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The first published attempt to use plasma emissions as a source for spectroscopic analysis were in 1956 by Eugen Bădărău. In 1964 Stanley Greenfield working at Albright & Wilson was the first to use ICP for non experimental analysis. The first commercial machine was produced by KONTRON in 1975. | 3 | Analytical Chemistry |
Users can design a rAAV vector to any target genomic locus and perform both gross and subtle endogenous gene alterations in mammalian somatic cell-types. These include gene knock-outs for functional genomics, or the ‘knock-in’ of protein tag insertions to track translocation events at physiological levels in live cells. Most importantly, rAAV targets a single allele at a time and does not result in any off-target genomic alterations. Because of this, it is able to routinely and accurately model genetic diseases caused by subtle SNPs or point mutations that are increasingly the targets of novel drug discovery programs. | 1 | Biochemistry |
Carbopalladations can be a description of the elementary step of a reaction catalyzed by a palladium catalyst (Mizoroki-Heck reaction) and can also refer to a carbometalation reaction with a palladium catalyst (alkene difunctionalization, hydrofunctionalization, or reductive Heck) | 0 | Organic Chemistry |
In biochemistry, two biopolymers are antiparallel if they run parallel to each other but with opposite directionality (alignments). An example is the two complementary strands of a DNA double helix, which run in opposite directions alongside each other. | 1 | Biochemistry |
Also during Phase II, copper and arsenical bronze production was practiced at the site.
Norşuntepe provides first clear and unambiguous evidence of arsenical bronze production in this general area before the 4th millennium. It demonstrates that some form of arsenic alloying was being deliberately practised. Since the slag identified at Norşuntepe contains no arsenic, this means that arsenic-bearing materials were added separately. The evidence was discovered at the levels with Ubaid style ceramics, where also were found a number of structures related to the Mesopotamian architectural traditions. A related site in the area from the same time period is Değirmentepe, where arsenic-bronze was also produced around 4200 BC.
The final Chalcolithic phases were characterized by small-scale single-room houses. Radiocarbon dating from the different Chalcolithic levels provided dates between 4300-3800 BC. | 8 | Metallurgy |
Alloys that are not bronze and brass have had a limited representation in the literature for archaeometallurgy. This is mostly due to lack of interest or evidence in the archaeological record. Arsenical copper is one such limited research topic with some experimental work done by Pollard, Thomas, and Williams. Through several experimental smeltings of copper ores including arsenic, Pollard, Thomas, and Williams found that arsenic in copper is retained in higher levels when a lower smelting temperature is used, implying that arsenical copper may have been the result of early smelting technologies where temperatures were unable to pass a certain point.
Lead experimentation has been limited mostly because of its ease in production. Ore containing lead can be easily smelted, re-melted, and worked and as such there is not much difficulty in understanding how past societies may have produced lead. When lead experiments are conducted, they are done much in the same fashion as copper smelting experiments taking notes on quantitative elements such as completion time, airflow rates, fuel usage, and the resulting amount and composition of metal from the smelt. In addition, lead is a toxic element and special care has to take place in order to experiment with it, which makes limitations on the experiments. | 8 | Metallurgy |
Levetiracetam, along with other anti-epileptic drugs, can increase the risk of suicidal behavior or thoughts. People taking levetiracetam should be monitored closely for signs of worsening depression, suicidal thoughts or tendencies, or any altered emotional or behavioral states. | 4 | Stereochemistry |
There are several spot tests that are infrequently used due to their limited applicability, but may be useful in situations where particular lichen metabolites need to be detected, or to distinguish between certain species when other tests are negative.
* A 10% solution of barium hydroxide (Ba(OH)) gives a violet colour when tested with diploschistesic acid, a chemical found in some Diploschistes species.
* A saturated solution of barium peroxide (BaO), when tested with olivetoric acid, will turn a yellow colour that becomes green after a few minutes.
* A 1% (weight per volume) solution of ferric chloride (FeCl) in ethanol produces several possible colours when tested with compounds that have phenolic groups.
* The N test uses a 35% solution of nitric acid, which can be used to distinguish species of Melanelia from brown species of Xanthoparmelia.
* The S test uses a sulphuric acid solution (0.5% to 10%) brushed over an acetone-extracted, dried sample from a lichen thallus, followed by heating over a flame for 30 seconds or until colour develops. A persistent violet to bright pink colour indicates the presence of miriquidic acid and can be used to distinguish between the two morphologically similar snow lichens, Stereocaulon alpinum and S. groenlandicum without having to resort to more laborious chemical analysis.
*The Beilstein test involves heating a small sample of the substance to be tested on a copper wire; halogenated compounds cause a temporary deep green flame colour. | 3 | Analytical Chemistry |
Germicidal UV for disinfection is most typically generated by a mercury-vapor lamp. Low-pressure mercury vapor has a strong emission line at 254 nm, which is within the range of wavelengths that demonstrate strong disinfection effect. The optimal wavelengths for disinfection are close to 260 nm.
Mercury vapor lamps may be categorized as either low-pressure (including amalgam) or medium-pressure lamps. Low-pressure UV lamps offer high efficiencies (approx. 35% UV-C) but lower power, typically 1 W/cm power density (power per unit of arc length). Amalgam UV lamps utilize an amalgam to control mercury pressure to allow operation at a somewhat higher temperature and power density. They operate at higher temperatures and have a lifetime of up to 16,000 hours. Their efficiency is slightly lower than that of traditional low-pressure lamps (approx. 33% UV-C output), and power density is approximately 2–3 W/cm. Medium-pressure UV lamps operate at much higher temperatures, up to about 800 degrees Celsius, and have a polychromatic output spectrum and a high radiation output but lower UV-C efficiency of 10% or less. Typical power density is 30 W/cm or greater.
Depending on the quartz glass used for the lamp body, low-pressure and amalgam UV emit radiation at 254 nm and also at 185 nm, which has chemical effects. UV radiation at 185 nm is used to generate ozone.
The UV lamps for water treatment consist of specialized low-pressure mercury-vapor lamps that produce ultraviolet radiation at 254 nm, or medium-pressure UV lamps that produce a polychromatic output from 200 nm to visible and infrared energy. The UV lamp never contacts the water; it is either housed in a quartz glass sleeve inside the water chamber or mounted externally to the water, which flows through the transparent UV tube. Water passing through the flow chamber is exposed to UV rays, which are absorbed by suspended solids, such as microorganisms and dirt, in the stream. | 5 | Photochemistry |
The genetic code within living organisms can potentially be co-opted to store information. Furthermore synthetic biology can be used to engineer cells with "molecular recorders" to allow the storage and retrieval of information stored in the cell's genetic material. CRISPR gene editing can also be used to insert artificial DNA sequences into the genome of the cell. For encoding developmental lineage data (molecular flight recorder), roughly 30 trillion cell nuclei per mouse * 60 recording sites per nucleus * 7-15 bits per site yields about 2 TeraBytes per mouse written (but only very selectively read). | 1 | Biochemistry |
The general reaction that occurs in the Pidgeon process is:
For industrial use, ferrosilicon is used because its cheaper and more readily available than silicon. The iron from the alloy is a spectator in the reaction. CaC may also be used as an even cheaper alternative for silicon and ferrosilicon, but is disadvantageous because it decreases the magnesium yield slightly.
The magnesium raw material of this type of reaction is magnesium oxide, which is obtained in many ways. In all cases, the raw materials have to be calcined to remove both water and carbon dioxide. Without doing so, the reaction would be gaseous at reaction temperatures and may even revert the reaction. Magnesium oxide can be obtained by sea or lake water magnesium chloride hydrolyzed to hydroxide. It is calcined to magnesium oxide by removing water. Another option is to use mined magnesite (MgCO) calcined to magnesium oxide by carbon dioxide removal.
The most used raw material is mined dolomite, a mixed (Ca,Mg)CO, where the calcium oxide present in the reaction zone scavenges the silica formed, releasing heat and consuming one of the products, ultimately helping push the equilibrium to the right.
(1) Dolomite calcination
(2) Reduction
The Pidgeon process is an endothermic reaction (H° ~183.0kJ/mol Si). Thermodynamically speaking, the temperatures decrease when the vacuum is used for both MgO and calcined dolomite. | 8 | Metallurgy |
Radical cyclization reactions produce mono- or polycyclic products through the action of radical intermediates. Because they are intramolecular transformations, they are often very rapid and selective. Selective radical generation can be achieved at carbons bound to a variety of functional groups, and reagents used to effect radical generation are numerous. The radical cyclization step usually involves the attack of a radical on a multiple bond. After this step occurs, the resulting cyclized radicals are quenched through the action of a radical scavenger, a fragmentation process, or an electron-transfer reaction. Five- and six-membered rings are the most common products; formation of smaller and larger rings is rarely observed.
Three conditions must be met for an efficient radical cyclization to take place:
* A method must be available to generate a radical selectively on the substrate.
* Radical cyclization must be faster than trapping of the initially formed radical.
* All steps must be faster than undesired side reactions such as radical recombination or reaction with solvent.
Advantages: because radical intermediates are not charged species, reaction conditions are often mild and functional group tolerance is high and orthogonal to that of many polar processes. Reactions can be carried out in a variety of solvents (including arenes, alcohols, and water), as long as the solvent does not have a weak bond that can undergo abstraction, and products are often synthetically useful compounds that can be carried on using existing functionality or groups introduced during radical trapping.
Disadvantages: the relative rates of the various stages of radical cyclization reactions (and any side reactions) must be carefully controlled so that cyclization and trapping of the cyclized radical is favored. Side reactions are sometimes a problem, and cyclization is especially slow for small and large rings (although macrocyclizations, which resemble intermolecular radical reactions, are often high yielding). | 0 | Organic Chemistry |
A putative gene is a segment of DNA that is believed to be a gene. Putative genes can share sequence similarities to already characterized genes and thus can be inferred to share a similar function, yet the exact function of putative genes remains unknown. Newly identified sequences are considered putative gene candidates when homologs of those sequences are found to be associated with the phenotype of interest. | 1 | Biochemistry |
Potentiometric solid state gas sensors have been generally classified into three broad groups.
*Type I sensors have an electrolyte containing mobile ions of the chemical species in the gas phase that it is monitoring. The commercial product, YSZ oxygen sensor, is an example of type I.
*Type II sensors do not have mobile ions of the chemical species to be sensed, but an ion related to the target gas can diffuse in the solid electrolyte to allow equilibration with the atmosphere. Therefore, type I and type II sensors have the same design with gas electrodes combined with metal and an electrolyte where oxidized or reduced ions can be electrochemically equilibrated through the electrochemical cell. In the third type of electrochemical sex, auxiliary phases are added to the electrodes to enhance the selectivity and stability.
*Type III sensors make the electrode concept even more confusing. With respect to the design of a solid state sensor, the auxiliary phase looks as part of the electrode. But it cannot be an electrode because auxiliary phase materials are not generally good electrical conductor. In spite of this confusion, type III design offers more feasibility in terms of designing various sensors with different auxiliary materials and electrolytes. | 7 | Physical Chemistry |
The Strep-tag system offers a selective tool to purify proteins under physiological conditions. The proteins obtained are bioactive and display a very high purity (above 95%). Also, the Strep-tag system can be used for protein detection in various assays. Depending on the experimental circumstances, Strep-tag antibodies or Strep-Tactin, with an enzymatic (e.g.horseradish peroxidase (HRP), alkaline phosphatase (AP)) or fluorescence (e.g. green fluorescent protein (GFP)) marker. If high purity is required, the lysate can be purified by first using Strep-Tactin and then perform a second run using antibodies against Strep-tag. This reduces the contamination with unspecific bound proteins, which might occur in some rare scenarios.
Following assays can be conducted using the Strep-tag detection system:
* one-step affinity purification
* Protein:protein interaction studies
* Colony blot, dot blot, Western blot and ELISA
* Screening for positive expression clones
* Immunocytochemistry and Immunohistochemistry
* Protein localization and targeting studies
Because the Strep-tag is capable of isolating protein complexes, strategies for the study of protein-protein interactions can also be conducted. Another option is the immobilization of Strep-tag proteins with a specific high affinity antibody on microplates or biochips.
Strep-Tag/StrepTactin system is also used in single-molecule optical tweezers and atomic force microscope experiments, showing high mechanical stability comparable to the strongest non-covalent linkages currently available. | 1 | Biochemistry |
Transposon mutagenesis was first studied by Barbara McClintock in the mid-20th century during her Nobel Prize-winning work with corn. McClintock received her BSc in 1923 from Cornell’s College of Agriculture. By 1927 she had her PhD in botany, and she immediately began working on the topic of maize chromosomes. In the early 1940s, McClintock was studying the progeny of self-pollinated maize plants which resulted from crosses having a broken chromosome 9. These plants were missing their telomeres. This research prompted the first discovery of a transposable element, and from there transposon mutagenesis has been exploited as a biological tool. | 1 | Biochemistry |
Gravimetric biosensors use the basic principle of a response to a change in mass. Most gravimetric biosensors use thin piezoelectric quartz crystals, either as resonating crystals (QCM), or as bulk/surface acoustic wave (SAW) devices. In the majority of these the mass response is inversely proportional to the crystal thickness. Thin polymer films are also used in which biomolecules can be added to the surface with known surface mass. Acoustic waves can be projected to the thin film to produce an oscillatory device, which then follows an equation that is nearly identical to the Sauerbrey equation used in the QCM method. Biomolecules, such as proteins or antibodies can bind and its change in mass gives a measureable signal proportional to the presence of the target analyte in the sample. | 1 | Biochemistry |
The central carbon in 1,3-dicarbonyl compound is known as an activated methylene group. This is because, owing to the structure, the carbon is especially acidic and can easily be deprotonated to form a methylene group. | 0 | Organic Chemistry |
Process analytical chemistry involves the following sub-disciplines of analytical chemistry: microanalytical systems, nanotechnology, chemical detection, electrochemistry or electrophoresis, chromatography, spectroscopy, mass spectrometry, process chemometrics, process control, flow injection analysis, ultrasound, and handheld sensors. | 7 | Physical Chemistry |
The trifluoromethyl group has a significant electronegativity that is often described as being intermediate between the electronegativities of fluorine and chlorine. For this reason, trifluoromethyl-substituted compounds are often strong acids, such as trifluoromethanesulfonic acid and trifluoroacetic acid. Conversely, the trifluoromethyl group lowers the basicity of compounds like trifluoroethanol. | 0 | Organic Chemistry |
Norman Hackerman (March 2, 1912 – June 16, 2007) was an American chemist, professor, and academic administrator who served as the 18th President of the University of Texas at Austin (1967–1970) and later as the 4th President of Rice University (1970–1985). He was an internationally known expert in metal corrosion. | 7 | Physical Chemistry |
A number of public and private companies are competing to develop a full genome sequencing platform that is commercially robust for both research and clinical use, including Illumina, Knome, Sequenom,
454 Life Sciences, Pacific Biosciences, Complete Genomics,
Helicos Biosciences, GE Global Research (General Electric), Affymetrix, IBM, Intelligent Bio-Systems, Life Technologies, Oxford Nanopore Technologies, and the Beijing Genomics Institute. These companies are heavily financed and backed by venture capitalists, hedge funds, and investment banks.
A commonly-referenced commercial target for sequencing cost until the late 2010s was $1,000USD, however, the private companies are working to reach a new target of only $100. | 1 | Biochemistry |
*Lomagundi-Jatuli event (2,300–2,080 Ma) Paleoproterozoic - Positive excursion
*Shunga-Francevillian event (2,080 Ma) Paleoproterozoic - Negative excursion
*Shuram-Wonoka excursion (570–551 Ma) Neoproterozoic - Negative excursion
*Steptoean positive carbon isotope excursion (494.6-492 Ma) Paleozoic - Positive excursion
*Ireviken event (433.4 Ma) Paleozoic - Positive excursion
*Mulde event (427 Ma) Paleozoic - Positive excursion
*Lau event (424 Ma) Paleozoic - Positive excursion
*Cenomanian-Turonian boundary event (93.9 Ma) Mesozoic - Positive excursion
*Paleocene–Eocene Thermal Maximum (55.5 Ma) Cenozoic - Negative excursion | 9 | Geochemistry |
Historically, in traditional medicine of Europe, Lobaria pulmonaria was collected in large quantities as "lungwort", due to its lung-like appearance (the "doctrine of signatures" suggesting that herbs can treat body parts that they physically resemble). Similarly, Peltigera leucophlebia ("ruffled freckled pelt") was used as a supposed cure for thrush, due to the resemblance of its cephalodia to the appearance of the disease.
Lichens produce metabolites being researched for their potential therapeutic or diagnostic value. Some metabolites produced by lichens are structurally and functionally similar to broad-spectrum antibiotics while few are associated respectively to antiseptic similarities. Usnic acid is the most commonly studied metabolite produced by lichens. It is also under research as a bactericidal agent against Escherichia coli and Staphylococcus aureus. | 2 | Environmental Chemistry |
It has been shown that the fundamental thermodynamic relation together with the following three postulates
is sufficient to build the theory of statistical mechanics without the equal a priori probability postulate.
For example, in order to derive the Boltzmann distribution, we assume the probability density of microstate satisfies . The normalization factor (partition function) is therefore
The entropy is therefore given by
If we change the temperature by while keeping the volume of the system constant, the change of entropy satisfies
where
Considering that
we have
From the fundamental thermodynamic relation, we have
Since we kept constant when perturbing , we have . Combining the equations above, we have
Physics laws should be universal, i.e., the above equation must hold for arbitrary systems, and the only way for this to happen is
That is
It has been shown that the third postulate in the above formalism can be replaced by the following:
However, the mathematical derivation will be much more complicated. | 7 | Physical Chemistry |
A subset X of a metric space is relatively dense if there exists a number r such that all points of X are within distance r of X, and it is uniformly discrete if there exists a number ε such that no two points of X are within distance ε of each other. A set that is both relatively dense and uniformly discrete is called a Delone set. When X is a subset of a vector space, its Minkowski difference X − X is the set {x − y | x, y in X} of differences of pairs of elements of X.
With these definitions, a Meyer set may be defined as a relatively dense set X for which X − X is uniformly discrete. Equivalently, it is a Delone set for which X − X is Delone, or a Delone set X for which there exists a finite set F with X − X ⊂ X + F
Some additional equivalent characterizations involve the set
defined for a given X and ε, and approximating (as ε approaches zero) the definition of the reciprocal lattice of a lattice. A relatively dense set X is a Meyer set if and only if
* For all ε > 0, X is relatively dense, or equivalently
* There exists an ε with 0 is relatively dense.
A character of an additively closed subset of a vector space is a function that maps the set to the unit circle in the plane of complex numbers, such that the sum of any two elements is mapped to the product of their images. A set X is a harmonious set if, for every character χ on the additive closure of X and every ε > 0, there exists a continuous character on the whole space that ε-approximates χ. Then a relatively dense set X is a Meyer set if and only if it is harmonious. | 3 | Analytical Chemistry |
In organic chemistry, a variety of synthetic procures are particularly useful in closing carbocyclic and other rings; these are termed ring-closing reactions. Examples include:
* alkyne trimerisation;
* the Bergman cyclization of an enediyne;
* the Diels–Alder, between a conjugated diene and a substituted alkene, and other cycloaddition reactions;
* the Nazarov cyclization reaction, originally being the cyclization of a divinyl ketone;
* various radical cyclizations;
* ring-closing metathesis reactions, which also can be used to accomplish a specific type of polymerization;
* the Ruzicka large ring synthesis, in which two carboxyl groups combine to form a carbonyl group with loss of and ;
* the Wenker synthesis converting a beta amino alcohol to an aziridine
* other reactions, such as an amino group reacting with a hydroxy group, as in the biosynthesis of solanine | 4 | Stereochemistry |
Compared to other biomedical fields, lipidology was long-neglected as the handling of oils, smears, and greases was unappealing to scientists and lipid separation was difficult. It was not until 2002 that lipidomics, the study of lipid networks and their interaction with other molecules, appeared in the scientific literature. Attention to the field was bolstered by the introduction of chromatography, spectrometry, and various forms of spectroscopy to the field, allowing lipids to be isolated and analyzed. The field was further popularized following the cytologic application of the electron microscope, which led scientists to find that many metabolic pathways take place within, along, and through the cell membrane - the properties of which are strongly influenced by lipid composition. | 1 | Biochemistry |
SERS from pyridine adsorbed on electrochemically roughened silver was first observed by Martin Fleischmann, Patrick J. Hendra and A. James McQuillan at the Department of Chemistry at the University of Southampton, UK in 1973. This initial publication has been cited over 6000 times. The 40th Anniversary of the first observation of the SERS effect has been marked by the Royal Society of Chemistry by the award of a National Chemical Landmark plaque to the University of Southampton. In 1977, two groups independently noted that the concentration of scattering species could not account for the enhanced signal and each proposed a mechanism for the observed enhancement. Their theories are still accepted as explaining the SERS effect. Jeanmaire and Richard Van Duyne
proposed an electromagnetic effect, while Albrecht and Creighton
proposed a charge-transfer effect. Rufus Ritchie, of Oak Ridge National Laboratory's Health Sciences Research Division, predicted the existence of the surface plasmon. | 7 | Physical Chemistry |
Crystal parting occurs when minerals break along planes of structural weakness due to external stress, along twin composition planes, or along planes of weakness due to the exsolution of another mineral. Parting breaks are very similar in appearance to cleavage, but the cause is different. Cleavage occurs because of design weakness while parting results from growth defects (deviations from the basic crystallographic design). Thus, cleavage will occur in all samples of a particular mineral, while parting is only found in samples with structural defects. Examples of parting include the octahedral parting of magnetite, the rhombohedral and basal parting in corundum, and the basal parting in pyroxenes. | 3 | Analytical Chemistry |
Surface physics can be roughly defined as the study of physical interactions that occur at interfaces. It overlaps with surface chemistry. Some of the topics investigated in surface physics include friction, surface states, surface diffusion, surface reconstruction, surface phonons and plasmons, epitaxy, the emission and tunneling of electrons, spintronics, and the self-assembly of nanostructures on surfaces. Techniques to investigate processes at surfaces include surface X-ray scattering, scanning probe microscopy, surface-enhanced Raman spectroscopy and X-ray photoelectron spectroscopy. | 7 | Physical Chemistry |
The ancient world lacked standardized forensic practices, which enabled criminals to escape punishment. Criminal investigations and trials relied heavily on forced confessions and witness testimony. However, ancient sources do contain several accounts of techniques that foreshadow concepts in forensic science developed centuries later.
The first written account of using medicine and entomology to solve criminal cases is attributed to the book of Xi Yuan Lu (translated as Washing Away of Wrongs), written in China in 1248 by Song Ci (, 1186–1249), a director of justice, jail and supervision, during the Song dynasty.
Song Ci introduced regulations concerning autopsy reports to court, how to protect the evidence in the examining process, and explained why forensic workers must demonstrate impartiality to the public. He devised methods for making antiseptic and for promoting the reappearance of hidden injuries to dead bodies and bones (using sunlight and vinegar under a red-oil umbrella); for calculating the time of death (allowing for weather and insect activity); described how to wash and examine the dead body to ascertain the reason for death. At that time the book had described methods for distinguishing between suicide and faked suicide. He wrote the book on forensics stating that all wounds or dead bodies should be examined, not avoided. The book became the first form of literature to help determine the cause of death.
In one of Song Cis accounts (Washing Away of Wrongs'), the case of a person murdered with a sickle was solved by an investigator who instructed each suspect to bring his sickle to one location. (He realized it was a sickle by testing various blades on an animal carcass and comparing the wounds.) Flies, attracted by the smell of blood, eventually gathered on a single sickle. In light of this, the owner of that sickle confessed to the murder. The book also described how to distinguish between a drowning (water in the lungs) and strangulation (broken neck cartilage), and described evidence from examining corpses to determine if a death was caused by murder, suicide or accident.
Methods from around the world involved saliva and examination of the mouth and tongue to determine innocence or guilt, as a precursor to the Polygraph test. In ancient India, some suspects were made to fill their mouths with dried rice and spit it back out. Similarly, in ancient China, those accused of a crime would have rice powder placed in their mouths. In ancient middle-eastern cultures, the accused were made to lick hot metal rods briefly. It is thought that these tests had some validity since a guilty person would produce less saliva and thus have a drier mouth; the accused would be considered guilty if rice was sticking to their mouths in abundance or if their tongues were severely burned due to lack of shielding from saliva. | 3 | Analytical Chemistry |
Some microbes are heterotrophic (more precisely chemoorganoheterotrophic), using organic compounds as both carbon and energy sources. Heterotrophic microbes live off of nutrients that they scavenge from living hosts (as commensals or parasites) or find in dead organic matter of all kind (saprophages). Microbial metabolism is the main contribution for the bodily decay of all organisms after death. Many eukaryotic microorganisms are heterotrophic by predation or parasitism, properties also found in some bacteria such as Bdellovibrio (an intracellular parasite of other bacteria, causing death of its victims) and Myxobacteria such as Myxococcus (predators of other bacteria which are killed and lysed by cooperating swarms of many single cells of Myxobacteria). Most pathogenic bacteria can be viewed as heterotrophic parasites of humans or the other eukaryotic species they affect. Heterotrophic microbes are extremely abundant in nature and are responsible for the breakdown of large organic polymers such as cellulose, chitin or lignin which are generally indigestible to larger animals. Generally, the oxidative breakdown of large polymers to carbon dioxide (mineralization) requires several different organisms, with one breaking down the polymer into its constituent monomers, one able to use the monomers and excreting simpler waste compounds as by-products, and one able to use the excreted wastes. There are many variations on this theme, as different organisms are able to degrade different polymers and secrete different waste products. Some organisms are even able to degrade more recalcitrant compounds such as petroleum compounds or pesticides, making them useful in bioremediation.
Biochemically, prokaryotic heterotrophic metabolism is much more versatile than that of eukaryotic organisms, although many prokaryotes share the most basic metabolic models with eukaryotes, e. g. using glycolysis (also called EMP pathway) for sugar metabolism and the citric acid cycle to degrade acetate, producing energy in the form of ATP and reducing power in the form of NADH or quinols. These basic pathways are well conserved because they are also involved in biosynthesis of many conserved building blocks needed for cell growth (sometimes in reverse direction). However, many bacteria and archaea utilize alternative metabolic pathways other than glycolysis and the citric acid cycle. A well-studied example is sugar metabolism via the keto-deoxy-phosphogluconate pathway (also called ED pathway) in Pseudomonas. Moreover, there is a third alternative sugar-catabolic pathway used by some bacteria, the pentose phosphate pathway. The metabolic diversity and ability of prokaryotes to use a large variety of organic compounds arises from the much deeper evolutionary history and diversity of prokaryotes, as compared to eukaryotes. It is also noteworthy that the mitochondrion, the small membrane-bound intracellular organelle that is the site of eukaryotic oxygen-using energy metabolism, arose from the endosymbiosis of a bacterium related to obligate intracellular Rickettsia, and also to plant-associated Rhizobium or Agrobacterium. Therefore, it is not surprising that all mitrochondriate eukaryotes share metabolic properties with these Pseudomonadota. Most microbes respire (use an electron transport chain), although oxygen is not the only terminal electron acceptor that may be used. As discussed below, the use of terminal electron acceptors other than oxygen has important biogeochemical consequences. | 1 | Biochemistry |
Esters are generally identified by gas chromatography, taking advantage of their volatility. IR spectra for esters feature an intense sharp band in the range 1730–1750 cm assigned to ν. This peak changes depending on the functional groups attached to the carbonyl. For example, a benzene ring or double bond in conjugation with the carbonyl will bring the wavenumber down about 30 cm. | 0 | Organic Chemistry |
N-heterocyclic carbenes are similar to cyanide in reactivity. Like cyanide, they have an unusual chemical ambivalence, which allows them to trigger umpolung in reactions where they are involved. The carbene has six electrons - two each in the carbon-nitrogen single bonds, two in its sp-hybridized orbital, and an empty p-orbital. The sp lone pair acts as an electron donor, whereas the empty p-orbital is capable as acting as an electron acceptor.
In this example, the β-carbon of the α,β-unsaturated ester 1 formally acts as a nucleophile, whereas normally it would be expected to be a Michael acceptor.
This carbene reacts with the α,β-unsaturated ester 1 at the β-position forming the intermediate enolate 2. Through tautomerization 2b can displace the terminal bromine atom to 3. An elimination reaction regenerates the carbene and releases the product 4.
For comparison: in the Baylis-Hillman reaction the same electrophilic β-carbon atom is attacked by a reagent but resulting in the activation of the α-position of the enone as the nucleophile. | 0 | Organic Chemistry |
An equation of state introduced by R. H. Cole
where is a reference density, is the adiabatic index, and is a parameter with pressure units. | 7 | Physical Chemistry |
For low values of the Reynolds number (<1), true for most aerosol motion, Stokes law describes the force of resistance on a solid spherical particle in a fluid. However, Stokes law is only valid when the velocity of the gas at the surface of the particle is zero. For small particles (< 1 μm) that characterize aerosols, however, this assumption fails. To account for this failure, one can introduce the Cunningham correction factor, always greater than 1. Including this factor, one finds the relation between the resisting force on a particle and its velocity:
where
: is the resisting force on a spherical particle
: is the dynamic viscosity of the gas
: is the particle velocity
: is the Cunningham correction factor.
This allows us to calculate the terminal velocity of a particle undergoing gravitational settling in still air. Neglecting buoyancy effects, we find:
where
: is the terminal settling velocity of the particle.
The terminal velocity can also be derived for other kinds of forces. If Stokes law holds, then the resistance to motion is directly proportional to speed. The constant of proportionality is the mechanical mobility (B') of a particle:
A particle traveling at any reasonable initial velocity approaches its terminal velocity exponentially with an e-folding time equal to the relaxation time:
where:
: is the particle speed at time t
: is the final particle speed
: is the initial particle speed
To account for the effect of the shape of non-spherical particles, a correction factor known as the dynamic shape factor is applied to Stokes' law. It is defined as the ratio of the resistive force of the irregular particle to that of a spherical particle with the same volume and velocity:
where:
: is the dynamic shape factor | 7 | Physical Chemistry |
The law of mass action forms the basis of the compartmental model of disease spread in mathematical epidemiology, in which a population of humans, animals or other individuals is divided into categories of susceptible, infected, and recovered (immune). The principle of mass action is at the heart of the transmission term of compartmental models in epidemiology, which provide a useful abstraction of disease dynamics. The law of mass action formulation of the SIR model corresponds to the following "quasichemical" system of elementary reactions:
:The list of components is S (susceptible individuals), I (infected individuals), and R (removed individuals, or just recovered ones if we neglect lethality);
:The list of elementary reactions is
:If the immunity is unstable then the transition from R to S should be added that closes the cycle (SIRS model):
A rich system of law of mass action models was developed in mathematical epidemiology by adding components and elementary reactions.
Individuals in human or animal populations unlike molecules in an ideal solution do not mix homogeneously. There are some disease examples in which this non-homogeneity is great enough such that the outputs of the classical SIR model and their simple generalizations like SIS or SEIR, are invalid. For these situations, more sophisticated compartmental models or distributed reaction-diffusion models may be useful. | 7 | Physical Chemistry |
Based on the manual curation done, BioCyc database family is divided into 3 tiers:
Tier 1: Databases which have received at least one year of literature based manual curation. Currently there are seven databases in Tier 1. Out of the seven, MetaCyc is a major database that contains almost 2500 metabolic pathways from many organisms. The other important Tier 1 database is HumanCyc which contains around 300 metabolic pathways found in humans. The remaining five databases include, EcoCyc (E. coli), AraCyc (Arabidopsis thaliana), YeastCyc (Saccharomyces cerevisiae), LeishCyc (Leishmania major Friedlin) and TrypanoCyc (Trypanosoma brucei).
Tier 2: Databases that were computationally predicted but have received moderate manual curation (most with 1–4 months curation). Tier 2 Databases are available for manual curation by scientists who are interested in any particular organism. Tier 2 databases currently contain 43 different organism databases.
Tier 3: Databases that were computationally predicted by PathoLogic and received no manual curation. As with Tier 2, Tier 3 databases are also available for curation for interested scientists. | 1 | Biochemistry |
Many crystals naturally grow in faceted shapes. For instance, common table salt forms cubes and quartz forms hexagonal prisms. These characteristic shapes are a consequence of the crystal structure of the material and the surface energy, as well as the general conditions under which the crystal formed.
The Bravais lattice of the crystal structure defines a set of possible "low-energy planes", which are usually planes on which the atoms are close-packed. For instance, a cubic crystal may have low-energy planes on the faces of the cube or on the diagonals. The planes are low-energy in the sense that if the crystal is cleaved along these planes, there will be relatively few broken bonds and a relatively small increase in energy over the unbroken crystal. Equivalently, these planes have a low surface energy. The planes with the lowest energy will form the largest facets, in order to minimize the overall thermodynamic free energy of the crystal. If the surface energy as a function of the planes is known, the equilibrium shape of the crystal may be found via the Wulff construction.
Growth conditions, including the surface the crystal is growing on top of (the substrate), may change the expected shape of the crystal; for instance, if the base of the crystal is under stress from the substrate, this may favor the crystal growing taller rather than growing outwards along the substrate. The surface energy, including the relative energies of the different planes, depend on many factors including the temperature, the composition of the surroundings (e.g. humidity), and the pressure. | 3 | Analytical Chemistry |
TEOS-10 covers all thermodynamic properties of liquid water, seawater, ice, water vapour and humid air within their particular ranges of validity as well as their mutual equilibrium composites such as sea ice or cloudy (wet and icy) air.
Additionally, TEOS-10 covers derived properties, for example the potential temperature and Conservative Temperature, the buoyancy frequency, the planetary vorticity and the Montgomery and Cunningham geostrophic streamfunctions. A complete list of featured properties can be found in the [http://www.teos-10.org/pubs/TEOS-10_Manual.pdf TEOS-10 Manual].
The handling of salinity was one of the novelties in TEOS-10. It defines the relationship between Reference Salinity and Practical Salinity, Chlorinity or Absolute Salinity and accounts for the different chemical compositions by adding a regionally variable 𝛿S (see Figure). TEOS-10 is valid for Vienna Standard Mean Ocean Water which accounts for different hydrogen- and oxygen-isotope compositions in water which affects the triple point and therefore phase transitions of water. | 7 | Physical Chemistry |
In geochemistry, a version of Henry's law applies to the solubility of a noble gas in contact with silicate melt. One equation used is
where
:C is the number concentrations of the solute gas in the melt and gas phases,
:β = 1/kT, an inverse temperature parameter (k is the Boltzmann constant),
:µ is the excess chemical potentials of the solute gas in the two phases. | 7 | Physical Chemistry |
The atoms in a gas which are emitting radiation will have a distribution of velocities. Each photon emitted will be "red"- or "blue"-shifted by the Doppler effect depending on the velocity of the atom relative to the observer. The higher the temperature of the gas, the wider the distribution of velocities in the gas. Since the spectral line is a combination of all of the emitted radiation, the higher the temperature of the gas, the broader the spectral line emitted from that gas. This broadening effect is described by a Gaussian profile and there is no associated shift. | 7 | Physical Chemistry |
Hypotonia and Parkinsonism were present in two Turkish siblings, brother and sister. By using exome sequencing, which sequences a selective coding region of the genome, researchers have found a homozygous five-nucleotide deletion in the SPR gene which confirmed both siblings were homozygous. It is predicted that this mutation leads to premature translational termination. Translation is the biological process through which proteins are manufactured. The homozygous mutation of the SPR gene in these two siblings exhibiting early-onset Parkinsonism showcases that SPR gene mutations can vary in combinations of clinical symptoms and movement. These differences result in a wider spectrum for the disease phenotype and increases the genetic heterogeneity causing difficulties in diagnosing the disease. | 1 | Biochemistry |
Short-interspersed nuclear elements are believed to have parasitic origins in eukaryotic genomes. These SINEs have mutated and replicated themselves a large number of times on an evolutionary time-scale and thus form many different lineages. Their early evolutionary origin has caused them to be ubiquitous in many eukaryotic lineages.
Alu elements, short-interspersed nuclear element of about 300 nucleotides, are the most common SINE in humans, with >1,000,000 copies throughout the genome, which is over 10 percent of the total genome; this is not uncommon among other species. Alu element copy number differences can be used to distinguish between and construct phylogenies of primate species. Canines differ primarily in their abundance of SINEC_Cf repeats throughout the genome, rather than other gene or allele level mutations. These dog-specific SINEs may code for a splice acceptor site, altering the sequences that appear as exons or introns in each species.
Apart from mammals, SINEs can reach high copy numbers in a range of species, including nonbony vertebrates (elephant shark) and some fish species (coelacanths). In plants, SINEs are often restricted to closely related species and have emerged, decayed, and vanished frequently during evolution. Nevertheless, some SINE families such as the Au-SINEs and the Angio-SINEs are unusually widespread across many often unrelated plant species. | 1 | Biochemistry |
FRAP can also be used to monitor proteins outside the membrane. After the protein of interest is made fluorescent, generally by expression as a GFP fusion protein, a confocal microscope is used to photobleach and monitor a region of the cytoplasm, mitotic spindle, nucleus, or another cellular structure. The mean fluorescence in the region can then be plotted versus time since the photobleaching, and the resulting curve can yield kinetic coefficients, such as those for the proteins binding reactions and/or the proteins diffusion coefficient in the medium where it is being monitored. Often the only dynamics considered are diffusion and binding/unbinding interactions, however, in principle proteins can also move via flow, i.e., undergo directed motion, and this was recognized very early by Axelrod et al. This could be due to flow of the cytoplasm or nucleoplasm, or transport along filaments in the cell such as microtubules by molecular motors.
The analysis is most simple when the fluorescence recovery is limited by either the rate of diffusion into the bleached area or by rate at which bleached proteins unbind from their binding sites within the bleached area, and are replaced by fluorescent protein. Let us look at these two limits, for the common case of bleaching a GFP fusion protein in a living cell. | 1 | Biochemistry |
Olga García Mancheño is an organic chemistry professor at the University of Münster in Germany. García Mancheño directs an organic chemistry research group at University of Münster that focuses on development of new catalytic methods with the goal of developing sustainable synthetic routes to accomplish carbon-hydrogen functionalization, organic chemical rearrangements, and photocatalyzed chemical reactions. | 0 | Organic Chemistry |
Animals that are capable of smell detect aroma compounds with their olfactory receptors. Olfactory receptors are cell-membrane receptors on the surface of sensory neurons in the olfactory system that detect airborne aroma compounds. Aroma compounds can then be identified by gas chromatography-olfactometry, which involves a human operator sniffing the GC effluent.
In mammals, olfactory receptors are expressed on the surface of the olfactory epithelium in the nasal cavity. | 0 | Organic Chemistry |
Filters are often used to collect bioaerosols because of their simplicity and low cost. Filter collection is especially useful for personal bioaerosol sampling since they are light and unobtrusive. Filters can be preceded by a size-selective inlet, such as a cyclone or impactor, to remove larger particles and provide size-classification of the bioaerosol particles. Aerosol filters are often described using the term "pore size" or "equivalent pore diameter". Note that the filter pore size does NOT indicate the minimum particle size that will be collected by the filter; in fact, aerosol filters generally will collect particles much smaller than the nominal pore size. | 7 | Physical Chemistry |
Initially, there had been questions of whether the solved DNA structures were artefacts of the X-ray crystallography techniques used. However, the structure of DNA was subsequently confirmed in solution via gel electrophoretic methods and later via solution NMR and AFM indicating that the crystallography process did not distort it. The structure of DNA in complex with nucleosomes, helicases, and numerous other DNA binding proteins also supported its biological relevance in vivo. | 1 | Biochemistry |
In this example, the following sentence with three-letter words makes sense when read from the beginning:
|Start|THE CAT AND THE MAN ARE FAT ...
|Start|123 123 123 123 123 123 123 ...
However, if the reading frame is shifted by one letter to between the T and H of the first word (effectively a +1 frameshift when considering the 0 position to be the initial position of T),
T|Start|HEC ATA NDT HEM ANA REF AT...
-|Start|123 123 123 123 123 123 12...
then the sentence reads differently, making no sense. | 1 | Biochemistry |
Similar to bromocresol green, the structure of bromocresol purple changes with pH. Changing the level of acidity causes a shift in the equilibrium between two different structures that have different colors. In near-neutral or alkaline solution, the chemical has a sulfonate structure that gives the solution a purple color. As the pH decreases, it converts to a sultone (cyclic sulfonic ester) that colors the solution yellow. In some microbiology tests, this change is used as an indicator of bacterial growth. | 3 | Analytical Chemistry |
In order to load a gas as a sample of pressure transmitting medium, the gas must be in a dense state, as to not shrink the sample chamber once pressure is induced. To achieve a dense state, gases can be liquefied at low temperatures or compressed. Cryogenic loading is a technique that uses liquefied gas as a means of filling the sample chamber. The DAC is directly immersed into the cryogenic fluid that fills the sample chamber. However, there are disadvantages to cryogenic loading. With the low temperatures indicative of cryogenic loading, the sample is subjected to temperatures that could irreversibly change it. Also, the boiling liquid could displace the sample or trap an air bubble in the chamber. It is not possible to load gas mixtures using the cryogenic method due to the different boiling points of most gases. Gas compression technique densifies the gases at room temperature. With this method, most of the problems seen with cryogenic loading are fixed. Also, loading gas mixtures becomes a possibility. The technique uses a vessel or chamber in which the DAC is placed and is filled with gas. Gases are pressurized and pumped into the vessel with a compressor. Once the vessel is filled and the desired pressure is reached the DAC is closed with a clamp system run by motor driven screws. | 7 | Physical Chemistry |
Filter papers are widely used in laboratory experiments across many different fields, from biology to chemistry. The type of filter used will differ according to the purpose of the procedure and the chemicals involved. Generally, filter papers are used with laboratory techniques such as gravity or vacuum filtration.
Historically, a type of soft, porous paper called charta emporetica was used in pharmacy as a filter and as packing paper. | 3 | Analytical Chemistry |
Many microbes (phototrophs) are capable of using light as a source of energy to produce ATP and organic compounds such as carbohydrates, lipids, and proteins. Of these, algae are particularly significant because they are oxygenic, using water as an electron donor for electron transfer during photosynthesis. Phototrophic bacteria are found in the phyla "Cyanobacteria", Chlorobiota, Pseudomonadota, Chloroflexota, and Bacillota. Along with plants these microbes are responsible for all biological generation of oxygen gas on Earth. Because chloroplasts were derived from a lineage of the Cyanobacteria, the general principles of metabolism in these endosymbionts can also be applied to chloroplasts. In addition to oxygenic photosynthesis, many bacteria can also photosynthesize anaerobically, typically using sulfide () as an electron donor to produce sulfate. Inorganic sulfur (), thiosulfate () and ferrous iron () can also be used by some organisms. Phylogenetically, all oxygenic photosynthetic bacteria are Cyanobacteria, while anoxygenic photosynthetic bacteria belong to the purple bacteria (Pseudomonadota), Green sulfur bacteria (e.g., Chlorobium), Green non-sulfur bacteria (e.g., Chloroflexus), or the heliobacteria (Low %G+C Gram positives). In addition to these organisms, some microbes (e.g. the Archaeon Halobacterium or the bacterium Roseobacter, among others) can utilize light to produce energy using the enzyme bacteriorhodopsin, a light-driven proton pump. However, there are no known Archaea that carry out photosynthesis.
As befits the large diversity of photosynthetic bacteria, there are many different mechanisms by which light is converted into energy for metabolism. All photosynthetic organisms locate their photosynthetic reaction centers within a membrane, which may be invaginations of the cytoplasmic membrane (Pseudomonadota), thylakoid membranes ("Cyanobacteria"), specialized antenna structures called chlorosomes (Green sulfur and non-sulfur bacteria), or the cytoplasmic membrane itself (heliobacteria). Different photosynthetic bacteria also contain different photosynthetic pigments, such as chlorophylls and carotenoids, allowing them to take advantage of different portions of the electromagnetic spectrum and thereby inhabit different niches. Some groups of organisms contain more specialized light-harvesting structures (e.g. phycobilisomes in Cyanobacteria and chlorosomes in Green sulfur and non-sulfur bacteria), allowing for increased efficiency in light utilization.
Biochemically, anoxygenic photosynthesis is very different from oxygenic photosynthesis. Cyanobacteria (and by extension, chloroplasts) use the Z scheme of electron flow in which electrons eventually are used to form NADH. Two different reaction centers (photosystems) are used and proton motive force is generated both by using cyclic electron flow and the quinone pool. In anoxygenic photosynthetic bacteria, electron flow is cyclic, with all electrons used in photosynthesis eventually being transferred back to the single reaction center. A proton motive force is generated using only the quinone pool. In heliobacteria, Green sulfur, and Green non-sulfur bacteria, NADH is formed using the protein ferredoxin, an energetically favorable reaction. In purple bacteria, NADH is formed by reverse electron flow due to the lower chemical potential of this reaction center. In all cases, however, a proton motive force is generated and used to drive ATP production via an ATPase.
Most photosynthetic microbes are autotrophic, fixing carbon dioxide via the Calvin cycle. Some photosynthetic bacteria (e.g. Chloroflexus) are photoheterotrophs, meaning that they use organic carbon compounds as a carbon source for growth. Some photosynthetic organisms also fix nitrogen (see below). | 1 | Biochemistry |
Copper is a fairly common element, with an estimated concentration of 50–70 ppm (0.005–0.007 percent) in Earths crust (1 kg of copper per 15–20 tons of crustal rock). A concentration of 60 ppm would multiply out to 1.66 quadrillion tonnes over the mass of the crust, or over 90 million years worth at the 2013 production rate of 18.3 MT per year. However, not all of it can be extracted profitably at the current level of technology and the current market value.
The USGS reported a current total reserve base of copper in potentially recoverable ores of 1.6 billion tonnes as of 2005, of which 950 million tonnes were considered economically recoverable. A 2013 global assessment identified "455 known deposits (with well-defined identified resources) that contain about 1.8 billion metric tons of copper", and predicted "a mean of 812 undiscovered deposits within the uppermost kilometer of the earth's surface" containing another 3.1 billion metric tons of copper "which represents about 180 times 2012 global copper production from all types of copper deposits." | 8 | Metallurgy |
CK1δ and CK1ε were thought to be generally redundant in circadian cycle length and protein stability. Recent research, however, has shown that CK1δ deficiency lengthens circadian period while CK1ε deficiency does not. Also, CK1α has recently been suggested to play a role redundant to CK1δ in phosphorylating PER1 although this is not consistent with other data | 1 | Biochemistry |
RNA polymerase II is inhibited by α-Amanitin and other amatoxins. α-Amanitin is a highly poisonous substance found in many mushrooms. The mushroom poison has different effects on each of the RNA Polymerases: I, II, III. RNAP I is completely unresponsive to the substance and will function normally while RNAP III has a moderate sensitivity. RNAP II, however, is completely inhibited by the toxin. Alpha-Amanitin inhibits RNAP II by strong interactions in the enzyme's "funnel", "cleft", and the key "bridge α-helix" regions of the RPB-1 subunit. | 1 | Biochemistry |
The institute also contributes to the undergraduate programs and university studies as well as continuing vocational trainings. Academic staff is involved in several master programs and coordinates two of them. The institute is also engaged in an Erasmus Mundus master, «EACH» (Excellence in Analytical Chemistry), and the «pNMR Marie Curie Initial network». Regarding vocational training, the institute provides several trainings in a wide range of analytical techniques. | 3 | Analytical Chemistry |
Gestonorone caproate is used in the palliative treatment of benign prostatic hypertrophy and endometrial cancer. It is used at a dose of 100 to 200 mg once a week by intramuscular injection. | 4 | Stereochemistry |
Intramolecular Diels–Alder (IMDA) reactions pair tethered dienes and dienophiles in a [4+2] fashion, the most common being terminal substitution. These transformations are popular in total synthesis and have seen a wide spread use in advance to numerous difficult synthetic targets. One such use is the application of an enantioselective IMDA transformation in the asymmetric synthesis of the marine toxin (10).
The synthesis of demonstrated the utility of cationic Cu(II)bis(oxazoline) complex catalyzed IMDA reactions to give bicyclic products with as many as four neighboring stereogenic centers (figure 3). A rather recent application of IMDA reactions in complex molecule synthesis is the IMDA approach to the tricyclic core of palhinine lycopodium alkaloids, a class of natural products isolated from nodding club moss.
N–heterocyclic carbenes (NHCs) are an emerging class of organocatalysts that are able to induce Umpolung reactivity as well as normal polarity transformations, however until recently these have not been broadly used in total synthesis due to limited substrate scope. An interesting expansion in the use of these organocatalysts is the NHC catalyzed olefin isomerization/IMDA cascade reaction to give unique bicyclic scaffolds. Dienyl esters such as 11 were transformed into substituted bicyclo[2.2.2]octanes via an isomerization step stabilized by a hemiacetal azolium intermediate (13). The activation barrier of isomerization of 1,3–hexadiene through a [1,5]–shift is 41 Kcal mol–1 and is expected to increase with conjugation to the ester, thus uncatalyzed isomerization is unlikely. This provides the advantage of bypassing a high barrier of activation, providing access to previously unobtainable IMDA derivatives. | 0 | Organic Chemistry |
In plants and microorganisms, threonine is synthesized from aspartic acid via α-aspartyl-semialdehyde and homoserine. Homoserine undergoes O-phosphorylation; this phosphate ester undergoes hydrolysis concomitant with relocation of the OH group. Enzymes involved in a typical biosynthesis of threonine include aspartokinase, β-aspartate semialdehyde dehydrogenase, homoserine dehydrogenase, homoserine kinase, threonine synthase.
The biosynthesis of threonine is regulated via allosteric regulation of its precursor, homoserine, by structurally altering the enzyme homoserine dehydrogenase. This reaction occurs at a key branch point in the pathway, with the substrate homoserine serving as the precursor for the biosynthesis of lysine, methionine, threonin and isoleucine. High levels of threonine result in low levels of homoserine synthesis. The synthesis of aspartate kinase (AK), which catalyzes the phosphorylation of aspartate and initiates its conversion into other amino acids, is feed-back inhibited by lysine, isoleucine, and threonine, which prevents the synthesis of the amino acids derived from aspartate. So, in addition to inhibiting the first enzyme of the aspartate families biosynthetic pathway, threonine also inhibits the activity of the first enzyme after the branch point, i.e. the enzyme that is specific for threonine's own synthesis. | 1 | Biochemistry |
There are at least four families of chromatin remodelers in eukaryotes: SWI/SNF, ISWI, NuRD/Mi-2/CHD, and INO80 with first two remodelers being very well studied so far, especially in the yeast model. Although all of remodelers share common ATPase domain, their functions are specific based on several biological processes (DNA repair, apoptosis, etc.). This is due to the fact that each remodeler complex has unique protein domains (Helicase, bromodomain, etc.) in their catalytic ATPase region and also has different recruited subunits. | 1 | Biochemistry |
In physics, chemistry and related fields, a kinetic scheme is a network of states and connections between them representing the scheme of a dynamical process. Usually a kinetic scheme represents a Markovian process, while for non-Markovian processes generalized kinetic schemes are used. Figure 1 shows an illustration of a kinetic scheme. | 7 | Physical Chemistry |
The conjugate base of hydroxamic acids forms is called a hydroxamate. Deprotonation occurs at the group, with the hydrogen atom being removed, resulting in a hydroxamate anion . The resulting conjugate base presents the metal with an anionic, conjugated O,O chelating ligand. Many hydroxamic acids and many iron hydroxamates have been isolated from natural sources.
They function as ligands, usually for iron. Nature has evolved families of hydroxamic acids to function as iron-binding compounds (siderophores) in bacteria. They extract iron(III) from otherwise insoluble sources (rust, minerals, etc.). The resulting complexes are transported into the cell, where the iron is extracted and utilized metabolically.
Ligands derived from hydroxamic acid and thiohydroxamic acid (a hydroxamic acid where one or both oxygens in the functional group are replaced by sulfur) also form strong complexes with lead(II). | 0 | Organic Chemistry |
ATP synthase consists of a F and F subunit. The F subunit contains alpha and beta subunits of its own which can assist in the formation of ATP, or hydrolyze it to serve as a proton pump. Though most catalytic actions happen on the beta subunits, the alpha subunits each contain an arginine finger. The role of the arginine finger in ATP synthase is akin to the function of the arginine finger residues of G proteins; to help split ATP. For example, if the arginine of the arginine finger is substituted by lysine, possibly due to a missense mutation, the αR364K mutant results. In the αR364K mutant, the ability of ATP synthase to hydrolyze ATP is decreased around a thousandfold compared to the wild type. | 1 | Biochemistry |
As a common noun, English heat or warmth (just as French chaleur, German Wärme, Latin calor, Greek θάλπος, etc.) refers to (the human perception of) either thermal energy or temperature. Speculation on thermal energy or "heat" as a separate form of matter has a long history, identified as caloric theory, phlogiston theory, and fire.
Heat has been discussed in ordinary language by philosophers. An example is this 1720 quote from John Locke:
:::::Heat, is a very brisk agitation of the insensible parts of the object, which produces in us that sensation from whence we denominate the object hot; so what in our sensation is heat, in the object is nothing but motion. This appears by the way, whereby heat is produc’d: for we see that the rubbing of a brass nail upon a board, will make it very hot; and the axle-trees of carts and coaches are often hot, and sometimes to a degree, that it sets them on fire, by the rubbing of the nave of the wheel upon it.
This source was repeatedly quoted by Joule.
John Tyndalls Heat Considered as Mode of Motion' (1863) was instrumental in popularizing the idea of heat as motion to the English-speaking public.
The theory was developed in academic publications in French, English and German. From an early time, the French technical term chaleur used by Carnot was taken as equivalent to the English heat and German Wärme (lit. "warmth", while the equivalent of heat would be German Hitze). | 7 | Physical Chemistry |
Feather meal is a byproduct of processing poultry; it is made from poultry feathers by partially grinding them under elevated heat and pressure, and then grinding and drying. Although total nitrogen levels are fairly high (up to 12%), the bioavailability of this nitrogen may be low. Feather meal is used in formulated animal feed and in organic fertilizer.
Worldwide, approximately 50 billion chickens were used for human consumption in 2014. Feather meal is made through a process called rendering. Steam pressure cookers with temperatures over are used to "cook" and sterilize the feathers. This partially hydrolyzes the proteins, which denatures them. It is then dried, cooled and ground into a powder for use as a nitrogen source for animal feed (mostly ruminants) or as an organic soil amendment.
Containing up to 12% nitrogen, it is a source of slow-release, organic, high-nitrogen fertilizer for organic gardens. It is not water-soluble and does not make a good liquid fertilizer. It can be used to:
*Increase green leaf growth
*Activate compost decomposition
*Improve soil structure
When adding it to a garden as a nitrogen source, it must be blended into the soil to start the decomposition to make the nitrogenous compounds available to the plants. As an organic garden fertilizer, it is not synthetic or petroleum-based. | 9 | Geochemistry |
Gram-positive bacteria that participate in quorum sensing typically use secreted oligopeptides as autoinducers. Peptide autoinducers usually result from posttranslational modification of a larger precursor molecule. In many Gram-positive bacteria, secretion of peptides requires specialized export mechanisms. For example, some peptide autoinducers are secreted by ATP-binding cassette transporters that couple proteolytic processing and cellular export. Following secretion, peptide autoinducers accumulate in extracellular environments. Once a threshold level of signal is reached, a histidine sensor kinase protein of a two-component regulatory system detects it and a signal is relayed into the cell. As with AHLs, the signal ultimately ends up altering gene expression. Unlike some AHLs, however, most oligopeptides do not act as transcription factors themselves. | 1 | Biochemistry |
The K/U Ratio is the ratio of a slightly volatile element, potassium (K), to a highly refractory element, uranium (U). It is a useful way to measure the presence of volatile elements on planetary surfaces. The K/U ratio helps explain the evolution of the planetary system and the origin of Earth's moon. | 9 | Geochemistry |
Darodipine is an experimental calcium channel blocker that based on animal models may reduce neuronal cytoskeletal alterations during aging and in neurodegenerative disorders. Studies performed on rats have shown darodipine to have an effect on brain serotonergic systems. Darodipine increased the 5-HIAA/5-HT ratio within various parts of the brain. Darodipine has also been shown to impair memory and learning processes on mice.
The longterm effect of darodipine was tested in the rats and it shows that there is no significant change in their body and brain weight values but, there is a significant change in their alkaline phosphate reactive capillary profile values. Alkaline phosphate enzymes plays an important role in the functioning of the cerebral capillary activities. The effect of darodipine on plasma concentration was also tested on a group of healthy male human volunteers. The result showed that darodipine resulted in the change in heart rate and diastolic blood pressure which is related to the plasma concentration.
Darodipine (50–500 nM), the sensitivity of DMPO‐COO.− adduct decreased by more than that of the DMPO‐OH adduct and the concentration-dependent drop in signal intensity. It has additional preventive effects, because of its calcium antagonistics, against free-radical mediated electrophysiological alterations; it is likely because of the trapping of such radical molecules. | 1 | Biochemistry |
The word methemoglobin derives from the Ancient Greek prefix μετα- (meta-: behind, later, subsequent) and the word hemoglobin.
The name hemoglobin is itself derived from the words heme and globin, each subunit of hemoglobin being a globular protein with an embedded heme group. | 1 | Biochemistry |
The following example deals with a beam of light scattering off a circle with radius and a perfectly reflecting boundary. The beam consists of a uniform density of parallel rays, and the beam-circle interaction is modeled within the framework of geometric optics. Because the problem is genuinely two-dimensional, the cross section has units of length (e.g., meters). Let be the angle between the light ray and the radius joining the reflection point of the ray with the center point of the mirror. Then the increase of the length element perpendicular to the beam is
The reflection angle of this ray with respect to the incoming ray is , and the scattering angle is
The differential relationship between incident and reflected intensity is
The differential cross section is therefore ()
Its maximum at corresponds to backward scattering, and its minimum at corresponds to scattering from the edge of the circle directly forward. This expression confirms the intuitive expectations that the mirror circle acts like a diverging lens. The total cross section is equal to the diameter of the circle: | 7 | Physical Chemistry |
As the temperature decreases, further physiological systems falter and heart rate, respiratory rate, and blood pressure all decrease. This results in an expected heart rate in the 30s at a temperature of .
There is often cold, inflamed skin, hallucinations, lack of reflexes, fixed dilated pupils, low blood pressure, pulmonary edema, and shivering is often absent. Pulse and respiration rates decrease significantly, but fast heart rates (ventricular tachycardia, atrial fibrillation) can also occur. Atrial fibrillation is not typically a concern in and of itself. | 1 | Biochemistry |
Faradays electrochemical paradox arises from his famous experiment of 1833. Concentrated nitric acid had been synthesized and although Faraday did not have a pH meter (the pH scale would not be developed for another seventy years), Faraday knew from various tests (e.g. taste and time of dissolution of calcite chips) that concentrated nitric acid was a much stronger acid than dilute nitric acid. Thus, when he placed the iron in the dilute acid, gas (now known to be hydrogen) was evolved from the surface and the iron dissolved. When he placed the iron in the concentrated nitric acid, he expected that it would dissolve at a higher rate, but no attack was observed. He then scratched the surface and a burst of bubbles was generated but then ceased. He stated that the surface had become "passive" and, therefore, he correctly assumed that the surface was oxidized and became covered with a protective oxide film. However, the oxide film did not dissolve and the attack did not continue in the concentrated nitric acid. This became known as Faradays electrochemical paradox, and was not solved until 1989.
The key to resolving the paradox is passivation. When the acid is concentrated enough, and because concentrated nitric acid is an oxidizing agent, the potential of the metal is raised to the point that a layer of metastable FeO forms on the surface and protects it from further corrosion, even though the pH is so low that stable FeO cannot exist. This explanation is supported by the observation that scratching the surface causes a burst of bubbles. Diluted nitric acid is not as strong an oxidizing agent and hence does not raise the potential of the metal to the extent that metastable FeO forms on the surface. In this case, the metal freely corrodes. | 7 | Physical Chemistry |
The IUBMB is committed to providing training opportunities to biochemists and molecular biologists around the world. The Wood Whelan Research fellowship, established in honor of past-Presidents Harland G. Wood and William Joseph Whelan, provides opportunities for students to travel to a laboratory in a different country to work on a specified project. Mid Career Fellowships provide a similar opportunity to early career investigators. The IUBMB collaborates with American Society of Biochemistry and Molecular Biology to offer PROLAB fellowships to provide opportunities for Latin American students to study in the US. | 1 | Biochemistry |
In 2009, Gaunts group reported a copper catalyzed meta-selective C–H arylation reaction on anilide derivatives. Despite the intrinsic ortho-/para- selectivity of the amido group, the arylation occurs exclusively on the meta position on a variety of anilide substrates. Remarkably, the regioselectivity is totally different from the earlier reported Pd catalyzed C-H functionalizations, where the amido group serve as a powerful ortho-directing group. The method is robust under mild reaction conditions. It is compatible with a spectrum of substituted anilide as well as different bisaryliodonium salts. However, the meta-selectivity is lost when highly ortho/para-directing methoxy group substitutes one of the meta'-hydrogen of the anilide, which marks the limitation of this method. Despite the limitation, the paper was of high impact. It has been highlighted in a number of journals and news and was voted as one of the top 12 papers of 2009 by Chemical and Engineering News.
In a more recent report from the same group, α-arylcarbonyl compounds were found to be good substrates for the copper catalyzed meta-selective C-H arylation. The power of the meta-selectivity overrides the electronic effect of different substituents, including the strong ortho/para-directing m-methoxy group.
Although the copper catalyzed meta-selective C–H arylation is quite successful, the mechanism behind the meta-selectivity is not completely understood. There are generally two proposed mechanisms both involving a Cu(I)/Cu(III) catalyst cycle.
In Gaunts original paper, he proposed a mechanism involving an anti-oxy-cupration step as the key to the meta-selectivity. First, the Cu(II) salt generates the active Cu(I) species through either disproportionation or reduction by nucleophile. The active Cu(I) species undergoes oxidative addition with diphenyliodonium salt to generate a highly electrophilic Cu(III) species. While the Cu(III) species activates the aromatic ring, the amide oxygen attacks the ortho position, breaking the aromaticity and allowing cupration at the meta position. The intermediate then rearomatizes with base and undergoes reductive elimination to afford the meta'-arylated product and regenerate the active Cu(I) catalyst.
Alternatively, Li and Wu, based on DFT calculations, proposed a mechanism involving a "Heck-like four-membered-ring transition state". The amide oxygen first coordinates to the Cu(III) species generated from oxidative addition of Cu(I) triflate and diphenyliodonium triflate. Then, the phenyl group bonded to copper interacts with the aromatic ring at the meta-position, forming a four-membered-ring transition state. According to their calculations, the aromaticity is not completely lost during the transformation. In the last step, the Cu(III)-C bond breaks to regenerate the Cu(I) catalyst while the triflate ion abstract the meta-hydrogen to recover the aromaticity and gives the product. | 0 | Organic Chemistry |
In most hydrogen-fusing stars, including the Sun, a chemical cycle involved in stellar nucleosynthesis occurs which is known as a carbon-nitrogen-oxygen or (CNO cycle). In addition to this cycle, stars also have a helium cycle. Various cycles involving gas and dust have been found to occur in galaxies. | 9 | Geochemistry |
During barcode sequencing, high molecular weight DNA samples that contain the targeted DNA sequence, ranging from fifty to several hundred kilobases in size, are combined with gel beads containing unique barcodes, enzymes, and sequencing reagents. Microfluidic device can partition input DNA molecules into individual nanoliter-sized droplets of water-in-oil emulsion, called GEMs. Each GEM contains gel beads coated with the same barcode and primers, and a small amount of DNA. The primers are complementary to specific regions of the DNA molecule, allowing for amplification of the DNA in the droplets through PCR. The barcodes enable the identification and grouping of sequencing reads that originate from the same long fragment, which is crucial for downstream analysis. | 1 | Biochemistry |
Organocerium chemistry is the science of organometallic compounds that contain one or more chemical bond between carbon and cerium. These compounds comprise a subset of the organolanthanides. Most organocerium compounds feature Ce(III) but some Ce(IV) derivatives are known. | 0 | Organic Chemistry |
BBE-like enzymes serve as a catalyzer for a wide range of reactions. All the way from two-electron oxidations as observed in (At)BBE-like 15 to four-electron oxidations as seen in Dbv29.
BBE-like enzymes are involved in the synthesis of plenty of isoquinoline alkaloids such as the conversion of (S)-reticuline to (S)-scoulerine or by guiding (S)-reticuline to protoberberine, protopine, benzophenanthridine, phthalide isoquinoline or rhoeadine metabolic pathways.
Research on this matter is rare since it is very complex and had never been looked into until recently. New studies reveal that BBE-like enzymes are involved in the biological synthesis of the alkaloids intermediates communesin as well as chanoclavine (I). The mechanism through which reactions are catalyzed by these BBE-like enzymes has not been found yet, but the resulting conformation of the products suggests that a similar coupling of substrate oxidation and ring formation occurs in these processes. | 1 | Biochemistry |
Transition state theory explains the reaction dynamics of reactions. The theory is based on the idea that there is an equilibrium between the activated complex and reactant molecules. The theory incorporates concepts from collision theory, which states that for a reaction to occur, reacting molecules must collide with a minimum energy and correct orientation. The reactants are first transformed into the activated complex before breaking into the products. From the properties of the activated complex and reactants, the reaction rate constant iswhere K is the equilibrium constant, is the Boltzmann constant, T is the thermodynamic temperature, and h is Planck's constant. Transition state theory is based on classical mechanics, as it assumes that as the reaction proceeds, the molecules will never return to the transition state. | 7 | Physical Chemistry |
The continental shelf pump is proposed as operating in the shallow waters of the continental shelves as a mechanism transporting carbon (dissolved or particulate) from the continental waters to the interior of the adjacent deep ocean. As originally formulated, the pump is thought to occur where the solubility pump interacts with cooler, and therefore denser water from the shelf floor which feeds down the continental slope into the neighbouring deep ocean. The shallowness of the continental shelf restricts the convection of cooling water, so the cooling can be greater for continental shelf waters than for neighbouring open ocean waters. These cooler waters promote the solubility pump and lead to an increased storage of dissolved inorganic carbon. This extra carbon storage is further augmented by the increased biological production characteristic of shelves. The dense, carbon-rich shelf waters then sink to the shelf floor and enter the sub-surface layer of the open ocean via isopycnal mixing. As the sea level rises in response to global warming, the surface area of the shelf seas will grow and in consequence the strength of the shelf sea pump should increase. | 9 | Geochemistry |
Airless spray equipment used for Dimetcote should have a fluid tip with orifice no smaller than 0.019 inch (0.48), and the minimum level of pump ratio is 28:1. Some standard airless sprays such as Spee-Flo, Graco, Nordson-Bede, and DeVilbiss meet these requirements. | 8 | Metallurgy |
The idea for the race was formulated by scientists Christian Joachim and in Toulouse, France in January 2013 in the ACS Nano journal. A call for applications was launched to give the participating teams time to prepare appropriate nanocars. The race is officially announced by the French National Centre for Scientific Research (CNRS) in November 2015 in Toulouse during Futurapolis1. On this occasion, five teams presented their prototype projects on November 27, 2015.
The first race in the world of this type, between four vehicles, started on the 28 April 2017 at the CEMES-CNRS in Toulouse and lasted 36 hours. The Toulouse organizers also agreed on the competition of two more vehicles, which will then be remotely controlled via Internet from the CEMES-CNRS race room on the microscope of their own laboratory. These relates to the vehicles from Ohio and Graz-Rice. | 6 | Supramolecular Chemistry |
In the early 20th century, galvanized piping replaced previously-used cast iron and lead in cold-water plumbing. Typically, galvanized piping rusts from the inside out, building up layers of plaque on the inside of the piping, causing both water pressure problems and eventual pipe failure. These plaques can flake off, leading to visible impurities in water and a slight metallic taste. The life expectancy of galvanized piping is about 40–50 years, but it may vary on how well the pipes were built and installed. Pipe longevity also depends on the thickness of zinc in the original galvanizing, which ranges on a scale from G01 to G360. | 8 | Metallurgy |
Demulsifiers, or emulsion breakers, are a class of specialty chemicals used to separate emulsions, for example, water in oil. They are commonly used in the processing of crude oil, which is typically produced along with significant quantities of saline water. This water (and salt) must be removed from the crude oil prior to refining. If the majority of the water and salt are not removed, significant corrosion problems can occur in the refining process.
Demulsifiers are typically based on the following chemistry:
* Acid catalysed phenol-formaldehyde resins
* Base catalysed phenol-formaldehyde resins
* Epoxy resins
* Polyethyleneimines
* Polyamines
* Di-epoxides
* Polyols
* dendrimer
The above are usually ethoxylated (and/or propoxylated) to provide the desired degree of water/oil solubility.
The addition of ethylene oxide increases water solubility, propylene oxide decreases it.
Commercially available demulsifier formulations are typically a mixture of two to four different chemistries, in carrier solvent(s) such as xylene, heavy aromatic naphtha (HAN), Isopropanol, methanol, 2-Ethylhexanol or diesel.
Demulsifiers are manufactured by chemical manufacturers including:
* Arkema
* Baker Hughes
* BASF
* ChampionX
* Clariant
* Dow Chemical Company
* Lubrizol
* Nouryon
* [https://purechemservices.com/ PureChem Services] ([https://www.cesenergysolutions.com/ CES])
* SI Group
* Chembiotec Additives
* Solvay
* Stepan
* Starborn Chemical
* Dorf Ketal Chemicals | 7 | Physical Chemistry |
Children may be at greater risk for adverse reactions to repellents, in part, because their exposure may be greater.
Children can be at greater risk of accidental eye contact or ingestion.
As with chemical exposures in general, pregnant women should take care to avoid exposures to repellents when practical, as the fetus may be vulnerable.
Some experts also recommend against applying chemicals such as DEET and sunscreen simultaneously since that would increase DEET penetration. Canadian researcher, Xiaochen Gu, a professor at the University of Manitoba's faculty of Pharmacy who led a study about mosquitos, advises that DEET should be applied 30 or more minutes later. Gu also recommends insect repellent sprays instead of lotions which are rubbed into the skin "forcing molecules into the skin".
Regardless of which repellent product used, it is recommended to read the label before use and carefully follow directions. Usage instructions for repellents vary from country to country. Some insect repellents are not recommended for use on younger children.
In the DEET Reregistration Eligibility Decision (RED) the United States Environmental Protection Agency (EPA) reported 14 to 46 cases of potential DEET associated seizures, including 4 deaths. The EPA states: "... it does appear that some cases are likely related to DEET toxicity," but observed that with 30% of the US population using DEET, the likely seizure rate is only about one per 100 million users.
The Pesticide Information Project of Cooperative Extension Offices of Cornell University states that, "Everglades National Park employees having extensive DEET exposure were more likely to have insomnia, mood disturbances and impaired cognitive function than were lesser exposed co-workers".
The EPA states that citronella oil shows little or no toxicity and has been used as a topical insect repellent for 60 years. However, the EPA also states that citronella may irritate skin and cause dermatitis in certain individuals. Canadian regulatory authorities concern with citronella based repellents is primarily based on data-gaps in toxicology, not on incidents.
Within countries of the European Union, implementation of Regulation 98/8/EC, commonly referred to as the Biocidal Products Directive, has severely limited the number and type of insect repellents available to European consumers. Only a small number of active ingredients have been supported by manufacturers in submitting dossiers to the EU Authorities.
In general, only formulations containing DEET, icaridin (sold under the trade name Saltidin and formerly known as Bayrepel or KBR3023), IR3535 and citriodiol (p-menthane-3,8-diol) are available. Most "natural" insect repellents such as citronella, neem oil, and herbal extracts are no longer permitted for sale as insect repellents in the EU due to their lack of effectiveness; this does not preclude them from being sold for other purposes, as long as the label does not indicate they are a biocide (insect repellent). | 1 | Biochemistry |
Shrinking the two-sphere model to the molecular level creates the problem that in the self-exchange reaction the charge can no longer be transferred in arbitrary amounts, but only as a single electron. However, the polarization still is determined by the total ensemble of the solvent molecules and therefore can still be treated classically, i.e. the polarization energy is not subject to quantum limitations. Therefore, the energy of solvent reorganization can be calculated as being due to a hypothetical transfer and back transfer of a partial elementary charge according to the Marcus formula. Thus the reorganization energy for chemical redox reactions, which is a Gibbs free energy, is also a parabolic function of Δe of this hypothetical transfer, For the self exchange reaction, where for symmetry reasons Δe = 0.5, the Gibbs free energy of activation is ΔG(0) = λ/4 (see Fig. 1 and Fig. 2 intersection of the parabolas I and f, f(0), respectively).
Up to now all was physics, now some chemistry enters. The self exchange reaction is a very specific redox reaction, most of the redox reactions are between different partners e.g.
and they have positive (endergonic) or negative (exergonic) Gibbs free energies of reaction .
As Marcus calculations refer exclusively to the electrostatic properties in the solvent (outer sphere) and are independent of one another and therefore can just be added up. This means that the Marcus parabolas in systems with different are shifted just up or down in the vs. diagram (Fig. 2). Variation of can be affected in experiments by offering different acceptors to the same donor.
Simple calculation of the intersection point between the parabolas i and give the Gibbs free energy of activation
where = and = c. The intersection of those parabolas represents an activation energy and not the energy of a transition state of fixed configuration of all nuclei in the system as is the case in the substitution and other reactions mentioned. The transition state of the latter reactions has to meet structural and energetic conditions, redox reactions have only to comply to the energy requirement. Whereas the geometry of the transition state in the other reactions is the same for all pairs of reactants, for redox pairs many polarization environments may meet the energetic conditions.
Marcus' formula shows a quadratic dependence of the Gibbs free energy of activation on the Gibbs free energy of reaction. It is general knowledge from the host of chemical experience that reactions usually are the faster the more negative is . In many cases even a linear free energy relation is found. According to the Marcus formula the rates increase also when the reactions are more exergonic, however only as long as is positive or slightly negative. It is surprising that for redox reactions according to the Marcus formula the activation energy should increase for very exergonic reaction, i.e. in the cases when is negative and its absolute value is greater than that of . This realm of Gibbs free energy of reaction is called "Marcus inverted region". In Fig. 2 it becomes obvious that the intersection of the parabolas i and f moves upwards in the left part of the graph when continues to become more negative, and this means increasing activation energy. Thus the total graph of vs. should have a maximum.
The maximum of the ET rate is expected at Here and (Fig. 2) which means that the electron may jump in the precursor complex at its equilibrium polarization. No thermal activation is necessary: the reaction is barrierless. In the inverted region the polarization corresponds to the difficult-to-imagine notion of a charge distribution where the donor has received and the acceptor given off charge. Of course, in real world this does not happen, it is not a real charge distribution which creates this critical polarization, but the thermal fluctuation in the solvent. This polarization necessary for transfer in the inverted region can be created – with some probability – as well as any other one. The electron is just waiting for it for jumping. | 7 | Physical Chemistry |
The laws of many countries permit IVF for only single individuals, lesbian couples, and persons participating in surrogacy arrangements. | 1 | Biochemistry |
Trace metals are the metals subset of trace elements; that is, metals normally present in small but measurable amounts in animal and plant cells and tissues. Some of these trace metals are a necessary part of nutrition and physiology. Some biometals are trace metals. Ingestion of, or exposure to, excessive quantities can be toxic. However, insufficient plasma or tissue levels of certain trace metals can cause pathology, as is the case with iron.
Trace metals within the human body include iron, lithium, zinc, copper, chromium, nickel, cobalt, vanadium, molybdenum, manganese and others.
Some of the trace metals are needed by living organisms to function properly and are depleted through the expenditure of energy by various metabolic processes of living organisms. They are replenished in animals through diet as well as environmental exposure, and in plants through the uptake of nutrients from the soil in which the plant grows. Human vitamin pills and plant fertilizers can be a source of trace metals.
Trace metals are sometimes referred to as trace elements, although the latter includes minerals and is a broader category. See also Dietary mineral. Trace elements are required by the body for specific functions. Things such as vitamins, sports drinks, fresh fruits and vegetables are sources. Taken in excessive amounts, trace elements can cause problems. For example, fluorine is required for the formation of bones and enamel on teeth. However, when taken in an excessive amount can cause a disease called "Fluorosis', in which bone deformations and yellowing of teeth are seen. Fluorine can occur naturally in some areas in ground water. | 9 | Geochemistry |
Several X-ray crystallographic and electron cryomicroscopic (cryo-EM) structures of IPRs from mouse, rat, and human have defined the overall architecture of the channel. The 1.2 MDa C4-symmetric assembly consists of an ER-embedded transmembrane domain (TMD) in a domain-swapped 6 transmembrane (6TM) cation channel fold that is capped by a large cytosolic domain (CD). In this manner, IPRs share significant homology with the much larger and distantly-related RyRs. The CD contains all known ligand binding sites, including the IP binding site, two Ca binding sites, an adenine nucleotide binding site, and a CH Zn finger fold. A comprehensive Ca-dependent conformational landscape has recently been defined by cryo-EM. | 1 | Biochemistry |
Amides are pervasive in nature and technology. Proteins and important plastics like Nylons, Aramid, Twaron, and Kevlar are polymers whose units are connected by amide groups (polyamides); these linkages are easily formed, confer structural rigidity, and resist hydrolysis. Amides include many other important biological compounds, as well as many drugs like paracetamol, penicillin and LSD. Low-molecular-weight amides, such as dimethylformamide, are common solvents. | 0 | Organic Chemistry |
The total protein concentration is readout by an increase in absorbance at 565 nm, which can then be measured using colorimetric techniques, including using microplate readers. Most common reagents, except thiols and SDS, are compatible with the assay. An optimized formulation for the assay to maximize sensitivity in microplate format was described. | 1 | Biochemistry |
The scattering cross section is related to the meteorological range :
The quantity is sometimes denoted , the scattering coefficient per unit length. | 7 | Physical Chemistry |
In January researchers reported that six choroideremia patients had been treated with adeno-associated virus with a copy of REP1. Over a six-month to two-year period all had improved their sight. By 2016, 32 patients had been treated with positive results and researchers were hopeful the treatment would be long-lasting. Choroideremia is an inherited genetic eye disease with no approved treatment, leading to loss of sight.
In March researchers reported that 12 HIV patients had been treated since 2009 in a trial with a genetically engineered virus with a rare mutation (CCR5 deficiency) known to protect against HIV with promising results.
Clinical trials of gene therapy for sickle cell disease were started in 2014.
In February LentiGlobin BB305, a gene therapy treatment undergoing clinical trials for treatment of beta thalassemia gained FDA "breakthrough" status after several patients were able to forgo the frequent blood transfusions usually required to treat the disease.
In March researchers delivered a recombinant gene encoding a broadly neutralizing antibody into monkeys infected with simian HIV; the monkeys' cells produced the antibody, which cleared them of HIV. The technique is named immunoprophylaxis by gene transfer (IGT). Animal tests for antibodies to ebola, malaria, influenza, and hepatitis were underway.
In March, scientists, including an inventor of CRISPR, Jennifer Doudna, urged a worldwide moratorium on germline gene therapy, writing "scientists should avoid even attempting, in lax jurisdictions, germline genome modification for clinical application in humans" until the full implications "are discussed among scientific and governmental organizations".
In December, scientists of major world academies called for a moratorium on inheritable human genome edits, including those related to CRISPR-Cas9 technologies but that basic research including embryo gene editing should continue. | 1 | Biochemistry |
Twice a year the EBF brings together representatives all member companies to discuss subjects well prepared in advance. The topics range from procedural to regulatory often resulting in internal benchmarking or surveys. Next to these general meetings, topic specific specialists meetings are also organized. All member companies assign one representative to these closed meetings. | 3 | Analytical Chemistry |
Energy expenditure is correlated to a number of factors, listed in alphabetical order.
*Age: Besides the epidemiologically correlated trends of aging, lowered physical activity, and loss of lean muscle mass, lessened cellular activity (the senescence thereof) may also contribute to lowering of REE. | 1 | Biochemistry |
PDE3A is mainly implicated in cardiovascular function and fertility but PDE3B is mainly implicated in lipolysis. Table 1 is an overview of localization of the PDE3 isoforms.
In general, PDE3 can be either cytosolic or membrane-bound and has been associated to plasma membrane, sarcoplasmic reticulum, golgi, and nucleus envelope.
PDE3B is predominantly membrane-associated, and is localized to endoplasmic reticulum and microsomal fractions.
PDE3A can be either membrane-associated or cytosolic, depending on the variant and the cell type it is expressed in. | 1 | Biochemistry |
In 2000, EPA drafted plans to phase out the use of MTBE nationwide over four years. Some states enacted MTBE prohibitions without waiting for federal restrictions. California banned MTBE as a gasoline additive in 2002. The State of New York banned the use of MTBE as a "fuel additive", effective in 2004. However, MTBE is still legal in the state for other industrial uses.
The Energy Policy Act of 2005, as approved by the U.S. House of Representatives, did not include a provision for shielding MTBE manufacturers from water contamination lawsuits. This provision was first proposed in 2003 and had been thought by some to be a priority of Tom DeLay and Rep. Joe Barton, then chairman of the Energy and Commerce Committee. This bill did include a provision that gave MTBE makers, including some major oil companies, $2 billion in transition assistance while MTBE was phased out over the following nine years. Due to opposition in the Senate, the conference report dropped all MTBE provisions. The final bill was signed into law by President George W. Bush. The lack of MTBE liability protection is resulting in a switchover to the use of ethanol as a gasoline additive. | 2 | Environmental Chemistry |
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