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The Contamination Indicator Decontamination Assurance System (CIDAS) is a technology used to identify chemical contamination. CIDAS is meant to help soldiers by detecting trace levels and finding the exact location of chemical weapon agents.
CIDAS is a component of a larger U.S. government initiative, run by the Joint Project Manager Protection at the Department of Defense, to improve decontamination processes associated with chemical, biological, and non-traditional warfare agents. Programs under this umbrella include the Joint Sensitive Equipment Wipe, General Purpose Decontaminants, and CIDAS. | 1 | Biochemistry |
VCl is a catalyst for the polymerization of alkenes, especially those useful in the rubber industry. The underlying technology is related to Ziegler–Natta catalysis, which involves the intermediacy of vanadium alkyls. | 0 | Organic Chemistry |
The Pfizer Award in Enzyme Chemistry, formerly known as the Paul-Lewis Award in Enzyme Chemistry was established in 1945. Consisting of a gold medal and honorarium, its purpose is to stimulate fundamental research in enzyme chemistry by scientists not over forty years of age. The award is administered by the Division of Biological Chemistry of the American Chemical Society and sponsored by Pfizer. The award was terminated in 2022. | 1 | Biochemistry |
Organometallic photosensitizers contain a metal atom chelated to at least one organic ligand. The photosensitizing capacities of these molecules result from electronic interactions between the metal and ligand(s). Popular electron-rich metal centers for these complexes include Iridium, Ruthenium, and Rhodium. These metals, as well as others, are common metal centers for photosensitizers due to their highly filled d-orbitals, or high d-electron counts, to promote metal to ligand charge transfer from pi-electron accepting ligands. This interaction between the metal center and the ligand leads to a large continuum of orbitals within both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) which allows for excited electrons to switch multiplicities via intersystem crossing.
While many organometallic photosensitizer compounds are made synthetically, there also exists naturally occurring, light-harvesting organometallic photosensitizers as well. Some relevant naturally occurring examples of organometallic photosensitizers include Chlorophyll A and Chlorophyll B. | 5 | Photochemistry |
Radical cyclization reactions are organic chemical transformations that yield cyclic products through radical intermediates. They usually proceed in three basic steps: selective radical generation, radical cyclization, and conversion of the cyclized radical to product. | 0 | Organic Chemistry |
Surfaces and interfaces are critical zones where major physical, chemical, and biological exchanges occur. As the ocean covers 362 million km, about 71% of the Earth's surface, the ocean-atmosphere interface is plausibly one of the largest and most important interfaces on the planet. Every substance entering or leaving the ocean from or to the atmosphere passes through this interface, which on the water-side -and to a lesser extent on the air-side- shows distinct physical, chemical, and biological properties. On the water side the uppermost 1 to 1000 μm of this interface are referred to as the sea surface microlayer (SML). Like a skin, the SML is expected to control the rates of exchange of energy and matter between air and sea, thereby potentially exerting both short-term and long-term impacts on various Earth system processes, including biogeochemical cycling, production and uptake of radiately active gases like or DMS, thus ultimately climate regulation. As of 2017, processes occurring within the SML, as well as the associated rates of material exchange through the SML, remained poorly understood and were rarely represented in marine and atmospheric numerical models.
An improved understanding of the biological, chemical, and physical processes at the ocean's upper surface could provide an essential contribution to the reduction of uncertainties regarding ocean-climate feedbacks. Due to its positioning between atmosphere and ocean, the SML is the first to be exposed to climate changes including temperature, climate relevant trace gases, wind speed, and precipitation as well as to pollution by human waste, including nutrients, toxins, nanomaterials, and plastic debris. | 7 | Physical Chemistry |
The chloroplast NADH dehydrogenase F (ndhF) gene is found in all vascular plant divisions and is highly conserved. Its DNA fragment resides in the small single-copy region of the chloroplast genome, and is thought to encode a hydrophobic protein containing 664 amino acids and to have a mass of 72.9 kDa. | 5 | Photochemistry |
MAPK pathways of fungi are also well studied. In yeast, the Fus3 MAPK is responsible for cell cycle arrest and mating in response to pheromone stimulation. The pheromone alpha-factor is sensed by a seven transmembrane receptor. The recruitment and activation of Fus3 pathway components are strictly dependent on heterotrimeric G-protein activation. The mating MAPK pathway consist of three tiers (Ste11-Ste7-Fus3), but the MAP2 and MAP3 kinases are shared with another pathway, the Kss1 or filamentous growth pathway. While Fus3 and Kss1 are closely related ERK-type kinases, yeast cells can still activate them separately, with the help of a scaffold protein Ste5 that is selectively recruited by the G-proteins of the mating pathway. The trick is that Ste5 can associate with and "unlock" Fus3 for Ste7 as a substrate in a tertiary complex, while it does not do the same for Kss1, leaving the filamentous growth pathway to be activated only in the absence of Ste5 recruitment.
Fungi also have a pathway reminiscent of mammalian JNK/p38 signaling. This is the Hog1 pathway: activated by high osmolarity (in Saccharomyces cerevisiae) or a number of other abiotic stresses (in Schizosaccharomyces pombe). The MAP2 kinase of this pathway is called Pbs2 (related to mammalian MKK3/4/6/7), the dedicated MAP3 kinases involved in activation are Ssk2 and SSk22. The system in S. cerevisiae is activated by a sophisticated osmosensing module consisting of the Sho1 and Sln1 proteins, but it is yet unclear how other stimuli can elicit activation of Hog1. Yeast also displays a number of other MAPK pathways without close homologs in animals, such as the cell wall integrity pathway (Mpk1/Slt2) or the sporulation pathway (Smk1). | 1 | Biochemistry |
Solid carbon dioxide (dry ice) sublimes rapidly along the solid-gas boundary (sublimation point) below the triple point (e.g., at the temperature of −78.5 °C, at atmospheric pressure), whereas its melting into liquid CO can occur along the solid-liquid boundary (melting point) at pressures and temperatures above the triple point (i.e., 5.1 atm, −56.6 °C). | 3 | Analytical Chemistry |
A nitronate (IUPAC: azinate) in organic chemistry is an anion with the general structure , containing the functional group, where R can be hydrogen, halogen, organyl group or other groups. It is the anion of nitronic acid (sometimes also called an aci-nitro compound, or an azinic acid), a tautomeric form of a nitro compound. Just as aldehydes and ketones can exist in equilibrium with their enol tautomer, nitro compounds exist in equilibrium with their nitronate tautomer under basic conditions. In practice they are formed by the deprotonation of the α-carbon, the pK of which is typically around 17.
Nitronates are formed as intermediates in the Henry reaction, Hass–Bender oxidation and Nef reaction, the latter of which also demonstrates the instability of the nitronic acid form. The nitronate has two different resonance structures, one with a negative charge on the α-carbon and a double bond between the nitrogen and one of the oxygens, and another resonance structure with a double bond between the nitrogen and the α-carbon, and single bonds between the nitrogen and the oxygens. | 0 | Organic Chemistry |
Thionyl chloride converts phosphonic acids and phosphonates into phosphoryl chlorides. It is for this type of reaction that thionyl chloride is listed as a Schedule 3 compound, as it can be used in the "di-di" method of producing G-series nerve agents. For example, thionyl chloride converts dimethyl methylphosphonate into methylphosphonic acid dichloride, which can be used in the production of sarin and soman. | 0 | Organic Chemistry |
:Automated diffraction tomography (ADT) uses software to collect diffraction patterns over a series of slight tilt increments. In this way, a three-dimensional (tomographic) data set of reciprocal lattice intensities can be generated and used for structure determination. By coupling this technique with PED, the range and quality of the data set can be improved. The combination of ADT-PED has been employed effectively to investigate complex framework structures and beam-sensitive organic crystals | 3 | Analytical Chemistry |
When (p)ppGpp is absent, pathogenicity is compromised for reasons that vary with the organism studied. Deleting relA and spoT genes, but not relA alone, gave a (p)ppGpp state that resulted in strong attenuation in mice and noninvasiveness in vitro. Vaccine tests reveal that 30 days after single immunization with the (p)ppGpp strain, mice were protected from challenge with wild-type Salmonella at a dose 10-fold above the established LD. | 1 | Biochemistry |
A stereogenic center (or stereocenter) is an atom such that swapping the positions of two ligands (connected groups) on that atom results in a molecule that is stereoisomeric to the original. For example, a common case is a tetrahedral carbon bonded to four distinct groups a, b, c, and d (Cabcd), where swapping any two groups (e.g., Cbacd) leads to a stereoisomer of the original, so the central C is a stereocenter. Many chiral molecules have point chirality, namely a single chiral stereogenic center that coincides with an atom. This stereogenic center usually has four or more bonds to different groups, and may be carbon (as in many biological molecules), phosphorus (as in many organophosphates), silicon, or a metal (as in many chiral coordination compounds). However, a stereogenic center can also be a trivalent atom whose bonds are not in the same plane, such as phosphorus in P-chiral phosphines (PRR′R″) and sulfur in S-chiral sulfoxides (OSRR′), because a lone-pair of electrons is present instead of a fourth bond.
Similarly, a stereogenic axis (or plane) is defined as an axis (or plane) in the molecule such that the swapping of any two ligands attached to the axis (or plane) gives rise to a stereoisomer. For instance, the C-symmetric species 1,1′-bi-2-naphthol (BINOL) and 1,3-dichloroallene have stereogenic axes and exhibit axial chirality, while (E)-cyclooctene and many ferrocene derivatives bearing two or more substituents have stereogenic planes and exhibit planar chirality.
Chirality can also arise from isotopic differences between atoms, such as in the deuterated benzyl alcohol PhCHDOH; which is chiral and optically active ([α] = 0.715°), even though the non-deuterated compound PhCHOH is not.
If two enantiomers easily interconvert, the pure enantiomers may be practically impossible to separate, and only the racemic mixture is observable. This is the case, for example, of most amines with three different substituents (NRR′R″), because of the low energy barrier for nitrogen inversion.
It is not necessary for the chiral substance to have a stereogenic element. Examples include certain helicenes, calixarenes and fullerenes, which have inherent chirality. Moreover, it is possible for a molecule to have a center of chirality that sits in a position that does not correspond to an atom. Such a molecule may be chiral without having any stereogenic centers. Examples include 1,3,5(,7)-substituted adamantanes such as (1S,3R,5R,7S)-3-methyl-5-phenyladamantane-1-carboxylic acid (pictured).
When the optical rotation for an enantiomer is too low for practical measurement, the species is said to exhibit cryptochirality.
Chirality is an intrinsic part of the identity of a molecule, so the systematic name includes details of the absolute configuration (R/S, , or other designations). | 4 | Stereochemistry |
Natural polymeric materials such as hemp, shellac, amber, wool, silk, and natural rubber have been used for centuries. A variety of other natural polymers exist, such as cellulose, which is the main constituent of wood and paper. | 7 | Physical Chemistry |
In a redox reaction an electron donor D must diffuse to the acceptor A, forming a precursor complex, which is labile but allows electron transfer to give successor complex. The pair then dissociates. For a one electron transfer the reaction is
(D and A may already carry charges). Here k, k and k are diffusion constants, k and k are rate constants of activated reactions. The total reaction may be diffusion controlled (the electron transfer step is faster than diffusion, every encounter leads to reaction) or activation controlled (the "equilibrium of association" is reached, the electron transfer step is slow, the separation of the successor complex is fast). The ligand shells around A and D are retained. This process is called outer sphere electron transfer. Outer sphere ET is the main focus of traditional Marcus Theory. The other kind or redox reactions is inner sphere where A and D are covalently linked by a bridging ligand. Rates for such ET reactions depend on ligand exchange rates. | 7 | Physical Chemistry |
Karrers early research concerned complex metal compounds but his most important work has concerned plant pigments, particularly the yellow carotenoids. He elucidated their chemical structure and showed that some of these substances are transformed in the body into vitamin A. His work led to the establishment of the correct constitutional formula for beta-carotene, the chief precursor of vitamin A; the first time that the structure of a vitamin or provitamin had been established. George Wald worked briefly in Karrers lab while studying the role of vitamin A in the retina. Later, Karrer confirmed the structure of ascorbic acid (vitamin C) and extended his researches into the vitamin B and E. His important contributions to the chemistry of the flavins led to identification of lactoflavin as part of the complex originally thought to be vitamin B.
Karrer published many papers, and received many honours and awards, including the Nobel Prize in 1937. His textbook Lehrbuch der Organischen Chemie (Textbook of Organic Chemistry) was published in 1927, went through thirteen editions, and was published in seven languages. | 0 | Organic Chemistry |
The exchange current is the current at equilibrium, i.e. the rate at which oxidized and reduced species transfer electrons with the electrode. In other words, the exchange current density is the rate of reaction at the reversible potential (when the overpotential is zero by definition). At the reversible potential, the reaction is in equilibrium meaning that the forward and reverse reactions progress at the same rates. This rate is the exchange current density.
The Tafel slope is measured experimentally. It can, however, be shown theoretically that when the dominant reaction mechanism involves the transfer of a single electron that
where A is defined as
where
* is Boltzmann's constant,
* is the absolute temperature,
* is the electric elementary charge of an electron,
* is the thermal voltage, and
* is the "charge transfer coefficient", the value of which must be between 0 and 1. | 7 | Physical Chemistry |
Heavy-fermion superconductivity was discovered already in the late 1970s (with CeCuSi being the first example), but the number of heavy-fermion compounds known to superconduct was still very small in the early 1990s, when Christoph Geibel in the group of Frank Steglich found two closely related heavy-fermion superconductors, UNiAl (T=1K) and UPdAl (T=2K), which were published in 1991. At that point, the T=2.0K of UPdAl was the highest critical temperature amongst all known heavy-fermion superconductors, and this record would stand for 10 years until CeCoIn was discovered in 2001. | 8 | Metallurgy |
Although the FGF family of paracrine factors has a broad range of functions, major findings support the idea that they primarily stimulate proliferation and differentiation. To fulfill many diverse functions, FGFs can be alternatively spliced or even have different initiation codons to create hundreds of different FGF isoforms.
One of the most important functions of the FGF receptors (FGFR) is in limb development. This signaling involves nine different alternatively spliced isoforms of the receptor. Fgf8 and Fgf10 are two of the critical players in limb development. In the forelimb initiation and limb growth in mice, axial (lengthwise) cues from the intermediate mesoderm produces Tbx5, which subsequently signals to the same mesoderm to produce Fgf10. Fgf10 then signals to the ectoderm to begin production of Fgf8, which also stimulates the production of Fgf10. Deletion of Fgf10 results in limbless mice.
Additionally, paracrine signaling of Fgf is essential in the developing eye of chicks. The fgf8 mRNA becomes localized in what differentiates into the neural retina of the optic cup. These cells are in contact with the outer ectoderm cells, which will eventually become the lens.
Phenotype and survival of mice after knockout of some FGFR genes: | 1 | Biochemistry |
Cell–cell adhesion complexes are essential for the formation of complex animal tissues. β-catenin is part of a protein complex that form adherens junctions. These cell–cell adhesion complexes are necessary for the creation and maintenance of epithelial cell layers and barriers. As a component of the complex, β-catenin can regulate cell growth and adhesion between cells. It may also be responsible for transmitting the contact inhibition signal that causes cells to stop dividing once the epithelial sheet is complete. The E-cadherin – β-catenin – α-catenin complex is weakly associated to actin filaments. Adherens junctions require significant protein dynamics in order to link to the actin cytoskeleton,
thereby enabling mechanotransduction.
An important component of the adherens junctions are the cadherin proteins. Cadherins form the cell–cell junctional structures known as adherens junctions as well as the desmosomes. Cadherins are capable of homophilic interactions through their extracellular cadherin repeat domains, in a Ca2+-dependent manner; this can hold adjacent epithelial cells together. While in the adherens junction, cadherins recruit β-catenin molecules onto their intracellular regions. β-catenin, in turn, associates with another highly dynamic protein, α-catenin, which directly binds to the actin filaments. This is possible because α-catenin and cadherins bind at distinct sites to β-catenin. The β-catenin – α-catenin complex can thus physically form a bridge between cadherins and the actin cytoskeleton. Organization of the cadherin–catenin complex is additionally regulated through phosphorylation and endocytosis of its components. | 1 | Biochemistry |
RopB regulation speB is a key determinant in the expression of the speB proteinase which is a primary virulence factor and the most abundant extracellular protein in Streptococcal secretions. SpeB cleaves host serum proteins that make up the human extracellular matrix and bacterial proteins including other secreted Streptococcal proteins. As previously mentioned, it is responsible for the dissemination of a host of infectious diseases including but not limited to pharyngitis, impetigo, streptococcal toxic shock syndrome, necrotizing fasciitis, and scarlet fever. Therefore, study of the inactivation of speB's many functional pathways and regulators are of critical importance in developing potential novel therapeutics. | 1 | Biochemistry |
Glycoside hydrolases catalyze the breakage of glycosidic bonds. They are used to modify the oligosaccharide structure of the glycan after it has been added onto the lipid. They can also remove glycans from glycolipids to turn them back into unmodified lipids. | 0 | Organic Chemistry |
The reverse process to photoinduced electron transfer is displayed by light emitting diodes (LED) and chemiluminescence, where potential gradients are used to create excited states that decay by light emission. | 5 | Photochemistry |
Protic ionic liquids are formed via a proton transfer from an acid to a base. In contrast to other ionic liquids, which generally are formed through a sequence of synthesis steps, protic ionic liquids can be created more easily by simply mixing the acid and base.
Phosphonium cations (RP) are less common but offer some advantageous properties. Some examples of phosphonium cations are trihexyl(tetradecyl)phosphonium (P) and tributyl(tetradecyl)phosphonium (P). | 7 | Physical Chemistry |
The thermodynamic square can also be used to find the first-order derivatives in the common Maxwell relations. The following procedure should be considered:
# Looking at the four corners of the square and make a shape with the quantities of interest.
# Read the shape in two different ways by seeing it as L and ⅃. The L will give one side of the relation and the ⅃ will give the other. Note that the partial derivative is taken along the vertical stem of L (and ⅃) while the last corner is held constant.
# Use L to find .
# Similarly, use ⅃ to find . Again, notice that the sign convention affects only the variable held constant in the partial derivative, not the differentials.
# Finally, use above equations to get the Maxwell relation: .
By rotating the shape (randomly, for example by 90 degrees counterclockwise into a shape) other relations such as:
can be found. | 7 | Physical Chemistry |
The nonspecificity of Jaffe's reaction causes falsely elevated creatinine results in the presence of protein, glucose, acetoacetate, ascorbic acid, guanidine, acetone, cephalosporins, aminoglycosides (mainly streptomycin), ketone bodies, α-keto acids, and other organic compounds. Ammonium is also an interferent; if the sample is plasma, care needs to be taken that ammonium heparin has not been used as an anticoagulant. Nonspecificity is markedly decreased in urine samples since urine creatinine levels are much higher than blood and it generally does not contain significant levels of interfering chromogens.
The Jaffe reaction's nonspecificity remains an important issue. Diabetes patients are a high-risk population to develop chronic kidney disease (CKD) and, therefore, interferences from glucose and acetoacetate are of particular importance.
Artifacts such as hemolysis, lipemia, and icteremia can also affect accuracy. Hemolysis releases Jaffe-reacting chromogens and therefore will falsely increase results. Lipemia and icteremia can inhibit optical readings and falsely decrease values. The procedure has been developed over time with the intention to minimize these interferents. | 1 | Biochemistry |
Hemolithin (sometimes confused with the similar space polymer Hemoglycin) is a proposed protein containing iron and lithium, of extraterrestrial origin, according to an unpublished preprint. The result has not been published in any peer-reviewed scientific journal. The protein was purportedly found inside two CV3 meteorites, Allende and Acfer-086, by a team of scientists led by Harvard University biochemist Julie McGeoch. The report of the discovery was met with some skepticism and suggestions that the researchers had extrapolated too far from incomplete data. | 9 | Geochemistry |
Attempts to model the formation of the "first" star from the pure hydrogen and helium gas clouds below about 10,000 K show that the heat generated in the gravitational contraction phase must be somehow radiatively released for further cooling to be possible. This is no problem as long as temperatures are still high enough so that free electrons exist: electrons are efficient emitters when interacting with neutrals (bremsstrahlung). However, at the lower temperatures in neutral gases, the recombination of hydrogen atoms to
H molecules is a process that generates enormous amounts of heat that must somehow be radiated away in CIE processes; if CIE were non-existing, molecule formation could not take place and temperatures could not fall further. Only CIE processes permit further cooling, so that molecular hydrogen will accumulate. A dense, cool environment will thus develop so that a gravitational collapse and star formation can actually proceed. | 7 | Physical Chemistry |
Mono Lake is a vital resting and eating stop for migratory shorebirds and has been recognized as a site of international importance by the Western Hemisphere Shorebird Reserve Network.
Nearly 2,000,000 waterbirds, including 35 species of shorebirds, use Mono Lake to rest and eat for at least part of the year. Some shorebirds that depend on the resources of Mono Lake include American avocets, killdeer, and sandpipers. One to two million eared grebes and phalaropes use Mono Lake during their long migrations.
Late every summer tens of thousands of Wilson's phalaropes and red-necked phalaropes arrive from their nesting grounds, and feed until they continue their migration to South America or the tropical oceans respectively.
In addition to migratory birds, a few species spend several months to nest at Mono Lake. Mono Lake has the second largest nesting population of California gulls, Larus californicus, second only to the Great Salt Lake in Utah. Since abandoning the landbridged Negit Island in the late 1970s, California gulls have moved to some nearby islets and have established new, if less protected, nesting sites. Cornell University and Point Blue Conservation Science have continued the study of nesting populations on Mono Lake that was begun 35 years ago. Snowy plovers also arrive at Mono Lake each spring to nest along the northern and eastern shores. | 2 | Environmental Chemistry |
The research on dnaA(Ts) mutants provided the first proof that the dnaA gene is autoregulated. DnaA protein is still produced at non-permissive temperatures where it is inactive, but in some mutants it can be made active again by returning to a temperature that is conducive to development. This reversible initiation capacity—which was larger than anticipated given the mass gain of the culture—could be seen in the absence of protein synthesis at the permissive temperature and suggested that the DnaA protein synthesis was derepressed at the high growth temperature. These results prompted a thorough investigation of the dnaA46 mutant under permissive, intermediate, and non-permissive development conditions. The studys findings revealed that as growth temperature increased, the DnaA46 proteins activity decreased, leading to progressively decreasing DNA and origin concentrations at intermediate temperatures. An increase in initiation capacity was seen concurrently with a decrease in DnaA protein activity. Hansen and Rasmussen (1977) argued that the DnaA protein had a positive effect in replication initiation aing transcripts entering the dnaA gene were found as a result of sequencing the dnaA promoter region and the dnaA gene. The DnaA promoter region has nine GATC sites within 225 base pairs, and a sequence that is similar to nd a negative role in its own synthesis based on these observations. Two promoters providrepetitions (DnaA-boxes) in the oriC region was found between the two promoters. According to several studies, the DnaA protein negatively regulates both promoters. In these research, it was discovered that the dnaA transcription was upregulated by 4- to 5-fold at non-permissive temperatures in dnaATs mutants and repressed by the same amount when DnaA protein was overproduced. The autoregulation of the dnaA gene requires the DnaA-box. The sequence of the dnaA2p promoter region has some intriguing characteristics that can be seen more clearly. This promoter contains two GATC sites, one in the 10 sequence and the other in the 35 sequence, and both in vivo and in vitro, methylation increases transcription from this promoter by a factor of two. In addition, DnaA protein binds to regions upstream of the dnaA2p promoter with a high affinity. | 1 | Biochemistry |
2-Furoic acid is an organic compound, consisting of a furan ring and a carboxylic acid side-group. Along with other furans, its name is derived from the Latin word furfur, meaning bran, from which these compounds were first produced. The salts and esters of furoic acids are known as furoates. 2-Furoic acid is most widely encountered in food products as a preservative and a flavouring agent, where it imparts a sweet, earthy flavour. | 0 | Organic Chemistry |
Ground substance is an amorphous gel-like substance in the extracellular space of animals that contains all components of the extracellular matrix (ECM) except for fibrous materials such as collagen and elastin. Ground substance is active in the development, movement, and proliferation of tissues, as well as their metabolism. Additionally, cells use it for support, water storage, binding, and a medium for intercellular exchange (especially between blood cells and other types of cells). Ground substance provides lubrication for collagen fibers.
The components of the ground substance vary depending on the tissue. Ground substance is primarily composed of water and large organic molecules, such as glycosaminoglycans (GAGs), proteoglycans, and glycoproteins. GAGs are polysaccharides that trap water, giving the ground substance a gel-like texture. Important GAGs found in ground substance include hyaluronic acid, heparan sulfate, dermatan sulfate, and chondroitin sulfate. With the exception of hyaluronic acid, GAGs are bound to proteins called proteoglycans. Glycoproteins are proteins that attach components of the ground substance to one another and to the surfaces of cells. Components of the ground substance are secreted by fibroblasts. Usually it is not visible on slides, because it is lost during staining in the preparation process.
Link proteins such as vinculin, spectrin and actomyosin stabilize the proteoglycans and organize elastic fibers in the ECM. Changes in the density of ground substance can allow collagen fibers to form aberrant cross-links. Loose connective tissue is characterized by few fibers and cells, and a relatively large amount of ground substance. Dense connective tissue has a smaller amount of ground substance compared to the fibrous material.
The meaning of the term has evolved over time. | 1 | Biochemistry |
Replication, in metallography, is the use of thin plastic films to nondestructively duplicate the microstructure of a component. The film is then examined at high magnifications.
Replication is a method of copying the topography of a surface by casting or impressing material onto the surface. It is the commonly used technique to duplicate surfaces that are inaccessible in metrology to other forms of nondestructive testing. Replicas can be used in biology as well:
The replicas may be imaged in the light microscope or coated with heavy metals, the replicating film melted away, and the heavy metal replica imaged in a Transmission Electron Microscope (TEM).
The same materials, cellulose acetate films, are used for creating replicas of biological materials such as bacteria.
Field Metallurgical Replication (FMR), in field metallography, is the use of metallurgical preparation on surfaces in the field, by polishing to a mirror image, along with application of acetate or other thin plastic films designed to nondestructively duplicate the microstructure of a part or structure in-situ. The FMR replica is then transferred to a glass slide for examination by optical microscopy, electron microscopy, and other methods. | 8 | Metallurgy |
The name "ellipsometry" stems from the fact that elliptical polarization of light is used. The term "spectroscopic" relates to the fact that the information gained is a function of the light's wavelength or energy (spectra). The technique has been known at least since 1888 by the work of Paul Drude and has many applications today.
The first documented use of the term "ellipsometry" was in 1945. | 7 | Physical Chemistry |
A growing number of scientists agree that there is an urgent need to protect the public by being able to forecast harmful algal blooms. One way they hope to do that is with sophisticated sensors which can help warn about potential blooms. The same types of sensors can also be used by water treatment facilities to help them prepare for higher toxic levels.
The only sensors now in use are located in the Gulf of Mexico. In 2008 similar sensors in the Gulf forewarned of an increased level of toxins that led to a shutdown of shellfish harvesting in Texas along with a recall of mussels, clams, and oysters, possibly saving many lives. With an increase in the size and frequency of HABs, experts state the need for significantly more sensors located around the country. The same kinds of sensors can also be used to detect threats to drinking water from intentional contamination.
Satellite and remote sensing technologies are growing in importance for monitoring, tracking, and detecting HABs. Four U.S. federal agencies—EPA, the National Aeronautics and Space Administration (NASA), NOAA, and the U.S. Geological Survey (USGS)—are working on ways to detect and measure cyanobacteria blooms using satellite data. The data may help develop early-warning indicators of cyanobacteria blooms by monitoring both local and national coverage. In 2016 automated early-warning monitoring systems were successfully tested, and for the first time proven to identify the rapid growth of algae and the subsequent depletion of oxygen in the water. | 3 | Analytical Chemistry |
Nitrocellulose slides are used mainly in proteomics to do protein microarrays with automated systems that print the slides and record results. Microarrays of cell analytes, arrays of cell lysate, antibody microarrays, tissue printing, immunoarrays, etc. are also possible with the slide. | 1 | Biochemistry |
Inorganic arsenic and its compounds, upon entering the food chain, are progressively metabolised (detoxified) through a process of methylation. The methylation occurs through alternating reductive and oxidative methylation reactions, that is, reduction of pentavalent to trivalent arsenic followed by addition of a methyl group (CH).
In mammals, methylation occurs in the liver by methyltransferases, the products being the (CH)AsOH (dimethylarsinous acid) and (CH)As(O)OH (dimethylarsinic acid), which have the oxidation states As(III) and As(V), respectively. Although the mechanism of methylation of arsenic in humans has not been elucidated, the source of methyl is methionine, which suggests a role of S-adenosyl methionine. Exposure to toxic doses begin when the liver's methylation capacity is exceeded or inhibited.
There are two major forms of arsenic that can enter the body, arsenic (III) and arsenic (V). Arsenic (III) enters the cells though aquaporins 7 and 9, which is a type of aquaglyceroporin. Arsenic (V) compounds use phosphate transporters to enter cells. The arsenic (V) can be converted to arsenic (III) by the enzyme purine nucleoside phosphorylase. This is classified as a bioactivation step, as although arsenic (III) is more toxic, it is more readily methylated.
There are two routes by which inorganic arsenic compounds are methylated. The first route uses Cyt19 arsenic methyltransferase to methylate arsenic (III) to a mono-methylated arsenic (V) compound. This compound is then converted to a mono-methylated arsenic (III) compound using Glutathione S-Transferase Omega-1 (GSTO1). The mono-methylated arsenic (V) compound can then be methylated again by Cyt19 arsenic methyltransferase, which forms a dimethyl arsenic (V) compound, which can be converted to a dimethyl arsenic (III) compound by Glutathione S-Transferase Omega-1 (GTSO1). The other route uses glutathione (GSH) to conjugate with arsenic (III) to form an arsenic (GS) complex. This complex can form a monomethylated arsenic (III) GS complex, using Cyt19 arsenic methyltransferase, and this monomethylated GS complex is in equilibrium with the monomethylated arsenic (III). Cyt19 arsenic methyltransferase can methylate the complex one more time, and this forms a dimethylated arsenic GS complex, which is in equilibrium with a dimethyl arsenic (III) complex. Both of the mono-methylated and di-methylated arsenic compounds can readily be excreted in urine. However, the monomethylated compound was shown to be more reactive and more toxic than the inorganic arsenic compounds to human hepatocytes (liver), keratinocytes in the skin, and bronchial epithelial cells (lungs).
Studies in experimental animals and humans show that both inorganic arsenic and methylated metabolites cross the placenta to the fetus, however, there is evidence that methylation is increased during pregnancy and that it could be highly protective for the developing organism.
Enzymatic methylation of arsenic is a detoxification process; it can be methylated to methylarsenite, dimethylarsenite or trimethylarsenite, all of which are trivalent. The methylation is catalyzed by arsenic methyltransferase (AS3MT) in mammals, which transfers a methyl group on the cofactor S-adenomethionine (SAM) to arsenic (III). An orthologue of AS3MT is found in bacteria and is called CmArsM. This enzyme was tested in three states (ligand free, arsenic (III) bound and SAM bound). Arsenic (III) binding sites usually use thiol groups of cysteine residues. The catalysis involves thiolates of Cys72, Cys174, and Cys224. In an SN2 reaction, the positive charge on the SAM sulfur atom pulls the bonding electron from the carbon of the methyl group, which interacts with the arsenic lone pair to form an As−C bond, leaving SAH. | 1 | Biochemistry |
There exists a wide range of characterization methods for COF materials. There are several COF single crystals synthesized to date. For these highly crystalline materials, X-ray diffraction (XRD) is a powerful tool capable of determining COF crystal structure. The majority of COF materials suffer from decreased crystallinity so powder X-ray diffraction (PXRD) is used. In conjunction with simulated powder packing models, PXRD can determine COF crystal structure.
In order to verify and analyze COF linkage formation, various techniques can be employed such as infrared (IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. Precursor and COF IR spectra enables comparison between vibrational peaks to ascertain that certain key bonds present in the COF linkages appear and that peaks of precursor functional groups disappear. In addition, solid-state NMR enables probing of linkage formation as well and is well suited for large, insoluble materials like COFs. Gas adsorption-desorption studies quantify the porosity of the material via calculation of the Brunauer–Emmett–Teller (BET) surface area and pore diameter from gas adsorption isotherms. Electron imagine techniques such as scanning electron microscope (SEM), and transmission electron microscopy (TEM) can resolve surface structure and morphology, and microstructural information, respectively. Scanning tunneling microscope (STM) and atomic force microscopy (AFM) have also been used to characterize COF microstructural information as well. Additionally, methods like X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), and combustion analysis can be used to identify elemental composition and ratios. | 6 | Supramolecular Chemistry |
Microarray data is difficult to exchange due to the lack of standardization in platform fabrication, assay protocols, and analysis methods. This presents an interoperability problem in bioinformatics. Various grass-roots open-source projects are trying to ease the exchange and analysis of data produced with non-proprietary chips:
For example, the "Minimum Information About a Microarray Experiment" (MIAME) checklist helps define the level of detail that should exist and is being adopted by many journals as a requirement for the submission of papers incorporating microarray results. But MIAME does not describe the format for the information, so while many formats can support the MIAME requirements, no format permits verification of complete semantic compliance. The "MicroArray Quality Control (MAQC) Project" is being conducted by the US Food and Drug Administration (FDA) to develop standards and quality control metrics which will eventually allow the use of MicroArray data in drug discovery, clinical practice and regulatory decision-making. The MGED Society has developed standards for the representation of gene expression experiment results and relevant annotations. | 1 | Biochemistry |
Susceptible cells are inoculated with serial logarithmic dilutions of samples in a 96-well plate. After viral growth, viral detection by IPA yields the infectious virus titer, expressed as tissue culture infectious dose (TCID50). This represents the dilution of a virus-containing sample at which half of a series of laboratory wells contain replicating viruses. This technique is a reliable method for the titration of human coronaviruses (HCoV) in biological samples (cells, tissues, or fluids). It is also reliable in the detection of antibodies to human cytomegalovirus. | 1 | Biochemistry |
A catalytic triad is a set of three coordinated amino acids that can be found in the active site of some enzymes. Catalytic triads are most commonly found in hydrolase and transferase enzymes (e.g. proteases, amidases, esterases, acylases, lipases and β-lactamases). An acid-base-nucleophile triad is a common motif for generating a nucleophilic residue for covalent catalysis. The residues form a charge-relay network to polarise and activate the nucleophile, which attacks the substrate, forming a covalent intermediate which is then hydrolysed to release the product and regenerate free enzyme. The nucleophile is most commonly a serine or cysteine amino acid, but occasionally threonine or even selenocysteine. The 3D structure of the enzyme brings together the triad residues in a precise orientation, even though they may be far apart in the sequence (primary structure).
As well as divergent evolution of function (and even the triad's nucleophile), catalytic triads show some of the best examples of convergent evolution. Chemical constraints on catalysis have led to the same catalytic solution independently evolving in at least 23 separate superfamilies. Their mechanism of action is consequently one of the best studied in biochemistry. | 1 | Biochemistry |
*Tetramethyl­phosphonium fluoride (CH)PF forms stable acetonitrile solutions. It is prepared from the ylide and potassium bifluoride:
:(CH)P=CH + KHF → (CH)PF + KF
:Gaseous tetramethylphosphonium fluoride exists as the phosphorane but autoionizes in acetonitrile solution. A more elaborate phosphazenium salt ([(CH)N)P]NF) is also known.
*Anhydrous Tetrabutylammonium fluoride has been prepared by the reaction of hexafluorobenzene and tetrabutylammonium cyanide. | 0 | Organic Chemistry |
Statistical mechanics played a significant role in the development of TST. However, the application of statistical mechanics to TST was developed very slowly given the fact that in mid-19th century, James Clerk Maxwell, Ludwig Boltzmann, and Leopold Pfaundler published several papers discussing reaction equilibrium and rates in terms of molecular motions and the statistical distribution of molecular speeds.
It was not until 1912 when the French chemist A. Berthoud used the Maxwell–Boltzmann distribution law to obtain an expression for the rate constant.
where a and b are constants related to energy terms.
Two years later, René Marcelin made an essential contribution by treating the progress of a chemical reaction as a motion of a point in phase space. He then applied Gibbs' statistical-mechanical procedures and obtained an expression similar to the one he had obtained earlier from thermodynamic consideration.
In 1915, another important contribution came from British physicist James Rice. Based on his statistical analysis, he concluded that the rate constant is proportional to the "critical increment". His ideas were further developed by Richard Chace Tolman. In 1919, Austrian physicist Karl Ferdinand Herzfeld applied statistical mechanics to the equilibrium constant and kinetic theory to the rate constant of the reverse reaction, k, for the reversible dissociation of a diatomic molecule.
He obtained the following equation for the rate constant of the forward reaction
where is the dissociation energy at absolute zero, k is the Boltzmann constant, h is the Planck constant, T is thermodynamic temperature, is vibrational frequency of the bond.
This expression is very important since it is the first time that the factor kT/h, which is a critical component of TST, has appeared in a rate equation.
In 1920, the American chemist Richard Chace Tolman further developed Rice's idea of the critical increment. He concluded that critical increment (now referred to as activation energy) of a reaction is equal to the average energy of all molecules undergoing reaction minus the average energy of all reactant molecules. | 7 | Physical Chemistry |
Comments in the New York Times about the healthfulness of coconut oil in late 2015 were covered in 200+ newspapers globally. Brenna opined that 21th century virgin coconut oil does not cause heart disease but that earlier coconut oils may cause heart disease due to process contaminants. | 3 | Analytical Chemistry |
This demonstration of the triplet nature of the genetic code, although carried out with bacteriophage, later proved to be universally applicable to all forms of life.
The results of this experiment inspired many to begin decoding the triplet code discovered by Brenner and Crick et al. Once this paper was published in 1961, researchers knew that there are 64 possible triplet codons, since there are four nitrogenous bases (4 x 4 x 4 = 64). Today, scientists have decoded what all 64 codons encode for, and the assignments have proven to be nearly universal. | 1 | Biochemistry |
George Simmons Hammond was born on May 22, 1921, in Auburn, Maine. Growing up in Auburn his family were charged with the operation of the neighborhood dairy farm on Hardscrapple Road. His father died when Hammond was thirteen. He was the oldest of seven children and was raised by a single mother. From an early age Hammond was charged with running the day-to-day operations of the dairy farm with his mother and older siblings. Hammond's parents were college graduates, but disliked the local schools in Auburn. As a result, he was homeschooled until the sixth grade. Afterwards, he was educated at various Auburn public schools before graduating in 1938. After graduating he took a gap year to continue operating his dairy farm. After his educational hiatus he applied to and was accepted into Bates College, in Lewiston, Maine. He graduated with a Bachelors of Science in chemistry magna cum laude and Phi Beta Kappa in January 1943. | 7 | Physical Chemistry |
Early proton-exchange membrane technology was developed in the early 1960s by Leonard Niedrach and Thomas Grubb, chemists working for the General Electric Company. Significant government resources were devoted to the study and development of these membranes for use in NASAs Project Gemini spaceflight program. A number of technical problems led NASA to forego the use of proton-exchange membrane fuel cells in favor of batteries as a lower capacity but more reliable alternative for Gemini missions 1-4. An improved generation of General Electrics PEM fuel cell was used in all subsequent Gemini missions, but was abandoned for the subsequent Apollo missions. The fluorinated ionomer Nafion, which is today the most widely utilized proton-exchange membrane material, was developed by DuPont plastics chemist Walther Grot. Grot also demonstrated its usefulness as an electrochemical separator membrane.
In 2014, Andre Geim of the University of Manchester published initial results on atom thick monolayers of graphene and boron nitride which allowed only protons to pass through the material, making them a potential replacement for fluorinated ionomers as a PEM material. | 7 | Physical Chemistry |
Carbyne molecules are generally found to be in electronic doublet states: the non-bonding electrons on carbon are arranged as one radical (unpaired electron) and one electron pair, leaving a vacant atomic orbital, rather than being a triradical (the quartet state). The simplest case is the CH radical, which has an electron configuration . Here the 1σ molecular orbital is essentially the carbon 1s atomic orbital, and the 2σ is the C–H bonding orbital formed by overlap of a carbon sp hybrid orbital with the hydrogen 1s orbital. The 3σ is a carbon non-bonding orbital pointing along the C–H axis away from the hydrogen, while there are two non-bonding 1π orbitals perpendicular to the C–H axis. However the 3σ is an sp hybrid which has lower energy than the 1π orbital which is pure p, so the 3σ is filled before the 1π. The CH radical is in fact isoelectronic with the nitrogen atom which does have three unpaired electrons in accordance with Hund's rule of maximum multiplicity. However the nitrogen atom has three degenerate p orbitals, in contrast to the CH radical where hybridization of one orbital (the 3σ) leads to an energy difference. | 0 | Organic Chemistry |
In its main applications, dithionite is generally prepared in situ by reduction of sulfur dioxide by sodium borohydride, described by the following idealized equation:.
Dithionite is a reducing agent. At pH 7, the potential is −0.66 V vs NHE. Redox occurs with formation of sulfite:
: + 2 HO → 2 + 2 e + 2 H
Dithionite undergoes acid hydrolytic disproportionation to thiosulfate and bisulfite:
:2 + HO → + 2
It also undergoes alkaline hydrolytic disproportionation to sulfite and sulfide:
:3 NaSO + 6 NaOH → 5 NaSO + NaS + 3 HO
It is formally derived from dithionous acid (HSO), but this acid does not exist in any practical sense. | 8 | Metallurgy |
Light microscopes are designed for placement of the specimen's polished surface on the specimen stage either upright or inverted. Each type has advantages and disadvantages. Most LOM work is done at magnifications between 50 and 1000X. However, with a good microscope, it is possible to perform examination at higher magnifications, e.g., 2000X, and even higher, as long as diffraction fringes are not present to distort the image. However, the resolution limit of the LOM will not be better than about 0.2 to 0.3 micrometers. Special methods are used at magnifications below 50X, which can be very helpful when examining the microstructure of cast specimens where greater spatial coverage in the field of view may be required to observe features such as dendrites.
Besides considering the resolution of the optics, one must also maximize visibility by maximizing image contrast. A microscope with excellent resolution may not be able to image a structure, that is there is no visibility, if image contrast is poor. Image contrast depends upon the quality of the optics, coatings on the lenses, and reduction of flare and glare; but, it also requires proper specimen preparation and good etching techniques. So, obtaining good images requires maximum resolution and image contrast. | 8 | Metallurgy |
Retention distance, or R, is a concept in thin layer chromatography, designed for quantitative measurement of equal-spreading of the spots on the chromatographic plate and one of the Chromatographic response functions. It is calculated from the following formula:
where n is the number of compounds separated, R are the Retention factor of the compounds sorted in non-descending order, R = 0 and R = 1. | 3 | Analytical Chemistry |
In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e.g. a battery), or sound (e.g. explosion heard when burning hydrogen). The term exothermic was first coined by 19th-century French chemist Marcellin Berthelot.
The opposite of an exothermic process is an endothermic process, one that absorbs energy usually in the form of heat. The concept is frequently applied in the physical sciences to chemical reactions where chemical bond energy is converted to thermal energy (heat). | 7 | Physical Chemistry |
Non-B DNA refers to DNA conformations that differ from the canonical B-DNA conformation, the most common form of DNA found in nature at neutral pH and physiological salt concentrations. Non-B DNA structures can arise due to various factors, including DNA sequence, length, supercoiling, and environmental conditions. Non-B DNA structures can have important biological roles, but they can also cause problems, such as genomic instability and disease. | 1 | Biochemistry |
Given the importance of glycan-protein interactions, there is an ongoing research dedicated to the a) creation of new tools to detect glycan-protein interactions and b) using those tools to decipher the so-called sugar code. | 1 | Biochemistry |
Photochromic compounds have the ability to switch between a range or variety of colors. Their ability to display different colors lies in how they absorb light. Different isomeric manifestations of the molecule absorbs different wavelengths of light, so that each isomeric species can display a different color based on its absorption. These include photoswitchable compounds, which are proteins that can switch from a non-fluorescent state to that of a fluorescent one given a certain environment.
The most common organic molecule to be used as a photochrome is diarylethene. Other examples of photoswitchable proteins include PADRON-C, rs-FastLIME-s and bs-DRONPA-s, which can be used in plant and mammalian cells alike to watch cells move into different environments. | 1 | Biochemistry |
Pockels spent much of her life caring for her sick parents, which she noted to be "very challenging". Her father died in 1906 and her mother died in 1914. By that time, Pockels was herself in ill health, necessitating a stay for a time in a sanatorium. She traveled in Europe for enjoyment. During Pockels' later years, she was known for her role as an aunt, "Auntie Agnes."
Pockels died in 1935 in Brunswick, Germany, in the town where she had lived for the duration of her career. | 7 | Physical Chemistry |
Etching reveals and delineates grain boundaries and other microstructural features that are not apparent on the as-polished surface. The two most common types of etching in ceramography are selective chemical corrosion, and a thermal treatment that causes relief. As an example, alumina can be chemically etched by immersion in boiling concentrated phosphoric acid for 30–60 s, or thermally etched in a furnace for 20–40 min at in air. The plastic encapsulation must be removed before thermal etching. The alumina in Fig. 1 was thermally etched.
Alternatively, non-cubic ceramics can be prepared as thin sections, also known as petrography, for examination by polarized transmitted light microscopy. In this technique, the specimen is sawed to ~1 mm thick, glued to a microscope slide, and ground or sawed (e.g., by microtome) to a thickness (x) approaching 30 µm. A cover slip is glued onto the exposed surface. The adhesives, such as epoxy or Canada balsam resin, must have approximately the same refractive index (η ≈ 1.54) as glass. Most ceramics have a very small absorption coefficient (α ≈ 0.5 cm for alumina in Fig. 2) in the Beer–Lambert law below, and can be viewed in transmitted light. Cubic ceramics, e.g. yttria-stabilized zirconia and spinel, have the same refractive index in all crystallographic directions and appear, therefore, black when the microscope's polarizer is 90° out of phase with its analyzer.
: (Beer–Lambert eqn)
Ceramographic specimens are electrical insulators in most cases, and must be coated with a conductive ~10-nm layer of metal or carbon for electron microscopy, after polishing and etching. Gold or Au-Pd alloy from a sputter coater or evaporative coater also improves the reflection of visible light from the polished surface under a microscope, by the Fresnel formula below. Bare alumina (η ≈ 1.77, k ≈ 10) has a negligible extinction coefficient and reflects only 8% of the incident light from the microscope, as in Fig. 1. Gold-coated (η ≈ 0.82, k ≈ 1.59 @ λ = 500 nm) alumina reflects 44% in air, 39% in immersion oil.
: (Fresnel eqn).. | 8 | Metallurgy |
Chiral Lewis acids have proven useful in the ene reaction. When catalyzed by an achiral Lewis acid, the reaction normally provides good diastereoselectivity.
Good enantioselectivity has been observed when a chiral Lewis acid catalyst is used.
The enantioselectivity is believed to be due to the steric interactions between the methyl and phenyl group, which makes the transition structure of the iso product considerably more favorable. | 4 | Stereochemistry |
According to metallurgist Jack Harris, "Oxidation is usually accompanied by a net expansion so that when it occurs in a confined space stresses are generated in the metal component itself or in any surrounding medium such as stone or cement. So much energy is released by oxidation that the stresses generated are of sufficient magnitude to deform or fracture all known materials."
As early as 1915, it was recognized that certain modern metal alloys are more susceptible to excessive oxidation when subjected to weathering than other metals. At that time, there was a trend to replace wrought iron fasteners with mild steel equivalents, which were less expensive. Unexpectedly, the mild steel fasteners failed in real world use much more quickly than anticipated, leading to a return to use of wrought iron in certain applications where length of service was important. | 8 | Metallurgy |
Vitamin D toxicity is rare. It is caused by supplementing with high doses of vitamin D rather than sunlight. The threshold for vitamin D toxicity has not been established; however, according to some research:
* 100μg/day (4k IU), have been show to not cause toxic levels. ages 9–71
* 240 μg/day (10k IU), over 5 months have been show not to cause toxicity.
* 1250μg/day (50k IU) over several months can increase serum 25-hydroxyvitamin D levels to 150ng/mL.
Those with certain medical conditions, such as primary hyperparathyroidism, are far more sensitive to vitamin D and develop hypercalcemia in response to any increase in vitamin D nutrition, while maternal hypercalcemia during pregnancy may increase fetal sensitivity to effects of vitamin D and lead to a syndrome of intellectual disability and facial deformities.
Idiopathic infantile hypercalcemia is caused by a mutation of the CYP24A1 gene, leading to a reduction in the degradation of vitamin D. Infants who have such a mutation have an increased sensitivity to vitamin D and in case of additional intake a risk of hypercalcaemia. The disorder can continue into adulthood.
A review published in 2015 noted that adverse effects have been reported only at 25(OH)D serum concentrations above 200nmol/L.
Published cases of toxicity involving hypercalcemia in which the vitamin D dose and the 25-hydroxy-vitamin D levels are known all involve an intake of ≥40,000IU (1,000μg) per day.
Those who are pregnant or breastfeeding should consult a doctor before taking a vitamin D supplement. The FDA advised manufacturers of liquid vitamin D supplements that droppers accompanying these products should be clearly and accurately marked for 400 international units (1IU is the biological equivalent of 25ng cholecalciferol/ergocalciferol). In addition, for products intended for infants, the FDA recommends the dropper hold no more than 400IU. For infants (birth to 12 months), the tolerable upper limit (maximum amount that can be tolerated without harm) is set at 25μg/day (1,000IU). One thousand micrograms per day in infants has produced toxicity within one month. After being commissioned by the Canadian and American governments, the Institute of Medicine (IOM) , has increased the tolerable upper limit (UL) to 2,500IU per day for ages 1–3 years, 3,000IU per day for ages 4–8 years and 4,000IU per day for ages 9–71+ years (including pregnant or lactating women).
Calcitriol itself is auto-regulated in a negative feedback cycle, and is also affected by parathyroid hormone, fibroblast growth factor 23, cytokines, calcium, and phosphate.
A study published in 2017 assessed the prevalence of high daily intake levels of supplemental vitamin D among adults ages 20+ in the United States, based on publicly available NHANES data from 1999 through 2014. Its data shows the following:
* Over 18% of the population exceeds the NIH daily recommended allowance (RDA) of 600–800 IU, by taking over 1000 IU, which suggests intentional supplement intake.
* Over 3% of the population exceeds the NIH daily tolerable upper intake level (UL) of 4000 IU, above which level the risk of toxic effects increases.
* The percentage of the population taking over 1000 IU/day, as well as the percentage taking over 4000 IU/day, have both increased since 1999, according to trend analysis. | 1 | Biochemistry |
In molecular biology, an oscillating gene is a gene that is expressed in a rhythmic pattern or in periodic cycles. Oscillating genes are usually circadian and can be identified by periodic changes in the state of an organism. Circadian rhythms, controlled by oscillating genes, have a period of approximately 24 hours. For example, plant leaves opening and closing at different times of the day or the sleep-wake schedule of animals can all include circadian rhythms. Other periods are also possible, such as 29.5 days resulting from circalunar rhythms or 12.4 hours resulting from circatidal rhythms. Oscillating genes include both core clock component genes and output genes. A core clock component gene is a gene necessary for to the pacemaker. However, an output oscillating gene, such as the AVP gene, is rhythmic but not necessary to the pacemaker. | 1 | Biochemistry |
Ribosomally synthesized and post-translationally modified peptides (RiPPs), also known as ribosomal natural products, are a diverse class of natural products of ribosomal origin. Consisting of more than 20 sub-classes, RiPPs are produced by a variety of organisms, including prokaryotes, eukaryotes, and archaea, and they possess a wide range of biological functions.
As a consequence of the falling cost of genome sequencing and the accompanying rise in available genomic data, scientific interest in RiPPs has increased in the last few decades. Because the chemical structures of RiPPs are more closely predictable from genomic data than are other natural products (e.g. alkaloids, terpenoids), their presence in sequenced organisms can, in theory, be identified rapidly. This makes RiPPs an attractive target of modern natural product discovery efforts. | 1 | Biochemistry |
Epitope binning is a competitive immunoassay used to characterize and then sort a library of monoclonal antibodies against a target protein. Antibodies against a similar target are tested against all other antibodies in the library in a pairwise fashion to see if antibodies block one another's binding to the epitope of an antigen. After each antibody has a profile created against all of the other antibodies in the library, a competitive blocking profile is created for each antibody relative to the others in the library. Closely related binning profiles indicate that the antibodies have the same or a closely related epitope and are "binned" together. Epitope binning is referenced in the literature under different names such as epitope mapping and epitope characterization. Regardless of the naming, epitope binning is prevalent in the pharmaceutical industry. Epitope Binning is used in the discovery and development of new therapeutics, vaccines, and diagnostics. | 1 | Biochemistry |
The meaning of the term has evolved. The original meaning of transfection was "infection by transformation", i.e., introduction of genetic material, DNA or RNA, from a prokaryote-infecting virus or bacteriophage into cells, resulting in an infection. For work with bacterial and archaeal cells transfection retains its original meaning as a special case of transformation. Because the term transformation had another sense in animal cell biology (a genetic change allowing long-term propagation in culture, or acquisition of properties typical of cancer cells), the term transfection acquired, for animal cells, its present meaning of a change in cell properties caused by introduction of DNA. | 1 | Biochemistry |
For each element, the following table shows the spectral lines which appear in the visible spectrum at about 400-700 nm. | 7 | Physical Chemistry |
Inspired from the dirhodium tetraacetate bimetallic salt, synthetic chemists decided to explore the synthesis of paddlewheel mixed heteronuclear bismuth-rhodium salts. The synthesis involves treatment of the [Rh(OCR)] salt with the dibusmuth tetrafluoroacetate [Bi(OCCF)] equivalent. Depending on the nature and sterics of the R ligand, the resulting mixed salt has either two Bu R-substituents resulting in the cis mixed salt or a single Me R-substituent provenient from the dirhodium precursor (see scheme to the right). The mixed salts display increased air and moisture compared to the parental dimetallic salts and show Lewis acidity at the rhodium center. | 0 | Organic Chemistry |
1,1-Dichloro-1-fluoroethane is a haloalkane with the formula . It is one of the three isomers of dichlorofluoroethane. It belongs to the hydrochlorofluorocarbon (HCFC) family of man-made compounds that contribute significantly to both ozone depletion and global warming when released into the environment. | 2 | Environmental Chemistry |
* Advective Transport formulation
* Dispersive Transport formulation
* Surface Heat Budget formulation
* Dissolved Oxygen Saturation formulation
* Reaeration formulation
* Carbonaceous Deoxygenation formulation
* Nitrogenous Biochemical Oxygen Demand formulation
* Sediment oxygen demand formulation (SOD)
* Photosynthesis and Respiration formulation
* pH and Alkalinity formulation
* Nutrients formulation (fertilizers)
* Algae formulation
* Zooplankton formulation
* Coliform bacteria formulation (e.g. Escherichia coli ) | 9 | Geochemistry |
The most common application of the Hellmann–Feynman theorem is the calculation of intramolecular forces in molecules. This allows for the calculation of equilibrium geometries – the nuclear coordinates where the forces acting upon the nuclei, due to the electrons and other nuclei, vanish. The parameter corresponds to the coordinates of the nuclei. For a molecule with electrons with coordinates , and nuclei, each located at a specified point and with nuclear charge , the clamped nucleus Hamiltonian is
The -component of the force acting on a given nucleus is equal to the negative of the derivative of the total energy with respect to that coordinate. Employing the Hellmann–Feynman theorem this is equal to
Only two components of the Hamiltonian contribute to the required derivative – the electron-nucleus and nucleus-nucleus terms. Differentiating the Hamiltonian yields
Insertion of this in to the Hellmann–Feynman theorem returns the -component of the force on the given nucleus in terms of the electronic density and the atomic coordinates and nuclear charges: | 6 | Supramolecular Chemistry |
Static testing sites provide testing services to clients at fixed locations away from events. Often these are in the entertainment districts of cities. Energy Control in Barcelona and DIMS in the Netherlands provide such services.
Off-site testing occurs away from events and away from clients. Clients submit samples by post or at drop-off locations. Those samples are analysed and then the results are publicised. Examples of this model include WEDINOS (the Welsh Emerging Drugs & Identification of Novel Substances Project) and DIMS in the Netherlands.
The UK's first trial of community-based drug safety testing was carried out in Bristol and Durham in 2018 in a church, a drugs service, and a youth and community centre. Users reported that they intended to carry out a range of harm reduction actions such as alerting friends and acquaintances, being more careful mixing substances, consuming lowered dosage, and disposing of substances.
Drug Checking Programs have been emerging across the Americas in recent years. A directory of these programs can be found at the Harm Reduction Innovation Lab's website. | 3 | Analytical Chemistry |
Waste heat can be used in district heating. Depending on the temperature of the waste heat and the district heating system, a heat pump must be used, to reach sufficient temperatures. An easy and cheap way to use waste heat in cold district heating systems, as these are operated at ambient temperatures and therefore even low-grade waste heat can be used without needing a heat pump at the producer side. | 7 | Physical Chemistry |
Grignard is most noted for devising a new method for generating carbon-carbon bonds using magnesium to couple ketones and alkyl halides. This reaction is valuable in organic synthesis. It occurs in two steps:
#Formation of the "Grignard reagent", which is an organomagnesium compound made by the reaction of an organohalide, R-X (R = alkyl or aryl; and X is a halide, usually bromide or iodide) with magnesium metal. The Grignard reagent is usually described with the general chemical formula R-Mg-X, although its structure is more complex.
#Addition of the carbonyl, in which a ketone or an aldehyde is added to the solution containing the Grignard reagent. The carbon atom that is bonded to Mg transfers to the carbonyl carbon atom, and the oxygen of the carbonyl carbon becomes attached to the magnesium to give an alkoxide. The process is an example of a nucleophilic addition to a carbonyl. After the addition, the reaction mixture is treated with aqueous acid to give an alcohol, and the magnesium salts are subsequently discarded. | 0 | Organic Chemistry |
An V1-morph is an organism that changes in shape during growth such that its surface area is proportional to its volume. In most cases both volume and surface area are proportional to length
The reason the concept is important in the context of the Dynamic Energy Budget theory is that food (substrate) uptake is proportional to surface area, and maintenance to volume. The surface area that is of importance is that part that is involved in substrate uptake. Since uptake is proportional to maintenance for V1-morphs, there is no size control, and an organism grows exponentially at constant food (substrate) availability.
Filaments, such as fungi that form hyphae growing in length, but not in diameter, are examples of V1-morphs. Sheets that extend, but do not change in thickness, like some colonial bacteria and algae, are another example.
An important property of V1-morphs is that the distinction between the individual and the population level disappears; a single long filament grows as fast as many small ones of the same diameter and the same total length. | 1 | Biochemistry |
One of the most well known examples of a short copy number variation is the trinucleotide repeat of the CAG base pairs in the huntingtin gene responsible for the neurological disorder Huntingtons disease. For this particular case, once the CAG trinucleotide repeats more than 36 times in a trinucleotide repeat expansion, Huntingtons disease will likely develop in the individual and it will likely be inherited by his or her offspring. The number of repeats of the CAG trinucleotide is inversely correlated with the age of onset of Huntingtons disease. These types of short repeats are often thought to be due to errors in polymerase activity during replication including polymerase slippage, template switching, and fork switching which will be discussed in detail later. The short repeat size of these copy number variations lends itself to errors in the polymerase as these repeated regions are prone to misrecognition by the polymerase and replicated regions may be replicated again, leading to extra copies of the repeat. In addition, if these trinucleotide repeats are in the same reading frame in the coding portion of a gene, it may lead to a long chain of the same amino acid, possibly creating protein aggregates in the cell, and if these short repeats fall into the non-coding portion of the gene, it may affect gene expression and regulation. On the other hand, a variable number of repeats of entire genes is less commonly identified in the genome. One example of a whole gene repeat is the alpha-amylase 1 gene (AMY1) that encodes alpha-amylase which has a significant copy number variation between different populations with different diets. Although the specific mechanism that allows the AMY1 gene to increase or decrease its copy number is still a topic of debate, some hypotheses suggest that the non-homologous end joining or the microhomology-mediated end joining is likely responsible for these whole gene repeats. Repeats of entire genes has immediate effects on expression of that particular gene, and the fact that the copy number variation of the AMY1' gene has been related to diet is a remarkable example of recent human evolutionary adaptation. Although these are the general groups that copy number variations are grouped into, the exact number of base pairs copy number variations affect depends on the specific loci of interest. Currently, using data from all reported copy number variations, the mean size of copy number variant is around 118kb, and the median is around 18kb.
In terms of the structural architecture of copy number variations, research has suggested and defined hotspot regions in the genome where copy number variations are four times more enriched. These hotspot regions were defined to be regions containing long repeats that are 90–100% similar known as segmental duplications either tandem or interspersed and most importantly, these hotspot regions have an increased rate of chromosomal rearrangement. It was thought that these large-scale chromosomal rearrangements give rise to normal variation and genetic diseases, including copy number variations. Moreover, these copy number variation hotspots are consistent throughout many populations from different continents, implying that these hotspots were either independently acquired by all the populations and passed on through generations, or they were acquired in early human evolution before the populations split, the latter seems more likely. Lastly, spatial biases of the location at which copy number variations are most densely distributed does not seem to occur in the genome. Although it was originally detected by fluorescent in situ hybridization and microsatellite analysis that copy number repeats are localized to regions that are highly repetitive such as telomeres, centromeres, and heterochromatin, recent genome-wide studies have concluded otherwise. Namely, the subtelomeric regions and pericentromeric regions are where most chromosomal rearrangement hotspots are found, and there is no considerable increase in copy number variations in that region. Furthermore, these regions of chromosomal rearrangement hotspots do not have decreased gene numbers, again, implying that there is minimal spatial bias of the genomic location of copy number variations. | 1 | Biochemistry |
Technomimetics are molecular systems that can mimic man-made devices. The term was first introduced in 1997. The current set of technomimetic molecules includes motors, rotors, gears, gyroscopes, tweezers, and other molecular devices. Technomimetics can be considered as the essential components of molecular machines and have the primary use in molecular nanotechnology. | 6 | Supramolecular Chemistry |
The prefix disiamyl is an abbreviation for "di-sec-isoamyl", where sec-isoamyl ("secondary isoamyl") is an archaic name for the 1,2-dimethylpropyl group (amyl being a obsolescent synonym of pentyl). | 0 | Organic Chemistry |
Good tilth shares a balanced relation between soil-aggregate tensile strength and friability, in which it has a stable mixture of aggregate soil particles that can be readily broken up by shallow non-abrasive tilling. A high tensile strength will result in large cemented clods of compacted soil with low friability. Proper management of agricultural soils can positively impact soil aggregation and improve tilth quality.
Aggregation is positively associated with tilth. With finer-textured soils, aggregates may in turn be made up of smaller aggregates. Aggregation implies substantial pores between individual aggregates.
Aggregation is important in the subsoil, the layer below tillage. Such aggregates involve larger (2- to 6-inch) blocks of soil that are more angular and not as distinctive. These aggregates are less impacted by biological activity than the tillage layer. Subsurface aggregates are important for root growth deep into the profile. Deep roots allow greater access to moisture, which helps in drought periods. Subsoil aggregates can also be compacted, mainly by heavy equipment on wet soil. Another significant source of subsoil compaction is the practice of plowing with tractor wheels in the open furrow. | 9 | Geochemistry |
Pentafluorophenyl (PFP) esters are chemical compounds with the generic formula RC(O)OCF. They are active esters derived from pentafluorophenol (HOCF).
PFP esters are useful for attaching fluorophores such as fluorescein or haptens to primary amines in biomolecules. They also are valuable in laboratory peptide synthesis. Pentafluorophenyl esters produce amide bonds as effectively as succinimidyl esters and various similar agents do, but PFP esters are particularly useful because they are less susceptible to spontaneous hydrolysis during conjugation reactions. | 0 | Organic Chemistry |
Beryllium can form a variety of organoberyllium compounds, including ring structures, alkyls, alkynyls, hydrides, methyls, halides, phosphines, carbenes, and nitrogen-based coordination such as NacNac.
Dimethylberyllium has the same crystal structure as dimethylmagnesium and can be used to synthesize beryllium azide and beryllium hydride. | 0 | Organic Chemistry |
Prothrombin fragment 1+2 (F1+2), also written as prothrombin fragment 1.2 (F1.2), is a polypeptide fragment of prothrombin (factor II) generated by the in vivo cleavage of prothrombin into thrombin (factor IIa) by the enzyme prothrombinase (a complex of factor Xa and factor Va). It is released from the N-terminus of prothrombin. F1+2 is a marker of thrombin generation and hence of coagulation activation. It is considered the best marker of in vivo thrombin generation.
F1+2 levels can be quantified with blood tests and is used in the diagnosis of hyper- and hypocoagulable states and in the monitoring of anticoagulant therapy. It was initially determined with a radioimmunoassay, but is now measured with several enzyme-linked immunosorbent assays.
The molecular weight of F1+2 is around 41 to 43 kDa. Its biological half-life is 90 minutes and it persists in blood for a few hours after formation. The half-life of F1+2 is relatively long, which makes it more reliable for measuring ongoing coagulation than other markers like thrombin–antithrombin complexes and fibrinopeptide A. Concentrations of F1+2 in healthy individuals range from 0.44 to 1.11 nM.
F1+2 levels increase with age. Levels of F1+2 have been reported to be elevated in venous thromboembolism, protein C deficiency, protein S deficiency, atrial fibrillation, unstable angina, acute myocardial infarction, acute stroke, atherosclerosis, peripheral arterial disease, and in smokers. Anticoagulants have been found to reduce F1+2 levels. F1+2 levels are increased with pregnancy and by ethinylestradiol-containing birth control pills. Conversely, they do not appear to be increased with estetrol- or estradiol-containing birth control pills. However, F1+2 levels have been reported to be increased with oral estrogen-based menopausal hormone therapy, whereas transdermal estradiol-based menpausal hormone therapy appears to result in less or no consistent increase. | 1 | Biochemistry |
Most organic reactions involve the breaking and making of bonds to a carbon; thus, it is reasonable to expect detectable carbon isotope effects. When C is used as the label, the change in mass of the isotope is only ~8%, though, which limits the observable kinetic isotope effects to much smaller values than the ones observable with hydrogen isotope effects. | 7 | Physical Chemistry |
The first ion funnel was created in 1997 in the Environmental Molecular Sciences Laboratory Pacific Northwest National Laboratory by the researchers in Richard D. Smiths lab. The ion funnel was implemented to replace the ion transmission-limited skimmer for more efficient ion capture in an ESI source. Many characteristics of the ion funnel are attributed to the stacked ring ion guide, however, the disks of an ion funnel vary in diameter down its long axis. There is a portion at the base of the ion funnel in which a series of cylindrical ring electrodes have decreasing diameters, which enables the ion cloud entering the ion funnel to be spatially dispersed. This allows for efficient transfer of the ion cloud through the conductance limiting orifice at the exit as the ion cloud becomes focused to a much smaller radial size. The DC electric field serves to push ions through the funnel. For positive ions, the front plate of the funnel has the most positive DC voltage, and subsequent plates have gradually decreasing DC components, providing added control. RF and DC electric fields are co-applied with a pseudopotential created with alternating RF polarities on adjacent electrodes. This “pseudo-potential” radially confines ions and causes instability in ions with a lower m/z (mass to charge ratio) while ions with a higher m/z are focused to the center of the funnel. The initial ion funnel design used in the Smith research lab proved inefficient for collecting ions with low m/z'. Simulations suggest that decreasing the spacing between the lenses so that they are less than the diameter of the smallest ring electrode could be a plausible solution to this problem. Another issue with the design is that the funnel is susceptible to noise with fast neutrals and charged droplets at many atmospheric interfaces during the initial vacuum phase. Modifications increase the efficiency and signal to noise ratio of the ion funnel.
Some of the earliest ion funnels struggled to control gas flow as the pressure in the ion vacuum chamber was not uniform due to gas dynamic effects. The pressure at the funnel's exit was estimated to be 2 to 3 times higher than the pressure from the pressure gauge. The higher pressure required greater pumping in downstream vacuum chambers to compensate for the larger injection of gas. The discrepancy between the measured pressure and the pressure at the exit of the funnel was caused by the a sizable portion of the supersonic gas jet from the injector continuing beyond the Mach disk or shock diamond at the beginning of the funnel and continuing through until the end. The most effective resolution is the us of a jet disrupter that consists of a 9 mm diameter brass disk suspended perpendicular to the gas flow in the center of the ion funnel. | 7 | Physical Chemistry |
Egg white ovalbumin: The unfolding of ovalbumin, a 45 kDa protein, as a function of guanidine hydrochloride (0-6M) occurred reversibly in one step. The protein fractions in native (N) and the denatured states (D) were characterized by UV spectrometry and viscosity measurements at defined temperatures in buffer pH 7.0. The thermodynamics of folding and possibly kinetics followed a two state transition (N->D). The data were consistent with the fact that the native state was stabilized by hydrophobic effect in aqueous solution; this effect was diminished by introducing Guanidine hydrochloride to protein solution with concomitant transition to denatured state, random coil conformation similar to a nascent polypeptide chain.
Egg white Ovomucoid: The unfolding of ovomucoid (N), a domain containing 28 kDa protein, by guanidine hydrochloride did not proceed in a single step but occurred in two steps; the transition at low denaturant was associated with an intermediate, native-like, structure (X), and at high denaturant, protein existed in random coil structure (D). The reversible unfolding at each step (N->X->D) followed a two state transition pattern, albeit with somewhat different folding rates for the intermediate and native structures (1978). The studies in his lab indicated that in vivo protein folding may not be explained by the amino acid sequence alone. Independently, the molecular biology of chaperones succeeded in the identification of additional folding factors in 1989. The latter studies marked the beginning of modern protein folding with manipulation in human health. | 1 | Biochemistry |
A contaminant is a substance present in nature at a level higher than fixed levels or that would not otherwise be there. This may be due to human activity and bioactivity. The term contaminant is often used interchangeably with pollutant, which is a substance that has a detrimental impact on the surrounding environment. Whilst a contaminant is sometimes defined as a substance present in the environment as a result of human activity, but without harmful effects, it is sometimes the case that toxic or harmful effects from contamination only become apparent at a later date.
The "medium" such as soil or organism such as fish affected by the pollutant or contaminant is called a receptor, whilst a sink is a chemical medium or species that retains and interacts with the pollutant such as carbon sink and its effects by microbes. | 2 | Environmental Chemistry |
The PI3K/AKT/mTOR pathway is an intracellular signaling pathway important in regulating the cell cycle. Therefore, it is directly related to cellular quiescence, proliferation, cancer, and longevity. PI3K activation phosphorylates and activates AKT, localizing it in the plasma membrane. AKT can have a number of downstream effects such as activating CREB, inhibiting p27, localizing FOXO in the cytoplasm, activating PtdIns-3ps, and activating mTOR which can affect transcription of p70 or 4EBP1. There are many known factors that enhance the PI3K/AKT pathway including EGF, shh, IGF-1, insulin, and CaM. Both leptin and insulin recruit PI3K signalling for metabolic regulation. The pathway is antagonized by various factors including PTEN, GSK3B, and HB9.
In many cancers, this pathway is overactive, thus reducing apoptosis and allowing proliferation. This pathway is necessary, however, to promote growth and proliferation over differentiation of adult stem cells, neural stem cells specifically. It is the difficulty in finding an appropriate amount of proliferation versus differentiation that researchers are trying to determine in order to utilize this balance in the development of various therapies. Additionally, this pathway has been found to be a necessary component in neural long term potentiation. | 1 | Biochemistry |
Temperature programmed desorption (TPD) is the method of observing desorbed molecules from a surface when the surface temperature is increased. When experiments are performed using well-defined surfaces of single-crystalline samples in a continuously pumped ultra-high vacuum (UHV) chamber, then this experimental technique is often also referred to as thermal desorption spectroscopy or thermal desorption spectrometry (TDS). | 7 | Physical Chemistry |
DLVO theory is a theory of colloidal dispersion stability in which zeta potential is used to explain that as two particles approach one another their ionic atmospheres begin to overlap and a repulsion force is developed. In this theory, two forces are considered to impact on colloidal stability: Van der Waals forces and electrical double layer forces.
The total potential energy is described as the sum of the attraction potential and the repulsion potential. When two particles approach each other, electrostatic repulsion increases and the interference between their electrical double layers increases. However, the Van der Waals attraction also increases as they get closer. At each distance, the net potential energy of the smaller value is subtracted from the larger value.
At very close distances, the combination of these forces results in a deep attractive well, which is referred to as the primary minimum. At larger distances, the energy profile goes through a maximum, or energy barrier, and subsequently passes through a shallow minimum, which is referred to as the secondary minimum.
At the maximum of the energy barrier, repulsion is greater than attraction. Particles rebound after interparticle contact, and remain dispersed throughout the medium. The maximum energy needs to be greater than the thermal energy. Otherwise, particles will aggregate due to the attraction potential. The height of the barrier indicates how stable the system is. Since particles have to overcome this barrier in order to aggregate, two particles on a collision course must have sufficient kinetic energy due to their velocity and mass. If the barrier is cleared, then the net interaction is all attractive, and as a result the particles aggregate. This inner region is often referred to as an energy trap since the colloids can be considered to be trapped together by Van der Waals forces.
For a colloidal system, the thermodynamic equilibrium state may be reached when the particles are in deep primary minimum. At primary minimum, attractive forces overpower the repulsive forces at low molecular distances. Particles coagulate and this process is not reversible. However, when the maximum energy barrier is too high to overcome, the colloid particles may stay in the secondary minimum, where particles are held together but more weakly than in the primary minimum. Particles form weak attractions but are easily redispersed. Thus, the adhesion at secondary minimum can be reversible. | 7 | Physical Chemistry |
The peptidoglycan layer within the bacterial cell wall is a crystal lattice structure formed from linear chains of two alternating amino sugars, namely N-acetylglucosamine (GlcNAc or NAG) and N-acetylmuramic acid (MurNAc or NAM). The alternating sugars are connected by a β-(1,4)-glycosidic bond. Each MurNAc is attached to a short (4- to 5-residue) amino acid chain, containing -alanine, -glutamic acid, meso-diaminopimelic acid, and -alanine in the case of Escherichia coli (a Gram-negative bacterium) or -alanine, -glutamine, -lysine, and -alanine with a 5-glycine interbridge between tetrapeptides in the case of Staphylococcus aureus (a Gram-positive bacterium). Peptidoglycan is one of the most important sources of D-amino acids in nature.
By enclosing the inner membrane, the peptidoglycan layer protects the cell from lysis caused by the turgor pressure of the cell. When the cell wall grows, it retains its shape throughout its life, so a rod shape will remain a rod shape, and a spherical shape will remain a spherical shape for life. This happens because the freshly added septal material of synthesis transforms into a hemispherical wall for the offspring cells.
Cross-linking between amino acids in different linear amino sugar chains occurs with the help of the enzyme DD-transpeptidase and results in a 3-dimensional structure that is strong and rigid. The specific amino acid sequence and molecular structure vary with the bacterial species.
The different peptidoglycan types of bacterial cell walls and their taxonomic implications have been described. Archaea (domain Archaea) do not contain peptidoglycan (murein). Some Archaea contain pseudopeptidoglycan (pseudomurein, see below).
Peptidoglycan is involved in binary fission during bacterial cell reproduction. L-form bacteria and mycoplasmas, both lacking peptidoglycan cell walls, do not proliferate by binary fission, but by a budding mechanism.
In the course of early evolution, the successive development of boundaries (membranes, walls) protecting first structures of life against their environment must have been essential for the formation of the first cells (cellularisation).
The invention of rigid peptidoglycan (murein) cell walls in bacteria (domain Bacteria) was probably the prerequisite for their survival, extensive radiation and colonisation of virtually all habitats of the geosphere and hydrosphere. | 1 | Biochemistry |
Carbodiimides are reagents for the Moffatt oxidation, a protocol for conversion of an alcohol to a carbonyl (ketone or aldehyde) using dimethyl sulfoxide as the oxidizing agent:
:(CH)SO + (CyN)C + RCHOH → (CH)S + (CyNH)CO + RC=O
Typically the sulfoxide and diimide are used in excess. The reaction generates dimethyl sulfide and a urea as byproducts. | 0 | Organic Chemistry |
The retroviruses include T-cell Leukemia virus type I, HIV, and Rous Sarcoma Virus (RSV). The viral gene tax is expressed when the T-cell Leukemia virus transforms a cell altering the expression of cellular growth control genes and causing the transformed cells to become cancerous. HIV works differently by not directly causing cells to become cancerous but by instead making those infected more susceptible to lymphoma and Kaposi's sarcoma. Many other retroviruses contain the three genes, gag, pol, and env, which do not directly cause transformation or tumor formation. | 1 | Biochemistry |
The Inglis–Teller equation represents an approximate relationship between the plasma density and the principal quantum number of the highest bound state of an atom. The equation was derived by [https://ahf.nuclearmuseum.org/ahf/profile/david-r-inglis/ David R. Inglis] and Edward Teller in 1939.
In a plasma, atomic levels are broadened and shifted due to the Stark effect, caused by electric microfields formed by the charged plasma particles (ions and electrons). The Stark broadening increases with the principal quantum number , while the energy separation between the nearby levels and decreases. Therefore, above a certain all levels become merged.
Assuming a neutral atomic radiator in a plasma consisting of singly charged ions (and neglecting the electrons), the equation reads
where is the ion particle density and is the Bohr radius.
The equation readily generalizes to cases of multiply charged plasma ions and/or charged radiator. Allowance for the effect of electrons is also possible, as was discussed already in the original study.
Spectroscopically, this phenomenon appears as discrete spectral lines merging into continuous spectrum. Therefore, by using the (appropriately generalized) Inglis–Teller equation it is possible to infer the density of laboratory and astrophysical plasmas. | 7 | Physical Chemistry |
From 1991-1993 a group of investigators, headed by Zvi Shkedi, in the state of Massachusetts, USA, built well-insulated cells and calorimeters which included the capability to measure the actual Faraday efficiency in real-time during the experiments. The cells were of the light-water type; with a fine-wire nickel cathode; a platinum anode; and KCO electrolyte.
The calorimeters were calibrated to an accuracy of 0.02% of input power. The long-term stability of the calorimeters was verified over a period of 9 months of continuous operation. In their publication, the investigators show details of their calorimeters' design and teach the technology of achieving high calorimetric accuracy. | 7 | Physical Chemistry |
3-Methylglutaconyl-CoA (MG-CoA), also known as β-methylglutaconyl-CoA, is an intermediate in the metabolism of leucine. It is metabolized into HMG-CoA. | 1 | Biochemistry |
The central dogma of molecular biology deals with the flow of genetic information within a biological system. It is often stated as "DNA makes RNA, and RNA makes protein", although this is not its original meaning. It was first stated by Francis Crick in 1957, then published in 1958:
He re-stated it in a Nature paper published in 1970: "The central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that such information cannot be transferred back from protein to either protein or nucleic acid."
A second version of the central dogma is popular but incorrect. This is the simplistic DNA → RNA → protein pathway published by James Watson in the first edition of The Molecular Biology of the Gene (1965). Watsons version differs from Cricks because Watson describes a two-step (DNA → RNA and RNA → protein) process as the central dogma. While the dogma as originally stated by Crick remains valid today, Watson's version does not. | 1 | Biochemistry |
Zerovalent iron (ZVI) is jargon that describes forms of iron metal that are proposed for used in Groundwater remediation.
ZVI operates by electron transfer from Fe toward some organochlorine compounds, a common class of pollutants. The remediation process is proposed to generate Fe and Cl and halide-free organic products, all of which are relatively innocuous. The technology is not however been implemented, despite many proofs of principle. | 2 | Environmental Chemistry |
Solar cells are typically named after the semiconducting material they are made of. These materials must have certain characteristics in order to absorb sunlight. Some cells are designed to handle sunlight that reaches the Earth's surface, while others are optimized for use in space. Solar cells can be made of a single layer of light-absorbing material (single-junction) or use multiple physical configurations (multi-junctions) to take advantage of various absorption and charge separation mechanisms.
Solar cells can be classified into first, second and third generation cells. The first generation cells—also called conventional, traditional or wafer-based cells—are made of crystalline silicon, the commercially predominant PV technology, that includes materials such as polysilicon and monocrystalline silicon. Second generation cells are thin film solar cells, that include amorphous silicon, CdTe and CIGS cells and are commercially significant in utility-scale photovoltaic power stations, building integrated photovoltaics or in small stand-alone power system. The third generation of solar cells includes a number of thin-film technologies often described as emerging photovoltaics—most of them have not yet been commercially applied and are still in the research or development phase. Many use organic materials, often organometallic compounds as well as inorganic substances. Despite the fact that their efficiencies had been low and the stability of the absorber material was often too short for commercial applications, there is research into these technologies as they promise to achieve the goal of producing low-cost, high-efficiency solar cells. As of 2016, the most popular and efficient solar cells were those made from thin wafers of silicon which are also the oldest solar cell technology. | 7 | Physical Chemistry |
Photodynamic therapy (PDT) uses photooxygenation to destroy cancerous tissue. A photosensitizer is injected into the tumor and then specific wavelengths of light are exposed to the tissue to excite the Sens. The excited Sens generally follows a type I or II photooxygenation mechanism to result in oxidative damage to cells. Extensive oxidative damage to tumor cells will kill tumor cells. Also oxidative damage to nearby blood vessels will cause local agglomeration and cut off nutrient supply to the tumor, thus starving the tumor.
An important consideration when selecting the Sens to be used in PDT is the specific wavelength of light the Sens will absorb to reach an excited state. Since the maximum penetration of tissues is achieved around wavelengths of 800 nm, selecting Sens that absorb around this range is advantageous as it allows for PDT to be affective on tumors beneath the outer most layer of the dermis. The window of 800 nm light is most effective at penetrating tissues because at wavelengths shorter than 800 nm the light starts to be scattered by the macromolecules of cells and at wavelengths longer than 800 nm water molecules will begin to absorb the light and convert it into heat. | 5 | Photochemistry |
As discussed in the operation section, the resolution bandwidth filter or RBW filter is the bandpass filter in the IF path. It's the bandwidth of the RF chain before the detector (power measurement device). It determines the RF noise floor and how close two signals can be and still be resolved by the analyzer into two separate peaks. Adjusting the bandwidth of this filter allows for the discrimination of signals with closely spaced frequency components, while also changing the measured noise floor. Decreasing the bandwidth of an RBW filter decreases the measured noise floor and vice versa. This is due to higher RBW filters passing more frequency components through to the envelope detector than lower bandwidth RBW filters, therefore a higher RBW causes a higher measured noise floor. | 7 | Physical Chemistry |
Erosion corrosion is a form of corrosion damage usually on a metal surface caused by turbulence of a liquid or solid containing liquid and the metal surface. Aluminum can be particularly susceptible due to the fact that the aluminum oxide layer which affords corrosion protection to the underlying metal is eroded away. | 8 | Metallurgy |
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