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The , developed in 1908 with Elias Anton Cappelen Smith, significantly improved the converting of copper matte.
Before this invention, the converter was a cylindrical barrel, lined with an acid refractory lining, made of sand and clay. It was developed by two French engineers, Pierre Manhès and from 1880 to 1884. Their copper-converting process, named the Manhès–David process, was directly derived from the Bessemer process. In this horizontal chemical reactor, where air was injected into copper matte, a molten sulfide material containing iron, sulphur and copper, to become molten blister, an alloy containing 99% copper. But the basic slag produced during the blowing combined with the acid silica refractory lining, thereby causing a very short lifetime of the lining.
By developing a basic refractory material adapted to the matte refining process (in magnesia bricks), Peirce and his engineer Smith found a way to drastically increase the lifetime of the lining. It has been stated that, in some cases, the process allowing an increase from 10 to 2500 tons of copper produced without relining the converters. A reduction of the cost of copper converting from 15–20 USD to 4–5 USD has been stated.
The Peirce-Smith converter quickly replaced the Manhès–David converter: by March 1912, the Peirce-Smith Converting Co claimed that "over 80% of the copper produced in [the U.S.] is being converted either in P-S type converters or on basic lining, under license, in the old acid shells".
It is still in use today, although the process has been significantly improved since then. In 2010, with 250 converters working in the world, the Peirce-Smith converters refine 90% of the copper matte. | 8 | Metallurgy |
According to the label on consumer products TarnX and Silver Dip, the liquid silver cleaning products contain thiourea along with a warning that thiourea is a chemical on California's list of carcinogens. A lixiviant for gold and silver leaching can be created by selectively oxidizing thiourea, bypassing the steps of cyanide use and smelting. | 0 | Organic Chemistry |
Amino acids are the building blocks of peptides and enzymes while sugar-peptide chains are the backbone of RNA and DNA. In biological organisms, amino acids appear almost exclusively in the left-handed form (-amino acids) and sugars in the right-handed form (R-sugars). Since the enzymes catalyze reactions, they enforce homochirality on a great variety of other chemicals, including hormones, toxins, fragrances and food flavors. Glycine is achiral, as are some other non-proteinogenic amino acids that are either achiral (such as dimethylglycine) or of the enantiomeric form.
Biological organisms easily discriminate between molecules with different chiralities. This can affect physiological reactions such as smell and taste. Carvone, a terpenoid found in essential oils, smells like mint in its L-form and caraway in its R-form. Limonene tastes like citrus when right-handed and pine when left-handed.
Homochirality also affects the response to drugs. Thalidomide, in its left-handed form, cures morning sickness; in its right-handed form, it causes birth defects. Unfortunately, even if a pure left-handed version is administered, some of it can convert to the right-handed form in the patient. Many drugs are available as both a racemic mixture (equal amounts of both chiralities) and an enantiopure drug (only one chirality). Depending on the manufacturing process, enantiopure forms can be more expensive to produce than stereochemical mixtures.
Chiral preferences can also be found at a macroscopic level. Snail shells can be right-turning or left-turning helices, but one form or the other is strongly preferred in a given species. In the edible snail Helix pomatia, only one out of 20,000 is left-helical. The coiling of plants can have a preferred chirality and even the chewing motion of cows has a 10% excess in one direction. | 4 | Stereochemistry |
Before the invention of artificial refrigeration technology, ice making by nocturnal cooling was common in both India and Iran.
In India, such apparatuses consisted of a shallow ceramic tray with a thin layer of water, placed outdoors with a clear exposure to the night sky. The bottom and sides were insulated with a thick layer of hay. On a clear night the water would lose heat by radiation upwards. Provided the air was calm and not too far above freezing, heat gain from the surrounding air by convection was low enough to allow the water to freeze.
In Iran, this involved making large flat ice pools, which consisted of a reflection pool of water built on a bed of highly insulative material surrounded by high walls. The high walls provided protection against convective warming, the insulative material of the pool walls would protect against conductive heating from the ground, the large flat plane of water would then permit evaporative and radiative cooling to take place. | 7 | Physical Chemistry |
For example, ammonia (NH) is soluble in both water (aq) and the organic solvent trichloromethane (CHCl) - two immiscible solvents. If ammonia is first dissolved in water, and then an equal volume of trichloromethane is added, and the two liquids shaken together, the following equilibrium is established:
:K = [NH ]/[NH] (where K is the equilibrium constant)
The equilibrium concentrations of ammonia in each layer can be established by titration with standard acid solution. It can thus be determined that K remains constant, with a value of 0.4 in this case. | 7 | Physical Chemistry |
Bacteria proteins, also known as effectors, have been shown to use AMPylation. Effectors such as VopS, IbpA, and DrrA, have been shown to AMPylate host GTPases and cause actin cytoskeleton changes. GTPases are common targets of AMPylators. Rho, Rab, and Arf GTPase families are involved in actin cytoskeleton dynamics and vesicular trafficking. They also play roles in cellular control mechanisms such as phagocytosis in the host cell.
The pathogen enhances or prevents its internalization by either inducing or inhibiting host cell phagocytosis. Vibrio parahaemolyticus is a Gram-negative bacterium that causes food poisoning as a result of raw or undercooked seafood consumption in humans. VopS, a type III effector found in Vibrio parahaemolyticus, contains a Fic domain that has a conserved HPFx(D/E)GN(G/K)R motif that contains a histidine residue essential for AMPylation. VopS blocks actin assembly by modifying threonine residue in the switch 1 region of Rho GTPases. The transfer of an AMP moiety using ATP to the threonine residue results in steric hindrance, and thus prevents Rho GTPases from interacting with downstream effectors. VopS also adenylates RhoA and cell division cycle 42 (CDC42), leading to a disaggregation of the actin filament network. As a result, the host cell's actin cytoskeleton control is disabled, leading to cell rounding.
IbpA is secreted into eukaryotic cells from H. somni, a Gram-negative bacterium in cattle that causes respiratory epithelium infection. This effector contains two Fic domains at the C-terminal region. AMPylation of the IbpA Fic domain of Rho family GTPases is responsible for its cytotoxicity. Both Fic domains have similar effects on host cells' cytoskeleton as VopS. The AMPylation on a tyrosine residue of the switch 1 region blocks the interaction of the GTPases with downstream substrates such as PAK.
DrrA is the Dot/Icm type IV translocation system substrate DrrA from Legionella pneumophila. It is the effector secreted by L. pneumophila to modify GTPases of the host cells. This modification increases the survival of bacteria in host cells. DrrA is composed of Rab1b specific guanine nucleotide exchange factor (GEF) domain, a C-terminal lipid binding domain and an N-terminal domain with unclear cytotoxic properties. Research works show that N-terminal and full-length DrrA shows AMPylators activity toward hosts Rab1b protein (Ras related protein), which is also the substrate of Rab1b GEF domain. Rab1b protein is the GTPase Rab to regulate vesicle transportation and membrane fusion. The adenylation by bacteria AMPylators prolong GTP-bound state of Rab1b. Thus, the role of effector DrrA is connected toward the benefits of bacterias vacuoles for their replication during the infection. | 1 | Biochemistry |
The Jameson Cell reportedly has the following advantages:
* relatively low energy use – the only energy that is required to operate the Cell is to pump the slurry through the slurry lens. This means that it requires significantly less electricity than conventional mechanical or column flotation cells. In addition, the better particle–bubble contact means that fewer Cells are required for the equivalent duty of mechanical cells, giving an even bigger power saving.
* high recovery of fines – The Cell is able to achieve final product specification from previously discarded coal fines at very high recoveries (95–98%) in a single pass. It has also been shown to be effective in recovering fine particles in base metals, potash and phosphate applications.
* effective froth washing – The Cell uses froth washing as standard to control concentrate grade. A conventional flotation cell has problems with recovering fine particles at high grades due to the entrainment of gangue minerals in the froth. The high throughput of the Jameson Cell means that the froth is produced in a small surface area so it is economic to apply froth washing to all cells
* easily scaled up – the hydrodynamic conditions for particle collection inside the downcomer and separation in the tank are identical between the laboratory, pilot plant and industrial-scale Jameson Cell, meaning that there is direct scale-up. This makes predicting plant performance for small-scale tests straightforward. In contrast, factors have to be used to scale-up the design of mechanical and column flotation cells.
* relatively small footprint – the high intensity of bubble-particle contact means that very low residence times are required in the Cell (residence time in the downcomer is 5–10 seconds and the separation tank volume is small compared with alternative technologies). This means that the total volume of the Cell is lower than the alternatives.
* fast response to process changes – process variables such as air flow rate, froth depth and wash water are all automated making optimisation straightforward. The small tank volumes means very short residence times in the tank (typically 1–3 minutes) so changes made, whether they are deliberate or from normal plant fluctuations, are observed almost instantly.
* rapid start-up and shutdown – the small volume of the tank means that the Cell can be filled and drained quickly so with plant upsets the Cell can reach steady state very quickly.
* low maintenance costs – the Cell has no moving parts and is designed to provide easy access to serviceable parts. The slurry lens orifice has a service life exceeding 5 years under normal operating conditions and the service life of the other wet-end wear parts is reported to be over 10 years under normal operating conditions.
* low capital cost – the small footprint of the Cell reduces the amount of steel required in its construction and, coupled with the simplicity of its design, has lower installation costs when compared with conventional or column flotation cells.
* low operating costs – the lack of moving parts with a consequent lower power consumption, long wear life and easy access results in low operating costs.
* short payback periods – Cell users typically report short payback periods for their investments in the technology. For example, the 2007 installation of a 5.4 m diameter Jameson Cell with 18 downcomers to treat preflotation concentrate recovered up to 90% of the zinc previously lost to the tailings disposal facility and had a payback of approximately one year at the zinc prices of the day. Peko Mines reported a payback period of two months for its Cell installation. The complete replacement of 32 mechanical cells with eight Jameson Cells at the Goonyella coal mine had a payback of 17 months. More recently, the installation of a Cell ahead of each of two cleaner trains at the Telfer Mine had a payback of between two and seven months. | 8 | Metallurgy |
Hyper–Rayleigh scattering optical activity ( ), a form of chiroptical harmonic scattering, is a nonlinear optical physical effect whereby chiral scatterers (such as nanoparticles or molecules) convert light (or other electromagnetic radiation) to higher frequencies via harmonic generation processes, in a way that the intensity of generated light depends on the chirality of the scatterers. "Hyper–Rayleigh scattering" is a nonlinear optical counterpart to Rayleigh scattering. "Optical activity" refers to any changes in light properties (such as intensity or polarization) that are due to chirality. | 4 | Stereochemistry |
With its future thus assured, in 1966 additional laboratories in a new building were opened on the Stoke Poges site. Also in that year Fulmer strengthened its expertise, particularly in electron metallography, by recruiting several key staff who transferred from Aeon Laboratories of Egham, Surrey.
In 1969 Mr Liddiard retired as Director of Research and Dr W E Duckworth was recruited from the British Iron and Steel Research Association and appointed in his place.
In 1970 Fulmer set up a new unit, Fulmer Technical Services (FTS), to provide a focus for its testing and consultancy services to industry.
During this period there was a gradual increase in income and a modest profit while staff numbers remained at about 120. | 8 | Metallurgy |
* Cytochrome P450 monooxygenase system
* Flavin-containing monooxygenase system
* Alcohol dehydrogenase and aldehyde dehydrogenase
* Monoamine oxidase
* Co-oxidation by peroxidases | 1 | Biochemistry |
For a beam of light traveling in air with an approximate index of refraction of 1.0, and encountering the surface of a material having an index of refraction of 1.5: | 7 | Physical Chemistry |
Accurate interpretation takes a variety of factors into account, such as the thyroid hormones i.e. thyroxine (T) and triiodothyronine (T), current medical status (such as pregnancy), certain medications like propylthiouracil, temporal effects including circadian rhythm and hysteresis, and other past medical history. | 1 | Biochemistry |
Unlike end point PCR (conventional PCR), real time PCR allows monitoring of the desired product at any point in the amplification process by measuring fluorescence (in real time frame, measurement is made of its level over a given threshold). A commonly employed method of DNA quantification by real-time PCR relies on plotting fluorescence against the number of cycles on a logarithmic scale. A threshold for detection of DNA-based fluorescence is set 3–5 times of the standard deviation of the signal noise above background. The number of cycles at which the fluorescence exceeds the threshold is called the threshold cycle (C) or, according to the MIQE guidelines, quantification cycle (C).
During the exponential amplification phase, the quantity of the target DNA template (amplicon) doubles every cycle. For example, a DNA sample whose C precedes that of another sample by 3 cycles contained 2 = 8 times more template. However, the efficiency of amplification is often variable among primers and templates. Therefore, the efficiency of a primer-template combination is assessed in a titration experiment with serial dilutions of DNA template to create a standard curve of the change in (C) with each dilution. The slope of the linear regression is then used to determine the efficiency of amplification, which is 100% if a dilution of 1:2 results in a (C) difference of 1. The cycle threshold method makes several assumptions of reaction mechanism and has a reliance on data from low signal-to-noise regions of the amplification profile that can introduce substantial variance during the data analysis.
To quantify gene expression, the (C) for an RNA or DNA from the gene of interest is subtracted from the (C) of RNA/DNA from a housekeeping gene in the same sample to normalize for variation in the amount and quality of RNA between different samples. This normalization procedure is commonly called the ΔC-method and permits comparison of expression of a gene of interest among different samples. However, for such comparison, expression of the normalizing reference gene needs to be very similar across all the samples. Choosing a reference gene fulfilling this criterion is therefore of high importance, and often challenging, because only very few genes show equal levels of expression across a range of different conditions or tissues. Although cycle threshold analysis is integrated with many commercial software systems, there are more accurate and reliable methods of analysing amplification profile data that should be considered in cases where reproducibility is a concern.
Mechanism-based qPCR quantification methods have also been suggested, and have the advantage that they do not require a standard curve for quantification. Methods such as MAK2 have been shown to have equal or better quantitative performance to standard curve methods. These mechanism-based methods use knowledge about the polymerase amplification process to generate estimates of the original sample concentration. An extension of this approach includes an accurate model of the entire PCR reaction profile, which allows for the use of high signal-to-noise data and the ability to validate data quality prior to analysis.
According to research of Ruijter et al. MAK2 assumes constant amplification efficiency during the PCR reaction. However, theoretical analysis of polymerase chain reaction, from which MAK2 was derived, has revealed that amplification efficiency is not constant throughout PCR. While MAK2 quantification provides reliable estimates of target DNA concentration in a sample under normal qPCR conditions, MAK2 does not reliably quantify target concentration for qPCR assays with competimeters. | 1 | Biochemistry |
Bromotrifluoromethane is commercially synthesized in a two-step process from chloroform. Chloroform is fluorinated with hydrogen fluoride.
CHCl3 + 3 HF → CHF3 + 3 HCl
The resulting Fluoroform is then reacted with elemental bromine.
CHF3 + Br2 → CF3Br + HBr | 2 | Environmental Chemistry |
Several TILLING centers exist over the world that focus on agriculturally important species:
*Rice – UC Davis (USA)
*Maize – Purdue University (USA)
*Brassica napus – University of British Columbia (CA)
*Brassica rapa – John Innes Centre (UK)
*Arabidopsis – Fred Hutchinson Cancer Research
*Soybean – Southern Illinois University (USA)
*Lotus and Medicago – John Innes Centre (UK)]
*Wheat – UC Davis (USA)
*Pea, Tomato - INRA (France)
*Tomato - RTGR, University of Hyderabad (India) | 1 | Biochemistry |
Ying Ge is a Chinese-American chemist who is a Professor of Cell and Regenerative Biology at the University of Wisconsin–Madison. Her research considers the molecular mechanisms that underpin cardiac disease. She has previously served on the board of directors of the American Society for Mass Spectrometry. In 2020 Ge was named on the Analytical Scientist Power List. | 1 | Biochemistry |
cAMP-dependent protein kinase type I-alpha regulatory subunit is an enzyme that in humans is encoded by the PRKAR1A gene. | 1 | Biochemistry |
Wild aquatic birds are the natural hosts for a large variety of influenza A viruses. Occasionally viruses are transmitted from this reservoir to other species and may then cause devastating outbreaks in domestic poultry or give rise to human influenza pandemics. | 1 | Biochemistry |
Aryl sulfonic acids are produced by the process of sulfonation. Usually the sulfonating agent is sulfur trioxide. A large scale application of this method is the production of alkylbenzenesulfonic acids:
In this reaction, sulfur trioxide is an electrophile and the arene is the nucleophile. The reaction is an example of electrophilic aromatic substitution.
Alkylsulfonic acids can be prepared by many methods. In sulfoxidation, alkanes are irradiated with a mixture of sulfur dioxide and oxygen. This reaction is employed industrially to produce alkyl sulfonic acids, which are used as surfactants.
Direct reaction of alkanes with sulfur trioxide is not generally useful, except for the conversion methanesulfonic acid to methanedisulfonic acid.
Many alkane sulfonic acids can be obtained by the addition of bisulfite to terminal alkenes. Bisulfite can also be alkylated by alkyl halides:
Sulfonic acids can be prepared by oxidation of thiols:
This pathway is the basis of the biosynthesis of taurine. | 0 | Organic Chemistry |
20β-Dihydroprogesterone (20β-DHP), also known as 20β-hydroxyprogesterone (20β-OHP), is an endogenous metabolite of progesterone which is formed by 20β-hydroxysteroid dehydrogenase (20β-HSD). It is a progestogen similarly to progesterone, with about 20 to 50% of the progestogenic activity of progesterone. It can be converted by 20β-HSD into progesterone in the uterus. The effects of 20β-HSD on the uterus, mammary glands, and in maintaining pregnancy have been studied. The progestogenic activity of 20β-HSD has also been characterized in women. | 1 | Biochemistry |
For liquid moving quickly over a surface, the contact angle can be altered from its value at rest. The advancing contact angle will increase with speed, and the receding contact angle will decrease. The discrepancies between static and dynamic contact angles are closely proportional to the capillary number, noted . | 7 | Physical Chemistry |
Monitoring the relative abundance of comonomer sequences is a common technique and is used, for example, to observe the progress of transesterification reactions between polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) in their blends.
During such a transesterification reaction, three resonances representing four diads can be distinguished via H NMR spectroscopy by different chemical shifts of the oxyethylene units: The diads -terephthalate-oxyethylene-terephthalate- (TET) and -naphthalate-oxyethylene-naphthalate- (NEN), which are also present in the homopolymers polyethylene naphthalate und polyethylene terephthalate, as well as the (indistinguishable) diads -terephthalate-oxyethylene-naphthalate- (TEN) and -naphthalate-oxyethylene-terephthalate- (NET), which are exclusively present in the copolymer. In the spectrum of a 1:1 physical PET/PEN mixture, only the resonances corresponding to the diads TET and NEN are present at 4.90 and 5.00 ppm, respectively. Once a transesterification reaction occurs, a new resonance at 4.95 ppm emerges that increases in intensity with the reaction time, corresponding to the TEN / NET sequences.
The example of polyethylene naphthalate and polyethylene terephthalate is relatively simple, as only the aromatic part of the polymers differ (naphthalate vs. terephthalate). In a blend of polyethylene naphthalate and polytrimethylene terephthalate, already six resonances can be distinguished, since both, oxyethylene and oxypropylene, form three resonances. The sequence patterns can become even more complex, when triads can be distinguished spectroscopically. The extractable information is limited by the difference in chemical shift and the resonance width. In addition to H NMR spectroscopy, also C NMR spectroscopy is a common method for the sequencing shown above, which is characterized in particular by a very narrow resonance width.
Deconvolution and assignment of these triad-based resonances allows a quantitative determination of the degree of randomness and the average block length via integration of the distinguishable resonances. In a 1:1 mixture of two linear two-component 1:1 polycondensates (AB) and (AB) (with molecular weight high enough to neglected chain-ends), the following two equations are valid:
[ A] = [B], wherein (i = 1,2) (1)
[ AB ] = [ AB] (2)
Equation 1 states that the molar ratio of all four repeat units is identical and equation 2 states that both types of copolymer are of identical concentration. In this case, the degree of randomness χ is calculated as given by equation 3:
, wherein (i, j = 1, 2) (3)
In the beginning of a transreaction process (e. g. transesterification or transamidation), the degree of randomness χ ≈ 0 as the system comprises a physical mixture of homopolymers or block copolymers. During the transreaction process χ increases up to χ = 1 for a fully random copolymer. If χ > 1 it indicates a tendency of the monomers to form alternating structure, up to χ = 2 for a completely alternating copolymer. The degree of randomness χ gives thereby statistical information about the polymer sequence. The calculation can be modified for three-component and four-component polycondensates. | 7 | Physical Chemistry |
K. C. Nicolaous group successfully synthesized endiandric acid, 1, in 1982 as a test of Blacks biosynthetic conjecture, using a biomimetic strategy involving series of stereocontrolled electrocyclic reactions. Specifically, they observed that the natural products endiandric acids A and C could have arisen from a common precursor, via slightly different 6π [4s+2s] cycloaddition (Diels-Alder) reactions. This key precursor was in turn accessible biosynthetically via two further thermally allowed sequential 6π electron and 8π electron electrocyclizations.
The Nicolaou group therefore sought to synthesize endiandric acid C from an acyclic symmetric diacetylenic diol precursor, 14 (as shown); they began with "mild hydrogenation" in the presence of Lindlar catalyst and quinoline, anticipating tetraene diol 15, cyclooctatriene 16, or the fully cyclized bicyclo[4.2.0]octadiene (bicyclic diol) 17. Remarkably, following this 3-6 hour, 25 °C process, a 45-55% yield of bicyclic diol 17 could be isolated. Hence, it was not necessary to do anything specific to promote the required sequence of 8π conrotatory and 6π disrotatory cyclizations (further highlighted in supplementary image); they occurred spontaneously on generation of tetraene-diol 15. Protection of a single alcohol moiety (as TBDPS) was accomplished using the silyl chloride via the corresponding tricyclic iodoether intermediate (not shown), with the internally masked remaining hydroxyl group being released on treatment with zinc dust in acetic acid (giving 18 in 70-80% yield). Bromination of the alcohol under Appel conditions followed by its displacement on treatment with sodium cyanide in HMPA gave nitrile 20, the key intermediate in all of this groups endiandric acid syntheses.'
The title compound was then pursued via DIBAL reduction of the nitrile at low temperature, followed by mild acidic hydrolysis to release aldehyde 21. A series of 7 further steps—condensation to form trans-butenoate 22, thermal intramolecular Diels-Alder reaction to create the tetracyclic endiantric core structure 23, desilylation to unmask alcohol 24, bromination and nitrile formation (as described above) to give 25 and 26, respectively, then hydrolysis of the methyl ester and repeat of the earlier DIBAL/acid hydrolysis sequence—generated the endiantric core structure with pendant aldehyde, 28, that was poised for the final step. Its treatment with diethyl cinnamylphosphonate and LDA at low temperature in THF (generating en route the anionic olefination reagent) formed the desired diene in good yield in a "geometrically controlled manner", thus providing the desired endiandric acid C product. | 0 | Organic Chemistry |
A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals. The input signal that most common spectrum analyzers measure is electrical; however, spectral compositions of other signals, such as acoustic pressure waves and optical light waves, can be considered through the use of an appropriate transducer. Spectrum analyzers for other types of signals also exist, such as optical spectrum analyzers which use direct optical techniques such as a monochromator to make measurements.
By analyzing the spectra of electrical signals, dominant frequency, power, distortion, harmonics, bandwidth, and other spectral components of a signal can be observed that are not easily detectable in time domain waveforms. These parameters are useful in the characterization of electronic devices, such as wireless transmitters.
The display of a spectrum analyzer has frequency displayed on the horizontal axis and the amplitude on the vertical axis. To the casual observer, a spectrum analyzer looks like an oscilloscope, which plots amplitude on the vertical axis but time on the horizontal axis. In fact, some lab instruments can function either as an oscilloscope or a spectrum analyzer. | 7 | Physical Chemistry |
Triethyl phosphonoacetate is a reagent for organic synthesis used in the Horner-Wadsworth-Emmons reaction (HWE) or the Horner-Emmons modification.
Triethyl phosphonoacetate can be added dropwise to sodium methoxide solution to prepare a phosphonate anion. It has an acidic proton that can easily be abstracted by a weak base. When used in an HWE reaction with a carbonyl the resulting alkene formed is usually the E alkene, and is generated with excellent regioselectivity. | 0 | Organic Chemistry |
In chemistry, one usually ignores distinctions between isotopes of the same element. However, in some situations (for instance in Raman, NMR, or microwave spectroscopy) one may treat different isotopes of the same element as different elements. In the second case, two molecules with the same number of atoms of each isotope but distinct bonding schemes are said to be structural isotopomers.
Thus, for example, ethene would have no structural isomers under the first interpretation; but replacing two of the hydrogen atoms (H) by deuterium atoms (H) may yield any of two structural isotopomers (1,1-dideuteroethene and 1,2-dideuteroethene), if both carbon atoms are the same isotope. If, in addition, the two carbons are different isotopes (say, C and C), there would be three distinct structural isotopomers, since 1-C-1,1-dideuteroethene would be different from 1-C-2,2-dideuteroethene.) And, in both cases, the 1,2-dideutero structural isotopomer would occur as two stereo isotopomers, cis and trans. | 4 | Stereochemistry |
Terrestrial planets are believed to have come from the same nebular material as the giant planets, but they have lost most of the lighter elements and have different histories. Planets closer to the Sun might be expected to have a higher fraction of refractory elements, but if their later stages of formation involved collisions of large objects with orbits that sampled different parts of the Solar System, there could be little systematic dependence on position.
Direct information on Mars, Venus and Mercury largely comes from spacecraft missions. Using gamma-ray spectrometers, the composition of the crust of Mars has been measured by the Mars Odyssey orbiter, the crust of Venus by some of the Venera missions to Venus, and the crust of Mercury by the MESSENGER spacecraft. Additional information on Mars comes from meteorites that have landed on Earth (the Shergottites, Nakhlites, and Chassignites, collectively known as SNC meteorites). Abundances are also constrained by the masses of the planets, while the internal distribution of elements is constrained by their moments of inertia.
The planets condensed from the solar nebula, and much of the details of their composition are determined by fractionation as they cooled. The phases that condense fall into five groups. First to condense are materials rich in refractory elements such as Ca and Al. These are followed by nickel and iron, then magnesium silicates. Below about 700 kelvins (700 K), FeS and volatile-rich metals and silicates form a fourth group, and in the fifth group FeO enter the magnesium silicates. The compositions of the planets and the Moon are chondritic, meaning that within each group the ratios between elements are the same as in carbonaceous chondrites.
The estimates of planetary compositions depend on the model used. In the equilibrium condensation model, each planet was formed from a feeding zone in which the compositions of solids were determined by the temperature in that zone. Thus, Mercury formed at 1400 K, where iron remained in a pure metallic form and there was little magnesium or silicon in solid form; Venus at 900 K, so all the magnesium and silicon condensed; Earth at 600 K, so it contains FeS and silicates; and Mars at 450 K, so FeO was incorporated into magnesium silicates. The greatest problem with this theory is that volatiles would not condense, so the planets would have no atmospheres and Earth no atmosphere.
In chondritic mixing models, the compositions of chondrites are used to estimate planetary compositions. For example, one model mixes two components, one with the composition of C1 chondrites and one with just the refractory components of C1 chondrites. In another model, the abundances of the five fractionation groups are estimated using an index element for each group. For the most refractory group, uranium is used; iron for the second; the ratios of potassium and thallium to uranium for the next two; and the molar ratio FeO/(FeO+MgO) for the last. Using thermal and seismic models along with heat flow and density, Fe can be constrained to within 10 percent on Earth, Venus, and Mercury. U can be constrained within about 30% on Earth, but its abundance on other planets is based on "educated guesses". One difficulty with this model is that there may be significant errors in its prediction of volatile abundances because some volatiles are only partially condensed. | 9 | Geochemistry |
Diorganophosphites are derivatives of phosphorus(V) and can be viewed as the di-esters of phosphorous acid ((HO)P(O)H). They exhibit tautomerism, however, the equilibrium overwhelmingly favours the right-hand (phosphonate-like) form:
:(RO)POH ⇌ (RO)P(O)H
The P-H bond is the site of high reactivity in these compounds (for example in the Atherton–Todd reaction and Hirao coupling), whereas in tri-organophosphites the lone pair on phosphorus is the site of high reactivity. Diorganophosphites do however undergo transesterification. | 0 | Organic Chemistry |
Fracturing is a brittle deformation process that creates permanent linear breaks, that are not accompanied by displacement within materials. These linear breaks or openings can be independent or interconnected. For fracturing to occur, the ultimate strength of the materials need to be exceeded to a point where the material ruptures. Rupturing is aided by the accumulations of high differential stress (the difference between the maximum and minimum stress acting on the object). Most fracture grow into faults. However, the term fault is only used when the fracture plane accommodate some degree of movement. Fracturing can happen across all scales, from microfractures to macroscopic fractures and joints in the rocks. | 8 | Metallurgy |
One of the innovations for night and all-weather flying used by the US, UK, Japan and Germany during World War II was the use of UV interior lighting to illuminate the instrument panel, giving a safer alternative to the radium-painted instrument faces and pointers, and an intensity that could be varied easily and without visible illumination that would give away an aircraft's position. This went so far as to include the printing of charts that were marked in UV-fluorescent inks, and the provision of UV-visible pencils and slide rules such as the E6B.
They may also be used to test for LSD, which fluoresces under black light while common substitutes such as 25I-NBOMe do not.
Strong sources of long-wave ultraviolet light are used in tanning beds. | 5 | Photochemistry |
Aequorin is a calcium-activated photoprotein isolated from the hydrozoan Aequorea victoria. Its bioluminescence was studied decades before the protein was isolated from the animal by Osamu Shimomura in 1962. In the animal, the protein occurs together with the green fluorescent protein to produce green light by resonant energy transfer, while aequorin by itself generates blue light.
Discussions of "jellyfish DNA" that can make "glowing" animals often refer to transgenic animals that express the green fluorescent protein, not aequorin, although both originally derive from the same animal.
Apoaequorin, the protein portion of aequorin, is an ingredient in the dietary supplement Prevagen. The US Federal Trade Commission (FTC) has charged the maker with false advertising for its memory improvement claims. | 1 | Biochemistry |
Lectins is a generic name for proteins with carbohydrate-recognizing domains (CRD). Although it became almost synonymous with glycan-binding proteins, it does not include antibodies which also belong to the class.
Lectins found in plants and fungi cells have been extensively used in research as a tool to detect, purify, and analyze glycans. However, useful lectins usually have sub-optimal specificities. For instance, Ulex europaeus agglutinin-1 (UEA-1), a plant-extracted lectin capable of binding to human blood type O antigen, can also bind to unrelated glycans such as 2'-fucosyllactose, GalNAcα1-4(Fucα1-2)Galβ1-4GlcNAc, and Lewis-Y antigen. | 1 | Biochemistry |
There is a market for vials of processed sperm and for various reasons a sperm bank may sell-on stocks of vials which it holds known as onselling. The costs of screening of donors and storage of frozen donor sperm vials are not insignificant and in practice most sperm banks will try to dispose of all samples from an individual donor. The onselling of sperm therefore enables a sperm bank to maximize the sale and disposal of sperm samples which it has processed. The reasons for onselling may also be where part of, or even the main business of, a particular sperm bank is to process and store sperm rather than to use it in fertility treatments, or where a sperm bank is able to collect and store more sperm than it can use within nationally set limits. In the latter case a sperm bank may onsell sperm from a particular donor for use in another jurisdiction after the number of pregnancies achieved from that donor has reached its national maximum.
Sperm banks may supply other sperm banks or a fertility clinic with donor sperm to be used for achieving pregnancies.
Sperm banks may also supply sperm for research or educational purposes. | 1 | Biochemistry |
Jean-Claude Duplessy, born in 1942, is a French geochemist. He is Director of Research Emeritus at the CNRS and a member of the French Academy of Sciences. | 9 | Geochemistry |
Prehistoric links between Mesoamerica and the Andes have been suggested on several occasions. Early Mesoamerican and Ecuadorian pottery style show some similarities, both in technique and motifs. Likewise, similarities in early burial styles (so-called "shaft tombs") present in Ecuador and western Mesoamerica have been pointed out. Even the origins of the Purépecha people in Michoacán have been suggested as lying in South America. However, none of these proposals are widely accepted by specialists. More widely accepted is the influence of South American metallurgy on Mesoamerica.
South American metallurgy itself can be divided into two traditions: one in Peru, southern Ecuador, and Bolivia, which used copper, tin, silver, gold, and arsenic in various alloys with a variety of uses; and a second in Colombia and southern Central America, the so-called Intermediate Area, which relied on gold and copper for largely artistic rather than utilitarian purposes. The metallurgical tradition of western Mesoamerica, though geographically closer to the Intermediate Zone, is much closer in form and function to the southern Ecuadorian tradition. The form and method of creating interlocking metal rings is identical in the two traditions, and even their archaeological context (placed around the cranium in burials) is remarkably similar. Fish-hooks, needles, and tweezers, also appear in both traditions. However, the wax-casting tradition of the Intermediate Area, which spread to other parts of Mesoamerica, also proved influential in the western Mesoamerican context, such as in the creation of copper-gold alloy bells. | 8 | Metallurgy |
Beryllide is an intermetallic compound of beryllium with other metals, e.g. zirconium, tantalum, titanium, nickel, or cobalt. Typical chemical formulae are BeTi and FeBe. These are hard, metal-like materials that display properties distinct from the constituents, especially with regards to their resilience toward oxidation. | 8 | Metallurgy |
The Hammett acidity function (H) is a measure of acidity that is used for very concentrated solutions of strong acids, including superacids. It was proposed by the physical organic chemist Louis Plack Hammett and is the best-known acidity function used to extend the measure of Brønsted–Lowry acidity beyond the dilute aqueous solutions for which the pH scale is useful.
In highly concentrated solutions, simple approximations such as the Henderson–Hasselbalch equation are no longer valid due to the variations of the activity coefficients. The Hammett acidity function is used in fields such as physical organic chemistry for the study of acid-catalyzed reactions, because some of these reactions use acids in very high concentrations, or even neat (pure). | 7 | Physical Chemistry |
Blood or urine tests measure hCG. These can be pregnancy tests. hCG-positive can indicate an implanted blastocyst and mammalian embryogenesis or can be detected for a short time following childbirth or pregnancy loss. Tests can be done to diagnose and monitor germ cell tumors and gestational trophoblastic diseases.
Concentrations are commonly reported in thousandth international units per milliliter (mIU/mL). The international unit of hCG was originally established in 1938 and has been redefined in 1964 and in 1980. At the present time, 1 international unit is equal to approximately 2.35×10 moles, or about 6×10 grams.
It is also possible to test for hCG to have an approximation of the gestational age. | 1 | Biochemistry |
One of the more classic applications of DKR is Noyori's asymmetric hydrogenation. The presence of an acidic center between two carbonyl groups allows for easy epimerization at the chiral center under basic conditions. To select for one of the four possible stereoisomers, a BINAP-Ru catalyst is used to control the outcome of the reaction through the steric bulk of the phosphorus ligand. Some of the early transformations are shown below.
To further understand the stereochemical outcome, one must look at the transition state geometry.
The steric bulk of the BINAP ligand coupled with the coordination of ruthenium to the carbonyl oxygen atoms results in high selectivity for hydrogen insertion on one face. This resulting stereochemistry of (R,S) and (R,R) is obtained in 94.5% yield while the other three stereoisomers range from 0.5-3% yield. Noyori's accomplishments of 1990 paved the way for even more useful applications of DKR. | 4 | Stereochemistry |
Heterogeneous nuclear ribonucleoproteins (hnRNPs) are complexes of RNA and protein present in the cell nucleus during gene transcription and subsequent post-transcriptional modification of the newly synthesized RNA (pre-mRNA). The presence of the proteins bound to a pre-mRNA molecule serves as a signal that the pre-mRNA is not yet fully processed and therefore not ready for export to the cytoplasm. Since most mature RNA is exported from the nucleus relatively quickly, most RNA-binding protein in the nucleus exist as heterogeneous ribonucleoprotein particles. After splicing has occurred, the proteins remain bound to spliced introns and target them for degradation.
hnRNPs are also integral to the 40S subunit of the ribosome and therefore important for the translation of mRNA in the cytoplasm. However, hnRNPs also have their own nuclear localization sequences (NLS) and are therefore found mainly in the nucleus. Though it is known that a few hnRNPs shuttle between the cytoplasm and nucleus, immunofluorescence microscopy with hnRNP-specific antibodies shows nucleoplasmic localization of these proteins with little staining in the nucleolus or cytoplasm. This is likely because of its major role in binding to newly transcribed RNAs. High-resolution immunoelectron microscopy has shown that hnRNPs localize predominantly to the border regions of chromatin, where it has access to these nascent RNAs.
The proteins involved in the hnRNP complexes are collectively known as heterogeneous ribonucleoproteins. They include protein K and polypyrimidine tract-binding protein (PTB), which is regulated by phosphorylation catalyzed by protein kinase A and is responsible for suppressing RNA splicing at a particular exon by blocking access of the spliceosome to the polypyrimidine tract. hnRNPs are also responsible for strengthening and inhibiting splice sites by making such sites more or less accessible to the spliceosome. Cooperative interactions between attached hnRNPs may encourage certain splicing combinations while inhibiting others. | 1 | Biochemistry |
The US National Academy of Medicine updated Dietary Reference Intakes (DRIs) in 2001 for vitamin A, which included Recommended Dietary Allowances (RDAs). For infants up to 12 months there was not sufficient information to establish a RDA, so Adequate Intake (AI) is shown instead. As for safety, tolerable upper intake levels (ULs) were also established. For ULs, carotenoids are not added when calculating total vitamin A intake for safety assessments.
The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL defined the same as in United States. For women and men of ages 15 and older, the PRIs are set respectively at 650 and 750 μg RE/day. PRI for pregnancy is 700 μg RE/day, for lactation 1300/day. For children of ages 1–14 years, the PRIs increase with age from 250 to 600 μg RE/day. These PRIs are similar to the US RDAs. The EFSA reviewed the same safety question as the United States, and set ULs at 800 for ages 1–3, 1100 for ages 4–6, 1500 for ages 7–10, 2000 for ages 11–14, 2600 for ages 15–17 and 3000 μg/day for ages 18 and older for preformed vitamin A, i.e., not including dietary contributions from carotenoids. | 1 | Biochemistry |
An organic acid anhydride is an acid anhydride that is also an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the parent acid is a carboxylic acid, the formula of the anhydride being (RC(O))O. Symmetrical acid anhydrides of this type are named by replacing the word acid in the name of the parent carboxylic acid by the word anhydride. Thus, (CHCO)O is called acetic anhydride. Mixed (or unsymmetrical) acid anhydrides, such as acetic formic anhydride (see below), are known, whereby reaction occurs between two different carboxylic acids. Nomenclature of unsymmetrical acid anhydrides list the names of both of the reacted carboxylic acids before the word "anhydride" (for example, the dehydration reaction between benzoic acid and propanoic acid would yield "benzoic propanoic anhydride").
One or both acyl groups of an acid anhydride may also be derived from another type of organic acid, such as sulfonic acid or a phosphonic acid. One of the acyl groups of an acid anhydride can be derived from an inorganic acid such as phosphoric acid. The mixed anhydride 1,3-bisphosphoglyceric acid, an intermediate in the formation of ATP via glycolysis, is the mixed anhydride of 3-phosphoglyceric acid and phosphoric acid. Acidic oxides are also classified as acid anhydrides. | 0 | Organic Chemistry |
Optical tweezers are capable of manipulating nanometer and micron-sized dielectric particles, and even individual atoms, by exerting extremely small forces via a highly focused laser beam. The beam is typically focused by sending it through a microscope objective. Near the narrowest point of the focused beam, known as the beam waist, the amplitude of the oscillating electric field varies rapidly in space. Dielectric particles are attracted along the gradient to the region of strongest electric field, which is the center of the beam. The laser light also tends to apply a force on particles in the beam along the direction of beam propagation. This is due to conservation of momentum: photons that are absorbed or scattered by the tiny dielectric particle impart momentum to the dielectric particle. This is known as the scattering force and results in the particle being displaced slightly downstream from the exact position of the beam waist, as seen in the figure.
Optical traps are very sensitive instruments and are capable of the manipulation and detection of sub-nanometer displacements for sub-micron dielectric particles. For this reason, they are often used to manipulate and study single molecules by interacting with a bead that has been attached to that molecule. DNA and the proteins and enzymes that interact with it are commonly studied in this way.
For quantitative scientific measurements, most optical traps are operated in such a way that the dielectric particle rarely moves far from the trap center. The reason for this is that the force applied to the particle is linear with respect to its displacement from the center of the trap as long as the displacement is small. In this way, an optical trap can be compared to a simple spring, which follows Hooke's law. | 1 | Biochemistry |
Various types of aggregates can undergo different chemical reactions and swell inside concrete, leading to damaging expansive phenomena.
;Alkali–silica reaction
The most common are those containing reactive amorphous silica, that can react in the presence of water with the cement alkalis (KO and NaO). Among the more reactive siliceous mineral components of some aggregates are opal, chalcedony, flint and strained quartz. Silica (in fact silicic acid when hydrated) is easily dissolved by sodium hydroxide (NaOH) to form sodium silicate (), a strong desiccant with a high affinity for water. This reaction is at the core of the alkali–silica reaction (ASR):
Following this reaction, a hygroscopic and expansive viscous silicagel phase forms inside the affected aggregates which swell and crack from inside. In its turn, the volumetric expansion of the swollen aggregates damages the concrete matrix and extensive cracks propagate causing structural damages in the concrete structure. On the surface of concrete pavements, the ASR can also cause pop-outs, i.e. the expulsion of small cones (up to in diameter), corresponding to aggregate particle size.
A quite similar reaction (alkali-silicate reaction) can occur when clay minerals are present in some impure aggregates, and it may also lead to destructive expansion.
;Alkali–carbonate reaction
With some aggregates containing dolomite, a dedolomitization reaction, also known as alkali-carbonate reaction (ACR), can occur where the magnesium carbonate () reacts with the hydroxyl ions () and yields magnesium hydroxide (brucite, ) and a carbonate ion (). The resulting expansion caused by the swelling of brucite can cause destruction of the material:
Often the alkali–silicate reaction and the dedolomitization reaction are masked by a much more severe alkali–silica reaction dominating the deleterious effects. Because the alkali-carbonate reaction (ACR) is often thwarted by a coexisting ASR reaction, it explains why ACR is no longer considered to be a major detrimental reaction.
;Pyrite oxidation
Far less common are degradation and pop-outs caused by the presence of pyrite (), a disulfide (S-S) very sensitive to oxidation by atmospheric oxygen, that generates expansion by forming less dense insoluble iron oxides (), iron oxy-hydroxides (FeO(OH), or ·n) and mildly soluble gypsum (·2).
When complete (i.e., when all ions are also oxidized into less soluble ions), pyrite oxidation can be globally written as follows:
The sulfuric acid released by pyrite oxidation then reacts with portlandite ()) present in the hardened cement paste to give gypsum:
When concrete is carbonated by atmospheric carbon dioxide (), or if limestone aggregates are used in concrete, reacts with calcite () and water to also form gypsum while releasing back to the atmosphere:
The dihydrated gypsum is relatively soluble in water at room temperature and thus mobile. It can easily be leached by infiltration water and can form efflorescences on the concrete surface while the insoluble ·n remain in place around the grains of oxidized pyrite they taint in red-ocre. | 8 | Metallurgy |
Although chlororespiration is not as efficient as photosynthesis in producing energy, its significance its attributed to its role as a survival adaptation for plants when placed in conditions lacking light and water or if placed in uncomfortable temperatures (note: optimum temperatures vary across different plant species). Additionally, Cournac and Peltier noticed that chlororespiratory ETCs play a role in balancing electron flow across respiratory and photosynthetic ETCs. This helps maintain water balance and regulate the plant's internal temperature. | 1 | Biochemistry |
Protein-RNA interactions may prevent or stabilize the formation of an anti-terminator structure. .. karima eric discovery | 1 | Biochemistry |
Glycoazodyes (or GADs) are a family of "naturalised" synthetic dyes, so called because they are the conjugation of common commercial azo dyes with a sugar through a "linker". This principle is summarised in the scheme below. | 0 | Organic Chemistry |
The monolayer formation time or monolayer time is the length of time required, on average, for a surface to be covered by an adsorbate, such as oxygen sticking to fresh aluminum. If the adsorbate has a unity sticking coefficient, so that every molecule which reaches the surface sticks to it without re-evaporating, then the monolayer time is very roughly:
where t is the time and P is the pressure. It takes about 1 second for a surface to be covered at a pressure of 300 µPa (2×10 Torr). | 7 | Physical Chemistry |
Especially when in concentrated form, organic peroxides can decompose by self-oxidation, since organic peroxides contain both an oxidizer (the O-O bond) and fuel (C-H and C-C bonds). A "self-accelerating decomposition" occurs when the rate of peroxide decomposition generates heat at a faster rate than it can be dissipated to the environment. Temperature is the main factor in the rate of decomposition. The lowest temperature at which a packaged organic peroxide will undergo a self-accelerating decomposition within a week is defined as the self-accelerating decomposition temperature (SADT). A large fire at the Arkema Chemical Plant in Crosby, Texas (USA) in 2017 was caused by the decomposition of various organic peroxides following power failure and subsequent loss of cooling systems. This occurred due to extreme flooding from Hurricane Harvey, which destroyed main and back-up power generators at the site. | 0 | Organic Chemistry |
In organic chemistry, brosyl (or para-bromophenylsulfonyl) group is a functional group with the chemical formula BrCHSO. This group is usually introduced using the compound brosyl chloride, BrCHSOCl, which forms sulfonyl esters and amides of p-bromophenylsulfonic acid. The term brosylate refers to the anion of p-bromophenylsulfonic acid (BrCHSO). | 0 | Organic Chemistry |
The number of mentally disabled veterans including those who have PTSD is increasing some of them increasingly showing signs of mental issues and the mental health conditions have worsened with age in others. | 1 | Biochemistry |
Metallic glasses based on the Mg-Zn-Ca ternary alloy system only consist of the elements which already exist inside the human body. As such, it is being explored as a potential bioresorbable biomaterial for use in orthopaedic applications. | 8 | Metallurgy |
The SELDI process is a combination of surface-enhanced neat desorption (SEND),surface-enhanced affinity-capture (SEAC), and surface-enhanced photolabile attachment and release (SEPAR) mass spectrometry. With SEND, analytes can be desorbed and ionized without adding a matrix; the matrix is incorporated into the sample surface. In SEAC, the sample surface is modified to bind the analyte of interest for analysis with laser desorption/ionization mass spectrometry (LDI-MS). SEPAR is a combination of SEND and SEAC; the modified sample surface also acts as an energy absorbing matrix for ionization. | 1 | Biochemistry |
Biocatalysis refers to the use of living (biological) systems or their parts to speed up (catalyze) chemical reactions. In biocatalytic processes, natural catalysts, such as enzymes, perform chemical transformations on organic compounds. Both enzymes that have been more or less isolated and enzymes still residing inside living cells are employed for this task. Modern biotechnology, specifically directed evolution, has made the production of modified or non-natural enzymes possible. This has enabled the development of enzymes that can catalyze novel small molecule transformations that may be difficult or impossible using classical synthetic organic chemistry. Utilizing natural or modified enzymes to perform organic synthesis is termed chemoenzymatic synthesis; the reactions performed by the enzyme are classified as chemoenzymatic reactions. | 0 | Organic Chemistry |
The density of seawater controls much of the movement of water, or the thermohaline flow, in the ocean. The density of seawater is primarily determined by the temperature and salinity of that water. Changes in these two main parameters, potential temperature Θ and salinity S, are multiplied with their thermal expansion or haline contraction coefficient equal to each other; and are both proportional to a change in density and are both terms of the linearized equation of state of the ocean (TEOS-10). This similarity is supposed to be relevant for understanding the consequences of sea water mixing.
The density doesn't change over an isopycnal. However, by mixing a change in temperature and salinity can occur. Therefore spiciness is introduced as variable that is proportional to thermal expansion and haline contraction. Integration of this variable along an isopycnal leads to the following equation.
Spiciness could be described as the isothermal gradient of the density that equals the isohaline gradient of the density.
The isopycnal gradient of spiciness should equal to the isopycnal gradient of temperature and salinity by multiplication with the derivative in the other variable of the density.
Another mathematical implication for the existence of a spiciness influence manifests itself in a -diagram, where the negative slope of the isopleths equals the ratio between the temperature- and salinity derivative of the spiciness. | 7 | Physical Chemistry |
Membrane emulsification (ME) is a relatively novel technique for producing all types of single and multiple emulsions for DDS (drug delivery systems), solid micro carriers for encapsulation of drug or nutrient, solder particles for surface-mount technology, mono dispersed polymer microspheres (for analytical column packing, enzyme carriers, liquid crystal display spacers, toner core particles). Membrane emulsification was introduced by Nakashima and Shimizu in the late 1980s in Japan. | 7 | Physical Chemistry |
In 1953, Charles Frank proposed a model to demonstrate that homochirality is a consequence of autocatalysis. In his model the and enantiomers of a chiral molecule are autocatalytically produced from an achiral molecule A
while suppressing each other through a reaction that he called mutual antagonism
In this model the racemic state is unstable in the sense that the slightest enantiomeric excess will be amplified to a completely homochiral state. This can be shown by computing the reaction rates from the law of mass action:
where is the rate constant for the autocatalytic reactions, is the rate constant for mutual antagonism reaction, and the concentration of A is kept constant for simplicity.
The analytical solutions for are found to be
Linear stability analysis of this equation shows that the racemic state is unstable. Starting from almost everywhere in the concentration space, the system evolves to a homochiral state.
It is generally understood that autocatalysis alone does not yield to homochirality, and the presence of the mutually antagonistic relationship between the two enantiomers is necessary for the instability of the racemic mixture. However, recent studies show that homochirality could be achieved from autocatalysis in the absence of the mutually antagonistic relationship, but the underlying mechanism for symmetry-breaking is different. | 4 | Stereochemistry |
Hexacoordinate phosphorus molecules involving nitrogen, oxygen, or sulfur ligands provide examples of Lewis acid-Lewis base hexacoordination. For the two similar complexes shown below, the length of the C–P bond increases with decreasing length of the N–P bond; the strength of the C–P bond decreases with increasing strength of the N–P Lewis acid–Lewis base interaction. | 4 | Stereochemistry |
PAC has 2 loxP sites, which can be used by phage recombinases to form the product from its cre-gene recognition during Cre-Lox recombination. This process circularizes the DNA strand, forming a plasmid, which can then be inserted into bacteria such as Escherichia coli. The transformation is usually done by electroporation, which uses electricity to allow the plasmids permeate into the cells. If high expression levels are desired, the P1 lytic replicon can be used in constructs. Electroporation allows for lysogeny of PACs so that they can replicate within cells without disturbing other chromosomes. | 1 | Biochemistry |
Ct filtration is a technique that uses the principles of DNA renaturation kinetics to separate the repetitive DNA sequences that dominate many eukaryotic genomes from "gene-rich" single/low-copy sequences. This allows DNA sequencing to concentrate on the parts of the genome that are most informative and interesting, which will speed up the discovery of new genes and make the process more efficient. | 1 | Biochemistry |
Figure 2 illustrates the most common type of DDRNAI DNA construct, designed to express a shRNA. This figure consists of a promoter sequence driving the expression of sense and antisense sequences separated by a loop sequence, followed by a transcriptional terminator. The antisense sequence processed from the shRNA can bind to the target RNA and specify its degradation. shRNA constructs typically encode sense and antisense sequences of 20–30 nucleotides. Flexibility in construct design is possible; for example, the positions of sense and antisense sequences can be reversed, and other modifications and additions can alter intracellular shRNA processing. Moreover, a variety of promoter loop and terminator sequences can be used.
A beneficial variant is a multi-cassette (Figure 2b). Designed to express two or more shRNAs, they can simultaneously target multiple sequences for degradation hence particularly a useful strategy for targeting viruses. Natural sequence variations can render a single shRNA-target site unrecognizable, preventing RNA degradation. Multi-cassette constructs that target multiple sites within the same viral RNA circumvent this issue. | 1 | Biochemistry |
In a similar way, the assembly of a molecular propeller and a molecular motor can form a nanoscale machine that can pump fluids or perform locomotion. Future applications of these nanosystems range from novel analytical tools in physics and chemistry, drug delivery and gene therapy in biology and medicine, advanced nanofluidic lab-on-a-chip techniques, to tiny robots performing various activities at the nanoscale or microscale. | 6 | Supramolecular Chemistry |
Polysialic acid is an unusual posttranslational modification that occurs on neural cell adhesion molecules (NCAM). Polysialic acid is considerably anionic. This strong negative charge gives this modification the ability to change the protein's surface charge and binding ability. In the synapse, polysialation of NCAM prevents its ability to bind to NCAMs on the adjacent membrane. | 1 | Biochemistry |
FEBS activities include: publishing journals; providing grants for scientific meetings such as an annual Congress, Young Scientists’ Forum and FEBS Advanced Courses; offering travel awards to early-stage scientists to participate in these events; offering research Fellowships for pre- and post-doctoral bioscientists; promoting molecular life science education; encouraging integration of scientists working in economically disadvantaged countries of the FEBS area; and awarding prizes and medals for research excellence. FEBS collaborates with related scientific societies such as its Constituent Societies, the International Union of Biochemistry and Molecular Biology (IUBMB) and the European Molecular Biology Organization (EMBO).
Awards presented by FEBS include the Sir Hans Krebs Medal, the FEBS/EMBO Women in Science Award (presented jointly with EMBO), the Datta medal and the Theodor Bücher medal. | 1 | Biochemistry |
The presence of a charged impermeant ion (for example, a protein) on one side of a membrane will result in an asymmetric distribution of permeant charged ions. The Gibbs–Donnan equation at equilibrium states (assuming permeant ions are Na and Cl):Equivalently, | 7 | Physical Chemistry |
Chowdhury was born on 1 August 1930 to Abdul Aziz Chowdhury, an educationist and Afifa Khatun of Kunja Sreepur village, in Comilla District, Bengal Presidency. | 7 | Physical Chemistry |
Purified extracts of the sweet chili pepper containing capsinoids have been extensively studied through rigorous safety tests, including evaluation of chronic toxicity, reproduction, genotoxicity, and teratology in animals, single oral administration and pharmacokinetics in humans.
Capsinoids are hydrolyzed before absorption and break down to fatty acids and to vanillyl alcohol. According to human studies conducted to date, intact capsinoids are not present in the bloodstream following oral administration, suggesting minimal concern about untoward activation of TRPV1 receptors in other parts of the body. Single dose oral administration of up to 30 mg capsinoids did not raise blood pressure or heart rate in healthy volunteers, nor did administration of CH-19 Sweet. | 1 | Biochemistry |
The dominant epoxides industrially are ethylene oxide and propylene oxide, which are produced respectively on the scales of approximately 15 and 3 million tonnes/year. | 0 | Organic Chemistry |
The first radio-receptor assay (RRA) was done in 1970 by Lefkowitz et al., using a radiolabeled hormone to determine the binding affinity for its receptor.
A radio-receptor assay requires the separation of the bound from the free ligand. This is done by filtration, centrifugation or dialysis.
A method that does not require separation is the scintillation proximity assay that relies on the fact that β-rays from H travel extremely short distances. The receptors are bound to beads coated with a polyhydroxy scintillator. Only the bound ligands to be detected.
Today, the fluorescence method is preferred to radioactive materials due to a much lower cost, lower hazard, and the possibility of multiplexing the reactions in a high-throughput manner. One problem is that fluorescent-labeled ligands have to bear a bulky fluorophore that may cause it to hinder the ligand binding. Therefore, the fluorophore used, the length of the linker, and its position must be carefully selected.
An example is by using FRET, where the ligand's fluorophore transfers its energy to the fluorophore of an antibody raised against the receptor.
Other detection methods such as surface plasmon resonance do not even require fluorophores. | 1 | Biochemistry |
A recent advance in the production of nucleosome core particles with enhanced stability involves site-specific disulfide crosslinks. Two different crosslinks can be introduced into the nucleosome core particle. A first one crosslinks the two copies of H2A via an introduced cysteine (N38C) resulting in histone octamer which is stable against H2A/H2B dimer loss during nucleosome reconstitution. A second crosslink can be introduced between the H3 N-terminal histone tail and the nucleosome DNA ends via an incorporated convertible nucleotide. The DNA-histone octamer crosslink stabilizes the nucleosome core particle against DNA dissociation at very low particle concentrations and at elevated salt concentrations. | 1 | Biochemistry |
In organic chemistry, Hückels rule predicts that a planar ring molecule will have aromatic properties if it has 4n + 2 π electrons, where n is a non-negative integer. The quantum mechanical basis for its formulation was first worked out by physical chemist Erich Hückel in 1931. The succinct expression as the 4n' + 2 rule has been attributed to W. v. E. Doering (1951), although several authors were using this form at around the same time.
In agreement with the Möbius–Hückel concept, a cyclic ring molecule follows Hückels rule when the number of its π-electrons equals 4n + 2, although clearcut examples are really only established for values of n = 0 up to about n = 6. Hückels rule was originally based on calculations using the Hückel method, although it can also be justified by considering a particle in a ring system, by the LCAO method and by the Pariser–Parr–Pople method.
Aromatic compounds are more stable than theoretically predicted using hydrogenation data of simple alkenes; the additional stability is due to the delocalized cloud of electrons, called resonance energy. Criteria for simple aromatics are:
# the molecule must have 4n + 2 (a so-called "Hückel number") π electrons (2, 6, 10, ...) in a conjugated system of p orbitals (usually on sp-hybridized atoms, but sometimes sp-hybridized);
# the molecule must be (close to) planar (p orbitals must be roughly parallel and able to interact, implicit in the requirement for conjugation);
# the molecule must be cyclic (as opposed to linear);
# the molecule must have a continuous ring of p atomic orbitals (there cannot be any sp atoms in the ring, nor do exocyclic p orbitals count). | 7 | Physical Chemistry |
Some mutations that lead to this disorder are:
# a Cytosine (C) to Guanine (G) substitution which converts a tyrosine to stop codon
# a 39 base pair deletion
# a 2 base pair deletion which creates an early stop codon
Endoglin levels have been found to be elevated in pregnant women who subsequently develop preeclampsia. | 1 | Biochemistry |
Sodium ion channels provide an integral service through the body, as they transmit depolarizing impulses at the cellular and intracellular level. This allows sodium ions to coordinate much more intensive processes such as movement and cognition. Sodium ion channels consist of various subunits, however, only the principle subunit is required for function. These sodium ion channels consist of four internally homologous domains, each of which containing six transmembrane segments and resembling a single subunit of a voltage-dependent potassium ion channel. The four domains fold together, forming a central pore. That central pore of the sodium ions dictates the selectivity of the channel: both ionic radius and ionic charge are key in channel selectivity. | 7 | Physical Chemistry |
The main way free oxygen is lost from the atmosphere is via respiration and decay, mechanisms in which animal life and bacteria consume oxygen and release carbon dioxide. | 5 | Photochemistry |
In the ocean, alkalinity is completely dominated by carbonate and bicarbonate plus a small contribution from borate.
Thus the chemical equation for alkalinity in seawater is:
: A = [HCO] + 2[CO] + [B(OH)]
There are many methods of alkalinity generation in the ocean. Perhaps the most well known is the dissolution of calcium carbonate to form Ca and (carbonate). The carbonate ion has the potential to absorb two hydrogen ions. Therefore, it causes a net increase in ocean alkalinity. Calcium carbonate dissolution occurs in regions of the ocean which are undersaturated with respect to calcium carbonate.
The increasing carbon dioxide level in the atmosphere, due to carbon dioxide emissions, results in increasing absorption of CO from the atmosphere into the oceans. This does not affect the ocean's alkalinity but it does result in a reduction in pH value (called ocean acidification). Ocean alkalinity enhancement has been proposed as one option to add alkalinity to the ocean and therefore buffer against pH changes.
Biological processes have a much greater impact on oceanic alkalinity on short (minutes to centuries) timescales. Aerobic respiration of organic matter can decrease alkalinity by releasing protons. Denitrification and sulfate reduction occur in oxygen-limited environments. Both of these processes consume hydrogen ions (thus increasing alkalinity) and release gases (N or HS), which eventually escape into the atmosphere. Nitrification and sulfide oxidation both decrease alkalinity by releasing protons as a byproduct of oxidation reactions. | 9 | Geochemistry |
Pyrex started to make laboratory equipment in 1916 and became a favorite brand for the scientific community due to the borosilicate glass's natural properties. These included strength against; chemicals, thermal shift, and mechanical stress. | 3 | Analytical Chemistry |
Single nucleotide polymorphisms (SNPs) play an important role in genome wide association studies because they act as primary biomarkers. SNPs are currently the marker of choice due to their large numbers in virtually all populations of individuals. The location of these biomarkers can be tremendously important in terms of predicting functional significance, genetic mapping and population genetics. Each SNP represents a nucleotide change between two individuals at a defined location. SNPs are the most common genetic variant found in all individual with one SNP every 100–300 bp in some species. Since there is a massive number of SNPs on the genome, there is a clear need to prioritize SNPs according to their potential effect in order to expedite genotyping and analysis.
Annotating large numbers of SNPs is a difficult and complex process, which need computational methods to handle such a large dataset. Many tools available have been developed for SNP annotation in different organisms: some of them are optimized for use with organisms densely sampled for SNPs (such as humans), but there are currently few tools available that are species non-specific or support non-model organism data. The majority of SNP annotation tools provide computationally predicted putative deleterious effects of SNPs. These tools examine whether a SNP resides in functional genomic regions such as exons, splice sites, or transcription regulatory sites, and predict the potential corresponding functional effects that the SNP may have using a variety of machine-learning approaches. But the tools and systems that prioritize functionally significant SNPs, suffer from few limitations: First, they examine the putative deleterious effects of SNPs with respect to a single biological function that provide only partial information about the functional significance of SNPs. Second, current systems classify SNPs into deleterious or neutral group.
Many annotation algorithms focus on single nucleotide variants (SNVs), considered more rare than SNPs as defined by their minor allele frequency (MAF). As a consequence, training data for the corresponding prediction methods may be different and hence one should be careful to select the appropriate tool for a specific purpose. For the purposes of this article, "SNP" will be used to mean both SNP and SNV, but readers should bear in mind the differences. | 1 | Biochemistry |
In chemical terms, actinism is the property of radiation that lets it be absorbed by a molecule and cause a photochemical reaction as a result. Albert Einstein was the first to correctly theorize that each photon would be able to cause only one molecular reaction. This distinction separates photochemical reactions from exothermic reduction reactions triggered by radiation.
For general purposes, photochemistry is the commonly used vernacular rather than actinic or actino-chemistry, which are again more commonly seen used for photography or imaging. | 7 | Physical Chemistry |
A cascade reaction, also known as a domino reaction or tandem reaction, is a chemical process that comprises at least two consecutive reactions such that each subsequent reaction occurs only in virtue of the chemical functionality formed in the previous step. In cascade reactions, isolation of intermediates is not required, as each reaction composing the sequence occurs spontaneously. In the strictest definition of the term, the reaction conditions do not change among the consecutive steps of a cascade and no new reagents are added after the initial step. By contrast, one-pot procedures similarly allow at least two reactions to be carried out consecutively without any isolation of intermediates, but do not preclude the addition of new reagents or the change of conditions after the first reaction. Thus, any cascade reaction is also a one-pot procedure, while the reverse does not hold true. Although often composed solely of intramolecular transformations, cascade reactions can also occur intermolecularly, in which case they also fall under the category of multicomponent reactions.
The main benefits of cascade sequences include high atom economy and reduction of waste generated by the several chemical processes, as well as of the time and work required to carry them out. The efficiency and utility of a cascade reaction can be measured in terms of the number of bonds formed in the overall sequence, the degree of increase in the structural complexity via the process, and its applicability to broader classes of substrates.
The earliest example of a cascade reaction is arguably the synthesis of tropinone reported in 1917 by Robinson. Since then, the use of cascade reactions has proliferated in the area of total synthesis. Similarly, the development of cascade-driven organic methodology has also grown tremendously. This increased interest in cascade sequences is reflected by the numerous relevant review articles published in the past couple of decades. A growing area of focus is the development of asymmetric catalysis of cascade processes by employing chiral organocatalysts or chiral transition-metal complexes.
Classification
of cascade reactions is sometimes difficult due to the diverse nature of the many
steps in the transformation. K. C. Nicolaou labels the cascades as
nucleophilic/electrophilic, radical, pericyclic or transition-metal-catalyzed,
based on the mechanism of the steps involved. In the cases in which two or more
classes of reaction are included in a cascade, the distinction becomes rather
arbitrary and the process is labeled according to what can be arguably
considered the “major theme”. In order to highlight the remarkable
synthetic utility of cascade reactions, the majority of the examples below come
from the total syntheses of complex molecules. | 0 | Organic Chemistry |
Melzer's is used by exposing fungal tissue or cells to the reagent, typically in a microscope slide preparation, and looking for any of three color reactions:
* Amyloid or Melzer's-positive reaction, in which the material reacts blue to black.
* Pseudoamyloid or dextrinoid reaction, in which the material reacts brown to reddish brown.
* Inamyloid or Melzer's-negative, in which the tissues do not change color, or react faintly yellow-brown.
Among the amyloid reaction, two types can be distinguished:
* Euamyloid reaction, in which the material turns blue without potassium hydroxide (KOH)-pretreatment.
* Hemiamyloid reaction, in which the material turns red in Lugols solution, but shows no reaction in Melzers reagent; when KOH-pretreated it turns blue in both reagents (hemiamyloidity).
Melzer's reactions are typically almost immediate, though in some cases the reaction may take up to 20 minutes to develop.
The function of the chemicals that make up Melzers reagent are several. The chloral hydrate is a clearing agent, bleaching and improving the transparency of various dark-colored microscopic materials. The potassium iodide is used to improve the solubility of the iodine, which is otherwise only semi-soluble in water. Iodine is thought to be the main active staining agent in Melzers; it is thought to react with starch-like polysaccharides in the cell walls of amyloid material, however, its mechanism of action is not entirely understood. It has been observed that hemiamyloid material reacts differently when exposed to Melzers than it does when exposed to other IKI solutions such as Lugols, and that in some cases an amyloid reaction is shown in material that had prior exposure to KOH, but an inamyloid reaction without such pretreatment.
An experiment in which spores from 35 species of basidiomycetes were tested for reactions to both Melzers and Lugols showed that spores in a large percentage of the species tested display very different reactions between the two reagents. These varied from being weakly or non-reactive in Lugols, to giving iodine-positive reactions in Lugols but not in Melzers, to even giving dextrinoid reactions in Lugols while giving amyloid reactions in Melzers.
Melzers degrades into a cloudy precipitate when combined with alkaline solutions, hence it cannot be used in combination or in direct series with such common mycological reagents such as potassium hydroxide or ammonium hydroxide solutions. When potassium hydroxide is used as a pretreatment, the alkalinity must be first neutralized before adding Melzers. | 3 | Analytical Chemistry |
Some η-aldehyde complexes insert alkenes to give five-membered metallacycles.
η-Complexes of alpha-beta unsaturated carbonyls exhibit enhanced reactivity toward dienes. This interaction is the basis of Lewis-acid catalyzed Diels-Alder reactions. | 0 | Organic Chemistry |
The Beilstein test is a simple qualitative chemical test for organic halides. It was developed by Friedrich Konrad Beilstein.
A copper wire is cleaned and heated in a Bunsen burner flame to form a coating of copper(II) oxide. It is then dipped in the sample to be tested and once again heated in a flame. A positive test is indicated by a green flame caused by the formation of a copper halide. The test does not detect fluorine/fluorides.
This test is no longer frequently used. One reason why it is not widely used is that it is possible to generate the highly toxic chloro-dioxins if the test material is a polychloroarene.
An alternative wet test for halide is the sodium fusion test — this test converts organic material to inorganic salts include the sodium halide. Addition of silver nitrate solution causes any halides to precipitate as the respective silver halide. | 3 | Analytical Chemistry |
A second category of reactions under Curtin–Hammett control includes those in which the less stable conformer reacts more quickly. In this case, despite an energetic preference for the less reactive species, the major product is derived from the higher-energy species. An important implication is that the product of a reaction can be derived from a conformer that is at sufficiently low concentration as to be unobservable in the ground state. | 7 | Physical Chemistry |
Petroleum production has been linked with conflict for many years, leading to thousands of deaths due to these wars/conflicts. Petroleum deposits are in hardly any countries around the world; mainly in Russia and some parts of the middle east. Conflicts may start when countries refuse to cut oil production in which other countries respond to such actions by increasing their production causing a trade war as experienced during the 2020 Russia–Saudi Arabia oil price war. Other conflicts start due to countries wanting petroleum resources or other reasons on oil resource territory experienced in the Iran–Iraq War. | 7 | Physical Chemistry |
CO absorbs the ground's thermal radiation mainly at wavelengths between 13 and 17 micron. At this wavelength range, it is almost solely responsible for the attenuation of radiation from the ground. The amount of ground radiation that is transmitted through the atmosphere in each wavelength is related to the optical depth of the atmosphere at this wavelength, OD, by:
The optical depth itself is given by Beer–Lambert law:
where σ is the absorption cross section of a single CO molecule, and n(y) is the
number density of these molecules at altitude y. Due to the high dependence of the cross section in wavelength, the OD changes from around 0.1 at 13 microns to ~10 at 14 microns and even higher beyond 100 at 15 microns, then dropping off to ~10 at 16 microns, ~1 at 17 microns and below 0.1 at 18 microns. Note that the OD depends on the total number of molecules per unit area in the atmosphere, and therefore rises linearly with its CO content.
Looked upon from outer space into the atmosphere at a specific wavelength, one would see to different degrees different layers of the atmosphere, but on average one would see down to an altitude such that the part of the atmosphere from this altitude and up has an optical depth of ~1. Earth will therefore radiate at this wavelength approximately according to the temperature of that altitude. The effect of increasing CO atmospheric content means that the optical depth increases, so that the altitude seen from outer space increases; as long as it increases within the troposphere, the radiation temperature drops and the radiation decreases. When it reaches the tropopause, any further increase in CO levels will have no noticeable effect, since the temperature no longer depends there on the altitude.
At wavelengths of 14 to 16 microns, even the tropopause, having ~0.12 of the amount of CO of the whole atmosphere, has OD>1. Therefore, at these wavelengths Earth radiates mainly in the tropopause temperature, and addition of CO does not change this. At wavelengths smaller than 13 microns or larger than 18 microns, the atmospheric absorption is negligible, and addition of CO hardly changes this. Therefore, the effect of CO increase on radiation is relevant in wavelengths 13–14 and 16–18 microns, and addition on CO mainly contributes to the opacity of the troposphere, changing the altitude that is effectively seen from outer space within the troposphere. | 2 | Environmental Chemistry |
*4.D.1 The Putative Vectorial Glycosyl Polymerization (VGP) Family
*4.D.2 The Glycosyl Transferase 2 (GT2) Family
*4.D.3 The Glycan Glucosyl Transferase (OpgH) Family | 1 | Biochemistry |
The most common example is selective leaching of zinc from brass alloys containing more than 15% zinc (dezincification) in the presence of oxygen and moisture, e.g. from brass taps in chlorine-containing water. Dezincification has been studied since the Civil War era, and the mechanism by which it occurs was under extensive examination by the 1960s. It is believed that both copper and zinc gradually dissolve out simultaneously, and copper precipitates back from the solution. The material remaining is a copper-rich sponge with poor mechanical properties, and a color changed from yellow to red. Dezincification can be caused by water containing sulfur, carbon dioxide, and oxygen. Stagnant or low velocity waters tend to promote dezincification.
To combat this, arsenic or tin can be added to brass, or gunmetal can be used instead. Dezincification resistant brass (DZR), also known as Brass C352 is an alloy used to make pipe fittings for use with potable water. Plumbing fittings that are resistant to dezincification are appropriately marked, with the letters "CR" (Corrosion Resistant) or DZR (dezincification resistant) in the UK, and the letters "DR" (dezincification resistant) in Australia. | 8 | Metallurgy |
Most nonparasitic copepods are holoplanktonic, meaning they stay planktonic for all of their lifecycles, although harpacticoids, although free-living, tend to be benthic rather than planktonic.
During mating, the male copepod grips the female with his first pair of antennae, which is sometimes modified for this purpose. The male then produces an adhesive package of sperm and transfers it to the females genital opening with his thoracic limbs. Eggs are sometimes laid directly into the water, but many species enclose them within a sac attached to the females body until they hatch. In some pond-dwelling species, the eggs have a tough shell and can lie dormant for extended periods if the pond dries up.
Eggs hatch into nauplius larvae, which consist of a head with a small tail, but no thorax or true abdomen. The nauplius moults five or six times, before emerging as a "copepodid larva". This stage resembles the adult, but has a simple, unsegmented abdomen and only three pairs of thoracic limbs. After a further five moults, the copepod takes on the adult form. The entire process from hatching to adulthood can take a week to a year, depending on the species and environmental conditions such as temperature and nutrition (e.g., egg-to-adult time in the calanoid Parvocalanus crassirostris is ~7 days at but 19 days at . | 2 | Environmental Chemistry |
Base editors used for prime editing require delivery of both a protein and RNA molecule into living cells. Introducing exogenous gene editing technologies into living organisms is a significant challenge. One potential way to introduce a base editor into animals and plants is to package the base editor into a viral capsid. The target organism can then be transduced by the virus to synthesize the base editor in vivo. Common laboratory vectors of transduction such as lentivirus cause immune responses in humans, so proposed human therapies often centered around adeno-associated virus (AAV) because AAV infections are largely asymptomatic. Unfortunately, the effective packaging capacity of AAV vectors is small, approximately 4.4kb not including inverted terminal repeats. As a comparison, an SpCas9-reverse transcriptase fusion protein is 6.3kb, which does not even account for the lengthened guide RNA necessary for targeting and priming the site of interest. However, successful delivery in mice has been achieved by splitting the editor into two AAV vectors or by using an adenovirus, which has a larger packaging capacity. | 1 | Biochemistry |
Lugol's iodine, also known as aqueous iodine and strong iodine solution, is a solution of potassium iodide with iodine in water. It is a medication and disinfectant used for a number of purposes. Taken by mouth it is used to treat thyrotoxicosis until surgery can be carried out, protect the thyroid gland from radioactive iodine, and to treat iodine deficiency. When applied to the cervix it is used to help in screening for cervical cancer. As a disinfectant it may be applied to small wounds such as a needle stick injury. A small amount may also be used for emergency disinfection of drinking water.
Side effects may include allergic reactions, headache, vomiting, and conjunctivitis. Long term use may result in trouble sleeping and depression. It should not typically be used during pregnancy or breastfeeding. Lugol's iodine is a liquid made up of two parts potassium iodide for every one part elemental iodine in water.
Lugols iodine was first made in 1829 by the French physician Jean Lugol. It is on the World Health Organizations List of Essential Medicines. Lugols iodine is available as a generic medication and over the counter. Lugols solution is available in different strengths of iodine. Large volumes of concentrations more than 2.2% may be subject to regulation. | 3 | Analytical Chemistry |
In instances where the biomass and enzyme concentrations are not appreciably changing in time, we can assume that biomass dynamics is negligible and that the total enzyme concentration is constant, and the GEBIK equations become
Eqs. () for isotopic compositions, Eq. () for the fractionation factor and Eq. () for the enrichment factor equally applies to the GEBIK equations under the BFEI hypothesis. | 7 | Physical Chemistry |
A fundamental assumption in this interpretation of the f-ratio is the spatial separation of primary production and nitrification. Indeed, in their original paper, Eppley & Peterson noted that: "To relate new production to export requires that nitrification in the euphotic zone be negligible." However, subsequent observational work on the distribution of nitrification has found that nitrification can occur at shallower depths, and even within the photic zone.
As the adjacent diagram shows, if ammonium is indeed nitrified to nitrate in the ocean's surface waters it essentially "short circuits" the deep pathway of nitrate. In practice, this would lead to an overestimation of new production and a higher f-ratio, since some of the ostensibly new production would actually be fuelled by recently nitrified nitrate that had never left the surface ocean. After including nitrification measurements in its parameterisation, an ecosystem model of the oligotrophic subtropical gyre region (specifically the BATS site) found that, on an annual basis, around 40% of surface nitrate was recently nitrified (rising to almost 90% during summer). A further study synthesising geographically diverse nitrification measurements found high variability but no relationship with depth, and applied this in a global-scale model to estimate that up to a half of surface nitrate is supplied by surface nitrification rather than upwelling.
Although measurements of the rate of nitrification are still relatively rare, they do suggest that the f-ratio is not as straightforward a proxy for the biological pump as was once thought. For this reason, some workers have proposed distinguishing between the f-ratio and the ratio of particulate export to primary production, which they term the pe-ratio. While quantitatively different from the f-ratio, the pe-ratio shows similar qualitative variation between high productivity/high biomass/high export regimes and low productivity/low biomass/low export regimes.
In addition, a further process that potentially complicates the use of the f-ratio to estimate "new" and "regenerated" production is dissimilatory nitrate reduction to ammonium (DNRA). In low oxygen environments, such as oxygen minimum zones and seafloor sediments, chemoorganoheterotrophic microbes use nitrate as an electron acceptor for respiration, reducing it to nitrite, then to ammonium. Since, like nitrification, DNRA alters the balance in the availability of nitrate and ammonium, it has the potential to introduce inaccuracy to the calculated f-ratio. However, as DNRA's occurrence is limited to anaerobic situations, its importance is less widespread than nitrification, although it can occur in association with primary producers. | 9 | Geochemistry |
Yellow H-A or Reactive Yellow 3 has a formula of CHClNOS and a molecular weight of 593 g/mol, containing a monochlorotriazine ring. On agarose as supporting matrix, it was seen to purify cholesteryl ester transfer protein. | 3 | Analytical Chemistry |
The density of aluminium granules ranges from 1.0 to 1.8 g/cm and is much higher compared to aluminium powder. | 8 | Metallurgy |
SOFIA provides, among other things, methods to diagnose prion diseases by detection of PrP in biological samples. Samples can be brain tissue, nerve tissue, blood, urine, lymphatic fluid, cerebrospinal fluid, or a combination thereof. Absence of PrP indicates no infection with the infectious agent up to the detection limits of the methods. Detection of a presence of PrP indicates infection with the infectious agent associated with prion disease. Infection with the prion agent may be detected in both presymptomatic and symptomatic stages of disease progression.
These and other improvements have been achieved with SOFIA. SOFIA's sensitivity and specificity eliminates the need for PK digestion to distinguish between the normal and abnormal PrP isoforms. Further detection of PrP in blood plasma has been addressed by limited protein misfolding cyclic amplification (PMCA) followed by SOFIA. Because of the sensitivity of SOFIA, PMCA cycles can be reduced, thus decreasing the chances of spontaneous PrP formation and the detection of false-positive samples. SOFIA meets the needs of increased sensitivity in the detection of prion diseases in both presymptomatic and symptomatic TSE infected animals, including humans, by providing methods of analysis using highly sensitive instrumentation, which requires less sample preparation than previously described methods, in combination with recently developed Mabs against PrP. The method of the present version of SOFIA provides sensitivity levels sufficient to detect PrP in brain tissue. When coupled with limited sPMCA, the methods of the present inventions provide sensitivity levels sufficient to detect PrP in blood plasma, tissue and other fluids collected antemortem.
The methods combine the specificity of the Mabs for antigen capture and concentration with the sensitivity of a surround optical fiber detection technology. In contrast to previously described methods for detection of PrP in brain homogenates, these techniques, when used to study brain homogenates, do not use seeded polymerization, amplification, or enzymatic digestion (for example, by proteinase K, or “PK”). This is important in that previous reports have indicated the existence of PrP isoforms with varied PK sensitivity, which decreases reliability of the assay. The sensitivity of this assay makes it suitable as a platform for rapid prion detection assay in biological fluids. In addition to prion diseases, the method may provide a means for rapid, high-throughput testing for a wide spectrum of infections and disorders.
While about 40 cycles of sPMCA combined with immunoprecipitation were found to be inadequate for PrP detection in plasma by ELISA or western blotting, the PrP has also been found to be readily measured by SOFIA methods. The limited numbers of cycles necessary for the present assay platform virtually eliminates the possibility of obtaining PMCA-related false-positive results such as those previously reported (Thorne and Terry, 2008). | 1 | Biochemistry |
The main technological driver for the exploration of multiferroics has been their potential for controlling magnetism using electric fields via their magneto electric coupling. Such a capability could be technologically transformative, since the production of electric fields is far less energy intensive than the production of magnetic fields (which in turn require electric currents) that are used in most existing magnetism-based technologies. There have been successes in controlling the orientation of magnetism using an electric field, for example in heterostructures of conventional ferromagnetic metals and multiferroic BiFeO, as well as in controlling the magnetic state, for example from antiferromagnetic to ferromagnetic in FeRh.
In multiferroic thin films, the coupled magnetic and ferroelectric order parameters can be exploited for developing magnetoelectronic devices. These include novel spintronic devices such as tunnel magnetoresistance (TMR) sensors and spin valves with electric field tunable functions. A typical TMR device consists of two layers of ferromagnetic materials separated by a thin tunnel barrier (~2 nm) made of a multiferroic thin film. In such a device, spin transport across the barrier can be electrically tuned. In another configuration, a multiferroic layer can be used as the exchange bias pinning layer. If the antiferromagnetic spin orientations in the multiferroic pinning layer can be electrically tuned, then magnetoresistance of the device can be controlled by the applied electric field. One can also explore multiple state memory elements, where data are stored both in the electric and the magnetic polarizations. | 7 | Physical Chemistry |
Anisotropic terahertz microspectrosopy (ATM) has found applications in structural biology and molecular fingerprinting of DNA and proteins. The technique is also suitable for drug discovery and studying THz frequency properties of thin film solid state materials.
Special attention is given to molecular motions in proteins where many structural changes occur at frequencies in the terahertz range of the spectrum (0.3 THz to 3 THz). These structural changes include hinge motions in which two regions of molecules are connected together by a flexible molecular structure that bends like a mechanical hinge or elbow. ATM is uniquely capable of measuring the spatial direction in which hinge motions occur because of its use of linearly polarized electric fields. | 7 | Physical Chemistry |
The following inclusion types can also be found in aluminium alloys: alumina needles (AlO), nitrides (AlN), iron oxides (FeO), manganese oxides (MnO), fluorides (NaAlF, NaF, CaF, …), aluminium borides (AlB, AlB), borocarbides (AlCB).
Bone ash (Ca(PO)) sometimes added to patch cracks in the trough can be found as inclusions in the melt. | 8 | Metallurgy |
Now, given the considerations of background, peak shape functions, integrated intensity, and non-linear least squares minimization, the parameters used in the Rietveld refinement which put these things together can be introduced. Below are the groups of independent least squares parameters generally refined in a Rietveld refinement.
* Background parameters: usually 1 to 12 parameters.
* Sample displacement: sample transparency, and zero shift corrections. (move peak position)
* Multiple peak shape parameters.
** FWHM parameters: i.e. Caglioti parameters (see section 3.1.2)
** Asymmetry parameters (FCJ parameters)
* Unit cell dimensions
** one to six parameters (a, b, c, α, β, γ), depending on the crystal family/system, for each present phase.
* Preferred orientation, and sometimes absorption, porosity, and extinction coefficients, which can be independent for each phase.
* Scale factors (for each phase)
* Positional parameters of all independent atoms in the crystal model (generally 0 to 3 per atom).
* Population parameters
** Occupation of site positions by atoms.
* Atomic displacement parameters
** Isotropic and anisotropic (temperature) parameters.
Each Rietveld refinement is unique and there is no prescribed sequence of parameters to include in a refinement. It is up to the user to determine and find the best sequence of parameters for refinement. It is worth noting that it is rarely possible to refine all relevant variables simultaneously from the beginning of a refinement, nor near the end since the least squares fitting will be destabilized or lead to a false minimum. It is important for the user to determine a stopping point for a given refinement. Given the complexity of Rietveld refinement it is important to have a clear grasp of the system being studied (sample, and instrumentation) to ensure that results are accurate, realistic, and meaningful. High data quality, a large enough range, and a good model – to serve as the initial approximation in the least squares fitting – are necessary for a successful, reliable, and meaningful Rietveld refinement. | 3 | Analytical Chemistry |
Dissociative photoionization processes can be generalized as:
If the enthalpies of formation of two of the three species are known, the third can be calculated with the help of the dissociative photoionization energy, E, using Hess's law. This approach was used, for instance, to determine the enthalpy of formation of the methyl ion, , which in turn was used to obtain the enthalpy of formation of iodomethane, as 15.23 kJ mol, with an uncertainty of only 0.3 kJ mol.
If different sample molecules produce shared fragment ions, a complete thermochemical chain can be constructed, as was shown for some methyl trihalides, where the uncertainty in e.g. the , (Halon-1021) heat of formation was reduced from 20 to 2 kJ mol. Furthermore, dissociative photoionization energies can be combined with calculated isodesmic reaction energies to build thermochemical networks. Such an approach was used to revise primary alkylamine enthalpies of formation. | 7 | Physical Chemistry |
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