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An experiment observing chilling stress on the tropical plant species, Spathiphyllum wallisii by scientists Maria Segura and Maria Quiles, showcased varying responses by chlororespiratory pathways when different parts of the plant were chilled at 10 degrees Celsius.
Segura and Quiles noticed that when the roots of the plant were subjected to low temperatures (10 degrees Celsius), the level of chlororespiratory molecules (NADPH and PTOX) slightly varied when compared to the level of NADPH and PTOX within the controlled plant. However, when the stem alone was cooled at 10 degrees Celsius, then the molecules NADPH, NDH and PTOX increased in amount as a result of reduced PS I activity. Segura and Quiles then compared this result, by subjecting only the leaves of the plant to 10 degrees Celsius. They noticed that this had caused the PS II activity to stop, and thus inhibit the process of photosynthesis. The lack in photosynthetic activity, in combination with the incline in NADPH and PTOX molecules, then triggered chlororespiratory pathways to begin chemical energy synthesis.
Furthermore, Segura and Quiles also noted that the simultaneous chilling of the leaves and heating of the roots (whilst the plant is under illumination), can cause the slowing and eventual inhibition of the ETC in PS II. This then led to an over-reduction in the PQ pool., which ultimately stimulated chlororespiration.
Segura and Quiles utilised the Fluorescence imaging technique to determine the level of photosynthetic activity in the leaves of the plants. By discerning the percentage of photosynthesis efficiency, Segura and Quiles were able to determine the likelihood of triggering chlororespiratory pathways. They noticed that the percentage of photosynthesis efficiency remained high in test subjects where:
* only the leaves were chilled
* only the stem was chilled
* only the roots were chilled
This high percentage of photosynthesis efficiency meant that the chances of chlororespiration taking place are slim. However, this was not true for the plant that underwent both stem chilling at 10 degrees Celsius and root heating at 24 degrees Celsius. The photosynthesis efficiency of this test subject was significantly lower when compared to the experimental control. This also indicated the inhibition of PS II activity which then caused chlororespiration to begin.
Segura and Quiles also used an immunoblot analysis to deduce the effect of varying temperatures on different parts of the plant. Specifically, the immunoblot measures the amount of PTOX and NDH complex accumulated within the thylakoid membrane of the chloroplast organelle. An increase in NDH complex was evident in the plant where the stem was chilled at 10 degrees Celsius and the root heated at 24 degrees Celsius. Chlororespiration was stimulated in this plant. Dissimilarly, the immunoblot analysis detected no variation in the levels NDH complex and PTOX molecules in test subjects where:
* only the leaves were chilled
* only the stem was chilled
* only the roots were chilled
These test subjects had similar concentrations of NDH and PTOX when compared to the concentration of NDH complex and PTOX molecules within the experimental control. | 1 | Biochemistry |
In the context of pharmacodynamics (how the drug affects the body), the hydrophobic effect is the major driving force for the binding of drugs to their receptor targets. On the other hand, hydrophobic drugs tend to be more toxic because they, in general, are retained longer, have a wider distribution within the body (e.g., intracellular), are somewhat less selective in their binding to proteins, and finally are often extensively metabolized. In some cases the metabolites may be chemically reactive. Hence it is advisable to make the drug as hydrophilic as possible while it still retains adequate binding affinity to the therapeutic protein target. For cases where a drug reaches its target locations through passive mechanisms (i.e., diffusion through membranes), the ideal distribution coefficient for the drug is typically intermediate in value (neither too lipophilic, nor too hydrophilic); in cases where molecules reach their targets otherwise, no such generalization applies. | 7 | Physical Chemistry |
In this shuttle, the enzyme called cytoplasmic glycerol-3-phosphate dehydrogenase 1 (GPD1 or cGPD) converts dihydroxyacetone phosphate (2) to glycerol 3-phosphate (1) by oxidizing one molecule of NADH to NAD as in the following reaction:
Glycerol-3-phosphate is converted back to dihydroxyacetone phosphate by an inner membrane-bound mitochondrial glycerol-3-phosphate dehydrogenase 2 (GPD2 or mGPD), this time reducing one molecule of enzyme-bound flavin adenine dinucleotide (FAD) to FADH. FADH then reduces coenzyme Q (ubiquinone to ubiquinol) whose electrons enter into oxidative phosphorylation. This reaction is irreversible. These electrons bypass Complex I of the electron transport chain, making the glycerol-3-phosphate shuttle less energetically efficient compared to oxidation of NADH by Complex I. | 1 | Biochemistry |
Acetone (propanone) is the simplest ketone and is separated into three groups in the Joback method: two methyl groups (−CH) and one ketone group (C=O). Since the methyl group is present twice, its contributions have to be added twice. | 7 | Physical Chemistry |
This involves sampling direct onto the focusing trap of the thermal desorber. It is generally used for situations where the analytes are too volatile to be retained on sorbent tubes.
*Bags – Commonly known as Tedlar bags, these are made from poly(vinyl fluoride) film.
*Canisters – These are available in a range of sizes up to 1 L, and are popular especially in the US and Japan for monitoring of air for compounds lighter than about n-dodecane (n-CH). The canister is evacuated and allowed to refill with the target atmosphere via a flow regulator.
*Headspace – The material is placed in a headspace vial or other sampling container, and the headspace introduced directly into the focusing trap. Multiple samplings onto the same trap allow sensitivity to be increased, but it is increasingly common for two-stage thermal desorption to be used instead.
*On-line – The target atmosphere is simply pumped directly onto the focusing trap.
*Purge-and-trap – A flow of gas is bubbled through an aqueous sample (a beverage or aqueous extract), and the gas stream then introduced directly into the focusing trap.
*Solid-phase microextraction – This is based on adsorption of analytes onto a polymer-coated fibre or cartridge. The small sample size taken onto fibres means that analytes are usually desorbed directly into the GC, while the larger cartridges are usually placed in a TD tube and subjected to single-stage thermal desorption. | 3 | Analytical Chemistry |
When drugs are covered under patent protection, only the pharmaceutical company that holds the patent is allowed to manufacture, market, and eventually profit from them. The lifetime of the patent varies between countries and also between drugs; in the United States, most drug patents last about twenty years. Once the patent has expired, the drug can be manufactured and sold by other companies - at which point, it is referred to as a generic drug. Its availability on the market as a generic drug removes the monopoly of the patent holder, thereby encouraging competition and causing a significant drop in drug prices, which ensures that life-saving and important drugs reach the general population at fair prices. However, the company holding the initial patent may get a new patent by forming a new version of the drug that is significantly changed compared to the original compound. Patentability of different isomers has been controversial over the past ten years and there have been a number of related legal issues. In making their determinations, courts have looked at factors including: (i) Whether the racemate was known in the prior art. (ii) The difficulty in resolving the enantiomers. (iii) The stereoselectivity of the relevant receptor. (iv) Other secondary considerations of non-obviousness such as commercial success, unexpected results, and satisfaction of long-felt needs in the art. The decisions made regarding these issues have varied and there is no clear answer to the legality of patenting stereoisomers. These issues have been resolved on a case-by-case basis. With the number of current pharmaceuticals currently being marketed as racemic mixtures, it is likely that patentability will continue to be debated in the near future.
There are examples of common drugs, like ibuprofen, where the use of chiral switching has caused controversy. Ibuprofen is a racemic mixture where the S-enantiomer is known to play a major role in reducing inflammation as it inhibits COX-2 (cooxygenase 2) compared to the R-enantiomer; the fact that the S-enantiomer is stronger is what led to the chiral switching. But, when the racemic ibuprofen enters the body, a little over half of the R-enantiomers experience chiral inversion and transform into the favored S-enantiomer. This observation has led to a conclusion that the racemic and the S-enantiomer are potentially biologically equivalent. Because of this and the more recent evidence suggesting that the R-enantiomer may actually contribute to COX-2 inhibition, as well, but at a slower rate, there is still debate on whether or not the chiral switching seen in ibuprofen is really advantageous or if it is just to give patent protections to the manufacturers. | 4 | Stereochemistry |
For smaller, mesoscopic, systems (for example, with only thousands of particles), the ground state term can be more explicitly approximated by adding in an actual discrete level at energy ε=0 in the grand potential:
which gives instead . Now, the behaviour is smooth when crossing the critical temperature, and z approaches 1 very closely but does not reach it.
This can now be solved down to absolute zero in temperature. Figure 1 shows the results of the solution to this equation for α=3/2, with k=ε=1 which corresponds to a gas of bosons in a box. The solid black line is the fraction of excited states 1-N/N for N =10,000 and the dotted black line is the solution for N =1000. The blue lines are the fraction of condensed particles N/N The red lines plot values of the
negative of the chemical potential μ and the green lines plot the corresponding values of z . The horizontal axis is the normalized temperature τ defined by
It can be seen that each of these parameters become linear in τ in the limit of low temperature and, except for the chemical potential, linear in 1/τ in the limit of high temperature. As the number of particles increases, the condensed and excited fractions tend towards a discontinuity at the critical temperature.
The equation for the number of particles can be written in terms of the normalized temperature as:
For a given N and τ, this equation can be solved for τ and then a series solution for z can be found by the method of inversion of series, either in powers of τ or as an asymptotic expansion in inverse powers of τ. From these expansions, we can find the behavior of the gas near T =0 and in the Maxwell–Boltzmann as T approaches infinity. In particular, we are interested in the limit as N approaches infinity, which can be easily determined from these expansions.
This approach to modelling small systems may in fact be unrealistic, however, since the variance in the number of particles in the ground state is very large, equal to the number of particles. In contrast, the variance of particle number in a normal gas is only the square-root of the particle number, which is why it can normally be ignored. This high variance is due to the choice of using the grand canonical ensemble for the entire system, including the condensate state. | 7 | Physical Chemistry |
Polyfluorenes often show both excimer and aggregate formation upon thermal annealing or when current is passed through them. Excimer formation involves the generation of dimerized units of the polymer which emit light at lower energies than the polymer itself. This hinders the use of polyfluorenes for most applications, including light-emitting diodes (LED). When excimer or aggregate formation occurs this lowers the efficiency of the LEDs by decreasing the efficiency of charge carrier recombination. Excimer formation also causes a red shift in the emission spectrum.
Polyfluorenes can also undergo decomposition. There are two known ways in which decomposition can occur. The first involves the oxidation of the polymer that leads to the formation of an aromatic ketone, quenching the fluorescence. The second decomposition process results in aggregation leading to a red-shifted fluorescence, reduced intensity, exciton migration and relaxation through excimers.
Researchers have attempted to eliminate excimer formation and enhance the efficiency of polyfluorenes by copolymerizing polyfluorene with anthracene and end-capping polyfluorenes with bulky groups which could sterically hinder excimer formation. Additionally, researchers have tried adding large substituents at the nine position of the fluorene in order to inhibit excimer and aggregate formation. Furthermore, researchers have tried to improve LEDs by synthesizing fluorene-triarylamine copolymers and other multilayer devices that are based on polyfluorenes that can be cross-linked. These have been found to have brighter fluorescence and reasonable efficiencies.
Aggregation has also been combated by varying the chemical structure. For example, when conjugated polymers aggregate, which is natural in the solid state, their emission can be self-quenched, reducing luminescent quantum yields and reducing luminescent device performance. In opposition to this tendency, researchers have used tri-functional monomers to create highly branched polyfluorenes which do not aggregate due to the bulkiness of the substituents. This design strategy has achieved luminescent quantum yields of 42% in the solid state.
This solution reduces the ease of processability of the material because branched polymers have increased chain entanglement and poor solubility.
Another problem commonly encountered by polyfluorenes is an observed broad green, parasitic emission which detracts from the color purity and efficiency needed for an OLED.
Initially attributed to excimer emission, this green emission has been shown to be due to the formation of ketone defects along the fluorene polymer backbone (oxidation of the nine position on the monomer) when there are incomplete substitution at the nine positions of the fluorene monomer. Routes to combat this involve ensuring full substitution of the monomer’s active site, or including aromatic substituents. These solutions may present structures that lack optimal bulkiness or may be synthetically difficult. | 7 | Physical Chemistry |
In lactic acid fermentation, each pyruvate molecule is directly reduced by NADH. The only byproduct from this type of fermentation is lactate. Lactic acid fermentation is used by human muscle cells as a means of generating ATP during strenuous exercise where oxygen consumption is higher than the supplied oxygen. As this process progresses, the surplus of lactate is brought to the liver, which converts it back to pyruvate. | 1 | Biochemistry |
In this assay the genome is digested by DpnI, which cuts only methylated GATCs. Double-stranded adapters with a known sequence are then ligated to the ends generated by DpnI. Ligation products are then digested by DpnII. This enzyme cuts non-methylated GATCs, ensuring that only fragments flanked by consecutive methylated GATCs are amplified in the subsequent PCR. A PCR with primers matching the adaptors is then carried out, leading to the specific amplification of genomic fragments flanked by methylated GATCs. | 1 | Biochemistry |
A superhelix is a molecular structure in which a helix is itself coiled into a helix. This is significant to both proteins and genetic material, such as overwound circular DNA.
The earliest significant reference in molecular biology is from 1971, by F. B. Fuller:
About the writhing number, mathematician W. F. Pohl says:
Contrary to intuition, a topological property, the linking number, arises from the geometric properties twist and writhe according to the following relationship:
:L= T + W,
where L is the linking number, W is the writhe and T is the twist of the coil.
The linking number refers to the number of times that one strand wraps around the other. In DNA this property does not change and can only be modified by specialized enzymes called topoisomerases. | 6 | Supramolecular Chemistry |
Jung et al. also describe a molecular mechanism for fibrinogen displacement involving pH cycling. Here the αC domains of fibrinogen change charge after pH cycling which results in conformational changes to the protein that leads to stronger interactions with the protein and the biomaterial. | 7 | Physical Chemistry |
In contrast to retrotransposons, retroposons never encode reverse transcriptase (RT) (but see below). Therefore, they are non-autonomous elements with regard to transposition activity (as opposed to transposons).
Non-long terminal repeat (LTR) retrotransposons such as the human LINE1 elements are sometimes falsely referred to as retroposons. However, this depends on the author. For example, Howard Temin published the following definition: Retroposons encode RT but are devoid of long terminal repeats (LTRs), for example long interspersed elements (LINEs). Retrotransposons also feature LTRs and retroviruses, in addition, are packaged as viral particles (virions). Retrosequences are non-autonomous elements devoid of RT. They are retroposed with the aid of the machinery of autonomous elements, such as LINEs; examples are short interspersed nuclear elements (SINEs) or mRNA-derived retro(pseudo)genes. | 1 | Biochemistry |
This protein is a member of a RNA-binding protein family that regulates transcription and RNA translation. It was first identified in cytotoxic lymphocyte (CTL) target cells. TIA1 acts in the nucleus to regulate splicing and transcription. TIA1 helps to recruit the splicesome to regulate RNA splicing, and it inhibits transcription of multiple genes, such as the cytokine Tumor necrosis factor alpha. In response to stress, TIA1 translocates from the nucleus to the cytoplasm, where it nucleates a type of RNA granule, termed the stress granule, and participates in the translational stress response. As part of the translational stress response, TIA1 works in cooperation with other RNA binding proteins to sequester RNA transcripts away from the ribosome, which allows the cell to focus its protein synthesis/RNA translation machinery on producing proteins that will address the particular stress. It has been suggested that this protein may be involved in the induction of apoptosis as it preferentially recognizes poly(A) homopolymers and induces DNA fragmentation in CTL targets. The major granule-associated species is a 15-kDa protein that is thought to be derived from the carboxyl terminus of the 40-kDa product by proteolytic processing. Alternative splicing resulting in different isoforms of this gene product have been described. | 1 | Biochemistry |
The Planck distribution can be used to find the spectral emissive power of a blackbody, as follows,
The total emissive power of a blackbody is then calculated as,The solution of the above integral yields a remarkably elegant equation for the total emissive power of a blackbody, the Stefan-Boltzmann law, which is given as,where is the Steffan-Boltzmann constant. | 7 | Physical Chemistry |
* Further muscle development (especially upper body)
* Increased sweat and changes in body odor
* Prominence of veins and coarser skin
* Alterations in blood lipids (cholesterol and triglycerides)
* Increased red blood cell count | 1 | Biochemistry |
Saturated vapor pressure, <br>
Actual vapor pressure,
: here e[T] is vapor pressure as a function of temperature, T.
::T = the dewpoint temperature at which water condenses.
::T = the temperature of a wet thermometer bulb from which water can evaporate to air.
::T = the temperature of a dry thermometer bulb in air. | 7 | Physical Chemistry |
Her research involves structural characterization of biopolymers using mass spectrometry-based techniques, such as liquid chromatography-mass spectrometry, thin-layer chromatography-mass spectrometry, Fourier-transform ion cyclotron resonance mass spectrometry, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, microfluidic capillary electrophoresis-mass spectrometry, and ion mobility spectrometry-mass spectrometry. She was one of the first scientists to characterize glycoconjugates with tandem mass spectrometry. Her 1988 article has been cited over two thousand times. She participated in the Human Proteome Project, the SysteMHC Atlas project, and the Minimum Information Required for a Glycomics Experiment (MIRAGE) project. | 1 | Biochemistry |
Aquatic organic matter can be further divided into two components: (1) dissolved organic matter (DOM), measured as colored dissolved organic matter (CDOM) or dissolved organic carbon (DOC), and (2) particulate organic matter (POM). They are typically differentiated by that which can pass through a 0.45 micrometre filter (DOM), and that which cannot (POM). | 0 | Organic Chemistry |
Phred is often used together with another software program called Phrap, which is a program for DNA sequence assembly. Phrap was routinely used in some of the largest sequencing projects in the Human Genome Sequencing Project and is currently one of the most widely used DNA sequence assembly programs in the biotech industry. Phrap uses Phred quality scores to determine highly accurate consensus sequences and to estimate the quality of the consensus sequences. Phrap also uses Phred quality scores to estimate whether discrepancies between two overlapping sequences are more likely to arise from random errors, or from different copies of a repeated sequence. | 1 | Biochemistry |
Alcohols are then classified into primary, secondary (sec-, s-), and tertiary (tert-, t-), based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl functional group. (The respective numeric shorthands 1°, 2°, and 3° are sometimes used in informal settings.) The primary alcohols have general formulas . The simplest primary alcohol is methanol (), for which R=H, and the next is ethanol, for which , the methyl group. Secondary alcohols are those of the form RRCHOH, the simplest of which is 2-propanol (). For the tertiary alcohols, the general form is RRR"COH. The simplest example is tert-butanol (2-methylpropan-2-ol), for which each of R, R, and R" is . In these shorthands, R, R, and R" represent substituents, alkyl or other attached, generally organic groups. | 0 | Organic Chemistry |
In general, the spontaneity of a process only determines whether or not a process can occur and makes no indication as to whether or not the process will occur. In other words, spontaneity is a necessary, but not sufficient, condition for a process to actually occur. Furthermore, spontaneity makes no implication as to the speed at which as spontaneous may occur.
As an example, the conversion of a diamond into graphite is a spontaneous process at room temperature and pressure. Despite being spontaneous, this process does not occur since the energy to break the strong carbon-carbon bonds is larger than the release in free energy. | 7 | Physical Chemistry |
While null in comparison to the concentrations found in indoor air, benzene, toluene, and methyl tert-butyl ether (MTBE) were found in samples of human milk and increase the concentrations of VOCs that we are exposed to throughout the day. A study notes the difference between VOCs in alveolar breath and inspired air suggesting that VOCs are ingested, metabolized, and excreted via the extra-pulmonary pathway. VOCs are also ingested by drinking water in varying concentrations. Some VOC concentrations were over the EPAs National Primary Drinking Water Regulations and Chinas National Drinking Water Standards set by the Ministry of Ecology and Environment. | 0 | Organic Chemistry |
Structural considerations play an important role in the proper design of copper applications. The primary concern is about thermal effects: movement and stresses related to temperature variations. Thermal effects can be accommodated by preventing movement and resisting cumulative stresses or by allowing movement at predetermined locations, thereby relieving anticipated thermal stresses.
Wind resistance is an important structural consideration. Underwriters Laboratories (UL) conducted a series of tests on copper roof systems. A copper standing-seam roof with test panels was subjected to the UL 580, Uplift Resistance Test Protocol. The copper system did not exhibit unusual deformation, the cleats did not loosen from the structural deck, and the system passed UL 580 requirements. UL-90 designation was granted. | 8 | Metallurgy |
For the 3D uniform Fermi gas, with fermions of spin-½, the number of particles as a function of the energy is obtained by substituting the Fermi energy by a variable energy :
from which the density of states (number of energy states per energy per volume) can be obtained. It can be calculated by differentiating the number of particles with respect to the energy:
This result provides an alternative way to calculate the total energy of a Fermi sphere of fermions (which occupy all energy states within the Fermi sphere): | 7 | Physical Chemistry |
A V0-morph is an organism whose surface area remains constant as the organism grows.
The reason why the concept is important in the context of the Dynamic Energy Budget theory is that food (substrate) uptake is proportional to surface area, and maintenance to volume. The surface area that is of importance is that part that is involved in substrate uptake.
Biofilms on a flat solid substrate are examples of V0-morphs; they grow in thickness, but not in surface area that is involved in nutrient exchange. Other examples are dinophyta and diatoms that have a cell wall that does not change during the cell cycle. During cell-growth, when the amounts of protein and carbohydrates increase, the vacuole shrinks. The outer membrane that is involved in nutrient uptake remains constant. At cell division, the daughter cells rapidly take up water, complete a new cell wall and the cycle repeats.
Rods (bacteria that have the shape of a rod and grow in length, but not in diameter) are a static mixture between a V0- and a V1-morph, where the caps act as V0-morphs and the cylinder between the caps as V1-morph.The mixture is called static because the weight coefficients of the contributions of the V0- and V1-morph terms in the shape correction function are constant during growth.
Crusts, such as lichens that grow on a solid substrate, are a dynamic mixture between a V0- and a V1-morph, where the inner part acts as V0-morph, and the outer annulus as V1-morph.The mixture is called dynamic because the weight coefficients of the contributions of the V0- and V1-morph terms in the shape correction function change during growth. The Dynamic Energy Budget theory explains why the diameter of crusts grow linearly in time at constant substrate availability. | 1 | Biochemistry |
William H. Peirce (died 1944) was an American civil engineer and metallurgist, who pioneered copper production in the early 20th century. Among his achievements was the , invented with Elias Anton Cappelen Smith. | 8 | Metallurgy |
Contract research organizations (CROs) provide services to the life science industries along product development. There are more than 2000 CROs operating worldwide, representing revenues of more than $20 billion. One distinguishes between "Product" and "Patient" CROs. Whereas the production sites of CMOs are multipurpose plants, allowing for the production of tens to hundreds of tons of fine chemicals, the work places of patient CROs are the test persons (volunteers) for the clinical trials and those of the product CROs are the laboratory benches. Major customers for CRO services are the large global pharmaceutical companies. Half a dozen companies (Pfizer, GlaxoSmithKline, Sanofi-Aventis, AstraZeneca, Johnson & Johnson, and Merck & Co.) alone absorb about one third of all CRO spending. As for CMOs also for CROs, biotech start-up companies with their dichotomy between ambitious drug development programs and limited resources are the second most promising prospects. Product CROs (chemical CROs) are providing primarily sample preparation, process research and development services. An overlap between the latter and CMOs exists with regard to pilot plants (100 kg quantities), which are part of the arsenal of both types of enterprise.
There are more 100 product CROs. Most of them are privately held and have revenues of $10–$20 million per year or less, adding up to a total business in the range of $1.5-$2 billion. Their tasks are described in Chapter 5,
Examples of are:
*In North America: Alphora; Delmar; NAEJA, all Canada. AMRI; Aptuit; Cambridge Major; ChemBridge; Innocentive; Irix Pharmaceuticals, PharmEco, all USA.
*In Europe; Carbogen-Amcis, Switzerland; Chemcomm, Germany; ChemDiv, Russia; Clauson-Kaas, Denmark; Enamine Ltd, Ukraine; Girindus, Germany; Nerviano Medical Sciences, Italy; Recipharm, Sweden; Serichim, Italy; Solvias, Switzerland, Netherlands.
*In Asia: BioDuro, Medicilon, Pharmaron; WuXi AppTec, all China; Acoris; Aptuit Laurus; Biocon / Syngene; Chembiotek; Chempartner; ProCitius, all India; NARD Institute, Riken, both Japan.
The business of CROs is usually done through a "pay for service" arrangement. Contrary to manufacturing companies, invoicing of CROs is not based on unit product price, but on full-time equivalents (FTEs), that is, the cost of a scientist working one year on a given customer assignment.
Companies offering both contract research and manufacturing services (CRAMS) combine the activities of CROs and CMOs. Their history is either a forward integration of a CRO, which adds industrial scale capabilities or backwards integration of a CMO. As there are only limited synergies (e.g. > 90% of the projects end at the sample preparation stage). It is questionable, though, whether one-stop shops really fulfil a need. Actually, the large fine chemical companies consider the preparation of samples more as marketing tool (and expense ...) rather than a profit contributor.
The offerings of Patient CROs (Clinical CROs) comprise more than 30 tasks addressing the clinical part of pharmaceutical development at the interface between drugs, physicians, hospitals, and patients, such as the clinical development and selection of lead new drug compounds. As clinical trials represent the largest expense in pharmaceutical research, the market for patient CROs is larger than for their product counterparts. Thus, the sales of the top tier firms, Charles River Laboratories, Covance, Parexel, PPD, Quintiles Transnational, all USA, and TCG Lifescience, India; are in the $1–$2 billion range, whereas the largest product CROs have revenues of a few 100 million dollars. | 0 | Organic Chemistry |
In organometallic chemistry, a transition metal alkene complex is a coordination compound containing one or more alkene ligands. The inventory is large. Such compounds are intermediates in many catalytic reactions that convert alkenes to other organic products. | 0 | Organic Chemistry |
3D optical data storage is any form of optical data storage in which information can be recorded or read with three-dimensional resolution (as opposed to the two-dimensional resolution afforded, for example, by CD).
This innovation has the potential to provide petabyte-level mass storage on DVD-sized discs (120mm). Data recording and readback are achieved by focusing lasers within the medium. However, because of the volumetric nature of the data structure, the laser light must travel through other data points before it reaches the point where reading or recording is desired. Therefore, some kind of nonlinearity is required to ensure that these other data points do not interfere with the addressing of the desired point.
No commercial product based on 3Doptical data storage has yet arrived on the mass market, although several companies are actively developing the technology and claim that it may become available soon. | 5 | Photochemistry |
The intramolecular Heck reaction (IMHR) in chemistry is the coupling of an aryl or alkenyl halide with an alkene in the same molecule. The reaction may be used to produce carbocyclic or heterocyclic organic compounds with a variety of ring sizes. Chiral palladium complexes can be used to synthesize chiral intramolecular Heck reaction products in non-racemic form. | 0 | Organic Chemistry |
Chemiluminescence is the emission of light by a chemical reaction. Some enzyme reactions produce light and this can be measured to detect product formation. These types of assay can be extremely sensitive, since the light produced can be captured by photographic film over days or weeks, but can be hard to quantify, because not all the light released by a reaction will be detected.
The detection of horseradish peroxidase by enzymatic chemiluminescence (ECL) is a common method of detecting antibodies in western blotting. Another example is the enzyme luciferase, this is found in fireflies and naturally produces light from its substrate luciferin. | 1 | Biochemistry |
In the United States, the Environmental Protection Agency has published pollution control regulations for smelters.
* Air pollution standards under the Clean Air Act
* Water pollution standards (effluent guidelines) under the Clean Water Act.
The RMI Conformant Smelter Program
As conflict mineral use grows, numerous initiatives have been launched to counteract the problem. They encourage responsible mineral sourcing practices in regions under circumstances of conflict, human rights abuse, or labour exploitation.
The Responsible Mineral Initiative, RMI, has developed a set of ideals and guidelines for smelter, including the Conformant Smelter Program. The program is a third-party audit and certification program that assesses the performance of smelters in the responsible sourcing of minerals. This program adheres to the Organization for Economic Co-operation and Development, OECD, guidelines. Published in the OECD Due Diligence Guidance for Responsible Supply Chains of Minerals from Conflict-Affected and High-Risk Areas. The OECD is a body focused on policies for bettering global practices.
The focus of the program is evaluating smelters on:
*Sourcing practices: Demonstrating sourced minerals do not contribute to active conflict, human rights issues, or environmental damage
*Due Diligence: Establishing a due diligence process to mitigate risks in the supply chain
*Transparency: Information being transparent about their sourcing
*Environmental and social performance: Minimizing the environmental impact and respecting workers' rights
Smelters that meet the RMI standards gain recognition on the RMI Conformant Smelter & Refiner Lists.
This is not the only program regulating the smelting industry, additional auditing programs include:
*The London Bullion Market Association, LBMA, focuses on gold, silver, platinum, and palladium. With successful smelters gaining recognition on the Good Suppliers List.
*Responsible Jewellery Council, RJC, promotes responsible practices in the jewellery supply chain. Successful smelters gaining recognition on the RJC members registry.
Similarly, to the RMI Conformant Smelter Program these entities comply with OECD guidelines and promote ethical and environmental supply chain management. However, the named organizations have varying additional guidelines therefore the only cross recognized audits with the RMI are:
*LBMA Responsible Gold Guidance
*RMI Responsible Minerals Assurance Process Gold Standard
*RJC Chain-of-Custody (CoC) Standard (provision 1 only)
*RJC Code of Practices (COP) Standard (provision 7 only) | 8 | Metallurgy |
Non-lytic insect cell expression is an alternative to the lytic baculovirus expression system. In non-lytic expression, vectors are transiently or stably transfected into the chromosomal DNA of insect cells for subsequent gene expression. This is followed by selection and screening of recombinant clones. The non-lytic system has been used to give higher protein yield and quicker expression of recombinant genes compared to baculovirus-infected cell expression. Cell lines used for this system include: Sf9, Sf21 from Spodoptera frugiperda cells, Hi-5 from Trichoplusia ni cells, and Schneider 2 cells and Schneider 3 cells from Drosophila melanogaster cells. With this system, cells do not lyse and several cultivation modes can be used. Additionally, protein production runs are reproducible. This system gives a homogeneous product. A drawback of this system is the requirement of an additional screening step for selecting viable clones. | 1 | Biochemistry |
Fluorenylidene reacts with olefins as predicted by the Skell-Woodworth rules. The stereochemistry of cycloaddition products depends on the relative rates of cyclopropanation (or other reactions) and intersystem crossing. Stabilization of specific spin states, and, by extension, increased stereospecificity can be achieved by using solvents of different polarities . | 0 | Organic Chemistry |
Regurgitation has been mentioned above under abomasum and crop, referring to crop milk, a secretion from the lining of the crop of pigeons and doves with which the parents feed their young by regurgitation.
Many sharks have the ability to turn their stomachs inside out and evert it out of their mouths in order to get rid of unwanted contents (perhaps developed as a way to reduce exposure to toxins).
Other animals, such as rabbits and rodents, practise coprophagia behaviours – eating specialised faeces in order to re-digest food, especially in the case of roughage. Capybara, rabbits, hamsters and other related species do not have a complex digestive system as do, for example, ruminants. Instead they extract more nutrition from grass by giving their food a second pass through the gut. Soft faecal pellets of partially digested food are excreted and generally consumed immediately. They also produce normal droppings, which are not eaten.
Young elephants, pandas, koalas, and hippos eat the faeces of their mother, probably to obtain the bacteria required to properly digest vegetation. When they are born, their intestines do not contain these bacteria (they are completely sterile). Without them, they would be unable to get any nutritional value from many plant components. | 1 | Biochemistry |
2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)pyrimidine is a metabolite in the purine metabolism, formed by the hydrolysis of GTP by GTP cyclohydrolase II. Alternatively two separate enzymes can carry out this reaction, initially GTP cyclohydrolase IIa hydrolyses the 8,9 bond to form 2-Amino-5-formylamino-6-(5-phospho-D-ribosylamino)pyrimidin-4(3H)-one, followed by de-formylation by 2-amino-5-formylamino-6-ribosylaminopyrimidin-4(3H)-one 5'-monophosphate deformylase. 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)pyrimidine is deaminated by Diaminohydroxyphosphoribosylaminopyrimidine deaminase to form 5-amino-6-(5-phosphoribosylamino)uracil. | 1 | Biochemistry |
The NDUFAF6 gene is located on the q arm of chromosome 8 in position 22.1 and spans 222,728 base pairs. The gene produces a 38.2 kDa protein composed of 333 amino acids. The protein contains a predicted phytoene synthase domain. | 1 | Biochemistry |
NBS can α-brominate carbonyl derivatives via either a radical pathway (as above) or via acid-catalysis. For example, hexanoyl chloride 1 can be brominated in the alpha-position by NBS using acid catalysis.
The reaction of enolates, enol ethers, or enol acetates with NBS is the preferred method of α-bromination as it is high-yielding with few side-products. | 0 | Organic Chemistry |
Early efforts to use rule-based modeling in simulation of biochemical systems include the stochastic simulation systems StochSim
A widely used tool for rule-based modeling of biochemical networks is BioNetGen It is released under the GNU GPL, version 3. BioNetGen includes a language to describe chemical substances, including the states they can assume and the bindings they can undergo. These rules can be used to create a reaction network model or to perform computer simulations directly on the rule set. The biochemical modeling framework Virtual Cell includes a BioNetGen interpreter.
A close alternative is the Kappa language. Another alternative is BioChemical Space language. | 1 | Biochemistry |
While the romantic picture of gold mining focuses on nuggets, the reality is that gold is typically recovered from ores containing >10 ppm of the metal. Thus, the main challenge is concentrating this trace amount. | 8 | Metallurgy |
The second analysis, taking into account the measured Faraday efficiency, yielded an actual excess heat of 0.13% +/- 0.48%. In other words, when the actual Faraday efficiency was measured and taken into account, the energy balance of the cells was zero, with no excess heat. | 7 | Physical Chemistry |
In addition to the above-mentioned classification based on energy, muon beams are also divided according to the time structure of the particle accelerator, i.e. continuous or pulsed.
For continuous muon sources no dominating time structure is present. By selecting an appropriate incoming muon rate, muons are implanted into the sample one-by-one. The main advantage is that the time resolution is solely determined by the detector construction and the read-out electronics. There are two main limitations for this type of source, however: (i) unrejected charged particles accidentally hitting the detectors produce non-negligible random background counts; this compromises measurements after a few muon lifetimes, when the random background exceeds the true decay events; and (ii) the requirement to detect muons one at a time sets a maximum event rate. The background problem can be reduced by the use of electrostatic deflectors to ensure that no muons enter the sample before the decay of the previous muon. PSI and TRIUMF host the two continuous muon sources available for µSR experiments.
At pulsed muon sources protons hitting the production target are bunched into short, intense, and widely separated pulses that provide a similar time structure in the secondary muon beam. An advantage of pulsed muon sources is that the event rate is only limited by detector construction. Furthermore, detectors are active only after the incoming muon pulse, strongly reducing the accidental background counts. The virtual absence of background allows the extension of the time window for measurements up to about ten times the muon mean lifetime. The principal downside is that the width of the muon pulse limits the time resolution. ISIS Neutron and Muon Source and J-PARC are the two pulsed muon sources available for µSR experiments. | 7 | Physical Chemistry |
In any forced convection situation, some amount of natural convection is always present whenever there are gravitational forces present (i.e., unless the system is in an inertial frame or free-fall). When the natural convection is not negligible, such flows are typically referred to as mixed convection. | 7 | Physical Chemistry |
Evergreening refers to the various strategies whereby owners (innovators/sponsors) of pharmaceutical products use patent laws and minor drug modifications to extend their monopoly privileges on the drug. An enantiomer patent is another form of evergreening based on a chiral switch strategy. Single-enantiomer drugs represent more than 50% of the top-selling 100 drugs worldwide. There are some studies which go to suggest that drug companies employ chiral switching for life-cycle management/patent protection of the parent racemic drug and also as a marketing strategy. Pharmaceutical companies support evergreening practices. Some chiral switches are performed to re-start the patent clock for a medication without reducing side effects or improving efficacy. A high price can then continue to be charged for a medication. Examples include citalopram and escitalopram, and omeprazole and esomeprazole. In both these medications, proposed theoretical benefits were used to market the enantiopure drugs, without any clinical trials being conducted to provide evidence that the racemic drugs improved patient centered outcomes. | 4 | Stereochemistry |
Dephosphorylation can play a key role in molecular biology, particularly cloning using restriction enzymes. The cut ends of a vector may re-ligate during a ligation step due to phosphorylation. By using a desphosphorylating phosphatase, re-ligation can be avoided. Alkaline phosphatases, which remove the phosphate group present at the 5′ terminus of a DNA molecule, are often sourced naturally, most commonly from calf intestine, and are abbreviated as CIP. | 1 | Biochemistry |
An artificial metalloenzyme (ArM) is a metalloprotein made in the laboratory which cannot be found in the nature and can catalyze certain desired chemical reactions. Despite fitting into classical enzyme categories, ArMs also have potential in chemical reactivity like catalyzing Suzuki coupling, metathesis and so on, which are never reported in natural enzymatic reaction. With the progress in organometallic synthesis and protein engineering, more and more new kind of design of ArMs came out, showing promising future in both academia and industrial aspects.
In 2018, one half of the Nobel Prize in Chemistry was awarded to Frances H. Arnold “for the directed evolution of enzymes”, which elegantly evolved the artificial metalloenzymes to realize efficient and highly selective abiotic chemical reaction in vitro and in vivo. | 0 | Organic Chemistry |
Large aggregates can become anoxic which gives rise to anaerobic metabolisms. Typically anaerobic metabolisms are confined to areas where it is more energetically favorable. Given the abundance of denitrifying and sulfate-reducing bacteria, it is thought that these metabolisms are able to thrive within marine snow aggregates. In a model developed by Bianchi et al., it shows the various redox potentials within an aggregate. | 9 | Geochemistry |
PDE3 is a phosphodiesterase. The PDEs belong to at least eleven related gene families, which are different in their primary structure, substrate affinity, responses to effectors, and regulation mechanism.
Most of the PDE families are composed of more than one gene. PDE3 is clinically significant because of its role in regulating heart muscle, vascular smooth muscle and platelet aggregation. PDE3 inhibitors have been developed as pharmaceuticals, but their use is limited by arrhythmic effects and they can increase mortality in some applications. | 1 | Biochemistry |
Staying in the U.S., Cheon was a postdoc in the University of California Berkeley. For the next three years, he was a staff research associate at UCLA before returning to Korea to work as an assistant and then associate professor at KAIST. His research at KAIST focused on geometrical shape control of nanoparticles and magnetic particles. This also marked his first publication on nanocrystals which is a reoccurring interest in his research career and a source of multiple highly cited articles.
He started working at Yonsei University as a full professor in 2002 and later became the Horace G. Underwood Professor in 2008. His research at Yonsei on nanoscale phenomena has led to nanomaterial applications in biology, including highly sensitive MRI contrast agents and nanoscale toolkits for cells. A notable study is from 2004, when he demonstrated the principle of size-dependent MRI contrast effects using nanoparticles which enabled the development of magnetism-engineered iron oxide (MEIO) as an ultra-sensitive nanoparticle MRI contrast agent which might help detect early stage cancer.
From 2010 to 2016, Cheon was the director of the National Creative Research Initiative Center for Evolutionary Nanoparticles. From 2015, he became the director of the newly established Yonsei-Institute of Basic Science Center for Nanomedicine at the Yonsei University Sinchon campus. | 0 | Organic Chemistry |
The site was occupied by the pre-Roman Britons, likely as part of an iron working industry. It was continually occupied throughout the Roman era, and the scale of industrial activity increased over the period. It is clear that there was a focus of settlement activity near Bromsash, but the area appears to some archaeologists to have contained dispersed centres of activity and settlement rather than a Roman town. Ariconiums only documented significance is as a station on Iter XIII of the Iter Britanniarum', with the single mention there being its only mention in classical history.
It seems to have been abandoned shortly after 360. Its sudden abandonment is consistent with a violent end, and may be related to the collapse of authority and widespread marauding at that time, as reported by Ammianus, a situation that lasted for almost a decade, and from which parts of Roman Britain never recovered. Evidence of later occupation of the site has not been found. | 8 | Metallurgy |
Heart rate is determined by the medulla oblongata and part of the pons, two organs located inferior to the hypothalamus on the brain stem. Heart rate is important for basal metabolic rate and resting metabolic rate because it drives the blood supply, stimulating the Krebs cycle. During exercise that achieves the anaerobic threshold, it is possible to deliver substrates that are desired for optimal energy utilization. The anaerobic threshold is defined as the energy utilization level of heart rate exertion that occurs without oxygen during a standardized test with a specific protocol for accuracy of measurement, such as the Bruce Treadmill protocol (see metabolic equivalent of task). With four to six weeks of targeted training the body systems can adapt to a higher perfusion of mitochondrial density for increased oxygen availability for the Krebs cycle, or tricarboxylic cycle, or the glycolytic cycle. This in turn leads to a lower resting heart rate, lower blood pressure, and increased resting or basal metabolic rate.
By measuring heart rate we can then derive estimations of what level of substrate utilization is actually causing biochemical metabolism in our bodies at rest or in activity. This in turn can help a person to maintain an appropriate level of consumption and utilization by studying a graphical representation of the anaerobic threshold. This can be confirmed by blood tests and gas analysis using either direct or indirect calorimetry to show the effect of substrate utilization. The measures of basal metabolic rate and resting metabolic rate are becoming essential tools for maintaining a healthy body weight. | 1 | Biochemistry |
The exact mechanism of the enhancement effect of SERS is still a matter of debate in the literature. There are two primary theories and while their mechanisms differ substantially, distinguishing them experimentally has not been straightforward. The electromagnetic theory proposes the excitation of localized surface plasmons, while the chemical theory proposes the formation of charge-transfer complexes. The chemical theory is based on resonance Raman spectroscopy, in which the frequency coincidence (or resonance) of the incident photon energy and electron transition greatly enhances Raman scattering intensity. Research in 2015 on a more powerful extension of the SERS technique called SLIPSERS (Slippery Liquid-Infused Porous SERS) has further supported the EM theory. | 7 | Physical Chemistry |
The prefix E/Z- can be used to indicate uncertainty in the E or Z isomers for an ene bond. For graphical representations, wavy single bonds are the standard way to represent unknown or unspecified stereochemistry or a mixture of isomers (as with tetrahedral stereocenters). A crossed double-bond has been used sometimes; it is no longer considered an acceptable style for general use by IUPAC but may still be required by computer software. | 4 | Stereochemistry |
Estradiol with levonorgestrel in the form of a skin patch is used under the brand name Climara Pro for hormone replacement therapy in postmenstrual women, treating symptoms such as hot flashes or osteoporosis. The simultaneous delivery of a progestogen such as levonorgestrel is necessary for the protection of the endometrium. | 4 | Stereochemistry |
LHCGR have been found in many types of extragonadal tissues, and the physiologic role of some has remained largely unexplored. Thus receptors have been found in the uterus, sperm, seminal vesicles, prostate, skin, breast, adrenals, thyroid, neural retina, neuroendocrine cells, and (rat) brain. | 1 | Biochemistry |
Sel gris (pl. sels gris, "gray salt" in French) is a coarse granular sea salt popularized by the French.
Sel gris comes from the same solar evaporation salt pans as fleur de sel but is harvested differently; it is allowed to come into contact with the bottom of the salt pan before being raked, hence its gray color. Sel gris is coarser than fleur de sel but is also a moist salt, typically containing 13 percent residual moisture. | 9 | Geochemistry |
α-Ketoisovalerate undergoes hydroxymethylation to give ketopantoate:
:(CH)CHC(O)CO + CHO → HOCH(CH)CC(O)CO
This conversion is catalyzed by ketopantoate hydroxymethyltransferase.
Like many α-ketoacids, α-ketoisovaleric acid is prone to decarboxylation to give isobutyraldehyde:
:(CH)CHC(O)COH → (CH)CHCHO + CO
Genetic engineering has been used to produce the biofuel isobutanol by reduction of isobutyraldehyde obtained from ketoisovalerate. | 1 | Biochemistry |
The -(+)-tartaric acid isomer of tartaric acid is industrially produced in the largest amounts. It is obtained from lees, a solid byproduct of fermentations. The former byproducts mostly consist of potassium bitartrate (KHCHO). This potassium salt is converted to calcium tartrate (CaCHO) upon treatment with calcium hydroxide "milk of lime" (Ca(OH)):
In practice, higher yields of calcium tartrate are obtained with the addition of calcium chloride. Calcium tartrate is then converted to tartaric acid by treating the salt with aqueous sulfuric acid: | 4 | Stereochemistry |
The discovery of the perfect liquid was a turning point in physics. Experiments at RHIC have revealed a wealth of information about this remarkable substance, which we now know to be a QGP. Nuclear matter at "room temperature" is known to behave like a superfluid. When heated the nuclear fluid evaporates and turns into a dilute gas of nucleons and, upon further heating, a gas of baryons and mesons (hadrons). At the critical temperature, T, the hadrons melt and the gas turns back into a liquid. RHIC experiments have shown that this is the most perfect liquid ever observed in any laboratory experiment at any scale. The new phase of matter, consisting of dissolved hadrons, exhibits less resistance to flow than any other known substance. The experiments at RHIC have, already in 2005, shown that the Universe at its beginning was uniformly filled with this type of material—a super-liquid—which once the Universe cooled below T evaporated into a gas of hadrons. Detailed measurements show that this liquid is a quark–gluon plasma where quarks, antiquarks and gluons flow independently.
In short, a quark–gluon plasma flows like a splat of liquid, and because it is not "transparent" with respect to quarks, it can attenuate jets emitted by collisions. Furthermore, once formed, a ball of quark–gluon plasma, like any hot object, transfers heat internally by radiation. However, unlike in everyday objects, there is enough energy available so that gluons (particles mediating the strong force) collide and produce an excess of the heavy (i.e., high-energy) strange quarks. Whereas, if the QGP did not exist and there was a pure collision, the same energy would be converted into a non-equilibrium mixture containing even heavier quarks such as charm quarks or bottom quarks.
The equation of state is an important input into the flow equations. The speed of sound (speed of QGP-density oscillations) is currently under investigation in lattice computations. The mean free path of quarks and gluons has been computed using perturbation theory as well as string theory. Lattice computations have been slower here, although the first computations of transport coefficients have been concluded. These indicate that the mean free time of quarks and gluons in the QGP may be comparable to the average interparticle spacing: hence the QGP is a liquid as far as its flow properties go. This is very much an active field of research, and these conclusions may evolve rapidly. The incorporation of dissipative phenomena into hydrodynamics is another active research area. | 7 | Physical Chemistry |
Using a thin coat of polish can prevent tarnish from forming over these metals. Tarnish can be removed by using steel wool, sandpaper, emery paper, baking soda or a file to rub or polish the metal's dull surface. Fine objects (such as silverware) may have the tarnish electrochemically reversed (non-destructively) by resting the objects on a piece of aluminium foil in a pot of boiling water with a small amount of salt or baking soda, or it may be removed with a special polishing compound and a soft cloth. Gentler abrasives, like calcium carbonate, are often used by museums to clean tarnished silver as they cannot damage or scratch the silver and will not leave unwanted residues. | 8 | Metallurgy |
Amino acids can also be classified according to how many different amino acids they can be exchanged by through single nucleotide substitution.
* Typical amino acids - there are several other amino acids which they can change into through single nucleotide substitution. Typical amino acids and their alternatives usually have similar physicochemical properties. Leucine is an example of a typical amino acid.
* Idiosyncratic amino acids - there are few similar amino acids that they can mutate to through single nucleotide substitution. In this case most amino acid replacements will be disruptive for protein function. Tryptophan is an example of an idiosyncratic amino acid. | 1 | Biochemistry |
A sample is continuously extracted from the gas stream being monitored using a titanium probe, which is water-cooled to below 70 °C. The sample flow rate is automatically adjusted to ensure isokinetic sampling (the velocity of gas entering the sampling system is equal to the velocity of the gas in the system under test). The sample gas is drawn through a quartz wool pre-filter and then across a cartridge filled with resin, such as XAD 2. The sample gas is also cooled to below 5 °C to condense and remove water vapour. All system parameters are recorded digitally during sampling. The resin cartridge and the condensate are removed at the end of a monitoring period, and the contents are analysed to determine levels of dioxins and furans. | 3 | Analytical Chemistry |
Cyanobacteria are a very large and diverse phylum of photosynthetic prokaryotes. They are defined by their unique combination of pigments and their ability to perform oxygenic photosynthesis. They often live in colonial aggregates that can take on a multitude of forms. Of particular interest are the filamentous species, which often dominate the upper layers of microbial mats found in extreme environments such as hot springs, hypersaline water, deserts and the polar regions, but are also widely distributed in more mundane environments as well. They are evolutionarily optimized for environmental conditions of low oxygen. Some species are nitrogen-fixing and live in a wide variety of moist soils and water, either freely or in a symbiotic relationship with plants or lichen-forming fungi (as in the lichen genus Peltigera).
Cyanobacteria are globally widespread photosynthetic prokaryotes and are major contributors to global biogeochemical cycles. They are the only oxygenic photosynthetic prokaryotes, and prosper in diverse and extreme habitats. They are among the oldest organisms on Earth with fossil records dating back at least 2.1 billion years. Since then, cyanobacteria have been essential players in the Earth's ecosystems. Planktonic cyanobacteria are a fundamental component of marine food webs and are major contributors to global carbon and nitrogen fluxes. Some cyanobacteria form harmful algal blooms causing the disruption of aquatic ecosystem services and intoxication of wildlife and humans by the production of powerful toxins (cyanotoxins) such as microcystins, saxitoxin, and cylindrospermopsin. Nowadays, cyanobacterial blooms pose a serious threat to aquatic environments and public health, and are increasing in frequency and magnitude globally.
Cyanobacteria are ubiquitous in marine environments and play important roles as primary producers. They are part of the marine phytoplankton, which currently contributes almost half of the Earth's total primary production. About 25% of the global marine primary production is contributed by cyanobacteria.
Within the cyanobacteria, only a few lineages colonized the open ocean: Crocosphaera and relatives, cyanobacterium UCYN-A, Trichodesmium, as well as Prochlorococcus and Synechococcus. From these lineages, nitrogen-fixing cyanobacteria are particularly important because they exert a control on primary productivity and the export of organic carbon to the deep ocean, by converting nitrogen gas into ammonium, which is later used to make amino acids and proteins. Marine picocyanobacteria (Prochlorococcus and Synechococcus) numerically dominate most phytoplankton assemblages in modern oceans, contributing importantly to primary productivity. While some planktonic cyanobacteria are unicellular and free living cells (e.g., Crocosphaera, Prochlorococcus, Synechococcus); others have established symbiotic relationships with haptophyte algae, such as coccolithophores. Amongst the filamentous forms, Trichodesmium are free-living and form aggregates. However, filamentous heterocyst-forming cyanobacteria (e.g., Richelia, Calothrix) are found in association with diatoms such as Hemiaulus, Rhizosolenia and Chaetoceros.
Marine cyanobacteria include the smallest known photosynthetic organisms. The smallest of all, Prochlorococcus, is just 0.5 to 0.8 micrometres across. In terms of numbers of individuals, Prochlorococcus is possibly the most plentiful genus on Earth: a single millilitre of surface seawater can contain 100,000 cells of this genus or more. Worldwide there are estimated to be several octillion (10, a billion billion billion) individuals. Prochlorococcus is ubiquitous between latitudes 40°N and 40°S, and dominates in the oligotrophic (nutrient-poor) regions of the oceans. The bacterium accounts for about 20% of the oxygen in the Earth's atmosphere. | 5 | Photochemistry |
The Petrochemical industry typically encounters aggressive corrosive media. These include sulfides and high temperatures. Corrosion control and solutions are thus necessary for the world economy. Scale formation in injection water presents its own problems with regard to corrosion and thus for the corrosion engineer. | 8 | Metallurgy |
The active site of malate dehydrogenase is a hydrophobic cavity within the protein complex that has specific binding sites for the substrate and its coenzyme, NAD. In its active state, MDH undergoes a conformational change that encloses the substrate to minimize solvent exposure and to position key residues in closer proximity to the substrate. The three residues in particular that comprise a catalytic triad are histidine (His-195), aspartate (Asp-168), both of which work together as a proton transfer system, and arginines (Arg-102, Arg-109, Arg-171), which secure the substrate.
Mechanistically, malate dehydrogenase catalyzes the oxidation of the hydroxyl group of malate by utilizing NAD as an electron acceptor. This oxidation step results in the elimination of a proton and a hydride ion from the substrate. NAD receives the hydride ion (specifically, the hydride ion is transferred to the nicotinamide ring of the NAD) and becomes reduced to NADH while concomitantly, the His-195 residue on the enzyme accepts the proton. The positively charged His-195 residue, which is involved in base catalysis of the substrate, is stabilized by the adjacent, negatively charged Asp-168 residue. This electrostatic stabilization helps facilitate the transfer of the proton. Arg-102, Arg-109, and Arg-171 (which are protonated, and thus positively charged) participate in electrostatic catalysis and help to bind the negatively charged carboxylates on the substrate. Additionally, the Arginine residues on the enzyme provide additional substrate specificity and binding through hydrogen bonding between the guanidinium side chain of the Arginine amino acid residues and the carboxylates of the substrate.
Studies have also identified a mobile loop in malate dehydrogenase that participates in the catalytic activity of the enzyme. The loop undergoes a conformational change to shield the substrate and catalytic amino acids from the solvent in response to the binding of the malate dehydrogenase:coenzyme complex to substrate. This flipping of the loop to the up position to cover the active site also promotes enhanced interaction of the catalytically important amino residues on the enzyme with the substrate. Additionally, the movement of the loop has been shown to correlate with the rate determining step of the enzyme. | 1 | Biochemistry |
The LysRS-ApA-MITF signaling pathway was first discovered in mast cells, in which, the A mitogen-activated protein kinase (MAPK) pathway is activated upon allergen stimulation. The binding of immunoglobulin E to the high-affinity IgE receptor (FcεRI) provides the stimulus that starts the cascade.
Lysyl-tRNA synthetase (LysRS) normally resides in the multisynthetase complex. This complex consists of nine different aminoacyl-tRNA synthetases and three scaffold proteins and has been termed the "signalosome" due to its non-catalytic signalling functions. After activation, LysRS is phosphorylated on Serine 207 in a MAPK-dependent manner. This phosphorylation causes LysRS to change its conformation, detach from the complex and translocate into the nucleus, where it associates with the encoding histidine triad nucleotide–binding protein 1 (HINT1) thus forming the MITF-HINT1 inhibitory complex. The conformational change also switches LysRS activity from aminoacylation of Lysine tRNA to diadenosine tetraphosphate (Ap4A) production. Ap4A, which is an adenosine joined to another adenosine through a 5‘-5’tetraphosphate bridge, binds to HINT1 and this releases MITF from the inhibitory complex, allowing it to transcribe its target genes. Specifically, Ap4A causes a polymerization of the HINT1 molecule into filaments. The polymerization blocks the interface for MITF and thus prevents the binding of the two proteins. This mechanism is dependent on the precise length of the phosphate bridge in the Ap4A molecule so other nucleotides such as ATP or AMP will not affect it.
MITF is also an integral part of melanocytes, where it regulates the expression of a number of proteins with melanogenic potential. Continuous expression of MITF at a certain level is one of the necessary factors for melanoma cells to proliferate, survive and avoid detection by host immune cells through the T-cell recognition of the melanoma-associated antigen (melan-A). Post-translational modifications of the HINT1 molecules have been shown to affect MITF gene expression as well as the binding of Ap4A. Mutations in HINT1 itself have been shown to be the cause of axonal neuropathies. The regulatory mechanism relies on the enzyme diadenosine tetraphosphate hydrolase, a member of the Nudix type 2 enzymatic family (NUDT2), to cleave Ap4A, allow the binding of HINT1 to MITF and thus suppress the expression of the MITF transcribed genes. NUDT2 itself has also been shown to be associated with human breast carcinoma, where it promotes cellular proliferation. The enzyme is 17 kDa large and can freely diffuse between the nucleus and cytosol explaining its presence in the nucleus. It has also been shown to be actively transported into the nucleus by directly interacting with the N-terminal domain of importin-β upon immunological stimulation of the mast cells. Growing evidence is pointing to the fact that the LysRS-Ap4A-MITF signalling pathway is in fact an integral aspect of controlling MITF transcriptional activity.
Activation of the LysRS-Ap4A-MITF signalling pathway by isoproterenol has been confirmed in cardiomyocytes. A heart specific isoform of MITF is a major regulator of cardiac growth and hypertrophy responsible for heart growth and for the physiological response of the cardiomyocytes to beta-adrenergic stimulation. | 1 | Biochemistry |
Mefloquine was formulated at Walter Reed Army Institute of Research (WRAIR) in the 1970s shortly after the end of the Vietnam war. Mefloquine was number 142,490 of a total of 250,000 antimalarial compounds screened during the study.
Mefloquine was the first Public-Private Venture (PPV) between the US Department of Defense and a pharmaceutical company. WRAIR transferred all its phase I and phase II clinical trial data to Hoffman-LaRoche and Smith Kline. FDA approval as a treatment for malaria was swift. Most notably, phase III safety and tolerability trials were skipped.
The drug was first approved in Switzerland in 1984 by Hoffmann-LaRoche, who brought it to market with the name Lariam.
However, mefloquine was not approved by the FDA for prophylactic use until 1989. This approval was based primarily on compliance, while safety and tolerability were overlooked. Because of the drug's very long half-life, the Centers for Disease Control originally recommended a mefloquine dosage of 250 mg every two weeks; however, this caused an unacceptably high malaria rate in the Peace Corps volunteers who participated in the approval study, so the drug regimen was switched to once a week.
By 1991, Hoffman was marketing the drug on a worldwide basis.
By the 1992 UNITAF, Canadian soldiers were being prescribed the drug en masse.
By 1994, medical professionals were noting "severe psychiatric side effects observed during prophylaxis and treatment with mefloquine", and recommending that "the absence of contraindications and minor side effects during an initial course of mefloquine should be confirmed before another course is prescribed." Other doctors at the University Hospital of Zurich noted in a case of "a 47-year-old, previously healthy Japanese tourist" who had severe neuropsychiatric side-effects from the drug that
The first randomized, controlled trial on a mixed population was performed in 2001. Prophylaxis with mefloquine was compared to prophylaxis with atovaquone-proguanil. Roughly 67% of participants in the mefloquine arm reported greater than or equal to one adverse event, versus 71% in the atovaquone-proguanil arm. In the mefloquine arm, 5% of the users reported severe events requiring medical attention, versus 1.2% in the atovaquone-proguanil arm.
In August 2009, Roche stopped marketing Lariam in the United States.
Retired soldier Johnny Mercer, who was later appointed Minister for Veterans Affairs by Boris Johnson, told in 2015 that he had received "a letter about once or twice a week" about ill-effects from the drug. In July 2016, Roche took this brand off the market in Ireland. | 4 | Stereochemistry |
After the electron has left Photosystem II it is transferred to a cytochrome b6f complex and then to plastocyanin, a blue copper protein and electron carrier. The plastocyanin complex carries the electron that will neutralize the pair in the next reaction center, Photosystem I.
As with Photosystem II and the bacterial reaction center, a pair of chlorophyll a molecules initiates photoinduced charge separation. This pair is referred to as P700, where 700 is a reference to the wavelength at which the chlorophyll molecules absorb light maximally. The P700 lies in the center of the protein. Once photoinduced charge separation has been initiated, the electron travels down a pathway through a chlorophyll α molecule situated directly above the P700, through a quinone molecule situated directly above that, through three 4Fe-4S clusters, and finally to an interchangeable ferredoxin complex. Ferredoxin is a soluble protein containing a 2Fe-2S cluster coordinated by four cysteine residues. The positive charge on the high-energy P700 is neutralized by the transfer of an electron from plastocyanin, which receives energy eventually used to convert QH back to Q. Thus the overall reaction catalyzed by Photosystem I is:
:Pc(Cu) + Fd + hν → Pc(Cu) + Fd
The cooperation between Photosystems I and II creates an electron and proton flow from HO to NADP, producing NADPH needed for glucose synthesis. This pathway is called the Z-scheme because the redox diagram from HO to NADP via P680 and P700 resembles the letter Z. | 5 | Photochemistry |
Cell-free production of proteins is performed in vitro using purified RNA polymerase, ribosomes, tRNA and ribonucleotides. These reagents may be produced by extraction from cells or from a cell-based expression system. Due to the low expression levels and high cost of cell-free systems, cell-based systems are more widely used. | 1 | Biochemistry |
The first nucleotide to be expanded was the purine adenine. Nelson J. Leonard and colleagues synthesized this original x-nucleotide, which was referred to as "expanded adenine". xA was used as a probe in the investigation of active sites of ATP-dependent enzymes, more specifically what modifications the substrate could take while still being functional. Almost two decades later, the other three bases were successfully expanded and later integrated into a double helix by Eric T. Kool and colleagues. Their goal was to create a synthetic genetic system which mimics and surpasses the functions of the natural genetic system, and to broaden the applications of DNA both in living cells and in experimental biochemistry. Once the expanded base set was created, the goal shifted to identifying or developing faithful replication enzymes and further optimizing the expanded DNA alphabet. | 1 | Biochemistry |
The primary translation product of SFRP1 contains an atypical signaling sequence, where a chain of 15 hydrophilic amino acids precede the hydrophobic domain. Looking at 7 tumors without the truncating mutation, the retained SFRP1 allele contained an in-frame three-base insertion after nucleotide 37. This is thought to lead to an extra alanine in the protein after codon 13. However, no significant association was found between the development of colorectal cancer and the presence of the 3-bp insertion. | 1 | Biochemistry |
Gene expression and RNA quantification studies have benefited from the increased precision and absolute quantification of dPCR. RNA quantification can be accomplished via RT-PCR, wherein RNA is reverse-transcribed into cDNA in the partitioned reaction itself, and the number of RNA molecules originating from each transcript (or allelic transcript) is quantified via dPCR.
One can often achieve greater sensitivity and precision by using dPCR rather than qPCR to quantify RNA molecules in part because it does not require use of a standard curve for quantification. dPCR is also more resilient to PCR inhibitors for the quantification of RNA than qPCR.
dPCR can detect and quantify more individual target species per detection channel than qPCR by virtue of being able to distinguish targets based on their differential fluorescence amplitude or by the use of distinctive color combinations for their detection. As an example of this, a 2-channel dPCR system has been used to detect in a single well the expression of four different splice variants of human telomerase reverse transcriptase, a protein that is more active in most tumor cells than in healthy cells. | 1 | Biochemistry |
E. coli - Ecotin - EIF-W2 protein domain - electrophoresis - electroporation - ELFV dehydrogenase - Ellis–van Creveld syndrome - end labeling - endonuclease - enhancer - enterobacter ribonuclease - enzyme - epitope - ethidium bromide - evolutionary clock - evolutionary footprinting - exon - exonuclease - exosome complex - expression - expression clone - expression vector - extended ELM2 domain - | 1 | Biochemistry |
Eigen and Rigler first introduced the fluorescence cross-correlation spectroscopy (FCCS) method in 1994. Later, in 1997, Schwille experimentally implemented this method. | 7 | Physical Chemistry |
The daily light integral (DLI) is the number of photosynthetically active photons (photons in the PAR range) accumulated in a square meter over the course of a day. It is a function of photosynthetic light intensity and duration (day length) and is usually expressed as moles of light (mol photons) per square meter (m) per day (d), or: mol·m·d.
DLI is usually calculated by measuring the photosynthetic photon flux density (PPFD) in μmol·m·s (number of photons in the PAR range received in a square meter per second) as it changes throughout the day, and then using that to calculate total estimated number of photons in the PAR range received over a 24-hour period for a specific area. In other words, DLI describes the sum of the per second PPFD measurements during a 24-hour period.
If the photosynthetic light intensity stays the same for the entire 24-hour period, DLI in mol m d can be estimated from the instantaneous PPFD from the following equation: μmol m s multiplied by 86,400 (number of seconds in a day) and divided by 10 (number of μmol in a mol). Thus, 1 μmol m s = 0.0864 mol m d if light intensity stays the same for the entire 24 hour period. | 5 | Photochemistry |
Textbooks in physical chemistry generally give two derivations of the title equation. One is the conventional derivation that goes back to Van der Waals, a mechanical equation of state that cannot be used to specify all thermodynamic functions; the other is a statistical mechanics derivation that makes explicit the intermolecular potential neglected in the first derivation. A particular advantage of the statistical mechanical derivation is that it yields the partition function for the system, and allows all thermodynamic functions to be specified (including the mechanical equation of state). | 7 | Physical Chemistry |
The Ramsauer–Townsend effect, also sometimes called the Ramsauer effect or the Townsend effect, is a physical phenomenon involving the scattering of low-energy electrons by atoms of a noble gas. This effect is a result of quantum mechanics. The effect is named for Carl Ramsauer and John Sealy Townsend, who each independently studied the collisions between atoms and low-energy electrons in 1921. | 7 | Physical Chemistry |
Farther from the sun, the temperature was low enough that volatile elements would precipitate as ices. The two are separated by a snow line controlled by the temperature distribution around the Sun.
Formed farthest from the sun, the carbonaceous chondrites have the highest K/U ratios. Ordinary chondrites which form closer in are only about 10% depleted in K relative to U.
The fine-grained matrix which fills spaces between the chondrules, however, appears to have formed at rather different temperatures in the various classes of chondrites. For this reason the volatile abundances of different classes of chondrites can vary. One particularly important class is the carbonaceous chondrites because of their high carbon content. In these meteorites, chondrules coexist with minerals that are only stable below 100 °C, so they contain materials that formed in both high- and low-temperature environments and were only later collected together. Further evidence for the primordial attributes of carbonaceous chondrites comes from the fact that they have compositions very similar to the nonvolatile element composition of the sun. | 9 | Geochemistry |
Isotopic ratio relative to each component in the system, each with its isotopic expression, with respect to the concentration of its most abundant isotopologue | 7 | Physical Chemistry |
The primary limitations of TMM cycloadditions employing diazenes are competitive MCP and dimer formation. To circumvent these problems, either very high concentrations of alkene must be used or the cycloaddition must be intramolecular. Stereoselectivity and site selectivity may also be higher in intramolecular variants of cycloadditions starting from diazenes.
Usually, unless a cyclic pi system is involved TMM cycloadditions exhibit 2π periselectivity and do not react with larger pi systems. Polar MCPs, for example, react only with the 2,3 double bond of polyunsaturated esters.
Transition-metal catalyzed reactions have the potential to quickly generate an interesting functionality. Propellanes have been generated from intramolecular cyclization under palladium catalysis.
Silylated allylic acetates may be employed for intra- or intermolecular applications. Carbonyl compounds may be used as the 2π component under the appropriate conditions. For instance, in the presence of an indium co-catalyst, the reactive 2π component of the cycloaddition below switches from the C-C to the C-O double bond.
Polarized trimethylenemethanes generated from polar MCPs are also useful substrates for (3+2) reactions with polar double bonds as the 2π component. Orthoester products are generally favored over ketene acetals. | 0 | Organic Chemistry |
A number of other unexpected applications have been identified in the last few years, mostly in multiferroic bismuth ferrite, that do not seem to be directly related to the coupled magnetism and ferroelectricity. These include a photovoltaic effect, photocatalysis, and gas sensing behaviour. It is likely that the combination of ferroelectric polarisation, with the small band gap composed partially of transition-metal d states are responsible for these favourable properties.
Multiferroic films with appropriate band gap structure into solar cells was developed which results in high energy conversion efficiency due to efficient ferroelectric polarization driven carrier separation and overband spacing generation photo-voltage. Various films have been researched, and there is also a new approach to effectively adjust the band gap of the double perovskite multilayer oxide by engineering the cation order for Bi2FeCrO6. | 7 | Physical Chemistry |
The operon must respond to changes in the metabolic state of the cell. It is subject to growth rate dependent control, stringent control (control during the various stresses the cell is exposed to) and other forms of control. Hence it stops biosynthesis if guanine can be obtained from the external medium, increases its expression if nucleotides are needed (for example during DNA replication) and balances the production of GMP with respect to AMP and the pyrimidine nucleotides.
The branch point at IMP mentioned above is tightly controlled rigid node so as to have a balanced production of AMP and GMP. The gua operon is repressed by GMP and is induced by AMP. Similarly AMP synthesis is repressed by AMP itself while it is activated by GMP. This dual control ensures that there is a balance of flux between AMP and GMP and the flux partition remains relatively constant even in the face of perturbations. Some mechanisms by which this control is achieved are discussed below. | 1 | Biochemistry |
There are several parameters to consider for optimization of binding-induced electrochemical signal gain. The aptamer probe packing density, the nature of the self-assembling monolayer, and the ACV frequency are factors that affect detecting and measuring of signal. Two main factors are considered when fabricating the packing density on the probe surface. The concentration of aptamer and the surface chemistry of the self-assembling monolayer (SAM) enable variations of desired probe packing density. | 7 | Physical Chemistry |
Periphyton communities are used in aquaculture food production systems for the removal of solid and dissolved pollutants. Their performance in filtration is established and their application as aquacultural feed is being researched.
Periphyton serves as an indicator of water quality because:
:*It has a naturally high number of species.
:*It has a fast response to changes.
:*It is easy to sample.
:*It is known for tolerance/sensitivity to change. | 2 | Environmental Chemistry |
Electric sonic amplitude was experimentally discovered by Cannon with co-authors in early 1980s. It is also widely used for characterizing ζ-potential in dispersions and emulsions. There is review of this effect theory, experimental verification and multiple applications published by Hunter. | 7 | Physical Chemistry |
The Biuret reagent is made of sodium hydroxide (NaOH) and hydrated copper(II) sulfate, together with potassium sodium tartrate, the latter of which is added to chelate and thus stabilize the cupric ions. The reaction of the cupric ions with the nitrogen atoms involved in peptide bonds leads to the displacement of the peptide hydrogen atoms under the alkaline conditions. A tri- or tetra-dentate chelation with the peptide nitrogen produces the characteristic color. This is found with dipeptides.
The reagent is commonly used in the biuret protein assay, a colorimetric test used to determine protein concentration by UV/VIS spectroscopy at wavelength 540 nm. | 3 | Analytical Chemistry |
Solder is a metallic material that is used to connect metal workpieces. The choice of specific solder alloys depends on their melting point, chemical reactivity, mechanical properties, toxicity, and other properties. Hence a wide range of solder alloys exist, and only major ones are listed below. Since early 2000s the use of lead in solder alloys is discouraged by several governmental guidelines in the European Union, Japan and other countries, such as Restriction of Hazardous Substances Directive and Waste Electrical and Electronic Equipment Directive. | 8 | Metallurgy |
The current interest in nontraditional methods for the generation of hydrogen has prompted a revisit of radiolytic splitting of water, where the interaction of various types of ionizing radiation (α, β, and γ) with water produces molecular hydrogen. This reevaluation was further prompted by the current availability of large amounts of radiation sources contained in the fuel discharged from nuclear reactors. This spent fuel is usually stored in water pools, awaiting permanent disposal or reprocessing. The yield of hydrogen resulting from the irradiation of water with β and γ radiation is low (G-values = <1 molecule per 100 electronvolts of absorbed energy) but this is largely due to the rapid reassociation of the species arising during the initial radiolysis. If impurities are present or if physical conditions are created that prevent the establishment of a chemical equilibrium, the net production of hydrogen can be greatly enhanced.
Another approach uses radioactive waste as an energy source for regeneration of spent fuel by converting sodium borate into sodium borohydride. By applying the proper combination of controls, stable borohydride compounds may be produced and used as hydrogen fuel storage medium.
A study conducted in 1976 found an order-of-magnitude estimate can be made of the average hydrogen production rate that could be obtained by utilizing the energy liberated via radioactive decay. Based on the primary molecular hydrogen yield of 0.45 molecules/100 eV, it would be possible to obtain 10 tons per day. Hydrogen production rates in this range are not insignificant, but are small compared with the average daily usage (1972) of hydrogen in the U.S. of about 2 x 10^4 tons. Addition of a hydrogen-atom donor could increase this about a factor of six. It was shown that the addition of a hydrogen-atom donor such as formic acid enhances the G value for hydrogen to about 2.4 molecules per 100 eV absorbed. The same study concluded that designing such a facility would likely be too unsafe to be feasible. | 5 | Photochemistry |
To explain each part of the terminology, "scattering" refers to the deflection of leptons' (electron, muon, etc.) off of hadrons. Measuring the angles of deflection gives information about the nature of the process. "Inelastic" means that the target absorbs some kinetic energy. In fact, at the very high energies of leptons used, the target is "shattered" and emits many new particles. These particles are hadrons and, to oversimplify greatly, the process is interpreted as a constituent quark of the target being "knocked out" of the target hadron, and due to quark confinement, the quarks are not actually observed but instead produce the observable particles by hadronization. "Deep" refers to the high energy of the lepton, which gives it a very short wavelength and hence the ability to probe distances that are small compared with the size of the target hadron, so it can probe "deep inside" the hadron. Also, note that in the perturbative approximation it is a high-energy virtual photon emitted from the lepton and absorbed by the target hadron which transfers energy to one of its constituent quarks, as in the adjacent diagram.
Povh and Rosina pointed out that the term “deep inelastic scattering against nucleons” was coined when the quark substructure of nucleons was unknown. They prefer the term “quasielastic lepton-quark scattering”. | 7 | Physical Chemistry |
Cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase-1 (mPGES-1) structures were studied using both photo-methionine (photo-activatable) and bifunctional cross linkers. Photo-methionine used in COX-2 had shown just as the bifunctional cross-linker that there was a dimeric structure which this was consistent with the crystal structure of the enzyme. In mPGES-1, the human cells (A549) had been treated with disuccinimidyl suberate (chemical cross-linker) had yielded a dimer of 33kDa and a trimer of 45kDa while it was treated with photo-methionine had yielded a dimer of the same molecular weight (33kDa) and two putative trimers (50kDa and 55kDa). Once a mPGES-1 inhibitor (MF63) was introduced; this had inhibited the formation of the 50kDa and 55kDa complexes. The dimer and trimer yielded by the chemical cross-linker was not affected by the inhibitor. Yet, photo-methionine nor disuccinimidyl suberate had not shown any protein-protein interactions between COX-2 and mPGES-1 and this could be due to various reasons. For photo-methionine; one could be due to the low incorporation at this time as it was 0.7%. So, for mPGES-1; this has 152 amino acids so only one photo-methionine would be incorporated per monomer. That also means not one specific methionine would be replaced so that results in a heterogeneous population of mPGES-1 resulting in different cross-linking. Even though it did not show any protein-protein interactions, it could be used to detect inhibitor-induced protein conformational changes in the cell membranes on top of determining oligomeric structures. | 5 | Photochemistry |
A chirality center (chiral center) is a type of stereocenter. A chirality center is defined as an atom holding a set of four different ligands (atoms or groups of atoms) in a spatial arrangement which is non-superposable on its mirror image. Chirality centers must be sp hybridized, meaning that a chirality center can only have single bonds. In organic chemistry, a chirality center usually refers to a carbon, phosphorus, or sulfur atom, though it is also possible for other atoms to be chirality centers, especially in areas of organometallic and inorganic chemistry.
The concept of a chirality center generalizes the concept of an asymmetric carbon atom (a carbon atom bonded to four different entities) to a broader definition of any atom with four different attachment groups in which an interchanging of any two attachment groups gives rise to an enantiomer. | 4 | Stereochemistry |
*G are involved in Rho family GTPase signaling (see Rho family of GTPases). This is through the RhoGEF superfamily involving the RhoGEF domain of the proteins' structures). These are involved in control of cell cytoskeleton remodeling, and thus in regulating cell migration. | 1 | Biochemistry |
Once the initiation complex is open, the first ribonucleotide is brought into the active site to initiate the polymerization reaction in the absence of a primer. This generates a nascent RNA chain that forms a hetero-duplex with the template DNA strand. However, before entering the elongation phase, polymerase may terminate prematurely and release a short, truncated transcript. This process is called abortive initiation. Many cycles of abortive initiation may occur before the transcript grows to sufficient length to promote polymerase escape from the promoter. Throughout abortive initiation cycles, RNA polymerase remains bound to the promoter and pulls downstream DNA into its catalytic cleft in a scrunching-kind of motion. | 1 | Biochemistry |
The BCA assay is largely incompatible with reducing agents and metal chelators, although trace quantities may be tolerated. The BCA assay also reportedly responds to common membrane lipids and phospholipids. | 1 | Biochemistry |
Monochromators are often calibrated in units of wavelength. Uniform rotation of a grating produces a sinusoidal change in wavelength, which is approximately linear for small grating angles, so such an instrument is easy to build. Many of the underlying physical phenomena being studied are linear in energy though, and since wavelength and photon energy have a reciprocal relationship, spectral patterns that are simple and predictable when plotted as a function of energy are distorted when plotted as a function of wavelength. Some monochromators are calibrated in units of reciprocal centimeters or some other energy units, but the scale may not be linear. | 7 | Physical Chemistry |
Cyanate esters can be cured and postcured by heating, either alone at elevated temperatures or at lower temperatures in presence of a suitable catalyst. The most common catalysts are transition metal complexes of cobalt, copper, manganese and zinc. The result is a thermoset material with a very high glass-transition temperature (T) of up to 400 °C, and a very low dielectric constant, providing excellent long term thermal stability at elevated end use temperatures, very good fire, smoke and toxicity performance and specific suitability for printed circuit boards installed in critical electrical devices. This is also due to its low moisture uptake.
This property, together with a higher toughness compared to epoxies, also makes it a valuable material in aerospace applications. For example, the Lynx Mark II spaceplane is primarily made of carbon/cyanate ester.
The chemistry of the cure reaction is a trimerization of three CN groups to a triazine ring. When the monomer contains two cyanate groups the resulting structure is a 3D polymer network. Thermoset polymer matrix properties can be fine tuned by the choice of substituents in the bisphenolic compound. Bisphenol A and novolac based cyanate esters are the major products; bisphenol F and bisphenol E are also used. The aromatic ring of the bisphenol can be substituted with an allylic group for improved toughness of the material. Cyanate esters can also be mixed with bismaleimides to form BT-resins or with epoxy resins to optimize the end use properties. | 0 | Organic Chemistry |
Reaction centers are present in all green plants, algae, and many bacteria. A variety in light-harvesting complexes exist across the photosynthetic species. Green plants and algae have two different types of reaction centers that are part of larger supercomplexes known as P700 in Photosystem I and P680 in Photosystem II. The structures of these supercomplexes are large, involving multiple light-harvesting complexes. The reaction center found in Rhodopseudomonas bacteria is currently best understood, since it was the first reaction center of known structure and has fewer polypeptide chains than the examples in green plants.
A reaction center is laid out in such a way that it captures the energy of a photon using pigment molecules and turns it into a usable form. Once the light energy has been absorbed directly by the pigment molecules, or passed to them by resonance transfer from a surrounding light-harvesting complex, they release electrons into an electron transport chain and pass energy to a hydrogen donor such as HO to extract electrons and protons from it. In green plants, the electron transport chain has many electron acceptors including pheophytin, quinone, plastoquinone, cytochrome bf, and ferredoxin, which result finally in the reduced molecule NADPH, while the energy used to split water results in the release of oxygen. The passage of the electron through the electron transport chain also results in the pumping of protons (hydrogen ions) from the chloroplast's stroma and into the lumen, resulting in a proton gradient across the thylakoid membrane that can be used to synthesize ATP using the ATP synthase molecule. Both the ATP and NADPH are used in the Calvin cycle to fix carbon dioxide into triose sugars. | 5 | Photochemistry |
In physics, optical depth or optical thickness is the natural logarithm of the ratio of incident to transmitted radiant power through a material.
Thus, the larger the optical depth, the smaller the amount of transmitted radiant power through the material.
Spectral optical depth or spectral optical thickness is the natural logarithm of the ratio of incident to transmitted spectral radiant power through a material. Optical depth is dimensionless, and in particular is not a length, though it is a monotonically increasing function of optical path length, and approaches zero as the path length approaches zero. The use of the term "optical density" for optical depth is discouraged.
In chemistry, a closely related quantity called "absorbance" or "decadic absorbance" is used instead of optical depth: the common logarithm of the ratio of incident to transmitted radiant power through a material. It is the optical depth divided by , because of the different logarithm bases used. | 7 | Physical Chemistry |
Some catalysts operate by "outer sphere mechanisms" such that the substrate never bonds directly to the metal but rather interacts with its ligands, which is often a metal hydride and a protic hydrogen on a ligand. As such, in most cases dihydrogen is split heterolytically, with the metal acting as a Lewis acid and either an external or internal base "deprotonating" the hydride.
For an example of this mechanism we can consider the BINAP-Ru-diamine system. The dihalide form of the catalyst is converted to the catalysts by reaction of H in the presence of base:
:RuCl(BINAP)(diamine) + 2 KOBu-t + 2 H → RuH(BINAP)(diamine) + 2 KCl + 2 HOBu-t
The resulting catalysts have three kinds of ligands:
*hydrides, which transfer to the unsaturated substrate
*diamines, which interact with substrate and with base activator by the second coordination sphere
*diphosphine, which confers asymmetry.
The "Noyori-class" of catalysts are often referred to as bifunctional catalysts to emphasize the fact that both the metal and the (amine) ligand are functional.
In the hydrogenation of C=O containing substates, the mechanism was long assumed to operate by a six membered pericyclic transition state/intermediate whereby the hydrido ruthenium hydride center (HRu-NH) interacts with the carbonyl substrate RC=O. More recent DFT and experimental studies have shown that this model is largely incorrect. Instead, the amine backbone interacts strongly with the base activator, which often is used in large excess. However in both cases, the substate does not bond directly with the metal centre, thus making it a great example of an outer sphere mechanism. | 0 | Organic Chemistry |
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