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From 2008 Kuipers is supervisor, coach and coordinator of the iGEM student team Groningen. iGEM is a worldwide competition in the field of synthetic biology between teams of students from all over the world. The team from Groningen won in the annual in Boston (United States) organized international competition several gold medals (2008 to 2016). In 2012, when the team from Groningen became world champion, the research concerned a study of an alternative method to determine whether food is spoiled: the Food warden . This method makes use of genetic engineered bacteria responsive to the volatiles of the decomposing meat. A pigment makes the decomposition visible. | 0 | Organic Chemistry |
Sit was born in 1941 and attended Tanjong Katong Girls' School. She studied science at the National University of Singapore and obtained first-class honours when she graduated top of her class. She obtained her PhD in biochemistry from McGill University. | 1 | Biochemistry |
There has been conflicting ideas to the purpose of the 800 copper plates. Although they have been assumed to be scales of armor from an Egyptian army unit, as proposed by archaeologist Shmuel Yeivin, recent reevaluations have confuted this claim. Archaeologist William A. Ward proposed that the scales were means of barter or a reserve supply of metal from the Syro-Palestinian area. Ward arrived at this conclusion through several pieces of evidence: the scales were not attached to any jacket, body armor was generally not used by the Egyptians until the New Kingdom, copper was still very rare, and the plates were too thin for body armor. | 8 | Metallurgy |
Ferritin concentrations increase drastically in the presence of an infection or cancer. Endotoxins are an up-regulator of the gene coding for ferritin, thus causing the concentration of ferritin to rise. By contrast, organisms such as Pseudomonas, although possessing endotoxin, cause plasma ferritin levels to drop significantly within the first 48 hours of infection. Thus, the iron stores of the infected body are denied to the infective agent, impeding its metabolism. | 1 | Biochemistry |
TiAl has the lowest density of 3.4 g/cm, the highest micro hardness of 465–670 kg/mm and the best oxidation resistance even at 1 000 °C. However, the applications of TiAl in the engineering and aerospace fields are limited by its poor ductility. In addition, the loss of ductility at ambient temperature is usually accompanied by a change of fracture mode from ductile transgranular to brittle intergranular or to brittle cleavage. Despite the fact that a lot of toughening strategies have been developed to improve their toughness, machining quality is still a difficult problem to tackle. Near-net shape manufacturing technology is considered as one of the best choices for preparing such materials. {date=July 2022} | 8 | Metallurgy |
*Aza-Cope rearrangement
*Beckmann rearrangement
*Duff reaction
*Mannich reaction
*Pictet-Spengler reaction
*Stephen aldehyde synthesis
*Stork enamine alkylation
*Vilsmeier-Haack reaction and Vilsmeier reagent | 0 | Organic Chemistry |
* Group 14 anions functionalized with organic groups: [GeMes], [Ge(CHCHCHNH)], [(CHCH)GeGe(CHCH)], [Ge(CHCHCHCH)Ge], [(CHCH)Ge(CH)Ge(CHCH)];
* Silated anions: GeHypTl, [GeHyp];
* Intermetalloid deltahedral clusters: [Co@Sn], [Ni@Pb], [Au@Pb], [Mn@Pb], [Rh@Sn];
* Exo coordinated transition metal complexes: [(ŋ-Sn)Hg(ŋ-Sn)], [GeNi(CO)], [SnTiCp], [(tol)NbSnNb(tol)];
* [NiSb] (NiSb ring inside Sb bowl). | 7 | Physical Chemistry |
Surface diffusion is a critically important concept in heterogeneous catalysis, as reaction rates are often dictated by the ability of reactants to "find" each other at a catalyst surface. With increased temperature adsorbed molecules, molecular fragments, atoms, and clusters tend to have much greater mobility (see equation 1). However, with increased temperature the lifetime of adsorption decreases as the factor kT becomes large enough for the adsorbed species to overcome the barrier to desorption, Q (see figure 2). Reaction thermodynamics aside because of the interplay between increased rates of diffusion and decreased lifetime of adsorption, increased temperature may in some cases decrease the overall rate of the reaction. | 7 | Physical Chemistry |
Nitriles are susceptible to hydrogenation over diverse metal catalysts. The reaction can afford either the primary amine () or the tertiary amine (), depending on conditions. In conventional organic reductions, nitrile is reduced by treatment with lithium aluminium hydride to the amine. Reduction to the imine followed by hydrolysis to the aldehyde takes place in the Stephen aldehyde synthesis, which uses stannous chloride in acid. | 0 | Organic Chemistry |
Modafinil was used by the French Foreign Legion, U.S. Air Force, and U.S. Marine infantry during the Gulf War to enhance "operational tempo" (a term that denotes the speed and intensity at which military operations or activities are executed), aiming to optimize the overall performance and efficiency of the unit.
Armed forces in various countries, including the United States, the United Kingdom, India, and France, have considered modafinil as an alternative to traditional amphetamines for managing sleep deprivation in combat or extended missions. The US military approved modafinil for specific Air Force missions, replacing amphetamines for fatigue management. The use of modafinil in military contexts without sleep deprivation is not recommended due to inconclusive evidence on its cognitive enhancement benefits and potential risks of adverse effects.
Modafinil is also available to astronauts aboard the International Space Station for the management of fatigue caused by circadian dyssynchrony in orbit. | 4 | Stereochemistry |
The alternative oxidase is an integral monotopic membrane protein that is tightly bound to the inner mitochondrial membrane from matrix side The enzyme has been predicted to contain a coupled diiron center on the basis of a conserved sequence motif consisting of the proposed iron ligands, four glutamate and two histidine amino acid residues. The electron spin resonance study of Arabidopsis thaliana alternative oxidase AOX1a showed that the enzyme contains a hydroxo-bridged mixed-valent Fe(II)/Fe(III) binuclear iron center. A catalytic cycle has been proposed that involves this di-iron center and at least one transient protein-derived free radical, which is probably formed on a tyrosine residue. | 1 | Biochemistry |
The following reactions describe the methanation of carbon monoxide and carbon dioxide respectively:
: -206 kJ/mol
: -164 kJ/mol
The methanation reactions are classified as exothermic and their energy of formations are listed.
There is disagreement on whether the CO methanation occurs by first associatively adsorbing an adatom hydrogen and forming oxygen intermediates before hydrogenation or dissociating and forming a carbonyl before being hydrogenated. CO is believed to be methanated through a dissociative mechanism where the carbon-oxygen bond is broken before hydrogenation with an associative mechanism only being observed at high H concentrations.
Methanation reaction over different carried metal catalysts including Ni, Ru and Rh has been widely investigated for the production of CH from syngas and other power to gas initiatives. Nickel is the most widely used catalyst due to its high selectivity and low cost. | 0 | Organic Chemistry |
During the submerged arc welding process, not all flux turns into slag. Depending on the welding process, 50% to 90% of the flux can be reused. | 8 | Metallurgy |
In a dynamic osmometer flow of solvent is measured and a counteracting pressure is created to stop the flow. Flow rate of the solvent is measured by the movement of an air bubble in a capillary tube of the solvent. The pressure of the solvent compartment is directly changed by raising or lowering a reservoir of solvent connected to the solvent compartment. The pressure difference between the two compartments is the osmotic pressure. This can be calculate by measuring the change in height or measured directly with a flexible diaphragm. Since the pressure is directly changed, an accurate measurement of osmotic pressure can be achieved in 10 – 30 minutes. | 7 | Physical Chemistry |
The strength, , of dislocation is dependent on the shear modulus, G, the magnitude of the Burgers vector, b, and the dislocation density, :
where is the intrinsic strength of the material with low dislocation density and is a correction factor specific to the material.
As shown in Figure 1 and the equation above, work hardening has a half root dependency on the number of dislocations. The material exhibits high strength if there are either high levels of dislocations (greater than 10 dislocations per m) or no dislocations. A moderate number of dislocations (between 10 and 10 dislocations per m) typically results in low strength. | 8 | Metallurgy |
Arenediazonium cations reduced by hypophosphorous acid, ethanol, sodium stannite or alkaline sodium thiosulphate gives benzene:
An alternative way suggested by Baeyer & Pfitzinger is to replace the diazo group with H is: first to convert it into hydrazine by treating with then to oxidize it into hydrocarbon by boiling with cupric sulphate solution. | 0 | Organic Chemistry |
Dicarbollide complexes have been investigated for many years, but commercial applications are rare. The bis(dicarbollide) has been used as a precipitant for removal of from radiowastes.
The medical applications of carboranes have been explored. C-functionalized carboranes represent a source of boron for boron neutron capture therapy.
The compound is a superacid, forming an isolable salt with protonated benzene cation, (benzenium cation). The formula of that salt is . The superacid protonates fullerene, . | 7 | Physical Chemistry |
Electron diffraction is a generic term for phenomena associated with changes in the direction of electron beams due to elastic interactions with atoms. It occurs due to elastic scattering, when there is no change in the energy of the electrons. The negatively charged electrons are scattered due to Coulomb forces when they interact with both the positively charged atomic core and the negatively charged electrons around the atoms. The resulting map of the directions of the electrons far from the sample is called a diffraction pattern, see for instance Figure 1. Beyond patterns showing the directions of electrons, electron diffraction also plays a major role in the contrast of images in electron microscopes.
This article provides an overview of electron diffraction and electron diffraction patterns, collective referred to by the generic name electron diffraction. This includes aspects of how in a general way electrons can act as waves, and diffract and interact with matter. It also involves the extensive history behind modern electron diffraction, how the combination of developments in the 19th century in understanding and controlling electrons in vacuum and the early 20th century developments with electron waves were combined with early instruments, giving birth to electron microscopy and diffraction in 1920–1935. While this was the birth, there have been a large number of further developments since then.
There are many types and techniques of electron diffraction. The most common approach is where the electrons transmit through a thin sample, from 1 nm to 100 nm (10 atoms to 1000 thick), where the results depending upon how the atoms are arranged in the material, for instance a single crystal, many crystals or different types of solids. Other cases such as larger repeats, no periodicity or disorder have their own characteristic patterns. There are many different ways of collecting diffraction information, from parallel illumination to a converging beam of electrons or where the beam is rotated or scanned across the sample which produce information that is often easier to interpret. There are also many other types of instruments. For instance, in a scanning electron microscope (SEM), electron backscatter diffraction can be used to determine crystal orientation across the sample. Electron diffraction patterns can also be used to characterize molecules using gas electron diffraction, liquids, surfaces using lower energy electrons, a technique called LEED, and by reflecting electrons off surfaces, a technique called RHEED.
There are also many levels of analysis of electron diffraction, including:
# The simplest approximation using the de Broglie wavelength for electrons, where only the geometry is considered and often Bragg's law is invoked. This approach only considers the electrons far from the sample, a far-field or Fraunhofer approach.
# The first level of more accuracy where it is approximated that the electrons are only scattered once, which is called kinematical diffraction and is also a far-field or Fraunhofer approach.
# More complete and accurate explanations where multiple scattering is included, what is called dynamical diffraction (e.g. refs). These involve more general analyses using relativistically corrected Schrödinger equation methods, and track the electrons through the sample, being accurate both near and far from the sample (both Fresnel and Fraunhofer diffraction).
Electron diffraction is similar to x-ray and neutron diffraction. However, unlike x-ray and neutron diffraction where the simplest approximations are quite accurate, with electron diffraction this is not the case. Simple models give the geometry of the intensities in a diffraction pattern, but dynamical diffraction approaches are needed for accurate intensities and the positions of diffraction spots. | 7 | Physical Chemistry |
Regulatory sequences for the insulin gene are:
* A5
* Z
* negative regulatory element (NRE)
* C2
* E2
* A3
* cAMP response element
* A2
* CAAT enhancer binding (CEB)
* C1
* E1
* G1 | 1 | Biochemistry |
The second part of the B ring synthesis (Scheme 5) was concerned with correct chemistry for the newly formed ethylene bridge connecting the A and C rings. After Scheme 4, this bridge contained an exocyclic methylene group, but in the ultimate taxol molecule this bridge is an α-acylketone. The required conversion was accomplished in the next 10 steps.
The tert-butylsilyl protecting group in diene 39 was not compatible in later reactions and was replaced by a triethylsilyl. Epoxidation of diene 40 with meta-chloroperoxybenzoic acid gave the oxirane ring. This served solely as a protecting group in preparation for modifications of the exocyclic alkene. In the next two steps, the benzyl protecting group in compound 41 was replaced by an acetyl group. Carbonate ester 43 was opened by reaction with phenyllithium to give alcohol 44. The cleavage of the exocyclic double bond was difficult and accomplished only with forcing conditions (19 equivalents of osmium tetroxide, 105 °C, 24 hours) by the putative osmate ester (45). Subsequent oxidative cleavage with lead tetraacetate gave ketone 46. The epoxide protecting group was removed with samarium (II) iodide to give α-ß-unsaturated ketone 47. The enolate was formed by the reaction of ketone 47 with potassium tert-butoxide, and subsequent reaction with phenylseleninic anhydride followed by acylation gave α-acylketone 49. | 0 | Organic Chemistry |
Small amounts of yttrium (0.1 to 0.2%) have been used to reduce the grain sizes of chromium, molybdenum, titanium, and zirconium. Yttrium is used to increase the strength of aluminium and magnesium alloys. The addition of yttrium to alloys generally improves workability, adds resistance to high-temperature recrystallization, and significantly enhances resistance to high-temperature oxidation (see graphite nodule discussion below).
Yttrium can be used to deoxidize vanadium and other non-ferrous metals. Yttria stabilizes the cubic form of zirconia in jewelry.
Yttrium has been studied as a nodulizer in ductile cast iron, forming the graphite into compact nodules instead of flakes to increase ductility and fatigue resistance. Having a high melting point, yttrium oxide is used in some ceramic and glass to impart shock resistance and low thermal expansion properties. Those same properties make such glass useful in camera lenses. | 8 | Metallurgy |
Nickel aluminide refers to either of two widely used intermetallic compounds, NiAl or NiAl, but the term is sometimes used to refer to any nickel–aluminium alloy. These alloys are widely used because of their high strength even at high temperature, low density, corrosion resistance, and ease of production. NiAl is of specific interest as a precipitate in nickel-based superalloys, where it is called the γ' (gamma prime) phase. It gives these alloys high strength and creep resistance up to 0.7–0.8 of its melting temperature. Meanwhile, NiAl displays excellent properties such as lower density and higher melting temperature than those of NiAl, and good thermal conductivity and oxidation resistance. These properties make it attractive for special high-temperature applications like coatings on blades in gas turbines and jet engines. However, both these alloys have the disadvantage of being quite brittle at room temperature, with NiAl remaining brittle at high temperatures as well. To address this problem, has been shown that NiAl can be made ductile when manufactured in single-crystal form rather than in polycrystalline form. | 8 | Metallurgy |
* Pacey, A. J. & Fisher, S. J. (1967) "Daniel Bernoulli and the vis viva of compressed air", The British Journal for the History of Science 3 (4), p. 388–392,
* British Transport Commission (1957) Handbook for Railway Steam Locomotive Enginemen, London : B.T.C., p. 81, (facsimile copy publ. Ian Allan (1977), ) | 7 | Physical Chemistry |
Several equations to predict the number of calories required by humans have been published from the early 20th–21st centuries. In each of the formulas below:
: P is total heat production at complete rest,
: m is mass (kg),
: h is height (cm),
: a is age (years).
;The original Harris–Benedict equation
Historically, the most notable formula was the Harris–Benedict equation, which was published in 1919:
: for men,
: for women,
The difference in BMR for men and women is mainly due to differences in body mass. For example, a 55-year-old woman weighing and tall would have a BMR of per day.
;The revised Harris–Benedict equation
In 1984, the original Harris–Benedict equations were revised using new data. In comparisons with actual expenditure, the revised equations were found to be more accurate:
: for men,
: for women,
It was the best prediction equation until 1990, when Mifflin et al. introduced the equation:
;The Mifflin St Jeor equation
where s is +5 for males and −161 for females.
According to this formula, the woman in the example above has a BMR of per day.
During the last 100 years, lifestyles have changed, and Frankenfield et al. showed it to be about 5% more accurate.
These formulas are based on body mass, which does not take into account the difference in metabolic activity between lean body mass and body fat. Other formulas exist which take into account lean body mass, two of which are the Katch–McArdle formula and Cunningham formula.
;The Katch–McArdle formula (resting daily energy expenditure)
The Katch–McArdle formula is used to predict resting daily energy expenditure (RDEE).
The Cunningham formula is commonly cited to predict RMR instead of BMR; however, the formulas provided by Katch–McArdle and Cunningham are the same.
where ℓ is the lean body mass (LBM in kg):
where f is the body fat percentage.
According to this formula, if the woman in the example has a body fat percentage of 30%, her resting daily energy expenditure (the authors use the term of basal and resting metabolism interchangeably) would be 1262 kcal per day. | 1 | Biochemistry |
* A consortium of Porsche, Siemens Energy, Enel, AME und ENAP plans to build production facilities for manufacturing of renewable methanol with wind power and CO from the air (as of July 2021). With assistance of ExxonMobil the methanol shall be transformed to further synthetic fuels. By 2024 the consortium wants to produce 55 million litres of eFuels and by 2026 around 550 million litres of eFuels. | 2 | Environmental Chemistry |
In order for seawater mineral and element extractions to take place while taking close consideration of sustainable practices, it is necessary for monitored management systems to be put in place. This requires management of ocean areas and their conditions, environmental planning, structured guidelines to ensure that extractions are controlled, regular assessments of the condition of the sea post-extraction, and constant monitoring. The use of technology, such as underwater drones, can facilitate sustainable extractions. The use of low-carbon infrastructure would also allow for more sustainable extraction processes while reducing the carbon footprint from mineral extractions.
Another practice that is being considered closely is the process of desalination in order to achieve a more sustainable water supply from seawater. Although desalination also comes with environmental concerns, such as costs and resources, researchers are working closely to determine more sustainable practices, such as creating more productive water plants that can deal with larger water supplies in areas where these plans weren't always available. Although seawater extractions can benefit society greatly, it is crucial to consider the environmental impact and to ensure that all extractions are conducted in a way that acknowledges and considers the associated risks to the sustainability of seawater ecosystems. | 9 | Geochemistry |
Triglycerides are synthesized by esterification of fatty acids to glycerol. Fatty acid esterification takes place in the endoplasmic reticulum of cells by metabolic pathways in which acyl groups in fatty acyl-CoAs are transferred to the hydroxyl groups of glycerol-3-phosphate and diacylglycerol. Three fatty acid chains are bonded to each glycerol molecule. Each of the three -OH groups of the glycerol reacts with the carboxyl end of a fatty acid chain (-COOH). Water is eliminated and the remaining carbon atoms are linked by an -O- bond through dehydration synthesis.
Both the adipose tissue and the liver can synthesize triglycerides. Those produced by the liver are secreted from it in the form of very-low-density lipoproteins (VLDL). VLDL particles are secreted directly into blood, where they function to deliver the endogenously derived lipids to peripheral tissues. | 1 | Biochemistry |
Every possible biosignature is associated with its own set of unique false positive mechanisms or non-biological processes that can mimic the detectable feature of a biosignature. An important example is using oxygen as a biosignature. On Earth, the majority of life is centred around oxygen. It is a byproduct of photosynthesis and is subsequently used by other life forms to breathe. Oxygen is also readily detectable in spectra, with multiple bands across a relatively wide wavelength range, therefore, it makes a very good biosignature. However, finding oxygen alone in a planet's atmosphere is not enough to confirm a biosignature because of the false-positive mechanisms associated with it. One possibility is that oxygen can build up abiotically via photolysis if there is a low inventory of non-condensable gasses or if the planet loses a lot of water. Finding and distinguishing a biosignature from its potential false-positive mechanisms is one of the most complicated parts of testing for viability because it relies on human ingenuity to break an abiotic-biological degeneracy, if nature allows. | 2 | Environmental Chemistry |
One of the simplest methods for finding reactivity ratios is plotting the copolymer equation and using nonlinear least squares analysis to find the , pair that gives the best fit curve. This is preferred as methods such as Kelen-Tüdős or Fineman-Ross (see below) that involve linearization of the Mayo–Lewis equation will introduce bias to the results. | 7 | Physical Chemistry |
The EPS process (see Figure 2) begins with hot rolled strip steel in coil form. This steel pays off of an uncoiler, then passes through a machine which serves the purpose of "scale breaker", "leveler" or both. This machine (see Figure 2) works the material between sets of hardened rollers. This has the effect of removing the curvature of the strip ("coil set") and breaking loose the outer layers of mill scale which encase the steel strip.
After passing through the "scale breaker/leveler" machine, the steel strip enters the first "EPS slurry blasting cell". Slurry blasting is a wet abrasive blasting process that combines a fine-particle metallic abrasive with a "carrier liquid" (the most common one being water). This abrasive + water slurry mixture is fed into a rotating impeller which propels it at high velocity across the object to be cleaned (see Figure 3). Slurry blasting is a method for removing rust/scale, for blast cleaning and shot peening. Cleaning agents can be introduced into the carrier liquid to reduce smut and aid in rust prevention.
An EPS slurry blasting cell is composed of eight of the slurry discharge heads shown in Figure 3 – four for the top surface and four for the bottom surface of the strip. Inside the slurry blasting cell, jets of water cleanse the steel strip of both the abrasive particles and the dislodged mill scale. An EPS production system may use multiple EPS slurry blasting cells arranged in tandem, so the steel strip passes from one cell into the next, then into the next, and so on. Multiple cells increase the exposure of the steel strip to the slurry blast streams, thereby allowing the strip to move faster, yet still achieve the necessary level of scale removal. The strip speed and, therefore, system output increases in rough proportion to the number of EPS slurry blasting cells used.
The strip emerges from the final blasting cell and is dried using high-velocity air blowers. At this point the strip passes beneath a real-time oxide detector camera, which provides feedback to the line control to assure full oxide removal is accomplished.
To conclude the process, the strip may, optionally, have an oil film or lubricant applied, then it is recoiled. Of note is that tension created by the force of the recoiler pulling the strip through the scale breaker/leveler serves to flatten the strip, removing bow, edge wave and minor coil breaks. Also, not shown in Figure 2 is the slurry delivery/recirculation/filtering system. This closed-loop system collects the carrier liquid, abrasive and removed scale, filters out the removed scale, other contaminants and "undersized" abrasive particles, and returns a cleansed slurry mixture back to the blasting cells. | 8 | Metallurgy |
Agarose gel is a three-dimensional matrix formed of helical agarose molecules in supercoiled bundles that are aggregated into three-dimensional structures with channels and pores through which biomolecules can pass. The 3-D structure is held together with hydrogen bonds and can therefore be disrupted by heating back to a liquid state. The melting temperature is different from the gelling temperature, depending on the sources, agarose gel has a gelling temperature of 35–42 °C and a melting temperature of 85–95 °C. Low-melting and low-gelling agaroses made through chemical modifications are also available.
Agarose gel has large pore size and good gel strength, making it suitable as an anticonvection medium for the electrophoresis of DNA and large protein molecules. The pore size of a 1% gel has been estimated from 100 nm to 200–500 nm, and its gel strength allows gels as dilute as 0.15% to form a slab for gel electrophoresis. Low-concentration gels (0.1–0.2%) however are fragile and therefore hard to handle. Agarose gel has lower resolving power than polyacrylamide gel for DNA but has a greater range of separation, and is therefore used for DNA fragments of usually 50–20,000 bp in size. The limit of resolution for standard agarose gel electrophoresis is around 750 kb, but resolution of over 6 Mb is possible with pulsed field gel electrophoresis (PFGE). It can also be used to separate large proteins, and it is the preferred matrix for the gel electrophoresis of particles with effective radii larger than 5–10 nm. A 0.9% agarose gel has pores large enough for the entry of bacteriophage T4.
The agarose polymer contains charged groups, in particular pyruvate and sulphate. These negatively charged groups create a flow of water in the opposite direction to the movement of DNA in a process called electroendosmosis (EEO), and can therefore retard the movement of DNA and cause blurring of bands. Higher concentration gels would have higher electroendosmotic flow. Low EEO agarose is therefore generally preferred for use in agarose gel electrophoresis of nucleic acids, but high EEO agarose may be used for other purposes. The lower sulphate content of low EEO agarose, particularly low-melting point (LMP) agarose, is also beneficial in cases where the DNA extracted from gel is to be used for further manipulation as the presence of contaminating sulphates may affect some subsequent procedures, such as ligation and PCR. Zero EEO agaroses however are undesirable for some applications as they may be made by adding positively charged groups and such groups can affect subsequent enzyme reactions. Electroendosmosis is a reason agarose is used in preference to agar as the agaropectin component in agar contains a significant amount of negatively charged sulphate and carboxyl groups. The removal of agaropectin in agarose substantially reduces the EEO, as well as reducing the non-specific adsorption of biomolecules to the gel matrix. However, for some applications such as the electrophoresis of serum proteins, a high EEO may be desirable, and agaropectin may be added in the gel used. | 1 | Biochemistry |
Trandolapril acts by competitive inhibition of angiotensin converting enzyme (ACE), a key enzyme in the renin–angiotensin system. which plays an important role in regulating blood pressure. | 4 | Stereochemistry |
The use of trifluoroperacetic acid with boron trifluoride causes oxidation of alkenes and aromatic rings with concomitant rearrangement of the molecular skeleton.
For alkenes, the reaction gives a ketone product, though the mechanistic process is not simply epoxidation followed by a BF-catalyzed Wagner–Meerwein rearrangement:
For aromatics, an example demonstrated in an Organic Syntheses report is the conversion of hexamethylbenzene to 2,3,4,5,6,6-hexamethyl-2,4-cyclohexadienone: | 0 | Organic Chemistry |
Plants use CAM to different degrees. Some are "obligate CAM plants", i.e. they use only CAM in photosynthesis, although they vary in the amount of they are able to store as organic acids; they are sometimes divided into "strong CAM" and "weak CAM" plants on this basis. Other plants show "inducible CAM", in which they are able to switch between using either the or mechanism and CAM depending on environmental conditions. Another group of plants employ "CAM-cycling", in which their stomata do not open at night; the plants instead recycle produced by respiration as well as storing some during the day.
Plants showing inducible CAM and CAM-cycling are typically found in conditions where periods of water shortage alternate with periods when water is freely available. Periodic drought – a feature of semi-arid regions – is one cause of water shortage. Plants which grow on trees or rocks (as epiphytes or lithophytes) also experience variations in water availability. Salinity, high light levels and nutrient availability are other factors which have been shown to induce CAM.
Since CAM is an adaptation to arid conditions, plants using CAM often display other xerophytic characters, such as thick, reduced leaves with a low surface-area-to-volume ratio; thick cuticle; and stomata sunken into pits. Some shed their leaves during the dry season; others (the succulents) store water in vacuoles. CAM also causes taste differences: plants may have an increasingly sour taste during the night yet become sweeter-tasting during the day. This is due to malic acid being stored in the vacuoles of the plants' cells during the night and then being used up during the day. | 5 | Photochemistry |
In the recent article published in 2021, Hansen and Vermeeren proposed the two requirements for an α-nucleophile to present the α-effect. The two proposed requirements were (1) minimization of steric Pauli repulsion via small HOMO lobes on the nucleophilic center and (2) small HOMO-LUMO orbital energy gap that ensures orbital overlap with the substrate. It was proposed that both of these two requirements should be fulfilled to have an α-effect, otherwise, the nucleophiles would show no or inverse α-effect (Figure 2). In this recent work, the six normal nucleophiles (HO, CHO, HN, CHHN, CHS, HS) followed the Brønsted-type correlation. α-nucleophiles with O, HN, and S in the α position were classified into three groups according to their degree and pattern of deviation from the Brønsted-type correlation in S2 reactions with the substrate, ethyl chloride (CHCl) (Figure 3).
First, the α-nucleophiles with downward deviation, in other words, higher reactivity shown considering the basicity or lower basicity given the reactivity, were grouped as nucleophiles showing α-effect. The second group had nucleophiles with small or no deviation from the line plotted by six normal nucleophiles. Lastly, the third group had nucleophiles showing inverse α-effect, meaning that they are above the plotted line or have less reactivity considering their high basicity. Relative density functional theory, activation strain model, energy decomposition analysis, and Kohn-Sham molecular orbital analysis the three groups had a distinction in HOMO lobes and HOMO-LUMO gaps.
To elaborate on the first requirement, the electronegative heteroatom reduces the electron density of the atom that attacks the nucleophile making the HOMO lobe smaller. This minimizes the Pauli repulsion between the substrate and the nucleophile. Nonetheless, these small HOMO lobes don't mean less orbital interaction than the parent normal nucleophile. This is because α-nucleophiles showing the α-effect have smaller HOMO(nucleophile)-LUMO(substrate) gap, in other words, high HOMO energy level that allows more orbital interaction.
Examples of α-nucleophiles with α-effects are shown in Figure 4. The α-nucleophiles have smaller HOMO lobes than the parent normal nucleophile.
Examples of α-nucleophiles with α-effect and inverse α-effect are shown in Figure 5. | 7 | Physical Chemistry |
CDAs are used with NMR spectroscopic analysis to determine enantiomeric excess and the absolute configuration of a substrate. Chiral discriminating agents are sometimes difficult to distinguish from chiral solvating agents (CSA) and some agents can be used as both. The speed of the exchange between the substrate and the metal center is the most important determining factor to differentiate between the use of a compound as a CDA or CSA. Generally, a CDA has a slow exchange whereas a CSA has a fast exchange. CDAs are more widely used than CSAs to determine absolute configurations because the covalent bonding to the substrate and auxiliary reagent produce species with greater conformational rigidity which creates greater differences in the NMR spectra. CDAs and CSAs can be used together to improve chiral recognition, although this is not a common.
NMR shift reagents such as EuFOD, Pirkle's alcohol, and TRISPHAT take advantage of the formation of diastereomeric complexes between the shift reagent and the analytical sample. | 4 | Stereochemistry |
Glycine is biosynthesized from serine, catalyzed by serine hydroxymethyltransferase (SHMT). The enzyme effectively replaces a hydroxymethyl group with a hydrogen atom.
SHMT is coded by the gene glyA. The regulation of glyA is complex and is known to incorporate serine, glycine, methionine, purines, thymine, and folates, The full mechanism has yet to be elucidated. The methionine gene product MetR and the methionine intermediate homocysteine are known to positively regulate glyA. Homocysteine is a coactivator of glyA and must act in concert with MetR. On the other hand, PurR, a protein which plays a role in purine synthesis and S-adeno-sylmethionine are known to down regulate glyA. PurR binds directly to the control region of glyA and effectively turns the gene off so that glycine will not be produced by the bacterium. | 1 | Biochemistry |
As of 2013, eighteen cases of overdoses had been reported with doses of up to 14.4 grams, none of them fatal. No specific antidote for overdose exists and treatment is purely supportive. | 4 | Stereochemistry |
The reaction of calcium carbide with water, producing acetylene and calcium hydroxide, was discovered by Friedrich Wöhler in 1862.
:CaC(s) + 2HO(l) → CH(g) + Ca(OH)(aq)
This reaction was the basis of the industrial manufacture of acetylene, and is the major industrial use of calcium carbide.
Today acetylene is mainly manufactured by the partial combustion of methane or appears as a side product in the ethylene stream from cracking of hydrocarbons. Approximately 400,000 tonnes are produced this way annually (see acetylene preparation).
In China, acetylene derived from calcium carbide remains a raw material for the chemical industry, in particular for the production of polyvinyl chloride. Locally produced acetylene is more economical than using imported oil. Production of calcium carbide in China has been increasing. In 2005 output was 8.94 million tons, with the capacity to produce 17 million tons.
In the United States, Europe, and Japan, consumption of calcium carbide is generally declining. Production levels in the US during the 1990s were 236,000 tons per year. | 8 | Metallurgy |
Polymerase chain reaction (PCR) is an extremely versatile technique for copying DNA. In brief, PCR allows a specific DNA sequence to be copied or modified in predetermined ways. The reaction is extremely powerful and under perfect conditions could amplify one DNA molecule to become 1.07 billion molecules in less than two hours. PCR has many applications, including the study of gene expression, the detection of pathogenic microorganisms, the detection of genetic mutations, and the introduction of mutations to DNA. The PCR technique can be used to introduce restriction enzyme sites to ends of DNA molecules, or to mutate particular bases of DNA, the latter is a method referred to as site-directed mutagenesis. PCR can also be used to determine whether a particular DNA fragment is found in a cDNA library. PCR has many variations, like reverse transcription PCR (RT-PCR) for amplification of RNA, and, more recently, quantitative PCR which allow for quantitative measurement of DNA or RNA molecules. | 1 | Biochemistry |
The peridinin-chlorophyll-protein complex (PCP or PerCP) is a soluble molecular complex consisting of the peridinin-chlorophyll a-protein bound to peridinin, chlorophyll, and lipids. The peridinin molecules absorb light in the blue-green wavelengths (470 to 550 nm) and transfer energy to the chlorophyll molecules with extremely high efficiency. PCP complexes are found in many photosynthetic dinoflagellates, in which they may be the primary light-harvesting complexes. | 5 | Photochemistry |
Lasso peptide biosynthesis requires at least three genes, referred to as the A, B, and C proteins. The A gene encodes the precursor peptide, which is modified by the B and C proteins into the mature natural product. The B protein is an adenosine triphosphate-dependent cysteine protease that cleaves the leader region from the precursor peptide. The C protein displays homology to asparagine synthetase and is thought to activate the carboxylic acid side chain of a glutamate or aspartate residue via adenylylation. The N-terminal amine formed by the B protein (protease) then reacts with this activated side chain to form the macrocycle-forming isopeptide bond. The exact steps and reaction intermediates in lasso peptide biosynthesis remain unknown due to experimental difficulties associated with the proteins. Commonly, the B protein is referred to as the lasso protease, and the C protein is referred to as the lasso cyclase.
Some lasso peptide biosynthetic gene clusters also require an additional protein of unknown function for biosynthesis. Additionally, lasso peptide gene clusters usually include an ABC transporter (D protein) or an isopeptidase, although these are not strictly required for lasso peptide biosynthesis and are sometimes absent. No X-ray crystal structure is yet known for any lasso peptide biosynthetic protein.
The biosynthesis of lasso peptides is particularly interesting due to the inaccessibility of the threaded-lasso topology to chemical peptide synthesis. | 1 | Biochemistry |
Synthetic polymers invariably consist of a mixture of macromolecular species with different degrees of polymerization and therefore of different molecular weights. There are different types of average polymer molecular weight, which can be measured in different experiments. The two most important are the number average (X) and the weight average (X).
The number-average degree of polymerization is a weighted mean of the degrees of polymerization of polymer species, weighted by the mole fractions (or the number of molecules) of the species. It is typically determined by measurements of the osmotic pressure of the polymer.
The weight-average degree of polymerization is a weighted mean of the degrees of polymerization, weighted by the weight fractions (or the overall weight of the molecules) of the species. It is typically determined by measurements of Rayleigh light scattering by the polymer. | 7 | Physical Chemistry |
The atomic number or nuclear charge number (symbol Z) of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (n) or the number of protons found in the nucleus of every atom of that element. The atomic number can be used to uniquely identify ordinary chemical elements. In an ordinary uncharged atom, the atomic number is also equal to the number of electrons.
For an ordinary atom which contains protons, neutrons and electrons, the sum of the atomic number Z and the neutron number N gives the atoms atomic mass number A. Since protons and neutrons have approximately the same mass (and the mass of the electrons is negligible for many purposes) and the mass defect of the nucleon binding is always small compared to the nucleon mass, the atomic mass of any atom, when expressed in daltons (making a quantity called the "relative isotopic mass"), is within 1% of the whole number A'.
Atoms with the same atomic number but different neutron numbers, and hence different mass numbers, are known as isotopes. A little more than three-quarters of naturally occurring elements exist as a mixture of isotopes (see monoisotopic elements), and the average isotopic mass of an isotopic mixture for an element (called the relative atomic mass) in a defined environment on Earth determines the element's standard atomic weight. Historically, it was these atomic weights of elements (in comparison to hydrogen) that were the quantities measurable by chemists in the 19th century.
The conventional symbol Z comes from the German word number, which, before the modern synthesis of ideas from chemistry and physics, merely denoted an elements numerical place in the periodic table, whose order was then approximately, but not completely, consistent with the order of the elements by atomic weights. Only after 1915, with the suggestion and evidence that this Z number was also the nuclear charge and a physical characteristic of atoms, did the word (and its English equivalent atomic number') come into common use in this context.
The rules above do not always apply to exotic atoms which contain short-lived elementary particles other than protons, neutrons and electrons. | 3 | Analytical Chemistry |
In medicine, actinic effects are generally described in terms of the dermis or outer layers of the body, such as eyes (see: Actinic conjunctivitis) and upper tissues that the sun would normally affect, rather than deeper tissues that higher-energy shorter-wavelength radiation such as x-ray and gamma might affect. Actinic is also used to describe medical conditions that are triggered by exposure to light, especially UV light (see actinic keratosis).
The term actinic rays is used to refer to this phenomenon. | 7 | Physical Chemistry |
Since laser diffraction analysis is not the sole way of measuring particles it has been compared to the sieve-pipette method, which is a traditional technique for grain size analysis. When compared, results showed that laser diffraction analysis made fast calculations that were easy to recreate after a one-time analysis, did not need large sample sizes, and produced large amounts of data. Results can easily be manipulated because the data is on a digital surface. Both the sieve-pipette method and laser diffraction analysis are able to analyze minuscule objects, but laser diffraction analysis resulted in having better precision than its counterpart method of particle measurement. | 7 | Physical Chemistry |
In the solvent extraction a mixture of an extractant in a diluent is used to extract a metal from one phase to another. In solvent extraction this mixture is often referred to as the "organic" because the main constituent (diluent) is some type of oil.
The PLS (pregnant leach solution) is mixed to emulsification with the stripped organic and allowed to separate. The metal will be exchanged from the PLS to the organic they are modified. The resulting streams will be a loaded organic and a raffinate. When dealing with electrowinning, the loaded organic is then mixed to emulsification with a lean electrolyte and allowed to separate. The metal will be exchanged from the organic to the electrolyte. The resulting streams will be a stripped organic and a rich electrolyte. The organic stream is recycled through the solvent extraction process while the aqueous streams cycle through leaching and electrowinning processes respectively. | 8 | Metallurgy |
The nitroso group has both a +M and -M effect, but the -M effect is more favorable.
Nitrogen has a lone pair of electrons. However, the lone pair of its monomer form is unfavourable to donate through resonance. Only the dimer form is available for +M effect. However, the dimer form is less stable in a solution. Therefore, the nitroso group is less available to donate electrons.
Oppositely, withdrawing electron density is more favourable: (see the picture on the right).As a result, the nitroso group is a deactivator. However, it has available to donate electron density to the benzene ring during the Wheland intermediate, making it still being an ortho / para director. | 0 | Organic Chemistry |
Vinylidene chloride and fluoride can be converted to linear polymers polyvinylidene chloride (PVDC) and polyvinylidene fluoride (PVDF). The polymerization reaction is:
: n CH=CX → (CH−CX)
These vinylidene polymers are isomeric with those produced from vinylene monomers. Thus polyvinylene fluoride from vinylene fluoride (HFC=CHF). | 0 | Organic Chemistry |
Accelerated studies have been in use since at least the mid-1950s, at least for biological reference materials. CRMs are typically monitored at a range of temperatures and the results are used to predict the rate of change at a proposed, usually low, storage temperature. Often, the prediction uses a well known degradation model such as an Arrhenius model. The advantage over real-time studies is that results are available sooner and predictions of stability over a much longer period than the stability study can be defended. For some applications, accelerated studies have been described as the only practical approach:
The principal disadvantage of accelerated studies is that reference materials, like any other material, can degrade for unexpected reasons over time, or can degrade following different kinetic models; predictions can then become unreliable. | 3 | Analytical Chemistry |
Ivar Karl Ugi (9 September 1930 in Saaremaa, Estonia – 29 September 2005 in Munich) was an Estonian-born German chemist who made major contributions to organic chemistry. He is known for the research on multicomponent reactions, yielding the Ugi reaction. | 0 | Organic Chemistry |
Laser diffraction analysis is originally based on the Fraunhofer diffraction theory, stating that the intensity of light scattered by a particle is directly proportional to the particle size. The angle of the laser beam and particle size have an inversely proportional relationship, where the laser beam angle increases as particle size decreases and vice versa. The Mie scattering model, or Mie theory, is used as alternative to the Fraunhofer theory since the 1990s.
Commercial laser diffraction analyzers leave to the user the choice of using either Fraunhofer or Mie theory for data analysis, hence the importance of understanding the strengths and limitations of both models. Fraunhofer theory only takes into account the diffraction phenomena occurring at the contour of the particle. Its main advantage is that it does not require any knowledge of the optical properties (complex refractive index) of the particle’s material. Hence is it typically applied to samples of unknown optical properties, or to mixtures of different materials. For samples of known optical properties, Fraunhofer theory should only be applied for particles of an expected diameter at least 10 times larger than the light source’s wavelength, and/or to opaque particles.
The Mie theory is based on measuring the scattering of electromagnetic waves on spherical particles. Hence, it is taking into account not only the diffraction at the particle’s contour, but also the refraction, reflection and absorption phenomena within the particle and at its surface. Thus, this theory is better suited than the Fraunhofer theory for particles that are not significantly larger than the wavelength of the light source, and to transparent particles. The model’s main limitation is that it requires precise knowledge of the complex refractive index (including the absorption coefficient) of the particle’s material. The lower theoretical detection limit of laser diffraction, using the Mie theory, is generally thought to lie around 10 nm. | 7 | Physical Chemistry |
The structure of biliproteins is typically characterised by bilin chromophores arranged in linear tetrapyrrolic formation, and the bilins are covalently bound to apoproteins via thioether bonds. Each type of biliprotein has a unique bilin that belongs to it (e.g. phycoerythrobilin is the chromophore of phycoerythrin and phycocyanobilin is the chromophore of phycocyanin). The bilin chromophores are formed by the oxidative cleavage of a haem ring and catalysed by haem oxygenases at one of four methine bridges, allowing four possible bilin isomers to occur. In all organisms known to have biliproteins, cleavage usually occurs at the α-bridge, generating biliverdin IXα.
Phycobiliproteins are grouped together in separate clusters, approximately 40nm in diameter, known as phycobilisomes. The structural changes involved in deriving bilins from their biliverdin IXα isomer determine the spectral range of light absorption.
The structure of biliproteins in insects differ slightly than those in plants and algae; they have a crystal structure and their chromophores are not covalently bound to the apoproteins. Unlike phycobiliproteins whose chromophores are held in an extended arrangement by specific interactions between chromophores and proteins, the chromophore in insect biliproteins has a cyclic helical crystal structure in the protein-bound state, as found in studies of the biliprotein extracted from the large white butterfly. | 1 | Biochemistry |
The effects of calcium on human cells are specific, meaning that different types of cells respond in different ways. However, in certain circumstances, its action may be more general. Ca ions are one of the most widespread second messengers used in signal transduction. They make their entrance into the cytoplasm either from outside the cell through the cell membrane via calcium channels (such as calcium-binding proteins or voltage-gated calcium channels), or from some internal calcium storages such as the endoplasmic reticulum and mitochondria. Levels of intracellular calcium are regulated by transport proteins that remove it from the cell. For example, the sodium-calcium exchanger uses energy from the electrochemical gradient of sodium by coupling the influx of sodium into cell (and down its concentration gradient) with the transport of calcium out of the cell. In addition, the plasma membrane Ca ATPase (PMCA) obtains energy to pump calcium out of the cell by hydrolysing adenosine triphosphate (ATP). In neurons, voltage-dependent, calcium-selective ion channels are important for synaptic transmission through the release of neurotransmitters into the synaptic cleft by vesicle fusion of synaptic vesicles.
Calcium's function in muscle contraction was found as early as 1882 by Ringer. Subsequent investigations were to reveal its role as a messenger about a century later. Because its action is interconnected with cAMP, they are called synarchic messengers. Calcium can bind to several different calcium-modulated proteins such as troponin-C (the first one to be identified) and calmodulin, proteins that are necessary for promoting contraction in muscle.
In the endothelial cells which line the inside of blood vessels, Ca ions can regulate several signaling pathways which cause the smooth muscle surrounding blood vessels to relax. Some of these Ca-activated pathways include the stimulation of eNOS to produce nitric oxide, as well as the stimulation of K channels to efflux K and cause hyperpolarization of the cell membrane. Both nitric oxide and hyperpolarization cause the smooth muscle to relax in order to regulate the amount of tone in blood vessels. However, dysfunction within these Ca-activated pathways can lead to an increase in tone caused by unregulated smooth muscle contraction. This type of dysfunction can be seen in cardiovascular diseases, hypertension, and diabetes.
Calcium coordination plays an important role in defining the structure and function of proteins. An example a protein with calcium coordination is von Willebrand factor (vWF) which has an essential role in blood clot formation process. It was discovered using single molecule optical tweezers measurement that calcium-bound vWF acts as a shear force sensor in the blood. Shear force leads to unfolding of the A2 domain of vWF whose refolding rate is dramatically enhanced in the presence of calcium. | 1 | Biochemistry |
CoQ is not approved by the U.S. Food and Drug Administration (FDA) for the treatment of any medical condition. However, it is sold as a dietary supplement not subject to the same regulations as medicinal drugs, and is an ingredient in some cosmetics. The manufacture of CoQ is not regulated, and different batches and brands may vary significantly. | 1 | Biochemistry |
In 1811, Amedeo Avogadro verified that equal volumes of pure gases contain the same number of particles. His theory was not generally accepted until 1858 when another Italian chemist Stanislao Cannizzaro was able to explain non-ideal exceptions. For his work with gases a century prior, the physical constant that bears his name (the Avogadro constant) is the number of atoms per mole of elemental carbon-12 (). This specific number of gas particles, at standard temperature and pressure (ideal gas law) occupies 22.40 liters, which is referred to as the molar volume.
Avogadro's law states that the volume occupied by an ideal gas is proportional to the amount of substance in the volume. This gives rise to the molar volume of a gas, which at STP is 22.4 dm/mol (liters per mole). The relation is given by
where n is the amount of substance of gas (the number of molecules divided by the Avogadro constant). | 7 | Physical Chemistry |
Similar to other d transition metals, Nb(III) produce adducts with alkynes. These derivatives are sometimes called Nb(V) alkenediyls metallacyclopropenes.
These alkendiyl complexes function as latent dianion equivalents. They react with electrophiles to give alkene derivatives. | 0 | Organic Chemistry |
The robustness of focal molography against environmental noise gives the method a platform character that enables many possible applications. They range from the investigation of a specific biomolecular interaction in basic biological research to the diagnosis of a critical health condition in an emergency.
The biological applications of molography categorize into five basic classes:
# Classical biomolecular interaction analysis (BIA), i.e. the measurement of on-rates, off-rates and binding constants as demonstrated in,
# Quantification of biomarkers in biological samples,
# Profiling of low-affinity binders on mologram arrays,
# Quantification of molecular interactions in living cells in real time, and
# Discovery of unknown biomolecular interactions by means of binding assays. | 1 | Biochemistry |
6-Methylisoxanthopterin (6MI) is a base analog for the nucleotide guanine. It is useful as a fluorescent indicator because unlike most other base analogs, quenching does not occur when it is incorporated into a double helix. In fact, it exhibits a 3 to 4-fold increase in quantum yield when it is incorporated into a duplex formation. This allows 6MI to be used to probe the dynamics of DNA or RNA helices using a technique such as fluorescence polarization anisotropy. | 1 | Biochemistry |
The table below describes properties of several different thermocouple types. Within the tolerance columns, T represents the temperature of the hot junction, in degrees Celsius. For example, a thermocouple with a tolerance of ±0.0025×T would have a tolerance of ±2.5 °C at 1000 °C.
Each cell in the Color Code columns depicts the end of a thermocouple cable, showing the jacket color and the color of the individual leads. The background color represents the color of the connector body. | 8 | Metallurgy |
For molecules in the gas phase, the principal effects are Doppler and pressure broadening. This applies to rotational spectroscopy, rotational-vibrational spectroscopy and vibronic spectroscopy.
For molecules in the liquid state or in solution, collision and proximity broadening predominate and lines are much broader than lines from the same molecule in the gas phase. Line maxima may also be shifted. Because there are many sources of broadening, the lines have a stable distribution, tending towards a Gaussian shape. | 7 | Physical Chemistry |
Reduced oxygen levels are expected to lead to increased seawater concentrations of redox-sensitive metals. The reductive dissolution of iron–manganese oxyhydroxides in seafloor sediments under low-oxygen conditions would release those metals and associated trace metals. Sulfate reduction in such sediments could release other metals such as barium. When heavy-metal-rich anoxic deep water entered continental shelves and encountered increased O levels, precipitation of some of the metals, as well as poisoning of the local biota, would have occurred. In the late Silurian mid-Pridoli event, increases are seen in the Fe, Cu, As, Al, Pb, Ba, Mo and Mn levels in shallow-water sediment and microplankton; this is associated with a marked increase in the malformation rate in chitinozoans and other microplankton types, likely due to metal toxicity. Similar metal enrichment has been reported in sediments from the mid-Silurian Ireviken event. | 9 | Geochemistry |
The regulation of translation in eukaryotes is more complex than in prokaryotes. Initially, the eIF4F complex is recruited to the 5′ cap, which in turn recruits the ribosomal complex to the 5′ UTR. Both eIF4E and eIF4G bind the 5′ UTR, which limits the rate at which translational initiation can occur. However, this is not the only regulatory step of translation that involves the 5′ UTR.
RNA-binding proteins sometimes serve to prevent the pre-initiation complex from forming. An example is regulation of the msl2 gene. The protein SXL attaches to an intron segment located within the 5′ UTR segment of the primary transcript, which leads to the inclusion of the intron after processing. This sequence allows the recruitment of proteins that bind simultaneously to both the 5′ and 3′ UTR, not allowing translation proteins to assemble. However, it has also been noted that SXL can also repress translation of RNAs that do not contain a poly(A) tail, or more generally, 3′ UTR. | 1 | Biochemistry |
Nesfatin-1 is a polypeptide encoded in the N-terminal region of the protein precursor, Nucleobindin-2 (NUCB2).
Recombinant human Nesfatin-1 is a 9.7 kDa protein containing 82 amino acid residues. Nesfatin-1 is expressed in the hypothalamus, in other areas of the brain, and in pancreatic islets, gastric endocrine cells and adipocytes. | 1 | Biochemistry |
* SOX gene family
** Sex-Determining Region Y Protein
** SOX1, SOX2, etc.
* TCF/LEF family (T cell factor/lymphoid enhancer factor family)
** LEF1 (Lymphoid enhancer-binding factor 1)
** TCF7 (TCF-1)
** TCF7L1 (TCF-3)
** TCF7L2 (TCF-4) | 1 | Biochemistry |
Structural work has determined that its 1,494 Dalton core unit (Glycine / Hydroxy-glycine / FeO) contains iron, but not lithium, leading to the more general term hemoglycin for these molecules. The hemoglycin core contains a total of 22 glycine residues in an anti-parallel beta sheet chain that is terminated at each end by an iron atom plus two oxygens. Four of these glycine residues are oxidized to hydroxy-glycine with hydroxy groups (-OH) on the alpha carbon. This structure was determined by mass spectrometry of meteoritic solvent extracts and has been confirmed in X-ray scattering by crystals of hemoglycin, and also by optical absorption. Crystals show a 480 nm characteristic absorption that can only exist when hydroxy-glycine residues have R chirality and are C-terminal bonded to iron. | 9 | Geochemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), and Valine (Val, V). | 1 | Biochemistry |
Once the selection has been performed, the primary structure of the proteins which display the appropriate characteristics must be determined. This is achieved by retrieval of the protein-encoding sequences (as originally inserted) from the cells showing the appropriate phenotype. | 1 | Biochemistry |
The Bragg condition is correct for very large crystals. Because the scattering of X-rays and neutrons is relatively weak, in many cases quite large crystals with sizes of 100 nm or more are used. While there can be additional effects due to crystal defects, these are often quite small. In contrast, electrons interact thousands of times more strongly with solids than X-rays, and also lose energy (inelastic scattering). Therefore samples used in transmission electron diffraction are much thinner. Typical diffraction patterns, for instance the Figure, show spots for different directions (plane waves) of the electrons leaving a crystal. The angles that Braggs law predicts are still approximately right, but in general there is a lattice of spots which are close to projections of the reciprocal lattice that is at right angles to the direction of the electron beam. (In contrast, Braggs law predicts that only one or perhaps two would be present, not simultaneously tens to hundreds.) With low-energy electron diffraction where the electron energies are typically 30-1000 electron volts, the result is similar with the electrons reflected back from a surface. Also similar is reflection high-energy electron diffraction which typically leads to rings of diffraction spots.
With X-rays the effect of having small crystals is described by the Scherrer equation. This leads to broadening of the Bragg peaks which can be used to estimate the size of the crystals. | 3 | Analytical Chemistry |
Tribocorrosion occurs in many engineering fields. It reduces the life-time of pipes, valves and pumps, of waste incinerators, of mining equipment or of medical implants, and it can affect the safety of nuclear reactors or of transport systems. On the other hand, tribocorrosion phenomena can also be applied to good use, for example in the chemical-mechanical planarization of wafers in the electronics industry or in metal grinding and cutting in presence of aqueous emulsions. Keeping this in mind, we may define tribocorrosion in a more general way independently of the notion of usefulness or damage or of the particular type of mechanical interaction: Tribocorrosion concerns the irreversible transformation of materials or of their function as a result of simultaneous mechanical and chemical/electrochemical interactions between surfaces in relative motion. | 8 | Metallurgy |
Suzanne A. Blum is an American professor of chemistry at the University of California, Irvine. Blum works on mechanistic chemistry, most recently focusing on borylation reactions and the development of single-molecule and single-particle fluorescence microscopy to study organic chemistry and catalysis. She received the American Chemical Society's Arthur C. Cope Scholar Award in 2023. | 0 | Organic Chemistry |
The Petasis reagent is prepared by the salt metathesis reaction of methylmagnesium chloride or methyllithium with titanocene dichloride:
: CpTiCl + 2 CHMgCl → CpTi(CH) + 2 MgCl
This compound is used for the transformation of carbonyl groups to terminal alkenes. It exhibits similar reactivity to the Tebbe reagent and Wittig reaction. Unlike the Wittig reaction, the Petasis reagent can react with a wide range of aldehydes, ketones and esters. The Petasis reagent is also very air stable, and is commonly used in solution with toluene or THF.
The Tebbe reagent and the Petasis reagent share a similar reaction mechanism. The active olefinating reagent, CpTiCH, is generated in situ upon heating. With the organic carbonyl, this titanium carbene forms a four membered oxatitanacyclobutane that releases the terminal alkene.
In contrast to the Tebbe reagent, homologs of the Petasis reagent are relatively easy to prepare by using the corresponding alkyllithium instead of methyllithium, allowing the conversion of carbonyl groups to alkylidenes. | 0 | Organic Chemistry |
Sublimation is a direct phase transition from the solid phase to the gas phase, skipping the intermediate liquid phase. Because it does not involve the liquid phase, it is not a form of vaporization. | 7 | Physical Chemistry |
The organic chemistry of nitrosamines is well developed with regard to their syntheses, their structures, and their reactions. They usually are produced by the reaction of nitrous acid () and secondary amines, although other nitrosyl sources (e.g. , , RONO) have the same effect:
The nitrous acid usually arises from protonation of a nitrite. This synthesis method is relevant to the generation of nitrosamines under some biological conditions. The nitrosation is also partially reversible; aryl nitrosamines rearrange to give a para-nitroso aryl amine in the Fischer-Hepp rearrangement.
With regards to structure, the core of nitrosamines is planar, as established by X-ray crystallography. The N-N and N-O distances are 132 and 126 pm, respectively in dimethylnitrosamine, one of the simplest members of a large class of N-nitrosamines
Nitrosamines are not directly carcinogenic. Metabolic activation is required to convert them to the alkylating agents that modify bases in DNA, inducing mutations. The specific alkylating agents vary with the nitrosamine, but all are proposed to feature alkyldiazonium centers. | 0 | Organic Chemistry |
For Schottky diodes, majority carrier traps are observed by the application of a reverse bias pulse, while minority carrier traps can be observed when the reverse bias voltage pulses are replaced with light pulses with the photon energy from the above semiconductor bandgap spectral range. This method is called Minority Carrier Transient Spectroscopy (MCTS). The minority carrier traps can be also observed for the p-n junctions by application of forward bias pulses, which inject minority carriers into the space charge region. In DLTS plots the minority carrier spectra usually are depicted with an opposite sign of amplitude in respect to the majority carrier trap spectra. | 7 | Physical Chemistry |
At this point, the lipoate-thioester functionality is translocated into the dihydrolipoyl transacetylase (E2) active site, where a transacylation reaction transfers the acetyl from the "swinging arm" of lipoyl to the thiol of coenzyme A. This produces acetyl-CoA, which is released from the enzyme complex and subsequently enters the citric acid cycle. E2 can also be known as lipoamide reductase-transacetylase. | 1 | Biochemistry |
EPA's analysis indicated the amount of existing inventory was between 22,700t and 45,400t.
In 2012 the EPA reduced the amount of R-22 by 45%, causing the price to rise by more than 300%. For 2013, the EPA has reduced the amount of R-22 by 29%. | 2 | Environmental Chemistry |
Silicified carbonates can appear as silicified carbonate rock layers, or in the form of silicified karsts. The Paleogene Madrid Basin in Central Spain is a foreland basin resulted from the Alpine uplift, an example of silicified carbonates in rock layers. The lithology consists of carbonate and detritus units that were formed in a lacustrine environment. The rock units are silicified where cherts, quartz, and opaline minerals are found in the layers. It is conformable with the underlying evaporitic beds, also dated from similar ages. It is found that there were two stages of silicification within the rock strata. The earlier stage of silicification provided a better condition and site for the precipitation of silica. The source of silica is still uncertain. There are no biogenic silica detected from the carbonates. However, microbial films in carbonates are found, which could suggest the presence of diatoms.
Karsts are carbonate caves formed from a dissolution of carbonate rocks such as limestones and dolomites. They are usually susceptible to groundwater and are dissolved in these drainage. Silicified karsts and cave deposits are formed when siliceous fluids enter karsts through faults and cracks. The Mid-Proterozoic Mescal Limestone from the Apache Group in central Arizona is classic examples of silicified karsts. A portion of the carbonates are replaced by cherts in early diagenesis and the remaining portion is completely silicified in later stages. The source of silica in carbonates are usually associated with the presence of biogenetic silica; however, the source of silica in Mescal Limestone is from weathering of overlying basalts, which are extrusive igneous rocks that have high silica content. | 9 | Geochemistry |
Like lansoprazole, dexlansoprazole permanently binds to the proton pump and blocks it, preventing the formation of gastric acid. | 4 | Stereochemistry |
In the 1980s the NCEC developed the Chemdata hazardous material database, which was provided to British fire services for use in case of chemical accidents.
Chemdata lists over 61,600 safety data sheets (SDS) for dangerous substances. It is published in six languages. | 2 | Environmental Chemistry |
The distinction between prokaryotes and eukaryotes was firmly established by the microbiologists Roger Stanier and C. B. van Niel in their 1962 paper The concept of a bacterium (though spelled procaryote and eucaryote there). That paper cites Édouard Chattons 1937 book Titres et Travaux Scientifiques' for using those terms and recognizing the distinction. One reason for this classification was so that what was then often called blue-green algae (now called cyanobacteria) would not be classified as plants but grouped with bacteria. | 1 | Biochemistry |
In all three spectroscopic methods, the sample usually needs to be present in solution, which may present problems during forensic examination because it necessarily involves sampling solid from the object to be examined.
In FTIR, three types of samples can be analyzed: solution (KBr), powder, or film. A solid film is the easiest and most straight forward sample type to test. | 7 | Physical Chemistry |
The C-terminal domain, also known as ropB-CTD, is a carboxy terminalligand-binding domain made of amino acids 56–280. RopB-CTD houses 5 TPR motifs and attaches to the SIP peptide in the innermost part of the SIP binding pocket in a sequence-specific manner without induction of polymerization. | 1 | Biochemistry |
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*Buchdahl, H.A. (1966). The Concepts of Classical Thermodynamics, Cambridge University Press, Cambridge UK.
* Callen, H.B. (1960/1985). Thermodynamics and an Introduction to Thermostatistics, (1st edition 1960) 2nd edition 1985, Wiley, New York, .
* A translation may be found [http://neo-classical-physics.info/uploads/3/0/6/5/3065888/caratheodory_-_thermodynamics.pdf here]. A mostly reliable translation is to be found at Kestin, J. (1976). The Second Law of Thermodynamics, Dowden, Hutchinson & Ross, Stroudsburg PA.
* Chandrasekhar, S. (1961). Hydrodynamic and Hydromagnetic Stability, Oxford University Press, Oxford UK.
* Clausius, R. (1854). Annalen der Physik (Poggendoffs Annalen), Dec. 1854, vol. xciii. p. 481; translated in the Journal de Mathematiques, vol. xx. Paris, 1855, and in the Philosophical Magazine', August 1856, s. 4. vol. xii, p. 81.
* Clausius, R. (1865/1867). [https://books.google.com/books?id=8LIEAAAAYAAJ&q=necessitating+any+other The Mechanical Theory of Heat – with its Applications to the Steam Engine and to Physical Properties of Bodies], London: John van Voorst. 1867. Also the second edition translated into English by W.R. Browne (1879) [https://archive.org/details/cu31924101120883 here] and [http://www3.nd.edu/~powers/ame.20231/clausius1879.pdf here].
* De Groot, S.R., Mazur, P. (1962). Non-equilibrium Thermodynamics, North-Holland, Amsterdam. Reprinted (1984), Dover Publications Inc., New York, .
* Denbigh, K. (1955/1981). The Principles of Chemical Equilibrium, Cambridge University Press, Cambridge .
* Greven, A., Keller, G., Warnecke (editors) (2003). Entropy, Princeton University Press, Princeton NJ, .
* , Lecture on Matter, Living Force, and Heat. 5 and 12 May 1847.
* Kittel, C. Kroemer, H. (1980). Thermal Physics, second edition, W.H. Freeman, San Francisco, .
* Kondepudi, D., Prigogine, I. (1998). Modern Thermodynamics: From Heat Engines to Dissipative Structures, John Wiley & Sons, Chichester, .
* Landau, L., Lifshitz, E.M. (1958/1969). [https://archive.org/details/StatisticalPhysics Statistical Physics], volume 5 of Course of Theoretical Physics, translated from the Russian by J.B. Sykes, M.J. Kearsley, Pergamon, Oxford.
* Lebon, G., Jou, D., Casas-Vázquez, J. (2008). Understanding Non-equilibrium Thermodynamics: Foundations, Applications, Frontiers, Springer-Verlag, Berlin, e-.
* Lieb, E.H., Yngvason, J. (2003). The Entropy of Classical Thermodynamics, Chapter 8 of Entropy, Greven, A., Keller, G., Warnecke (editors) (2003).
* Pippard, A.B. (1957/1966). Elements of Classical Thermodynamics for Advanced Students of Physics, original publication 1957, reprint 1966, Cambridge University Press, Cambridge.
* Planck, M., (1897/1903). [https://archive.org/details/treatiseonthermo00planrich Treatise on Thermodynamics], translated by A. Ogg, first English edition, Longmans, Green and Co., London.
* Planck. M. (1914). [https://archive.org/details/theoryofheatradi00planrich The Theory of Heat Radiation], a translation by Masius, M. of the second German edition, P. Blakiston's Son & Co., Philadelphia.
* Planck, M., (1923/1927). Treatise on Thermodynamics, translated by A. Ogg, third English edition, Longmans, Green and Co., London.
* Shavit, A., Gutfinger, C. (1995). Thermodynamics. From Concepts to Applications, Prentice Hall, London, .
* Truesdell, C. (1969). Rational Thermodynamics: a Course of Lectures on Selected Topics, McGraw-Hill Book Company, New York.
* Truesdell, C. (1980). The Tragicomical History of Thermodynamics 1822–1854, Springer, New York, . | 7 | Physical Chemistry |
Kovacs reagent is a biochemical reagent consisting of isoamyl alcohol, para-dimethylaminobenzaldehyde (DMAB), and concentrated hydrochloric acid. It is used for the diagnostical indole test, to determine the ability of the organism to split indole from the amino acid tryptophan. The indole produced yields a red complex with para-dimethylaminobenzaldehyde under the given conditions. This was invented by the Hungarian physician Nicholas Kovacs and was published in 1928. This reagent is used in the confirmation of E. coli and many other pathogenic microorganisms. | 1 | Biochemistry |
Ligand cone angles are measures of the size of ligands in coordination chemistry. It is defined as the solid angle formed with the metal at the vertex and the hydrogen atoms at the perimeter of the cone (see figure). | 4 | Stereochemistry |
The Reformatsky reaction (sometimes transliterated as Reformatskii reaction) is an organic reaction which condenses aldehydes or ketones with α-halo esters using metallic zinc to form β-hydroxy-esters:
The organozinc reagent, also called a Reformatsky enolate, is prepared by treating an alpha-halo ester with zinc dust. Reformatsky enolates are less reactive than lithium enolates or Grignard reagents and hence nucleophilic addition to the ester group does not occur. The reaction was discovered by Sergey Nikolaevich Reformatsky.
Some reviews have been published.
In addition to aldehydes and ketones, it has also been shown that the Reformatsky enolate is able to react with acid chlorides, imines, nitriles (see Blaise reaction), and nitrones. Moreover, metals other than zinc have also been used, including magnesium, iron, cobalt, nickel, germanium, cadmium, indium, barium, and cerium. Additionally, metal salts are also applicable in place of metals, notably samarium(II) iodide, chromium(II) chloride, titanium(II) chloride, cerium(III) halides such as cerium(III) iodide, and titanocene(III) chloride. | 0 | Organic Chemistry |
Rasagiline (Azilect, Azipron) is an irreversible inhibitor of monoamine oxidase-B used as a monotherapy to treat symptoms in early Parkinson's disease or as an adjunct therapy in more advanced cases.
The racemic form of the drug was invented by Aspro Nicholas in the early 1970s. Moussa B.H. Youdim identified it as a potential drug for Parkinson's disease, and working with collaborators at Technion – Israel Institute of Technology in Israel and the drug company, Teva Pharmaceuticals, identified the R-isomer as the active form of the drug. Teva brought it to market in partnership with Lundbeck in Europe and Eisai in the US and elsewhere. It was approved in Europe in 2005 and in the US in 2006.
Rasagiline is used to treat symptoms of Parkinson's disease both alone and in combination with other drugs. It has shown efficacy in both early and advanced Parkinsons, and appears to be especially useful in dealing with non-motor symptoms like fatigue.
Rasagiline has not been tested in pregnant women and is Pregnancy Category C in the US. | 4 | Stereochemistry |
Using this notation, Woodward and Hoffmann state in their 1969 review the general formulation for all pericyclic reactions as follows:
and (4r) components is odd.</blockquote>
Here, (4q + 2) and (4r) refer to suprafacial (4q + 2)-electron and antarafacial (4r)-electron components, respectively. Moreover, this criterion should be interpreted as both sufficient (stated above) as well as necessary (not explicitly stated above, see: if and only if) | 7 | Physical Chemistry |
The absorption of dietary iron is a variable and dynamic process. The amount of iron absorbed compared to the amount ingested is typically low, but may range from 5% to as much as 35% depending on circumstances and type of iron. The efficiency with which iron is absorbed varies depending on the source. Generally, the best-absorbed forms of iron come from animal products. Absorption of dietary iron in iron salt form (as in most supplements) varies somewhat according to the body's need for iron, and is usually between 10% and 20% of iron intake. Absorption of iron from animal products, and some plant products, is in the form of heme iron, and is more efficient, allowing absorption of from 15% to 35% of intake. Heme iron in animals is from blood and heme-containing proteins in meat and mitochondria, whereas in plants, heme iron is present in mitochondria in all cells that use oxygen for respiration.
Like most mineral nutrients, the majority of the iron absorbed from digested food or supplements is absorbed in the duodenum by enterocytes of the duodenal lining. These cells have special molecules that allow them to move iron into the body. To be absorbed, dietary iron can be absorbed as part of a protein such as heme protein or iron must be in its ferrous Fe form. A ferric reductase enzyme on the enterocytes brush border, duodenal cytochrome B (Dcytb), reduces ferric Fe to Fe. A protein called divalent metal transporter 1 (DMT1), which can transport several divalent metals across the plasma membrane, then transports iron across the enterocytes cell membrane into the cell. If the iron is bound to heme it is instead transported across the apical membrane by heme carrier protein 1 (HCP1).
These intestinal lining cells can then either store the iron as ferritin, which is accomplished by Fe binding to apoferritin (in which case the iron will leave the body when the cell dies and is sloughed off into feces), or the cell can release it into the body via the only known iron exporter in mammals, ferroportin. Hephaestin, a ferroxidase that can oxidize Fe to Fe and is found mainly in the small intestine, helps ferroportin transfer iron across the basolateral end of the intestine cells. In contrast, ferroportin is post-translationally repressed by hepcidin, a 25-amino acid peptide hormone. The body regulates iron levels by regulating each of these steps. For instance, enterocytes synthesize more Dcytb, DMT1 and ferroportin in response to iron deficiency anemia. Iron absorption from diet is enhanced in the presence of vitamin C and diminished by excess calcium, zinc, or manganese.
The human body's rate of iron absorption appears to respond to a variety of interdependent factors, including total iron stores, the extent to which the bone marrow is producing new red blood cells, the concentration of hemoglobin in the blood, and the oxygen content of the blood. The body also absorbs less iron during times of inflammation, in order to deprive bacteria of iron. Recent discoveries demonstrate that hepcidin regulation of ferroportin is responsible for the syndrome of anemia of chronic disease. | 1 | Biochemistry |
Semi-solid metal (SSM) casting is a modified die casting process that reduces or eliminates the residual porosity present in most die castings. Rather than using liquid metal as the feed material, SSM casting uses a higher viscosity feed material that is partially solid and partially liquid. A modified die casting machine is used to inject the semi-solid slurry into reusable hardened steel dies. The high viscosity of the semi-solid metal, along with the use of controlled die filling conditions, ensures that the semi-solid metal fills the die in a non-turbulent manner so that harmful porosity can be essentially eliminated.
Used commercially mainly for aluminium and magnesium alloys, SSM castings can be heat treated to the T4, T5 or T6 tempers. The combination of heat treatment, fast cooling rates (from using uncoated steel dies) and minimal porosity provides excellent combinations of strength and ductility. Other advantages of SSM casting include the ability to produce complex shaped parts net shape, pressure tightness, tight dimensional tolerances and the ability to cast thin walls. | 8 | Metallurgy |
The EPS process produces scale-free steel strip which is interchangeable with acid-pickled steel strip, yet the EPS process entails lower capital and operating (variable) cost than an acid-pickling line of equivalent output. For this reason the EPS process is considered to be a direct replacement of acid pickling.
In addition, the EPS process is considered less damaging to the environment than acid pickling for these reasons:
* Lower energy consumption;
* No hazardous/acidic substances used in the process;
* No potential exposure to acid fumes for people, equipment or buildings;
* No hazardous or polluting outputs or byproducts of the process with disposal or fume stack liabilities. | 8 | Metallurgy |
The Born series for the scattering states reads
It can be derived by iterating the Lippmann–Schwinger equation
Note that the Green's operator for a free particle can be retarded/advanced or standing wave operator for retarded advanced or standing wave scattering states .
The first iteration is obtained by replacing the full scattering solution with free particle wave function on the right hand side of the Lippmann-Schwinger equation and it gives the first Born approximation.
The second iteration substitutes the first Born approximation in the right hand side and the result is called the second Born approximation. In general the n-th Born approximation takes n-terms of the series into account. The second Born approximation is sometimes used, when the first Born approximation vanishes, but the higher terms are rarely used. The Born series can formally be summed as geometric series with the common ratio equal to the operator , giving the formal solution to Lippmann-Schwinger equation in the form | 7 | Physical Chemistry |
Because cycling probe technology does not involve the amplification of target DNA, CPT has a lower risk of cross contamination than PCR. In addition, CPT is faster than PCR and doesn't require a specialized thermocycler. CPT also does not require running CPT products on a gel. | 1 | Biochemistry |
Spectroradiometers, which operate almost like the visible region spectrophotometers, are designed to measure the spectral density of illuminants. Applications may include evaluation and categorization of lighting for sales by the manufacturer, or for the customers to confirm the lamp they decided to purchase is within their specifications. Components:
# The light source shines onto or through the sample.
# The sample transmits or reflects light.
# The detector detects how much light was reflected from or transmitted through the sample.
# The detector then converts how much light the sample transmitted or reflected into a number. | 7 | Physical Chemistry |
OCO-3 is constructed from spare equipment from the OCO-2 mission. Thus its physical characteristics are similar, but with some adaptations. A 2-axis pointing mirror was added, which will allow targeting of cities and other areas on order of for area mapping (also called "snapshot mode"). A resolution context camera was also added. An onboard cryocooler will maintain detector temperatures of around . Entrance optics were modified to maintain a similar ground footprint to OCO-2.
Similar to OCO and OCO-2, the main measurement will be of reflected near-IR sunlight. Grating spectrometers separate incoming light energy into different components of the electromagnetic spectrum (or wavelengths or "colors"). Because and molecular oxygen absorb light at specific wavelengths, the signal or absorption levels at different wavelengths provide information on the amount of gases. Three bands are used called Weak (around 1.6 μm), Strong (around 2.0 μm), and Oxygen-A (around 0.76 μm). There are 1,016 spectral elements per band, and measurements are made simultaneously at 8 side-by-side locations or "footprints" each about or smaller, 3 times per second. | 2 | Environmental Chemistry |
The Otto Warburg Medal is awarded annually by the German Society for Biochemistry and Molecular Biology (German: Gesellschaft für Biochemie und Molekularbiologie or GBM) to honour scientists who have contributed important work in the field of biological chemistry. It is named after Otto Warburg, a renowned German physiologist and Nobel Prize laureate. It was first awarded on his 80th birthday on 8 October 1963.
Up to 2013, nine Warburg Medal recipients have also been awarded the Nobel Prize. | 1 | Biochemistry |
Bacterial bioluminescence is seen in Photobacterium species, Vibrio fischeri, Vibrio haweyi, and Vibrio harveyi. Light emission in some bioluminescent bacteria utilizes antenna such as lumazine protein to accept the energy from the primary excited state on the luciferase, resulting in an excited lulnazine chromophore which emits light that is of a shorter wavelength (more blue), while in others use a yellow fluorescent protein (YFP) with flavin mononucleotide (FMN) as the chromophore and emits light that is red-shifted relative to that from luciferase. | 1 | Biochemistry |
Chemical structure of the herbicide is of primary affecting efficacy. 2,4-D, mecoprop, and dicamba control many broadleaf weeds but remain ineffective against turf grasses.
Chemical additives influence selectivity. Surfactants alter the physical properties of the spray solution and the overall phytotoxicity of the herbicide, increasing translocation. Herbicide safeners enhance the selectivity by boosting herbicide resistance by the crop but allowing the herbicide to damage the weed.
Selectivity is determined by the circumstances and technique of application. Climatic factors affect absorption including humidity, light, precipitation, and temperature. Foliage-applied herbicides will enter the leaf more readily at high humidity by lengthening the drying time of the spray droplet and increasing cuticle hydration. Light of high intensity may break down some herbicides and cause the leaf cuticle to thicken, which can interfere with absorption. Precipitation may wash away or remove some foliage-applied herbicides, but it will increase root absorption of soil-applied herbicides. Drought-stressed plants are less likely to translocate herbicides. As temperature increases, herbicides' performance may decrease. Absorption and translocation may be reduced in very cold weather. | 2 | Environmental Chemistry |
In the experiment a droplet of mercury is placed in a watch glass, immersed in an electrolyte such as sulfuric acid which contains an oxidizing agent such as hydrogen peroxide, potassium permanganate, or potassium dichromate. The tip of an iron nail is positioned almost touching the mercury. If the position of the nail tip is just right, the mercury blob begins to oscillate, changing shape. | 7 | Physical Chemistry |
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