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The notions that not all enhancers are transcribed at the same time and that eRNA transcription correlates with enhancer-specific activity support the idea that individual eRNAs carry distinct and relevant biological functions. However, there is still no consensus on the functional significance of eRNAs. Furthermore, eRNAs can easily be degraded through exosomes and nonsense-mediated decay, which limits their potential as important transcriptional regulators. To date, four main models of eRNA function have been proposed, each supported by different lines of experimental evidence. | 1 | Biochemistry |
Beneath the layer of microwells is an ion sensitive layer, below which is an ISFET ion sensor. All layers are contained within a CMOS semiconductor chip, similar to that used in the electronics industry.
Each chip contains an array of microwells with corresponding ISFET detectors.
Each released hydrogen ion then triggers the ISFET ion sensor. The series of electrical pulses transmitted from the chip to a computer is translated into a DNA sequence, with no intermediate signal conversion required. Because nucleotide incorporation events are measured directly by electronics, the use of labeled nucleotides and optical measurements are avoided. Signal processing and DNA assembly can then be carried out in software. | 1 | Biochemistry |
This depends upon a relationship between the specific surface area and the resistance to gas-flow of a porous bed of powder. The method is simple and quick, and yields a result that often correlates well with the chemical reactivity of a powder. However, it fails to measure much of the deep surface texture. | 7 | Physical Chemistry |
Further modifications on N-myristoylated proteins can add another level of regulation for myristoylated protein. Dual acylation can facilitate more tightly regulated protein localization, specifically targeting proteins to lipid rafts at membranes or allowing dissociation of myristoylated proteins from membranes.
Myristoylation and palmitoylation are commonly coupled modifications. Myristoylation alone can promote transient membrane interactions that enable proteins to anchor to membranes but dissociate easily. Further palmitoylation allows for tighter anchoring and slower dissociation from membranes when required by the cell. This specific dual modification is important for G protein-coupled receptor pathways and is referred to as the dual fatty acylation switch.
Myristoylation is often followed by phosphorylation of nearby residues. Additional phosphorylation of the same protein can decrease the electrostatic affinity of the myristoylated protein for the membrane, causing translocation of that protein to the cytoplasm following dissociation from the membrane. | 1 | Biochemistry |
Deficiency of ETF-QO results in a disorder known as glutaric acidemia type II (also known as MADD for multiple acyl-CoA dehydrogenase deficiency), in which there is an improper buildup of fats and proteins in the body. Complications can involve acidosis or hypoglycemia, with other symptoms such as general weakness, liver enlargement, increased heart failure, and carnitine deficiency. More severe cases involve congenital defects and full metabolic crisis. Genetically, it is an autosomal recessive disorder, making its occurrence fairly rare. Most affected patients are the result of single point mutations around the FAD ubiquinone interface. Milder forms of the disorder have been responsive to riboflavin therapy and are coined riboflavin-responsive MADD (RR-MADD), although due to the varying mutations causing the disease treatment and symptoms can vary considerably. | 1 | Biochemistry |
* Infrared spectroscopy: the C=O double bond absorbs infrared light at wavenumbers between approximately 1600–1900 cm(5263 nm to 6250 nm). The exact location of the absorption is well understood with respect to the geometry of the molecule. This absorption is known as the "carbonyl stretch" when displayed on an infrared absorption spectrum. In addition, the ultraviolet-visible spectra of propanone in water gives an absorption of carbonyl at 257 nm.
* Nuclear magnetic resonance: the C=O double-bond exhibits different resonances depending on surrounding atoms, generally a downfield shift. The C NMR of a carbonyl carbon is in the range of 160–220 ppm. | 0 | Organic Chemistry |
Bond forming reactions between carbon and nitrogen are the most widely used in dynamic covalent chemistry. They have been used more broadly in materials chemistry for molecular switches, covalent organic frameworks, and in self-sorting systems.
Imine formation takes place between an aldehyde or ketone and a primary amine. Similarly, aminal formation takes place between an aldehyde or ketone and a vicinal secondary amine. Both reactions are commonly used in DCvC. While both reactions can initially be categorized as formation reactions, in the presence of one or more of either reagent, the dynamic equilibrium between carbonyl and amine becomes an exchange reaction. | 6 | Supramolecular Chemistry |
Glutaminolysis takes place in all proliferating cells, such as lymphocytes, thymocytes, colonocytes, adipocytes and especially in tumor cells. Glutaminolysis has been targeted for therapeutic purposes. In tumor cells the citric acid cycle is truncated due to an inhibition of the enzyme aconitase (EC 4.2.1.3) by high concentrations of reactive oxygen species (ROS) Aconitase catalyzes the conversion of citrate to isocitrate.
On the other hand, tumor cells over express phosphate dependent glutaminase and NAD(P)-dependent malate decarboxylase, which in combination with the remaining reaction steps of the citric acid cycle from α-ketoglutarate to citrate impart the possibility of a new energy producing pathway, the degradation of the amino acid glutamine to glutamate, aspartate, pyruvate CO, lactate and citrate.
Besides glycolysis in tumor cells glutaminolysis is another main pillar for energy production. High extracellular glutamine concentrations stimulate tumor growth and are essential for cell transformation. On the other hand, a reduction of glutamine correlates with phenotypical and functional differentiation of the cells. | 1 | Biochemistry |
Tramadol and desmetramadol may be quantified in blood, plasma, serum, or saliva to monitor for abuse, confirm a diagnosis of poisoning or assist in the forensic investigation of a sudden death. Most commercial opiate immunoassay screening tests do not cross-react significantly with tramadol or its major metabolites, so chromatographic techniques must be used to detect and quantitate these substances. The concentration of desmetramadol in the blood or plasma of a person who has taken tramadol is generally 10–20% those of the parent drug. | 4 | Stereochemistry |
The biosynthesis of longifolene begins with farnesyl diphosphate (1) (also called farnesyl pyrophosphate) by means of a cationic polycyclization cascade. Loss of the pyrophosphate group and cyclization by the distal alkene gives intermediate 3, which by means of a 1,3-hydride shift gives intermediate 4. After two additional cyclizations, intermediate 6 produces longifolene by a 1,2-alkyl migration. | 0 | Organic Chemistry |
In 1893, the American botanist Charles Reid Barnes proposed two terms, photosyntax and photosynthesis, for the biological process of synthesis of complex carbon compounds out of carbonic acid, in the presence of chlorophyll, under the influence of light. The term photosynthesis is derived from the Greek phōs (φῶς, gleam) and sýnthesis (σύνθεσις, arranging together), while another word that he designated was photosyntax, from sýntaxis (σύνταξις, configuration). Over time, the term photosynthesis came into common usage. Later discovery of anoxygenic photosynthetic bacteria and photophosphorylation necessitated redefinition of the term. | 5 | Photochemistry |
Following the discovery in 1952 that the tuberculosis drug iproniazid elevated the mood of people taking it, and the subsequent discovery that the effect was likely due to inhibition of MAO, many people and companies started trying to discover MAO inhibitors to use as antidepressants. Selegiline was discovered by Zoltan Ecseri at the Hungarian drug company, Chinoin (part of Sanofi since 1993), which they called E-250. Chinoin received a patent on the drug in 1962 and the compound was first published in the scientific literature in English in 1965. Work on the biology and effects of E-250 in animals and humans was conducted by a group led by József Knoll at Semmelweis University which was also in Budapest.
Deprenyl is a racemic compound (a mixture of two isomers called enantiomers). Further work determined that the levorotatory enantiomer was a more potent MAO-inhibitor, which was published in 1967, and subsequent work was done with the single enantiomer -deprenyl.
In 1971, Knoll showed that selegiline selectively inhibits the B-isoform of monoamine oxidase (MAO-B) and proposed that it is unlikely to cause the infamous "cheese effect" (hypertensive crisis resulting from consuming foods containing tyramine) that occurs with non-selective MAO inhibitors. A few years later, two Parkinsons disease researchers based in Vienna, Peter Riederer and Walther Birkmayer, realized that selegiline could be useful in Parkinsons disease. One of their colleagues, Prof. Moussa B.H. Youdim, visited Knoll in Budapest and took selegiline from him to Vienna. In 1975, Birkmayers group published the first paper on the effect of selegiline in Parkinsons disease.
In the 1970s there was speculation that it could be useful as an anti-aging drug or aphrodisiac.
In 1987 Somerset Pharmaceuticals in New Jersey, which had acquired the US rights to develop selegiline, filed a new drug application (NDA) with the FDA to market the drug for Parkinsons disease in the US. While the NDA was under review, Somerset was acquired in a joint venture by two generic drug companies, Mylan and Bolan Pharmaceuticals. Selegiline was approved for Parkinsons disease by the FDA in 1989.
In the 1990s, J. Alexander Bodkin at McLean Hospital, an affiliate of Harvard Medical School, began a collaboration with Somerset to develop delivery of selegiline via a transdermal patch in order to avoid the well known dietary restrictions of MAO inhibitors. Somerset obtained FDA approval to market the patch in 2006. | 4 | Stereochemistry |
In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell.
Synapses are essential to the transmission of nervous impulses from one neuron to another, playing a key role in enabling rapid and direct communication by creating circuits. In addition, a synapse serves as a junction where both the transmission and processing of information occur, making it a vital means of communication between neurons. Neurons are specialized to pass signals to individual target cells, and synapses are the means by which they do so. At a synapse, the plasma membrane of the signal-passing neuron (the presynaptic neuron) comes into close apposition with the membrane of the target (postsynaptic) cell. Both the presynaptic and postsynaptic sites contain extensive arrays of molecular machinery that link the two membranes together and carry out the signaling process. In many synapses, the presynaptic part is located on an axon and the postsynaptic part is located on a dendrite or soma. Astrocytes also exchange information with the synaptic neurons, responding to synaptic activity and, in turn, regulating neurotransmission. Synapses (at least chemical synapses) are stabilized in position by synaptic adhesion molecules (SAMs) projecting from both the pre- and post-synaptic neuron and sticking together where they overlap; SAMs may also assist in the generation and functioning of synapses. Moreover, SAMs coordinate the formation of synapses, with various types working together to achieve the remarkable specificity of synapses. In essence, SAMs function in both excitatory and inhibitory synapses, likely serving as devices for signal transmission. | 1 | Biochemistry |
The surface chemistry of paper is responsible for many important paper properties, such as gloss, waterproofing, and printability. Many components are used in the paper-making process that affect the surface. | 7 | Physical Chemistry |
Early theories of the origin of life included spontaneous generation from non-living matter and panspermia, the arrival of life on earth from other bodies in space. The question of how life originated became urgent when Charles Darwins 1859 On the Origin of Species' became widely accepted by biologists. The evolution of new species by splitting off from older ones implied that all life forms were derived from a few such forms, perhaps only one, as Darwin had suggested at the end of his book. Darwin suggested that life could have originated in some "warm little pond" containing a suitable mixture of chemical compounds. The question has continued to be debated into the 21st century.
Nick Lane is a biochemist at University College London; he researches "evolutionary biochemistry and bioenergetics, focusing on the origin of life and the evolution of complex cells." He has become known as a science writer, having written four books about evolutionary biochemistry. | 1 | Biochemistry |
In phase change cycles and engines, the working fluids are gases and liquids. The engine converts the working fluid from a gas to a liquid, from liquid to gas, or both, generating work from the fluid expansion or compression.
*Rankine cycle (classical steam engine)
*Regenerative cycle (steam engine more efficient than Rankine cycle)
*Organic Rankine cycle (Coolant changing phase in temperature ranges of ice and hot liquid water)
*Vapor to liquid cycle (drinking bird, injector, Minto wheel)
*Liquid to solid cycle (frost heaving – water changing from ice to liquid and back again can lift rock up to 60 cm.)
*Solid to gas cycle (firearms – solid propellants combust to hot gases.) | 7 | Physical Chemistry |
The total radiation intensity of a black body rises as the fourth power of the absolute temperature, as expressed by the Stefan–Boltzmann law. A kitchen oven, at a temperature about double room temperature on the absolute temperature scale (600 K vs. 300 K) radiates 16 times as much power per unit area. An object at the temperature of the filament in an incandescent light bulb—roughly 3000 K, or 10 times room temperature—radiates 10,000 times as much energy per unit area.
As for photon statistics, thermal light obeys Super-Poissonian statistics. | 7 | Physical Chemistry |
Unbound bilirubin (Bf) levels can be used to predict the risk of neurodevelopmental handicaps within infants. Unconjugated hyperbilirubinemia in a newborn can lead to accumulation of bilirubin in certain brain regions (particularly the basal nuclei) with consequent irreversible damage to these areas manifesting as various neurological deficits, seizures, abnormal reflexes and eye movements. This type of neurological injury is known as kernicterus. The spectrum of clinical effect is called bilirubin encephalopathy. The neurotoxicity of neonatal hyperbilirubinemia manifests because the blood–brain barrier has yet to develop fully, and bilirubin can freely pass into the brain interstitium, whereas more developed individuals with increased bilirubin in the blood are protected. Aside from specific chronic medical conditions that may lead to hyperbilirubinemia, neonates in general are at increased risk since they lack the intestinal bacteria that facilitate the breakdown and excretion of conjugated bilirubin in the feces (this is largely why the feces of a neonate are paler than those of an adult). Instead the conjugated bilirubin is converted back into the unconjugated form by the enzyme β-glucuronidase (in the gut, this enzyme is located in the brush border of the lining intestinal cells) and a large proportion is reabsorbed through the enterohepatic circulation. In addition, recent studies point towards high total bilirubin levels as a cause for gallstones regardless of gender or age. | 1 | Biochemistry |
Product heterogeneity is common in monoclonal antibodies and other recombinant biological products and is typically introduced either upstream during expression or downstream during manufacturing.
These variants are typically aggregates, deamidation products, glycosylation variants, oxidized amino acid side chains, as well as amino and carboxyl terminal amino acid additions. These seemingly minute structural changes can affect preclinical stability and process optimization as well as therapeutic product potency, bioavailability and immunogenicity. The generally accepted purification method of process streams for monoclonal antibodies includes capture of the product target with protein A, elution, acidification to inactivate potential mammalian viruses, followed by ion chromatography, first with anion beads and then with cation beads.
Displacement chromatography has been used to identify and characterize these often unseen variants in quantities that are suitable for subsequent preclinical evaluation regimens such as animal pharmacokinetic studies. Knowledge gained during the preclinical development phase is critical for enhanced product quality understanding and provides a basis for risk management and increased regulatory flexibility. The recent Food and Drug Administration's Quality by Design initiative attempts to provide guidance on development and to facilitate design of products and processes that maximizes efficacy and safety profile while enhancing product manufacturability. | 1 | Biochemistry |
A volatile corrosion inhibitor (VCI) is a material that protects metals from corrosion. Corrosion inhibitors are chemical compounds that can decrease the corrosion rate of a material, typically a metal or an alloy. NACE International Standard TM0208 defines volatile corrosion inhibitor (VCI) as a chemical substance that acts to reduce corrosion by a combination of volatilization from a VCI material, vapor transport in the atmosphere of an enclosed environment, and condensation onto surface in the space, including absorption, dissolution, and hydrophobic effects on metal surfaces, where the rate of corrosion of metal surfaces is thereby inhibited. They also called vapor-phase inhibitors, vapor-phase corrosion inhibitors, and vapor-transported corrosion inhibitors.
VCIs come in various formulations that are dependent on the type of system they will be used in; for example, films, oils, coatings, cleaners, etc. There are also variety of formulations that provide protection in ferrous, nonferrous, or multi-metal applications. Other variables include the amount of vapor phase compared to contact phase inhibitors. Because they are volatile at ambient temperature, VCI compounds can reach inaccessible crevices in metallic structures.
V.VCI is also called Vacuum VCI meaning they have special properties of performance in vacuum as well as corrosion protection properties. | 8 | Metallurgy |
Sulfoxides, especially DMSO, form coordination complexes with transition metals. Depending on the hard-soft properties of the metal, the sulfoxide binds through either the sulfur or the oxygen atom. The latter is particularly common. | 0 | Organic Chemistry |
The IIR produces an electronic monthly newsletter that features news and updates on the refrigeration sector: regulation, events, economic data, monitoring, technological progress, etc.
It provides a detailed overview of the general developments within the sector worldwide and as acts a regular information tool for readers. | 7 | Physical Chemistry |
Solomon is well known for several of his research achievements. In particular his work on free radical polymerization revolutionized the field through the development of the first living free-radical polymerization technique; Nitroxide Mediated Polymerization (NMP). He also led the team, and was principal inventor of the world's first polymer banknote. | 7 | Physical Chemistry |
Arsenic is a cause of mortality throughout the world; associated problems include heart, respiratory, gastrointestinal, liver, nervous and kidney diseases.
Arsenic interferes with cellular longevity by allosteric inhibition of an essential metabolic enzyme pyruvate dehydrogenase (PDH) complex, which catalyzes the oxidation of pyruvate to acetyl-CoA by NAD. With the enzyme inhibited, the energy system of the cell is disrupted resulting in a cellular apoptosis episode. Biochemically, arsenic prevents use of thiamine resulting in a clinical picture resembling thiamine deficiency. Poisoning with arsenic can raise lactate levels and lead to lactic acidosis.
Genotoxicity involves inhibition of DNA repair and DNA methylation. The carcinogenic effect of arsenic arises from the oxidative stress induced by arsenic. Arsenic's high toxicity naturally led to the development of a variety of arsenic compounds as chemical weapons, e.g. dimethylarsenic chloride. Some were employed as chemical warfare agents, especially in World War I. This threat led to many studies on antidotes and an expanded knowledge of the interaction of arsenic compounds with living organisms. One result was the development of antidotes such as British anti-Lewisite. Many such antidotes exploit the affinity of As(III) for thiolate ligands, which convert highly toxic organoarsenicals to less toxic derivatives. It is generally assumed that arsenates bind to cysteine residues in proteins.
By contrast, arsenic oxide is an approved and effective chemotherapeutic drug for the treatment of acute promyelocytic leukemia (APL). | 1 | Biochemistry |
In microbial communities like soil, the C:N ratio is a key indicator as it describes a balance between energetic foods (represented by carbon) and material to build protein with (represented by nitrogen). An optimal C:N ratio of around 24:1 provides for higher microbial activity.
The C:N ratio of soil can be modified by the addition of materials such as compost, manure, and mulch. A feedstock with a near-optimal C:N ratio will be consumed quickly. Any excess C will cause the N originally in the soil to be consumed, competing with the plant for nutrients (immobilization) – at least temporarily until the microbes die. Any excess N, on the other hand, will usually just be left behind (mineralization), but too much excess may result in losses to leaching. The recommended C:N ratio for soil materials is therefore 30:1. A soil test may be done to find the C:N ratio of soil itself.
The C:N ratio of microbes themselves is generally around 10:1. A lower ratio is correlated with higher soil productivity. | 9 | Geochemistry |
* EPA. [http://www.epa.gov/volunteer/stream/vms511.html "Monitoring and Assessing Water Quality: Fecal Bacteria."] | 3 | Analytical Chemistry |
All members of Group VI use virally encoded reverse transcriptase, an RNA-dependent DNA polymerase, to produce DNA from the initial virion RNA genome. This DNA is often integrated into the host genome, as in the case of retroviruses and pseudoviruses, where it is replicated and transcribed by the host.
Group VI includes:
* Order Ortervirales
** Family Belpaoviridae
** Family Metaviridae
** Family Pseudoviridae
** Family Retroviridae – Retroviruses, e.g. HIV
** Family Caulimoviridae – a VII group virus family (see below)
The family Retroviridae was previously divided into three subfamilies (Oncovirinae, Lentivirinae, and Spumavirinae), but are now divided into two: Orthoretrovirinae and Spumaretrovirinae. The term oncovirus is now commonly used to describe a cancer-causing virus. This family now includes the following genera:
* Subfamily Orthoretrovirinae:
** Genus Alpharetrovirus; including Avian leukosis virus and Rous sarcoma virus
** Genus Betaretrovirus; including Mouse mammary tumour virus
** Genus Gammaretrovirus; including Murine leukemia virus and Feline leukemia virus
** Genus Deltaretrovirus; including Bovine leukemia virus and the cancer-causing Human T-lymphotropic virus
** Genus Epsilonretrovirus
** Genus Lentivirus; including Human immunodeficiency virus 1 and Simian and Feline immunodeficiency viruses
* Subfamily Spumaretrovirinae:
** Genus Bovispumavirus
** Genus Equispumavirus
** Genus Felispumavirus
** Genus Prosimiispumavirus
** Genus Simiispumavirus
Note that according to ICTV 2017, genus Spumavirus has been divided into five genera, and its former type species Simian foamy virus is now upgraded to genus Simiispumavirus with not less than 14 species, including new type species Eastern chimpanzee simian foamy virus. | 1 | Biochemistry |
Because the timescale for the development of reconstructions is so recent, most reconstructions have been built manually. However, now, there are quite a few resources that allow for the semi-automatic assembly of these reconstructions that are utilized due to the time and effort necessary for a reconstruction. An initial fast reconstruction can be developed automatically using resources like PathoLogic or ERGO in combination with encyclopedias like MetaCyc, and then manually updated by using resources like PathwayTools. These semi-automatic methods allow for a fast draft to be created while allowing the fine tune adjustments required once new experimental data is found. It is only in this manner that the field of metabolic reconstructions will keep up with the ever-increasing numbers of annotated genomes. | 1 | Biochemistry |
Autocrine signaling is a form of cell signaling in which a cell secretes a hormone or chemical messenger (called the autocrine agent) that binds to autocrine receptors on that same cell, leading to changes in the cell. This can be contrasted with paracrine signaling, intracrine signaling, or classical endocrine signaling. | 1 | Biochemistry |
* Line or stick – atomic nuclei are not represented, just the bonds as sticks or lines. As in 2D molecular structures of this type, atoms are implied at each vertex.
* Electron density plot – shows the electron density determined either crystallographically or using quantum mechanics rather than distinct atoms or bonds.
* Ball and stick – atomic nuclei are represented by spheres (balls) and the bonds as sticks.
* Spacefilling models or CPK models (also an atomic coloring scheme in representations) – the molecule is represented by overlapping spheres representing the atoms.
* Cartoon – a representation used for proteins where loops, beta sheets, and alpha helices are represented diagrammatically and no atoms or bonds are explicitly represented (e.g. the protein backbone is represented as a smooth pipe).
The greater the amount of lone pairs contained in a molecule, the smaller the angles between the atoms of that molecule. The VSEPR theory predicts that lone pairs repel each other, thus pushing the different atoms away from them. | 4 | Stereochemistry |
The Portland Press Excellence in Science Award was an annual award instituted in 1964 to recognize notable research in any branch of biochemistry undertaken in the UK or Republic of Ireland. It was initially called the CIBA Medal and Prize, then the Novartis Medal and Prize. The prize consists of a medal and a £3000 cash award. The winner is invited to present a lecture at a Society conference and submit an article to one of the Society's publications. Notable recipients include the Nobel laureates John E. Walker, Paul Nurse, Sydney Brenner, César Milstein, Peter D. Mitchell, Rodney Porter, and John Cornforth.
The Novartis Medal and Prize was last presented in 2019 and will be replaced from 2021 by the Portland Press Excellence in Science Award. Portland Press is the publishing arm of the Biochemical Society. | 1 | Biochemistry |
Flocculation is widely employed to measure the progress of curd formation in the initial stages of cheese making to determine how long the curds must set. The reaction involving the rennet micelles are modeled by Smoluchowski kinetics. During the renneting of milk the micelles can approach one another and flocculate, a process that involves hydrolysis of molecules and macropeptides.
Flocculation is also used during cheese wastewater treatment. Three different coagulants are mainly used:
* FeSO (iron(II) sulfate)
* Al(SO) (aluminium sulfate)
* FeCl (iron(III) chloride) | 8 | Metallurgy |
The principle intracellular signalling protein is Imd, a death domain-containing protein that binds with FADD and Dredd to form a complex. Dredd is activated following ubiquitination by the Iap2 complex (involving Iap2, UEV1a, bend, and eff), which allows Dredd to cleave the 30 residue N-terminus of Imd, allowing it to also be ubiquitinated by Iap2. Following this, the Tak1/TAB2 complex binds to the activated form of Imd and subsequently activates the IKKγ/Ird5 complex through phosphorylation. This IKKγ complex activates Relish by phosphorylation, leading to cleavage of Relish and thereby producing both N-terminal and C-terminal Relish fragments. The N-terminal Relish fragments dimerize leading to their translocation into the nucleus where these dimers bind to Relish-family NF-κB binding sites. Binding of Relish promotes the transcription of effectors such as antimicrobial peptides.
While Relish is integral for transcription of Imd pathway effectors, there is additional cooperation with other pathways such as Toll and JNK. The TAK1/TAB2 complex is key to propagating intracellular signalling of not only the Imd pathway, but also the JNK pathway. As a result, mutants for JNK signalling have severely reduced expression of Imd pathway antimicrobial peptides. | 1 | Biochemistry |
The coliform index is a rating of the purity of water based on a count of fecal bacteria. It is one of many tests done to assure sufficient water quality. Coliform bacteria are microorganisms that primarily originate in the intestines of warm-blooded animals. By testing for coliforms, especially the well known Escherichia coli (E. coli), which is a thermotolerant coliform, one can determine if the water has possibly been exposed to fecal contamination; that is, whether it has come in contact with human or animal feces. It is important to know this because many disease-causing organisms are transferred from human and animal feces to water, from where they can be ingested by people and infect them. Water that has been contaminated by feces usually contains pathogenic bacteria, which can cause disease. Some types of coliforms cause disease, but the coliform index is primarily used to judge if other types of pathogenic bacteria are likely to be present in the water.
The coliform index is used because it is difficult to test for pathogenic bacteria directly. There are many different types of disease-causing bacteria, and they are usually present in low numbers which do not always show up in tests. Thermotolerant coliforms are present in higher numbers than individual types of pathogenic bacteria and they can be tested relatively easily.
However, the coliform index is far from perfect. Thermotolerant coliforms can survive in water on their own, especially in tropical regions, so they do not always indicate fecal contamination. Furthermore, they do not give a good indication of how many pathogenic bacteria are present in the water, and they give no idea at all of whether there are pathogenic viruses or protozoa which also cause diseases and are rarely tested for. Therefore, it does not always give accurate or useful results regarding the purity of water. | 3 | Analytical Chemistry |
Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule.
Photodissociation is not limited to visible light. Any photon with sufficient energy can affect the chemical bonds of a chemical compound. Since a photon's energy is inversely proportional to its wavelength, electromagnetic radiations with the energy of visible light or higher, such as ultraviolet light, X-rays, and gamma rays can induce such reactions. | 5 | Photochemistry |
The production of ferronickel from laterites takes place in a context that is much more favorable to the Krupp-Renn process than to the steel industry. Lateritic ores in the form of saprolite are poor, very basic and contain iron. Production volumes are moderate, and the nickel chemistry is remarkably amenable to rotary kiln reduction. The process is therefore attractive, but regardless of the metal extracted, mastering all the physical and chemical transformations in a single reactor is a real challenge. The failure of the Larco plant at Lárymna, Greece, illustrates the risk involved in adopting this process: it was only when the ore was ready for industrial processing that it proved incompatible with the Krupp-Renn process.
As a result, lower-temperature reduction followed by electric furnace smelting allows each stage to have its own dedicated tool for greater simplicity and efficiency. Developed in 1950 at the in New Caledonia, this combination has proven to be both cost-effective and, above all, more robust. Large rotating drums (5 m in diameter and 100 m or even 185 m long) are used to produce a dry powder from nickel ore concentrate. This powder contains 1.5 to 3% nickel. It leaves the drum at 800–900 °C and is immediately melted in electric furnaces. Only partial reduction takes place in the drums: a quarter of the nickel comes out in metallic form, the rest is still oxidized. Only 5% of the iron is reduced to metal, leaving unburned coal as fuel for the subsequent melting stage in the electric furnace. This proven process (also known as the RKEF process, for Rotary Kiln-Electric Furnace) has become the norm: at the beginning of the 21st century, it accounted for almost all nickel laterite processing.
In the early 21st century, however, the Nihon Yakin Kogyo foundry in Ōeyama, Japan, continued to use the Krupp-Renn process to produce intermediate grade ferronickel (23% nickel), sometimes called nickel pig iron. With a monthly output of 1,000 tons of Luppen and a production capacity of 13 kt/year, the plant is operating at full capacity. It is the only plant in the world using this process. It is also the only plant using a direct reduction process to extract nickel from laterite. The process, which has been significantly upgraded, is called the "Ōeyama process".
The Ōeyama process differs from the Krupp-Renn process in the use of limestone and the briquetting of the ore prior to charging. It retains its advantages, which are the concentration of all pyrometallurgical reactions in a single reactor and the use of standard (i.e. non-coking) coal, which covers 90% of the energy requirements of the process. Coal consumption is only 140 kg per ton of dry laterite, and the quality of the ferronickel obtained is compatible with direct use by the steel industry. Although marginal, the Krupp-Renn process remains a modern, high-capacity process for the production of nickel pig iron. In this context, it remains a systematically studied alternative to the RKEF process and the "sinter plant-blast furnace" combination. | 8 | Metallurgy |
The stack effect or chimney effect is the movement of air into and out of buildings through unsealed openings, chimneys, flue-gas stacks, or other containers, resulting from air buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. The result is either a positive or negative buoyancy force. The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect helps drive natural ventilation, air infiltration, and fires (e.g. the Kaprun tunnel fire, King's Cross underground station fire and the Grenfell Tower fire). | 7 | Physical Chemistry |
The theory of response reactions (RERs) was elaborated for systems in which several physico-chemical processes run simultaneously in mutual interaction, with local thermodynamic equilibrium, and in which state variables called extents of reaction are allowed, but thermodynamic equilibrium proper is not required. It is based on detailed analysis of the Hessian determinant, using either the Gibbs or the De Donder method of analysis. The theory derives the sensitivity coefficient as the sum of the contributions of individual RERs. Thus phenomena which are in contradiction to over-general statements of the Le Chatelier principle can be interpreted. With the help of RERs the equilibrium coupling was defined. RERs could be derived based either on the species, or on the stoichiometrically independent reactions of a parallel system. The set of RERs is unambiguous in a given system; and the number of them (M) is , where S denotes the number of species and C refers to the number of components. In the case of three-component systems, RERs can be visualized on a triangle diagram. | 7 | Physical Chemistry |
The pigments in photoreceptor proteins either change their conformation or undergo photoreduction when they absorb a photon. This change in the conformation or redox state of the chromophore then affects the protein conformation or activity and triggers a signal transduction cascade.
Examples of photoreceptor pigments include:
*retinal (in rhodopsin)
*flavin (in cryptochrome)
*bilin (in phytochrome) | 1 | Biochemistry |
Often in informal, non-technical language, concentration is described in a qualitative way, through the use of adjectives such as "dilute" for solutions of relatively low concentration and "concentrated" for solutions of relatively high concentration. To concentrate a solution, one must add more solute (for example, alcohol), or reduce the amount of solvent (for example, water). By contrast, to dilute a solution, one must add more solvent, or reduce the amount of solute. Unless two substances are miscible, there exists a concentration at which no further solute will dissolve in a solution. At this point, the solution is said to be saturated. If additional solute is added to a saturated solution, it will not dissolve, except in certain circumstances, when supersaturation may occur. Instead, phase separation will occur, leading to coexisting phases, either completely separated or mixed as a suspension. The point of saturation depends on many variables, such as ambient temperature and the precise chemical nature of the solvent and solute.
Concentrations are often called levels, reflecting the mental schema of levels on the vertical axis of a graph, which can be high or low (for example, "high serum levels of bilirubin" are concentrations of bilirubin in the blood serum that are greater than normal). | 3 | Analytical Chemistry |
The first recorded observation of capillary action was by Leonardo da Vinci. A former student of Galileo, Niccolò Aggiunti, was said to have investigated capillary action. In 1660, capillary action was still a novelty to the Irish chemist Robert Boyle, when he reported that "some inquisitive French Men" had observed that when a capillary tube was dipped into water, the water would ascend to "some height in the Pipe". Boyle then reported an experiment in which he dipped a capillary tube into red wine and then subjected the tube to a partial vacuum. He found that the vacuum had no observable influence on the height of the liquid in the capillary, so the behavior of liquids in capillary tubes was due to some phenomenon different from that which governed mercury barometers.
Others soon followed Boyle's lead. Some (e.g., Honoré Fabri, Jacob Bernoulli) thought that liquids rose in capillaries because air could not enter capillaries as easily as liquids, so the air pressure was lower inside capillaries. Others (e.g., Isaac Vossius, Giovanni Alfonso Borelli, Louis Carré, Francis Hauksbee, Josia Weitbrecht) thought that the particles of liquid were attracted to each other and to the walls of the capillary.
Although experimental studies continued during the 18th century, a successful quantitative treatment of capillary action was not attained until 1805 by two investigators: Thomas Young of the United Kingdom and Pierre-Simon Laplace of France. They derived the Young–Laplace equation of capillary action. By 1830, the German mathematician Carl Friedrich Gauss had determined the boundary conditions governing capillary action (i.e., the conditions at the liquid-solid interface). In 1871, the British physicist Sir William Thomson (later Lord Kelvin) determined the effect of the meniscus on a liquid's vapor pressure—a relation known as the Kelvin equation. German physicist Franz Ernst Neumann (1798–1895) subsequently determined the interaction between two immiscible liquids.
Albert Einsteins first paper, which was submitted to Annalen der Physik' in 1900, was on capillarity. | 7 | Physical Chemistry |
The problem of finding a reaction centre in a protein matrix is formally equivalent to many problems in computing. Mapping computing problems onto reaction center searches may allow light harvesting to work as a computational device, improving computational speeds at room temperature, yielding 100-1000x efficiency. | 5 | Photochemistry |
sarcoplasmic reticulum - satellite DNA - scientific notation - SDS-PAGE - second messenger - second messenger system - secondary structure - secretin - selectin - sensory receptor - sequence (biology) - sequence homology - sequence motif - sequencing - serine - serotonin - serotonin receptor - serpin - sexual reproduction - SH3 domain - SI - sigma factor - signal peptide - signal recognition particle - signal sequence - signal transduction - sincalide - skeleton - skin - smooth ER - sodium channel - sodium-hydrogen antiporter - soluble - solution - solvation - solvent - somatomedin - somatomedin receptor - somatostatin - somatostatin receptor - somatotropin - somatotropin receptor - somatotropin-releasing hormone - somatropin - sp1 transcription factor - spectrin - spectroscopy - src gene - src-family kinase - SSRI - starch - stem cell - stereochemistry - steroid 17alpha-monooxygenase - steroid 21-monooxygenase - steroid receptor - stimulatory gs G-protein - stoichiometry - structural biology - structural domain - Structural formula - structural motif - substance P - substrate - sugar - sulfur - supercoil - superfamily - superoxide - surface immunoglobulin - surface plasmon resonance - suspension (chemistry) - synapse - synthetic vaccine - systems biology | 1 | Biochemistry |
The regulation of Ler and its transcript, ler, is complex and many-fold. The plasmid encoded regulator (per) directly activates the region of the LEE1 operon which encodes Ler. Integration host factor is also a direct activator of ler and binds upstream of its promoter.
Jeannette Barba and her colleagues at the National Autonomous University of Mexico elucidated a positive regulatory loop between Ler, ler, GrlA, and grlRA. GrlA is also a LEE encoded regulator of the LEE pathogenicity island. They found that GrlA activates ler, and that Ler activates grlRA indicating a loop of activation wherein a protein product activates a transcript whose protein product activates the transcript of the original protein. Ler activates grlRA only if H-NS is present, this is not the case for GrlA activation of ler.
Quorum sensing plays a role in Ler regulation. LuxS is an important protein involved in quorum sensing, particularly in the synthesis of autoinducer molecules. Quorum-sensing E. coli regulator A (QseA) is found in LuxS systems and activates transcription of ler. Fis, a nucleoid associated protein essential for EPEC's ability to form attaching and effacing lesions, partly acts through activation of Ler expression. BipA, a ribosomal binding GTPase and prolific regulator of EPEC virulence, transcriptionally regulates Ler from an upstream position where it also regulates other genes.
The Ler protein also represses its own transcript on the LEE1 operon through DNA looping which prevents RNA polymerase from completing transcription. | 1 | Biochemistry |
Clay is a very fine-grained geologic material that develops plasticity when wet, but becomes hard, brittle and non–plastic upon drying or firing. It is a very common material, and is the oldest known ceramic. Prehistoric humans discovered the useful properties of clay and used it for making pottery. The chemistry of clay, including its capacity to retain nutrient cations such as potassium and ammonium, is important to soil fertility.
Because the individual particles in clay are less than in size, they cannot be characterized by ordinary optical or physical methods. The crystallographic structure of clay minerals became better understood in the 1930s with advancements in the x-ray diffraction (XRD) technique indispensable to deciphering their crystal lattice. Clay particles were found to be predominantly sheet silicate (phyllosilicate) minerals, now grouped together as clay minerals. Their structure is based on flat hexagonal sheets similar to those of the mica group of minerals. Standardization in terminology arose during this period as well, with special attention given to similar words that resulted in confusion, such as sheet and plane.
Because clay minerals are usually (but not necessarily) ultrafine-grained, special analytical techniques are required for their identification and study. In addition to X-ray crystallography, these include electron diffraction methods, various spectroscopic methods such as Mössbauer spectroscopy, infrared spectroscopy, Raman spectroscopy, and SEM-EDS or automated mineralogy processes. These methods can be augmented by polarized light microscopy, a traditional technique establishing fundamental occurrences or petrologic relationships. | 9 | Geochemistry |
Six essential amino acids and three nonessential are synthesized from oxaloacetate and pyruvate. Aspartate and alanine are formed from oxaloacetate and pyruvate, respectively, by transamination from glutamate. Asparagine is synthesized by amidation of aspartate, with glutamine donating the NH4.
These are nonessential amino acids, and their simple biosynthetic pathways occur in all organisms. Methionine, threonine, lysine, isoleucine, valine, and leucine are essential amino acids in humans and most vertebrates. Their biosynthetic pathways in bacteria are complex and interconnected. | 1 | Biochemistry |
In normal configuration, the light beam samples perpendicularly the electrode surface. Normal configuration provides optical information related to the changes that take place in the solution adjacent to the electrode and on the electrode surface. The optical path length coincides with the diffusion layer thickness, which is usually in the order of micrometers. This arrangement is the most suitable when the compound of interest is deposited or adsorbed on the working electrode, because it provides information about all processes occurring on the electrode surface.
UV-Vis absorption SEC in normal arrangement can be performed using both transmission and reflection phenomena.
* Normal transmission
In normal transmission, the light beam passes through a optically transparent working electrode, collecting information about the phenomena that take place on the surface of the electrode and on the solution adjacent to it. Electrodes in this configuration must be composed of materials that have great electrical conductivity and adequate optical transparency in the spectral region of interest.
The external reflection mode was proposed to improve the sensitivity and to use non-transparent electrodes.
<br />
* Normal reflection
In normal reflection, the light beam travels in a perpendicular direction to the working electrode surface on which the reflection occurs. The reflected beam is collected to be analyzed in the spectrometer. It is also possible to work with other incidence and collection angles. This configuration is an alternative when the working electrode is non-transparent. In this configuration, the optical path-length in solution is on the order of twice the diffusion layer thickness. It should be noticed that growth of films on the electrode surface could cause optical interference phenomena. As it is based on reflection phenomenon, in many cases reflectance is used as unit of measurement instead of absorbance.
<br /> | 7 | Physical Chemistry |
A hydrogen carrier is an organic macromolecule that transports atoms of hydrogen from one place to another inside a cell or from cell to cell for use in various metabolical processes. Examples include NADPH, NADH, and FADH. The main role of these is to transport hydrogen atom to electron transport chain which will change ADP to ATP by adding one phosphate during metabolic processes (e.g. photosynthesis and respiration). Hydrogen carrier participates in an oxidation-reduction reaction by getting reduced due to the acceptance of a Hydrogen. The enzyme used in Glycolysis, Dehydrogenase is used to attach the hydrogen to one of the hydrogen carrier. | 1 | Biochemistry |
According to the Oxford English Dictionary, the suffix ‘omics’ refers to ‘the totality of some sort’. In biology, ‘omics’ techniques are used for the high-throughput analysis of DNA sequences and epigenetic modifications (genomics), mRNA and miRNA transcripts (transcriptomics), expressed proteins (proteomics), as well as synthesised metabolites (metabolomics) in a biological system (cell, tissue, organism, etc.) under a given set of experimental conditions.
Due to the high number of variables that are measured simultaneously, these techniques provide large and complex datasets that require adapted tools for data analysis and interpretation. | 0 | Organic Chemistry |
In stereochemistry, cryptochirality is a special case of chirality in which a molecule is chiral but its specific rotation is non-measurable. The underlying reason for the lack of rotation is the specific electronic properties of the molecule. The term was introduced by Kurt Mislow in 1977.
For example, the alkane 5-ethyl-5-propylundecane found in certain species of Phaseolus vulgaris is chiral at its central quaternary carbon, but neither enantiomeric form has any observable optical rotation:
It is still possible to distinguish between the two enantiomers by using them in asymmetric synthesis of another chemical whose stereochemical nature can be measured. For example, the Soai reaction of 2-(3,3-dimethylbut-1-ynyl)pyrimidine-5-carbaldehyde with diisopropylzinc performed in the presence of 5-ethyl-5-propylundecane forms a secondary alcohol with a high enantiomeric excess based on the major enantiomer of the alkane that was used.
Even a slight enantiomeric excess of the alkane is rapidly amplified due to the autocatalytic nature of this reaction.
Cryptochirality also occurs in polymeric systems growing from chiral initiators, for example in dendrimers having lobes of different sizes attached to a central core.
The term is also used to describe a situation where an enantiomeric excess lies far below the observational horizon, but is still relevant, e.g. in highly enantiosensitive, self-amplifying reactions. | 4 | Stereochemistry |
Karl Barry Sharpless (born April 28, 1941) is an American stereochemist. He is a two-time Nobel laureate in Chemistry known for his work on stereoselective reactions and click chemistry.
Sharpless was awarded half of the 2001 Nobel Prize in Chemistry "for his work on chirally catalysed oxidation reactions", and one third of the 2022 prize, jointly with Carolyn R. Bertozzi and Morten P. Meldal, "for the development of click chemistry and bioorthogonal chemistry". Sharpless is the fifth person (in addition to two organizations), to have twice been awarded a Nobel prize, along with Marie Curie, John Bardeen, Linus Pauling and Frederick Sanger, and the third to have been awarded two prizes in the same discipline (after Bardeen and Sanger). | 4 | Stereochemistry |
Another possible effect would be an increase in harmful algal bloom events, which could contribute to the accumulation of toxins (domoic acid, brevetoxin, saxitoxin) in small organisms such as anchovies and shellfish, in turn increasing occurrences of amnesic shellfish poisoning, neurotoxic shellfish poisoning and paralytic shellfish poisoning. Although algal blooms can be harmful, other beneficial photosynthetic organisms may benefit from increased levels of carbon dioxide. Most importantly, seagrasses will benefit. Research found that as seagrasses increased their photosynthetic activity, calcifying algae's calcification rates rose, likely because localized photosynthetic activity absorbed carbon dioxide and elevated local pH. | 9 | Geochemistry |
Source:
Battery (BATT)
Topical Interest Area (TIA): Batteries and Energy Storage (established 1947)
High-Temperature Energy, Materials, & Processes (H-TEMP)
TIA: Fuel Cells, Electrolyzers, and Energy Conversion (established 1921)
Corrosion (CORR)
TIA: Corrosion Science and Technology (established 1942)
Industrial Electrochemistry and Electrochemical Engineering (IE&EE)
TIA: Electrochemical Engineering (established 1943)
Dielectric Science and Technology (DS&T)
TIA: Dielectric Science and Materials (established 1945)
Luminescence and Display Materials (LDM)
TIA: Luminescence and Display Materials, Devices, and Processing (established 1982)
Electrodeposition (ELDP)
TIA: Electrochemical/Electroless Deposition (established 1921)
Nanocarbons (NANO)
TIA: Carbon Nanostructures and Devices (established 1993)
Electronics and Photonics (EPD)
TIA: Electronic Materials and Processing and Electronic and Photonic Devices and Systems (established 1931)
Organic and Biological Electrochemistry (OBE)
TIA: Organic and Bioelectrochemistry (established 1940)
Energy Technology (ETD)
TIA: Fuel Cells, Electrolyzers, and Energy Conversion (established 1983)
Physical and Analytical Electrochemistry (PAE)
TIA: Physical and Analytical Electrochemistry, Electrocatalysis, and Photoelectrochemistry (established 1936)
Sensor (SENS)
TIA: Sensors (established 1988) | 7 | Physical Chemistry |
Besides the smelters named so far, the BBOC has been licensed to the operators of the Trail smelter in British Columbia, the Belledune smelter in New Brunswick, the Noyelles Godault smelter in France, the Korea Zinc zinc smelter in Onsan, South Korea, and the lead smelter at Chanderiya in India. | 8 | Metallurgy |
The active part of 3D optical storage media is usually an organic polymer either doped or grafted with the photochemically active species. Alternatively, crystalline and sol-gel materials have been used. | 5 | Photochemistry |
According to Web of Science the three most cited papers in the journal are:
# Chiappe C, Pieraccini D. Ionic liquids: solvent properties and organic reactivity, 18(4): 275–297, 2005
# Carmichael AJ, Seddon KR. Polarity study of some 1-alkyl-3-methylimidazolium ambient-temperature ionic liquids with the solvatochromic dye, Nile Red, 13(10): 591–595, 2000
# Matyjaszewski K, Ziegler MJ, Arehart SV, et al. Gradient copolymers by atom transfer radical copolymerization, 13(12): 775–786, 2000 | 7 | Physical Chemistry |
ABE fermentation is attracting renewed interest with a focus on butanol as a renewable biofuel.
Sustainability is by far the topic of major concern over the last years. The energy challenge is the key point of the environmental friendly policies adopted by all the most developed and industrialized countries worldwide. For this purpose Horizon 2020, the biggest EU Research and Innovation programme, was funded by the European Union over the 2014–2020 period.
The International Energy Agency defines renewables as the centre of the transition to a less carbon-intensive and more sustainable energy system. Biofuels are believed to represent around 30% of energy consumption in transport by 2060. Their role is particularly important in sectors which are difficult to decarbonise, such as aviation, shipping and other long-haul transport. That is why several bioprocesses have seen a renewed interest in recent years, both from a research and an industrial perspective.
For this reason, the ABE fermentation process has been reconsidered from a different perspective. Although it was originally conceived to produce acetone, it is considered as a suitable production pathway for biobutanol that has become the product of major interest.
Biogenic butanol is a possible substitute of bioethanol or even better and it is already employed both as fuel additive and as pure fuel instead of standard gasoline because, differently from ethanol, it can be directly and efficiently used in gasoline engines. Moreover, it has the advantage that it can be shipped and distributed through existing pipelines and filling stations.
Finally biobutanol is widely used as a direct solvent for paints, coatings, varnishes, resins, dyes, camphor, vegetable oils, fats, waxes, shellac, rubbers and alkaloids due to its higher energy density, lower volatility, and lower hygroscopicity. It can be produced from different kinds of cellulosic biomass and can be used for further processing of advanced biofuels such as butyl levulinate as well.
The application of n-butanol in the production of butyl acrylate has a wide scope for its expansion, which in turn would help in increasing the consumption of n-butanol globally. Butyl acrylate was the biggest n-butanol application in 2014 and is projected to be worth US$3.9 billion by 2020. | 1 | Biochemistry |
RASSLs and DREADDs are families of designer G-protein-coupled receptors (GPCRs) built specifically to allow for precise spatiotemporal control of GPCR signaling in vivo. These engineered GPCRs are unresponsive to endogenous ligands but can be activated by nanomolar concentrations of pharmacologically inert, drug-like small molecules. Currently, RASSLs exist for the interrogation of several GPCR signaling pathways, including those activated by Gs, Gi, Gq, Golf and β-arrestin. A major cause for success of RASSL resources has been open exchange of DNA constructs, and RASSL related resources.
The hM4Di-DREADDs inhibitory effects are a result of the CNOs stimulation and resulting activation of the G-protein inwardly rectifying potassium (GIRK) channels. This causes hyperpolarization of the targeted neuronal cell and thus attenuates subsequent activity. | 1 | Biochemistry |
The distribution of the different laminin isoforms is tissue-specific. Laminin–111 is predominantly expressed in the embryonic epithelium, but can also be found in some adult epithelium such as the kidney, liver, testis, ovaries, and brain blood vessels. Different levels of expression of α chains have a large influence on the differential expression of laminin, thereby determining the isoform produced. From studying a mouse model, it was found that transcription factors present in the parietal endoderm regulate the expression of the α1 and large amounts of laminin-111 are produced. | 0 | Organic Chemistry |
In organic chemistry, a sulfide (British English sulphide) or thioether is an organosulfur functional group with the connectivity as shown on right. Like many other sulfur-containing compounds, volatile sulfides have foul odors. A sulfide is similar to an ether except that it contains a sulfur atom in place of the oxygen. The grouping of oxygen and sulfur in the periodic table suggests that the chemical properties of ethers and sulfides are somewhat similar, though the extent to which this is true in practice varies depending on the application. | 0 | Organic Chemistry |
Toc75 is the most abundant protein on the outer chloroplast envelope. It is a transmembrane tube that forms most of the TOC pore itself. Toc75 is a β-barrel channel lined by 16 β-pleated sheets. The hole it forms is about 2.5 nanometers wide at the ends, and shrinks to about 1.4–1.6 nanometers in diameter at its narrowest point—wide enough to allow partially folded chloroplast preproteins to pass through.
Toc75 can also bind to chloroplast preproteins, but is a lot worse at this than Toc34 or Toc159.
Arabidopsis thaliana has multiple isoforms of Toc75 that are named by the chromosomal positions of the genes that code for them. AtToc75 III is the most abundant of these. | 5 | Photochemistry |
(born 1950) is a Japanese organic chemist. He is a university lecturer in the Applied Chemistry Department of Tokyo University of Science.
Soai studied at the University of Tokyo, where he received his Ph.D. in 1979 in organic synthesis under Teruaki Mukaiyama and was a fellow of the Japan Society for the Promotion of Science. He conducted his postdoctoral studies with Ernest L. Eliel at the University of North Carolina. In 1981, he became a lecturer at Tokyo University of Science, and was promoted to associate professor (1986) and full professor (1991).
He is involved in asymmetric and enantioselective synthesis, asymmetric autocatalysis, origin of chirality,
The Soai reaction for alkylation of pyrimidine-5-carbaldehyde with diisopropylzinc is named after him.
Soai was a visiting professor to many universities such as the ESPCI Paris (2001), Kyushu University (2005), Waseda University (2007-2010), University of Strasbourg (2008), and Jilin University (2010-2015). | 4 | Stereochemistry |
Organometallic complexes are commonly used in catalysis. Major industrial processes include hydrogenation, hydrosilylation, hydrocyanation, olefin metathesis, alkene polymerization, alkene oligomerization, hydrocarboxylation, methanol carbonylation, and hydroformylation. Organometallic intermediates are also invoked in many heterogeneous catalysis processes, analogous to those listed above. Additionally, organometallic intermediates are assumed for Fischer–Tropsch process.
Organometallic complexes are commonly used in small-scale fine chemical synthesis as well, especially in cross-coupling reactions that form carbon-carbon bonds, e.g. Suzuki-Miyaura coupling, Buchwald-Hartwig amination for producing aryl amines from aryl halides, and Sonogashira coupling, etc. | 0 | Organic Chemistry |
Racemic amphetamine was first synthesized under the chemical name "phenylisopropylamine" in Berlin, 1887 by the Romanian chemist Lazăr Edeleanu. It was not widely marketed until 1932, when the pharmaceutical company Smith, Kline & French (now known as GlaxoSmithKline) introduced it in the form of the Benzedrine inhaler for use as a bronchodilator. Notably, the amphetamine contained in the Benzedrine inhaler was the liquid free-base, not a chloride or sulfate salt.
Three years later, in 1935, the medical community became aware of the stimulant properties of amphetamine, specifically the dextroamphetamine isomer, and in 1937 Smith, Kline, and French introduced tablets under the brand name Dexedrine. In the United States, Dexedrine was approved to treat narcolepsy and attention disorders. In Canada indications once included epilepsy and parkinsonism. Dextroamphetamine was marketed in various other forms in the following decades, primarily by Smith, Kline, and French, such as several combination medications including a mixture of dextroamphetamine and amobarbital (a barbiturate) sold under the tradename Dexamyl and, in the 1950s, an extended release capsule (the "Spansule"). Preparations containing dextroamphetamine were also used in World War II as a treatment against fatigue.
It quickly became apparent that dextroamphetamine and other amphetamines had a high potential for misuse, although they were not heavily controlled until 1970, when the Comprehensive Drug Abuse Prevention and Control Act was passed by the United States Congress. Dextroamphetamine, along with other sympathomimetics, was eventually classified as Schedule II, the most restrictive category possible for a drug with a government-sanctioned, recognized medical use. Internationally, it has been available under the names AmfeDyn (Italy), Curban (US), Obetrol (Switzerland), Simpamina (Italy), Dexedrine/GSK (US & Canada), Dexedrine/UCB (United Kingdom), Dextropa (Portugal), and Stild (Spain). It became popular on the mod scene in England in the early 1960s, and carried through to the Northern Soul scene in the north of England to the end of the 1970s.
In October 2010, GlaxoSmithKline sold the rights for Dexedrine Spansule to Amedra Pharmaceuticals (a subsidiary of CorePharma).
The U.S. Air Force uses dextroamphetamine as one of its "go pills", given to pilots on long missions to help them remain focused and alert. Conversely, "no-go pills" are used after the mission is completed, to combat the effects of the mission and "go-pills". The Tarnak Farm incident was linked by media reports to the use of this drug on long term fatigued pilots. The military did not accept this explanation, citing the lack of similar incidents. Newer stimulant medications or awakeness promoting agents with different side effect profiles, such as modafinil, are being investigated and sometimes issued for this reason. | 4 | Stereochemistry |
Different transition metals have been used to catalyze carboamination reactions, including palladium, copper, and rhodium etc. The reaction mechanism varies with different transition metals. For palladium-catalyzed carboamination reactions, Pd(0)/Pd(II) and Pd(II)/Pd(IV) catalytic cycles are the most common mechanisms that have been proposed.
The reaction mode for the key aminopalladation step is different in these two cases. In Wolfe’s chemistry, which is known as the Pd(0)/Pd(II) catalytic system, syn-aminopalladation is observed. While in the Pd(II)/Pd(IV) catalytic system, which was developed by Forrest Michael, anti-aminopalladation was observed. It is believed that the pH of the reaction will affect the existing form of the amine nucleophile, which will determine whether the nitrogen coordinates with palladium center or not during the aminopalladation step. For the C–H activation step in Pd(II)/Pd(IV) chemistry, since there is no directing effect on the aromatic ring, large excess of arenes are required.
In 2015, Rovis and coworkers reported a rhodium-catalyzed intermolecular carboamination. In this reaction, enoxyphthalimide was used to serve as both the nitrogen and carbon source. The reaction mechanism is proposed in the paper (vide infra).
In 2017, Liu and coworkers reported a copper-catalyzed three component carboamination reaction of styrenes. In the meantime, Engle and coworkers published a palladium-catalyzed three component carboamination reaction using directing group strategy. These two works are the very rare examples of three component carboamination reactions. | 0 | Organic Chemistry |
Commercially, homoserine can serve as precursor to the synthesis of isobutanol and 1,4-butanediol. Purified homoserine is used in enzyme structural studies. Also, homoserine has played important roles in studies to elucidate peptide synthesis and synthesis of proteoglycan glycopeptides. Bacterial cell lines can make copious amounts of this amino acid. | 1 | Biochemistry |
From studies and predictions such as Dreyer and Bennett's, it shows that the light chains and heavy chains are encoded by separate multigene families on different chromosomes. They are referred to as gene segments and are separated by non-coding regions. The rearrangement and organization of these gene segments during the maturation of B cells produce functional proteins. The entire process of rearrangement and organization of these gene segments is the vital source where our body immune system gets its capabilities to recognize and respond to variety of antigens. | 1 | Biochemistry |
Due to the special property of photo-switchable fluorescence, Kaede protein possesses several advantages as an optical cell marker.
After the photoconversion, the photoconverted Kaede protein emits bright and stable red fluorescence. This fluorescence can last for months without anaerobic conditions. As this red state of Kaede is bright and stable compared to the green state, and because the unconverted green Kaede emits very low intensity of red fluorescence, the red signals provides contrast.
Besides, before the photoconversion, Kaede emits bright green fluorescence which enables the visualization of the localization of the non-photoacivated protein. This is superior to other fluorescent proteins such as PA-GFP and KFP1, which only show low fluorescence before photoactivation.
In addition, as both green and red fluorescence of Kaede are excited by blue light at 480 nm for observation, this light will not induce photoconversion. Therefore, illumination lights for observation and photoconversion can be separated completely. | 1 | Biochemistry |
Siderophores usually form a stable, hexadentate, octahedral complex preferentially with Fe compared to other naturally occurring abundant metal ions, although if there are fewer than six donor atoms water can also coordinate. The most effective siderophores are those that have three bidentate ligands per molecule, forming a hexadentate complex and causing a smaller entropic change than that caused by chelating a single ferric ion with separate ligands. Fe is a strong Lewis acid, preferring strong Lewis bases such as anionic or neutral oxygen atoms to coordinate with. Microbes usually release the iron from the siderophore by reduction to Fe which has little affinity to these ligands.
Siderophores are usually classified by the ligands used to chelate the ferric iron. The major groups of siderophores include the catecholates (phenolates), hydroxamates and carboxylates (e.g. derivatives of citric acid). Citric acid can also act as a siderophore. The wide variety of siderophores may be due to evolutionary pressures placed on microbes to produce structurally different siderophores which cannot be transported by other microbes' specific active transport systems, or in the case of pathogens deactivated by the host organism. | 1 | Biochemistry |
One mechanism, considered important for small atomic numbers is the scattering of a free electron at the shell electrons of an atom or molecule. Since electron–electron bremsstrahlung is a function of and the usual electron-nucleus bremsstrahlung is a function of electron–electron bremsstrahlung is negligible for metals. For air, however, it plays an important role in the production of terrestrial gamma-ray flashes. | 7 | Physical Chemistry |
Several groups of bacteria can conduct anoxygenic photosynthesis: green sulfur bacteria (GSB), red and green filamentous phototrophs (FAPs e.g. Chloroflexia), purple bacteria, acidobacteriota, and heliobacteria.
Some archaea (e.g. Halobacterium) capture light energy for metabolic function and are thus phototrophic but none are known to "fix" carbon (i.e. be photosynthetic). Instead of a chlorophyll-type receptor and electron transport chain, proteins such as halorhodopsin capture light energy with the aid of diterpenes to move ions against a gradient and produce ATP via chemiosmosis in the manner of mitochondria. | 5 | Photochemistry |
He married Catherine Connelly (also a biochemist) in Holyoke, Massachusetts, On September 16, 1961. He raised a family of four children: Miguel Luis, Juan Ignacio, Jorge Eduardo and Maria Amparo and has 13 grandchildren.
With his wife, Catherine Connelly, he was on sabbatical at the University of California at San Diego, when the 1973 coup in Chile took place. He returned to Chile in May 1974 and was one of the main defenders of the University of Chile's autonomy, endangered by the military intervention in academic life. In December 1975 he co-signed, with other academics, a letter entitled "University under surveillance" opposing military intervention in the University of Chile. The letter was written by philosopher Jorge Millas and published in the newspaper "El Mercurio". The letter was the first appearance of a public statement by a group of academics who criticized the handling of the University of Chile by the military government. | 1 | Biochemistry |
Dislocation creep is a non-linear (plastic) deformation mechanism in which vacancies in the crystal glide and climb past obstruction sites within the crystal lattice. These migrations within the crystal lattice can occur in one or more directions and are triggered by the effects of increased differential stress. It occurs at lower temperatures relative to diffusion creep. The mechanical process presented in dislocation creep is called slip. The principal direction in which dislocation takes place are defined by a combination of slip planes and weak crystallographic orientations resulting from vacancies and imperfections in the atomic structure. Each dislocation causes a part of the crystal to shift by one lattice point along the slip plane, relative to the rest of the crystal. Each crystalline material has different distances between atoms or ions in the crystal lattice, resulting in different lengths of displacement. The vector that characterizes the length and orientation of the displacement is called the Burgers vector. The development of strong lattice preferred orientation can be interpreted as evidence for dislocation creep as dislocations move only in specific lattice planes.
Dislocation glide cannot act on its own to produce large strains due to the effects of strain-hardening, where a dislocation ‘tangle’ can inhibit the movement of other dislocations, which then pile up behind the blocked ones causing the crystal to become difficult to deform. Diffusion and dislocation creep can occur simultaneously. The effective viscosity of a stressed material under given conditions of temperature, pressure, and strain rate will be determined by the mechanism that delivers the smallest viscosity. Some form of recovery process, such as dislocation climb or grain-boundary migration must also be active. Slipping of the dislocation results in a more stable state for the crystal as the pre-existing imperfection is removed. It requires much lower differential stress than that required for brittle fracturing. This mechanism does not damage the mineral or reduce the internal strength of crystals. | 8 | Metallurgy |
Biocatalysis is used to produce a number of food products. More than five biilion tons of high fructose corn syrup are produced annually by the action of the immobilized enzyme glucose isomerase of corn-derived glucose. Emerging technologies are numerous, including enzymes for clarifying or debittering of fruit juices.
A variety of potentially useful chemicals are obtained by engineered plants. Bioremediation is a green route to biodegradation. | 1 | Biochemistry |
Absinthin's (1) complex structure is classified as a sesquiterpene lactone, meaning it belongs to a large category of natural products chemically derived from 5-carbon "building blocks" (3) derived from isoprene (4). The complete structure consists of two identical monomers (2) that are attached via a suspected naturally occurring Diels Alder reaction occurring at the alkenes on the 5-membered ring of the guaianolide. | 0 | Organic Chemistry |
There are about 2 dozen computational NMR services available that can be divided into:
* Processing: MDD NMR
* Assignment: Auto Assign • MARS • UNIO
* Analysis: TALOS+ • AnisoFIT • MaxOcc • iCing
* Structure Calculation: CS-ROSETTA • CYANA • UNIO • Xplor-NIH
* Molecular Dynamics: AMBER • GROMACS
* Modelling: 3D-DART • HADDOCK
* Tools: Format Converter • SHIFTX2 • Antechamber • PREDITOR • RCI • UPLABEL | 1 | Biochemistry |
There is no simple relationship between the scattering cross section and the physical size of the particles, as the scattering cross section depends on the wavelength of radiation used. This can be seen when looking at a halo surrounding the Moon on a decently foggy evening: Red light photons experience a larger cross sectional area of water droplets than photons of higher energy. The halo around the Moon thus has a perimeter of red light due to lower energy photons being scattering further from the center of the Moon. Photons from the rest of the visible spectrum are left within the center of the halo and perceived as white light. | 7 | Physical Chemistry |
Single molecule fluorescent sequencing is one method of DNA sequencing. The core principle is the imaging of individual fluorophore molecules, each corresponding to one base. By working on single molecule level, amplification of DNA is not required, avoiding amplification bias. The method lends itself to parallelization by probing many sequences simultaneously, imaging all of them at the same time.
The principle can be applied stepwise (e.g. the Helicos implementation), or in real time (as in the Pacific Biosciences implementation). | 1 | Biochemistry |
Haworth projections are a related chemical notation used to represent sugars in ring form. The groups on the right hand side of a Fischer projection are equivalent to those below the plane of the ring in Haworth projections. Fischer projections should not be confused with Lewis structures, which do not contain any information about three dimensional geometry. Newman projections are another system that can be used as they showcase the structure of a molecule in the staggered or eclipsed conformation states. The wedge and dash notation will help to showcase the stereochemistry within a specific molecule. | 4 | Stereochemistry |
Tesoro was a member of several committees of the National Academy of Sciences and the National Research Council concerning toxic materials and fire safety. Other committees she was a part of include: the Fiber Society (founder/president in 1974), Sigma Xi, a Gordon Research Conference committee, the American Chemical Society, the American Association of Textile Chemists and Colorists, the American Institute of Chemists, and the American Association for the Advancement of Science. In 1963, Tesoro was awarded the Olney Medal of the American Association of Textile Chemists and Colorists. She was the recipient of the Society of Women Engineers’ Achievement Award in 1978. Additionally, Tesoro earned the American Dyestuff Reporter Award. | 0 | Organic Chemistry |
During 2010, the United States Department of Energy established the Joint Center for Artificial Photosynthesis. The mission of JCAP is to find a cost-effective method to produce fuels using only sunlight, water, and carbon-dioxide as inputs. JCAP is managed by a team from the California Institute of Technology (Caltech), directed by Professor Nathan Lewis and brings together more than 120 scientists and engineers from Caltech and its main partner, Lawrence Berkeley National Laboratory. JCAP also draws on the expertise and capabilities of key partners from Stanford University, the University of California at Berkeley, UCSB, University of California, Irvine, and University of California at San Diego, and the Stanford Linear Accelerator. Additionally, JCAP serves as a central hub for other solar fuels research teams across the United States, including 20 DOE Energy Frontier Research Center. The program had a budget of $122M over five years, subject to Congressional appropriation | 5 | Photochemistry |
The organization of the components for artificial photosynthesis is crucial. Natural photosynthesis can be divided in three steps:
* Light-harvesting complexes in bacteria and plants capture photons and transduce them into electrons, injecting them into the photosynthetic chain.
* Proton-coupled electron transfer along several cofactors of the photosynthetic chain, causing local, spatial charge separation.
* Redox catalysis, which uses the aforementioned transferred electrons to oxidize water to dioxygen and protons; these protons can in some species be utilized for dihydrogen production.
These processes could be replicated by a triad assembly, which could oxidize water at one catalyst, reduce protons at another, and have a photosensitizer molecule to power the whole system | 5 | Photochemistry |
In spectroscopy, remission refers to the reflection or back-scattering of light by a material. While seeming similar to the word "re-emission", it is the light which is scattered back from a material, as opposed to that which is "transmitted" through the material. The word "re-emission" connotes no such directional character. Based on the origin of the word "emit", which means "to send out or away", "re-emit" means "to send out again", "transmit" means "to send across or through", and "remit" means "to send back". | 7 | Physical Chemistry |
Search capacities of crystallographic databases differ widely. Basic functionality comprises search by keywords, physical properties, and chemical elements. Of particular importance is search by compound name and lattice parameters. Very useful are search options that allow the use of wildcard characters and logical connectives in search strings. If supported, the scope of the search can be constrained by the exclusion of certain chemical elements.
More sophisticated algorithms depend on the material type covered. Organic compounds might be searched for on the basis of certain molecular fragments. Inorganic compounds, on the other hand, might be of interest with regard to a certain type of coordination geometry. More advanced algorithms deal with conformation analysis (organics), supramolecular chemistry (organics), interpolyhedral connectivity (‘non-organics’) and higher-order molecular structures (biological macromolecules). Search algorithms used for a more complex analysis of physical properties, e.g. phase transitions or structure-property relationships, might apply group-theoretical concepts.
Modern versions of crystallographic databases are based on the relational database model. Communication with the database usually happens via a dialect of the Structured Query Language (SQL). Web-based databases typically process the search algorithm on the server interpreting supported scripting elements, while desktop-based databases run locally installed and usually precompiled search engines. | 7 | Physical Chemistry |
The deuteron has spin +1 ("triplet state") and is thus a boson. The NMR frequency of deuterium is significantly different from common light hydrogen. Infrared spectroscopy also easily differentiates many deuterated compounds, due to the large difference in IR absorption frequency seen in the vibration of a chemical bond containing deuterium, versus light hydrogen. The two stable isotopes of hydrogen can also be distinguished by using mass spectrometry.
The triplet deuteron nucleon is barely bound at E = , and none of the higher energy states are bound. The singlet deuteron is a virtual state, with a negative binding energy of . There is no such stable particle, but this virtual particle transiently exists during neutron-proton inelastic scattering, accounting for the unusually large neutron scattering cross-section of the proton. | 9 | Geochemistry |
In the jump method, the top cylinder is mounted to a pair of cantilever springs, while the bottom cylinder is brought up towards the top cylinder. While the bottom cylinder approaches the top, there comes a point when they will "jump" into contact with each other. The measurements, in this case, are based on the distance from which they jump and the spring constant. These measurements are usually between surfaces 1.25 nm and 20 nm apart. | 6 | Supramolecular Chemistry |
Superheating can occur when an undisturbed container of water is heated in a microwave oven. At the time the container is removed, the lack of nucleation sites prevents boiling, leaving the surface calm. However, once the water is disturbed, some of it violently flashes to steam, potentially spraying boiling water out of the container. The boiling can be triggered by jostling the cup, inserting a stirring device, or adding a substance like instant coffee or sugar. The chance of superheating is greater with smooth containers, because scratches or chips can house small pockets of air, which serve as nucleation points. Superheating is more likely after repeated heating and cooling cycles of an undisturbed container, as when a forgotten coffee cup is re-heated without being removed from a microwave oven. This is due to heating cycles releasing dissolved gases such as oxygen and nitrogen from the solvent. There are ways to prevent superheating in a microwave oven, such as putting a non-metallic object (such as a stir stick) into the container beforehand or using a scratched container. To avoid a dangerous sudden boiling, it is recommended not to microwave water for an excessive amount of time. | 7 | Physical Chemistry |
Alkali metal nitrates are chemical compounds consisting of an alkali metal (lithium, sodium, potassium, rubidium and caesium) and the nitrate ion. Only two are of major commercial value, the sodium and potassium salts. They are white, water-soluble salts with melting points ranging from 255 °C () to 414 °C () on a relatively narrow span of 159 °C
The melting point of the alkali metal nitrates tends to increase from 255 °C to 414 °C (with an anomaly for rubidium being not properly aligned in the series) as the atomic mass and the ionic radius (naked cation) of the alkaline metal increases, going down in the column. Similarly, but not presented here in the table, the solubility of these salts in water also decreases with the atomic mass of the metal. | 7 | Physical Chemistry |
A DNA walker is a class of nucleic acid nanomachines where a nucleic acid "walker" is able to move along a nucleic acid "track". The concept of a DNA walker was first defined and named by John H. Reif in 2003.
A nonautonomous DNA walker requires external changes for each step, whereas an autonomous DNA walker progresses without any external changes. Various nonautonomous DNA walkers were developed, for example Shin controlled the motion of DNA walker by using control strands which needed to be manually added in a specific order according to the template's sequence in order to get the desired path of motion.
In 2004 the first autonomous DNA walker, which did not require external changes for each step, was experimentally demonstrated by the Reif group.
DNA walkers have functional properties such as a range of motion extending from linear to 2 and 3-dimensional, the ability to pick up and drop off molecular cargo, performing DNA-templated synthesis, and increased velocity of motion. DNA walkers have potential applications ranging from nanomedicine to nanorobotics. Many different fuel options have been studied including DNA hybridization, hydrolysis of DNA or ATP, and light. The DNA walker's function is similar to that of the proteins dynein and kinesin. | 6 | Supramolecular Chemistry |
Hydrocyanation was first reported by Arthur and Pratt in 1954, when they homogeneously catalyzed the hydrocyanation of linear alkenes.
The industrial process for catalytic hydrocyanation of butadiene to adiponitrile was invented by William C. Drinkard. | 0 | Organic Chemistry |
In the early 1960s, Woodward began work on what was the most complex natural product synthesized to date—vitamin B. In a remarkable collaboration with his colleague Albert Eschenmoser in Zurich, a team of almost one hundred students and postdoctoral workers worked for many years on the synthesis of this molecule. The work was finally published in 1973, and it marked a landmark in the history of organic chemistry. The synthesis included almost a hundred steps, and involved the characteristic rigorous planning and analyses that had always characterised Woodwards work. This work, more than any other, convinced organic chemists that the synthesis of any complex substance was possible, given enough time and planning (see also palytoxin, synthesized by the research group of Yoshito Kishi, one of Woodwards postdoctoral students). As of 2019, no other total synthesis of Vitamin B has been published.
That same year, based on observations that Woodward had made during the B synthesis, he and Roald Hoffmann devised rules (now called the Woodward–Hoffmann rules) for elucidating the stereochemistry of the products of organic reactions. Woodward formulated his ideas (which were based on the symmetry properties of molecular orbitals) based on his experiences as a synthetic organic chemist; he asked Hoffman to perform theoretical calculations to verify these ideas, which were done using Hoffmann's Extended Hückel method. The predictions of these rules, called the "Woodward–Hoffmann rules" were verified by many experiments. Hoffmann shared the 1981 Nobel Prize for this work along with Kenichi Fukui, a Japanese chemist who had done similar work using a different approach; Woodward had died in 1979 and Nobel Prizes are not awarded posthumously. | 4 | Stereochemistry |
The atoms, molecules or ions that make up solids may be arranged in an orderly repeating pattern, or irregularly. Materials whose constituents are arranged in a regular pattern are known as crystals. In some cases, the regular ordering can continue unbroken over a large scale, for example diamonds, where each diamond is a single crystal. Solid objects that are large enough to see and handle are rarely composed of a single crystal, but instead are made of a large number of single crystals, known as crystallites, whose size can vary from a few nanometers to several meters. Such materials are called polycrystalline. Almost all common metals, and many ceramics, are polycrystalline.
In other materials, there is no long-range order in the position of the atoms. These solids are known as amorphous solids; examples include polystyrene and glass.
Whether a solid is crystalline or amorphous depends on the material involved, and the conditions in which it was formed. Solids that are formed by slow cooling will tend to be crystalline, while solids that are frozen rapidly are more likely to be amorphous. Likewise, the specific crystal structure adopted by a crystalline solid depends on the material involved and on how it was formed.
While many common objects, such as an ice cube or a coin, are chemically identical throughout, many other common materials comprise a number of different substances packed together. For example, a typical rock is an aggregate of several different minerals and mineraloids, with no specific chemical composition. Wood is a natural organic material consisting primarily of cellulose fibers embedded in a matrix of organic lignin. In materials science, composites of more than one constituent material can be designed to have desired properties. | 7 | Physical Chemistry |
The Pinner triazine synthesis describes the preparation of 2-hydroxyl-4,6-diaryl-s-triazines by reaction of aryl amidines and phosgene. This reaction may be extended to halogenated aliphatic amidines.
This reaction was first reported by Adolf Pinner in 1890 | 0 | Organic Chemistry |
The formation of chiral quaternary carbon centers has been a synthetic challenge. Chemists have developed asymmetric Diels–Alder reactions, Heck reaction, Enyne cyclization, cycloaddition reactions, C–H activation, Allylic substitution, Pauson–Khand reaction, etc. to construct asymmetric quaternary carbon atoms. | 0 | Organic Chemistry |
Lithium tert-butoxide is commercially available as a solution and as a solid, but it is often generated in situ for laboratory use because samples are so sensitive and older samples are often of poor quality. It can be obtained by treating tert-butanol with butyl lithium. | 0 | Organic Chemistry |
In March 2014, NASA's Jet Propulsion Laboratory demonstrated a unique way to study the origins of life: fuel cells. Fuel cells are similar to biological cells in that electrons are also transferred to and from molecules. In both cases, this results in electricity and power. The study of fuel cells suggest that an important factor in protocell development was that the Earth provides electrical energy at the seafloor. "This energy could have kick-started life and could have sustained life after it arose. Now, we have a way of testing different materials and environments that could have helped life arise not just on Earth, but possibly on Mars, Europa and other places in the Solar System." | 9 | Geochemistry |
Molecular gyroscopes are chemical compounds or supramolecular complexes containing a rotor that moves freely relative to a stator, and therefore act as gyroscopes. Though any single bond or triple bond permits a chemical group to freely rotate, the compounds described as gyroscopes may protect the rotor from interactions, such as in a crystal structure with low packing density or by physically surrounding the rotor avoiding steric contact. A qualitative distinction can be made based on whether the activation energy needed to overcome rotational barriers is higher than the available thermal energy. If the activation energy required is higher than the available thermal energy, the rotor undergoes "site exchange", jumping in discrete steps between local energy minima on the potential energy surface. If there is thermal energy sufficiently higher than that needed to overcome the barrier to rotation, the molecular rotor can behave more like a macroscopic freely rotating inertial mass.
For example, several studies in 2002 with a p-phenylene rotor found that some structures using variable-temperature (VT) solid-state C CPMAS and quadrupolar echo H NMR were able to detect a two-site exchange rate of 1.6 MHz (over 10/second at 65 °C), described as "remarkably fast for a phenylene group in a crystalline solid", with steric barriers of 12–14 kcal/mol. However, tert-butyl modification of the rotor increased the exchange rate to over 10 per second at room temperature, and the rate for inertially rotating p-phenylene without barriers is estimated to be approximately 2.4 x 10 revolutions per second. | 6 | Supramolecular Chemistry |
There are two options for realizing apertureless NSOM-Raman technique: TERS and SERS. TERS is frequently used for apertureless NSOM-Raman and can significantly enhance the spatial resolution. This technique requires a metal tip to enhance the signal of the sample. That is why an AFM metal tip is usually used for enhancing the electric field for molecule excitation. Raman spectroscopy was combined with AFM in 1999. A very narrow aperture of the tip was required to obtain a relatively high spatial resolution; such aperture reduced the signal and was difficult to prepare. In 2000, Stȍckle et al. first designed a setup combining apertureless NSOM, Raman and AFM techniques, in which the tip had a 20 nm thick granular silver film on it. They reported a large gain in the Raman scattering intensity of a dye film (brilliant cresyl blue) deposited on a glass substrate if a metal-coated AFM tip was brought very close to the sample. About 2000-fold enhancement of Raman scattering and a spatial resolution of ~55 nm were achieved.
Similarly, Nieman et al. used an illuminated AFM tip coated with a 100 nm thick film of gold to enhance Raman scattering from polymers samples and achieved a resolution of 100 nm. In the early research of TERS, the most commonly used coating materials for the tip probe were silver and gold. High-resolution spatial maps of Raman signals were obtained with this technique from molecular films of such compounds as brilliant cresyl blue, malachite green isothiocyanate and rhodamine 6G, as well as individual carbon nanotubes. | 7 | Physical Chemistry |
Either enantiomer of tert-butanesulfinamide can be reached from tert-butyl disulfide in two steps: a catalytic asymmetric oxidation reaction gives the disulfide oxidation product (thiosulfinate) in high yield and enantiomeric excess. Treatment of this compound with lithium amide in ammonia affords optically pure inverted product.
<br />
Condensation of tert-butanesulfinamide with an aldehyde or ketone proceeds in high yield and affords only the (E)-isomer of the corresponding N-sulfinyl imines.
<br /> | 4 | Stereochemistry |
The induced vortices have many applications in various aspects of electrokinetic microfluidics. There are many micro-mixers that are designed and fabricated based on the existence of their induced vortices in the microfluidics devices. Such micro-mixers which are used for biochemical, medicine, biology applications has no mechanical parts and only use conducting surfaces to generate induced vortices to mix the different fluid streams.
This phenomenon even is used to trap the micron and submicron particles floating in flow inside a micro-channel. This method can be used to manipulate, detect, handle, and concentrate cells and virus in biomedical field; or, for colloidal particle assembly.
In addition the induced vortices around the conducting surfaces in a microfluidic system can be used as a micro-valve, micro-actuator, micro-motor and micro-regulator to control the direction and manipulation. | 7 | Physical Chemistry |
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