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*Antimony potassium tartrate, an anion, that forms diastereomeric salts with chiral cations.
*Camphorsulfonic acid, an acid that forms diastereomeric salts with chiral amines
*1-Phenylethylamine, a base that forms diastereomeric salts with chiral acids. Many related chiral amines have been demonstrated.
The chiral pool consists of many widely available resolving agents. | 4 | Stereochemistry |
In stereochemistry, mutarotation is the change in optical rotation of a chiral material in a solution due to a change in proportion of the two constituent anomers (i.e. the interconversion of their respective stereocenters) until equilibrium is reached. Cyclic sugars show mutarotation as α and β anomeric forms interconvert.
The optical rotation of the solution depends on the optical rotation of each anomer and their ratio in the solution.
Mutarotation was discovered by French chemist Augustin-Pierre Dubrunfaut in 1844, when he noticed that the specific rotation of aqueous sugar solution changes with time. | 4 | Stereochemistry |
Di-tert-butyl dicarbonate is inexpensive, so it is usually purchased. Classically, this compound is prepared from tert-butanol, carbon dioxide, and phosgene, using DABCO as a base:
This route is currently employed commercially by manufacturers in China and India. European and Japanese companies use the reaction of sodium tert-butoxide with carbon dioxide, catalysed by p-toluenesulfonic acid or methanesulfonic acid. This process involves a distillation of the crude material yielding a very pure grade.
Boc anhydride is also available as a 70% solution in toluene or THF. As boc anhydride may melt at ambient temperatures, its storage and handling is sometimes simplified by using a solution. | 0 | Organic Chemistry |
Consistent with these compounds being alkylating agents, the α-halide is readily substituted, e.g. by azide. Similarly, the α-bromocarboxylic acid undergo nucleophilic substitution with ammonia to give the amino acid,
The Darzens reaction involves a ketone or aldehyde with an α-haloester in the presence of a base to form an α,β-epoxy ester, also called a "glycidic ester". The reaction process begins with deprotonation at the halogenated position. In a related reaction, α-halo carboxylic esters can be reduced by lithium aluminium hydride to the α-halo alcohols, which can be converted to the α-epoxides.
α-Halo-esters can be converted to vinyl halides. upon reaction with ketones and chromous chloride. | 0 | Organic Chemistry |
Lithium toxicity, which is also called lithium overdose and lithium poisoning, is the condition of having too much lithium in the blood. This condition also happens in persons that are taking lithium in which the lithium levels are affected by drug interactions in the body.
In acute toxicity, people have primarily gastrointestinal symptoms such as vomiting and diarrhea, which may result in volume depletion. During acute toxicity, lithium distributes later into the central nervous system resulting in mild neurological symptoms, such as dizziness.
In chronic toxicity, people have primarily neurological symptoms which include nystagmus, tremor, hyperreflexia, ataxia, and change in mental status. During chronic toxicity, the gastrointestinal symptoms seen in acute toxicity are less prominent. The symptoms are often vague and nonspecific.
If the lithium toxicity is mild or moderate, lithium dosage is reduced or stopped entirely. If the toxicity is severe, lithium may need to be removed from the body. | 1 | Biochemistry |
Binary (involving one other metal) and ternary (involving two other metals) intermetallic stannides have been investigated. Niobium stannide, NbSn is perhaps the best known superconducting tin intermetallics. This is more commonly called "niobium-tin". | 7 | Physical Chemistry |
Junk DNA is DNA that has no biologically relevant function such as pseudogenes and fragments of once active transposons. Bacteria and viral genomes have very little junk DNA but some eukaryotic genomes may have a substantial amount of junk DNA. The exact amount of nonfunctional DNA in humans and other species with large genomes has not been determined and there is considerable controversy in the scientific literature.
The nonfunctional DNA in bacterial genomes is mostly located in the intergenic fraction of non-coding DNA but in eukaryotic genomes it may also be found within introns. It is important to note that there are many examples of functional DNA elements in non-coding DNA and that it is erroneous to equate non-coding DNA with junk DNA. | 1 | Biochemistry |
Coupled substitution is the geological process by which two elements simultaneous substitute into a crystal in order to maintain overall electrical neutrality and keep the charge constant. In forming a solid solution series, ionic size is more important than ionic charge, as this can be compensated for elsewhere in the structure. | 3 | Analytical Chemistry |
A screw displacement (also screw operation or rotary translation) is the composition of a rotation by an angle φ about an axis (called the screw axis) with a translation by a distance d along this axis. A positive rotation direction usually means one that corresponds to the translation direction by the right-hand rule. This means that if the rotation is clockwise, the displacement is away from the viewer. Except for φ = 180°, we have to distinguish a screw displacement from its mirror image. Unlike for rotations, a righthand and lefthand screw operation generate different groups.
The combination of a rotation about an axis and a translation in a direction perpendicular to that axis is a rotation about a parallel axis. However, a screw operation with a nonzero translation vector along the axis cannot be reduced like that. Thus the effect of a rotation combined with any translation is a screw operation in the general sense, with as special cases a pure translation, a pure rotation and the identity. Together these are all the direct isometries in 3D.
In crystallography, a screw axis symmetry is a combination of rotation about an axis and a translation parallel to that axis which leaves a crystal unchanged. If φ = 360°/n for some positive integer n, then screw axis symmetry implies translational symmetry with a translation vector which is n times that of the screw displacement.
Applicable for space groups is a rotation by 360°/n about an axis, combined with a translation along the axis by a multiple of the distance of the translational symmetry, divided by n. This multiple is indicated by a subscript. So, 6 is a rotation of 60° combined with a translation of 1/2 of the lattice vector, implying that there is also 3-fold rotational symmetry about this axis. The possibilities are 2, 3, 4, 4, 6, 6, and 6, and the enantiomorphous 3, 4, 6, and 6.
Considering a screw axis n, if g is the greatest common divisor of n and m, then there is also a g-fold rotation axis. When n/g screw operations have been performed, the displacement will be m/g, which since it is a whole number means one has moved to an equivalent point in the lattice, while carrying out a rotation by 360°/g. So 4, 6 and 6 create two-fold rotation axes, while 6 creates a three-fold axis.
A non-discrete screw axis isometry group contains all combinations of a rotation about some axis and a proportional translation along the axis (in rifling, the constant of proportionality is called the twist rate); in general this is combined with k-fold rotational isometries about the same axis (k ≥ 1); the set of images of a point under the isometries is a k-fold helix; in addition there may be a 2-fold rotation about a perpendicularly intersecting axis, and hence a k-fold helix of such axes. | 3 | Analytical Chemistry |
Block or graft copolymers are commonly used as compatibilizing agents. The copolymer used is made of the two components in the immiscible blend. The respective portions of the copolymer are able to interact with the two phases of the blend to make the phase morphology more stable. The increased stability is caused by reducing the size of the phase-separated particles in the blend. The size reduction comes from the lower interfacial tension, due to accumulating block copolymers at the many interfaces between the two copolymers. This helps the immiscible blends break up into smaller particles in the melt phase. In turn, these phase separated particles will not be as inclined to consolidate and grow because the interfacial tension is now much lower. This stabilizes the polymer blend to a usable product.
An example of this are Ethylene/propylene copolymers. They are able to act as good compatibilizing agents for blends of polypropylene and low density polyethylene. In this specific application, longer ethylene sequences are preferred in the copolymer. This is because cocrystallization also factors into this case, and the longer ethylene sequences will retain some residual crystallinity. | 7 | Physical Chemistry |
Hormonal effects are dependent on where they are released, as they can be released in different manners. Not all hormones are released from a cell and into the blood until it binds to a receptor on a target. The major types of hormone signaling are: | 1 | Biochemistry |
In this approach, an enantiomerically pure compound, the chiral selector, is added to the mobile phase and separation happens on a conventional achiral column. When a mixture of enantiomers is introduced into the chromatographic system, the individual enantiomers form transient diastereomeric complexes with the chiral mobile phase additive. In the chiral mobile phase additive technique, two possible mechanisms may operate: one possibility is that CMPA and the enantiomers may form diastereomers in the mobile phase. Another is that the stationary phase may be coated with the CMPA, leading to diastereomeric interactions with the enantiomeric pairs during chromatographic separation process. It is observed that both the mechanisms may happen depending on the characteristic of the stationary phase and mobile phase employed. Of late this method finds limited application. | 4 | Stereochemistry |
All viruses bind to their hosts and introduce their genetic material into the host cell as part of their replication cycle. This genetic material contains basic instructions of how to produce more copies of these viruses, hacking the bodys normal production machinery to serve the needs of the virus. The host cell will carry out these instructions and produce additional copies of the virus, leading to more and more cells becoming infected. Some types of viruses insert their genome into the hosts cytoplasm, but do not actually enter the cell. Others penetrate the cell membrane disguised as protein molecules and enter the cell.
There are two main types of virus infection: lytic and lysogenic. Shortly after inserting its DNA, viruses of the lytic cycle quickly produce more viruses, burst from the cell and infect more cells. Lysogenic viruses integrate their DNA into the DNA of the host cell and may live in the body for many years before responding to a trigger. The virus reproduces as the cell does and does not inflict bodily harm until it is triggered. The trigger releases the DNA from that of the host and employs it to create new viruses. | 1 | Biochemistry |
In May the FDA approved Vyjuvek for the treatment of wounds in patients with dystrophic epidermolysis bullosa (DEB) which is applied as a topical gel that delivers a herpes-simplex virus type 1 (HSV-1) vector encoding the collagen type VII alpha 1 chain (COL7A1) gene that is dysfunctional on those affected by DEB . One trial found 65% of the Vyjuvek-treated wounds completely closed while only 26% of the placebo-treated at 24 weeks. It has been also reported its use as a eyedrops for a patient with DEB that had vision loss due to the widespread blistering with good results.
In June the FDA gave an accelerated approval to Elevidys for Duchenne muscular dystrophy (DMD) only for boys 4 to 5 years old as they are more likely to benefit from the therapy which consists of one-time intravenous infusion of a virus (AAV rh74 vector) that delivers a functioning “microdystrophin” gene (138 kDa) into the muscle cells to act in place of the normal dystrophin (427 kDa) that is found mutated in this disease.
In July it was reported that it had been developed a new method to affect genetic expressions through direct current. | 1 | Biochemistry |
Gymnochrome E is a cytotoxic phenanthroperylenequinone isolated from a deep-water crinoid called Holopus rangii. | 1 | Biochemistry |
BMR is a flexible trait (it can be reversibly adjusted within individuals), with, for example, lower temperatures generally resulting in higher basal metabolic rates for both birds and rodents. There are two models to explain how BMR changes in response to temperature: the variable maximum model (VMM) and variable fraction model (VFM). The VMM states that the summit metabolism (or the maximum metabolic rate in response to the cold) increases during the winter, and that the sustained metabolism (or the metabolic rate that can be indefinitely sustained) remains a constant fraction of the former. The VFM says that the summit metabolism does not change, but that the sustained metabolism is a larger fraction of it. The VMM is supported in mammals, and, when using whole-body rates, passerine birds. The VFM is supported in studies of passerine birds using mass-specific metabolic rates (or metabolic rates per unit of mass). This latter measurement has been criticized by Eric Liknes, Sarah Scott, and David Swanson, who say that mass-specific metabolic rates are inconsistent seasonally.
In addition to adjusting to temperature, BMR also may adjust before annual migration cycles. The red knot (ssp. islandica) increases its BMR by about 40% before migrating northward. This is because of the energetic demand of long-distance flights. The increase is likely primarily due to increased mass in organs related to flight. The end destination of migrants affects their BMR: yellow-rumped warblers migrating northward were found to have a 31% higher BMR than those migrating southward.
In humans, BMR is directly proportional to a persons lean body mass. In other words, the more lean body mass a person has, the higher their BMR; but BMR is also affected by acute illnesses and increases with conditions like burns, fractures, infections, fevers, etc. In menstruating females, BMR varies to some extent with the phases of their menstrual cycle. Due to the increase in progesterone, BMR rises at the start of the luteal phase and stays at its highest until this phase ends. There are different findings in research how much of an increase usually occurs. Small sample, early studies, found various figures, such as; a 6% higher postovulatory sleep metabolism, a 7% to 15% higher 24 hour expenditure following ovulation, and an increase and a luteal phase BMR increase by up to 12%. A study by the American Society of Clinical Nutrition found that an experimental group of female volunteers had an 11.5% average increase in 24 hour energy expenditure in the two weeks following ovulation, with a range of 8% to 16%. This group was measured via simultaneously direct and indirect calorimetry and had standardized daily meals and sedentary schedule in order to prevent the increase from being manipulated by change in food intake or activity level. A 2011 study conducted by the Mandya Institute of Medical Sciences found that during a womans follicular phase and menstrual cycle is no significant difference in BMR, however the calories burned per hour is significantly higher, up to 18%, during the luteal phase. Increased state anxiety (stress level) also temporarily increased BMR. | 1 | Biochemistry |
The Kesternich test is a common name for the corrosion test with sulfur dioxide (SO) under general moisture condensation. This test was developed in 1951 by Wilhelm Kesternich to simulate the damaging effects of acid rain.
Acid rain and acidic industrial pollutants are corrosive and can degrade coatings and plated surfaces. Kesternich testing, or sulfur dioxide testing, simulates acid rain or industrial chemical exposure to evaluate the relative corrosion resistance of the coating, substrate, or part itself. The test can be used for coatings or for base materials.
The test method is defined by various standards, DIN EN ISO 6988, DIN 50018, ASTM G87, ISO 3231, ISO 22479 are the most common. The parts to be tested are placed in a test chamber with a capacity of 300L and exposed to warm, moist air in combination with a certain amount of sulfur dioxide
Note: Sulfur is interchangeable with Sulphur and SO2 is the abbreviation for Sulfur/Sulphur Dioxide | 8 | Metallurgy |
All living organisms are dependent on three essential biopolymers for their biological functions: DNA, RNA and proteins. Each of these molecules is required for life since each plays a distinct, indispensable role in the cell. The simple summary is that DNA makes RNA, and then RNA makes proteins.
DNA, RNA, and proteins all consist of a repeating structure of related building blocks (nucleotides in the case of DNA and RNA, amino acids in the case of proteins). In general, they are all unbranched polymers, and so can be represented in the form of a string. Indeed, they can be viewed as a string of beads, with each bead representing a single nucleotide or amino acid monomer linked together through covalent chemical bonds into a very long chain.
In most cases, the monomers within the chain have a strong propensity to interact with other amino acids or nucleotides. In DNA and RNA, this can take the form of Watson–Crick base pairs (G–C and A–T or A–U), although many more complicated interactions can and do occur. | 7 | Physical Chemistry |
The Caspian Sea is the worlds largest inland body of water, often described as the worlds largest lake and sometimes referred to as a full-fledged sea. An endorheic basin, it lies between Europe and Asia: east of the Caucasus, west of the broad steppe of Central Asia, south of the fertile plains of Southern Russia in Eastern Europe, and north of the mountainous Iranian Plateau. It covers a surface area of (excluding the highly saline lagoon of Garabogazköl to its east), an area approximately equal to that of Japan, with a volume of . It has a salinity of approximately 1.2% (12 g/L), about a third of the salinity of average seawater. It is bounded by Kazakhstan to the northeast, Russia to the northwest, Azerbaijan to the southwest, Iran to the south, and Turkmenistan to the southeast.
The sea stretches from north to south, with an average width of . Its gross coverage is and the surface is about below sea level. Its main freshwater inflow, Europe's longest river, the Volga, enters at the shallow north end. Two deep basins form its central and southern zones. These lead to horizontal differences in temperature, salinity, and ecology. The seabed in the south reaches below sea level, which is the second-lowest natural non-oceanic depression on Earth after Lake Baikal ().
Written accounts from the ancient inhabitants of its coast perceived the Caspian Sea as an ocean, probably because of its salinity and large size. With a surface area of , the Caspian Sea is nearly five times as big as Lake Superior (). The Caspian Sea is home to a wide range of species and is famous for its caviar and oil industries. Pollution from the oil industry and dams on rivers that drain into it have harmed its ecology. It is predicted that during the 21st century, the depth of the sea will decrease by 9–18 m (30–60 ft) due to global warming and the process of desertification, causing an ecocide. | 2 | Environmental Chemistry |
Elastin-like polypeptides (ELPs) are synthetic biopolymers with potential applications in the fields of cancer therapy, tissue scaffolding, metal recovery, and protein purification. For cancer therapy, the addition of functional groups to ELPs can enable them to conjugate with cytotoxic drugs. Also, ELPs may be able to function as polymeric scaffolds, which promote tissue regeneration. This capacity of ELPs has been studied particularly in the context of bone growth. ELPs can also be engineered to recognize specific proteins in solution. The ability of ELPs to undergo morphological changes at certain temperatures enables specific proteins that are bound to the ELPs to be separated out from the rest of the solution via experimental techniques such as centrifugation.
The general structure of polymeric ELPs is (VPGXG), where the monomeric unit is Val-Pro-Gly-X-Gly, and the "X" denotes a variable amino acid that can have consequences on the general properties of the ELP, such as the transition temperature (T). Specifically, the hydrophilicity or hydrophobicity and the presence or absence of a charge on the guest residue play a great role in determining the T Also, the solubilization of the guest residue can effect the T The "n" denotes the number of monomeric units that comprise the polymer. In general, these polymers are linear below the T, but aggregate into spherical clumps above the T. | 7 | Physical Chemistry |
Several systems have been proposed which combine MRI capability with lanthanides probes in dual assays. The luminescent probe may for instance serve to localize the MRI contrast agent. This has helped to visualize the delivery of nucleic acids into cultured cells. Lanthanides are not used for their fluorescence but their magnetic qualities. | 1 | Biochemistry |
A number of proteins are known to be associated with TAD formation including the protein CTCF and the protein complex cohesin. It is also unknown what components are required at TAD boundaries; however, in mammalian cells, it has been shown that these boundary regions have comparatively high levels of CTCF binding. In addition, some types of genes (such as transfer RNA genes and housekeeping genes) appear near TAD boundaries more often than would be expected by chance.
Computer simulations have shown that chromatin loop extrusion driven by cohesin motors can generate TADs. In the loop extrusion model, cohesin binds chromatin, pulls it in, and extrudes chromatin to progressively grow a loop. Chromatin on both sides of the cohesin complex is extruded until cohesin encounters a chromatin-bound CTCF protein, typically located at the boundary of a TAD. In this way, TAD boundaries can be brought together as the anchors of a chromatin loop. Indeed, in vitro, cohesin has been observed to processively extrude DNA loops in an ATP-dependent manner and stall at CTCF. However, some in vitro data indicates that the observed loops may be artifacts. Importantly, since cohesins can dynamically unbind from chromatin, this model suggests that TADs (and associated chromatin loops) are dynamic, transient structures, in agreement with in vivo observations.
Other mechanisms for TAD formation have been suggested. For example, some simulations suggest that transcription-generated supercoiling can relocalize cohesin to TAD boundaries or that passively diffusing cohesin “slip links” can generate TADs. | 1 | Biochemistry |
Temperature plays a key role in the ecology, physiology and metabolism of aquatic species. The rate of PCB metabolism was temperature dependent in yellow perch (Perca flavescens). In fall and winter, only 11 out of 72 introduced PCB congeners were excreted and had halflives of more than 1,000 days. During spring and summer when the average daily water temperature was above 20 °C, persistent PCBs had halflives of 67 days. The main excretion processes were fecal egestion, growth dilution and loss across respiratory surfaces. The excretion rate of PCBs matched with the perch's natural bioenergetics, where most of their consumption, respiration and growth rates occur during the late spring and summer. Since the perch is performing more functions in the warmer months, it naturally has a faster metabolism and has less PCB accumulation. However, multiple cold-water periods mixed with toxic PCBs with coplanar chlorine molecules can be detrimental to perch health. | 2 | Environmental Chemistry |
Shneider-Miles scattering (also referred to as collisional scattering or quasi-Rayleigh scattering) is the quasi-elastic scattering of electromagnetic radiation by charged particles in a small-scale medium with frequent particle collisions. Collisional scattering typically occurs in coherent microwave scattering of high neutral density, low ionization degree microplasmas such as atmospheric pressure laser-induced plasmas. Shneider-Miles scattering is characterized by a 90° phase shift between the incident and scattered waves and a scattering cross section proportional to the square of the incident driving frequency (). Scattered waves are emitted in a short dipole radiation pattern. The variable phase shift present in semi-collisional scattering regimes allows for determination of a plasma's collisional frequency through coherent microwave scattering. | 7 | Physical Chemistry |
In chemistry, acylation is a broad class of chemical reactions in which an acyl group () is added to a substrate. The compound providing the acyl group is called the acylating agent. The substrate to be acylated and the product include the following:
*alcohols, esters
*amines, amides
*arenes, ketones
A particularly common type of acylation is acetylation, the addition of the acetyl group. Closely related to acylation is formylation, which employ sources of "HCO in place of "RCO". | 0 | Organic Chemistry |
Phenols are susceptible to Electrophilic aromatic substitutions. Condensation with formaldehyde gives resinous materials, famously Bakelite.
Another industrial-scale electrophilic aromatic substitution is the production of bisphenol A, which is produced by the condensation with acetone. | 0 | Organic Chemistry |
In pharmacology, an active moiety is the part of a molecule or ion – excluding appended inactive portions – that is responsible for the physiological or pharmacological action of a drug substance. Inactive appended portions of the drug substance may include either the alcohol or acid moiety of an ester, a salt (including a salt with hydrogen or coordination bonds), or other noncovalent derivative (such as a complex, chelate, or clathrate). The parent drug may itself be an inactive prodrug and only after the active moiety is released from the parent in free form does it become active. | 0 | Organic Chemistry |
Disrupted functioning of cAMP has been noted as one of the mechanisms of several bacterial exotoxins.
They can be subgrouped into two distinct categories:
* Toxins that interfere with enzymes ADP-ribosyl-transferases, and
* invasive adenylate cyclases. | 1 | Biochemistry |
Clinopyroxene thermobarometry is usually used by mining industries. It is particularly helpful to the diamond industry, so many stakeholders possess pressure and temperature data regarding the formation of rocks that contain diamonds. This is important because diamonds are usually found in kimberlites, but kimberlites do not always contain diamonds. Instead of mining every kimberlite found, they can be sampled to see if they formed in an environment that would have favored the crystallization of diamonds.
Other applications are largely scientific; pressure and temperature data about magma can be used to propose detailed models of the lithosphere and mantle. These models enhance understanding of geological and volcanic activity, which may contribute to scientists' ability to predict events such as eruptions or earthquakes. | 9 | Geochemistry |
S-Nitrosothiols, also known as thionitrites, are compounds containing a nitroso group attached to the sulfur atom of a thiol, e.g. R−S−N=O. They have received considerable attention in biochemistry because they serve as donors of the nitrosonium ion, NO, and nitric oxide, NO, which may serve as signaling molecules in living systems, especially related to vasodilation. | 9 | Geochemistry |
The Journal of Physical Chemistry C publishes scientific articles reporting research on several subdisciplines of physical chemistry:
*Nanoparticles and nanostructures
*surfaces, interfaces, and catalysis
*Electron transport, optical and electronic devices
*Energy conversion and storage
It was created in 2007 when The Journal of Physical Chemistry B was split in two, largely due to the recent growth in the area of nanotechnology. The journal is published weekly, with the first issue on January 11, 2007. Like The Journal of Physical Chemistry A and B, it is published by the American Chemical Society.
The journal is indexed in: Chemical Abstracts Service (CAS) and British Library. According to the Journal Citation Reports, the journal had a 2022 impact factor of 3.7. | 7 | Physical Chemistry |
DNA methylation, referring to the reversible methylation of the 5 position of cytosine by methyltransferases, is a major epigenetic modification in multicellular organisms. In mammals, this modification primarily occurs at CpG sites, which in turn tend to cluster in regions called CpG islands. There is a small fraction of CpG islands that can overlap or be in close proximity to promoter regions of transcription start sites. The modification may also occur at other sites, but methylation at either of these sites can repress gene expression by either interfering with the binding of transcription factors or modifying chromatin structure to a repressive state.
Disease condition studies have largely fueled the effort in understanding the role of DNA methylation. Currently, the major research interest lies in investigating disease conditions such as cancer to identify regions of the DNA that has undergone extensive methylation changes. The genes contained in these regions are of functional interest as they may offer a mechanistic explanation to the underlying genetic causes of a disease. For instance, the abnormal methylation pattern of cancer cells was initially shown to be a mechanism through which tumor suppressor-like genes are silenced, although it was later observed that a much broader range of gene types are affected. | 1 | Biochemistry |
The phosphorus atom in phosphines has a formal oxidation state −3 (σλ) and are the phosphorus analogues of amines. Like amines, phosphines have a trigonal pyramidal molecular geometry although often with smaller C-E-C angles (E = N, P), at least in the absence of steric effects. The C-P-C bond angle is 98.6° for trimethylphosphine increasing to 109.7° when the methyl groups are replaced by tert-butyl groups. When used as ligands, the steric bulk of tertiary phosphines is evaluated by their cone angle. The barrier to pyramidal inversion is also much higher than nitrogen inversion to occur, and therefore phosphines with three different substituents can be resolved into thermally stable optical isomers. Phosphines are often less basic than corresponding amines, for instance the phosphonium ion itself has a pK of −14 compared to 9.21 for the ammonium ion; trimethylphosphonium has a pK of 8.65 compared to 9.76 for trimethylammonium. However, triphenylphosphine (pK 2.73) is more basic than triphenylamine (pK −5), mainly because the lone pair of the nitrogen in NPh is partially delocalized into the three phenyl rings. Whereas the lone pair on nitrogen is delocalized in pyrrole, the lone pair on phosphorus atom in the phosphorus equivalent of pyrrole (phosphole) is not. The reactivity of phosphines matches that of amines with regard to nucleophilicity in the formation of phosphonium salts with the general structure PRX. This property is used in the Appel reaction for converting alcohols to alkyl halides. Phosphines are easily oxidized to the corresponding phosphine oxides, whereas amine oxides are less readily generated. In part for this reason, phosphines are very rarely encountered in nature. | 0 | Organic Chemistry |
Whether or not a given individuals brain can deal effectively with stress, and thus their susceptibility to depression, depends on the β-catenin in each persons brain, according to a study conducted at the Icahn School of Medicine at Mount Sinai and published November 12, 2014, in the journal Nature. Higher β-catenin signaling increases behavioral flexibility, whereas defective β-catenin signaling leads to depression and reduced stress management. | 1 | Biochemistry |
Fungi, thanks to their non-specific enzymes, are able to break down many kinds of substances including pharmaceuticals and fragrances that are normally recalcitrant to bacteria degradation, such as paracetamol (also known as acetaminophen). For example, using Mucor hiemalis, the breakdown of products which are toxic in traditional water treatment, such as phenols and pigments of wine distillery wastewater, X-ray contrast agents, and ingredients of personal care products, can be broken down in a non-toxic way.
Mycoremediation is a cheaper method of remediation, and it doesn't usually require expensive equipment. For this reason, it is often used in small scale applications, such as mycofiltration of domestic wastewater, and industrial effluent filtration.
According to a 2015 study, mycoremediation can even help with the polycyclic aromatic hydrocarbons (PAH) soil biodegradation. Soils soaked with creosote contain high concentrations of PAH and in order to stop the spread, mycoremediation has proven to be the most successful strategy. | 2 | Environmental Chemistry |
Chlorodifluoromethane or difluoromonochloromethane is a hydrochlorofluorocarbon (HCFC). This colorless gas is better known as HCFC-22, or R-22, or . It was commonly used as a propellant and refrigerant. These applications were phased out under the Montreal Protocol in developed countries in 2020 due to the compound's ozone depletion potential (ODP) and high global warming potential (GWP), and in developing countries this process will be completed by 2030. R-22 is a versatile intermediate in industrial organofluorine chemistry, e.g. as a precursor to tetrafluoroethylene. | 2 | Environmental Chemistry |
Isolated photosystems offer the most direct connection between water photolysis and anode reduction. Typically, photosystems are isolated and adsorbed to a conductive surface. A soluble redox mediator (a small molecule capable of accepting and donating electrons) may be required to improve the electrical communication between photosystem and anode. Because other cellular components required for repair are absent, biological photovoltaic systems based on isolated photosystems have relatively short lifetimes (a few hours) and often require low temperatures to improve stability. | 7 | Physical Chemistry |
Foodomics greatly helps the scientists in an area of food science and nutrition to gain a better access to data, which is used to analyze the effects of food on human health, etc. It is believed to be another step towards better understanding of development and application of technology and food. Moreover, the study of foodomics leads to other omics sub-disciplines, including nutrigenomics which is the integration of the study of nutrition, gene and omics. | 1 | Biochemistry |
Trichrome stains are normally used to differentiate between collagen and muscle tissues. Some studies that benefit from its application include end stage liver disease (cirrhosis), myocardial infarction, muscular dystrophy, and tumor analysis. | 1 | Biochemistry |
After ingestion, is converted to following dissociation of the calcium moiety in the gut. When the HMB-Ca dosage form is ingested, the magnitude and time at which the peak plasma concentration of HMB occurs depends on the dose and concurrent food intake. Higher HMB-Ca doses increase the rate of absorption, resulting in a peak plasma HMB level (C) that is disproportionately greater than expected of a linear dose-response relationship and which occurs sooner relative to lower doses. Consumption of HMB-Ca with sugary substances slows the rate of HMB absorption, resulting in a lower peak plasma HMB level that occurs later. | 1 | Biochemistry |
Carbon tetraiodide is slightly reactive towards water, giving iodoform and I. It is soluble in nonpolar organic solvents. It decomposes thermally and photochemically to , CI. Its synthesis entails AlCl-catalyzed halide exchange, which is conducted at room temperature:
The product crystallizes from the reaction solution.
Carbon tetraiodide is used as an iodination reagent, often upon reaction with bases. Ketones are converted to 1,1-diiodoalkenes upon treatment with triphenylphosphine (PPh) and carbon tetraiodide. Alcohols are converted in and to iodide, by a mechanism similar to the Appel reaction. In an Appel reaction, carbon tetrachloride is used to generate alkyl chlorides from alcohols. | 0 | Organic Chemistry |
In general, in a group across the periodic table, the more basic the ion (the higher the pK of the conjugate acid) the more reactive it is as a nucleophile. Within a series of nucleophiles with the same attacking element (e.g. oxygen), the order of nucleophilicity will follow basicity. Sulfur is in general a better nucleophile than oxygen. | 7 | Physical Chemistry |
DNA banking is used to conserve genetic material, especially that of organisms that face extinction. This is a more prominent issue today due to deforestation and climate change, which serve as a threat to biodiversity. The genetic information can be stored within lambda phage and plasma vectors. The National Institute of Agrobiological Sciences (NIAS) DNA Bank, for example, collects the DNA of agricultural organisms, such as rice and fish, for scientific research. Most DNA provided by DNA banks is used for studies to attempt to develop more productive or more environmentally friendly agricultural species. Some DNA banks also store the DNA of rare or endangered species to ensure their survival.
The DNA bank can be used to compare and analyze DNA samples. Comparison of DNA samples allowed scientists to work on the Human Genome Project, which maps out many of the genes on human DNA. It has also led to the development of preventive genetics. Samples from the DNA bank have been used to identify patterns and determine which genes lead to specific disorders. Once people know which genes lead to disorders, people can take steps to lessen the effects of that disorder. This can occur through adjustments in lifestyle, as demonstrated in preventive healthcare, or even through gene therapy. DNA can be banked at any time during a person's life.
DNA banks were introduced to the criminal justice system in the 1980s. This system makes it possible to rule out or confirm the verdict of a suspect based on their personal genetic code. Once an individual’s DNA is stored, it remains in the system permanently; allowing law enforcement to identify and track criminals more easily. There is some controversy about this topic as some individuals believe the storage of citizen's DNA is an invasion of privacy.
DNA banking capsules are also starting to be used for retaining the DNA of the deceased, a service offered by some funeral homes. | 1 | Biochemistry |
The backbone and side-chain dihedral angles of protein and RNA have been shown to have specific combinations of angles which are allowed (or forbidden). For protein backbone dihedrals (φ, ψ), this has been addressed by the legendary Ramachandran Plot while for side-chain dihedrals (χ's), one should refer to the Dunbrack Backbone-dependent rotamer library.
Though, mRNA structures are generally short-lived and single-stranded, there are an abundance of non-coding RNAs with different secondary and tertiary folding (tRNA, rRNA etc.) which contain a preponderance of the canonical Watson-Crick (WC) base-pairs, together with significant number of non-Watson Crick (NWC) base-pairs - for which such RNA also qualify for regular structural validation that apply for nucleic acid helices. The standard practice is to analyse the intra- (Transnational: Shift, Slide, Rise; Rotational: Tilt, Roll, Twist) and inter-base-pair geometrical parameters (Transnational: Shear, Stagger, Stretch, Rotational: Buckle, Propeller, Opening) - whether in-range or out-of-range with respect to their suggested values. These parameters describe the relative orientations of the two paired bases with respect to each other in two strands (intra) along with those of the two stacked base pairs (inter) with respect to each other, and, hence, together, they serve to validate nucleic acid structures in general. Since, RNA-helices are small in length (average: 10-20 bps), the use of electrostatic surface potential as a validation parameter has been found to be beneficial, particularly for modelling purposes. | 1 | Biochemistry |
In metallurgy, hot working refers to processes where metals are plastically deformed above their recrystallization temperature. Being above the recrystallization temperature allows the material to recrystallize during deformation. This is important because recrystallization keeps the materials from strain hardening, which ultimately keeps the yield strength and hardness low and ductility high. This contrasts with cold working.
Many kinds of working, including rolling, forging, extrusion, and drawing, can be done with hot metal. | 8 | Metallurgy |
Modern high-pressure thermal cracking operates at absolute pressures of about 7,000 kPa. An overall process of disproportionation can be observed, where "light", hydrogen-rich products are formed at the expense of heavier molecules which condense and are depleted of hydrogen. The actual reaction is known as homolytic fission and produces alkenes, which are the basis for the economically important production of polymers.
Thermal cracking is currently used to "upgrade" very heavy fractions or to produce light fractions or distillates, burner fuel and/or petroleum coke. Two extremes of the thermal cracking in terms of the product range are represented by the high-temperature process called "steam cracking" or pyrolysis (ca. 750 °C to 900 °C or higher) which produces valuable ethylene and other feedstocks for the petrochemical industry, and the milder-temperature delayed coking (ca. 500 °C) which can produce, under the right conditions, valuable needle coke, a highly crystalline petroleum coke used in the production of electrodes for the steel and aluminium industries.
William Merriam Burton developed one of the earliest thermal cracking processes in 1912 which operated at and an absolute pressure of and was known as the Burton process. Shortly thereafter, in 1921, C.P. Dubbs, an employee of the Universal Oil Products Company, developed a somewhat more advanced thermal cracking process which operated at and was known as the Dubbs process. The Dubbs process was used extensively by many refineries until the early 1940s when catalytic cracking came into use. | 0 | Organic Chemistry |
Circuit-breakers can be placed at portions of a circuit in series to the path of current it will affect. If more current than expected goes through the circuit-breaker, the circuit breaker "opens" the circuit and stops all current. A fuse is a common type of circuit breaker that involves direct effect of Joule-overheating. A fuse is always placed in series with the path of current it will affect. Fuses usually consist of a thin strand of wire of definite-material. When more that the rated current flows through the fuse, the wire melts and breaks the circuit. | 7 | Physical Chemistry |
Dideoxynucleotides are used in sequencing. These nucleoside triphosphates possess a non-canonical sugar, dideoxyribose, which lacks the 3 hydroxyl group normally present in DNA and therefore cannot bond with the next base. The lack of the 3 hydroxyl group terminates the chain reaction as the DNA polymerases mistake it for a regular deoxyribonucleotide. Another chain-terminating analogue that lacks a 3' hydroxyl and mimics adenosine is called cordycepin. Cordycepin is an anticancer drug that targets RNA replication. Another analogue in sequencing is a nucleobase analogue, 7-deaza-GTP and is used to sequence CG rich regions, instead 7-deaza-ATP is called tubercidin, an antibiotic. | 1 | Biochemistry |
Protein methylation typically takes place on arginine or lysine amino acid residues in the protein sequence. Arginine can be methylated once (monomethylated arginine) or twice, with either both methyl groups on one terminal nitrogen (asymmetric dimethylarginine) or one on both nitrogens (symmetric dimethylarginine), by protein arginine methyltransferases (PRMTs). Lysine can be methylated once, twice, or three times by lysine methyltransferases. Protein methylation has been most studied in the histones. The transfer of methyl groups from S-adenosyl methionine to histones is catalyzed by enzymes known as histone methyltransferases. Histones that are methylated on certain residues can act epigenetically to repress or activate gene expression. Protein methylation is one type of post-translational modification. | 0 | Organic Chemistry |
Mitogen-activated protein kinase (MAPK) networks are the pathways and signaling of MAPK, which is a protein kinase that consists of amino acids serine and threonine. MAPK pathways have both a positive and negative regulation in plants. A positive regulation of MAPK networks is to help in assisting with stresses from the environment. A negative regulation of MAPK networks is pertaining to a high quantity of reactive oxygen species (ROS) in the plant. | 1 | Biochemistry |
RP-CARS takes advantage of the polarization-dependent selection rules to detect the local microscopic orientation of the chemical bonds under investigation. By means of RP-CARS it is possible to visualize the
degree of orientation anisotropy of selected molecular bonds and to detect their average orientation direction.
It is possible by continuously rotating the orientation of the polarization plane of the incident light with a rotating waveplate and then, sequentially, for each image pixel, analysing the orientation dependence of the CARS signal intensity. This allows measuring for each pixel the average-orientation plane of the molecular bonds of interest and the degree of this spatial anisotropy in the point-spread-function volume. | 3 | Analytical Chemistry |
Post-translational modification is the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis for many proteins. | 1 | Biochemistry |
Section D ON Storage and Transport of the IIR is involved in the controlled-temperature logistics and distribution of temperature-sensitive products, from foodstuffs to health products (medicines, vaccines, blood products, organs ...) from artwork to chemicals.
It addresses all issues of equipment and solutions for a durable cold chain from the production or manufacture, to the consumption or use of these products.
Section D thus covers the issues of storage, transportation by land, air or water, packaging, distribution and delivery of these products to the consumer, and the traceability of the cold chain.
The Section is involved in warehouse and platform equipment, devices for temperature-controlled transport, coolants or cool packs, small coolers and refrigerated containers, chillers, refrigerated furnishings, refrigerated cabinets, climate chambers, refrigerators and freezers, but also to thermometers and temperature recorders.
The cold chain involves many temperature ranges, both positive and negative, from -80 °C to + 63 °C.
* Commission D1: Refrigerated Storage
Commission D1 on Refrigerated Storage deals with the storage of all products which require temperature control, such as food and pharmaceuticals. Industrial, commercial and residential storage are also taken into account so that, in cooperation with Commission D2 Refrigerated Transport, the entire cold chain is treated, from raw materials to the final product at our home. Refrigeration plays an essential role for perishable products. While the estimated capacity of refrigerated warehouses was over 500 million cubic meters worldwide in 2014, in some countries global food losses due to the lack of a cold chain are still very important and can reach as much as 20% of the global food supply. At the same time, in heavily industrialised countries, the use of commercial and domestic refrigerators accounts for up to 6% of global electricity consumption.
As a result, the Commission faces important issues in order to promote widespread, energy efficient and environmentally friendly storage systems. New refrigerants, synergies to save or exchange energy with other systems and new technologies are the main focus of its activity. One of the most important themes in these days for this commission is energy efficiency
* Commission D2: Refrigerated Transport
The IIRs Commission D2 on Refrigerated Transport is extremely active. In addition to the IIRs four yearly congress, Commission D2 participates in the IIR Conference on Sustainability and the Cold Chain, held out of synchronisation to the congress.
Every year, Commission D2 CERTE test engineers meet in a European country to discuss refrigerated transport technology and testing issues. This group subsequently advises the United Nations working party on transport of perishable foodstuffs held each year in Geneva. Commission D2 is currently addressing the “Cold Chain for Pharmaceutical Products” and will add this to regular transport discussion and advisory topics. Commission D2 also helps to produce Informatory Notes to assist in areas of technical or regulatory difficulty.
The role of the IIR is well recognized, and in particular, the expertise of the members of Commission D2 makes an important contribution to refrigerated transport issues: reducing food wastage and minimizing emissions. | 7 | Physical Chemistry |
Cellular models are instrumental in dissecting a complex pathological process into simpler molecular events. Parkinson's disease (PD) is multifactorial and clinically heterogeneous; the aetiology of the sporadic (and most common) form is still unclear and only a few molecular mechanisms have been clarified so far in the neurodegenerative cascade. In such a multifaceted picture, it is particularly important to identify experimental models that simplify the study of the different networks of proteins and genes involved. Cellular models that reproduce some of the features of the neurons that degenerate in PD have contributed to many advances in our comprehension of the pathogenic flow of the disease. In particular, the pivotal biochemical pathways (i.e. apoptosis and oxidative stress, mitochondrial impairment and dysfunctional mitophagy, unfolded protein stress and improper removal of misfolded proteins) have been widely explored in cell lines, challenged with toxic insults or genetically modified. The central role of a-synuclein has generated many models aiming to elucidate its contribution to the dysregulation of various cellular processes. Classical cellular models appear to be the correct choice for preliminary studies on the molecular action of new drugs or potential toxins and for understanding the role of single genetic factors. Moreover, the availability of novel cellular systems, such as cybrids or induced pluripotent stem cells, offers the chance to exploit the advantages of an in vitro investigation, although mirroring more closely the cell population being affected. | 7 | Physical Chemistry |
The oxygen minimum zone (OMZ), sometimes referred to as the shadow zone, is the zone in which oxygen saturation in seawater in the ocean is at its lowest. This zone occurs at depths of about , depending on local circumstances. OMZs are found worldwide, typically along the western coast of continents, in areas where an interplay of physical and biological processes concurrently lower the oxygen concentration (biological processes) and restrict the water from mixing with surrounding waters (physical processes), creating a "pool" of water where oxygen concentrations fall from the normal range of 4–6 mg/L to below 2 mg/L. | 9 | Geochemistry |
was a Japanese organic chemist. One of the most prolific chemists of the 20th century in the field of organic synthesis, Mukaiyama helped establish the field of organic chemistry in Japan after World War II. | 0 | Organic Chemistry |
There are three known mammalian tachykinin receptors termed NK, NK and NK. All are members of the 7 transmembrane G-protein coupled receptor family and induce the activation of phospholipase C, producing inositol triphosphate (so called G-coupled).
Inhibitors of NK-1, known as NK-1 receptor antagonists, can be used as antiemetic agents, such as the drug aprepitant. | 1 | Biochemistry |
Acetoacetic ester synthesis is a chemical reaction where ethyl acetoacetate is alkylated at the α-carbon to both carbonyl groups and then converted into a ketone, or more specifically an α-substituted acetone. This is very similar to malonic ester synthesis. | 0 | Organic Chemistry |
Passing–Bablok regression is a method from robust statistics for nonparametric regression analysis suitable for method comparison studies introduced by Wolfgang Bablok and Heinrich Passing in 1983. The procedure is adapted to fit linear errors-in-variables models. It is symmetrical and is robust in the presence of one or few outliers.
The Passing-Bablok procedure fits the parameters and of the linear equation using non-parametric methods. The coefficient is calculated by taking the shifted median of all slopes of the straight lines between any two points, disregarding lines for which the points are identical or . The median is shifted based on the number of slopes where to create an approximately consistent estimator. The estimator is therefore close in spirit to the Theil-Sen estimator. The parameter is calculated by .
In 1986, Passing and Bablok extended their method introducing an equivariant extension for method transformation which also works when the slope is far from 1.
It may be considered a robust version of reduced major axis regression. The slope estimator is the median of the absolute values of all pairwise slopes.
The original algorithm is rather slow for larger data sets as its computational complexity is . However, fast quasilinear algorithms of complexity ln have been devised.
Passing and Bablok define a method for calculating a 95% confidence interval (CI) for both and in their original paper, which was later refined, though bootstrapping the parameters is the preferred method for in vitro diagnostics (IVD) when using patient samples. The Passing-Bablok procedure is valid only when a linear relationship exists between and , which can be assessed by a CUSUM test. Further assumptions include the error ratio to be proportional to the slope and the similarity of the error distributions of the and distributions.
The results are interpreted as follows. If 0 is in the CI of , and 1 is in the CI of , the two methods are comparable within the investigated concentration range. If 0 is not in the CI of there is a systematic difference and if 1 is not in the CI of then there is a proportional difference between the two methods.
However, the use of Passing–Bablok regression in method comparison studies has been criticized because it ignores random differences between methods. | 3 | Analytical Chemistry |
UV degradation is one form of polymer degradation that affects plastics exposed to sunlight. The problem appears as discoloration or fading, cracking, loss of strength or disintegration. The effects of attack increase with exposure time and sunlight intensity. The addition of UV absorbers inhibits the effect.
Sensitive polymers include thermoplastics and speciality fibers like aramids. UV absorption leads to chain degradation and loss of strength at sensitive points in the chain structure. Aramid rope must be shielded with a sheath of thermoplastic if it is to retain its strength.
Many pigments and dyes absorb UV and change colour, so paintings and textiles may need extra protection both from sunlight and fluorescent lamps, two common sources of UV radiation. Window glass absorbs some harmful UV, but valuable artifacts need extra shielding. Many museums place black curtains over watercolour paintings and ancient textiles, for example. Since watercolours can have very low pigment levels, they need extra protection from UV. Various forms of picture framing glass, including acrylics (plexiglass), laminates, and coatings, offer different degrees of UV (and visible light) protection. | 5 | Photochemistry |
The central issue of the formation of a quark–gluon plasma is the research for the onset of deconfinement. From the beginning of the research on formation of QGP, the issue was whether energy density can be achieved in nucleus-nucleus collisions. This depends on how much energy each nucleon loses. An influential reaction picture was the scaling solution presented by Bjorken. This model applies to ultra-high energy collisions. In experiments carried out at CERN SPS and BNL RHIC more complex situation arose, usually divided into three stages:
* Primary parton collisions and baryon stopping at the time of complete overlapping of the colliding nuclei.
* Redistribution of particle energy and new particles born in the QGP fireball.
* The fireball of QGP matter equilibrates and expands before hadronizing.
More and more experimental evidence points to the strength of QGP formation mechanisms—operating even in LHC-energy scale proton-proton collisions. | 7 | Physical Chemistry |
Depending on the environment developed in the crevice and the nature of the metal, the crevice corrosion can take a form of:
* pitting (i.e., formation of pits), but note pitting and crevice corrosion are not the same phenomenon,
* filiform corrosion (this type of crevice corrosion that may occur on a metallic surface underneath an organic coating),
* intergranular attack, or,
* stress corrosion cracking. | 8 | Metallurgy |
The insertion of alkenes into both metal-carbon is important. The insertion of ethylene and propylene into titanium alkyls is the cornerstone of Ziegler–Natta catalysis, the main source of polyethylene and polypropylene. The majority of this technology involves heterogeneous catalysts, but it is widely assumed that the principles and observations on homogeneous systems are applicable to the solid-state versions. Related technologies include the Shell Higher Olefin Process which produces detergent precursors. | 0 | Organic Chemistry |
Also shown on the map is a typical steady state working (or operating/running) line. This is a locus of the operating points of the engine, as it is throttled.
Being a high pressure ratio device, the working line is relatively shallow. If the unit had no variable geometry, there would be handling problems, because the surge line would be very steep and cross the working line at part-flow.
During a slam-acceleration from a mid-throttle setting, the compressor working line will move rapidly towards surge and then slowly approach the steady state operating point, further up the map. The reverse effect occurs during a slam-deceleration. These effects are caused by the sluggish response of the spool (i.e. inertia effects) to rapid changes in engine fuel flow. Compressor surge is a particular problem during slam-accelerations and can be overcome by suitable adjustments to the fueling schedule and/or use of blow-off (bleeding air off the compressor, for handling purposes).
In the particular example shown, a slam-acceleration from ground idle would cause a high-pressure compressor surge. Opening the blow-off would help, but some changes to the variable stator schedule might also be required.
Because a high-pressure compressor sees the choked flow capacity of the high-pressure turbine, the compressor working line is hardly affected by flight conditions. The slope of the working line approximates to a constant corrected outlet flow. | 7 | Physical Chemistry |
2-Chlorocarboxylic acids can be reduced with lithium aluminium hydride to the 2-chloroalcohols. The required 2-chlorocarboxylic acids are obtained in a variety of ways, including the Hell–Volhard–Zelinsky halogenation. 2-Chloropropionic acid is produced by chlorination of propionyl chloride followed by hydrolysis of the 2-chloropropionyl chloride. Enantiomerically pure (S)-2-chloropropionic acid and several related compounds can be prepared from amino acids via diazotization. | 0 | Organic Chemistry |
Anthoxanthins (flavones and flavonols) are a type of flavonoid pigments in plants. Anthoxanthins are water-soluble pigments which range in color from white or colorless to a creamy to yellow, often on petals of flowers. These pigments are generally whiter in an acid medium and yellowed in an alkaline medium. They are very susceptible to color changes with minerals and metal ions, similar to anthocyanins. | 2 | Environmental Chemistry |
Plasmonic nanoparticles are particles whose electron density can couple with electromagnetic radiation of wavelengths that are far larger than the particle due to the nature of the dielectric-metal interface between the medium and the particles: unlike in a pure metal where there is a maximum limit on what size wavelength can be effectively coupled based on the material size.
What differentiates these particles from normal surface plasmons is that plasmonic nanoparticles also exhibit interesting scattering, absorbance, and coupling properties based on their geometries and relative positions. These unique properties have made them a focus of research in many applications including solar cells, spectroscopy, signal enhancement for imaging, and cancer treatment. Their high sensitivity also identifies them as good candidates for designing mechano-optical instrumentation.
Plasmons are the oscillations of free electrons that are the consequence of the formation of a dipole in the material due to electromagnetic waves. The electrons migrate in the material to restore its initial state; however, the light waves oscillate, leading to a constant shift in the dipole that forces the electrons to oscillate at the same frequency as the light. This coupling only occurs when the frequency of the light is equal to or less than the plasma frequency and is greatest at the plasma frequency that is therefore called the resonant frequency. The scattering and absorbance cross-sections describe the intensity of a given frequency to be scattered or absorbed. Many fabrication processes or chemical synthesis methods exist for preparation of such nanoparticles, depending on the desired size and geometry.
The nanoparticles can form clusters (the so-called "plasmonic molecules") and interact with each other to form cluster states. The symmetry of the nanoparticles and the distribution of the electrons within them can affect a type of bonding or antibonding character between the nanoparticles similarly to molecular orbitals. Since light couples with the electrons, polarized light can be used to control the distribution of the electrons and alter the mulliken term symbol for the irreducible representation. Changing the geometry of the nanoparticles can be used to manipulate the optical activity and properties of the system, but so can the polarized light by lowering the symmetry of the conductive electrons inside the particles and changing the dipole moment of the cluster. These clusters can be used to manipulate light on the nano scale. | 7 | Physical Chemistry |
Mass cytometry is a mass spectrometry technique based on inductively coupled plasma mass spectrometry and time of flight mass spectrometry used for the determination of the properties of cells (cytometry). In this approach, antibodies are conjugated with isotopically pure elements, and these antibodies are used to label cellular proteins. Cells are nebulized and sent through an argon plasma, which ionizes the metal-conjugated antibodies. The metal signals are then analyzed by a time-of-flight mass spectrometer. The approach overcomes limitations of spectral overlap in flow cytometry by utilizing discrete isotopes as a reporter system instead of traditional fluorophores which have broad emission spectra. | 3 | Analytical Chemistry |
The introduction of whole genome sequencing may have ethical implications. On one hand, genetic testing can potentially diagnose preventable diseases, both in the individual undergoing genetic testing and in their relatives. On the other hand, genetic testing has potential downsides such as genetic discrimination, loss of anonymity, and psychological impacts such as discovery of non-paternity.
Some ethicists insist that the privacy of individuals undergoing genetic testing must be protected, and is of particular concern when minors undergo genetic testing. Illuminas CEO, Jay Flatley, claimed in February 2009 that "by 2019 it will have become routine to map infants genes when they are born". This potential use of genome sequencing is highly controversial, as it runs counter to established ethical norms for predictive genetic testing of asymptomatic minors that have been well established in the fields of medical genetics and genetic counseling. The traditional guidelines for genetic testing have been developed over the course of several decades since it first became possible to test for genetic markers associated with disease, prior to the advent of cost-effective, comprehensive genetic screening.
When an individual undergoes whole genome sequencing, they reveal information about not only their own DNA sequences, but also about probable DNA sequences of their close genetic relatives. This information can further reveal useful predictive information about relatives' present and future health risks. Hence, there are important questions about what obligations, if any, are owed to the family members of the individuals who are undergoing genetic testing. In Western/European society, tested individuals are usually encouraged to share important information on any genetic diagnoses with their close relatives, since the importance of the genetic diagnosis for offspring and other close relatives is usually one of the reasons for seeking a genetic testing in the first place. Nevertheless, a major ethical dilemma can develop when the patients refuse to share information on a diagnosis that is made for serious genetic disorder that is highly preventable and where there is a high risk to relatives carrying the same disease mutation. Under such circumstances, the clinician may suspect that the relatives would rather know of the diagnosis and hence the clinician can face a conflict of interest with respect to patient-doctor confidentiality.
Privacy concerns can also arise when whole genome sequencing is used in scientific research studies. Researchers often need to put information on patient's genotypes and phenotypes into public scientific databases, such as locus specific databases. Although only anonymous patient data are submitted to locus specific databases, patients might still be identifiable by their relatives in the case of finding a rare disease or a rare missense mutation. Public discussion around the introduction of advanced forensic techniques (such as advanced familial searching using public DNA ancestry websites and DNA phenotyping approaches) has been limited, disjointed, and unfocused. As forensic genetics and medical genetics converge toward genome sequencing, issues surrounding genetic data become increasingly connected, and additional legal protections may need to be established. | 1 | Biochemistry |
An initial assumption is that the number of molecular orbitals is equal to the number of atomic orbitals included in the linear expansion. In a sense, n atomic orbitals combine to form n molecular orbitals, which can be numbered i = 1 to n and which may not all be the same. The expression (linear expansion) for the i th molecular orbital would be:
or
where is a molecular orbital represented as the sum of n atomic orbitals , each multiplied by a corresponding coefficient , and r (numbered 1 to n) represents which atomic orbital is combined in the term. The coefficients are the weights of the contributions of the n atomic orbitals to the molecular orbital. The Hartree–Fock method is used to obtain the coefficients of the expansion.
The orbitals are thus expressed as linear combinations of basis functions, and the basis functions are single-electron functions which may or may not be centered on the nuclei of the component atoms of the molecule. In either case the basis functions are usually also referred to as atomic orbitals (even though only in the former case this name seems to be adequate). The atomic orbitals used are typically those of hydrogen-like atoms since these are known analytically i.e. Slater-type orbitals but other choices are possible such as the Gaussian functions from standard basis sets or the pseudo-atomic orbitals from plane-wave pseudopotentials.
By minimizing the total energy of the system, an appropriate set of coefficients of the linear combinations is determined. This quantitative approach is now known as the Hartree–Fock method. However, since the development of computational chemistry, the LCAO method often refers not to an actual optimization of the wave function but to a qualitative discussion which is very useful for predicting and rationalizing results obtained via more modern methods. In this case, the shape of the molecular orbitals and their respective energies are deduced approximately from comparing the energies of the atomic orbitals of the individual atoms (or molecular fragments) and applying some recipes known as level repulsion and the like. The graphs that are plotted to make this discussion clearer are called correlation diagrams. The required atomic orbital energies can come from calculations or directly from experiment via Koopmans' theorem.
This is done by using the symmetry of the molecules and orbitals involved in bonding, and thus is sometimes called symmetry adapted linear combination (SALC). The first step in this process is assigning a point group to the molecule. Each operation in the point group is performed upon the molecule. The number of bonds that are unmoved is the character of that operation. This reducible representation is decomposed into the sum of irreducible representations. These irreducible representations correspond to the symmetry of the orbitals involved.
Molecular orbital diagrams provide simple qualitative LCAO treatment. The Hückel method, the extended Hückel method and the Pariser–Parr–Pople method, provide some quantitative theories. | 7 | Physical Chemistry |
Free radicals derived from mercaptans, called thiyl radicals, are commonly invoked to explain reactions in organic chemistry and biochemistry. They have the formula RS where R is an organic substituent such as alkyl or aryl. They arise from or can be generated by a number of routes, but the principal method is H-atom abstraction from thiols. Another method involves homolysis of organic disulfides. In biology thiyl radicals are responsible for the formation of the deoxyribonucleic acids, building blocks for DNA. This conversion is catalysed by ribonucleotide reductase (see figure). Thiyl intermediates also are produced by the oxidation of glutathione, an antioxidant in biology. Thiyl radicals (sulfur-centred) can transform to carbon-centred radicals via hydrogen atom exchange equilibria. The formation of carbon-centred radicals could lead to protein damage via the formation of C−C bonds or backbone fragmentation.
Because of the weakness of the S−H bond, thiols can function as scavengers of free radicals. | 0 | Organic Chemistry |
#Antibody coating: Throughout the ELISpot Assay technique, different substances are added to and washed away from wells. Wells are found on a laboratory plate with tiny dishes/bowls that can be filled with a substance to be examined; the amount of wells on a plate varies, but it usually ranges from 16-100. The first substance added to the wells are cytokine specific monoclonal antibodies. These antibodies coat the walls of the wells for future binding to cytokine. The monoclonal antibodies means that the antibody is produced from a single cell lineage, and is only able to bind to one protein epitope. Polyclonal antibodies, on the other hand, are capable of binding to multiple epitopes of the same protein.
#Cell incubation: The desired cells being observed and analyzed are added to the wells. Each well can have the presence or absence of stimuli that activate the secretion of cytokine in cells. During cell incubation, the cells are allowed to react to any present stimuli and secrete cytokine. There are many procedures and methods to follow to ensure proper cell handling. To make sure that cells are of high quality, cells in blood samples should be lightly agitated if stored for longer than 3 hours, the blood samples should be diluted in PBS (phosphate buffered saline) before being stored, and the blood samples should not have granulocytes. Any cells that have been cryopreserved and thawed should be allowed to rest for an hour or more at 37 degrees Celsius (the typical temperature of the human body). There are also many things that should be taken into consideration when incubating the cells, such as making sure that the cells do not experience sudden movements that could affect spot formation, or that the incubator's humidity is high enough to avoid excessive evaporation and drying out the wells.
#Cytokine capture: Since the cells are surrounded by cytokine specific monoclonal antibodies that coat the walls of the wells, cytokine that has been secreted by the incubated cells will start to attach to the antibodies at a specific epitope.
#Detection antibodies: At this point, the wells must be rinsed in order to get rid of the cells and any other undesirable substances. All that should remain are the cytokine specific monoclonal antibodies and any cytokine that bonded to the antibodies. Biotinylated cytokine-specific detection antibodies are then added to the well. These cytokine-specific detection antibodies will bind to any cytokine that is left in the well since the cytokine is still attached to the first set of antibodies used. Since the cytokine attached to the first set of antibodies coating the wells, the cytokine was not washed away when the wells were rinsed.
#Streptavidin-enzyme conjugate: Streptavidin-enzyme conjugate is added to the wells in order to bind with the detection antibodies. The purpose of biotinylating the cytokine-specific detection antibodies added to the wells in the previous step is so that the antibody can bind to the new streptavidin-enzyme conjugate. Biotinylation basically creates a strong affinity between the biotin on the cytokine-specific antibody and the streptavidin on the conjugate.
#Addition of substrate: A substrate is added to the wells, and is catalyzed by the enzyme conjugate added in the previous step. This reaction forms insoluble precipitate that forms spots in the wells. The substrate that you use in this step will depend on the type of enzyme used in the previous step. If streptavidin-ALP (streptavidin and alkaline phosphatase conjugate) is used, then using BCIP/NBT-plus (a mixture of 5-bromo-4-chloro-3-indolyl phosphate and nitroblue tetrazolium chloride) as a substrate will produce more distinct spots that are easier to analyze. If streptavidin-HRP (streptavidin and horseradish peroxidase conjugate) is used, then using TMB (tetramethylbenzidine) as a substrate will produce better results.
#Analysis: The spots that are formed can then be read on an automated ELISpot reader, or counted under a dissection microscope, and further used to calculate the frequency of cytokine secretion. | 1 | Biochemistry |
This way of evaluation deals with agar-agar or gelatine containing semi-solid layers made prior to the experiment. Small wells are cut into the layer and filled with cells and the test substance. Cells can migrate towards the chemical gradient in the semi solid layer or under the layer as well. Some variations of the technique deal also with wells and parallel channels connected by a cut at the start of the experiment (PP-technique). Radial arrangement of PP-technique (3 or more channels) provides the possibility to compare chemotactic activity of different cell populations or study preference between ligands.
Counting of cells: positive responder cells could be counted from the front of migrating cells, after staining or in native conditions in light microscope. | 1 | Biochemistry |
During the late 1940s, Woodward synthesized many complex natural products including quinine, cholesterol, cortisone, strychnine, lysergic acid, reserpine, chlorophyll, cephalosporin, and colchicine. With these, Woodward opened up a new era of synthesis, sometimes called the Woodwardian era in which he showed that natural products could be synthesized by careful applications of the principles of physical organic chemistry, and by meticulous planning.
Many of Woodwards syntheses were described as spectacular by his colleagues and before he did them, it was thought by some that it would be impossible to create these substances in the lab. Woodwards syntheses were also described as having an element of art in them, and since then, synthetic chemists have always looked for elegance as well as utility in synthesis. His work also involved the exhaustive use of the then newly developed techniques of infrared spectroscopy and later, nuclear magnetic resonance spectroscopy. Another important feature of Woodwards syntheses was their attention to stereochemistry or the particular configuration of molecules in three-dimensional space. Most natural products of medicinal importance are effective, for example as drugs, only when they possess a specific stereochemistry. This creates the demand for stereoselective synthesis', producing a compound with a defined stereochemistry. While today a typical synthetic route routinely involves such a procedure, Woodward was a pioneer in showing how, with exhaustive and rational planning, one could conduct reactions that were stereoselective. Many of his syntheses involved forcing a molecule into a certain configuration by installing rigid structural elements in it, another tactic that has become standard today. In this regard, especially his syntheses of reserpine and strychnine were landmarks.
During World War II, Woodward was an advisor to the War Production Board on the penicillin project. Although often given credit for proposing the beta-lactam structure of penicillin, it was actually first proposed by chemists at Merck and Edward Abraham at Oxford and then investigated by other groups, as well (e.g., Shell). Woodward at first endorsed an incorrect tricyclic (thiazolidine fused, amino bridged oxazinone) structure put forth by the penicillin group at Peoria. Subsequently, he put his imprimatur on the beta-lactam structure, all of this in opposition to the thiazolidine–oxazolone structure proposed by Robert Robinson, the then leading organic chemist of his generation. Ultimately, the beta-lactam structure was shown to be correct by Dorothy Hodgkin using X-ray crystallography in 1945.
Woodward also applied the technique of infrared spectroscopy and chemical degradation to determine the structures of complicated molecules. Notable among these structure determinations were santonic acid, strychnine, magnamycin and terramycin. In each one of these cases, Woodward again showed how rational facts and chemical principles, combined with chemical intuition, could be used to achieve the task.
In the early 1950s, Woodward, along with the British chemist Geoffrey Wilkinson, then at Harvard, postulated a novel structure for ferrocene, a compound consisting of a combination of an organic molecule with iron. This marked the beginning of the field of transition metal organometallic chemistry which grew into an industrially very significant field. Wilkinson won the Nobel Prize for this work in 1973, along with Ernst Otto Fischer. Some historians think that Woodward should have shared this prize along with Wilkinson. Remarkably, Woodward himself thought so, and voiced his thoughts in a letter sent to the Nobel Committee.
Woodward won the Nobel Prize in 1965 for his synthesis of complex organic molecules. He had been nominated a total of 111 times from 1946 to 1965. In his Nobel lecture, he described the total synthesis of the antibiotic cephalosporin, and claimed that he had pushed the synthesis schedule so that it would be completed around the time of the Nobel ceremony. | 4 | Stereochemistry |
;Surrounding animals
:Although the pheromone may diffuse off as a territorial representation of the foraging organism, that does not secure the safety of the organism. In fact, this act may do the opposite and attract competing wildlife. With more surrounding predators, or competitors, comes more difficulty with foraging for a food source. Especially in cases were food is scarce, surrounding organism. Depending on the cost vs benefits tradeoff, an organism, in a situation where it may need the food supply, may be willing to risk the dangers to obtain it. Also, with more predators or competitors out there, the risks of foraging increase.
;Surrounding plants
:Factors such as type and abundance of surrounding plants in an environment may certainly affect the degree of trail pheromone potency. Plants residing in close proximity to the odor trail may emit an abundance of chemicals which can either mask, change, or possibly even help propagate the signal. Additionally, areas saturated with plant life may block or alter trail pheromone diffusion. | 1 | Biochemistry |
In the 1980s and 1990s, silicon carbide was studied in several research programs for high-temperature gas turbines in Europe, Japan and the United States. The components were intended to replace nickel superalloy turbine blades or nozzle vanes. However, none of these projects resulted in a production quantity, mainly because of its low impact resistance and its low fracture toughness.
Like other hard ceramics (namely alumina and boron carbide), silicon carbide is used in composite armor (e.g. Chobham armor), and in ceramic plates in bulletproof vests. Dragon Skin, which was produced by Pinnacle Armor, used disks of silicon carbide. Improved fracture toughness in SiC armor can be facilitated through the phenomenon of abnormal grain growth or AGG. The growth of abnormally long silicon carbide grains may serve to impart a toughening effect through crack-wake bridging, similar to whisker reinforcement. Similar
AGG-toughening effects have been reported in Silicon nitride (SiN).
Silicon carbide is used as a support and shelving material in high temperature kilns such as for firing ceramics, glass fusing, or glass casting. SiC kiln shelves are considerably lighter and more durable than traditional alumina shelves.
In December 2015, infusion of silicon carbide nano-particles in molten magnesium was mentioned as a way to produce a new strong and plastic alloy suitable for use in aeronautics, aerospace, automobile and micro-electronics. | 8 | Metallurgy |
The Mark IV Cell design was introduced in 2009. It included the following improvements:
* a flexible hose for easier alignment of the downcomer
* clamping of the slurry lens onto the downcomer (see Figure 10)
* stainless steel quick-release clamps in the downcomer assembly
* long-lasting rubber flaps in the AISE valves. | 8 | Metallurgy |
Log reduction is a measure of how thoroughly a decontamination process reduces the concentration of a contaminant.
It is defined as the common logarithm of the ratio of the levels of contamination before and after the process, so an increment of 1 corresponds to a reduction in concentration by a factor of 10.
In general, an -log reduction means that the concentration of remaining contaminants is only times that of the original. So for example, a 0-log reduction is no reduction at all, while a 1-log reduction corresponds to a reduction of 90 percent from the original concentration, and a 2-log reduction corresponds to a reduction of 99 percent from the original concentration. | 3 | Analytical Chemistry |
The European Association of Geochemistry gives the following awards:
* The Urey Medal (European Association of Geochemistry) for outstanding contributions advancing geochemistry over a career.
* The Science Innovation Award for an important and innovative breakthrough in geochemistry.
* The Houtermans Award for exceptional contributions to geochemistry made by scientists under 35 years old.
* Geochemical Fellows – Awarded annually by the Geochemical Society and the European Association of Geochemistry to outstanding scientists who have, over some years, made a major contribution to the field of geochemistry. | 9 | Geochemistry |
In Population-based rule evaluation, rules are applied to populations. All molecules of the same species in the same state are pooled together. Application of a specific rule reduces or increases the size of one of the pools, possibly at the expense of another.
Some of the best-known classes of simulation approaches in computational biology belong to the population-based family, including those based on the numerical integration of ordinary and partial differential equations and the Gillespie stochastic simulation algorithm.
Differential equations describe changes in molecular concentrations over time in a deterministic manner. Simulations based on differential equations usually do not attempt to solve those equations analytically, but employ a suitable numerical solver.
The stochastic Gillespie algorithm changes the composition of pools of molecules through a progression of randomness reaction events, the probability of which is computed from reaction rates and from the numbers of molecules, in accordance with the stochastic master equation.
In population-based approaches, one can think of the system being modeled as being in a given state at any given time point, where a state is defined according to the nature and size of the populated pools of molecules. This means that the space of all possible states can become very large. With some simulation methods implementing numerical integration of ordinary and partial differential equations or the Gillespie stochastic algorithm, all possible pools of molecules and the reactions they undergo are defined at the start of the simulation, even if they are empty. Such "generate-first" methods scale poorly with increasing numbers of molecular states. For instance, it has recently been estimated that even for a simple model of CaMKII with just 6 states per subunits and 10 subunits, it would take 290 years to generate the entire reaction network on a 2.54 GHz Intel Xeon processor. In addition, the model generation step in generate-first methods does not necessarily terminate, for instance when the model includes assembly of proteins into complexes of arbitrarily large size, such as actin filaments. In these cases, a termination condition needs to be specified by the user.
Even if a large reaction system can be successfully generated, its simulation using population-based rule evaluation can run into computational limits. In a recent study, a powerful computer was shown to be unable to simulate a protein with more than 8 phosphorylation sites ( phosphorylation states) using ordinary differential equations.
Methods have been proposed to reduce the size of the state space. One is to consider only the states adjacent to the present state (i.e. the states that can be reached within the next iteration) at each time point. This eliminates the need for enumerating all possible states at the beginning. Instead, reactions are generated "on-the-fly" at each iteration. These methods are available both for stochastic and deterministic algorithms. These methods still rely on the definition of an (albeit reduced) reaction network - in contrast to the "network-free" methods discussed below.
Even with "on-the-fly" network generation, networks generated for population-based rule evaluation can become quite large, and thus difficult - if not impossible - to handle computationally. An alternative approach is provided by particle-based rule evaluation. | 1 | Biochemistry |
Commonly used indicator bacteria include total coliforms, or a subset of this group, fecal coliforms, which are found in the intestinal tracts of warm blooded animals. Total coliforms were used as fecal indicators by public agencies in the US as early as the 1920s. These organisms can be identified based on the fact that they all metabolize the sugar lactose, producing both acid and gas as byproducts. Fecal coliforms are more useful as indicators in recreational waters than total coliforms which include species that are naturally found in plants and soil; however, there are even some species of fecal coliforms that do not have a fecal origin, such as Klebsiella pneumoniae. Perhaps the biggest drawback to using coliforms as indicators is that they can grow in water under certain conditions.
Escherichia coli (E. coli) and enterococci are also used as indicators. | 3 | Analytical Chemistry |
Levofloxacin is not approved in most countries for the treatment of children except in unique and life-threatening infections because it is associated with an elevated risk of musculoskeletal injury in this population, a property it shares with other fluoroquinolones.
In the United States levofloxacin is approved for the treatment of anthrax and plague in children over six months of age.
Levofloxacin is recommended by the Pediatric Infectious Disease Society and the Infectious Disease Society of America as a first-line treatment for pediatric pneumonia caused by penicillin-resistant Streptococcus pneumoniae, and as a second-line agent for the treatment of penicillin-sensitive cases.
In one study, 1534 juvenile patients (age 6 months to 16 years) treated with levofloxacin as part of three efficacy trials were followed up to assess all musculoskeletal events occurring up to 12 months post-treatment. At 12 months follow-up the cumulative incidence of musculoskeletal adverse events was 3.4%, compared to 1.8% among 893 patients treated with other antibiotics. In the levafloxacin-treated group, approximately two-thirds of these musculoskeletal adverse events occurred in the first 60 days, 86% were mild, 17% were moderate, and all resolved without long-term sequelae. | 4 | Stereochemistry |
G proteins are important signal transducing molecules in cells. "Malfunction of GPCR [G Protein-Coupled Receptor] signaling pathways are involved in many diseases, such as diabetes, blindness, allergies, depression, cardiovascular defects, and certain forms of cancer. It is estimated that about 30% of the modern drugs' cellular targets are GPCRs." The human genome encodes roughly 800 G protein-coupled receptors, which detect photons of light, hormones, growth factors, drugs, and other endogenous ligands. Approximately 150 of the GPCRs found in the human genome still have unknown functions.
Whereas G proteins are activated by G protein-coupled receptors, they are inactivated by RGS proteins (for "Regulator of G protein signalling"). Receptors stimulate GTP binding (turning the G protein on). RGS proteins stimulate GTP hydrolysis (creating GDP, thus turning the G protein off). | 1 | Biochemistry |
Similar to Cu(I) chemistry mentioned above, Rh(I) complexes can also transmetallate with arylboronic esters to get aryl rhodium intermediates, to which CO is inserted giving carboxylic acids. Later, Iwasawa et al. described C-H carboxylation strategy. Rh(I) undergoes oxidative addition to aryl C-H bond followed by transmetallation with alkyl aluminum species. Ar-Rh(I) regenerates by reductive elimination releasing methane. Ar-Rh(I) attacks CO then transmetallates with aryl boronic acid to release the boronic acid of product, giving final carboxylic acid by hydrolysis. Directed and non-directed versions are both achieved.
Iwasawa and co-workers developed Rh(I) catalyzed carbonation reaction initiated by Rh-H insertion to vinylarenes. In order to regenerate reactive Rh-H after nucleophilic addition to CO, photocatalytic proton-coupled electron transfer approach was adopted. In this system, excess amount of diethylpropylethylamine works as sacrificial electron donor (Scheme 5). | 0 | Organic Chemistry |
The effect of the sigma electron displacement towards the more electronegative atom by which one end becomes positively charged and the other end negatively charged is known as the inductive effect. The -I effect is a permanent effect & generally represented by an arrow on the bond.
However, some groups, such as the alkyl group, are less electron-withdrawing than hydrogen and are therefore considered as electron-releasing/ electron-donating groups. This is electron-releasing character and is indicated by the +I effect. In short, alkyl groups tend to give electrons, leading to the induction effect. However, such an effect has been questioned.
As the induced change in polarity is less than the original polarity, the inductive effect rapidly dies out and is significant only over a short distance. Moreover, the inductive effect is permanent but feeble since it involves the shift of strongly held σ-bond electrons and other stronger factors may overshadow this effect. | 7 | Physical Chemistry |
Initially, pyruvate and thiamine pyrophosphate (TPP or vitamin B) are bound by pyruvate dehydrogenase subunits. The thiazolium ring of TPP is in a zwitterionic form, and the anionic C2 carbon performs a nucleophilic attack on the C2 (ketone) carbonyl of pyruvate. The resulting hemithioacetal undergoes decarboxylation to produce an acyl anion equivalent (see cyanohydrin or aldehyde-dithiane umpolung chemistry, as well as benzoin condensation). This anion attacks S1 of an oxidized lipoate species that is attached to a lysine residue. In a ring-opening S2-like mechanism, S2 is displaced as a sulfide or sulfhydryl moiety. Subsequent collapse of the tetrahedral hemithioacetal ejects thiazole, releasing the TPP cofactor and generating a thioacetate on S1 of lipoate. The E1-catalyzed process is the rate-limiting step of the whole pyruvate dehydrogenase complex. | 1 | Biochemistry |
Base excess can be estimated from the bicarbonate concentration ([HCO]) and pH by the equation:
with units of mEq/L. The same can be alternatively expressed as
Calculations are based on the Henderson-Hasselbalch equation:
Ultimately the end result is: | 1 | Biochemistry |
Agents that break disulfide bonds by reduction include:
* 2-Mercaptoethanol
* Dithiothreitol
* TCEP (tris(2-carboxyethyl)phosphine) | 1 | Biochemistry |
CHAPS is a zwitterionic surfactant used in the laboratory to solubilize biological macromolecules such as proteins. It may be synthesized from cholic acid and is zwitterionic due to its quaternary ammonium and sulfonate groups; it is structurally similar to certain bile acids, such as taurodeoxycholic acid and taurochenodeoxycholic acid. It is used as a non-denaturing detergent in the process of protein purification and is especially useful in purifying membrane proteins, which are often sparingly soluble or insoluble in aqueous solution due to their native hydrophobicity.
CHAPS is an abbreviation for 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate. A related detergent, called CHAPSO, has the same basic chemical structure with an additional hydroxyl functional group; its full chemical name is 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonate. Both detergents have low light absorbance in the ultraviolet region of the electromagnetic spectrum, which is useful for monitoring ongoing chemical reactions or protein-protein binding with UV/Vis spectroscopy. | 1 | Biochemistry |
Antarctic fungi species such as Metschnikowia sp., Cryptococcus gilvescens, Cryptococcus victoriae, Pichia caribbica and Leucosporidium creatinivorum can withstand extreme cold and still provide efficient biodegradation of contaminants. Due to the nature of colder, remote environments like Antarctica, usual methods of contaminant remediation, such as the physical removal of contaminated media, can prove costly. Most species of psychrophilic Antarctic fungi are resistant to the decreased levels of ATP (adenosine triphosphate) production causing reduced energy availability, decreased levels of oxygen due to the low permeability of frozen soil, and nutrient transportation disruption caused by freeze-thaw cycles. These species of fungi are able to assimilate and degrade compounds such as phenols, n-Hexadecane, toluene, and polycyclic aromatic hydrocarbons in these harsh conditions. These compounds are found in crude oil and refined petroleum.
Some fungi species, like Rhodotorula taiwanensis, are resistant to the extremely low pH (acidic) and radioactive medium found in radioactive waste and can successfully grow in these conditions, unlike most other organisms. They can also thrive in the presence of high concentrations of mercury and chromium. Fungi such as Rhodotorula taiwanensis can possibly be used in the bioremediation of radioactive waste due to their low pH and radiation resistant properties. Certain species of fungi are able to absorb and retain radionuclides such as Cs, Sr, Eu, Pu and Am. In fact, cell walls of some species of dead fungi can be used as a filter that can adsorb heavy metals and radionuclides present in industrial effluents, preventing them from being released into the environment. | 2 | Environmental Chemistry |
In May, the FDA approved onasemnogene abeparvovec (Zolgensma) for treating spinal muscular atrophy in children under two years of age. The list price of Zolgensma was set at per dose, making it the most expensive drug ever.
In May, the EMA approved betibeglogene autotemcel (Zynteglo) for treating beta thalassemia for people twelve years of age and older.
In July, Allergan and Editas Medicine announced phase I/II clinical trial of AGN-151587 for the treatment of Leber congenital amaurosis 10. This is the first study of a CRISPR-based in vivo human gene editing therapy, where the editing takes place inside the human body. The first injection of the CRISPR-Cas System was confirmed in March 2020. | 1 | Biochemistry |
Metal carbene complexes are often classified into two types. The Fischer carbenes, named after Ernst Otto Fischer, feature strong π-acceptors at the metal and are electrophilic at the carbene carbon atom. Schrock carbenes, named after Richard R. Schrock, are characterized by more nucleophilic carbene carbon centers; these species typically feature higher oxidation state (valency) metals. N-Heterocyclic carbenes (NHCs) were popularized following Arduengo's isolation of a stable free carbene in 1991. Reflecting the growth of the area, carbene complexes are now known with a broad range of different reactivities and diverse substituents. Often it is not possible to classify a carbene complex solely with regards to its electrophilicity or nucleophilicity. | 0 | Organic Chemistry |
In organic chemistry, syn- and anti-addition are different ways in which substituent molecules can be added to an alkene () or alkyne (). The concepts of syn and anti addition are used to characterize the different reactions of organic chemistry by reflecting the stereochemistry of the products in a reaction.
The type of addition that occurs depends on multiple different factors of a reaction, and is defined by the final orientation of the substituents on the parent molecule. Syn and anti addition are related to Markovnikovs rule for the orientation of a reaction, which refers to the bonding preference of different substituents for different carbons on an alkene or alkyne. In order for a reaction to follow Markovnikovs rule, the intermediate carbocation of the mechanism of a reaction must be on the more-substituted carbon, allowing the substituent to bond to the more-stable carbocation and the more-substituted carbon.
Syn addition is the addition of two substituents to the same side (or face) of a double bond or triple bond, resulting in a decrease in bond order but an increase in number of substituents. Generally the substrate will be an alkene or alkyne. An example of syn addition would be the oxidation of an alkene to a diol by way of a suitable oxidizing agent such as osmium tetroxide, , or potassium permanganate, .
Anti addition is in direct contrast to syn addition. In anti addition, two substituents are added to opposite sides (or faces) of a double bond or triple bond, once again resulting in a decrease in bond order and increase in number of substituents. The classical example of this is bromination (any halogenation) of alkenes. An anti addition reaction results in a trans-isomer of the products, as the substituents are on opposite faces of the bond.
Depending on the substrate double bond, addition can have different effects on the molecule. After addition to a straight-chain alkene such as ethene (), the resulting alkane will rapidly and freely rotate around its single sigma bond under normal conditions (i.e. room temperature). Thus whether substituents are added to the same side (syn) or opposite sides (anti) of a double can usually be ignored due to free rotation. However, if chirality or the specific absolute orientation of the substituents needs to be taken into account, knowing the type of addition is significant. Unlike straight-chain alkenes, cycloalkene syn addition allows stable addition of substituents to the same side of the ring, where they remain together. The cyclic locked ring structure prevents free rotation.
Syn elimination and anti elimination are the reverse processes of syn and anti addition. These result in a new double bond, such as in E elimination. | 4 | Stereochemistry |
The Melt Flow Index (MFI) is a measure of the ease of flow of the melt of a thermoplastic polymer. It is defined as the mass of polymer, in grams, flowing in ten minutes through a capillary of a specific diameter and length by a pressure applied via prescribed alternative gravimetric weights for alternative prescribed temperatures. Polymer processors usually correlate the value of MFI with the polymer grade that they have to choose for different processes, and most often this value is not accompanied by the units, because it is taken for granted to be g/10min. Similarly, the test conditions of MFI measurement are normally expressed in kilograms rather than any other units. The method is described in the similar standards ASTM D1238 and ISO 1133.
Melt flow rate is an indirect measure of molecular weight, with high melt flow rate corresponding to low molecular weight. At the same time, melt flow rate is a measure of the ability of the material's melt to flow under pressure. Melt flow rate is inversely proportional to viscosity of the melt at the conditions of the test, though it should be borne in mind that the viscosity for any such material depends on the applied force. Ratios between two melt flow rate values for one material at different gravimetric weights are often used as a measure for the broadness of the molecular weight distribution.
Melt flow rate is very commonly used for polyolefins, polyethylene being measured at 190 °C and polypropylene at 230 °C. The plastics engineer should choose a material with a melt index high enough that the molten polymer can be easily formed into the article intended, but low enough that the mechanical strength of the final article will be sufficient for its use. | 7 | Physical Chemistry |
Detonation spraying is one of the many forms of thermal spraying techniques that are used to apply a protective coating at supersonic velocities to a material in order to change its surface characteristics. This is primarily to improve the durability of a component. It was first invented in 1955 by H.B. Sargent, R.M. Poorman and H. Lamprey and is applied to a component using a specifically designed detonation gun (D-gun). The component being sprayed must be prepared correctly by removing all surface oils, greases, debris and roughing up the surface in order to achieve a strongly bonded detonation spray coating. This process involves the highest velocities (≈3500 m/s shockwave that propels the coating materials) and temperatures (≈4000 °C) of coating materials compared to all other forms of thermal spraying techniques. Which means detonation spraying is able to apply low porous (below 1%) and low oxygen content (between 0.1 and 0.5%) protective coatings that protect against corrosion, abrasion and adhesion under low load.
This process allows the application of very hard and dense surface coatings which are useful as wear resistant coatings. For this reason, detonation spraying is commonly used for protective coatings in aircraft engines, plug and ring gauges, cutting edges (skiving knives), tubular drills, rotor and stator blades, guide rails or any other metallic material that is subject to high wear and tear. Commonly the materials that are sprayed onto components during detonation spraying are powders of metals, metal alloys and cermets; as well as their oxides (aluminum, copper, iron, etc.).
Detonation spraying is an industrial process that can be dangerous if not performed correctly and in a safe environment. As such there are many safety precautions that must be adhered to when using this thermal spraying technique. | 8 | Metallurgy |
Imipenem (trade name Primaxin among others) is a synthetic β-lactam antibiotic belonging to the carbapenems chemical class. developed by Merck scientists Burton Christensen, William Leanza, and Kenneth Wildonger in the mid-1970s. Carbapenems are highly resistant to the β-lactamase enzymes produced by many multiple drug-resistant Gram-negative bacteria, thus playing a key role in the treatment of infections not readily treated with other antibiotics. It is usually administered through intravenous injection.
Imipenem was patented in 1975 and approved for medical use in 1985. It was developed via a lengthy trial-and-error search for a more stable version of the natural product thienamycin, which is produced by the bacterium Streptomyces cattleya. Thienamycin has antibacterial activity, but is unstable in aqueous solution, thus it is practically of no medicinal use. Imipenem has a broad spectrum of activity against aerobic and anaerobic, Gram-positive and Gram-negative bacteria. It is particularly important for its activity against Pseudomonas aeruginosa and Enterococcus species. However, it is not active against MRSA. | 4 | Stereochemistry |
* Thioacetone (2-propanethione) A lightly studied organosulfur. Its smell is so potent it can be detected several hundred meters downwind mere seconds after a container is opened.
* Allyl thiol (2-propenethiol; allyl mercaptan; CH=CHCHSH) (garlic volatiles and garlic breath)
* (Methylthio)methanethiol (CHSCHSH), the "mouse thiol", found in mouse urine and functions as a semiochemical for female mice
* Ethanethiol, commonly called ethyl mercaptan (added to propane or other liquefied-petroleum gases used as fuel gases)
* 2-Methyl-2-propanethiol, commonly called tert-butyl mercaptan, is added as a blend of other components to natural gas used as fuel gas.
* Butane-1-thiol, commonly called butyl mercaptan, is a chemical intermediate.
* Grapefruit mercaptan (grapefruit)
* Methanethiol, commonly called methyl mercaptan (after eating Asparagus)
* Furan-2-ylmethanethiol, also called furfuryl mercaptan (roasted coffee)
* Benzyl mercaptan (leek or garlic-like) | 0 | Organic Chemistry |
In electrochemistry, a half-cell is a structure that contains a conductive electrode and a surrounding conductive electrolyte separated by a naturally occurring Helmholtz double layer. Chemical reactions within this layer momentarily pump electric charges between the electrode and the electrolyte, resulting in a potential difference between the electrode and the electrolyte. The typical anode reaction involves a metal atom in the electrode being dissolved and transported as a positive ion across the double layer, causing the electrolyte to acquire a net positive charge while the electrode acquires a net negative charge. The growing potential difference creates an intense electric field within the double layer, and the potential rises in value until the field halts the net charge-pumping reactions. This self-limiting action occurs almost instantly in an isolated half-cell; in applications two dissimilar half-cells are appropriately connected to constitute a Galvanic cell.
A standard half-cell consists of a metal electrode in an aqueous solution where the concentration of the metal ions is 1 molar (1 mol/L) at 298 kelvins (25 °C). In the case of the standard hydrogen electrode (SHE), a platinum electrode is used and is immersed in an acidic solution where the concentration of hydrogen ions is 1M, with hydrogen gas at 1atm being bubbled through solution. The electrochemical series, which consists of standard electrode potentials and is closely related to the reactivity series, was generated by measuring the difference in potential between the metal half-cell in a circuit with a standard hydrogen half-cell, connected by a salt bridge.
The standard hydrogen half-cell:
:2H(aq) + 2e → H(g)
The half-cells of a Daniell cell:
:Original equation
::Zn + Cu → Zn + Cu
:Half-cell (anode) of Zn
::Zn → Zn + 2e
:Half-cell (cathode) of Cu
::Cu + 2e → Cu | 7 | Physical Chemistry |
One study tested the effects of ephaptic coupling by using both neurotransmitter antagonists to block chemical synapses and gap junction blockers to block electrical synapses. It was found that rhythmic electrical discharge associated with fetal neurons in the rat spinal cord and medulla was still sustained. This suggests that connections between the neurons still exist and work to spread signals even without traditional synapses. These findings support a model in which ephaptic coupling works alongside canonical synapses to propagate signals across neuronal networks. | 1 | Biochemistry |
For thermal transport between two contacting bodies, such as particles in a granular medium, the contact pressure is the factor of most influence on overall contact conductance. As contact pressure grows, true contact area increases and contact conductance grows (contact resistance becomes smaller).
Since the contact pressure is the most important factor, most studies, correlations and mathematical models for measurement of contact conductance are done as a function of this factor.
The thermal contact resistance of certain sandwich kinds of materials that are manufactured by rolling under high temperatures may sometimes be ignored because the decrease in thermal conductivity between them is negligible. | 7 | Physical Chemistry |
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