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A heptose is a monosaccharide with seven carbon atoms.
They have either an aldehyde functional group in position 1 (aldoheptoses) or a ketone functional group in position 2, 3 or 4 (ketoheptoses). Ketoheptoses have 4 chiral centers, whereas aldoheptoses have 5. | 1 | Biochemistry |
NbGe was discovered to be a superconductor in 1973 and for 13 years (until the discovery in 1986 of the cuprate superconductors) it held the record as having the highest critical temperature.
It has not been as widely used for superconductive applications as niobium–tin or niobium–titanium. | 8 | Metallurgy |
The study of deformation is essential for the development of new materials. Deformation in metals depends on temperature, type of stress applied, strain rate, oxidation, and corrosion. Deformation-induced EMR can be divided into three categories: effects in ionic crystal materials, effects in rocks and granites, and effects in metals and alloys. EMR emission depends on the orientation of the grains in individual crystals since material properties are different in differing directions. Amplitude of the EMR pulse increases as long as the crack grows as new atomic bonds are broken, leading to EMR. The Pulse starts to decay as the cracking halts. Observations from experiments showed that emitted EMR signals contain mixed frequency components. | 5 | Photochemistry |
In eukaryotes, genomic DNA is highly compacted in order to be able to fit it into the nucleus. This is accomplished by winding the DNA around protein octamers called histones, which has consequences for the physical accessibility of parts of the genome at any given time. Significant portions are silenced through histone modifications, and thus are inaccessible to the polymerases or their cofactors. The highest level of transcription regulation occurs through the rearrangement of histones in order to expose or sequester genes, because these processes have the ability to render entire regions of a chromosome inaccessible such as what occurs in imprinting.
Histone rearrangement is facilitated by post-translational modifications to the tails of the core histones. A wide variety of modifications can be made by enzymes such as the histone acetyltransferases (HATs), histone methyltransferases (HMTs), and histone deacetylases (HDACs), among others. These enzymes can add or remove covalent modifications such as methyl groups, acetyl groups, phosphates, and ubiquitin. Histone modifications serve to recruit other proteins which can either increase the compaction of the chromatin and sequester promoter elements, or to increase the spacing between histones and allow the association of transcription factors or polymerase on open DNA. For example, H3K27 trimethylation by the polycomb complex PRC2 causes chromosomal compaction and gene silencing. These histone modifications may be created by the cell, or inherited in an epigenetic fashion from a parent. | 1 | Biochemistry |
In thermodynamics, a critical line is the higher-dimensional equivalent of a critical point. It is the
locus of contiguous critical points in a phase diagram. These lines cannot occur for
a single substance due to the phase rule, but they can be observed in systems with more variables, such as mixtures. Two critical lines may meet and terminate in a tricritical point. | 7 | Physical Chemistry |
Human cloning is the creation of a genetically identical copy of a human. The term is generally used to refer to artificial human cloning, which is the reproduction of human cells and tissues. It does not refer to the natural conception and delivery of identical twins. The possibility of human cloning has raised controversies. These ethical concerns have prompted several nations to pass legislation regarding human cloning and its legality. As of right now, scientists have no intention of trying to clone people and they believe their results should spark a wider discussion about the laws and regulations the world needs to regulate cloning.
Two commonly discussed types of theoretical human cloning are therapeutic cloning and reproductive cloning. Therapeutic cloning would involve cloning cells from a human for use in medicine and transplants, and is an active area of research, but is not in medical practice anywhere in the world, . Two common methods of therapeutic cloning that are being researched are somatic-cell nuclear transfer and, more recently, pluripotent stem cell induction. Reproductive cloning would involve making an entire cloned human, instead of just specific cells or tissues. | 1 | Biochemistry |
In optical physics, transmittance of the surface of a material is its effectiveness in transmitting radiant energy. It is the fraction of incident electromagnetic power that is transmitted through a sample, in contrast to the transmission coefficient, which is the ratio of the transmitted to incident electric field.
Internal transmittance refers to energy loss by absorption, whereas (total) transmittance is that due to absorption, scattering, reflection, etc. | 7 | Physical Chemistry |
The molecular weight of polymers has a large influence on their properties and therefore determines the applications. Among others the flow behavior, the solubility, the mechanical properties but also the lifetime are influenced by the molecular weight. For high duty polymers – polymers that have to fulfill elevated demands – not only the molecular weight but also the molecular weight distribution is important. This especially holds true if low and/or high molecular material disturbs a given task. | 7 | Physical Chemistry |
Potassium is the main intracellular ion for all types of cells, while having a major role in maintenance of fluid and electrolyte balance. Potassium is necessary for the function of all living cells, and is thus present in all plant and animal tissues. It is found in especially high concentrations within plant cells, and in a mixed diet, it is most highly concentrated in fruits. The high concentration of potassium in plants, associated with comparatively very low amounts of sodium there, historically resulted in potassium first being isolated from the ashes of plants (potash), which in turn gave the element its modern name. The high concentration of potassium in plants means that heavy crop production rapidly depletes soils of potassium, and agricultural fertilizers consume 93% of the potassium chemical production of the modern world economy.
The functions of potassium and sodium in living organisms are quite different. Animals, in particular, employ sodium and potassium differentially to generate electrical potentials in animal cells, especially in nervous tissue. Potassium depletion in animals, including humans, results in various neurological dysfunctions. Characteristic concentrations of potassium in model organisms are: 30–300mM in E. coli, 300mM in budding yeast, 100mM in mammalian cell and 4mM in blood plasma. | 1 | Biochemistry |
Children and adolescents who use tanning beds are at greater risk because of biological vulnerability to UV radiation. Epidemiological studies have shown that exposure to artificial tanning increases the risk of malignant melanoma and that the longer the exposure, the greater the risk, particularly in individuals exposed before the age of 30 or who have been sunburned.
One study conducted among college students found that awareness of the risks of tanning beds did not deter the students from using them. Teenagers are frequent targets of tanning industry marketing, which includes offers of coupons and placing ads in high-school newspapers. Members of the United States House Committee on Energy and Commerce commissioned a "sting" operation in 2012, in which callers posing as a 16-year-old woman who wanted to tan for the first time called 300 tanning salons in the US. Staff reportedly failed to follow FDA recommendations, denied the risks of tanning, and offered misleading information about benefits. | 5 | Photochemistry |
Cryoimmunotherapy, also referred to as cryoimmunology, is an oncological treatment for various cancers that combines cryoablation of tumor with immunotherapy treatment. In-vivo cryoablation of a tumor, alone, can induce an immunostimulatory, systemic anti-tumor response, resulting in a cancer vaccine—the abscopal effect. Thus, cryoablation of tumors is a way of achieving autologous, in-vivo tumor lysate vaccine and treat metastatic disease. However, cryoablation alone may produce an insufficient immune response, depending on various factors, such as high freeze rate. Combining cryotherapy with immunotherapy enhances the immunostimulating response and has synergistic effects for cancer treatment.
Although, cryoblation and immunotherapy has been used successfully in oncological clinical practice for over 100 years, and can treat metastatic disease with curative intent, it has been ignored in modern practice. Only recently has cryoimmunotherapy been resurrected to become the gold standard in cancer treatment of all stages of disease. | 1 | Biochemistry |
The half-chair conformation indicates that attack occurs stereoselectively on the diastereomer where the electrophilic carbon can receive the nucleophile and proceed to the favored chair conformation. | 4 | Stereochemistry |
Volatiles are present in nearly all magma in different concentrations. Examples of volatiles within magma include water, carbon dioxide, and halogen gases. High pressures allow these volatiles to stay relatively stable within solution. However, over time, as the magmatic pressure decreases, volatiles will rise out of solution in the gaseous phase, further decreasing the magmatic pressure. These pressure differences cause drastic differences in the volume of a magma. Pressure difference causes some forms of volcanoes to be highly explosive and others to be effusive. | 9 | Geochemistry |
The DrugWipe is a moist wipe used to detect drug residue on surfaces, or on the forehead, palm, or tongue of an individual. An integrated ampule is broken, which is the medium for transporting the collected analyte to the antigen-binding site. The DrugWipe can be configured to detect cannabis, cocaine, opiates, amphetamines, MDMA, and benzodiazepines. Immunoassay strips containing antibodies bind to components of the different drugs. | 3 | Analytical Chemistry |
Polymer solutions are solutions containing dissolved polymers. These may be (e.g. in ), or solid solutions (e.g. a substance which has been plasticized).
The introduction into the polymer of small amounts of a solvent (plasticizer) reduces the temperature of glass transition, the yield temperature, and the viscosity of a melt.
An understanding of the thermodynamics of a polymer solution is critical to prediction of its behavior in manufacturing processes — for example, its shrinkage or expansion in injection molding processes, or whether pigments and solvents will mix evenly with a polymer in the manufacture of paints and coatings. A recent theory on the viscosity of polymer solutions gives a physical explanation for various well-known empirical relations and numerical values including the Huggins constant, but reveals also novel simple concentration and molar mass dependence. | 7 | Physical Chemistry |
In general, TST has provided researchers with a conceptual foundation for understanding how chemical reactions take place. Even though the theory is widely applicable, it does have limitations. For example, when applied to each elementary step of a multi-step reaction, the theory assumes that each intermediate is long-lived enough to reach a Boltzmann distribution of energies before continuing to the next step. When the intermediates are very short-lived, TST fails. In such cases, the momentum of the reaction trajectory from the reactants to the intermediate can carry forward to affect product selectivity. An example of such a reaction is the ring closure of cyclopentane biradicals generated from the gas-phase thermal decomposition of 2,3-diazabicyclo[2.2.1]hept-2-ene.
Transition state theory is also based on the assumption that atomic nuclei behave according to classical mechanics. It is assumed that unless atoms or molecules collide with enough energy to form the transition structure, then the reaction does not occur. However, according to quantum mechanics, for any barrier with a finite amount of energy, there is a possibility that particles can still tunnel across the barrier. With respect to chemical reactions this means that there is a chance that molecules will react, even if they do not collide with enough energy to overcome the energy barrier. While this effect is negligible for reactions with large activation energies, it becomes an important phenomenon for reactions with relatively low energy barriers, since the tunneling probability increases with decreasing barrier height.
Transition state theory fails for some reactions at high temperature. The theory assumes the reaction system will pass over the lowest energy saddle point on the potential energy surface. While this description is consistent for reactions occurring at relatively low temperatures, at high temperatures, molecules populate higher energy vibrational modes; their motion becomes more complex and collisions may lead to transition states far away from the lowest energy saddle point. This deviation from transition state theory is observed even in the simple exchange reaction between diatomic hydrogen and a hydrogen radical.
Given these limitations, several alternatives to transition state theory have been proposed. A brief discussion of these theories follows. | 7 | Physical Chemistry |
Radon concentrations found in natural environments are much too low to be detected by chemical means: for example, a 1000 Bq/m (relatively high) concentration corresponds to 0.17 picogram per cubic meter. The average concentration of radon in the atmosphere is about 6 atoms of radon for each molecule in the air, or about 150 atoms in each mL of air. The entire radon activity of the Earth's atmosphere at any one time is due to some tens of grams of radon, constantly being replaced by decay of larger amounts of radium and uranium. Its concentration can vary greatly from place to place. In the open air, it ranges from 1 to 100 Bq/m, even less (0.1 Bq/m) above the ocean. In caves, aerated mines, or poorly ventilated dwellings, its concentration can climb to 20–2,000 Bq/m.
In mining contexts, radon concentrations can be much higher. Ventilation regulations try to maintain concentrations in uranium mines under the "working level", and under 3 WL (546 pCi per liter of air; 20.2 kBq/m measured from 1976 to 1985) 95 percent of the time.
The concentration in the air at the (unventilated) Gastein Healing Gallery averages 43 kBq/m (about 1.2 nCi/L) with maximal value of 160 kBq/m (about 4.3 nCi/L).
Radon emanates naturally from the ground and from some building materials all over the world, wherever there are traces of uranium or thorium, and particularly in regions with soils containing granite or shale, which have a higher concentration of uranium. In every 1 square mile of surface soil, the first (of depth) contains about 0.035 oz of radium (0.4 g per km) which releases radon in small amounts to the atmosphere. Sand used in making concrete is the major source of radon in buildings.
On a global scale, it is estimated that 2,400 million curies (91 TBq) of radon are released from soil annually. Not all granitic regions are prone to high emissions of radon. Being an unreactive noble gas, it usually migrates freely through faults and fragmented soils, and may accumulate in caves or water. Due to its very small half-life (four days for ), its concentration decreases very quickly when the distance from the production area increases.
Its atmospheric concentration varies greatly depending on the season and conditions. For instance, it has been shown to accumulate in the air if there is a meteorological inversion and little wind.
Because atmospheric radon concentrations are very low, radon-rich water exposed to air continually loses radon by volatilization. Hence, ground water generally has higher concentrations of than surface water, because the radon is continuously replenished by radioactive decay of present in rocks. Likewise, the saturated zone of a soil frequently has a higher radon content than the unsaturated zone because of diffusional losses to the atmosphere. As a below-ground source of water, some springs—including hot springs—contain significant amounts of radon. The towns of Boulder, Montana; Misasa; Bad Kreuznach, and the country of Japan have radium-rich springs which emit radon. To be classified as a radon mineral water, radon concentration must be above a minimum of 2 nCi/L (7 Bq/L). The activity of radon mineral water reaches 2,000 Bq/L in Merano and 4,000 Bq/L in the village of Lurisia (Ligurian Alps, Italy).
Radon is also found in some petroleum. Because radon has a similar pressure and temperature curve to propane, and oil refineries separate petrochemicals based on their boiling points, the piping carrying freshly separated propane in oil refineries can become partially radioactive due to radon decay particles. Residues from the oil and gas industry often contain radium and its daughters. The sulfate scale from an oil well can be radium rich, while the water, oil, and gas from a well often contains radon. The radon decays to form solid radioisotopes which form coatings on the inside of pipework. In an oil processing plant, the area of the plant where propane is processed is often one of the more contaminated areas, because radon has a similar boiling point to propane. | 2 | Environmental Chemistry |
Solomon is co-author of nine books, including an historical account of the development of plastic banknotes (The Plastic Banknote: From Concept to Reality) and several text books (including The Chemistry of Radical Polymerization). He is also co-author of over 250 journal papers and 45 patents. | 7 | Physical Chemistry |
This is a derivation to obtain an expression for for an ideal gas.
An ideal gas has the equation of state:
where
:P = pressure
:V = volume
:n = number of moles
:R = universal gas constant
:T = temperature
The ideal gas equation of state can be arranged to give:
: or
The following partial derivatives are obtained from the above equation of state:
The following simple expressions are obtained for thermal expansion coefficient :
and for isothermal compressibility :
One can now calculate for ideal gases from the previously obtained general formula:
Substituting from the ideal gas equation gives finally:
where n = number of moles of gas in the thermodynamic system under consideration and R = universal gas constant. On a per mole basis, the expression for difference in molar heat capacities becomes simply R for ideal gases as follows:
This result would be consistent if the specific difference were derived directly from the general expression for . | 7 | Physical Chemistry |
Elgiloy (Co-Cr-Ni Alloy) is a "super-alloy" consisting of 39-41% cobalt, 19-21% chromium, 14-16% nickel, 11.3-20.5% iron, 6-8% molybdenum, 1.5-2.5% manganese and 0.15% max. carbon.
It is used to make springs that are corrosion resistant and exhibit high strength, ductility, and good fatigue life. These same properties led to it being used for control cables in the Lockheed SR-71 Blackbird airplane, as they needed to cope with repeated stretching and contracting.
Elgiloy meets specifications AMS 5876, AMS 5833, and UNS R30003.
Due to its chemical composition, Elgiloy is highly resistant to sulfide stress corrosion cracking and pitting, and can operate at temperatures up to 454 °C.
Elgiloy is a trade name for this super alloy. Phynox is another trade name for the same super alloy. | 8 | Metallurgy |
The GYG1 gene is located on the long arm of the chromosome 3, between positions 24 and 25, from base pair 148,709,194 to base pair 148,745,455.
Transcription of human glycogenin-1 is mainly initiated at 80bp and 86bp upstream the translator’s codon beginning. Transcriptions factors have different binding sites for its development, some examples are: GATA, activator protein 1 and 2 (AP-1 and AP-2), and numerous potential Octamer-1 binding sites. | 1 | Biochemistry |
The capping enzyme is part of the covalent nucleotidyl transferases superfamily, which also includes DNA ligases and RNA ligases. The enzymes of this superfamily share the following similarities:
* Conserved regions known as motifs I, II, III, IIIa, IV, V and VI, which are arranged in the same order and similar spacing
* A lysine containing motif KxDG (motif I)
* A covalent lysyl-NMP intermediate
The capping enzyme is composed of two domains, a nucleotidyl transferase (NTase) domain and a C-terminal oligonucleotide binding (OB) domain. The NTase domain, conserved in capping enzymes, DNA and RNA ligases, is made up 5 motifs, I, III, IIIa, IV and V. Motif I or KxDG is the active site where the covalent (lysyl)-N-GMP intermediate is formed. Both the NTase and OB domains undergo conformational changes that assist in the capping reaction.
Capping enzymes are found in the nucleus of eukaryotic cells. Depending on the organism, the capping enzyme is either a monofunctional or bifunctional polypeptide. The guanylyltransferases (Ceg1) of Saccharomyces cerevisiae is encoded by the CEG1 gene and is composed of 459 amino acids (53-kD). The RNA triphosphatase (Cet1) is a separate 549 amino acid polypeptide (80-kD), encoded by the CET1 gene. The human capping enzyme is an example of a bifunctional polypeptide, which has both triphosphatase (N-terminal) and guanylyltransferase (C-terminal) domains. The human mRNA guanylyltransferase domain of the capping enzyme is composed of seven helices and fifteen β strands that are grouped into three, five and seven strands, arranged as antiparallel β sheets. The enzyme structure has three sub-domains referred to hinge, base and lid. The GTP binding site is located between the hinge and base domain. The lid domain determines the conformation of the active site cleft, which consists of the GTP binding site, phosphoamide linking lysine and surrounding residues. The guanylyltransferase domain is linked to the triphosphatase domain via a 25 amino acid flexible loop structure. | 1 | Biochemistry |
Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective insecticides, although some are extremely toxic to humans, including sarin and VX nerve agents.
Phosphorus, like nitrogen, is in group 15 of the periodic table, and thus phosphorus compounds and nitrogen compounds have many similar properties. The definition of organophosphorus compounds is variable, which can lead to confusion. In industrial and environmental chemistry, an organophosphorus compound need contain only an organic substituent, but need not have a direct phosphorus-carbon (P-C) bond. Thus a large proportion of pesticides (e.g., malathion), are often included in this class of compounds.
Phosphorus can adopt a variety of oxidation states, and it is general to classify organophosphorus compounds based on their being derivatives of phosphorus(V) vs phosphorus(III), which are the predominant classes of compounds. In a descriptive but only intermittently used nomenclature, phosphorus compounds are identified by their coordination number σ and their valency λ. In this system, a phosphine is a σλ compound. | 0 | Organic Chemistry |
FAST (Fluorescence-Activating and absorption-Shifting Tag) is a small, genetically-encoded, protein tag which allows for fluorescence reporting of proteins of interest. Unlike natural fluorescent proteins and derivates such as GFP or mCherry, FAST is not fluorescent by itself. It can bind selectively a fluorogenic chromophore derived from 4-hydroxybenzylidene rhodanine (HBR), which is itself non fluorescent unless bound. Once bound, the pair of molecules goes through a unique fluorogen activation mechanism based on two spectroscopic changes, increase of fluorescence quantum yield and absorption red shift, hence providing high labeling selectivity. The FAST-fluorogen reporting system can be used in fluorescence microscopy, flow cytometry and any other fluorometric method to explore the living world: biosensors, protein trafficking.
FAST, a small 14 kDa protein, was engineered from the photoactive yellow protein (PYP) by directed evolution. It was reported for the first time in 2016 by researchers from Ecole normale supérieure de Paris.
__TOC__ | 1 | Biochemistry |
Tris(trimethylsilyl)methyl group is also a very bulky group that is often used to stabilize a multiple bond between heavy elements. By dropwise addition of to sodium napthelenide. P, H and C spectra all proved the formulation of this alkyl-group stabilized diphosphene. | 0 | Organic Chemistry |
The B Horizon has dark layer where minerals, organic matter and bases are being illuviated (washed in/accumulated). Below this is a red/orange layer of iron and aluminium sesquioxides deposit. Some bases remain in the soil, though others may be lost by throughflow. In many podsols, Iron Pans are created. This can cause water logging which may then saturate the A horizon leading to mottling or a gleyed podsol.
Also useful: soil chemistry | 9 | Geochemistry |
The Crick, Brenner et al. experiment (1961) was a scientific experiment performed by Francis Crick, Sydney Brenner, Leslie Barnett and R.J. Watts-Tobin.
It was a key experiment in the development of what is now known as molecular biology and led to a publication entitled "The General Nature of the Genetic Code for Proteins" and according to the historian of Science Horace Judson is "regarded...as a classic of intellectual clarity, precision and rigour". This study demonstrated that the genetic code is made up of a series of three base pair codons which code for individual amino acids. The experiment also elucidated the nature of gene expression and frame-shift mutations. | 1 | Biochemistry |
is used in the semiconductor industry in plasma etching of silicon oxide and silicon nitride. Known as R-23 or HFC-23, it was also a useful refrigerant, sometimes as a replacement for chlorotrifluoromethane (CFC-13) and is a byproduct of its manufacture.
When used as a fire suppressant, the fluoroform carries the DuPont trade name, FE-13. is recommended for this application because of its low toxicity, its low reactivity, and its high density. HFC-23 has been used in the past as a replacement for Halon 1301(CFC-13B1) in fire suppression systems as a total flooding gaseous fire suppression agent. | 2 | Environmental Chemistry |
Consider the force F(h) between two identical spheres of radius R as an illustration. The surfaces of the two respective spheres are thought to be sliced into infinitesimal disks of width dr and radius r as shown in the figure. The force is given by the sum of the corresponding swelling pressures between the two disks
where x is the distance between the disks and dA the area of one of these disks. This distance can be expressed as x=h+2y. By considering the Pythagorean theorem on the grey triangle shown in the figure one has
Expanding this expression and realizing that y ≪ R one finds that the area of the disk can be expressed as
The force can now be written as
where W(h) is the surface free energy per unit area introduced above. When introducing the equation above, the upper integration limit was replaced by infinity, which is approximately correct as long as h ≪ R. | 7 | Physical Chemistry |
Originally used with a different meaning, the term took its current definition after Lwoff and collaborators (1946). | 5 | Photochemistry |
The time evolution of a single electronic wave function in an atom, is described by the Schrödinger equation (in atomic units):
where the light-matter interaction Hamiltonian, , can be expressed in the length gauge, within the dipole approximation, as:
where is the Coulomb potential of the atomic species considered; are the momentum and position operator, respectively; and is the total electric field evaluated in the neighbor of the atom.
The formal solution of the Schrödinger equation is given by the propagator formalism:
where , is the electron wave function at time .
This exact solution cannot be used for almost any practical purpose.
However, it can be proved, using Dyson's equations that the previous solution can also be written as:
where,
is the bounded Hamiltonian and
is the interaction Hamiltonian.
The formal solution of Eq. , which previously was simply written as Eq. , can now be regarded in Eq. as a superposition of different quantum paths (or quantum trajectory), each one of them with a peculiar interaction time with the electric field.
In other words, each quantum path is characterized by three steps:
# An initial evolution without the electromagnetic field. This is described by the left-hand side term in the integral.
# Then, a "kick" from the electromagnetic field, that "excite" the electron. This event occurs at an arbitrary time that uni-vocally characterizes the quantum path .
#A final evolution driven by both the field and the Coulomb potential, given by .
In parallel, you also have a quantum path that do not perceive the field at all, this trajectory is indicated by the right-hand side term in Eq. .
This process is entirely time-reversible, i.e. can also occur in the opposite order.
Equation is not straightforward to handle. However, physicists use it as the starting point for numerical calculation, more advanced discussion or several approximations.
For strong-field interaction problems, where ionization may occur, one can imagine to project Eq. in a certain continuum state (unbounded state or free state) , of momentum , so that:
where <math>|c_{\textbf{p}}(t)|^2
, the electron in the continuum states .
If this probability amplitude is greater than zero, the electron is photoionized.
For the majority of application, the second term in is not considered, and only the first one is used in discussions, hence:
Equation is also known as time reversed S-matrix amplitude and it gives the probability of photoionization by a generic time-varying electric field. | 7 | Physical Chemistry |
Omar M. Yaghi and William A. Goddard III reported COFs as exceptional hydrogen storage materials. They predicted the highest excess H uptakes at 77 K are 10.0 wt % at 80 bar for COF-105, and 10.0 wt % at 100 bar for COF-108, which have higher surface area and free volume, by grand canonical Monte Carlo (GCMC) simulations as a function of temperature and pressure. This is the highest value reported for associative H storage of any material. Thus 3D COFs are most promising new candidates in the quest for practical H storage materials. In 2012, the lab of William A. Goddard III reported the uptake for COF102, COF103, and COF202 at 298 K and they also proposed new strategies to obtain higher interaction with H. Such strategy consists of metalating the COF with alkali metals such as Li. These complexes composed of Li, Na and K with benzene ligands (such as 1,3,5-benzenetribenzoate, the ligand used in MOF-177) have been synthesized by Krieck et al. and Goddard showed that the THF is important to their stability. If the metalation with alkali meals is performed in the COFs, Goddard et al. calculated that some COFs can reach 2010 DOE gravimetric target in delivery units at 298 K of 4.5 wt %: COF102-Li (5.16 wt %), COF103-Li (4.75 wt %), COF102-Na (4.75 wt %) and COF103-Na (4.72 wt %). COFs also perform better in delivery units than MOFs because the best volumetric performance is for COF102-Na (24.9), COF102-Li (23.8), COF103-Na (22.8), and COF103-Li (21.7), all using delivery g H/L units for 1–100 bar. These are the highest gravimetric molecular hydrogen uptakes for a porous material under these thermodynamic conditions. | 6 | Supramolecular Chemistry |
In chemistry, the capped octahedral molecular geometry describes the shape of compounds where seven atoms or groups of atoms or ligands are arranged around a central atom defining the vertices of a gyroelongated triangular pyramid. This shape has C symmetry and is one of the three common shapes for heptacoordinate transition metal complexes, along with the pentagonal bipyramid and the capped trigonal prism.
Examples of the capped octahedral molecular geometry are the heptafluoromolybdate () and the heptafluorotungstate () ions.
The "distorted octahedral geometry" exhibited by some AXE molecules such as xenon hexafluoride (XeF) is a variant of this geometry, with the lone pair occupying the "cap" position. | 4 | Stereochemistry |
The Fas receptor, also known as Fas, FasR, apoptosis antigen 1 (APO-1 or APT), cluster of differentiation 95 (CD95) or tumor necrosis factor receptor superfamily member 6 (TNFRSF6), is a protein that in humans is encoded by the FAS gene. Fas was first identified using a monoclonal antibody generated by immunizing mice with the FS-7 cell line. Thus, the name Fas is derived from FS-7-associated surface antigen.
The Fas receptor is a death receptor on the surface of cells that leads to programmed cell death (apoptosis) if it binds its ligand, Fas ligand (FasL). It is one of two apoptosis pathways, the other being the mitochondrial pathway. | 1 | Biochemistry |
A partial extraction procedure was developed in 1935 which involved reacting the compound with benzoyl chloride to allow it to be separated from the water-soluble components. The compound was first isolated and purified to crystals by Osamu Shimomura. The structure of the compound was confirmed some years later. Feeding experiments suggest that the compound is synthesized in the animal from three amino-acids: tryptophan, isoleucine, and arginine. | 1 | Biochemistry |
The Food and Drug Administration (FDA) classifies tanning beds as "moderate risk" devices (changed in 2014 from "low risk"). It requires that devices carry a black box warning that they should not be used by individuals under the age of 18, but it has not banned their use by minors. , California, Delaware, the District of Columbia, Hawaii, Illinois, Kansas, Louisiana, Massachusetts, Minnesota, Nevada, New Hampshire, North Carolina, Oregon, Texas, Vermont and Washington have banned the use of tanning beds for minors under the age of 18. Other states strictly regulate indoor tanning under the age of 18, with most banning indoor tanning for persons under the age of 14 unless medically required, and some requiring the consent of a guardian for those aged 14–17. In 2010 under the Affordable Care Act, a 10% "tanning tax" was introduced, which is added to the fees charged by tanning facilities; it was expected to raise $2.7 billion for health care over ten years.
Tanning beds are regulated in the United States by the federal governments Code of Federal Regulations (21 CFR 1040.20). This is designed to ensure that the devices adhere to a set of safety rules, with the primary focus on sunbed and lamp manufacturers regarding maximum exposure times and product equivalence. Additionally, must have a "Recommended Exposure Schedule" posted on both the front of the tanning bed and in the owners manual, and list the original lamp that was certified for that particular tanning bed. Salon owners are required to replace the lamps with either exactly the same lamp, or a lamp that is certified by the lamp manufacturer to be.
States control regulations for salons, regarding operator training, sanitization of sunbeds and eyewear, and additional warning signs. Many states also ban or regulate the use of tanning beds by minors under the age of 18.
American osteopathic physician Joseph Mercola was prosecuted in 2016 by the Federal Trade Commission (FTC) for selling tanning beds to "reverse your wrinkles" and "slash your risk of cancer". The settlement meant that consumers who had purchased the devices were eligible for refunds totalling $5.3 million. Mercola had falsely claimed that the FDA "endorsed indoor tanning devices as safe", and had failed to disclose that he had paid the Vitamin D Council for its endorsement of his devices. The FTC said that it was deceptive for the defendants to fail to disclose that tanning is not necessary to produce vitamin D. | 5 | Photochemistry |
Hydrodimerization is an organic reaction that couples two alkenes to give a symmetrical hydrocarbon. The reaction is often implemented electrochemically; in that case the reaction is called electrodimerization. The reaction can also be induced with samarium diiodide, a one-electron reductant.
Hydrodimerization is the basis of the Monsanto adiponitrile synthesis:
:2CH=CHCN + 2e + 2H → NCCHCHCHCHCN
The reaction applies to a number electrophilic alkenes (Michael acceptors). | 7 | Physical Chemistry |
Janet Jones was once married to Robert Osteryoung, who was also an award-winning chemist. In April 2010, she married Chris Cobb in Washington, D.C. Together, Jones and Cobb established the Comis Foundation, a family philanthropic foundation to benefit children and youth. | 3 | Analytical Chemistry |
For example, a commonly used reaction to profile hydrogen with an energetic N ion beam is
:N + H → C + α + γ (4.43 MeV)
with a sharp resonance in the reaction cross section at 6.385 MeV of only 1.8 keV. Since the incident N ion loses energy along its trajectory in the material it must have an energy higher than the resonance energy to induce the nuclear reaction with hydrogen nuclei deeper in the target.
This reaction is usually written H(N,αγ)C. It is inelastic because the Q-value is not zero (in this case it is 4.965 MeV). Rutherford backscattering (RBS) reactions are elastic (Q = 0), and the interaction (scattering) cross-section σ given by the famous formula derived by Lord Rutherford in 1911. But non-Rutherford cross-sections (so-called EBS, elastic backscattering spectrometry) can also be resonant: for example, the O(α,α)O reaction has a strong and very useful resonance at 3038.1 ± 1.3 keV.
In the H(N,αγ)C reaction (or indeed the N(p,αγ)C inverse reaction), the energetic emitted γ ray is characteristic of the reaction and the number that are detected at any incident energy is proportional to the hydrogen concentration at the respective depth in the sample. Due to the narrow peak in the reaction cross section primarily ions of the resonance energy undergo a nuclear reaction. Thus, information on the hydrogen distribution can be straight forward obtained by varying the N incident beam energy.
Hydrogen is an element inaccessible to Rutherford backscattering spectrometry since nothing can backscatter from H (since all atoms are heavier than hydrogen!). But it is often analysed by elastic recoil detection. | 7 | Physical Chemistry |
The following is an overview of each cycle in the optical sequencing process.
Step 1: DNA barcoding<br />
Cells are lysed to release genomic DNA. These DNA molecules are untangled, placed onto optical mapping surface containing microfluidic channels and the DNA is allowed to flow through the channels. These molecules are then barcoded by restriction enzymes to allow for genomic localization through the technique of optical mapping. See the above section on "Technology" for those steps.
Step 2: Template nicking<br />
DNase I is added to randomly nick the mounted DNA molecules. A wash is then performed to remove the DNase I. The mean number of nicks that occur per template is dependent on the concentration of DNase I as well as the incubation time.
Step 3: Gap formation<br />
T7 exonuclease is added which uses the nicks in the DNA molecules to expand the gaps in a 5–3 direction. Amount of T7 exonuclease must be carefully controlled to avoid overly high levels of double-stranded breaks.
Step 4: Fluorochrome incorporation<br />
DNA polymerase is used to incorporate fluorochrome-labelled nucleotides (FdNTPs) into the multiple gapped sites along each DNA molecule. During each cycle, the reaction mixture contains a single type of FdNTP and allows for multiple additions of that nucleotide type. Various washes are then performed to remove unincorporated fdNTPs in preparation for imaging and the next cycle of FdNTP addition.
Step 5: Imaging<br />
This step counts the number of incorporated fluorochrome-labeled nucleotides at the gap regions using fluorescence microscopy.
Step 6: Photobleaching<br />
The laser illumination that is used to excite the fluorochrome is also used here to destroy the fluorochrome signal. This essentially resets the fluorochrome counter, and prepares the counter for the next cycle. This step is a unique aspect of optical sequencing as it does not actually remove the fluorochrome label of the nucleotide after its incorporation. not removing the fluorochrome label makes sequencing more economical, but it results in the need to incorporate fluorochrome labels consecutively which can result in problems due to the bulkiness of the labels.
Step 7: Repeat steps 4–6<br />
Steps 4-6 are repeated with step 4 using a reaction mixture that contains a different fluorochrome-labeled nucleotide (FdNTP) each time. This is repeated until the desired region is sequenced. | 1 | Biochemistry |
X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy for complete structural analysis of complex glycans is a difficult and complex field. However, the structure of the binding site of numerous lectins, enzymes and other carbohydrate-binding proteins has revealed a wide variety of the structural basis for glycome function. The purity of test samples have been obtained through chromatography (affinity chromatography etc.) and analytical electrophoresis (PAGE (polyacrylamide electrophoresis), capillary electrophoresis, affinity electrophoresis, etc.). | 0 | Organic Chemistry |
Butyrate has numerous effects on energy homeostasis and related diseases (diabetes and obesity), inflammation, and immune function (e.g., it has pronounced antimicrobial and anticarcinogenic effects) in humans. These effects occur through its metabolism by mitochondria to generate during fatty acid metabolism or through one or more of its histone-modifying enzyme targets (i.e., the class I histone deacetylases) and G-protein coupled receptor targets (i.e., FFAR2, FFAR3, and Hydroxycarboxylic acid receptor 2|). | 1 | Biochemistry |
Ligands of proteins can be characterized also by the number of protein chains they bind. "Monodesmic" ligands (μόνος: single, δεσμός: binding) are ligands that bind a single protein chain, while "polydesmic" ligands (πολοί: many) are frequent in protein complexes, and are ligands that bind more than one protein chain, typically in or near protein interfaces. Recent research shows that the type of ligands and binding site structure has profound consequences for the evolution, function, allostery and folding of protein compexes. | 1 | Biochemistry |
Thermodynamic potentials are different quantitative measures of the stored energy in a system. Potentials are used to measure the energy changes in systems as they evolve from an initial state to a final state. The potential used depends on the constraints of the system, such as constant temperature or pressure. For example, the Helmholtz and Gibbs energies are the energies available in a system to do useful work when the temperature and volume or the pressure and temperature are fixed, respectively.
The five most well known potentials are:
where is the temperature, the entropy, the pressure, the volume, the chemical potential, the number of particles in the system, and is the count of particles types in the system.
Thermodynamic potentials can be derived from the energy balance equation applied to a thermodynamic system. Other thermodynamic potentials can also be obtained through Legendre transformation. | 7 | Physical Chemistry |
WAC protein domain - Western blot - Wfdc15a - WHEP-TRS protein domain - WIF domain - wildtype - wobble position - Wolfram syndrome - WWE protein domain - | 1 | Biochemistry |
The name γ-glutamyltransferase is preferred by the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology. The Expert Panel on Enzymes of the International Federation of Clinical Chemistry also used this name. The older name is gamma-glutamyl transpeptidase (GGTP). | 1 | Biochemistry |
LAAM was approved in 1993 by the U.S. Food and Drug Administration for use in the treatment of opioid dependence. In 2001, LAAM was removed from the European market due to reports of life-threatening ventricular rhythm disorders. In 2003, Roxane Laboratories, Inc. discontinued Orlaam in the US. | 4 | Stereochemistry |
El-Shall was the first to apply the Resonant Enhanced Multiphoton Ionization (REMPI) technique to selectively generate molecular ions within supersaturated host vapors and study the phenomena of ion-induced nucleation on well-defined ions. He also focused his study on the formation mechanisms of gold–zinc oxide hexagonal nanopyramids through heterogeneous nucleation using microwave synthesis. In 2018, he demonstrated nucleation and growth process of gold nanoparticles initiated by nanosecond and femtosecond laser irradiation of aqueous solutions of [AuCl4]−. | 7 | Physical Chemistry |
Researchers at the Université de Montréal are working with Photon etc. and Optina Diagnostics to test the use of hyperspectral photography in the diagnosis of retinopathy and macular edema before damage to the eye occurs. The metabolic hyperspectral camera will detect a drop in oxygen consumption in the retina, which indicates potential disease. An ophthalmologist will then be able to treat the retina with injections to prevent any potential damage. | 7 | Physical Chemistry |
Hard solders are used for brazing, and melt at higher temperatures. Alloys of copper with either zinc or silver are the most common.
In silversmithing or jewelry making, special hard solders are used that will pass assay. They contain a high proportion of the metal being soldered and lead is not used in these alloys. These solders vary in hardness, designated as "enameling", "hard", "medium" and "easy". Enameling solder has a high melting point, close to that of the material itself, to prevent the joint desoldering during firing in the enameling process. The remaining solder types are used in decreasing order of hardness during the process of making an item, to prevent a previously soldered seam or joint desoldering while additional sites are soldered. Easy solder is also often used for repair work for the same reason. Flux is also used to prevent joints from desoldering.
Silver solder is also used in manufacturing to join metal parts that cannot be welded. The alloys used for these purposes contain a high proportion of silver (up to 40%), and may also contain cadmium. | 8 | Metallurgy |
A quantum heat engine is a device that generates power from the heat flow between hot and cold reservoirs.
The operation mechanism of the engine can be described by the laws of quantum mechanics.
The first realization of a quantum heat engine was pointed out by Scovil and Schulz-DuBois in 1959, showing the connection of efficiency of the Carnot engine and the 3-level maser.
Quantum refrigerators share the structure of quantum heat engines with the purpose of pumping heat from a cold to a hot bath consuming power
first suggested by Geusic, Schulz-DuBois, De Grasse and Scovil. When the power is supplied by a laser the process is termed optical pumping or laser cooling, suggested by Wineland and Hänsch.
Surprisingly heat engines and refrigerators can operate up to the scale of a single particle thus justifying the need for a quantum theory termed quantum thermodynamics. | 7 | Physical Chemistry |
Upon irradiation with UV light, diazirines form reactive carbene species. The carbene may exist in the singlet form, in which the two free electrons occupy the same orbital, or the triplet form, with two unpaired electrons in different orbitals. | 5 | Photochemistry |
Amino acids contain both amino and carboxylic acid functional groups. (In biochemistry, the term amino acid is used when referring to those amino acids in which the amino and carboxylate functionalities are attached to the same carbon, plus proline which is not actually an amino acid).
Modified amino acids are sometimes observed in proteins; this is usually the result of enzymatic modification after translation (protein synthesis). For example, phosphorylation of serine by kinases and dephosphorylation by phosphatases is an important control mechanism in the cell cycle. Only two amino acids other than the standard twenty are known to be incorporated into proteins during translation, in certain organisms:
* Selenocysteine is incorporated into some proteins at a UGA codon, which is normally a stop codon.
* Pyrrolysine is incorporated into some proteins at a UAG codon. For instance, in some methanogens in enzymes that are used to produce methane.
Besides those used in protein synthesis, other biologically important amino acids include carnitine (used in lipid transport within a cell), ornithine, GABA and taurine. | 0 | Organic Chemistry |
Oxyhemoglobin is formed during physiological respiration when oxygen binds to the heme component of the protein hemoglobin in red blood cells. This process occurs in the pulmonary capillaries adjacent to the alveoli of the lungs. The oxygen then travels through the blood stream to be dropped off at cells where it is utilized as a terminal electron acceptor in the production of ATP by the process of oxidative phosphorylation. It does not, however, help to counteract a decrease in blood pH. Ventilation, or breathing, may reverse this condition by removal of carbon dioxide, thus causing a shift up in pH.
Hemoglobin exists in two forms, a taut (tense) form (T) and a relaxed form (R). Various factors such as low pH, high CO and high 2,3 BPG at the level of the tissues favor the taut form, which has low oxygen affinity and releases oxygen in the tissues. Conversely, a high pH, low CO, or low 2,3 BPG favors the relaxed form, which can better bind oxygen. The partial pressure of the system also affects O affinity where, at high partial pressures of oxygen (such as those present in the alveoli), the relaxed (high affinity, R) state is favoured. Inversely, at low partial pressures (such as those present in respiring tissues), the (low affinity, T) tense state is favoured. Additionally, the binding of oxygen to the iron(II) heme pulls the iron into the plane of the porphyrin ring, causing a slight conformational shift. The shift encourages oxygen to bind to the three remaining heme units within hemoglobin (thus, oxygen binding is cooperative).
Classically, the iron in oxyhemoglobin is seen as existing in the iron(II) oxidation state. However, the complex of oxygen with heme iron is diamagnetic, whereas both oxygen and high-spin iron(II) are paramagnetic. Experimental evidence strongly suggests heme iron is in the iron(III) oxidation state in oxyhemoglobin, with the oxygen existing as superoxide anion (O) or in a covalent charge-transfer complex. | 7 | Physical Chemistry |
The acidity of tellurols can be inferred by the acidity and dissociation constant of hydrogen telluride, , which has a (first) pK of 2.64 corresponding to a dissociation constant of 2.3 × 10. has a lower pK and higher dissociation constant than and . The pKa is 9.3 for vs 10.8 for .
The absence of hydrogen-bonding explains the low boiling temperature of tellurols. | 0 | Organic Chemistry |
A cDNA library is a collection of expressed DNA genes that are seen as a useful reference tool in gene identification and cloning processes. cDNA libraries are constructed from mRNA using RNA-dependent DNA polymerase reverse transcriptase (RT), which transcribes an mRNA template into DNA. Therefore, a cDNA library can only contain inserts that are meant to be transcribed into mRNA. This process relies on the principle of DNA/RNA complementarity. The end product of the libraries is double stranded DNA, which may be inserted into plasmids. Hence, cDNA libraries are a powerful tool in modern research. | 1 | Biochemistry |
Dielectric constant is the most important factor in determining the occurrence of ion association. A table of some typical values can be found under dielectric constant.
Water has a relatively high dielectric constant value of 78.7 at 298K (25 °C), so in aqueous solutions at ambient temperatures 1:1 electrolytes such as NaCl do not form ion pairs to an appreciable extent except when the solution is very concentrated. 2:2 electrolytes (q = 2, q = 2) form ion pairs more readily. Indeed, the solvent-shared ion pair [Mg(HO)]SO was famously discovered to be present in seawater, in equilibrium with the contact ion pair [Mg(HO)(SO)] Trivalent ions such as Al, Fe and lanthanide ions form weak complexes with monovalent anions.
The dielectric constant of water decreases with increasing temperature to about 55 at 100 °C and about 5 at the critical temperature (217.7 °C). Thus ion pairing will become more significant in superheated water.
Solvents with a dielectric constant in the range, roughly, 20–40, show extensive ion-pair formation. For example, in acetonitrile both contact and solvent-shared ion pairs of Li(NCS) have been observed. In methanol the 2:1 electrolyte Mg(NCS) is partially dissociated into a contact ion pair, [Mg(NCS)] and the thiocyanate ion.
The dielectric constant of liquid ammonia decreases from 26 at its freezing point (−80 °C) to 17 at 20 °C (under pressure). Many simple 1:1 electrolytes form contact ion pairs at ambient temperatures. The extent of ion pairing decreases as temperature decreases. With lithium salts there is evidence to show that both inner-sphere and outer-sphere complexes exist in liquid-ammonia solutions.
Of the solvents with dielectric constant of 10 or less, tetrahydrofuran (THF) is particularly relevant in this context, as it solvates cations strongly with the result that simple electrolytes have sufficient solubility to make the study of ion association possible. In this solvent ion association is the rule rather than the exception. Indeed, higher associates such as tetramers are often formed. Triple cations and triple anions have also been characterized in THF solutions.
Ion association is an important factor in phase-transfer catalysis, since a species such as RPCl is formally neutral and so can dissolve easily in a non-polar solvent of low dielectric constant. In this case it also helps that the surface of the cation is hydrophobic.
In S1 reactions the carbocation intermediate may form an ion pair with an anion, particularly in solvents of low dielectric constant, such as diethylether. This can affect both the kinetic parameters of the reaction and the stereochemistry of the reaction products. | 7 | Physical Chemistry |
First studied in 2010 via this method, a recent investigation used SRCD to examine the differences in structure in solution and when at the oil-water interface, of peptides derived from seaweed, bacteria and potatoes as potential emulsifying agents. Of these studied, the peptide from bacteria proved to be the most effective at being both an emulsifying agent and stabilising antioxidant compound. | 7 | Physical Chemistry |
Alastair Ian Scott married Elizabeth Wilson Walters at the University of Glasgow Memorial Chapel, on 4 March 1950. They had two children: Anne and William.
Alastair died in Texas on 18 April 2007, following a heart attack. He was survived by his wife, two children and six grandchildren.
Elizabeth died at her home in Grapevine on 13 September 2016, aged 89. | 0 | Organic Chemistry |
Tacticity describes the relative stereochemistry of chiral centers in neighboring structural units within a macromolecule. There are three types of tacticity: isotactic (all substituents on the same side), atactic (random placement of substituents), and syndiotactic (alternating placement of substituents). | 7 | Physical Chemistry |
The selectivity of an ion-exchange membrane is due to Donnan equilibrium and not due to physically blocking or electrostatically excluding specific charged species.
The selectivity to the transport of ions of opposite charges is called its permselectivity. | 3 | Analytical Chemistry |
Protein degradation may take place intracellularly or extracellularly. In digestion of food, digestive enzymes may be released into the environment for extracellular digestion whereby proteolytic cleavage breaks proteins into smaller peptides and amino acids so that they may be absorbed and used. In animals the food may be processed extracellularly in specialized organs or guts, but in many bacteria the food may be internalized via phagocytosis. Microbial degradation of protein in the environment can be regulated by nutrient availability. For example, limitation for major elements in proteins (carbon, nitrogen, and sulfur) induces proteolytic activity in the fungus Neurospora crassa as well as in of soil organism communities.
Proteins in cells are broken into amino acids. This intracellular degradation of protein serves multiple functions: It removes damaged and abnormal proteins and prevents their accumulation. It also serves to regulate cellular processes by removing enzymes and regulatory proteins that are no longer needed. The amino acids may then be reused for protein synthesis. | 1 | Biochemistry |
The induction of NMDA receptor-dependent long-term potentiation (LTP) in chemical synapses in the brain occurs via a fairly straightforward mechanism. A substantial and rapid rise in calcium ion concentration inside the postsynaptic cell (or more specifically, within the dendritic spine) is most possibly all that is required to induce LTP. But the mechanism of calcium delivery to the postsynaptic cell in inducing LTP is more complicated. | 1 | Biochemistry |
One of the best studied graphite intercalation compounds, , is prepared by melting potassium over graphite powder. The potassium is absorbed into the graphite and the material changes color from black to bronze. The resulting solid is pyrophoric. The composition is explained by assuming that the potassium to potassium distance is twice the distance between hexagons in the carbon framework. The bond between anionic graphite layers and potassium cations is ionic. The electrical conductivity of the material is greater than that of α-graphite. is a superconductor with a very low critical temperature T = 0.14 K. Heating leads to the formation of a series of decomposition products as the K atoms are eliminated:
Via the intermediates (blue in color), , , ultimately the compound results.
The stoichiometry is observed for M = K, Rb and Cs. For smaller ions M = , , , , , and , the limiting stoichiometry is . Calcium graphite is obtained by immersing highly oriented pyrolytic graphite in liquid Li–Ca alloy for 10 days at 350 °C. The crystal structure of belongs to the Rm space group. The graphite interlayer distance increases upon Ca intercalation from 3.35 to 4.524 Å, and the carbon-carbon distance increases from 1.42 to 1.444 Å.
With barium and ammonia, the cations are solvated, giving the stoichiometry ((stage 1)) or those with caesium, hydrogen and potassium ((stage 1)).
In situ adsorption on free-standing graphene and intercalation in bilayer graphene of the alkali metals K, Cs, and Li was observed by means of low-energy electron microscopy.
Different from other alkali metals, the amount of Na intercalation is very small. Quantum-mechanical calculations show that this originates from a quite general phenomenon: among the alkali and alkaline earth metals, Na and Mg generally have the weakest chemical binding to a given substrate, compared with the other elements in the same group of the periodic table. The phenomenon arises from the competition between trends in the ionization energy and the ion–substrate coupling, down the columns of the periodic table. However, considerable Na intercalation into graphite can occur in cases when the ion is wrapped in a solvent shell through the process of co-intercalation. A complex magnesium(I) species has also been intercalated into graphite. | 6 | Supramolecular Chemistry |
Phred quality scores are used for assessment of sequence quality, recognition and removal of low-quality sequence (end clipping), and determination of accurate consensus sequences.
Originally, Phred quality scores were primarily used by the sequence assembly program Phrap. Phrap was routinely used in some of the largest sequencing projects in the Human Genome Sequencing Project and is currently one of the most widely used DNA sequence assembly programs in the biotech industry. Phrap uses Phred quality scores to determine highly accurate consensus sequences and to estimate the quality of the consensus sequences. Phrap also uses Phred quality scores to estimate whether discrepancies between two overlapping sequences are more likely to arise from random errors, or from different copies of a repeated sequence.
Within the Human Genome Project, the most important use of Phred quality scores was for automatic determination of consensus sequences. Before Phred and Phrap, scientists had to carefully look at discrepancies between overlapping DNA fragments; often, this involved manual determination of the highest-quality sequence, and manual editing of any errors. Phrap's use of Phred quality scores effectively automated finding the highest-quality consensus sequence; in most cases, this completely circumvents the need for any manual editing. As a result, the estimated error rate in assemblies that were created automatically with Phred and Phrap is typically substantially lower than the error rate of manually edited sequence.
In 2009, many commonly used software packages make use of Phred quality scores, albeit to a different extent. Programs like Sequencher use quality scores for display, end clipping, and consensus determination; other programs like CodonCode Aligner also implement quality-based consensus methods. | 1 | Biochemistry |
Several components of the signaling cascade that mediates the HMB-induced increase in human skeletal muscle protein synthesis have been identified in vivo. Similar to HMBs metabolic precursor, , HMB has been shown to increase protein synthesis in human skeletal muscle via phosphorylation of the mechanistic target of rapamycin (mTOR) and subsequent activation of , which leads to protein biosynthesis in cellular ribosomes via phosphorylation of mTORC1s immediate targets (i.e., the p70S6 kinase and the translation repressor protein 4EBP1). Supplementation with HMB in several non-human animal species has been shown to increase the serum concentration of growth hormone and insulin-like growth factor 1 (IGF-1) via an unknown mechanism, in turn promoting protein synthesis through increased mTOR phosphorylation. Based upon limited clinical evidence in humans, supplemental HMB appears to increase the secretion of growth hormone and IGF-1 in response to resistance exercise.
, the signaling cascade that mediates the HMB-induced reduction in muscle protein breakdown has not been identified in living humans, although it is well-established that it attenuates proteolysis in humans in vivo. Unlike , HMB attenuates muscle protein breakdown in an insulin-independent manner in humans. HMB is believed to reduce muscle protein breakdown in humans by inhibiting the 19S and 20S subunits of the ubiquitin–proteasome system in skeletal muscle and by inhibiting apoptosis of skeletal muscle nuclei via unidentified mechanisms.
Based upon animal studies, HMB appears to be metabolized within skeletal muscle into cholesterol, which may then be incorporated into the muscle cell membrane, thereby enhancing membrane integrity and function. The effects of HMB on muscle protein metabolism may help stabilize muscle cell structure. One review suggested that the observed HMB-induced reduction in the plasma concentration of muscle damage biomarkers (i.e., muscle enzymes such as creatine kinase and lactate dehydrogenase) in humans following intense exercise may be due to a cholesterol-mediated improvement in muscle cell membrane function.
HMB has been shown to stimulate the proliferation, differentiation, and fusion of human myosatellite cells in vitro, which potentially increases the regenerative capacity of skeletal muscle, by increasing the protein expression of certain myogenic regulatory factors (e.g., myoD and myogenin) and gene transcription factors (e.g., MEF2). HMB-induced human myosatellite cell proliferation in vitro is mediated through the phosphorylation of the mitogen-activated protein kinases ERK1 and ERK2. HMB-induced human myosatellite differentiation and accelerated fusion of myosatellite cells into muscle tissue in vitro is mediated through the phosphorylation of Akt, a serine/threonine-specific protein kinase. | 1 | Biochemistry |
Aromatic compounds play key roles in the biochemistry of all living things. The four aromatic amino acids histidine, phenylalanine, tryptophan, and tyrosine each serve as one of the 20 basic building-blocks of proteins. Further, all 5 nucleotides (adenine, thymine, cytosine, guanine, and uracil) that make up the sequence of the genetic code in DNA and RNA are aromatic purines or pyrimidines. The molecule heme contains an aromatic system with 22 π electrons. Chlorophyll also has a similar aromatic system.
Aromatic compounds are important in industry. Key aromatic hydrocarbons of commercial interest are benzene, toluene, ortho-xylene and para-xylene. About 35 million tonnes are produced worldwide every year. They are extracted from complex mixtures obtained by the refining of oil or by distillation of coal tar, and are used to produce a range of important chemicals and polymers, including styrene, phenol, aniline, polyester and nylon. | 7 | Physical Chemistry |
The dissociation rate in chemistry, biochemistry, and pharmacology is the rate or speed at which a ligand dissociates from a protein, for instance, a receptor. It is an important factor in the binding affinity and intrinsic activity (efficacy) of a ligand at a receptor. The dissociation rate for a particular substrate can be applied to enzyme kinetics, including the Michaelis-Menten model. Substrate dissociation rate contributes to how large or small the enzyme velocity will be. In the Michaelis-Menten model, the enzyme binds to the substrate yielding an enzyme substrate complex, which can either go backwards by dissociating or go forward by forming a product. The dissociation rate constant is defined using K.
The Michaelis-Menten constant is denoted by K and is represented by the equation K= (K + K)/ K. The rates that the enzyme binds and dissociates from the substrate are represented by K and K respectively. K is also defined as the substrate concentration at which enzymatic velocity reaches half of its maximal rate. The tighter a ligand binds to a substrate, the lower the dissociation rate will be. K and K are proportional, thus at higher levels of dissociation, the Michaelis-Menten constant will be larger. | 7 | Physical Chemistry |
Being a major hotspots of biodiversity, coral reefs are very important to the ecosystem and livelihood of marine and human life. Countries around the world depend on reefs as a source of food and income, especially for civilizations that inhabit small islands. With over a 60% decrease in available fishing around coral reefs, many countries, will be forced to adapt. Coral Reefs are also important for a countries economy, as reefs provide various forms of tourist activities, that can generate a lot of revenue for the economy. These can also contribute to individual levels of wellness, as the owners of these business, profit off of increased visitation and usage. Coral Reefs also provide, a form of coastal infrastructure, that acts as a barrier between us a major ocean catastrophes, such as tsunamis and coastal storms. | 9 | Geochemistry |
A growing number of ligands that can be used to activate RASSLs / DREADDs are commercially available.
CNO is the prototypical DREADD activator. CNO activates the excitatory Gq- coupled DREADDs: hM3Dq, hM1Dq and hM5Dq and also the inhibitory hM4Di and hM2Di G-coupled DREADDs. CNO also activates the G-coupled DREADD (GsD) and the β-arrestin preferring DREADD: rM3Darr (Rq(R165L).
Recent findings suggest that systemically administered CNO does not readily cross the blood-brain-barrier in vivo and converts to clozapine which itself activates DREADDs. Clozapine is an atypical antipsychotic which has been indicated to show high DREADD affinity and potency. Subthreshold injections of clozapine itself can be utilised to induce preferential DREADD-mediated behaviors. Therefore, when using CNO, care must be taken in experimental design and proper controls should be incorporated.
DREADD agonist 21, also known as Compound 21, represents an alternative agonist for muscarinic-based DREADDs and an alternative to CNO. It has been reported that Compound 21 has excellent bioavailability, pharmacokinetic properties and brain penetrability and does not undergo reverse metabolism to clozapine. Another known agonist is perlapine, a hypnotic drug approved for treating insomnia in Japan. It acts as an activator of G-, G-, and G DREADDs that has structural similarity to CNO. A more recent agonist of hM3Dq and hM4Di is deschloroclozapine (DCZ).
On the other hand, SalB B is a potent and selective activator of KORD.
JHU37160 and JHU37152 have been marketed commercially as novel DREADD ligands, active in vivo, with high potency and affinity for hM3Dq and hM4Di DREADDs.
Diihydrochloride salts of DREADDs ligands that are water-soluble (but with differing stabilities in solution) have also been commercially developed (see for aqueous stability). | 1 | Biochemistry |
In mathematics, a stereographic projection is a perspective projection of the sphere, through a specific point on the sphere (the pole or center of projection), onto a plane (the projection plane) perpendicular to the diameter through the point. It is a smooth, bijective function from the entire sphere except the center of projection to the entire plane. It maps circles on the sphere to circles or lines on the plane, and is conformal, meaning that it preserves angles at which curves meet and thus locally approximately preserves shapes. It is neither isometric (distance preserving) nor equiareal (area preserving).
The stereographic projection gives a way to represent a sphere by a plane. The metric induced by the inverse stereographic projection from the plane to the sphere defines a geodesic distance between points in the plane equal to the spherical distance between the spherical points they represent. A two-dimensional coordinate system on the stereographic plane is an alternative setting for spherical analytic geometry instead of spherical polar coordinates or three-dimensional cartesian coordinates. This is the spherical analog of the Poincaré disk model of the hyperbolic plane.
Intuitively, the stereographic projection is a way of picturing the sphere as the plane, with some inevitable compromises. Because the sphere and the plane appear in many areas of mathematics and its applications, so does the stereographic projection; it finds use in diverse fields including complex analysis, cartography (see stereographic map projection), geology, and photography. Sometimes stereographic computations are done graphically using a special kind of graph paper called a stereographic net, shortened to stereonet, or Wulff net. | 3 | Analytical Chemistry |
In normal usage, the rate-limiting step or rate-determining step is defined as the slowest step of a chemical reaction that determines the speed (rate) at which the overall reaction proceeds. The flux control coefficients do not measure this kind of rate-limitingness. For example, in a linear chain of reactions at steady-state, all steps carry the same flux. That is, there is no slow or fast step with respect to the rate or speed of a reaction. The flux control coefficient, instead, measures how much influence a given step has on the steady-state flux. A step with a high flux control coefficient means that changing the activity of the step (by changing the expression level of the enzyme) will have a large effect on the steady-state flux through the pathway and vice versa.
Historically the concept of the rate-limiting steps was also related to the notion of the master step. However, this drew much criticism due to a misunderstanding of the concept of the steady-state. | 1 | Biochemistry |
Organic halides, extractable organic halides (EOX), and total organic halides (TOX) are related content for this topic. EOX provides information on how halides can be extracted using a solvent while TOX provides information about the total organic halide content in the sample. This value can be used to estimate biochemical oxygen demand (BOD) or chemical oxygen demand (COD), a key factor in estimating the required oxygen to burn the organic compounds to estimate the percentage of AOX’s and Extractable organic halides. | 2 | Environmental Chemistry |
Strong bases catalyze hydroamination, an example being the ethylation of piperidine using ethene:
Such base catalyzed reactions proceed well with ethene but higher alkenes are less reactive. | 0 | Organic Chemistry |
In August 1997, the plant was included in the list of enterprises of strategic importance for the economy and security of Ukraine.
In 1998, for the first time, the plant was certified as a manufacturer of steel and semi-finished products from it (slabs and open-hearth ingots from carbon and carbon-manganese steel grades of normal and increased strength) according to the rules of the English Lloyd's Register.
In August 2002, on the basis of the blast-furnace and open-hearth shops of the Donetsk Metallurgical Plant, the Donetskstal Metallurgical Plant PJSC was established. The company specializes in the production of:
* foundry and pig iron
* more than 100 varieties of carbon, structural, low-alloyed, alloyed ordinary quality, high-quality and high-quality steel grades
* church bells made of non-ferrous high-quality alloy
* steel electric-welded longitudinal pipes and metal furniture frames
* slag-forming mixtures, granulated slag and building materials
Slabs made of normal strength marine structural steel grades GL-A and GL-B are certified according to the rules of Deutsche Lloyd.
In 2003, the church of St. Ignatius of Mariupol was built on the territory of the plant.
The plant completed 2013 with a net profit of UAH 83.322 million. | 8 | Metallurgy |
The ASTM D5511-12 and ASTM D5526-12 are testing methods that comply with international standards such as the ISO DIS 15985 for the biodegradability of plastic. | 7 | Physical Chemistry |
Samarium–neodymium is an isotope system which can be utilised to provide a date as well as isotopic fingerprints of geological materials, and various other materials including archaeological finds (pots, ceramics).
Sm decays to produce Nd with a half life of 1.06x10 years.
Dating is achieved usually by trying to produce an isochron of several minerals within a rock specimen. The initial Nd/Nd ratio is determined.
This initial ratio is modelled relative to CHUR (the Chondritic Uniform Reservoir), which is an approximation of the chondritic material which formed the solar system. CHUR was determined by analysing chondrite and achondrite meteorites.
The difference in the ratio of the sample relative to CHUR can give information on a model age of extraction from the mantle (for which an assumed evolution has been calculated relative to CHUR) and to whether this was extracted from a granitic source (depleted in radiogenic Nd), the mantle, or an enriched source. | 9 | Geochemistry |
The most common case is case (a) in which is electrostatically coupled to the internuclear axis, and is coupled to by spin-orbit coupling. Then both and have well-defined axial components, and respectively. As they are written with the same Greek symbol, the spin component should not be confused with states, which are states with orbital angular component equal to zero. defines a vector of magnitude pointing along the internuclear axis. Combined with the rotational angular momentum of the nuclei , we have . In this case, the precession of and around the nuclear axis is assumed to be much faster than the nutation of and around .
The good quantum numbers in case (a) are , , , and . However is not a good quantum number because the vector is strongly coupled to the electrostatic field and therefore precesses rapidly around the internuclear axis with an undefined magnitude. We express the rotational energy operator as , where is a rotational constant. There are, ideally, fine-structure states, each with rotational levels having relative energies starting with . For example, a Π state has a Π term (or fine structure state) with rotational levels = 1/2, 3/2, 5/2, 7/2, ... and a Π term with levels = 3/2, 5/2, 7/2, 9/2.... Case (a) requires > 0 and so does not apply to any Σ states, and also > 0 so that it does not apply to any singlet states.
The selection rules for allowed spectroscopic transitions depend on which quantum numbers are good. For Hund's case (a), the allowed transitions must have and and and and . In addition, symmetrical diatomic molecules have even (g) or odd (u) parity and obey the Laporte rule that only transitions between states of opposite parity are allowed. | 7 | Physical Chemistry |
A thermogravitational cycle is a reversible thermodynamic cycle using the gravitational works of weight and buoyancy to respectively compress and expand a working fluid. | 7 | Physical Chemistry |
The National Atmospheric Deposition Program (NADP) is a Cooperative Research Support Program of the State Agricultural Experiment Stations (NRSP-3). Housed at the Wisconsin State Laboratory of Hygiene at the University of Wisconsin–Madison, the NADP is a collaborative effort between many different groups, such as: Federal, state, tribal, local governmental agencies, educational institutions, private companies, and non-governmental agencies. These organizations work together in order to operate monitoring sites and report deposition data. The NADP provides free access to all of its data, including seasonal and annual averages, trend plots, deposition maps, reports, manuals, and educational brochures. | 2 | Environmental Chemistry |
N-Fluoropyridinium triflate is an organofluorine compound with the formula [CHNF]OSCF. It is a white solid with low solubility in polar organic solvents. The compound is used as an electrophilic fluorinating agent. It is a salt, consisting of the N-fluoropyridinium cation ([CHNF]) and the triflate anion. Related reagents include Selectfluor, which is also an N-fluorinated salt.
N-Fluoropyridinium cations are not only electrophilic fluorinating agents (i.e., sources of "F"), they are also one-electron oxidants. | 0 | Organic Chemistry |
ChemPRO 100 Chemical Detection System is a handheld chemical detector for field detection and classification of Chemical Warfare Agents. If mail arrives with an unidentified substance, this hand held detector can be used to immediately identify the chemical.
Hardened Mobile Trace Explosive Particle tests for a wide range of explosives and narcotics in seconds. The system will identify explosives in packages or envelopes that are often undetectable by x-ray machines. This handheld detector expands the range of target explosives you can identify in a single sample for faster more comprehensive screening. As noted, this system also detects a wide range of narcotics. The system tests for explosives and narcotics simultaneously in a single sample, for faster, more comprehensive screening. | 3 | Analytical Chemistry |
An epitaxial layer can be doped during deposition by adding impurities to the source gas, such as arsine, phosphine, or diborane. Dopants in the source gas, liberated by evaporation or wet etching of the surface, may also diffuse into the epitaxial layer and cause autodoping. The concentration of impurity in the gas phase determines its concentration in the deposited film. Doping can also be achieved by a site-competition technique, where the growth precursor ratios are tuned to enhance the incorporation of vacancies, specific dopant species or vacant-dopant clusters into the lattice. Additionally, the high temperatures at which epitaxy is performed may allow dopants to diffuse into the growing layer from other layers in the wafer (out-diffusion). | 3 | Analytical Chemistry |
Custom capture panels tailored to specific cancer types or personalized selectors were utilized in EPIC-seq. The capture panels targeted transcription start site regions of genes of interest. Enrichment for EPIC-seq was performed following established laboratory protocols. Subsequently, hybridization captures were pooled, and the pooled samples underwent sequencing using short read sequencing. | 1 | Biochemistry |
As an architectural metal, copper provides excellent corrosion resistance. Copper surfaces form tough oxide-sulfate patina coatings that protect underlying copper surfaces and resist corrosion for a very long time.
Copper corrodes at negligible rates in unpolluted air, water, de-aerated non-oxidizing acids, and when exposed to saline solutions, alkaline solutions, and organic chemicals. Copper roofing in rural atmospheres corrodes at rates of less than in 200 years.
Unlike most other metals, copper does not suffer from underside corrosion that can cause premature failures in roofing. With a copper roof, supporting substrates and structures usually fail long before the copper on the roof.
Architectural copper is, however, susceptible to corrosive attack under certain conditions. Oxidizing acids, oxidizing heavy-metal salts, alkalis, sulfur and nitrogen oxides, ammonia, and some sulfur and ammonium compounds can expedite copper corrosion. Precipitation in areas with a pH less than 5.5 may corrode copper, possibly before a patina or protective oxide film has the time to form. Acidic precipitation, known as acid rain, is due to emissions from fossil fuel combustion, chemical manufacturing, or other processes that release sulfur and nitrogen oxides into the atmosphere. Erosion corrosion may occur when acidic water from a non-copper roof that does not neutralise the acidity, such as tile, slate, wood, or asphalt, falls on a small area of copper. Line corrosion can occur if the drip edge of an inert roofing material rests directly on copper. A solution to this may be to raise the lower edge of the shingles with a cant strip, or to provide a replaceable reinforcing strip between the shingles and the copper. Proper water-shedding design and detailing, which reduces the dwell time of acidic water on metal surfaces, can prevent the majority of atmospheric corrosion problems.
Brass, an alloy of copper and zinc, has good resistance to atmospheric corrosion, alkalis, and organic acids. In some potable waters and in seawater, however, brass alloys with 20% or more zinc may suffer corrosive attack. | 8 | Metallurgy |
Sulfilimine bonds stabilize collagen IV strands found in the extracellular matrix and arose at least 500 mya. These bonds covalently connect hydroxylysine and methionine residues of adjacent polypeptide strands to form a larger collagen trimer. | 0 | Organic Chemistry |
Faradaic loss is only one form of energy loss in an electrochemical system. Another is overpotential, the difference between the theoretical and actual electrode voltages needed to drive the reaction at the desired rate. Even a rechargeable battery with 100% faradaic efficiency requires charging at a higher voltage than it produces during discharge, so its overall energy efficiency is the product of voltage efficiency and faradaic efficiency. Voltage efficiencies below 100% reflect the thermodynamic irreversibility of every real-world chemical reaction. | 7 | Physical Chemistry |
Studies have shown that blocking antibodies can bind to and prevent thyrotropin binding, resulting in reduced cAMP levels in human thyroid cells. This interaction has been used primarily as a method of indicating that Graves' disease immunoglobulins are pluritopic, meaning that they have multiple effects, rather than indicating a possible treatment for this disease. | 1 | Biochemistry |
Glucagon-like peptide-2 (GLP-2) is a 33 amino acid peptide with the sequence HADGSFSDEMNTILDNLAARDFINWLIQTKITD (see Proteinogenic amino acid) in humans. GLP-2 is created by specific post-translational proteolytic cleavage of proglucagon in a process that also liberates the related glucagon-like peptide-1 (GLP-1). GLP-2 is produced by the intestinal endocrine L cell and by various neurons in the central nervous system. Intestinal GLP-2 is co-secreted along with GLP-1 upon nutrient ingestion.
When externally administered, GLP-2 produces a number of effects in humans and rodents, including intestinal growth, enhancement of intestinal function, reduction in bone breakdown and neuroprotection. GLP-2 may act in an endocrine fashion to link intestinal growth and metabolism with nutrient intake. GLP-2 and related analogs may be treatments for short bowel syndrome, Crohn's disease, osteoporosis and as adjuvant therapy during cancer chemotherapy.
GLP-2 has an antidepressant effect in a mouse model of depression when delivered via intracerebroventricular injection. However, a GLP-2 derivative (PAS-CPP-GLP-2) was shown to be efficiently delivered to the brain intranasally, with similar efficacy. | 1 | Biochemistry |
Melting curve analysis is an assessment of the dissociation characteristics of double-stranded DNA during heating. As the temperature is raised, the double strand begins to dissociate leading to a rise in the absorbance intensity, hyperchromicity. The temperature at which 50% of DNA is denatured is known as the melting temperature. Measurement of melting temperature can help us predict species by just studying the melting temperature. This is because every organism has a specific melting curve.
The information gathered can be used to infer the presence and identity of single-nucleotide polymorphisms (SNP). This is because G-C base pairing have 3 hydrogen bonds between them while A-T base pairs have only 2. DNA with mutations from either A or T to either C or G will create a higher melting temperature.
The information also gives vital clues to a molecules mode of interaction with DNA. Molecules such as intercalators slot in between base pairs and interact through pi stacking. This has a stabilizing effect on DNAs structure which leads to a raise in its melting temperature. Likewise, increasing salt concentrations helps diffuse negative repulsions between the phosphates in the DNAs backbone. This also leads to a rise in the DNAs melting temperature. Conversely, pH can have a negative effect on DNA's stability which may lead to a lowering of its melting temperature. | 1 | Biochemistry |
Conceived to work in concert with next-gen sequencing platforms such as Illumina dye sequencing, GUIDE-Seq relies on the integration of a blunt, double-stranded oligodeoxynucleotide (dsODN) that has been phosphothioated on two of the phosphate linkages on the 5' end of both strands. The dsODN cassette integrates into any site in the genome that contains a double-stranded break (DSB). This means that along with the target and off-target sites that may exist as a result of the activity of a nuclease, the dsODN cassette will also integrate into any spurious sites in the genome that have a DSB. This makes it critical to have a dsODN only condition that controls for errant and naturally occurring DSBs, and is required to use the GUIDE-seq bioinformatic pipeline.
After integration of the dsODN cassette, genomic DNA (gDNA) is extracted from the cell culture and sheared to 500bp fragments via sonication. The resulting sheared gDNA undergoes end-repair and adapter ligation. From here, DNA specifically containing the dsODN insert is amplified via two rounds of polymerase chain reaction (PCR) that proceeds in a unidirectional manner starting from the primers that are complementary to the dsODN. This process allows for the reading of the adjacent sequences, both the sense and anti-sense strands, flanking the insert. The final product is a panoply of amplicons, describing the DSB distribution, containing indices for sample differentiation, p5 and p7 Illumina flow-cell adapters, and the sequences flanking the dsODN cassette.
GUIDE-Seq is able to achieve detection of rare DSBs that occur with a 0.1% frequency, however this may be as a result of the limitations of next-generation sequencing platforms. The greater the depth of reads an instrument is able to achieve, the better it can detect rarer events. Additionally, GUIDE-Seq is able to detect sites not predicted by the "in silico" methods which often will predict sites based on sequence similarity and percent mismatch. There have been cases of GUIDE-Seq not detecting any off-targets for certain guide RNAs, suggesting that some RNA-guided nucleases may have no associated off-targets. GUIDE-Seq has been used to show that engineered variants of Cas9 can have reduced off-target effects. | 1 | Biochemistry |
Cast iron farm tools and weapons were widespread in China by the 5th century BC, employing workforces of over 200 men in iron smelters from the 3rd century onward. The earliest known blast furnaces are attributed to the Han dynasty in the 1st century AD. These early furnaces had clay walls and used phosphorus-containing minerals as a flux. Chinese blast furnaces ranged from around two to ten meters in height, depending on the region. The largest ones were found in modern Sichuan and Guangdong, while the 'dwarf" blast furnaces were found in Dabieshan. In construction, they are both around the same level of technological sophistication
There is no evidence of the bloomery in China after the appearance of the blast furnace and cast iron. In China, blast furnaces produced cast iron, which was then either converted into finished implements in a cupola furnace, or turned into wrought iron in a fining hearth. If iron ores are heated with carbon to 1420–1470 K, a molten liquid is formed, an alloy of about 96.5% iron and 3.5% carbon. This product is strong, can be cast into intricate shapes, but is too brittle to be worked, unless the product is decarburized to remove most of the carbon. The vast majority of Chinese iron manufacture, from the late Zhou dynasty onward, was of cast iron. However forged swords began to be made in the Warring-States-period: "Earliest iron and steel Jian also appear, made by the earliest and most basic forging and folding techniques." Iron would become, by around 300 BCE, the preferred metal for tools and weapons in China.
The primary advantage of the early blast furnace was in large scale production and making iron implements more readily available to peasants. Cast iron is more brittle than wrought iron or steel, which required additional fining and then cementation or co-fusion to produce, but for menial activities such as farming it sufficed. By using the blast furnace, it was possible to produce larger quantities of tools such as ploughshares more efficiently than the bloomery. In areas where quality was important, such as warfare, wrought iron and steel were preferred. Nearly all Han period weapons are made of wrought iron or steel, with the exception of axe-heads, of which many are made of cast iron.
The effectiveness of the Chinese human and horse powered blast furnaces was enhanced during this period by the engineer Du Shi (c. AD 31), who applied the power of waterwheels to piston-bellows in forging cast iron. Early water-driven reciprocators for operating blast furnaces were built according to the structure of horse powered reciprocators that already existed. That is, the circular motion of the wheel, be it horse driven or water driven, was transferred by the combination of a belt drive, a crank-and-connecting-rod, other connecting rods, and various shafts, into the reciprocal motion necessary to operate a push bellow.
Donald Wagner suggests that early blast furnace and cast iron production evolved from furnaces used to melt bronze. Certainly, though, iron was essential to military success by the time the State of Qin had unified China (221 BC). Usage of the blast and cupola furnace remained widespread during the Song and Tang dynasties. By the 11th century, the Song dynasty Chinese iron industry made a switch of resources from charcoal to coke in casting iron and steel, sparing thousands of acres of woodland from felling. This may have happened as early as the 4th century AD.
Blast furnaces were also later used to produce gunpowder weapons such as cast iron bomb shells and cast iron cannons during the Song dynasty. | 8 | Metallurgy |
Taking the natural logarithm of Arrhenius equation yields:
Rearranging yields:
This has the same form as an equation for a straight line:
where x is the reciprocal of T.
So, when a reaction has a rate constant that obeys the Arrhenius equation, a plot of ln k versus T gives a straight line, whose gradient and intercept can be used to determine E and A. This procedure has become so common in experimental chemical kinetics that practitioners have taken to using it to define the activation energy for a reaction. That is, the activation energy is defined to be (−R) times the slope of a plot of ln k vs. (1/T): | 7 | Physical Chemistry |
The glycocalyx is located on the apical surface of vascular endothelial cells which line the lumen. When vessels are stained with cationic dyes such as Alcian blue stain, transmission electron microscopy shows a small, irregularly shaped layer extending approximately 50–100 nm into the lumen of a blood vessel. Another study used osmium tetroxide staining during freeze substitution, and showed that the endothelial glycocalyx could be up to 11 μm thick. It is present throughout a diverse range of microvascular beds (capillaries) and macrovessels (arteries and veins). The glycocalyx also consists of a wide range of enzymes and proteins that regulate leukocyte and thrombocyte adherence, since its principal role in the vasculature is to maintain plasma and vessel-wall homeostasis. These enzymes and proteins include:
*Endothelial nitric oxide synthase (endothelial NOS)
*Extracellular superoxide dismutase (SOD3)
*Angiotensin converting enzyme
*Antithrombin-III
*Lipoprotein lipase
*Apolipoproteins
*Growth factors
*Chemokines
The enzymes and proteins listed above serve to reinforce the glycocalyx barrier against vascular and other diseases. Another main function of the glycocalyx within the vascular endothelium is that it shields the vascular walls from direct exposure to blood flow, while serving as a vascular permeability barrier. Its protective functions are universal throughout the vascular system, but its relative importance varies depending on its exact location in the vasculature. In microvascular tissue, the glycocalyx serves as a vascular permeability barrier by inhibiting coagulation and leukocyte adhesion. Leukocytes must not stick to the vascular wall because they are important components of the immune system that must be able to travel to a specific region of the body when needed. In arterial vascular tissue, the glycocalyx also inhibits coagulation and leukocyte adhesion, but through mediation of shear stress-induced nitric oxide release. Another protective function throughout the cardiovascular system is its ability to affect the filtration of interstitial fluid from capillaries into the interstitial space.
The glycocalyx, which is located on the apical surface of endothelial cells, is composed of a negatively charged network of proteoglycans, glycoproteins, and glycolipids. Along the luminal surface of the vascular glycocalyx exists an empty layer that excludes red blood cells. | 1 | Biochemistry |
Polymers can be fractionated on an analytical scale by size exclusion chromatography (SEC), Matrix-assisted laser desorption/ionization (MALDI) or field flow fractionation (FFF). These methods are used to determine the molecular weight distribution. | 7 | Physical Chemistry |
In early "straight-through" urea plants, reactant recovery (the first step in "recycling") was done by letting down the system pressure to atmospheric to let the carbamate decompose back to ammonia and carbon dioxide. Originally, because it was not economic to recompress the ammonia and carbon dioxide for recycle, the ammonia at least would be used for the manufacture of other products such as ammonium nitrate or ammonium sulfate, and the carbon dioxide was usually wasted. Later process schemes made recycling unused ammonia and carbon dioxide practical. This was accomplished by the "total recycle process", developed in the 1940s to 1960s and now called the "conventional recycle process". It proceeds by depressurizing the reaction solution in stages (first to 18–25 bar and then to 2–5 bar) and passing it at each stage through a steam-heated carbamate decomposer, then recombining the resulting carbon dioxide and ammonia in a falling-film carbamate condenser and pumping the carbamate solution back into the urea reaction vessel. | 0 | Organic Chemistry |
The balance of dissimilatory nitrate reduction to ammonium and denitrification alters the accuracy of f-ratio calculations. The f-ratio is used to quantify the efficiency of the biological pump, which reflects sequestering of carbon from the atmosphere to the deep sea. The f-ratio is calculated using estimates of new production (primary productivity stimulated by nutrients entering the photic zone from outside the photic zone, for example from the deep ocean) and regenerated production (primary productivity stimulated by nutrients already in the photic zone, released by remineralisation). Calculations of the f-ratio use the nitrogen species stimulating primary productivity as a proxy for the type of production occurring; productivity stimulated by NH rather than NO is regenerated production. DNRA also produces NH (in addition to remineralisation) but from organic matter which has been exported from the photic zone; this may be subsequently reintroduced by mixing or upwelling of deeper water back to the surface, thereby, stimulating primary productivity; thus, in areas where high amounts of DNRA is occurring, f-ratio calculations will not be accurate. | 1 | Biochemistry |
The Eschweiler–Clarke reaction is a method for methylation of amines. This method avoids the risk of quaternization, which occurs when amines are methylated with methyl halides. | 0 | Organic Chemistry |
Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, crops, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 (completely dry) to the value of the materials' porosity at saturation. It can be given on a volumetric or mass (gravimetric) basis. | 7 | Physical Chemistry |
CcrM is a type II DNA Methyltransferase, that transfer a methyl group from the methyl donor SAM to the N6 of an adenine in a 5-GANTC-3 recognition sites of hemimethylated DNA. Based on the order of the conserved motifs that form the SAM binding, the active site and the target recognition domain in the sequence of CcrM it can be classified as a β-class adenine N6 Methyltransferase. CcrM homologs in Alphaproteobacteria have an 80 residues C terminal domain, with non well characterized function.
CcrM is characterized by a high degree of sequence discrimination, showing a very high specificity for GANTC sites over AANTC sites , being able to recognize and methylate this sequence in both double and single strand DNA. CcrM in complex with a dsDNA structure was resolved, showing that the enzyme presents a novel DNA interaction mechanism, opening a bubble in the DNA recognition site (The concerted mechanism of Methyltransferases relies in the flip of the target base), the enzyme interacts with DNA forming an homodimer with differential monomer interactions.
CcrM is a highly efficient enzyme capable of methylating a high number of 5-GANTC-3 sites in low time, however if the enzyme is processive (the enzyme binds to the DNA and methylate several methylation sites before dissociation) or distributive (the enzyme dissociates from DNA after each methylation) it is still in discussion. First reports indicated the second case, however more recent characterisation of CcrM indicate that it is a processive enzyme. | 1 | Biochemistry |
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