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The Systems Biology Pathway Exchange (SBPAX) allows SBO terms to be added to Biological Pathway Exchange (BioPAX). This links BioPAX to information useful for modelling, especially by adding quantitative descriptions described by SBO. | 1 | Biochemistry |
Fluoride-containing compounds, such as sodium fluoride or sodium monofluorophosphate are used in topical and systemic fluoride therapy for preventing tooth decay, but the exact biochemical reason is unknown. They are used for water fluoridation and in many products associated with oral hygiene. Originally, sodium fluoride was used to fluoridate water; hexafluorosilicic acid (HSiF) and its salt sodium hexafluorosilicate (NaSiF) are more commonly used additives, especially in the United States. The fluoridation of water is known to prevent tooth decay and is considered by the U.S. Centers for Disease Control and Prevention to be "one of 10 great public health achievements of the 20th century". In some countries where large, centralized water systems are uncommon, fluoride is delivered to the populace by fluoridating table salt. For the method of action for cavity prevention, see Fluoride therapy. Fluoridation of water has its critics (see water fluoridation controversy). Fluoridated toothpaste is in common use. Meta-analysis show the efficacy of 500 ppm fluoride in toothpastes. However, no beneficial effect can be detected when more than one fluoride source is used for daily oral care. | 1 | Biochemistry |
The Society for Mining, Metallurgy & Exploration publishes the monthly magazine Mining Engineering since 1949. | 8 | Metallurgy |
Herbivores are dependent on plants for food and have evolved mechanisms to obtain this food despite the evolution of a diverse arsenal of plant defenses. Herbivore adaptations to plant defense have been likened to offensive traits and consist of adaptations that allow increased feeding and use of a host plant. Relationships between herbivores and their host plants often result in reciprocal evolutionary change, called co-evolution. When an herbivore eats a plant, it selects for plants that can mount a defensive response. In cases where this relationship demonstrates specificity (the evolution of each trait is due to the other) and reciprocity (both traits must evolve), the species are thought to have co-evolved.
The "escape and radiation" mechanism for co-evolution presents the idea that adaptations in herbivores and their host plants have been the driving force behind speciation and have played a role in the radiation of insect species during the age of angiosperms. Some herbivores have evolved ways to hijack plant defenses to their own benefit by sequestering these chemicals and using them to protect themselves from predators. Plant defenses against herbivores are generally not complete, so plants also tend to evolve some tolerance to herbivory. | 1 | Biochemistry |
In biochemical signaling, diacylglycerol functions as a second messenger signaling lipid, and is a product of the hydrolysis of the phospholipid phosphatidylinositol 4,5-bisphosphate (PIP) by the enzyme phospholipase C (PLC) (a membrane-bound enzyme) that, through the same reaction, produces inositol trisphosphate (IP). Although inositol trisphosphate diffuses into the cytosol, diacylglycerol remains within the plasma membrane, due to its hydrophobic properties. IP stimulates the release of calcium ions from the smooth endoplasmic reticulum, whereas DAG is a physiological activator of protein kinase C (PKC). The production of DAG in the membrane facilitates translocation of PKC from the cytosol to the plasma membrane. | 1 | Biochemistry |
Biallelic recessive mutations in the sialic acid synthesis gene, N-acetyl-neuraminic acid synthase (NANS) in humans may result in a severe disease featuring intellectual disability and short stature, highlighting the importance of sialic acid in brain development. A therapeutic trial with a short-term supplementation of sialic acid given orally has failed to show a significant beneficial effect on biochemical parameters | 0 | Organic Chemistry |
A number of distinct reactions are associated with the term ATP-dependent chromatin remodeling. Remodeling enzymes have been shown to slide nucleosomes along DNA, disrupt histone-DNA contacts to the extent of destabilizing the H2A/H2B dimer and to generate negative superhelical torsion in DNA and chromatin. Recently, the Swr1 remodeling enzyme has been shown to introduce the variant histone H2A.Z into nucleosomes. At present, it is not clear if all of these represent distinct reactions or merely alternative outcomes of a common mechanism. What is shared between all, and indeed the hallmark of ATP-dependent chromatin remodeling, is that they all result in altered DNA accessibility.
Studies looking at gene activation in vivo and, more astonishingly, remodeling in vitro have revealed that chromatin remodeling events and transcription-factor binding are cyclical and periodic in nature. While the consequences of this for the reaction mechanism of chromatin remodeling are not known, the dynamic nature of the system may allow it to respond faster to external stimuli. A recent study indicates that nucleosome positions change significantly during mouse embryonic stem cell development, and these changes are related to binding of developmental transcription factors. | 1 | Biochemistry |
The Ray–Dutt twist is a mechanism proposed for the racemization of octahedral complexes containing three bidentate chelate rings. Such complexes typically adopt an octahedral molecular geometry in their ground states, in which case they possess helical chirality. The pathway entails formation of an intermediate of C point group symmetry. An alternative pathway that also does not break any metal-ligand bonds is called the Bailar twist. Both of these mechanism product complexes wherein the ligating atoms (X in the scheme) are arranged in an approximate trigonal prism.
This pathway is called the Ray–Dutt twist in honor of Priyadaranjan Ray (not Prafulla Chandra Ray) and N. K. Dutt, inorganic chemists at the Indian Association for the Cultivation of Science abbr. IACS who proposed this process. | 4 | Stereochemistry |
A lithium–ammonia solution at −60 °C is saturated at about 15 mol% metal (MPM). When the concentration is increased in this range electrical conductivity increases from 10 to 10 Ωcm (larger than liquid mercury). At around 8 MPM, a "transition to the metallic state" (TMS) takes place (also called a "metal-to-nonmetal transition" (MNMT)). At 4 MPM a liquid-liquid phase separation takes place: the less dense gold-colored phase becomes immiscible from a denser blue phase. Above 8 MPM the solution is bronze/gold-colored. In the same concentration range the overall density decreases by 30%. | 0 | Organic Chemistry |
Ferritin is used in materials science as a precursor in making iron nanoparticles for carbon nanotube growth by chemical vapor deposition.
Cavities formed by ferritin and mini-ferritins (Dps) proteins have been successfully used as the reaction chamber for the fabrication of metal nanoparticles (NPs). Protein shells served as a template to restrain particle growth and as a coating to prevent coagulation/aggregation between NPs. Using various sizes of protein shells, various sizes of NPs can be easily synthesized for chemical, physical and bio-medical applications.
Experimental COVID-19 vaccines have been produced that display the spike protein's receptor binding domain on the surface of ferritin nanoparticles. | 1 | Biochemistry |
Diatoms can also be used to study oxygen isotopes and are especially useful in regions of the ocean where foraminifera do not preserve in marine sediments. One example of vital effects in diatoms is a difference in δO between two different species, Coscinodiscus marginatus and Coscinodiscus radiatus, which is attributed to their difference in size. | 9 | Geochemistry |
Purple of Cassius is a purple pigment formed by the reaction of gold salts with tin(II) chloride. It has been used to impart glass with a red coloration (see cranberry glass), as well as to determine the presence of gold as a chemical test.
Generally, the preparation of this material involves gold being dissolved in aqua regia, then reacted with a solution of tin(II) chloride. The tin(II) chloride reduces the chloroauric acid from the dissolution of gold in aqua regia to a colloid of elemental gold supported on tin dioxide to give a purple precipitate or coloration.
When used as a test, the intensity of the color correlates with the concentration of gold present. This test was first observed and refined by a German physician and alchemist, Andreas Cassius (1600–1676) of Hamburg, in 1665. Berzelius later made a detailed study of the purple of Cassius. The colour also attracted attention from Faraday.
Richard Adolf Zsigmondy, who earned the 1926 Nobel Prize for chemistry, says that "Several of the red gold divisions prepared with formaldehyde as well as those reduced with phosphorus appeared perfectly clear in ordinary daylight (like good red wine). They did not settle out their gold, and I was therefore able to call them rightly chemical solutions. In Thomas Graham’s dialysis, however, they behaved like colloidal suspensions: the gold particles did not pass through the parchment membrane. This showed my gold divisions their proper place, namely, that they belonged to the colloidal suspensions." | 3 | Analytical Chemistry |
Accurately measuring V̇O max involves a physical effort sufficient in duration and intensity to fully tax the aerobic energy system. In general clinical and athletic testing, this usually involves a graded exercise test in which exercise intensity is progressively increased while measuring:
* ventilation and
* oxygen and carbon dioxide concentration of the inhaled and exhaled air.
V̇O max is measured during a cardiopulmonary exercise test (CPX test). The test is done on a treadmill or cycle ergometer. In untrained subjects, V̇O max is 10% to 20% lower when using a cycle ergometer compared with a treadmill. However, trained cyclists' results on the cycle ergometer are equal to or even higher than those obtained on the treadmill.
The classic V̇O max, in the sense of Hill and Lupton (1923), is reached when oxygen consumption remains at a steady state ("plateau") despite an increase in workload. The occurrence of a plateau is not guaranteed and may vary by person and sampling interval, leading to modified protocols with varied results. | 1 | Biochemistry |
In the presence of base or cyanide, 3-sulfolene isomerizes to a mixture of 2-sulfolene and 3-sulfolene.
At 50 °C an equilibrium mixture is obtained containing 42% 3-sulfolene and 58% 2-sulfolene. The thermodynamically more stable 2-sulfolene can be isolated from the mixture of isomers as pure substance in the form of white plates (m.p. 48-49 °C) by heating for several days at 100 °C, because of the thermal decomposition of the 3-sulfolene at temperatures above 80 °C. | 0 | Organic Chemistry |
Increased endocannabinoid signaling within the central nervous system promotes sleep-inducing effects. Intercerebroventricular administration of anandamide in rats has been shown to decrease wakefulness and increase slow-wave sleep and REM sleep. Administration of anandamide into the basal forebrain of rats has also been shown to increase levels of adenosine, which plays a role in promoting sleep and suppressing arousal. REM sleep deprivation in rats has been demonstrated to increase CB1 receptor expression in the central nervous system. Furthermore, anandamide levels possess a circadian rhythm in the rat, with levels being higher in the light phase of the day, which is when rats are usually asleep or less active, since they are nocturnal. | 1 | Biochemistry |
nc-AFM was the first form of AFM to achieve true atomic resolution images, rather than averaging over multiple contacts, both on non-reactive and reactive surfaces.
nc-AFM was the first form of microscopy to achieve subatomic resolution images, initially on tip atoms and later on single iron adatoms on copper.
nc-AFM was the first technique to directly image chemical bonds in real space, see inset image. This resolution was achieved by picking up a single CO molecule on the apex of the tip.
nc-AFM has been used to probe the force interaction between a single pair of molecules. | 6 | Supramolecular Chemistry |
The agricultural water balances are calculated for each soil reservoir separately as shown in the article Hydrology (agriculture). The excess water leaving one reservoir is converted into incoming water for the next reservoir. The three soil reservoirs can be assigned different thickness and storage coefficients, to be given as input data. When, in a particular situation the transition zone or the aquifer is not present, they must be given a minimum thickness of 0.1 m.
The depth of the water table at the end of the previous time step, calculated from the water balances, is assumed to be the same within each polygon. If this assumption is not acceptable, the area must be divided into a larger number of polygons.
Under certain conditions, the height of the water table influences the water-balance components. For example, a rise of the water table towards the soil surface may lead to an increase of capillary rise, actual evaporation, and subsurface drainage, or a decrease of percolation losses. This, in turn, leads to a change of the water-balance, which again influences the height of the water table, etc. This chain of reactions is one of the reasons why Sahysmod has been developed into a computer program, in which the computations are made day by day to account for the chain of reactions with a sufficient degree of accuracy. | 9 | Geochemistry |
Ferroxyl indicator is a solution containing potassium hexacyanoferrate(III) and phenolphthalein. It turns blue in the presence of Fe ions, and pink in the presence of hydroxide ions. It can be used to detect metal oxidation, and is often used to detect rusting in various situations.
It can be prepared by dissolving 10g sodium chloride and 1g potassium hexacyanoferrate(III) in distilled water, adding 10 cm phenolphthalein indicator, then making up to 500 cm with distilled water. | 8 | Metallurgy |
Biometals are metals normally present, in small but important and measurable amounts, in biology, biochemistry, and medicine. The metals copper, zinc, iron, and manganese are examples of metals that are essential for the normal functioning of most plants and the bodies of most animals, such as the human body. A few (calcium, potassium, sodium) are present in relatively larger amounts, whereas most others are trace metals, present in smaller but important amounts (the image shows the percentages for humans). Approximately 2/3 of the existing periodic table is composed of metals with varying properties, accounting for the diverse ways in which metals (usually in ionic form) have been utilized in nature and medicine. | 1 | Biochemistry |
Nagai was born in Myōdō District, Awa Province in what is now Tokushima Prefecture, as the son of a doctor and started studying rangaku medicine at the Dutch Medical School of Nagasaki (Igaku-Denshujo) in 1864. While in Nagasaki, he made the acquaintance of Ōkubo Toshimichi, Itō Hirobumi, and other future leaders of the Meiji government. | 0 | Organic Chemistry |
Wiesner received a Guggenheim Fellowship in 1952, the Chemical Institute of Canadas Palladium Medal in 1963, the Royal Society of Chemistrys Centenary Prize in 1976, the American Chemical Society's Ernest Guenther Award in 1983, and the Izaak Walton Killam Memorial Prize in 1986. He was elected to the Royal Society of Canada in 1957, to the Royal Society in 1969, and admitted to the Pontifical Academy of Sciences in 1978. He was awarded the Order of Canada on June 25, 1975. He also received the Marin Drinov Medal of the Bulgarian Academy of Sciences. | 0 | Organic Chemistry |
The POCIS system is continually evaluated for the potential to sample a wide range of contaminants. Calibration data and analyte recovery methods are currently being generated by researchers around the world. Techniques to merge the POCIS device with bioassays are also under development. The POCIS sampler already serves as a versatile, economical, and robust tool for monitoring studies and observing trends in both space and time. However, sampling rates are not yet robust enough to supply reliable contaminant concentrations, particularly when regarding environmental quality standards. A limited number of sampling rates have been determined for chemicals and the determination of additional sampling rate data is necessary for the advancement of passive sampling technology. | 3 | Analytical Chemistry |
The general outline for the organic synthesis of a CBS catalyst is shown below. The first leg of the reaction sequence starts from the azeotropic dehydration of a boronic acid (1) such as one based on toluene to a boroxine (2). This boroxine reacts with the proline derivative (3d) to form the basic oxazaborolidine CBS catalyst (4). The oxazaborolidine was first developed as a ketone reducing agent by the laboratory of Itsuno, and thus is more properly called the Itsuno-Corey oxazaborolidine. Proline derivative 3d is prepared in a separate leg from a Grignard reaction with Grignard reagent 3c and proline ester 3b. A Lewis acid superacid salt (6) can be obtained with the aid of triflic acid (5). Many other such catalysts exist with different derivatives of these reactants. | 0 | Organic Chemistry |
* ASBMB Student Chapters Regional Meeting Award
* Outstanding Chapter Award
* Student Chapter Outreach Grant
* ASBMB Undergraduate Research Award
* Student Chapters Award | 1 | Biochemistry |
In 2017, Russia banned imports of beef from New Zealand after finding ractopamine in New Zealand beef. Ractopamine is not registered for use in cattle in New Zealand. | 4 | Stereochemistry |
Sulfenamides are usually prepared by the reaction of sulfenyl chlorides and amines:
:RSCl + RNH → RSNR + HCl
The S-N bond formation generally obeys standard bimolecular nucleophilic substitution rules, with the basic nitrogen centre being the nucleophile. Primary sulfenamide formation as shown above occurs with the reaction of the sulfenyl halide with ammonia. Additionally primary as well as secondary and tertiary amines form sulfenamides through reaction with, thiols, disulfides, and sulfenyl thiocyanates. In one illustrative synthesis, triphenylmethanesulphenyl chloride and butylamine react in benzene at 25 C:
:PhCSCl + 2BuNH → PhCSN(H)Bu + BuNHCl
Many other routes to sulfenamides are known, starting from thiols and disulfides.
:RSSR + 2RNH + Ag → RSNR + AgSR + R'NH | 0 | Organic Chemistry |
From the titration of protonatable group, one can read the so-called pK which is equal to the pH value where the group is half-protonated (i.e. when 50% such groups would be protonated). The pK is equal to the Henderson–Hasselbalch pK (pK) if the titration curve follows the Henderson–Hasselbalch equation. Most pK calculation methods silently assume that all titration curves are Henderson–Hasselbalch shaped, and pK values in pK calculation programs are therefore often determined in this way. In the general case of multiple interacting protonatable sites, the pK value is not thermodynamically meaningful. In contrast, the Henderson–Hasselbalch pK value can be computed from the protonation free energy via
and is thus in turn related to the protonation free energy of the site via
The protonation free energy can in principle be computed from the protonation probability of the group (pH) which can be read from its titration curve
Titration curves can be computed within a continuum electrostatics approach with formally exact but more elaborate analytical or Monte Carlo (MC) methods, or inexact but fast approximate methods. MC methods that have been used to compute titration curves are Metropolis MC or Wang–Landau MC. Approximate methods that use a mean-field approach for computing titration curves are the Tanford–Roxby method and hybrids of this method that combine an exact statistical mechanics treatment within clusters of strongly interacting sites with a mean-field treatment of intercluster interactions.
In practice, it can be difficult to obtain statistically converged and accurate protonation free energies from titration curves if is close to a value of 1 or 0. In this case, one can use various free energy calculation methods to obtain the protonation free energy such as biased Metropolis MC, free-energy perturbation, thermodynamic integration, the non-equilibrium work method or the Bennett acceptance ratio method.
Note that the pK value does in general depend on the pH value.
This dependence is small for weakly interacting groups like well solvated amino acid side chains on the protein surface, but can be large for strongly interacting groups like those buried in enzyme active sites or integral membrane proteins.
While many protein pKa prediction methods are available, their accuracies often differ significantly due to subtle and often drastic differences in strategy. | 7 | Physical Chemistry |
A basic, phenomenological understanding of the transition dipole moment can be obtained by analogy with a classical dipole. While the comparison can be very useful, care must be taken to ensure that one does not fall into the trap of assuming they are the same.
In the case of two classical point charges, and , with a displacement vector, , pointing from the negative charge to the positive charge, the electric dipole moment is given by
In the presence of an electric field, such as that due to an electromagnetic wave, the two charges will experience a force in opposite directions, leading to a net torque on the dipole. The magnitude of the torque is proportional to both the magnitude of the charges and the separation between them, and varies with the relative angles of the field and the dipole:
Similarly, the coupling between an electromagnetic wave and an atomic transition with transition dipole moment depends on the charge distribution within the atom, the strength of the electric field, and the relative polarizations of the field and the transition. In addition, the transition dipole moment depends on the geometries and relative phases of the initial and final states. | 5 | Photochemistry |
Expanded bed adsorption (EBA) is a preparative chromatographic technique which makes processing of viscous and particulate liquids possible. | 1 | Biochemistry |
There are three types of shrinkage: shrinkage of the liquid, solidification shrinkage and patternmakers shrinkage. The shrinkage of the liquid is rarely a problem because more material is flowing into the mold behind it. Solidification shrinkage occurs because metals are less dense as a liquid than a solid, so during solidification the metal density dramatically increases. Patternmakers shrinkage refers to the shrinkage that occurs when the material is cooled from the solidification temperature to room temperature, which occurs due to thermal contraction. | 8 | Metallurgy |
Hydrolysis is the reverse reaction of formation with regeneration of the carbonyl compound.
In the Shapiro reaction tosylhydrazones are used as a leaving group in elimination reactions. This reaction requires a strong base. If sodium methoxide is used as the base the reaction is called a Bamford–Stevens reaction. Tosylhydrazones can be reduced to the corresponding alkanes with reagents such as sodium borohydride and borane.
Tosylhydrazone salts can react with metals to form metal carbenes and used in cyclopropanations and epoxidations. An example of a transition metal-catalyzed cyclopropanation is a synthesis of tranylcypromine, in which the sodium salt of benzaldehyde tosylhydrazone is converted to a rhodium metal carbene through the diazo intermediate.
Tosylhydrazones are also starting materials for certain cross-coupling reactions. In the first report on this reaction type the coupling partners were a tosylhydrazone, an aryl halide with catalyst system dibenzylideneacetone / XPhos. As part of the catalytic cycle the diazo intermediateformed by decomposition of the tosylhydrazone forms a palladium-carbene complex with the oxidative addition complex of palladium with the aryl halide.
Using this powerful method it is possible to access bioactive compounds. | 0 | Organic Chemistry |
A convenient synthesis of chloromethyl methyl ether in situ involves the reaction of dimethoxymethane and acetyl chloride in the presence of a Lewis acid catalyst This route affords a methyl acetate solution of chloromethyl methyl ether of high purity. A similar method, using a high-boiling acyl chloride, can be used to prepare pure, dimethoxymethane being the only contaminant. In contrast, the classical procedure reported in Organic Syntheses employing formaldehyde, methanol, and hydrogen chloride yields material significantly contaminated with the dangerous bis(chloromethyl) ether and requires fractional distillation. | 0 | Organic Chemistry |
Mitotic spindle assembly checkpoint protein MAD1 is a protein that in humans is encoded by the MAD1L1 gene.
MAD1L1 is also known as Human Accelerated Region 3. It may have played a key role in the evolution of humans from apes. | 1 | Biochemistry |
Supercells are also commonly used in computational models of crystal defects to allow the use of periodic boundary conditions. | 3 | Analytical Chemistry |
*one ATP by direct phosphorylation of GDP
*two ATP from oxidation of FADH
*three ATP at a time for the NADH + H produced within the α-ketoglutarate dehydrogenase reaction, the malate dehydrogenase reaction and the malate decarboxylase reaction.
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Due to low glutamate dehydrogenase and glutamate pyruvate transaminase activities, in tumor cells the conversion of glutamate to alpha-ketoglutarate mainly takes place via glutamate oxaloacetate transaminase. | 1 | Biochemistry |
Pathogenic bacteria commonly produce a bacterial capsule, a thick, mucous-like, layer of polysaccharide. The capsule cloaks antigenic proteins on the bacterial surface that would otherwise provoke an immune response and thereby lead to the destruction of the bacteria. Capsular polysaccharides are water-soluble, commonly acidic, and have molecular weights on the order of 100,000 to 2,000,000 daltons. They are linear and consist of regularly repeating subunits of one to six monosaccharides. There is enormous structural diversity; nearly two hundred different polysaccharides are produced by E. coli alone. Mixtures of capsular polysaccharides, either conjugated or native, are used as vaccines.
Bacteria and many other microbes, including fungi and algae, often secrete polysaccharides to help them adhere to surfaces and to prevent them from drying out. Humans have developed some of these polysaccharides into useful products, including xanthan gum, dextran, welan gum, gellan gum, diutan gum and pullulan.
Most of these polysaccharides exhibit useful visco-elastic properties when dissolved in water at very low levels. This makes various liquids used in everyday life, such as some foods, lotions, cleaners, and paints, viscous when stationary, but much more free-flowing when even slight shear is applied by stirring or shaking, pouring, wiping, or brushing. This property is named pseudoplasticity or shear thinning; the study of such matters is called rheology.
Aqueous solutions of the polysaccharide alone have a curious behavior when stirred: after stirring ceases, the solution initially continues to swirl due to momentum, then slows to a standstill due to viscosity and reverses direction briefly before stopping. This recoil is due to the elastic effect of the polysaccharide chains, previously stretched in solution, returning to their relaxed state.
Cell-surface polysaccharides play diverse roles in bacterial ecology and physiology. They serve as a barrier between the cell wall and the environment, mediate host-pathogen interactions. Polysaccharides also play an important role in formation of biofilms and the structuring of complex life forms in bacteria like Myxococcus xanthus.
These polysaccharides are synthesized from nucleotide-activated precursors (called nucleotide sugars) and, in most cases, all the enzymes necessary for biosynthesis, assembly and transport of the completed polymer are encoded by genes organized in dedicated clusters within the genome of the organism. Lipopolysaccharide is one of the most important cell-surface polysaccharides, as it plays a key structural role in outer membrane integrity, as well as being an important mediator of host-pathogen interactions.
The enzymes that make the A-band (homopolymeric) and B-band (heteropolymeric) O-antigens have been identified and the metabolic pathways defined. The exopolysaccharide alginate is a linear copolymer of β-1,4-linked -mannuronic acid and -guluronic acid residues, and is responsible for the mucoid phenotype of late-stage cystic fibrosis disease. The pel and psl loci are two recently discovered gene clusters that also encode exopolysaccharides found to be important for biofilm formation. Rhamnolipid is a biosurfactant whose production is tightly regulated at the transcriptional level, but the precise role that it plays in disease is not well understood at present. Protein glycosylation, particularly of pilin and flagellin, became a focus of research by several groups from about 2007, and has been shown to be important for adhesion and invasion during bacterial infection. | 0 | Organic Chemistry |
Most metal-hypophosphite complexes are unstable, owing to the tendency of hypophosphites to reduce metal cations back into the bulk metal. Some examples have been characterised, including the important nickel salt [Ni(HO)](HPO). | 0 | Organic Chemistry |
pH in rivers is affected by the geology of the water source, atmospheric inputs and a range of other chemical contaminants. pH is only likely to become an issue on very poorly buffered upland rivers where atmospheric sulphur and nitrogen oxides may very significantly depress the pH as low as pH4 or in eutrophic alkaline rivers where photosynthetic bi-carbonate ion production in photosynthesis may drive the pH up above pH10. | 2 | Environmental Chemistry |
familial Mediterranean fever - farnesol dehydrogenase - Fat storage-inducing transmembrane protein 2 - FDC-SP - FHIPEP protein family - fibroblasts - fluorescence in situ hybridization -fluorophore-assisted carbohydrate electrophoresis - footprinting - formylmethanofuran dehydrogenase - Fragile site, folic acid type, rare, fra(2)(q13) - Fragile X syndrome - frameshift mutation - fructose 5-dehydrogenase - fucoidanase - fungal fruit body lectin family - fusion protein - | 1 | Biochemistry |
Copper and its alloys are readily joined by mechanical techniques, such as crimping, staking, riveting, and bolting; or by bonding techniques, such as soldering, brazing and welding. Selection of the best joining technique is determined by service requirements, joint configuration, thickness of components, and alloy composition.
Soldering is the preferred joining method where strong, watertight joints are required, such as for internal gutters, roofing, and flashing applications. A soldered seam joins two pieces of copper into a cohesive unit that expands and contracts as one piece. Well-soldered seams are often stronger than the original base material and provide many years of service.
Mechanical fasteners, such as screws, bolts, and rivets, are often used to strengthen the joints and seams. Continuous, long runs of soldered seams can cause stress fractures and should therefore be avoided.
Common 50-50 tin-lead bar solder is often used for uncoated copper; 60-40 tin-lead solder is used for lead-coated copper. Many lead-free solders are also acceptable.
Adhesives can be used in certain applications. Relatively thin sheet alloys can be bonded to plywood or certain types of foam which act as rigid insulation.
Brazing is the preferred method for joining pipe and tube copper alloys. Copper metal sections are joined with a non-ferrous filler material with a melting point above 800 degrees Fahrenheit but below the melting point of the base metals. Blind or concealed joints are recommended since the color match of silver filler material is fair to poor.
Welding is a process where pieces of copper are effectively melted together, either by flame, electricity, or high pressure. With increasing availability of modern TIG welding equipment, welding of even light-gauge copper decorative elements is gaining acceptance.
Instructional videos are available regarding fluxing and soldering techniques; how to make flat seam solder joints, double-lock standing seams, lap seams, soldering vertical sheet copper lap seams, and stitches (including the butterfly stitch); as well as copper tinning, bending, flaring, and brazing. | 8 | Metallurgy |
Folch was born in Barcelona, Spain. His father Rafel Folch was a lawyer and a Catalan poet, and his mother Maria Pi a teacher. His mother spoke French, Folch went to high school at the Lycée Français of Barcelona, from which he graduated in 1927. He then undertook Medicine studies and received an M.D. degree from the University of Barcelona Medical school in 1932. | 1 | Biochemistry |
NASA used additive manufacturing to synthesize an alloy they termed GRX-810, which survived temperatures over . The alloy also featured improved strength, malleability, and durability. The printer dispersed oxide particles uniformly throughout the metal matrix. The alloy was identified using 30 simulations of thermodynamic modeling. | 8 | Metallurgy |
Conjugated systems not only have low energy excitations in the visible spectral region but they also accept or donate electrons easily. Phthalocyanines, which, like Phthalocyanine Blue BN and Phthalocyanine Green G, often contain a transition metal ion, exchange an electron with the complexed transition metal ion that easily changes its oxidation state. Pigments and dyes like these are charge-transfer complexes. | 7 | Physical Chemistry |
In 1941, Beadle and Tatum proposed on the basis of their study of mutants of the fungus Neurospora sitophila that genes control specific biochemical reactions. They suggested that the functioning of an organism depends on an integrated system of chemical reactions controlled in some manner by genes. They further noted that “It is entirely tenable to suppose that these genes, which are themselves a part of the system, control or regulate specific reactions in the system either by acting directly as enzymes or by determining the specificity of enzymes.” This line of reasoning gave rise to the “one gene–one enzyme hypothesis”. In a retrospective article, Beadle discussed the status of the one gene-one enzyme hypothesis 10 years after it was proposed. Beadle commented on the Cold Spring Harbor Symposium meeting of biologists in 1951. He noted “I have the impression that the number whose faith in one gene-one enzyme remained steadfast could be counted on the fingers of one hand—with a couple of fingers left over.” However by the early 1960s the concept that the DNA base sequence of a gene specifies the amino acid sequence of a protein became well established on the basis of numerous experiments. For example, an experiment by Crick, Brenner, Barnett and Watts-Tobin in 1961 demonstrated that each amino acid in a protein is encoded by a corresponding sequence of three bases in DNA (called a codon). Soon after this, the specific codon assignments for each amino acid were determined (see Genetic code). | 1 | Biochemistry |
Adsorbed proteins are among the most difficult food soils to remove from food contact surfaces. In particular, heat-denatured proteins (such as those found in dairy industry applications) adhere tightly to surfaces and require strong alkaline cleaners for removal. It is important that cleaning methods are capable of removing both visible and non-visible protein soils. Nutrients for bacterial growth must be removed as well as biofilms that may have built up on the food contact surface. Proteins are water-insoluble, slightly soluble in acidic solutions and soluble in alkaline solutions, which limits the type of cleaner that can be used to remove protein from the surface. Generally speaking, highly alkaline cleaners with peptizing and wetting agents are most effective in protein removal on food contact surfaces. Cleaning temperature is also a concern for effective protein removal. As temperature increases, the activity of the cleaning compound increases, making soil removal easier. However, at higher temperatures (> 55 °C) proteins denature and cleaning efficacy is reduced. | 1 | Biochemistry |
In the early 1990s, at least thirty separate groups were working on the total synthesis of the chemotherapy medicine paclitaxel (Taxol), culminating with the groups of Robert A. Holton and K. C. Nicolaou publishing nearly simultaneously in 1994. By then, Mukaiyama had retired from the University of Tokyo after reaching the mandatory age of 60 and set up an academic lab at the Tokyo University of Science. The Mukaiyama taxol total synthesis was published between the years of 1997 and 1999 after five years of research, making the Mukaiyama lab the sixth group to report results.
This total synthesis is largely a linear synthesis which forms the four rings of taxol in the order C, B, A, D. It is differentiated from the others from its use of L-serine as a starting material and for being the only total synthesis not to use the Ojima lactam to create the amide tail. Instead, the tail is created from scratch by converting benzyloxyacetic acid into a silyl enol ether, joining it with benzaldehyde with a Mukaiyama aldol addition, and creating the amide from the alcohol via a Mitsunobu reaction followed by benzoylation.
The synthesis also made use of three Swern oxidations during the synthesis of the C ring. This reaction is typically performed at very low temperatures (< -50 °C) to stabilize its activated DMSO intermediate and constantly evolves the strong-smelling DMS, making it very difficult to work with at large scales. The difficulties encountered during their total synthesis prompted Mukaiyama to pursue an alternative method, and in 2001 a room-temperature oxidation involving N-chlorosuccinimide and a catalytic amount of N-t-butylbenzenesulfenamide was developed. The more electronegative nitrogen adjacent to the sulfur in the sulfenamide increased the stability of the intermediate relative to that formed from the sulfur-carbon bond of DMSO and was inspired by his earlier work with sulfenamides while still at the Tokyo Institute of Technology. | 0 | Organic Chemistry |
Flow-accelerated corrosion (FAC), also known as flow-assisted corrosion, is a corrosion mechanism in which a normally protective oxide layer on a metal surface dissolves in a fast flowing water. The underlying metal corrodes to re-create the oxide, and thus the metal loss continues.
By definition, the rate of FAC depends on the flow velocity. FAC often affects carbon steel piping carrying ultra-pure, deoxygenated water or wet steam. Stainless steel does not suffer from FAC. FAC of carbon steel halts in the presence of small amount of oxygen dissolved in water. FAC rates rapidly decrease with increasing water pH.
FAC has to be distinguished from erosion corrosion because the fundamental mechanisms for the two corrosion modes are different. FAC does not involve impingement of particles, bubbles, or cavitation which cause the mechanical (often crater-like) wear on the surface. By contrast to mechanical erosion, FAC involves dissolution of normally poorly soluble oxide by combined electrochemical, water chemistry and mass-transfer phenomena. Nevertheless, the terms FAC and erosion are sometimes used interchangeably because the actual mechanism may, in some cases, be unclear.
FAC was the cause of several high-profile accidents in power plants, for example, a rupture of a high-pressure condensate line in Virginia Power's Surry nuclear plant in 1986, that resulted in four fatalities and four injuries. | 8 | Metallurgy |
In podsolisation, chelating agents break down clay and release minerals such as iron and aluminium. When iron and aluminium are hydrated they become sesquioxides. The sesquioxides are translocated from the A Horizon, a zone of out-washing, to the B Horizon, a zone of illuviation. Many bases such as calcium and potassium are also leached from the zone along with organic matter and silica. Often minerals like quartz and silica are left behind in the A horizon. What is significantly different about podsols in comparison to other soils is that the bottom of A horizon is known as the AE horizon, which is an eluviated area which has lost sesquioxides. It tends to be an ash gray colour. | 9 | Geochemistry |
Rubber elasticity refers to a property of crosslinked rubber: it can be stretched by up to a factor of 10 from its original length and, when released, returns very nearly to its original length. This can be repeated many times with no apparent degradation to the rubber. Rubber is a member of a larger class of materials called elastomers and it is difficult to overestimate their economic and technological importance. Elastomers have played a key role in the development of new technologies in the 20th century and make a substantial contribution to the global economy. Rubber elasticity is produced by several complex molecular processes and its explanation requires a knowledge of advanced mathematics, chemistry and statistical physics, particularly the concept of entropy. Entropy may be thought of as a measure of the thermal energy that is stored in a molecule.
Common rubbers, such as polybutadiene and polyisoprene (also called natural rubber), are produced by a process called polymerization. Very long molecules (polymers) are built up sequentially by adding short molecular backbone units through chemical reactions. A rubber polymer follows a random, zigzag path in three dimensions, intermingling with many other rubber molecules. An elastomer is created by the addition of a few percent of a cross linking molecule such as sulfur. When heated, the crosslinking molecule causes a reaction that chemically joins (bonds) two of the rubber molecules together at some point (a crosslink). Because the rubber molecules are so long, each one participates in many crosslinks with many other rubber molecules forming a continuous molecular network.
As a rubber band is stretched, some of the network chains are forced to become straight and this causes a decrease in their entropy. It is this decrease in entropy that gives rise to the elastic force in the network chains. | 7 | Physical Chemistry |
Supercritical hydrolysis is a method of converting all biomass polysaccharides as well the associated lignin into low molecular compounds by contacting with water alone under supercritical conditions. The supercritical water, acts as a solvent, a supplier of bond-breaking thermal energy, a heat transfer agent and as a source of hydrogen atoms. All polysaccharides are converted into simple sugars in near-quantitative yield in a second or less. The aliphatic inter-ring linkages of lignin are also readily cleaved into free radicals that are stabilized by hydrogen originating from the water. The aromatic rings of the lignin are unaffected under short reaction times so that the lignin-derived products are low molecular weight mixed phenols. To take advantage of the very short reaction times needed for cleavage a continuous reaction system must be devised. The amount of water heated to a supercritical state is thereby minimized. | 7 | Physical Chemistry |
The Mg(I) dimer formula, LMgMgL, has undergone multiple theoretical investigations regarding the bonds. Furthermore, L, a monoanionic ligand, can also include halides, hydrogen, small alkyl groups, aryl groups, cyclopentadienyl with respective derivatives and chelating monoanionic nitrogen ligands. Mg—Mg bonded molecules underwent the primary investigation, with the bond length found to be 2.76-2.89 Å. Additionally, the bond dissociation energy was found to be between 45 and 48 kcal mol. Specifically, for ClMgMgCl, it was found to be 47.1 kcal mol. | 7 | Physical Chemistry |
Many cofactors (non-protein-based helper molecules) feature thiols. The biosynthesis and degradation of fatty acids and related long-chain hydrocarbons is conducted on a scaffold that anchors the growing chain through a thioester derived from the thiol Coenzyme A. The biosynthesis of methane, the principal hydrocarbon on Earth, arises from the reaction mediated by coenzyme M, 2-mercaptoethyl sulfonic acid. Thiolates, the conjugate bases derived from thiols, form strong complexes with many metal ions, especially those classified as soft. The stability of metal thiolates parallels that of the corresponding sulfide minerals. | 0 | Organic Chemistry |
Abnormal grain growth (AGG) is encountered in metallic or ceramic systems exhibiting one or more of several characteristics:
# Systems with secondary phase inclusions, precipitates or impurities above a certain threshold concentration.
# Systems with a highly anisotropic surface energy.
# Systems far from chemical equilibrium.
Abnormal grain growth occurs due to very high local rates of interface migration and is enhanced by the localized formation of liquid at grain boundaries. In 2023, Liss et al.
have shown that the spontaneous activation of a grain boundary opens diffusion pathways, leading to the activation of one grain in an otherwise inactive microstructure and allowing the grain to rotate and coalesce with a neighbor grain. However, due to competition with the surrounding grains, rotation may proceed erratically. Coupled with spontaneous activation, this makes abnormal grain growth a largely erratic process. While the activation of grain boundaries (leading to rotation and growth) can occur at temperatures well below the temperatures required for partial melting of the grain boundaries, the effect is emphasized when melting occurs. | 3 | Analytical Chemistry |
In the general context, strange matter might occur inside neutron stars, if the pressure at their core is high enough to provide a sufficient gravitational force (i.e. above the critical pressure). At the sort of densities and high pressures we expect in the center of a neutron star, the quark matter would probably be strange matter. It could conceivably be non-strange quark matter, if the effective mass of the strange quark were too high. Charm quarks and heavier quarks would only occur at much higher densities.
Strange matter comes about as a way to relieve degeneracy pressure. The Pauli exclusion principle forbids fermions such as quarks from occupying the same position and energy level. When the particle density is high enough that all energy levels below the available thermal energy are already occupied, increasing the density further requires raising some to higher, unoccupied energy levels. This need for energy to cause compression manifests as a pressure. Neutrons consist of twice as many down quarks (charge − e) as up quarks (charge + e), so the degeneracy pressure of down quarks usually dominates electrically neutral quark matter. However, when the required energy level is high enough, an alternative becomes available: half of the down quarks can be transmuted to strange quarks (charge − e). The higher rest mass of the strange quark costs some energy, but by opening up an additional set of energy levels, the average energy per particle can be lower, making strange matter more stable than non-strange quark matter.
A neutron star with a quark matter core is often called a hybrid star. However, it is difficult to know whether hybrid stars really exist in nature because physicists currently have little idea of the likely value of the critical pressure or density. It seems plausible that the transition to quark matter will already have occurred when the separation between the nucleons becomes much smaller than their size, so the critical density must be less than about 100 times nuclear saturation density. But a more precise estimate is not yet available, because the strong interaction that governs the behavior of quarks is mathematically intractable, and numerical calculations using lattice QCD are currently blocked by the fermion sign problem.
One major area of activity in neutron star physics is the attempt to find observable signatures by which we could tell whether neutron stars have quark matter (probably strange matter) in their core.
During the merger of two neutron stars, strange matter may be ejected out into the space around the stars, which may allow for the studying of strange matter. However, the rate at which strange matter decays is unknown, and there are very few binary pairs of neutron stars nearby to the Solar System, which could make the official discovery of strange matter very difficult. | 7 | Physical Chemistry |
Aluminum, copper, molybdenum, cobalt, mercury reserves and most importantly electricity for the smelting process has led to the development of non-ferrous metallurgy. The Zeylik mine in Daskasan district is the main provider of the alunite for aluminum production. The extracted ore here transported through Guschu-Alabashli railway to the aluminum plant located in Ganja city. The obtained aluminum oxide is brought to Sumgayit aluminum plant in order produce aluminum. Ganja Aluminum Plant produces sulfuric acid, aluminum oxide, and potassium fertilizer through extracted ore from Zalik deposit in Dashkesen. Aluminum oxide is also produced in Sumgait. AzerGold CJSC (created by the Presidential Decree No. 1047 on February 11, 2015) implements exploration, management, and also extraction, processing and sale of precious and non-ferrous metal ore deposits located within the borders of the country. In 2017, the volume of exports of precious metals carried out by this company amounted to 77340 million dollars. | 8 | Metallurgy |
For example, the molecule 2,3-dibromobutane carries two vicinal bromine atoms and 1,3-dibromobutane does not. Mostly, the use of the term vicinal is restricted to two identical functional groups.
Likewise in a gem-dibromide the prefix gem, an abbreviation of geminal, signals that both bromine atoms are bonded to the same atom (i.e., in a 1,1-relationship). For example, 1,1-dibromobutane is geminal. While comparatively less common, the term hominal has been suggested as a descriptor for groups in a 1,3-relationship.
Like other descriptors, such as syn, anti, exo or endo, the description vicinal helps explain how different parts of a molecule are related to each other either structurally or spatially. The vicinal adjective is sometimes restricted to those molecules with two identical functional groups. The use of the term can also be extended to substituents on aromatic rings. | 4 | Stereochemistry |
Particulate organic carbon (POC) is operationally defined as all combustible, non-carbonate carbon that can be collected on a filter. The oceanographic community has historically used a variety of filters and pore sizes, most commonly 0.7, 0.8, or 1.0 μm glass or quartz fiber filters. The biomass of living zooplankton is intentionally excluded from POC through the use of a pre-filter or specially designed sampling intakes that repel swimming organisms. Sub-micron particles, including most marine prokaryotes, which are 0.2–0.8 μm in diameter, are often not captured but should be considered part of POC rather than dissolved organic carbon (DOC), which is usually operationally defined as < 0.2 μm. Typically POC is considered to contain suspended and sinking particles ≥ 0.2 μm in size, which therefore includes biomass from living microbial cells, detrital material including dead cells, fecal pellets, other aggregated material, and terrestrially-derived organic matter. Some studies further divide POC operationally based on its sinking rate or size, with ≥ 51 μm particles sometimes equated to the sinking fraction. Both DOC and POC play major roles in the carbon cycle, but POC is the major pathway by which organic carbon produced by phytoplankton is exported – mainly by gravitational settling – from the surface to the deep ocean and eventually to sediments, and is thus a key component of the biological pump. | 9 | Geochemistry |
In molecular biology, prostanoids are active lipid mediators that regulate inflammatory response. Prostanoids are a subclass of eicosanoids consisting of the prostaglandins (mediators of inflammatory and anaphylactic reactions), the thromboxanes (mediators of vasoconstriction), and the prostacyclins (active in the resolution phase of inflammation). Prostanoids are seen to target NSAIDS which allow for therapeutic potential. Prostanoids are present within areas of the body such as the gastrointestinal tract, urinary tract, respiratory and cardiovascular systems, reproductive tract and vascular system. Prostanoids can even be seen with aid to the water and ion transportation within cells. | 1 | Biochemistry |
In acid-base titrations, an unfitting pH indicator may induce a color change in the indicator-containing solution before or after the actual equivalence point. As a result, different equivalence points for a solution can be concluded based on the pH indicator used. This is because the slightest color change of the indicator-containing solution suggests the equivalence point has been reached. Therefore, the most suitable pH indicator has an effective pH range, where the change in color is apparent, that encompasses the pH of the equivalence point of the solution being titrated. | 7 | Physical Chemistry |
An amylase () is an enzyme that catalyses the hydrolysis of starch (Latin ) into sugars. Amylase is present in the saliva of humans and some other mammals, where it begins the chemical process of digestion. Foods that contain large amounts of starch but little sugar, such as rice and potatoes, may acquire a slightly sweet taste as they are chewed because amylase degrades some of their starch into sugar. The pancreas and salivary gland make amylase (alpha amylase) to hydrolyse dietary starch into disaccharides and trisaccharides which are converted by other enzymes to glucose to supply the body with energy. Plants and some bacteria also produce amylase. Specific amylase proteins are designated by different Greek letters. All amylases are glycoside hydrolases and act on α-1,4-glycosidic bonds. | 1 | Biochemistry |
2,6-Dichlorophenolindophenol (DCPIP, DCIP or DPIP) is a chemical compound used as a redox dye. When oxidized, DCPIP is blue with a maximal absorption at 600 nm; when reduced, DCPIP is colorless.
DCPIP can be used to measure the rate of photosynthesis. It is part of the Hill reagents family. When exposed to light in a photosynthetic system, the dye is decolorised by chemical reduction. DCPIP has a higher affinity for electrons than ferredoxin and the photosynthetic electron transport chain can reduce DCPIP as a substitute for NADP, that is normally the final electron carrier in photosynthesis. As DCPIP is reduced and becomes colorless, the resultant increase in light transmittance can be measured using a spectrophotometer.
DCPIP can also be used as an indicator for vitamin C. If vitamin C, which is a good reducing agent, is present, the blue dye, which turns pink in acid conditions, is reduced to a colorless compound by ascorbic acid. This reaction is a redox reaction: vitamin C (ascorbic acid) is oxidized to dehydroascorbic acid, and DCPIP is reduced to the colorless compound DCPIPH
:DCPIP (blue) + H → DCPIPH (pink)
:DCPIPH (pink) + vitamin C → DCPIPH (colorless)
In this titration, when all the ascorbic acid in the solution has been used up, there will not be any electrons available to reduce the DCPIPH and the solution remains pink due to the DCPIPH. The end point is a pink color that persists for 10 seconds or more, if there is not enough ascorbic acid to reduce all of the DCPIPH. Pharmacological experiments suggest that DCPIP may serve as a pro-oxidant chemotherapeutic targeting human cancer cells in an animal model of human melanoma; DCPIP-induced cancer cell death occurs by depletion of intracellular glutathione and upregulation of oxidative stress. | 3 | Analytical Chemistry |
The Wilfley Table is commonly used for the concentration of heavy minerals from the laboratory up to the industrial scale. It has a traditional shaking (oscillating) table design with a riffled deck. It is one of several brands of wet tables used for the separation and concentration of heavy ore minerals which include the Deister Table and Holman Table, all built to handle either coarse or fine feeds for mineral processing.
The Wilfley Table became a design used world-wide due to the fact it significantly increased the recovery of silver, gold and other precious metals. Such was the tables widespread use that it was included in Websters Dictionary, and has been in constant use by miners and metallurgists since its invention. | 8 | Metallurgy |
Murray studied chemistry at St. Marys University in Halifax, Nova Scotia, Canada from 1985, graduating with a Bachelors Degree with Honors in Chemistry in 1988. He spent a year as a Rotary International Fellow at the University of Auckland in 1989. From 1990 he studied at the Massachusetts Institute of Technology (MIT), where he received his doctorate in chemistry in 1995. | 7 | Physical Chemistry |
Reaction systems that are less efficient or entirely inactive in the absence of carboxylate acids and bases are likely to occur through a concerted metalation protonation reaction pathway. An example of such a reaction with an sp C–H bond that was reported in 2007 by Keith Fagnou and coworkers is an intramolecular cyclization that uses a palladium catalyst.
A notable example of a reaction that is catalyzed by ruthenium in which directed metalation occurs through CMD was reported by Igor Larossa and coworkers in 2018. The ruthenium catalyst is functional group tolerant and enables the late stage synthesis of pharmaceutically relevant biaryls. | 0 | Organic Chemistry |
Because the Zeeman interaction is a function of magnetic field and Larmor frequency, it can be obstructed or amplified by altering the external magnetic or the Larmor frequency with experimental instruments that generate oscillating fields. It has been observed that migratory birds lose their navigational abilities in such conditions where the Zeeman interaction is obstructed in radical-pairs. | 7 | Physical Chemistry |
Combustion analysis is a method used in both organic chemistry and analytical chemistry to determine the elemental composition (more precisely empirical formula) of a pure organic compound by combusting the sample under conditions where the resulting combustion products can be quantitatively analyzed. Once the number of moles of each combustion product has been determined the empirical formula or a partial empirical formula of
the original compound can be calculated.
Applications for combustion analysis involve only the elements of carbon (C), hydrogen (H), nitrogen (N), and sulfur (S) as combustion of materials containing them convert these elements to their oxidized form (CO, HO, NO or NO, and SO) under high temperature high oxygen conditions. Notable interests for these elements involve measuring total nitrogen in food or feed to determine protein percentage, measuring sulfur in petroleum products, or measuring total organic carbon (TOC) in water. | 0 | Organic Chemistry |
Glutamate-1-semialdehyde is a molecule formed from by the reduction of tRNA bound glutamate, catalyzed by glutamyl-tRNA reductase. It is isomerized by glutamate-1-semialdehyde 2,1-aminomutase to give aminolevulinic acid in the biosynthesis of porphyrins, including heme and chlorophyll. | 1 | Biochemistry |
Albert Rakoto Ratsimamanga was born on 28 December 1907, in Antananarivo, Madagascar, to Razanadrakoto Ratsimamanga and Lala Ralisoa. He was the grandson of Prince Ratsimamanga, uncle and advisor to Queen Ranavalona III, who was executed in 1897 at the beginning of the French colonisation of Madagascar. When Albert was only eleven years old, his father died in 1918 from heavy drinking.
He received his early education at the Faculty of Medicine, University of Antananarivo, until he became a doctor of Indigenous Medicine in 1924. Ratsimamanga was a member of the Malagasy delegation to the 1930 Colonial Exhibition in Paris, during which he decided to join the University of Paris to become a Doctor of Science (MS) and a Doctor of Medicine (MD). He also graduated from the Institute of Exotic Medicine and the Pasteur Institut, and founded the association of Malagasy Students in France. | 1 | Biochemistry |
Amine oxidation with benzoyl peroxide is the most common method to synthesize hydroxylamines. Care must be taken to prevent over-oxidation to a nitrone. Other methods include:
* Hydrogenation of an oxime
* Alkylating a precursor hydroxylamine
* Amine oxide pyrolysis (the Cope reaction) | 0 | Organic Chemistry |
The BGIT is based on empirical data and heat of formation. Some groups are too hard to measure, so not all the existing groups are available in the table. Sometimes approximation should be made when those unavailable groups are encountered. For example, we need to approximate C as C and N as N in C≡N, which clearly cause more inaccuracy, which is another drawback. | 7 | Physical Chemistry |
When an area element is radiating as a result of being illuminated by an external source, the irradiance (energy or photons /time/area) landing on that area element will be proportional to the cosine of the angle between the illuminating source and the normal. A Lambertian scatterer will then scatter this light according to the same cosine law as a Lambertian emitter. This means that although the radiance of the surface depends on the angle from the normal to the illuminating source, it will not depend on the angle from the normal to the observer. For example, if the moon were a Lambertian scatterer, one would expect to see its scattered brightness appreciably diminish towards the terminator due to the increased angle at which sunlight hit the surface. The fact that it does not diminish illustrates that the moon is not a Lambertian scatterer, and in fact tends to scatter more light into the oblique angles than a Lambertian scatterer.
The emission of a Lambertian radiator does not depend on the amount of incident radiation, but rather from radiation originating in the emitting body itself. For example, if the sun were a Lambertian radiator, one would expect to see a constant brightness across the entire solar disc. The fact that the sun exhibits limb darkening in the visible region illustrates that it is not a Lambertian radiator. A black body is an example of a Lambertian radiator. | 7 | Physical Chemistry |
A new formula describing size effect was proposed. This formula has a form
where is the nanoparticle radius and is wave number. It is supposed here that the time dependence of the electromagnetic field is given by the factor In this paper Bruggemans approach was used, but electromagnetic field for electric-dipole oscillation mode inside the picked particle was computed without applying quasi-static approximation. Thus the function is due to the field nonuniformity inside the picked particle. In quasi-static region (, i.e. for Ag this function becomes constant and formula (5) becomes identical with Bruggemans formula. | 7 | Physical Chemistry |
For light, as in other settings, the scattering cross section for particles is generally different from the geometrical cross section of the particle, and it depends upon the wavelength of light and the permittivity, shape, and size of the particle. The total amount of scattering in a sparse medium is proportional to the product of the scattering cross section and the number of particles present.
In the interaction of light with particles, many processes occur, each with their own cross sections, including absorption, scattering, and photoluminescence. The sum of the absorption and scattering cross sections is sometimes referred to as the attenuation or extinction cross section.
The total extinction cross section is related to the attenuation of the light intensity through the Beer–Lambert law, which says that attenuation is proportional to particle concentration:
where is the attenuation at a given wavelength , is the particle concentration as a number density, and is the path length. The absorbance of the radiation is the logarithm (decadic or, more usually, natural) of the reciprocal of the transmittance :
Combining the scattering and absorption cross sections in this manner is often necessitated by the inability to distinguish them experimentally, and much research effort has been put into developing models that allow them to be distinguished, the Kubelka-Munk theory being one of the most important in this area. | 7 | Physical Chemistry |
An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts:
* The chemical gradient, or difference in solute concentration across a membrane.
* The electrical gradient, or difference in charge across a membrane.
When there are unequal concentrations of an ion across a permeable membrane, the ion will move across the membrane from the area of higher concentration to the area of lower concentration through simple diffusion. Ions also carry an electric charge that forms an electric potential across a membrane. If there is an unequal distribution of charges across the membrane, then the difference in electric potential generates a force that drives ion diffusion until the charges are balanced on both sides of the membrane.
Electrochemical gradients are essential to the operation of batteries and other electrochemical cells, photosynthesis and cellular respiration, and certain other biological processes. | 7 | Physical Chemistry |
Enediols are alkenes with a hydroxyl group on each carbon of the C=C double bond. Normally such compounds are disfavored components in equilibria with acyloins. One special case is catechol, where the C=C subunit is part of an aromatic ring. In some other cases however, enediols are stabilized by flanking carbonyl groups. These stabilized enediols are called reductones. Such species are important in glycochemistry, e.g., the Lobry de Bruyn-van Ekenstein transformation.
Ribulose-1,5-bisphosphate is a key substrate in the Calvin cycle of photosynthesis. In the Calvin cycle, the ribulose equilibrates with the enediol, which then binds carbon dioxide. The same enediol is also susceptible to attack by oxygen (O) in the (undesirable) process called photorespiration. | 0 | Organic Chemistry |
Methyl metabolism is very ancient and can be found in all organisms on earth, from bacteria to humans, indicating the importance of methyl metabolism for physiology. Indeed, pharmacological inhibition of global methylation in species ranging from human, mouse, fish, fly, roundworm, plant, algae, and cyanobacteria causes the same effects on their biological rhythms, demonstrating conserved physiological roles of methylation during evolution. | 0 | Organic Chemistry |
* Hartree–Fock method (closed-shell and restricted open-shell)
* Multi-configurational self-consistent field (MCSCF) (quadratic convergence and state averaging)
* Multi-reference CISD for an arbitrary set of reference configurations (including a massively parallel version)
* Configuration interaction calculations are based on Graphical Unitary Group Approach (GUGA).
* Analytic gradients for MCSCF, MR-CISD, MR-ACPF and MR-AQCC
* Analytic MCSCF and MR-CISD nonadiabatic coupling vectors
* Support for electrostatic embedding QM/MM calculations
* Automatic geometry optimization, saddle-point searches
* Automatic searches for the minima on conical intersection seams.
* Spin/orbit configuration interaction | 7 | Physical Chemistry |
Smith worked on the development of technically and environmentally sound mineral and waste processing technologies. He laid the groundwork for various technical innovations, including the carbochlorination technique used in the processing of lunar anorthite. Alongside colleagues, he confirmed graphite's ability, with or without catalysts, to selectively reduce iron oxide in synthetic ilmenite, observed through isothermal weight loss over time from 850 °C to 1200 °C under argon atmosphere. Additionally, he explored reduction roasting processes using various reductants and desulfurizers to convert sulfide minerals to metallic form without sulfur dioxide emissions, capturing sulfur as either calcium sulfide or sodium sulfide. | 8 | Metallurgy |
Addiction to indoor tanning has been recognized as a psychiatric disorder. The disorder is characterized as excessive indoor tanning that causes the subject personal distress; it has been associated with anxiety, eating disorders and smoking. The media has described the addiction as tanorexia. According to the Canadian Pediatric Society, "repeated UVR exposures, and the use of indoor tanning beds specifically, may have important systemic and behavioural consequences, including mood changes, compulsive disorders, pain and physical dependency." | 5 | Photochemistry |
As a type of emergency contraception, levonorgestrel is used after unprotected intercourse to reduce the risk of pregnancy. However, it can serve different hormonal purposes in its different methods of delivery. It is available for use in a variety of forms: | 4 | Stereochemistry |
Relative entropy is directly related to the Fisher information metric. This can be made explicit as follows. Assume that the probability distributions and are both parameterized by some (possibly multi-dimensional) parameter . Consider then two close by values of and so that the parameter differs by only a small amount from the parameter value . Specifically, up to first order one has (using the Einstein summation convention)
with a small change of in the direction, and the corresponding rate of change in the probability distribution. Since relative entropy has an absolute minimum 0 for , i.e. , it changes only to second order in the small parameters . More formally, as for any minimum, the first derivatives of the divergence vanish
and by the Taylor expansion one has up to second order
where the Hessian matrix of the divergence
must be positive semidefinite. Letting vary (and dropping the subindex 0) the Hessian defines a (possibly degenerate) Riemannian metric on the parameter space, called the Fisher information metric. | 7 | Physical Chemistry |
Crown ethers, like cyclodextrin-type CSPs contain a chiral cavity. Crown ethers are immobilized on the silica surface to form chiral stationary phase. Crown ethers contain oxygen atoms within the cavity. The cyclic structure that contains apolar ethylene groups between oxygen forms hydrophobic inner cavity. Cram et al., introduced CSP based on chiral crown ethers and accomplished separation of amino acid. The crucial chiral recognition principle underlying crown ether-based enantiomer separation is based on the formation of numerous hydrogen bonds between the protonated primary amino group of the analyte and the ether oxygens of the crown structure. This structural requirement confines the application of crown ether-type CSPs to chiral compounds having primary amino groups adjoining the chiral centers, such as amino acids, amino acid derivatives. Progress in the field of crown ether-type CSPs have been reviewed. | 4 | Stereochemistry |
Hollow fiber membranes (HFMs) are a class of artificial membranes containing a semi-permeable barrier in the form of a hollow fiber. Originally developed in the 1960s for reverse osmosis applications, hollow fiber membranes have since become prevalent in water treatment, desalination, cell culture, medicine, and tissue engineering. Most commercial hollow fiber membranes are packed into cartridges which can be used for a variety of liquid and gaseous separations. | 7 | Physical Chemistry |
Micro-compounding is the mixing or processing of polymer formulations in the melt on a very small scale, typically several milliliters. The advantage of the use of a micro-compounder for R&D are significant: it gives faster, yet reliable results with much smaller samples and at much less investment costs, thus speeding up the innovation process in R&D of polymer materials, pharmaceutical, biomedical and nutritional applications.
Micro-compounding is typically performed with a table top, twin screw micro-compounder or -extruder with a working volume of 5 or 15 milliliters. With such small volumes it is almost impossible to have sufficient mixing in a continuous extruder. Therefore, state of the art micro-compounders have a batch mode (recirculation) and a conical shape. The L/D of a continuous twin screw extruder is mimicked in a batch micro-compounder by the recirculation mixing time, which is controlled by a manual valve. With this valve the recirculation can be interrupted to unload the formulation in either a strand, or an injection moulder, a film device or a fiber line. Typical recirculation times are 1-3 min, dependent on the ease of dispersive and distributive mixing of the formulation. | 7 | Physical Chemistry |
The settling particles can contact each other and arise when approaching the floor of the sedimentation tanks at very high particle concentration. So that further settling will only occur in adjust matrix as the sedimentation rate decreasing. This is can be illustrated by the lower region of the zone-settling diagram (Figure 3). In Compression zone, the settled solids are compressed by gravity (the weight of solids), as the settled solids are compressed under the weight of overlying solids, and water is squeezed out while the space gets smaller. | 3 | Analytical Chemistry |
Electron-stimulated desorption occurs as a result of an electron beam incident upon a surface in vacuum, as is common in particle physics and industrial processes such as scanning electron microscopy (SEM). At atmospheric pressure, molecules may weakly bond to surfaces in what is known as adsorption. These molecules may form monolayers at a density of 10 atoms/cm for a perfectly smooth surface,. One monolayer or several may form, depending on the bonding capabilities of the molecules. If an electron beam is incident upon the surface, it provides energy to break the bonds of the surface with molecules in the adsorbed monolayer(s), causing pressure to increase in the system. Once a molecule is desorbed into the vacuum volume, it is removed via the vacuum's pumping mechanism (re-adsorption is negligible). Hence, fewer molecules are available for desorption, and an increasing number of electrons are required to maintain constant desorption.
One of the leading models on electron stimulated desorption is described by Peter Antoniewicz In short, his theory is that the adsorbate becomes ionized by the incident electrons and then the ion experiences an image charge potential which attracts it towards the surface. As the ion moves closer to the surface, the possibility of electron tunnelling from the substrate increases and through this process ion neutralisation can occur. The neutralised ion still has kinetic energy from before, and if this energy plus the gained potential energy is greater than the binding energy then the ion can desorb from the surface. As ionisation is required for this process, this suggests the atom cannot desorb at low excitation energies, which agrees with experimental data on electron simulated desorption. Understanding electron stimulated desorption is crucial for accelerators such as the Large Hadron Collider, where surfaces are subjected to an intense bombardment of energetic electrons. In particular, in the beam vacuum systems the desorption of gases can strongly impact the accelerators performance by modifying the secondary electron yield of the surfaces. | 7 | Physical Chemistry |
Fuculose or 6-deoxy-tagatose is a ketohexose deoxy sugar. Fuculose is involved in the process of sugar metabolism. -Fuculose can be formed from -fucose by -fucose isomerase and converted to L-fuculose-1-phosphate by -fuculose kinase. | 1 | Biochemistry |
The formation reactions for most organic compounds are hypothetical. For instance, carbon and hydrogen will not directly react to form methane (), so that the standard enthalpy of formation cannot be measured directly. However the standard enthalpy of combustion is readily measurable using bomb calorimetry. The standard enthalpy of formation is then determined using Hess's law. The combustion of methane:
is equivalent to the sum of the hypothetical decomposition into elements followed by the combustion of the elements to form carbon dioxide () and water ():
Applying Hess's law,
Solving for the standard of enthalpy of formation,
The value of is determined to be −74.8 kJ/mol. The negative sign shows that the reaction, if it were to proceed, would be exothermic; that is, methane is enthalpically more stable than hydrogen gas and carbon.
It is possible to predict heats of formation for simple unstrained organic compounds with the heat of formation group additivity method. | 7 | Physical Chemistry |
The database was pulled from the internet by the Trump administration in December 2019. The NLM said in a statement that much of the information remained available from the original sources, and that thus the database could be removed; critics, such as the Environmental Data & Governance Initiative, suggested it was part of a larger effort on the part of the administration to obfuscate the detrimental results of the rollback of Obama-era environmental regulations.
The data underlying TOXMAP remains accessible through their original resources: Government of Canada National Pollutant Release Inventory (NPRI), U.S. Census Bureau, U.S. EPA Clean Air Markets Program, U.S. EPA Geospatial Applications, U.S. EPA Facilities Registry System (FRS), U.S. EPA Superfund Program, U.S. EPA Toxics Release Program (TRI), U.S. NIH NCI Surveillance, Epidemiology, and End Results Program (SEER), U.S. Nuclear Regulatory Commission (NRC). | 1 | Biochemistry |
The Bengal Iron Works was founded at Kulti, Bengal, in 1870 which began its production in 1874 followed by The Tata Iron and Steel Company (TISCO) was established by Dorabji Tata in 1907, as part of his father's conglomerate. By 1939 it operated the largest steel plant in the British Empire. The company launched a major modernization and expansion program in 1951.
Prime Minister Jawaharlal Nehru, a believer in socialism, decided that the technological revolution in India needed maximization of steel production. He, therefore, formed a government owned company, Hindustan Steel Limited (HSL) and set up three steel plants in the 1950s.
The Indian steel industry began expanding into Europe in the 21st century. In January 2007 Indias Tata Steel made a successful $11.3 billion offer to buy European steel maker Corus Group. In 2006 Mittal Steel (based in London but with Indian management) merged with Arcelor after a takeover bid for $34.3 billion to become the worlds biggest steel maker, ArcelorMittal (based in Luxembourg City), with 10% of the world's output. | 8 | Metallurgy |
The molecular term symbol is a shorthand expression of the angular momenta that characterize the electronic quantum states of a diatomic molecule, which are also eigenstates of the electronic molecular Hamiltonian. It is also convenient, and common, to represent a diatomic molecule as two-point masses connected by a massless spring. The energies involved in the various motions of the molecule can then be broken down into three categories: the translational, rotational, and vibrational energies.The theoretical study of the rotational energy levels of the diatomic molecules can be described using the below description of the rotational energy levels. While the study of vibrational energy level of the diatomic molecules can be described using the harmonic oscillator approximation or using the quantum vibrational interaction potentials. These potentials give more accurate energy levels because they take multiple vibrational effects into account.
Concerning history, the first treatment of diatomic molecules with quantum mechanics was made by Lucy Mensing in 1926. | 4 | Stereochemistry |
SOCS are negative regulators of the JAK-STAT signaling pathway. SOCS have also been implicated in the regulation of cytokines, growth factors, and tumor suppression. | 1 | Biochemistry |
Surface runoff is defined as precipitation (rain, snow, sleet, or hail) that reaches a surface stream without ever passing below the soil surface. It is distinct from direct runoff, which is runoff that reaches surface streams immediately after rainfall or melting snowfall and excludes runoff generated by the melting of snowpack or glaciers.
Snow and glacier melt occur only in areas cold enough for these to form permanently. Typically snowmelt will peak in the spring and glacier melt in the summer, leading to pronounced flow maxima in rivers affected by them. The determining factor of the rate of melting of snow or glaciers is both air temperature and the duration of sunlight. In high mountain regions, streams frequently rise on sunny days and fall on cloudy ones for this reason.
In areas where there is no snow, runoff will come from rainfall. However, not all rainfall will produce runoff because storage from soils can absorb light showers. On the extremely ancient soils of Australia and Southern Africa, proteoid roots with their extremely dense networks of root hairs can absorb so much rainwater as to prevent runoff even with substantial amounts of rainfall. In these regions, even on less infertile cracking clay soils, high amounts of rainfall and potential evaporation are needed to generate any surface runoff, leading to specialised adaptations to extremely variable (usually ephemeral) streams. | 2 | Environmental Chemistry |
Anomalous diffusion is a diffusion process with a non-linear relationship between the mean squared displacement (MSD), , and time. This behavior is in stark contrast to Brownian motion, the typical diffusion process described by Einstein and Smoluchowski, where the MSD is linear in time (namely, with d being the number of dimensions and D the diffusion coefficient).
It has been found that equations describing normal diffusion are not capable of characterizing some complex diffusion processes, for instance, diffusion process in inhomogeneous or heterogeneous medium, e.g. porous media. Fractional diffusion equations were introduced in order to characterize anomalous diffusion phenomena.
Examples of anomalous diffusion in nature have been observed in ultra-cold atoms, harmonic spring-mass systems, scalar mixing in the interstellar medium, telomeres in the nucleus of cells, ion channels in the plasma membrane, colloidal particle in the cytoplasm, moisture transport in cement-based materials, and worm-like micellar solutions. | 7 | Physical Chemistry |
Ammonia oxidation to nitrate in a single step within one organism was predicted in 2006 and discovered in 2015 in the species Nitrospira inopinata. A pure culture of the organism was obtained in 2017, representing a revolution in our understanding of the nitrification process. | 1 | Biochemistry |
Chain shuttling polymerization makes use of two catalysts and a chain shuttling agent (CSA) to generate copolymers of alternating tacticity. Catalyst 1 (Cat1) propagates a polyolefin of a desired tacticity. Catalyst 2 (Cat2) generates another chain of a different tacticity. The two chains are allowed to co-propagate in a single reactor in the same living polymer fashion as before. To alternate the tacticity, a CSA will transfer the polymer chain from its respective catalyst. The CSA can then bind to Cat2 and attach the chain to Cat2. When the chain attaches to Cat2, the polymerization of that chain continues, except it now propagates with the tacticity dictated by Cat2, not Cat1. The general result is that the chain will alternate between two different tacticities. As the forward and reverse reactions occur, the polymer chain is “shuttled” back and forth between the two catalysts and a block copolymer is formed.
The shuttling of chains back and forth from catalysts via a CSA can be viewed as a competing chemical equilibrium. Note that the forward and reverse reactions of CSA binding and leaving either Cat1 or Cat2 are possible. This competition means that a chain can leave Cat1 via a CSA and the reattach to Cat1, polymerizing the same tacticity. The rate at which the reattachment of Cat1 occurs can be controlled by altering the relative concentrations of Cat1, Cat2 and CSA. For example, if one wanted to produce a polymer with the properties mainly resulting from the use of Cat1 and only wanted to influence its properties slightly by the presence of Cat2, a greater concentration of Cat1 would be used than for Cat2. The rate of alternation between tacticity can be controlled by altering the concentration of CSA relative to Cat1 and Cat2; having a higher concentration of CSA means that the chains will shuttle back and forth more rapidly, creating shorter units of alternating tacticity. | 7 | Physical Chemistry |
As illustrated by the diagram on the right, additional carbon dioxide () is absorbed by the ocean and reacts with water, carbonic acid () is formed and broken down into both bicarbonate () and hydrogen () ions (gray arrow), which reduces bioavailable carbonate () and decreases ocean pH (black arrow). This is likely to enhance nitrogen fixation by diazotrophs (gray arrow), which utilize ions to convert nitrogen into bioavailable forms such as ammonia () and ammonium ions (). However, as pH decreases, and more ammonia is converted to ammonium ions (gray arrow), there is less oxidation of ammonia to nitrite (NO), resulting in an overall decrease in nitrification and denitrification (black arrows). This in turn would lead to a further build-up of fixed nitrogen in the ocean, with the potential consequence of eutrophication. Gray arrows represent an increase while black arrows represent a decrease in the associated process. | 1 | Biochemistry |
Two simple examples are . The MB cores (M = Fe or Co) of these two compounds adopt structures expected for nido 5-vertex clusters. The iron compound is produced by reaction of diiron nonacarbonyl with pentaborane. and cyclobutadieneiron tricarbonyl have similar structures. | 7 | Physical Chemistry |
Enantioselective cycloaddition of azomethine ylides using chiral catalysts was first described in a seminal work by Allway and Grigg in 1991. This powerful method was further developed by Jørgensen and Zhang. These reactions generally use zinc, silver, copper, nickel, and calcium complexes.
Using chiral phosphine catalysts, enantiomerically pure spiroindolinones can be synthesized. The method described by Gong, et al. leads to an unexpected regiochemical outcome that does not follow electronic effects. This is attributed to favorable pi stacking with the catalyst. | 0 | Organic Chemistry |
In thermodynamics, the Joule–Thomson effect (also known as the Joule–Kelvin effect or Kelvin–Joule effect) describes the temperature change of a real gas or liquid (as differentiated from an ideal gas) when it is forced through a valve or porous plug while keeping it insulated so that no heat is exchanged with the environment. This procedure is called a throttling process or Joule–Thomson process. At room temperature, all gases except hydrogen, helium, and neon cool upon expansion by the Joule–Thomson process when being throttled through an orifice; these three gases experience the same effect but only at lower temperatures. Most liquids such as hydraulic oils will be warmed by the Joule–Thomson throttling process.
The gas-cooling throttling process is commonly exploited in refrigeration processes such as liquefiers in air separation industrial process. In hydraulics, the warming effect from Joule–Thomson throttling can be used to find internally leaking valves as these will produce heat which can be detected by thermocouple or thermal-imaging camera. Throttling is a fundamentally irreversible process. The throttling due to the flow resistance in supply lines, heat exchangers, regenerators, and other components of (thermal) machines is a source of losses that limits their performance.
Since it is a constant-enthalpy process, it can be used to experimentally measure the lines of constant enthalpy (isenthalps) on the diagram of a gas. Combined with the specific heat capacity at constant pressure it allows the complete measurement of the thermodynamic potential for the gas. | 7 | Physical Chemistry |
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