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While the first reports of its use dated to 1980, it was a further two decades before the technique of SRCD took off largely due to the work of Bonnie Wallace at Birkbeck College, University of London. From around 2000, her aims in the field focused on both enhancing the collection of quality data through technical improvements, and on demonstrating "proof-of-principle" application studies, illustrating the novel information that SRCD offers. The construction on the Synchrotron Radiation Source (SRS) of the CD12 beamline at Daresbury Laboratory, opened in 2005 under the auspices of the Centre for Protein and Membrane Structure and Dynamics (CPMSD) of which Wallace was the Director, represented the first of the new, dedicated, second-generation SRCD beamlines. It was quickly identified that the high photon flux from CD12 was causing denaturation of the protein sample but that this was resolvable by reducing the sample area being irradiated. Later studies have identified the flux threshold limits that induce SRCD protein denaturation. The input from the Wallace lab to the early years of SRCD development also included the introduction of calibration and standardization of SRCD and cCD spectrophotometers, the creation of software to process the spectral data using CDtool, and CDtoolX, and to analyse the data using DichroWeb, and the generation of reference data sets of proteins to support these data analyses. Additionally, her lab produced sample cells with reduced pathlengths, and using material, (CaF), transparent to VUV radiation which significantly enhanced the collection of data into the SRCD lower wavelength regions.
New SRCD beamlines were constructed on various synchrotrons around the world. ring, in the Department of Physics and Astronomy of Aarhus University in Denmark, became a dedicated second-generation synchrotron in 2005. Ultimately this ring had two SRCD beamlines, [https://www.isa.au.dk/facilities/astrid/beamlines/uv1/uv1.asp UV1] and [https://www.isa.au.dk/facilities/astrid/beamlines/cd1/cd1.asp CD1], which migrated to the new third-generation ring, ASTRID2, in 2013/14, as [https://www.isa.au.dk/facilities/astrid2/beamlines/AU-uv/AU-uv.asp AU-UV] and [https://www.isa.au.dk/facilities/astrid2/beamlines/AU-cd/AU-cd.asp AU-CD]. SOLEIL synchrotron, near Paris, France, commissioned a dedicated SRCD beamline, [https://www.synchrotron-soleil.fr/en/beamlines/disco DISCO], around 2005. At Hiroshima Synchrotron Radiation Center, also known as HiSOR, a VUVCD beamline was constructed over the same period, while a little later in 2009, an SRCD beamline was commissioned in Beijing, China. This particular beamline is unique in that the synchrotron which acts as its light source is also the electron carrying ring of the Beijing Electron Positron Collider. The SRS closed in 2008 being superseded in the UK by the Diamond Light Source on which an SRCD beamline opened for use in 2010. With the SRS closure the CD12 SRCD beamline was moved to, and installed on, the ANKA Synchrotron Radiation Facility, (now called [https://www.ibpt.kit.edu/kara.php KARA]), part of Karlsruhe Institute of Technology (KIT), in Karlsruhe, Germany. This beamline opened for users in 2011 but was closed in 2021. Currently under construction (as of June 2023) on the Sirius synchrotron light source in Campinas, Brazil, is a new SRCD beamline, CEDRO. | 7 | Physical Chemistry |
Eukaryotes have a much larger genome and thus have different methods of gene regulation than in prokaryotes. All cells in a eukaryotic organism have the same DNA but are specified through differential gene expression, a phenomenon known as genetic totipotency. However, in order for a cell to express the genes for proper functioning, the genes must be closely regulated to express the correct properties. Genes in eukaryotes are controlled on the transcriptional, post-transcriptional, translational, and post-translational levels. On the transcriptional level, gene expression is regulated by altering transcription rates. Genes that encode proteins include exons which will encode the polypeptides, introns that are removed from mRNA before the translation of proteins, a transcriptional start site in which RNA polymerase binds, and a promoter. | 1 | Biochemistry |
Manufacturers recommend that carbon tetraiodide be stored near . As a ready source of iodine, it is an irritant. Its LD on rats is 18 mg/kg. In general, organic compounds should be considered toxic, with the narrow exception of small perfluoroalkanes (essentially inert due to the strength of the C-F bond). | 0 | Organic Chemistry |
Redox gradients form based on resource availability and physiochemical conditions (pH, salinity, temperature) and support stratified communities of microbes. Microbes carry out differing respiration processes (methanogenesis, sulfate reduction, etc.) based on the conditions around them and further amplify redox gradients present in the environment. However, distribution of microorganisms cannot solely be determined from thermodynamics (redox ladder), but is also influenced by ecological and physiological factors.
Redox gradients form along contaminant plumes, in both aquatic and terrestrial settings, as a function of the contaminant concentration and the impacts it has on relevant chemical processes and microbial communities. The highest rates of organic pollutant degradation along a redox gradient are found at the oxic-anoxic interface. In groundwater, this oxic-anoxic environment is referred to as the capillary fringe, where the water table meets soil and fills empty pores. Because this transition zone is both oxic and anoxic, electron acceptors and donors are in high abundance and there is a high level of microbial activity, leading to the highest rates of contaminant biodegradation.
Benthic sediments are heterogeneous in nature and subsequently exhibit redox gradients. Due to this heterogeneity, gradients of reducing and oxidizing chemical species do not always overlap enough to support electron transport needs of niche microbial communities. Cable bacteria have been characterized as sulfide-oxidizing bacteria that assist in connecting these areas of undersupplied and excess electrons to complete the electron transport for otherwise unavailable redox reactions.
Biofilms, found in tidal flats, glaciers, hydrothermal vents, and at the bottoms of aquatic environments, also exhibit redox gradients. The community of microbes—often metal- or sulfate-reducing bacteria—produces redox gradients on the micrometer scale as a function of spatial physiochemical variability.
See sulfate-methane transition zone for coverage of microbial processes in SMTZs. | 7 | Physical Chemistry |
The hydroamination reaction is approximately thermochemically neutral. The reaction however suffers from a high activation barrier, perhaps owing to the repulsion of the electron-rich substrate and the amine nucleophile. The intermolecular reaction also is accompanied by highly negative changing entropy, making it unfavorable at higher temperatures.
Consequently, catalysts are necessary for this reaction to proceed. As usual in chemistry, intramolecular processes occur at faster rates than intermolecular versions. | 0 | Organic Chemistry |
In a nanorecording application, a certain rotaxane is deposited as a Langmuir–Blodgett film on ITO-coated glass. When a positive voltage is applied with the tip of a scanning tunneling microscope probe, the rotaxane rings in the tip area switch to a different part of the dumbbell and the resulting new conformation makes the molecules stick out 0.3 nanometer from the surface. This height difference is sufficient for a memory dot. It is not yet known how to erase such a nanorecording film. | 6 | Supramolecular Chemistry |
For humans, porcine endogenous retroviruses (PERVs) pose a concern when using porcine tissues and organs in xenotransplantion, the transplanting of living cells, tissues, and organs from an organism of one species to an organism of different species. Although pigs are generally the most suitable donors to treat human organ diseases due to practical, financial, safety, and ethical reasons, PERVs previously could not be removed from pigs, due to their viral ability to integrate into the host genome and to be passed into offspring, until the year 2017, when one lab, using CRISPR-Cas9, removed all 62 retroviruses from the pig genome. The consequences of cross-species transmission remain unexplored and have dangerous potential.
Researchers have indicated that infection of human tissues by PERVs is very possible, especially in immunosuppressed individuals. An immunosuppressed condition could potentially permit a more rapid and tenacious replication of viral DNA, and would later have less difficulty adapting to human-to-human transmission. Although known infectious pathogens present in the donor organ/tissue can be eliminated by breeding pathogen-free herds, unknown retroviruses can be present in the donor. These retroviruses are often latent and asymptomatic in the donor, but can become active in the recipient. Some examples of endogenous viruses that can infect and multiply in human cells are from baboons (BaEV), cats (RD114), and mice.
There are three different classes of PERVs, PERV-A, PERV-B, and PERV-C. PERV-A and PERV-B are polytropic and can infect human cells in vitro, while PERV-C is ecotropic and does not replicate on human cells. The major differences between the classes is in the receptor binding domain of the env protein and the long terminal repeats (LTRs) that influence the replication of each class. PERV-A and PERV-B display LTRs that have repeats in the U3 region. However, PERV-A and PERV-C show repeatless LTRs. Researchers found that PERVs in culture actively adapted to the repeat structure of their LTR in order to match the best replication performance a host cell could perform. At the end of their study, researchers concluded that repeatless PERV LTR evolved from the repeat-harboring LTR. This was likely to have occurred from insertional mutation and was proven through use of data on LTR and env/Env. It is thought that the generation of repeatless LTRs could be reflective of an adaptation process of the virus, changing from an exogenous to an endogenous lifestyle.
A clinical trial study performed in 1999 sampled 160 patients who were treated with different living pig tissues and observed no evidence of a persistent PERV infection in 97% of the patients for whom a sufficient amount of DNA was available to PCR for amplification of PERV sequences. This study stated that retrospective studies are limited to find the true incidence of infection or associated clinical symptoms, however. It suggested using closely monitored prospective trials, which would provide a more complete and detailed evaluation of the possible cross-species PERV transmission and a comparison of the PERV. | 1 | Biochemistry |
Manganese-mediated coupling reactions are radical coupling reactions between enolizable carbonyl compounds and unsaturated compounds initiated by a manganese(III) salt, typically manganese(III) acetate. Copper(II) acetate is sometimes used as a co-oxidant to assist in the oxidation of intermediate radicals to carbocations.
Manganese(III) acetate is effective for the one-electron oxidation of enolizable carbonyl compounds to α-oxoalkyl or α,α'-dioxoalkyl radicals. Radicals generated in this manner may then undergo inter- or intramolecular addition to carbon-carbon multiple bonds. Pathways available to the adduct radical include further oxidation to a carbocation (and subsequent β-elimination or trapping with a nucleophile) and hydrogen abstraction to generate a saturated carbonyl compound containing a new carbon-carbon bond. Copper(II) acetate is sometimes needed to facilitate the oxidation of adduct radicals to carbocations. Yields of these reactions are generally moderate, particularly in the intermolecular case, but tandem intramolecular radical cyclizations initiated by Mn(III) oxidation may generate complex carbocyclic frameworks. Because of the limited functional group compatibility of Mn(OAc), radical couplings employing this reagent have mainly been applied to the synthesis of hydrocarbon natural products, such as pheromones. | 0 | Organic Chemistry |
Elimination, bimolecular reactions are one step, concerted reaction where both base and substrate participate in the rate limiting step. In an E2 mechanism, a base takes a proton near the leaving group, forcing the electrons down to make a double bond, and forcing off the leaving group-all in one concerted step. The rate law depends on the first order concentration of two reactants, making it a 2nd order (bimolecular) elimination reaction. Factors that affect the rate determining step are stereochemistry, leaving groups, and base strength.
A theory, for an E2 reaction, by Joseph Bunnett suggests the lowest pass through the energy barrier between reactants and products is gained by an adjustment between the degrees of C-H and C-X rupture at the transition state. The adjustment involves much breaking of the bond more easily broken, and a small amount of breaking of the bond which requires more energy. This conclusion by Bunnett is a contradiction from the Hammond postulate. The Hammond postulate is the opposite of what Bunnett theorized. In the transition state of a bond breaking step it involves little breaking when the bond is easily broken and much breaking when it is difficult to break. Despite these differences, the two postulates are not in conflict since they are concerned with different sorts of processes. Hammond focuses on reaction steps where one bond is made or broken, or the breaking of two or more bonds is done with no time taken occur simultaneously. The E2 theory transition state concerns a process when bond formation or breaking are not simultaneous. | 7 | Physical Chemistry |
The N-methyl-D-aspartate receptor (NMDA receptor) – a type of ionotropic glutamate receptor – is a ligand-gated ion channel that is gated by the simultaneous binding of glutamate and a co-agonist (i.e., either D-serine or glycine). Studies show that the NMDA receptor is involved in regulating synaptic plasticity and memory.
The name "NMDA receptor" is derived from the ligand N-methyl-D-aspartate (NMDA), which acts as a selective agonist at these receptors. When the NMDA receptor is activated by the binding of two co-agonists, the cation channel opens, allowing Na and Ca to flow into the cell, in turn raising the cell's electric potential. Thus, the NMDA receptor is an excitatory receptor. At resting potentials, the binding of Mg or Zn at their extracellular binding sites on the receptor blocks ion flux through the NMDA receptor channel. "However, when neurons are depolarized, for example, by intense activation of colocalized postsynaptic AMPA receptors, the voltage-dependent block by Mg is partially relieved, allowing ion influx through activated NMDA receptors. The resulting Ca influx can trigger a variety of intracellular signaling cascades, which can ultimately change neuronal function through activation of various kinases and phosphatases". Ligands include:
* Primary endogenous co-agonists: glutamate and either D-serine or glycine
* Other agonists : aminocyclopropanecarboxylic acid; D-cycloserine; L-aspartate; quinolinate, etc.
* Partial agonists : N-methyl-D-aspartic acid (NMDA); NRX-1074; 3,5-dibromo-L-phenylalanine, etc.
* Antagonists: ketamine, PCP, dextropropoxyphene, ketobemidone, tramadol, kynurenic acid (endogenous), etc. | 1 | Biochemistry |
Transparent wood derives its mechanical properties and performance primarily from its cellulose fiber content and the geometric orientation of the fiber tube cells (radial and tangential) structure, providing the structural base for the design of advanced materials applications.
One aspect of the transparent wood mechanical property is the strength of the material. According to Zhu and his colleagues, transparent wood in the longitudinal direction has an elastic modulus of 2.37 GPa and strength of 45.38 MPa (both which are lower than for pure PMMA) and twice as high as those perpendicular to the longitudinal direction, 1.22 GPa and 23.38 MPa respectively. They conclude that longitudinal to transverse properties decreased for transparent wood, which they expected as the presence of the polymer resin suppresses the cavity space. Also, the plastic nature of transparent wood composite provides advantages compare to other brittle materials like glass, meaning it does not shatter upon impact. | 7 | Physical Chemistry |
Dynamic kinetic resolution in chemistry is a type of kinetic resolution where 100% of a racemic compound can be converted into an enantiopure compound. It is applied in asymmetric synthesis. Asymmetric synthesis has become a much explored field due to the challenge of creating a compound with a single 3D structure. Even more challenging is the ability to take a racemic mixture and have only one chiral product left after a reaction. One method that has become an exceedingly useful tool is dynamic kinetic resolution (DKR). DKR utilizes a center of a particular molecule that can be easily epimerized so that the (R) and (S) enantiomers can interconvert throughout the reaction process. At this point the catalyst can selectively lower the transition state energy of a single enantiomer, leading to almost 100% yield of one reaction pathway over the other. The figure below is an example of an energy diagram for a compound with an (R) and (S) isomer.
If a catalyst is able to increase ΔΔG to a sufficient degree, then one pathway will dominate over the other, leading to a single chiral product. Manipulating kinetics therefore becomes a powerful way to achieve asymmetric products from racemic starting materials. There have been numerous uses of DKR in the literature that have provided new methods in pharmaceuticals as well as routes to natural products. | 4 | Stereochemistry |
Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial (positive allelopathy) or detrimental (negative allelopathy) effects on the target organisms and the community. Allelopathy is often used narrowly to describe chemically-mediated competition between plants; however, it is sometimes defined more broadly as chemically-mediated competition between any type of organisms. Allelochemicals are a subset of secondary metabolites, which are not directly required for metabolism (i.e. growth, development and reproduction) of the allelopathic organism.
Allelopathic interactions are an important factor in determining species distribution and abundance within plant communities, and are also thought to be important in the success of many invasive plants. For specific examples, see black walnut (Juglans nigra), tree of heaven (Ailanthus altissima), black crowberry (Empetrum nigrum), spotted knapweed (Centaurea stoebe), garlic mustard (Alliaria petiolata), Casuarina/Allocasuarina spp., and nutsedge.
It can often be difficult in practice to distinguish allelopathy from resource competition. While the former is caused by the addition of a harmful chemical agent to the environment, the latter is caused by the removal of essential nutrients (or water). Often, both mechanisms can act simultaneously. Moreover, some allelochemicals may function by reducing nutrient availability. Further confounding the issue, the production of allelochemicals can itself be affected by environmental factors such as nutrient availability, temperature and pH. Today, most ecologists recognize the existence of allelopathy, however many particular cases remain controversial. | 1 | Biochemistry |
While the methods above are designed to reduce PD formation, another approach aims to minimize signal generated from PDs in quantitative PCR. This approach is useful as long as there are few PDs formed and their inhibitory effect on product accumulation is minor.
Four steps PCR: used when working with nonspecific dyes, such as SYBR Green I. It is based on the different length, and hence, different melting temperature of the PDs and the target sequence. In this method the signal is acquired below the melting temperature of the target sequence, but above the melting temperature of the PDs.
Sequence-specific probes: TaqMan and molecular beacon probes generate signal only in the presence of their target (complementary) sequence, and this enhanced specificity precludes signal acquisition (but not possible inhibitory effects on product accumulation) from PDs. | 1 | Biochemistry |
Adverse effects of dextromethorphan in overdose at doses 3 to 10 times the recommended therapeutic dose:
At doses 11 to 75 times the recommended therapeutic dose:
Episodic acute psychosis can occur when high doses of dextromethorphan are taken for recreational use, and an abundance of psychiatric symptoms can result, including dissociation and other PCP-like symptoms. | 4 | Stereochemistry |
Most commonly the term is used for the piles of waste earth materials removed during an excavation process.
* In surface mining (commonly called strip mining) for coal or other underground deposits, earth materials removed to expose the targeted deposit are piled up alongside the excavation site (commonly a strip mining pit) in spoil banks.
* A dredge in placer mining is used to dig up volumes of gravel and other earth materials, which are sent through sluices to remove gold or other minerals, and the remaining earth materials ("tailings") are deposited behind the dredge in spoil banks.
* In hydraulic mining, high-pressure jets of water dislodge earth materials, which are put through sluices to sort out gold or other minerals, and the residual earth materials are left in spoil banks.
* The excavation of ditches and canals results in spoil banks being left along the side of the canal or ditch.
Spoil banks can also refer to refuse heaps formed from removal of excess surface materials. For example, alongside livestock lots, spoil banks are formed of manure and other slurry periodically removed from the surface of the livestock lot areas. | 8 | Metallurgy |
When an ecosystem experiences an increase in nutrients, primary producers reap the benefits first. In aquatic ecosystems, species such as algae experience a population increase (called an algal bloom). Algal blooms limit the sunlight available to bottom-dwelling organisms and cause wide swings in the amount of dissolved oxygen in the water. Oxygen is required by all aerobically respiring plants and animals and it is replenished in daylight by photosynthesizing plants and algae. Under eutrophic conditions, dissolved oxygen greatly increases during the day, but is greatly reduced after dark by the respiring algae and by microorganisms that feed on the increasing mass of dead algae. When dissolved oxygen levels decline to hypoxic levels, fish and other marine animals suffocate. As a result, creatures such as fish, shrimp, and especially immobile bottom dwellers die off. In extreme cases, anaerobic conditions ensue, promoting growth of bacteria. Zones where this occurs are known as dead zones. | 2 | Environmental Chemistry |
The triangle of death and the waste management crisis are primarily a result of government failure to control illegal waste dumping. The government had attempted to mandate recycling and waste management programs, but were unable to, causing the expansion of opportunities for illegal activities, which caused further barriers to solve the waste crisis.
Pollutants such as dioxins are found in the area, particularly around Acerra, as well as illegal waste disposal, even in the business district of Montefibre. As early as 1987, a decree of the Ministry of Environment marked Acerra "at high risk of environmental crisis".
High levels of polychlorinated biphenyls (PCBs) were detected both in the soil and in the inhabitants of the region. It is hypothesized that industrial slurry originating from Porto Marghera (industrial docklands near Venice) was disguised as compost and spread on fields in the Acerra countryside by the Casalesi clan, often with help from the landowners.
In one case, a company had its assets seized during a 2006 investigation in which it was alleged that the company had illegally disposed of waste from industries in the regions of Veneto and Tuscany in the territories of Bacoli, Giugliano and Qualiano. Approximately one million tonnes of toxic waste are said to have been disposed of, earning €27 million. The company was already the subject of a 2003 investigation. In another case, a tank full of toxic substances was found buried in an illegal dump, in Marigliano.
The illegal burning of waste, for example to recover copper from wiring, is known to release dioxins into the atmosphere. Such fires are easily hidden among legitimate incineration resulting from the more general waste disposal problem, and the illegal burning of hazardous materials was particularly noted during 2007 and 2008. The presence of fires in the north area of Naples led author Roberto Saviano to use Terra dei fuochi ("Land of pyres") as a chapter title in his book Gomorrah.
In 2000, a Parliamentary Commission inquiry about waste discovered some 800,000 tonnes of mud in Pianura landfill, coming from ACNA of Cengio in Naples, and the Italian Procura della Repubblica found (through telephone wiretappings) some irregularities in the waste disposal into the landfill of Villaricca, managed by FIBA (a company of the Impregilo group). | 2 | Environmental Chemistry |
Asthma is characterized by eosinophil-induced inflammation motivated by a type 2 helper T cell (Th2). By targeting the transcription factor, GATA3, of the Th2 pathway, with DNAzyme it may be possible to negate the inflammation. The safety and efficacy of SB010, a novel 10-23 DNAzyme was evaluated, and found to have the ability to cleave and inactivate GATA3 messenger RNA in phase IIa clinical trials. Treatment with SB010 significantly offset both late and early asthmatic responses after allergen aggravation in male patients with allergic asthma.
The transcription factor GATA-3 is also an interesting target, of the DNAzyme topical formulation SB012, for a novel therapeutic strategy in ulcerative colitis (UC). UC is an idiopathic inflammatory bowel diseases defined by chronically relapsing inflammations of the gastrointestinal tract, and characterized by a superficial, continuous mucosal inflammation, which predominantly affects the large intestine. Patients that do not effectively respond to current UC treatment strategies exhibit serious drawbacks one of which may lead to colorectal surgery, and can result in a severely compromised quality of life. Thus, patients with moderate or severe UC may significantly benefit from these new therapeutic alternatives, of which SB012 is in phase I clinical trials.
Atopic dermatitis (AD) is a chronic inflammatory skin disorder, in which patients suffer from eczema, often severe pruritus on the affected skin, as well as complications and secondary infections. AD surfaces from an upregulation of Th2-modified immune responses, therefore a novel AD approach using DNAzymes targeting GATA-3 is a plausible treatment option. The topical DNAzyme SB011 is currently in phase II clinical trials.
DNAzyme research for the treatment of cancer is also underway. The development of a 10-23 DNAzyme that can block the expression of IGF-I (Insulin-like growth factor I, a contributor to normal cell growth as well as tumorigenesis) by targeting its mRNA could be useful for blocking the secretion of IGF-I from prostate storm primary cells ultimately inhibiting prostate tumor development. Additionally, with this treatment it is expected that hepatic metastasis would also be inhibited, via the inhibition of IGF-I in the liver (the major source of serum IGF-I). | 7 | Physical Chemistry |
Meropenem is bactericidal except against Listeria monocytogenes, where it is bacteriostatic. It inhibits bacterial cell wall synthesis like other β-lactam antibiotics. In contrast to other beta-lactams, it is highly resistant to degradation by β-lactamases or cephalosporinases. In general, resistance arises due to mutations in penicillin-binding proteins, production of metallo-β-lactamases, or resistance to diffusion across the bacterial outer membrane. Unlike imipenem, it is stable to dehydropeptidase-1, so can be given without cilastatin.
In 2016, a synthetic peptide-conjugated PMO (PPMO) was found to inhibit the expression of New Delhi metallo-beta-lactamase, an enzyme that many drug-resistant bacteria use to destroy carbapenems.
While β-lactam ring in meropenem is more accessible to water molecules than in the other β-lactam antibiotics, that facilitates the hydrolysis process and faster degradation of meropenem's antibacterial properties in aqueous solutions, it is more resistant to degradation by β-lactamase enzymes produced by bacteria than the other β-lactam antibiotics. | 4 | Stereochemistry |
Selenium has bimodal biological action depending on the concentration. At low nutritional doses, selenium acts as an antioxidant through selenoproteins, scavenging ROS, supporting cell survival and growth; while, at supra-nutritional higher pharmacological doses, selenium acts as a pro-oxidant generating ROS and inducing cell death. In cancer, studies have been conducted mostly on the benefits of selenium intake in reducing the risk of cancer incidence at the nutritional level; however, fewer studies have explored the effects of supra-nutritional or pharmacological doses of selenium on cancer.
"Although an inverse association between selenium exposure and the risk of some types of cancer was found in some observational studies, this cannot be taken as evidence of a causal relation, and these results should be interpreted with caution... Conflicting results including inverse, null and direct associations have been reported for some cancer types... RCTs assessing the effects of selenium supplementation on cancer risk have yielded inconsistent results... To date, no convincing evidence suggests that selenium supplements can prevent cancer in humans." | 1 | Biochemistry |
Using the Bessemer process, it took between 10 and 20 minutes to convert three to five tons of iron into steel — it would previously take at least a full day of heating, stirring and reheating to achieve this. | 8 | Metallurgy |
Energy quality is a measure of the ease with which a form of energy can be converted to useful work or to another form of energy: i.e. its content of thermodynamic free energy. A high quality form of energy has a high content of thermodynamic free energy, and therefore a high proportion of it can be converted to work; whereas with low quality forms of energy, only a small proportion can be converted to work, and the remainder is dissipated as heat. The concept of energy quality is also used in ecology, where it is used to track the flow of energy between different trophic levels in a food chain and in thermoeconomics, where it is used as a measure of economic output per unit of energy. Methods of evaluating energy quality often involve developing a ranking of energy qualities in hierarchical order. | 7 | Physical Chemistry |
The carbonate–silicate geochemical cycle, also known as the inorganic carbon cycle, describes the long-term transformation of silicate rocks to carbonate rocks by weathering and sedimentation, and the transformation of carbonate rocks back into silicate rocks by metamorphism and volcanism. Carbon dioxide is removed from the atmosphere during burial of weathered minerals and returned to the atmosphere through volcanism. On million-year time scales, the carbonate-silicate cycle is a key factor in controlling Earth's climate because it regulates carbon dioxide levels and therefore global temperature.
The rate of weathering is sensitive to factors that change how much land is exposed. These factors include sea level, topography, lithology, and vegetation changes. Furthermore, these geomorphic and chemical changes have worked in tandem with solar forcing, whether due to orbital changes or stellar evolution, to determine the global surface temperature. Additionally, the carbonate-silicate cycle has been considered a possible solution to the faint young Sun paradox. | 9 | Geochemistry |
To understand the photoreceptor's behavior to light intensities, it is necessary to understand the roles of different currents.
There is an ongoing outward potassium current through nongated K-selective channels. This outward current tends to hyperpolarize the photoreceptor at around −70 mV (the equilibrium potential for K).
There is also an inward sodium current carried by cGMP-gated sodium channels. This "dark current" depolarizes the cell to around −40 mV. This is significantly more depolarized than most other neurons.
A high density of Na-K pumps enables the photoreceptor to maintain a steady intracellular concentration of Na and K.
When light intensity increases, the potential of the membrane decreases (hyperpolarization). Because as the intensity increases, the release of the stimulating neurotransmitter glutamate of the photoreceptors is reduced. When light intensity decreases, that is, in the dark environment, glutamate release by photoreceptors increases. This increases the membrane potential and produces membrane depolarization. | 1 | Biochemistry |
A ketenyl anion contains a C=C=O allene-like functional group, similar to ketene, with a negative charge on either terminal carbon or oxygen atom, forming resonance structures by moving a lone pair of electrons on C-C-O bond. Ketenes have been sources for many organic compounds with its reactivity despite a challenge to isolate them as crystal. Precedent method to obtain this product has been at gas phase or at reactive intermediate, and synthesis of ketene is used be done in extreme conditions (i.e., high temperature, low pressure). Recently found stabilized ketenyl anions become easier to prepare compared to precedent synthetic procedure. A major feature about stabilized ketene is that it can be prepared from carbon monoxide (CO) reacting with main-group starting materials such as ylides, silylene, and phosphinidene to synthesize and isolate for further steps. As CO becomes a more common carbon source for various type of synthesis, this recent finding about stabilizing ketene with main-group elements opens a variety of synthetic routes to target desired products. | 0 | Organic Chemistry |
Because hypophosphorous acid can reduce elemental iodine to form hydroiodic acid, which is a reagent effective for reducing ephedrine or pseudoephedrine to methamphetamine, the United States Drug Enforcement Administration designated hypophosphorous acid (and its salts) as a List I precursor chemical effective November 16, 2001. Accordingly, handlers of hypophosphorous acid or its salts in the United States are subject to stringent regulatory controls including registration, recordkeeping, reporting, and import/export requirements pursuant to the Controlled Substances Act and 21 CFR §§ 1309 and 1310. | 0 | Organic Chemistry |
Although antibodies exhibit nanomolar affinities toward protein antigens, the specificity against glycans is very limited. In fact, available antibodies may bind only <4% of the 7000 mammalian glycan antigens; moreover, most of those antibodies have low affinity and exhibit cross-reactivity. | 1 | Biochemistry |
Indene is deprotonated by butyl lithium and related reagents to give the equivalent of the indenyl anion:
:CH + BuLi → LiCH + BuH
The resulting lithium indenide can be used to prepare indenyl complexes by salt metathesis reactions of metal halides. When the metal halide is easily reduced, the trimethylstannylindenyl can be used as a source of indenyl anion:
:MeSnCH + TiCl → MeSnCl + CHTiCl
The M-C distances in indenyl complexes are comparable to those in cyclopentadienyl complexes. For the metallocenes M(Ind), ring slipping is evident for the case of M = Co and especially Ni, but not for M = Fe. A number of chelating or ansa-bis(indenyl complexes are known, such as those derived from 2,2'-bis(2-indenyl) biphenyl | 0 | Organic Chemistry |
Although the MPTP has been studied mainly in mitochondria from mammalian sources, mitochondria from diverse species also undergo a similar transition. While its occurrence can be easily detected, its purpose still remains elusive. Some have speculated that the regulated opening of the MPT pore may minimize cell injury by causing ROS-producing mitochondria to undergo selective lysosome-dependent mitophagy during nutrient starvation conditions. Under severe stress/pathologic conditions, MPTP opening would trigger injured cell death mainly through necrosis.
There is controversy about the question of whether the MPTP is able to exist in a harmless, "low-conductance" state. This low-conductance state would not induce MPT and would allow certain molecules and ions to cross the mitochondrial membranes. The low-conductance state may allow small ions like Ca to leave mitochondria quickly, in order to aid in the cycling of Ca in healthy cells. If this is the case, MPT may be a harmful side effect of abnormal activity of a usually beneficial MPTP.
MPTP has been detected in mitochondria from plants, yeasts, such as Saccharomyces cerevisiae, birds, such as guinea fowl and primitive vertebrates such as the Baltic lamprey. While the permeability transition is evident in mitochondria from these sources, its sensitivity to its classic modulators may differ when compared with mammalian mitochondria. Nevertheless, CsA-insensitive MPTP can be triggered in mammalian mitochondria given appropriate experimental conditions strongly suggesting this event may be a conserved characteristic throughout the eukaryotic domain. | 1 | Biochemistry |
2,2-Dimethylpropanoyl chloride is a branched-chain acyl chloride. It was first made by Aleksandr Butlerov in 1874 by reacting pivalic acid with phosphorus pentachloride.
Pivaloyl chloride is used as an input in the manufacture of some drugs, insecticides and herbicides. | 0 | Organic Chemistry |
At a certain voltage E, equilibrium will attain and the forward and backward rates (v and v) will be equal. This is represented by the green curve in the above figure. The equilibrium rate constants will be written as k and k, and the equilibrium concentrations will be written c and c. The equilibrium currents (j and j) will be equal and are written as j, which is known as the exchange current density.
Note that the net current density at equilibrium will be zero. The equilibrium rate constants are then:
Solving the above for k and k in terms of the equilibrium concentrations c and c and the exchange current density j, the current density j as a function of applied potential E may now be written:
Assuming that equilibrium holds in the bulk solution, with concentrations and , it follows that and , and the above expression for the current density j is then the Butler–Volmer equation. Note that E-E is also known as η, the activation overpotential. | 7 | Physical Chemistry |
The Stöber process is a chemical process used to prepare silica () particles of controllable and uniform size for applications in materials science. It was pioneering when it was reported by Werner Stöber and his team in 1968, and remains today the most widely used wet chemistry synthetic approach to silica nanoparticles. It is an example of a sol-gel process wherein a molecular precursor (typically tetraethylorthosilicate) is first reacted with water in an alcoholic solution, the resulting molecules then joining together to build larger structures. The reaction produces silica particles with diameters ranging from 50 to 2000 nm, depending on conditions. The process has been actively researched since its discovery, including efforts to understand its kinetics and mechanisma particle aggregation model was found to be a better fit for the experimental data than the initially hypothesized LaMer model. The newly acquired understanding has enabled researchers to exert a high degree of control over particle size and distribution and to fine-tune the physical properties of the resulting material in order to suit intended applications.
In 1999 a two-stage modification was reported that allowed the controlled formation of silica particles with small holes. The process is undertaken at low pH in the presence of a surface-active molecule. The hydrolysis step is completed with the formation of a microemulsion before adding sodium fluoride to start the condensation process. The non-ionic surfactant is burned away to produce empty pores, increasing the surface area and altering the surface characteristics of the resulting particles, allowing for much greater control over the physical properties of the material. Development work has also been undertaken for larger pore structures such as macroporous monoliths, shell-core particles based on polystyrene, cyclen, or polyamines, and carbon spheres.
Silica produced using the Stöber process is an ideal material to serve as a model for studying colloid phenomena because of the monodispersity (uniformity) of its particle sizes. Nanoparticles prepared using the Stöber process have found applications including in the delivery of medications to within cellular structures and in the preparation of biosensors. Porous silica Stöber materials have applications in catalysis and liquid chromatography due to their high surface area and their uniform, tunable, and highly ordered pore structures. Highly effective thermal insulators known as aerogels can also be prepared using Stöber methods, and Stöber techniques have been applied to prepare non-silica aerogel systems. Applying supercritical drying techniques, a Stöber silica aerogel with a specific surface area of 700 m g and a density of 0.040 g cm can be prepared. NASA has prepared silica aerogels with a Stöber-process approach for both the Mars Pathfinder and Stardust missions. | 7 | Physical Chemistry |
The term wetware is used to describe the protocols and molecular devices used in molecular biology and synthetic biology.
Where biological components and systems are treated in a similar manner to software, and similar development models and methodologies are applied, the term wetware can be used to imply an approach to their problems as bugs and their beneficial aspects as features. In this manner, genetic code can be subjected to Version Control Systems such as Git, for the development of improvements and new gene edits, therapeutic components and therapies. | 1 | Biochemistry |
The New Jersey Zinc Company invented this process in 1930.
The process take advantage of the relatively low boiling point of zinc () as compared to the impurities being removed in the first "column": iron and aluminium. Therefore, in the first column the zinc is heated above its boiling point and allowed to rise to a condenser. The iron and aluminium impurities sink to the bottom in the form of a solid or liquid. There are still lead and cadmium vapor impurities. In order to remove the lead 2-3% of the vapor is condensed, which draws the majority of the lead out of the vapor; down to the point where it is only 0.003% of the total contents. Finally the vapor is pumped into the cadmium column where it is cooled to an intermediate temperature below the boiling point zinc, but still above the boiling point of cadmium (). The zinc leaves out the bottom as a refined liquid, while the cadmium leaves out the top as vapor. | 8 | Metallurgy |
A single-stranded genome that is used in both positive-sense and negative-sense capacities is said to be ambisense. Some viruses have ambisense genomes. Bunyaviruses have three single-stranded RNA (ssRNA) fragments, some of them containing both positive-sense and negative-sense sections; arenaviruses are also ssRNA viruses with an ambisense genome, as they have three fragments that are mainly negative-sense except for part of the 5′ ends of the large and small segments of their genome. | 1 | Biochemistry |
Molecular distillation is a type of short-path vacuum distillation, characterized by an extremely low vacuum pressure, 0.01 torr or below, which is performed using a molecular still. It is a process of separation, purification and concentration of natural products, complex and thermally sensitive molecules for example vitamins and polyunsaturated fatty acids. This process is characterized by short term exposure of the distillate liquid to high temperatures in high vacuum (around mmHg) in the distillation column and a small distance between the evaporator and the condenser around 2 cm. In molecular distillation, fluids are in the free molecular flow regime, i.e. the mean free path of molecules is comparable to the size of the equipment. The gaseous phase no longer exerts significant pressure on the substance to be evaporated, and consequently, rate of evaporation no longer depends on pressure. The motion of molecules is in the line of sight, because they do not form a continuous gas anymore. Thus, a short path between the hot surface and the cold surface is necessary, typically by suspending a hot plate covered with a film of feed next to a cold plate with a line of sight in between.
This process has the advantages of avoiding the problem of toxicity that occurs in techniques that use solvents as the separating agent, and also of minimizing losses due to thermal decomposition. and can be used in a continuous feed process to harvest distillate without having to break vacuum.
Molecular distillation is used industrially for purification of oils. It is also used to enrich borage oil in γ-linolenic acid (GLA) and also to recover tocopherols from deodorizer distillate of soybean oil (DDSO). Molecular stills were historically used by Wallace Carothers in the synthesis of larger polymers, as a reaction product, water, interfered with polymerization by undoing the reaction via hydrolysis, but the water could be removed by the molecular still. | 3 | Analytical Chemistry |
The mass-flux fraction (or Hirschfelder-Curtiss variable or Kármán-Penner variable) is the ratio of mass-flux of a particular chemical species to the total mass flux of a gaseous mixture. It includes both the convectional mass flux and the diffusional mass flux. It was introduced by Joseph O. Hirschfelder and Charles F. Curtiss in 1948 and later by Theodore von Kármán and Sol Penner in 1954. The mass-flux fraction of a species i is defined as
where
* is the mass fraction
* is the mass average velocity of the gaseous mixture
* is the average velocity with which the species i diffuse relative to
* is the density of species i
* is the gas density.
It satisfies the identity
similar to the mass fraction, but the mass-flux fraction can take both positive and negative values. This variable is used in steady, one-dimensional combustion problems in place of the mass fraction. For one-dimensional ( direction) steady flows, the conservation equation for the mass-flux fraction reduces to
where is the mass production rate of species i. | 3 | Analytical Chemistry |
Light consists of electromagnetic radiation of different wavelengths. Therefore, when the elements or their compounds are heated either on a flame or by an electric arc they emit energy in the form of light. Analysis of this light, with the help of a spectroscope gives us a discontinuous spectrum. A spectroscope or a spectrometer is an instrument which is used for separating the components of light, which have different wavelengths. The spectrum appears in a series of lines called the line spectrum. This line spectrum is called an atomic spectrum when it originates from an atom in elemental form. Each element has a different atomic spectrum. The production of line spectra by the atoms of an element indicate that an atom can radiate only a certain amount of energy. This leads to the conclusion that bound electrons cannot have just any amount of energy but only a certain amount of energy.
The emission spectrum can be used to determine the composition of a material, since it is different for each element of the periodic table. One example is astronomical spectroscopy: identifying the composition of stars by analysing the received light.
The emission spectrum characteristics of some elements are plainly visible to the naked eye when these elements are heated. For example, when platinum wire is dipped into a sodium nitrate solution and then inserted into a flame, the sodium atoms emit an amber yellow color. Similarly, when indium is inserted into a flame, the flame becomes blue. These definite characteristics allow elements to be identified by their atomic emission spectrum. Not all emitted lights are perceptible to the naked eye, as the spectrum also includes ultraviolet rays and infrared radiation.
An emission spectrum is formed when an excited gas is viewed directly through a spectroscope.
Emission spectroscopy is a spectroscopic technique which examines the wavelengths of photons emitted by atoms or molecules during their transition from an excited state to a lower energy state. Each element emits a characteristic set of discrete wavelengths according to its electronic structure, and by observing these wavelengths the elemental composition of the sample can be determined. Emission spectroscopy developed in the late 19th century and efforts in theoretical explanation of atomic emission spectra eventually led to quantum mechanics.
There are many ways in which atoms can be brought to an excited state. Interaction with electromagnetic radiation is used in fluorescence spectroscopy, protons or other heavier particles in Particle-Induced X-ray Emission and electrons or X-ray photons in Energy-dispersive X-ray spectroscopy or X-ray fluorescence. The simplest method is to heat the sample to a high temperature, after which the excitations are produced by collisions between the sample atoms. This method is used in flame emission spectroscopy, and it was also the method used by Anders Jonas Ångström when he discovered the phenomenon of discrete emission lines in the 1850s.
Although the emission lines are caused by a transition between quantized energy states and may at first look very sharp, they do have a finite width, i.e. they are composed of more than one wavelength of light. This spectral line broadening has many different causes.
Emission spectroscopy is often referred to as optical emission spectroscopy because of the light nature of what is being emitted. | 7 | Physical Chemistry |
Alessio Zaccone and collaborators investigated the effects of shear-flow on particle aggregation which can play an important role in applications e.g. microfluidics, chemical reactors, atmospheric and environmental flows. Their work showed a characteristic lag-time in the shear-induced aggregation of the particles, which decreases exponentially with the shear rate. | 7 | Physical Chemistry |
Benzyl chloroformate, also known as benzyl chlorocarbonate or Z-chloride, is the benzyl ester of chloroformic acid. It can be also described as the chloride of the benzyloxycarbonyl (Cbz or Z) group. In its pure form it is a water-sensitive oily colorless liquid, although impure samples usually appear yellow. It possesses a characteristic pungent odor and degrades in contact with water.
The compound was first prepared by Leonidas Zervas in the early 1930s who used it for the introduction of the benzyloxycarbonyl protecting group, which became the basis of the Bergmann-Zervas carboxybenzyl method of peptide synthesis he developed with Max Bergmann. This was the first successful method of controlled peptide chemical synthesis and for twenty years it was the dominant procedure used worldwide until the 1950s. To this day, benzyl chloroformate is often used for amine group protection. | 0 | Organic Chemistry |
Common examples of RATs or RADTs include:
* COVID-19 testing-related rapid tests
* Rapid strep tests (for streptococcal antigens)
* Rapid influenza diagnostic tests (RIDTs) (for influenza virus antigens)
* Malaria antigen detection tests (for Plasmodium antigens) | 1 | Biochemistry |
The partial volume of a particular gas is a fraction of the total volume occupied by the gas mixture, with unchanged pressure and temperature. In gas mixtures, e.g. air, the partial volume allows focusing on one particular gas component, e.g. oxygen.
It can be approximated both from partial pressure and molar fraction:
* V is the partial volume of any individual gas component (X)
* V is the total volume in gas mixture
* P is the partial pressure of gas X
* P is the total pressure in gas mixture
* n is the amount of substance of a gas (X)
* n is the total amount of substance in gas mixture | 7 | Physical Chemistry |
The main durations of embryo culture are until cleavage stage (day two to four after co-incubation) or the blastocyst stage (day five or six after co-incubation). Embryo culture until the blastocyst stage confers a significant increase in live birth rate per embryo transfer, but also confers a decreased number of embryos available for transfer and embryo cryopreservation, so the cumulative clinical pregnancy rates are increased with cleavage stage transfer. Transfer day two instead of day three after fertilisation has no differences in live birth rate. There are significantly higher odds of preterm birth (odds ratio 1.3) and congenital anomalies (odds ratio 1.3) among births having from embryos cultured until the blastocyst stage compared with cleavage stage. | 1 | Biochemistry |
Prior to the Montreal Protocol, large quantities of carbon tetrachloride were used to produce the chlorofluorocarbon refrigerants R-11 (trichlorofluoromethane) and R-12 (dichlorodifluoromethane). However, these refrigerants play a role in ozone depletion and have been phased out. Carbon tetrachloride is still used to manufacture less destructive refrigerants. | 2 | Environmental Chemistry |
The Peng–Robinson equation of state relates the three interdependent state properties pressure P, temperature T, and molar volume V. From the state properties (P, V, T), one may compute the departure function for enthalpy per mole (denoted h) and entropy per mole (s):
where is defined in the Peng-Robinson equation of state, T is the reduced temperature, P is the reduced pressure, Z is the compressibility factor, and
Typically, one knows two of the three state properties (P, V, T), and must compute the third directly from the equation of state under consideration. To calculate the third state property, it is necessary to know three constants for the species at hand: the critical temperature T, critical pressure P, and the acentric factor ω. But once these constants are known, it is possible to evaluate all of the above expressions and hence determine the enthalpy and entropy departures. | 7 | Physical Chemistry |
UPdAl is a heavy-fermion superconductor with a hexagonal crystal structure and critical temperature T=2.0K that was discovered in 1991. Furthermore, UPdAl orders antiferromagnetically at T=14K, and UPdAl thus features the unusual behavior that this material, at temperatures below 2K, is simultaneously superconducting and magnetically ordered.
Later experiments demonstrated that superconductivity in UPdAl is magnetically mediated, and UPdAl therefore serves as a prime example for non-phonon-mediated superconductors. | 8 | Metallurgy |
Carboxylic acids are Brønsted–Lowry acids because they are proton (H) donors. They are the most common type of organic acid.
Carboxylic acids are typically weak acids, meaning that they only partially dissociate into Hydronium| cations and Carboxylate| anions in neutral aqueous solution. For example, at room temperature, in a 1-molar solution of acetic acid, only 0.001% of the acid are dissociated (i.e. 10 moles out of 1 mol). Electron-withdrawing substituents, such as -CF group, give stronger acids (the pK of acetic acid is 4.76 whereas trifluoroacetic acid, with a trifluoromethyl substituent, has a pK of 0.23). Electron-donating substituents give weaker acids (the pK of formic acid is 3.75 whereas acetic acid, with a methyl substituent, has a pK of 4.76)
Deprotonation of carboxylic acids gives carboxylate anions; these are resonance stabilized, because the negative charge is delocalized over the two oxygen atoms, increasing the stability of the anion. Each of the carbon–oxygen bonds in the carboxylate anion has a partial double-bond character. The carbonyl carbon's partial positive charge is also weakened by the -/ negative charges on the 2 oxygen atoms. | 0 | Organic Chemistry |
Upon illumination with blue-green light, OCP switches from an orange form (OCP) to a red form (OCP). The reversion of OCP to OCP is light independent and occurs slowly in darkness. OCP is considered the dark, stable form of the protein, and does not contribute to phycobilisome quenching. OCP is considered to be essential for induction of the photoprotection mechanism. The photoconversion from the orange to red form has a poor light efficiency (very low quantum yield), which helps to ensure the protein's photoprotective role only functions during high light conditions; otherwise, the dissipative NPQ process could unproductively divert light energy away from photosynthesis under light-limiting conditions. | 5 | Photochemistry |
In organometallic chemistry, (η-CH) piano stool compounds are half-sandwich compounds with (η-CH)ML structure (M = Cr, Mo, W, Mn(I), Re(I) and L = typically CO). (η-CH) piano stool complexes are stable 18-electron coordination compounds with a variety of chemical and material applications. Early studies on (η-CH)Cr(CO) were carried out by Natta, Ercoli and Calderazzo, and Fischer and Ofele, and the crystal structure was determined by Corradini and Allegra in 1959. The X-ray data indicate that the plane of the benzene ring is nearly parallel to the plane defined by the oxygen atoms of the carbonyl ligands, and so the structure resembles a benzene seat mounted on three carbonyl legs tethered by the metal atom. | 0 | Organic Chemistry |
Microarrays usually consist of a grid of short nucleotide oligomers, known as "probes", typically arranged on a glass slide. Transcript abundance is determined by hybridisation of fluorescently labelled transcripts to these probes. The fluorescence intensity at each probe location on the array indicates the transcript abundance for that probe sequence. Groups of probes designed to measure the same transcript (i.e., hybridizing a specific transcript in different positions) are usually referred to as "probesets".
Microarrays require some genomic knowledge from the organism of interest, for example, in the form of an annotated genome sequence, or a library of ESTs that can be used to generate the probes for the array. | 1 | Biochemistry |
In 2008, Place et al. identified targets for miRNA miR-373 on the promoters of several human genes and found that introduction of miR-373 mimics into human cells induced the expression of its predicted target genes. This study provided the first example that RNAa could be mediated by naturally occurring non-coding RNA (ncRNA). In 2011, Huang et al. further demonstrated in mouse cells that endogenous RNAa mediated by miRNAs functions in a physiological context and is possibly exploited by cancer cells to gain a growth advantage. Since then, a number of miRNAs have been shown to upregulate gene expression by targeting gene promoters or enhancers, thereby, exerting important biological roles. A good example is miR-551b-3p which is overexpressed in ovarian cancer due to amplification. By targeting the promoter of STAT3 to increase its transcription, miR-551b-3p confers to ovarian cancer cells resistance to apoptosis and a proliferative advantage.
In C. elegans hypodermal seam cells, the transcription of lin-4 miRNA is positively regulated by lin-4 itself which binds to a conserved lin-4 complementary element in its promoter, constituting a positive autoregulatory loop.
In C. elegans, Argonaute CSR-1 interacts with 22G small RNAs derived from RNA-dependent RNA polymerase and antisense to germline-expressed transcripts to protect these mRNAs from Piwi-piRNA mediated silencing via promoting epigenetic activation.
It is currently unknown how widespread gene regulation by endogenous RNAa is in mammalian cells. Studies have shown that both miRNAs and Ago proteins (Ago1) bind to numerous sites in human genome, especially promoter regions, to exert a largely positive effect on gene transcription. | 1 | Biochemistry |
mA is not the only RNA modification that can be found in viral RNAs. For instance, N,2-O-dimethyladenosine (mA) can be found in influenza and herpes simplex virus type 1, even though the effect this mark has on the life cycle of these viruses remains unknown. NAT10 mediated acetylation of cytidines on HIV-1 RNA was recently reported. Another modification commonly found in coronaviruses, flaviviruses and poxviruses (all of them are cytoplasmic viruses) is the 2-O-methylation of ribose moieties. The addition of this mark is catalyzed by a viral methyltransferase. 2-O-methylation binds to and inhibits Toll-like receptor 7 (TLR-7), which is involved in activating the production of inflammatory cytokines. Moreover, this modification enables viral RNAs to evade the antiviral actions of the IFIT proteins, a family of interferon-induced proteins that limit viral replication. | 1 | Biochemistry |
Thioesters are prominent active esters, as illustrated by the esters of coenzyme A.
In synthetic chemistry, active esters include derivatives of nitrophenols and pentafluorophenol. Active esters are often used in peptide synthesis, e.g., N-hydroxysuccinimide, hydroxybenzotriazole. Active esters of acrylic acid are precursors to polymers with reactive side chains.
The concept of active esters extends to esters of phosphoric and sulfuric acids. One such case is dimethylsulfate, a strong methylating agent. | 0 | Organic Chemistry |
The notion of chromium as a potential regulator of glucose metabolism began in the 1950s when Walter Mertz and his co-workers performed a series of experiments controlling the diet of rats. The experimenters subjected the rats to a chromium deficient diet, and witnessed an inability of the organisms to respond effectively to increased levels of glucose within the blood. They then included "acid-hydrolyzed porcine kidney and Brewers yeast" in the diet of these rats, and found that the rats were now able to effectively metabolize glucose. Both the porcine kidney and Brewers yeast were rich in chromium, and so it was from these findings that began the study of chromium as a regulator of blood glucose.
The idea of chromium being used for the treatment of type II diabetes was first sparked in the 1970s. A patient receiving total parenteral nutrition (TPN) had developed "severe signs of diabetes", and was administered chromium supplements based on previous studies that proved the effectiveness of this metal in modulating blood glucose levels. The patient was administered chromium for a total of two weeks, and by the end of this time-period, their ability to metabolize glucose had increased significantly; they also now required less insulin ("exogenous insulin requirements decreased from 45 units/day to none"). It was these experiments that were performed in the 1950s and 1970s that paved the foundation for future studies on chromium and diabetes.
In 2005, the U.S. Food and Drug Administration approved a Qualified Health Claim for chromium picolinate with a requirement for very specific label wording: "One small study suggests that chromium picolinate may reduce the risk of insulin resistance, and therefore possibly may reduce the risk of type 2 diabetes. FDA concludes, however, that the existence of such a relationship between chromium picolinate and either insulin resistance or type 2 diabetes is highly uncertain." In 2010, chromium(III) picolinate was approved by Health Canada to be used in dietary supplements. Approved labeling statements included: "...provides support for healthy glucose metabolism." The European Food Safety Authority (EFSA) approved claims in 2010 that chromium contributed to normal macronutrient metabolism and maintenance of normal blood glucose concentration.
A 2016 review of meta-analyses concluded that whereas there may be modest decreases in fasting plasma glucose or glycosylated hemoglobin that achieve statistical significance, the changes were rarely large enough to be expected to be relevant to clinical outcome. | 1 | Biochemistry |
Thermal hydrolysis is a two-stage process combining high-pressure boiling of waste or sludge followed by a rapid decompression. This combined action sterilizes the sludge and makes it more biodegradable, which improves digestion performance. Sterilization destroys pathogens in the sludge resulting in it exceeding the stringent requirements for land application (agriculture).
In addition, the treatment adjusts the rheology to such an extent that loading rates to sludge anaerobic digesters can be doubled, and also dewaterability of the sludge is significantly improved. The first full-scale application of this process for sewage sludge was installed in Hamar, Norway in 1996. Since then, there have been over 30 additional installations globally. | 7 | Physical Chemistry |
This involves "screening" for the sequences of interest. There are multiple possible methods to achieve this. | 1 | Biochemistry |
When tissue cells are in a protein-containing fluid, the Donnan effect of the cytoplasmic proteins is equal and opposite to the Donnan effect of the extracellular proteins. The opposing Donnan effects cause chloride ions to migrate inside the cell, increasing the intracellular chloride concentration. The Donnan effect may explain why some red blood cells do not have active sodium pumps; the effect relieves the osmotic pressure of plasma proteins, which is why sodium pumping is less important for maintaining the cell volume . | 7 | Physical Chemistry |
In 1856, Robert Forester Mushet "used manganese to improve the ability of steel produced by the Bessemer process to withstand rolling and forging at elevated temperatures."
In 1860, Henry Bessemer invented the use of ferromanganese as a method of introducing manganese in controlled proportions during the production of steel. The advantage of combining powdered iron oxide and manganese oxide together is the lower melting point of the combined alloy compared to pure manganese oxide.
In 1872, Lambert von Pantz produced ferromanganese in a blast furnace, with significantly higher manganese content than was previously possible (37% instead of the previous 12%). This won his company international recognition, including a gold medal at the 1873 World Exposition in Vienna and a certificate of award at the 1876 Centennial Exposition in Pennsylvania.
In an 1876 article, MF Gautier explained that the magnetic oxide needs to be slagged off by the addition of manganese (then in the form of spiegel iron) in order to befit it for rolling. | 8 | Metallurgy |
The first glycal was synthesized by Hermann Emil Fischer and Karl Zach in 1913. They synthesized this 1,2-unsaturated sugar from D-glucose and named their product D-glucal. Fischer believed he had synthesized an aldehyde, and therefore he gave the product a name that suggested this. By the time he discovered his mistake, the name "glycal" was adopted as a general name for all sugars with a double bond between carbon atoms 1 and 2. | 0 | Organic Chemistry |
As shown below, the SCODA principle applies to any particle driven by a force field in which the particle's mobility is altered in sync with the driving field. | 1 | Biochemistry |
Colorimetric analysis is a method of determining the concentration of a chemical element or chemical compound in a solution with the aid of a color reagent. It is applicable to both organic compounds and inorganic compounds and may be used with or without an enzymatic stage. The method is widely used in medical laboratories and for industrial purposes, e.g. the analysis of water samples in connection with industrial water treatment. | 3 | Analytical Chemistry |
In many examples of 3D optical data storage systems, several wavelengths (colors) of light are used (e.g. reading laser, writing laser, signal; sometimes even two lasers are required just for writing). Therefore, as well as coping with the high laser power and variable spherical aberration, the optical system must combine and separate these different colors of light as required. | 5 | Photochemistry |
In 2020, evidence was provided that the cores of neutron stars with mass ~2M were likely composed of quark matter. Their result was based on neutron-star tidal deformability during a neutron star merger as measured by gravitational-wave observatories, leading to an estimate of star radius, combined with calculations of the equation of state relating the pressure and energy density of the star's core. The evidence was strongly suggestive but did not conclusively prove the existence of quark matter. | 7 | Physical Chemistry |
One rock, "Bounce Rock," found sitting on the sandy plains was found to be ejecta from an impact crater. Its chemistry was different from the bedrocks. Containing mostly pyroxene and plagioclase and no olivine, it closely resembled a part, Lithology B, of the shergottite meteorite EETA 79001, a meteorite known to have come from Mars. Bounce rock received its name by being near an airbag bounce mark. | 9 | Geochemistry |
Phase transitions (phase changes) that help describe polymorphism include polymorphic transitions as well as melting and vaporization transitions. According to IUPAC, a polymorphic transition is "A reversible transition of a solid crystalline phase at a certain temperature and pressure (the inversion point) to another phase of the same chemical composition with a different crystal structure." Additionally, Walter McCrone described the phases in polymorphic matter as "different in crystal structure but identical in the liquid or vapor states." McCrone also defines a polymorph as “a crystalline phase of a given compound resulting from the possibility of at least two different arrangements of the molecules of that compound in the solid state.” These defining facts imply that polymorphism involves changes in physical properties but cannot include chemical change. Some early definitions do not make this distinction.
Eliminating chemical change from those changes permissible during a polymorphic transition delineates polymorphism. For example, isomerization can often lead to polymorphic transitions. However, tautomerism (dynamic isomerization) leads to chemical change, not polymorphism. As well, allotropy of elements and polymorphism have been linked historically. However, allotropes of an element are not always polymorphs. A common example is the allotropes of carbon, which include graphite, diamond, and londsdaleite. While all three forms are allotropes, graphite is not a polymorph of diamond and londsdaleite. The reason is that graphite is chemically distinct, having sp hybridized bonding, while diamond, and londsdaleite are chemically identical, both having sp hybridized bonding. Diamond and londsdaleite differ in their crystal structures but do not differ chemically. Isomerization and allotropy are only two of the phenomena linked to polymorphism. For additional information about identifying polymorphism and distinguishing it from other phenomena, see the review by Brog et al.
Polymorphism is of practical relevance to pharmaceuticals, agrochemicals, pigments, dyestuffs, foods, and explosives. | 3 | Analytical Chemistry |
Another form of translational regulation in eukaryotes comes from unique elements on the 5′ UTR called upstream open reading frames (uORF). These elements are fairly common, occurring in 35–49% of all human genes. A uORF is a coding sequence located in the 5′ UTR located upstream of the coding sequences initiation site. These uORFs contain their own initiation codon, known as an upstream AUG (uAUG). This codon can be scanned for by ribosomes and then translated to create a product, which can regulate the translation of the main protein coding sequence or other uORFs that may exist on the same transcript.
The translation of the protein within the main ORF after a uORF sequence has been translated is known as reinitiation. The process of reinitiation is known to reduce the translation of the ORF protein. Control of protein regulation is determined by the distance between the uORF and the first codon in the main ORF. A uORF has been found to increase reinitiation with the longer distance between its uAUG and the start codon of the main ORF, which indicates that the ribosome needs to reacquire translation factors before it can carry out translation of the main protein. For example, ATF4 regulation is performed by two uORFs further upstream, named uORF1 and uORF2, which contain three amino acids and fifty-nine amino acids, respectively. The location of uORF2 overlaps with the ATF4 ORF. During normal conditions, the uORF1 is translated, and then translation of uORF2 occurs only after eIF2-TC has been reacquired. Translation of the uORF2 requires that the ribosomes pass by the ATF4 ORF, whose start codon is located within uORF2. This leads to its repression. However, during stress conditions, the 40S ribosome will bypass uORF2 because of a decrease in concentration of eIF2-TC, which means the ribosome does not acquire one in time to translate uORF2. Instead, ATF4 is translated. | 1 | Biochemistry |
The reaction mechanism for complex III (cytochrome bc1, coenzyme Q: cytochrome C oxidoreductase) is known as the ubiquinone ("Q") cycle. In this cycle four protons get released into the positive "P" side (inter membrane space), but only two protons get taken up from the negative "N" side (matrix). As a result, a proton gradient is formed across the membrane. In the overall reaction, two ubiquinols are oxidized to ubiquinones and one ubiquinone is reduced to ubiquinol. In the complete mechanism, two electrons are transferred from ubiquinol to ubiquinone, via two cytochrome c intermediates.
Overall:
* 2 x QH oxidised to Q
* 1 x Q reduced to QH
* 2 x Cyt c reduced
* 4 x H released into intermembrane space
* 2 x H picked up from matrix
The reaction proceeds according to the following steps:
Round 1:
# Cytochrome b binds a ubiquinol and a ubiquinone.
# The 2Fe/2S center and B heme each pull an electron off the bound ubiquinol, releasing two protons into the intermembrane space.
# One electron is transferred to cytochrome c from the 2Fe/2S centre, whilst another is transferred from the B heme to the B Heme.
# Cytochrome c transfers its electron to cytochrome c (not to be confused with cytochrome c1), and the B Heme transfers its electron to a nearby ubiquinone, resulting in the formation of a ubisemiquinone.
# Cytochrome c diffuses. The first ubiquinol (now oxidised to ubiquinone) is released, whilst the semiquinone remains bound.
Round 2:
# A second ubiquinol is bound by cytochrome b.
# The 2Fe/2S center and B heme each pull an electron off the bound ubiquinol, releasing two protons into the intermembrane space.
# One electron is transferred to cytochrome c from the 2Fe/2S centre, whilst another is transferred from the B heme to the B Heme.
# Cytochrome c then transfers its electron to cytochrome c, whilst the nearby semiquinone produced from round 1 picks up a second electron from the B heme, along with two protons from the matrix.
# The second ubiquinol (now oxidised to ubiquinone), along with the newly formed ubiquinol are released. | 1 | Biochemistry |
The applications of biopolymers can be categorized under two main fields, which differ due to their biomedical and industrial use. | 1 | Biochemistry |
MAPs have been divided into several different categories and sub-categories. There are "structural" MAPs which bind along the microtubules and "+TIP" MAPs which bind to the growing end of the microtubules. Structural MAPs have been divided into MAP1, MAP2, MAP4, and Tau families. +TIP MAPs are motor proteins such as kinesin, dyneins, and other MAPs. | 1 | Biochemistry |
Signal transduction mediated by the superfamily of GPCRs dates back to the origin of multicellularity. Mammalian-like GPCRs are found in fungi, and have been classified according to the GRAFS classification system based on GPCR fingerprints. Identification of the superfamily members across the eukaryotic domain, and comparison of the family-specific motifs, have shown that the superfamily of GPCRs have a common origin. Characteristic motifs indicate that three of the five GRAFS families, Rhodopsin, Adhesion, and Frizzled, evolved from the Dictyostelium discoideum cAMP receptors before the split of opisthokonts. Later, the Secretin family evolved from the Adhesion GPCR receptor family before the split of nematodes. Insect GPCRs appear to be in their own group and Taste2 is identified as descending from Rhodopsin. Note that the Secretin/Adhesion split is based on presumed function rather than signature, as the classical Class B (7tm_2, ) is used to identify both in the studies. | 1 | Biochemistry |
Plants are exposed to many stress factors such as disease, temperature changes, herbivory, injury and more. Therefore, in order to respond or be ready for any kind of physiological state, they need to develop some sort of system for their survival in the moment and/or for the future. Plant communication encompasses communication using volatile organic compounds, electrical signaling, and common mycorrhizal networks between plants and a host of other organisms such as soil microbes, other plants (of the same or other species), animals, insects, and fungi. Plants communicate through a host of volatile organic compounds (VOCs) that can be separated into four broad categories, each the product of distinct chemical pathways: fatty acid derivatives, phenylpropanoids/benzenoids, amino acid derivatives, and terpenoids. Due to the physical/chemical constraints most VOCs are of low molecular mass (< 300 Da), are hydrophobic, and have high vapor pressures. The responses of organisms to plant emitted VOCs varies from attracting the predator of a specific herbivore to reduce mechanical damage inflicted on the plant to the induction of chemical defenses of a neighboring plant before it is being attacked. In addition, the host of VOCs emitted varies from plant to plant, where for example, the Venus Fly Trap can emit VOCs to specifically target and attract starved prey. While these VOCs typically lead to increased resistance to herbivory in neighboring plants, there is no clear benefit to the emitting plant in helping nearby plants. As such, whether neighboring plants have evolved the capability to "eavesdrop" or whether there is an unknown tradeoff occurring is subject to much scientific debate.
As related to the aspect of meaning-making, the field is also identified as phytosemiotics. | 1 | Biochemistry |
Professor Cerling, helped by James Ehleringer and Christopher Remien (two University of Utah colleagues), George Wittemyer of Colorado State University and member of "Save the Elephants" in Nairobi, and Iain Douglas-Hamilton, who founded the association "Save the Elephants", conducted a research around the Samburu and Buffalo Springs national reserves in northern Kenya analyzing carbon and other stable isotopes in elephant tail hair to discover where and what Victoria, Anastasia and Cleopatra, three daughters of a mother elephant named Queen Elizabeth, usually eat over a six-years period (2000–2006). In order to monitor their life, the elephants were equipped with a Global Positioning System that recorded their positions every hour for the whole research period. For getting the sample of tail hair, elephants were immobilized with drug-filled dart guns when necessary. Considering that the hair grows about an inch per month, a single hair contained isotopic information to diet during an 18-month period. | 9 | Geochemistry |
In physics, emission is the process by which a higher energy quantum mechanical state of a particle becomes converted to a lower one through the emission of a photon, resulting in the production of light. The frequency of light emitted is a function of the energy of the transition.
Since energy must be conserved, the energy difference between the two states equals the energy carried off by the photon. The energy states of the transitions can lead to emissions over a very large range of frequencies. For example, visible light is emitted by the coupling of electronic states in atoms and molecules (then the phenomenon is called fluorescence or phosphorescence). On the other hand, nuclear shell transitions can emit high energy gamma rays, while nuclear spin transitions emit low energy radio waves.
The emittance of an object quantifies how much light is emitted by it. This may be related to other properties of the object through the Stefan–Boltzmann law.
For most substances, the amount of emission varies with the temperature and the spectroscopic composition of the object, leading to the appearance of color temperature and emission lines. Precise measurements at many wavelengths allow the identification of a substance via emission spectroscopy.
Emission of radiation is typically described using semi-classical quantum mechanics: the particles energy levels and spacings are determined from quantum mechanics, and light is treated as an oscillating electric field that can drive a transition if it is in resonance with the systems natural frequency. The quantum mechanics problem is treated using time-dependent perturbation theory and leads to the general result known as Fermi's golden rule. The description has been superseded by quantum electrodynamics, although the semi-classical version continues to be more useful in most practical computations. | 7 | Physical Chemistry |
In covalent imprinting, the template molecule is covalently bonded to the functional monomers that are then polymerized together. After polymerization, the polymer matrix is cleaved from the template molecule, leaving a cavity shaped as the template. Upon rebinding with the original molecule, the binding sites will interact with the target molecule, reestablishing the covalent bonds. During this reestablishment, kinetics associated with bond binding and bond breakage are obtained back. The imprinted molecule is then released from the template, in which it would then rebind with the target molecule, forming the same covalent bonds that were formed before polymerization. Advantages through utilizing this approach include the functional group being solely associated with the binding sites, avoiding any non-specific binding. The imprinted molecule also displays a homogenous distribution of binding sites, increasing the stability of the template-polymer complex. However, there are a few number of compounds that can be used to imprint with template molecules via covalent bonding, such as alcohols, aldehydes and ketones, all of which have high formation kinetics. In some cases, the rebinding of the polymer matrix with the template can be very slow, making this approach time inefficient for applications that require fast kinetics, such as chromatography. | 6 | Supramolecular Chemistry |
The practice of designating hemes with upper case letters was formalized in a footnote in a paper by Puustinen and Wikstrom, which explains under which conditions a capital letter should be used: "we prefer the use of capital letters to describe the heme structure as isolated. Lowercase letters may then be freely used for cytochromes and enzymes, as well as to describe individual protein-bound heme groups (for example, cytochrome bc, and aa3 complexes, cytochrome b, heme c of the bc complex, heme a of the aa complex, etc)." In other words, the chemical compound would be designated with a capital letter, but specific instances in structures with lowercase. Thus cytochrome oxidase, which has two A hemes (heme a and heme a) in its structure, contains two moles of heme A per mole protein. Cytochrome bc, with hemes b, b, and c, contains heme B and heme C in a 2:1 ratio. The practice seems to have originated in a paper by Caughey and York in which the product of a new isolation procedure for the heme of cytochrome aa3 was designated heme A to differentiate it from previous preparations: "Our product is not identical in all respects with the heme a obtained in solution by other workers by the reduction of the hemin a as isolated previously (2). For this reason, we shall designate our product heme A until the apparent differences can be rationalized." In a later paper, Caughey's group uses capital letters for isolated heme B and C as well as A. | 1 | Biochemistry |
Electrolysis of water in a supercritical state, reduces the overpotentials found in other electrolysers, thereby improving the electrical efficiency of the production of oxygen and hydrogen.
Increased temperature reduces thermodynamic barriers and increases kinetics. No bubbles of oxygen or hydrogen are formed on the electrodes, therefore no insulating layer is formed between catalyst and water, reducing the ohmic losses. The gas-like properties provide rapid mass transfer. | 7 | Physical Chemistry |
During the same period, Santorio Santorio came up with one of the earliest thermoscopes. In 1612 he published his results on the heating effects from the Sun, and attempts to measure heat from the Moon.
Earlier 1589, Giambattista della Porta reported on the heat resented by his face, emitted by a remote candle and facilitated by a concave metallic mirror. He also reported the cooling felt from a solid ice block Della Porta experiment would be replicated many times with increasing accuracy. It was replicated by astronomers Giovanni Antonio Magini and Christopher Heydon in 1603, and supplied instructions for Rudolf II, Holy Roman Emperor who performed it in 1611. In 1660, della Porta experiment was updated by the Accademia del Cimento using a thermometer invented by Ferdinand II, Grand Duke of Tuscany. | 7 | Physical Chemistry |
Separation processes are of great economic importance as they are accounting for 40 – 90% of capital and operating costs in industry. The separation processes of mixtures are including besides others washing, extraction, pressing, drying, clarification, evaporation, crystallization and filtration. Often several separation processes are performed successively. Separation operations are having several different functions:
* Purification of raw materials and products and recovery of by-products
* Recycling of solvents and unconverted reactants
* Removal of contaminants from effluents | 3 | Analytical Chemistry |
Nitrobenzyl-based PPGs are often considered the most commonly used PPGs. These PPGs are traditionally identified as Norrish Type II reaction as their mechanism was first described by Norrish in 1935. Norrish elucidated that an incident photon (200 nm –10 s. Following resonance of the π-electrons, a five-membered ring is formed before the PPG is cleaved yielding 2-nitrosobenzaldehyde and a carboxylic acid.
Overall, nitrobenzyl-based PPGs are highly general. The list of functional groups that can be protected include, but are not limited to, phosphates, carboxylates, carbonates, carbamates, thiolates, phenolates and alkoxides. Additionally, while the rate varies with a number of variables, including choice of solvent and pH, the photodeprotection has been exhibited in both solution and in the solid-state. Under optimal conditions, the photorelease can proceed with >95% yield. Nevertheless, the photoproducts of this PPG are known to undergo imine formation when irradiated at wavelengths above 300 nm. This side product often competes for incident radiation, which may lead to decreased chemical and quantum yields. | 5 | Photochemistry |
Solar cells are commonly encapsulated in a transparent polymeric resin to protect the delicate solar cell regions for coming into contact with moisture, dirt, ice, and other conditions expected either during operation or when used outdoors. The encapsulants are commonly made from polyvinyl acetate or glass. Most encapsulants are uniform in structure and composition, which increases light collection owing to light trapping from total internal reflection of light within the resin. Research has been conducted into structuring the encapsulant to provide further collection of light. Such encapsulants have included roughened glass surfaces, diffractive elements, prism arrays, air prisms, v-grooves, diffuse elements, as well as multi-directional waveguide arrays. Prism arrays show an overall 5% increase in the total solar energy conversion. Arrays of vertically aligned broadband waveguides provide a 10% increase at normal incidence, as well as wide-angle collection enhancement of up to 4%, with optimized structures yielding up to a 20% increase in short circuit current. Active coatings that convert infrared light into visible light have shown a 30% increase. Nanoparticle coatings inducing plasmonic light scattering increase wide-angle conversion efficiency up to 3%. Optical structures have also been created in encapsulation materials to effectively "cloak" the metallic front contacts. | 7 | Physical Chemistry |
* The Tishchenko reaction of acetaldehyde gives the commercially important solvent ethyl acetate. The reaction is catalyzed by aluminium alkoxides.
* The Tishchenko reaction is used to obtain isobutyl isobutyrate, a specialty solvent.
* Hydroxypivalic acid neopentyl glycol ester is produced by a Tishchenko reaction from hydroxypivaldehyde in the presence of a basic catalyst (e.g., aluminium oxide).
* The Tishchenko reaction of paraformaldehyde in the presence of aluminum methylate or magnesium methylate forms methyl formate.
* Paraformaldehyde reacts with boric acid to form methyl formate. The key step in the reaction mechanism for this reaction is a 1,3-hydride shift in the hemiacetal intermediate formed from two successive nucleophilic addition reactions, the first one from the catalyst. The hydride shift regenerates the alkoxide catalyst. | 0 | Organic Chemistry |
Monomeric metal carbyne complexes exhibit fairly linear M–C–R linkages according to X-ray crystallography. The M–C distances are typically shorter than the M–C bonds found in metal carbenes. The bond angle is generally between 170° and 180° Analogous to Fischer and Schrock carbenes; Fischer and Schrock carbynes are also known. Fischer carbynes usually have lower oxidation state metals and the ligands are π-accepting/electron-withdrawing ligands. Schrock carbynes on the other hand typically have higher oxidation state metals and electron-donating/anionic ligands. In a Fischer carbyne the C-carbyne exhibits electrophilic behavior while Schrock carbynes display nucleophilic reactivity on the carbyne carbon Carbyne complexes have also been characterized by many methods including infrared Spectroscopy, Raman spectroscopy. Bond lengths, bond angles and structures can be inferred from these and other analytical techniques.
Metal carbyne complexes also exhibit a large trans effect, where the ligand opposite the carbyne is typically labile. | 0 | Organic Chemistry |
Boron porphyrins first appeared in the literature during the 1960s and 1970s, in initially available literature the complex was never well characterized. The Boron porphyrin compounds can be synthesized either from the free base porphyrin or from a lithium porphyrin complex as starting material. Two representative examples are shown here. The first is the porphyrin free base reacted with BX in the presence of water.
The second is Li(ttp) reacted with BX. The (BX)(por) can undergo reduction to form a B-B bond and eliminate X, giving (BX)(por). From here, the halides can be replaced with BuLi to give (B-Bu)(por), reacted with alcohols to give (B-OR)(por), or even undergo halogen abstraction via weakly-coordinating anions to give [(B-B)(por)]. | 5 | Photochemistry |
In a traditional chemical formula notation, a buckminsterfullerene (C) with an atom (M) was simply represented as MC regardless of whether M was inside or outside the fullerene. In order to allow for more detailed discussions with minimal loss of information, a more explicit notation was proposed in 1991,
where the atoms listed to the left of the @ sign are situated inside the network composed of the atoms listed to the right. The example above would then be denoted M@C if M were inside the carbon network. A more complex example is K(K@CB), which denotes "a 60-atom fullerene cage with one boron atom substituted for a carbon in the geodesic network, a single potassium trapped inside, and two potassium atoms adhering to the outside."
The choice of the symbol has been explained by the authors as being concise, readily printed and transmitted electronically (the at sign is included in ASCII, which most modern character encoding schemes are based on), and the visual aspects suggesting the structure of an endohedral fullerene. | 6 | Supramolecular Chemistry |
If we place two detectors at the same angle from the target, one on the right and one on the left, they will generally measure a different number of electrons and . Consequently it is possible to define the asymmetry , as
The Sherman function is a measure of the probability of a spin-up electron to be scattered, at a specific angle , to the right or to the left of the target, due to spin-orbit coupling. It can assume values ranging from -1 (spin-up electron is scattered with 100% probability to the left of the target) to +1 (spin-up electron is scattered with 100% probability to the right of the target). The value of the Sherman function depends on the energy of the incoming electron, evaluated via the parameter . When , spin-up electrons will be scattered with the same probability to the right and to the left of the target.
Then it is possible to write
Plugging these formulas inside the definition of asymmetry, it is possible to obtain a simple expression for the evaluation of the asymmetry at a specific angle , i.e.:
Theoretical calculations are available for different atomic targets and for a specific target, as a function of the angle. | 7 | Physical Chemistry |
The crystallographic directions are geometric lines linking nodes (atoms, ions or molecules) of a crystal. Likewise, the crystallographic planes are geometric planes linking nodes. Some directions and planes have a higher density of nodes. These high density planes have an influence on the behavior of the crystal as follows:
*Optical properties: Refractive index is directly related to density (or periodic density fluctuations).
*Adsorption and reactivity: Physical adsorption and chemical reactions occur at or near surface atoms or molecules. These phenomena are thus sensitive to the density of nodes.
*Surface tension: The condensation of a material means that the atoms, ions or molecules are more stable if they are surrounded by other similar species. The surface tension of an interface thus varies according to the density on the surface.
*Microstructural defects: Pores and crystallites tend to have straight grain boundaries following higher density planes.
*Cleavage: This typically occurs preferentially parallel to higher density planes.
*Plastic deformation: Dislocation glide occurs preferentially parallel to higher density planes. The perturbation carried by the dislocation (Burgers vector) is along a dense direction. The shift of one node in a more dense direction requires a lesser distortion of the crystal lattice.
Some directions and planes are defined by symmetry of the crystal system. In monoclinic, trigonal, tetragonal, and hexagonal systems there is one unique axis (sometimes called the principal axis) which has higher rotational symmetry than the other two axes. The basal plane is the plane perpendicular to the principal axis in these crystal systems. For triclinic, orthorhombic, and cubic crystal systems the axis designation is arbitrary and there is no principal axis. | 3 | Analytical Chemistry |
A sigma factor (σ factor or specificity factor) is a protein needed for initiation of transcription in bacteria. It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase (RNAP) to gene promoters. It is homologous to archaeal transcription factor B and to eukaryotic factor TFIIB. The specific sigma factor used to initiate transcription of a given gene will vary, depending on the gene and on the environmental signals needed to initiate transcription of that gene. Selection of promoters by RNA polymerase is dependent on the sigma factor that associates with it. They are also found in plant chloroplasts as a part of the bacteria-like plastid-encoded polymerase (PEP).
The sigma factor, together with RNA polymerase, is known as the RNA polymerase holoenzyme. Every molecule of RNA polymerase holoenzyme contains exactly one sigma factor subunit, which in the model bacterium Escherichia coli is one of those listed below. The number of sigma factors varies between bacterial species. E. coli has seven sigma factors. Sigma factors are distinguished by their characteristic molecular weights. For example, σ is the sigma factor with a molecular weight of 70 kDa.
The sigma factor in the RNA polymerase holoenzyme complex is required for the initiation of transcription, although once that stage is finished, it is dissociated from the complex and the RNAP continues elongation on its own. | 1 | Biochemistry |
Pepper spray is an inflammatory agent. It inflames the mucous membranes in the eyes, nose, throat and lungs. It causes immediate closing of the eyes, difficulty breathing, runny nose, and coughing. The duration of its effects depends on the strength of the spray; the average full effect lasts from 20 to 90 minutes, but eye irritation and redness can last for up to 24 hours.
The Journal of Investigative Ophthalmology and Visual Science published a study that concluded that single exposure of the eye to OC is harmless, but repeated exposure can result in long-lasting changes in corneal sensitivity. They found no lasting decrease in visual acuity.
The European Parliament Scientific and Technological Options Assessment (STOA) published in 1998 "An Appraisal of Technologies of Political Control"
The STOA appraisal states:
::"Past experience has shown that to rely on manufacturers unsubstantiated claims about the absence of hazards is unwise. In the US, companies making crowd control weapons, (e.g. pepper-gas manufacturer Zarc International), have put their technical data in the public domain without loss of profitability."
:and
::"Research on chemical irritants should be published in open scientific journals before authorization for any usage is permitted and that the safety criteria for such chemicals should be treated as if they were drugs rather than riot control agents;"
For those taking drugs, or those subjected to restraining techniques that restrict the breathing passages, there is a risk of death. In 1995, the Los Angeles Times reported at least 61 deaths associated with police use of pepper spray since 1990 in the USA. The American Civil Liberties Union (ACLU) documented 27 people in police custody who died after exposure to pepper spray in California since 1993. However, the ACLU report counts all deaths occurring within hours of exposure to pepper spray regardless of prior interaction, taser use, or if drugs are involved. In all 27 cases listed by the ACLU, the coroners' report listed other factors as the primary cause of death; in a few cases the use of pepper spray may have been a contributing factor.
The US Army performed studies in 1993 at Aberdeen Proving Ground, and a UNC study in 2000 stated that the compound in peppers, capsaicin, is mildly mutagenic, and 10% of mice exposed to it developed cancer. Where the study also found many beneficial effects of capsaicin, the Occupational Safety and Health Administration released statements declaring exposure of employees to OC is an unnecessary health risk. As of 1999, it was in use by more than 2,000 public safety agencies.
The head of the FBIs Less-Than-Lethal Weapons Program at the time of the 1991 study, Special Agent Thomas W. W. Ward, was fired by the FBI and was sentenced to two months in prison for receiving payments from a pepper-gas manufacturer while conducting and authoring the FBI study that eventually approved pepper spray for FBI use. Prosecutors said that from December 1989 through 1990, Ward received about $5,000 a month for a total of $57,500, from Luckey Police Products, a Fort Lauderdale, Florida-based company that was a major producer and supplier of pepper spray. The payments were paid through a Florida company owned by Wards wife.
Direct close-range spray can cause more serious eye irritation by attacking the cornea with a concentrated stream of liquid (the so-called "hydraulic needle" effect). Some brands have addressed this problem by means of an elliptically cone-shaped spray pattern.
Pepper spray has been associated with positional asphyxiation of individuals in police custody. There is much debate over the actual cause of death in these cases. There have been few controlled clinical studies of the human health effects of pepper spray marketed for police use, and those studies are contradictory. Some studies have found no harmful effects beyond the effects described above. Due to these studies and deaths, many law enforcement agencies have moved to include policies and training to prevent positional deaths. However, there are some scientific studies that argue the positional asphyxiation claim is a myth due to pinpoint pressure on a person. The study by two universities stressed that no pressure should be applied to the neck area. They concluded that the persons own weight is not scientifically enough to stop a persons breathing with the rest of their body supported. | 1 | Biochemistry |
The context for understanding the thermodynamics of quark matter is the standard model of particle physics, which contains six different flavors of quarks, as well as leptons like electrons and neutrinos. These interact via the strong interaction, electromagnetism, and also the weak interaction which allows one flavor of quark to turn into another. Electromagnetic interactions occur between particles that carry electrical charge; strong interactions occur between particles that carry color charge.
The correct thermodynamic treatment of quark matter depends on the physical context. For large quantities that exist for long periods of time (the "thermodynamic limit"), we must take into account the fact that the only conserved charges in the standard model are quark number (equivalent to baryon number), electric charge, the eight color charges, and lepton number. Each of these can have an associated chemical potential. However, large volumes of matter must be electrically and color-neutral, which determines the electric and color charge chemical potentials. This leaves a three-dimensional phase space, parameterized by quark chemical potential, lepton chemical potential, and temperature.
In compact stars quark matter would occupy cubic kilometers and exist for millions of years, so the thermodynamic limit is appropriate. However, the neutrinos escape, violating lepton number, so the phase space for quark matter in compact stars only has two dimensions, temperature (T) and quark number chemical potential μ. A strangelet is not in the thermodynamic limit of large volume, so it is like an exotic nucleus: it may carry electric charge.
A heavy-ion collision is in neither the thermodynamic limit of large volumes nor long times. Putting aside questions of whether it is sufficiently equilibrated for thermodynamics to be applicable, there is certainly not enough time for weak interactions to occur, so flavor is conserved, and there are independent chemical potentials for all six quark flavors. The initial conditions (the impact parameter of the collision, the number of up and down quarks in the colliding nuclei, and the fact that they contain no quarks of other flavors) determine the chemical potentials. (Reference for this section:). | 7 | Physical Chemistry |
It catalyzes the reduction of cytochrome c by
oxidation of coenzyme Q (CoQ) and the concomitant pumping of 4 protons from the mitochondrial matrix to the intermembrane space:
: QH + 2 cytochrome c (Fe) + 2 H → Q + 2 cytochrome c (Fe) + 4 H
In the process called Q cycle, two protons are consumed from the matrix (M), four protons are released into the inter membrane space (IM) and two electrons are passed to cytochrome c. | 1 | Biochemistry |
Solid state fermentation (SSF) is a biomolecule manufacturing process used in the food, pharmaceutical, cosmetic, fuel and textile industries. These biomolecules are mostly metabolites generated by microorganisms grown on a solid support selected for this purpose. This technology for the culture of microorganisms is an alternative to liquid or submerged fermentation, used predominantly for industrial purposes. | 1 | Biochemistry |
For two N particle systems 0 and 1 with partition function and ,
from
get the thermodynamic free energy difference is
For every configuration visited during this sampling of system 1 we can compute the potential energy U as a function of the configuration space, and the potential energy difference is
Now construct a probability density of the potential energy from the above equation:
where in is a configurational part of a partition function
since
now define two functions:
thus that
and can be obtained by fitting and | 7 | Physical Chemistry |
In addition to the variety of verified DNA structures, there have been a range of proposed DNA models that have either been disproven, or lack evidence.
Some of these structures were proposed during the 1950s before the structure of the double helix was solved, most famously by Linus Pauling. Non-helical or "side-by-side" models of DNA were proposed in the 1970s to address what appeared at the time to be problems with the topology of circular DNA chromosomes during replication (subsequently resolved via the discovery of enzymes that modify DNA topology). These were also rejected due to accumulating experimental evidence from X-ray crystallography, solution NMR, and atomic force microscopy (of both DNA alone, and bound to DNA-binding proteins). Although localised or transient non-duplex helical structures exist, non-helical models are not currently accepted by the mainstream scientific community. Finally, there exists a persistent set of contemporary fringe theories proposing a range of unsupported models. | 1 | Biochemistry |
The first example of laser cooling, and also still the most common method (so much so that it is still often referred to simply as laser cooling) is Doppler cooling. | 7 | Physical Chemistry |
International treaties on the long-range transport of atmospheric pollutants have been agreed upon by western countries for some time now. Beginning in 1979, European countries convened in order to ratify general principles discussed during the UNECE Convention. The purpose was to combat Long-Range Transboundary Air Pollution. The 1985 Helsinki Protocol on the Reduction of Sulfur Emissions under the Convention on Long-Range Transboundary Air Pollution furthered the results of the convention. Results of the treaty have already come to fruition, as evidenced by an approximate 40 percent drop in particulate matter in North America. The effectiveness of the Convention in combatting acid rain has inspired further acts of international commitment to prevent the proliferation of particulate matter. Canada and the US signed the Air Quality Agreement in 1991. Most European countries and Canada signed the treaties. Activity of the Long-Range Transboundary Air Pollution Convention remained dormant after 1999, when 27 countries convened to further reduce the effects of acid rain. In 2000, foreign cooperation to prevent acid rain was sparked in Asia for the first time. Ten diplomats from countries ranging throughout the continent convened to discuss ways to prevent acid rain. Following these discussions, the Acid Deposition Monitoring Network in East Asia (EANET) was established in 2001 as an intergovernmental initiative to provide science-based inputs for decision makers and promote international cooperation on acid deposition in East Asia. In 2023, the EANET member countries include Cambodia, China, Indonesia, Japan, Lao PDR, Malaysia, Mongolia, Myanmar, the Philippines, Republic of Korea, Russia, Thailand and Vietnam. | 2 | Environmental Chemistry |
In 2007 the New Zealand Society of Plant Biologists renamed their annual award after Slack. The award is made to society members to recognise an outstanding contribution to the study of plant biology. It was renamed in recognition of his outstanding contribution as a plant biologist and biochemist in New Zealand, his role in the discovery of C4 photosynthesis (also known as the Hatch Slack Pathway), and his contribution as an early member of the New Zealand Society of Plant Biologists. | 1 | Biochemistry |
The level 1 destination vector determines the position and orientation of each gene in the final construct. There are fourteen available level 1 vectors, which differ only by the sequence of the flanking fusion sites while being identical in the internal fusion sites. Hence, all vectors can assemble the same level 0 parts.
As all level 1 vectors are binary plasmids, they are used for Agrobacterium mediated temporary expression in plants. | 1 | Biochemistry |
The material properties of the metal interconnects have a strong influence on the life span. The characteristics are predominantly the composition of the metal alloy and the dimensions of the conductor. The shape of the conductor, the crystallographic orientation of the grains in the metal, procedures for the layer deposition, heat treatment or annealing, characteristics of the passivation and the interface to other materials also affect the durability of the interconnects. There are also important differences with time dependent current: direct current or different alternating current waveforms cause different effects. | 7 | Physical Chemistry |
Prime editor 5 utilizes the same machinery as PE3, but also includes a plasmid that encodes for dominant negative MLH1. Like PE4, this allows for a knockdown of endogenous MMR response, increasing the efficiency of prime editing. | 1 | Biochemistry |
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