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A yeast commonly used for protein production is Pichia pastoris. Examples of yeast expression vector in Pichia are the pPIC series of vectors, and these vectors use the AOX1 promoter which is inducible with methanol. The plasmids may contain elements for insertion of foreign DNA into the yeast genome and signal sequence for the secretion of expressed protein. Proteins with disulphide bonds and glycosylation can be efficiently produced in yeast. Another yeast used for protein production is Kluyveromyces lactis and the gene is expressed, driven by a variant of the strong lactase LAC4 promoter.
Saccharomyces cerevisiae is particularly widely used for gene expression studies in yeast, for example in yeast two-hybrid system for the study of protein-protein interaction. The vectors used in yeast two-hybrid system contain fusion partners for two cloned genes that allow the transcription of a reporter gene when there is interaction between the two proteins expressed from the cloned genes. | 1 | Biochemistry |
Prions are proteins of particular amino acid sequences in particular conformations. They propagate themselves in host cells by making conformational changes in other molecules of protein with the same amino acid sequence, but with a different conformation that is functionally important or detrimental to the organism. Once the protein has been transconformed to the prion folding it changes function. In turn it can convey information into new cells and reconfigure more functional molecules of that sequence into the alternate prion form. In some types of prion in fungi this change is continuous and direct; the information flow is Protein → Protein.
Some scientists such as Alain E. Bussard and Eugene Koonin have argued that prion-mediated inheritance violates the central dogma of molecular biology. However, Rosalind Ridley in Molecular Pathology of the Prions (2001) has written that "The prion hypothesis is not heretical to the central dogma of molecular biology—that the information necessary to manufacture proteins is encoded in the nucleotide sequence of nucleic acid—because it does not claim that proteins replicate. Rather, it claims that there is a source of information within protein molecules that contributes to their biological function, and that this information can be passed on to other molecules." | 1 | Biochemistry |
Lake Chichoj is located within 2 km of the Chixoy-Polochic fault, a major fault of the North America-Caribbean plate boundary, which constitutes the closest and largest seismic hazard for San Cristóbal Verapaz, but lies within a broader array of large to intermediate seismogenic faults. The latest noticeable earthquakes include a M 4.1 quake in 2006 on the Polochic fault and a M4.8 in June 2009 on a secondary fault, NW of the lake. The sediments of the lake host a rich record of disruptions produced by past earthquakes, most notably the M 7.8 February 4th 1978 earthquake on the Motagua fault as well as a series of older M 7 earthquakes along the Polochic fault between 850 CE and 1450 CE. The lake adds hazard to the ground shaking of earthquakes. The low-lying marshlands that surround the lake are increasingly filled and urbanized. They are susceptible to seismic wave amplification, seismic wave refraction, and soil liquefaction during earthquakes, but also susceptible to flooding during earthquakes if the lake spillovers. Large waves can be produced during earthquakes, either as a result of landslides affecting the lake inner slopes, or by seismic resonance (seiche waves). | 2 | Environmental Chemistry |
Fineman and Ross rearranged the copolymer equation into a linear form:
where and
Thus, a plot of versus yields a straight line with slope and intercept | 7 | Physical Chemistry |
The total energy of the system is where S is entropy, and the are the other extensive parameters of the system (e.g. volume, particle number, etc.). The entropy of the system may likewise be written as a function of the other extensive parameters as . Suppose that X is one of the which varies as a system approaches equilibrium, and that it is the only such parameter which is varying. The principle of maximum entropy may then be stated as:
: and at equilibrium.
The first condition states that entropy is at an extremum, and the second condition states that entropy is at a maximum. Note that for the partial derivatives, all extensive parameters are assumed constant except for the variables contained in the partial derivative, but only U, S, or X are shown. It follows from the properties of an exact differential (see equation 8 in the exact differential article) and from the energy/entropy equation of state that, for a closed system:
It is seen that the energy is at an extremum at equilibrium. By similar but somewhat more lengthy argument it can be shown that
which is greater than zero, showing that the energy is, in fact, at a minimum. | 7 | Physical Chemistry |
In organic chemistry, the propargyl group is a functional group of 2-propynyl with the structure . It is an alkyl group derived from propyne ().
The term propargylic refers to a saturated position (sp-hybridized) on a molecular framework next to an alkynyl group. The name comes from mix of propene and argentum, which refers to the typical reaction of the terminal alkynes with silver salts.
The term homopropargylic designates in the same manner
* a saturated position on a molecular framework next to a propargylic group and thus two bonds from an alkyne moiety.
* a 3-butynyl fragment, , or substituted homologue. | 0 | Organic Chemistry |
In chemical separation terminology, the raffinate (from French raffiner, to refine) is a product which has had a component or components removed. The product having the removed materials is referred to as the extract. For example, in solvent extraction, the raffinate is the liquid stream which remains after solutes from the original liquid are removed through contact with an immiscible liquid. In metallurgy, raffinating refers to a process in which impurities are removed from liquid material.
In pressure swing adsorption the raffinate refers to the gas which is not adsorbed during the high pressure stage. The species which is desorbed from the adsorbent at low pressure may be called the "extract" product. | 3 | Analytical Chemistry |
The alpha effect refers to the increased nucleophilicity of an atom due to the presence of an adjacent (alpha) atom with lone pair electrons. This first atom does not necessarily exhibit increased basicity compared with a similar atom without an adjacent electron-donating atom, resulting in a deviation from the classical Brønsted-type reactivity-basicity relationship. In other words, the alpha effect refers to nucleophiles presenting higher nucleophilicity than the predicted value obtained from the Brønsted basicity. The representative examples would be high nucleophilicities of hydroperoxide (HO) and hydrazine (NH). The effect is now well established with numerous examples and became an important concept in mechanistic chemistry and biochemistry. However, the origin of the effect is still controversial without a clear winner. | 7 | Physical Chemistry |
- For visible light,
- For neutrons,
- For "hard" X-rays,
while typical values for polymers range in . This makes small-angle measurements in neutrons and X-rays a bit more tedious, as very small angles are needed, and the data in those angles is often "overpowered" by the spot emerging in usual scattering experiments. The problem is mitigated by conducting longer experiments with more exposure time, which allows the required data to "intensify". One must take care though, as to not allow the prolonged exposure to high levels of radiation damage the polymers (which might be a real problem when considering biological polymer samples – proteins, for example).
On the other hand, to resolve smaller polymers and structurals subtleties, one cannot always resort to using the long-wavelength rays, as the diffraction limit comes into play. | 7 | Physical Chemistry |
De Silva and McClenaghan designed a proof-of-principle arithmetic device based on molecular logic gates. As depicted in Figure 10 A, Compound A is a push-pull olefin with the top receptor containing four carboxylic acid anion groups (and non-disclosed counter cations) capable of binding to calcium. The bottom part is a quinoline molecule which is a receptor for hydrogen ions. The logic gate operates as follows. Without any chemical input of Ca or H, the chromophore shows a maximum absorbance in UV/VIS spectroscopy at 390 nm. When calcium is introduced a hypsochromic shift (blue shift) takes place and the absorbance at 390 nm decreases. Likewise, addition of protons causes a bathochromic shift (red shift), and when both cations are in the water, the net result is absorption at the original 390 nm wavelength. This system represents an XNOR logic gate in absorption and an XOR logic gate in transmittance.
In another XOR logic gate system, the chemistry is based on the pseudorotaxane depicted in Figure 11. In organic solution the electron-deficient diazapyrenium salt (rod) and the electron-rich 2,3-dioxynaphthalene units of the crown ether (ring) self-assemble by formation of a charge transfer complex. An added tertiary amine like tributylamine forms a 1:2 adduct with the diazapyrene and the complex gets dethreaded. This process is accompanied by an increase in emission intensity at 343 nm resulting from freed crown ether. Added trifluoromethanesulfonic acid reacts with the amine and the process is reverted. Excess acid locks the crown ether by protonation and again the complex is de-threaded. | 6 | Supramolecular Chemistry |
Mikhail Semyonovich Tsvet, also spelt Tsvett, Tswett, Tswet, Zwet, and Cvet (Russian: Михаил Семёнович Цвет; 14 May 1872 – 26 June 1919) was a Russian-Italian botanist who invented chromatography. His last name is Russian for "colour" and is also the root word of "flower." | 3 | Analytical Chemistry |
In the study of heat transfer, critical heat flux (CHF) is the heat flux at which boiling ceases to be an effective form of transferring heat from a solid surface to a liquid. | 7 | Physical Chemistry |
The biopolymer poly-3-hydroxybutyrate (PHB) is a polyester produced by certain bacteria processing glucose, corn starch or wastewater. Its characteristics are similar to those of the petroplastic polypropylene (PP). PHB production is increasing. The South American sugar industry, for example, has decided to expand PHB production to an industrial scale. PHB is distinguished primarily by its physical characteristics. It can be processed into a transparent film with a melting point higher than 130 degrees Celsius, and is biodegradable without residue. | 7 | Physical Chemistry |
Selenols are important in certain biological processes. Three enzymes found in mammals contain selenols at their active sites: glutathione peroxidase, iodothyronine deiodinase, and thioredoxin reductase. The selenols in these proteins are part of the essential amino acid selenocysteine. The selenols function as reducing agents to give selenenic acid derivative (), which in turn are re-reduced by thiol-containing enzymes. Methaneselenol (commonly named "methylselenol") (), which can be produced in vitro by incubating selenomethionine with a bacterial methionine gamma-lyase (METase) enzyme, by biological methylation of selenide ion or in vivo by reduction of methaneseleninic acid (), has been invoked to explain the anticancer activity of certain organoselenium compounds. Precursors of methaneselenol are under active investigation in cancer prevention and therapy. In these studies, methaneselenol is found to be more biologically active than ethaneselenol () or 2-propaneselenol (). | 0 | Organic Chemistry |
A fourth international conference on the Gaia hypothesis, sponsored by the Northern Virginia Regional Park Authority and others, was held in October 2006 at the Arlington, VA campus of George Mason University.
Martin Ogle, Chief Naturalist, for NVRPA, and long-time Gaia hypothesis proponent, organized the event. Lynn Margulis, Distinguished University Professor in the Department of Geosciences, University of Massachusetts-Amherst, and long-time advocate of the Gaia hypothesis, was a keynote speaker. Among many other speakers: Tyler Volk, co-director of the Program in Earth and Environmental Science at New York University; Dr. Donald Aitken, Principal of Donald Aitken Associates; Dr. Thomas Lovejoy, President of the Heinz Center for Science, Economics and the Environment; Robert Corell, Senior Fellow, Atmospheric Policy Program, American Meteorological Society and noted environmental ethicist, J. Baird Callicott. | 9 | Geochemistry |
Buffer capacity is a quantitative measure of the resistance to change of pH of a solution containing a buffering agent with respect to a change of acid or alkali concentration. It can be defined as follows:
where is an infinitesimal amount of added base, or
where is an infinitesimal amount of added acid. pH is defined as −log[H], and d(pH) is an infinitesimal change in pH.
With either definition the buffer capacity for a weak acid HA with dissociation constant K can be expressed as
where [H] is the concentration of hydrogen ions, and is the total concentration of added acid. K is the equilibrium constant for self-ionization of water, equal to 1.0. Note that in solution H exists as the hydronium ion HO, and further aquation of the hydronium ion has negligible effect on the dissociation equilibrium, except at very high acid concentration.
This equation shows that there are three regions of raised buffer capacity (see figure 2).
* In the central region of the curve (coloured green on the plot), the second term is dominant, and Buffer capacity rises to a local maximum at pH = pK. The height of this peak depends on the value of pK. Buffer capacity is negligible when the concentration [HA] of buffering agent is very small and increases with increasing concentration of the buffering agent. Some authors show only this region in graphs of buffer capacity. Buffer capacity falls to 33% of the maximum value at pH = pK ± 1, to 10% at pH = pK ± 1.5 and to 1% at pH = pK ± 2. For this reason the most useful range is approximately pK ± 1. When choosing a buffer for use at a specific pH, it should have a pK value as close as possible to that pH.
* With strongly acidic solutions, pH less than about 2 (coloured red on the plot), the first term in the equation dominates, and buffer capacity rises exponentially with decreasing pH: This results from the fact that the second and third terms become negligible at very low pH. This term is independent of the presence or absence of a buffering agent.
* With strongly alkaline solutions, pH more than about 12 (coloured blue on the plot), the third term in the equation dominates, and buffer capacity rises exponentially with increasing pH: This results from the fact that the first and second terms become negligible at very high pH. This term is also independent of the presence or absence of a buffering agent. | 7 | Physical Chemistry |
When carbon dioxide is the substrate, the product of the carboxylase reaction is an unstable six-carbon phosphorylated intermediate known as 3-keto-2-carboxyarabinitol-1,5-bisphosphate, which decays rapidly into two molecules of glycerate-3-phosphate. This product, also known as 3-phosphoglycerate, can be used to produce larger molecules such as glucose.
When molecular oxygen is the substrate, the products of the oxygenase reaction are phosphoglycolate and 3-phosphoglycerate. Phosphoglycolate is recycled through a sequence of reactions called photorespiration, which involves enzymes and cytochromes located in the mitochondria and peroxisomes (this is a case of metabolite repair). In this process, two molecules of phosphoglycolate are converted to one molecule of carbon dioxide and one molecule of 3-phosphoglycerate, which can reenter the Calvin cycle. Some of the phosphoglycolate entering this pathway can be retained by plants to produce other molecules such as glycine. At ambient levels of carbon dioxide and oxygen, the ratio of the reactions is about 4 to 1, which results in a net carbon dioxide fixation of only 3.5. Thus, the inability of the enzyme to prevent the reaction with oxygen greatly reduces the photosynthetic capacity of many plants. Some plants, many algae, and photosynthetic bacteria have overcome this limitation by devising means to increase the concentration of carbon dioxide around the enzyme, including carbon fixation, crassulacean acid metabolism, and the use of pyrenoid.
Rubisco side activities can lead to useless or inhibitory by-products. Important inhibitory by-products include xylulose 1,5-bisphosphate and glycero-2,3-pentodiulose 1,5-bisphosphate, both caused by "misfires" halfway in the enolisation-carboxylation reaction. In higher plants, this process causes RuBisCO self-inhibition, which can be triggered by saturating and RuBP concentrations and solved by Rubisco activase (see below). | 5 | Photochemistry |
The research shortened photosynthetic pathways in tobacco. Engineered crops grew taller and faster, yielding up to 40% more biomass. The study employed synthetic biology to construct new metabolic pathways and assessed their efficiency with and without transporter RNAi. The most efficient pathway increased light-use efficiency by 17%. | 5 | Photochemistry |
Wood particles used to make various types of products rely on particle-size analysis to maintain high quality standards. By doing so, companies reduce waste and become more productive. | 3 | Analytical Chemistry |
The viral vectors described above have natural host cell populations that they infect most efficiently. Retroviruses have limited natural host cell ranges, and although adenovirus and adeno-associated virus are able to infect a relatively broader range of cells efficiently, some cell types are resistant to infection by these viruses as well. Attachment to and entry into a susceptible cell is mediated by the protein envelope on the surface of a virus. Retroviruses and adeno-associated viruses have a single protein coating their membrane, while adenoviruses are coated with both an envelope protein and fibers that extend away from the surface of the virus. The envelope proteins on each of these viruses bind to cell-surface molecules such as heparin sulfate, which localizes them upon the surface of the potential host, as well as with the specific protein receptor that either induces entry-promoting structural changes in the viral protein, or localizes the virus in endosomes wherein acidification of the lumen induces this refolding of the viral coat. In either case, entry into potential host cells requires a favorable interaction between a protein on the surface of the virus and a protein on the surface of the cell.
For the purposes of gene therapy, one might either want to limit or expand the range of cells susceptible to transduction by a gene therapy vector. To this end, many vectors have been developed in which the endogenous viral envelope proteins have been replaced by either envelope proteins from other viruses, or by chimeric proteins. Such chimera would consist of those parts of the viral protein necessary for incorporation into the virion as well as sequences meant to interact with specific host cell proteins. Viruses in which the envelope proteins have been replaced as described are referred to as pseudotyped viruses. For example, the most popular retroviral vector for use in gene therapy trials has been the lentivirus Simian immunodeficiency virus coated with the envelope proteins, G-protein, from Vesicular stomatitis virus. This vector is referred to as VSV G-pseudotyped lentivirus, and infects an almost universal set of cells. This tropism is characteristic of the VSV G-protein with which this vector is coated. Many attempts have been made to limit the tropism of viral vectors to one or a few host cell populations. This advance would allow for the systemic administration of a relatively small amount of vector. The potential for off-target cell modification would be limited, and many concerns from the medical community would be alleviated. Most attempts to limit tropism have used chimeric envelope proteins bearing antibody fragments. These vectors show great promise for the development of "magic bullet" gene therapies. | 1 | Biochemistry |
It is assumed that the Beer–Lambert law applies.
where is the optical path length, is a molar absorbance at unit path length and is a concentration. More than one of the species may contribute to the absorbance. In principle absorbance may be measured at one wavelength only, but in present-day practice it is common to record complete spectra. | 7 | Physical Chemistry |
Photophoresis denotes the phenomenon that small particles suspended in gas (aerosols) or liquids (hydrocolloids) start to migrate when illuminated by a sufficiently intense beam of light. The existence of this phenomenon is owed to a non-uniform distribution of temperature of an illuminated particle in a fluid medium. Separately from photophoresis, in a fluid mixture of different kinds of particles, the migration of some kinds of particles may be due to differences in their absorptions of thermal radiation and other thermal effects collectively known as thermophoresis. In laser photophoresis, particles migrate once they have a refractive index different from their surrounding medium. The migration of particles is usually possible when the laser is slightly or not focused. A particle with a higher refractive index compared to its surrounding molecule moves away from the light source due to momentum transfer from absorbed and scattered light photons. This is referred to as a radiation pressure force. This force depends on light intensity and particle size but has nothing to do with the surrounding medium. Just like in Crookes radiometer, light can heat up one side and gas molecules bounce from that surface with greater velocity, hence push the particle to the other side. Under certain conditions, with particles of diameter comparable to the wavelength of light, the phenomenon of a negative indirect photophoresis occurs, due to the unequal heat generation on the laser irradiation between the back and front sides of particles, this produces a temperature gradient in the medium around the particle such that molecules at the far side of the particle from the light source may get to heat up more, causing the particle to move towards the light source.
If the suspended particle is rotating, it will also experience the Yarkovsky effect.
Discovery of photophoresis is usually attributed to Felix Ehrenhaft in the 1920s, though earlier observations were made by others including Augustin-Jean Fresnel. | 7 | Physical Chemistry |
Alkaliphiles promise several interesting uses for biotechnology and future research. Alkaliphilic methods of regulating pH and producing ATP are of interest in the scientific community. However, perhaps the greatest area of interest from alkaliphiles lies in their enzymes: alkaline proteases; starch-degrading enzymes; cellulases; lipases; xylanases; pectinases; chitinases and their metabolites, including: 2-phenylamine; carotenoids; siderophores; cholic acid derivatives and organic acids. It is hoped that further research into alkaliphilic enzymes will allow scientists to harvest alkaliphiles' enzymes for use in basic conditions. Research aimed at discovering alkaliphile-produced antibiotics showed some success, yet has been held at bay by the fact that some products produced at high pH are unstable and unusable at a physiological pH range. | 1 | Biochemistry |
The extended double-stranded adapters are cleaved by HpyCH4III at a specific restriction site located at 3’ side of the tag sequence and will result in a 3’-dT overhang that will be ligated to the 3’-dA overhang on DNA libraries in the adapter ligation step (Figure 1). | 1 | Biochemistry |
Anomers can be interconverted through a process known as mutarotation. The anomeric effect more accurately called the endo-anomeric effect is the propensity for heteroatoms at C-1 to be oriented axially. This is counter intuitive as one would expect the equatorially anomer to be the thermodynamic product. This effect has been rationalized through dipole–dipole repulsion and n–σ* arguments. | 0 | Organic Chemistry |
Levorphanol is the INN, BAN, and DCF. As the medically used tartrate salt, the drug is also known as levorphanol tartrate (USAN, BANM). The former developmental code name of levorphanol at Roche was Ro 1-5431. | 4 | Stereochemistry |
* Hoerr, John P. And the Wolf Finally Came: The Decline of the American Steel Industry (1988) [https://www.amazon.com/Wolf-Finally-Came-American-Industry/dp/0822953986/ excerpt and text search]
* Hogan, William T. Economic History of the Iron and Steel Industry in the United States (5 vol 1971) monumental detail
* Ingham, John N. The Iron Barons: A Social Analysis of an American Urban Elite, 1874-1965 (1978)
* Krass, Peter. Carnegie (2002). .
* Livesay, Harold C. Andrew Carnegie and the Rise of Big Business, 2nd Edition (1999). .
* Misa, Thomas J. A Nation of Steel: The Making of Modern America, 1865–1925 (1995) Chapter 1 "[http://www.tc.umn.edu/~tmisa//NOS/1.1_intro.html The Dominance of Rails]"
* Nasaw, David. Andrew Carnegie (The Penguin Press, 2006).
* Paskoff, Paul F. Iron and Steel in the Nineteenth Century (Encyclopedia of American Business History and Biography) (1989) 385 pp; biographies and brief corporate histories
* Rogers, Robert P. An Economic History of the American Steel Industry (2009) [https://www.amazon.com/Economic-American-Industry-Routledge-Explorations/dp/0415777607/ excerpt and text search]
* Scamehorn, H. Lee. Mill & Mine: The Cf&I in the Twentieth Century University of Nebraska Press, 1992
* Scheuerman, William. The Steel Crisis: The Economics and Politics of a Declining Industry (1986)
* Skrabec Jr, Quentin R. The Carnegie Boys: The Lieutenants of Andrew Carnegie that Changed America (McFarland, 2012).
* Seely, Bruce E., ed The Iron and Steel Industry in the 20th Century (1994) (Encyclopedia of American Business History and Biography)
* Temin, Peter. Iron and Steel in Nineteenth-Century America, An Economic Inquiry (1964)
* Wall, Joseph Frazier. Andrew Carnegie (1989). .
* Warren, Kenneth, Big Steel: The First Century of the United States Steel Corporation, 1901–2001. (University of Pittsburgh Press, 2001) [https://web.archive.org/web/20070211162744/http://eh.net/bookreviews/library/0558.shtml online review]
* Warren, Kenneth. Bethlehem Steel: Builder and Arsenal of America (2010) [https://www.amazon.com/gp/reader/0822960672/ excerpt and text search]
* Warren, Kenneth. The American Steel Industry, 1850–1970: A Geographical Interpretation (1973) ()
* Whaples, Robert. "Andrew Carnegie", EH.Net Encyclopedia of Economic and Business History [https://web.archive.org/web/20061216082029/http://eh.net/encyclopedia/article/Whaples.Carnegie online]
* [https://web.archive.org/web/20110717180737/http://www.ussteel.com/corp/about.htm#The%20History%20of%20United%20States%20Steel U.S. Steel's History of U.S. Steel]
* Urofsky, Melvin I. Big Steel and the Wilson Administration: A Study in Business-Government Relations (1969) | 8 | Metallurgy |
Structural isomers have the same number of atoms of each element (hence the same molecular formula), but the atoms are connected in distinct ways. | 4 | Stereochemistry |
Lithol Rubine BK is a reddish synthetic azo dye. It has the appearance of a red powder and is magenta when printed. It is slightly soluble in hot water, insoluble in cold water, and insoluble in ethanol. When dissolved in dimethylformamide, its absorption maximum lies at about 442 nm. It is usually supplied as a calcium salt. It is prepared by azo coupling with 3-hydroxy-2-naphthoic acid.
It is used to dye plastics, paints, printing inks, and for textile printing. It is normally used as a standard magenta in the three and four color printing processes.
When used as a food dye, it has E number E180. It is used to color cheese rind, and it is a component in some lip balms. | 0 | Organic Chemistry |
There are four basic techniques for acquiring the three-dimensional (x, y, λ) dataset of a hyperspectral cube. The choice of technique depends on the specific application, seeing that each technique has context-dependent advantages and disadvantages. | 7 | Physical Chemistry |
RIP140 is part of the chain by which tumors can cause cachexia.
Levels of RIP140 expression in various tissues varies during aging in mice, suggesting changes in metabolic function. RIP140 is implicated in certain human disease processes. In morbid obesity, RIP140 levels are down-regulated in visceral adipose tissue. In breast cancer, RIP140 is involved in regulation of E2F1, an oncogene which discriminates between luminal and basal types of tumours. RIP140 has an influence upon cancer phenotype and prognosis. In addition, RIP140 has a role in inflammation, since it acts as a coactivator for NFkappaB/RelA-dependent cytokine gene expression. Lack of RIP140 leads to an inhibition of proinflammatory pathways in macrophages. | 1 | Biochemistry |
CaCrO is a frustrated kagome bilayer magnet, which does not develop long-range order even below 1 K, and has a diffuse spectrum of gapless excitations. | 7 | Physical Chemistry |
: M–R + M–X → M–X + M–R.
In redox-transmetalation/ligand exchange the ligands of two metal complexes switch places with each other, bonding with the other metal center. The R ligand can be an alkyl, aryl, alkynyl, or allyl group and the X ligand can be a halogen, pseudo-halogen, alkyl, or aryl group. The reaction can proceed by two possible intermediate steps. The first is an associative intermediate, where the R and X ligands bridge the two metals, stabilizing the transition state. The second and less common intermediate is the formation of a cation where R is bridging the two metals and X is anionic. The RTLE reaction proceeds in a concerted manner. Like in RT reactions, the reaction is driven by electronegativity values. The X ligand is attracted to highly electropositive metals. If M is a more electropositive metal than M, it is thermodynamically favorable for the exchange of the R and X ligands to occur. | 0 | Organic Chemistry |
Due to the location of the active origin OriL in the dimer junction, synthesis of new copies of the left-end hairpin in the correct, i.e.flip, orientation is not straightforward since a replication fork moving from this site through the linear bridge structure should synthesize new DNA in the flop orientation. Instead, the left-hand MVM dimer junction is resolved asymmetrically in a process that creates a cruciform intermediate. This maneuver accomplishes two things: it allows synthesis of the new DNA in the correct sequence orientation, and it creates a structure that can be resolved by NS1. This "heterocruciform" model of synthesis suggests that resolution is driven by the NS1 helicase activity and depends on the inherent instability of the duplex palindrome, a property that allows it to switch between its linear and cruciform configurations.
NS1 initially introduces a single-strand nick in OriL in the B ("right") arm of the junction and becomes covalently attached to the DNA on the 5′ side of the nick, exposing a basepaired 3′ nucleotide. Two outcomes can then occur, depending on the speed with which a replication fork is assembled. If assembly is rapid, then while the junction is in its linear configuration, "read-through" synthesis copies the upper strand, which regenerates the duplex junction and displaces a positive-sense strand that feeds back into the replicative pool. This promotes MVM DNA amplification but does not lead to synthesis of new terminal sequences in the correct orientation or to junction resolution.
To create a resolvable structure, the initial nicking must be followed by melting and rearrangement of the dimer junction into a cruciform. This is driven by the 3′-to-5′ helicase activity of the 5′-linked NS1 complex. Once this cruciform extends to include sequences beyond the nick site, the exposed primer at the nick site in OriL undergoes template switching by annealing with its complement in the lower arm of the cruciform. If a fork assembles after this point, then the subsequent synthesis unfolds and copies the lower cruciform arm. This creates a heterocruciform intermediate that contains the newly synthesized telomere in the flip sequence orientation that is attached to the lower strand of the B arm. This modified junction is called MJ2.
The lower arm of MJ2 is an extended-form duplex palindrome that is essentially identical to those generated during terminal resolution. Once MJ2 is synthesized, the lower arm becomes susceptible to rabbit-ear formation. This repositions the 3′ nucleotide of the newly synthesized copy of the lower arm so that it pairs with inboard sequences on the junction's B arm to prime strand displacement synthesis. If a replication fork is created at this 3′ nucleotide, then the lower strand of the B arm is copied, creating an intermediate junction called MJ1 and progressively displacing the upper strand. This leads to the release of the newly synthesized B turn-around (B-ta) sequence. The residual cruciform, called δJ, is partially single-stranded at the upper part of the B arm and contains the intact upper strand of the junction paired to the lower strand of the A ("left") arm, with an intact copy of the left-end hairpin, ending in a 5′ NS1 complex. Since δJ carries the NS1 helicase, it is presumed to periodically alter configuration.
The next step is less certain but can be inferred based on what is known about the process thus far. The NS1 helicase is expected to create a dynamic structure in which the nick site in δJ in the normally inactive A side is temporarily but repeatedly exposed in a single-stranded form during duplex-to-hairpin rearrangements, which allows NS1 to engage the nick site in the origin OriL without the help of a cofactor. The nick would leave NS1 covalently attached to the positive-sense "B" strand of δJ and lead to the release of this strand. Nicking also leaves open a basepaired 3′ nucleotide on the "A" strand of δJ to prime DNA synthesis. If a replication fork is established here, then the A strand is unfolded and copied to create its duplex extended form.
When MVM genomes replicate in vivo, the aforementioned nick may not occur because both ends of the dimer replicative form contain an efficient number of right-end hairpin origins. Therefore, replication forks may progress back toward the dimer junction from the genomes right end, copying the top strand of the B arm before the final resolution nick. This bypasses dimer bridge resolution and recycles the top strand into a replicating duplex dimer pool. In a closely related virus, LuIII, the single-strand nick releases a positive-sense strand with its left-end hairpin in the flop orientation. Unlike MVM, LuIII packages strands of both sense with equal frequency. In the negative-sense strands, the left-end hairpins are all in the flip orientation, while in the positive-sense strands, there are an equal number of flip and flop orientations. Compared to MVM, LuIII contains a two-base insertion immediately 3′ of the nick site in the right origin, which impairs its efficiency. Because of this, the reduced efficiency of replication fork assembly in the genomes right end may favor single-strand nicking by giving it more time to occur. | 1 | Biochemistry |
RT-PCR is commonly used in research methods to measure gene expression. For example, Lin et al. used qRT-PCR to measure expression of Gal genes in yeast cells. First, Lin et al. engineered a mutation of a protein suspected to participate in the regulation of Gal genes. This mutation was hypothesized to selectively abolish Gal expression. To confirm this, gene expression levels of yeast cells containing this mutation were analyzed using qRT-PCR. The researchers were able to conclusively determine that the mutation of this regulatory protein reduced Gal expression. Northern blot analysis is used to study the RNA's gene expression further. | 1 | Biochemistry |
* Due to the structure, the pressure difference is theoretically limited to atmospheric pressure (1 bar), and in practice somewhat lower.
* Besides the drum, other accessories, for example, agitators and vacuum pump, vacuum receivers, slurry pumps are required.
* The discharge cake contains residual moisture.
* The cake tends to crack due to their air drawn through by the vacuum system, so that washing and drying are not efficient.
* High energy consumption by the vacuum pump. | 3 | Analytical Chemistry |
Screening falls under two general categories: dry screening, and wet screening. From these categories, screening separates a flow of material into grades, these grades are then either further processed to an intermediary product or a finished product. Additionally, the machines can be categorized into a moving screen and static screen machines, as well as by whether the screens are horizontal or inclined. | 8 | Metallurgy |
A glide plane is a reflection in a plane, followed by a translation parallel with that plane. This is noted by , , or , depending on which axis the glide is along. There is also the glide, which is a glide along the half of a diagonal of a face, and the glide, which is a fourth of the way along either a face or space diagonal of the unit cell. The latter is called the diamond glide plane as it features in the diamond structure. In 17 space groups, due to the centering of the cell, the glides occur in two perpendicular directions simultaneously, i.e. the same glide plane can be called b or c, a or b, a or c. For example, group Abm2 could be also called Acm2, group Ccca could be called Cccb. In 1992, it was suggested to use symbol e for such planes. The symbols for five space groups have been modified: | 4 | Stereochemistry |
The illustrations to the right shows the main regions that may be present in a glow discharge. Regions described as "glows" emit significant light; regions labeled as "dark spaces" do not. As the discharge becomes more extended (i.e., stretched horizontally in the geometry of the illustrations), the positive column may become striated. That is, alternating dark and bright regions may form. Compressing the discharge horizontally will result in fewer regions. The positive column will be compressed while the negative glow will remain the same size, and, with small enough gaps, the positive column will disappear altogether. In an analytical glow discharge, the discharge is primarily a negative glow with dark region above and below it. | 3 | Analytical Chemistry |
Cicadia wings have a surface of hexagonally close packed nanopillars that have been shown to have self-cleaning properties. Similarly templated nanopatterned silica arrays have been shown to have hydrophobic, anti-reflective, and self-cleaning properties. These silica arrays begin as non-close packed monolayers, and are patterned in a series of etching steps involving chlorine and oxygen reactive ion etching, and a hydrofluoric acid wash. These properties have implicated that this surface pattern may prove to be useful in solar cell applications. Biomimetic materials based on the cicadia wing have also been made from polytetrafluoroethylene films with carbon/epoxy supports treated with argon and oxygen ion beams. A nanoimprint patterned surface based on the cicadia wings has been made by electrochemically templating and aluminum sheet with alumina oxide, and using this template to pattern a polymer surface. | 7 | Physical Chemistry |
The most critical eyespot proteins are the photoreceptor proteins that sense light. The photoreceptors found in unicellular organisms fall into two main groups: flavoproteins and retinylidene proteins (rhodopsins). Flavoproteins are characterized by containing flavin molecules as chromophores, whereas retinylidene proteins contain retinal. The photoreceptor protein in Euglena is likely a flavoprotein. In contrast, Chlamydomonas phototaxis is mediated by archaeal-type rhodopsins.
Besides photoreceptor proteins, eyespots contain a large number of structural, metabolic and signaling proteins. The eyespot proteome of Chlamydomonas cells consists of roughly 200 different proteins. | 1 | Biochemistry |
Scytovirin is a 95-amino acid antiviral protein isolated from the cyanobacteria Scytonema varium. It has been cultured in E. coli and its structure investigated in detail. Scytovirin is thought to be produced by the bacteria to protect itself from viruses that might otherwise attack it, but as it has broad-spectrum antiviral activity against a range of enveloped viruses, scytovirin has also been found to be useful against a range of major human pathogens, most notably HIV / AIDS but also including SARS coronavirus and filoviruses such as Ebola virus and Marburg virus. While some lectins such as cyanovirin and Urtica dioica agglutinin are thought likely to be too allergenic to be used internally in humans, studies so far on scytovirin and griffithsin have not shown a similar level of immunogenicity. Scytovirin and griffithsin are currently being investigated as potential microbicides for topical use. | 1 | Biochemistry |
Photoreceptor cells are unusual cells in that they depolarize in response to absence of stimuli or scotopic conditions (darkness). In photopic conditions (light), photoreceptors hyperpolarize to a potential of −60 mV.
In the dark, cGMP levels are high and keep cGMP-gated sodium channels open allowing a steady inward current, called the dark current. This dark current keeps the cell depolarized at about −40 mV, leading to glutamate release which inhibits excitation of neurons.
The depolarization of the cell membrane in scotopic conditions opens voltage-gated calcium channels. An increased intracellular concentration of Ca causes vesicles containing glutamate, a neurotransmitter, to merge with the cell membrane, therefore releasing glutamate into the synaptic cleft, an area between the end of one cell and the beginning of another neuron. Glutamate, though usually excitatory, functions here as an inhibitory neurotransmitter.
In the cone pathway, glutamate:
* Hyperpolarizes on-center bipolar cells. Glutamate that is released from the photoreceptors in the dark binds to metabotropic glutamate receptors (mGluR6), which, through a G-protein coupling mechanism, causes non-specific cation channels in the cells to close, thus hyperpolarizing the bipolar cell.
* Depolarizes off-center bipolar cells. Binding of glutamate to ionotropic glutamate receptors results in an inward cation current that depolarizes the bipolar cell. | 1 | Biochemistry |
In order to get a meaningful sulfur signal from the analysis, the buffer should not contain sulfur (i.e. no BES, DDT, HEPES, MES, MOPSO or PIPES compounds). Excessive amounts of chlorine in the buffer should also be avoided, since this will overlap with the sulfur peak; KBr and NaBr are suitable alternatives. | 7 | Physical Chemistry |
Hydrocarbons, primarily paraffins (CH) and lipids but also sugar alcohols.
* Advantages
** Freeze without much supercooling
** Ability to melt congruently
** Self nucleating properties
** Compatibility with conventional material of construction
** No segregation
** Chemically stable
** Safe and non-reactive
* Disadvantages
** Low thermal conductivity in their solid state. High heat transfer rates are required during the freezing cycle. Nano composites were found to yield an effective thermal conductivity increase up to 216%.
** Volumetric latent heat storage capacity can be low
** Flammable. This can be partially alleviated by specialised containment. | 7 | Physical Chemistry |
Liquid is one of the four primary states of matter, with the others being solid, gas and plasma. A liquid is a fluid. Unlike a solid, the molecules in a liquid have a much greater freedom to move. The forces that bind the molecules together in a solid are only temporary in a liquid, allowing a liquid to flow while a solid remains rigid.
A liquid, like a gas, displays the properties of a fluid. A liquid can flow, assume the shape of a container, and, if placed in a sealed container, will distribute applied pressure evenly to every surface in the container. If liquid is placed in a bag, it can be squeezed into any shape. Unlike a gas, a liquid is nearly incompressible, meaning that it occupies nearly a constant volume over a wide range of pressures; it does not generally expand to fill available space in a container but forms its own surface, and it may not always mix readily with another liquid. These properties make a liquid suitable for applications such as hydraulics.
Liquid particles are bound firmly but not rigidly. They are able to move around one another freely, resulting in a limited degree of particle mobility. As the temperature increases, the increased vibrations of the molecules causes distances between the molecules to increase. When a liquid reaches its boiling point, the cohesive forces that bind the molecules closely together break, and the liquid changes to its gaseous state (unless superheating occurs). If the temperature is decreased, the distances between the molecules become smaller. When the liquid reaches its freezing point the molecules will usually lock into a very specific order, called crystallizing, and the bonds between them become more rigid, changing the liquid into its solid state (unless supercooling occurs). | 7 | Physical Chemistry |
Quantities, Units and Symbols in Physical Chemistry, also known as the Green Book, is a compilation of terms and symbols widely used in the field of physical chemistry. It also includes a table of physical constants, tables listing the properties of elementary particles, chemical elements, and nuclides, and information about conversion factors that are commonly used in physical chemistry. The Green Book is published by the International Union of Pure and Applied Chemistry (IUPAC) and is based on published, citeable sources. Information in the Green Book is synthesized from recommendations made by IUPAC, the International Union of Pure and Applied Physics (IUPAP) and the International Organization for Standardization (ISO), including recommendations listed in the IUPAP Red Book Symbols, Units, Nomenclature and Fundamental Constants in Physics and in the ISO 31 standards. | 3 | Analytical Chemistry |
There is one Public Analyst Laboratory in each of Guernsey, Isle of Man and Jersey serving the needs of these islands. | 2 | Environmental Chemistry |
The Caspian Sea is at its South Caspian Basin, like the Black Sea, a remnant of the ancient Paratethys Sea. Its seafloor is, therefore, a standard oceanic basalt and not a continental granite body. It is estimated to be about 30 million years old, and became landlocked in the Late Miocene, about 5.5 million years ago, due to tectonic uplift and a fall in sea level. The Caspian Sea was a comparatively small endorheic lake during the Pliocene, but its surface area increased fivefold around the time of the Pliocene-Pleistocene transition. During warm and dry climatic periods, the landlocked sea almost dried up, depositing evaporitic sediments like halite that were covered by wind-blown deposits and were sealed off as an evaporite sink when cool, wet climates refilled the basin. (Comparable evaporite beds underlie the Mediterranean.) Due to the current inflow of fresh water in the north, the Caspian Sea water is almost fresh in its northern portions, getting more brackish toward the south. It is most saline on the Iranian shore, where the catchment basin contributes little flow. Currently, the mean salinity of the Caspian is one third that of Earth's oceans. The Garabogazköl lagoon, which dried up when water flow from the main body of the Caspian was blocked in the 1980s but has since been restored, routinely exceeds oceanic salinity by a factor of 10. | 2 | Environmental Chemistry |
Accurate detection and quantification are the most vital components of the TOC analysis process. Conductivity and non-dispersive infrared (NDIR) are the two common detection methods used in modern TOC analyzers. | 3 | Analytical Chemistry |
Atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES) is a spectroanalytical procedure for the quantitative determination of chemical elements by free atoms in the gaseous state. Atomic absorption spectroscopy is based on absorption of light by free metallic ions.
In analytical chemistry the technique is used for determining the concentration of a particular element (the analyte) in a sample to be analyzed. AAS can be used to determine over 70 different elements in solution, or directly in solid samples via electrothermal vaporization, and is used in pharmacology, biophysics,
archaeology and toxicology research.
Atomic emission spectroscopy (AAS) was first used as an analytical technique, and the underlying principles were established in the second half of the 19th century by Robert Wilhelm Bunsen and Gustav Robert Kirchhoff, both professors at the University of Heidelberg, Germany.
The modern form of AAS was largely developed during the 1950s by a team of Australian chemists. They were led by Sir Alan Walsh at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Division of Chemical Physics, in Melbourne, Australia.
Atomic absorption spectrometry has many uses in different areas of chemistry such as clinical analysis of metals in biological fluids and tissues such as whole blood, plasma, urine, saliva, brain tissue, liver, hair, muscle tissue. Atomic absorption spectrometry can be used in qualitative and quantitative analysis. | 3 | Analytical Chemistry |
Organic ionic plastic crystals – are a type organic salts exhibiting mesophases (i.e. a state of matter intermediate between liquid and solid), in which mobile ions are orientationally or rotationally disordered while their centers are located at the ordered sites in the crystal structure. They have various forms of disorder due to one or more solid–solid phase transitions below the melting point and have therefore plastic properties and good mechanical flexibility as well as improved electrode|electrolyte interfacial contact. In particular, protic organic ionic plastic crystals (POIPCs), which are solid protic organic salts formed by proton transfer from a Brønsted acid to a Brønsted base and in essence are protic ionic liquids in the molten state, have found to be promising solid-state proton conductors for fuel cells. Examples include 1,2,4-triazolium perfluorobutanesulfonate and imidazolium methanesulfonate. | 7 | Physical Chemistry |
The endothelial protease vasohibin uses a cysteine as the nucleophile, but a serine to coordinate the histidine base. Despite the serine being a poor acid, it is still effective in orienting the histidine in the catalytic triad. Some homologues alternatively have a threonine instead of serine at the acid location. | 1 | Biochemistry |
A thermodynamic system consisting of a single phase, in the absence of external forces, in its own state of internal thermodynamic equilibrium, is homogeneous. This means that the material in any region of the system can be interchanged with the material of any congruent and parallel region of the system, and the effect is to leave the system thermodynamically unchanged. The thermodynamic operation of scaling is the creation of a new homogeneous system whose size is a multiple of the old size, and whose intensive variables have the same values. Traditionally the size is stated by the mass of the system, but sometimes it is stated by the entropy, or by the volume. For a given such system , scaled by the real number to yield a new one , a state function, , such that , is said to be extensive. Such a function as is called a homogeneous function of degree 1. There are two different concepts mentioned here, sharing the same name: (a) the mathematical concept of degree-1 homogeneity in the scaling function; and (b) the physical concept of the spatial homogeneity of the system. It happens that the two agree here, but that is not because they are tautologous. It is a contingent fact of thermodynamics. | 7 | Physical Chemistry |
Sucrose esters were first mentioned in 1880 by Herzfeld who described the preparation of sucrose octaacetate. The substance is still in use today as a food additive. In 1921, Hess and Messner synthesized sucrose octapalmitate and sucrose octastearate. Both are sucrose fatty acid esters.
Rosenthal, in 1924, synthesized highly substituted sucrose fatty acid esters using the classical condensation reaction between sucrose and the acid chloride of the drying oil fatty acid; pyridine was used as a solvent. Rheineck, Rabin, and Long followed the same procedure using alternative polyhydroxyl molecules such as mannitol. These condensation gave low yields, and the products, which were dark in color, needed extensive purification. Moreover, pyridine is a toxic solvent, so the synthesis was not commercially successful.
In 1939, Cantor, who patented a production route of sucrose fatty acid esters from starch factory by-products, claimed that the products could be used as emulsifying agents or fats. The classical esterification was used with a mixture of pyridine and either chloroform or carbontetrachloride as a solvent.
Later, the concept of synthesizing sucrose ester from sucrose and fatty acids was patented in 1952. The new synthesis pathway, which involved transesterification of triglycerides and sucrose in the new solvent dimethylformamide or DMF, was invented and seemed promising.
In 1950s, Foster Snell and his team conducted research on the production of several mono- and di-substituted sucrose esters. Many processes are still used in commercial production today. | 0 | Organic Chemistry |
The reaction mechanism of allylic C-H acetoxylation has been studied. The first step in the catalytic cycle is cleavage of the allylic C-H bond. The sulfoxide ligand is thought to promote this step by generating a highly electrophilic, possibly cationic palladium species in situ. This species coordinates to the alkene and acidifies the adjacent C-H bond, which allows acetate to abstract the proton and forms a π-allyl palladium complex (II). Subsequently, a π-acid such as benzoquinone coordinates to the palladium, activating the π-allyl complex to nucleophilic attack (III). A nucleophile, in this case acetate, attacks to reductively eliminate palladium, generating the product and palladium(0) (IV). The palladium(0) is reoxidized to palladium(II) by benzoquinone and the sulfoxide ligand reassociates, closing the catalytic cycle. | 0 | Organic Chemistry |
The word pesticide derives from the Latin pestis (plague) and caedere (kill).
The Food and Agriculture Organization (FAO) has defined pesticide as:
: any substance or mixture of substances intended for preventing, destroying, or controlling any pest, including vectors of human or animal disease, unwanted species of plants or animals, causing harm during or otherwise interfering with the production, processing, storage, transport, or marketing of food, agricultural commodities, wood and wood products or animal feedstuffs, or substances that may be administered to animals for the control of insects, arachnids, or other pests in or on their bodies. The term includes substances intended for use as a plant growth regulator, defoliant, desiccant, or agent for thinning fruit or preventing the premature fall of fruit. Also used as substances applied to crops either before or after harvest to protect the commodity from deterioration during storage and transport. | 2 | Environmental Chemistry |
In discussing these figures, it should be kept in mind that both the radon distribution in dwelling and its effect at low exposures are not precisely known, and the radon health effect has to be computed (deaths caused by radon domestic exposure cannot be observed as such). These estimations are strongly dependent on the model retained.
According to these models, radon exposure is thought to be the second major cause of lung cancer after smoking.
Iowa has the highest average radon concentration in the United States; studies performed there have demonstrated a 50% increased lung cancer risk with prolonged radon exposure above the EPA's action level of 4 pCi/L.
Based on studies carried out by the National Academy of Sciences in the United States, radon would thus be the second leading cause of lung cancer after smoking, and accounts for 15,000 to 22,000 cancer deaths per year in the US alone.
The United States Environmental Protection Agency (EPA) says that radon is the number one cause of lung cancer among non-smokers.
The general population is exposed to small amounts of polonium as a radon daughter in indoor air; the isotopes Po and Po are thought to cause the majority of the estimated 15,000–22,000 lung cancer deaths in the US every year that have been attributed to indoor radon.
The Surgeon General of the United States has reported that over 20,000 Americans die each year of radon-related lung cancer.
In the United Kingdom, residential radon would be, after cigarette smoking, the second most frequent cause of lung cancer deaths: according to models, 83.9% of deaths are attributed to smoking only, 1.0% to radon only, and 5.5% to a combination of radon and smoking.
The World Health Organization has recommended a radon reference concentration of 100 Bq/m (2.7 pCi/L). The European Union recommends that action should be taken starting from concentrations of 400 Bq/m (11 pCi/L) for older dwellings and 200 Bq/m (5 pCi/L) for newer ones. After publication of the North American and European Pooling Studies, Health Canada proposed a new guideline that lowers their action level from 800 to 200 Bq/m (22 to 5 pCi/L).
The United States Environmental Protection Agency (EPA) strongly recommends action for any dwelling with a concentration higher than 148 Bq/m (4 pCi/L),
and encourages action starting at 74 Bq/m (2 pCi/L).
EPA recommends that all homes should be monitored for radon. If testing shows levels less than 4 picocuries radon per liter of air (160 Bq/m), then no action is necessary. For levels of 20 picocuries radon per liter of air (800 Bq/m) or higher, the home owner should consider some type of procedure to decrease indoor radon levels. For instance, as radon has a half-life of four days, opening the windows once a day can cut the mean radon concentration to one fourth of its level.
The United States Environmental Protection Agency (EPA) recommends homes be fixed if an occupant's long-term exposure will average 4 picocuries per liter (pCi/L) that is 148 Bq/m. EPA estimates that one in 15 homes in the United States has radon levels above the recommended guideline of 4 pCi/L.
EPA radon risk level tables including comparisons to other risks encountered in life are available in their citizen's guide.
The EPA estimates that nationally, 8% to 12% of all dwellings are above their maximum "safe levels" (four picocuries per liter—the equivalent to roughly 200 chest x-rays). The United States Surgeon General and the EPA both recommend that all homes be tested for radon.
The limits retained do not correspond to a known threshold in the biological effect, but are determined by a cost-efficiency analysis. EPA believes that a 150 Bq/m level (4 pCi/L) is achievable in the majority of homes for a reasonable cost, the average cost per life saved by using this action level is about $700,000.
For radon concentration in drinkable water, the World Health Organization issued as guidelines (1988) that remedial action should be considered when the radon activity exceeded 100 kBq/m in a building, and remedial action should be considered without long delay if exceeding 400 kBq/m. | 2 | Environmental Chemistry |
Steroid 21-hydroxylase is a cytochrome P450 enzyme that is notable for its substrate specificity and relatively high catalytic efficiency.
Like other cytochrome P450 enzymes, steroid 21-hydroxylase participates in the cytochrome P450 catalytic cycle and engages in one-electron transfer with NADPH-P450 reductase. Steroid 21-hydroxylase is highly specific for hydroxylation of progesterone and 17-hydroxyprogesterone. This is in marked contrast to the evolutionarily and functionally related P450 enzyme 17-hydroxylase, which has a broad range of substrates.
The chemical reaction in which steroid 21-hydroxylase catalyzes the addition of hydroxyl (-OH) to the C21 position of progesterone, 17α-hydroxyprogesterone and 21-desoxycortisone was first described in 1952.
Studies of the human enzyme expressed in yeast initially classified 17-hydroxyprogesterone as the preferred substrate for steroid 21-hydroxylase, however, later analysis of the purified human enzyme found a lower K and greater catalytic efficiency for progesterone over 17-hydroxyprogesterone.
The catalytic efficiency of steroid 21-hydroxylase for conversion of progesterone in humans is approximately 1.3 x 10 Ms at 37 °C. This makes it the most catalytically efficient P450 enzyme of those reported to date, and catalytically more efficient than the closely related bovine steroid 21-hydroxylase enzyme. C-H bond breaking to create a primary carbon radical is thought to be the rate-limiting step in the hydroxylation. | 1 | Biochemistry |
In the field of energetics, an energy carrier is produced by human technology from a primary energy source. Only the energy sector uses primary energy sources. Other sectors of society use an energy carrier to perform useful activities (end-uses). The distinction between "Energy Carriers" (EC) and "Primary Energy Sources" (PES) is extremely important. An energy carrier can be more valuable (have a higher quality) than a primary energy source. For example 1 megajoule (MJ) of electricity produced by a hydroelectric plant is equivalent to 3 MJ of oil. Sunlight is a main source of primary energy, which can be transformed into plants and then into coal, oil and gas. Solar power and wind power are other derivatives of sunlight. Note that although coal, oil and natural gas are derived from sunlight, they are considered primary energy sources which are extracted from the earth (fossil fuels). Natural uranium is also a primary energy source extracted from the earth but does not come from the decomposition of organisms (mineral fuel). | 7 | Physical Chemistry |
A primary alcohol is an alcohol in which the hydroxy group is bonded to a primary carbon atom. It can also be defined as a molecule containing a “–CHOH” group.
In contrast, a secondary alcohol has a formula “–CHROH” and a tertiary alcohol has a formula “–CROH”, where “R” indicates a carbon-containing group.
Examples of primary alcohols include ethanol and 1-butanol.
Methanol is also generally regarded as a primary alcohol, including by the 1911 edition of the Encyclopædia Britannica. | 0 | Organic Chemistry |
In theoretical electrolysis of water, a voltage of only 1.23 V is required to split water into hydrogen and oxygen, The formation of an EDL increases this to its thermo-neutral voltage of 1.45 V. Minimising the EDL formed during pulse electrolysis is advantageous, as it can reduce the thermo-neutral voltage and the energy input required, increasing energy efficiency. | 7 | Physical Chemistry |
The calcium cycle is a transfer of calcium between dissolved and solid phases. There is a continuous supply of calcium ions into waterways from rocks, organisms, and soils. Calcium ions are consumed and removed from aqueous environments as they react to form insoluble structures such as calcium carbonate and calcium silicate, which can deposit to form sediments or the exoskeletons of organisms. Calcium ions can also be utilized biologically, as calcium is essential to biological functions such as the production of bones and teeth or cellular function. The calcium cycle is a common thread between terrestrial, marine, geological, and biological processes. Calcium moves through these different media as it cycles throughout the Earth. The marine calcium cycle is affected by changing atmospheric carbon dioxide due to ocean acidification. | 1 | Biochemistry |
When discussing the properties of acids it is usual to specify equilibrium constants as acid dissociation constants, denoted by K, with numerical values given the symbol pK.
On the other hand, association constants are used for bases.
However, general purpose computer programs that are used to derive equilibrium constant values from experimental data use association constants for both acids and bases. Because stability constants for a metal-ligand complex are always specified as association constants, ligand protonation must also be specified as an association reaction. The definitions show that the value of an acid dissociation constant is the reciprocal of the value of the corresponding association constant:
Notes
# For a given acid or base in water, , the self-ionization constant of water.
# The association constant for the formation of a supramolecular complex may be denoted as K; in such cases "a" stands for "association", not "acid".
# For polyprotic acids, the numbering of stepwise association constants is the reverse of the numbering of the dissociation constants. For example, for phosphoric acid (details in the polyprotic acids section below): | 7 | Physical Chemistry |
The siRNA-induced post transcriptional gene silencing is initiated by the assembly of the RNA-induced silencing complex (RISC). The complex silences certain gene expression by cleaving the mRNA molecules coding the target genes. To begin the process, one of the two siRNA strands, the guide strand (anti-sense strand), will be loaded into the RISC while the other strand, the passenger strand (sense strand), is degraded. Certain Dicer enzymes may be responsible for loading the guide strand into RISC. Then, the siRNA scans for and directs RISC to perfectly complementary sequence on the mRNA molecules. The cleavage of the mRNA molecules is thought to be catalyzed by the Piwi domain of Argonaute proteins of the RISC. The mRNA molecule is then cut precisely by cleaving the phosphodiester bond between the target nucleotides which are paired to siRNA residues 10 and 11, counting from the 5end. This cleavage results in mRNA fragments that are further degraded by cellular exonucleases. The 5 fragment is degraded from its 3 end by exosome while the 3 fragment is degraded from its 5 end by 5 -3' exoribonuclease 1(XRN1). Dissociation of the target mRNA strand from RISC after the cleavage allow more mRNA to be silenced. This dissociation process is likely to be promoted by extrinsic factors driven by ATP hydrolysis.
Sometimes cleavage of the target mRNA molecule does not occur. In some cases, the endonucleolytic cleavage of the phosphodiester backbone may be suppressed by mismatches of siRNA and target mRNA near the cleaving site. Other times, the Argonaute proteins of the RISC lack endonuclease activity even when the target mRNA and siRNA are perfectly paired. In such cases, gene expression will be silenced by an miRNA induced mechanism instead
Piwi-interacting RNAs are responsible for the silencing of transposons and are not siRNAs. PIWI-interacting RNAs (piRNAs) are a recently-discovered class of small non-coding RNAs (ncRNAs) with a length of 21-35 nucleotides. They play a role in gene expression regulation, transposon silencing, and viral infection inhibition. Once considered as "dark matter" of ncRNAs, piRNAs emerged as important players in multiple cellular functions in different organisms. | 1 | Biochemistry |
Hydrogels have the remarkable ability to swell in water and aqueous solvents. During the process of swelling, surface instability can occur. This instability depends on the thickness of the hydrogel layers and the surface tension. A higher surface tension stabilizes the flat surface of the hydrogel, which is the outer-most layer. The swelling ratio of the flat layer can be calculated using the following equation derived from the Flory–Huggins theory of free surface energy in hydrogels:
Where λ is the swelling ratio, μ is the chemical potential, p is pressure, k is the Boltzmann constant, and χ and N are unitless hydrogel constants.
As swelling increases, mechanical properties generally suffer. | 7 | Physical Chemistry |
It has been suggested certain microbial dark matter genetic material could belong to a new (i.e., fourth) domain of life, although other explanations (e.g., viral origin) are also possible, which has ties with the issue of a hypothetical shadow biosphere. | 1 | Biochemistry |
Catherine E. Costello is the William Fairfield Warren distinguished professor in the department of biochemistry, Cell Biology and Genomics, and the director of the Center for Biomedical Mass Spectrometry at the Boston University School of Medicine. | 1 | Biochemistry |
In 1756 Thomas Melvill observed the emission of distinct patterns of colour when salts were added to alcohol flames. By 1785 James Gregory discovered the principles of diffraction grating and American astronomer David Rittenhouse made the first engineered diffraction grating. In 1821 Joseph von Fraunhofer solidified this significant experimental leap of replacing a prism as the source of wavelength dispersion improving the spectral resolution and allowing for the dispersed wavelengths to be quantified.
In 1835, Charles Wheatstone reported that different metals could be distinguished by bright lines in the emission spectra of their sparks, thereby introducing an alternative to flame spectroscopy.
In 1849, J. B. L. Foucault experimentally demonstrated that absorption and emission lines at the same wavelength are both due to the same material, with the difference between the two originating from the temperature of the light source.
In 1853, the Swedish physicist Anders Jonas Ångström presented observations and theories about gas spectra. Ångström postulated that an incandescent gas emits luminous rays of the same wavelength as those it can absorb. At the same time George Stokes and William Thomson (Kelvin) were discussing similar postulates. Ångström also measured the emission spectrum from hydrogen later labeled the Balmer lines.
In 1854 and 1855, David Alter published observations on the spectra of metals and gases, including an independent observation of the Balmer lines of hydrogen.
By 1859, Gustav Kirchhoff and Robert Bunsen noticed that several Fraunhofer lines (lines in the solar spectrum) coincide with characteristic emission lines identified in the spectra of heated elements. It was correctly deduced that dark lines in the solar spectrum are caused by absorption by chemical elements in the solar atmosphere. | 7 | Physical Chemistry |
Reports on the "classical" pharmacology of pempidine have been published. The Spinks group, at ICI, compared pempidine, its N-ethyl analogue, and mecamylamine in considerable detail, with additional data related to several structurally simpler compounds. | 0 | Organic Chemistry |
An inexact differential or imperfect differential is a differential whose integral is path dependent. It is most often used in thermodynamics to express changes in path dependent quantities such as heat and work, but is defined more generally within mathematics as a type of differential form. In contrast, an integral of an exact differential is always path independent since the integral acts to invert the differential operator. Consequently, a quantity with an inexact differential cannot be expressed as a function of only the variables within the differential. I.e., its value cannot be inferred just by looking at the initial and final states of a given system. Inexact differentials are primarily used in calculations involving heat and work because they are path functions, not state functions. | 7 | Physical Chemistry |
The mother liquor (or spent liquor) is the solution remaining after a component has been removed by a some process such as filtration or more commonly crystallization. It is encountered in chemical processes including sugar refining.
In crystallization, a solid (usually impure) is dissolved in a solvent at high temperature, taking advantage of the fact that most solids are more soluble at higher temperatures. As the solution cools, the solubility of the solute in the solvent will gradually become smaller. The resultant solution is described as supersaturated, meaning that there is more solute dissolved in the solution than would be predicted by its solubility at that temperature. Crystallization can then be induced from this supersaturated solution and the resultant pure crystals removed by such methods as filtration and centrifugal separators. The remaining solution, once the crystals have been filtered out, is known as the mother liquor, and will contain a portion of the original solute (as predicted by its solubility at that temperature) as well as any impurities that were not filtered out. Second and third crops of crystals can then be harvested from the mother liquor.
An alternative to second cropping is continuous recycle of a portion of the mother liquors from one batch into in subsequent batches in which an increased product yield is expected, and also leads to an accumulation of impurities. It can be shown that the impurity profile of the mother liquors, at moderate recycle levels (i.e. when x>1), quickly reaches a steady state according to (1 − x)/(1 − x), where n is the number of times the process is operated and x is the fraction of mother liquors recycled (Fig. 1). The aforementioned approach is idealised and assumes that the build up of impurities in the mother liquor does not exceed the impurity/impurities solubility. The approach has been confirmed experimentally. | 3 | Analytical Chemistry |
Amyotrophic lateral sclerosis (ALS), also called Lou Gehrig's disease, is a motor neuron disease that affects the brain and spinal cord. The disease causes motor neurons to degenerate, which eventually leads to neuron death and muscular degeneration. Hundreds of mutations in the Cu/Zn superoxide dismutase (SOD1) gene have been found to cause ALS. Gene silencing has been used to knock down the SOD1 mutant that is characteristic of ALS. In specific, siRNA molecules have been successfully used to target the SOD1 mutant gene and reduce its expression through allele-specific gene silencing. | 1 | Biochemistry |
Third-generation Glycoazodyes are synthesized using amino sugars such as 6-amino-6-deoxy-D-galactose or 6 amino-6-deoxylactose. The point of the amide bond is controlled by protecting the alcohol groups on the sugar and allowing the free amine to react. The point of the ester group is controlled by choosing a azo dye with a different alcohol group position. Either the dye or the sugar is reacted with succinic anhydride. This forms an amide group with the sugar or an ester group with the dye. The free carboxylic acid may then react with the alcohol group or amine group on the corresponding dye or sugar. The condensation product is then deprotected. | 0 | Organic Chemistry |
Few commercial applications exist for bioplastics. Cost and performance remain problematic. Typical is the example of Italy, where biodegradable plastic bags are compulsory for shoppers since 2011 with the introduction of a specific law. Beyond structural materials, electroactive bioplastics are being developed that promise to carry electric current.
Bioplastics are used for disposable items, such as packaging, crockery, cutlery, pots, bowls, and straws.
Biopolymers are available as coatings for paper rather than the more common petrochemical coatings.
Bioplastics called drop-in bioplastics are chemically identical to their fossil-fuel counterparts but made from renewable resources. Examples include bio-PE, bio-PET, bio-propylene, bio-PP, and biobased nylons. Drop-in bioplastics are easy to implement technically, as existing infrastructure can be used. A dedicated bio-based pathway allows to produce products that cannot be obtained through traditional chemical reactions and can create products which have unique and superior properties, compared to fossil-based alternatives. | 7 | Physical Chemistry |
In metallurgy, gas flushing removes dissolved gases from the molten metal prior to the material being processed. For example, before casting aluminium alloys, argon bubbles are injected into liquid aluminium using a rotary degasser. The argon bubbles rise to the surface, bringing with them some of the dissolved hydrogen. The degassing step reduces the occurrence of hydrogen gas porosity. In the steel making process, this method is used very commonly for duplex steel and some high reactivity metals. | 8 | Metallurgy |
For an isolated spherical solid particle of diameter in its own liquid, the Gibbs–Thomson equation for the structural melting point depression can be written:
where:
* T = bulk melting temperature
* σ = solid–liquid interface energy (per unit area)
* H = bulk enthalpy of fusion (per gram of material)
* ρ = density of solid
* r = radius of the nanoparticle | 7 | Physical Chemistry |
The dithiodialkyphosphinic acids (RPSH) are related to the diorganodithiophosphates with the formula (RO)PSH, which are also used as complexing agents in the purification of metals. The phosphates are more prone to hydrolysis owing to the greater lability of the RO-P linkage vs the direct C-P bond. | 0 | Organic Chemistry |
As illustrated in Retrosynthetic Scheme I, Taxol was derived from diol 7.2 by an ester bond formation, according to the Ojima-Holton method. This diol comes from carbonate 6.3 by the addition of phenyllithium. The oxetane ring in compound 6.3 was obtained via an S2 reaction involving a mesylate derived from acetal 4.9. Ring B was closed via a McMurry reaction involving dialdehyde 4.8 which ultimately was derived from aldehyde 4.2 and hydrazone 3.6 using a Shapiro coupling reaction.
Retrosynthetic Scheme II indicates that both the aldehyde and the hydrazone used in the Shapiro coupling reaction were synthesized using Diels-Alder reactions. | 0 | Organic Chemistry |
In cancers, loss of expression of genes occurs about 10 times more frequently by transcription silencing (caused by promoter hypermethylation of CpG islands) than by mutations. As Vogelstein et al. point out, in a colorectal cancer there are usually about 3 to 6 driver mutations and 33 to 66 hitchhiker or passenger mutations. In contrast, in colon tumors compared to adjacent normal-appearing colonic mucosa, there are about 600 to 800 heavily methylated CpG islands in promoters of genes in the tumors while these CpG islands are not methylated in the adjacent mucosa.
Using gene set enrichment analysis, 569 out of 938 gene sets were hypermethylated and 369 were hypomethylated in cancers. Hypomethylation of CpG islands in promoters results in increased transcription of the genes or gene sets affected.
One study listed 147 specific genes with colon cancer-associated hypermethylated promoters and 27 with hypomethylated promoters, along with the frequency with which these hyper/hypo-methylations were found in colon cancers. At least 10 of those genes had hypermethylated promoters in nearly 100% of colon cancers. They also indicated 11 microRNAs whose promoters were hypermethylated in colon cancers at frequencies between 50% and 100% of cancers. MicroRNAs (miRNAs) are small endogenous RNAs that pair with sequences in messenger RNAs to direct post-transcriptional repression. On average, each microRNA represses or inhibits transcriptional expression of several hundred target genes. Thus microRNAs with hypermethylated promoters may be allowing enhanced transcription of hundreds to thousands of genes in a cancer. | 1 | Biochemistry |
McCrones work as a microscopist first attracted widespread public attention when he helped exonerate Lloyd Eldon Miller, a cabdriver who had been sentenced to death for the 1955 murder of an 8-year-old girl in Canton, Illinois. McCrone was able to show that the stains in a pair of undershorts that the prosecution had presented to the jury as blood were actually red paint. Millers conviction was overturned by the US Supreme Court in 1967. In later life, McCrone microscopically examined the physical evidence (hairs, fibers, blood, etc.) that led to the conviction of Wayne Williams as the Atlanta child killer. That work earned him the 1982 Certificate of Merit from the Forensic Sciences Foundation.
On occasion, McCrone was given hair samples of famous people to analyze. Based on such analysis, he rejected the hypothesis that Napoleon had been poisoned with arsenic, but concluded that Beethoven had suffered from lead poisoning. | 3 | Analytical Chemistry |
Different rules (4n, 5n, or 6n) are invoked depending on the number of electrons per vertex.
The 4n rules are reasonably accurate in predicting the structures of clusters having about 4 electrons per vertex, as is the case for many boranes and carboranes. For such clusters, the structures are based on deltahedra, which are polyhedra in which every face is triangular. The 4n clusters are classified as closo-, nido-, arachno- or hypho-, based on whether they represent a complete (closo-) deltahedron, or a deltahedron that is missing one (nido-), two (arachno-) or three (hypho-) vertices.
However, hypho clusters are relatively uncommon due to the fact that the electron count is high enough to start to fill antibonding orbitals and destabilize the 4n structure. If the electron count is close to 5 electrons per vertex, the structure often changes to one governed by the 5n rules, which are based on 3-connected polyhedra.
As the electron count increases further, the structures of clusters with 5n electron counts become unstable, so the 6n rules can be implemented. The 6n clusters have structures that are based on rings.
A molecular orbital treatment can be used to rationalize the bonding of cluster compounds of the 4n, 5n, and 6n types. | 7 | Physical Chemistry |
In polymerase chain reaction (PCR) experiments, the GC-content of short oligonucleotides known as primers is often used to predict their annealing temperature to the template DNA. A higher GC-content level indicates a relatively higher melting temperature.
Many sequencing technologies, such as Illumina sequencing, have trouble reading high-GC-content sequences. Bird genomes are known to have many such parts, causing the problem of "missing genes" expected to be present from evolution and phenotype but never sequenced — until improved methods were used. | 1 | Biochemistry |
* Nesmeyanov A.N. D.I. Mendeleev's Periodic Table of Elements and Organic Chemistry. Series: Reports at the plenary session/ VIII Mendeleev Congress on General and Applied Chemistry. Moscow: Publishing House Acad. Sciences of the USSR, 1959.
* Nesmeyanov A.N. Ed. acad. A. V. Topchiev Selected Works. Moscow: Publishing House Acad. Sciences of the USSR, 1959.
* Ioffe S.T. and Nesmeyanov A.N. Ed. A. N. Nesmeyanova and К. A. Kocheshkova Magnesium, beryllium, calcium, strontium, barium. Series: Methods of elemental organic chemistry. Moscow: Publishing House Acad. Sciences of the USSR, 1963.
* Nesmeyanov A.N. and Sokolik R.A. Ed. A. N. Nesmeyanova and К. A. Kocheshkova Bor. Aluminum. Gallium. Indium. Thallium. Series: Methods of elemental organic chemistry. Moscow: Publishing House Acad. Sciences of the USSR, 1964.
* Makarova L.G. and Nesmeyanov A.N. Ed. A. N. Nesmeyanova and К. A. Kocheshkova Mercury. Series: Methods of elemental organic chemistry. Moscow: Publishing House Acad. Sciences of the USSR, 1965.
* Nesmeyanov A.N., Belikov V.M.Problem of food synthesis. Series: Report at the plenary session / XI Mendeleev Congress on General and Applied Chemistry. Moscow: Nauka, 1965.
* Nesmeyanov A.N.Research in Organic Chemistry. Selected works 1959-1969. Moscow: Nauka, 1971.
* Nesmeyanov A.N. and Nesmeyanov N.A. The Beginnings of Organic Chemistry. In two books. Moscow: Chemistry, 1969.
* Nesmeyanov A.N. and Nesmeyanov N.A. The Beginnings of Organic Chemistry. In two books. Moscow: Chemistry, 1970. | 0 | Organic Chemistry |
Conventional SNP typing methods are typically time-consuming and expensive, requiring several probe based assays to be multiplexed together or the use of DNA microarrays. HRM is more cost-effective and reduces the need to design multiple pairs of primers and the need to purchase expensive probes. The HRM method has been successfully used to detect a single G to A substitution in the gene Vssc (Voltage Sensitive Sodium Channel) which confers resistance to the acaricide permethrin in Scabies mite. This mutation results in a coding change in the protein (G1535D). The analysis of scabies mites collected from suspected permethrin susceptible and tolerant populations by HRM showed distinct melting profiles. The amplicons from the sensitive mites were observed to have a higher melting temperature relative to the tolerant mites, as expected from the higher thermostability of the GC base pair
In a field more relevant to clinical diagnostics, HRM has been shown to be suitable in principle for the detection of mutations in the breast cancer susceptibility genes BRCA1 and BRCA2. More than 400 mutations have been identified in these genes.<br />The sequencing of genes is the gold standard for identifying mutations. Sequencing is time-consuming and labour-intensive and is often preceded by techniques used to identify heteroduplex DNA, which then further amplify these issues. HRM offers a faster and more convenient closed-tube method of assessing the presence of mutations and gives a result which can be further investigated if it is of interest. In a study carried out by Scott et al. in 2006, 3 cell lines harbouring different BRCA mutations were used to assess the HRM methodology. It was found that the melting profiles of the resulting PCR products could be used to distinguish the presence or absence of a mutation in the amplicon. Similarly in 2007 Krypuy et al. showed that the careful design of HRM assays (with regards to primer placement) could be successfully employed to detect mutations in the TP53 gene, which encodes the tumour suppressor protein p53 in clinical samples of breast and ovarian cancer. Both these studies highlighted the fact that changes in the melting profile can be in the form of a shift in the melting temperature or an obvious difference in the shape of the melt curve. Both of these parameters are a function of the amplicon sequence.
The consensus is that HRM is a cost efficient method that can be employed as an initial screen for samples suspected of harbouring polymorphisms or mutations. This would reduce the number of samples which need to be investigated further using more conventional methods. | 1 | Biochemistry |
The thylakoid lumen is a continuous aqueous phase enclosed by the thylakoid membrane. It plays an important role for photophosphorylation during photosynthesis. During the light-dependent reaction, protons are pumped across the thylakoid membrane into the lumen making it acidic down to pH 4. | 5 | Photochemistry |
Wu was born 1 January 1928 in Jinan, Shandong, Republic of China. He graduated from the Department of Chemistry of Fudan University in 1951, and was hired as a faculty member by the university. In September 1954, he began his graduate studies in the Department of Chemistry of the Moscow State University, and earned his associate doctor degree (Ph.D. equivalent) in June 1958.
After returning to China, Wu was assigned to the newly founded Zhengzhou University to help establish its chemistry department, where he worked for the rest of his career. He later served as chairman of the department and a doctoral advisor.
Wu published more than 160 research articles. He won a National Science Congress Award in 1978, and the Henan Science and Technology Progress Award (First Class) in 2001. He was elected an academician of the Chinese Academy of Sciences in 2003. | 0 | Organic Chemistry |
He briefly taught physical chemistry at the London University before moving to Pakistan. Upon his return, he joined the Pakistan Atomic Energy Commission (PAEC) and took the professorship of nuclear chemistry at the Pakistan Institute of Nuclear Science and Technology (PINSTECH). Subsequently, he joined the clandestine atomic bomb project's chemistry section led by fellow chemist Iqbal Hussain Qureshi.
Munir Ahmad Khan, chairman PAEC, had him partially take over the "R-Labs" at PAEC to engage research in chemical explosives. Initially, the research was concentrated towards development of the HMX, a non-toxic explosive that was produced as a by-product of the RDX process. In the 1970s, he founded the Metallurgical Laboratory (ML) where he also moved majority of the staff to undertake research in metallurgy. He then led a team of chemists who supervised the physical conversion of UF into solid metal before coating and machining the metal. During this time, he also led the research on using chemical and metallurgical industrial techniques and reduction furnaces to produce metal from the Highly enriched uranium. Due to the sensitivity of the project and concerns of fellow theorist Dr. AQ Khan, the program was moved to KRL in the 1980s. | 7 | Physical Chemistry |
* Weber et al. 2005 determined that the inactive X-chromosome in females is hypermethylated on a chromosome wide level using MeDIP coupled with microarray.
* Keshet et al. 2006 performed a study on colon and prostate cancer cells using MeDIP-chip. The result is a genome-wide analysis of genes lying in hypermethylated regions as well as conclude that there is an instructive mechanism of de novo methylation in cancer cells.
* Zhang et al. 2006 obtained a high resolution methylome mapping in Arabidopsis using MeDIP-chip.
* Novak et al. 2006 used the MeDIP-chip approach to investigate human breast cancer for methylation associated silencing and observed the inactivation of the HOXA gene cluster | 1 | Biochemistry |
The structural changes that occur during 72-hour hypothermic storage of previously uninjured kidneys have been described by Mackay who showed how there was progressive vacuolation of the cytoplasm of the cells which particularly affected the proximal tubules. On electron microscopy the mitochondria were seen to become swollen with early separation of the internal cristal membranes and later loss of all internal structure. Lysosomal integrity was well preserved until late, and the destruction of the cell did not appear to be caused by lytic enzymes because there was no more injury immediately adjacent to the lysosomes than in the rest of the cell.
Woods and Liu – when describing successful 5 and 7 day kidney storage - described the light microscopic changes seen at the end of perfusion and at post mortem, but found few gross abnormalities apart from some infiltration with lymphocytes and occasional tubular atrophy.
The changes during short perfusions of human kidneys prior to reimplantation have been described by Hill who also performed biopsies 1 hour after reimplantation. On electron microscopy Hill found endothelial damage which correlated with the severity of the fibrin deposition after reimplantation. The changes that Hill saw in the glomeruli on light microscopy were occasional fibrin thrombi and infiltration with polymorphs. Hill suspected that these changes were an immunologically induced lesion, but found that there was no correlation between the severity of the histological lesion and the presence or absence of immunoglobulin deposits.
There are several reports of the analysis of urine produced by kidneys during perfusion storage. Kastagir analysed urine produced during 24-hour perfusion and found it to be an ultrafiltrate of the perfusate, Scott found a trace of protein in the urine during 24-hour storage, and Pederson found only a trace of protein after 36 hours perfusion storage. Pederson mentioned that he had found heavy proteinuria during earlier experiments. Woods noted protein casts in the tubules of viable kidneys after 5 day storage, but he did not analyse the urine produced during perfusion. In Cohen's study there was a progressive increase in urinary protein concentration during 8 day preservation until the protein content of the urine equalled that of the perfusate. This may have been related to the swelling of the glomerular basement membranes and the progressive fusion of epithelial cell foot processes that was also observed during the same period of perfusion storage. | 1 | Biochemistry |
SLS has been proposed as a potentially effective topical microbicide, for intravaginal use, to inhibit and possibly prevent infection by various enveloped and non-enveloped viruses such as the herpes simplex viruses, HIV, and the Semliki Forest virus.
Liquid membranes formed from SDS in water have been demonstrated to work as unusual particle separators. The device acts as a reverse filter, allowing large particles to pass while capturing smaller particles. | 1 | Biochemistry |
In general, prehistoric extraction of metals, particularly copper, involved two fundamental stages: first, the smelting of copper ore at temperatures exceeding 700 °C is needed to separate the gangue from the copper; second, melting the copper, which requires temperatures exceeding its melting point of 1080 °C. Given the available technology at the time, accomplishing these extreme temperatures posed a significant challenge. Early smelters developed ways to effectively increase smelting temperatures by feeding the fire with forced flows of oxygen.
Copper extraction in particular is of great interest in archeometallurgical studies since it dominated other metals in Mesopotamia from the early Chalcolithic until the mid-to-late sixth century BC. There is a lack of consensus among archaeometallurgists on the origin of non-ferrous extractive metallurgy. Some scholars believe that extractive metallurgy may have been simultaneously or independently discovered in several parts of the world. The earliest known use of pyrometallurgical extraction of copper occurred in Belovode, eastern Serbia, from the late sixth to early fifth millennium BC. However, there is also evidence of copper smelting in Tal-i-Iblis, southeastern Iran, which dates back to around the same period. During this period, copper smelters used large in-grown pits filled with coal, or crucibles to extract copper, but by the fourth millennium BC this practice had begun to phase out in favor of the smelting furnace, which had a larger production capacity. From the third millennium onward, the invention of the reusable smelting furnace was crucial to the success of large-scale copper production and the robust expansion of the copper trade through the Bronze Age.
The earliest silver objects began appearing in the late fourth millennium BC in Anatolia, Turkey. Prehistoric silver extraction is strongly associated with the extraction of the less valuable metal, lead; although evidence of lead extraction technology predates silver by at least 3 millennia. Silver and lead extractions are also associated because the argentiferous (silver-bearing) ores used in the process often contains both elements.
In general, prehistoric silver recovery was broken down into three phases: First, the silver-lead ore is roasted to separate the silver and lead from the gangue. The metals are then melted at high temperature ( greater than 1100 °C) in the crucible while air is blown over the molten metal (cupellation). Finally, lead is oxidized to form lead monoxide (PbO) or is absorbed into the walls of the crucible, leaving the refined silver behind.
The silver-lead cupellation method was first used in Mesopotamia between 4000 and 3500 BC. Silver artifacts, dating around 3600 BC, were discovered in Naqada, Egypt. Some of these cast silver artifacts contained less than 0.5% lead, which strongly indicates cupellation. | 8 | Metallurgy |
The use of equivalent weights in general chemistry has largely been superseded by the use of molar masses. Equivalent weights may be calculated from molar masses if the chemistry of the substance is well known:
*sulfuric acid has a molar mass of 98.078(5) , and supplies two moles of hydrogen ions per mole of sulfuric acid, so its equivalent weight is 98.078(5) /2 = 49.039(3) .
*potassium permanganate has a molar mass of 158.034(1) , and reacts with five moles of electrons per mole of potassium permanganate, so its equivalent weight is 158.034(1) /5 = 31.6068(3) .
Historically, the equivalent weights of the elements were often determined by studying their reactions with oxygen. For example, 50 g of zinc will react with oxygen to produce 62.24 g of zinc oxide, implying that the zinc has reacted with 12.24 g of oxygen (from the Law of conservation of mass): the equivalent weight of zinc is the mass which will react with eight grams of oxygen, hence 50 g × 8 g/12.24 g = 32.7 g.
Some contemporary general chemistry textbooks make no mention of equivalent weights. Others explain the topic, but point out that it is merely an alternate method of doing calculations using moles. | 7 | Physical Chemistry |
Crucibles used for copper smelting were generally wide shallow vessels made from clay that lacks refractory properties which is similar to the types of clay used in other ceramics of the time. During the Chalcolithic period, crucibles were heated from the top by using blowpipes. Ceramic crucibles from this time had slight modifications to their designs such as handles, knobs or pouring spouts allowing them to be more easily handled and poured. Early examples of this practice can be seen in Feinan, Jordan. These crucibles have added handles to allow for better manipulation, however, due to the poor preservation of the crucibles there is no evidence of a pouring spout. The main purpose of the crucible during this period was to keep the ore in the area where the heat was concentrated to separate it from impurities before shaping.
A crucible furnace dating to 2300–1900 BC for bronze casting has been found at a religious precinct of Kerma. | 3 | Analytical Chemistry |
In Europe, the Water Framework Directive (WFD) went into effect on October 23, 2000. It requires all EU member states to show that all surface and groundwater bodies are in good status. The WFD requires member states to implement monitoring systems to estimate the integrity of biological stream components for specific sub-surface water categories. This requirement increased the incidence of biometrics applied to ascertain stream health in Europe A remote online biomonitoring system was designed in 2006. It is based on bivalve molluscs and the exchange of real-time data between a remote intelligent device in the field (able to work for more than 1 year without in-situ human intervention) and a data centre designed to capture, process and distribute the web information derived from the data. The technique relates bivalve behaviour, specifically shell gaping activity, to water quality changes. This technology has been successfully used for the assessment of coastal water quality in various countries (France, Spain, Norway, Russia, Svalbard (Ny-Ålesund) and New Caledonia).
In the United States, the Environmental Protection Agency (EPA) published Rapid Bioassessment Protocols, in 1999, based on measuring macroinvertebrates, as well as periphyton and fish for assessment of water quality.
In South Africa, the Southern African Scoring System (SASS) method is based on benthic macroinvertebrates, and is used for the assessment of water quality in South African rivers. The SASS aquatic biomonitoring tool has been refined over the past 30 years and is now on the fifth version (SASS5) in accordance with the ISO/IEC 17025 protocol. The SASS5 method is used by the South African Department of Water Affairs as a standard method for River Health Assessment, which feeds the national River Health Programme and the national Rivers Database.
The imposex phenomenon in the dog conch species of sea snail leads to the abnormal development of a penis in females, but does not cause sterility. Because of this, the species has been suggested as a good indicator of pollution with organic man-made tin compounds in Malaysian ports. | 2 | Environmental Chemistry |
The Barbier–Wieland degradation is a procedure for shortening the carbon chain of a carboxylic acid by one carbon. It only works when the carbon adjacent to the carboxyl is a simple methylene bridge (an aliphatic carbon with no substituents). The reaction sequence involves conversion of the carboxyl and alpha carbon into an alkene, which is then cleaved by oxidation to convert the former alpha position into a carboxyl itself. | 0 | Organic Chemistry |
Some forms of mutations are hereditary (germline mutations), or passed on from a parent to its offspring. Such mutated coding regions are present in all cells within the organism. Other forms of mutations are acquired (somatic mutations) during an organisms lifetime, and may not be constant cell-to-cell. These changes can be caused by mutagens, carcinogens, or other environmental agents (ex. UV). Acquired mutations can also be a result of copy-errors during DNA replication and are not passed down to offspring. Changes in the coding region can also be de novo (new); such changes are thought to occur shortly after fertilization, resulting in a mutation present in the offsprings DNA while being absent in both the sperm and egg cells. | 1 | Biochemistry |
The Hoopes process is a metallurgical process, used to obtain aluminium metal of very high purity (about 99.99% pure). The process was patented by William Hoopes, a chemist of the Aluminum Company of America (ALCOA), in 1925. | 8 | Metallurgy |
The radio spectrum scope (also radio panoramic receiver, panoramic adapter, pan receiver, pan adapter, panadapter, panoramic radio spectroscope, panoramoscope, panalyzor and band scope) was invented by Marcel Wallace - and measures and shows the magnitude of an input signal versus frequency within one or more radio bands - e.g. shortwave bands. A spectrum scope is normally a lot cheaper than a spectrum analyzer, because the aim is not high quality frequency resolution - nor high quality signal strength measurements.
The spectrum scope use can be to:
* find radio channels quickly of known and unknown signals when receiving.
* find radio amateurs activity quickly e.g. with the intent of communicating with them.
Modern spectrum scopes, like the Elecraft P3, also plot signal frequencies and amplitudes over time, in a rolling format called a waterfall plot. | 7 | Physical Chemistry |
Metal carbonyls are used in a number of industrially important carbonylation reactions. In the oxo process, an alkene, hydrogen gas, and carbon monoxide react together with a catalyst (such as dicobalt octacarbonyl) to give aldehydes. Illustrative is the production of butyraldehyde from propylene:
:CHCH=CH + H + CO → CHCHCHCHO
Butyraldehyde is converted on an industrial scale to 2-ethylhexanol, a precursor to PVC plasticizers, by aldol condensation, followed by hydrogenation of the resulting hydroxyaldehyde. The "oxo aldehydes" resulting from hydroformylation are used for large-scale synthesis of fatty alcohols, which are precursors to detergents. The hydroformylation is a reaction with high atom economy, especially if the reaction proceeds with high regioselectivity.
Another important reaction catalyzed by metal carbonyls is the hydrocarboxylation. The example below is for the synthesis of acrylic acid and acrylic acid esters:
Also the cyclization of acetylene to cyclooctatetraene uses metal carbonyl catalysts:
In the Monsanto and Cativa processes, acetic acid is produced from methanol, carbon monoxide, and water using hydrogen iodide as well as rhodium and iridium carbonyl catalysts, respectively. Related carbonylation reactions afford acetic anhydride. | 0 | Organic Chemistry |