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The important sulfur cycle is a biogeochemical cycle in which the sulfur moves between rocks, waterways and living systems. It is important in geology as it affects many minerals and in life because sulfur is an essential element (CHNOPS), being a constituent of many proteins and cofactors, and sulfur compounds can be used as oxidants or reductants in microbial respiration. The global sulfur cycle involves the transformations of sulfur species through different oxidation states, which play an important role in both geological and biological processes.
Steps of the sulfur cycle are:
* Mineralization of organic sulfur into inorganic forms, such as hydrogen sulfide (HS), elemental sulfur, as well as sulfide minerals.
* Oxidation of hydrogen sulfide, sulfide, and elemental sulfur (S) to sulfate ().
* Reduction of sulfate to sulfide.
* Incorporation of sulfide into organic compounds (including metal-containing derivatives).
* Disproportionation of sulfur compounds (elemental sulfur, sulfite, thiosulfate) into sulfate and hydrogen sulfide.
These are often termed as follows:
:Assimilative sulfate reduction (see also sulfur assimilation) in which sulfate () is reduced by plants, fungi and various prokaryotes. The oxidation states of sulfur are +6 in sulfate and –2 in R–SH.
:Desulfurization in which organic molecules containing sulfur can be desulfurized, producing hydrogen sulfide gas (HS, oxidation state = –2). An analogous process for organic nitrogen compounds is deamination.
:Oxidation of hydrogen sulfide produces elemental sulfur (S), oxidation state = 0. This reaction occurs in the photosynthetic green and purple sulfur bacteria and some chemolithotrophs. Often the elemental sulfur is stored as polysulfides.
:Oxidation in elemental sulfur by sulfur oxidizers produces sulfate.
:Dissimilative sulfur reduction in which elemental sulfur can be reduced to hydrogen sulfide.
:Dissimilative sulfate reduction in which sulfate reducers generate hydrogen sulfide from sulfate. | 0 | Theoretical and Fundamental Chemistry |
By definition, strain implies discomfiture, so it should follow that molecules with large amounts of transannular strain should have higher energies than those without. Cyclohexane, for the most part, is without strain and is therefore quite stable and low in energy. Rings smaller than cyclohexane, like cyclopropane and cyclobutane, have significant tension caused by small-angle strain, but there is no transannular strain. While there is no small-angle strain present in medium-sized rings, there does exist something called large-angle strain. Some angle and torsional strain is used by rings with more than nine members to relieve some of the distress caused by transannular strain.
As the plot to the left indicates, the relative energies of cycloalkanes increases as the size of the ring increases, with a peak at cyclononane (with nine members in its ring.) At this point, the flexibility of the rings increases with increasing size; this allows for conformations that can significantly mitigate transannular interactions. | 0 | Theoretical and Fundamental Chemistry |
Completion of the C ring required complete reduction of the arene, placement of para oxygen atoms and importantly introduction of the C19 methyl group. The first assault on the aromatic ring in 3.1 (scheme 3) was launched with Birch reduction (potassium, ammonia, tetrahydrofuran, -78 °C, then ethanol) to diene 3.2. Deprotection (TBAF) to diol 3.3, reprotection as the benzaldehyde acetal 3.4 and reduction (sodium borohydride) to alcohol 3.5 allowed the oxidation of the diene to the 1,4-butenediol 3.6. In this photochemical [4+2]cycloaddition, singlet oxygen was generated from oxygen and rose bengal and the intermediate peroxide was reduced with thiourea. The next order of business was introduction of the C19 fragment: the new diol group was protected as the PMP acetal 3.7 (PMP stands for p-methoxyphenyl) allowing the oxidation of the C4 alcohol to ketone 3.8 with the Dess-Martin periodinane. Diethylaluminum cyanide reacted in a conjugate addition to the enone group to nitrile 3.9. The enol was protected as the TBS ether 3.10 allowing for the reduction of the nitrile group first to the aldehyde with DIBAL and then on to the alcohol 3.11 with Lithium aluminium hydride. The alcohol group was replaced by bromine in an Appel reaction which caused an elimination reaction (loss of HBr) to cyclopropane 3.12. Treatment with hydrochloric acid formed ketone 3.13, reaction with Samarium(II) iodide gave ring-opening finally putting the C19 methyl group in place in 3.14 and deprotection (TBAF) and enol-ketone conversion gave hydroxyketone 3.15 | 0 | Theoretical and Fundamental Chemistry |
[RhH(CO)(PPh)] is a catalyst for the selective hydroformylation of 1-olefins to produce aldehydes at low pressures and mild temperatures. The selectivity for n-aldehydes increases in the presence of excess PPh and at low CO partial pressures. The first step in the hydroformylation process is the dissociative substitution of an alkene for a PPh. The migratory insertion of this 18-electron complex can result in either a primary or secondary rhodium alkyl. This step sets the regiochemistry of the product, however it is rapidly reversible. The 16-electron alkyl complex undergoes migratory insertion of a CO to form the coordinately unsaturated acyl. This species once again gives an 18-electron acyl complex. The last step involves β-H elimination via hydrogenolysis which results in the cleavage of the aldehyde product and regeneration of the rhodium catalyst. | 0 | Theoretical and Fundamental Chemistry |
Perchloromethyl mercaptan () reacts with bonds in the presence of base to give the sulfenamides:
This method is used in the production of the fungicides Captan and Folpet.
Sulfenyl chlorides add across alkenes, for example ethylene:
They undergo chlorination to the trichlorides:
Sulfenyl chlorides react with water and alcohols to give sulfenyl esters (): | 0 | Theoretical and Fundamental Chemistry |
In molecular biology and genetics, upstream and downstream both refer to relative positions of genetic code in DNA or RNA. Each strand of DNA or RNA has a 5 end and a 3 end, so named for the carbon position on the deoxyribose (or ribose) ring. By convention, upstream and downstream relate to the 5 to 3 direction respectively in which RNA transcription takes place. Upstream is toward the 5 end of the RNA molecule and downstream is toward the 3 end. When considering double-stranded DNA, upstream is toward the 5 end of the coding strand for the gene in question and downstream is toward the 3 end. Due to the anti-parallel nature of DNA, this means the 3 end of the template strand is upstream of the gene and the 5 end is downstream.
Some genes on the same DNA molecule may be transcribed in opposite directions. This means the upstream and downstream areas of the molecule may change depending on which gene is used as the reference.
The terms upstream and downstream are sometimes also applied to a polypeptide sequence, where upstream refers to a region N-terminal and downstream to residues C-terminal of a reference point. | 1 | Applied and Interdisciplinary Chemistry |
Geophysical mass flows such as avalanches and debris flows take place on inclined slopes which then merge into gentle and flat run-out zones.
So, these flows are associated with the elevation of the topographic slopes that induce the gravity potential energy together with the pressure potential energy during the flow. Therefore, the classical Froude number should include this additional effect. For such a situation, Froude number needs to be re-defined. The extended Froude number is defined as the ratio between the kinetic and the potential energy:
where is the mean flow velocity, , ( is the earth pressure coefficient, is the slope), , is the channel downslope position and is the distance from the point of the mass release along the channel to the point where the flow hits the horizontal reference datum; and are the pressure potential and gravity potential energies, respectively. In the classical definition of the shallow-water or granular flow Froude number, the potential energy associated with the surface elevation, , is not considered. The extended Froude number differs substantially from the classical Froude number for higher surface elevations. The term emerges from the change of the geometry of the moving mass along the slope. Dimensional analysis suggests that for shallow flows , while and are both of order unity. If the mass is shallow with a virtually bed-parallel free-surface, then can be disregarded. In this situation, if the gravity potential is not taken into account, then is unbounded even though the kinetic energy is bounded. So, formally considering the additional contribution due to the gravitational potential energy, the singularity in Fr is removed. | 1 | Applied and Interdisciplinary Chemistry |
*1968–2008 - Institute of Biochemistry and Biotechnology, Georgian Academy of Sciences
*1968–1999 - Professor at Tbilisi State University, Georgia
*2008–2010 - Professor at Ilia State University, Tbilisi, Georgia
*2010–2011 - Professor at Free University of Tbilisi, Georgia
*2012–2021- Director of Institute of Molecular Genetics, Agricultural University of Georgia
*2012–present - Professor at Agricultural University of Georgia, Tbilisi, Georgia | 1 | Applied and Interdisciplinary Chemistry |
Nicolson–Ross–Weir method is a measurement technique for determination of complex permittivities and permeabilities of material samples for microwave frequencies. The method is based on insertion of a material sample with a known thickness inside a waveguide, such as a coaxial cable or a rectangular waveguide, after which the dispersion data is extracted from the resulting scattering parameters. The method is named after A. M. Nicolson and G. F. Ross, and W. B. Weir, who developed the approach in 1970 and 1974, respectively.
The technique is one of the most common procedures for material characterization in microwave engineering. | 0 | Theoretical and Fundamental Chemistry |
Eigen et al. and Woese proposed that the genomes of early protocells were composed of single-stranded RNA, and that individual genes corresponded to separate RNA segments, rather than being linked end-to-end as in present-day DNA genomes. A protocell that was haploid (one copy of each RNA gene) would be vulnerable to damage, since a single lesion in any RNA segment would be potentially lethal to the protocell (e.g., by blocking replication or inhibiting the function of an essential gene).
Vulnerability to damage could be reduced by maintaining two or more copies of each RNA segment in each protocell, i.e., by maintaining diploidy or polyploidy. Genome redundancy would allow a damaged RNA segment to be replaced by an additional replication of its homolog. However, for such a simple organism, the proportion of available resources tied up in the genetic material would be a large fraction of the total resource budget. Under limited resource conditions, the protocell reproductive rate would likely be inversely related to ploidy number. The protocell's fitness would be reduced by the costs of redundancy. Consequently, coping with damaged RNA genes while minimizing the costs of redundancy would likely have been a fundamental problem for early protocells.
A cost-benefit analysis was carried out in which the costs of maintaining redundancy were balanced against the costs of genome damage. This analysis led to the conclusion that, under a wide range of circumstances, the selected strategy would be for each protocell to be haploid, but to periodically fuse with another haploid protocell to form a transient diploid. The retention of the haploid state maximizes the growth rate. The periodic fusions permit mutual reactivation of otherwise lethally damaged protocells. If at least one damage-free copy of each RNA gene is present in the transient diploid, viable progeny can be formed. For two, rather than one, viable daughter cells to be produced would require an extra replication of the intact RNA gene homologous to any RNA gene that had been damaged prior to the division of the fused protocell. The cycle of haploid reproduction, with occasional fusion to a transient diploid state, followed by splitting to the haploid state, can be considered to be the sexual cycle in its most primitive form. In the absence of this sexual cycle, haploid protocells with damage in an essential RNA gene would simply die.
This model for the early sexual cycle is hypothetical, but it is very similar to the known sexual behavior of the segmented RNA viruses, which are among the simplest organisms known. Influenza virus, whose genome consists of 8 physically separated single-stranded RNA segments, is an example of this type of virus. In segmented RNA viruses, "mating" can occur when a host cell is infected by at least two virus particles. If these viruses each contain an RNA segment with a lethal damage, multiple infection can lead to reactivation providing that at least one undamaged copy of each virus gene is present in the infected cell. This phenomenon is known as "multiplicity reactivation". Multiplicity reactivation has been reported to occur in influenza virus infections after induction of RNA damage by UV-irradiation, and ionizing radiation. | 0 | Theoretical and Fundamental Chemistry |
According to Mu-ming Poo, the principal significance of this event is that it could be used to create genetically identical monkeys for use in animal experiments. Crab-eating macaques are already an established model organism for studies of atherosclerosis, though Poo chose to emphasize neuroscience, naming Parkinsons disease and Alzheimers disease when he appeared on the radio news program All Things Considered in January 2018.
The birth of the two cloned primates also raised concerns from bioethicists. Insoo Hyun of Case Western Reserve University questioned whether this meant that human cloning would be next. Poo told All Things Considered that "Technically speaking one can clone human[s] ... But were not going to do it. Theres absolutely no plan to do anything on humans." | 1 | Applied and Interdisciplinary Chemistry |
In this field, the following directions were developed in V. G. Khlopin's works:
1. radioelements migration, in particular - relatively short-lived in the Earth's crust;
2. study of radium-mesothorium containing waters;
3. Determination of geologic age on the basis of radioactive data;
4. distribution of helium and argon in natural gases of the country;
5. effects of natural waters in geochemistry of noble gases;
6. distribution of boron in natural waters. | 0 | Theoretical and Fundamental Chemistry |
As with all airborne particulates, wood dust particle sizes are classified with regard to effect on the human respiratory system. For this classification, the unit for measurement of particle sizes is the micrometre or micron (μm), where 1 micrometre = 1 micron. Particles below 50 μm are not normally visible to the naked human eye. Particles of concern for human respiratory health are those <100 μm (where the symbol < means ‘less than’).
Zhang (2004) has defined the size of indoor particulates according to respiratory fraction:
Particles which precipitate in the vicinity of the mouth and eyes, and get into the organism, are defined as the inhalable fraction, that is total dust. Smaller fractions, penetrating into the non-cartilage respiratory tract, are defined as respirable dust. Dust emitted in the wood industry is characterized by the dimensional disintegration of particles up to 5 μm, and that
is why they precipitate mostly in the nasal cavity, increasing the risk of cancer of the upper respiratory tract. | 1 | Applied and Interdisciplinary Chemistry |
The earliest known Chinese manual on materia medica is the Shennong Ben Cao Jing (The Divine Farmers Herb-Root Classic'), dating back to the first century AD. It was compiled during the Han dynasty and was attributed to the mythical Shennong. Earlier literature included lists of prescriptions for specific ailments, exemplified by a manuscript "Recipes for 52 Ailments", found in the Mawangdui, sealed in 168 BC. Present-day Chinese pharmacy is a result of pharmaceutical exchanges between China and the rest of the world in the past centuries.
The earliest known compilation of medicinal substances in Indian traditional medicine dates to the third or fourth century AD (attributed to Sushruta, who is recorded as a physician of the sixth century BC).
There is a stone sign for a pharmacy with a tripod, a mortar, and a pestle opposite one for a doctor in the Arcadian Way in Ephesus, Turkey.
In Japan, at the end of the Asuka period (538–710) and the early Nara period (710–794), the men who fulfilled roles similar to those of modern pharmacists were highly respected. The place of pharmacists in society was expressly defined in the Taihō Code (701) and re-stated in the Yōrō Code (718). Ranked positions in the pre-Heian Imperial court were established; and this organizational structure remained largely intact until the Meiji Restoration (1868). In this highly stable hierarchy, the pharmacists—and even pharmacist assistants—were assigned status superior to all others in health-related fields such as physicians and acupuncturists. In the Imperial household, the pharmacist was even ranked above the two personal physicians of the Emperor. | 1 | Applied and Interdisciplinary Chemistry |
Rasagiline is broken down via CYP1A2, part of the cytochrome P450 metabolic path in the liver. It is contraindicated in patients with hepatic insufficiency and its use should be monitored carefully in patients taking other drugs that alter the normal effectiveness of this metabolic path. | 0 | Theoretical and Fundamental Chemistry |
The pzc is the same as the isoelectric point (iep) if there is no adsorption of other ions than the potential determining H/OH at the surface. This is often the case for pure ("pristine surface") oxides in water. In the presence of specific adsorption, pzc and isoelectric point generally have different values. | 0 | Theoretical and Fundamental Chemistry |
Linked-read sequencing, a type of DNA sequencing technology, uses specialized technique that tags DNA molecules with unique barcodes before fragmenting them. Unlike traditional sequencing technology, where DNA is broken into small fragments and then sequenced individually, resulting in short read lengths that has difficulties in accurately reconstructing the original DNA sequence, the unique barcodes of linked-read sequencing allows scientists to link together DNA fragments that come from the same DNA molecule. A pivotal benefit of this technology lies in the small quantities of DNA required for large genome information output, effectively combining the advantages of long-read and short-read technologies. | 1 | Applied and Interdisciplinary Chemistry |
Carbon-14 has a half-life of years and a decay rate of 14 disintegrations per minute (dpm) per gram of natural carbon.
If an artifact is found to have radioactivity of 4 dpm per gram of its present C, we can find the approximate age of the object using the above equation:
where: | 0 | Theoretical and Fundamental Chemistry |
RNF123 was found to be an interacting protein of FAM227B through Affinity Capture – MS. RAB3A was found to be an interacting protein of FAM227B through tandem affinity purification. | 1 | Applied and Interdisciplinary Chemistry |
Nucleophilic displacement of alkyl halides by alkoxides
: R–ONa + R′–X → R–O–R′ + NaX
This reaction, the Williamson ether synthesis, involves treatment of a parent alcohol with a strong base to form the alkoxide, followed by addition of an appropriate aliphatic compound bearing a suitable leaving group (R–X). Although popular in textbooks, the method is usually impractical on scale because it cogenerates significant waste.
Suitable leaving groups (X) include iodide, bromide, or sulfonates. This method usually does not work well for aryl halides (e.g. bromobenzene, see Ullmann condensation below). Likewise, this method only gives the best yields for primary halides. Secondary and tertiary halides are prone to undergo E2 elimination on exposure to the basic alkoxide anion used in the reaction due to steric hindrance from the large alkyl groups.
In a related reaction, alkyl halides undergo nucleophilic displacement by phenoxides. The R–X cannot be used to react with the alcohol. However phenols can be used to replace the alcohol while maintaining the alkyl halide. Since phenols are acidic, they readily react with a strong base like sodium hydroxide to form phenoxide ions. The phenoxide ion will then substitute the –X group in the alkyl halide, forming an ether with an aryl group attached to it in a reaction with an S2 mechanism.
: CHOH + OH → CH–O + HO
: CH–O + R–X → CHOR
The Ullmann condensation is similar to the Williamson method except that the substrate is an aryl halide. Such reactions generally require a catalyst, such as copper. | 0 | Theoretical and Fundamental Chemistry |
The International Molecular Exchange Consortium (IMEx) is a group of the major public providers of molecular interaction data to provide a single, non-redundant set of molecular interactions. Data is captured using a detailed curation model and made available in the PSI-MI standard formats. Participating databases include DIP, IntAct, the Molecular Interaction Database (MINT), MatrixDB, InnateDB, IID, HPIDB, UCL Cardiovascular Gene Annotation, MBInfo, Molecular Connections and UniProt. The group collates the interaction data and prevents duplicate entries in the various databases. The IMEx consortium also supports and contributes to the development of the HUPO-PSI-MI XML format, which is now widely implemented. | 1 | Applied and Interdisciplinary Chemistry |
WikiPathways is a community resource for contributing and maintaining content dedicated to biological pathways. Any registered WikiPathways user can contribute, and anybody can become a registered user. Contributions are monitored by a group of admins, but the bulk of peer review, editorial curation, and maintenance is the responsibility of the user community. WikiPathways is originally built using MediaWiki software, a custom graphical pathway editing tool (PathVisio) and integrated BridgeDb databases covering major gene, protein, and metabolite systems. WikiPathways was founded in 2008 by Thomas Kelder, Alex Pico, Martijn Van Iersel, Kristina Hanspers, Bruce Conklin and Chris Evelo. Current architects are Alex Pico and Martina Summer-Kutmon. | 1 | Applied and Interdisciplinary Chemistry |
In the sand packing process the pipe is filled with fine sand and the ends are capped. The filled pipe is heated in a furnace to or higher. Then it is placed on a slab with pins set in it, and bent around the pins using a winch, crane, or some other mechanical force. The sand in the pipe minimizes distortion in the pipe cross section. | 1 | Applied and Interdisciplinary Chemistry |
A realtime spectrum analyser does not have any blind time—up to some maximum span, often called the "realtime bandwidth". The analyser is able to sample the incoming RF spectrum in the time domain and convert the information to the frequency domain using the FFT process. FFT's are processed in parallel, gapless and overlapped so there are no gaps in the calculated RF spectrum and no information is missed. | 0 | Theoretical and Fundamental Chemistry |
Wet storage stain is a white, crumbly, and porous substance that is a mixture of three chemical compounds: 2ZnCO·3Zn(OH), ZnO, and β-Zn(OH). Underneath the white coating is usually a dark gray surface. The corrosion product is very voluminous; it is approximately 100 times greater in volume than the zinc consumed. Because of this the corrosion is not usually detrimental to the usability of the item, unless the zinc surface is only a thin coating, such as zinc electroplating.
Wet storage stain only occurs in situations where there is a lack of oxygen or carbon dioxide, because it usually forms zinc oxide and zinc hydroxide in open air environments. These oxides are usually present on zinc surfaces, but do not protect them from wet storage stain because they are only loosely adherent to the surface and any moisture can attack the oxides from underneath. Also, chlorides and sulfates accelerate the formation of corrosion. | 1 | Applied and Interdisciplinary Chemistry |
Before proceeding further it is necessary to introduce the concept of a jump condition – a condition that holds at a discontinuity or abrupt change.
Consider a 1D situation where there is a jump in the scalar conserved physical quantity , which is governed by integral conservation law
for any , , , and, therefore, by partial differential equation
for smooth solutions.
Let the solution exhibit a jump (or shock) at , where and , then
The subscripts 1 and 2 indicate conditions just upstream and just downstream of the jump respectively, i.e. and
Note, to arrive at equation () we have used the fact that and .
Now, let and , when we have and , and in the limit
where we have defined (the system characteristic or shock speed), which by simple division is given by
Equation () represents the jump condition for conservation law (). A shock situation arises in a system where its characteristics intersect, and under these conditions a requirement for a unique single-valued solution is that the solution should satisfy the admissibility condition or entropy condition. For physically real applications this means that the solution should satisfy the Lax entropy condition
where and represent characteristic speeds at upstream and downstream conditions respectively. | 1 | Applied and Interdisciplinary Chemistry |
* Increased ruggedness: Bonding a sheet of glass on top of the display increases the ruggedness of the display.
* Improved durability: A bonded display is better able to resist scratches, fluids, stains and dirt.
* Condensation: The elimination of an air gap between the cover glass and the display means that moisture cannot penetrate and cause fogging on display’s surface.
* Extended temperature range and EMI filtering: The temperature range of the display can be extended by incorporating ITO heaters on the cover glass; EMI filters can be added via the same mechanism. | 0 | Theoretical and Fundamental Chemistry |
Silverquant is a labeling and detection method for DNA microarrays or protein microarrays. A synonym is <colorimetric> detection.
In contrast to the classical signal detection on microarrays by using fluorescence, the colorimetric detection is more sensitive and ozone-stable. | 1 | Applied and Interdisciplinary Chemistry |
Diastereomers are distinct molecular configurations that are a broader category. They usually differ in physical characteristics as well as chemical properties. If two molecules with more than one chiral centre differ in one or more (but not all) centres, they are diastereomers. All stereoisomers that are not enantiomers are diastereomers. Diastereomerism also exists in alkenes. Alkenes are designated Z or E depending on group priority on adjacent carbon atoms. E/Z notation describes the absolute stereochemistry of the double bond. Cis/trans notation is also used to describe the relative orientations of groups. | 0 | Theoretical and Fundamental Chemistry |
Homochirality is the geometric uniformity of materials composed of chiral (non-mirror-symmetric) units. Living organisms use molecules that have the same chirality (handedness): with almost no exceptions, amino acids are left-handed while nucleotides and sugars are right-handed. Chiral molecules can be synthesized, but in the absence of a chiral source or a chiral catalyst, they are formed in a 50/50 (racemic) mixture of both forms. Known mechanisms for the production of non-racemic mixtures from racemic starting materials include: asymmetric physical laws, such as the electroweak interaction; asymmetric environments, such as those caused by circularly polarized light, quartz crystals, or the Earth's rotation, statistical fluctuations during racemic synthesis, and spontaneous symmetry breaking.
Once established, chirality would be selected for. A small bias (enantiomeric excess) in the population can be amplified into a large one by asymmetric autocatalysis, such as in the Soai reaction. In asymmetric autocatalysis, the catalyst is a chiral molecule, which means that a chiral molecule is catalyzing its own production. An initial enantiomeric excess, such as can be produced by polarized light, then allows the more abundant enantiomer to outcompete the other.
Homochirality may have started in outer space, as on the Murchison meteorite the amino acid L-alanine is more than twice as frequent as its D form, and L-glutamic acid is more than three times as abundant as its D counterpart. Amino acids from meteorites show a left-handed bias, whereas sugars show a predominantly right-handed bias, as found in living organisms, suggesting an abiogenic origin of these compounds.
In 2010, an experiment by Robert Root-Bernstein shows that "two D-RNA-oligonucleotides having inverse base sequences (D-CGUA and D-AUGC) and their corresponding L-RNA-oligonucleotides (L-CGUA and L-AUGC) were synthesized and their affinity determined for Gly and eleven pairs of L- and D-amino acids". This suggests that homochirality, including codon directionality, might have "emerged as a function of the origin of the genetic code". | 0 | Theoretical and Fundamental Chemistry |
This particular function is considered a scaffold's most basic function. Scaffolds assemble signaling components of a cascade into complexes. This assembly may be able to enhance signaling specificity by preventing unnecessary interactions between signaling proteins, and enhance signaling efficiency by increasing the proximity and effective concentration of components in the scaffold complex. A common example of how scaffolds enhance specificity is a scaffold that binds a protein kinase and its substrate, thereby ensuring specific kinase phosphorylation. Additionally, some signaling proteins require multiple interactions for activation and scaffold tethering may be able to convert these interactions into one interaction that results in multiple modifications. Scaffolds may also be catalytic as interaction with signaling proteins may result in allosteric changes of these signaling components. Such changes may be able to enhance or inhibit the activation of these signaling proteins. An example is the Ste5 scaffold in the mitogen-activated protein kinase (MAPK) pathway. Ste5 has been proposed to direct mating signaling through the Fus3 MAPK by catalytically unlocking this particular kinase for activation by its MAPKK Ste7. | 1 | Applied and Interdisciplinary Chemistry |
The paradox does not arise in the Big Bang or its successful Lambda-CDM refinement, which posit that the universe began roughly 13.8 billion years ago, not long enough ago for the universe to have approached thermodynamic equilibrium. Some proposed further refinements, termed eternal inflation, restore Kelvin's idea of unending time in the more complicated form of an eternal, exponentially-expanding multiverse in which mutually-inaccessible baby universes, some of which resemble the universe we inhabit, are continually being born. | 0 | Theoretical and Fundamental Chemistry |
In a common situation, the diffusion coefficient is constant, there are no sources or sinks, and the velocity field describes an incompressible flow (i.e., it has zero divergence). Then the formula simplifies to:
In this form, the convection–diffusion equation combines both parabolic and hyperbolic partial differential equations.
In this case the equation can be put in the simple convective form:
Where, the derivative of the left hand side is the material derivative of the variable c.
In non-interacting material, (for example, when temperature is close to absolute zero, dilute gas has almost zero mass diffusivity), hence the transport equation is simply the continuity equation:
Using Fourier transform in both temporal and spatial domain (that is, with integral kernel ), its characteristic equation can be obtained:
which gives the general solution:
where is any differentiable scalar function. This is the basis of temperature measurement for near Bose–Einstein condensate via time of flight method. | 1 | Applied and Interdisciplinary Chemistry |
A topogenic sequence is a collective term used for a peptide sequence present at nascent proteins essential for their insertion and orienting in cellular membranes. The sequences are also used to translocate proteins across various intracellular membranes, and ensure they are transported to the correct organelle after synthesis. The position of the sequence may be at the end, e.g. N-terminal signal sequence, or in mid parts of the nascent protein, e.g. stop-transfer anchor sequences and signal-anchor sequences. If the sequence is at the end of the polypeptide, it is cleaved off after entering the ER-lumen (via a translocon) by a signal peptidase, and subsequently degraded.
As an example, the vast majority of all known complex plastid preproteins (an unactivated protein) encoded in the nucleus possess a topogenic sequence. | 1 | Applied and Interdisciplinary Chemistry |
Passive daytime radiative cooling has "the potential to simultaneously alleviate the two major problems of energy crisis and global warming" while being an "environmental protection refrigeration technology." PDRCs thereby have an array of potential applications, but are now most often applied to various aspects of the built environment, such as building envelopes, cool pavements, and other surfaces to decrease energy demand, costs, and emissions. PDRC has been tested and applied for indoor space cooling, outdoor urban cooling, solar cell efficiency, power plant condenser cooling, among other applications. For outdoor applications, the lifetime of PDRCs should be adequately estimated, both for high humidity and heat as well as for UV stability. | 0 | Theoretical and Fundamental Chemistry |
Several other methods exist for the synthesis of imines.
* Reaction of organic azides with metal carbenoids (produced from diazocarbonyl compounds).
* Condensation of carbon acids with nitroso compounds.
* The rearrangement of trityl N-haloamines in the Stieglitz rearrangement.
* By reaction of alkenes with hydrazoic acid in the Schmidt reaction.
* By reaction of a nitrile, hydrochloric acid, and an arene in the Hoesch reaction.
* Multicomponent synthesis of 3-thiazolines in the Asinger reaction.
* Thermal decomposition of oximes. | 0 | Theoretical and Fundamental Chemistry |
The main application of Ellingham diagrams is in the extractive metallurgy industry, where it helps to select the best reducing agent for various ores in the extraction process, purification and grade setting for steel manufacturing. It also helps to guide the purification of metals, especially the removal of trace elements. The direct reduction process for making iron rests firmly on the guidance of Ellingham diagrams, which show that hydrogen by itself can reduce iron oxides to the metal. | 1 | Applied and Interdisciplinary Chemistry |
The stereochemical term diastereotopic refers to the relationship between two groups in a molecule which, if replaced, would generate compounds that are diastereomers. Diastereotopic groups are often, but not always, identical groups attached to the same atom in a molecule containing at least one chiral center.
For example, the two hydrogen atoms of the CH moiety in (S)-2-bromobutane are diastereotopic. Replacement of one hydrogen atom (colored blue) with a bromine atom will produce (2S,3R)-2,3-dibromobutane. Replacement of the other hydrogen atom (colored red) with a bromine atom will produce the diastereomer (2S,3S)-2,3-dibromobutane.
In chiral molecules containing diastereotopic groups, such as in 2-bromobutane, there is no requirement for enantiomeric or optical purity; no matter its proportion, each enantiomer will generate enantiomeric sets of diastereomers upon substitution of diastereotopic groups (though, as in the case of substitution by bromine in 2-bromobutane, meso isomers have, strictly speaking, no enantiomer).
Diastereotopic groups are not mirror images of one another about any plane. They are always different, in any environment, but may not be distinguishable. For instance, both pairs of CH hydrogens in ethyl phenylalaninate hydrochloride (PhCHCH(NH)COOCHCH Cl) are diastereotopic and both give pairs of distinct H-NMR signals in DMSO-d at 300 MHz, but in the similar ethyl 2-nitrobutanoate (CHCHCH(NO)COOCHCH), only the CH group next to the chiral center gives distinct signals from its two hydrogens with the same instrument in CDCl. Such signals are often complex because of small differences in chemical shift, overlap and an additional strong coupling between geminal hydrogens. On the other hand, the two CH groups of ipsenol, which are three bonds away from the chiral center, give separate H doublets at 300 MHz and separate C-NMR signals in CDCl, but the diastereotopic hydrogens in ethyl alaninate hydrochloride (CHCH(NH)COOCHCH Cl), also three bonds away from the chiral center, show barely distinguishable H-NMR signals in DMSO-d.
Diastereotopic groups also arise in achiral molecules. For instance, any one pair of CH hydrogens in 3-pentanol (Figure 1) are diastereotopic, as the two CH carbons are enantiotopic. Substitution of any one of the four CH hydrogens creates two chiral centers at once, and the two possible hydrogen substitution products at any one CH carbon will be diastereomers. This kind of relationship is often easier to detect in cyclic molecules. For instance, any pair of CH hydrogens in cyclopentanol (Figure 2) are similarly diastereotopic, and this is easily discerned as one of the hydrogens in the pair will be cis to the OH group (on the same side of the ring face) while the other will be trans to it (on the opposite side).
The term diastereotopic is also applied to identical groups attached to the same end of an alkene moiety which, if replaced, would generate geometric isomers (also falling in the category of diastereomers). Thus, the CH hydrogens of propene are diastereotopic, one being cis to the CH group, and the other being trans to it, and replacement of one or the other with CH would generate cis- or trans--2-butene.
Diastereotopicity is not limited to organic molecules, nor to groups attached to carbon, nor to molecules with chiral tetrahedral (sp-hybridized) centers: for instance, the pair of hydrogens in any CH or NH group in tris(ethylenediamine)chromium(III) ion (Cr(en)), where the metal center is chiral, are diastereotopic (Figure 2).
The terms enantiotopic and diastereotopic can also be applied to the faces of planar groups (especially carbonyl groups and alkene moieties). See Cahn-Ingold-Prelog priority rule. | 0 | Theoretical and Fundamental Chemistry |
Each of the ten possible d electron counts has an associated Tanabe–Sugano diagram describing gradations of possible ligand field environments a metal center could experience in an octahedral geometry. The Tanabe–Sugano diagram with a small amount of information accurately predicts absorptions in the UV and visible electromagnetic spectrum resulting from d to d orbital electron transitions. It is these d–d transitions, ligand to metal charge transfers (LMCT), or metal to ligand charge transfers (MLCT) that generally give metals complexes their vibrant colors. | 0 | Theoretical and Fundamental Chemistry |
Sleeves can be made of:
* sections of steel pipe.
* plastic.
* sheet metal.
* proprietary devices that are listed firestop components. | 1 | Applied and Interdisciplinary Chemistry |
Key adaptations are adaptations that allow a group of organisms to diversify. Daphnia lumholtzi is a water flea that is able to form rigid head spines in response to chemicals released when fish are present. These phenotypically plastic traits serve as an induced defense against these predators. A study showed that Daphnia pulicaria is competitively superior to D. lumholtzi in the absence of predators. However, in the presence of fish predation the invasive species formed its defenses and became the dominant water flea in the region. This switch in dominance suggests that the induced defense against fish predation could represent a key adaptation for the invasion success of D. lumholtzi. A defensive trait that qualifies as a key adaptation is most likely an example of escape and radiate coevolution. | 1 | Applied and Interdisciplinary Chemistry |
Research has examined integrating RO with electrodialysis to improve recovery of valuable deionized products, or to reduce concentrate volumes. | 0 | Theoretical and Fundamental Chemistry |
A compressor map shows the operating range of a compressor and how well it works within its operating range. Two fundamental requirements for the gas flowing through a compressor explain why it works best at a design condition and not so well at other conditions, known as off-design. First, the exit area has to be smaller than the inlet area because the compressed gas has a higher density. The exit area is sized to pass the specific volume at the design condition. Second, all the rotor and stator blades in an axial compressor, and impeller inducer and diffuser vanes in a centrifugal compressor, are angled to meet approaching air head-on at the design condition to minimize incidence losses. Incidence losses reduce the efficiency of compression. Satisfactory operation of the compressor relies on controlling the angle at which the gas approaches rotating and stationary blades to within an acceptable range. Deviating from the optimum first results in increased losses/reduced efficiency then either stalling or sonic velocity/choking which occur in the blade passages at opposite ends of an axial compressor at the same time. They also occur in a centrifugal compressor at entry to the impeller and in the diffuser.
The compressor design point will be in an area of high efficiency whether the compressor is part of a gas turbine engine or whether it is used for pumping air into a blast furnace. However the compressor has to provide suitable performance at other operating conditions imposed on it which means a high efficiency is required over a wider range of operation. In the case of a gas turbine engine it must permit the engine to be started readily and accelerated rapidly to the design speed which means operating at lower speeds than the design speed. At speeds and flows away from the design point the compressor flow area reduction is not appropriate for the actual density rise. A NACA report illustrates pictorially the difference in contraction required at the design condition and at low speed. At lower speeds, for example, the gas hasn't been compressed enough to exit the compressor without adversely affecting the blade angles of attack through the compressor. Away from the design point the middle stages of an axial compressor continue to operate at about the optimum angle of attack but the front stages deviate one way, towards stall, and the rear stages in the opposite direction towards choke. The deviation was acceptable up to a design pressure ratio of about 5:1, producing only a loss in efficiency. At higher design pressure ratios prevention of rotating stall, which occurs at low corrected speeds, and choking was required with the introduction of inlet guide vanes which partially closed at low speeds, or by removing air part-way along the compressor at low speeds. Rows of variable stators or split compressors, which allowed the front stages to speed up and the rear to slow down relative to each other, would also be introduced for the same reason. When pressure ratios reached about 12:1 compressors would incorporate more than one of these features together. | 0 | Theoretical and Fundamental Chemistry |
In humans, consumption of cobalt-containing vitamin B meets all needs for cobalt. For cattle and sheep, which meet vitamin B needs via synthesis by resident bacteria in the rumen, there is a function for inorganic cobalt. In the early 20th century, during the development of farming on the North Island Volcanic Plateau of New Zealand, cattle suffered from what was termed "bush sickness". It was discovered that the volcanic soils lacked the cobalt salts essential for the cattle food chain. The "coast disease" of sheep in the Ninety Mile Desert of the Southeast of South Australia in the 1930s was found to originate in nutritional deficiencies of trace elements cobalt and copper. The cobalt deficiency was overcome by the development of "cobalt bullets", dense pellets of cobalt oxide mixed with clay given orally for lodging in the animal's rumen. | 1 | Applied and Interdisciplinary Chemistry |
* X-ray photoelectron spectroscopy
* Auger electron spectroscopy
* Electron energy loss spectroscopy
* Ultraviolet photoelectron spectroscopy | 0 | Theoretical and Fundamental Chemistry |
Polyaniline nanofibers are a high aspect form of polyaniline, a polymer consisting of aniline monomers, which appears as discrete long threads with an average diameter between 30 nm and 100 nm. Polyaniline is one of the oldest known conducting polymers, being known for over 150 years. Polyaniline nanofibers are often studied for their potential to enhance the properties of polyaniline or have additional beneficial properties due to the addition of a nanostructure to the polymer. Properties that make polyaniline useful can be seen in the nanofiber form as well, such as facile synthesis, environmental stability, and simple acid/base doping/dedoping chemistry. These and other properties have led to the formation of various applications for polyaniline nanofibers as actuators memory devices, and sensors. | 0 | Theoretical and Fundamental Chemistry |
Aromatic polyamides and polyamides are practical compounds due to their temperature resistance, electrical or insulating characteristics, and their mechanical strength. Some of the polyamides and polyimides that can be synthesized by o-Cresophthalein are polycarbonate, polyacrylate, and epoxy-resin.
The diether-diamine 3,3-bis[4-(4-amino-phenoxy)-3-methylphenyl]phthalide, or BNMP, is synthesized by 12 g o-cresophthalein, 11.5 g p-chloronitrobenzene, 5.1 g anhydrous potassium carbonate, and 55 mL of DMF. The compounds should be refluxed together at 160 °C for eight hours. Once it is done and has cooled, it should be mixed with 0.3 L methanol. A precipitate should form and be vacuum filtered to obtain a solid. It should then be washed with water and dried, yielding a yellow product. It should then be recrystallized from glacial acetic acid to yield yellow needles. The product is BNMP. The reaction can go further by combining 15.5 g of BNMP with 0.18 g 10% Pd/C and 50 mL ethanol. They should be stirred at 80 °C. 7 mL of hydrazine monohydrate should be added drop by drop for one hour. The solution should then be mixed for eight hours. It should then be filtered to separated from the Pd/C and concentrated. The concentrated solution should be added to water, and a precipitate should be formed. It should then be vacuum filtered to isolate the solid, yelding 3,3-Bis[4-(4-aminophenoxy)-3-methylphenyl]pthalide, or BAMP, as a white solid. It should then be purified by water and ethanol. | 0 | Theoretical and Fundamental Chemistry |
The shape of a surfactant molecule can be described by its surfactant packing parameter, (Israelachvili, 1976). The packing parameter takes into account the volume of the hydrophobic chain (), the equilibrium area per molecule at
the aggregate interface (), and the length of the hydrophobic chain ():
The packing parameter for a specific surfactant is not a constant. It is dependent on various conditions which affect each the volume of the hydrophobic chain, the cross sectional area of the hydrophilic head group, and the length of the hydrophobic chain. Things that can affect these include, but are not limited to, the properties of the solvent, the solvent temperature, and the ionic strength of the solvent. | 0 | Theoretical and Fundamental Chemistry |
The and pH of a solution are related by the Nernst equation as commonly represented by a Pourbaix diagram . explicitly denotes expressed versus the standard hydrogen electrode (SHE). For a half cell equation, conventionally written as a reduction reaction (i.e., electrons accepted by an oxidant on the left side):
The equilibrium constant of this reduction reaction is:
where curly braces { } indicate activities (), rectangle braces [ ] denote molar or molal concentrations (), represent the activity coefficients, and the stoichiometric coefficients are shown as exponents.
Activities correspond to thermodynamic concentrations and take into account the electrostatic interactions between ions present in solution. When the concentrations are not too high, the activity () can be related to the measurable concentration () by a linear relationship with the activity coefficient ():
The half-cell standard reduction potential is given by
where is the standard Gibbs free energy change, is the number of electrons involved, and is the Faraday's constant. The Nernst equation relates pH and as follows:
In the following, the Nernst slope (or thermal voltage) is used, which has a value of 0.02569... V at STP. When base-10 logarithms are used, V λ = 0.05916... V at STP where λ = ln[10] = 2.3026.
This equation is the equation of a straight line for as a function of pH with a slope of volt (pH has no units).
This equation predicts lower at higher pH values. This is observed for the reduction of O into HO, or OH, and for reduction of H into H. is then often noted as to indicate that it refers to the standard hydrogen electrode (SHE) whose = 0 by convention under standard conditions (T = 298.15 K = 25 °C = 77 F, P = 1 atm (1.013 bar), concentrations = 1 M and thus pH = 0). | 0 | Theoretical and Fundamental Chemistry |
Methanogenesis is the final step in the decay of organic matter. During the decay process, electron acceptors (such as oxygen, ferric iron, sulfate, and nitrate) become depleted, while hydrogen (H) and carbon dioxide accumulate. Light organics produced by fermentation also accumulate. During advanced stages of organic decay, all electron acceptors become depleted except carbon dioxide. Carbon dioxide is a product of most catabolic processes, so it is not depleted like other potential electron acceptors.
Only methanogenesis and fermentation can occur in the absence of electron acceptors other than carbon. Fermentation only allows the breakdown of larger organic compounds, and produces small organic compounds. Methanogenesis effectively removes the semi-final products of decay: hydrogen, small organics, and carbon dioxide. Without methanogenesis, a great deal of carbon (in the form of fermentation products) would accumulate in anaerobic environments. | 1 | Applied and Interdisciplinary Chemistry |
The Peter Debye Award in Physical Chemistry is awarded annually by the American Chemical Society "to encourage and reward outstanding research in physical chemistry". The award is named after Peter Debye and
granted without regard to age or nationality. | 0 | Theoretical and Fundamental Chemistry |
In the experiment a droplet of mercury is placed in a watch glass, immersed in an electrolyte such as sulfuric acid which contains an oxidizing agent such as hydrogen peroxide, potassium permanganate, or potassium dichromate. The tip of an iron nail is positioned almost touching the mercury. If the position of the nail tip is just right, the mercury blob begins to oscillate, changing shape. | 0 | Theoretical and Fundamental Chemistry |
Quinapril, sold under the brand name Accupril by the Pfizer corporation. It a medication used to treat high blood pressure (hypertension), heart failure, and diabetic kidney disease. It is a first line treatment for high blood pressure. It is taken by mouth.
Common side effects include headaches, dizziness, feeling tired, and cough. Serious side effects may include liver problems, low blood pressure, angioedema, kidney problems, and high blood potassium. Use in pregnancy and breastfeeding is not recommended. It is among a class of drugs called ACE inhibitors and works by decreasing renin-angiotensin-aldosterone system activity.
Quinapril was patented in 1980 and came into medical use in 1989. It is available as a generic medication. In 2020, it was the 253rd most commonly prescribed medication in the United States, with more than 1million prescriptions. | 0 | Theoretical and Fundamental Chemistry |
Acylhydrazines are derivatives of carboxylic acids, although they are typically prepared by the reaction of esters with hydrazine: | 0 | Theoretical and Fundamental Chemistry |
Thionoesters are isomeric with thioesters. In a thionoester, sulfur replaces the carbonyl oxygen in an ester. Methyl thionobenzoate is CHC(S)OCH. Such compounds are typically prepared by the reaction of the thioacyl chloride with an alcohol.
They can also be made by the reaction of Lawesson's reagent with esters or by treating pinner salts with hydrogen sulphide. An alternatively, various thionoesters may be prepared through the transesterification of an existing methyl thionoester with an alcohol under base-catalyzed conditions.
Xanthates and thioamides can be transformed to thionoesters under metal-catalyzed cross-coupling conditions. | 0 | Theoretical and Fundamental Chemistry |
The MACS method allows cells to be separated by using magnetic nanoparticles coated with antibodies against a particular surface antigen. This causes the cells expressing this antigen to attach to the magnetic nanoparticles. After incubating the beads and cells, the solution is transferred to a column in a strong magnetic field. In this step, the cells attached to the nanoparticles (expressing the antigen) stay on the column, while other cells (not expressing the antigen) flow through. With this method, the cells can be separated positively or negatively with respect to the particular antigen(s). | 1 | Applied and Interdisciplinary Chemistry |
In comparison with terrestrial-based biofuel crops such as corn or soybeans, microalgal production results in a much less significant land footprint due to the higher oil productivity from the microalgae than all other oil crops. Algae can also be grown on marginal lands useless for ordinary crops and with low conservation value, and can use water from salt aquifers that is not useful for agriculture or drinking. Algae can also grow on the surface of the ocean in bags or floating screens. Thus microalgae could provide a source of clean energy with little impact on the provisioning of adequate food and water or the conservation of biodiversity. Algae cultivation also requires no external subsidies of insecticides or herbicides, removing any risk of generating associated pesticide waste streams. In addition, algal biofuels are much less toxic, and degrade far more readily than petroleum-based fuels. However, due to the flammable nature of any combustible fuel, there is potential for some environmental hazards if ignited or spilled, as may occur in a train derailment or a pipeline leak. This hazard is reduced compared to fossil fuels, due to the ability for algal biofuels to be produced in a much more localized manner, and due to the lower toxicity overall, but the hazard is still there nonetheless. Therefore, algal biofuels should be treated in a similar manner to petroleum fuels in transportation and use, with sufficient safety measures in place at all times.
Studies have determined that replacing fossil fuels with renewable energy sources, such as biofuels, have the capability of reducing emissions by up to 80%. An algae-based system could capture approximately 80% of the emitted from a power plant when sunlight is available. Although this will later be released into the atmosphere when the fuel is burned, this would have entered the atmosphere regardless. The possibility of reducing total emissions therefore lies in the prevention of the release of from fossil fuels. Furthermore, compared to fuels like diesel and petroleum, and even compared to other sources of biofuels, the production and combustion of algal biofuel does not produce any sulfur oxides or nitrous oxides, and produces a reduced amount of carbon monoxide, unburned hydrocarbons, and reduced emission of other harmful pollutants. Since terrestrial plant sources of biofuel production simply do not have the production capacity to meet current energy requirements, microalgae may be one of the only options to approach complete replacement of fossil fuels.
Microalgae production also includes the ability to use saline waste or waste streams as an energy source. This opens a new strategy to produce biofuel in conjunction with waste water treatment, while being able to produce clean water as a byproduct. When used in a microalgal bioreactor, harvested microalgae will capture significant quantities of organic compounds as well as heavy metal contaminants absorbed from wastewater streams that would otherwise be directly discharged into surface and ground-water. Moreover, this process also allows the recovery of phosphorus from waste, which is an essential but scarce element in nature – the reserves of which are estimated to have depleted in the last 50 years. Another possibility is the use of algae production systems to clean up non-point source pollution, in a system known as an algal turf scrubber (ATS). This has been demonstrated to reduce nitrogen and phosphorus levels in rivers and other large bodies of water affected by eutrophication, and systems are being built that will be capable of processing up to 110 million liters of water per day. ATS can also be used for treating point source pollution, such as the waste water mentioned above, or in treating livestock effluent. | 1 | Applied and Interdisciplinary Chemistry |
In plants, animals and bacteria the glycine cleavage system catalyzes the following reversible reaction:
: Glycine + Hfolate + NAD ↔ 5,10-methylene-Hfolate + CO + NH + NADH + H
In the enzymatic reaction, H-protein activates the P-protein, which catalyzes the decarboxylation of glycine and attaches the intermediate molecule to the H-protein to be shuttled to the T-protein. The H-protein forms a complex with the T-protein that uses tetrahydrofolate and yields ammonia and 5,10-methylenetetrahydrofolate. After interaction with the T-protein, the H-protein is left with two fully reduced thiol groups in the lipoate group. The glycine protein system is regenerated when the H-protein is oxidized to regenerate the disulfide bond in the active site by interaction with the L-protein, which reduces NAD to NADH and H.
When coupled to serine hydroxymethyltransferase, the glycine cleavage system overall reaction becomes:
: 2 glycine + NAD + HO → serine + CO + NH + NADH + H
In humans and most vertebrates, the glycine cleavage system is part of the most prominent glycine and serine catabolism pathway. This is due in large part to the formation 5,10-methylenetetrahydrofolate, which is one of the few C donors in biosynthesis. In this case the methyl group derived from the catabolism of glycine can be transferred to other key molecules such as purines and methionine.
This reaction, and by extension the glycine cleavage system, is required for photorespiration in C plants. The glycine cleavage system takes glycine, which is created from an unwanted byproduct of the Calvin cycle, and converts it to serine which can reenter the cycle. The ammonia generated by the glycine cleavage system, is assimilated by the Glutamine synthetase-Glutamine oxoglutarate aminotransferase cycle but costs the cell one ATP and one NADPH. The upside is that one CO is produced for every two O that are mistakenly taken up by the cell, generating some value in an otherwise energy depleting cycle. Together the proteins involved in these reactions comprise about half the proteins in mitochondria from spinach and pea leaves. The glycine cleavage system is constantly present in the leaves of plants, but in small amounts until they are exposed to light. During peak photosynthesis, the concentration of the glycine cleavage system increases ten-fold.
In the anaerobic bacteria, Clostridium acidiurici, the glycine cleavage system runs mostly in the direction of glycine synthesis. While glycine synthesis through the cleavage system is possible due to the reversibility of the overall reaction, it is not readily seen in animals. | 1 | Applied and Interdisciplinary Chemistry |
For very long nonlinear waves, with the parameter m close to one, m → 1, the Jacobi elliptic function cn can be approximated by
: with
Here sinh, cosh, tanh and sech are hyperbolic functions. In the limit m = 1:
with sech(z) = 1 / cosh(z).
Further, for the same limit of m → 1, the complete elliptic integral of the first kind K(m) goes to infinity, while the complete elliptic integral of the second kind E(m) goes to one. This implies that the limiting values of the phase speed c and minimum elevelation η become:
: and
Consequently, in terms of the width parameter Δ, the solitary wave solution to both the KdV and BBM equation is:
The width parameter, as found for the cnoidal waves and now in the limit m → 1, is different for the KdV and the BBM equation:
But the phase speed of the solitary wave in both equations is the same, for a certain combination of height H and depth h. | 1 | Applied and Interdisciplinary Chemistry |
The small size of nanoenzymes (or nanozymes) (1–100 nm) has provided them with unique optical, magnetic, electronic, and catalytic properties. Moreover, the control of surface functionality of nanoparticles and the predictable nanostructure of these small-sized enzymes have allowed them to create a complex structure on their surface that can meet the needs of specific applications | 0 | Theoretical and Fundamental Chemistry |
Compilation of data into secure and readily searchable databases ensures ease of use and is fundamental to the success of the programme. The [http://www.bodc.ac.uk/geotraces/ GEOTRACES Data Assembly Centre] (GDAC) is responsible for the compilation, quality control and secure archiving of data received from national data centers and from core international GEOTRACES cruises. It has as its main aims the integration of core GEOTRACES data into global data sets, and making this data accessible to participating scientist and the larger science community according to the GEOTRACES data policy. The GDAC is hosted at the British Oceanographic Data Centre and a dedicated committee with international representation oversees it. | 0 | Theoretical and Fundamental Chemistry |
A lithium–ammonia solution at −60 °C is saturated at about 15 mol% metal (MPM). When the concentration is increased in this range electrical conductivity increases from 10 to 10 Ωcm (larger than liquid mercury). At around 8 MPM, a "transition to the metallic state" (TMS) takes place (also called a "metal-to-nonmetal transition" (MNMT)). At 4 MPM a liquid-liquid phase separation takes place: the less dense gold-colored phase becomes immiscible from a denser blue phase. Above 8 MPM the solution is bronze/gold-colored. In the same concentration range the overall density decreases by 30%. | 0 | Theoretical and Fundamental Chemistry |
CF allows the single/low copy sequences and the repetitive sequences of a genome to be studied independently of each other. It can also be used to fractionate highly repetitive DNA from moderately repetitive sequences or to further fractionate isolated kinetic components. CF is most accurately performed if fractionation is based upon the results of a Cot analysis. | 1 | Applied and Interdisciplinary Chemistry |
Transport theory provides an alternative interpretation of viscosity in terms of momentum transport: viscosity is the material property which characterizes momentum transport within a fluid, just as thermal conductivity characterizes heat transport, and (mass) diffusivity characterizes mass transport. This perspective is implicit in Newtons law of viscosity, , because the shear stress has units equivalent to a momentum flux, i.e., momentum per unit time per unit area. Thus, can be interpreted as specifying the flow of momentum in the direction from one fluid layer to the next. Per Newtons law of viscosity, this momentum flow occurs across a velocity gradient, and the magnitude of the corresponding momentum flux is determined by the viscosity.
The analogy with heat and mass transfer can be made explicit. Just as heat flows from high temperature to low temperature and mass flows from high density to low density, momentum flows from high velocity to low velocity. These behaviors are all described by compact expressions, called constitutive relations, whose one-dimensional forms are given here:
where is the density, and are the mass and heat fluxes, and and are the mass diffusivity and thermal conductivity. The fact that mass, momentum, and energy (heat) transport are among the most relevant processes in continuum mechanics is not a coincidence: these are among the few physical quantities that are conserved at the microscopic level in interparticle collisions. Thus, rather than being dictated by the fast and complex microscopic interaction timescale, their dynamics occurs on macroscopic timescales, as described by the various equations of transport theory and hydrodynamics. | 1 | Applied and Interdisciplinary Chemistry |
Mainly associated with abnormalities that result in neurodegenerative diseases. Tau proteins stabilize microtubules, and thus shift the reaction kinetics in favor of addition of new subunits, accelerating microtubule growth. Tau has the additional function of facilitating bundling of microtubules within the nerve cell. The function of tau has been linked to the neurological condition Alzheimers disease. In the nervous tissue of Alzheimers patients, tau forms abnormal aggregates. This aggregated tau is often severely modified, most commonly through hyperphosphorylation. As described above, phosphorylation of MAPs causes them to detach from microtubules. Thus, the hyperphosphorylation of tau leads to massive detachment, which in turn greatly reduces the stability of microtubules in nerve cells.[9] This increase in microtubule instability may be one of the main causes of the symptoms of Alzheimer's disease. | 1 | Applied and Interdisciplinary Chemistry |
was first prepared in 1835 by M. Gregory by the reaction of disulfur dichloride with ammonia, a process that has been optimized:
Coproducts of this reaction include heptasulfur imide () and elemental sulfur. A related synthesis employs instead:
An alternative synthesis entails the use of as a precursor with pre-formed S–N bonds. is prepared by the reaction of lithium bis(trimethylsilyl)amide and sulfur dichloride|.
The reacts with the combination of and sulfuryl chloride| to form , trimethylsilyl chloride, and sulfur dioxide: | 0 | Theoretical and Fundamental Chemistry |
When studying or discussing explosive safety, or the safety of systems containing explosives, the terms deflagration, detonation and deflagration-to-detonation transition (commonly referred to as DDT) must be understood and used appropriately to convey relevant information. As explained above, a deflagration is a subsonic reaction, whereas a detonation is a supersonic (greater than the [https://www.nde-ed.org/Physics/Sound/vibration.xhtml sound speed of the material]) reaction. Distinguishing between a deflagration or a detonation can be difficult to impossible to the casual observer. Rather, confidently differentiating between the two requires instrumentation and diagnostics to ascertain reaction speed in the affected material. Therefore, when an unexpected event or an accident occurs with an explosive material or an explosive-containing system it is usually impossible to know whether the explosive deflagrated or detonated as both can appear as very violent, energetic reactions. Therefore, the energetic materials community coined the term "high explosive violent reaction" or "HEVR" to describe a violent reaction that, because it lacked diagnostics to measure sound-speed, could have been either a deflagration or a detonation. | 0 | Theoretical and Fundamental Chemistry |
An initial metabolic reconstruction of a genome is typically far from perfect due to the high variability and diversity of microorganisms. Often, metabolic pathway databases such as KEGG and MetaCyc will have "holes", meaning that there is a conversion from a substrate to a product (i.e., an enzymatic activity) for which there is no known protein in the genome that encodes the enzyme that facilitates the catalysis. What can also happen in semi-automatically drafted reconstructions is that some pathways are falsely predicted and don't actually occur in the predicted manner. Because of this, a systematic verification is made in order to make sure no inconsistencies are present and that all the entries listed are correct and accurate. Furthermore, previous literature can be researched in order to support any information obtained from one of the many metabolic reaction and genome databases. This provides an added level of assurance for the reconstruction that the enzyme and the reaction it catalyzes do actually occur in the organism.
Enzyme promiscuity and spontaneous chemical reactions can damage metabolites. This metabolite damage, and its repair or pre-emption, create energy costs that need to be incorporated into models. It is likely that many genes of unknown function encode proteins that repair or pre-empt metabolite damage, but most genome-scale metabolic reconstructions only include a fraction of all genes.
Any new reaction not present in the databases needs to be added to the reconstruction. This is an iterative process that cycles between the experimental phase and the coding phase. As new information is found about the target organism, the model will be adjusted to predict the metabolic and phenotypical output of the cell. The presence or absence of certain reactions of the metabolism will affect the amount of reactants/products that are present for other reactions within the particular pathway. This is because products in one reaction go on to become the reactants for another reaction, i.e. products of one reaction can combine with other proteins or compounds to form new proteins/compounds in the presence of different enzymes or catalysts.
Francke et al. provide an excellent example as to why the verification step of the project needs to be performed in significant detail. During a metabolic network reconstruction of Lactobacillus plantarum, the model showed that succinyl-CoA was one of the reactants for a reaction that was a part of the biosynthesis of methionine. However, an understanding of the physiology of the organism would have revealed that due to an incomplete tricarboxylic acid pathway, Lactobacillus plantarum does not actually produce succinyl-CoA, and the correct reactant for that part of the reaction was acetyl-CoA.
Therefore, systematic verification of the initial reconstruction will bring to light several inconsistencies that can adversely affect the final interpretation of the reconstruction, which is to accurately comprehend the molecular mechanisms of the organism. Furthermore, the simulation step also ensures that all the reactions present in the reconstruction are properly balanced. To sum up, a reconstruction that is fully accurate can lead to greater insight about understanding the functioning of the organism of interest. | 1 | Applied and Interdisciplinary Chemistry |
BUN is usually reported in mg/dL in some countries (e.g. United States, Mexico, Italy, Austria, and Germany). Elsewhere, the concentration of urea is reported in SI units as mmol/L.
represents the mass of nitrogen within urea/volume, not the mass of whole urea. Each molecule of urea has two nitrogen atoms, each having molar mass 14 g/mol. To convert from mg/dL of blood urea nitrogen to mmol/L of urea:
Note that molar concentrations of urea and urea nitrogen are equal, because both nitrogen gas and urea has two nitrogen atoms.
Convert BUN to urea in mg/dL by using following formula:
Where 60 represents MW of urea and 14*2 MW of urea nitrogen. | 1 | Applied and Interdisciplinary Chemistry |
21st Century Medicine (21CM) is a California cryobiological research company which has as its primary focus the development of perfusates and protocols for viable long-term cryopreservation of human organs, tissues and cells at temperatures below −100 °C through the use of vitrification. 21CM was founded in 1993.
In 2004 21CM received a $900,000 grant from the U.S. National Institutes of Health (NIH) to study a preservation solution developed by the University of Rochester in New York for extending simple cold storage time of human hearts removed for transplant.
At the July 2005 annual conference of the Society for Cryobiology, 21st Century Medicine announced the vitrification of a rabbit kidney to −135 °C with their vitrification mixture. The kidney was successfully transplanted upon rewarming to a rabbit, the rabbit being euthanized on the 48th day for histological follow-up.
On February 9, 2016, 21st Century Medicine won the Small Mammal Brain Preservation Prize. On March 13, 2018, they won the Large Mammal Brain Preservation Prize. | 1 | Applied and Interdisciplinary Chemistry |
He received his degree at the University of Barcelona in 1944, his doctorate in Madrid, and finished his training at Harvard University in 1951. In 1944 he formed a team at the Spanish National Research Council. His work has largely been in kinetics and organic chemistry. | 0 | Theoretical and Fundamental Chemistry |
Four drugs from the class of direct Xa inhibitors are marketed worldwide. Rivaroxaban (Xarelto) was the first approved FXa inhibitor to become commercially available in Europe and Canada in 2008. The second one was apixaban (Eliquis), approved in Europe in 2011 and in the United States in 2012. The third one edoxaban (Lixiana, Savaysa) was approved in Japan in 2011 and in Europe and the US in 2015. Betrixaban (Bevyxxa) was approved in the US in 2017. | 1 | Applied and Interdisciplinary Chemistry |
Many reactions involving nucleophiles attacking electrophiles can be usefully assessed from the perspective of an incipient charge-transfer complex. Examples include electrophilic aromatic substitution, the addition of Grignard reagents to ketones, and brominolysis of metal-alkyl bonds. | 0 | Theoretical and Fundamental Chemistry |
It is important to note that the list given above is qualitative and describes trends. The ability of a group to leave is contextual. For example, in SAr reactions, the rate is generally increased when the leaving group is fluoride relative to the other halogens. This effect is due to the fact that the highest energy transition state for this two step addition-elimination process occurs in the first step, where fluoride's greater electron withdrawing capability relative to the other halides stabilizes the developing negative charge on the aromatic ring. The departure of the leaving group takes place quickly from this high energy Meisenheimer complex, and since the departure is not involved in the rate limiting step, it does not affect the overall rate of the reaction. This effect is general to conjugate base eliminations.
Even when the departure of the leaving group is involved in the rate limiting step of a reaction there can still exist contextual differences that can change the order of leaving group ability. In Friedel-Crafts alkylations, the normal halogen leaving group order is reversed so that the rate of the reaction follows RF > RCl > RBr > RI. This effect is due to their greater ability to complex the Lewis acid catalyst, and the actual group that leaves is an "ate" complex between the Lewis acid and the departing leaving group. This situation is broadly defined as leaving group activation.
There can still exist contextual differences in leaving group ability in the purest form, that is when the actual group that leaves is not affected by the reaction conditions (by protonation or Lewis acid complexation) and the departure of the leaving group occurs in the rate determining step. In the situation where other variables are held constant (nature of the alkyl electrophile, solvent, etc.), a change in nucleophile can lead to a change in the order of reactivity for leaving groups. In the case below, tosylate is the best leaving group when ethoxide is the nucleophile, but iodide and even bromide become better leaving groups in the case of the thiolate nucleophile. | 0 | Theoretical and Fundamental Chemistry |
A molecular vibration is a periodic motion of the atoms of a molecule relative to each other, such that the center of mass of the molecule remains unchanged. The typical vibrational frequencies range from less than 10 Hz to approximately 10 Hz, corresponding to wavenumbers of approximately 300 to 3000 cm and wavelengths of approximately 30 to 3 µm.
For a diatomic molecule A−B, the vibrational frequency in s is given by , where k is the force constant in dyne/cm or erg/cm and μ is the reduced mass given by . The vibrational wavenumber in cm is where c is the speed of light in cm/s.
Vibrations of polyatomic molecules are described in terms of normal modes, which are independent of each other, but each normal mode involves simultaneous vibrations of different parts of the molecule. In general, a non-linear molecule with N atoms has 3N – 6 normal modes of vibration, but a linear molecule has 3N – 5 modes, because rotation about the molecular axis cannot be observed. A diatomic molecule has one normal mode of vibration, since it can only stretch or compress the single bond.
A molecular vibration is excited when the molecule absorbs energy, ΔE, corresponding to the vibrations frequency, ν, according to the relation ΔE = hν, where h is Plancks constant. A fundamental vibration is evoked when one such quantum of energy is absorbed by the molecule in its ground state. When multiple quanta are absorbed, the first and possibly higher overtones are excited.
To a first approximation, the motion in a normal vibration can be described as a kind of simple harmonic motion. In this approximation, the vibrational energy is a quadratic function (parabola) with respect to the atomic displacements and the first overtone has twice the frequency of the fundamental. In reality, vibrations are anharmonic and the first overtone has a frequency that is slightly lower than twice that of the fundamental. Excitation of the higher overtones involves progressively less and less additional energy and eventually leads to dissociation of the molecule, because the potential energy of the molecule is more like a Morse potential or more accurately, a Morse/Long-range potential.
The vibrational states of a molecule can be probed in a variety of ways. The most direct way is through infrared spectroscopy, as vibrational transitions typically require an amount of energy that corresponds to the infrared region of the spectrum. Raman spectroscopy, which typically uses visible light, can also be used to measure vibration frequencies directly. The two techniques are complementary and comparison between the two can provide useful structural information such as in the case of the rule of mutual exclusion for centrosymmetric molecules.
Vibrational excitation can occur in conjunction with electronic excitation in the ultraviolet-visible region. The combined excitation is known as a vibronic transition, giving vibrational fine structure to electronic transitions, particularly for molecules in the gas state.
Simultaneous excitation of a vibration and rotations gives rise to vibration–rotation spectra. | 0 | Theoretical and Fundamental Chemistry |
In fluid mechanics, Kelvin's circulation theorem (named after William Thomson, 1st Baron Kelvin who published it in 1869) states:
Stated mathematically:
where is the circulation around a material contour Stated more simply, this theorem says that if one observes a closed contour at one instant, and follows the contour over time (by following the motion of all of its fluid elements), the circulation over the two locations of this contour are equal.
This theorem does not hold in cases with viscous stresses, nonconservative body forces (for example the Coriolis force) or non-barotropic pressure-density relations. | 1 | Applied and Interdisciplinary Chemistry |
Strep Tamer is a technology which allows the reversible isolation and staining of antigen-specific T-cells. This technology combines a current T-cell isolation method with the Strep-Tag technology. In principle, the T-cells are separated by establishing a specific interaction between the T-cell of interest and a molecule, that is conjugated to a marker which enables the isolation. The reversibility of this interaction and the low temperatures at which it is performed allow for the isolation and characterization of functional T-cells. Because T-cells remain phenotypically and functionally indistinguishable from untreated cells, this method offers modern strategies in clinical and basic T-cell research. | 1 | Applied and Interdisciplinary Chemistry |
Many adhesion GPCRs undergo proteolytic events posttranslationally at highly conserved Cys-rich motifs known as GPCR proteolysis sites (GPS), located next to the first transmembrane region. This site is called the HL-S(T) site. Once this protein is cleaved, the pieces are expressed at the cell surface as a heterodimer. This cleavage is thought to happen from within the protein itself, through the conserved GAIN domain. This process seems to be similar to those found in other auto-proteolytic proteins such as the Ntn hydrolases and hedgehog proteins. | 1 | Applied and Interdisciplinary Chemistry |
Sandwich assays are generally used for larger analytes because they tend to have multiple binding sites. As the sample migrates through the assay it first encounters a conjugate, which is an antibody specific to the target analyte labelled with a visual tag, usually colloidal gold. The antibodies bind to the target analyte within the sample and migrate together until they reach the test line. The test line also contains immobilized antibodies specific to the target analyte, which bind to the migrated analyte bound conjugate molecules. The test line then presents a visual change due to the concentrated visual tag, hence confirming the presence of the target molecules. The majority of sandwich assays also have a control line which will appear whether or not the target analyte is present to ensure proper function of the lateral flow pad.
The rapid, low-cost sandwich-based assay is commonly used for home pregnancy tests which detect human chorionic gonadotropin, hCG, in the urine of pregnant women. | 1 | Applied and Interdisciplinary Chemistry |
Transition metal-based bioconjugation had been challenging due to the nature of biological conditions – aqueous solution, room temperature, mild pH, and low substrate concentrations – which are generally challenging for organometallic reactions. However, recently, besides [[CuAAC|copper-catalyzed [3 + 2] azide alkyne cycloaddition]] reaction, more and more diverse transition metal-mediated chemical transformations have been applied for bioconjugation reactions, introducing olefin metathesis, alkylation, C–H arylation, C–C, C–S, and C–N cross-coupling reactions. | 1 | Applied and Interdisciplinary Chemistry |
In linear elasticity, the stress and strain are related by Hooke's law, i.e.,
or, using Voigt notation,
The condition for material symmetry in linear elastic materials is.
where | 0 | Theoretical and Fundamental Chemistry |
The cellular reproduction process of meiosis was discovered by Oscar Hertwig in 1876. Mitosis was discovered several years later in 1882 by Walther Flemming.
Hertwig studied sea urchins, and noticed that each egg contained one nucleus prior to fertilization and two nuclei after. This discovery proved that one spermatozoon could fertilize an egg, and therefore proved the process of meiosis. Hermann Fol continued Hertwig's research by testing the effects of injecting several spermatozoa into an egg, and found that the process did not work with more than one spermatozoon.
Flemming began his research of cell division starting in 1868. The study of cells was an increasingly popular topic in this time period. By 1873, Schneider had already begun to describe the steps of cell division. Flemming furthered this description in 1874 and 1875 as he explained the steps in more detail. He also argued with Schneider's findings that the nucleus separated into rod-like structures by suggesting that the nucleus actually separated into threads that in turn separated. Flemming concluded that cells replicate through cell division, to be more specific mitosis.
Matthew Meselson and Franklin Stahl are credited with the discovery of DNA replication. Watson and Crick acknowledged that the structure of DNA did indicate that there is some form of replicating process. However, there was not a lot of research done on this aspect of DNA until after Watson and Crick. People considered all possible methods of determining the replication process of DNA, but none were successful until Meselson and Stahl. Meselson and Stahl introduced a heavy isotope into some DNA and traced its distribution. Through this experiment, Meselson and Stahl were able to prove that DNA reproduces semi-conservatively. | 1 | Applied and Interdisciplinary Chemistry |
Photo-reflectance is a particularly convenient type of modulation spectroscopy, as it may be performed at room temperature and only requires the sample have a reflecting surface. It is an established tool for non-contact determination of material and electronic properties of semiconductor films. In photo-reflectance, a pump laser beam is used to modulate the free charge density in a semiconductor sample (via photo-injection), thereby modulating one or more physical quantities (e.g. the internal electric field). The measured signal ΔR is the change in amplitude of the reflected probe light as the intensity modulated pump radiation interacts with the sample. The normalized signal is ΔR/R, i.e. the pump-induced change in reflectance (AC) divided by the baseline reflectance (DC). The conventional photo-reflectance apparatus uses a spectroscopic source for the probe beam, such that the signal may be recorded as a function of the probe light's wavelength. Generally, the signal may be written:
where ΔR/R is the normalized change in reflectance, α (≡1/R×∂R/∂ε) and β (≡1/R×∂R/∂ε) are the "Seraphin coefficients" which contain filmstack information, and Δε and Δε are the pump induced changes in the complex dielectric function. However, in conventional photo-reflectance analysis, it is not necessary to independently determine the refractive and absorptive components (the first and second terms in ΔR/R, respectively) of the signal. Rather, a fit to the overall signal is performed using the third derivative functional form given by Aspnes. This fit procedure yields the interband transition energies, amplitudes, and widths. However, because the signal depends on the uniformity of the perturbation, the extraction of such parameters must be treated with care. | 0 | Theoretical and Fundamental Chemistry |
HDPE piping is estimated to last 50 years. However, technical white papers written by the Plastics Industry Pipe Association assert that HDPE pipe systems can be reasonably expected to last up to, or over 100 years. | 1 | Applied and Interdisciplinary Chemistry |
5-Methyluridine triphosphate or mUTP is one of five nucleoside triphosphates. It is the ribonucleoside triphosphate of thymidine, but the nomenclature with "5-methyluridine" is used because the term thymidine triphosphate is used for the deoxyribonucleoside by convention. | 1 | Applied and Interdisciplinary Chemistry |
Common effects (1–10% incidence) include:
* Abnormal dreams
* Anisocoria
* Anorgasmia
* Anxiety
* Arthralgia (joint pain)
* Constipation
* Decreased or increased appetite
* Diarrhea
* Dilated pupils
* Dizziness
* Dry mouth
* Excessive sweating
* Fatigue
* Impotence (erectile dysfunction)
* Libido changes
* Myalgia (muscular aches and pains)
* Paraesthesia (abnormal skin sensation)
* Pyrexia (fever)
* Restlessness
* Sinusitis (nasal congestion)
* Tremor
* Vomiting
* Yawning | 0 | Theoretical and Fundamental Chemistry |
As shown in Eq. 2, the neutral pathway of the Heck reaction begins with the oxidative addition of the aryl or alkenyl halide into a coordinatively unsaturated palladium(0) complex (typically bound to two phosphine ligands) to give complex I. Dissociation of a phosphine ligand followed by association of the alkene yields complex II, and migratory insertion of the alkene into the carbon-palladium bond establishes the key carbon-carbon bond.
Insertion takes place in a suprafacial fashion, but the dihedral angle between the alkene and palladium-carbon bond during insertion can vary from 0° to ~90°. After insertion, β-hydride elimination affords the product and a palladium(II)-hydrido complex IV, which is reduced by base back to palladium(0). | 0 | Theoretical and Fundamental Chemistry |
The distribution coefficient, log D, is the ratio of the sum of the concentrations of all forms of the compound (ionized plus un-ionized) in each of the two phases, one essentially always aqueous; as such, it depends on the pH of the aqueous phase, and log D = log P for non-ionizable compounds at any pH. For measurements of distribution coefficients, the pH of the aqueous phase is buffered to a specific value such that the pH is not significantly perturbed by the introduction of the compound. The value of each log D is then determined as the logarithm of a ratio—of the sum of the experimentally measured concentrations of the solute's various forms in one solvent, to the sum of such concentrations of its forms in the other solvent; it can be expressed as
In the above formula, the superscripts "ionized" each indicate the sum of concentrations of all ionized species in their respective phases. In addition, since log D is pH-dependent, the pH at which the log D was measured must be specified. In areas such as drug discovery—areas involving partition phenomena in biological systems such as the human body—the log D at the physiologic pH = 7.4 is of particular interest.
It is often convenient to express the log D in terms of P, defined above (which includes P as state ), thus covering both un-ionized and ionized species. For example, in octanol–water:
which sums the individual partition coefficients (not their logarithms), and where indicates the pH-dependent mole fraction of the -th form (of the solute) in the aqueous phase, and other variables are defined as previously. | 0 | Theoretical and Fundamental Chemistry |
Typical stages in 5S rRNA (also termed class I) gene initiation:
*TFIIIA (Transcription Factor for polymerase III A) binds to the intragenic (lying within the transcribed DNA sequence) 5S rRNA control sequence, the C Block (also termed box C).
*TFIIIA serves as a platform that replaces the A and B Blocks for positioning TFIIIC in an orientation with respect to the start site of transcription that is equivalent to what is observed for tRNA genes.
*Once TFIIIC is bound to the TFIIIA-DNA complex, the assembly of TFIIIB proceeds as described for tRNA transcription. | 1 | Applied and Interdisciplinary Chemistry |
Mieli was a member of the Socialist Party, which led to his election as town councillor in Chianciano in 1901. He left in 1903. Mieli claimed in his autobiography that he left the Socialist movement due to the lack of sincerity and idealism in the movement. Police records, however, showed that Mielis homosexuality, referred to as manifest immorality' was well known in the local area, which would have severely inhibited his political career.
Secret police raided his flat in Rome in 1929, just a few months after he had moved to France. Mieli's friend Gino Chiappini, a typographer, and his friend Angelo Pisani were living there at the time. By 1930, police records marked him as a "dangerous socialist". | 1 | Applied and Interdisciplinary Chemistry |
An enzyme inhibitor is a molecule that binds to an enzyme and blocks its activity. Enzymes are proteins that speed up chemical reactions necessary for life, in which substrate molecules are converted into products. An enzyme facilitates a specific chemical reaction by binding the substrate to its active site, a specialized area on the enzyme that accelerates the most difficult step of the reaction.
An enzyme inhibitor stops ("inhibits") this process, either by binding to the enzymes active site (thus preventing the substrate itself from binding) or by binding to another site on the enzyme such that the enzymes catalysis of the reaction is blocked. Enzyme inhibitors may bind reversibly or irreversibly. Irreversible inhibitors form a chemical bond with the enzyme such that the enzyme is inhibited until the chemical bond is broken. By contrast, reversible inhibitors bind non-covalently and may spontaneously leave the enzyme, allowing the enzyme to resume its function. Reversible inhibitors produce different types of inhibition depending on whether they bind to the enzyme, the enzyme-substrate complex, or both.
Enzyme inhibitors play an important role in all cells, since they are generally specific to one enzyme each and serve to control that enzyme's activity. For example, enzymes in a metabolic pathway may be inhibited by molecules produced later in the pathway, thus curtailing the production of molecules that are no longer needed. This type of negative feedback is an important way to maintain balance in a cell. Enzyme inhibitors also control essential enzymes such as proteases or nucleases that, if left unchecked, may damage a cell. Many poisons produced by animals or plants are enzyme inhibitors that block the activity of crucial enzymes in prey or predators.
Many drug molecules are enzyme inhibitors that inhibit an aberrant human enzyme or an enzyme critical for the survival of a pathogen such as a virus, bacterium or parasite. Examples include methotrexate (used in chemotherapy and in treating rheumatic arthritis) and the protease inhibitors used to treat HIV/AIDS. Since anti-pathogen inhibitors generally target only one enzyme, such drugs are highly specific and generally produce few side effects in humans, provided that no analogous enzyme is found in humans. (This is often the case, since such pathogens and humans are genetically distant.) Medicinal enzyme inhibitors often have low dissociation constants, meaning that only a minute amount of the inhibitor is required to inhibit the enzyme. A low concentration of the enzyme inhibitor reduces the risk for liver and kidney damage and other adverse drug reactions in humans. Hence the discovery and refinement of enzyme inhibitors is an active area of research in biochemistry and pharmacology. | 1 | Applied and Interdisciplinary Chemistry |
UDP-glucuronic acid is a sugar used in the creation of polysaccharides and is an intermediate in the biosynthesis of ascorbic acid (except in primates and guinea pigs). It also participates in the heme degradation process of human.
It is made from UDP-glucose by UDP-glucose 6-dehydrogenase (EC 1.1.1.22) using NAD+ as a cofactor. It is the source of the glucuronosyl group in glucuronosyltransferase reactions. | 1 | Applied and Interdisciplinary Chemistry |
p-Dimethylaminobenzaldehyde reacts with hydrazine to form p-Dimethylaminobenzalazine azo-dye which has a distinct yellow color. It is therefore used for spectrophotometric determination of hydrazine in aqueous solutions at 457 nm. | 0 | Theoretical and Fundamental Chemistry |
The (Z) group is another carbamate-type amine protecting group, discovered by Leonidas Zervas in the early 1930s and usually added via reaction with benzyl chloroformate.
It is removed under harsh conditions using HBr in acetic acid, or milder conditions of catalytic hydrogenation.
This methodology was first used in the synthesis of oligopeptides by Zervas and Max Bergmann in 1932. Hence, this became known as the Bergmann-Zervas synthesis, which was characterised "epoch-making" and helped establish synthetic peptide chemistry as a distinct field. It constituted the first useful lab method for controlled peptide synthesis, enabling the synthesis of previously unattainable peptides with reactive side-chains, while Z-protected amino acids are also prevented form undergoing racemization.
The use of the Bergmann-Zervas method remained the standard practice in peptide chemistry for two full decades after its publication, superseded by newer methods (such as the Boc protecting group) in the early 1950s. Nowadays, while it has been used periodically for α-amine protection, it is much more commonly used for side chain protection. | 1 | Applied and Interdisciplinary Chemistry |
Most monitoring programmes involve the periodic collection of low volume spot samples (bottle or grab) of water, which is challenging, particularly where levels fluctuate over time and when chemicals are only present at trace, yet toxicologically relevant concentrations. Chemcatcher® is used to measure time-weighted average (TWA) or equilibrium concentrations of a wide range of pollutants in water. This allows the end user to obtain a more representative picture of the chemicals that may be present in the aquatic environment. | 0 | Theoretical and Fundamental Chemistry |
The structure of vitamin B was the first low-molecular weight natural product determined by x-ray analysis rather than by chemical degradation. Thus, while the structure of this novel type of complex biomolecule was established, its chemistry remained essentially unknown; exploration of this chemistry became one of the tasks of the vitamin's chemical synthesis. In the 1960s, synthesis of such an exceptionally complex and unique structure presented the major challenge at the frontier of research in organic natural product synthesis.
Already in 1960, the research group of the biochemist in Stuttgart had reconstituted vitamin B from one of its naturally occurring derivatives, cobyric acid, by stepwise construction of the vitamin's nucleotide loop. This work amounted to a partial synthesis of vitamin B from a natural product containing all the structural elements of vitamin B except the nucleotide loop. Therefore, cobyric acid was chosen as the target molecule for a total synthesis of vitamin B.
Collaborative work of research groups at Harvard and at ETH resulted in two cobyric acid syntheses, both concomitantly accomplished in 1972, one at Harvard, and the other at ETH. A "competitive collaboration" of that size, involving 103 graduate students and postdoctoral researchers for a total almost 177 person-years, is so far unique in the history of organic synthesis. The two syntheses are intricately intertwined chemically, yet they differ basically in the way the central macrocyclic corrin ligand system is constructed. Both strategies are patterned after two model corrin syntheses developed at ETH. The first, published in 1964, achieved the construction of the corrin chromophore by combining an A-D-component with a B-C-component via iminoester/enamine-C,C-condensations, the final corrin-ring closure being attained between rings A and B. The second model synthesis, published 1969, explored a novel photochemical cycloisomerization process to create the direct A/D-ring junction as final corrin-ring closure between rings A and D.
The A/B approach to the cobyric acid syntheses was collaboratively pursued and accomplished in 1972 at Harvard. It combined a bicyclic Harvard A-D-component with an ETH B-C-component, and closed the macrocyclic corrin ring between rings A and B. The A/D approach to the synthesis, accomplished at ETH and finished at the same time as the A/B approach also in 1972, successively adds rings D and A to the B-C-component of the A/B approach and attains the corrin ring closure between rings A and D. The paths of the two syntheses met in a common corrinoid intermediate. The final steps from this intermediate to cobyric acid were carried out in the two laboratories again collaboratively, each group working with material prepared via their own approach, respectively. | 0 | Theoretical and Fundamental Chemistry |
It was excavated between 1968 and 1974 under the direction of German archaeologist Harald Hauptmann as part of the salvage project to document archaeological sites that would be flooded by the construction of the Keban Dam. Excavation of the site focused on three areas: the western slope, the so-called "acropolis" area, and the south terrace. | 1 | Applied and Interdisciplinary Chemistry |
The effect is named after Tanzanian scientist Erasto Mpemba. He described it in 1963 in Form 3 of Magamba Secondary School, Tanganyika; when freezing a hot ice cream mix in a cookery class, he noticed that it froze before a cold mix. He later became a student at Mkwawa Secondary (formerly High) School in Iringa. The headmaster invited Dr. Denis Osborne from the University College in Dar es Salaam to give a lecture on physics. After the lecture, Mpemba asked him, "If you take two similar containers with equal volumes of water, one at and the other at , and put them into a freezer, the one that started at freezes first. Why?" Mpemba was at first ridiculed by both his classmates and his teacher. After initial consternation, however, Osborne experimented on the issue back at his workplace and confirmed Mpemba's finding. They published the results together in 1969, while Mpemba was studying at the College of African Wildlife Management.
Mpemba and Osborne described placing samples of water in beakers in the icebox of a domestic refrigerator on a sheet of polystyrene foam. They showed the time for freezing to start was longest with an initial temperature of and that it was much less at around . They ruled out loss of liquid volume by evaporation and the effect of dissolved air as significant factors. In their setup, most heat loss was found to be from the liquid surface. | 0 | Theoretical and Fundamental Chemistry |
Typically, settled sewage flow enters at a high level and flows through the primary settlement tank. The supernatant from the tank flows into a dosing device, often a tipping bucket which delivers flow to the arms of the filter. The flush of water flows through the arms and exits through a series of holes pointing at an angle downwards. This propels the arms around distributing the liquid evenly over the surface of the filter media.
Most are uncovered (unlike the accompanying diagram) and are freely ventilated to the atmosphere.
The removal of pollutants from the waste water stream involves both absorption and adsorption of organic compounds and some inorganic species (such as nitrite and nitrate ions) by the layer of microbial biofilm. The filter media is typically chosen to provide a very high surface-to-volume ratio. Typical materials are often porous and have considerable internal surface area, in addition to the external surface of the medium. Passage of the wastewater over the media provides dissolved oxygen, which the biofilm layer requires for the biochemical oxidation of the organic compounds and releases carbon dioxide gas, water and other oxidized end products. As the biofilm layer thickens, it eventually sloughs off into the liquid flow and subsequently forms part of the secondary sludge. Typically, a trickling filter is followed by a clarifier or sedimentation tank for the separation and removal of the sloughed film. Filters utilizing higher-density media, such as sand, foam and peat moss do not produce a sludge that must be removed, but may require forced air blowers, backwashing, and/or an enclosed anaerobic environment. | 1 | Applied and Interdisciplinary Chemistry |
Of the known chemical elements, 80 elements have at least one stable nuclide. These comprise the first 82 elements from hydrogen to lead, with the two exceptions, technetium (element 43) and promethium (element 61), that do not have any stable nuclides. As of 2023, there were a total of 251 known "stable" nuclides. In this definition, "stable" means a nuclide that has never been observed to decay against the natural background. Thus, these elements have half-lives too long to be measured by any means, direct or indirect.
Stable isotopes:
* 1 element (tin) has 10 stable isotopes
* 5 elements have 7 stable isotopes apiece
* 7 elements have 6 stable isotopes apiece
* 11 elements have 5 stable isotopes apiece
* 9 elements have 4 stable isotopes apiece
* 5 elements have 3 stable isotopes apiece
* 16 elements have 2 stable isotopes apiece
* 26 elements have 1 single stable isotope.
These last 26 are thus called monoisotopic elements. The mean number of stable isotopes for elements which have at least one stable isotope is 251/80 = 3.1375. | 0 | Theoretical and Fundamental Chemistry |
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