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In general, action potentials that reach the synaptic knobs cause a neurotransmitter to be released into the synaptic cleft. Neurotransmitters are small molecules that may open ion channels in the postsynaptic cell; most axons have the same neurotransmitter at all of their termini. The arrival of the action potential opens voltage-sensitive calcium channels in the presynaptic membrane; the influx of calcium causes vesicles filled with neurotransmitter to migrate to the cell's surface and release their contents into the synaptic cleft. This complex process is inhibited by the neurotoxins tetanospasmin and botulinum toxin, which are responsible for tetanus and botulism, respectively. | 7 | Physical Chemistry |
Chemical structures of BNA monomers containing a bridge at the 2, 4-position of the ribose to afford a 2, 4-BNA monomer as synthesized by Takeshi Imanishi's group. The nature of the bridge can vary for different types of monomers. The 3D structures for A-RNA and B-DNA were used as a template for the design of the BNA monomers. The goal for the design was to find derivatives that possess high binding affinities with complementary RNA and/or DNA strands.
An increased conformational inflexibility of the sugar moiety in nucleosides (oligonucleotides) results in a gain of high binding affinity with complementary single-stranded RNA and/or double-stranded DNA. The first 2,4-BNA (LNA) monomers were first synthesized by Takeshi Imanishis group in 1997 followed independently by Jesper Wengels group in 1998.
BNA nucleotides can be incorporated into DNA or RNA oligonucleotides at any desired position. Such oligomers are synthesized chemically and are now commercially available. The bridged ribose conformation enhances base stacking and pre-organizes the backbone of the oligonucleotide significantly increasing their hybridization properties.
The incorporation of BNAs into oligonucleotides allows the production of modified synthetic oligonucleotides with
equal or higher binding affinity against a DNA or RNA complement with excellent single-mismatch discriminating power;
better RNA selective binding;
stronger and more sequence selective triplex-forming characters;
pronounced higher nuclease resistance, even higher than Sp-phosphorothioate analogues; and
good aqueous solubility of the resulting oligonucleotides when compared to regular DNA or RNA oligonucleotides.
New BNA analogs introduced by Imanishis group were designed by taking the length of the bridged moiety into account. A six-membered bridged structure with a unique structural feature (N-O bond) in the sugar moiety was designed to have a nitrogen atom. This atom improves the formation of duplexes and triplexes by lowering the repulsion between the negatively charged backbone phosphates. These modifications allow to control the affinity towards complementary strands, regulate resistance against nuclease degradation and the synthesis of functional molecules designed for specific applications in genomics. The properties of these analogs were investigated and compared to those of previous 2,4-BNA (LNA) modified oligonucleotides by Imanishis group. Imanishis results show that "2,4'-BNA-modified oligonucleotides with these profiles show great promise for applications in antisense and antigene technologies." | 1 | Biochemistry |
Copper-free click chemistry is a bioorthogonal reaction as a variant of an azide-alkyne Huisgen cycloaddition. By eliminating cytotoxic copper catalysts, the reaction proceeds without live-cell toxicity. It was developed as a faster alternative to the Staudinger ligation with the first generation of Cu-free click chemistry, producing rate constants over 63 times faster.
Although the reaction produces a regioisomeric mixture of triazoles, the lack of regioselectivity in the reaction is not a major concern for its applications in bioorthogonal chemistry. More regiospecific and less bioorthogonal requirements are best served by the traditional Huisgen cycloaddition, especially given the low yield and synthetic difficulty of synthesizing a strained cyclooctyne (compared to the addition of a terminal alkyne).
The bioorthogonality of the reaction has allowed the Cu-free click reaction to be applied within cultured cells, live zebrafish, and mice.
The absence of exogenous metal catalysts makes the Cu-free chemical reactions suitable for the in vivo applications of bioorthogonal chemistry or bioorthogonal click chemistry. | 0 | Organic Chemistry |
Pseudomonas aeruginosa is a known opportunistic pathogen. One of its virulence factors is its ability to produce pyocyanin, a toxin released to kill both microbes and mammalian cells alike. The pyocyanin production occurs when activated by PhoB. This implies that P. aeruginosa uses the low Pi as a signal that the host has been damaged and to start producing toxin to improve chances of its survival.
In contrast to P. aeruginosa, Vibrio cholerae has its toxin genes repressed by PhoB. It is thought that PhoB in V. cholerae is activated when Pi is low to prevent the production of toxins. It could be activated by other signals in the environment, but it has been shown that PhoB directly inhibits the toxins production by binding to the tcpPH promoter and stopping the ToxR regulon from being activated. Evidence supporting Pi as the signal is given by how the regulon is not repressed under high Pi conditions. The regulatory cascade is only repressed under low Pi conditions. | 1 | Biochemistry |
Another regulatory element located upstream of the gene is an enhancer. Enhancers function as a "turn on" switch in gene expression and will activate the promoter region of a particular gene while silencers act as the "turn off" switch. Though these two regulatory elements work against each other, both sequence types affect the promoter region in very similar ways. Because silencers have not been thoroughly identified and analyzed, the extensive research on enhancers has aided biologists in understanding the mechanics of the silencer. Enhancers can be found in many of the same areas that silencers are found, such as upstream of the promoter by many kilobase pairs, or even downstream within the intron of the gene. DNA looping is also a model function used by enhancers in order to shorten the proximity of the promoter to the enhancer. Enhancers also function with transcription factors in order to initiate expression, much like silencers can with repressors. | 1 | Biochemistry |
Electroacoustic phenomena arise when ultrasound propagates through a fluid containing ions. The associated particle motion generates electric signals because ions have electric charge. This coupling between ultrasound and electric field is called electroacoustic phenomena. The fluid might be a simple Newtonian liquid, or complex heterogeneous dispersion, emulsion or even a porous body. There are several different electroacoustic effects depending on the nature of the fluid.
*Ion vibration current (IVI) and potential, an electric signal that arises when an acoustic wave propagates through a homogeneous fluid.
*Streaming vibration current (SVI) and potential, an electric signal that arises when an acoustic wave propagates through a porous body in which the pores are filled with fluid.
*Colloid vibration current (CVI) and potential, an electric signal that arises when ultrasound propagates through a heterogeneous fluid, such as a dispersion or emulsion.
*Electric sonic amplitude (ESA), the inverse of the CVI effect, in which an acoustic field arises when an electric field propagates through a heterogeneous fluid. | 7 | Physical Chemistry |
Sulfating roasting oxidizes certain sulfide ores to sulfates in a supply of air to enable leaching of the sulfate for further processing. | 8 | Metallurgy |
The viscosity of liquid metals can vary greatly depending on the atomic composition of the liquid, especially in the case of alloys. In particular, the temperature dependence of the viscosity of liquid metals may range from the standard Arrhenius law dependence, to a much steeper (non-Arrhenius) dependence such as that given empirically by the Vogel-Fulcher-Tammann equation.
A physical model for the viscosity of liquid metals, which captures this great variability in terms of the underlying interatomic interactions, was also developed.
The electrical resistance of a liquid metal can be estimated by means of the Ziman formula, which gives the resistance in terms of the static structure factor of the liquid as can be determined by neutron or X-ray scattering measurements. | 8 | Metallurgy |
A preliminary zeroth order analysis may be performed to answer fundamental questions about the nature of the unknown material. Methods that might be used for the preliminary analysis include spectroscopic methods, such as infrared spectroscopy or x-ray fluorescence spectroscopy. The results of the zeroth order characterization of the material inform subsequent choices in later stages of analysis.
A formulated chemical mixture may contain multiple phases, such as suspended or emulsified material. A first-order analysis of the material may involve the separation of phases. Centrifugation, extraction, and filtration are examples of methods which separate material in different phases. Centrifugation is effective to separate phases that differ in density. Extraction is effective to separate immiscible liquid phases. Filtration is effective to separate dispersed particles that are sufficiently large in size to be trapped in a filter. This initial separation may require the selection of appropriate solvents to either dissolve solid components or to act as a diluent for liquids. The quantitative determination of phases is often determined gravimetrically.
Once separated, each material phase is itself a chemical mixture to be further analyzed. A second-order analysis of each phase will typically involve a selection among available analytical methods to further separate these components. Analytical methods used on liquid phases might include distillation or one of a variety of chromatographic separation methods. Distillation separates the components of a liquid mixture according to differences in their boiling points. Chomatography separates components of a liquid or gaseous mixture according to differences in retention time as the mixture interacts with a stationary phase. Individual components thus separated can then be identified by a variety of detection methods, including infrared spectroscopy, Raman spectroscopy, mass spectrometry, and nuclear magnetic resonance spectrometry. Methods used to further analyze solids might include thermal analysis (such as thermogravimetric analysis or differential scanning calorimetry), x-ray diffraction to characterize crystalline solids, microscopy, pyrolysis, combustion analysis, or surface spectroscopic methods.
In some contexts further stages of analysis of the separated components may be required. The active ingredients of a formulated chemical product that differentiate it from another similar material may include proprietary ingredients or specific functional additives. Such ingredients that play a key role in the performance of the material in an application may require a third-order analysis to more completely characterize them. Some examples of functional additives include surfactants, emulsifiers, dispersants, adhesion promoters, leveling agents, dyes and pigments, antioxidants, preservatives, and optical brighteners. Practically every type of chemically formulated product is associated with its own formulary of likely functional additive choices that can fulfill some critical role in performance. Deformulation may thus require both a breakdown of material composition and also identification of the functional role of key ingredients. | 3 | Analytical Chemistry |
Enantioselective synthesis, also called asymmetric synthesis, is a form of chemical synthesis. It is defined by IUPAC as "a chemical reaction (or reaction sequence) in which one or more new elements of chirality are formed in a substrate molecule and which produces the stereoisomeric (enantiomeric or diastereomeric) products in unequal amounts."
Put more simply: it is the synthesis of a compound by a method that favors the formation of a specific enantiomer or diastereomer. Enantiomers are stereoisomers that have opposite configurations at every chiral center. Diastereomers are stereoisomers that differ at one or more chiral centers.
Enantioselective synthesis is a key process in modern chemistry and is particularly important in the field of pharmaceuticals, as the different enantiomers or diastereomers of a molecule often have different biological activity. | 4 | Stereochemistry |
Fluoride is naturally present in groundwater, fresh and saltwater sources, as well as in rainwater, particularly in urban areas. Seawater fluoride levels are usually in the range of 0.86 to 1.4 mg/L, and average 1.1 mg/L (milligrams per litre). For comparison, chloride concentration in seawater is about 19 g/L. The low concentration of fluoride reflects the insolubility of the alkaline earth fluorides, e.g., CaF.
Concentrations in fresh water vary more significantly. Surface water such as rivers or lakes generally contains between 0.01 and 0.3 mg/L. Groundwater (well water) concentrations vary even more, depending on the presence of local fluoride-containing minerals. For example, natural levels of under 0.05 mg/L have been detected in parts of Canada but up to 8 mg/L in parts of China; in general levels rarely exceed 10 mg/litre
* In parts of Asia the groundwater can contain dangerously high levels of fluoride, leading to serious health problems.
* Worldwide, 50 million people receive water from water supplies that naturally have close to the "optimal level".
* In other locations the level of fluoride is very low, sometimes leading to fluoridation of public water supplies to bring the level to around 0.7–1.2 ppm.
*Mining can increase local fluoride levels
Fluoride can be present in rain, with its concentration increasing significantly upon exposure to volcanic activity or atmospheric pollution derived from burning fossil fuels or other sorts of industry, particularly aluminium smelters. | 1 | Biochemistry |
RNA polymerase II holoenzyme is a form of eukaryotic RNA polymerase II that is recruited to the promoters of protein-coding genes in living cells. It consists of RNA polymerase II, a subset of general transcription factors, and regulatory proteins known as . | 1 | Biochemistry |
The glutathione peroxidase family of enzymes (abbreviated GSH-Px) catalyze reduction of hydrogen peroxide and organic hydroperoxides:
:2GSH + HO → GSSG + 2 HO
The two H atoms are donated by thiols in a process that begins with oxidation of a selenol side chain in GSH-Px. The organoselenium compound ebselen is a drug used to supplement the action of GSH-Px. It functions as a catalyst for the destruction of hydrogen peroxide.
A related selenium-containing enzyme in some plants and in animals (thioredoxin reductase) generates reduced thioredoxin, a dithiol that serves as an electron source for peroxidases and also the important reducing enzyme ribonucleotide reductase that makes DNA precursors from RNA precursors. | 1 | Biochemistry |
Titer has the same origin as the word "title", from the French word titre, meaning "title" but referring to the documented purity of a substance, often gold or silver. This comes from the Latin word titulus, also meaning "title". | 1 | Biochemistry |
A protein phosphatase is a phosphatase enzyme that removes a phosphate group from the phosphorylated amino acid residue of its substrate protein. Protein phosphorylation is one of the most common forms of reversible protein posttranslational modification (PTM), with up to 30% of all proteins being phosphorylated at any given time. Protein kinases (PKs) are the effectors of phosphorylation and catalyse the transfer of a γ-phosphate from ATP to specific amino acids on proteins. Several hundred PKs exist in mammals and are classified into distinct super-families. Proteins are phosphorylated predominantly on Ser, Thr and Tyr residues, which account for 79.3, 16.9 and 3.8% respectively of the phosphoproteome, at least in mammals. In contrast, protein phosphatases (PPs) are the primary effectors of dephosphorylation and can be grouped into three main classes based on sequence, structure and catalytic function. The largest class of PPs is the phosphoprotein phosphatase (PPP) family comprising PP1, PP2A, PP2B, PP4, PP5, PP6 and PP7, and the protein phosphatase Mg- or Mn-dependent (PPM) family, composed primarily of PP2C. The protein Tyr phosphatase (PTP) super-family forms the second group, and the aspartate-based protein phosphatases the third. The protein pseudophosphatases form part of the larger phosphatase family, and in most cases are thought to be catalytically inert, instead functioning as phosphate-binding proteins, integrators of signalling or subcellular traps. Examples of membrane-spanning protein phosphatases containing both active (phosphatase) and inactive (pseudophosphatase) domains linked in tandem are known, conceptually similar to the kinase and pseudokinase domain polypeptide structure of the JAK pseudokinases. A complete comparative analysis of human phosphatases and pseudophosphatases has been completed by Manning and colleagues, forming a companion piece to the ground-breaking analysis of the human kinome, which encodes the complete set of ~536 human protein kinases. | 1 | Biochemistry |
Due to the biological complexity of gene expression, the considerations of experimental design that are discussed in the expression profiling article are of critical importance if statistically and biologically valid conclusions are to be drawn from the data.
There are three main elements to consider when designing a microarray experiment. First, replication of the biological samples is essential for drawing conclusions from the experiment. Second, technical replicates (e.g. two RNA samples obtained from each experimental unit) may help to quantitate precision. The biological replicates include independent RNA extractions. Technical replicates may be two aliquots of the same extraction. Third, spots of each cDNA clone or oligonucleotide are present as replicates (at least duplicates) on the microarray slide, to provide a measure of technical precision in each hybridization. It is critical that information about the sample preparation and handling is discussed, in order to help identify the independent units in the experiment and to avoid inflated estimates of statistical significance. | 1 | Biochemistry |
The New Jersey Zinc process is no longer used to produce primary zinc in the U.S., in Europe and Japan, but it still is used to treat secondary operations. This process peaked in 1960, when it accounted for 5% of world zinc production. A modified version of this process is still used at Huludao, China, which produced 65,000 metric tons per year.
This process begins by roasting concentrates that are mixed with coal and briquetted in two stages. The briquettes are then heated in an autogenous coker at and then charged into the retort. There are three reasons to briquette the calcine: to ensure free downward movement of the charge; to permit heat transfer across a practical size cross-section; to allow adequate porosity for the passage of reduced zinc vapour to the top of the retort. The reduced zinc vapour that is collected at the top of the retort is then condensed to a liquid.
Overpelt improved upon this design by using only one large condensation chamber, instead of many small ones, as it was originally designed. This allowed for the carbon monoxide to be recirculated into the furnaces for heating the retorts.
This process was licensed to the Imperial Smelting Corporation (ISC), based in Avonmouth, England, which had a large vertical retort (VR) plant in production for many years. It was used until the mid-1970s when it was superseded by the company's Imperial Smelting Furnace (ISF) plant. The VR plant was demolished in 1975. | 8 | Metallurgy |
In some materials, superspots will occur at positions that do not represent a simple fraction, say q=(0.5234,0,0). In this case the structure strictly speaking has lost all translational symmetry in a particular direction. This is called an incommensurate structure. | 3 | Analytical Chemistry |
In stereochemistry, prochiral molecules are those that can be converted from achiral to chiral in a single step. An achiral species which can be converted to a chiral in two steps is called proprochiral.
If two identical substituents are attached to a sp-hybridized atom, the descriptors pro-R and pro-S are used to distinguish between the two. Promoting the pro-R substituent to higher priority than the other identical substituent results in an R chirality center at the original sp-hybridized atom, and analogously for the pro-S substituent.
A trigonal planar sp-hybridized atom can be converted to a chiral center when a substituent is added to the re or si () face of the molecule. A face is labeled re if, when looking at that face, the substituents at the trigonal atom are arranged in increasing Cahn-Ingold-Prelog priority order (1 to 2 to 3) in a clockwise order, and si if the priorities increase in anti-clockwise order; note that the designation of the resulting chiral center as S or R depends on the priority of the incoming group.
The concept of prochirality is necessary for understanding some aspects of enzyme stereospecificity. Alexander Ogston pointed out that when a symmetrical molecule is placed in an asymmetric environment, such as the surface of an enzyme, supposedly identically placed groups become distinguishable. In this way he showed that earlier exclusion of non-chiral citrate as a possible intermediate in the tricarboxylate cycle was mistaken. | 4 | Stereochemistry |
Microspectrophotometry is the measure of the spectra of microscopic samples using different wavelengths of electromagnetic radiation (e.g. ultraviolet, visible and near infrared, etc.) It is accomplished with microspectrophotometers, cytospectrophotometers, microfluorometers, Raman microspectrophotometers, etc. A microspectrophotometer can be configured to measure transmittance, absorbance, reflectance, light polarization, fluorescence (or other types of luminescence such as photoluminescence) of sample areas less than a micrometer in diameter through a modified optical microscope. | 7 | Physical Chemistry |
Because converting RNA into cDNA, ligation, amplification, and other sample manipulations have been shown to introduce biases and artifacts that may interfere with both the proper characterization and quantification of transcripts, single molecule direct RNA sequencing has been explored by companies including Helicos (bankrupt), Oxford Nanopore Technologies, and others. This technology sequences RNA molecules directly in a massively-parallel manner. | 1 | Biochemistry |
Evelyn Brower Man (October 7, 1904 – September 3, 1992) was an American biochemist. She was a leading woman in developing the first test to detect hormone levels in the thyroid gland. | 1 | Biochemistry |
Photogeochemical reactions may be classified based on thermodynamics and/or the nature of the materials involved. In addition, when ambiguity exists regarding an analogous reaction involving light and living organisms (phototrophy), the term "photochemical" may be used to distinguish a particular abiotic reaction from the corresponding photobiological reaction. For example, "photooxidation of iron(II)" can refer to either a biological process driven by light (phototrophic or photobiological iron oxidation) or a strictly chemical, abiotic process (photochemical iron oxidation). Similarly, an abiotic process that converts water to O under the action of light may be designated "photochemical oxidation of water" rather than simply "photooxidation of water", in order to distinguish it from photobiological oxidation of water potentially occurring in the same environment (by algae, for example). | 5 | Photochemistry |
The Hawaii Ocean Time-series (HOT) program is a long-term oceanographic study based at the University of Hawaii at Manoa. In 2015, the American Society for Microbiology designated the HOT Program's field site Station ALOHA (A Long-Term Oligotrophic Habitat Assessment; ()) a "Milestone in Microbiology", for playing "a key role in defining the discipline of microbial oceanography and educating the public about the vital role of marine microbes in global ecosystems."
Scientists working on the Hawaii Ocean Time-series (HOT) program have been making repeated observations of the hydrography, chemistry and biology of the water column at a station north of Oahu, Hawaii since October 1988. The objective of this research is to provide a comprehensive description of the ocean at a site representative of the North Pacific Subtropical Gyre. Cruises are made approximately once per month to the deep-water Station ALOHA located 100 km north of Oahu, Hawaii. Measurements of the thermohaline structure, water column chemistry, currents, optical properties, primary production, plankton community structure, and rates of particle export are made on each cruise. The HOT program also uses autonomous underwater vehicles, including floats and gliders, to collect data at Station ALOHA between cruises. | 9 | Geochemistry |
Lichens often have a regular but very slow growth rate of less than a millimeter per year.
In crustose lichens, the area along the margin is where the most active growth is taking place. Most crustose lichens grow only 1–2 mm in diameter per year. | 2 | Environmental Chemistry |
Spectral responsivity is a similar measurement, but it has different units: amperes per watt (A/W); (i.e. how much current comes out of the device per unit of incident light power). Responsivity is ordinarily specified for monochromatic light (i.e. light of a single wavelength). Both the quantum efficiency and the responsivity are functions of the photons' wavelength (indicated by the subscript λ).
To convert from responsivity (, in A/W) to QE (on a scale 0 to 1):
where is the wavelength in nm, h is the Planck constant, c is the speed of light in vacuum, and e is the elementary charge. Note that the unit W/A (watts per ampere) is equivalent to V (volts). | 7 | Physical Chemistry |
The general steps to prepare a complementary DNA (cDNA) library for sequencing are described below, but often vary between platforms.
# RNA Isolation: RNA is isolated from tissue and mixed with Deoxyribonuclease (DNase). DNase reduces the amount of genomic DNA. The amount of RNA degradation is checked with gel and capillary electrophoresis and is used to assign an RNA integrity number to the sample. This RNA quality and the total amount of starting RNA are taken into consideration during the subsequent library preparation, sequencing, and analysis steps.
#RNA selection/depletion: To analyze signals of interest, the isolated RNA can either be kept as is, enriched for RNA with 3 polyadenylated (poly(A)) tails to include only eukaryotic mRNA, depleted of ribosomal RNA (rRNA), and/or filtered for RNA that binds specific sequences (RNA selection and depletion methods table, below). RNA molecules having 3 poly(A) tails in eukaryotes are mainly composed of mature, processed, coding sequences. Poly(A) selection is performed by mixing RNA with oligomers covalently attached to a substrate, typically magnetic beads. Poly(A) selection has important limitations in RNA biotype detection. Many RNA biotypes are not polyadenylated, including many noncoding RNA and histone-core protein transcripts, or are regulated via their poly(A) tail length (e.g., cytokines) and thus might not be detected after poly(A) selection. Furthermore, poly(A) selection may display increased 3' bias, especially with lower quality RNA. These limitations can be avoided with ribosomal depletion, removing rRNA that typically represents over 90% of the RNA in a cell. Both poly(A) enrichment and ribosomal depletion steps are labor intensive and could introduce biases, so more simple approaches have been developed to omit these steps. Small RNA targets, such as miRNA, can be further isolated through size selection with exclusion gels, magnetic beads, or commercial kits.
#cDNA synthesis: RNA is reverse transcribed to cDNA because DNA is more stable and to allow for amplification (which uses DNA polymerases) and leverage more mature DNA sequencing technology. Amplification subsequent to reverse transcription results in loss of strandedness, which can be avoided with chemical labeling or single molecule sequencing. Fragmentation and size selection are performed to purify sequences that are the appropriate length for the sequencing machine. The RNA, cDNA, or both are fragmented with enzymes, sonication, or nebulizers. Fragmentation of the RNA reduces 5 bias of randomly primed-reverse transcription and the influence of primer binding sites, with the downside that the 5 and 3' ends are converted to DNA less efficiently. Fragmentation is followed by size selection, where either small sequences are removed or a tight range of sequence lengths are selected. Because small RNAs like miRNAs are lost, these are analyzed independently. The cDNA for each experiment can be indexed with a hexamer or octamer barcode, so that these experiments can be pooled into a single lane for multiplexed sequencing. | 1 | Biochemistry |
Herbicide resistance became a critical problem in Australian agriculture, after many Australian sheep farmers began to exclusively grow wheat in their pastures in the 1970s. Introduced varieties of ryegrass, while good for grazing sheep, compete intensely with wheat. Ryegrasses produce so many seeds that, if left unchecked, they can completely choke a field. Herbicides provided excellent control, while reducing soil disrupting because of less need to plough. Within little more than a decade, ryegrass and other weeds began to develop resistance. In response Australian farmers changed methods. By 1983, patches of ryegrass had become immune to Hoegrass (diclofop-methyl), a family of herbicides that inhibit an enzyme called acetyl coenzyme A carboxylase.
Ryegrass populations were large, and had substantial genetic diversity, because farmers had planted many varieties. Ryegrass is cross-pollinated by wind, so genes shuffle frequently. To control its distribution farmers sprayed inexpensive Hoegrass, creating selection pressure. In addition, farmers sometimes diluted the herbicide in order to save money, which allowed some plants to survive application. When resistance appeared farmers turned to a group of herbicides that block acetolactate synthase. Once again, ryegrass in Australia evolved a kind of "cross-resistance" that allowed it to rapidly break down a variety of herbicides. Four classes of herbicides become ineffective within a few years. In 2013 only two herbicide classes, called Photosystem II and long-chain fatty acid inhibitors, were effective against ryegrass. | 2 | Environmental Chemistry |
Molybdenum is an essential element in most organisms; a 2008 research paper speculated that a scarcity of molybdenum in the Earth's early oceans may have strongly influenced the evolution of eukaryotic life (which includes all plants and animals).
At least 50 molybdenum-containing enzymes have been identified, mostly in bacteria. Those enzymes include aldehyde oxidase, sulfite oxidase and xanthine oxidase. With one exception, Mo in proteins is bound by molybdopterin to give the molybdenum cofactor. The only known exception is nitrogenase, which uses the FeMoco cofactor, which has the formula FeMoSC.
In terms of function, molybdoenzymes catalyze the oxidation and sometimes reduction of certain small molecules in the process of regulating nitrogen, sulfur, and carbon. In some animals, and in humans, the oxidation of xanthine to uric acid, a process of purine catabolism, is catalyzed by xanthine oxidase, a molybdenum-containing enzyme. The activity of xanthine oxidase is directly proportional to the amount of molybdenum in the body. An extremely high concentration of molybdenum reverses the trend and can inhibit purine catabolism and other processes. Molybdenum concentration also affects protein synthesis, metabolism, and growth.
Mo is a component in most nitrogenases. Among molybdoenzymes, nitrogenases are unique in lacking the molybdopterin. Nitrogenases catalyze the production of ammonia from atmospheric nitrogen:
The biosynthesis of the FeMoco active site is highly complex.
Molybdate is transported in the body as MoO. | 1 | Biochemistry |
Microscale thermophoresis (MST) is a technology for the biophysical analysis of interactions between biomolecules. Microscale thermophoresis is based on the detection of a temperature-induced change in fluorescence of a target as a function of the concentration of a non-fluorescent ligand. The observed change in fluorescence is based on two distinct effects. On the one hand it is based on a temperature related intensity change (TRIC) of the fluorescent probe, which can be affected by binding events. On the other hand, it is based on thermophoresis, the directed movement of particles in a microscopic temperature gradient. Any change of the chemical microenvironment of the fluorescent probe, as well as changes in the hydration shell of biomolecules result in a relative change of the fluorescence detected when a temperature gradient is applied and can be used to determine binding affinities. MST allows measurement of interactions directly in solution without the need of immobilization to a surface (immobilization-free technology). | 1 | Biochemistry |
By the time of the American Civil War, as telegraph traffic increased, the Grove cell's tendency to discharge poisonous nitrogen dioxide (NO) fumes proved increasingly hazardous to health, and as telegraphs became more complex, the need for constant voltage became critical. The Grove cell was limited in this respect, because as the cell discharged, voltage reduced. Eventually, Grove cells were replaced in use by Daniell cells. | 3 | Analytical Chemistry |
In stoichiometry of a chemical reaction to produce a chemical product, it may be observed or predicted that with amounts supplied in specified proportions, one of the reactants will be consumed by the reaction before the others. The amount of product is thus limited by the supply of this reagent. This limiting reagent determines the theoretical yield of the reaction. The other reactants are said to be non-limiting or in excess. This distinction makes sense only when the chemical equilibrium so favors the products to cause the complete consumption of one of the reactants.
In studies of reaction kinetics, the rate of progress of the reaction may be limited by the concentration of one of the reactants or catalyst. In multi-step reactions, a step may be rate-limiting in terms of production of the final product. In vivo, in an organism or in an ecologic system, such factors as those may be rate-limiting, or in the overall analysis of a multi-step process including biologic, geologic, hydrologic, or atmospheric transport and chemical reactions, transport of a reactant may be limiting. | 7 | Physical Chemistry |
In organic chemistry, the chloromethyl group is a functional group that has the chemical formula . The naming of this group is derived from the methyl group (which has the formula ), by replacing one hydrogen atom by a chlorine atom. Compounds with this group are a subclass of the organochlorines.
The way of introducing a chloromethyl group into aromatic compounds is the chloromethylation by the Blanc reaction. | 0 | Organic Chemistry |
Having properly sized particles allow aggregate companies to create long-lasting roads and other products. Particle size analysis is also routinely conducted on bitumen emusions to predict their stability and their behavior. | 3 | Analytical Chemistry |
Aerogels are highly porous ultralight materials in which the liquid component of a gel has been replaced with a gas, and are noteworthy for being solids that are extremely effective thermal insulators with very low density. Aerogels can be prepared in a variety of ways, and though most have been based on silica, materials based on zirconia, titania, cellulose, polyurethane, and resorcinol—formaldehyde systems, amongst others, have been reported and explored. The prime disadvantage of a silica-based aerogel is its fragility, though NASA has used them for insulation on Mars rovers, the Mars Pathfinder and they have been used commercially for insulating blankets and between glass panes for translucent day-lighting panels. Particulate gels prepared by the Stöber process can be dehydrated rapidly to produce highly effective silica aerogels, as well as xerogels. They key step is the use of supercritical fluid extraction to remove water from the gel while maintaining the gel structure, which is typically done with supercritical carbon dioxide, as NASA does. The resulting aerogels are very effective thermal insulators because of their high porosity with very small pores (in the nanometre range). Conduction of heat through the gas phase is poor, and as the structure greatly inhibits movement of air molecules through the structure, heat transfer through the material is poor, as can be seen in the image at right where heat from a Bunsen burner transfers so poorly that crayons resting on the aerogel do not melt. Due to their low density, aerogels have also been used to capture interstellar dust particles with minimal heat changes in slowing them down (to prevent heat-induced changes in the particles) as part of the Stardust mission.
One method to produce a silica aerogel uses a modified Stöber process and supercritical drying. The product appears translucent with a blue tinge as a consequence of Rayleigh scattering; when placed in front of a light source, it becomes yellowish due to Mie scattering. This aerogel has a surface area of 700 m g and a density of 0.040 g cm; by way of contrast, the density of air is 0.0012 g cm (at 15 °C and 1 atm).
Silica aerogels held 15 entries for materials properties in the Guinness World Records in 2011, including for best insulator and lowest-density solid, though aerographite took the latter title in 2012.
Aerographene, with a density of just 13% of that of room temperature air and less dense than helium gas, became the lowest-density solid yet developed in 2013. Stöber-like methods have been applied in the preparation of aerogels in non-silica systems. NASA has developed silica aerogels with a polymer coating to reinforce the structure, producing a material roughly two orders of magnitude stronger for the same density, and also polymer aerogels, which are flexible and can be formed into a bendable thin film. | 7 | Physical Chemistry |
Attempts to correct for changes in thyroid binding globulin due to liver disease, protein losing states, pregnancy or various drugs
It is used to calculate free thyroxine index (total T4 x T3 uptake), an estimate of free T4. Free thyroxine index may be calculated with increased diagnostic accuracy using direct TBG measurement when the total hormone concentration is abnormally elevated | 1 | Biochemistry |
Palytoxin was first isolated, named and described from Palythoa toxica by Moore and Scheuer in a study published in 1971. They measured that its molar mass is approximately 3300 g/mol. They also identified it to be the substance that was probably responsible for the toxicity of P. toxica, but it was uncertain at the time if the coral also had other toxic compounds in it. It was then assessed by Walsh and Bowers that the limu-make-o-Hana was not a seaweed but a zoanthid coral, subsequently described as Palythoa toxica. Moore and Scheuer were aware of the study that Walsh and Bowers were writing. | 0 | Organic Chemistry |
In synaptic vesicles, some neurochemists have suggested that vesicles occasionally may not completely fuse with presynaptic membranes in neurotransmitter release into the synaptic cleft. The controversy lies in whether or not endocytosis always occurs in vesicle reforming after release of the neurotransmitter. Another proposed mechanism for release of vesicle contents into extracellular fluid is called kiss-and-run fusion.
There is some indication that vesicles may only form a small pore in the presynaptic membrane allowing contents to be released by standard diffusion for a short while before retreating back into the presynaptic cell. This mechanism may be a way around clathrin-mediated endocytosis. It is also proposed that the vesicle does not need to return to an endosome to refill, though it is not thoroughly understood by which mechanism it would refill. This does not exclude full vesicle fusion, but only states that both mechanisms may operate in synaptic clefts.
"Kiss and run" has been shown to occur in endocrine cells, though it has not been directly witnessed in synaptic gaps. | 1 | Biochemistry |
Holmes undergraduate studies and masters research were conducted at the University of Melbourne where he was resident at Ormond College. Travelling to the UK on a Shell Overseas Science Scholarship, he performed his PhD work at University College London under the supervision of Franz Sondheimer. | 0 | Organic Chemistry |
Phanes are abstractions of highly complex organic molecules introduced for simplification of the naming of these highly complex molecules.
Systematic nomenclature of organic chemistry consists of building a name for the structure of an organic compound by a collection of names of its composite parts but describing also its relative positions within the structure. Naming information is summarised by IUPAC:
Whilst the cyclophane name describes only a limited number of sub-structures of benzene rings interconnected by individual atoms or chains, phane is a class name which includes others, hence heterocyclic rings as well. Therefore, the various cyclophanes are perfectly good for the general class of phanes as well keeping in mind that the cyclic structures in phanes could have much greater diversity. | 0 | Organic Chemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), Valine (Val, V) | 1 | Biochemistry |
Fluorinations with DAST can be carried out in conventional glass equipment, although etching of the glass may result from reaction byproducts. Reactions are typically carried out in aprotic or non-polar solvents. Moisture and atmospheric oxygen should be excluded from the reaction. Reactions are generally started at -78 °C and warmed to room temperature or above; however, reactions should not be heated above 80 °C, as decomposition of the fluorinating reagent begins to occur at this temperature. Workup usually involves pouring the reaction mixture over water or ice, followed by neutralization of acidic byproducts with sodium bicarbonate. Standard purification methods can be used to isolate the desired fluorinated products. | 0 | Organic Chemistry |
The transcriptome can be seen as a subset of the proteome, that is, the entire set of proteins expressed by a genome.
However, the analysis of relative mRNA expression levels can be complicated by the fact that relatively small changes in mRNA expression can produce large changes in the total amount of the corresponding protein present in the cell. One analysis method, known as gene set enrichment analysis, identifies coregulated gene networks rather than individual genes that are up- or down-regulated in different cell populations.
Although microarray studies can reveal the relative amounts of different mRNAs in the cell, levels of mRNA are not directly proportional to the expression level of the proteins they code for. The number of protein molecules synthesized using a given mRNA molecule as a template is highly dependent on translation-initiation features of the mRNA sequence; in particular, the ability of the translation initiation sequence is a key determinant in the recruiting of ribosomes for protein translation. | 1 | Biochemistry |
The PCP protein has been identified in dinoflagellate genomes in at least two forms, a homodimeric form composed of two 15-kD monomers, and a monomeric form of around 32kD believed to have evolved from the homodimeric form via gene duplication. The monomeric form consists of two pseudosymmetrical eight-helix domains in which the helices are packed in a complex topology resembling that of the beta sheets in a jelly roll fold. The three-dimensional arrangement of helices forms a boat-shaped molecule with a large central cavity in which the pigments and lipids are bound. Each eight-helix segment typically binds four peridinin molecules, one chlorophyll a molecule, and one lipid molecule such as digalactosyl diacyl glycerol; however, this stoichiometry varies among species and among PCP isoforms. The most common 4:1 peridinin:chlorophyll ratio was predicted by spectroscopy in the 1970s, but was unconfirmed until the crystal structure of the Amphidinium carterae PCP complex was solved in the 1990s. Whether formed from a protein monomer or dimer, the assembled protein-pigment complex is sometimes known as bPCP (for "building block") and is the minimal stable unit. In at least some PCP forms, including that from A. carterae, these building blocks assemble into a trimer thought to be the biologically functional state.
When the X-ray crystallography structure of PCP was solved in 1997, it represented a novel protein fold, and its topology remains unique among known proteins. The structure is referred to by the CATH database, which systematically classifies protein structures, as an "alpha solenoid" fold; however, elsewhere in the literature the term alpha solenoid is used for open and less compact helical protein structures. | 5 | Photochemistry |
The Elbs reaction is an organic reaction describing the pyrolysis of an ortho methyl substituted benzophenone to a condensed polyaromatic. The reaction is named after its inventor, the German chemist Karl Elbs, also responsible for the Elbs oxidation. The reaction was published in 1884. Elbs however did not correctly interpret the reaction product due to a lack of knowledge about naphthalene structure. | 0 | Organic Chemistry |
Where two rivers meet at a confluence there exists a mixing zone. A mixing zone may be very large and extend for many miles as in the case of the Mississippi and Missouri rivers in the United States and the River Clwyd and River Elwy in North Wales. In a mixing zone water chemistry may be very variable and can be difficult to predict. The chemical interactions are not just simple mixing but may be complicated by biological processes from submerged macrophytes and by water joining the channel from the hyporheic zone or from springs draining an aquifer. | 2 | Environmental Chemistry |
Petroleum is a fossil fuel derived from fossilized organic materials, such as zooplankton and algae. Vast amounts of these remains settled to sea or lake bottoms where they were covered in stagnant water (water with no dissolved oxygen) or sediments such as mud and silt faster than they could decompose aerobically. Approximately 1 m below this sediment, water oxygen concentration was low, below 0.1 mg/L, and anoxic conditions existed. Temperatures also remained constant.
As further layers settled into the sea or lake bed, intense heat and pressure built up in the lower regions. This process caused the organic matter to change, first into a waxy material known as kerogen, found in various oil shales around the world, and then with more heat into liquid and gaseous hydrocarbons via a process known as catagenesis. Formation of petroleum occurs from hydrocarbon pyrolysis in a variety of mainly endothermic reactions at high temperatures or pressures, or both. These phases are described in detail below. | 7 | Physical Chemistry |
TRIM28 has been shown to interact with:
* CBX5,
* CEBPB,
* Glucocorticoid receptor,
* SETDB1 and
* ZNF10. | 1 | Biochemistry |
Sticking coefficient is the term used in surface physics to describe the ratio of the number of adsorbate atoms (or molecules) that adsorb, or "stick", to a surface to the total number of atoms that impinge upon that surface during the same period of time. Sometimes the symbol S is used to denote this coefficient, and its value is between 1 (all impinging atoms stick) and 0 (no atoms stick). The coefficient is a function of surface temperature, surface coverage (θ) and structural details as well as the kinetic energy of the impinging particles. The original formulation was for molecules adsorbing from the gas phase and the equation was later extended to adsorption from the liquid phase by comparison with molecular dynamics simulations. For use in adsorption from liquids the equation is expressed based on solute density (molecules per volume) rather than the pressure. | 7 | Physical Chemistry |
Although metal centers (e.g., Li, Zn, Sc, etc.) are most commonly cationic and electrophilic (Lewis acidic) in nature, certain metal centers (particularly ones in a low oxidation state and/or carrying a negative charge) are among the strongest recorded nucleophiles and are sometimes referred to as "supernucleophiles." For instance, using methyl iodide as the reference electrophile, PhSn is about 10000 times more nucleophilic than I, while the Co(I) form of vitamin B (vitamin B) is about 10 times more nucleophilic. Other supernucleophilic metal centers include low oxidation state carbonyl metalate anions (e.g., CpFe(CO)). | 7 | Physical Chemistry |
During anoxia, provision of ATP by substrate-level phosphorylation in the matrix is important not only as a mere means of energy, but also to prevent mitochondria from straining glycolytic ATP reserves by maintaining the adenine nucleotide translocator in ‘forward mode’ carrying ATP towards the cytosol. | 1 | Biochemistry |
An aminopolycarboxylic acid (sometimes abbreviated APCA) is a chemical compound containing one or more nitrogen atoms connected through carbon atoms to two or more carboxyl groups. Aminopolycarboxylates that have lost acidic protons form strong complexes with metal ions. This property makes aminopolycarboxylic acids useful complexone in a wide variety of chemical, medical, and environmental applications. | 7 | Physical Chemistry |
Due to their ability to scatter light back into the photovoltaic structure and low absorption, plasmonic nanoparticles are under investigation as a method for increasing solar cell efficiency. Forcing more light to be absorbed by the dielectric increases efficiency.
Plasmons can be excited by optical radiation and induce an electric current from hot electrons in materials fabricated from gold particles and light-sensitive molecules of porphin, of precise sizes and specific patterns. The wavelength to which the plasmon responds is a function of the size and spacing of the particles. The material is fabricated using ferroelectric nanolithography. Compared to conventional photoexcitation, the material produced three to 10 times the current. | 7 | Physical Chemistry |
In coordination chemistry, a spectator ligand is a ligand that does not participate in chemical reactions of the complex. Instead, spectator ligands (vs "actor ligands") occupy coordination sites. Spectator ligands tend to be of polydentate, such that the M-spectator ensemble is inert kinetically. Although they do not participate in reactions of the metal, spectator ligands influence the reactivity of the metal center to which they are bound. These ligands are sometimes referred to as ancillary ligands.
Several different classes of ligand exist that can be considered spectator ligands. A few examples include trispyrazolylborates (Tp), cyclopentadienyl ligands (Cp), and many chelating diphosphines such as 1,2-bis(diphenylphosphino)ethane ligands (dppe). Varying the substituents on the spectator ligands greatly influences the solubility, stability, electronic, and steric properties of the metal complex. In the area of platinum-based antineoplastic agents, spectator (and nonspectator) ligands greatly affect efficacy. | 0 | Organic Chemistry |
Bronze and brass are both copper alloys that are solid solution strengthened. Bronze is the result of adding about 12% tin to copper while brass is the result of adding about 34% zinc to copper. Both of these alloys are being utilized in coins production, ship hardware, and art. | 8 | Metallurgy |
Multiangle light scattering (MALS) describes a technique for measuring the light scattered by a sample into a plurality of angles. It is used for determining both the absolute molar mass and the average size of molecules in solution, by detecting how they scatter light. A collimated beam from a laser source is most often used, in which case the technique can be referred to as multiangle laser light scattering (MALLS). The insertion of the word laser was intended to reassure those used to making light scattering measurements with conventional light sources, such as Hg-arc lamps that low-angle measurements could now be made. Until the advent of lasers and their associated fine beams of narrow width, the width of conventional light beams used to make such measurements prevented data collection at smaller scattering angles. In recent years, since all commercial light scattering instrumentation use laser sources, this need to mention the light source has been dropped and the term MALS is used throughout.
The "multi-angle" term refers to the detection of scattered light at different discrete angles as measured, for example, by a single detector moved over a range that includes the particular angles selected or an array of detectors fixed at specific angular locations. A discussion of the physical phenomenon related to this static light scattering, including some applications, data analysis methods and graphical representations associated therewith are presented. | 7 | Physical Chemistry |
There are three types of thermogravimetry:
*Isothermal or static thermogravimetry: In this technique, the sample weight is recorded as a function of time at a constant temperature.
*Quasistatic thermogravimetry: In this technique, the sample temperature is raised in sequential steps separated by isothermal intervals, during which the sample mass reaches stability before the start of the next temperature ramp.
*Dynamic thermogravimetry: In this technique, the sample is heated in an environment whose temperature is changed in a linear manner. | 7 | Physical Chemistry |
Studies suggest dexmedetomidine for sedation in mechanically ventilated adults may reduce time to extubation and ICU stay.
Compared with other sedatives, some studies suggest dexmedetomidine may be associated with less delirium. However, this finding is not consistent across multiple studies. At the very least, when aggregating many study results together, use of dexmedetomidine appears to be associated with less neurocognitive dysfunction compared to other sedatives. Whether this observation has a beneficial psychological impact is unclear. From an economic perspective, dexmedetomidine is associated with lower ICU costs, largely due to a shorter time to extubation. | 4 | Stereochemistry |
In addition to its well-known roles in the electron transport chain and cell apoptosis, according to a recent study cytochrome c can also act as an antioxidative enzyme in the mitochondria; it does so by removing superoxide (O) and hydrogen peroxide (HO) from mitochondria. Therefore, not only is cytochrome c required in the mitochondria for cellular respiration, but it is also needed in the mitochondria to limit the production of O and HO. | 1 | Biochemistry |
Although the apertureless mode is more promising than the aperture mode, the latter is more widely used because of easier instrumental setup and operation. To obtain a high resolution Raman micrograph/spectrum, the following conditions should be met: (1) the size of the aperture must be on the order of the wavelength of the excitation light. (2) The distance from the tip of the probe to the sample must be smaller than excitation wavelength. (3) The instrument must remain stable over a long time. An important AFM feature is the ability to accurately control the distance between the sample and probe tip, which is the reason why the AFM-Raman combination is preferred for realizing Raman-NSOM. | 7 | Physical Chemistry |
Some of the earliest, published studies on sweat composition date back to the 19th century. Further studies in the 20th century began to solidify understanding of the physiology and pharmacology of the eccrine sweat gland. In-vivo and in-vitro studies from this time period, and even those continuing today, have identified numerous structural nuances and new molecules present within sweat. The first commercially adopted use for sweat diagnostics included testing of sodium and chloride levels in children for the diagnosis of cystic fibrosis. Today, one of the most popular devices for this testing is the Macroduct Sweat Collection System from ELITechGroup. | 1 | Biochemistry |
A fan is a powered machine used to create a flow of air. A fan consists of a rotating arrangement of vanes or blades, generally made of wood, plastic, or metal, which act on the air. The rotating assembly of blades and hub is known as an impeller, rotor, or runner. Usually, it is contained within some form of housing, or case. This may direct the airflow, or increase safety by preventing objects from contacting the fan blades. Most fans are powered by electric motors, but other sources of power may be used, including hydraulic motors, handcranks, and internal combustion engines.
Mechanically, a fan can be any revolving vane, or vanes used for producing currents of air. Fans produce air flows with high volume and low pressure (although higher than ambient pressure), as opposed to compressors which produce high pressures at a comparatively low volume. A fan blade will often rotate when exposed to an air-fluid stream, and devices that take advantage of this, such as anemometers and wind turbines, often have designs similar to that of a fan.
Typical applications include climate control and personal thermal comfort (e.g., an electric table or floor fan), vehicle engine cooling systems (e.g., in front of a radiator), machinery cooling systems (e.g., inside computers and audio power amplifiers), ventilation, fume extraction, winnowing (e.g., separating chaff from cereal grains), removing dust (e.g. sucking as in a vacuum cleaner), drying (usually in combination with a heat source) and providing draft for a fire. Some fans may be indirectly used for cooling in the case of industrial heat exchangers.
While fans are effective at cooling people, they do not cool air, but rather work by evaporative cooling of sweat and increased heat convection into the surrounding air, due to the airflow from the fans. Thus, fans may become less effective at cooling the body if the surrounding air is near body temperature and contains high humidity. | 7 | Physical Chemistry |
An extensive range of recommended values for the Margules parameters can be found in the literature. Selected values are provided in the table below. | 7 | Physical Chemistry |
The use of supercritical carbon dioxide, instead of water, has been examined as a geothermal working fluid. | 7 | Physical Chemistry |
Berylliosis is an occupational disease. Relevant occupations are those where beryllium is mined, processed or converted into metal alloys, or where machining of metals containing beryllium and recycling of scrap alloys occurs. It is associated with aerospace manufacturing, microwave semiconductor electronics, beryllium mining or manufacturing of fluorescent light bulbs (which once contained beryllium compounds in their internal phosphor coating). Beryllia was used in lamp manufacture because of ceramic's obvious virtues for insulation and heat resistance, and also because beryllia could be made transparent. Certain welding anodes along with other electrical contacts and even non-sparking tools are made of beryllium copper alloy and the subsequent machining of such materials would cause the disease as well. | 1 | Biochemistry |
Deoxyadenosine monophosphate (dAMP), also known as deoxyadenylic acid or deoxyadenylate in its conjugate acid and conjugate base forms, respectively, is a derivative of the common nucleic acid AMP, or adenosine monophosphate, in which the -OH (hydroxyl) group on the 2 carbon on the nucleotides pentose has been reduced to just a hydrogen atom (hence the "deoxy-" part of the name). Deoxyadenosine monophosphate is abbreviated dAMP. It is a monomer used in DNA. | 1 | Biochemistry |
Amination of nucleophiles with N-unsubstituted oxaziridines is quite versatile in the breadth of possible nucleophiles and corresponding products. Hydrazines may be derived from the amination of secondary or tertiary amines, hydroxylamine and thiohydroxamines may be formed from their corresponding alcohols and thiols, sulfimides may be formed from thioethers and α-aminoketones may be formed by attack of corresponding enolates. | 0 | Organic Chemistry |
The most commonly studied system to date is the system, consisting of a proton bound with a ion. The system was first observed in 2000 by a group at the University of Waterloo in Canada.
The formation of the ion can be understood classically; as the single electron in a hydrogen atom cannot fully shield the positively charged nucleus, another electron brought into close proximity will feel an attractive force. While this classical description is nice for getting a feel for the interactions involved, it is an oversimplification; many other atoms have a greater electron affinity than hydrogen. In general the process of forming a negative ion is driven by the filling of atomic electron shells to form a lower energy configuration.
Only a small number of molecules have been used to produce heavy Rydberg systems although in principle any atom with a positive electron affinity can bind with a positive ion. Species used include , and . Fluorine and oxygen are particularly favoured due to their high electron affinity, high ionisation energy and consequently high electronegativity. | 7 | Physical Chemistry |
The hydroxymethyl group is the name for a substituent with the structural formula . It consists of a methylene bridge ( unit) bonded to a hydroxyl group (). This makes the hydroxymethyl group an alcohol. It has the identical chemical formula with the methoxy group () that differs only in the attachment site and orientation to the rest of the molecule. However, their chemical properties are different.
Hydroxymethyl is the side chain of encoded amino acid serine. | 0 | Organic Chemistry |
The biosynthetic pathway of phycocyanobilin begins with 5-Aminolevulinic acid (5-ALA). Two molecules of 5-ALA undergo a condensation reaction catalyzed by Porphobilinogen (PBG) Synthase to yield a molecule of Porphobilinogen (PBG) (not shown). Four molecules of PBG are polymerized into a linear tetrapyrrole by Porphobilinogen deaminase. This reaction releases four ammonia molecules in the process. Completion of the tetrapyrrole is performed by Uroporphyrinogen III synthase which results in the macrocyclic Uroporphyrinogen III. Uroporphyrinogen III is then converted to a Heme by a Uroporphyrinogen III decarboxylase. The heme molecule is converted to Biliverdin IX α. Biliverdin is then finally reduced to Phycocyanobilin (PCB) by the Phycocyanin Ferredoxin Oxidoreductase PcyA. Literature circa 1989 includes phytochromobilin as an intermediate in this final conversion. | 1 | Biochemistry |
In other less formal contexts, an alcohol is often called with the name of the corresponding alkyl group followed by the word "alcohol", e.g., methyl alcohol, ethyl alcohol. Propyl alcohol may be n-propyl alcohol or isopropyl alcohol, depending on whether the hydroxyl group is bonded to the end or middle carbon on the straight propane chain. As described under systematic naming, if another group on the molecule takes priority, the alcohol moiety is often indicated using the "hydroxy-" prefix.
In archaic nomenclature, alcohols can be named as derivatives of methanol using "-carbinol" as the ending. For instance, can be named trimethylcarbinol. | 0 | Organic Chemistry |
A racemic mixture is denoted by the prefix (±)- or dl- (for sugars the prefix - may be used), indicating an equal (1:1) mixture of dextro and levo isomers. Also the prefix rac- (or racem-) or the symbols RS and SR (all in italic letters) are used.
If the ratio is not 1:1 (or is not known), the prefix (+)/(−), - or d/l- (with a slash) is used instead.
The usage of d and l is discouraged by IUPAC. | 4 | Stereochemistry |
The ionotropic glutamate receptors bind the neurotransmitter glutamate. They form tetramers, with each subunit consisting of an extracellular amino terminal domain (ATD, which is involved tetramer assembly), an extracellular ligand binding domain (LBD, which binds glutamate), and a transmembrane domain (TMD, which forms the ion channel). The transmembrane domain of each subunit contains three transmembrane helices as well as a half membrane helix with a reentrant loop. The structure of the protein starts with the ATD at the N terminus followed by the first half of the LBD which is interrupted by helices 1,2 and 3 of the TMD before continuing with the final half of the LBD and then finishing with helix 4 of the TMD at the C terminus. This means there are three links between the TMD and the extracellular domains. Each subunit of the tetramer has a binding site for glutamate formed by the two LBD sections forming a clamshell like shape. Only two of these sites in the tetramer need to be occupied to open the ion channel. The pore is mainly formed by the half helix 2 in a way which resembles an inverted potassium channel. | 1 | Biochemistry |
Bioorganometallic chemistry is the study of biologically active molecules that contain carbon directly bonded to metals or metalloids. The importance of main-group and transition-metal centers has long been recognized as important to the function of enzymes and other biomolecules. However, only a small subset of naturally-occurring metal complexes and synthetically prepared pharmaceuticals are organometallic; that is, they feature a direct covalent bond between the metal(loid) and a carbon atom. The first, and for a long time, the only examples of naturally occurring bioorganometallic compounds were the cobalamin cofactors (vitamin B) in its various forms. In the 21st century, as a result of the discovery of new systems containing carbon–metal bonds in biology, bioorganometallic chemistry is rapidly emerging as a distinct subdiscipline of bioinorganic chemistry that straddles organometallic chemistry and biochemistry. Naturally occurring bioorganometallics include enzymes and sensor proteins. Also within this realm are synthetically prepared organometallic compounds that serve as new drugs and imaging agents (technetium-99m sestamibi) as well as the principles relevant to the toxicology of organometallic compounds (e.g., methylmercury). Consequently, bioorganometallic chemistry is increasingly relevant to medicine and pharmacology. | 0 | Organic Chemistry |
An anion exchange membrane (AEM) is a semipermeable membrane generally made from ionomers and designed to conduct anions but reject gases such as oxygen or hydrogen. | 7 | Physical Chemistry |
Multiple challenges exist in assessing exposure to pesticides in the general population, and many others that are specific to occupational exposures of agricultural workers. Beyond farm workers, estimating exposure to family members and children presents additional challenges, and may occur through "take-home" exposure from pesticide residues collected on clothing or equipment belonging to parent farm workers and inadvertently brought into the home. Children may also be exposed to pesticides prenatally from mothers who are exposed to pesticides during pregnancy. Characterizing children's exposure resulting from drift of airborne and spray application of pesticides is similarly challenging, yet well documented in developing countries. Because of critical development periods of the fetus and newborn children, these non-working populations are more vulnerable to the effects of pesticides, and may be at increased risk of developing neurocognitive effects and impaired development.
While measuring biomarkers or markers of biological effects may provide more accurate estimates of exposure, collecting these data in the field is often impractical and many methods are not sensitive enough to detect low-level concentrations. Rapid cholinesterase test kits exist to collect blood samples in the field. Conducting large scale assessments of agricultural workers in remote regions of developing countries makes the implementation of these kits a challenge. The cholinesterase assay is a useful clinical tool to assess individual exposure and acute toxicity. Considerable variability in baseline enzyme activity among individuals makes it difficult to compare field measurements of cholinesterase activity to a reference dose to determine health risk associated with exposure. Another challenge researchers face in deriving a reference dose is identifying health endpoints that are relevant to exposure. More epidemiological research is needed to identify critical health endpoints, particularly among populations who are occupationally exposed. | 2 | Environmental Chemistry |
Some miRNAs in plants have been seen to contain 2'-O-methylation, a modification to the ribose sugar that is added by the methyltransferase HEN1. This modification is thought to protect the miRNA against polyuridylation, which would result in its subsequent degradation.
In addition, pri-miRNAs have been shown to contain mA. This reversible modification may affect their cellular localization and function during miRNA processing. | 1 | Biochemistry |
Protein adsorption can also occur as a direct result of heating a mixture. Protein adsorption in milk processing is often used as a model for this type of adsorption in other situations. Milk is composed mainly of water, with less than 20% of suspended solids or dissolved proteins. Proteins make up only 3.6% of milk in total, and only 26% of the components that are not water. These proteins are all responsible for fouling that occurs during pasteurization.
As milk is heated during pasteurization many of the proteins in the milk are denatured. Pasteurization temperatures can reach 161 °F (71.7 °C). This temperature is high enough to denature the proteins below, lowering the nutritional value of the milk and causing fouling. Milk is heated to these high temperatures for a short time (15–20 seconds) to reduce the amount of denaturization. However fouling from denatured proteins is still a significant problem.
Denaturation exposes hydrophobic amino acid residues in the protein, which had been previously protected by the protein. The exposed hydrophobic amino acids decrease the entropy of the water surrounding them, making it favorable for surface adsorption. Some of the β-lactoglobulin (β-lg) will adsorb directly onto the surface of a heat exchanger or container. Other denatured β-lg molecules adsorb to casein micelles, which are also present in the milk. As more and more β-lg proteins bind to the casein micelle it forms an aggregate, which will then diffuse to the heat exchanger and/or surface of the container. | 1 | Biochemistry |
The replication cycle of a retrovirus entails the insertion ("integration") of a DNA copy of the viral genome into the nuclear genome of the host cell. Most retroviruses infect somatic cells, but occasional infection of germline cells (cells that produce eggs and sperm) can also occur. Rarely, retroviral integration may occur in a germline cell that goes on to develop into a viable organism. This organism will carry the inserted retroviral genome as an integral part of its own genome—an "endogenous" retrovirus (ERV) that may be inherited by its offspring as a novel allele. Many ERVs have persisted in the genome of their hosts for millions of years. However, most of these have acquired inactivating mutations during host DNA replication and are no longer capable of producing the virus. ERVs can also be partially excised from the genome by a process known as recombinational deletion, in which recombination between the identical sequences that flank newly integrated retroviruses results in deletion of the internal, protein-coding regions of the viral genome.
The general retrovirus genome consists of three genes vital for the invasion, replication, escape, and spreading of its viral genome. These three genes are gag (encodes for structural proteins for the viral core), pol (encodes for reverse transcriptase, integrase, and protease), and env (encodes for coat proteins for the viruss exterior). These viral proteins are encoded as polyproteins. In order to carry out their life cycle, the retrovirus relies heavily on the host cells machinery. Protease degrades peptide bonds of the viral polyproteins, making the separate proteins functional. Reverse transcriptase functions to synthesize viral DNA from the viral RNA in the host cell's cytoplasm before it enters the nucleus. Integrase guides the integration of viral DNA into the host genome.
Over time, the genome of ERVs not only acquire point mutations, but also shuffle and recombine with other ERVs. ERVs with a decayed sequence for the env become more likely to propagate. | 1 | Biochemistry |
CCL7 was first characterized from osteosarcoma supernatant. CCL7 consists of 99 amino acids, which contains 23-amino acid signal peptide. The mature protein about 76 amino acids is secreted after cleavage of the signal peptide. In contrast to most chemokines, CCL7 exists in a general monomeric form, differing from the dimer formed in a highly concentrated solution.
CCL7 can exist in four different glycotypes with a molecular weight 11, 13, 17 and 18 kDa in COS cells.
CCL7 mediates effects on the immune cell types through binding to numerous receptors, including CCR1, CCR2, CCR3, CCR5, and CCR10. These receptors belongs to the G protein-coupled seven-transmembrane receptors. CCL7 can also interact with cell surface glycosaminoglycans (GAGs) present on all animal cell surfaces. | 1 | Biochemistry |
Salimuzzaman was born in Subeha (Barabanki District) near Lucknow on 19 October 1897. His father's name was Chaudhry Muhammad Zaman and his elder brother Chaudhry Khaliquzzaman was a distinguished All India Muslim League leader and one of the founding fathers of Pakistan. He received his early education from Lucknow, both in the Urdu and Persian languages, and soon developed interest in literature, poetry, and calligraphy from his father Sheikh Muhammad Zaman. He graduated in Philosophy and Persian language, from Muhammadan Anglo-Oriental College (that would later become Aligarh Muslim University) in 1920.
In 1920, Siddiqui proceeded to University College London to study medicine. However, after one year of pre-medical studies, he moved to Frankfurt University in 1921 to study chemistry. In 1924, he married his German classmate, Ethel Wilhelmina Schneeman. He received Doctor of Philosophy under the supervision of Julius Von Braun in 1927. During his college days in Germany in the 1920s, Germany experienced high inflation and he went through some hard economic times. In these tough times, Indias then eminent philanthropist Hakim Ajmal Khan used to send him Rupees400 every month. Many years later, as a successful scientist in Pakistan, Siddiqui repaid Hakeem Ajmal Khans kindness by dedicating his discoveries to him.
On his return, he established the Ayurvedic and Unani Tibbi Research Institute at the Tibbia College Delhi, under the guidance of Hakim Ajmal Khan. He was appointed its first director. However, soon after the death of Hakim Ajmal Khan, Siddiqui left the post. In 1940, he joined Indian Council for Scientific and Industrial Research where he worked until 1951 when he migrated to Pakistan on the request of Prime Minister Liaquat Ali Khan. | 0 | Organic Chemistry |
Expressome may refer to:
*A supramolecular complex consisting of RNA polymerase and a trailing ribosome linked by a shared mRNA. The expressome complex mediates a mechanism of gene expression regulation termed transcription-translation coupling.
*The whole set of gene expression in a cell, tissue, organ, organisms, and species. Expressome is a slightly larger concept than transcriptome. The transcriptome is the set of transcripts, while expressome includes transcripts, proteins and other ligands (abundance or concentration). | 1 | Biochemistry |
Some researchers have speculated that Earth may have been seeded by organic compounds early in its development by tholin-rich comets, providing the raw material necessary for life to develop (see Miller–Urey experiment for discussion related to this). Tholins do not exist naturally on present-day Earth due to the oxidizing properties of the free oxygen component of its atmosphere ever since the Great Oxygenation Event around 2.4 billion years ago.
Laboratory experiments suggest that tholins near large pools of liquid water that might persist for thousands of years could facilitate the formation of prebiotic chemistry to take place, and has implications on the origins of life on Earth and possibly other planets. Also, as particles in the atmosphere of an exoplanet, tholins affect the light scatter and act as a screen for protecting planetary surfaces from ultraviolet radiation, affecting habitability. Laboratory simulations found derived residues related to amino acids as well as urea, with important astrobiological implications.
On Earth, a wide variety of soil bacteria are able to use laboratory-produced tholins as their sole source of carbon. Tholins could have been the first microbial food for heterotrophic microorganisms before autotrophy evolved. | 9 | Geochemistry |
When generating THz radiation via a photoconductive emitter, an ultrafast pulse (typically 100 femtoseconds or shorter) creates charge carriers (electron-hole pairs) in a semiconductor material. This incident laser pulse abruptly changes the antenna from an insulating state into a conducting state. Due to an electric bias applied across the antenna, a sudden electric current transmits across the antenna. This changing current lasts for about a picosecond, and thus emits terahertz radiation since the Fourier transform of a picosecond length signal will contain THz components.
Typically the two antenna electrodes are patterned on a low temperature gallium arsenide (LT-GaAs), semi-insulating gallium arsenide (SI-GaAs), or other semiconductor (such as InP) substrate.
In a commonly used scheme, the electrodes are formed into the shape of a simple dipole antenna with a gap of a few micrometers and have a bias voltage up to 40 V between them. The ultrafast laser pulse must have a wavelength that is short enough to excite electrons across the bandgap of the semiconductor substrate. This scheme is suitable for illumination with a Ti:sapphire oscillator laser with photon energies of 1.55 eV and pulse energies of about 10 nJ. For use with amplified Ti:sapphire lasers with pulse energies of about 1 mJ, the electrode gap can be increased to several centimeters with a bias voltage of up to 200 kV.
More recent advances towards cost-efficient and compact THz-TDS systems are based on mode-locked fiber laser sources emitting at a center wavelength of 1550 nm. Therefore, the photoconductive emitters must be based on semiconductor materials with smaller band gaps of approximately 0.74 eV such as Fe-doped indium gallium arsenide or indium gallium arsenide/indium aluminum arsenide heterostructures.
The short duration of THz pulses generated (typically ~2 ps) are primarily due to the rapid rise of the photo-induced current in the semiconductor and short carrier lifetime semiconductor materials (e.g., LT-GaAs). This current may persist for only a few hundred femtoseconds to several nanoseconds depending on the substrate material. This is not the only means of generation but is currently () the most common.
Pulses produced by this method have average power levels on the order of several tens of microwatts. The peak power during pulses can be many orders of magnitude higher due to the low duty cycle of mostly >1%, which is dependent on the repetition rate of the laser source. The maximum bandwidth of the resulting THz pulse is primarily limited by the duration of the laser pulse, while the frequency position of the maximum of the Fourier spectrum is determined by the carrier lifetime of the semiconductor. | 7 | Physical Chemistry |
The valence bonds do not have to be formed by nearest neighbors only and their distributions may vary in different materials. Ground states with large contributions of long range valence bonds have more low-energy spin excitations, as those valence bonds are easier to break up. On breaking, they form two free spins. Other excitations rearrange the valence bonds, leading to low-energy excitations even for short-range bonds. Something very special about spin liquids is that they support exotic excitations, meaning excitations with fractional quantum numbers. A prominent example is the excitation of spinons which are neutral in charge and carry spin . In spin liquids, a spinon is created if one spin is not paired in a valence bond. It can move by rearranging nearby valence bonds at low energy cost. | 7 | Physical Chemistry |
Ptaquiloside has unstable chemical structure and readily undergoes glucose liberation. The resulting ptaquilodienone is the active form of ptaquiloside and accounts for the observed biological effects. The cyclopropyl group in the dienone is highly reactive as an electrophile, not only because it is conjugated with the keto group, but because it also constitutes a cyclopropyl carbinol system, from which the facile formation of the stable non-classical cation is well-known. | 0 | Organic Chemistry |
The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for zinc in 2001. The current EARs for zinc for women and men ages 14 and up is 6.8 and 9.4 mg/day, respectively. The RDAs are 8 and 11 mg/day. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy is 11 mg/day. RDA for lactation is 12 mg/day. For infants up to 12 months the RDA is 3 mg/day. For children ages 1–13 years the RDA increases with age from 3 to 8 mg/day. As for safety, the IOM sets Tolerable upper intake levels (ULs) for vitamins and minerals when evidence is sufficient. In the case of zinc the adult UL is 40 mg/day (lower for children). Collectively the EARs, RDAs, AIs and ULs are referred to as Dietary Reference Intakes (DRIs).
The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL are defined the same as in the United States. For people ages 18 and older the PRI calculations are complex, as the EFSA has set higher and higher values as the phytate content of the diet increases. For women, PRIs increase from 7.5 to 12.7 mg/day as phytate intake increases from 300 to 1200 mg/day; for men the range is 9.4 to 16.3 mg/day. These PRIs are higher than the U.S. RDAs. The EFSA reviewed the same safety question and set its UL at 25 mg/day, which is much lower than the U.S. value.
For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (%DV). For zinc labeling purposes 100% of the Daily Value was 15 mg, but on May 27, 2016, it was revised to 11 mg. A table of the old and new adult daily values is provided at Reference Daily Intake. | 1 | Biochemistry |
Biological molecular machines have been known and studied for years given their vital role in sustaining life, and have served as inspiration for synthetically designed systems with similar useful functionality. The advent of conformational analysis, or the study of conformers to analyze complex chemical structures, in the 1950s gave rise to the idea of understanding and controlling relative motion within molecular components for further applications. This led to the design of "proto-molecular machines" featuring conformational changes such as cog-wheeling of the aromatic rings in triptycenes. By 1980, scientists could achieve desired conformations using external stimuli and utilize this for different applications. A major example is the design of a photoresponsive crown ether containing an azobenzene unit, which could switch between cis and trans isomers on exposure to light and hence tune the cation-binding properties of the ether. In his seminal 1959 lecture Theres Plenty of Room at the Bottom', Richard Feynman alluded to the idea and applications of molecular devices designed artificially by manipulating matter at the atomic level. This was further substantiated by Eric Drexler during the 1970s, who developed ideas based on molecular nanotechnology such as nanoscale "assemblers", though their feasibility was disputed.
Though these events served as inspiration for the field, the actual breakthrough in practical approaches to synthesize artificial molecular machines (AMMs) took place in 1991 with the invention of a "molecular shuttle" by Sir Fraser Stoddart. Building upon the assembly of mechanically linked molecules such as catenanes and rotaxanes as developed by Jean-Pierre Sauvage in the early 1980s, this shuttle features a rotaxane with a ring that can move across an "axle" between two ends or possible binding sites (hydroquinone units). This design realized the well-defined motion of a molecular unit across the length of the molecule for the first time. In 1994, an improved design allowed control over the motion of the ring by pH variation or electrochemical methods, making it the first example of an AMM. Here the two binding sites are a benzidine and a biphenol unit; the cationic ring typically prefers staying over the benzidine ring, but moves over to the biphenol group when the benzidine gets protonated at low pH or if it gets electrochemically oxidized. In 1998, a study could capture the rotary motion of a decacyclene molecule on a copper-base metallic surface using a scanning tunneling microscope. Over the following decade, a broad variety of AMMs responding to various stimuli were invented for different applications. In 2016, the Nobel Prize in Chemistry was awarded to Sauvage, Stoddart, and Bernard L. Feringa for the design and synthesis of molecular machines. | 6 | Supramolecular Chemistry |
Nb.BbvCI is a nicking endonuclease used to cut one strand of double-stranded DNA. It has been successfully used to incorporate fluorochrome-labeled nucleotides into specific spots of a DNA sequence via nick translation. | 1 | Biochemistry |
The groups in phosphoric acids can also condense with the hydroxyl groups of alcohols to form phosphate esters. Since orthophosphoric acid has three groups, it can esterify with one, two, or three alcohol molecules to form a mono-, di-, or triester. See the general structure image of an ortho- (or mono-) phosphate ester below on the left, where any of the R groups can be a hydrogen or an organic radical. Di- and tripoly- (or tri-) phosphate esters, etc. are also possible. Any groups on the phosphates in these ester molecules may lose ions to form anions, again depending on the pH in a solution. In the biochemistry of living organisms, there are many kinds of (mono)phosphate, diphosphate, and triphosphate compounds (essentially esters), many of which play a significant role in metabolism such as adenosine diphosphate (ADP) and triphosphate (ATP). | 0 | Organic Chemistry |
Dilution of sample or reducing the volume of sample injected may give a reduction of ion suppression by reducing the quantity of interfering species present, although the quantity of analyte of interest will also be reduced, making this an undesirable approach for trace analysis.
Similar is the effect of reducing the mobile phase flow rate to the nanolitre-per-minute range since, in addition to resulting in improved desolvation, the smaller droplets formed are more tolerant to the presence of non-volatile species in the sample matrix. | 3 | Analytical Chemistry |
Enone–alkene cycloadditions often suffer from side reactions, e.g. those associated with the diradical intermediate. These side reactions can often be minimized by a judicious choice of reaction conditions.
Dissolved oxygen is avoided since it is photo reactive.
A variety of solvents can be used. Acetone is a useful solvent, because it can serve as a triplet sensitizer. Alkane-based solvents are selected to be free of alkenes. Excitation wavelength is important. For intermolecular reactions, excess of the alkene can be employed to avoid competitive dimerization of the enone. | 5 | Photochemistry |
Pumps vary in pressure capacity, but their performance is measured on their ability to yield a consistent and reproducible volumetric flow rate. Pressure may reach as high as 60 MPa (6000 lbf/in), or about 600 atmospheres. Modern HPLC systems have been improved to work at much higher pressures, and therefore are able to use much smaller particle sizes in the columns (), or about 1200 atmospheres. The term "UPLC" is a trademark of the Waters Corporation, but is sometimes used to refer to the more general technique of UHPLC. | 3 | Analytical Chemistry |
Alain Viel is the director of Northwest Undergraduate Laboratories and senior lecturer in the Department of Molecular and Cellular Biology at Harvard University. | 1 | Biochemistry |
Fumaric acid was developed as a medicine to treat the autoimmune condition psoriasis in the 1950s in Germany as a tablet containing 3 esters, primarily dimethyl fumarate, and marketed as Fumaderm by Biogen Idec in Europe. Biogen would later go on to develop the main ester, dimethyl fumarate, as a treatment for multiple sclerosis.
In patients with relapsing-remitting multiple sclerosis, the ester dimethyl fumarate (BG-12, Biogen) significantly reduced relapse and disability progression in a phase 3 trial. It activates the Nrf2 antioxidant response pathway, the primary cellular defense against the cytotoxic effects of oxidative stress. | 1 | Biochemistry |
In outer sphere redox reactions no bonds are formed or broken; only an electron transfer (ET) takes place. A quite simple example is the Fe/Fe redox reaction, the self exchange reaction which is known to be always occurring in an aqueous solution containing the aquo complexes [Fe(HO)] and [Fe(HO)6]. Redox occurs with Gibbs free reaction energy .
From the reaction rates temperature dependence an activation energy is determined, and this activation energy is interpreted as the energy of the transition state in a reaction diagram. The latter is drawn, according to Arrhenius and Eyring, as an energy diagram with the reaction coordinate as the abscissa. The reaction coordinate describes the minimum energy path from the reactants to the products, and the points of this coordinate are combinations of distances and angles between and in the reactants in the course of the formation and/or cleavage of bonds. The maximum of the energy diagram, the transition state, is characterized by a specific configuration of the atoms. Moreover, in Eyrings TST a quite specific change of the nuclear coordinates is responsible for crossing the maximum point, a vibration in this direction is consequently treated as a translation.
For outer sphere redox reactions there cannot be such a reaction path, but nevertheless one does observe an activation energy. The rate equation for activation-controlled reactions has the same exponential form as the Eyring equation,
is the Gibbs free energy of the formation of the transition state, the exponential term represents the probability of its formation, A contains the probability of crossing from precursor to successor complex. | 7 | Physical Chemistry |
Promoters of active genes have nucleosome free regions (NFR). This allows for promoter DNA accessibility to various proteins, such as transcription factors. Nucleosome free region typically spans for 200 nucleotides in S. cerevisiae Well-positioned nucleosomes form boundaries of NFR. These nucleosomes are called +1-nucleosome and −1-nucleosome and are located at canonical distances downstream and upstream, respectively, from transcription start site. +1-nucleosome and several downstream nucleosomes also tend to incorporate H2A.Z histone variant. | 1 | Biochemistry |
Normative mineralogy is an estimate of the mineralogy of the rock. It usually differs from the visually observable mineralogy, at least as much as the types of mineral species, especially amongst the ferromagnesian minerals and feldspars, where it is possible to have many solid solution series of minerals, or minerals with similar Fe and Mg ratios substituting, especially with water (e.g.; amphibole and biotite replacing pyroxene).
However, in aphanites, or rocks with phenocrysts clearly out of equilibrium with the groundmass, a normative mineral calculation is often the best to understand the evolution of the rock and its relationship to other igneous rocks in the region. | 9 | Geochemistry |
In 2016 a new study showed that flat roofs in urban areas are fruitful places to extract micrometeorites. The "urban" cosmic spherules have a shorter terrestrial age and are less altered than the previous findings.
Amateur collectors may find micrometeorites in areas where dust from a large area has been concentrated, such as from a roof downspout. | 9 | Geochemistry |
Hammond married Ellen Sarah Sophia Clarke (1833–1905), the sister-in-law of Samuel Warren, in 1874. Hammond survived her by three years upon her death in 1905.
Along with New York architect Alexander Twombly, who was the engineer and draftsman of Forest Paper Company, Hammond designed what is today known as Camp Hammond, set back from Yarmouths Main Street and from which Hammond could see his mill. Twombly also designed several buildings in Boston. Frederick Law Olmsted, who designed Central Park in New York City, designed the gardens of the property. With the Hammonds splitting their time between Boston and Yarmouth, the property became known as the Camp'.
The Hammonds also formed the Antiquarian Society in order to facilitate the 1890 purchase of the North Yarmouth and Freeport Baptist Meetinghouse on Yarmouth's Hillside Street. It became a library and museum, known as the Hillside Library.
Among the many roles Hammond took on without payment was as president of the Yarmouth Water Committee, established in 1895, which sourced its water supply from Hammond Spring on the property of Forest Paper Company. Hammond donated Forest Paper Company land for the 1903 construction of Merrill Memorial Library, on Main Street, which was designed by Alexander Longfellow, a nephew of the poet Henry Wadsworth Longfellow.
Hammond served in the Maine Legislature between 1868 and 1870, was on the Maine Board of Agriculture and the board of trustees of North Yarmouth Academy, was a member of the American Association for the Advancement of Science, the Society of Chemical Industry, the American Institute of Mining, Metallurgical, and Petroleum Engineers, The Society of Arts and Crafts of Boston, the Massachusetts Historical Society, the New England Historic Genealogical Society (from January 1876), The Bostonian Society and the Franklin Institute. He was also a Freemason.
A member of the American Horticultural Society, he was a keen arborist, and his knowledge of trees and plants earned him a place on the Overseers Committee at Harvard Universitys Gray Herbarium between 1888 and the time of his death.
The Hammonds were members of Yarmouths First Parish Congregational Church and Bostons Trinity Church. | 8 | Metallurgy |
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