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A sophorolipid is a surface-active glycolipid compound that can be synthesized by a selected number of non-pathogenic yeast species. They are potential bio-surfactants due to their biodegradability and low eco-toxicity. | 0 | Organic Chemistry |
At least five different kinds of snRNPs join the spliceosome to participate in splicing. They can be visualized by gel electrophoresis and are known individually as: U1, U2, U4, U5, and U6. Their snRNA components are known, respectively, as: U1 snRNA, U2 snRNA, U4 snRNA, U5 snRNA, and U6 snRNA.
In the mid-1990s, it was discovered that a variant class of snRNPs exists to help in the splicing of a class of introns found only in metazoans, with highly conserved 5' splice sites and branch sites. This variant class of snRNPs includes: U11 snRNA, U12 snRNA, U4atac snRNA, and U6atac snRNA. While different, they perform the same functions as do U1, U2, U4, and U6, respectively.
Additionally, U7 snRNP is made of U7 small nuclear RNA and associated proteins and is involved in the processing of the 3′ stem-loop of histone pre-mRNA. | 1 | Biochemistry |
In biogeochemistry, remineralisation (or remineralization) refers to the breakdown or transformation of organic matter (those molecules derived from a biological source) into its simplest inorganic forms. These transformations form a crucial link within ecosystems as they are responsible for liberating the energy stored in organic molecules and recycling matter within the system to be reused as nutrients by other organisms.
Remineralisation is normally viewed as it relates to the cycling of the major biologically important elements such as carbon, nitrogen and phosphorus. While crucial to all ecosystems, the process receives special consideration in aquatic settings, where it forms a significant link in the biogeochemical dynamics and cycling of aquatic ecosystems. | 9 | Geochemistry |
These occur between alkenes and electrophiles, often halogens as in halogen addition reactions. Common reactions include use of bromine water to titrate against a sample to deduce the number of double bonds present. For example, ethene + bromine → 1,2-dibromoethane:
:CH + Br → BrCHCHBr
This takes the form of 3 main steps shown below;
#Forming of a π-complex
#:The electrophilic Br-Br molecule interacts with electron-rich alkene molecule to form a π-complex 1.
#Forming of a three-membered bromonium ion
#:The alkene is working as an electron donor and bromine as an electrophile. The three-membered bromonium ion 2 consisted of two carbon atoms and a bromine atom forms with a release of Br.
#Attacking of bromide ion
#:The bromonium ion is opened by the attack of Br from the back side. This yields the vicinal dibromide with an antiperiplanar configuration. When other nucleophiles such as water or alcohol are existing, these may attack 2 to give an alcohol or an ether.
This process is called Ad2 mechanism ("addition, electrophilic, second-order"). Iodine (I), chlorine (Cl), sulfenyl ion (RS), mercury cation (Hg), and dichlorocarbene (:CCl) also react through similar pathways. The direct conversion of 1 to 3 will appear when the Br is large excess in the reaction medium. A β-bromo carbenium ion intermediate may be predominant instead of 3 if the alkene has a cation-stabilizing substituent like phenyl group. There is an example of the isolation of the bromonium ion 2. | 7 | Physical Chemistry |
Ibuprofen, polyunsaturated fatty acids, and beta-blockers have been reported in some preliminary studies to decrease REE, which may allow patients to meet their caloric needs and gain weight. | 1 | Biochemistry |
A mutation in genes encoding 11β-hydroxylase is associated with congenital adrenal hyperplasia due to 11β-hydroxylase deficiency.
11β-hydroxylase is involved in the metabolism of 17α-hydroxyprogesterone to 21-deoxycortisol, in cases of congenital adrenal hyperplasia due to 21-hydroxylase deficiency. | 1 | Biochemistry |
The global cooling potential of various areas around the world varies primarily based on climate zones and the presence of weather patterns and events. Dry and hot regions generally have a higher radiative cooling power (estimated up to 120 W/m2), while colder regions or those with high humidity or cloud cover generally have lower global cooling potentials. The cooling potential of various regions can also change from winter to summer due to shifts in humidity and cloud cover. Studies mapping the daytime radiative cooling potential have been done for China and India, the United States, and on a continental scale across Europe. | 7 | Physical Chemistry |
In condensed matter physics, second sound is a quantum mechanical phenomenon in which heat transfer occurs by wave-like motion, rather than by the more usual mechanism of diffusion. Its presence leads to a very high thermal conductivity. It is known as "second sound" because the wave motion of entropy and temperature is similar to the propagation of pressure waves in air (sound). The phenomenon of second sound was first described by Lev Landau in 1941. | 7 | Physical Chemistry |
Functions can be binding motifs that bind another macromolecule or small compound, that induce a covalent modification of minimotif, or are involved in the protein trafficking of the protein containing the minimotif. The basic premise of Minimotif Miner is that is a short peptide sequence is known to have a function in one protein, may have a similar function in another query protein. The current release of the MnM 3.0 database has ~300,000 minimotifs and can be searched at the website.
There are two workflows that are of interest to scientists that use Minimotif Miner 1) Entering any query protein into Minimotif Miner returns a table with a list of minimotif sequence and functions that have a sequence pattern match with the protein query sequence. These provide potential new functions in the protein query. 2) By using the view single nucleotide polymorphism (SNP) function, SNPs from dbSNP are mapped in the sequence window. A user can select any set of the SNPs and then identify any minimotif that is introduced or eliminated by the SNP or mutation. This helps to identify minimotifs involved in generating organism diversity or those that may be associated with a disease.
Typical results of MnM predict more than 50 new minimotifs for a protein query. A major limitation in this type of analysis is that the low sequence complexity of short minimotifs produces false positive predictions where the sequence occurs in a protein by random chance and not because it contains the predicted function. MnM 3.0 introduces a library of advanced heuristics and filters, which enable vast reduction of false positive predictions. These filters use minimotif complexity, protein surface location, molecular processes, cellular processes, protein-protein interactions, and genetic interactions. We recently combined all of these heuristics into a single, compound filter which makes significant progress toward solving this problem with high accuracy of minimotif prediction as measured by a performance benchmarking study which evaluated both sensitivity and specificity. | 1 | Biochemistry |
With nuclear magnetic resonance (NMR) spectra the observed chemical shift value, , arising from a given atom contained in a reagent molecule and one or more complexes of that reagent, will be the concentration-weighted average of all shifts of those chemical species. Chemical exchange is assumed to be rapid on the NMR time-scale.
terms of mole fractions,
is the chemical shift of the ith chemical species which contains the nucleus and is the concentration /mole fraction ( c is a concentration / mol dm) of that species. This expression has the same mathematical form as Beer's law. Chemical shift values may be obtained for more than one nucleus in an analogous way that absorbance may be measured at more than one wavelength. Typical isotopes that may be used in this context are H,C and P. It is usual to use a deuterated solvent when measuring H chemical shift values. | 6 | Supramolecular Chemistry |
To encode arbitrary data in DNA, the data is typically first converted into ternary (base 3) data rather than binary (base 2) data. Each digit (or "trit") is then converted to a nucleotide using a lookup table. To prevent homopolymers (repeating nucleotides), which can cause problems with accurate sequencing, the result of the lookup also depends on the preceding nucleotide. Using the example lookup table below, if the previous nucleotide in the sequence is T (thymine), and the trit is 2, the next nucleotide will be G (guanine).
Various systems may be incorporated to partition and address the data, as well as to protect it from errors. One approach to error correction is to regularly intersperse synchronization nucleotides between the information-encoding nucleotides. These synchronization nucleotides can act as scaffolds when reconstructing the sequence from multiple overlapping strands. | 1 | Biochemistry |
Atomic-force microscopy (AFM) is a powerful microscopy technique used for studying samples at a nanoscale and is often used to image protein distribution on a surface. It consists of a cantilever with a tip to scan over the surface. It is a valuable tool for measuring protein-protein and protein-surface interaction. However, the limiting factor of many AFM studies is that imaging is often performed after drying the surface which might affect protein folding and the structure of the protein layer. Moreover, the cantilever tip can dislodge a protein or corrugate the protein layer. | 1 | Biochemistry |
Primary (1°) phosphines, with the formula RPH, are typically prepared by alkylation of phosphine. Simple alkyl derivatives such as methylphosphine (CHPH) are prepared by alkylation of alkali metal derivatives MPH (M is Li, Na, or K). Another synthetic route involves treatment of the corresponding chlorophosphines with hydride reagents. For example, reduction of dichlorophenylphosphine with lithium aluminium hydride affords phenylphosphine (PhPH).
Primary (RPH) and secondary phosphines (RRPH and RPH) add to alkenes in presence of a strong base (e.g., KOH in DMSO). Markovnikov's rules apply. Similar reactions occur involving alkynes. Base is not required for electron-deficient alkenes (e.g., derivatives of acrylonitrile) and alkynes. | 0 | Organic Chemistry |
*Karl Fischer titration: A potentiometric method to analyze trace amounts of water in a substance. A sample is dissolved in methanol, and titrated with Karl Fischer reagent (consists of iodine, sulfur dioxide, a base and a solvent, such as alcohol). The reagent contains iodine, which reacts proportionally with water. Thus, the water content can be determined by monitoring the electric potential of excess iodine. | 3 | Analytical Chemistry |
All bacterial species that have been reported to possess bioluminescence belong within the families Vibrionaceae, Shewanellaceae, or Enterobacteriaceae, all of which are assigned to the class Gammaproteobacteria.
(List from Dunlap and Henryk (2013), "Luminous Bacteria", The Prokaryotes ) | 1 | Biochemistry |
Much of the chemistry of glycosides is explained in the article on glycosidic bonds. For example, the glycone and aglycone portions can be chemically separated by hydrolysis in the presence of acid and can be hydrolyzed by alkali. There are also numerous enzymes that can form and break glycosidic bonds. The most important cleavage enzymes are the glycoside hydrolases, and the most important synthetic enzymes in nature are glycosyltransferases. Genetically altered enzymes termed glycosynthases have been developed that can form glycosidic bonds in excellent yield.
There are many ways to chemically synthesize glycosidic bonds. Fischer glycosidation refers to the synthesis of glycosides by the reaction of unprotected monosaccharides with alcohols (usually as solvent) in the presence of a strong acid catalyst. The Koenigs-Knorr reaction is the condensation of glycosyl halides and alcohols in the presence of metal salts such as silver carbonate or mercuric oxide. | 0 | Organic Chemistry |
Acarbose is a pseudotetrasaccharide mimicking maltotetraose (a substructure of starch). One of the glucose units has been replaced by valienamine - a carbasugar, linked to the next carbohydrate by an amine bridge. Another of the glucose units appears as a 6-deoxy variant. Acarbose is an enzyme inhibitor that is used as a drug against type 2 diabetes. | 1 | Biochemistry |
Under thermal effect, the end of polymer chain departs, and forms low free radical which has low activity. Then according to the chain reaction mechanism, the polymer loses the monomer one by one. However, the molecular chain doesn't change a lot in a short time. The reaction is shown below. This process is common for polymethymethacrylate (perspex).
CH-C(CH)COOCH-CH-C*(CH)COOCH→CH-C*(CH)COOCH + CH=C(CH)COOCH | 7 | Physical Chemistry |
Any reaction in the domain of photogeochemistry, either observed in the environment or studied in the laboratory, may be broadly classified according to the nature of the materials involved.
# Reactions among naturally occurring compounds. Photogeochemistry, both observational and exploratory, is concerned with reactions among materials known to occur naturally, as this reflects what happens or may happen on Earth.
# Reactions in which one or more of the reactants are not known to occur naturally. Studies of reactions among materials related to naturally occurring materials may contribute to understanding of natural processes. These complementary studies are relevant to photogeochemistry in that they illustrate reactions that may have a natural counterpart. For example, it has been shown that soils, when irradiated, can generate reactive oxygen species and that clay minerals present in soils can accelerate the degradation of synthetic chemicals; it may therefore be postulated that naturally occurring compounds are similarly affected by sunlight acting on soil. The conversion of N to NH has been observed upon irradiation in the presence of the iron titanate FeTiO. While such a compound is not known to occur naturally, it is related to ilmenite (FeTiO) and pseudobrookite (FeTiO), and can form upon heating of ilmenite; this may imply a similar reaction with N for the naturally occurring minerals. | 5 | Photochemistry |
CAF commonly occurs between adjacent vias (i.e. plated through holes) inside a PCB, as the copper migrates along the glass/resin interface from anode to cathode. CAF failures can manifest as current leakage, intermittent electrical shorts, and even dielectric breakdown between conductors in printed circuit boards. This often makes CAF very difficult to detect, especially when it occurs as an intermittent issue. There are a few things that can be done to isolate the fault location and confirm CAF as a root cause of a failure. If the issue is intermittent then putting the sample of interest under combined temperature-humidity-bias (THB) may help recreate the failure mode. In addition, techniques such as cross sectioning or superconducting quantum interference device (SQUID) can be used to identify the failure. | 7 | Physical Chemistry |
* Shakiness
* Dry cough
* Dizziness and light-headedness due to low blood pressure
* Fatigue, especially in the early stages
* Mouth dryness in the early stages
* Nausea
* Fainting
* Signs of infection (e.g., fever, chills, persistent sore throat)
* Chest pain
* Neutropenia (low white blood cells)
* Impotence (erectile dysfunction)
* Hyperkalemia
Serious allergic reactions to this drug are unlikely, but immediate medical attention must be sought if they occur. Symptoms of a serious allergic reaction include, but are not limited to a rash or swelling of the face, mouth, tongue, or throat. In extreme cases, ramipril may lead to potentially fatal liver problems. | 4 | Stereochemistry |
Historically, flammable, inflammable and combustible meant capable of burning. The word "inflammable" came through French from the Latin inflammāre = "to set fire to", where the Latin preposition "in-" means "in" as in "indoctrinate", rather than "not" as in "invisible" and "ineligible".
The word "inflammable" may be erroneously thought to mean "non-flammable". The erroneous usage of the word "inflammable" is a significant safety hazard. Therefore, since the 1950s, efforts to put forward the use of "flammable" in place of "inflammable" were accepted by linguists, and it is now the accepted standard in American English and British English. Antonyms of "flammable" or "inflammable" include: non-flammable, non-inflammable, incombustible, non-combustible, not flammable, and fireproof.
Flammable applies to combustible materials that ignite easily and thus are more dangerous and more highly regulated. Less easily ignited less-vigorously burning materials are combustible. For example, in the United States flammable liquids, by definition, have a flash point below —where combustible liquids have a flash point above . Flammable solids are solids that are readily combustible, or may cause or contribute to fire through friction. Readily combustible solids are powdered, granular, or pasty substances that easily ignite by brief contact with an ignition source, such as a burning match, and spread flame rapidly. The technical definitions vary between countries so the United Nations created the Globally Harmonized System of Classification and Labeling of Chemicals, which defines the flash point temperature of flammable liquids as between 0 and and combustible liquids between and . | 7 | Physical Chemistry |
Two main subunits of PSI, PsaA and PsaB, are closely related proteins involved in the binding of the vital electron transfer cofactors P, Acc, A, A, and F. PsaA and PsaB are both integral membrane proteins of 730 to 750 amino acids that contain 11 transmembrane segments. A [[4Fe-4S|[4Fe-4S] iron-sulfur cluster]] called F is coordinated by four cysteines; two cysteines are provided each by PsaA and PsaB. The two cysteines in each are proximal and located in a loop between the ninth and tenth transmembrane segments. A leucine zipper motif seems to be present downstream of the cysteines and could contribute to dimerisation of PsaA/PsaB. The terminal electron acceptors F and F, also [4Fe-4S] iron-sulfur clusters, are located in a 9-kDa protein called PsaC that binds to the PsaA/PsaB core near F. | 5 | Photochemistry |
A risk for periphyton stems from urbanization. Increased turbidity levels associated with urban sprawl can smother periphyton causing its detachment from the rocks on which it lives. It can be important for the clearance of harmful chemicals and reducing turbidity. | 2 | Environmental Chemistry |
*[https://i-aps.org Inter-American Photochemical Society]
*[https://www.photochemistry.eu European Photochemistry Association]
*Asian and Oceanian Photochemistry Association | 5 | Photochemistry |
When a melt undergoes cooling along the liquid line of descent, the results are limited to the production of a homogeneous solid body of intrusive rock, with uniform mineralogy and composition, or a partially differentiated cumulate mass with layers, compositional zones and so on. This behaviour is fairly predictable and easy enough to prove with geochemical investigations. In such cases, a magma chamber will form a close approximation of the ideal Bowen's reaction series. However, most magmatic systems are polyphase events, with several pulses of magmatism. In such a case, the liquid line of descent is interrupted by the injection of a fresh batch of hot, undifferentiated magma. This can cause extreme fractional crystallisation because of three main effects:
* Additional heat provides additional energy to allow more vigorous convection, allows resorption of existing mineral phases back into the melt, and can cause a higher-temperature form of a mineral or other higher-temperature minerals to begin precipitating
* Fresh magma changes the composition of the melt, changing the chemistry of the phases which are being precipitated. For instance, plagioclase conforms to the liquid line of descent by forming initial anorthite which, if removed, changes the equilibrium mineral composition to oligoclase or albite. Replenishment of the magma can see this trend reversed, so that more anorthite is precipitated atop cumulate layers of albite.
* Fresh magma destabilises minerals which are precipitating as solid solution series or on a eutectic; a change in composition and temperature can cause extremely rapid crystallisation of certain mineral phases which are undergoing a eutectic crystallisation phase. | 9 | Geochemistry |
The Serine-Histidine-Aspartate motif is one of the most thoroughly characterised catalytic motifs in biochemistry. The triad is exemplified by chymotrypsin, a model serine protease from the PA superfamily which uses its triad to hydrolyse protein backbones. The aspartate is hydrogen bonded to the histidine, increasing the pK of its imidazole nitrogen from 7 to around 12. This allows the histidine to act as a powerful general base and to activate the serine nucleophile. It also has an oxyanion hole consisting of several backbone amides which stabilises charge build-up on intermediates. The histidine base aids the first leaving group by donating a proton, and also activates the hydrolytic water substrate by abstracting a proton as the remaining OH attacks the acyl-enzyme intermediate.
The same triad has also convergently evolved in α/β hydrolases such as some lipases and esterases, however orientation of the triad members is reversed. Additionally, brain acetyl hydrolase (which has the same fold as a small G-protein) has also been found to have this triad. The equivalent Ser-His-Glu triad is used in acetylcholinesterase. | 1 | Biochemistry |
Common high-activity activators are mineral acids, often together with halides, amines, water or alcohols:
* hydrochloric acid, most common
* phosphoric acid, less common, use limited by its polymerization at higher temperatures
Inorganic acids are highly corrosive to metals even at room temperature, which causes issues during storage, handling and applications. As soldering involves high temperatures, compounds that decompose or react, with acids as products, are frequently used:
* zinc chloride, which at high temperatures reacts with moisture, forming oxychloride and hydrochloric acid
* ammonium chloride, thermally decomposing to ammonia and hydrochloric acid
* amine hydrochlorides, decomposing to the amine and hydrochloric acid | 8 | Metallurgy |
Trace amounts of up to 16 µg·m have been detected in tobacco smoke.
Minor amounts of pyridine are released into environment from some industrial processes such as steel manufacture, processing of oil shale, coal gasification, coking plants and incinerators. The atmosphere at oil shale processing plants can contain pyridine concentrations of up to 13 µg·m, and 53 µg·m levels were measured in the groundwater in the vicinity of a coal gasification plant. According to a study by the US National Institute for Occupational Safety and Health, about 43,000 Americans work in contact with pyridine. | 0 | Organic Chemistry |
eIF2 is a heterotrimer of a total molar mass of 126 kDa that is composed of the three sub-units: α (sub-unit 1), β (sub-unit 2), and γ (sub-unit 3).
The sequences of all three sub-units are highly conserved (pairwise amino acid identities for each sub-unit range from 47 to 72% when comparing the proteins of Homo sapiens and Saccharomyces cerevisiae).
The α-subunit contains the main target for phosphorylation, a serine at position 51. It also contains a S1 motif domain, which is a potential RNA binding-site. Therefore, the α-subunit can be considered the regulatory subunit of the trimer.
The β-subunit contains multiple phosphorylation sites (residues 2, 13, 67, 218). What is important to consider is that there are also three lysine clusters in the N-terminal domain (NTD), which are important for the interaction with eIF2B. Moreover, the sequence of the protein comprises a zinc finger motif that was shown to play a role in both ternary complex and 43S preinitiation complex formation. There are also two guanine nucleotide-binding sequences that have not been shown to be involved in the regulation of eIF2 activity. The β-subunit is also believed to interact with both tRNA and mRNA.
The γ-subunit comprises three guanine nucleotide-binding sites and is known to be the main docking site for GTP/GDP. It also contains a tRNA-binding cavity that has been shown by X-ray crystallography. A zinc knuckle motif is able to bind one Zn cation. It is related to some elongation factors like EF-Tu. | 1 | Biochemistry |
We will present a simplified version of the calculation. It differs from the full calculation in three ways:
# The ideal gas consists of particles confined to one spatial dimension.
# We keep only the terms of order , dropping all terms of size n or less, where n is the number of particles. For our purposes, this is enough, because this is where the Gibbs paradox shows up and where it must be resolved. The neglected terms play a role when the number of particles is not very large, such as in computer simulation and nanotechnology. Also, they are needed in deriving the Sackur–Tetrode equation.
# The subdivision of phase space into units of the Planck constant (h) is omitted. Instead, the entropy is defined using an integral over the "accessible" portion of phase space. This serves to highlight the purely classical nature of the calculation.
We begin with a version of Boltzmann's entropy in which the integrand is all of accessible phase space:
The integral is restricted to a contour of available regions of phase space, subject to conservation of energy. In contrast to the one-dimensional line integrals encountered in elementary physics, the contour of constant energy possesses a vast number of dimensions. The justification for integrating over phase space using the canonical measure involves the assumption of equal probability. The assumption can be made by invoking the ergodic hypothesis as well as the Liouville's theorem of Hamiltonian systems.
(The ergodic hypothesis underlies the ability of a physical system to reach thermal equilibrium, but this may not always hold for computer simulations (see the Fermi–Pasta–Ulam–Tsingou problem) or in certain real-world systems such as non-thermal plasmas.)
Liouvilles theorem assumes a fixed number of dimensions that the system explores'. In calculations of entropy, the number dimensions is proportional to the number of particles in the system, which forces phase space to abruptly change dimensionality when particles are added or subtracted. This may explain the difficulties in constructing a clear and simple derivation for the dependence of entropy on the number of particles.
For the ideal gas, the accessible phase space is an (n − 1)-sphere (also called a hypersphere) in the n-dimensional space:
To recover the paradoxical result that entropy is not extensive, we integrate over phase space for a gas of monatomic particles confined to a single spatial dimension by . Since our only purpose is to illuminate a paradox, we simplify notation by taking the particles mass and the Boltzmann constant equal to unity: . We represent points in phase-space and its x and v parts by n and 2n' dimensional vectors:
: where and
To calculate entropy, we use the fact that the (n-1)-sphere, has an -dimensional "hypersurface volume" of
For example, if n = 2, the 1-sphere is the circle , a "hypersurface" in the plane. When the sphere is even-dimensional (n odd), it will be necessary to use the gamma function to give meaning to the factorial; see below. | 7 | Physical Chemistry |
* Institute of Organoelement Compounds. A. N. Nesmeyanov RAS. In front of Institute building a memorial bust was installed (sculptor Oleg Komov). At the Institute of the annual annual day of memory of A. N. Nesmeyanov with relatives and graduate students.
* On September 26, 1980, one of the streets of the Gagarinsky district of Moscow was named after Alexander Nikolayevich.
* Russian Academy of Sciences was founder Prize named after A.N. Nesmeyanov, awarded since 1994 for outstanding work in the field of chemistry of organoelement compounds.
* In December 1980, a stamp in memory of A. N. Nesmeyanov was issued in the USSR.
* Alexander Petrovich Kazantsev dedicated to him the novel The Dome of Hope felt the phrase: “To the vivid memory of America, the Hero of Socialist Labor, Academician Alexander Nikolayevich NESMEYANOV, as a token of admiration for his life and work, I dedicate this novel-dream. Author». | 0 | Organic Chemistry |
Fick's first law relates the diffusive flux to the gradient of the concentration. It postulates that the flux goes from regions of high concentration to regions of low concentration, with a magnitude that is proportional to the concentration gradient (spatial derivative), or in simplistic terms the concept that a solute will move from a region of high concentration to a region of low concentration across a concentration gradient. In one (spatial) dimension, the law can be written in various forms, where the most common form (see) is in a molar basis:
where
* is the diffusion flux, of which the dimension is the amount of substance per unit area per unit time. measures the amount of substance that will flow through a unit area during a unit time interval.
* is the diffusion coefficient or diffusivity. Its dimension is area per unit time.
* is the concentration gradient
* (for ideal mixtures) is the concentration, with a dimension of amount of substance per unit volume.
* is position, the dimension of which is length.
is proportional to the squared velocity of the diffusing particles, which depends on the temperature, viscosity of the fluid and the size of the particles according to the Stokes–Einstein relation. In dilute aqueous solutions the diffusion coefficients of most ions are similar and have values that at room temperature are in the range of . For biological molecules the diffusion coefficients normally range from 10 to 10 m/s.
In two or more dimensions we must use , the del or gradient operator, which generalises the first derivative, obtaining
where denotes the diffusion flux vector.
The driving force for the one-dimensional diffusion is the quantity , which for ideal mixtures is the concentration gradient. | 7 | Physical Chemistry |
In this approach, the sample is spiked with a species (internal standard) which is used to normalise the response of analyte, compensating for variables at any stage of the sample preparation and analysis, including ion suppression.
It is important that the internal standard displays very similar (ideally identical) properties, with respect to detector response (i.e. ionisation), as the analyte of interest. To simplify the selection of internal standard, most laboratories use an analogous stable isotope in an isotope dilution type analysis. The stable isotope is almost guaranteed to be chemically and physically as close as possible to the analyte of interest, hence producing an almost identical detector response in addition to behaving identically during sample preparation and chromatographic resolution. To this end, the ion suppression experienced by both the analyte and the internal standard should be identical. It is important to note that an excessively high concentration of stable isotope internal standard may cause ion suppression itself, since it will co-elute with the analyte of interest. Hence, the internal standard should be added at an appropriate concentration. | 3 | Analytical Chemistry |
In the diagram on the right, phytoplankton convert CO, which has dissolved from the atmosphere into the surface oceans (90 Gt yr), into particulate organic carbon (POC) during primary production (~ 50 Gt C yr). Phytoplankton are then consumed by copepods, krill and other small zooplankton grazers, which in turn are preyed upon by higher trophic levels. Any unconsumed phytoplankton form aggregates, and along with zooplankton faecal pellets, sink rapidly and are exported out of the mixed layer ( 14). Krill, copepods, zooplankton and microbes intercept phytoplankton in the surface ocean and sinking detrital particles at depth, consuming and respiring this POC to CO (dissolved inorganic carbon, DIC), such that only a small proportion of surface-produced carbon sinks to the deep ocean (i.e., depths > 1000 m). As krill and smaller zooplankton feed, they also physically fragment particles into small, slower- or non-sinking pieces (via sloppy feeding, coprorhexy if fragmenting faeces), retarding POC export. This releases dissolved organic carbon (DOC) either directly from cells or indirectly via bacterial solubilisation (yellow circle around DOC). Bacteria can then remineralise the DOC to DIC (CO, microbial gardening).
The biological carbon pump is one of the chief determinants of the vertical distribution of carbon in the oceans and therefore of the surface partial pressure of CO governing air-sea CO exchange. It comprises phytoplankton cells, their consumers and the bacteria that assimilate their waste and plays a central role in the global carbon cycle by delivering carbon from the atmosphere to the deep sea, where it is concentrated and sequestered for centuries. Photosynthesis by phytoplankton lowers the partial pressure of CO in the upper ocean, thereby facilitating the absorption of CO from the atmosphere by generating a steeper CO gradient. It also results in the formation of particulate organic carbon (POC) in the euphotic layer of the epipelagic zone (0–200 m depth). The POC is processed by microbes, zooplankton and their consumers into fecal pellets, organic aggregates (“marine snow”) and other forms, which are thereafter exported to the mesopelagic (200–1000 m depth) and bathypelagic zones by sinking and vertical migration by zooplankton and fish. Although primary production includes both dissolved and particulate organic carbon (DOC and POC respectively), only POC leads to efficient carbon export to the ocean interior, whereas the DOC fraction in surface waters is mostly recycled by bacteria. However, a more biologically resistant DOC fraction produced in the euphotic zone (accounting for 15–20% of net community productivity), is not immediately mineralized by microbes and accumulates in the ocean surface as biologically semi-labile DOC. This semi-labile DOC undergoes net export to the deep ocean, thus constituting a dynamic part of the biological carbon pump. The efficiency of DOC production and export varies across oceanographic regions, being more prominent in the oligotrophic subtropical oceans. The overall efficiency of the biological carbon pump is mostly controlled by the export of POC. | 9 | Geochemistry |
10-acetyl-3,7-dihydroxyphenoxazine (also known as Amplex Red), structurally related to resazurin, reacts with HO in a 1:1 stoichiometry to produce the same by-product resorufin (used in many assays combining for example horseradish peroxidase (HRP), or NADH, NADPH using enzymes).
7-ethoxyresorufin, a compound used as the substrate in the measurement of cytochrome P450 (CYP1A1) induction using the ethoxyresorufin-O-deethylase (EROD) assay system in cell culture and environmental samples, produced in response to exposure to aryl hydrocarbons. The compound is catalysed by the enzyme to produce the same fluorescent product, resorufin.
1,3-dichloro-7-hydroxy-9,9-dimethylacridin-2(9H)-one (DDAO dye), a fluorescent dye used for oligonucleotide labeling. | 3 | Analytical Chemistry |
Thermal radiation is electromagnetic radiation emitted by the thermal motion of particles in matter. Thermal radiation transmits as an electromagnetic wave through both matter and vacuum. When matter absorbs thermal radiation its temperature will tend to rise. All matter with a temperature greater than absolute zero emits thermal radiation. The emission of energy arises from a combination of electronic, molecular, and lattice oscillations in a material. Kinetic energy is converted to electromagnetism due to charge-acceleration or dipole oscillation. At room temperature, most of the emission is in the infrared (IR) spectrum. Thermal radiation is one of the fundamental mechanisms of heat transfer, along with conduction and convection.
The primary method by which the Sun transfers heat to the Earth is thermal radiation. This energy is partially absorbed and scattered in the atmosphere, the latter process being the reason why the sky is visibly blue. Much of the Sun's radiation transmits through the atmosphere to the surface where it is either absorbed or reflected.
Thermal radiation can be used to detect objects or phenomena normally invisible to the human eye. Thermographic cameras create an image by sensing infrared radiation. These images can represent the temperature gradient of a scene and are commonly used to locate objects at a higher temperature than their surroundings. In a dark environment where visible light is at low levels, infrared images can be used to locate animals or people due to their body temperature. Cosmic microwave background radiation is another example of thermal radiation.
Blackbody radiation is a concept used to analyze thermal radiation in idealized systems. This model applies if a radiation object meets the physical characteristics of a black body in thermodynamic equilibrium. Plancks law describes the spectrum of blackbody radiation, and relates the radiative heat flux from a body to its temperature. Wiens displacement law determines the most likely frequency of the emitted radiation, and the Stefan–Boltzmann law gives the radiant intensity. Where blackbody radiation is not an accurate approximation, emission and absorption can be modeled using quantum electrodynamics (QED). | 7 | Physical Chemistry |
Recently, a nickel-catalyzed Sonogashira coupling has been developed which allows for the coupling of non-activated alkyl halides to acetylene without the use of palladium, although a copper co-catalyst is still needed. It has also been reported that gold can be used as a heterogeneous catalyst, which was demonstrated in the coupling of phenylacetylene and iodobenzene with an Au/CeO catalyst. In this case, catalysis occurs heterogeneously on the Au nanoparticles, with Au(0) as the active site. Selectivity to the desirable cross coupling product was also found to be enhanced by supports such as CeO and LaO. Additionally, iron-catalyzed Sonogashira couplings have been investigated as relatively cheap and non-toxic alternatives to palladium. Here, FeCl is proposed to act as the transition-metal catalyst and CsCO as the base, thus theoretically proceeding through a palladium-free and copper-free mechanism.
While the copper-free mechanism has been shown to be viable, attempts to incorporate the various transition metals mentioned above as less expensive alternatives to palladium catalysts have shown a poor track record of success due to contamination of the reagents with trace amounts of palladium, suggesting that these theorized pathways are extremely unlikely, if not impossible, to achieve.
Studies have shown that organic and inorganic starting materials can also contain enough (ppb level) palladium for the coupling. | 0 | Organic Chemistry |
Melt spinning is used to manufacture thin metal sheets or ribbons that are near amorphous or non-crystalline. The unique resulting electric and magnetic properties of melt-spun metals are a consequence of this structure as well as the composition of the alloy or metal that was used to form the ribbon. | 8 | Metallurgy |
Cram expanded upon Charles Pedersens ground-breaking synthesis of crown ethers, two-dimensional organic compounds that are able to recognize and selectively combine with the ions of certain metal elements. He synthesized molecules that took this chemistry into three dimensions, creating an array of differently shaped molecules that could interact selectively with other chemicals because of their complementary three-dimensional structures. Crams work represented a large step toward the synthesis of functional laboratory-made mimics of enzymes and other natural molecules whose special chemical behavior is due to their characteristic structure. He also did work in stereochemistry and Cram's rule of asymmetric induction is named after him.
In 1973, Cram collaborated on research with Irish chemist Francis Leslie Scott. | 4 | Stereochemistry |
Twinning is a form of symmetrical intergrowth between two or more adjacent crystals of the same mineral. It differs from the ordinary random intergrowth of mineral grains in a mineral deposit, because the relative orientations of the two crystal segments show a fixed relationship that is characteristic of the mineral structure. The relationship is defined by a symmetry operation called a twin operation.
The twin operation is not one of the normal symmetry operations of the untwinned crystal structure. For example, the twin operation may be reflection across a plane that is not a symmetry plane of the single crystal.
On the microscopic level, the twin boundary is characterized by a set of atomic positions in the crystal lattice that are shared between the two orientations. These shared lattice points give the junction between the crystal segments much greater strength than that between randomly oriented grains, so that the twinned crystals do not easily break apart. | 3 | Analytical Chemistry |
Many enzymes and proteins play a role in degrading mRNA. For example, in Escherichia coli there are three enzymes: RNase II, PNPase, and RNase R. RNase R is a 3’-5’ exoribonuclease that is recruited to degrade a defective mRNA. RNase R has two structural domains, an N-terminal putative helix-turn-helix (HTH) and a C-terminal lysine(K-rich) domain. These two domains are unique to RNase R, and are attributed as being the determining factors for the selectivity and specificity of the protein. Evidence has been shown that the K-rich domain is involved in the degradation of non-stop mRNA. These domains are not present in other RNases. Both RNase II and RNase R are members of RNR family, and they share a noteworthy similarity in primary sequence and domain architecture. However, RNase R has the ability to efficiently degrade mRNA, while RNase II has less efficiency in the degrading process. Nevertheless, the specific mechanics of degrading mRNA via RNase R has remained a mystery. | 1 | Biochemistry |
The human body has many defense mechanisms against pathogens, one of which is humoral immunity. This defence mechanism produces antibodies (large glycoproteins) in response to an immune stimulus. Many cells of the immune system are required for this process, including lymphocytes (T-cells and B-cells) and antigen presenting cells. These cells coordinate an immune response upon the detection of foreign proteins (antigens), producing antibodies that bind to these antigens. In normal physiology, lymphocytes that recognise human proteins (autoantigens) either undergo programmed cell death (apoptosis) or become non-functional. This self-tolerance means that lymphocytes should not incite an immune response against human cellular antigens. Sometimes, however, this process malfunctions and antibodies are produced against human antigens, which may lead to autoimmune disease. | 1 | Biochemistry |
The U.S. Bureau of Mines (USBM), developed by Donaldson et al. in 1969, is a method to measure wettability of petroleum reservoir rocks. In this method, the areas under the forced displacement Capillary pressure curves of oil and water drive processes are denoted as and to calculate the USBM index.
USBM index is positive for water-wet rocks, and negative for oil-wet systems. | 7 | Physical Chemistry |
The van der Waals radius, r, of an atom is the radius of an imaginary hard sphere representing the distance of closest approach for another atom.
It is named after Johannes Diderik van der Waals, winner of the 1910 Nobel Prize in Physics, as he was the first to recognise that atoms were not simply points and to demonstrate the physical consequences of their size through the van der Waals equation of state. | 6 | Supramolecular Chemistry |
In order to find theoretically the deuterium magnetic dipole moment μ, one uses the formula for a nuclear magnetic moment
with
g and g are g-factors of the nucleons.
Since the proton and neutron have different values for g and g, one must separate their contributions. Each gets half of the deuterium orbital angular momentum and spin . One arrives at
where subscripts p and n stand for the proton and neutron, and .
By using the same identities as here and using the value , we arrive at the following result, in units of the nuclear magneton μ
For the , state (), we obtain
For the , state (), we obtain
The measured value of the deuterium magnetic dipole moment, is , which is 97.5% of the value obtained by simply adding moments of the proton and neutron. This suggests that the state of the deuterium is indeed to a good approximation , state, which occurs with both nucleons spinning in the same direction, but their magnetic moments subtracting because of the neutron's negative moment.
But the slightly lower experimental number than that which results from simple addition of proton and (negative) neutron moments shows that deuterium is actually a linear combination of mostly , state with a slight admixture of , state.
The electric dipole is zero as usual.
The measured electric quadrupole of the deuterium is . While the order of magnitude is reasonable, since the deuterium radius is of order of 1 femtometer (see below) and its electric charge is e, the above model does not suffice for its computation. More specifically, the electric quadrupole does not get a contribution from the l =0 state (which is the dominant one) and does get a contribution from a term mixing the l =0 and the l =2 states, because the electric quadrupole operator does not commute with angular momentum.
The latter contribution is dominant in the absence of a pure contribution, but cannot be calculated without knowing the exact spatial form of the nucleons wavefunction inside the deuterium.
Higher magnetic and electric multipole moments cannot be calculated by the above model, for similar reasons. | 9 | Geochemistry |
P. Sikivie and Q. Yang showed that cold dark matter axions would form a Bose–Einstein condensate by thermalisation because of gravitational self-interactions. Axions have not yet been confirmed to exist. However the important search for them has been greatly enhanced with the completion of upgrades to the Axion Dark Matter Experiment (ADMX) at the University of Washington in early 2018.
In 2014, a potential dibaryon was detected at the Jülich Research Center at about 2380 MeV. The center claimed that the measurements confirm results from 2011, via a more replicable method. The particle existed for 10 seconds and was named d*(2380). This particle is hypothesized to consist of three up and three down quarks. It is theorized that groups of d* (d-stars) could form Bose–Einstein condensates due to prevailing low temperatures in the early universe, and that BECs made of such hexaquarks with trapped electrons could behave like dark matter. | 7 | Physical Chemistry |
Minze Stuiver was born in Vlagtwedde, the Netherlands, on 25 October 1929. As a boy he narrowly missed being taken into German forced labor toward the end of the Second World War, but, because he was away delivering milk by bicycle, he escaped the round-up that took most of the young men and older boys from the village. His secondary school education was disrupted by the war when the school was occupied by German soldiers and air raids interrupted classes in makeshift rooms. After the war he went to the University of Groningen, where he studied physics, mathematics and astronomy, focusing on nuclear physics. After graduation he joined the biophysics group led by the pre-eminent researcher Hessel de Vries and received a Ph.D. in Biophysics in 1958 with a thesis on the Biophysics of the Sense of Smell. Shortly thereafter he began working in the rapidly developing field of radiocarbon dating with de Vries, who found variations in the concentration of radiocarbon in the atmosphere which challenged the assumptions of the radiocarbon dating method. In 1959, together with his wife, Anneke, Minze went to Yale University for a one-year fellowship position but was called back to Groningen to take over as director of the radiocarbon facility when De Vries died. However Minze chose to remain in the United States at the Geochrometric Laboratory at Yale University. There he developed high-precision methods in radiocarbon that enabled him, along with Hans Suess, to verify De Vries’ “wiggly” nature of the atmospheric concentration of radiocarbon in the past from tree-rings. Stuiver and Suess created one of the first curves for calibration of radiocarbon dates. In 1969 Minze moved to the newly founded Quaternary Research Center at the University of Washington (UW) in Seattle. There he built the Quaternary Isotope Lab with a lead-lined room 30 feet below ground to shield the hand-built gas counters from detecting spurious events due to cosmic rays.
In the 1970s Minze began measuring C in dissolved inorganic carbon in ocean water as part of The Geochemical Ocean Sections Study (GEOSECS) to study the distribution of carbon in the ocean. In addition he was involved in a number of studies on the glacial histories of Antarctica and North America. He was the senior editor of the journal Radiocarbon from 1977 to 1988 and broadened the scope of the publication to include articles about scientific knowledge derived from radiocarbon measurements. By then the terminology for various ways to calculate and present radiocarbon data was becoming rather confusing. Together with Henry Polach, he formulated the equations and conventions for reporting radiocarbon data that is still widely used.
His work investigating atmospheric C changes gave rise to a greater understanding of the changes in solar activity over time and potential links to climate change as well as the extent of fossil fuel input.
In the mid-1980s he led the development of the first high-precision radiocarbon calibration curve extending back nearly 10,000 years ago based on C measurements of tree-rings with known calendar ages from dendrochronology. This data still forms the backbone of the Holocene portion of the current international radiocarbon calibration curve which is used by archaeologists and geoscientists around the world. He also oversaw the development of the CALIB computer software to automate the calibration process.
In the 1990s, in addition to continued work on radiocarbon calibration and solar variability, he began work on oxygen isotopes from Greenland ice cores together with Pieter Grootes. Their sub-annual resolution stable isotopes measurements provided confirmation of the rapid nature of major climatic changes at the end of the last glaciation.
Stuiver died on 26 December 2020, at the age of 91. | 9 | Geochemistry |
See Vitamin, Mineral (nutrient), Protein (nutrient)
An inadequate amount of a nutrient is a deficiency. Deficiencies can be due to a number of causes including an inadequacy in nutrient intake, called a dietary deficiency, or any of several conditions that interfere with the utilization of a nutrient within an organism. Some of the conditions that can interfere with nutrient utilization include problems with nutrient absorption, substances that cause a greater than normal need for a nutrient, conditions that cause nutrient destruction, and conditions that cause greater nutrient excretion. Nutrient toxicity occurs when excess consumption of a nutrient does harm to an organism.
In the United States and Canada, recommended dietary intake levels of essential nutrients are based on the minimum level that "will maintain a defined level of nutriture in an individual", a definition somewhat different from that used by the World Health Organization and Food and Agriculture Organization of a "basal requirement to indicate the level of intake needed to prevent pathologically relevant and clinically detectable signs of a dietary inadequacy".
In setting human nutrient guidelines, government organizations do not necessarily agree on amounts needed to avoid deficiency or maximum amounts to avoid the risk of toxicity. For example, for vitamin C, recommended intakes range from 40 mg/day in India to 155 mg/day for the European Union. The table below shows U.S. Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for vitamins and minerals, PRIs for the European Union (same concept as RDAs), followed by what three government organizations deem to be the safe upper intake. RDAs are set higher than EARs to cover people with higher than average needs. Adequate Intakes (AIs) are set when there is not sufficient information to establish EARs and RDAs. Countries establish tolerable upper intake levels, also referred to as upper limits (ULs), based on amounts that cause adverse effects. Governments are slow to revise information of this nature. For the U.S. values, with the exception of calcium and vitamin D, all of the data date from 1997 to 2004.
The daily recommended amounts of niacin and magnesium are higher than the tolerable upper limit because, for both nutrients, the ULs identify the amounts which will not increase risk of adverse effects when the nutrients are consumed as a serving of a dietary supplement. Magnesium supplementation above the UL may cause diarrhea. Supplementation with niacin above the UL may cause flushing of the face and a sensation of body warmth. Each country or regional regulatory agency decides on a safety margin below when symptoms may occur, so the ULs may differ based on source.
EAR U.S. Estimated Average Requirements.
RDA U.S. Recommended Dietary Allowances; higher for adults than for children, and may be even higher for women who are pregnant or lactating.
AI U.S. Adequate Intake; AIs established when there is not sufficient information to set EARs and RDAs.
PRI Population Reference Intake is European Union equivalent of RDA; higher for adults than for children, and may be even higher for women who are pregnant or lactating. For Thiamin and Niacin, the PRIs are expressed as amounts per megajoule (239 kilocalories) of food energy consumed.
Upper Limit Tolerable upper intake levels.
ND ULs have not been determined.
NE EARs, PRIs or AIs have not yet been established or will not be (EU does not consider chromium an essential nutrient). | 9 | Geochemistry |
The MODAL strategy defines overlap sequences known as "linkers" to reduce the amount of customisation that needs to be done with each DNA fragment. The linkers were designed using the [https://omictools.com/r2odna-designer-tool R2oDNA Designer] software and the overlap regions were designed to be 45 bp long to be compatible with Gibson assembly and other overlap assembly methods. To attach these linkers to the parts to be assembled, PCR is carried using part-specific primers containing 15 bp prefix and suffix adaptor sequences. The linkers are then attached to the adaptor sequences via a second PCR reaction. To position the DNA fragments, the same linker will be attached to the suffix of the desired upstream fragment and the prefix of the desired downstream fragments. Once the linkers are attached, Gibson assembly, CPEC, or the other overlap assembly methods can all be used to assemble the DNA fragments in the desired order. | 1 | Biochemistry |
The complex is the simplest PPC appearing in nature and therefore a suitable test object for the development of methods that can be transferred to more complex systems like photosystem I. Engel and co-workers observed that the FMO complex exhibits remarkably long quantum coherence, but after about a decade of debate, it was shown that this quantum coherence has no significance to the functioning of the complex. Furthermore, it was shown that the reported long lived oscillations observed in the spectra are solely due to groundstate vibrational dynamics and do not reflect any energy transfer dynamics. | 5 | Photochemistry |
Nevado was born in Madrid and grew up in Spain. She was the first scientist in her family. At high school she was inspired by her chemistry and physics teachers to pursue a career in science. She eventually studied chemistry at the Autonomous University of Madrid, and earned her bachelor's degree in 2000. During one summer holiday she worked at the Menéndez Pelayo International University, where she met international students and realised the scientific community was global. She remained at the Autonomous University for her doctoral research, where she worked on organic chemistry and the cyclisation of enynes that had been catalysed by gold and platinum complexes. After earning her doctorate, Nevado moved to the Max Planck Institute for Coal Research, where she worked as a postdoctoral fellow with Alois Fürstner. Her postdoctoral research considered natural product synthesis. She spent three months working alongside Eiichi Nakamura at the University of Tokyo. | 0 | Organic Chemistry |
As the study of isochores was de facto abandoned by most scientists, an alternative theory was proposed to describe the compositional organization of genomes in accordance with the most recent genomic studies. The Compositional Domain Model depicts genomes as a medley of short and long homogeneous and nonhomogeneous domains. The theory defines "compositional domains" as genomic regions with distinct GC-contents as determined by a computational segmentation algorithm. The homogeneity of compositional domains is compared to that of the chromosome on which they reside using the F-test, which separated them into compositionally homogeneous domains and compositionally nonhomogeneous domains based on the outcome of test. Compositionally homogeneous domains that are sufficiently long (≥ 300 kb) are termed isochores or isochoric domains. These terms are in accordance with the literature as they provide clear distinction between isochoric- and nonisochoric-domains.
A comprehensive study of the human genome unraveled a genomic organization where two-thirds of the genome is a mixture of many short compositionally homogeneous domains and relatively few long ones. The remaining portion of the genome is composed of nonhomogeneous domains. In terms of coverage, only 1% of the total number of compositionally homogeneous domains could be considered "isochores" which covered less than 20% of the genome.
Since its inception the theory received wide attention and was extensively used to explain findings emerging from over dozen new genome sequencing studies.
However, many important questions remain open, such as which evolutionary forces shaped the structure of compositional domains and the ways they differ between different species. | 1 | Biochemistry |
Eco pickled surface (EPS) is a process applied to hot rolled sheet steel to remove all surface oxides (mill scale) and clean the steel surface. Steel which has undergone the EPS process acquires a high degree of resistance to subsequent development of surface oxide (rust), so long as it does not come into direct contact with moisture. EPS was developed by The Material Works, Ltd., which has filed several patent applications covering the process. It is primarily intended to be a replacement of the acid pickling process wherein steel strip is immersed in solutions of hydrochloric and sulfuric acids to chemically remove oxides. | 8 | Metallurgy |
A missense mRNA arises from a missense mutation, in the event of which a DNA nucleotide base pair in the coding region of a gene is changed such that it results in the substitution of one amino acid for another. The point mutation is nonsynonymous because it alters the RNA codon in the mRNA transcript such that translation results in amino acid change. An amino acid change may not result in appreciable changes in protein structure depending on whether the amino acid change is conservative or non-conservative. This owes to the similar physicochemical properties exhibited by some amino acids.
Missense mRNAs may be detected as a result of two different types of point mutations - spontaneous mutations and induced mutations. Spontaneous mutations occur during the DNA replication process where a non-complementary nucleotide is deposited by the DNA polymerase in the extension phase. The consecutive round of replication would result in a point mutation. If the resulting mRNA codon is one that changes the amino acid, a missense mRNA would be detected. A hypergeometric distribution study involving DNA polymerase β replication errors in the APC gene revealed 282 possible substitutions that could result in missense mutations. When the APC mRNA was analyzed in the mutational spectrum, it showed 3 sites where the frequency of substitutions were high.
Induced mutations caused by mutagens can give rise to missense mutations. Nucleoside analogues such as 2-aminopurine and 5-bromouracil can insert in place of A and T respectively. Ionizing radiation like x-rays and γ-rays can deaminate cytosine to uracil.
Missense mRNAs may be applied synthetically in forward and reverse genetic screens used to interrogate the genome. Site-directed mutagenesis is a technique often employed to create knock-in and knock-out models that express missense mRNAs. For example, in knock-in studies, human orthologs are identified in model organisms to introduce missense mutations, or a human gene with a substitution mutation is integrated into the genome of the model organism. The subsequent loss-of-function or gain-of-function phenotypes are measured to model genetic diseases and discover novel drugs. While homologous recombination has been widely used to generate single-base substitutions, novel technologies that co-inject gRNA and hCas9 mRNA of the CRISPR/Cas9 system, in conjunction with single-strand oligodeoxynucleotide (ssODN) donor sequences have shown efficiency in generating point mutations in the genome. | 1 | Biochemistry |
Starfish is a set of software tools developed in 2019 by a consortium of scientists to analyze data from nine different variations of FISH, since all variations produce the same set of data—gene expression values mapped to x and y coordinates in a cell. The software, created for all scientists, not just bioinformaticians, reads a set of images, removes noise, and identifies RNA molecules. This approach has set out to define a standard analysis scheme of FISH datasets in a similar way to single-cell transcriptomics analysis. | 1 | Biochemistry |
Sandra Pizzarello's research over the last forty years involved the analysis of organic compounds in several carbonaceous chondrites, particularly molecular, chiral, and isotopic characterization of amino acids. Because the formation of these organic-rich meteorites pre-date the origin of life, they had been under investigation as potential sites of primal organic compounds which could shed light on abiogenesis, specifically the origin of biological homochirality. Such studies, however, had been inconclusive until 1997 when Cronin and Pizzarello detected 7-9% L-enantiomeric excesses of three abiological amino acids while analyzing the Murchison meteorite.
Given Earths history of meteoric impacts and the observation that meteors contain an excess of the biologically relevant L-stereoisomer of certain amino acids, Pizzarello studied the effect of meteoritic amino acids in enantiomeric excess on the formation of other biological molecules. In one study, Pizzarello found that nonracemic solutions of abiological isovaline and proteinogenic alanine can direct the condensation of glycolaldehyde to produce nonracemic solutions of threose and erythrose via an aldol reaction concluding that amino acids can act as asymmetric catalysts in carbohydrate synthesis. These findings support the origin of life hypothesis that homochirality originated prior to life and from extraterrestrial origins. However, Pizzarellos theoretical inquiries into cosmochemical evolution remain debated based on suspect analytical evidence of meteoritic enantiomeric excesses. | 1 | Biochemistry |
The injection valve is a motorized valve which links the mixer and sample loop to the column. Typically the valve has three positions for loading the sample loop, for injecting the sample from the loop into the column, and for connecting the pumps directly to the waste line to wash them or change buffer solutions. The injection valve has a sample loading port through which the sample can be loaded into the injection loop, usually from a hypodermic syringe using a Luer-lock connection. | 3 | Analytical Chemistry |
Complementarity can be found between short nucleic acid stretches and a coding region or a transcribed gene, and results in base pairing. These short nucleic acid sequences are commonly found in nature and have regulatory functions such as gene silencing. | 1 | Biochemistry |
Technicon published method sheets for a wide range of analyses and a few of these are listed below. These methods and later methods are available from SEAL Analytical. Method lists for manufacturers instruments are readily available on their websites. | 3 | Analytical Chemistry |
Coronavir is the brand name of favipiravir used in Russia, where it is approved for the treatment of COVID-19. It is produced and sold by R-Pharm. Coronavir was approved for use in Russia in hospitals in July 2020, and in September 2020 it received approval for prescription sales for outpatient use. | 4 | Stereochemistry |
mTOR promotes the protein synthesis required for synaptic plasticity. Studies in cell cultures and hippocampal slices indicate that mTOR inhibition reduces long-term potentiation. mTOR activation can protect against certain neurodegeneration associated with certain disease conditions. On the other hand, promotion of autophagy by mTOR inhibition may reduce cognitive decline associated with neurodegeneration.
Moderate reduction of mTOR activity by 25-30% has been shown to improve brain function, suggesting that the relation between mTOR and cognition is optimized with intermediate doses (2.24 mg/kg/day in mice, human equivalent about 0.19 mg/kg/day), where very high or very low doses impair cognition. Reduction of the inflammatory cytokine Interleukin 1 beta (IL-1β) in mice by mTOR inhibition (with rapamycin in doses of 20 mg/kg/day, human equivalent about 1.6 mg/kg/day) has been shown to enhance learning and memory. Although IL-1β is required for memory, IL-1β normally increases with age, impairing cognitive function. | 1 | Biochemistry |
Haloalkanes are a class of molecule that is defined by a carbon–halogen bond. This bond can be relatively weak (in the case of an iodoalkane) or quite stable (as in the case of a fluoroalkane). In general, with the exception of fluorinated compounds, haloalkanes readily undergo nucleophilic substitution reactions or elimination reactions. The substitution on the carbon, the acidity of an adjacent proton, the solvent conditions, etc. all can influence the outcome of the reactivity. | 0 | Organic Chemistry |
In the synthesis of spirotryprostatin B, an azomethine ylide is formed from condensation of an amine with an aldehyde. The ylide then reacts with an electron-deficient alkene on an indolinone, resulting in formation of a spirocyclic pyrrolidine and four contiguous stereocenters. | 0 | Organic Chemistry |
Sulfonyl halide groups occur when a sulfonyl functional group is singly bonded to a halogen atom. They have the general formula R−SO−X where X is a halide, usually chloride or fluoride. Chlorides are produced by chlorination of sulfonic acids using thionyl chloride. Sulfonyl fluorides can be produced by treating sulfonic acids with sulfur tetrafluoride: | 0 | Organic Chemistry |
Isolated restriction enzymes are used to manipulate DNA for different scientific applications.
They are used to assist insertion of genes into plasmid vectors during gene cloning and protein production experiments. For optimal use, plasmids that are commonly used for gene cloning are modified to include a short polylinker sequence (called the multiple cloning site, or MCS) rich in restriction enzyme recognition sequences. This allows flexibility when inserting gene fragments into the plasmid vector; restriction sites contained naturally within genes influence the choice of endonuclease for digesting the DNA, since it is necessary to avoid restriction of wanted DNA while intentionally cutting the ends of the DNA. To clone a gene fragment into a vector, both plasmid DNA and gene insert are typically cut with the same restriction enzymes, and then glued together with the assistance of an enzyme known as a DNA ligase.
Restriction enzymes can also be used to distinguish gene alleles by specifically recognizing single base changes in DNA known as single-nucleotide polymorphisms (SNPs). This is however only possible if a SNP alters the restriction site present in the allele. In this method, the restriction enzyme can be used to genotype a DNA sample without the need for expensive gene sequencing. The sample is first digested with the restriction enzyme to generate DNA fragments, and then the different sized fragments separated by gel electrophoresis. In general, alleles with correct restriction sites will generate two visible bands of DNA on the gel, and those with altered restriction sites will not be cut and will generate only a single band. A DNA map by restriction digest can also be generated that can give the relative positions of the genes. The different lengths of DNA generated by restriction digest also produce a specific pattern of bands after gel electrophoresis, and can be used for DNA fingerprinting.
In a similar manner, restriction enzymes are used to digest genomic DNA for gene analysis by Southern blot. This technique allows researchers to identify how many copies (or paralogues) of a gene are present in the genome of one individual, or how many gene mutations (polymorphisms) have occurred within a population. The latter example is called restriction fragment length polymorphism (RFLP).
Artificial restriction enzymes created by linking the FokI DNA cleavage domain with an array of DNA binding proteins or zinc finger arrays, denoted zinc finger nucleases (ZFN), are a powerful tool for host genome editing due to their enhanced sequence specificity. ZFN work in pairs, their dimerization being mediated in-situ through the FokI domain. Each zinc finger array (ZFA) is capable of recognizing 9–12 base pairs, making for 18–24 for the pair. A 5–7 bp spacer between the cleavage sites further enhances the specificity of ZFN, making them a safe and more precise tool that can be applied in humans. A recent Phase I clinical trial of ZFN for the targeted abolition of the CCR5 co-receptor for HIV-1 has been undertaken.
Others have proposed using the bacteria R-M system as a model for devising human anti-viral gene or genomic vaccines and therapies since the RM system serves an innate defense-role in bacteria by restricting tropism by bacteriophages. There is research on REases and ZFN that can cleave the DNA of various human viruses, including HSV-2, high-risk HPVs and HIV-1, with the ultimate goal of inducing target mutagenesis and aberrations of human-infecting viruses. The human genome already contains remnants of retroviral genomes that have been inactivated and harnessed for self-gain. Indeed, the mechanisms for silencing active L1 genomic retroelements by the three prime repair exonuclease 1 (TREX1) and excision repair cross complementing 1(ERCC) appear to mimic the action of RM-systems in bacteria, and the non-homologous end-joining (NHEJ) that follows the use of ZFN without a repair template. | 1 | Biochemistry |
The GC-ratio within a genome is found to be markedly variable. These variations in GC-ratio within the genomes of more complex organisms result in a mosaic-like formation with islet regions called isochores. This results in the variations in staining intensity in chromosomes. GC-rich isochores typically include many protein-coding genes within them, and thus determination of GC-ratios of these specific regions contributes to mapping gene-rich regions of the genome. | 1 | Biochemistry |
The process of electrochlorination is a simple application based on the chloralkali process (in an unpartitioned cell).
It is the electrolysis of saltwater to produce a chlorinated solution. The first step is removing any solids from the saltwater. Next, the saltwater streams through an electrolyzer cell's channel of decreasing thickness. One side of the channel is a cathode, the other is an anode. A low voltage DC current is applied, electrolysis happens producing sodium hypochlorite and hydrogen gas (H). The solution travels to a tank that separates the hydrogen gas based on its low density. Only water and sodium chloride are used. The simplified chemical reaction is:
:NaCl + HO + energy → NaOCl + H
That is, energy is added to sodium chloride (table salt) in water, producing sodium hypochlorite and hydrogen gas.
Because the reaction takes place in an unpartitioned cell and NaOH is present in the same solution as the Cl:
:2 NaCl + 2 HO → 2 NaOH + H + Cl
any Cl disproportionates to hypochlorite and chloride
:Cl + 2 NaOH → NaCl + NaClO + HO
resulting in a hypochlorite solution. | 7 | Physical Chemistry |
Before powered fans were widely accessible, their use related to the social divide between social classes. In Britain and China, they were initially only installed in the buildings of Parliament and in noble homes. In Ancient Egypt (3150 BC), servants were required to fan Pharaohs and important figures.
In parts of the world such as India, where the temperature reaches above , standing and electric box fans are essential in the business world for customer comfort and an efficient work environment. Fans have become solar powered, energy efficient and battery powered in places with unreliable energy sources.
In South Korea, fans play a part in an old wives tale. Many older South Korean citizens believe in the unscientific and unsupported myth of fan death due to excessive use of an electric fan; Korean electric fans usually turn off after a few hours to protect from fan death.
Typical room electrical fans consume 50 to 100 watts of power, while air-conditioning units use 500 to 4000 watts; fans use less electricity but do not cool the air, simply providing evaporative cooling of sweat. Commercial fans are louder than AC units and can be to disruptively loud. According to the U.S. Consumer Product Safety Commission, reported incidents related to box fans include, fire (266 incidents), potential fire (29 incidents), electrocution (15), electric shock (4 incidents), and electrical hazard (2 incidents). Injuries related to AC units mostly relate to their falling from buildings. | 7 | Physical Chemistry |
Through the seasonal vertical migration of zooplankton, the lipid pump creates a net difference between lipids transported to the deep during the fall (when zooplankton enter diapause) and what returns to the surface during the spring, resulting in the sequestration of lipid carbon at depth. The biological pump encompasses many processes that sequester the CO taken up in the surface ocean by phytoplankton through the export of POC to the deep ocean. Although zooplankton are known to play important roles in the biological pump through grazing and the repackaging of particulate matter, the active transport of seasonally-migrating zooplankton through the lipid pump has not been incorporated into global estimates of the biological pump. | 9 | Geochemistry |
Formaldehyde can be determined in electroless copper plating solutions by the addition of an excess of sodium sulfite solution and titrating the liberated hydroxyl ion with standard acid.
: HC=O + HSO + HO → [HO-CH-SO] + OH | 3 | Analytical Chemistry |
Articles made of Corinthian bronze are mentioned in the Bible. The Beautiful Gate (or Nicanor Gate) of the Second Temple in Jerusalem, mentioned in the Book of Acts 3:2–10, was a large, 18 metre (60 feet) wide structure said to be either solid, or covered in plates of, Corinthian brass. Another Biblical reference, in Book of Ezra 8:27, is usually translated "fine copper [or bronze], precious as gold".
Similar alloys are found outside Europe. The Hông-hee vases (1426) of China were said to be made of a similarly mixed metal allegedly formed when the Imperial palace was burnt to the ground. These vessels are of priceless value. An alloy of gold and copper, known as tumbaga was in widespread use in Pre-columbian Mesoamerica, and has an essentially identical composition to Corinthian brass. A similar metallurgical process for "the colouration [chrôsis] of gold" is described in the 15th recipe in the Leyden papyrus X, from Thebes in Egypt, dated to the 4th century AD. | 8 | Metallurgy |
Metal pollution in soil will induce high toxicity in hemp plants. Cadmium (Cd) toxicity has been proven to be long term and irreversible in plants. Cd specifically results in oxidative stress and increase in free radicals. Free radicals are found to cause oxidative stress, cell damage, and death. Hemp plants in Cd polluted soils were found to help detoxify the metal while the plants were still conserved. While growth in these hemp plants were slightly reduced when planted in Cd concentration soil, continued plant growth indicated hemp plants were able to detoxify some Cd. Specifically, transporter proteins would move Cd into the cell wall and differentially expressed genes (DEGs) would activate, bind, and defend against Cd stress. These DEGs were found to be involved in cell wall metabolism and were most active when in contact with Cd. The plant hormone ABA plays an important role in activating signal transduction cascades and cell cycling and growth. An increase of ABC transporters in hemp plants contributes to increases in calcium concentration, indicating that calcium-binding proteins can control Cd concentration and absorption. | 1 | Biochemistry |
The first rule holds that a double-stranded DNA molecule, globally has percentage base pair equality: A% = T% and G% = C%. The rigorous validation of the rule constitutes the basis of Watson–Crick base pairs in the DNA double helix model. | 1 | Biochemistry |
The exact mechanism of the action of general anaesthetics has not been delineated. Halothane activates GABA and glycine receptors. It also acts as an NMDA receptor antagonist, inhibits nACh and voltage-gated sodium channels, and activates 5-HT and twin-pore K channels. It does not affect the AMPA or kainate receptors. | 4 | Stereochemistry |
Phorbol is a natural product found in many plants, especially those of the Euphorbiaceae and Thymelaeaceae families. Phorbol is the active constituent of the highly toxic New World tropical manchineel or beach apple, Hippomane mancinella. It is very soluble in most polar organic solvents, as well as in water. In the manchineel, this leads to an additional exposure risk during rain, where liquid splashing from an undamaged tree may also be injurious. Contact with the tree or consumption of its fruit can lead to symptoms such as severe pain and swelling.
The purging croton, Croton tiglium, is the source of croton oil from which phorbol was initially isolated. Its seeds and oil have been used for hundreds of years in traditional medicine, generally as a purgative, and the seeds were mentioned in Chinese herbal texts 2000 years ago. The purgative effects of the oil are largely attributed to the high percentage of phorbol esters contained in the oil. Phorbol was isolated from C. tiglium seeds in 1934. The structure of the compound was determined in 1967, and a total synthesis was described in 2015. | 0 | Organic Chemistry |
Triethyloxonium tetrafluoroborate is the organic oxonium compound with the formula . It is often called Meerweins reagent or Meerweins salt after its discoverer Hans Meerwein. Also well known and commercially available is the related trimethyloxonium tetrafluoroborate. The compounds are white solids that dissolve in polar organic solvents. They are strong alkylating agents. Aside from the tetrafluoroborate| salt, many related derivatives are available. | 0 | Organic Chemistry |
The protein encoded by this gene mediates transcriptional control by interaction with the activation function 2 (AF2) region of several nuclear receptors, including the estrogen, retinoic acid, and vitamin D receptors. The protein localizes to nuclear bodies and is thought to associate with chromatin and heterochromatin-associated factors. The protein is a member of the tripartite motif (TRIM) family. The TRIM motif includes three zinc-binding domains – a RING, a B-box type 1 and a B-box type 2 – and a coiled-coil region. Two alternatively spliced transcript variants encoding different isoforms have been described for this gene. | 1 | Biochemistry |
Transcription elongation is not a smooth ride along double stranded DNA, as RNA polymerase undergoes extensive co-transcriptional pausing during transcription elongation. In general, RNA polymerase II does not transcribe through a gene at a constant pace. Rather it pauses periodically at certain sequences, sometimes for long periods of time before resuming transcription. This pausing is especially pronounced at nucleosomes, and arises in part through the polymerase entering a transcriptionally incompetent backtracked state. The duration of these pauses ranges from seconds to minutes or longer, and exit from long-lived pauses can be promoted by elongation factors such as TFIIS.
This pausing is also sometimes used for proofreading; here the polymerase backs up, erases some of the RNA it has already made and has another go at transcription. In extreme cases, for example, when the polymerase encounters a damaged nucleotide, it comes to a complete halt. More often, an elongating polymerase is stalled near the promoter. Promoter-proximal pausing during early elongation is a commonly used mechanism for regulating genes poised to be expressed rapidly or in a coordinated fashion. Pausing is mediated by a complex called NELF (negative elongation factor) in collaboration with DSIF (DRB-sensitivity-inducing factor containing SPT4/SPT5). The blockage is released once the polymerase receives an activation signal, such as the phosphorylation of Ser-2 of CTD tail by P-TEFb. Other elongation factors such as ELL and TFIIS stimulate the rate of elongation by limiting the length of time that polymerase pauses. | 1 | Biochemistry |
Advantages of electrofusion welding:
* Simple process capable of producing consistent joints
* Process is entirely contained, reducing the risk of joint contamination
* Process allows repair without the need to remove pipes
Disadvantages of electrofusion welding:
* A special sleeve is required, so it is more expensive than other pipe joining methods such as hot plate joining
* Implanted coils make recycling of parts more difficult | 7 | Physical Chemistry |
Arsenical bronze has seen little use in the modern period. It appears that the closest equivalent goes by the name of arsenical copper, defined as copper with under 0.5 wt% As, below the accepted percentage in archaeological artefacts. The presence of 0.5 wt% arsenic in copper lowers the electrical conductivity to 34% of that of pure copper, and even as little as 0.05 wt% decreases it by 15%. | 8 | Metallurgy |
Although CoQ has been used to treat purported muscle-related side effects of statin medications, a 2015 meta-analysis found that CoQ had no effect on statin myopathy. A 2018 meta-analysis concluded that there was preliminary evidence for oral CoQ reducing statin-associated muscle symptoms, including muscle pain, muscle weakness, muscle cramps and muscle tiredness. | 1 | Biochemistry |
Some enzymatic nitrification inhibitors, such as nitrapyrin, can also inhibit the oxidation of methane in methanotrophic bacteria. AMO shows similar kinetic turnover rates to methane monooxygenase (MMO) found in methanotrophs, indicating that MMO is a similar catalyst to AMO for the purpose of methane oxidation. Furthermore, methanotrophic bacteria share many similarities to oxidizers such as Nitrosomonas. The inhibitor profile of particulate forms of MMO (pMMO) shows similarity to the profile of AMO, leading to similarity in properties between MMO in methanotrophs and AMO in autotrophs. | 1 | Biochemistry |
The inducer in the lac operon is allolactose. If lactose is present in the medium, then a small amount of it will be converted to allolactose by a few molecules of β-galactosidase that are present in the cell. Allolactose binds to the repressor and decreases the repressor's affinity for the operator site.
However, when lactose and glucose are both available in the system, the lac operon is repressed. This is because glucose actively prevents the induction of lacZYA. | 0 | Organic Chemistry |
Metal nitrosyls, compounds featuring NO ligands, are numerous. In contrast to metal carbonyls, however, homoleptic metal nitrosyls are rare. NO is a stronger π-acceptor than CO. Well known nitrosyl carbonyls include CoNO(CO) and Fe(NO)(CO), which are analogues of Ni(CO). | 0 | Organic Chemistry |
Efforts are reported in asymmetric synthesis of halo carbonyls through organocatalysis. In one study an acid chloride is converted into an α-halo ester with a strong base (sodium hydride), a bromine donor and an organocatalyst based on proline and quinine:
In the proposed reaction mechanism the base first converts the acid chloride to the ketene, the organocatalyst then introduces chirality through its quinonoid tertiary amine, forming a ketene adduct. | 0 | Organic Chemistry |
Reaction centers are multi-protein complexes found within the thylakoid membrane.
At the heart of a photosystem lies the reaction center, which is an enzyme that uses light to reduce and oxidize molecules (give off and take up electrons). This reaction center is surrounded by light-harvesting complexes that enhance the absorption of light.
In addition, surrounding the reaction center are pigments which will absorb light. The pigments which absorb light at the highest energy level are found furthest from the reaction center. On the other hand, the pigments with the lowest energy level are more closely associated with the reaction center. Energy will be efficiently transferred from the outer part of the antenna complex to the inner part. This funneling of energy is performed via resonance transfer, which occurs when energy from an excited molecule is transferred to a molecule in the ground state. This ground state molecule will be excited, and the process will continue between molecules all the way to the reaction center. At the reaction center, the electrons on the special chlorophyll molecule will be excited and ultimately transferred away by electron carriers. (If the electrons were not transferred away after excitation to a high energy state, they would lose energy by fluorescence back to the ground state, which would not allow plants to drive photosynthesis.) The reaction center will drive photosynthesis by taking light and turning it into chemical energy that can then be used by the chloroplast.
Two families of reaction centers in photosystems can be distinguished: type I reaction centers (such as photosystem I (P700) in chloroplasts and in green-sulfur bacteria) and type II reaction centers (such as photosystem II (P680) in chloroplasts and in non-sulfur purple bacteria). The two photosystems originated from a common ancestor, but have since diversified.
Each of the photosystem can be identified by the wavelength of light to which it is most reactive (700 nanometers for PSI and 680 nanometers for PSII in chloroplasts), the amount and type of light-harvesting complex present, and the type of terminal electron acceptor used.
Type I photosystems use ferredoxin-like iron-sulfur cluster proteins as terminal electron acceptors, while type II photosystems ultimately shuttle electrons to a quinone terminal electron acceptor. Both reaction center types are present in chloroplasts and cyanobacteria, and work together to form a unique photosynthetic chain able to extract electrons from water, creating oxygen as a byproduct. | 5 | Photochemistry |
Airborne Real-time Cueing Hyperspectral Enhanced Reconnaissance, also known by the acronym ARCHER, is an aerial imaging system that produces ground images far more detailed than plain sight or ordinary aerial photography can.
It is the most sophisticated unclassified hyperspectral imaging system available, according to U.S. Government officials.
ARCHER can automatically scan detailed imaging for a given signature of the object being sought (such as a missing aircraft), for abnormalities in the surrounding area, or for changes from previous recorded spectral signatures.
It has direct applications for search and rescue, counterdrug, disaster relief and impact assessment, and homeland security, and has been deployed by the Civil Air Patrol (CAP) in the US on the Australian-built Gippsland GA8 Airvan fixed-wing aircraft. CAP, the civilian auxiliary of the United States Air Force, is a volunteer education and public-service non-profit organization that conducts aircraft search and rescue in the US. | 7 | Physical Chemistry |
Hydroamination has been examined with a variety of amines, unsaturated substrates, and vastly different catalysts. Amines that have been investigated span a wide scope including primary, secondary, cyclic, acyclic, and anilines with diverse steric and electronic substituents. The unsaturated substrates that have been investigated include alkenes, dienes, alkynes, and allenes. For intramolecular hydroamination, various aminoalkenes have been examined. | 0 | Organic Chemistry |
A rock hyrax midden is a stratified accumulation of fecal pellets and a brown amber-like a urinary product known as hyraceum excreted by the rock hyrax and closely related species.
Hyrax middens form very slowly (ranging from ~5 years to >1000 years for 1 mm of hyraceum accumulation), over long periods of time, with many spanning tens of thousands of years and some dating as far back as ~70,000 years. Hyrax middens contain a diverse range of paleoenvironmental proxies, including fossil pollen and stable carbon, nitrogen and hydrogen isotopes. Combined with the antiquity of hyrax middens, and the often-continuous nature of their deposition, hyrax middens have become a valuable means of reconstructing past environmental and climate change
Rock hyraxes are known to use communal latrines. These sites are often found in sheltered locations, where the threat of predation is limited, and middens form when they are protected from the elements. At well-protected sites, it may accumulate in deposits in excess of a meter thick and several meters across. The thickness of hyrax middens depends on the nature of the shelter and the regional climate history and geology. Hyraceum shows hygroscopic properties and periods of increased precipitation or elevated ambient humidity will destroy existing middens, while more arid periods allow their development/preservation. Thicker formations tend to occur in shallow shelters that during more arid periods, presumably provided sufficient shelter from rainfall for substantial midden accumulations, but under wetter conditions no longer provide adequate protection, resulting in the removal of the more soluble components of the midden. At poorly protected sites in arid regions hyrax urine leaves a white, calcium carbonate precipitate on the rocks. Varying degrees of protection result in varying degrees of midden preservation. Small overhangs, vertical fractures in cap rocks, and groundwater flow along weakness in the shelter’s architecture may lead to midden degradation if rainfall exceeds a certain amount and/or intensity. The thickest middens have been found at sites composed of massive, horizontally bedded rock such as granite and quartzites with between ~30 and 480 mm of annual rainfall. In more humid environments (>800 mm mean annual rainfall), there is little to no evidence of hyraceum accumulation, and middens typically resemble piles of compost, as the masticated plant material in the pellets rapidly decomposes. Hyraceum-rich middens do not typically form in coastal situations, despite the presence of hyraxes, and it is considered that the ambient humidity of the air and the occurrence of coastal fogs preclude midden development | 9 | Geochemistry |
In the case catalytic or adsorbent systems where a metal species is dispersed upon a support (or carrier) material (often quasi-inert oxides, such as alumina or silica), it is possible for an adsorptive species to indirectly adsorb to the support surface under conditions where such adsorption is thermodynamically unfavorable. The presence of the metal serves as a lower-energy pathway for gaseous species to first adsorb to the metal and then diffuse on the support surface. This is possible because the adsorbed species attains a lower energy state once it has adsorbed to the metal, thus lowering the activation barrier between the gas phase species and the support-adsorbed species.
Hydrogen spillover is the most common example of an adsorptive spillover. In the case of hydrogen, adsorption is most often accompanied with dissociation of molecular hydrogen (H) to atomic hydrogen (H), followed by spillover of the hydrogen atoms present.
The spillover effect has been used to explain many observations in heterogeneous catalysis and adsorption. | 7 | Physical Chemistry |
Members of the Hedgehog protein family act by binding to a transmembrane "Patched" receptor, which is bound to the "Smoothened" protein, by which the Hedgehog signal can be transduced. In the absence of Hedgehog, the Patched receptor inhibits Smoothened action. Inhibition of Smoothened causes the Cubitus interruptus (Ci), Fused, and Cos protein complex attached to microtubules to remain intact. In this conformation, the Ci protein is cleaved so that a portion of the protein is allowed to enter the nucleus and act as a transcriptional repressor. In the presence of Hedgehog, Patched no longer inhibits Smoothened. Then active Smoothened protein is able to inhibit PKA and Slimb, so that the Ci protein is not cleaved. This intact Ci protein can enter the nucleus, associate with CPB protein and act as a transcriptional activator, inducing the expression of Hedgehog-response genes. | 1 | Biochemistry |
PCBs are fairly chemically unreactive, this property being attractive for its application as an inert material. They resist oxidation.
Many chemical compounds are available to destroy or reduce the PCBs. Commonly, PCBs are degraded by basic mixtures of glycols, which displace some or all chloride. Also effective are reductants such as sodium or sodium naphthalene. Vitamin B12 has also shown promise. | 2 | Environmental Chemistry |
An experimental iodine clock sequence has also been established for a system consisting of iodine potassium-iodide, sodium chlorate and perchloric acid that takes place through the following reactions.
Triiodide is present in equilibrium with iodide anion and molecular iodine:
Chlorate ion oxidizes iodide ion to hypoiodous acid and chlorous acid in the slow and rate-determining step:
Chlorate consumption is accelerated by reaction of hypoiodous acid to iodous acid and more chlorous acid:
More autocatalysis when newly generated iodous acid also converts chlorate in the fastest reaction step:
In this clock the induction period is the time it takes for the autocatalytic process to start after which the concentration of free iodine falls rapidly as observed by UV–visible spectroscopy. | 7 | Physical Chemistry |
In chemistry, conformational isomerism is a form of stereoisomerism in which the isomers can be interconverted just by rotations about formally single bonds (refer to figure on single bond rotation). While any two arrangements of atoms in a molecule that differ by rotation about single bonds can be referred to as different conformations, conformations that correspond to local minima on the potential energy surface are specifically called conformational isomers or conformers. Conformations that correspond to local maxima on the energy surface are the transition states between the local-minimum conformational isomers. Rotations about single bonds involve overcoming a rotational energy barrier to interconvert one conformer to another. If the energy barrier is low, there is free rotation and a sample of the compound exists as a rapidly equilibrating mixture of multiple conformers; if the energy barrier is high enough then there is restricted rotation, a molecule may exist for a relatively long time period as a stable rotational isomer or rotamer (an isomer arising from hindered single-bond rotation). When the time scale for interconversion is long enough for isolation of individual rotamers (usually arbitrarily defined as a half-life of interconversion of 1000 seconds or longer), the isomers are termed atropisomers (see: atropisomerism). The ring-flip of substituted cyclohexanes constitutes another common form of conformational isomerism.
Conformational isomers are thus distinct from the other classes of stereoisomers (i. e. configurational isomers) where interconversion necessarily involves breaking and reforming of chemical bonds. For example, /- and R/S- configurations of organic molecules have different handedness and optical activities, and can only be interconverted by breaking one or more bonds connected to the chiral atom and reforming a similar bond in a different direction or spatial orientation. They also differ from geometric (cis/trans) isomers, another class of stereoisomers, which require the π-component of double bonds to break for interconversion. (Although the distinction is not always clear-cut, since certain bonds that are formally single bonds actually have double bond character that becomes apparent only when secondary resonance contributors are considered, like the C–N bonds of amides, for instance.) Due to rapid interconversion, conformers are usually not isolable at room temperature.
The study of the energetics between different conformations is referred to as conformational analysis. It is useful for understanding the stability of different isomers, for example, by taking into account the spatial orientation and through-space interactions of substituents. In addition, conformational analysis can be used to predict and explain product selectivity, mechanisms, and rates of reactions. Conformational analysis also plays an important role in rational, structure-based drug design. | 4 | Stereochemistry |
Plasmids are the most-commonly used bacterial cloning vectors. These cloning vectors contain a site that allows DNA fragments to be inserted, for example a multiple cloning site or polylinker which has several commonly used restriction sites to which DNA fragments may be ligated. After the gene of interest is inserted, the plasmids are introduced into bacteria by a process called transformation. These plasmids contain a selectable marker, usually an antibiotic resistance gene, which confers on the bacteria an ability to survive and proliferate in a selective growth medium containing the particular antibiotics. The cells after transformation are exposed to the selective media, and only cells containing the plasmid may survive. In this way, the antibiotics act as a filter to select only the bacteria containing the plasmid DNA. The vector may also contain other marker genes or reporter genes to facilitate selection of plasmids with cloned inserts. Bacteria containing the plasmid can then be grown in large amounts, harvested, and the plasmid of interest may then be isolated using various methods of plasmid preparation.
A plasmid cloning vector is typically used to clone DNA fragments of up to 15 kbp. To clone longer lengths of DNA, lambda phage with lysogeny genes deleted, cosmids, bacterial artificial chromosomes, or yeast artificial chromosomes are used. | 1 | Biochemistry |
*Heat treatment − Treating food with heat, such as blanching or roasting, de-naturates enzymes and destroys the reactants responsible for browning. Blanching is used, for example, in winemaking, tea processing, storing nuts and bacon, and preparing vegetables for freezing preservation. Meat is often partially browned under high heat before being incorporated into a larger preparation to be cooked at a lower temperature which produces less browning.
*Cold treatment − Refrigeration and freezing are the most common ways of storing food, preventing decay. The activity of browning enzymes, i.e., rate of reaction, drops in low temperatures. Thus, refrigeration helps to keep the initial look, color, and flavour of fresh vegetables and fruits. Refrigeration is also used during distribution and retailing of fruits and vegetables.
*Oxygen elimination − Presence of oxygen is crucial for enzymatic browning, therefore eliminating oxygen from the environment helps to slow down the browning reaction. Withdrawing air or replacing it with other gases (e.g., N or CO) during preservation, such as in vacuum-packaging or modified atmosphere packaging, wine or juice bottling, using impermeable films or edible coatings, dipping into salt or sugar solutions, keeps the food away from direct contact with oxygen. Impermeable films made of plastic or other materials prevent food being exposed to oxygen in the air and avoid moisture loss. There is an increasing activity in developing packaging materials impregnated with antioxidants, antimicrobial, and antifungal substances, such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), tocopherols, hinokitiol, lysozyme, nisin, natamycin, chitosan, and ε-polylysine. Edible coatings can be made of polysaccharides, proteins, lipids, vegetable skins, plants or other natural products.
*Irradiation − Food irradiation using UV-C, gamma rays, x-rays, and electron beams is another method to extend the food shelf life. Ionizing radiation inhibits the vitality of microorganisms responsible for food spoilage and delays the maturation and sprouting of preserving vegetables and fruits. | 1 | Biochemistry |
Temperature programmed desorption (TPD) is one of the most widely used surface analysis techniques available for materials research science. It has several applications such as knowing the desorption rates and binding energies of chemical compounds and elements, evaluation of active sites on catalyst surfaces and the understanding of the mechanisms of catalytic reactions including adsorption, surface reaction and desorption, analysing material compositions, surface interactions and surface contaminates. Therefore, TPD is increasingly important in many industries including, but not limited to, quality control and industrial research on products such as polymers, pharmaceuticals, clays and minerals, food packaging, and metals and alloys.
When TPD is used with the aim of knowing desorption rates of products that were previously adsorbed on a surface, it consists of heating a cold crystal surface that adsorbed a gas or a mixture of gases at a controlled rate. Then, the adsorbates will react as they are heated and then they will desorb from the surface. The results of applying TPD are the desorption rates of each of the product species that have been desorbed as a function of the temperature of the surface, this is called the TPD spectrum of the product. Also, as the temperature at which each of the surface compounds has been desorbed is known, it is possible to compute the energy that bounded the desorbed compound to the surface, the activation energy. | 7 | Physical Chemistry |
Thioamides are also a class of drugs that are used to control thyrotoxicosis.
Thioamides have been incorporated into peptides as isosteres for the amide bond. Peptide modifications are analogues of the native peptide, which can reveal the structure-activity relationship (SAR). Analogues of peptides can also be used as drugs with an improved oral bioavailability.
Thioamides inhibit the enzyme thyroid peroxidase in the thyroid, reducing the synthesis of triiodothyronine (T) and thyroxine (T), thereby blocking uptake of iodotyrosines from the colloid. They also block iodine release from peripheral hormone. Maximum effects occur only after a month, since hormone depletion is caused by reduced synthesis, which is a slow process. | 0 | Organic Chemistry |
When an isosbestic plot is constructed by the superposition of the absorption spectra of two species (whether by using molar absorptivity for the representation, or by using absorbance and keeping the same molar concentration for both species), the isosbestic point corresponds to a wavelength at which these spectra cross each other.
A pair of substances can have several isosbestic points in their spectra.
When a 1-to-1 (one mole of reactant gives one mole of product) chemical reaction (including equilibria) involves a pair of substances with an isosbestic point, the absorbance of the reaction mixture at this wavelength remains invariant, regardless of the extent of reaction (or the position of the chemical equilibrium). This occurs because the two substances absorb light of that specific wavelength to the same extent, and the analytical concentration remains constant.
For the reaction:
the analytical concentration is the same at any point in the reaction:
The absorbance of the reaction mixture (assuming it depends only on X and Y) is:
But at the isosbestic point, both molar absorptivities are the same:
Hence, the absorbance
does not depend on the extent of reaction (i.e., on the particular concentrations of X and Y)
The requirement for an isosbestic point to occur is that the two species involved are related linearly by stoichiometry, such that the absorbance is invariant at a certain wavelength. Thus, ratios other than 1-to-1 are possible. The presence of an isosbestic point typically indicates that only two species that vary in concentration contribute to the absorption around the isosbestic point. If a third one is partaking in the process, the spectra typically intersect at varying wavelengths as concentrations change, creating the impression that the isosbestic point is out of focus, or that it will shift as conditions change. The reason for this is that it would be very unlikely for three compounds to have extinction coefficients linked in a linear relationship by chance for one particular wavelength. | 7 | Physical Chemistry |
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