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One of the most common methods is the cumulant method, from which in addition to the sum of the exponentials above, more information can be derived about the variance of the system as follows:
where is the average decay rate and is the second order polydispersity index (or an indication of the variance). A third-order polydispersity index may also be derived but this is necessary only if the particles of the system are highly polydisperse. The z-averaged translational diffusion coefficient may be derived at a single angle or at a range of angles depending on the wave vector .
One must note that the cumulant method is valid for small and sufficiently narrow . One should seldom use parameters beyond µ, because overfitting data with many parameters in a power-series expansion will render all the parameters, including and µ, less precise.
The cumulant method is far less affected by experimental noise than the methods below. | 0 | Theoretical and Fundamental Chemistry |
Thermogravimetric analysis is often combined with other processes or used in conjunction with other analytical methods.
For example, the TGA instrument continuously weighs a sample as it is heated to temperatures of up to 2000 °C for coupling with Fourier-transform infrared spectroscopy (FTIR) and mass spectrometry gas analysis. As the temperature increases, various components of the sample are decomposed and the weight percentage of each resulting mass change can be measured. | 0 | Theoretical and Fundamental Chemistry |
* Expert Guide: Materialography/Metallography, QATM Academy, ATM Qness GmbH, 2022.
* Metallographic Preparation of Ceramic and Cermet Materials, [https://web.archive.org/web/20101007084342/http://leco.com/resources/met_tips/met_tip19.pdf Leco Met-Tips No. 19], 2008.
* Sample Preparation of Ceramic Material, [http://www.buehler.com/ Buehler Ltd.], 1990.
* Structure, Volume 33, [https://web.archive.org/web/20071203130459/http://www.struers.com/default.asp?top_id=5&main_id=43&doc_id=307&target=_self Struers A/S], 1998, p 3–20.
* [http://www.struers.com/default.asp?top_id=5&main_id=19&sub_id=25&doc_id=89 Struers Metalog Guide]
* S. Binkowski, R. Paul & M. Woydt, "Comparing Preparation Techniques Using Microstructural Images of Ceramic Materials," Structure, Vol 39, 2002, p 8–19.
* R.E. Chinn, Ceramography, ASM International and the American Ceramic Society, 2002, .
* D.J. Clinton, A Guide to Polishing and Etching of Technical and Engineering Ceramics, The Institute of Ceramics, 1987.
* [http://www.udri.udayton.edu/DLCM/Home.asp/ Digital Library of Ceramic Microstructures], University of Dayton, 2003.
* G. Elssner, H. Hoven, G. Kiessler & P. Wellner, translated by R. Wert, Ceramics and Ceramic Composites: Materialographic Preparation, Elsevier Science Inc., 1999, .
* R.M. Fulrath & J.A. Pask, ed., Ceramic Microstructures: Their Analysis, Significance, and Production, Robert E. Krieger Publishing Co., 1968, .
* K. Geels in collaboration with D.B. Fowler, W-U Kopp & M. Rückert, Metallographic and Materialographic Specimen Preparation, Light Microscopy, Image Analysis and Hardness Testing, ASTM International, 2007, .
* H. Insley & V.D. Fréchette, Microscopy of Ceramics and Cements, Academic Press Inc., 1955.
* W.E. Lee and W.M. Rainforth, Ceramic Microstructures: Property Control by Processing, Chapman & Hall, 1994.
* I.J. McColm, Ceramic Hardness, Plenum Press, 2000, .
* [http://products.asminternational.org/mgo/index.jsp Micrograph Center], ASM International, 2005.
* H. Mörtel, "Microstructural Analysis," Engineered Materials Handbook, Volume 4: Ceramics and Glasses, ASM International, 1991, p 570–579, .
* G. Petzow, Metallographic Etching, 2nd Edition, ASM International, 1999, .
* G.D. Quinn, "Indentation Hardness Testing of Ceramics," ASM Handbook, Volume 8: Mechanical Testing and Evaluation, ASM International, 2000, p 244–251, .
* A.T. Santhanam, "Metallography of Cemented Carbides," ASM Handbook Volume 9: Metallography and Microstructures, ASM International, 2004, p 1057–1066, .
* U. Täffner, V. Carle & U. Schäfer, "Preparation and Microstructural Analysis of High-Performance Ceramics," ASM Handbook Volume 9: Metallography and Microstructures, ASM International, 2004, p 1057–1066, .
* D.C. Zipperian, Metallographic Handbook, PACE Technologies, 2011. | 1 | Applied and Interdisciplinary Chemistry |
Dextroamphetamine (INN:dexamfetamine) is a potent central nervous system (CNS) stimulant and enantiomer of amphetamine that is prescribed for the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. It is also used as an athletic performance and cognitive enhancer, and recreationally as an aphrodisiac and euphoriant.
The amphetamine molecule exists as two enantiomers, levoamphetamine and dextroamphetamine. Dextroamphetamine is the dextrorotatory, or right-handed, enantiomer and exhibits more pronounced effects on the central nervous system than levoamphetamine. Pharmaceutical dextroamphetamine sulfate is available as both a brand name and generic drug in a variety of dosage forms. Dextroamphetamine is sometimes prescribed as the inactive prodrug lisdexamfetamine dimesylate, which is converted into dextroamphetamine after absorption.
Dextroamphetamine, like other amphetamines, elicits its stimulating effects via several distinct actions: it inhibits or reverses the transporter proteins for the monoamine neurotransmitters (namely the serotonin, norepinephrine and dopamine transporters) either via trace amine-associated receptor 1 (TAAR1) or in a TAAR1 independent fashion when there are high cytosolic concentrations of the monoamine neurotransmitters and it releases these neurotransmitters from synaptic vesicles via vesicular monoamine transporter 2. It also shares many chemical and pharmacological properties with human trace amines, particularly phenethylamine and , the latter being an isomer of amphetamine produced within the human body. It is available as a generic medication. In 2021, it was the 17th most commonly prescribed medication in the United States, with more than 30.3million prescriptions. | 0 | Theoretical and Fundamental Chemistry |
In chemical thermodynamics, an endergonic reaction (; also called a heat absorbing nonspontaneous reaction or an unfavorable reaction) is a chemical reaction in which the standard change in free energy is positive, and an additional driving force is needed to perform this reaction. In layman's terms, the total amount of useful energy is negative (it takes more energy to start the reaction than what is received out of it) so the total energy is a net negative result, as opposed to a net positive result in an exergonic reaction. Another way to phrase this is that useful energy must be absorbed from the surroundings into the workable system for the reaction to happen.
Under constant temperature and constant pressure conditions, this means that the change in the standard Gibbs free energy would be positive,
for the reaction at standard state (i.e. at standard pressure (1 bar), and standard concentrations (1 molar) of all the reagents).
In metabolism, an endergonic process is anabolic, meaning that energy is stored; in many such anabolic processes, energy is supplied by coupling the reaction to adenosine triphosphate (ATP) and consequently resulting in a high energy, negatively charged organic phosphate and positive adenosine diphosphate. | 0 | Theoretical and Fundamental Chemistry |
RajanBabu has over 160 publications to date and has co-authored several reviews and patents. His H-index is 56.
Notable publications include:
* Group-transfer polymerization. 1. A new concept for addition polymerization with organosilicon initiators
* Selective Generation of Free Radicals from Epoxides Using a Transition-Metal Radical. A Powerful New Tool for Organic Synthesis
* Transition-metal-centered radicals in organic synthesis. Titanium(III)-induced cyclization of epoxy olefins
* Ligand Electronic Effects in Asymmetric Catalysis: Enhanced Enantioselectivity in the Asymmetric Hydrocyanation of Vinylarenes
* Beyond Nature's Chiral Pool - Enantioselective Catalysis in Industry | 0 | Theoretical and Fundamental Chemistry |
In premixed turbulent combustion, Bray–Moss–Libby (BML) model is a closure model for a scalar field, built on the assumption that the reaction sheet is infinitely thin compared with the turbulent scales, so that the scalar can be found either at the state of burnt gas or unburnt gas. The model is named after Kenneth Bray, J. B. Moss and Paul A. Libby. | 1 | Applied and Interdisciplinary Chemistry |
The journal is abstracted and indexed in:
According to the Journal Citation Reports, the journal has a 2020 impact factor of 2.408. | 0 | Theoretical and Fundamental Chemistry |
The determination of trace acids in organic matrices is a common analytical task assigned to titrimetry. Examples are Total Acid Number (TAN) in mineral and lubricating oils and Free Fatty Acids (FFA) in edible fats and oils. Automated potentiometric titration procedures have been granted standard method status, for example by ASTM for TAN and AOAC for FFA. The methodology is similar in both instances. The sample is dissolved in a suitable solvent mixture; say a hydrocarbon and an alcohol which also must contain a small amount of water. The water is intended to enhance the electrical conductivity of the solution. The trace acids are titrated with standard base in an alcohol. The sample environment is essentially hostile to the pH electrode used to sense the titration. The electrode must be taken out of service on a regular basis to rehydrate the glass sensing membrane, which is also in danger of fouling by the oily sample solution.
A recent thermometric titrimetric procedure for the determination of FFA developed by Cameiro et al. (2002) has been shown to be particularly amenable to automation. It is fast, highly precise, and results agree very well with those obtained by the official AOAC method. The temperature change for the titration of very weak acids such as oleic acid by 0.1 mol/L KOH in propan-2-ol is too small to yield an accurate endpoint. In this procedure, a small amount of paraformaldehyde as a fine powder is added to the titrand before the titration. At the endpoint, the first excess of hydroxyl ions catalyzes the depolymerization of paraformaldehyde. The reaction is strongly endothermic and yields a sharp inflection. The titration plot is illustrated in Figure 13. The speed of this titration coupled with its precision and accuracy makes it ideal for the analysis of FFA in biodiesel feedstocks and product. | 0 | Theoretical and Fundamental Chemistry |
DnaA has the ability to bind its own promoter. When DnaA binds to its own promoter it blocks RNA polymerase from binding the promoter and inhibits initiation of transcription. In this way, DnaA is able to regulate its own expression. This process is called autoregulation. | 1 | Applied and Interdisciplinary Chemistry |
The 2006 Nobel Prize in Chemistry was awarded to Roger D. Kornberg for creating detailed molecular images of RNA polymerase during various stages of the transcription process.
In most prokaryotes, a single RNA polymerase species transcribes all types of RNA. RNA polymerase "core" from E. coli consists of five subunits: two alpha (α) subunits of 36 kDa, a beta (β) subunit of 150 kDa, a beta prime subunit (β′) of 155 kDa, and a small omega (ω) subunit. A sigma (σ) factor binds to the core, forming the holoenzyme. After transcription starts, the factor can unbind and let the core enzyme proceed with its work. The core RNA polymerase complex forms a "crab claw" or "clamp-jaw" structure with an internal channel running along the full length. Eukaryotic and archaeal RNA polymerases have a similar core structure and work in a similar manner, although they have many extra subunits.
All RNAPs contain metal cofactors, in particular zinc and magnesium cations which aid in the transcription process. | 1 | Applied and Interdisciplinary Chemistry |
Methylaluminoxane, commonly called MAO, is a mixture of organoaluminium compounds with the approximate formula (Al(CH)O). It is usually encountered as a solution in (aromatic) solvents, commonly toluene but also xylene, cumene, or mesitylene, Used in large excess, it activates precatalysts for alkene polymerization. | 0 | Theoretical and Fundamental Chemistry |
The first example of laser cooling, and also still the most common method (so much so that it is still often referred to simply as laser cooling) is Doppler cooling. | 0 | Theoretical and Fundamental Chemistry |
For an incompressible flow , but with variable density, Chia-Shun Yih derived the necessary equation. The velocity field is first transformed using Yih transformation
where is some reference density, with corresponding Stokes streamfunction defined such that
Let us include the gravitational force acting in the negative direction. The Yih equation is then given by
where | 1 | Applied and Interdisciplinary Chemistry |
Bacteria related to the nitrogen fixing Rhizobia are an interesting case of inter-kingdom conjugation. For example, the tumor-inducing (Ti) plasmid of Agrobacterium and the root-tumor inducing (Ri) plasmid of A. rhizogenes contain genes that are capable of transferring to plant cells. The expression of these genes effectively transforms the plant cells into opine-producing factories. Opines are used by the bacteria as sources of nitrogen and energy. Infected cells form crown gall or root tumors. The Ti and Ri plasmids are thus endosymbionts of the bacteria, which are in turn endosymbionts (or parasites) of the infected plant.
The Ti and Ri plasmids can also be transferred between bacteria using a system (the tra, or transfer, operon) that is different and independent of the system used for inter-kingdom transfer (the vir, or virulence, operon). Such transfers create virulent strains from previously avirulent strains. | 1 | Applied and Interdisciplinary Chemistry |
Gold occurs principally as a native metal, i.e., gold itself. Sometimes it is alloyed to a greater or lesser extent with silver, which is called electrum. Native gold can occur as sizeable nuggets, as fine grains or flakes in alluvial deposits, or as grains or microscopic particles (known as colour) embedded in rock minerals. Other forms of gold are the minerals calaverite (AuTe), aurostibnite (AuSb), and maldonite (AuBi). These latter three, although rarer that native gold, can be slow to react with cyanide and thus difficult to process. Still other gold-containing ores include various tellurides (sylvanite, nagyagite, petzite, and krennerite).
Certain contaminants in ores can interfere with the extractability of gold by cyanide. These interfering agents are called "preg-robbing ores". For example, gold can bind tightly to carbon, resisting normal cyanide extraction. Gold cyanides bind also to some clays. | 1 | Applied and Interdisciplinary Chemistry |
A reaction center comprises several (about 25-30) protein subunits, which provide a scaffold for a series of cofactors. The cofactors can be pigments (like chlorophyll, pheophytin, carotenoids), quinones, or iron-sulfur clusters.
Each photosystem has two main subunits: an antenna complex (a light harvesting complex or LHC) and a reaction center. The antenna complex is where light is captured, while the reaction center is where this light energy is transformed into chemical energy. At the reaction center, there are many polypeptides that are surrounded by pigment proteins. At the center of the reaction center is a special pair of chlorophyll molecules.
Each PSII has about 8 LHCII. These contain about 14 chlorophyll a and chlorophyll b molecules, as well as about four carotenoids. In the reaction center of PSII of plants and cyanobacteria, the light energy is used to split water into oxygen, protons, and electrons. The protons will be used in proton pumping to fuel the ATP synthase at the end of an electron transport chain. A majority of the reactions occur at the D1 and D2 subunits of PSII. | 0 | Theoretical and Fundamental Chemistry |
Benzylic activation and stereocontrol in tricarbonyl(arene)chromium complexes refers to the enhanced rates and stereoselectivities of reactions at the benzylic position of aromatic rings complexed to chromium(0) relative to uncomplexed arenes. Complexation of an aromatic ring to chromium stabilizes both anions and cations at the benzylic position and provides a steric blocking element for diastereoselective functionalization of the benzylic position. A large number of stereoselective methods for benzylic and homobenzylic functionalization have been developed based on this property. | 0 | Theoretical and Fundamental Chemistry |
Mill scale can be used as a raw material in granular refractory. When this refractory is cast and preheated, these scales provide escape routes for the evaporating water vapor, thus preventing cracks and resulting in a strong, monolithic structure. | 1 | Applied and Interdisciplinary Chemistry |
In the light-independent (or "dark") reactions, the enzyme RuBisCO captures CO from the atmosphere and, in a process called the Calvin cycle, uses the newly formed NADPH and releases three-carbon sugars, which are later combined to form sucrose and starch. The overall equation for the light-independent reactions in green plants is
Carbon fixation produces the three-carbon sugar intermediate, which is then converted into the final carbohydrate products. The simple carbon sugars photosynthesis produces are then used to form other organic compounds, such as the building material cellulose, the precursors for lipid and amino acid biosynthesis, or as a fuel in cellular respiration. The latter occurs not only in plants but also in animals when the carbon and energy from plants is passed through a food chain.
The fixation or reduction of carbon dioxide is a process in which carbon dioxide combines with a five-carbon sugar, ribulose 1,5-bisphosphate, to yield two molecules of a three-carbon compound, glycerate 3-phosphate, also known as 3-phosphoglycerate. Glycerate 3-phosphate, in the presence of ATP and NADPH produced during the light-dependent stages, is reduced to glyceraldehyde 3-phosphate. This product is also referred to as 3-phosphoglyceraldehyde (PGAL) or, more generically, as triose phosphate. Most (five out of six molecules) of the glyceraldehyde 3-phosphate produced are used to regenerate ribulose 1,5-bisphosphate so the process can continue. The triose phosphates not thus "recycled" often condense to form hexose phosphates, which ultimately yield sucrose, starch, and cellulose, as well as glucose and fructose. The sugars produced during carbon metabolism yield carbon skeletons that can be used for other metabolic reactions like the production of amino acids and lipids. | 0 | Theoretical and Fundamental Chemistry |
The reaction is catalyzed by a base and a divalent metal such as calcium. The intermediary steps taking place are aldol reactions, reverse aldol reactions, and aldose-ketose isomerizations. Intermediates are glycolaldehyde, glyceraldehyde, dihydroxyacetone, and tetrose sugars. In 1959, Breslow proposed a mechanism for the reaction, consisting of the following steps:
The reaction exhibits an induction period, during which only the nonproductive Cannizzaro disproportionation of formaldehyde (to methanol and formate) occurs. The initial dimerization of formaldehyde to give glycolaldehyde (1) occurs via an unknown mechanism, possibly promoted by light or through a free radical process and is very slow. However, the reaction is autocatalytic: 1 catalyzes the condensation of two molecules of formaldehyde to produce an additional molecule of 1. Hence, even a trace (as low as 3 ppm) of glycolaldehyde is enough to initiate the reaction. The autocatalytic cycle begins with the aldol reaction of 1 with formaldehyde to make glyceraldehyde (2). An aldose-ketose isomerization of 2 forms dihydroxyacetone (3). A further aldol reaction of 3 with formaldehyde produces tetrulose (6), which undergoes another ketose-aldose isomerization to form aldotetrose 7 (either threose or erythrose). The retro-aldol reaction of 7 generates two molecules of 1, resulting in the net production of a molecule of 1 from two molecules of formaldehyde, catalyzed by 1 itself (autocatalysis). During this process, 3 can also react with 1 to form ribulose (4), which can isomerize to give rise to ribose (5), an important building block of ribonucleic acid. The reaction conditions must be carefully controlled, otherwise the alkaline conditions will cause the aldoses to undergo the Cannizzaro reaction.
The aldose-ketose isomerization steps are promoted by chelation to calcium. However, these steps have been shown to proceed through a hydride shift mechanism by isotope labeling studies, instead of via an intermediate enediolate, as previously proposed. | 0 | Theoretical and Fundamental Chemistry |
SLS has been proposed as a potentially effective topical microbicide, for intravaginal use, to inhibit and possibly prevent infection by various enveloped and non-enveloped viruses such as the herpes simplex viruses, HIV, and the Semliki Forest virus.
Liquid membranes formed from SDS in water have been demonstrated to work as unusual particle separators. The device acts as a reverse filter, allowing large particles to pass while capturing smaller particles. | 1 | Applied and Interdisciplinary Chemistry |
Spontaneous deamination is the hydrolysis reaction of cytosine into uracil, releasing ammonia in the process. This can occur in vitro through the use of bisulfite, which deaminates cytosine, but not 5-methylcytosine. This property has allowed researchers to sequence methylated DNA to distinguish non-methylated cytosine (shown up as uracil) and methylated cytosine (unaltered).
In DNA, this spontaneous deamination is corrected for by the removal of uracil (product of cytosine deamination and not part of DNA) by uracil-DNA glycosylase, generating an abasic (AP) site. The resulting abasic site is then recognised by enzymes (AP endonucleases) that break a phosphodiester bond in the DNA, permitting the repair of the resulting lesion by replacement with another cytosine. A DNA polymerase may perform this replacement via nick translation, a terminal excision reaction by its 5⟶3 exonuclease activity, followed by a fill-in reaction by its polymerase activity. DNA ligase then forms a phosphodiester bond to seal the resulting nicked duplex product, which now includes a new, correct cytosine (Base excision repair). | 1 | Applied and Interdisciplinary Chemistry |
Metal borate thin films have been grown by a variety of techniques, including liquid-phase epitaxy (e.g. FeBO, β‐BaBO), electron-beam evaporation (e.g. CrBO, β‐BaBO), pulsed laser deposition (e.g. β‐BaBO, Eu(BO)), and atomic layer deposition (ALD). Growth by ALD was achieved using precursors composed of the tris(pyrazolyl)borate ligand and either ozone or water as the oxidant to deposit CaBO, SrBO, BaBO, Mn(BO), and CoBO films. | 0 | Theoretical and Fundamental Chemistry |
Unlike other endonucleases, the MmeI (type IIS) and EcoP15I (type III) restriction endonucleases cut downstream of their target binding sites. MmeI cuts 18/20 base pairs downstream and EcoP15I cuts 25/27 base pairs downstream. As these restriction enzymes bind at their target sequences located in the adaptors, they cut and release vectors that contain short sequences of the fragment or cDNA ligated to them, producing PETs. | 1 | Applied and Interdisciplinary Chemistry |
In the 1920s, the Russian embryologist Alexander Gurwitsch reported "ultraweak" photon emissions from living tissues in the UV-range of the spectrum. He named them "mitogenetic rays" because his experiments convinced him that they had a stimulating effect on cell division.
In the 1970s Fritz-Albert Popp and his research group at the University of Marburg (Germany) showed that the spectral distribution of the emission fell over a wide range of wavelengths, from 200 to 750 nm. Popps work on the biophoton emissions statistical properties, namely the claims on its coherence, was criticised for lack of scientific rigour.
One biophoton mechanism focuses on injured cells that are under higher levels of oxidative stress, which is one source of light, and can be deemed to constitute a "distress signal" or background chemical process, but this mechanism is yet to be demonstrated. The difficulty of teasing out the effects of any supposed biophotons amid the other numerous chemical interactions between cells makes it difficult to devise a testable hypothesis. A 2010 review article discusses various published theories on this kind of signaling.
The hypothesis of cellular communication by biophotons was highly criticised for failing to explain how could cells detect photonic signals several orders of magnitude weaker than the natural background illumination. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, a precursor is a compound that participates in a chemical reaction that produces another compound.
In biochemistry, the term "precursor" often refers more specifically to a chemical compound preceding another in a metabolic pathway, such as a protein precursor. | 1 | Applied and Interdisciplinary Chemistry |
The popularity of the Karl Fischer titration (henceforth referred to as KF) is due in large part to several practical advantages that it holds over other methods of moisture determination, such as accuracy, speed and selectivity.
KF is selective for water, because the titration reaction itself consumes water. In contrast, measurement of mass loss on drying will detect the loss of any volatile substance. However, the strong redox chemistry () means that redox-active sample constituents may react with the reagents. For this reason, KF is unsuitable for solutions containing e.g. dimethyl sulfoxide.
KF has a high accuracy and precision, typically within 1% of available water, e.g. 3.00% appears as 2.97–3.03%. Although KF is a destructive analysis, the sample quantity is small and is typically limited by the accuracy of weighing. For example, in order to obtain an accuracy of 1% using a scale with the typical accuracy of 0.2 mg, the sample must contain 20 mg water, which is e.g. 200 mg for a sample with 10% water. For coulometers, the measuring range is from 1–5 ppm to about 5%. Volumetric KF readily measures samples up to 100%, but requires impractically large amounts of sample for analytes with less than 0.05% water. The KF response is linear. Therefore, single-point calibration using a calibrated 1% water standard is sufficient and no calibration curves are necessary.
Little sample preparation is needed: a liquid sample can usually be directly injected using a syringe. The analysis is typically complete within a minute. However, KF suffers from an error called drift, which is an apparent water input that can confuse the measurement. The glass walls of the vessel adsorb water, and if any water leaks into the cell, the slow release of water into the titration solution can continue for a long time. Therefore, before measurement, it is necessary to carefully dry the vessel and run a 10–30-minute "dry run" in order to calculate the rate of drift. The drift is then subtracted from the result.
KF is suitable for measuring liquids and, with special equipment, gases. The major disadvantage with solids is that the water has to be accessible and easily brought into methanol solution. Many common substances, especially foods such as chocolate, release water slowly and with difficulty, requiring additional efforts to reliably bring the total water content into contact with the Karl Fischer reagents. For example, a high-shear mixer may be installed to the cell in order to break the sample. KF has problems with compounds with strong binding to water, as in water of hydration, for example with lithium chloride, so KF is unsuitable for the special solvent LiCl/DMAc.
KF is suitable for automation. Generally, KF is conducted using a separate KF titrator, or for volumetric titration, a KF titration cell installed into a general-purpose titrator. There are also oven attachments that can be used for materials that have problems being analyzed normally in the cell. The important aspect about the oven attachment is that the material doesn't decompose into water when heated to release the water. The oven attachment also supports automation of samples.
Using volumetric titration with visual detection of a titration endpoint is also possible with coloured samples by UV/VIS spectrophotometric detection. | 0 | Theoretical and Fundamental Chemistry |
The most common example is selective leaching of zinc from brass alloys containing more than 15% zinc (dezincification) in the presence of oxygen and moisture, e.g. from brass taps in chlorine-containing water. Dezincification has been studied since the Civil War era, and the mechanism by which it occurs was under extensive examination by the 1960s. It is believed that both copper and zinc gradually dissolve out simultaneously, and copper precipitates back from the solution. The material remaining is a copper-rich sponge with poor mechanical properties, and a color changed from yellow to red. Dezincification can be caused by water containing sulfur, carbon dioxide, and oxygen. Stagnant or low velocity waters tend to promote dezincification.
To combat this, arsenic or tin can be added to brass, or gunmetal can be used instead. Dezincification resistant brass (DZR), also known as Brass C352 is an alloy used to make pipe fittings for use with potable water. Plumbing fittings that are resistant to dezincification are appropriately marked, with the letters "CR" (Corrosion Resistant) or DZR (dezincification resistant) in the UK, and the letters "DR" (dezincification resistant) in Australia. | 1 | Applied and Interdisciplinary Chemistry |
Residual topology is a descriptive stereochemical term to classify a number of intertwined and interlocked molecules, which cannot be disentangled in an experiment without breaking of covalent bonds, while the strict rules of mathematical topology allow such a disentanglement. Examples of such molecules are rotaxanes, catenanes with covalently linked rings (so-called pretzelanes), and open knots (pseudoknots) which are abundant in proteins.
The term "residual topology" was suggested on account of a striking similarity of these compounds to the well-established topologically nontrivial species, such as catenanes and knotanes (molecular knots). The idea of residual topological isomerism introduces a handy scheme of modifying the molecular graphs and generalizes former efforts of systemization of mechanically bound and bridged molecules. | 0 | Theoretical and Fundamental Chemistry |
* Line or stick – atomic nuclei are not represented, just the bonds as sticks or lines. As in 2D molecular structures of this type, atoms are implied at each vertex.
* Electron density plot – shows the electron density determined either crystallographically or using quantum mechanics rather than distinct atoms or bonds.
* Ball and stick – atomic nuclei are represented by spheres (balls) and the bonds as sticks.
* Spacefilling models or CPK models (also an atomic coloring scheme in representations) – the molecule is represented by overlapping spheres representing the atoms.
* Cartoon – a representation used for proteins where loops, beta sheets, and alpha helices are represented diagrammatically and no atoms or bonds are explicitly represented (e.g. the protein backbone is represented as a smooth pipe).
The greater the amount of lone pairs contained in a molecule, the smaller the angles between the atoms of that molecule. The VSEPR theory predicts that lone pairs repel each other, thus pushing the different atoms away from them. | 0 | Theoretical and Fundamental Chemistry |
Disubstituted alkenes react with HCN in the presence of strong acids to give formamides, which can be decarbonylated. This method, the Ritter reaction, is used industrially to produce tertiary amines such as tert-octylamine.
Hydroamination of alkenes is also widely practiced. The reaction is catalyzed by zeolite-based solid acids. | 0 | Theoretical and Fundamental Chemistry |
The longevity of a soap bubble is limited by the ease of rupture of the very thin layer of water which constitutes its surface, namely a micrometer-thick soap film.
It is thus sensitive to :
* Drainage within the soap film: water falls down due to gravity. This can be slowed by increasing the water viscosity, for instance by adding glycerol. Still, there is an ultimate height limit, which is the capillary length, very high for soap bubbles: around 13 feet (4 meters). In principle, there is no limit in the length it can reach.
* Evaporation: This can be slowed by blowing bubbles in a wet atmosphere, or by adding some sugar to the water.
* Dirt and fat: When the bubble touches an object, it usually ruptures the soap film. This can be prevented by wetting these surfaces with water (preferably containing some soap).
After experiments, researchers found that a solution containing:
* 85.9 % water
* 10 % glycerol
* 4 % dishwashing liquid
* 0.1 % guar gum
gave the longest lasting results as it minimised the Marangoni Effect. | 1 | Applied and Interdisciplinary Chemistry |
In a loss-of-coolant accident (LOCA) it is thought that the surface of the cladding could reach a temperature between 800 and 1400 K, and the cladding will be exposed to steam for some time before water is reintroduced into the reactor to cool the fuel. During this time when the hot cladding is exposed to steam some oxidation of the zirconium will occur to form a zirconium oxide which is more zirconium rich than zirconia. This Zr(O) phase is the α-phase, further oxidation forms zirconia. The longer the cladding is exposed to steam the less ductile it will be. One measure of the ductility is to compress a ring along a diameter (at a constant rate of displacement, in this case 2 mm min) until the first crack occurs, then the ring will start to fail. The elongation which occurs between when the maximum force is applied and when the mechanical load is declined to 80% of the load required to induce the first crack is the L value in mm. The more ductile a sample is the greater this L value will be.
In one experiment the zirconium is heated in steam to 1473 K, the sample is slowly cooled in steam to 1173 K before being quenched in water. As the heating time at 1473 K is increased the zirconium becomes more brittle and the L value declines. | 0 | Theoretical and Fundamental Chemistry |
Vitalism was a widespread conception that substances found in organic nature are formed from the chemical elements by the action of a "vital force" or "life-force" (vis vitalis) that only living organisms possess.
In the 1810s, Jöns Jacob Berzelius argued that a regulative force must exist within living bodies. Berzelius also contended that compounds could be distinguished by whether they required any organisms in their synthesis (organic compounds) or whether they did not (inorganic compounds). Vitalism taught that formation of these "organic" compounds were fundamentally different from the "inorganic" compounds that could be obtained from the elements by chemical manipulations in laboratories.
Vitalism survived for a short period after the formulation of modern ideas about the atomic theory and chemical elements. It first came under question in 1824, when Friedrich Wöhler synthesized oxalic acid, a compound known to occur only in living organisms, from cyanogen. A further experiment was Wöhlers 1828 synthesis of urea from the inorganic salts potassium cyanate and ammonium sulfate. Urea had long been considered an "organic" compound, as it was known to occur only in the urine of living organisms. Wöhlers experiments were followed by many others, in which increasingly complex "organic" substances were produced from "inorganic" ones without the involvement of any living organism, thus disproving vitalism. | 0 | Theoretical and Fundamental Chemistry |
The MNR2 gene encodes a protein closely related to the Alr proteins, but includes conserved features that define a distinct subgroup of CorA proteins in fungal genomes, suggesting a distinct role in Mg homeostasis. Like an alr1 mutant, growth of an mnr2 mutant was sensitive to Mg-deficient conditions, but the mnr2 mutant was observed to accumulate more Mg than a wild-type strain under these conditions. These phenotypes suggested that Mnr2 may regulate Mg storage within an intracellular compartment. Consistent with this interpretation, the Mnr2 protein was localized to the membrane of the vacuole, an internal compartment implicated in the storage of excess mineral nutrients by yeast. A direct role of Mnr2 in Mg transport was suggested by the observation that increased Mnr2 expression, which redirected some Mnr2 protein to the cell surface, also suppressed the Mg-requirement of an alr1 alr2 double mutant strain. The mnr2 mutation also altered accumulation of other divalent cations, suggesting this mutation may increase Alr gene expression or protein activity. Recent work supported this model, by showing that Alr1 activity was increased in an mnr2 mutant strain, and that the mutation was associated with induction of Alr1 activity at a higher external Mg concentration than was observed for an Mnr2 wild-type strain. These effects were observed without any change in Alr1 protein accumulation, again indicating that Alr1 activity may be regulated directly by the Mg concentration within the cell. | 1 | Applied and Interdisciplinary Chemistry |
X-ray absorption fine-structure spectroscopy is an atomic scale probe making it useful for studying materials lacking in long range order. Spectra obtained using this method provide information on the oxidation state, coordination number, and species surrounding the atom in question as well as the distances at which they are found. | 0 | Theoretical and Fundamental Chemistry |
Gas-phase nephelometers are also used in the detection of smoke and other particles of combustion. In such use, the apparatus is referred to as an aspirated smoke detector. These have the capability to detect extremely low particle concentrations (to 0.005%) and are therefore highly suitable to protecting sensitive or valuable electronic equipment, such as mainframe computers and telephone switches. | 0 | Theoretical and Fundamental Chemistry |
Although most experiments use cellular response as a measure of the effect, the effect is, in essence, a result of the binding kinetics; so, in order to illustrate the mechanism, ligand binding is used. A ligand A will bind to a receptor R according to an equilibrium constant :
Although the equilibrium constant is more meaningful, texts often mention its inverse, the affinity constant (K = k/k): A better binding means an increase of binding affinity.
The equation for simple ligand binding to a single homogeneous receptor is
This is the Hill-Langmuir equation, which is practically the Hill equation described for the agonist binding. In chemistry, this relationship is called the Langmuir equation, which describes the adsorption of molecules onto sites of a surface (see adsorption).
is the total number of binding sites, and when the equation is plotted it is the horizontal asymptote to which the plot tends; more binding sites will be occupied as the ligand concentration increases, but there will never be 100% occupancy. The binding affinity is the concentration needed to occupy 50% of the sites; the lower this value is the easier it is for the ligand to occupy the binding site.
The binding of the ligand to the receptor at equilibrium follows the same kinetics as an enzyme at steady-state (Michaelis–Menten equation) without the conversion of the bound substrate to product.
Agonists and antagonists can have various effects on ligand binding. They can change the maximum number of binding sites, the affinity of the ligand to the receptor, both effects together or even more bizarre effects when the system being studied is more intact, such as in tissue samples. (Tissue absorption, desensitization, and other non equilibrium steady-state can be a problem.)
A surmountable drug changes the binding affinity:
* competitive ligand:
* cooperative allosteric ligand:
A nonsurmountable drug changes the maximum binding:
* noncompetitive binding:
* irreversible binding
The Schild regression also can reveal if there are more than one type of receptor and it can show if the experiment was done wrong as the system has not reached equilibrium. <br/> | 1 | Applied and Interdisciplinary Chemistry |
The Supervising Scientist is a statutory office under Australian law, originally created to assist in the monitoring of what was then one of the worlds largest uranium mines, the Ranger Uranium Mine. It now provides advice more generally on a wide range of scientific matters and mining-related environmental issues of national importance, including; radiological matters and tropical wetlands conservation and management'. The Supervising Scientist is administered as a division within the Department of the Environment, Water, Heritage and the Arts. | 0 | Theoretical and Fundamental Chemistry |
The first precession electron diffraction system was developed by Vincent and Midgley in Bristol, UK and published in 1994. Preliminary investigation into the ErGeO crystal structure demonstrated the feasibility of the technique at reducing dynamical effects and providing quasi-kinematical patterns that could be solved through direct methods to determine crystal structure. Over the next ten years, a number of university groups developed their own precession systems and verified the technique by solving complex crystal structures, including the groups of J. Gjønnes (Oslo), Migliori (Bologna), and L. Marks (Northwestern).
In 2004, [http://nanomegas.com/ NanoMEGAS] developed the first commercial precession system capable of being retrofit to any modern TEM. This hardware solution enabled more widespread implementation of the technique and spurred its more mainstream adoption into the crystallography community. Software methods have also been developed to achieve the necessary scanning and descanning using the built-in electronics of the TEM. HREM Research Inc has developed the [http://www.hremresearch.com/index.html QED plug-in] for the DigitalMicrograph software. This plug-in enables the widely used software package to collect precession electron diffraction patterns without additional modifications to the microscope.
According to NanoMEGAS, as of June, 2015, more than 200 publications have relied on the technique to solve or corroborate crystal structures; many on materials that could not be solved by other conventional crystallography techniques like x-ray diffraction. Their retrofit hardware system is used in more than 75 laboratories across the world. | 0 | Theoretical and Fundamental Chemistry |
Mycobacterium tuberculosis, the causative agent of tuberculosis, expresses at least six different forms of epoxide hydrolase (forms A-F). The structure of epoxide hydrolase B reveals that the enzyme is a monomer and contains an alpha/beta hydrolase fold. In addition to providing insights into the enzyme mechanism, this hydrolase currently serves as a platform for rational drug design of potent inhibitors. In particular, urea based inhibitors have been developed. These inhibitors directly target the catalytic cavity. It is hypothesized that the structure of epoxide hydrolase B may allow for drug design to inhibit all other Mycobacterium tuberculosis hydrolases as long as they contain similar alpha/beta folds. The structure of hydrolase B contains a cap domain, which is hypothesized to regulate the active site of the hydrolase. Furthermore, Asp104, His333, and Asp302 form the catalytic triad of the protein and is critical to function of the protein. At present, other structures of Mycobacterium tuberculosis hydrolase have not been solved. Model studies on pharmacological susceptibility of these epoxide hydrolases continue. | 1 | Applied and Interdisciplinary Chemistry |
Another example of the apparent molar volume of the second component is less than its molar volume as a pure substance is the case of ethanol in water. For example, at 20 mass percents ethanol, the solution has a volume of 1.0326 liters per kg at 20 °C, while pure water is 1.0018 L/kg (1.0018 cc/g). The apparent volume of the added ethanol is 1.0326 L – 0.8 kg x 1.0018 L/kg = 0.2317 L. The number of moles of ethanol is 0.2 kg / (0.04607 kg/mol) = 4.341 mol, so that the apparent molar volume is 0.2317 L / 4.341 mol = 0.0532 L / mol = 53.2 cc/mole (1.16 cc/g). However pure ethanol has a molar volume at this temperature of 58.4 cc/mole (1.27 cc/g).
If the solution were ideal, its volume would be the sum of the unmixed components. The volume of 0.2 kg pure ethanol is 0.2 kg x 1.27 L/kg = 0.254 L, and the volume of 0.8 kg pure water is 0.8 kg x 1.0018 L/kg = 0.80144 L, so the ideal solution volume would be 0.254 L + 0.80144 L = 1.055 L. The nonideality of the solution is reflected by a slight decrease (roughly 2.2%, 1.0326 rather than 1.055 L/kg) in the volume of the combined system upon mixing. As the percent ethanol goes up toward 100%, the apparent molar volume rises to the molar volume of pure ethanol. | 0 | Theoretical and Fundamental Chemistry |
Perfluoroalkanes are very stable because of the strength of the carbon–fluorine bond, one of the strongest in organic chemistry.
Its strength is a result of the electronegativity of fluorine imparting partial ionic character through partial charges on the carbon and fluorine atoms, which shorten and strengthen the bond (compared to carbon-hydrogen bonds) through favorable covalent interactions. Additionally, multiple carbon–fluorine bonds increase the strength and stability of other nearby carbon–fluorine bonds on the same geminal carbon, as the carbon has a higher positive partial charge. Furthermore, multiple carbon–fluorine bonds also strengthen the "skeletal" carbon–carbon bonds from the inductive effect. Therefore, saturated fluorocarbons are more chemically and thermally stable than their corresponding hydrocarbon counterparts, and indeed any other organic compound. They are susceptible to attack by very strong reductants, e.g. Birch reduction and very specialized organometallic complexes.
Fluorocarbons are colorless and have high density, up to over twice that of water. They are not miscible with most organic solvents (e.g., ethanol, acetone, ethyl acetate, and chloroform), but are miscible with some hydrocarbons (e.g., hexane in some cases). They have very low solubility in water, and water has a very low solubility in them (on the order of 10 ppm). They have low refractive indices.
As the high electronegativity of fluorine reduces the polarizability of the atom, fluorocarbons are only weakly susceptible to the fleeting dipoles that form the basis of the London dispersion force. As a result, fluorocarbons have low intermolecular attractive forces and are lipophobic in addition to being hydrophobic and non-polar. Reflecting the weak intermolecular forces these compounds exhibit low viscosities when compared to liquids of similar boiling points, low surface tension and low heats of vaporization. The low attractive forces in fluorocarbon liquids make them compressible (low bulk modulus) and able to dissolve gas relatively well. Smaller fluorocarbons are extremely volatile. There are five perfluoroalkane gases: tetrafluoromethane (bp −128 °C), hexafluoroethane (bp −78.2 °C), octafluoropropane (bp −36.5 °C), perfluoro-n-butane (bp −2.2 °C) and perfluoro-iso-butane (bp −1 °C). Nearly all other fluoroalkanes are liquids; the most notable exception is perfluorocyclohexane, which sublimes at 51 °C. Fluorocarbons also have low surface energies and high dielectric strengths. | 1 | Applied and Interdisciplinary Chemistry |
The Parkes process, patented in 1850 uses molten zinc. Zinc is not miscible with lead and when the two molten metals are mixed the zinc separates and floats to the top carrying only some 2% lead. However silver preferentially dissolves in zinc, so the zinc that floats to the top carries a significant proportion of the silver. The melt is then cooled until the zinc solidifies and the zinc crust is skimmed off. The silver is then recovered by volatalising the zinc. The Parkes process largely replaced the Pattinson process, except where the lead contained insufficient silver, in which case the Pattinson process provided a method to enrich it in silver to about 40 to 60 ounces per ton, at which concentration it could be treated using the Parkes' process. | 1 | Applied and Interdisciplinary Chemistry |
Wittig was born in Berlin, Germany and shortly after his birth moved with his family to Kassel, where his father was professor at the applied arts high school. He attended school in Kassel and started studying chemistry at the University of Tübingen 1916. He was drafted and became a lieutenant in the cavalry of Hesse-Kassel (or Hesse-Cassel). After being an Allied prisoner of war from 1918 until 1919, Wittig found it hard to restart his chemistry studies owing to overcrowding at the universities. By a direct plea to Karl von Auwers, who was professor for organic chemistry at the University of Marburg at the time, he was able to resume university study and after 3 years was awarded the Ph.D. in organic chemistry.
Karl von Auwers was able to convince him to start an academic career, leading to his habilitation in 1926. He became a close friend of Karl Ziegler, who was also doing his habilitation with Auwers during that time. The successor of Karl von Auwers, Hans Meerwein, accepted Wittig as lecturer, partly because he was impressed by the new 400-page book on stereochemistry that Wittig had written. In 1931 Wittig married Waltraud Ernst, a colleague from the Auwers working group. The invitation of Karl Fries brought him as professor to the TU Braunschweig in 1932. The time in Braunschweig became more and more problematic as the Nazis tried to get rid of Karl Fries and Wittig showed solidarity with him. After the forced retirement of Fries, in 1937 Hermann Staudinger offered Wittig a position at the University of Freiburg, partly because he knew Wittig from his book on stereochemistry in which he supported Staudingers highly criticized theory of macromolecules. The foundations of carbanion chemistry were laid during Wittigs time in Freiburg.
In 1944 he succeeded the head of the organic chemistry department Wilhelm Schlenk at the University of Tübingen. Most of his scientific work, including the development of the Wittig reaction, was performed during this time in Tübingen. The 1956 appointment of the nearly sixty-year-old Wittig as head of the organic chemistry department at the University of Heidelberg as successor of Karl Freudenberg was exceptional even at that time. The newly built department and the close connection to the BASF convinced Wittig to take this opportunity. He worked at the University of Heidelberg even after his retirement in 1967 and published papers until 1980. Most of his awards were presented during this time at Heidelberg, such as the honorary doctorate of the Sorbonne in 1956 and the Nobel Prize in Chemistry in 1979. | 0 | Theoretical and Fundamental Chemistry |
The phrase pseudokinase was first coined in 2002. They were subsequently sub-classified into different classes. Several pseudokinase-containing families are found in the human kinome, including the Tribbles pseudokinases, which are at the interface between kinase and ubiquitin E3 ligase signalling.
The human pseudokinases (and their pseudophosphatase cousins) are implicated in a wide variety of diseases, which has made them potential drug targets and antitargets). Pseudokinases are made up of an evolutionary mixture of eukaryotic protein kinase (ePK) and non ePK-related pseudoenzyme proteins (e.g., FAM20A, which binds ATP and is pseudokinase due to a conserved glutamate to glutamine swap in the alpha-C helix. FAM20A is implicated in periodontal disease, and serves to control the catalytic activity of FAM20C, an important physiological casein kinase that controls phosphorylation of proteins in the Golgi apparatus that are destined for secretion, such as the milk protein casein.
A comprehensive evolutionary analysis confirms that pseudokinases group into multiple subfamilies, and these are found in the annotated kinome of organisms across the kingdoms of life, including prokaryotes, archaea and all eukaryotic lineages with an annotated proteome; this data is searchable in ProKino (http://vulcan.cs.uga.edu/prokino/about/browser). | 1 | Applied and Interdisciplinary Chemistry |
*Bisulfite sequencing – the biochemical method used to determine the presence or absence of methyl groups on a DNA sequence
*MethDB DNA Methylation Database
*Microscale thermophoresis – a biophysical method to determine the methylisation state of DNA
*Remethylation, the reversible removal of methyl group in methionine and 5-methylcytosine | 0 | Theoretical and Fundamental Chemistry |
Shpolskii systems are low-temperature host–guest systems – they are typically rapidly frozen solutions of polycyclic aromatic hydrocarbons in suitable low molecular weight normal alkanes. The emission and absorption spectra of lowest energy electronic transitions in the Shpolskii systems exhibit narrow lines instead of the inhomogeneously broadened features normally associated with spectra of chromophores in liquids and amorphous solids. The effect was first described by Eduard Shpolskii in the 1950s and 1960s in the journals Transactions of the U.S.S.R. Academy of Sciences and Soviet Physics Uspekhi'.
Subsequent detailed studies of concentration and speed of cooling behavior of Shpolskii systems by L. A. Nakhimovsky and coauthors led to a hypothesis that these systems are metastable segregational solid solutions formed when one or more chromophores replace two or more molecules in the host crystalline lattice. The solid state quasi-equilibrium solubility in most Shpolskii systems is very low. When the Shpolskii effect is manifested, the solid state solubility increases two to three orders of magnitude. Isothermic annealing of the supersaturated rapidly frozen solutions of dibenzofuran in heptane was performed, and it was shown that the return of the metastable system to equilibrium in time reasonable for laboratory observation required the annealing temperature to be close to the melting temperature of the metastable frozen solution. Thus the Shpolskii systems are an example of a persistent metastable state.
A good match between the chromophore and the host lattice leads to a uniform environment for all the chromophores and hence greatly reduces the inhomogeneous broadening of the electronic transition's pure electronic and vibronic lines. In addition to the weak inhomogeneous broadening of the transitions, the quasi-lines observed at very low temperatures are phonon-less transitions. Since phonons originate in the lattice, an additional requirement is weak chromophore-lattice coupling. Weak coupling increases the probability of phonon-less transitions and hence favors the narrow zero phonon lines. The weak coupling is usually expressed in terms of the Debye-Waller factor, where a maximum value of one indicates no coupling between the chromophore and the lattice phonons. The narrow lines characteristic of the Shpolskii systems are only observed at cryogenic temperatures because at higher temperatures many phonons are active in the lattice and all of the amplitude of the transition shifts to the broad phonon sideband. The original observation of the Shpolskii effect was made at liquid nitrogen temperature (77 kelvins), but using temperatures close to that of liquid helium (4.2 K) yields much sharper spectral lines and is the usual practice.
Low molecular weight normal alkanes absorb light at energies higher than the absorption of all pi-pi electronic transitions of aromatic hydrocarbons. They interact weakly with the chromophores and crystallize when frozen. The length of the alkanes is often chosen to approximately match at least one of the dimensions of the chromophore, and are usually in the size range between n-pentane and n-dodecane. | 0 | Theoretical and Fundamental Chemistry |
Popular growth models include:
* KPZ equation
* Dimer model
* Eden growth model
* SOS model
*Self-avoiding walk
*Abelian sandpile model
*Kuramoto–Sivashinsky equation (or the flame equation, for studying the surface of a flame front)
They are studied for their fractal properties, scaling behavior, critical exponents, universality classes, and relations to chaos theory, dynamical system, non-equilibrium / disordered / complex systems.
Popular tools include statistical mechanics, renormalization group, rough path theory, etc. | 0 | Theoretical and Fundamental Chemistry |
1,10-Phenanthroline (phen) is a heterocyclic organic compound. It is a white solid that is soluble in organic solvents. The 1,10 refer to the location of the nitrogen atoms that replace CH's in the hydrocarbon called phenanthrene.
Abbreviated "phen", it is used as a ligand in coordination chemistry, forming strong complexes with most metal ions. It is often sold as the monohydrate. | 0 | Theoretical and Fundamental Chemistry |
Phosphine is a precursor to many organophosphorus compounds. It reacts with formaldehyde in the presence of hydrogen chloride to give tetrakis(hydroxymethyl)phosphonium chloride, which is used in textiles. The hydrophosphination of alkenes is versatile route to a variety of phosphines. For example, in the presence of basic catalysts adds of Michael acceptors. Thus with acrylonitrile, it reacts to give tris(cyanoethyl)phosphine:
Acid catalysis is applicable to hydrophosphination with isobutylene and related analogues:
where R is , alkyl, etc. | 0 | Theoretical and Fundamental Chemistry |
Atalla was the chairman of A4 System, as of 2003.
He lived in Atherton, California. Atalla died on December 30, 2009, in Atherton. | 0 | Theoretical and Fundamental Chemistry |
* [http://www.mikomma.de/schroe/quantumjumps.htm Are there quantum jumps?]
* «[http://www.rzuser.uni-heidelberg.de/~as3/no-quantum-jumps.pdf There are no quantum jumps, nor are there particles!]» by H. D. Zeh, Physics Letters A172, 189 (1993).
* [http://www.mikomma.de/fh/hydrod/h71.html Der Quantensprung im Bohrschen Atommodell] Frühe Quantenphysik
* [http://www.zeit.de/1996/19/quanten.txt.19960503.xml Der Quantensprung] Die zweifelhafte Karriere eines Fachausdrucks (ZEIT 1996)
* [http://www.arxiv.org/abs/quant-ph/9702007 M.B. Plenio und P.L. Knight The Quantum Jump Approach to Dissipative Dynamics in Quantum Optics], vgl. auch Rev. Mod. Phys. 70 101–144 (1998). (Beschreibung der Dynamik offener Systeme mittels Quantensprüngen)
* [http://www.mikomma.de/soqsp/soqsp.htm Historisches zum Quantensprung], Sommerfeld und Einstein 1911 | 0 | Theoretical and Fundamental Chemistry |
Patients also on diuretics may experience an excessive reduction of blood pressure after initiation of therapy with trandolapril. It can reduce potassium loss caused by thiazide diuretics and increase serum potassium when used alone. Therefore, hyperkalemia is a possible risk. Increased serum lithium levels can occur in patients who are also on lithium. | 0 | Theoretical and Fundamental Chemistry |
Planar Flow Casting (PFC) is a commonly used melt spinning process for the industrial fabrication of wide metallic glass sheets. In this process, the primary modification is that a much wider nozzle is used to eject the melt from the crucible. As a result, the melt puddle covers a larger area of the drum, which in turn forms a larger area of ribbon. PFC is commonly cast in a vacuum to avoid oxidation of the molten material, which would affect the quality of the resulting product. Ribbons up to 200 mm wide have been industrially achieved using PFC. | 1 | Applied and Interdisciplinary Chemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), and Valine (Val, V). | 1 | Applied and Interdisciplinary Chemistry |
A catabolic pathway is a series of reactions that bring about a net release of energy in the form of a high energy phosphate bond formed with the energy carriers adenosine diphosphate (ADP) and guanosine diphosphate (GDP) to produce adenosine triphosphate (ATP) and guanosine triphosphate (GTP), respectively. The net reaction is, therefore, thermodynamically favorable, for it results in a lower free energy for the final products. A catabolic pathway is an exergonic system that produces chemical energy in the form of ATP, GTP, NADH, NADPH, FADH2, etc. from energy containing sources such as carbohydrates, fats, and proteins. The end products are often carbon dioxide, water, and ammonia. Coupled with an endergonic reaction of anabolism, the cell can synthesize new macromolecules using the original precursors of the anabolic pathway. An example of a coupled reaction is the phosphorylation of fructose-6-phosphate to form the intermediate fructose-1,6-bisphosphate by the enzyme phosphofructokinase accompanied by the hydrolysis of ATP in the pathway of glycolysis. The resulting chemical reaction within the metabolic pathway is highly thermodynamically favorable and, as a result, irreversible in the cell. | 1 | Applied and Interdisciplinary Chemistry |
In fluid mechanics, the center of pressure is the point where the total sum of a pressure field acts on a body, causing a force to act through that point. The total force vector acting at the center of pressure is the surface integral of the pressure vector field across the surface of the body. The resultant force and center of pressure location produce an equivalent force and moment on the body as the original pressure field.
Pressure fields occur in both static and dynamic fluid mechanics. Specification of the center of pressure, the reference point from which the center of pressure is referenced, and the associated force vector allows the moment generated about any point to be computed by a translation from the reference point to the desired new point. It is common for the center of pressure to be located on the body, but in fluid flows it is possible for the pressure field to exert a moment on the body of such magnitude that the center of pressure is located outside the body. | 1 | Applied and Interdisciplinary Chemistry |
Wootz is characterized by a pattern caused by bands of clustered particles made by melting of low levels of carbide-forming elements. Wootz contains greater carbonaceous matter than common qualities of cast steel.
The distinct patterns of Wootz steel that can be made through forging are wave, ladder, and rose patterns with finely spaced bands. However, with hammering, dyeing, and etching further customized patterns were made.
The presence of cementite nanowires and carbon nanotubes has been identified by Peter Pepler of TU Dresden in the microstructure of wootz steel. There is a possibility of an abundance of ultrahard metallic carbides in the steel matrix precipitating out in bands.Wootz swords were renowned for their sharpness and toughness. | 1 | Applied and Interdisciplinary Chemistry |
The first synthetic ion channel was constructed by partial substitution on the primary rim of β-cyclodextrin. Other substituted β-cyclodextrins have since been reported, including thiol-modified cyclodextrins, an anion-selective oligobutylene channel, and various poly-ethyleneoxide linked starburst oligomers. Structure-activity relationships for a large suite of cyclodextrin "half-channels" prepared by "click"-chemistry has been recently reported. | 0 | Theoretical and Fundamental Chemistry |
A method that is the less well-known is the metabisulfite method, in which metabisulfite is placed at the bottom of a beaker and 12.6 molar concentration hydrochloric acid is added. The resulting gas is bubbled through nitric acid, which will release brown/red vapors of nitrogen dioxide as the reaction proceeds. The completion of the reaction is indicated by the ceasing of the fumes. This method does not produce an inseparable mist, which is quite convenient.
Burning sulfur together with saltpeter (potassium nitrate, ), in the presence of steam, has been used historically. As saltpeter decomposes, it oxidizes the sulfur to , which combines with water to produce sulfuric acid.
Alternatively, dissolving sulfur dioxide in an aqueous solution of an oxidizing metal salt such as copper(II) or iron(III) chloride:
Two less well-known laboratory methods of producing sulfuric acid, albeit in dilute form and requiring some extra effort in purification. A solution of copper(II) sulfate can be electrolyzed with a copper cathode and platinum/graphite anode to give spongy copper at cathode and evolution of oxygen gas at the anode, the solution of dilute sulfuric acid indicates completion of the reaction when it turns from blue to clear (production of hydrogen at cathode is another sign):
More costly, dangerous, and troublesome yet novel is the electrobromine method, which employs a mixture of sulfur, water, and hydrobromic acid as the electrolytic solution. The sulfur is pushed to bottom of container under the acid solution. Then the copper cathode and platinum/graphite anode are used with the cathode near the surface and the anode is positioned at the bottom of the electrolyte to apply the current. This may take longer and emits toxic bromine/sulfur bromide vapors, but the reactant acid is recyclable. Overall, only the sulfur and water are converted to sulfuric acid and hydrogen (omitting losses of acid as vapors):
: (electrolysis of aqueous hydrogen bromide)
: (initial tribromide production, eventually reverses as depletes)
: (bromine reacts with sulfur to form disulfur dibromide)
: (oxidation and hydration of disulfur dibromide)
Prior to 1900, most sulfuric acid was manufactured by the lead chamber process. As late as 1940, up to 50% of sulfuric acid manufactured in the United States was produced by chamber process plants.
In the early to mid 19th century "vitriol" plants existed, among other places, in Prestonpans in Scotland, Shropshire and the Lagan Valley in County Antrim Ireland, where it was used as a bleach for linen. Early bleaching of linen was done using lactic acid from sour milk but this was a slow process and the use of vitriol sped up the bleaching process. | 0 | Theoretical and Fundamental Chemistry |
In theory, the speed of the particles (and, therefore, the vorticity) in a vortex may vary with the distance from the axis in many ways. There are two important special cases, however:
* If the fluid rotates like a rigid body – that is, if the angular rotational velocity is uniform, so that increases proportionally to the distance from the axis – a tiny ball carried by the flow would also rotate about its center as if it were part of that rigid body. In such a flow, the vorticity is the same everywhere: its direction is parallel to the rotation axis, and its magnitude is equal to twice the uniform angular velocity of the fluid around the center of rotation.
* If the particle speed is inversely proportional to the distance from the axis, then the imaginary test ball would not rotate over itself; it would maintain the same orientation while moving in a circle around the vortex axis. In this case the vorticity is zero at any point not on that axis, and the flow is said to be irrotational. | 1 | Applied and Interdisciplinary Chemistry |
LD uses linearly polarized light, which is light that has been polarized in one direction only. This produces a wave, the electric field vector, which oscillates in only one plane, giving rise to a classic sinusoidal wave shape as the light travels through space. By using light parallel and perpendicular to the orientation direction it is possible to measure how much more energy is absorbed in one dimension of the molecule relative to the other, providing information to the experimentalist.
As light interacts with the molecule being investigated, should the molecule start absorbing the light then electron density inside the molecule will be shifted as the electron becomes photoexcited. This movement of charge is known as an electronic transition, the direction of which is called the electric transition polarisation. It is this property for which LD is a measurement.
The LD of an oriented molecule can be calculated using the following equation:-
:LD = A- A
Where A is the absorbance parallel to the orientation axis and A is the absorbance perpendicular to the orientation axis.
Note that light of any wavelength can be used to generate an LD signal.
The LD signal generated therefore has two limits upon the signal that can be generated. For a chemical system whose electric transition is parallel to the orientation axis, the following equation can be written:
:LD = A- A = A > 0
For most chemical systems this represents an electric transition polarised across the length of the molecule (i.e. parallel to the orientation axis).
Alternatively, the electric transition polarisation can be found to be perfectly perpendicular to the orientation of the molecule, giving rise to the following equation:
:LD = A- A = - A < 0
This equation represents the LD signal recorded if the electric transition is polarised across the width of the molecule (i.e. perpendicular to the orientation axis), which in the case of LD is the smaller of the two investigable axes.
LD can therefore be used in two ways. If the orientation of the molecules in flow is known, then the experimentalist can look at the direction of polarisation in the molecule (which gives an insight into the chemical structure of a molecule), or if the polarisation direction is unknown it can be used as a means of working out how oriented in flow a molecule is. | 0 | Theoretical and Fundamental Chemistry |
Being an essential element, calcium is obtained through dietary sources, the majority of which comes from dairy products. The three most significant mechanisms controlling calcium use within the body are intestinal absorption, renal absorption and bone turnover, which is controlled predominantly by hormones and their corresponding receptors in the gut, kidneys and bones respectively. This allows for calcium use throughout the body, namely in bone growth, cellular signalling, blood clotting, muscle contraction and neuron function.
Calcium is one of the essential components of bone, contributing to its strength and structure in addition to being the main site at which it is stored within the body. Within the muscles, its primary use is to enable contractions. Muscle cells draw calcium from the blood, allowing it to bind with troponin, a component of the muscle fibre that signals for a contraction by moving actin and myosin. After a contraction, calcium dissipates and the filaments move back to a resting state before the release of more calcium for the next contraction. Furthermore, calcium plays a significant role in allowing nerve impulses to be transmitted between neurons. The release of calcium ions from voltage gated ion channels signals for the release of neurotransmitters into the synapse. This allows for the depolarisation of a neuron, thus transmitting the signal to the next neuron where this process is once again repeated. Without the presence of calcium ions, the release of neurotransmitters would not occur, preventing signals from being sent and hindering body processes.
Negative feedback mechanisms are implemented in order to control calcium levels. When low calcium levels are detected in the body, the parathyroid releases parathyroid hormone (PTH) which travels through the bloodstream to the bones and kidneys. In the bones, the presence of PTH stimulates osteoclasts. These cells break down bone to release calcium into the bloodstream where it can be used by the rest of the body in the above processes. In the kidneys, PTH stimulates re-absorption of calcium so it in not lost from the body through urine and returned to the bloodstream instead. Lastly, PTH acts on the intestines by indirectly promoting enzymes that activate vitamin D, a signal for the intestines to absorb more calcium, further increasing blood calcium levels. This will continue until the body releases too much calcium into the bloodstream. Excess calcium then promotes the release of calcitonin from the thyroid gland, effectively reversing the process of PTH. Osteoclast activity is stopped and osteoblasts take over, utilising the excess calcium in the bloodstream to form new bone. Calcium re-absorption in the kidney is prevented, allowing the excretion of excess calcium through the urine. Through these hormonal mechanisms, calcium homeostasis is maintained within the body. | 1 | Applied and Interdisciplinary Chemistry |
In 1913, amateur Dutch physicist Antonius van den Broek was the first to propose that the atomic number (nuclear charge) determined the placement of elements in the periodic table. He correctly determined the atomic number of all elements up to atomic number 50 (tin), though he made several errors with heavier elements. However, Van den Broek did not have any method to experimentally verify the atomic numbers of elements; thus, they were still believed to be a consequence of atomic weight, which remained in use in ordering elements.
Moseley was determined to test Van den Broeks hypothesis. After a year of investigation of the Fraunhofer lines of various elements, he found a relationship between the X-ray wavelength of an element and its atomic number. With this, Moseley obtained the first accurate measurements of atomic numbers and determined an absolute sequence to the elements, allowing him to restructure the periodic table. Moseleys research immediately resolved discrepancies between atomic weight and chemical properties, where sequencing strictly by atomic weight would result in groups with inconsistent chemical properties. For example, his measurements of X-ray wavelengths enabled him to correctly place argon (Z = 18) before potassium (Z = 19), cobalt (Z = 27) before nickel (Z = 28), as well as tellurium (Z = 52) before iodine (Z = 53), in line with periodic trends. The determination of atomic numbers also clarified the order of chemically similar rare-earth elements; it was also used to confirm that Georges Urbain's claimed discovery of a new rare-earth element (celtium) was invalid, earning Moseley acclamation for this technique.
Swedish physicist Karl Siegbahn continued Moseleys work for elements heavier than gold (Z' = 79), and found that the heaviest known element at the time, uranium, had atomic number 92. In determining the largest identified atomic number, gaps in the atomic number sequence were conclusively determined where an atomic number had no known corresponding element; the gaps occurred at atomic numbers 43 (technetium), 61 (promethium), 72 (hafnium), 75 (rhenium), 85 (astatine), and 87 (francium). | 1 | Applied and Interdisciplinary Chemistry |
A Paul trap that uses an oscillating quadrupole field to trap ions radially and a static potential to confine ions axially. The quadrupole field is realized by four parallel electrodes laying in the -axis positioned at the corners of a square in the -plane. Electrodes diagonally opposite each other are connected and an a.c. voltage is applied. Using Maxwells equations, the electric field produced by this potential is electric field . Applying Newtons second law to an ion of charge and mass in this a.c. electric field, we can find the force on the ion using . We wind up with
Assuming that the ion has zero initial velocity, two successive integrations give the velocity and displacement as
where is a constant of integration. Thus, the ion oscillates with angular frequency and amplitude proportional to the electric field strength and is confined radially.
Working specifically with a linear Paul trap, we can write more specific equations of motion. Along the -axis, an analysis of the radial symmetry yields a potential
The constants and are determined by boundary conditions on the electrodes and satisfies Laplace's equation . Assuming the length of the electrodes is much greater than their separation , it can be shown that
Since the electric field is given by the gradient of the potential, we get that
Defining , the equations of motion in the -plane are a simplified form of the Mathieu equation, | 0 | Theoretical and Fundamental Chemistry |
Perhaps the most direct measurement of s character in a bonding orbital between hydrogen and carbon is via the H−C coupling constants determined from NMR spectra. Theory predicts that J values correlates with s character. In particular, the one bond C-H coupling constant J is related to the fractional s character of the carbon hybrid orbital used to form the bond through the empirical relationship , where is the s character. (For instance the pure sp hybrid atomic orbital found in the C-H bond of methane would have 25% s character resulting in an expected coupling constant of 500 Hz × 0.25 = 125 Hz, in excellent agreement with the experimentally determined value.)
As the electronegativity of the substituent increases, the amount of p character directed towards the substituent increases as well. This leaves more s character in the bonds to the methyl protons, which leads to increased J coupling constants. | 0 | Theoretical and Fundamental Chemistry |
Simple cations formed by adding a hydron to a hydride of a halogen, chalcogen or pnictogen are named by adding the suffix "-onium" to the element's root: is ammonium, is oxonium, and H2F+ is fluoronium. Ammonium was adopted instead of nitronium, which commonly refers to .
If the cationic center of the hydride is not a halogen, chalcogen or pnictogen then the suffix "-ium" is added to the name of the neutral hydride after dropping any final e. is methanium, is dioxidanium (HO-OH is dioxidane), and is diazanium ( is diazane). | 0 | Theoretical and Fundamental Chemistry |
All vertebrate and chordate species require vitamin A, either as dietary carotenoids or preformed retinol from consuming other animals. Deficiencies have been reported in laboratory-raised and pet dogs, cats, birds, reptiles and amphibians, also commercially raised chickens and turkeys. Herbivore species such as horses, cattle and sheep can get sufficient β-carotene from green pasture to be healthy, but the content in pasture grass dry due to drought and long-stored hay can be too low, leading to vitamin A deficiency. Omnivore and carnivore species, especially those toward the top of the food chain, can accrue large amounts of retinyl esters in their livers, or else excrete retinyl esters in urine as a means of dealing with surplus. Before the era of synthetic retinol, cod liver oil, high in vitamins A and D, was a commonly consumed dietary supplement. Invertebrates cannot synthesize carotenoids or retinol, and thus must accrue these essential nutrients from consumption of algae, plants or animals. | 1 | Applied and Interdisciplinary Chemistry |
Once the selection has been performed, the primary structure of the proteins which display the appropriate characteristics must be determined. This is achieved by retrieval of the protein-encoding sequences (as originally inserted) from the cells showing the appropriate phenotype. | 1 | Applied and Interdisciplinary Chemistry |
Intestinal organoids grown from rectal biopsies using culture protocols established by the Clevers group have been used to model cystic fibrosis, and led to the first application of organoids for personalised treatment. Cystic fibrosis is an inherited disease that is caused by gene mutations of the cystic fibrosis transmembrane conductance regulator gene that encodes an epithelial ion channel necessary for healthy epithelial surface fluids. Studies by the laboratory of Jeffrey Beekman (Wilhelmina Childrens Hospital, University Medical Center Utrecht, The Netherlands) described in 2013 that stimulation of colorectal organoids with cAMP-raising agonists such as forskolin or cholera toxin induced rapid swelling of organoids in a fully CFTR dependent manner. Whereas organoids from non-cystic fibrosis subjects swell in response to forskolin as a consequence of fluid transport into the organoids lumens, this is severely reduced or absent in organoids derived from people with cystic fibrosis. Swelling could be restored by therapeutics that repair the CFTR protein (CFTR modulators), indicating that individual responses to CFTR modulating therapy could be quantitated in a preclinical laboratory setting. Schwank et al. also demonstrated that the intestinal cystic fibrosis organoid phenotype could be repaired by CRISPR-Cas9 gene editing in 2013.
Follow-up studies by Dekkers et al. in 2016 revealed that quantitative differences in forskolin-induced swelling between intestinal organoids derived from people with cystic fibrosis associate with known diagnostic and prognostic markers such as CFTR gene mutations or in vivo biomarkers of CFTR function. In addition, the authors demonstrated that CFTR modulator responses in intestinal organoids with specific CFTR mutations correlated with published clinical trial data of these treatments. This led to preclinical studies where organoids from patients with extremely rare CFTR mutations for who no treatment was registered were found to respond strongly to a clinically available CFTR modulator. The suggested clinical benefit of treatment for these subjects based on the preclinical organoid test was subsequently confirmed upon clinical introduction of treatment by members of the clinical CF center under supervision of Kors van der Ent (Department of Paediatric Pulmonology, Wilhelmina Children's Hospital, University Medical Center Utrecht, The Netherlands). These studies show for the first time that organoids can be used for the individual tailoring of therapy or personalised medicine. | 1 | Applied and Interdisciplinary Chemistry |
The formation of chiral quaternary carbon centers has been a synthetic challenge. Chemists have developed asymmetric Diels–Alder reactions, Heck reaction, Enyne cyclization, cycloaddition reactions, C–H activation, Allylic substitution, Pauson–Khand reaction, etc. to construct asymmetric quaternary carbon atoms. | 0 | Theoretical and Fundamental Chemistry |
Peter Trefonas is a son of Louis Marco Trefonas, also a chemist, and Gail Thames. He was inspired by Star Trek and the writings of Isaac Asimov, and created his own chemistry lab at home.
Trefonas attended the University of New Orleans, receiving his Bachelor of Science in chemistry in 1980.
While an undergraduate, Trefonas earned money by writing video games for early personal computers. These included Worm, a clone of the 1976 arcade video game Blockade, and a clone of the arcade game Hustle (1977), which itself was based on Blockcade. Worm was the first of what would become many games in the snake video game genre for home computers. Trefonas also wrote a game based on Dungeons & Dragons.
Trefonas studied at the University of Wisconsin-Madison with Robert West, completing a Ph.D. in inorganic chemistry in late 1984. Trefonas became interested in electronic materials after working with West and chip makers from IBM to create organosilicon bilayer photoresists. His thesis topic was "Synthesis, properties and chemistry of organosilane and organogermane high polymers" (1985). | 0 | Theoretical and Fundamental Chemistry |
The Caspian Sea is the largest inland body of water in the world by area and accounts for 40–44% of the total lake waters of the world, and covers an area larger than Germany. The coastlines of the Caspian are shared by Azerbaijan, Iran, Kazakhstan, Russia, and Turkmenistan. The Caspian is divided into three distinct physical regions: the Northern, Middle, and Southern Caspian. The Northern–Middle boundary is the Mangyshlak Threshold, which runs through Chechen Island and Cape Tiub-Karagan. The Middle–Southern boundary is the Apsheron Threshold, a sill of tectonic origin between the Eurasian continent and an oceanic remnant, that runs through Zhiloi Island and Cape Kuuli. The Garabogazköl Bay is the saline eastern inlet of the Caspian, which is part of Turkmenistan and at times has been a lake in its own right due to the isthmus that cuts it off from the Caspian.
Differences between the three regions are dramatic. The Northern Caspian only includes the Caspian shelf, and is very shallow; it accounts for less than 1% of the total water volume with an average depth of only . The sea noticeably drops off towards the Middle Caspian, where the average depth is . The Southern Caspian is the deepest, with oceanic depths of over , greatly exceeding the depth of other regional seas, such as the Persian Gulf. The Middle and Southern Caspian account for 33% and 66% of the total water volume, respectively. The northern portion of the Caspian Sea typically freezes in the winter, and in the coldest winters ice forms in the south as well.
Over 130 rivers provide inflow to the Caspian, the Volga River being the largest. A second affluent, the Ural River, flows in from the north, and the Kura River from the west. In the past, the Amu Darya (Oxus) of Central Asia in the east often changed course to empty into the Caspian through a now-desiccated riverbed called the Uzboy River, as did the Syr Darya farther north. The Caspian has several small islands, primarily located in the north with a collective land area of roughly . Adjacent to the North Caspian is the Caspian Depression, a low-lying region below sea level. The Central Asian steppes stretch across the northeast coast, while the Caucasus mountains hug the western shore. The biomes to both the north and east are characterized by cold, continental deserts. Conversely, the climate to the southwest and south are generally warm with uneven elevation due to a mix of highlands and mountain ranges; the drastic changes in climate alongside the Caspian have led to a great deal of biodiversity in the region.
The Caspian Sea has numerous islands near the coasts, but none in the deeper parts of the sea. Ogurja Ada is the largest island. The island is long, with gazelles roaming freely on it. In the North Caspian, the majority of the islands are small and uninhabited, like the Tyuleniy Archipelago, an Important Bird Area (IBA). | 1 | Applied and Interdisciplinary Chemistry |
Ammonia borane (also systematically named ammoniotrihydroborate), also called borazane, is the chemical compound with the formula . The colourless or white solid is the simplest molecular boron-nitrogen-hydride compound. It has attracted attention as a source of hydrogen fuel, but is otherwise primarily of academic interest. | 0 | Theoretical and Fundamental Chemistry |
Peak oil is a term applied to the projection that future petroleum production, whether for individual oil wells, entire oil fields, whole countries, or worldwide production, will eventually peak and then decline at a similar rate to the rate of increase before the peak as these reserves are exhausted. The peak of oil discoveries was in 1965, and oil production per year has surpassed oil discoveries every year since 1980. However, this does not mean that potential oil production has surpassed oil demand.
It is difficult to predict the oil peak in any given region, due to the lack of knowledge and/or transparency in the accounting of global oil reserves. Based on available production data, proponents have previously predicted the peak for the world to be in the years 1989, 1995, or 1995–2000. Some of these predictions date from before the recession of the early 1980s, and the consequent lowering in global consumption, the effect of which was to delay the date of any peak by several years. Just as the 1971 U.S. peak in oil production was only clearly recognized after the fact, a peak in world production will be difficult to discern until production clearly drops off.
In 2020, according to BP's Energy Outlook 2020, peak oil had been reached, due to the changing energy landscape coupled with the economic toll of the COVID-19 pandemic.
While there has been much focus historically on peak oil supply, the focus is increasingly shifting to peak demand as more countries seek to transition to renewable energy. The GeGaLo index of geopolitical gains and losses assesses how the geopolitical position of 156 countries may change if the world fully transitions to renewable energy resources. Former oil exporters are expected to lose power, while the positions of former oil importers and countries rich in renewable energy resources is expected to strengthen. | 0 | Theoretical and Fundamental Chemistry |
Janice Musfeldt is a professor at University of Tennessee, Knoxville in physical and materials chemistry and experimental physics. She received her B.S. degree in chemical engineering from the University of Illinois in 1987 and a Ph.D. in physical chemistry from the University of Florida in 1992. She served as a post-doctoral research associate at the Departement de Physique, Universite de Sherbrooke in 1993-1994. She received the 2001 Creativity award from the Division of Materials Research, National Science Foundation and the 2010 Chancellor's award for research and creative achievement at the University of Tennessee. She has served on the user committee of the National High Magnetic Field Laboratory between 2010 and 2013 and between 2018 and the present and was elected its chair in 2010. In 2014 she founded the biannual Gordon Research Conference on Multiferroics and Magnetoelectric materials. In 2017, she was elected as a Fellow of the American Physical Society for her contribution to the spectroscopy of quantum materials with an emphasis on high magnetic field effects in multiferroics, quantum magnets, and nanomaterials. | 0 | Theoretical and Fundamental Chemistry |
Mollapour’s laboratory has discovered the tumor suppressor TSC1 and FNIPs function as the new co-chaperones of Hsp90. These two proteins are involved in Tuberous Sclerosis Complex and Birt–Hogg–Dubé syndrome (BHD) syndromes respectively. His research has identified a cross-talk between these two co-chaperones and demonstrated interconnectivity and compensatory mechanisms between the BHD and TSC pathways. | 1 | Applied and Interdisciplinary Chemistry |
Vladimir Prelog (23 July 1906 – 7 January 1998) was a Croatian-Swiss organic chemist who received the 1975 Nobel Prize in chemistry for his research into the stereochemistry of organic molecules and reactions. Prelog was born and grew up in Sarajevo. He lived and worked in Prague, Zagreb and Zürich during his lifetime. | 0 | Theoretical and Fundamental Chemistry |
In 2009, Stephen Bustin led an international group of scientists including Mikael Kubista to put together a set of guidelines on how to perform qPCR and what forms of data should be collected and published in the process. This also allowed editors and reviewers of scientific journals to employ the guidelines when looking over a submitted paper that included qPCR data. Thus, the guidelines were set up as a sort of checklist for each step of the procedure with certain items being marked as essential (E) when submitting data for publication and others marked as just desirable (D).
An additional version of the guidelines was published in September 2010 for use with fluorescence-based quantitative real-time PCR. It also acted as a précis for the broader form of the guidelines. Other researchers have been creating further versions for specific forms of qPCR that may require a supplementary or different set of items to check, including single-cell qPCR and digital PCR (dPCR). Appropriate adherence to the existing MIQE guidelines has also been overviewed in other scientific areas, including photobiomodulation and clinical biomarkers.
It was noted by Bustin in 2014 (and again by him in 2017) that there was some amount of uptake and usage of the MIQE guidelines within the scientific community, but there were still far too many published papers with qPCR experiments that lacked even the most basic of data presentation and proper confirmation of effectiveness for said data. These studies retained major reproducibility issues, where the conclusions of their evidence could not be replicated by other researchers, throwing the initial results into doubt. All of this was despite many papers directly citing Bustin's original MIQE publication, but not following through on the guideline checklist of material in their own experiments. However, some researchers have pointed out at least some success, with a number of papers being rejected by academic journals for publication due to failing to pass MIQE checklists. Other studies have been retracted after the fact once their lack of proper data to pass the MIQE guidelines was noted and publicly pointed out to the journal editors. | 1 | Applied and Interdisciplinary Chemistry |
Tamm et al. have shown that survivin inhibits both Bax and Fas-induced apoptotic pathways. The experiment involved transfecting HEK 293 cells with a Bax-encoding plasmid, which resulted in an increase in apoptosis (~7 fold) as measured by DAPI staining. They then contransfected the 293 cells with Bax-encoding plasmid and survivin-encoding plasmids. They observed that cells transfected along with the survivin showed a significant decrease in apoptosis (~3 fold). A similar result also showed for cells transfected with the Fas-overexpressing plasmid. Immunoblots were performed and confirmed that survivin does not inhibit by mechanism of preventing Bax or Fas protein from being made into fully functional proteins. Therefore, survivin should be acting somewhere downstream of the Bax or Fas signaling pathway to inhibit apoptosis through these pathways. | 1 | Applied and Interdisciplinary Chemistry |
The onset of acidosis during periods of intense exercise is commonly attributed to accumulation of hydrogens that are dissociated from lactate. Previously, lactic acid was thought to cause fatigue. From this reasoning, the idea of lactate production being a primary cause of muscle fatigue during exercise was widely adopted. A closer, mechanistic analysis of lactate production under “anaerobic” conditions shows that there is no biochemical evidence for the production of lactate through LDH contributing to acidosis. While LDH activity is correlated to muscle fatigue, the production of lactate by means of the LDH complex works as a system to delay the onset of muscle fatigue. George Brooks and Colleagues at UC Berkeley where the lactate shuttle was discovered showed that lactate was actually a metabolic fuel not a waste product or the cause of fatigue.
LDH works to prevent muscular failure and fatigue in multiple ways. The lactate-forming reaction generates cytosolic NAD+, which feeds into the glyceraldehyde 3-phosphate dehydrogenase reaction to help maintain cytosolic redox potential and promote substrate flux through the second phase of glycolysis to promote ATP generation. This, in effect, provides more energy to contracting muscles under heavy workloads. The production and removal of lactate from the cell also ejects a proton consumed in the LDH reaction- the removal of excess protons produced in the wake of this fermentation reaction serves to act as a buffer system for muscle acidosis. Once proton accumulation exceeds the rate of uptake in lactate production and removal through the LDH symport, muscular acidosis occurs. | 1 | Applied and Interdisciplinary Chemistry |
Vallot, first physician to Louis XIV, appointed him demonstrator of chemistry at the Jardin du Roi, Paris; Diarist John Evelyn is recorded as having attended a course of his lectures there in February 1647. In 1660 he was appointed Professor of Chemistry to Charles II of England in 1660, Apothecary in Ordinary to the Royal Family in 1660 and Manager of the laboratory at St James's Palace, London. | 1 | Applied and Interdisciplinary Chemistry |
Within the field of molecular biology, the epitranscriptome includes all the biochemical modifications of the RNA (the transcriptome) within a cell. In analogy to epigenetics that describes "functionally relevant changes to the genome that do not involve a change in the nucleotide sequence", epitranscriptomics involves all functionally relevant changes to the transcriptome that do not involve a change in the ribonucleotide sequence. Thus, the epitranscriptome can be defined as the ensemble of such functionally relevant changes.
There are several types of RNA modifications that impact gene expression. These modifications happen to many types of cellular RNA including, but not limited to, ribosomal RNA (rRNA), transfer RNA (tRNA), messenger RNA (mRNA), and small nuclear RNA (snRNA). The most common and well-understood mRNA modification at present is N-Methyladenosine (mA), which has been observed to occur an average of three times in every mRNA molecule.
Currently, work is focused on determining the types of and location of RNA modifications, determining if these modification have function, and if so, what is their mechanism of action. Similar to the epigenome, the epitranscriptome has "writers" and "erasers" that mark RNA and "readers" that translate those marks into function. One function that has been elucidated involves the enzyme adenosine deaminase (ADAR), which acts on RNA. ADAR affects a series of cellular processes, including alternative splicing, microRNAs, the innate immune system, and leads to protein recoding especially for important receptors in the central nervous system. | 1 | Applied and Interdisciplinary Chemistry |
* – documentary on rogue wave sizes, impacts, and causes by Facts in Motion (YouTuber).
* [https://web.archive.org/web/20060219163057/http://www.kayotix.com/tmp/newsfeeds/21.08.04/waveresearch/ BBC News Report on Wave Research], 21 August 2004
* [http://www.bbc.co.uk/science/horizon/2002/freakwave.shtml The BBC's Horizon "Freak waves" first aired in November 2002]
* [https://web.archive.org/web/20081206165607/http://www.gresham.ac.uk/event.asp?PageId=45&EventId=729 Giant Waves on the Open Sea], lecture by Professor Paul H Taylor at Gresham College, 13 May 2008 (available for video, audio or text download)
* [https://web.archive.org/web/20101113032038/http://www.janson.com/rights/2009/06/25/when-nature-strikes-back-freak-waves/ TV program description]
* [https://web.archive.org/web/20151021011540/http://users.ox.ac.uk/~spet1235/Site/Freak_waves.html Non-technical description of some of the causes of rogue waves]
* [http://seastead.org/localres/misc-articles/lawton_newsci_06_30_01.html New Scientist article 06/2001]
* [http://www.oceanwave.jp/index.php?Research%2FFreak%20(Rogue)%20Wave%20Prediction Freak Wave Research in Japan]
* [https://physics.anu.edu.au/theophys/osg/ Optical Science Group, Research School of Physics and Engineering at the Australian National University]
* [https://www.nytimes.com/2006/07/11/science/11wave.html "Rogue Giants at Sea"], The New York Times, July 11, 2006
* Illustrations of the ways rogue waves can form – with descriptions for layman, photos and animations.
* [http://mosaicimagesphoto.photoshelter.com/image/I0000T2wfLusQ4h8 "The Wave" – photograph of a solitary and isolated rogue wave appearing in otherwise calm ocean waters (photographer: G Foulds)]
* Katherine Noyes (25 February 2016), "[http://www.cio.com/article/3038356/a-new-algorithm-from-mit-could-protect-ships-from-rogue-waves-at-sea.html A new algorithm from MIT could protect ships from rogue waves at sea] ", CIO magazine.
* Wood, Charles, [https://www.quantamagazine.org/the-grand-unified-theory-of-rogue-waves-20200205/ The Grand Unified Theory of Rogue Waves]. Rogue waves – enigmatic giants of the sea – were thought to be caused by two different mechanisms. But a new idea that borrows from the hinterlands of probability theory has the potential to predict them all. February 5, 2020. Quanta Magazine. | 1 | Applied and Interdisciplinary Chemistry |
Speculations about the chemical structure and properties of hypothetical non-carbon-based life have been a recurring theme in science fiction. Silicon is often used as a substitute for carbon in fictional lifeforms because of its chemical similarities. In cinematic and literary science fiction, when man-made machines cross from non-living to living, this new form is often presented as an example of non-carbon-based life. Since the advent of the microprocessor in the late 1960s, such machines are often classed as "silicon-based life". Other examples of fictional "silicon-based life" can be seen in the 1967 episode "The Devil in the Dark" from Star Trek: The Original Series, in which a living rock creatures biochemistry is based on silicon. In the 1994 The X-Files' episode "Firewalker", in which a silicon-based organism is discovered in a volcano.
In the 1984 film adaptation of Arthur C. Clarkes 1982 novel 2010: Odyssey Two', a character argues, "Whether we are based on carbon or on silicon makes no fundamental difference; we should each be treated with appropriate respect."
In JoJolion, the eighth part of the larger JoJos Bizarre Adventure' series, a mysterious race of silicon-based lifeforms "Rock Humans" serve as the primary antagonists. | 1 | Applied and Interdisciplinary Chemistry |
Amines are often used as epoxy resin curing agents. These include dimethylethylamine, cyclohexylamine, and a variety of diamines such as 4,4-diaminodicyclohexylmethane. Multifunctional amines such as tetraethylenepentamine and triethylenetetramine are also widely used in this capacity. The reaction proceeds by the lone pair of electrons on the amine nitrogen attacking the outermost carbon on the oxirane ring of the epoxy resin. This relieves ring strain on the epoxide and is the driving force of the reaction. | 0 | Theoretical and Fundamental Chemistry |
Window shutter hardware, usually made of iron, are hinges and latches that attach to the shutter and a window frame (and in some cases directly attached to stone or brick). The hinges hold the shutter to the structure and allow the shutter to open and close over the window. The latches secure the shutter in the closed (over the window) position. Tie-back hardware can be used to hold the shutter in the open position.
Exterior shutters were vital elements of homes in the colonies. Raised panel shutters provided security against access from ground level. Exterior shutters also proved a first barrier against the elements. In cities, shutters provided privacy screens for the residents. Louvered upstairs shutters were often later additions to the home.
This article describes the evolution of early exterior window shutter hardware, terms and terminology related to shutter hardware and blacksmithing, and American regional styles of installation. | 1 | Applied and Interdisciplinary Chemistry |
Level -1 fragments are used to help cloning large level 0 modules. To clone level -1 fragments, blunt-end cloning with restriction ligation can be used. The vector used in cloning level -1 fragments cannot contain Type IIS restriction site BpiI that is used for the following assembly step. Moreover, the vector should also have a different selection marker from the destination vector in next assembly step, for example, if spectinomycin resistance is used in level 0 modules, level -1 fragments should have another antibiotic resistance like ampicillin. | 1 | Applied and Interdisciplinary Chemistry |
Thiocarboxylic acids (RC(O)SH) and dithiocarboxylic acids (RC(S)SH) are well known. They are structurally similar to carboxylic acids but more acidic. Thioamides are analogous to amides. | 0 | Theoretical and Fundamental Chemistry |
The ore concentrate is first introduced into an IsaMill. This comminution step places a high degree of strain on the mineral lattice and causes an increase in the number of grain boundary fractures and lattice defects of several orders of magnitude. The increase in the number of defects within the mineral lattice "activates" the mineral, facilitating leaching. The rate of leaching is also enhanced, due to the increase in the mineral surface area.
The oxidative leaching stage is carried out in agitated tanks operating at atmospheric pressure. Oxygen is introduced to the leach slurry to assist the oxidation. Leaching is autothermal, not requiring any external heat. Temperature is controlled by the rate of addition of oxygen, and by the leach slurry density. | 1 | Applied and Interdisciplinary Chemistry |
EosFP has been used to track cell movements during embryonic development of Xenopus laevis. At the two-cell/ early gastrula stage, capped mRNA coding for a dimeric EosFP (d2EosFP) was injected into cells and locally photoconverted using fluorescence microscopy. These fluorescent embryos demonstrated the dynamics of cell movement during neurulation. EosFP was found in part of the notochord which shows the possibility of EosFP to be used in fate-mapping experiments. | 1 | Applied and Interdisciplinary Chemistry |
A prominent α-halo carboxylic acid is chloroacetic acid, which is used to produce carboxymethyl cellulose, carboxymethyl starch, as well as several phenoxy herbicides. 2,2-Dichloropropionic acid ("Dalapon") is an herbicide. | 0 | Theoretical and Fundamental Chemistry |
A direct numerical simulation (DNS) is a simulation in computational fluid dynamics (CFD) in which the Navier–Stokes equations are numerically solved without any turbulence model. This means that the whole range of spatial and temporal scales of the turbulence must be resolved. All the spatial scales of the turbulence must be resolved in the computational mesh, from the smallest dissipative scales (Kolmogorov microscales), up to the integral scale , associated with the motions containing most of the kinetic energy. The Kolmogorov scale, , is given by
where is the kinematic viscosity and is the rate of kinetic energy dissipation. On the other hand, the integral scale depends usually on the spatial scale of the boundary conditions.
To satisfy these resolution requirements, the number of points along a given mesh direction with increments , must be
so that the integral scale is contained within the computational domain, and also
so that the Kolmogorov scale can be resolved.
Since
where is the root mean square (RMS) of the velocity, the previous relations imply that a three-dimensional DNS requires a number of mesh points satisfying
where is the turbulent Reynolds number:
Hence, the memory storage requirement in a DNS grows very fast with the Reynolds number. In addition, given the very large memory necessary, the integration of the solution in time must be done by an explicit method. This means that in order to be accurate, the integration, for most discretization methods, must be done with a time step, , small enough such that a fluid particle moves only a fraction of the mesh spacing in each step. That is,
( is here the Courant number). The total time interval simulated is generally proportional to the turbulence time scale given by
Combining these relations, and the fact that must be of the order of , the number of time-integration steps must be proportional to . On the other hand, from the definitions for , and given above, it follows that
and consequently, the number of time steps grows also as a power law of the Reynolds number.
One can estimate that the number of floating-point operations required to complete the simulation is proportional to the number of mesh points and the number of time steps, and in conclusion, the number of operations grows as .
Therefore, the computational cost of DNS is very high, even at low Reynolds numbers. For the Reynolds numbers encountered in most industrial applications, the computational resources required by a DNS would exceed the capacity of the most powerful computers currently available. However, direct numerical simulation is a useful tool in fundamental research in turbulence. Using DNS it is possible to perform "numerical experiments", and extract from them information difficult or impossible to obtain in the laboratory, allowing a better understanding of the physics of turbulence. Also, direct numerical simulations are useful in the development of turbulence models for practical applications, such as sub-grid scale models for large eddy simulation (LES) and models for methods that solve the Reynolds-averaged Navier–Stokes equations (RANS). This is done by means of "a priori" tests, in which the input data for the model is taken from a DNS simulation, or by "a posteriori" tests, in which the results produced by the model are compared with those obtained by DNS. | 1 | Applied and Interdisciplinary Chemistry |
Two waste products, dust and chips, form at the working surface during woodworking operations such as sawing, milling and sanding. These operations both shatter lignified wood cells and break out whole cells and groups of cells. Shattering of wood cells creates dust, while breaking out of whole groups of wood cells creates chips. The more cell-shattering that occurs, the finer the dust particles that are produced. For example, sawing and milling are mixed cell shattering and chip forming processes, whereas sanding is almost exclusively cell shattering. | 1 | Applied and Interdisciplinary Chemistry |
Transcription factor II E (TFE) is one of several general transcription factors that make up the RNA polymerase II preinitiation complex. It is a tetramer of two alpha and two beta chains and interacts with TAF6/TAFII80, ATF7IP, and varicella-zoster virus IE63 protein.
TFE recruits TFH to the initiation complex and stimulates the RNA polymerase II C-terminal domain kinase and DNA-dependent ATPase activities of TFH. Both TFH and TFE are required for promoter clearance by RNA polymerase. Transcription factor II E is encoded by the GTF2E1 and GTF2E2 genes. TFE is thought to be involved in DNA melting at the promoter: it contains a zinc ribbon motif that can bind single stranded DNA. | 1 | Applied and Interdisciplinary Chemistry |
N terminus - N-acetylhexosamine 1-dehydrogenase - N-acylmannosamine 1-dehydrogenase - N-formylmethionylaminoacyl-tRNA deformylase - N-isopropylammelide isopropylaminohydrolase - Na+-transporting two-sector ATPase - NADH:ubiquinone reductase (Na+-transporting) - native gel - nematode Her-1 - neolactotetraosylceramide alpha-2,3-sialyltransferase - nested PCR - neurofibromatosis - NH41 - nick (DNA) - nick translation - NIDDM1 - Niemann-Pick disease, type C - nitrate-transporting ATPase - non-coding DNA - non-coding strand - non-directiveness - nonconservative substitution - nonpolar-amino-acid-transporting ATPase - nonsense codon - nonsense mutation - nontranslated RNA - Northern blot - NT - nuclear run-on - nuclease - nuclease protection assay - nucleoplasmin ATPase - nucleoside - nucleoside-triphosphate diphosphatase - nucleotide - Nucleotide universal IDentifier - nucleus - | 1 | Applied and Interdisciplinary Chemistry |
Spin states relate to chemical and biochemical reaction mechanisms because bonds can be formed only between two electrons of opposite spin (Hund's rules). Sometimes when a bond is broken in a particular manner, for example, when struck by photons, each electron in the bond relocates to each respective molecule, and a radical-pair is formed. Furthermore, the spin of each electron previously involved in the bond is conserved, which means that the radical-pair now formed is a singlet (each electron has opposite spin, as in the origin bond). As such, the reverse reaction, i.e. the reforming of a bond, called recombination, readily occurs. The radical-pair mechanism explains how external magnetic fields can prevent radical-pair recombination with Zeeman interactions, the interaction between spin and an external magnetic field, and shows how a higher occurrence of the triplet state accelerates radical reactions because triplets can proceed only to products, and singlets are in equilibrium with the reactants as well as with the products.
Zeeman interactions can “flip” only one of the radicals electrons spin if the radical-pair is anisotropic, thereby converting singlet radical-pairs to triplets.
The Zeeman interaction is an interaction between spin and external magnetic field, and is given by the equation
where is the energy of the Zeeman interaction, is the Larmor frequency, is the external magnetic field, is the Bohr magneton, is Planck's constant, and is the g-factor of a free electron, 2.002319, which is slightly different in different radicals.
It is common to see the Zeeman interaction formulated in other ways. | 0 | Theoretical and Fundamental Chemistry |
Hypothiocyanite is the anion [OSCN] and the conjugate base of hypothiocyanous acid (HOSCN). It is an organic compound part of the thiocyanates as it contains the functional group SCN. It is formed when an oxygen is singly bonded to the thiocyanate group. Hypothiocyanous acid is a fairly weak acid; its acid dissociation constant (pK) is 5.3.
Hypothiocyanite is formed by peroxidase catalysis of hydrogen peroxide and thiocyanate:
: HO + SCN → OSCN + HO | 1 | Applied and Interdisciplinary Chemistry |
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