determined by the motion of the system through that col.
It has been typically assumed that the rate-limiting or lowest saddle point is located on the same energy surface as the initial ground state. However, it was recently found that this could be incorrect for processes occurring in semiconductors and insulators, where an initial excited state could go through a saddle point lower than the one on the surface of the initial ground state. | 7 | Physical Chemistry |
Until recent decades it was common to assume that the release of hydrogen and oxygen gas during electrolysis of water always has a Faraday efficiency of 100%. Pons and Fleischmann, and other investigators who reported the finding of anomalous excess heat in electrolytic cells, all relied on this popular assumption. No one bothered to measure the Faraday efficiency in their cells during the experiments. Many publications reporting the finding of excess heat included an explicit statement like: "The Faraday efficiency is assumed to be unity." Even if not explicitly stated so, these publications included this implicit assumption in the formulas used to calculate the cells' energy balance. | 7 | Physical Chemistry |
This pathway is a part of the glutamate family of amino acid biosynthetic pathways. The reaction steps in the pathway are similar to the citric acid cycle.
The first step in the pathway is condensation of acetyl-CoA with α-ketoglutarate, which gives homocitrate. This reaction is catalyzed by homocitrate synthase. Homocitrate is then converted to homoaconitate by homoaconitase and then to homoisocitrate. This is then decarboxylated by homoisocitrate dehydrogenase, which results in α-ketoadipate. A nitrogen atom is added from glutamate by aminoadipate aminotransferase to form the α-aminoadipate, from which this pathway gets its name. This is then reduced by aminoadipate reductase via an acyl-enzyme intermediate to a semialdehyde. Reaction with glutamate by one class of saccharopine dehydrogenase yields saccharopine which is then cleaved by a second saccharopine dehydrogenase to yield lysine and oxoglutarate.
Conversion of lysine to α-ketoadipate during degradation of lysine proceeds via the same steps, but in reverse. | 1 | Biochemistry |
Chitin (CHON) ( ) is a long-chain polymer of N-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chitin are produced each year in the biosphere. It is a primary component of cell walls in fungi (especially filamentous and mushroom forming fungi), the exoskeletons of arthropods such as crustaceans and insects, the radulae, cephalopod beaks and gladii of molluscs and in some nematodes and diatoms.
It is also synthesised by at least some fish and lissamphibians. Commercially, chitin is extracted from the shells of crabs, shrimps, shellfish and lobsters, which are major by-products of the seafood industry. The structure of chitin is comparable to cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein keratin. Chitin has proved useful for several medicinal, industrial and biotechnological purposes. | 1 | Biochemistry |
A variety of oxygen-transport and -binding proteins exist in organisms throughout the animal and plant kingdoms. Organisms including bacteria, protozoans, and fungi all have hemoglobin-like proteins whose known and predicted roles include the reversible binding of gaseous ligands. Since many of these proteins contain globins and the heme moiety (iron in a flat porphyrin support), they are often called hemoglobins, even if their overall tertiary structure is very different from that of vertebrate hemoglobin. In particular, the distinction of "myoglobin" and hemoglobin in lower animals is often impossible, because some of these organisms do not contain muscles. Or, they may have a recognizable separate circulatory system but not one that deals with oxygen transport (for example, many insects and other arthropods). In all these groups, heme/globin-containing molecules (even monomeric globin ones) that deal with gas-binding are referred to as oxyhemoglobins. In addition to dealing with transport and sensing of oxygen, they may also deal with NO, CO, sulfide compounds, and even O scavenging in environments that must be anaerobic. They may even deal with detoxification of chlorinated materials in a way analogous to heme-containing P450 enzymes and peroxidases.
The structure of hemoglobins varies across species. Hemoglobin occurs in all kingdoms of organisms, but not in all organisms. Primitive species such as bacteria, protozoa, algae, and plants often have single-globin hemoglobins. Many nematode worms, molluscs, and crustaceans contain very large multisubunit molecules, much larger than those in vertebrates. In particular, chimeric hemoglobins found in fungi and giant annelids may contain both globin and other types of proteins.
One of the most striking occurrences and uses of hemoglobin in organisms is in the giant tube worm (Riftia pachyptila, also called Vestimentifera), which can reach 2.4 meters length and populates ocean volcanic vents. Instead of a digestive tract, these worms contain a population of bacteria constituting half the organisms weight. The bacteria oxidize HS from the vent with O from the water to produce energy to make food from HO and CO. The worms upper end is a deep-red fan-like structure ("plume"), which extends into the water and absorbs HS and O for the bacteria, and CO for use as synthetic raw material similar to photosynthetic plants. The structures are bright red due to their content of several extraordinarily complex hemoglobins that have up to 144 globin chains, each including associated heme structures. These hemoglobins are remarkable for being able to carry oxygen in the presence of sulfide, and even to carry sulfide, without being completely "poisoned" or inhibited by it as hemoglobins in most other species are. | 7 | Physical Chemistry |
When building on top of bay mud layers or when dredging estuary bottoms, a variety of regulatory frameworks may arise. Normally in the United States, an Environmental Impact Report as well as a geotechnical investigation are conducted precedent to any major construction over bay mud. Combined, these reports have developed much of the data base extant on bay mud characteristics, frequently yielding original field data from soil borings. These data have demonstrated that in many locations the shallower bay muds contain concentrations of mercury, lead, chromium, petroleum hydrocarbons, PCBs, pesticides and other chemicals which exceed toxic limits: a geological record of human activities of the last century. These data are particularly important to consider when dredging of bay muds is contemplated as part of a development project. Such dredging can have impacts to receiving lands as soil contamination, but also water column impacts from sediment disturbance.
In the case of dredging within the United States, a permit is almost always required from the United States Army Corps of Engineers, after submission of extensive data on the project limits, chemical properties of the bay muds to be disturbed, a dredge disposal plan and often a complete Environmental Impact Statement pursuant to the National Environmental Policy Act. Further review by the United States Coast Guard would normally be required. Within individual state jurisdictions, such as California, an Environmental Impact Report must be filed for dredging of any significance; furthermore, agency reviews by the California Coastal Commission and the Regional Water Quality Control Board would normally be mandated. All of these regulatory bodies serve an important role in deciding whether an area may be dredged or not. However, the most important body is the California Environmental Quality Act (CEQA). This guiding legislation is the reason for Environmental Impact Reports, costly mitigation measures and arduous review processes. One of CEQA's main goals is to promote interagency cooperation in the review process of a project. This is one of the main reasons why it is the overseer of all projects in California.
For buildings proposed over bay mud layers, typically the municipality involved will, in addition to the usual engineering and design review issues common to all building projects (which are more complicated because of the site conditions), require an Environmental Impact Report [https://web.archive.org/web/20060906222150/http://ceres.ca.gov/topic/env_law/ceqa/guidelines/]. This process would include reviews by that city's building department, as well as applicable regional and state agencies such as those cited above for dredging projects, except that Coast Guard agencies would not typically be concerned. In developing in California, proposed development over bay mud layers would also have to go through a planning commission and a city council in order to be allowed. This process would respect the EIR, CEQA, and all the other bodies discussed above. In the case of San Francisco the project would have to get approved by the San Francisco Board of Supervisors.
In regards to San Francisco, some interesting negative externalities are being experienced due to the dredging of land by the Bay. The Millennium Towers, which were completed in 2008, are currently sinking. This has had a negative impact on the residents of this building. In response to this subsidence, San Francisco's city attorney has decided to file a lawsuit against the developer, because the developer failed to inform the residents of the accelerated speed that the building was sinking at. If this lawsuit results in success for San Francisco this could lead to policy changes being made in the future surrounding transparency between developers and potential buyers of the developed land. | 2 | Environmental Chemistry |
In a plasma, a Coulomb collision rarely results in a large deflection. The cumulative effect of the many small angle collisions, however, is often larger than the effect of the few large angle collisions that occur, so it is instructive to consider the collision dynamics in the limit of small deflections.
We can consider an electron of charge and mass passing a stationary ion of charge and much larger mass at a distance with a speed . The perpendicular force is at the closest approach and the duration of the encounter is about . The product of these expressions divided by the mass is the change in perpendicular velocity:
Note that the deflection angle is proportional to . Fast particles are "slippery" and thus dominate many transport processes. The efficiency of velocity-matched interactions is also the reason that fusion products tend to heat the electrons rather than (as would be desirable) the ions. If an electric field is present, the faster electrons feel less drag and become even faster in a "run-away" process.
In passing through a field of ions with density , an electron will have many such encounters simultaneously, with various impact parameters (distance to the ion) and directions. The cumulative effect can be described as a diffusion of the perpendicular momentum. The corresponding diffusion constant is found by integrating the squares of the individual changes in momentum. The rate of collisions with impact parameter between and is , so the diffusion constant is given by
Obviously the integral diverges toward both small and large impact parameters. The divergence at small impact parameters is clearly unphysical since under the assumptions used here, the final perpendicular momentum cannot take on a value higher than the initial momentum. Setting the above estimate for equal to , we find the lower cut-off to the impact parameter to be about
We can also use as an estimate of the cross section for large-angle collisions. Under some conditions there is a more stringent lower limit due to quantum mechanics, namely the de Broglie wavelength of the electron, where is Planck's constant.
At large impact parameters, the charge of the ion is shielded by the tendency of electrons to cluster in the neighborhood of the ion and other ions to avoid it. The upper cut-off to the impact parameter should thus be approximately equal to the Debye length: | 7 | Physical Chemistry |
21st Century Medicine (21CM) is a California cryobiological research company which has as its primary focus the development of perfusates and protocols for viable long-term cryopreservation of human organs, tissues and cells at temperatures below −100 °C through the use of vitrification. 21CM was founded in 1993.
In 2004 21CM received a $900,000 grant from the U.S. National Institutes of Health (NIH) to study a preservation solution developed by the University of Rochester in New York for extending simple cold storage time of human hearts removed for transplant.
At the July 2005 annual conference of the Society for Cryobiology, 21st Century Medicine announced the vitrification of a rabbit kidney to −135 °C with their vitrification mixture. The kidney was successfully transplanted upon rewarming to a rabbit, the rabbit being euthanized on the 48th day for histological follow-up.
On February 9, 2016, 21st Century Medicine won the Small Mammal Brain Preservation Prize. On March 13, 2018, they won the Large Mammal Brain Preservation Prize. | 1 | Biochemistry |
With the development of native chemical ligation in 1994, total chemical synthesis of pairs of D-protein and L-protein enantiomers became feasible. In the first practical application to solving an unknown structure, racemic and quasi-racemic X-ray crystallography were used to determine the structure of snow flea anti-freeze protein. In the course of that work it was observed that racemic and even quasi-racemic protein mixtures dramatically facilitated the formation of diffraction quality, centrosymmetric crystals. Quasi-racemates are formed by mirror image protein molecules that are not true enantiomers but which are sufficiently similar mirror image objects to form ordered pseudo-centrosymmetric arrays.
Subsequently, pairs of racemic and quasi-racemic protein molecules prepared by total chemical synthesis have been shown to dramatically increase the rate of success in forming diffraction-quality crystals from a wide range of globular protein molecules.
Rv1738, a protein of Mycobacterium tuberculosis is the most up-regulated gene product when M. tb enters persistent dormancy. Preparations of recombinantly expressed Rv1738 L-protein resisted extensive attempts to form crystals. A racemic mixture of the chemically synthesized D-protein and L-protein forms of Rv1738 gave crystals in the centrosymmetric space group C2/c. The structure, containing L-protein and D-protein dimers in a centrosymmetric space group, revealed structural similarity to hibernation-promoting factors that can bind to ribosomes and suppress translation.
Crystallization of ubiquitin protein was successfully done using racemic crystallography. Crystallization of either D-ubiquitin or L-ubiquitin alone is difficult, whereas a racemic mixture of D-ubiquitin and L-ubiquitin was readily crystallized and diffraction quality crystals were obtained overnight in almost half the conditions tested in a standard commercial crystallization screen.
Crystallization of racemates of disulfide-containing microprotein molecules was used to determine the structure of trypsin inhibitor SFTI-1 (14 amino acids,1 disulfide), conotoxin cVc1.1 (22 amino acids, 2 disul-fides) and cyclotide kB1 (29 amino acids, 3 disulfides). Using X-ray diffraction, it was found that the racemates crystallized in the centrosymmetric spacegroups P3(bar), Pbca and P1(bar).
Interestingly, achiral "peptoid" chains were found to fold as racemic pairs and crystallize in highly preferred centrosymmetric space groups.
A high-resolution crystal structure of the racemate of a heterochiral D-protein complex with vascular endothelial growth factor A (VEGF-A). The mirror image D-protein form of VEGF-A was used in phage display to identify a 56 residue L-protein binder with nanomolar affinity; the chemically synthesized D-protein binder had the same affinity for the L-protein form of VEGF-A. A mixture of chemically synthesized proteins consisting of D-VEGF-A, L-VEGF-A, and two equivalents each of the D-protein binder and L-protein binder, gave racemic crystals in the centrosymmetric space group P21/n. The structure of this 71kDa heterochiral protein complex was solved at a resolution of 1.6 Å | 3 | Analytical Chemistry |
The Kurnakov test is sometimes used to detect transplatin in samples of the drug cisplatin. In hot aqueous solution, the cis-compound reacts with aqueous thiourea (tu) to give a deeper yellow solution, from which yellow needles of [Pt(tu)]Cl chloride deposit on cooling. The trans-compound gives a colourless solution, from which snow-white needles of trans-[Pt(tu)(NH)]Cl deposit on cooling. | 3 | Analytical Chemistry |
Ted Ellis is involved with various causes and charitable organizations including United Way, ICLS, African American Visual Arts Association, Jack and Jill of America Inc., the United Negro College Fund, Heritage Christian Academy, and various public school districts. He was the featured artist of Big Brothers Big Sisters 2012 "Houston's Big Black Tie Ball" fundraiser gala and is a partner of the Houston Child Protective Services Black History Program. | 3 | Analytical Chemistry |
Volatile acyl halides are lachrymatory because they can react with water at the surface of the eye producing hydrohalic and organic acids irritating to the eye. Similar problems can result if one inhales acyl halide vapors. In general, acyl halides (even non-volatile compounds such as tosyl chloride) are irritants to the eyes, skin and mucous membranes. | 0 | Organic Chemistry |
Dihalophospaalkenes of the general form R-P=CX, where X is Cl, Br, or I, undergo lithium-halogen exchange with organolithium reagents to yield intermediates of the form R-P=CXLi. These species then eject the corresponding lithium halide salt, LiX, to putatively give a phospha-isocyanide, which can rearrange, much in the same way as an isocyanide, to yield the corresponding phosphaalkyne. This rearrangement has been evaluated using the tools of computational chemistry, which has shown that this isomerization process should proceed very rapidly, in line with current experimental evidence showing that phosphaisonitriles are unobservable intermediates, even at –85 °C (–121 °C). | 0 | Organic Chemistry |
Transcriptome instability is a genome-wide, pre-mRNA splicing-related characteristic of certain cancers. In general, pre-mRNA splicing is dysregulated in a high proportion of cancerous cells. For certain types of cancer, like in colorectal and prostate, the number of splicing errors per cancer has been shown to vary greatly between individual cancers, a phenomenon referred to as transcriptome instability. Transcriptome instability correlates significantly with reduced expression level of splicing factor genes. Mutation of DNMT3A contributes to development of hematologic malignancies, and DNMT3A-mutated cell lines exhibit transcriptome instability as compared to their isogenic wildtype counterparts. | 1 | Biochemistry |
In a recent publication, REMS technology has received the attention of the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases ([http://www.esceo.org/ ESCEO]). In this work, all the available technologies for bone strength assessment and fracture risk estimation have been reviewed and discussed in relation to the clinical needs currently unmet. In this context, REMS has been considered a valuable approach for osteoporosis diagnosis and for fracture risk assessment, at the same time overcoming several of the current limitations acknowledged for the currently available bone health assessment technologies. One example is the work of Degennaro et al. in which a significant BMD reduction has been detected in pregnant women compared to non-pregnant women for the very first time. Several international working groups has used REMS technology for research purposes: Bojincă et al. has proven the effectiveness of REMS BMD estimates in patients affected by rheumatoid arthritis. Kirilova et al. assessed the values of lumbar spine and hip REMS-based BMD in premenopausal and postmenopausal women. In Khu et al. REMS has been used for characterizing the relationship between body mass index and bone health. The growing interest towards REMS is also demonstrated by the publication of scientific review papers focused on this technology. | 7 | Physical Chemistry |
Germanns first scholarly publications reported his undergraduate electrochemistry research under the direction of Frank Curry Mathers (1881–1973). His M.Sc. research at Wisconsin was with Joseph Howard Mathews (1881–1970). His Sc.D. thesis was published as Albert-F.-O. Germann, Révision de la densité de loxygène, contribution à la détermination de la densité lair à Genève, thèse no. 514 (Genève: Imprimerie Albert Κündig, 1913, 63 pp.); Journal de Chimie physique,' vol. 12 (1914), pp. 66–108.
Germann was on the chemistry faculties of Western Reserve University, Cleveland, Ohio (1913–1921), Stanford University, Palo Alto, California (1921–1925), and Valparaiso University, Valparaiso, Indiana (1926–1927).
At Western Reserve, he extended his doctoral research, and then began cryoscopic studies of non-aqueous systems involving boron trifluoride or phosgene. Five students conducted these experiments. Harold Simmons Booth (1891–1953) had already completed his doctoral program at Cornell University. In September 1920, Booth became a member of the Western Reserve chemistry faculty, and was to have a distinguished career as an inorganic chemist at Western Reserve. He served as department chair. He was Editor-in-Chief of the inaugural volume (in 1939) of Inorganic Syntheses, a prestigious series that continues. He was promoted to Hurlbut Professor of Chemistry in 1947. Vernon Jersey (1898–1984) had received the A.B. in chemistry from Western Reserve in 1920, and had begun graduate research with Germann on phosgene. He studied solutions of phosgene and chlorine, obtaining cryoscopic evidence for ten different compounds, including chlorine octaphosgenate. Jersey's interests evolved into biochemistry, and he earned a Ph.D. in 1935 from Western Reserve. He then joined with Germann to form Nutritional Research Associates, Inc. Wendell Phillips was beginning his senior year, and would be awarded the A.B. degree in 1921. Leland Roy Smith had received the A.B. degree in 1920, and was beginning graduate studies at Western Reserve; he received the A.M. in 1921, and received the A.M. degree from Harvard University in 1923. Marion Cleaveland (1898–1975) had received the B.A. in chemistry in 1920, and would be awarded the M.A. in 1921. She pursued doctoral studies at Columbia University from 1926 to 1928, receiving the Ph.D. Except for her time at Columbia, she taught at Western Reserve from 1921 to 1946.
At Stanford, Germann focused on phosgene as a liquid solvent. His goal was to develop a solvent-system definition of acids and bases that would apply to compounds dissolved in solvents such as phosgene.
In 1925, Germann became research director of Laboratory Products Company. Brothers William Otto Frohring (1893–1959) and Paul R. Frohring (1903–1998) "did groundbreaking laboratory work at the Laboratory Products Co. in Cleveland that produced the first ready-prepared infant formula." Recognizing that the infant-food field was becoming crowded, the Frohring brothers began to diversify research and operations. Germann was recruited to lead the company into specialty biochemicals.
Germann was granted a year leave to take an active role in Lutheranizing a faltering Valparaiso University. He became professor of chemistry at Valparaiso, head of the department of chemistry, and acting dean of the school of pharmacy. Germann was acting president of Valparaiso University from May to September, 1927. During that time, the school of pharmacy was accepted as a member of the American Association of Colleges of Pharmacy, and judged to be conforming to the Association's standards.
Back in Cleveland at Laboratory Products Company, Germann assembled his own research group. The specialty biochemical carotene was prominent in his plans. His associates were Vernon Jersey, Robert John Cross (1884–1955), Otto Ungnade (1883–1963), and Harold Barnett (1903–1956). They intended to capitalize on the vitamin revolution. Germann, Jersey, Cross, and Ungnade founded Nutritional Research Associates, Inc. in 1935 with Albert Germann President. They established research and production facilities in South Whitley, Indiana, for extraction, purification, and stabilization of Vitamin A from carrots and Vitamin E from wheat germ. | 7 | Physical Chemistry |
Stability is among the essential properties of a CRM (see definitions above), and stability assessment is accordingly required for certified reference materials. Stability under long term storage and also under conditions of transport are both expected to be assessed. "Assessment" is not synonymous with "testing"; some materials - for example, many minerals and metal alloys - may be so stable that experimental tests are not considered necessary. Other reference materials will usually undergo experimental tests of stability at some point prior to the material being distributed for sale.
Where reference materials are certified for more than one property, stability is expected to be demonstrated for every certified property.
There are two important strategies for CRM stability testing; simple real-time studies and accelerated testing. Real-time studies simply keep units of the material at their planned storage temperature for a suitable period of time and observe the material at intervals. Accelerated studies use a range of more stringent conditions, most commonly increased temperature, to test whether the material is likely to be stable over longer time scales. | 3 | Analytical Chemistry |
In a flat horizontal uniformly layered radiative field, the hemispheric fluxes, upwards and downwards, at a point, can be subtracted to yield what is often called the net flux. The net flux then has a value equal to the magnitude of the full spherical flux vector at that point, as described above. | 7 | Physical Chemistry |
This compound is prepared by oxidation of 4-aminodimethylaniline in the presence of sodium thiosulfate to give the quinonediiminothiosulfonic acid, reaction with dimethylaniline, oxidation to the indamine, and cyclization to give the thiazine:
A green electrochemical procedure, using only dimethyl-4-phenylenediamine and sulfide ions has been proposed. | 3 | Analytical Chemistry |
The active zone is present in all chemical synapses examined so far and is present in all animal species. The active zones examined so far have at least two features in common, they all have protein dense material that project from the membrane and tethers synaptic vesicles close to the membrane and they have long filamentous projections originating at the membrane and terminating at vesicles slightly farther from the presynaptic membrane. The protein dense projections vary in size and shape depending on the type of synapse examined. One striking example of the dense projection is the ribbon synapse (see below) which contains a "ribbon" of protein dense material that is surrounded by a halo of synaptic vesicles and extends perpendicular to the presynaptic membrane and can be as long as 500 nm. The glutamate synapse contains smaller pyramid like structures that extend about 50 nm from the membrane. The neuromuscular synapse contains two rows of vesicles with a long proteinaceous band between them that is connected to regularly spaced horizontal ribs extending perpendicular to the band and parallel with the membrane. These ribs are then connected to the vesicles which are each positioned above a peg in the membrane (presumably a calcium channel). Previous research indicated that the active zone of glutamatergic neurons contained a highly regular array of pyramid shaped protein dense material and indicated that these pyramids were connected by filaments. This structure resembled a geometric lattice where vesicles were guided into holes of the lattice. This attractive model has come into question by recent experiments. Recent data shows that the glutamatergic active zone does contain the dense protein material projections but these projections were not in a regular array and contained long filaments projecting about 80 nm into the cytoplasm.
There are at least five major scaffold proteins that are enriched in the active zone; UNC13B/Munc13, RIMS1 (Rab3-interacting molecule), Bassoon, Piccolo/aczonin, ELKS, and liprins-α. These scaffold proteins are thought to be the constituents of the dense pyramid like structures of the active zone and are thought to bring the synaptic vesicles into close proximity to the presynaptic membrane and the calcium channels. The protein ELKS binds to the cell adhesion protein, β-neurexin, and other proteins within the complex such as Piccolo and Bassoon. β-neurexin then binds to cell adhesion molecule, neuroligin located on the postsynaptic membrane. Neuroligin then interacts with proteins that bind to postsynaptic receptors. Protein interactions like that seen between Piccolo/ELKS/β-neurexin/neuroligin ensures that machinery that mediates vesicle fusion is in close proximity to calcium channels and that vesicle fusion is adjacent to postsynaptic receptors. This close proximity vesicle fusion and postsynaptic receptors ensures that there is little delay between the activation of the postsynaptic receptors and the release of neurotransmitters. | 1 | Biochemistry |
The radical-pair mechanism explains how a magnetic field can affect reaction kinetics by affecting electron spin dynamics. Most commonly demonstrated in reactions of organic compounds involving radical intermediates, a magnetic field can speed up a reaction by decreasing the frequency of reverse reactions. | 7 | Physical Chemistry |
The Soviet Alfa-class submarines used LBE as a coolant for their nuclear reactors throughout the Cold War.
OKB Gidropress (the Russian developers of the VVER-type Light-water reactors) has expertise in LBE reactors. The SVBR-75/100, a modern design of this type, is one example of the extensive Russian experience with this technology.
Gen4 Energy (formerly Hyperion Power Generation), a United States firm connected with Los Alamos National Laboratory, announced plans in 2008 to design and deploy a uranium nitride fueled small modular reactor cooled by lead-bismuth eutectic for commercial power generation, district heating, and desalinization. The proposed reactor, called the Gen4 Module, is planned as a 70 MW reactor of the sealed modular type, factory assembled and transported to site for installation, and transported back to factory for refueling. | 8 | Metallurgy |
Multipoles beyond the quadrupole can correct for spherical aberration and in particle accelerators the dipole bending magnets are really composed of a large number of elements with different superpositions of multipoles.
Usually the dependency is given for the kinetic energy itself depending on the power of the velocity.
So for an electrostatic lens the focal length varies with the second power of the kinetic energy,
while for a magnetostatic lens the focal length varies proportional to the kinetic energy.
And a combined quadrupole can be achromatic around a given energy.
If a distribution of particles with different kinetic energies is accelerated by a longitudinal electric field, the relative energy spread is reduced leading to less chromatic error. An example of this is in the electron microscope. | 7 | Physical Chemistry |
Strychnine total synthesis in chemistry describes the total synthesis of the complex biomolecule strychnine. The first reported method by the group of Robert Burns Woodward in 1954 is considered a classic in this research field.
At the time it formed the natural conclusion to an elaborate process of molecular structure elucidation that started with the isolation of strychnine from the beans of Strychnos ignatii by Pierre Joseph Pelletier and Joseph Bienaimé Caventou in 1818. Major contributors to the entire effort were Sir Robert Robinson with over 250 publications and Hermann Leuchs with another 125 papers in a time span of 40 years. Robinson was awarded the Nobel Prize in Chemistry in 1947 for his work on alkaloids, strychnine included.
The process of chemical identification was completed with publications in 1946 by Robinson and later confirmed by Woodward in 1947. X-ray structures establishing the absolute configuration became available between 1947 and 1951 with publications from Johannes Martin Bijvoet and J. H. Robertson
Woodward published a very brief account on the strychnine synthesis in 1954 (just 3 pages) and a lengthy one (42 pages) in 1963.
Many more methods exist and reported by the research groups of Magnus, Overman, Kuehne, Rawal, Bosch, Vollhardt, Mori, Shibasaki, Li, Fukuyama Vanderwal and MacMillan. Synthetic (+)-strychnine is also known. Racemic synthesises were published by Padwa in 2007 and in 2010 by Andrade and by Reissig.
In his 1963 publication Woodward quoted Sir Robert Robinson who said for its molecular size it is the most complex substance known. | 0 | Organic Chemistry |
Like its relative [[annulene|[12]annulene]], hexadehydro-[12]annulene is also antiaromatic. Its structure has been studied computationally via ab initio and density functional theory calculations and is confirmed to be antiaromatic. | 7 | Physical Chemistry |
In 2013, Dr. Earle McBride, a researcher studying sandstone diagenesis and the textual and compositional maturation of sand during transportation, mixed samples collected from Omaha Beach in 1988 with a blue epoxy, creating an "artificial sandstone", before slicing it into thin sections. Utilising an optical microscope and an external light source, shiny, opaque grains could be identified. Although wave action had elicited rounding on the edges of some coarser grains, the shard-like angularity and corrosion of both coarse and fine grains suggested these grains were man-made. It is believed that the roughness of said grains was imparted by microporous surfaces produced during production and corrosion products post-explosion.
This inspection, alongside tests revealing that the grains were magnetic, led McBride to conclude these grains were pieces of shrapnel. | 2 | Environmental Chemistry |
Repressor proteins bind to the DNA strand and prevent RNA polymerase from being able to attach to the DNA and synthesize mRNA. Inducers bind to repressors, causing them to change shape and preventing them from binding to DNA. Therefore, they allow transcription, and thus gene expression, to take place.
For a gene to be expressed, its DNA sequence must be copied (in a process known as transcription) to make a smaller, mobile molecule called messenger RNA (mRNA), which carries the instructions for making a protein to the site where the protein is manufactured (in a process known as translation). Many different types of proteins can affect the level of gene expression by promoting or preventing transcription. In prokaryotes (such as bacteria), these proteins often act on a portion of DNA known as the operator at the beginning of the gene. The promoter is where RNA polymerase, the enzyme that copies the genetic sequence and synthesizes the mRNA, attaches to the DNA strand.
Some genes are modulated by activators, which have the opposite effect on gene expression as repressors. Inducers can also bind to activator proteins, allowing them to bind to the operator DNA where they promote RNA transcription.
Ligands that bind to deactivate activator proteins are not, in the technical sense, classified as inducers, since they have the effect of preventing transcription. | 0 | Organic Chemistry |
When a crystal is composed of crystallites with varying lattice orientation, topographic contrast arises: In plane-wave topography, only selected crystallites will be in diffracting position, thus yielding diffracted intensity only in some parts of the image. Upon sample rotation, these will disappear, and other crystallites will appear in the new topograph as strongly diffracting. In white-beam topography, all misoriented crystallites will be diffracting simultaneously (each at a different wavelength). However, the exit angles of the respective diffracted beams will differ, leading to overlapping regions of enhanced intensity as well as to shadows in the image, thus again giving rise to contrast.
While in the case of tilted crystallites, domain walls, grain boundaries etc. orientation contrast occurs on a macroscopic scale, it can also be generated more locally around defects, e.g. due to curved lattice planes around a dislocation core. | 3 | Analytical Chemistry |
Light-harvesting complex I is permanently bound to photosystem I via the plant-specific subunit PsaG. It is made up of four proteins: Lhca1, Lhca2, Lhca3, and Lhca4, all of which belong to the LHC or chlorophyll a/b-binding family. The LHC wraps around the PS1 reaction core. | 5 | Photochemistry |
New technologies in genomics have changed the way researchers approach both basic and translational research. With approaches such as exome sequencing, it is possible to significantly enhance the data generated from individual genomes which has put forth a series of questions on how to deal with the vast amount of information. Should the individuals in these studies be allowed to have access to their sequencing information? Should this information be shared with insurance companies? This data can lead to unexpected findings and complicate clinical utility and patient benefit. This area of genomics still remains a challenge and researchers are looking into how to address these questions. | 1 | Biochemistry |
To determine the energy levels, the polygon corresponding to the cyclic annulene is desired is inscribed in the circle of radius 2β and centered at α (the energy of an isolated p orbital). The y-coordinate of the vertices of the polygon are the simple Hückel theory orbital energies. For systems with Hückel topology, the vertex is positioned at the circle bottom as suggested by Frost; for systems with Möbius topology, a polygon side is positioned at the circle bottom. In other words, for an N carbon system, the Möbius Frost circle is rotated by π/N radians compared to the Hückel system. It is seen that with one MO at the bottom and then groups of degenerate pairs, the Hückel systems will accommodate 4n + 2 electrons, following the ordinary Hückel rule. However, in contrast, the Möbius Systems have degenerate pairs of molecular orbitals starting at the circle bottom and thus will accommodate 4n electrons. For cyclic annulenes one then predicts which species will be favored. The method applies equally to cyclic reaction intermediates and transition states for pericyclic processes. | 7 | Physical Chemistry |
The test was used in forensics for many years to test for the traces of nitroglycerine. Caustic soda is used to break down sample containing nitroglycerine to produce nitrite ions.
The test involves the taking of a sample with ether and its division into two bowls. Caustic soda is added to the first bowl followed by the Griess reagent; if the solution turns pink within ten seconds, this indicates the presence of nitrites. The test itself is positive if, after adding only Griess reagent to the second bowl, the solution there remains clear.
The convictions of Judith Ward and the Birmingham Six were assisted by Frank Skuse's flawed interpretation of Griess test results. | 3 | Analytical Chemistry |
Different types of corrosion inhibitor exist. Among them, oxidizing species such as chromate () and nitrite () were the first used to re-establish the state of passivation in the protective oxide layer. In the specific case of steel, the cation being a relatively soluble species, it contributes to favor the dissolution of the oxide layer which so loses its passivity. To restore the passivity, the principle simply consists to prevent the dissolution of the oxide layer by converting the soluble divalent cation into the much less soluble trivalent cation. This approach is also at the basis of the chromate conversion coating used to passivate steel, aluminium, zinc, cadmium, copper, silver, titanium, magnesium, and tin alloys.
As hexavalent chromate is a known carcinogen, its aqueous effluents can no longer be freely discharged into the environment and its maximum concentration acceptable in water is very low.
Nitrite is also an oxidizing species and has been used as corrosion inhibitor since the 1950's.
Under the basic conditions prevailing in concrete pore water nitrite converts the relatively soluble ions into the much less soluble ions, and so protects the carbon-steel reinforcement bars by forming a new and denser layer of γ- as follows:
Corrosion inhibitors, when present in sufficient amount, can provide protection against pitting. However, too low level of them can aggravate pitting by forming local anodes. | 8 | Metallurgy |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.