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Solar energy conversion has the potential to be a very cost-effective technology. It is cheaper as compared to non-conventional energy sources. The [https://www.learnarrow.com/2020/01/top-8-most-popular-uses-of-solar-energy.html use of solar energy] help to increase employment and development of the transportation & agriculture sector. Solar installations are becoming cheaper and more readily available to countries where energy demand is high, but supply is low due to economic circumstances. A 1 GW solar power plant can produce almost 10 times as much power as a fossil fuel combustion power plant that would cost twice as much to establish. Solar power plants have been projected to be the leader of the energy production by the year 2050. | 7 | Physical Chemistry |
While it is useful to study bulk cell entities, there is an underlying need to study an individual or single cell as it will provide a better understanding of how it contributes to the entity as a whole. It was found that the utilization of electrochemical techniques could analyze cells without interrupting cellular activity as well as provide a highly resolute spectrum. This analysis method was first completed by Wightman in 1982. In this method of analysis, a carbon microfiber electrode is placed near the studied cell; this electrode can monitor the call via methods of voltammetry or amperometry. Before the measure can be taken, the cell must be stimulated by an ejection pipette to cause a cellular release. This can be cellular release can be measured via the aforementioned methods. From this method, it was seen that instrumental advances were needed in order to perform quality SEE measurements. | 7 | Physical Chemistry |
Eshelby work helped shape the fields of defect mechanics and micromechanics of inhomogeneous solids for fifty years, including the controlling mechanisms of plastic deformation and fracture.The scientific phenomenon called Eshelby's inclusion is named after this scientist, and points at an ellipsoidal subdomain in an infinite homogeneous body, subjected to a uniform transformation strain. | 8 | Metallurgy |
In practice, the Joule–Thomson effect is achieved by allowing the gas to expand through a throttling device (usually a valve) which must be very well insulated to prevent any heat transfer to or from the gas. No external work is extracted from the gas during the expansion (the gas must not be expanded through a turbine, for example).
The cooling produced in the Joule–Thomson expansion makes it a valuable tool in refrigeration. The effect is applied in the Linde technique as a standard process in the petrochemical industry, where the cooling effect is used to liquefy gases, and in many cryogenic applications (e.g. for the production of liquid oxygen, nitrogen, and argon). A gas must be below its inversion temperature to be liquefied by the Linde cycle. For this reason, simple Linde cycle liquefiers, starting from ambient temperature, cannot be used to liquefy helium, hydrogen, or neon. They must first be cooled to their inversion temperatures, which are -233 C (helium), -71 C (hydrogen), and -42 C (neon). | 7 | Physical Chemistry |
Crystallography has 230 space groups to distinguish, far more than the 17 wallpaper groups, but many of the symmetries in the groups are the same. Thus one can use a similar notation for both kinds of groups, that of Carl Hermann and Charles-Victor Mauguin. An example of a full wallpaper name in Hermann-Mauguin style (also called IUCr notation) is p31m, with four letters or digits; more usual is a shortened name like cmm or pg.
For wallpaper groups the full notation begins with either p or c, for a primitive cell or a face-centred cell; these are explained below. This is followed by a digit, n, indicating the highest order of rotational symmetry: 1-fold (none), 2-fold, 3-fold, 4-fold, or 6-fold. The next two symbols indicate symmetries relative to one translation axis of the pattern, referred to as the "main" one; if there is a mirror perpendicular to a translation axis that is the main one (or if there are two, one of them). The symbols are either m, g, or 1, for mirror, glide reflection, or none. The axis of the mirror or glide reflection is perpendicular to the main axis for the first letter, and either parallel or tilted 180°/n (when n > 2) for the second letter. Many groups include other symmetries implied by the given ones. The short notation drops digits or an m that can be deduced, so long as that leaves no confusion with another group.
A primitive cell is a minimal region repeated by lattice translations. All but two wallpaper symmetry groups are described with respect to primitive cell axes, a coordinate basis using the translation vectors of the lattice. In the remaining two cases symmetry description is with respect to centred cells that are larger than the primitive cell, and hence have internal repetition; the directions of their sides is different from those of the translation vectors spanning a primitive cell. Hermann-Mauguin notation for crystal space groups uses additional cell types.
;Examples
* p2 (p2): Primitive cell, 2-fold rotation symmetry, no mirrors or glide reflections.
* p4gm (p4gm): Primitive cell, 4-fold rotation, glide reflection perpendicular to main axis, mirror axis at 45°.
* c2mm (c2mm): Centred cell, 2-fold rotation, mirror axes both perpendicular and parallel to main axis.
* p31m (p31m): Primitive cell, 3-fold rotation, mirror axis at 60°.
Here are all the names that differ in short and full notation.
The remaining names are p1, p2, p3, p3m1, p31m, p4, and p6. | 3 | Analytical Chemistry |
Iron export occurs in a variety of cell types, including neurons, red blood cells, macrophages and enterocytes. The latter two are especially important since systemic iron levels depend upon them. There is only one known iron exporter, ferroportin. It transports ferrous iron out of the cell, generally aided by ceruloplasmin and/or hephaestin (mostly in enterocytes), which oxidize iron to its ferric state so it can bind ferritin in the extracellular medium. Hepcidin causes the internalization of ferroportin, decreasing iron export. Besides, hepcidin seems to downregulate both TFR1 and DMT1 through an unknown mechanism. Another player assisting ferroportin in effecting cellular iron export is GAPDH. A specific post translationally modified isoform of GAPDH is recruited to the surface of iron loaded cells where it recruits apo-transferrin in close proximity to ferroportin so as to rapidly chelate the iron extruded.
The expression of hepcidin, which only occurs in certain cell types such as hepatocytes, is tightly controlled at the transcriptional level and it represents the link between cellular and systemic iron homeostasis due to hepcidin's role as "gatekeeper" of iron release from enterocytes into the rest of the body. Erythroblasts produce erythroferrone, a hormone which inhibits hepcidin and so increases the availability of iron needed for hemoglobin synthesis. | 1 | Biochemistry |
Sulfuryl fluoride is marketed in the U.S. by three manufacturers, under four different brand names. Vikane (Dow) (EPA Reg. No. 62719- 4-ZA) has been commercially available since the early 1960s, with Zythor (marketed by competitor Ensystex of North Carolina) (EPA Reg. No. 81824- 1-AA) being more recently introduced gradually as its use is approved by individual states (in Florida circa 2004, but not in California until October 2006, for example). Sulfuryl fluoride has been marketed as a post-harvest fumigant for dry fruits, nuts, and grains under the trade name ProFume (U.S. EPA Reg. No. 62719- 376-AA). Most recently Drexel Chemical Company has registered Master Fume (EPA Reg. No. 19713-596-AA) for the structural market, competing against Vikane and Zythor. | 2 | Environmental Chemistry |
Rescue fusion hybridization is a process used to manufacture some therapeutic cancer vaccines in which individual tumor cells obtained through biopsy are fused with an antibody-secreting cell to form a heterohybridoma. This cell then secretes the unique idiotype, or immunoglobulin antigen characteristic of the individual tumor, which is purified for use as the vaccine. It is used to produce the BiovaxID vaccine for follicular lymphoma. | 1 | Biochemistry |
In molecular biology, a histone octamer is the eight-protein complex found at the center of a nucleosome core particle. It consists of two copies of each of the four core histone proteins (H2A, H2B, H3, and H4). The octamer assembles when a tetramer, containing two copies of H3 and two of H4, complexes with two H2A/H2B dimers. Each histone has both an N-terminal tail and a C-terminal histone-fold. Each of these key components interacts with DNA in its own way through a series of weak interactions, including hydrogen bonds and salt bridges. These interactions keep the DNA and the histone octamer loosely associated, and ultimately allow the two to re-position or to separate entirely. | 1 | Biochemistry |
There is a lower limit for the length of the interconnect that will allow higher current carrying capability. It is known as "Blech length". Any wire that has a length below this limit will have a stretched limit for electromigration. Here, a mechanical stress buildup causes an atom back flow process which reduces or even compensates the effective material flow towards the anode. The Blech length must be considered when designing test structures to evaluate electromigration. This minimum length is typically some tens of microns for chip traces, and interconnections shorter than this are sometimes referred to as electromigration immortal. | 7 | Physical Chemistry |
Senapathy proposed that the gene-expression regulatory sequences (promoter and poly-A addition site sequences) also could have originated from stop codons. A conserved sequence, AATAAA, exists in almost every gene a short distance downstream from the end of the protein-coding message and serves as a signal for the addition of poly(A) in the mRNA copy of the gene. This poly(A) sequence signal contains a stop codon, TAA. A sequence shortly downstream from this signal, thought to be part of the complete poly(A) signal, also contains the TAG and TGA stop codons.
Eukaryotic RNA-polymerase-II-dependent promoters can contain a TATA box (consensus sequence TATAAA), which contains the stop codon TAA. Bacterial promoter elements at ~10 bases exhibits a TATA box with a consensus of TATAAT (which contains the stop codon TAA), and at -35 bases exhibits a consensus of TTGACA (containing the stop codon TGA). Thus, the evolution of the whole RNA processing mechanism seems to have been influenced by the too-frequent occurrence of stop codons, thus making the stop codons the focal points for RNA processing. | 1 | Biochemistry |
Halogenation of saturated hydrocarbons is a substitution reaction. The reaction typically requires free radical pathways. The regiochemistry of the halogenation of alkanes is largely determined by the relative weakness of the C–H bonds. This trend is reflected by the faster reaction at tertiary and secondary positions.
Fluorinations with elemental fluorine () are particularly exothermic, so much so that highly specialised conditions and apparatus are required. The method electrochemical fluorination generates small amounts of elemental fluorine in situ from hydrogen fluoride. The method avoids the hazards of handling fluorine gas. Many commercially important organic compounds are fluorinated using this technology. Aside from and its electrochemically generated equivalent, cobalt(III) fluoride is used as sources of fluorine radicals.
Free radical chlorination is used for the industrial production of some solvents:
Naturally-occurring organobromine compounds are usually produced by free radical pathway catalyzed by the enzyme bromoperoxidase. The reaction requires bromide in combination with oxygen as an oxidant. The oceans are estimated to release 1–2 million tons of bromoform and 56,000 tons of bromomethane annually.
The iodoform reaction, which involves degradation of methyl ketones, proceeds by the free radical iodination. | 0 | Organic Chemistry |
This is a modification of the method of oxidative tethering to a para-methoxybenzyl ether. The difference here is that the para-alkoxybenzyl group is attached to a solid support; the β-mannoside product is released into the solution phase in the last step, while the by-products remain attached to the solid phase. This makes the purification of the β-glycoside easier; it is formed as the almost exclusive product. | 0 | Organic Chemistry |
In 1963, Ralph Pearson proposed a qualitative concept known as the Hard and Soft Acids and Bases principle. later made quantitative with help of Robert Parr in 1984. Hard applies to species that are small, have high charge states, and are weakly polarizable. Soft applies to species that are large, have low charge states and are strongly polarizable. Acids and bases interact, and the most stable interactions are hard–hard and soft–soft. This theory has found use in organic and inorganic chemistry. | 7 | Physical Chemistry |
LAAM is indicated as a second-line treatment for the treatment and management of opioid dependence if patients fail to respond to drugs like methadone or buprenorphine.
LAAM is used as an oral solution of LAAM hydrochloride at a concentration of 10 mg/mL in bottles of 120 and 500 mL under the brand name Orlaam. The first dose of LAAM for patients who have not started treatment with methadone is 20–40 mg. The first dose for patients who have been receiving methadone will be a little higher than the amount of methadone that was being taken every day, but not more than 120 mg. Afterwards, the dosage may be adjusted as needed. Unlike methadone, which requires daily administration, LAAM is administered two to three times a week. | 4 | Stereochemistry |
Epigenetic Therapy is the use of drugs or other epigenome-influencing techniques to treat medical conditions.
It is recently regarded as promising therapy to NSCLC.
As can be seen in the above, SFRP1 was downregulated epigenetically in NSCLC and was recently proposed as one of epigenetic therapy target. | 1 | Biochemistry |
The presence of ptaquiloside has been detected in a variety of ferns, including the species in the genera Pteridium (bracken), Pteris, Microlepia, and Hypolepis. Pteridium aquilinum (commonly known as bracken fern) is the most common ptaquiloside-containing fern with a wide geographical and ecological distribution. It is present in all continents from subtropic to subarctic areas. Bracken fern is a very adaptable plant and is capable of forming dense, rapidly expanding populations in course of the first phases of the ecological succession in forest cleanings and other disturbed rural areas. Its aggressive growth, characterized by an extensive rhizome system and rapidly growing fronds, sometimes enables it to be a dominant species in certain plant communities.
The ptaquiloside content of bracken varies widely across species and changes with the part of the plant, the plant growing site and the collecting season. According to previous studies, the concentrations of ptaquiloside in bracken varied between 0 to 1% of the dry weight of the plant. Generally, ptaquiloside is found to occur in the highest concentrations in the young developing parts of bracken, such as the croziers and unfolding parts during the spring and early summer, while the concentrations of ptaquiloside in the rhizomes are rather low. However, studies on the concentrations of ptaquiloside in Danish bracken by Rasmussen et al. showed that the concentrations of ptaquiloside in the rhizomes were significantly higher than the previously reported values.
Ptaquiloside can pass into the milk produced by bracken-fed cows and sheep. In 1996, Alonso-Amelot, Smith and co-workers found that ptaquiloside was excreted in milk at a concentration of 8.6 ± 1.2% of the amount ingested by a cow from bracken, and was linearly dose-dependent. On the basis of their experiments and the assumption that a person drinks 0.5 litres of milk daily, they estimated that this person might ingest about 10 mg of ptaquiloside per day, although only some of that amount will be absorbed. Ptaquiloside can also leach from the bracken leaves into water and soil. Numerous studies have reported the presence of ptaquiloside in the underground/surface water, and soil near bracken vegetation. The degradation speed of ptaquiloside in the soil is affected by the acidity, clay content, carbon content, temperature and presumably microbioactivity. Acidic condition (pH<4) and high temperature (at least 25°C) facilitate ptaquiloside degradation, while the half-life of ptaquiloside in less acidic sandy soil is reported to be between 150 and 180 hours. | 0 | Organic Chemistry |
In chemistry, an electrofuge is a leaving group which does not retain the lone pair of electrons from its previous bond with another species (in contrast to a nucleofuge, which does). It can result from the heterolytic breaking of covalent bonds.
After this reaction an electrofuge may possess either a positive or a neutral charge; this is governed by the nature of the specific reaction.
An example would be the loss of from a molecule of benzene during nitration.
The word electrofuge is commonly found in older literature, but its use in contemporary organic chemistry is now uncommon. | 0 | Organic Chemistry |
In chemistry, a molecule experiences strain when its chemical structure undergoes some stress which raises its internal energy in comparison to a strain-free reference compound. The internal energy of a molecule consists of all the energy stored within it. A strained molecule has an additional amount of internal energy which an unstrained molecule does not. This extra internal energy, or strain energy, can be likened to a compressed spring. Much like a compressed spring must be held in place to prevent release of its potential energy, a molecule can be held in an energetically unfavorable conformation by the bonds within that molecule. Without the bonds holding the conformation in place, the strain energy would be released. | 4 | Stereochemistry |
Fatty acid synthesis starts with acetyl-CoA and builds up by the addition of two-carbon units. Fatty acid synthesis occurs in the cytoplasm of cells while oxidative degradation occurs in the mitochondria. Many of the enzymes for the fatty acid synthesis are organized into a multienzyme complex called fatty acid synthase. The major sites of fatty acid synthesis are adipose tissue and the liver. | 1 | Biochemistry |
The third annual Empowering Women in Organic Chemistry Conference was held virtually on Thursday, June 24, and Friday, June 25, 2021.
2021 Career Panel featured Kay Brummond (Univ of Pittsburgh), Martha A. Sarpong (GlaxoSmithKline), Emma Radoux (Royal Society of Chemistry), Callie Bryan (Janssen), Kimberly Steward (Cargill) and Daisy Rosas Vargas (Ithaca College). | 0 | Organic Chemistry |
As shown in the table below, the three chief national producers of copper, respectively, in 2002, were Chile, Indonesia, and the United States. In 2013, they were Chile, China, and Peru. Twenty-one of the 28 largest copper mines in the world (as of 2006) are not amenable to expansion. | 8 | Metallurgy |
Photoactivated adenylyl cyclase (PAC) is a protein consisting of an adenylyl cyclase enzyme domain directly linked to a BLUF (blue light receptor using FAD) type light sensor domain. When illuminated with blue light, the enzyme domain becomes active and converts ATP to cAMP, an important second messenger in many cells. In the unicellular flagellate Euglena gracilis, PACα and PACβ (euPACs) serve as a photoreceptor complex that senses light for photophobic responses and phototaxis. Small but potent PACs were identified in the genome of the bacteria Beggiatoa (bPAC) and Oscillatoria acuminata (OaPAC). While natural bPAC has some enzymatic activity in the absence of light, variants with no dark activity have been engineered (PACmn). | 1 | Biochemistry |
Water-use efficiency (WUE) refers to the ratio of plant biomass to water lost by transpiration, can be defined either at the leaf, at the whole plant or a population/stand/field level:
*leaf level : photosynthetic water-use efficiency (also called instantaneous water-use efficiency WUE), which is defined as the ratio of the rate of net CO carbon assimilation (photosynthesis) to the rate of transpiration or stomatal conductance, then called intrinsic water-use efficiency (iWUE or W)
*plant level : water-use efficiency of productivity (also called integrated water-use efficiency or transpiration efficiency,TE), which is typically defined as the ratio of dry biomass produced to the rate of transpiration.
* field level : based on measurements of CO and water fluxes over a field of a crop or a forest, using the eddy covariance technique
Research to improve the water-use efficiecy of crop plants has been ongoing from the early 20th century, however with difficulties to actually achieve crops with increased water-use efficiency.
Intrinsic water-use efficiency W usually increases during soil drought, due to stomatal closure and a reduction in transpiration, and is therefore often linked to drought tolerance. Observatios from several authors have however suggested that WUE would rather be linked to different drought response strategies, where
* low WUE plants could either correspond to a drought tolerance strategy, for example by anatomical adaptations reducing vulnerability to xylem cavitation, or to a drought avoidance/water spender strategy through a wide soil exploration by roots or a drought escape strategy due to early flowering
* whereas high WUE plants could correspond to a drought avoidance/water saving strategy, through drought-sensitive, early closing stomata.
Increases in water-use efficiency are commonly cited as a response mechanism of plants to moderate to severe soil water deficits and have been the focus of many programs that seek to increase crop tolerance to drought. However, there is some question as to the benefit of increased water-use efficiency of plants in agricultural systems, as the processes of increased yield production and decreased water loss due to transpiration (that is, the main driver of increases in water-use efficiency) are fundamentally opposed. If there existed a situation where water deficit induced lower transpirational rates without simultaneously decreasing photosynthetic rates and biomass production, then water-use efficiency would be both greatly improved and the desired trait in crop production.
Water-use efficiency is also a much studied trait in Plant ecology, where it has been used already in the early 20th century to study the ecological requirements of Herbaceous plants or forest trees, and is still used today, for example related to a drought-induced limitation of tree growth | 9 | Geochemistry |
Downregulation of gene expression via siRNA has been an important research tool in in vitro studies. Susceptibility of siRNAs to nuclease degradation, though, makes use of them in vivo problematic. In 2005, researchers working with hepatitis B virus(HBV) in rodents, determined that certain modifications of the siRNA prevented degradation by nucleases within the plasma and lead to increased gene silencing compared to unmodified siRNA. Modifications to the sense and antisense strands were made differentially. With respect to both sense and antisense strands, 2-OH was substituted with 2-fluoro at all pyrimidine positions. In addition, sense strands were modified at all purine positions with deoxyribose, antisense strands modified with 2-O-methyl at the same positions. The 5 and 3 ends of the sense strand were capped with abasic inverted repeats, while a phosphorothioate linkage was incorporated at the 3 end of the antisense strand.
Although this research demonstrated a potential RNAi therapy using modified siRNA, the 90% reduction in HBV DNA in rodents resulted from a 30 mg/kg dosage with frequent administration. Because this is not a viable dosing regime, this same group looked at the effects of encapsulating the siRNA in a PEGylated lipid bilayer, or SNALP. Specifically, the lipid bilayer facilitates uptake into the cell and subsequent release from the endosome, the PEGylated outer layer providing stability during formulation due to the resulting hydrophilicity of the exterior. According to this 2005 study, researchers obtained 90% reduction in HBV DNA with a 3 mg/kg/day dose of siRNA for three days, a dose substantially lower than the earlier study. In addition, in contrast to unmodified or modified and non-encapsulated siRNA, administration of SNALP-delivered siRNA resulted in no detectable levels of interferons, such as IFN-a, or inflammatory cytokines associated with immunostimulation. Even so, researchers acknowledged that more work was necessary in order to reach a feasible dose and dosing regime.
In 2006, researchers working on silencing of apolipoprotein B(ApoB) in non-human primates achieved 90% silencing with a single dose of 2.5 mg/kg of SNALP-delivered APOB-specific siRNA. ApoB is a protein involved with the assembly and secretion of very-low-density lipoprotein(VLDL) and low-density lipoprotein(LDL), and it is expressed primarily in the liver and jejunum. Both VLDL and LDL are important in cholesterol transport and its metabolism. Not only was this degree of silencing observed very quickly, in about 24 hours post-administration, but the silencing effects maintained for over 22 days after only a single dose. Researchers tested a 1 mg/kg single dose, too, obtaining a 68% silencing of the target gene, indicating dose-dependent silencing. This dose-dependent silencing was evident not only on the degree of silencing but the duration of silencing, expression of the target gene recovering 72 hours post-administration.
Although SNALPs having a 100 nm diameter have been used effectively to target specific genes for silencing, there are a variety of systemic barriers that relate specifically to size. For example, diffusion into solid tumors is impeded by large SNALPs and, similarly, inflamed cells having enhanced permeation and retention make it difficult for large SNALPs to enter. In addition, reticuloendothelial elimination, blood–brain barrier size-selectivity and limitations of capillary fenestrae all necessitate a smaller SNALP in order to effectively deliver target-specific siRNA. In 2012, scientists in Germany developed what they termed "mono-NALPs" using a fairly simple solvent exchange method involving progressive dilution of a 50% isopropanol solution. What results is a very stable delivery system similar to traditional SNALPs, but one having only a diameter of 30 nm. The mono-NALPs developed here, however, are inactive, but can become active carriers by implementing specific targeting and release mechanisms used by similar delivery systems. | 1 | Biochemistry |
The theory is based on the assumption that the reaction can be described by a reaction coordinate, and that we can apply Boltzmann distribution at least in the reactant state.
A new, especially reactive segment of the reactant, called the saddle domain, is introduced, and the rate constant is factored:
where α is the conversion factor between the reactant state and saddle domain, while k is the rate constant from the saddle domain. The first can be simply calculated from the free energy surface, the latter is easily accessible from short molecular dynamics simulations | 7 | Physical Chemistry |
Monothiophosphate is the anion [POS], which has C symmetry. A common salt is sodium monothiophosphate (NaPOS). Monothiophosphate is used in research as an analogue of phosphate in biochemistry. Monothiophosphate esters are biochemical reagents used in the study of transcription, substitution interference assays. Sometimes, "monothiophosphate" refers to esters such as (CHO)POS. | 0 | Organic Chemistry |
In Batesian mimicry, potential prey organisms will mimic chemicals emitted by an organism that poses a greater risk to the predator in order to deter attack. Most commonly this form of chemical mimicry is seen in plant species through the release of mimicked defense chemicals. The organism being mimicked may contain noxious chemicals used to deter predators from consuming them as it will lead to the predator becoming ill. By using Batesian mimicry the operator will mimic a chemical aspect, such as “defense signals" used by plants, in order to deceive the herbivore or predator into avoiding an edible organism. | 1 | Biochemistry |
Electrodes, especially stimulating electrodes and the high current density they discharge, can raise electrochemical issues. Electrodes will be surrounded by tissue and electrolytes; stimulation, resultant electric fields, and induced polarizations will change local ion concentrations and local pH which can then cause problems such as material corrosion and electrode fouling.
Pourbiax diagrams will show the phases that a material will take in an aqueous environment, based on electrical potential and pH. The brain maintains a pH of around 7.2 to 7.4, and from the Pourbaix diagram of platinum it can be seen that at around 0.8 volts Pt at the surface will oxidize to PtO, and at around 1.6 volts, PtO will oxidize to PtO. These voltages do not seem to be outside of reasonable range for neural stimulation. The voltage required for stimulation may change significantly over the life of a single electrode. This change is required to maintain a consistent current output through variations in the surrounding environmental resistance. The changes in resistance may be due to: adsorption of material onto the electrode, corrosion of the electrode, encapsulation of the electrode in fibrous tissue – known as a glial scar, or changes in the chemical environment around the electrode. Ohms law V = I * R' shows the interdependence of voltage, current and resistance. When voltage change causes a crossing of equilibrium lines as seen in a Pourbaix diagram during a stimulation, the changing polarization of the electrode is no longer linear. Undesirable polarization can lead to adverse effects such as corrosion, fouling, and toxicity. Because of this equilibrium potential, pH, and required current density should be considered when making material choice since these can affect the surface chemistry and biocompatibility of the implant. | 7 | Physical Chemistry |
The volume of a thermodynamic system typically refers to the volume of the working fluid, such as, for example, the fluid within a piston. Changes to this volume may be made through an application of work, or may be used to produce work. An isochoric process however operates at a constant-volume, thus no work can be produced. Many other thermodynamic processes will result in a change in volume. A polytropic process, in particular, causes changes to the system so that the quantity is constant (where is pressure, is volume, and is the polytropic index, a constant). Note that for specific polytropic indexes, a polytropic process will be equivalent to a constant-property process. For instance, for very large values of approaching infinity, the process becomes constant-volume.
Gases are compressible, thus their volumes (and specific volumes) may be subject to change during thermodynamic processes. Liquids, however, are nearly incompressible, thus their volumes can be often taken as constant. In general, compressibility is defined as the relative volume change of a fluid or solid as a response to a pressure, and may be determined for substances in any phase. Similarly, thermal expansion is the tendency of matter to change in volume in response to a change in temperature.
Many thermodynamic cycles are made up of varying processes, some which maintain a constant volume and some which do not. A vapor-compression refrigeration cycle, for example, follows a sequence where the refrigerant fluid transitions between the liquid and vapor states of matter.
Typical units for volume are (cubic meters), (liters), and (cubic feet). | 7 | Physical Chemistry |
Adsorption and desorption can both be promoted by exposure of trans metal oxides to light, the predominant process being controlled by experimental conditions. Adsorption of oxygen by illumination of TiO or ZnO at room temperature with low pressure results in the adsorption of oxygen, while at high pressures illumination leads to photo-assisted desorption. At high temperatures the opposite effect is observed, with low pressure leading to desorption, and high pressure causing adsorption.
Kase et al. conducted a study of the photo-assisted chemisorption of NO on ZnO, finding that under dark conditions a negligible amount of NO was adsorbed to the metal oxide, however under illumination ZnO irreversibly adsorbs NO, their sample showing no desorption after irradiation was stopped.
The process by which adsorption and desorption on metal oxide surfaces takes place is related to the photo generation of holes on the solid surface, which are believed to be trapped by hydroxyl groups on the surface of a transition metal oxides. These trapped holes allow photo-excited electrons to be available for chemisorption. Doping of a cation of either higher or lower valence can change the electronic properties of the metal oxide. Doping with a higher valence cation typically results in an increase in n-type semi-conductivity, or raises its Fermi energy, while doping with a lower valence cation should lower the Fermi energy level and reduce the metal oxides n'-type semi-conductivity. The process of doping indicates that a cation other than the transition metal cation experienced in the majority of the bulk is incorporated into the crystal structure of the semiconductor, either by replacing the cation, or interstitially adding to the matrix. Doping of ZnO with Li leads to greater photo-adsorption of oxygen, while doping with Ga or Al suppresses photo-adsorption of oxygen. Trends in photo-adsorption tend to follow trends in photo-oxidative catalysis, as shown by the high degree of photo-oxidative catalytic activity of TiO and ZnO, while other transition elements like VO shows no photo-oxidative catalytic response as well as no photo-activated adsorption of oxygen. | 7 | Physical Chemistry |
Hardenability is the depth to which a steel is hardened after putting it through a heat treatment process. It should not be confused with hardness, which is a measure of a sample's resistance to indentation or scratching. It is an important property for welding, since it is inversely proportional to weldability, that is, the ease of welding a material. | 8 | Metallurgy |
For adhesive bonding of materials, wetting of the surface, which can be measured by the contact angle, is critical to successful adhesive application. To determine how well a liquid wets a solid surface is proportional to the contact angle from the liquid while on the solid. This is determined by the respective surface tensions of the solid and liquid. William Zisman's contribution to adhesives in the way of his Zisman Plot, which has a variation today that graphs 1-cos(θ) vs γ . In this variation the X-intercept gives the critical surface tension of the liquid needed to effectively wet the solid surface. There are two steps when graphing the data which are to neglect all the points around zero on the y-axis to initially plot the line of best fit to find γ ; however, when graphing the line initially if a point near 0 lands to the right of the intersection redo the regression including that point to make the measurement of the critical surface tension, γ, more accurate. A table of variables and an example can be seen below. | 7 | Physical Chemistry |
An aglycone (aglycon or genin) is the chemical compound remaining after the glycosyl group on a glycoside is replaced by a hydrogen atom. For example, the aglycone of a cardiac glycoside would be a steroid molecule. | 0 | Organic Chemistry |
The program runs either with fixed input data for the number of years determined by the user. This option can be used to predict future developments based on long-term average input values, e.g. rainfall, as it will be difficult to assess the future values of the input data year by year.
The program also offers the possibility to follow historic records with annually changing input values (e.g. rainfall, irrigation, cropping rotations), the calculations must be made year by year. If this possibility is chosen, the program creates a transfer file by which the final conditions of the previous year (e.g. water table and salinity) are automatically used as the initial conditions for the subsequent period. This facility makes it also possible to use various generated rainfall sequences drawn randomly from a known rainfall probability distribution and to obtain a stochastic prediction of the resulting output parameters.
Some input parameters should not be changed, like the nodal network relations, the system geometry, the thickness of the soil layers, and the total porosity, otherwise illogical jumps occur in the water and salt balances. These parameters are also stored in the transfer file, so that any impermissible change is overruled by the transfer data. In some cases of incorrect changes, the program will stop and request the user to adjust the input. | 9 | Geochemistry |
Nicholas J. Turro (May 18, 1938 – November 24, 2012) was an American chemist, Wm. P. Schweitzer Professor of Chemistry at Columbia University. He was a world renowned organic chemist and leading world expert on organic photochemistry. He was the recipient of the 2011 Arthur C. Cope Award in Organic Chemistry, given annually "to recognize outstanding achievement in the field of organic chemistry, the significance of which has become apparent within the five years preceding the year in which the award will be considered." He was also the recipient of the 2000 Willard Gibbs Award, which recognizes "eminent chemists who...have brought to the world developments that enable everyone to live more comfortably and to understand this world better."
He received his B.A. degree summa cum laude from Wesleyan University in 1960. He attended graduate school at Caltech where he received his Ph.D. degree with George S. Hammond in 1963. Following a postdoctoral year at Harvard with P. D. Bartlett, he joined the faculty at Columbia University where he was the Wm. P. Schweitzer Professor of Chemistry.
Although he worked in many areas of chemistry, he was most well known for his work in photochemistry and spectroscopy, which he applied to studies involving small molecules in solution, interfaces, thin films, polymers, biological systems including DNA and carbohydrates, nanomaterials, supramolecular and "super-duper" molecular systems. His success in these areas is evident by his co-authorship of over 1000 papers. His expertise in photochemistry, spectroscopy and organic chemistry lead to a large network of international collaborators, including Fortune 500 companies such as Procter and Gamble.
He authored the influential books Molecular Photochemistry published in 1965, considered the "bible" of the field for several generations by organic photochemists, and Modern Molecular Photochemistry published in 1978. The latter was comprehensively revised as Principles of Molecular Photochemistry: An Introduction in 2008 and later as Modern Molecular Photochemistry of Organic Molecules in 2010 both of which were co-authored with V. Ramamurthy at University of Miami and J.C. Scaiano at the University of Ottawa. Turro has been selected as one of the most highly cited chemists for the past two decades, and has published over 900 research papers. He was a member of both the National Academy of Sciences and the American Academy of Arts and Sciences. | 5 | Photochemistry |
In chemistry the reactivity–selectivity principle or RSP states that a more reactive chemical compound or reactive intermediate is less selective in chemical reactions. In this context selectivity represents the ratio of reaction rates.
This principle was generally accepted until the 1970s when too many exceptions started to appear. The principle is now considered obsolete.
A classic example of perceived RSP found in older organic chemistry textbooks concerns the free radical halogenation of simple alkanes. Whereas the relatively unreactive bromine reacts with 2-methylbutane predominantly to 2-bromo-2-methylbutane, the reaction with much more reactive chlorine results in a mixture of all four regioisomers.
Another example of RSP can be found in the selectivity of the reaction of certain carbocations with azides and water. The very stable triphenylmethyl carbocation derived from solvolysis of the corresponding triphenylmethyl chloride reacts 100 times faster with the azide anion than with water. When the carbocation is the very reactive tertiary adamantane carbocation (as judged from diminished rate of solvolysis) this difference is only a factor of 10.
Constant or inverse relationships are just as frequent. For example, a group of 3- and 4-substituted pyridines in their reactivity quantified by their pKa show the same selectivity in their reactions with a group of alkylating reagents.
The reason for the early success of RSP was that the experiments involved very reactive intermediates with reactivities close to kinetic diffusion control and as a result the more reactive intermediate appeared to react slower with the faster substrate.
General relationships between reactivity and selectivity in chemical reactions can successfully be explained by Hammond's postulate.
When reactivity-selectivity relationships do exist they signify different reaction modes. In one study the reactivity of two different free radical species (A, sulfur, B carbon) towards addition to simple alkenes such as acrylonitrile, vinyl acetate and acrylamide was examined.
The sulfur radical was found to be more reactive (6*10 vs. 1*10 M.s) and less selective (selectivity ratio 76 vs 1200) than the carbon radical. In this case, the effect can be explained by extending the Bell–Evans–Polanyi principle with a factor accounting for transfer of charge from the reactants to the transition state of the reaction which can be calculated in silico:
with the activation energy and the reaction enthalpy change. With the electrophilic sulfur radical the charge transfer is largest with electron-rich alkenes such as acrylonitrile but the resulting reduction in activation energy (β is negative) is offset by a reduced enthalpy. With the nucleophilic carbon radical on the other hand both enthalpy and polar effects have the same direction thus extending the activation energy range. | 7 | Physical Chemistry |
About 164,000,000 tons were produced in 2019. It is obtained as the "heavy" (i.e., difficult to distill) fraction. Material with a boiling point greater than around 500 °C is considered asphalt. Vacuum distillation separates it from the other components in crude oil (such as naphtha, gasoline and diesel). The resulting material is typically further treated to extract small but valuable amounts of lubricants and to adjust the properties of the material to suit applications. In a de-asphalting unit, the crude bitumen is treated with either propane or butane in a supercritical phase to extract the lighter molecules, which are then separated. Further processing is possible by "blowing" the product: namely reacting it with oxygen. This step makes the product harder and more viscous.
Bitumen is typically stored and transported at temperatures around . Sometimes diesel oil or kerosene are mixed in before shipping to retain liquidity; upon delivery, these lighter materials are separated out of the mixture. This mixture is often called "bitumen feedstock", or BFS. Some dump trucks route the hot engine exhaust through pipes in the dump body to keep the material warm. The backs of tippers carrying asphalt, as well as some handling equipment, are also commonly sprayed with a releasing agent before filling to aid release. Diesel oil is no longer used as a release agent due to environmental concerns. | 7 | Physical Chemistry |
It is assumed that the scattered light intensity is a linear function of species’ concentrations.
where is a proportionality constant. | 7 | Physical Chemistry |
Copy number analysis is the process of analyzing data produced by a test for DNA copy number variation in an organism's sample. One application of such analysis is the detection of chromosomal copy number variation that may cause or may increase risks of various critical disorders. Copy number variation can be detected with various types of tests such as fluorescent in situ hybridization, comparative genomic hybridization and with high-resolution array-based tests based on array comparative genomic hybridization (or aCGH), SNP array technologies and high resolution microarrays that include copy number probes as well an SNPs. Array-based methods have been accepted as the most efficient in terms of their resolution and high-throughput nature and the highest coverage (choose an array with over 2 million probes) and they are also referred to as virtual karyotype. Data analysis for an array-based DNA copy number test can be very challenging though due to very high volume of data that come out of an array platform.
BAC (Bacterial Artificial Chromosome) arrays were historically the first microarray platform to be used for DNA copy number analysis. This platform is used to identify gross deletions or amplifications in DNA. Such anomalies for example are common in cancer and can be used for diagnosis of many developmental disorders. Data produced by such platforms are usually low to medium resolution in terms of genome coverage. Usually, log-ratio measurements are produced by this technology to represent deviation of patient's copy number state from normal. Such measurements then are studied and those that significantly differ from zero value are announced to represent a part of a chromosome with an anomaly (an abnormal copy number state). Positive log-ratios indicate a region of DNA copy number gain and negative log-ratio values mark a region of DNA copy number loss. Even a single data point can be declared an indication of a copy number gain or a copy number loss in BAC arrays. | 1 | Biochemistry |
A method for phenolic content quantification is volumetric titration. An oxidizing agent, permanganate, is used to oxidize known concentrations of a standard solution, producing a standard curve. The content of the unknown phenols is then expressed as equivalents of the appropriate standard.
Some methods for quantification of total phenolic content are based on colorimetric measurements. Total phenols (or antioxidant effect) can be measured using the Folin-Ciocalteu reaction. Results are typically expressed as gallic acid equivalents (GAE). Ferric chloride (FeCl) test is also a colorimetric assay.
Lamaison and Carnet have designed a test for the determination of the total flavonoid content of a sample (AlCI method). After proper mixing of the sample and the reagent, the mixture is incubated for 10 minutes at ambient temperature and the absorbance of the solution is read at 440 nm. Flavonoid content is expressed in mg/g of quercetin.
Quantitation results produced by the means of diode array detector-coupled HPLC are generally given as relative rather than absolute values as there is a lack of commercially available standards for every phenolic molecules. The technique can also be coupled with mass spectrometry (for example, HPLC–DAD–ESI/MS) for more precise molecule identification. | 0 | Organic Chemistry |
Several properties make NiSi an important local contact material in the area of microelectronics, among them a reduced thermal budget, low resistivity of 13–14 μΩ·cm and a reduced Si consumption when compared to alternative compounds. | 8 | Metallurgy |
At the end of World War II, the Allies occupied Germany and found large stockpiles of chemical weapons that they did not know how to dispose of or deal with. Ultimately, the Allies disposed large quantities of these chemical weapons into the Baltic Sea, including 32 000 tonnes of chemical munitions and chemical warfare agents dumped into the Bornholm Basin, and another 2000 tonnes of chemical weapons in the Gotland Basin.
The majority of these chemical munitions were dumped into the sea while contained in simple wooden crates, leading to a rapid proliferation of chemicals. Chemical Weapons being disposed in the ocean during the 20th century is not unique to the Baltic Sea, and other heavily contaminated areas where disposal occurred are the European, Japanese, Russian, and United States coasts. These chemical weapons dumped in the ocean pose a continual environmental and human health risk, and chemical agents and breakdown products from said agents have been recently been identified in ocean sediment near historical dumping sites. When chemical weapons are dumped or otherwise improperly disposed of, the chemical agents are quickly distributed over a wide range. The long term impacts of this wide-scale distribution are unknown, but known to be negative. In the Vietnam War of 1955–1975, a chemical weapon called agent orange was widely used by United States forces. The United States utilized agent orange as a type of tactical herbicide, aiming to destroy Vietnamese foliage and plant life to ease military access. This usage of agent orange has left lasting impacts that are still observable today in the Vietnamese environment, causing disease, stunted growth, and deformities. | 1 | Biochemistry |
Elly Schwab-Agallidis (born Elly Agallidis, , ; – ) was a Greek physicist/physical chemist and one of the first women in Greece to be awarded a PhD in the field. She was the wife of Georg-Maria Schwab, who met her in Munich as the supervisor of the experimental work for her doctoral thesis; the couple then worked together as researchers in the Kanellopoulos Institute after they emigrated in Greece. Her most famous work concerned the properties and reactivity of parahydrogen. | 7 | Physical Chemistry |
Sagan and Khare note the presence of tholins through multiple locations: "as a constituent of the Earth's primitive oceans and therefore relevant to the origin of life; as a component of red aerosols in the atmospheres of the outer planets and Titan; present in comets, carbonaceous chondrites asteroids, and pre-planetary solar nebulae; and as a major constituent of the interstellar medium." The surfaces of comets, centaurs, and many icy moons and Kuiper-belt objects in the outer Solar System are rich in deposits of tholins. | 9 | Geochemistry |
High-frequency vibrating screening equipment is a shaker whose frame is fixed and the drive vibrates only the screen cloth. High frequency vibration equipment is for particles that are in this particle size range of an 1/8 in (3 mm) down to a +150 mesh. Traditional shaker screeners have a difficult time making separations at sizes like 44 microns. At the same time, other high energy sieves like the Elcan Industries' advanced screening technology allow for much finer separations down to as fine as 10um and 5um, respectively.
These shakers usually make a secondary cut for further processing or make a finished product cut.
These shakers are usually set at a steep angle relative to the horizontal level plane. Angles range from 25 to 45 degrees relative to the horizontal level plane. | 8 | Metallurgy |
A useful way to study the interaction of an atom in a Gaussian beam is to look at the harmonic potential approximation of the intensity profile the atom experiences. In the case of the two-level atom, the potential experienced is related to its AC Stark Shift,
where is the natural line width of the excited state, is the electric dipole coupling, is the frequency of the transition, and is the detuning or difference between the laser frequency and the transition frequency.
The intensity of a gaussian beam profile is characterized by the wavelength , minimum waist , and power of the beam . The following formulas define the beam profile:
To approximate this Gaussian potential in both the radial and axial directions of the beam, the intensity profile must be expanded to second order in and for and respectively and equated to the harmonic potential . These expansions are evaluated assuming fixed power.
This means that when solving for the harmonic frequencies (or trap frequencies when considering optical traps for atoms), the frequencies are given as:
so that the relative trap frequencies for the radial and axial directions as a function of only beam waist scale as: | 1 | Biochemistry |
Ultrasound attenuation spectroscopy is a method for characterizing properties of fluids and dispersed particles. It is also known as acoustic spectroscopy.
There is an international standard for this method.
Measurement of attenuation coefficient versus ultrasound frequency yields raw data for further calculation of various system properties. Such raw data are often used in the calculation of the particle size distribution in heterogeneous systems such as emulsions and colloids. In the case of acoustic rheometers, the raw data are converted into extensional viscosity or volume viscosity.
Instruments that employ ultrasound attenuation spectroscopy are referred to as Acoustic spectrometers. | 7 | Physical Chemistry |
Vargulin (with the associated luciferase) has applications in biotechnology:
* in a variety of assays, to report gene or gene expression after luciferase have been genetically introduced in cells,
* to detect ATP, that is used in the vargulin/luciferase reaction (cell viability assays).
Although less stable, the Cypridina system is useful because can be used in multiplex assays with other (red-emitting) luciferin assays. | 1 | Biochemistry |
ANCAP reports that some RHD cars imported to Australia did not perform as well on crash tests as the LHD versions, although the cause is unknown, and may be due to differences in testing methodology. | 4 | Stereochemistry |
Seraj has established a well-equipped plant biotechnology laboratory at the University of Dhaka. She has been a co-principal investigator in several projects, such as the Generation Challenge Program (GCP)—an initiative to use molecular biology to help boost agricultural production.
Seraj has not only worked on fine mapping of the major QTLs for salinity tolerance in Pokkali, but also characterized traditional rice landraces with the aim of finding genetic loci responsible for salt tolerance and applying markers linked to these loci to aid breeding programs for incorporation of salinity tolerance in rice. She also works on developing genetically modified rice varieties with improved salt tolerance suitable for growing in the coastal region of Bangladesh. She was the recipient of the PEER award (joint USAID-NSF initiative) for using next generation sequencing technologies to find the basis of salt tolerance of a rice landrace endemic to the Bangladesh coast, where University of Texas at Austin served as the host for collaborative work.
Seraj has been a visiting scientist in [http://beta.irri.org/solutions/index.php?option=com_content&task=view&id=51&Itemid=69 PBGB, IRRI] (Constructs for salinity tolerance with Dr. John Bennett Jan-March 1998), PBGB & CSWS Division, IRRI (IRRI-PETRRA Bangladesh project on development of MV rice for the coastal wetlands of Bangladesh, June 11–29, 2002 and June 16–20, 2003), USDA research station at Beaumont, Texas, USA ( Aug. 4–16, 2003) and at the Department of Molecular, Cell and Developmental Biology, University of Texas, Austin, USA as Norman Borlaug Fellow (August 15-December 15, 2005). She has been honored with Visiting researcher status at University of Texas at Austin (October 2014-September, 2020). She was awarded the Annanya Award, 2017 for her scientific research. She was invited for a Tedx talk on how to save crops from sea level rise and salinity (Jan 16, 2018). She was featured in NHK TV, Japan in a talk on Science for Sustainable Earth in 2019. | 1 | Biochemistry |
In thermodynamics, the limit of local stability with respect to small fluctuations is clearly defined by the condition that the second derivative of Gibbs free energy is zero.
The locus of these points (the inflection point within a G-x or G-c curve, Gibbs free energy as a function of composition) is known as the spinodal curve. For compositions within this curve, infinitesimally small fluctuations in composition and density will lead to phase separation via spinodal decomposition. Outside of the curve, the solution will be at least metastable with respect to fluctuations. In other words, outside the spinodal curve some careful process may obtain a single phase system. Inside it, only processes far from thermodynamic equilibrium, such as physical vapor deposition, will enable one to prepare single phase compositions. The local points of coexisting compositions, defined by the common tangent construction, are known as a binodal coexistence curve, which denotes the minimum-energy equilibrium state of the system. Increasing temperature results in a decreasing difference between mixing entropy and mixing enthalpy, and thus the coexisting compositions come closer. The binodal curve forms the basis for the miscibility gap in a phase diagram. The free energy of mixing changes with temperature and concentration, and the binodal and spinodal meet at the critical or consolute temperature and composition. | 7 | Physical Chemistry |
The Young's modulus of a mineral can be predicted by varying one cell parameter at a time and observing the evolution of the stress tensor. Because the raw output of a simulation includes energy and volume, the integrated version of the Birch-Murnaghan equation of state is often used to determine bulk modulus. | 3 | Analytical Chemistry |
The sorbent tube and the focusing trap may be packed with one or more sorbents. The type and number of sorbents depends on a number of factors including the sampling setup, the analyte volatility range, analyte concentration, and the humidity of the sample.
One of the most versatile and popular sorbents for thermal desorption is poly(2,6-diphenyl-p-phenylene oxide), known by its trademark Tenax. | 3 | Analytical Chemistry |
While there are many abiotic sources and sinks for O, the presence of the profuse concentration of free oxygen in modern Earth's atmosphere and ocean is attributed to O production from the biological process of oxygenic photosynthesis in conjunction with a biological sink known as the biological pump and a geologic process of carbon burial involving plate tectonics. Biology is the main driver of O flux on modern Earth, and the evolution of oxygenic photosynthesis by bacteria, which is discussed as part of the Great Oxygenation Event, is thought to be directly responsible for the conditions permitting the development and existence of all complex eukaryotic metabolism. | 5 | Photochemistry |
Hyperconjugation is the stabilizing interaction that results from the interaction of the electrons in a sigma bond (usually C-H or C-C) with an adjacent empty (or partially filled) non-bonding p-orbital or antibonding π orbital or an antibonding sigma orbital to give an extended molecular orbital that increases the stability of the system. Hyperconjugation can be used to explain phenomena such as the gauche effect and anomeric effect.
Orbital symmetry is important when dealing with orbitals that contain directional components like p and d. An example of such an effect is square planar low-spin d transition metal complexes. These complexes exist as square planar complexes due to the directionality of the metal center's d orbitals despite fewer steric congestion in a tetrahedral geometric structure. This is simple one example of many varied examples, including aspects of pericyclic reactions such as the Diels-Alder reaction, among others.
Electrostatic interactions include both attractive and repulsive forces associated with the build-up of charge in a molecule. Electrostatic interactions are generally too weak to be considered traditional bonds or are prevented from forming a traditional bond, possibly by a steric effect. A bond is usually defined as two atoms approaching closer than the sum of their Van der Waal radii. Hydrogen bonding borders on being an actual "bond" and an electrostatic interaction. While an attractive electrostatic interaction is considered a "bond" if it gets too strong, a repulsive electrostatic interaction is always an electrostatic effect regardless of strength. An example of a repulsive effect is a molecule contorting to minimize the coulombic interactions of atoms that hold like charges.
Electronic spin state at it simplest describes the number of unpaired electrons in a molecule. Most molecules including the proteins, carbohydrates, and lipids that make up the majority of life have no unpaired electrons even when charged. Such molecules are called singlet molecules, since their paired electrons have only one spin state. In contrast, dioxygen under ambient conditions has two unpaired electrons. Dioxygen is a triplet molecule, since the two unpaired electrons allow for three spin states. The reaction of a triplet molecule with a singlet molecule is spin-forbidden in quantum mechanics. This is the major reasons there is a very high reaction barrier for the extremely thermodynamically favorable reaction of singlet organic molecules with triplet oxygen. This kinetic barrier prevents life from bursting into flames at room temperature.
Electronic spin states are more complex for transition metals. To understand the reactivity of transition metals, it is essential to understand the concept of d electron configuration as well as high-spin and low-spin configuration. For example, a low-spin d transition metal complex is usually square planar substitutionally inert with no unpaired electrons. In contrast, a high-spin d transition metal complex is usually octahedral, substitutionally labile, with two unpaired electrons.
Jahn–Teller effect is the geometrical distortion of non-linear molecules under certain situations. Any non-linear molecule with a degenerate electronic ground state will undergo a geometrical distortion that removes that degeneracy. This has the effect of lowering the overall energy. The Jahn–Teller distortion is especially common in certain transition metal complexes; for example, copper(II) complexes with 9 d electrons.
Trans influence is the influence that a ligand in a square or octahedral complex has on the bond to the ligand trans to it. It is caused by electronic effects, and manifests itself as the lengthening of the trans bonds and as an effect on the overall energy of the complex. | 7 | Physical Chemistry |
Photoredox catalysis is a branch of photochemistry that uses single-electron transfer. Photoredox catalysts are generally drawn from three classes of materials: transition-metal complexes, organic dyes, and semiconductors. While organic photoredox catalysts were dominant throughout the 1990s and early 2000s, soluble transition-metal complexes are more commonly used today. | 5 | Photochemistry |
To be representative, the layer must meet the following criteria:
• The volume fraction of each type of particle is the same in the representative layer as in the sample as a whole.
• The surface area fraction of each type of particle is the same in the representative layer as in the sample as a whole.
• The void fraction of the representative layer is the same as in the sample.
• The representative layer is nowhere more than one particle thick. Note this means the “thickness” of the representative layer is not uniform. This criterion is imposed so that we can assume that a given photon of light has only one interaction with the layer. It might be transmitted, remitted, or absorbed as a result of this interaction, but it is assumed not to interact with a second particle within the same layer.
In the above discussion, when we talk about a “type” of particle, we must clearly distinguish between particles of different composition. In addition, however, we must distinguish between particles of different sizes. Recall that scattering is envisioned as a surface phenomenon and absorption is envisioned as occurring at the molecular level throughout the particle. Consequently, our expectation is that the contribution of a “type” of particle to absorption will be proportional to the volume fraction of that particle in the sample, and the contribution of a “type” of particle to scattering will be proportional to the surface area fraction of that particle in the sample. This is why our “representative layer” criteria above incorporate both volume fraction and surface area fraction. Since small particles have larger surface area-to-volume ratios than large particles, it is necessary to distinguish between them. | 7 | Physical Chemistry |
In contrast to the oxidative citric acid cycle, the reverse or reductive cycle has a few key differences. There are three enzymes specific to the reductive citric acid cycle – citrate lyase, fumarate reductase, and α-ketoglutarate synthase.
The splitting of citric acid to oxaloacetate and acetate is in catalyzed by citrate lyase, rather than the reverse reaction of citrate synthase. Succinate dehydrogenase is replaced by fumarate reductase and α-ketoglutarate synthase replaces α-ketoglutarate dehydrogenase.
The conversion of succinate to 2-oxoglutarate is also different. In the oxidative reaction this step is coupled to the reduction of NADH. However, the oxidation of 2-oxoglutarate to succinate is so energetically favorable, that NADH lacks the reductive power to drive the reverse reaction. In the rTCA cycle, this reaction has to use a reduced low potential ferredoxin. | 1 | Biochemistry |
Retinal guanylyl cyclase 1 also known as guanylate cyclase 2D, retinal is an enzyme that in humans is encoded by the GUCY2D (guanylate cyclase 2D) gene. | 1 | Biochemistry |
* halocarbonates, including carbonate fluorides, carbonate chlorides, carbonate bromides
* phosphates, including fluoride phosphates, chloride phosphate, phosphate molybdates, phosphate arsenates
* borates
** halide borates, including fluoride borates borate chlorides, borate bromides, borate iodides
** chalcogenide borates, including sulfide borates
** borate carbonates, borate nitrates, borate sulfates, borate phosphates
** borate acetates
** Condensed borates: borosulfates, boroselenates, borotellurates, boroantimonates, borophosphates, boroselenites
* sulfates
** sulfate fluorides, sulfate chlorides
** sulfate arsenate
* selenite fluorides
* iodate fluorides
* Silicates
** sulfide silicates | 7 | Physical Chemistry |
On blood tests, an elevated level of lactate dehydrogenase usually indicates tissue damage, which has multiple potential causes, reflecting its widespread tissue distribution:
*Hemolytic anemia
*Vitamin B12 deficiency anemia
*Infections such as infectious mononucleosis, meningitis, encephalitis, HIV/AIDS. It is notably increased in sepsis.
*Infarction, such as bowel infarction, myocardial infarction and lung infarction
*Acute kidney disease
*Acute liver disease
*Rhabdomyolysis
*Pancreatitis
*Bone fractures
*Cancers, notably testicular cancer and lymphoma. A high LDH after chemotherapy may indicate that it has not been successful.
*Severe shock
*Hypoxia
Low and normal levels of LDH do not usually indicate any pathology. Low levels may be caused by large intake of vitamin C.
LDH is a protein that normally appears throughout the body in small amounts. | 1 | Biochemistry |
A special case of a chemical synapse is the neuromuscular junction, in which the axon of a motor neuron terminates on a muscle fiber. In such cases, the released neurotransmitter is acetylcholine, which binds to the acetylcholine receptor, an integral membrane protein in the membrane (the sarcolemma) of the muscle fiber. However, the acetylcholine does not remain bound; rather, it dissociates and is hydrolyzed by the enzyme, acetylcholinesterase, located in the synapse. This enzyme quickly reduces the stimulus to the muscle, which allows the degree and timing of muscular contraction to be regulated delicately. Some poisons inactivate acetylcholinesterase to prevent this control, such as the nerve agents sarin and tabun, and the insecticides diazinon and malathion. | 7 | Physical Chemistry |
Products using amphetamine base are now marketed. Dyanavel XR, a liquid suspension form became available in 2015, and contains about 24% levoamphetamine. Adzenys XR, an orally dissolving tablet came to market in 2016 and contains 25% levoamphetamine. | 4 | Stereochemistry |
In terms of mechanism, the insertion of alkenes into M–H bond and into M–C bonds are described similarly. Both involve four-membered transition states that place the less substituted carbon on the metal.
The reverse of olefin insertion into a metal-hydrogen bond is β-hydride elimination. The Principle of Microscopic Reversibility requires that the mechanism of β-hydride elimination follow the same pathway as the insertion of alkenes into metal hydride bonds. The first requirement for β-hydride elimination is the presence of a hydrogen at a position that is β with respect to the metal. β-elimination requires a vacant coordination position on the metal that will accommodate the hydrogen that is abstracted. | 0 | Organic Chemistry |
Loss-of-function mutations in the STAT3 gene result in hyperimmunoglobulin E syndrome, associated with recurrent infections as well as disordered bone and tooth development.
Gain-of-function mutations in the STAT3 gene have been reported to cause multi-organ early onset auto-immune diseases; such as thyroid disease, diabetes, intestinal inflammation, and low blood counts, while constitutive STAT3 activation is associated with various human cancers and commonly suggests poor prognosis. It has anti-apoptotic as well as proliferative effects.
STAT3 can promote oncogenesis by being constitutively active through various pathways as mentioned elsewhere. A tumor suppressor role of STAT3 has also been reported. In the report on human glioblastoma tumor, or brain cancer, STAT3 was shown to have an oncogenic or a tumor suppressor role depending upon the mutational background of the tumor. A direct connection between the PTEN-Akt-FOXO axis (suppressive) and the leukemia inhibitory factor receptor beta (LIFRbeta)-STAT3 signaling pathway (oncogenic) was shown.
Increased activity of STAT3 in cancer cells, leads to changes in the function of protein complexes that control expression of inflammatory genes, with result profound change in the secretome and the cell phenotypes, their activity in the tumor, and their capacity for metastasis. | 1 | Biochemistry |
FDA stock solution is prepared by dissolving 5 mg of fluorescein diacetate in 1 ml acetone, and sucrose may be added for live cell viability testing. FDA stain must be kept in the dark at 4°C or it will spoil. | 1 | Biochemistry |
Chemically, phosphatidylethanols are phospholipids carrying two fatty acid chains, which are variable in structure, and one phosphate ethyl ester. | 1 | Biochemistry |
In most vertebrates, digestion is a multistage process in the digestive system, starting from ingestion of raw materials, most often other organisms. Ingestion usually involves some type of mechanical and chemical processing. Digestion is separated into four steps:
# Ingestion: placing food into the mouth (entry of food in the digestive system),
# Mechanical and chemical breakdown: mastication and the mixing of the resulting bolus with water, acids, bile and enzymes in the stomach and intestine to break down complex chemical species into simple structures,
# Absorption: of nutrients from the digestive system to the circulatory and lymphatic capillaries through osmosis, active transport, and diffusion, and
# Egestion (Excretion): Removal of undigested materials from the digestive tract through defecation.
Underlying the process is muscle movement throughout the system through swallowing and peristalsis. Each step in digestion requires energy, and thus imposes an "overhead charge" on the energy made available from absorbed substances. Differences in that overhead cost are important influences on lifestyle, behavior, and even physical structures. Examples may be seen in humans, who differ considerably from other hominids (lack of hair, smaller jaws and musculature, different dentition, length of intestines, cooking, etc.).
The major part of digestion takes place in the small intestine. The large intestine primarily serves as a site for fermentation of indigestible matter by gut bacteria and for resorption of water from digests before excretion.
In mammals, preparation for digestion begins with the cephalic phase in which saliva is produced in the mouth and digestive enzymes are produced in the stomach. Mechanical and chemical digestion begin in the mouth where food is chewed, and mixed with saliva to begin enzymatic processing of starches. The stomach continues to break food down mechanically and chemically through churning and mixing with both acids and enzymes. Absorption occurs in the stomach and gastrointestinal tract, and the process finishes with defecation. | 1 | Biochemistry |
Sulfolipids are sulfur containing lipids. Sulfoquinovosyl diacylglycerols are the predominant sulfolipids present in plants. In leaves its content comprises up to 3 - 6% of the total sulfur present. This sulfolipid is present in plastid membranes and likely is involved in chloroplast functioning. The route of biosynthesis and physiological function of sulfoquinovosyl diacylglycerol is still under investigation. From recent studies it is evident that sulfite it the likely sulfur precursor for the formation of the sulfoquinovose group of this lipid. | 1 | Biochemistry |
The specific heat capacity of LAGP materials with general formula fits into the Maier-Kelley polynomial law in the temperature range from room temperature to 700 °C:
where
: is the absolute temperature,
: are fitting constants.
Typical values are in the range of 0.75 - 1.5 J⋅g⋅K in the temperature interval 25 - 100 °C. The constants increase with the x value, i.e. with both the aluminium and the lithium content, while the constant does not follow a precise trend. As a result, the specific heat capacity of LAGP is expected to increase as the Al content grows and the Ge content decreases, which is consistent with data about the relative specific heats of aluminium and germanium compounds.
In addition, the thermal diffusivity of LAGP follows a decreasing trend with increasing temperature, irrespective of the aluminium content:
The aluminium level affects the exponent , which varies from 0.08 (high Al content) to 0.11 (low Al content). Such small values suggest the presence of a large number of point defects in the material, which is highly beneficial for solid ionic conductors. Finally, the expression for the thermal conductivity can be written:
where
: is the heat capacity per unit volume,
: is the average phonon group velocity,
: is the phonon mean free path,
: is the density of the material.
Taking everything into account, as the aluminium content in LAGP increases, the ionic conductivity increases as well, while the thermal conductivity decreases, since a larger number of lithium ions enhances the phonon scattering, thus reducing the phonon mean free path and the thermal transport in the material. Therefore, thermal and ionic transports in LAGP ceramics are not correlated: the corresponding conductivities follow opposite trends as a function of the aluminium content and are affected in a different way by temperature variations (e.g., the ionic conductivity increases by one order of magnitude upon an increase from room temperature to 100 °C, while the thermal conductivity increases by only 6%). | 7 | Physical Chemistry |
Hydrothermal vents contribute dissolved Si to the ocean Si reservoir. Currently, it is challenging to determine the magnitude of hydrothermal Si fluxes, due to lack of data on the δSi values associated with this flux. There are only two published data points of the δSi value of hydrothermal vents (−0.4‰ and −0.2‰). | 9 | Geochemistry |
In 1922, Bowen became a Fellow in Chemistry of University College, Oxford, succeeding R. B. Bourdillon, who was briefly Fellow in Chemistry at the College from 1919 to 1921, but who subsequently changed his field of interest from chemistry to medicine. Bowen also served as Domestic Bursar of University College and as Junior Proctor of Oxford University in 1936.
Created a Fellow of the Royal Society in 1935 for his research into fluorescence, he was awarded the Davy Medal in 1963. He wrote a seminal book called The Chemical Aspects of Light. He was Vice-President of the Faraday Society and of the Chemical Society.
Much of Bowens research work was carried out at the Balliol-Trinity Laboratories in Oxford. He was an accomplished glass blower for his chemical apparatus and even produced artworks in glass. His 1966 Liversidge Lecture on Fluorescence was based on his lifes research. After retirement in June 1965, he was elected as an Honorary Fellow of University College on 6 October 1965. He was one of the longest serving Fellows of that college (43 years as an ordinary Fellow and a total of 59 years). There is a room in the college named after him. He was also a prominent Worcester Old Elizabethan serving on its Committee for many years and organising the Oxford branch of that club.
During May 1931, Bowen, then a University don, attended a series of three lectures given by Albert Einstein at Rhodes House in Oxford. After the second lecture on 16 May, he helped rescue the blackboard used by Einstein; Sir Francis Wylie (Warden of Rhodes House) formally presented it to the Museum of the History of Science in Oxford where it remains on prominent display to this day.
As well as chemistry, Bowen also had an interest in geology, especially around Ringstead Bay on the Jurassic Coast in Dorset on the south coast of England. Perisphinctes boweni, an ammonite from the Jurassic period, is named after him. Bowen was involved with the Oxford University Museum of Natural History and produced a scale model of the sun, earth, and moon, for the upper galleries in the museum. | 5 | Photochemistry |
Fe–Ni metal clusters are crucial for energy production in many bacteria. A primary source of energy in bacteria is the oxidation and reduction of H which is performed by hydrogenase enzymes.
These enzymes are able to create a charge gradient across the cell membrane which serves as an energy store. In aerobic environments, the oxidation and reduction of oxygen is the primary energy source. However, many bacteria are capable of living in environments where O supply is limited and use H as their primary energy source . The hydrogense enzymes which provide energy to the bacteria are centered around either a Fe–Fe or Fe–Ni active site. H metabolism is not used by humans or other complex life forms, but proteins in the mitochondria of mammalian life appear to have evolved from hydrogenase enzymes, indicating that hydrogenase is a crucial step in the evolutionary development of metabolism.
The active site of Fe–Ni containing hydrogenase enzymes often is composed of one or more bridging sulfur ligands, carbonyl, cyanide and terminal sulfur ligands. The non-bridging sulfur ligands are often cystine amino acid residues that attach the active site to the protein backbone. Metal–metal bonds between the Fe and Ni have not been observed. Several oxidation states of the Fe–Ni core have been observed in a variety of enzymes, though not all appear to be catalytically relevant.
The extreme oxygen and carbon monoxide sensitivity of these enzymes presents a challenge when studying the enzymes, but many crystallographic studies have been performed. Crystal structures for enzymes isolated from D. gigas, Desulfovibrio vulgaris, Desulfovibrio fructosovorans, Desulfovibrio desulfuricans, and Desulfomicrobium baculatum have been obtained, among others. A few bacteria, such as R. eutropha, have adapted to survive under ambient oxygen levels.
These enzymes have inspired study of structural and functional model complexes in hopes of making synthetic catalysis for hydrogen production (see Fe–Ni and hydrogen production, below, for more detail). | 7 | Physical Chemistry |
Electroreflectance (also: electromodulated reflectance) is the change of reflectivity of a solid due to the influence of an electric field close to, or at the interface of the solid with a liquid. The change in reflectivity is most noticeable at very specific ranges of photon energy, corresponding to the band gaps at critical points of the Brillouin zone.
The electroreflectance effect can be used to get a clearer picture of the band structure at critical points where there is a lot of near degeneracy. Normally, the band structure at critical points (points of special interest) has to be measured within a background of adsorption from non-critical points at the Brillouin zone boundary. Using a strong electric field, the adsorption spectrum can be changed to a spectrum that shows peaks at these critical points, essentially lifting the critical points from the background.
The effect was first discovered and understood in semiconductor materials, but later research proved that metals also exhibit electroreflectance. An early observation of the changing optical reflectivity of gold due to a present electric field was attributed to a change in refractive index of the neighboring liquid. However, it was shown that this could not be the case. The new conclusion was that the effect had to come from a modulation of the near-surface layer of the gold. | 7 | Physical Chemistry |
A galactosylceramide, or galactocerebroside is a type of cerebroside consisting of a ceramide with a galactose residue at the 1-hydroxyl moiety.
The galactose is cleaved by galactosylceramidase.
Galactosylceramide is a marker for oligodendrocytes in the brain, whether or not they form myelin. | 1 | Biochemistry |
Lightly crosslinked refers to the lightly woven polymer portion of the scavenger. This type of resin becomes swollen in a particular solvent, allowing an impurity to react with a specified functional group. In many times single solvents are not sufficient to expand the resin, in which case a second solvent must be added. Examples of a secondary solvent, or co-solvent, would be Tetrahydrofuran, or THF. Typically contain 1–3% of divinylbenzene. | 0 | Organic Chemistry |
A thermodynamic limit does not exist in all cases. Usually, a model is taken to the thermodynamic limit by increasing the volume together with the particle number while keeping the particle number density constant. Two common regularizations are the box regularization, where matter is confined to a geometrical box, and the periodic regularization, where matter is placed on the surface of a flat torus (i.e. box with periodic boundary conditions). However, the following three examples demonstrate cases where these approaches do not lead to a thermodynamic limit:
* Particles with an attractive potential that (unlike the Van der Waals force between molecules) doesn't turn around and become repulsive even at very short distances: In such a case, matter tends to clump together instead of spreading out evenly over all the available space. This is the case for gravitational systems, where matter tends to clump into filaments, galactic superclusters, galaxies, stellar clusters and stars.
* A system with a nonzero average charge density: In this case, periodic boundary conditions cannot be used because there is no consistent value for the electric flux. With a box regularization, on the other hand, matter tends to accumulate along the boundary of the box instead of being spread more or less evenly with only minor fringe effects.
* Certain quantum mechanical phenomena near absolute zero temperature present anomalies; e.g., Bose–Einstein condensation, superconductivity and superfluidity.
* Any system that is not H-stable; this case is also called catastrophic. | 7 | Physical Chemistry |
An interesting alternative synthesis of azlocillin involves activation of the substituted phenylglycine analogue 1 with 1,3-dimethyl-2-chloro-1-imidazolinium chloride (2) and then condensation with 6-APA. | 4 | Stereochemistry |
The aerosolization of bacteria in dust contributes heavily to the transport of bacterial pathogens. A well-known case of disease outbreak by bioaerosol was the meningococcal meningitis outbreak in sub-Saharan Africa, which was linked to dust storms during dry seasons.
Other outbreaks have been reportedly linked to dust events including Mycoplasma pneumonia and tuberculosis. Another instance of bioaerosol-spread health issues was an increase in human respiratory problems for Caribbean-region residents that may have been caused by traces of heavy metals, microorganism bioaerosols, and pesticides transported via dust clouds passing over the Atlantic Ocean.
Common sources of bioaerosols include soil, water, and sewage. Bioaerosols can transmit microbial pathogens, endotoxins, and allergens and can excrete both endotoxins and exotoxins. Exotoxins can be particularly dangerous when transported through the air and distribute pathogens to which humans are sensitive. Cyanobacteria are particularly prolific in their pathogen distribution and are abundant in both terrestrial and aquatic environments. | 7 | Physical Chemistry |
The Schilling test was a medical investigation used for patients with vitamin B (cobalamin) deficiency. The purpose of the test was to determine how well a patient is able to absorb B12 from their intestinal tract. The test is now considered obsolete and is rarely performed, and is no longer available at many medical centers. It is named for Robert F. Schilling. | 1 | Biochemistry |
The simplest liquid crystal phase is the nematic. In a nematic phase, organic molecules lack a crystalline positional order, but do self-align with their long axes roughly parallel. The molecules are free to flow and their center of mass positions are randomly distributed as in a liquid, but their orientation is constrained to form a long-range directional order.
The word nematic comes from the Greek (), which means "thread". This term originates from the disclinations: thread-like topological defects observed in nematic phases.
Nematics also exhibit so-called "hedgehog" topological defects. In two dimensions, there are topological defects with topological charges and . Due to hydrodynamics, the defect moves considerably faster than the defect. When placed close to each other, the defects attract; upon collision, they annihilate.
Most nematic phases are uniaxial: they have one axis (called a directrix) that is longer and preferred, with the other two being equivalent (can be approximated as cylinders or rods). However, some liquid crystals are biaxial nematic, meaning that in addition to orienting their long axis, they also orient along a secondary axis. Nematic crystals have fluidity similar to that of ordinary (isotropic) liquids but they can be easily aligned by an external magnetic or electric field. Aligned nematics have the optical properties of uniaxial crystals and this makes them extremely useful in liquid-crystal displays (LCD).
Nematic phases are also known in non-molecular systems: at high magnetic fields, electrons flow in bundles or stripes to create an "electronic nematic" form of matter. | 7 | Physical Chemistry |
Wilhelm Roentgen is credited with the discovery of radioactivity in 1895 with many others such as Antoine Henri Becquerel, Pierre Curie, and Marie Curie following closely behind to further advance the field of radioactivity. John Lawrence, a physicist at The University of California Berkeley, first used nuclear medicine in humans came in 1936 after extensive use of radioactive phosphorus in mouse models. Often called the father of nuclear medicine, Lawrence treated a leukemia patient with radiophosphorus, which was the first time a radioactive isotope has been used to treat human patients. Another pioneer in the field, Sam Seidlin, in partnership with Saul Hertz, treated a case of thyroid cancer with radioactive iodine (I-131) 1946. In the 1950s, nuclear medicine began to gain traction as a medical specialty with the Society of Nuclear Medicine forming in 1954 and later releasing the first copy of the Journal of Nuclear Medicine in 1960. The use of radioligands and nuclear tagging started to gain popularity in in the early 1960s when Elwood Jensen and Herbert Jacobsen (1962) and later Jack Gorksi, David Toft, G, Shymala, Donald Smith, and Angelo Notides (1968) attempted to identify the estrogen receptor. The American Medical Association (AMA) officially recognized Nuclear Medicine as a medical specialty in 1970 and the American Board of Nuclear Medicine was established in 1972. Progress came quickly in 1973 when Edward Hoffman, Michael M. Ter-Pogossian, and Michael E. Phelps invented the first PET camera for human use. The 1980s brought early radioligand studies for neuroendocrine tumors (NETs) which continued into the early 2000s. In 2017 the European Union (EU) approved the use of radioligand therapy for NETs with the U.S. following close behind in 2018. | 1 | Biochemistry |
Histamine has important roles in human physiology as both a hormone and a neurotransmitter. As a hormone, it is involved in the inflammatory response and itching. It regulates physiological functions in the gut and acts on the brain, spinal cord, and uterus. As a neurotransmitter, histamine promotes arousal and regulates appetite and the sleep-wake cycle. It also affects vasodilation, fluid production in tissues like the nose and eyes, gastric acid secretion, sexual function, and immune responses.
HNMT is the only enzyme in the human body responsible for metabolizing histamine within the CNS, playing a crucial role in brain function.
HNMT plays a crucial role in maintaining the proper balance of histamine in the human body. HNMT is responsible for the breakdown and metabolism of histamine, converting it into an inactive metabolite, N-methylhistamine, which inhibits HNMT gene expression in a negative feedback loop. By metabolizing histamine, HNMT helps prevent excessive levels of histamine from accumulating in various tissues and organs. This enzymatic activity ensures that histamine remains at appropriate levels to carry out its physiological functions without causing unwanted effects or triggering allergic reactions. In the central nervous system, HNMT plays an essential role in degrading histamine, where it acts as a neurotransmitter, since HNMT is the only enzyme in the body that can metabolize histamine in the CNS, ending its neurotransmitter activity.
HNMT also plays a role in the airway response to harmful particles, which is the body's physiological reaction to immune allergens, bacteria, or viruses in the respiratory system. Histamine is stored in granules in mast cells, basophils, and in the synaptic vesicles of histaminergic neurons of the airways. When exposed to immune allergens or harmful particles, histamine is released from these storage granules and quickly diffuses into the surrounding tissues. However, the released histamine needs to be rapidly deactivated for proper regulation, which is a function of HNMT. | 1 | Biochemistry |
Scavenger resins are polymers (resins) with bound functional groups that react with specific by-products, impurities, or excess reagents produced in a reaction. Polymer-bound functional groups permit the use of many different scavengers, as the functional groups are confined within a resin or are simply bound to the solid support of a bead. Simply, the functional groups of one scavenger will react minimally with the functional groups of another. | 0 | Organic Chemistry |
Assisted by Lewis acid catalyst, Friedel-Crafts methylsulfonation of aryl ring can be achieved by MsO. In contrast to MsCl, either activated or deactivated benzene derivatives can form the corresponding sulfonatesin satisfactory yields with MsO.
Examples of aromatic sulfonation with MsO:
* Sulfonation of chlorobenzene resulted in addition of methylsulfonyl group at para and ortho positions (with respect to chloride), with a ratio of 2 to 1, respectively; while reaction with Meta-dichlorobenzene gave monosulfonylated product at C4 position.
* With sulfuric acid, di-aryl sulfones were synthesized. | 0 | Organic Chemistry |
The maintenance of heterochromatin regions by RITS complexes has been described as a self-reinforcing feedback loop, in which RITS complexes stably bind the methylated histones of a heterochromatin region using the Chp1 protein and induce co-transcriptional degradation of any nascent messenger RNA (mRNA) transcripts, which are then used as RNA-dependent RNA polymerase substrates to replenish the complement of siRNA molecules to form more RITS complexes. The RITS complex localizes to heterochromatic regions through the base pairing of the nascent heterochromatic transcripts as well as through the Chp chromodomain which recognizes methylated histones found in heterochromatin. Once incorporated into the heterochromatin, the RITS complex is also known to play a role in the recruitment of other RNAi complexes as well as other chromatin modifying enzymes to specific genomic regions. Heterochromatin formation, but possibly not maintenance, is dependent on the ribonuclease protein dicer, which is used to generate the initial complement of siRNAs. | 1 | Biochemistry |
Metal-induced embrittlement (MIE) is the embrittlement caused by diffusion of metal, either solid or liquid, into the base material. Metal induced embrittlement occurs when metals are in contact with low-melting point metals while under tensile stress. The embrittler can be either solid (SMIE) or liquid (liquid metal embrittlement). Under sufficient tensile stress, MIE failure occurs instantaneously at temperatures just above melting point. For temperatures below the melting temperature of the embrittler, solid-state diffusion is the main transport mechanism. This occurs in the following ways:
* Diffusion through grain boundaries near the crack of matrix
* Diffusion of first monolayer heterogeneous surface embrittler atoms
* Second monolayer heterogenous surface diffusion of embrittler
* Surface diffusion of the embrittler over a layer of embrittler
The main mechanism of transport for SMIE is surface self-diffusion of the embrittler over a layer of embrittler that’s thick enough to be characterized as self-diffusion at the crack tip. In comparison, LMIE dominant mechanism is bulk liquid flow that penetrates at the tips of cracks. | 8 | Metallurgy |
siRNAs transfection into cells typically lowers the expression of many genes, however, the upregulation of genes is also observed. The upregulation of gene expression can partially be explained by the predicted gene targets of endogenous miRNAs. Computational analyses of more than 150 siRNA transfection experiments support a model where exogenous siRNAs can saturate the endogenous RNAi machinery, resulting in the de-repression of endogenous miRNA-regulated genes. Thus, while siRNAs can produce unwanted off-target effects, i.e. unintended downregulation of mRNAs via a partial sequence match between the siRNA and target, the saturation of RNAi machinery is another distinct nonspecific effect, which involves the de-repression of miRNA-regulated genes and results in similar problems in data interpretation and potential toxicity. | 1 | Biochemistry |
SNP detection through molecular beacons makes use of a specifically engineered single-stranded oligonucleotide probe. The oligonucleotide is designed such that there are complementary regions at each end and a probe sequence located in between. This design allows the probe to take on a hairpin, or stem-loop, structure in its natural, isolated state. Attached to one end of the probe is a fluorophore and to the other end a fluorescence quencher. Because of the stem-loop structure of the probe, the fluorophore is close to the quencher, thus preventing the molecule from emitting any fluorescence. The molecule is also engineered such that only the probe sequence is complementary to the genomic DNA that will be used in the assay (Abravaya et al. 2003).
If the probe sequence of the molecular beacon encounters its target genomic DNA during the assay, it will anneal and hybridize. Because of the length of the probe sequence, the hairpin segment of the probe will be denatured in favour of forming a longer, more stable probe-target hybrid. This conformational change permits the fluorophore and quencher to be free of their tight proximity due to the hairpin association, allowing the molecule to fluoresce.
If on the other hand, the probe sequence encounters a target sequence with as little as one non-complementary nucleotide, the molecular beacon will preferentially stay in its natural hairpin state and no fluorescence will be observed, as the fluorophore remains quenched.
The unique design of these molecular beacons allows for a simple diagnostic assay to identify SNPs at a given location. If a molecular beacon is designed to match a wild-type allele and another to match a mutant of the allele, the two can be used to identify the genotype of an individual. If only the first probes fluorophore wavelength is detected during the assay then the individual is homozygous to the wild type. If only the second probes wavelength is detected then the individual is homozygous to the mutant allele. Finally, if both wavelengths are detected, then both molecular beacons must be hybridizing to their complements and thus the individual must contain both alleles and be heterozygous. | 1 | Biochemistry |
Rather than directly measuring concentrations of carbon dioxide in the atmosphere, OCO-2 records how much of the sunlight reflected off the Earth is absorbed by molecules in an air column. OCO-2 makes measurements in three different spectral bands over four to eight different footprints of approximately each. About 24 soundings are collected per second while in sunlight and over 10% of these are sufficiently cloud free for further analysis. One spectral band is used for column measurements of oxygen (A-band 0.765 microns), and two are used for column measurements of carbon dioxide (weak band 1.61 microns, strong band 2.06 microns).
In the retrieval algorithm measurements from the three bands are combined to yield column-averaged dry-air mole fractions of carbon dioxide. Because these are dry-air mole fractions, these measurements do not change with water content or surface pressure. Because the molecular oxygen content of the atmosphere (i.e. excluding the oxygen in water vapour) is well known to be 20.95%, oxygen is used as a measure of the total dry air column. To ensure these measurements are traceable to the World Meteorological Organization, OCO-2 measurements are carefully compared with measurements by the Total Carbon Column Observing Network (TCCON). | 2 | Environmental Chemistry |
Retrosynthetic analysis is a technique for solving problems in the planning of organic syntheses. This is achieved by transforming a target molecule into simpler precursor structures regardless of any potential reactivity/interaction with reagents. Each precursor material is examined using the same method. This procedure is repeated until simple or commercially available structures are reached. These simpler/commercially available compounds can be used to form a synthesis of the target molecule. E.J. Corey formalized this concept in his book The Logic of Chemical Synthesis.
The power of retrosynthetic analysis becomes evident in the design of a synthesis. The goal of retrosynthetic analysis is a structural simplification. Often, a synthesis will have more than one possible synthetic route. Retrosynthesis is well suited for discovering different synthetic routes and comparing them in a logical and straightforward fashion. A database may be consulted at each stage of the analysis, to determine whether a component already exists in the literature. In that case, no further exploration of that compound would be required. If that compound exists, it can be a jumping point for further steps developed to reach a synthesis. | 0 | Organic Chemistry |
Saturation binding measures the specific binding of a radioligand at varying concentrations while at equilibrium. Through this method, the number of receptors can be determined as well as affinity of the ligand to these receptors. Saturation binding experiments are often called "Scatchard experiments" as they can be graphed as a Scatchard plot. | 1 | Biochemistry |
* The reaction 2 H + O → 2 HO provides an example of chain branching. The propagation is a sequence of two steps whose net effect is to replace an H atom by another H atom plus two OH radicals. This leads to an explosion under certain conditions of temperature and pressure.
** H• + O → •OH + •O•
** •O• + H → •OH + H•
* In chain-growth polymerization, the propagation step corresponds to the elongation of the growing polymer chain. Chain transfer corresponds to transfer of the activity from this growing chain, whose growth is terminated, to another molecule which may be a second growing polymer chain. For polymerization, the kinetic chain length defined above may differ from the degree of polymerization of the product macromolecule.
* Polymerase chain reaction, a technique used in molecular biology to amplify (make many copies of) a piece of DNA by in vitro enzymatic replication using a DNA polymerase. | 7 | Physical Chemistry |
The process of repolarization causes an overshoot in the potential of the cell. Potassium ions continue to move out of the axon so much so that the resting potential is exceeded and the new cell potential becomes more negative than the resting potential. The resting potential is ultimately re-established by the closing of all voltage-gated ion channels and the activity of the sodium potassium ion pump. | 7 | Physical Chemistry |
Laboratory cultures of marine phytoplankton (Phaeodactylum tricornutum, Phaeocystis sp., Thalassiosira weissflogii, Chaetoceros calcitrans, Isochrysis sp., Porphyridium sp., Synechococcus sp., Tetraselmis sp., Prorocentrum sp., and Emiliana huxleyi) produce CHCl, but in relatively insignificant amounts. An extensive study of 30 species of polar macroalgae revealed the release of significant amounts of CHCl in only Gigartina skottsbergii and Gymnogongrus antarcticus. | 2 | Environmental Chemistry |
There are actually two versions in mathematics of the abstract dual lattice concept, for a given lattice L in a real vector space V, of finite dimension.
The first, which generalises directly the reciprocal lattice construction, uses Fourier analysis. It may be stated simply in terms of Pontryagin duality. The dual group V^ to V is again a real vector space, and its closed subgroup L^ dual to L turns out to be a lattice in V^. Therefore, L^ is the natural candidate for dual lattice, in a different vector space (of the same dimension).
The other aspect is seen in the presence of a quadratic form Q on V; if it is non-degenerate it allows an identification of the dual space V of V with V. The relation of V to V is not intrinsic; it depends on a choice of Haar measure (volume element) on V. But given an identification of the two, which is in any case well-defined up to a scalar, the presence of Q allows one to speak to the dual lattice to L while staying within V.
In mathematics, the dual lattice of a given lattice L in an abelian locally compact topological group G is the subgroup L of the dual group of G consisting of all continuous characters that are equal to one at each point of L.
In discrete mathematics, a lattice is a locally discrete set of points described by all integral linear combinations of linearly independent vectors in R. The dual lattice is then defined by all points in the linear span of the original lattice (typically all of R) with the property that an integer results from the inner product with all elements of the original lattice. It follows that the dual of the dual lattice is the original lattice.
Furthermore, if we allow the matrix B to have columns as the linearly independent vectors that describe the lattice, then the matrix has columns of vectors that describe the dual lattice. | 3 | Analytical Chemistry |
* Southern blot for DNA
* northern blot for RNA
* reverse northern blot for RNA
* western blot for proteins
* far-western blot for protein–protein interactions
* eastern blot for post-translational modification
* far-eastern blot for glycolipids
* dot blot | 1 | Biochemistry |
In chemistry, the pentagonal planar molecular geometry describes the shape of compounds where five atoms, groups of atoms, or ligands are arranged around a central atom, defining the vertices of a pentagon. | 4 | Stereochemistry |
* Cryogenics, the study of the production and behaviour of materials at very low temperatures and the study of producing extremely low temperatures
* Cryoelectronics, the study of superconductivity under cryogenic conditions and its applications
* Cryosphere, those portions of Earth's surface where water ice naturally occurs
* Cryotron, a switch that uses superconductivity
* Cryovolcano, a theoretical type of volcano that erupts volatiles instead of molten rock | 1 | Biochemistry |
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