text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
The transition dipole moment or transition moment, usually denoted for a transition between an initial state, , and a final state, , is the electric dipole moment associated with the transition between the two states. In general the transition dipole moment is a complex vector quantity that includes the phase factors associated with the two states. Its direction gives the polarization of the transition, which determines how the system will interact with an electromagnetic wave of a given polarization, while the square of the magnitude gives the strength of the interaction due to the distribution of charge within the system. The SI unit of the transition dipole moment is the Coulomb-meter (Cm); a more conveniently sized unit is the Debye (D). | 5 | Photochemistry |
Peroxins (or peroxisomal/peroxisome biogenesis factors) represent several protein families found in peroxisomes. Deficiencies are associated with several peroxisomal disorders. Peroxins serve several functions including the recognition of cytoplasmic proteins that contain peroxisomal targeting signals (PTS) that tag them for transport by peroxisomal proteins to the peroxisome. Peroxins are structurally diverse and have been classified to different protein families. Some of them were predicted to be single-pass transmembrane proteins, for example Peroxisomal biogenesis factor 11. | 1 | Biochemistry |
Base excision repair (BER) is responsible for removing damaged bases in DNA. This mechanism specifically works on excising small base lesions which do not distort the DNA double helix, in contrast to the nucleotide excision repair pathway which is employed in correcting more prominent distorting lesions. DNA glycosylases initiate BER by both recognizing the faulty or incorrect bases and then removing them, forming AP sites lacking any purine or pyrimidine. AP endonuclease then cleaves the AP site, and the single-strand break is either processed by short-patch BER to replace a single nucleotide long-patch BER to create 2-10 replacement nucleotides. | 1 | Biochemistry |
In addition to the obvious data on quantities, units and symbols, the compilation contains some less obvious but very useful information on related topics. | 3 | Analytical Chemistry |
In host–guest chemistry, a carceplex is a class of chemical structures in the carcerand family that are hinged, and can be closed using reagents that react with the carceplex and trap precursors of reactive intermediates, and are unreactive with the trapped precursor or reactive intermediate. This is useful for determining the spectroscopic and crystallographic properties of reactive intermediates in relative isolation, particularly compounds prone to dimerization like cyclobutadiene. | 6 | Supramolecular Chemistry |
RAN translation produces a variety of dipeptide repeat proteins by translation of expanded hexanucleotide repeats present in an intron of the C9orf72 gene. The expansion of the hexanucleotide repeats and thus accumulation of dipeptide repeat proteins are thought to cause cellular toxicity that leads to neurodegeneration in ALS disease. | 1 | Biochemistry |
In combination with indapamide, perindopril has been shown to significantly reduce the progression of chronic kidney disease and renal complications in patients with type 2 diabetes. In addition, the Perindopril pROtection aGainst REcurrent Stroke Study (PROGRESS) found that whilst perindopril monotherapy demonstrated no significant benefit in reducing recurrent strokes when compared to placebo, the addition of low dose indapamide to perindopril therapy was associated with larger reductions in both blood pressure lowering and recurrent stroke risk in patients with pre-existing cerebrovascular disease, irrespective of their blood pressure. There is evidence to support the use of perindopril and indapamide combination over perindopril monotherapy to prevent strokes and improve mortality in patients with a history of stroke, transient ischaemic attack or other cardiovascular disease. | 4 | Stereochemistry |
The π orbitals of an alkene can stabilize a transition state by helping to delocalize the positive charge of the carbocation. For instance the unsaturated tosylate will react more quickly (10 times faster for aqueous solvolysis) with a nucleophile than the saturated tosylate.
The carbocationic intermediate will be stabilized by resonance where the positive charge is spread over several atoms. In the diagram below this is shown.
Here is a different view of the same intermediates.
Even if the alkene is more remote from the reacting center the alkene can still act in this way. For instance in the following alkyl benzenesulfonate the alkene is able to delocalise the carbocation. | 7 | Physical Chemistry |
Acyl halides are rather reactive compounds often synthesized to be used as intermediates in the synthesis of other organic compounds. For example, an acyl halide can react with:
*water, to form a carboxylic acid. This hydrolysis is the most heavily exploited reaction for acyl halides as it occurs in the industrial synthesis of acetic acid.
*an alcohol to form an ester
*an amine to form an amide
*an aromatic compound, using a Lewis acid catalyst such as AlCl, to form an aromatic ketone. See Friedel-Crafts acylation.
*carboxylic acids to form an organic acid anhydrides.
In the above reactions, HX (hydrogen halide or hydrohalic acid) is also formed. For example, if the acyl halide is an acyl chloride, HCl (hydrogen chloride or hydrochloric acid) is also formed. | 0 | Organic Chemistry |
Current association studies have focused on common variation across the genome, as these are the easiest to identify with our current assays. However, disease-causing variants of large effect have been found to lie within exomes in candidate gene studies, and because of negative selection, are found in much lower allele frequencies and may remain untyped in current standard genotyping assays. Whole genome sequencing is a potential method to assay novel variant across the genome. However, in complex disorders (such as autism), a large number of genes are thought to be associated with disease risk. This heterogeneity of underlying risk means that very large sample sizes are required for gene discovery, and thus whole genome sequencing is not particularly cost-effective. This sample size issue is alleviated by the development of novel advanced analytic methods, which effectively map disease genes despite the genetic mutations are rare at variant level. In addition, variants in coding regions have been much more extensively studied and their functional implications are much easier to derive, making the practical applications of variants within the targeted exome region more immediately accessible.
Exome sequencing in rare variant gene discovery remains a very active and ongoing area of research, and there is growing evidence that a significant burden of risk is observed across sets of genes. The exome sequencing has been reported rare variants in KRT82 gene in the autoimmune disorder Alopecia Areata. | 1 | Biochemistry |
Prehistoric man inhabited the Portlethen Moss area as evidenced by well preserved Iron Age stone circles and other excavated artifacts nearby. Obviously only the outcrops and ridge areas would have been habitable, but the desirability of primitive habitation would have been enhanced by proximity to the sea and natural defensive protection of the moss to impede intruders. From Tacitus accounts of the Roman general Agricola, it is known that the Romans were daunted by Portlethen Moss, Netherley Red Moss, Cookney Moss and other local bogs that hindered travel. This is also evidenced by the Roman Camp of Raedykes having been established immediately south of this cluster of mosses; the Romans not being able to progress further north, turned inland toward Netherley.The Portlethen Moss is near the Grampian Mountains.
The ancient Causey Mounth passage specifically connected the Bridge of Dee to the town of Stonehaven. This route was used to access the historic meeting of the Covenanters at Muchalls Castle in the year 1638 AD as they opposed the Bishops of Aberdeen. The route was also that taken by the William Keith, 7th Earl Marischal and James Graham, 1st Marquess of Montrose when they led a Covenanter army of 9000 men in the biggest battle of the Bishops' Wars in 1639
Further to the east of Portlethen Moss lie three original coastal fishing villages: Findon, Portlethen Village and Downies. In the period 1960 to 2005, Portlethen has developed as a dormitory town to Aberdeen and a location for retail superstores. | 2 | Environmental Chemistry |
Iron porphyrin complexes ("hemes") are the dominant metalloporphyrin complexes in nature. Consequently, synthetic iron porphyrin complexes are well investigated. Common derivatives are those of Fe(III) and Fe(II). Complexes of the type Fe(P)Cl are square-pyramidal and high spin with idealized C symmetry. Base hydrolysis affords the "mu-oxo dimers" with the formula [Fe(P)]O. These complexes have been widely investigated as oxidation catalysts. Typical stoichiometries of ferrous porphyrins are Fe(P)L where L is a neutral ligand such as pyridine and imidazole. Cobalt(II) porphyrins behave similarly to the ferrous derivatives. They bind O to form dioxygen complexes. | 1 | Biochemistry |
Some of the job skills and abilities that one needs to attain to be successful in this field of work include science, mathematics, reading comprehension, writing, and critical thinking. These skills are critical because of the nature of the experimental techniques of the occupation. One will also need to convey trends found in research in written and oral forms.
A degree in biochemistry or a related science such as chemistry is the minimum requirement for any work in this field. This is sufficient for a position as a technical assistant in industry or in academic settings. A Ph.D. (or equivalent) is generally required to pursue or direct independent research. To advance further in commercial environments, one may need to acquire skills in management.
Biochemists must pass a qualifying exam or a preliminary exam to continue their studies when receiving a Ph.D. in biochemistry.
Biochemistry requires an understanding of organic and inorganic chemistry. All types of chemistry are required, with emphasis on biochemistry, organic chemistry and physical chemistry. Basic classes in biology, including microbiology, molecular biology, molecular genetics, cell biology, and genomics, are focused on. Some instruction in experimental techniques and quantification is also part of most curricula.
In the private industries for businesses, it is imperative to possess strong business management skills as well as communication skills. Biochemists must also be familiar with regulatory rules and management techniques.
Biochemistry Blog publishes high quality research articles, papers, posts and jobs related to biochemistry. Biochemistry 2019, biochemistry papers latest.
Due to the reliance on most principles of the basic science of Biochemistry, early contemporary physicians were informally qualified to perform research on their own in mainly this (today also related biomedical sciences) field. | 1 | Biochemistry |
The thermic effect of food should be measured for a period of time greater than or equal to five hours.
The American Journal of Clinical Nutrition published that TEF lasts beyond six hours for the majority of people. | 1 | Biochemistry |
The term "doublet" dates back to the 19th century, when it was observed that certain spectral lines of an ionized, excited gas would split into two under the influence of a strong magnetic field, in an effect known as the anomalous Zeeman effect. Such spectral lines were observed not only in the laboratory, but also in astronomical spectroscopy observations, allowing astronomers to deduce the existence of, and measure the strength of magnetic fields around the Sun, stars and galaxies. Conversely, it was the observation of doublets in spectroscopy that allowed physicists to deduce that the electron had a spin, and that furthermore, the magnitude of the spin had to be 1/2. See the history section of the article on Spin (physics) for greater detail.
Doublets continue to play an important role in physics. For example, the healthcare technology of magnetic resonance imaging is based on nuclear magnetic resonance. In this technology, a spectroscopic doublet occurs in a spin-1/2 atomic nucleus, whose doublet splitting is in the radio-frequency range. By applying both a magnetic field and carefully tuning a radio-frequency transmitter, the nuclear spins will flip and re-emit radiation, in an effect known as the Rabi cycle. The strength and frequency of the emitted radio waves allows the concentration of such nuclei to be measured. Another potential application is the use of doublets as the emitting layer in light emitting diodes (LEDs). These materials have the advantage of having 100% theoretical quantum efficiency based on spin statistics whereas singlet systems and triplet systems have significantly lower efficiencies or rely on noble metals such as Pt and Ir to emit light. | 7 | Physical Chemistry |
Hydrogen bonding plays an important role in determining the three-dimensional structures and the properties adopted by many proteins. Compared to the , , and bonds that comprise most polymers, hydrogen bonds are far weaker, perhaps 5%. Thus, hydrogen bonds can be broken by chemical or mechanical means while retaining the basic structure of the polymer backbone. This hierarchy of bond strengths (covalent bonds being stronger than hydrogen-bonds being stronger than van der Waals forces) is relevant in the properties of many materials. | 6 | Supramolecular Chemistry |
The first reported steps towards the discovery of the shape-memory effect were taken in the 1930s. According to Otsuka and Wayman, Arne Ölander discovered the pseudoelastic behavior of the Au-Cd alloy in 1932. Greninger and Mooradian (1938) observed the formation and disappearance of a martensitic phase by decreasing and increasing the temperature of a Cu-Zn alloy. The basic phenomenon of the memory effect governed by the thermoelastic behavior of the martensite phase was widely reported a decade later by Kurdjumov and Khandros (1949) and also by Chang and Read (1951).
The nickel-titanium alloys were first developed in 1962–1963 by the United States Naval Ordnance Laboratory and commercialized under the trade name Nitinol (an acronym for Nickel Titanium Naval Ordnance Laboratories). Their remarkable properties were discovered by accident. A sample that was bent out of shape many times was presented at a laboratory management meeting. One of the associate technical directors, Dr. David S. Muzzey, decided to see what would happen if the sample was subjected to heat and held his pipe lighter underneath it. To everyone's amazement the sample stretched back to its original shape.
There is another type of SMA, called a ferromagnetic shape-memory alloy (FSMA), that changes shape under strong magnetic fields. These materials are of particular interest as the magnetic response tends to be faster and more efficient than temperature-induced responses.
Metal alloys are not the only thermally-responsive materials; shape-memory polymers have also been developed, and became commercially available in the late 1990s. | 8 | Metallurgy |
Charge transfer coefficient, and symmetry factor (symbols α and β, respectively) are two related parameters used in description of the kinetics of electrochemical reactions. They appear in the Butler–Volmer equation and related expressions.
The symmetry factor and the charge transfer coefficient are dimensionless.
According to an IUPAC definition, for a reaction with a single rate-determining step, the charge transfer coefficient for a cathodic reaction (the cathodic transfer coefficient, α) is defined as:
The anodic transfer coefficient (α) is defined by analogy:
where:
*: stoichiometric number, i.e., the number of activated complexes formed and destroyed in the overall reaction (with n electrons)
* : universal gas constant
* : absolute temperature
* : number of electrons involved in the electrode reaction
* : Faraday constant
* : electrode potential
* : partial cathodic (anodic) current | 7 | Physical Chemistry |
The AIRMoN sites were primarily used to assess the impacts of emission changes such as potential effects from new sources, federal Clean Air Act controls, and source-receptor relationships in atmospheric models. The network measured the same contaminants as the NTN, but sampling occurred daily during precipitation to provide greater temporal resolution. This consistent, high-resolution sampling improved the researchers’ ability to evaluate the data and, therefore, provide reliable results. The network was discontinued in September 2019. | 2 | Environmental Chemistry |
In principle, any technologies used for metabolomics can be used for exometabolomics. However, liquid chromatography–mass spectrometry (LC–MS) has been the most widely used. As with typical metabolomic measurements, metabolites are identified based on accurate mass, retention time, and their MS/MS fragmentation patterns, in comparison to authentic standards. Chromatographies typically used are hydrophilic interaction liquid chromatography for the measurement of polar metabolites, or reversed-phase (C18) chromatography for the measurement of non-polar compounds, lipids, and secondary metabolites. Gas chromatography–mass spectrometry can also be used to measure sugars and other carbohydrates, and to obtain complete metabolic profiles.
Because LC–MS does not give spatial data on metabolite localization, it can be complemented with mass spectrometry imaging (MSI). | 1 | Biochemistry |
NMH is formed by N-methylation of histamine, catalyzed by the enzyme Histamine N-methyltransferase.
NMH is excreted in the urine and can be measured as a biomarker of histamine activity. While NMH has some biological activity on its own, it is much weaker than histamine. It can bind to histamine receptors, still, NMH has a lower affinity and efficacy than histamine for these receptors, meaning that it binds less strongly and activates them less effectively. Depending on the receptor subtype and the tissue context, NMH may act as a partial agonist or an antagonist for some histamine receptors. NMH may have some modulatory effects on histamine signalling, but it is unlikely to cause significant allergic or inflammatory reactions by itself. NMH may also serve as a feedback mechanism to regulate histamine levels and prevent excessive histamine release.
In clinical settings, urinary NMH can be measured when systemic mastocytosis is suspected. Systemic mastocytosis and anaphylaxis are typically associated with at least a two-fold increase in urinary NMH levels, which are also increased in patients taking monoamine oxidase inhibitors and in patients on histamine-rich diets. | 1 | Biochemistry |
Time resolved microwave conductivity (TRMC) is an experimental technique used to evaluate the electronic properties of semiconductors. Specifically, it is used to evaluate a proxy for charge carrier mobility and a representative carrier lifetime from light-induced changes in conductance. The technique works by photo-generating electrons and holes in a semiconductor, allowing these charge carriers to move under a microwave field, and detecting the resulting changes in the electric field. TRMC systems cannot be purchased as a single unit, and are generally "home-built" from individual components. One advantage of TRMC over alternative techniques is that it does not require direct physical contact to the material. | 7 | Physical Chemistry |
Dihydroprogesterone may refer to:
* 5α-Dihydroprogesterone
* 5β-Dihydroprogesterone
* 20α-Dihydroprogesterone (20α-hydroxyprogesterone)
* 20β-Dihydroprogesterone (20β-hydroxyprogesterone)
* 3α-Dihydroprogesterone
* 3β-Dihydroprogesterone
* 17α,21-Dihydroprogesterone (11-deoxycortisol)
* 11β,21-Dihydroprogesterone (corticosterone) | 1 | Biochemistry |
Crystalline material may be divided into single crystals, twin crystals, polycrystals, and crystal powder. In a single crystal, the arrangement of atoms, ions, or molecules is defined by a single crystal structure in one orientation. Twin crystals, on the other hand, consist of single-crystalline twin domains, which are aligned by twin laws and separated by domain walls.
Polycrystals are made of a large number of small single crystals, or crystallites, held together by thin layers of amorphous solid. Crystal powder is obtained by grinding crystals, resulting in powder particles, made up of one or more crystallites. Both polycrystals and crystal powder consist of many crystallites with varying orientation.
Crystal phases are defined as regions with the same crystal structure, irrespective of orientation or twinning. Single and twinned crystalline specimens therefore constitute individual crystal phases. Polycrystalline or crystal powder samples may consist of more than one crystal phase. Such a phase comprises all the crystallites in the sample with the same crystal structure.
Crystal phases can be identified by successfully matching suitable crystallographic parameters with their counterparts in database entries. Prior knowledge of the chemical composition of the crystal phase can be used to reduce the number of database entries to a small selection of candidate structures and thus simplify the crystal phase identification process considerably. | 7 | Physical Chemistry |
One limitation is the energy loss in methane-producing bioelectrochemical systems. This occurs as a result of overpotentials occurring at the anode, membrane, and biocathode. The energy loss reduces efficiency significantly. Another limitation is the biocathode. Because the biocathode is so important in electron exchange and methane formation, its make-up can have a dramatic effect on the efficiency of the reaction. Efforts are being made to improve the biocathodes used in electromethanogenesis through combining new and existing materials, reshaping the materials, or applying different "pre-treatments" to the biocathode surface, thereby increasing biocompatibility. | 7 | Physical Chemistry |
Members of the HNF4 subfamily are nuclear receptors and bind to DNA either as homodimers or RXR heterodimers.
* HNF4α/TCF14/MODY1
* HNF4γ | 1 | Biochemistry |
Silver nanoparticles are thermodynamically unstable in oxic environments. In seawater, silver oxide is not thermodynamically favored when chloride and sulfur are present. On the surface where O is present in much greater quantities than chloride or sulfur, silver reacts to form a silver oxide surface layer. This oxidation has been shown to occur in nanoparticles as well, despite their shell.O in Water:O + HO → 2Ag + 2OH value of 4×10. → Ag+ + O → 4Ag + 2O + ½ O + 2H ⇌ 2Ag + H2O ions are a concern for environmental health, as these ions freely interact with other organic compounds, such as humic acids, and disrupt the normal balance of an ecosystem. These Ag ions will also react with Cl to form complexes such as AgCl, AgCl, and AgCl, which are bioavailable forms of silver that are potentially more toxic to bacteria and fish than silver nanoparticles. The etched structure of silver nanoparticles provides the chloride with the preferred atomic steps for nucleation to occur. + Cl → AgCl + Cl → AgCl ions will react with HS in the water to form the precipitate AgS. + HS → AgS + H S is not the only source of sulfur that Ag will readily bind to. Organosulfur compounds, which are produced by aquatic organisms, form extremely stable sulfide complexes with silver. Silver outcompetes other metals for the available sulfide, leading to an overall decrease in bioavailable sulfur in the community. Thus, the formation of AgS limits the amount of bioavailable sulfur and contributes to a reduction in toxicity of silver nanoparticles to nitrifying bacteria. | 2 | Environmental Chemistry |
The optical properties of semiconductors are directly related to the dielectric constant of the material. This dielectric constant gives the ratio between the electric permeability of a material in relation to the permeability of a vacuum. The imaginary refractive index of a material is given by the square root of the dielectric constant. The reflectance of a material can be calculated using the Fresnel equations. A present electric field alters the dielectric constant and therefore alters the optical properties of the material, like the reflectance. | 7 | Physical Chemistry |
For small scale reactions, SF can be inconvenient since it is a gas and stainless steel reaction vessels are required. Many transformations require elevated temperatures. The reaction generates hydrogen fluoride. These concerns have led to interest in alternative fluorinating reagents. Selenium tetrafluoride, a liquid at room temperature, behaves similarly to SF. Diethylaminosulfur trifluoride (DAST) is a derivative of SF that is easier to handle, albeit more expensive. | 0 | Organic Chemistry |
Broadband viscoelastic spectroscopy (BVS) is a technique for studying viscoelastic solids in both bending and torsion. It provides the ability to measure viscoelastic behavior over eleven decades (orders of magnitude) of time and frequency: from 10 to 10 Hz. BVS is typically either used to investigate viscoelastic properties isothermally over a large frequency range or as a function of temperature at a single frequency. It is capable of measuring mechanical properties directly over these frequency and temperature ranges; as such, it does not require time-temperature superposition or the assumption that material properties obey an Arrhenius-type temperature dependence. As a result, it can be used for heterogeneous and anisotropic specimens for which these assumptions do not apply. BVS is often used for the determination of attenuation coefficients, dynamic moduli, and especially damping ratios.
BVS was developed primarily to overcome shortcomings in the functional ranges of other viscoelastic characterization techniques. For example, resonant ultrasound spectroscopy (RUS), another popular technique for studying viscoelastic solids, experiences difficulty in determining a material's parameters below its resonant frequency. Furthermore, BVS is less sensitive to sample preparation than RUS. | 7 | Physical Chemistry |
The biuret test is a chemical test for proteins and polypeptides. It is based on the biuret reagent, a blue solution that turns violet upon contact with proteins, or any substance with peptide bonds. The test and reagent do not actually contain biuret; they are so named because both biuret and proteins have the same response to the test. | 0 | Organic Chemistry |
Perera completed his primary and secondary education at the Royal Primary School and the Royal College, Colombo and thereafter gained BSc (Honours) from the University of Sri Lanka, Colombo in May 1975, followed by a joint MSc from the University of Colombo and the University of Birmingham, England in July 1977. He thereby qualified professionally in the field of Analytical Chemistry, specialising in the subject of Quality Assurance, in which field his outstanding contributions were internationally recognised and awarded with an honorary PhD. | 3 | Analytical Chemistry |
Suksin Lee (; 6 October 1896/7 – 12 December 1944) was a Korean biochemist and physician. He is considered a pioneer of biochemistry in Korea, having been the first Korean to obtain a Ph.D. and to hold a full-time professorship in that field. His studies of glucose metabolism and the chemical composition of common foods contributed to the scientific analysis of nutrition in the Korean diet. | 1 | Biochemistry |
CO at high pressures has antimicrobial properties. While its effectiveness has been shown for various applications, the mechanisms of inactivation have not been fully understood although they have been investigated for more than 60 years. | 7 | Physical Chemistry |
Ion exchange chromatography can be used to separate proteins because they contain charged functional groups. The ions of interest (in this case charged proteins) are exchanged for another ions (usually H) on a charged solid support. The solutes are most commonly in a liquid phase, which tends to be water. Take for example proteins in water, which would be a liquid phase that is passed through a column. The column is commonly known as the solid phase since it is filled with porous synthetic particles that are of a particular charge. These porous particles are also referred to as beads, may be aminated (containing amino groups) or have metal ions in order to have a charge. The column can be prepared using porous polymers, for macromolecules of a mass of over 100 000 Da, the optimum size of the porous particle is about 1 μm. This is because slow diffusion of the solutes within the pores does not restrict the separation quality. The beads containing positively charged groups, which attract the negatively charged proteins, are commonly referred to as anion exchange resins. The amino acids that have negatively charged side chains at pH 7 (pH of water) are glutamate and aspartate. The beads that are negatively charged are called cation exchange resins, as positively charged proteins will be attracted. The amino acids that have positively charged side chains at pH 7 are lysine, histidine and arginine.
The isoelectric point is the pH at which a compound - in this case a protein - has no net charge. A protein's isoelectric point or PI can be determined using the pKa of the side chains, if the amino (positive chain) is able to cancel out the carboxyl (negative) chain, the protein would be at its PI. Using buffers instead of water for proteins that do not have a charge at pH 7, is a good idea as it enables the manipulation of pH to alter ionic interactions between the proteins and the beads. Weakly acidic or basic side chains are able to have a charge if the pH is high or low enough respectively. Separation can be achieved based on the natural isoelectric point of the protein. Alternatively a peptide tag can be genetically added to the protein to give the protein an isoelectric point away from most natural proteins (e.g., 6 arginines for binding to a cation-exchange resin or 6 glutamates for binding to an anion-exchange resin such as DEAE-Sepharose).
Elution by increasing ionic strength of the mobile phase is more subtle. It works because ions from the mobile phase interact with the immobilized ions on the stationary phase, thus "shielding" the stationary phase from the protein, and letting the protein elute.
Elution from ion-exchange columns can be sensitive to changes of a single charge- chromatofocusing. Ion-exchange chromatography is also useful in the isolation of specific multimeric protein assemblies, allowing purification of specific complexes according to both the number and the position of charged peptide tags. | 3 | Analytical Chemistry |
*dextran, α-1,6-glucan
*glycogen, α-1,4- and α-1,6-glucan
*pullulan, α-1,4- and α-1,6-glucan
*starch, α-1,4- (such as amylose) and α-1,6-glucan (including amylopectin) | 1 | Biochemistry |
Based on the method developed by Poliak and Jonas, a few models are developed in order to describe the critical strain for the onset of DRX as a function of the peak strain of the stress–strain curve. The models are derived for the systems with single peak, i.e. for the materials with medium to low stacking fault energy values. The models can be found in the following papers:
* [https://arxiv.org/abs/1405.0196 Determination of flow stress and the critical strain for the onset of dynamic recrystallization using a sine function]
* [https://dx.doi.org/10.1016/j.matdes.2013.08.055 Determination of flow stress and the critical strain for the onset of dynamic recrystallization using a hyperbolic tangent function]
* [https://dx.doi.org/10.1016/j.matdes.2009.09.001 Determination of critical strain for initiation of dynamic recrystallization]
* [https://www.researchgate.net/publication/260337084_Characteristic_points_of_stressstrain_curve_at_high_temperature Characteristic points of stress–strain curve at high temperature]
The DRX behavior for systems with multiple peaks (and single peak as well) can be modeled considering the interaction of multiple grains during deformation. I. e. the ensemble model describes the transition between single and multi peak behavior based on the initial grain size. It can also describe the effect of transient changes of the strain rate on the shape of the flow curve. The model can be found in the following paper:
* [https://doi.org/10.1016/j.msea.2015.08.085 A new unified approach for modeling recrystallization during hot rolling of steel] | 8 | Metallurgy |
SU-8 is composed of Bisphenol A Novolac epoxy that is dissolved in an organic solvent (gamma-butyrolactone GBL or cyclopentanone, depending on the formulation) and up to 10 wt% of mixed Triarylsulfonium/hexafluoroantimonate salt as the photoacid generator.
SU-8 absorbs light in the UV region, allowing fabrication of relatively thick (hundreds of micrometers) structures with nearly vertical side walls. The fact that a single photon can trigger multiple polymerizations makes the SU-8 a chemically amplified resist which is polymerized by photoacid generation. The light irradiated on the resist interacts with the salt in the solution, creating hexafluoroantimonic acid that then protonates the epoxides groups in the resin monomers. The monomer are thus activated but the polymerization will not proceed significantly until the temperature is raised as part of the post-expose bake. It is at this stage that the epoxy groups in the resin cross-link to form the cured structure. When fully cured, the high crosslinking degree gives to the resist its excellent mechanical properties.
The processing of SU-8 is similar to other negative resists with particular attention on the control of the temperature in the baking steps. The baking times depend on the SU-8 layer thickness; the thicker the layer, the longer the baking time. The temperature is controlled during the baking in order to reduce stress formation in the thick layer (leading to cracks) as the solvent evaporates.
The soft bake is the most important of the bake steps for stress formation. It is performed after spin coating. Its function is to remove the solvent from the resist and make the layer solid. Typically at least 5% of the solvent remains in the layer after the soft bake, however the thicker the coating, the harder it becomes to remove the solvent, as evaporating solvent through thick layers becomes increasingly difficult with coating thickness. The bake is performed on a programmable hot plate to reduce the skinning effect of solvent depletion at the surface creating a dense layer which makes the remainder of the solvent more difficult to remove. In order to reduce stress, the bake procedure is generally a two-step process made up of holding at 65 °C before ramping to 95 °C and holding again for a time dependent on the layer thickness. The temperature is then lowered slowly to room temperature.
When dry films are used, the photoresist is laminated rather than spin-coated. As this formulation is essentially solventless (less than 1% solvent remaining), it does not require a soft bake step and does not suffer stress or skinning. For enhanced adhesion, a post lamination bake can be added. This step is carried out in a similar way to the solution based resist - i.e. holding at 65 °C then 95 °C, the time dependent on film thickness.
After this stage the SU-8 layer can now be exposed. Typically this is through a photomask with an inverse pattern, as the resist is negative. The exposure time is a function of exposure dose and film thickness. After exposure the SU-8 needs to be baked again to complete the polymerization. This baking step is not as critical as the prebake but the rising of the temperature (again to 95 °C) needs to be slow and controlled. At this point the resist is ready to be developed.
The main developer for SU-8 is 1-methoxy-2-propanol acetate. Development time is primarily a function of SU-8 thickness.
After exposing and developing, its highly cross-linked structure gives it high stability to chemicals and radiation damage - hence the name "resist". Cured cross-linked SU-8 shows very low levels of outgassing in a vacuum.
However it is very difficult to remove, and tends to outgas in an unexposed state. | 7 | Physical Chemistry |
Two properties that have a large effect on the functionality of a biomaterial is the surface and bulk properties.
Bulk properties refers to the physical and chemical properties that compose the biomaterial for its entire lifetime. They can be specifically generated to mimic the physiochemical properties of the tissue that the material is replacing. They are mechanical properties that are generated from a material's atomic and molecular construction.
Important bulk properties:
* Chemical Composition
* Microstructure
* Elasticity
* Tensile Strength
* Density
* Hardness
* Electrical Conductivity
* Thermal Conductivity
Surface properties refers to the chemical and topographical features on the surface of the biomaterial that will have direct interaction with the host blood/tissue. Surface engineering and modification allows clinicians to better control the interactions of a biomaterial with the host living system.
Important surface properties:
* Wettability (surface energy)
* Surface chemistry
* Surface textures (smooth/rough)
** Topographical factors including: size, shape, alignment, structure determine the roughness of a material.
* Surface Tension
* Surface Charge | 1 | Biochemistry |
This process is not 100% efficient. At the Lautenthal, Altenau, and Sankt Andreasberg smelting-works in the Upper Harz between 1857 and 1860 25% of the silver, 25.1% of the lead and 9.3% of the copper was lost. Some of this is lost in slag that is not worth reusing, some is lost by what is termed ‘burning’, and some of the silver is lost to the refined copper. It is clear therefore that a constant supply of lead was needed to make up for that lost at various stages. | 8 | Metallurgy |
Although van der Waals postulated the intermolecular interaction in 1873, in 1894, Fischer built a philosophical root for supramolecular chemistry. He pointed out that enzyme-protein interactions behave in a "lock-and-key" manner. This interaction is the foundation to host-guest chemistry. With the deeper understanding of the non-covalent interactions, for example, the clear elucidation of DNA structure, chemists started to emphasize the importance of non-covalent interactions. In 1967, Charles J. Pedersen discovered crown ethers, which are ring-like structures capable of chelating certain metal ions. Then, in 1969, Jean-Marie Lehn discovered a class of molecules similar to crown ethers, called cryptands. After that, Donald J. Cram synthesized many variations to crown ethers, on top of separate molecules capable of selective interaction with certain chemicals. The three scientists were awarded the Nobel Prize in Chemistry in 1987 for "development and use of molecules with structure-specific interactions of high selectivity”. In 2016, Bernard L. Feringa, Sir J. Fraser Stoddart, and Jean-Pierre Sauvage were awarded the Nobel Prize in Chemistry, "for the design and synthesis of molecular machines".
Supramolecular chemistry refers to the chemical systems that contains discrete number chemical components. The strengths of the systems vary from the intermolecular forces to covalent bindings. The researchers mentioned above created and enlarged the area of host-guest interaction, one of the most important concepts of the supramolecular chemistry fields. There are two significant components in the host-guest interaction. One is the "host molecules", which usually have "pore-like" structure that is able to capture some other molecules. The other one is the "guest molecules", which are generally smaller than the host molecules, and capable of binding the host molecules. The driving forces of the interaction might vary in different cases, such as hydrophobic effect, chelate effect, van der Waals force, et al. Different bindings will provide variant properties for the materials, i.e., stimuli-responsiveness, self-healing, matrix rigidification. As a consequence, the host-guest interaction can be applied for self-healing materials, stimuli-responsive materials, room-temperature phosphorescence (RTP), improvement of mechanical properties, et al. The sizes of the host and guest molecules play an essential role in the interactions, and some typical examples of the host interactions will be discussed as follows.
Host–guest chemistry is a branch of supramolecular chemistry in which a host molecule binds a so-called guest molecule or ion. The two components of the complex interact by non-covalent forces, most commonly by hydrogen-bonding. Binding between host and guest can be highly selective, in which case the interaction is called molecular recognition. Often, a dynamic equilibrium exist between the unbound and the bound states:
:H ="host", G ="guest", HG ="host–guest complex"
The "host" component is often the larger molecule, and it encloses the smaller, "guest", molecule. In biological systems, the analogous terms of host and guest are commonly referred to as enzyme and substrate respectively. | 6 | Supramolecular Chemistry |
If a receptor in an active state encounters a G protein, it may activate it. Some evidence suggests that receptors and G proteins are actually pre-coupled. For example, binding of G proteins to receptors affects the receptor's affinity for ligands. Activated G proteins are bound to GTP.
Further signal transduction depends on the type of G protein. The enzyme adenylate cyclase is an example of a cellular protein that can be regulated by a G protein, in this case the G protein G. Adenylate cyclase activity is activated when it binds to a subunit of the activated G protein. Activation of adenylate cyclase ends when the G protein returns to the GDP-bound state.
Adenylate cyclases (of which 9 membrane-bound and one cytosolic forms are known in humans) may also be activated or inhibited in other ways (e.g., Ca2+/calmodulin binding), which can modify the activity of these enzymes in an additive or synergistic fashion along with the G proteins.
The signaling pathways activated through a GPCR are limited by the primary sequence and tertiary structure of the GPCR itself but ultimately determined by the particular conformation stabilized by a particular ligand, as well as the availability of transducer molecules. Currently, GPCRs are considered to utilize two primary types of transducers: G-proteins and β-arrestins. Because β-arr's have high affinity only to the phosphorylated form of most GPCRs (see above or below), the majority of signaling is ultimately dependent upon G-protein activation. However, the possibility for interaction does allow for G-protein-independent signaling to occur. | 1 | Biochemistry |
Rasagiline is broken down via CYP1A2, part of the cytochrome P450 metabolic path in the liver. It is contraindicated in patients with hepatic insufficiency and its use should be monitored carefully in patients taking other drugs that alter the normal effectiveness of this metabolic path. | 4 | Stereochemistry |
Ferrous metallurgy includes extraction of iron, smelting and refining of iron ore, rolling and ferroalloys production. The ferrous metallurgy production of the country started to meet the demand of oil and gas industry (due to pipe production) and grew further in order to improve other branches of the industry. Dashkasan iron ore in 4 deposits (Dashkesen, South Dashkasan, Hamanchay, Demiroglu) in the valley of Goshagarchay plays a key role in development of ferrous metallurgy. The cities of Baku, Sumgait and Dashkesan are major centers of metallurgy in terms of extraction and processing of iron ore. The Sumgait Pipe-Rolling Plant produces drill pipes, casing, tubing, oil and gas pipes, etc. Bentonite clay deposits in the village of Dash Salakhly, Gazakh district, is used in steel smelting. Baku Steel Company, the largest metallurgical enterprise in Azerbaijan, was opened in 2001 on the initiative of Heydar Aliyev. With two electric arc furnaces and three rolling lines the annual steel production capacity of company increased to 1,000,000 tons. | 8 | Metallurgy |
The general use and design of CDAs obey the following rules so that the CDA can effectively determine the stereochemistry of an analyte:
# The CDA must be enantiomerically pure, or (less satisfactorily) its enantiomeric purity must be accurately known.
#The reaction of the CDA with both enantiomers should go to completion under reaction conditions. This acts to avoid enrichment or depletion of one enantiomer of the analyte by kinetic resolution.
# CDA must not racemize under derivatization or analysis conditions. Its attachment should be mild enough so that the substrate does not racemize either. If analysis is completed by HPLC, the CDA must contain a chromophore to enhance detectability.
# If analysis is completed by NMR, the CDA should have a functional group that gives a singlet in the resultant NMR spectrum, where the singlet must be remote from other peaks. | 4 | Stereochemistry |
The primary UK legislation is the Food Safety Act 1990. All local authorities are required to appoint a Public Analyst, although there have always been fewer Public Analysts and their laboratories than local authorities, most being shared by a number of local authorities. On the UK mainland there has always been a mixture of public sector and private sector laboratories. This remains the case today - but they all provide an equivalent service, and avoidance of conflicts of interest are ensured by the statutory terms of appointment. There is a statutory qualification requirement for Public Analysts, known as the Mastership in Chemical Analysis (MChemA), awarded by the Royal Society of Chemistry. This is a specialist postgraduate qualification by examination that verifies knowledge and understanding of food and its potential defects, interpretation of food law, and the application and interpretation of chemical analysis for food law enforcement.
The Public Analysts’ laboratories must be third-party accredited to International Standard BS EN ISO/IEC 17025:2017.
In the mid 1980s there were some 40 Public Analyst Laboratories in the UK with over 100 appointed Public Analysts. By 1993 that had reduced to 34 Laboratories and around 80 Public Analysts, and by 2010 the number of Public Analyst Laboratories had reduced to 22 with only about 26 Public Analysts. As of 2022 there are 15 Public Analyst laboratories remaining in the UK. In part, the reduction in number of laboratories over the decades has been due to rationalisation and benefits from economies of scale; however, by a larger part, it has arisen due to lack of adequate funding. Although some of the remaining laboratories are larger than many that no longer exist, the overall capacity of the system is now far less than it used to be.
Enforcement of food law in the UK is done by local authorities, principally their environmental health officers and trading standards officers. Whilst these officers are empowered to take samples of food, the actual assessment in terms of chemical analysis or microbiological examination and subsequent interpretation that are necessary to determine whether a food complies with legislation, is carried out by Public Analysts and Food Examiners respectively, scientists whose qualifications and experience are specified by regulations. | 2 | Environmental Chemistry |
As illustrated by the peroxisomal intracellular lactate shuttle described above, the interconversion of lactate and pyruvate between cellular compartments plays a key role in the oxidative state of the cell. Specifically, the interconversion of NAD+ and NADH between compartments has been hypothesized to occur in the mitochondria. However, the evidence for this is lacking, as both lactate and pyruvate are quickly metabolized inside the mitochondria. However, the existence of the peroxisomal lactate shuttle suggests that this redox shuttle could exist for other organelles. | 1 | Biochemistry |
Copper tubes are made from the large billets of copper that are gradually worked and drawn down to the required size. As the tubes are drawn they are heat treated to produce the correct mechanical properties. The organic oils and greases used to lubricate the tubes during the drawing processes are broken down during the heat treatment and gradually coat the tube with a film of carbon. If the carbon is left in the bore of the tube then it disrupts the formation of the protective scale and allows the initiation of pits in the wall. The presence of deleterious films, such as carbon, has been prohibited by the British Standards in copper tubes since 1969. All copper tubes for water service are treated, usually by sand (or other nonferrous medium) blasting or acid pickling, to remove any films produced during manufacture with the result that Type 1 pitting initiated by carbon films is now very rare. | 8 | Metallurgy |
DNA structure is dominated by the well-known double helix formed by Watson-Crick base-pairing of C with G and A with T. This is known as B-form DNA, and is overwhelmingly the most favorable and common state of DNA; its highly specific and stable base-pairing is the basis of reliable genetic information storage. DNA can sometimes occur as single strands (often needing to be stabilized by single-strand binding proteins) or as A-form or Z-form helices, and occasionally in more complex 3D structures such as the crossover at Holliday junctions during DNA replication.
RNA, in contrast, forms large and complex 3D tertiary structures reminiscent of proteins, as well as the loose single strands with locally folded regions that constitute messenger RNA molecules. Those RNA structures contain many stretches of A-form double helix, connected into definite 3D arrangements by single-stranded loops, bulges, and junctions. Examples are tRNA, ribosomes, ribozymes, and riboswitches. These complex structures are facilitated by the fact that RNA backbone has less local flexibility than DNA but a large set of distinct conformations, apparently because of both positive and negative interactions of the extra OH on the ribose. Structured RNA molecules can do highly specific binding of other molecules and can themselves be recognized specifically; in addition, they can perform enzymatic catalysis (when they are known as "ribozymes", as initially discovered by Tom Cech and colleagues). | 0 | Organic Chemistry |
In 1973, the Freeport-McMoRan Copper and Gold ("Freeport") smelter at Miami, Arizona, installed a 51 MW electric furnace at its Miami smelter. The decision was based on a long-term electrical power contract with the Salt River Project that provided the company with a very low rate for electricity. This contract expired in 1990 and the resulting increase in electricity prices prompted the owners of the smelter, Cyprus Miami Mining Corporation ("Cyprus"), to seek alternative smelting technologies for lower operating costs.
The technologies evaluated included:
* Contop flame cyclone reactor
* Inco flash furnace
* ISASMELT
* Mitsubishi furnace
* Noranda reactor
* Outokumpu flash furnace
* Teniente furnace.
The Contop, Inco, Mitsubishi and Outokumpu processes "were all eliminated primarily because of their high dust levels, high capital costs and poor adaptability to the existing facility". The Teniente converter was ruled out because it required the use of the electric furnace for partial smelting. The Noranda reactor was not selected "because of its high refractory wear and its poor adaptability to the existing plant due to the handling of the reactor slag". ISASMELT was chosen as the preferred technology and a licence agreement was signed with MIM in October 1990. The major factor in the decision to select the ISASMELT technology was the ability to fit it into the existing plant and to maximise the use of existing equipment and infrastructure, while the major disadvantage was seen to be the risks associated with scaling up the technology from the Mount Isa demonstration plant.
The Miami copper ISASMELT furnace was designed to treat 590,000 t/y (650,000 short tons per year) of copper concentrate, a treatment rate that was constrained by the capacity of the sulfuric acid plant used to capture the sulfur dioxide from the smelter's waste gases. The existing electric furnace was converted from smelting duties to a slag cleaning furnace and providing matte surge capacity for the converters. The ISASMELT furnace was commissioned on 11 June 1992 and in 2002 treated over 700,000 t/y of concentrate. The modernisation of the Miami smelter cost an estimated US$95 million.
In 1993, the Cyprus Minerals Company merged with AMAX to form the Cyprus Amax Minerals company, which was in turn taken over by the Phelps Dodge Corporation in late 1999. After the take-over, Phelps Dodge closed its Hidalgo and Chino smelters. Phelps Dodge was acquired by Freeport in 2006.
The Miami smelter is one of only two remaining operating copper smelters in the United States, down from 16 in 1979. | 8 | Metallurgy |
Silencing of transposon transcripts can vary in completeness of silencing as well as in duration of alteration. Plants employ a number of methods, which range from elimination of transcripts to complete epigenetic silencing. In general, these can be sorted into two strategies:
* Gene silencing#Post-transcriptional gene silencing PTGS], post-transcriptional gene silencing, in which siRNA or miRNA derived from transposon activity are loaded onto an RNA-induced silencing complex (RISC), which cleaves targeted mRNA transcripts
* Gene silencing#Transcriptional gene silencing TGS], transcriptional gene silencing, in which siRNA transposon transcript is loaded onto an RNA-Directed DNA Methylation complex, which methylates the region of DNA which is reactive to the siRNA used in the complex. This can lead to histone modification and, if further epigenetic modification occurs, heterochromatin formation. This process is not well understood, as almost all information regarding it comes to us from the study of the FWA gene in Arabidopsis thaliana, a relatively TE-poor example in the plant kingdom. This paucity of information is further complicated by the relatively small genome and the low variability of the Arabidopsis epigenetic code.
In general, initiation of transposon silencing has yet to be fully explained. For example, there have been recorded incidences of spontaneous silencing in maize, which carries a high number of transposons (~85% of the genome), though the mechanism by which this occurs is unknown. While it is known that heritable methylation occurs, and must occur with frequency, and must be initiated, triggered by some distinct factor, the only known example of this is in the case of Mu killer (Muk), a gene in maize that silences MuDR, a class II autonomous transposable element. Muk encodes a natural inverted derivative of the transposase coding sequence in MuDR, which, when transcribed, forms a dsRNA that is subsequently cut into siRNA, which renders MUDR incapable of cutting and pasting itself by way of RNAi interference of the transposase. Muk also engages RNAi-Directed Methylation to create a stable and heritable suppression. | 1 | Biochemistry |
Another strategy that has been explored is the stabilization of reactions that develop partial negative charges in the transition state. Examples of successful applications are most commonly reactions that are approximated concerted and pericyclic in nature. During the course of the reaction, one fragment develops partial negative character and the transition state can be stabilized by accepting hydrogen bond(s).
A demonstrative example is the catalysis of Claisen rearrangements of ester-substituted allyl vinyl ethers reported by the Jacobsen research group. A chiral guanidinium catalyst was found to successfully promote the reaction near room temperature with high enantioselectivity. During the transition state, the fragment coordinated to the amidinium catalyst develops partial anionic character due to the electronegativity of the oxygen and the electron-withdrawing ester group. This increases the strength of hydrogen bonding and lowers the transition state energy, thus accelerating the reaction.
Similarly, negative charge can develop in cycloaddition reactions such as the Diels-Alder reaction, when the partners are appropriately substituted. As a representative example, Rawal and coworkers developed a chiral catalyst based on α,α,α,α-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL) that could catalyze Diels-Alder reactions. In the following example, the reaction with a highly electron-rich diene and an electron-poor dienophile is thought to develop significant negative charge on the enal fragment, and is the transition state is stabilized by increased hydrogen bonding to the TADDOL (Ar = 1-naphthyl). | 0 | Organic Chemistry |
Multiplexed error-robust fluorescence in situ hybridization is a highly multiplexed version of smFISH. It uses combinatorial labeling, followed by imaging, and then error-resistant encoding to capture a high number of RNA molecules and spatial localization within the cell. The capture of a large number of RNA molecules enables elucidation of gene regulatory networks, prediction of function of unannotated genes, and identification of RNA molecule distribution patterns, which correlate with their associated proteins. | 1 | Biochemistry |
Based on the principle of counter-current piston flow, these processes are the closest to the blast furnace or, more accurately, the stückofen. Hot reducing gases are obtained from natural gas, in a separate unit from the shaft, and injected at the bottom of the shaft, while the ore is charged at the top. The pre-reduced materials are extracted hot, but in solid form, from the bottom of the shaft. This similarity to a blast furnace without its crucible made it one of the first processes explored by metallurgists, but the failures of the German Gurlt in 1857, and the French Eugène Chenot (son of Adrien) around 1862, led to the conclusion that "the reduction of iron ore [...] is therefore [not] possible in large quantities by gas alone".
Developed in the 1970s, the Midrex process is the best example of a continuous direct reduction process. As much a technical success as a commercial one, since 1980 it has accounted for around two-thirds of the world's production of pre-reduced materials. Its similarity to the blast furnace means that it shares some of its advantages, such as high production capacity, and some disadvantages, such as the relative difficulty of controlling several simultaneous reactions in a single reactor (since the nature of the product changes considerably as it travels through the vessel). The strategy of selling turnkey units, combined with a cautious increase in production capacity, has given this process good financial and technical visibility... compared with the often dashed hopes of competing processes.
Its direct competitor, the HYL III process, is the result of a research effort by the Tenova Group (de), heir to the Mexican Hylsa pioneers. Accounting for almost 20% of pre-reduced product production, it differs from the Midrex process in that it features an in-house reforming unit for the production of reducing gases.
Other processes have been developed based on this continuous reactor principle. Some, like ULCORED, are still at the study stage. Most have only been developed in a single country, or by a single company. Others were failures, such as the NSC process, of which a single plant was built in 1984 and converted to HYL III in 1993, ARMCO (a single unit commissioned in 1963 and shut down in 1982) or PUROFER (3 units operational from 1970 to 1979, small-scale production resumed in 1988).
Coal-fired processes are variants of natural gas processes, where the gas can be synthesized from coal in an additional unit. Among these variants, the MXCOL, of which one unit has been operational since 1999 and two are under construction, is a Midrex fed by a coal gasification unit. Technically mature but more complex, they are at a disadvantage compared with equivalent gas-fired processes, which require slightly less investment. | 8 | Metallurgy |
Because the compounds that exhibit bioluminescence are typically fluorescent, fluorescence can be used to identify photocytes in organisms. | 1 | Biochemistry |
Quorum sensing has been engineered using synthetic biological circuits in different systems. Examples include rewiring the AHL components to toxic genes to control population size in bacteria; and constructing an auxin-based system to control population density in mammalian cells. Synthetic quorum sensing circuits have been proposed to enable applications like controlling biofilms or enabling drug delivery. Quorum sensing based genetic circuits have been used to convert AI-2 signals to AI-1 and then subsequently use the AI-1 signal to alter bacterial growth rate, thereby changing the composition of a consortium. | 1 | Biochemistry |
Amoxicillin (α-amino-p-hydroxybenzyl penicillin) is a semisynthetic derivative of penicillin with a structure similar to ampicillin but with better absorption when taken by mouth, thus yielding higher concentrations in blood and in urine. Amoxicillin diffuses easily into tissues and body fluids. It will cross the placenta and is excreted into breastmilk in small quantities. It is metabolized by the liver and excreted into the urine. It has an onset of 30 minutes and a half-life of 3.7 hours in newborns and 1.4 hours in adults.
Amoxicillin attaches to the cell wall of susceptible bacteria and results in their death. It is effective against streptococci, pneumococci, enterococci, Haemophilus influenzae, Escherichia coli, Proteus mirabilis, Neisseria meningitidis, Neisseria gonorrhoeae, Shigella, Chlamydia trachomatis, Salmonella, Borrelia burgdorferi, and Helicobacter pylori. As a derivative of ampicillin, amoxicillin is a member of the penicillin family and, like penicillins, is a β-lactam antibiotic. It inhibits cross-linkage between the linear peptidoglycan polymer chains that make up a major component of the bacterial cell wall.
It has two ionizable groups in the physiological range (the amino group in alpha-position to the amide carbonyl group and the carboxyl group). | 4 | Stereochemistry |
Various PPGs, often featuring the 2-nitrobenzyl motif, have been used to generate numerous gels. In one example, researchers incorporated PPGs into a silica-based sol-gel. In a second example, a hydrogel was synthesized to include protected Ca ions. Finally, PPGs have been utilized to cross-link numerous photodegradable polymers, which have featured linear, multi-dimensional network, dendrimer, and branched structures. | 5 | Photochemistry |
Brassica species contain glucosinolates, which are sulfur-containing secondary compounds. Glucosinolates are composed of a β-thioglucose moiety, a sulfonated oxime and a side chain. The synthesis of glucosinolates starts with the oxidation of the parent amino acid to an aldoxime, followed by the addition of a thiol group (through conjugation with glutathione) to produce thiohydroximate. The transfer of a glucose and a sulfate moiety completes the formation of the glucosinolates.
The physiological significance of glucosinolates is still ambiguous, though they are considered to function as sink compounds in situations of sulfur excess. Upon tissue disruption glucosinolates are enzymatically degraded by myrosinase and may yield a variety of biologically active products such as isothiocyanates, thiocyanates, nitriles and oxazolidine-2-thiones. The glucosinolate-myrosinase system is assumed to play a role in plant-herbivore and plant-pathogen interactions.
Furthermore, glucosinolates are responsible for the flavor properties of Brassicaceae and recently
have received attention in view of their potential anti-carcinogenic properties.
Allium species contain γ-glutamylpeptides and alliins (S-alk(en)yl cysteine sulfoxides). The content of these sulfur-containing secondary compounds strongly depends on stage of development of the plant, temperature, water availability and the level of nitrogen and sulfur nutrition. In onion bulbs their content may account for up to 80% of the organic sulfur fraction. Less is known about the content of secondary sulfur compounds in the seedling stage of the plant.
It is assumed that alliins are predominantly synthesized in the leaves, from where they are subsequently transferred to the attached bulb scale. The biosynthetic pathways of synthesis of γ-glutamylpeptides and alliins are still ambiguous. γ-Glutamylpeptides can be formed from cysteine (via γ-glutamylcysteine or glutathione) and can be metabolized into the corresponding alliins via oxidation and subsequent hydrolyzation by γ-glutamyl transpeptidases.
However, other possible routes of the synthesis of γ-glutamylpeptides and alliins may not be excluded. Alliins and γ-glutamylpeptides are known to have therapeutic utility and might have potential value as phytopharmaceutics. The alliins and their breakdown products (e.g. allicin) are the flavor precursors for the odor and taste of species. Flavor is only released when plant cells are disrupted and the enzyme alliinase from the vacuole is able to degrade the alliins, yielding a wide variety of volatile and non-volatile sulfur-containing compounds. The physiological function of γ-glutamylpeptides and alliins is rather unclear. | 1 | Biochemistry |
In chemistry, Bema Hapothle is an extended acronym for Bell–Marcus–Hammond–Polanyi–Thornton–Leffler, referring to the combined contribution of the theories of these chemists to the rationalization of changes in transition state structure to perturbations, such as change of reaction solvent. | 7 | Physical Chemistry |
In situ chemical reduction (ISCR) is a type of environmental remediation technique used for soil and/or groundwater remediation to reduce the concentrations of targeted environmental contaminants to acceptable levels. It is the mirror process of In Situ Chemical Oxidation (ISCO). ISCR is usually applied in the environment by injecting chemically reductive additives in liquid form into the contaminated area or placing a solid medium of chemical reductants in the path of a contaminant plume. It can be used to remediate a variety of organic compounds, including some that are resistant to natural degradation.
The in situ in ISCR is just Latin for "in place", signifying that ISCR is a chemical reduction reaction that occurs at the site of the contamination. Like ISCO, it is able to decontaminate many compounds, and, in theory, ISCR could be more effective in ground water remediation than ISCO.
Chemical reduction is one half of a redox reaction, which results in the gain of electrons. One of the reactants in the reaction becomes oxidized, or loses electrons, while the other reactant becomes reduced, or gains electrons. In ISCR, reducing compounds, compounds that accept electrons given by other compounds in a reaction, are used to change the contaminants into harmless compounds.
__TOC__ | 2 | Environmental Chemistry |
Heme, an important prosthetic group present in Complexes I, II, and IV can also be targeted, since heme biosynthesis and uptake have been correlated with increased cancer progression. Various molecules can inhibit heme via different mechanisms. For instance, succinylacetone has been shown to decrease heme concentrations by inhibiting δ-aminolevulinic acid in murine erythroleukemia cells. The primary structure of heme-sequestering peptides, such as HSP1 and HSP2, can be modified to downregulate heme concentrations and reduce proliferation of non-small lung cancer cells. | 1 | Biochemistry |
The advantage of NMR for end groups is that it allows for not only the identification of the end group units, but also allows for the quantification of the number-average length of the polymer. End-group analysis with NMR requires that the polymer be soluble in organic or aqueous solvents. Additionally, the signal on the end-group must be visible as a distinct spectral frequency, i.e. it must not overlap with other signals. As molecular weight increases, the width of the spectral peaks also increase. As a result of this, methods which rely on resolution of the end-group signal are mostly used for polymers of low molecular weight (roughly less than 20,000 g/mol number-average molecular weight). By using the information obtained from the integration of a H NMR spectrum, the degree of polymerization (X) can be calculated. With knowledge of the identity of the end groups/repeat unit and the number of protons contained on each, the X can then be calculated. For this example above, once the 1H NMR has been integrated and the values have been normalized to 1, the degree of polymerization is calculated by simply dividing the normalized value for the repeat unit by the number of protons continued in the repeat unit. For this case, X = n = 100/2, and therefore X = 50, or there are 50 repeat units in this monomer. | 7 | Physical Chemistry |
By extension, a [uvw] zone-axis pattern (ZAP) is a diffraction pattern taken with an incident beam, e.g. of electrons, X-rays or neutrons traveling along a lattice direction specified by the zone-axis indices [uvw]. Because of their small wavelength λ, high energy electrons used in electron microscopes have a very large Ewald sphere radius (1/λ), so that electron diffraction generally "lights up" diffraction spots with g-vectors (hkl) that are perpendicular to [uvw].
One result of this, as illustrated in the figure above, is that "low-index" zones are generally perpendicular to "low-Miller index" lattice planes, which in turn have small spatial frequencies (g-values) and hence large lattice periodicities (d-spacings). A possible intuition behind this is that in electron microscopy, for electron beams to be directed down wide (i.e. easily visible) tunnels between columns of atoms in a crystal, directing the beam down a low-index (and by association high-symmetry) zone axis may help. | 3 | Analytical Chemistry |
Grote–Hynes theory is a theory of reaction rate in a solution phase. This rate theory was developed by James T. Hynes with his graduate student Richard F. Grote in 1980.
The theory is based on the generalized Langevin equation (GLE). This theory introduced the concept of frequency dependent friction for chemical rate processes in solution phase. Because of inclusion of the frequency dependent friction instead of constant friction, the theory successfully predicts the rate constant including where the reaction barrier is large and of high frequency, where the diffusion over the barrier starts decoupling from viscosity of the medium. This was the weakness of Kramer's rate theory, which underestimated the reaction rate having large barrier with high frequency. | 7 | Physical Chemistry |
In die casting the most common defects are misruns and cold shuts. These defects can be caused by cold dies, low metal temperature, dirty metal, lack of venting, or excessive lubricant. Other possible defects are gas porosity, shrinkage porosity, hot tears, and flow marks. Flow marks are marks left on the surface of the casting due to poor gating, sharp corners or excessive lubricant. | 8 | Metallurgy |
A dominant role for the mitochondria is the production of ATP, as reflected by the large number of proteins in the inner membrane for this task. This is done by oxidizing the major products of glucose: pyruvate, and NADH, which are produced in the cytosol. This type of cellular respiration, known as aerobic respiration, is dependent on the presence of oxygen. When oxygen is limited, the glycolytic products will be metabolized by anaerobic fermentation, a process that is independent of the mitochondria. The production of ATP from glucose and oxygen has an approximately 13-times higher yield during aerobic respiration compared to fermentation. Plant mitochondria can also produce a limited amount of ATP either by breaking the sugar produced during photosynthesis or without oxygen by using the alternate substrate nitrite. ATP crosses out through the inner membrane with the help of a specific protein, and across the outer membrane via porins. After conversion of ATP to ADP by dephosphorylation that releases energy, ADP returns via the same route. | 1 | Biochemistry |
Dippel's oil (sometimes referred to as bone oil) is a nitrogenous by-product of the destructive distillation of bones. A dark, viscous, tar-like liquid with an unpleasant smell, it is named after its inventor, Johann Konrad Dippel. The oil consists of aliphatic chains, with nitrogen functional groups including pyrroles, pyridines and nitriles, as well as other nitrogenous compounds.
Dippel's oil had a number of uses, which are mostly obsolete. Its primary use was as an animal and insect repellent. It saw limited use as a chemical warfare harassing agent during the desert campaign of World War II. The oil was used to render wells undrinkable and thus deny their use to the enemy.
By not being lethal, the oil was claimed to not be in breach of the Geneva Protocol. | 0 | Organic Chemistry |
Abrasion is the property of the coal which describes its propensity and ability to wear away machinery and undergo autonomous grinding. While carbonaceous matter in coal is relatively soft, quartz and other mineral constituents in coal are quite abrasive. This is tested in a calibrated mill, containing four blades of known mass. The coal is agitated in the mill for 12,000 revolutions at a rate of 1,500 revolutions per minute.(I.E 1500 revolution for 8 min.) The abrasion index is determined by measuring the loss of mass of the four metal blades. | 3 | Analytical Chemistry |
Ogston studied potentiometric titration of amino acids in non-aqueous solvents. He was particularly interested in sinovial fluid, and fibrous proteins. More generally, he worked on the use of physico-chemical methods to study the size, weight and structure of molecules, such as ultracentrifugation, which he applied to insulin, for example, and electrophoresis. In this context he made many improvement to equipment used for studying the physical chemistry of proteins. For example, he devised a novel type of apparatus for measuring viscosity. He made many studies of enzymes such as peroxidase and creatine phosphotransferase. He contributed to the general field of enzyme kinetics by studying activation and inhibition.
He made a sceptical study of the suggestions of a repetitive structure of proteins made by Bergmann and Niemann and by Wrinch that were widely discussed in the 1940s. | 4 | Stereochemistry |
Adding to the transition metal-bismuth carbonyl clusters, the dibismuth clusters with transition metals have also been explored by synthetic chemists. The core of such compounds is represented in the form of dibismuthene or dibismithyne unit, in which the Bi atoms contain the inert 6s lone pair and through π-bond-donation are able to coordinate to carbonyl moieties of transition metals .
The common synthetic precursor is the trimethylsilylmethyl-cyclobismuthane. Upon reaction with tungsten pentacarbonyl, the resulting side-on adduct preserved the dibismuthene unit, while reaction with diiron noncarbonyl yields the a tetracylic heteronuclear iron-bismuth carbonyl compound (see scheme to the right).
The complexity of the dibismuthene complexes ranges from incorporation of cobalt ions to generate a prismatic cobalto carbonyl dicapped structure in the [(CO)CoBi] structure to iron incorporation to yield diiron dibismuth tetracyclic moiety side-on capped with cobaltocarbonyl unit. A similar structure was synthesized with tungsten replacing the iron units and this time capped with a bismuth-iron carbonyl-Cp unit. Finally, another example comes in the form of a side-on coordinated zirconium dicyclopentadienyl unit to the dibismuth mesitylene moiety (see figure). | 0 | Organic Chemistry |
Passive daytime radiative cooling is not a carbon dioxide removal (CDR) or solar radiation management (SRM) method, but rather enhances longwave infrared thermal radiation heat transfer on the Earth's surface through the infrared window with the coldness of outer space to achieve daytime cooling. Solar radiation is reflected by the PDRC surface to minimize heat gain and to maximize thermal emittance. PDRC differs from SRM because it increases radiative heat emission rather than merely reflecting the absorption of solar radiation. PDRC has been referred to as an alternative or "third approach" to geoengineering. PDRC has also been classified as a sustainable and renewable cooling technology. | 7 | Physical Chemistry |
In chemistry, a phosphodiester bond occurs when exactly two of the hydroxyl groups () in phosphoric acid react with hydroxyl groups on other molecules to form two ester bonds. The "bond" involves this linkage . Discussion of phosphodiesters is dominated by their prevalence in DNA and RNA, but phosphodiesters occur in other biomolecules, e.g. acyl carrier proteins, phospholipids and the cyclic forms of GMP and AMP (cGMP and cAMP). | 1 | Biochemistry |
The rate of curing of concrete depends on the fineness of the cement and of the components used in its manufacture, which may include fly ash, silica fume and other materials, in addition to the calcinated limestone which causes it to harden. Although the Blaine air permeability method is often preferred, due to its simplicity and low cost, the nitrogen BET method is also used.
When hydrated cement hardens, the calcium silicate hydrate (or C-S-H), which is responsible for the hardening reaction, has a large specific surface area because of its high porosity. This porosity is related to a number of important properties of the material, including the strength and permeability, which in turn affect the properties of the resulting concrete. Measurement of the specific surface area using the BET method is useful for comparing different cements. This may be performed using adsorption isotherms measured in different ways, including the adsorption of water vapour at temperatures near ambient, and adsorption of nitrogen at 77 K (the boiling point of liquid nitrogen). Different methods of measuring cement paste surface areas often give very different values, but for a single method the results are still useful for comparing different cements. | 7 | Physical Chemistry |
Subspecialty areas of organometallic chemistry include:
* Period 2 elements: organolithium chemistry, organoberyllium chemistry, organoborane chemistry
* Period 3 elements: organosodium chemistry, organomagnesium chemistry, organoaluminium chemistry, organosilicon chemistry
* Period 4 elements: organocalcium chemistry, organoscandium chemistry, organotitanium chemistry, organovanadium chemistry, organochromium chemistry, organomanganese chemistry, organoiron chemistry, organocobalt chemistry, organonickel chemistry, organocopper chemistry, organozinc chemistry, organogallium chemistry, organogermanium chemistry, organoarsenic chemistry, organoselenium chemistry
* Period 5 elements: organoyttrium chemistry, organozirconium chemistry, organoniobium chemistry, organomolybdenum chemistry, organotechnetium chemistry, organoruthenium chemistry, organorhodium chemistry, organopalladium chemistry, organosilver chemistry, organocadmium chemistry, organoindium chemistry, organotin chemistry, organoantimony chemistry, organotellurium chemistry
* Period 6 elements: organolanthanide chemistry, organocerium chemistry, organotantalum chemistry, organotungsten chemistry, organorhenium chemistry, organoosmium chemistry, organoiridium chemistry, organoplatinum chemistry, organogold chemistry, organomercury chemistry, organothallium chemistry, organolead chemistry, organobismuth chemistry, organopolonium chemistry
* Period 7 elements: organoactinide chemistry, organothorium chemistry, organouranium chemistry, organoneptunium chemistry | 0 | Organic Chemistry |
An inductively coupled plasma (ICP) or transformer coupled plasma (TCP) is a type of plasma source in which the energy is supplied by electric currents which are produced by electromagnetic induction, that is, by time-varying magnetic fields. | 7 | Physical Chemistry |
The sophistication of the active site network causes residues involved in catalysis (and residues in contact with these) to be highly evolutionarily conserved. However, there are examples of divergent evolution in catalytic triads, both in the reaction catalysed, and the residues used in catalysis. The triad remains the core of the active site, but it is evolutionarily adapted to serve different functions. Some proteins, called pseudoenzymes, have non-catalytic functions (e.g. regulation by inhibitory binding) and have accumulated mutations that inactivate their catalytic triad. | 1 | Biochemistry |
In atomic physics, a dark state refers to a state of an atom or molecule that cannot absorb (or emit) photons. All atoms and molecules are described by quantum states; different states can have different energies and a system can make a transition from one energy level to another by emitting or absorbing one or more photons. However, not all transitions between arbitrary states are allowed. A state that cannot absorb an incident photon is called a dark state. This can occur in experiments using laser light to induce transitions between energy levels, when atoms can spontaneously decay into a state that is not coupled to any other level by the laser light, preventing the atom from absorbing or emitting light from that state.
A dark state can also be the result of quantum interference in a three-level system, when an atom is in a coherent superposition of two states, both of which are coupled by lasers at the right frequency to a third state. With the system in a particular superposition of the two states, the system can be made dark to both lasers as the probability of absorbing a photon goes to 0. | 7 | Physical Chemistry |
The Rfam database can be used for a variety of functions. For each ncRNA family, the interface allows users to: view and download multiple sequence alignments; read annotation; and examine species distribution of family members. There are also links provided to literature references and other RNA databases.
Rfam also provides links to Wikipedia so that entries can be created or edited by users.
The interface at the Rfam website allows users to search ncRNAs by keyword, family name, or genome as well as to search by ncRNA sequence or EMBL accession number.
The database information is also available for download, installation and use using the INFERNAL software package. The INFERNAL package can also be used with Rfam to annotate sequences (including complete genomes) for homologues to known ncRNAs. | 1 | Biochemistry |
This describes the preparation of what Agricola calls "juices": salt, soda, nitre, alum, vitriol, saltpetre, sulphur and bitumen. Finally glass making is covered. Agricola seems less secure about this process. He is not clear about making glass from the raw ingredients but clearer about remelting glass to make objects.
Prof. Philippus Bechius (1521–1560), a friend of Agricola, translated De re metallica libri XII into German. It was published with the German title Vom Bergkwerck XII Bücher in 1557. The Hoovers describe the translation as "a wretched work, by one who knew nothing of the science," but it, like the Latin original, saw further editions. In 1563 Agricola's publisher, Froben and Bischoff ("Hieronimo Frobenio et Nicolao Episcopio") in Basel, published an Italian translation by Michelangelo Florio as well. | 8 | Metallurgy |
In chemistry, the Natta projection (named for Italian chemist Giulio Natta) is a way to depict molecules with complete stereochemistry in two dimensions in a skeletal formula. In a hydrocarbon molecule with all carbon atoms making up the backbone in a tetrahedral molecular geometry, the zigzag backbone is in the paper plane (chemical bonds depicted as solid line segments) with the substituents either sticking out of the paper toward the viewer (chemical bonds depicted as solid wedges) or away from the viewer (chemical bonds depicted as dashed wedges). The Natta projection is useful for representing the tacticity of a polymer. | 4 | Stereochemistry |
Examples include the active sites of a number of enzymes:
* Nitrogenase include two P-clusters ([8Fe-7S]) and two FeMocos ([7Fe-9S-C-Mo-R homocitrate]).
* Carbon monoxide dehydrogenase and acetyl coenzyme-A synthase each features an Fe-N-iS clusters.
* [FeFe]-hydrogenase features an "H-cluster", consisting of a FeS bridge to Fe via a cystine. The Fe half features unique ligands: 3 CO, 2 CN, and an azadithiolate HN(CHS).
* A special 6 cysteine-coordinated [FeS] cluster was found in oxygen-tolerant membrane-bound [NiFe] hydrogenases.
* The "double cubane cluster" [FeS], found in some nitrogenase-related ATPases, consists of two [FeS] bridged by a cysteine. The functions of such proteins remain unclear. | 7 | Physical Chemistry |
A privileged scaffold is a molecular framework or chemical moiety that is statistically recurrent among known drugs or among a specific array of biologically active compounds. These privileged elements can be used as a basis for designing new active biological compounds or compound libraries. | 1 | Biochemistry |
In an extension of the application of PED to imaging, electron tomography can benefit from the reduction of dynamic contrast effects. Tomography entails collecting a series of images (2-D projections) at various tilt angles and combining them to reconstruct the three dimensional structure of the specimen. Because many dynamical contrast effects are highly sensitive to the orientation of the crystalline sample with respect to the incident beam, these effects can convolute the reconstruction process in tomography. Similarly to single imaging applications, by reducing dynamical contrast, interpretation of the 2-D projections and thus the 3-D reconstruction are more straightforward. | 3 | Analytical Chemistry |
Porphyrin-based compounds are of interest as possible components of molecular electronics and photonics. Synthetic porphyrin dyes have been incorporated in prototype dye-sensitized solar cells. | 1 | Biochemistry |
A nitroalkene, or nitro olefin, is a functional group combining the functionality of its constituent parts, an alkene and nitro group, while displaying its own chemical properties through alkene activation, making the functional group useful in specialty reactions such as the Michael reaction or Diels-Alder additions. | 0 | Organic Chemistry |
The GUS assay does not require the presence of any cofactors or ions for function. Beta-glucuronidase can function through a wide range of pH values, and is fairly resistant to thermal inactivation. However, GUS is susceptible to inhibition from certain heavy metal ions, such as Cu and Zn.
Additionally, the interpretation of the assay is limited by the movement of diX-indigo throughout the cell. DiX-indigo, can associate with lipids to diffuse far from the site of enzyme activity, which shows a lack of cytosolic localization and irregularity of substrate penetration. This can potentially lead to an incorrect interpretation of GUS protein localization. Despite a lack of cellular localization, nuclear localization of GUS has been well observed. GUS assays can be carried out in the presence of potassium ferricyanide to prevent the stain from diffusing. | 1 | Biochemistry |
In organic chemistry, a primary carbon is a carbon atom which is bound to only one other carbon atom. It is thus at the end of a carbon chain. In case of an alkane, three hydrogen atoms are bound to a primary carbon (see propane in the figure on the right). A hydrogen atom could also be replaced by a hydroxy group (), which would make the molecule a primary alcohol. | 0 | Organic Chemistry |
Diphosphene is a type of organophosphorus compound that has a phosphorus–phosphorus double bond, denoted by R-P=P-R'. These compounds are not common but are of theoretical interest. Normally, compounds with the empirical formula RP exist as rings. However, like other multiple bonds between heavy main-group elements, P=P double bonds can be stabilized by a large steric hindrance from the substitutions. The first isolated diphosphene bis(2,4,6-tri-tert-butylphenyl)diphosphene was exemplified by Masaaki Yoshifuji and his coworkers in 1981, in which diphosphene is stabilized by two bulky phenyl group. | 0 | Organic Chemistry |
The reading of data from 3D optical memories has been carried out in many different ways. While some of these rely on the nonlinearity of the light-matter interaction to obtain 3D resolution, others use methods that spatially filter the media's linear response. Reading methods include:
Two photon absorption (resulting in either absorption or fluorescence). This method is essentially two-photon microscopy.
Linear excitation of fluorescence with confocal detection. This method is essentially confocal laser scanning microscopy. It offers excitation with much lower laser powers than does two-photon absorbance, but has some potential problems because the addressing light interacts with many other data points in addition to the one being addressed.
Measurement of small differences in the refractive index between the two data states. This method usually employs a phase-contrast microscope or confocal reflection microscope. No absorption of light is necessary, so there is no risk of damaging data while reading, but the required refractive index mismatch in the disc may limit the thickness (i.e., number of data layers) that the media can reach due to the accumulated random wavefront errors that destroy the focused spot quality.
Second-harmonic generation has been demonstrated as a method to read data written into a poled polymer matrix.
Optical coherence tomography has also been demonstrated as a parallel reading method. | 5 | Photochemistry |
Cucurbiturils are amidals (less precisely aminals) and synthesized from urea 1 and a dialdehyde (e.g., glyoxal 2) via a nucleophilic addition to give the intermediate glycoluril 3. This intermediate is condensed with formaldehyde to give hexamer cucurbit[6]uril above 110 °C. Ordinarily, multifunctional monomers such as 3 would undergo a step-growth polymerization that would give a distribution of products, but due to favorable strain and an abundance of hydrogen bonding, the hexamer is the only reaction product isolated after precipitation.
Decreasing the temperature of the reaction to between 75 and 90 °C can be used to access other sizes of cucurbiturils including CB[5], CB[7], CB[8], and CB[10]. CB[6] is still the major product; the other ring sizes are formed in smaller yields. The isolation of sizes other than CB[6] requires fractional crystallization and dissolution. CB[5], CB[6], CB[7], and CB[8] are all currently commercially available. The larger sizes are a particularly active area of research since they can bind larger and more interesting guest molecules, thus expanding their potential applications.
Cucurbit[10]uril is particularly difficult to isolate. It was first discovered by Day and coworkers in 2002 as an inclusion complex containing CB[5] by fractional crystallization of the cucurbituril reaction mixture. The CB[10]·CB[5] was unambiguously identified by single crystal X-ray structural analysis that revealed the complex resembled a molecular gyroscope. In this case, the free rotation of the CB[5] within the CB[10] cavity mimics the independent rotation of a flywheel within the frame of a gyroscope.
Isolation of pure CB[10] could not be accomplished by direct separation methods since the compound has such a high affinity for CB[5]. The strong binding affinity for the CB[5] can be understood since it has a complementary size and shape to the cavity of the CB[10]. Pure CB[10] was isolated by Isaacs and coworkers in 2005 by introducing a more strongly binding melamine diamine guest that is capable of displacing the CB[5]. The melamine diamine guest was then separated from the CB[10] by reaction with acetic anhydride that converted the positively charged amine groups to neutrally charged amides. Cucurbiturils strongly bind cationic guests, but by removing the positive charge from the melamine diamine guest reduces the association constant to the point it can be removed by washing with methanol, DMSO, and water. The CB[10] has an unusually large cavity (870 Å) that's free and capable of binding extraordinarily large guests including a cationic [[calixarene|calix[4]arene]]. | 6 | Supramolecular Chemistry |
Propionyl-CoA production through the catabolism of fatty acids is also associated with thioesterifcation. In a study concerning Aspergillus nidulans, it was found that with the inhibition of a methylcitrate synthase gene, mcsA, of the pathway described above, production of distinct polyketides was inhibited as well. Therefore, the utilization of propionyl-CoA through the methylcitrate cycle decreases its concentration, while subsequently increasing the concentration of polyketides. A polyketide is a structure commonly found in fungi that is made of acetyl- and malonyl-CoAs, providing a product with alternating carbonyl groups and methylene groups. Polyketides and polyketide derivatives are often highly structurally complex, and several are highly toxic. This has led to research on limiting polyketide toxicity to crops in agriculture through phytopathogenic fungi. | 1 | Biochemistry |
The physical properties of the isomers of xylene differ slightly. The melting point ranges from (m-xylene) to (p-xylene)—as usual, the para isomer's melting point is much higher because it packs more readily in the crystal structure. The boiling point for each isomer is around . The density of each isomer is around and thus is less dense than water. The odor of xylene is detectable at concentrations as low as 0.08 to 3.7 ppm (parts of xylene per million parts of air) and can be tasted in water at 0.53 to 1.8 ppm.
Xylenes form azeotropes with water and a variety of alcohols. The azeotrope with water consists of 60% xylenes and boils at 94.5 °C. As with many alkylbenzene compounds, xylenes form complexes with various halocarbons. The complexes of different isomers often have dramatically different properties from each other. | 2 | Environmental Chemistry |
There are several different pathways through which propionyl-CoA can be produced:
* Propionyl-CoA, a three-carbon structure, is considered to be a minor species of propionic acid. Therefore, odd-number chains of fatty acids are oxidized to yield both propionyl-CoA as well as acetyl-CoA. Propionyl-CoA is later converted into succinyl-CoA through biotin-dependant propionyl-CoA carboxylase (PCC) and b12-dependant methylmalonyl-CoA mutase (MCM), sequentially.
* Propionyl-CoA is not only produced from the oxidation of odd-chain fatty acids, but also by the oxidation of amino acids including methionine, valine, isoleucine, and threonine. Furthermore, catabolism of amino acids can also be a result of the conversion of propionyl-CoA to methylmalonyl-CoA by propionyl-CoA carboxylase.
* Cholesterol oxidation, which forms bile acids, also forms propionyl-CoA as a side product. In an experiment performed by Suld et al., when combining liver mitochondria and propionic acid with the addition of coenzyme A, labeled isotopes of psionic acid were degraded. However, following 5β-cholestane-3α,7α,12α,26-tetrol-26,27-C14 incubation, propionyl CoA was able to be rescued along with the formation of bile. | 1 | Biochemistry |
Due to their high surface roughness, conventional white nitrocellulose films scatter and reflect large amounts of excitation and emission light during the fluorescence detection in the microarray scanner. In addition, nitrocellulose exhibits a natural autofluorescence at the detection wavelengths commonly used. Both these factors lead to a high background fluorescent signal from these membrane slides. To overcome this problem, a new process has been developed to generate black membranes that absorb the scattered light, significantly reducing the background auto-fluorescence and thus offering a very low and homogenous auto-fluorescence to achieve a significantly improved dynamic range. These slides are commercially available through Schott AG. Nevertheless, conventional white nitrocellulose films continue to be the dominant surface for many protein microarray applications because the claims above have not proved relevant to end user requirements. Regardless, nitrocellulose slide manufacturers like Grace Bio-Labs continue to develop new nitrocellulose surfaces to further optimize their use in protein microarrays.
A method for protein quantitation on nitrocellulose coated glass slides uses near-IR fluorescent detection with quantum dots. Traditional porous nitrocellulose signal to noise is limited by auto-fluorescence of the nitrocellulose at the respective required wavelengths of excitation and emission for standard organic fluorescent detection probes. Near IR detection probes are excited and read at emission wavelengths outside the range of nitrocellulose fluorescence. | 1 | Biochemistry |
* 1999 Marie Curie Fellowship, University of Cambridge, United Kingdom.
* 2000 Junior Research Fellowship, Wolfson College, Cambridge, United Kingdom.
* 2001 Royal Society University Research Fellowship, University of Cambridge, United Kingdom.
* 2011 ERC Starting Grant (subsidy) from the European Research Council for research into: Self-replication in dynamic molecular networks
* 2013 Vici grant from the Dutch Research Council (NWO) for research into: the Darwinian evolution of molecules. (Vici grants are intended for excellent senior researchers who can demonstrably develop their own innovative research lines and who are suitable for coaching early-career researchers.
* 2013 Appointed as Fellow of the Royal Society of Chemistry.
* 2013 Visiting professor, University of Strasbourg, France.
* 2017 ERC Advanced Grant (subsidy) from the European Research Council.
* 2018 Visiting professor, Ludwig Maximilian University of Munich, Germany.
* 2018 Supramolecular chemistry prize of the Royal Society of Chemistry.
* 2020 Member of the Royal Dutch Academy of Science ([https://knaw.nl/en/news/news/royal-academy-selects-eighteen-new-members link]).
* 2023 ERC Synergy Grant (subsidy) from the European Research Council. | 0 | Organic Chemistry |
In order to identify and quantify metabolites produced by the body, various detection methods have been employed. Most often, these involve the use of nuclear magnetic resonance (NMR) spectroscopy or mass spectrometry (MS), providing universal detection, identification and quantification of metabolites in individual patient samples. Although both processes are used in pharmacometabolomic analyses, there are advantages and disadvantages for using either nuclear magnetic resonance (NMR) spectroscopy- or mass spectrometry (MS)-based platforms in this application. | 1 | Biochemistry |
In thermodynamics, the heat capacity at constant volume, , and the heat capacity at constant pressure, , are extensive properties that have the magnitude of energy divided by temperature. | 7 | Physical Chemistry |
Cys-loop receptors have structural elements that are well conserved, with a large extracellular domain (ECD) harboring an alpha-helix and 10 beta-strands. Following the ECD, four transmembrane segments (TMSs) are connected by intracellular and extracellular loop structures. Except the TMS 3-4 loop, their lengths are only 7-14 residues. The TMS 3-4 loop forms the largest part of the intracellular domain (ICD) and exhibits the most variable region between all of these homologous receptors. The ICD is defined by the TMS 3-4 loop together with the TMS 1-2 loop preceding the ion channel pore. Crystallization has revealed structures for some members of the family, but to allow crystallization, the intracellular loop was usually replaced by a short linker present in prokaryotic cys-loop receptors, so their structures as not known. Nevertheless, this intracellular loop appears to function in desensitization, modulation of channel physiology by pharmacological substances, and posttranslational modifications. Motifs important for trafficking are therein, and the ICD interacts with scaffold proteins enabling inhibitory synapse formation. | 1 | Biochemistry |
Proposed mechanisms:
*Reduced expression of penicillin binding proteins during stationary growth phase
*Induction of microbial resistance mechanisms (such as beta lactamases with short half-lives) by high drug concentrations
*Precipitation of antimicrobial drug in vitro, possibly also leading to the crystallized drug being mis-detected as colonies of the microbe.
*Self-antagonising the receptor with which it binds (penicillin binding proteins, for example, in the case of a penicillin).
Penicillin is a bactericidal antibiotic that works by inhibiting cell wall synthesis but this synthesis only occurs when bacteria are actively replicating (or in the log phase of growth). In cases of extremely high bacterial burden (such as with Group A Strep), bacteria may be in the stationary phase of growth. In this instance since no bacteria are actively replicating (presumably due to nutrient restriction) penicillin has no activity. This is why adding an antibiotic like clindamycin, which acts ribosomally, kills some of the bacteria and returns them to the log phase of growth. | 1 | Biochemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.