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Otherwise-intermolecular reactions can be made temporarily intramolecular by linking both reactants by a tether with all the advantages associated to it. Popular choices of tether contain a carbonate ester, boronic ester, silyl ether, or a silyl acetal link (silicon tethers) which are fairly inert in many organic reactions yet can be cleaved by specific reagents. The main hurdle for this strategy to work is selecting the proper length for the tether and making sure reactive groups have an optimal orientation with respect to each other. An examples is a Pauson–Khand reaction of an alkene and an alkyne tethered together via a silyl ether.
In this particular reaction, the tether angle bringing the reactive groups together is effectively reduced by placing isopropyl groups on the silicon atom via the Thorpe–Ingold effect. No reaction takes place when these bulky groups are replaced by smaller methyl groups. Another example is a photochemical [2+2]cycloaddition with two alkene groups tethered through a silicon acetal group (racemic, the other enantiomer not depicted), which is subsequently cleaved by TBAF yielding the endo-diol.
Without the tether, the exo isomer forms. | 0 | Theoretical and Fundamental Chemistry |
The thermodynamic potentials also satisfy
where is the chemical potential defined as (for constant n</sub> with j≠i):
This last partial derivative is the same as , the partial molar Gibbs free energy. This means that the partial molar Gibbs free energy and the chemical potential, one of the most important properties in thermodynamics and chemistry, are the same quantity. Under isobaric (constant P) and isothermal (constant T ) conditions, knowledge of the chemical potentials, , yields every property of the mixture as they completely determine the Gibbs free energy. | 0 | Theoretical and Fundamental Chemistry |
Both PXA and PXB were discovered in 2001, and their preparation by isolation from Phomopsis fungal cultures was described in the corresponding publication. Briefly, a MeOH extract of a Phomopsis culture is mixed with HO and washed with hexane. The aqueous phase is then dried and the residue is dissolved in EtOAc, washed with HO, concentrated and repeatedly purified by size-exclusion chromatography. The resulting mixture of PXA and PXB is separated by HPLC. A modified method, in which the initial extraction is done with EtOAc instead of MeOH and the drying step is skipped, was described in 2013. | 1 | Applied and Interdisciplinary Chemistry |
In fluid dynamics, the fluid flow is often decomposed into a mean flow and deviations from the mean. The averaging can be done either in space or in time, or by ensemble averaging. | 1 | Applied and Interdisciplinary Chemistry |
Helium-3 was trapped in the planet when it formed. Some He is being added by meteoric dust, primarily collecting on the bottom of oceans (although due to subduction, all oceanic tectonic plates are younger than continental plates). However, He will be degassed from oceanic sediment during subduction, so cosmogenic He is not affecting the concentration or noble gas ratios of the mantle.
Helium-3 is created by cosmic ray bombardment, and by lithium spallation reactions which generally occur in the crust. Lithium spallation is the process by which a high-energy neutron bombards a lithium atom, creating a He and a He ion. This requires significant lithium to adversely affect the He/He ratio.
All degassed helium is lost to space eventually, due to the average speed of helium exceeding the escape velocity for the Earth. Thus, it is assumed the helium content and ratios of Earth's atmosphere have remained essentially stable.
It has been observed that He is present in volcano emissions and oceanic ridge samples. How He is stored in the planet is under investigation, but it is associated with the mantle and is used as a marker of material of deep origin.
Due to similarities in helium and carbon in magma chemistry, outgassing of helium requires the loss of volatile components (water, carbon dioxide) from the mantle, which happens at depths of less than 60 km. However, He is transported to the surface primarily trapped in the crystal lattice of minerals within fluid inclusions.
Helium-4 is created by radiogenic production (by decay of uranium/thorium-series elements). The continental crust has become enriched with those elements relative to the mantle and thus more He is produced in the crust than in the mantle.
The ratio (R) of He to He is often used to represent He content. R usually is given as a multiple of the present atmospheric ratio (Ra).
Common values for R/Ra:
* Old continental crust: less than 1
* mid-ocean ridge basalt (MORB): 7 to 9
* Spreading ridge rocks: 9.1 plus or minus 3.6
* Hotspot rocks: 5 to 42
* Ocean and terrestrial water: 1
* Sedimentary formation water: less than 1
* Thermal spring water: 3 to 11
He/He isotope chemistry is being used to date groundwaters, estimate groundwater flow rates, track water pollution, and provide insights into hydrothermal processes, igneous geology and ore genesis.
* [http://www.geotrack.com.au/uthhe/u-th-he-techinfo.htm (U-Th)/He dating of apatite as a thermal history tool]
* [https://web.archive.org/web/20050210172919/http://lvo.wr.usgs.gov/helium.html USGS: Helium Discharge at Mammoth Mountain Fumarole (MMF)] | 0 | Theoretical and Fundamental Chemistry |
Let the principle of detailed balance be valid. Then, for small deviations from equilibrium, the kinetic response of the system can be approximated as linearly related to its deviation from chemical equilibrium, giving the reaction rates for the generalized mass action law as:
Therefore, again in the linear response regime near equilibrium, the kinetic equations are ():
This is exactly the Onsager form: following the original work of Onsager, we should introduce the thermodynamic forces and the matrix of coefficients in the form
The coefficient matrix is symmetric:
These symmetry relations, , are exactly the Onsager reciprocal relations. The coefficient matrix is non-positive. It is negative on the linear span of the stoichiometric vectors .
So, the Onsager relations follow from the principle of detailed balance in the linear approximation near equilibrium. | 0 | Theoretical and Fundamental Chemistry |
Ester pyrolysis in organic chemistry is a vacuum pyrolysis reaction converting esters containing a β-hydrogen atom into the corresponding carboxylic acid and the alkene. The reaction is an E elimination and operates in a syn fashion.
Examples include the synthesis of acrylic acid from ethyl acrylate at 590 °C, the synthesis of 1,4-pentadiene from 1,5-pentanediol diacetate at 575 °C or the construction of a cyclobutene framework at 700 °C | 0 | Theoretical and Fundamental Chemistry |
Doubly labeled water is water in which both the hydrogen and the oxygen have been partly or completely replaced (i.e. labeled) with an uncommon isotope of these elements for tracing purposes.
In practice, for both practical and safety reasons, almost all recent applications of the "doubly labeled water" method use water labeled with heavy but non-radioactive forms of each element (deuterium and oxygen-18). In theory, radioactive heavy isotopes of the elements could be used for such labeling; this was the case in many early applications of the method.
In particular, doubly labeled water (DLW) can be used for a method to measure the average daily metabolic rate of an organism over a period of time (often also called the Field metabolic rate, or FMR, in non-human animals). This is done by administering a dose of DLW, then measuring the elimination rates of deuterium and oxygen-18 in the subject over time (through regular sampling of heavy isotope concentrations in body water, by sampling saliva, urine, or blood). At least two samples are required: an initial sample (after the isotopes have reached equilibrium in the body), and a second sample some time later. The time between these samples depends on the size of the animal. In small animals, the period may be as short as 24 hours; in larger animals (such as adult humans), the period may be as long as 14 days.
The method was invented in the 1950s by Nathan Lifson and colleagues at the University of Minnesota. However, its use was restricted to small animals until the 1980s because of the high cost of the oxygen-18 isotope. Advances in mass spectrometry during the 1970s and early 1980s reduced the amount of isotope required, which made it feasible to apply the method to larger animals, including humans. The first application to humans was in 1982, by Dale Schoeller, over 25 years after the method was initially discovered. A complete summary of the technique is provided in a book by British biologist John Speakman. | 0 | Theoretical and Fundamental Chemistry |
Like the other members in the CMTM protein family, CMTM6 has a structure that contains domains (i.e. parts) similar to those in chemokine proteins; tetraspanin proteins (also termed transmembrane-4 superfamily proteins); the myelin and lymphocyte protein (also termed MAR protein); proteins that direct membrane vesicle trafficking; and proteins that are embedded across cell membranes. CMTM6 proteins are expressed in virtually all tissues and are located in cell plasma membranes (i.e. cell surface membranes), lysosomes, endosomes, cytosol, attached to the cell's cytoskeleton, and in extracellular spaces. | 1 | Applied and Interdisciplinary Chemistry |
MLST has provided a more richly textured picture of bacteria within human populations and on strain variants that may be pathogenic to human, plants and animals. MLST technique was first used by Maiden et al. (1) to characterize Neisseria meningitidis using six loci. The application of MLST has clearly resolved the major meningococcal lineages known to be responsible for invasive disease around the world. To improve the level of discriminatory power between the major invasive lineages, seven loci are now being used and have been accepted by many laboratories as the method of choice for characterizing meningococcal isolates. It is a well known fact that recombinational exchanges commonly occur in N. meningitidis, leading to rapid diversification of meningococcal clones. MLST has successfully provided a reliable method for characterization of clones within other bacterial species in which the rates of clonal diversification are generally lower. | 1 | Applied and Interdisciplinary Chemistry |
** Decision to construct the National Ignition Facility "beamlet" laser at LLNL is made.
** The START Tokamak fusion experiment begins in Culham. The experiment would eventually achieve a record beta (plasma pressure compared to magnetic field pressure) of 40% using a neutral beam injector. It was the first design that adapted the conventional toroidal fusion experiments into a tighter spherical design.
** The JT-60 tokamak was upgraded to JT-60U in March.
** The Engineering Design Activity for the ITER starts with participants EURATOM, Japan, Russia and United States. It ended in 2001.
** The United States and the former republics of the Soviet Union cease nuclear weapons testing.
** The TFTR tokamak at Princeton (PPPL) experiments with a 50% deuterium, 50% tritium mix, eventually producing as much as 10 megawatts of power from a controlled fusion reaction.
** NIF Beamlet laser is completed and begins experiments validating the expected performance of NIF.
** The USA declassifies information about indirectly driven (hohlraum) target design.
** Comprehensive European-based study of HIF driver begins, centered at the Gesellschaft für Schwerionenforschung (GSI) and involving 14 laboratories, including USA and Russia. The Heavy Ion Driven Inertial Fusion (HIDIF) study will be completed in 1997.
** A record is reached at Tore Supra: a plasma duration of two minutes with a current of almost 1 million amperes driven non-inductively by 2.3 MW of lower hybrid frequency waves (i.e. 280 MJ of injected and extracted energy). This result was possible due to the actively cooled plasma-facing components installed in the machine.
** The JT-60U tokamak achieves extrapolated breakeven at Q = 1.05.
** The JET tokamak in the UK produces 16 MW of fusion power - this remains the world record for fusion power until 2022 when JET sets an even higher record. Four megawatts of alpha particle self-heating was achieved.
** LLNL study compared projected costs of power from ICF and other fusion approaches to the projected future costs of existing energy sources.
** Groundbreaking ceremony held for the National Ignition Facility (NIF).
** The JT-60 tokamak in Japan produced a high performance reversed shear plasma with the equivalent fusion amplification factor of 1.25 - the current world record of Q, fusion energy gain factor.
** Results of European-based study of heavy ion driven fusion power system (HIDIF, GSI-98-06) incorporates telescoping beams of multiple isotopic species. This technique multiplies the 6-D phase space usable for the design of HIF drivers.
** The United States withdraws from the ITER project.
** The START experiment is succeeded by MAST. | 0 | Theoretical and Fundamental Chemistry |
Polyamine-based cryptands can be converted to polyammonium cages, which exhibit high affinities for anions. | 0 | Theoretical and Fundamental Chemistry |
For a d-dimensional system, the ideal gas pressure is:
where is the volume of the d-dimensional domain in which the gas exists. The dimensions of the pressure changes with dimensionality. | 0 | Theoretical and Fundamental Chemistry |
Thyroid-stimulating hormone (TSH, thyrotropin) is generally increased in hypothyroidism and decreased in hyperthyroidism, making it the most important test for early detection of both of these conditions. The result of this assay is suggestive of the presence and cause of thyroid disease, since a measurement of elevated TSH generally indicates hypothyroidism, while a measurement of low TSH generally indicates hyperthyroidism. However, when TSH is measured by itself, it can yield misleading results, so additional thyroid function tests must be compared with the result of this test for accurate diagnosis.
TSH is produced in the pituitary gland. The production of TSH is controlled by thyrotropin-releasing hormone (TRH), which is produced in the hypothalamus. TSH levels may be suppressed by excess free T3 (fT3) or free T4 (fT4) in the blood. | 1 | Applied and Interdisciplinary Chemistry |
A 2006 meta analysis concluded that compared to other proton pump inhibitors, esomeprazole confers a modest overall benefit in esophageal healing and symptom relief. When broken down by disease severity, the benefit of esomeprazole relative to other proton pump inhibitors was negligible in people with mild disease (number needed to treat 50), but appeared more in those with severe disease (number needed to treat 8). A second meta analysis also found increases in erosive esophageal healing (>95% healing rate) when compared to standardized doses in broadly selected patient populations. A 2017 study found esomeprazole to be among a number of effective PPIs. | 0 | Theoretical and Fundamental Chemistry |
To be able to use external cullet in production, any contaminants should be removed as much as possible. Typical contaminations are:
* Organics: Paper, plastics, caps, rings, PVB foils for flat glass
* Inorganics: Stones, ceramics, porcelains
* Metals: Ferrous and non-ferrous metals
* Heat resistant and lead glass
Manpower or machinery can be used in different stages of purification. Since they melt at higher temperatures than glass, separation of inorganics, the removal of heat resistant glass and lead glass is critical. In the modern recycling facilities, dryer systems and optical sorting machines are used. The input material should be sized and cleaned for the highest efficiency in automatic sorting. More than one free fall or conveyor belt sorter can be used, depending on the requirements of the process. Different colors can be sorted by optical sorting machines. | 0 | Theoretical and Fundamental Chemistry |
Most organic solvents are flammable or highly flammable, depending on their volatility. Exceptions are some chlorinated solvents like dichloromethane and chloroform. Mixtures of solvent vapors and air can explode. Solvent vapors are heavier than air; they will sink to the bottom and can travel large distances nearly undiluted. Solvent vapors can also be found in supposedly empty drums and cans, posing a flash fire hazard; hence empty containers of volatile solvents should be stored open and upside down.
Both diethyl ether and carbon disulfide have exceptionally low autoignition temperatures which increase greatly the fire risk associated with these solvents. The autoignition temperature of carbon disulfide is below 100 °C (212 °F), so objects such as steam pipes, light bulbs, hotplates, and recently extinguished bunsen burners are able to ignite its vapors.
In addition some solvents, such as methanol, can burn with a very hot flame which can be nearly invisible under some lighting conditions. This can delay or prevent the timely recognition of a dangerous fire, until flames spread to other materials. | 1 | Applied and Interdisciplinary Chemistry |
Organometallic nucleophiles used for conjugate additions are most often prepared in situ. The use of anhydrous equipment and inert atmosphere is necessary. Because these factors are sometimes difficult to control and the strength of freshly prepared reagents can vary substantially, titration methods are necessary to verify the purity of reagents. A number of efficient titration methodologies exist.
Usually, vicinal difunctionalizations are carried out in one pot, without the intermediacy of a neutral protected enolate. However, in specific cases it may be necessary to protect the intermediate of β-addition. Before reaching this point, however, solvent and nucleophile screens, order of addition adjustments, and counterion adjustments can be made to optimize the one-pot process for a particular combination of carbonyl compound, nucleophile, and alkylating (or acylating) agent. Solvent adjustments between the two steps are common; if one solvent is used, tetrahydrofuran is the solvent of choice. Polar aprotic solvents should be avoided for the conjugate addition step. Concerning temperature, conjugate additions are usually carried out at low temperatures (-78 °C), while alkylations are carried out at slightly higher temperatures (0 to -30 °C). Less reactive alkylating agents may require room temperature. | 0 | Theoretical and Fundamental Chemistry |
The conversion efficiency of biological photovoltaic devices is presently too low for scaled-up versions to achieve grid parity. Genetic engineering approaches are being employed to increase the current output from photosynthetic organisms for use in biological photovoltaic systems. | 0 | Theoretical and Fundamental Chemistry |
* Fellow, Royal Society of Canada, 1959
* Doctor of Letters, Trent University, 1980
* Officer, Order of Canada, 1988
* Prix Marie-Victorin, Prix du Québec, 1990 | 0 | Theoretical and Fundamental Chemistry |
An ionic liquid can be described simply as a salt in a liquid state, exhibiting triboelectric properties which allow it to be used as a lubricant. Traditional solvents are composed of oils or synthetic compounds, like fluorocarbons which, when airborne, can act as a greenhouse gas. Ionic liquids are nonvolatile and have high thermal stability and, as Lei states, "They present a “greener” alternative to standard solvents". Ionic liquids can also be used for carbon dioxide capture or as a component in bioethanol production in the gasification process. | 1 | Applied and Interdisciplinary Chemistry |
The Gibbs–Thomson equation may be written in a compact form:
where the Gibbs–Thomson coefficient assumes different values for different liquids and different interfacial geometries (spherical/cylindrical/planar).
In more detail:,
where:
* is a geometric constant dependent on the interfacial shape,
* is a constant involving parameters specific to the crystalline solid of solid–liquid system, and
* is an interfacial energy term. | 0 | Theoretical and Fundamental Chemistry |
The compressibility of water is a function of pressure and temperature. At 0 °C, at the limit of zero pressure, the compressibility is . At the zero-pressure limit, the compressibility reaches a minimum of around 45 °C before increasing again with increasing temperature. As the pressure is increased, the compressibility decreases, being at 0 °C and .
The bulk modulus of water is about 2.2 GPa. The low compressibility of non-gasses, and of water in particular, leads to their often being assumed as incompressible. The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume.
The bulk modulus of water ice ranges from 11.3 GPa at 0 K up to 8.6 GPa at 273 K. The large change in the compressibility of ice as a function of temperature is the result of its relatively large thermal expansion coefficient compared to other common solids. | 1 | Applied and Interdisciplinary Chemistry |
The MPS method is used to solve the Navier-Stokes equations in a Lagrangian framework. A fractional step method is applied which consists of splitting each time step in two steps of prediction and correction. The fluid is represented with particles, and the motion of each particle is calculated based on the interactions with the neighboring particles by means of a kernel function. The MPS method is similar to the SPH (smoothed-particle hydrodynamics) method (Gingold and Monaghan, 1977; Lucy, 1977) in that both methods provide approximations to the strong form of the partial differential equations (PDEs) on the basis of integral interpolants. However, the MPS method applies simplified differential operator models solely based on a local weighted averaging process without taking the gradient of a kernel function. In addition, the solution process of MPS method differs to that of the original SPH method as the solutions to the PDEs are obtained through a semi-implicit prediction-correction process rather than the fully explicit one in original SPH method. | 1 | Applied and Interdisciplinary Chemistry |
Urea (46-0-0) accounts for more than fifty percent of the world's nitrogenous fertilizers. It is found in granular or prill form, which allows urea to be easily stored, transported and applied in agricultural settings. It is also the cheapest form of granular nitrogen fertilizer. Since urea is not an oxidizer at standard temperature and pressure, it is safer to handle and less of a security risk than other common nitrogen fertilizers, such as ammonium nitrate. However, if urea is applied to the soil surface, a meaningful fraction of applied fertilizer nitrogen may be lost to the atmosphere as ammonia gas; this only occurs under certain conditions. | 0 | Theoretical and Fundamental Chemistry |
Lavoisier showed at the end of the 18th century that organic substances consisted of a limited number of elements: primarily carbon and hydrogen and supplemented by oxygen and nitrogen. He quickly focused on the isolation of these substances, often because they had an interesting pharmacological activity. Plants were the main source of such compounds, especially alkaloids and glycosides. It was long been known that opium, a sticky mixture of alkaloids (including codeine, morphine, noscapine, thebaine, and papaverine) from the opium poppy (Papaver somniferum), possessed a narcotic and at the same time mind-altering properties. By 1805, morphine had already been isolated by the German chemist Friedrich Sertürner and in the 1870s it was discovered that boiling morphine with acetic anhydride produced a substance with a strong pain suppressive effect: heroin. In 1815, Eugène Chevreul isolated cholesterol, a crystalline substance, from animal tissue that belongs to the class of steroids, and in 1819 strychnine, an alkaloid was isolated. | 1 | Applied and Interdisciplinary Chemistry |
:The information in this section was obtained from a US EPA published fact sheet.
Flue gas desulfurization scrubbers have been applied to combustion units firing coal and oil that range in size from 5 MW to 1,500 MW. Scottish Power are spending £400 million installing FGD at Longannet power station, which has a capacity of over 2,000 GW. Dry scrubbers and spray scrubbers have generally been applied to units smaller than 300 MW.
FGD has been fitted by RWE npower at Aberthaw Power Station in south Wales using the seawater process and works successfully on the 1,580 MW plant.
Approximately 85% of the flue gas desulfurization units installed in the US are wet scrubbers, 12% are spray dry systems, and 3% are dry injection systems.
The highest removal efficiencies (greater than 90%) are achieved by wet scrubbers and the lowest (less than 80%) by dry scrubbers. However, the newer designs for dry scrubbers are capable of achieving efficiencies in the order of 90%.
In spray drying and dry injection systems, the flue gas must first be cooled to about 10–20 °C above adiabatic saturation to avoid wet solids deposition on downstream equipment and plugging of baghouses.
The capital, operating and maintenance costs per short ton of removed (in 2001 US dollars) are:
*For wet scrubbers larger than 400 MW, the cost is $200 to $500 per ton
*For wet scrubbers smaller than 400 MW, the cost is $500 to $5,000 per ton
*For spray dry scrubbers larger than 200 MW, the cost is $150 to $300 per ton
*For spray dry scrubbers smaller than 200 MW, the cost is $500 to $4,000 per ton | 1 | Applied and Interdisciplinary Chemistry |
Circulation can be related to curl of a vector field and, more specifically, to vorticity if the field is a fluid velocity field,
By Stokes theorem, the flux of curl or vorticity vectors through a surface S' is equal to the circulation around its perimeter,
Here, the closed integration path is the boundary or perimeter of an open surface , whose infinitesimal element normal is oriented according to the right-hand rule. Thus curl and vorticity are the circulation per unit area, taken around a local infinitesimal loop.
In potential flow of a fluid with a region of vorticity, all closed curves that enclose the vorticity have the same value for circulation. | 1 | Applied and Interdisciplinary Chemistry |
Major uses of I include the treatment of thyrotoxicosis (hyperthyroidism) due to Graves disease, and sometimes hyperactive thyroid nodules (abnormally active thyroid tissue that is not malignant). The therapeutic use of radioiodine to treat hyperthyroidism from Graves disease was first reported by Saul Hertz in 1941. The dose is typically administered orally (either as a liquid or capsule), in an outpatient setting, and is usually 400–600 megabecquerels (MBq). Radioactive iodine (iodine-131) alone can potentially worsen thyrotoxicosis in the first few days after treatment. One side effect of treatment is an initial period of a few days of increased hyperthyroid symptoms. This occurs because when the radioactive iodine destroys the thyroid cells, they can release thyroid hormone into the blood stream. For this reason, sometimes patients are pre-treated with thyrostatic medications such as methimazole, and/or they are given symptomatic treatment such as propranolol. Radioactive iodine treatment is contraindicated in breast-feeding and pregnancy | 0 | Theoretical and Fundamental Chemistry |
The CD V-700 Model 7 is a kit to upgrade and modernize the Lionel Model 6B, Lionel/Anton Model 6, or Electro-Neutronics 6B with electronics derived from a recent version of the Ludlum Model 3 Geiger counter. The kit includes a new main electronics board with rotary switch, a connector for a detachable external probe, a wiring harness and switches to add new functionality and improved reliability to aging CD V-700s. The upgrade requires substantial modifications to the case. The State of Florida Department of Public Health has modified a large number of their CD V-700s to this standard.
The kit has the following ranges:
* x1 (0-0.5 mR/h or 0-300 C/m)
* x10 (0-5 mR/h or 0-3000 C/m)
* x100 (0-50 mR/h or 0-30000 C/m)
* x1000 (0-500 mR/h or 0-300000 C/m) | 0 | Theoretical and Fundamental Chemistry |
Wei-Shou Hu is a Taiwanese-American chemical engineer. He earned his B.S. in agricultural chemistry from National Taiwan University in 1974 and his Ph.D. in biochemical engineering from the Massachusetts Institute of Technology under the guidance of Daniel I.C. Wang in 1983. He has been a professor with the University of Minnesota since 1983. Dr. Hu has long impacted the field of cell culture bioprocessing since its infancy by steadfastly introducing quantitative and systematic analysis into this field. His work, which covers areas such as modeling and controlling cell metabolism, modulating glycosylation, and process data mining, has helped shape the advances of biopharmaceutical process
technology. He recently led an industrial consortium to embark on genomic research on Chinese hamster ovary cells, the main workhorse of biomanufacturing, and to promote post-genomic research in cell bioprocessing. His research focuses on the field of cell culture bioprocessing, particularly metabolic control of the physiological state of the cell. In addition to his work with Chinese hamster ovary cells, his work has enabled the use of process engineering for cell therapy, especially with liver cells. Dr.Hu has written four different biotechnology books. Also, one of his articles is cited by 63.
He is the 2005 recipient of the Marvin Johnson Award from the American Chemical Society, the distinguished service award of Society of Biological Engineers, a special award from Asia Pacific Biochemical Engineering Conference (2009), and the Amgen Award from Engineering Conferences International, as well as both the distinguished service award and the Division award from the Food, Pharmaceuticals and Bioengineering Division of the American Institute of Chemical Engineers. He has authored the books Bioseparations, Cell Culture Technology for Pharmaceutical and Cell-Based Therapies and Cell Culture Bioprocess Engineering
He is currently the Distinguished McKnight University Professor of Chemical Engineering and Material Science at the University of Minnesota | 1 | Applied and Interdisciplinary Chemistry |
ROMeoRigorous Online Modelling and Equation Based Optimization is an advanced online chemical process optimizer of SimSci, a brand of Aveva software It is mainly used by process engineers in the chemical, petroleum and natural gas industries.
It includes a chemical component library, thermodynamic property prediction methods, and unit operations such as distillation columns, heat exchangers, compressors, and reactors as found in the chemical processing industries.
It can perform steady state mass and energy balance calculations for modeling, simulating and optimizing continuous processes.
ROMeo 6.0 has been released with increased access to native Refinery Process Models based on technology from ExxonMobil.
From ROMeo 7.0, ROMeo changed from 32 bit to 64bit.
ROMeo changed the name to AVEVA Process Optimization from 2020 version. | 1 | Applied and Interdisciplinary Chemistry |
Cadmium sulfide nanoparticle synthesis by yeast involves sequestration of Cd by glutathione-related peptides followed by reduction within the cell. Ahmad et al. (2002) reported that cadmium sulfide nanoparticle synthesis by Fusarium oxysporum was based on a sulfate reductase (enzyme) process. | 0 | Theoretical and Fundamental Chemistry |
The principle of detailed balance was explicitly introduced for collisions by Ludwig Boltzmann. In 1872, he proved his H-theorem using this principle. The arguments in favor of this property are founded upon microscopic reversibility.
Five years before Boltzmann, James Clerk Maxwell used the principle of detailed balance for gas kinetics with the reference to the principle of sufficient reason. He compared the idea of detailed balance with other types of balancing (like cyclic balance) and found that "Now it is impossible to assign a reason" why detailed balance should be rejected (pg. 64).
Albert Einstein in 1916 used the principle of detailed balance in a background for his quantum theory of emission and absorption of radiation.
In 1901, Rudolf Wegscheider introduced the principle of detailed balance for chemical kinetics. In particular, he demonstrated that the irreversible cycles are impossible and found explicitly the relations between kinetic constants that follow from the principle of detailed balance. In 1931, Lars Onsager used these relations in his works, for which he was awarded the 1968 Nobel Prize in Chemistry.
The principle of detailed balance has been used in Markov chain Monte Carlo methods since their invention in 1953. In particular, in the Metropolis–Hastings algorithm and in its important particular case, Gibbs sampling, it is used as a simple and reliable condition to provide the desirable equilibrium state.
Now, the principle of detailed balance is a standard part of the university courses in statistical mechanics, physical chemistry, chemical and physical kinetics. | 0 | Theoretical and Fundamental Chemistry |
1,1,1-Trichloroethane was one of the volatile organochlorides that have been tried as alternatives to chloroform in anaesthesia.
In the 1880s, it was found to be a safe and strong substitute for chloroform but its production was expensive and difficult.
In 1880, 1,1,1-Trichloroethane was suggested as an anaesthetic. It was first referred to as "methyl-chloroform" in the same year. At the time, the narcotic effects of chloral hydrate were owed to a hypothetical metabolic pathway to chloroform in "alkaline blood". Trichloroethane was studied for its structural similarity to chloral and potential anaesthetic effects. However, trichloroethane did not exhibit any conversion to chloroform in laboratory experiments. The 1,1,2-trichloroethane isomer, which lacked a trichloromethyl group, exhibited anaesthetic effects even stronger than the 1,1,1 isomer. | 1 | Applied and Interdisciplinary Chemistry |
Ernst was a foreign fellow of the Estonian Academy of Sciences (elected 2002), the US National Academy of Sciences, the Royal Academy of Sciences, London, the German National Academy of Sciences Leopoldina, the Russian Academy of Sciences, the Korean Academy of Science and Technology and Bangladesh Academy of Sciences. He was elected a Foreign Member of the Royal Society (ForMemRS) in 1993. He was awarded the John Gamble Kirkwood Medal in 1989.
In 1991, Ernst was on an aeroplane flying over the Atlantic when he discovered he had been awarded The Nobel Prize in Chemistry. He was invited into the cockpit, where he was given a radio to talk to the Nobel committee. Here they told him he was being honoured "for his contributions to the development of the methodology of high resolution nuclear magnetic resonance (NMR) spectroscopy".
Ernst was member of the World Knowledge Dialogue Scientific Board. He was awarded the Marcel Benoist Prize in 1986, the Wolf Prize for Chemistry in 1991, and Louisa Gross Horwitz Prize of Columbia University in 1991. He was also awarded the Tadeus Reichstein Medal in 2000 and the Order of the Star of Romania in 2004. He also held Honorary Doctorates from the Technical University of Munich, EPF Lausanne, University of Zurich, University Antwerpen, Babes-Bolyai University, and University Montpellier.
The 2009 Bel Air Film Festival featured the world premiere of a documentary film on Ernst Science Plus Dharma Equals Social Responsibility. Produced by Carlo Burton, the film takes place in Ernst's hometown in Switzerland. In 2022, another movie about Richard R. Ernst premiered at the Cameo cinema in Winterthur, produced by Lukas Schwarzenbacher and Susanne Schmid. The documentary contains a retrospective of Richard R. Ernsts life, which is filmed only a few months before his death. | 0 | Theoretical and Fundamental Chemistry |
The attack takes the form of a reaction between ammonia and copper to form the cuprammonium ion, formula [Cu(NH)], a chemical complex which is water-soluble, and hence washed from the growing cracks. The problem of cracking can therefore also occur in copper and any other copper alloy, such as bronze. The tendency of copper to react with ammonia was exploited in making rayon, and the deep blue colour of the aqueous solution of copper(II) oxide in ammonia is known as Schweizer's reagent. | 1 | Applied and Interdisciplinary Chemistry |
Blast waves are generated in research environments using explosive or compressed-gas driven shock tubes in an effort to replicate the environment of a military conflict to better understand the physics of blasts and injuries that may result, and to develop better protection against blast exposure. Blast waves are directed against structures (such as vehicles), materials, and biological specimens or surrogates. High-speed pressure sensors and/or high speed cameras are often used to quantify the response to blast exposure. Anthropomorphic test devices (ATDs or test dummies) initially developed for the automotive industry are being used, sometimes with added instrumentation, to estimate the human response to blast events. For examples, personnel in vehicles and personnel on demining teams have been simulated using these ATDs.
Combined with experiments, complex mathematical models have been made of the interaction of blast waves with inanimate and biological structures. Validated models are useful for "what if" experiments – predictions of outcomes for different scenarios. Depending on the system being modeled, it can be difficult to have accurate input parameters (for example, the material properties of a rate-sensitive material at blast rates of loading). Lack of experimental validation severely limits the usefulness of any numerical model. | 1 | Applied and Interdisciplinary Chemistry |
Multi-wavelength anomalous diffraction (sometimes Multi-wavelength anomalous dispersion; abbreviated MAD) is a technique used in X-ray crystallography that facilitates the determination of the three-dimensional structure of biological macromolecules (e.g. DNA, drug receptors) via solution of the phase problem.
MAD was developed by Wayne Hendrickson while working as a postdoctoral researcher under Jerome Karle at the United States Naval Research Laboratory. The mathematics upon which MAD (and progenitor Single-wavelength anomalous diffraction) was based were developed by Jerome Karle, work for which he was awarded the 1985 Nobel Prize in Chemistry (along with Herbert Hauptman).
Compared to the predecessor SAD, MAD has greatly elevated phasing power from using multiple wavelengths close to the edge. However, because it requires a synchrotron beamline, a longer exposure (risking radiation damage), and only allows a limited choice of heavy atoms (those with edges reachable by a synchrotron), MAD has declined in popularity relative to SAD. | 0 | Theoretical and Fundamental Chemistry |
* Methylphosphine and dimethylphosphine (garlic-metallic, two of the most potent odorants known)
* Phosphine (zinc phosphide poisoned bait)
* Diacetyl (butter flavor)
* Acetoin (butter flavor)
* Nerolin (orange flowers)
* Tetrahydrothiophene (added to natural gas)
* 2,4,6-Trichloroanisole (cork taint)
* Substituted pyrazines | 0 | Theoretical and Fundamental Chemistry |
Some caries excavation methods lead to leaving caries-affected dentin behind to serve as the bonding substrate, mostly in indirect pulp capping.
It is reported that the immediate bond strengths to caries-affected dentin are 20-50% lower than to sound dentin, and even lower with caries-infected dentin. How does caries progression correlates with this? First, it reduces mineral content, increases porosity and changes the dentinal collagen structure and its distribution too. These changes can cause a significant reduction in the mechanical properties in dentin e.g. hardness, stiffness, tensile strength, modulus of elasticity, and shrinkage during drying, which makes dentin in and under hybrid layer more prone to cohesive failures under occlusal forces.
Lower mineral content of the caries-affected dentin will allow phosphoric acid or acidic monomers to demineralize matrix more deeply than in normal dentin, which results in even more residual water in exposed collagen matrix. | 0 | Theoretical and Fundamental Chemistry |
Aminoallyl nucleosides can be synthesized via Heck coupling as shown in the image below.
In the image above, on the left is a modified nucleoside with an iodine (the iodine is added via electrophilic halogenation) in the fifth carbon in the pyrimidine ring. Its formation can be associated with a reaction with an allylamine and various reagents via heck coupling are able to remove the halogen group from the base and add the allylamine to become the aminoallyl nucleoside shown on the right. The product on the right is then used to in molecular biology in RNA synthesis.
Other reactions include using a single pot synthesis with other halogens. | 1 | Applied and Interdisciplinary Chemistry |
For over 30 years, several research groups actively pursued the total synthesis of dodecahedrane. A review article published in 1978 described the different strategies that existed up to then. The first attempt was initiated in 1964 by R.B. Woodward with the synthesis of the compound triquinacene which was thought to be able to simply dimerize to dodecahedrane. Other groups were also in the race, for example that of Philip Eaton and Paul von Ragué Schleyer.
Leo Paquette's group at Ohio State University was the first to succeed, by a complex 29-step route that mostly builds the dodecahedral skeleton one ring at a time, and finally closes the last hole.
In 1987, more versatile alternative synthesis route was found by the Horst Prinzbach's group. Their approach was based on the isomerization pagodane, obtained from isodrin (isomer of aldrin) as starting material i.a. through [6+6]photocycloaddition. Schleyer had followed a similar approach in his synthesis of adamantane.
Following that idea, joint efforts of the Prinzbach team and the Schleyer group succeeded but obtained only 8% yield for the conversion at best. In the following decade the group greatly optimized that route, so that dodecahedrane could be obtained in multi-gram quantities. The new route also made it easier to obtain derivatives with selected substitutions and unsaturated carbon-carbon bonds. Two significant developments were the discovery of σ-bishomoaromaticity and the formation of C fullerene from highly brominated dodecahedrane species. | 0 | Theoretical and Fundamental Chemistry |
Due to the existence of the 2 possible final states, each β decay is a mixture of the two decay types. This essentially means that some of the time the remaining nucleus is in an excited state and other times the decay is directly to the ground state.
Unlike Fermi transitions, Gamow–Teller transitions occur via an operator that operates only if the initial nuclear wavefunction and final nuclear wavefunction are defined.
The Isospin and Angular Momentum selection rules can be deduced from the operator and the identification of allowed and forbidden decays can be found.
;Examples:
or
The above reaction involves "mirror nuclei", nuclei in which the numbers of protons and neutrons are interchanged.
One can measure the angular distributions of β particles with respect to the axis of nuclear spin polarization to determine what the mixture is between the two decay types (Fermi and Gamow–Teller).
The mixture can be expressed as a ratio of matrix elements (Fermi's golden rule relates transitions to matrix elements)
The interesting observation is that y for mirror nuclei is on the order of the value of y for neutron decay while non-mirror nuclear decays tend to be an order of magnitude less. | 0 | Theoretical and Fundamental Chemistry |
Raman spectroelectrochemistry (Raman-SEC) is a technique that studies the inelastic scattering or Raman scattering of monochromatic light related to chemical compounds involved in an electrode process. This technique provides information about vibrational energy transitions of molecules, using a monochromatic light source, usually from a laser that belongs to the UV, Vis or NIR region. Raman spectroelectrochemistry provides specific information about structural changes, composition and orientation of the molecules on the electrode surface involved in an electrochemical reaction, being the Raman spectra registered a real fingerprint of the compounds.
When a monochromatic light beam samples the electrode/solution interface, most of the photons are scattered elastically, with the same energy than the incident light. However, a small fraction is scattered inelastically, being the energy of the laser photons shifted up or down. When the scattering is elastic, the phenomenon is denoted as Rayleigh scattering, while when it is inelastic it is called Raman scattering. Raman spectroscopy combined with electrochemical techniques, makes Raman spectroelectrochemistry a powerful technique in the identification, characterization and quantification of molecules.
The main advantage of Raman spectroelectrochemistry is that it is not limited to the selected solvent, and aqueous and organic solutions can be used. However, the main disadvantage is the intrinsic low Raman signal intensity. Different methods as well as new substrates were developed to improve the sensitivity and selectivity of this multirresponse technique.
For researchers, a few experimental considerations related to Raman spectroelectrochemistry include electrode preparation, cell design, laser parameters, electrochemical sequence and data process. | 0 | Theoretical and Fundamental Chemistry |
A bridged nucleic acid (BNA) is a modified RNA nucleotide. They are sometimes also referred to as constrained or inaccessible RNA molecules. BNA monomers can contain a five-membered, six-membered or even a seven-membered bridged structure with a "fixed" C-endo sugar puckering. The bridge is synthetically incorporated at the 2, 4-position of the ribose to afford a 2, 4'-BNA monomer. The monomers can be incorporated into oligonucleotide polymeric structures using standard phosphoramidite chemistry. BNAs are structurally rigid oligo-nucleotides with increased binding affinities and stability. | 1 | Applied and Interdisciplinary Chemistry |
One particularly notable use of glass-ceramics is in the processing of ceramic matrix composites. For many ceramic matrix composites typical sintering temperatures and times cannot be used, as the degradation and corrosion of the constituent fibres becomes more of an issue as temperature and sintering time increase.
One example of this is SiC fibres, which can start to degrade via pyrolysis at temperatures above 1470K. One solution to this is to use the glassy form of the ceramic as the sintering feedstock rather than the ceramic, as unlike the ceramic the glass pellets have a softening point and will generally flow at much lower pressures and temperatures. This allows the use of less extreme processing parameters, making the production of many new technologically important fibre-matrix combinations by sintering possible. | 0 | Theoretical and Fundamental Chemistry |
Before 1918, many professionals and scientists using the metric system of units defined the standard reference conditions of temperature and pressure for expressing gas volumes as being and . During those same years, the most commonly used standard reference conditions for people using the imperial or U.S. customary systems was and 14.696 psi (1 atm) because it was almost universally used by the oil and gas industries worldwide. The above definitions are no longer the most commonly used in either system of units. | 0 | Theoretical and Fundamental Chemistry |
A photochromic lens is an optical lens that darkens on exposure to light of sufficiently high frequency, most commonly ultraviolet (UV) radiation. In the absence of activating light, the lenses return to their clear state. Photochromic lenses may be made of polycarbonate, or another plastic. Glass lenses use visible light to darken. They are principally used in glasses that are dark in bright sunlight, but clear, or more rarely, lightly tinted in low ambient light conditions. They darken significantly within about a minute of exposure to bright light and take somewhat longer to clear. A range of clear and dark transmittances is available.
In one sort of technology, molecules of silver chloride or another silver halide are embedded in photochromic lenses. They are transparent to visible light without significant ultraviolet component, which is normal for artificial lighting. In another sort of technology, organic photochromic molecules, when exposed to ultraviolet (UV) rays as in direct sunlight, undergo a chemical process that causes them to change shape and absorb a significant percentage of the visible light, i.e., they darken. These processes are reversible; once the lens is removed from strong sources of UV rays the photochromic compounds return to their transparent state. | 0 | Theoretical and Fundamental Chemistry |
The soil management practices required to maintain soil tilth are a function of the type of soil. Sandy and gravelly soils are naturally deficient in small pores and are therefore drought prone, whereas loams and clays can retain and thus supply crops with more water. | 0 | Theoretical and Fundamental Chemistry |
Adverse events include hypoglycemia, pruritis (itching), nasopharyngitis, headache, and upper respiratory tract infection. It may also cause joint pain that can be severe and disabling. Like other DDP-4 inhibitors, alogliptin is weight-neutral.
A 2014 letter to the editor claimed alogliptin is not associated with increased risk of cardiovascular events. In April 2016, the U.S. Food and Drug Administration (FDA) added a warning about increased risk of heart failure. | 0 | Theoretical and Fundamental Chemistry |
Fittings are also used to split or join a number of pipes together, and for other purposes. A broad variety of standardized pipe fittings are available; they are generally broken down into either a tee, an elbow, a branch, a reducer/enlarger, or a wye. Valves control fluid flow and regulate pressure. The piping and plumbing fittings and valves articles discuss them further. | 1 | Applied and Interdisciplinary Chemistry |
* Chemical Engineering Research and Design
* Process Safety and Environmental Protection
* Food and Bioproducts Processing
* Education for Chemical Engineers
* Molecular Systems Design and Engineering (joint with the Royal Society of Chemistry)
* Sustainable Production and Consumption
* South African Journal of Chemical Engineering | 1 | Applied and Interdisciplinary Chemistry |
The term "pyrometer" was coined in the 1730s by Pieter van Musschenbroek, better known as the inventor of the Leyden jar. His device, of which no surviving specimens are known, may be now called a dilatometer because it measured the dilation of a metal rod.
The earliest example of a pyrometer thought to be in existence is the [https://collection.sciencemuseumgroup.org.uk/objects/co1668/hindleys-pyrometer-pyrometers-dilatometers Hindley Pyrometer] held by the London Science Museum, dating from 1752, produced for the Royal collection. The pyrometer was a well known enough instrument that it was described in some detail by the mathematician Euler in 1760.
Around 1782 potter Josiah Wedgwood invented a different type of pyrometer (or rather a pyrometric device) to measure the temperature in his kilns, which first compared the color of clay fired at known temperatures, but was eventually upgraded to measuring the shrinkage of pieces of clay, which depended on kiln temperature (see Wedgwood scale for details). Later examples used the expansion of a metal bar.
In 1860s–1870s brothers William and Werner Siemens developed a platinum resistance thermometer, initially to measure temperature in undersea cables, but then adapted for measuring temperatures in metallurgy up to 1000 °C, hence deserving a name of a pyrometer.
The first disappearing-filament pyrometer was built by L. Holborn and F. Kurlbaum in 1901. This device had a thin electrical filament between an observer's eye and an incandescent object. The current through the filament was adjusted until it was of the same colour (and hence temperature) as the object, and no longer visible; it was calibrated to allow temperature to be inferred from the current.
The temperature returned by the vanishing-filament pyrometer and others of its kind, called brightness pyrometers, is dependent on the emissivity of the object. With greater use of brightness pyrometers, it became obvious that problems existed with relying on knowledge of the value of emissivity. Emissivity was found to change, often drastically, with surface roughness, bulk and surface composition, and even the temperature itself.
To get around these difficulties, the ratio or two-color pyrometer was developed. They rely on the fact that Plancks law, which relates temperature to the intensity of radiation emitted at individual wavelengths, can be solved for temperature if Plancks statement of the intensities at two different wavelengths is divided. This solution assumes that the emissivity is the same at both wavelengths and cancels out in the division. This is known as the gray-body assumption. Ratio pyrometers are essentially two brightness pyrometers in a single instrument. The operational principles of the ratio pyrometers were developed in the 1920s and 1930s, and they were commercially available in 1939.
As the ratio pyrometer came into popular use, it was determined that many materials, of which metals are an example, do not have the same emissivity at two wavelengths. For these materials, the emissivity does not cancel out, and the temperature measurement is in error. The amount of error depends on the emissivities and the wavelengths where the measurements are taken. Two-color ratio pyrometers cannot measure whether a material's emissivity is wavelength-dependent.
To more accurately measure the temperature of real objects with unknown or changing emissivities, multiwavelength pyrometers were envisioned at the US National Institute of Standards and Technology and described in 1992. Multiwavelength pyrometers use three or more wavelengths and mathematical manipulation of the results to attempt to achieve accurate temperature measurement even when the emissivity is unknown, changing or differs according to wavelength of measurement. | 1 | Applied and Interdisciplinary Chemistry |
The term ‘acid sulfate soils’ (ASS) was coined by the Working Party on Nomenclature and Methods for the first International Symposium on Acid Sulfate Soils (1972, Wageningen) to mean soils that contain, or have the potential to produce, sulfuric acid in quantities that cause significant and long-lasting changes in key soil properties. This term was gradually adopted by the international scientific community for the sake of international consistency and cooperation. Prior to this, different regions used colloquial terms such as:
* argilla vitriolacea (Latin, ‘clay with sulfuric acid’ – coined by Carl Linnaeus);
* Kattekleigronden or Katte Klei (Dutch, ‘cat clay’);
* Gifterde (German, ‘cursed / poisoned earth’); and
* Maibolt (an Austro-Germanic spirit or creature that, when angered, would curse the soil to spoil crops).
The term ‘acid sulfate soil’ is useful for general discussion, but fails to capture nuances required for technical classification of soils. Additional terms such as ‘potential acid sulfate soil’ (PASS), ‘active acid sulfate soil’ (AASS) and ‘post-active acid sulfate soil’ (PAASS) helped researchers distinguish between the following:
* PASS: non-acidic soils that did not contain substantial quantities of sulfuric acid, but contained the necessary materials to produce it under certain conditions;
* AASS: soils that were acidic due to the presence of sulfuric acid; and
* PAASS: soils that were once active acid sulfate soils, but have since weathered or ‘ripened’ to the point they were similar to ‘normal’ sub-aerial soil in terms of their chemical and physical properties (e.g., pH and drainage).
As a single soil profile may contain PASS, AASS, and PAASS at different depths, the term ‘material’ was added as a modifier (i.e., PASS-material, AASS-material, and PAASS-material) to allow for more nuanced descriptions of complex soils. However, these terms are still somewhat awkward and unsuitable for technical classification. Additionally, acid sulfate soils and the variations thereof imply that acid sulfate soils are an altogether different type or class of soil, rather than a feature soils may exhibit under certain conditions. Consequently, there has been a gradual movement away from these terms in favour of more standardised, operationally-defined definitions. | 0 | Theoretical and Fundamental Chemistry |
Diffraction topography (short: "topography") is a imaging technique based on Bragg diffraction.
Diffraction topographic images ("topographies") record the intensity profile of a beam of X-rays (or, sometimes, neutrons) diffracted by a crystal.
A topography thus represents a two-dimensional spatial intensity mapping (image) of the X-rays diffracted in a specific direction, so regions which diffract substantially will appear brighter than those which do not. This is equivalent to the spatial fine structure of a Laue reflection.
Topographs often reveal the irregularities in a non-ideal crystal lattice.
X-ray diffraction topography is one variant of X-ray imaging, making use of diffraction contrast rather than absorption contrast which is usually used in radiography and computed tomography (CT). Topography is exploited to a lesser extends with neutrons, and is the same concept as dark field imaging in an electron microscope.
Topography is used for monitoring crystal quality and visualizing defects in many different crystalline materials.
It has proved helpful e.g. when developing new crystal growth methods, for monitoring growth and the crystal quality achieved, and for iteratively optimizing growth conditions.
In many cases, topography can be applied without preparing or otherwise damaging the sample; it is therefore one variant of non-destructive testing. | 0 | Theoretical and Fundamental Chemistry |
Cryosurgery (with cryo from the Ancient Greek ) is the use of extreme cold in surgery to destroy abnormal or diseased tissue; thus, it is the surgical application of cryoablation.
Cryosurgery has been historically used to treat a number of diseases and disorders, especially a variety of benign and malignant skin conditions. | 1 | Applied and Interdisciplinary Chemistry |
Sodium methylsulfinylmethylide (also called NaDMSO or dimsyl sodium) is the sodium salt of the conjugate base of dimethyl sulfoxide. This unusual salt has some uses in organic chemistry as a base and nucleophile.
Since the first publication in 1965 by Corey et al., a number of additional uses for this reagent have been identified. | 0 | Theoretical and Fundamental Chemistry |
A variant of the 3-hydroxypropionate cycle was found to operate in the aerobic extreme thermoacidophile archaeon Metallosphaera sedula. This pathway is called the 3-hydroxypropionate/4-hydroxybutyrate cycle.
Yet another variant of the 3-hydroxypropionate cycle is the dicarboxylate/4-hydroxybutyrate cycle. It was discovered in anaerobic archaea.
It was proposed in 2008 for the hyperthermophile archeon Ignicoccus hospitalis. | 0 | Theoretical and Fundamental Chemistry |
Silicon wafers can be etched in hydrofluoric acid (HF) to remove the native oxide and form a hydrogen-terminated silicon surface. The hydrogen-terminated surfaces undergo hydrosilation with unsaturated compounds (such as terminal alkenes and alkynes), to form a stable monolayer on the surface. For example:
:Si-H + HC=CH(CH)CH → Si-CHCHH-(CH)CH
The hydrosilylation reaction can be initiated with UV light at room temperature or with heat (typical reaction temperature 120-200 °C), under moisture- and oxygen-free conditions. The resulting monolayer, which is stable and inert, inhibits oxidation of the base silicon layer, relevant to various device applications. | 0 | Theoretical and Fundamental Chemistry |
Ancyronyx, commonly known as spider water beetles or spider riffle beetles, is a genus of aquatic riffle beetles from North America, South Asia, China, and Southeast Asia. They are small beetles with extremely long legs ending in strong claws. Both the adults and the larvae are found underwater in the shallow riffles of streams and rivers, clinging to rocks or submerged wood. They feed on algae and decaying wood tissue. The genus contains twenty-one species, eleven of which are endemic to the Philippines. | 1 | Applied and Interdisciplinary Chemistry |
Alcohols react with phosgene to yield carbonate esters according to the following reaction:
:2 ROH + COCl → ROC(O)OR + 2 HCl
Phenols react similarly. Polycarbonate derived from bisphenol A is produced in this manner. This process is high yielding. However, toxic phosgene is used, and stoichiometric quantities of base (e.g. pyridine) are required to neutralize the hydrogen chloride that is cogenerated. Chloroformate esters are intermediates in this process. Rather than reacting with additional alcohol, they may disproportionate to give the desired carbonate diesters and one equivalent of phosgene:
: PhOH + COCl → PhOC(O)Cl + HCl
: 2 PhOC(O)Cl → PhOC(O)OPh + COCl
Overall reaction is:
: 2 PhOH + COCl → PhOC(O)OPh + 2 HCl | 0 | Theoretical and Fundamental Chemistry |
Capsiate (4-hydroxy-3-methoxybenzyl (E)-8-methyl-6-nonenoate) (CAS No. 205687-01-0)
Dihydrocapsiate (4-hydroxy-3-methoxybenzyl 8-methylnonanoate) (CAS No. 205687-03-2)
Nordihydrocapsiate (4-hydroxy-3-methoxybenzyl 7-methyloctanoate) (CAS No. 220012-53-3) | 1 | Applied and Interdisciplinary Chemistry |
In general, catalytic cycles can be divided into 3 stages:
# Coordination of the starting material(s)
# Catalytic transformation of the starting material(s) to the product(s)
# Displacement of the product(s) to regain the catalyst (or pre-catalyst)
<br>
Traditionally the focus of catalytic research has been on the reaction taking place in the second stage, however there will be energy changes associated with the beginning and end steps due to their effect on the coordination sphere and geometry of the complex, as well as its oxidation number in cases of oxidative addition and reductive elimination. When these energy changes are large they can dictate the turn-over rate of the catalyst and hence its effectiveness.
Hemilabile ligands reduce the activation energy of these changes by readily undergoing partial and reversible displacement from the metal centre. Hence a co-ordinately saturated hemilabile complex will readily reorganise to allow the coordination of reagents but will also promote the ejection of products due to re-coordination of the labile section of the ligand. The low energy barrier between the fully and hemi coordinated states results in frequent inverconvertion between the two, which promotes a fast catalytic turn-over rate.
Hemilabile ligands dissociate in one of three main ways; an "on/off" mechanism where they are constantly dissociating and re-associating, a displacement mechanism where they dissociate easily when exposed to a competing substrate, or redox switching where the oxidation state of the ligand is used to tune its affinity for the metal center. | 0 | Theoretical and Fundamental Chemistry |
The manifold topographic techniques can be categorized according to several criteria.
One of them is the distinction between restricted-beam techniques on the one hand (such as section topography or pinhole topography) and extended-beam techniques on the other hand, which use the full width and intensity of the incoming beam. Another, independent distinction is between integrated-wave topography, making use of the full spectrum of incoming X-ray wavelengths and divergences, and plane-wave (monochromatic) topopgraphy, more selective in both wavelengths and divergence. Integrated-wave topography can be realized as either single-crystal or double-crystal topography. Further distinctions include the one between topography in reflection geometry (Bragg-case) and in transmission geometry (Laue case).
For a full discussion and a graphical hierarchy of topographic techniques, see
[https://web.archive.org/web/20041107130433/http://www.esrf.fr/exp_facilities/ID19/homepage/DiffTopo/X-raytopography.htm]. | 0 | Theoretical and Fundamental Chemistry |
USAID has supported efforts to introduce scheduled desludging services in some countries in Southeast Asia. The first of these was in Dumaguete in the Philippines. The program was run jointly by the city government and the Dumaguete City Water District, with the former operating the treatment plant and the Water District conducting the desludging. The cost of the scheme was covered by adding a tariff of 2 pesos (about 5 US cents) to the water bill for each cubic meter of water consumed (about one US dollar per family per month). This approach was possible because around 95% of residents had a connection to the Water District reticulation system. Trucks were to move from neighborhood to neighborhood on a scheduled cycle, emptying pits on a regular 3–4 year cycle. This approach requires a database of all pits and septic tanks requiring desludging. However, Dumaguete has by 2018 reverted to an on-call system, the cost of which is still covered by the surcharge on the water tariff. It seems that users prefer this small regular payment to having to make large payments when tanks require desludging. | 1 | Applied and Interdisciplinary Chemistry |
Newlands was born in London in England, at West Square in Southwark, the son of a Scottish Presbyterian minister and his Italian wife.
Newlands was home-schooled by his father, and later studied at the Royal College of Chemistry, now part of Imperial College London. He was interested in social reform and during 1860 served as a volunteer with Giuseppe Garibaldi in his military campaign to unify Italy. Returning to London, Newlands established himself as an analytical chemist in 1864. In 1868 he became chief chemist of James Duncan's London sugar refinery, where he introduced a number of improvements in processing. Later he quit the refinery and again became an analyst with his brother, Benjamin.
Newlands was the first person to devise a periodic table of chemical elements arranged in order of their relative atomic masses published in Chemical News in February 1863. Continuing Johann Wolfgang Döbereiners work with triads and Jean-Baptiste Dumas families of similar elements, he published in 1865 his "Law of Octaves", which stated that "any given element will exhibit analogous behaviour to the eighth element following it in the table." Newlands arranged all of the known elements, starting with hydrogen and ending with thorium (atomic weight 232), into eight groups of seven, which he likened to octaves of music. In Newlands' table, the elements were ordered by the atomic weights that were known at the time and were numbered sequentially to show their order. Groups were shown going across the table, with periods going down – the opposite from the modern form of the periodic table.
The incompleteness of the table alluded to the possible existence of additional, undiscovered elements. However, the Law of Octaves was ridiculed by some of Newlands' contemporaries, and the Society of Chemists did not accept his work for publication.
After Dmitri Mendeleev and Lothar Meyer received the Davy Medal from the Royal Society for their later discovery of the periodic table in 1882, Newlands fought for recognition of his earlier work and eventually received the Davy Medal in 1887.
John Newlands died due to complications of surgery at his home in Lower Clapton, Middlesex and was buried at West Norwood Cemetery. His businesses was continued after his death by his younger brother, Benjamin. | 0 | Theoretical and Fundamental Chemistry |
Elaidinization is any chemical reaction which convert a cis- olefin to a trans- olefin in unsaturated fatty acids. This is often performed on fats and oils to increase both the melting point and the shelf life without reducing the degree of unsaturation. The term originates from elaidic acid, the trans-isomer of oleic acid. | 0 | Theoretical and Fundamental Chemistry |
Proton emission (also known as proton radioactivity) is a rare type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case the process is known as beta-delayed proton emission, or can occur from the ground state (or a low-lying isomer) of very proton-rich nuclei, in which case the process is very similar to alpha decay. For a proton to escape a nucleus, the proton separation energy must be negative (Sp < 0)—the proton is therefore unbound, and tunnels out of the nucleus in a finite time. The rate of proton emission is governed by the nuclear, Coulomb, and centrifugal potentials of the nucleus, where centrifugal potential affects a large part of the rate of proton emission. Half-life of proton emission is affected by the proton energy and its orbital angular momentum. Proton emission is not seen in naturally occurring isotopes; proton emitters can be produced via nuclear reactions, usually using linear particle accelerators.
Although prompt (i.e. not beta-delayed) proton emission was observed from an isomer in cobalt-53 as early as 1969, no other proton-emitting states were found until 1981, when the proton radioactive ground states of lutetium-151 and thulium-147 were observed at experiments at the GSI in West Germany. Research in the field flourished after this breakthrough, and to date more than 25 isotopes have been found to exhibit proton emission. The study of proton emission has aided the understanding of nuclear deformation, masses, and structure, and it is a pure example of quantum tunneling.
In 2002, the simultaneous emission of two protons was observed from the nucleus iron-45 in experiments at GSI and GANIL (Grand Accélérateur National d'Ions Lourds at Caen). In 2005 it was experimentally determined (at the same facility) that zinc-54 can also undergo double proton decay. | 0 | Theoretical and Fundamental Chemistry |
People who are exposed to PFASs through their jobs typically have higher levels of PFASs in their blood than the general population. While the general population is exposed to PFASs through ingested food and water, occupational exposure includes accidental ingestion, inhalation exposure, and skin contact in settings where PFAS become volatile. The severity of PFAS-associated health effects can vary based on the length of exposure, level of exposure, and health status. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, acetophenide is a functional group which is composed of the cyclic ketal of a diol with acetophenone. In pharmaceutical chemistry, it is present in algestone acetophenide (dihydroxyprogesterone acetophenide) and amcinafide (triamcinolone acetophenide). | 0 | Theoretical and Fundamental Chemistry |
The general principle of a biosurface is a solid surface with an additional layer of biological macromolecules. Because this molecular layer will reversibly respond to changes in the environment of the surface, it is also called “stimuli-responsive monolayer”. The external stimuli can be for example changes in temperature, changes in magnetic fields, mechanical forces or changes in electric fields.
Different strategies can be used to attach a monolayer of biomolecules to a surface, for example atomic layer deposition or layer-by-layer deposition. Another option is the fabrication of self-assembled monolayers (SAM). The surface used most often with this strategy is a gold electrode. SAM form by spontaneous organization of the molecules, for example alkanethiolates, on the substrate. SAM can be used as surface layers for nanoparticles, e.g. in MRI contrast agents, they can protect metal films from corrosion, and have many other applications in electrochemistry and nanoscience. For their application as a biosensor, one of the most often used molecules self-assembling on gold electrodes is DNA. Due to its molecular structure, double stranded DNA molecules are negatively charged and rigid. By applying an alternating potential to the biosurface, the attached DNA strands can be moved systematically because they will switch between an upright position and a flat position. This enables the usage of the biosurface as a biosensor. | 1 | Applied and Interdisciplinary Chemistry |
Spectrum analyzers are widely used to measure the frequency response, noise and distortion characteristics of all kinds of radio-frequency (RF) circuitry, by comparing the input and output spectra. For example, in RF mixers, spectrum analyzer is used to find the levels of third order inter-modulation products and conversion loss. In RF oscillators, spectrum analyzer is used to find the levels of different harmonics.
In telecommunications, spectrum analyzers are used to determine occupied bandwidth and track interference sources. For example, cell planners use this equipment to determine interference sources in the GSM frequency bands and UMTS frequency bands.
In EMC testing, a spectrum analyzer is used for basic precompliance testing; however, it can not be used for full testing and certification. Instead, an EMI receiver is used.
A spectrum analyzer is used to determine whether a wireless transmitter is working according to defined standards for purity of emissions. Output signals at frequencies other than the intended communications frequency appear as vertical lines (pips) on the display. A spectrum analyzer is also used to determine, by direct observation, the bandwidth of a digital or analog signal.
A spectrum analyzer interface is a device that connects to a wireless receiver or a personal computer to allow visual detection and analysis of electromagnetic signals over a defined band of frequencies. This is called panoramic reception and it is used to determine the frequencies of sources of interference to wireless networking equipment, such as Wi-Fi and wireless routers.
Spectrum analyzers can also be used to assess RF shielding. RF shielding is of particular importance for the siting of a magnetic resonance imaging machine since stray RF fields would result in artifacts in an MR image. | 0 | Theoretical and Fundamental Chemistry |
Bent's rule provides an additional level of accuracy to valence bond theory. Valence bond theory proposes that covalent bonds consist of two electrons lying in overlapping, usually hybridised, atomic orbitals from two bonding atoms. The assumption that a covalent bond is a linear combination of atomic orbitals of just the two bonding atoms is an approximation (see molecular orbital theory), but valence bond theory is accurate enough that it has had and continues to have a major impact on how bonding is understood.
In valence bond theory, two atoms each contribute an atomic orbital and the electrons in the orbital overlap form a covalent bond. Atoms do not usually contribute a pure hydrogen-like orbital to bonds. If atoms could only contribute hydrogen-like orbitals, then the experimentally confirmed tetrahedral structure of methane would not be possible as the 2s and 2p orbitals of carbon do not have that geometry. That and other contradictions led to the proposing of orbital hybridisation. In that framework, atomic orbitals are allowed to mix to produce an equivalent number of orbitals of differing shapes and energies. In the aforementioned case of methane, the 2s and three 2p orbitals of carbon are hybridized to yield four equivalent sp orbitals, which resolves the structure discrepancy. Orbital hybridisation allowed valence bond theory to successfully explain the geometry and properties of a vast number of molecules.
In traditional hybridisation theory, the hybrid orbitals are all equivalent. Namely the atomic s and p orbital(s) are combined to give four orbitals, three orbitals, or two orbitals. These combinations are chosen to satisfy two conditions. First, the total amount of s and p orbital contributions must be equivalent before and after hybridisation. Second, the hybrid orbitals must be orthogonal to each other. If two hybrid orbitals were not orthogonal, by definition they would have nonzero orbital overlap. Electrons in those orbitals would interact and if one of those orbitals were involved in a covalent bond, the other orbital would also have a nonzero interaction with that bond, violating the two electron per bond tenet of valence bond theory.
To construct hybrid s and p orbitals, let the first hybrid orbital be given by , where p is directed towards a bonding group and λ determines the amount of p character this hybrid orbital has. This is a weighted sum of the wavefunctions. Now choose a second hybrid orbital , where p is directed in some way and λ is the amount of p character in this second orbital. The value of λ and direction of p must be determined so that the resulting orbital can be normalized and so that it is orthogonal to the first hybrid orbital. The hybrid can certainly be normalized, as it is the sum of two normalized wavefunctions. Orthogonality must be established so that the two hybrid orbitals can be involved in separate covalent bonds. The inner product of orthogonal orbitals must be zero and computing the inner product of the constructed hybrids gives the following calculation.
The s orbital is normalized and so the inner product . Also, the s orbital is orthogonal to the p and p orbitals, which leads to two terms in the above equaling zero. Finally, the last term is the inner product of two normalized functions that are at an angle of to each other, which gives by definition. However, the orthogonality of bonding orbitals demands that , so we get Coulson's theorem as a result:
This means that the four s and p atomic orbitals can be hybridised in arbitrary directions provided that all of the coefficients λ satisfy the above condition pairwise to guarantee the resulting orbitals are orthogonal.
Bents rule, that central atoms direct orbitals of greater p character towards more electronegative substituents, is easily applicable to the above by noting that an increase in the λ coefficient increases the p character of the hybrid orbital. Thus, if a central atom A is bonded to two groups X and Y and Y is more electronegative than X, then A will hybridise so that . More sophisticated theoretical and computation techniques beyond Bents rule are needed to accurately predict molecular geometries from first principles, but Bent's rule provides an excellent heuristic in explaining molecular structures.
Henry Bent originally proposed his rule in 1960 on empirical grounds, but a few years later it was supported by molecular orbital calculations by Russell Drago. | 0 | Theoretical and Fundamental Chemistry |
Zeise returned to Denmark in the autumn of 1819. The prospects were not bright for an appointment at the University, although he was likely the only scientifically trained chemist in the country at that time. However, he learned at the end of the year that he had received public funds to support his work in science. That same year the university rented an apartment in Nørregade for use as a physics workshop and for physics education. Ørsted converted the apartment kitchen into a menial little laboratory, over which Zeise was made responsible. In this, the so-called "Royal Science Laboratory", Zeise received 10 students in the first year to whom he lectured, both in the laboratory and partly in the physical workshop. In June 1822 Zeise was appointed extraordinary Professor of Chemistry. In 1824, Professor Ørsted selected a nearby farm as the site for what would later become the Danish Polytechnic Education Institution. It was decided to transform the large stable building in the courtyard into a dedicated chemical laboratory. When the Polytechnic College was eventually founded in 1829, Zeise was instrumental in getting the chemical laboratory expanded and organised.
In 1823 while still in the small laboratory at Nørregade he identified a new family of sulfur-containing compounds, calling them xanthates (xanthus, Greek "yellow") on account of the predominantly yellow colour of xanthate salts. Zeise was accordingly awarded a silver medal by the Royal Danish Academy of Sciences and Letters, and he became a member of that body the following year on the recommendation of Ørsted. In 1836 he became a Knight of the Order of the Dannebrog, a very high honour bestowed by the Danish monarch.
As a teacher Zeise demanded strict accuracy from his pupils; together with conscientiousness, order and diligence - the same qualities which so strongly animated him.
In February 1842 he married Maren Martine Bjerring. Zeise's health was fragile for much of his life and he suffered greatly, possibly due to his handling of noxious chemicals in poorly ventilated rooms. He died of tuberculosis in Copenhagen on 12 November 1847 and was buried in Assistens Cemetery in the same city. | 0 | Theoretical and Fundamental Chemistry |
Most analytical methods for hydrogen embrittlement involve evaluating the effects of (1) internal hydrogen from production and/or (2) external sources of hydrogen such as cathodic protection. For steels, it is important to test specimens in the lab that are at least as hard (or harder) than the final parts will be. Ideally, specimens should be made of the final material or the nearest possible representative, as fabrication can have a profound impact on resistance to hydrogen-assisted cracking.
There are numerous ASTM standards for testing for hydrogen embrittlement:
* ASTM B577 is the Standard Test Methods for Detection of Cuprous Oxide (Hydrogen Embrittlement Susceptibility) in Copper. The test focuses on hydrogen embrittlement of copper alloys, including a metallographic evaluation (method A), testing in a hydrogen charged chamber followed by metallography (method B), and method C is the same as B but includes a bend test.
* ASTM B839 is the Standard Test Method for Residual Embrittlement in Metallic Coated, Externally Threaded Articles, Fasteners, and Rod-Inclined Wedge Method.
* ASTM F519 is the Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments. There are 7 different samples designs and the two most commons tests are (1) the rapid test, the Rising step load testing (RSL) method per ASTM F1624 and (2) the sustained load test, which takes 200 hours. The sustained load test is still included in many legacy standards, but the RSL method is increasingly being adopted due to speed, repeatability, and the quantitative nature of the test. The RSL method provides an accurate ranking of the effect of hydrogen from both internal and external sources.
* ASTM F1459 is the Standard Test Method for Determination of the Susceptibility of Metallic Materials to Hydrogen Gas Embrittlement (HGE) Test. The test uses a diaphragm loaded with a differential pressure.
* ASTM G142 is the Standard Test Method for Determination of Susceptibility of Metals to Embrittlement in Hydrogen Containing Environments at High Pressure, High Temperature, or Both. The test uses a cylindrical tensile specimen tested into an enclosure pressurized with hydrogen or helium.
* ASTM F1624 is the Standard Test Method for Measurement of Hydrogen Embrittlement Threshold in Steel by the Incremental Step Loading Technique. The test uses the incremental step loading (ISL) or Rising step load testing (RSL) method for quantitatively testing for the Hydrogen Embrittlement threshold stress for the onset of Hydrogen-Induced Cracking due to platings and coatings from Internal Hydrogen Embrittlement (IHE) and Environmental Hydrogen Embrittlement (EHE). F1624 provides a rapid, quantitative measure of the effects of hydrogen both from internal sources and external sources (which is accomplished by applying a selected voltage in an electrochemical cell). The F1624 test is performed by comparing a standard fast-fracture tensile strength to the fracture strength from a Rising step load testing practice where the load is held for hour(s) at each step. In many cases it can be performed in 30 hours or less.
* ASTM F1940 is the Standard Test Method for Process Control Verification to Prevent Hydrogen Embrittlement in Plated or Coated Fasteners. While the title now explicitly includes the word fasteners, F1940 was not originally intended for these purposes. F1940 is based on the F1624 method and is similar to F519 but with different root radius and stress concentration factors. When specimens exhibit a threshold cracking of 75% of the net fracture strength, the plating bath is considered to be non-embrittling.
There are many other related standards for hydrogen embrittlement:
* NACE TM0284-2003 (NACE International) Resistance to Hydrogen-Induced Cracking
* ISO 11114-4:2005 (ISO)Test methods for selecting metallic materials resistant to hydrogen embrittlement.
* Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments | 0 | Theoretical and Fundamental Chemistry |
Organosulfur compounds can be classified according to the sulfur-containing functional groups, which are listed (approximately) in decreasing order of their occurrence. | 0 | Theoretical and Fundamental Chemistry |
The difference between reversible and irreversible events has particular explanatory value in complex systems (such as living organisms, or ecosystems). According to the biologists Humberto Maturana and Francisco Varela, living organisms are characterized by autopoiesis, which enables their continued existence. More primitive forms of self-organizing systems have been described by the physicist and chemist Ilya Prigogine. In the context of complex systems, events which lead to the end of certain self-organising processes, like death, extinction of a species or the collapse of a meteorological system can be considered as irreversible. Even if a clone with the same organizational principle (e.g. identical DNA-structure) could be developed, this would not mean that the former distinct system comes back into being. Events to which the self-organizing capacities of organisms, species or other complex systems can adapt, like minor injuries or changes in the physical environment are reversible. However, adaptation depends on import of negentropy into the organism, thereby increasing irreversible processes in its environment. Ecological principles, like those of sustainability and the precautionary principle can be defined with reference to the concept of reversibility. | 0 | Theoretical and Fundamental Chemistry |
The adsorption of a very weakly basic or acidic probe molecule can serve to give a picture of Brønsted and Lewis acid–base sites. Infrared spectroscopy of surface sites and adsorbed molecules can then be used to monitor the change in the vibrational frequencies upon adsorption. A very weakly acidic probe molecule can be used to minimize disturbing neighboring sites so that a more accurate measure of surface acidity or basicity can be obtained. A variety of probe molecules can be used including: ammonia, pyridine, acetonitrile, carbon monoxide, and carbon dioxide. | 0 | Theoretical and Fundamental Chemistry |
Many polymer degradation mechanisms can be followed using IR spectroscopy, such as UV degradation and oxidation, among many other failure modes. | 0 | Theoretical and Fundamental Chemistry |
Aldehyde substituents suffer nucleophilic addition in the presence of organolithium compounds; however, adducts of aldehydes with lithium diamines can serve as effective directing groups for lateral lithiation. Subsequent treatment with an electrophilic primary alkyl halide and elimination of the diamine provides functionalized aryl aldehydes.
Tertiary amides are highly effective directing groups. After treatment of the resulting benzylic anion with an aldehyde, cyclization leads to lactones. Carboxamides, in which the amide is attached to the aromatic ring through nitrogen rather than carbon, are also effective directing groups.
Related O-aryl carbamates are good directing groups; upon warming, the resulting organolithiums undergo rearrangement to benzylic amides (the Snieckus-Fries rearrangement) via migration of the carbonyl carbon from oxygen to carbon.
Secondary N-aryl carbamates (along with secondary amides, ketones, and other directing groups containing acidic hydrogens) must be treated with two equivalents of organolithium reagent for lateral lithiation to occur. In the case below, sec-butyllithium is used to avoid competitive addition to the Boc group.
Sulfonamides require two equivalents of an organolithium reagent for lateral lithiation, but represent a useful class of directing groups. Treatment with ketones leads to tertiary alcohols in high yield. | 0 | Theoretical and Fundamental Chemistry |
In the first step of the porphyrin biosynthesis pathway, porphobilinogen is generated from aminolevulinate (ALA) by the enzyme ALA dehydratase. | 1 | Applied and Interdisciplinary Chemistry |
Standard CD/DVD readers can be used to read the assays. The CD/DVD readers contain a laser, set of optical elements which shape and focus the laser, a disk driver, and a signal detector that function as follows:
# The laser produces light of a selected wavelength.
# The beam of light hits the analyte in the spots of the microarrays and refracts. The mass of the analyte causes the angle of reflected light to be different from the angle of incident light. The reflective properties of the CD/DVD change based on the quantity of analyte in the sample.
# The attenuated signal reaches the photodiode of the drive's pickup.
# Analog signals are extracted, digitized, and converted to an image.
The signal or optical density of the image is inversely proportional to concentration. The refractive index of light, which is directly proportional to concentration, can also be measured. A readable signal is only generated if the sample is at least 200 nm, otherwise it is too small to significantly disrupt reflection of incident laser light.
DVD diagnostic software programs such as Kprobe, ODC, and PlexUtilities can also be used for testing arrays and assays prepared on DVDs. These programs rely on a basic DVD error correcting algorithm. DVDs are organized by sectors which each consist of 2064 bytes. A logical error correction code (ECC) block consists of 16 data sectors. The ECC block is the basic unit for testing disk quality by counting the number of parity inner errors (PIE) or parity inner failures (PIF). The software programs can analyze PIF density which is proportional to analyte concentration. | 1 | Applied and Interdisciplinary Chemistry |
In the late 1960s it was discovered that illuminated organic dyes can generate electricity at oxide electrodes in electrochemical cells. In an effort to understand and simulate the primary processes in photosynthesis the phenomenon was studied at the University of California at Berkeley with chlorophyll extracted from spinach (bio-mimetic or bionic approach). On the basis of such experiments electric power generation via the dye sensitization solar cell (DSSC) principle was demonstrated and discussed in 1972. The instability of the dye solar cell was identified as a main challenge. Its efficiency could, during the following two decades, be improved by optimizing the porosity of the electrode prepared from fine oxide powder, but the instability remained a problem.
A modern n-type DSSC, the most common type of DSSC, is composed of a porous layer of titanium dioxide nanoparticles, covered with a molecular dye that absorbs sunlight, like the chlorophyll in green leaves. The titanium dioxide is immersed under an electrolyte solution, above which is a platinum-based catalyst. As in a conventional alkaline battery, an anode (the titanium dioxide) and a cathode (the platinum) are placed on either side of a liquid conductor (the electrolyte).
The working principle for n-type DSSCs can be summarized into a few basic steps. Sunlight passes through the transparent electrode into the dye layer where it can excite electrons that then flow into the conduction band of the n-type semiconductor, typically titanium dioxide. The electrons from titanium dioxide then flow toward the transparent electrode where they are collected for powering a load. After flowing through the external circuit, they are re-introduced into the cell on a metal electrode on the back, also known as the counter electrode, and flow into the electrolyte. The electrolyte then transports the electrons back to the dye molecules and regenerates the oxidized dye.
The basic working principle above, is similar in a p-type DSSC, where the dye-sensitised semiconductor is of p-type nature (typically nickel oxide). However, instead of injecting an electron into the semiconductor, in a p-type DSSC, a hole flows from the dye into the valence band of the p-type semiconductor.
Dye-sensitized solar cells separate the two functions provided by silicon in a traditional cell design. Normally the silicon acts as both the source of photoelectrons, as well as providing the electric field to separate the charges and create a current. In the dye-sensitized solar cell, the bulk of the semiconductor is used solely for charge transport, the photoelectrons are provided from a separate photosensitive dye. Charge separation occurs at the surfaces between the dye, semiconductor and electrolyte.
The dye molecules are quite small (nanometer sized), so in order to capture a reasonable amount of the incoming light the layer of dye molecules needs to be made fairly thick, much thicker than the molecules themselves. To address this problem, a nanomaterial is used as a scaffold to hold large numbers of the dye molecules in a 3-D matrix, increasing the number of molecules for any given surface area of cell. In existing designs, this scaffolding is provided by the semiconductor material, which serves double-duty. | 0 | Theoretical and Fundamental Chemistry |
PCL consists in introducing a somatic adult or senescent cell nucleus or entire cell with enlarged membrane pores in an (activated) oocyte and to withdraw this treated cell before its de-differentiation and first cell division occurs. Thus, the progressive rejuvenation capability of the oocyte is used only temporarily in order to obtain a partial natural rejuvenation. PCL permits to envisage a chosen degree of partial rejuvenation in changing the duration of the introduction of the treated cell in the oocyte. Using PCL cell de-differentiation and its age reprogramming might be, at least partially, separable. Thus the existence of an isolated ageing clock would be confirmed at least during a certain part of the cellular evolution and involution. | 1 | Applied and Interdisciplinary Chemistry |
Methyl violet is a family of organic compounds that are mainly used as dyes. Depending on the number of attached methyl groups, the color of the dye can be altered. Its main use is as a purple dye for textiles and to give deep violet colors in paint and ink. It is also used as a hydration indicator for silica gel. Methyl violet 10B is also known as crystal violet (and many other names) and has medical uses. | 0 | Theoretical and Fundamental Chemistry |
According to structural and functional similarity, many local hormones fall into either the gastrin or the secretin family. | 1 | Applied and Interdisciplinary Chemistry |
DEPT (Distortionless Enhancement by Polarisation Transfer) is a pulse sequence used to distinguish between the multiplicity of hydrogen bonded to carbon, that is it can separate C, CH, CH and CH groups. It does this by exploiting the heteronuclear carbon-hydrogen -coupling and varying the tip angle of the final pulse in the sequence. The basic pulse sequence is shown below.
Under the weak coupling assumption, the chemical shift terms commute with the -coupling term in the Hamiltonian. Hence we can ignore the refocussed chemical shift (see ) in the two intervals containing -pulses, namely and , and additionally refrain from evaluating the chemical shift evolution in the last period . The pulse separation time is adjusted to the coupling strength (with associated Hamiltonian coefficient ) such that it satisfies
because then the first term in the evolved density operator in Equation vanishes under the pure coupling evolution between the pulses. | 0 | Theoretical and Fundamental Chemistry |
Sepro-Sizetec Screens are used for a variety of particle size separation and dewatering duties in mineral processing and aggregate applications. In mineral processing applications, particle size separation is of utmost importance in order to optimize crushing, grinding and gravity separation as well as many other processes. In aggregate applications, proper size separation and dewatering is essential to generate a saleable product. High capacity capable and featuring interchangeable screen decks, Sepro-Sizetec Screens are used for gold ore processing, fine aggregates, industrial minerals, soil remediation and coal processing applications. | 1 | Applied and Interdisciplinary Chemistry |
A Newtonian fluid is a fluid in which the viscous stresses arising from its flow are at every point linearly correlated to the local strain rate — the rate of change of its deformation over time. Stresses are proportional to the rate of change of the fluid's velocity vector.
A fluid is Newtonian only if the tensors that describe the viscous stress and the strain rate are related by a constant viscosity tensor that does not depend on the stress state and velocity of the flow. If the fluid is also isotropic (mechanical properties are the same along any direction), the viscosity tensor reduces to two real coefficients, describing the fluid's resistance to continuous shear deformation and continuous compression or expansion, respectively.
Newtonian fluids are the easiest mathematical models of fluids that account for viscosity. While no real fluid fits the definition perfectly, many common liquids and gases, such as water and air, can be assumed to be Newtonian for practical calculations under ordinary conditions. However, non-Newtonian fluids are relatively common and include oobleck (which becomes stiffer when vigorously sheared) and non-drip paint (which becomes thinner when sheared). Other examples include many polymer solutions (which exhibit the Weissenberg effect), molten polymers, many solid suspensions, blood, and most highly viscous fluids.
Newtonian fluids are named after Isaac Newton, who first used the differential equation to postulate the relation between the shear strain rate and shear stress for such fluids. | 1 | Applied and Interdisciplinary Chemistry |
* Principles of Nuclear Magnetic Resonance in One and Two Dimensions, Clarendon Press, 1987
* Richard R. Ernst: Nobelpreisträger aus Winterthur, Hier und Jetzt, Baden 2020
* Alois Feusi: [https://www.nzz.ch/zuerich/richard-ernst-chemiker-aus-winterthur-revolutioniert-die-medizin-ld.1556522 Richard Ernst: Der Selbstzweifler, dem der Nobelpreis peinlich war. Summary of his autobiography.] Neue Zürcher Zeitung, 21 May 2020. Retrieved 22 May 2020 | 0 | Theoretical and Fundamental Chemistry |
Pycnonuclear fusion () is a type of nuclear fusion reaction which occurs due to zero-point oscillations of nuclei around their equilibrium point bound in their crystal lattice. In quantum physics, the phenomenon can be interpreted as overlap of the wave functions of neighboring ions, and is proportional to the overlapping amplitude. Under the conditions of above-threshold ionization, the reactions of neutronization and pycnonuclear fusion can lead to the creation of absolutely stable environments in superdense substances.
The term "pycnonuclear" was coined by A.G.W. Cameron in 1959, but research showing the possibility of nuclear fusion in extremely dense and cold compositions was published by W. A. Wildhack in 1940. | 0 | Theoretical and Fundamental Chemistry |
Despite the highly attractive nature of 3D optical data storage, the development of commercial products has taken a significant length of time. This results from limited financial backing in the field, as well as technical issues, including:
Destructive reading. Since both the reading and the writing of data are carried out with laser beams, there is a potential for the reading process to cause a small amount of writing. In this case, the repeated reading of data may eventually serve to erase it (this also happens in phase change materials used in some DVDs). This issue has been addressed by many approaches, such as the use of different absorption bands for each process (reading and writing), or the use of a reading method that does not involve the absorption of energy.
Thermodynamic stability. Many chemical reactions that appear not to take place in fact happen very slowly. In addition, many reactions that appear to have happened can slowly reverse themselves. Since most 3D media are based on chemical reactions, there is therefore a risk that either the unwritten points will slowly become written or that the written points will slowly revert to being unwritten. This issue is particularly serious for the spiropyrans, but extensive research was conducted to find more stable chromophores for 3D memories.
Media sensitivity. two-photon absorption is a weak phenomenon, and therefore high power lasers are usually required to produce it. Researchers typically use Ti-sapphire lasers or Nd:YAG lasers to achieve excitation, but these instruments are not suitable for use in consumer products. | 0 | Theoretical and Fundamental Chemistry |
A hybrid scaffold is a skin substitute based on a combination of synthetic and natural materials. Examples of hybrid scaffolds are HYAFF and Laserskin. These hybrid scaffolds have been shown to have good in-vitro and in-vivo biocompatibilities and their biodegradability is controllable. | 1 | Applied and Interdisciplinary Chemistry |
The commercially most relevant field of application for HCl regeneration processes is the recovery of HCl from waste pickle liquors from carbon-steel pickling lines. Other applications include the production of metal oxides such as, but not limited, to AlO and MgO, as well as rare-earth oxides, by pyrohydrolysis of aqueous metal chloride or rare-earth chloride solutions.
A number of different process routes are available. The most widely used is based on pyrohydrolysis and adiabatic absorption of hydrogen chloride in water, a process invented in the 1960s. However tightening environmental standards and stringent air permit policies render it increasingly difficult to establish new pyrohydrolysis-based acid regeneration plants. | 0 | Theoretical and Fundamental Chemistry |
Thermal desorption is an environmental remediation technology that utilizes heat to increase the volatility of contaminants such that they can be removed (separated) from the solid matrix (typically soil, sludge or filter cake). The volatilized contaminants are then either collected or thermally destroyed. A thermal desorption system therefore has two major components; the desorber itself and the offgas treatment system.
Thermal desorption is not incineration. | 1 | Applied and Interdisciplinary Chemistry |
Often, reactive intermediates such as carbocations and free radicals have more delocalized structure than their parent reactants, giving rise to unexpected products. The classical example is allylic rearrangement. When 1 mole of HCl adds to 1 mole of 1,3-butadiene, in addition to the ordinarily expected product 3-chloro-1-butene, we also find 1-chloro-2-butene. Isotope labelling experiments have shown that what happens here is that the additional double bond shifts from 1,2 position to 2,3 position in some of the product. This and other evidence (such as NMR in superacid solutions) shows that the intermediate carbocation must have a highly delocalized structure, different from its mostly classical (delocalization exists but is small) parent molecule. This cation (an allylic cation) can be represented using resonance, as shown above.
This observation of greater delocalization in less stable molecules is quite general. The excited states of conjugated dienes are stabilised more by conjugation than their ground states, causing them to become organic dyes.
A well-studied example of delocalization that does not involve π electrons (hyperconjugation) can be observed in the non-classical 2-Norbornyl cation Another example is methanium (). These can be viewed as containing three-center two-electron bonds and are represented either by contributing structures involving rearrangement of σ electrons or by a special notation, a Y that has the three nuclei at its three points.
Delocalized electrons are important for several reasons; a major one is that an expected chemical reaction may not occur because the electrons delocalize to a more stable configuration, resulting in a reaction that happens at a different location. An example is the Friedel–Crafts alkylation of benzene with 1-chloro-2-methylpropane; the carbocation rearranges to a tert-butyl group stabilized by hyperconjugation, a particular form of delocalization. | 0 | Theoretical and Fundamental Chemistry |
The modern era of pharmaceutical industry began with local apothecaries that expanded from their traditional role of distributing botanical drugs such as morphine and quinine to wholesale manufacture in the mid-1800s, and from discoveries resulting from applied research. Intentional drug discovery from plants began with the isolation between 1803 and 1805 of morphine – an analgesic and sleep-inducing agent – from opium by the German apothecary assistant Friedrich Sertürner, who named this compound after the Greek god of dreams, Morpheus. By the late 1880s, German dye manufacturers had perfected the purification of individual organic compounds from tar and other mineral sources and had also established rudimentary methods in organic chemical synthesis. The development of synthetic chemical methods allowed scientists to systematically vary the structure of chemical substances, and growth in the emerging science of pharmacology expanded their ability to evaluate the biological effects of these structural changes. | 1 | Applied and Interdisciplinary Chemistry |
In 1864, William Sellers, then president of Franklin Institute, presented a standard for nuts, bolts, and screws. Out of this effort came the first United States Standard threads, including pipe threads. | 1 | Applied and Interdisciplinary Chemistry |
Quantitative systems pharmacology (QSP) is a discipline within biomedical research that uses mathematical computer models to characterize biological systems, disease processes and drug pharmacology. QSP can be viewed as a sub-discipline of pharmacometrics that focuses on modeling the mechanisms of drug pharmacokinetics (PK), pharmacodynamics (PD), and disease processes using a systems pharmacology point of view. QSP models are typically defined by systems of ordinary differential equations (ODE) that depict the dynamical properties of the interaction between the drug and the biological system.
QSP can be used to generate biological/pharmacological hypotheses in silico to aid in the design of in vitro or in vivo non-clinical and clinical experiments. This can help to guide biomedical experiments so that they yield more meaningful data. QSP is increasingly being used for this purpose in pharmaceutical research & development to help guide the discovery and development of new therapies. QSP has been used by the FDA in a clinical pharmacology review. | 1 | Applied and Interdisciplinary Chemistry |
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