text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
In the Ziegler process, linear alcohols are produced from ethylene and triethylaluminium followed by oxidation and hydrolysis. An idealized synthesis of 1-octanol is shown:
The process generates a range of alcohols that are separated by distillation.
Many higher alcohols are produced by hydroformylation of alkenes followed by hydrogenation. When applied to a terminal alkene, as is common, one typically obtains a linear alcohol:
Such processes give fatty alcohols, which are useful for detergents. | 0 | Organic Chemistry |
Potassium ethyl xanthate is used in the mining industry as flotation agent for extraction of the ores of copper, nickel, and silver. The method exploits the affinity of these "soft" metals for the organosulfur ligand.
Potassium xanthate is a useful reagent for preparing xanthate esters from alkyl and aryl halides. The resulting xanthate esters are useful intermediates in organic synthesis. | 8 | Metallurgy |
Motor proteins are the driving force behind most active transport of proteins and vesicles in the cytoplasm. Kinesins and cytoplasmic dyneins play essential roles in intracellular transport such as axonal transport and in the formation of the spindle apparatus and the separation of the chromosomes during mitosis and meiosis. Axonemal dynein, found in cilia and flagella, is crucial to cell motility, for example in spermatozoa, and fluid transport, for example in trachea. The muscle protein myosin "motors" the contraction of muscle fibers in animals. | 6 | Supramolecular Chemistry |
The effect of corrosion on a smooth-specimen S-N diagram is shown schematically on the right. Curve A shows the fatigue behavior of a material tested in air. A fatigue threshold (or limit) is seen in curve A, corresponding to the horizontal part of the curve. Curves B and C represent the fatigue behavior of the same material in two corrosive environments. In curve B, the fatigue failure at high stress levels is retarded, and the fatigue limit is eliminated. In curve C, the whole curve is shifted to the left; this indicates a general lowering in fatigue strength, accelerated initiation at higher stresses and elimination of the fatigue limit.
To meet the needs of advancing technology, higher-strength materials are developed through heat treatment or alloying. Such high-strength materials generally exhibit higher fatigue limits, and can be used at higher service stress levels even under fatigue loading. However, the presence of a corrosive environment during fatigue loading eliminates this stress advantage, since the fatigue limit becomes almost insensitive to the strength level for a particular group of alloys. This effect is schematically shown for several steels in the diagram on the left, which illustrates the debilitating effect of a corrosive environment on the functionality of high-strength materials under fatigue.
Corrosion fatigue in aqueous media is an electrochemical behavior. Fractures are initiated either by pitting or persistent slip bands. Corrosion fatigue may be reduced by alloy additions, inhibition and cathodic protection, all of which reduce pitting. Since corrosion-fatigue cracks initiate at a metals surface, surface treatments like plating, cladding, nitriding and shot peening were found to improve the materials resistance to this phenomenon. | 8 | Metallurgy |
The pre-mRNA processing at the 3 end of the RNA molecule involves cleavage of its 3 end and then the addition of about 250 adenine residues to form a poly(A) tail. The cleavage and adenylation reactions occur primarily if a polyadenylation signal sequence (5- AAUAAA-3) is located near the 3 end of the pre-mRNA molecule, which is followed by another sequence, which is usually (5-CA-3') and is the site of cleavage. A GU-rich sequence is also usually present further downstream on the pre-mRNA molecule. More recently, it has been demonstrated that alternate signal sequences such as UGUA upstream off the cleavage site can also direct cleavage and polyadenylation in the absence of the AAUAAA signal.
It is important to understand that these two signals are not mutually independent and often coexist. After the synthesis of the sequence elements, several multi-subunit proteins are transferred to the RNA molecule. The transfer of these sequence specific binding proteins cleavage and polyadenylation specificity factor (CPSF), Cleavage Factor I (CF I) and cleavage stimulation factor (CStF) occurs from RNA Polymerase II. The three factors bind to the sequence elements. The AAUAAA signal is directly bound by CPSF. For UGUA dependent processing sites, binding of the multi protein complex is done by Cleavage Factor I (CF I). The resultant protein complex formed contains additional cleavage factors and the enzyme Polyadenylate Polymerase (PAP). This complex cleaves the RNA between the polyadenylation sequence and the GU-rich sequence at the cleavage site marked by the (5-CA-3) sequences. Poly(A) polymerase then adds about 200 adenine units to the new 3 end of the RNA molecule using ATP as a precursor. As the poly(A) tail is synthesized, it binds multiple copies of poly(A)-binding protein, which protects the 3end from ribonuclease digestion by enzymes including the CCR4-Not complex. | 1 | Biochemistry |
N-, P-, and S-alkylation are important processes for the formation of carbon-nitrogen, carbon-phosphorus, and carbon-sulfur bonds,
Amines are readily alkylated. The rate of alkylation follows the order tertiary amine < secondary amine < primary amine. Typical alkylating agents are alkyl halides. Industry often relies on green chemistry methods involving alkylation of amines with alcohols, the byproduct being water. Hydroamination is another green method for N-alkylation.
In the Menshutkin reaction, a tertiary amine is converted into a quaternary ammonium salt by reaction with an alkyl halide. Similar reactions occur when tertiary phosphines are treated with alkyl halides, the products being phosphonium salts.
Thiols are readily alkylated to give thioethers via the thiol-ene reaction. The reaction is typically conducted in the presence of a base or using the conjugate base of the thiol. Thioethers undergo alkylation to give sulfonium ions. | 0 | Organic Chemistry |
Both steps are producing energy to be coupled to ATP synthesis. Nitrifying organisms are chemoautotrophs, and use carbon dioxide as their carbon source for growth. Some AOB possess the enzyme, urease, which catalyzes the conversion of the urea molecule to two ammonia molecules and one carbon dioxide molecule. Nitrosomonas europaea, as well as populations of soil-dwelling AOB, have been shown to assimilate the carbon dioxide released by the reaction to make biomass via the Calvin Cycle, and harvest energy by oxidizing ammonia (the other product of urease) to nitrite. This feature may explain enhanced growth of AOB in the presence of urea in acidic environments.
In most environments, organisms are present that will complete both steps of the process, yielding nitrate as the final product. However, it is possible to design systems in which nitrite is formed (the Sharon process).
Nitrification is important in agricultural systems, where fertilizer is often applied as ammonia. Conversion of this ammonia to nitrate increases nitrogen leaching because nitrate is more water-soluble than ammonia.
Nitrification also plays an important role in the removal of nitrogen from municipal wastewater. The conventional removal is nitrification, followed by denitrification. The cost of this process resides mainly in aeration (bringing oxygen in the reactor) and the addition of an external carbon source (e.g., methanol) for the denitrification.
Nitrification can also occur in drinking water. In distribution systems where chloramines are used as the secondary disinfectant, the presence of free ammonia can act as a substrate for ammonia-oxidizing microorganisms. The associated reactions can lead to the depletion of the disinfectant residual in the system. The addition of chlorite ion to chloramine-treated water has been shown to control nitrification.
Together with ammonification, nitrification forms a mineralization process that refers to the complete decomposition of organic material, with the release of available nitrogen compounds. This replenishes the nitrogen cycle. | 1 | Biochemistry |
The idea of corresponding states originated when van der Waals cast his equation in the dimensionless form, . However, as Boltzmann noted, such a simple representation could not correctly describe all substances. Indeed, the saturation analysis of this form produces , namely all substances have the same dimensionless coexistence curve. In order to avoid this paradox an extended principle of corresponding states has been suggested in which where is a substance dependent dimensionless parameter related to the only physical feature associated with an individual substance, its critical point.
The first candidate for was the critical compressibility factor , but because that quantity is difficult to measure accurately, the acentric factor developed by Kenneth Pitzer, , is more useful. The saturation pressure in this situation is represented by a one parameter family of curves, . Several investigators have produced correlations of saturation data for a number of substances, the best is that of Dong and Lienhard,
which has an rms error of over the range
Figure 3 is a plot of vs . for various values of as given by this equation. The ordinate is logarithmic in order to show the behavior at pressures far below the critical where differences among the various substances (indicated by varying values of ) are more pronounced.
Figure 4 is another plot of the same equation showing as a function of for various values of . It includes data from 51 substances including the vdW fluid over the range . This plot shows clearly that the vdW fluid () is a member of the class of real fluids; indeed it quantitatively describes the behavior of the liquid metals cesium () and mercury () whose values of are close to the vdW value. However, it describes the behavior of other fluids only qualitatively, because specific numerical values are modified by differing values of their Pitzer factor, . | 7 | Physical Chemistry |
Metalation was first observed in the laboratory by Edward Frankland during a synthesis of diethylzinc in 1849. While this development eventually led to the development of organometallic compounds of other metals, these compounds saw little use in the laboratory because of their expense and (in the case of organozinc compounds) their highly pyrophoric nature. Metalation reactions (particularly in the form of transmetalation) only began to see more widespread use in synthetic laboratories after François Auguste Victor Grignard’s synthesized organomagnesium halides directly from metallic magnesium and organic halides. These newfound organomagnesium reagents extreme versatility in organic synthesis caused metalation to see widespread use in laboratory science. Organolithium reagents were synthesized for the first time in 1917 by Schlenk and Holtz, though these reagents did not see widespread use as metallating agents or reagents in organic synthesis until Karl Ziegler, Henry Gilman, and Georg Wittig — among others — developed synthetic methods that improved upon this initial synthesis. After these improvements in synthesis came to be known, interest in the compounds increased significantly, as they are generally more reactive than organomagnesium compounds. The first use of an organolithium reagent as a metalation reagent occurred in 1928, with Schlenk and Bergmanns metalation of fluorene with ethyllithium. | 0 | Organic Chemistry |
During operation of an electrochemical cell, chemical energy is transformed into electrical energy. This can be expressed mathematically as the product of the cells emf E measured in volts (V) and the electric charge Q' transferred through the external circuit.
:Electrical energy = EQ
Q is the cell current integrated over time and measured in coulombs (C); it can also be determined by multiplying the total number n of electrons transferred (measured in moles) times Faradays constant (F').
The emf of the cell at zero current is the maximum possible emf. It can be used to calculate the maximum possible electrical energy that could be obtained from a chemical reaction. This energy is referred to as electrical work and is expressed by the following equation:
where work is defined as positive when it increases the energy of the system.
Since the free energy is the maximum amount of work that can be extracted from a system, one can write:
A positive cell potential gives a negative change in Gibbs free energy. This is consistent with the cell production of an electric current from the cathode to the anode through the external circuit. If the current is driven in the opposite direction by imposing an external potential, then work is done on the cell to drive electrolysis.
A spontaneous electrochemical reaction (change in Gibbs free energy less than zero) can be used to generate an electric current in electrochemical cells. This is the basis of all batteries and fuel cells. For example, gaseous oxygen (O) and
hydrogen (H) can be combined in a fuel cell to form water and energy, typically a combination of heat and electrical energy.
Conversely, non-spontaneous electrochemical reactions can be driven forward by the application of a current at sufficient voltage. The electrolysis of water into gaseous oxygen and hydrogen is a typical example.
The relation between the equilibrium constant, K, and the Gibbs free energy for an electrochemical cell is expressed as follows:
Rearranging to express the relation between standard potential and equilibrium constant yields
At T = 298 K, the previous equation can be rewritten using the Briggsian logarithm as follows: | 7 | Physical Chemistry |
In physics, atomic spectroscopy is the study of the electromagnetic radiation absorbed and emitted by atoms. Since unique elements have unique emission spectra, atomic spectroscopy is applied for determination of elemental compositions. It can be divided by atomization source or by the type of spectroscopy used. In the latter case, the main division is between optical and mass spectrometry. Mass spectrometry generally gives significantly better analytical performance, but is also significantly more complex. This complexity translates into higher purchase costs, higher operational costs, more operator training, and a greater number of components that can potentially fail. Because optical spectroscopy is often less expensive and has performance adequate for many tasks, it is far more common. Atomic absorption spectrometers are one of the most commonly sold and used analytical devices. | 7 | Physical Chemistry |
Oxidative phosphorylation produces 26 of the 30 equivalents of ATP generated in cellular respiration by transferring electrons from NADH or FADH2 to O through electron carriers. The energy released when electrons are passed from higher-energy NADH or FADH2 to the lower-energy O is required to phosphorylate ADP and once again generate ATP. It is this energy coupling and phosphorylation of ADP to ATP that gives the electron transport chain the name oxidative phosphorylation. | 1 | Biochemistry |
POSCO, one of the world's biggest steel production companies, in 1986, initiated a founding of a science and technology university in the city of Pohang, about 200 miles southeast of Seoul, the capital city of Korea. Pohang University of Science and Technology (POSTECH) has now become one of the top research universities in Asia. GIFT was founded to provide an academic environment for education and research on ferrous materials. | 8 | Metallurgy |
The difference between pitting and micropitting is the size of the pits after surface fatigue. Pits formed by micropitting are approximately 10–20 μm in depth, and micropitted metal often has a frosted or gray appearance. Normal pitting creates larger and more visible pits. Micropits are originated from the local contact of asperities produced by improper lubrication. | 8 | Metallurgy |
Aerobic organisms use a process called aerobic respiration to create ATP from ADP and a phosphate. Glucose (a monosaccharide) is oxidized to power the electron transport chain:
This equation is a summary of what happens in three series of biochemical reactions: glycolysis, the Krebs cycle (also known as the Citric acid cycle), and oxidative phosphorylation.
:CHO + 6 O + 38 ADP + 38 phosphate → 6 CO + 44 HO + 38 ATP
In Oxidative phosphorylation, ATP is synthesized from ADP and a phosphate using ATP synthase. ATP synthase is powered by a proton-motive force created by using the energy generated from the electron transport chain. A hydrogen ion (H) has a positive charge and if separated by a cellular membrane, it creates a difference in charge between the inside and outside of the membrane. Oxidative phosphorylation occurs in the mitochondria of eukaryotes.
Aerobic respiration needs O because it acts as the terminal electron acceptor in prokaryotes' electron transport chain. Molecular Oxygen is reduced to water in this process. | 1 | Biochemistry |
In the marine environment, nitrogen is often the limiting nutrient, so the nitrogen cycle in the ocean is of particular interest. The nitrification step of the cycle is of particular interest in the ocean because it creates nitrate, the primary form of nitrogen responsible for "new" production. Furthermore, as the ocean becomes enriched in anthropogenic CO, the resulting decrease in pH could lead to decreasing rates of nitrification. Nitrification could potentially become a "bottleneck" in the nitrogen cycle.
Nitrification, as stated above, is formally a two-step process; in the first step ammonia is oxidized to nitrite, and in the second step nitrite is oxidized to nitrate. Diverse microbes are responsible for each step in the marine environment. Several groups of ammonia-oxidizing bacteria (AOB) are known in the marine environment, including Nitrosomonas, Nitrospira, and Nitrosococcus. All contain the functional gene ammonia monooxygenase (AMO) which, as its name implies, is responsible for the oxidation of ammonia. Subsequent metagenomic studies and cultivation approaches have revealed that some Thermoproteota (formerly Crenarchaeota) possess AMO. Thermoproteota are abundant in the ocean and some species have a 200 times greater affinity for ammonia than AOB, contrasting with the previous belief that AOB are primarily responsible for nitrification in the ocean. Furthermore, though nitrification is classically thought to be vertically separated from primary production because the oxidation of nitrate by bacteria is inhibited by light, nitrification by AOA does not appear to be light inhibited, meaning that nitrification is occurring throughout the water column, challenging the classical definitions of "new" and "recycled" production.
In the second step, nitrite is oxidized to nitrate. In the oceans, this step is not as well understood as the first, but the bacteria Nitrospina and Nitrobacter are known to carry out this step in the ocean. | 1 | Biochemistry |
The role of the surface is strongly reaction-specific: in fact, one site can catalyze certain reactions and inhibit other ones.<br>
According to TSK model, surface atoms in nanocrystals can occupy terrace, step or kink positions: each site has a different tendency to adsorb reactants and to let them move along the surface. Generally, sites having lower coordination number (steps and kinks) are more reactive due to their high free energy. High energy sites, however, are less thermodynamically stable and nanocrystals have a tendency to transform to their equilibrium shape.
Thanks to the progress in nanoparticles synthesis it is now possible to have a single-crystal approach to surface science, allowing more precise research on the effect of a given surface. Studies have been conducted on nanoelectrodes exposing a (100), (110) or (111) plane to a solution containing the reactants, in order to define the surface effect on reaction rate and selectivity of the most common electrochemical reactions. | 7 | Physical Chemistry |
The European Coil Coating Association (ECCA) is an international non-profit association dedicated to the diffusion of the use of coil and/or sheet coated metal. | 8 | Metallurgy |
The syndrome primarily affects young males. Preliminary studies suggest that prevalence may be 1.8 per 10,000 live male births. 50% of those affected do not live beyond 25 years of age, with deaths attributed to the impaired immune function. | 1 | Biochemistry |
Ferrier proposed the following reaction mechanism:
In this mechanism, the terminal olefin undergoes hydroxymercuration to produce the first intermediate, compound 2, a hemiacetal. Next, methanol is lost and the dicarbonyl compound cyclizes through an attack on the electrophilic aldehyde to form the carbocycle as the product. A downside to this reaction is that the loss of CHOH at the anomeric position (carbon-1) results in a mixture of α- and β-anomers. The reaction also works for substituted alkenes (e. g. having an -OAc group on the terminal alkene).
Ferrier also reported that the final product, compound 5, could be converted into a conjugated ketone (compound 6) by reaction with acetic anhydride (AcO) and pyridine, as shown below. | 0 | Organic Chemistry |
At normal temperatures pumping mechanisms in cell walls retain intracellular potassium at high levels and extrude sodium. If these pumps fail sodium is taken up by the cell and potassium lost. Water follows the sodium passively and results in swelling of the cells. The importance of this control of cell swelling was demonstrated by McLoughlin who found a significant correlation between canine renal cortical water content and the ability of kidneys to support life after 36-hour storage. The pumping mechanism is driven by the enzyme system known as Na+K+- activated ATPase and is inhibited by cold. Levy found that metabolic activity at 10 °C, as indicated by oxygen consumption measurements, was reduced to about 5% of normal and, because all enzyme systems are affected in a similar way by hypothermia, ATPase activity is markedly reduced at 10 °C.
There are, however, tissue and species differences in the cold sensitivity of this ATPase which may account for the differences in the ability of tissues to withstand hypothermia. Martin has shown that in dog kidney cortical cells some ATPase activity is still present at 10 °C but not at 0 °C. In liver and heart cells activity was completely inhibited at 10 °C and this difference in the cold sensitivity of ATPase correlated with the greater difficulty in controlling cell swelling during hypothermic storage of liver and heart cells. A distinct ATPase is found in vessel walls, and this was shown by Belzer to be completely inhibited at 10 °C, when at this temperature kidney cortical cells ATPase is still active. These experiments were performed on aortic endothelium, but if the vascular endothelium of the kidney has the same properties, then vascular injury may be the limiting factor in prolonged kidney storage.
Willis has shown how hibernators derive some of their ability to survive low temperatures by having a Na+K+-ATPase which is able to transport sodium and potassium actively across their cell membranes, at 5 °C, about six times faster than in non-hibernators; this transport rate is sufficient to prevent cell swelling.
The rate of cooling of a tissue may also be significant in the production of injury to enzyme systems. Francavilla showed that when liver slices were rapidly cooled (immediate cooling to 12 °C in 6 minutes) anaerobic glycolysis, as measured on rewarming to 37 °C, was inhibited by about 67% of the activity that was demonstrated in slices that had been subjected to delayed cooling. However, dog kidney slices were less severely affected by the rapid cooling than were the liver slices. | 1 | Biochemistry |
Disulfide is also used to refer to compounds that contain two sulfide (S) centers. The compound carbon disulfide, CS is described with the structural formula i.e. S=C=S. This molecule is not a disulfide in the sense that it lacks a S-S bond. Similarly, molybdenum disulfide, MoS, is not a disulfide in the sense again that its sulfur atoms are not linked. | 0 | Organic Chemistry |
Numerical and theoretical considerations prompted the development of bimodal AFM. The method was initially thought to enhance topographic contrast in air environments. Three subsequent advances such as the capability to detect non-topography properties such electrostatic and magnetic interactions; imaging in liquid and ultra-high vacuum and its genuine quantitative features set the stage for further developments and applications. | 6 | Supramolecular Chemistry |
The Wnt signaling pathways are initiated by the binding of the Wnt ligand to the Fz receptor. There are three different molecular pathways downstream of the Wnt/Fz interaction. The majority of research has focused on the Wnt/β-catenin pathway (also known as the "canonical" Wnt pathway), which manages cell fate determination by regulating gene expression. The Wnt/Ca and Wnt/polarity pathways are known as the "non-canonical pathways". The decision of which pathway is activated most likely depends on which Wnt ligand and Fz receptor are present, as well as the cellular context. Nineteen Wnt ligands and ten different members of the Fz seven-transmembrane receptor family have been described in the human genome. As a result, a large variety of responses could be initiated from the Wnt/Fz interactions.
The Wnt/β-catenin pathway starts with the binding of Wnt to a receptor complex encompassing a Fz receptor and LRP co-receptor. After Wnt binds, an intracellular protein named Dishevelled (Dvl) is activated via phosphorylation. β-catenin degradation complexes in the cytoplasm are composed of adenomatous polyposis coli (APC), glycogen synthase kinase 3β (GSK3β) and Axin. APC promotes the degradation of β-catenin by increasing the affinity of the degradation complex to β-catenin. Axin is a scaffolding protein which holds the degradation complex together. The activated Dvl associates with Axin and prevents GSK3β and casein kinase 1α (CK1α) from phosphorylating critical substrates, such as β-catenin. Phosphorylation of β-catenin marks the protein for ubiquitylation and rapid degradation by proteasomes. Thus, the binding of Wnt to the receptor results in a non-phosphorylated form of β-catenin which localizes to the nucleus and, after displacing the Groucho corepressor protein, forms a complex with Tcf/Lef transcription factors and co-activators (such as CREB binding protein) and induces the expression of downstream target genes.
β-catenin is actively stabilized in over 50% of breast cancers and its nuclear localization correlates with poor patient prognosis. Several target genes of the Wnt signaling pathway, such as cyclin D1, are activated in a significant proportion of breast tumours. It has been shown that SFRP1 transcription can be driven by B-catenin in normal intestinal epithelial cells. Neoplastic epithelial cells were treated with lithium chloride, which inhibits GSK3B and thus stabilizes B-catenin. Lithium chloride is widely used to mimic Wnt signaling. Rather than suppressing SFRP1 expression, B-catenin/TCF activity was associated with the induction of SFRP1. This is consistent with a negative feedback response restricting the exposure of a normal cell to a prolonged Wnt growth factor signal.
Hedgehog signaling in the intestinal epithelium represses the canonical Wnt signaling to restrict expression of Wnt target genes to stem or progenitor cells. It was thought that the Hedgehog signaling pathway does this via the induction of the secreted-type Wnt inhibitor. Katoh et al. searched for the GLI-binding site within the promoter region of Wnt inhibitor genes. GLI are transcription factors that activate the transcription of Hedgehog target genes. The GLI-binding site was identified within the 5’-flanking promoter region of the human SFRP1 gene. The GLI-binding site was conserved among promoter regions of mammalian SFRP1 orthologs. These facts indicate that the SFRP1 gene was identified as the evolutionarily conserved target of the Hedgehog-GLI signaling pathway. SFRP1 was found to be expressed in mesenchymal cells. Hedgehog is secreted from differentiated epithelial cells to induce SFRP1 expression in mesenchymal cells, which keeps differentiated epithelial cells away from the effect of canonical Wnt signaling. Thus, SFRP1 is most likely the Hedgehog target to confine canonical Wnt signaling within stem or progenitor cells. Epigenetic CpG hypermethylation of the SFRP1 promoter during chronic persistent inflammation and aging leads to the occurrence of gastrointestinal cancers, such as colorectal cancer and gastric cancer, through the breakdown of Hedgehog-dependent Wnt signal inhibition. | 1 | Biochemistry |
In the panel it is shown an example of the working principle of a Mott detector, supposing a value for . If an electron beam with a 3:1 ratio of spin-up over spin-down electrons collide with the target, it will be splitted with a ratio 5:3, according to previous equation, with an asymmetry of 25%. | 7 | Physical Chemistry |
In general, electronegativity increases on passing from left to right along a period and decreases on descending a group. Hence, fluorine is the most electronegative of the elements (not counting noble gases), whereas caesium is the least electronegative, at least of those elements for which substantial data is available. This would lead one to believe that caesium fluoride is the compound whose bonding features the most ionic character.
There are some exceptions to this general rule. Gallium and germanium have higher electronegativities than aluminium and silicon, respectively, because of the d-block contraction. Elements of the fourth period immediately after the first row of the transition metals have unusually small atomic radii because the 3d-electrons are not effective at shielding the increased nuclear charge, and smaller atomic size correlates with higher electronegativity (see Allred-Rochow electronegativity and Sanderson electronegativity above). The anomalously high electronegativity of lead, in particular when compared to thallium and bismuth, is an artifact of electronegativity varying with oxidation state: its electronegativity conforms better to trends if it is quoted for the +2 state with a Pauling value of 1.87 instead of the +4 state. | 3 | Analytical Chemistry |
Aggregation pheromones function in mate choice, overcoming host resistance by mass attack, and defense against predators. A group of individuals at one location is referred to as an aggregation, whether consisting of one sex or both sexes. Male-produced sex attractants have been called aggregation pheromones, because they usually result in the arrival of both sexes at a calling site and increase the density of conspecifics surrounding the pheromone source. Most sex pheromones are produced by the females; only a small percentage of sex attractants are produced by males. Aggregation pheromones have been found in members of the Coleoptera, Collembola, Diptera, Hemiptera, Dictyoptera, and Orthoptera. In recent decades, aggregation pheromones have proven useful in the management of many pests, such as the boll weevil (Anthonomus grandis), the pea and bean weevil (Sitona lineatus, and stored product weevils (e.g. Sitophilus zeamais, Sitophilus granarius, and Sitophilus oryzae). Aggregation pheromones are among the most ecologically selective pest suppression methods. They are non-toxic and effective at very low concentrations. | 1 | Biochemistry |
In the food processing industry, hyperspectral imaging, combined with intelligent software, enables digital sorters (also called optical sorters) to identify and remove defects and foreign material (FM) that are invisible to traditional camera and laser sorters. By improving the accuracy of defect and FM removal, the food processor’s objective is to enhance product quality and increase yields.
Adopting hyperspectral imaging on digital sorters achieves non-destructive, 100 percent inspection in-line at full production volumes. The sorter’s software compares the hyperspectral images collected to user-defined accept/reject thresholds, and the ejection system automatically removes defects and foreign material.
The recent commercial adoption of hyperspectral sensor-based food sorters is most advanced in the nut industry where installed systems maximize the removal of stones, shells and other foreign material (FM) and extraneous vegetable matter (EVM) from walnuts, pecans, almonds, pistachios, peanuts and other nuts. Here, improved product quality, low false reject rates and the ability to handle high incoming defect loads often justify the cost of the technology.
Commercial adoption of hyperspectral sorters is also advancing at a fast pace in the potato processing industry where the technology promises to solve a number of outstanding product quality problems. Work is under way to use hyperspectral imaging to detect “sugar ends,” “hollow heart” and “common scab,” conditions that plague potato processors. | 7 | Physical Chemistry |
In a crossed molecular beam apparatus, two collimated beams of gas-phase atoms or molecules, each dilute enough to ignore collisions within each beam, intersect in a vacuum chamber. The direction and velocity of the resulting product molecules are then measured, and are frequently coupled with mass spectrometric data. These data yield information about the partitioning of energy among translational, rotational, and vibrational modes of the product molecules. | 7 | Physical Chemistry |
In size exclusion chromatography, where the separation process is driven by entropy, it is not possible to increase the resolution attained by a column via temperature or solvent gradients. Consequently, these separations often require SMB, to extend usable retention time differences between the molecules or particles being separated. SMB is also very useful in the pharmaceutical industry, where separation of molecules having different chirality must be done on a very large scale. For the purification of fructose, e.g. in high fructose corn syrup, or amino-acids, biological-acids, etc. on an industrial scale, simulated moving bed chromatography is used in order to improve the economics of the production. | 3 | Analytical Chemistry |
As observed through the literature, survivin is found to be over-expressed across many tumour types. Scientists are not sure of the mechanism that causes this abnormal over-expression of survivin; however, p53 is downregulated in almost all cancers, so it is tempting to suggest that survivin over-expression is due to p53 inactivity. Wagner et al. investigated the possible molecular mechanism involved with the over expression of survivin in acute myeloid leukemia (AML). In their experiments, they did both an epigenetic and a genetic analysis of the survivin gene promoter region in AML patients and compared the observations to what was seen in peripheral blood mononuclear cells (PBMCs) that have been shown to express no survivin. Assuming that the molecular mechanism of survivin re-expression in cancerous cells is at the transcriptional level, the authors decided to look at particular parts of the promoter region of survivin in order to see what happens in cancer cells that does not happen in normal cells that causes such a high level of survivin to be expressed. With regards to an epigenetic mechanism of survivin gene regulation, the authors measured the methylation status of the survivin promoter, since it is accepted that methylation of genes plays an important role in carcinogenesis by silencing of certain genes or vice versa. The authors used methylation specific polymerase chain reaction with bisulfite sequencing methods to measure the promoter methylation status in AML and PBMCs and found unmethylated survivin promoters in both groups. This result shows that DNA methylation status is not an important regulator of survivin re-expression during leukemogenesis. However, De Carvalho et al. performed a DNA methylation screening and identified that DNA methylation of IRAK3 plays a key role in survivin up-regulation in different types of Cancer, suggesting that epigenetic mechanisms plays an indirect role on abnormal over-expression of survivin. With regard to genetic analysis of the survivin promoter region, the isolated DNA of AML and PBMCs were treated with bisulfite, and the survivin promoter region sequence was amplified out with PCR and sequenced to look for any particular genetic changes in the DNA sequence between the two groups. Three single-nucleotide polymorphisms (SNPs) were identified and were all present both in AML patients and in healthy donors. This result suggests that the occurrence of these SNPs in the promoter region of the survivin gene also appears to be of no importance to survivin expression. However, it has not been ruled out yet that there may be other possible epigenetic mechanisms that may be responsible for a high level of survivin expression observed in cancer cells and not in normal cells. For example, the acetylation profile of the survivin promoter region can also be looked at. Different cancer and tissue types may have slight or significant differences in the way survivin expression is regulated in the cell, and, thus, the methylation status or genetic differences in the survivin promoter may be observed to be different in different tissues. Thus, further experiments assessing the epigenetic and genetic profile of different tumour types must be investigated. | 1 | Biochemistry |
When in biotic conditions, anaerobic corrosion can be facilitated by the metabolic activity of microorganisms in the surrounding environment. This process is known as microbiologically-influenced corrosion or bacterial anaerobic corrosion. Most notably, the production of dissolved sulfides by sulfate-reducing bacteria (SRB) react with solid metals and hydrogen ions to form metal sulfides in a redox reaction. | 8 | Metallurgy |
The insertion of membrane proteins into a lipid membrane has been monitored using LD, supplying the experimentalist with information about the orientation of the protein relative to the lipid membrane at different time points.
In addition, other types of molecule have been analysed by UV LD, including carbon nanotubes and their associated ligand complexes. | 7 | Physical Chemistry |
One simplified example of a synexpression group is the genes cdc6, cdc3, cdc46, and swi4 in yeast, which are all co-expressed early in the G-1 stage of the cell cycle., These genes share one common cis-regulatory element, called ECB, which serves as a binding site for the MCM1 trans-acting protein. Although these genes are not spatially clustered, co-regulation seems to be achieved via this common cis and trans control mechanism. Most synexpression groups are more complicated than the ECB group in yeast, involving myriad cis and trans control elements. | 1 | Biochemistry |
Enzymes are generally in a state that is not only a compromise between stability and catalytic efficiency, but also for specificity and evolvability, the latter two dictating whether an enzyme is a generalist (highly evolvable due to large promiscuity, but low main activity) or a specialist (high main activity, poorly evolvable due to low promiscuity). Examples of these are enzymes for primary and secondary metabolism in plants (§ Plant secondary metabolism below). Other factors can come into play, for example the glycerophosphodiesterase (gpdQ) from Enterobacter aerogenes shows different values for its promiscuous activities depending on the two metal ions it binds, which is dictated by ion availability.
In some cases promiscuity can be increased by relaxing the specificity of the active site by enlarging it with a single mutation as was the case of a D297G mutant of the E. coli L-Ala-D/L-Glu epimerase (ycjG) and E323G mutant of a pseudomonad muconate lactonizing enzyme II, allowing them to promiscuously catalyse the activity of O-succinylbenzoate synthase (menC). Conversely, promiscuity can be decreased as was the case of γ-humulene synthase (a sesquiterpene synthase) from Abies grandis that is known to produce 52 different sesquiterpenes from farnesyl diphosphate upon several mutations.
Studies on enzymes with broad-specificity—not promiscuous, but conceptually close—such as mammalian trypsin and chymotrypsin, and the bifunctional isopropylmalate isomerase/homoaconitase from Pyrococcus horikoshii have revealed that active site loop mobility contributes substantially to the catalytic elasticity of the enzyme. | 1 | Biochemistry |
Multiomics, multi-omics, integrative omics, "panomics" or "pan-omics" is a biological analysis approach in which the data sets are multiple "omes", such as the genome, proteome, transcriptome, epigenome, metabolome, and microbiome (i.e., a meta-genome and/or meta-transcriptome, depending upon how it is sequenced); in other words, the use of multiple omics technologies to study life in a concerted way. By combining these "omes", scientists can analyze complex biological big data to find novel associations between biological entities, pinpoint relevant biomarkers and build elaborate markers of disease and physiology. In doing so, multiomics integrates diverse omics data to find a coherently matching geno-pheno-envirotype relationship or association. The OmicTools service lists more than 99 softwares related to multiomic data analysis, as well as more than 99 databases on the topic.
Systems biology approaches are often based upon the use of panomic analysis data. The American Society of Clinical Oncology (ASCO) defines panomics as referring to "the interaction of all biological
functions within a cell and with other body functions, combining data collected by targeted tests ... and global assays (such as genome sequencing) with other patient-specific information." | 1 | Biochemistry |
Judd–Ofelt intensity parameters from absorption spectrum of any lanthanide can be calculated by the RELIC application software.
Judd–Ofelt intensity parameters and derived quantities (oscillator strengths, radiative transition probabilities, luminescence branching ratios, excited state radiative lifetimes, and estimates of quantum efficiencies) from the emission spectrum of Eu doped compounds, can be obtained by the JOES application software. | 7 | Physical Chemistry |
Levamlodipine (INN), also known as levoamlodipine or S-amlodipine is a pharmacologically active enantiomer of amlodipine. Amlodipine belongs to the dihydropyridine group of calcium channel blocker used as an antihypertensive and antianginal agent. It was approved by the U.S. FDA in December 2019 and is currently marketed under the brand name Conjupri. | 4 | Stereochemistry |
Current living forms on Earth are essentially composed of four types of molecular entities: (i) nucleic acids, (ii) proteins, (iii) carbohydrates, and (iv) lipids. Nucleic acids (DNA and RNA) embody and express the genetic information and, together, constitute the genome and the apparatus for its expression (the genotype). Proteins, carbohydrates, and lipids form the structures, which harness and handle energy from the environment for organizing matter according to the instructions specified by the genotype, aiming to its conservation and transmission. The ensemble of proteins, carbohydrates, lipids and nucleic acids constitute the phenotype. Life is thus made of the interaction of metabolism and genetics, of the genotype with the phenotype. Both are built around the chemistry of the most common elements of the universe (hydrogen, oxygen, nitrogen, and carbon), important although ancillary roles being played by phosphorus and sulphur, and by other elements.
Given the overwhelming variety of the chemically conceivable molecules, the fact that in biological systems we observe only a small subset of organic molecules has raised questions how and which different reaction pathways could have plausibly lead to the synthesis of pre-biological molecules on the primordial Earth. These are the main objectives of prebiotic chemistry research. | 9 | Geochemistry |
The set of translations and rotations together form the rigid motions or rigid displacements. This set forms a group under composition, the group of rigid motions, a subgroup of the full group of Euclidean isometries. | 3 | Analytical Chemistry |
Mutations in the NDUFAF6 gene are associated with complex I enzymatic deficiency and lead to Leigh syndrome, which is characterized by lesions in the central nervous system and rapid deterioration of cognitive and motor functions. In Acadians, a non-coding mutation in NDUFAF6 has been shown to cause Acadian variant Fanconi Syndrome, symptoms of which include pulmonary interstitial fibrosis and proximal tubular dysfunction accompanied by slowly progressive kidney disease. Inheritance of mutations in the NDUFAF6 gene is autosomal recessive. | 1 | Biochemistry |
Conductive measurements began as early as the 18th century, when Andreas Baumgartner noticed that salt and mineral waters from Bad Gastein in Austria conducted electricity. As such, using conductometry to determine water purity, which is often used today to test the effectiveness of water purification systems, began in 1776. Friedrich Kohlrausch further developed conductometry in the 1860s when he applied alternating current to water, acids, and other solutions. It was also around this time when Willis Whitney, who was studying the interactions of sulfuric acid and chromium sulfate complexes, found the first conductometric endpoint. These finding culminated into potentiometric titrations and the first instrument for volumetric analysis by Robert Behrend in 1883 while titrating chloride and bromide with HgNO. This development allowed for testing the solubility of salts and hydrogen ion concentration, as well as acid/base and redox titrations. Conductometry was further improved with the development of the glass electrode, which began in 1909. | 3 | Analytical Chemistry |
Chemically, lichenin is a mixed-linkage glucan, consisting of repeating glucose units linked by β-1,3 and β-1,4 glycosidic bonds. | 1 | Biochemistry |
Edward Roberts FRSC., is a British-born American scientist with expertise in biochemistry and synthetic organic chemistry. He is recognized for his significant contributions to medicinal chemistry, the design and discovery of new medicines in the development of novel therapeutics. | 0 | Organic Chemistry |
Certain amphiphilic block copolymer micelles display a similar behavior as surfactant micelles. These are generally called dynamic micelles and are characterized by the same relaxation processes assigned to surfactant exchange and micelle scission/recombination. Although the relaxation processes are the same between the two types of micelles, the kinetics of unimer exchange are very different. While in surfactant systems the unimers leave and join the micelles through a diffusion-controlled process, for copolymers the entry rate constant is slower than a diffusion controlled process. The rate of this process was found to be a decreasing power-law of the degree of polymerization of the hydrophobic block to the power 2/3. This difference is due to the coiling of the hydrophobic block of a copolymer exiting the core of a micelle.
Block copolymers which form dynamic micelles are some of the tri-block poloxamers under the right conditions. | 6 | Supramolecular Chemistry |
The graphic display of an operon contains all the genes of its different transcription units, as well as all the regulatory elements involved in the transcription and regulation of those TUs. An operon is here conceived as a structural unit encompassing all genes and regulatory elements. An operon with several promoters located near each other may also have dual binding sites, indicating that such a site can activate one particular promoter, but repress a second one.
In the same page, the collection of the different TUs is displayed below the operon. The graphic display of an operon contains all the genes of its different transcription units, as well as all the regulatory elements involved in the transcription and regulation of those TUs.
The graphic display of a TU will always contain only one promoter -when known- with the binding sites that regulate its activity, followed by the transcribed genes. Note that dual sites are frequently displayed at a TU as repressors or activators. This is because the site will have a particular effect on the promoter of that TU. | 1 | Biochemistry |
Of primary interest among the intracellular components are microbial enzymes: catalase, amylase, protease, pectinase, cellulase, hemicellulase, lipase, lactase, streptokinase and many others. Recombinant proteins, such as insulin, hepatitis B vaccine, interferon, granulocyte colony-stimulating factor, streptokinase and others are also made this way. The largest difference between this process and the others is that the cells must be ruptured (lysed) at the end of fermentation, and the environment must be manipulated to maximize the amount of the product. Furthermore, the product (typically a protein) must be separated from all of the other cellular proteins in the lysate to be purified. | 1 | Biochemistry |
Signal-correlation techniques were first experimentally applied to fluorescence in 1972 by Magde, Elson, and Webb, who are therefore commonly credited as the "inventors" of FCS. The technique was further developed in a group of papers by these and other authors soon after, establishing the theoretical foundations and types of applications.
Around 1990, with the ability of detecting sufficiently small number of fluorescence particles, two issues emerged: A non-Gaussian distribution of the fluorescence intensity and the three-dimensional confocal Measurement Volume of a laser-microscopy system. The former led to an analysis of distributions and moments of the fluorescent signals for extracting molecular information, which eventually became a collection of methods known as Brightness Analyses. See Thompson (1991) for a review of that period.
Beginning in 1993, a number of improvements in the measurement techniques—notably using confocal microscopy, and then two-photon microscopy—to better define the measurement volume and reject background—greatly improved the signal-to-noise ratio and allowed single molecule sensitivity. Since then, there has been a renewed interest in FCS, and as of August 2007 there have been over 3,000 papers using FCS found in Web of Science. See Krichevsky and Bonnet for a review. In addition, there has been a flurry of activity extending FCS in various ways, for instance to laser scanning and spinning-disk confocal microscopy (from a stationary, single point measurement), in using cross-correlation (FCCS) between two fluorescent channels instead of autocorrelation, and in using Förster Resonance Energy Transfer (FRET) instead of fluorescence. | 7 | Physical Chemistry |
Abortive initiation occurs prior to promoter clearance.
# RNA polymerase binds to promoter DNA to form an RNA polymerase-promoter closed complex
# RNA polymerase then unwinds one turn of DNA surrounding the transcription start site to yield an RNA polymerase-promoter open complex
# RNA polymerase enters into abortive cycles of synthesis and releases short RNA products (contains less than 10 nucleotides)
# RNA polymerase escapes the promoter and enters into the elongation step of transcription | 1 | Biochemistry |
For logic gates with a single input, there are four possible output patterns. When the input is 0, the output can be either a 0 or 1. When the input is 1, the output can again be 0 or 1. The four output bit patterns that can arise corresponds to a specific logic type: PASS 0, YES, NOT, and PASS 1. PASS 0 always outputs 0, whatever the input. PASS 1 always outputs 1, whatever the input. YES outputs a 1 when the input is 1, and NOT is the inverse of YES – it outputs a 0 when the input is 1.
AND, OR, XOR, NAND, NOR, XNOR, and INH are two-input logic gates. The AND, OR, and XOR gates are fundamental logic gates, and the NAND, NOR, and XNOR gates are complementary to AND, OR, and XOR gates, respectively. An INHIBIT (INH) gate is a special conditional logic gate that includes a prohibitory input. When the prohibitory input is absent, the output produced depends solely on the other input. | 6 | Supramolecular Chemistry |
In electric discharges, for example as laboratory discharges between two electrodes or as lightning discharges between cloud and ground or within clouds, electrons produce Bremsstrahlung photons while scattering off air molecules. These photons become manifest in terrestrial gamma-ray flashes and are the source for beams of electrons, positrons, neutrons and protons. The appearance of Bremsstrahlung photons also influences the propagation and morphology of discharges in nitrogen-oxygen mixtures with low percentages of oxygen. | 7 | Physical Chemistry |
In molecular spectroscopy, a Jablonski diagram is a diagram that illustrates the electronic states and often the vibrational levels of a molecule, and also the transitions between them. The states are arranged vertically by energy and grouped horizontally by spin multiplicity. Nonradiative transitions are indicated by squiggly arrows and radiative transitions by straight arrows. The vibrational ground states of each electronic state are indicated with thick lines, the higher vibrational states with thinner lines.
The diagram is named after the Polish physicist Aleksander Jabłoński who first proposed it in 1933. | 7 | Physical Chemistry |
In materials science and soil mechanics, a slip line field or slip line field theory is a technique often used to analyze the stresses and forces involved in the major deformation of metals or soils. In essence, in some problems including plane strain and plane stress elastic-plastic problems, elastic part of the material prevent unrestrained plastic flow but in many metal-forming processes, such as rolling, drawing, gorging, etc., large unrestricted plastic flows occur except for many small elastic zones. In effect we are concerned with a rigid-plastic material under condition of plane strain. it turns out that the simplest way of solving stress equations is to express them in terms of a coordinate system that is along potential slip (or failure) surfaces. It is for this reason that this type of analysis is termed slip line analysis or the theory of slip line fields in the literature. | 8 | Metallurgy |
To quantify microstructural features, both morphological and material property must be characterized. Image processing is a robust technique for determination of morphological features such as volume fraction, inclusion morphology, void and crystal orientations. To acquire micrographs, optical as well as electron microscopy are commonly used.
To determine material property, Nanoindentation is a robust technique for determination of properties in micron and submicron level for which conventional testing are not feasible. Conventional mechanical testing such as tensile testing or dynamic mechanical analysis (DMA) can only return macroscopic properties without any indication of microstructural properties. However, nanoindentation can be used for determination of local microstructural properties of homogeneous as well as heterogeneous materials. Microstructures can also be characterized using high-order statistical models through which a set of complicated statistical properties are extracted from the images. Then, these properties can be used to produce various other stochastic models. | 8 | Metallurgy |
Gene function can be investigated by systematically "knocking out" genes one by one. This is done by either deletion or disruption of function (such as by insertional mutagenesis) and the resulting organisms are screened for phenotypes that provide clues to the function of the disrupted gene. Knock-outs have been produced for whole genomes, i.e. by deleting all genes in a genome. For essential genes, this is not possible, so other techniques are used, e.g. deleting a gene while expressing the gene from a plasmid, using an inducible promoter, so that the level of gene product can be changed at will (and thus a "functional" deletion achieved). | 1 | Biochemistry |
The citrate-malate shuttle is a series of chemical reactions, commonly referred to as a biochemical cycle or system, that transports acetyl-CoA in the mitochondrial matrix across the inner and outer mitochondrial membranes for fatty acid synthesis. Mitochondria are enclosed in a double membrane. As the inner mitochondrial membrane is impermeable to acetyl-CoA, the shuttle system is essential to fatty acid synthesis in the cytosol. It plays an important role in the generation of lipids in the liver (hepatic lipogenesis).
The name of the citrate-malate shuttle is derived from the two intermediates – short-lived chemicals that are generated in a reaction step and consumed entirely in the next – citrate and malate that carry the acetyl-CoA molecule across the mitochondrial double membrane.
The citrate–malate shuttle is present in humans and other higher eukaryotic organisms and is closely related to the Krebs cycle. The system is responsible for the transportation of malate into the mitochondrial matrix to serve as an intermediate in the Krebs cycle and the transportation of citrate into the cytosol for secretion in Aspergillus niger, a fungus used in the commercial production of citric acid. | 1 | Biochemistry |
The full biosynthesis of Absinthin in Artemisia absinthium has not been elucidated, but a great portion of it can be inferred from the natural product precursors required to access Absinthin. While terpenoids like Absinthin can be said to consist of isoprene "units," isoprene by itself is too stable and does not react directly. Rather, the isoprene units are transferred and reacted as diphosphates. As the nomenclature for terpenes suggests, the first Absinthin precursor farnesyl diphosphate [A] contains 15 carbons, or 3 isoprene units. Diphosphate departure (1) generates a carbo-cation within the synthase, which can then be attacked by a carbon-carbon double bond at the opposing end of the molecule (2). The first stable intermediate in the biosynthesis pathway in Artemisia is likely Germacrene A [B], which has been previously identified in plant sesquiterpene pathways as a precursor to guaianolides. From there, hydroxylation (3) occurs, followed by oxidation (4) to an aldehyde directly followed by further hydroxylation (5) and formation of a carboxyl group. It is important to note the disappearance of the terminal carbon-carbon double bond after (4), as the reduction of this bond in the final product differentiates the Absinthin monomer from other Germacrene A downstream products. This reduction does not necessarily occur at step (4), but may occur further downstream. With the carboxyl and hydroxyl group in position, the guaiano-lactone [C] formation via dehydration (7) can occur, as proposed for a general guaianolide pathway. Formation of the Absinthin sesquiterpene guaianolide monomer [D] from hydroxylation and double bond rearrangement (8,9) is then postulated to directly precede dimerization to Absinthin [E] via a naturally occurring Diels-Alder reaction [10], which is likely facilitated by the associated synthase even though the reaction itself can occur in good yields spontaneously, albeit slower than typical natural product biosynthesis.
While no synthases specific to Artemisia absinthium have been sufficiently isolated to recreate this particular sesquiterpene formation in vitro, the general reaction scheme presented here portrays a likely scenario for Absinthin biosynthesis through the use of terpene intermediates utilized in the biosynthesis of Germacrene A, another sesquiterpene lactone. Enzymatic analogs from terpene biosynthesis which help rationalize the above proposed numbered biosynthetic steps are as follows:
# Farnesyl diphosphate departure via a generic sesquiterpene synthase
# Ring closure via a generic sesquiterpene synthase (as for #1)
# Hydroxylation of terminal allylic carbon via Germacrene A hydroxylase, a cytochrome P450 enzyme.
# Oxidation of alcohol to aldol, via -germacrene A hydroxylase.
# Hydroxylation of alcohol to carboxyl group, via Germacrene A hydroxylase.
# NADPH-mediated hydroxylation of allylic carbon via a postulated hydroxylation to precede lactone ring closure
# Lactone formation/ring closure
# Hydroxylation at carbon-carbon tertiary double bond.
# Additional 5-membered ring formation/cyclization
# Diels-Alder coupling via an unidentified enzyme in Artemisia absinthium. | 0 | Organic Chemistry |
Multipstep ultrasensitivity occurs when a single effector acts on several steps in a cascade. Successive cascade signals can result in higher levels of noise being introduced into the signal that can interfere with the final output. This is especially relevant for large cascades, such as the flagellar regulatory system in which the master regulator signal is transmitted through multiple intermediate regulators before activating transcription. Cascade ultrasensitivity can reduce noise and therefore require less input for activation. Additionally, multiple phosphorylation events are an example of ultrasensitivity. Recent modeling has shown that multiple phosphorylation sites on membrane proteins could serve to locally saturate enzyme activity. Proteins at the membrane are greatly reduced in mobility compared to those in the cytoplasm, this means that a membrane tethered enzyme acting upon a membrane protein will take longer to diffuse away. With the addition of multiple phosphorylation sites upon the membrane substrate, the enzyme can - by a combination of increased local concentration of enzyme and increased substrates - quickly reach saturation. | 1 | Biochemistry |
The FDA label contains warnings that rasagiline may cause severe hypertension or hypotension, may make people sleepy, may make motor control worse in some people, may cause hallucinations and psychotic-like behavior, may cause impulse control disorder, may increase the risk of melanoma, and upon withdrawal may cause high fever or confusion.
Side effects when the drug is taken alone include flu-like symptoms, joint pain, depression, stomach upset, headache, dizziness, and insomnia. When taken with L-DOPA, side effects include increased movement problems, accidental injury, sudden drops in blood pressure, joint pain and swelling, dry mouth, rash, abnormal dreams and digestive problems including vomiting, loss of appetite, weight loss, abdominal pain, nausea, constipation. When taken with Parkinson's drugs other than L-DOPA, side effects include peripheral edema, fall, joint pain, cough, and insomnia. | 4 | Stereochemistry |
The 1963 Nobel Prize in Chemistry was awarded to German Karl Ziegler, for his discovery of first titanium-based catalysts, and Italian Giulio Natta, for using them to prepare stereoregular polymers from propylene. Ziegler–Natta catalysts have been used in the commercial manufacture of various polyolefins since 1956. As of 2010, the total volume of plastics, elastomers, and rubbers produced from alkenes with these and related (especially Phillips) catalysts worldwide exceeds 100 million tonnes. Together, these polymers represent the largest-volume commodity plastics as well as the largest-volume commodity chemicals in the world.
In the early 1950s workers at Phillips Petroleum discovered that chromium catalysts are highly effective for the low-temperature polymerization of ethylene, which launched major industrial technologies culminating in the Phillips catalyst. A few years later, Ziegler discovered that a combination of titanium tetrachloride (TiCl) and diethylaluminium chloride (Al(CH)Cl) gave comparable activities for the production of polyethylene. Natta used crystalline α-TiCl in combination with Al(CH) to produce first isotactic polypropylene. Usually Ziegler catalysts refer to titanium-based systems for conversions of ethylene and Ziegler–Natta catalysts refer to systems for conversions of propylene.
Also, in the 1960s, BASF developed a gas-phase, mechanically-stirred polymerization process for making polypropylene. In that process, the particle bed in the reactor was either not fluidized or not fully fluidized. In 1968, the first gas-phase fluidized-bed polymerization process, the Unipol process, was commercialized by Union Carbide to produce polyethylene. In the mid-1980s, the Unipol process was further extended to produce polypropylene.
In the 1970s, magnesium chloride (MgCl) was discovered to greatly enhance the activity of the titanium-based catalysts. These catalysts were so active that the removal of unwanted amorphous polymer and residual titanium from the product (so-called deashing) was no longer necessary, enabling the commercialization of linear low-density polyethylene (LLDPE) resins and allowed the development of fully amorphous copolymers.
The fluidized-bed process remains one of the two most widely used processes for producing polypropylene. | 7 | Physical Chemistry |
In 1905, in an article entitled "Radiation through a foggy atmosphere", Arthur Schuster published a solution to the equation of radiative transfer, which describes the propagation of radiation through a medium, affected by absorption, emission, and scattering processes. His mathematics used a two flux approximation; i.e., all light is assumed to travel with a component either in the same direction as the incident beam, or in the opposite direction. He used the word scattering rather than reflection, and considered scatter to be in all directions. He used the symbols k and s for absorption and isotropic scattering coefficients, and repeatedly refers to radiation entering a "layer", which ranges in size from infinitesimal to infinitely thick. In his treatment, the radiation enters the layers at all possible angles, referred to as "diffuse illumination". | 7 | Physical Chemistry |
Glucuronidation occurs mainly in the liver, although the enzyme responsible for its catalysis, UDP-glucuronyltransferase, has been found in all major body organs (e.g., intestine, kidneys, brain, adrenal gland, spleen, and thymus). | 0 | Organic Chemistry |
Pregnanediol glucuronide, or 5β-pregnane-3α,20α-diol 3α-glucuronide, is the major metabolite of progesterone and the C3α glucuronide conjugate of pregnanediol (5β-pregnane-3α,20α-diol). Approximately 15 to 30% of a parenteral dose of progesterone is metabolized into pregnanediol glucuronide. While this specific isomer is referred to as pregnanediol glucuronide and is the most major form, there are actually many possible isomers of the metabolite. | 1 | Biochemistry |
Percoll was previously used in assisted reproductive technology (ART) to select sperm from semen by density gradient centrifugation, for use in techniques such as in vitro fertilization or intrauterine insemination. However, in 1996, Pharmacia sent out a letter to laboratories stating that Percoll should be used for research purposes only, not clinical. Pharmacia had not marketed it as a sperm preparation product; it had been repackaged and sold as such by third-party manufacturers. The FDA Warning Letter was due to concerns that PVP might cause damage to sperm (an unknown issue), and also that some batches of Percoll contained high levels of endotoxin (a known issue). The latter concern also applies to the use of Percoll with any other cells that might be injected back into a patient, since endotoxin can cause severe inflammation and fever. Since then it has been replaced with other colloids in the ART industry. | 1 | Biochemistry |
Treatment of tantalum pentachloride with hexamethylbenzene (CMe), aluminium, and aluminium trichloride gives [M(η-CMe)AlCl].
Tantalum-alkyne complexes catalyze cyclotrimerizations. Some tantalum-alkyne complexes are precursors to allylic alcohols. Tantalacyclopropenes are invoked as intermediates. | 0 | Organic Chemistry |
ppGpp and pppGpp were first identified by Michael Cashel in 1969. These nucleotides were found to accumulate rapidly in Escherichia coli cells starved for amino acids and inhibit synthesis of ribosomal and transfer RNAs. It is now known that (p)ppGpp is also produced in response to other stressors including carbon and phosphate starvation. Historically, literature surrounding (p)ppGpp have given conflicting findings and information on its role in bacterial stress responses. | 1 | Biochemistry |
Other climate change factors to consider that might influence these lipid-rich copepods are shifts of current systems, storm activity and sea-ice cover. In some regions of the arctic, specifically the Bering Sea, studies have forecasted a decrease in storms due to warming. This impacts the mixing of the water column that brings nutrient-rich water upwards. Copepods consume primary producers that require nutrients to survive. Limiting the amount of nutrients in the water column could decrease the abundance of these primary producers and subsequently reduce Calanus spp. abundance as well.
Changes in the water masses and temperature could have a direct effect on the zooplanktons vertical migration. The distribution of the zooplankton in the water column is controlled by the currents. The Calanus spp. use the water column for their vertical migration. Changes to the currents while Calanus spp. are in diapause could result in a reduction in the abundance of the copepods in the Norwegian Sea. Since the lipid pump is controlled through the movement of copepods, particularly Calanus' spp., impacts of climate change that affect copepod abundance or seasonal migration will directly impact the lipid pump and carbon export to the deep ocean. | 9 | Geochemistry |
Manganese is also important in photosynthetic oxygen evolution in chloroplasts in plants. The oxygen-evolving complex (OEC) is a part of photosystem II contained in the thylakoid membranes of chloroplasts; it is responsible for the terminal photooxidation of water during the light reactions of photosynthesis, and has a metalloenzyme core containing four atoms of manganese. To fulfill this requirement, most broad-spectrum plant fertilizers contain manganese. | 1 | Biochemistry |
Reagent test results develop very quickly and due to reactions with moisture and oxygen in air, any changes after the first 60 seconds should be discarded. | 3 | Analytical Chemistry |
A problem with transition state analogue selection approach is that catalytic activity is not a screening criterion. TSAs do not necessarily represent real transition states and so a catalyst obtained from screening could just be the best receptor for a TSA but is not necessarily the best catalyst. To circumvent this problem, catalytic activity needs to be measured directly and also quickly. To develop a high-throughput screen, substrates could be designed to change color or release a fluorescent product upon reaction. For example, Crabtree and coworkers utilized this method in screening for a hydrosylation catalysts for alkene and imine. Unfortunately the prerequisite for such substrates narrow down the range of reactions for study. | 6 | Supramolecular Chemistry |
In biochemistry, in the biological context of organisms' regulation of gene expression and production of gene products, downregulation is the process by which a cell decreases the production and quantities of its cellular components, such as RNA and proteins, in response to an external stimulus. The complementary process that involves increase in quantities of cellular components is called upregulation.
An example of downregulation is the cellular decrease in the expression of a specific receptor in response to its increased activation by a molecule, such as a hormone or neurotransmitter, which reduces the cell's sensitivity to the molecule. This is an example of a locally acting (negative feedback) mechanism.
An example of upregulation is the response of liver cells exposed to such xenobiotic molecules as dioxin. In this situation, the cells increase their production of cytochrome P450 enzymes, which in turn increases degradation of these dioxin molecules.
Downregulation or upregulation of an RNA or protein may also arise by an epigenetic alteration. Such an epigenetic alteration can cause expression of the RNA or protein to no longer respond to an external stimulus. This occurs, for instance, during drug addiction or progression to cancer. | 1 | Biochemistry |
Cefuroxime is generally well tolerated, and its side effects are usually transient. If ingested after food, this antibiotic is both better absorbed and less likely to cause its most common side effects of diarrhea, nausea, vomiting, headaches/migraines, dizziness, and abdominal pain compared to most antibiotics in its class.
Although a widely stated cross-allergic risk of about 10% exists between cephalosporins and penicillin, an assessment in 2006 have shown no increased risk for a cross-allergic reaction for cefuroxime and several other second-generation or later cephalosporins. | 4 | Stereochemistry |
The leuco dye variant is typically composed of leuco dyes with additional chemicals to add different desired effects. It is the most commonly used type because it is easier to manufacture. They can be designed to react to changes in temperature that range from -15 °C to 60 °C. Most common applications of the ink have activation temperatures at -10 °C (cold), 31 °C (body temperature), or 43 °C (warm). At lower temperatures, the ink appears to be a certain color, and once the temperature increases, the ink becomes either translucent or lightly colored, allowing hidden patterns to be seen. This gives the effect of a change in color, and the process can also be reversed by lowering the temperature again. | 7 | Physical Chemistry |
Failures due to service or operation conditions includes using a component outside of its intended conditions, such as an impact force or a high load. It can also include failures due to unexpected conditions in usage, such as an unexpected contact point that causes wear and abrasion or an unexpected humidity level or chemical presence that causes corrosion. These factors result in the component failing at an earlier time than expected. | 8 | Metallurgy |
Barley yellow dwarf virus 5' UTR is a non-coding RNA element containing structural elements required for translation of the genome of the plant disease pathogen Barley yellow dwarf virus.
Unlike eukaryotic mRNA, this virus lacks a 5 cap and a poly(A) tail but still circularises its mRNA through base pairing between two stem loops, one located in the 5 untranslated region (UTR) and the other within the 3 UTR. The structure within the 3 UTR has been previously characterised as the 3 cap-independent translation element (3 TE element) and the 5 UTR of barley yellow dwarf virus has been predicted to contain 4 stem loop structures. Mutagenesis showed that stem loop 4 is essential for base pairing with 3TE and only 5 bases are needed to base pair for mRNA circularization to occur. | 1 | Biochemistry |
Serial analysis of gene expression (SAGE) is an alternate method of analysis based on RNA sequencing rather than hybridization. SAGE relies on the sequencing of 10–17 base pair tags which are unique to each gene. These tags are produced from poly-A mRNA and ligated end-to-end before sequencing. SAGE gives an unbiased measurement of the number of transcripts per cell, since it does not depend on prior knowledge of what transcripts to study (as microarrays do). | 1 | Biochemistry |
18-Crown-6 is an organic compound with the formula [CHO] and the IUPAC name of 1,4,7,10,13,16-hexaoxacyclooctadecane. It is a white, hygroscopic crystalline solid with a low melting point. Like other crown ethers, 18-crown-6 functions as a ligand for some metal cations with a particular affinity for potassium cations (binding constant in methanol: 10 M). The point group of 18-crown-6 is S. The dipole moment of 18-crown-6 varies in different solvent and under different temperature. Under 25 °C, the dipole moment of 18-crown-6 is in cyclohexane and in benzene. The synthesis of the crown ethers led to the awarding of the Nobel Prize in Chemistry to Charles J. Pedersen. | 6 | Supramolecular Chemistry |
He was born in Balsall Heath, Birmingham, Warwickshire, (now the West Midlands), England, the son of Joseph Henry Pickard, a tool maker, and Alice his wife, the daughter of Robert Howson of Birmingham. From 1883-1891 he attended King Edward VIs Grammar School. In 1891 he studied chemistry at Mason Science College (which later became the University of Birmingham), under Percy F. Frankland and obtained a first class BSc, then awarded by the University of London. In 1896 he attended the University of Munich as an 1851 Exhibitioner being awarded a PhD summa cum laude' in 1898. | 4 | Stereochemistry |
Maltose, cellobiose, and chitobiose are hydrolysis products of the polysaccharides starch, cellulose, and chitin, respectively.
Less common disaccharides include: | 0 | Organic Chemistry |
In aquatic sediments, several reactions can transform the chemicals released by the creosote preservatives into more dangerous chemicals. Most creosote preservative compounds have hazards associated with them before they are transformed. Cresol (m-, p-, and o-), phenol, guaiacol, and xylenol (1,3,4- and 1,3,5-) all are acute aquatic hazards prior to going through chemical reactions with the sediments. Alkylation reactions allows for the compounds to transition into more toxic compounds with the addition of R-groups to the major compounds found in creosote preservatives. Compounds formed through alkylation include: 3,4-dimethylphenol, 2,3-dimethylphenol, and 2,5-dimethylphenol, which are all listed as acute environmental hazards. Biodegradation controls the rate at which the sediment holds the chemicals, and the number of reactions that are able to take place. The biodegradation process can take place under many different conditions, and vary depending on the compounds that are released. Oxidation-reduction reactions allow for the compounds to be broken down into new forms of more toxic molecules. Studies have shown oxidation-reduction reactions of creosote preservative compounds included compounds that are listed as environmental hazards, such as p-benzoquinone in the oxidation of phenol. Not only are the initial compounds in creosote hazardous to the environment, but the byproducts of the chemical reactions are environmental hazardous as well. | 7 | Physical Chemistry |
Caspases are an important group of proteases involved in apoptosis or programmed cell death. The precursors of caspase, procaspase, may be activated by proteolysis through its association with a protein complex that forms apoptosome, or by granzyme B, or via the death receptor pathways. | 1 | Biochemistry |
There is a simplified special case for the spectroscopic parameters of a sheet. This sheet consists of three plane parallel layers (1:front surface, 2:interior, 3:rear surface) in which the surfaces both have the same remission fraction when illuminated from either direction, regardless of the relative refractive indices of the two media on either side of the surface. For the case of zero absorption in the interior, the total remission and transmission from the layer can be determined from the infinite series, where is the remission from the surface:
These formulas can be modified to account for absorption. Alternatively, the spectroscopic parameters of a sheet (or slab) can be built up from the spectroscopic parameters of the individual pieces that compose the layer: surface, interior, surface. This can be done using an approach developed by Kubelka for treatment of inhomogeneous layers. Using the example from the previous section: { , , } {, , }.
We will assume the interior of the sheet is composed of a material that has Napierian absorption coefficient of 0.5 cm, and the sheet is 1 mm thick (). For this case, on a single trip through the interior, according to the Bouguer-Lambert law, , which according to our assumptions yields and . Thus { , , }.
Then one of Benford's equations can be applied. If , and are known for layer and and are known for layer , the ART fractions for a sample composed of layer and layer are:
:(The symbol means the reflectance of layer when the direction of illumination is antiparallel to that of the incident beam. The difference in direction is important when dealing with inhomogeneous layers. This consideration was added by Paul Kubelka in 1954. He also pointed out that transmission was independent of the direction of illumination, but absorption and remission were not.) | 7 | Physical Chemistry |
Kelly Chibale PhD, MASSAf, FAAS, Fellow of UCT, FRSSAf, FRSC (born 1964) is professor of organic chemistry at the University of Cape Town, and the founder and director of [http://www.h3d.uct.ac.za/ H3D research center] and [https://h3dfoundation.org H3D Foundation NPC]. In 2018 he was recognised as one of Fortune magazines top 50 Worlds Greatest Leaders. His research focuses on drug discovery and the development of tools and models to contribute to improving treatment outcomes in people of African descent or heritage. | 0 | Organic Chemistry |
In 1937, Xing returned to China. He moved to Kunming since eastern China was occupied by Japanese invaders. There, he spent some efforts on the refining of Quinine. Then Xing joined the New Fourth Army as a teacher in its military medical school. Moreover, he assisted the army to product medicine.
In 1946, Xing went back to Beijing and accepted an appointment as a professor at Peking University.
In 1950s, Xing designed a new method to synthesize the chloramphenicol.
During 1964–65, Xing participated in the total synthesis of bovine insulin project, co-operating with Shanghai Institutes for Biological Sciences.
In 1980, Xing was elected as an academician of the Chinese Academy of Sciences.
During 1981–87, Xing focused on the activation methods for the carboxyl group in the peptide synthesis, and developed related chemical reagents. | 0 | Organic Chemistry |
As early as 1895 in the UK it was being noted that the heyday of the Bessemer process was over and that the open hearth method predominated. The Iron and Coal Trades Review said that it was "in a semi-moribund condition. Year after year, it has not only ceased to make progress, but it has absolutely declined." It has been suggested, both at that time and more recently, that the cause of this was the lack of trained personnel and investment in technology rather than anything intrinsic to the process itself. For example, one of the major causes of the decline of the giant ironmaking company Bolckow Vaughan of Middlesbrough was its failure to upgrade its technology. The basic process, the Thomas-Gilchrist process, remained in use longer, especially in Continental Europe, where iron ores were of high phosphorus content and the open-hearth process was not able to remove all phosphorus; almost all inexpensive construction steel in Germany was produced with this method in the 1950s and 1960s. It was eventually superseded by basic oxygen steelmaking.
In the U.S., commercial steel production using this method stopped in 1968. It was replaced by processes such as the basic oxygen (Linz–Donawitz) process, which offered better control of final chemistry. The Bessemer process was so fast (10–20 minutes for a heat) that it allowed little time for chemical analysis or adjustment of the alloying elements in the steel. Bessemer converters did not remove phosphorus efficiently from the molten steel; as low-phosphorus ores became more expensive, conversion costs increased. The process permitted only limited amount of scrap steel to be charged, further increasing costs, especially when scrap was inexpensive. Use of electric arc furnace technology competed favourably with the Bessemer process resulting in its obsolescence.
Basic oxygen steelmaking is essentially an improved version of the Bessemer process (decarburization by blowing oxygen as gas into the heat rather than burning the excess carbon away by adding oxygen carrying substances into the heat). The advantages of pure oxygen blast over air blast were known to Henry Bessemer, but 19th-century technology was not advanced enough to allow for the production of the large quantities of pure oxygen necessary to make it economical. | 8 | Metallurgy |
All igneous magmas contain dissolved gases (water, carbonic acid, hydrogen sulfide, chlorine, fluorine, boric acid, etc.). Of these water is the principal, and was formerly believed to have percolated downwards from the Earth's surface to the heated rocks below, but is now generally admitted to be an integral part of the magma. Many peculiarities of the structure of the plutonic rocks as contrasted with the lavas may reasonably be accounted for by the operation of these gases, which were unable to escape as the deep-seated masses slowly cooled, while they were promptly given up by the superficial effusions. The acid plutonic or intrusive rocks have never been reproduced by laboratory experiments, and the only successful attempts to obtain their minerals artificially have been those in which special provision was made for the retention of the "mineralizing" gases in the crucibles or sealed tubes employed. These gases often do not enter into the composition of the rock-forming minerals, for most of these are free from water, carbonic acid, etc. Hence as crystallization goes on the residual melt must contain an ever-increasing proportion of volatile constituents. It is conceivable that in the final stages the still uncrystallized part of the magma has more resemblance to a solution of mineral matter in superheated steam than to a dry igneous fusion. Quartz, for example, is the last mineral to form in a granite. It bears much of the stamp of the quartz which we know has been deposited from aqueous solution in veins, etc. It is at the same time the most infusible of all the common minerals of rocks. Its late formation shows that in this case it arose at comparatively low temperatures and points clearly to the special importance of the gases of the magma as determining the sequence of crystallization.
When solidification is nearly complete the gases can no longer be retained in the rock and make their escape through fissures towards the surface. They are powerful agents in attacking the minerals of the rocks which they traverse, and instances of their operation are found in the kaolinization of granites, tourmalinization and formation of greisen, deposition of quartz veins, and the group of changes known as propylitization. These "pneumatolytic" processes are of the first importance in the genesis of many ore deposits. They are a real part of the history of the magma itself and constitute the terminal phases of the volcanic sequence. | 9 | Geochemistry |
For a two-phase system consisting of the and phase in equilibrium with a surface dividing the phases, the total Gibbs free energy of a system can be written as:
where is the Gibbs free energy.
The equation of the Gibbs Adsorption Isotherm can be derived from the “particularization to the thermodynamics of the Euler theorem on homogeneous first-order forms.” The Gibbs free energy of each phase , phase , and the surface phase can be represented by the equation:
where is the internal energy, is the pressure, is the volume, is the temperature, is the entropy, and is the chemical potential of the -th component.
By taking the total derivative of the Euler form of the Gibbs equation for the phase, phase and the surface phase:
where is the area of the dividing surface, and is the surface tension.
For reversible processes, the first law of thermodynamics requires that:
where is the heat energy and is the work.
Substituting the above equation into the total derivative of the Gibbs energy equation and by utilizing the result is equated to the non-pressure volume work when surface energy is considered:
by utilizing the fundamental equation of Gibbs energy of a multicomponent system:
The equation relating the phase, phase and the surface phase becomes:
When considering the bulk phases ( phase, phase), at equilibrium at constant temperature and pressure the Gibbs–Duhem equation requires that:
The resulting equation is the Gibbs adsorption isotherm equation:
The Gibbs adsorption isotherm is an equation which could be considered an adsorption isotherm that connects surface tension of a solution with the concentration of the solute.
For a binary system containing two components the Gibbs Adsorption Equation in terms of surface excess is: | 7 | Physical Chemistry |
The construct-specific detection methods can either be DNA or protein based. DNA based detection looks for a part of the foreign DNA inserted in a GMO. For technical reasons, certain DNA sequences are shared by several GMOs. Protein-based methods detect the product of the transgene, for example the Bt toxin. Since different GMOs may produce the same protein, construct-specific detection can test a sample for several GMOs in one step, but is unable to tell precisely which of the similar GMOs are present. Especially in the USA, protein-based detection is used for the construct-specific approach. | 1 | Biochemistry |
The Wenzel model (Robert N. Wenzel, 1936) describes the homogeneous wetting regime, as seen in Figure 7, and is defined by the following equation for the contact angle on a rough surface:
where is the apparent contact angle which corresponds to the stable equilibrium state (i.e. minimum free energy state for the system). The roughness ratio, r, is a measure of how surface roughness affects a homogeneous surface. The roughness ratio is defined as the ratio of true area of the solid surface to the apparent area.
θ is the Young contact angle as defined for an ideal surface. Although Wenzel's equation demonstrates the contact angle of a rough surface is different from the intrinsic contact angle, it does not describe contact angle hysteresis. | 7 | Physical Chemistry |
Gary M. Hieftje is an analytical chemist, Distinguished Professor, and the Robert & Marjorie Mann Chair of Chemistry at Indiana University in Bloomington, Indiana. Gary M. Hieftje received his A.B. degree at Hope College in Holland, Michigan in 1964, and his PhD from University of Illinois at Urbana–Champaign in 1969. In 1969, he started his career in teaching and research at Indiana University. Hieftje was named a Distinguished Professor in 1985, and entered emeritus status in 2018. As of 2018, Dr. Hieftje has been involved in over 600 publications.
Research in the Hieftje Group mainly focuses on studying and improving the mechanisms and methods of atomic emission and absorption, fluorescence, and mass spectrometry. He also works to develop new methods of analysis for atoms, molecules, and biomolecules. His group even developed an online computer program to control their experiments. Some areas of interest to his research are: finding new applications of lasers, linear response theory, near-infrared correlation methods of analysis, time-resolved luminescence, and fiber-optic sensors.
Professor Hieftje has authored many books. Perhaps, the most well-known is “Chemical Separations and Measurements - The Theory and Practice of Analytical Chemistry” with colleagues Dennis G. Peters and John M. Hayes published by Saunders in Philadelphia in 1974. | 3 | Analytical Chemistry |
The addition of a benzene spacer in x-nucleobases affects the bases' optical absorption spectra. Time-dependent density functional theory (TDDFT) applied to xDNA revealed that the benzene component of the highest occupied molecular orbitals (HOMO) in the x-bases pins the absorption onset at an earlier point than natural bases. Another unusual feature of xDNA absorption spectra is the red-shifted excimers of xA in the low range. In terms of stacking fingerprints, there is a more pronounced hypochromicity seen in consecutive xA-T base pairs.
Implications of xDNA's altered absorption include applications in nanoelectronic technology and nanobiotechnology. The reduced spacing between x-nucleotides makes the helix stiffer, thus it is not as easily affected by substrate, electrode, and functional nanoparticle forces. Other alterations to natural nucleotides resulting in different absorption spectra will broaden these applications in the future. | 1 | Biochemistry |
The degree of dissociation in gases is denoted by the symbol , where refers to the percentage of gas molecules which dissociate. Various relationships between and exist depending on the stoichiometry of the equation. The example of dinitrogen tetroxide () dissociating to nitrogen dioxide () will be taken.
If the initial concentration of dinitrogen tetroxide is 1 mole per litre, this will decrease by at equilibrium giving, by stoichiometry, moles of . The equilibrium constant (in terms of pressure) is given by the equation
where represents the partial pressure. Hence, through the definition of partial pressure and using to represent the total pressure and to represent the mole fraction;
The total number of moles at equilibrium is , which is equivalent to . Thus, substituting the mole fractions with actual values in term of and simplifying;
This equation is in accordance with Le Chatelier's principle. will remain constant with temperature. The addition of pressure to the system will increase the value of , so must decrease to keep constant. In fact, increasing the pressure of the equilibrium favours a shift to the left favouring the formation of dinitrogen tetroxide (as on this side of the equilibrium there is less pressure since pressure is proportional to number of moles) hence decreasing the extent of dissociation . | 7 | Physical Chemistry |
Salcatonin is composed of 32 amino acids, of which 13 differ from human calcitonin. The structure of human calcitonin and salcatonin is as follows:
Human calcitonin:
H-Cys-Gly-Asn-Leu-Ser-Thr-Cys-Met-Leu-Gly-Thr-Tyr-Thr-Gln-Asp-Phe-Asn-Lys-Phe-His-Thr-Phe-Pro-Gln-Thr-Ala-lle-Gly-Val-Gly-Ala-Pro-NH
Salcatonin:
H-Cys-Ser-Asn-Leu-Ser-Thr-Cys-Val-Leu-Gly-Lys-Leu-Ser-Gln-Glu-Leu-His-Lys-Leu-Gln-Thr-Tyr-Pro-Arg-Thr-Asn-Thr-Gly-Ser-Gly-Thr-Pro-NH
The cysteine in the first and seventh positions form a disulfide bond. | 1 | Biochemistry |
The Hiyama coupling can be applied to the formation of C-C (e.g. aryl–aryl) bonds as well as C-C (e.g. aryl–alkyl) bonds. Good synthetic yields are obtained with couplings of aryl halides, vinyl halides, and allylic halides and organo­iodides afford the best yields.
The scope of this reaction was expanded to include closure of medium-sized rings by Scott E. Denmark.
The coupling of alkyl halides with organo­halo­silanes as alternative organo­silanes has also been performed. Organo­chloro­silanes allow couplings with aryl chlorides, which are abundant and generally more eco­nomical than aryl iodides. A nickel catalyst allows for access to new reactivity of organo­trifluoro­silanes as reported by GC Fu et al. Secondary alkyl halides are coupled with aryl silanes with good yields using this reaction. | 0 | Organic Chemistry |
In organic chemistry, a directing group (DG) is a substituent on a molecule or ion that facilitates reactions by interacting with a reagent. The term is usually applied to C–H activation of hydrocarbons, where it is defined as a "coordinating moiety (an internal ligand), which directs a metal catalyst into the proximity of a certain C–H bond." In a well known example, the ketone group () in acetophenone is the DG in the Murai reaction.
The Murai reaction is related to directed ortho metalation, a reaction is typically applied to the lithiation of substituted aromatic rings.
A wide variety of functional groups can serve as directing groups. | 0 | Organic Chemistry |
The central solenoid and toroidal field superconducting magnets for the planned experimental ITER fusion reactor use niobium–tin as a superconductor. The central solenoid coil will produce a field of . The toroidal field coils will operate at a maximum field of 11.8 T. Estimated use is of NbSn strands and 250 metric tonnes of NbTi strands.
At the Large Hadron Collider at CERN, extra-strong quadrupole magnets (for focussing beams) made with niobium–tin are being installed in key points of the accelerator between late 2018 and early 2020. Niobium tin had been proposed in 1986 as an alternative to niobium–titanium, since it allowed coolants less complex than superfluid helium, but this was not pursued in order to avoid delays while competing with the then-planned US-led Superconducting Super Collider. | 8 | Metallurgy |
The Edwards equation in organic chemistry is a two-parameter equation for correlating nucleophilic reactivity, as defined by relative rate constants, with the basicity of the nucleophile (relative to protons) and its polarizability. This equation was first developed by John O. Edwards in 1954 and later revised based on additional work in 1956.
The general idea is that most nucleophiles are also good bases because the concentration of negatively charged electron density that defines a nucleophile will strongly attract positively charged protons, which is the definition of a base according to Brønsted–Lowry acid-base theory. Additionally, highly polarizable nucleophiles will have greater nucleophilic character than suggested by their basicity because their electron density can be shifted with relative ease to concentrate in one area. | 7 | Physical Chemistry |
The apparatus consists of a gas chromatograph equipped with an odour port (ODP), in place of or in addition to conventional detectors, from with human assessors sniff the eluates. The odour port is characterised by its nose-cone design connected to the GC instrument by a transfer line. The odour port is commonly glass or polytetrafluoroethylene. It is generally placed 30–60 cm away from the instrument, extending from the side such that it is not affected by the hot GC oven. The deactivated silica transfer line is generally heated to prevent the condensation of less-volatile compounds. It is flexible so that the assessor can adjust it according to their comfortable sitting position. As traditional warm and dry carrier gases may dehydrate the mucous membrane of the nose, volatiles are delivered via auxiliary gas or humidified carrier gas, with relative humidity (RH) of 50–75%, to ease the dehydration.
The olfactometric detector may be coupled with, or connected in parallel to, a flame ionization detector (FID) or mass spectrometer (MS). Moreover, multiple odour ports may be set-up. In these cases, the eluate is generally split evenly between the detectors to allow it to reach the detectors simultaneously. | 3 | Analytical Chemistry |
An open-label clinical study for infantile neuroaxonal dystrophy evaluating long-term evaluation of efficacy, safety, tolerability, and pharmacokinetics of deulinoleate ethyl, which, when taken with food, can protect the neuronal cells from degeneration, started in the Summer 2018. | 1 | Biochemistry |
Random chimeragenesis on transient templates (RACHITT) is a method to perform molecular mutagenesis at a high recombination rate. For example, RACHITT can be used to generate increased rate and extent of biodesulfurization of diesel by modification of dibenzothiophene mono-oxygenase. DNA shuffling is a similar but less powerful method used in directed evolution experiments. | 1 | Biochemistry |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.