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The pressure dependence of fugacity (at constant temperature) is given by
and is always positive.
The temperature dependence at constant pressure is
where is the change in molar enthalpy as the gas expands, liquid vaporizes, or solid sublimates into a vacuum. Also, if the pressure is , then
Since the temperature and entropy are positive, decreases with increasing temperature. | 7 | Physical Chemistry |
Each of the groups in this section has two cell structure diagrams, which are to be interpreted as follows (it is the shape that is significant, not the colour):
On the right-hand side diagrams, different equivalence classes of symmetry elements are colored (and rotated) differently.
The brown or yellow area indicates a fundamental domain, i.e. the smallest part of the pattern that is repeated.
The diagrams on the right show the cell of the lattice corresponding to the smallest translations; those on the left sometimes show a larger area. | 3 | Analytical Chemistry |
Hypothiocyanite is the anion [OSCN] and the conjugate base of hypothiocyanous acid (HOSCN). It is an organic compound part of the thiocyanates as it contains the functional group SCN. It is formed when an oxygen is singly bonded to the thiocyanate group. Hypothiocyanous acid is a fairly weak acid; its acid dissociation constant (pK) is 5.3.
Hypothiocyanite is formed by peroxidase catalysis of hydrogen peroxide and thiocyanate:
: HO + SCN → OSCN + HO | 1 | Biochemistry |
Toxicity assessment/toxicology by metabolic profiling (especially of urine or blood plasma samples) detects the physiological changes caused by toxic insult of a chemical (or mixture of chemicals). In many cases, the observed changes can be related to specific syndromes, e.g. a specific lesion in liver or kidney. This is of particular relevance to pharmaceutical companies wanting to test the toxicity of potential drug candidates: if a compound can be eliminated before it reaches clinical trials on the grounds of adverse toxicity, it saves the enormous expense of the trials.
For functional genomics, metabolomics can be an excellent tool for determining the phenotype caused by a genetic manipulation, such as gene deletion or insertion. Sometimes this can be a sufficient goal in itself—for instance, to detect any phenotypic changes in a genetically modified plant intended for human or animal consumption. More exciting is the prospect of predicting the function of unknown genes by comparison with the metabolic perturbations caused by deletion/insertion of known genes. Such advances are most likely to come from model organisms such as Saccharomyces cerevisiae and Arabidopsis thaliana. The Cravatt laboratory at the Scripps Research Institute has recently applied this technology to mammalian systems, identifying the N-acyltaurines as previously uncharacterized endogenous substrates for the enzyme fatty acid amide hydrolase (FAAH) and the monoalkylglycerol ethers (MAGEs) as endogenous substrates for the uncharacterized hydrolase KIAA1363.
Metabologenomics is a novel approach to integrate metabolomics and genomics data by correlating microbial-exported metabolites with predicted biosynthetic genes. This bioinformatics-based pairing method enables natural product discovery at a larger-scale by refining non-targeted metabolomic analyses to identify small molecules with related biosynthesis and to focus on those that may not have previously well known structures.
Fluxomics is a further development of metabolomics. The disadvantage of metabolomics is that it only provides the user with abundances or concentrations of metabolites, while fluxomics determines the reaction rates of metabolic reactions and can trace metabolites in a biological system over time.
Nutrigenomics is a generalised term which links genomics, transcriptomics, proteomics and metabolomics to human nutrition. In general, in a given body fluid, a metabolome is influenced by endogenous factors such as age, sex, body composition and genetics as well as underlying pathologies. The large bowel microflora are also a very significant potential confounder of metabolic profiles and could be classified as either an endogenous or exogenous factor. The main exogenous factors are diet and drugs. Diet can then be broken down to nutrients and non-nutrients. Metabolomics is one means to determine a biological endpoint, or metabolic fingerprint, which reflects the balance of all these forces on an individual's metabolism. Thanks to recent cost reductions, metabolomics has now become accessible for companion animals, such as pregnant dogs.
Plant metabolomics is designed to study the overall changes in metabolites of plant samples and then conduct deep data mining and chemometric analysis. Specialized metabolites are considered components of plant defense systems biosynthesized in response to biotic and abiotic stresses. Metabolomics approaches have recently been used to assess the natural variance in metabolite content between individual plants, an approach with great potential for the improvement of the compositional quality of crops. | 1 | Biochemistry |
Several fluorescent protein exist in nature, but the most important one as a research tool is Green Fluorescent Protein (GFP) from the jellyfish Aequorea victoria, which spontaneously fluoresces upon folding via specific serine-tyrosine-glycine residues. The benefit that GFP and other fluorescent proteins have over organic dyes or quantum dots is that they can be expressed exogenously in cells alone or as a fusion protein, a protein that is created by ligating the fluorescent gene (e.g., GFP) to another gene and whose expression is driven by a housekeeping gene promoter or another specific promoter. This approach allows fluorescent proteins to be used as reporters for any number of biological events, such as sub-cellular localization and expression patterns.
A variant of GFP is naturally found in corals, specifically the Anthozoa, and several mutants have been created to span the visible spectra and fluoresce longer and more stably.
Other proteins are fluorescent but require a fluorophore cofactor, and hence can only be used in vitro; these are often found in plants and algae (phytofluors, phycobiliprotein such as allophycocyanin). | 1 | Biochemistry |
Besides simple strand displacement schemes, DNA computers have also been constructed using the concept of toehold exchange. In this system, an input DNA strand binds to a sticky end, or toehold, on another DNA molecule, which allows it to displace another strand segment from the molecule. This allows the creation of modular logic components such as AND, OR, and NOT gates and signal amplifiers, which can be linked into arbitrarily large computers. This class of DNA computers does not require enzymes or any chemical capability of the DNA. | 1 | Biochemistry |
Elementary reaction steps with order 3 (called ternary reactions) are rare and unlikely to occur. However, overall reactions composed of several elementary steps can, of course, be of any (including non-integer) order.
Here stands for concentration in molarity (mol · L), for time, and for the reaction rate constant. The half-life of a first-order reaction is often expressed as t = 0.693/k (as ln(2)≈0.693). | 7 | Physical Chemistry |
Out of the available endocrine-disrupting compounds looked at, flutamide has a notable effect on anogenital distance in rats.) | 4 | Stereochemistry |
The preferred geometries of the benzene dimer have been modeled at a high level of theory with MP2-R12/A computations and very large counterpoise-corrected aug-cc-PVTZ basis sets. The two most stable conformations are the parallel displaced and T-shaped, which are essentially isoenergetic. In contrast, the sandwich configuration maximizes overlap of the pi system, which destabilizes the interaction. The sandwich configuration represents an energetic saddle point, which is consistent with the relative rarity of this configuration in x-ray crystal data.
The relative binding energies of these three geometric configurations of the benzene dimer can be explained by a balance of quadrupole/quadrupole and London dispersion forces. While benzene does not have a dipole moment, it has a strong quadrupole moment. The local C–H dipole means that there is positive charge on the atoms in the ring and a correspondingly negative charge representing an electron cloud above and below the ring. The quadrupole moment is reversed for hexafluorobenzene due to the electronegativity of fluorine. The benzene dimer in the sandwich configuration is stabilized by London dispersion forces but destabilized by repulsive quadrupole/quadrupole interactions. By offsetting one of the benzene rings, the parallel displaced configuration reduces these repulsive interactions and is stabilized. The large polarizability of aromatic rings lead to dispersive interactions as major contribution to stacking effects. These play a major role for interactions of nucleobases e.g. in DNA. The T-shaped configuration enjoys favorable quadrupole/quadrupole interactions, as the positive quadrupole of one benzene ring interacts with the negative quadrupole of the other. The benzene rings are furthest apart in this configuration, so the favorable quadrupole/quadrupole interactions evidently compensate for diminished dispersion forces. | 6 | Supramolecular Chemistry |
As reacts with water it can be used to dehydrate various metal chloride hydrates, such magnesium chloride (), aluminium chloride (), and iron(III) chloride (). This conversion involves treatment with refluxing thionyl chloride and follows the following general equation: | 0 | Organic Chemistry |
Assume that a beam of light enters a material sample. Define as an axis parallel to the direction of the beam. Divide the material sample into thin slices, perpendicular to the beam of light, with thickness sufficiently small that one particle in a slice cannot obscure another particle in the same slice when viewed along the direction. The radiant flux of the light that emerges from a slice is reduced, compared to that of the light that entered, by where is the (Napierian) attenuation coefficient, which yields the following first-order linear, ordinary differential equation:
The attenuation is caused by the photons that did not make it to the other side of the slice because of scattering or absorption. The solution to this differential equation is obtained by multiplying the integrating factorthroughout to obtainwhich simplifies due to the product rule (applied backwards) to
Integrating both sides and solving for for a material of real thickness , with the incident radiant flux upon the slice and the transmitted radiant flux givesand finally
Since the decadic attenuation coefficient is related to the (Napierian) attenuation coefficient by we also have
To describe the attenuation coefficient in a way independent of the number densities of the attenuating species of the material sample, one introduces the attenuation cross section has the dimension of an area; it expresses the likelihood of interaction between the particles of the beam and the particles of the species in the material sample:
One can also use the molar attenuation coefficients where is the Avogadro constant, to describe the attenuation coefficient in a way independent of the amount concentrations of the attenuating species of the material sample: | 7 | Physical Chemistry |
This theory is a little similar to the Lock and Key Theory, but at this time the active site is preprogrammed to bind perfectly to substrate in transition state rather than in ground state. The formation of transition state within the solution requires a large amount of energy to relocate solvent molecules and the reaction is slowed. So the active site can substitute solvent molecules and surround the substrates to minimize the counterproductive effect imposed by the solution. The presence of charged groups with the active site will attract substrates and ensure electrostatic complementarity. | 1 | Biochemistry |
Paul Walden (; ; ; 26 July 1863 – 22 January 1957) was a Russian, Latvian and German chemist known for his work in stereochemistry and history of chemistry. In particular, he discovered the Walden rule, he invented the stereochemical reaction known as Walden inversion and synthesized the first room-temperature ionic liquid, ethylammonium nitrate. | 4 | Stereochemistry |
For DNB type of boiling crisis, the flow is characterized by creeping vapor fluid between liquid and the wall. On top of the convective heat transfer, radiation heat transfer contributes to the heat transfer. After the dryout, the flow regime is shifted from an inverted annular to mist flow. | 7 | Physical Chemistry |
Ruthenium-iridium nanosized corals (RuIr-NC) are electrodes consisting of nanosized anisotropic ruthenium-iridium sheets for efficient electrolysis of water in acid discovered in the Kyoto University.
The RuIr-NC were discovered unintentionally at the Kyoto University, but then investigated and refined for the purpose of efficient electrolysis of water in acid and found to have very promising qualities in terms of performance and durability.
As of 2021 the researchers at Kyoto University report their RuIr-NC are composed of 94% ruthenium and 6% iridium with the exposed hexagonal atomic arrangement corresponding to a hexagonal closed-packed (HCP) crystalline lattice plane crystal structure. The nanosheets take the form of 3 nm thick sheets with a mean diameter of 57 ± 7 nm. The researchers found them suitable for use as both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) electrodes.
Their water splitting cell using RuIr-NC as both OER and HER electrodes is able to achieve 10 mA cm at 1.485 V for 120 h without noticeable degradation. They report that, of the electrodes they evaluated for water electrolysis in acid, the RuIr-NC shows the highest intrinsic activity and stability.
The RuIr-NC is obtained by adding a mixture of RuCl3·nH2O and H2IrCl6 aqueous solutions to triethylene glycol solution containing polyvinylpyrrolidone at 230 °C.
The research team at Kyoto University published their work in February 2021 and presented it at the Chemical Society of Japan 101. General Meeting in March 2021. | 7 | Physical Chemistry |
Donetsk Metallurgical Plant also called Donetsk Iron and Steel Works is an enterprise of Donetsk, Ukraine. It is a ferrous metallurgy enterprise that is located in the Leninskyi district of Donetsk. | 8 | Metallurgy |
The LHCG receptor's main function is the regulation of steroidogenesis. This is accomplished by increasing the intracellular levels of the enzyme cholesterol side chain cleaving enzyme, a member of the cytochrome P450 family. This leads to increased conversion of cholesterol into androgen precursors required to make many steroid hormones, including testosterone and estrogens. | 1 | Biochemistry |
Evaporation suppressing monolayers are materials that when applied to the air/water interface, will spread (or self-assemble) and form a thin film across the surface of the water. The purpose of these materials is to reduce evaporative water loss from dams and reservoirs. | 7 | Physical Chemistry |
A Gilman reagent is a diorganocopper compound with the formula Li[CuR], where R is an alkyl or aryl. They are colorless solids. | 0 | Organic Chemistry |
The Gibbs adsorption isotherm for multicomponent systems is an equation used to relate the changes in concentration of a component in contact with a surface with changes in the surface tension, which results in a corresponding change in surface energy. For a binary system, the Gibbs adsorption equation in terms of surface excess is:
where
: is the surface tension,
: is the surface excess concentration of component i,
: is the chemical potential of component i. | 7 | Physical Chemistry |
* Wolfram Saenger, Principles of Nucleic Acid Structure, 1984, Springer-Verlag New York Inc.
* Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter Molecular Biology of the Cell, 2007, . Fourth edition is available online through the NCBI Bookshelf: [https://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=mboc4 link]
* Jeremy M Berg, John L Tymoczko, and Lubert Stryer, Biochemistry 5th edition, 2002, W H Freeman. Available online through the NCBI Bookshelf: [https://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=stryer link] | 1 | Biochemistry |
The Weismann barrier, proposed by August Weismann in 1892, distinguishes between the "immortal" germ cell lineages (the germ plasm) which produce gametes and the "disposable" somatic cells. Hereditary information moves only from germline cells to somatic cells (that is, somatic mutations are not inherited). This, before the discovery of the role or structure of DNA, does not predict the central dogma, but does anticipate its gene-centric view of life, albeit in non-molecular terms. | 1 | Biochemistry |
Seipin is a homo-oligomeric integral membrane protein in the endoplasmic reticulum (ER) that concentrates at junctions with cytoplasmic lipid droplets (LDs). Alternatively, seipin can be referred to as Berardinelli–Seip congenital lipodystrophy type 2 protein (BSCL2), and it is encoded by the corresponding gene of the same name, i.e. BSCL2. At protein level, seipin is expressed in cortical neurons in the frontal lobes, as well as motor neurons in the spinal cord. It is highly expressed in areas like the brain, testis and adipose tissue. Seipin's function is still unclear but it has been localized close to lipid droplets, and cells knocked out in seipin have anomalous droplets. Hence, recent evidence suggests that seipin plays a crucial role in lipid droplet biogenesis. | 1 | Biochemistry |
As shrink fitting requires a uniform heating of the component to be expanded, it is best to try to use the lowest practical frequency when approaching heating for shrink fitting. Again the exception to this rule can be when removing parts from shafts. | 8 | Metallurgy |
In an alkene ring that does not contain an oxygen atom, any large substituent prefers to be in an equatorial position, in order to minimize steric effects. It has been observed in rings containing oxocarbenium ions that electronegative substituents prefer the axial or pseudo-axial positions. When the electronegative atom is in the axial position, its electron density can be donated through space to the positively charged oxygen atom in the ring. This electronic interaction stabilizes the axial conformation. Hydroxyl groups, ethers and halogens are examples of substituents that exhibit this phenomenon. Stereoelectronic effects must be taken into consideration when determining the lowest energy conformation in the analysis for nucleophilic addition to an oxocarbenium ion. | 0 | Organic Chemistry |
Semiconductor detectors, also called solid-state detectors, are fundamentally different from scintillation detectors: They rely on detection of the charge carriers (electrons and holes) generated in semiconductors by energy deposited by gamma ray photons.
In semiconductor detectors, an electric field is applied to the detector volume. An electron in the semiconductor is fixed in its valence band in the crystal until a gamma ray interaction provides the electron enough energy to move to the conduction band. Electrons in the conduction band can respond to the electric field in the detector, and therefore move to the positive contact that is creating the electrical field. The gap created by the moving electron is called a "hole", and is filled by an adjacent electron. This shuffling of holes effectively moves a positive charge to the negative contact. The arrival of the electron at the positive contact and the hole at the negative contact produces the electrical signal that is sent to the preamplifier, the MCA, and on through the system for analysis. The movement of electrons and holes in a solid-state detector is very similar to the movement of ions within the sensitive volume of gas-filled detectors such as ionization chambers.
Common semiconductor-based detectors include germanium, cadmium telluride, and cadmium zinc telluride.
Germanium detectors provide significantly improved energy resolution in comparison to sodium iodide detectors, as explained in the preceding discussion of resolution. Germanium detectors produce the highest resolution commonly available today. However, a disadvantage is the requirement of cryogenic temperatures for the operation of germanium detectors, typically by cooling with liquid nitrogen. | 7 | Physical Chemistry |
A Stöber-like process has been used to produce monodisperse carbon spheres using resorcinol-formaldehyde resin in place of a silica precursor. The modified process allows production of carbon spheres with smooth surfaces and a diameter ranging from 200 to 1000 nm. Unlike the silica-based Stöber process, this reaction is completed at neutral pH and ammonia has a role in stabilizing the individual carbon particles by preventing self-adhesion and aggregation, as well as acting as a catalyst. | 7 | Physical Chemistry |
In 1877, Köhler and Michaelis claimed that they synthesized the first isolated diphosphene (PhP=PPh). However, the molecular weight determination and X-ray crystallographic analysis later proved that this "diphosphene" only had a P-P single bond. Then the research to diphosphenes kept silent over almost 120 years until Masaaki Yoshifuji and his coworkers isolated an unprecedented diphosphene, bis(2,4,6-tri-tert-butylphenyl)diphosphene, in 1981. They first synthesized the (2,4,6-tri-tert-butylphenyl)phosphorus dichloride by adding phosphorus trichloride to (2,4,6-tri-butylphenyl)lithium that was the product of the lithium and halogen exchange. The phosphorus dichloride dimerized to a diphosphene after magnesium extracted two chlorine atoms from (2,4,6-tri-tert-butylphenyl)phosphorus dichloride. The P-P bond distance is 2.034 Å, which is much shorter than the average bond length in (CHP) (2.217 Å) and (CHP) (2.237 Å), indicating its double bond character. This research was a milestone in diphosphene studies because the product here was the first reported compound that had the isolated localized P=P bond. Moreover, this bulky structure provided a instructive pathway for the future synthesis of diphosphenes. | 0 | Organic Chemistry |
Sonogashira couplings are employed in a wide array of synthetic reactions, primarily due to their success in facilitating the following challenging transformations: | 0 | Organic Chemistry |
This gene product is a component of a nucleolar small nuclear ribonucleoprotein (snRNP) particle thought to participate in the first step in processing pre-ribosomal (r)RNA. It is associated with the U3, U8, and U13 small nucleolar RNAs and is located in the dense fibrillar component (DFC) of the nucleolus. The encoded protein contains an N-terminal repetitive domain that is rich in glycine and arginine residues, like fibrillarins in other species. Its central region resembles an RNA-binding domain and contains an RNP consensus sequence. Antisera from approximately 8% of humans with the autoimmune disease scleroderma recognize fibrillarin.
Fibrillarin is a component of several ribonucleoproteins including a nucleolar small nuclear ribonucleoprotein (SnRNP) and one of the two classes of small nucleolar ribonucleoproteins (snoRNPs). SnRNAs function in RNA splicing while snoRNPs function in ribosomal RNA processing.
Fibrillarin is associated with U3, U8 and U13 small nuclear RNAs in mammals and is similar to the yeast NOP1 protein. Fibrillarin has a well conserved sequence of around 320 amino acids, and contains 3 domains, an N-terminal Gly/Arg-rich region; a central domain resembling other RNA-binding proteins and containing an RNP-2-like consensus sequence; and a C-terminal alpha-helical domain. An evolutionarily related pre-rRNA processing protein, which lacks the Gly/Arg-rich domain, has been found in various archaea.
A study by Schultz et al. indicated that the K-turn binding 15.5-kDa protein (called Snu13 in yeast) interacts with spliceosome proteins hPRP31, hPRP3, hPRP4, CYPH and the small nucleolar ribonucleoproteins NOP56, NOP58, and fibrillarin. The 15.5-kDa protein has sequence similarity to other RNA-binding proteins such as ribosomal proteins S12, L7a, and L30 and the snoRNP protein NHP2. The U4/U6 snRNP contains 15.5-kDa protein. The 15.5-kDa protein also exists in a ribonucleoprotein complex that binds the U3 box B/C motif. The 15.5-kDa protein also exists as one of the four core proteins of the C/D small nucleolar ribonucleoprotein that mediates methylation of pre-ribosomal RNAs.
Structural evidence supporting the idea that fibrillarin is the snoRNA methyltransferase has been reviewed. | 1 | Biochemistry |
Bacteria of the genera Chromobacterium, Janthinobacterium, and Pseudoalteromonas produce a toxic secondary metabolite, violacein, to deter protozoan predation. Violacein is released when bacteria are consumed, killing the protozoan. Another bacteria, Pseudomonas aeruginosa, aggregates into quorum sensing biofilms which may aid the coordinated release of toxins to protect against predation by protozoans. Flagellates were allowed to grow and were present in a biofilm of P. aeruginosa grown for three days, but no flagellates were detected after seven days. This suggests that concentrated and coordinated release of extracellular toxins by biofilms has a greater effect than unicellular excretions. Bacterial growth is inhibited not only by bacterial toxins, but also by secondary metabolites produced by fungi as well. The most well-known of these, first discovered and published by Alexander Fleming in 1929, described the antibacterial properties of a "mould juice" isolated from Penicillium notatum. He named the substance penicillin, and it became the worlds first broad-spectrum antibiotic. Many fungi are either pathogenic saprophytic, or live within plants without harming them as endophytes, and many of these have been documented to produce chemicals with antagonistic effects against a variety of organisms, including fungi, bacteria, and protozoa. Studies of coprophilous fungi have found antifungal agents which reduce the fitness of competing fungi. In addition, sclerotia of Aspergillus flavus contained a number of previously unknown aflavinines which were much more effective at reducing predation by the fungivorous beetle, Carpophilus hemipterus, than aflatoxins which A. flavus also produced and it has been hypothesized that ergot alkaloids, mycotoxins produced by Claviceps purpurea', may have evolved to discourage herbivory of the host plant. | 1 | Biochemistry |
Willauer started researching biphasic systems and phase transitions after graduating from Berry College. In 1998 she studied aqueous biphasic systems (ABS) for the potential of recapturing valuable dyes from textile manufacturing effluent. She investigated ions and catalysts.
In the 2000s, Willauer began studying methods for extracting CO and H from seawater, for the purpose of reacting these molecules into hydrocarbons by using the Fischer–Tropsch process. She also investigated modified iron (Fe) catalysts and studied zeolite (nanoporous aluminosilicate) catalyst supports for recombining these molecules into jet fuel.
Previous studies had concluded that CO, under the form of the bicarbonate anion (HCO) dominant (96% mole fraction) in the seawater inorganic carbon species could not be economically removed from seawater. However, by acidifying seawater by means of an adapted electrolysis cell with cation permeable membranes (dubbed a three-chambered electrochemical acidification cell), it is possible to economically convert HCO into CO at a pH lower than 6 and to increase the extraction yield. In January 2011, the NRL installed a prototype of seawater electrolysis cell at Naval Air Station Key West in Florida.
In 2017, Willauer et al. were granted a patent for a extraction device from seawater, in the form of an electrolytic-cation exchange module (E-CEM). The E-CEM is seen as a "key step" in the production of synthetic fuel from seawater. Other researchers named in the patent are Felice DiMascio, Dennis R. Hardy, Jeffrey Baldwin, Matthew Bradley, James Morris, Ramagopal Ananth and Frederick W. Williams. | 3 | Analytical Chemistry |
Diphenylamine may be used as a wet chemical test for the presence of the nitrate ion. In this test, a solution of diphenylamine and ammonium chloride in sulfuric acid is used. In the presence of nitrates, diphenylamine is oxidized, giving a blue coloration. This reaction has been used to test for organic nitrates as well, and has found use in gunshot residue kits detecting nitroglycerine and nitrocellulose. | 3 | Analytical Chemistry |
Some of the most common amine protecting groups, such as BOC, FMOC, benzyl chloroformate and trichloroethyl chloroformate are carbamates. | 0 | Organic Chemistry |
Tuberculostearic acid (D-10-Methylstearic acid) is a saturated fatty acid that is known to be produced by Mycobacterium spp. and two species of Streptomyces. It is formed from the precursor oleic acid (a monounsaturated fatty acid). After oleic acid is esterified to a phospholipid, S-adenosyl-methionine donates a methyl group to the double bond of oleic acid. This methylation reaction forms the intermediate 10-methylene-octadecanoyal. Successive reduction of the residue, with NADPH as a cofactor, results in 10-methylstearic acid | 1 | Biochemistry |
Surfactants are classified into four main types, each with different properties and applications: anionic, cationic, nonionic and zwitterionic (or amphoteric). Anionic surfactants are compounds that contain an anionic polar group. Examples of anionic surfactants include sodium dodecyl sulfate and dioctyl sodium sulfosuccinate. Included in this class of surfactants are sodium alkylcarboxylates (soaps). Cationic surfactats are similar in nature to anionic surfactants, except the surfactant molecules carry a positive charge at the hydrophilic portion. Many of these compounds are quaternary ammonium salts, as well as cetrimonium bromide (CTAB). Non-ionic surfactants are non-charged and together with anionic surfactants make up the majority of oil-dispersant formulations. The hydrophilic portion of the surfactant contains polar functional groups, such as -OH or -NH. Zwitterionic surfactants are the most expensive, and are used for specific applications. These compounds have both positively and negatively charged components. An example of a zwitterionic compound is phosphatidylcholine, which as a lipid is largely insoluble in water. | 2 | Environmental Chemistry |
Dexbrompheniramine is an antihistamine with anticholinergic properties used to treat allergic conditions such as hay fever or urticaria. It is the pharmacologically active dextrorotatory isomer of brompheniramine. It was formerly marketed in combination with pseudoephedrine under the name Drixoral in the US and Canada. It is an alkylamine antihistamine.
Dexbrompheniramine is a first generation antihistamine that reduces the effects of the neurotransmitter histamine in the body; sneezing, itching, watery eyes, and runny nose. | 4 | Stereochemistry |
The chemical potential, , of a substance B in an ideal mixture of liquids or an ideal solution is given by
where μ is the chemical potential of a pure substance , and is the mole fraction of the substance in the mixture.
This is generalised to include non-ideal behavior by writing
when is the activity of the substance in the mixture,
where is the activity coefficient, which may itself depend on . As approaches 1, the substance behaves as if it were ideal. For instance, if ≈ 1, then Raoults law is accurate. For > 1 and < 1, substance B shows positive and negative deviation from Raoults law, respectively. A positive deviation implies that substance B is more volatile.
In many cases, as goes to zero, the activity coefficient of substance B approaches a constant; this relationship is Henry's law for the solvent. These relationships are related to each other through the Gibbs–Duhem equation.
Note that in general activity coefficients are dimensionless.
In detail: Raoult's law states that the partial pressure of component B is related to its vapor pressure (saturation pressure) and its mole fraction in the liquid phase,
with the convention
In other words: Pure liquids represent the ideal case.
At infinite dilution, the activity coefficient approaches its limiting value, . Comparison with Henry's law,
immediately gives
In other words: The compound shows nonideal behavior in the dilute case.
The above definition of the activity coefficient is impractical if the compound does not exist as a pure liquid. This is often the case for electrolytes or biochemical compounds. In such cases, a different definition is used that considers infinite dilution as the ideal state:
with
and
The symbol has been used here to distinguish between the two kinds of activity coefficients. Usually it is omitted, as it is clear from the context which kind is meant. But there are cases where both kinds of activity coefficients are needed and may even appear in the same equation, e.g., for solutions of salts in (water + alcohol) mixtures. This is sometimes a source of errors.
Modifying mole fractions or concentrations by activity coefficients gives the effective activities of the components, and hence allows expressions such as Raoult's law and equilibrium constants to be applied to both ideal and non-ideal mixtures.
Knowledge of activity coefficients is particularly important in the context of electrochemistry since the behaviour of electrolyte solutions is often far from ideal, due to the effects of the ionic atmosphere. Additionally, they are particularly important in the context of soil chemistry due to the low volumes of solvent and, consequently, the high concentration of electrolytes. | 7 | Physical Chemistry |
Hydrogen is a chemical element with an atomic number of 1. It has just one proton and one electron. Deuterium is the heavier naturally occurring, non-radioactive, stable isotope of hydrogen. Deuterium contains one proton, one electron, and a neutron, effectively doubling the mass of the deuterium isotope without changing its properties significantly. Substituting deuterium for hydrogen yields deuterated compounds that are similar in size and shape to hydrogen-based compounds.
One of the most pernicious and irreparable types of oxidative damage inflicted by reactive oxygen species (ROS) upon biomolecules involves the carbon-hydrogen bond cleavage (hydrogen abstraction). In theory, replacing hydrogen with deuterium "reinforces" the bond due to the kinetic isotope effect, and such reinforced biomolecules taken up by the body will be more resistant to ROS.
The deuterium-reinforced lipids resists the non-enzymatic lipid peroxidation (LPO) through isotope effect — a non-antioxidant based mechanism that protects mitochondrial, neuronal and other lipid membranes, thereby greatly reducing the levels of numerous LPO-derived toxic products such as reactive carbonyls.
Treating cells with deuterium-containing PUFAs (D-PUFAs) can prevent of ferroptosis. This treatment stops the autoxidation process through the kinetic isotope effect (KIE), as shown in Table 1 [66]. The efficacy of D-PUFAs in preventing ferroptosis has been demonstrated in models induced by erastin and RSL3, and has shown promising results in various disease models, especially those related to neurodegenerative disorders. | 1 | Biochemistry |
EQCM can be used to monitor the chemical reaction occurring on the electrode, which offers the optimized reaction condition by comparing the influence factors during the synthesis process. Some previous work has already investigated the polymerization process and charge transport properties, polymer film growth on gold electrode surface, and polymerization process of polypyrrole and its derivatives. EQCM was used to study electro-polymerization process and doping/de-doping properties of polyaniline film on gold electrode surface as well. To investigate the electrosynthesis process, sometimes it is necessary to combine other characterization technologies, such as using FTIR and EQCM to study the effect of different conditions on the formation of poly(3,4-ethylenedioxythiophene) film structure, and using EQCM, together with AFM, FTIR, EIS, to investigate the film formation process in the alkyl carbonate/lithium salt electrolyte solution on precious metal electrodes surfaces. | 7 | Physical Chemistry |
Lipid profiling is a targeted metabolomics platform that provides a comprehensive analysis of lipid species within a cell or tissue. Profiling based on electrospray ionization tandem mass spectrometry (ESI-MS/MS) is capable of providing quantitative data and is adaptable to high throughput analyses. The powerful approach of transgenics, namely deletion and/or overexpression of a gene product coupled with lipidomics, can give valuable insights into the role of biochemical pathways. Lipid profiling techniques have also been applied to plants and microorganisms such as yeast. A combination of quantitative lipidomic data in conjunction with the corresponding transcriptional data (using gene-array methods) and proteomic data (using tandem MS) enables a systems biology approach to a more in-depth understanding of the metabolic or signaling pathways of interest. | 1 | Biochemistry |
Diebold holds dual citizenship of both Austria and the US. She is married to Gerhard Piringer with whom she has two sons, Thomas (born 1996) and Niklas (born 1999). | 7 | Physical Chemistry |
Nitridoiron and imidoiron compounds are closely related to iron-dinitrogen chemistry. The biological significance of nitridoiron(V) porphyrins has been reviewed. A widely applicable method to generate high-valent nitridoiron species is the thermal or photochemical oxidative elimination of molecular nitrogen from an azide complex. | 7 | Physical Chemistry |
Penicillamine is a chiral drug with one chiral center and exists as a pair of enantiomers. (S)-penicillamine is the eutomer with the desired antiarthritic activity while the (R)-penicillamine is extremely toxic. | 4 | Stereochemistry |
Although they are classically thought of working only together, GPCRs may signal through G-protein-independent mechanisms, and heterotrimeric G-proteins may play functional roles independent of GPCRs. GPCRs may signal independently through many proteins already mentioned for their roles in G-protein-dependent signaling such as β-arrs, GRKs, and Srcs. Such signaling has been shown to be physiologically relevant, for example, β-arrestin signaling mediated by the chemokine receptor CXCR3 was necessary for full efficacy chemotaxis of activated T cells. In addition, further scaffolding proteins involved in subcellular localization of GPCRs (e.g., PDZ-domain-containing proteins) may also act as signal transducers. Most often the effector is a member of the MAPK family. | 1 | Biochemistry |
For an incident plane wave at a single frequency (and the angular frequency ) on a crystal, the diffracted waves from the crystal can be thought as the sum of outgoing plane waves from the crystal. (In fact, any wave can be represented as the sum of plane waves, see Fourier Optics.) The incident wave and one of plane waves of the diffracted wave are represented as
where and are wave vectors for the incident and outgoing plane waves, is the position vector, and is a scalar representing time, and and are initial phases for the waves. For simplicity we take waves as scalars here, even though the main case of interest is an electromagnetic field, which is a vector. We can think these scalar waves as components of vector waves along a certain axis (x, y, or z axis) of the Cartesian coordinate system.
The incident and diffracted waves propagate through space independently, except at points of the lattice of the crystal, where they resonate with the oscillators, so the phases of these waves must coincide. At each point of the lattice , we have
or equivalently, we must have
for some integer , that depends on the point . Since this equation holds at , at some integer . So
(We still use instead of since both the notations essentially indicate some integer.) By rearranging terms, we get
Now, it is enough to check that this condition is satisfied at the primitive vectors (which is exactly what the Laue equations say), because, at any lattice point , we have
where is the integer . The claim that each parenthesis, e.g. , is to be a multiple of (that is each Laue equation) is justified since otherwise does not hold for any arbitrary integers .
This ensures that if the Laue equations are satisfied, then the incoming and outgoing (diffracted) wave have the same phase at each point of the crystal lattice, so the oscillations of atoms of the crystal, that follows the incoming wave, can at the same time generate the outgoing wave at the same phase of the incoming wave. | 3 | Analytical Chemistry |
The hypothesis was postulated by the Nobel laureate Otto Heinrich Warburg in 1924. He hypothesized that cancer, malignant growth, and tumor growth are caused by the fact that tumor cells mainly generate energy (as e.g., adenosine triphosphate / ATP) by non-oxidative breakdown of glucose (a process called glycolysis). This is in contrast to healthy cells which mainly generate energy from oxidative breakdown of pyruvate. Pyruvate is an end-product of glycolysis, and is oxidized within the mitochondria. Hence, according to Warburg, carcinogenesis stems from the lowering of mitochondrial respiration. Warburg regarded the fundamental difference between normal and cancerous cells to be the ratio of glycolysis to respiration; this observation is also known as the Warburg effect.
In the somatic mutation theory of cancer, malignant proliferation is caused by mutations and altered gene expression, in a process called malignant transformation, resulting in an uncontrolled growth of cells. The metabolic difference observed by Warburg adapts cancer cells to the hypoxic (oxygen-deficient) conditions inside solid tumors, and results largely from the same mutations in oncogenes and tumor suppressor genes that cause the other abnormal characteristics of cancer cells. Therefore, the metabolic change observed by Warburg is not so much the cause of cancer, as he claimed, but rather, it is one of the characteristic effects of cancer-causing mutations.
Warburg articulated his hypothesis in a paper entitled The Prime Cause and Prevention of Cancer which he presented in lecture at the meeting of the Nobel-Laureates on June 30, 1966 at Lindau, Lake Constance, Germany. In this speech, Warburg presented additional evidence supporting his theory that the elevated anaerobiosis seen in cancer cells was a consequence of damaged or insufficient respiration. Put in his own words, "the prime cause of cancer is the replacement of the respiration of oxygen in normal body cells by a fermentation of sugar."
The body often kills damaged cells by apoptosis, a mechanism of self-destruction that involves mitochondria, but this mechanism fails in cancer cells where the mitochondria are shut down. The reactivation of mitochondria in cancer cells restarts their apoptosis program. | 1 | Biochemistry |
"Methylmercury" is a shorthand for the hypothetical "methylmercury cation", sometimes written methylmercury(1+) cation or methylmercury(II) cation. This functional group is composed of a methyl group bonded to an atom of mercury. Its chemical formula is (sometimes written as ).The Methylmercury compound has an overall charge of +1, with Hg in the +2 oxidation state. Methylmercury exists as a substituent in many complexes of the type (L = Lewis base) and MeHgX (X = anion).
As a positively charged ion, it readily combines with anions such as chloride (), hydroxide () and nitrate (). It has particular affinity for sulfur-containing anions, particularly thiols (). Thiols are generated when the amino acid cysteine and the peptide glutathione form strong complexes with methylmercury: | 0 | Organic Chemistry |
In vivo, when alacepril undergoes deacetylation, it loses a molecule similar to the amino acid phenylalanine which transforms it into captopril. Captopril then provides its blood pressure lowering effect through two way. First, it inhibits the conversion of angiotensin 1, a precursor molecule, to angiotensin II, a vasoconstrictor that narrows blood vessels. Secondly, captopril prevents the breakdown of bradykinin, a vasodilator peptide that naturally relaxes blood vessels. | 4 | Stereochemistry |
Bents rule can be used to explain trends in both molecular structure and reactivity. After determining how the hybridisation of the central atom should affect a particular property, the electronegativity of substituents can be examined to see if Bents rule holds. | 4 | Stereochemistry |
Along with other NSAIDs, ibuprofen has been associated with the onset of bullous pemphigoid or pemphigoid-like blistering. As with other NSAIDs, ibuprofen has been reported to be a photosensitising agent, but it is considered a weak photosensitising agent compared to other members of the 2-arylpropionic acid class. Like other NSAIDs, ibuprofen is an extremely rare cause of the autoimmune disease Stevens–Johnson syndrome (SJS). Ibuprofen is also an extremely rare cause of toxic epidermal necrolysis. | 4 | Stereochemistry |
Traumatic brain injury is defined as a “direct physical impact or trauma to
the head followed by a dynamic series of injury and repair events”. Recently, neuroproteomics have been applied to studying the disability that over 5.4 million Americans live with. In addition to physically injuring the brain tissue, traumatic brain injury induces the release of glutamate that interacts with ionotropic glutamate receptors (iGluRs). These glutamate receptors acidify the surrounding intracranial fluid, causing further injury on the molecular level to nearby neurons. The death of the surrounding neurons is induced through normal apoptosis mechanisms, and it is this cycle that is being studied with neuroproteomics. Three different cysteine protease derivatives are involved in the apoptotic pathway induced by the acidic environment triggered by glutamate. These cysteine proteases include calpain, caspase, and cathepsin. These three proteins are examples of detectable signs of traumatic brain injury that are much more specific than temperature, oxygen level, or intracranial pressure.
Proteomics thus also offers a tracking mechanism by which researchers can monitor the progression of traumatic brain injury, or a chronic disease such as Alzheimer’s or Parkinson’s. Especially in Parkinson’s, in which neurotransmitters play a large role, recent proteomic research has involved the study of synaptotagmin. Synaptotagmin is involved in the calcium-induced budding of vesicle containing neurotransmitters from the presynaptic membrane. By studying the intracellular mechanisms involved in neural apoptosis after traumatic brain injury, researchers can create a map that genetic changes can follow later on. | 1 | Biochemistry |
In chemistry, molecular Borromean rings are an example of a mechanically-interlocked molecular architecture in which three macrocycles are interlocked in such a way that breaking any macrocycle allows the others to dissociate. They are the smallest examples of Borromean rings. The synthesis of molecular Borromean rings was reported in 2004 by the group of J. Fraser Stoddart. The so-called Borromeate is made up of three interpenetrated macrocycles formed through templated self assembly as complexes of zinc.
The synthesis of the macrocyclic systems involves self-assembles of two organic building blocks: 2,6-diformylpyridine (an aromatic compound with two aldehyde groups positioned ortho to the nitrogen atom of the pyridine ring) and a symmetric diamine containing a meta-substituted 2,2'-bipyridine group. Zinc acetate is added as the template for the reaction, resulting in one zinc cation in each of the six pentacoordinate complexation sites. Trifluoroacetic acid (TFA) is added to catalyse the imine bond-forming reactions. The preparation of the tri-ring Borromeate involves a total of 18 precursor molecules and is only possible because the building blocks self-assemble through 12 aromatic pi-pi interactions and 30 zinc to nitrogen dative bonds. Because of these interactions, the Borromeate is thermodynamically the most stable reaction product out of potentially many others. As a consequence of all the reactions taking place being equilibria, the Borromeate is the predominant reaction product.
Reduction with sodium borohydride in ethanol affords the neutral Borromeand. With the zinc removed, the three macrocycles are no longer chemically bonded but remain "mechanically entangled in such a way that that if only one of the rings is removed the other two can part company." The Borromeand is thus a true Borromean system as cleavage of just one imine bond (to an amine and an acetal) in this structure breaks the mechanical bond between the three constituent macrocycles, releasing the other two individual rings. A borromeand differs from a [[catenane|[3]catenane]] in that none of its three macrocycles is concatenated with another other; if one bond in a [3]catenane is broken and a cycle removed, a [2]catenane can remain.
Organic synthesis of this seemingly complex compound is in reality fairly simple; for this reason, the Stoddart group has suggested it as a gram-scale laboratory activity for undergraduate organic chemistry courses. | 6 | Supramolecular Chemistry |
Purėnas participated in revolution held in 1905–1907, therefore he was prosecuted by the police. In 1918 he joined LSDP, Lithuanian teachers union and teachers association "Naujoji mokykla". In 1920 he was a delegate of LSDP in Constituent Assembly of Lithuania, Chairman of educational committee. | 0 | Organic Chemistry |
Enzymes are proteins that catalyze (i.e. accelerate) chemical reactions. They are natural catalysts and are ubiquitous, in plants, animals and microorganisms where they catalyze processes that are vital to living organisms. They are intimately involved in numerous biotechnological processes, such as cheese making, beer brewing and winemaking, that date back to the dawn of civilization. Recent advances in biotechnology, particularly in genetic and protein engineering, and genetics have provided the basis for the efficient development of enzymes with improved properties for established applications and novel, tailor-made enzymes for completely new applications where enzymes were not previously used.
Today, enzymes are widely applied in many different industries and the number of applications continues to increase. Examples include food (baking, dairy products, starch conversion) and beverage (beer, wine, fruit and vegetable juices) processing, animal feed, textiles, pulp and paper, detergents, biosensors, cosmetics, health care and nutrition, waste water treatment, pharmaceutical and chemical manufacture and, more recently, biofuels such as biodiesel. The main driver for the widespread application of enzymes is their small environmental footprint.
Many traditional chemical conversions used in various industries suffer from inherent drawbacks from both an economic and environmental viewpoint. Non-specific reactions can afford low product yields, copious amounts of waste and impure products. The need for elevated temperatures and pressures leads to high energy consumption and high capital investment costs. Disposal of unwanted by-products may be difficult and/or expensive and hazardous solvents may be required. In stark contrast, enzymatic reactions are performed under mild conditions of temperature and pressure, in water as solvent, and exhibit very high rates and are often highly specific. Moreover, they are produced from renewable raw materials and are biodegradable. In addition, the mild operating conditions of enzymatic processes mean that they can be performed in relatively simple equipment and are easy to control. In short, they reduce the environmental footprint of manufacturing by reducing the consumption of energy and chemicals and concomitant generation of waste.
In the production of fine chemicals, flavors and fragrances, agrochemicals and pharmaceuticals an important benefit of enzymes is the high degree of chemoselectivity, regioselectivity and enantioselectivity which they exhibit. Particularly, their ability to catalyze the formation of products in high enantiopurity, by an exquisite stereochemical control, is of the utmost importance in these industries.
Notwithstanding all these desirable characteristic features of enzymes, their widespread industrial application is often hampered by their lack of long term operational stability and shelf-storage life, as well as by their cumbersome recovery and re-use. These drawbacks can be generally overcome by enzyme immobilization. A major present challenge in industrial biocatalysis is the development of stable, robust and preferably insoluble biocatalysts. | 4 | Stereochemistry |
Counterflow centrifugal elutriation (CCE) is a liquid clarification technique. This method enables scientists to separate different cells with different sizes. Since cell size is correlated with cell cycle stages this method also allows the separation of cells at different stages of the cell cycle. | 3 | Analytical Chemistry |
A powerful mixer is required for Dimetcote. To meet the high pressure requirement, the mixer should be powered by an explosion-proof electric motor or air motor. Workers can attain optimal spray characteristics by adjusting the tip size or pressure of the spray. | 8 | Metallurgy |
CTCF insulators affect the expression of genes implicated in cell cycle regulation processes that are important for cell growth, cell differentiation, and programmed cell death (apoptosis). Two of these cell cycle regulation genes that are known to interact with CTCF are hTERT and C-MYC. In these cases, a loss of function mutation to the CTCF insulator gene changes the expression patterns and may affect the interplay between cell growth, differentiation and apoptosis and lead to tumourigenesis or other problems.
CTCF is also required for the expression of tumour repressor retinoblastoma (Rb) gene and mutations and deletions of this gene are associated with inherited malignancies. When the CTCF binding site is removed expression of Rb is decreased and tumours are able to thrive.
Other genes that encode cell cycle regulators include BRCA1, and p53, which are growth suppressors that are silenced in many cancer types, and whose expression is controlled by CTCF. Loss of function of CTCF in these genes leads to the silencing of the growth suppressor and contributes to the formation of cancer.
The aberrant activation of insulators can modulate the expression of cancer-related genes, including matrix metalloproteinases involved in cancer cell invasion. | 1 | Biochemistry |
The process requirements for (Pb-free) SAC solders and Sn-Pb solders are different both materially and logistically for electronic assembly. In addition, the reliability of Sn-Pb solders is well established, while SAC solders are still undergoing study, (though much work has been done to justify the use of SAC solders, such as the iNEMI Lead Free Solder Project).
One important difference is that Pb-free soldering requires higher temperatures and increased process control to achieve the same results as that of the tin-lead method. The melting point of SAC alloys is 217–220°C, or about 34°C higher than the melting point of the eutectic tin-lead (63/37) alloy. This requires peak temperatures in the range of 235–245°C to achieve wetting and wicking.
Some of the components susceptible to SAC assembly temperatures are electrolytic capacitors, connectors, opto-electronics, and older style plastic components. However, a number of companies have started offering 260 °C compatible components to meet the requirements of Pb-free solders. iNEMI has proposed that a good target for development purposes would be around 260°C.
Also, SAC solders are alloyed with a larger number of metals so there is the potential for a far wider variety of intermetallics to be present in a solder joint. These more complex compositions can result in solder joint microstructures that are not as thoroughly studied as current tin-lead solder microstructures. These concerns are magnified by the unintentional use of lead-free solders in either processes designed solely for tin-lead solders or environments where material interactions are poorly understood. For example, the reworking of a tin-lead solder joint with Pb-free solder. These mixed-finish possibilities could negatively impact the solder's reliability. | 8 | Metallurgy |
When aluminum makes contact with water, hydrogen gas is produced as a result of hydrolysis. However, at the same time, water oxidizes the aluminum and causes a thin protective layer of aluminum oxide to rapidly form on the surface of the metal, preventing further hydrolysis. In order for the aluminum to continuously produce hydrogen gas, scientists had to forcefully remove or at least fracture the aluminum oxide layer, typically dissolving it in water with the help of hazardous compounds such as hydrochloric acid, sodium hydroxide, or expensive elements such as gallium/indium. Other methods apply external energy in the form of an electric current or superheated steam to slowly force the reaction at elevated temperatures. The aluminum based nanogalvanic alloy, a particulate material invented by the U.S. Army Research Laboratory (ARL), is able to generate hydrogen by hydrolysis at room temperature with any liquid that contains water (e.g. naturally scavenged water, coffee, energy drinks, urine, etc.) without relying on any other chemicals, catalysts, or externally supplied power. The nanostructured galvanic couple, with aluminum as the anode and another element (e.g. tin, bismuth, etc.) as the cathode, rapidly disturbs the formation of the native oxide layer and thus continually exposes fresh aluminum surfaces to hydrolysis. | 2 | Environmental Chemistry |
bHLH transcription factors have been shown to have a wide array of functions in developmental processes. More precisely, they have critical roles in the control of cellular differentiation, proliferation and regulation of oncogenesis. To date, 242 eukaryotic proteins belonging to the HLH superfamily have been reported. They have varied expression patterns in all eukaryotes from yeast to humans.
Structurally, bHLH proteins are characterised by a “highly conserved domain containing a stretch of basic amino acids adjacent to two amphipathic α-helices separated by a loop”.
These helices have important functional properties, forming part of the DNA binding and transcription activating domains. With respect to scleraxis, the bHLH region spans amino acid residues 78 to 131. A proline rich region is also predicted to lie between residues 161–170. A stretch of basic residues, which aids in DNA binding, is found closer to the N terminal end of scleraxis.
HLH proteins that lack this basic domain have been shown to negatively regulate the activities of bHLH proteins and are called inhibitors of differentiation (Id). Basic HLH proteins function normally as dimers and bind to a specific hexanucleotide DNA sequence (CAANTG) known as an E-box thus switching on the expression of various genes involved in cellular development and survival. | 1 | Biochemistry |
Liquid junction potential (shortly LJP) occurs when two solutions of electrolytes of different concentrations are in contact with each other. The more concentrated solution will have a tendency to diffuse into the comparatively less concentrated one. The rate of diffusion of each ion will be roughly proportional to its speed in an electric field, or their ion mobility. If the anions diffuse more rapidly than the cations, they will diffuse ahead into the dilute solution, leaving the latter negatively charged and the concentrated solution positively charged. This will result in an electrical double layer of positive and negative charges at the junction of the two solutions. Thus at the point of junction, a potential difference will develop because of the ionic transfer. This potential is called liquid junction potential or diffusion potential which is non-equilibrium potential. The magnitude of the potential depends on the relative speeds of the ions' movement. | 7 | Physical Chemistry |
* 1848 – William Thomson extends the concept of absolute zero from gases to all substances
* 1849 – William John Macquorn Rankine calculates the correct relationship between saturated vapour pressure and temperature using his hypothesis of molecular vortices
* 1850 – Rankine uses his vortex theory to establish accurate relationships between the temperature, pressure, and density of gases, and expressions for the latent heat of evaporation of a liquid; he accurately predicts the surprising fact that the apparent specific heat of saturated steam will be negative
* 1850 – Rudolf Clausius coined the term "entropy" (das Wärmegewicht, symbolized S) to denote heat lost or turned into waste. ("Wärmegewicht" translates literally as "heat-weight"; the corresponding English term stems from the Greek τρέπω, "I turn".)
* 1850 – Clausius gives the first clear joint statement of the first and second law of thermodynamics, abandoning the caloric theory, but preserving Carnot's principle
* 1851 – Thomson gives an alternative statement of the second law
* 1852 – Joule and Thomson demonstrate that a rapidly expanding gas cools, later named the Joule–Thomson effect or Joule–Kelvin effect
* 1854 – Helmholtz puts forward the idea of the heat death of the universe
* 1854 – Clausius establishes the importance of dQ/T (Clausius's theorem), but does not yet name the quantity
* 1854 – Rankine introduces his thermodynamic function, later identified as entropy
* 1856 – August Krönig publishes an account of the kinetic theory of gases, probably after reading Waterston's work
* 1857 – Clausius gives a modern and compelling account of the kinetic theory of gases in his On the nature of motion called heat
* 1859 – James Clerk Maxwell discovers the distribution law of molecular velocities
* 1859 – Gustav Kirchhoff shows that energy emission from a black body is a function of only temperature and frequency
* 1862 – "Disgregation", a precursor of entropy, was defined in 1862 by Clausius as the magnitude of the degree of separation of molecules of a body
* 1865 – Clausius introduces the modern macroscopic concept of entropy
* 1865 – Josef Loschmidt applies Maxwell's theory to estimate the number-density of molecules in gases, given observed gas viscosities.
* 1867 – Maxwell asks whether Maxwell's demon could reverse irreversible processes
* 1870 – Clausius proves the scalar virial theorem
* 1872 – Ludwig Boltzmann states the Boltzmann equation for the temporal development of distribution functions in phase space, and publishes his H-theorem
* 1873 - Johannes Diderik van der Waals formulates his equation of state
* 1874 – Thomson formally states the second law of thermodynamics
* 1876 – Josiah Willard Gibbs publishes the first of two papers (the second appears in 1878) which discuss phase equilibria, statistical ensembles, the free energy as the driving force behind chemical reactions, and chemical thermodynamics in general.
* 1876 – Loschmidt criticises Boltzmanns H theorem as being incompatible with microscopic reversibility (Loschmidts paradox).
* 1877 – Boltzmann states the relationship between entropy and probability
* 1879 – Jožef Stefan observes that the total radiant flux from a blackbody is proportional to the fourth power of its temperature and states the Stefan–Boltzmann law
* 1884 – Boltzmann derives the Stefan–Boltzmann blackbody radiant flux law from thermodynamic considerations
* 1888 – Henri-Louis Le Chatelier states his principle that the response of a chemical system perturbed from equilibrium will be to counteract the perturbation
* 1889 – Walther Nernst relates the voltage of electrochemical cells to their chemical thermodynamics via the Nernst equation
* 1889 – Svante Arrhenius introduces the idea of activation energy for chemical reactions, giving the Arrhenius equation
* 1893 – Wilhelm Wien discovers the displacement law for a blackbody's maximum specific intensity | 7 | Physical Chemistry |
Organisms may secrete bioadhesives for use in attachment, construction and obstruction, as well as in predation and defense. Examples include their use for:
* Colonization of surfaces (e.g. bacteria, algae, fungi, mussels, barnacles, rotifers)
* Mussel's byssal threads
* Tube building by polychaete worms, which live in underwater mounds
* Insect egg, larval or pupal attachment to surfaces (vegetation, rocks), and insect mating plugs
* Host attachment by blood-feeding ticks
* Nest-building by some insects, and also by some fish (e.g. the three-spined stickleback)
* Defense by Notaden frogs and by sea cucumbers
* Prey capture in spider webs and by velvet worms
Some bioadhesives are very strong. For example, adult barnacles achieve pull-off forces as high as 2 MPa (2 N/mm). A similarly strong, rapidly adhering glue - which contains 171 different proteins and can adhere to wet, moist and impure surfaces - is produced by the very hard limpet species Patella vulgata; this adhesive material is a very interesting subject of research in the development of surgical adhesives and several other applications. Silk dope can also be used as a glue by arachnids and insects. | 1 | Biochemistry |
Archaeological evidence indicates that the earliest metal objects in China were made in the late fourth millennium BCE. Copper was generally the earliest metal to be used by humanity, and was used in China since at least 3000 BCE.
Early metal-using communities have been found at the Qijia and Siba sites in Gansu. The metal knives and axes recovered in Qijia apparently point to some interactions with Siberian and Central Asian cultures, in particular with the Seima-Turbino complex, or the Afanasievo culture. Archeological evidence points to plausible early contact between the Qijia culture and Central Asia. Similar sites have been found in Xinjiang in the west and Shandong, Liaoning and Inner Mongolia in the east and north. The Central Plain sites associated with the Erlitou culture also contain early metalworks.
Copper manufacturing, more complex than jade working, gradually appeared in the Yangshao period (5000–3000 BCE). Jiangzhai is the only place where copper artifacts were found in the Banpo culture. Archaeologists have found remains of copper metallurgy in various cultures from the late fourth to the early third millennia BCE. These include the copper-smelting remains and copper artifacts of the Hongshan culture (4700–2900) and copper slag at the Yuanwozhen site. This indicates that inhabitants of the Yellow River valley had already learned how to make copper artifacts by the later Yangshao period.
The Qijia culture (c. 2500–1900) of Qinghai, Gansu, and western Shaanxi produced copper and bronze utilitarian items and gold, copper, and bronze ornaments. The earliest metalworks in this region are found at a Majiayao site at Linjia, Dongxiang, Gansu. "Their dates range from 2900 to 1600 BCE. These metal objects represent the Majiayao 馬家窯 type of the Majiayao culture (c. 3100–2700 BCE), Zongri 宗日 Culture (c. 3600–2050 BCE), Machang 馬廠 Type (c. 2300–2000 BCE), Qijia 齊家 Culture (c. 2050–1915 BCE), and Siba 四壩 Culture (c. 2000–1600 BCE)."
At Dengjiawan, in the Shijiahe site complex in Hubei, some pieces of copper were discovered; they are the earliest copper objects discovered in southern China. The Linjia site (林家遺址, Línjiā yízhǐ) has the earliest evidence for bronze in China, dating to c. 3000 BCE. | 8 | Metallurgy |
The thanator (Palulukan in Navi) is a large hexapodal land predator that is believed, by the RDA, to be the apex land predator. It is scientifically known as Bestiapanthera ferox. Cameron personally designed the creature. The thanator is first seen when Jake wanders off into the jungle and touches multiple helicoradian leaves, at which they retract to reveal a family of hammerhead titanotheres behind. The thanator frightens the titanotheres and pursues Jake. Jake later escapes the thanator by jumping off a cliff into pool below. It later appears during the climax where it assists Neytiri and later battles Quaritchs AMP Suit Beyond Glory, but is killed by the AMP suit's knife. The thanator is black with white fleshy skin under each hand. Its appearance is similar to a panther; Cameron describes the thanator as "the panther from hell". The thanator has ten sensory quills connected to six pads at the rear of the skull that flare up before it attacks the prey. The director explained how the thanator is the most fearsome creature on Pandora, "The thanator could eat a T-Rex and have the Alien for dessert." | 1 | Biochemistry |
Diazonium salts can be reduced with stannous chloride () to the corresponding hydrazine derivatives. This reaction is particularly useful in the Fischer indole synthesis of triptan compounds and indometacin. The use of sodium dithionite is an improvement over stannous chloride since it is a cheaper reducing agent with fewer environmental problems. | 0 | Organic Chemistry |
The structure–correlation principle states that structural changes that occur along the reaction coordinate can reveal themselves in the ground state as deviations of bond distances and angles from normal values along the reaction coordinate. According to this theory if one particular bond length on reaching the transition state increases then this bond is already longer in its ground state compared to a compound not sharing this transition state. One demonstration of this principle is found in the two bicyclic compounds depicted below. The one on the left is a bicyclo[2.2.2]octene, which, at 200 °C, extrudes ethylene in a retro-Diels–Alder reaction.
Compared to the compound on the right (which, lacking an alkene group, is unable to give this reaction) the bridgehead carbon-carbon bond length is expected to be shorter if the theory holds, because on approaching the transition state this bond gains double bond character. For these two compounds the prediction holds up based on X-ray crystallography. | 7 | Physical Chemistry |
Chloroformates are a class of organic compounds with the formula ROC(O)Cl. They are formally esters of chloroformic acid. Most are colorless, volatile liquids that degrade in moist air. A simple example is methyl chloroformate, which is commercially available.
Chloroformates are used as reagents in organic chemistry. For example, benzyl chloroformate is used to introduce the Cbz (carboxybenzyl) protecting group and fluorenylmethyloxycarbonyl chloride is used to introduce the FMOC protecting group. Chloroformates are popular in the field of chromatography as derivatization agents. They convert polar compounds into less polar more volatile derivatives. In this way, chloroformates enable relatively simple transformation of large array of metabolites (aminoacids, amines, carboxylic acids, phenols) for analysis by gas chromatography / mass spectrometry. | 0 | Organic Chemistry |
A salt with associated water of crystallization is known as a hydrate. The structure of hydrates can be quite elaborate, because of the existence of hydrogen bonds that define polymeric structures.
Historically, the structures of many hydrates were unknown, and the dot in the formula of a hydrate was employed to specify the composition without indicating how the water is bound. Per IUPAC's recommendations, the middle dot is not surrounded by spaces when indicating a chemical adduct. Examples:
* – copper(II) sulfate pentahydrate
* – cobalt(II) chloride hexahydrate
* – tin(II) (or stannous) chloride dihydrate
For many salts, the exact bonding of the water is unimportant because the water molecules are made labile upon dissolution. For example, an aqueous solution prepared from and anhydrous behave identically. Therefore, knowledge of the degree of hydration is important only for determining the equivalent weight: one mole of weighs more than one mole of . In some cases, the degree of hydration can be critical to the resulting chemical properties. For example, anhydrous is not soluble in water and is relatively useless in organometallic chemistry whereas is versatile. Similarly, hydrated is a poor Lewis acid and thus inactive as a catalyst for Friedel-Crafts reactions. Samples of must therefore be protected from atmospheric moisture to preclude the formation of hydrates.
Crystals of hydrated copper(II) sulfate consist of centers linked to ions. Copper is surrounded by six oxygen atoms, provided by two different sulfate groups and four molecules of water. A fifth water resides elsewhere in the framework but does not bind directly to copper. The cobalt chloride mentioned above occurs as and . In tin chloride, each Sn(II) center is pyramidal (mean angle is 83°) being bound to two chloride ions and one water. The second water in the formula unit is hydrogen-bonded to the chloride and to the coordinated water molecule. Water of crystallization is stabilized by electrostatic attractions, consequently hydrates are common for salts that contain +2 and +3 cations as well as −2 anions. In some cases, the majority of the weight of a compound arises from water. Glauber's salt, , is a white crystalline solid with greater than 50% water by weight.
Consider the case of nickel(II) chloride hexahydrate. This species has the formula . Crystallographic analysis reveals that the solid consists of subunits that are hydrogen bonded to each other as well as two additional molecules of . Thus one third of the water molecules in the crystal are not directly bonded to , and these might be termed "water of crystallization". | 3 | Analytical Chemistry |
A black light lamp emits long-wave UV‑A radiation and little visible light. Fluorescent black light lamps work similarly to other fluorescent lamps, but use a phosphor on the inner tube surface which emits UV‑A radiation instead of visible light. Some lamps use a deep-bluish-purple Woods glass optical filter that blocks almost all visible light with wavelengths longer than 400 nanometers. The purple glow given off by these tubes is not the ultraviolet itself, but visible purple light from mercurys 404 nm spectral line which escapes being filtered out by the coating. Other black lights use plain glass instead of the more expensive Wood's glass, so they appear light-blue to the eye when operating.
Incandescent black lights are also produced, using a filter coating on the envelope of an incandescent bulb that absorbs visible light (see section below). These are cheaper but very inefficient, emitting only a small fraction of a percent of their power as UV. Mercury-vapor black lights in ratings up to 1 kW with UV-emitting phosphor and an envelope of Wood's glass are used for theatrical and concert displays.
Black lights are used in applications in which extraneous visible light must be minimized; mainly to observe fluorescence, the colored glow that many substances give off when exposed to UV light. UV‑A / UV‑B emitting bulbs are also sold for other special purposes, such as tanning lamps and reptile-husbandry. | 5 | Photochemistry |
In organometallic chemistry, the isolobal principle (more formally known as the isolobal analogy) is a strategy used to relate the structure of organic and inorganic molecular fragments in order to predict bonding properties of organometallic compounds. Roald Hoffmann described molecular fragments as isolobal "if the number, symmetry properties, approximate energy and shape of the frontier orbitals and the number of electrons in them are similar – not identical, but similar." One can predict the bonding and reactivity of a lesser-known species from that of a better-known species if the two molecular fragments have similar frontier orbitals, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Isolobal compounds are analogues to isoelectronic compounds that share the same number of valence electrons and structure. A graphic representation of isolobal structures, with the isolobal pairs connected through a double-headed arrow with half an orbital below, is found in Figure 1.
For his work on the isolobal analogy, Hoffmann was awarded the Nobel Prize in Chemistry in 1981, which he shared with Kenichi Fukui. In his Nobel Prize lecture, Hoffmann stressed that the isolobal analogy is a useful, yet simple, model and thus is bound to fail in certain instances. | 0 | Organic Chemistry |
The standard biochemistry and molecular biology textbooks describe non-coding nucleotides in mRNA located between the 5 end of the gene and the translation initiation codon. These regions are called 5-untranslated regions or 5-UTRs. Similar regions called 3-untranslated regions (3-UTRs) are found at the end of the gene. The 5-UTRs and 3UTRs are very short in bacteria but they can be several hundred nucleotides in length in eukaryotes. They contain short elements that control the initiation of translation (5-UTRs) and transcription termination (3'-UTRs) as well as regulatory elements that may control mRNA stability, processing, and targeting to different regions of the cell. | 1 | Biochemistry |
Reverse transcriptase creates double-stranded DNA from an RNA template.
In virus species with reverse transcriptase lacking DNA-dependent DNA polymerase activity, creation of double-stranded DNA can possibly be done by host-encoded DNA polymerase δ, mistaking the viral DNA-RNA for a primer and synthesizing a double-stranded DNA by a similar mechanism as in primer removal, where the newly synthesized DNA displaces the original RNA template.
The process of reverse transcription, also called retrotranscription or retrotras, is extremely error-prone, and it is during this step that mutations may occur. Such mutations may cause drug resistance. | 1 | Biochemistry |
Mass cytometry has research applications in medical fields including immunology, hematology, and oncology. It has been used in studies of hematopoiesis, cell cycle, cytokine expression, and differential signaling responses.
MC has been used in various research fields, such as cancer biology, immunology, and neuroscience, to provide a more comprehensive understanding of tissue architecture and cellular interactions. | 3 | Analytical Chemistry |
Possible complications may include: infection, bleeding, dysrhythmias and high blood sugar. One review found an increased risk of pneumonia and sepsis but not the overall risk of infection. Another review found a trend towards increased bleeding but no increase in severe bleeding. Hypothermia induces a "cold diuresis" which can lead to electrolyte abnormalities – specifically hypokalemia, hypomagnesaemia, and hypophosphatemia, as well as hypovolemia. | 1 | Biochemistry |
The following example illustrates how a Boolean network can model a GRN together with its gene products (the outputs) and the substances from the environment that affect it (the inputs). Stuart Kauffman was amongst the first biologists to use the metaphor of Boolean networks to model genetic regulatory networks.
# Each gene, each input, and each output is represented by a node in a directed graph in which there is an arrow from one node to another if and only if there is a causal link between the two nodes.
# Each node in the graph can be in one of two states: on or off.
# For a gene, "on" corresponds to the gene being expressed; for inputs and outputs, "on" corresponds to the substance being present.
# Time is viewed as proceeding in discrete steps. At each step, the new state of a node is a Boolean function of the prior states of the nodes with arrows pointing towards it.
The validity of the model can be tested by comparing simulation results with time series observations. A partial validation of a Boolean network model can also come from testing the predicted existence of a yet unknown regulatory connection between two particular transcription factors that each are nodes of the model. | 1 | Biochemistry |
Acid–base titrations depend on the neutralization between an acid and a base when mixed in solution. In addition to the sample, an appropriate pH indicator is added to the titration chamber, representing the pH range of the equivalence point. The acid–base indicator indicates the endpoint of the titration by changing color. The endpoint and the equivalence point are not exactly the same because the equivalence point is determined by the stoichiometry of the reaction while the endpoint is just the color change from the indicator. Thus, a careful selection of the indicator will reduce the indicator error. For example, if the equivalence point is at a pH of 8.4, then the phenolphthalein indicator would be used instead of Alizarin Yellow because phenolphthalein would reduce the indicator error. Common indicators, their colors, and the pH range in which they change color are given in the table above. When more precise results are required, or when the reagents are a weak acid and a weak base, a pH meter or a conductance meter are used.
For very strong bases, such as organolithium reagent, metal amides, and hydrides, water is generally not a suitable solvent and indicators whose pKa are in the range of aqueous pH changes are of little use. Instead, the titrant and indicator used are much weaker acids, and anhydrous solvents such as THF are used.
The approximate pH during titration can be approximated by three kinds of calculations. Before beginning of titration, the concentration of is calculated in an aqueous solution of weak acid before adding any base. When the number of moles of bases added equals the number of moles of initial acid or so called equivalence point, one of hydrolysis and the pH is calculated in the same way that the conjugate bases of the acid titrated was calculated. Between starting and end points, is obtained from the Henderson-Hasselbalch equation and titration mixture is considered as buffer. In Henderson-Hasselbalch equation the and are said to be the molarities that would have been present even with dissociation or hydrolysis. In a buffer, can be calculated exactly but the dissociation of , the hydrolysis of and self-ionization of water must be taken into account. Four independent equations must be used:
In the equations, and are the moles of acid () and salt ( where X is the cation), respectively, used in the buffer, and the volume of solution is . The law of mass action is applied to the ionization of water and the dissociation of acid to derived the first and second equations. The mass balance is used in the third equation, where the sum of and must equal to the number of moles of dissolved acid and base, respectively. Charge balance is used in the fourth equation, where the left hand side represents the total charge of the cations and the right hand side represents the total charge of the anions: is the molarity of the cation (e.g. sodium, if sodium salt of the acid or sodium hydroxide is used in making the buffer). | 3 | Analytical Chemistry |
The analysis of honey shows:
Typical honey analysis
* Fructose: 38%
* Glucose: 31%
* Sucrose: 1%
* Water: 17%
* Other sugars: 9% (maltose, melezitose)
* Ash: 0.17%
In this example the ash would include all the minerals in honey.
Ashing is also performed prior to chemical analysis by inductively coupled plasma emission spectrometry. | 3 | Analytical Chemistry |
The adsorption regeneration process is divided into three key elements which occur in different parts of the cell. All three occur continuously and simultaneously, with parameters such as charge passed, rate of effluent in/outflow and air inlet rate varied according to pollutant type and concentration. | 7 | Physical Chemistry |
The microstructure of a polymer (sometimes called configuration) relates to the physical arrangement of monomer residues along the backbone of the chain. These are the elements of polymer structure that require the breaking of a covalent bond in order to change. Various polymer structures can be produced depending on the monomers and reaction conditions: A polymer may consist of linear macromolecules containing each only one unbranched chain. In the case of unbranched polyethylene, this chain is a long-chain n-alkane. There are also branched macromolecules with a main chain and side chains, in the case of polyethylene the side chains would be alkyl groups. In particular unbranched macromolecules can be in the solid state semi-crystalline, crystalline chain sections highlighted red in the figure below.
While branched and unbranched polymers are usually thermoplastics, many elastomers have a wide-meshed cross-linking between the "main chains". Close-meshed crosslinking, on the other hand, leads to thermosets. Cross-links and branches are shown as red dots in the figures. Highly branched polymers are amorphous and the molecules in the solid interact randomly. | 7 | Physical Chemistry |
Acute beryllium poisoning is an occupational disease. Relevant occupations are those where beryllium is mined, processed or converted into metal alloys, or where machining of metals containing beryllium or recycling of scrap alloys occurs.
Metallographic preparation equipment and laboratory work surfaces must be damp-wiped occasionally to inhibit buildup of particles. Cutting, grinding, and polishing procedures that generate dust or fumes must be handled within sufficiently vented coverings supplied with particulate filters. | 1 | Biochemistry |
As of November 15, 2021, seven states in the USA declared ten cases of illnesses from an E. coli O157:H7 strain. These cases were reported from October 15, 2021 through October 27, 2021 and an investigation was carried out by the Minnesota Department of Agriculture and FDA. It was concluded that packages of spinach collected from homes of infected people were contaminated with a strain of E. coli that matched the strain causing illness. This was determined by performing whole genome sequencing on the strain extracted from the spinach and comparing it to the strain taken from infected individuals.
As of February 7, 2022, the provinces of Alberta and Saskatchewan in Canada reported a collective fourteen confirmed cases of E. coli O157 strain illnesses. These were reported between December 2021 and January 2022, and the Public Health Agency of Canada (PHAC), the Canadian Food Inspection Agency (CFIA), and Health Canada were able to determine a specific brand of Original Kimchi to be the source of the organism. On January 28, 2022 and February 6, 2022, the CFIA issued a recall on Hankook Original Kimchi. | 3 | Analytical Chemistry |
SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, structural, and evolutionary units that form proteins. Domains of common Ancestry are grouped into superfamilies. The domains and domain superfamilies are defined and described in SCOP. Superfamilies are groups of proteins which have structural evidence to support a common evolutionary ancestor but may not have detectable sequence homology. | 1 | Biochemistry |
Ethanol is the most commonly used biofuel and can be produced on large scale via fermentation. The maximum theoretical yield for the production of ethanol was achieved around 20 years. A plasmid that carried the pyruvate decarboxylase and alcohol dehydrogenase genes from the bacteria Z. mobilis was used by scientists. This was inserted into E. coli and resulted in an increased yield of ethanol. The genome of this E. coli strain, KO11, has more recently been sequenced and mapped. | 1 | Biochemistry |
In 1915, the reason for nuclear charge being quantized in units of Z, which were now recognized to be the same as the element number, was not understood. An old idea called Prouts hypothesis had postulated that the elements were all made of residues (or "protyles") of the lightest element hydrogen, which in the Bohr-Rutherford model had a single electron and a nuclear charge of one. However, as early as 1907, Rutherford and Thomas Royds had shown that alpha particles, which had a charge of +2, were the nuclei of helium atoms, which had a mass four times that of hydrogen, not two times. If Prouts hypothesis were true, something had to be neutralizing some of the charge of the hydrogen nuclei present in the nuclei of heavier atoms.
In 1917, Rutherford succeeded in generating hydrogen nuclei from a nuclear reaction between alpha particles and nitrogen gas, and believed he had proven Prout's law. He called the new heavy nuclear particles protons in 1920 (alternate names being proutons and protyles). It had been immediately apparent from the work of Moseley that the nuclei of heavy atoms have more than twice as much mass as would be expected from their being made of hydrogen nuclei, and thus there was required a hypothesis for the neutralization of the extra protons presumed present in all heavy nuclei. A helium nucleus was presumed to be composed of four protons plus two "nuclear electrons" (electrons bound inside the nucleus) to cancel two of the charges. At the other end of the periodic table, a nucleus of gold with a mass 197 times that of hydrogen was thought to contain 118 nuclear electrons in the nucleus to give it a residual charge of +79, consistent with its atomic number. | 3 | Analytical Chemistry |
In chemistry, a dynamic equilibrium exists once a reversible reaction occurs. Substances transition between the reactants and products at equal rates, meaning there is no net change. Reactants and products are formed at such a rate that the concentration of neither changes. It is a particular example of a system in a steady state.
In physics, concerning thermodynamics, a closed system is in thermodynamic equilibrium when reactions occur at such rates that the composition of the mixture does not change with time. Reactions do in fact occur, sometimes vigorously, but to such an extent that changes in composition cannot be observed. Equilibrium constants can be expressed in terms of the rate constants for reversible reactions. | 7 | Physical Chemistry |
Thiourea is employed as a source of sulfide, such as for converting alkyl halides to thiols. The reaction capitalizes on the high nucleophilicity of the sulfur center and easy hydrolysis of the intermediate isothiouronium salt:
In this example, ethane-1,2-dithiol is prepared from 1,2-dibromoethane:
Like other thioamides, thiourea can serve as a source of sulfide upon reaction with metal ions. For example, mercury sulfide forms when mercuric salts in aqueous solution are treated with thiourea:
These sulfiding reactions, which have been applied to the synthesis of many metal sulfides, require water and typically some heating. | 0 | Organic Chemistry |
Hydroxycorticosteroids (OHCSs) are corticosteroids that have an additional hydroxy (-OH) group.
There are two main positions where the hydroxy group may be added: at carbon atom 11, and at carbon atom 17. | 0 | Organic Chemistry |
Multicolumn countercurrent solvent gradient purification (MCSGP) is a form of chromatography that is used to separate or purify biomolecules from complex mixtures. It was developed at the Swiss Federal Institute of Technology Zürich by Aumann and Morbidelli. The process consists of two to six chromatographic columns which are connected to one another in such a way that as the mixture moves through the columns the compound is purified into several fractions. | 3 | Analytical Chemistry |
The term electrochemical potential is sometimes used to mean an electrode potential (either of a corroding electrode, an electrode with a non-zero net reaction or current, or an electrode at equilibrium). In some contexts, the electrode potential of corroding metals is called "electrochemical corrosion potential", which is often abbreviated as ECP, and the word "corrosion" is sometimes omitted. This usage can lead to confusion. The two quantities have different meanings and different dimensions: the dimension of electrochemical potential is energy per mole while that of electrode potential is voltage (energy per charge). | 7 | Physical Chemistry |
DNA repair genes are frequently repressed in cancers due to hypermethylation of CpG islands within their promoters. In head and neck squamous cell carcinomas at least 15 DNA repair genes have frequently hypermethylated promoters; these genes are XRCC1, MLH3, PMS1, RAD51B, XRCC3, RAD54B, BRCA1, SHFM1, GEN1, FANCE, FAAP20, SPRTN, SETMAR, HUS1, and PER1. About seventeen types of cancer are frequently deficient in one or more DNA repair genes due to hypermethylation of their promoters. As summarized in one review article, promoter hypermethylation of the DNA repair gene MGMT occurs in 93% of bladder cancers, 88% of stomach cancers, 74% of thyroid cancers, 40%-90% of colorectal cancers and 50% of brain cancers. Promoter hypermethylation of LIG4 occurs in 82% of colorectal cancers. This review article also indicates promoter hypermethylation of NEIL1 occurs in 62% of head and neck cancers and in 42% of non-small-cell lung cancers; promoter hypermetylation of ATM occurs in 47% of non-small-cell lung cancers; promoter hypermethylation of MLH1 occurs in 48% of squamous cell carcinomas; and promoter hypermethylation of FANCB occurs in 46% of head and neck cancers.
On the other hand, the promoters of two genes, PARP1 and FEN1, were hypomethylated and these genes were over-expressed in numerous cancers. PARP1 and FEN1 are essential genes in the error-prone and mutagenic DNA repair pathway microhomology-mediated end joining. If this pathway is over-expressed, the excess mutations it causes can lead to cancer. PARP1 is over-expressed in tyrosine kinase-activated leukemias, in neuroblastoma, in testicular and other germ cell tumors, and in Ewing's sarcoma, FEN1 is over-expressed in the majority of cancers of the breast, prostate, stomach, neuroblastomas, pancreatic, and lung.
DNA damage appears to be the primary underlying cause of cancer. If accurate DNA repair is deficient, DNA damages tend to accumulate. Such excess DNA damage can increase mutational errors during DNA replication due to error-prone translesion synthesis. Excess DNA damage can also increase epigenetic alterations due to errors during DNA repair. Such mutations and epigenetic alterations can give rise to cancer (see malignant neoplasms). Thus, CpG island hyper/hypo-methylation in the promoters of DNA repair genes are likely central to progression to cancer. | 1 | Biochemistry |
Faradaic efficiency of a cell design is usually measured through bulk electrolysis where a known quantity of reagent is stoichiometrically converted to product, as measured by the current passed. This result is then compared to the observed quantity of product measured through another analytical method. | 7 | Physical Chemistry |
Copper does not require complex ventilation measures. It is suitable for both unventilated warm and ventilated cold roof constructions. | 8 | Metallurgy |
Benzylpenicillin, also known as penicillin G (PenG) or BENPEN, is an antibiotic used to treat a number of bacterial infections. This includes pneumonia, strep throat, syphilis, necrotizing enterocolitis, diphtheria, gas gangrene, leptospirosis, cellulitis, and tetanus. It is not a first-line agent for pneumococcal meningitis. Due to benzylpenicillin's limited bioavailability for oral medications, it is generally taken as an injection in the form of a sodium, potassium, benzathine, or procaine salt. Benzylpenicillin is given by injection into a vein or muscle. Two long-acting forms benzathine benzylpenicillin and procaine benzylpenicillin are available for use by injection into a muscle only.
Side effects include diarrhea, seizures, and allergic reactions including anaphylaxis. When used to treat syphilis or Lyme disease a reaction known as Jarisch–Herxheimer may occur. It is not recommended in those with a history of penicillin allergy. Use during pregnancy is generally safe in the penicillin and β-lactam class of medications.
Benzylpenicillin is on the World Health Organization's List of Essential Medicines. | 4 | Stereochemistry |
Chelating resins operate similarly to ordinary ion-exchange resins.
Most chelating resins are polymers (copolymers to be precise) with reactive functional groups that chelate to metal ions. The variation in chelating resins arises from the nature of the chelating agents pendant from the polymer backbone. Dowex chelating resin A-1, also known as Chelex 100, is based on iminodiacetic acid in a styrene-divinylbenzene matrix. Dowex A-1 is available commercially and is widely used to determine general properties of chelating resins such as rate determining step and pH dependence, etc. Dowex A-1 is produced from chloromethylated styrene-divinylbenzene copolymer via amination with aminodiacetic acid.
Poly metal chelating resin has almost negligible affinity to both alkali and alkaline earth metals; small quantities of resin can be utilized to concentrate trace metals in natural water systems or biological fluids, in which there are three or four orders of magnitude greater alkali and alkaline earth metal concentration than the trace metal concentrations.
Other functional groups bound to chelating resins are aminophosphonic acids, thiourea, and 2-picolylamine. | 3 | Analytical Chemistry |
One of the earliest steps towards atomic physics was the recognition that matter was composed of atoms, in modern terms the basic unit of a chemical element. This theory was developed by John Dalton in the 18th century. At this stage, it wasn't clear what atoms were - although they could be described and classified by their observable properties in bulk; summarized by the developing periodic table, by John Newlands and Dmitri Mendeleyev around the mid to late 19th century.
Later, the connection between atomic physics and optical physics became apparent, by the discovery of spectral lines and attempts to describe the phenomenon - notably by Joseph von Fraunhofer, Fresnel, and others in the 19th century.
From that time to the 1920s, physicists were seeking to explain atomic spectra and blackbody radiation. One attempt to explain hydrogen spectral lines was the Bohr atom model.
Experiments including electromagnetic radiation and matter - such as the photoelectric effect, Compton effect, and spectra of sunlight the due to the unknown element of Helium, the limitation of the Bohr model to Hydrogen, and numerous other reasons, lead to an entirely new mathematical model of matter and light: quantum mechanics. | 7 | Physical Chemistry |
Absorption coefficients for 200 nm and 900 nm are almost equal at 6.9 m (attenuation length of 14.5 cm). Very weak light absorption, in the visible region, by liquid water has been measured using an integrating cavity absorption meter (ICAM). The absorption was attributed to a sequence of overtone and combination bands whose intensity decreases at each step, giving rise to an absolute minimum at 418 nm, at which wavelength the attenuation coefficient is about 0.0044 m, which is an attenuation length of about 227 meters. These values correspond to pure absorption without scattering effects. The attenuation of, e.g., a laser beam would be slightly stronger. | 7 | Physical Chemistry |
As a gasoline (petrol) additive, benzene increases the octane rating and reduces knocking. As a consequence, gasoline often contained several percent benzene before the 1950s, when tetraethyl lead replaced it as the most widely used antiknock additive. With the global phaseout of leaded gasoline, benzene has made a comeback as a gasoline additive in some nations. In the United States, concern over its negative health effects and the possibility of benzene entering the groundwater has led to stringent regulation of gasoline's benzene content, with limits typically around 1%. European petrol specifications now contain the same 1% limit on benzene content. The United States Environmental Protection Agency introduced new regulations in 2011 that lowered the benzene content in gasoline to 0.62%.
In some European languages, the word for petroleum or gasoline is an exact cognate of "benzene". For instance in Catalan the word benzina can be used for gasoline, though now it is relatively rare. | 2 | Environmental Chemistry |
Intramolecular aldol condensation is between two aldehyde groups or ketone groups in the same molecule. Five- or six-membered , -unsaturated ketone or aldehydes are formed as products. This reaction is an important approach to the formation of carbon-carbon bonds in organic molecules containing ring systems. As an example, under strong basic conditions (e.g. sodium hydroxide), hexane-2,5-dione (compound A in Figure 1) can cyclize via intramolecular aldol reaction to form the 3-methylcyclopent-2-en-1-one (compound B).
The mechanism of the intramolecular aldol reaction involves formation of a key enolate intermediate followed by an intramolecular nucleophilic addition process.
First, hydroxide abstracts the α-hydrogen on a terminal carbon to form the enolate. Next, a nucleophilic attack of the enolate on the other keto group forms a new carbon-carbon bond (red) between carbons 2 and 6. This forms the Adol addition product.
Then, usually under heating conditions, the elimination of water molecule yields the cyclized α,β-unsaturated ketone, the aldol condensation product.
Intramolecular aldol reactions have been widely used in total syntheses of various natural products, especially alkaloids and steroids. An example is the application of an intramolecular aldol reaction in the ring closure step for total synthesis of (+)-Wortmannin by Shigehisa, et al. (Figure 2). | 0 | Organic Chemistry |
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