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Phycobilisomes are protein complexes (up to 600 polypeptides) anchored to thylakoid membranes. They are made of stacks of chromophorylated proteins, the phycobiliproteins, and their associated linker polypeptides. Each phycobilisome consists of a core made of allophycocyanin, from which several outwardly oriented rods made of stacked disks of phycocyanin and (if present) phycoerythrin(s) or phycoerythrocyanin. The spectral property of phycobiliproteins are mainly dictated by their prosthetic groups, which are linear tetrapyrroles known as phycobilins including phycocyanobilin, phycoerythrobilin, phycourobilin and phycobiliviolin. The spectral properties of a given phycobilin are influenced by its protein environment. | 5 | Photochemistry |
Light sources emitting in the UV spectral region are widely used in techniques involving photo-chemical processes, e.g., curing of inks, adhesives, varnishes and coatings, photolithography, UV induced growth of dielectrics, UV induced surface modification, and cleaning or material deposition. Incoherent sources of UV radiation have some advantages over laser sources because of their lower cost, a huge area of irradiation, and ease of use, especially when large-scale industrial processes are envisaged.
Mercury lamps (λ = 253.7 nm) are widely spread UV sources, but their production, use, and disposal of old lamps pose a threat to human health and environmental pollution. Comparing with commonly used mercury lamps, excimer lamps have a number of advantages. A specific feature of an excimer molecule is the absence of a strong bond in the ground electronic state. Thanks to this, high-intensity UV radiation can be extracted from a plasma without significant self-absorption. This makes possible to convert efficiently energy deposited to the active medium into UV radiation.
Excimer lamps are referred to cold sources of UV radiation since the radiating surface of excimer lamps remains at relatively low temperatures in contrast with traditional UV lamps like a mercury one. Because the medium does not need to be heated, excimer lamps reach their peak output almost immediately after they are turned on.
Rare gas and rare gas-halide excimer lamps generally radiate in the ultraviolet (UV) and vacuum-ultraviolet (VUV) spectral regions (see table). Their unique narrow-band emission characteristics, high quantum efficiency, and high-energy photons make them suitable for applications such as absorption spectroscopy, UV curing, UV coating, disinfection, ozone generation, destruction of gaseous organic waste, photo-etching and photo-deposition and more other applications.
Light sources emitting photons in the energy range of 3.5–10 eV find applications in many fields due to the ability of high-energy photons to cleave most chemical bonds and kill microbes destroying nucleic acids and disrupting their DNA. Examples of excimer lamp applications include purification and disinfection of drinking water, pool water, air, sewage purification, decontamination of industrial waste, photochemical synthesis and degradation of organic compounds in flue gases and water, photopolymerization of organic coatings and paints, and photo-enhanced chemical vapor deposition. In all cases UV photons excite species or cleave chemical bonds, resulting in the formation of radicals or other chemical reagents, which initiate a required reaction.
An excimer lamp has selective action. UV radiation of a given wavelength can selectively excite species or generate required radicals. Such lamps can be useful for photophysical and photochemical processing such as UV curing of paints, varnishes, and adhesives, cleansing and modifying surface properties, polymerization of lacquers and paints, and photo-degradation of a variety of pollutants. Photo-etching of polymers is possible using different wavelengths: 172 nm by xenon excimer, 222 nm by krypton chloride, and 308 nm by xenon chloride. Excimer UV sources can be used for microstructuring large-area polymer surfaces. XeCl-excimer lamps (308 nm) are especially suitable to get tan.
Fluorescence spectroscopy is one of the most common methods for detecting biomolecules. Biomolecules can be labeled with fluoroprobe, which then is excited by a short pulse of UV light, leading to re-emission in the visible spectral region. Detecting this re-emitted light, one can judge the density of labeled molecules. Lanthanide complexes are commonly used as fluoroprobes. Due to their long lifetime, they play an important role in Förster resonance energy transfer (FRET) analysis.
At present, excimer lamps are coming into use in ecology, photochemistry, photobiology, medicine, criminalistics, petrochemistry, physics, microelectronics, different engineering tasks, wide-ranging technologies, science, various branches of industry including the food industry, and many others. | 5 | Photochemistry |
Presence of un-phosphorylated pRb drives cell cycle exit and maintains senescence. At the end of mitosis, PP1 dephosphorylates hyper-phosphorylated pRb directly to its un-phosphorylated state. Furthermore, when cycling C2C12 myoblast cells differentiated (by being placed into a differentiation medium), only un-phosphorylated pRb was present. Additionally, these cells had a markedly decreased growth rate and concentration of DNA replication factors (suggesting G0 arrest).
This function of un-phosphorylated pRb gives rise to a hypothesis for the lack of cell cycle control in cancerous cells: Deregulation of Cyclin D - Cdk 4/6 phosphorylates un-phosphorylated pRb in senescent cells to mono-phosphorylated pRb, causing them to enter G1. The mechanism of the switch for Cyclin E activation is not known, but one hypothesis is that it is a metabolic sensor. Mono-phosphorylated pRb induces an increase in metabolism, so the accumulation of mono-phosphorylated pRb in previously G0 cells then causes hyper-phosphorylation and mitotic entry. Since any un-phosphorylated pRb is immediately phosphorylated, the cell is then unable to exit the cell cycle, resulting in continuous division.
DNA damage to G0 cells activates Cyclin D - Cdk 4/6, resulting in mono-phosphorylation of un-phosphorylated pRb. Then, active mono-phosphorylated pRb causes repression of E2F-targeted genes specifically. Therefore, mono-phosphorylated pRb is thought to play an active role in DNA damage response, so that E2F gene repression occurs until the damage is fixed and the cell can pass the restriction point. As a side note, the discovery that damages causes Cyclin D - Cdk 4/6 activation even in G0 cells should be kept in mind when patients are treated with both DNA damaging chemotherapy and Cyclin D - Cdk 4/6 inhibitors. | 1 | Biochemistry |
Transient expression, more frequently referred to "transient gene expression", is the temporary expression of genes that are expressed for a short time after nucleic acid, most frequently plasmid DNA encoding an expression cassette, has been introduced into eukaryotic cells with a chemical delivery agent like calcium phosphate (CaPi) or polyethyleneimine (PEI). However, unlike "stable expression," the foreign DNA does not fuse with the host cell DNA, resulting in the inevitable loss of the vector after several cell replication cycles. The majority of transient gene expressions are done with cultivated animal cells. The technique is also used in plant cells; however, the transfer of nucleic acids into these cells requires different methods than those with animal cells. In both plants and animals, transient expression should result in a time-limited use of transferred nucleic acids, since any long-term expression would be called "stable expression."
Methodology varies depending on the organism to transform. While plants can be transformed with a construct introduced into Agrobacterium tumefaciens via agroinfiltration or floral dip, most animal cells would require a viral vector. In humans, the field of transient transformation advanced rapidly during the 2020–2021 COVID-19 pandemic with major COVID-19 vaccines using either direct mRNA transfer into human or adenovirus vectors, with the RNA being expressed in the host human to produce spike proteins that induce an immune response. | 1 | Biochemistry |
* Jim Wittke's class notes at Northern Arizona University
* John Fournelle's class notes at the University of Wisconsin–Madison
* John Donovan's class notes at the University of Oregon | 3 | Analytical Chemistry |
Aziridine is an organic compound consisting of the three-membered heterocycle . It is a colorless, toxic, volatile liquid that is of significant practical interest. Aziridine was discovered in 1888 by the chemist Siegmund Gabriel. Its derivatives, also referred to as aziridines, are of broader interest in medicinal chemistry. | 0 | Organic Chemistry |
Lawessons reagent has a four membered ring of alternating sulfur and phosphorus atoms. The central phosphorus/sulfur four-membered ring dissociates to form two reactive dithiophosphine ylides (R-PS). Much of the chemistry of Lawessonss reagent is in fact the chemistry of this reactive intermediate.
In general, the more electron rich a carbonyl is, the faster the carbonyl group will be converted into the corresponding thiocarbonyl by Lawesson's reagent. | 0 | Organic Chemistry |
Diel Vertical Migration (DVM) is a well-studied phenomenon, widespread in the temperate and tropical oceans, and previously understood to be the most significant contributor to the active export of carbon as a result of zooplankton migration. The most common form is the nocturnal DVM, a night-time ascent to the upper pelagic and a daytime descent to deeper waters. A relatively unique variation of this form is the twilight DVM, where the ascent happens during dusk and the descent around midnight (i.e., midnight sinking).
While DVM occurs on a daily basis, overwintering diapause (hibernation) occurs on an annual time-scale and enables zooplankton species, particularly Calanus spp., to adapt to seasonal variation in primary productivity in specific ocean basins. Individuals enter diapause and migrate deeper in the water column to overwinter below the thermocline. During diapause they survive on stored lipid reserves that are generated at the end of their time at the surface when nutrients are widely available. The seasonal end of diapause must be closely timed with the beginning of the spring phytoplankton bloom to enable acquisition of food to permit proper egg development and hatching. If the timing is disrupted, eggs that are hatched during diapause will have limited growth time and a lower likelihood of surviving overwintering, as thus is an example of match-mismatch hypothesis. Calanus spp. in ocean basins with shorter growth seasons will be increasingly sensitive to the timing of the spring bloom, such as polar regions.
In the Arctic and Antarctic environments, the productive season is typically short and certain copepods species vertically migrate during overwintering diapause. During the productive seasons of spring and summer, younger developmental stages of these copepods usually thrive in food-rich, warmer, near-surface waters, and they rapidly develop and grow. During late summer and fall, grazing pressure, nutrient limitation, and annual variations of irradiance combine to limit the pelagic primary production. Consequently, the food supply fades toward fall, and overwintering diapause initiates. These copepods migrate to deeper waters with accumulated lipid reserves for overwintering. The overwintering diapause stages remain in deeper waters with limited physical and physiological activity and ascend back to the near-surface waters and complete the life cycle at the onset of the following productive season. | 9 | Geochemistry |
Germacranolides are a group of natural chemical compounds classified as sesquiterpene lactones. They are found in a variety of plant sources. | 0 | Organic Chemistry |
In SARS-CoV-2 (COVID-19) infected Caco-2 cells, the phosphorylase activity of CK2 is increased resulting in phosphorylation of several cytoskeletal proteins. These infected cells also display CK2-containing filopodia protrusions associated with budding viral particles. Hence the protrusions may assist the virus in infecting adjacent cells. In these same cells, the CK2 inhibitor silmitasertib displayed potent antiviral activity. Senhwa Biosciences and the US National Institutes of Health have announced that they will evaluate the efficacy of silmitasertib in treating COVID-19 infections. | 1 | Biochemistry |
In the context of climate change and in particular mitigation, a sink is defined as "Any process, activity or mechanism which removes a greenhouse gas, an aerosol or a precursor of a greenhouse gas from the atmosphere".
In the case of non- greenhouse gases, sinks need not store the gas. Instead they can break it down into substances that have a reduced effect on global warming. For example, nitrous oxide can be reduced to harmless N.
Related terms are "carbon pool, reservoir, sequestration, source and uptake". The same publication defines carbon pool as "a reservoir in the Earth system where elements, such as carbon [...], reside in various chemical forms for a period of time."
Both carbon pools and carbon sinks are important concepts in understanding the carbon cycle, but they refer to slightly different things. A carbon pool can be thought of as the overarching term, and carbon sink is then a particular type of carbon pool: A carbon pool is all the places where carbon can be (for example the atmosphere, oceans, soil, plants, and fossil fuels). A carbon sink, on the other hand, is a type of carbon pool that has the capability to take up more carbon from the atmosphere than it releases. | 5 | Photochemistry |
One potential application of ARS involves the rapid and nondestructive identification of drug tablet verification. Currently, there are no unfailing methods to eliminate contaminated or mislabeled products, a process which sometimes results in millions of pills having to be recalled. More studies need to be completed to determine if ARS could be used as a process analytical technique in industry to prevent problems with pills before they are shipped. ARS may also be useful for quantifying the active ingredient in pharmaceutical ointments and gels. | 7 | Physical Chemistry |
Many governments impose strict regulations regarding the maximum chemical oxygen demand allowed in waste water before they can be returned to the environment. For example, in Switzerland, a maximum oxygen demand between 200 and 1000 mg/L must be reached before waste water or industrial water can be returned to the environment [https://web.archive.org/web/20040310122559/http://www.csem.ch/corporate/Report2002/pdf/p56.pdf]. | 9 | Geochemistry |
The karat (US spelling, symbol k or Kt) or carat (UK spelling, symbol c or Ct) is a fractional measure of purity for gold alloys, in parts fine per 24 parts whole. The karat system is a standard adopted by US federal law. | 8 | Metallurgy |
High-throughput analyses of ESTs often encounter similar data management challenges. A first challenge is that tissue provenance of EST libraries is described in plain English in dbEST. This makes it difficult to write programs that can unambiguously determine that two EST libraries were sequenced from the same tissue. Similarly, disease conditions for the tissue are not annotated in a computationally friendly manner. For instance, cancer origin of a library is often mixed with the tissue name (e.g., the tissue name "glioblastoma" indicates that the EST library was sequenced from brain tissue and the disease condition is cancer). With the notable exception of cancer, the disease condition is often not recorded in dbEST entries. The TissueInfo project was started in 2000 to help with these challenges. The project provides curated data (updated daily) to disambiguate tissue origin and disease state (cancer/non cancer), offers a tissue ontology that links tissues and organs by "is part of" relationships (i.e., formalizes knowledge that hypothalamus is part of brain, and that brain is part of the central nervous system) and distributes open-source software for linking transcript annotations from sequenced genomes to tissue expression profiles calculated with data in dbEST. | 1 | Biochemistry |
A disadvantage to MIKES is that observations are made later in the ion flight path when compared to other methods. Also, a smaller number of ions will typically decompose. This will in turn cause the sensitivity to be lower than other kinetic energy spectroscopy methods. | 7 | Physical Chemistry |
Proteins perform several functions in living organisms, including catalytic reactions and transport of molecules or ions within the cells, the organs or the whole body. The understanding of the processes in human organisms, which are mainly driven by biochemical reactions and protein-protein interactions, depends to a great extent on the ability to isolate active proteins in biological samples for more detailed examination of chemical structure and physiological function. This essential information can imply an important indication of a patient's state of health.
As about 30–40% of all known proteins contain one or more metal ion cofactors (e.g., ceruloplasmin, ferritin, amyloid-beta precursor protein, matrix metalloproteinase, or metallochaperones), especially native and denatured metalloproteins have to be isolated, identified and quantified after liquid biopsy. Many of these cofactors (e.g., iron, copper, or zinc) play a key role in vital enzymatic catalytic processes or stabilize globular protein molecules. Therefore, the high-precision gel electrophoresis and comparable separation techniques are highly relevant as initial step of protein and trace metal speciation analysis, subsequently, followed by modern mass spectrometric and magnetic resonance methods for quantifying and identifying the soluble proteins of interest. | 3 | Analytical Chemistry |
Each cell typically contains several hundred of a special class of enhancers that stretch over many kilobases long DNA sequences, called "super-enhancers". These enhancers contain a large number of binding sites for sequence-specific, inducible transcription factors, and regulate expression of genes involved in cell differentiation. During inflammation, the transcription factor NF-κB facilitates remodeling of chromatin in a manner that selectively redistributes cofactors from high-occupancy enhancers, thereby repressing genes involved in maintaining cellular identify whose expression they enhance; at the same time, this F-κB-driven remodeling and redistribution activates other enhancers that guide changes in cellular function through inflammation. As a result, inflammation reprograms cells, altering their interactions with the rest of tissue and with the immune system. In cancer, proteins that control NF-κB activity are dysregulated, permitting malignant cells to decrease their dependence on interactions with local tissue, and hindering their surveillance by the immune system. | 1 | Biochemistry |
The intense coloring of the molecule is generated by the absorption of specific wavelengths of light by the pi bonds. These bonds are ordinarily excited by light in the orange region of the spectrum, causing the molecule to appear blue. When the molecule interacts with protons from an acid the bonds become harder to excite and thus absorb green light which has a shorter wavelength. This is what causes the molecule to appear red in the presence of an acid. | 3 | Analytical Chemistry |
The word "benzene" derives from "gum benzoin" (benzoin resin), an aromatic resin known since ancient times in Southeast Asia, and later to European pharmacists and perfumers in the 16th century via trade routes. An acidic material was derived from benzoin by sublimation, and named "flowers of benzoin", or benzoic acid. The hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene. Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen. In 1833, Eilhard Mitscherlich produced it by distilling benzoic acid (from gum benzoin) and lime. He gave the compound the name benzin. In 1836, the French chemist Auguste Laurent named the substance "phène"; this word has become the root of the English word "phenol", which is hydroxylated benzene, and "phenyl", the radical formed by abstraction of a hydrogen atom from benzene.
In 1845, Charles Blachford Mansfield, working under August Wilhelm von Hofmann, isolated benzene from coal tar. Four years later, Mansfield began the first industrial-scale production of benzene, based on the coal-tar method. Gradually, the sense developed among chemists that a number of substances were chemically related to benzene, comprising a diverse chemical family. In 1855, Hofmann was the first to apply the word "aromatic" to designate this family relationship, after a characteristic property of many of its members. In 1997, benzene was detected in deep space. | 2 | Environmental Chemistry |
If the plasma is optically thin, the bremsstrahlung radiation leaves the plasma, carrying part of the internal plasma energy. This effect is known as the bremsstrahlung cooling. It is a type of radiative cooling. The energy carried away by bremsstrahlung is called bremsstrahlung losses and represents a type of radiative losses. One generally uses the term bremsstrahlung losses in the context when the plasma cooling is undesired, as e.g. in fusion plasmas. | 7 | Physical Chemistry |
Measurements (performed using a soy bean SCS) indicate an optimal temperature of 37 °C and an optimal pH of 7.0-8.0. | 1 | Biochemistry |
The Sleeping Beauty transposon system (SBTS) is the first successful non-viral vector for incorporation of a gene cassette into a vertebrate genome. Up until the development of this system, the major problems with non-viral gene therapy have been the intracellular breakdown of the transgene due to it being recognized as Prokaryotes and the inefficient delivery of the transgene into organ systems. The SBTS revolutionized these issues by combining the advantages of viruses and naked DNA. It consists of a transposon containing the cassette of genes to be expressed, as well as its own transposase enzyme. By transposing the cassette directly into the genome of the organism from the plasmid, sustained expression of the transgene can be attained. This can be further refined by enhancing the transposon sequences and the transposase enzymes used. SB100X is a hyperactive mammalian transposase which is roughly 100x more efficient than the typical first-generation transposase. Incorporation of this enzyme into the cassette results in even more sustained transgene expression (over one year). Additionally, transgenesis frequencies can be as high as 45% when using pronuclear injection into mouse zygotes.
The mechanism of the SBTS is similar to the Tn5 transposon system, however the enzyme and gene sequences are eukaryotic in nature as opposed to prokaryotic. The systems tranposase can act in trans as well as in cis, allowing a diverse collection of transposon structures. The transposon itself is flanked by inverted repeat sequences, which are each repeated twice in a direct fashion, designated IR/DR sequences. The internal region consists of the gene or sequence to be transposed, and could also contain the transposase gene. Alternatively, the transposase can be encoded on a separate plasmid or injected in its protein form. Yet another approach is to incorporate both the transposon and the transposase genes into a viral vector, which can target a cell or tissue of choice. The transposase protein is extremely specific in the sequences that it binds, and is able to discern its IR/DR sequences from a similar sequence by three base pairs. Once the enzyme is bound to both ends of the transposon, the IR/DR sequences are brought together and held by the transposase in a Synaptic Complex Formation (SCF). The formation of the SCF is a checkpoint ensuring proper cleavage. HMGB1 is a non-histone protein from the host which is associated with eukaryotic chromatin. It enhances the preferential binding of the transposase to the IR/DR sequences and is likely essential for SCF complex formation/stability. Transposase cleaves the DNA at the target sites, generating 3 overhangs. The enzyme then targets TA dinucleotides in the host genome as target sites for integration. The same enzymatic catalytic site which cleaved the DNA is responsible for integrating the DNA into the genome, duplicating the region of the genome in the process. Although transposase is specific for TA dinucleotides, the high frequency of these pairs in the genome indicates that the transposon undergoes fairly random integration. | 1 | Biochemistry |
GBE is encoded by the GBE1 gene.
Through Southern blot analysis of DNA derived from human/rodent somatic cell hybrids, GBE1 has been identified as an autosomal gene located on the short arm of chromosome 3 at position 12.3. The human GBE gene was also isolated by a function complementation of the Saccharomyces cerevisiae GBE deficiency. From the isolated cDNA, the length of the gene was found to be approximately 3 kb. Additionally, the coding sequence was found to comprise 2,106 base pairs and encode a 702-amino acid long GBE. The molecular mass of human GBE was calculated to be 80,438 Da. | 1 | Biochemistry |
Henry Clifton Sorby, in 1858, was the first to document microscopic melt inclusions in crystals. The study of melt inclusions has been driven more recently by the development of sophisticated chemical analysis techniques. Scientists from the former Soviet Union lead the study of melt inclusions in the decades after World War II, and developed methods for heating melt inclusions under a microscope, so changes could be directly observed. A.T. Anderson explored analysis of melt inclusions from basaltic magmas from Kilauea Volcano in Hawaii to determine initial volatile concentrations of magma at depth. | 9 | Geochemistry |
Applications:
* The rotary filter is most suitable for continuous operation on large quantities of slurry.
* If the slurry contains considerable amount of solids, that is, in the range of 15-30%.
* Examples of pharmaceutical applications include the collection of calcium carbonate, magnesium carbonate and starch.
* The separation of the mycelia from the fermentation liquor in the manufacture of antibiotics.
* block and instant yeast production. | 3 | Analytical Chemistry |
Many isothiocyanates from plants are produced by enzymatic conversion of metabolites called glucosinolates. A prominent natural isothiocyanate is allyl isothiocyanate, also known as mustard oils.
Cruciferous vegetables, such as bok choy, broccoli, cabbage, cauliflower, kale, and others, are rich sources of glucosinolate precursors of isothiocyanates. | 0 | Organic Chemistry |
Oncometabolism is the field of study that focuses on the metabolic changes that occur in cells that make up the tumor microenvironment (TME) and accompany oncogenesis and tumor progression toward a neoplastic state.
Cells with increased growth and survivability differ from non-tumorigenic cells in terms of metabolism. The Warburg Effect, which describes how cancer cells change their metabolism to become more oncogenic in order to proliferate and eventually invade other tissues in a process known as metastasis.
The chemical reactions associated with oncometabolism are triggered by the alteration of oncogenes, which are genes that have the potential to cause cancer. These genes can be functional and active during physiological conditions, producing normal amounts of metabolites. Their upregulation as a result of DNA damage can result in an overabundance of these metabolites, and lead to tumorigenesis. These metabolites are known as oncometabolites, and can act as biomarkers. | 1 | Biochemistry |
In a delay line detector the electrons are accelerated to 500 eV between the back of the last MCP and a grid. They then fly for 5 mm and are dispersed over an area of 2 mm. A grid follows. Each element has a diameter of 1 mm and consists of an electrostatic lens focusing arriving electrons through a 30 µm hole of a grounded sheet of aluminium. Behind that, a cylinder of the same size follows. The electron cloud induces a 300 ps negative pulse when entering the cylinder and a positive when leaving. After that another sheet, a second cylinder follows, and a last sheet follows. Effectively the cylinders are fused into the center-conductor of a stripline. The sheets minimize cross talk between the layers and adjacent lines in the same layer, which would lead to signal dispersion and ringing. These striplines meander across the anode to connect all cylinders, to offer each cylinder 50 Ω impedance, and to generate a position dependent delay. Because the turns in the stripline adversely affect the signal quality their number is limited and for higher resolutions multiple independent striplines are needed. At both ends the meanders are connected to detector electronics. These electronics convert the measured delays into X- (first layer) and Y-coordinates (second layer). Sometimes a hexagonal grid and 3 coordinates are used. This redundancy reduces the dead space-time by reducing the maximum travel distance and thus the maximum delay, allowing for faster measurements. The microchannel plate detector must not operate over around 60 degree Celsius, otherwise it will degrade rapidly, bakeout without voltage has no influence. | 7 | Physical Chemistry |
Cathepsin zymography is a technique for quantifying enzymatic activity of the cathepsin family of cysteine proteases. It is based on SDS-PAGE whereby samples tested for cathepsin activity are loaded into a polyacrylamide gel and then separated by molecular weight. Gelatin is embedded in the gel itself, providing a substrate for the enzymes to hydrolyze.
While the proform of cathepsins are generally stable, once activated, proteases such as cathepsin K are vulnerable to inactivation in neutral pH environments. This loss of activity complicates detection of these enzymes. Zymography, through its high sensitivity and multiplex nature allows for the simultaneous distinction between multiple cathepsins. Very small amounts of enzymatic activity can be elucidated and is capable of resolving a femtomole of cathepsin K activity. | 1 | Biochemistry |
The People's Republic of China defines a VOC as those compounds that have "originated from automobiles, industrial production and civilian use, burning of all types of fuels, storage and transportation of oils, fitment finish, coating for furniture and machines, cooking oil fume and fine particles (PM 2.5)", and similar sources. The Three-Year Action Plan for Winning the Blue Sky Defence War released by the State Council in July 2018 creates an action plan to reduce 2015 VOC emissions 10% by 2020. | 0 | Organic Chemistry |
Consider two probability distributions and . Usually, represents the data, the observations, or a measured probability distribution. Distribution represents instead a theory, a model, a description or an approximation of . The Kullback–Leibler divergence is then interpreted as the average difference of the number of bits required for encoding samples of using a code optimized for rather than one optimized for . Note that the roles of and can be reversed in some situations where that is easier to compute, such as with the expectation–maximization algorithm (EM) and evidence lower bound (ELBO) computations. | 7 | Physical Chemistry |
The heat death paradox, also known as thermodynamic paradox, Clausius paradox, and Kelvins paradox, is a reductio ad absurdum argument that uses thermodynamics to show the impossibility of an infinitely old universe. It was formulated in February 1862 by Lord Kelvin and expanded upon by Hermann von Helmholtz and William John Macquorn Rankine. | 7 | Physical Chemistry |
Geologists often refer to the temperature range in which oil forms as an "oil window". Below the minimum temperature oil remains trapped in the form of kerogen. Above the maximum temperature the oil is converted to natural gas through the process of thermal cracking. Sometimes, oil formed at extreme depths may migrate and become trapped at a much shallower level. The Athabasca oil sands are one example of this. | 7 | Physical Chemistry |
Thionyl chloride is mainly used in the industrial production of organochlorine compounds, which are often intermediates in pharmaceuticals and agrichemicals. It usually is preferred over other reagents, such as phosphorus pentachloride, as its by-products (HCl and ) are gaseous, which simplifies purification of the product.
Many of the products of thionyl chloride are themselves highly reactive and as such it is involved in a wide range of reactions. | 0 | Organic Chemistry |
To observe one-to-one binding between a single host (H) and guest (G) using UV/Vis absorbance, the Benesi–Hildebrand method can be employed. The basis behind this method is that the acquired absorbance should be a mixture of the host, guest, and the host–guest complex.
With the assumption that the initial concentration of the guest (G) is much larger than the initial concentration of the host (H), then the absorbance from H should be negligible.
The absorbance can be collected before and following the formation of the HG complex. This change in absorbance (ΔA) is what is experimentally acquired, with A being the initial absorbance before the interaction of HG and A being the absorbance taken at any point of the reaction.
Using the Beer–Lambert law, the equation can be rewritten with the absorption coefficients and concentrations of each component.
Due to the previous assumption that , one can expect that [G] = [G]. Δε represents the change in value between ε and ε.
A binding isotherm can be described as "the theoretical change in the concentration of one component as a function of the concentration of another component at constant temperature." This can be described by the following equation:
By substituting the binding isotherm equation into the previous equation, the equilibrium constant K can now be correlated to the change in absorbance due to the formation of the HG complex.
Further modifications results in an equation where a double reciprocal plot can be made with 1/ΔA as a function of 1/[G]. Δε can be derived from the intercept while K can be calculated from the slope. | 7 | Physical Chemistry |
In organic chemistry, enolates are organic anions derived from the deprotonation of carbonyl () compounds. Rarely isolated, they are widely used as reagents in the synthesis of organic compounds. | 0 | Organic Chemistry |
Enalapril is used to treat hypertension, symptomatic heart failure, and asymptomatic left ventricular dysfunction. ACE-inhibitors (including enalapril) have demonstrated ability to reduce the progression and worsening of existing chronic kidney disease in the presence of proteinuria/microalbuminuria (protein in the urine, a biomarker for chronic kidney disease). This renal protective effect is not seen in the absence of proteinuria/microalbuminuria, including in diabetic populations. The benefit has been particularly demonstrated in patients with hypertension and/or diabetes, and is likely to be seen in other populations (although further studies and subgroup analyses of existing studies are needed) It is widely used in chronic kidney failure. Furthermore, enalapril is an emerging treatment for psychogenic polydipsia. A double-blind, placebo-controlled trial showed that when used for this purpose, enalapril led to decreased water consumption (determined by urine output and osmolality) in 60% of patients. | 4 | Stereochemistry |
Conjugation increases the allylic strain because it forces substituents into a configuration that causes their atoms to be in closer proximity, increasing the strength of repulsive Van der Waals forces. This situation occurs most noticeably when carboxylic acid or ketone is involved as a substituent of the allylic group. Resonance effect on the carboxylic group shifts the CO double bond to a hydroxy group. The carboxylic group will thus function as a hydroxyl group that will cause a large allylic strain to form and cancel the stabilization effects of the extended conjugation. This is very common in enolization reactions and can be viewed in the figure below under "Acidic Conditions."
In situations where the molecule can either be in a conjugated system or avoid allylic strain, it has been shown that the molecule's major form will be the one that avoids strain. This has been found via the cyclization in the figure below. Under treatment of perchloric acid, molecule A cyclizes into the conjugated system show in molecule B. However, the molecule will rearrange (due to allylic strain) into molecule C, causing molecule C to be the major species. Thus, the magnitude of destabilization via the allylic strain outweighs the stabilization caused by the conjugated system. | 4 | Stereochemistry |
The third class of PTPs contains three cell cycle regulators, CDC25A, CDC25B and CDC25C, which dephosphorylate CDKs at their N-terminal, a reaction required to drive progression of the cell cycle. They are themselves regulated by phosphorylation and are degraded in response to DNA damage to prevent chromosomal abnormalities. | 1 | Biochemistry |
The term glycosynthase refers to a class of proteins that have been engineered to catalyze the formation of a glycosidic bond. Glycosynthase are derived from glycosidase enzymes, which catalyze the hydrolysis of glycosidic bonds. They were traditionally formed from retaining glycosidase by mutating the active site nucleophilic amino acid (usually an aspartate or glutamate) to a small non-nucleophilic amino acid (usually alanine or glycine). More modern approaches use directed evolution to screen for amino acid substitutions that enhance glycosynthase activity. | 0 | Organic Chemistry |
Tetracyclics are cyclic chemical compounds that contain four fused rings of atoms, for example, Tröger's base.
Some tricyclic compounds having three fused and one tethered ring (connected to main nucleus by a single bond) can also classified as tetracyclic, for example, ciclazindol.
Tetracyclic compounds have various pharmaceutical uses, such as:
*tetracycline antibiotics
**Doxycycline
**Tigecycline
**Omadacycline
**Eravacycline
*tetracyclic antidepressants
**Benzoctamine
**Loxapine
**Mazindol
**Mianserin
**Mirtazapine | 0 | Organic Chemistry |
Haloalkanes generally resemble the parent alkanes in being colorless, relatively odorless, and hydrophobic. The melting and boiling points of chloro-, bromo-, and iodoalkanes are higher than the analogous alkanes, scaling with the atomic weight and number of halides. This effect is due to the increased strength of the intermolecular forces—from London dispersion to dipole-dipole interaction because of the increased polarizability. Thus tetraiodomethane () is a solid whereas tetrachloromethane () is a liquid. Many fluoroalkanes, however, go against this trend and have lower melting and boiling points than their nonfluorinated analogues due to the decreased polarizability of fluorine. For example, methane () has a melting point of −182.5 °C whereas tetrafluoromethane () has a melting point of −183.6 °C.
As they contain fewer C–H bonds, haloalkanes are less flammable than alkanes, and some are used in fire extinguishers. Haloalkanes are better solvents than the corresponding alkanes because of their increased polarity. Haloalkanes containing halogens other than fluorine are more reactive than the parent alkanes—it is this reactivity that is the basis of most controversies. Many are alkylating agents, with primary haloalkanes and those containing heavier halogens being the most active (fluoroalkanes do not act as alkylating agents under normal conditions). The ozone-depleting abilities of the CFCs arises from the photolability of the C–Cl bond. | 0 | Organic Chemistry |
In its simplest form, photosynthesis is adding water to to produce sugars and oxygen, but a complex chemical pathway is involved, facilitated along the way by a range of enzymes and co-enzymes. The enzyme RuBisCO is responsible for "fixing" – that is, it attaches it to a carbon-based molecule to form a sugar, which can be used by the plant, releasing an oxygen molecule along the way. However, the enzyme is notoriously inefficient, and just as effectively will also fix oxygen instead of in a process called photorespiration. This is energetically costly as the plant has to use energy to turn the products of photorespiration back into a form that can react with . | 5 | Photochemistry |
Dissolved load can provide valuable information about the rate of soil formation and other processes of chemical erosion. In particular, the mass balance between the dissolved load and solid phase is helpful in determining surface dynamics. In addition, dissolved load can be used to reconstruct the climate of the Earth in the past. This is because chemical weathering is the major contributor to the dissolved load of a stream. The chemical weathering of silicate rocks is the primary sink for carbon dioxide in the atmosphere, because atmospheric carbon dioxide is converted into carbonate rocks in the carbonate–silicate cycle. Carbon dioxide concentrations are the primary control of the greenhouse effect, which determines the temperature of the Earth. | 9 | Geochemistry |
A second application in cement for the bulk material analyzer is raw mix proportioning. An analyzer placed just upstream of the raw mill can monitor the chemistry of the raw mix and automatically trigger an adjustment in the proportions of the reclaimed stockpile and the correctives. By doing so, the plant is able to reduce the variability in the raw mix, and later on the kiln feed. Consistent kiln feed chemistry in turn leads to lower fuel consumption per ton of clinker produced. | 3 | Analytical Chemistry |
Dead zones are hypoxic (low-oxygen) areas in the world's oceans and large lakes. Hypoxia occurs when dissolved oxygen (DO) concentration falls to or below 2 mg of O/liter. When a body of water experiences hypoxic conditions, aquatic flora and fauna begin to change behavior in order to reach sections of water with higher oxygen levels. Once DO declines below 0.5 ml O/liter in a body of water, mass mortality occurs. With such a low concentration of DO, these bodies of water fail to support the aquatic life living there. Historically, many of these sites were naturally occurring. However, in the 1970s, oceanographers began noting increased instances and expanses of dead zones. These occur near inhabited coastlines, where aquatic life is most concentrated.
Coastal regions, such as the Baltic Sea, the northern Gulf of Mexico, and the Chesapeake Bay, as well as large enclosed water bodies like Lake Erie, have been affected by deoxygenation due to eutrophication. Excess nutrients are input into these systems by rivers, ultimately from urban and agricultural runoff and exacerbated by deforestation. These nutrients lead to high productivity that produces organic material that sinks to the bottom and is respired. The respiration of that organic material uses up the oxygen and causes hypoxia or anoxia.
The UN Environment Programme reported 146 dead zones in 2004 in the world's oceans where marine life could not be supported due to depleted oxygen levels. Some of these were as small as a square kilometer (0.4 mi), but the largest dead zone covered 70,000 square kilometers (27,000 mi). A 2008 study counted 405 dead zones worldwide. | 9 | Geochemistry |
Acyl chlorides react with low-valent metal centers to give transition metal acyl complexes. Illustrative is the oxidative addition of acetyl chloride to Vaska's complex, converting square planar Ir(I) to octahedral Ir(III): | 0 | Organic Chemistry |
The alkynylation reaction of aryl halides using aromatic acetylenes was reported in 1975 in three independent contributions by Cassar, Dieck and Heck as well as Sonogashira, Tohda and Hagihara. All of the reactions employ palladium catalysts to afford the same reaction products. However, the protocols of Cassar and Heck are performed solely by the use of palladium and require harsh reaction conditions (i.e. high reaction temperatures). The use of copper-cocatalyst in addition to palladium complexes in Sonogashiras procedure enabled the reactions to be carried under mild reaction conditions in excellent yields. A rapid development of the Pd/Cu systems followed and enabled myriad synthetic applications, while Cassar-Heck conditions were left, maybe unjustly, all but forgotten. The reactions remarkable utility can be evidenced by the amount of research still being done on understanding and optimizing its synthetic capabilities as well as employing the procedures to prepare various compounds of synthetic, medicinal or material/industrial importance. Among the cross-coupling reactions it follows in the number of publications right after Suzuki and Heck reaction and a search for the term "Sonogashira" in SciFinder provides over 1500 references for journal publications between 2007 and 2010.
The Sonogashira reaction has become so well known that often all reactions that use modern organometallic catalyst to couple alkyne motifs are termed some variant of "Sonogashira reaction", despite the fact that these reactions are not carried out under true Sonogashira reaction conditions. | 0 | Organic Chemistry |
* Advantages
** By using uniform droplets to deliver therapeutic payloads to specific locations in the body, researchers can achieve greater precision and control over drug delivery while also minimizing toxicity and harmful side effects. For example, these droplets can be quickly loaded during the polymerization process and can be varied in porosity to control the time it takes to release a drug. Microdroplets-based drug delivery also has a significant advantage over traditional systems in that they can minimize side effects, reduce the need for invasive procedures, and even improve a drug's efficacy. Overall, microdroplet-based drug delivery systems show great promise for revolutionizing medicine with significant potential for targeted drug delivery.
* Limitations
** Nevertheless, it is essential to note some common challenges associated with microdroplet-based drug delivery systems, including their biocompatibility, toxicity, and scalability. The biocompatibility and toxicity of Microdroplets are essential to consider because these can affect a drug's safety and overall efficacy, causing unwanted side effects and possibly death. On the other hand, scalability is another crucial challenge to consider because this aspect can lead to increased manufacturing costs, problems with quality control, and limitations in equipment used. All in all, even with great promise to revolutionize targeted drug delivery, researchers must keep in mind the biocompatibility, toxicity, and scalability of microdroplet-based drug delivery systems when using them. | 1 | Biochemistry |
Triphenylphosphine dichloride is usually prepared fresh by the addition of chlorine to triphenylphosphine.
:PhP + Cl → PhPCl
Both reagents are typically used in solution to ensure the correct stoichiometry.
PhPCl can also be obtained by the reaction of iodobenzene dichloride (PhICl) and triphenylphosphine.
Alternatively, PhPCl can be obtained by chlorination of triphenylphosphine oxide with, for example, phosphorus trichloride, as in Grignard's original 1931 synthesis. | 0 | Organic Chemistry |
Sulfones are prepared under conditions used for Friedel–Crafts reactions using sources of derived from sulfonyl halides and sulfonic acid anhydrides. Lewis acid catalysts such as and are required.
Sulfones have been prepared by nucleophilic displacement of halides by sulfinates: | 0 | Organic Chemistry |
The first "pure" Bose–Einstein condensate was created by Eric Cornell, Carl Wieman, and co-workers at JILA on 5 June 1995. They cooled a dilute vapor of approximately two thousand rubidium-87 atoms to below 170 nK using a combination of laser cooling (a technique that won its inventors Steven Chu, Claude Cohen-Tannoudji, and William D. Phillips the 1997 Nobel Prize in Physics) and magnetic evaporative cooling. About four months later, an independent effort led by Wolfgang Ketterle at MIT condensed sodium-23. Ketterle's condensate had a hundred times more atoms, allowing important results such as the observation of quantum mechanical interference between two different condensates. Cornell, Wieman and Ketterle won the 2001 Nobel Prize in Physics for their achievements.
A group led by Randall Hulet at Rice University announced a condensate of lithium atoms only one month following the JILA work. Lithium has attractive interactions, causing the condensate to be unstable and collapse for all but a few atoms. Hulet's team subsequently showed the condensate could be stabilized by confinement quantum pressure for up to about 1000 atoms. Various isotopes have since been condensed. | 7 | Physical Chemistry |
Elementoid clusters are ligand-stabilized clusters of metal atoms that possess more direct element-element than element-ligand contacts. Examples of structurally characterized clusters feature ligand stabilized cores of Al, Ga, and Pd. | 7 | Physical Chemistry |
Many different affinity media exist for a variety of possible uses.
Briefly, they are (generalized) activated/functionalized that work as a functional spacer, support matrix, and eliminates handling of toxic reagents.
Amino acid media is used with a variety of serum proteins, proteins, peptides, and enzymes, as well as rRNA and dsDNA. Avidin biotin media is used in the purification process of biotin/avidin and their derivatives.
Carbohydrate bonding is most often used with glycoproteins or any other carbohydrate-containing substance; carbohydrate is used with lectins, glycoproteins, or any other carbohydrate metabolite protein. Dye ligand media is nonspecific but mimics biological substrates and proteins. Glutathione is useful for separation of GST tagged recombinant proteins. Heparin is a generalized affinity ligand, and it is most useful for separation of plasma coagulation proteins, along with nucleic acid enzymes and lipases
Hydrophobic interaction media are most commonly used to target free carboxyl groups and proteins.
Immunoaffinity media (detailed below) utilizes antigens and antibodies high specificity to separate; immobilized metal affinity chromatography is detailed further below and uses interactions between metal ions and proteins (usually specially tagged) to separate; nucleotide/coenzyme that works to separate dehydrogenases, kinases, and transaminases.
Nucleic acids function to trap mRNA, DNA, rRNA, and other nucleic acids/oligonucleotides. Protein A/G method is used to purify immunoglobulins.
Speciality media are designed for a specific class or type of protein/co enzyme; this type of media will only work to separate a specific protein or coenzyme. | 3 | Analytical Chemistry |
* Grüner, George. Density Waves in Solids. Addison-Wesley, 1994.
* Review of experiments as of 2013 by Pierre Monceau. [https://arxiv.org/abs/1307.0929 Electronic crystals: an experimental overview]. | 7 | Physical Chemistry |
The James Webb Space Telescope uses radiative cooling to reach its operation temperature of about 50 K. To do this, its large reflective sunshield blocks radiation from the Sun, Earth, and Moon. The telescope structure, kept permanently in shadow by the sunshield, then cools by radiation. | 7 | Physical Chemistry |
Synapses are functional connections between neurons, or between neurons and other types of cells. A typical neuron gives rise to several thousand synapses, although there are some types that make far fewer. Most synapses connect axons to dendrites, but there are also other types of connections, including axon-to-cell-body, axon-to-axon, and dendrite-to-dendrite. Synapses are generally too small to be recognizable using a light microscope except as points where the membranes of two cells appear to touch, but their cellular elements can be visualized clearly using an electron microscope.
Chemical synapses pass information directionally from a presynaptic cell to a postsynaptic cell and are therefore asymmetric in structure and function. The presynaptic axon terminal, or synaptic bouton, is a specialized area within the axon of the presynaptic cell that contains neurotransmitters enclosed in small membrane-bound spheres called synaptic vesicles (as well as a number of other supporting structures and organelles, such as mitochondria and endoplasmic reticulum). Synaptic vesicles are docked at the presynaptic plasma membrane at regions called active zones.
Immediately opposite is a region of the postsynaptic cell containing neurotransmitter receptors; for synapses between two neurons the postsynaptic region may be found on the dendrites or cell body. Immediately behind the postsynaptic membrane is an elaborate complex of interlinked proteins called the postsynaptic density (PSD).
Proteins in the PSD are involved in anchoring and trafficking neurotransmitter receptors and modulating the activity of these receptors. The receptors and PSDs are often found in specialized protrusions from the main dendritic shaft called dendritic spines.
Synapses may be described as symmetric or asymmetric. When examined under an electron microscope, asymmetric synapses are characterized by rounded vesicles in the presynaptic cell, and a prominent postsynaptic density. Asymmetric synapses are typically excitatory. Symmetric synapses in contrast have flattened or elongated vesicles, and do not contain a prominent postsynaptic density. Symmetric synapses are typically inhibitory.
The synaptic cleft—also called synaptic gap—is a gap between the pre- and postsynaptic cells that is about 20 nm (0.02 μ) wide. The small volume of the cleft allows neurotransmitter concentration to be raised and lowered rapidly.
An autapse is a chemical (or electrical) synapse formed when the axon of one neuron synapses with its own dendrites. | 1 | Biochemistry |
Zolghadr and co-workers presented a fluorescent two-hybrid system that uses two hybrid proteins that are fused to different fluorescent proteins as well as LacI, the lac repressor. The structure of the fusion proteins looks like this: FP2-LacI-bait and FP1-prey where the bait and prey proteins interact and bring the fluorescent proteins (FP1 = GFP, FP2=mCherry) in close proximity at the binding site of the LacI protein in the host cell genome. The system can also be used to screen for inhibitors of protein–protein interactions. | 1 | Biochemistry |
The synthesis reported by Bodwell/Li (racemic, 2002) was a formal synthesis as it produced a compound already prepared by Rawal (no. 5 in the Rawal synthesis). The key step was an inverse electron demand Diels–Alder reaction of cyclophane 1 by heating in N,N-diethylaniline (dinitrogen is expulsed) followed by reduction of double bond in 2 to 3 by sodium borohydride / triflic acid and removal of the carbamate protecting group (PDC / celite) to 4.
The method is disputed by Reissig (see Reissig synthesis). | 0 | Organic Chemistry |
While the original effort failed to produce useful products, follow-on work in Europe did produce usable astronomical detectors
but without apparent use of this technology. In other areas, however, the approach seems to be competitive, with prior art for making various end-products, since it has been used as a fabrication step for experimental devices and structures. Many groups have used the approach to grow homoepitaxial diamond and subsequently release the thin-films with a variety of "lift-off" processes.
It has also been considered in contexts such as carbon microelectromechanical systems production and different materials applications, for example with non-contacted palladium deposition and extensions. While not citing Marchywka et al.'s original paper, these continue to cite non-contactedness as a feature,
"The electrode assembly and the conductive surface may be positioned in close proximity to, but without contacting, one another". references a much earlier patent covering related attempts to achieve non-contacted electro-etching, "The present invention relates to a method of and apparatus for electrochemically processing metallic surfaces of workpieces arranged in a contact-free manner with regard to the cathode and anode[...]."
The effect has been mentioned in passing with regard to novel devices such
as quantum coherent devices while patents on emerging uses for amorphous carbon
and
diamond thermal conductors by manufacturers of high density electronic chips reference the related lift-off technology. | 7 | Physical Chemistry |
There are two primary approaches to the organic synthesis of catenanes. The first is to simply perform a ring-closing reaction with the hope that some of the rings will form around other rings giving the desired catenane product. This so-called "statistical approach" led to the first synthesis of a catenane; however, the method is highly inefficient, requiring high dilution of the "closing" ring and a large excess of the pre-formed ring, and is rarely used.
The second approach relies on supramolecular preorganization of the macrocyclic precursors utilizing hydrogen bonding, metal coordination, hydrophobic effect, or coulombic interactions. These non-covalent interactions offset some of the entropic cost of association and help position the components to form the desired catenane upon the final ring-closing. This "template-directed" approach, together with the use of high-pressure conditions, can provide yields of over 90%, thus improving the potential of catenanes for applications. An example of this approach used bis-bipyridinium salts which form strong complexes threaded through crown ether bis(para-phenylene)-34-crown-10.
Template directed syntheses are mostly performed under kinetic control, when the macrocyclization (catenation) reaction is irreversible. More recently, the groups of Sanders and Otto have shown that dynamic combinatorial approaches using reversible chemistry can be particularly successful in preparing new catenanes of unpredictable structure. The thermodynamically controlled synthesis provides an error correction mechanism; even if a macrocycle closes without forming a catenane it can re-open and yield the desired interlocked structure later. The approach also provides information on the affinity constants between different macrocycles thanks to the equilibrium between the individual components and the catenanes, allowing a titration-like experiment. | 6 | Supramolecular Chemistry |
The Boltzmann constant ( or ) is the proportionality factor that relates the average relative thermal energy of particles in a gas with the thermodynamic temperature of the gas. It occurs in the definitions of the kelvin and the gas constant, and in Plancks law of black-body radiation and Boltzmanns entropy formula, and is used in calculating thermal noise in resistors. The Boltzmann constant has dimensions of energy divided by temperature, the same as entropy. It is named after the Austrian scientist Ludwig Boltzmann.
As part of the 2019 redefinition of SI base units, the Boltzmann constant is one of the seven "defining constants" that have been given exact definitions. They are used in various combinations to define the seven SI base units. The Boltzmann constant is defined to be exactly . | 7 | Physical Chemistry |
In polymer chemistry, the kinetic chain length () of a polymer is the average number of units called monomers added to a growing chain during chain-growth polymerization. During this process, a polymer chain is formed when monomers are bonded together to form long chains known as polymers. Kinetic chain length is defined as the average number of monomers that react with an active center such as a radical from initiation to termination.
This definition is a special case of the concept of chain length in chemical kinetics. For any chemical chain reaction, the chain length is defined as the average number of times that the closed cycle of chain propagation steps is repeated. It is equal to the rate of the overall reaction divided by the rate of the initiation step in which the chain carriers are formed. For example, the decomposition of ozone in water is a chain reaction which has been described in terms of its chain length.
In chain-growth polymerization the propagation step is the addition of a monomer to the growing chain. The word kinetic is added to chain length in order to distinguish the number of reaction steps in the kinetic chain from the number of monomers in the final macromolecule, a quantity named the degree of polymerization. In fact the kinetic chain length is one factor which influences the average degree of polymerization, but there are other factors as described below. The kinetic chain length and therefore the degree of polymerization can influence certain physical properties of the polymer, including chain mobility, glass-transition temperature, and modulus of elasticity. | 7 | Physical Chemistry |
Another way to form primitive compartments that may lead to the formation of a protocell is polyesters membraneless structures that have the ability to host biochemicals (proteins and RNA) and/or scaffold the assemblies of lipids around them. While these droplets are leaky towards genetic materials, this leakiness could have facilitated the progenote hypothesis. | 9 | Geochemistry |
The presence of conserved moieties can affect how computer simulation models are constructed. Moiety-conserved cycles will reduce the number of differential equations required to solve a system. For example, a simple cycle has only one independent variable. The other variable can be computed using the difference between the total mass and the independent variable. The set of differential equations for the two-cycle is given by:
These can be reduced to one differential equation and one linear algebraic equation: | 1 | Biochemistry |
A chafery is a variety of hearth used in ironmaking for reheating a bloom of iron, in the course of its being drawn out into a bar of wrought iron.
The equivalent term for a bloomery was string hearth, except in 17th century Cumbria, where the terminology was that of the finery forge.
A finery forge for the Walloon process would typically have one chafery to work two fineries (but sometimes one or three fineries).
Chaferies were also used in the potting and stamping forges of the industrial revolution. | 8 | Metallurgy |
Iron acquisition poses a problem for aerobic organisms because ferric iron is poorly soluble near neutral pH. Thus, these organisms have developed means to absorb iron as complexes, sometimes taking up ferrous iron before oxidising it back to ferric iron. In particular, bacteria have evolved very high-affinity sequestering agents called siderophores.
After uptake in human cells, iron storage is precisely regulated. A major component of this regulation is the protein transferrin, which binds iron ions absorbed from the duodenum and carries it in the blood to cells. Transferrin contains Fe in the middle of a distorted octahedron, bonded to one nitrogen, three oxygens and a chelating carbonate anion that traps the Fe ion: it has such a high stability constant that it is very effective at taking up Fe ions even from the most stable complexes. At the bone marrow, transferrin is reduced from Fe and Fe and stored as ferritin to be incorporated into hemoglobin.
The most commonly known and studied bioinorganic iron compounds (biological iron molecules) are the heme proteins: examples are hemoglobin, myoglobin, and cytochrome P450. These compounds participate in transporting gases, building enzymes, and transferring electrons. Metalloproteins are a group of proteins with metal ion cofactors. Some examples of iron metalloproteins are ferritin and rubredoxin. Many enzymes vital to life contain iron, such as catalase, lipoxygenases, and IRE-BP.
Hemoglobin is an oxygen carrier that occurs in red blood cells and contributes their color, transporting oxygen in the arteries from the lungs to the muscles where it is transferred to myoglobin, which stores it until it is needed for the metabolic oxidation of glucose, generating energy. Here the hemoglobin binds to carbon dioxide, produced when glucose is oxidized, which is transported through the veins by hemoglobin (predominantly as bicarbonate anions) back to the lungs where it is exhaled. In hemoglobin, the iron is in one of four heme groups and has six possible coordination sites; four are occupied by nitrogen atoms in a porphyrin ring, the fifth by an imidazole nitrogen in a histidine residue of one of the protein chains attached to the heme group, and the sixth is reserved for the oxygen molecule it can reversibly bind to. When hemoglobin is not attached to oxygen (and is then called deoxyhemoglobin), the Fe ion at the center of the heme group (in the hydrophobic protein interior) is in a high-spin configuration. It is thus too large to fit inside the porphyrin ring, which bends instead into a dome with the Fe ion about 55 picometers above it. In this configuration, the sixth coordination site reserved for the oxygen is blocked by another histidine residue.
When deoxyhemoglobin picks up an oxygen molecule, this histidine residue moves away and returns once the oxygen is securely attached to form a hydrogen bond with it. This results in the Fe ion switching to a low-spin configuration, resulting in a 20% decrease in ionic radius so that now it can fit into the porphyrin ring, which becomes planar. (Additionally, this hydrogen bonding results in the tilting of the oxygen molecule, resulting in a Fe–O–O bond angle of around 120° that avoids the formation of Fe–O–Fe or Fe–O–Fe bridges that would lead to electron transfer, the oxidation of Fe to Fe, and the destruction of hemoglobin.) This results in a movement of all the protein chains that leads to the other subunits of hemoglobin changing shape to a form with larger oxygen affinity. Thus, when deoxyhemoglobin takes up oxygen, its affinity for more oxygen increases, and vice versa. Myoglobin, on the other hand, contains only one heme group and hence this cooperative effect cannot occur. Thus, while hemoglobin is almost saturated with oxygen in the high partial pressures of oxygen found in the lungs, its affinity for oxygen is much lower than that of myoglobin, which oxygenates even at low partial pressures of oxygen found in muscle tissue. As described by the Bohr effect (named after Christian Bohr, the father of Niels Bohr), the oxygen affinity of hemoglobin diminishes in the presence of carbon dioxide.
Carbon monoxide and phosphorus trifluoride are poisonous to humans because they bind to hemoglobin similarly to oxygen, but with much more strength, so that oxygen can no longer be transported throughout the body. Hemoglobin bound to carbon monoxide is known as carboxyhemoglobin. This effect also plays a minor role in the toxicity of cyanide, but there the major effect is by far its interference with the proper functioning of the electron transport protein cytochrome a. The cytochrome proteins also involve heme groups and are involved in the metabolic oxidation of glucose by oxygen. The sixth coordination site is then occupied by either another imidazole nitrogen or a methionine sulfur, so that these proteins are largely inert to oxygen – with the exception of cytochrome a, which bonds directly to oxygen and thus is very easily poisoned by cyanide. Here, the electron transfer takes place as the iron remains in low spin but changes between the +2 and +3 oxidation states. Since the reduction potential of each step is slightly greater than the previous one, the energy is released step-by-step and can thus be stored in adenosine triphosphate. Cytochrome a is slightly distinct, as it occurs at the mitochondrial membrane, binds directly to oxygen, and transports protons as well as electrons, as follows:
:4 Cytc + O + 8H → 4 Cytc + 2 HO + 4H
Although the heme proteins are the most important class of iron-containing proteins, the iron–sulfur proteins are also very important, being involved in electron transfer, which is possible since iron can exist stably in either the +2 or +3 oxidation states. These have one, two, four, or eight iron atoms that are each approximately tetrahedrally coordinated to four sulfur atoms; because of this tetrahedral coordination, they always have high-spin iron. The simplest of such compounds is rubredoxin, which has only one iron atom coordinated to four sulfur atoms from cysteine residues in the surrounding peptide chains. Another important class of iron–sulfur proteins is the ferredoxins, which have multiple iron atoms. Transferrin does not belong to either of these classes.
The ability of sea mussels to maintain their grip on rocks in the ocean is facilitated by their use of organometallic iron-based bonds in their protein-rich cuticles. Based on synthetic replicas, the presence of iron in these structures increased elastic modulus 770 times, tensile strength 58 times, and toughness 92 times. The amount of stress required to permanently damage them increased 76 times. | 1 | Biochemistry |
A review in 2013 came to the result that infants resulting from IVF (with or without ICSI) have a relative risk of birth defects of 1.32 (95% confidence interval 1.24–1.42) compared to naturally conceived infants. In 2008, an analysis of the data of the National Birth Defects Study in the US found that certain birth defects were significantly more common in infants conceived through IVF, notably septal heart defects, cleft lip with or without cleft palate, esophageal atresia, and anorectal atresia; the mechanism of causality is unclear. However, in a population-wide cohort study of 308,974 births (with 6,163 using assisted reproductive technology and following children from birth to age five) researchers found: "The increased risk of birth defects associated with IVF was no longer significant after adjustment for parental factors." Parental factors included known independent risks for birth defects such as maternal age, smoking status, etc. Multivariate correction did not remove the significance of the association of birth defects and ICSI (corrected odds ratio 1.57), although the authors speculate that underlying male infertility factors (which would be associated with the use of ICSI) may contribute to this observation and were not able to correct for these confounders. The authors also found that a history of infertility elevated risk itself in the absence of any treatment (odds ratio 1.29), consistent with a Danish national registry study and "implicates patient factors in this increased risk." The authors of the Danish national registry study speculate: "our results suggest that the reported increased prevalence of congenital malformations seen in singletons born after assisted reproductive technology is partly due to the underlying infertility or its determinants." | 1 | Biochemistry |
Tin deposits exist in many parts of South America, with minor deposits in southern Peru, Colombia, Brazil, and northwestern Argentina, and major deposits of exploitable cassiterite in northern Bolivia. These deposits were exploited as early as 1000 AD in the manufacture of tin bronze by Andean cultures, including the later Inca Empire, which considered tin bronze the "imperial alloy". In North America, the only known exploitable source of tin during ancient times is located in the Zacatecas tin province of north central Mexico which supplied west Mexican cultures with enough tin for bronze production. | 8 | Metallurgy |
Acylium ions are cations of the formula . The carbon–oxygen bond length in these cations is near 1.1 Å (110-112 pm), which is shorter than the 112.8 pm of carbon monoxide and indicates triple-bond character.
The carbon centres of acylium ions generally have a linear geometry and sp atomic hybridization, and are best represented by a resonance structure bearing a formal positive charge on the oxygen (rather than carbon): . They are characteristic fragments observed in EI-mass spectra of ketones.
Acylium ions are common reactive intermediates, for example in the Friedel–Crafts acylation and many other organic reactions such as the Hayashi rearrangement. Salts containing acylium ions can be generated by removal of the halide from acyl halides:
Acyl radicals are readily generated from aldehydes by hydrogen-atom abstraction. However, they undergo rapid decarbonylation to afford the alkyl radical:
Acyl anions are almost always unstable—usually too unstable to be exploited synthetically. They readily react with the neutral aldehyde to form an acyloin dimer. Hence, synthetic chemists have developed various acyl anion synthetic equivalents, such as dithianes, as surrogates. However, as a partial exception, hindered dialkylformamides (e.g., diisopropylformamide, HCONiPr) can undergo deprotonation at low temperature (−78 °C) with lithium diisopropylamide as the base to form a carbamoyl anion stable at these temperatures. | 0 | Organic Chemistry |
Under the Acronym Biofector the European Union supports the Research of Bioeffectors under the leadership of the University of Hohenheim. Coordinator Guenter Neumann, Projectmembers: Jiří Balík, Borbala Biro, Karl Fritz Lauer, Uwe Ludewig, Torsten Müller, Alessandro Piccolo, Manfred G. Raupp, Kornelia Smalla, Pavel Tlustoš, Markus Weinmann.
The results of the project will be evaluated by the members of the Association Biostimulants in Agriculture (ABISTA) and provided agriculture for use and EU institutions for the legislative and registration procedures.
Other Biostimulants Organisations are European Biostimulant Industry Council, International Biocontrol Manufacturers' Association and Annual Biocontrol Industry Meeting. | 1 | Biochemistry |
Another advantage of poly(pseudo)rotaxanes is the ability for long-term release of drugs or genes. Some polyrotaxanes can used to form a physical hydrogel, which is called supramolecular hydrogel. In these cases, a three-dimensional physically crosslinked network formed by the poly(pseudo)rotaxanes, can be obtained, which is able to retain a large amount of water inside this network. If water-soluble drugs or genes are added in the solution, it could be capsulated in the supramolecular hydrogels. Also, functional units can be employed in the units of the poly(pseudo)rotaxanes, which enhances the interaction between the poly(pseudo)rotaxanes and capsulated drugs/genes and provides the carriers with other predetermined functions. As the network is further swollen in the water-based environment, part of the carrier will be dissolved gradually, so the capsulated drug or gene can be released from the hydrogels over a long period of time. | 6 | Supramolecular Chemistry |
Due to the inert pair effect of the heavy, organometallic compounds of Bi (III) show Lewis acid properties given the lower ability of the 6s electron pair to mix with molecular orbitals and form σ-bonds. The search for non-toxic equivalents of boronic acids in advancing the Suzuki-Miyaura carbon-carbon coupling reactions and expand the scope of carbon-nitrogen and carbon-oxygen coupling ones turned chemists' attention to organometallic bismuth chemistry. Two catalytic mechanisms were proposed in the C-C bond formation catalyzed by bismuth organometallic compounds. The major difference arises from the rate of the oxidative addition to Pd(0) into a C-Bi bond or C-O one, yielding cycles A and B, respectively (see image). | 0 | Organic Chemistry |
Kennedy J. P. Orton (1872 - 1930) was a British chemist. Initially he studied medicine at St. Thomas Hospital, but there he became interested in chemistry and moved to St. Johns College, Cambridge. He then obtained a Ph.D. summa cum laude in Heidelberg under Karl von Auwers, before working for a year with Sir William Ramsey at University College, London. He was then lecturer and demonstrator of Chemistry at St. Bartholomew's Hospital, before in 1903 being appointed Professor of Chemistry at University College of North Wales, Bangor, where he headed the department until his death. He was elected a Fellow of the Royal Society in 1921.
Besides being a chemist, he was a keen climber and ornithologist, and a biannual ornithological lecture was endowed in his name. | 7 | Physical Chemistry |
The simplest method of manufacturing the molding of a disk in one piece is a possibility for some systems. A more complex method of media manufacturing is for the media to be constructed layer by layer. This is required if the data is to be physically created during manufacture. However, layer-by-layer construction need not mean the sandwiching of many layers together. Another alternative is to create the medium in a form analogous to a roll of adhesive tape. | 5 | Photochemistry |
Until 1969 there was no obvious relationship except that the two methods lead to the same predictions. As noted earlier, the Woodward–Hoffmann method requires symmetry. But in 1969 and 1970 a general formulation was published, namely, A ground-state pericyclic change is symmetry-allowed when the total number of (4q + 2) and (4r) components is odd. The 1969–1970 Woodward–Hoffmann general formulation is seen to be equivalent to the Zimmerman Möbius–Hückel concept. Thus each (4r) component provides one plus-minus overlap in the cyclic array (i.e. an odd number) for 4n electrons. The (4q + 2) component just makes certain that the number of electrons in symmetric bonds is 4n + 2.
The equivalency of the more recent formulation of the Woodward–Hoffmann rules has been discussed. | 7 | Physical Chemistry |
PTT utilizes photothermal transduction agents (PTAs) which can transform light energy to heat through photothermal effect to raise the temperature of tumor area and thus cause the ablation of tumor cells. Specifically, ideal PTAs should have high photothermal conversion efficiency (PCE), excellent optical stability and biocompatibility, and strong light adsorption in the near-infrared (NIR) region (650-1350 nm) due to the deep-tissue penetration and minimal absorption of NIR light in the biological tissues. PTAs mainly include inorganic materials and organic materials. Inorganic PTAs, such as noble metal materials, carbon-based nanomaterials, and other 2D materials, have high PCE and excellent photostability, but they are not biodegradable and thus have potential long-term toxicity in vivo. Organic PTAs including small molecule dyes and conjugated polymers (CPs) have good biocompatibility and biodegradability, but poor photostability. Among them, small molecule dyes, such as cyanine, porphyrin, phthalocyanine, are limited in the field of cancer treatment because of their susceptibility to photobleaching and poor tumor enrichment ability. Conjugated polymers with large π−π conjugated skeleton and a high electron delocalization structure show potential for PTT due to their strong NIR absorption, excellent photostability, low cytotoxicity, outstanding PCE, good dispersibility in aqueous medium, increased accumulation at tumor site, and long blood circulation time. Moreover, conjugated polymers can be easily combined with other imaging agents and drugs to construct multifunctional nanomaterials for selective and synergistic cancer therapy.
The CPs used for tumor PTT mainly include polyaniline (PANI), polypyrrole (PPy), polythiophene (PTh), polydopamine (PDA), donor−acceptor (D-A) conjugated polymers, and poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS). | 5 | Photochemistry |
The context of a photogeochemical reaction is implicitly the surface of Earth, since that is where sunlight is available (although other sources of light such as chemiluminescence would not be strictly excluded from photogeochemical study). Reactions may occur among components of land such as rocks, soil and detritus; components of surface water such as sediment and dissolved organic matter; and components of the atmospheric boundary layer directly influenced by contact with land or water, such as mineral aerosols and gases. Visible and medium- to long-wave ultraviolet radiation is the main source of energy for photogeochemical reactions; wavelengths of light shorter than about 290 nm are completely absorbed by the present atmosphere, and are therefore practically irrelevant, except in consideration of atmospheres different from that of Earth today.
Photogeochemical reactions are limited to chemical reactions not facilitated by living organisms. The reactions comprising photosynthesis in plants and other organisms, for example, are not considered photogeochemistry, since the physiochemical context for these reactions is installed by the organism, and must be maintained in order for these reactions to continue (i.e. the reactions cease if the organism dies). In contrast, if a certain compound is produced by an organism, and the organism dies but the compound remains, this compound may still participate independently in a photogeochemical reaction even though its origin is biological (e.g. biogenic mineral precipitates or organic compounds released from plants into water).
The study of photogeochemistry is primarily concerned with naturally occurring materials, but may extend to include other materials, inasmuch as they are representative of, or bear some relation to, those found on Earth. For example, many inorganic compounds have been synthesized in the laboratory to study photocatalytic reactions. Although these studies are usually not undertaken in the context of environmental or Earth sciences, the study of such reactions is relevant to photogeochemistry if there is a geochemical implication (i.e. similar reactants or reaction mechanisms occur naturally). Similarly, photogeochemistry may also include photochemical reactions of naturally occurring materials that are not touched by sunlight, if there is the possibility that these materials may become exposed (e.g. deep soil layers uncovered by mining).
Except for several isolated instances, studies that fit the definition of photogeochemistry have not been explicitly specified as such, but have been traditionally categorized as photochemistry, especially at the time when photochemistry was an emerging field or new facets of photochemistry were being explored. Photogeochemical research, however, may be set apart in light of its specific context and implications, thereby bringing more exposure to this "poorly explored area of experimental geochemistry". Past studies that fit the definition of photogeochemistry may be designated retroactively as such. | 5 | Photochemistry |
Prp24 has a molecular weight of 50 kDa and has been shown to contain four RNA recognition motifs (RRMs) and a conserved 12-amino acid sequence at the C-terminus. RRMs 1 and 2 have been shown to be important for high-affinity binding of U6, while RRMs 3 and 4 bind at lower affinity sites on U6. The first three RRMs interact extensively with each other and contain canonical folds that contain a four-stranded beta-sheet and two alpha-helices. The electropositive surface of RRMs 1 and 2 is a RNA annealing domain while the cleft between RRMs 1 and 2 including the beta-sheet face of RRM2 is a sequence-specific RNA binding site. The C-terminal motif is required for association with LSm proteins and contributes to substrate (U6) binding and not the catalytic rate of splicing. | 1 | Biochemistry |
The C-terminal glucase enzymatic unit contains extra binding sites, which allows for it to bind to larger substrates for catalytic digestion. It was originally understood that maltase-glucoamylase's crystalline structure was inherently similar throughout the N and C-termini. Further studies have found that the C-terminus is composed of 21 more amino acid residues than the N-terminus, which account for its difference in function. Sucrase-Isomaltase –– located on chromosome 3q26–– has a similar crystalline structure to maltase-glucoamylase and work in tandem in the human small intestine. They have been derived from a common ancestor, as they both come from the same GH31 family. As a result of having similar properties, both of these enzymes work together in the small intestine in order to convert consumed starch into glucose for metabolic energy. The difference between these two enzymes is that maltase-glucoamylase has a specific activity at the 1-4 linkage of sugar, where at SI has a specific activity at the 1-6 linkage. | 1 | Biochemistry |
This reaction shows the oxidation of p-cresol in a sulfate-enriched environment. P-cresol was seen to be the easiest to degrade through the sulfate-enriched environment, while m-cresol and o-cresol where inhibited. In the chart above, p-cresol was oxidized under an anaerobic sulfate reducing condition and formed four different intermediates. After the formation of the intermediates, the study reported further degradation of the intermediates leading to the production of carbon dioxide and methane. The p-hydroxylbenzyl alcohol, p-hydroxylbenzaldehye, p-hyrdoxylbenzoate, and benzoate intermediates all are produced from this oxidation and released into the sediments. Similar results were also produced by different studies using other forms of oxidation such as: iron-reducing organisms, Copper/Manganese Oxide catalyst, and nitrate- reducing conditions. | 7 | Physical Chemistry |
Flashover is one of the most feared phenomena among firefighters. Firefighters are taught to recognize the signs of imminent rollovers and flashovers and to avoid backdrafts. For example, there are certain routines for opening closed doors to buildings and compartments on fire, known as door entry procedures, ensuring fire crew safety where possible. | 7 | Physical Chemistry |
In exceptionally preserved fossils, such as those of the Burgess shale, soft parts of organisms may be preserved. Since these fossils are often compressed into a planar film, it can be difficult to distinguish the features: a famous example is the triangular extensions in Opabinia, which were interpreted as either legs or extensions of the gut. Elemental mapping showed that their composition was similar to the gut, favoring that interpretation. Because of the thinness of carbon films, only low voltages (5-15 kV) can be used on them. | 3 | Analytical Chemistry |
The International Standard for making artificial seawater can be found at ASTM International. The current standard is named ASTM D1141-98 (The original standard was ASTM D1141-52) and describes the standard practice for the preparation of substitute ocean water.
The ASTM D1141-98 standard comes in a ready-made artificial seawater form or a "Sea Salt" mix that can be prepared by engineers and hobbyists. Generally, the ready-made artificial seawater comes in 1 gallon and 5 gallon containers, whereas the "Sea Salt" mix comes in 20lb pails (makes approximately 57 gallons) and 50lb pails (makes approximately 143 gallons). | 9 | Geochemistry |
"Polarity" is a gene expression mechanism in which transcription terminates prematurely due to a loss of coupling between transcription and translation. Transcription outpaces translation when the ribosome pauses or encounters a premature stop codon. This allows the transcription termination factor Rho to bind the mRNA and terminate mRNA synthesis. Consequently, genes that are downstream in the operon are not transcribed, and therefore not expressed. Polarity serves as mRNA quality control, allowing unused transcripts to be terminated prematurely, rather than synthesized and degraded.
The term "polarity" was introduced to describe the observation that the order of genes within an operon is important: a nonsense mutation within an upstream gene effects the transcription of downstream genes. Furthermore, the position of the nonsense mutation within the upstream gene modulates the "degree of polarity", with nonsense mutations at the start of the upstream genes exerting stronger polarity (more reduced transcription) on downstream genes.
Unlike the mechanism of attenuation, which involves intrinsic termination of transcription at well-defined programmed sites, polarity is Rho-dependent and termination occurs at variable position. | 1 | Biochemistry |
* O. K. Berdiev
* I. N. Khlopin
* Boris Kuftin
* Gorislava Nikolaevna Lisit︠s︡yna
* Mikhail Evgenievich Masson
* Vadim Mikhailovich Masson
* G. E. Markov
* Alexey Okladnikov
* Viktor Sarianidi | 8 | Metallurgy |
Neuraminidase inhibitors are useful for combating influenza infection: zanamivir, administered by inhalation; oseltamivir, administered orally; peramivir administered parenterally, that is through intravenous or intramuscular injection; and laninamivir which is in phase III clinical trials.
There are two major proteins on the surface of influenza virus particles. One is the lectin haemagglutinin protein with three relatively shallow sialic acid-binding sites and the other is enzyme sialidase with the active site in a pocket. Because of the relative deep active site in which low-molecular-weight inhibitors can make multiple favorable interactions and approachable methods of designing transition-state analogues in the hydrolysis of sialosides, the sialidase becomes more attractive anti-influenza drug target than the haemagglutinin. After the X-ray crystal structures of several influenza virus sialidases were available, the structure-based inhibitor design was applied to discover potent inhibitors of this enzyme.
The unsaturated sialic acid (N-acetylneuraminic acid [Neu5ac]) derivative 2-deoxy-2, 3-didehydro--N-acetylneuraminic acid (Neu5Ac2en), a sialosyl cation transition-state (Figure 2) analogue, is believed the most potent inhibitor core template. Structurally modified Neu5Ac2en derivatives may give more effective inhibitors.
Many Neu5Ac2en-based compounds have been synthesized and tested for their influenza virus sialidase inhibitory potential. For example:
The 4-substituted Neu5Ac2en derivatives (Figure 3), 4-amino-Neu5Ac2en (Compound 1), which showed two orders of magnitude better inhibition of influenza virus sialidase than Neu5Ac2en5 and 4-guanidino-Neu5Ac2en (Compound 2), known as Zanamivir, which is now marketed for treatment of influenza virus as a drug, have been designed by von Itzstein and coworkers. A series of amide-linked C9 modified Neu5Ac2en have been reported by Megesh and colleagues as NEU1 inhibitors. | 0 | Organic Chemistry |
In 1938, he married Irja Pullman; they had two daughters: Siiri Anna (b. 1939) and Jean Kirsten (b. 1944). In 1946, he married Eudoxia Muller, an artist and technician whom he met at the Polaroid Corp. This marriage, which lasted until 1972, produced a daughter, and a son: Crystal Elisabeth (b. 1947), and Eric Richard Arthur (b. 1953). | 4 | Stereochemistry |
The thermal expansion coefficients depends on the modification of zirconia as follows:
* Monoclinic: 7·10/K
* Tetragonal: 12·10/K
* YO stabilized: 10,5·10/K | 7 | Physical Chemistry |
An MPS gas is a mixture of two or more of propane, butane, butadiene, methylacetylene (propyne, CHC≡CH) and propadiene (CH=C=CH). They are marketed under different names including: "MPS", "Chem-O-Lean", "Apachi Gas", "FG-2 Gas", "Flamex" and "natural gas". The most commonly known type of MPS gas is the discontinued MAPP gas.
As a fuel gas, it burns hotter than propylene, propane or natural gas. | 0 | Organic Chemistry |
The partition coefficient, abbreviated P, is defined as a particular ratio of the concentrations of a solute between the two solvents (a biphase of liquid phases), specifically for un-ionized solutes, and the logarithm of the ratio is thus log P. When one of the solvents is water and the other is a non-polar solvent, then the log P value is a measure of lipophilicity or hydrophobicity. The defined precedent is for the lipophilic and hydrophilic phase types to always be in the numerator and denominator respectively; for example, in a biphasic system of n-octanol (hereafter simply "octanol") and water:
To a first approximation, the non-polar phase in such experiments is usually dominated by the un-ionized form of the solute, which is electrically neutral, though this may not be true for the aqueous phase. To measure the partition coefficient of ionizable solutes, the pH of the aqueous phase is adjusted such that the predominant form of the compound in solution is the un-ionized, or its measurement at another pH of interest requires consideration of all species, un-ionized and ionized (see following).
A corresponding partition coefficient for ionizable compounds, abbreviated log P , is derived for cases where there are dominant ionized forms of the molecule, such that one must consider partition of all forms, ionized and un-ionized, between the two phases (as well as the interaction of the two equilibria, partition and ionization). M is used to indicate the number of ionized forms; for the -th form () the logarithm of the corresponding partition coefficient, , is defined in the same manner as for the un-ionized form. For instance, for an octanol–water partition, it is
To distinguish between this and the standard, un-ionized, partition coefficient, the un-ionized is often assigned the symbol log P, such that the indexed expression for ionized solutes becomes simply an extension of this, into the range of values . | 7 | Physical Chemistry |
In the electronics industry, octafluoropropane is mixed with oxygen and used as a plasma etching material for SiO layers in semiconductor applications, as oxides are selectively etched versus their metal substrates.
In medicine, octafluoropropane may compose the gas cores of microbubble contrast agents used in contrast-enhanced ultrasound. Octafluoropropane microbubbles reflect sound waves well and are used to improve the ultrasound signal backscatter.
It is used in eye surgery, such as pars plana vitrectomy procedures where a retina hole or tear is repaired. The gas provides a long-term tamponade, or plug, of a retinal hole or tear and allows re-attachment of the retina to occur over the several days following the procedure.
Under the name R-218, octafluoropropane is used in other industries as a component of refrigeration mixtures.
It has been featured in some plans for terraforming Mars. With a greenhouse gas effect 24,000 times greater than carbon dioxide (CO), octafluoropropane could dramatically reduce the time and resources it takes to terraform Mars.
It is the active liquid in PICO-2L dark matter bubble detector (joined PICASSO and COUPP collaborations). | 2 | Environmental Chemistry |
Simulation and modeling techniques are often combined with experimental methods to characterize structures of amorphous materials. Commonly used computational techniques include density functional theory, molecular dynamics, and reverse Monte Carlo. | 7 | Physical Chemistry |
qPCR using reverse transcription (RT-qPCR) can be used to detect GMOs given its sensitivity and dynamic range in detecting DNA. Alternatives such as DNA or protein analysis are usually less sensitive. Specific primers are used that amplify not the transgene but the promoter, terminator or even intermediate sequences used during the process of engineering the vector. As the process of creating a transgenic plant normally leads to the insertion of more than one copy of the transgene its quantity is also commonly assessed. This is often carried out by relative quantification using a control gene from the treated species that is only present as a single copy. | 1 | Biochemistry |
In 1908, Lawrence Joseph Henderson derived an equation to calculate the hydrogen ion concentration of a bicarbonate buffer solution, which rearranged looks like this:
In 1909 Søren Peter Lauritz Sørensen introduced the pH terminology, which allowed Karl Albert Hasselbalch to re-express Henderson's equation in logarithmic terms, resulting in the Henderson–Hasselbalch equation. | 7 | Physical Chemistry |
There have been several efforts to map eukaryotic interactomes through HTP methods. While no biological interactomes have been fully characterized, over 90% of proteins in Saccharomyces cerevisiae have been screened and their interactions characterized, making it the best-characterized interactome. Species whose interactomes have been studied in some detail include
* Schizosaccharomyces pombe
* Caenorhabditis elegans
* Drosophila melanogaster
* Homo sapiens
Recently, the pathogen-host interactomes of Hepatitis C Virus/Human (2008), Epstein Barr virus/Human (2008), Influenza virus/Human (2009) were delineated through HTP to identify essential molecular components for pathogens and for their host's immune system. | 1 | Biochemistry |
A novel myokine osteonectin, or SPARC (secreted protein acidic and rich in cysteine), plays a vital role in bone mineralization, cell-matrix interactions, and collagen binding. Osteonectin inhibits tumorigenesis in mice. Osteonectin can be classed as a myokine, as it was found that even a single bout of exercise increased its expression and secretion in skeletal muscle in both mice and humans. | 1 | Biochemistry |
The United States Environmental Protection Agency has set a maximum contaminant level for benzene in drinking water at 0.0005 mg/L (5 ppb), as promulgated via the U.S. National Primary Drinking Water Regulations. This regulation is based on preventing benzene leukemogenesis. The maximum contaminant level goal (MCLG), a nonenforceable health goal that would allow an adequate margin of safety for the prevention of adverse effects, is zero benzene concentration in drinking water. The EPA requires that spills or accidental releases into the environment of 10 pounds (4.5 kg) or more of benzene be reported.
The U.S. Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit of 1 part of benzene per million parts of air (1 ppm) in the workplace during an 8-hour workday, 40-hour workweek. The short term exposure limit for airborne benzene is 5 ppm for 15 minutes. These legal limits were based on studies demonstrating compelling evidence of health risk to workers exposed to benzene. The risk from exposure to 1 ppm for a working lifetime has been estimated as 5 excess leukemia deaths per 1,000 employees exposed. (This estimate assumes no threshold for benzene's carcinogenic effects.) OSHA has also established an action level of 0.5 ppm to encourage even lower exposures in the workplace.
The U.S. National Institute for Occupational Safety and Health (NIOSH) revised the Immediately Dangerous to Life and Health (IDLH) concentration for benzene to 500 ppm. The current NIOSH definition for an IDLH condition, as given in the NIOSH Respirator Selection Logic, is one that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment. The purpose of establishing an IDLH value is (1) to ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment and (2) is considered a maximum level above which only a highly reliable breathing apparatus providing maximum worker protection is permitted. In September 1995, NIOSH issued a new policy for developing recommended exposure limits (RELs) for substances, including carcinogens. As benzene can cause cancer, NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding the REL (10-hour) of 0.1 ppm. The NIOSH short-term exposure limit (STEL – 15 min) is 1 ppm.
American Conference of Governmental Industrial Hygienists (ACGIH) adopted Threshold Limit Values (TLVs) for benzene at 0.5 ppm TWA and 2.5 ppm STEL. | 2 | Environmental Chemistry |
Viaspan was the trademark under which the University of Wisconsin cold storage solution (also known as University of Wisconsin solution or UW solution) was sold. Currently, UW solution is sold under the Belzer UW trademark and others like Bel-Gen or StoreProtect. UW solution was the first solution designed for use in organ transplantation, and became the first intracellular-like preservation medium. Developed in the late 1980s by Folkert Belzer and James Southard for pancreas preservation, the solution soon displaced EuroCollins solution as the preferred medium for cold storage of livers and kidneys, as well as pancreas. The solution has also been used for hearts and other organs. University of Wisconsin cold storage solution remains what is often called the gold standard for organ preservation, despite the development of other solutions that are in some respects superior. | 1 | Biochemistry |