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The partial volume of a particular gas in a mixture is the volume of one component of the gas mixture. It is useful in gas mixtures, e.g. air, to focus on one particular gas component, e.g. oxygen.
It can be approximated both from partial pressure and molar fraction:
* V is the partial volume of an individual gas component X in the mixture
* V is the total volume of the gas mixture
* p is the partial pressure of gas X
* p is the total pressure of the gas mixture
* n is the amount of substance of gas X
* n is the total amount of substance in the gas mixture | 7 | Physical Chemistry |
Irisin (fibronectin type III domain-containing protein 5 or FNDC5), a recently described myokine hormone produced and secreted by acutely exercising skeletal muscles, is thought to bind white adipose tissue cells via undetermined receptors. Irisin has been reported to promote a brown adipose tissue-like phenotype upon white adipose tissue by increasing cellular mitochondrial density and expression of uncoupling protein-1, thereby increasing adipose tissue energy expenditure via thermogenesis. This is considered important, because excess visceral adipose tissue in particular distorts the whole body energy homeostasis, increases the risk of cardiovascular disease and raises exposure to a milieu of adipose tissue-secreted hormones (adipokines) that promote inflammation and cellular aging. The authors enquired whether the favorable impact of irisin on white adipose tissue might be associated with maintenance of telomere length, a well-established genetic marker in the aging process. They conclude that these data support the view that irisin may have a role in the modulation not only of energy balance but also the aging process.
However, exogenous irisin may aid in heightening energy expenditure, and thus in reducing obesity. Boström et al. reported on December 14, 2012: "Since the conservation of calories would likely provide an overall survival advantage for mammals, it appears paradoxical that exercise would stimulate the secretion of a polypeptide hormone that increases thermogenesis and energy expenditure. One explanation for the increased irisin expression with exercise in mouse and man may have evolved as a consequence of muscle contraction during shivering. Muscle secretion of a hormone that activates adipose thermogenesis during this process might provide a broader, more robust defense against hypothermia. The therapeutic potential of irisin is obvious. Exogenously administered irisin induces the browning of subcutaneous fat and thermogenesis, and it presumably could be prepared and delivered as an injectable polypeptide. Increased formation of brown or beige/brite fat has been shown to have anti-obesity, anti-diabetic effects in multiple murine models, and adult humans have significant deposits of UCP1-positive brown fat. (Our data show) that even relatively short treatments of obese mice with irisin improves glucose homeostasis and causes a small weight loss. Whether longer treatments with irisin and/or higher doses would cause more weight loss remains to be determined. The worldwide, explosive increase in obesity and diabetes strongly suggests exploring the clinical utility of irisin in these and related disorders. Another potentially important aspect of this work relates to other beneficial effects of exercise, especially in some diseases for which no effective treatments exist. The clinical data linking exercise with health benefits in many other diseases suggests that irisin could also have significant effects in these disorders."
While the murine findings reported by Boström et al. appear encouraging, other researchers have questioned whether irisin operates in a similar manner in humans. For example, Timmons et al. noted that over 1,000 genes are upregulated by exercise and examined how expression of FNDC5 was affected by exercise in ~200 humans. They found that it was upregulated only in highly active elderly humans, casting doubt on the conclusions of Boström et al. Further discussion of this issue can be found in . | 1 | Biochemistry |
The test relies upon a microbial ecosystem with enzymes capable of oxidizing the available organic material. Some waste waters, such as those from biological secondary sewage treatment, will already contain a large population of microorganisms acclimated to the water being tested. An appreciable portion of the waste may be utilized during the holding period prior to commencement of the test procedure. On the other hand, organic wastes from industrial sources may require specialized enzymes. Microbial populations from standard seed sources may take some time to produce those enzymes. A specialized seed culture may be appropriate to reflect conditions of an evolved ecosystem in the receiving waters. | 3 | Analytical Chemistry |
In biology, abiogenesis (from Greek ἀ- a- not + βῐ́ος bios life + γένεσις genesis origin) or the origin of life is the natural process by which life has arisen from non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to living entities on Earth was not a single event, but a process of increasing complexity involving the formation of a habitable planet, the prebiotic synthesis of organic molecules, molecular self-replication, self-assembly, autocatalysis, and the emergence of cell membranes. The transition from non-life to life has never been observed experimentally, but many proposals have been made for different stages of the process.
The study of abiogenesis aims to determine how pre-life chemical reactions gave rise to life under conditions strikingly different from those on Earth today. It primarily uses tools from biology and chemistry, with more recent approaches attempting a synthesis of many sciences. Life functions through the specialized chemistry of carbon and water, and builds largely upon four key families of chemicals: lipids for cell membranes, carbohydrates such as sugars, amino acids for protein metabolism, and nucleic acid DNA and RNA for the mechanisms of heredity. Any successful theory of abiogenesis must explain the origins and interactions of these classes of molecules. Many approaches to abiogenesis investigate how self-replicating molecules, or their components, came into existence. Researchers generally think that current life descends from an RNA world, although other self-replicating molecules may have preceded RNA.
The classic 1952 Miller–Urey experiment demonstrated that most amino acids, the chemical constituents of proteins, can be synthesized from inorganic compounds under conditions intended to replicate those of the early Earth. External sources of energy may have triggered these reactions, including lightning, radiation, atmospheric entries of micro-meteorites and implosion of bubbles in sea and ocean waves. Other approaches ("metabolism-first" hypotheses) focus on understanding how catalysis in chemical systems on the early Earth might have provided the precursor molecules necessary for self-replication.
While the last universal common ancestor (LUCA) is thought to have been quite different from the origin of life, investigations into LUCA can guide research into early universal characteristics. A genomics approach has sought to characterise LUCA of modern organisms by identifying the genes shared by Archaea and Bacteria, members of the two major branches of life (where the Eukaryotes belong to the archaean branch in the two-domain system). 355 genes appear to be common to all life; their nature implies that the LUCA was anaerobic with the Wood–Ljungdahl pathway, deriving energy by chemiosmosis, and maintaining its hereditary material with DNA, the genetic code, and ribosomes. Although the LUCA lived over 4 billion years ago (4 Gya), researchers do not believe it was the first form of life. Earlier cells might have had a leaky membrane and been powered by a naturally occurring proton gradient near a deep-sea white smoker hydrothermal vent.
Earth remains the only place in the universe known to harbor life. Geochemical and fossil evidence from the Earth informs most studies of abiogenesis. The Earth was formed at 4.54 Gya, and the earliest evidence of life on Earth dates from at least 3.8 Gya from Western Australia. Fossil micro-organisms appear to have lived within hydrothermal vent precipitates dated 3.77 to 4.28 Gya from Quebec, soon after ocean formation 4.4 Gya during the Hadean. | 9 | Geochemistry |
M. acetivorans has been noted for its ability to metabolize carbon monoxide to form acetate and formate. It can also oxidize carbon monoxide into carbon dioxide. The carbon dioxide can then be converted into methane in a process which M. acetivorans uses to conserve energy. It has been suggested that this pathway may be similar to metabolic pathways used by primitive cells.
However, in the presence of minerals containing iron sulfides, as might have been found in sediments in a primordial environment, acetate would be catalytically converted into acetate thioester, a sulfur-containing derivative. Primitive microbes could obtain biochemical energy in the form of adenosine triphosphate (ATP) by converting acetate thioester back into acetate using PTS and ACK, which would then be converted back into acetate thioester to complete the process. In such an environment, a primitive "protocell" could easily produce energy through this metabolic pathway, excreting acetate as waste. Furthermore, ACK catalyzes the synthesis of ATP directly. Other pathways generate energy from ATP only through complex multi-enzyme reactions involving protein pumps and osmotic imbalances across a membrane. | 1 | Biochemistry |
There is much debate to whether transcription factories assemble because of the transcriptional demands of the genome or if they are stable structures that are conserved over time. Experimentally, it appears that they remain fixed over a short period of time; newly made mRNA were pulse labelled over 15 minutes and it showed no new transcription factories appearing. This is also supported by inhibition experiments. In these studies heat shock was used to turn off transcription which resulted in no change in the number of polymerases detected. Upon further analysis of western blot data it was suggested that there was in fact a slight decrease over time of transcription factories. Therefore, it could be claimed that polymerase molecules are released gently over time from the factory when there is a lack of transcription which would eventually lead to the complete loss of the transcription factory.
There is also several pieces of evidence that promotes the idea of transcription factories assembling de novo due to transcriptional demands. GFP polymerase fluorescence experiments have shown that the inducement of transcription in Drosophila polytene nuclei leads to the formation of a factory which contradicts the notion of a stable and secure structure. | 1 | Biochemistry |
The class IA phospholipid kinase, PI-3 kinase, is activated by the majority of RTKs. Similarly to other SH2 domain-containing proteins, PI-3 kinase forms a complex with PY sites on activated receptors. The main function of PI3K activation is the generation of PIP3, which functions as a second messenger to activate downstream tyrosine kinases Btk and Itk, the Ser/Thr kinases PDK1 and Akt (PKB). The major biological functions of Akt activation can be classified into three categories – survival, proliferation and cell growth. Akt is also known to be implicated in several cancers, particularly breast. PLCγ is immediately recruited by an activated RTK through the binding of its SH2 domains to phosphotyrosine sites of the receptor. After activation, PLCγ hydrolyses its substrate PtdIns(4,5)P2 and forms two second messengers, diacylglycerol and Ins(1,4,5)P3. Ins(1,4,5)P3 stimulates the release of Ca 2+ from intracellular supplies. Ca 2+ then binds to calmodulin, which subsequently activates a family of calmodulindependent protein kinases (CamKs). In addition, both diacylglycerol and Ca 2+ activate members of the PKC family. The second messengers generated by PtdIns(4,5)P2 hydrolysis stimulate a variety of intracellular processes such as proliferation, angiogenesis, cell motility. | 1 | Biochemistry |
The influence of thermal phonons and their interaction with electronic structure is a topic that was appropriately introduced in a discussion of the resistance of liquid metals. Lindemann's theory of melting is referenced, and it is suggested that the drop in conductivity in going from the crystalline to the liquid state is due to the increased scattering of conduction electrons as a result of the increased amplitude of atomic vibration. Such theories of localization have been applied to transport in metallic glasses, where the mean free path of the electrons is very small (on the order of the interatomic spacing).
The formation of a non-crystalline form of a gold-silicon alloy by the method of splat quenching from the melt led to further considerations of the influence of electronic structure on glass forming ability, based on the properties of the metallic bond.
Other work indicates that the mobility of localized electrons is enhanced by the presence of dynamic phonon modes. One claim against such a model is that if chemical bonds are important, the nearly free electron models should not be applicable. However, if the model includes the buildup of a charge distribution between all pairs of atoms just like a chemical bond (e.g., silicon, when a band is just filled with electrons) then it should apply to solids.
Thus, if the electrical conductivity is low, the mean free path of the electrons is very short. The electrons will only be sensitive to the short-range order in the glass since they do not get a chance to scatter from atoms spaced at large distances. Since the short-range order is similar in glasses and crystals, the electronic energies should be similar in these two states. For alloys with lower resistivity and longer electronic mean free paths, the electrons could begin to sense that there is disorder in the glass, and this would raise their energies and destabilize the glass with respect to crystallization. Thus, the glass formation tendencies of certain alloys may therefore be due in part to the fact that the electron mean free paths are very short, so that only the short-range order is ever important for the energy of the electrons.
It has also been argued that glass formation in metallic systems is related to the "softness" of the interaction potential between unlike atoms. Some authors, emphasizing the strong similarities between the local structure of the glass and the corresponding crystal, suggest that chemical bonding helps to stabilize the amorphous structure.
Other authors have suggested that the electronic structure yields its influence on glass formation through the directional properties of bonds. Non-crystallinity is thus favored in elements with a large number of polymorphic forms and a high degree of bonding anisotropy. Crystallization becomes more unlikely as bonding anisotropy is increased from isotropic metallic to anisotropic metallic to covalent bonding, thus suggesting a relationship between the group number in the periodic table and the glass forming ability in elemental solids. | 7 | Physical Chemistry |
Protein folding in a cell is a highly complex process that involves transport of the newly synthesized proteins to appropriate cellular compartments through targeting, permanent misfolding, temporarily unfolded states, post-translational modifications, quality control, and formation of protein complexes facilitated by chaperones.
Some proteins need the assistance of chaperone proteins to fold properly. It has been suggested that this disproves Anfinsen's dogma. However, the chaperones do not appear to affect the final state of the protein; they seem to work primarily by preventing aggregation of several protein molecules prior to the final folded state of the protein. However, at least some chaperones are required for the proper folding of their subject proteins.
Many proteins can also undergo aggregation and misfolding. For example, prions are stable conformations of proteins which differ from the native folding state. In bovine spongiform encephalopathy, native proteins re-fold into a different stable conformation, which causes fatal amyloid buildup. Other amyloid diseases, including Alzheimers disease and Parkinsons disease, are also exceptions to Anfinsen's dogma.
Some proteins have multiple native structures, and change their fold based on some external factors. For example, the KaiB protein complex switches fold throughout the day, acting as a clock for cyanobacteria. It has been estimated that around 0.5–4% of PDB proteins switch folds. The switching between alternative structures is driven by interactions of the protein with small ligands or other proteins, by chemical modifications (such as phosphorylation) or by changed environmental conditions, such as temperature, pH or membrane potential. Each alternative structure may either correspond to the global minimum of free energy of the protein at the given conditions or be kinetically trapped in a higher local minimum of free energy. | 1 | Biochemistry |
Finally, the potential at the center of each side is a natural function of the variables at the corner of that side. So, is a natural function of and , and is a natural function of and . | 7 | Physical Chemistry |
Some species release a volatile substance when attacked by a predator that can trigger flight (in aphids) or aggression (in ants, bees, termites, and wasps) in members of the same species. For example, Vespula squamosa use alarm pheromones to alert others to a threat. In Polistes exclamans, alarm pheromones are also used as an alert to incoming predators. Pheromones also exist in plants: Certain plants emit alarm pheromones when grazed upon, resulting in tannin production in neighboring plants. These tannins make the plants less appetizing to herbivores.
An alarm pheromone has been documented in a mammalian species. Alarmed pronghorn, Antilocapra americana flair their white rump hair and exposes two highly odoriferous glands that releases a compound described having the odor "reminiscent of buttered popcorn". This sends a message to other pronghorns by both sight and smell about a present danger. This scent has been observed by humans 20 to 30 meters downwind from alarmed animals. The major odour compound identified from this gland is 2-pyrrolidinone. | 1 | Biochemistry |
To determine saponification value, the sample is treated with an excess of alkali (usually an ethanolic solution of potassium hydroxide) for half an hour under reflux. The KOH is consumed by reaction with triglycerides, which consume three equivalents of base. Diglycerides consume two equivalents of KOH. Monoglycerides and free fatty acids, as well as by other esters such as lactones consume one equivalent of base At the end of the reaction the quantity of KOH is determined by titration using standard solution of hydrochloric acid (HCl). Key to the method is the use of phenolphthalein indicator, which indicates the consumption of strong base (KOH) by the acid, not the weak base (potassium carboxylates). The SV (mg KOH/ g of sample) is calculated as following:
:where:
: is the volume of HCl solution used for the blank run, in mL;
: is the volume of HCl solution used for the tested sample, in mL;
: is the molarity of HCl solution, in mol / L;
: is the molecular weight of KOH, in g / mol;
: is the weight of sample, in g.
For example, standard methods for determination of SV of vegetable and animal fats are as follows:
The SV can also be calculated from the fatty acid composition as determined by gas chromatography (AOCS Cd 3a-94).
Handmade soap makers who aim for bar soap use sodium hydroxide (NaOH), commonly known as lye, rather than KOH (caustic potash) which produces soft paste, gel or liquid soaps. In order to calculate the lye amount needed to make bar soap, KOH values of SV can be converted to NaOH values by dividing KOH values by the ratio of the molecular weights of KOH and NaOH (1.403). | 3 | Analytical Chemistry |
Burning glasses are known to date back to about 700 BC. One of the first accurately mentions of burning glasses appears in Aristophaness comedy, The Clouds, written in 423 BC. According to the Archimedes heat ray anecdote, Archimedes is purported to have developed mirrors to concentrate heat rays in order to burn attacking Roman ships during the Siege of Syracuse ( 213–212 BC), but no sources from the time have been confirmed. Catoptrics is a book attributed to Euclid on how to focus light in order to produce heat, but the book might have been written in 300 AD. | 7 | Physical Chemistry |
The only dose-effect relationship available are those of miners cohorts (for much higher exposures), exposed to radon. Studies of Hiroshima and Nagasaki survivors are less informative (the exposure to radon is chronic, localized, and the ionizing radiations are alpha rays).
Although low-exposed miners experienced exposures comparable to long-term residence in high-radon dwellings, the mean cumulative exposure among miners is approximately 30-fold higher than that associated with long-term residency in a typical home. Moreover, the smoking is a significant confounding factor in all miners' studies. It can be concluded from miner studies that when the radon exposure in dwellings compares to that in mines (above 1000 Bq/m), radon is a proven health hazard; but in the 1980s very little was known on the dose-effect relationship, both theoretically and statistical.
Studies have been made since the 1980s, both on epidemiological studies and in the radiobiology field.
In the radiobiology and carcinogenesis studies, progress has been made in understanding the first steps of cancer development, but not to the point of validating a reference dose-effect model. The only certainty gained is that the process is very complex, the resulting dose-effect response being complex, and most probably not a linear one.
Biologically based models have also been proposed that could project substantially reduced carcinogenicity at low doses.
In the epidemiological field, no definite conclusion has been reached. However, from the evidence now available, a threshold exposure, that is, a level of exposure below which there is no effect of radon, cannot be excluded.
Given the radon distribution observed in dwellings, and the dose-effect relationship proposed by a given model, a theoretical number of victims can be calculated, and serve as a basis for public health policies.
With the BEIR VI model, the main health effect (nearly 75% of the death toll) is to be found at low radon concentration exposures, because most of the population (about 90%) lives in the 0–200 Bq/m range. Under this modeling, the best policy is obviously to reduce the radon levels of all homes where the radon level is above average, because this leads to a significant decrease of radon exposure on a significant fraction of the population; but this effect is predicted in the 0–200 Bq/m range, where the linear model has its maximum uncertainty. From the statistical evidence available, a threshold exposure cannot be excluded; if such a threshold exists, the real radon health effect would in fact be limited to those homes where the radon concentrations reaches that observed in mines—at most a few percent. If a radiation hormesis effect exists after all, the situation would be even worse: under that hypothesis, suppressing the natural low exposure to radon (in the 0–200 Bq/m range) would actually lead to an increase of cancer incidence, due to the suppression of this (hypothetical) protecting effect. As the low-dose response is unclear, the choice of a model is very controversial.
No conclusive statistics being available for the levels of exposure usually found in homes, the risks posed by domestic exposures is usually estimated on the basis of observed lung-cancer deaths caused by higher exposures in mines, under the assumption that the risk of developing lung-cancer increases linearly as the exposure increases. This was the basis for the model proposed by BEIR IV in the 1980s. The linear no-threshold model has since been kept in a conservative approach by the UNSCEAR report and the BEIR VI and BEIR VII publications, essentially for lack of a better choice: | 2 | Environmental Chemistry |
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl group (e.g., alkyl, alkenyl, aryl), or hydrogen, or other groups. Carboxylic acids occur widely. Important examples include the amino acids and fatty acids. Deprotonation of a carboxylic acid gives a carboxylate anion. | 0 | Organic Chemistry |
Unlike most other commodity plastics polyethylene terephthalate (PET) is able to absorb the near ultraviolet rays in sunlight. Absorption begins at 360 nm, becoming stronger below 320 nm and is very significant below 300 nm. Despite this PET has better resistance to photo-oxidation than other commodity plastics, this is due to a poor quantum yield or the absorption. The degradation chemistry is complicated due to simultaneous photodissociation (i.e. not involving oxygen) and photo-oxidation reactions of both the aromatic and aliphatic parts of the molecule. Chain scission is the dominant process, with chain branching and the formation of coloured impurities being less common. Carbon monoxide, carbon dioxide, and carboxylic acids are the main products.
The photo-oxidation of other linear polyesters such as polybutylene terephthalate and polyethylene naphthalate proceeds similarly.
Photodissociation involves the formation of an excited terephthalic acid unit which undergoes Norrish reactions. The type I reaction dominates, which cause chain scission at the carbonyl unit to give a range of products.
Type II Norrish reactions are less common but give rise to acetaldehyde by way of vinyl alcohol esters. This has an exceedingly low odour and taste threshold and can cause an off-taste in bottled water.
Radicals formed by photolysis may initiate the photo-oxidation in PET. Photo-oxidation of the aromatic terephthalic acid core results in its step-wise oxidation to 2,5-dihydroxyterephthalic acid. The photo-oxidation process at aliphatic sites is similar to that seen for polyolefins, with the formation of hydroperoxide species eventually leading to beta-scission of the polymer chain. | 5 | Photochemistry |
Targeted drug delivery is one of many ways researchers seek to improve drug delivery systems' overall efficacy, safety, and delivery. Within this medical field is a special reversal form of drug delivery called chemotactic drug targeting. By using chemical agents to help guide a drug carrier to a specific location within the body, this innovative approach seeks to improve precision and control during the drug delivery process, decrease the risk of toxicity, and potentially lower the required medical dosage needed. The general components of the conjugates are designed as follows: (i) carrier – regularly possessing promoter effect also on internalization into the cell; (ii) chemotactically active ligands acting on the target cells; (iii) drug to be delivered in a selective way and (iv) spacer sequence which joins drug molecule to the carrier and due to it enzyme labile moiety makes possible the intracellular compartment specific release of the drug. Careful selection of chemotactic component of the ligand not only the chemoattractant character could be expended, however, chemorepellent ligands are also valuable as they are useful to keep away cell populations degrading the conjugate containing the drug. In a larger sense, chemotactic drug-targeting has the potential to improve cancer, inflammation, and arthritis treatment by taking advantage of the difference in environment between the target site and its surroundings. Therefore, this Wikipedia article aims to provide a brief overview of chemotactic drug targeting, the principles behind the approach, possible limitations and advantages, and its application to cancer and inflammation. | 1 | Biochemistry |
Sodium peroxide is added to the compound to oxidise phosphorus to sodium phosphate. It is boiled with concentrated HNO and then ammonium molybdate is added. A yellow precipitate (ammonium phosphomolybdate) indicates the presence of phosphorus.
</blockquote>
</blockquote> | 3 | Analytical Chemistry |
Stevens is the author or co-author of over 70 scientific publications and books. These include:
* Carly Stevens, The impact of atmospheric nitrogen deposition on grasslands: species composition and biogeochemistry, VDM Verlag, 2009. ISBN 978-3639144147
* Carly J Stevens, Nancy B Dise, J Owen Mountford, David J Gowing (2004) Impact of nitrogen deposition on the species richness of grasslands. Science 303 1876-1879 | 9 | Geochemistry |
Science fiction has used cloning, most commonly and specifically human cloning, to raise the controversial questions of identity. A Number is a 2002 play by English playwright Caryl Churchill which addresses the subject of human cloning and identity, especially nature and nurture. The story, set in the near future, is structured around the conflict between a father (Salter) and his sons (Bernard 1, Bernard 2, and Michael Black) – two of whom are clones of the first one. A Number was adapted by Caryl Churchill for television, in a co-production between the BBC and HBO Films.
In 2012, a Japanese television series named "Bunshin" was created. The storys main character, Mariko, is a woman studying child welfare in Hokkaido. She grew up always doubtful about the love from her mother, who looked nothing like her and who died nine years before. One day, she finds some of her mothers belongings at a relative's house, and heads to Tokyo to seek out the truth behind her birth. She later discovered that she was a clone.
In the 2013 television series Orphan Black, cloning is used as a scientific study on the behavioral adaptation of the clones. In a similar vein, the book The Double by Nobel Prize winner José Saramago explores the emotional experience of a man who discovers that he is a clone. | 1 | Biochemistry |
The rate of living theory postulates that the faster an organism’s metabolism, the shorter its lifespan. First proposed by Max Rubner in 1908, the theory was based on his observation that smaller animals had faster metabolisms and shorter lifespans compared to larger animals with slower metabolisms. The theory gained further credibility through the work of Raymond Pearl, who conducted experiments on drosophila and cantaloupe seeds, which supported Rubners initial observation. Pearls findings were later published in his book, The Rate of Living, in 1928, in which he expounded upon Rubner's theory and demonstrated a causal relationship between the slowing of metabolism and an increase in lifespan.
The theory gained additional credibility with the discovery of Max Kleibers law in 1932. Kleiber found that an organisms basal metabolic rate could be predicted by taking 3/4 the power of the organism's body weight. This finding was noteworthy because the inversion of the scaling exponent, between 0.2 and 0.33, also demonstrated the scaling for both lifespan and metabolic rate, and was colloquially called the "mouse-to-elephant" curve. | 1 | Biochemistry |
Dry polymer electrolytes – differ from liquid and gel electrolytes in the sense that salt is dissolved directly into the solid medium. Usually it is a relatively high dielectric constant polymer (PEO, PMMA, PAN, polyphosphazenes, siloxanes, etc.) and a salt with low lattice energy. In order to increase the mechanical strength and conductivity of such electrolytes, very often composites are used, and inert ceramic phase is introduced. There are two major classes of such electrolytes: polymer-in-ceramic, and ceramic-in-polymer. | 7 | Physical Chemistry |
Ethanol contained in alcoholic beverages is produced by means of fermentation induced by yeast.
* Wine is produced by fermentation of the natural sugars present in grapes; cider and perry are produced by similar fermentation of natural sugar in apples and pears, respectively; and other fruit wines are produced from the fermentation of the sugars in any other kinds of fruit. Brandy and eaux de vie (e.g. slivovitz) are produced by distillation of these fruit-fermented beverages.
* Mead is produced by fermentation of the natural sugars present in honey.
* Beer, whiskey, and sometimes vodka are produced by fermentation of grain starches that have been converted to sugar by the enzyme amylase, which is present in grain kernels that have been malted (i.e. germinated). Other sources of starch (e.g. potatoes and unmalted grain) may be added to the mixture, as the amylase will act on those starches as well. It may also be amylase-induce fermented with saliva in a few countries. Whiskey and vodka are also distilled; gin and related beverages are produced by the addition of flavoring agents to a vodka-like feedstock during distillation.
* Rice wines (including sake) are produced by the fermentation of grain starches converted to sugar by the mold Aspergillus oryzae. Baijiu, soju, and shōchū are distilled from the product of such fermentation.
* Rum and some other beverages are produced by fermentation and distillation of sugarcane. Rum is usually produced from the sugarcane product molasses.
In all cases, fermentation must take place in a vessel that allows carbon dioxide to escape but prevents outside air from coming in. This is to reduce risk of contamination of the brew by unwanted bacteria or mold and because a buildup of carbon dioxide creates a risk the vessel will rupture or fail, possibly causing injury or property damage. | 1 | Biochemistry |
Finally, biology is not the sole domain of MAs. The fields of supramolecular chemistry and nanotechnology each have areas that have developed to elaborate and extend the principles first demonstrated in biologic MAs. Of particular interest in these areas has been elaborating the fundamental processes of molecular machines, and extending known machine designs to new types and processes. | 1 | Biochemistry |
In type III reactions, there is an electron transfer that occurs between the Sens* and the substrate resulting in an anionic Sens and a cationic substrate. Another electron transfer then occurs where the anionic Sens transfers an electron to O to form the superoxide anion, O. This transfer returns the Sens to its ground state. The superoxide anion and cationic substrate then interact to form the oxygenated product. | 5 | Photochemistry |
For mutually insoluble compounds, Dalton's law states that the partial pressure of a non aqueous phase liquid (NAPL) is equal to its vapor pressure, and that the NAPL in contact with water will boil when the vapor pressure of water plus the vapor pressure of the VOC is equal to ambient pressure. When a VOC-steam bubble is formed the composition of the bubble is proportional to the composite’s respective vapor pressures. | 2 | Environmental Chemistry |
Baloola was born on April 14, 1981, in Abu Dhabi, United Arab Emirates.
Baloola received a Bachelor of Science in biomedical engineering from Ajman University of Science and Technology in September 2009. Then he joined Ajman University as a teaching assistant in the Faculty of Engineering. He won many awards during his studies and after graduating. | 7 | Physical Chemistry |
While the mechanism by which survivin may regulate cell mitosis and cytokinesis is not known, the observations made on its localization during mitosis suggests strongly that it is involved in some way in the cytokinetic process.
Proliferating Daoy cells were placed on a glass coverslip, fixed and stained with fluorescent antibodies for survivin and alpha-tubulin. Immunoflourescence using confocal microscopy was used to look at the localization of survivin and tubulin during the cell-cycle to look for any patterns of survivin expression. Survivin was absent in interphase, but present in the G2-M phase.
During the different stages of mitosis, one could see that survivin follows a certain localization pattern. At prophase and metaphase, survivin is mainly nuclear in location. During prophase, as the chromatin condenses so that it is visible under the microscope, survivin starts to move to the centromeres. At prometaphase when the nuclear membrane dissociates and spindle microtubules cross over the nuclear region, survivin stays put at the centromeres. At metaphase, when the chromosomes align at the middle plate and are pulled with high tension to either pole by the kinetochore attachments, survivin then associates with the kinetochores. At anaphase as separation of the chromatids happens, the kinetochore microtubules shorten as the chromosomes move towards to the spindle poles and survivin also moves along to the midplate. Survivin thus accumulates at the midplate at telophase. Finally, survivin localizes to the midbody at the cleavage furrow. | 1 | Biochemistry |
Diarrhea is more common and sometimes more severe with flutamide than with other NSAAs. In a comparative trial of combined androgen blockade for prostate cancer, the rate of diarrhea was 26% for flutamide and 12% for bicalutamide. Moreover, 6% of flutamide-treated patients discontinued the medication due to diarrhea, whereas only 0.5% of bicalutamide-treated patients did so. In the case of antiandrogen monotherapy for prostate cancer, the rates of diarrhea are 5 to 20% for flutamide, 2 to 5% for bicalutamide, and 2 to 4% for nilutamide. In contrast to diarrhea, the rates of nausea and vomiting are similar among the three medications. | 4 | Stereochemistry |
Investigation on dinoflagellate cyst in the Mediterranean Sea has identified warm and cold temperate dinocyst species and these species have been used to reconstruct the paleoclimate changes during the past 30,000 years. | 9 | Geochemistry |
The primary cause of change in the composition of a magma is cooling, which is an inevitable consequence of the magma being formed and migrating from the site of partial melting into an area of lower stress - generally a cooler volume of the crust.
Cooling causes the magma to begin to crystallize minerals from the melt or liquid portion of the magma. Most magmas are a mixture of liquid rock (melt) and crystalline minerals (phenocrysts).
Contamination is another cause of magma differentiation. Contamination can be caused by assimilation of wall rocks, mixing of two or more magmas or even by replenishment of the magma chamber with fresh, hot magma.
The whole gamut of mechanisms for differentiation has been referred to as the FARM process, which stands for fractional crystallization, assimilation, replenishment and magma mixing. | 9 | Geochemistry |
A general d-orbital splitting diagram for square planar (D) transition metal complexes can be derived from the general octahedral (O) splitting diagram, in which the d−y, d and d orbitals. When the two axial ligands are removed to generate a square planar geometry, the d, d and d orbitals because of the torus shaped lobe of the d, d and d orbitals are generally presented as degenerate but they have to split into two different energy levels with respect to the irreducible representations of the point group D. Their relative ordering depends on the nature of the particular complex. Furthermore, the splitting of d-orbitals is perturbed by π-donating ligands in contrast to octahedral complexes. In the square planar case strongly π-donating ligands can cause the d and d orbitals to be higher in energy than the d</sub> orbital, whereas in the octahedral case π-donating ligands only affect the magnitude of the d-orbital splitting and the relative ordering of the orbitals is conserved. | 4 | Stereochemistry |
The completed assembly of the holoenzyme with transcription factors and RNA polymerase II bound to the promoter forms the eukaryotic transcription initiation complex. Transcription in the archaea domain is similar to transcription in eukaryotes.
Transcription begins with matching of NTPs to the first and second in the DNA sequence. This, like most of the remainder of transcription, is an energy-dependent process, consuming adenosine triphosphate (ATP) or other NTP. | 1 | Biochemistry |
Studies of ephaptic coupling have also focused on its role in the synchronization and timing of action potentials in neurons. In the simpler case of adjacent fibers that experience simultaneous stimulation the impulse is slowed because both fibers are limited to exchange ions solely with the interstitial fluid (increasing the resistance of the nerve). Slightly offset impulses (conduction velocities differing by less than 10%) are able to exchange ions constructively and the action potentials propagate slightly out of phase at the same velocity.
More recent research, however, has focused on the more general case of electric fields that affect a variety of neurons. It has been observed that local field potentials in cortical neurons can serve to synchronize neuronal activity. Although the mechanism is unknown, it is hypothesized that neurons are ephaptically coupled to the frequencies of the local field potential. This coupling may effectively synchronize neurons into periods of enhanced excitability (or depression) and allow for specific patterns of action potential timing (often referred to as spike timing). This effect has been demonstrated and modeled in a variety of cases.
A hypothesis or explanation behind the mechanism is "one-way", "master-slave", or "unidirectional synchronization" effect as mathematical and fundamental property of non-linear dynamic systems (oscillators like neurons) to synchronize under certain criteria. Such phenomenon was proposed and predicted to be possible between two HR neurons, since 2010 in simulations and modeling work by Hrg. It was also shown that such unidirectional synchronization or copy/paste transfer of neural dynamics from master to slave neurons, could be exhibited in different ways. Hence the phenomenon is of not only fundamental interest but also applied one from treating epilepsy to novel learning systems. A study in July 2023 found that mathematical models of ephaptic coupling predicted in vivo data of neural activity. The authors likened the electric field to a conductor of an orchestra and neurons to the musicians. Then the field,like the conductor, listens to the music and guides the musicians accordingly. In an opinion paper, they also suggested that not only neurons but other parts of the cytoskeleton generate electromagnetic fields that influence individual neurons, and called this cytoelectric coupling. Synchronization of neurons is in principle unwanted behavior, as brain would have zero information or be simply a bulb if all neurons would synchronize. Hence it is a hypothesis that neurobiology and evolution of brain coped with ways of preventing such synchronous behavior on large scale, using it rather in other special cases.
As models of brain function using only neuronal and gap junction connections fail to explain its complexity, ephaptic coupling is being added more to the equation to try and explain the isopotentiality of cortical astrocytes to maintain the bioelectromagnetic crosstalk between neurons and astrocytes in the neocortex. | 1 | Biochemistry |
Plasma transferred wire arc (PTWA) is another form of wire arc spray which deposits a coating on the internal surface of a cylinder, or on the external surface of a part of any geometry. It is predominantly known for its use in coating the cylinder bores of an engine, enabling the use of Aluminum engine blocks without the need for heavy cast iron sleeves. A single conductive wire is used as "feedstock" for the system. A supersonic plasma jet melts the wire, atomizes it and propels it onto the substrate. The plasma jet is formed by a transferred arc between a non-consumable cathode and the type of a wire. After atomization, forced air transports the stream of molten droplets onto the bore wall. The particles flatten when they impinge on the surface of the substrate, due to the high kinetic energy. The particles rapidly solidify upon contact. The stacked particles make up a high wear resistant coating. The PTWA thermal spray process utilizes a single wire as the feedstock material. All conductive wires up to and including 0.0625" (1.6mm) can be used as feedstock material, including "cored" wires. PTWA can be used to apply a coating to the wear surface of engine or transmission components to replace a bushing or bearing. For example, using PTWA to coat the bearing surface of a connecting rod offers a number of benefits including reductions in weight, cost, friction potential, and stress in the connecting rod. | 8 | Metallurgy |
The existence of nonradioactive isotopes of lighter elements had been suspected in studies of neon as early as 1913, and proven by mass spectrometry of light elements in 1920. At that time the neutron had not yet been discovered, and the prevailing theory was that isotopes of an element differ by the existence of additional protons in the nucleus accompanied by an equal number of nuclear electrons. In this theory, the deuterium nucleus with mass two and charge one would contain two protons and one nuclear electron. However, it was expected that the element hydrogen with a measured average atomic mass very close to , the known mass of the proton, always has a nucleus composed of a single proton (a known particle), and could not contain a second proton. Thus, hydrogen was thought to have no heavy isotopes. | 9 | Geochemistry |
Waste of the by-product heat is reduced if a cogeneration system is used, also known as a Combined Heat and Power (CHP) system. Limitations to the use of by-product heat arise primarily from the engineering cost/efficiency challenges in effectively exploiting small temperature differences to generate other forms of energy. Applications utilizing waste heat include swimming pool heating and paper mills. In some cases, cooling can also be produced by the use of absorption refrigerators for example, in this case it's called trigeneration or CCHP (combined cooling, heat and power). | 7 | Physical Chemistry |
In the S-matrix formulation of particle physics, which was pioneered by John Archibald Wheeler among others, all physical processes are modeled according to the following paradigm.
One begins with a non-interacting multiparticle state in the distant past. Non-interacting does not mean that all of the forces have been turned off, in which case for example protons would fall apart, but rather that there exists an interaction-free Hamiltonian H, for which the bound states have the same energy level spectrum as the actual Hamiltonian . This initial state is referred to as the in state. Intuitively, it consists of elementary particles or bound states that are sufficiently well separated that their interactions with each other are ignored.
The idea is that whatever physical process one is trying to study may be modeled as a scattering process of these well separated bound states. This process is described by the full Hamiltonian , but once its over, all of the new elementary particles and new bound states separate again and one finds a new noninteracting state called the out state'. The S-matrix is more symmetric under relativity than the Hamiltonian, because it does not require a choice of time slices to define.
This paradigm allows one to calculate the probabilities of all of the processes that we have observed in 70 years of particle collider experiments with remarkable accuracy. But many interesting physical phenomena do not obviously fit into this paradigm. For example, if one wishes to consider the dynamics inside of a neutron star sometimes one wants to know more than what it will finally decay into. In other words, one may be interested in measurements that are not in the asymptotic future. Sometimes an asymptotic past or future is not even available. For example, it is very possible that there is no past before the Big Bang.
In the 1960s, the S-matrix paradigm was elevated by many physicists to a fundamental law of nature. In S-matrix theory, it was stated that any quantity that one could measure should be found in the S-matrix for some process. This idea was inspired by the physical interpretation that S-matrix techniques could give to Feynman diagrams restricted to the mass-shell, and led to the construction of dual resonance models. But it was very controversial, because it denied the validity of quantum field theory based on local fields and Hamiltonians. | 7 | Physical Chemistry |
Centrifugal partition chromatography has been extensively used for isolation and purification of natural products for 40 years. Due to the ability to get very high selectivity, and the ability to tolerate samples containing particulated matter, it is possible to work with direct extracts of biomass, opposed to traditional liquid chromatography, where impurities degrade the solid stationary phase so that separation become impossible.
There are numerous laboratory scale centrifugal partition chromatography manufacturers around the world, like Gilson (Armen Instrument), Kromaton (Rousselet Robatel), and AECS-QUIKPREP. These instruments operate at flow rates of 1–500 mL/min. with stationary phase retentions of 40–80%. | 3 | Analytical Chemistry |
The source for APCI is similar to ESI except that ions are formed by the interaction of the heated analyte solvent with a corona discharge needle set at a high electrical potential. Primary ions are formed immediately surrounding the needle, and these interact with the solvent to form secondary ions that ultimately ionize the sample. APCI is particularly useful for the analysis of nonpolar lipids such as triacylglycerols, sterols, and fatty acid esters. | 1 | Biochemistry |
Reversible solid oxide cells are receiving increased attention as energy storage solutions for the weekly or the monthly scale. Other technologies for large scale electrical storage such as pumped-storage hydroelectricity and compressed air energy storage are characterized by geographical limitations. On the other hand, Li-ion batteries suffer from limited discharge capabilities. In this regard, hydrogen storage is a promising alternative, since the produced fuel can be compressed and stored for months. Among all hydrogen technologies, rSOCs are definitely the best candidates for producing and converting back hydrogen into electricity. Due to their high operating temperature, they are characterized by higher efficiency, compared to technologies like PEM fuel cells or PEM electrolyzers. Moreover, the possibility to operate both the fuel oxidation and the electrolysis on the same device is beneficial on the capacity factor of the system, helping at reducing its specific investment cost. | 7 | Physical Chemistry |
Due to its regulatory role in the cell cycle, targeting the DREAM complex might enhance anticancer treatments such as imatinib. | 1 | Biochemistry |
While most failures in practice have been through fast failure, there is experimental evidence that hydrogen also affects the fatigue properties of steels. This is entirely expected given the nature of the embrittlement mechanisms proposed for fast fracture. In general hydrogen embrittlement has a strong effect on high-stress, low-cycle fatigue and very little effect on high-cycle fatigue. | 7 | Physical Chemistry |
Virtual karyotyping is another cost-effective, clinically available alternative to FISH panels using thousands to millions of probes on a single array to detect copy number changes, genome-wide, at unprecedented resolution. Currently, this type of analysis will only detect gains and losses of chromosomal material and will not detect balanced rearrangements, such as translocations and inversions which are hallmark aberrations seen in many types of leukemia and lymphoma. | 1 | Biochemistry |
The process efficiency of sensor-based ore sorting is described in detail by C. Robben in 2014. The total process efficiency is subdivided into the following sub-process efficiencies; Platform efficiency, preparation efficiency, presentation efficiency, detection efficiency and separation efficiency. All the sub-process contribute to the total process efficiency, of course in combination with the liberation characteristics of the bulk material that the technology is applied to. The detailed description of the sib-processes and their contribution to the total process efficiency can be found in the literature. | 3 | Analytical Chemistry |
For the deprotonation of acids, K is known as K, the acid dissociation constant. Strong acids, such as sulfuric or phosphoric acid, have large dissociation constants; weak acids, such as acetic acid, have small dissociation constants.
The symbol K, used for the acid dissociation constant, can lead to confusion with the association constant, and it may be necessary to see the reaction or the equilibrium expression to know which is meant.
Acid dissociation constants are sometimes expressed by pK, which is defined by
This notation is seen in other contexts as well; it is mainly used for covalent dissociations (i.e., reactions in which chemical bonds are made or broken) since such dissociation constants can vary greatly.
A molecule can have several acid dissociation constants. In this regard, that is depending on the number of the protons they can give up, we define monoprotic, diprotic and triprotic acids. The first (e.g., acetic acid or ammonium) have only one dissociable group, the second (e.g., carbonic acid, bicarbonate, glycine) have two dissociable groups and the third (e.g., phosphoric acid) have three dissociable groups. In the case of multiple pK values they are designated by indices: pK, pK, pK and so on. For amino acids, the pK constant refers to its carboxyl (–COOH) group, pK refers to its amino (–NH) group and the pK is the pK value of its side chain. | 7 | Physical Chemistry |
miR-324-5p likely regulates cell growth and survival through interaction with multiple pathways. Published research demonstrates that this miRNA interacts with the Hedgehog (HH) signaling pathway via interactions with HH transcription factor Gli1 and HH protein receptor Smo, often contributing to tumorigenesis. miR-324-5p's activating interaction with the protein NfkB also regulates numerous components of cell survival, including cell cycle control, enzyme synthesis, and cell adhesion. In addition, miR-324-5p regulates components of the MAPK pathway, influencing cell growth, proliferation, and survival. Specifically, miR-324-5p downregulates RAF and ERK and is necessary for normal levels of cell growth. Reduced expression leads to increased cell growth and proliferation, and overexpression limits growth, leading to its role in oncogenesis. | 1 | Biochemistry |
RAPD markers are decamer (10 nucleotides long) DNA fragments from PCR amplification of random segments of genomic DNA with a single primer of arbitrary nucleotide sequence and which are able to differentiate between genetically distinct individuals, although not necessarily in a reproducible way.
It is used to analyze the genetic diversity of an individual by using random primers. Due to problems in experiment reproducibility, many scientific journals do not accept experiments merely based on RAPDs anymore.
RAPD requires only one primer for amplification. | 1 | Biochemistry |
Unique VUV absorbance spectra not only enable unambiguous compound identification, and allows GC run times to be deliberately shortened. VUV detectors operate at ambient pressure and are thus not flow rate limited. GC run times can be reduced by increasing the GC column flow and oven temperature program rates.
Flow rate-enhanced chromatographic compression utilizes VUV spectral deconvolution to resolve any co-elution that may result from shortening GC runtimes. VUV absorption is additive, meaning that overlapping peaks give a spectrum that corresponds to the sum absorbance of each compound. The individual contribution of each analyte can be determined if the VUV spectra for co-eluting compounds are stored in the VUV library. The ability to differentiate coeluting analyte spectra and use them to deconvolve the overlapping signals is demonstrated in Figure 4. The individual spectra of terpenes limonene and p-Cymene are shown in Panel A along with the summed absorbance of the selected retention time window (blue region in Panel B) and the fit with VUV library spectra. The R >0.999 fit result confirms their identities, and enables the deconvolution of these and other terpenes analyzed by GC-VUV as featured in Panel B.
Testing for the presence of residual solvents in Active Pharmaceutical Ingredients (APIs) is critical for patient safety and commonly follows United States Pharmacopeia (USP) Method <467> guidelines, or more broadly, International Council for Harmonization (ICH) Guideline Q3C(R6). The gas chromatography (GC) runtime suggested by USP Method 467 is approximately 60 min. A generic method for residual solvent analysis by GC-MS describes conditions that include a runtime of approximately 30 minutes. A GC-VUV and static headspace method was developed using a chromatographic compression strategy that resulted in a GC runtime of 8 minutes. The GC-VUV method uses a flow rate of 4 mL/min and an oven ramp of 35 °C (held for 1 min), followed by an increase to 245 °C at a rate of 30 °C/min.
Figure 5 compares the results when the general conditions of the GC-MS method were followed against the GC-VUV method run with Class 2 residual solvents. Tetralin eluted at approximately 35 minutes using the GC-MS method conditions, whereas the analyte had a retention time of less than 7 minutes when the GC-VUV method was applied. The co-elution of m- and p-xylene occurred in both GC-MS and GC-VUV method runs. VUV software matched the analyte absorbance of both isomers with VUV library spectra (Figure 2) to deconvolve the overlapping signals as displayed in Figure 6. Goodness of fit information ensures that the correct compound assignment takes place during the post-run data analysis.
The flow rate-enhanced chromatographic compression strategy has been applied to a diverse set of applications since the development of the GC-VUV method for residual solvents analysis. The fast GC-VUV approach reduced GC runtimes for terpene analysis from 30 minutes to 9 minutes (the deconvolution of monoterpene isomers is shown in Figure 4). It has also been demonstrated that GC runtimes as short as 14 minutes can be used for PIONA compound analysis of gasoline samples. Typical GC separation times range between 1 – 2 hours using alternative methods. | 7 | Physical Chemistry |
In rotational-vibrational and electronic spectroscopy of diatomic molecules, Hund's coupling cases are idealized descriptions of rotational states in which specific terms in the molecular Hamiltonian and involving couplings between angular momenta are assumed to dominate over all other terms. There are five cases, proposed by Friedrich Hund in 1926-27 and traditionally denoted by the letters (a) through (e). Most diatomic molecules are somewhere between the idealized cases (a) and (b). | 7 | Physical Chemistry |
Tumor antigens are those antigens that are presented by MHC class I or MHC class II molecules on the surface of tumor cells. Antigens found only on such cells are called tumor-specific antigens (TSAs) and generally result from a tumor-specific mutation. More common are antigens that are presented by tumor cells and normal cells, called tumor-associated antigens (TAAs). Cytotoxic T lymphocytes that recognize these antigens may be able to destroy tumor cells.
Tumor antigens can appear on the surface of the tumor in the form of, for example, a mutated receptor, in which case they are recognized by B cells.
For human tumors without a viral etiology, novel peptides (neo-epitopes) are created by tumor-specific DNA alterations. | 1 | Biochemistry |
PAC is commonly used as a large capacity vector which allows propagation of large DNA inserts in Escherichia coli. This feature has been commonly used for:
* building genome libraries for human, mouse, etc, helps with projects such as Human Genome Project
* libraries served as the template for gene sequencing (example: used as gene template in mouse gene function analysis)
* genome analysis on specific functions of different genes for more complex organisms (plants, animals etc.)
* facilitate gene expression
Since PAC was derived from phages, PAC and its variants are also useful in the PAC-based phage therapy and antibiotic studies. | 1 | Biochemistry |
Dibasic ester or DBE is an ester of a dicarboxylic acid. Depending on the application, the alcohol may be methanol or higher molecular weight monoalcohols.
Mixtures of different methyl dibasic esters are commercially produced from short-chain acids such as adipic acid, glutaric acid, and succinic acid. They are non-flammable, readily biodegradable, non-corrosive, and have a mild, fruity odour.
Dibasic esters of phthalates, adipates, and azelates with C8 - C10 alcohols have found commercial use as lubricants, spin finishes, and additives. | 0 | Organic Chemistry |
Chromatography is a physical method of separation that distributes the components you want to separate between two phases, one stationary (stationary phase), the other (the mobile phase) moving in a definite direction. Cold ethanol precipitation, developed by Cohn in 1946, manipulates pH, ionic strength, ethanol concentration and temperature to precipitate different protein fractions from plasma. Chromatographic techniques utilise ion exchange, gel filtration and affinity resins to separate proteins. Since the 1980s it has emerged as an effective method of purifying blood components for therapeutic use. | 3 | Analytical Chemistry |
Studies show that the EPOC effect exists after both aerobic exercise and anaerobic exercise. In a 1992 Purdue study, results showed that high intensity, anaerobic type exercise resulted in a significantly greater magnitude of EPOC than aerobic exercise of equal work output. For exercise regimens of comparable duration and intensity, aerobic exercise burns more calories during the exercise itself, but the difference is partly offset by the higher increase in caloric expenditure that occurs during the EPOC phase after anaerobic exercise. Anaerobic exercise in the form of high-intensity interval training was also found in one study to result in greater loss of subcutaneous fat, even though the subjects expended fewer than half as many calories during exercise. Whether this result was caused by the EPOC effect has not been established, and the caloric content of the participants' diet was not controlled during this particular study period.
Most researchers use a measure of EPOC as a natural part of the quantification or measurement of exercise and recovery energy expenditure; to others this is not deemed necessary. After a single bout or set of weight lifting, Scott et al. found considerable contributions of EPOC to total energy expenditure. In their 2004 survey of the relevant literature, Meirelles and Gomes found: "In summary, EPOC resulting from a single resistance exercise session (i.e., many lifts) does not represent a great impact on energy balance; however, its cumulative effect may be relevant". This is echoed by Reynolds and Kravitz in their survey of the literature where they remarked: "the overall weight-control benefits of EPOC, for men and women, from participation in resistance exercise occur over a significant time period, since kilocalories are expended at a low rate in the individual post-exercise sessions."
The EPOC effect clearly increases with the intensity of the exercise, and (at least in the case of aerobic exercise, perhaps also for anaerobic) the duration of the exercise.
Studies comparing intermittent and continuous exercise consistently show a greater EPOC response for higher intensity, intermittent exercise. | 1 | Biochemistry |
ATP synthase, also called complex V, is the final enzyme in the oxidative phosphorylation pathway. This enzyme is found in all forms of life and functions in the same way in both prokaryotes and eukaryotes. The enzyme uses the energy stored in a proton gradient across a membrane to drive the synthesis of ATP from ADP and phosphate (P). Estimates of the number of protons required to synthesize one ATP have ranged from three to four, with some suggesting cells can vary this ratio, to suit different conditions.
This phosphorylation reaction is an equilibrium, which can be shifted by altering the proton-motive force. In the absence of a proton-motive force, the ATP synthase reaction will run from right to left, hydrolyzing ATP and pumping protons out of the matrix across the membrane. However, when the proton-motive force is high, the reaction is forced to run in the opposite direction; it proceeds from left to right, allowing protons to flow down their concentration gradient and turning ADP into ATP. Indeed, in the closely related vacuolar type H+-ATPases, the hydrolysis reaction is used to acidify cellular compartments, by pumping protons and hydrolysing ATP.
ATP synthase is a massive protein complex with a mushroom-like shape. The mammalian enzyme complex contains 16 subunits and has a mass of approximately 600 kilodaltons. The portion embedded within the membrane is called F and contains a ring of c subunits and the proton channel. The stalk and the ball-shaped headpiece is called F and is the site of ATP synthesis. The ball-shaped complex at the end of the F portion contains six proteins of two different kinds (three α subunits and three β subunits), whereas the "stalk" consists of one protein: the γ subunit, with the tip of the stalk extending into the ball of α and β subunits. Both the α and β subunits bind nucleotides, but only the β subunits catalyze the ATP synthesis reaction. Reaching along the side of the F portion and back into the membrane is a long rod-like subunit that anchors the α and β subunits into the base of the enzyme.
As protons cross the membrane through the channel in the base of ATP synthase, the F proton-driven motor rotates. Rotation might be caused by changes in the ionization of amino acids in the ring of c subunits causing electrostatic interactions that propel the ring of c subunits past the proton channel. This rotating ring in turn drives the rotation of the central axle (the γ subunit stalk) within the α and β subunits. The α and β subunits are prevented from rotating themselves by the side-arm, which acts as a stator. This movement of the tip of the γ subunit within the ball of α and β subunits provides the energy for the active sites in the β subunits to undergo a cycle of movements that produces and then releases ATP.
This ATP synthesis reaction is called the binding change mechanism and involves the active site of a β subunit cycling between three states. In the "open" state, ADP and phosphate enter the active site (shown in brown in the diagram). The protein then closes up around the molecules and binds them loosely – the "loose" state (shown in red). The enzyme then changes shape again and forces these molecules together, with the active site in the resulting "tight" state (shown in pink) binding the newly produced ATP molecule with very high affinity. Finally, the active site cycles back to the open state, releasing ATP and binding more ADP and phosphate, ready for the next cycle.
In some bacteria and archaea, ATP synthesis is driven by the movement of sodium ions through the cell membrane, rather than the movement of protons. Archaea such as Methanococcus also contain the AA synthase, a form of the enzyme that contains additional proteins with little similarity in sequence to other bacterial and eukaryotic ATP synthase subunits. It is possible that, in some species, the AA form of the enzyme is a specialized sodium-driven ATP synthase, but this might not be true in all cases. | 1 | Biochemistry |
Joule heating is caused by interactions between charge carriers (usually electrons) and the body of the conductor.
A potential difference (voltage) between two points of a conductor creates an electric field that accelerates charge carriers in the direction of the electric field, giving them kinetic energy. When the charged particles collide with the quasi-particles in the conductor (i.e. the canonically quantized, ionic lattice oscillations in the harmonic approximation of a crystal), energy is being transferred from the electrons to the lattice (by the creation of further lattice oscillations). The oscillations of the ions are the origin of the radiation ("thermal energy") that one measures in a typical experiment. | 7 | Physical Chemistry |
Protein crystallization is the process of formation of a regular array of individual protein molecules stabilized by crystal contacts. If the crystal is sufficiently ordered, it will diffract. Some proteins naturally form crystalline arrays, like aquaporin in the lens of the eye.
In the process of protein crystallization, proteins are dissolved in an aqueous environment and sample solution until they reach the supersaturated state. Different methods are used to reach that state such as vapor diffusion, microbatch, microdialysis, and free-interface diffusion. Developing protein crystals is a difficult process influenced by many factors, including pH, temperature, ionic strength in the crystallization solution, and even gravity. Once formed, these crystals can be used in structural biology to study the molecular structure of the protein, particularly for various industrial or medical purposes. | 3 | Analytical Chemistry |
The carbonyl groups of reducing sugars react with the amino groups of amino acids in the Maillard reaction, a complex series of reactions that occurs when cooking food. Maillard reaction products (MRPs) are diverse; some are beneficial to human health, while others are toxic. However, the overall effect of the Maillard reaction is to decrease the nutritional value of food. One example of a toxic product of the Maillard reaction is acrylamide, a neurotoxin and possible carcinogen that is formed from free asparagine and reducing sugars when cooking starchy foods at high temperatures (above 120 °C). However, evidence from epidemiological studies suggest that dietary acrylamide is unlikely to raise the risk of people developing cancer. | 0 | Organic Chemistry |
Starting as a biomass technology licensor In Summer of 2012 SGC Energia (SGCE) successfully commissioned a pilot multi tubular Fischer–Tropsch process unit and associated product upgrading units at the Pasadena, Tx Technology Center. The technology center focused on the development and operations of their XTLH solution which optimized processing of low value carbon waste streams into advanced fuels and wax products. This unit also serves as an operations training environment for the 1100 BPD Juniper GTL facility constructed in Westlake, LA. | 0 | Organic Chemistry |
A volumetric pipette, bulb pipette, or belly pipette allows extremely accurate measurement (to four significant figures) of the volume of a solution. It is calibrated to deliver accurately a fixed volume of liquid.
These pipettes have a large bulb with a long narrow portion above with a single graduation mark as it is calibrated for a single volume (like a volumetric flask). Typical volumes are 1, 2, 5, 10, 20, 25, 50 and 100 mL. Volumetric pipettes are commonly used in analytical chemistry to make laboratory solutions from a base stock as well as to prepare solutions for titration.
ASTM standard E969 defines the standard tolerance for volumetric transfer pipettes. The tolerance depends on the size: a 0.5-mL pipette has a tolerance of ±0.006 mL, while a 50-mL pipette has a tolerance of ±0.05 mL. (These are for Class A pipettes; Class B pipettes are given a tolerance of twice that for the corresponding Class A.)
A specialized example of a volumetric pipette is the microfluid pipette (capable of dispensing as little as 10 µL) designed with a circulating liquid tip that generates a self-confining volume in front of its outlet channels. | 3 | Analytical Chemistry |
In the early 11th century, the Islamic medical philosopher Avicenna wrote extensively on many subjects including medicine. Forty of these treatises on medicine survive, and in the most famous one titled the Canon of Medicine he discusses "rising gas". Avicenna believed that digestive system dysfunction was responsible for the overproduction of gas in the gastrointestinal tract. He suggested lifestyle changes and a compound of herbal drugs for its treatment.
In 1497, Alessandro Benedetti viewed the stomach as an unclean organ separated off by the diaphragm. This view of the stomach and intestines as being base organs was generally held until the mid-17th century.
In the Renaissance of the 16th century, Leonardo da Vinci produced some early drawings of the stomach and intestines. He thought that the digestive system aided the respiratory system. Andreas Vesalius provided some early anatomical drawings of the abdominal organs in the 16th century.
In the middle of the 17th century, a Flemish physician Jan Baptist van Helmont offered the first chemical account of digestion which was later described as being very close to the later conceptualised enzyme.
In 1653, William Harvey described the intestines in terms of their length, their blood supply, the mesenteries, and fat (adenylyl cyclase).
In 1823, William Prout discovered hydrochloric acid in the gastric juice. In 1895, Ivan Pavlov described its secretion as being stimulated by a neurologic reflex with the vagus nerve having a crucial role. Black in the 19th century suggested an association of histamine with this secretion. In 1916, Popielski described histamine as a gastric secretagogue of hydrochloric acid.
William Beaumont was an army surgeon who in 1825, was able to observe digestion as it took place in the stomach. This was made possible by experiments on a man with a stomach wound that did not fully heal leaving an opening into the stomach. The churning motion of the stomach was described among other findings.
In the 19th century, it was accepted that chemical processes were involved in the process of digestion. Physiological research into secretion and the gastrointestinal tract was pursued with experiments undertaken by Claude Bernard, Rudolph Heidenhain and Ivan Pavlov.
The rest of the 20th century was dominated by research into enzymes. The first to be discovered was secretin by Ernest Starling in 1902, with ensuing results from John Edkins in 1905 who first suggested gastrin with its structure being determined in 1964. Andre Latarjet and Lester Dragstedt found a role for acetylcholine in the digestive system. In 1972, H2 receptor agonists were described by J. Black, that block the action of histamine and decrease the production of hydrochloric acid. In 1980, proton pump inhibitors were described by Sachs. In 1983, the role of Helicobacter pylori in the formation of ulcers was described by Barry Marshall, and Robin Warren.
Art historians have often noted that banqueters on iconographic records of ancient Mediterranean societies almost always appear to be lying down on their left sides. One possible explanation could lie in the anatomy of the stomach and in the digestive mechanism. When lying on the left, the food has room to expand because the curvature of the stomach is enhanced in that position. | 1 | Biochemistry |
Raymond's daughter Janet Lemieux was Canadian champion soccer player and was inducted to the Canada Soccer Hall of Fame in 2021. | 0 | Organic Chemistry |
Mineral separation is hampered by several factors, with particle size being particularly important. As the slurry feed grainsize increases, the efficiency of separation tends to decrease. Separation efficiency is also affected by the stroke of the table (frequency and length); fine feed requires a higher speed and shorter stroke than a coarse feed. A frequency of 200 to 325 strokes per minute is typical.
When Wilfley tables were originally employed to rework tailing dumps, the tables were found to enhance mineral recovery by some 3540% percent compared to existing processes, though this is not always the case.
Optimisation of table setup can have a significant impact on the recovery of ore. Using magnetite as a synthetic ore to test recovery on a Wilfley Table, Mackay et al. (2015) found that an optimised table setup (i.e. table inclination, wash-water flow rate, material feed rate, table speed, stroke amplitude, feed grade and feed density) increased magnetite recovery by a factor of 3.7.
The Wilfley table, like any wet table, is one of the most metallurgically efficient forms of gravity concentration, being used to treat the smaller, more difficult flow-streams, and to produce finished concentrates from the products of other forms of gravity system. Additional efficiencies are gained in the treatment of low grade feeds where two or even three decks are stacked one above the other allowing for continuous feeding. | 8 | Metallurgy |
Mucoadhesion involves several types of bonding mechanisms, and it is the interaction between each process that allows for the adhesive process. The major categories are wetting theory, adsorption theory, diffusion theory, electrostatic theory, and fracture theory. Specific processes include mechanical interlocking, electrostatic, diffusion interpenetration, adsorption and fracture processes. | 1 | Biochemistry |
[RhH(CO)(PPh)] is a catalyst for the selective hydroformylation of 1-olefins to produce aldehydes at low pressures and mild temperatures. The selectivity for n-aldehydes increases in the presence of excess PPh and at low CO partial pressures. The first step in the hydroformylation process is the dissociative substitution of an alkene for a PPh. The migratory insertion of this 18-electron complex can result in either a primary or secondary rhodium alkyl. This step sets the regiochemistry of the product, however it is rapidly reversible. The 16-electron alkyl complex undergoes migratory insertion of a CO to form the coordinately unsaturated acyl. This species once again gives an 18-electron acyl complex. The last step involves β-H elimination via hydrogenolysis which results in the cleavage of the aldehyde product and regeneration of the rhodium catalyst. | 0 | Organic Chemistry |
Olfactory processing of chemical signals like pheromones exists in all animal phyla and is thus the oldest of the senses. It has been suggested that it serves survival by generating appropriate behavioral responses to the signals of threat, sex and dominance status among members of the same species.
Furthermore, it has been suggested that in the evolution of unicellular prokaryotes to multicellular eukaryotes, primordial pheromone signaling between individuals may have evolved to paracrine and endocrine signaling within individual organisms.
Some authors assume that approach-avoidance reactions in animals, elicited by chemical cues, form the phylogenetic basis for the experience of emotions in humans. | 1 | Biochemistry |
Spin column-based nucleic acid purification is a solid phase extraction method to quickly purify nucleic acids. This method relies on the fact that nucleic acid will bind to the solid phase of silica under certain conditions. | 1 | Biochemistry |
Carbon in pulp (CIP) is an extraction technique for recovery of gold which has been liberated into a cyanide solution as part of the gold cyanidation process.
Introduced in the early 1980s, Carbon in Pulp is regarded as a simple and cheap process. As such it is used in most industrial applications where the presence of competing silver or copper does not prohibit its use. In the case of high (i.e., 1%) copper content, froth flotation is more typical.
Activated carbon acts like a sponge to dicyanoaurate, the main soluble gold species in gold extraction technologies. Hard carbon particles (much larger than the ore particle sizes) can be mixed with the solution. The gold cyanide complex adsorb onto the carbon and is proposed to be reduced back to the metal. Because the carbon particles are much larger than the ore particles, the coarse carbon can then be separated from the slurry by screening using a wire mesh. | 8 | Metallurgy |
A Chi site or Chi sequence is a short stretch of DNA in the genome of a bacterium near which homologous recombination is more likely to occur than on average across the genome. Chi sites serve as stimulators of DNA double-strand break repair in bacteria, which can arise from radiation or chemical treatments, or result from replication fork breakage during DNA replication. The sequence of the Chi site is unique to each group of closely related organisms; in E. coli and other enteric bacteria, such as Salmonella, the core sequence is 5-GCTGGTGG-3 plus important nucleotides about 4 to 7 nucleotides to the 3 side of the core sequence. The existence of Chi sites was originally discovered in the genome of bacteriophage lambda, a virus that infects E. coli, but is now known to occur about 1000 times in the E. coli' genome.
The Chi sequence serves as a signal to the RecBCD helicase-nuclease that triggers a major change in the activities of this enzyme. Upon encountering the Chi sequence as it unwinds DNA, RecBCD cuts the DNA a few nucleotides to the 3’ side of Chi, within the important sequences noted above; depending on the reaction conditions, this cut is either a simple nick on the 3'-ended strand or the change of nuclease activity from cutting the 3’-ended strand to cutting the 5’-ended strand. In either case the resulting 3’ single-stranded DNA (ssDNA) is bound by multiple molecules of RecA protein that facilitate "strand invasion," in which one strand of a homologous double-stranded DNA is displaced by the RecA-associated ssDNA. Strand invasion forms a joint DNA molecule called a D-loop. Resolution of the D-loop is thought to occur by replication primed by the 3’ end generated at Chi (in the D-loop). Alternatively, the D-loop may be converted into a Holliday junction by cutting of the D-loop and a second exchange of DNA strands; the Holliday junction can be converted into linear duplex DNA by cutting of the Holliday junction and ligation of the resultant nicks. Either type of resolution can generate recombinant DNA molecules if the two interacting DNAs are genetically different, as well as repair the initially broken DNA.
Chi sites are sometimes referred to as "recombination hot spots". The name "Chi" is an abbreviation of In reference to E. coli phage lambda, the term is sometimes written as "χ site", using the Greek letter chi; for E. coli and other bacteria the term "Chi" is proper. | 1 | Biochemistry |
Each cell division cycle triggers a new round of chromosome replication by DnaA, the initiator protein. It is crucial to regulate DnaA-ATP monomer interactions with oriC during helicase loading and unwinding of origin DNA for precise timing. DnaA recognition sites in Escherichia coli are arranged in OriC to facilitate staged pre-replication complex assembling, with DnaA interacting with low affinity sites at it oligomerizes to fill the gaps between high affinity sites as it oligomerizes. There may be numerous gap-filling strategies to link OriC functions to bacterial lifestyles in nature, which may account for the wide variability of OriC DnaA recognition site patterns. The two forms of DnaA, the active ATP- and ADP-form are regulated. The ATP-form is converted to the ADP-form through either Regulatory inactivation of DnaA (RIDA), which in turn consists of the Hda protein and the β sliding clamp (DnaN) and datA-dependent DnaA-ATP hydrolysis. The ADP-form is converted to the ATP-form by DnaA-reactivating sequences 1 and 2 (DARS1 and DARS2). | 1 | Biochemistry |
Freshwaters are surprisingly difficult to sample because they are rarely homogeneous and their quality varies during the day and during the year. In addition the most representative sampling locations are often at a distance from the shore or bank increasing the logistic complexity. | 2 | Environmental Chemistry |
Some filters, notably welding glass, are rated by shade number (SN), which is 7/3 times the absorbance plus one:
For example, if the filter has 0.1% transmittance (0.001 transmittance, which is 3 absorbance units), its shade number would be 8. | 7 | Physical Chemistry |
Installations can destroy and/or relocate ecological habitats by covering large tracts of land and promoting habitat fragmentation. Solar facilities constructed on Native American reservations have interrupted traditional practices and have also had negative impact on the local ecosphere. | 7 | Physical Chemistry |
Despite its highly pyrophoric nature, diethylzinc is an important chemical reagent. It is used in organic synthesis as a source of the ethyl carbanion in addition reactions to carbonyl groups. For example, the asymmetric addition of an ethyl group to benzaldehyde and imines.
Additionally, it is commonly used in combination with diiodomethane as a Simmons-Smith reagent to convert alkenes into cyclopropyl groups. It is less nucleophilic than related alkyllithium and Grignard reagents, so it may be used when a "softer" nucleophile is needed.
It is also used extensively in materials science chemistry as a zinc source in the synthesis of nanoparticles. Particularly in the formation of the zinc sulfide shell for core/shell-type quantum dots.
While in polymer chemistry, it can be used as part of the catalyst for a chain shuttling polymerization reaction, whereby it participates in living polymerization.
Diethylzinc is not limited to only being used in chemistry. Because of its high reactivity toward air, it was used in small quantities as a hypergolic or "self igniting" liquid rocket fuel—it ignites on contact with oxidizer, so the rocket motor need only contain a pump, without a spark source for ignition. Diethylzinc was also investigated by the United States Library of Congress as a potential means of mass deacidification of books printed on wood pulp paper. Diethylzinc vapour would, in theory, neutralize acid residues in the paper, leaving slightly alkaline zinc oxide residues. Although initial results were promising, the project was abandoned. A variety of adverse results prevented the method's adoption. Most infamously, the final prototype suffered damage in a series of diethylzinc explosions from trace amounts of water vapor in the chamber. This led the authors of the study to humorously comment:
In microelectronics, diethylzinc is used as a doping agent.
For corrosion protection in nuclear reactors of the light water reactor design, depleted zinc oxide is produced by first passing diethylzinc through an enrichment centrifuge.
The pyrophoricity of diethylzinc can be used to test the inert atmosphere inside a glovebox. An oxygen concentration of only a few parts per million will cause a bottle of diethylzinc to fume when opened. | 0 | Organic Chemistry |
Samples of proteorhodopsin expressing bacteria have been obtained from the Eastern Pacific Ocean, Central North Pacific Ocean and Southern Ocean, Antarctica. Subsequently, genes of proteorhodopsin variants have been identified in samples from the Mediterranean, Red Seas, the Sargasso Sea, and Sea of Japan, and the North Sea.
Proteorhodopsin variants are not spread randomly, but disperse along depth gradients based on the maximal absorption-tuning of the particular holoprotein sequence; this is mainly due to the electromagnetic absorption by water which creates wavelength gradients relative to depth. Oxyrrhis marina is a dinoflagellate protist with green-absorbing proteorhodopsin (a result of the L109 Group) that exists mostly in shallow tide pools and shores, where green light is still available. Karlodinium micrum, another dinolagelate, expresses a blue tuned proteorhodopsin (E109) which may be related to its deep water vertical migrations. O. marina was originally believed to be a heterotroph, however the proteorhodopsin may well partake in a functionally significant manner, as it was the most abundantly expressed nuclear gene and, furthermore, is dispersed unevenly in the organism, suggesting some organelle membrane function. Previously the only known eukaryotic solar energy transducing proteins were Photosystem I and Photosystem II. It has been hypothesized that lateral gene transfer is the method by which proteorhodopsin has made its way into numerous phyla. Bacteria, archaea and eukarya all colonize the photic zone where they come to light; Proteorhodopsin has been able to disseminate through this zone, but not to other portions of the water column. | 5 | Photochemistry |
There are multiple technologies available that identify genetic variants. Each technology has advantages and disadvantages in terms of technical and financial factors. Two such technologies are microarrays and whole-genome sequencing. | 1 | Biochemistry |
The Pasteur effect describes how available oxygen inhibits ethanol fermentation, driving yeast to switch toward aerobic respiration for increased generation of the energy carrier adenosine triphosphate (ATP). More generally, in the medical literature, the Pasteur effect refers to how the cellular presence of oxygen causes in cells a decrease in the rate of glycolysis and also a suppression of lactate accumulation. The effect occurs in animal tissues, as well as in microorganisms belonging to the fungal kingdom. | 1 | Biochemistry |
The Racah parameters are defined as
where are Slater integrals
and are the Slater-Condon parameters
where is the normalized radial part of an electron orbital, and | 7 | Physical Chemistry |
The SI unit of conductivity is S/m and, unless otherwise qualified, it refers to 25 °C. More generally encountered is the traditional unit of μS/cm.
The commonly used standard cell has a width of 1 cm, and thus for very pure water in equilibrium with air would have a resistance of about 10 ohms, known as a megohm. Ultra-pure water could achieve 18 megohms or more. Thus in the past, megohm-cm was used, sometimes abbreviated to "megohm". Sometimes, conductivity is given in "microsiemens" (omitting the distance term in the unit). While this is an error, it can often be assumed to be equal to the traditional μS/cm. Often, by typographic limitations μS/cm is expressed as uS/cm.
The conversion of conductivity to the total dissolved solids depends on the chemical composition of the sample and can vary between 0.54 and 0.96. Typically, the conversion is done assuming that the solid is sodium chloride; 1 μS/cm is then equivalent to about 0.64 mg of NaCl per kg of water.
Molar conductivity has the SI unit S m mol. Older publications use the unit Ω cm mol. | 7 | Physical Chemistry |
Wittig reagents are found to react as nucleophiles in S2' substitution:
The initial addition reaction is followed by an elimination reaction. | 0 | Organic Chemistry |
Remote surface-enhanced Raman spectroscopy (SERS) consists of using metallic nanowaveguides supporting propagating surface plasmon polaritons (SPPs) to perform SERS at a distant location different to the one of the incident laser.
Propagating SPPs supported by nanowires has been used to show the remote excitation., as well as the remote detection of SERS. A silver nanowire was also used to show remote excitation and detection using graphene as Raman scatterer
Applications
Different plasmonic systems have already been used to show Raman detection of biomolecules in vivo in cells and remote excitation of surface catalytic reactions. | 7 | Physical Chemistry |
Reaction progress data may often most simply be presented as plot of substrate concentration ([A]) vs. time (t) or fraction conversion (F) vs. time (t). The latter requires minor algebraic manipulation to convert concentration/absorbance values to fractional conversion (F), by:
:F =
where [A] is the amount, absorbance, or concentration of substrate initially present and [A] is the amount, absorbance, or concentration of that reagent at time, t. Normalizing data to fractional conversion may be particularly helpful as it allows multiple reactions run with different absolute amounts or concentrations to be compared on the same plot.
Data may also commonly be presented as a plot of reaction rate (v) vs. time (t). Again, simple algebraic manipulation is required; for example, calorimetric experiments give:
:v =
where q is the instantaneous heat transfer, ΔH is the known enthalpy change of the reaction, and V is the reaction volume.
Data from reaction progress kinetics experiments are also often presented via a rate (v) vs. substrate concentration ([S]) plot. This requires obtaining and combining both the [S] vs. t and the v vs. t plots described above (note that one may be obtained from the other by simple differentiation or integration.) The combination leads to a standard set of curves in which reaction progress is read from right to left along the x-axis and reaction rate is read from bottom to top along the y-axis. While these plots often provide a visually compelling demonstration of basic kinetic trends, differential methods are generally superior for extracting numerical rate constants. (see below) | 7 | Physical Chemistry |
In its simplest form, equilibrium unfolding assumes that the molecule may belong to only two thermodynamic states, the folded state (typically denoted N for "native" state) and the unfolded state (typically denoted U). This "all-or-none" model of protein folding was first proposed by Tim Anson in 1945, but is believed to hold only for small, single structural domains of proteins (Jackson, 1998); larger domains and multi-domain proteins often exhibit intermediate states. As usual in statistical mechanics, these states correspond to ensembles of molecular conformations, not just one conformation.
The molecule may transition between the native and unfolded states according to a simple kinetic model
:N U
with rate constants and for the folding () and unfolding () reactions, respectively. The dimensionless equilibrium constant can be used to determine the conformational stability by the equation
where is the gas constant and is the absolute temperature in kelvin. Thus, is positive if the unfolded state is less stable (i.e., disfavored) relative to the native state.
The most direct way to measure the conformational stability of a molecule with two-state folding is to measure its kinetic rate constants and under the solution conditions of interest. However, since protein folding is typically completed in milliseconds, such measurements can be difficult to perform, usually requiring expensive stopped flow or (more recently) continuous-flow mixers to provoke folding with a high time resolution. Dual polarisation interferometry is an emerging technique to directly measure conformational change and . | 7 | Physical Chemistry |
Acid anhydrides are a source of reactive acyl groups, and their reactions and uses resemble those of acyl halides. In reactions with protic substrates, the reactions afford equal amounts of the acylated product and the carboxylic acid:
:RC(O)OC(O)R + HY → RC(O)Y + RCOH
for HY = HOR (alcohols), HNR' (ammonia, primary, secondary amines), aromatic ring (see Friedel-Crafts acylation).
Acid anhydrides tend to be less electrophilic than acyl chlorides, and only one acyl group is transferred per molecule of acid anhydride, which leads to a lower atom efficiency. The low cost, however, of acetic anhydride makes it a common choice for acetylation reactions. | 0 | Organic Chemistry |
The Étang de Berre (, "Lagoon of Berre"; in Provençal Occitan: estanh de Bèrra / mar de Bèrra according to classical orthography, estang de Berro / mar de Berro according to Mistralian orthography) is a brackish water lagoon on the Mediterranean coast of France, about north-west of Marseille. | 2 | Environmental Chemistry |
The repulsive effects of the two lone pairs on the oxygen atom cause water to have a bent, not linear, molecular structure, allowing it to be polar. The hydrogen–oxygen–hydrogen angle is 104.45°, which is less than the 109.47° for ideal sp hybridization. The valence bond theory explanation is that the oxygen atoms lone pairs are physically larger and therefore take up more space than the oxygen atoms bonds to the hydrogen atoms. The molecular orbital theory explanation (Bents rule) is that lowering the energy of the oxygen atoms nonbonding hybrid orbitals (by assigning them more s character and less p character) and correspondingly raising the energy of the oxygen atoms hybrid orbitals bonded to the hydrogen atoms (by assigning them more p character and less s character) has the net effect of lowering the energy of the occupied molecular orbitals because the energy of the oxygen atoms nonbonding hybrid orbitals contributes completely to the energy of the oxygen atoms lone pairs while the energy of the oxygen atoms other two hybrid orbitals contributes only partially to the energy of the bonding orbitals (the remainder of the contribution coming from the hydrogen atoms' 1s orbitals). | 2 | Environmental Chemistry |
By definition, strain implies discomfiture, so it should follow that molecules with large amounts of transannular strain should have higher energies than those without. Cyclohexane, for the most part, is without strain and is therefore quite stable and low in energy. Rings smaller than cyclohexane, like cyclopropane and cyclobutane, have significant tension caused by small-angle strain, but there is no transannular strain. While there is no small-angle strain present in medium-sized rings, there does exist something called large-angle strain. Some angle and torsional strain is used by rings with more than nine members to relieve some of the distress caused by transannular strain.
As the plot to the left indicates, the relative energies of cycloalkanes increases as the size of the ring increases, with a peak at cyclononane (with nine members in its ring.) At this point, the flexibility of the rings increases with increasing size; this allows for conformations that can significantly mitigate transannular interactions. | 4 | Stereochemistry |
From 1787 to 1802, it was determined by Jacques Charles (unpublished), John Dalton, and Joseph Louis Gay-Lussac that, at constant pressure, ideal gases expanded or contracted their volume linearly (Charless law) by about 1/273 parts per degree Celsius of temperatures change up or down, between 0° and 100 °C. This suggested that the volume of a gas cooled at about −273 °C would reach zero.
In October 1848, William Thomson, a 24 year old professor of Natural Philosophy at the University of Glasgow, published the paper On an Absolute Thermometric Scale.
In a footnote Thomson calculated that "infinite cold" (absolute zero) was equivalent to −273 °C (he called the temperature in °C as the "temperature of the air thermometers" of the time). This value of "−273" was considered to be the temperature at which the ideal gas volume reaches zero. By considering a thermal expansion linear with temperature (i.e. a constant coefficient of thermal expansion), the value of absolute zero was linearly extrapolated as the negative reciprocal of 0.366/100 °C – the accepted average coefficient of thermal expansion of an ideal gas in the temperature interval 0–100 °C, giving a remarkable consistency to the currently accepted value of −273.15 °C. | 7 | Physical Chemistry |
Chemical exchange is assumed to be rapid on the NMR time-scale. An individual chemical shift is the mole-fraction-weighted average of the shifts of nuclei in contributing species.
Example: the pK of the hydroxyl group in citric acid has been determined from C chemical shift data to be 14.4. Neither potentiometry nor ultraviolet–visible spectroscopy could be used for this determination. | 7 | Physical Chemistry |
Gene structure is the organisation of specialised sequence elements within a gene. Genes contain most of the information necessary for living cells to survive and reproduce. In most organisms, genes are made of DNA, where the particular DNA sequence determines the function of the gene. A gene is transcribed (copied) from DNA into RNA, which can either be non-coding (ncRNA) with a direct function, or an intermediate messenger (mRNA) that is then translated into protein. Each of these steps is controlled by specific sequence elements, or regions, within the gene. Every gene, therefore, requires multiple sequence elements to be functional. This includes the sequence that actually encodes the functional protein or ncRNA, as well as multiple regulatory sequence regions. These regions may be as short as a few base pairs, up to many thousands of base pairs long.
Much of gene structure is broadly similar between eukaryotes and prokaryotes. These common elements largely result from the shared ancestry of cellular life in organisms over 2 billion years ago. Key differences in gene structure between eukaryotes and prokaryotes reflect their divergent transcription and translation machinery. Understanding gene structure is the foundation of understanding gene annotation, expression, and function. | 1 | Biochemistry |
A transversely isotropic material is one with physical properties that are symmetric about an axis that is normal to a plane of isotropy. This transverse plane has infinite planes of symmetry and thus, within this plane, the material properties are the same in all directions. Hence, such materials are also known as "polar anisotropic" materials. In geophysics, vertically transverse isotropy (VTI) is also known as radial anisotropy.
This type of material exhibits hexagonal symmetry (though technically this ceases to be true for tensors of rank 6 and higher), so the number of independent constants in the (fourth-rank) elasticity tensor are reduced to 5 (from a total of 21 independent constants in the case of a fully anisotropic solid). The (second-rank) tensors of electrical resistivity, permeability, etc. have two independent constants. | 3 | Analytical Chemistry |
Iphigenia Photaki (, ; also known after marriage as Iphigenia Vourvidou-Photaki, ; 1921–1983) was a Greek organic chemist remembered for her contributions in peptide chemical synthesis, especially in the synthesis of biologically/enzymatically active peptides.
Photaki was in 1965 the fourth woman overall to be habilitated in a scientific discipline in Greece, and the second to do so in the field of Chemistry. She specialised in peptide synthesis, influenced by her mentor and doctoral advisor Leonidas Zervas, a global authority on the subject. After distinguished research in Basel, Athens, and later Cornell, Photaki eventually rose to Professor of Organic Chemistry and Head of the Laboratory of Organic Chemistry of the University of Athens. | 0 | Organic Chemistry |
Phosphatidic acid consists of a glycerol backbone, with, in general, a saturated fatty acid bonded to carbon-1, an unsaturated fatty acid bonded to carbon-2, and a phosphate group bonded to carbon-3. | 1 | Biochemistry |
Following oral administration, dextromethorphan is rapidly absorbed from the gastrointestinal tract, where it enters the bloodstream and crosses the blood–brain barrier.
At therapeutic doses, dextromethorphan acts centrally (meaning that it acts on the brain) as opposed to locally (on the respiratory tract). It elevates the threshold for coughing, without inhibiting ciliary activity. Dextromethorphan is rapidly absorbed from the gastrointestinal tract and converted into the active metabolite dextrorphan in the liver by the cytochrome P450 enzyme CYP2D6. The average dose necessary for effective antitussive therapy is between 10 and 45 mg, depending on the individual. The International Society for the Study of Cough recommends "an adequate first dose of medication is 60 mg in the adult and repeat dosing should be infrequent rather than qds recommended."
Dextromethorphan has an elimination half-life of approximately 4 hours in individuals with an extensive metabolizer phenotype; this is increased to approximately 13 hours when dextromethorphan is given in combination with quinidine. The duration of action after oral administration is about three to eight hours for dextromethorphan hydrobromide, and 10 to 12 hours for dextromethorphan polistirex. Around one in 10 of the Caucasian population has little or no CYP2D6 enzyme activity, leading to long-lived high drug levels. | 4 | Stereochemistry |
Three factors define an ideal plasma:
*The plasma approximation: The plasma approximation applies when the plasma parameter Λ, representing the number of charge carriers within the Debye sphere is much higher than unity. It can be readily shown that this criterion is equivalent to smallness of the ratio of the plasma electrostatic and thermal energy densities. Such plasmas are called weakly coupled.
*Bulk interactions: The Debye length is much smaller than the physical size of the plasma. This criterion means that interactions in the bulk of the plasma are more important than those at its edges, where boundary effects may take place. When this criterion is satisfied, the plasma is quasineutral.
*Collisionlessness: The electron plasma frequency (measuring plasma oscillations of the electrons) is much larger than the electron–neutral collision frequency. When this condition is valid, electrostatic interactions dominate over the processes of ordinary gas kinetics. Such plasmas are called collisionless. | 7 | Physical Chemistry |
* 2016 Georges Guiochon Faculty Fellowship
* 2018 H. I. Romnes Faculty Fellowship
* 2019 Analytical Scientist Power List
* 2020 American Society for Mass Spectrometry Biemann Medal
* 2020 Analytical Scientist Power List
*2021 Human Proteome Organization (HUPO) Clinical and Translational Proteomics Award
*2021 Analytical Scientist Power List | 1 | Biochemistry |
Zearalanone (ZAN) is a mycoestrogen that is a derivative of zearalenone (ZEN). Zearalanone can be extracted from medical herbs and edible herbs along with aflatoxins in the same time by a specific immunoaffinity column. | 1 | Biochemistry |
Iron salts are used commonly in Russula and Bolete identification. It is best to dissolve the salts in water (typically a 10% solution) and then apply to the flesh, but it is sometimes possible to apply the dry salts directly to see a color change. For example, the white flesh of Boletus chrysenteron stains lemon-yellow or olive. Three results are expected with the iron salts tests: no change indicates a negative reaction; a color change to olive, green or blackish green; or a color change to reddish-pink. | 3 | Analytical Chemistry |
* Lamprophyres and melilitic rocks
* Kimberlite
* Lamproite
* Orangeite (see Group II kimberlite)
* Feldspathoid-bearing rocks such as leucitites
* K-feldspar enriched leucogranites
* Vaugnerite and Durbachite | 9 | Geochemistry |
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