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LISICON is an acronym for LIthium Super Ionic CONductor, which refers to a family of solids with the chemical formula LiZnGeO.
The first example of this structure was discovered in 1977 with , providing a chemical formula of LiZn(GeO). The crystal structure of LISICON consists of a network of [LiZn(GeO)] as well as 3 loosely bonded Li. The weaker bonds allow for the lithium ions to easily move from site to site, not needing to break strong bonds to do so. Also, this structure forms large “bottlenecks” between the interstitial positions which these ions occupy, additionally lowering the energy required to move from site to site. These two factors allow for the lithium ions to diffuse quickly and easily through the structure. However, because of the shape of the channels through which these lithium ions can diffuse, they are limited to 2 dimensional diffusion. LISICON compounds have relatively high ionic conductivity, on the order of 10 S/cm at 25 °C. LISICONs readily react with lithium metal and atmospheric gases such as CO; as a result, their conductivity decreases with time. | 7 | Physical Chemistry |
Ruthenium forms highly active catalysts. Allowing milder operating pressures and temperatures, Ru-based materials are referred to as second-generation catalysts. Such catalysts are prepared by the decomposition of triruthenium dodecacarbonyl on graphite. A drawback of activated-carbon-supported ruthenium-based catalysts is the methanation of the support in the presence of hydrogen. Their activity is strongly dependent on the catalyst carrier and the promoters. A wide range of substances can be used as carriers, including carbon, magnesium oxide, aluminium oxide, zeolites, spinels, and boron nitride.
Ruthenium-activated carbon-based catalysts have been used industrially in the KBR Advanced Ammonia Process (KAAP) since 1992. The carbon carrier is partially degraded to methane; however, this can be mitigated by a special treatment of the carbon at 1500 °C, thus prolonging the catalyst lifetime. In addition, the finely dispersed carbon poses a risk of explosion. For these reasons and due to its low acidity, magnesium oxide has proven to be a good choice of carrier. Carriers with acidic properties extract electrons from ruthenium, make it less reactive, and have the undesirable effect of binding ammonia to the surface. | 7 | Physical Chemistry |
Most chalconatronite formed on bronze and silver that have been treated with either sodium sesquicarbonate or sodium cyanide to prevent corrosion and bronze disease. The mineral has also been proven to form on the surface of copper artifacts after being treated with aqueous sodium carbonate. This formation by using sodium sesquicarbonate is undesirable by many antique collectors, as the mineral changes the patinas of copper artifacts. When the mineral forms, it can replace copper salts within the patina, and turn the color from a rich green to a blue-green or even black. | 8 | Metallurgy |
Dicumyl peroxide is an organic compound with the formula (Me = CH). Classified as a dialky peroxide, it is produced on a large scale industrially for use in polymer chemistry. It serves as an initiator and crosslinking agent in the production of low density polyethylene. | 0 | Organic Chemistry |
Rotational spectroscopy is concerned with the measurement of the energies of transitions between quantized rotational states of molecules in the gas phase. The rotational spectrum (power spectral density vs. rotational frequency) of polar molecules can be measured in absorption or emission by microwave spectroscopy or by far infrared spectroscopy. The rotational spectra of non-polar molecules cannot be observed by those methods, but can be observed and measured by Raman spectroscopy. Rotational spectroscopy is sometimes referred to as pure rotational spectroscopy to distinguish it from rotational-vibrational spectroscopy where changes in rotational energy occur together with changes in vibrational energy, and also from ro-vibronic spectroscopy (or just vibronic spectroscopy) where rotational, vibrational and electronic energy changes occur simultaneously.
For rotational spectroscopy, molecules are classified according to symmetry into a spherical top, linear and symmetric top; analytical expressions can be derived for the rotational energy terms of these molecules. Analytical expressions can be derived for the fourth category, asymmetric top, for rotational levels up to J=3, but higher energy levels need to be determined using numerical methods. The rotational energies are derived theoretically by considering the molecules to be rigid rotors and then applying extra terms to account for centrifugal distortion, fine structure, hyperfine structure and Coriolis coupling. Fitting the spectra to the theoretical expressions gives numerical values of the angular moments of inertia from which very precise values of molecular bond lengths and angles can be derived in favorable cases. In the presence of an electrostatic field there is Stark splitting which allows molecular electric dipole moments to be determined.
An important application of rotational spectroscopy is in exploration of the chemical composition of the interstellar medium using radio telescopes. | 7 | Physical Chemistry |
The LAL test is a major source of animal product dependence in the biomedical industry, and a challenge to the Three Rs of science in relation to the use of animals in testing. With reports of higher-than anticipated mortality rates it has been considered more ethical to devise alternatives to the test. Since 2003, a recombinant protein substitute for use in the LAL test has been commercially available. Named the recombinant factor C (rFC) assay, it is based on the same Limulus clotting factor C protein, but produced by genetically modified insect cells (the specific factor C sequence used does not necessarily come from the Atlantic horseshoe crab).
Instead of emulating the whole clotting pathway, rFC tests let factor C cleave a synthetic fluorogenic substrate, so that the sample lights up when endotoxin activates the factor. Since it does not contain factor G, (1,3)-β-D-glucan will not cause false-positives. As of 2018, available evidence shows that the rFC test is no worse than the LAL test.
The adoption of the rFC test was slow, which began to change in 2012 when the US FDA and the European health ministry acknowledged it as an accepted alternative. Its lack of mention in Pharmacopeias remained an issue, as there was no good standard for running the test in production. In 2016, it was added to the European Pharmacopoeia. A patent on rFC also limited adoption until its expiration in 2018.
On 1 June 2020, the United States Pharmacopeia (USP) decided to cancel the proposal to include recombinant technology for endotoxin testing in chapter 85, Bacterial Endotoxins, and start the development of a separate chapter that expands on the use, validation, and comparability of endotoxin tests based on recombinantly derived reagents. A separate guidance-only chapter 1085.1 was proposed by the USP, though comments and feedback published on 11 December 2020 show that pharmaceutical companies and the FDA do not support this chapter, and request for compendial status. | 3 | Analytical Chemistry |
Scholars previously believed that sub-Saharan Africans either did not have a period of using copper until the nineteenth century (going from the Stone Age directly into the Iron Age), or that they started smelting iron and copper at the same time. Copper smelting is thought to have been practiced in Nubia, during the early Old Kingdom c. 2686–2181 BC.
The principal evidence for this claim is an Egyptian outpost established in Buhen (near today's Sudanese-Egyptian border) around 2600 BC to smelt copper ores from Nubia. Alongside this, a crucible furnace dating to 2300–1900 BC for bronze casting has been found at the temple precinct at Kerma (in present-day northern Sudan), however the source of the tin remains unknown. Over the next millennium Nubians developed great skill in working copper and other known metals.
Discoveries in the Agadez Region of Niger evidence signs of copper metallurgy as early as 2000 BC. This date pre-dates the use of iron by a thousand years. Copper metallurgy seems to have been an indigenous invention in this area, because there is no clear evidence of influences from Northern Africa, and the Saharan wet phase was coming to an end, hindering human interactions across the Saharan region. It appeared to not be fully developed copper metallurgy, which suggests it was not from external origins. The people used native copper at first, and experimented with different furnace styles in order to smelt the ore between 2500 and 1500 BC.
Copper metallurgy has been recorded at Akjoujt in western Mauritania. The Akjoujt site is later than Agadez, dating back to around 850 BC. There is evidence of mining between 850 and 300 BC. Radiocarbon dates from the Grotte aux Chauves-souris mine shows that the extraction and smelting of malachite goes back to the early fifth century BC. A number of copper artifacts—including arrow points, spearheads, chisels, awls and plano-convex axes as well as bracelets, bead and earrings—were found at Neolithic sites in the region.
Collecting dates from Tropical Africa has been extremely difficult. No dates are available for the copper mine in pre-colonial Nigeria, and the earliest dates available south of the equator are around 345 AD at Naviundu springs near Lubumbashi in the Democratic Republic of Congo (DRC). Kansanshi mine in Zambia and Kipushi mine in the DRC date to between the fifth and twelfth centuries. Sites further south have produced later dates, for example the Thakadu mines in Botswana date to between 1480 and 1680; other major mines in Botswana, Namibia, and South Africa remain undated. | 8 | Metallurgy |
Supplemental HMB has been used in clinical trials as a treatment for preserving lean body mass in muscle wasting conditions, particularly sarcopenia, and has been studied in clinical trials as an adjunct therapy in conjunction with resistance exercise. Based upon two medical reviews and a meta-analysis of seven randomized controlled trials, HMB supplementation can preserve or increase lean muscle mass and muscle strength in sarcopenic older adults. HMB does not appear to significantly affect fat mass in older adults. Preliminary clinical evidence suggests that HMB supplementation may also prevent muscle atrophy during bed rest. A growing body of evidence supports the efficacy of HMB in nutritional support for reducing, or even reversing, the loss of muscle mass, muscle function, and muscle strength that occurs in hypercatabolic disease states such as cancer cachexia; consequently, the authors of two 2016 reviews of the clinical evidence recommended that the prevention and treatment of sarcopenia and muscle wasting in general include supplementation with HMB, regular resistance exercise, and consumption of a high-protein diet.
Clinical trials that used HMB for the treatment of muscle wasting have involved the administration of 3 grams of HMB per day under different dosing regimens. According to one review, an optimal dosing regimen is to administer it in one 1 gram dose, three times a day, since this ensures elevated plasma concentrations of HMB throughout the day; however, the best dosing regimen for muscle wasting conditions is still being investigated.
Some branded products that contain HMB (i.e., certain formulations of Ensure and Juven) are medical foods that are intended to be used to provide nutritional support under the care of a doctor in individuals with muscle wasting due to HIV/AIDS or cancer, to promote wound healing following surgery or injury, or when otherwise recommended by a medical professional. Juven, a nutrition product which contains 3 grams of , 14 grams of -arginine, and 14 grams of -glutamine per two servings, has been shown to improve lean body mass during clinical trials in individuals with AIDS and cancer, but not rheumatoid cachexia. Further research involving the treatment of cancer cachexia with Juven over a period of several months is required to adequately determine treatment efficacy. | 1 | Biochemistry |
In addition to chlorophylls, another group of yellow–orange pigments called carotenoids are also found in the photosystems. There are about thirty photosynthetic carotenoids. They help transfer and dissipate excess energy, and their bright colors sometimes override the chlorophyll green, like during the fall, when the leaves of some land plants change color. β-carotene is a bright red-orange carotenoid found in nearly all chloroplasts, like chlorophyll a. Xanthophylls, especially the orange-red zeaxanthin, are also common. Many other forms of carotenoids exist that are only found in certain groups of chloroplasts. | 5 | Photochemistry |
The primary mechanism of virokine interference with immune signaling is thought to be competitive inhibition of the binding of host signaling molecules to their target receptors. Virokines occupy binding sites on host receptors, thereby inhibiting access by signaling molecules. Viroceptors mimic host receptors and thus divert signaling molecules from finding their targets. Cytokine-binding proteins bind to and sequester cytokines, occluding the binding surface through which they interact with receptors. The effect is to attenuate and subvert host immune response. | 1 | Biochemistry |
Consistent with its high oxidizing power, VCl reacts with HBr at -50 °C to produce VBr. The reaction proceeds via VBr, which releases Br during warming to room temperature.
:2 VCl + 8 HBr → 2 VBr + 8 HCl + Br
VCl forms adducts with many donor ligands, for example, VCl(THF).
It is the precursor to vanadocene dichloride. | 0 | Organic Chemistry |
Consideration of the structure factor (and our assumption about translational invariance) is complicated by the fact that atoms in the crystal may be displaced from their respective lattice sites. Taking the scattering potential to be proportional to the density of scattering matter, we rewrite the structure factor.
The integral from here onwards is understood to be taken over the unit cell. is the density of scattering matter. The angle brackets indicate a temporal average of each unit cell followed by a spatial average over every unit cell. We further assume that each atom is displaced independently of the other atoms.
The number of atoms in the unit cell is and the occupancy factor for atom is . represents the point in the unit cell for which we would like to know the density of scattering matter. is the density of scattering matter from atom at a position separated from the nuclear position by a vector . is the probability density function for displacement. is the reference lattice site from which atom may be displaced to a new position . If is symmetrical enough (e.g. spherically symmetrical), is simply the mean nuclear position. When considering X-ray scattering, the scattering matter density consists of electron density around the nucleus. For neutron scattering, we have -functions weighted by a scattering length for the respective nucleus (see Fermi pseudopotential). Note that in the above discussion, we assumed the atoms were not deformable. With this in mind, (9) may be plugged into expression (8) for the structure factor.
Now we see the overall structure factor may be represented as a weighted sum of structure factors corresponding to each atom. Set the displacement between the location in space for which we would like to know the scattering density and the reference position for the nucleus equal to a new variable . Do the same for the displacement between the displaced and reference nuclear positions . Substitute into (10).
Within the square brackets of (11), we convolve the density of scattering matter of atom with the probability density function for some nuclear displacement. Then, in the curly brackets, we Fourier transform the resulting convolution. The final step is to multiply by a phase depending on the reference (e.g. mean) position of atom . But, according to the convolution theorem, Fourier transforming a convolution is the same as multiplying the two Fourier transformed functions. Set the displacement between the location in space for which we would like to know the scattering density and the position for the nucleus equal to a new variable .
Substitute (12) into (10).
That is:
is the atomic form factor of the atom ; it determines how the distribution of scattering matter about the nuclear position influences scattering. is the atomic Debye–Waller factor; it determines how the propensity for nuclear displacement from the reference lattice position influences scattering. The expression given for in the article's opening is different because of 1) the decision to take the thermal or time average, 2) the arbitrary choice of negative sign in the exponential, and 3) the decision to square the factor (which more directly connects it to the observed intensity). | 7 | Physical Chemistry |
The Paternò–Büchi reaction, named after Emanuele Paternò and George Büchi, who established its basic utility and form, is a photochemical reaction, specifically a 2+2 photocycloaddition, which forms four-membered oxetane rings from an excited carbonyl and reacting with an alkene.
With substrates benzaldehyde and 2-methyl-2-butene the reaction product is a mixture of structural isomers:
Another substrate set is benzaldehyde and furan or heteroaromatic ketones and fluorinated alkenes.
The alternative strategy for the above reaction is called the Transposed Paternò−Büchi reaction. | 5 | Photochemistry |
* Hypophosphorous acid (or phosphinic acid), (or ), a monoprotic acid (meaning that only one of the hydrogen atoms is acidic). Its salts and esters are called hypophosphites or phosphinates. | 0 | Organic Chemistry |
In general, hematocrit is the number of red blood cells (RBC) in circulation and is highly variable among fish species. Active fish, like the blue marlin, tend to have higher hematocrits, whereas less active fish, such as the starry flounder exhibit lower hematocrits. Hematocrit may be increased in response to both short-term (acute) or long-term (chronic) hypoxia exposure and results in an increase in the total amount of oxygen the blood can carry, also known as the oxygen carrying capacity of the blood. Acute changes in hematocrit are the result of circulating stress hormones (see - catecholamines) activating receptors on the spleen that cause the release of RBCs into circulation. During chronic hypoxia exposure, the mechanism used to increase hematocrit is independent of the spleen and results from hormonal stimulation of the kidney by erythropoetin (EPO). Increasing hematocrit in response to erythropoietin is observed after approximately one week and is therefore likely under genetic control of hypoxia inducible factor hypoxia inducible factor (HIF).
While increasing hematocrit means that the blood can carry a larger total amount of oxygen, a possible advantage during hypoxia, increasing the number of RBCs in the blood can also lead to certain disadvantages. First, A higher hematocrit results in more viscous blood (especially in cold water) increasing the amount of energy the cardiac system requires to pump the blood through the system and secondly depending on the transit time of the blood across the branchial arch and the diffusion rate of oxygen, an increased hematocrit may result in less efficient transfer of oxygen from the environment to the blood. | 9 | Geochemistry |
Gas generation by radiolytic decomposition of hydrogen-containing materials has been an area of concern for the transport and storage of radioactive materials and waste for a number of years. Potentially combustible and corrosive gases can be generated while at the same time, chemical reactions can remove hydrogen, and these reactions can be enhanced by the presence of radiation. The balance between these competing reactions is not well known at this time. | 5 | Photochemistry |
If we introduce a large number of particles with uniformly distributed impact parameters, the rate at which they exit the system is known as the decay rate. We can calculate the decay rate by simulating the system over many trials and forming a histogram of the delay time, T. For the GR system, it is easy to see that the delay time and the length of the particle trajectory are equivalent but for a multiplication coefficient. A typical choice for the impact parameter is the y-coordinate, while the trajectory angle is kept constant at zero degrees—horizontal. Meanwhile, we say that the particle has "exited the system" once it passes a border some arbitrary, but sufficiently large, distance from the centre of the system.
We expect the number of particles remaining in the system, N(T), to vary as:
Thus the decay rate, , is given as:
where n is the total number of particles.
Figure 3 shows a plot of the path-length versus the number of particles for a simulation of one million (1e6) particles started with random impact parameter, b. A fitted straight line of negative slope, is overlaid. The path-length, s, is equivalent to the decay time, T, provided we scale the (constant) speed appropriately.
Note that an exponential decay rate is a property specifically of hyperbolic chaotic scattering. Non-hyperbolic scatterers may have an arithmetic decay rate. | 7 | Physical Chemistry |
One possible model for fusion pore formation is the lipid-line pore theory. In this model, once the membranes have been brought into sufficiently close proximity via the "zipper" mechanism of the SNARE complex, membrane fusion occurs spontaneously. It has been shown that when the two membranes are brought within a critical distance, it is possible for hydrophilic lipid headgroups of one membrane to merge with the opposing membrane. In the lipid-lined fusion pore model, the SNARE complex acts as a scaffold, pulling on the membrane, causing both membranes to pucker so they may reach the critical fusion distance. As the two membranes begin to fuse, a lipid-lined stalk is produced, expanding radially outward as fusion proceeds.
While a lipid-lined pore is possible and can achieve all the same properties observed in early pore formation, sufficient data does not exist to prove it is the sole method of formation. There is not currently a proposed mechanism on inter-cellular regulation for fluctuation of lipid-lined pores, and they would have a substantially more difficult time producing effects such as the "kiss-and-run" when compared with their protein-lined counterparts. Lipid-lined pores effectiveness would also be highly dependent on the composition of both membranes, and its success or failure could vary wildly with changes in elasticity and rigidity. | 1 | Biochemistry |
Cation exchange sorbents are derivatized with functional groups that interact and retain positively charged cations, such as bases. Strong cation exchange sorbents contain aliphatic sulfonic acid groups that are always negatively charged in aqueous solution, and weak cation exchange sorbents contain aliphatic carboxylic acids, which are charged when the pH is above about 5. Strong cation exchange sorbents are useful because any strongly basic impurities in the sample will bind to the sorbent and usually will not be eluted with the analyte of interest; to recover a strong base a weak cation exchange cartridge should be used. To elute the analyte from either the strong or weak sorbent, the stationary phase is washed with a solvent that neutralizes ionic interaction between the analyte and the stationary phase. | 3 | Analytical Chemistry |
Some semicarbazones, such as nitrofurazone, and thiosemicarbazones are known to have anti-viral and anti-cancer activity, usually mediated through binding to copper or iron in cells. Many semicarbazones are crystalline solids, useful for the identification of the parent aldehydes/ketones by melting point analysis.
A thiosemicarbazone is an analog of a semicarbazone which contains a sulfur atom in place of the oxygen atom. | 0 | Organic Chemistry |
A common example of galvanic corrosion occurs in galvanized iron, a sheet of iron or steel covered with a zinc coating. Even when the protective zinc coating is broken, the underlying steel is not attacked. Instead, the zinc is corroded because it is less "noble". Only after it has been consumed can rusting of the base metal occur. By contrast, with a conventional tin can, the opposite of a protective effect occurs: because the tin is more noble than the underlying steel, when the tin coating is broken, the steel beneath is immediately attacked preferentially. | 8 | Metallurgy |
Generally speaking, chemotactic drug-targeting is a drug delivery strategy with promising avenues for treating diseases such as cancer and inflammation. This approach mimics the biological process of chemotaxis, which biological organisms use to detect, maneuver, and react to chemical signals in their environment. By applying this technique to targeted drug delivery, researchers aim to create drugs that can precisely reach their intended targets, minimizing the potential for side effects, improving drug efficacy, and decreasing drug dosage. Some examples include but are not limited to microdroplets, protocells, biological and bio-hybrid drug carriers, leukocytes, and neutrophils.
While chemotactic drug targeting holds great promise for drug delivery, there are key advantages and limitations that must be considered. One main advantage is that these systems can precisely target specific cells, tissues, or organs within the body while minimizing their disruptive effects on healthy tissue. Moreover, by delivering the drug directly to the desired target, researchers can effectively reduce the required drug dosage needed. However, some limitations to chemotactic drug targeting include issues with biocompatibility, drug-carrying capacity, and the life span of specific carriers. Another major challenge with this approach is motility, when either the chemical stimuli diminish, or the attached enzymes become oversaturated. This can limit the effectiveness of the drug delivery system and may require additional modifications to improve its performance. Thus, although these approaches have shown great promise, more research is still needed to fully understand chemotaxis mechanisms and optimize this property for targeted drug delivery strategies. | 1 | Biochemistry |
As mentioned in the previous section, early repolarization is known as appearing as elevated wave segments on ECGs. Recent studies have shown a connection between early repolarization and sudden cardiac death, which is identified as early repolarization syndrome. The condition is shown in both ventricular fibrillation without other structural heart defects as well as an early depolarization pattern, which can be seen on ECG.
The primary root of early repolarization syndrome stems from malfunctions of electrical conductance in ion channels, which may be due to genetic factors. Malfunctions of the syndrome include fluctuating sodium, potassium, and calcium currents. Changes in these currents may result in overlap of myocardial regions undergoing different phases of the action potential simultaneously, leading to risk of ventricular fibrillation and arrhythmias.
Upon being diagnosed, most individuals do not need immediate intervention, as early repolarization on an ECG does not indicate any life-threatening medical emergency. Three to thirteen percent of healthy individuals have been observed to have early repolarization on an ECG. However, patients who display early repolarization after surviving an event of early repolarization syndrome (a sudden-cardiac death experience), an implantable cardioverter-defibrillator (ICD) is strongly recommended. In addition, a patient may be more prone to atrial fibrillation if the individual has early repolarization syndrome and is under sixty years of age. | 7 | Physical Chemistry |
Attempts at treatment for cancer cells with constitutively phosphorylated STAT5 have included both indirect and direct inhibition of STAT5 activity. While more medicinal work has been done in indirect inhibition, this approach can lead to increased toxicity in cells and can also result in non-specific effects, both of which are better handled by direct inhibition.
Indirect inhibition targets kinases associated with STAT5, or targets proteases that carry out terminal truncation of proteins. Different inhibitors have been designed to target different kinases:
* Inhibition of BCR/ABl constitutes the basis of the functioning of drugs like imatinib
* Inhibition of FLT3 is carried out by drugs like lestaurtinib
* Inhibition of JAK2 is carried out by the drug CYT387, which was successful in preclinical trials and is currently undergoing clinical trials.
Direct inhibition of STAT5 activity makes use of small molecule inhibitors that prevent STAT5 from properly binding to DNA or prevent proper dimerization. The inhibiting of DNA binding utilizes RNA interference, antisense oligodeoxynucleotide, and short hairpin RNA. The inhibition of proper dimerization, on the other hand, is brought about by the use of small molecules that target the SH2 domain. Recent work on drug development in the latter field have proved particularly effective. | 1 | Biochemistry |
The nomenclature of organic acid anhydrides is derived from the names of the constituent carboxylic acids. In symmetrical acid anhydrides, only the prefix of the original carboxylic acid is used and the suffix "anhydride" is added. For most unsymmetrical acid anhydrides - also called mixed anhydrides- the prefixes from both acids reacted are listed before the suffix, e.g., benzoic propanoic anhydride. | 0 | Organic Chemistry |
François Diederich (9 July 1952, in Ettelbruck – 23 September 2020) was a Luxembourgian chemist specializing in organic chemistry. | 0 | Organic Chemistry |
Excitatory amino acids (EAA) will activate post-synaptic cells. inhibitory amino acids (IAA) depress the activity of post-synaptic cells. | 1 | Biochemistry |
Avidin and biotinylated artificial metal cofactor the most commonly used supramolecular strategy to make an ArM. In the example showed below, the ligand of Ru(I) complex was modified with biotin and than the whole complex was loaded onto streptavidin by biotin-avidin interaction. The resulted ArM can catalyze the reduction of prochiral ketones. Taking advantages of protein context, different mutants of strepavidin can achieve different stereochemistry selectivity by direct evolution. For example, Mutant L124V can selectively reduce certain ketone into R-alcohol while S112A-K121N can reduce the same substance into S-alcohol.<nowiki/>
Besides biotin-avidin based ArMs, another important attempt utilizing supuramolecular interaction is antigen-antibody recognition. First reported in 1989 by Lerner, a monoclonal antibody-based ArM is raised to hydrolyze specific peptide. | 0 | Organic Chemistry |
Pure water containing no exogenous ions is an excellent electronic insulator, but not even "deionized" water is completely free of ions. Water undergoes autoionization in the liquid state when two water molecules form one hydroxide anion () and one hydronium cation (). Because of autoionization, at ambient temperatures pure liquid water has a similar intrinsic charge carrier concentration to the semiconductor germanium and an intrinsic charge carrier concentration three orders of magnitude greater than the semiconductor silicon, hence, based on charge carrier concentration, water can not be considered to be a completely dielectric material or electrical insulator but to be a limited conductor of ionic charge.
Because water is such a good solvent, it almost always has some solute dissolved in it, often a salt. If water has even a tiny amount of such an impurity, then the ions can carry charges back and forth, allowing the water to conduct electricity far more readily.
It is known that the theoretical maximum electrical resistivity for water is approximately 18.2 MΩ·cm (182 kΩ·m) at 25 °C. This figure agrees well with what is typically seen on reverse osmosis, ultra-filtered and deionized ultra-pure water systems used, for instance, in semiconductor manufacturing plants. A salt or acid contaminant level exceeding even 100 parts per trillion (ppt) in otherwise ultra-pure water begins to noticeably lower its resistivity by up to several kΩ·m.
In pure water, sensitive equipment can detect a very slight electrical conductivity of 0.05501 ± 0.0001 μS/cm at 25.00 °C. Water can also be electrolyzed into oxygen and hydrogen gases but in the absence of dissolved ions this is a very slow process, as very little current is conducted. In ice, the primary charge carriers are protons (see proton conductor). Ice was previously thought to have a small but measurable conductivity of 1 S/cm, but this conductivity is now thought to be almost entirely from surface defects, and without those, ice is an insulator with an immeasurably small conductivity. | 2 | Environmental Chemistry |
There are four main experimental methods. For less commonly used methods, see Rossotti and Rossotti. In all cases the range can be extended by using the competition method. An example of the application of this method can be found in palladium(II) cyanide. | 7 | Physical Chemistry |
Above the liquidus temperature, the material is homogeneous and liquid at equilibrium. As the system is cooled below the liquidus temperature, more and more crystals will form in the melt if one waits a sufficiently long time, depending on the material. Alternately, homogeneous glasses can be obtained through sufficiently fast cooling, i.e., through kinetic inhibition of the crystallization process.
The crystal phase that crystallizes first on cooling a substance to its liquidus temperature is termed primary crystalline phase or primary phase. The composition range within which the primary phase remains constant is known as primary crystalline phase field.
The liquidus temperature is important in the glass industry because crystallization can cause severe problems during the glass melting and forming processes, and it also may lead to product failure. | 7 | Physical Chemistry |
: Once genes or markers are identified, they can be used for genotyping and selection decisions can be made. | 1 | Biochemistry |
In many bacteria, both mRNAs and non-coding RNAs can be polyadenylated. This poly(A) tail promotes degradation by the degradosome, which contains two RNA-degrading enzymes: polynucleotide phosphorylase and RNase E. Polynucleotide phosphorylase binds to the 3′ end of RNAs and the 3′ extension provided by the poly(A) tail allows it to bind to the RNAs whose secondary structure would otherwise block the 3′ end. Successive rounds of polyadenylation and degradation of the 3′ end by polynucleotide phosphorylase allows the degradosome to overcome these secondary structures. The poly(A) tail can also recruit RNases that cut the RNA in two. These bacterial poly(A) tails are about 30 nucleotides long.
In as different groups as animals and trypanosomes, the mitochondria contain both stabilising and destabilising poly(A) tails. Destabilising polyadenylation targets both mRNA and noncoding RNAs. The poly(A) tails are 43 nucleotides long on average. The stabilising ones start at the stop codon, and without them the stop codon (UAA) is not complete as the genome only encodes the U or UA part. Plant mitochondria have only destabilising polyadenylation. Mitochondrial polyadenylation has never been observed in either budding or fission yeast.
While many bacteria and mitochondria have polyadenylate polymerases, they also have another type of polyadenylation, performed by polynucleotide phosphorylase itself. This enzyme is found in bacteria, mitochondria, plastids and as a constituent of the archaeal exosome (in those archaea that have an exosome). It can synthesise a 3′ extension where the vast majority of the bases are adenines. Like in bacteria, polyadenylation by polynucleotide phosphorylase promotes degradation of the RNA in plastids and likely also archaea. | 1 | Biochemistry |
FDA-approved
In 2019 the FDA approved the first drug targeting melanocortin receptors, Vyleesi (Bremelanotide) which was developed by Palatin Technologies, Inc. The Melanocortin system has been largely unexplored in drug development but recent approvals, its novelty and wide-spread application across indications has led it to the frontier of new discoveries in medicine. Since Vyleesi approval multiple companies have initiated drug discovery programs targeting the melanocortin system. Bremelanotide (Vyleesi) is approved for treatment of acquired, generalized hypoactive sexual desire disorder (HSDD) in premenopausal women. At therapeutic dose levels, it activates MC1R and MC4R.
Setmelanotide (Imcivree) is an MC4R agonist approved for chronic weight management in patients with genetic obesity.
Afamelanotide (Scenesse) is an MC1R agonist approved for patients with erythropoietic protoporphyria to increase pain-free light exposure.
Clinical trials
PL9643, an ophthalmic solution, is being tested in phase 3 clinical trials to determine safety and efficacy in patients with dry eye. PL9643 activates MC1R, MC3R, MC4R and MC5R. Completed Phase 2 studies demonstrated positive results for the treatment of dry eye disease.
Dersimelagon (MT-7117) is an orally administered MC1R agonist being tested in phase 3 clinical trials to evaluate safety and tolerability in patients with erythropoietic protoporphyria or X-linked protoporphyria.
Resomelagon (AP1189) is an orally administered MC1R and MC3R agonist being tested in three phase 2 clinical trials to study safety and efficacy in patients with rheumatoid arthritis and idiopathic membranous nephropathy. | 1 | Biochemistry |
Phorbol derivatives work primarily by interacting with protein kinase C (PKC), although they can interact with other phospholipid membrane receptors. The esters bind to PKC in a similar way to its natural ligand, diacylglycerol, and activate the kinase. Diacylglycerol is degraded quickly by the body, allowing PKC to be reversibly activated. When phorbol esters bind to the receptor, they are not degraded as efficiently by the body, leading to constitutively active PK. PKC is involved in a number of important cell signaling pathways. Thus, phorbol ester exposure can show a wide range of results.
The main results of phorbol exposure are tumor promotion and inflammatory response. Although phorbol is not a carcinogen itself, it greatly enhances the action of other substances and promotes tumor proliferation. PKC is a key component in biological pathways controlling cell growth and differentiation. When phorbol esters bind to PKC, cell proliferation pathways are activated. This effect greatly promotes tumors when the cells are exposed to even a sub-carcinogenic amount of a substance.
PKC is also involved in activation of inflammation pathways such as the NF-κB pathway. Thus, exposure to phorbol products can induce an inflammatory response in tissues. Symptoms can include edema and pain, especially to the skin and mucus membranes.
While phorbol itself does not have irritant activity, nearly all phorbol esters are highly irritant, with a wide range of half-maximal inhibitory concentration (IC) values. The median lethal dose (LD) of phorbol esters for male mice was found to be about 27 mg/kg, with the mice showing hemorrhage and congestion of pulmonary blood vessels, as well as lesions throughout the body. | 0 | Organic Chemistry |
K. C. Nicolaou and coworkers at Scripps Research Institute generated the chiral hydrazone through Enders hydrazone alkylation reaction with high stereoselectivity (de' > 95%). The subsequent ozonolysis and Wittig reaction led to the side chain fragment of zaragozic acid A, which is a potent medicine for coronary heart disease. | 0 | Organic Chemistry |
Englishman William Haynes patented a process in 1860 for separating sulfide and gangue minerals using oil. Later writers have pointed to Haynes's as the first "bulk oil flotation" patent, though there is no evidence of its being field tested, or used commercially. In 1877 the brothers Bessel (Adolph and August) of Dresden, Germany, introduced their commercially successful oil and froth flotation process for extracting graphite, considered by some the root of froth flotation. However, the Bessel process became uneconomical after the discovery of high-grade graphite in Sri Lanka and was largely forgotten.
Inventor Hezekiah Bradford of Philadelphia invented a "method of saving floating material in ore-separation” and received US patent No. 345951 on July 20, 1886. He would later go on to patent the Bradford Breaker, currently in use by the coal industry, in 1893. His "Bradford washer," patented 1870, was used to concentrate iron, copper and lead-zinc ores by specific gravity, but lost some of the metal as float off the concentration process. The 1886 patent was to capture this "float" using surface tension, the first of the skin-flotation process patents that were eclipsed by oil froth flotation.
On August 24, 1886, Carrie Everson received a patent for her process calling for oil[s] but also an acid or a salt, a significant step in the evolution of the process history. By 1890, tests of the Everson process had been made at Georgetown and Silver Cliff, Colorado, and Baker, Oregon. She abandoned the work upon the death of her husband, and before perfecting a commercially successful process. Later, during the height of legal disputes over the validity of various patents during the 1910s, Everson's was often pointed to as the initial flotation patent - which would have meant that the process was not patentable again by later contestants. Much confusion has been clarified recently by historian Dawn Bunyak. | 8 | Metallurgy |
SFRS1 is a proto-oncogene, and thus ASF/SF2 can act as an oncoprotein; it can alter the splicing patterns of crucial cell cycle regulatory genes and suppressor genes. ASF/SF2 controls the splicing of various tumor suppressor genes, kinases, and kinase receptors, all of which have the potential to be alternatively spliced into oncogenic isoforms. As such, ASF/SF2 is an important target for cancer therapy, as it is over-expressed in many tumors.
Modifications and defects in the alternative splicing pathway are associated with a variety of human diseases.
ASF/SF2 is involved in the replication of HIV-1, as HIV-1 needs a delicate balance of spliced and unspliced forms of its viral DNA. ASF/SF2 action in the replication of HIV-1 is a potential target for HIV therapy. ASF/SF2 is also implicated in the production of T cell receptors in Systemic Lupus Erythematosus, altering specific chain expression in T cell receptors through alternative splicing. | 1 | Biochemistry |
The phenomenon was first noticed in 1983 in hoop-wound fibre-reinforced aluminium alloy cylinders, which burst in use in the USA. The alloy was 6351 with a relatively high lead content (400 ppm), but even after the lead content was lowered, the problem recurred, and subsequently the problem was detected in monolithic aluminium cylinders. The first incidence of an SLC crack in the cylindrical part of a cylinder was reported in 1999. | 8 | Metallurgy |
Two launch facilities at Malmstrom Air Force Base showed PCB levels higher than the thresholds recommended by the Environmental Protection Agency when extensive sampling began of active U.S. intercontinental ballistic missile bases to address specific cancer concerns in 2023. | 2 | Environmental Chemistry |
NMR spectroscopy is a technique that has been used over the years to study important dynamic aspects of base flipping. This technique allows researchers to determine the physical and chemical properties of atoms and other molecules by utilizing the magnetic properties of atomic nuclei. In addition, NMR can provide a variety of information including structure, reaction states, chemical environment of the molecules, and dynamics. During the DNA base flipping discovery experiment, researchers utilized NMR spectroscopy to investigate the enzyme-induced base flipping of HhaI methyltransferase. In order to accomplish this experiment, two 5-fluorocytosine residues were incorporated into the target and the reference position with the DNA substrate so the F chemical shift analysis could be performed. Once the F chemical shift analysis was evaluated, it was then concluded that the DNA complexes existed with multiple forms of the target 5-fluorocytosine along the base flipping pathway. | 1 | Biochemistry |
Plant defenses can be classified as constitutive or induced. Constitutive defenses are always present, while induced defenses are produced or mobilized to the site where a plant is injured. There is wide variation in the composition and concentration of constitutive defenses; these range from mechanical defenses to digestibility reducers and toxins. Many external mechanical defenses and quantitative defenses are constitutive, as they require large amounts of resources to produce and are costly to mobilize. A variety of molecular and biochemical approaches are used to determine the mechanisms of constitutive and induced defensive responses.
Induced defenses include secondary metabolites and morphological and physiological changes. An advantage of inducible, as opposed to constitutive defenses, is that they are only produced when needed, and are therefore potentially less costly, especially when herbivory is variable. Modes of induced defence include systemic acquired resistance and plant-induced systemic resistance. | 1 | Biochemistry |
The term lacunary is applied to ions which have a fragment missing, sometimes called defect structures. Examples are the and formed by the removal from the Keggin structure of sufficient Mo and O atoms to eliminate 1 or 3 adjacent octahedra. The Dawson structure is made up of two Keggin lacunary fragments with 3 missing octahedra. | 7 | Physical Chemistry |
It is useful to recognize that the only states within ~ of the Fermi level contribute significantly to the entropy. Other states are either fully occupied, , or completely unoccupied, . In either case, these states do not contribute to the entropy. If one assumes that the density of states is constant within of the Fermi level, one can derive that the electron heat capacity, equal to:
where is the density of states (number of levels per unit energy) at the Fermi level. Several other approximations can be made, but they all indicate that the electronic entropy should, to first order, be proportional to the temperature and the density of states at the Fermi level. As the density of states at the Fermi level varies widely between systems, this approximation is a reasonable heuristic for inferring when it may be necessary to include electronic entropy in the thermodynamic description of a system; only systems with large densities of states at the Fermi level should exhibit non-negligible electronic entropy (where large may be approximately defined as ). | 7 | Physical Chemistry |
Being strong acids, sulfonic acids are also used as catalysts. The simplest examples are methanesulfonic acid, CHSOOH and p-toluenesulfonic acid, which are regularly used in organic chemistry as acids that are lipophilic (soluble in organic solvents). Polymeric sulfonic acids are also useful. Dowex resin are sulfonic acid derivatives of polystyrene and is used as catalysts and for ion exchange (water softening). Nafion, a fluorinated polymeric sulfonic acid is a component of proton exchange membranes in fuel cells. | 0 | Organic Chemistry |
Chronic administration of zuclopenthixol (30 mg/kg/day for two years) in rats resulted in small, but significant, increases in the incidence of thyroid parafollicular carcinomas and, in females, of mammary adenocarcinomas and of pancreatic islet cell adenomas and carcinomas. An increase in the incidence of mammary adenocarcinomas is a common finding for D antagonists which increase prolactin secretion when administered to rats. An increase in the incidence of pancreatic islet cell tumours has been observed for some other D antagonists. The physiological differences between rats and humans with regard to prolactin make the clinical significance of these findings unclear.
Withdrawal syndrome: Abrupt cessation of therapy may cause acute withdrawal symptoms (eg, nausea, vomiting, or insomnia). Symptoms usually begin in 1 to 4 days of withdrawal and subside within 1 to 2 weeks.
Other permanent side effects are similar to many other typical antipsychotics, namely extrapyramidal symptoms as a result of dopamine blockade in subcortical areas of the brain. This may result in symptoms similar to those seen in Parkinson's disease and include a restlessness and inability to sit still known as akathisia, a slow tremor and stiffness of the limbs. Zuclopenthixol is thought to be more sedating than the related flupentixol, though possibly less likely to induce extrapyramidal symptoms than other typical depots. As with other dopamine antagonists, zuclopenthixol may sometimes elevate prolactin levels; this may occasionally result in amenorrhoea or galactorrhoea in severe cases. Neuroleptic malignant syndrome is a rare but potentially fatal side effect. Any unexpected deterioration in mental state with confusion and muscle stiffness should be seen by a physician.
Zuclopenthixol decanoate induces a transient dose-dependent sedation. However, if the patient is switched to maintenance treatment with zuclopenthixol decanoate from oral zuclopenthixol or from i.m. zuclopenthixol acetate the sedation will be no problem. Tolerance to the unspecific sedative effect develops rapidly.
;Very common Adverse Effects (≥10% incidence)
* Dry Mouth
* Somnolence
* Akathisia
* Hyperkinesia
* Hypokinesia
;Common (1–10%)
* Tachycardia
* Heart palpitations
* Vertigo
* Accommodation disorder
* Abnormal vision
* Salivary hypersecretion
* Constipation
* Vomiting
* Dyspepsia
* Diarrhoea
* Asthenia
* Fatigue
* Malaise
* Pain (at the injection site)
* Increased appetite
* Weight gain
* Myalgia
* Tremor
* Dystonia
* Hypertonia
* Dizziness
* Headache
* Paraesthesia
* Disturbance in attention
* Amnesia
* Abnormal gait
* Insomnia
* Depression
* Anxiety
* Abnormal dreams
* Agitation
* Decreased libido
* Nasal congestion
* Dyspnoea
* Hyperhidrosis
* Pruritus
;Uncommon (0.1–1%)
* Hyperacusis
* Tinnitus
* Mydriasis
* Abdominal pain
* Nausea
* Flatulence
* Thirst
* Injection site reaction
* Hypothermia
* Pyrexia
* Abnormal liver function tests
* Decreased appetite
* Weight loss
* Muscle rigidity
* Trismus
* Torticollis
* Tardive dyskinesia
* Hyperreflexia
* Dyskinesia
* Parkinsonism
* Syncope
* Ataxia
* Speech disorder
* Hypotonia
* Convulsion
* Migraine
* Apathy
* Nightmares
* Libido increased
* Confused state
* Ejaculation failure
* Erectile dysfunction
* Female orgasmic disorder
* Vulvovaginal
* Dryness
* Rash
* Photosensitivity
* Pigmentation disorder
* Seborrhoea
* Dermatitis
* Purpura
* Hypotension
* Hot flush
;Rare (0.01–0.1%)
* Thrombocytopenia
* Neutropenia
* Leukopenia
* Agranulocytosis
* QT prolongation
* Hyperprolactinaemia
* Hypersensitivity
* Anaphylactic reaction
* Hyperglycaemia
* Glucose tolerance impaired
* Hyperlipidaemia
* Gynaecomastia
* Galactorrhoea
* Amenorrhoea
* Priapism
* Withdrawal symptoms
;Very rare (<0.01%)
* Cholestatic hepatitis
* Jaundice
* Neuroleptic malignant syndrome
* Venous thromboembolism | 4 | Stereochemistry |
In cancers, loss of expression of genes occurs about 10 times more frequently by hypermethylation of promoter CpG islands than by mutations. For instance, in colon tumors compared to adjacent normal-appearing colonic mucosa, about 600 to 800 heavily methylated CpG islands occur in promoters of genes in the tumors while these CpG islands are not methylated in the adjacent mucosa. In contrast, as Vogelstein et al. point out, in a colorectal cancer there are typically only about 3 to 6 driver mutations and 33 to 66 hitchhiker or passenger mutations. | 1 | Biochemistry |
The most general description of a chemical reaction network considers a number of distinct chemical species reacting via reactions.
The chemical equation of the -th reaction can then be written in the generic form
which is often written in the equivalent form
Here
* is the reaction index running from 1 to ,
* denotes the -th chemical species,
* is the rate constant of the -th reaction and
* and are the stoichiometric coefficients of reactants and products, respectively.
The rate of such a reaction can be inferred by the law of mass action
which denotes the flux of molecules per unit time and unit volume. Here is the vector of concentrations. This definition includes the elementary reactions:
; zero order reactions
:for which for all ,
; first order reactions
:for which for a single ,
; second order reactions
:for which for exactly two ; that is, a bimolecular reaction, or for a single ; that is, a dimerization reaction.
Each of these is discussed in detail below. One can define the stoichiometric matrix
denoting the net extent of molecules of in reaction . The reaction rate equations can then be written in the general form
This is the product of the stoichiometric matrix and the vector of reaction rate functions.
Particular simple solutions exist in equilibrium, , for systems composed of merely reversible reactions. In this case, the rate of the forward and backward reactions are equal, a principle called detailed balance. Detailed balance is a property of the stoichiometric matrix alone and does not depend on the particular form of the rate functions . All other cases where detailed balance is violated are commonly studied by flux balance analysis, which has been developed to understand metabolic pathways. | 7 | Physical Chemistry |
Alcohol can be converted to haloalkanes. Direct reaction with a hydrohalic acid rarely gives a pure product, instead generating ethers. However, some exceptions are known: ionic liquids suppress the formation or promote the cleavage of ethers, hydrochloric acid converts tertiary alcohols to choloroalkanes, and primary and secondary alcohols convert similarly in the presence of a Lewis acid activator, such as zinc chloride. The latter is exploited in the Lucas test.
In the laboratory, more active deoxygenating and halogenating agents combine with base to effect the conversion. In the "Darzens halogenation", thionyl chloride () with pyridine converts less reactive alcohols to chlorides. Both phosphorus pentachloride () and phosphorus trichloride () function similarly, and alcohols convert to bromoalkanes under hydrobromic acid or phosphorus tribromide (PBr). The heavier halogens do not require preformed reagents: A catalytic amount of may be used for the transformation using phosphorus and bromine; is formed in situ. Iodoalkanes may similarly be prepared using red phosphorus and iodine (equivalent to phosphorus triiodide).
One family of named reactions relies on the deoxygenating effect of triphenylphosphine. In the Appel reaction, the reagent is tetrahalomethane and triphenylphosphine; the co-products are haloform and triphenylphosphine oxide. In the Mitsunobu reaction, the reagents are any nucleophile, triphenylphosphine, and a diazodicarboxylate; the coproducts are triphenyl­phosphine oxide and a hydrazodiamide. | 0 | Organic Chemistry |
Techniques are used for finding the source rock (the solid material in which the petroleum is found), as well as the type and amount of the petroleum within. They are also used to note migration timing and pathways, which are then used to predict when and where petroleum can be found; petroleum sources can be predicted if material associated with source rock is found. | 9 | Geochemistry |
Atmospheric methane is an important greenhouse gas with a global warming potential 25 times greater than carbon dioxide (averaged over 100 years), and methanogenesis in livestock and the decay of organic material is thus a considerable contributor to global warming. It may not be a net contributor in the sense that it works on organic material which used up atmospheric carbon dioxide when it was created, but its overall effect is to convert the carbon dioxide into methane which is a much more potent greenhouse gas.
Methanogenesis can also be beneficially exploited, to treat organic waste, to produce useful compounds, and the methane can be collected and used as biogas, a fuel. It is the primary pathway whereby most organic matter disposed of via landfill is broken down. | 1 | Biochemistry |
Geologists describe four qualitative levels of crystallinity:
* holocrystalline rocks are completely crystalline;
* hypocrystalline rocks are partially crystalline, with crystals embedded in an amorphous or glassy matrix;
* hypohyaline rocks are partially glassy;
* holohyaline rocks (such as obsidian) are completely glassy. | 7 | Physical Chemistry |
Compound 48/80 is a polymer produced by the condensation of N-methyl-p-methoxyphenethylamine with formaldehyde. It promotes histamine release, and in biochemical research, compound 48/80 is used to promote mast cell degranulation. | 1 | Biochemistry |
Multiple chemical shift databases and related services have been created to aid structural elucidation of and expert analysis of their NMR spectra. Of them, several informatics tools are dedicated solely to carbohydrates:
*GlycoSCIENCES.de
**over 2000 NMR spectra of mammalian glycans
**search of structure by NMR signals and vice versa
*CSDB (carbohydrate structure database) contains:
**over 4000 NMR spectra of bacterial, plant and fungal glycans,
**search of structure by NMR signals and vice versa
**empirical spectra simulation routine optimized for carbohydrates,
**statistical chemical shift estimation based on HOSE algorithm optimized for carbohydrates,
**structure generation and NMR-based ranking tool.
*CASPER (computer assisted spectrum evaluation of regular polysaccharides). contains:
**chemical shift database,
**empirical spectra simulation routine optimized for carbohydrates,
**online interface.
**structure matching tool. Both proton and carbon C and H chemical shifts can be used to access structural information. | 0 | Organic Chemistry |
DNA computing is an emerging branch of unconventional computing which uses DNA, biochemistry, and molecular biology hardware, instead of the traditional electronic computing. Research and development in this area concerns theory, experiments, and applications of DNA computing. Although the field originally started with the demonstration of a computing application by Len Adleman in 1994, it has now been expanded to several other avenues such as the development of storage technologies, nanoscale imaging modalities, synthetic controllers and reaction networks, etc. | 1 | Biochemistry |
*[http://www.efunda.com/ Diffusion Treatment Hardening]. eFunda. Retrieved 19 April 2008.
*[http://steel.keytometals.com Surface Hardening of Steels]. Key to Metals. Retrieved 19 April 2008. | 8 | Metallurgy |
In parallel to the advances in highthroughput biology, machine learning applications to biomedical data analysis are flourishing. The integration of multi-omics data analysis and machine learning has led to the discovery of new biomarkers. For example, one of the methods of the [http://mixomics.org/ mixOmics] project implements a method based on sparse Partial Least Squares regression for selection of features (putative biomarkers). A unified and flexible statistical framewok for heterogeneous data integration called "Regularized Generalized Canonical Correlation Analysis" (RGCCA ) enables identifying such putative biomarkers. This framework is implemented and made freely avalaible within the [https://cran.r-project.org/web/packages/RGCCA/ RGCCA R package] . | 1 | Biochemistry |
sAC is encoded in a single Homo sapiens gene identified as ADCY10 or Adenylate cyclase 10 (soluble). This gene packed down 33 exons that comprise greater than 100kb; though, it seems to utilize multiple promoters, and its mRNA undergoes extensive alternative splicing. | 1 | Biochemistry |
Discussion of cloning in the popular media often presents the subject negatively. In an article in the 8 November 1993 article of Time, cloning was portrayed in a negative way, modifying Michelangelos Creation of Adam to depict Adam with five identical hands. Newsweek' 10 March 1997 issue also critiqued the ethics of human cloning, and included a graphic depicting identical babies in beakers.
The concept of cloning, particularly human cloning, has featured a wide variety of science fiction works. An early fictional depiction of cloning is Bokanovskys Process which features in Aldous Huxleys 1931 dystopian novel Brave New World. The process is applied to fertilized human eggs in vitro, causing them to split into identical genetic copies of the original. Following renewed interest in cloning in the 1950s, the subject was explored further in works such as Poul Andersons 1953 story UN-Man, which describes a technology called "exogenesis", and Gordon Rattray Taylors book The Biological Time Bomb, which popularised the term "cloning" in 1963.
Cloning is a recurring theme in a number of contemporary science fiction films, ranging from action films such as Anna to the Infinite Power, The Boys from Brazil, Jurassic Park (1993), Alien Resurrection (1997), The 6th Day (2000), Resident Evil (2002), Star Wars: Episode II – Attack of the Clones (2002), The Island (2005) and Moon (2009) to comedies such as Woody Allens 1973 film Sleeper'.
The process of cloning is represented variously in fiction. Many works depict the artificial creation of humans by a method of growing cells from a tissue or DNA sample; the replication may be instantaneous, or take place through slow growth of human embryos in artificial wombs. In the long-running British television series Doctor Who, the Fourth Doctor and his companion Leela were cloned in a matter of seconds from DNA samples ("The Invisible Enemy", 1977) and then – in an apparent homage to the 1966 film Fantastic Voyage – shrunk to microscopic size to enter the Doctors body to combat an alien virus. The clones in this story are short-lived, and can only survive a matter of minutes before they expire. Science fiction films such as The Matrix and Star Wars: Episode II – Attack of the Clones' have featured scenes of human foetuses being cultured on an industrial scale in mechanical tanks.
Cloning humans from body parts is also a common theme in science fiction. Cloning features strongly among the science fiction conventions parodied in Woody Allens Sleeper, the plot of which centres around an attempt to clone an assassinated dictator from his disembodied nose. In the 2008 Doctor Who story "Journeys End", a duplicate version of the Tenth Doctor spontaneously grows from his severed hand, which had been cut off in a sword fight during an earlier episode.
After the death of her beloved 14-year-old Coton de Tulear named Samantha in late 2017, Barbra Streisand announced that she had cloned the dog, and was now "waiting for [the two cloned pups] to get older so [she] can see if they have [Samantha's] brown eyes and her seriousness". The operation cost $50,000 through the pet cloning company ViaGen. | 1 | Biochemistry |
Photosystem II light-harvesting proteins are the intrinsic transmembrane proteins CP43 (PsbC) and CP47 (PsbB) occurring in the reaction centre of photosystem II (PSII). These polypeptides bind to chlorophyll a and β-Carotene and pass the excitation energy on to the reaction centre.
This family also includes the iron-stress induced chlorophyll-binding protein CP43, encoded by the IsiA gene, which evolved in cyanobacteria from a PSII protein to cope with light limitations and stress conditions. Under iron-deficient growth conditions, CP43 associates with photosystem I (PSI) to form a complex that consists of a ring of 18 or more CP43 molecules around a PSI trimer, which significantly increases the light-harvesting system of PSI. The IsiA' protein can also provide photoprotection for PSII.
Plants, algae and some bacteria use two photosystems, PSI with P700 and PSII with P680. Using light energy, PSII acts first to channel an electron through a series of acceptors that drive a proton pump to generate adenosine triphosphate (ATP), before passing the electron on to PSI. Once the electron reaches PSI, it has used most of its energy in producing ATP, but a second photon of light captured by P700 provides the required energy to channel the electron to ferredoxin, generating reducing power in the form of NADPH. The ATP and NADPH produced by PSII and PSI, respectively, are used in the light-independent reactions for the formation of organic compounds. This process is non-cyclic, because the electron from PSII is lost and is only replenished through the oxidation of water. Hence, there is a constant flow of electrons and associated hydrogen atoms from water for the formation of organic compounds. It is this stripping of hydrogens from water that produces the oxygen we breathe.
IsiA has an inverse relationship with the iron stress repressed RNA (IsrR). IsrR is an antisense RNA that acts as a reversible switch that responds to changes in environmental conditions to modulate the expression of IsiA. | 5 | Photochemistry |
In a solid, only those particles that are at the surface can be involved in a reaction. Crushing a solid into smaller parts means that more particles are present at the surface, and the frequency of collisions between these and reactant particles increases, and so reaction occurs more rapidly. For example, Sherbet (powder) is a mixture of very fine powder of malic acid (a weak organic acid) and sodium hydrogen carbonate. On contact with the saliva in the mouth, these chemicals quickly dissolve and react, releasing carbon dioxide and providing for the fizzy sensation. Also, fireworks manufacturers modify the surface area of solid reactants to control the rate at which the fuels in fireworks are oxidised, using this to create diverse effects. For example, finely divided aluminium confined in a shell explodes violently. If larger pieces of aluminium are used, the reaction is slower and sparks are seen as pieces of burning metal are ejected. | 7 | Physical Chemistry |
A Bjerrum defect is a crystallographic defect which is specific to ice, and which is partly responsible for the electrical properties of ice. It was first proposed by Niels Bjerrum in 1952 in order to explain the electrical polarization of ice in an electric field. A hydrogen bond normally has one proton, but a hydrogen bond with a Bjerrum defect will have either two protons (D defect, from "doppel" in German, meaning "double") or no proton (L defect, from "leer" in German, meaning "empty"). D-defects are more energetically favorable than L-defects. The unfavorable defect strain is resolved when a water molecule pivots about an oxygen atom to produce hydrogen bonds with single protons. Dislocations of ice Ih along a slip plane create pairs of Bjerrum defects, one D defect and one L defect.
Nonpolar molecules such as methane can form clathrate hydrates with water, especially under high pressure. Although there is no hydrogen bonding of water molecules when methane is the guest molecule of the clathrate, guest-host hydrogen bonding often forms with guest molecules in clathrates of many larger organic molecules, such as pinacolone and tetrahydrofuran. In such cases the guest-host hydrogen bonds result in the formation of L-type Bjerrum defect in the clathrate lattice. Oxygen atoms (in alcohol or carbonyl functional groups) and nitrogen atoms (in amine functional groups) in the guest molecules lead to transient hydrogen bonds and misoriented water molecules in the hydrate lattice. | 7 | Physical Chemistry |
Kinetic theory provides insight into the macroscopic properties of gases by considering their molecular composition and motion. Starting with the definitions of momentum and kinetic energy, one can use the conservation of momentum and geometric relationships of a cube to relate macroscopic system properties of temperature and pressure to the microscopic property of kinetic energy per molecule. The theory provides averaged values for these two properties.
The kinetic theory of gases can help explain how the system (the collection of gas particles being considered) responds to changes in temperature, with a corresponding change in kinetic energy.
For example: Imagine you have a sealed container of a fixed-size (a constant volume), containing a fixed-number of gas particles; starting from absolute zero (the theoretical temperature at which atoms or molecules have no thermal energy, i.e. are not moving or vibrating), you begin to add energy to the system by heating the container, so that energy transfers to the particles inside. Once their internal energy is above zero-point energy, meaning their kinetic energy (also known as thermal energy) is non-zero, the gas particles will begin to move around the container. As the box is further heated (as more energy is added), the individual particles increase their average speed as the system's total internal energy increases. The higher average-speed of all the particles leads to a greater rate at which collisions happen (i.e. greater number of collisions per unit of time), between particles and the container, as well as between the particles themselves.
The macroscopic, measurable quantity of pressure, is the direct result of these microscopic particle collisions with the surface, over which, individual molecules exert a small force, each contributing to the total force applied within a specific area. (Read "Pressure" in the above section "Macroscopic view of gases".)
Likewise, the macroscopically measurable quantity of temperature, is a quantification of the overall amount of motion, or kinetic energy that the particles exhibit. (Read "Temperature" in the above section "Macroscopic view of gases".) | 7 | Physical Chemistry |
Ionic surfactants require special considerations, as they are electrolytes:
* In absence of extra electrolytes
where refers to the surface concentration of surfactant molecules, without considering the counter ion.
* In presence of added electrolytes | 7 | Physical Chemistry |
The main difference is in the reversal of these two types of neuromuscular-blocking drugs.
* Non-depolarizing blockers are reversed by acetylcholinesterase inhibitor drugs since non-depolarizing blockers are competitive antagonists at the ACh receptor so can be reversed by increases in ACh.
* The depolarizing blockers already have ACh-like actions, so these agents have prolonged effect under the influence of acetylcholinesterase inhibitors. Administration of depolarizing blockers initially produces fasciculations (a sudden twitch just before paralysis occurs). This is due to depolarization of the muscle. Also, post-operative pain is associated with depolarizing blockers.
The tetanic fade is the failure of muscles to maintain a fused tetany at sufficiently high frequencies of electrical stimulation.
* Non-depolarizing blockers have this effect on patients, probably by an effect on presynaptic receptors.
* Depolarizing blockers do not cause the tetanic fade. However, a clinically similar manifestation called Phase II block occurs with repeated doses of suxamethonium.
This discrepancy is diagnostically useful in case of intoxication of an unknown neuromuscular-blocking drug. | 1 | Biochemistry |
A plasmid partition system is a mechanism that ensures the stable inheritance of plasmids during bacterial cell division. Each plasmid has its independent replication system which controls the number of copies of the plasmid in a cell. The higher the copy number, the more likely the two daughter cells will contain the plasmid. Generally, each molecule of plasmid diffuses randomly, so the probability of having a plasmid-less daughter cell is 2, where N is the number of copies. For instance, if there are 2 copies of a plasmid in a cell, there is 50% chance of having one plasmid-less daughter cell. However, high-copy number plasmids have a cost for the hosting cell. This metabolic burden is lower for low-copy plasmids, but those have a higher probability of plasmid loss after a few generations. To control vertical transmission of plasmids, in addition to controlled-replication systems, bacterial plasmids use different maintenance strategies, such as multimer resolution systems, post-segregational killing systems (addiction modules), and partition systems. | 1 | Biochemistry |
Anandamide (ANA), also known as N-arachidonoylethanolamine (AEA), an N-acylethanolamine (NAE), is a fatty acid neurotransmitter. Anandamide was the first endocannabinoid to be discovered: it participates in the bodys endocannabinoid system by binding to cannabinoid receptors, the same receptors that the psychoactive compound THC in cannabis acts on. Anandamide is found in nearly all tissues in a wide range of animals. Anandamide has also been found in plants, including small amounts in chocolate. The name anandamide is taken from the Sanskrit word ananda', which means "joy, bliss, delight", plus amide.
Anandamide is derived from the non-oxidative metabolism of arachidonic acid, an essential omega-6 fatty acid. It is synthesized from N-arachidonoyl phosphatidylethanolamine by multiple pathways. It is degraded primarily by the fatty acid amide hydrolase (FAAH) enzyme, which converts anandamide into ethanolamine and arachidonic acid. As such, inhibitors of FAAH lead to elevated anandamide levels and are being pursued for therapeutic use.
Anandamide is also being explored for its role in diabetic neuropathy/neuropathy, as cannabinoids as well as exogenous or endogenous anandamide, demonstrate broad-spectrum antinociceptive properties in a model of painful diabetic neuropathy, mediated through peripheral activation of both cannabinoid receptors, i.e. CB1 and CB2, beside involvement of transient receptor vanilloid type-1 (TRPV1) channels in the pain modulation, as endovanilloid signalling modulates local pain, as well as in reduction of inflammation associated with renal injury. | 1 | Biochemistry |
Glycosynthase have been useful for the preparation of oligosaccharides; however, their use suffers from certain limitations. First, glycosynthase can only be used to synthesize glycosidic linkages for which there is a known glycosidase. That glycosidase must also be first converted into a glycosynthase, which is not always possible. Second, the product of the glycosynthase reaction is often a better substrate for the glycosynthase then the starting material, resulting in the formation of multiple products of varying lengths. Finally, glycosynthase are specific for the donor sugar but often have loose specificity for the acceptor sugar. This can result in different regioselectivity depending on the acceptor resulting in products with different glycosidic linkages. One example is the Agrobacterium sp. β-glucosynthase, which forms a β-1,4-glycoside with glucose as the acceptor, but forms a β-1,3-glycoside with xylose as the acceptor. | 0 | Organic Chemistry |
The way bacteriorhodopsin generates a proton gradient in Archaea is through a proton pump. The proton pump relies on proton carriers to drive protons from the side of the membrane with a low H concentration to the side of the membrane with a high H concentration. In bacteriorhodopsin, the proton pump is activated by absorption of photons of 568nm wavelength, which leads to isomerization of the Schiff base (SB) in retinal forming the K state. This moves SB away from Asp85 and Asp212, causing H transfer from the SB to Asp85 forming the M1 state. The protein then shifts to the M2 state by separating Glu204 from Glu194 which releases a proton from Glu204 into the external medium. The SB is reprotonated by Asp96 which forms the N state. It is important that the second proton comes from Asp96 since its deprotonated state is unstable and rapidly reprotonated with a proton from the cytosol. The protonation of Asp85 and Asp96 causes re-isomerization of the SB, forming the O state. Finally, bacteriorhodopsin returns to its resting state when Asp85 releases its proton to Glu204. | 7 | Physical Chemistry |
The ISASMELT process is an energy-efficient smelting process that was jointly developed from the 1970s to the 1990s by Mount Isa Mines (a subsidiary of MIM Holdings and now part of Glencore) and the Government of Australia's CSIRO. It has relatively low capital and operating costs for a smelting process.
ISASMELT technology has been applied to lead, copper, and nickel smelting. As of 2021, 22 plants were in operation in eleven countries, along with three demonstration plants located at Mt Isa. The installed capacity of copper/nickel operating plants in 2020 was 9.76 million tonnes per year of feed materials and 750 thousand tonnes per year across lead operating plants.
Smelters based on the copper ISASMELT process are among the lowest-cost copper smelters in the world. | 8 | Metallurgy |
Traditional CRP measurement only detected CRP in the range of 10 to 1,000 mg/L, whereas high sensitivity CRP (hs-CRP) detects CRP in the range of 0.5 to 10 mg/L. hs-CRP can detect cardiovascular disease risk when in excess of 3 mg/L, whereas below 1 mg/L would be low risk. Traditional CRP measurement is faster and less costly than hs-CRP, and can be adequate for some applications, such as monitoring hemodialysis patients. | 1 | Biochemistry |
The parent metallacyclobenzene has the formula LM(CH). They can be viewed as derivatives of benzene wherein a CH center has been replaced by a transition metal complex. Most metallabenzenes do not feature the M(CH) ring itself, but, instead, some of the H atoms are replaced by other substituents. | 0 | Organic Chemistry |
Transitions between redox species Cu and Cu fractionate Cu isotopes. Cu is preferentially reduced over Cu, leaving the residual Cu enriched in Cu. The equilibrium fractionation factor for speciation between Cu and Cu (α) is 1.00403 (i.e., dissolved Cu is enriched in Cu by ~+4‰ relative to Cu). | 9 | Geochemistry |
In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group . Their formula is usually written , where R is a side chain. They are reactive derivatives of carboxylic acids (). A specific example of an acyl chloride is acetyl chloride, . Acyl chlorides are the most important subset of acyl halides. | 0 | Organic Chemistry |
Adenine and guanine are the two nucleotides classified as purines. In purine synthesis, PRPP is turned into inosine monophosphate, or IMP. Production of IMP from PRPP requires glutamine, glycine, aspartate, and 6 ATP, among other things. IMP is then converted to AMP (adenosine monophosphate) using GTP and aspartate, which is converted into fumarate. While IMP can be directly converted to AMP, synthesis of GMP (guanosine monophosphate) requires an intermediate step, in which NAD+ is used to form the intermediate xanthosine monophosphate, or XMP. XMP is then converted into GMP by using the hydrolysis of 1 ATP and the conversion of glutamine to glutamate. AMP and GMP can then be converted into ATP and GTP, respectively, by kinases that add additional phosphates.
ATP stimulates production of GTP, while GTP stimulates production of ATP. This cross regulation keeps the relative amounts of ATP and GTP the same. Excess of either nucleotide could increase the likelihood of DNA mutations, where the wrong purine nucleotide is inserted.
Lesch–Nyhan syndrome is caused by a deficiency in hypoxanthine-guanine phosphoribosyltransferase or HGPRT, the enzyme that catalyzes the reversible reaction of producing guanine from GMP. This is a sex-linked congenital defect that causes overproduction of uric acid along with mental retardation, spasticity, and an urge to self-mutilate. | 1 | Biochemistry |
In case of measuring the hydration rim using the depth profiling ability of the secondary ion mass spectrometry technique, the sample is mounted on a holder without any preparation or cutting. This method of measurement is non-destructive.
There are two general SIMS modes: static mode and dynamic mode, depending on the primary ion current density, and three different types of mass spectrometers: magnetic sector, quadrupole and time-of-flight (TOF).
Any mass-spectrometer can work in static mode (very low ion current, a top mono-atomic layer analysis), and dynamic mode (a high ion current density, in-depth analysis).
Although relatively infrequent the use of SIMS on obsidian surface investigations has produced great progress in OHD dating. SIMS in general refers to four instrumental categories according to their operation; static, dynamic, quadrupole, and time-of-flight, TOF. In essence it is a technique with a large resolution on a plethora of chemical elements and molecular structures in an essentially non destructive manner. An approach to OHD with a completely new rationale suggests that refinement of the technique is possible in a manner which improves both its accuracy and precision and potentially expands the utility by generating reliable chronological data. Anovitz et al. presented a model which relied solely on compositionally-dependent diffusion, following numerical solutions (finite difference (FD), or finite element) elaborating on the H+ profile acquired by SIMS. A test of the model followed using results from Mount 65, Chalco in Mexico by Riciputi et al. This technique used numerical calculation to model the formation of the entire diffusion profile as a function of time and fitted the derived curve to the hydrogen profile. The FD equations are based on a number of assumptions about the behavior of water as it diffused into the glass and characteristic points of the SIMS H+ diffusion profile.
In Rhodes, Greece, under the direction and invention of Ioannis Liritzis,
the dating approach is based on modeling the S-like hydrogen profile by SIMS, following Fick's diffusion law, and an understanding of the surface saturation layer (see Figure). In fact, the saturation layer on the surface forms up to a certain depth depending on factors that include the kinetics of the diffusion mechanism for the water molecules, the specific chemical structure of obsidian, as well as the external conditions affecting diffusion (temperature, relative humidity, and pressure). Together these factors result in the formation of an approximately constant, boundary concentration value, in the external surface layer. Using the end product of diffusion, a phenomenological model has been developed, based on certain initial and boundary conditions and appropriate physicochemical mechanisms, that express the HO concentration versus depth profile as a diffusion/time equation.
This latest advance, the novel secondary ion mass spectrometry–surface saturation (SIMS-SS), thus, involves modelling the hydrogen concentration profile of the surface versus depth, whereas the age determination is reached via equations describing the diffusion process, while topographical effects have been confirmed and monitored through atomic force microscopy. | 9 | Geochemistry |
Thyroids secretory capacity (G, also referred to as SPINA-GT) is the maximum stimulated amount of thyroxine the thyroid can produce in one second. G' is elevated in hyperthyroidism and reduced in hypothyroidism.
G is calculated with
or
: Dilution factor for T4 (reciprocal of apparent volume of distribution, 0.1 l)<br />
: Clearance exponent for T4 (1.1e-6 sec)<br />
K: Dissociation constant T4-TBG (2e10 L/mol)<br />
K: Dissociation constant T4-TBPA (2e8 L/mol)<br />
D: EC for TSH (2.75 mU/L) | 1 | Biochemistry |
There are two limiting cases of the Butler–Volmer equation:
* the low overpotential region (called "polarization resistance", i.e., when E ≈ E), where the Butler–Volmer equation simplifies to:
* the high overpotential region, where the Butler–Volmer equation simplifies to the Tafel equation. When , the first term dominates, and when , the second term dominates.
: for a cathodic reaction, when E , or
: for an anodic reaction, when E >> E
where and are constants (for a given reaction and temperature) and are called the Tafel equation constants. The theoretical values of the Tafel equation constants are different for the cathodic and anodic processes. However, the Tafel slope can be defined as:
where is the faradaic current, expressed as , being and the cathodic and anodic partial currents, respectively. | 7 | Physical Chemistry |
A predominance diagram purports to show the conditions of concentration and pH where a chemical species has the highest concentration in solutions in which there are multiple acid-base equilibria. The lines on a predominance diagram indicate where adjacent species have the same concentration. Either side of such a line one species or the other predominates, that is, has higher concentration relative to the other species.
To illustrate a predominance diagram, part of the one for chromate is shown at the right. pCr stands for minus the logarithm of the chromium concentration and pH stands for minus the logarithm of the hydrogen ion concentration. There are two independent equilibria, with equilibrium constants defined as follows.
A third equilibrium constant can be derived from K and K.
The species and are only formed at very low pH so they do not appear on this diagram. Published values for log K and log K are 5.89 and 2.05, respectively. Using these values and the equality conditions, the concentrations of the three species, chromate , hydrogen chromate and dichromate can be calculated, for various values of pH, by means of the equilibrium expressions. The chromium concentration is calculated as the sum of the species' concentrations in terms of chromium content.
The three species all have concentrations equal to at pH = pK, for which [Cr] = . The three lines on this diagram meet at that point.
; Green line: Chromate and hydrogen chromate have equal concentrations. Setting [] equal to [] in eq. , [] = , or pH = log K. This relationship is independent of pCr, so it requires a vertical line to be drawn on the predominance diagram.
; Red line: Hydrogen chromate and dichromate have equal concentrations. Setting [] equal to [] in Eq. , [] = ; from Eq. , then, [] = .
; Blue line: Chromate and dichromate have equal concentrations. Setting [] equal to [] in Eq. gives [] = .
The predominance diagram is interpreted as follows. The chromate ion is the predominant species in the region to the right of the green and blue lines. Above pH ~6.75 it is always the predominant species. At pH ) the hydrogen chromate ion is predominant in dilute solution but the dichromate ion is predominant in more concentrated solutions.
Predominance diagrams can become very complicated when many polymeric species can be formed as, for example, with vanadate, molybdate and tungstate. Another complication is that many of the higher polymers are formed extremely slowly, such that equilibrium may not be attained even in months, leading to possible errors in the equilibrium constants and the predominance diagram. | 7 | Physical Chemistry |
There are two types of free-radical photoinitators: A two component system where the radical is generated through abstraction of a hydrogen atom from a donor compound (also called co-initiator), and a one-component system where two radicals are generated by cleavage. Examples of each type of free-radical photoinitiator is shown below.
Benzophenone, xanthones, and quinones are examples of abstraction type photoinitiators, with common donor compounds being aliphatic amines. The resulting R• species from the donor compound becomes the initiator for the free radical polymerization process, while the radical resulting from the starting photoinitiator (benzophenone in the example shown above) is typically unreactive.
Benzoin ethers, Acetophenones, Benzoyl Oximes, and Acylphosphines are some examples of cleavage-type photoinitiators. Cleavage readily occurs for the species, giving two radicals upon absorption of light, and both radicals generated can typically initiate polymerization. Cleavage type photoinitiators do not require a co-initiator, such as aliphatic amines. This can be beneficial since amines are also effective chain transfer species. Chain-transfer processes reduce the chain length and ultimately the crosslink density of the resulting film. | 5 | Photochemistry |
Tandem mass spectrometry (Tandem MS or MS/MS) uses two mass analyzers in sequence to separate more complex mixtures of analytes. The advantage of tandem MS is that it can be much faster than other two-dimensional methods, with times ranging from milliseconds to seconds. Because there is no dilution with solvents in MS, there is less probability of interference, so tandem MS can be more sensitive and have a higher signal-to-noise ratio compared to other two-dimensional methods. The main disadvantage associated with tandem MS is the high cost of the instrumentation needed. Prices can range from $500,000 to over $1 million. Many form of tandem MS involve a mass selection step and a fragmentation step. The first mass analyzer can be programmed to only pass molecules of a specific mass-to-charge ratio. Then the second mass analyzer can fragment the molecule to determine its identity. This can be especially useful for separating molecules of the same mass (i.e. proteins of the same mass or molecular isomers). Different types of mass analyzers can be coupled to achieve varying effects. One example would be a TOF-Quadrupole system. Ions can be sequentially fragmented and/or analyzed in a quadrupole as they leave the TOF in order of increasing m/z. Another prevalent tandem mass spectrometer is the quadrupole-quadrupole-quadrupole (Q-Q-Q) analyzer. The first quadrupole separates by mass, collisions take place in the second quadrupole, and the fragments are separated by mass in the third quadrupole. | 3 | Analytical Chemistry |
Protein digestion occurs in the stomach and duodenum in which 3 main enzymes, pepsin secreted by the stomach and trypsin and chymotrypsin secreted by the pancreas, break down food proteins into polypeptides that are then broken down by various exopeptidases and dipeptidases into amino acids. The digestive enzymes however are mostly secreted as their inactive precursors, the zymogens. For example, trypsin is secreted by pancreas in the form of trypsinogen, which is activated in the duodenum by enterokinase to form trypsin. Trypsin then cleaves proteins to smaller polypeptides. | 1 | Biochemistry |
# Urea + water --(enzyme urease)--> ammonium carbonate
# Ammonium carbonate + phenol + hypochlorite ----> colored complex
In this case, only the first stage of the reaction is catalyzed by an enzyme. The second stage is non-enzymatic. | 3 | Analytical Chemistry |
With time, various chemical notations for the hydroperoxyl (perhydroxyl) radical coexist in the literature. Haber, Wilstätter and Weiss simply wrote HO or OH, but sometimes HO or OH can also be found to stress the radical character of the species.
The hydroperoxyl radical is a weak acid and gives rise to the superoxide radical (O) when it loses a proton:
:HO → H + O
:sometimes also written as:
:HO → H + O
A first pK value of 4.88 for the dissociation of the hydroperoxyl radical was determined in 1970. The presently accepted value is 4.7. This pK value is close to that of acetic acid. Below a pH of 4.7, the protonated hydroperoxyl radical will dominate in solution while at pH above 4.7 the superoxide radical anion will be the main species. | 2 | Environmental Chemistry |
An excellent example system is the "Gaspard–Rice" (GR) scattering system
—also known simply as the "three-disc" system—which embodies many of the important concepts in chaotic scattering while being simple and easy to understand and simulate. The concept is very simple: we have three hard discs arranged in some triangular formation, a point particle is sent in and undergoes perfect, elastic collisions until it exits towards infinity. In this discussion, we will only consider GR systems having equally sized discs, equally spaced around the points of an equilateral triangle.
Figure 1 illustrates this system while Figure 2 shows two example trajectories. Note first that the trajectories bounce around the system for some time before finally exiting. Note also, that if we consider the impact parameters to be the start of the two perfectly horizontal lines at left (the system is completely reversible: the exit point could also be the entry point), the two trajectories are initially so close as to be almost identical. By the time they exit, they are completely different, thus illustrating the strong sensitivity to initial conditions. This system will be used as an example throughout the article. | 7 | Physical Chemistry |
*Hattori, K. (1993). High-sulfur magma, a product of fluid discharge from underlying mafic magma: evidence from Mount Pinatubo, Philippines. Geology, 21(12), 1083–1086.
*Hattori, K. H., & Keith, J. D. (2001). Contribution of mafic melt to porphyry copper mineralization: evidence from Mount Pinatubo, Philippines, and Bingham Canyon, Utah, USA. Mineralium Deposita, 36, 799–806.
*Hattori, K. H., & Guillot, S. (2003, April). Volcanic fronts as a consequence of serpentinite dehydration in the mantle wedge. In EGS-AGU-EUG Joint Assembly.
*Takahashi, Y., Minamikawa, R., Hattori, K. H., Kurishima, K., Kihou, N., & Yuita, K. (2004). Arsenic behavior in paddy fields during the cycle of flooded and non-flooded periods. Environmental Science & Technology, 38(4), 1038–1044.
*Guillot, S., Hattori, K., 2013. Serpentinites: Essential roles in geodynamics, arc volcanism, sustainable development, and the origin of life. Elements, 9 (2),. 95-98. Doi: 10.2113/gselements.9.2.25
*Hattori, K. H., & Guillot, S. (2003l). Volcanic fronts as a consequence of serpentinite dehydration in the mantle wedge.Geology, 31 (6), 525-528.
*Hattori, K., Takahashi, Y., Guillot, S., & Johanson, B. (2005). Occurrence of arsenic (V) in forearc mantle serpentinites based on X-ray absorption spectroscopy study. Geochimica et Cosmochimica Acta, 69(23), 5585–5596.
*Pagé, L., & Hattori, K. (2017). Tracing halogen and B cycling in subduction zones based on obducted, subducted and forearc serpentinites of the Dominican Republic. Scientific Reports, 7(1), 17776. | 9 | Geochemistry |
The joule per mole (symbol: J·mol or J/mol) is the unit of energy per amount of substance in the International System of Units (SI), such that energy is measured in joules, and the amount of substance is measured in moles.
It is also an SI derived unit of molar thermodynamic energy defined as the energy equal to one joule in one mole of substance. For example, the Gibbs free energy of a compound in the area of thermochemistry is often quantified in units of kilojoules per mole (symbol: kJ·mol or kJ/mol), with 1 kilojoule = 1000 joules.
Physical quantities measured in J·mol usually describe quantities of energy transferred during phase transformations or chemical reactions. Division by the number of moles facilitates comparison between processes involving different quantities of material and between similar processes involving different types of materials. The precise meaning of such a quantity is dependent on the context (what substances are involved, circumstances, etc.), but the unit of measurement is used specifically to describe certain existing phenomena, such as in thermodynamics it is the unit of measurement that describes molar energy.
Since 1 mole = 6.02214076 particles (atoms, molecules, ions etc.), 1 joule per mole is equal to 1 joule divided by 6.02214076 particles, ≈1.660539 joule per particle. This very small amount of energy is often expressed in terms of an even smaller unit such as the kJ·mol, because of the typical order of magnitude for energy changes in chemical processes. For example, heats of fusion and vaporization are usually of the order of 10 kJ·mol, bond energies are of the order of 100 kJ·mol, and ionization energies of the order of 1000 kJ·mol. For this reason, it is common within the field of chemistry to quantify the enthalpy of reaction in units of kJ·mol.
Other units sometimes used to describe reaction energetics are kilocalories per mole (kcal·mol), electron volts per particle (eV), and wavenumbers in inverse centimeters (cm). 1 kJ·mol is approximately equal to 1.04 eV per particle, 0.239 kcal·mol, or 83.6 cm. At room temperature (25 °C, or 298.15 K) 1 kJ·mol is approximately equal to 0.4034 . | 3 | Analytical Chemistry |
Raman spectroelectrochemistry (Raman-SEC) is a technique that studies the inelastic scattering or Raman scattering of monochromatic light related to chemical compounds involved in an electrode process. This technique provides information about vibrational energy transitions of molecules, using a monochromatic light source, usually from a laser that belongs to the UV, Vis or NIR region. Raman spectroelectrochemistry provides specific information about structural changes, composition and orientation of the molecules on the electrode surface involved in an electrochemical reaction, being the Raman spectra registered a real fingerprint of the compounds.
When a monochromatic light beam samples the electrode/solution interface, most of the photons are scattered elastically, with the same energy than the incident light. However, a small fraction is scattered inelastically, being the energy of the laser photons shifted up or down. When the scattering is elastic, the phenomenon is denoted as Rayleigh scattering, while when it is inelastic it is called Raman scattering. Raman spectroscopy combined with electrochemical techniques, makes Raman spectroelectrochemistry a powerful technique in the identification, characterization and quantification of molecules.
The main advantage of Raman spectroelectrochemistry is that it is not limited to the selected solvent, and aqueous and organic solutions can be used. However, the main disadvantage is the intrinsic low Raman signal intensity. Different methods as well as new substrates were developed to improve the sensitivity and selectivity of this multirresponse technique.
For researchers, a few experimental considerations related to Raman spectroelectrochemistry include electrode preparation, cell design, laser parameters, electrochemical sequence and data process. | 7 | Physical Chemistry |
Low dimensional van der Waals bonded materials display a fundamental material unit, usually depicted as the simplest molecular formula obeying stoichiometry. A series of such fundamental units align in the bulk material phase due to weak van der Waals interactions. Overall, key advantages conferred by the chemical structure are the ease to scale the materials down to nanostructures under simultaneous conservation of the bulk structure and the reduction in defects amount.
Belonging to the larger class of quasi 1-dimensional van der Waals bonded materials, β-BiI has been recently reported as a novel topological insulator. The binary bismuth-iodine family class includes the known bismuth(III) iodide along with additional representatives such as α-BiI, BiI, BiI, and BiI. Having the same stoichiometric chemical formula, α-BiI and β-BiI show similar solid-state structures yet critically different physicochemical properties. Specifically, α-BiI represents the trivial insulator phase, while stacking of the bismuth atoms along the b crystallographic axis in the β-BiI phase yield a different topological insulator phase. Both isoforms crystallyse in the C2/m space group, with α-BiI having a unit cell volume almost double of its topological insulator counterpart. The β crytallographic angle is higher in the β-BiI: 107.87 vs 92.96, making the β-BiI more tilted (see images above). | 7 | Physical Chemistry |
Sources of manganese ore generally also contain iron oxides. As manganese is harder to reduce than iron, during the reduction of manganese ore, iron is also reduced and mixed with the manganese in the melt, unlike other oxides such as SiO, AlO and CaO.
Reduction is achieved using a submerged arc furnance. There are two main industrial procedures to perform the reduction, the discard slag method (or flux method) and the duplex method (or fluxless method). Despite the name, the differences in the method are not in the addition of flux, but rather in the number of stages required. In the flux method, basic fluxes such as CaO are added in order to electrolytically reduce the manganese ore:
The remaining slag after the reduction process has approximately 15-20% manganese content, which is usually discarded.
In the fluxless method, carbon reduction is also used in the first stage, but the fluxes added do not necessarily increase the activity of the manganese. As a result, the remaining slag has a concentration of 30% to 50% of the manganese. This is then reprocessed with quartzite to make silicomanganese alloys. The resultant discarded slag has a manganese content of less than 5%, increasing the yield. As a result, this method is used more often in industry.
In both methods, due to the addition of carbon as an reducing agent, the alloy produced is referred to as high-carbon ferromanganese (HCFM), with a carbon content of up to 6%.
A correct mix of coke, flux and ore composition is required to give high yield and reliable furnance operation, by achieving the desired chemical properties, viscosity and smelting temperature in the resulting melt. Since the iron to manganese ratio of natural manganese sources vary greatly, mixing ores from several sources is sometimes done to give a certain desired ratio.
In the manufacture of steel, low-carbon ferromanganese (LCFM) is preferred due to the ability to accurately control the amount of carbon in the resultant steel. To arrive at LCFM from HCFM, there are also two main methods: silicothermal reduction and oxygen refinement.
In silicothermal reduction, silicomanganese from the second step of the duplex process is used as a reductant. After a variety of mixing and meting steps to reduce the silicon content, a low-carbon allow with less than 0.8% carbon and 1% silicon by weight can be obtained.
In the oxygen refinement method, HCFM is melted and heated to a high temperature of . Oxygen is then blown in to oxidise the carbon into CO and CO. The disadvantage of this process is that the metal is also oxidised at these high temperatures. Manganese oxide collects mainly in the form of MnO in the dust blown out from the crucible. | 8 | Metallurgy |
At molecular weights between 6 and 10 kilodaltons the R-PEG hydrogel acts as a Maxwell material, which means the fluid has both viscosity and elasticity. This is determined by measuring the plateau modulus, the elastic modulus for a viscoelastic polymer is constant or "relaxed" when deformed, at a range of frequencies via oscillatory rheology. Plotting the first- vs second-order integrals of the modulus values, a Cole-Cole plot is obtained, which, when fitted to a Maxwell model, provides the following relationship:
Where
* is the plateau modulus
* is the oscillation frequency in radians per second | 7 | Physical Chemistry |
Direct translation from DNA to protein has been demonstrated in a cell-free system (i.e. in a test tube), using extracts from E. coli that contained ribosomes, but not intact cells. These cell fragments could synthesize proteins from single-stranded DNA templates isolated from other organisms (e.g., mouse or toad), and neomycin was found to enhance this effect. However, it was unclear whether this mechanism of translation corresponded specifically to the genetic code. | 1 | Biochemistry |
Georg Wittig (; 16 June 1897 – 26 August 1987) was a German chemist who reported a method for synthesis of alkenes from aldehydes and ketones using compounds called phosphonium ylides in the Wittig reaction. He shared the Nobel Prize in Chemistry with Herbert C. Brown in 1979. | 4 | Stereochemistry |
A starting point for the development can be taken as the virial equation of state for a gas.
where is the pressure, is the volume, is the temperature and ... are known as virial coefficients. The first term on the right-hand side is for an ideal gas. The remaining terms quantify the departure from the ideal gas law with changing pressure, . It can be shown by statistical mechanics that the second virial coefficient arises from the intermolecular forces between pairs of molecules, the third virial coefficient involves interactions between three molecules, etc. This theory was developed by McMillan and Mayer.
Solutions of uncharged molecules can be treated by a modification of the McMillan-Mayer theory. However, when a solution contains electrolytes, electrostatic interactions must also be taken into account. The Debye–Hückel theory was based on the assumption that each ion was surrounded by a spherical "cloud" or ionic atmosphere made up of ions of the opposite charge. Expressions were derived for the variation of single-ion activity coefficients as a function of ionic strength. This theory was very successful for dilute solutions of 1:1 electrolytes and, as discussed below, the Debye–Hückel expressions are still valid at sufficiently low concentrations. The values calculated with Debye–Hückel theory diverge more and more from observed values as the concentrations and/or ionic charges increases. Moreover, Debye–Hückel theory takes no account of the specific properties of ions such as size or shape.
Brønsted had independently proposed an empirical equation,
in which the activity coefficient depended not only on ionic strength, but also on the concentration, m, of the specific ion through the parameter β. This is the basis of SIT theory. It was further developed by Guggenheim. Scatchard extended the theory to allow the interaction coefficients to vary with ionic strength. Note that the second form of Brønsted's equation is an expression for the osmotic coefficient. Measurement of osmotic coefficients provides one means for determining mean activity coefficients. | 7 | Physical Chemistry |
During his tenure, Lee has worked to create new research institutes, advance scientific research within Taiwan, and to recruit and cultivate top scholars for the Academic Sinica.
In 2010, Lee said that global warming would be much more serious than scientists previously thought, and that Taiwanese people needed to cut their per-capita carbon emissions from the current 12 tons per year to just three. This would take more than a few slogans, turning off the lights for one hour, or cutting meat consumption, noting: "We will have to learn to live the simple lives of our ancestors." Without such efforts, he said, "Taiwanese will be unable to survive long into the future".
He has been involved with the Malta Conferences, an initiative designed to bring together Middle Eastern scientists. As part of the initiative, he offered six fellowships to work on the synchrotron in Taiwan.
He is also a member of International Advisory Council in Universiti Tunku Abdul Rahman. | 7 | Physical Chemistry |
Molten chloride salt mixtures are commonly used as quenching baths for various alloy heat treatments, such as annealing and martempering of steel. Cyanide and chloride salt mixtures are used for surface modification of alloys such as carburizing and nitrocarburizing of steel.
Cryolite (a fluoride salt) is used as a solvent for aluminium oxide in the production of aluminium in the Hall-Héroult process.
Fluoride, chloride, and hydroxide salts can be used as solvents in pyroprocessing of nuclear fuel. | 8 | Metallurgy |
Tilt filling, also known as tilt casting, is an uncommon filling technique where the crucible is attached to the gating system and both are slowly rotated so that the metal enters the mold cavity with little turbulence. The goal is to reduce porosity and inclusions by limiting turbulence. For most uses tilt filling is not feasible because the following inherent problem: if the system is rotated slow enough to not induce turbulence, the front of the metal stream begins to solidify, which results in mis-runs. If the system is rotated faster it induces turbulence, which defeats the purpose. Durville of France was the first to try tilt casting, in the 1800s. He tried to use it to reduce surface defects when casting coinage from aluminium bronze. | 8 | Metallurgy |
Homovanillic acid (HVA) is a major catecholamine metabolite that is produced by a consecutive action of monoamine oxidase and catechol-O-methyltransferase on dopamine. Homovanillic acid is used as a reagent to detect oxidative enzymes, and is associated with dopamine levels in the brain.
In psychiatry and neuroscience, brain and cerebrospinal fluid levels of HVA are measured as a marker of metabolic stress caused by 2-deoxy--glucose. HVA presence supports a diagnosis of neuroblastoma and malignant pheochromocytoma.
Fasting plasma levels of HVA are known to be higher in females than in males. This does not seem to be influenced by adult hormonal changes, as the pattern is retained in the elderly and post-menopausal as well as transgender people according to their genetic sex, both before and during cross-sex hormone administration. Differences in HVA have also been correlated to tobacco usage, with smokers showing significantly lower amounts of plasma HVA. | 1 | Biochemistry |
Blood test results should always be interpreted using the reference ranges provided by the laboratory that performed the results. Example reference ranges are listed below. | 0 | Organic Chemistry |
Goldschmidts tolerance factor (from the German word Toleranzfaktor') is an indicator for the stability and distortion of crystal structures. It was originally only used to describe the perovskite ABO structure, but now tolerance factors are also used for ilmenite.
Alternatively the tolerance factor can be used to calculate the compatibility of an ion with a crystal structure.
The first description of the tolerance factor for perovskite was made by Victor Moritz Goldschmidt in 1926. | 3 | Analytical Chemistry |
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