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Ultra- and High Shear in-line or batch reactors allow production of biodiesel continuously, semi- continuously, and in batch-mode. This drastically reduces production time and increases production volume.
The reaction takes place in the high-energetic shear zone of the Ultra- and High Shear mixer by reducing the droplet size of the immiscible liquids such as oil or fats and methanol. Therefore, the smaller the droplet size the larger the surface area the faster the catalyst can react. | 0 | Organic Chemistry |
The mechanism of electromethanogenesis is outlined in Figure 1. Water is introduced into the system with the anode, biocathode, and microbes. At the anode, microbes attract HO molecules which are then oxidized after an electrical current is turned on from the power source. Oxygen is released from the anode side. The protons and electrons oxidized from the HO move across the membrane where they move into the material that makes up the biocathode. The new microbe on the biocathode has the ability to transfer the new electrons from the biocathode material and convert them into protons. These protons are then used in the major pathway that drives methane production in electromethanogenesis—CO reduction. CO is brought in on the biocathode side of the system where it is reduced by the protons produced by the microorganisms to yield HO and methane (CH). Methane is produced and can then be released from the biocathode side and stored. | 7 | Physical Chemistry |
Many kinds of molecular-weight size markers exist, and each possess unique characteristics, lending to their involvement in a number of biological techniques. Selection of a molecular-weight size marker depends upon the marker type (DNA, RNA, or protein) and the length range it offers (e.g. 1kb). Before selecting a molecular-weight size marker, it is important to become familiar with these characteristics and properties. In a particular instance one type may be more appropriate than another. Although specific markers can vary between protocols for a given technique, this section will outline general markers and their roles. | 1 | Biochemistry |
Förster resonance energy transfer (FRET)-based Cl indicators consist of two fluorescent proteins, Cyan fluorescent protein (CFP) and YFP connected via a polypeptide linker. This allows ratiometric Cl measurements based on the Cl sensitivity of YFP and Cl insensivity of CFP. Clomeleon and Cl Sensor are FRET-based Cl indicators that allow ratiometric non-invasive monitoring of chloride activity in living cells. | 3 | Analytical Chemistry |
Arsenic containing concentrates are roasted in a fluidized bed to remove 60% to 70% of the arsenic present as arsenic oxide (AsO). The roasted ores can be treated with hydrochloric acid and chlorine or with sulfuric acid to give a leach solution that can be purified by hydrometallurgical methods and from which cobalt can be recovered by electro refining or by carbonate precipitation. If hydrochloric acid is used then cobalt may be extracted using alamine 336 in meta-xylene. Cobalt can be extracted also using dialkylphosphinic acid. When cobalt carbonate (CoCO) is heated (calcined) above 400 °C it decomposes into carbon dioxide (CO) and cobalt(II) oxide (CoO) and can be refined as an oxide concentrate (see above). | 8 | Metallurgy |
Neuromuscular blocking agents need to fit in a space close to 2 nanometres, which resembles the molecular length of decamethonium. Some molecules of decamethonium congeners may bind only to one receptive site. Flexible molecules have a greater chance of fitting receptive sites. However, the most populated conformation may not be the best-fitted one. Very flexible molecules are, in fact, weak neuromuscular inhibitors with flat dose-response curves. On the other hand, stiff or rigid molecules tend to fit well or not at all. If the lowest-energy conformation fits, the compound has high potency because there is a great concentration of molecules close to the lowest-energy conformation. Molecules can be thin but yet rigid. Decamethonium for example needs relatively high energy to change the N-N distance.
In general, molecular rigidity contributes to potency, while size affects whether a muscle relaxant shows a polarizing or a depolarizing effect. Cations must be able to flow through the trans-membrane tube of the ion-channel to depolarize the endplate. Small molecules may be rigid and potent but unable to occupy or block the area between the receptive sites. Large molecules, on the other hand, may bind to both receptive sites and hinder depolarizing cations independent of whether the ion-channel is open or closed below. Having a lipophilic surface pointed towards the synapse enhances this effect by repelling cations. The importance of this effect varies between different muscle relaxants and classifying depolarizing from non-depolarizing blocks is a complex issue. The onium heads are usually kept small and the chains connecting the heads usually keep the N-N distance at 10 N or O atoms. Keeping the distance in mind the structure of the chain can vary (double bonded, cyclohexyl, benzyl, etc.)
Succinylcholine has a 10-atom distance between its N atoms, like decamethonium. Yet it has been reported that it takes two molecules, as with acetylcholine, to open one nicotinic ion channel. The conformational explanation for this is that each acetylcholine moiety of succinylcholine prefers the gauche (bent, cis) state. The attraction between the N and O atoms is greater than the onium head repulsion. In this most populated state, the N-N distance is shorter than the optimal distance of ten carbon atoms and too short to occupy both receptive sites. This similarity between succinyl- and acetyl-choline also explains its acetylcholine-like side-effects.
Comparing molecular lengths, the pachycurares dimethyltubocurarine and d-tubocurarine both are very rigid and measure close to 1.8 nm in total length. Pancuronium and vecuronium measure 1.9 nm, whereas pipecuronium is 2.1 nm. The potency of these compounds follows the same rank of order as their length. Likewise, the leptocurares prefer a similar length. Decamethonium, which measures 2 nm, is the most potent in its category, whereas C11 is slightly too long. Gallamine despite having low bulk and rigidity is the most potent in its class, and it measures 1.9 nm. Based on this information one can conclude that the optimum length for neuromuscular blocking agents, depolarizing or not, should be 2 to 2.1 nm.
The CAR for long-chain bisquaternary tetrahydroisoquinolines like atracurium, cisatracurium, mivacurium, and doxacurium is hard to determine because of their bulky onium heads and large number of rotatable bonds and groups. These agents must follow the same receptive topology as others, which means that they do not fit between the receptive sites without bending. Mivacurium for example has a molecular length of 3.6 nm when stretched out, far from the 2 to 2.1 nm optimum. Mivacurium, atracurium, and doxacurium have greater N-N distance and molecular length than d-tubocurarine even when bent. To make them fit, they have flexible connections that give their onium heads a chance to position themselves beneficially. This bent N-N scenario probably does not apply to laudexium and decamethylene bisatropium, which prefer a straight conformation. | 1 | Biochemistry |
A severe shortage of potassium in body fluids may cause a potentially fatal condition known as hypokalemia. Hypokalemia typically results from loss of potassium through diarrhea, diuresis, or vomiting. Symptoms are related to alterations in membrane potential and cellular metabolism. Symptoms include muscle weakness and cramps, paralytic ileus, ECG abnormalities, intestinal paralysis, decreased reflex response and (in severe cases) respiratory paralysis, alkalosis and arrhythmia.
In rare cases, habitual consumption of large amounts of black licorice has resulted in hypokalemia. Licorice contains a compound (Glycyrrhizin) that increases urinary excretion of potassium. | 1 | Biochemistry |
The earliest surviving bimetallic strip was made by the eighteenth-century clockmaker John Harrison who is generally credited with its invention. He made it for his third marine chronometer (H3) of 1759 to compensate for temperature-induced changes in the balance spring. It should not be confused with the bimetallic mechanism for correcting for thermal expansion in his gridiron pendulum. His earliest examples had two individual metal strips joined by rivets but he also invented the later technique of directly fusing molten brass onto a steel substrate. A strip of this type was fitted to his last timekeeper, H5. Harrison's invention is recognized in the memorial to him in Westminster Abbey, England. | 8 | Metallurgy |
This method was developed by British physicists Oliver Lodge in 1886 and William Cecil Dampier in 1893. It depends on the movement of the boundary between two adjacent electrolytes under the influence of an electric field. If a colored solution is used and the interface stays reasonably sharp, the speed of the moving boundary can be measured and used to determine the ion transference numbers.
The cation of the indicator electrolyte should not move faster than the cation whose transport number is to be determined, and it should have same anion as the principle electrolyte. Besides the principal electrolyte (e.g., HCl) is kept light so that it floats on indicator electrolyte. serves best because is less mobile than and is common to both and the principal electrolyte HCl.
For example, the transport numbers of hydrochloric acid (HCl(aq)) may be determined by electrolysis between a cadmium anode and an Ag-AgCl cathode. The anode reaction is so that a cadmium chloride () solution is formed near the anode and moves toward the cathode during the experiment. An acid-base indicator such as bromophenol blue is added to make visible the boundary between the acidic HCl solution and the near-neutral solution. The boundary tends to remain sharp since the leading solution HCl has a higher conductivity that the indicator solution , and therefore a lower electric field to carry the same current. If a more mobile ion diffuses into the solution, it will rapidly be accelerated back to the boundary by the higher electric field; if a less mobile ion diffuses into the HCl solution it will decelerate in the lower electric field and return to the solution. Also the apparatus is constructed with the anode below the cathode, so that the denser solution forms at the bottom.
The cation transport number of the leading solution is then calculated as
where is the cation charge, the concentration, the distance moved by the boundary in time , the cross-sectional area, the Faraday constant, and the electric current. | 7 | Physical Chemistry |
MG (pyrimido[1,2-a]purin-10(3H)-one) is a heterocyclic compound which is a by-product of base excision repair (BER) of a specific type of DNA adduct called MdG. The MdG adduct in turn is formed by a condensation reaction between guanosine nucleotides in DNA and either malondialdehyde (propanedial) or acrolein. If not repaired, these adducts are mutagenic and carcinogenic.
Malondialdehyde is an end product of lipid peroxidation while acrolein is a result of DNA peroxidation.
MdG is the major endogenous DNA adduct in humans. MdG adducts have been detected in cell DNA in liver, leucocytes, pancreas and breast in concentrations of 1-120 per 10 nucleotides. Detection and quantification of MdG adducts in the body as measured by free MG is a tool for detecting DNA damage that may lead to cancer. Free MG is also biomarker for oxidative stress. | 1 | Biochemistry |
The reaction of cyclopropylmethamine with sodium nitrite in dilute aqueous perchloric acid solution yielded a mixture of 48% cyclopropylmethyl alcohol, 47% cyclobutanol, and 5% homoallylic alcohol (but-3-en-1-ol). In the non-classical perspective, the positive charge is delocalized throughout the carbocation intermediate structure via resonance, resulting in partial (electron-deficient) bonds. Evidently, the relatively low yield of the homoallylic alcohol implies that the homoallylic structure is the weakest resonance contributor. | 7 | Physical Chemistry |
Self-splicing occurs for rare introns that form a ribozyme, performing the functions of the spliceosome by RNA alone. There are three kinds of self-splicing introns, Group I, Group II and Group III. Group I and II introns perform splicing similar to the spliceosome without requiring any protein. This similarity suggests that Group I and II introns may be evolutionarily related to the spliceosome. Self-splicing may also be very ancient, and may have existed in an RNA world present before protein.
Two transesterifications characterize the mechanism in which group I introns are spliced:
# 3OH of a free guanine nucleoside (or one located in the intron) or a nucleotide cofactor (GMP, GDP, GTP) attacks phosphate at the 5 splice site.
# 3OH of the 5 exon becomes a nucleophile and the second transesterification results in the joining of the two exons.
The mechanism in which group II introns are spliced (two transesterification reaction like group I introns) is as follows:
# The 2OH of a specific adenosine in the intron attacks the 5 splice site, thereby forming the lariat
# The 3OH of the 5 exon triggers the second transesterification at the 3' splice site, thereby joining the exons together. | 1 | Biochemistry |
* DMSO
* Ethylene glycol
* Glycerol
* 2-Methyl-2,4-pentanediol (MPD)
* Propylene glycol
* Sucrose
* Trehalose
*Heavy water [7] | 1 | Biochemistry |
For imides derived from ammonia, the N–H center is weakly acidic. Thus, alkali metal salts of imides can be prepared by conventional bases such as potassium hydroxide. The conjugate base of phthalimide is potassium phthalimide. These anion can be alkylated to give N-alkylimides, which in turn can be degraded to release the primary amine. Strong nucleophiles, such as potassium hydroxide or hydrazine are used in the release step.
Treatment of imides with halogens and base gives the N-halo derivatives. Examples that are useful in organic synthesis are N-chlorosuccinimide and N-bromosuccinimide, which respectively serve as sources of "Cl" and "Br" in organic synthesis. | 0 | Organic Chemistry |
* Flavor: the artificial sweetener aspartame has two enantiomers. -aspartame tastes sweet whereas -aspartame is tasteless.
* Odor: R-(–)-carvone smells like spearmint whereas S-(+)-carvone smells like caraway.
* Drug effectiveness: the antidepressant drug citalopram is sold as a racemic mixture. However, studies have shown that only the (S)-(+) enantiomer (escitalopram) is responsible for the drug's beneficial effects.
* Drug safety: ‑penicillamine is used in chelation therapy and for the treatment of rheumatoid arthritis whereas ‑penicillamine is toxic as it inhibits the action of pyridoxine, an essential B vitamin. | 4 | Stereochemistry |
Urea is used in Selective Non-Catalytic Reduction (SNCR) and Selective Catalytic Reduction (SCR) reactions to reduce the nitrogen oxide| pollutants in exhaust gases from combustion from diesel, dual fuel, and lean-burn natural gas engines. The BlueTec system, for example, injects a water-based urea solution into the exhaust system. Ammonia () produced by the hydrolysis of urea reacts with nitrogen oxides () and is converted into nitrogen gas () and water within the catalytic converter. The conversion of noxious to innocuous is described by the following simplified global equation:
When urea is used, a pre-reaction (hydrolysis) occurs to first convert it to ammonia:
Being a solid highly soluble in water (545 g/L at 25 °C), urea is much easier and safer to handle and store than the more irritant, caustic and hazardous ammonia (), so it is the reactant of choice. Trucks and cars using these catalytic converters need to carry a supply of diesel exhaust fluid, also sold as AdBlue, a solution of urea in water. | 0 | Organic Chemistry |
The Cieplak effect relies on the stabilizing interaction of mixing full and empty orbitals to delocalize electrons, known as hyperconjugation. When the highest occupied molecular orbital (HOMO) of one system and the lowest unoccupied molecular orbital (LUMO) of another system have comparable energies and spatial overlap, the electrons can delocalize and sink into a lower energy level. Often, the HOMO of a system is a full σ (bonding) orbital and the LUMO is an empty σ* (antibonding) orbital. This mixing is a stabilizing interaction and has been widely used to explain such phenomena as the anomeric effect. A common requirement of hyperconjugation is that the bonds donating and accepting electron density are antiperiplanar to each other, to allow for maximum orbital overlap.
The Cieplak effect uses hyperconjugation to explain the face-selective addition of nucleophiles to carbonyl carbons. Specifically, donation into the low-lying σ* bond by antiperiplanar electron-donating substituents is the stabilizing interaction which lowers the transition state energy of one stereospecific reaction pathway and thus increases the rate of attack from one side. In the simplest model, a conformationally constrained cyclohexanone is reduced to the corresponding alcohol. Reducing agents add a hydride to the carbonyl carbon via attack along the Burgi–Dunitz angle, which can come from the top along a pseudo-axial trajectory or from below, along a pseudo-equatorial trajectory. It has long been known that large reducing agents add hydride to the equatorial position to avoid steric interactions with axial hydrogens on the ring. Small hydride sources, however, add hydride to an axial position for reasons which are still disputed.
The Cieplak effect explains this phenomenon by postulating that hyperconjugation of the forming σ* orbital with geometrically aligned σ orbitals is the stabilizing interaction that controls stereoselectivity. In an equatorial approach, the bonds that are geometrically aligned antiperiplanar to the forming C–H bond are the C–C bonds of the ring, so they donate electron density to σ*. In an axial approach, the neighboring axial C–H bonds are aligned antiperiplanar to the forming C–H bond, so they donate electron density to σ*. Because C-H bonds are better electron donors than C–C bonds, they are better able to participate in this stabilizing interaction and so this pathway is favored. | 0 | Organic Chemistry |
The reactions are most usually carried out in test tubes into which a gel is formed that contains a dilute solution of one of the reactants.
If a hot solution of agar gel also containing a dilute solution of potassium dichromate is poured in a test tube, and after the gel solidifies a more concentrated solution of silver nitrate is poured on top of the gel, the silver nitrate will begin to diffuse into the gel. It will then encounter the potassium dichromate and will form a continuous region of precipitate at the top of the tube.
After some hours, the continuous region of precipitation is followed by a clear region with no sensible precipitate, followed by a short region of precipitate further down the tube. This process continues down the tube forming several, up to perhaps a couple dozen, alternating regions of clear gel and precipitate rings. | 7 | Physical Chemistry |
Pharmacologic down-regulation of (mTOR) pathway during chemotherapy in a mouse model prevents activation of primordial follicles, preserves ovarian function, and maintains normal fertility using clinically available inhibitors INK and RAD. In that way, it helps to maintain fertility while undergoing chemotherapy treatments. These mTOR inhibitors, when administered as pretreatment or co-treatment with standard gonadotoxic chemotherapy, helps to maintain ovarian follicles in their primordial state. | 1 | Biochemistry |
A typical experiment, consists of a glass tube of volume V, and of cross-section A, which is open on one of its end. A ball (or sometimes a piston) of mass m with the same cross-section, creating an air-tight seal, is allowed to fall under gravity g. The entrapped gas is first compressed by the weight of the piston, which leads to an increase in temperature. In the course of the piston falling, a gas cushion is created, and the piston bounces. Harmonic oscillation occurs, which slowly damps. The result is a rapid sequence of expansion and compression of the gas. The picture shows a revised version of the original Rüchardt setup: the sphere oscillating inside the tube is here replaced by a "breast-pump" which acts as an oscillating glass-piston; in this new setup three sensors allow to measure in real-time the piston oscillations as well as the pressure and temperature oscillations of the air inside the bottle (more details may be found in )
According to Figure 1, the piston inside the tube is in equilibrium if the pressure P inside the glass bottle is equal to the sum of the atmospheric pressure P and the pressure increase due to the piston weight :
When the piston moves beyond the equilibrium by a distance dx, the pressure changes by dp. A force F will be exerted on the piston, equal to
According to Newtons second law of motion, this force will create an acceleration a' equal to
As this process is adiabatic, the equation for ideal gas (Poisson's equation) is:
It follows using differentiation from the equation above that:
If the piston moves by a distance in the glass tube, the corresponding change in volume will be
By substituting equation into equation , we can rewrite as follows:
Solving this equation and rearranging terms yields the differential equation of a harmonic oscillation from which the angular frequency ω can be deduced:
From this, the period T of harmonic oscillation performed by the ball is:
Measuring the period of oscillation T and the relative pressure P in the tube yields the equation for the adiabatic exponent: | 7 | Physical Chemistry |
Malaria and vitamin A deficiency are both common among young children in sub-Saharan Africa. Vitamin A supplementation to children in regions where vitamin A deficiency is common has repeatedly been shown to reduce overall mortality rates, especially from measles and diarrhea. For malaria, clinical trial results are mixed, either showing that vitamin A treatment did not reduce the incidence of probable malarial fever, or else did not affect incidence, but did reduce slide-confirmed parasite density and reduced the number of fever episodes. The question was raised as to whether malaria causes vitamin A deficiency, or vitamin A deficiency contributes to the severity of malaria, or both. Researchers proposed several mechanisms by which malaria (and other infections) could contribute to vitamin A deficiency, including a fever-induced reduction in synthesis of retinal-binding protein (RBP) responsible for transporting retinol from liver to plasma and tissues, but reported finding no evidence for a transient depression or restoration of plasma RBP or retinol after a malarial infection was eliminated. | 1 | Biochemistry |
Glutaminolysis partially recruits reaction steps from the citric acid cycle and the malate-aspartate shuttle. | 1 | Biochemistry |
A settling chamber where the two phases separate by static decantation. Coalescence plates facilitate the separation of the emulsion into two phases (heavy and light). The two phases then pass to continuous stages by overflowing the light phase and heavy phase weirs. The height of the heavy phase weir can be adjusted in order to position the heavy/light interphase in the settling chamber based on the density of each one of the phases.
The settler is a calm pool downstream of the mixer where the liquids are allowed to separate by gravity. The liquids are then removed separately from the end of the mixer. | 3 | Analytical Chemistry |
The three prime untranslated regions (3UTRs) of messenger RNAs (mRNAs) often contain regulatory sequences that post-transcriptionally cause gene silencing. Such 3-UTRs often contain both binding sites for microRNAs (miRNAs) as well as for regulatory proteins. By binding to specific sites within the 3-UTR, a large number of specific miRNAs decrease gene expression of their particular target mRNAs by either inhibiting translation or directly causing degradation of the transcript, using a mechanism similar to RNA interference (see MicroRNA). The 3-UTR also may have silencer regions that bind repressor proteins that inhibit the expression of an mRNA.
The 3-UTR often contains microRNA response elements (MREs). MREs are sequences to which miRNAs bind and cause gene silencing. These are prevalent motifs within 3-UTRs. Among all regulatory motifs within the 3'-UTRs (e.g. including silencer regions), MREs make up about half of the motifs.
As of 2014, the miRBase web site, an archive of miRNA sequences and annotations, listed 28,645 entries in 233 biologic species. Of these, 1,881 miRNAs were in annotated human miRNA loci. miRNAs were predicted to each have an average of about four hundred target mRNAs (causing gene silencing of several hundred genes). Freidman et al. estimate that >45,000 miRNA target sites within human mRNA 3'UTRs are conserved above background levels, and >60% of human protein-coding genes have been under selective pressure to maintain pairing to miRNAs.
Direct experiments show that a single miRNA can reduce the stability of hundreds of unique mRNAs. Other experiments show that a single miRNA may repress the production of hundreds of proteins, but that this repression often is relatively mild (less than 2-fold).
The effects of miRNA dysregulation of gene expression seem to be important in cancer. For instance, in gastrointestinal cancers, nine miRNAs have been identified as epigenetically altered and effective in down regulating DNA repair enzymes.
The effects of miRNA dysregulation of gene expression also seem to be important in neuropsychiatric disorders, such as schizophrenia, bipolar disorder, major depression, Parkinsons disease, Alzheimers disease and autism spectrum disorders. | 1 | Biochemistry |
A liquid-impregnated surface consists of two distinct layers. The first is a highly textured or porous substrate with features spaced sufficiently close to stably contain the second layer which is an impregnating liquid that fills in the spaces between the features. The liquid must have a surface energy well-matched to the substrate in order to form a stable film. These surfaces bioimitate the carnivorous Venezuelan pitcher plant, which uses microscale hairs to create a water slide that causes ants to slip to their death. Slippery surfaces are finding applications in commercial products, anti-fouling surfaces, anti-icing and biofilm-resistant medical devices. | 7 | Physical Chemistry |
Adenylate-uridylate-rich elements (AU-rich elements; AREs) are found in the 3' untranslated region (UTR) of many messenger RNAs (mRNAs) that code for proto-oncogenes, nuclear transcription factors, and cytokines. AREs are one of the most common determinants of RNA stability in mammalian cells.
AREs are defined as a region with frequent adenine and uridine bases in a mRNA. They usually target the mRNA for rapid degradation.
ARE-directed mRNA degradation is influenced by many exogenous factors, including phorbol esters, calcium ionophores, cytokines, and transcription inhibitors. These observations suggest that AREs play a critical role in the regulation of gene transcription during cell growth and differentiation, and the immune response.
AREs have been divided into three classes with different sequences. The best characterised adenylate uridylate (AU)-rich Elements have a core sequence of AUUUA within U-rich sequences (for example WWWU(AUUUA)UUUW where W is A or U). This lies within a 50–150 base sequence, repeats of the core AUUUA element are often required for function.
A number of different proteins (e.g. HuA, HuB, HuC, HuD, HuR) bind to these elements and stabilise the mRNA while others (AUF1, TTP, BRF1, TIA-1, TIAR, and KSRP) destabilise the mRNA, miRNAs may also bind to some of them. HuD (also called ELAVL4) binds to AREs and increases the half-life of ARE-bearing mRNAs in neurons during brain development and plasticity.
AREsite—a database for ARE containing genes—has recently been developed with the aim to provide detailed bioinformatic characterization of AU-rich elements. | 1 | Biochemistry |
The location of FAM227B, 15q21.2, was found to be associated with oral cancer. The 15q21.2 locus is mentioned in other literature as well. FGF7 is a neighbour of FAM227B in the 15q21.2 locus (rs10519227), and encodes for the fibroblast growth factor, which is involved in processes such as embryonic development, cell growth, tissue repair, tumor growth, invasion, and morphogenesis. FGF works as a signal for thyroid gland development, and an SNP on intron 2 of FGF7 has been associated with thyroid growth/goiter growth. This association was only significant at the genome level in males. It was found that the abnormal goiter growth is likely due to variant signals that cause increased levels of TSH. FAM227B was found to be related to at least some of the 48 significant DMRs (differentially methylated regions) between HF (high fertile) and LF (low fertile) groups in the genome of spermatozoa from boar animal model. FAM227B was found to be upregulated in LOXL2 knockdown. Knocking down LOXL2 results in lower levels of H3K4ox, resulting in chromatin decompaction, thus continuing activation of DNA damage response. This results in anticancer agents being more effective against cancerous cell lines. FAM227B was found to be a genetic risk variant in breast cancer. FAM227B was differentially expressed in prostrate genes of Esr2 knockout rats compared to wildtype rats. Esr2 is involved in anti-proliferation and differentiation. FAM227B was part of 20 upregulated genes in chorionic girdle during trophoblast development in horses. Protein FAM227B was differentially expressed in cardiovascular disease. FAM227B was found to be a candidate causal gene for lung cancer. FAM227B has a predicted p53 binding site. | 1 | Biochemistry |
In quantum mechanics the free rotation of a molecule is quantized, so that the rotational energy and the angular momentum can take only certain fixed values, which are related simply to the moment of inertia, , of the molecule. For any molecule, there are three moments of inertia: , and about three mutually orthogonal axes A, B, and C with the origin at the center of mass of the system. The general convention, used in this article, is to define the axes such that , with axis corresponding to the smallest moment of inertia. Some authors, however, define the axis as the molecular rotation axis of highest order.
The particular pattern of energy levels (and, hence, of transitions in the rotational spectrum) for a molecule is determined by its symmetry. A convenient way to look at the molecules is to divide them into four different classes, based on the symmetry of their structure. These are | 7 | Physical Chemistry |
Mathematically, the pressure of a mixture of non-reactive gases can be defined as the summation:
where , , ..., represent the partial pressures of each component.
where is the mole fraction of the ith component in the total mixture of n components . | 7 | Physical Chemistry |
If an antigen can be recognized by more than one component of its structure, it is less likely to be "missed" by the immune system. Mutation of pathogenic organisms can result in modification of antigen—and, hence, epitope—structure. If the immune system "remembers" what the other epitopes look like, the antigen, and the organism, will still be recognized and subjected to the body's immune response. Thus, the polyclonal response widens the range of pathogens that can be recognized. | 1 | Biochemistry |
From a thermodynamics point of view, at the melting point the change in Gibbs free energy ∆G of the substances is zero, but there are non-zero changes in the enthalpy (H) and the entropy (S), known respectively as the enthalpy of fusion (or latent heat of fusion) and the entropy of fusion. Melting is therefore classified as a first-order phase transition. Melting occurs when the Gibbs free energy of the liquid becomes lower than the solid for that material. The temperature at which this occurs is dependent on the ambient pressure.
Low-temperature helium is the only known exception to the general rule. Helium-3 has a negative enthalpy of fusion at temperatures below 0.3 K. Helium-4 also has a very slightly negative enthalpy of fusion below 0.8 K. This means that, at appropriate constant pressures, heat must be removed from these substances in order to melt them. | 7 | Physical Chemistry |
Neuromodulation is the physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons. Neuromodulators typically bind to metabotropic, G-protein coupled receptors (GPCRs) to initiate a second messenger signaling cascade that induces a broad, long-lasting signal. This modulation can last for hundreds of milliseconds to several minutes. Some of the effects of neuromodulators include: altering intrinsic firing activity, increasing or decreasing voltage-dependent currents, altering synaptic efficacy, increasing bursting activity and reconfigurating synaptic connectivity.
Major neuromodulators in the central nervous system include: dopamine, serotonin, acetylcholine, histamine, norepinephrine, nitric oxide, and several neuropeptides. Cannabinoids can also be powerful CNS neuromodulators. Neuromodulators can be packaged into vesicles and released by neurons, secreted as hormones and delivered through the circulatory system. A neuromodulator can be conceptualized as a neurotransmitter that is not reabsorbed by the pre-synaptic neuron or broken down into a metabolite. Some neuromodulators end up spending a significant amount of time in the cerebrospinal fluid (CSF), influencing (or "modulating") the activity of several other neurons in the brain. | 1 | Biochemistry |
Yet another method called the harmonic oscillator model of aromaticity (HOMA) is defined as a normalized sum of squared deviations of bond lengths from the optimal value, which is assumed to be realized for a fully aromatic system. An aromatic compound has HOMA value 1 whereas a non-aromatic compound has value 0. For all-carbon systems, the HOMA value is defined as:
where V=257.7 Å is the normalization value, n is the number of carbon–carbon bonds, and d are bond lengths (d=1.388 Å is the optimum value and d are the observed or computed values). | 7 | Physical Chemistry |
ATSDR has seven goals:
# Protect the public from environmental hazards and toxic exposures.
# Promote healthy environments.
# Advance the science of environmental public health.
# Support environmental public health practice.
# Educate communities, partners, and policy makers about environmental health risks and protective measures.
# Promote environmental justice and reduce health disparities associated with environmental exposures.
# Provide unique scientific and technical expertise to advance public health science and practice. | 1 | Biochemistry |
Photosynthesis is the process in which light energy is absorbed and converted to chemical energy. This chemical energy is eventually used in the conversion of carbon dioxide to sugar in plants. | 5 | Photochemistry |
Often a multi-disciplinary approach is taken in compiling all the components of a Phase I study, since skills in chemistry, atmospheric physics, geology, microbiology and even botany are frequently required. Many of the preparers are environmental scientists who have been trained to integrate these diverse disciplines. Many states have professional registrations which are applicable to the preparers of Phase I ESAs; for example, the state of California had a registration entitled "California Registered Environmental Assessor Class I or Class II" until July 2012, when it removed this REA certification program due to budget cuts.
Under ASTM E 1527-13 parameters were set forth as to who is qualified to perform Phase I ESAs. An Environmental Professional is someone with:
# a current Professional Engineers or Professional Geologists license or registration from a state or U.S. territory with 3 years equivalent full-time experience; or
# a Baccalaureate or higher degree from an accredited institution of higher education in a discipline of engineering or science and 5 years equivalent full-time experience; or
# have the equivalent of 10 years full-time experience.
A person not meeting one or more of those qualifications may assist in the conduct of a Phase I ESA if the individual is under the supervision or responsible charge of a person meeting the definition of an Environmental Professional when concluding such activities.
Most site assessments are conducted by private companies independent of the owner or potential purchaser of the land. | 2 | Environmental Chemistry |
In 1825, Johann Friedrich Engelhart discovered that the ratio of iron to protein is identical in the hemoglobins of several species. From the known atomic mass of iron, he calculated the molecular mass of hemoglobin to n × 16000 (n = number of iron atoms per hemoglobin molecule, now known to be 4), the first determination of a proteins molecular mass. This "hasty conclusion" drew ridicule from colleagues who could not believe that any molecule could be so large. However, Gilbert Smithson Adair confirmed Engelharts results in 1925 by measuring the osmotic pressure of hemoglobin solutions.
Although blood had been known to carry oxygen since at least 1794, the oxygen-carrying property of hemoglobin was described by Hünefeld in 1840. In 1851, German physiologist Otto Funke published a series of articles in which he described growing hemoglobin crystals by successively diluting red blood cells with a solvent such as pure water, alcohol or ether, followed by slow evaporation of the solvent from the resulting protein solution. Hemoglobin's reversible oxygenation was described a few years later by Felix Hoppe-Seyler.
With the development of X-ray crystallography, it became possible to sequence protein structures. In 1959, Max Perutz determined the molecular structure of hemoglobin. For this work he shared the 1962 Nobel Prize in Chemistry with John Kendrew, who sequenced the globular protein myoglobin.
The role of hemoglobin in the blood was elucidated by French physiologist Claude Bernard.
The name hemoglobin is derived from the words heme and globin, reflecting the fact that each subunit of hemoglobin is a globular protein with an embedded heme group. Each heme group contains one iron atom, that can bind one oxygen molecule through ion-induced dipole forces. The most common type of hemoglobin in mammals contains four such subunits. | 7 | Physical Chemistry |
RNA sequencing is a next-generation sequencing technology; as such it requires only a small amount of RNA and no previous knowledge of the genome. It allows for both qualitative and quantitative analysis of RNA transcripts, the former allowing discovery of new transcripts and the latter a measure of relative quantities for transcripts in a sample.
The three main steps of sequencing transcriptomes of any biological samples include RNA purification, the synthesis of an RNA or cDNA library and sequencing the library. The RNA purification process is different for short and long RNAs. This step is usually followed by an assessment of RNA quality, with the purpose of avoiding contaminants such as DNA or technical contaminants related to sample processing. RNA quality is measured using UV spectrometry with an absorbance peak of 260 nm. RNA integrity can also be analyzed quantitatively comparing the ratio and intensity of 28S RNA to 18S RNA reported in the RNA Integrity Number (RIN) score. Since mRNA is the species of interest and it represents only 3% of its total content, the RNA sample should be treated to remove rRNA and tRNA and tissue-specific RNA transcripts.
The step of library preparation with the aim of producing short cDNA fragments, begins with RNA fragmentation to transcripts in length between 50 and 300 base pairs. Fragmentation can be enzymatic (RNA endonucleases), chemical (trismagnesium salt buffer, chemical hydrolysis) or mechanical (sonication, nebulisation). Reverse transcription is used to convert the RNA templates into cDNA and three priming methods can be used to achieve it, including oligo-DT, using random primers or ligating special adaptor oligos. | 1 | Biochemistry |
The advantage of this method is that it is fairly objective and the measurement yields data which is inherently averaged over the wetted length. Although this does not help determine heterogeneity, it does automatically give a more accurate average value. Its disadvantages, aside from being more complicated than the goniometer method, include the fact that sample of an appropriate size must be produced with a uniform cross section in the submersion direction, and the wetted length must be measured with some precision. In addition, this method is only appropriate if both sides of the sample are identical, otherwise the measured data will be a result of two completely different interactions.
Strictly speaking, this is not a sessile drop technique, as we are using a small submerging pool, rather than a droplet. However, the calculations described in the following sections, which were derived for the relation of the sessile drop contact angle to the surface energy, apply just as well. | 7 | Physical Chemistry |
AR3 is expressed by Halorubrum sodomense. The organism was first identified in the Dead Sea in 1980 and requires a higher concentration of Mg ions for growth than related halophiles. The aop3 gene was cloned by Ihara and colleagues at Nagoya University in 1999 and the protein was found to share 59% sequence identity with bacteriorhodopsin. The crystal structure of AR3 was solved by Anthony Watts at Oxford University and Isabel Moraes at the National Physical Laboratory, together with collaborators at Diamond Light Source.
Mutants of Archaerhodopsin-3 (AR3) are widely used as tools in optogenetics for neuroscience research.
AR3 has recently been introduced as a fluorescent voltage sensor. | 5 | Photochemistry |
Processing of mRNA differs greatly among eukaryotes, bacteria, and archaea. Non-eukaryotic mRNA is, in essence, mature upon transcription and requires no processing, except in rare cases. Eukaryotic pre-mRNA, however, requires several processing steps before its transport to the cytoplasm and its translation by the ribosome. | 1 | Biochemistry |
The first small molecule CID system was developed in 1993 and used FK1012, a derivative of the drug tacrolimus (FK506), to induce homo-dimerization of FKBP. This system was used in vivo to induce binding between cell surface receptors which could not bind in the normal way because they lacked the transmembrane and extracellular domain. Addition of FK1012 to the cells caused signal transduction. | 1 | Biochemistry |
The process begins by preparing the puddling furnace. This involves bringing the furnace to a low temperature and then fettling it. Fettling is the process of painting the grate and walls around it with iron oxides, typically hematite; this acts as a protective coating keeping the melted metal from burning through the furnace. Sometimes finely pounded cinder was used instead of hematite. In this case the furnace must be heated for 4–5 hours to melt the cinder and then cooled before charging.
Either white cast iron or refined iron is then placed in hearth of the furnace, a process known as charging. For wet puddling, scrap iron and/or iron oxide is also charged. This mixture is then heated until the top melts, allowing for the oxides to begin mixing; this usually takes 30 minutes. This mixture is subjected to a strong current of air and stirred by long bars with hooks on one end, called puddling bars or rabbles, through doors in the furnace. This helps the iron-III (the species acting as an oxidiser) from the oxides to react with impurities in the pig iron, notably silicon, manganese (to form slag) and to some degree sulfur and phosphorus, which form gases that escape with the exhaust of the furnace.
More fuel is then added and the temperature is raised. The iron completely melts and the carbon starts to burn off. When wet puddling, the formation of carbon monoxide (CO) and carbon dioxide () due to reactions with the added iron oxide will cause bubbles to form that cause the mass to appear to boil. This process causes the slag to puff up on top, giving the rabbler a visual indication of the progress of the combustion. As the carbon burns off, the melting temperature of the mixture rises from , so the furnace has to be continually fed during this process. The melting point increases since the carbon atoms within the mixture act as a solute in solution which lowers the melting point of the iron mixture (like road salt on ice).
Working as a two-man crew, a puddler and helper could produce about 1500 kg of iron in a 12-hour shift. The strenuous labour, heat and fumes caused puddlers to have a very short life expectancy, with most dying in their 30s. Puddling was never able to be automated because the puddler had to sense when the balls had "come to nature". | 8 | Metallurgy |
In the presence of the group 3 homoleptic catalyst Y[N(SiMe)], triphenylphosphonium methylide can be coupled with phenylsilane. This reaction produces H gas as a byproduct, and forms a silyl-stabilised ylide. | 0 | Organic Chemistry |
In 1961, Nesmeyanov formulated the idea of obtaining food by synthetic methods, bypassing agriculture. The idea was based on the works of D. I. Mendeleev and M. Berthelot , as well as an awareness of the modern possibilities of organic synthesis, the problems of preserving the environment and the efficiency of food production. The main areas of work were: the development of highly efficient methods for obtaining nutrients; reproduction of the appearance, taste, smell, color, shape, consistency and other properties of natural products in synthetic food substances. As a result of research at INEOS , processes have been developed for obtaining black caviar, new forms of potato products, pasta and cereals and combined meat products based on vegetable and animal proteins. | 0 | Organic Chemistry |
In general, SEC is considered a low-resolution chromatography as it does not discern similar species very well, and is therefore often reserved for the final step of a purification. The technique can determine the quaternary structure of purified proteins that have slow exchange times, since it can be carried out under native solution conditions, preserving macromolecular interactions. SEC can also assay protein tertiary structure, as it measures the hydrodynamic volume (not molecular weight), allowing folded and unfolded versions of the same protein to be distinguished. For example, the apparent hydrodynamic radius of a typical protein domain might be 14 Å and 36 Å for the folded and unfolded forms, respectively. SEC allows the separation of these two forms, as the folded form elutes much later due to its smaller size. | 1 | Biochemistry |
Infrared spectroscopy is based on the fact that molecules absorb electromagnetic radiation at characteristic frequencies related to their vibrational structure. Infrared (IR) spectroelectrochemistry is a technique that allows the characterization of molecules based on the resistance, stiffness and number of bonds present. It also detects the presence of compounds, determines the concentration of species during a reaction, the structure of compounds, the properties of the chemical bonds, etc. | 7 | Physical Chemistry |
Chloroplasts are a special type of a plant cell organelle called a plastid, though the two terms are sometimes used interchangeably. There are many other types of plastids, which carry out various functions. All chloroplasts in a plant are descended from undifferentiated proplastids found in the zygote, or fertilized egg. Proplastids are commonly found in an adult plant's apical meristems. Chloroplasts do not normally develop from proplastids in root tip meristems—instead, the formation of starch-storing amyloplasts is more common.
In shoots, proplastids from shoot apical meristems can gradually develop into chloroplasts in photosynthetic leaf tissues as the leaf matures, if exposed to the required light. This process involves invaginations of the inner plastid membrane, forming sheets of membrane that project into the internal stroma. These membrane sheets then fold to form thylakoids and grana.
If angiosperm shoots are not exposed to the required light for chloroplast formation, proplastids may develop into an etioplast stage before becoming chloroplasts. An etioplast is a plastid that lacks chlorophyll, and has inner membrane invaginations that form a lattice of tubes in their stroma, called a prolamellar body. While etioplasts lack chlorophyll, they have a yellow chlorophyll precursor stocked. Within a few minutes of light exposure, the prolamellar body begins to reorganize into stacks of thylakoids, and chlorophyll starts to be produced. This process, where the etioplast becomes a chloroplast, takes several hours. Gymnosperms do not require light to form chloroplasts.
Light, however, does not guarantee that a proplastid will develop into a chloroplast. Whether a proplastid develops into a chloroplast some other kind of plastid is mostly controlled by the nucleus and is largely influenced by the kind of cell it resides in. | 5 | Photochemistry |
Jameson's research into flotation began when he was at Imperial College London, in 1969. A colleague, Dr J. A. Kitchener of the Royal School of Mines, pointed out that many of the new mineral deposits being found around the world required fine grinding to separate the valuable particles from the rock in which they were embedded, and the flotation technologies available at the time were relatively inefficient for recovering fine particles. Kitchener felt that improvements could best be achieved by an increased knowledge of the physics of flotation, rather than the chemistry of the reagents. Jameson had gained some expertise in the properties of bubbles and particles in suspensions whilst a PhD student at Cambridge. He began research into the fluid mechanics of the flotation process and set in train a series of experimental projects into the effect of particle diameter and bubble size on the flotation rate constant. Much of the research was conducted by honours students in chemical engineering. Jameson accepted the challenge of coming up with practical solutions to remedy the situation, if these could be identified.
Jameson's research showed that the kinetics of flotation of fine particles was a strong function of the bubble diameter and that the way to improve recoveries was to use small bubbles in the order of 300 microns (μm) in diameter. What was needed was a practical method of making such bubbles in large quantities, of the order of billions per second. The device needed to be simple to construct and operate, capable of running for long periods with minimal maintenance, and should be resistant to blockage by stray large particles in the feed. He began to look at the theory of bubble breakup in sheared flows, that is, in flow fields in which layers of liquid slide over each other. Lewis and Davidson had recently published a theory to predict the maximum size of bubbles in a well-characterised flow environment. By balancing the forces acting on a bubble in a shearing flow, including the disruptive dynamic stresses from the liquid motion and the restoring force of surface tension, it was possible to predict the critical shear rate required to produce a bubble of given size. Jameson then looked for simple and practical ways of generating the required shear rates, and found inspiration in the kitchen sink. If a jet of water from a tap plunges into a basin full of water, a shear layer develops around the jet, that entrains air from the atmosphere into the water, and at the same time, breaks up the entrained air into fine bubbles. The effect is magnified if there is a detergent in the water. Detergents, known as frothers, are used in flotation to prevent bubble coalescence, and to create stable froths. By the correct choice of jet velocity and diameter, it is possible to provide a controlled shear environment that can generate bubbles of a suitable size for flotation, with the added advantage that the air is naturally aspirated by the jet, so there is no need for a compressor or blower. Thus the idea of the Jameson Cell was born.
After a number of failures, the radical new process for flotation emerged in the laboratory at the University of Newcastle. Jameson filed a provisional patent application in 1986. After an initial trial at the Renison Bell tin mine in Tasmania, certain design features were modified. He led a further plant trial with a small cell in the lead-zinc concentrator at Mt Isa Mines Ltd in Queensland, initially working alone. The plant metallurgists took an interest in the technology and helped to refine it, particularly checking the scale-up procedures that Jameson had devised. In 1988 a recent graduate was assigned full-time for a year to verify and validate the performance of the Cell. In 1989 a worldwide exclusive license was negotiated between Tunra Ltd on behalf of the University of Newcastle, Jameson, and MIM Holdings Limited, for the use of the Cell for metallurgical purposes. Summary papers on the theory and practice have been published.
There have been ongoing significant changes to the design of the Cell since it was first developed in the late 1980s. | 8 | Metallurgy |
The RNAP occasionally stops and starts moving backwards when it encounters a roadblock or some difficult sequences. When this happens, the EC gets stuck because the reactive 3 edge of the RNA is out of the active site. The transcript cleavage factor TFS (a TFIIS homolog) helps resolve this issue by generating a cut so that a new 3 end is available in the active site. Some archaeon have up to 4 paralogs of TFS with divergent functions. | 1 | Biochemistry |
Deuterium occurs in trace amounts naturally as deuterium gas (H or D), but most deuterium atoms in the Universe are bonded with H to form a gas called hydrogen deuteride (HD or HH). Similarly, natural water contains deuterated molecules, almost all as semiheavy water HDO with only one deuterium atom.
The existence of deuterium on Earth, elsewhere in the Solar System (as confirmed by planetary probes), and in the spectra of stars, is also an important datum in cosmology. Gamma radiation from ordinary nuclear fusion dissociates deuterium into protons and neutrons, and there are no known natural processes other than the Big Bang nucleosynthesis that might have produced deuterium at anything close to its observed natural abundance. Deuterium is produced by the rare cluster decay, and occasional absorption of naturally occurring neutrons by light hydrogen, but these are trivial sources. There is thought to be little deuterium in the interior of the Sun and other stars, as at these temperatures the nuclear fusion reactions that consume deuterium happen much faster than the proton-proton reaction that creates deuterium. However, deuterium persists in the outer solar atmosphere at roughly the same concentration as in Jupiter, and this has probably been unchanged since the origin of the Solar System. The natural abundance of deuterium seems to be a very similar fraction of hydrogen, wherever hydrogen is found, unless there are obvious processes at work that concentrate it.
The existence of deuterium at a low but constant primordial fraction in all hydrogen is another one of the arguments in favor of the Big Bang theory over the Steady State theory of the Universe. The observed ratios of hydrogen to helium to deuterium in the universe are difficult to explain except with a Big Bang model. It is estimated that the abundances of deuterium have not evolved significantly since their production about 13.8 billion years ago. Measurements of Milky Way galactic deuterium from ultraviolet spectral analysis show a ratio of as much as 23 atoms of deuterium per million hydrogen atoms in undisturbed gas clouds, which is only 15% below the WMAP estimated primordial ratio of about 27 atoms per million from the Big Bang. This has been interpreted to mean that less deuterium has been destroyed in star formation in the Milky Way galaxy than expected, or perhaps deuterium has been replenished by a large in-fall of primordial hydrogen from outside the galaxy. In space a few hundred light years from the Sun, deuterium abundance is only 15 atoms per million, but this value is presumably influenced by differential adsorption of deuterium onto carbon dust grains in interstellar space.
The abundance of deuterium in the atmosphere of Jupiter has been directly measured by the Galileo space probe as 26 atoms per million hydrogen atoms. ISO-SWS observations find 22 atoms per million hydrogen atoms in Jupiter. and this abundance is thought to represent close to the primordial Solar System ratio. This is about 17% of the terrestrial deuterium-to-hydrogen ratio of 156 deuterium atoms per million hydrogen atoms.
Cometary bodies such as Comet Hale-Bopp and Halleys Comet have been measured to contain relatively more deuterium (about 200 atoms D per million hydrogens), ratios which are enriched with respect to the presumed protosolar nebula ratio, probably due to heating, and which are similar to the ratios found in Earth seawater. The recent measurement of deuterium amounts of 161 atoms D per million hydrogen in Comet 103P/Hartley (a former Kuiper belt object), a ratio almost exactly that in Earths oceans, emphasizes the theory that Earths surface water may be largely comet-derived. Most recently the deuterium–protium (H–H) ratio of 67P/Churyumov–Gerasimenko as measured by Rosetta is about three times that of Earth water, a figure that is high. This has caused renewed interest in suggestions that Earths water may be partly of asteroidal origin.
Deuterium has also been observed to be concentrated over the mean solar abundance in other terrestrial planets, in particular Mars and Venus. | 9 | Geochemistry |
Inositol trisphosphate receptor (InsP3R) is a membrane glycoprotein complex acting as a Ca channel activated by inositol trisphosphate (InsP3). InsP3R is very diverse among organisms, and is necessary for the control of cellular and physiological processes including cell division, cell proliferation, apoptosis, fertilization, development, behavior, learning and memory. Inositol triphosphate receptor represents a dominant second messenger leading to the release of Ca from intracellular store sites. There is strong evidence suggesting that the InsP3R plays an important role in the conversion of external stimuli to intracellular Ca signals characterized by complex patterns relative to both space and time, such as Ca waves and oscillations. | 1 | Biochemistry |
Equilibrium thermodynamics is the study of transfers of matter and energy in systems or bodies that, by agencies in their surroundings, can be driven from one state of thermodynamic equilibrium to another. The term thermodynamic equilibrium indicates a state of balance, in which all macroscopic flows are zero; in the case of the simplest systems or bodies, their intensive properties are homogeneous, and their pressures are perpendicular to their boundaries. In an equilibrium state there are no unbalanced potentials, or driving forces, between macroscopically distinct parts of the system. A central aim in equilibrium thermodynamics is: given a system in a well-defined initial equilibrium state, and given its surroundings, and given its constitutive walls, to calculate what will be the final equilibrium state of the system after a specified thermodynamic operation has changed its walls or surroundings. | 7 | Physical Chemistry |
The symbol used to represent pressure in equations is "p" or "P" with SI units of pascals.
When describing a container of gas, the term pressure (or absolute pressure) refers to the average force per unit area that the gas exerts on the surface of the container. Within this volume, it is sometimes easier to visualize the gas particles moving in straight lines until they collide with the container (see diagram at top of the article). The force imparted by a gas particle into the container during this collision is the change in momentum of the particle. During a collision only the normal component of velocity changes. A particle traveling parallel to the wall does not change its momentum. Therefore, the average force on a surface must be the average change in linear momentum from all of these gas particle collisions.
Pressure is the sum of all the normal components of force exerted by the particles impacting the walls of the container divided by the surface area of the wall. | 7 | Physical Chemistry |
The older German DIN 8511 specification is still often in use in shops. In the table below, note that the correspondence between DIN 8511 and ISO 9454-1 codes is not one-to-one. | 8 | Metallurgy |
Aside from its synthetic versatility (see above), sulfolene is used as an additive in electrochemical fluorination. It can increase the yield of perfluorooctanesulfonyl fluoride by about 70%. It is "highly soluble in anhydrous HF and increases the conductivity of the electrolyte solution". In this application, it undergoes a ring opening and is fluorinated to form perfluorobutanesulfonyl fluoride. | 0 | Organic Chemistry |
IVF may be used to overcome female infertility when it is due to problems with the fallopian tubes, making in vivo fertilisation difficult. It can also assist in male infertility, in those cases where there is a defect in sperm quality; in such situations intracytoplasmic sperm injection (ICSI) may be used, where a sperm cell is injected directly into the egg cell. This is used when sperm has difficulty penetrating the egg. ICSI is also used when sperm numbers are very low. When indicated, the use of ICSI has been found to increase the success rates of IVF.
According to UK's National Institute for Health and Care Excellence (NICE) guidelines, IVF treatment is appropriate in cases of unexplained infertility for people who have not conceived after 2 years of regular unprotected sexual intercourse.
In people with anovulation, it may be an alternative after 7–12 attempted cycles of ovulation induction, since the latter is expensive and more easy to control. | 1 | Biochemistry |
Because they have many applications and are easily prepared, halomethanes have been of intense commercial interest. | 2 | Environmental Chemistry |
Daniel Koshland's theory of enzyme-substrate binding is that the active site and the binding portion of the substrate are not exactly complementary. The induced fit model is a development of the lock-and-key model and assumes that an active site is flexible and changes shape until the substrate is completely bound. This model is similar to a person wearing a glove: the glove changes shape to fit the hand. The enzyme initially has a conformation that attracts its substrate. Enzyme surface is flexible and only the correct catalyst can induce interaction leading to catalysis. Conformational changes may then occur as the substrate is bound. After the reaction products will move away from the enzyme and the active site returns to its initial shape. This hypothesis is supported by the observation that the entire protein domain could move several nanometers during catalysis. This movement of protein surface can create microenvironments that favour the catalysis. | 1 | Biochemistry |
Small hole drilling EDM is used in a variety of applications.
On wire-cut EDM machines, small hole drilling EDM is used to make a through hole in a workpiece through which to thread the wire for the wire-cut EDM operation. A separate EDM head specifically for small hole drilling is mounted on a wire-cut machine and allows large hardened plates to have finished parts eroded from them as needed and without pre-drilling.
Small hole EDM is used to drill rows of holes into the leading and trailing edges of turbine blades used in jet engines. Gas flow through these small holes allows the engines to use higher temperatures than otherwise possible. The high-temperature, very hard, single crystal alloys employed in these blades makes conventional machining of these holes with high aspect ratio extremely difficult, if not impossible.
Small hole EDM is also used to create microscopic orifices for fuel system components, spinnerets for synthetic fibers such as rayon, and other applications.
There are also stand-alone small hole drilling EDM machines with an x–y axis also known as a super drill or hole popper that can machine blind or through holes. EDM drills bore holes with a long brass or copper tube electrode that rotates in a chuck with a constant flow of distilled or deionized water flowing through the electrode as a flushing agent and dielectric. The electrode tubes operate like the wire in wire-cut EDM machines, having a spark gap and wear rate. Some small-hole drilling EDMs are able to drill through 100 mm of soft or hardened steel in less than 10 seconds, averaging 50% to 80% wear rate. Holes of 0.3 mm to 6.1 mm can be achieved in this drilling operation. Brass electrodes are easier to machine but are not recommended for wire-cut operations due to eroded brass particles causing "brass on brass" wire breakage, therefore copper is recommended. | 8 | Metallurgy |
* Boudrant, J. (1990): Microbial processes for ascorbic acid biosynthesis: a review. In: Enzyme Microb Technol. 12(5); 322–9; ;
* Bremus, C. et al. (2006): The use of microorganisms in L-ascorbic acid production. In: J Biotechnol. 124(1); 196–205; ; | 0 | Organic Chemistry |
An acetoxy group may be used as a protection for an alcohol functionality in a synthetic route although the protecting group itself is called an acetyl group. | 0 | Organic Chemistry |
*For biodiesel fuel: waste vegetable oil (WVO) must be neutralized before a batch may be processed. A portion of WVO is titrated with a base to determine acidity, so the rest of the batch may be neutralized properly. This removes free fatty acids from the WVO that would normally react to make soap instead of biodiesel fuel.
*Kjeldahl method: a measure of nitrogen content in a sample. Organic nitrogen is digested into ammonia with sulfuric acid and potassium sulfate. Finally, ammonia is back titrated with boric acid and then sodium carbonate.
*Acid value: the mass in milligrams of potassium hydroxide (KOH) required to titrate fully an acid in one gram of sample. An example is the determination of free fatty acid content.
*Saponification value: the mass in milligrams of KOH required to saponify a fatty acid in one gram of sample. Saponification is used to determine average chain length of fatty acids in fat.
*Ester value (or ester index): a calculated index. Ester value = Saponification value – Acid value.
*Amine value: the mass in milligrams of KOH equal to the amine content in one gram of sample.
*Hydroxyl value: the mass in milligrams of KOH corresponding to hydroxyl groups in one gram of sample. The analyte is acetylated using acetic anhydride then titrated with KOH. | 3 | Analytical Chemistry |
Scientists at the University of Alberta have been systematically characterizing specific biofluid metabolomes including the serum metabolome, the urine metabolome, the cerebrospinal fluid (CSF) metabolome and the saliva metabolome. These efforts have involved both experimental metabolomic analysis (involving NMR, GC-MS, ICP-MS, LC-MS and HPLC assays) as well as extensive literature mining. According to their data, the human serum metabolome contains at least 4,200 different compounds (including many lipids), the human urine metabolome contains at least 3,000 different compounds (including hundreds of volatiles and gut microbial metabolites), the human CSF metabolome contains nearly 500 different compounds while the human saliva metabolome contains approximately 400 different metabolites, including many bacterial products. | 1 | Biochemistry |
A particularly efficient way of generating hydrogen (10 kWh/kg) is the methane plasmalysis. In this process, methane (e.g. from natural gas) is decomposed in the plasma under oxygen exclusion, forming hydrogen and elemental carbon, as in the following reaction equation:
Methane plasmalysis offers, among other things, the possibility of decentralized decarbonization of natural gas or, if biogas is used, also the realization of a CO2 sink, whereby, in contrast to the CCS process commonly used to date, no gas has to be compressed and stored, but the elemental carbon produced can be bound in product form.
This technology can also be used to prevent the flaring of so-called "flare gases" by using them as a feedstock for the production of hydrogen and carbon. | 7 | Physical Chemistry |
Preparation of the diluted acid can be dangerous due to the heat released in the dilution process. To avoid splattering, the concentrated acid is usually added to water and not the other way around. A saying used to remember this is "Do like you oughta, add the acid to the water". Water has a higher heat capacity than the acid, and so a vessel of cold water will absorb heat as acid is added.
Also, because the acid is denser than water, it sinks to the bottom. Heat is generated at the interface between acid and water, which is at the bottom of the vessel. Acid will not boil, because of its higher boiling point. Warm water near the interface rises due to convection, which cools the interface, and prevents boiling of either acid or water.
In contrast, addition of water to concentrated sulfuric acid results in a thin layer of water on top of the acid. Heat generated in this thin layer of water can boil, leading to the dispersal of a sulfuric acid aerosol or worse, an explosion.
Preparation of solutions greater than 6 M (35%) in concentration is dangerous, unless the acid is added slowly enough to allow the mixture sufficient time to cool. Otherwise, the heat produced may be sufficient to boil the mixture. Efficient mechanical stirring and external cooling (such as an ice bath) are essential.
Reaction rates double for about every 10-degree Celsius increase in temperature. Therefore, the reaction will become more violent as dilution proceeds, unless the mixture is given time to cool. Adding acid to warm water will cause a violent reaction.
On a laboratory scale, sulfuric acid can be diluted by pouring concentrated acid onto crushed ice made from de-ionized water. The ice melts in an endothermic process while dissolving the acid. The amount of heat needed to melt the ice in this process is greater than the amount of heat evolved by dissolving the acid so the solution remains cold. After all the ice has melted, further dilution can take place using water. | 7 | Physical Chemistry |
MIKES is a powerful technique used for structural studies of organic compounds, gaseous ions, and also for direct analysis of complex mixtures without separation of the components. In other words, it is used for molecular structure studies. The reason why MIKES is good for molecular structure studies is due to the reverse-geometry of MIKES. The MIKES Schematic shows that the ion species in the source goes into the magnetic field. After which, the chemistry is later studied in the second field-free region (FFR) by scanning the electric sector which defines the nature of the fragments by measuring their kinetic energy. This causes competitive unimolecular fragmentations that can be observed in the MIKE spectra. Furthermore, if gas is brought into the second FFR, more dissociation will be induced by collision, that will later appear in the MIKE spectra. | 7 | Physical Chemistry |
A number of factors can affect the migration of nucleic acids: the dimension of the gel pores, the voltage used, the ionic strength of the buffer, and the concentration intercalating dye such as ethidium bromide if used during electrophoresis. | 1 | Biochemistry |
To begin, proteins of interest are prepared for the SDS-PAGE technique and subsequently loaded onto the gel for separation on the basis of molecular size. Large proteins will have difficulty navigating through the mesh-like structure of the gel as they can not fit through the pores with the ease that smaller proteins can. As a result, large proteins do not travel very far on the gel in comparison to smaller proteins that travel further. After enough time, this results in distinct bands that can be visualized from a number of post-gel electrophoresis staining procedures. The bands are at different positions on the gel relative to the well that they were loaded into.
Next, proteins are to be renatured followed by the gel being subjected to pressed between two nitrocellulose filters which rely on diffusion to transfer the proteins from the gel to the membrane filters. At this point replicas of the gel have been created of which each serves a particular purpose. One membrane filter can be stained to see the protein bands that were created from gel electrophoresis and the other is used in the actual process of hybridizing with prepared P radioactively labeled specific oligonucleotide probes. To detect any protein-DNA interactions, autoradiography is commonly used. | 1 | Biochemistry |
Once the two solutions are forced out of their syringes they enter a mixing system that has baffles to ensure complete mixing, with turbulent flow rather than laminar flow, which would allow the two solutions to flow side by side with incomplete mixing. | 7 | Physical Chemistry |
In this type of plot (Figure 1), each axis represents a unique reaction coordinate, the corners represent local minima along the potential surface such as reactants, products or intermediates and the energy axis projects vertically out of the page. Changing a single reaction parameter can change the height of one or more of the corners of the plot. These changes are transmitted across the surface such that the position of the transition state (the saddle point) is altered.
Consider a generic example in which the initial transition state along a concerted pathway is represented by a black dot on a red diagonal (Figure 1). Changing the height of the corners can have two effects on the position of the transition state: it can move along the diagonal, reflecting a change in the Gibbs free energy of the reaction (ΔG°), or perpendicular to it, reflecting a change in the energy of competing pathways. Thus, in accordance with the Hammond postulate, the transition state moves along the diagonal towards the corner that is raised in energy (a Hammond effect) and perpendicular to the diagonal towards the corner that is lowered (an anti-Hammond effect). In this example, R is raised in energy and I(2) is lowered in energy. The transition state moves accordingly and the vector sum of both movements gives the real change in its position. | 7 | Physical Chemistry |
Columnar structures appear in various research fields on a broad range of length scales from metres down to the nanoscale. On the largest scale, such structures can be found in botany where seeds of a plant assemble around the stem. On a smaller scale bubbles of equal size crystallise to columnar foam structures when confined in a glass tube. In nanoscience such structures can be found in man-made objects which are on length scales from a micron to the nanoscale. | 3 | Analytical Chemistry |
†The value is exact but not expressible as a finite decimal; approximated to 9 decimal places only.
Since is a proportionality factor between temperature and energy, its numerical value depends on the choice of units for energy and temperature. The small numerical value of the Boltzmann constant in SI units means a change in temperature by 1 K only changes a particle's energy by a small amount. A change of is defined to be the same as a change of . The characteristic energy is a term encountered in many physical relationships.
The Boltzmann constant sets up a relationship between wavelength and temperature (dividing hc/k by a wavelength gives a temperature) with one micrometer being related to , and also a relationship between voltage and temperature (kT in units of eV corresponds to a voltage) with one volt being related to . The ratio of these two temperatures, / ≈ 1.239842, is the numerical value of hc in units of eV⋅μm. | 7 | Physical Chemistry |
AK1 genetic ablation decreases tolerance to metabolic stress. AK1 deficiency induces fiber-type specific variation in groups of transcripts in glycolysis and mitochondrial metabolism. This supports muscle energy metabolism. | 1 | Biochemistry |
The first symptoms of apitoxin (bee venom), that are now thought to be caused by apamin, were described back in 1936 by Hahn and Leditschke. Apamin was first isolated by Habermann in 1965 from Apis mellifera, the Western honey bee. Apamin was named after this bee. Bee venom contains many other compounds, like histamine, phospholipase A2, hyaluronidase, MCD peptide, and the main active component melittin. Apamin was separated from the other compounds by gel filtration and ion exchange chromatography. | 1 | Biochemistry |
The coding region of a gene, also known as the coding sequence (CDS), is the portion of a gene's DNA or RNA that codes for a protein. Studying the length, composition, regulation, splicing, structures, and functions of coding regions compared to non-coding regions over different species and time periods can provide a significant amount of important information regarding gene organization and evolution of prokaryotes and eukaryotes. This can further assist in mapping the human genome and developing gene therapy. | 1 | Biochemistry |
In ventilation systems a jet fan, also known as an impulse or induction fan, ejects a stream of air which entrains ambient air along with it, in order to circulate the ambient air. The system takes up less space than conventional ventilation ducting and can significantly increase the rates of inflow of fresh air and expulsion of stale air. | 7 | Physical Chemistry |
Of special interest are ion-abundant liquid media (such as ionic liquids, molten salts, liquid electrolytes, etc.), which represent “liquid ions” with excellent tunable properties for different applications. The systems are famous for their ability to solvent-solute self-organization phenomena and are often employed in chemistry, biochemistry and pharmaceutical research. One of the most important features of ion-abundant liquid media is their huge potential to be fine-tuned. Thus, one can design an ionic liquid with virtually any combination of physicochemical or biochemical properties.
Research in the area of “liquid ions” is a rapidly developing scientific field, and numerous data on their properties and activities have been accumulated so far. Currently, the concept finds applications in catalysis, electrochemistry, analytics, fuel production, biomass processing, biotechnology, biochemistry and pharmaceutics. | 1 | Biochemistry |
In 2015 the use of highly porous, catalyst-decorated COFs for converting carbon dioxide into carbon monoxide was reported. MOF under solvent-free conditions can also be used for catalytic activity in the cycloaddition of CO and epoxides into cyclic organic carbonates with enhanced catalyst recyclability. | 6 | Supramolecular Chemistry |
Until recently, real-time monitoring of BOD was unattainable owing to its complex nature. Recent research by a leading UK university has discovered the link between multiple water quality parameters including electrical conductivity, turbidity, TLF and CDOM. These parameters are all capable of being monitored in real-time through a combination of traditional methods (electrical conductivity via electrodes) and newer methods such as fluorescence. The monitoring of tryptophan-like fluorescence (TLF) has been successfully utilised as a proxy for biological activity and enumeration, particularly with a focus on Escherichia coli (E. Coli). TLF based monitoring is applicable across a wide range of environments, including but by no means limited to sewage treatment works and freshwaters. Therefore, there has been a significant movement towards combined sensor systems that can monitor parameters and use them, in real-time, to provide a reading of BOD that is of laboratory quality. | 3 | Analytical Chemistry |
As already pointed out above, there is a difference between medium-resolution spectrometers that are used for LS AAS and high-resolution spectrometers that are designed for CS AAS. The spectrometer includes the spectral sorting device (monochromator) and the detector. | 3 | Analytical Chemistry |
*Theodor Körner Prize for Science and Art in Austria, 1970
*Ernst Späth Prize of the Austrian Academy of Sciences, 1976
*Sandoz Prize, 1977
*Election to corresponding member of the New York Academy of Sciences, 1989
*Election to corresponding member of the Mathematical and Natural Sciences Class of the Austrian Academy of Sciences, 1992
*Upper Austrian Prize for Science, 1993
*Election to full member of the Mathematical and Natural Sciences Class of the Austrian Academy of Sciences, 1997
*Josef Loschmidt Medal of the Austrian Chemical Society, 1998
*Scientific award of the Rudolf Trauner Stiftung, 2003
*Silver medal of the government of Upper Austria, 2009 | 0 | Organic Chemistry |
In most solids, ions rigidly occupy fixed positions, strongly embraced by neighboring atoms or ions. In some solids, selected ions are highly mobile allowing ionic conduction. The mobility increases with temperature. Materials exhibiting this property are used in batteries. A well-known ion conductive solid is β-alumina ("BASE"), a form of aluminium oxide that has channels through which sodium cations can hop. When this ceramic is complexed with a mobile ion, such as Na, it behaves as so-called fast ion conductor. BASE is used as a membrane in several types of molten salt electrochemical cell. | 7 | Physical Chemistry |
The movement of so many chloroplast genes to the nucleus means that many chloroplast proteins that were supposed to be translated in the chloroplast are now synthesized in the cytoplasm. This means that these proteins must be directed back to the chloroplast, and imported through at least two chloroplast membranes.
Curiously, around half of the protein products of transferred genes arent even targeted back to the chloroplast. Many became exaptations, taking on new functions like participating in cell division, protein routing, and even disease resistance. A few chloroplast genes found new homes in the mitochondrial genome—most became nonfunctional pseudogenes, though a few tRNA genes still work in the mitochondrion. Some transferred chloroplast DNA protein products get directed to the secretory pathway (though many secondary plastids are bounded by an outermost membrane derived from the hosts cell membrane, and therefore topologically outside of the cell, because to reach the chloroplast from the cytosol, you have to cross the cell membrane, just like if you were headed for the extracellular space. In those cases, chloroplast-targeted proteins do initially travel along the secretory pathway).
Because the cell acquiring a chloroplast already had mitochondria (and peroxisomes, and a cell membrane for secretion), the new chloroplast host had to develop a unique protein targeting system to avoid having chloroplast proteins being sent to the wrong organelle. | 5 | Photochemistry |
This technique is also used for detection of illicit drugs in various samples. The most common method of drug detection has been an immunoassay. This method is much more convenient. However, convenience comes at the cost of specificity and coverage of a wide range of drugs, therefore, HPLC has been used as well as an alternative method. As HPLC is a method of determining (and possibly increasing) purity, using HPLC alone in evaluating concentrations of drugs was somewhat insufficient. Therefore, HPLC in this context is often performed in conjunction with mass spectrometry. Using liquid chromatography-mass spectrometry (LC-MS) instead of gas chromatography-mass spectrometry (GC-MS) circumvents the necessity for derivitizing with acetylating or alkylation agents, which can be a burdensome extra step. LC-MS has been used to detect a variety of agents like doping agents, drug metabolites, glucuronide conjugates, amphetamines, opioids, cocaine, BZDs, ketamine, LSD, cannabis, and pesticides. Performing HPLC in conjunction with mass spectrometry reduces the absolute need for standardizing HPLC experimental runs. | 3 | Analytical Chemistry |
Akin to enamines, enol ethers are electron-rich alkenes by virtue of the electron-donation from the heteroatom via pi-bonding. Enol ethers have oxonium ion character. By virtue of their bonding situation, enol ethers display distinctive reactivity. In comparison with simple alkenes, enol ethers exhibit enhanced susceptibility to attack by electrophiles such as Bronsted acids. Similarly, they undergo inverse demand Diels-Alder reactions.
The reactivity of enol ethers is highly dependent on the presence of substituents alpha to oxygen. The vinyl ethers are susceptible to polymerization to give polyvinyl ethers. They also react readily with thiols in the thiol-ene reaction to form thioethers. This makes enol ether-functionalized monomers ideal for polymerization with thiol-based monomers to form thiol-ene networks.
Some vinyl ethers find some use as inhalation anesthetics. Enol ethers bearing α substituents do not polymerize readily. They are mainly of academic interest, e.g. as intermediates in the synthesis of more complex molecules.
The acid-catalyzed addition of hydrogen peroxide to vinyl ethers gives the hydroperoxide:
:CHOCH=CH + HO → CHOCH(OOH)CH | 0 | Organic Chemistry |
Both slow variants (GCaMP6s, jGCaMP7s) and fast variants (GCaMP6f, jGCaMP7f) are used in biological and neuroscience research. The slow variants are brighter and more sensitive to small changes in Ca levels, such as single action potentials; on the other hand, the fast variants are less sensitive but respond more quickly, making them useful for tracking changes in Ca levels over precise timescales. GCaMP6 also has a medium variant, GCaMP6m, whose kinetics are intermediate between GCaMP6s and GCaMP6f. Other variants of jGCaMP7 are also employed: jGCaMP7b exhibits bright baseline fluorescence and is used for imaging dendrites and axons, while jGCaMP7c exhibits greater contrast between maximal and baseline fluorescence and is advantageous for imaging large populations of neurons.
In 2018, Yang et al. reported the development of GCaMP-X, generated by the addition of a calmodulin-binding motif. Since the GCaMP calmodulin domain, when unbound, disrupts L-type calcium channel gating, the added calmodulin-binding motif prevents GCaMP-X from interfering with calcium-dependent signaling mechanisms.
In 2020, Zhang et al. reported the development of jGCaMP8, including sensitive, medium, and fast variants, which exhibit faster kinetics and greater sensitivity than the corresponding jGCaMP7 variants.
Red fluorescent indicators have also been developed: jRCaMP1a and jRCaMP1b use a circular permutation of the red fluorescent protein mRuby instead of GFP, while jRGECO1a is based on the red fluorescent protein mApple. Since the blue light used to excite GCaMP is scattered by tissue and the emitted green light is absorbed by blood, red fluorescent indicators provide more penetration and imaging depth in vivo than GCaMP. Use of red fluorescent indicators also avoids the photodamage caused by blue excitation light. Moreover, red fluorescent indicators allow for concurrent use of optogenetics, which is difficult with GCaMP because the excitation wavelengths of GCaMP overlap with those of channelrhodopsin-2 (ChR2). Simultaneous use of red and green GECIs can provide two-color visualization of different subcellular regions or cell populations. | 1 | Biochemistry |
Methylthioadenosine nucleosidase are enzymes that catalyse the hydrolytic deadenylation reaction of 5'-methylthioadenosine and S-adenosylhomocysteine. It is also regarded as an important target for antibacterial drug discovery because it is important in the metabolic system of bacteria and only produced by bacteria. Given the different distance between nitrogen atom of adenine and the ribose anomeric carbon (see in the diagram in this section), the transition state structure can be defined by early or late dissociation stage. Based on the finding of different transition state structures, Schramm and coworkers designed two transition state analogues mimicking the early and late dissociative transition state. The early and late transition state analogue shown binding affinity (Kd) of 360 and 140 pM, respectively. | 1 | Biochemistry |
Water vapor has lower density than that of air and is therefore buoyant in air but has lower vapor pressure than that of air. When water vapor is used as a lifting gas by a thermal airship the water vapor is heated to form steam so that its vapor pressure is greater than the surrounding air pressure in order to maintain the shape of a theoretical "steam balloon", which yields approximately 60% the lift of helium and twice that of hot air. | 2 | Environmental Chemistry |
Foods and beverages contain numerous aromatic compounds, some naturally present in the raw materials and some forming during processing. GC–MS is extensively used for the analysis of these compounds which include esters, fatty acids, alcohols, aldehydes, terpenes etc. It is also used to detect and measure contaminants from spoilage or adulteration which may be harmful and which is often controlled by governmental agencies, for example pesticides. | 3 | Analytical Chemistry |
Mutations in the HNF4A gene have been linked to maturity onset diabetes of the young 1 (MODY1).
This seems to be caused by HNF4-a's [http://jme.endocrinology-journals.org/content/43/1/19.full.pdf] role in the synthesis of SHBG, which is known to be severely diminished in patients with insulin-resistance. | 1 | Biochemistry |
In biochemistry, the molar absorption coefficient of a protein at depends almost exclusively on the number of aromatic residues, particularly tryptophan, and can be predicted from the sequence of amino acids. Similarly, the molar absorption coefficient of nucleic acids at can be predicted given the nucleotide sequence.
If the molar absorption coefficient is known, it can be used to determine the concentration of a protein in solution. | 3 | Analytical Chemistry |
Levosulpiride is used in the treatment of:
* Psychosis
* Negative symptoms of schizophrenia
* Anxiety disorders
* Dysthymia
* Vertigo
* Dyspepsia
* Irritable bowel syndrome
* Premature ejaculation.
Levosulpiride is not currently licensed for treatment of premature ejaculation in the UK or other European countries. | 4 | Stereochemistry |
Some elements like potassium, uranium, and thorium are naturally radioactive and give off gamma rays as they decay. Electromagnetic radiation from these isotopes can be detected by a Gamma-Ray Spectrometer (GRS) dropped toward the planetary surface or observed from orbit. An orbiting instrument can map the surface distribution of many elements for an entire planet.
Uncrewed spacecraft programs such as Venera and the Vega program have flown to Venus and sent back data allowing estimates of the K/U ratio of the surface rocks.
The Lunar Prospector mission used a GRS to map the Earth's Moon.
To determine the elemental makeup of the Martian surface, the Mars Odyssey used a GRS and two neutron detectors.
These GRS readings can be compared to direct elemental measurements of chondrites meteorites, Earth, and Moon samples brought back from Apollo program missions, as well as to meteorites that are believed to have come from Mars. | 9 | Geochemistry |
Ionic imprinting, which involves metal ions, serves as an approach to enhance template molecule and functional monomer interaction in water. Typically, metal ions serve as a mediator during the imprinting process. Cross-linking polymers that are in the presence of a metal ion will form a matrix that is capable of metal binding. Metal ions can also mediate molecular imprinting by binding to a range of functional monomers, where ligands donate electrons to the outermost orbital of the metal ion. In addition to mediating imprinting, metal ions can be utilized in the direct imprinting. For example, a metal ion can serve as the template for the imprinting process. | 6 | Supramolecular Chemistry |
The mass of the atoms forming a chemical bond affects the bond’s strength. When two different isotopes of the same element exist, the heavier ones form stronger bonds. Stronger bonds make bond cleavage reactions run more slowly, leading to the kinetic isotope effect, a well-studied concept in physical chemistry. To illustrate this with an example from soccer, if one of the two identical soccer balls is filled up with air and another one with water, they will look identical on the ground, but a stronger kick would be required to send the water-filled ball the same distance as the air-filled one. Of the two stable isotopes of hydrogen (H), Deuterium (H) is twice as heavy as protium (H), thus giving the largest kinetic isotope effect of all stable (non-radioactive) atoms.
The kinetic isotope effect is sometimes applied in another context in drug development, modulating drug properties in a favorable/patient-friendly way (deuterated drugs). Small molecules used as drugs are recognized as “foreign” to the body, and an organism’s defense systems often mount a response. Typically, drug metabolism alters the drug molecule through oxidation into derivatives that are easier to excrete, reducing the drug’s half-life. This can be slowed down by deuteration, hence improving pharmacokinetics and pharmacodynamics. | 7 | Physical Chemistry |
Thioketenes can be stabilized by either steric protection or by electronic effects. Thus, di-tert-butylthioketene is easily isolated and air-stable. Several examples have been characterized by X-ray crystallography. The C=S distance is 157 pm and the C=C distance is 124 pm, both bonds being suitable for the C=C=S assignment. The violet color characteristic of thioketenes indicates the small HOMO-LUMO gap. These compound are prepared by treatment of the acid chloride with phosphorus pentasulfide as described by the following idealized equation:
Bis(trifluoromethyl)thioketene () is an example of an electronically stabilized thioketene. | 0 | Organic Chemistry |
ADP cycling supplies the energy needed to do work in a biological system, the thermodynamic process of transferring energy from one source to another. There are two types of energy: potential energy and kinetic energy. Potential energy can be thought of as stored energy, or usable energy that is available to do work. Kinetic energy is the energy of an object as a result of its motion. The significance of ATP is in its ability to store potential energy within the phosphate bonds. The energy stored between these bonds can then be transferred to do work. For example, the transfer of energy from ATP to the protein myosin causes a conformational change when connecting to actin during muscle contraction.
It takes multiple reactions between myosin and actin to effectively produce one muscle contraction, and, therefore, the availability of large amounts of ATP is required to produce each muscle contraction. For this reason, biological processes have evolved to produce efficient ways to replenish the potential energy of ATP from ADP.
Breaking one of ATP's phosphorus bonds generates approximately 30.5 kilojoules per mole of ATP (7.3 kcal). ADP can be converted, or powered back to ATP through the process of releasing the chemical energy available in food; in humans, this is constantly performed via aerobic respiration in the mitochondria. Plants use photosynthetic pathways to convert and store energy from sunlight, also conversion of ADP to ATP. Animals use the energy released in the breakdown of glucose and other molecules to convert ADP to ATP, which can then be used to fuel necessary growth and cell maintenance. | 1 | Biochemistry |
In physics, tunnel ionization is a process in which electrons in an atom (or a molecule) tunnel through the potential barrier and escape from the atom (or molecule). In an intense electric field, the potential barrier of an atom (molecule) is distorted drastically. Therefore, as the length of the barrier that electrons have to pass decreases, the electrons can escape from the atom's potential more easily. Tunneling ionization is a quantum mechanical phenomenon since in the classical picture an electron does not have sufficient energy to overcome the potential barrier of the atom.
When the atom is in a DC external field, the Coulomb potential barrier is lowered and the electron has an increased, non-zero probability of tunnelling through the potential barrier. In the case of an alternating electric field, the direction of the electric field reverses after the half period of the field. The ionized electron may come back to its parent ion. The electron may recombine with the nucleus (nuclei) and its kinetic energy is released as light (high harmonic generation). If the recombination does not occur, further ionization may proceed by collision between high-energy electrons and a parent atom (molecule). This process is known as non-sequential ionization. | 7 | Physical Chemistry |
Distribution law or the Nernst's distribution law gives a generalisation which governs the distribution of a solute between two immiscible solvents. This law was first given by Nernst who studied the distribution of several solutes between different appropriate pairs of solvents.
C/C = K
Where K is called the distribution coefficient or the partition coefficient.
Concentration of X in solvent A/concentration of X in solvent B=Kď
If C denotes the concentration of solute X in solvent A & C denotes the concentration of solute X in solvent B; Nernst's distribution law can be expressed as C/C = K. This law is only valid if the solute is in the same molecular form in both the solvents. Sometimes the solute dissociates or associates in the solvent.
In such cases the law is modified as,
D(Distribution factor)=concentration of solute in all forms in solvent 1/concentration of solute in all forms in solvent 2. | 7 | Physical Chemistry |
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