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A sample injector is a device used in conjunction with injecting samples into high-performance liquid chromatography (HPLC) or similar chromatography apparati. | 3 | Analytical Chemistry |
The rank product is a biologically motivated rank test for the detection of differentially expressed genes in replicated microarray experiments.
It is a simple non-parametric statistical method based on ranks of fold changes. In addition to its use in expression profiling, it can be used to combine ranked lists in various application domains, including proteomics, metabolomics, statistical meta-analysis, and general feature selection. | 1 | Biochemistry |
Photosynthetic water splitting (or oxygen evolution) is one of the most important reactions on the planet, since it is the source of nearly all the atmosphere's oxygen. Moreover, artificial photosynthetic water-splitting may contribute to the effective use of sunlight as an alternative energy-source.
The mechanism of water oxidation is understood in substantial detail. The oxidation of water to molecular oxygen requires extraction of four electrons and four protons from two molecules of water. The experimental evidence that oxygen is released through cyclic reaction of oxygen evolving complex (OEC) within one PSII was provided by Pierre Joliot et al. They have shown that, if dark-adapted photosynthetic material (higher plants, algae, and cyanobacteria) is exposed to a series of single turnover flashes, oxygen evolution is detected with typical period-four damped oscillation with maxima on the third and the seventh flash and with minima on the first and the fifth flash (for review, see). Based on this experiment, Bessel Kok and co-workers introduced a cycle of five flash-induced transitions of the so-called S-states, describing the four redox states of OEC: When four oxidizing equivalents have been stored (at the S-state), OEC returns to its basic S-state. In the absence of light, the OEC will "relax" to the S state; the S state is often described as being "dark-stable". The S state is largely considered to consist of manganese ions with oxidation states of Mn, Mn, Mn, Mn. Finally, the intermediate S-states were proposed by Jablonsky and Lazar as a regulatory mechanism and link between S-states and tyrosine Z.
In 2012, Renger expressed the idea of internal changes of water molecules into typical oxides in different S-states during water splitting. | 5 | Photochemistry |
The noncanonical PCP pathway regulates cell morphology, division, and movement. Once again Wnt proteins binds to and activates Frizzled so that Frizzled activates a Dishevelled protein that is tethered to the plasma membrane through a Prickle protein and transmembrane Stbm protein. The active Dishevelled activates RhoA GTPase through Dishevelled associated activator of morphogenesis 1 (Daam1) and the Rac protein. Active RhoA is able to induce cytoskeleton changes by activating Roh-associated kinase (ROCK) and affect gene transcription directly. Active Rac can directly induce cytoskeleton changes and affect gene transcription through activation of JNK. | 1 | Biochemistry |
Rotation around the C-5/C-6 bond is described by the angle ω. Three possible staggered conformations are possible:: gauche–trans (gt), gauche–gauche (gg), and trans–gauche (tg). The name indicates the interaction between O-5 and OH-6 first followed by the interaction between OH-6 and C-4. | 0 | Organic Chemistry |
Dally (division abnormally delayed) is the name of a gene that encodes a HS-modified-protein found in the fruit fly (Drosophila melanogaster). The protein has to be processed after being codified, and in its mature form it is composed by 626 amino acids, forming a proteoglycan rich in heparin sulfate which is anchored to the cell surface via covalent linkage to glycophosphatidylinositol (GPI), so we can define it as a glypican. For its normal biosynthesis it requires sugarless (sgl), a gene that encodes an enzyme which plays a critical role in the process of modification of dally. | 1 | Biochemistry |
The PSD of a material can be important in understanding its physical and chemical properties. It affects the strength and load-bearing properties of rocks and soils. It affects the reactivity of solids participating in chemical reactions, and needs to be tightly controlled in many industrial products such as the manufacture of printer toner, cosmetics, and pharmaceutical products. | 7 | Physical Chemistry |
It is common to place a drop of the test solution on a metal disk which is then dried out to give a uniform coating on the disk. This is then used as the test sample. If the thickness of the layer formed on the disk is too thick then the lines of the spectrum are broadened to lower energies. This is because some of the energy of the alpha particles is lost during their movement through the layer of active material. | 7 | Physical Chemistry |
Changes in Arc mRNA and/or protein are correlated with a number of behavioral changes including cued fear conditioning, contextual fear conditioning, spatial memory, operant conditioning, and inhibitory avoidance. The mRNA is notably upregulated following electrical stimulation in LTP-induction procedures such as high frequency stimulation (HFS), and is massively and globally induced by maximal electroconvulsive shock (MECS). | 1 | Biochemistry |
When phosphorylated by an unknown kinase, PRR5 and PRR3 proteins demonstrate increased binding to TIMING OF CAB2 EXPRESSION 1 ( TOC1). This interaction stabilizes both TOC1 and PRR5 and prevents their degradation by the F-box protein ZEITLUPE (ZTL). Through this mechanism, PRR5 is indirectly activated by light, as ZTL is inhibited by light. Additionally, PRR5 contributes to the transcriptional repression of the genes encoding the single MYB transcription factors CCA1 and LHY. | 1 | Biochemistry |
The MLN can provide an important component of mercury dry deposition to a forested landscape. The importance of litterfall mercury data for quantifying atmospheric mercury deposition to forests was demonstrated with studies at NADP sites in the eastern USA from 2007-2009 and 2007 to 2014. | 2 | Environmental Chemistry |
There are a number of effects which control spectral line shape. A spectral line extends over a tiny spectral band with a nonzero range of frequencies, not a single frequency (i.e., a nonzero spectral width). In addition, its center may be shifted from its nominal central wavelength. There are several reasons for this broadening and shift. These reasons may be divided into two general categories – broadening due to local conditions and broadening due to extended conditions. Broadening due to local conditions is due to effects which hold in a small region around the emitting element, usually small enough to assure local thermodynamic equilibrium. Broadening due to extended conditions may result from changes to the spectral distribution of the radiation as it traverses its path to the observer. It also may result from the combining of radiation from a number of regions which are far from each other. | 7 | Physical Chemistry |
Although this term is also sometimes used interchangeably with exon, it is not the exact same thing: the exon is composed of the coding region as well as the 3 and 5 untranslated regions of the RNA, and so therefore, an exon would be partially made up of coding regions. The 3 and 5 untranslated regions of the RNA, which do not code for protein, are termed non-coding regions and are not discussed on this page.
There is often confusion between coding regions and exomes and there is a clear distinction between these terms. While the exome refers to all exons within a genome, the coding region refers to a singular section of the DNA or RNA which specifically codes for a certain kind of protein. | 1 | Biochemistry |
Fischmeister studied physics, mathematics, and chemistry at the University of Graz from 1945 to 1951 and received his doctorate in physical chemistry with Otto Kratky in 1951. From 1953, he was a research assistant at the Institute of Inorganic Chemistry at Uppsala University. In 1956, he became head of the Physics and Materials groups at the Development Laboratory of LM Ericsson in Stockholm. From 1958, he led the Laboratory of Powder Metallurgy at the Swedish Institute for Metals Research (Institutet för Metallforskning) in Stockholm. In 1961, he qualified as a university lecturer at Uppsala University in the field of general and inorganic chemistry. From 1961, he headed the research department for cemented carbides at the stainless steel works of Stora Kopparbergs Bergslags AB in Söderfors, subsequently leading the entire research, development, and quality assurance of the stainless steel works in Söderfors (today Erasteel Kloster AB and Alleima Söderfors).
In 1965, Fischmeister accepted a call to the chair and head of the Institute of Metallic Materials at Chalmers University of Technology in Gothenburg. In 1975, he was appointed chair and head of the Institute of Metallurgy and Materials Testing at the University of Leoben. In 1981, he became a scientific member of the Max Planck Society and director of the Institute of Materials Sciences at the Max Planck Institute for Metals Research in Stuttgart (now the Max Planck Institute for Intelligent Systems). In addition to his leadership role at the Max Planck Institute for Metals Research, he was also the founding director of the Max Planck Institute of Microstructure Physics in Halle (Saale) from 1991 to 1993. In 1995, he retired from the Max Planck Institute for Metals Research.
Fischmeister was a member of the Austrian Universities' Board of Trustees (Universitätenkuratorium) from 1993 till 2003 and was a member of the Austrian Science Council (Wissenschaftsrat) from 2004 to 2009. | 8 | Metallurgy |
In the United States, sperm banks are regulated as Human Cell and Tissue or Cell and Tissue Bank Product (HCT/Ps) establishments by the Food and Drug Administration (FDA) with new guidelines in effect May 25, 2005. Many states also have regulations in addition to those imposed by the FDA, including New York and California.
In the European Union a sperm bank must have a license according to the EU Tissue Directive which came into effect on April 7, 2006. In the United Kingdom, sperm banks are regulated by the Human Fertilisation and Embryology Authority.
In countries where sperm banks are allowed to operate, the sperm donor will not usually become the legal father of the children produced from the sperm he donates, but he will be the biological father of such children. In cases of surrogacy involving embryo donation, a form of gestational surrogacy, the commissioning mother or the commissioning parents will not be biologically related to the child and may need to go through an adoption procedure.
As with other forms of third party reproduction, the use of donor sperm from a sperm bank gives rise to a number of moral, legal, and ethical issues, including, but not limited to the right of the sperm donor remaining anonymous, and the child's right to know their familial background.
Furthermore, as local regulations reduce the size of the donor pool and, in some cases, exclude entire classes of potential buyers such as single women and lesbian couples, restricting donations to only heterosexual couples who are married. Some customers choose to buy abroad or on the internet, having the samples delivered at home. | 1 | Biochemistry |
Solder (; NA: ) is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable for use as solder should have a lower melting point than the pieces to be joined. The solder should also be resistant to oxidative and corrosive effects that would degrade the joint over time. Solder used in making electrical connections also needs to have favorable electrical characteristics.
Soft solder typically has a melting point range of , and is commonly used in electronics, plumbing, and sheet metal work. Alloys that melt between are the most commonly used. Soldering performed using alloys with a melting point above is called "hard soldering", "silver soldering", or brazing.
In specific proportions, some alloys are eutectic — that is, the alloys melting point is the lowest possible for a mixture of those components, and coincides with the freezing point. Non-eutectic alloys can have markedly different solidus and liquidus' temperatures, as they have distinct liquid and solid transitions. Non-eutectic mixtures often exist as a paste of solid particles in a melted matrix of the lower-melting phase as they approach high enough temperatures. In electrical work, if the joint is disturbed while in this "pasty" state before it fully solidifies, a poor electrical connection may result; use of eutectic solder reduces this problem. The pasty state of a non-eutectic solder can be exploited in plumbing, as it allows molding of the solder during cooling, e.g. for ensuring watertight joint of pipes, resulting in a so-called "wiped joint".
For electrical and electronics work, solder wire is available in a range of thicknesses for hand-soldering (manual soldering is performed using a soldering iron or soldering gun), and with cores containing flux. It is also available as a room temperature paste, as a preformed foil shaped to match the workpiece which may be more suited for mechanized mass-production, or in small "tabs" that can be wrapped around the joint and melted with a flame where an iron isn't usable or available, as for instance in field repairs. Alloys of lead and tin were commonly used in the past and are still available; they are particularly convenient for hand-soldering. Lead-free solders have been increasing in use due to regulatory requirements plus the health and environmental benefits of avoiding lead-based electronic components. They are almost exclusively used today in consumer electronics.
Plumbers often use bars of solder, much thicker than the wire used for electrical applications, and apply flux separately; many plumbing-suitable soldering fluxes are too corrosive (or conductive) to be used in electrical or electronic work. Jewelers often use solder in thin sheets, which they cut into snippets. | 8 | Metallurgy |
Dendrimers have the potential to completely change the pharmacokinetic and pharmacodynamic (PK/PD) profiles of a drug. As carriers, the PK/PD is no longer determined by the drug itself but by the dendrimer’s localization, drug release, and dendrimer excretion. ADME properties are very highly tunable by varying dendrimer size, structure, and surface characteristics. While G9 dendrimers biodistribute very heavily to the liver and spleen, G6 dendrimers tend to biodistribute more broadly. As molecular weight increases, urinary clearance and plasma clearance decrease while terminal half-life increases. | 6 | Supramolecular Chemistry |
Soil is well developed in the forest as suggested by the thick humus layers, rich diversity of large trees and animals that live there. Forest soils can form a thick soil carbon sponge. In forests, precipitation exceeds evapotranspiration which results in an excess of water that percolates downward through the soil layers. Slow rates of decomposition leads to large amounts of fulvic acid, greatly enhancing chemical weathering. The downward percolation, in conjunction with chemical weathering leaches Mg, Fe, and aluminium (Al) from the soil and transports them downward, a process known as podzolization. This process leads to marked contrasts in the appearance and chemistry of the soil layers. | 9 | Geochemistry |
A cumulative or overall constant, given the symbol β, is the constant for the formation of a complex from reagents. For example, the cumulative constant for the formation of ML is given by
:M + 2 L ML; [ML] = β[M][L]
The stepwise constant, K, for the formation of the same complex from ML and L is given by
:ML + L ML; [ML] = K[ML][L] = Kβ[M][L]
It follows that
:β = Kβ
A cumulative constant can always be expressed as the product of stepwise constants. There is no agreed notation for stepwise constants, though a symbol such as K is sometimes found in the literature. It is best always to define each stability constant by reference to an equilibrium expression. | 7 | Physical Chemistry |
Elections for membership are held annually with candidates for membership being nominated and elected exclusively by existing EMBO members, membership cannot be applied for directly. Three types of membership exist:
# EMBO Member, for scientists living (or who have lived) in a European Molecular Biology Conference (EMBC) Member State
# EMBO Associate Member, for scientists living outside of the EMBC Member States
# EMBO Young Investigator | 1 | Biochemistry |
Copepods vary considerably, but are typically long, with a teardrop-shaped body and large antennae. Like other crustaceans, they have an armoured exoskeleton, but they are so small that in most species, this thin armour and the entire body is almost totally transparent. Some polar copepods reach . Most copepods have a single median compound eye, usually bright red and in the centre of the transparent head. Subterranean species may be eyeless, and members of the genera Copilia and Corycaeus possess two eyes, each of which has a large anterior cuticular lens paired with a posterior internal lens to form a telescope. Like other crustaceans, copepods possess two pairs of antennae; the first pair is often long and conspicuous.
Free-living copepods of the orders Calanoida, Cyclopoida, and Harpacticoida typically have a short, cylindrical body, with a rounded or beaked head, although considerable variation exists in this pattern. The head is fused with the first one or two thoracic segments, while the remainder of the thorax has three to five segments, each with limbs. The first pair of thoracic appendages is modified to form maxillipeds, which assist in feeding. The abdomen is typically narrower than the thorax, and contains five segments without any appendages, except for some tail-like "rami" at the tip. Parasitic copepods (the other seven orders) vary widely in morphology and no generalizations are possible.
Because of their small size, copepods have no need of any heart or circulatory system (the members of the order Calanoida have a heart, but no blood vessels), and most also lack gills. Instead, they absorb oxygen directly into their bodies. Their excretory system consists of maxillary glands. | 2 | Environmental Chemistry |
To ensure consistency and repeatability, the methods use in the chemical analysis of water samples are often agreed and published at a national or state level. By convention these are often referred to as "Blue book"s.
Certain analyses are performed in-field (e.g. pH, specific conductance) while others involve sampling and laboratory testing.
The methods defined in the relevant standards can be broadly classified as:
* Conventional wet chemistry including the Winkler method for dissolved oxygen, precipitation, filtration for solids, acidification, neutralisation, titration etc. Colourimetric methods such as MBAS assay which indicates anionic surfactants in water and on site comparator methods to determine chlorine and chloramines. Nephelometers are used to measure solids concentrations as turbidity. These methods are generally robust and well tried and inexpensive, giving a reasonable degree of accuracy at modest sensitivity.
*Electro chemistry including pH, conductivity and dissolved oxygen using oxygen electrode. These methods yield accurate and precise results using electronic equipment capable of feeding results directly into a laboratory data management system
*Spectrophotometry is used particularly for metallic elements in solution producing results with very high sensitivity, but which may require some sample preparation prior to analysis and may also need specialised sampling methods to avoid sample deterioration in transit.
*Chromatography is used for many organic species which are volatile or which can yield a characteristic volatile component of after initial chemical processing.
*Ion chromatography is a sensitive and stable technique that can measure lithium, ammonium NH and many other low molecular weight ions using ion exchange technology.
*Gas chromatography can be used to determine methane, carbon dioxide, cyanide, oxygen, nitrogen and many other volatile components at reasonable sensitivities.
*Mass spectrometry is used where very high sensitivity is required and is sometimes used as a back-end process after gas liquid chromatography for detecting trace organic chemicals.
Depending on the components, different methods are applied to determine the quantities or ratios of the components. While some methods can be performed with standard laboratory equipment, others require advanced devices, such as inductively coupled plasma mass spectrometry (ICP-MS). | 9 | Geochemistry |
Mathews married Ella Gillfillan (B.A. 1907, University of Wisconsin) on June 26, 1909. They had two children: Marian and Jean. Marian married M. H. Withey of Madison. Jean married Charles C. Watson, a collaborator with her father and with John Warren Williams in establishing the colloid chemistry research group at the University of Wisconsin. | 7 | Physical Chemistry |
Psychrotrophic microbes are able to grow at temperatures below , but have better growth rates at higher temperatures. Psychrotrophic bacteria and fungi are able to grow at refrigeration temperatures, and can be responsible for food spoilage and as foodborne pathogens such as Yersinia. They provide an estimation of the product's shelf life, but also they can be found in soils, in surface and deep sea waters, in Antarctic ecosystems, and in foods.
Psychrotrophic bacteria are of particular concern to the dairy industry. Most are killed by pasteurization; however, they can be present in milk as post-pasteurization contaminants due to less than adequate sanitation practices. According to the Food Science Department at Cornell University, psychrotrophs are bacteria capable of growth at temperatures at or less than . At freezing temperatures, growth of psychrotrophic bacteria becomes negligible or virtually stops.
All three subunits of the RecBCD enzyme are essential for physiological activities of the enzyme in the Antarctic Pseudomonas syringae, namely, repairing of DNA damage and supporting the growth at low temperature. The RecBCD enzymes are exchangeable between the psychrophilic P. syringae and the mesophilic E. coli when provided with the entire protein complex from same species. However, the RecBC proteins (RecBCPs and RecBCEc) of the two bacteria are not equivalent; the RecBCEc is proficient in DNA recombination and repair, and supports the growth of P. syringae at low temperature, while RecBCPs is insufficient for these functions. Finally, both helicase and nuclease activity of the RecBCDPs are although important for DNA repair and growth of P. syringae at low temperature, the RecB-nuclease activity is not essential in vivo. | 1 | Biochemistry |
Schwartz's reagent is the common name for the organozirconium compound with the formula (CH)ZrHCl, sometimes called zirconocene hydrochloride or zirconocene chloride hydride, and is named after Jeffrey Schwartz, a chemistry professor at Princeton University. This metallocene is used in organic synthesis for various transformations of alkenes and alkynes. | 0 | Organic Chemistry |
Rutherford backscattering spectrometry (RBS) is an analytical technique used in materials science. Sometimes referred to as high-energy ion scattering (HEIS) spectrometry, RBS is used to determine the structure and composition of materials by measuring the backscattering of a beam of high energy ions (typically protons or alpha particles) impinging on a sample. | 7 | Physical Chemistry |
The chemical components of orcein were elucidated only in the 1950s by Hans Musso. The structures are shown below. A paper originally published in 1961, embodying most of Musso's work on components of orcein and litmus, was translated into English and published in 2003 in a special issue of the journal Biotechnic & Histochemistry (Vol 78, No. 6) devoted to the dye. A single alternative structural formula for orcein, possibly incorrect, is given by the National Library of Medicine and Emolecules.
Orcein is a reddish-brown dye, orchil is a purple-blue dye. Orcein is also used as a stain in microscopy to visualize chromosomes, elastic fibers, Hepatitis B surface antigens, and copper-associated proteins.
Orcein is not approved as a food dye (banned in Europe since January 1977), with E number E121 before 1977 and E182 after. Its CAS number is . Its chemical formula is CHNO. It forms dark brown crystals. It is a mixture of phenoxazone derivates - hydroxyorceins, aminoorceins, and aminoorceinimines. | 3 | Analytical Chemistry |
Perstraction is the separation technique developed from liquid-liquid extraction. Due to the presence of the membrane a wider selection of extractants can be used, this can include the use of miscible solutions, for example the recovery of ammonia from waste water using sulphuric acid.
This process is analogous to pervaporation in some ways. But the permeate is in liquid phase. Perstraction technique eliminates the problem of phase dispersion and separation altogether.
A basic perstraction is called the single perstraction or membrane perstraction. An advantage is minimizing toxic damage to microorganisms or enzymes. Nevertheless, perstraction includes problems like expensive membranes, clogging and fouling of membranes. | 3 | Analytical Chemistry |
Important derivatives of tartaric acid include:
*Sodium ammonium tartrate, the first material separated into its enantiomers
*cream of tartar (potassium bitartrate), used in cooking
*Rochelle salt (potassium sodium tartrate), which has unusual optical properties
*tartar emetic (antimony potassium tartrate), a resolving agent. Diisopropyl tartrate is used as a co-catalyst in asymmetric synthesis.
Tartaric acid is a muscle toxin, which works by inhibiting the production of malic acid, and in high doses causes paralysis and death. The median lethal dose (LD) is about 7.5 grams/kg for a human, 5.3 grams/kg for rabbits, and 4.4 grams/kg for mice. Given this figure, it would take over to kill a person weighing with 50% probability, so it may be safely included in many foods, especially sour-tasting sweets. As a food additive, tartaric acid is used as an antioxidant with E number E334; tartrates are other additives serving as antioxidants or emulsifiers.
When cream of tartar is added to water, a suspension results which serves to clean copper coins very well, as the tartrate solution can dissolve the layer of copper(II) oxide present on the surface of the coin. The resulting copper(II)-tartrate complex is easily soluble in water. | 4 | Stereochemistry |
The U.S. National Academy of Medicine (NAM), on behalf of both the U.S. and Canada, sets Dietary Reference Intakes, including Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs), or Adequate Intakes (AIs) for when there is not sufficient information to set EARs and RDAs.
For both males and females under 9 years of age, the AIs for potassium are: 400mg of potassium for 0 to 6-month-old infants, 860mg of potassium for 7 to 12-month-old infants, 2,000mg of potassium for 1 to 3-year-old children, and 2,300mg of potassium for 4 to 8-year-old children.
For males 9 years of age and older, the AIs for potassium are: 2,500mg of potassium for 9 to 13-year-old males, 3,000mg of potassium for 14 to 18-year-old males, and 3,400mg for males that are 19 years of age and older.
For females 9 years of age and older, the AIs for potassium are: 2,300mg of potassium for 9 to 18-year-old females, and 2,600mg of potassium for females that are 19 years of age and older.
For pregnant and lactating females, the AIs for potassium are: 2,600mg of potassium for 14 to 18-year-old pregnant females, 2,900mg for pregnant females that are 19 years of age and older; furthermore, 2,500mg of potassium for 14 to 18-year-old lactating females, and 2,800mg for lactating females that are 19 years of age and older. As for safety, the NAM also sets tolerable upper intake levels (ULs) for vitamins and minerals, but for potassium the evidence was insufficient, so no UL was established.
In 2019, the National Academies of Sciences, Engineering, and Medicine revised the Adequate Intake for potassium to 2,600 mg/day for females 19 years of age and older who are not pregnant or lactating, and 3,400 mg/day for males 19 years of age and older.
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 defined the same as in United States. For people ages 15 and older the AI is set at 3,500 mg/day. AIs for pregnancy is 3,500 mg/day, for lactation 4,000 mg/day. For children ages 1–14 years the AIs increase with age from 800 to 2,700 mg/day. These AIs are lower than the U.S. RDAs. The EFSA reviewed the same safety question and decided that there was insufficient data to establish a UL for potassium. | 1 | Biochemistry |
Magnesium alloys. A putative flux for soldering these alloys at low temperature is molten acetamide. Acetamide dissolves surface oxides on both aluminium and magnesium; promising experiments were done with its use as a flux for a tin-indium solder on magnesium. | 8 | Metallurgy |
The nucleosome repeat length, (NRL) is the average distance between the centers of neighboring nucleosomes. NRL is an important physical chromatin property that determines its biological function. NRL can be determined genome-wide for the chromatin in a given cell type and state, or locally for a large enough genomic region containing several nucleosomes.
In chromatin, neighbouring nucleosomes are separated by the linker DNA and in many cases also by the linker histone H1 as well as non-histone proteins. Since the size of the nucleosome is typically fixed (146-147 base pairs), NRL is mostly determined by the size of the linker region between nucleosomes. Alternatively, partial DNA unwrapping from the histone octamer or partial disassembly of the histone octamer can decrease the effective nucleosome size and thus affect NRL.
Past studies going back to 1970s showed that, in general, NRL is different for different species and even for different cell types of the same organism. In addition, recent publications reported NRL variations for different genomic regions of the same cell type.
Recent works have compared the NRL around yeast transcription start sites (TSSs) in vivo and that for the reconstituted chromatin on the same DNA sequences in vitro. It was shown that ordered nucleosome positioning arises only in the presence of ATP-dependent chromatin remodeling. Furthermore, it was reported that the NRL determined around yeast TSSs is an invariant value universal for a given wild type yeast strain, although it can change when one of chromatin remodelers is missing. In general, NRL depends on the DNA sequence, concentrations of histones and non-histone proteins, as well as long-range interactions between nucleosomes. NRL determines geometric properties of the nucleosome array, and therefore the higher-order packing of the DNA into the chromatin fiber, which might affect gene expression. | 1 | Biochemistry |
Transketolase is widely expressed in a wide range of organisms including bacteria, plants, and mammals. The following human genes encode proteins with transketolase activity:
* TKT (transketolase)
* TKTL1 (transketolase-like protein 1)
* TKTL2 (transketolase-like protein 2) | 5 | Photochemistry |
In 1975, Draper's house, known as the Henry Draper Observatory, in Hastings was designated a National Historic Landmark.
In 1976, New York University founded the John W. Draper Interdisciplinary Master's Program in Humanities and Social Thought (Draper Program) in honor of his lifelong commitment to interdisciplinary study.
In 2001, Draper and the founding of the American Chemical Society were designated a National Historic Chemical Landmark at New York University. | 5 | Photochemistry |
The C:N ratio of mixed feedstocks is calculated by summing their C and N amounts together and dividing the two results. For compost, moisture is also an important factor. | 9 | Geochemistry |
Integration of SBUs into a covalent framework results in the synergistic emergence of conductivities much greater than the monomeric values. The nature of the SBUs can improve conductivity. Through the use of highly conjugated linkers throughout the COF scaffold, the material can be engineered to be fully conjugated, enabling high charge carrier density as well as through- and in-plane charge transport. For instance, Mirica and coworkers synthesized a COF material (NiPc-Pyr COF) from nickel phthalocyanine (NiPc) and pyrene organic linkers that had a conductivity of 2.51 x 10 S/m, which was several orders of magnitude larger than the undoped molecular NiPc, 10 S/m. A similar COF structure made by Jiang and coworkers, CoPc-Pyr COF, exhibited a conductivity of 3.69 x 10 S/m. In both previously mentioned COFs, the 2D lattice allows for full π-conjugation in the x and y directions as well as π-conduction along the z axis due to the fully conjugated, aromatic scaffold and π-π stacking, respectively. Emergent electrical conductivity in COF structures is especially important for applications such as catalysis and energy storage where quick and efficient charge transport is required for optimal performance. | 6 | Supramolecular Chemistry |
In a variety of animal models, PEA seems to have some promise; researchers have been able to demonstrate relevant clinical efficacy in a variety of disorders, from multiple sclerosis to neuropathic pain.
In the mouse forced swimming test, palmitoylethanolamide was comparable to fluoxetine for depression. An Italian study published in 2011 found that PEA reduced the raised intraocular pressure of glaucoma. In a spinal trauma model, PEA reduced the resulting neurological deficit via the reduction of mast cell infiltration and activation. PEA in this model also reduced the activation of microglia and astrocytes. Its activity as an inhibitor of inflammation counteracts reactive astrogliosis induced by beta-amyloid peptide, in a model relevant for neurodegeneration, probably via the PPAR-α mechanism of action. In models of stroke and other CNS trauma, PEA exerted neuroprotective properties. | 1 | Biochemistry |
The thanatotranscriptome denotes all RNA transcripts produced from the portions of the genome still active or awakened in the internal organs of a body following its death. It is relevant to the study of the biochemistry, microbiology, and biophysics of thanatology, in particular within forensic science. Some genes may continue to be expressed in cells for up to 48 hours after death, producing new mRNA. Certain genes that are generally inhibited since the end of fetal development may be expressed again at this time. | 1 | Biochemistry |
Cosmid vectors are plasmids that contain a small region of bacteriophage λ DNA called the cos sequence. This sequence allows the cosmid to be packaged into bacteriophage λ particles. These particles- containing a linearized cosmid- are introduced into the host cell by transduction. Once inside the host, the cosmids circularize with the aid of the host's DNA ligase and then function as plasmids. Cosmids are capable of carrying inserts up to 40kb in size. | 1 | Biochemistry |
*1990 Günter Snatzke, Germany
*1991 Hannes Aiginger, Austria; Peter Wobrauschek]], Austria; Joachim Knoth]], Germany; Heinrich Schwenke]], Germany
*1992 Kurt Laqua, Germany; Arnulf Röseler]], Germany
*1993 Boris L'vov, Russia
*1994 D. Bruce Chase, United States; W. J. Orville-Thomas, Great Britain
*1995 Paul W.J.M. Boumans, Netherlands
*1998 Annemie Bogaerts, Belgium
*2000 Dieter Fischer, Germany
*2001 John A. McLean, United States
*2002 Jürgen Popp, Germany
*2003 Sergei Boulyga, Germany
*2004 Ewa Bulska, Poland
*2005 Nicolas Bings, Germany
*2006 Volker Deckert, Germany
*2007 Jörg Bettmer, Germany
*2008 Sebastian Schlücke, Germany
*2009 Joachim Koch, Switzerland
*2010 Janina Kneipp, Germany
*2011 Daniel Pröfrock, Germany
*2012 Christoph Haisch, Germany
*2013 Maria Montes-Bayón, Spain
*2014 Oliver Reich, Germany
*2015 Martín Resano, Spain
*2016 Torsten Frosch, Germany
*2017 Jacob T. Shelley, United States
*2018 , Hungary
*2020 Natalia P. Ivleva
*2022 Carlos Abad Andrade | 3 | Analytical Chemistry |
Combination simply means that two radicals are joined together, destroying the radical character of each and forming one polymeric chain. With no chain transfer, the average degree of polymerization is then twice the average kinetic chain length | 7 | Physical Chemistry |
Thomas Gilbert Henry Jones was born on 14 July 1895 in Owens Gap, Hunter Valley, New South Wales, the son of Thomas Jones a schoolteacher and his wife Margaret Bell. He attended Newcastle High School where he won prizes in his Junior and Senior years. He entered the University of Sydney in 1912 where he studied his B.Sc graduating with first class honours in mathematics and chemistry in 1915 and winning the Levy Scholarship for chemistry and physics, the Slade Prize for practical chemistry, the Caird Scholarship for chemistry II and the University medals for mathematics and chemistry. In 1915, Jones was awarded a government research scholarship and was appointed an assistant lecturer and demonstrator at the University of Queensland. | 0 | Organic Chemistry |
With a specific gravity greater than 1 (denser than water), trichloroethylene can be present as a dense non-aqueous phase liquid (DNAPL) if sufficient quantities are spilt in the environment.
The first known report of TCE in groundwater was given in 1949 by two English public chemists who described two separate instances of well contamination by industrial releases of TCE. Based on available federal and state surveys, between 9% and 34% of the drinking water supply sources tested in the US may have some TCE contamination, though EPA has reported that most water supplies comply with the maximum contaminant level (MCL) of 5 ppb.
Generally, atmospheric levels of TCE are highest in areas of concentrated industry and population. Atmospheric levels tend to be lowest in rural and remote regions. Average TCE concentrations measured in air across the United States are generally between 0.01 ppb and 0.3 ppb, although mean levels as high as 3.4 ppb have been reported. TCE levels in the low parts per billion range have been measured in food; however, levels as high as 140 ppb were measured in a few samples of food. TCE levels above background have been found in homes undergoing renovation. | 2 | Environmental Chemistry |
While a verdant Arctic Ocean is a viable working model, skeptical scientists point out that it would be possible for Azolla colonies in river deltas or freshwater lagoons to be swept into the Arctic Ocean by strong currents, removing the necessity for a freshwater layer. | 2 | Environmental Chemistry |
A major application of photochlorination is the production of chloroparaffins. Mixtures of complex composition consisting of several chlorinated paraffins are formed. Chlorinated paraffins have the general sum formula CHCl and are categorized into three groups: Low molecular weight chlorinated paraffins are short chain chloroparaffins (SCCP) with 10 to 13 carbon atoms, followed by medium chain chloroparaffins (MCCP) with carbon chain lengths of 14 to 17 carbon atoms and long chain chlorinated paraffins (LCCP), owing a carbon chainwith more than 17 carbon atoms. Approximately 70% of the chloroparaffins produced are MCCPs with a degree of chlorination from 45 to 52%. The remaining 30% are divided equally between SCCP and LCCP. Short chain chloroparaffins have high toxicity and easily accumulate in the environment. The European Union has classified SCCP as a category III carcinogen and restricted its use.
In 1985 the world production was 300,000 tonnes; since then the production volumes are falling in Europe and North America. In China, on the other hand, production rose sharply. China produced more than 600,000 tonnes of chlorinated paraffins in 2007, while in 2004 it was less than 100,000 tonnes.
The quantum yield for the photochlorination of n-heptane is about 7000, for example. In photochlorination plants, the quantum yield is about 100. In contrast to the thermal chlorination, which can utilize the formed reaction energy, the energy required to maintain the photochemical reaction must be constantly delivered.
The presence of inhibitors, such as oxygen or nitrogen oxides, must be avoided. Too high chlorine concentrations lead to high absorption near the light source and have a disadvantageous effect. | 5 | Photochemistry |
After two years of post-doctoral research with Merle Battiste at the University of Florida, where he worked on small ring chemistry, Halton was appointed as a faculty member in the Department of Chemistry at Victoria University of Wellington in 1968, eventually rising to become a full professor. When he retired in 2004, he was conferred the title of professor emeritus.
Haltons research was centred on the synthesis and investigation of highly strained and fused aromatic compounds and their unstable cyclopropanated derivatives, known as cycloproparenes, which included highly strained didehydrobenzenes and some exceptionally fluorescent compounds. in 1987, Halton was conferred with the degree of Doctor of Science by Victoria University of Wellington, on the basis of his submission of 57 papers, collectively titled Studies of some strained organic molecules', published between 1971 and 1987.
Halton was active in the New Zealand Institute of Chemistry (NZIC), serving as chair of the Wellington branch, editor of Chemistry in New Zealand between 2002 and 2012, and president of the NZIC from 1986 to 1987. He represented New Zealand on the organising committee of Pacifichem, the international chemical congress of Pacific basin societies, for 18 years. | 0 | Organic Chemistry |
Aminoxyl denotes a radical functional group with general structure RN–O. It is commonly known as a nitroxyl radical or a nitroxide, however IUPAC discourages the use of these terms, as they erroneously suggest the presence of a nitro group. Aminoxyls are structurally related to hydroxylamines and N-oxoammonium salts, with which they can interconvert via a series of redox steps.
Sterically unhindered aminoxyls bearing α-hydrogens are unstable and undergo rapid disproportionation to nitrones and hydroxylamines. Sterically hindered aminoxyls without α-hydrogens, such TEMPO and TEMPOL, and are persistent (stable) radicals and find use in a range of applications, both on the laboratory scale and in industry. Their ability to reversibly bind to other radical compounds makes them important as both spin labels and spin traps. They are used to selectively oxidise carbonyl groups via oxoammonium-catalyzed oxidations. They are also used as polymer stabilizers such as hindered amine light stabilizers or as transient reactive species in p-phenylenediamine based antiozonants. They are used both to form polymers via nitroxide-mediated radical polymerization and prevent their formation as polymerization inhibitors. Various other reagents, such as N-hydroxyphthalimide can also be converted into aminoxyl radicals as part of their chemistry. | 0 | Organic Chemistry |
While chemically pure materials have a single melting point, chemical mixtures often partially melt at the solidus temperature (T or T), and fully melt at the higher liquidus temperature (T or T). The solidus is always less than or equal to the liquidus, but they need not coincide. If a gap exists between the solidus and liquidus it is called the freezing range, and within that gap, the substance consists of a mixture of solid and liquid phases (like a slurry). Such is the case, for example, with the olivine (forsterite-fayalite) system, which is common in Earth's mantle. | 7 | Physical Chemistry |
Marine Chemistry is an international peer-reviewed scientific journal for publications in the field of chemistry in the marine environment. The journal is currently published by Elsevier. Its editor-in-chief is T.S. Bianchi. According to the Journal Citation Reports, Marine Chemistry has a 2020 impact factor of 3.807. | 9 | Geochemistry |
This phenomenon was first described by Snow and Frey in 1943. The thermodynamic explanation is due to Frederick Dainton and K. J. Ivin, who proposed that the chain propagation step of the polymerization is reversible.
At the ceiling temperature, there will always be excess monomers in the polymer due to the equilibrium between polymerization and depolymerization. Polymers derived from simple vinyl monomers have such high ceiling temperatures that only a small amount of monomers remain in the polymer at ordinary temperatures. The situation for α-methylstyrene, PhC(Me)=CH, is an exception to this trend. Its ceiling temperature is around 66 °C. Steric hindrance is significant in polymers derived from α-methylstyrene because the phenyl and methyl groups are bonded to the same carbon. These steric effects in combination with stability of the tertiary benzylic α-methylstyryl radical give α-methylstyrene its relatively low ceiling temperature. When a polymer has a very high ceiling temperature, it degrades via bond cleavage reactions instead of depolymerization. A similar effect explains the relatively low ceiling temperature for polyisobutylene. | 7 | Physical Chemistry |
Changing the concentration of a chemical will shift the equilibrium to the side that would counter that change in concentration. The chemical system will attempt to partly oppose the change affected to the original state of equilibrium. In turn, the rate of reaction, extent, and yield of products will be altered corresponding to the impact on the system.
This can be illustrated by the equilibrium of carbon monoxide and hydrogen gas, reacting to form methanol.
:CO + 2 H ⇌ CHOH
Suppose we were to increase the concentration of CO in the system. Using Le Chatelier's principle, we can predict that the concentration of methanol will increase, decreasing the total change in CO. If we are to add a species to the overall reaction, the reaction will favor the side opposing the addition of the species. Likewise, the subtraction of a species would cause the reaction to "fill the gap" and favor the side where the species was reduced. This observation is supported by the collision theory. As the concentration of CO is increased, the frequency of successful collisions of that reactant would increase also, allowing for an increase in forward reaction, and generation of the product. Even if the desired product is not thermodynamically favored, the end-product can be obtained if it is continuously removed from the solution.
The effect of a change in concentration is often exploited synthetically for condensation reactions (i.e., reactions that extrude water) that are equilibrium processes (e.g., formation of an ester from carboxylic acid and alcohol or an imine from an amine and aldehyde). This can be achieved by physically sequestering water, by adding desiccants like anhydrous magnesium sulfate or molecular sieves, or by continuous removal of water by distillation, often facilitated by a Dean-Stark apparatus. | 7 | Physical Chemistry |
In 1961, Israeli archaeologist Pessah Bar-Adon discovered a hoard of Chalcolithic artifacts in a cave on the northern side of Nahal Mishmar, known since as the Treasure Cave. The hoard consisted of 442 decorated objects made of copper and bronze (429 of them), ivory and stone, including 240 mace heads, about 100 scepters, 5 crowns, powder horns, tools and weapons. Archaeologist David Ussishkin has suggested the hoard was the cultic furniture of the abandoned Chalcolithic Temple of Ein Gedi. Prominent finds from the hoard are currently on display in the archaeology wing of the Israel Museum in Jerusalem.
Items in the hoard belong to the Ghassulian culture and the Nahal Mishmar hoard is the only hoard of this culture. It is probable that the copper used for producing them was mined in Wadi Feynan.
Due to the dry climate numerous textile and plaited remains were found at the site. The remains of over 20 individuals were found in the caves. They were members of a sedentary Chalcolithic population who became refugees and their lives ended under tragic circumstances which is indicated by the fact they had numerous injuries and that the wrappings were stained with blood.
Many of these copper objects were made using the lost-wax process, one of the earliest known uses of this complex technique. Carbon-14 dating of the reed mat which was used to wrap the objects points that it was used circa 3500 B.C.E. During this period the use of copper became widespread throughout the Levant which also led to social changes in the region. | 8 | Metallurgy |
Carnivory in plants has evolved at least six times independently, some examples include the Venus flytrap, pitcher plant, and butterwort. Although many outside of the scientific community usually believe these plants excel in defenses, many of these plants have evolved in poor nutrient soil. In order to get sufficient nutrients in these conditions they must use an alternative method. They use insects and small birds as a way to gain the minerals they need through carnivory. Carnivorous plants do not use carnivory as self-defense, but to get the nutrients they need. | 1 | Biochemistry |
Uroguanylin is a 16 amino acid peptide that is secreted by enterochromaffin cells in the duodenum and proximal small intestine. Guanylin acts as an agonist of the guanylyl cyclase receptor guanylate cyclase 2C (GC-C), and regulates electrolyte and water transport in intestinal and renal epithelia. By agonizing this guanylyl cyclase receptor, uroguanylin and guanylin cause intestinal secretion of chloride and bicarbonate to dramatically increase; this process is helped by the second messenger cGMP. Its sequence is H-Asn-Asp-Asp-Cys(1)-Glu-Leu-Cys(2)-Val-Asn-Val-Ala-Cys(1)-Thr-Gly-Cys(2)-Leu-OH.
In humans, the uroguanylin peptide is encoded by the GUCA2B gene. Uroguanylin may be involved in appetite and perceptions of fullness after eating meals, as suggested by a study into mice. | 1 | Biochemistry |
All living cells have the ability to receive and process signals that originate outside their membranes, which they do by means of proteins called receptors, often located at the cells surface imbedded in the plasma membrane. When such signals interact with a receptor, they effectively direct the cell to do something, such as dividing, dying, or allowing substances to be created, or to enter or exit the cell. A cells ability to respond to a chemical message depends on the presence of receptors tuned to that message. The more receptors a cell has that are tuned to the message, the more the cell will respond to it.
Receptors are created, or expressed, from instructions in the DNA of the cell, and they can be increased, or upregulated, when the signal is weak, or decreased, or downregulated, when it is strong. Their level can also be up or down regulated by modulation of systems that degrade receptors when they are no longer required by the cell.
Downregulation of receptors can also occur when receptors have been chronically exposed to an excessive amount of a ligand, either from endogenous mediators or from exogenous drugs. This results in ligand-induced desensitization or internalization of that receptor. This is typically seen in animal hormone receptors. Upregulation of receptors, on the other hand, can result in super-sensitized cells, especially after repeated exposure to an antagonistic drug or prolonged absence of the ligand.
Some receptor agonists may cause downregulation of their respective receptors, while most receptor antagonists temporarily upregulate their respective receptors. The disequilibrium caused by these changes often causes withdrawal when the long-term use of a drug is discontinued.
Upregulation and downregulation can also happen as a response to toxins or hormones. An example of upregulation in pregnancy is hormones that cause cells in the uterus to become more sensitive to oxytocin. | 1 | Biochemistry |
The Mesozoic is well known for its distinct Ocean Anoxic Events (OAEs) which resulted in the burial of layers of black shale. Although these OAEs are not stand alone evidence for euxinia, many do contain biomarkers which support euxinic formation. Again, evidence is not universal. OAEs may have spurred the spread of existing euxinia, especially in upwelling regions or semi-restricted basins, but photic zone euxinia did not happen everywhere. | 9 | Geochemistry |
A pepper-spray projectile, also called a pepper-spray ball, pepper-ball, pepper bomb, or pepper-spray pellet, is a frangible projectile containing a powdered chemical that irritates the eyes and nose in a manner similar to pepper spray. These projectiles are fired from specially designed forced compliance weapons or modified paintball guns. | 1 | Biochemistry |
Bekbölet joined the faculty at Boğaziçi University in 1985 as an instructor in the Institute of Environmental Sciences. She was promoted to assistant professor in 1986, associate professor in 1991 and professor in 1997.
Bekbölet's researches oxidation techniques, photocatalytic and photolytic reactions, adsorption/bio-oxidation processes in aquatic systems, and drinking water quality. | 5 | Photochemistry |
Cryoablation of tumor induces necrosis of tumor cells. The immunotherapeutic effect of cryoablation of tumor is the result of the release of intracellular tumor antigens from within the necrotized tumor cells. The released tumor antigens help activate anti-tumor T cells, which destroy remaining malignant cells. Thus, cryoablation of tumor elicits a systemic anti-tumor immunologic response.
The resulting immunostimulation from cryoablation may not be sufficient to induce sustained, systemic regression of metastases, and can be synergised with the combination of immunotherapy treatment and vaccine adjuvants.
Various adjuvant immunotherapy and chemotherapy treatments can be combined with cryoablation to sustain systemic anti-tumor response with regression of metastases, including:
* Injection of immunomodulating drugs (i.e.: therapeutic antibodies) and vaccine adjuvants (saponins) directly into the cryoablated, necrotized tumor lysate, immediately after cryoablation
* Administration of autologous immune enhancement therapy, including: dendritic cell therapy, CIK cell therapy | 1 | Biochemistry |
While new production of these refrigerants has been banned, large volumes still exist in older systems and have been said to pose an immediate threat to our environment. Preventing the release of these harmful refrigerants has been ranked as one of the single most effective actions we can take to mitigate catastrophic climate change. | 2 | Environmental Chemistry |
HeAR is expressed by Halorubrum ejinorense. The organism was first isolated from Lake Ejinor in Inner Mongolia, China. | 5 | Photochemistry |
The maximum-term method is a consequence of the large numbers encountered in statistical mechanics. It states that under appropriate conditions the logarithm of a summation is essentially equal to the logarithm of the maximum term in the summation.
These conditions are (see also proof below) that (1) the number of terms in the sum is large and (2) the terms themselves scale exponentially with this number. A typical application is the calculation of a thermodynamic potential from a partition function. These functions often contain terms with factorials which scale as (Stirling's approximation). | 7 | Physical Chemistry |
The convergence of observed BD angles can be viewed as arising from the need to maximize overlap between the highest occupied molecular orbital (HOMO) of the nucleophile, and the lowest unoccupied molecular orbital (LUMO) of the unsaturated, trigonal center of the electrophile. (See, in comparison, the related inorganic chemistry concept of the angular overlap model.)
In the case of addition to a carbonyl, the HOMO is often a p-type orbital (e.g., on an amine nitrogen or halide anion), and the LUMO is generally understood to be the antibonding π* molecular orbital perpendicular to the plane containing the ketone C=O bond and its substituents (see figure at right above). The BD angle observed for nucleophilic attack is believed to approach the angle that would produce optimal overlap between HOMO and LUMO (based on the principle of the lowering of resulting new molecular orbital energies after such mixing of orbitals of similar energy and symmetry from the participating reactants). At the same time, the nucleophile avoids overlap with other orbitals of the electrophilic group that are unfavorable for bond formation (not apparent in image at right, above, because of the simplicity of the R=R'=H in formaldehyde). | 7 | Physical Chemistry |
Atmospheric concentrations fluctuate slightly with the seasons, falling during the Northern Hemisphere spring and summer as plants consume the gas and rising during northern autumn and winter as plants go dormant or die and decay. The level drops by about 6 or 7 ppm (about 50 Gt) from May to September during the Northern Hemisphere's growing season, and then goes up by about 8 or 9 ppm. The Northern Hemisphere dominates the annual cycle of concentration because it has much greater land area and plant biomass than the Southern Hemisphere. Concentrations reach a peak in May as the Northern Hemisphere spring greenup begins, and decline to a minimum in October, near the end of the growing season.
Concentrations also vary on a regional basis, most strongly near the ground with much smaller variations aloft. In urban areas concentrations are generally higher and indoors they can reach 10 times background levels. | 2 | Environmental Chemistry |
The folded protein complexes of interest separate cleanly and predictably without the risk of denaturation due to the specific properties of the polyacrylamide gel, electrophoresis buffer solution, electrophoretic equipment and standardized parameters used. The separated proteins are continuously eluted into a physiological eluent and transported to a fraction collector. In four to five PAGE fractions each the different metal cofactors can be identified and absolutely quantified by high-resolution ICP-MS. The associated structures of the isolated metalloproteins in these fractions can be specifically determined by solution NMR spectroscopy. | 1 | Biochemistry |
* Can be made from any organic material using proven technology going through syngas. There is no need to use food crops and compete with food production. The amount of methanol that can be generated from biomass is much greater than ethanol.
* Can compete with and complement ethanol in a diversified energy marketplace. Methanol obtained from fossil fuels has a lower price than ethanol.
* Can be blended in gasoline like ethanol. In 2007, China blended more than of methanol into fuel and will introduce methanol fuel standard by mid-2008. M85, a mixture of 85% methanol and 15% gasoline can be used much like E85 sold in some gas stations today. | 2 | Environmental Chemistry |
Nonenzymatic peroxidation occurs through the action of reactive oxygen species (ROS), specifically hydroxyl (HO) and hydroperoxyl (HO) radicals, which initiate the oxidation of polyunsaturated fatty acids. Other initiators of lipid peroxidation include ozone (O), nitrogen oxide (NO), nitrogen dioxide (NO), and sulfur dioxide. The process of nonenzymatic peroxidation can be divided into three phases: initiation, propagation, and termination.
During the initiation phase, fatty acid radicals are generated, which can propagate peroxidation to other molecules. This occurs when a free radical removes a hydrogen atom from a fatty acid, resulting in a lipid radical (L) with an unpaired electron.
In the propagation phase, the lipid radical reacts with oxygen (O) or a transition metal, forming a peroxyl radical (LOO). This peroxyl radical continues the chain reaction by reacting with a new unsaturated fatty acid, producing a new lipid radical (L) and lipid hydroperoxide (LOOH). These primary products can further decompose into secondary products.
The termination phase involves the interaction of a radical with an antioxidant molecule, such as α-tocopherol (vitamin E), which inhibits the propagation of chain reactions, thus terminating peroxidation. Another method of termination is the reaction between a lipid radical and a lipid peroxide, or the combination of two lipid peroxide molecules, resulting in stable nonreactive molecules. Reinforced lipids that become part of the membrane if consumed with heavy isotope diet also inhibit peroxidation. | 1 | Biochemistry |
With an appropriate exercise program, dietary supplementation with 3 grams of HMB per day has been shown to increase exercise-induced gains in muscle size, muscle strength and power, and lean body mass, reduce exercise-induced skeletal muscle damage, and expedite recovery from high-intensity exercise. Based upon limited clinical research, HMB supplementation may also improve aerobic exercise performance and increase gains in aerobic fitness when combined with high-intensity interval training. These effects of HMB are more pronounced in untrained individuals and athletes who perform high intensity resistance or aerobic exercise. In resistance-trained populations, the effects of HMB on muscle strength and lean body mass are limited. HMB affects muscle size, strength, mass, power, and recovery in part by stimulating myofibrillar muscle protein synthesis and inhibiting muscle protein breakdown through various mechanisms, including the activation of mechanistic target of rapamycin complex 1 (mTORC1) and inhibition of proteasome-mediated proteolysis in skeletal muscles.
The efficacy of HMB supplementation for reducing skeletal muscle damage from prolonged or high-intensity exercise is affected by the time that it is used relative to exercise. The greatest reduction in skeletal muscle damage from a single bout of exercise has been shown to occur when is ingested hours prior to exercise or is ingested minutes prior to exercise.
In 2006, only about 2% of college student athletes in the United States used HMB as a dietary supplement. As of 2017, HMB has found widespread use as an ergogenic supplement among athletes. HMB has not been banned by the National Collegiate Athletic Association, World Anti-Doping Agency, or any other prominent national or international athletic organization. | 1 | Biochemistry |
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic, stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time. The satellite view of weather around Robinson Crusoe Islands illustrates one example. | 7 | Physical Chemistry |
Spontaneous absolute asymmetric synthesis is a chemical phenomenon that stochastically generates chirality based on autocatalysis and small fluctuations in the ratio of enantiomers present in a racemic mixture. In certain reactions which initially do not contain chiral information, stochastically distributed enantiomeric excess can be observed. The phenomenon is different from chiral amplification, where enantiomeric excess is present from the beginning and not stochastically distributed. Hence, when the experiment is repeated many times, the average enantiomeric excess approaches 0%. The phenomenon has important implications concerning the origin of homochirality in nature. | 4 | Stereochemistry |
carbon fixation is the most common of three metabolic pathways for carbon fixation in photosynthesis, the other two being C4 carbon fixation| and CAM. This process converts carbon dioxide and ribulose bisphosphate (RuBP, a 5-carbon sugar) into two molecules of 3-phosphoglycerate through the following reaction:
:CO + HO + RuBP → (2) 3-phosphoglycerate
This reaction was first discovered by Melvin Calvin, Andrew Benson and James Bassham in 1950. C carbon fixation occurs in all plants as the first step of the Calvin–Benson cycle. (In and CAM plants, carbon dioxide is drawn out of malate and into this reaction rather than directly from the air.)
Plants that survive solely on fixation ( plants) tend to thrive in areas where sunlight intensity is moderate, temperatures are moderate, carbon dioxide concentrations are around 200 ppm or higher, and groundwater is plentiful. The plants, originating during Mesozoic and Paleozoic eras, predate the C4 carbon fixation| plants and still represent approximately 95% of Earth's plant biomass, including important food crops such as rice, wheat, soybeans and barley.
plants cannot grow in very hot areas at today's atmospheric CO level (significantly depleted during hundreds of millions of years from above 5000 ppm) because RuBisCO incorporates more oxygen into RuBP as temperatures increase. This leads to photorespiration (also known as the oxidative photosynthetic carbon cycle, or C2 photosynthesis), which leads to a net loss of carbon and nitrogen from the plant and can therefore limit growth.
plants lose up to 97% of the water taken up through their roots by transpiration. In dry areas, plants shut their stomata to reduce water loss, but this stops from entering the leaves and therefore reduces the concentration of in the leaves. This lowers the :O ratio and therefore also increases photorespiration. and CAM plants have adaptations that allow them to survive in hot and dry areas, and they can therefore out-compete plants in these areas.
The isotopic signature of plants shows higher degree of C depletion than the plants, due to variation in fractionation of carbon isotopes in oxygenic photosynthesis across plant types. Specifically, plants do not have PEP carboxylase like plants, allowing them to only utilize ribulose-1,5-bisphosphate carboxylase (Rubisco) to fix through the Calvin cycle. The enzyme Rubisco largely discriminates against carbon isotopes, evolving to only bind to C isotope compared to C (the heavier isotope), attributing to why there's a low C depletion seen in plants compared to plants especially since the pathway uses PEP carboxylase in addition to Rubisco. | 5 | Photochemistry |
Biochemistry laboratories often use in vitro studies to explore ATP-dependent molecular processes. ATP analogs are also used in X-ray crystallography to determine a protein structure in complex with ATP, often together with other substrates.
Enzyme inhibitors of ATP-dependent enzymes such as kinases are needed to examine the binding sites and transition states involved in ATP-dependent reactions.
Most useful ATP analogs cannot be hydrolyzed as ATP would be; instead, they trap the enzyme in a structure closely related to the ATP-bound state. Adenosine 5′-(γ-thiotriphosphate) is an extremely common ATP analog in which one of the gamma-phosphate oxygens is replaced by a sulfur atom; this anion is hydrolyzed at a dramatically slower rate than ATP itself and functions as an inhibitor of ATP-dependent processes. In crystallographic studies, hydrolysis transition states are modeled by the bound vanadate ion.
Caution is warranted in interpreting the results of experiments using ATP analogs, since some enzymes can hydrolyze them at appreciable rates at high concentration. | 1 | Biochemistry |
In an Arabidopsis thaliana study, hundreds of different proteins demonstrated the possibility to bind to CaM in plants. | 1 | Biochemistry |
Louis Pasteur a French chemist, supported the idea that fermentation was a biological process. Justus von Liebig, a German chemist, supported the idea that fermentation was a mechanical process. Both chemists had different methods of experimentation, and they focused on different aspects of fermentation because they had different ideas about where the fermentation began in an organism.
The Liebig–Pasteur feud started in 1857 when Pasteur said that fermentation can occur in the absence of oxygen. The two were aware of the other's works, but continued working with their own theories. The two mention each other, as well as other scientists, in articles and other publications about the processes and causes of fermentation. | 1 | Biochemistry |
Pouring metal defects include misruns, cold shuts, and inclusions. A misrun occurs when the liquid metal does not completely fill the mould cavity, leaving an unfilled portion. Cold shuts occur when two fronts of liquid metal do not fuse properly in the mould cavity, leaving a weak spot. Both are caused by either a lack of fluidity in the molten metal or cross-sections that are too narrow. The fluidity can be increased by changing the chemical composition of the metal or by increasing the pouring temperature. Another possible cause is back pressure from improperly vented mould cavities.
Misruns and cold shuts are closely related and both involve the material freezing before it completely fills the mould cavity. These types of defects are serious because the area surrounding the defect is significantly weaker than intended. The castability and viscosity of the material can be important factors with these problems. Fluidity affects the minimum section thickness that can be cast, the maximum length of thin sections, fineness of feasibly cast details, and the accuracy of filling mould extremities. There are various ways of measuring the fluidity of a material, although it usually involves using a standard mould shape and measuring the distance the material flows. Fluidity is affected by the composition of the material, freezing temperature or range, surface tension of oxide films, and, most importantly, the pouring temperature. The higher the pouring temperature, the greater the fluidity; however, excessive temperatures can be detrimental, leading to a reaction between the material and the mould; in casting processes that use a porous mould material the material may even penetrate the mould material.
The point at which the material cannot flow is called the coherency point. The point is difficult to predict in mould design because it is dependent on the solid fraction, the structure of the solidified particles, and the local shear strain rate of the fluid. Usually this value ranges from 0.4 to 0.8.
An inclusion is a metal contamination of dross, if solid, or slag, if liquid. These usually are impurities in the pour metal (generally oxides, less frequently nitrides, carbides, or sulfides), material that is eroded from furnace or ladle linings, or contaminates from the mould. In the specific case of aluminium alloys, it is important to control the concentration of inclusions by measuring them in the liquid aluminium and taking actions to keep them to the required level.
There are a number of ways to reduce the concentration of inclusions. In order to reduce oxide formation the metal can be melted with a flux, in a vacuum, or in an inert atmosphere. Other ingredients can be added to the mixture to cause the dross to float to the top where it can be skimmed off before the metal is poured into the mould. If this is not practical, then a special ladle that pours the metal from the bottom can be used. Another option is to install ceramic filters into the gating system. Otherwise swirl gates can be formed which swirl the liquid metal as it is poured in, forcing the lighter inclusions to the center and keeping them out of the casting. If some of the dross or slag is folded into the molten metal then it becomes an entrainment defect. | 8 | Metallurgy |
First attempts to synthesize 2DPs date back to the 1930s when Gee reported interfacial polymerizations at the air/water interface in which a monolayer of an unsaturated fatty acid derivative was laterally polymerized to give a 2D cross-linked material. Since then a number of important attempts were reported in terms of cross-linking polymerization of monomers confined to layered templates or various interfaces. These approaches provide easy accesses to sheet-like polymers. However, the sheets' internal network structures are intrinsically irregular and the term "repeat unit" is not applicable (See for example:). In organic chemistry, creation of 2D periodic network structures has been a dream for decades. Another noteworthy approach is "on-surface polymerization" whereby 2DPs with lateral dimensions not exceeding some tens of nanometers were reported. Laminar crystals are readily available, each layer of which can ideally be regarded as latent 2DP. There have been a number of attempts to isolate the individual layers by exfoliation techniques (see for example:). | 7 | Physical Chemistry |
Flowability, also known as powder flow is a property that defines an ability of a powdered material to flow, related to cohesion.
Powder flowability depends on many traits:
* the shape and size of the powder particles due to intermolecular force,
* porosity
* electrostatic activity
* hygroscopy
* bulk density
* angle of repose
* presence of glidants
* oxidation rate (of a metallic powder)
* humidity
ISO 4490:2018 norm (and its precedent, ISO 4490:2014) standardizes a method for determining the flow rate of metallic powders. It uses a normalized/calibrated funnel, named Hall flowmeter. | 6 | Supramolecular Chemistry |
FI6 is an antibody that targets a protein found on the surface of all influenza A viruses called hemagglutinin. FI6 is the only known antibody found to bind all 16 subtypes of the influenza A virus hemagglutinin and is hoped to be useful for a universal influenza virus therapy.
The antibody binds to the F domain HA trimer, and prevents the virus from attaching to the host cell. The antibody has been refined in order to remove any excess, unstable mutations that could negatively affect its neutralising ability, and this new version of the antibody has been termed "FI6v3" | 1 | Biochemistry |
Available evidence from geobiological studies of Archean (>2500 Ma) sedimentary rocks indicates that life existed 3500 Ma. Fossils of what are thought to be filamentous photosynthetic organisms have been dated at 3.4 billion years old, consistent with recent studies of photosynthesis. Early photosynthetic systems, such as those from green and purple sulfur and green and purple nonsulfur bacteria, are thought to have been anoxygenic, using various molecules as electron donors. Green and purple sulfur bacteria are thought to have used hydrogen and hydrogen sulfide as electron and hydrogen donors. Green nonsulfur bacteria used various amino and other organic acids. Purple nonsulfur bacteria used a variety of nonspecific organic and inorganic molecules. It is suggested that photosynthesis likely originated at low-wavelength geothermal light from acidic hydrothermal vents, Zn-tetrapyrroles were the first photochemically active pigments, the photosynthetic organisms were anaerobic and relied on without relying on H emitted by alkaline hydrothermal vents. The divergence of anoxygenic photosynthetic organisms at the photic zone could have led to the ability to strip electrons from more efficiently under ultraviolet radiation. There is geochemical evidence that suggests that anaerobic photosynthesis emerged 3.3 to 3.5 billion years ago. The organisms later developed a Chlorophyll F synthase. They could have also stripped electrons from soluble metal ions although it is unknown.
The first oxygenic photosynthetic organisms are proposed to be -dependent. It is also suggested photosynthesis originated under sunlight, using emitted by volcanoes and hydrothermal vents which ended the need for scarce H emitted by alkaline hydrothermal vents. Oxygenic photosynthesis uses water as an electron donor, which is oxidized to molecular oxygen () in the photosynthetic reaction center. The biochemical capacity for oxygenic photosynthesis evolved in a common ancestor of extant cyanobacteria. The first appearance of free oxygen in the atmosphere is sometimes referred to as the oxygen catastrophe. The geological record indicates that this transforming event took place during the Paleoproterozoic era at least 2450–2320 million years ago (Ma), and, it is speculated, much earlier. A clear paleontological window on cyanobacterial evolution opened about 2000 Ma, revealing an already-diverse biota of blue-greens. Cyanobacteria remained principal primary producers throughout the Proterozoic Eon (2500–543 Ma), in part because the redox structure of the oceans favored photoautotrophs capable of nitrogen fixation. Green algae joined blue-greens as major primary producers on continental shelves near the end of the Proterozoic, but only with the Mesozoic (251–65 Ma) radiations of dinoflagellates, coccolithophorids, and diatoms did primary production in marine shelf waters take modern form. Cyanobacteria remain critical to marine ecosystems as primary producers in oceanic gyres, as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine algae. Modern photosynthesis in plants and most photosynthetic prokaryotes is oxygenic. | 5 | Photochemistry |
An overdose of modafinil can lead to a range of symptoms and complications. Psychiatric symptoms may include psychosis, mania, hallucinations, and suicidal ideation, which can occur even in individuals without a history of mental illness and may persist after discontinuation of the drug. Neurological complications, such as seizures, tremors, dystonia, and dyskinesia, may arise from modafinil's interaction with various neurotransmitter systems.
Allergic reactions such as rash, angioedema, anaphylaxis, and Stevens–Johnson syndrome may be triggered by an immunological response to modafinil or its metabolites. Cardiovascular complications like hypertension, tachycardia, chest pain, and arrhythmias may also be observed due to modafinil's sympathomimetic action.
In animal studies, the median lethal dose (LD) of modafinil varies among species and depends on the route of administration. In mice and rats, the LD is approximately if administered via an injection, but the oral LD for rats is . The LD value for humans have not been established. Human clinical trials have involved total daily doses up to for 7–21 days. Acute one-time total overdoses up to have not been life-threatening but resulted in symptoms like agitation, insomnia, tremor, palpitations, and gastrointestinal disturbances.
The management of modafinil overdose involves supportive care, monitoring of vital signs, and treatment of specific complications. In cases of recent consumption, activated charcoal, gastric lavage, or hemodialysis may be used. There is no specific antidote for modafinil overdose. The main way to deal with modafinil overdose is supportive care, which includes sedating the patient and stabilizing their blood pressure, and muscle activity in case of manifestations such as agitation or tremor. | 4 | Stereochemistry |
Steel superalloys are of interest because some present creep and oxidation resistance similar to Ni-based superalloys, at far less cost.
Gamma (γ): Fe-based alloys feature a matrix phase of austenite iron (FCC). Alloying elements include: Al, B, C, Co, Cr, Mo, Ni, Nb, Si, Ti, W, and Y. Al (oxidation benefits) must be kept at low weight fractions (wt.%) because Al stabilizes a ferritic (BCC) primary phase matrix, which is undesirable, as it is inferior to the high temperature strength exhibited by an austenitic (FCC) primary phase matrix.
Gamma-prime (γ): This phase is introduced as precipitates to strengthen the alloy. γ-Ni3Al precipitates can be introduced with the proper balance of Al, Ni, Nb, and Ti additions. | 8 | Metallurgy |
ICOS consists of a network of standardized, long-term, high-precision integrated monitoring of atmospheric greenhouse gas concentrations and fluxes. The infrastructure integrates terrestrial and atmospheric observations at various sites into a single, coherent, highly precise dataset. This data allows a unique regional top-down assessment of fluxes from atmospheric data, and a bottom-up assessment from ecosystem measurements and fossil fuel inventories. Target is a daily mapping of sources and sinks at scales down to about 10 km, as a basis for understanding the exchange processes between the atmosphere, the terrestrial surface and the ocean. ICOS contributes to the implementation of the Integrated Global Carbon Observation System IGCO. | 2 | Environmental Chemistry |
The reductive acetyl CoA pathway (CoA) pathway, also known as the Wood-Ljungdahl pathway uses CO as electron acceptor and carbon source, and H as an electron donor to form acetic acid. This metabolism is wide spread within the phylum Bacillota, especially in the Clostridia.
The pathway is also used by methanogens, which are mainly Euryarchaeota, and several anaerobic chemolithoautotrophs, such as sulfate-reducing bacteria and archaea. It is probably performed also by the Brocadiales, an order of Planctomycetota that oxidize ammonia in anaerobic condition. Hydrogenotrophic methanogenesis, which is only found in certain archaea and accounts for 80% of global methanogenesis, is also based on the reductive acetyl CoA pathway.
The Carbon Monoxide Dehydrogenase/Acetyl-CoA Synthase is the oxygen-sensitive enzyme that permits the reduction of CO to CO and the synthesis of acetyl-CoA in several reactions.
One branch of this pathway, the methyl branch, is similar but non-homologous between bacteria and archaea. In this branch happens the reduction of CO to a methyl residue bound to a cofactor. The intermediates are formate for bacteria and formyl-methanofuran for archaea, and also the carriers, tetrahydrofolate and tetrahydropterins respectively in bacteria and archaea, are different, such as the enzymes forming the cofactor-bound methyl group.
Otherwise, the carbonyl branch is homologous between the two domains and consists of the reduction of another molecule of CO to a carbonyl residue bound to an enzyme, catalyzed by the CO dehydrogenase/acetyl-CoA synthase. This key enzyme is also the catalyst for the formation of acetyl-CoA starting from the products of the previous reactions, the methyl and the carbonyl residues.
This carbon fixation pathway requires only one molecule of ATP for the production of one molecule of pyruvate, which makes this process one of the main choice for chemolithoautotrophs limited in energy and living in anaerobic conditions. | 5 | Photochemistry |
In soil mechanics and petroleum engineering the water saturation or degree of saturation, , is defined as
where is the porosity, in terms of the volume of void or pore space and the total volume of the substance . Values of S can range from 0 (dry) to 1 (saturated). In reality, S never reaches 0 or 1 - these are idealizations for engineering use.
The normalized water content, , (also called effective saturation or ) is a dimensionless value defined by van Genuchten as:
where is the volumetric water content; is the residual water content, defined as the water content for which the gradient becomes zero; and, is the saturated water content, which is equivalent to porosity, . | 7 | Physical Chemistry |
Stuntman and comedian Steve-O has publicly spoken of his involvement as a test subject in an early ractopamine study whose aim was to determine the stress limits of ractopamine saturation in humans. Glover says "Based on how dangerous the study was, the more money you get." | 4 | Stereochemistry |
Protein topology is a property of protein molecule that does not change under deformation (without cutting or breaking a bond). | 6 | Supramolecular Chemistry |
If the reactions occurring during crosslinking are exothermic, the crosslinking rate can be related to the heat released during the process. Higher is the number of bonds created, higher is the heat released in the reaction. At the end of the reaction, no more heat will be released. To measure the heat flow differential scanning calorimetry can be used.
Assuming that each bond formed during the crosslinking releases the same amount of energy, the degree of curing, , can be defined as follows:
where is the heat released up to a certain time , is the instantaneous rate of heat and is the total amount of heat released in , when the reaction finishes.
Also in this case the degree of curing goes from zero (no bonds created) to one (no more reactions occur) with a slope that changes in time and has its maximum about at half of the reaction. | 7 | Physical Chemistry |
Friedel's law, named after Georges Friedel, is a property of Fourier transforms of real functions.
Given a real function , its Fourier transform
has the following properties.
where is the complex conjugate of .
Centrosymmetric points are called Friedel's pairs.
The squared amplitude () is centrosymmetric:
The phase of is antisymmetric:
Friedels law is used in X-ray diffraction, crystallography and scattering from real potential within the Born approximation. Note that a [http://reference.iucr.org/dictionary/Twin_operation twin operation] ( Opération de maclage) is equivalent to an inversion centre and the intensities from the individuals are equivalent under Friedels law. | 3 | Analytical Chemistry |
As of 2020, YwIE is the only known active PAP in B.Subtilis, although Fuhrmann et al. (2013). identified a YwIE homolog in Drosophila, but its role in the specie is still unknown. In contrast, Suzuki et al. (2013) identified the presence of McsB in over 150 bacteria species | 1 | Biochemistry |
Institute of Geochemistry (), which is located in Guiyang, the capital of Guizhou Province of China, was founded in 1966 by the Beijing Institute of Geology, Chinese Academy of Sciences (now Institute of Geology and Geophysics, Chinese Academy of Sciences). | 9 | Geochemistry |
Equilibrium chemistry is concerned with systems in chemical equilibrium. The unifying principle is that the free energy of a system at equilibrium is the minimum possible, so that the slope of the free energy with respect to the reaction coordinate is zero. This principle, applied to mixtures at equilibrium provides a definition of an equilibrium constant. Applications include acid–base, host–guest, metal–complex, solubility, partition, chromatography and redox equilibria. | 7 | Physical Chemistry |
Some promoters are called constitutive as they are active in all circumstances in the cell, while others are regulated, becoming active in the cell only in response to specific stimuli. | 1 | Biochemistry |
Fluid models describe plasmas in terms of smoothed quantities, like density and averaged velocity around each position (see Plasma parameters). One simple fluid model, magnetohydrodynamics, treats the plasma as a single fluid governed by a combination of Maxwell's equations and the Navier–Stokes equations. A more general description is the two-fluid plasma, where the ions and electrons are described separately. Fluid models are often accurate when collisionality is sufficiently high to keep the plasma velocity distribution close to a Maxwell–Boltzmann distribution. Because fluid models usually describe the plasma in terms of a single flow at a certain temperature at each spatial location, they can neither capture velocity space structures like beams or double layers, nor resolve wave-particle effects. | 7 | Physical Chemistry |
An important aspect of improving chemical reactions is the understanding of the underlying reaction mechanism. To answer this question for C-H activation, time-resolved spectroscopic techniques can be used to follow the dynamics of the chemical reaction. This technique requires a trigger for initiating the process, which is in most cases illumination of the compound. Photoinitiated reactions of transition metal complexes with alkanes serve as a powerful model systems for understanding the cleavage of the strong C-H bond.
In such systems, the sample is illuminated with UV-light which excites an electron from the metal center to an unoccupied, antibonding ligand orbitals (MLCT), leading to ligand dissociation. This creates a highly reactive, electron deficient 16-electron intermediate, with a vacant coordination site. This species then binds to an alkane molecule, forming a σ-complex coordinating to a C-H bond. In a third step, the metal atom inserts into the C-H bond, cleaving it and yielding the C-H bond activated product.
The intermediates and their kinetics can be observed using different time-resolved spectroscopic techniques (e.g. TR-IR, TR-XAS, TR-RIXS). Time-resolved infrared spectroscopy (TR-IR) is a rather convenient method to observe these intermediates. However, it is only limited to complexes which have IR-active ligands and is prone to correct assignments on the femtosecond timescale due to underlying vibrational cooling. To answer the question of difference in reactivity for distinct complexes, the electronic structure of those needs to be investigated. This can be achieved by X-ray absorption spectroscopy (XAS) or resonant inelastic X-ray scattering (RIXS). These methods have been successfully used to follow the steps of C-H activation with orbital resolution and provide detailed insights into the responsible interactions for the C-H bond breaking.
Full characterization of the structure of methane bound to a metal center was reported by Girolami in 2023: isotopic perturbation of equilibrium (IPE) studies involving deuterated isotopologs showed that methane binds to the metal center through a single M···H-C bridge; changes in the J coupling constants indicate clearly that the structure of the methane ligand is significantly perturbed relative to the free molecule. | 0 | Organic Chemistry |
Optimized configuration of pyroelectric sensors in optoelectronic technology. It has been shown that in the case of constant laser power, the response of the pyroelectric sensor would not depend on the spatial distribution of the intensity of the laser beam. Therefore, depending on the voltage model, the signal amplitude will be inversely proportional to the effective range of the sensor. In addition, the thermoelectric signal may increase once the effective area decreases and the total area of the sensor remains constant. Based on this, by optimizing the metal electrode structure of the sensor, a method is proposed to improve the PPE signal measured in voltage mode. The experiment shows that this improved method can increase the signal amplitude by 10 times without increasing the electrical noise. | 7 | Physical Chemistry |
There are many classes of neutral homoaromatic compounds although there is much debate as to whether they truly exhibit homoaromatic character or not.
One class of neutral homoaromatics are called monohomoaromatics, one of which is cycloheptatriene, and numerous complex monohomoaromatics have been synthesized. One particular example is a 60-carbon fulleroid derivative that has a single methylene bridge. UV and NMR analysis have shown that the aromatic character of this modified fulleroid is not disrupted by the addition of a homoconjugate linkage, therefore this compound is definitively homoaromatic.
Substituted neutral barbaralane derivatives (homoannulenes) have been disclosed as stable ground state homoaromatic molecules in 2023. Evidence for the homoaromatic character in this class of molecules stems from bond length analysis (X-Ray structural analysis) as well as shifts in the NMR spectrum. The homoannulenes also act as photoswitches by which means a local 6π homoaromaticity can be switched to a global 10π homoaromaticity. | 7 | Physical Chemistry |
In a suspension roaster, the concentrates are blown into a combustion chamber very similar to that of a pulverized coal furnace. The roaster consists of a refractory-lined cylindrical steel shell, with a large combustion space at the top and 2 to 4 hearths in the lower portion, similar to those of a multiple hearth furnace. Additional grinding, beyond that required for a multiple hearth furnace, is normally required to ensure that heat transfer to the material is sufficiently rapid for the desulfurization and oxidation reactions to occur in the furnace chamber. Suspension roasters are unpressurized and operate at about . | 8 | Metallurgy |
Zn is present in the active sites of most hydrolytic enzymes, and is used as an electrophilic catalyst to activate water molecules that ultimately hydrolyze chemical bonds. Examples of zinc-based enzymes include superoxide dismutase (SOD), metallothionein, carbonic anhydrase, Zn finger proteins, alcohol dehydrogenase and carboxypeptidase. | 9 | Geochemistry |
Fumaric acid is used in the manufacture of polyester resins and polyhydric alcohols and as a mordant for dyes.
When fumaric acid is added to their feed, lambs produce up to 70% less methane during digestion. | 1 | Biochemistry |
*Violanthrone
*Isoviolanthrone
*Fluorescein
*Rubrene
*9,10-Diphenylanthracene
*Tetracene
*13,13'-Dibenzantronile
*Levulinic Acid | 7 | Physical Chemistry |
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