text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
Prokaryotic ribosomes begin translation of the mRNA transcript while DNA is still being transcribed. Thus translation and transcription are parallel processes. Bacterial mRNA are usually polycistronic and contain multiple ribosome binding sites. Translation initiation is the most highly regulated step of protein synthesis in prokaryotes.
The rate of translation depends on two factors:
* the rate at which a ribosome is recruited to the RBS
* the rate at which a recruited ribosome is able to initiate translation (i.e. the translation initiation efficiency)
The RBS sequence affects both of these factors. | 1 | Biochemistry |
NCOA4 has been shown to interact with:
* Androgen receptor, and
* Peroxisome proliferator-activated receptor gamma
* Ferritin
* ATG8 | 1 | Biochemistry |
The interconversion of chair conformers is called ring flipping or chair-flipping. Carbon–hydrogen bonds that are axial in one configuration become equatorial in the other, and vice versa. At room temperature the two chair conformations rapidly equilibrate. The proton NMR spectrum of cyclohexane is a singlet at room temperature, with no separation into separate signals for axial and equatorial hydrogens.
In one chair form, the dihedral angle of the chain of carbon atoms (1,2,3,4) is positive whereas that of the chain (1,6,5,4) is negative, but in the other chair form, the situation is the opposite. So both these chains have to undergo a reversal of dihedral angle. When one of these two four-atom chains flattens to a dihedral angle of zero, we have the half-chair conformation, at a maximum energy along the conversion path. When the dihedral angle of this chain then becomes equal (in sign as well as magnitude) to that of the other four-atom chain, the molecule has reached the continuum of conformations, including the twist boat and the boat, where the bond angles and lengths can all be at their normal values and the energy is therefore relatively low. After that, the other four-carbon chain has to switch the sign of its dihedral angle in order to attain the target chair form, so again the molecule has to pass through the half-chair as the dihedral angle of this chain goes through zero. Switching the signs of the two chains sequentially in this way minimizes the maximum energy state along the way (at the half-chair state) — having the dihedral angles of both four-atom chains switch sign simultaneously would mean going through a conformation of even higher energy due to angle strain at carbons 1 and 4.
The detailed mechanism of the chair-to-chair interconversion has been the subject of much study and debate. The half-chair state (D, in figure below) is the key transition state in the interconversion between the chair and twist-boat conformations. The half-chair has C symmetry. The interconversion between the two chair conformations involves the following sequence: chair → half-chair → twist-boat → half-chair′ → chair′. | 4 | Stereochemistry |
Large amounts of research have focused recently on the use of enzymes as a catalyst for the transesterification. Researchers have found that very good yields could be obtained from crude and used oils using lipases. The use of lipases makes the reaction less sensitive to high free fatty-acid content, which is a problem with the standard biodiesel process. One problem with the lipase reaction is that methanol cannot be used because it inactivates the lipase catalyst after one batch. However, if methyl acetate is used instead of methanol, the lipase is not in-activated and can be used for several batches, making the lipase system much more cost-effective. | 0 | Organic Chemistry |
Mitochondrial creatine kinase (CK) is present in the mitochondrial intermembrane space, where it regenerates phosphocreatine (PCr) from mitochondrially generated ATP and creatine (Cr) imported from the cytosol. Apart from the two mitochondrial CK isoenzyme forms, that is, ubiquitous mtCK (present in non-muscle tissues) and sarcomeric mtCK (present in sarcomeric muscle), there are three cytosolic CK isoforms present in the cytosol, depending on the tissue. Whereas MM-CK is expressed in sarcomeric muscle, that is, skeletal and cardiac muscle, MB-CK is expressed in cardiac muscle, and BB-CK is expressed in smooth muscle and in most non-muscle tissues.
Mitochondrial mtCK and cytosolic CK are connected in a so-called PCr/Cr-shuttle or circuit. PCr generated by mtCK in mitochondria is shuttled to cytosolic CK that is coupled to ATP-dependent processes, e.g. ATPases, such as acto-myosin ATPase and calcium ATPase involved in muscle contraction, and sodium/potassium ATPase involved in sodium retention in the kidney. The bound cytosolic CK accepts the PCr shuttled through the cell and uses ADP to regenerate ATP, which can then be used as an energy source by the ATPases (CK is associated intimately with the ATPases, forming a functionally coupled microcompartment). PCr is not only an energy buffer, but also a cellular transport form of energy between subcellular sites of energy (ATP) production (mitochondria and glycolysis) and those of energy utilization (ATPases).
Thus, CK enhances skeletal, cardiac, and smooth muscle contractility, and is involved in the generation of blood pressure. Further, the ADP-scavenging action of creatine kinase has been implicated in bleeding disorders: persons with highly elevated plasma CK could be prone to major bleeding. | 1 | Biochemistry |
If the crystal diffracts to high resolution (<1.2 Å), the initial phases can be estimated using direct methods. Direct methods can be used in x-ray crystallography, neutron crystallography, and electron crystallography.
A number of initial phases are tested and selected by this method. The other is the Patterson method, which directly determines the positions of heavy atoms. The Patterson function gives a large value in a position which corresponds to interatomic vectors. This method can be applied only when the crystal contains heavy atoms or when a significant fraction of the structure is already known.
For molecules whose crystals provide reflections in the sub-Ångström range, it is possible to determine phases by brute force methods, testing a series of phase values until spherical structures are observed in the resultant electron density map. This works because atoms have a characteristic structure when viewed in the sub-Ångström range. The technique is limited by processing power and data quality. For practical purposes, it is limited to "small molecules" and peptides because they consistently provide high-quality diffraction with very few reflections. | 3 | Analytical Chemistry |
Veterinary virology is the study of viruses in non-human animals. It is an important branch of veterinary medicine. | 1 | Biochemistry |
Standard conditions for using NBS in allylic and/or benzylic bromination involves refluxing a solution of NBS in anhydrous CCl with a radical initiator—usually azobisisobutyronitrile (AIBN) or benzoyl peroxide, irradiation, or both to effect radical initiation. The allylic and benzylic radical intermediates formed during this reaction are more stable than other carbon radicals and the major products are allylic and benzylic bromides. This is also called the Wohl–Ziegler reaction.
The carbon tetrachloride must be maintained anhydrous throughout the reaction, as the presence of water may likely hydrolyze the desired product. Barium carbonate is often added to maintain anhydrous and acid-free conditions.
In the above reaction, while a mixture of isomeric allylic bromide products are possible, only one is created due to the greater stability of the 4-position radical over the methyl-centered radical. | 0 | Organic Chemistry |
Diebold has served in a number of editorial roles and on a number of advisory boards for scientific journals. These include:
* 2003–present Surface Science Reports advisory editorial board
* 2006 – 2007 Journal of Physics: Condensed Matter Surface, Interface and Atomic-Scale Science editorial board
* 2006 – 2007 Chemical Physics, guest editor of special issue "Doping and Functionalization of Photoactive Semiconducting Metal Oxides" with C. Di Valentin and A. Selloni
* 2007 – 2010 Open Journal of Physical Chemistry, advisory editorial board
* 2009 - 2009 Journal of Physics: Condensed Matter "guest editor of special issue on Non-thermal Processes on Surfaces, dedicated to the memory of Theodore E Madey and perspectives on surface science" with Thomas M. Orlando
* 2016–present npj Quantum Materials, advisory editorial board member
* 2017 – 2019 ACS Energy Letters, editorial advisory board
* 2019 – 2021 Physical Review Research, editorial board
* 2020 – 2021 Science, board of reviewing editors | 7 | Physical Chemistry |
Isla San José is the second largest island in the Pearl Islands, off the Pacific coast of Panama. The privately owned island has an area of . At the 2000 census, it had a population of only 10. Thousands of wild pigs and deer populate Isla San Jose, which has a rugged, rocky shoreline and over 50 beaches.
A unit of U.S. soldiers tested chemical arms from 1945 to 1947 on the then deserted island, leaving behind at least eight unexploded 500 and 1,000-pound bombs. A U.S. military text states that the larger bombs contained phosgene and cyanogen chloride, and smaller ones mustard gas. Other reports state that the soldiers also tested VX nerve gas and sarin. Claims of abandoned mine fields containing thousands of armed chemical mines have been made, but no evidence of this has been presented. An unknown but large amount of munitions was also dropped into the sea around the island. Earl Tupper, the inventor of Tupperware, was owner of the island.
The island is served by San José Airport. | 1 | Biochemistry |
RNA polymerase plays a very crucial role in all steps including post-transcriptional changes in RNA.
As shown in the image in the right it is evident that the CTD (C Terminal Domain) is a tail that changes its shape; this tail will be used as a carrier of splicing, capping and polyadenylation, as shown in the image on the left. | 1 | Biochemistry |
Thermogravimetric analysis is often combined with other processes or used in conjunction with other analytical methods.
For example, the TGA instrument continuously weighs a sample as it is heated to temperatures of up to 2000 °C for coupling with Fourier-transform infrared spectroscopy (FTIR) and mass spectrometry gas analysis. As the temperature increases, various components of the sample are decomposed and the weight percentage of each resulting mass change can be measured. | 7 | Physical Chemistry |
There was originally a simple and widely accepted argument that the genetic code should be universal: namely, that any variation in the genetic code would be lethal to the organism (although Crick had stated that viruses were an exception). This is known as the "frozen accident" argument for the universality of the genetic code. However, in his seminal paper on the origins of the genetic code in 1968, Francis Crick still stated that the universality of the genetic code in all organisms was an unproven assumption, and was probably not true in some instances. He predicted that "The code is universal (the same in all organisms) or nearly so". The first variation was discovered in 1979, by researchers studying human mitochondrial genes. Many slight variants were discovered thereafter, including various alternative mitochondrial codes. These minor variants for example involve translation of the codon UGA as tryptophan in Mycoplasma species, and translation of CUG as a serine rather than leucine in yeasts of the "CTG clade" (such as Candida albicans). Because viruses must use the same genetic code as their hosts, modifications to the standard genetic code could interfere with viral protein synthesis or functioning. However, viruses such as totiviruses have adapted to the host's genetic code modification. In bacteria and archaea, GUG and UUG are common start codons. In rare cases, certain proteins may use alternative start codons.
Surprisingly, variations in the interpretation of the genetic code exist also in human nuclear-encoded genes: In 2016, researchers studying the translation of malate dehydrogenase found that in about 4% of the mRNAs encoding this enzyme the stop codon is naturally used to encode the amino acids tryptophan and arginine. This type of recoding is induced by a high-readthrough stop codon context and it is referred to as functional translational readthrough.
Despite these differences, all known naturally occurring codes are very similar. The coding mechanism is the same for all organisms: three-base codons, tRNA, ribosomes, single direction reading and translating single codons into single amino acids. The most extreme variations occur in certain ciliates where the meaning of stop codons depends on their position within mRNA. When close to the 3 end they act as terminators while in internal positions they either code for amino acids as in Condylostoma magnum or trigger ribosomal frameshifting as in Euplotes'.
The origins and variation of the genetic code, including the mechanisms behind the evolvability of the genetic code, have been widely studied, and some studies have been done experimentally evolving the genetic code of some organisms. | 1 | Biochemistry |
This is a highly competitive area and a number of people claim patents in the field, most notably Alere (formerly Inverness Medical Innovations, now owned by Abbott) who own patents originally filed by Unipath. The US 6,485,982 patent, that has been litigated, expired in 2019. A number of other companies also hold patents in this arena. A group of competitors are challenging the validity of the patents. The original patent is apparently from 1988. | 1 | Biochemistry |
During the 1980s, a class of thermal spray processes called high velocity oxy-fuel spraying was developed. A mixture of gaseous or liquid fuel and oxygen is fed into a combustion chamber, where they are ignited and combusted continuously. The resultant hot gas at a pressure close to 1 MPa emanates through a converging–diverging nozzle and travels through a straight section. The fuels can be gases (hydrogen, methane, propane, propylene, acetylene, natural gas, etc.) or liquids (kerosene, etc.). The jet velocity at the exit of the barrel (>1000 m/s) exceeds the speed of sound. A powder feed stock is injected into the gas stream, which accelerates the powder up to 800 m/s. The stream of hot gas and powder is directed towards the surface to be coated. The powder partially melts in the stream, and deposits upon the substrate. The resulting coating has low porosity and high bond strength.
HVOF coatings may be as thick as 12 mm (1/2"). It is typically used to deposit wear and corrosion resistant coatings on materials, such as ceramic and metallic layers. Common powders include WC-Co, chromium carbide, MCrAlY, and alumina. The process has been most successful for depositing cermet materials (WC–Co, etc.) and other corrosion-resistant alloys (stainless steels, nickel-based alloys, aluminium, hydroxyapatite for medical implants, etc.). | 8 | Metallurgy |
For superalloys operating at high temperatures and exposed to corrosive environments, oxidation behavior is a concern. Oxidation involves chemical reactions of the alloying elements with oxygen to form new oxide phases, generally at the alloy surface. If unmitigated, oxidation can degrade the alloy over time in a variety of ways, including:
* sequential surface oxidation, cracking, and spalling, eroding the alloy over time
* surface embrittlement through the introduction of oxide phases, promoting crack formation and fatigue failure
* depletion of key alloying elements, affecting mechanical properties and possibly compromising performance
Selective oxidation is the primary strategy used to limit these deleterious processes. The ratio of alloying elements promotes formation of a specific oxide phase that then acts as a barrier to further oxidation. Most commonly, aluminum and chromium are used in this role, because they form relatively thin and continuous oxide layers of alumina (AlO) and chromia (CrO), respectively. They offer low oxygen diffusivities, effectively halting further oxidation beneath this layer. In the ideal case, oxidation proceeds through two stages. First, transient oxidation involves the conversion of various elements, especially the majority elements (e.g. nickel or cobalt). Transient oxidation proceeds until the selective oxidation of the sacrificial element forms a complete barrier layer.
The protective effect of selective oxidation can be undermined. The continuity of the oxide layer can be compromised by mechanical disruption due to stress or may be disrupted as a result of oxidation kinetics (e.g. if oxygen diffuses too quickly). If the layer is not continuous, its effectiveness as a diffusion barrier to oxygen is compromised. The stability of the oxide layer is strongly influenced by the presence of other minority elements. For example, the addition of boron, silicon, and yttrium to superalloys promotes oxide layer adhesion, reducing spalling and maintaining continuity.
Oxidation is the most basic form of chemical degradation superalloys may experience. More complex corrosion processes are common when operating environments include salts and sulfur compounds, or under chemical conditions that change dramatically over time. These issues are also often addressed through comparable coatings. | 8 | Metallurgy |
Different annotations capture diverse aspects of variant function. Simultaneous use of multiple, varied functional annotations could improve rare variants association analysis power of whole exome and whole genome sequencing studies. Some tools have been developed to enable functionally-informed phenotype-genotype association analysis for common and rare variants by incorporating functional annotations in biobank-scale cohorts. | 1 | Biochemistry |
A YAC is built using an initial circular DNA plasmid, which is typically cut into a linear DNA molecule using restriction enzymes; DNA ligase is then used to ligate a DNA sequence or gene of interest into the linearized DNA, forming a single large, circular piece of DNA. [https://doi.org/10.1073/pnas.87.11.4256] The basic generation of linear yeast artificial chromosomes can be broken down into 6 main steps: | 1 | Biochemistry |
There has been a significant amount of work experimentally to observe both the structure and measure the properties of grain boundaries but the five dimensional degrees of freedom of grain boundaries within complex polycrystalline networks has not yet been fully understood and thus there is currently no method to control the structure and properties of most metals and alloys with atomic precision. Part of the problem is related to the fact that much of the theoretical work to understand grain boundaries is based upon construction of bicrystal (two) grains which do not represent the network of grains typically found in a real system and the use of classical force fields such as the embedded atom method often do not describe the physics near the grains correctly and density functional theory could be required to give realistic insights. Accurate modelling of grain boundaries both in terms of structure and atomic interactions could have the effect of improving engineering which could reduce waste and increase efficiency in terms of material usage and performance. From a computational point of view much of the research on grain boundaries has focused on bi-crystal systems, these are systems which only consider two grain boundaries. There has been recent work which has made use of novel grain evolution models which show that there are substantial differences in the material properties associated with whether curved or planar grains are present. | 8 | Metallurgy |
It is common in electrochemistry and solid-state physics to discuss both the chemical potential and the electrochemical potential of the electrons. However, in the two fields, the definitions of these two terms are sometimes swapped. In electrochemistry, the electrochemical potential of electrons (or any other species) is the total potential, including both the (internal, nonelectrical) chemical potential and the electric potential, and is by definition constant across a device in equilibrium, whereas the chemical potential of electrons is equal to the electrochemical potential minus the local electric potential energy per electron. In solid-state physics, the definitions are normally compatible with this, but occasionally the definitions are swapped.
This article uses the electrochemistry definitions. | 7 | Physical Chemistry |
The earliest record of trichloroethylene synthesis dates back to 1836. It was obtained from the action of potassium hydroxide on 1,1,2,2-tetrachloroethane and 1,1,1,2-tetrachloroethane by Auguste Laurent and notated as (then the atomic weight of carbon was thought to be the half of it really was). Laurent did not investigate the compound further.
Trichloroethylene's discovery is widely attributed to E. Fischer who made it in 1864 via the reduction of hexachloroethane with hydrogen. Fischer investigated TCE and noted its boiling point as between 87 and 90 degrees Celsius. Commercial production began in Germany, in 1920 and in the US in 1925.
Pioneered by Imperial Chemical Industries in Britain, under the trade name "Trilene" (from trichloroethylene) , its development was hailed as an anesthetic revolution. It was mostly known as "Trimar" in the United States. The –mar suffix indicates study and development at the University of Maryland, e.g., "Fluoromar" for fluroxene and "Vinamar" for ethyl vinyl ether".
Originally thought to possess less hepatotoxicity than chloroform, and without the unpleasant pungency and flammability of ether, TCE use was nonetheless soon found to have several pitfalls. These included promotion of cardiac arrhythmias, low volatility and high solubility preventing quick anesthetic induction, reactions with soda lime used in carbon dioxide absorbing systems, prolonged neurologic dysfunction when used with soda lime, and evidence of hepatotoxicity as had been found with chloroform.
The introduction of halothane in 1956 greatly diminished the use of TCE as a general anesthetic. TCE was still used as an inhalation analgesic in childbirth given by self-administration. Fetal toxicity and concerns about the carcinogenic potential of TCE led to its abandonment in developed countries by the 1980s.
The use of trichloroethylene in the food and pharmaceutical industries has been banned in much of the world since the 1970s due to concerns about its toxicity. Legislation has forced the replacement of trichloroethylene in many processes in Europe as the chemical was classified as a carcinogen carrying an R45 risk phrase, May cause cancer. Many degreasing chemical alternatives are being promoted such as Ensolv and Leksol; however, each of these is based on n-propyl bromide which carries an R60 risk phrase of May impair fertility, and would not be a legally acceptable substitute. | 2 | Environmental Chemistry |
Charles' law, or the law of volumes, was founded in 1787 by Jacques Charles. It states that, for a given mass of an ideal gas at constant pressure, the volume is directly proportional to its absolute temperature, assuming in a closed system.
The statement of Charles' law is as follows:
the volume (V) of a given mass of a gas, at constant pressure (P), is directly proportional to its temperature (T). | 7 | Physical Chemistry |
Some phenolic compounds produced from previous reactions worked as bactericides and the actinomycetales order of bacteria also produced antibiotic compounds (e.g., streptomycin). Thus the action of anaerobic bacteria ceased at about 10 m below the water or sediment. The mixture at this depth contained fulvic acids, unreacted and partially reacted fats and waxes, slightly modified lignin, resins and other hydrocarbons. As more layers of organic matter settled into the sea or lake bed, intense heat and pressure built up in the lower regions. As a consequence, compounds of this mixture began to combine in poorly understood ways to kerogen. Combination happened in a similar fashion as phenol and formaldehyde molecules react to urea-formaldehyde resins, but kerogen formation occurred in a more complex manner due to a bigger variety of reactants. The total process of kerogen formation from the beginning of anaerobic decay is called diagenesis, a word that means a transformation of materials by dissolution and recombination of their constituents. | 7 | Physical Chemistry |
Around 1750, colonial raw materials poured into the British Isles, and factories began to appear. The earlier hardware with its chiseled and filed details fast gave way to less expensive, but equally functional hardware of similar but unadorned design. H and HL hinges are a good example of this transition.
After the American Revolution machines were invented to make screws and to produce rolled iron in thin sheets. By about 1800 cheap screws were readily available. Cast iron technology had long been available – now machine-made screws allowed such hardware to be economically mounted. Butt type hinges can be seen during this "Federal" Period (1800–1830) – but they quickly fell from favor, probably because they were subject to breakage.
A more obvious change in the shutter hardware was noted in shutter bolts. The common slide plate and keeper style of bolt started to appear. It was simpler to fabricate and operate than the earlier "strap style lock". This bolt relied on both the new cheap fasteners and the readily available plate iron. This bolt also relied on machines and "dies." This form of shutter bolt has been made continually ever since.
Strap hinges continued to dominate in the marketplace for hanging shutters. Drive pintles started to be replaced by similar pintles cut off and mounted on a piece of thin plate material and again fastened with the new screws. This is the precursor of the "plate pintle".
Changes in construction have been noted in the same period. Structures were built with openings into which pre-fabricated windows were installed. The earliest examples date from around 1810 and used a variation on the strap hinge. Instead of mounting the pintle to the surface of the structure, a new form was designed. This pintle was a flat plate of about two inches high and notched to one half of its height and formed to a female barrel. Holes were punched in the side of the pintle, and it was screwed directly to the side of the window before the window was installed on the structure. The strap hinges were modified to match the new pintles and the hinge was of the same width as the pintle and notched to one half of its height. A pin to mate with the female pintle was welded in the hinge. Examples of this type proved to be very durable and were in regular and widespread use through the 1870s.
Often when the shutters were removed – usually in the 20th century – cast type pintles were hit with a hammer and broken off flush with the edge of the window. The shutters often found their way into the basements of the home to provide coal bins for newly installed central heat or were nailed up in the barn to partition off pig sties or calf pens.
Cast iron tie-backs became much more popular during the Federal period – usually mounted on arms extending from the window sills. The "Federal Shell" was the dominant pattern in this period. | 8 | Metallurgy |
For an enzyme immobilised on an electrode, the value of the current at a certain potential equates , where is the number of electrons exchanged in the catalytic reaction, is the electrode surface, is the electroactive coverage, and TOF is the turnover frequency (or "turnover number"), that is, the number of substrate molecules transformed per second and per molecule of adsorbed enzyme).The latter can be deduced from the absolute value of the current only on condition that is known, which is rarely the case. However, information is obtained by analysing the relative change in current that results from changing the experimental conditions.
The factors that may influence the TOF are (i) the mass transport of substrate towards the electrode where the enzyme is immobilised (diffusion and convection), (ii) the rate of electron transfer between the electrode and the enzyme (interfacial electron transfer), and (iii) the "intrinsic" activity of the enzyme, all of which may depend on electrode potential.
The enzyme is often immobilized on a rotating disk working electrode (RDE) that is spun quickly to prevent the depletion of the substrate near the electrode. In that case, mass transport of substrate towards the electrode where the enzyme is adsorbed may not be influential. | 7 | Physical Chemistry |
In land plants, chloroplasts are generally lens-shaped, 3–10 μm in diameter and 1–3 μm thick. Corn seedling chloroplasts are ≈20 µm in volume. Greater diversity in chloroplast shapes exists among the algae, which often contain a single chloroplast that can be shaped like a net (e.g., Oedogonium), a cup (e.g., Chlamydomonas), a ribbon-like spiral around the edges of the cell (e.g., Spirogyra), or slightly twisted bands at the cell edges (e.g., Sirogonium). Some algae have two chloroplasts in each cell; they are star-shaped in Zygnema, or may follow the shape of half the cell in order Desmidiales. In some algae, the chloroplast takes up most of the cell, with pockets for the nucleus and other organelles, for example, some species of Chlorella have a cup-shaped chloroplast that occupies much of the cell.
All chloroplasts have at least three membrane systems—the outer chloroplast membrane, the inner chloroplast membrane, and the thylakoid system. Chloroplasts that are the product of secondary endosymbiosis may have additional membranes surrounding these three. Inside the outer and inner chloroplast membranes is the chloroplast stroma, a semi-gel-like fluid that makes up much of a chloroplast's volume, and in which the thylakoid system floats.
There are some common misconceptions about the outer and inner chloroplast membranes. The fact that chloroplasts are surrounded by a double membrane is often cited as evidence that they are the descendants of endosymbiotic cyanobacteria. This is often interpreted as meaning the outer chloroplast membrane is the product of the hosts cell membrane infolding to form a vesicle to surround the ancestral cyanobacterium—which is not true—both chloroplast membranes are homologous to the cyanobacteriums original double membranes.
The chloroplast double membrane is also often compared to the mitochondrial double membrane. This is not a valid comparison—the inner mitochondria membrane is used to run proton pumps and carry out oxidative phosphorylation across to generate ATP energy. The only chloroplast structure that can considered analogous to it is the internal thylakoid system. Even so, in terms of "in-out", the direction of chloroplast H ion flow is in the opposite direction compared to oxidative phosphorylation in mitochondria. In addition, in terms of function, the inner chloroplast membrane, which regulates metabolite passage and synthesizes some materials, has no counterpart in the mitochondrion. | 5 | Photochemistry |
Bharat is the author or co-author of over 46 scientific publications. These include:
* Jan Böhning, Mnar Ghrayeb, Conrado Pedebos, Daniel K. Abbas, Syma Khalid, Liraz Chai & Tanmay A. M. Bharat (2022) [https://www.nature.com/articles/s41467-022-34700-z Donor-strand exchange drives assembly of the TasA scaffold in Bacillus subtilis biofilms.] Nature Communications volume 13, article number 7082.
* Tanmay A.M. Bharat, Andriko von Kügelgen & Vikram Alva (2021) [https://pubmed.ncbi.nlm.nih.gov/33121898/ Molecular Logic of Prokaryotic Surface Layer Structures.] Trends in Microbiology May;29(5):405-415.
* Charlotte Melia, Jani Bolla, Stefan Lanwermeyer, Daniel Mihaylov, Patrick Hoffmann, Jiandong Huo, Michael Wozny, Louis Elfari, Jan Böhning, Ray Owens, Carol Robinson, George O’Toole & Tanmay A.M. Bharat (2021) [https://www.biorxiv.org/content/10.1101/2021.02.08.430230v1 Architecture of cell-cell junctions in situ reveals a mechanism for bacterial biofilm inhibition.] Proceedings of the National Academy of Sciences of the United States of America 118(31):
* Andriko von Kügelgen, Vikram Alva and Tanmay A.M. Bharat (2021) [https://www.cell.com/cell-reports/fulltext/S2211-1247(21)01538-2 Complete atomic structure of a native archaeal cell surface.] Cell Reports volume 37, issue 8, 110052.
* Abul K. Tarafder, Andriko von Kügelgen, Adam J. Mellul & Tanmay A. M. Bharat (2020) [https://www.pnas.org/doi/full/10.1073/pnas.1917726117 Phage liquid crystalline droplets form occlusive sheaths that encapsulate and protect infectious rod-shaped bacteria.] Proceedings of the National Academy of Sciences of the United States of America volume 117, issue 9, pages 4724-4731.
* Andriko von Kügelgen, Haiping Tang., Gail Hardy, Danguole Kureisaite-Ciziene, Yves Brun, Phillip Stansfeld, Carol Robinson, & Tanmay A.M. Bharat (2020) [https://pubmed.ncbi.nlm.nih.gov/31883796/ In Situ Structure of an Intact Lipopolysaccharide-Bound Bacterial Surface Layer.] Cell 180(2): 348-358
* Tanmay A.M. Bharat, Christopher J. Russo, Jan Löwe, Lori A. Passmore & Sjors H.W. Scheres (2015) [https://www.cell.com/structure/fulltext/S0969-2126(15)00279-8 Advances in Single-Particle Electron Cryomicroscopy Structure Determination applied to Sub-tomogram Averaging] Structure volume 23, issue 9, pages 1743-1753.
* Tanmay A. M. Bharat, James D. Riches, Larissa Kolesnikova, Sonja Welsch, Verena Krähling, Norman Davey, Marie-Laure Parsy, Stephan Becker & John A. G. Briggs (2011) [https://doi.org/10.1371/journal.pbio.1001196 Cryo-Electron Tomography of Marburg Virus Particles and Their Morphogenesis within Infected Cells.] PLOS Biology | 1 | Biochemistry |
According to IUPAC convention, by precedence (stylized electronegativity), hydrogen falls between group 15 and group 16 elements. Therefore, we have NH, "nitrogen hydride" (ammonia), versus HO, "hydrogen oxide" (water). This convention is sometimes broken for polonium, which on the grounds of polonium's metallicity is often referred to as "polonium hydride" instead of the expected "hydrogen polonide". | 0 | Organic Chemistry |
The SQT approach has been praised for a variety of reasons as a technique for characterizing sediment conditions. Relative to the depth of information it provides, and the inclusive nature, it is very cost effective. It can be applied to all sediment classifications, and even adapted to soil and water column assessments (Chapman and McDonald 2005). A decision matrix can be employed such that all three measures be analyzed simultaneously, and a deduction of possible ecological impacts be made (USEPA 1994)
Other advantages of the SQT include information on the potential bioaccumulation and biomagnifcation effects of contaminants, and its flexibility in application, resulting from its design as a framework rather than a formula or standard method. By using multiple lines of evidence, there are a host of ways to manipulate and interpret SQT data (Bay and Weisberg 2012). It has been accepted on an international scale as the most comprehensive approach to assessing sediment (Chapman and McDonald 2005). The SQT approach to sediment testing has been used in North America, Europe, Australia, South America, and the Antarctic. | 2 | Environmental Chemistry |
The scintillation process in inorganic materials is due to the electronic band structure found in crystals and is not molecular in nature as is the case with organic scintillators. An incoming particle can excite an electron from the valence band to either the conduction band or the exciton band (located just below the conduction band and separated from the valence band by an energy gap; see [http://upload.wikimedia.org/wikipedia/commons/4/46/Bandgap_in_semiconductor.svg picture]). This leaves an associated hole behind, in the valence band. Impurities create electronic levels in the forbidden gap. The excitons are loosely bound electron-hole pairs which wander through the crystal lattice until they are captured as a whole by impurity centers. The latter then rapidly de-excite by emitting scintillation light (fast component). The activator impurities are typically chosen so that the emitted light is in the visible range or near-UV where photomultipliers are effective. The holes associated with electrons in the conduction band are independent from the latter. Those holes and electrons are captured successively by impurity centers exciting certain metastable states not accessible to the excitons. The delayed de-excitation of those metastable impurity states again results in scintillation light (slow component).
BGO (bismuth germanium oxide) is a pure inorganic scintillator without any activator impurity. There, the scintillation process is due to an optical transition of the bismuth| ion, a major constituent of the crystal. In tungstate scintillators calcium tungstate| and cadmium tungstate| the emission is due to radiative decay of self-trapped excitons.
The scintillation process in GaAs doped with silicon and boron impurities is different from conventional scintillators in that the silicon n-type doping provides a built-in population of delocalized electrons at the bottom of the conduction band. Some of the boron impurity atoms reside on arsenic sites and serve as acceptors. A scintillation photon is produced whenever an acceptor atom such as boron captures an ionization hole from the valence band and that hole recombines radiatively with one of the delocalized electrons. Unlike many other semiconductors, the delocalized electrons provided by the silicon are not “frozen out” at cryogenic temperatures. Above the Mott transition concentration of free carriers per cm, the “metallic” state is maintained at cryogenic temperatures because mutual repulsion drives any additional electrons into the next higher available energy level, which is in the conduction band. The spectrum of photons from this process is centered at 930 nm (1.33 eV) and there are three other emission bands centered at 860, 1070, and 1335 nm from other minor processes. Each of these emission bands has a different luminosity and decay time. The high scintillation luminosity is surprising because (1) with a refractive index of about 3.5, escape is inhibited by total internal reflection and (2) experiments at 90K report narrow-beam infrared absorption coefficients of several per cm. Recent Monte Carlo and Feynman path integral calculations have shown that the high luminosity could be explained if most of the narrow beam absorption is actually a novel optical scattering from the conduction electrons with a cross section of about 5 x 10 cm that allows scintillation photons to escape total internal reflection. This cross section is about 10 times larger than Thomson scattering but comparable to the optical cross section of the conduction electrons in a metal mirror. | 5 | Photochemistry |
The Akula is a Dunkleosteus like creature. They have 3 sets of jaws and is the apex predator of the Pandoran ocean. They are introduced in Avatar: The Way of Water, where Jakes son Loak fights of one after he is stranded in the ocean, before being saved by Payakan. | 1 | Biochemistry |
The Mixtec civilization have long been thought to be the dominant goldsmiths of post-classic Mesoamerica. A large number of gold artifacts found in central and southern Mexico have been attributed to the Mixtec. | 8 | Metallurgy |
RopB transcriptional regulator, also known as RopB/Rgg transcriptional regulator is a transcriptional regulator protein that regulates expression of the extracellularly secreted cysteine protease streptococcal pyrogenic exotoxin B (speB) [See Also: erythrogenic toxins] which is an important virulence factor of Streptococcus pyogenes and is responsible for the dissemination of a host of infectious diseases including strep throat, impetigo, streptococcal toxic shock syndrome, necrotizing fasciitis, and scarlet fever. Functional studies suggest that the ropB multigene regulon is responsible for not only global regulation of virulence but also a wide range of functions from stress response, metabolic function, and two-component signaling. Structural studies implicate ropB's regulatory action being reliant on a complex interaction involving quorum sensing with the leaderless peptide signal speB-inducing peptide (SIP) acting in conjunction with a pH sensitive histidine switch.
See Photo: | 1 | Biochemistry |
Crystallite size in monodisperse microstructures is usually approximated from X-ray diffraction patterns and grain size by other experimental techniques like transmission electron microscopy. Solid objects large enough to see and handle are rarely composed of a single crystal, except for a few cases (gems, silicon single crystals for the electronics industry, certain types of fiber, single crystals of a nickel-based superalloy for turbojet engines, and some ice crystals which can exceed 0.5 meters in diameter). The crystallite size can vary from a few nanometers to several millimeters. | 8 | Metallurgy |
Lead ore (galena) in relatively pure form is present geologically in a number of places in North America. Some native populations mined and used the lead. | 8 | Metallurgy |
The classes of enzymes that have manganese cofactors include oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases. Other enzymes containing manganese are arginase and Mn-containing superoxide dismutase (Mn-SOD). Also the enzyme class of reverse transcriptases of many retroviruses (though not lentiviruses such as HIV) contains manganese. Manganese-containing polypeptides are the diphtheria toxin, lectins and integrins. | 1 | Biochemistry |
Different influences at the interface may cause changes in the composition of the near-surface layer. Substances may either accumulate near the surface or, conversely, move into the bulk. The movement of the molecules characterizes the phenomena of adsorption. Adsorption influences changes in surface tension and colloid stability. Adsorption layers at the surface of a liquid dispersion medium may affect the interactions of the dispersed particles in the media and consequently these layers may play crucial role in colloid stability The adsorption of molecules of liquid phase at an interface occurs when this liquid phase is in contact with other immiscible phases that may be gas, liquid, or solid | 7 | Physical Chemistry |
The HPCE-based viral titer assay uses a proprietary, high-performance capillary electrophoresis system to determine baculovirus titer.
The Trofile assay is used to determine HIV tropism.
The viral plaque assay is to calculate the number of viruses present in a sample. In this technique the number of viral plaques formed by a viral inoculum is counted, from which the actual virus concentration can be determined. | 1 | Biochemistry |
Calcination is thermal decomposition of a material. Examples include decomposition of hydrates such as ferric hydroxide to ferric oxide and water vapor, the decomposition of calcium carbonate to calcium oxide and carbon dioxide as well as iron carbonate to iron oxide:
:CaCO → CaO + CO
Calcination processes are carried out in a variety of furnaces, including shaft furnaces, rotary kilns, and fluidized bed reactors. | 8 | Metallurgy |
Ethyl chloroformate is an organic compound with the chemical formula . It is the ethyl ester of chloroformic acid. It is a colorless, corrosive and highly toxic liquid. It is a reagent used in organic synthesis for the introduction of the ethyl carbamate protecting group and for the formation of carboxylic anhydrides. | 0 | Organic Chemistry |
The CompTox Chemicals Dashboard database contains high quality chemical structures and information that have been extensively curated and quality checked, which can be used as a resource for analytical scientists involved in structure identification.
Chemical hazard data in the dashboard comes from both traditional laboratory animal studies and high-throughput screening. Biological data from high-throughput screening is generated by EPA's ToxCast program, the ToxCast data in the database provides information about the assays used and their response potency and efficacy. These data can be found in the bioactivity tab.
The Chemicals Dashboard can be accessed via a web interface or sets of data within it can be downloaded for use offline. The Lists tab can be used to browse and download groups of related chemicals based on their relevance to a specific research topic (such as [https://comptox.epa.gov/dashboard/chemical_lists/CIGARETTES additives in cigarettes] or [https://comptox.epa.gov/dashboard/chemical_lists/DNTEFFECTS chemicals demonstrating effects on neurodevelopmental effects]) or the specific assay endpoints they are covered by.
Within the online dashboard searches can be performed by product/use categories, assay/gene, systematic name, synonym, CAS number, DSSTox Substance ID or InChiKey. Under the Advanced Search tab chemicals can be searched based on their mass or molecular formula. Searches can also be performed for groups of chemicals based on Chemical Name CASRN, InChIKey, DSSTox Substance ID, DSSTox Compound ID, InChIKey Skeleton, MS-Ready Formula, Exact Formula, or Monoisotopic Mass using the batch search function. | 2 | Environmental Chemistry |
Demethylation of 5-methylcytosine to generate 5-hydroxymethylcytosine (5hmC) very often initially involves oxidation of 5mC (see Figure in this section) by ten-eleven translocation methylcytosine dioxygenases (TET enzymes). The molecular steps of this initial demethylation are shown in detail in TET enzymes. In successive steps (see Figure) TET enzymes further hydroxylate 5hmC to generate 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC). Thymine-DNA glycosylase (TDG) recognizes the intermediate bases 5fC and 5caC and excises the glycosidic bond resulting in an apyrimidinic site (AP site). This is followed by base excision repair (stage 3). In an alternative oxidative deamination pathway, 5hmC can be oxidatively deaminated by APOBEC (AID/APOBEC) deaminases to form 5-hydroxymethyluracil (5hmU). Also, 5mC can be converted to thymine (Thy). 5hmU can be cleaved by TDG, MBD4, NEIL1 or SMUG1. AP sites and T:G mismatches are then repaired by base excision repair (BER) enzymes to yield cytosine (Cyt). The TET family of dioxygenases are employed in the most frequent type of demethylation reactions. | 1 | Biochemistry |
The extent to which a solid is crystalline (crystallinity) has important effects on its physical properties. Sulfur, while usually polycrystalline, may also occur in other allotropic forms with completely different properties. Although crystallites are referred to as grains, powder grains are different, as they can be composed of smaller polycrystalline grains themselves. Generally, polycrystals cannot be superheated; they will melt promptly once they are brought to a high enough temperature. This is because grain boundaries are amorphous, and serve as nucleation points for the liquid phase. By contrast, if no solid nucleus is present as a liquid cools, it tends to become supercooled. Since this is undesirable for mechanical materials, alloy designers often take steps against it (by grain refinement).
Material fractures can be either intergranular or a transgranular fracture. There is an ambiguity with powder grains: a powder grain can be made of several crystallites. Thus, the (powder) "grain size" found by laser granulometry can be different from the "grain size" (rather, crystallite size) found by X-ray diffraction (e.g. Scherrer method), by optical microscopy under polarised light, or by scanning electron microscopy (backscattered electrons).
If the individual crystallites are oriented completely at random, a large enough volume of polycrystalline material will be approximately isotropic. This property helps the simplifying assumptions of continuum mechanics to apply to real-world solids. However, most manufactured materials have some alignment to their crystallites, resulting in texture that must be taken into account for accurate predictions of their behavior and characteristics. When the crystallites are mostly ordered with a random spread of orientations, one has a mosaic crystal. Abnormal grain growth, where a small number of crystallites are significantly larger than the mean crystallite size, is commonly observed in diverse polycrystalline materials, and results in mechanical and optical properties that diverge from similar materials having a monodisperse crystallite size distribution with a similar mean crystallite size.
Coarse grained rocks are formed very slowly, while fine grained rocks are formed quickly, on geological time scales. If a rock forms very quickly, such as from the solidification of lava ejected from a volcano, there may be no crystals at all. This is how obsidian forms. | 8 | Metallurgy |
An ionotropic effect is the effect of a transmitter substance or hormone that activates or deactivates ionotropic receptors (ligand-gated ion channels). The effect can be either positive or negative, specifically a depolarization or a hyperpolarization respectively. This term is commonly confused with an inotropic effect, which refers to a change in the force of contraction (e.g. in heart muscle) produced by transmitter substances or hormones. | 1 | Biochemistry |
Land animals, including livestock and pets have been affected. Dogs have died from the toxins after swimming in algal blooms. Warnings have come from government agencies in the state of Ohio, which noted that many dogs and livestock deaths resulted from HAB exposure in the U.S. and other countries. They also noted in a 2003 report that during the previous 30 years, they have seen more frequent and longer-lasting harmful algal blooms." In 50 countries and 27 states that year there were reports of human and animal illnesses linked to algal toxins. In Australia, the department of agriculture warned farmers that the toxins from a HAB had the "potential to kill large numbers of livestock very quickly."
Marine mammals have also been seriously harmed, as over 50 percent of unusual marine mammal deaths are caused by harmful algal blooms. In 1999, over 65 bottlenose dolphins died during a coastal HAB in Florida. In 2013 a HAB in southwest Florida killed a record number of Manatee. Whales have also died in large numbers. During the period from 2005 to 2014, Argentina reported an average 65 baby whales dying which experts have linked to algal blooms. A whale expert there expects the whale population to be reduced significantly. In 2003 off Cape Cod in the North Atlantic, at least 12 humpback whales died from toxic algae from a HAB. In 2015 Alaska and British Columbia reported many humpback whales had likely died from HAB toxins, with 30 having washed ashore in Alaska. "Our leading theory at this point is that the harmful algal bloom has contributed to the deaths," said a NOAA spokesperson.
Birds have died after eating dead fish contaminated with toxic algae. Rotting and decaying fish are eaten by birds such as pelicans, seagulls, cormorants, and possibly marine or land mammals, which then become poisoned. The nervous systems of dead birds were examined and had failed from the toxin's effect. On the Oregon and Washington coast, a thousand scoters, or sea ducks, were also killed in 2009. "This is huge," said a university professor. As dying or dead birds washed up on the shore, wildlife agencies went into "an emergency crisis mode."
It has even been suggested that harmful algal blooms are responsible for the deaths of animals found in fossil troves, such as the dozens of cetacean skeletons found at Cerro Ballena. | 3 | Analytical Chemistry |
Fig. 5 shows a so-called DC SQUID. It consists of two superconductors connected by two weak links. The fluxoid quantization of a loop through the two bulk superconductors and the two weak links demands
If the self-inductance of the loop can be neglected the magnetic flux in the loop Φ is equal to the applied flux
with B the magnetic field, applied perpendicular to the surface, and A the surface area of the loop. The total supercurrent is given by
Substitution of Eq() in () gives
Using a well known geometrical formula we get
Since the sin-function can vary only between −1 and +1 a steady solution is only possible if the applied current is below a critical current given by
Note that the critical current is periodic in the applied flux with period . The dependence of the critical current on the applied flux is depicted in Fig. 6. It has a strong resemblance with the interference pattern generated by a laser beam behind a double slit. In practice the critical current is not zero at half integer values of the flux quantum of the applied flux. This is due to the fact that the self-inductance of the loop cannot be neglected. | 7 | Physical Chemistry |
Nidogens, formerly known as entactins, are a family of sulfated monomeric glycoproteins located in the basal lamina of parahoxozoans. Two nidogens have been identified in humans: nidogen-1 (NID1) and nidogen-2 (NID2). Remarkably, vertebrates are still capable of stabilizing basement membrane in the absence of either identified nidogen. In contrast, those lacking both nidogen-1 and nidogen-2 typically die prematurely during embryonic development as a result of defects existing in the heart and lungs. Nidogen have been shown to play a crucial role during organogenesis in late embryonic development, particularly in cardiac and lung development. From an evolutionary perspective, nidogens are highly conserved across vertebrates and invertebrates, retaining their ability to bind laminin.
In nematodes, nidogen-1 is necessary for axon guidance, but not for basement membrane assembly. | 1 | Biochemistry |
Poly(3,4-ethylenedioxythiophene) (PEDOT) is another conducting polymer that is being investigated for coating an electrode surface. Some benefits of PEDOT over PPy is that it is more stable to oxidation and more conductive; however PPy is much cheaper. As with PPy, PEDOT has been shown to decrease the electrical impedance. In one article, a PEDOT coating was electrochemically deposited on to gold recording electrodes. The results showed that impedance of the electrode decreased significantly when the PEDOT coating was added. The unmodified gold electrodes had an impedance of 500–1000 kΩ, while the modified gold electrode with the PEDOT coating had an impedance of 3–6 kΩ. The paper also showed that the interaction between the polymer and neurons improved the stability and durability of the electrode. The study concluded that by adding a conductive polymer the impedance of the electrode system decreased, which increased the charge transfer making a more effective electrode. The ease and control of electrochemically depositing conducting coatings onto electrode surfaces makes it a very attractive surface modification for neural electrodes. | 7 | Physical Chemistry |
C/N ratios in the range 4-10:1 are usually from marine sources, whereas higher ratios are likely to come from a terrestrial source. Vascular plants from terrestrial sources tend to have C/N ratios greater than 20. The lack of cellulose, which has a chemical formula of (CHO), and greater amount of proteins in algae versus vascular plants causes this significant difference in the C/N ratio. | 9 | Geochemistry |
Imaging biomarkers allow earlier detection of disease compared to molecular biomarkers, and streamline translational research in the drug discovery marketplace. For example, one could determine the percent of receptors a drug targets, shortening the time and money of research during the new drug development stage. Imaging biomarkers also are non-invasive, which is a clinical advantage over molecular biomarkers. Some of the image-based biomarkers are X-Ray, Computed Tomography (CT), Positron Emission Tomography (PET), Single Photo Emission Computed Tomography (SPECT) and Magnetic Resonance Imaging (MRI).
Many new biomarkers are being developed that involve imaging technology. Imaging biomarkers have many advantages. They are usually noninvasive, and they produce intuitive, multidimensional results. Yielding both qualitative and quantitative data, they are usually relatively comfortable for patients. When combined with other sources of information, they can be very useful to clinicians seeking to make a diagnosis.
Cardiac imaging is an active area of biomarker research. Coronary angiography, an invasive procedure requiring catheterization, has long been the gold standard for diagnosing arterial stenosis, but scientists and doctors hope to develop noninvasive techniques. Many believe that cardiac computed tomography (CT) has great potential in this area, but researchers are still attempting to overcome problems related to "calcium blooming," a phenomenon in which calcium deposits interfere with image resolution. Other intravascular imaging techniques involving magnetic resonance imaging (MRI), optical coherence tomography (OCT), and near infrared spectroscopy are also being investigated.
Another new imaging biomarker involves radiolabeled fludeoxyglucose. Positron emission tomography (PET) can be used to measure where in the body cells take up glucose. By tracking glucose, doctors can find sites of inflammation because macrophages there take up glucose at high levels. Tumors also take up a lot of glucose, so the imaging strategy can be used to monitor them as well. Tracking radiolabeled glucose is a promising technique because it directly measures a step known to be crucial to inflammation and tumor growth. | 1 | Biochemistry |
The stoichiometric structure and mass-conservation properties of biochemical pathways gives rise to a series of theorems or relationships between the control coefficients and the control coefficients and elasticities. There are a large number of such relationships depending on the pathway configuration (e.g. linear, branched or cyclic) which have been documented and discovered by various authors. The term theorem has been used to describe these relationships because they can be proved in terms of more elementary concepts. The operational proofs in particular are of this nature.
The most well known of these theorems are the summation theorems for the control coefficients and the connectivity theorems which relate control coefficients to the elasticities. The focus of this page are the connectivity theorems.
When deriving the summation theorems, a thought experiment was conducted that involved manipulating enzyme activities such that concentrations were unaffected but fluxes changed. The connectivity theorems use the opposite thought experiment, that is enzyme activities are changed such that concentrations change but fluxes are unchanged. This is an important observation that highlights the orthogonal nature of these two sets of theorem.
As with the summation theorems, the connectivity theorems can also be proved using more rigorous mathematical approaches involving calculus and linear algebra. Here the more intuitive and operational proofs will be used to prove the connectivity theorems. | 1 | Biochemistry |
Horizontal gene transfer (HGT) from host to virus allows for AMGs to be acquired. Gene transfer from host eukaryotes to viruses occur about twice as frequently as virus to host gene transfers due to a higher number viral recipients than donors. The vast majority of gene transfer occurs in double-stranded DNA viruses since they have large and flexible genomes, co-evolution with eukaryotes, and wide host breadth. Additionally, unicellular hosts more commonly transfer genes. | 1 | Biochemistry |
Glycoconjugate is the covalently bonded product of oligosaccharides to the biomolecules such as proteins and lipids. They play indispensable role in the biological activities of mammalian cells from energy generation to cell signalling. These glycoconjugates with short oligosaccharide structures are important for the characterization and purification in the course glycoconjucate vaccine developements. Therefore, research in the engineering of the glycosyl precursors that create oligosaccharides with controlled size is important in carbohydrate synthesis. | 0 | Organic Chemistry |
One of the most developed areas of phosphaalkyne chemistry is that of cycloadditions. Like other multiply bonded molecular fragments, phosphaalkynes undergo myriad reactions such as [1+2] cycloadditions, [3+2] cycloadditions, and [4+2] cycloadditions. This reactivity is summarized in graphical format below, which includes some examples of 1,2-addition reactivity (which is not a form of cycloaddition). | 0 | Organic Chemistry |
Nitrates do not affect infants and pregnant women. Blue baby syndrome is caused by a number of other factors such as gastric upset, such as diarrheal infection, protein intolerance, heavy metal toxicity etc., with nitrates playing a minor role. | 0 | Organic Chemistry |
The formula of monomeric oxyanions, , is dictated by the oxidation state of the element A and its position in the periodic table. Elements of the first row are limited to a maximum coordination number of 4. However, none of the first row elements has a monomeric oxyanion with that coordination number. Instead, carbonate () and nitrate () have a trigonal planar structure with π bonding between the central atom and the oxygen atoms. This π bonding is favoured by the similarity in size of the central atom and oxygen.
The oxyanions of second-row elements in the group oxidation state are tetrahedral. Tetrahedral units are found in olivine minerals, , but the anion does not have a separate existence as the oxygen atoms are surrounded tetrahedrally by cations in the solid state. Phosphate (), sulfate (), and perchlorate () ions can be found as such in various salts. Many oxyanions of elements in lower oxidation state obey the octet rule and this can be used to rationalize the formulae adopted. For example, chlorine(V) has two valence electrons so it can accommodate three electron pairs from bonds with oxide ions. The charge on the ion is +5 − 3 × 2 = −1, and so the formula is . The structure of the ion is predicted by VSEPR theory to be pyramidal, with three bonding electron pairs and one lone pair. In a similar way,
The oxyanion of chlorine(III) has the formula , and is bent with two lone pairs and two bonding pairs.
In the third and subsequent rows of the periodic table, 6-coordination is possible, but isolated octahedral oxyanions are not known because they would carry too high an electrical charge. Thus molybdenum(VI) does not form , but forms the tetrahedral molybdate anion, . MoO units are found in condensed molybdates. Fully protonated oxyanions with an octahedral structure are found in such species as and . In addition, orthoperiodate can be only partially deprotonated, with
: having pK=11.60. | 7 | Physical Chemistry |
Columnar structures were first studied in botany due to their diverse appearances in plants. D'Arcy Thompson analysed such arrangement of plant parts around the stem in his book "On Growth and Form" (1917). But they are also of interest in other biological areas, including bacteria, viruses, microtubules, and the notochord of the zebra fish.
One of the largest flowers where the berries arrange in a regular cylindrical form is the titan arum. This flower can be up to 3m in height and is natively solely found in western Sumatra and western Java.
On smaller length scales, the berries of the Arum maculatum form a columnar structure in autumn. Its berries are similar to that of the corpse flower, since the titan arum is its larger relative. However, the cuckoo-pint is much smaller in height (height ≈ 20 cm). The berry arrangement varies with the stem to berry size.
Another plant that can be found in many gardens of residential areas is the Australian bottlebrush. It assembles its seed capsules around a branch of the plant. The structure depends on the seed capsule size to branch size. | 3 | Analytical Chemistry |
Some authors refer to the grand potential as the Landau free energy or Landau potential and write its definition as:
named after Russian physicist Lev Landau, which may be a synonym for the grand potential, depending on system stipulations. For homogeneous systems, one obtains . | 7 | Physical Chemistry |
A "transient complex" model was first proposed by Huetz et al. to explain this competitive exchange. This transient complex exchange occurs in three distinct steps. Initially a protein embeds itself into the monolayer of an already adsorbed homogenous protein monolayer. The aggregation of this new heterogenous protein mixture causes the "turning" of the double-protein complex which exposes the initially adsorbed protein to the solution. In the third step, the protein that was initially adsorbed can now diffuse out into the solution and the new protein takes over. This 3 part "transient complex mechanism" is further explained and verified through AFM imaging by Hirsh et al. | 7 | Physical Chemistry |
A prokaryote (, also spelled procaryote) is a single-cell organism whose cell lacks a nucleus and other membrane-bound organelles. The word prokaryote comes from the Ancient Greek πρό () before and κάρυον () nut, kernel. In the two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota. But in the three-domain system, based upon molecular analysis, prokaryotes are divided into two domains: Bacteria (formerly Eubacteria) and Archaea (formerly Archaebacteria). Organisms with nuclei are placed in a third domain, Eukaryota.
Prokaryotes evolved before eukaryotes, and lack nuclei, mitochondria or most of the other distinct organelles that characterize the eukaryotic cell. It was once thought that prokaryotic cellular components were unenclosed within the cytoplasm except for an outer cell membrane, but bacterial microcompartments, which are thought to be quasi-organelles enclosed in protein shells (such as the encapsulin protein cages), have been discovered, along with other prokaryotic organelles. While being unicellular, some prokaryotes, such as cyanobacteria, may form colonies held together by biofilms, and large colonies can create multilayered microbial mats. Others, such as myxobacteria, have multicellular stages in their life cycles. Prokaryotes are asexual, reproducing via binary fission without any fusion of gametes, although horizontal gene transfer may take place.
Molecular studies have provided insight into the evolution and interrelationships of the three domains of life. The division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization; only eukaryotic cells have an enveloped nucleus that contains its chromosomal DNA, and other characteristic membrane-bound organelles including mitochondria. Distinctive types of prokaryotes include extremophiles and methanogens; these are common in some extreme environments. | 1 | Biochemistry |
Hua-Zhong "Hogan" Yu (于化忠) is presently a professor of materials and analytical chemistry at Simon Fraser University in metro Vancouver, Canada, where he leads a research laboratory working on Surfaces and Materials for Sensing. He is also an associate editor for Analyst, the journal for Analytical and Bioanalytical Sciences from the Royal Society of Chemistry in UK, and an adjunct professor in the College of Biomedical Engineering, Taiyuan University of Technology in Shanxi, China. | 3 | Analytical Chemistry |
M is the molar mass and G are the group contributions (different for all three properties) for functional groups of a molecule. | 7 | Physical Chemistry |
The lactate shuttle hypothesis describes the movement of lactate intracellularly (within a cell) and intercellularly (between cells). The hypothesis is based on the observation that lactate is formed and utilized continuously in diverse cells under both anaerobic and aerobic conditions. Further, lactate produced at sites with high rates of glycolysis and glycogenolysis can be shuttled to adjacent or remote sites including heart or skeletal muscles where the lactate can be used as a gluconeogenic precursor or substrate for oxidation. The hypothesis was proposed by professor George Brooks of the University of California at Berkeley.
In addition to its role as a fuel source predominantly in the muscles, heart, brain, and liver, the lactate shuttle hypothesis also relates the role of lactate in redox signalling, gene expression, and lipolytic control. These additional roles of lactate have given rise to the term ‘lactormone’, pertaining to the role of lactate as a signalling hormone. | 1 | Biochemistry |
Superconductor material classes include chemical elements (e.g. mercury or lead), alloys (such as niobium–titanium, germanium–niobium, and niobium nitride), ceramics (YBCO and magnesium diboride), superconducting pnictides (like fluorine-doped LaOFeAs) or organic superconductors (fullerenes and carbon nanotubes; though perhaps these examples should be included among the chemical elements, as they are composed entirely of carbon). | 7 | Physical Chemistry |
Lithium aluminium germanium phosphate, typically known with the acronyms LAGP or LAGPO, is an inorganic ceramic solid material whose general formula is . LAGP belongs to the NASICON (Sodium Super Ionic Conductors) family of solid conductors and has been applied as a solid electrolyte in all-solid-state lithium-ion batteries. Typical values of ionic conductivity in LAGP at room temperature are in the range of 10 - 10 S/cm, even if the actual value of conductivity is strongly affected by stoichiometry, microstructure, and synthesis conditions. Compared to lithium aluminium titanium phosphate (LATP), which is another phosphate-based lithium solid conductor, the absence of titanium in LAGP improves its stability towards lithium metal. In addition, phosphate-based solid electrolytes have superior stability against moisture and oxygen compared to sulfide-based electrolytes like (LGPS) and can be handled safely in air, thus simplifying the manufacture process.
Since the best performances are encountered when the stoichiometric value of x is 0.5, the acronym LAGP usually indicates the particular composition of , which is also the typically used material in battery applications. | 7 | Physical Chemistry |
IIR Working Groups operate on a temporary basis, bringing together specialists, to work on projects arising from current issues.
Their aim is to promote development, provide knowledge and give recommendations in these spheres. In order to achieve these objectives, they hold conferences and workshops, write publications and provide recommendations. Members of WGs are IIR members from industry, academia, national administrations and research. | 7 | Physical Chemistry |
In electrochemistry, there are two types of ideal electrode, the ideal polarizable electrode and the ideal non-polarizable electrode. Simply put, the ideal polarizable electrode is characterized by charge separation at the electrode-electrolyte boundary and is electrically equivalent to a capacitor, while the ideal non-polarizable electrode is characterized by no charge separation and is electrically equivalent to a short. | 7 | Physical Chemistry |
The GFAJ-1 bacterium was discovered by geomicrobiologist Felisa Wolfe-Simon, a NASA astrobiology fellow in residence at the US Geological Survey in Menlo Park, California. GFAJ stands for "Give Felisa a Job". The organism was isolated and cultured beginning in 2009 from samples she and her colleagues collected from sediments at the bottom of Mono Lake, California, U.S.A. Mono Lake is hypersaline (about 90 grams/liter) and highly alkaline (pH 9.8). It also has one of the highest natural concentrations of arsenic in the world (200 μM). The discovery was widely publicized on 2 December 2010. | 1 | Biochemistry |
Immunological effects resulting from the cryoablation of tumors was first observed in the 1960s. Since the 1960s, Tanaka treated metastatic breast cancer patients with cryotherapy and reported cryoimmunological reaction resulting from cryotherapy. In the 1970s, systemic immunological response from local cryoablation of prostate cancer was also clinically observed. In the 1980s, Tanaka, of Japan, continued to advance the clinical practice of cryoimmunology with combination treatments including: cryochemotherapy and cryoimmunotherapy. In 1997, Russian scientists confirmed the efficacy of cryoimmunotherapy in inhibiting metastases in advanced cancer. In 2000s, China, following closely with the exciting developments, enthusiastically embraced cryoablation treatment for cancer and has been leading the practice ever since with cryoimmunotherapy treatments available for cancer patients in numerous hospitals and medical clinics throughout China. In the 2010s, American researchers and medical professionals, started to explore cryoimmunotherapy for systemic treatment of cancer. | 1 | Biochemistry |
One application for sodium tert-butoxide is as a non-nucleophilic base. It has been widely used in the Buchwald–Hartwig amination, as in this typical example:
Sodium tert-butoxide is used to prepare tert-butoxide complexes. For example hexa(tert-butoxy)ditungsten(III) is thus obtained by the salt metathesis reaction from a ditungsten heptachloride:
:NaWCl(THF) + 6 NaOBu-t → W(OBu-t) + 7 NaCl + 5 THF | 0 | Organic Chemistry |
Landes joined the University of Houston at an assistant professor in 2006, and moved to Rice University in 2009. She was appointed Kenneth S. Pitzer-Schlumberger Chair in 2021. Her early independent work considered super-resolution single molecule spectroscopy for the characterization of biomolecules using FRET with membrane receptors and diffusion within polymer brushes and porous hydrogel materials. She has pioneered the application of super-resolution microscopy to understand chromatography and has focused on tuning the plasmonic properties of nanomaterials using electrochemistry and stimuli-responsive polymers. She has also shown how silver ions disperse from the tips of gold-silver nanoparticle alloys, which may improve catalytic activity. Her biophysical chemistry work has demonstrated that single-molecule approaches could be used to better understand cancer metastasis.
Landes established the NSF Center for Adapting Flaws into Features (CAFF) in 2021 and serves as its director. The center investigates the defects in silicon-based electronics that hold promise for improving device performance, explore the structural and optoelectronic processes that make these flaws influential, and realize technologies that incorporate and exploit these flaws.
Landes was elected Chair of the Physical Chemistry Division in 2020.
Landes joined the University of Illinois Urbana-Champaign in 2023. | 7 | Physical Chemistry |
Immunotherapy is a treatment used to produce immunity to a disease or enhance the resistance of the immune system to an active disease process, such as cancer
Wnt and Fz genes are frequently overexpressed in head and neck squamous cell carcinoma (HNSCC). Treatment of a HNSCC cell line (SNU 1076) with anti-Wnt1 antibodies reduced the activity of the Wnt/Fz dependent transcription factor LEF/TCF and diminished the expression of cyclin D1 and B-catenin proteins. Similar to anti-Wnt antibodies, treatment with recombinant SFRP1 inhibited growth of SNU 1076 cells as well. This suggests that Wnt and Fz receptors may be attractive targets for immunotherapy and drug therapy of HNSCC. | 1 | Biochemistry |
The above problem raises the question for α > 1: if a Bose gas with a fixed number of particles is lowered down below the critical temperature, what happens?
The problem here is that the Thomas–Fermi approximation has set the degeneracy of the ground state to zero, which is wrong. There is no ground state to accept the condensate and so particles simply disappear from the continuum of states. It turns out, however, that the macroscopic equation gives an accurate estimate of the number of particles in the excited states, and it is not a bad approximation to simply "tack on" a ground state term to accept the particles that fall out of the continuum:
where N is the number of particles in the ground state condensate.
Thus in the macroscopic limit, when T , the value of z is pinned to 1 and N takes up the remainder of particles. For T > T there is the normal behaviour, with N = 0. This approach gives the fraction of condensed particles in the macroscopic limit: | 7 | Physical Chemistry |
Also in 1989, Peko Mines, then a division of North Broken Hill Peko Limited, also engaged Jameson to undertake test work in its Warrego concentrator near Tennant Creek in Australias Northern Territory. The objective was to determine the Jameson Cells performance in cleaning copper concentrate to improve its grade by removing gangue minerals, including pyrite, magnetite, hematite and quartz. Peko Mines personnel also tested a conventional flotation column for comparison. Following the test work, Peko Mines installed two full-scale, 1.4 m diameter Jameson Cells in the concentrator, each with three downcomers.
Peko Mines' decision was based on:
* metallurgical performance during pilot plant test work
* lower capital expenditure and installation costs
* shorter construction and installation times
* ease of operation and lower expected maintenance costs.
Peko Mines reported a payback on the investment in the Cells of two months. | 8 | Metallurgy |
Electrometallurgy is the field concerned with the processes of metal electrodeposition. There are seven categories of these processes:
*Electrolysis
*Electrowinning, the extraction of metal from ores
*Electrorefining, the purification of metals. Metal powder production by electrodeposition is included in this category, or sometimes electrowinning, or a separate category depending on application.
*Electroplating, the deposition of a layer of one metal on another
*Electroforming, the manufacture of, usually thin, metal parts through electroplating
*Electropolishing, the removal of material from a metallic workpiece
*Etching, industrially known to Wikipedia as chemical milling | 8 | Metallurgy |
The unit sphere in three-dimensional space is the set of points such that . Let be the "north pole", and let be the rest of the sphere. The plane runs through the center of the sphere; the "equator" is the intersection of the sphere with this plane.
For any point on , there is a unique line through and , and this line intersects the plane in exactly one point , known as the stereographic projection of onto the plane.
In Cartesian coordinates on the sphere and on the plane, the projection and its inverse are given by the formulas
In spherical coordinates on the sphere (with the zenith angle, , and the azimuth, ) and polar coordinates on the plane, the projection and its inverse are
Here, is understood to have value when = 0. Also, there are many ways to rewrite these formulas using trigonometric identities. In cylindrical coordinates on the sphere and polar coordinates on the plane, the projection and its inverse are | 3 | Analytical Chemistry |
In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos(−) = 109.4712206...° ≈ 109.5° when all four substituents are the same, as in methane () as well as its heavier analogues. Methane and other perfectly symmetrical tetrahedral molecules belong to point group T, but most tetrahedral molecules have lower symmetry. Tetrahedral molecules can be chiral. | 4 | Stereochemistry |
DSSCs are currently the most efficient third-generation (2005 Basic Research Solar Energy Utilization 16) solar technology available. Other thin-film technologies are typically between 5% and 13%, and traditional low-cost commercial silicon panels operate between 14% and 17%. This makes DSSCs attractive as a replacement for existing technologies in "low density" applications like rooftop solar collectors, where the mechanical robustness and light weight of the glass-less collector is a major advantage. They may not be as attractive for large-scale deployments where higher-cost higher-efficiency cells are more viable, but even small increases in the DSSC conversion efficiency might make them suitable for some of these roles as well.
There is another area where DSSCs are particularly attractive. The process of injecting an electron directly into the TiO is qualitatively different from that occurring in a traditional cell, where the electron is "promoted" within the original crystal. In theory, given low rates of production, the high-energy electron in the silicon could re-combine with its own hole, giving off a photon (or other form of energy) which does not result in current being generated. Although this particular case may not be common, it is fairly easy for an electron generated by another atom to combine with a hole left behind in a previous photoexcitation.
In comparison, the injection process used in the DSSC does not introduce a hole in the TiO, only an extra electron. Although it is energetically possible for the electron to recombine back into the dye, the rate at which this occurs is quite slow compared to the rate that the dye regains an electron from the surrounding electrolyte. Recombination directly from the TiO to species in the electrolyte is also possible although, again, for optimized devices this reaction is rather slow. On the contrary, electron transfer from the platinum coated electrode to species in the electrolyte is necessarily very fast.
As a result of these favorable "differential kinetics", DSSCs work even in low-light conditions. DSSCs are therefore able to work under cloudy skies and non-direct sunlight, whereas traditional designs would suffer a "cutout" at some lower limit of illumination, when charge carrier mobility is low and recombination becomes a major issue. The cutoff is so low they are even being proposed for indoor use, collecting energy for small devices from the lights in the house.
A practical advantage which DSSCs share with most thin-film technologies, is that the cell's mechanical robustness indirectly leads to higher efficiencies at higher temperatures. In any semiconductor, increasing temperature will promote some electrons into the conduction band "mechanically". The fragility of traditional silicon cells requires them to be protected from the elements, typically by encasing them in a glass box similar to a greenhouse, with a metal backing for strength. Such systems suffer noticeable decreases in efficiency as the cells heat up internally. DSSCs are normally built with only a thin layer of conductive plastic on the front layer, allowing them to radiate away heat much easier, and therefore operate at lower internal temperatures. | 5 | Photochemistry |
There are different chemical families of corrosion inhibitors used in the oil industry, among them are the following:
Fatty Imidazolines: These are imidazole-based compounds, usually with a long unsaturated chain length, derived mainly from oleic acid. They are very effective in preventing acid corrosion of carbon steel (Figure 1).
Fatty amines: These corrosion inhibitors are organic compounds that contain an amino group and an alkyl group. They act as cathodic inhibitors and form a protective layer on the metal surface.They work efficiently against corrosion brought about by carbon dioxide (CO2) and hydrogen sulfide (H2S). Also, ethoxylated amines are widely applied for the same purpose (Figure 2).
Organic Acids: Organic acids such as acetic acid, formic aci,d and citric acid are used as corrosion inhibitors. These acids react with metal ions to form insoluble compounds that protect the metal surface. These inhibitors are often used in combination with other corrosion inhibitors and techniques, such as cathodic protection and coatings, to provide comprehensive corrosion protection. CO2 and H2S are regularly seen in oilfields and are notorious for causing corrosion of metal sections. Fortunately, they can be kept under control with measures that have been found to be effective (Figure 3).
Pyridines: Some studies have shown that certain pyridines can inhibit corrosion caused by the presence of acid gases, such as carbon dioxide and hydrogen sulfide, which are common in the oil industry. Pyridine and its derivatives have been shown to be effective inhibitors for a wide range of metals, such as carbon steel, stainless steel, and copper alloys. They act by adsorbing to the metal surface and forming a protective film, which can be physical or chemical in nature. Pyridine and its derivatives are also effective in inhibiting localized corrosion, such as pitting and crevice corrosion (Figure 4).
Azoles: Azoles, such as triazole and benzotriazole, oxazole and benzoxazoles, thioazoles, and benzothioazoles, are organic compounds used as corrosion inhibitors in the petroleum industry. They act as anodic inhibitors and form a protective layer on the metal surface (Figure 5).
Polymers: Polymers are large molecules used in the petroleum industry as corrosion inhibitors. These polymers can adsorb onto the metal surface and form a protective coating. They can also be used as dispersants to prevent the formation of corrosive deposits. Some examples are:
Aminated polymers: These polymers are used for corrosion protection of metal surfaces in the oil industry. They are highly effective in preventing salt water and hydrogen sulfide (H2S) corrosion.
Acrylic polymers: These polymers are used as corrosion inhibitors in the industry due to their good compatibility with oil and drilling fluids. They are effective against corrosion caused by the presence of hydrochloric acid (HCl) in drilling fluids.
Maleate polymers: These polymers are used as corrosion inhibitors in the industry due to their good adsorption capacity on metal surfaces and their high solubility in oil and drilling fluids. They offer protection against the corrosive effects of hydrogen sulfide (H2S) present in the drilling fluid. (Figure 6).
Other organic products used as corrosion inhibitors in the oil industry are nitriles, amides, oximes, ureas and, thioureas, and phosphonate salts. Inorganic inhibitors such as lanthanides, molybdates, silicates, boric and phosphoric acids, and combinations of nitrates and nitrites are also widely employed. Environmentally friendly inhibitors such as some biomass wastes, amino acids, and ionic liquids have been investigated.
It is critical to choose the right corrosion inhibitor based on environmental conditions (temperature, pressure, and type of metal to be protected) and to ensure that the right amount is applied for maximum protection. The corrosion progress should also be monitored periodically to adjust the dosage of the inhibitor if necessary. | 0 | Organic Chemistry |
According to the assumptions of the kinetic theory of ideal gases, one can consider that there are no intermolecular attractions between the molecules, or atoms, of an ideal gas. In other words, its potential energy is zero. Hence, all the energy possessed by the gas is the kinetic energy of the molecules, or atoms, of the gas.
This corresponds to the kinetic energy of n moles of a monoatomic gas having 3 degrees of freedom; x, y, z. The table here below gives this relationship for different amounts of a monoatomic gas. | 7 | Physical Chemistry |
Methylotrophs use the electron transport chain to conserve energy produced from the oxidation of compounds. An additional activation step is required in methanotrophic metabolism to allow degradation of chemically-stable methane. This oxidation to methanol is catalyzed by MMO, which incorporates one oxygen atom from into methane and reduces the other oxygen atom to water, requiring two equivalents of reducing power. Methanol is then oxidized to formaldehyde through the action of methanol dehydrogenase (MDH) in bacteria, or a non-specific alcohol oxidase in yeast. Electrons from methanol oxidation are passed to a membrane-associated quinone of the electron transport chain to produce .
In dissimilatory processes, formaldehyde is completely oxidized to <chem>CO2
associated dehydrogenases, is produced.
Finally, formate is oxidized to by cytoplasmic or membrane-bound Formate dehydrogenase (FDH), producing and . | 0 | Organic Chemistry |
Convection-cooling is sometimes loosely assumed to be described by Newton's law of cooling.
Newtons law states that the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings while under the effects of a breeze'. The constant of proportionality is the heat transfer coefficient. The law applies when the coefficient is independent, or relatively independent, of the temperature difference between object and environment.
In classical natural convective heat transfer, the heat transfer coefficient is dependent on the temperature. However, Newton's law does approximate reality when the temperature changes are relatively small, and for forced air and pumped liquid cooling, where the fluid velocity does not rise with increasing temperature difference. | 7 | Physical Chemistry |
The muons are implanted into the sample of interest where they lose energy very quickly. Fortunately, this deceleration process occurs in such a way that it does not jeopardize a μSR measurement. On one side it is very fast (much faster than 100 ps), which is much shorter than a typical μSR time window (up to 20 μs), and on the other side, all the processes involved during the deceleration are Coulombic (ionization of atoms, electron scattering, electron capture) in origin and do not interact with the muon spin, so that the muon is thermalized without any significant loss of polarization.
The positive muons usually adopt interstitial sites of the crystallographic lattice, markedly distinguished by their electronic (charge) state. The spectroscopy of a muon chemically bound to an unpaired electron is remarkably different from that of all other muon states, which motivates the historical distinction in paramagnetic and diamagnetic states. Note that many diamagnetic muon states really behave like paramagnetic centers, according to the standard definition of a paramagnet. For example, in most metallic samples, which are Pauli paramagnets, the muons positive charge is collectively screened by a cloud of conduction electrons. Thus, in metals, the muon is not bound to a single electron, hence it is in the so-called diamagnetic state and behaves like a free muon. In insulators or semiconductors a collective screening cannot take place and the muon will usually pick up one electron and form a so-called muonium (Mu=μ+e), which has similar size (Bohr radius), reduced mass, and ionization energy to the hydrogen atom. This is the prototype of the so-called paramagnetic' state. | 7 | Physical Chemistry |
Discovery of the novel antioxidant function of coenzyme A highlights its protective role during cellular stress. Mammalian and Bacterial cells subjected to oxidative and metabolic stress show significant increase in the covalent modification of protein cysteine residues by coenzyme A. This reversible modification is termed protein CoAlation (Protein-S-SCoA), which plays a similar role to protein S-glutathionylation by preventing the irreversible oxidation of the thiol group of cysteine residues.
Using anti-coenzyme A antibody and liquid chromatography tandem mass spectrometry (LC-MS/MS) methodologies, more than 2,000 CoAlated proteins were identified from stressed mammalian and bacterial cells. The majority of these proteins are involved in cellular metabolism and stress response. Different research studies have focused on deciphering the coenzyme A-mediated regulation of proteins. Upon protein CoAlation, inhibition of the catalytic activity of different proteins (e.g. metastasis suppressor NME1, peroxiredoxin 5, GAPDH, among others) is reported. To restore the protein's activity, antioxidant enzymes that reduce the disulfide bond between coenzyme A and the protein cysteine residue play an important role. This process is termed protein deCoAlation. So far, two bacterial proteins, Thioredoxin A and Thioredoxin-like protein (YtpP), are shown to deCoAlate proteins. | 1 | Biochemistry |
The effective fragment potential (EFP) method is a computational approach designed to describe intermolecular interactions and environmental effects. It is a computationally inexpensive means to describe interactions in non-bonded systems. It was originally formulated to describe the solvent effects in complex chemical systems. But it has undergone vast improvements in the past two decades, and is currently used to represent intermolecular interactions (represented as rigid fragments), and in molecular dynamics (MD) simulations as well. | 6 | Supramolecular Chemistry |
The role that plastoquinone plays in photosynthesis, more specifically in the light-dependent reactions of photosynthesis, is that of a mobile electron carrier through the membrane of the thylakoid.
Plastoquinone is reduced when it accepts two electrons from photosystem II and two hydrogen cations (H) from the stroma of the chloroplast, thereby forming plastoquinol (PQH). It transfers the electrons further down the electron transport chain to plastocyanin, a mobile, water-soluble electron carrier, through the cytochrome bf protein complex. The cytochrome bf protein complex catalyzes the electron transfer between plastoquinone and plastocyanin, but also transports the two protons into the lumen of thylakoid discs. This proton transfer forms an electrochemical gradient, which is used by ATP synthase at the end of the light dependent reactions in order to form ATP from ADP and P. | 5 | Photochemistry |
Leaves are normally extensively vascularized and typically have networks of vascular bundles containing xylem, which supplies water for photosynthesis, and phloem, which transports the sugars produced by photosynthesis. Many leaves are covered in trichomes (small hairs) which have diverse structures and functions. | 5 | Photochemistry |
Albert Rakoto Ratsimamanga is considered one of Madagascars most renowned scholars. A commemorative stamp was issued in his memory in 2002, and the Institut de France minted a coin tribute to Ratsimamanga. Ratsimamangas legacy can be seen as a | 1 | Biochemistry |
Wootz steel originated in the mid-1st millennium BC in India, in present-day Tiruchirappalli, Kodumanal, Erode, Tamil Nadu. There are several ancient Tamil, North Indian, Greek, Chinese and Roman literary references to high-carbon Tamil steel. In later times, wootz steel was also made in Golconda in Telangana, Karnataka and Sri Lanka. The steel was exported as cakes of steely iron that came to be known as "Wootz". The method was to heat black magnetite ore in the presence of carbon in a sealed clay crucible inside a charcoal furnace to completely remove slag. An alternative was to smelt the ore first to give wrought iron, then heat and hammer it to remove slag. The carbon source was bamboo and leaves from plants such as Avārai. Locals in Sri Lanka adopted the production methods of creating wootz steel from the Chera Tamils by the 5th century BC. Joseph Needham in 1971 claimed China produced a similar steel also by the 5th century BCE but more recent research in China (2009) showed that Needham erroneously identified the ancient Chinese steel as hyper-eutectoid and similar to wootz but it was really produced via co-fusion process instead (smelting cast iron and wrought iron together). Genuine wootz in China was mentioned for the first time much later, during the Bei Wei Dynasty (386-534 CE) under the name “Bintie” or “Pin t’ieh” as being produced in India, ingots were initially given by Persian Kings as valuable presents, later the Chinese called "bintie" the various co-fusion hard steels they produced. In Sri Lanka, this early steel-making method employed a unique wind furnace, driven by the monsoon winds. Production sites from antiquity have emerged, in places such as Anuradhapura, Tissamaharama and Samanalawewa, as well as imported artifacts of ancient iron and steel from Kodumanal. Recent archaeological excavations (2018) of the Yodhawewa site (in Mannar District) discovered a lower half-spherical furnace, crucible fragments, and lid fragments related to the crucible steel production through the carburization process. A 200 BC Tamil trade guild in Tissamaharama, in the South East of Sri Lanka, brought with them some of the oldest iron and steel artifacts and production processes to the island from the classical period.
Trade between India and Sri Lanka through the Arabian Sea introduced wootz steel to Arabia. The term muhannad مهند or hendeyy هندي in pre-Islamic and early Islamic Arabic refers to sword blades made from Indian steel, which were highly prized, and are attested in Arabic poetry. Further trade spread the technology to the city of Damascus, where an industry developed for making weapons of this steel. This led to the development of Damascus steel. The 12th century Arab traveler Edrisi mentioned the "Hinduwani" or Indian steel as the best in the world. Arab accounts also point to the fame of Teling steel, which can be taken to refer to the region of Telangana. The Golconda region of Telangana clearly being the nodal centre for the export of wootz steel to West Asia.
Another sign of its reputation is seen in a Persian phraseto give an "Indian answer", meaning "a cut with an Indian sword". Wootz steel was widely exported and traded throughout ancient Europe and the Arab world, and became particularly famous in the Middle East. | 8 | Metallurgy |
Marshes, intertidal ecosystems dominated by herbaceous vegetation, can be found globally on coastlines from the arctic to the subtropics. In the tropics, marshes are replaced by mangroves as the dominant coastal vegetation.
Marshes have high productivity, with a large portion of primary production in belowground biomass. This belowground biomass can form deposits up to 8m deep. Marshes provide valuable habitat for plants, birds, and juvenile fish, protect coastal habitat from storm surge and flooding, and can reduce nutrient loading to coastal waters. Similarly to mangrove and seagrass habitats, marshes also serve as important carbon sinks. Marshes sequester C in underground biomass due to high rates of organic sedimentation and anaerobic-dominated decomposition. Salt marshes cover approximately 22,000 to 400,000 km globally, with an estimated carbon burial rate of 210 g C m yr.
Salt marshes may not be expansive worldwide in relation to forests, but they have a C burial rate that is over 50 times faster than tropical rainforests. Rates of burial have been estimated at up to 87.2 ± 9.6 Tg C yr which is greater than that of tropical rainforests, 53 ± 9.6 Tg C yr. Since the 1800s salt marshes have been disturbed due to development and a lack of understanding of their importance. The 25% decline since that time has led to a decrease in potential C sink area coupled with the release of once buried C. Consequences of increasingly degraded marsh habitat are a decrease in C stock in sediments, a decrease in plant biomass and thus a decrease in photosynthesis reducing the amount of CO taken up by the plants, failure of C in plant blades to be transferred into the sediment, possible acceleration of erosive processes due to the lack of plant biomass, and acceleration of buried C release to the atmosphere.
Tidal marshes have been impacted by humans for centuries, including modification for grazing, haymaking, reclamation for agriculture, development and ports, evaporation ponds for salt production, modification for aquaculture, insect control, tidal power and flood protection. Marshes are also susceptible to pollution from oil, industrial chemicals, and most commonly, eutrophication. Introduced species, sea-level rise, river damming and decreased sedimentation are additional longterm changes that affect marsh habitat, and in turn, may affect carbon sequestration potential. | 9 | Geochemistry |
Iron(II) is oxidized by hydrogen peroxide to iron(III), forming a hydroxyl radical and a hydroxide ion in the process. Iron(III) is then reduced back to iron(II) by another molecule of hydrogen peroxide, forming a hydroperoxyl radical and a proton. The net effect is a disproportionation of hydrogen peroxide to create two different oxygen-radical species, with water (H + OH) as a byproduct.
The free radicals generated by this process engage in secondary reactions. For example, the hydroxyl is a powerful, non-selective oxidant. Oxidation of an organic compound by Fenton's reagent is rapid and exothermic and results in the oxidation of contaminants to primarily carbon dioxide and water.
Reaction () was suggested by Haber and Weiss in the 1930s as part of what would become the Haber–Weiss reaction.
Iron(II) sulfate is typically used as the iron catalyst. The exact mechanisms of the redox cycle are uncertain, and non-OH oxidizing mechanisms of organic compounds have also been suggested. Therefore, it may be appropriate to broadly discuss Fenton chemistry rather than a specific Fenton reaction.
In the electro-Fenton process, hydrogen peroxide is produced in situ from the electrochemical reduction of oxygen.
Fenton's reagent is also used in organic synthesis for the hydroxylation of arenes in a radical substitution reaction such as the classical conversion of benzene into phenol.
An example hydroxylation reaction involves the oxidation of barbituric acid to alloxane. Another application of the reagent in organic synthesis is in coupling reactions of alkanes. As an example tert-butanol is dimerized with Fentons reagent and sulfuric acid to 2,5-dimethyl-2,5-hexanediol. Fentons reagent is also widely used in the field of environmental science for water purification and soil remediation. Various hazardous wastewater were reported to be effectively degraded through Fenton's reagent. | 2 | Environmental Chemistry |
The Hiyama–Denmark coupling is the modification of the Hiyama coupling that does not require a fluoride additive to utilize organosilanols and organic halides as coupling partners. The general reaction scheme is shown below, showcasing the utilization of a Brønsted base as the activating agent as opposed to fluoride, phosphine ligands are also used on the metal center.
A specific example of this reaction is shown with reagents. If fluoride had been used, as in the original Hiyama protocol, the tert-butyldimethylsilyl (TBS) ether would have likely been destroyed. | 0 | Organic Chemistry |
Chibaite is a rare silicate mineral. It is a silica clathrate with formula (n = 3/17 (max)). The mineral is cubic (diploidal class, m) and the silica hosts or traps various hydrocarbon molecules, such as methane, ethane, propane and isobutane.
Chibaite was first described for specimens collected from Arakawa, Minamibōsō, Chiba Prefecture, Honshu Island, Japan. The mineral was approved by the IMA in 2009. | 6 | Supramolecular Chemistry |
One important characteristic of a crystalline structure is its atomic packing factor (APF). This is calculated by assuming that all the atoms are identical spheres, with a radius large enough that each sphere abuts on the next. The atomic packing factor is the proportion of space filled by these spheres which can be worked out by calculating the total volume of the spheres and dividing by the volume of the cell as follows:
Another important characteristic of a crystalline structure is its coordination number (CN). This is the number of nearest neighbours of a central atom in the structure.
The APFs and CNs of the most common crystal structures are shown below:
The 74% packing efficiency of the FCC and HCP is the maximum density possible in unit cells constructed of spheres of only one size. | 3 | Analytical Chemistry |
Two dimensional space has the same number of crystal systems, crystal families, and lattice systems. In 2D space, there are four crystal systems: oblique, rectangular, square, and hexagonal. | 3 | Analytical Chemistry |
Magnesium can affect muscle relaxation through direct action on cell membranes. Mg ions close certain types of calcium channels, which conduct positively charged calcium ions into neurons. With an excess of magnesium, more channels will be blocked and nerve cells activity will decrease. | 1 | Biochemistry |
1H-NMR (300 MHz, CDCl3): δ 7.59 (d, J = 9.5 Hz, 1H, aromatic), 7.22 (s, 1H, aromatic), 6.75 (d, J = 21.6 Hz, 1H, aromatic), 6.20 (d, J = 9.5 Hz, 1H, aromatic), 4.74 (t, J = 8.8 Hz, 1H, CH), 3.28-3.15 (m, 2H, CH2), 1.87 (s, 1H, OH), 1.37 (s, 3H, CH3), 1.24 (s, 3H, CH3) ppm. | 1 | Biochemistry |
Coal analysis techniques are specific analytical methods designed to measure the particular physical and chemical properties of coals. These methods are used primarily to determine the suitability of coal for coking, power generation or for iron ore smelting in the manufacture of steel. | 3 | Analytical Chemistry |
Thiophenes are a special class of sulfide-containing heterocyclic compounds. Because of their aromatic character, they are non-nucleophilic. The nonbonding electrons on sulfur are delocalized into the π-system. As a consequence, thiophene exhibits few properties expected for a sulfide – thiophene is non-nucleophilic at sulfur and, in fact, is sweet-smelling. Upon hydrogenation, thiophene gives tetrahydrothiophene, CHS, which indeed does behave as a typical sulfide. | 0 | Organic Chemistry |
Malonyl-CoA plays a special role in the mitochondrial clearance of toxic malonic acid in the metabolic disorder combined malonic and methylmalonic aciduria (CMAMMA). In CMAMMA due to ACSF3, malonyl-CoA synthetase is decreased, which can generate malonyl-CoA from malonic acid, which can then be converted to acetyl-CoA by malonyl-CoA decarboxylase. In contrast, in CMAMMA due to malonyl-CoA decarboxylase deficiency, malonyl-CoA decarboxylase is decreased, which converts malonyl-CoA to acetyl-CoA. | 1 | Biochemistry |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.