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In hydrodynamics, the Perrin friction factors are multiplicative adjustments to the translational and rotational friction of a rigid spheroid, relative to the corresponding frictions in spheres of the same volume. These friction factors were first calculated by Jean-Baptiste Perrin.
These factors pertain to spheroids (i.e., to ellipsoids of revolution), which are characterized by the axial ratio p = (a/b), defined here as the axial semiaxis a
(i.e., the semiaxis along the axis of revolution) divided by the equatorial semiaxis b. In prolate spheroids, the axial ratio p > 1 since the axial semiaxis is longer than the equatorial semiaxes. Conversely, in oblate spheroids, the axial ratio p < 1 since the axial semiaxis is shorter than the equatorial semiaxes. Finally, in spheres, the axial ratio p = 1, since all three semiaxes are equal in length.
The formulae presented below assume "stick" (not "slip") boundary conditions, i.e., it is assumed that the velocity of the fluid is zero at the surface of the spheroid. | 1 | Applied and Interdisciplinary Chemistry |
Friction stir processing can also be used to improve the microstructural properties of powder metal objects. In particular, when dealing with aluminium powder metal alloys, the aluminium oxide film on the surface of each granule is detrimental to the ductility, fatigue properties and fracture toughness of the workpiece. While conventional techniques for removing this film include forging and extrusion, friction stir processing is suited for situations where localized treatment is desired. | 1 | Applied and Interdisciplinary Chemistry |
Consider the two equilibria, in aqueous solution, between the copper(II) ion, Cu and ethylenediamine (en) on the one hand and methylamine, MeNH on the other.
In the first reaction the bidentate ligand ethylene diamine forms a chelate complex with the copper ion. Chelation results in the formation of a five-membered ring. In the second reaction the bidentate ligand is replaced by two monodentate methylamine ligands of approximately the same donor power, meaning that the enthalpy of formation of Cu–N bonds is approximately the same in the two reactions. Under conditions of equal copper concentrations and when the concentration of methylamine is twice the concentration of ethylenediamine, the concentration of the bidentate complex will be greater than the concentration of the complex with 2 monodentate ligands. The effect increases with the number of chelate rings so the concentration of the EDTA complex, which has six chelate rings, is much higher than a corresponding complex with two monodentate nitrogen donor ligands and four monodentate carboxylate ligands. Thus, the phenomenon of the chelate effect is a firmly established empirical fact: under comparable conditions, the concentration of a chelate complex will be higher than the concentration of an analogous complex with monodentate ligands.
The thermodynamic approach to explaining the chelate effect considers the equilibrium constant for the reaction: the larger the equilibrium constant, the higher the concentration of the complex.
When the analytical concentration of methylamine is twice that of ethylenediamine and the concentration of copper is the same in both reactions, the concentration [Cu(en)] is much higher than the concentration [Cu(MeNH)] because
The difference between the two stability constants is mainly due to the difference in the standard entropy change, ΔS. In the reaction with the chelating ligand there are two particles on the left and one on the right, whereas in equation with the monodentate ligand there are three particles on the left and one on the right. This means that less entropy of disorder is lost when the chelate complex is formed than when the complex with monodentate ligands is formed. This is one of the factors contributing to the entropy difference. Other factors include solvation changes and ring formation. Some experimental data to illustrate the effect are shown in the following table.
These data show that the standard enthalpy changes are indeed approximately equal for the two reactions and that the main reason why the chelate complex is so much more stable is that the standard entropy term is much less unfavourable, indeed, it is favourable in this instance. In general it is difficult to account precisely for thermodynamic values in terms of changes in solution at the molecular level, but it is clear that the chelate effect is predominantly an effect of entropy. Other explanations, including that of Schwarzenbach, are discussed in Greenwood and Earnshaw.
The chelate effect increases as the number of chelate rings increases. For example, the complex [Ni(dien))] is more stable than the complex [Ni(en))]; both complexes are octahedral with six nitrogen atoms around the nickel ion, but dien (diethylenetriamine, 1,4,7-triazaheptane) is a tridentate ligand and en is bidentate. The number of chelate rings is one less than the number of donor atoms in the ligand. EDTA (ethylenediaminetetracetic acid) has six donor atoms so it forms very strong complexes with five chelate rings. Ligands such as DTPA, which have eight donor atoms are used to form complexes with large metal ions such as lanthanide or actinide ions which usually form 8- or 9-coordinate complexes.
5-membered and 6-membered chelate rings give the most stable complexes. 4-membered rings are subject to internal strain because of the small inter-bond angle is the ring. The chelate effect is also reduced with 7- and 8- membered rings, because the larger rings are less rigid, so less entropy is lost in forming them. | 0 | Theoretical and Fundamental Chemistry |
Ion pairs are formed when a cation and anion, which are present in a solution of an ionizable substance, come together to form a discrete chemical species. There are three distinct types of ion pairs, depending on the extent of solvation of the two ions. For example, magnesium sulfate exists as both contact and solvent-shared ion-pairs in seawater.
In the schematic representation above, the circles represent spheres. The sizes are arbitrary and not necessarily similar as illustrated. The cation is coloured red and the anion is coloured blue. The green area represents solvent molecules in a primary solvation shell; secondary solvation is ignored. When both ions have a complete primary solvation sphere, the ion pair may be termed fully solvated (separated ion pair, SIP). When there is about one solvent molecule between cation and anion, the ion pair may be termed solvent-shared. Lastly, when the ions are in contact with each other, the ion pair is termed a contact ion pair (CIP). Even in a contact ion pair, however, the ions retain most of their solvation shell. The nature of this solvation shell is generally not known with any certainty. In aqueous solution and in other donor solvents, metal cations are surrounded by between 4 and 9 solvent molecules in the primary solvation shell,
An alternative name for a solvent-shared ion pair is an outer-sphere complex. This usage is common in coordination chemistry and denotes a complex between a solvated metal cation and an anion. Similarly, a contact ion pair may be termed an inner-sphere complex. The essential difference between the three types is the closeness with which the ions approach each other: fully solvated > solvent-shared > contact. With fully solvated and solvent-shared ion pairs the interaction is primarily electrostatic, but in a contact ion pair some covalent character in the bond between cation and anion is also present.
An ion triplet may be formed from one cation and two anions or from one anion and two cations. Higher aggregates, such as a tetramer , may be formed.
Ternary ion associates involve the association of three species. Another type, named intrusion ion pair, has also been characterized. | 0 | Theoretical and Fundamental Chemistry |
In steady state, the third order virial equation becomes
If the axis of rotation is chosen in direction, the equation becomes | 1 | Applied and Interdisciplinary Chemistry |
To understand the how the MRI works, we must first understand the conditions inside a perfectly conducting fluid in motion. This is often a good approximation to astrophysical gases. In the presence of a magnetic field a moving conductor responds by trying to eliminate the Lorentz force on the free charges. The magnetic force acts in such a way as to locally rearrange these charges to produce an internal electric field of In this way, the direct Lorentz force on the charges vanishes. (Alternatively, the electric field in the local rest frame of the moving charges vanishes.) This induced electric field can now itself induce further changes in the magnetic field according to Faraday's law,
Another way to write this equation is that if in time the fluid makes a displacement then the magnetic field changes by
The equation of a magnetic field in a perfect conductor in motion has a special property: the combination of Faraday induction and zero Lorentz force makes the field lines behave as though they were painted, or "frozen," into the fluid. In particular, if is initially nearly constant and is a divergence-free displacement, then our equation reduces to
because of the vector calculus identity
Out of these 4 terms, is one of Maxwell's equations. By the divergence-free assumption, . because B is assumed to be nearly constant. Equation shows that changes only when there is a shearing displacement along the field line.
To understand the MRI, it is sufficient to consider the case in which is uniform in vertical direction, and varies as Then
where it is understood that the real part of this equation expresses its physical content. (If is proportional to for example, then is proportional to )
A magnetic field exerts a force per unit volume on an electrically neutral, conducting fluid equal to Amperes circuital law gives because Maxwells correction is neglected in the MHD approximation. The force per unit volume becomes
where we have used the same vector calculus identity. This equation is fully general, and makes no assumptions about the strength or direction of the magnetic field.
The first term on the right is analogous to a pressure gradient. In our problem it may be neglected because it exerts no force in the plane of the disk, perpendicular to The second term acts like a magnetic tension force, analogous to a taut string. For a small disturbance it exerts an acceleration given by force divided by mass, or equivalently, force per unit volume divided by mass per unit volume:
Thus, a magnetic tension force gives rise to a return force which is directly proportional to the displacement. This means that the oscillation frequency for small displacements in the plane of rotation of a disk with a uniform magnetic field in the vertical direction satisfies an equation ("dispersion relation") exactly analogous to equation , with the "spring constant"
As before, if there is an exponentially growing root of this equation for wavenumbers satisfying
This corresponds to the MRI.
Notice that the magnetic field appears in equation only as the product Thus, even if is very small, for very large wavenumbers this magnetic tension can be important. This is why the MRI is so sensitive to even very weak magnetic fields: their effect is amplified by multiplication by Moreover, it can be shown that MRI is present regardless of the magnetic field geometry, as long as the field is not too strong.
In astrophysics, one is generally interested in the case for which the disk is supported by rotation against the gravitational attraction of a central mass. A balance between the Newtonian gravitational force and the radial centripetal force immediately gives
where is the Newtonian gravitational constant, is the central mass, and is radial location in the disk. Since this so-called Keplerian disk is unstable to the MRI . Without a weak magnetic field, the flow would be stable.
For a Keplerian disk, the maximum growth rate is which occurs at a wavenumber satisfying
is very rapid, corresponding to an amplification factor of more than 100 per rotation period.
The nonlinear development of the MRI into fully developed turbulence may be followed via large scale numerical computation. | 1 | Applied and Interdisciplinary Chemistry |
One way to visualize the internal standard method is to create one calibration curve that doesn't use the method and one calibration curve that does. Suppose there are known concentrations of nickel in a set of calibration solutions: 0 ppm, 1.6 ppm, 3.2 ppm, 4.8 ppm, 6.4 ppm, and 8 ppm. Each solution also has 5 ppm yttrium to act as an internal standard. If these solutions are measured using ICP-OES, the intensity of the yttrium signal should be consistent across all solutions. If not, the intensity of the nickel signal is likely imprecise as well.
The calibration curve that does not use the internal standard method ignores the uncertainty between measurements. The coefficient of determination (R) for this plot is 0.9985.
In the calibration curve that uses the internal standard, the y-axis is the ratio of the nickel signal to the yttrium signal. This ratio is unaffected by uncertainty in the nickel measurements, as it should affect the yttrium measurements in the same way. This results in a higher R, 0.9993. | 0 | Theoretical and Fundamental Chemistry |
The Greek Ministry of Finance has now installed a green roof on the Treasury in Constitution Square in Athens. The so-called "oikostegi" (Greek – oiko, , meaning building-ecological, and stegi, pronounced staygee, meaning roof-abode-shelter) was inaugurated in September 2008. Studies of the thermodynamics of the roof in September 2008 concluded that the thermal performance of the building was significantly affected by the installation. In further studies, in August 2009, energy savings of 50% were observed for air conditioning in the floor directly below the installation. The ten-floor building has a total floor space of . The oikostegi covers , equalling 52% of the roof space and 8% of the total floor space. Despite this, energy savings totalling €5,630 per annum were recorded, which translates to a 9% saving in air conditioning and a 4% saving in heating bills for the whole building. An additional observation and conclusion of the study was that the thermodynamic performance of the oikostegi had improved as biomass was added over the 12 months between the first and second study. This suggests that further improvements will be observed as the biomass increases still further. The study also stated that while measurements were being made by thermal cameras, a plethora of beneficial insects were observed on the roof, such as butterflies, honey bees and ladybirds. Obviously this was not the case before installation. Finally, the study suggested that both the micro-climate and biodiversity of Constitution Square, in Athens, Greece had been improved by the oikostegi. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, racemization is a conversion, by heat or by chemical reaction, of an optically active compound into a racemic (optically inactive) form. This creates a 1:1 molar ratio of enantiomers and is referred to as a racemic mixture (i.e. contain equal amount of (+) and (−) forms). Plus and minus forms are called Dextrorotation and levorotation. The D and L enantiomers are present in equal quantities, the resulting sample is described as a racemic mixture or a racemate. Racemization can proceed through a number of different mechanisms, and it has particular significance in pharmacology as different enantiomers may have different pharmaceutical effects. | 0 | Theoretical and Fundamental Chemistry |
Okano’s group expanded on their success by using different modifiers to enhance hydrophobicity through the attachment of butyl methacrylate (BMA), a hydrophobic comonomer. For simplification the resultant polymer has been labeled as IBc (isopropylacrylamide butyl methacrylate copolymer). The polymers were synthesized using radical telomerization with varying BMA content. Where pure PNIPAAm was unable to resolve hydrophobic steroids at any temperature, IBc-grafted silica stationary phases were able to resolve steroid peaks with increasingly retarded retention times in correlation to both increased BMA content and increased temperature. They went on to develop a method to separate phenylthiohydantoin(PTH)-amino acids using their IBc stationary phase with a stronger emphasis of implementing environmentally friendly conditions using a purely aqueous phase in HPLC. Another group separated catechins using PNIPAAm. | 0 | Theoretical and Fundamental Chemistry |
Unlike conventional composites, which typically fail catastrophically, RCCM fail incrementally because of the non-linear deformation phase and the multiplicity of joints and links. These results matched finite-element simulations with finely-meshed rigid body models. In addition to convergence to the observed coordinated buckling mode, these simulations accurately predict the relative strength scaling observed in load test experiments. These results are consistent with the observation that open-cell lattice materials fail through micro-structural strut bending failures with σmax ∝. The simulations also suggest that the coordinated buckling phenomenon as well as the modulus measurements are not dominated by edge effects, with minimal influence on overall results beyond characteristic lengths exceeding several units.
Varying the locations of more and less rigid elements can trigger pure axial compression, simple uni-directional Euler buckling and complex buckling. | 0 | Theoretical and Fundamental Chemistry |
Aggregate exposures to consumers (direct and indirect dermal contact, ingestion, and inhalation) have been estimated to be 1.42 ug/Kg bw/day.
Calcium xylene sulfonate and sodium cumene sulfonate have been shown to cause temporary, slight eye irritation in animals. Studies have not found hydrotropes to be mutagenic, carcinogenic or have reproductive toxicity. | 0 | Theoretical and Fundamental Chemistry |
Gamma rays detected in a spectroscopic system produce peaks in the spectrum. These peaks can also be called lines by analogy to optical spectroscopy. The width of the peaks is determined by the resolution of the detector, a very important characteristic of gamma spectroscopic detectors, and high resolution enables the spectroscopist to separate two gamma lines that are close to each other. Gamma spectroscopy systems are designed and adjusted to produce symmetrical peaks of the best possible resolution. The peak shape is usually a Gaussian distribution. In most spectra the horizontal position of the peak is determined by the gamma ray's energy, and the area of the peak is determined by the intensity of the gamma ray and the efficiency of the detector.
The most common figure used to express detector resolution is full width at half maximum (FWHM). This is the width of the gamma ray peak at half of the highest point on the peak distribution. Resolution figures are given with reference to specified gamma ray energies. Resolution can be expressed in absolute (i.e., eV or MeV) or relative terms. For example, a sodium iodide (NaI) detector may have a FWHM of 9.15 keV at 122 keV, and 82.75 keV at 662 keV. These resolution values are expressed in absolute terms. To express the resolution in relative terms, the FWHM in eV or MeV is divided by the energy of the gamma ray and usually shown as percentage. Using the preceding example, the resolution of the detector is 7.5% at 122 keV, and 12.5% at 662 keV. A germanium detector may give resolution of 560 eV at 122 keV, yielding a relative resolution of 0.46%. | 0 | Theoretical and Fundamental Chemistry |
Rigid polyurethane foam has many desirable properties which has enabled increased use in various applications, some of which are quite demanding. These properties include low thermal conduction making it useful as an insulator. It also has low density compared to metals and other materials and also good dimensional stability. A metal will expand on heating whereas rigid PU foam does not. They have excellent strength to weight ratios. Like many applications, there has been a trend to make rigid PU foam from renewable raw materials in place of the usual polyols.
They are used in vehicles, planes and buildings in structural applications. They have also been used in fire-retardant applications. | 0 | Theoretical and Fundamental Chemistry |
DAA developers face foreseeable challenges in the years to come. Therapeutic gaps for individuals with complicating conditioned such as chronic kidney disease and cirrhosis will need to be bridged. Shorter therapies with milder side effects would yield greater adherence, and the ever present spectre of drug resistance is looming. The highly adaptive HCV has evolved into a number of different genomes that all need to be adequately treated, preferably with pan-genotypic regimens.
Some of these challenges already have possible solutions in sight. The protease inhibitor ABT-493 and the next-generation NS5A inhibitor ABT-530 are considered active against all HCV genotypes, including the hard to treat genotype 3. In vitro, ABT-530 showed potency against the resistance associated variants which are immune to the first generations of NS5A inhibitors, including ledipasvir, daclatasvir and ombitasvir. Because this drug combination has the additional quality of being hepatically cleared, it holds the promise that patients with chronic kidney disease and HCV could receive a safe, non-sofosbuvir-based treatment in the near future.
At least three drug combinations for the treatment of HCV are in the pipeline to be approved in 2016-2017: Sofosbuvir in combination with velpatasvir, ABT-493 in combination with ABT-530, and grazoprevir in combination with elbasvir, of which velpatasvir, ABT-530 and elbasvir are NS5A inhibitors. | 1 | Applied and Interdisciplinary Chemistry |
The two main tasks of transcription initiation are to provide RNA polymerase with an access to the promoter and to assemble general transcription factors with polymerase into a transcription initiation complex. Diverse mechanisms of initiating transcription by overriding inhibitory signals at the gene promoter have been identified. Eukaryotic genes have acquired extensive regulatory sequences that encompass a large number of regulator-binding sites and spread overall kilobases (sometimes hundreds of kilobases) from the promoter–-both upstream and downstream. The regulator binding sites are often clustered together into units called enhancers. Enhancers can facilitate highly cooperative action of several transcription factors (which constitute enhanceosomes). Remote enhancers allow transcription regulation at a distance. Insulators situated between enhancers and promoters help define the genes that an enhancer can or cannot influence.
Eukaryotic transcriptional activators have separate DNA-binding and activating functions. Upon binding to its cis-element, an activator can recruit polymerase directly or recruit other factors needed by the transcriptional machinery. An activator can also recruit nucleosome modifiers that alter chromatin in the vicinity of the promoter and thereby help initiation. Multiple activators can work together, either by recruiting a common or two mutually dependent components of the transcriptional machinery, or by helping each other bind to their DNA sites. These interactions can synergize multiple signaling inputs and produce intricate transcriptional responses to address cellular needs. | 1 | Applied and Interdisciplinary Chemistry |
In contradistinction with electrophoresis, motion of particle in homogeneous electric field only, electrodiffusiophoresis occurs in the areas of the dispersion that experience concentration polarization due to, for instance, electrochemical reactions, see electrochemistry. There are concentration gradients in such areas that affect particles motion strongly. First of all they create inhomogeneity in the electric field. Secondly, they cause diffusiophoresis. This peculiarities of the particles motion in the areas subjected to the concentration polarization justifies introduction of the special term for this electrokinetic effect - electrodiffusiophoresis.
One of the most important differences of the electrodiffusioporesis from the electrophoresis is that exists as directed particles drift in the alternating electric field. Electrophoresis, in contrary, causes only particles oscillation on the same spot. This difference opens opportunities for important applications.
Electrodiffusiophoresis was theoretically predicted in 1980 - 82.
It was experimentally observed microscopically in 1982.
The first application of this effect was explanation of particles depositing at some distance from the surface of the ion selective membrane.
These earlier experiments and theory were described in the review published in 1990. This review presents also application of electrodiffusiophoresis for making bactericidal coatings.
This effect has attracted new attention in 2010 with regard to microfluidics. | 0 | Theoretical and Fundamental Chemistry |
Albert believed that all natural things were compositions of matter and form, he referred to it as quod est and quo est. Albert also believed that God alone is the absolute ruling entity. Albert's version of hylomorphism is very similar to the Aristotelian doctrine. | 1 | Applied and Interdisciplinary Chemistry |
The predominant form of lining for water applications is cement mortar centrifugally applied during manufacturing. The cement mortar comprises a mixture of cement and sand to a ratio of between 1:2 and 1:3.5. For potable water, portland cement is used; for sewage it is common to use sulfate resisting or high alumina cement.
Cement mortar linings have been found to dramatically reduce internal corrosion. A DIPRA survey has demonstrated that the Hazen-Williams factor of cement lining remains between 130 and 151 with only slight reduction with age. | 1 | Applied and Interdisciplinary Chemistry |
Creation of canals would need large areas of land resulting in large scale deforestation in certain areas. | 1 | Applied and Interdisciplinary Chemistry |
The K factor or characterization factor is defined from Rankine boiling temperature °R=1.8Tb[k] and relative to water density ρ at 60°F:
K(UOP) =
The K factor is a systematic way of classifying a crude oil according to its paraffinic, naphthenic, intermediate or aromatic nature. 12.5 or higher indicate a crude oil of predominantly paraffinic constituents, while 10 or lower indicate a crude of more aromatic nature. The K(UOP) is also referred to as the UOP K factor or just UOPK. | 0 | Theoretical and Fundamental Chemistry |
Yuri Andreyevich Zhdanov (; 20 August 1919 – 19 December 2006) was a Soviet and Russian chemistry professor and rector of the University of Rostov. He was the son of Soviet politician Andrei Zhdanov and a former husband of Joseph Stalin's daughter, Svetlana Alliluyeva. | 0 | Theoretical and Fundamental Chemistry |
Hazards posed by titanium tetrachloride generally arise from its reaction with water that releases hydrochloric acid, which is severely corrosive itself and whose vapors are also extremely irritating. is a strong Lewis acid, which exothermically forms adducts with even weak bases such as THF and water. | 0 | Theoretical and Fundamental Chemistry |
The erythromycin breath test (ERMBT) is a method used to measure metabolism (oxidation and elimination from the system) by a part of the cytochrome P450 system. Erythromycin produces CO and this CO can be measured to study drugs that interact with the cytochrome P450 system. Erythromycin is tagged with carbon-14 and given as an intravenous injection; after 20 minutes the subject blows up a balloon and the carbon dioxide exhaled that is tagged with carbon-14 shows the activity of the CYP3A4 isoenzyme on the erythromycin. ERMBT can be used to determine how drugs that the CYP3A4 isoenzyme metabolizes will function in a given individual.
Erythromycin is a drug that treats bacterial infections like bronchitis, sexually transmitted diseases, and pneumonia. The medication is in a capsule form and takes on a "delayed-release," to ensure it is only broken down once it reaches the intestine and not by stomach acids.
The test allows doctors to determine or predict an individual’s drug treatment outcome. Will a patient develop serious or fatal side effects from a certain drug? Which foods and drugs should not be taken together? With this and other tests a physician may determine treatment outcomes in advance or study the effects of new drugs.
Some patients have a congenital inability to synthesize certain enzymes, so drugs may build up to toxic levels in their system or other drugs and foods a patient is taking may consume all of their ability to metabolize certain foods and drugs. An example is: when a person taking a cholesterol-lowering statin drug then drinking grapefruit juice, they may have a poor treatment outcome (adverse drug reaction) and sustain liver damage or kidney failure due to drug induced rhabdomyolysis (the breaking up of muscle tissue). | 1 | Applied and Interdisciplinary Chemistry |
In molecular biology, linker DNA is double-stranded DNA (38-53 base pairs long) in between two nucleosome cores that, in association with histone H1, holds the cores together. Linker DNA is seen as the string in the "beads and string model", which is made by using an ionic solution on the chromatin. Linker DNA connects to histone H1 and histone H1 sits on the nucleosome core. Nucleosome is technically the consolidation of a nucleosome core and one adjacent linker DNA; however, the term nucleosome is used freely for solely the core. Linker DNA may be degraded by endonucleases.
The linkers are short double stranded DNA segments which are formed of oligonucleotides. These contain target sites for the action of one or more restriction enzymes. The linkers can be synthesized chemically and can be ligated to the blunt end of foreign DNA or vector DNA. These are then treated with restriction endonuclease enzyme to produce cohesive ends of DNA fragments. The commonly used linkers are EcoRI-linkers and sal-I linkers. | 0 | Theoretical and Fundamental Chemistry |
Miglustat is an iminosugar in which the ring oxygen is replaced by nitrogen. Miglustat a drug used to treat some rare lysosomal storage disorder diseases. | 1 | Applied and Interdisciplinary Chemistry |
The Campaign to Electrify Britain's Railway (CEBR) is an internet-based campaign group formed in 2018 whose aim is to convince the government to completely electrify the British Railway network. Its slogan is "Down with Dirty Diesel." The campaign promotes a rolling programme of electrification, which it considers essential to improve UK railways and help to decarbonise transport. It collaborates with groups such as the Railway Industry Association, Rail Delivery Group, Birmingham Centre for Railway Research and Education, Campaign for Better Transport, Institute of Electrical Engineers and the Permanent Way Institution. The group has given evidence to the Transport Select Committee. Huw Merriman the committee chair at the time, put it writing he agreed with their view. Merriman was appointed as Minister of State for Rail and HS2 in October 2022. The desire to achieve net zero carbon in transport has increased calls for electrification. | 1 | Applied and Interdisciplinary Chemistry |
Atmospheric Methane Removal is a category of potential approaches being researched to accelerate the breakdown of methane once in the atmosphere to mitigate some of the impacts of climate change.
Different methods to remove methane from the atmosphere include thermal-catalytic oxidation, photocatalytic oxidation, biological methanotrophic methane removal, concentration with zeolites or other porous solids, and separation by membranes. | 1 | Applied and Interdisciplinary Chemistry |
The yield of a system can be measured by either its value or its net benefit. For a water supply system, the true value or the net benefit is a reliable water supply service having adequate quantity and good quality of the product. For example, if the existing water supply of a city needs to be extended to supply a new municipality, the impact of the new branch of the system must be designed to supply the new needs, while maintaining supply to the old system. | 1 | Applied and Interdisciplinary Chemistry |
FEBS publishes four scientific journals: The FEBS Journal, FEBS Letters, Molecular Oncology and FEBS Open Bio. The FEBS Journal was previously entitled the European Journal of Biochemistry. Molecular Oncology and FEBS Open Bio are open-access journals. | 1 | Applied and Interdisciplinary Chemistry |
Two very similar expressions for are in wide use in hydrology. Both have the form ‰ (‰ = permil or parts per thousand) where s and a are the relative abundances of N in respectively the sample and the atmosphere. The difference is whether the relative abundance is with respect to all the nitrogen, i.e. N plus N, or just to N. Since the atmosphere is 99.6337% N and 0.3663% N, a is 0.003663 in the former case and 0.003663/0.996337 = 0.003676 in the latter. However s varies similarly; for example if in the sample N is 0.385% and N is 99.615%, s is 0.003850 in the former case and 0.00385/0.99615 = 0.003865 in the latter. The value of is then 51.05‰ in the former case and 51.38‰ in the latter, an insignificant difference in practice given the typical range of -20 to 80 for . | 0 | Theoretical and Fundamental Chemistry |
Archaea have a single type of RNAP, responsible for the synthesis of all RNA. Archaeal RNAP is structurally and mechanistically similar to bacterial RNAP and eukaryotic nuclear RNAP I-V, and is especially closely structurally and mechanistically related to eukaryotic nuclear RNAP II.
The history of the discovery of the archaeal RNA polymerase is quite recent. The first analysis of the RNAP of an archaeon was performed in 1971, when the RNAP from the extreme halophile Halobacterium cutirubrum was isolated and purified. Crystal structures of RNAPs from Sulfolobus solfataricus and Sulfolobus shibatae set the total number of identified archaeal subunits at thirteen.
Archaea has the subunit corresponding to Eukaryotic Rpb1 split into two. There is no homolog to eukaryotic Rpb9 (POLR2I) in the S. shibatae complex, although TFS (TFIIS homolog) has been proposed as one based on similarity. There is an additional subunit dubbed Rpo13; together with Rpo5 it occupies a space filled by an insertion found in bacterial β′ subunits (1,377–1,420 in Taq). An earlier, lower-resolution study on S. solfataricus structure did not find Rpo13 and only assigned the space to Rpo5/Rpb5. Rpo3 is notable in that it's an iron–sulfur protein. RNAP I/III subunit AC40 found in some eukaryotes share similar sequences, but does not bind iron. This domain, in either case, serves a structural function.
Archaeal RNAP subunit previously used an "RpoX" nomenclature where each subunit is assigned a letter in a way unrelated to any other systems. In 2009, a new nomenclature based on Eukaryotic Pol II subunit "Rpb" numbering was proposed. | 1 | Applied and Interdisciplinary Chemistry |
A cooling curve is a line graph that represents the change of phase of matter, typically from a gas to a solid or a liquid to a solid. The independent variable (X-axis) is time and the dependent variable (Y-axis) is temperature. Below is an example of a cooling curve used in castings.
The initial point of the graph is the starting temperature of the matter, here noted as the "pouring temperature". When the phase change occurs, there is a "thermal arrest"; that is, the temperature stays constant. This is because the matter has more internal energy as a liquid or gas than in the state that it is cooling to. The amount of energy required for a phase change is known as latent heat. The "cooling rate" is the slope of the cooling curve at any point.
Alloy have range of melting point. It solidifies as above. First, molten alloy reaches to liquidus temperature and then freezing range starts. At solidus temperature, molten alloys becomes solid. | 0 | Theoretical and Fundamental Chemistry |
The overwhelming majority of aromatic compounds are compounds of carbon, but they need not be hydrocarbons. | 0 | Theoretical and Fundamental Chemistry |
In the analysis of sediments, C/N ratios are a proxy for paleoclimate research, having different uses whether the sediment cores are terrestrial-based or marine-based. Carbon-to-nitrogen ratios are an indicator for nitrogen limitation of plants and other organisms and can identify whether molecules found in the sediment under study come from land-based or algal plants. Further, they can distinguish between different land-based plants, depending on the type of photosynthesis they undergo. Therefore, the C/N ratio serves as a tool for understanding the sources of sedimentary organic matter, which can lead to information about the ecology, climate, and ocean circulation at different times in Earth's history. | 0 | Theoretical and Fundamental Chemistry |
Possibly the most exciting potential use for PECO is producing hydrogen to be used as a source of renewable energy. Photoelectrochemical oxidation reactions that take place within PEC cells are the key to water splitting for hydrogen production. While the main concern with this technology is stability, systems that use PECO technology to create hydrogen from vapor rather than liquid water has demonstrated potential for greater stability. Early researchers working on vapor fed systems developed modules with 14% solar to hydrogen (STH) efficiency, while remaining stable for 1000+ hours. More recently, further technological developments have been made, demonstrated by the direct air electrolysis (DAE) module developed by Jining Guo and his team, which produces 99% pure hydrogen from the air and has demonstrated stability of 8 months thus far.
Promising research and technological advancement using PECO for different applications like water and air treatment and hydrogen production suggests that it is a valuable tool that can be utilized in a variety of ways. | 0 | Theoretical and Fundamental Chemistry |
Static fatigue describes how prolonged and constant cyclic stress weakens a material until it breaks apart, which is called failure. Static fatigue is sometimes called "delayed fracture". The damage occurs at a lower stress level than the stress level needed to create a normal tensile fracture. Static fatigue can involve plastic deformation or crack growth. For example, repeated stress can create small cracks that grow and eventually break apart plastic, glass, or ceramic materials. The material reaches failure faster by increasing cyclic stress. Static fatigue varies with material type and environmental factors, such as moisture presence and temperature. | 1 | Applied and Interdisciplinary Chemistry |
Oxyhydrogen is a mixture of hydrogen (H) and oxygen (O) gases. This gaseous mixture is used for torches to process refractory materials and was the first
gaseous mixture used for welding. Theoretically, a ratio of 2:1 hydrogen:oxygen is enough to achieve maximum efficiency; in practice a ratio 4:1 or 5:1 is needed to avoid an oxidizing flame.
This mixture may also be referred to as (Scandinavian and German ; ), although some authors define knallgas to be a generic term for the mixture of fuel with the precise amount of oxygen required for complete combustion, thus 2:1 oxyhydrogen would be called "hydrogen-knallgas".
"Brown's gas" and HHO are terms for oxyhydrogen originating in pseudoscience, although is preferred due to meaning . | 0 | Theoretical and Fundamental Chemistry |
Although enol ethers can be considered the ether of the corresponding enolates, they are not prepared by alkylation of enolates. Some enol ethers are prepared from saturated ethers by elimination reactions.
Alternatively, vinyl ethers can be prepared from alcohols by iridium-catalyzed transesterification of vinyl esters, especially the widely available vinyl acetate:
:ROH + CH=CHOAc → ROCH=CH + HOAc
Vinyl ethers can be prepared by reaction of acetylene and alcohols in presence of a base. | 0 | Theoretical and Fundamental Chemistry |
There are 3 types of tumor suppressor genes:
* Genes that affect cell growth
* Genes that limit the cell cycle and induce apoptosis
* Genes that repair damaged DNA
SFRP1 appears to fall in the first category of genes, those that affect cell growth.
The role of SFRP1 as a tumor suppressor has been proposed in many cancers, based on its loss in patient tumors. Its frequent inactivation by methylation-induced silencing is consistent with it behaving as a tumor suppressor. Also, the SFRP1 gene is located in a region on chromosome 8 that is frequently lost in many cancer types. Expression levels of several targets of the Wnt signaling pathways are increased in tumor tissue compared with normal, and the expression of SFRP1 is lost in patient tumor samples. The role for the Wnt/β-catenin signaling in cancer has been well defined: β-catenin drives transcription of genes that contribute to the tumor phenotype by regulating processes such as proliferation, survival and invasion.
Gumz et al. showed that SFRP1 expression in UMRC3 cells (clear cell renal cell carcinoma cell line) resulted in a growth-inhibited phenotype. SFRP1 expression not only reduced the expression of Wnt target genes, but also markedly inhibited tumor cell growth in culture, soft agar and xenografts in athymic nude mice. Growth in culture and anchorage-independent growth were inhibited in SFRP1-expressing UMRC3 cells. The growth-inhibitory effects of SFRP1 were due primarily to decreased cell proliferation rather than an increase in apoptosis. This was consistent with the effect of SFRP1 on cellular proliferation as seen in prostate cancer, where retroviral-mediated expression of SFRP1 resulted in inhibited cellular proliferation but had no effect on apoptosis. Also, restoration of SFRP1 expression attenuated the malignant phenotype of cRCC; moreover, other studies showed reexpression of SFRP1 resulted in decreased colony formation in colon and lung cancer models. | 1 | Applied and Interdisciplinary Chemistry |
Large thermal reactors with low flux coupling between regions may experience spatial power oscillations because of the non-uniform presence of xenon-135. Xenon-induced spatial power oscillations occur as a result of rapid perturbations to power distribution that cause the xenon and iodine distribution to be out of phase with the perturbed power distribution. This results in a shift in xenon and iodine distributions that causes the power distribution to change in an opposite direction from the initial perturbation.
The instantaneous production rate of xenon-135 is dependent on the iodine-135 concentration and therefore on the local neutron flux history. On the other hand, the destruction rate of xenon-135 is dependent on the instantaneous local neutron flux.
The combination of delayed generation and high neutron-capture cross section produces a diversity of impacts on nuclear reactor operation. The mechanism is described in the following four steps.
# An initial lack of symmetry (for example, axial symmetry, in the case of axial oscillations) in the core power distribution (for example as a result of significant control rods movement) causes an imbalance in fission rates within the reactor core, and therefore, in the iodine-135 buildup and the xenon-135 absorption.
# In the high-flux region, xenon-135 burnout allows the flux to increase further, while in the low-flux region, the increase in xenon-135 causes a further reduction in flux. The iodine concentration increases where the flux is high and decreases where the flux is low. This shift in the xenon distribution is such as to increase (decrease) the multiplication properties of the region in which the flux has increased (decreased), thus enhancing the flux tilt.
# As soon as the iodine-135 levels build up sufficiently, decay to xenon reverses the initial situation. Flux decreases in this area, and the former low-flux region increases in power.
# Repetition of these patterns can lead to xenon oscillations moving about the core with periods on the order of about 24 hours.
With little change in overall power level, these oscillations can significantly change the local power levels. This oscillation may go unnoticed and reach dangerous local flux levels if only the total power of the core is monitored. Therefore, most PWRs use tandem power range excore neutron detectors to monitor upper and lower halves of the core separately. | 0 | Theoretical and Fundamental Chemistry |
The Henry adsorption constant is the constant appearing in the linear adsorption isotherm, which formally resembles Henrys law; therefore, it is also called Henrys adsorption isotherm. It is named after British chemist William Henry. This is the simplest adsorption isotherm in that the amount of the surface adsorbate is represented to be proportional to the partial pressure of the adsorptive gas:
where:
* X - surface coverage,
* P - partial pressure,
* K - Henry's adsorption constant.
For solutions, concentrations, or activities, are used instead of the partial pressures.
The linear isotherm can be used to describe the initial part of many practical isotherms. It is typically taken as valid for low surface coverages, and the adsorption energy being independent of the coverage (lack of inhomogeneities on the surface).
The Henry adsorption constant can be defined as:
where:
* is the number density at free phase,
* is the surface number density, | 0 | Theoretical and Fundamental Chemistry |
Transannular strain can be eliminated by the simple addition of a carbon bridge. E,Z,E,Z,Z-[10]-annulene is quite unstable; while it has the requisite number of π-electrons to be aromatic, they are for the most part isolated. Ultimately, the molecule itself is very difficult to observe. However, by the simple addition of a methylene bridge between the 1 and 6 positions, a stable, flat, aromatic molecule can be made and observed. | 0 | Theoretical and Fundamental Chemistry |
An overlayer is a layer of adatoms adsorbed onto a surface, for instance onto the surface of a single crystal. | 0 | Theoretical and Fundamental Chemistry |
Although RNA polymerase holoenzyme shows high affinity to non-specific sites of the DNA, this characteristic does not allow us to clarify the process of promoter location. This process of promoter location has been attributed to the structure of the holoenzyme to DNA and sigma 4 to DNA complexes. | 1 | Applied and Interdisciplinary Chemistry |
A centisome is a unit of length defined as one percent of the length of a particular chromosome. This course unit of physical DNA length began to be used in the early exploration of genomes through molecular biology before the resolution of the nucleic acid sequences of chromosomes was possible.
One of the main uses for this unit was for describing the locus of a gene by giving a distance in centisomes from a reference point on the chromosome. For instance, when the complete genome of the bacterium Escherichia coli was finally completed in 1997, it was presented with a scale given in centisomes (as well as one in kilobases). Since bacterial chromosomes are circular, the reference point cannot be an end of the DNA molecule, but must be some point that has some easily determinable unique characteristic. Often this point is the origin of replication, although for E. coli it is the origin of transfer during conjugation. Hence, the reference point for centisome positions is simply a convention established for each individual species of organism.
For the most part, modern scientific literature uses "centisome" as part of a shorthand way of referring to a particular region of interest on the chromosome of particular organisms. For instance, much research has been done on the "Centisome 63" area of the chromosomes of Salmonella species. | 1 | Applied and Interdisciplinary Chemistry |
The average wholesale price (AWP) for oxacillin products are provided as follows. The prices listed below are intended to serve as reference values and do not represent the pricing determined by any single manufacturer or entity.
*Bactocill in Dextrose Intravenous
**1 g/50 mL: $20.37
**2 g/50 mL: $32.48
*Oxacillin Sodium Injection
**1 g: $17.52
**2 g: $33.99
**10 g: $138.77 | 0 | Theoretical and Fundamental Chemistry |
The calcium cycle links ionic and non ionic calcium together in both marine and terrestrial environments and is essential for the functioning of all living organisms. In animals, calcium enables neurons to transmit signals by opening voltage gated channels that allow neurotransmitters to reach the next cell, bone formation and development and kidney function, whilst being maintained by hormones that ensure calcium homeostasis is reached. In plants, calcium promotes enzyme activity and ensures cell wall function, providing stability to plants. It also enables crustaceans to form shells and corals to exist, as calcium provides structure, rigidity and strength to structures when complexed (combined) to other atoms. Without its presence in the environment, many life-preserving processes would not exist. In the modern context, calcium also enables many industrial processes to occur, promoting further technological developments.
With its close relation to the carbon cycle and the effects of greenhouse gasses, both calcium and carbon cycles are predicted to change in the coming years. Tracking calcium isotopes enables the prediction of environmental changes, with many sources suggesting increasing temperatures in both the atmosphere and marine environment. As a result, this will drastically alter the breakdown of rock, the pH of oceans and waterways and thus calcium sedimentation, hosting an array of implications on the calcium cycle.
Due to the complex interactions of calcium with many facets of life, the effects of altered environmental conditions are unlikely to be known until they occur. Predictions can however be tentatively made, based upon evidence-based research. Increasing carbon dioxide levels and decreasing ocean pH will alter calcium solubility, preventing corals and shelled organisms from developing their calcium-based exoskeletons, thus making them vulnerable or unable to survive. | 1 | Applied and Interdisciplinary Chemistry |
A siphon rain gauge is a rain gauge that can record rainfall over an extended period. A siphon is used to automatically empty the gauge. It is often simply called a "siphon gauge" and is not to be confused with a siphon pressure gauge. | 1 | Applied and Interdisciplinary Chemistry |
Enhancers or cis-regulatory modules/elements (CRM/CRE) are non-coding DNA sequences containing multiple activator and repressor binding sites. Enhancers range from 200 bp to 1 kb in length and can be either proximal, 5’ upstream to the promoter or within the first intron of the regulated gene, or distal, in introns of neighboring genes or intergenic regions far away from the locus. Through DNA looping, active enhancers contact the promoter dependently of the core DNA binding motif promoter specificity. Promoter-enhancer dichotomy provides the basis for the functional interaction between transcription factors and transcriptional core machinery to trigger RNA Pol II escape from the promoter. Whereas one could think that there is a 1:1 enhancer-promoter ratio, studies of the human genome predict that an active promoter interacts with 4 to 5 enhancers. Similarly, enhancers can regulate more than one gene without linkage restriction and are said to “skip” neighboring genes to regulate more distant ones. Even though infrequent, transcriptional regulation can involve elements located in a chromosome different from one where the promoter resides. Proximal enhancers or promoters of neighboring genes can serve as platforms to recruit more distal elements. | 1 | Applied and Interdisciplinary Chemistry |
# Multimedia filters use multiple layers of different filter media to achieve more effective and efficient filtration than single-media filters like sand filters.
# They can remove a wider range of particle sizes and types than single-media filters, resulting in more efficient filtration and longer filter life.
# They are effective at removing suspended solids, turbidity, and other contaminants from water.
# They can be used for a wide range of flow rates and particle sizes. They can be easily backwashed to clean the filter media and restore filtration efficiency.
# They require little to no electricity to operate. | 1 | Applied and Interdisciplinary Chemistry |
* Alfred P. Sloan Fellow, 1961-65
* NSF Senior Postdoctoral Fellow, 1968-69
* Heinrich Hertz Fellow (West Germany)
* Meyerhoff Fellow (Israel)
* Fellow of the American Physical Society, citation: For his many contributions to the statistical mechanics of transport processes, especially to the understanding of Brownian motion and the couplings of moving molecules, 1983. | 0 | Theoretical and Fundamental Chemistry |
Transferrins are glycoproteins that are often found in biological fluids of vertebrates. When a transferrin protein loaded with iron encounters a transferrin receptor on the surface of a cell, e.g., erythroid precursors in the bone marrow, it binds to it and is transported into the cell in a vesicle by receptor-mediated endocytosis. The pH of the vesicle is reduced by hydrogen ion pumps ( ATPases) to about 5.5, causing transferrin to release its iron ions. Iron release rate is dependent on several factors including pH levels, interactions between lobes, temperature, salt, and chelator. The receptor with its ligand bound transferrin is then transported through the endocytic cycle back to the cell surface, ready for another round of iron uptake.
Each transferrin molecule has the ability to carry two iron ions in the ferric form (). | 1 | Applied and Interdisciplinary Chemistry |
The Boltzmann equation is valid only under several assumptions. For instance, the particles are assumed to be pointlike, i.e. without having a finite size. There exists a generalization of the Boltzmann equation that is called the Enskog equation. The collision term is modified in Enskog equations such that particles have a finite size, for example they can be modelled as spheres having a fixed radius.
No further degrees of freedom besides translational motion are assumed for the particles. If there are internal degrees of freedom, the Boltzmann equation has to be generalized and might possess inelastic collisions.
Many real fluids like liquids or dense gases have besides the features mentioned above more complex forms of collisions, there will be not only binary, but also ternary and higher order collisions. These must be derived by using the BBGKY hierarchy.
Boltzmann-like equations are also used for the movement of cells. Since cells are composite particles that carry internal degrees of freedom, the corresponding generalized Boltzmann equations must have inelastic collision integrals. Such equations can describe invasions of cancer cells in tissue, morphogenesis, and chemotaxis-related effects. | 1 | Applied and Interdisciplinary Chemistry |
Organostannane addition reactions comprise the nucleophilic addition of an allyl-, allenyl-, or propargylstannane to an aldehyde, imine, or, in rare cases, a ketone. The reaction is widely used for carbonyl allylation.
Organostannane addition to carbonyl groups constitutes one of the most common and efficient methods for the construction of contiguous, oxygen-containing stereocenters in organic molecules. As many molecules containing this motif—polypropionates and polyacetates, for instance—are desired by natural products chemists, the title reaction has become important synthetically and has been heavily studied over the years. Substituted allylstannanes may create one or two new stereocenters, often with a very high degree of stereocontrol.
Organostannanes are known for their stability, ease of handling, and selective reactivity. Chiral allylstannanes often react with good stereoselectivity to give single diastereomers. Models explaining the sense of selectivity are reliable. In terms of disadvantages, stoichiometric amounts of metal-containing byproducts are generated. Additions to sterically encumbered pi bonds, such as those of ketones, are uncommon. | 0 | Theoretical and Fundamental Chemistry |
The continuous process of applying up to three separate coating layers onto one or both sides of a metal strip substrate occurs on a coil coating line. These lines vary greatly in size, with widths from and speeds from ; however, all coil-coating lines share the same basic process steps.
A typical organic coil coating line consists of decoilers, entry strip accumulator, cleaning, chemical pretreatment, primer coat application, curing, final coat application, curing, exit accumulator and recoilers.
The following steps take place on a modern coating line:
* Mechanical stitching of the strip to its predecessor
* Cleaning the strip
* Power brushing
* Surface treatment by chemical conversion
* Drying the strip
* Application of primer on one or both sides
* Passage through the first curing oven (between 15 and 60 seconds)
* Cooling the strip
* Coating the finish on one or both sides
* Passage through the second curing oven (between 15 and 60 seconds)
* Cooling down to room temperature
* Rewinding of the coated coil | 1 | Applied and Interdisciplinary Chemistry |
An example of a short-lived fission product is iodine-131, this can also be formed as an activation product by the neutron activation of tellurium.
In both bomb fallout and a release from a power reactor accident, the short-lived isotopes cause the dose rate on day one to be much higher than that which will be experienced at the same site many days later. This holds true even if no attempts at decontamination are made. In the graphs below, the total gamma dose rate and the share of the dose due to each main isotope released by the Chernobyl accident are shown. | 0 | Theoretical and Fundamental Chemistry |
Druglikeness is a qualitative concept used in drug design for how "druglike" a substance is with respect to factors like bioavailability. It is estimated from the molecular structure before the substance is even synthesized and tested. A druglike molecule has properties such as:
*Solubility in both water and fat, as an orally administered drug needs to pass through the intestinal lining after it is consumed, be carried in aqueous blood and penetrate the lipid-based cell membrane to reach the inside of a cell. A model compound for the lipophilic cellular membrane is 1-octanol (a lipophilic medium-chain fatty alcohol), so the logarithm of the octanol-water partition coefficient, known as LogP, is used to predict the solubility of a potential oral drug. This coefficient can be experimentally measured or predicted computationally, in which case it is sometimes called "cLogP". As the lipophilicity of ionizable compounds is strongly dependent of pH, the distribution coefficient logD, or a logP vs pH curve may be used instead.
*Potency at the biological target. High potency (high value of pIC) is a desirable attribute in drug candidates, as it reduces the risk of non-specific, off-target pharmacology at a given concentration. When associated with low clearance, high potency also allows for low total dose, which lowers the risk of idiosyncratic drug reactions.
*Ligand efficiency and lipophilic efficiency.
*Molecular weight: The smaller the better, because diffusion is directly affected. The great majority of drugs on the market have molecular weights between 200 and 600 daltons, and particularly <500; they belong to the group of small molecules.
A traditional method to evaluate druglikeness is to check compliance of Lipinski's Rule of Five, which covers the numbers of hydrophilic groups, molecular weight and hydrophobicity.
Since the drug is transported in aqueous media like blood and intracellular fluid, it has to be sufficiently water-soluble in the absolute sense (i.e. must have a minimum chemical solubility in order to be effective). Solubility in water can be estimated from the number of hydrogen bond donors vs. alkyl sidechains in the molecule. Low water solubility translates to slow absorption and action. Too many hydrogen bond donors, on the other hand, lead to low fat solubility, so that the drug cannot penetrate the cell membrane to reach the inside of the cell.
Based on one definition, a drug-like molecule has a logarithm of partition coefficient (log P) between -0.4 and 5.6, molecular weight 160-480 g/mol, molar refractivity of 40–130, which is related to the volume and molecular weight of the molecule and has 20-70 atoms.
Substructures with known toxic, mutagenic or teratogenic properties affect the usefulness of a designed molecule. However, several poisons have a good druglikeness. Natural toxins are used in pharmacological research to find out their mechanism of action, and if it could be exploited for beneficial purposes. Alkylnitro compounds tend to be irritants, and Michael acceptors, such as enones, are alkylating agents and thus potentially mutagenic and carcinogenic.
Druglikeness indices are inherently limited tools. Druglikeness can be estimated for any molecule, and does not evaluate the actual specific effect that the drug achieves (biological activity). Simple rules are not always accurate and may unnecessarily limit the chemical space to search: many best-selling drugs have features that cause them to score low on various druglikeness indices. Furthermore, first-pass metabolism, which is biochemically selective, can destroy the pharmacological activity of a compound despite good druglikeness.
Druglikeness is not relevant for most biologics, since they are usually proteins that need to be injected, because proteins are digested if eaten. | 1 | Applied and Interdisciplinary Chemistry |
# Magnetic materials e.g. alnico, sendust, Permendur, FeCo, Terfenol-D
# Superconductors e.g. A15 phases, niobium-tin
# Hydrogen storage e.g. AB compounds (nickel metal hydride batteries)
# Shape memory alloys e.g. Cu-Al-Ni (alloys of CuAl and nickel), Nitinol (NiTi)
# Coating materials e.g. NiAl
# High-temperature structural materials e.g. nickel aluminide, NiAl
# Dental amalgams, which are alloys of intermetallics AgSn and CuSn
# Gate contact/ barrier layer for microelectronics e.g. TiSi
# Laves phases (AB), e.g., MgCu, MgZn and MgNi.
The formation of intermetallics can cause problems. For example, intermetallics of gold and aluminium can be a significant cause of wire bond failures in semiconductor devices and other microelectronics devices. The management of intermetallics is a major issue in the reliability of solder joints between electronic components. | 1 | Applied and Interdisciplinary Chemistry |
Contact angle, or wetting angle, is a very important parameter in real systems where perfect wetting ( = 0) is hardly ever achieved. The Young equation provides reasoning for contact angle involvement in capillary condensation. The Young Equation explains that the surface tension between the liquid and vapor phases is scaled to the cosine of the contact angle. As shown in the figure to the right, the contact angle between a condensed liquid and the inner wall of a capillary can affect the radius of curvature a great deal. For this reason, contact angle is coupled inherently to the curvature term of the Kelvin equation. As the contact angle increases, the radius of curvature will increase as well. This is to say that a system with perfect wetting will exhibit a larger amount of liquid in its pores than a system with non-perfect wetting ( > 0). Also, in systems where = 0 the radius of curvature is equal to the capillary radius. Due to these complications caused by contact angle, scientific studies are often designed to assume = 0. | 1 | Applied and Interdisciplinary Chemistry |
Nilson was professor of analytical chemistry at Uppsala from 1878 until 1883, when he became professor of chemistry of the Royal Swedish Academy of Agriculture and Forestry in Stockholm. As an agricultural chemist and Director of the Agricultural Chemical Experiment Station, he published nearly sixty papers concerning topics such as soils and manures. As a result of his inquiries many of the swamps of Gothland were drained and cultivated. The sugar beet was introduced and became a major crop, as chalky moors were treated with potash fertilizers.
He also conducted studies of cow's milk and various plants for cattle fodder.
Nilson was elected a foreign member of the Chemical Society of Great Britain on February 2, 1888.
Nilson was a member of several other academies as well. He received several awards, including the Order of the Polar Star. | 1 | Applied and Interdisciplinary Chemistry |
In 1908, Lawrence Joseph Henderson derived an equation to calculate the hydrogen ion concentration of a bicarbonate buffer solution, which rearranged looks like this:
In 1909 Søren Peter Lauritz Sørensen introduced the pH terminology, which allowed Karl Albert Hasselbalch to re-express Henderson's equation in logarithmic terms, resulting in the Henderson–Hasselbalch equation. | 0 | Theoretical and Fundamental Chemistry |
Cosmid vectors are plasmids that contain a small region of bacteriophage λ DNA called the cos sequence. This sequence allows the cosmid to be packaged into bacteriophage λ particles. These particles- containing a linearized cosmid- are introduced into the host cell by transduction. Once inside the host, the cosmids circularize with the aid of the host's DNA ligase and then function as plasmids. Cosmids are capable of carrying inserts up to 40kb in size. | 1 | Applied and Interdisciplinary Chemistry |
Grid spectroscopy is an extension of force spectroscopy described above. In grid spectroscopy multiple force spectra are taken in a grid over a surface, to build up a three-dimensional force map above the surface. These experiments can take a considerable time, often over 24 hours, thus the microscope is usually cooled with liquid helium or an atom tracking method is employed to correct for drift. | 0 | Theoretical and Fundamental Chemistry |
An orifice plate is a device used for measuring flow rate, for reducing pressure or for restricting flow (in the latter two cases it is often called a ). | 1 | Applied and Interdisciplinary Chemistry |
Spontaneous deamination of 5-methylcytosine results in thymine and ammonia. This is the most common single nucleotide mutation. In DNA, this reaction, if detected prior to passage of the replication fork, can be corrected by the enzyme thymine-DNA glycosylase, which removes the thymine base in a G/T mismatch. This leaves an abasic site that is repaired by AP endonucleases and polymerase, as with uracil-DNA glycosylase. | 1 | Applied and Interdisciplinary Chemistry |
PEMFCs have some advantages over other types of fuel cells such as solid oxide fuel cells (SOFC). PEMFCs operate at a lower temperature, are lighter and more compact, which makes them ideal for applications such as cars.
However, some disadvantages are: the ~80 °C operating temperature is too low for cogeneration like in SOFCs, and that the electrolyte for PEMFCs must be water-saturated. However, some fuel-cell cars, including the Toyota Mirai, operate without humidifiers, relying on rapid water generation and the high rate of back-diffusion through thin membranes to maintain the hydration of the membrane, as well as the ionomer in the catalyst layers.
High-temperature PEMFCs operate between 100 °C and 200 °C, potentially offering benefits in electrode kinetics and heat management, and better tolerance to fuel impurities, particularly CO in reformate. These improvements potentially could lead to higher overall system efficiencies. However, these gains have yet to be realized, as the gold-standard perfluorinated sulfonic acid (PFSA) membranes lose function rapidly at 100 °C and above if hydration drops below ~100%, and begin to creep in this temperature range, resulting in localized thinning and overall lower system lifetimes. As a result, new anhydrous proton conductors, such as protic organic ionic plastic crystals (POIPCs) and protic ionic liquids, are actively studied for the development of suitable PEMs.
The fuel for the PEMFC is hydrogen, and the charge carrier is the hydrogen ion (proton). At the anode, the hydrogen molecule is split into hydrogen ions (protons) and electrons. The hydrogen ions permeate across the electrolyte to the cathode, while the electrons flow through an external circuit and produce electric power. Oxygen, usually in the form of air, is supplied to the cathode and combines with the electrons and the hydrogen ions to produce water. The reactions at the electrodes are as follows:
:Anode reaction:
::2H → 4H + 4e
:Cathode reaction:
::O + 4H + 4e → 2HO
:Overall cell reaction:
::2H + O → 2HO + heat + electrical energy
The theoretical exothermic potential is +1.23 V overall. | 0 | Theoretical and Fundamental Chemistry |
* Photosynthesis, a process whereby carbon dioxide and water are transformed into a number of organic molecules in plant cells.
* Nitrogen fixation from the soil into organic molecules by symbiotic bacteria which live in the roots of certain plants, such as Leguminosae.
* Magnesium supplements orotate, oxide, sulfate, citrate, and glycerate are all structurally similar. However, oxide and sulfate are not water-soluble and do not enter the bloodstream, while orotate and glycerate have normal exiguous liver conversion. Chlorophyll sources or magnesium citrate are highly bioassimilable.
* The absorption of nutrients into the body after digestion in the intestine and its transformation in biological tissues and fluids. | 1 | Applied and Interdisciplinary Chemistry |
The first cast iron pipe was produced in horizontal moulds, the core of the mould would be supported on small iron rods which would become part of the pipe. Horizontal casting resulted in an uneven distribution of metal around the pipe circumference. Typically slag would collect at the crown of the pipe creating a much weaker section. | 1 | Applied and Interdisciplinary Chemistry |
Pepper spray typically comes in canisters, which are often small enough to be carried or concealed in a pocket or purse. Pepper spray can also be purchased concealed in items such as rings. There are also pepper spray projectiles available, which can be fired from a paintball gun or similar platform. It has been used for years against demonstrators and aggressive animals like bears. There are also many types such as foam, gel, foggers, and spray. | 1 | Applied and Interdisciplinary Chemistry |
The English word amber derives from the Arabic word (; ultimately from Middle Persian ambar, also ambergris), via Middle Latin ambar and Middle French ambre. The word "amber", in its sense of "ambergris", was adopted in Middle English in the 14th century.
The word "ambergris" comes from the Old French ambre gris or "grey amber". The addition of "grey" came about when, in the Romance languages, the sense of the word "amber" was extended to Baltic amber (fossil resin), as white or yellow amber (ambre jaune), from as early as the late 13th century. This fossilized resin subsequently became the dominant (and now exclusive) sense of "amber", leaving "ambergris" as the word for the whale secretion.
The archaic alternate spelling "ambergrease" arose as an eggcorn from the phonetic pronunciation of "ambergris," encouraged by the substance's waxy texture. | 1 | Applied and Interdisciplinary Chemistry |
For deprotection (regeneration of the alcohol)
* Aqueous base (pH >9)
* Aqueous acid (pH <2), may have to be heated
* Anhydrous base such as sodium methoxide in methanol. Very useful when a methyl ester of a carboxylic acid is also present in the molecule, as it will not hydrolyze it like an aqueous base would. (Same also holds with an ethoxide in ethanol with ethyl esters) | 0 | Theoretical and Fundamental Chemistry |
Although untrue from an historical perspective (see the history of the steroid, cortisone), total synthesis in the modern age has largely been an academic endeavor (in terms of manpower applied to problems). Industrial chemical needs often differ from academic focuses. Typically, commercial entities may pick up particular avenues of total synthesis efforts and expend considerable resources on particular natural product targets, especially if semi-synthesis can be applied to complex, natural product-derived drugs. Even so, for decades there has been a continuing discussion regarding the value of total synthesis as an academic enterprise. While there are some outliers, the general opinions are that total synthesis has changed in recent decades, will continue to change, and will remain an integral part of chemical research. Within these changes, there has been increasing focus on improving the practicality and marketability of total synthesis methods. The Phil S. Baran group at Scripps, a notable pioneer of practical synthesis have endeavored to create scalable and high efficiency syntheses that would have more immediate uses outside of academia. | 0 | Theoretical and Fundamental Chemistry |
Silvana Konermann is a Swiss-American biochemist whose research involves CRISPR, Cas9, and their use in genome editing. She is an assistant professor of biochemistry at Stanford University, as well as the Director and co-founder of the Arc Institute in Palo Alto. | 1 | Applied and Interdisciplinary Chemistry |
On August 18, 1926, Otto Raubenheimer from the US, the Austrian Ludwig Winkler and the Germans Fritz Ferchl, Georg Urdang, Walther Zimmermann, founded the Gesellschaft für Geschichte der Pharmazie (Society for the History of Pharmacy) in Innsbruck, Austria
The Second World War interrupted the societys activities but after that it reformed and in 1949 gave itself the name Internationale Gesellschaft für Geschichte der Pharmazie and also appears under equivalent English- or French-language names: International Society for the History of Pharmacy or Société Internationale dHistoire de la Pharmacie. | 1 | Applied and Interdisciplinary Chemistry |
The AR is defined as the collection all possible outcomes for all conceivable reactor combinations. Geometrically, the AR may (for instance) be represented as a convex region in state space representing all possible outlet compositions for all reactor combinations. A combination of reactors is often termed a reactor structure. An example of the reactors that are considered for this theory are Continuous flow stirred-tank reactor (CSTR) and a Plug flow reactor model (PFR).
Knowledge of the AR helps to address two areas in chemical reactor design:
# The reactor network synthesis problem: Given a system of reactions and feed point, construction of the AR assists with determining an optimal reactor structure that achieves a desired duty or objective function. That is, AR theory assists with understanding specifically what type and combination of the chemical reactors are best suited for a particular system and duty.
# Performance targeting: Given an existing reactor design, knowledge of the AR assists with understanding if there are other reactor structures that could achieve superior performance, by comparison to its location in the AR. Seeing as the AR represents all reactor designs by definition, different proposed reactor designs must lie as a point in or on the AR in state space. The effectiveness of each design may then all be assessed by comparison the AR and their relation to objective functions if any. | 1 | Applied and Interdisciplinary Chemistry |
Williams Haynes was born in Detroit, where his father, David Oliphant Haynes, was the publisher of The Pharmaceutical Era, as well as the president and the general manager of D. O. Haynes & Co. In 1896 D. O. Haynes established in New York City the New York Commercial as a daily newspaper on business.
Williams Haynes worked as a reporter for the New York Sun and as an editor for Field and Fancy from 1906 to 1907. He enrolled in 1908 as a special student at Johns Hopkins University, where he studied economics, biology, and chemistry, but left in 1911 without a degree. He married his first wife in June 1911. From 1911 to 1916 he was a contributor to magazines and newspapers and at various times visited Canada and Europe as a journalist. From 1914 to 1915 he was editor-in-chief of the Northampton, Massachusetts Herald (a daily newspaper). In 1916 he became the editorial director of D. O. Haynes & Co. As editorial director he was responsible for the chemical industry journal Drug and Chemical Markets and in 1920 became the journals publisher. In 1926 he split the journal into two journals: Drugs and Cosmetics Industry and Chemical Industries (later called Chemical Week under the ownership of McGraw-Hill). In 1926 he also began publishing Plastic Products (renamed Modern Plastics, published from 1934 to 2004). In 1928 he established the book series Chemical Who’s Who' and was editor-in-chief of the series until 1951. In 1939 Haynes sold his interest in the trade journals in order to focus his efforts as an author and editor. He moved to a property near Stonington in eastern Connecticut. The property, which had been in his family for several generations, had a farmhouse built in 1750.
As a journalist he contributed to The Outlook, The Nation, The Dial, Science, and Outing, among other publications. His extensive photo collection of chemists came to the Science History Institute through The Chemists' Club of New York.
In 1950 Haynes was awarded the Honorable Cornelius Amory Pugsley Bronze Medal for his work in protecting the natural environment. In 1957 he received the Dexter Award for his work as a historian of the American chemical industry.
He was married twice. There were two daughters from his second marriage. | 1 | Applied and Interdisciplinary Chemistry |
Organic solar cells and polymer solar cells are built from thin films (typically 100 nm) of organic semiconductors including polymers, such as polyphenylene vinylene and small-molecule compounds like copper phthalocyanine (a blue or green organic pigment) and carbon fullerenes and fullerene derivatives such as PCBM.
They can be processed from liquid solution, offering the possibility of a simple roll-to-roll printing process, potentially leading to inexpensive, large-scale production. In addition, these cells could be beneficial for some applications where mechanical flexibility and disposability are important. Current cell efficiencies are, however, very low, and practical devices are essentially non-existent.
Energy conversion efficiencies achieved to date using conductive polymers are very low compared to inorganic materials. However, Konarka Power Plastic reached efficiency of 8.3% and organic tandem cells in 2012 reached 11.1%.
The active region of an organic device consists of two materials, one electron donor and one electron acceptor. When a photon is converted into an electron hole pair, typically in the donor material, the charges tend to remain bound in the form of an exciton, separating when the exciton diffuses to the donor-acceptor interface, unlike most other solar cell types. The short exciton diffusion lengths of most polymer systems tend to limit the efficiency of such devices. Nanostructured interfaces, sometimes in the form of bulk heterojunctions, can improve performance.
In 2011, MIT and Michigan State researchers developed solar cells with a power efficiency close to 2% with a transparency to the human eye greater than 65%, achieved by selectively absorbing the ultraviolet and near-infrared parts of the spectrum with small-molecule compounds. Researchers at UCLA more recently developed an analogous polymer solar cell, following the same approach, that is 70% transparent and has a 4% power conversion efficiency. These lightweight, flexible cells can be produced in bulk at a low cost and could be used to create power generating windows.
In 2013, researchers announced polymer cells with some 3% efficiency. They used block copolymers, self-assembling organic materials that arrange themselves into distinct layers. The research focused on P3HT-b-PFTBT that separates into bands some 16 nanometers wide. | 0 | Theoretical and Fundamental Chemistry |
Carboxylation of benzyl halides has been reported. The reaction mechanism is proposed to involve oxidative addition of benzyl chloride to Ni(0). The Ni(II) benzyl complex is reduced to Ni(I), e.g., by zinc, which inserts CO delivering the nickel carboxylate. Reduction of the Ni(I) carboxylate to Ni(0) releases the zinc carboxylate (Scheme 6). Similarly, such carboxylation has been achieved on aryl and benzyl pivalate, alkyl halides, and allyl esters. | 0 | Theoretical and Fundamental Chemistry |
Vomiting agents are chemical weapon agents causing vomiting. Prolonged exposure can be lethal. They were used for the first time during WWI. | 1 | Applied and Interdisciplinary Chemistry |
Over more than a ten-year span, engineers in former Yugoslavian Institute of Thermal and Nuclear Technology (ITEN), Energoinvest Co., Sarajevo, had built the first experimental Magneto-Hydrodynamic facility power generator in 1989. It was here it was first patented. | 1 | Applied and Interdisciplinary Chemistry |
The formation evaluation gamma ray log is a record of the variation with depth of the natural radioactivity of earth materials in a wellbore. Measurement of natural emission of gamma rays in oil and gas wells are useful because shales and sandstones typically have different gamma ray levels. Shales and clays are responsible for most natural radioactivity, so gamma ray log often is a good indicator of such rocks. In addition, the log is also used for correlation between wells, for depth correlation between open and cased holes, and for depth correlation between logging runs. | 0 | Theoretical and Fundamental Chemistry |
* Hoffman-La Roche Award from the Canadian Society for Chemistry (1997)
* Ottawa Life Sciences Council Achievement Award (2001)
* Rotary International Paul Harris Fellowship (2001)
* National Research Council of Canada Royalty Sharing Award (2001)
* Melville L. Wolfrom Award from the American Chemical Society Division of Carbohydrate Chemistry (2003)
* Gold Medal from the World Intellectual Property Organization (WIPO) (2005)
* Tech Museum Award – Technology Benefiting Humanity the Hib Vaccine team (2005)
* Probst Memorial Lecturer – Southern Illinois University (2006)
* Award of Excellence in research from the Foundation of Stars - Montreal Children’s Hospital (2008)
* Médaille (medal) de l’Université du Québec À Montréal (UQAM) (2009)
* Léo-Pariseau Prize of the Association francophone pour le savoir (2010)
* "Prix Cercle d’Excellence” of the Université du Québec (2011)
* Canada Research Chair in Medicinal Chemistry (2004-2017) | 0 | Theoretical and Fundamental Chemistry |
The possum belly is used to slow the flow of returning drilling fluid before it hits the shale shakers. This enables the shale shaker to clean the cuttings out of the drilling fluid before it is returned to the pits for circulation. | 1 | Applied and Interdisciplinary Chemistry |
Tetrakis(hydroxymethyl)phosphonium chloride has industrial importance in the production of crease-resistant and flame-retardant finishes on cotton textiles and other cellulosic fabrics. A flame-retardant finish can be prepared from THPC by the Proban Process, in which THPC is treated with urea. The urea condenses with the hydroxymethyl groups on THPC. The phosphonium structure is converted to phosphine oxide as the result of this reaction. | 0 | Theoretical and Fundamental Chemistry |
Cos sequences are ~200 base pairs long and essential for packaging. They contain a cosN site where DNA is nicked at each strand, 12 bp apart, by terminase. This causes linearization of the circular cosmid with two "cohesive" or "sticky ends" of 12bp. (The DNA must be linear to fit into a phage head.) The cosB site holds the terminase while it is nicking and separating the strands. The cosQ site of next cosmid (as rolling circle replication often results in linear concatemers) is held by the terminase after the previous cosmid has been packaged, to prevent degradation by cellular DNases. | 1 | Applied and Interdisciplinary Chemistry |
After the fall of the Roman Empire, the focus of alchemical development moved to the Islamic World. Much more is known about Islamic alchemy because it was better documented: indeed, most of the earlier writings that have come down through the years were preserved as Arabic translations. The word alchemy itself was derived from the Arabic word al-kīmiyā (الكيمياء). The early Islamic world was a melting pot for alchemy. Platonic and Aristotelian thought, which had already been somewhat appropriated into hermetical science, continued to be assimilated during the late 7th and early 8th centuries through Syriac translations and scholarship.
In the late ninth and early tenth centuries, the Arabic works attributed to Jābir ibn Hayyān (Latinized as "Geber" or "Geberus") introduced a new approach to alchemy. Paul Kraus, who wrote the standard reference work on Jabir, put it as follows:
Islamic philosophers also made great contributions to alchemical hermeticism. The most influential author in this regard was arguably Jabir. Jabirs ultimate goal was Takwin, the artificial creation of life in the alchemical laboratory, up to, and including, human life. He analysed each Aristotelian element in terms of four basic qualities of hotness, coldness, dryness, and moistness. According to Jabir, in each metal two of these qualities were interior and two were exterior. For example, lead was externally cold and dry, while gold was hot and moist. Thus, Jabir theorized, by rearranging the qualities of one metal, a different metal would result. By this reasoning, the search for the philosophers stone was introduced to Western alchemy. Jabir developed an elaborate numerology whereby the root letters of a substances name in Arabic, when treated with various transformations, held correspondences to the elements physical properties.
The elemental system used in medieval alchemy also originated with Jabir. His original system consisted of seven elements, which included the five classical elements (aether, air, earth, fire, and water) in addition to two chemical elements representing the metals: sulphur, "the stone which burns", which characterized the principle of combustibility, and mercury, which contained the idealized principle of metallic properties. Shortly thereafter, this evolved into eight elements, with the Arabic concept of the three metallic principles: sulphur giving flammability or combustion, mercury giving volatility and stability, and salt giving solidity. The atomic theory of corpuscularianism, where all physical bodies possess an inner and outer layer of minute particles or corpuscles, also has its origins in the work of Jabir.
From the 9th to 14th centuries, alchemical theories faced criticism from a variety of practical Muslim chemists, including Alkindus, Abū al-Rayhān al-Bīrūnī, Avicenna and Ibn Khaldun. In particular, they wrote refutations against the idea of the transmutation of metals.
From the 14th century onwards, many materials and practices originally belonging to Indian alchemy (Rasayana) were assimilated in the Persian texts written by Muslim scholars. | 1 | Applied and Interdisciplinary Chemistry |
VMAT1 also has effects on the modulation of gastrin processing in G cells. These intestinal endocrine cells process amine precursors, and VMAT1 pulls them into vesicles for storage. The activity of VMAT1 in these cells has a seemingly inhibitory effect on the processing of gastrin. Essentially, this means that certain compounds in the gut can be taken into these G cells and either amplify or inhibit the function of VMAT1, which will impact gastrin processing (conversion from G34 to G17).
Additionally, VMAT1 is known to play a role in the uptake and secretion of serotonin in the gut. Enterochromaffin cells in the intestines will secrete serotonin in response to the activation of certain mechanosensors. The regulation of serotonin in the gut is critically important, as it modulates appetite and controls intestinal contraction. | 1 | Applied and Interdisciplinary Chemistry |
UV curing is used for converting or curing inks, adhesives, and coatings. UV-cured adhesive has become a high speed replacement for two-part adhesives, eliminating the need for solvent removal, ratio mixing, and potential life concern. It is used in flexographic, offset, pad, and screen printing processes; where UV curing systems are used to polymerize images on screen-printed products, ranging from T-shirts to 3D and cylindrical parts. It is used in fine instrument finishing (guitars, violins, ukuleles, etc.), pool cue manufacturing and other wood craft industries. Printing with UV curable inks provides the ability to print on a very wide variety of substrates such as plastics, paper, canvas, glass, metal, foam boards, tile, films, and many other materials.
Industries that use UV curing include medicine, automobiles, cosmetics (for example artificial fingernails and gel nail polish), food, science, education, and art. UV curable inks have successfully met the demands of the publication sector in terms of print quality, durability, and compatibility with different substrates, making them a suitable choice for printing applications in this industry. | 0 | Theoretical and Fundamental Chemistry |
The first Empowering Women in Organic Chemistry Conference took place on Friday, June 28, 2019, at the University of Pennsylvania, Philadelphia, PA.
2019 Career Panel featured Sarah Wengryniuk (Temple University), Emily McLaughlin (Bard College), Nikki Goodwin (GlaxoSmithKline), Jamie McCabe Dunn (Merck), Zhenzhen Dong (Adesis), Nicole Camasso (JACS). | 0 | Theoretical and Fundamental Chemistry |
Reactions used in DCvC must generate thermodynamically stable products to overcome the entropic cost of self-assembly. The reactions must form covalent linkages between building blocks. Finally, all possible intermediates must be reversible, and the reaction ideally proceeds under conditions that are tolerant of functional groups elsewhere in the molecule.
Reactions that can be used in DCvC are diverse and can be placed into two general categories. Exchange reactions involve the substitution of one reaction partner in an intermolecular reaction for another with an identical type of bonding. Some examples of this are shown in schemes 5 and 8, in an ester exchange, and disulfide exchange reactions. The second type, formation reactions, rely on the formation of new covalent bonds. Some examples include Diels–Alder and aldol reactions. In some cases, a reaction can pertain to both categories. For example, Schiff base formation can be categorized as a forming new covalent bonds between a carbonyl and primary amine. However, in the presence of two different amines the reaction becomes an exchange reaction where the two imine derivatives compete in equilibrium.
Exchange and formation reactions can be further broken down into three categories:
# Bonding between carbon–carbon
# Bonding between carbon–heteroatom
# Bonding between heteroatom–heteroatom | 0 | Theoretical and Fundamental Chemistry |
The following outline is provided as an overview of and topical guide to air pollution dispersion:
In environmental science, air pollution dispersion is the distribution of air pollution into the atmosphere. Air pollution is the introduction of particulates, biological molecules, or other harmful materials into Earths atmosphere, causing disease, death to humans, damage to other living organisms such as food crops, and the natural or built environment. Air pollution may come from anthropogenic or natural sources. Dispersion' refers to what happens to the pollution during and after its introduction; understanding this may help in identifying and controlling it.
Air pollution dispersion has become the focus of environmental conservationists and governmental environmental protection agencies (local, state, province and national) of many countries (which have adopted and used much of the terminology of this field in their laws and regulations) regarding air pollution control. | 1 | Applied and Interdisciplinary Chemistry |
Features, Events, and Processes (FEP) are terms used in the fields of radioactive waste management, carbon capture and storage, and hydraulic fracturing to define relevant scenarios for safety assessment studies. For a radioactive waste repository, features would include the characteristics of the site, such as the type of soil or geological formation the repository is to be built on or under. Events would include things that may or will occur in the future, like, e.g., glaciations, droughts, earthquakes, or formation of faults. Processes are things that are ongoing, such as the erosion or subsidence of the landform where the site is located on, or near.
Several catalogues of FEP's are publicly available, a.o., this one elaborated for the NEA Clay Club dealing with the disposal of radioactive waste in deep clay formations,
and those compiled for deep crystalline rocks (granite) by Svensk Kärnbränslehantering AB, SKB, the Swedish Nuclear Fuel and Waste Management Company. | 0 | Theoretical and Fundamental Chemistry |
Chiral recognition implies the ability of chiral stationery phases to interact differently with mirror-image molecules, leading to their separation. The mechanism of enantiomeric resolution using CSPs is generally attributed to the “three-point" interaction model (fig.1.) between the analyte and the chiral selector in the stationary phase. Also known as the Dalgliesh model. Under this model, for chiral recognition, and hence enantiomeric resolution to happen on a CSP one of the enantiomers of the analyte must be involved in three simultaneous interactions. This means to say the one of enantiomers is able to have a good interaction with the complimentary sites on the chiral selector attached to the CSP. While Its mirror-image partner may only interact at two or one such sites. In the figure, enantiomer (a), has the correct configuration of the ligands (X, Y and Z) for three-point interactions with the complimentary sites (X’, Y’ and Z’) on the CSP, while its mirror image (b) can only interact at one site. The dotted lines (-----) indicate interaction with complimentary sites.
The diastereomeric complexes thus formed will have different energies of interaction. The enantiomer forming the more stable complex will have less energy and stay longer in the stationary phase compared to the less stable complex with higher energy. The success of chiral separation basically depends in manipulating the subtle energy differences between the reversibly formed non-covalent transient diastereomeric complexes. The energy difference reflects the magnitude of enantioselectivity. Mobile phase has a major role in stabilizing the diastereomeric complex and thus in chiral separation. This simplified bimolecular interaction model is a treatment suitable for theoretical purposes. Mobile phase plays a key role in chiral recognition mechanism. Components of MP (such as bulk solvents, modifiers, buffer salts, additives) not only influence the conformational flexibility of CS and CA molecules but also their degree of ionization. The types of interaction involved in the analyte-selector interaction vary depending on the nature of the CSP used. These may include hydrogen bonding, dipole-dipole, π-π, electrostatic, hydrophobic or steric interactions, and inclusion complex formation. | 0 | Theoretical and Fundamental Chemistry |
In the pump-probe method the reaction is first triggered (pump) by photolysis (most often laser light) and then a diffraction pattern is collected by an X-ray pulse (probe) at a specific time delay. This makes it possible to obtain many images at different time delays after reaction triggering, and thereby building up a chronological series of images describing the events during reaction.
To obtain a reasonable signal to noise ratio this pump-probe cycle has to be performed many times for each spatial rotation of the crystal, and many times for the same time delay. Therefore, the reaction that one wishes to study with pump-probe must be able to relax back to its original conformation after triggering, enabling many measurements on the same sample.
The time resolution of the observed phenomena is dictated by the time width of the probing pulse (full width at half maximum). All processes that happen on a faster time scale than that are going to be averaged out by the convolution of the probe pulse intensity in time with the intensity of the actual x-ray reflectivity of the sample. | 0 | Theoretical and Fundamental Chemistry |
Per- and polyfluoroalkyl substances (PFAS or PFASs) are a group of synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain. The PubChem database lists more than 6 million unique compounds in this group. PFASs started being used in the mid-20th century to make fluoropolymer coatings and products that resist heat, oil, stains, grease, and water. They are used in a variety of products including waterproof clothing, furniture, adhesives, food packaging, heat-resistant non-stick cooking surfaces, and the insulation of electrical wire. They have played a key economic role for companies such as DuPont, 3M, and W. L. Gore & Associates that use them to produce widely known materials such as Teflon or Gore-Tex.
Only since the start of the 21st century has the environmental impact and toxicity to human and mammalian life been studied in depth. Many PFAS such as PFOS, PFOA are a concern because they do not break down via natural processes and are commonly described as persistent organic pollutants or "forever chemicals". They can also move through soils and contaminate drinking water sources and can build up (bioaccumulate) in fish and wildlife. Residues have been detected in humans and wildlife. Due to the large number of PFAS it is challenging to study and assess the potential human health and environmental risks; more research is necessary. According to the United States Environmental Protection Agency, exposure to some PFAS in the environment may be linked to harmful health effects in humans and animals. The International Agency for Research on Cancer (IARC) has classified PFOA as carcinogenic to humans and PFOS as possibly carcinogenic. According to the National Academies of Sciences, Engineering, and Medicine, PFAS exposure is linked to increased risk of dyslipidemia (abnormally high cholesterol), suboptimal antibody response, reduced infant and fetal growth, and higher rates of kidney cancer.
Health concerns related to PFASs have resulted in numerous litigations (see Timeline of events related to per- and polyfluoroalkyl substances). PFAS producers such as 3M, Chemours, DuPont and Corteva have reached billion dollar agreements to settle claims against them. The use of PFAS is regulated in several parts of the world, with some plans to phase them out entirely from products. | 0 | Theoretical and Fundamental Chemistry |
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 | Applied and Interdisciplinary Chemistry |
The chalcophile elements include Ag, As, Bi, Cd, Cu, Ga, Ge, Hg, In, Pb, S, Sb, Se, Sn, Te, Tl and Zn.
Chalcophile elements are those that remain on or close to the surface because they combine readily with sulfur and some other chalcogen other than oxygen, forming compounds which do not sink into the Earth's core.
Chalcophile elements are those metals and heavier nonmetals that have a low affinity for oxygen and prefer to bond with sulfur as highly insoluble sulfides. Chalcophile derives from Greek khalkós (χαλκός), meaning "ore" (it also meant "bronze" or "copper", but in this case "ore" is the relevant meaning), and is taken to mean "chalcogen-loving" by various sources.
Because these sulfides are much denser than the silicate minerals formed by lithophile elements, chalcophile elements separated below the lithophiles at the time of the first crystallization of the Earths crust. This has led to their depletion in the Earths crust relative to their solar abundances, though because the minerals they form are nonmetallic, this depletion has not reached the levels found with siderophile elements.
However, because they formed volatile hydrides on the primitive Earth when the controlling redox reaction was the oxidation or reduction of hydrogen, the less metallic chalcophile elements are strongly depleted on Earth as a whole relative to cosmic abundances. This is most especially true of the chalcogens selenium and tellurium (which formed volatile hydrogen selenide and hydrogen telluride, respectively), which for this reason are among the rarest elements found in the Earth's crust (to illustrate, tellurium is only about as abundant as platinum).
The most metallic chalcophile elements (of the copper, zinc and boron groups) may mix to some degree with iron in the Earth's core. They are not likely to be depleted on Earth as a whole relative to their solar abundances since they do not form volatile hydrides. Zinc and gallium are somewhat "lithophile" in nature because they often occur in silicate or related minerals and form quite strong bonds with oxygen. Gallium, notably, is sourced mainly from bauxite, an aluminum hydroxide ore in which gallium ion substitutes for chemically similar aluminum.
Although no chalcophile element is of high abundance in the Earths crust, chalcophile elements constitute the bulk of commercially important metals. This is because, whereas lithophile elements require energy-intensive electrolysis for extraction, chalcophiles can be easily extracted by reduction with coke, and chalcophiles geochemical concentration – which in extreme cases can exceed 100,000 times average crustal abundance. These greatest enrichments occur in high plateaux like the Tibetan Plateau and the Bolivian Altiplano where large quantities of chalcophile elements have been uplifted through plate collisions. A side-effect of this in modern times is that the rarest chalcophiles (like mercury) are so completely exploited that their value as minerals has almost completely disappeared. | 0 | Theoretical and Fundamental Chemistry |
Spectral optical depth in frequency and spectral optical depth in wavelength of a material, denoted and respectively, are given by:
where
* is the spectral radiant flux in frequency transmitted by that material;
* is the spectral radiant flux in frequency received by that material;
* is the spectral transmittance in frequency of that material;
* is the spectral radiant flux in wavelength transmitted by that material;
* is the spectral radiant flux in wavelength received by that material;
* is the spectral transmittance in wavelength of that material.
Spectral absorbance is related to spectral optical depth by:
where
* is the spectral absorbance in frequency;
* is the spectral absorbance in wavelength. | 0 | Theoretical and Fundamental Chemistry |
The photocyte of Arachnocampa luminosa was found to contain a circular nucleus, and large amounts of ribosomes, smooth endoplasmic reticulum, mitochondria, and microtubules. Instead of having photocyte granules, the photocytes of the organism were shown to undergo the luciferase reaction in their cytoplasm. The cells do not have a golgi apparatus or rough endoplasmic reticulum and were found to be 250 micrometers by 120 micrometers overall with a depth of 25 to 30 micrometers. | 1 | Applied and Interdisciplinary Chemistry |
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