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At high pressures, water has a complex phase diagram with 15 known phases of ice and several triple points, including 10 whose coordinates are shown in the diagram. For example, the triple point at 251 K (−22 °C) and 210 MPa (2070 atm) corresponds to the conditions for the coexistence of ice Ih (ordinary ice), ice III and liquid water, all at equilibrium. There are also triple points for the coexistence of three solid phases, for example ice II, ice V and ice VI at 218 K (−55 °C) and 620 MPa (6120 atm).
For those high-pressure forms of ice which can exist in equilibrium with liquid, the diagram shows that melting points increase with pressure. At temperatures above 273 K (0 °C), increasing the pressure on water vapor results first in liquid water and then a high-pressure form of ice. In the range , ice I is formed first, followed by liquid water and then ice III or ice V, followed by other still denser high-pressure forms. | 0 | Theoretical and Fundamental Chemistry |
Lipid bilayers are structures of lipid molecules consisting of a hydrophobic tail and a hydrophilic head group. Therefore, these structures experience all the characteristic Interbilayer forces involved in that regime. | 0 | Theoretical and Fundamental Chemistry |
Hyperconjugation is the stabilizing interaction that results from the interaction of the electrons in a sigma bond (usually C-H or C-C) with an adjacent empty (or partially filled) non-bonding p-orbital or antibonding π orbital or an antibonding sigma orbital to give an extended molecular orbital that increases the stability of the system. Hyperconjugation can be used to explain phenomena such as the gauche effect and anomeric effect.
Orbital symmetry is important when dealing with orbitals that contain directional components like p and d. An example of such an effect is square planar low-spin d transition metal complexes. These complexes exist as square planar complexes due to the directionality of the metal center's d orbitals despite fewer steric congestion in a tetrahedral geometric structure. This is simple one example of many varied examples, including aspects of pericyclic reactions such as the Diels-Alder reaction, among others.
Electrostatic interactions include both attractive and repulsive forces associated with the build-up of charge in a molecule. Electrostatic interactions are generally too weak to be considered traditional bonds or are prevented from forming a traditional bond, possibly by a steric effect. A bond is usually defined as two atoms approaching closer than the sum of their Van der Waal radii. Hydrogen bonding borders on being an actual "bond" and an electrostatic interaction. While an attractive electrostatic interaction is considered a "bond" if it gets too strong, a repulsive electrostatic interaction is always an electrostatic effect regardless of strength. An example of a repulsive effect is a molecule contorting to minimize the coulombic interactions of atoms that hold like charges.
Electronic spin state at it simplest describes the number of unpaired electrons in a molecule. Most molecules including the proteins, carbohydrates, and lipids that make up the majority of life have no unpaired electrons even when charged. Such molecules are called singlet molecules, since their paired electrons have only one spin state. In contrast, dioxygen under ambient conditions has two unpaired electrons. Dioxygen is a triplet molecule, since the two unpaired electrons allow for three spin states. The reaction of a triplet molecule with a singlet molecule is spin-forbidden in quantum mechanics. This is the major reasons there is a very high reaction barrier for the extremely thermodynamically favorable reaction of singlet organic molecules with triplet oxygen. This kinetic barrier prevents life from bursting into flames at room temperature.
Electronic spin states are more complex for transition metals. To understand the reactivity of transition metals, it is essential to understand the concept of d electron configuration as well as high-spin and low-spin configuration. For example, a low-spin d transition metal complex is usually square planar substitutionally inert with no unpaired electrons. In contrast, a high-spin d transition metal complex is usually octahedral, substitutionally labile, with two unpaired electrons.
Jahn–Teller effect is the geometrical distortion of non-linear molecules under certain situations. Any non-linear molecule with a degenerate electronic ground state will undergo a geometrical distortion that removes that degeneracy. This has the effect of lowering the overall energy. The Jahn–Teller distortion is especially common in certain transition metal complexes; for example, copper(II) complexes with 9 d electrons.
Trans influence is the influence that a ligand in a square or octahedral complex has on the bond to the ligand trans to it. It is caused by electronic effects, and manifests itself as the lengthening of the trans bonds and as an effect on the overall energy of the complex. | 0 | Theoretical and Fundamental Chemistry |
Background BOD or benthic oxygen demand is the diffuse source of BOD represented by the decay of organic matter that has already settled on the bottom. This will give rise to a constant diffuse input thus the change in BOD over time will be
where
* is the rate for oxygen consumption by BOD, usually in .
* is the BOD from organic matter in the water .
* is the background BOD input . | 1 | Applied and Interdisciplinary Chemistry |
Due to it being a lesser understood post-translational modification, arginylation and its regulation in vivo still remains largely esoteric. The expression of ATE1 can vary significantly within different tissues, but its levels within these tissues peak at mid-development but begin to decline as an organism ages. It has also been observed that a variety of physiological compounds and drugs are able to affect the incorporation of arginine in vivo, but it is hypothesized that this occurs in a non-specific manner. As such, it has been theorized that inhibitors and activators which regulate ATE1 activity, and therefore arginylation, may exist in vivo.
Arginylation's ability to make proteins metabolically unstable, as observed in yeast, makes proteins which have been modified in this way an attractive target for removal. One of the well characterized arginylation regulators is the ubiquitin dependent protein degradation which quickly degrades and removes harmful proteins. This important regulator of arginylation facilitates the specificity of this post-translational modification and efficiently removes proteins which were not meant to be arginylated in vivo.
Lastly, an unproven but highly attractive mechanism of regulating arginylation in vivo suggests the use of de-arginylation enzymes which may be able to remove an arginine that has been added post-translationally to proteins. Enzymes such as Aminopeptidase B and Carboxypeptidase B are able to remove arginine from a proteins N-terminus and from side chain carboxyl groups, respectively, but do not specifically target arginylated sites. The proposed de-arginylation enzymes are theorized to act in the same way as the previously mentioned enzymes Aminopeptidase B and Carboxypeptidase B, but would differ in the fact that they specifically target arginylated protein substrates. Although these enzymes have not been discovered as of yet, the search for and discovery of these enzymes is an exciting path for further studies. | 1 | Applied and Interdisciplinary Chemistry |
The molecular mechanism of ATP (Adenosine triphosphate) generation in chloroplasts is similar to that in mitochondria and takes the required energy from the proton motive force (PMF). However, chloroplasts rely more on the chemical potential of the PMF to generate the potential energy required for ATP synthesis. The PMF is the sum of a proton chemical potential (given by the proton concentration gradient) and a transmembrane electrical potential (given by charge separation across the membrane). Compared to the inner membranes of mitochondria, which have a significantly higher membrane potential due to charge separation, thylakoid membranes lack a charge gradient. To compensate for this, the 10,000 fold proton concentration gradient across the thylakoid membrane is much higher compared to a 10 fold gradient across the inner membrane of mitochondria. The resulting chemiosmotic potential between the lumen and stroma is high enough to drive ATP synthesis using the ATP synthase. As the protons travel back down the gradient through channels in ATP synthase, ADP + P are combined into ATP. In this manner, the light-dependent reactions are coupled to the synthesis of ATP via the proton gradient. | 0 | Theoretical and Fundamental Chemistry |
Autocrine signaling is a form of cell signaling in which a cell secretes a hormone or chemical messenger (called the autocrine agent) that binds to autocrine receptors on that same cell, leading to changes in the cell. This can be contrasted with paracrine signaling, intracrine signaling, or classical endocrine signaling. | 1 | Applied and Interdisciplinary Chemistry |
Chemical milling or industrial etching is the subtractive manufacturing process of using baths of temperature-regulated etching chemicals to remove material to create an object with the desired shape. Other names for chemical etching include photo etching, chemical etching, photo chemical etching and photochemical machining. It is mostly used on metals, though other materials are increasingly important. It was developed from armor-decorating and printing etching processes developed during the Renaissance as alternatives to engraving on metal. The process essentially involves bathing the cutting areas in a corrosive chemical known as an etchant, which reacts with the material in the area to be cut and causes the solid material to be dissolved; inert substances known as maskants are used to protect specific areas of the material as resists. | 1 | Applied and Interdisciplinary Chemistry |
The B-B bond adds across alkenes and alkynes to give the 1,2-diborylated alkanes and alkenes. Using various organorhodium or organoiridium catalysts, it can also be installed onto saturated hydrocarbons:
:CH(CH)CH + [pinB] → pinBH + CH(CH)Bpin
These reactions proceed via boryl complexes.
Bis(pinacolato)diboron can also be used as reducing agent for example in transition metal catalyzed hydrogenations of alkenes and alkynes. | 0 | Theoretical and Fundamental Chemistry |
Perovskite solar cells are solar cells that include a perovskite-structured material as the active layer. Most commonly, this is a solution-processed hybrid organic-inorganic tin or lead halide based material. Efficiencies have increased from below 5% at their first usage in 2009 to 25.5% in 2020, making them a very rapidly advancing technology and a hot topic in the solar cell field. Researchers at University of Rochester reported in 2023 that significant further improvements in cell efficiency can be achieved by utilizing Purcell effect.
Perovskite solar cells are also forecast to be extremely cheap to scale up, making them a very attractive option for commercialisation. So far most types of perovskite solar cells have not reached sufficient operational stability to be commercialised, although many research groups are investigating ways to solve this. Energy and environmental sustainability of perovskite solar cells and tandem perovskite are shown to be dependent on the structures. Photonic front contacts for light management can improve the perovskite cells' performance, via enhanced broadband absorption, while allowing better operational stability due to protection against the harmful high-energy (above Visible) radiation. The inclusion of the toxic element lead in the most efficient perovskite solar cells is a potential problem for commercialisation. | 0 | Theoretical and Fundamental Chemistry |
Protein misfolding cyclic amplification (PMCA) is an amplification technique (conceptually like polymerase chain reaction (PCR) but not involving nucleotides) to multiply misfolded prions originally developed by Soto and colleagues. It is a test for spongiform encephalopathies like chronic wasting disease (CWD) or bovine spongiform encephalopathy (BSE). | 1 | Applied and Interdisciplinary Chemistry |
An abnormal basal metabolic rate is not necessarily indicative of disease; a number of physiological factors can alter the BMR by influencing cellular metabolic activity. For instance, males are more likely than females to have a high BMR, and in women, the BMR may rise to abnormal levels during pregnancy or lactation. An individual's BMR varies greatly with age: infants and children typically have a high BMR, required for growth, while the elderly have a low BMR. Tall, thin people have a higher BMR than their shorter counterparts, even with the same weight, due to the greater surface area of their skin. The metabolic rate also decreases during sleep and increases in exercise, and individuals who exercise regularly have a higher BMR than those who are sedentary. Environmental temperature also has an effect: the BMR is increased in both heat and cold. | 1 | Applied and Interdisciplinary Chemistry |
Amyl nitrite is administered to treat cyanide poisoning. It works by converting hemoglobin to methemoglobin, which allows for the binding of cyanide (CN) anions by ferric (Fe) cations and the formation of cyanomethemoglobin. The immediate goal of forming this cyanide adduct is to prevent the binding of free cyanide to the cytochrome a group in cytochrome c oxidase. | 1 | Applied and Interdisciplinary Chemistry |
Carbon monoxide can be produced from CORR over various precious metal catalysts. Steel has proven to be one such catalyst., or hydrogen.
Mechanistically, carbon monoxide arises from the metal bonded to the carbon of CO (see metallacarboxylic acid). Oxygen is lost as water. | 1 | Applied and Interdisciplinary Chemistry |
Although the applications of pharmacometabolomics to personalized medicine are largely only being realized now, the study of an individual's metabolism has been used to treat disease since the Middle Ages. Early physicians employed a primitive form of metabolomic analysis by smelling, tasting and looking at urine to diagnose disease. Obviously the measurement techniques needed to look at specific metabolites were unavailable at that time, but such technologies have evolved dramatically over the last decade to develop precise, high-throughput devices, as well as the accompanying data analysis software to analyze output. Currently, sample purification processes, such as liquid or gas chromatography, are coupled with either mass spectrometry (MS)-based or nuclear magnetic resonance (NMR)-based analytical methods to characterize the metabolite profiles of individual patients. Continually advancing informatics tools allow for the identification, quantification and classification of metabolites to determine which pathways may influence certain pharmaceutical interventions. One of the earliest studies discussing the principle and applications of pharmacometabolomics was conducted in an animal model to look at the metabolism of paracetamol and liver damage. NMR spectroscopy was used to analyze the urinary metabolic profiles of rats pre- and post-treatment with paracetamol. The analysis revealed a certain metabolic profile associated with increased liver damage following paracetamol treatment. At this point, it was eagerly anticipated that such pharmacometabolomics approaches could be applied to personalized human medicine. Since this publication in 2006, the Pharmacometabolomics Research Network led by Duke University researchers and that included partnerships between centers of excellence in metabolomics, pharmacogenomics and informatics (over sixteen academic centers funded by NIGMS) has been able to illustrate for the first time the power of the pharmacometabolomics approach in informing about treatment outcomes in large clinical studies and with use of drugs that include antidepressants, statins, antihypertensives, antiplatelet therapies and antipsychotics. Totally new concepts emerged from these studies on use of pharmacometabolomics as a tool that can bring a paradigm shift in the field of pharmacology. It illustrated how pharmacometabolomics can enable a Quantitative and Systems Pharmacology approach.
Pharmacometabolomics has been applied for the treatment of numerous human diseases, such as schizophrenia, diabetes, neural disease, depression and cancer. | 1 | Applied and Interdisciplinary Chemistry |
Monoamine precursors are precursors of monoamines and monoamine neurotransmitters in the body. The amino acids -tryptophan and -5-hydroxytryptophan (5-HTP; oxitriptan) are precursors of serotonin and melatonin, while the amino acids -phenylalanine, -tyrosine, and -DOPA (levodopa) are precursors of dopamine, epinephrine (adrenaline), and norepinephrine (noradrenaline). Administration of monoamine precursors can increase the levels of monoamine neurotransmitters in the body and brain. Monoamine precursors may be used in combination with peripherally selective aromatic -amino acid decarboxylase inhibitors (AAAD inhibitors; also known as DOPA decarboxylase (DDC) inhibitors) such as carbidopa and benserazide. Carbidopa/levodopa is used to increase brain dopamine levels in the treatment of Parkinson's disease while carbidopa/oxitriptan (EVX-101) is under development as an antidepressant for possible use in the treatment of depression. | 1 | Applied and Interdisciplinary Chemistry |
P680 receives excitation energy either by directly absorbing a photon of suitable frequency or indirectly from other chlorophylls within photosystem II, thereby exciting an electron to a higher energy level. The resulting P680 with a loosened electron is designated as P680*, which is a strong reducing agent. | 0 | Theoretical and Fundamental Chemistry |
The process of pseudorotation occurs when the two axial ligands close like a pair of scissors pushing their way in between two of the equatorial groups which scissor out to accommodate them. Both the axial and equatorial constituents move at the same rate of increasing the angle between the other axial or equatorial constituent. This forms a square based pyramid where the base is the four interchanging ligands and the tip is the pivot ligand, which has not moved. The two originally equatorial ligands then open out until they are 180 degrees apart, becoming axial groups perpendicular to where the axial groups were before the pseudorotation. This requires about 3.6 kcal/mol in PF.
This rapid exchange of axial and equatorial ligands renders complexes with this geometry unresolvable (unlike carbon atoms with four distinct substituents), except at low temperatures or when one or more of the ligands is bi- or poly-dentate. | 0 | Theoretical and Fundamental Chemistry |
The nuclear medicine technique commonly called the bone scan usually uses Tc. It is not to be confused with the "bone density scan", DEXA, which is a low-exposure X-ray test measuring bone density to look for osteoporosis and other diseases where bones lose mass without rebuilding activity. The nuclear medicine technique is sensitive to areas of unusual bone rebuilding activity, since the radiopharmaceutical is taken up by osteoblast cells which build bone. The technique therefore is sensitive to fractures and bone reaction to bone tumors, including metastases. For a bone scan, the patient is injected with a small amount of radioactive material, such as of Tc-medronic acid and then scanned with a gamma camera. Medronic acid is a phosphate derivative which can exchange places with bone phosphate in regions of active bone growth, so anchoring the radioisotope to that specific region. To view small lesions (less than ) especially in the spine, the SPECT imaging technique may be required, but currently in the United States, most insurance companies require separate authorization for SPECT imaging. | 0 | Theoretical and Fundamental Chemistry |
This equation is used:
In this equation, α (Greek letter "alpha") is the measured rotation in degrees, l is the path length in decimeters, and ρ (Greek letter "rho") is the density of the liquid in g/mL, for a sample at a temperature T (given in degrees Celsius) and wavelength λ (in nanometers). If the wavelength of the light used is 589 nanometers (the sodium D line), the symbol “D” is used. The sign of the rotation (+ or −) is always given. | 0 | Theoretical and Fundamental Chemistry |
Membrane fusion is a key biophysical process that is essential for the functioning of life itself. It is defined as the event where two lipid bilayers approach each other and then merge to form a single continuous structure. In living beings, cells are made of an outer coat made of lipid bilayers; which then cause fusion to take place in events such as fertilization, embryogenesis and even infections by various types of bacteria and viruses. It is therefore an extremely important event to study. From an evolutionary angle, fusion is an extremely controlled phenomenon. Random fusion can result in severe problems to the normal functioning of the human body. Fusion of biological membranes is mediated by proteins. Regardless of the complexity of the system, fusion essentially occurs due to the interplay of various interfacial forces, namely hydration repulsion, hydrophobic attraction and van der Waals forces. | 0 | Theoretical and Fundamental Chemistry |
Mitochondria can repair oxidative DNA damage by mechanisms analogous to those occurring in the cell nucleus. The proteins employed in mtDNA repair are encoded by nuclear genes, and are translocated to the mitochondria. The DNA repair pathways in mammalian mitochondria include base excision repair, double-strand break repair, direct reversal and mismatch repair. Alternatively, DNA damage may be bypassed, rather than repaired, by translesion synthesis.
Of the several DNA repair process in mitochondria, the base excision repair pathway has been most comprehensively studied. Base excision repair is carried out by a sequence of enzyme-catalyzed steps that include recognition and excision of a damaged DNA base, removal of the resulting abasic site, end processing, gap filling and ligation. A common damage in mtDNA that is repaired by base excision repair is 8-oxoguanine produced by oxidation of guanine.
Double-strand breaks can be repaired by homologous recombinational repair in both mammalian mtDNA and plant mtDNA. Double-strand breaks in mtDNA can also be repaired by microhomology-mediated end joining. Although there is evidence for the repair processes of direct reversal and mismatch repair in mtDNA, these processes are not well characterized. | 1 | Applied and Interdisciplinary Chemistry |
If the peptides are not cleaved from the solid support we deal with a mixture of beads, each bead containing a single peptide. Smith and his colleagues showed earlier that peptides could be tested in tethered form, too. This approach was also used in screening peptide libraries. The tethered peptide library was tested with a dissolved target protein. The beads to which the protein was attached were picked out, removed the protein from the bead then the tethered peptide was identified by sequencing.
A somewhat different approach was followed by Taylor and Morken. They used infrared thermography to identify catalysts in non-peptide tethered libraries. The method is based on the heat that is evolved in the beads that contain a catalyst when the tethered library immersed into a solution of a substrate. When the beads are examined through an infrared microscope the catalyst containing beads appear as bright spots and can be picked out. | 1 | Applied and Interdisciplinary Chemistry |
Optical magnetometry makes use of various optical techniques to measure magnetization. One such technique, Kerr magnetometry makes use of the magneto-optic Kerr effect, or MOKE. In this technique, incident light is directed at the samples surface. Light interacts with a magnetized surface nonlinearly so the reflected light has an elliptical polarization, which is then measured by a detector. Another method of optical magnetometry is Faraday rotation magnetometry. Faraday rotation magnetometry utilizes nonlinear magneto-optical rotation to measure a samples magnetization. In this method a Faraday modulating thin film is applied to the sample to be measured and a series of images are taken with a camera that senses the polarization of the reflected light. To reduce noise, multiple pictures are then averaged together. One advantage to this method is that it allows mapping of the magnetic characteristics over the surface of a sample. This can be especially useful when studying such things as the Meissner effect on superconductors. Microfabricated optically pumped magnetometers (µOPMs) can be used to detect the origin of brain seizures more precisely and generate less heat than currently available superconducting quantum interference devices, better known as SQUIDs. The device works by using polarized light to control the spin of rubidium atoms which can be used to measure and monitor the magnetic field. | 0 | Theoretical and Fundamental Chemistry |
The underlying premise of spectroscopy is that light is made of different wavelengths and that each wavelength corresponds to a different frequency. The importance of spectroscopy is centered around the fact that every element in the periodic table has a unique light spectrum described by the frequencies of light it emits or absorbs consistently appearing in the same part of the electromagnetic spectrum when that light is diffracted. This opened up an entire field of study with anything that contains atoms which is all matter. Spectroscopy is the key to understanding the atomic properties of all matter. As such spectroscopy opened up many new sub-fields of science yet undiscovered. The idea that each atomic element has its unique spectral signature enabled spectroscopy to be used in a broad number of fields each with a specific goal achieved by different spectroscopic procedures. The National Institute of Standards and Technology maintains a public Atomic Spectra Database that is continually updated with precise measurements.
The broadening of the field of spectroscopy is due to the fact that any part of the electromagnetic spectrum may be used to analyze a sample from the infrared to the ultraviolet telling scientists different properties about the very same sample. For instance in chemical analysis, the most common types of spectroscopy include atomic spectroscopy, infrared spectroscopy, ultraviolet and visible spectroscopy, Raman spectroscopy and nuclear magnetic resonance. In nuclear magnetic resonance (NMR), the theory behind it is that frequency is analogous to resonance and its corresponding resonant frequency. Resonances by the frequency were first characterized in mechanical systems such as pendulums which have a frequency of motion noted famously by Galileo. | 0 | Theoretical and Fundamental Chemistry |
Conversion electron Mössbauer spectroscopy (CEMS) is a Mössbauer spectroscopy technique based on conversion electron.
The CEM spectrum can be obtained either by collecting essentially all the electrons leaving the surface (integral technique), or by selecting the ones in a given energy range by means of a beta ray spectrometer (differential or depth selective CEMS).
This method allows the use of simple and inexpensive detecting equipment, mainly flow-type proportional detectors in which large counting rates can be obtained. This last characteristic makes possible the study of samples with the natural abundance of the Mössbauer isotope. The information furnished by the integral measurements can be increased by using various angles of incidence or by depositing thin layers of inert material on the sample. | 0 | Theoretical and Fundamental Chemistry |
Ultra- and High Shear in-line or batch reactors allow production of biodiesel continuously, semi- continuously, and in batch-mode. This drastically reduces production time and increases production volume.
The reaction takes place in the high-energetic shear zone of the Ultra- and High Shear mixer by reducing the droplet size of the immiscible liquids such as oil or fats and methanol. Therefore, the smaller the droplet size the larger the surface area the faster the catalyst can react. | 0 | Theoretical and Fundamental Chemistry |
Escitalopram appears to be effective in treating generalized anxiety disorder, with relapse on escitalopram at 20% rather than placebo at 50%, which translates to a number needed to treat of 3.33. Escitalopram appears effective in treating social anxiety disorder as well. | 0 | Theoretical and Fundamental Chemistry |
The Uncompahgre Ute indigenous people from Central Colorado are one of the first documented groups of people in the world credited with the application of mechanoluminescence involving the use of quartz crystals to generate light. The Ute constructed unique ceremonial rattles made from buffalo rawhide which they filled with clear quartz crystals collected from the mountains of Colorado and Utah. When the rattles were shaken at night during ceremonies, the friction and mechanical stress of the quartz crystals impacting together produced flashes of light visible through the translucent buffalo hide. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, materials science, and physics, the liquidus temperature specifies the temperature above which a material is completely liquid, and the maximum temperature at which crystals can co-exist with the melt in thermodynamic equilibrium. The solidus is the locus of temperatures (a curve on a phase diagram) below which a given substance is completely solid (crystallized). The solidus temperature, specifies the temperature below which a material is completely solid, and the minimum temperature at which a melt can co-exist with crystals in thermodynamic equilibrium.
Liquidus and solidus are mostly used for impure substances (mixtures) such as glasses, metal alloys, ceramics, rocks, and minerals. Lines of liquidus and solidus appear in the phase diagrams of binary solid solutions, as well as in eutectic systems away from the invariant point. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, a methine group or methine bridge is a trivalent functional group , derived formally from methane. It consists of a carbon atom bound by two single bonds and one double bond, where one of the single bonds is to a hydrogen. The group is also called methyne or methene, but its IUPAC systematic name is methylylidene or methanylylidene.
This group is sometimes called "methylidyne", however that name belongs properly to either the methylidyne group (connected to the rest of the molecule by a triple bond) or to the methylidyne radical (the two atoms as a free molecule with dangling bonds).
The name "methine" is also widely used in non-systematic nomenclature for the methanetriyl group (IUPAC): a carbon atom with four single bonds, where one bond is to a hydrogen atom (). | 0 | Theoretical and Fundamental Chemistry |
Schlögl was born October 5, 1924, in Vienna. Schlögl's first contact with organic chemistry happened during his middle-school education, when his father - the principal and teacher for natural sciences - took young Karl to school after hours to do experiments together.
Schlögl graduated from high-school in 1943 and was declared unfit for service by the Wehrmacht due to his asthma.
He started studying chemistry at the University of Vienna under Ernst Späth, where he completed his dissertation in 1950.
From 1954 to 1955 Schlögl began working on ferrocenes at the University of Manchester during a British council scholarship.
After his return to the University of Vienna he achieved the habilitation for organic chemistry in 1959.
In 1970 Schlögl was promoted to associate professor and in 1971 to full professor for organic chemistry.
Since 1974 he was director, and since 1978 chairman of the [http://www.univie.ac.at/orgchem/ Institute of Organic Chemistry] at the University of Vienna. From 1977 through 1979 he was the first elected Dean of the Faculty of Formal and Natural Sciences at the University of Vienna.
The Austrian Academy of Sciences elected Schlögl as a corresponding member in 1978 and as a full member in 1982. From 1991 to 1995 Schlögl was general secretary of the academy, and from 1997 to 2000 he was vice-president of the Austrian Academy of Sciences. Furthermore, Schlögl was a corresponding member of the Nordrhein-Westfälische Akademie der Wissenschaften as well as the New York Academy of Sciences. | 0 | Theoretical and Fundamental Chemistry |
Nanocasting is a method based on soft lithography which uses elastomeric molds to make nano-structured surfaces. For example, polydimethylsiloxane (PDMS) was cast over the lotus leaf and used to make a negative PDMS template. PDMS was then coated with an anti-stick monolayer of trimethylchlorosilane and used to make a positive PDMS template from the first. As the natural lotus leaf structure enables pronounced self-cleaning ability, this templating technique was able to replicate the nanostructure, resulting in a surface wettability similar to the lotus leaf. Further, the ease of this methodology enables translation to mass replication of nano-structured surfaces. | 0 | Theoretical and Fundamental Chemistry |
Known relaxases are metal ion dependent tyrosine transesterases. This means that they use a metal ion to aid the transfer of an ester bond from the DNA phosphodiester backbone to a catalytic tyrosine side chain, resulting in a long-lived covalent phosphotyrosine intermediate that essentially unified the nicked DNA strand and the enzyme as one molecule. Preliminary reports of relaxase inhibition by small molecules that mimic intermediates of this reaction were first reported in 2007. Such inhibition has implications related to preventing the propagation of antibiotic resistance in clinical settings.
The first relaxase x-ray crystal and NMR structures – of Rep relaxases from tomato yellow leaf curl virus (TYLCV) and adeno associated virus serotype 5 (AAV-5) – were solved in 2002. These revealed compact molecules composed of five-stranded, antiparallel beta sheet cores and peripheral alpha helices. A histidine-rich motif, previously identified by sequence conservation, was shown to be a metal ion binding site located on the beta sheet core, nearby the carboxy-terminal catalytic tyrosine residue. Later structures of the Mob relaxases TrwC from plasmid R388 and TraI from the F-plasmid confirmed that the Mob and Rep classes are evolutionarily related to one another through circular permutation. This means that they share a general fold, but the amino-terminal sequence of one is homologous to the C-terminus of the other, and vice versa. Thus the Catalytic tyrosines of TraI and TrwC are amino-terminal rather than carboxy-terminal. | 1 | Applied and Interdisciplinary Chemistry |
Take a system in a certain super (i.e. Gibbs) state. By performing a Metropolis Monte Carlo walk it is possible to sample the landscape of states that the system moves between, using the equation
where ΔU = U(State) − U(State) is the difference in potential energy, β = 1/kT (T is the temperature in kelvins, while k is the Boltzmann constant), and is the Metropolis function.
The resulting states are then sampled according to the Boltzmann distribution of the super state at temperature T.
Alternatively, if the system is dynamically simulated in the canonical ensemble (also called the NVT ensemble), the resulting states along the simulated trajectory are likewise distributed.
Averaging along the trajectory (in either formulation) is denoted by angle brackets
Suppose that two super states of interest, A and B, are given. We assume that they have a common configuration space, i.e., they share all of their micro states, but the energies associated to these (and hence the probabilities) differ because of a change in some parameter (such as the strength of a certain interaction).
The basic question to be addressed is, then, how can the Helmholtz free energy change (ΔF = F − F) on moving between the two super states be calculated from sampling in both ensembles? The kinetic energy part in the free energy is equal between states so can be ignored. Also the Gibbs free energy corresponds to the NpT ensemble. | 0 | Theoretical and Fundamental Chemistry |
In general, the luminous intensity of a point on a surface varies by direction; for a Lambertian surface, that distribution is defined by the cosine law, with peak luminous intensity in the normal direction. Thus when the Lambertian assumption holds, we can calculate the total luminous flux, , from the peak luminous intensity, , by integrating the cosine law:
and so
where is the determinant of the Jacobian matrix for the unit sphere, and realizing that is luminous flux per steradian. Similarly, the peak intensity will be of the total radiated luminous flux. For Lambertian surfaces, the same factor of relates luminance to luminous emittance, radiant intensity to radiant flux, and radiance to radiant emittance. Radians and steradians are, of course, dimensionless and so "rad" and "sr" are included only for clarity.
Example: A surface with a luminance of say 100 cd/m (= 100 nits, typical PC monitor) will, if it is a perfect Lambert emitter, have a luminous emittance of 100π lm/m. If its area is 0.1 m (~19" monitor) then the total light emitted, or luminous flux, would thus be 31.4 lm. | 0 | Theoretical and Fundamental Chemistry |
In 1845, the English physicist James Joule wrote a paper On the mechanical equivalent of heat for the British Association meeting in Cambridge. In this paper, he reported his best-known experiment, in which the mechanical power released through the action of a "weight falling through a height" was used to turn a paddle-wheel in an insulated barrel of water.
In this experiment, the motion of the paddle wheel, through agitation and friction, heated the body of water, so as to increase its temperature. Both the temperature change of the water and the height of the fall of the weight were recorded. Using these values, Joule was able to determine the mechanical equivalent of heat. Joule estimated a mechanical equivalent of heat to be 819 ft•lbf/Btu (4.41 J/cal). The modern day definitions of heat, work, temperature, and energy all have connection to this experiment. In this arrangement of apparatus, it never happens that the process runs in reverse, with the water driving the paddles so as to raise the weight, not even slightly. Mechanical work was done by the apparatus of falling weight, pulley, and paddles, which lay in the surroundings of the water. Their motion scarcely affected the volume of the water. A quantity of mechanical work, measured as force × distance in the surroundings, that does not change the volume of the water, is said to be isochoric. Such work reaches the system only as friction, through microscopic modes, and is irreversible. It does not count as thermodynamic work. The energy supplied by the fall of the weight passed into the water as heat. | 0 | Theoretical and Fundamental Chemistry |
Photosynthetic prokaryotic organisms that produced O as a waste product lived long before the first build-up of free oxygen in the atmosphere, perhaps as early as 3.5 billion years ago. The oxygen they produced would have been rapidly removed from the oceans by weathering of reducing minerals, most notably iron. This rusting led to the deposition of iron oxide on the ocean floor, forming banded iron formations. Thus, the oceans rusted and turned red. Oxygen only began to persist in the atmosphere in small quantities about 50 million years before the start of the Great Oxygenation Event. | 0 | Theoretical and Fundamental Chemistry |
As the chemicals being separated may be colourless, several methods exist to visualise the spots:
* Placing the plate under blacklight (366 nm light) makes fluorescent compounds glow
* TLC plates containing a small amount of fluorescent compound (usually manganese-activated zinc silicate) in the adsorbent layer allow for visualisation of some compounds under UV-C light (254 nm). The adsorbent layer will fluoresce light-green, while spots containing compounds that absorb UV-C light will not.
* Placing the plate in a container filled with iodine vapours temporarily stains the spots. They typically become a yellow or brown colour.
* The TLC plate can either be dipped in or sprayed with a stain and sometimes heated depending on the stain used. Many stains exist for a large range of chemical moieties but some examples include:
** Potassium permanganate (no heating, for oxidisable groups)
** Ninhydrin (heating, amines and amino-acids)
** Acidic vanillin (heating, general reagent)
** Phosphomolybdic acid (no heating, general reagent)
* In the case of lipids, the chromatogram may be transferred to a polyvinylidene fluoride membrane and then subjected to further analysis, for example, mass spectrometry. This technique is known as far-eastern blot. | 0 | Theoretical and Fundamental Chemistry |
Asphalt made with vegetable oil based binders was patented by Colas SA in France in 2004.
A number of homeowners seeking an environmentally friendly alternative to asphalt for paving have experimented with waste vegetable oil as a binder for driveways and parking areas in single-family applications. The earliest known test occurred in 2002 in Ohio, where the homeowner combined waste vegetable oil with dry aggregate to create a low-cost and less polluting paving material for his 200-foot driveway. After five years, he reports the driveway is performing as well or better than petroleum-based materials.
Shell Oil Company paved two public roads in Norway in 2007 with vegetable-oil-based asphalt. Results of this study are still premature.
[http://www.halik.biz HALIK Asphalts LTD] from Israel has been experimenting with recycled and secondary road building since 2003. The company is using various wastes such as vegetable fats & oils, wax and thermoplastic elastomers to build and repair roads. The results reported are so far satisfying.
On October 6, 2010, a bicycle path in Des Moines, Iowa, was paved with bio-oil based asphalt through a partnership between Iowa State University, the City of Des Moines, and [http://www.avellobioenergy.com/ Avello Bioenergy] Inc. Research is being conducted on the asphalt mixture, derived from plants and trees to replace petroleum-based mixes.
Bioasphalt is a registered trademark of Avello Bioenergy Inc.
Dr. Elham H. Fini, at North Carolina A&T University, has been spearheading research that has successfully produced bio asphalt from swine manure.
Since November 2014 the Dutch Wageningen University & Research centre is running a pilot in the Dutch province of Zeeland with bioasphalt in which the binder of bitumen was substituted by lignin.
In 2015, French researchers published their results about the usage of microalgaes as a source of asphalt binding material. | 0 | Theoretical and Fundamental Chemistry |
Initially traffic was slow and very sparse, but, as early as 1856, a newspaper said, "The cart was near to the right hand kerb. According to the rules of the road, it should have been on the left side. In turning sharp round a right-hand corner, a driver should keep away to the opposite side." That rule was codified when the first Highway Code was written in 1936. | 0 | Theoretical and Fundamental Chemistry |
Aside from the academic world, during all these years, George Hammond, "made many public speeches on controversial themes, both political (e.g., the invasion of Cambodia, delivered in 1971 at a public rally on Caltechs Olive Walk) and scientific (e.g., the future of chemistry)" Many of these controversial speeches affected his career negatively. For example, after his speech at Olive Walk, president Richard Nixons administration removed his name from nomination for a major NSF post. Nevertheless, he did not back down and continued to criticize the government, and not limiting to delivering speeches, he wrote a letter to the editor of a newspaper saying: “A June 30 front-page article describes the potential bonanza in arms sales to new members as the North Atlantic Treaty Organization expands. I was favorably inclined toward expansion because of my naive assumption that bringing most of the nations of Europe and North America together as a cooperating group would decrease the likelihood of war. I cannot believe this will be the case if a prerequisite for entry is that countries buy new armaments from present members. At whom will the guns be aimed? Russia? Then we will probably re-create the cold war." The way this excerpt was written says many things about George Hammond, starting with his passionate character. Hammond fought for everything he believed in. He cared about his nation and he was also a little reckless about the consequences he could suffer for defying the government. Also, in the excerpt, a sarcastic side of Hammond can be perceived, a man of strong character with the ability to recognize when he is wrong. | 0 | Theoretical and Fundamental Chemistry |
Sewage liquor is run into deep tanks with diffuser grid aeration systems that are attached to the floor. These are like the diffused airstone used in tropical fish tanks but on a much larger scale. Air is pumped through the blocks and the curtain of bubbles formed both oxygenates the liquor and also provides the necessary mixing action. Where capacity is limited or the sewage is unusually strong or difficult to treat, oxygen may be used instead of air. Typically, the air is generated by some type of air blower. | 1 | Applied and Interdisciplinary Chemistry |
In recent years, expression vectors have been used to introduce specific genes into plants and animals to produce transgenic organisms, for example in agriculture it is used to produce transgenic plants. Expression vectors have been used to introduce a vitamin A precursor, beta-carotene, into rice plants. This product is called golden rice. This process has also been used to introduce a gene into plants that produces an insecticide, called Bacillus thuringiensis toxin or Bt toxin which reduces the need for farmers to apply insecticides since it is produced by the modified organism. In addition expression vectors are used to extend the ripeness of tomatoes by altering the plant so that it produces less of the chemical that causes the tomatoes to rot. There have been controversies over using expression vectors to modify crops due to the fact that there might be unknown health risks, possibilities of companies patenting certain genetically modified food crops, and ethical concerns. Nevertheless, this technique is still being used and heavily researched.
Transgenic animals have also been produced to study animal biochemical processes and human diseases, or used to produce pharmaceuticals and other proteins. They may also be engineered to have advantageous or useful traits. Green fluorescent protein is sometimes used as tags which results in animal that can fluoresce, and this have been exploited commercially to produce the fluorescent GloFish. | 1 | Applied and Interdisciplinary Chemistry |
Marinobufagenin (marinobufagin) is a cardiotonic bufadienolide steroid. It can be found in the plasma and urine of human subjects with myocardial infarction, kidney failure, and heart failure. It is also secreted by the toad Bufo rubescens and other related species such as Bufo marinus. It is a vasoconstrictor with effects similar to digitalis. | 1 | Applied and Interdisciplinary Chemistry |
Borate anions (and functional groups) consist of trigonal planar and/or tetrahedral structural units, joined together via shared oxygen atoms (corners) or atom pairs (edges) into larger clusters so as to construct various ions such as , , , , , etc. These anions may be cyclic or linear in structure, and can further polymerize into infinite chains, layers, and tridimensional frameworks. The terminal (unshared) oxygen atoms in the borate anions may be capped with hydrogen atoms () or may carry a negative charge ().
The planar units may be stacked in the crystal lattice so as to have π-conjugated molecular orbitals, which often results in useful optical properties such as strong harmonics generation, birefringence, and UV transmission.
Polymeric borate anions may have linear chains of 2, 3 or 4 trigonal structural units, each sharing oxygen atoms with adjacent unit(s). as in lithium metaborate|, contain chains of trigonal structural units. Other anions contain cycles; for instance, Sodium metaborate| and contain the cyclic ion, consisting of a six-membered ring of alternating boron and oxygen atoms with one extra oxygen atom attached to each boron atom.
The thermal expansion of crystalline borates is dominated by the fact that and polyhedra and rigid groups consisting of these polyhedra practically do not change their configuration and size upon heating, but sometimes rotate like hinges, which results in greatly anisotropic thermal expansion including linear negative expansion. | 0 | Theoretical and Fundamental Chemistry |
Isotope-ratio mass spectrometry (IRMS) is a specialization of mass spectrometry, in which mass spectrometric methods are used to measure the relative abundance of isotopes in a given sample.
This technique has two different applications in the earth and environmental sciences. The analysis of stable isotopes is normally concerned with measuring isotopic variations arising from mass-dependent isotopic fractionation in natural systems. On the other hand, radiogenic isotope analysis involves measuring the abundances of decay-products of natural radioactivity, and is used in most long-lived radiometric dating methods. | 0 | Theoretical and Fundamental Chemistry |
Amorphous phases are important constituents of thin films. Thin films are solid layers of a few nanometres to tens of micrometres thickness that are deposited onto a substrate. So-called structure zone models were developed to describe the microstructure of thin films as a function of the homologous temperature (T), which is the ratio of deposition temperature to melting temperature. According to these models, a necessary condition for the occurrence of amorphous phases is that (T) has to be smaller than 0.3. The deposition temperature must be below 30% of the melting temperature. | 0 | Theoretical and Fundamental Chemistry |
The weighted sum of partial specific volumes of a mixture or solution is an inverse of density of the mixture namely the specific volume of the mixture. | 1 | Applied and Interdisciplinary Chemistry |
Levonorgestrel-containing emergency contraception is available over-the-counter in some countries, such as the United States. On some college campuses, Plan B is available from vending machines.
A policy update in 2015, required all pharmacies, clinics, and emergency departments run by Indian Health Services (for Native Americans) to have Plan B One-Step in stock, to distribute it to any woman (or her representative) who asked for it without a prescription, age verification, registration or any other requirement, to provide orientation training to all staff regarding the medication, to provide unbiased and medically accurate information about emergency contraception, and to make someone available at all times to distribute the pill in case the primary staffer objected to providing it on religious or moral grounds. | 0 | Theoretical and Fundamental Chemistry |
Eddy saturation and eddy compensation are phenomena found in the Southern Ocean. Both are limiting processes where eddy activity increases due to the momentum of strong westerlies, and hence do not enhance their respective mean currents. Where eddy saturations impacts the Antarctic Circumpolar Current (ACC), eddy compensation influences the associated Meridional Overturning Circulation (MOC).
In recent decades wind stresses in the Southern Ocean have increased partly due to greenhouse gases and ozone depletion in the stratosphere. Because the ACC and MOC play an important role in the global climate; affecting the stratification of the ocean, uptake of heat, carbon dioxide and other passive tracers. Addressing how these increased zonal winds affect the MOC and the ACC will help understand whether the uptakes will change in the future, which could have serious impact on the carbon cycle. This remains an important and critical research topic. | 1 | Applied and Interdisciplinary Chemistry |
For an isothermal gaseous star, the pressure is due to the kinetic pressure and radiation pressure
whe
* is the density
* is the Boltzmann constant
* is the mean molecular weight
* is the mass of the proton
* is the temperature of the star
* is the Stefan–Boltzmann constant
* is the speed of light
The equation for equilibrium of the star requires a balance between the pressure force and gravitational force
where is the radius measured from the center and is the gravitational constant. The equation is re-written as
Introducing the transformation
where is the central density of the star, leads to
The boundary conditions are
For , the solution goes like | 1 | Applied and Interdisciplinary Chemistry |
Metanil Yellow (Acid Yellow 36) is a dye of the azo class. In analytical chemistry, it is used as a pH indicator and it has a color change from red to yellow between pH 1.2 and 3.2.
Although it is an unpermitted food dye, because of its bright yellow color, Metanil Yellow has been used as an adulterant in turmeric powder and arhar dal, particularly in India.
Animal studies have suggested that Metanil Yellow is neurotoxic and hepatotoxic. | 0 | Theoretical and Fundamental Chemistry |
There are three stages in the post-Soviet history of Ural metallurgy:
* 1991-1994 - adaptation to market conditions, search for sources of raw materials and sales markets, accumulation of working capital.
* 1994-2003 - formation of vertically integrated companies and their development.
* since 2003 - modernization of enterprises within vertically integrated companies.
Restructuring and the transition to market conditions led to a 2-fold reduction in production at the Ural metallurgical enterprises. The Nizhniy Tagil and Orsko-Khalilovsky plants went bankrupt. Some enterprises went through bankruptcy proceedings several times. The privatization and corporatization of the enterprises of the Ural metallurgy were completed in 1992-1994. In the late 1990s - early 2000s, vertically integrated structures began to form around large enterprises, including all stages of a closed technological cycle. In addition to the Magnitogorsk Metallurgical Combine, the MMK Group includes: the Magnitogorsk Hardware, Metallurgical, and Calibration Plants; the Mechel group united the Chelyabinsk Metallurgical Plant, Yuzhuralnickel, Beloretsk Metallurgical Plant, Izhstal, and Korshunovsky Mining and Processing Plant; NTMK and Kachkanarsky Mining and Processing Plant, together with the West Siberian and Kuznetsk metallurgical plants, entered Evraz-holding; Chelyabinsk Pipe Rolling Plant and Pervouralsk Novotrubny Plants were merged into the ChTPZ Group; copper smelters became part of UMMC and Russian Copper Company; aluminum - Rusal and SUAL, united in 2007.
The main directions of development of ferrous metallurgy in the Urals in the market conditions were the reconstruction of blast furnaces with optimization of the profile and process control systems, the replacement of open-hearth furnaces with oxygen converters and electric furnaces, the widespread introduction of out-of-furnace steel processing, evacuation of steel before casting, as well as an increase in the share of continuous casting of steel. From 1985 to 2000, the share of the Ural steel smelted by the open-hearth method decreased from 78.2% to 46.9%; the share of converter steel in the same period increased from 15% to 46.9%, the share of continuously cast steel - from 1.2% to 33.1%. The share of electric steel in the same period remained at the level of about 6-7%.
After the reconstruction and launch of new capacities, about 85% of the Ural steel was produced at the 4 largest metallurgical plants: MMK (39.1% of the total steel volume in 2006), NTMK (17.6%), Mechel (15.2% ), and Ural steel (11.4%).
In the late 20th - early 21st century, the Ural metallurgical plants are developing taking into account the interests of holding structures. The main directions of development are the automation of production and the minimization of costs. Key investment development projects are the reconstruction of the converter shop and the construction of a pulverized coal injection unit at NTMK in 2010-2012, the launch in 2010 of the "Vysota 239" large-diameter pipe production shop at ChTPZ, as well as the launch in 2009 of Mill-5000 at MMK, which supplies workpieces including for the new ChelPipe workshop. By 2014, the share of Ural steel processed by the out-of-furnace method and poured at the continuous casting machine was brought to 100%.
In 2008, the Ural plants produced 43.1% of all-Russian pig iron, 43.4% of steel, 43.4% of rolled products, 46.4% of pipes, 47.9% of hardware, 72.8% of ferroalloys, about 80% of bauxite, 60% of alumina, 36% of refined copper, 100% of titanium and magnesium alloys, 64% of zinc, 15% of lead, and 8% of aluminum. The largest contribution to the metallurgy of the region is made by enterprises of the Chelyabinsk and Sverdlovsk Oblasts. As of 2013, the contribution of the Ural enterprises was estimated at 38% of steel and rolled products and about 50% of steel pipes. | 1 | Applied and Interdisciplinary Chemistry |
The Akula is a Dunkleosteus like creature. They have 3 sets of jaws and is the apex predator of the Pandoran ocean. They are introduced in Avatar: The Way of Water, where Jakes son Loak fights of one after he is stranded in the ocean, before being saved by Payakan. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, the rate equation (also known as the rate law or empirical differential rate equation) is an empirical differential mathematical expression for the reaction rate of a given reaction in terms of concentrations of chemical species and constant parameters (normally rate coefficients and partial orders of reaction) only. For many reactions, the initial rate is given by a power law such as
where and are the molar concentrations of the species and usually in moles per liter (molarity, ). The exponents and are the partial orders of reaction for and and the overall reaction order is the sum of the exponents. These are often positive integers, but they may also be zero, fractional, or negative. The order of reaction is a number which quantifies the degree to which the rate of a chemical reaction depends on concentrations of the reactants. In other words, the order of reaction is the exponent to which the concentration of a particular reactant is raised. The constant is the reaction rate constant or rate coefficient and at very few places velocity constant or specific rate of reaction. Its value may depend on conditions such as temperature, ionic strength, surface area of an adsorbent, or light irradiation. If the reaction goes to completion, the rate equation for the reaction rate applies throughout the course of the reaction.
Elementary (single-step) reactions and reaction steps have reaction orders equal to the stoichiometric coefficients for each reactant. The overall reaction order, i.e. the sum of stoichiometric coefficients of reactants, is always equal to the molecularity of the elementary reaction. However, complex (multi-step) reactions may or may not have reaction orders equal to their stoichiometric coefficients. This implies that the order and the rate equation of a given reaction cannot be reliably deduced from the stoichiometry and must be determined experimentally, since an unknown reaction mechanism could be either elementary or complex. When the experimental rate equation has been determined, it is often of use for deduction of the reaction mechanism.
The rate equation of a reaction with an assumed multi-step mechanism can often be derived theoretically using quasi-steady state assumptions from the underlying elementary reactions, and compared with the experimental rate equation as a test of the assumed mechanism. The equation may involve a fractional order, and may depend on the concentration of an intermediate species.
A reaction can also have an undefined reaction order with respect to a reactant if the rate is not simply proportional to some power of the concentration of that reactant; for example, one cannot talk about reaction order in the rate equation for a bimolecular reaction between adsorbed molecules: | 0 | Theoretical and Fundamental Chemistry |
Facultative anaerobes are able to grow in both the presence and absence of oxygen due to the expression of both aerobic and anaerobic respiratory chains using either oxygen or an alternative electron acceptor. For example, in the absence of oxygen, E. coli can use fumarate, nitrate, nitrite, dimethyl sulfoxide, or trimethylamine oxide as an electron acceptor. This flexibility allows facultative anaerobes to survive in a number of environments, and in environments with frequently changing conditions.
Several species of protists use a facultative anaerobic metabolism to enhance their ATP production, and some can produce dihydrogen through this process. | 1 | Applied and Interdisciplinary Chemistry |
In conventional seasoning, the oil or fat is converted into a hard surface at or above the high temperatures used for cooking, analogous to the reaction of drying oils. When oils or fats are heated, multiple degradation reactions occur, including decomposition, autoxidation, thermal oxidation, polymerization, and cyclization.
Often cookware's seasoning is uneven, and over time it will spread to the whole item. Heating the cookware (such as in a hot oven or on a stovetop) facilitates the oxidation of the iron; the fats and/or oils protect the metal from contact with the air during the reaction, which would otherwise cause rust to form. Some cast iron users advocate heating the cookware slightly before applying the fat or oil to ensure it is completely dry.
The seasoned surface is hydrophobic and highly attractive to oils and fats used for cooking (oleophilic). These form a layer that prevents foods, which typically contain water, from touching and cooking on to the hydrophilic metallic cooking surface underneath.
The seasoned surface will deteriorate at the temperature where the coating breaks down. This is typically higher than the smoke point of the original oils and fats used to season the cookware. Thus old seasoning can be removed at a sufficiently high temperature (~500 °C), as found in oven self-cleaning cycles. | 0 | Theoretical and Fundamental Chemistry |
The smelting of gold began sometime around 6000 – 3000 BC. According to one source the technique began to be in use in Mesopotamia or Syria. In ancient Greece, Heraclitus wrote on the subject.
According to de Lecerda and Salomons (1997) mercury was first in use for extraction at about 1000 BC, according to Meech and others (1998), mercury was used in obtaining gold until the latter period of the first millennia.
A technique known to Pliny the Elder was extraction by way of crushing, washing, and then applying heat, with the resultant material powdered. | 1 | Applied and Interdisciplinary Chemistry |
That is, the change in the internal energy of the substance within a volume is the negative of the amount carried out of the volume by the flow of material across the boundary plus the work done compressing the material on the boundary minus the flow of heat out through the boundary. More generally, it is possible to incorporate source terms. | 0 | Theoretical and Fundamental Chemistry |
Because chemical diffusion is a net transport process, the system in which it takes place is not an equilibrium system (i.e. it is not at rest yet). Many results in classical thermodynamics are not easily applied to non-equilibrium systems. However, there sometimes occur so-called quasi-steady states, where the diffusion process does not change in time, where classical results may locally apply. As the name suggests, this process is a not a true equilibrium since the system is still evolving.
Non-equilibrium fluid systems can be successfully modeled with Landau-Lifshitz fluctuating hydrodynamics. In this theoretical framework, diffusion is due to fluctuations whose dimensions range from the molecular scale to the macroscopic scale.
Chemical diffusion increases the entropy of a system, i.e. diffusion is a spontaneous and irreversible process. Particles can spread out by diffusion, but will not spontaneously re-order themselves (absent changes to the system, assuming no creation of new chemical bonds, and absent external forces acting on the particle). | 1 | Applied and Interdisciplinary Chemistry |
Several molecular biology studies during the 1950s indicated that RNA played some kind of role in protein synthesis, but that role was not clearly understood. For instance, in one of the earliest reports, Jacques Monod and his team showed that RNA synthesis was necessary for protein synthesis, specifically during the production of the enzyme β-galactosidase in the bacterium E. coli. Arthur Pardee also found similar RNA accumulation in 1954. In 1953, Alfred Hershey, June Dixon, and Martha Chase described a certain cytosine-containing DNA (indicating it was RNA) that disappeared quickly after its synthesis in E. coli. In hindsight, this may have been one of the first observations of the existence of mRNA but it was not recognized at the time as such.
The idea of mRNA was first conceived by Sydney Brenner and Francis Crick on 15 April 1960 at Kings College, Cambridge, while François Jacob was telling them about a recent experiment conducted by Arthur Pardee, himself, and Monod (the so-called PaJaMo experiment, which did not prove mRNA existed but suggested the possibility of its existence). With Cricks encouragement, Brenner and Jacob immediately set out to test this new hypothesis, and they contacted Matthew Meselson at the California Institute of Technology for assistance. During the summer of 1960, Brenner, Jacob, and Meselson conducted an experiment in Meselson's laboratory at Caltech which was the first to prove the existence of mRNA. That fall, Jacob and Monod coined the name "messenger RNA" and developed the first theoretical framework to explain its function.
In February 1961, James Watson revealed that his Harvard-based research group had been right behind them with a series of experiments whose results pointed in roughly the same direction. Brenner and the others agreed to Watsons request to delay publication of their research findings. As a result, the Brenner and Watson articles were published simultaneously in the same issue of Nature in May 1961, while that same month, Jacob and Monod published their theoretical framework for mRNA in the Journal of Molecular Biology'. | 1 | Applied and Interdisciplinary Chemistry |
Tissue engineered heart valves (TEHV) offer a new and advancing proposed treatment of creating a living heart valve for people who are in need of either a full or partial heart valve replacement. Currently, there are over a quarter of a million prosthetic heart valves implanted annually, and the number of patients requiring replacement surgeries is only suspected to rise and even triple over the next fifty years. While current treatments offered such as mechanical valves or biological valves are not deleterious to ones health, they both have their own limitations in that mechanical valves necessitate the lifelong use of anticoagulants while biological valves are susceptible to structural degradation and reoperation. Thus, in situ (in its original position or place) tissue engineering of heart valves serves as a novel approach that explores the use creating a living heart valve composed of the hosts own cells that is capable of growing, adapting, and interacting within the human body's biological system.
Research has not yet reached the stage of clinical trials. | 1 | Applied and Interdisciplinary Chemistry |
eIF-2 - eIF-2 kinase - electrochemical potential - electron - electron capture - electron configuration - electron microscopy - electron shell - electron transport chain - electron volt - electronegativity - electrophile - electrophoresis - electrophysiology - element - element symbol - ELISA - ELISPOT - embryo - embryonal development - emulsion - endergonic reaction - endodermis - endomembrane system - endoplasmic reticulum - endothelin receptor - endothelin-1 - energy decomposition cycles - energy level - enhancer - enkephalin - enthalpy - entomology - entropy - env gene product - environmental chemistry - enzyme - epidermal growth factor - epidermal growth factor receptor - epidiorite - epigenetics - epinephrine - equine gonadotropin - erbA gene - erbB gene - erbB-2 gene - erbB-2 receptor - erythropoietin - erythropoietin receptor - essential amino acid - ester - estradiol receptor - estrogen receptor - ethanol - ether - eukaryote - evolution - evolutionary biology - evolutionary developmental biology - evolutionary tree - excretion - exergonic reaction - exon - extracellular matrix protein - eye proteins | 1 | Applied and Interdisciplinary Chemistry |
Studies have shown that deletion of KAP1 in mice before gastrulation results in death (implicating it as a necessary protein for proliferation) while deletion in adult mice results in increased anxiety and stress-induced alterations in learning and memory. KAP1 has been shown to participate in the maintenance of pluripotency of embryonic stem cells and to promote and inhibit cellular differentiation of adult cell lines. Increased levels of KAP1 have been found in liver, gastric, breast, lung, and prostate cancers as well, indicating that it may play an important role in tumor cell proliferation (possibly by inhibiting apoptosis). | 1 | Applied and Interdisciplinary Chemistry |
A standard coinduction regimen for an adult might consist of a benzodiazepine sedative amnesic such as midazolam, followed by an opioid analgesic with further sedating properties such as fentanyl which has a fast onset, then an intravenous induction agent: propofol. A muscle relaxant such as atracurium would be administered after this, though this would not strictly be a part of coinduction. For a child on the other hand, a commonly used regimen would be fentanyl, ketamin and rocuronium. In all cases the choice of agents would be tailored to the situation; for a neonatal intubation the aforementioned regimes would be inappropriate as sedation and especially amnesia are less important. Fentanyl alone would be used, followed by the short-action muscle relaxant suxamethonium: coinduction is typically not used in neonatal anesthesia. | 1 | Applied and Interdisciplinary Chemistry |
The herpesviruses, Kaposis sarcoma-associated herpesvirus and Epstein-Barr virus, are believed to cause cancer in humans, such as Kaposis sarcoma, Burkitt's lymphoma, and nasopharyngeal carcinoma. Although genes have been identified in these viruses that cause transformation, the manner in which the virus transforms and replicates the host cell is not understood. | 1 | Applied and Interdisciplinary Chemistry |
These angles are best construed to mean the angles observed (measured) for a given system, and not an historically observed range in values (e.g., as in the range of the original Bürgi–Dunitz aminoketones), or an idealized value computed for a particular system (such as the = 0° for hydride addition to formaldehyde). That is, the and angles of the hydride-formadehyde system have one pair of values, while the angles observed for other systems—combinations of nucelophile and electrophile, in combination with catalyst and other variables that define the experimental condition, including whether the reaction is in solutio or otherwise—are fully expected (and are reported) to vary, at least somewhat, from the theoretical, symmetric hydride-formaldehyde case.
A stated convention for is that it is positive (>0°) when it deviates in direction:
* away from the larger substituent attached to the electrophilic center,
* away from the more electron-rich substituent (where these two and other factors can be in a complex competition, see below);
hence, as noted, for reaction of a simple nucleophile with a symmetrically substituted carbonyl (R = R, or other symmetric planar electrophile) is expected to be 0° in vacuo or in solutio', e.g., as in the case of the computed and experimental addition of hydride (H) to formaldehyde (HC=O). | 0 | Theoretical and Fundamental Chemistry |
Thermodynamics is principally based on a set of four laws which are universally valid when applied to systems that fall within the constraints implied by each. In the various theoretical descriptions of thermodynamics these laws may be expressed in seemingly differing forms, but the most prominent formulations are the following. | 0 | Theoretical and Fundamental Chemistry |
Capping is a three-step process that utilizes the enzymes RNA triphosphatase, guanylyltransferase, and methyltransferase. Through a series of three steps, the cap is added to the first nucleotides 5 hydroxyl group of the growing mRNA strand while transcription is still occurring. First, RNA 5 triphosphatase hydrolyzes the 5 triphosphate group to make diphosphate-RNA. Then, the addition of GMP by guanylyltransferase produces the guanosine cap. Last, RNA methyltransferase transfers a methyl group to the guanosine cap to yield 7-methylguanosine cap that is attached to the 5' end of the transcript. These three enzymes, collectively called the capping enzymes, are only able to catalyze their respective reactions when attached to RNA polymerase II, an enzyme necessary for the transcription of DNA into pre-mRNA. When this complex of RNA polymerase II and the capping enzymes is achieved, the capping enzymes are able to add the cap to the mRNA while it is produced by RNA polymerase II. | 1 | Applied and Interdisciplinary Chemistry |
In thermodynamics and fluid mechanics, the compressibility (also known as the coefficient of compressibility or, if the temperature is held constant, the isothermal compressibility) is a measure of the instantaneous relative volume change of a fluid or solid as a response to a pressure (or mean stress) change. In its simple form, the compressibility (denoted in some fields) may be expressed as
where is volume and is pressure. The choice to define compressibility as the negative of the fraction makes compressibility positive in the (usual) case that an increase in pressure induces a reduction in volume. The reciprocal of compressibility at fixed temperature is called the isothermal bulk modulus. | 1 | Applied and Interdisciplinary Chemistry |
James N. Pitts Jr. (January 10, 1921 – June 19, 2014) was an American chemist and researcher known for his work in the fields of photochemistry and atmospheric chemistry. Pitts was a pioneer in the study of smog and air pollution, especially in Los Angeles County. Pitts co-founded the Statewide Air Pollution Research Center at the University of California, Riverside in 1961 and served as the center's director from 1970 to 1988. He authored more than 400 scientific publications and four books on the subjects, especially smog.
Pitts research formed the basis for Californias air quality laws. According to the chair of the Air Resources Board, Mary Nichols, "Jim Pitts was probably the single person most responsible for the understanding of what strategies we need to clean up Southern California's air...He was able to explain all of this in English to policymakers so that they would be able to accept that it was going to take extensive and difficult actions to control emissions." He often invited state and federal officials to his smog chamber at UC Irvine, including Jerry Brown and Ronald Reagan, to demonstrate the effects of smog and air pollution. In a common demonstration, Pitts would fill an Erlenmeyer flask with ozone and then twist a slice of lemon onto the flask. The ensuing chemical reaction, which quickly produced a fog, demonstrated the formation of smog in the atmosphere.
Pitts refused funding from industry groups, which increased his center's credibility. He was the recipient of numerous awards and recognitions from the California State Assembly, the United States Congress, the Coalition for Clean Air, the South Coast Air Quality Management District, and the California state air board.
Pitts was born on January 10, 1921, in Salt Lake City, Utah, to Esther (née Bengtson) and James N. Pitts. The family moved to West Los Angeles when he was just six months old. A high school teacher sparked his interest in chemistry during his junior year.
Pitts enrolled as a chemistry student at University of California, Los Angeles (UCLA) in 1939. He left during World War II, joining a group of young scientists who conducted classified chemical warfare field tests. Their work led to the development of more effective gas mask for Allied forces during the war. He returned to UCLA, where he received a bachelor's degree in chemistry in 1945 and a doctorate in 1949. Pitts initially worked as a faculty member of Northwestern University. He was at the time married to a woman by the name of Nancy Ann Quirt. James and Nancy had three daughters Linda, Christie and Beckie.
Pitts was hired as a founding professor at UC Riverside in 1954.
Pitts married his second wife, UC Irvine chemist and professor Barbara Finlayson-Pitts in 1970. He followed her to the University of California, Irvine in 1994, where the two collaborated of research and co-authored books and other publications.
James Pitts died of natural causes at his home in Irvine, California, on June 19, 2014, at the age of 93. He was survived by his wife, Barbara Finlayson-Pitts, and three daughters, Linda Lee, Christie Hoffman and Beckie St. George. He was also survived by five grandchildren Kristin Cohn, Brianna Hoffman, Trevin Hoffman, Mallory St George and Ryan Giordano. His great-grandchildren include Brandon, Kyle, Austin and Riley. | 0 | Theoretical and Fundamental Chemistry |
The above equations can also be written using quantities related to the number of nuclide particles in a sample;
* The activity: .
* The amount of substance: .
* The mass: .
where = is the Avogadro constant, is the molar mass of the substance in kg/mol, and the amount of the substance is in moles. | 0 | Theoretical and Fundamental Chemistry |
Bay muds originate from two generalized sources. First alluvial deposits of clays, silts and sand occur from streams tributary to a given bay. The extent of these unconsolidated interglacial deposits typically ranges throughout a given bay to the extent of the historical perimeter marshlands. Second, in periods of high glaciation, deposits of silts, sands and organic plus inorganic detritus (e.g. decomposition of estuarine diatoms) may form a separate distinct layer. Thus bay muds are important time records of glacial activity and streamflow throughout the Quaternary period.
Some depositional formation is quite recent, such as in the case of Florida Bay, where much of the bay mud has accumulated since 2000 BCE, and consists of primarily decayed organic material. In the case of Florida Bay these bay muds can accrete as much as 0.5 to 2.0 centimeters per annum, although the dynamic equilibrium of erosion, wave action redistribution and deposition complicate the net rate of layer growth. In the case of the Bristol Channel in the United Kingdom bay, mud formation has been occurring at least since the Eemian Stage (known as the Sangamonian Stage in North America), or about 130,000 years ago. In other cases such as with San Francisco Bay, deposition has been interrupted by sea-level changes, and strata of vastly different vintages are found. In the San Francisco Bay Area, these are called Young bay mud and Older bay mud by geologists. Human activities can also affect deposition; close to half of the Young Bay Mud in San Francisco Bay was placed in the period 1855–1865, as a result of placer mining in the Sierra Nevada foothills. | 1 | Applied and Interdisciplinary Chemistry |
Pharmacometabolomics may decrease the burden on the healthcare system by better gauging the correct choice of treatment drug and dosage in order to optimize the response of a patient to a treatment. Hopefully, this approach will also ultimately limit the number of adverse drug reactions (ADRs) associated with many treatment regimens. Overall, physicians would be better able to apply more personalized, and potentially more effective, treatments to their patients. It is important to consider, however, that the processing and analysis of the patient samples takes time, resulting in delayed treatment.
Another concern about the application of pharmacometabolomics analyses to individual patient care, is deciding who should and who should not receive this in-depth, personalized treatment protocol. Certain diseases and stages of disease would have to be classified according to their requirement of such a treatment plan, but there are no criteria for this classification. Furthermore, not all hospitals and treatment institutes can afford the equipment to process and analyze patient samples on site, but sending out samples takes time and ultimately delays treatment.
Health insurance coverage of such procedures may also be an issue. Certain insurance companies may discriminate against the application of this type of sample analysis and metabolite characterization. Furthermore, there would have to be regulations put in place to ensure that there was no discrimination by insurance companies against the metabolic profiles of individual patients (“high metabolizers” vs. risky “low metabolizers”). | 1 | Applied and Interdisciplinary Chemistry |
The boundary between one grain and its neighbour (grain boundary) is a defect in the crystal structure and so it is associated with a certain amount of energy. As a result, there is a thermodynamic driving force for the total area of boundary to be reduced. If the grain size increases, accompanied by a reduction in the actual number of grains per volume, then the total area of grain boundary will be reduced.
In the classic theory, the local velocity of a grain boundary at any point is proportional to the local curvature of the grain boundary, i.e.:
where is the velocity of grain boundary, is grain boundary mobility (generally depends on orientation of two grains), is the grain boundary energy and is the sum of the two principal surface curvatures. For example, shrinkage velocity of a spherical grain embedded inside another grain is
where is radius of the sphere. This driving pressure is very similar in nature to the Laplace pressure that occurs in foams.
In comparison to phase transformations the energy available to drive grain growth is very low and so it tends to occur at much slower rates and is easily slowed by the presence of second phase particles or solute atoms in the structure.
Recently, in contrast to the classic linear relation between grain boundary velocity and curvature, grain boundary velocity and curvature are observed to be not correlated in Ni polycrystals, which conflicting results has been revealed and be theoretically interpreted by a general model of grain boundary (GB) migration in the previous literature. According to the general GB migration model, the classical linear relation can only be used in a specical case. | 1 | Applied and Interdisciplinary Chemistry |
Numerous methods exist to synthesize phenylboronic acid. One of the most common synthesis uses phenylmagnesium bromide and trimethyl borate to form the ester PhB(OMe), which is then hydrolyzed to the product.
:PhMgBr + B(OMe) → PhB(OMe) + MeOMgBr
:PhB(OMe) + HO → PhB(OH) + MeOH
Other routes to phenylboronic acid involve electrophilic borates to trap phenylmetal intermediates from phenyl halides or from directed ortho-metalation. Phenylsilanes and phenylstannanes transmetalate with BBr, followed by hydrolysis form phenylboronic acid. Aryl halides or triflates can be coupled with diboronyl reagents using transition metal catalysts. Aromatic C-H functionalization can also be done using transition metal catalysts. | 0 | Theoretical and Fundamental Chemistry |
* An ingredient in diesel exhaust fluid (DEF), which is 32.5% urea and 67.5% de-ionized water. DEF is sprayed into the exhaust stream of diesel vehicles to break down dangerous emissions into harmless nitrogen and water.
* A component of animal feed, providing a relatively cheap source of nitrogen to promote growth
* A non-corroding alternative to rock salt for road de-icing. It is often the main ingredient of pet friendly salt substitutes although it is less effective than traditional rock salt or calcium chloride.
* A main ingredient in hair removers such as Nair and Veet
* A browning agent in factory-produced pretzels
* An ingredient in some skin cream, moisturizers, hair conditioners, and shampoos
* A cloud seeding agent, along with other salts
* A flame-proofing agent, commonly used in dry chemical fire extinguisher charges such as the urea-potassium bicarbonate mixture
* An ingredient in many tooth whitening products
* An ingredient in dish soap
* Along with diammonium phosphate, as a yeast nutrient, for fermentation of sugars into ethanol
* A nutrient used by plankton in ocean nourishment experiments for geoengineering purposes
* As an additive to extend the working temperature and open time of hide glue
* As a solubility-enhancing and moisture-retaining additive to dye baths for textile dyeing or printing
* As an optical parametric oscillator in nonlinear optics | 0 | Theoretical and Fundamental Chemistry |
Unit Operations of Chemical Engineering, first published in 1956, is one of the oldest chemical engineering textbooks still in widespread use. The current Seventh Edition, published in 2004, continues its successful tradition of being used as a textbook in university undergraduate chemical engineering courses. It is widely used in colleges and universities throughout the world, and often referred just "McCabe-Smith-Harriott" or "MSH". | 1 | Applied and Interdisciplinary Chemistry |
Future Medicinal Chemistry is a peer-reviewed medical journal covering all aspects of medicinal chemistry, including drug discovery, pharmacology, in silico drug design, structural characterization techniques, ADME-Tox investigations, and science policy, economic and intellectual property issues. It was established in 2009 and is published by Future Science. The editors-in-chief are Iwao Ojima (The State University of New York at Stony Brook) and Jonathan Baell (Monash University). | 1 | Applied and Interdisciplinary Chemistry |
The molar gas constant (also known as the gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol or . It is the molar equivalent to the Boltzmann constant, expressed in units of energy per temperature increment per amount of substance, rather than energy per temperature increment per particle. The constant is also a combination of the constants from Boyles law, Charless law, Avogadros law, and Gay-Lussacs law. It is a physical constant that is featured in many fundamental equations in the physical sciences, such as the ideal gas law, the Arrhenius equation, and the Nernst equation.
The gas constant is the constant of proportionality that relates the energy scale in physics to the temperature scale and the scale used for amount of substance. Thus, the value of the gas constant ultimately derives from historical decisions and accidents in the setting of units of energy, temperature and amount of substance. The Boltzmann constant and the Avogadro constant were similarly determined, which separately relate energy to temperature and particle count to amount of substance.
The gas constant R is defined as the Avogadro constant N multiplied by the Boltzmann constant k (or k):
Since the 2019 redefinition of SI base units, both N and k are defined with exact numerical values when expressed in SI units. As a consequence, the SI value of the molar gas constant is exactly .
Some have suggested that it might be appropriate to name the symbol R the Regnault constant in honour of the French chemist Henri Victor Regnault, whose accurate experimental data were used to calculate the early value of the constant. However, the origin of the letter R to represent the constant is elusive. The universal gas constant was apparently introduced independently by Clausius' student, A.F. Horstmann (1873) and Dmitri Mendeleev who reported it first on Sep. 12, 1874. Using his extensive measurements of the properties of gases,
Mendeleev also calculated it with high precision, within 0.3% of its modern value.
The gas constant occurs in the ideal gas law:
where P is the absolute pressure, V is the volume of gas, n is the amount of substance, m is the mass, and T is the thermodynamic temperature. R is the mass-specific gas constant. The gas constant is expressed in the same unit as are molar entropy and molar heat. | 0 | Theoretical and Fundamental Chemistry |
To understand the prospects for life to exist elsewhere in the universe, astrobiologists are interested in measuring the chemical composition of extraplanetary bodies. Because of their small size and wide-ranging functionality, microfluidic devices are uniquely suited for these remote sample analyses. From an extraterrestrial sample, the organic content can be assessed using microchip capillary electrophoresis and selective fluorescent dyes. These devices are capable of detecting amino acids, peptides, fatty acids, and simple aldehydes, ketones, and thiols. These analyses coupled together could allow powerful detection of the key components of life, and hopefully inform our search for functioning extraterrestrial life. | 1 | Applied and Interdisciplinary Chemistry |
Typical photovoltaics work by creating a p–n junction near the front surface of a thin semiconductor material. When photons above the bandgap energy of the material hit atoms within the bulk lower layer, below the junction, an electron is photoexcited and becomes free of its atom. The junction creates an electric field that accelerates the electron forward within the cell until it passes the junction and is free to move to the thin electrodes patterned on the surface. Connecting a wire from the front to the rear allows the electrons to flow back into the bulk and complete the circuit.
Photons with less energy than the bandgap do not eject electrons. Photons with energy above the bandgap will eject higher-energy electrons which tend to thermalize within the material and lose their extra energy as heat. If the cell's bandgap is raised, the electrons that are emitted will have higher energy when they reach the junction and thus result in a higher voltage, but this will reduce the number of electrons emitted as more photons will be below the bandgap energy and thus generate a lower current. As electrical power is the product of voltage and current, there is a sweet spot where the total output is maximized.
Terrestrial solar radiation is typically characterized by a standard known as Air Mass 1.5, or AM1.5. This is very close to 1,000 W of energy per square meter at an apparent temperature of 5780 K. At this temperature, about half of all the energy reaching the surface is in the infrared. Based on this temperature, energy production is maximized when the bandgap is about 1.4 eV, in the near infrared. This just happens to be very close to the bandgap in doped silicon, at 1.1 eV, which makes solar PV inexpensive to produce.
This means that all of the energy in the infrared and lower, about half of AM1.5, goes to waste. There has been continuing research into cells that are made of several different layers, each with a different bandgap, and thus tuned to a different part of the solar spectrum. , cells with overall efficiencies in the range of 40% are commercially available, although they are extremely expensive and have not seen widespread use outside of specific roles like powering spacecraft, where cost is not a significant consideration. | 0 | Theoretical and Fundamental Chemistry |
Organic azides engage in useful organic reactions. The terminal nitrogen is mildly nucleophilic. Generally, nucleophiles attack the azide at the terminal nitrogen N, while electrophiles react at the internal atom N. Azides easily extrude diatomic nitrogen, a tendency that is exploited in many reactions such as the Staudinger ligation or the Curtius rearrangement.
Azides may be reduced to amines by hydrogenolysis or with a phosphine (e.g., triphenylphosphine) in the Staudinger reaction. This reaction allows azides to serve as protected -NH synthons, as illustrated by the synthesis of 1,1,1-tris(aminomethyl)ethane:
In the azide alkyne Huisgen cycloaddition, organic azides react as 1,3-dipoles, reacting with alkynes to give substituted 1,2,3-triazoles.
Some azide reactions are shown in the following scheme. Probably the most famous is the reaction with phosphines, which leads to iminophosphoranes 22; these can be hydrolysed into primary amines 23 (the Staudinger reaction), react with carbonyl compounds to give imines 24 (the aza-Wittig reaction), or undergo other transformations. Thermal decomposition of azides gives nitrenes, which participate in a variety of reactions; vinyl azides 19 decompose into 2H-azirines 20. Alkyl azides with low nitrogen-content ((nC + nO) / nN ≥ 3) are relatively stable and decompose only above ca. 175 °C.
Direct photochemical decomposition of alkyl azides leads almost exclusively to imines (e.g. 25 and 26). It is proposed that the azide group is promoted to the singlet excited state and then undergoes concerted rearrangement without the intermediacy of nitrenes. The presence of triplet sensitisers, however, may change the reaction mechanism and result in the formation of triplet nitrenes. The latter were observed directly by ESR spectroscopy at −269 °C as well as inferred in some photolyses. Triplet methyl nitrene is 31 kJ/mol more stable than its singlet form, and thus is most likely the ground state.
The (3+2)-cycloaddition of azides to double or triple bonds is one of the most utilised cycloadditions in organic chemistry and affords triazolines (e.g. 17) or triazoles, respectively. The uncatalysed reaction is a concerted pericyclic process, in which the configuration of the alkene component is transferred to the triazoline product. The Woodward–Hoffmann denomination is [π4s+π2s] and the reaction is symmetry-allowed. According to Sustmann, this is a Type II cycloaddition, which means the two HOMOs and the two LUMOs have comparable energies, and thus both electron-withdrawing and electron-donating substituents may lead to an increase in the reaction rate. The reaction is generally free from significant solvent effects because both the reactants and the transition state (TS) are non-polar.
Another azide regular is tosyl azide here in reaction with norbornadiene in a nitrogen insertion reaction: | 0 | Theoretical and Fundamental Chemistry |
A number of different classification systems of the patterns of leaf veins (venation or veination) have been described, starting with Ettingshausen (1861), together with many different descriptive terms, and the terminology has been described as "formidable". One of the commonest among these is the Hickey system, originally developed for "dicotyledons" and using a number of Ettingshausens terms derived from Greek (1973–1979): (see also': Simpson Figure 9.12, p. 468) | 0 | Theoretical and Fundamental Chemistry |
HCN4 is the main isoform expressed in the sinoatrial node, but low levels of HCN1 and HCN2 have also been reported.
The current through HCN channels, called the pacemaker current (I), plays a key role in the generation and modulation of cardiac rhythmicity, as they are responsible for the spontaneous depolarization in pacemaker action potentials in the heart. HCN4 isoforms are regulated by cCMP and cAMP and these molecules are agonists at I. | 1 | Applied and Interdisciplinary Chemistry |
the health effects of using hash oil were poorly documented. Cannabis extracts have less plant matter and create less harmful smoke. However, trace amounts of impurities are not generally regarded as safe (GRAS). In 2019 following an outbreak of illnesses additives added to vape pen mixtures were found to be causing breathing problems, lung damage, and deaths. | 0 | Theoretical and Fundamental Chemistry |
Since the generic term polyol is only derived from chemical nomenclature and just indicates the presence of several hydroxyl groups, no common properties can be assigned to all polyols. However, polyols are usually viscous at room temperature due to hydrogen bonding. | 0 | Theoretical and Fundamental Chemistry |
In the same way that detecting a biosignature would be a significant discovery about a planet, finding evidence that life is not present can also be an important discovery about a planet. Life relies on redox imbalances to metabolize the resources available into energy. The evidence that nothing on an earth is taking advantage of the "free lunch" available due to an observed redox imbalance is called antibiosignatures. | 1 | Applied and Interdisciplinary Chemistry |
In 2005, a mode of desorption was discovered by John Weaver et al. that has elements of both thermal and electron stimulated desorption. This mode is of particular interest as desorption can occur in a closed system without external stimulus. The mode was discovered whilst investigating bromine absorbed on silicone using scanning tunnelling microscopy. In the experiment, the Si-Br wafers were heated to temperatures ranging from 620 to 775 K. However, it was not simple thermal desorption bond breaking that was observed as the activation energies calculated from Arrhenius plots were found to be lower than the Si-Br bond strength. Instead, the optical phonons of the Silicon weaken the surface bond through vibrations and also provide the energy for electron to excite to the antibonding state. | 0 | Theoretical and Fundamental Chemistry |
With a gyromagnetic ratio 40.5% of that for H, P-NMR signals are observed near 202 MHz on an 11.7-Tesla magnet (used for 500 MHz H-NMR measurements). Chemical shifts are typically referenced to 85% phosphoric acid, which is assigned the chemical shift of 0, and appear at positive values (downfield of the standard). Due to the inconsistent nuclear Overhauser effect, integrations are not useful. Most often, spectra are recorded with protons decoupled. | 0 | Theoretical and Fundamental Chemistry |
4-Iodophenol (p-iodophenol) is an aromatic organic compound. A colorless solid, it is one of three monoiodophenols. 4-Iodophenol undergoes a variety of coupling reactions in which the iodine substituent is replaced by a new carbon group para to the hydroxy group of the phenol. It is also used to enhance chemiluminescence for detection of cancer cells and in the Eclox assay.
4-Iodophenol can be prepared from 4-aminophenol via the diazonium salt. An alternative synthesis involves reaction of salicylic acid with iodine, followed by decarboxylation. | 0 | Theoretical and Fundamental Chemistry |
A soda geyser is a physical reaction between a carbonated beverage, usually Diet Coke, and Mentos mints that causes the beverage to be expelled from its container. The candies catalyze the release of gas from the beverage, which creates an eruption that pushes most of the liquid up and out of the bottle. Lee Marek and "Mareks Kid Scientists" were the first to publicly demonstrate the experiment on the Late Show with David Letterman in 1999. Steve Spanglers televised demonstration of the eruption in 2005 became popular on YouTube, launching a chain of several other Diet Coke and Mentos experiment viral videos. Experiments carried out at altitudes ranging from below sea level in Death Valley to the summit of Pikes Peak have demonstrated that the reaction works better at higher elevations. | 1 | Applied and Interdisciplinary Chemistry |
In 1932, it was reported that dinitrogen gas was generated via an unknown mechanism during fermentation in the sediments of Lake Mendota, Wisconsin, USA. In 1965, F. A. Richards noticed that most of the ammonium that should be produced during the anaerobic remineralization of organic matter was unaccounted for. As there was no known biological pathway for this transformation, biological anaerobic oxidation of ammonium received little further attention.
In 1977, Engelbert Broda predicted the existence of two chemolithoautotrophic microorganisms capable of oxidizing ammonium to dinitrogen gas on the basis of thermodynamic calculations. It was thought that anaerobic oxidation of ammonium would not be feasible, assuming that the predecessors had tried and failed to establish a biological basis for those reactions. By the 1990s, Arnold Mulders observations were just consistent with Richards suggestion. In their anoxic denitrifying pilot reactor, ammonium disappeared at the expense of nitrite with a clear nitrogen production. The reactor used the effluent from a methanogenic pilot reactor, which contained ammonium, sulphide and other compounds, and nitrate from a nitrifying plant as the influent. The process was named "anammox," and was realized to have great significance in the removal of unwanted ammonium.
The discovery of the anammox process was first publicly presented at the 5th European congress on biotechnology. By the mid-1990s, the discovery of anammox in the fluidized bed reactor was published. A maximum ammonium removal rate of 0.4 kg N/m/d was achieved. It was shown that for every mole of ammonium consumed, 0.6 mol of nitrate was required, resulting in the formation of 0.8 mol of gas.
In 1995, the biological nature of anammox was identified. Labeling experiments with in combination with showed that was the dominant product making up 98.2% of the total labeled . It was realized that, instead of nitrate, nitrite was assumed as the oxidizing agent of ammonium in anammox reaction. Based on a previous study, Strous et al. calculated the stoichiometry of anammox process by mass balancing, which is widely accepted by other groups. Later, anammox bacteria were identified as Planctomycetota, and the first identified anammox organism was named Candidatus "Brocadia anammoxidans."
Before 2002, anammox was assumed to be a minor player in the nitrogen cycle within natural ecosystems. In 2002 however, anammox was found to play an important part in the biological nitrogen cycle, accounting for 24–67% of the total production in the continental shelf sediments that were studied. The discovery of anammox process modified the concept of biological nitrogen cycle, as depicted in Figure 2. | 1 | Applied and Interdisciplinary Chemistry |
A common and practical expression of the Beer–Lambert law relates the optical attenuation of a physical material containing a single attenuating species of uniform concentration to the optical path length through the sample and absorptivity of the species. This expression is:where
* is the absorbance
* is the molar attenuation coefficient or absorptivity of the attenuating species
* is the optical path length
* is the concentration of the attenuating species
A more general form of the Beer–Lambert law states that, for attenuating species in the material sample,or equivalently thatwhere
* is the attenuation cross section of the attenuating species in the material sample;
* is the number density of the attenuating species in the material sample;
* is the molar attenuation coefficient or absorptivity of the attenuating species in the material sample;
* is the amount concentration of the attenuating species in the material sample;
* is the path length of the beam of light through the material sample.
In the above equations, the transmittance of material sample is related to its optical depth and to its absorbance by the following definitionwhere
* is the radiant flux transmitted by that material sample;
* is the radiant flux received by that material sample.
Attenuation cross section and molar attenuation coefficient are related byand number density and amount concentration byor equivalentlyCases of non-uniform attenuation occur in atmospheric science applications and radiation shielding theory for instance.
The law tends to break down at very high concentrations, especially if the material is highly scattering. Absorbance within range of 0.2 to 0.5 is ideal to maintain linearity in the Beer–Lambert law. If the radiation is especially intense, nonlinear optical processes can also cause variances. The main reason, however, is that the concentration dependence is in general non-linear and Beer's law is valid only under certain conditions as shown by derivation below. For strong oscillators and at high concentrations the deviations are stronger. If the molecules are closer to each other interactions can set in. These interactions can be roughly divided into physical and chemical interactions. Physical interaction do not alter the polarizability of the molecules as long as the interaction is not so strong that light and molecular quantum state intermix (strong coupling), but cause the attenuation cross sections to be non-additive via electromagnetic coupling. Chemical interactions in contrast change the polarizability and thus absorption. | 0 | Theoretical and Fundamental Chemistry |
The capacity of a sacrificial metal may be calculated from first principle as follows:
* 1 kg Al = 1000/27 moles Al
* 1 kg Al = 3 x 1000/27 moles of electrons
* 1 kg Al = 3 x 1000/27 x 96494 coulombs of charge (by Faraday principles)
* = 10.72 x 10 Amp.seconds of charge per Kg Al (1 Coulomb = 1 Amp.Second)
* = 10.72 x 10/3600 = 2978 Amp.Hours per Kg
By similar calculations Zinc and Magnesium have a capacity of 825 and 2206 Amp.Hours per Kg respectively. | 0 | Theoretical and Fundamental Chemistry |
A splicing factor is a protein involved in the removal of introns from strings of messenger RNA, so that the exons can bind together; the process takes place in particles known as spliceosomes. Genes are progressively switched off as people age, and splicing factors can reverse this trend. Splicing factors regulate the binding of the snRNPs U1 and U2 to the 3 and 5 ends of the intron during splicing and can either be splicing promoters or splicing repressors.
In a research paper, splicing factors were found to be produced upon application of resveratrol analogues, which induced senescent cells to rejuvenate. | 1 | Applied and Interdisciplinary Chemistry |
Temporins are a family of peptides isolated originally from the skin secretion of the European red frog, Rana temporaria. Peptides belonging to the temporin family have been isolated also from closely related North American frogs, such as Rana sphenocephala. | 1 | Applied and Interdisciplinary Chemistry |
In those without signs of life, cardiopulmonary resuscitation (CPR) should be continued during active rewarming. For ventricular fibrillation or ventricular tachycardia, a single defibrillation should be attempted. However, people with severe hypothermia may not respond to pacing or defibrillation. It is not known if further defibrillation should be withheld until the core temperature reaches . In Europe, epinephrine is not recommended until the person's core temperature reaches , while the American Heart Association recommends up to three doses of epinephrine before a core temperature of is reached. Once a temperature of has been reached, normal ACLS protocols should be followed. | 1 | Applied and Interdisciplinary Chemistry |
Tetrafluoromethane, like other fluorocarbons, is very stable due to the strength of its carbon–fluorine bonds. The bonds in tetrafluoromethane have a bonding energy of 515 kJ⋅mol. As a result, it is inert to acids and hydroxides. However, it reacts explosively with alkali metals. Thermal decomposition or combustion of CF produces toxic gases (carbonyl fluoride and carbon monoxide) and in the presence of water will also yield hydrogen fluoride.
It is very slightly soluble in water (about 20 mg⋅L), but miscible with organic solvents. | 1 | Applied and Interdisciplinary Chemistry |
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