text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
Linolelaidic acid is an omega-6 trans fatty acid (TFA) and is a cis–trans isomer of linoleic acid. It is found in partially hydrogenated vegetable oils. It is a white (or colourless) viscous liquid.
TFAs are classified as conjugated and nonconjugated, corresponding usually to the structural elements and , respectively. Nonconjugated TFAs are represented by elaidic acid and linolelaidic acid. Their presence is linked heart diseases. The TFA vaccenic acid, which is of animal origin, poses less of a health risk. | 0 | Organic Chemistry |
Carbon tetrachloride was originally synthesized in 1820 by Michael Faraday, who named it "protochloride of carbon", by decomposition of hexachloroethane ("perchloride of carbon") which he synthesized by chlorination of ethylene. The protochloride of carbon has been previously misidentified as tetrachloroethylene because it was made with the same reaction of hexachloroethane. Later in the 19th century, the name protochloride of carbon was used for tetrachloroethylene, and carbon tetrachloride was called "bichloride of carbon" or "perchloride of carbon". Henri Victor Regnault developed another method to synthesise carbon tetrachloride from chloroform, chloroethane or methanol with excess chlorine in 1839.
Kolbe made carbon tetrachloride in 1845 by passing chlorine over carbon disulfide through a porcelain tube. Prior to the 1950s, carbon tetrachloride was manufactured by the chlorination of carbon disulfide at 105 to 130 °C:
:CS + 3 Cl → CCl + SCl
But now it is mainly produced from methane:
:CH + 4 Cl → CCl + 4 HCl
The production often utilizes by-products of other chlorination reactions, such as from the syntheses of dichloromethane and chloroform. Higher chlorocarbons are also subjected to this process named "chlorinolysis":
:CCl + Cl → 2 CCl
The production of carbon tetrachloride has steeply declined since the 1980s because of environmental concerns and the decreased demand for CFCs, which were derived from carbon tetrachloride. In 1992, production in the U.S./Europe/Japan was estimated at 720,000 tonnes. | 2 | Environmental Chemistry |
The general principle of a biosurface is a solid surface with an additional layer of biological macromolecules. Because this molecular layer will reversibly respond to changes in the environment of the surface, it is also called “stimuli-responsive monolayer”. The external stimuli can be for example changes in temperature, changes in magnetic fields, mechanical forces or changes in electric fields.
Different strategies can be used to attach a monolayer of biomolecules to a surface, for example atomic layer deposition or layer-by-layer deposition. Another option is the fabrication of self-assembled monolayers (SAM). The surface used most often with this strategy is a gold electrode. SAM form by spontaneous organization of the molecules, for example alkanethiolates, on the substrate. SAM can be used as surface layers for nanoparticles, e.g. in MRI contrast agents, they can protect metal films from corrosion, and have many other applications in electrochemistry and nanoscience. For their application as a biosensor, one of the most often used molecules self-assembling on gold electrodes is DNA. Due to its molecular structure, double stranded DNA molecules are negatively charged and rigid. By applying an alternating potential to the biosurface, the attached DNA strands can be moved systematically because they will switch between an upright position and a flat position. This enables the usage of the biosurface as a biosensor. | 1 | Biochemistry |
Rhodizonic acid was discovered by Austrian chemist Johann Heller in 1837, by analyzing the products of heating a mixture of potassium carbonate and charcoal. The name comes from Greek (rhodizō, "to tinge red"), on account of the color of its salts. | 3 | Analytical Chemistry |
Pomeroys report contains errors in the equation: the pipeline slope (S, p. 8) is quoted as m/100m, but should be m/m. This introduces a factor of 10 underestimate in the calculation of the Z factor', used to indicate if there is a risk of sulphide-induced corrosion, if the published units are used. The web link is to the revised 1992 edition, which contains the units error - the 1976 edition has the correct units. | 8 | Metallurgy |
The substrate(s) and physiological function of Peg1/MEST are not known; however, the protein may play a role in mammalian development and abnormalities in its expression by its gene (PEG1/MEST)by, for example, loss of Genomic imprinting, overexpression, or promoter switching, has been linked to certain types of cancer and tumors in humans such as invasive cervical cancer, uterine leiomyomas, and cancers of the breast, lung, and colon (see MEST (gene)). | 1 | Biochemistry |
In 2012, scientists at the University of New South Wales were able to use phosphine to precisely, deterministically eject a single silicon atom onto a surface of epitaxial silicon. This resulting adatom created what is described as a single-atom transistor. Thus, inasmuch as chemical empirical formulas pinpoint the locations of branching ions that are attached to a particular molecule, the dopant of silicon based transistors and other such electronic components will have the location identified of each dopant atom or molecule, along with the associated characteristic of the device based on the named locations. Thus, the mapping of the dopant substances will give exact characteristics of any given semiconductor device, once all is known.
With the technology available nowadays it is possible to create a linear chain of adatoms on top of an epitaxial film. With this, one can analyse theoretical situations.
Furthermore, Usami et al. were able to create quantum wells by adding Si atoms to a SiGe bulk crystal. Within these wells they observed photoluminescence of excitons that were confined in these wells. | 7 | Physical Chemistry |
Each nerve is composed of a bundle of axons. Each axon is surrounded by the endoneurium connective tissue layer. These axons are bundled into fascicles surrounded by the perineurium connective tissue layer. Multiple fascicles are then surrounded by the epineurium, which is the outermost connective tissue layer of the nerve. The axons of myelinated nerves have a myelin sheath made up of Schwann cells that coat the axon. | 1 | Biochemistry |
C-type lectin-like receptors (CLRs) contain one or more C-type lectin (Ca2+ dependent carbohydrate-binding lectin) domains. Example pairs include:
* CD94/NKG2, expressed in NK and some T cells and interacts with the ligand HLA-E.
* Dendritic cell immunoreceptor (DCIR)/dendritic cell immunoactivating receptor (DCAR), characterized as a pair in mice, though no human DCAR has been identified.
* NKR-P1 (CD161) is a member of a paired receptor group in rodents, but the human genome contains only one, inhibitory receptor, NKRP1A (KLRB1).
* The Ly49 family in mice has been extensively studied for its role in NK activation using laboratory mice as a model organism, but has no homologous gene cluster in the human genome. The KIR family is the functional equivalent. | 1 | Biochemistry |
The Flippin–Lodge angle is one of two angles used by organic and biological chemists studying the relationship between a molecules chemical structure and ways that it reacts, for reactions involving "attack" of an electron-rich reacting species, the nucleophile, on an electron-poor reacting species, the electrophile. Specifically, the angles—the Bürgi–Dunitz, , and the Flippin–Lodge, —describe the "trajectory" or "angle of attack" of the nucleophile as it approaches the electrophile, in particular when the latter is planar in shape. This is called a nucleophilic addition reaction and it plays a central role in the biological chemistry taking place in many biosyntheses in nature, and is a central "tool" in the reaction toolkit of modern organic chemistry, e.g., to construct new molecules such as pharmaceuticals. Theory and use of these angles falls into the areas of synthetic and physical organic chemistry, which deals with chemical structure and reaction mechanism, and within a sub-specialty called structure correlation'.
Because chemical reactions take place in three dimensions, their quantitative description is, in part, a geometry problem. Two angles, first the Bürgi–Dunitz angle, , and later the Flippin–Lodge angle, , were developed to describe the approach of the reactive atom of a nucleophile (a point off of a plane) to the reactive atom of an electrophile (a point on a plane). The is an angle that estimates the displacement of the nucleophile, at its elevation, toward or away from the particular R and R' substituents attached to the electrophilic atom (see image). The is the angle between the approach vector connecting these two atoms and the plane containing the electrophile (see the Bürgi–Dunitz article). Reactions addressed using these angle concepts use nucleophiles ranging from single atoms (e.g., chloride anion, Cl) and polar organic functional groups (e.g., primary amines, R"-NH), to complex chiral catalyst reaction systems and enzyme active sites. These nucleophiles can be paired with an array of planar electrophiles: aldehydes and ketones, carboxylic acid-derivatives, and the carbon-carbon double bonds of alkenes. Studies of and can be theoretical, based on calculations, or experimental (either quantitative, based on X-ray crystallography, or inferred and semiquantitative, rationalizing results of particular chemical reactions), or a combination of these.
The most prominent application and impact of the Flippin–Lodge angle has been in the area of chemistry where it was originally defined: in practical synthetic studies of the outcome of carbon-carbon bond-forming reactions in solution. An important example is the aldol reaction, e.g., addition of ketone-derived nucleophiles (enols, enolates), to electrophilic aldehydes that have attached groups varying in size and polarity. Of particular interest, given the three-dimensional nature of the concept, is understanding how the combined features on the nucleophile and electrophile impact the stereochemistry of reaction outcomes (i.e., the "handedness" of new chiral centers created by a reaction). Studies invoking Flippin–Lodge angles in synthetic chemistry have improved the ability of chemists to predict outcomes of known reactions, and to design better reactions to produce particular stereoisomers (enantiomers and diastereomers) needed in the construction of complex natural products and drugs. | 7 | Physical Chemistry |
The word intron is derived from the terms intragenic region, and intracistron, that is, a segment of DNA that is located between two exons of a gene. The term intron refers to both the DNA sequence within a gene and the corresponding sequence in the unprocessed RNA transcript. As part of the RNA processing pathway, introns are removed by RNA splicing either shortly after or concurrent with transcription. Introns are found in the genes of most organisms and many viruses. They can be located in a wide range of genes, including those that generate proteins, ribosomal RNA (rRNA), and transfer RNA (tRNA).
Within introns, a donor site (5 end of the intron), a branch site (near the 3 end of the intron) and an acceptor site (3 end of the intron) are required for splicing. The splice donor site includes an almost invariant sequence GU at the 5 end of the intron, within a larger, less highly conserved region. The splice acceptor site at the 3 end of the intron terminates the intron with an almost invariant AG sequence. Upstream (5-ward) from the AG there is a region high in pyrimidines (C and U), or polypyrimidine tract. Further upstream from the polypyrimidine tract is the branchpoint, which includes an adenine nucleotide involved in lariat formation. The consensus sequence for an intron (in IUPAC nucleic acid notation) is: G-G-[cut]-G-U-R-A-G-U (donor site) ... intron sequence ... Y-U-R-A-C (branch sequence 20-50 nucleotides upstream of acceptor site) ... Y-rich-N-C-A-G-[cut]-G (acceptor site). However, it is noted that the specific sequence of intronic splicing elements and the number of nucleotides between the branchpoint and the nearest 3’ acceptor site affect splice site selection. Also, point mutations in the underlying DNA or errors during transcription can activate a cryptic splice site in part of the transcript that usually is not spliced. This results in a mature messenger RNA with a missing section of an exon. In this way, a point mutation, which might otherwise affect only a single amino acid, can manifest as a deletion or truncation in the final protein. | 1 | Biochemistry |
A major issue is how many embryos should be transferred, since placement of multiple embryos carries a risk of multiple pregnancy. While the past physicians placed multiple embryos to increase the chance of pregnancy, this approach has fallen out of favor. Professional societies, and legislatures in many countries, have issued guidelines or laws to curtail the practice. There is low to moderate evidence that making a double embryo transfer during one cycle achieves a higher live birth rate than a single embryo transfer; but making two single embryo transfers in two cycles has the same live birth rate and would avoid multiple pregnancies.
The appropriate number of embryos to be transferred depends on the age of the woman, whether it is the first, second or third full IVF cycle attempt and whether there are top-quality embryos available. According to a guideline from The National Institute for Health and Care Excellence (NICE) in 2013, the number of embryos transferred in a cycle should be chosen as in following table: | 1 | Biochemistry |
*Prastarika: metal trader
*Sulbhadhatusastra: science of metals
*panchaloha, sarva loha: the five base metals (tin, lead, iron, copper, silver) | 8 | Metallurgy |
Solid-phase extraction (SPE) is a solid-liquid extractive technique, by which compounds that are dissolved or suspended in a liquid mixture are separated, isolated or purified, from other compounds in this mixture, according to their physical and chemical properties. Analytical laboratories use solid phase extraction to concentrate and purify samples for analysis. Solid phase extraction can be used to isolate analytes of interest from a wide variety of matrices, including urine, blood, water, beverages, soil, and animal tissue.
SPE uses the affinity of solutes, dissolved or suspended in a liquid (known as the mobile phase), to a solid packing inside a small column, through which the sample is passed (known as the stationary phase), to separate a mixture into desired and undesired components. The result is that either the desired analytes of interest or undesired impurities in the sample are retained on the stationary phase. The portion that passes through the stationary phase is collected or discarded, depending on whether it contains the desired analytes or undesired impurities. If the portion retained on the stationary phase includes the desired analytes, they can then be removed from the stationary phase for collection in an additional step, in which the stationary phase is rinsed with an appropriate eluent.
It is possible to have an incomplete recovery of the analytes by SPE caused by incomplete extraction or elution. In the case of an incomplete extraction, the analytes do not have enough affinity for the stationary phase and part of them will remain in the permeate. In an incomplete elution, part of the analytes remain in the sorbent because the eluent used does not have a strong enough affinity.
Many of the adsorbents/materials are the same as in chromatographic methods, but SPE is distinctive, with aims separate from chromatography, and so has a unique niche in modern chemical science. | 3 | Analytical Chemistry |
A Nanocoulombmeter in combination with a Faraday cup can be used
to detect and measure the beams emitted from ion guns. | 7 | Physical Chemistry |
In 2003 an alternative mechanism was devised by Nadine Abraham and Peter Palffy-Muhoray of Ohio, USA, that utilizes capillary action combined with evaporation to produce motion, but has no volatile working fluid. Their paper "A Dunking Bird of the Second Kind", was submitted to the American Journal of Physics, and published in June 2004. It describes a mechanism which, while similar to the original drinking bird, operates without a temperature difference. Instead it utilizes a combination of capillary action, gravitational potential difference and the evaporation of water to power the device.
This bird works as follows: it is balanced such that, when dry, it tips into a head-down position. The bird is placed next to a water source such that this position brings its beak into contact with water. Water is then lifted into the beak by capillary action (the authors used a triangular sponge) and carried by capillary action past the fulcrum to a larger sponge reservoir which they fashioned to resemble wings. When enough water has been absorbed by the reservoir, the now-heavy bottom causes the bird to tip into a head-up position. With the beak out of the water, eventually enough water evaporates from the sponge that the original balance is restored and the head tips down again. Although a small drop in temperature may occur due to evaporative cooling, this does not contribute to the motion of the bird. The device operates relatively slowly with 7 hours 22 minutes being the average cycle time measured. | 7 | Physical Chemistry |
The secondary structure of nucleic acid molecules can often be uniquely decomposed into stems and loops. The stem-loop structure (also often referred to as an "hairpin"), in which a base-paired helix ends in a short unpaired loop, is extremely common and is a building block for larger structural motifs such as cloverleaf structures, which are four-helix junctions such as those found in transfer RNA. Internal loops (a short series of unpaired bases in a longer paired helix) and bulges (regions in which one strand of a helix has "extra" inserted bases with no counterparts in the opposite strand) are also frequent.
There are many secondary structure elements of functional importance to biological RNAs; some famous examples are the Rho-independent terminator stem-loops and the tRNA cloverleaf. Active research is on-going to determine the secondary structure of RNA molecules, with approaches including both experimental and computational methods (see also the List of RNA structure prediction software). | 4 | Stereochemistry |
Solenopsin is a lipophilic alkaloid with the molecular formula CHN found in the venom of fire ants (Solenopsis). It is considered the primary toxin in the venom and may be the component responsible for the cardiorespiratory failure in people who experience excessive fire ant stings.
Structurally solenopsins are a piperidine ring with a methyl group substitution at position 2 and a long hydrophobic chain at position 6. They are typically oily at room temperature, water-insoluble, and present an absorbance peak at 232 nanometers. Fire ant venom contains other chemically related piperidines which make purification of solenopsin from ants difficult. Therefore, solenopsin and related compounds have been the target of organic synthesis from which pure compounds can be produced for individual study. Originally synthesized in 1993, several groups have designed novel and creative methods of synthesizing enantiopure solenopsin and other alkaloidal components of ant venom. | 0 | Organic Chemistry |
As the name suggests, eslicarbazepine acetate is the acetate ester prodrug of eslicarbazepine. Eslicarbazepine itself is the pharmacologically more active of the two stereoisomers of licarbazepine. More specifically, it is (S)-(+)-licarbazepine.
;Related drugs and active metabolites for comparison: | 4 | Stereochemistry |
Biological photovoltaics, also called biophotovoltaics or BPV, is an energy-generating technology which uses oxygenic photoautotrophic organisms, or fractions thereof, to harvest light energy and produce electrical power. Biological photovoltaic devices are a type of biological electrochemical system, or microbial fuel cell, and are sometimes also called photo-microbial fuel cells or “living solar cells”. In a biological photovoltaic system, electrons generated by photolysis of water are transferred to an anode. A relatively high-potential reaction takes place at the cathode, and the resulting potential difference drives current through an external circuit to do useful work. It is hoped that using a living organism (which is capable of self-assembly and self-repair) as the light harvesting material, will make biological photovoltaics a cost-effective alternative to synthetic light-energy-transduction technologies such as silicon-based photovoltaics. | 7 | Physical Chemistry |
Developments in mass spectrometry led to the adoption of oxygen-16 as the standard substance, in lieu of natural oxygen.
The oxygen-16 definition was replaced with one based on carbon-12 during the 1960s. The mole was defined by International Bureau of Weights and Measures as "the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12." Thus, by that definition, one mole of pure C had a mass of exactly 12 g. The four different definitions were equivalent to within 1%.
Because a dalton, a unit commonly used to measure atomic mass, is exactly 1/12 of the mass of a carbon-12 atom, this definition of the mole entailed that the mass of one mole of a compound or element in grams was numerically equal to the average mass of one molecule or atom of the substance in daltons, and that the number of daltons in a gram was equal to the number of elementary entities in a mole. Because the mass of a nucleon (i.e. a proton or neutron) is approximately 1 dalton and the nucleons in an atom's nucleus make up the overwhelming majority of its mass, this definition also entailed that the mass of one mole of a substance was roughly equivalent to the number of nucleons in one atom or molecule of that substance.
Since the definition of the gram was not mathematically tied to that of the dalton, the number of molecules per mole N (the Avogadro constant) had to be determined experimentally. The experimental value adopted by CODATA in 2010 is .
In 2011 the measurement was refined to .
The mole was made the seventh SI base unit in 1971 by the 14th CGPM. | 3 | Analytical Chemistry |
Heteroduplex analysis (HDA) is a method in biochemistry used to detect point mutations in DNA (Deoxyribonucleic acid) since 1992. Heteroduplexes are dsDNA molecules that have one or more mismatched pairs, on the other hand homoduplexes are dsDNA which are perfectly paired. This method of analysis depend up on the fact that heteroduplexes shows reduced mobility relative to the homoduplex DNA. heteroduplexes are formed between different DNA alleles. In a mixture of wild-type and mutant amplified DNA, heteroduplexes are formed in mutant alleles and homoduplexes are formed in wild-type alleles. There are two types of heteroduplexes based on type and extent of mutation in the DNA. Small deletions or insertion create bulge-type heteroduplexes which is stable and is verified by electron microscope. Single base substitutions creates more unstable heteroduplexes called bubble-type heteroduplexes, because of low stability it is difficult to visualize in electron microscopy. HDA is widely used for rapid screening of mutation of the 3 bp p.F508del deletion in the CFTR gene. | 1 | Biochemistry |
Copper extraction refers to the methods used to obtain copper from its ores. The conversion of copper ores consists of a series of physical, chemical and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations, and other factors. | 8 | Metallurgy |
Ulrike Diebold is well known for her influential work in the fields of surface science, materials and physical chemistry, and condensed matter physics. In particular, she has contributed greatly to the understanding of atomic-scale surface structure and electronic surface structure of metal oxides. For her work, she mainly employs Ultra-high vacuum technology and Scanning Tunneling Microscopy. | 7 | Physical Chemistry |
An alternative approach used to measure the relative abundance of radiogenic isotopes when working with a solid surface is secondary-ion mass spectrometry (SIMS). This type of ion-microprobe analysis normally works by focusing a primary (oxygen) ion beam on a sample in order to generate a series of secondary positive ions that can be focused and measured based on their mass/charge ratios.
SIMS is a common method used in U-Pb analysis, as the primary ion beam is used to bombard the surface of a single zircon grain in order to yield a secondary beam of Pb ions. The Pb ions are analyzed using a double focusing mass spectrometer that comprises both an electrostatic and magnetic analyzer. This assembly allows the secondary ions to be focused based on their kinetic energy and mass-charge ratio in order to be accurately collected using a series of Faraday cups.
A major issue that arises in SIMS analysis is the generation of isobaric interference between sputtered molecular ions and the ions of interest. This issue occurs with U–Pb dating as Pb ions have essentially the same mass as HfO. In order to overcome this problem, a sensitive high-resolution ion microprobe (SHRIMP) can be used. A SHRIMP is a double-focusing mass spectrometer that allows for a large spatial separation between different ion masses based on its relatively large size. For U-Pb analysis, the SHRIMP allows for the separation of Pb from other interfering molecular ions, such as HfO. | 9 | Geochemistry |
Most HIV-based co-receptor research focuses on the CCR5 co-receptor. The majority of HIV strains use the CCR5 receptor. HIV-2 strains can also use the CXCR4 receptor though the CCR5 receptor is the more predominantly targeted of the two.
Both the CCR5 and the CXCR4 co-receptors are seven-trans-membrane (7TM) G protein-coupled receptors.
Different strains of HIV work on different co-receptors, although the virus can switch to utilizing other co-receptors. For example, R5X4 receptors can become the dominant HIV co-receptor target in main strains. HIV-1 and HIV-2 can both use the CCR8 co-receptor. The crossover of co-receptor targets for different strains and the ability for the strains to switch from their dominant co-receptor can impede clinical treatment of HIV. Treatments such as WR321 mAb can inhibit some strains of CCR5 HIV-1, preventing cell infection. The mAb causes the release of HIV-1-inhibitory b-chemokines, preventing other cells from becoming infected. | 1 | Biochemistry |
There are three known thrombin receptors (ThrR), termed PAR1, PAR3 and PAR4 (PAR for protease-activated receptor).
G-protein-coupled receptors that are responsible for the coagulation effects and responses of thrombin on cells are known as protease-activated receptors, or PARs. These receptors are members of the 7-transmembrane g protein-coupled family of receptors, however, their method of activation is unique. Unlike most G-protein-coupled receptors, PARs are irreversibly activated by proteolytic mechanism and therefore, are strictly regulated.
Thrombin is an allosteric serine protease that is an essential effector of coagulation that is produced at sites of vascular injury and plays a critical role in cellular response to blood-related diseases. It binds to and cleaves the extracellular N-terminal domain of the receptor. A tethered ligand corresponding to the new N-terminus, SFLLRN, is then unmasked, binding to the second extracellular loop of the receptor and activating it. | 1 | Biochemistry |
An important piece of early evidence in support of the homotropylium cation structure that did not rely on the magnetic properties of the molecule involved the acquisition of its UV spectrum. Winstein et al. determined that the absorption maxima for the homotropylium cation exhibited a considerably shorter wavelength than would be precited for the classical cyclooctatrienyl cation or the bicyclo[5.1.0]octadienyl compound with the fully formed internal cyclopropane bond (and a localized electronic structure). Instead, the UV spectrum most resembled that of the aromatic tropylium ion. Further calculations allowed Winstein to determine that the bond order between the two carbon atoms adjacent to the outlying methylene bridge is comparable to that of the π-bond separating the corresponding carbon atoms in the tropylium cation. Although this experiment proved to be highly illuminating, UV spectra are generally considered to be poor indicators of aromaticity or homoaromaticity. | 7 | Physical Chemistry |
Squibb developed the first ACE inhibitor, captopril, but it had adverse effects such as a metallic taste (which, as it turned out, was due to the sulfhydryl group). Merck developed enalapril as a competing product.
Enalaprilat was developed first, partly to overcome these limitations of captopril. The sulfhydryl moiety was replaced by a carboxylate moiety, but additional modifications were required in its structure-based design to achieve a potency similar to captopril. Enalaprilat, however, had a problem of its own in that it had poor oral availability. This was overcome by the Merck researchers through the esterification of enalaprilat with ethanol to produce enalapril.
Merck introduced enalapril to market in 1981; it became Merck's first billion dollar-selling drug in 1988. The patent expired in 2000, opening the way for generics. | 4 | Stereochemistry |
James Thomas Brenna (born October 15, 1959) is an American scientist specializing in analytical chemistry, and in human nutrition and foods, specifically fats. He is a professor of Paediatrics at Dell Medical School, having previously been a professor of human nutrition, chemistry, chemical biology and food science at Cornell University. | 3 | Analytical Chemistry |
For assembly, a purified amphiphilic polypeptoid of specific sequence is dissolved in aqueous solution. These form a monolayer (Langmuir–Blodgett film) on the air-water interface with their hydrophobic side chains oriented in air and hydrophilic side chains in the water. When this mono-layer is shrunk, it buckles into a bilayer with the hydrophobic groups forming the interior core of the peptoid nanosheet. This method has been standardized in the Zuckermann laboratory by repetitively tilting vials of peptoid solution at 85° before returning the vials to the upright position. This repetitive vial “rocking” motion lessens the interfacial area of the air-water interface inside the vial, compressing the peptoid mono-layer by a factor of four and causing the mono-layer to buckle into peptoid nanosheets. Using this method, nanosheets are produced in high yield, and 95% of the peptoid polymer starting material is efficiently converted into peptoid nanosheets after rocking the vials several hundred times. | 0 | Organic Chemistry |
TEOS-10 (Thermodynamic Equation of Seawater - 2010) is the international standard for the use and calculation of the thermodynamic properties of seawater, humid air and ice. It supersedes the former standard EOS-80 (Equation of State of Seawater 1980). TEOS-10 is used by oceanographers and climate scientists to calculate and model properties of the oceans such as heat content in an internationally comparable way. | 7 | Physical Chemistry |
While gene knock-in technology has proven to be a powerful technique for the generation of models of human disease and insight into proteins in vivo, numerous limitations still exist. Many of these are shared with the limitations of knockout technology. First, combinations of knock-in genes lead to growing complexity in the interactions that inserted genes and their products have with other sections of the genome and can therefore lead to more side effects and difficult-to-explain phenotypes. Also, only a few loci, such as the ROSA26 locus have been characterized well enough where they can be used for conditional gene knock-ins; making combinations of reporter and transgenes in the same locus problematic. The biggest disadvantage of using gene knock-in for human disease model generation is that mouse physiology is not identical to that of humans and human orthologs of proteins expressed in mice will often not wholly reflect the role of a gene in human pathology. This can be seen in mice produced with the ΔF508 fibrosis mutation in the CFTR gene, which accounts for more than 70% of the mutations in this gene for the human population and leads to cystic fibrosis. While ΔF508 CF mice do exhibit the processing defects characteristic of the human mutation, they do not display the pulmonary pathophysiological changes seen in humans and carry virtually no lung phenotype. Such problems could be ameliorated by the use of a variety of animal models, and pig models (pig lungs share many biochemical and physiological similarities with human lungs) have been generated in an attempt to better explain the activity of the ΔF508 mutation. | 1 | Biochemistry |
Many methods of transfection and transformation – two ways of expressing a foreign or modified gene in an organism – are effective in only a small percentage of a population subjected to the techniques. Thus, a method for identifying those few successful gene uptake events is necessary. Reporter genes used in this way are normally expressed under their own promoter (DNA regions that initiates gene transcription) independent from that of the introduced gene of interest; the reporter gene can be expressed constitutively (that is, it is "always on") or inducibly with an external intervention such as the introduction of Isopropyl β-D-1-thiogalactopyranoside (IPTG) in the β-galactosidase system. As a result, the reporter genes expression is independent of the gene of interests expression, which is an advantage when the gene of interest is only expressed under certain specific conditions or in tissues that are difficult to access.
In the case of selectable-marker reporters such as CAT, the transfected population of bacteria can be grown on a substrate that contains chloramphenicol. Only those cells that have successfully taken up the construct containing the CAT gene will survive and multiply under these conditions. | 1 | Biochemistry |
Recent work has investigated the role of enhancers in morphological changes in threespine stickleback fish. Sticklebacks exist in both marine and freshwater environments, but sticklebacks in many freshwater populations have completely lost their pelvic fins (appendages homologous to the posterior limb of tetrapods).<br> Pitx1 is a homeobox gene involved in posterior limb development in vertebrates. Preliminary genetic analyses indicated that changes in the expression of this gene were responsible for pelvic reduction in sticklebacks. Fish expressing only the freshwater allele of Pitx1 do not have pelvic spines, whereas fish expressing a marine allele retain pelvic spines. A more thorough characterization showed that a 500 base pair enhancer sequence is responsible for turning on Pitx1 expression in the posterior fin bud. This enhancer is located near a chromosomal fragile site—a sequence of DNA that is likely to be broken and thus more likely to be mutated as a result of imprecise DNA repair. This fragile site has caused repeated, independent losses of the enhancer responsible for driving Pitx1 expression in the pelvic spines in isolated freshwater population, and without this enhancer, freshwater fish fail to develop pelvic spines. | 1 | Biochemistry |
Food Authenticity Methods (FAM) program focuses on identifying analytical tools to better characterize the intentional and economically motivated adulteration of foods. | 3 | Analytical Chemistry |
Ro60 is not part of the TRIM family. Ro60 is encoded by a gene 32 kb in length and acts to regulate the fate of misfolded RNA within the host cell. Ro60 forms a ribonucleoprotein complex with one molecule of noncoding Y1, Y3, Y4, or Y5RNA, all of which are approximately 100 nucleotides in length, to form the epitope that Anti-Ro60 recognizes. The absence of Ro60 results in an elevated immune response and decreased resilience to immune-related stress.
The epitope of the Ro60 protein is similar to that of the Epstein-Barr virus, and the presence of the virus may enhance the autoimmune response to Ro60, as anti-Epstein Barr antibodies can target the protein. | 1 | Biochemistry |
Reduction of with aluminium results in one-electron reduction. The trichloride (Titanium(III) chloride|) and tetrachloride have contrasting properties: the trichloride is a colored solid, being a coordination polymer, and is paramagnetic. When the reduction is conducted in THF solution, the Ti(III) product converts to the light-blue adduct . | 0 | Organic Chemistry |
Abiotic foldamers are again organic molecules designed to exhibit dynamic folding. They exploit a few known key intermolecular interactions, as optimized by their design. One example is oligopyrroles that organize upon binding anions like chloride through hydrogen bonding (see figure). Folding is induced in the presence of an anion: the polypyrrole groups have little conformational restriction otherwise. | 6 | Supramolecular Chemistry |
S&S has also been used in RNA splicing research in many animals and plants.
The mRNA splicing plays a fundamental role in gene functional regulation. Very recently, it has been shown that A to G conversions at splice sites can lead to mRNA mis-splicing in Arabidopsis. The splicing and exon–intron junction prediction coincided with the GT/AG rule (S&S) in the Molecular characterization and evolution of carnivorous sundew (Drosera rotundifolia L.) class V b-1,3-glucanase. Unspliced (LSDH) and spliced (SSDH) transcripts of NAD+ dependent sorbitol dehydroge nase (NADSDH) of strawberry (Fragaria ananassa Duch., cv. Nyoho) were investigated for phytohormonal treatments.
Ambra1 is a positive regulator of autophagy, a lysosome-mediated degradative process involved both in physiological and pathological conditions. Nowadays, this function of Ambra1 has been characterized only in mammals and zebrafish. Diminution of rbm24a or rbm24b gene products by morpholino knockdown resulted in significant disruption of somite formation in mouse and zebrafish. Dr.Senapathy algorithm used extensively to study intron-exon organization of fut8 genes. The intron-exon boundaries of Sf9 fut8 were in agreement with the consensus sequence for the splicing donor and acceptor sites concluded using S&S. | 1 | Biochemistry |
Capacitance sensors (or Dielectric sensors) use capacitance to measure the dielectric permittivity of a surrounding medium.
The configuration is like the neutron probe where an access tube made of PVC is installed in the soil; probes can also be modular (comb-like) and connected to a logger. The sensing head consists of an oscillator circuit, the frequency is determined by an annular electrode, fringe-effect capacitor, and the dielectric constant of the soil.
Each capacitor sensor consists of two metal rings mounted on the circuit board at some distance from the top of the access tube. These rings are a pair of electrodes, which form the plates of the capacitor with the soil acting as the dielectric in between. The plates are connected to an oscillator, consisting of an inductor and a capacitor. The oscillating electrical field is generated between the two rings and extends into the soil medium through the wall of the access tube. The capacitor and the oscillator form a circuit, and changes in dielectric constant of surrounding media are detected by changes in the operating frequency. The capacitance sensors are designed to oscillate in excess of 100 MHz inside the access tube in free air. The output of the sensor is the frequency response of the soil’s capacitance due to its soil moisture level. | 7 | Physical Chemistry |
In fluid mechanics, specific weight represents the force exerted by gravity on a unit volume of a fluid. For this reason, units are expressed as force per unit volume (e.g., N/m or lbf/ft). Specific weight can be used as a characteristic property of a fluid. | 7 | Physical Chemistry |
Chemosensors have been incorporated through surface functionalization onto particles and beads such as metal based nanoparticles, quantum dots, carbon-based particles and into soft materials such as polymers to facilitate their various applications.
Other receptors are sensitive not to a specific molecule but to a molecular compound class, these chemosensors are used in array- (or microarray) based sensors. Array-based sensors utilise analyte binding by the differential receptors. One example is the grouped analysis of several tannic acids that accumulate in ageing Scotch whisky in oak barrels. The grouped results demonstrated a correlation with the age but the individual components did not. A similar receptor can be used to analyze tartrates in wine.
The application of chemosensors in cellular imaging is particularly promising as most biological process are now monitored by using imaging technologies such as confocal fluorescence and superresolution microscopy, among others.
The compound saxitoxin is a neurotoxin found in shellfish and a chemical weapon. An experimental sensor for this compound is again based on PET. Interaction of saxitoxin with the sensor's crown ether moiety kills its PET process towards the fluorophore and fluorescence is switched from off to on. The unusual boron moiety makes sure the fluorescence takes place in the visible light part of the electromagnetic spectrum. | 6 | Supramolecular Chemistry |
A piece of alloy metal containing a precious metal may also have the weight of its precious component referred to as its "fine weight". For example, 1 troy ounce of 18 karat gold (which is 75% gold) may be said to have a fine weight of 0.75 troy ounces.
Most modern government-issued bullion coins specify their fine weight. For example, the American Gold Eagle is embossed One Oz. Fine Gold and weighs 1.091 troy oz. | 8 | Metallurgy |
HNMT could be a potential target for the treatment of symptoms of methamphetamine overdose. It is a central nervous system stimulant, which can be abused up to the lethal consequences: numerous deaths related to methamphetamine overdoses have been reported. The reasoning behind this is that such overdose often leads to behavioral abnormalities, and it has been observed that elevated levels of histamine in the brain can attenuate these methamphetamine-induced behaviors. Therefore, by targeting HNMT, it might be possible to increase the levels of histamine in the brain, which could, in turn, help to mitigate the effects of a methamphetamine overdose. This effect could be achieved by using HNMT inhibitors. Studies predict that one such inhibitor can be metoprine, which crosses the blood-brain barrier and can potentially increase brain histamine levels by inhibiting HNMT; still, treatment of methamphetamine overdose by HNMT inhibitors is still an area of research. | 1 | Biochemistry |
Corepressors present many potential avenues for drugs to target a vast range of diseases.
BCL6 upregulation is observed in cancers such as diffuse large B-cell lymphomas (DLBCLs), colorectal cancer, and lung cancer. BCL-6 corepressor, SMRT, NCoR, and other corepressors are able to interact with and transcriptionally repress BCL6. Small-molecule compounds, such as synthetic peptides that target BCL6 and corepressor interactions, as well as other protein-protein interaction inhibitors, have been shown to effectively kill cancer cells.
Activated liver X receptor (LXR) forms a complex with corepressors to suppress the inflammatory response in rheumatoid arthritis, making LXR agonists like GW3965 a potential therapeutic strategy. Ursodeoxycholic acid (UDCA), by upregulating the corepressor small heterodimer partner interacting leucine zipper protein (SMILE), inhibits the expression of IL-17, an inflammatory cytokine, and suppresses Th17 cells, both implicated in rheumatoid arthritis. This effect is dose-dependent in humans, and UCDA is thought to be another prospective agent of rheumatoid arthritis therapy. | 1 | Biochemistry |
The bromodomain is a motif that is responsible for acetylated lysine recognition on histones by nucleosome remodelling proteins. Posttranslational modifications of N- and C-terminal histone tails attracts various transcription initiation factors that contain bromodomains, including human transcriptional coactivator PCAF, TAF1, GCN5 and CREB-binding protein (CBP), to the promoter and have a significance in regulating gene expression. Structural analysis of transcription factors has shown that highly conserved bromodomains are essential for protein to bind to acetylated lysine. This suggests that specific histone site acetylation has a regulatory role in gene transcriptional activation. | 0 | Organic Chemistry |
Monosaccharides are the simplest form of carbohydrates with only one simple sugar. They essentially contain an aldehyde or ketone group in their structure. The presence of an aldehyde group in a monosaccharide is indicated by the prefix aldo-. Similarly, a ketone group is denoted by the prefix keto-. Examples of monosaccharides are the hexoses, glucose, fructose, Trioses, Tetroses, Heptoses, galactose, pentoses, ribose, and deoxyribose. Consumed fructose and glucose have different rates of gastric emptying, are differentially absorbed and have different metabolic fates, providing multiple opportunities for two different saccharides to differentially affect food intake. Most saccharides eventually provide fuel for cellular respiration.
Disaccharides are formed when two monosaccharides, or two single simple sugars, form a bond with removal of water. They can be hydrolyzed to yield their saccharin building blocks by boiling with dilute acid or reacting them with appropriate enzymes. Examples of disaccharides include sucrose, maltose, and lactose.
Polysaccharides are polymerized monosaccharides, or complex carbohydrates. They have multiple simple sugars. Examples are starch, cellulose, and glycogen. They are generally large and often have a complex branched connectivity. Because of their size, polysaccharides are not water-soluble, but their many hydroxy groups become hydrated individually when exposed to water, and some polysaccharides form thick colloidal dispersions when heated in water. Shorter polysaccharides, with 3 to 10 monomers, are called oligosaccharides.
A fluorescent indicator-displacement molecular imprinting sensor was developed for discriminating saccharides. It successfully discriminated three brands of orange juice beverage. The change in fluorescence intensity of the sensing films resulting is directly related to the saccharide concentration. | 0 | Organic Chemistry |
Chetsanga was born in Murewa, Zimbabwe on 22 August 1935, and was baptised in 1948. In his youth, he was educated at Nhowe Mission, and went on to study at University of California, Berkeley where he received his BSc in 1965. Chetsanga also studied for a period at Pepperdine University. In 1969, he received his MSc and PhD in biochemistry and molecular biology from University of Toronto before becoming a post doctoral fellow at Harvard University between 1969 and 1972. Between 1972 and 1983 he became a professor at the University of Michigan, then in 1983 he left to become the senior lecturer in Biochemistry for University of Zimbabwe. In 1990, President Robert Mugabe awarded him President’s Award for Distinguished Contribution to Science and Technology. Has also awarded the Order of the Star of Zimbabwe. He is presently the vice chancellor at Zimbabwe Ezekiel Guti University.
In 2004, when the Zimbabwe Academy of Sciences was formed, Chetsanga was appointed the first president of the academy. Chetsanga advocated the use of genetically modified food sources as a possible solution for food shortages in Africa in 2020. | 1 | Biochemistry |
Ubiquitin-AMC is prepared by the C-terminal derivatization of ubiquitin with 7-amino-4-methylcoumarin and has been shown to be a useful and sensitive fluorogenic substrate for wide range of deubiquitinylating enzymes (DUBs), including ubiquitin C-terminal hydrolases (UCHs) and ubiquitin specific proteases (USPs).
Ubiquitin-AMC has been shown to be a sensitive substrate for UCH-L3 (Km = 0.039µM) and for Isopeptidase-T (Km = 0.17-1.4µM), and is particularly useful for studying deubiquitinylating activity where detection sensitivity or continuous monitoring of activity is essential.
Typical assay set-up: Assay substrate concentration: 0.01-1.0µM. Enzyme concentrations, UCH-L3: 10-100pM, isopeptidase-T: 10-100nM. Release of AMC fluorescence by DUB enzymes can be monitored using 380 nm excitation and 460 nm emission wavelengths. | 1 | Biochemistry |
Seasoning is the process of coating the surface of cookware with fat which is heated in order to produce a corrosion resistant layer of polymerized fat. It is required for raw cast-iron cookware and carbon steel, which otherwise rust rapidly in use, but is also used for many other types of cookware. An advantage of seasoning is that it helps prevent food sticking.
Some cast-iron and carbon steel cookware is pre-seasoned by manufacturers to protect the pan from oxidation (rust), but will need to be further seasoned by the end-users for the cookware to become ready for best nonstick cooking results. To form a strong seasoning, the raw iron item is thoroughly cleaned, coated in a very thin layer of unsaturated fat or oil, and then heated until the bioplastic layer forms, and left to completely cool. Multiple layers are required for the best long-term results.
Stainless steel and aluminium cookware do not require protection from corrosion, but seasoning reduces sticking, and can help with browning as the seasoning coating has high thermal emissivity. Other cookware surfaces are generally not seasoned.
A seasoned surface is hydrophobic and highly attractive to oils and fats used for cooking. These form a layer that prevents foods, which typically contain water, from touching and cooking onto the hydrophilic metallic cooking surface underneath. These properties are useful when frying, roasting and baking. | 7 | Physical Chemistry |
The term sequestration is based on the Latin sequestrare, which means set aside or surrender. It is derived from sequester, a depositary or trustee, one in whose hands a thing in dispute was placed until the dispute was settled. In English "sequestered" means secluded or withdrawn.
In law, sequestration is the act of removing, separating, or seizing anything from the possession of its owner under process of law for the benefit of creditors or the state. | 5 | Photochemistry |
If we differentiate this last equation with respect to at constant we get:
Since we know from the Gibbs potential equation that:
with the molar volume , these last two equations put together give:
Since all this, done as a pure substance, is valid in an ideal mix just adding the subscript to all the intensive variables and changing to , with optional overbar, standing for partial molar volume:
Applying the first equation of this section to this last equation we find:
which means that the partial molar volumes in an ideal mix are independent of composition. Consequently, the total volume is the sum of the volumes of the components in their pure forms: | 7 | Physical Chemistry |
*1988 Japan IBM Science Prize
*1992 Chu-Nichi Culture Award
*2002 Medals with Purple ribbon
*2003 Fellow of the American Association for the Advancement of Science (AAAS)
*2004 Yamada-Koga Prize
*2006 Tetrahedron Prize for Creativity in Organic Chemistry & BioMedicinal Chemistry
*2007 Japan Academy Prize (academics)
*2007 Humboldt Prize
*2011 The Ryoji Noyori Prize
*2012 Fujihara Award
*2017 The Roger Adams Award (American Chemical Society)
*2018 Person of Cultural Merit | 0 | Organic Chemistry |
NV centers emit bright red light (E→A transitions), if excited off-resonantly by visible green light (A →E transitions). This can be done with convenient light sources such as argon or krypton lasers, frequency doubled Nd:YAG lasers, dye lasers, or He-Ne lasers. Excitation can also be achieved at energies below that of zero phonon emission.
As the relaxation time from the excited state is small (~10 ns), the emission happens almost instantly after the excitation. At room temperature the NV center's optical spectrum exhibits no sharp peaks due to thermal broadening. However, cooling the NV centers with liquid nitrogen or liquid helium dramatically narrows the lines down to a width of a few MHz. At low temperature it also becomes possible to specifically address the zero-phonon line (ZPL).
An important property of the luminescence from individual NV centers is its high temporal stability. Whereas many single-molecular emitters bleach (i.e. change their charge state and become dark) after emission of 10–10 photons, bleaching is unlikely for NV centers at room temperature. Strong laser illumination, however, may also convert some NV into NV centers.
Because of these properties, the ideal technique to address the NV centers is confocal microscopy, both at room temperature and at low temperature. | 7 | Physical Chemistry |
The harmonic trap potential:
is a model system with many applications in modern physics. The density of states (or more accurately, the degree of degeneracy) for a given spin species is:
where is the harmonic oscillation frequency.
The Fermi energy for a given spin species is: | 7 | Physical Chemistry |
The Q temperature coefficient is a measure of temperature sensitivity based on the chemical reactions.
The Q is calculated as:
where;
: R is the rate
: T is the temperature in Celsius degrees or kelvin.
Rewriting this equation, the assumption behind Q is that the reaction rate R depends exponentially on temperature:
Q is a unitless quantity, as it is the factor by which a rate changes, and is a useful way to express the temperature dependence of a process.
For most biological systems, the Q value is ~ 2 to 3. | 7 | Physical Chemistry |
Various signalling pathways, as FGF, WNT and TGF-β pathways, regulate the processes involved in embryogenesis.
FGF (Fibroblast Growth Factor) ligands bind to receptors tyrosine kinase, FGFR (Fibroblast Growth Factor Receptors), and form a stable complex with co-receptors HSPG (Heparan Sulphate Proteoglycans) that will promote autophosphorylation of the intracellular domain of FGFR and consequent activation of four main pathways: MAPK/ERK, PI3K, PLCγ and JAK/STAT.
* MAPK/ERK (Mitogen-Activated Protein Kinase/Extracellular Signal-Regulated Kinase) regulates gene transcription through successive kinase phosphorylation and in human embryonic stem cells it helps maintaining pluripotency. However, in the presence of Activin A, a TGF-β ligand, it causes the formation of mesoderm and neuroectoderm.
* Phosphorylation of membrane phospholipids by PI3K (Phosphatidylinositol 3-Kinase) results in activation of AKT/PKB (Protein Kinase B). This kinase is involved in cell survival and inhibition of apoptosis, cellular growth and maintenance of pluripotency, in embryonic stem cells.
* PLCγ (Phosphoinositide Phospholipase C γ) hydrolyzes membrane phospholipids to form IP3 (Inositoltriphosphate) and DAG (Diacylglycerol), leading to activation of kinases and regulating morphogenic movements during gastrulation and neurulation.
* STAT (Signal Trandsducer and Activator of Transcription) is phosphorylated by JAK (Janus Kinase) and regulates gene transcription, determining cell fates. In mouse embryonic stem cells, this pathway helps maintaining pluripotency.
The WNT pathway allows β-catenin function in gene transcription, once the interaction between WNT ligand and G protein-coupled receptor Frizzled inhibits GSK-3 (Glycogen Synthase Kinase-3) and thus formation of β-catenin destruction complex. Although there is some controversy about the effects of this pathway in embryogenesis, it is thought that WNT signalling induces primitive streak, mesoderm and endoderm formation.
In TGF-β (Transforming Growth Factor β) pathway, BMP (Bone Morphogenic Protein), Activin and Nodal ligands bind to their receptors and activate Smads that bind to DNA and promote gene transcription. Activin is necessary for mesoderm and specially endoderm differentiation, and Nodal and BMP are involved in embryo patterning. BMP is also responsible for formation of extra-embryonic tissues before and during gastrulation, and for early mesoderm differentiation, when Activin and FGF pathways are activated. | 7 | Physical Chemistry |
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases.
Nucleophilic describes the affinity of a nucleophile to bond with positively charged atomic nuclei. Nucleophilicity, sometimes referred to as nucleophile strength, refers to a substance's nucleophilic character and is often used to compare the affinity of atoms. Neutral nucleophilic reactions with solvents such as alcohols and water are named solvolysis. Nucleophiles may take part in nucleophilic substitution, whereby a nucleophile becomes attracted to a full or partial positive charge, and nucleophilic addition. Nucleophilicity is closely related to basicity. The difference between the two is, that basicity is a thermodynamic property (i.e. relates to an equilibrium state), but nucleophilicity is a kinetic property, which relates to rates of certain chemical reactions. | 7 | Physical Chemistry |
DNA methylation involves the addition of a methyl group to the carbon-5 position of the cytosine ring in the CpG dinucleotide and converting it to methylcytosine. This process is catalyzed by DNA methyltransferase. In numerous cancers, the CpG islands of selected genes are aberrantly methylated (hypermethylated) which results in transcriptional repression. This may be an alternate mechanism of gene inactivation.
Multiple genes have been discovered to be frequently methylated in cancers and leukemias. More specifically, the deregulation of the Wnt signaling pathway has been implicated in a wide array of cancers that is mainly seen as a result of loss-of-function mutations of APC and axin or as a gain-of-function mutation of CTNNB1 (B-catenin). The GC content of the SFRP1 promoter in humans is 56.3%.
It has been found that the overexpression of B-catenin may lead to enhanced proliferation in myeloma plasma cells; thus, soluble Wnt inhibitors are potential tumor suppressor genes and, if inactivated, may contribute to myeloma pathogenesis. This led Chim et al. to investigate the role of aberrant gene methylation of a panel of soluble Wnt antagonists, including SFRP1. Complete methylation led to silencing of respective genes (no transcripts), whereas absence of gene methylation was associated with constitutive gene expression. Methylation of soluble Wnt antagonists would be important in the pathogenesis of multiple myeloma if Wnt signaling was regulated by an autocrine loop by Wnt and Fz. If an autocrine loops exists, then both the ligand (Wz) and receptor (Fzd) should be simultaneously expressed in myeloma cells and growth of tumour cells should be inhibited upon addition of SFRP1. Chim et al. demonstrated simultaneous expression of Wz and Fzd in myeloma plasma cells. Moreover, treatment with recombinant SFRP1 inhibited the growth of myeloma cells in a dose-dependent manner. These findings implicate soluble Wnt inhibitors as tumor suppressors that could be inactivated by methylation.
Veeck and colleagues found all of their eight breast cancer cell lines had complete methylation in the SFRP1 promoter region, while no methylation was detectable in non-malignant cell lines. After treatment with 5-Aza-2’-deoxycytidine (DAC), an inhibitor of DNA methyltransferase, SFRP1 expression was restored in all four treated breast cancer cell lines, supporting the hypothesis of methylation-mediated SFRP1 gene silencing in breast cancer.
Furthermore, the transcriptional silencing mechanism underlying DNA methylation which is brought about through the hypermethylation of CpG-rich islands present in the promoter region of genes, can cooperate with histone deacetylation to change chromatin structure to a repressed form. Lo and colleagues looked at the effects of DAC and trichostatin A (TSA, selectively inhibits the mammalian histone deacetylase family of enzymes) on cancer cells. In 4 breast cancer cell lines, SFRP1 expression was significantly restored after treatment with DAC alone. TSA, only in combination with DAC, had a slightly enhanced effect on SFRP1 expression in these cell lines. A different breast cancer cell line (SKBR3, showed loss of SFRP1 expression without significant methylation of the SFRP1 promoter. Lo et al. hypothesized that this may be due to silencing via histone deacetylation. After SKBR3 cells were treated with TSA, SFRP1 expression was restored in a dose- and time-dependent manner. Yet another breast cancer cell line (T47D) required both DAC and TSA to upregulate SFRP1 expression. This indicates that T47D cells are tightly regulated by two layers of epigenetic control (DNA methylation and histion deacetylation) and relieving inhibition by both mechanisms is necessary for reactivation of SFRP1. This study shows that both the epigenetic mechanisms, DNA methylation and histone deacetylation, are involved in silencing of SFRP1. | 1 | Biochemistry |
GGT is expressed in high levels in many different tumors. It is known to accelerate tumor growth and to increase resistance to cisplatin in tumors. | 1 | Biochemistry |
Another information-theoretic metric is variation of information, which is roughly a symmetrization of conditional entropy. It is a metric on the set of partitions of a discrete probability space. | 7 | Physical Chemistry |
and are normally the temperature and the pressure of the triple point, but the normal melting temperature at atmospheric pressure are also commonly used as reference point because the normal melting point is much more easily accessible. Typically is then set to 0. and are component-specific parameters.
The Simon–Glatzel equation can be viewed as a combination of the Murnaghan equation of state and the Lindemann law, and an alternative form was proposed by J. J. Gilvarry (1956):
where is general at , is pressure derivative at , is Grüneisen ratio, and is the coefficient in Morse potential. | 7 | Physical Chemistry |
The principle may be used for the calculation of the scattering amplitude in the similar way like the variational principle for bound states, i.e. the form of the wave functions is guessed, with some free parameters, that are determined from the condition of stationarity of the functional. | 7 | Physical Chemistry |
The Overman synthesis (1993) took a chiral cyclopentene compound as starting material obtained by enzymatic hydrolysis of cis-1,4-diacetoxycyclopent-2-ene. This starting material was converted in several steps to trialkylstannane 2 which was then coupled with an aryl iodide 1 in a Stille reaction in presence of carbon monoxide (tris(dibenzylideneacetone)dipalladium(0), triphenylarsine). The internal double in 3 was converted to an epoxide using tert-Butyl hydroperoxide, the carbonyl group was then converted to an alkene in a Wittig reaction using PhP=CH and the TIPS group was hydrolyzed (TBAF) and replaced by a trifluoroacetamide group (NHCOCF, NaH) in 4. Cyclization (NaH) took place next, opening the epoxide ring and the trifluoroacetyl group was removed using KOH affording azabicyclooctane 5.
The key step was an aza-Cope-Mannich reaction initiated by an amine-carbonyl condensation using formaldehyde and forming 6 in a quantitative yield:
In the final sequence strychnine was obtained through the Wieland-Gumlich aldehyde (10):
Intermediate 6 was acylated using methyl cyanoformate and two protective groups (tert-butyl and ) were removed using HCl / MeOH in 7. The C8C13 double bond was reduced with zinc (MeOH/H) to saturated ester 8 (mixture). Epimerization at C13 with sodium methoxide in MeOH produced beta-ester 9 which was reduced with diisobutylaluminium hydride to Wieland-Gumlich aldehyde 10. Conversion of this compound with malonic acid to (−)-strychnine 11 was already known as a procedure. | 0 | Organic Chemistry |
One approach is the collision theory of chemical reactions, developed by Max Trautz and William Lewis in the years 1916–18. In this theory, molecules are supposed to react if they collide with a relative kinetic energy along their line of centers that exceeds E. The number of binary collisions between two unlike molecules per second per unit volume is found to be
where N is the Avogadro constant, d is the average diameter of A and B, T is the temperature which is multiplied by the Boltzmann constant k to convert to energy, and μ is the reduced mass.
The rate constant is then calculated as , so that the collision theory predicts that the pre-exponential factor is equal to the collision number z. However for many reactions this agrees poorly with experiment, so the rate constant is written instead as . Here is an empirical steric factor, often much less than 1.00, which is interpreted as the fraction of sufficiently energetic collisions in which the two molecules have the correct mutual orientation to react. | 7 | Physical Chemistry |
Eudistomins are β-carboline derivatives, isolated from ascidians (marine tunicates of the family Ascidiacea), like Ritterella sigillinoides, Lissoclinum fragile, or Pseudodistoma aureum. | 1 | Biochemistry |
The synthesis of borjatriol involved the rare isolation of a migrated epoxide. The diastereomeric mixture of rearrangement products was carried through the remainder of the synthesis.
The final two steps in the total synthesis of spatol involved intramolecular electrophilic trapping of an alkoxide derived from a rearranged epoxide. Attack of the intermediate alkoxide on the adjacent mesylate afforded a bis(epoxide), and debenzylation provided the target compound. | 0 | Organic Chemistry |
Because of the non-covalent host-guest interaction, the polymer backbone can have enough flexibility to diffuse. If a crack exists in the materials, after compressing the two materials around the crack, because of the fast exchange of the host-guest molecular structure, the crack will rejoin again revealing good self-healing properties. Harada et al reported a self-healing hydrogel constructed by vinyl-group-modified cyclodextrin and adamantane. Another strategy is to use the interaction between the polymer backbone and host molecule (host molecule threading onto the polymer). If the threading process is fast enough, self-healing can also be achieved. | 6 | Supramolecular Chemistry |
As shown in Figure 5, ketenyl anion has two major resonance structures: ketenyl form and ynolate form. Due to the resonance structures, alkali metal cations can be coordinated to either at central carbon atom or terminal oxygen atom depending on its electronic structure. A series of structural analysis revealed both ketene and ynolate structures evenly contribute to the overall electronic structure of ketenyl anion.
From an example in Gessners paper, the crystal structure of the ketenyl anion K[PPh(=S)CCO] had the bond length of C-C bond (1.245 Å) and C-O bond (1.215 Å). By comparing these bond length with Pyykkős analysis on bond, C-C bond is in between double bond and triple bond whereas C-O bond is in between single bond and double bond. In natural bond orbital (NBO) analysis, Wiberg bond index is found to be 2.06 and 1.72 for C-C bond and C-O bond, respectively. These values also suggests that both double and triple bond character for C-C bond (range of 1.20 - 1.34 Å) and both single bond and double bond character for C-O bond (range of 1.24 - 1.38 Å). The characteristic of allene-like (C=C=C) structure is also applied other ketenyl anion compounds so far. Inoue's silica-ketenyl anion product, shown in Figure 3, had Wiberg bond index of 1.68 and 1.76 for Si-C bond and C-O bond, respectively. Their bond indices demonstrate that both Si-C and C-O bonds have part of double bond character that contributes of Si=C=O structure.
This ketenyl anion can dimerize in solid state as oxygen atoms interacts with alkali metal cation. This dimer can be broken up by adding M(18-crown-6) (where M = alkali metal cation), resulting in isolation of single ketenyl anion structure. Intrinsic bond orbitals (IBO) of the molecule [K(PPh(=S)CCO] reveal molecular orbital describing π-orbital of C-C and C-O and delocalized orbital on oxygen atom.
The stability of ketenyl anion is come from the decrease of charge on ketene carbon from parent ketene to ketenyl anion. In Gessner's study, parent ketenyl anion [H-C=C=O] has smaller positive charge (+4.0 e) on C compared to parent ketene [HC=C=O] (+7.0 e on C). This drops of charge makes the ketene less amphiphilic, leading to a more stable compound. | 0 | Organic Chemistry |
Being an essential element, calcium is obtained through dietary sources, the majority of which comes from dairy products. The three most significant mechanisms controlling calcium use within the body are intestinal absorption, renal absorption and bone turnover, which is controlled predominantly by hormones and their corresponding receptors in the gut, kidneys and bones respectively. This allows for calcium use throughout the body, namely in bone growth, cellular signalling, blood clotting, muscle contraction and neuron function.
Calcium is one of the essential components of bone, contributing to its strength and structure in addition to being the main site at which it is stored within the body. Within the muscles, its primary use is to enable contractions. Muscle cells draw calcium from the blood, allowing it to bind with troponin, a component of the muscle fibre that signals for a contraction by moving actin and myosin. After a contraction, calcium dissipates and the filaments move back to a resting state before the release of more calcium for the next contraction. Furthermore, calcium plays a significant role in allowing nerve impulses to be transmitted between neurons. The release of calcium ions from voltage gated ion channels signals for the release of neurotransmitters into the synapse. This allows for the depolarisation of a neuron, thus transmitting the signal to the next neuron where this process is once again repeated. Without the presence of calcium ions, the release of neurotransmitters would not occur, preventing signals from being sent and hindering body processes.
Negative feedback mechanisms are implemented in order to control calcium levels. When low calcium levels are detected in the body, the parathyroid releases parathyroid hormone (PTH) which travels through the bloodstream to the bones and kidneys. In the bones, the presence of PTH stimulates osteoclasts. These cells break down bone to release calcium into the bloodstream where it can be used by the rest of the body in the above processes. In the kidneys, PTH stimulates re-absorption of calcium so it in not lost from the body through urine and returned to the bloodstream instead. Lastly, PTH acts on the intestines by indirectly promoting enzymes that activate vitamin D, a signal for the intestines to absorb more calcium, further increasing blood calcium levels. This will continue until the body releases too much calcium into the bloodstream. Excess calcium then promotes the release of calcitonin from the thyroid gland, effectively reversing the process of PTH. Osteoclast activity is stopped and osteoblasts take over, utilising the excess calcium in the bloodstream to form new bone. Calcium re-absorption in the kidney is prevented, allowing the excretion of excess calcium through the urine. Through these hormonal mechanisms, calcium homeostasis is maintained within the body. | 1 | Biochemistry |
For transcription to take place, the enzyme that synthesizes RNA, known as RNA polymerase, must attach to the DNA near a gene. Promoters contain specific DNA sequences such as response elements that provide a secure initial binding site for RNA polymerase and for proteins called transcription factors that recruit RNA polymerase. These transcription factors have specific activator or repressor sequences of corresponding nucleotides that attach to specific promoters and regulate gene expression.
;In bacteria: The promoter is recognized by RNA polymerase and an associated sigma factor, which in turn are often brought to the promoter DNA by an activator protein's binding to its own DNA binding site nearby.
;In eukaryotes: The process is more complicated, and at least seven different factors are necessary for the binding of an RNA polymerase II to the promoter.
Promoters represent critical elements that can work in concert with other regulatory regions (enhancers, silencers, boundary elements/insulators) to direct the level of transcription of a given gene.
A promoter is induced in response to changes in abundance or conformation of regulatory proteins in a cell, which enable activating transcription factors to recruit RNA polymerase. | 1 | Biochemistry |
Electrode potential and other environmental factors such as temperature, pH and degree of aeration can greatly impact the results off this accelerated stress corrosion cracking test, as can the specimen surface finish and metallurgical condition. | 8 | Metallurgy |
The photochlorination of hydrocarbon is unselective, although the reactivity of the C-H bonds is tertiary>secondary>primary. At 30 °C the relative reaction rates of primary, secondary and tertiary hydrogen atoms are in a relative ratio of approximately 1 to 3.25 to 4.43. The C-C bonds remain unaffected.
Upon radiation the reaction involves alkyl and chlorine radicals following a chain reaction according to the given scheme:
Chain termination occurs by recombination of chlorine atoms. Impurities such as oxygen (present in electrochemically obtained chlorine) also cause chain termination.
The selectivity of photochlorination (with regard to substitution of primary, secondary or tertiary hydrogens) can be controlled by the interaction of the chlorine radical with the solvent, such as benzene, tert-butylbenzene or carbon disulfide. Selectivity increases in aromatic solvents. By varying the solvent the ratio of primary to secondary hydrogens can be tailored to ratios between 1: 3 to 1: 31. At higher temperatures, the reaction rates of primary, secondary and tertiary hydrogen atoms equalize. Therefore, photochlorination is usually carried out at lower temperatures. | 5 | Photochemistry |
Dettre and Johnson discovered in 1964 that the superhydrophobic lotus effect phenomenon was related to rough hydrophobic surfaces, and they developed a theoretical model based on experiments with glass beads coated with paraffin or TFE telomer. The self-cleaning property of superhydrophobic micro-nanostructured surfaces was reported in 1977. Perfluoroalkyl, perfluoropolyether, and RF plasma -formed superhydrophobic materials were developed, used for electrowetting and commercialized for bio-medical applications between 1986 and 1995. Other technology and applications have emerged since the mid-1990s. A durable superhydrophobic hierarchical composition, applied in one or two steps, was disclosed in 2002 comprising nano-sized particles ≤ 100 nanometers overlaying a surface having micrometer-sized features or particles ≤ 100 micrometers. The larger particles were observed to protect the smaller particles from mechanical abrasion.
In recent research, superhydrophobicity has been reported by allowing alkylketene dimer (AKD) to solidify into a nanostructured fractal surface. Many papers have since presented fabrication methods for producing superhydrophobic surfaces including particle deposition, sol-gel techniques, plasma treatments, vapor deposition, and casting techniques. Current opportunity for research impact lies mainly in fundamental research and practical manufacturing. Debates have recently emerged concerning the applicability of the Wenzel and Cassie–Baxter models. In an experiment designed to challenge the surface energy perspective of the Wenzel and Cassie–Baxter model and promote a contact line perspective, water drops were placed on a smooth hydrophobic spot in a rough hydrophobic field, a rough hydrophobic spot in a smooth hydrophobic field, and a hydrophilic spot in a hydrophobic field. Experiments showed that the surface chemistry and geometry at the contact line affected the contact angle and contact angle hysteresis, but the surface area inside the contact line had no effect. An argument that increased jaggedness in the contact line enhances droplet mobility has also been proposed.
Many hydrophobic materials found in nature rely on Cassie's law and are biphasic on the submicrometer level with one component air. The lotus effect is based on this principle. Inspired by it, many functional superhydrophobic surfaces have been prepared.
An example of a bionic or biomimetic superhydrophobic material in nanotechnology is nanopin film.
One study presents a vanadium pentoxide surface that switches reversibly between superhydrophobicity and superhydrophilicity under the influence of UV radiation. According to the study, any surface can be modified to this effect by application of a suspension of rose-like VO particles, for instance with an inkjet printer. Once again hydrophobicity is induced by interlaminar air pockets (separated by 2.1 nm distances). The UV effect is also explained. UV light creates electron-hole pairs, with the holes reacting with lattice oxygen, creating surface oxygen vacancies, while the electrons reduce V to V. The oxygen vacancies are met by water, and it is this water absorbency by the vanadium surface that makes it hydrophilic. By extended storage in the dark, water is replaced by oxygen and hydrophilicity is once again lost.
A significant majority of hydrophobic surfaces have their hydrophobic properties imparted by structural or chemical modification of a surface of a bulk material, through either coatings or surface treatments. That is to say, the presence of molecular species (usually organic) or structural features results in high contact angles of water. In recent years, rare earth oxides have been shown to possess intrinsic hydrophobicity. The intrinsic hydrophobicity of rare earth oxides depends on surface orientation and oxygen vacancy levels, and is naturally more robust than coatings or surface treatments, having potential applications in condensers and catalysts that can operate at high temperatures or corrosive environments. | 6 | Supramolecular Chemistry |
There are certain advantages of using sinters as opposed to using other materials which include recycling the fines and other waste products, to include flue dust, mill scale, lime dust and sludge. Processing sinter helps eliminate raw flux, which is a binding material used to agglomerate materials, which saves the heating material, coke, and improves furnace productivity.
Improvements and efficiency can be gained from higher softening temperature and narrower softening in the melting zone, which increases the volume of the granular zone and shrinks the width of the cohesive zone. A lower silica content and higher hot metal temperature contributes to more sulphur removal. | 8 | Metallurgy |
In 1865, the first "PCB-like" chemical was discovered, and was found to be a byproduct of coal tar. Years later in 1876, German chemist Oscar Döbner (Doebner) synthesized the first PCB in a laboratory. Since then, large amounts of PCBs were released into the environment, to the extent that there are even measurable amounts of PCBs in feathers of birds currently held in museums before the production of PCBs peaked.
In 1935, Monsanto Chemical Company (now Solutia Inc) took over commercial production of PCBs from Swann Chemical Company which had begun in 1929. PCBs, originally termed "chlorinated diphenyls", were commercially produced as mixtures of isomers at different degrees of chlorination. The electric industry used PCBs as a non-flammable replacement for mineral oil to cool and insulate industrial transformers and capacitors. PCBs were also commonly used as heat stabilizer in cables and electronic components to enhance the heat and fire resistance of PVC.
In the 1930s, the toxicity associated with PCBs and other chlorinated hydrocarbons, including polychlorinated naphthalenes, was recognized because of a variety of industrial incidents. Between 1936 and 1937, there were several medical cases and papers released on the possible link between PCBs and its detrimental health effects. In 1936 a U.S. Public health Service official described the wife and child of a worker from the Monsanto Industrial Chemical Company who exhibited blackheads and pustules on their skin. The official attributed these symptoms to contact with the worker's clothing after he returned from work. In 1937, a conference about the hazards was organized at Harvard School of Public Health, and a number of publications referring to the toxicity of various chlorinated hydrocarbons were published before 1940.
In 1947, Robert Brown reminded chemists that Arochlors were "objectionably toxic": "Thus the maximum permissible concentration for an 8-hr. day is 1 mg. per cu.m. [] of air. They also produce a serious and disfiguring dermatitis".
In 1954, Kanegafuchi Chemical Co. Ltd. (Kaneka Corporation) first produced PCBs, and continued until 1972.
Through the 1960s Monsanto Chemical Company knew increasingly more about PCBs' harmful effects on humans and the environment, per internal leaked documents released in 2002, yet PCB manufacture and use continued with few restraints until the 1970s.
In 1966, PCBs were determined by Swedish chemist Sören Jensen to be an environmental contaminant. Jensen, according to a 1994 article in Sierra, named chemicals PCBs, which previously, had simply been called "phenols" or referred to by various trade names, such as Aroclor, Kanechlor, Pyrenol, Chlorinol and others. In 1972, PCB production plants existed in Austria, West Germany, France, the UK, Italy, Japan, Spain, the USSR and the US.
In the early 1970s, Ward B. Stone of the New York State Department of Environmental Conservation (NYSDEC) first published his findings that PCBs were leaking from transformers and had contaminated the soil at the bottom of utility poles.
There have been allegations that Industrial Bio-Test Laboratories engaged in data falsification in testing relating to PCBs. In 2003, Monsanto and Solutia Inc., a Monsanto corporate spinoff, reached a US$700 million settlement with the residents of West Anniston, Alabama who had been affected by the manufacturing and dumping of PCBs. In a trial lasting six weeks, the jury found that "Monsanto had engaged in outrageous behavior, and held the corporations and its corporate successors liable on all six counts it considered – including negligence, nuisance, wantonness and suppression of the truth."
Existing products containing PCBs which are "totally enclosed uses" such as insulating fluids in transformers and capacitors, vacuum pump fluids, and hydraulic fluid, are allowed to remain in use in the US. The public, legal, and scientific concerns about PCBs arose from research indicating they are likely carcinogens having the potential to adversely impact the environment and, therefore, undesirable as commercial products. Despite active research spanning five decades, extensive regulatory actions, and an effective ban on their production since the 1970s, PCBs still persist in the environment and remain a focus of attention. | 2 | Environmental Chemistry |
snRNPs (pronounced "snurps"), or mall uclear iboucleoroteins, are RNA-protein complexes that combine with unmodified pre-mRNA and various other proteins to form a spliceosome, a large RNA-protein molecular complex upon which splicing of pre-mRNA occurs. The action of snRNPs is essential to the removal of introns from pre-mRNA, a critical aspect of post-transcriptional modification of RNA, occurring only in the nucleus of eukaryotic cells.
Additionally, U7 snRNP is not involved in splicing at all, as U7 snRNP is responsible for processing the 3′ stem-loop of histone pre-mRNA.
The two essential components of snRNPs are protein molecules and RNA. The RNA found within each snRNP particle is known as small nuclear RNA, or snRNA, and is usually about 150 nucleotides in length. The snRNA component of the snRNP gives specificity to individual introns by "recognizing" the sequences of critical splicing signals at the 5 and 3 ends and branch site of introns. The snRNA in snRNPs is similar to ribosomal RNA in that it directly incorporates both an enzymatic and a structural role.
SnRNPs were discovered by Michael R. Lerner and Joan A. Steitz.
Thomas R. Cech and Sidney Altman also played a role in the discovery, winning the Nobel Prize for Chemistry in 1989 for their independent discoveries that RNA can act as a catalyst in cell development. | 1 | Biochemistry |
BIND contains information on three types of data: interactions, molecular complexes and pathways.
# Interactions are the basic component of BIND and describe how 2 or more objects (A and B) interact with each other. The objects can be a variety of things: DNA, RNA, genes, proteins, ligands, or photons. The interaction entry contains the most information about a molecule; it provides information on its name and synonyms, where it is found (e.g. where in the cell, what species, when it is active, etc.), and its sequence or where its sequence can be found. The interaction entry also outlines the experimental conditions required to observe binding in vitro, chemical dynamics (including thermodynamics and kinetics).
# The second type of BIND entries are the molecular complexes. Molecular complexes are defined as an aggregate of molecules that are stable and have a function when bound to each other. The record may also contain some information on the role of the complex in various interactions and the molecular complex entry links data from 2 or more interaction records.
# The third component of BIND is the pathway record section. A pathway consists of a network of interactions that are involved in the regulation of cellular processes. This section may also contain information on phenotypes and diseases related to the pathway.
<br />The minimum amount of information needed to create an entry in BIND is a PubMed publication reference and an entry in another database (e.g. GenBank). Each entry within the database provides references/authors for the data. As BIND is a constantly growing database, all components of BIND track updates and changes.
BIND is based on a data specification written using Abstract Syntax Notation 1 (ASN.1) language. ASN.1 is used also by NCBI when storing data for their Entrez system and because of this BIND uses the same standards as NCBI for data representation. The ASN.1 language is preferred because it can be easily translated into other data specification languages (e.g. XML), can easily handle complex data and can be applied to all biological interactions – not just proteins. Bader and Hogue (2000) have prepared a detailed manuscript on the ASN.1 data specification used by BIND. | 1 | Biochemistry |
SI-compliant units that can be used as alternatives are shown in the chart below. Expressions that the BIPM explicitly does not recognize as being suitable for denoting dimensionless quantities with the SI are marked with .
Note that the notations in the "SI units" column above are for the most part dimensionless quantities; that is, the units of measurement factor out in expressions like "1 nm/m" (1 n/ =1 × 10) so the ratios are pure-number coefficients with values less than 1. | 2 | Environmental Chemistry |
Animal models are used to learn more about a disease, its diagnosis and its treatment, with animal models predicting human toxicity in up to 71% of cases. The human equivalent dose (HED) or human equivalent concentration (HEC) is the quantity of a chemical that, when administered to humans, produces an effect equal to that produced in test animals by a smaller dose. Calculating the HED is a step in carrying out a clinical trial of a pharmaceutical drug. | 1 | Biochemistry |
Inclusions are one of the most important factors when it comes to gem valuation. In many gemstones, such as diamonds, inclusions affect the clarity of the gem, diminishing the value. In some gems, however, such as star sapphires, the inclusion actually increases the value of the gem.
Many colored gemstones are expected to have inclusions, and the inclusions do not greatly affect the stone's value. Colored gemstones are categorized into three types as follows:
*Type I colored gems include gems with very little or no inclusions. They include aquamarines, topaz and zircon.
*Type II colored gems include those that often have a few inclusions. They include sapphire, ruby, garnet and spinel.
*Type III colored gems include those that almost always have inclusions. Gems in this category include emerald and tourmaline. | 8 | Metallurgy |
The cyclization of the enediyne functional group creates a transient reactive 1,4-benzenoid diradical that acts as a nucleophile and attacks electrophiles in order to achieve a more stable form. In biological systems, once the diradical is positioned in the minor groove of double-stranded DNA, it abstracts two hydrogen atoms from the sugars opposite strands at either the C1, C4, or C5 positions. The DNA radicals that form can then cause interstrand crosslinks or react with O, leading to double- or single-stranded DNA cleavage. | 0 | Organic Chemistry |
In these glycosides, the aglycone part is a steroid nucleus. These glycosides are found in the plant genera Digitalis, Scilla, and Strophanthus. They are used in the treatment of heart diseases, e.g., congestive heart failure (historically as now recognised does not improve survivability; other agents are now preferred) and arrhythmia. | 0 | Organic Chemistry |
Modafinil is commercially available in and oral tablet forms. Additionally, it is offered as the (R)-enantiomer, known as armodafinil, and as a prodrug named adrafinil. | 4 | Stereochemistry |
Born in Kobe, Japan, Yamamoto earned a B.S. at Kyoto University in 1967 and a Ph.D. at Harvard University in 1971.
He was a professor at Nagoya University from 1983 until 2002 and has since been a professor within the Department of Chemistry at the University of Chicago. His research work is largely in the chemistry of acid catalysts that play an important role in triggering or driving chemical reactions, specifically Lewis and Brønsted acid catalysts used in selective organic synthesis. Yamamoto has authored or co-authored several books on topics in modern synthetic organic chemistry. As of 2021, his h-index equals to 120 with more than 64,000 citations. | 0 | Organic Chemistry |
The Winkler test is used to determine the concentration of dissolved oxygen in water samples. Dissolved oxygen (D.O.) is widely used in water quality studies and routine operation of water reclamation facilities to analyze its level of oxygen saturation.
In the test, an excess of manganese(II) salt, iodide (I) and hydroxide (OH) ions are added to a water sample causing a white precipitate of Mn(OH) to form. This precipitate is then oxidized by the oxygen that is present in the water sample into a brown manganese-containing precipitate with manganese in a more highly oxidized state (either Mn(III) or Mn(IV)).
In the next step, a strong acid (either hydrochloric acid or sulfuric acid) is added to acidify the solution. The brown precipitate then converts the iodide ion (I) to iodine. The amount of dissolved oxygen is directly proportional to the titration of iodine with a thiosulfate solution. Today, the method is effectively used as its colorimetric modification, where the trivalent manganese produced on acidifying the brown suspension is directly reacted with ethylenediaminetetraacetic acid to give a pink color. As manganese is the only common metal giving a color reaction with ethylenediaminetetraacetic acid, it has the added effect of masking other metals as colorless complexes. | 3 | Analytical Chemistry |
CDP recognizes companies with high-quality disclosure in its annual scoring process, with top companies making it onto CDP's so-called A-list.
Scores are calculated according to a standardized method which measures whether and how well a company responds to each question. A company goes through four main steps, starting with disclosure of their current position, moving to awareness which looks at whether a company is conscious of its environmental impact, to management, and finally leadership.
A high CDP score is supposed to be indicative of a company's environmental awareness, advanced sustainability governance and leadership to address climate change. | 2 | Environmental Chemistry |
Method development of chiral chromatography is still done by screening of columns from the various classes of chiral columns. While chiral separation mechanisms are understandable in certain scenarios, and the retention characteristics of analytes within the chromatographic columns can occasionally be elucidated, the precise combination of chiral stationary phases (CSPs) and mobile-phase compositions that required to effectively resolve a specific enantiomeric pair often remains elusive.
The chemistry of CSP ligands significantly influences the creation of in-situ diastereomeric complexes upon the stationary phase surface. However, other methods conditions, such as mobile-phase solvents, their composition, mobile phase additives and column temperature can play equally critical roles. The final resolution of the enantiomers is the outcome of combination of intermolecular forces, and even a subtle change in them can determine the success or failure of separation. This complexity prevents from establishing routine method-development protocols that are universally applicable to a diverse range of enantiomers. In fact, sometimes the outcome of previous unsuccessful experiments do not provide any clue for the subsequent steps. Therefore, in practice, a chiral method development laboratory settings, acts like a high-throughput screening protocol, of conducting a systematic screening of various CSPs by advanced column switching devices, trying automatically and systematically various mobile-phase combinations, effectively employing a trial-and-error strategy.
Because of the highly complex retention mechanism of a chiral stationary-phase due to chiral recognition, whose principles have not been deciphered, it is often difficult, if not impossible to predict in advance the steps that can be successfully applied to the enantiomers at hand as part of method development. That's why the standard approach in the method development is high throughput screening, to evaluate or examine a series of stationary phases, using various mobile-phase combinations, to increase the chance of finding a suitable separation condition. | 4 | Stereochemistry |
It takes a few days until plankton organisms have filtered the particles and incorporated the toxins into their body fat and tissue: In the southwards flow of the waters of the Hudson off the coast of New Jersey, the highest levels of mercury in copepods have not been found directly in front of the river off New York but 150 km south, off Atlantic City.
Many copepods are then captured by mysidae, krill and smallest fish like the juveniles of atlantic herring - and in each step of the foodchain the toxin concentrations increase by the factor of 10. The milk of mothers (Homo sapiens) consuming fish and related products like margarine and eggs in such areas have so high toxin levels that it would be impossible to sell such milk on markets - their babies have much more birth-defects and/or retarded brains and have later difficulties to learn and/or reproduce. Many die at an early age.
Filter of krill: The first degree filter setae carry in v-form two rows of second degree setae, pointing towards the inside of the feeding basket. The purple ball is one micrometer in size. To display the total area of this fascinating particle filtration structure one would have to [http://www.ecoscope.com/krill/filter/filter7/index.htm tile] 7500 times this image.
Filter basket of a mysid. These 3 cm long animals live close to shore and hover above the sea floor, constantly collecting particles. Mysids are an important food source for herring, cod, flounder, striped bass. In polluted areas they have high toxin levels in their tissue but they are very robust and require much poison to die. | 2 | Environmental Chemistry |
Glycoprotein hormones may be removed by the liver from the bloodstream when the passage of time causes the breaking-off of carbohydrates from the glycoproteins. | 0 | Organic Chemistry |
Carboximidates can act as protecting group for alcohols. For example, the base catalyzed reaction of benzyl alcohol upon trichloroacetonitrile yields a trichloroacetimidate. This species has orthogonal stability to acetate and TBS protections and may be cleaved by acid hydrolysis. | 0 | Organic Chemistry |
Beletskaya was born in Leningrad (St. Petersburg, Russia) in 1933. She graduated from the Department of Chemistry of Lomonosov Moscow State University in 1955 where she focused her undergraduate research on organoarsenic chemistry. She obtained the Candidate of Chemistry (analogous to Ph.D.) degree in 1958. For this degree she investigated electrophilic substitution reactions. More specifically, she explored the influence of ammonia on a-bromomercurophenylacetic acid reactions. In 1963 she received her Dr.Sci. degree from the same institution. In 1970 she became a Full Professor of Chemistry at Moscow State University, where she currently serves as head of the [http://www.chem.msu.su/eng/lab/orgcomp.html Organoelement Chemistry Laboratory]. Beletskaya was elected a corresponding member of the Academy of Science of USSR in 1974. In 1992 she became a full member (academician) of the Russian Academy of Sciences. Between 1991 and 1993 she served as president of the Division of Organic Chemistry of IUPAC. Until 2001 she served on the IUPAC Committee on Chemical Weapons Destruction Technology (CWDT). She is editor-in chief of the [https://link.springer.com/journal/11178 Russian Journal of Organic Chemistry].
Beletskaya initially researched the reaction mechanisms of organic reactions, focusing on compounds with metal-carbon bonds. Her research included Grignard-like reactions and lanthanide complexes in the context of catalysts. She and Prof. O. Reutov worked on electrophilic reactions at saturated carbon. She also investigated the reaction mechanisms of organometallic compounds. She also researched carbanion reactivity, emphasizing the reactivity and structure of ion pairs. Once more advanced in her career, Beltskaya focused more on transition metal catalysts and developing economically favorable catalysts. Currently, she serves as the head of the Laboratory of Organoelement Compounds within the Department of Chemistry at Moscow State University, where she has concentrated her research on carbon dioxide utilization and its utility in renewable energy and reactions with epoxides. | 0 | Organic Chemistry |
Many of the other quantities of information theory can be interpreted as applications of relative entropy to specific cases. | 7 | Physical Chemistry |
Testing and scientific certainty were desired at the end of the 1940s. To that end products meant to be used by humans were tested with model animals to speed trials. Eddy & McGregor 1949 and Wiesmann & Lotmar 1949 used mice, Wasicky et al. 1949 canaries and guinea pigs, Kasman et al. 1953 also guinea pigs, Starnes & Granett 1953 rabbits, and many used cattle. | 1 | Biochemistry |
In many magnetic ferrous alloys, the Curie point, the temperature at which magnetic materials cease to behave magnetically, occurs at nearly the same temperature as the austenite transformation. This behavior is attributed to the paramagnetic nature of austenite, while both martensite and ferrite are strongly ferromagnetic. | 8 | Metallurgy |
William Zismans contribution of what is called today as the Zisman Plot revolutionized the world of adhesive bonding and surface chemistry by giving a fast, effective, and quantitative way to measure the wettability or critical surface tension of a solid. This spawned the work of many others over the past few decades. This spans from Danns work in the late 1960s to David and Neumann's work in 2014. The Zisman Plot is still used today, and it has many variations since the y-axis is unitless and can be found more easily and accurately using modern regression software packages. | 7 | Physical Chemistry |
Townsend put forward the hypothesis that positive ions also produce ion pairs, introducing a coefficient expressing the number of ion pairs generated per unit length by a positive ion (cation) moving from anode to cathode. The following formula was found
since , in very good agreement with experiments.
The first Townsend coefficient ( α ), also known as first Townsend avalanche coefficient is a term used where secondary ionisation occurs because the primary ionisation electrons gain sufficient energy from the accelerating electric field, or from the original ionising particle. The coefficient gives the number of secondary electrons produced by primary electron per unit path length. | 7 | Physical Chemistry |
The stereochemistry of macromolecules can be defined even more precisely with the introduction of triads. An isotactic triad (mm) is made up of two adjacent meso diads, a syndiotactic triad (also spelled syndyotactic) (rr) consists of two adjacent racemo diads, and a heterotactic triad (rm) is composed of a racemo diad adjacent to a meso diad. The mass fraction of isotactic (mm) triads is a common quantitative measure of tacticity.
When the stereochemistry of a macromolecule is considered to be a Bernoulli process, the triad composition can be calculated from the probability P of a diad being meso. For example, when this probability is 0.25 then the probability of finding:
*an isotactic triad is P, or 0.0625
*an heterotactic triad is 2P(1–P), or 0.375
*a syndiotactic triad is (1–P), or 0.5625
with a total probability of 1. Similar relationships with diads exist for tetrads. | 4 | Stereochemistry |
Indirect enantiomer separation involves the interaction between the chiral analyte (CA) of interest and the suitable reactive CS (in this case it is an enantiopure chiral derivatizing agent, CDA) leading to the formation of a covalent diastereomeric complex that can be separated with an achiral chromatographic technique. Therapeutic agents often contain reactive functional groups (amino, hydroxyl, epoxy, carbonyl and carboxylic acid, etc.) in their structures. They are converted into covalently bonded diastereomeric derivatives using enantiomerically pure chiral derivatizing agent. The diastereomers thus formed unlike enantiomers, exhibit different physicochemical properties in an achiral environment and are eventually separated as a result of differential retention time on a stationary phase. The success of this approach depends on the availability of stable enantiopure chiral derivatizing agent (CDA) and on the presence of a suitable reactive functional group in the chiral drug molecule for covalent formation of diastereomeric derivative. The reaction of a racemic, (R,S)- Drug with a chirally and chemically pure chiral derivatizing agent, (R’)-CDA, will afford diastereomeric products, (R)-Drug-(R')-CDA + (S)-Drug-(R’)- CDA. The chiral derivatization reaction scheme is illustrated in the box on the right hand side.
In contrast to enantiomers, diastereomers have different physicochemical properties that make them separable on regular achiral stationary phases. The major benefit of the indirect methodology is that conventional achiral stationary phase/mobile phase system may be used for the separation of the generated diastereomers. Thus, considerable flexibility in chromatographic conditions is available to achieve the desired separation and to eliminate interferences from metabolites and endogenous substances. Moreover, the sensitivity of the method can be enhanced by sensible choice of the CDA and the chromatographic detection system. But this indirect approach to enantiomeric analysis has some potential problems. These include availability of a suitable functional group on the enantiomer for derivatization, enantiomeric purity of the CDA, racemization of the CDA during derivatization, and racemization of the analyte during the derivatization. Currently, however, the application of indirect analytical approaches is in decline. | 4 | Stereochemistry |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.