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Dicloxacillin is a narrow-spectrum β-lactam antibiotic of the penicillin class. It is used to treat infections caused by susceptible (non-resistant) Gram-positive bacteria. It is active against beta-lactamase-producing organisms such as Staphylococcus aureus, which would otherwise be resistant to most penicillins. Dicloxacillin is available under a variety of trade names including Diclocil (BMS).
It was patented in 1961 and approved for medical use in 1968. It is available as a generic medication. | 4 | Stereochemistry |
The Academy of Nutrition and Dietetics (AND) provides clinical guidance for preparing a subject for RMR measures, in order to mitigate possible confounding factors from feeding, stressful physical activities, or exposure to stimulants such as caffeine or nicotine:
Further, the correct use of a well-maintained indirect calorimeter includes achieving a natural and steady breathing pattern in order to reveal oxygen consumption and carbon dioxide production rates under a reproducible resting condition. Indirect calorimetry is considered the gold-standard method to measure RMR. Indirect calorimeters are usually found in laboratory and clinical settings, but technological advancements are bringing RMR measurement to free-living conditions. | 1 | Biochemistry |
A second major group of British bun ingots date to the Roman period and are found mostly in the copper-rich highland areas of Wales and in Scotland. They are heavier than the LBA examples, with weights ranging between 12 and 22 kg.
Some have stamps clearly dating them to the Roman period including an example that reads SOCIO ROMAE NATSOL. The term "socio" suggests that the ingots were cast by a private company rather than by the state. Fraser Hunter reassessed the context of the Scottish examples and some of the unstamped Welsh examples and argues that they could in fact date to the Iron Age or at least reflect native rather than Roman copper working. Although ingots of any sort are not common in the British Iron Age, planoconvex or bun-shaped ingots exist, e.g. a tin ingot discovered within the Iron Age hillfort at Chun Castle, Cornwall. | 8 | Metallurgy |
In comparison with its better-known archaeal homolog bacteriorhodopsin, most of the active site residues of known importance to the bacteriorhodopsin mechanism are conserved in proteorhodopsin. Sequence similarity is not significantly conserved however, from either halo- or bacterio- rhodopsin. Homologues of the active site residues Arg82, Asp85 (the primary proton acceptor), Asp212 and Lys216 (the retinal Schiff base binding site) in bacteriorhodopsin are conserved as Arg94, Asp97, Asp227 and Lys231 in proteorhodopsin. However, in proteorhodopsin, there are no carboxylic acid residues directly homologous to Glu194 or Glu204 of bacteriorhodopsin (or Glu 108 and 204 depending on the bacRhodopsin variant), which are thought to be involved in the proton release pathway at the extracellular surface. However, Asp97 and Arg94 may replace this functionality without the close residue proximity as in bacteriorhodopsin. The department of chemistry at Syracuse University decisively showed Asp97 cannot be the proton release group as the release happened at forcing conditions under which the aspartic acid group remained protonated. | 5 | Photochemistry |
In 2006, Pilot Pens Inc. developed a pen with erasable ink that utilized thermochromic ink. It was composed of a solvent, a colorant, and a resin film-forming agent. At temperatures below 65 °C, the ink stayed in a colored state. Once temperatures went above 65 °C, the ink began to melt and became colorless, creating the effect of erasable ink. The ink was able to return to its colored state by cooling the temperature down to below -10 °C. | 7 | Physical Chemistry |
The sources of silica can be divided into two categories: silica in organic and inorganic materials. The former category is also known as biogenic silica, which is a ubiquitous material in animals and plants. The latter category is the second most abundant element in Earth's crust. Silicate minerals are the major components of 95% of presently identified rocks. | 9 | Geochemistry |
The Proterozoic is the transition era between anoxic and oxygenated oceans. The classic model is that the end of the Banded iron formations (BIFs) was due to the injection of oxygen into the deep ocean, an approximately 0.6 billion year lag behind the Great Oxygenation Event. Canfield, however, argued that anoxia lasted much longer, and the end of the banded iron formations was due to the introduction of sulfide. Supporting Canfield's original hypothesis, 1.84 billion year old sedimentary records have been found in the Animike group in Canada that exhibit close to full pyritization on top of the last of the banded iron formations, showing evidence of a transition to euxinic conditions in that basin. In order for full pyritization to happen, nearly all of the sulfate in the water was reduced to sulfide, which stripped the iron from the water, forming pyrite. Because this basin was open to the ocean, deep euxinia was interpreted as being a widespread phenomena. This euxinia is hypothesized to have lasted until about 0.8 billion years ago, making basin bottom euxinia a potentially widespread feature throughout the Boring Billion.
Further evidence for euxinia was discovered in the McArthur Basin in Australia, where similar iron chemistry was found. The degree of pyritization and the δS were both high, supporting the presence of anoxia and sulfide, as well as the depletion of sulfate. A different study found biomarkers for green sulfur bacteria and purple sulfur bacteria in the same area, providing further evidence for the reduction of sulfate to hydrogen sulfide.
Molybdenum isotopes have been used to examine the distribution of euxinia in the Proterozoic eon, and suggest that perhaps euxinia was not as widespread as Canfield initially postulated. Bottom waters may have been more widely suboxic than anoxic, and there could have been negative feedback between euxinia and the high levels of surface primary production needed to sustain euxinic conditions. Further work has suggested that from 700 million years ago (late Proterozoic) and onward, the deep oceans may have actually been anoxic and iron rich with conditions similar to those during the formation of BIFs. | 9 | Geochemistry |
This is the simplest method of non-viral transfection. Clinical trials carried out of intramuscular injection of a naked DNA plasmid have occurred with some success; however, the expression has been very low in comparison to other methods of transfection. In addition to trials with plasmids, there have been trials with naked PCR product, which have had similar or greater success. Cellular uptake of naked DNA is generally inefficient. Research efforts focusing on improving the efficiency of naked DNA uptake have yielded several novel methods, such as electroporation, sonoporation, and the use of a "gene gun", which shoots DNA coated gold particles into the cell using high pressure gas. | 1 | Biochemistry |
Chloridometers are used to determine the concentration of chloride ions in biological fluids. For example, fish plasma chloride ion concentration is measured to gauge the effects of stress on osmoregulation in aquacultures. A small quantity of plasma (10 μL) combined with an acid reagent results in a chemical reaction that ultimately provides a concentration measure of chloride ions in meq/L.
Because they require alternating current, chloridometers are not portable and are better suited to a "bench-top location". This may necessitate freezing biological fluid specimens collected in the field for later analysis.
Chloridometers represent the most common use of coulometry in clinical biochemistry. | 3 | Analytical Chemistry |
Alkyl-lithium compounds are stored under inert gas to prevent loss of activity and for reasons of safety. n-BuLi reacts violently with water:
:CHLi + HO → CH + LiOH
This is an exergonic and highly exothermic reaction. If oxygen is present the butane produced may ignite.
BuLi also reacts with CO to give lithium pentanoate:
:CHLi + CO → CHCOLi | 0 | Organic Chemistry |
One of the widely used ways to excite emission of excimer molecules is an electric discharge. There are a lot of discharge types used for pumping excimer lamps. Some examples are glow discharge, pulsed discharge, capacitive discharge, longitudinal and transverse discharges, volume discharge, spark discharge, and microhollow discharge.
, dielectric barrier discharge (DBD), a type of capacitive discharge, is the most common type used in commercial lamps. A benefit of the DBD excimer lamps is that the electrodes are not in direct contact with the active medium (plasma). Absence of interaction between the electrodes and the discharge eliminates electrode corrosion as well as contamination of the active medium by sputtered electrode material, which considerably increases the lifetime of DBD excimer lamps in comparison with others. Moreover, a dielectric barrier discharge ensures effective excitation of a gas mixture in a wide range of working pressures from a few torrs to more than one atmosphere. Excimer lamps can be made in any desired shape of the radiating surface, satisfying requirements of a specific task. | 5 | Photochemistry |
Via the absorption of light, photosensitizers can utilize triplet state transfer to reduce small molecules, such as water, to generate Hydrogen gas. As of right now, photosensitizers have generated hydrogen gas by splitting water molecules at a small, laboratory scale. | 5 | Photochemistry |
In 1952, Stanley Miller and Harold Urey carried out a chemical experiment to demonstrate how organic molecules could have formed spontaneously from inorganic precursors under prebiotic conditions like those posited by the Oparin–Haldane hypothesis. It used a highly reducing (lacking oxygen) mixture of gases—methane, ammonia, and hydrogen, as well as water vapor—to form simple organic monomers such as amino acids. Bernal said of the Miller–Urey experiment that "it is not enough to explain the formation of such molecules, what is necessary, is a physical-chemical explanation of the origins of these molecules that suggests the presence of suitable sources and sinks for free energy." However, current scientific consensus describes the primitive atmosphere as weakly reducing or neutral, diminishing the amount and variety of amino acids that could be produced. The addition of iron and carbonate minerals, present in early oceans, however, produces a diverse array of amino acids. Later work has focused on two other potential reducing environments: outer space and deep-sea hydrothermal vents. | 9 | Geochemistry |
Nitric acid reacts with most metals, but the details depend on the concentration of the acid and the nature of the metal. Dilute nitric acid behaves as a typical acid in its reaction with most metals. Magnesium, manganese, and zinc liberate Hydrogen|:
Nitric acid can oxidize non-active metals such as copper and silver. With these non-active or less electropositive metals the products depend on temperature and the acid concentration. For example, copper reacts with dilute nitric acid at ambient temperatures with a 3:8 stoichiometry:
The nitric oxide produced may react with atmospheric oxygen to give nitrogen dioxide. With more concentrated nitric acid, nitrogen dioxide is produced directly in a reaction with 1:4 stoichiometry:
Upon reaction with nitric acid, most metals give the corresponding nitrates. Some metalloids and metals give the oxides; for instance, Sn, As, Sb, and Ti are oxidized into Tin(IV) oxide|, Arsenic pentoxide|, Antimony pentoxide|, and Titanium dioxide| respectively.
Some precious metals, such as pure gold and platinum-group metals do not react with nitric acid, though pure gold does react with aqua regia, a mixture of concentrated nitric acid and hydrochloric acid. However, some less noble metals (Ag, Cu, ...) present in some gold alloys relatively poor in gold such as colored gold can be easily oxidized and dissolved by nitric acid, leading to colour changes of the gold-alloy surface. Nitric acid is used as a cheap means in jewelry shops to quickly spot low-gold alloys (< 14 karats) and to rapidly assess the gold purity.
Being a powerful oxidizing agent, nitric acid reacts with many non-metallic compounds, sometimes explosively. Depending on the acid concentration, temperature and the reducing agent involved, the end products can be variable. Reaction takes place with all metals except the noble metals series and certain alloys. As a general rule, oxidizing reactions occur primarily with the concentrated acid, favoring the formation of nitrogen dioxide (). However, the powerful oxidizing properties of nitric acid are thermodynamic in nature, but sometimes its oxidation reactions are rather kinetically non-favored. The presence of small amounts of nitrous acid () greatly increases the rate of reaction.
Although chromium (Cr), iron (Fe), and aluminium (Al) readily dissolve in dilute nitric acid, the concentrated acid forms a metal-oxide layer that protects the bulk of the metal from further oxidation. The formation of this protective layer is called passivation. Typical passivation concentrations range from 20% to 50% by volume (see ASTM A967-05). Metals that are passivated by concentrated nitric acid are iron, cobalt, chromium, nickel, and aluminium. | 3 | Analytical Chemistry |
A lattice system is a group of lattices with the same set of lattice point groups. The 14 Bravais lattices are grouped into seven lattice systems: triclinic, monoclinic, orthorhombic, tetragonal, rhombohedral, hexagonal, and cubic. | 3 | Analytical Chemistry |
Although ectopic expression can be caused by a natural condition, it is uncommonly seen in nature because it is a product of defects in gene regulation. In fact, ectopic expression is more commonly used for research purposes. Artificially induced gene expression helps to determine the function of a gene of interest. Common techniques such as overexpressing or misexpressing the genes by UAS-[http://flystocks.bio.indiana.edu/Browse/uas/uashome.htm Gal4] system in D. melanogaster are used. In model organisms, such techniques are used to perform genetic screens to identify a function of the gene involved in specific cellular or developmental processes.
Ectopic expression using these techniques is a useful tool because phenotypes induced in a tissue or cell type where are not normally expressed are easily distinguishable compared to a tissue or cell type where the gene is normally expressed. By the comparison with its basal expression, the function of a gene of interest can be identified.
Although the understanding of ectopic expressions deals with endogenous genes in an organism, it can be expended to a similar concept like transgenesis, which an exogenous gene is introduced to a cell or tissue type in which the gene is not usually expressed. Practices of ectopic expression in biological science is not only limited to identifying a function of the gene in a known cell or tissue type but also implemented to discover unknown or additional functions of the gene by ectopic expression. | 1 | Biochemistry |
Industrial product applications include, sealants, adhesives, extenders for putties used for sealing roofs and windows, coatings, polymer modification, tackified polyethylene films, personal care, polybutene emulsions. Hydrogenated polybutenes are used in a wide variety of cosmetic preparations, such as lipstick and lip gloss. It is used in adhesives owing to its tackiness. Polybutene finds a niche use in bird and squirrel repellents and is ubiquitous as the active agent in mouse and insect "sticky traps".
An important physical property is that higher molecular weight grades thermally degrade to lower-molecular weight polybutenes; those evaporate as well as degrade to butene monomers which can also evaporate. This depolymerization mechanism which allows clean and complete volatization is in contrast to mineral oils which leave gum and sludge or thermoplastics which melt and spread. The property is very valuable for a variety of applications. For smoke inhibition in two stroke engine fuels, the lubricant can degrade at temperatures below the combustion temperature. For electrical lubricants and carriers which might be subject to overheating or fires, polybutene does not result in increased insulation (accelerating the overheating) or conductive carbon deposits. | 7 | Physical Chemistry |
The solved structures of yeast FAS and mammalian FAS show two distinct organizations of highly conserved catalytic domains/enzymes in this multi-enzyme cellular machine. Yeast FAS has a highly efficient rigid barrel-like structure with 6 reaction chambers which synthesize fatty acids independently, while the mammalian FAS has an open flexible structure with only two reaction chambers. However, in both cases the conserved ACP acts as the mobile domain responsible for shuttling the intermediate fatty acid substrates to various catalytic sites. A first direct structural insight into this substrate shuttling mechanism was obtained by cryo-EM analysis, where ACP is observed bound to the various catalytic domains in the barrel-shaped yeast fatty acid synthase. The cryo-EM results suggest that the binding of ACP to various sites is asymmetric and stochastic, as also indicated by computer-simulation studies | 1 | Biochemistry |
In the past 5 years plasmonic nanoparticles have been explored as a method for high resolution spectroscopy. One group utilized 40 nm gold nanoparticles that had been functionalized such that they would bind specifically to epidermal growth factor receptors to determine the density of those receptors on a cell. This technique relies on the fact that the effective geometry of the particles change when they appear within one particle diameter (40 nm) of each other. Within that range, quantitative information on the EGFR density in the cell membrane can be retrieved based on the shift in resonant frequency of the plasmonic particles. | 7 | Physical Chemistry |
Some quantities decay by two exponential-decay processes simultaneously. In this case, the actual half-life can be related to the half-lives and that the quantity would have if each of the decay processes acted in isolation:
For three or more processes, the analogous formula is:
For a proof of these formulas, see Exponential decay § Decay by two or more processes. | 7 | Physical Chemistry |
In 1935, the first scientific work devoted to the thermodynamics of biological systems was published - the book of the Hungarian-Russian theoretical biologist Erwin S. Bauer (1890-1938) "Theoretical Biology". E. Bauer formulated the "Universal Law of Biology" in the following edition: "All and only living systems are never in equilibrium and perform constant work at the expense of their free energy against the equilibrium required by the laws of physics and chemistry under existing external conditions". This law can be considered the 1st law of thermodynamics of biological systems.
In 1957, German-British physician and biochemist Hans Krebs and British-American biochemist Hans Kornberg in the book "Energy Transformations in Living Matter" first described the thermodynamics of biochemical reactions. In their works, H. Krebs and Hans Kornberg showed how in living cells, as a result of biochemical reactions, adenosine triphosphate (ATP) is synthesized from food, which is the main source of energy of living organisms (the Krebs–Kornberg cycle).
In 2006, the Israeli-Russian scientist Boris Dobroborsky (1945) published the book "Thermodynamics of Biological Systems", in which the general principles of functioning of living organisms from the perspective of nonequilibrium thermodynamics were formulated for the first time and the nature and properties of their basic physiological functions were explained. | 7 | Physical Chemistry |
Spectrophotometry is a tool that hinges on the quantitative analysis of molecules depending on how much light is absorbed by colored compounds. Important features of spectrophotometers are spectral bandwidth (the range of colors it can transmit through the test sample), the percentage of sample transmission, the logarithmic range of sample absorption, and sometimes a percentage of reflectance measurement.
A spectrophotometer is commonly used for the measurement of transmittance or reflectance of solutions, transparent or opaque solids, such as polished glass, or gases. Although many biochemicals are colored, as in, they absorb visible light and therefore can be measured by colorimetric procedures, even colorless biochemicals can often be converted to colored compounds suitable for chromogenic color-forming reactions to yield compounds suitable for colorimetric analysis. However, they can also be designed to measure the diffusivity on any of the listed light ranges that usually cover around 200–2500 nm using different controls and calibrations. Within these ranges of light, calibrations are needed on the machine using standards that vary in type depending on the wavelength of the photometric determination.
An example of an experiment in which spectrophotometry is used is the determination of the equilibrium constant of a solution. A certain chemical reaction within a solution may occur in a forward and reverse direction, where reactants form products and products break down into reactants. At some point, this chemical reaction will reach a point of balance called an equilibrium point. To determine the respective concentrations of reactants and products at this point, the light transmittance of the solution can be tested using spectrophotometry. The amount of light that passes through the solution is indicative of the concentration of certain chemicals that do not allow light to pass through.
The absorption of light is due to the interaction of light with the electronic and vibrational modes of molecules. Each type of molecule has an individual set of energy levels associated with the makeup of its chemical bonds and nuclei and thus will absorb light of specific wavelengths, or energies, resulting in unique spectral properties. This is based upon its specific and distinct makeup.
The use of spectrophotometers spans various scientific fields, such as physics, materials science, chemistry, biochemistry, chemical engineering, and molecular biology. They are widely used in many industries including semiconductors, laser and optical manufacturing, printing and forensic examination, as well as in laboratories for the study of chemical substances. Spectrophotometry is often used in measurements of enzyme activities, determinations of protein concentrations, determinations of enzymatic kinetic constants, and measurements of ligand binding reactions. Ultimately, a spectrophotometer is able to determine, depending on the control or calibration, what substances are present in a target and exactly how much through calculations of observed wavelengths.
In astronomy, the term spectrophotometry refers to the measurement of the spectrum of a celestial object in which the flux scale of the spectrum is calibrated as a function of wavelength, usually by comparison with an observation of a spectrophotometric standard star, and corrected for the absorption of light by the Earth's atmosphere. | 7 | Physical Chemistry |
Amoxicillin is also sometimes used as an antibiotic for animals. The use of amoxicillin for animals intended for human consumption (chickens, cattle, and swine for example) has been approved. | 4 | Stereochemistry |
Nucleic acid secondary structure is the basepairing interactions within a single nucleic acid polymer or between two polymers. It can be represented as a list of bases which are paired in a nucleic acid molecule.
The secondary structures of biological DNAs and RNAs tend to be different: biological DNA mostly exists as fully base paired double helices, while biological RNA is single stranded and often forms complex and intricate base-pairing interactions due to its increased ability to form hydrogen bonds stemming from the extra hydroxyl group in the ribose sugar.
In a non-biological context, secondary structure is a vital consideration in the nucleic acid design of nucleic acid structures for DNA nanotechnology and DNA computing, since the pattern of basepairing ultimately determines the overall structure of the molecules. | 4 | Stereochemistry |
The favored azaenolate is the dominant starting molecule for the subsequent alkylation reaction. There are two possible faces of accessing for any electrophile to react with. The steric interaction between the pyrrolidine ring and the electrophilic reagent hinders the attack of the electrophile from the top face. On the contrary, when the electrophile attacks from the bottom face, such unfavorable interaction does not exist. Therefore, the electrophilic attack proceeds from the sterically more accessible face. | 0 | Organic Chemistry |
While it is well established that the skin provides an ideal site for the administration of local and systemic drugs, it presents a formidable barrier to the permeation of most substances. Isotropic formulations have been used to deliver drugs locally and systemically via the skin appendages, intercellular and transcellular routes. | 7 | Physical Chemistry |
Oxidative addition of vinylcyclopropanes primarily occurs at the proximal position, giving pi-allyl intermediates. Through subsequent insertion reactions (e.g. with alkynes, alkenes, and carbon monoxide), rings of various sizes and fused ring systems can be formed. | 0 | Organic Chemistry |
It has been suggested that zero-order ultrasensitivity may generate thresholds during development allowing for the conversion of a graded morphogen input to a binary switch-like response. Melen et al. (2005) have found evidence for such a system in the patterning of the Drosophila embryonic ventral ectoderm. In this system, graded mitogen activated protein kinase (MAPK) activity is converted to a binary output, the all-or-none degradation of the Yan transcriptional repressor. They found that MAPK phosphorylation of Yan is both essential and sufficient for Yan's degradation. Consistent with zero-order ultrasensitivity an increase in Yan protein lengthened the time required for degradation but had no effect on the border of Yan degradation in developing embryos. Their results are consistent with a situation where a large pool of Yan becomes either completely degraded or maintained. The particular response of each cell depends on whether or not the rate of reversible Yan phosphorylation by MAPK is greater or less than dephosphorylation. Thus, a small increase in MAPK phosphorylation can cause it to be the dominant process in the cell and lead to complete degradation of Yan. | 1 | Biochemistry |
In principle, full genome sequencing can provide the raw nucleotide sequence of an individual organism's DNA at a single point in time. However, further analysis must be performed to provide the biological or medical meaning of this sequence, such as how this knowledge can be used to help prevent disease. Methods for analyzing sequencing data are being developed and refined.
Because sequencing generates a lot of data (for example, there are approximately six billion base pairs in each human diploid genome), its output is stored electronically and requires a large amount of computing power and storage capacity.
While analysis of WGS data can be slow, it is possible to speed up this step by using dedicated hardware. | 1 | Biochemistry |
Half sandwich complexes containing cyclopentadienyl ligands are common. Well studied examples include (η-CH)V(CO), (η-CH)Cr(CO)H, (η-CHCH)Mn(CO), (η-CH)Cr(CO)H, [(η-CH)Fe(CO)], (η-CH)V(CO)I, and (η-CH)Ru(NCMe). (η-CH)Co(CO) is a two-legged piano stool complex. Bulky cyclopentadienyl ligands such as 1,2,4-CH(tert-Bu) form unusual half-sandwich complexes. | 0 | Organic Chemistry |
Nitroso compounds can be prepared by the reduction of nitro compounds or by the oxidation of hydroxylamines.
Ortho-nitrosophenols may be produced by the Baudisch reaction. In the Fischer–Hepp rearrangement aromatic 4-nitrosoanilines are prepared from the corresponding nitrosamines. | 0 | Organic Chemistry |
Semi-synthetic bio-hybrid channels constructed by modifications of natural ion channels had been constructed. Leveraging modern synthetic organic chemistry, these allows pinpoint modifications of existing structures to either elucidate their transport mechanisms or to graft on new functionalities.
Gramicidin and alamethicin had been popular starting points for selective modifications. The above diagram illustrates one example, where a crown-ether was fixed across the mouth of the ion-passing portal. This channel shows discrete conductance but different ion selectivity than wild type gramicidin in voltage-clamp experiments.
While modification of large protein channels using mutagenesis are generally considered out of the scope of synthetic channels, the demarcation is not sharp, as supramolecular or covalent bonding of cyclodextrins to alpha-hemolysin demonstrates. | 6 | Supramolecular Chemistry |
In type I rearrangements (Y-A-B-X conversion to X-A-B-Y) the two migrating groups are oriented trans to each other and as a result of the rearrangement they migrate to opposite sides. The first example of a dyotropic rearrangement involving a carbon-carbon bond was reported by Cyril A. Grob and Saul Winstein. They observed the interconversion of 2 bromine atoms in a certain steroid.
In a straightforward example the two bromine atoms in 3-tert-butyl-trans-1,2-dibromohexane mutarotate by heating. In the transition state both bromine atoms connect symmetrically to both carbon atoms on opposite sides and the reaction is concerted. Stepwise mechanisms in dyotropic reactions have also been investigated.
In organic synthesis an important application is the conversion of 4-substituted-gamma-lactones to butyrolactones. Type I dyotropic rearrangements also occur around carbon-oxygen bonds, such as the thermal equilibration of (RSi)RC-O-SiR to (RSi)RC-O-SiR. The 1,2-Wittig rearrangement can also be considered an example of this reaction type. More dyotropic reactions are found involving N-O bonds and N-N bonds. | 0 | Organic Chemistry |
Benzyne complexes react with a variety of electrophiles, resulting in insertion into one M-C bond. With trifluoroacetic acid, benzene is lost to give the trifluoroacetate Ni(OCF)(dcpe). | 0 | Organic Chemistry |
The sessile drop technique has various applications for both materials engineering and straight characterization. In general, it is useful in determining the surface tension of liquids through the use of reference solids, with a similar technique being the Captive Bubble Method. There are various other specific applications which can be subdivided according to which of the above theories is most likely to be applicable to the circumstances:
The Zisman theory is mostly used for low energy surfaces and characterizes only the total surface energy. As such, it is probably most useful in cases that recall the conventional definition of surfaces, for example if a chemical engineer wants to know what the energy associated with fabricating a surface is. It may also be useful in cases where the surface energy has some effect on a spectroscopic technique being used on the solid in question.
The two component theories would most likely be applicable to materials engineering questions about the practical interactions of liquids and solids. The Fowkes theory, since it is more suited for higher energy solid surfaces, and since much of it is rooted in theories about adhesion, would likely be suited for the characterization of interactions where the solids and liquids have a high affinity for one another, such as, logically enough, adhesives and adhesive coatings. The Owens/Wendt theory, which deals in low energy solid surfaces, would be helpful in characterizing the interactions where the solids and liquids do not have a strong affinity for one another – for example, the effectiveness of waterproofing. Polyurethanes and PVC are good examples of waterproof plastics.
The Schultz theory is best used for the characterization of very high energy surfaces for which the other theories are ineffective, the most significant example being bare metals.
The van Oss theory is most suitable for cases in which acid/base interaction is an important consideration. Examples include pigments, pharmaceuticals, and paper. Specifically, notable examples include both paper used for the regular purpose of printing, and the more specialized case of litmus paper, which in itself is used to characterize acidity and basicity. | 7 | Physical Chemistry |
This assay was patented in 2006 by Randall Nelson, Peter Williams and Jennifer Reeve Krone. The idea first came about with the development of ELISA and RIA. An earlier patent method suggested tagging antigens or antibodies with stable isotopes or long-lived radioactive elements. But limitations to both methods called for a better detection methods of a protein or proteins. The invention combines antigen-antibody binding with a mass spectrometer which aids in identifying qualitatively and quantifying analytes respectively.
An early MSIA experiment was done on a venom laced human blood sample for the Antigen myotoxin. The experiment was successful in that the mass spectrum resulting from the analysis showed a distinct response for myotoxin at the molecular weight corresponding to 4,822 Da (a). The m/z ratio at 5,242 Da (b) is the molecular weight of the modified variant H-myotoxina, used as an internal reference species. The figure of the mass spectrum is shown below. | 1 | Biochemistry |
Since 1975 ion chromatography has been widely used in many branches of industry. The main beneficial advantages are reliability, very good accuracy and precision, high selectivity, high speed, high separation efficiency, and low cost of consumables. The most significant development related to ion chromatography are new sample preparation methods; improving the speed and selectivity of analytes separation; lowering of limits of detection and limits of quantification; extending the scope of applications; development of new standard methods; miniaturization and extending the scope of the analysis of a new group of substances. Allows for quantitative testing of electrolyte and proprietary additives of electroplating baths. It is an advancement of qualitative hull cell testing or less accurate UV testing. Ions, catalysts, brighteners and accelerators can be measured. Ion exchange chromatography has gradually become a widely known, universal technique for the detection of both anionic and cationic species. Applications for such purposes have been developed, or are under development, for a variety of fields of interest, and in particular, the pharmaceutical industry. The usage of ion exchange chromatography in pharmaceuticals has increased in recent years, and in 2006, a chapter on ion exchange chromatography was officially added to the United States Pharmacopia-National Formulary (USP-NF). Furthermore, in 2009 release of the USP-NF, the United States Pharmacopia made several analyses of ion chromatography available using two techniques: conductivity detection, as well as pulse amperometric detection. Majority of these applications are primarily used for measuring and analyzing residual limits in pharmaceuticals, including detecting the limits of oxalate, iodide, sulfate, sulfamate, phosphate, as well as various electrolytes including potassium, and sodium. In total, the 2009 edition of the USP-NF officially released twenty eight methods of detection for the analysis of active compounds, or components of active compounds, using either conductivity detection or pulse amperometric detection. | 3 | Analytical Chemistry |
A membraneless battery relies on laminar flow in which two liquids are pumped through a channel, where they undergo electrochemical reactions to store or release energy. The solutions stream through in parallel, with little mixing. The flow naturally separates the liquids, eliminating the need for a membrane.
Membranes are often the most costly and least reliable components of batteries, as they can be corroded by repeated exposure to certain reactants. The absence of a membrane enables the use of a liquid bromine solution and hydrogen: this combination is problematic when membranes are used, because they form hydrobromic acid that can destroy the membrane. Both materials are available at low cost. The design uses a small channel between two electrodes. Liquid bromine flows through the channel over a graphite cathode and hydrobromic acid flows under a porous anode. At the same time, hydrogen gas flows across the anode. The chemical reaction can be reversed to recharge the battery – a first for any membraneless design.
One such membraneless flow battery published in August 2013 produced a maximum power density of 0.795 mW/cm, three times as much power as other membraneless systems— and an order of magnitude higher than lithium-ion batteries.
In 2018, a macroscale membraneless redox flow battery capable of recharging and recirculation of the same electrolyte streams for multiple cycles has been demonstrated. The battery is based on immiscible organic catholyte and aqueous anolyte liquids, which exhibits high capacity retention and Coulombic efficiency during cycling. | 7 | Physical Chemistry |
Two RNA genomes are packaged into each retrovirus particle, but, after an infection, each virus generates only one provirus. After infection, reverse transcription is accompanied by template switching between the two genome copies (copy choice recombination). There are two models that suggest why RNA transcriptase switches templates. The first, the forced copy-choice model, proposes that reverse transcriptase changes the RNA template when it encounters a nick, implying that recombination is obligatory to maintaining virus genome integrity. The second, the dynamic choice model, suggests that reverse transcriptase changes templates when the RNAse function and the polymerase function are not in sync rate-wise, implying that recombination occurs at random and is not in response to genomic damage. A study by Rawson et al. supported both models of recombination. From 5 to 14 recombination events per genome occur at each replication cycle. Template switching (recombination) appears to be necessary for maintaining genome integrity and as a repair mechanism for salvaging damaged genomes. | 1 | Biochemistry |
The atomic structure of human uncoupling protein 1 UCP1 has been solved by cryogenic-electron microscopy. The structure has the typical fold of a member of the SLC25 family. UCP1 is locked in a cytoplasmic-open state by guanosine triphosphate in a pH-dependent manner, preventing proton leak. | 1 | Biochemistry |
In sedimentary layers throughout the Arctic basin, a unit reaching at least 8 m in thickness (the bottom of the longest core was not recovered, but it may have reached 20 m+) is discernible. This unit consists of alternating layers; siliceous clastic layers representing the background sedimentation of planktonic organisms, usual to marine sediments, switch with millimetre-thick laminations comprising fossilised Azolla matter. This organic matter can also be detected in the form of a gamma radiation spike, that has been noted throughout the Arctic basin, making the event a useful aid in lining up cores drilled at different locations. Palynological controls and calibration with the high-resolution geomagnetic reversal record allows the duration of the event to be estimated at 800,000 years. The event coincides precisely with a catastrophic decline in carbon dioxide levels, which fell from 3500 ppm in the early Eocene to 650 ppm during this event. | 2 | Environmental Chemistry |
Allopolyploids are species whose increased complement of genetic material is the result of hybridization of two closely related species. Thus homeologous chromosomes in allopolyploids are equivalent, but not identical. These differences mean that the precise pattern of silencing and expression can have important phenotypic effects. Reciprocal silencing on the population level refers to the case where two populations are each descended from the same allopolyploid. In one population, one of the two equivalent locci (A) is expressed while the other (B) has been silenced, while in the other population the reciprocal pattern occurs, with B being expressed and A silenced. It is important to note that this refers to equivalent loci, specific locations within the genome, rather than the entire homeologous chromosome.
Reciprocal silencing on the population level has been proposed as a means of allopatric speciation following a polyploid event. Allopatric speciation occurs when two populations of the same species become spatially separated and accumulate enough genetic differences to lose the ability to interbreed. As redundant genes are silenced in allopolyploids there is the potential for rapid genetic differences to accumulate through reciprocal silencing. These differences can lead to the loss of ability to interbreed between separated populations at a faster rate than other methods of speciation, given the relative speed with which genes are silenced following a polyploid event. Faster still, redundant genes can be silenced through epigenetic means, although the importance of this phenomenon is not fully understood. | 1 | Biochemistry |
In the absence of liver disease, high levels of total bilirubin confers various health benefits. Studies have also revealed that levels of serum bilirubin (SBR) are inversely related to risk of certain heart diseases. While the poor solubility and potential toxicity of bilirubin limit its potential medicinal applications, current research is being done on whether bilirubin encapsulated silk fibrin nanoparticles can alleviate symptoms of disorders such as acute pancreatitis. In addition to this, there has been recent discoveries linking bilirubin and its ε-polylysine-bilirubin conjugate (PLL-BR), to more efficient insulin medication. It seems that bilirubin exhibits protective properties during the islet transplantation process when drugs are delivered throughout the bloodstream. | 1 | Biochemistry |
A classic method for the synthesis of azides is the Dutt–Wormall reaction in which a diazonium salt reacts with a sulfonamide first to a diazoaminosulfinate and then on hydrolysis the azide and a sulfinic acid. | 0 | Organic Chemistry |
Ocean acidity due to carbon dioxide has already increased by 25% since the industrial revolution. As carbon dioxide emissions continually increase and accumulate, this will negatively affect the lives of many marine ecosystems. The calcium carbonate used to form many marine organisms' exoskeletons will begin to break down, leaving these animals vulnerable and unable to live in their habitats. This ultimately has a flow on effect to predators, further affecting the function of many food webs globally. | 1 | Biochemistry |
Genetic codes is a simple ASN.1 database hosted by the National Center for Biotechnology Information and listing all the known Genetic codes. | 1 | Biochemistry |
Dihydrokaempferol 4-reductase uses cis-3,4-leucopelargonidin and NADP to produce (+)-aromadendrin, NADPH, and H.
Leucoanthocyanidin reductase transforms cis-3,4-leucopelargonidin into afzelechin. | 1 | Biochemistry |
Moving wire IRMS is useful for analyzing carbon-13 ratios of compounds in a solution, such as after purification by liquid chromatography. The solution (or outflow from the chromatography) is dried onto a nickel or stainless steel wire. After the residue is deposited on the wire, it enters a furnace where the sample is converted to CO and water by combustion. The gas stream finally enters a capillary, is dried, ionized, and analyzed. This process allows a mixture of compounds to be purified and analyzed continuously, which can decrease the analysis time by a factor of four. Moving wire IRMS is quite sensitive, and samples containing as little as 1 nanomole of carbon can yield precise (within 1‰) results. | 9 | Geochemistry |
Valence tautomerism is a type of tautomerism in which single and/or double bonds are rapidly formed and ruptured, without migration of atoms or groups. It is distinct from prototropic tautomerism, and involves processes with rapid reorganisation of bonding electrons.
A pair of valence tautomers with formula CHO are benzene oxide and oxepin.
Other examples of this type of tautomerism can be found in bullvalene, and in open and closed forms of certain heterocycles, such as organic azides and tetrazoles, or mesoionic münchnone and acylamino ketene.
Valence tautomerism requires a change in molecular geometry and should not be confused with canonical resonance structures or mesomers. | 4 | Stereochemistry |
Spray and fuse uses high heat to increase the bond between the thermal spray coating and the substrate of the part. Unlike other types of thermal spray, spray and fuse creates a metallurgical bond between the coating and the surface. This means that instead of relying on friction for coating adhesion, it melds the surface and coating material into one material. Spray and fuse comes down to the difference between adhesion and cohesion.
This process usually involves spraying a powdered material onto the component then following with an acetylene torch. The torch melts the coating material and the top layer of the component material; fusing them together. Due to the high heat of spray and fuse, some heat distortion may occur, and care must be taken to determine if a component is a good candidate. These high temperatures are akin to those used in welding. This metallurgical bond creates an extremely wear and abrasion resistant coating. Spray and fuse delivers the benefits of hardface welding with the ease of thermal spray. | 8 | Metallurgy |
Eukaryotic cells are composed of the following organelles:
* Nucleus: The nucleus of the cell functions as the genome and genetic information storage for the cell, containing all the DNA organized in the form of chromosomes. It is surrounded by a nuclear envelope, which includes nuclear pores allowing for the transportation of proteins between the inside and outside of the nucleus. This is also the site for replication of DNA as well as transcription of DNA to RNA. Afterwards, the RNA is modified and transported out to the cytosol to be translated to protein.
* Nucleolus: This structure is within the nucleus, usually dense and spherical. It is the site of ribosomal RNA (rRNA) synthesis, which is needed for ribosomal assembly.
* Endoplasmic reticulum (ER): This functions to synthesize, store, and secrete proteins to the Golgi apparatus. Structurally, the endoplasmic reticulum is a network of membranes found throughout the cell and connected to the nucleus. The membranes are slightly different from cell to cell and a cell's function determines the size and structure of the ER.
* Mitochondria: Commonly known as the powerhouse of the cell is a double membrane bound cell organelle. This functions for the production of energy or ATP within the cell. Specifically, this is the place where the Krebs cycle or TCA cycle for the production of NADH and FADH occurs. Afterwards, these products are used within the electron transport chain (ETC) and oxidative phosphorylation for the final production of ATP.
* Golgi apparatus: This functions to further process, package, and secrete the proteins to their destination. The proteins contain a signal sequence that allows the Golgi apparatus to recognize and direct it to the correct place. Golgi apparatus also produce glycoproteins and glycolipids.
* Lysosome: The lysosome functions to degrade material brought in from the outside of the cell or old organelles. This contains many acid hydrolases, proteases, nucleases, and lipases, which break down the various molecules. Autophagy is the process of degradation through lysosomes which occurs when a vesicle buds off from the ER and engulfs the material, then, attaches and fuses with the lysosome to allow the material to be degraded.
* Ribosomes: Functions to translate RNA to protein. it serves as a site of protein synthesis.
* Cytoskeleton: Cytoskeleton is a structure that helps to maintain the shape and general organization of the cytoplasm. It anchors organelles within the cells and makes up the structure and stability of the cell. The cytoskeleton is composed of three principal types of protein filaments: actin filaments, intermediate filaments, and microtubules, which are held together and linked to subcellular organelles and the plasma membrane by a variety of accessory proteins.
* Cell membrane: The cell membrane can be described as a phospholipid bilayer and is also consisted of lipids and proteins. Because the inside of the bilayer is hydrophobic and in order for molecules to participate in reactions within the cell, they need to be able to cross this membrane layer to get into the cell via osmotic pressure, diffusion, concentration gradients, and membrane channels.
* Centrioles: Function to produce spindle fibers which are used to separate chromosomes during cell division.
Eukaryotic cells may also be composed of the following molecular components:
* Chromatin: This makes up chromosomes and is a mixture of DNA with various proteins.
* Cilia: They help to propel substances and can also be used for sensory purposes. | 1 | Biochemistry |
After a cell has been depolarized, it undergoes one final change in internal charge. Following depolarization, the voltage-gated sodium ion channels that had been open while the cell was undergoing depolarization close again. The increased positive charge within the cell now causes the potassium channels to open. Potassium ions (K) begin to move down the electrochemical gradient (in favor of the concentration gradient and the newly established electrical gradient). As potassium moves out of the cell the potential within the cell decreases and approaches its resting potential once more. The sodium potassium pump works continuously throughout this process. | 7 | Physical Chemistry |
It is possible to perform a CD4 co-receptor blockade, using antibodies, in order to lower T cell activation and counteract autoimmune disorders. This blockade appears to elicit a "dominant" effect, that is to say, once blocked, the T cells do not regain their ability to become active. This effect then spreads to native T cells which then switch to a CD4+CD25+GITR+FoxP3+ T regulatory phenotype. | 1 | Biochemistry |
All RiPPs are synthesized first at the ribosome as a precursor peptide. This peptide consists of a core peptide segment which is typically preceded (and occasionally followed) by a leader peptide segment and is typically ~20-110 residues long. The leader peptide is usually important for enabling enzymatic processing of the precursor peptide via aiding in recognition of the core peptide by biosynthetic enzymes and for cellular export. Some RiPPs also contain a recognition sequence C-terminal to the core peptide; these are involved in excision and cyclization. Additionally, eukaryotic RiPPs may contain a signal segment of the precursor peptide which helps direct the peptide to cellular compartments.
During RiPP biosynthesis, the unmodified precursor peptide (containing an unmodified core peptide, UCP) is recognized and chemically modified sequentially by biosynthetic enzymes (PRPS). Examples of modifications include dehydration (i.e. lanthipeptides, thiopeptides), cyclodehydration (i.e. thiopeptides), prenylation (i.e. cyanobactins), and cyclization (i.e. lasso peptides), among others. The resulting modified precursor peptide (containing a modified core peptide, MCP) then undergoes proteolysis, wherein the non-core regions of the precursor peptide are removed. This results in the mature RiPP. | 1 | Biochemistry |
* Halliday, Alex N., Der-Chuen Lee, John N. Christensen, Mark Rehkämper, Wen Yi, Xiaozhong Luo, Chris M. Hall, Chris J. Ballentine, Thomas Pettke, and Claudine Stirling. "Applications of multiple collector-ICPMS to cosmochemistry, geochemistry, and paleoceanography." Geochimica et Cosmochimica Acta 62, no. 6 (1998): 919–940.
* Amelin, Yuri, Angela Kaltenbach, Tsuyoshi Iizuka, Claudine H. Stirling, Trevor R. Ireland, Michail Petaev, and Stein B. Jacobsen. "U–Pb chronology of the Solar System's oldest solids with variable 238U/235U." Earth and Planetary Science Letters 300, no. 3-4 (2010): 343–350.
* Stirling, Claudine H., Morten B. Andersen, Emma-Kate Potter, and Alex N. Halliday. "Low-temperature isotopic fractionation of uranium." Earth and Planetary Science Letters 264, no. 1-2 (2007): 208–225.
* Gutjahr, Marcus, Martin Frank, Claudine H. Stirling, Veronika Klemm, Tina Van de Flierdt, and Alex N. Halliday. "Reliable extraction of a deepwater trace metal isotope signal from Fe–Mn oxyhydroxide coatings of marine sediments." Chemical Geology 242, no. 3-4 (2007): 351–370.
* Rehkämper, Mark, Maria Schönbächler, and Claudine H. Stirling. "Multiple collector ICP‐MS: Introduction to instrumentation, measurement techniques and analytical capabilities." Geostandards Newsletter 25, no. 1 (2001): 23–40. | 9 | Geochemistry |
Bacteria use two different strategies for transcription termination – Rho-independent termination and Rho-dependent termination. In Rho-independent transcription termination, RNA transcription stops when the newly synthesized RNA molecule forms a G-C-rich hairpin loop followed by a run of Us. When the hairpin forms, the mechanical stress breaks the weak rU-dA bonds, now filling the DNA–RNA hybrid. This pulls the poly-U transcript out of the active site of the RNA polymerase, terminating transcription. In Rho-dependent termination, Rho, a protein factor, destabilizes the interaction between the template and the mRNA, thus releasing the newly synthesized mRNA from the elongation complex.
Transcription termination in eukaryotes is less well understood than in bacteria, but involves cleavage of the new transcript followed by template-independent addition of adenines at its new 3' end, in a process called polyadenylation.
Beyond termination by a terminator sequences (which is a part of a gene), transcription may also need to be terminated when it encounters conditions such as DNA damage or an active replication fork. In bacteria, the Mfd ATPase can remove a RNA polymerase stalled at a lesion by prying open its clamp. It also recruits nucleotide excision repair machinery to repair the lesion. Mfd is proposed to also resolve conflicts between DNA replication and transcription. In eukayrotes, ATPase TTF2 helps to suppress the action of RNAP I and II during mitosis, preventing errors in chromosomal segregation. In archaea, the Eta ATPase is proposed to play a similar role. | 1 | Biochemistry |
Cleaning is the preparatory process of ensuring that the surface to be etched is free of contaminants which could negatively impact the quality of the finished part. An improperly cleaned surface could result in poor adhesion of the maskant, causing areas to be etched erroneously, or a non-uniform etch rate which could result in inaccurate final dimensions. The surface must be kept free from oils, grease, primer coatings, markings and other residue from the marking out process, scale (oxidation), and any other foreign contaminants. For most metals, this step can be performed by applying a solvent substance to the surface to be etched, washing away foreign contaminants. The material may also be immersed in alkaline cleaners or specialized de-oxidizing solutions. It is common practice in modern industrial chemical etching facilities that the workpiece never be directly handled after this process, as oils from human skin could easily contaminate the surface. | 8 | Metallurgy |
Pedagogical work was an important part of the life of Pigulevsky. From 1911 to 1964, with a break for the duration of the war, he taught at Leningrad State University and lectured at other universities and institutes. During this time, he read many lecture courses: “Fats and oils”, “About derivatives of aliphatic terpenes”, “Resins”, “Terpenes”, “Essential oils”, etc.
Pigulevsky was a member of the Academic Council of the Leningrad branch of the D.I. Mendeleev All-Union Chemical Society, as well as a member of the Central Council of the D.I. Mendeleev All-Union Chemical Society. In 1946-1947, he was a member of the editorial board of the journal "Sovietskaya Botanica". From 1937 until the end of his life, he was a member of the editorial committee of the Journal of Applied Chemistry of the USSR. | 0 | Organic Chemistry |
* Filed: December 2, 2010. Granted: November 17, 2011.
* Filed: June 25, 2009. Granted: November 20, 2012.
* Filed: October 28, 2010. Granted: February 25, 2014.
* Filed August 10, 2012. Granted March 4, 2014. | 3 | Analytical Chemistry |
The MeDIP-seq approach, i.e. the coupling of MeDIP with next generation, short-read sequencing technologies such as 454 pyrosequencing or Illumina (Solexa), was first described by Down et al. in 2008. The high-throughput sequencing of the methylated DNA fragments produces a large number of short reads (36-50bp or 400 bp, depending on the technology). The short reads are aligned to a reference genome using alignment software such as Mapping and Assembly with Quality ([http://maq.sf.net Maq]), which uses a Bayesian approach, along with base and mapping qualities to model error probabilities for the alignments. The reads can then be extended to represent the ~400 to 700 bp fragments from the sonication step. The coverage of these extended reads can be used to estimate the methylation level of the region. A genome browser such as [http://www.ensembl.org Ensembl] can also be used to visualize the data.
Validation of the approach to assess quality and accuracy of the data can be done with quantitative PCR. This is done by comparing a sequence from the MeDIP sample against an unmethylated control sequence. The samples are then run on a gel and the band intensities are compared. The relative intensity serves as the guide for finding enrichment. The results can also be compared with MeDIP-chip results to help determine coverage needed. | 1 | Biochemistry |
Hexacyclinol is a natural metabolite of a fungus, Panus rudis. Significant controversy surrounded its proposed structure until its total synthesis by John Porco, Jr. in 2006. | 0 | Organic Chemistry |
Arketamine (developmental code names PCN-101, HR-071603), also known as (R)-ketamine or (R)-(−)-ketamine, is the (R)-(−) enantiomer of ketamine. Similarly to racemic ketamine and esketamine, the S(+) enantiomer of ketamine, arketamine is biologically active; however, it is less potent as an NMDA receptor antagonist and anesthetic and thus has never been approved or marketed for clinical use as an enantiopure drug. Arketamine is currently in clinical development as a novel antidepressant.
Relative to esketamine, arketamine possesses 4 to 5 times lower affinity for the PCP site of the NMDA receptor. In accordance, arketamine is significantly less potent than racemic ketamine and especially esketamine in terms of anesthetic, analgesic, and sedative-hypnotic effects. Racemic ketamine has weak affinity for the sigma receptor, where it acts as an agonist, whereas esketamine binds negligibly to this receptor, and so the sigma receptor activity of racemic ketamine lies in arketamine. It was suggested that this action of arketamine may play a role in the hallucinogenic effects of racemic ketamine and that it may be responsible for the lowering of the seizure threshold seen with racemic ketamine. However several subsequent studies have indicated that esketamine is more likely to induce dissociative events, while studies in patients undergoing electroconvulsive therapy suggested that esketamine is a potent inducer of seizures. Esketamine inhibits the dopamine transporter about 8-fold more potently than does arketamine, and so is about 8 times more potent as a dopamine reuptake inhibitor. Arketamine and esketamine possess similar potency for interaction with the muscarinic acetylcholine receptors. | 4 | Stereochemistry |
In 1969, one such method was performed by Mary Lou Pardue and Joseph G. Gall at the Yale University through radioactivity where it involved the hybridization of a radioactive test DNA in solution to the stationary DNA of a cytological preparation, which is identified as autoradiography. | 1 | Biochemistry |
Addition of acid and inert-gas sparging allows all bicarbonate and carbonate ions to be converted to carbon dioxide, and this IC product vented along with any purgeable organic carbon (POC) that was present. | 3 | Analytical Chemistry |
The World Health Organization says that "there does not appear to be any convincing evidence that water hardness causes adverse health effects in humans". In fact, the United States National Research Council has found that hard water serves as a dietary supplement for calcium and magnesium.
Some studies have shown a weak inverse relationship between water hardness and cardiovascular disease in men, up to a level of 170 mg calcium carbonate per litre of water. The World Health Organization has reviewed the evidence and concluded the data was inadequate to recommend a level of hardness.
Recommendations have been made for the minimum and maximum levels of calcium (40–80 ppm) and magnesium (20–30 ppm) in drinking water, and a total hardness expressed as the sum of the calcium and magnesium concentrations of 2–4 mmol/L.
Other studies have shown weak correlations between cardiovascular health and water hardness.
The prevalence of atopic dermatitis (eczema) in children may be increased by hard drinking water. Living in areas with hard water may also play a part in the development of AD in early life. However, when AD is already established, using water softeners at home does not reduce the severity of the symptoms. | 3 | Analytical Chemistry |
While telomeres play an important role in cellular senescence, the intricate biological details of telomeres still require further investigation. The complex interactions between telomeres, different proteins and the cellular environment must be fully understood in order to develop precise and safe interventions to change it. Understanding the long-term effects of telomere extension on the body is complex and risky. Prediction of long-term consequences, including potential unanticipated side effects or interactions with other cellular processes, requires thorough and long-term investigation. | 1 | Biochemistry |
Gene sequence-based methods depend on the recognition of exclusive gene sequences particular to specific strains of organisms. Polymerase chain reaction (PCR) and fluorescence in situ hybridization (FISH) are gene sequence-based methods currently being used to detect specific strains of indicator bacteria. | 3 | Analytical Chemistry |
The electro-optic effect is a change in the optical properties of an optically active material in response to changes in an electric field. This interaction usually results in a change in the birefringence, and not simply the refractive index of the medium. In a Kerr cell, the change in birefringence is proportional to the square of the electric field, and the material is usually a liquid. In a Pockels cell, the change in birefringence varies linearly with the electric field, and the material is usually a crystal. Non-crystalline, solid electro-optical materials have generated interest because of their low cost of production. These organic, polymer-based materials are also known as organic EO material, plastic EO material, or polymer EO material. They consist of nonlinear optical chromophores in a polymer lattice. The nonlinear optical chromophores can produce Pockels effect. | 7 | Physical Chemistry |
In ultrashort pulse physics, a so-called nonthermal melting may take place. It occurs not because of the increase of the atomic kinetic energy, but because of changes of the interatomic potential due to excitation of electrons. Since electrons are acting like a glue sticking atoms together, heating electrons by a femtosecond laser alters the properties of this "glue", which may break the bonds between the atoms and melt a material even without an increase of the atomic temperature.
In genetics, melting DNA means to separate the double-stranded DNA into two single strands by heating or the use of chemical agents, polymerase chain reaction. | 7 | Physical Chemistry |
Gemperline came to the notice of a larger scientific community in 1984 with the publication of a paper describing DISNET in the Journal of Automated Methods and Management in Chemistry. (The journal title was changed to Journal of Analytical Methods in Chemistry in 2013.) Gemperline and his colleagues provided methodologies which underlay the improvements in calibration accuracy, computer-based data acquisition and mathematical analysis in chemometrics. The qualitative advances helped open new scientific fields such as molecular modeling and QSAR, cheminformatics, the ‘-omics’ fields of genomics, proteomics, metabonomics and metabolomics, process modeling and process analytical technology.
Gemperline is a self-taught chemometrician, and he has been most influential by dispersing knowledge of his chemometric methodologies through his publications. Perhaps the best example of this is his book, Practical Guide to Chemometrics, for which he served as both editor and as a contributor. Better process methods can create inflection points that became the foundation for radical improvements and transitions in the scientific enterprise. It can be decades before the implications of particular advances are intuited, especially those related to the basic training of the next generations of chemists. His research in chemometrics has been "focused on development of new algorithms and software tools for analysis of multivariate spectroscopic measurements using pattern recognition methods, artificial neural networks, multivariate statistical methods, multivariate calibration, and non-linear model estimation." Sandia National Laboratories researcher, David Haaland, called Gemperline a "chemometrician extraordinaire," with a "deep understanding of chemometrics" and "wide-ranging" contributions to the research literature, and said after his first meeting with Gemperline he "always read his publications and attended his talks at conferences knowing that I would learn something new every time."
According to former graduate student, Patrick Cutler, another important aspect of Gemperlines research and teaching career has been his ability to collaborate with industry, which allowed "opportunities for students to gain invaluable experience." Cutler mentions pharmaceutical company Burroughs Wellcome in particular which at one time operated a production plant in Greenville, North Carolina, in close proximity to East Carolina University. Gemperline collaborated with Burroughs Wellcome in the 1980s to develop software for multivariate pattern recognition analysis of near-infrared reflectance spectra for rapid, non-destructive testing of pharmaceutical ingredients and products. His research and publications in this area furthered his international recognition. Cutler notes that Gemperline, "built his career and has produced world-renowned chemometrics research with the limited resources of mostly undergraduates and masters level students."
Gemperline also has had research collaborations with Pfizer, Inc. and GlaxoSmithKline and he has received "significant" funding for his research from the National Science Foundation (NSF) and the Measurement and Control Engineering Center (MCEC) at University of Tennessee, Knoxville, an NSF-sponsored Industry-University Cooperative Research Center (IUCRC). He collaborated with David Haaland at Sandia National Laboratories to develop chemometric tools to study kinetics in cells using hyperspectral fluorescence imaging. Their efforts were judged successful, and led to the 2010 Meggers Award for them and coauthors Patrick Cutler and Erik Andres for their two 2009 publications in Applied Spectroscopy about their research.
Gemperline served as the editor-in-chief of Journal of Chemometrics for ten years, from 2007 to 2017, and before that as the North American editor for five years, from 1996 to 2001. The journal honored him with a special issue in July 2020. He joined the editorial advisory board of Spectroscopy Magazine in 2020. | 3 | Analytical Chemistry |
The ionization in the cathode dark space results in a high electron density, but slower electrons, making it easier for the electrons to recombine with positive ions, leading to intense light, through a process called bremsstrahlung radiation. | 3 | Analytical Chemistry |
Quark–gluon plasma is a state of matter in which the elementary particles that make up the hadrons of baryonic matter are freed of their strong attraction for one another under extremely high energy densities. These particles are the quarks and gluons that compose baryonic matter. In normal matter quarks are confined; in the QGP quarks are deconfined. In classical quantum chromodynamics (QCD), quarks are the fermionic components of hadrons (mesons and baryons) while the gluons are considered the bosonic components of such particles. The gluons are the force carriers, or bosons, of the QCD color force, while the quarks by themselves are their fermionic matter counterparts.
Quark–gluon plasma is studied to recreate and understand the high energy density conditions prevailing in the Universe when matter formed from elementary degrees of freedom (quarks, gluons) at about 20 μs after the Big Bang. Experimental groups are probing over a large distance the (de)confining quantum vacuum structure, the present day relativistic æther, which determines prevailing form of matter and laws of nature. The experiments give insight to the origin of matter and mass: the matter and antimatter is created when the quark–gluon plasma hadronizes and the mass of matter originates in the confining vacuum structure. | 7 | Physical Chemistry |
1-Hydroxy-7-azabenzotriazole (HOAt) is a triazole used as a peptide coupling reagent. It suppresses racemization that can otherwise occur during the reaction.
HOAt has a melting point between 213 and 216 degrees Celsius. As a liquid, it is transparent and without any color. | 1 | Biochemistry |
* Williams, H. (trans.), A sixteenth-century German treatise: Von Stahel und Eysen. 1532, Technical studies in the field of the fine arts, 4.2 (October, 1935), 63-92.
* Smith, Cyril Stanley (ed.), Sources for the History of the Science of Steel, 1532-1786, Society for the History of Technology, 4 (Cambridge, Mass.: Society for the History of Technology, 1968), pp. 7–19. | 8 | Metallurgy |
The Koschevnikov gland is a gland of the honeybee located near the sting shaft. The gland produces an alarm pheromone that is released when a bee stings. The pheromone contains more than 40 different compounds, including pentylacetate, butyl acetate, 1-hexanol, n-butanol, 1-octanol, hexylacetate, octylacetate, and 2-nonanol. These components have a low molar mass and evaporate quickly. This collection of compounds is the least specific of all pheromones. The alarm pheromone is released when a honey bee stings another animal to attract other bees to attack, as well. The release of the alarm pheromone may entice more bees to sting at the same location. Smoking the bees can reduce the pheromone's efficacy. | 1 | Biochemistry |
Signal transduction is realized by activation of specific receptors and consequent production/delivery of second messengers, such as Ca or cAMP. These molecules operate as signal transducers, triggering intracellular cascades and in turn amplifying the initial signal.
Two main signal transduction mechanisms have been identified, via nuclear receptors, or via transmembrane receptors. In the first one, first messenger cross through the cell membrane, binding and activating intracellular receptors localized at nucleus or cytosol, which then act as transcriptional factors regulating directly gene expression. This is possible due to the lipophilic nature of those ligands, mainly hormones. In the signal transduction via transmembrane receptors, the first messenger binds to the extracellular domain of transmembrane receptor, activating it. These receptors may have intrinsic catalytic activity or may be coupled to effector enzymes, or may also be associated to ionic channels. Therefore, there are four main transmembrane receptor types: G protein coupled receptors (GPCRs), tyrosine kinase receptors (RTKs), serine/threonine kinase receptors (RSTKs), and ligand-gated ion channels (LGICs).
Second messengers can be classified into three classes:
# Hydrophilic/cytosolic – are soluble in water and are localized at the cytosol, including cAMP, cGMP, IP3, Ca, cADPR and S1P. Their main targets are protein kinases as PKA and PKG, being then involved in phosphorylation mediated responses.
# Hydrophobic/membrane-associated – are insoluble in water and membrane-associated, being localized at intermembrane spaces, where they can bind to membrane-associated effector proteins. Examples: PIP3, DAG, phosphatidic acid, arachidonic acid and ceramide. They are involved in regulation of kinases and phosphatases, G protein associated factors and transcriptional factors.
# Gaseous – can be widespread through cell membrane and cytosol, including nitric oxide and carbon monoxide. Both of them can activate cGMP and, besides of being capable of mediating independent activities, they also can operate in a coordinated mode. | 7 | Physical Chemistry |
*To produce 1,3-bisphospho-D-glycerate in glycolysis.
D-glyceraldehyde 3-phosphate is also of some importance since this is how glycerol (as DHAP) enters the glycolytic and gluconeogenic pathways. Furthermore, it is a participant in and a product of the pentose phosphate pathway. | 5 | Photochemistry |
The purification process utilizes the cementation process to further purify the zinc. It uses zinc dust and steam to remove copper, cadmium, cobalt, and nickel, which would interfere with the electrolysis process. After purification, concentrations of these impurities are limited to less than 0.05 milligram per liter (4×10 pound per U.S. gallon). Purification is usually conducted in large agitated tanks. The process takes place at temperatures ranging from , and pressures ranging from atmospheric to (absolute scale). The by-products are sold for further refining.
The zinc sulfate solution must be very pure for electrowinning to be at all efficient. Impurities can change the decomposition voltage enough to where the electrolysis cell produces largely hydrogen gas rather than zinc metal. | 8 | Metallurgy |
Shiny metal surfaces, have low emissivities both in the visible wavelengths and in the far infrared. Such surfaces can be used to reduce heat transfer in both directions; an example of this is the multi-layer insulation used to insulate spacecraft.
Since any electromagnetic radiation, including thermal radiation, conveys momentum as well as energy, thermal radiation also induces very small forces on the radiating or absorbing objects. Normally these forces are negligible, but they must be taken into account when considering spacecraft navigation. The Pioneer anomaly, where the motion of the craft slightly deviated from that expected from gravity alone, was eventually tracked down to asymmetric thermal radiation from the spacecraft. Similarly, the orbits of asteroids are perturbed since the asteroid absorbs solar radiation on the side facing the Sun, but then re-emits the energy at a different angle as the rotation of the asteroid carries the warm surface out of the Sun's view (the YORP effect). | 7 | Physical Chemistry |
ECgene in computational biology is a database of genomic annotations taking alternative splicing events into consideration. | 1 | Biochemistry |
Proposed by Gottfried Leibniz over the period 1676–1689, the theory was controversial as it seemed to oppose the theory of conservation of quantity of motion advocated by René Descartes. Descartes quantity of motion was different from momentum, but Newton defined the quantity of motion as the conjunction of the quantity of matter and velocity in Definition II of his Principia. In Definition III, he defined the force that resists a change in motion as the vis inertia of Descartes. Newton’s Third Law of Motion (for every action there is an equal and opposite reaction) is also equivalent to the principle of conservation of momentum. Leibniz accepted the principle of conservation of momentum, but rejected the Cartesian version of it. The difference between these ideas was whether the quantity of motion was simply related to a bodys resistance to a change in velocity (vis inertia) or whether a body's amount of force due to its motion (vis viva) was related to the square of its velocity.
The theory was eventually absorbed into the modern theory of energy, though the term still survives in the context of celestial mechanics through the vis viva equation. The English equivalent "living force" was also used, for example by George William Hill.
The term is due to German Gottfried Wilhelm Leibniz, who was the first to attempt a mathematical formulation from 1676 to 1689. Leibniz noticed that in many mechanical systems (of several masses, m each with velocity v) the quantity
was conserved. He called this quantity the vis viva or "living force" of the system. The principle represented an accurate statement of the conservation of kinetic energy in elastic collisions that was independent of the conservation of momentum.
However, many physicists at the time were unaware of this fact and, instead, were influenced by the prestige of Sir Isaac Newton in England and of René Descartes in France, both of whom advanced the conservation of momentum as a guiding principle. Thus the momentum:
was held by the rival camp to be the conserved vis viva. It was largely engineers such as John Smeaton, Peter Ewart, Karl Holtzmann, Gustave-Adolphe Hirn and Marc Seguin who objected that conservation of momentum alone was not adequate for practical calculation and who made use of Leibniz's principle. The principle was also championed by some chemists such as William Hyde Wollaston.
The French mathematician Émilie du Châtelet, who had a sound grasp of Newtonian mechanics, developed Leibnizs concept and, combining it with the observations of Willem s Gravesande, showed that vis viva was dependent on the square of the velocities.
Members of the academic establishment such as John Playfair were quick to point out that kinetic energy is clearly not conserved. This is obvious to a modern analysis based on the second law of thermodynamics, but in the 18th and 19th centuries, the fate of the lost energy was still unknown. Gradually it came to be suspected that the heat inevitably generated by motion was another form of vis viva. In 1783, Antoine Lavoisier and Pierre-Simon Laplace reviewed the two competing theories of vis viva and caloric theory. Count Rumfords 1798 observations of heat generation during the boring of cannons added more weight to the view that mechanical motion could be converted into heat. Vis viva began to be known as energy' after Thomas Young first used the term in 1807.
The recalibration of vis viva to include the coefficient of a half, namely:
was largely the result of the work of Gaspard-Gustave Coriolis and Jean-Victor Poncelet over the period 1819–1839, although the present-day definition can occasionally be found earlier (e.g., in Daniel Bernoulli's texts).
The former called it the quantité de travail (quantity of work) and the latter, travail mécanique (mechanical work) and both championed its use in engineering calculation. | 7 | Physical Chemistry |
The idea of photostimulation as a method of controlling biomolecule function was developed in the 1970s. Two researchers, Walther Stoeckenius and Dieter Oesterhelt discovered an ion pump known as bacteriorhodopsin which functions in the presence of light in 1971. In 1978, J.F. Hoffman invented the term “caging”. Unfortunately, this term caused some confusion among scientists due to the fact that the term is often used to describe a molecule which is trapped within another molecule. It could also be confused with the “caged effect” in the recombination of radicals. Therefore, some authors decided to use the term “light-activated” instead of “caging”. Both terms are currently in use. The first “caged molecule” synthesized by Hoffman et al. at Yale was the caged precursor to ATP derivative 1. | 1 | Biochemistry |
Thermal hydrolysis is a process used for treating industrial waste, municipal solid waste and sewage sludge. | 7 | Physical Chemistry |
Light-dependent reactions are certain photochemical reactions involved in photosynthesis, the main process by which plants acquire energy. There are two light dependent reactions: the first occurs at photosystem II (PSII) and the second occurs at photosystem I (PSI).
PSII absorbs a photon to produce a so-called high energy electron which transfers via an electron transport chain to cytochrome bf and then to PSI. The then-reduced PSI, absorbs another photon producing a more highly reducing electron, which converts NADP to NADPH. In oxygenic photosynthesis, the first electron donor is water, creating oxygen (O) as a by-product. In anoxygenic photosynthesis, various electron donors are used.
Cytochrome bf and ATP synthase work together to produce ATP (photophosphorylation) in two distinct ways. In non-cyclic photophosphorylation, cytochrome bf uses electrons from PSII and energy from PSI to pump protons from the stroma to the lumen. The resulting proton gradient across the thylakoid membrane creates a proton-motive force, used by ATP synthase to form ATP. In cyclic photophosphorylation, cytochrome bf uses electrons and energy from PSI to create more ATP and to stop the production of NADPH. Cyclic phosphorylation is important to create ATP and maintain NADPH in the right proportion for the light-independent reactions.
The net-reaction of all light-dependent reactions in oxygenic photosynthesis is:
:2 + 2 + 3ADP + 3P → + 2 H + 2NADPH + 3ATP
PSI and PSII are light-harvesting complexes. If a special pigment molecule in a photosynthetic reaction center absorbs a photon, an electron in this pigment attains the excited state and then is transferred to another molecule in the reaction center. This reaction, called photoinduced charge separation, is the start of the electron flow and transforms light energy into chemical forms. | 5 | Photochemistry |
Potential Sulfidic Acidity (PSA) is a function of the concentration of Reduced Inorganic Sulfur (RIS) in a soil sample. If RIS were the only pool of sulfur present in a sample, PSA could be directly estimated from the total concentration of sulfur. In some cases this may possible. However, sulfate minerals (e.g., gypsum, epsomite, and jarosite) and organic matter typically constitute additional sources of sulfur in most sulfidic and sulfuric soils. Chromium Reducible Sulfur (S or CRS) accurately measures RIS without significant interference from these other sources of sulfur. The chromium reduction method is summarized in Soil Chemical Methods:S by a hot acidic CrCl solution; the evolved gas is trapped quantitatively in a Zn acetate solution as solid ZnS. The ZnS is then treated with HCl to release HS into solution, which must then be quickly titrated with I solution to the blue-coloured end point indicated by the reaction of I with starch.) - is calculated as the difference between the sulfur determined via peroxide digestion (S) and sulfur extracted with a 1 M KCl solution (S).
S is a measure of sulfur associated with relativity soluble sulfates (e.g., gyspum and epsomite). S is a measure of sulfur associated with both RIS and organic matter. As such, S may overestimate PSA where samples contain even relatively small amounts of organic matter. Therefore, S is recommended for samples containing > 0.06% organic carbon.
Neither S nor S provide a measure of sulfur associated with sparingly soluble sulfate minerals such as jarosite. | 9 | Geochemistry |
The A-domains have 8 amino acid-long non-ribosomal signatures.
LTKVGHIG → Asp (Aspartic acid)
VGEIGSID → Orn (Orinithine)
AWMFAAVL → Val (Valine) | 1 | Biochemistry |
*pimaric acid
**pimara-8(14),15-dien-18-oic acid
*isopimaric acids
*simplified formula CHO or CHCOOH
*molecular weight 302 | 1 | Biochemistry |
PIPES (piperazine-N,N-bis(2-ethanesulfonic acid)) is a frequently used buffering agent in biochemistry. It is an ethanesulfonic acid buffer developed by Good et al. in the 1960s. | 1 | Biochemistry |
In an 1847 lecture entitled On Matter, Living Force, and Heat, James Prescott Joule characterized the terms latent heat and sensible heat as components of heat each affecting distinct physical phenomena, namely the potential and kinetic energy of particles, respectively.
He described latent energy as the energy possessed via a distancing of particles where attraction was over a greater distance, i.e. a form of potential energy, and the sensible heat as an energy involving the motion of particles, i.e. kinetic energy.
Latent heat is the heat released or absorbed by a chemical substance or a thermodynamic system during a change of state that occurs without a change in temperature. Such a process may be a phase transition, such as the melting of ice or the boiling of water. | 7 | Physical Chemistry |
In the male the LHCGR has been identified on the Leydig cells that are critical for testosterone production, and support spermatogenesis.
Normal LHCGR functioning is critical for male fetal development, as the fetal Leydig cells produce androstenedione which is converted to testosterone in fetal Sertoli cells to induce masculinization. | 1 | Biochemistry |
Hunter returned to New Zealand to begin his academic career. He was a lecturer in bioorganic chemistry at the University of Otago from 1989 to 1991. He then returned to the United Kingdom and joined the University of Sheffield. He was a lecturer from 1991 to 1994 and reader from 1994 to 1997. He was promoted to professor of chemistry in 1997. He held a Lister Institute Research Fellowship from 1994 to 1999, and an Engineering and Physical Sciences Research Council Senior Research Fellowship from 2005 to 2010.
In September 2013, he was selected as the next Herchel Smith Professor of Organic Chemistry. He joined the University of Cambridge in early 2014 to take up the appointment. There, he is a member of the Synthetic Chemistry Research Interest Group. He is also a Fellow of Emmanuel College, Cambridge. | 0 | Organic Chemistry |
As a gemstone used in jewelry, silicon carbide is called "synthetic moissanite" or just "moissanite" after the mineral name. Moissanite is similar to diamond in several important respects: it is transparent and hard (9–9.5 on the Mohs scale, compared to 10 for diamond), with a refractive index between 2.65 and 2.69 (compared to 2.42 for diamond). Moissanite is somewhat harder than common cubic zirconia. Unlike diamond, moissanite can be strongly birefringent. For this reason, moissanite jewels are cut along the optic axis of the crystal to minimize birefringent effects. It is lighter (density 3.21 g/cm vs. 3.53 g/cm), and much more resistant to heat than diamond. This results in a stone of higher luster, sharper facets, and good resilience. Loose moissanite stones may be placed directly into wax ring moulds for lost-wax casting, as can diamond, as moissanite remains undamaged by temperatures up to . Moissanite has become popular as a diamond substitute, and may be misidentified as diamond, since its thermal conductivity is closer to diamond than any other substitute. Many thermal diamond-testing devices cannot distinguish moissanite from diamond, but the gem is distinct in its birefringence and a very slight green or yellow fluorescence under ultraviolet light. Some moissanite stones also have curved, string-like inclusions, which diamonds never have. | 8 | Metallurgy |
The ascorbate ion is the predominant species at typical biological pH values. It is a mild reducing agent and antioxidant. It is oxidized with loss of one electron to form a radical cation and then with loss of a second electron to form dehydroascorbic acid. It typically reacts with oxidants of the reactive oxygen species, such as the hydroxyl radical.
Ascorbic acid is special because it can transfer a single electron, owing to the resonance-stabilized nature of its own radical ion, called semidehydroascorbate. The net reaction is:
:RO + → RO + CHO → ROH + CHO
On exposure to oxygen, ascorbic acid will undergo further oxidative decomposition to various products including diketogulonic acid, xylonic acid, threonic acid and oxalic acid.
Reactive oxygen species are damaging to animals and plants at the molecular level due to their possible interaction with nucleic acids, proteins, and lipids. Sometimes these radicals initiate chain reactions. Ascorbate can terminate these chain radical reactions by electron transfer. The oxidized forms of ascorbate are relatively unreactive and do not cause cellular damage.
However, being a good electron donor, excess ascorbate in the presence of free metal ions can not only promote but also initiate free radical reactions, thus making it a potentially dangerous pro-oxidative compound in certain metabolic contexts.
Ascorbic acid and its sodium, potassium, and calcium salts are commonly used as antioxidant food additives. These compounds are water-soluble and, thus, cannot protect fats from oxidation: For this purpose, the fat-soluble esters of ascorbic acid with long-chain fatty acids (ascorbyl palmitate or ascorbyl stearate) can be used as antioxidant food additives. | 1 | Biochemistry |
Over the decades huge number of precipitation reactions have been used to study the phenomenon, and it seems quite general. Chromates, metal hydroxides, carbonates, and sulfides, formed with lead, copper, silver, mercury and cobalt salts are sometimes favored by investigators, perhaps because of the pretty, colored precipitates formed.
The gels used are usually gelatin, agar or silicic acid gel.
The concentration ranges over which the rings form in a given gel for a precipitating system can usually be found for any system by a little systematic empirical experimentation in a few hours. Often the concentration of the component in the agar gel should be substantially less concentrated (perhaps an order of magnitude or more) than the one placed on top of the gel.
The first feature usually noted is that the bands which form farther away from the liquid-gel interface are generally farther apart. Some investigators measure this distance and report in some systems, at least, a systematic formula for the distance that they form at. The most frequent observation is that the distance apart that the rings form is proportional to the distance from the liquid-gel interface. This is by no means universal, however, and sometimes they form at essentially random, irreproducible distances.
Another feature often noted is that the bands themselves do not move with time, but rather form in place and stay there.
For very many systems the precipitate that forms is not the fine coagulant or flocs seen on mixing the two solutions in the absence of the gel, but rather coarse, crystalline dispersions. Sometimes the crystals are well separated from one another, and only a few form in each band.
The precipitate that forms a band is not always a binary insoluble compound, but may be even a pure metal. Water glass of density 1.06 made acidic by sufficient acetic acid to make it gel, with 0.05 N copper sulfate in it, covered by a 1 percent solution of hydroxylamine hydrochloride produces large tetrahedrons of metallic copper in the bands.
It is not possible to make any general statement of the effect of the composition of the gel. A system that forms nicely for one set of components, might fail altogether and require a different set of conditions if the gel is switched, say, from agar to gelatin. The essential feature of the gel required is that thermal convection in the tube be prevented altogether.
Most systems will form rings in the absence of the gelling system if the experiment is carried out in a capillary, where convection does not disturb their formation. In fact, the system does not have to even be liquid. A tube plugged with cotton with a little ammonium hydroxide at one end, and a solution of hydrochloric acid at the other will show rings of deposited ammonium chloride where the two gases meet, if the conditions are chosen correctly. Ring formation has also been observed in solid glasses containing a reducible species. For example, bands of silver have been generated by immersing silicate glass in molten AgNO for extended periods of time (Pask and Parmelee, 1943). | 7 | Physical Chemistry |
Plant viruses need to be transmitted by a vector, most often insects such as leafhoppers. One class of viruses, the Rhabdoviridae, has been proposed to actually be insect viruses that have evolved to replicate in plants. The chosen insect vector of a plant virus will often be the determining factor in that virus's host range: it can only infect plants that the insect vector feeds upon. This was shown in part when the old world white fly made it to the United States, where it transferred many plant viruses into new hosts. Depending on the way they are transmitted, plant viruses are classified as non-persistent, semi-persistent and persistent. In non-persistent transmission, viruses become attached to the distal tip of the stylet of the insect and on the next plant it feeds on, it inoculates it with the virus. Semi-persistent viral transmission involves the virus entering the foregut of the insect. Those viruses that manage to pass through the gut into the haemolymph and then to the salivary glands are known as persistent. There are two sub-classes of persistent viruses: propagative and circulative. Propagative viruses are able to replicate in both the plant and the insect (and may have originally been insect viruses), whereas circulative can not. Circulative viruses are protected inside aphids by the chaperone protein symbionin, produced by bacterial symbionts. Many plant viruses encode within their genome polypeptides with domains essential for transmission by insects. In non-persistent and semi-persistent viruses, these domains are in the coat protein and another protein known as the helper component. A bridging hypothesis has been proposed to explain how these proteins aid in insect-mediated viral transmission. The helper component will bind to the specific domain of the coat protein, and then the insect mouthparts – creating a bridge. In persistent propagative viruses, such as tomato spotted wilt virus (TSWV), there is often a lipid coat surrounding the proteins that is not seen in other classes of plant viruses. In the case of TSWV, 2 viral proteins are expressed in this lipid envelope. It has been proposed that the viruses bind via these proteins and are then taken into the insect cell by receptor-mediated endocytosis. | 1 | Biochemistry |
In 1913, the German chemist Max Bodenstein first put forth the idea of chemical chain reactions. If two molecules react, not only molecules of the final reaction products are formed, but also some unstable molecules which can further react with the parent molecules with a far larger probability than the initial reactants. (In the new reaction, further unstable molecules are formed besides the stable products, and so on.)
In 1918, Walther Nernst proposed that the photochemical reaction between hydrogen and chlorine is a chain reaction in order to explain what is known as the quantum yield phenomena. This means that one photon of light is responsible for the formation of as many as 10 molecules of the product HCl. Nernst suggested that the photon dissociates a Cl molecule into two Cl atoms which each initiate a long chain of reaction steps forming HCl.
In 1923, Danish and Dutch scientists J. A. Christiansen and Hendrik Anthony Kramers, in an analysis of the formation of polymers, pointed out that such a chain reaction need not start with a molecule excited by light, but could also start with two molecules colliding violently due to thermal energy as previously proposed for initiation of chemical reactions by van' t Hoff.
Christiansen and Kramers also noted that if, in one link of the reaction chain, two or more unstable molecules are produced, the reaction chain would branch and grow. The result is in fact an exponential growth, thus giving rise to explosive increases in reaction rates, and indeed to chemical explosions themselves. This was the first proposal for the mechanism of chemical explosions.
A quantitative chain chemical reaction theory was created later on by Soviet physicist Nikolay Semyonov in 1934. Semyonov shared the Nobel Prize in 1956 with Sir Cyril Norman Hinshelwood, who independently developed many of the same quantitative concepts. | 7 | Physical Chemistry |
* Ushinsky Medal
* Honored Science Worker of the RSFSR (1967)
* Latvian SSR State Prize
* Order of the Patriotic War, 2nd class
* Order of the Red Banner of Labour | 0 | Organic Chemistry |
Hemispherical transmittance of a surface, denoted T, is defined as
where
*Φ is the radiant flux transmitted by that surface;
*Φ is the radiant flux received by that surface. | 7 | Physical Chemistry |
Podsolisation is an extreme form of leaching which causes the eluviation of iron and aluminium sesquioxides.
The process generally occurs in areas where precipitation is greater than evapotranspiration. The minerals are removed by a process known as leaching.
When organic material is broken down nutrients are released, but at the same time organic acids are released. These organic acids are known as chelating agents. Many podsol soils form underneath coniferous forests, the fact that pine trees are evergreen causes a very thin litter layer inhibiting the production of humus. As a result, an acidic (pH 4.5) mor humus is produced which provides a greater amount of chelating agents. | 9 | Geochemistry |
Nucleotides are the fundamental molecules that combine in series to form RNA. They consist of a nitrogenous base attached to a sugar-phosphate backbone. RNA is made of long stretches of specific nucleotides arranged so that their sequence of bases carries information. The RNA world hypothesis holds that in the primordial soup (or sandwich), there existed free-floating nucleotides. These nucleotides regularly formed bonds with one another, which often broke because the change in energy was so low. However, certain sequences of base pairs have catalytic properties that lower the energy of their chain being created, enabling them to stay together for longer periods of time. As each chain grew longer, it attracted more matching nucleotides faster, causing chains to now form faster than they were breaking down.
These chains have been proposed by some as the first, primitive forms of life. In an RNA world, different sets of RNA strands would have had different replication outputs, which would have increased or decreased their frequency in the population, i.e., natural selection. As the fittest sets of RNA molecules expanded their numbers, novel catalytic properties added by mutation, which benefitted their persistence and expansion, could accumulate in the population. Such an autocatalytic set of ribozymes, capable of self-replication in about an hour, has been identified. It was produced by molecular competition (in vitro evolution) of candidate enzyme mixtures.
Competition between RNA may have favored the emergence of cooperation between different RNA chains, opening the way for the formation of the first protocell. Eventually, RNA chains developed with catalytic properties that help amino acids bind together (a process called peptide-bonding). These amino acids could then assist with RNA synthesis, giving those RNA chains that could serve as ribozymes the selective advantage. The ability to catalyze one step in protein synthesis, aminoacylation of RNA, has been demonstrated in a short (five-nucleotide) segment of RNA.
In March 2015, NASA scientists reported that, for the first time, complex DNA and RNA organic compounds of life, including uracil, cytosine, and thymine, have been formed in the laboratory under conditions found only in outer space, using starting chemicals, like pyrimidine, found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), may have been formed in red giant stars or in interstellar dust and gas clouds, according to the scientists.
In 2018, researchers at Georgia Institute of Technology identified three molecular candidates for the bases that might have formed an earliest version of proto-RNA: barbituric acid, melamine, and 2,4,6-triaminopyrimidine (TAP). These three molecules are simpler versions of the four bases in current RNA, which could have been present in larger amounts and could still be forward-compatible with them but may have been discarded by evolution in exchange for more optimal base pairs. Specifically, TAP can form nucleotides with a large range of sugars. Both TAP and melamine base pair with barbituric acid. All three spontaneously form nucleotides with ribose. | 9 | Geochemistry |
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