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A photochemical logic gate is based on the photochemical intersystem crossing and molecular electronic transition between photochemically active molecules, leading to logic gates that can be produced. | 5 | Photochemistry |
CAF-1 functions as a histone chaperone that mediates the first step in nucleosome formation by tetramerizing and depositing newly synthesized histone H3/H4 onto DNA rapidly behind replication forks. H3 and H4 are synthesized in the cytoplasm. Several studies have shown that the interaction between CAF-1 and PCNA (proliferating cell nuclear antigen, which stabilizes CAF-1 at replication forks, is important for CAF-1's role in nucleosome assembly
The three subunits work together to make the complex function. The human subunit (p150) interacts with PCNA, which acts as a sliding clamp, to help the CAF-1 complex interact with the DNA replication fork. Additionally, p150 along with PCNA performs nucleotide excision repair to fix any damaged DNA. P60 interacts with ASF1a/b, which is a histone chaperone for H3/H4. p48 has roles outside of CAF-1, but when involved with the complex, it binds to H4.
p60 attracts ASF1a/b which is a chaperone for H3/H4 and this is in the complex with p150 which interacts with PCNA to attach to the replication fork. The CAF-1 complex adds the histones to the DNA ahead of the replication fork.
A mutation in p150 that results in a loss of function would lead to double stranded breaks, interruptions in the replication fork and translocations. In p60, loss of function would mean the histone chaperone for H3/H4 would not interact with the complex. A mutation like this in either subunit would result in loss of function for the CAF-1 complex as a whole. However, loss of function in p48 would alter how well the complex is able to chaperone chromatin, but would not stop it as a whole. | 1 | Biochemistry |
The light reactions of photosynthesis generate ATP by the action of chemiosmosis. The photons in sunlight are received by the antenna complex of Photosystem II, which excites electrons to a higher energy level. These electrons travel down an electron transport chain, causing protons to be actively pumped across the thylakoid membrane into the thylakoid lumen. These protons then flow down their electrochemical potential gradient through an enzyme called ATP-synthase, creating ATP by the phosphorylation of ADP to ATP. The electrons from the initial light reaction reach Photosystem I, then are raised to a higher energy level by light energy and then received by an electron acceptor and reduce NADP to NADPH. The electrons lost from Photosystem II get replaced by the oxidation of water, which is "split" into protons and oxygen by the oxygen-evolving complex (OEC, also known as WOC, or the water-oxidizing complex). To generate one molecule of diatomic oxygen, 10 photons must be absorbed by Photosystems I and II, four electrons must move through the two photosystems, and 2 NADPH are generated (later used for carbon dioxide fixation in the Calvin Cycle). | 1 | Biochemistry |
The electrophoretic SCODA force is gentle enough to maintain the integrity of high molecular weight DNA as it is concentrated towards the center of the SCODA gel. Depending on the length of the DNA in the sample different protocols can be used to concentrate DNA over 1 Mb in length. | 1 | Biochemistry |
In biochemistry, denaturation is a process in which proteins or nucleic acids lose the quaternary structure, tertiary structure, and secondary structure which is present in their native state, by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent (e.g., alcohol or chloroform), agitation and radiation, or heat. If proteins in a living cell are denatured, this results in disruption of cell activity and possibly cell death. Protein denaturation is also a consequence of cell death. Denatured proteins can exhibit a wide range of characteristics, from conformational change and loss of solubility or dissociation of cofactors to aggregation due to the exposure of hydrophobic groups. The loss of solubility as a result of denaturation is called coagulation. Denatured proteins lose their 3D structure, and therefore, cannot function.
Proper protein folding is key to whether a globular or membrane protein can do its job correctly; it must be folded into the native shape to function. However, hydrogen bonds and cofactor-protein binding, which play a crucial role in folding, are rather weak, and thus, easily affected by heat, acidity, varying salt concentrations, chelating agents, and other stressors which can denature the protein. This is one reason why cellular homeostasis is physiologically necessary in most life forms.
This concept is unrelated to denatured alcohol, which is alcohol that has been mixed with additives to make it unsuitable for human consumption. | 1 | Biochemistry |
Typically, metallacycles are cyclic compounds with two metal carbon bonds.
Many compounds containing metals in rings are known, for example chelate rings. Usually, such compounds are not classified as metallacycles, but the naming conventions are not rigidly followed. Within the area of coordination chemistry and supramolecular chemistry, examples include metallacrowns, metallacryptands, metallahelices, and molecular wheels. | 0 | Organic Chemistry |
Expected progeny differences (EPD) are an evaluation of an animal’s genetic worth as a parent. They are based on animal models which combine all information known about an individual and its relatives to create a genetic profile of the animal’s merits. These profiles are then compared to other individuals of the same breed. | 1 | Biochemistry |
Haemozoin is a disposal product formed from the digestion of blood by some blood-feeding parasites. These hematophagous organisms such as malaria parasites (Plasmodium spp.), Rhodnius and Schistosoma digest haemoglobin and release high quantities of free heme, which is the non-protein component of haemoglobin. Heme is a prosthetic group consisting of an iron atom contained in the center of a heterocyclic porphyrin ring. Free heme is toxic to cells, so the parasites convert it into an insoluble crystalline form called hemozoin. In malaria parasites, hemozoin is often called malaria pigment.
Since the formation of hemozoin is essential to the survival of these parasites, it is an attractive target for developing drugs and is much-studied in Plasmodium as a way to find drugs to treat malaria (malarias Achilles heel). Several currently used antimalarial drugs, such as chloroquine and mefloquine, are thought to kill malaria parasites by inhibiting haemozoin biocrystallization. | 1 | Biochemistry |
Medieval Islamic chemists like the authors writing under the name of Jabir ibn Hayyan (died c. 806 – c. 816 AD, known in Latin as Geber), Abu Bakr al-Razi (865 – 925 AD, known in Latin as Rhazes), Ibn Sina (980 – 1037 AD, known in Latin as Avicenna), and Muhammad ibn Ibrahim al-Watwat (1234 – 1318 AD) included vitriol in their mineral classification lists.
The Jabirian authors and al-Razi experimented extensively with the distillation of various substances, including vitriols. In one recipe recorded in his (Book of Secrets), al-Razi may have created sulfuric acid without being aware of it:
In an anonymous Latin work variously attributed to Aristotle (under the title , Book of Aristotle), to al-Razi (under the title , Great Light of Lights), or to Ibn Sina, the author speaks of an oil () obtained through the distillation of iron(II) sulfate (green vitriol), which was likely oil of vitriol or sulfuric acid. The work refers multiple times to Jabir ibn Hayyans Book of Seventy' (), one of the few Arabic Jabir works that were translated into Latin. The author of the version attributed to al-Razi also refers to the as his own work, showing that he erroneously believed the to be a work by al-Razi. There are several indications that the anonymous work was an original composition in Latin, although according to one manuscript it was translated by a certain Raymond of Marseilles, meaning that it may also have been a translation from the Arabic.
According to Ahmad Y. al-Hassan, three recipes for sulfuric acid occur in an anonymous Karshuni manuscript containing a compilation taken from several authors and dating from before . One of them runs as follows:
A recipe for the preparation of sulfuric acid is mentioned in , an Arabic treatise falsely attributed to the Shii Imam Jafar al-Sadiq (died 765). Julius Ruska dated this treatise to the 13th century, but according to Ahmad Y. al-Hassan it likely dates from an earlier period: | 7 | Physical Chemistry |
Denatured proteins can exhibit a wide range of characteristics, from loss of solubility to protein aggregation. | 1 | Biochemistry |
Since the motions of the atoms in a molecule are determined by quantum mechanics, "motion" must be defined in a quantum mechanical way. The overall (external) quantum mechanical motions translation and rotation hardly change the geometry of the molecule. (To some extent rotation influences the geometry via Coriolis forces and centrifugal distortion, but this is negligible for the present discussion.) In addition to translation and rotation, a third type of motion is molecular vibration, which corresponds to internal motions of the atoms such as bond stretching and bond angle variation. The molecular vibrations are harmonic (at least to good approximation), and the atoms oscillate about their equilibrium positions, even at the absolute zero of temperature. At absolute zero all atoms are in their vibrational ground state and show zero point quantum mechanical motion, so that the wavefunction of a single vibrational mode is not a sharp peak, but approximately a Gaussian function (the wavefunction for n = 0 depicted in the article on the quantum harmonic oscillator). At higher temperatures the vibrational modes may be thermally excited (in a classical interpretation one expresses this by stating that "the molecules will vibrate faster"), but they oscillate still around the recognizable geometry of the molecule.
To get a feeling for the probability that the vibration of molecule may be thermally excited,
we inspect the Boltzmann factor , where ΔE is the excitation energy of the vibrational mode, k the Boltzmann constant and T the absolute temperature. At 298 K (25 °C), typical values for the Boltzmann factor β are:
* β = 0.089 for ΔE = 500 cm
* β = 0.008 for ΔE = 1000 cm
* β = 0.0007 for ΔE = 1500 cm.
(The reciprocal centimeter is an energy unit that is commonly used in infrared spectroscopy; 1 cm corresponds to ). When an excitation energy is 500 cm, then about 8.9 percent of the molecules are thermally excited at room temperature. To put this in perspective: the lowest excitation vibrational energy in water is the bending mode (about 1600 cm). Thus, at room temperature less than 0.07 percent of all the molecules of a given amount of water will vibrate faster than at absolute zero.
As stated above, rotation hardly influences the molecular geometry. But, as a quantum mechanical motion, it is thermally excited at relatively (as compared to vibration) low temperatures. From a classical point of view it can be stated that at higher temperatures more molecules will rotate faster,
which implies that they have higher angular velocity and angular momentum. In quantum mechanical language: more eigenstates of higher angular momentum become thermally populated with rising temperatures. Typical rotational excitation energies are on the order of a few cm. The results of many spectroscopic experiments are broadened because they involve an averaging over rotational states. It is often difficult to extract geometries from spectra at high temperatures, because the number of rotational states probed in the experimental averaging increases with increasing temperature. Thus, many spectroscopic observations can only be expected to yield reliable molecular geometries at temperatures close to absolute zero, because at higher temperatures too many higher rotational states are thermally populated. | 4 | Stereochemistry |
Mixed oxides of nitrogen (MON) are solutions of nitric oxide (NO) in dinitrogen tetroxide/nitrogen dioxide (NO and NO). It may be used as an oxidizing agent in rocket propulsion systems. A broad range of compositions is available, and can be denoted as MONi, where i represents the percentage of nitric oxide in the mixture (e.g. MON3 contains 3% nitric oxide, MON25 25% nitric oxide). An upper limit is MON40 (40% by weight). In Europe MON 1.3 is mostly used for rocket propulsion systems, while NASA seems to prefer MON 3. A higher percentage of NO decreases the corrosiveness and oxidation potential of the liquid, but increases costs.
The addition of nitric oxide also reduces the freezing point to a more desirable temperature. The freezing point of pure nitrogen tetroxide is , while MON3 is and MON25 is . | 7 | Physical Chemistry |
In the pharmaceutical industry, ICP-MS is used for detecting inorganic impurities in pharmaceuticals and their ingredients. New and reduced maximum permitted exposure levels of heavy metals from dietary supplements, introduced in USP (United States Pharmacopeia) «〈232〉Elemental Impurities—Limits» and USP «〈232〉Elemental Impurities—Procedures», will increase the need for ICP-MS technology, where, previously, other analytic methods have been sufficient.
Cosmetics, such as lipstick, recovered from a crime scene may provide valuable forensic information. Lipstick smears left on cigarette butts, glassware, clothing, bedding; napkins, paper, etc. may be valuable evidence. Lipstick recovered from clothing or skin may also indicate physical contact between individuals. Forensic analysis of recovered lipstick smear evidence can provide valuable information on the recent activities of a victim or suspect. Trace elemental analysis of lipstick smears could be used to complement existing visual comparative procedures to determine the lipstick brand and color.
Single Particle Inductively Coupled Plasma Mass Spectroscopy (SP ICP-MS) was designed for particle suspensions in 2000 by Claude Degueldre. He first tested this new methodology at the Forel Institute of the University of Geneva and presented this new analytical approach at the Colloid 2oo2 symposium during the spring 2002 meeting of the EMRS, and in the proceedings in 2003. This study presents the theory of SP ICP-MS and the results of tests carried out on clay particles (montmorillonite) as well as other suspensions of colloids. This method was then tested on thorium dioxide nanoparticles by Degueldre & Favarger (2004), zirconium dioxide by Degueldre et al (2004) and gold nanoparticles, which are used as a substrate in nanopharmacy, and published by Degueldre et al (2006). Subsequently, the study of uranium dioxide nano- and micro-particles gave rise to a detailed publication, Ref. Degueldre et al (2006). Since 2010 the interest for SP ICP-MS has exploded.
Previous forensic techniques employed for the organic analysis of lipsticks by compositional comparison include thin layer chromatography (TLC), gas chromatography (GC), and high-performance liquid chromatography (HPLC). These methods provide useful information regarding the identification of lipsticks. However, they all require long sample preparation times and destroy the sample. Nondestructive techniques for the forensic analysis of lipstick smears include UV fluorescence observation combined with purge-and-trap gas chromatography, microspectrophotometry and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and Raman spectroscopy. | 3 | Analytical Chemistry |
Catalysts for artificial photosynthesis are expected to effect turn over numbers in the millions. Catalysts often corrode in water, especially wen irradiated. Thus, they may be less stable than photovoltaics over long periods of time. Hydrogen catalysts are very sensitive to oxygen, being inactivated or degraded in its presence; also, photodamage may occur over time. | 5 | Photochemistry |
Dioxiranes may either be prepared in advance or generated in situ for epoxidation reactions. In most cases, a two-phase system must be set up for in situ epoxidations, as KHSO is not soluble in organic solvents. Thus, substrates or products sensitive to hydrolysis will not survive in situ epoxidations. This section describes epoxidation conditions for alkenes with electron-donating or -withdrawing substituents, both of which may be epoxidized with dioxiranes in either the stoichiometric or catalytic mode.
Although dioxiranes are highly electrophilic, they epoxidize both electron-rich and electron-poor alkenes in good yield (although the latter react much more slowly). Electron-poor epoxide products also exhibit enhanced hydrolytic stability, meaning that they can often survive in situ conditions. Epoxidations of electron-rich double bonds have yielded intermediates of Rubottom oxidation. Upon hydrolysis, these siloxyepoxides yield α-hydroxyketones.
Electron-poor double bonds take much longer to epoxidize. Heating may be used to encourage oxidation, although the reaction temperature should never exceed 50 °C, to avoid decomposition of the dioxirane.
Alkenes bound to both electron-withdrawing and -donating groups tend to behave like the former, requiring long oxidation times and occasionally some heating. Like electron-poor epoxides, epoxide products from this class of substrates are often stable with respect to hydrolysis.
In substrates containing multiple double bonds, the most electron-rich double bond can usually be selectively epoxidized.
Epoxidations employing aqueous Oxone and a catalytic amount of ketone are convenient if a specialized dioxirane must be used (as in asymmetric applications) or if isolation of the dioxirane is inconvenient. Hydrolytic decomposition of the epoxidation product may be used to good advantage. | 0 | Organic Chemistry |
The Froehde reagent is used as a simple spot-test to presumptively identify alkaloids, especially opioids, as well as other compounds. It is composed of a mixture of molybdic acid or a molybdate salt dissolved in hot, concentrated sulfuric acid, which is then dripped onto the substance being tested.
The United States Department of Justice method for producing the reagent is the addition of 100 ml of hot, concentrated (95–98%) sulfuric acid to 0.5 g of sodium molybdate or molybdic acid.
The Virginia Department of Forensic Science method uses 0.5 g ammonium molybdate per 100 ml HSO (conc.)
Unheated sulfuric acid can be used to prepare the reagent in a less dangerous manner, but 2–4 hours must be allowed for the molybdate to dissolve. | 3 | Analytical Chemistry |
Ali Musa oglu Guliyev (31 May 1912, Yelizavetpol – 29 January 1989, Baku) was a Soviet and Azerbaijani scientist. | 0 | Organic Chemistry |
The immobilized whole cell system is an alternative to enzyme immobilization. Unlike enzyme immobilization, where the enzyme is attached to a solid support (such as calcium alginate or activated PVA or activated PEI), in immobilized whole cell systems, the target cell is immobilized. Such methods may be implemented when the enzymes required are difficult or expensive to extract, an example being intracellular enzymes. Also, if a series of enzymes are required in the reaction; whole cell immobilization may be used for convenience. This is only done on a commercial basis when the need for the product is more justified.
Multiple enzymes may be introduced into the reaction, thus eliminating the need for immobilization of multiple enzymes. Furthermore, intracellular enzymes need not be extracted prior to the reaction; they may be used directly. However, some enzymes may be used for the metabolic needs of the cell, leading to reduced yield of the cell. | 1 | Biochemistry |
Hydrocarbon mixtures are composed of petroleum ethers and other hydrocarbons. Petroleum ether should not be confused with the class of organic compounds called ethers; and equally, going under its alternative name of benzine, it should not be confused with benzene. (Benzine is a mixture of alkanes, such as pentane, hexane, and heptane; whereas benzene is a cyclic, aromatic hydrocarbon.)
A hydrocarbon is any chemical compound that consists only of the elements carbon (C) and hydrogen (H). They all contain a carbon frame, and have hydrogen atoms attached to the frame. Often the term is used as a shortened form of the term aliphatic hydrocarbon. Most hydrocarbons are combustible.
Petroleum ether is obtained from petroleum refineries as the portion of the distillate which is intermediate between the lighter naphtha and the heavier kerosene. It has a specific gravity of between 0.6 and 0.8 depending on its composition. | 0 | Organic Chemistry |
Within molecular and cell biology membrane ruffling (also known as cell ruffling) is the formation of a motile cell surface that contains a meshwork of newly polymerized actin filaments. It can also be regarded as one of the earliest structural changes observed in the cell. The GTP-binding protein Rac is the regulator of this membrane ruffling. Changes in the Polyphosphoinositide metabolism and changes in Ca level of the cell may also play an important role. A number of actin-binding and organizing proteins localize to membrane ruffles and potentially target to transducing molecules. | 1 | Biochemistry |
The activity coefficient of component i is found by differentiation of the excess Gibbs energy towards x.
This yields, when applied only to the first term and using the Gibbs–Duhem equation,:
In here A and A are constants which are equal to the logarithm of the limiting activity coefficients: and respectively.
When , which implies molecules of same molecular size but different polarity, the equations reduce to the one-parameter Margules activity model:
In that case the activity coefficients cross at x=0.5 and the limiting activity coefficients are equal. When A=0 the model reduces to the ideal solution, i.e. the activity of a compound is equal to its concentration (mole fraction). | 7 | Physical Chemistry |
Informally, a Euclidean plane isometry is any way of transforming the plane without "deforming" it. For example, suppose that the Euclidean plane is represented by a sheet of transparent plastic sitting on a desk. Examples of isometries include:
* Shifting the sheet one inch to the right.
* Rotating the sheet by ten degrees around some marked point (which remains motionless).
* Turning the sheet over to look at it from behind. Notice that if a picture is drawn on one side of the sheet, then after turning the sheet over, we see the mirror image of the picture.
These are examples of translations, rotations, and reflections respectively. There is one further type of isometry, called a glide reflection (see below under classification of Euclidean plane isometries).
However, folding, cutting, or melting the sheet are not considered isometries. Neither are less drastic alterations like bending, stretching, or twisting. | 3 | Analytical Chemistry |
Most human cancers have been found to have gains and losses of chromosomes that may be due to chromosomal instability (CIN). One of the things that cause CIN is the inactivation of genes that control the proper segregation of the sister chromatids during mitosis. In gaining a better understanding of survivin's function in mitotic regulation, scientists have looked into the area of genomic instability. It is known that survivin associates with microtubules of the mitotic spindle at the start of mitosis.
It has been shown in the literature that knocking out survivin in cancer cells will disrupt microtubule formation and result in polyploidy as well as massive apoptosis. It has also been shown that survivin-depleted cells exit mitosis without achieving proper chromosome alignment and then reforms single tetraploid nuclei. Further evidence also suggests that survivin is needed for sustaining mitotic arrest upon encounter with mitosis problems. The evidence mentioned above implicates that survivin plays an important regulatory role both in the progression of mitosis and sustaining mitotic arrest. This seems strange, as survivin is known to be highly upregulated in most cancer cells (that usually contain chromosome instability characteristics), and its function is that which promotes proper regulation of mitosis. | 1 | Biochemistry |
Aside from the KIX domain, CBP and P300 contain many other protein binding domains that should not be confused (numbers are aa numberings):
* CH1/TAZ1 domain, CBP[347–433], P300[323-423]
* KIX domain, CBP[587–666], P300[566–645]
* Bromodomain, CBP[1103–1175], P300[1067–1139]
* CH2 domain (), CBP[1191–1317], P300[1155-1280].
* HAT domain, CBP[1323–1700], P300[1287–1663]
* CH3/ZZ domain, CBP[1701-1744], P300[1664-1707]
* CH3/TAZ2 domain, CBP[1765–1846], P300[1728-1809]
* IRF-3 binding (i-BiD), nuclear receptor coactivator binding (NCBD), or SRC1 interaction domain (SID; ), CBP[2020-2113], P300[1992-2098].
All three CH (cysteine/histidine-rich) domains are zinc fingers. | 1 | Biochemistry |
Mitochondrial diseases are usually caused by mutation in mitochondrial DNA. These genes regulate different proteins synthesis, including carrier proteins and certain enzymes.
The replication of mitochondrial DNA follows binary fission. In this process, 1 set of genes would divide into 2 sets. The mitochondrial gene of children is inherited from their mother only. If there are any genetic defects or mutations in the mother’s mitochondrial DNA, it would be inherited by the children. If those changes in genes can cause mitochondrial diseases, the children have a 100% possibility of acquiring the diseases.
For the malate-oxaloacetate shuttle, 4 major genes are involved. They are PMDH1, MDH, PMDH2, mMDH1. PMDH-1 and PMDH-2 encode two different enzymes that provide NAD for the oxidation of malate. In addition, MDH and mMDH1 encode for an enzyme that directly oxidizes malate. | 1 | Biochemistry |
Another role for these receptors is at the junction of the innervated tissues and the postganglionic neurons in the parasympathetic division of the autonomic nervous system. Here acetylcholine is again used as a neurotransmitter, and muscarinic receptors form the principal receptors on the innervated tissue. | 1 | Biochemistry |
Homogeneous means that the components of the mixture form a single phase. Heterogeneous means that the components of the mixture are of different phase. The properties of the mixture (such as concentration, temperature, and density) can be uniformly distributed through the volume but only in absence of diffusion phenomena or after their completion. Usually, the substance present in the greatest amount is considered the solvent. Solvents can be gases, liquids, or solids. One or more components present in the solution other than the solvent are called solutes. The solution has the same physical state as the solvent. | 7 | Physical Chemistry |
* Temperature (T) represents the average kinetic energy of the particles in a system. It's a measure of how hot or cold a system is.
* Pressure (P) is the force exerted by the particles of a system on a unit area of the container walls.
* Volume (V) refers to the space occupied by the system.
* Composition defines the amount of each component present for systems with more than one component (e.g., mixtures). | 7 | Physical Chemistry |
Culcheth Laboratories was a British metallurgical and nuclear research institute that researched the structural design of nuclear reactors and reactor pressure vessels in Culcheth, Cheshire, then in south Lancashire and now in the borough of Warrington. | 8 | Metallurgy |
Sucrose esters are used as food additives in a variety of food. European Parliament and Council Directive No 95/2/EC limited the use of sucrose esters under E 473 in each kind of food. No longer in force, Date of end of validity: 20/01/2010; Repealed by [https://eur-lex.europa.eu/legal-content/en/TXT/?uri=CELEX:32008R1333 32008R1333] . | 0 | Organic Chemistry |
OA was first used after World War II by the US railroad industry to monitor the health of locomotives. In 1946 the Denver and Rio Grande Railroad's research laboratory successfully detected diesel engine problems through wear metal analysis of used oils. A key factor in their success was the development of the spectrograph, an instrument which replaced several wet chemical methods for detecting and measuring individual chemical element such as iron or copper. This practice was soon accepted and used extensively throughout the railroad industry.
By 1955 OA had matured to the point that the United States Bureau of Naval Weapons began a major research program to adopt wear metal analysis for use in aircraft component failure prediction. These studies formed the basis for a Joint Oil Analysis Program (JOAP) involving all branches of the U.S. Armed Forces. The JOAP results proved conclusively that increases in component wear could be confirmed by detecting corresponding increases in the wear metal content of the lubricating oil. In 1958 Pacific Intermountain Express (P.I.E.) was the first trucking company to set up an in-house used oil analysis laboratory to control vehicle maintenance costs which was managed by Bob Herguth. In 1960 the first independent commercial oil analysis laboratory was started by Edward Forgeron in Oakland, CA. | 3 | Analytical Chemistry |
Liquation is a metallurgical method for separating metals from an ore or alloy. The material must be heated until one of the metals starts to melt and drain away from the other and can be collected. This method was largely used to remove lead containing silver from copper, but it can also be used to remove antimony from ore minerals, and refine tin.
The 16th-century process of separating copper and silver using liquation, described by Georg Agricola in his 1556 treatise De re metallica, remained almost unchanged until the 19th century when it was replaced by cheaper and more efficient processes such as sulphatization and eventually electrolytic methods. | 8 | Metallurgy |
The hydrogenation of alkenes to alkanes is exothermic. The amount of energy released during a hydrogenation reaction, known as the heat of hydrogenation, is inversely related to the stability of the starting alkene: the more stable the alkene, the lower its heat of hydrogenation. Examining the heats of hydrogenation for various alkenes reveals that stability increases with the amount of substitution.
The increase in stability associated with additional substitutions is the result of several factors. Alkyl groups are electron donating by inductive effect, and increase the electron density on the sigma bond of the alkene. Also, alkyl groups are sterically large, and are most stable when they are far away from each other. In an alkane, the maximum separation is that of the tetrahedral bond angle, 109.5°. In an alkene, the bond angle increases to near 120°. As a result, the separation between alkyl groups is greatest in the most substituted alkene.
Hyperconjugation, which describes the stabilizing interaction between the HOMO of the alkyl group and the LUMO of the double bond, also helps explain the influence of alkyl substitutions on the stability of alkenes. In regards to orbital hybridization, a bond between an sp carbon and an sp carbon is stronger than a bond between two sp-hybridized carbons. Computations reveal a dominant stabilizing hyperconjugation effect of 6 kcal/mol per alkyl group. | 7 | Physical Chemistry |
Colletto et al. developed a regioselective -arylation of benzo[b]thiophenes at room temperature with aryl iodides as coupling partners and sought to understand the mechanism of this reaction by performing natural abundance kinetic isotope effect measurements via single pulse NMR.
The observation of a primary C isotope effect at C3, an inverse H isotope effect, a secondary C isotope effect at C2, and the lack of an H isotope effect at C2 lead Colletto et al. to suggest a Heck-type reaction mechanism for the regioselective -arylation of benzo[b]thiophenes at room temperature with aryl iodides as coupling partners.
Frost et al. sought to understand the effects of Lewis acid additives on the mechanism of enantioselective palladium catalyzed C-N bond activation using natural abundance kinetic isotope effect measurements via single pulse NMR.
The primary C kinetic isotope effect observed in the absence of BPh suggests a reaction mechanism with rate limiting cis oxidation into the C–CN bond of the cyanoformamide. The addition of BPh causes a relative decrease in the observed C kinetic isotope effect which led Frost et al. to suggest a change in the rate limiting step from cis oxidation to coordination of palladium to the cyanoformamide. | 7 | Physical Chemistry |
Organic reactions can be categorized based on the type of functional group involved in the reaction as a reactant and the functional group that is formed as a result of this reaction. For example, in the Fries rearrangement the reactant is an ester and the reaction product an alcohol.
An overview of functional groups with their preparation and reactivity is presented below: | 0 | Organic Chemistry |
A composite cross population (CCP) is created by crossing a number of plants from different lines, and subsequently bulking seeds from the resulting offspring. This makes a CCP a population of plants with a lot of inherent genetic diversity, in contrast to monocultures where all plants are clones and homozygous at all loci (fully inbred). In recent years CCPs have been proposed as a way to create modern landraces of wheat, barley and oats. Research is done to explore whether they are better suited for organic farming than the modern cultivars.
They are suited for participatory breeding of crops, which is in contrast to cultivars owned by big breeding companies.
The idea of using CCPs in plant breeding was published in 1956 based on the barley composite cross devised by Harry Harlan and Mary Martini in 1929. Yield data for 4 different populations for 8–28 years were presented in the article and after 8–15 years of repeated breeding under natural selection, the populations out-yielded the reference cultivar. | 1 | Biochemistry |
Though veterinarians and bovine farmers point to the effectiveness of transfaunation for treating digestive disease, many animal rights groups argue that the practice is unnecessarily harmful to the quality of life of the cannulated cow. Use of a rumen-fluid collector instead of fistulation is well tolerated by the donor cow. People for the Ethical Treatment of Animals points to the surgerys four- to six-week recovery period and suggests that arguments for the health benefits of cannulation obscure the profit motive of the dairy industry: "While some claim that this transfer can improve the health of cows, the procedure seems mostly to benefit the meat and dairy industries bottom lines—optimizing food and digestion for animals who will ultimately be exploited and slaughtered." Similarly, The New Zealand Anti-Vivisection Society describes the practice as "cruel, insensitive and barbaric [...] the epitome of using cows as mere objects, like cars with gas tanks."
The fact-checking site Snopes has determined that the description of a circulating video of a cannulated cow as "abuse" is a "miscategorization," saying that cannulation "is neither a form of abuse nor a method to increase dairy production." However, rumen cannulation has long been used by the dairy industry to study methods that improve milk production. For instance, a 1940 study used cannulated cows to determine that a vitamin-rich diet makes for more antiscorbutic milk than a vitamin-poor diet, and a 2004 study used cannulated cows to evaluate treatments for a pH imbalance called subacute ruminal acidosis that is of concern to dairy farmers primarily because it damages milk production. | 1 | Biochemistry |
Proline-catalyzed aldol additions proceed via a six-membered enamine transition state according to the Zimmerman-Traxler model. Addition of 20-30 mol% proline to acetone or hydroxyacetone catalyzes their addition to a diverse set of aldehydes with high (>99%) enantioselectivity yielding diol products.
Proline and proline derivatives have been implemented as organocatalysts to promote asymmetric condensation reactions. An example of such a reaction proceeding through a six membered transition state is modelled as follows.
Intramolecular aldolization reactions that are catalyzed by proline likewise go through six-membered transition states. These transition states can enable the formation of either the enolexo or the enolendo product. | 0 | Organic Chemistry |
A restriction enzyme, restriction endonuclease, REase, ENase or restrictase is an enzyme that cleaves DNA into fragments at or near specific recognition sites within molecules known as restriction sites. Restriction enzymes are one class of the broader endonuclease group of enzymes. Restriction enzymes are commonly classified into five types, which differ in their structure and whether they cut their DNA substrate at their recognition site, or if the recognition and cleavage sites are separate from one another. To cut DNA, all restriction enzymes make two incisions, once through each sugar-phosphate backbone (i.e. each strand) of the DNA double helix.
These enzymes are found in bacteria and archaea and provide a defense mechanism against invading viruses. Inside a prokaryote, the restriction enzymes selectively cut up foreign DNA in a process called restriction digestion; meanwhile, host DNA is protected by a modification enzyme (a methyltransferase) that modifies the prokaryotic DNA and blocks cleavage. Together, these two processes form the restriction modification system.
More than 3,600 restriction endonucleases are known which represent over 250 different specificities. Over 3,000 of these have been studied in detail, and more than 800 of these are available commercially. These enzymes are routinely used for DNA modification in laboratories, and they are a vital tool in molecular cloning. | 1 | Biochemistry |
Number of chiral environments are created within the polymer. Cavities are formed between adjacent glucose units, and spaces/channels between polysaccharide chains. These chiral cavities or channels give the chiral discrimination capability to polysaccharide CSPs. The mechanism of Chiral discrimination is not well understood but believed to involve hydrogen bonding and dipole-dipole interaction between the analyte molecule and the ester or carbamate linkage of the CSP. | 4 | Stereochemistry |
Diazirines are widely used in receptor labeling studies. This is because diazirine-containing analogs of various ligands can be synthesized and incubated with their respective receptors, and then subsequently exposed to light to produce reactive carbenes. The carbene will covalently bond to residues in the binding site of the receptor. The carbene compound may include a bioorthogonal tag or handle by which the protein of interest can be isolated. The protein can then be digested and sequenced by mass spectrometry in order to identify which residues the carbene containing ligand is bound to, and hence the identity of the binding site in the receptor.
Examples of diazirines used in receptor labeling studies include:
* The discovery of a brassinosteroid receptor for brassinosteroid plant hormones by Kinoshita et al. Researchers used a plant hormone analog with a diazirine crosslinking moiety and a biotin tag for isolation to identity the new receptor. This study led to a number of similar studies conducted with regards to other plant hormones.
* The discovery of novel non-CB1/CB2 cannabinoid receptors using anandamide analog probes containing a diazirine group by Balas et al.
* The binding cavity of the hypnotic agent propofol in the GABA receptor using a diazirine containing propofol analog. | 5 | Photochemistry |
Phonons can scatter through several mechanisms as they travel through the material. These scattering mechanisms are: Umklapp phonon-phonon scattering, phonon-impurity scattering, phonon-electron scattering, and phonon-boundary scattering. Each scattering mechanism can be characterised by a relaxation rate 1/ which is the inverse of the corresponding relaxation time.
All scattering processes can be taken into account using Matthiessen's rule. Then the combined relaxation time can be written as:
The parameters , , , are due to Umklapp scattering, mass-difference impurity scattering, boundary scattering and phonon-electron scattering, respectively. | 7 | Physical Chemistry |
The last model involves transcriptional regulation by eRNAs at distant chromosomal locations. Through the differential recruitment of protein complexes, eRNAs can affect the transcriptional competency of specific loci. Evf-2 represents a good example of such trans regulatory eRNA as it can induce the expression of Dlx2, which in turn can increase the activity of the Dlx5 and Dlx6 enhancers. Trans-acting eRNAs might also be working in cis, and vice versa. | 1 | Biochemistry |
Graham Charles Wood FRS (6 February 1934—4 November 2016) was an English corrosion scientist.
Born in Farnborough, he went on to study metallurgy at Cambridge. Following postdoctoral work at Cambridge, he moved to Manchester, where his career in corrosion science would be based, starting at the Manchester College of Science and Technology (now the University of Manchester) where he joined the Department of Chemical Engineering as a lecturer in corrosion science. In 1972 he established and led the Corrosion and Protection Centre at UMIST (University of Manchester Institute of Science and Technology) as professor of corrosion science. In 1973 he helped to establish a consulting organisation, Corrosion and Protection Centre Industrial Service (CAPCIS – now part of Intertek).
Graham served terms as President of the Corrosion and Protection Association and the Institution of Corrosion Science and Technology ([https://www.icorr.org/ Institute of Corrosion]), and chaired the National Council for Corrosion Societies. He also served as a UK representative on the International Corrosion Council for 15 years, for which he also served as vice-chair and chair.
At UMIST, he held several administerial roles, including vice-principal for academic development, dean, and pro-vice chancellor.
He was elected Fellow of the Royal Academy of Engineering in 1990, and Fellow of the Royal Society in 1997. | 8 | Metallurgy |
Also known as luminophors, these compounds absorb the scintillation of the base and then emit at larger wavelength, effectively converting the ultraviolet radiation of the base into the more easily transferred visible light. Further increasing the attenuation length can be accomplished through the addition of a second fluor, referred to as a spectrum shifter or converter, often resulting in the emission of blue or green light.
Common fluors include polyphenyl hydrocarbons, oxazole and oxadiazole aryls, especially, n-terphenyl (PPP), 2,5-diphenyloxazole (PPO), 1,4-di-(5-phenyl-2-oxazolyl)-benzene (POPOP), 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD), and 2-(4’-tert-butylphenyl)-5-(4’’-biphenylyl)-1,3,4-oxadiazole (B-PBD). | 5 | Photochemistry |
The Weibull distribution, now named for Waloddi Weibull was first identified by and first applied by to describe particle size distributions. It is still widely used in mineral processing to describe particle size distributions in comminution processes.
where
:: Particle size
:: 80th percentile of the particle size distribution
:: Parameter describing the spread of the distribution
The inverse distribution is given by:
where
:: Mass fraction | 7 | Physical Chemistry |
The presence of AU-rich elements in some mammalian mRNAs tends to destabilize those transcripts through the action of cellular proteins that bind these sequences and stimulate poly(A) tail removal. Loss of the poly(A) tail is thought to promote mRNA degradation by facilitating attack by both the exosome complex and the decapping complex. Rapid mRNA degradation via AU-rich elements is a critical mechanism for preventing the overproduction of potent cytokines such as tumor necrosis factor (TNF) and granulocyte-macrophage colony stimulating factor (GM-CSF). AU-rich elements also regulate the biosynthesis of proto-oncogenic transcription factors like c-Jun and c-Fos. | 1 | Biochemistry |
From these values, we know that:
where
* CO = Cardiac Output
* C = Oxygen content of arterial blood
* C = Oxygen content of mixed venous blood
This allows us to say
and hence calculate cardiac output.
Note that (C – C) is also known as the arteriovenous oxygen difference. | 1 | Biochemistry |
Honeybees have very controlled patterns of movement, such as the waggle or tremble dance which serve to deliver specific coordinates of fruitful sources to potential foragers. Bumblebee movement is comparatively random and does not supply coordinates to other bees. Other experiments by Dornhaus and Chittka (2001) showed increased movement of successful foraging bees upon returning to the nest. Successful bees ran faster and longer compared to unsuccessful bees. A bee may spend several minutes running around the nest before flying out again. As the bee runs, it has been hypothesized that the bee may also offer a form of communication based on the buzzing sounds made from her wings. These excited runs serve in part to rouse other bees into foraging. | 1 | Biochemistry |
Electrode fouling is a major hindrance on the performance of electrodes. Few materials are completely bioinert, as in they trigger no bodily reaction. Some material that may be bioinert in theory fails to be ideal in practice because of defects in their formation, processing, manufacturing or sterilization. Fouling can be caused by adsorption of proteins, fibrous tissue, trapped cells or dead cell fragments, bacteria, or any other reactive particle. Protein adsorption is influenced by the nature and geometry of domains including hydrophobicity, polar and ionic interactions of the material and surrounding particles, charge distribution, kinetic movement, and pH. Phagocytosis of bacteria and other particles is mainly affected by surface charge, hydrophobicity, and chemical composition of the implant. It is important to note that the initial environment the implant is subjected to after implantation is different and unique compared to the environment after some time has passed since the area will undergo wound repair; the body's natural healing of the trauma will cause changes in local pH, electrolyte concentrations, and the presence and activity of biological compounds. | 7 | Physical Chemistry |
Austenitization means to heat the iron, iron-based metal, or steel to a temperature at which it changes crystal structure from ferrite to austenite. The more-open structure of the austenite is then able to absorb carbon from the iron-carbides in carbon steel. An incomplete initial austenitization can leave undissolved carbides in the matrix.
For some iron metals, iron-based metals, and steels, the presence of carbides may occur during the austenitization step. The term commonly used for this is two-phase austenitization. | 8 | Metallurgy |
The utilization of UVGI for air disinfection began in earnest in the mid-1930s. William F. Wells demonstrated in 1935 that airborne infectious organisms, specifically aerosolized B. coli exposed to 254 nm UV, could be rapidly inactivated. This built upon earlier theories of infectious droplet nuclei transmission put forth by Carl Flüugge and Wells himself. Prior to this, UV radiation had been studied predominantly in the context of liquid or solid media, rather than airborne microbes.
Shortly after Wells' initial experiments, high-intensity UVGI was employed to disinfect a hospital operating room at Duke University in 1936. The method proved a success, reducing postoperative wound infections from 11.62% without the use of UVGI to 0.24% with the use of UVGI. Soon, this approach was extended to other hospitals and infant wards using UVGI "light curtains", designed to prevent respiratory cross-infections, with noticeable success.
Adjustments in the application of UVGI saw a shift from "light curtains" to upper-room UVGI, confining germicidal irradiation above human head level. Despite its dependency on good vertical air movement, this approach yielded favorable outcomes in preventing cross-infections. This was exemplified by Wells' successful usage of upper-room UVGI between 1937 and 1941 to curtail the spread of measles in suburban Philadelphia day schools. His study found that 53.6% of susceptibles in schools without UVGI became infected, while only 13.3% of susceptibles in schools with UVGI were infected.
Richard L. Riley, initially a student of Wells, continued the study of airborne infection and UVGI throughout the 1950s and 60s, conducting significant experiments in a Veterans Hospital TB ward. Riley successfully demonstrated that UVGI could efficiently inactivate airborne pathogens and prevent the spread of tuberculosis.
Despite initial successes, the use of UVGI declined in the second half of the 20th century era due to various factors, including a rise in alternative infection control and prevention methods, inconsistent efficacy results, and concerns regarding its safety and maintenance requirements. However, recent events like a rise in multiple drug-resistant bacteria and the COVID-19 pandemic have renewed interest in UVGI for air disinfection. | 5 | Photochemistry |
Friedrich Deusch used the impressed mark "Deusch 1000 / 1000" on the early items. This mark was punched directly into the silver. Very often one may also find a red three-digit number on the bottom of the porcelain or glass which indicates this early production. Later, it was replaced by a red stamp which shows a coffeepot and the name Deusch. In addition, to these marks, the following marks may also be found: "1000 / 1000 Silber" or "1000 / 1000 Feinsilber". Later items may have the additional mark "Made in Western Germany".
Alfred and Manfred Veyhl used many different marks, stamps and labels (always placed on the bottom of the item). Vehyl's work often shows the "1000/1000 silver" mark included in the body of the design. Some rare items are signed by handwritten monogram (MV for Manfred Veyhl) and the word "Handgemalt" (handpainted).
Friedrich Wilhelm Spahr mostly used marks impressed directly into the silver. The very earliest and rarest of Spahr's marks began with "MSG 1000 10" ("MSG" standing for "Manufaktur Schwäbisch Gmünd"). This mark was followed by "Spahr 1000 10" (sometimes stamped in black letters on a porcelain base), later with "Spahr 1000", and finally with transparent plastic labels on the bottom printed "Spahr Feinsilberauflage 1000 / 1000".
Alvin Corporation, which was later owned by the Gorham Mfg. Co. after 1928, also used special marks. They manufactures pieces of sterling silver flatware, as well as hollowware and special toilet ware.
The La Pierre Manufacturing Company also sued special marks. It was established by Frank H. La Pierre in 1885, and headquartered at 18 East 14th Street, NY. It relocated its offices to Newark, NJ before its incorporation in 1895. Their special marks appear on their silver overlay item such as hollowware and novelty items.
The Rockwell Silver Company established in Meriden, CT around 1905 created a number designs which featured silver overlay, however they were merged with Silver City Glass Company in 1978, so even though they have done extensive work, there are no unique marks associated with the company.
The Gorham Manufacturing Co. which was active from 1848 till 1865 used a lion as their mark. They also used a rams head and the phrase "coin" to mark their items. | 8 | Metallurgy |
Window shutter hardware, usually made of iron, are hinges and latches that attach to the shutter and a window frame (and in some cases directly attached to stone or brick). The hinges hold the shutter to the structure and allow the shutter to open and close over the window. The latches secure the shutter in the closed (over the window) position. Tie-back hardware can be used to hold the shutter in the open position.
Exterior shutters were vital elements of homes in the colonies. Raised panel shutters provided security against access from ground level. Exterior shutters also proved a first barrier against the elements. In cities, shutters provided privacy screens for the residents. Louvered upstairs shutters were often later additions to the home.
This article describes the evolution of early exterior window shutter hardware, terms and terminology related to shutter hardware and blacksmithing, and American regional styles of installation. | 8 | Metallurgy |
The surface advances by the lateral motion of steps which are one interplanar spacing in height (or some integral multiple thereof). An element of surface undergoes no change and does not advance normal to itself except during the passage of a step, and then it advances by the step height. It is useful to consider the step as the transition between two adjacent regions of a surface which are parallel to each other and thus identical in configuration—displaced from each other by an integral number of lattice planes. Note here the distinct possibility of a step in a diffuse surface, even though the step height would be much smaller than the thickness of the diffuse surface. | 3 | Analytical Chemistry |
In crystallography, the diamond cubic crystal structure is a repeating pattern of 8 atoms that certain materials may adopt as they solidify. While the first known example was diamond, other elements in group 14 also adopt this structure, including α-tin, the semiconductors silicon and germanium, and silicon–germanium alloys in any proportion. There are also crystals, such as the high-temperature form of cristobalite, which have a similar structure, with one kind of atom (such as silicon in cristobalite) at the positions of carbon atoms in diamond but with another kind of atom (such as oxygen) halfway between those (see :Category:Minerals in space group 227).
Although often called the diamond lattice, this structure is not a lattice in the technical sense of this word used in mathematics. | 3 | Analytical Chemistry |
In contrast to the flux summation theorem, the concentration summation theorem sums to zero. The implications of this are that some enzymes will cause a given metabolite to increase while others, in order to satisfy the summation to zero, must cause the same metabolite to decrease. This is particularly noticeable in a linear chain of enzyme reactions where, given a metabolite located in the center of the pathway, an increase in expression of any enzyme upstream of the metabolite will cause the metabolite to increase in concentration. In contrast, an increase in expression of any enzyme downstream of the metabolite will cause the given metabolite to decrease in concentration. | 1 | Biochemistry |
It is easiest to describe the flux of metabolites through a pathway by considering the reaction steps individually. The flux of the metabolites through each reaction (J) is the rate of the forward reaction (V), less that of the reverse reaction (V):
At equilibrium, there is no flux. Furthermore, it is observed that throughout a steady-state pathway, the flux is determined to varying degrees by all steps in the pathway. The degree of influence is measured by the flux control coefficient. | 1 | Biochemistry |
Vitrification is the progressive partial fusion of a clay, or of a body, as a result of a firing process. As vitrification proceeds, the proportion of glassy bond increases and the apparent porosity of the fired product becomes progressively lower. Vitreous bodies have open porosity, and may be either opaque or translucent. In this context, "zero porosity" may be defined as less than 1% water absorption. However, various standard procedures define the conditions of water absorption. An example is by ASTM, who state "The term vitreous generally signifies less than 0.5% absorption, except for floor and wall tile and low-voltage electrical insulators, which are considered vitreous up to 3% water absorption."
Pottery can be made impermeable to water by glazing or by vitrification. Porcelain, bone china, and sanitaryware are examples of vitrified pottery, and are impermeable even without glaze. Stoneware may be vitrified or semi-vitrified; the latter type would not be impermeable without glaze. | 1 | Biochemistry |
The Langmuir adsorption model explains adsorption by assuming an adsorbate behaves as an ideal gas at isothermal conditions. According to the model, adsorption and desorption are reversible processes. This model even explains the effect of pressure i.e. at these conditions the adsorbate's partial pressure is related to its volume adsorbed onto a solid adsorbent. The adsorbent, as indicated in the figure, is assumed to be an ideal solid surface composed of a series of distinct sites capable of binding the adsorbate. The adsorbate binding is treated as a chemical reaction between the adsorbate gaseous molecule and an empty sorption site . This reaction yields an adsorbed species with an associated equilibrium constant :
From these basic hypotheses the mathematical formulation of the Langmuir adsorption isotherm can be derived in various independent and complementary ways: by the kinetics, the thermodynamics, and the statistical mechanics approaches respectively (see below for the different demonstrations).
The Langmuir adsorption equation is
where is the fractional occupancy of the adsorption sites, i.e., the ratio of the volume of gas adsorbed onto the solid to the volume of a gas molecules monolayer covering the whole surface of the solid and completely occupied by the adsorbate. A continuous monolayer of adsorbate molecules covering a homogeneous flat solid surface is the conceptual basis for this adsorption model. | 7 | Physical Chemistry |
With metal ions, thiolates behave as ligands to form transition metal thiolate complexes. The term mercaptan is derived from the Latin mercurium captans (capturing mercury) because the thiolate group bonds so strongly with mercury compounds. According to hard/soft acid/base (HSAB) theory, sulfur is a relatively soft (polarizable) atom. This explains the tendency of thiols to bind to soft elements and ions such as mercury, lead, or cadmium. The stability of metal thiolates parallels that of the corresponding sulfide minerals. | 0 | Organic Chemistry |
T. rotula has been known to produce many types of polyunsaturated aldehydes, including (2E,4E/Z)-hepta-2,4-dienal, (2E,4E/Z,7Z)-deca-2,4,7-trienal, (2E,4E/Z)-octa-2,4-dienal, and (2E,4E/Z,7Z)-octa-2,4,7-trienal. These particular aldehydes are also produced by Stephanopyxis turris and Skeletonema costatum in response to wounding. Phaeocystis pouchetii and Skeletonema marinoi also produce various octadienal and heptadienal isomers. | 1 | Biochemistry |
The hydrodynamic resistance force is evaluated following the Stokes’ law.
The electrophoretic force is evaluated following the Coulomb’s law.
In these equations r presents the hydrodynamic radius of the colloids, – the speed of electrophoretic migration, – the dynamic viscosity of the solutions, – dielectric constant in vacuum, is water’s relative dielectric constant at 298 K, is the zeta potential, E is the electric field. The hydrodynamic radius is the sum of particles’ radiuses and the stationary solvent interface.
By steady state electrophoretic migration of charged colloids the electrophoretic force and the hydrodynamic resistance force are in equilibrium, described by:
:F + F = 0
Those effects influence the electrofiltration of biopolymers, which could be also charged, not only by the hydrodynamic resistance force but also by the electric field force. Focusing on the cathode side reveals that the negatively charged particles are affected by the electric field force, which is opposite to the hydrodynamic resistance force. In this manner the formation of filter cake on this side is impeded or in ideal situation filter cake is not formed at all. In this case the electric field is referred as critical electric field E. As a result of the equilibrium of those forces, liquids subjected to the influence of electric force become charged. In addition to the applied hydraulic pressure ∆pH the process is influenced also by the electro-osmotic pressure P.
Modifying the Darcy’s basic equation, describing filter cake formation, with electro-kinetic effects by integration under assumption of using the constants of electro-osmotic pressure P, the critical electric field E and the electric field E results:
Previous scientific works conducted in the [http://www.bio-ag.de/ Dept. of Bioprocess Engineering, Institute of Engineering in Life Sciences, University of Karlsruhe] demonstrated that electrofiltration is effective for the concentration of charged biopolymers. Very promising results concerning purification of the charged polysaccharide xanthan are already obtained. Figure 2 represents xanthan filter cake. | 3 | Analytical Chemistry |
Lead can form a low-melting slag capable of fluxing protective oxide scales. Lead is more often known for causing stress corrosion cracking in common materials that are exposed to molten lead. The cracking tendency of lead has been known for some time, since most iron based alloys, including those used in steel containers and vessels for molten lead baths, usually fail due to cracking. | 8 | Metallurgy |
The bond length in a heavy Rydberg system is 10,000 times larger than in a typical diatomic molecule. As well as producing the characteristic hydrogen-like behaviour, this also makes them extremely sensitive to perturbation by external electric and magnetic fields.
Heavy Rydberg systems have a relatively large reduced mass, given by:
This leads to a very slow time evolution, which makes them easy to manipulate both spatially and energetically, while their low binding energy makes them relatively simple to detect through field dissociation and detection of the resulting ions, in a process known as threshold ion-pair production spectroscopy.
Kepler's third law states that the period of an orbit is proportional to the cube of the semi-major axis; this can be applied to the Coulomb force:
where is the time-period, is the reduced mass, is the semi-major axis and .
Classically we can say that a system with a large reduced mass has a long orbital period. Quantum mechanically, a large reduced mass in a system leads to narrow spacing of the energy levels and the rate of time-evolution of the wavefunction depends on this energy spacing. This slow time-evolution makes heavy Rydberg systems ideal for experimentally probing the dynamics of quantum systems. | 7 | Physical Chemistry |
Sulfonic acids are strong acids. They are commonly cited as being around a million times stronger than the corresponding carboxylic acid. For example, p-Toluenesulfonic acid and methanesulfonic acid have pK values of −2.8 and −1.9, respectively, while those of benzoic acid and acetic acid are 4.20 and 4.76, respectively. However, as a consequence of their strong acidity, their pK values cannot be measured directly, and values commonly quoted should be regarded as indirect estimates with significant uncertainties. For instance, various sources have reported the pK of methanesulfonic acid to be as high as −0.6 or as low as −6.5. Sulfonic acids are known to react with solid sodium chloride (salt) to form the sodium sulfonate and hydrogen chloride. This property implies an acidity within two or three orders of magnitude of that of HCl, whose pK was recently accurately determined (pK = −5.9).
Because of their polarity, sulfonic acids tend to be crystalline solids or viscous, high-boiling liquids. They are also usually colourless and nonoxidizing, which makes them suitable for use as acid catalysts in organic reactions. Their polarity, in conjunction with their high acidity, renders short-chain sulfonic acids water-soluble, while longer-chain ones exhibit detergent-like properties.
The structure of sulfonic acids is illustrated by the prototype, methanesulfonic acid. The sulfonic acid group, RSOOH features a tetrahedral sulfur centre, meaning that sulfur is at the center of four atoms: three oxygens and one carbon. The overall geometry of the sulfur centre is reminiscent of the shape of sulfuric acid. | 0 | Organic Chemistry |
For a finite crystal means that the sums in equations 1-7 are now over a finite . The effect is most easily demonstrated with a 1-D lattice of points. The sum of the phase factors is a geometric series and the structure factor becomes:
This function is shown in the Figure for different values of .
When the scattering from every particle is in phase, which is when the scattering is at a reciprocal lattice point , the sum of the amplitudes must be and so the maxima in intensity are . Taking the above expression for and estimating the limit using, for instance, LHôpitals rule) shows that as seen in the Figure. At the midpoint (by direct evaluation) and the peak width decreases like . In the large limit, the peaks become infinitely sharp Dirac delta functions, the reciprocal lattice of the perfect 1-D lattice.
In crystallography when is used, is large, and the formal size effect on diffraction is taken as , which is the same as the expression for above near to the reciprocal lattice points, . Using convolution, we can describe the finite real crystal structure as [lattice] [basis] rectangular function, where the rectangular function has a value 1 inside the crystal and 0 outside it. Then [crystal structure] = [lattice] [basis] [rectangular function]; that is, scattering [reciprocal lattice] [structure factor] [ sinc function]. Thus the intensity, which is a delta function of position for the perfect crystal, becomes a function around every point with a maximum , a width , area . | 3 | Analytical Chemistry |
The primary uses of lovastatin is for the treatment of dyslipidemia and the prevention of cardiovascular disease. It is recommended to be used only after other measures, such as diet, exercise, and weight reduction, have not improved cholesterol levels. | 0 | Organic Chemistry |
Since 1980 two theories were worked on to explain adsorption and obtain equations that work. These two are referred to as the chi hypothesis, the quantum mechanical derivation, and excess surface work, ESW. Both these theories yield the same equation for flat surfaces:
Where U is the unit step function. The definitions of the other symbols is as follows:
where "ads" stands for "adsorbed", "m" stands for "monolayer equivalence" and "vap" is reference to the vapor pressure ("ads" and "vap" are the latest IUPAC convention but "m" has no IUAPC equivalent notation) of the liquid adsorptive at the same temperature as the solid sample. The unit function creates the definition of the molar energy of adsorption for the first adsorbed molecule by:
The plot of adsorbed versus is referred to as the chi plot. For flat surfaces, the slope of the chi plot yields the surface area. Empirically, this plot was notice as being a very good fit to the isotherm by Polanyi and also by deBoer and Zwikker but not pursued. This was due to criticism in the former case by Einstein and in the latter case by Brunauer. This flat surface equation may be used as a "standard curve" in the normal tradition of comparison curves, with the exception that the porous sample's early portion of the plot of versus acts as a self-standard. Ultramicroporous, microporous and mesoporous conditions may be analyzed using this technique. Typical standard deviations for full isotherm fits including porous samples are typically less than 2%.
A typical fit to good data on a homogeneous non-porous surface is shown in figure 3. The data is by Payne, Sing and Turk and was used to create the -s standard curve. Unlike the BET, which can only be at best fit over the range of 0.05 to 0.35 of P/P, the range of the fit is the full isotherm. | 7 | Physical Chemistry |
A 4n + 2 electrocyclic ring opening reaction is also a 2-component pericyclic reaction which is suprafacial with respect to the π-system. Thus, in order for the reaction to be allowed, the number of antarafacial components must be 0, i.e. it must be suprafacial with respect to the breaking σ-bond as well. Thus a disrotatory mechanism is symmetry-allowed. | 7 | Physical Chemistry |
Everhardus Jacobus Ariëns (29 January 1918 – 3 March 2002) was a Dutch pharmacologist and professor at the Catholic University of Nijmegen (now Radboud University Nijmegen). He made important contributions to the function of receptors and the mathematical description of ligand–receptor interactions (receptor theory). Moreover, Everhardus Ariëns was a pioneer of the consideration of stereochemistry in drug development, such as the development of enantiopure drugs. | 4 | Stereochemistry |
A critical role for the ER in calcium signaling was acknowledged before such a role for the mitochondria was widely accepted, in part because the low affinity of Ca channels localized to the outer mitochondrial membrane seemed to contradict this organelle's purported responsiveness to changes in intracellular Ca flux. But the presence of the MAM resolves this apparent contradiction: the close physical association between the two organelles results in Ca microdomains at contact points that facilitate efficient Ca transmission from the ER to the mitochondria. Transmission occurs in response to so-called "Ca puffs" generated by spontaneous clustering and activation of IP3R, a canonical ER membrane Ca channel.
The fate of these puffs—in particular, whether they remain restricted to isolated locales or integrated into Ca waves for propagation throughout the cell—is determined in large part by MAM dynamics. Although reuptake of Ca by the ER (concomitant with its release) modulates the intensity of the puffs, thus insulating mitochondria to a certain degree from high Ca exposure, the MAM often serves as a firewall that essentially buffers Ca puffs by acting as a sink into which free ions released into the cytosol can be funneled. This Ca tunneling occurs through the low-affinity Ca receptor VDAC1, which recently has been shown to be physically tethered to the IP3R clusters on the ER membrane and enriched at the MAM. The ability of mitochondria to serve as a Ca sink is a result of the electrochemical gradient generated during oxidative phosphorylation, which makes tunneling of the cation an exergonic process. Normal, mild calcium influx from cytosol into the mitochondrial matrix causes transient depolarization that is corrected by pumping out protons.
But transmission of Ca is not unidirectional; rather, it is a two-way street. The properties of the Ca pump SERCA and the channel IP3R present on the ER membrane facilitate feedback regulation coordinated by MAM function. In particular, the clearance of Ca by the MAM allows for spatio-temporal patterning of Ca signaling because Ca alters IP3R activity in a biphasic manner. SERCA is likewise affected by mitochondrial feedback: uptake of Ca by the MAM stimulates ATP production, thus providing energy that enables SERCA to reload the ER with Ca for continued Ca efflux at the MAM. Thus, the MAM is not a passive buffer for Ca puffs; rather it helps modulate further Ca signaling through feedback loops that affect ER dynamics.
Regulating ER release of Ca at the MAM is especially critical because only a certain window of Ca uptake sustains the mitochondria, and consequently the cell, at homeostasis. Sufficient intraorganelle Ca signaling is required to stimulate metabolism by activating dehydrogenase enzymes critical to flux through the citric acid cycle. However, once Ca signaling in the mitochondria passes a certain threshold, it stimulates the intrinsic pathway of apoptosis in part by collapsing the mitochondrial membrane potential required for metabolism. Studies examining the role of pro- and anti-apoptotic factors support this model; for example, the anti-apoptotic factor Bcl-2 has been shown to interact with IP3Rs to reduce Ca filling of the ER, leading to reduced efflux at the MAM and preventing collapse of the mitochondrial membrane potential post-apoptotic stimuli. Given the need for such fine regulation of Ca signaling, it is perhaps unsurprising that dysregulated mitochondrial Ca has been implicated in several neurodegenerative diseases, while the catalogue of tumor suppressors includes a few that are enriched at the MAM. | 1 | Biochemistry |
Besides the ex vivo approach by the City of Hope National Medical Center discussed above, the Center for Infection and Immunity Amsterdam (CINIMA), the University of Amsterdam, the Netherlands, is extensively researching the composition of multi-cassette DNA constructs to tackle HIV. | 1 | Biochemistry |
Transcription of the cloned gene is a necessary component of the vector when expression of the gene is required: one gene may be amplified through transcription to generate multiple copies of mRNAs, the template on which protein may be produced through translation. A larger number of mRNAs would express a greater amount of protein, and how many copies of mRNA are generated depends on the promoter used in the vector. The expression may be constitutive, meaning that the protein is produced constantly in the background, or it may be inducible whereby the protein is expressed only under certain condition, for example when a chemical inducer is added. These two different types of expression depend on the types of promoter and operator used.
Viral promoters are often used for constitutive expression in plasmids and in viral vectors because they normally force constant transcription in many cell lines and types reliably. Inducible expression depends on promoters that respond to the induction conditions: for example, the murine mammary tumor virus promoter only initiates transcription after dexamethasone application and the Drosophila heat shock promoter only initiates after high temperatures.
Some vectors are designed for transcription only, for example for in vitro mRNA production. These vectors are called transcription vectors. They may lack the sequences necessary for polyadenylation and termination, therefore may not be used for protein production. | 1 | Biochemistry |
Cross sections commonly calculated using Mie theory include efficiency coefficients for extinction , scattering , and Absorption cross sections. These are normalized by the geometrical cross sections of the particle as
The cross section is defined by
where is the energy flow through the surrounding surface, and is the intensity of the incident wave. For a plane wave the intensity is going to be , where is the impedance of the host medium.
The main approach is based on the following. Firstly, we construct an imaginary sphere of radius (surface ) around the particle (the scatterer). The net rate of electromagnetic energy crosses the surface is
where is the time averaged Poynting vector. If energy is absorbed within the sphere, otherwise energy is being created within the sphere. We will not consider this case here. If the host medium is non-absorbing, the energy must be absorbed by the particle. We decompose the total field into incident and scattered parts , and the same for the magnetic field . Thus, we can decompose into the three terms , where
Where , , and .
All the field can be decomposed into the series of vector spherical harmonics (VSH). After that, all the integrals can be taken.
In the case of a uniform sphere of radius , permittivity , and permeability the problem has a precise solution. The scattering and extinction coefficients are | 7 | Physical Chemistry |
Diastereoselective DMD epoxidation of a chiral unsaturated ketone was applied to the synthesis of verrucosan-2β-ol.
Enantioselective dioxirane epoxidation is critical in a synthetic sequence leading to an analogue of glabrescol. The sequence produced the glabrescol analogue in 31% overall yield in only two steps. | 0 | Organic Chemistry |
A spectrophotometer built with a high quality double monochromator can produce light of sufficient purity and intensity that the instrument can measure a narrow band of optical attenuation of about one million fold (6 AU, Absorbance Units). | 7 | Physical Chemistry |
* gamma-Decalactone intense peach flavor
* gamma-Nonalactone coconut odor, popular in suntan lotions
* delta-Octalactone creamy note
* Jasmine lactone powerful fatty-fruity peach and apricot
* Massoia lactone powerful creamy coconut
* Wine lactone sweet coconut odor
* Sotolon (maple syrup, curry, fenugreek) | 0 | Organic Chemistry |
The E. Coli Metabolome Database is a freely accessible, online database of >2,700 small molecule metabolites found in or produced by Escherichia coli (E. coli strain K12, MG1655). The ECMDB contains two kinds of information:
# Chemical information and
# Biochemical information.
The chemical information includes more than 2,700 metabolite structures with detailed metabolite descriptions, extensive chemical classifications, synthesis information and observed/calculated chemical properties. It also contains nearly 5,000 NMR, GC-MS and LC-MS spectra from more than 600 different metabolites. The biochemical information includes >1,600 protein (and DNA) sequences and >3,100 biochemical reactions that are linked to these metabolite entries. The ECMDB supports many different types of online queries including text searches, chemical structure searches, sequence similarity searches and spectral similarity searches. This makes it particularly useful for metabolomic researchers who are studying E. coli as a model organism.
Secondary electrospray ionization (SESI-MS) can discriminate between eleven E. Coli strains thanks to the volatile organic compound profiling. | 1 | Biochemistry |
The Repligen Award in Chemistry of Biological Processes was established in 1985 and consists of a silver medal and honorarium. Its purpose is to acknowledge and encourage outstanding contributions to the understanding of the chemistry of biological processes, with particular emphasis on structure, function, and mechanism. The Award is administered by the Division of Biological Chemistry of the American Chemical Society.
The award was suspended in 2018 until a patron can be found. | 1 | Biochemistry |
ADP/ATP translocase is very specifically inhibited by two families of compounds. The first family, which includes atractyloside (ATR) and carboxyatractyloside (CATR), binds to the ADP/ATP translocase from the cytoplasmic side, locking it in a cytoplasmic side open conformation. In contrast, the second family, which includes bongkrekic acid (BA) and isobongkrekic acid (isoBA), binds the translocase from the matrix, locking it in a matrix side open conformation. The negatively charged groups of the inhibitors bind strongly to the positively charged residues deep within the binding pocket. The high affinity (K in the nanomolar range) makes each inhibitor a deadly poison by obstructing cellular respiration/energy transfer to the rest of the cell. There are structures available that show the translocator locked in a cytoplasmic state by the inhibitor carboxyatractyloside, or in the matrix state by the inhibitor bongkrekic acid. | 1 | Biochemistry |
In biochemistry, sulfotransferases (SULTs) are transferase enzymes that catalyze the transfer of a sulfo group () from a donor molecule to an acceptor alcohol () or amine (). The most common sulfo group donor is 3-phosphoadenosine-5-phosphosulfate (PAPS). In the case of alcohol as acceptor, the product is a sulfate ():
whereas an amine leads to a sulfamate ():
Both reactive groups for a sulfonation via sulfotransferases may be part of a protein, lipid, carbohydrate or steroid. | 1 | Biochemistry |
In 1993, Schreiber and his co-workers reported the first total synthesis of the unnatural antipode (-)-discodermolide and determined the absolute stereochemistry of the natural product. The Schreiber team recognized three fragments of roughly equal complexity that are separated by olefinic units in discodermolide. The two starting materials, homoallylic alcohols, are both readily derived from 3-hydroxy-2-methylpropionate.
The trisubstituted (Z)-alkene of first fragment was generated by using the Still-Gennari reagent. Gilbert's reagent was then used to homologate it to an acetylene. Goekjian and Kishi method was then used to get the desired fragment, iodoacetylene. The same homoallylic alcohol was converted to diol in four steps. After oxidation to keto-aldehyde, it was homololated to dienes by a palladium-catalyzed coupling with vinylzinc bromide to generated the second fragment. The six-membered ring subunit was transformed from an acetal, which was obtained by an intramolecular 1,4-addition of a presumed hemiacetal intermediate.
The Schreiber team found that the NiCl and CrCl promoted addition of alkynyl iodide to aldehyde effectively. The reaction provides a 2:1 mixture of desired product and its isomer. However, the undesired isomer can be recycled to the desired epimer in three steps, including Swern oxidation and Corey's asymmetric reduction. Pd catalyzed partial hydrogenation of the alkyne to establish the Z-configuration at C(8)–C(9). The pivaloyloxy group was then converted to a bromide for the final coupling. A stereoselective enolate alkylation between the allylic bromide with the lithium enolate derived from the second fragment provided a 3:1 mixture of isomers and completed the backbone assembly of (-)-discodermolide. During the final conversion, the NaBH reduction of ketone provided a separable 2.5:1 mixture of isomers. The Schreiber synthesis of (-)-discodermolide has an overall yield of 3.2% with a longest linear sequence of 24 steps and 36 total steps. In 1996, the Schreiber group published the total synthesis of natural discodermolide with similar synthetic strategy (4.3% overall yield, 36 steps, 24 steps longest linear sequence. | 0 | Organic Chemistry |
ATP is one of four monomers required in the synthesis of RNA. The process is promoted by RNA polymerases. A similar process occurs in the formation of DNA, except that ATP is first converted to the deoxyribonucleotide dATP. Like many condensation reactions in nature, DNA replication and DNA transcription also consume ATP. | 1 | Biochemistry |
In organic chemistry, a sulfoxide, also called a sulphoxide, is an organosulfur compound containing a sulfinyl () functional group attached to two carbon atoms. It is a polar functional group. Sulfoxides are oxidized derivatives of sulfides. Examples of important sulfoxides are alliin, a precursor to the compound that gives freshly crushed garlic its aroma, and dimethyl sulfoxide (DMSO), a common solvent. | 0 | Organic Chemistry |
For atoms in the gas phase the principal effects are Doppler and pressure broadening. Lines are relatively sharp on the scale of measurement so that applications such as atomic absorption spectroscopy (AAS) and Inductively coupled plasma atomic emission spectroscopy (ICP) are used for elemental analysis. Atoms also have distinct x-ray spectra that are attributable to the excitation of inner shell electrons to excited states. The lines are relatively sharp because the inner electron energies are not very sensitive to the atom's environment. This is applied to X-ray fluorescence spectroscopy of solid materials. | 7 | Physical Chemistry |
As previously mentioned, cis-isomers of cycloalkenes exhibit more stability than trans-isomers; however, on an experimental and computational level, this property is only applicable to cycloalkenes with 10 carbons or less. As the number of carbons increase, the possibility of a trans-isomer occurring also increase. The geometrical considerations as analyzed by computational analysis are as follows.
The most stable trans-isomers of 10 ring or greater cycloalkenes exhibit 4 irregularities from standard geometric norms. The first irregularity is twisted planes of substituents along the C=C. Using C=C as the stable axis, 2 substituents of 1 carbon can be visualized on the same plane, equally applied to the other carbon. These planes are not planar and instead one carbon substituent plane twists along the axis away or toward the other carbon’s plane. This twisting leads to pyramidalization forming a pyramidal alkene which is the second irregularity. A greater angle of twisting, usually results in lower carbon number rings and decreases as the carbon number increases. Pyramidalization is important in highered number rings, because it increases p-orbital overlap for stability, and reduces torsional strain.
Bond length between the C=C and corresponding vinylic carbons also vary. In smaller cycloalkenes, it is expected for the bonds to be greater in length uniformly to account for increased strain, but for example, trans-cycloheptane has varying bond lengths. Also, the vinylic carbons on trans cyclohexanes exhibit longer bond lengths than their respective cis isomer for trans-cycloheptane through trans-cyclononene (7 carbon and 9 carbon cycloalkenes). | 0 | Organic Chemistry |
Methyl red (2-(N,N-dimethyl-4-aminophenyl) azobenzenecarboxylic acid), also called C.I. Acid Red 2, is an indicator dye that turns red in acidic solutions. It is an azo dye, and is a dark red crystalline powder. Methyl red is a pH indicator; it is red in pH under 4.4, yellow in pH over 6.2, and orange in between, with a pK of 5.1. Murexide and methyl red are investigated as promising enhancers of sonochemical destruction of chlorinated hydrocarbon pollutants. Methyl red is classed by the IARC in group 3 - unclassified as to carcinogenic potential in humans. | 3 | Analytical Chemistry |
Broadly, aptamers are small molecules composed of either single-stranded DNA or RNA and are typically 20-100 nucleotides in length, or ~3-60 kDa. Because of their single-stranded nature, aptamers are capable of forming many secondary structures, including pseudoknots, stem loops, and bulges, through intra-strand base pairing interactions. The combinations of secondary structures present in an aptamer confer it a particular tertiary structure which in turn dictates the specific target the aptamer will selectively bind to. Because of the selective binding ability of aptamers, they are considering a promising biomolecule for use in pharmaceuticals. Additionally, aptamers exhibit tight binding to targets, with dissociation constants often in the pM to nM range. Besides their strong binding ability, aptamers are also valued because they can be used on targets that are not capable of being bound by small peptides generated by phage display or by antibodies, and they are able to differentiate between conformational isomers and amino acid substitutions. Also, because aptamers are nucleic-acid based, they can be directly synthesized, eliminating the need for cell-based expression and extraction as is the case in antibody production. RNA aptamers in particular are capable of producing a myriad of different structures, leading to speculations that they are more discriminating in their target affinity compared to DNA aptamers. | 1 | Biochemistry |
The regulatory subunit dimer of PKA is important for localizing the kinase inside the cell. The dimerization and docking (D/D) domain of the dimer binds to the A-kinase binding (AKB) domain of A-kinase anchor protein (AKAP). The AKAPs localize PKA to various locations (e.g., plasma membrane, mitochondria, etc.) within the cell.
AKAPs bind many other signaling proteins, creating a very efficient signaling hub at a certain location within the cell. For example, an AKAP located near the nucleus of a heart muscle cell would bind both PKA and phosphodiesterase (hydrolyzes cAMP), which allows the cell to limit the productivity of PKA, since the catalytic subunit is activated once cAMP binds to the regulatory subunits. | 1 | Biochemistry |
Alcohol is absorbed throughout the gastrointestinal tract, but more slowly in the stomach than in the small or large intestine. For this reason, alcohol consumed with food is absorbed more slowly, because it spends a longer time in the stomach. Furthermore, alcohol dehydrogenase is present in the stomach lining. After absorption, the alcohol passes to the liver through the hepatic portal vein, where it undergoes a first pass of metabolism before entering the general bloodstream.
Alcohol is removed from the bloodstream by a combination of metabolism, excretion, and evaporation. Alcohol is metabolized mainly by the group of six enzymes collectively called alcohol dehydrogenase. These convert the ethanol into acetaldehyde (an intermediate more toxic than ethanol). The enzyme acetaldehyde dehydrogenase then converts the acetaldehyde into non-toxic acetic acid.
Many physiologically active materials are removed from the bloodstream (whether by metabolism or excretion) at a rate proportional to the current concentration, so that they exhibit exponential decay with a characteristic half-life (see pharmacokinetics). This is not true for alcohol, however. Typical doses of alcohol actually saturate the enzymes capacity, so that alcohol is removed from the bloodstream at an approximately constant rate. This rate varies considerably between individuals. Another sex-based difference is in the elimination of alcohol. For females, the concentration of alcohol in breast milk produced during lactation is closely correlated to the individuals blood alcohol content. People under 25, women, or people with liver disease may process alcohol more slowly. Falsely high BAC readings may be seen in patients with kidney or liver disease or failure.
Such persons also have impaired acetaldehyde dehydrogenase, which causes acetaldehyde levels to peak higher, producing more severe hangovers and other effects such as flushing and tachycardia. Conversely, members of certain ethnicities that traditionally did not use alcoholic beverages have lower levels of alcohol dehydrogenases and thus "sober up" very slowly but reach lower aldehyde concentrations and have milder hangovers. The rate of detoxification of alcohol can also be slowed by certain drugs which interfere with the action of alcohol dehydrogenases, notably aspirin, furfural (which may be found in fusel alcohol), fumes of certain solvents, many heavy metals, and some pyrazole compounds. Also suspected of having this effect are cimetidine, ranitidine, and acetaminophen (paracetamol).
Currently, the only known substance that can increase the rate of alcohol metabolism is fructose. The effect can vary significantly from person to person, but a 100 g dose of fructose has been shown to increase alcohol metabolism by an average of 80%. Fructose also increases false positives of high BAC readings in anyone with proteinuria and hematuria, due to kidney-liver metabolism.
The peak of blood alcohol level (or concentration of alcohol) is reduced after a large meal. | 1 | Biochemistry |
In materials science, the sessile drop technique is a method used for the characterization of solid surface energies, and in some cases, aspects of liquid surface energies. The main premise of the method is that by placing a droplet of liquid with a known surface energy and contact angle, the surface energy of the solid substrate can be calculated. The liquid used for such experiments is referred to as the probe liquid, and the use of several different probe liquids is required. | 7 | Physical Chemistry |
Phosphoenolpyruvate and erythrose-4-phosphate condense to form 3-deoxy--arabinoheptulosonate-7-phosphate (DAHP), in a reaction catalyzed by the enzyme DAHP synthase. DAHP is then transformed to 3-dehydroquinate (DHQ), in a reaction catalyzed by DHQ synthase. Although this reaction requires nicotinamide adenine dinucleotide (NAD) as a cofactor, the enzymic mechanism regenerates it, resulting in the net use of no NAD.
DHQ is dehydrated to 3-dehydroshikimic acid by the enzyme 3-dehydroquinate dehydratase, which is reduced to shikimic acid by the enzyme shikimate dehydrogenase, which uses nicotinamide adenine dinucleotide phosphate (NADPH) as a cofactor. | 1 | Biochemistry |
* EIA/JEDEC Standard EIA/JESD61: Isothermal Electromigration Test Procedure.
* EIA/JEDEC Standard EIA/JESD63: Standard method for calculating the electromigration model parameters for current density and temperature.
* [https://www.ifte.de/books/em/em_chap2.pdf Fundamentals of electromigration, Chapter 2] | 7 | Physical Chemistry |
The translations form a normal abelian subgroup of rank 3, called the Bravais lattice (so named after French physicist Auguste Bravais). There are 14 possible types of Bravais lattice. The quotient of the space group by the Bravais lattice is a finite group which is one of the 32 possible point groups. | 4 | Stereochemistry |
Coomber's relationship can be used to describe how the internal pressure and dielectric constant of a non-polar liquid are related.
As , which defines the internal pressure of a liquid, it can be found that:
where
* is equal to the number of molecules
* is the ionization potential of the liquid
* is a temperature dependent relation based on numerical constants of the pair summation from inter-particle geometry
* is the polarizability
* is the volume of the liquid
where for most non-polar liquids | 7 | Physical Chemistry |
Cold hardening is the physiological and biochemical process by which an organism prepares for cold weather. | 1 | Biochemistry |
Louis Georges Gouy in 1910 and David Leonard Chapman in 1913 both observed that capacitance was not a constant and that it depended on the applied potential and the ionic concentration. The "Gouy–Chapman model" made significant improvements by introducing a diffuse model of the DL. In this model, the charge distribution of ions as a function of distance from the metal surface allows Maxwell–Boltzmann statistics to be applied. Thus the electric potential decreases exponentially away from the surface of the fluid bulk.
Gouy-Chapman layers may bear special relevance in bioelectrochemistry. The observation of long-distance inter-protein electron transfer through the aqueous solution has been attributed to a diffuse region between redox partner proteins (cytochromes c and c) that is depleted of cations in comparison to the solution bulk, thereby leading to reduced screening, electric fields extending several nanometers, and currents decreasing quasi exponentially with the distance at rate ~1 nm. This region is termed "Gouy-Chapman conduit" and is strongly regulated by phosphorylation, which adds one negative charge to the protein surface that disrupts cationic depletion and prevents long-distance charge transport. Similar effects are observed at the redox active site of photosynthetic complexes. | 7 | Physical Chemistry |
The nucleus accumbens (NAc) has a significant role in addiction. In the nucleus accumbens of mice, repeated cocaine exposure resulted in reduced TET1 messenger RNA (mRNA) and reduced TET1 protein expression. Similarly, there was a ~40% decrease in TET1 mRNA in the NAc of human cocaine addicts examined postmortem.
As indicated above in learning and memory, a short hairpin RNA (shRNA) is an artificial RNA molecule with a tight hairpin turn that can be used to silence target gene expression via RNA interference. Feng et al. injected shRNA targeted to TET1 in the NAc of mice. This could reduce TET1 expression in the same manner as reduction of TET1 expression with cocaine exposure. They then used an indirect measure of addiction, conditioned place preference. Conditioned place preference can measure the amount of time an animal spends in an area that has been associated with cocaine exposure, and this can indicate an addiction to cocaine. Reduced Tet1 expression caused by shRNA injected into the NAc robustly enhanced cocaine place conditioning. | 1 | Biochemistry |
For an optically thin plasma composed of a single, neutral atomic species in local thermal equilibrium (LTE), the density of photons emitted by a transition from level i to level j is
where :
* is the emission rate density of photons (in m sr s)
* is the number of neutral atoms in the plasma (in m)
* is the transition probability between level i and level j (in s)
* is the degeneracy of the upper level i (2J+1)
* is the partition function (unitless)
* is the energy level of the upper level i (in eV)
* is the Boltzmann constant (in eV/K)
* is the temperature (in K)
* is the line profile such that
* is the wavelength (in nm)
The partition function is the statistical occupation fraction of every level of the atomic species : | 7 | Physical Chemistry |
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