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To stop the corrosion from continuing the object just needs to be aired out to remove any moisture and allow the normal layer of protection to form. Washing and a wire brush will remove most of the corrosion. For complete removal, 10% acetic acid or a mixture of polishing chalk and 20–40% NaOH can be used. Both require a thorough water rinsing afterward and do not restore lustrous surface finish if one was previously present. | 8 | Metallurgy |
Spiral separators of the wet type, also called spiral concentrators, are devices to separate solid components in a slurry, based upon a combination of the solid particle density as well as the particle's hydrodynamic properties (e.g. drag). The device consists of a tower, around which is wound a sluice, from which slots or channels are placed in the base of the sluice to extract solid particles that have come out of suspension.
As larger and heavier particles sink to the bottom of the sluice faster and experience more drag from the bottom, they travel slower, and so move towards the center of the spiral. Conversely, light particles stay towards the outside of the spiral, with the water, and quickly reach the bottom. At the bottom, a "cut" is made with a set of adjustable bars, channels, or slots, separating the low and high density parts. | 3 | Analytical Chemistry |
SH2 domains are not present in yeast and appear at the boundary between protozoa and animalia in organisms such as the social amoeba Dictyostelium discoideum.
A detailed bioinformatic examination of SH2 domains of human and mouse reveals 120 SH2 domains contained within 115 proteins encoded by the human genome, representing a rapid rate of evolutionary expansion among the SH2 domains.
A large number of SH2 domain structures have been solved and many SH2 proteins have been knocked out in mice. | 1 | Biochemistry |
Crystallographic directions are lines linking nodes (atoms, ions or molecules) of a crystal. Similarly, crystallographic planes are planes linking nodes. Some directions and planes have a higher density of nodes; these dense planes have an influence on the behavior of the crystal:
*optical properties: in condensed matter, light "jumps" from one atom to the other with the Rayleigh scattering; the velocity of light thus varies according to the directions, whether the atoms are close or far; this gives the birefringence
*adsorption and reactivity: adsorption and chemical reactions can occur at atoms or molecules on crystal surfaces, 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
** Pores and crystallites tend to have straight grain boundaries following dense planes
**cleavage
*dislocations (plastic deformation)
**the dislocation core tends to spread on dense planes (the elastic perturbation is "diluted"); this reduces the friction (Peierls–Nabarro force), the sliding occurs more frequently on dense planes;
**the perturbation carried by the dislocation (Burgers vector) is along a dense direction: the shift of one node in a dense direction is a lesser distortion;
**the dislocation line tends to follow a dense direction, the dislocation line is often a straight line, a dislocation loop is often a polygon.
For all these reasons, it is important to determine the planes and thus to have a notation system. | 3 | Analytical Chemistry |
A number of organism-specific transcriptome databases have been constructed and annotated to aid in the identification of genes that are differentially expressed in distinct cell populations.
RNA-seq is emerging (2013) as the method of choice for measuring transcriptomes of organisms, though the older technique of DNA microarrays is still used. RNA-seq measures the transcription of a specific gene by converting long RNAs into a library of cDNA fragments. The cDNA fragments are then sequenced using high-throughput sequencing technology and aligned to a reference genome or transcriptome which is then used to create an expression profile of the genes. | 1 | Biochemistry |
A fourth group has also been discovered and members have three amino acids between the two cysteines and is termed CXC chemokine (or d-chemokines). The only CXC chemokine discovered to date is called fractalkine (or CXCL1). It is both secreted and tethered to the surface of the cell that expresses it, thereby serving as both a chemoattractant and as an adhesion molecule. | 1 | Biochemistry |
In fluid mechanics, dewetting is one of the processes that can occur at a solid–liquid, solid–solid or liquid–liquid interface. Generally, dewetting describes the process of retraction of a fluid from a non-wettable surface it was forced to cover. The opposite process—spreading of a liquid on a substrate—is called wetting. The factor determining the spontaneous spreading and dewetting for a drop of liquid placed on a solid substrate with ambient gas, is the so-called spreading coefficient :
where is the solid-gas surface tension, is the solid-liquid surface tension and is the liquid-gas surface tension (measured for the mediums before they are brought in contact with each other).
When , the spontaneous spreading occurs, and if , partial wetting is observed, meaning the liquid will only cover the substrate to some extent.
The equilibrium contact angle is determined from the Young–Laplace equation.
Spreading and dewetting are important processes for many applications, including adhesion, lubrication, painting, printing, and protective coating. For most applications, dewetting is an unwanted process, because it destroys the applied liquid film.
Dewetting can be inhibited or prevented by photocrosslinking the thin film prior to annealing, or by incorporating nanoparticle additives into the film.
Surfactants can have a significant effect on the spreading coefficient. When a surfactant is added, its amphiphilic properties cause it to be more energetically favorable to migrate to the surface, decreasing the interfacial tension and thus increasing the spreading coefficient (i.e. making S more positive). As more surfactant molecules are absorbed into the interface, the free energy of the system decreases in tandem to the surface tension decreasing, eventually causing the system to become completely wetting.
In biology, by analogy with the physics of liquid dewetting, the process of tunnel formation through endothelial cells has been referred to as cellular dewetting. | 7 | Physical Chemistry |
From the structural perspective, haloalkanes can be classified according to the connectivity of the carbon atom to which the halogen is attached. In primary (1°) haloalkanes, the carbon that carries the halogen atom is only attached to one other alkyl group. An example is chloroethane (). In secondary (2°) haloalkanes, the carbon that carries the halogen atom has two C–C bonds. In tertiary (3°) haloalkanes, the carbon that carries the halogen atom has three C–C bonds.
Haloalkanes can also be classified according to the type of halogen on group 17 responding to a specific halogenoalkane. Haloalkanes containing carbon bonded to fluorine, chlorine, bromine, and iodine results in organofluorine, organochlorine, organobromine and organoiodine compounds, respectively. Compounds containing more than one kind of halogen are also possible. Several classes of widely used haloalkanes are classified in this way chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). These abbreviations are particularly common in discussions of the environmental impact of haloalkanes. | 0 | Organic Chemistry |
Tumor angiogenesis rely on interactions between endothelial vascular growth factors which can all activate the PI3K/AKT/mTOR in endothelial cells, pericytes, or cancer cells. Example of these growth factors are angiopoietin 1 (ANG1), ANG 2, basic fibroblast growth factor (bFGF), ephrin-B2, vascular endothelial growth factor (VEGF), and members of the tumor growth factor-β (TGFβ) superfamily. One of the major stimuli of angiogenesis is hypoxia, resulting in activation of hypoxia-inducible transcription factors (HIFs) and expression of ANG2, bFGF, PDGF, VEGF, and VEGFR. Inhibition of HIF1α translation by preventing PDGF/PDGFR and VEGF/VEGFR can result from mTOR inhibition. A G0-G1 cell-cycle blockage can be the consequence of inactivation of mTOR in hypoxia-activated pericytes and endothelial cells.
There is some evidence that extended therapy with rapamycin may have effect on AKT and mTORC2 as well. | 1 | Biochemistry |
Small interfering (siRNA) are short, 19-23 base-pair (with a 3 overhang of two nucleotides), double-stranded pieces of RNA that participate in the RNA-induced silencing complex (RISC) for gene silencing. Specifically, siRNA is bound by the RISC complex where it is unwound using ATP hydrolysis. It is then used as a guide by the enzyme "Slicer" to target mRNAs for degradation based on complementary base-pairing to the target mRNA. As a therapeutic, siRNA is able to be delivered locally, through the eye or nose, to treat various diseases. Local delivery benefits from simple formulation and drug delivery and high bioavailability of the drug. Systemic delivery is necessary to target cancers and other diseases. Targeting the siRNA when delivered locally is one of the main challenges in siRNA therapeutics. While it is possible to use intravenous injection to deliver siRNA therapies, concerns have been raised about the large volumes used in the injection, as these must often be ~20-30% of the total blood volume. Other methods of delivery include liposome packaging, conjugation to membrane-permeable peptides, and direct tissue/organ electroporation. Additionally, it has been found that exogeneous siRNAs only last a few days (a few weeks at most in non-dividing cells) in vivo'. If siRNA is able to successfully reach its target, it has the potential to therapeutically regulate gene expression through its ability to base-pair to mRNA targets and promote their degradation through the RISC system Currently, siRNA-based therapy is in a phase I clinical trial for the treatment of age-related macular degeneration, although it is also being explored for use in cancer therapy. For instance, siRNA can be used to target mRNAs that code for proteins that promote tumor growth such as the VEGF receptor and telomerase enzyme. | 1 | Biochemistry |
In atomic, molecular and optical physics, the Araki–Sucher correction is a leading-order correction to the energy levels of atoms and molecules due to effects of quantum electrodynamics (QED). It is named after Huzihiro Araki and Joseph Sucher, who first calculated it for the helium atom in 1957. The method is based on a perturbative expansion of the energy in the Bethe–Salpeter equation, and have since been used to calculate corrections for atoms other than helium (e.g. beryllium and lithium), and for systems with more than two electrons. The correction typically involves the fine-structure constant and may sometimes include terms of third order and higher . | 7 | Physical Chemistry |
*Arc discharge: this is a high power thermal discharge of very high temperature (≈10,000 K). It can be generated using various power supplies. It is commonly used in metallurgical processes. For example, it is used to smelt minerals containing AlO to produce aluminium.
*Corona discharge: this is a non-thermal discharge generated by the application of high voltage to sharp electrode tips. It is commonly used in ozone generators and particle precipitators.
*Dielectric barrier discharge (DBD): this is a non-thermal discharge generated by the application of high voltages across small gaps wherein a non-conducting coating prevents the transition of the plasma discharge into an arc. It is often mislabeled "Corona" discharge in industry and has similar application to corona discharges. A common usage of this discharge is in a plasma actuator for vehicle drag reduction. It is also widely used in the web treatment of fabrics. The application of the discharge to synthetic fabrics and plastics functionalizes the surface and allows for paints, glues and similar materials to adhere. The dielectric barrier discharge was used in the mid-1990s to show that low temperature atmospheric pressure plasma is effective in inactivating bacterial cells. This work and later experiments using mammalian cells led to the establishment of a new field of research known as plasma medicine. The dielectric barrier discharge configuration was also used in the design of low temperature plasma jets. These plasma jets are produced by fast propagating guided ionization waves known as plasma bullets.
*Capacitive discharge: this is a nonthermal plasma generated by the application of RF power (e.g., 13.56 MHz) to one powered electrode, with a grounded electrode held at a small separation distance on the order of 1 cm. Such discharges are commonly stabilized using a noble gas such as helium or argon.
*"Piezoelectric direct discharge plasma:" is a nonthermal plasma generated at the high-side of a piezoelectric transformer (PT). This generation variant is particularly suited for high efficient and compact devices where a separate high voltage power supply is not desired. | 7 | Physical Chemistry |
The contribution of each gas to the enhanced greenhouse effect is determined by the characteristics of that gas, its abundance, and any indirect effects it may cause. For example, the direct radiative effect of a mass of methane is about 84 times stronger than the same mass of carbon dioxide over a 20-year time frame. Since the 1980s, greenhouse gas forcing contributions (relative to year 1750) are also estimated with high accuracy using IPCC-recommended expressions derived from radiative transfer models.
The concentration of a greenhouse gas is typically measured in parts per million (ppm) or parts per billion (ppb) by volume. A concentration of 420 ppm means that 420 out of every million air molecules is a molecule. The first 30 ppm increase in concentrations took place in about 200 years, from the start of the Industrial Revolution to 1958; however the next 90 ppm increase took place within 56 years, from 1958 to 2014. Similarly, the average annual increase in the 1960s was only 37% of what it was in 2000 through 2007.
Many observations are available online in a variety of Atmospheric Chemistry Observational Databases. The table below shows the most influential long-lived, well-mixed greenhouse gases, along with their tropospheric concentrations and direct radiative forcings, as identified by the Intergovernmental Panel on Climate Change (IPCC). Abundances of these trace gases are regularly measured by atmospheric scientists from samples collected throughout the world. It excludes water vapor because changes in its concentrations are calculated as a climate change feedback indirectly caused by changes in other greenhouse gases, as well as ozone, whose concentrations are only modified indirectly by various refrigerants that cause ozone depletion. Some short-lived gases (e.g. carbon monoxide, NOx) and aerosols (e.g. mineral dust or black carbon) are also excluded because of limited role and strong variation, alongwith minor refrigerants and other halogenated gases, which have been mass-produced in smaller quantities than those in the table. and Annex III of the 2021 IPCC WG1 Report
Mole fractions: μmol/mol = ppm = parts per million (10); nmol/mol = ppb = parts per billion (10); pmol/mol = ppt = parts per trillion (10).
The IPCC states that "no single atmospheric lifetime can be given" for CO. This is mostly due to the rapid growth and cumulative magnitude of the disturbances to Earth's carbon cycle by the geologic extraction and burning of fossil carbon. As of year 2014, fossil CO emitted as a theoretical 10 to 100 GtC pulse on top of the existing atmospheric concentration was expected to be 50% removed by land vegetation and ocean sinks in less than about a century, as based on the projections of coupled models referenced in the AR5 assessment. A substantial fraction (20–35%) was also projected to remain in the atmosphere for centuries to millennia, where fractional persistence increases with pulse size.
Values are relative to year 1750. AR6 reports the effective radiative forcing which includes effects of rapid adjustments in the atmosphere and at the surface. | 2 | Environmental Chemistry |
Jaroslav Heyrovský () (December 20, 1890 – March 27, 1967) was a Czech chemist and inventor. Heyrovský was the inventor of the polarographic method, father of the electroanalytical method, and recipient of the Nobel Prize in 1959 for his invention and development of the polarographic methods of analysis. His main field of work was polarography. | 3 | Analytical Chemistry |
In 2005, Suskiewicz et al. classified the enzyme YwIE as a tyrosine phosphatase. And Kirstein et al. (2005) found that McsB is a tyrosine kinase that needs McsA to become activated. They also found that the interaction of McsA and McsB with CtsR results in the formation of a 3-protein complex that stops the binding of CtsR to its target DNA and leads to subsequent phosphorylation of McsB, McsA, and CtsR. | 1 | Biochemistry |
A mode of toxic action is a common set of physiological and behavioral signs that characterize a type of adverse biological response. A mode of action should not be confused with mechanism of action, which refer to the biochemical processes underlying a given mode of action. Modes of toxic action are important, widely used tools in ecotoxicology and aquatic toxicology because they classify toxicants or pollutants according to their type of toxic action. There are two major types of modes of toxic action: non-specific acting toxicants and specific acting toxicants. Non-specific acting toxicants are those that produce narcosis, while specific acting toxicants are those that are non-narcotic and that produce a specific action at a specific target site. | 1 | Biochemistry |
The ohmic resistance appears in series with the electrode impedance of the reaction and the Nyquist diagram is translated to the right. | 7 | Physical Chemistry |
Any of the thermodynamic potentials may be held constant during a process. For example:
* An isenthalpic process introduces no change in enthalpy in the system. | 7 | Physical Chemistry |
Sea salt is mentioned in the Vinaya Pitaka, a Buddhist scripture compiled in the mid-5th century BC. The principle of production is evaporation of the water from the sea brine. In warm and dry climates this may be accomplished entirely by using solar energy, but in other climates fuel sources have been used. Modern sea salt production is almost entirely found in Mediterranean and other warm, dry climates.
Such places are today called salt works, instead of the older English word saltern. An ancient or medieval saltern was established where there was:
# Access to a market for the salt
# A gently shelving coast, protected from exposure to the open sea
# An inexpensive and easily worked fuel supply, or preferably the sun
# Another trade, such as pastoral farming or tanning—which benefited from proximity to the saltern (by producing leather, salted meat, etc.) and provided the saltern with a local market
In this way, salt marsh, pasture (salting), and salt works (saltern) enhanced each other economically. This was the pattern during the Roman and medieval periods around The Wash, in eastern England. There, the tide brought the brine, the extensive saltings provided the pasture, the fens and moors provided the peat fuel, and the sun sometimes shone.
The dilute brine of the sea was largely evaporated by the sun. In Roman areas, this was done using ceramic containers known as briquetage. Workers scraped up the concentrated salt and mud slurry and washed it with clean sea water to settle impurities out of the now concentrated brine. They poured the brine into shallow pans (lightly baked from local marine clay) and set them on fist-sized clay pillars over a peat fire for final evaporation. Then they scraped out the dried salt and sold it.
In traditional salt production in the Visayas Islands of the Philippines, salt are made from coconut husks, driftwood, or other plant matter soaked in seawater for at least several months. These are burned into ash then seawater is run through the ashes on a filter. The resulting brine is then evaporated in containers. Coconut milk is sometimes added to the brine before evaporation. The practice is endangered due to competition with cheap industrially-produced commercial salt. Only two traditions survive to the present day: asín tibuok and túltul (or dúkdok).
In the colonial New World, slaves were brought from Africa to rake salt on various islands in the West Indies, Bahamas and particularly Turks and Caicos Islands.
Today, salt labelled "sea salt" in the US might not have actually come from the sea, as long as it meets the FDA's purity requirements. All mined salts were originally sea salts since they originated from a marine source at some point in the distant past, usually from an evaporating shallow sea. | 9 | Geochemistry |
The word "litmus" comes from an Old Norse word for “moss used for dyeing”. About 1300, the Spanish physician Arnaldus de Villa Nova began using litmus to study acids and bases.
From the 16th century onwards, the blue dye was extracted from some lichens, especially in the Netherlands. | 3 | Analytical Chemistry |
In FRAP, a region is briefly exposed to intense light, irrecoverably photobleaching fluorophores, and the fluorescence recovery due to diffusion of nearby (non-bleached) fluorophores is imaged. A primary advantage of FRAP over FCS is the ease of interpreting qualitative experiments common in cell biology. Differences between cell lines, or regions of a cell, or before and after application of drug, can often be characterized by simple inspection of movies. FCS experiments require a level of processing and are more sensitive to potentially confounding influences like: rotational diffusion, vibrations, photobleaching, dependence on illumination and fluorescence color, inadequate statistics, etc. It is much easier to change the measurement volume in FRAP, which allows greater control. In practice, the volumes are typically larger than in FCS. While FRAP experiments are typically more qualitative, some researchers are studying FRAP quantitatively and including binding dynamics. A disadvantage of FRAP in cell biology is the free radical perturbation of the cell caused by the photobleaching. It is also less versatile, as it cannot measure concentration or rotational diffusion, or co-localization. FRAP requires a significantly higher concentration of fluorophores than FCS. | 7 | Physical Chemistry |
The Crich β-mannosylation in organic chemistry is a synthetic strategy which is used in carbohydrate synthesis to generate a 1,2-cis-glycosidic bond. This type of linkate is generally very difficult to make, and specific methods like the Crich β-mannosylation are used to overcome these issues. The technique takes its name from its developer, Professor David Crich. | 0 | Organic Chemistry |
In thermodynamics, a thermodynamicist is someone who studies thermodynamic processes and phenomena, i.e. the physics that deal with mechanical action and relations of heat.
Among the well-known number of famous thermodynamicists, include Sadi Carnot, Rudolf Clausius, Willard Gibbs, Hermann von Helmholtz, and Max Planck. | 7 | Physical Chemistry |
Hydroalumination of alkynes may be either stereospecifically cis or trans depending on the conditions employed. When a dialkylalane such as di(isobutyl)aluminium hydride (DIBAL-H) is used, the hydrogen and aluminium delivered from the reagent end up cis in the resulting alkenylalane. This stereospecificity can be explained by invoking a concerted addition of the H–Al bond across the triple bond. In the transition state, partial positive charge builds up on the carbon forming a bond to hydrogen; thus, the carbon better able to stabilize a positive charge becomes attached to hydrogen in the product alkenylalane. Hydroaluminations of terminal alkynes typically produce terminal alkenylalanes as a result. Selectivity in hydroaluminations of internal alkynes is typically low, unless an electronic bias exists in the substrate (such as a phenyl ring in conjugation with the alkyne).
Stereospecific trans hydroalumination is possible through the use of lithium aluminium hydride. The mechanism of this transformation involves the addition of hydride to the carbon less able to stabilize the developing negative charge (viz., in the β position to an electron-withdrawing group). Coordination of aluminium to the resulting trans vinyl carbanion leads to the observed trans configuration of the product. | 0 | Organic Chemistry |
This detector is mostly used with alkali atoms, having a low ionization potential, with applications in mass spectrometry and atomic clocks. | 3 | Analytical Chemistry |
Anabolic processes build organs and tissues. These processes produce growth and differentiation of cells and increase in body size, a process that involves synthesis of complex molecules. Examples of anabolic processes include the growth and mineralization of bone and increases in muscle mass. | 1 | Biochemistry |
Computational methods have been applied to search for parameters (e.g. residue propensity, hydrophobicity, planarity) that could distinguish glycan-binding proteins from other surface patches. For example, a model trained on 19 non-homologous carbohydrate binding structures was able to predict carbohydrate-binding domains (CRDs) with an accuracy of 65% for non-enzymatic structures and 87% for enzymatic ones. Further studies have employed calculations of Van der Waals energies of protein-probe interactions and amino acid propensities to identify CRDs with 98% specificity at 73% sensitivity. More recent methods can predict CRDs even from protein sequences, by comparing the sequence with those for which structures are already known. | 1 | Biochemistry |
Unlike other GDNF family of ligands, persephin only contains one RXXR cleavage site, rather than multiple, indicating that it can only make one length of functional peptide. | 1 | Biochemistry |
Microwave radiation was applied in electrochemical methods in 1998 when Frank Marken and Richard G. Compton in Oxford placed a piece of platinum wire inside a microwave cavity in small electrochemical cell. | 5 | Photochemistry |
An area denial weapon is a defensive device used to prevent an adversary from occupying or traversing an area of land, sea or air. The specific method may not be totally effective in preventing passage, but is sufficient to severely restrict, slow down, or endanger the opponent. Some area denial weapons pose risks to civilians entering the area even long after combat has ended, and consequently are often controversial.
An area denial weapon can be part of an anti-access/area denial (A2/AD) strategy. | 1 | Biochemistry |
The discovery of the Nef reaction and the papers about divalent carbon (carbenes) were his major achievements. | 0 | Organic Chemistry |
The nucleophilic lysine residue is commonly targeted site in protein bioconjugation, typically through amine-reactive N-hydroxysuccinimidyl (NHS) esters. To obtain optimal number of deprotonated lysine residues, the pH of the aqueous solution must be below the pKa of the lysine ammonium group, which is around 10.5, so the typical pH of the reaction is about 8 and 9. The common reagent for the coupling reaction is NHS-ester (shown in the first reaction below in Figure 1), which reacts with nucleophilic lysine through a lysine acylation mechanism. Other similar reagents are isocyanates and isothiocyanates that undergo a similar mechanism (shown in the second and third reactions in Figure 1 below). Benzoyl fluorides (shown in the last reaction below in Figure 1), which allows for lysine modification of proteins under mild conditions (low temperature, physiological pH), were recently proposed as an alternative to classically used lysine specific reagents. | 1 | Biochemistry |
Chromatin Immunoprecipitation results in production of complex mixtures of relatively short DNA fragments, which is challenging to amplify with MDA without causing a bias in the fragment representation. A method to circumvent this problem was proposed, which is based on conversion of these mixtures to circular concatemers using ligation, followed by Φ29 DNA polymerase-mediated MDA. | 1 | Biochemistry |
Hexosaminidases (Hex) are important glycoside hydrolases for the generation of plant-specific paucimannosidic proteins across Plantae. HEXO1-HEXO3 have been reported to be key mediators of paucimannose expression in various plant species including Nicotiana benthamiana, A.thaliana and L. japonicus. Moreover, α1,3-fucosyltransferase (FUT11/12) and β1,2-xylosyltransferase as well as α-mannosidase II were also reported to play critical roles in the generation of the paucimannosidic proteins expressed by plants. | 1 | Biochemistry |
Metabolic labeling of glycans can be used as a way to detect glycan structures. A well-known strategy involves the use of azide-labeled sugars which can be reacted using the Staudinger ligation. This method has been used for in vitro and in vivo imaging of glycans. | 0 | Organic Chemistry |
Scolytus multistriatus, one of the vectors of the Dutch elm disease, uses vanillin as a signal to find a host tree during oviposition. | 0 | Organic Chemistry |
DNA is precipitated by first ensuring that the correct concentration of positive ions is present in solution (too much will result in a lot of salt co-precipitating with DNA, too little will result in incomplete DNA recovery) and then adding two to three volumes of at least 95% ethanol. Many protocols advise storing DNA at low temperature at this point, but there are also observations that it may not improve DNA recovery, and may even lower precipitation efficiency while using over-night incubation time. Therefore, good efficiency can be achieved at room temperature, but when possible degradation is taken into account, it is probably better to incubate DNA on wet ice. Optimal incubation time depends on the length and concentration of DNA. Smaller fragments and lower concentrations will require longer times to achieve acceptable recovery. For very small lengths and low concentrations over-night incubation is recommended. In such cases use of carriers like tRNA, glycogen or linear polyacrylamide can greatly improve recovery.
During incubation DNA and some salts will precipitate from solution, in the next step this precipitate is collected by centrifugation in a microcentrifuge tube at high speeds (~12,000g). Time and speed of centrifugation has the biggest effect on DNA recovery rates. Again smaller fragments and higher dilutions require longer and faster centrifugation. Centrifugation can be done either at room temperature or in 4 °C or 0 °C.
During centrifugation precipitated DNA has to move through ethanol solution to the bottom of the tube, lower temperatures increase viscosity of the solution and larger volumes make the distance longer, so both those factors lower efficiency of this process requiring longer centrifugation for the same effect.
After centrifugation the supernatant solution is removed, leaving a pellet of crude DNA. Whether the pellet is visible depends on the amount of DNA and on its purity (dirtier pellets are easier to see) or the use of co-precipitants.
In the next step, 70% ethanol is added to the pellet, and it is gently mixed to break the pellet loose and wash it. This removes some of the salts present in the leftover supernatant and bound to DNA pellet making the final DNA cleaner. This suspension is centrifuged again to once again pellet DNA and the supernatant solution is removed. This step is repeated once.
Finally, the pellet is air-dried and the DNA is resuspended in water or other desired buffer. It is important not to over-dry the pellet as it may lead to denaturation of DNA and make it harder to resuspend.
Isopropanol can also be used instead of ethanol; the precipitation efficiency of the isopropanol is higher making one volume enough for precipitation. However, isopropanol is less volatile than ethanol and needs more time to air-dry in the final step. The pellet might also adhere less tightly to the tube when using isopropanol. | 1 | Biochemistry |
The type of a mass spectrometer most widely used with MALDI is the time-of-flight mass spectrometer (TOF), mainly due to its large mass range. The TOF measurement procedure is also ideally suited to the MALDI ionization process since the pulsed laser takes individual shots rather than working in continuous operation. MALDI-TOF instruments are often equipped with a reflectron (an "ion mirror") that reflects ions using an electric field. This increases the ion flight path, thereby increasing time of flight between ions of different m/z and increasing resolution. Modern commercial reflectron TOF instruments reach a resolving power m/Δm of 50,000 FWHM (full-width half-maximum, Δm defined as the peak width at 50% of peak height) or more.
MALDI has been coupled with IMS-TOF MS to identify phosphorylated and non-phosphorylated peptides.
MALDI-FT-ICR MS has been demonstrated to be a useful technique where high resolution MALDI-MS measurements are desired. | 1 | Biochemistry |
Adverse effects include nausea, indigestion, diarrhea, constipation, gastrointestinal ulceration, headache, dizziness, rash, salt and fluid retention, and high blood pressure.
Infrequent adverse effects include esophageal ulceration, heart failure, high blood levels of potassium, kidney impairment, confusion, and bronchospasm. Ibuprofen can exacerbate asthma, sometimes fatally.
Allergic reactions, including anaphylaxis and anaphylactic shock, may occur. Ibuprofen may be quantified in blood, plasma, or serum to demonstrate the presence of the drug in a person having experienced an anaphylactic reaction, confirm a diagnosis of poisoning in people who are hospitalized, or assist in a medicolegal death investigation. A monograph relating ibuprofen plasma concentration, time since ingestion, and risk of developing renal toxicity in people who have overdosed has been published.
In October 2020, the US FDA required the drug label to be updated for all NSAID medications to describe the risk of kidney problems in unborn babies that result in low amniotic fluid. | 4 | Stereochemistry |
The development of methods to detect and identify biomolecules has been motivated by the ability to improve the study of molecular structure and interactions. Before the advent of fluorescent labeling, radioisotopes were used to detect and identify molecular compounds. Since then, safer methods have been developed that involve the use of fluorescent dyes or fluorescent proteins as tags or probes as a means to label and identify biomolecules. Although fluorescent tagging in this regard has only been recently utilized, the discovery of fluorescence has been around for a much longer time.
Sir George Stokes developed the Stokes Law of Fluorescence in 1852 which states that the wavelength of fluorescence emission is greater than that of the exciting radiation. Richard Meyer then termed fluorophore in 1897 to describe a chemical group associated with fluorescence. Since then, Fluorescein was created as a fluorescent dye by Adolph von Baeyer in 1871 and the method of staining was developed and utilized with the development of fluorescence microscopy in 1911.
Ethidium bromide and variants were developed in the 1950s, and in 1994, fluorescent proteins or FPs were introduced. Green fluorescent protein or GFP was discovered by Osamu Shimomura in the 1960s and was developed as a tracer molecule by Douglas Prasher in 1987. FPs led to a breakthrough of live cell imaging with the ability to selectively tag genetic protein regions and observe protein functions and mechanisms. For this breakthrough, Shimomura was awarded the Nobel Prize in 2008.
New methods for tracking biomolecules have been developed including the use of colorimetric biosensors, photochromic compounds, biomaterials, and electrochemical sensors. Fluorescent labeling is also a common method in which applications have expanded to enzymatic labeling, chemical labeling, protein labeling, and genetic labeling. | 1 | Biochemistry |
In some cases in the EU MRLs are also used for ornamental produce, and checked against MRLs for food crops. While this is a sound approach for the general environmental impact, it doesnt reflect potential exposure of people handling ornamentals. A swap test can eliminate this gap. MRLs for ornamental produce can sometimes result in a conflicting outcome because of the absence of pre harvest intervals (PHI) or withholding periods for ornamentals, specifically in crops where harvesting is continuous, like roses. This happens when a grower is following the label recommendations and the produce is sampled shortly after. | 2 | Environmental Chemistry |
References to silicon carbide heating elements exist from the early 20th century when they were produced by Acheson's Carborundum Co. in the U.S. and EKL in Berlin. Silicon carbide offered increased operating temperatures compared with metallic heaters. Silicon carbide elements are used today in the melting of glass and non-ferrous metal, heat treatment of metals, float glass production, production of ceramics and electronics components, igniters in pilot lights for gas heaters, etc. | 8 | Metallurgy |
Polyurea is a type of elastomer that is derived from the reaction product of an isocyanate component and an amine component. The isocyanate can be aromatic or aliphatic in nature. It can be monomer, polymer, or any variant reaction of isocyanates, quasi-prepolymer or a prepolymer. The prepolymer, or quasi-prepolymer, can be made of an amine-terminated polymer resin, or a hydroxyl-terminated polymer resin.
The resin blend may be made up of amine-terminated polymer resins, and/or amine-terminated chain extenders. The amine-terminated polymer resins do not have any intentional hydroxyl moieties. Any hydroxyls are the result of incomplete conversion to the amine-terminated polymer resins. The resin blend may also contain additives or non-primary components. These additives may contain hydroxyls, such as pre-dispersed pigments in a polyol carrier. Normally, the resin blend does not contain a catalyst(s). | 7 | Physical Chemistry |
The discovery of mTOR was made in 1994 while investigating the mechanism of action of its inhibitor, rapamycin. Rapamycin was first discovered in 1975 in a soil sample from Easter Island of South Pacific, also known as Rapa Nui, from where its name is derived. Rapamycin is a macrolide, produced by the microorganism Streptomyces hygroscopicus and showed antifungal properties. Shortly after its discovery, immunosuppressive properties were detected, which later led to the establishment of rapamycin as an immunosuppressant. In the 1980s, rapamycin was also found to have anticancer activity although the exact mechanism of action remained unknown until many years later.
In the 1990s there was a dramatic change in this field due to studies on the mechanism of action of rapamycin and the identification of the drug target. It was found that rapamycin inhibited cellular proliferation and cell cycle progression. Research on mTOR inhibition has been a growing branch in science and has promising results. | 1 | Biochemistry |
In case (b), the spin-orbit coupling is weak or non-existent (in the case ). In this case, we take and and assume precesses quickly around the internuclear axis.
The good quantum numbers in case (b) are , , , and . We express the rotational energy operator as , where is a rotational constant. The rotational levels therefore have relative energies starting with . For example, a Σ state has rotational levels = 0, 1, 2, 3, 4, ..., and each level is divided by spin-orbit coupling into two levels = ± 1/2 (except for = 0 which corresponds only to = 1/2 because cannot be negative).
Another example is the Σ ground state of dioxygen, which has two unpaired electrons with parallel spins. The coupling type is Hund's case b), and each rotational level N is divided into three levels = , , .
For case b) the selection rules for quantum numbers , , and and for parity are the same as for case a). However for the rotational levels, the rule for quantum number does not apply and is replaced by the rule . | 7 | Physical Chemistry |
Cation-exchange capacity is measured by displacing all the bound cations with a concentrated solution of another cation, and then measuring either the displaced cations or the amount of added cation that is retained. Barium (Ba) and ammonium (NH) are frequently used as exchanger cations, although many other methods are available.
CEC measurements depend on pH, and therefore are often made with a buffer solution at a particular pH value. If this pH differs from the natural pH of the soil, the measurement will not reflect the true CEC under normal conditions. Such CEC measurements are called "potential CEC". Alternatively, measurement at the native soil pH is termed "effective CEC", which more closely reflects the real value, but can make direct comparison between soils more difficult. | 9 | Geochemistry |
Dalton's law expresses the fact that the total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of the individual gases in the mixture. This equality arises from the fact that in an ideal gas, the molecules are so far apart that they do not interact with each other. Most actual real-world gases come very close to this ideal. For example, given an ideal gas mixture of nitrogen (N), hydrogen (H) and ammonia (NH):
where:
* = total pressure of the gas mixture
* = partial pressure of nitrogen (N)
* = partial pressure of hydrogen (H)
* = partial pressure of ammonia (NH) | 7 | Physical Chemistry |
The list of synthetic polymers, roughly in order of worldwide demand, includes polyethylene, polypropylene, polystyrene, polyvinyl chloride, synthetic rubber, phenol formaldehyde resin (or Bakelite), neoprene, nylon, polyacrylonitrile, PVB, silicone, and many more. More than 330 million tons of these polymers are made every year (2015).
Most commonly, the continuously linked backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene (polythene in British English), whose repeat unit or monomer is ethylene. Many other structures do exist; for example, elements such as silicon form familiar materials such as silicones, examples being Silly Putty and waterproof plumbing sealant. Oxygen is also commonly present in polymer backbones, such as those of polyethylene glycol, polysaccharides (in glycosidic bonds), and DNA (in phosphodiester bonds). | 7 | Physical Chemistry |
In chemistry, "activation" refers to the reversible transition of a molecule into a nearly identical chemical or physical state, with the defining characteristic being that this resultant state exhibits an increased propensity to undergo a specified chemical reaction. Thus, activation is conceptually the opposite of protection, in which the resulting state exhibits a decreased propensity to undergo a certain reaction.
The energy of activation specifies the amount of free energy the reactants must possess (in addition to their rest energy) in order to initiate their conversion into corresponding products—that is, in order to reach the transition state for the reaction. The energy needed for activation can be quite small, and often it is provided by the natural random thermal fluctuations of the molecules themselves (i.e. without any external sources of energy).
The branch of chemistry that deals with this topic is called chemical kinetics. | 7 | Physical Chemistry |
A number of formal [2+2+2] cycloadditions have been realized under Nb catalysis, including alkyne trimerizations and couplings of alkynes with alkenes or nitriles to form cyclohexadienes or pyridines, respectively. Typically a Nb(III) catalyst will form a Nb(V) metallocyclopropene with a terminal alkyne component and then engage in sequential migratory insertions and reductive elimination to furnish the six membered ring and regenerate the Nb(III).
An organoniobium catalyst has also been developed for (Z)-selective semihydrogenation of alkynes. The mechanistic pathway for this reaction is distinct from other transition metal catalyzed hydrogenations, proceeding through the Nb(V) metallocyclopropene which engages with hydrogen either through direct sigma-bond metathesis or outer sphere 1,2-addition. | 0 | Organic Chemistry |
Enantiopure tert-butanesulfinamide can be prepared by enantioselective oxidation of inexpensive di-tert-butyl disulfide to the thiosulfinate followed by disulfide bond cleavage by lithium amide. In the original scope the chiral ligand used together with vanadyl acetylacetonate was prepared by condensing an optically pure chiral aminoindanol with 3,5-di-tert-butyl salicylaldehyde. | 0 | Organic Chemistry |
Thermochemical equations can be changed, as mentioned above, by multiplying by any numerical coefficient. All agents must be multiplied, including ΔH. Using the thermochemical equation of variables as above, one gets the following example.
:A + B → C
:ΔH= (±) #
One must assume that A needs to be multiplied by two in order for the thermochemical equation to be used. All the agents in the reaction must then be multiplied by the same coefficient, like so:
:2A + 2B → 2C
:2ΔH= 2[(±) #]
This is again considered to be logical when the First Law of Thermodynamics is considered. Twice as much product is produced, so twice as much heat is removed or given off. The division of coefficients functions in the same way. | 7 | Physical Chemistry |
The gradation of soils, or soil texture, affects water and nutrient holding and drainage capabilities. For sand-based soils, particle size can be the dominant characteristic affecting soil performances and hence crop. Sieving has long been the technique of choice for soil texture analysis, although laser diffraction instruments are increasingly used as they considerably speed up the analytical process, and provide highly reproducible results.
Particle size analysis in the agriculture industry is paramount because unwanted materials will contaminate products if they are not detected. By having an automated particle size analyzer, companies can closely monitor their processes. | 3 | Analytical Chemistry |
Organic Letters is a biweekly peer-reviewed scientific journal covering research in organic chemistry. It was established in 1999 and is published by the American Chemical Society. In 2014, the journal moved to a hybrid open access publishing model. The founding editor-in-chief was Amos Smith. The current editor-in-chief is Marisa C. Kozlowski. The journal is abstracted and indexed in: the Science Citation Index Expanded, Scopus, Academic Search Premier, BIOSIS Previews, Chemical Abstracts Service, EMBASE, and MEDLINE. | 0 | Organic Chemistry |
High-energy ion beams produced by particle accelerators are used in atomic physics, nuclear physics and particle physics. | 7 | Physical Chemistry |
Lithium is structurally similar to other cations such as sodium, potassium, magnesium and calcium, this causes lithium to activate potassium channels which inhibit neuromuscular transmission. Patients who take lithium can have a prolonged response to both depolarising and nondepolarising NMBAs. | 1 | Biochemistry |
Ultraviolet in sewage treatment is commonly replacing chlorination. This is in large part because of concerns that reaction of the chlorine with organic compounds in the waste water stream could synthesize potentially toxic and long lasting chlorinated organics and also because of the environmental risks of storing chlorine gas or chlorine containing chemicals. Individual wastestreams to be treated by UVGI must be tested to ensure that the method will be effective due to potential interferences such as suspended solids, dyes, or other substances that may block or absorb the UV radiation. According to the World Health Organization, "UV units to treat small batches (1 to several liters) or low flows (1 to several liters per minute) of water at the community level are estimated to have costs of US$20 per megaliter, including the cost of electricity and consumables and the annualized capital cost of the unit."
Large-scale urban UV wastewater treatment is performed in cities such as Edmonton, Alberta. The use of ultraviolet light has now become standard practice in most municipal wastewater treatment processes. Effluent is now starting to be recognized as a valuable resource, not a problem that needs to be dumped. Many wastewater facilities are being renamed as water reclamation facilities, whether the wastewater is discharged into a river, used to irrigate crops, or injected into an aquifer for later recovery. Ultraviolet light is now being used to ensure water is free from harmful organisms. | 5 | Photochemistry |
We have to distinguish between line source AAS (LS AAS) and continuum source AAS (CS AAS). In classical LS AAS, as it has been proposed by Alan Walsh, the high spectral resolution required for AAS measurements is provided by the radiation source itself that emits the spectrum of the analyte in the form of lines that are narrower than the absorption lines. Continuum sources, such as deuterium lamps, are only used for background correction purposes. The advantage of this technique is that only a medium-resolution monochromator is necessary for measuring AAS; however, it has the disadvantage that usually a separate lamp is required for each element that has to be determined. In CS AAS, in contrast, a single lamp, emitting a continuum spectrum over the entire spectral range of interest is used for all elements. Obviously, a high-resolution monochromator is required for this technique, as will be discussed later. | 3 | Analytical Chemistry |
The MAM is a critical signaling, metabolic, and trafficking hub in the cell that allows for the integration of ER and mitochondrial physiology. Coupling between these organelles is not simply structural but functional as well and critical for overall cellular physiology and homeostasis. The MAM thus offers a perspective on mitochondria that diverges from the traditional view of this organelle as a static, isolated unit appropriated for its metabolic capacity by the cell. Instead, this mitochondrial-ER interface emphasizes the integration of the mitochondria, the product of an endosymbiotic event, into diverse cellular processes. Recently it has also been shown, that mitochondria and MAM-s in neurons are anchored to specialised intercellular communication sites (so called somatic-junctions). Microglial processes monitor and protect neuronal functions at these sites, and MAM-s are supposed to have an important role in this type of cellular quality-control. | 1 | Biochemistry |
Cyanosulfidic prebiotic synthesis is a proposed mechanism for the origin of the key chemical building blocks of life. It involves a systems chemistry approach to synthesize the precursors of amino acids, ribonucleotides, and lipids using the same starting reagents and largely the same plausible early Earth conditions. Cyanosulfidic prebotic synthesis was developed by John Sutherland and co-workers at the Laboratory of Molecular Biology in Cambridge, England. | 9 | Geochemistry |
The geologic component of the carbon cycle operates slowly in comparison to the other parts of the global carbon cycle. It is one of the most important determinants of the amount of carbon in the atmosphere, and thus of global temperatures.
Most of the Earths carbon is stored inertly in the Earths lithosphere. Much of the carbon stored in the Earth's mantle was stored there when the Earth formed. Some of it was deposited in the form of organic carbon from the biosphere. Of the carbon stored in the geosphere, about 80% is limestone and its derivatives, which form from the sedimentation of calcium carbonate stored in the shells of marine organisms. The remaining 20% is stored as kerogens formed through the sedimentation and burial of terrestrial organisms under high heat and pressure. Organic carbon stored in the geosphere can remain there for millions of years.
Carbon can leave the geosphere in several ways. Carbon dioxide is released during the metamorphism of carbonate rocks when they are subducted into the earth's mantle. This carbon dioxide can be released into the atmosphere and ocean through volcanoes and hotspots. It can also be removed by humans through the direct extraction of kerogens in the form of fossil fuels. After extraction, fossil fuels are burned to release energy and emit the carbon they store into the atmosphere. | 5 | Photochemistry |
Caldoramide is a pentapeptide isolated from the cyanobacteria Caldora penicillata. It has cytotoxic effects on cancer cells and has been the subject of extensive oncological research. It is structurally analogous to belamide A and dolastatin 15. Its appearance is that of a powdery, white, substance. | 1 | Biochemistry |
Platelet-derived growth factor receptors (PDGF-R) are cell surface tyrosine kinase receptors for members of the platelet-derived growth factor (PDGF) family. PDGF subunits -A and -B are important factors regulating cell proliferation, cellular differentiation, cell growth, development and many diseases including cancer. There are two forms of the PDGF-R, alpha and beta each encoded by a different gene. Depending on which growth factor is bound, PDGF-R homo- or heterodimerizes. | 1 | Biochemistry |
Not every interaction between a photon and an atom, or molecule, will result in photoionization. The probability of photoionization is related to the photoionization cross section of the species – the probability of an ionization event conceptualized as a hypothetical cross-sectional area. This cross section depends on the energy of the photon (proportional to its wavenumber) and the species being considered i.e. it depends on the structure of the molecular species. In the case of molecules, the photoionization cross-section can be estimated by examination of Franck-Condon factors between a ground-state molecule and the target ion. This can be initialized by computing the vibrations of a molecule and associated cation (post ionization) using quantum chemical software e.g. QChem. For photon energies below the ionization threshold, the photoionization cross-section is near zero. But with the development of pulsed lasers it has become possible to create extremely intense, coherent light where multi-photon ionization may occur via sequences of excitations and relaxations. At even higher intensities (around of infrared or visible light), non-perturbative phenomena such as barrier suppression ionization and rescattering ionization are observed. | 7 | Physical Chemistry |
The Secretin family are peptides that act as local hormones which regulate activity of G-protein coupled receptors. Most often found in the pancreas and the intestines. Secretin was discovered in 1902 by E. H. Starling. It was later linked to chemical regulation and was the first substance to be deemed a hormone.
#Secretin
#Glucagon
#Glicentin (GLI)
#Vasoactive intestinal peptide (VIP)
#Gastric inhibitory polypeptide (GIP) | 1 | Biochemistry |
Nicotinamide adenine dinucleotide has several essential roles in metabolism. It acts as a coenzyme in redox reactions, as a donor of ADP-ribose moieties in ADP-ribosylation reactions, as a precursor of the second messenger molecule cyclic ADP-ribose, as well as acting as a substrate for bacterial DNA ligases and a group of enzymes called sirtuins that use NAD to remove acetyl groups from proteins. In addition to these metabolic functions, NAD emerges as an adenine nucleotide that can be released from cells spontaneously and by regulated mechanisms, and can therefore have important extracellular roles. | 5 | Photochemistry |
The genome of the P1 phage is moderately large, around 93Kbp in length (compared to the genomes of e.g. T4 - 169Kbp, lambda - 48Kbp and Ff - 6.4Kbp). In the viral particle it is in the form of a linear double stranded DNA molecule. Once inserted into the host it circularizes and replicates as a plasmid.
In the viral particle the DNA molecule is longer (110Kbp) than the actual length of the genome. It is created by cutting an appropriately sized fragment from a concatemeric DNA chain having multiple copies of the genome (see the section below on lysis for how this is made). Due to this the ends of the DNA molecule are identical. This is referred to as being terminally redundant. This is important for the DNA to be circularized in the host. Another consequence of the DNA being cut out of a concatemer is that a given linear molecule can start at any location on the circular genome. This is called a cyclic permutation.
The genome is especially rich in Chi sequences recognized by the bacterial recombinase RecBCD. The genome contains two origins of replication: oriR which replicates it during the lysogenic cycle and oriL which replicates it during the lytic stage. The genome of P1 encodes three tRNAs which are expressed in the lytic stage.
Proteome. The genome of P1 encodes 112 proteins and 5 untranslated genes and is this about twice the size of bacteriophage lambda. | 1 | Biochemistry |
The 1,3-enyne moiety is an important structural unit for biologically active and natural compounds. It can be derived from vinylic systems and terminal acetylenes by using a configuration-retention stereospecific procedure such as the Sonogashira reaction. Vinyl iodides are the most reactive vinyl halides to Pd oxidative addition, and their use is therefore most frequent for Sonogashira cross-coupling reactions due to the usually milder conditions employed. Some examples include:
*The coupling of 2-iodoprop-2-en-1-ol with a wide range of acetylenes.
*The preparation of alk-2-ynylbuta-1,3-dienes from the cross-coupling of a diiodide and phenylacetylene, as shown below. | 0 | Organic Chemistry |
Norsteroids (nor-, L. norma, from "normal" in chemistry, indicating carbon removal) are a structural class of steroids that have had an atom or atoms (typically carbon) removed, biosynthetically or synthetically, from positions of branching off of rings or side chains (e.g., removal of methyl groups), or from within rings of the steroid ring system. For instance, 19-norsteroids (e.g., 19-norprogesterone) constitute an important class of natural and synthetic steroids derived by removal of the methyl group of the natural product progesterone; the equivalent change between testosterone and 19-nortestosterone (nandrolone) is illustrated below. | 1 | Biochemistry |
The NDUFAF6 gene encodes a protein that localizes to mitochondria. The encoded protein plays an important role in the assembly of complex I (NADH-ubiquinone oxidoreductase) of the mitochondrial respiratory chain through regulation of subunit ND1 biogenesis. | 1 | Biochemistry |
Although only being able to produce short hydrogel fibers, production of hydrogel fiber by polymerizing the hydrogel network inside a tubular mold and push out the fiber forcefully can also be achieved. But the friction will increase with the increasing length, and only short hydrogel fibers are feasible.
A case would be the production of poly(acrylamide-co-poly(ethylene glycol) diacrylate) fiber reported by yun et al. The pregel solution was a mixture of AAM, [https://www.sigmaaldrich.com/catalog/product/aldrich/455008?lang=en®ion=US poly(ethylene glycol) diacrylate] (PEGDA, crosslinker), and [https://www.sigmaaldrich.com/catalog/product/aldrich/405655?lang=en®ion=US&cm_sp=Insite-_-caSrpResults_srpRecs_srpModel_2-hydroxy-2-methylpropiophenone-_-srpRecs3-1 2-hydroxy-2-methylpropiophenone] (photoinitiator). The mixture was injected into a tubular mold and extracted through hydrostatic force afterwards. | 7 | Physical Chemistry |
When two or more types of ligands (L, L, ...) are coordinated to an octahedral metal centre (M), the complex can exist as isomers. The naming system for these isomers depends upon the number and arrangement of different ligands. | 4 | Stereochemistry |
A kairomone (a coinage using the Greek καιρός opportune moment, paralleling pheromone) is a semiochemical, emitted by an organism, which mediates interspecific interactions in a way that benefits an individual of another species which receives it and harms the emitter. This "eavesdropping" is often disadvantageous to the producer (though other benefits of producing the substance may outweigh this cost, hence its persistence over evolutionary time). The kairomone improves the fitness of the recipient and in this respect differs from an allomone (which is the opposite: it benefits the producer and harms the receiver) and a synomone (which benefits both parties). The term is mostly used in the field of entomology (the study of insects). Two main ecological cues are provided by kairomones; they generally either indicate a food source for the receiver, or the presence of a predator, the latter of which is less common or at least less studied. | 1 | Biochemistry |
Boiling is also a phase transition from the liquid phase to gas phase, but boiling is the formation of vapor as bubbles of vapor below the surface of the liquid. Boiling occurs when the equilibrium vapor pressure of the substance is greater than or equal to the atmospheric pressure. The temperature at which boiling occurs is the boiling temperature, or boiling point. The boiling point varies with the pressure of the environment. | 7 | Physical Chemistry |
In 1834, Théophile-Jules Pelouze distilled tartaric acid and isolated glutaric acid and another unknown organic acid. Jöns Jacob Berzelius characterized this other acid the following year and named pyruvic acid because it was distilled using heat. The correct molecular structure was deduced by the 1870s.
Pyruvic acid is a colorless liquid with a smell similar to that of acetic acid and is miscible with water. In the laboratory, pyruvic acid may be prepared by heating a mixture of tartaric acid and potassium hydrogen sulfate, by the oxidation of propylene glycol by a strong oxidizer (e.g., potassium permanganate or bleach), or by the hydrolysis of acetyl cyanide, formed by reaction of acetyl chloride with potassium cyanide:
:CHCOCl + KCN → CHCOCN + KCl
:CHCOCN → CHCOCOOH | 1 | Biochemistry |
Methanogenesis or biomethanation is the formation of methane coupled to energy conservation by microbes known as methanogens. Organisms capable of producing methane for energy conservation have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with anaerobic bacteria. The production of methane is an important and widespread form of microbial metabolism. In anoxic environments, it is the final step in the decomposition of biomass. Methanogenesis is responsible for significant amounts of natural gas accumulations, the remainder being thermogenic. | 1 | Biochemistry |
An inclusion is a solid particle in liquid aluminium alloy. It is usually non-metallic and can be of different nature depending on its source. | 8 | Metallurgy |
Rudd joined the glycobiology institute at the University of Oxford in 1985. At the time, it was difficult for women scientists to secure jobs as academic personnel, and Rudd joined as a glass washer. She learned how to work with glycoproteins and large sugars and eventually completed a doctorate on glycoforms at the Open University in 1995. Rudd moved to the Scripps Research institute, and held a visiting position at the Ben-Gurion University of the Negev. She commercialised her work on liquid chromatography–mass spectrometry (LCMS) with Waters Corporation.
Rudd has worked to miniaturise technologies for glycol analysis. For example, she has used genome-wide association studies (GWAS) to link individual genomes to their serum glycome and individual proteins. She moved to University College Dublin in 2006, where was made head of the Dublin-Oxford glycobiology laboratory research group. She opened the National Institute for Bioprocessing Research and Training (NIBRT), where she developed new processes for protein glycosylation in an attempt to characterise recombinant protein drugs. | 1 | Biochemistry |
*A phase is a form of matter that is homogeneous in chemical composition and physical state. Typical phases are solid, liquid and gas. Two immiscible liquids (or liquid mixtures with different compositions) separated by a distinct boundary are counted as two different phases, as are two immiscible solids.
*The number of components (C) is the number of chemically independent constituents of the system, i.e. the minimum number of independent species necessary to define the composition of all phases of the system.
*The number of degrees of freedom (F) in this context is the number of intensive variables which are independent of each other.
The basis for the rule is that equilibrium between phases places a constraint on the intensive variables. More rigorously, since the phases are in thermodynamic equilibrium with each other, the chemical potentials of the phases must be equal. The number of equality relationships determines the number of degrees of freedom. For example, if the chemical potentials of a liquid and of its vapour depend on temperature (T) and pressure (p), the equality of chemical potentials will mean that each of those variables will be dependent on the other. Mathematically, the equation , where , the chemical potential, defines temperature as a function of pressure or vice versa. (Caution: do not confuse as pressure with , number of phases.)
To be more specific, the composition of each phase is determined by intensive variables (such as mole fractions) in each phase. The total number of variables is , where the extra two are temperature T and pressure p. The number of constraints is , since the chemical potential of each component must be equal in all phases. Subtract the number of constraints from the number of variables to obtain the number of degrees of freedom as .
The rule is valid provided the equilibrium between phases is not influenced by gravitational, electrical or magnetic forces, or by surface area, and only by temperature, pressure, and concentration. | 7 | Physical Chemistry |
In heterotrimeric G proteins, catalysis of GTP can be assisted by aluminum tetrafluoride () and RGS4. Heterotrimeric G proteins are larger three-part proteins serve in signal transduction of many pathways. The catalytic mechanism for GTP hydrolysis in heterotrimeric G proteins consists of an active state where catalysis is likely to occur and an inactive state where catalysis is unlikely. In the active state, stabilizes the transition state and points the arginine finger residue towards GTP. This causes increased charge density on the beta phosphate of GTP and planarization of the gamma phosphate, which creates an opening and reduces steric hindrance for water to hydrolyze the phosphoanhydride beta-gamma bond. This is because the gamma phosphate's bond to the beta phosphate bends, exposing its connection and allowing the subsequent nucleophilic substitution reaction initiated by water. The complex formed with RGS4 assists in this process by creating strain on the bond between the gamma and beta phosphates and assisting in distributing more charge onto the beta phosphate. | 1 | Biochemistry |
was a Japanese organic chemist and marine biologist, and professor emeritus at Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts and Boston University School of Medicine. He was awarded the Nobel Prize in Chemistry in 2008 for the discovery and development of green fluorescent protein (GFP) with two American scientists: Martin Chalfie of Columbia University and Roger Tsien of the University of California-San Diego. | 0 | Organic Chemistry |
Type J (iron–constantan) has a more restricted range (−40 °C to +750 °C) than type K but higher sensitivity of about 50 μV/°C. The Curie point of the iron (770 °C) causes a smooth change in the characteristic, which determines the upper temperature limit. Note, the European/German Type L is a variant of the type J, with a different specification for the EMF output (reference DIN 43712:1985-01). | 8 | Metallurgy |
Very little is known about the initiation of epigenetic silencing of transposable elements, and aside from the rare exception to this rule, as in the gene Muk, present as an initiator of regulatory epigenetic modification in maize, there are many other unclear aspects of how transposons are regulated in plant genomes. Might they be a first step in evolution that we never knew about? [1] Might they be, simply, a kink in the chain of genetic coding, one that will eventually be worked out? Again, given the lack of information it is hard to say. Future research into this field will see the changing of our conceptions of transposons and their role in eukaryote development, one way or another. | 1 | Biochemistry |
EXPOSE has several objectives, specific to each experiments, but all linked to the astrobiology domain. Their collective objective is to better understand the nature and evolution of organic matter present in extraterrestrial environments and their potential implications in astrobiology. These experiments mostly study molecules of cometary interest in order to understand the results of the Rosetta mission, the chemistry of Titan (Cassini–Huygens mission), or the organic chemistry of the Martian environment (Mars Science Laboratory and ExoMars project). | 1 | Biochemistry |
Kinesin-13 MCAK (Mitotic Centromere-Associated Kinesin) is a KRP that is involved in resolving errors during mitosis involving kinetochore-microtubules. This process is associated with Aurora B Protein Kinase. When Aurora Bs function is disrupted, MCAK ability to locate centromeres, which play a critical role in separation of chromosomes during mitosis, was suppressed. There are other environments in which MCAKs function is impaired, absent impact on its associated kinase. For example, alpha-tubulin detyrosination has been demonstrated to impact MCAK's mitotic repair capabilities, suggesting a potential cause of chromosomal instability. | 1 | Biochemistry |
The best Lewis structure for an oxocarbenium ion contains an oxygen–carbon double bond, with the oxygen atom attached to an additional group and consequently taking on a formal positive charge. In the language of canonical structures (or "resonance"), the polarization of the π bond is described by a secondary carbocationic resonance form, with a formal positive charge on carbon (see above). In terms of frontier molecular orbital theory, the Lowest Unoccupied Molecular Orbital (LUMO) of the oxocarbenium ion is a π* orbital that has the large lobe on the carbon atom; the more electronegative oxygen contributes less to the LUMO. Consequently, in an event of a nucleophilic attack, the carbon is the electrophilic site. Compared to a ketone, the polarization of an oxocarbenium ion is accentuated: they more strongly resemble a "true" carbocation, and they are more reactive toward nucleophiles. In organic reactions, ketones are commonly activated by the coordination of a Lewis acid or Brønsted acid to the oxygen to generate an oxocarbenium ion as an intermediate.
Numerically, a typical partial charge (derived from Hartree-Fock computations) for the carbonyl carbon of a ketone RC=O (like acetone) is δ+ = 0.51. With the addition of an acidic hydrogen to the oxygen atom to produce [RC=OH], the partial charge increases to δ+ = 0.61. In comparison, the nitrogen analogues of ketones and oxocarbenium ions, imines (RC=NR) and iminium ions ([RC=NRH]), respectively, have partial charges of δ+ = 0.33 and δ+ = 0.54, respectively. The order of partial positive charge on the carbonyl carbon is therefore imine < ketone < iminium < oxocarbenium.
This is also the order of electrophilicity for species containing C=X (X = O, NR) bonds. This order is synthetically significant and explains, for example, why reductive aminations are often best carried out at pH = 5 to 6 using sodium cyanoborohydride (Na[HB(CN)]) or sodium triacetoxyborohydride (Na[HB(OAc)]) as a reagent. Bearing an electron-withdrawing group, sodium cyanoborohydride and sodium triacetoxyborohydride are poorer reducing agents than sodium borohydride, and their direct reaction with ketones is generally a slow and inefficient process. However, the iminium ion (but not the imine itself) formed in situ during a reductive amination reaction is a stronger electrophile than the ketone starting material and will react with the hydride source at a synthetically useful rate. Importantly, the reaction is conducted under mildly acidic conditions that protonate the imine intermediate to a significant extent, forming the iminium ion, while not being strongly acidic enough to protonate the ketone, which would form the even more electrophilic oxocarbenium ion. Thus, the reaction conditions and reagent ensure that amine is formed selectively from iminium reduction, instead of direct reduction of the carbonyl group (or its protonated form) to form an alcohol. | 0 | Organic Chemistry |
Beginning with this initial sequence:<br />
The complement created by base pairing is:<br />
The reverse complement is:<br />
And, the inverted repeat sequence is:<br />
"nnnnnn" represents any number of intervening nucleotides. | 1 | Biochemistry |
Phillips started his academic career as an assistant professor at the University of Illinois Urbana-Champaign, followed by his appointment as a professor of biochemistry at Rice University in 1987. In 1993, he assumed the position of Rice Scientia Lecturer, subsequently receiving the Robert A. Welch Lecturer appointment in 2001. He joined the University of Wisconsin-Madison in 2000 as a professor of Biochemistry and took on the role of professor emeritus in 2012. He has been serving as a professor of chemistry, as well as the Ralph and Dorothy Looney Professor of Biochemistry and Cell Biology at Rice University. | 1 | Biochemistry |
Another potential route to ecosystem impacts is through bioacoustics. This may occur as ocean acidification can alter the acoustic properties of seawater, allowing sound to propagate further, and increasing ocean noise. This impacts all animals that use sound for echolocation or communication. | 9 | Geochemistry |
In biology, iron plays a number of roles. Iron is widespread in most living organisms and is essential for their function. In microbes, iron redox chemistry is utilized as an electron donor or receptor in microbial metabolism, allowing microbes to generate energy. In the oceans, iron is essential for the growth and survival of phytoplankton, which use iron to fix nitrogen. Iron is also important in plants, given that they need iron to transfer electrons during photosynthesis. Finally, in animals, iron plays many roles, however, its most essential function is to transport oxygen in the bloodstream throughout the body. Thus, iron undergoes many biological processes, each of which have variations in which isotopes of iron they preferentially use. While iron isotopic fractionations are observed in many organisms, they are still not well understood. Improvements in the understanding the iron isotope fractionations observed in biology will enable the development of a more complete knowledge of the enzymatic, metabolic, and other biologic pathways in different organisms. Below, the known iron isotopic variations for different classes of organisms are described. | 9 | Geochemistry |
Progesterone, like pregnenolone and dehydroepiandrosterone (DHEA), belongs to an important group of endogenous steroids called neurosteroids. It can be metabolized within all parts of the central nervous system.
Neurosteroids are neuromodulators, and are neuroprotective, neurogenic, and regulate neurotransmission and myelination. The effects of progesterone as a neurosteroid are mediated predominantly through its interactions with non-nuclear PRs, namely the mPRs and PGRMC1, as well as certain other receptors, such as the σ and nACh receptors. | 0 | Organic Chemistry |
Floral scent emissions of most flowering plants vary predictably throughout the day, following a circadian rhythm. This variation is controlled by light intensity. Maximal emissions coincide with peaks of the highest activity of visiting pollinators. For instance, snapdragon flowers, mostly pollinated by bees, have the highest emissions at noon, whereas nocturnally-visited tobacco plants have the highest emissions at night.
Floral scent emissions also vary along with floral development, with the highest emissions at anthesis, i.e. when the flower is fecund (highly fertile), and reduced emissions after pollination, probably due to mechanisms linked with fecundation. In tropical orchids, floral scent emission is terminated immediately following pollination, reducing the expenditure of energy on fragrance production. In petunia flowers, ethylene is released to stop the synthesis of benzenoid floral volatiles after successful pollination.
Abiotic factors, such as temperature, atmospheric concentration, hydric stress, and soil nutrient status also impact the regulation of floral scent. For instance, increased temperatures in the environment can increase the emission of VOCs in flowers, potentially altering communication between plants and pollinators.
Finally, biotic interactions may also affect the floral scent. Plant leaves attacked by herbivores emit new VOCs in response to the attack, the so-called herbivore-induced plant volatiles (HIPVs). Similarly, damaged flowers have a modified floral scent compared to undamaged ones. Micro-organisms present in nectar may alter floral scent emissions as well. | 1 | Biochemistry |
Agreed-upon reference materials are required so that reported δ values are comparable among studies. For the sulfur isotope system, δS values are reported on the Vienna-Cañon Diablo Troilite (VCDT) scale. The original CDT scale was based on a sample of the mineral troilite recovered from the Canyon Diablo meteorite at Meteor Crater, Arizona, US. The Cañon Diablo Troilite was assigned a δS value of 0‰. However, troilite from the Canyon Diablo meteorite was later discovered to have variable sulfur isotope composition. As a result, VCDT was established as a hypothetical sulfur isotope reference with a R value of 0.044151 and δS of 0‰, but no physical sample of VCDT exists. Samples are now measured in comparison to International Atomic Energy Agency (IAEA) reference materials, which are well-characterized, lab-prepared compounds with known δS values. A commonly-used IAEA reference material is IAEA-S-1, a silver sulfide reference material with a δS value of −0.30‰ VCDT. S and S abundance can also be measured relative to IAEA reference materials and reported on the VCDT scale. For these isotopes, too, VCDT is established as having δS and δS values of 0‰. The R value of VCDT is 0.007877 and the R value is 0.0002. IAEA-S-1 has a R value of 0.0007878 and a δS value of −0.05‰ VCDT; it has a δS value of −0.6‰ VCDT. | 9 | Geochemistry |
A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes (alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility:
* Heterogeneous supported catalysts based on titanium compounds are used in polymerization reactions in combination with cocatalysts, organoaluminum compounds such as triethylaluminium, Al(CH). This class of catalyst dominates the industry.
* Homogeneous catalysts usually based on complexes of the group 4 metals titanium, zirconium or hafnium. They are usually used in combination with a different organoaluminum cocatalyst, methylaluminoxane (or methylalumoxane, MAO). These catalysts traditionally contain metallocenes but also feature multidentate oxygen- and nitrogen-based ligands.
Ziegler–Natta catalysts are used to polymerize terminal alkenes (ethylene and alkenes with the vinyl double bond):
:n CH=CHR → −[CH−CHR]−; | 7 | Physical Chemistry |
Undervirilization can occur if a genetic male cannot produce enough androgen or the body tissues cannot respond to it. Extreme undervirilization occurs when no significant androgen hormones can be produced or the body is completely insensitive to androgens. Both result in a female body. Partial undervirilization produces ambiguous genitalia part-way between male and female. Examples of undervirilization are androgen insensitivity syndrome, 5 alpha reductase deficiency, and some forms of congenital adrenal hyperplasia. | 1 | Biochemistry |
Ferrosilicon is an alloy of iron and silicon with a typical silicon content by weight of 15–90%. It contains a high proportion of iron silicides. | 8 | Metallurgy |
Tumor development is a complex process that requires cell division, growth, and survival. One approach used by tumors to upregulate growth and survival is through autocrine production of growth and survival factors. Autocrine signaling plays critical roles in cancer activation and also in providing self-sustaining growth signals to tumors. | 1 | Biochemistry |
Aliphatic compounds can be saturated, joined by single bonds (alkanes), or unsaturated, with double bonds (alkenes) or triple bonds (alkynes). If other elements (heteroatoms) are bound to the carbon chain, the most common being oxygen, nitrogen, sulfur, and chlorine, it is no longer a hydrocarbon, and therefore no longer an aliphatic compound. However, such compounds may still be referred to as aliphatic if the hydrocarbon portion of the molecule is aliphatic, e.g. aliphatic amines, to differentiate them from aromatic amines.
The least complex aliphatic compound is methane (CH). | 0 | Organic Chemistry |
A complete description of hypervalent molecules arises from consideration of molecular orbital theory through quantum mechanical methods. An LCAO in, for example, sulfur hexafluoride, taking a basis set of the one sulfur 3s-orbital, the three sulfur 3p-orbitals, and six octahedral geometry symmetry-adapted linear combinations (SALCs) of fluorine orbitals, a total of ten molecular orbitals are obtained (four fully occupied bonding MOs of the lowest energy, two fully occupied intermediate energy non-bonding MOs and four vacant antibonding MOs with the highest energy) providing room for all 12 valence electrons. This is a stable configuration only for SX molecules containing electronegative ligand atoms like fluorine, which explains why SH is not a stable molecule. In the bonding model, the two non-bonding MOs (1e) are localized equally on all six fluorine atoms. | 4 | Stereochemistry |
The diaphragm is an important part of the body's digestive system. The muscular diaphragm separates the thoracic cavity from the abdominal cavity where most of the digestive organs are located. The suspensory muscle attaches the ascending duodenum to the diaphragm. This muscle is thought to be of help in the digestive system in that its attachment offers a wider angle to the duodenojejunal flexure for the easier passage of digesting material. The diaphragm also attaches to, and anchors the liver at its bare area. The esophagus enters the abdomen through a hole in the diaphragm at the level of T10. | 1 | Biochemistry |
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