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Some thiosemicarbazones have medicinal properties, e.g. the antiviral metisazone and the antibiotic thioacetazone. Thiosemicarbazones are also widely used as ligands in coordination chemistry. The affinity of thiosemicarbazones for metal ions is exploited in controlling iron overload. | 0 | Organic Chemistry |
Two compounds are said to be enantiomers if their molecules are mirror images of each other, that cannot be made to coincide only by rotations or translations – like a left hand and a right hand. The two shapes are said to be chiral.
A classical example is bromochlorofluoromethane (). The two enantiomers can be distinguished, for example, by whether the path turns clockwise or counterclockwise as seen from the hydrogen atom. In order to change one conformation to the other, at some point those four atoms would have to lie on the same plane – which would require severely straining or breaking their bonds to the carbon atom. The corresponding energy barrier between the two conformations is so high that there is practically no conversion between them at room temperature, and they can be regarded as different configurations.
The compound chlorofluoromethane , in contrast, is not chiral: the mirror image of its molecule is also obtained by a half-turn about a suitable axis.
Another example of a chiral compound is 2,3-pentadiene a hydrocarbon that contains two overlapping double bonds. The double bonds are such that the three middle carbons are in a straight line, while the first three and last three lie on perpendicular planes. The molecule and its mirror image are not superimposable, even though the molecule has an axis of symmetry. The two enantiomers can be distinguished, for example, by the right-hand rule. This type of isomerism is called axial isomerism.
Enantiomers behave identically in chemical reactions, except when reacted with chiral compounds or in the presence of chiral catalysts, such as most enzymes. For this latter reason, the two enantiomers of most chiral compounds usually have markedly different effects and roles in living organisms. In biochemistry and food science, the two enantiomers of a chiral molecule – such as glucose – are usually identified, and treated as very different substances.
Each enantiomer of a chiral compound typically rotates the plane of polarized light that passes through it. The rotation has the same magnitude but opposite senses for the two isomers, and can be a useful way of distinguishing and measuring their concentration in a solution. For this reason, enantiomers were formerly called "optical isomers". However, this term is ambiguous and is discouraged by the IUPAC.
Stereoisomers that are not enantiomers are called diastereomers. Some diastereomers may contain chiral center, some not.
Some enantiomer pairs (such as those of trans-cyclooctene) can be interconverted by internal motions that change bond lengths and angles only slightly. Other pairs (such as CHFClBr) cannot be interconverted without breaking bonds, and therefore are different configurations. | 4 | Stereochemistry |
Ferredoxin (Fd) is a soluble protein that facilitates reduction of to NADPH. Fd moves to carry an electron either to a lone thylakoid or to an enzyme that reduces . Thylakoid membranes have one binding site for each function of Fd. The main function of Fd is to carry an electron from the iron-sulfur complex to the enzyme ferredoxin– reductase. | 5 | Photochemistry |
In the last step of duplex sequencing library preparation, Illumina sequencing adapters are added to the tagged double stranded libraries by PCR amplification using primers containing sequencing adapters. During PCR amplification, both complementary strands of DNA are amplified and generate two types of PCR products. Product 1 derives from strand 1's which have a unique tag sequence (called α in Figure 2) next to the Illumina adapter 1 and product 2 has a unique tag (called β in Figure 2) next to the Illumina adapter 1. (In each strand, tag α is the reverse complement of tag β and vice versa). The libraries containing duplex tags and Illumina adapters are sequenced using the Illumina TruSeq system. Reads that are originating from every single strand of DNA form a group of reads (tag families) that share the same tag. The detected families of reads will be used in the next step for analyzing sequencing data. | 1 | Biochemistry |
In the context of solids, amorphous and crystalline are terms used to describe the structure of materials. Amorphous solids are the opposite of crystalline. The atoms or molecules in amorphous substances are arranged randomly without any long-range order. As a result, they do not have a sharp melting point. The phase transition from solid to liquid occurs over a range of temperatures. Some examples include glass, rubber and some plastics. | 7 | Physical Chemistry |
Experimental data on association reactions of H and HO suggest that radiative association involving atomic and diatomic neutral radicals may be considered as an effective mechanism for the production of small neutral molecules in the interstellar clouds. The formation of O occurs in the gas phase via the neutral exchange reaction between O and HO, which is also the main sink for HO in dense regions.
We can see that atomic oxygen takes part both in the production and destruction of HO, so the abundance of HO depends mainly on the H abundance. Then, important chemical pathways leading from HO radicals are:
HO + O → O + H (1A) Neutral-neutral
HO + C → CO + H (2A) Ion-neutral
HO + N → NO + H (3A) Neutral-neutral
HO + C → CO + H (4A) Neutral-neutral
HO + H → HO + photon (5A) Neutral-neutral | 2 | Environmental Chemistry |
Ridges (regions of increased gene expression) are domains of the genome with a high gene expression; the opposite of ridges are antiridges. The term was first used by Caron et al. in 2001. Characteristics of ridges are:
*Gene dense
*Contain many C and G nucleobases
*Genes have short introns
*High SINE repeat density
*Low LINE repeat density | 1 | Biochemistry |
A common means of expressing the length of a chain is the degree of polymerization, which quantifies the number of monomers incorporated into the chain. As with other molecules, a polymers size may also be expressed in terms of molecular weight. Since synthetic polymerization techniques typically yield a statistical distribution of chain lengths, the molecular weight is expressed in terms of weighted averages. The number-average molecular weight (M) and weight-average molecular weight (M) are most commonly reported. The ratio of these two values (M / M) is the dispersity (Đ'), which is commonly used to express the width of the molecular weight distribution.
The physical properties of polymer strongly depend on the length (or equivalently, the molecular weight) of the polymer chain. One important example of the physical consequences of the molecular weight is the scaling of the viscosity (resistance to flow) in the melt. The influence of the weight-average molecular weight () on the melt viscosity () depends on whether the polymer is above or below the onset of entanglements. Below the entanglement molecular weight, , whereas above the entanglement molecular weight, . In the latter case, increasing the polymer chain length 10-fold would increase the viscosity over 1000 times. Increasing chain length furthermore tends to decrease chain mobility, increase strength and toughness, and increase the glass-transition temperature (T). This is a result of the increase in chain interactions such as van der Waals attractions and entanglements that come with increased chain length. These interactions tend to fix the individual chains more strongly in position and resist deformations and matrix breakup, both at higher stresses and higher temperatures. | 7 | Physical Chemistry |
The Laves graph has been suggested as an allotrope of carbon, analogous to the more common graphene and graphite carbon structure which also have three bonds per atom at 120° angles. In graphene, adjacent atoms have the same bonding planes as each other, whereas in the Laves graph structure the bonding planes of adjacent atoms are twisted by an angle of approximately 70.5° around the line of the bond. However, this hypothetical carbon allotrope turns out to be unstable.
The Laves graph may also give a crystal structure for boron, one which computations predict should be stable. Other chemicals that may form this structure include SrSi (from which the "srs net" name derives) and elemental nitrogen, as well as certain metal–organic frameworks and cyclic hydrocarbons.
The electronic band structure for the tight-binding model of the Laves graph has been studied, showing the existence of Dirac and Weyl points in this structure. | 3 | Analytical Chemistry |
Living organisms produce retinal by irreversible oxidative cleavage of carotenoids.
For example:
:beta-carotene + O → 2 retinal,
catalyzed by a beta-carotene 15,15-monooxygenase or a beta-carotene 15,15-dioxygenase.
Just as carotenoids are the precursors of retinal, retinal is the precursor of the other forms of vitamin A. Retinal is interconvertible with retinol, the transport and storage form of vitamin A:
:retinal + NADPH + H retinol + NADP
:retinol + NAD retinal + NADH + H,
catalyzed by retinol dehydrogenases (RDHs) and alcohol dehydrogenases (ADHs).
Retinol is called vitamin A alcohol or, more often, simply vitamin A. Retinal can also be oxidized to retinoic acid:
:retinal + NAD + HO → retinoic acid + NADH + H (catalyzed by RALDH)
:retinal + O + HO → retinoic acid + HO (catalyzed by retinal oxidase),
catalyzed by retinal dehydrogenases also known as retinaldehyde dehydrogenases (RALDHs) as well as retinal oxidases.
Retinoic acid, sometimes called vitamin A acid, is an important signaling molecule and hormone in vertebrate animals. | 1 | Biochemistry |
An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H ions) across a membrane. Many of the enzymes in the electron transport chain are embedded within the membrane.
The flow of electrons through the electron transport chain is an exergonic process. The energy from the redox reactions creates an electrochemical proton gradient that drives the synthesis of adenosine triphosphate (ATP). In aerobic respiration, the flow of electrons terminates with molecular oxygen as the final electron acceptor. In anaerobic respiration, other electron acceptors are used, such as sulfate.
In an electron transport chain, the redox reactions are driven by the difference in the Gibbs free energy of reactants and products. The free energy released when a higher-energy electron donor and acceptor convert to lower-energy products, while electrons are transferred from a lower to a higher redox potential, is used by the complexes in the electron transport chain to create an electrochemical gradient of ions. It is this electrochemical gradient that drives the synthesis of ATP via coupling with oxidative phosphorylation with ATP synthase.
In eukaryotic organisms, the electron transport chain, and site of oxidative phosphorylation, is found on the inner mitochondrial membrane. The energy released by reactions of oxygen and reduced compounds such as cytochrome c and (indirectly) NADH and FADH2 is used by the electron transport chain to pump protons into the intermembrane space, generating the electrochemical gradient over the inner mitochondrial membrane. In photosynthetic eukaryotes, the electron transport chain is found on the thylakoid membrane. Here, light energy drives electron transport through a proton pump and the resulting proton gradient causes subsequent synthesis of ATP. In bacteria, the electron transport chain can vary between species but it always constitutes a set of redox reactions that are coupled to the synthesis of ATP through the generation of an electrochemical gradient and oxidative phosphorylation through ATP synthase. | 1 | Biochemistry |
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 | Biochemistry |
In polymer chemistry, a repeat unit or repeating unit (or mer) is a part of a polymer whose repetition would produce the complete polymer chain (except for the end-groups) by linking the repeat units together successively along the chain, like the beads of a necklace.
A repeat unit is sometimes called a mer (or mer unit). "Mer" originates from the Greek word meros, which means "a part". The word polymer derives its meaning from this, which means "many mers". A repeat unit (mer) is not to be confused with the term monomer, which refers to the small molecule from which a polymer is synthesized.
One of the simplest repeat units is that of the addition polymer polyvinyl chloride,
-[CH-CHCl]-, whose repeat unit is -[CH-CHCl]-.
In this case the repeat unit has the same atoms as the monomer vinyl chloride CH=CHCl. When the polymer is formed, the C=C double bond in the monomer is replaced by a C-C single bond in the polymer repeat unit, which links by two new bonds to adjoining repeat units.
In condensation polymers (see examples below), the repeat unit contains fewer atoms than the monomer or monomers from which it is formed.
The subscript "n" denotes the degree of polymerisation, that is, the number of units linked together. The molecular mass of the repeat unit, M, is simply the sum of the atomic masses of the atoms within the repeat unit. The molecular mass of the chain is just the product nM. Other than monodisperse polymers, there is normally a molar mass distribution caused by chains of different length.
In copolymers there are two or more types of repeat unit, which may be arranged in alternation, or at random, or in other more complex patterns. | 7 | Physical Chemistry |
The essence of NSOM/FTIR is that it allows the detection of non-propagating evanescent waves in the near-field (less than one wavelength from the sample), thus yielding high spatial resolution. Depending on the detection modes of these non-propagating evanescent waves, two NSOM/FTIR instrumentations are available: apertureless NSOM/FTIR and aperture-based NSOM/FTIR.
;Aperture-based NSOM/FTIR
In aperture-based NSOM/FTIR, the probe is a waveguide with a tapered tip with a very small, sub-wavelength size aperture. When the aperture is brought into the near-field, it collects the non-propagating light and guides it to the detector. In general, there are two modes when the aperture is scanned over the sample: illumination mode and collection mode (Figure 7).
The high-quality infrared fiber tip is very important in realizing NSOM/FTIR technique. There are several types of fibers, such as sapphire, chalcogenide glass, fluoride glass and hollow silica guides. Chalcogenide glasses are widely used because of their high transmittance in the broad IR range of 2–12 μm. The fluoride fibers also exhibit low transmitting losses beyond 3.0 μm.
;Apertureless NSOM/FTIR
The probe is a sharp metal tip ending with a single or a few atoms. The sample is illuminated from far-field and the radiation is focused at the contact area between probe and sample. When this tip approaches the sample, usually within 10 nm, the incident electromagnetic field is enhanced due to the resonant surface plasma excitation as well as due to hot-spots in the sharp tip. The dipole interaction between the tip and sample change the non-propagating waves into propagating waves by scattering, and a detector collects the signal in the far-field. An apertureless NSOM/FTIR usually has better resolution (~5–30 nm) compared with aperture-based NSOM/FTIR (~50–150 nm). One main challenge in apertureless NSOM/FTIR is a strong background signal because the scattering is obtained from both near-field and remote area of the probe. Thus, the small near-field contribution to the signal has to be extracted from the background. One solution is to use a very flat sample with only optical spatial fluctuation. Another solution is to apply constant-height mode scanning or pseudo-constant-height mode scanning.
;Experimental scheme of aperture-based NSOM/FTIR
Figure 8 shows the experimental setup used in NSOM/FTIR in the external reflection mode. FEL source is focused on the sample from the far-field using a mirror. The distance between the probe and a sample is kept at a few nanometers during scanning.
Figure 9 is the cross-section of a NSOM/FTIR instrument. As shown below, sample is placed on a piezo-electric tube scanner, in which the x-y tube has four parts, namely x+, x-, y+ and y-. Lateral (x-y plane) oscillation of the fiber tip is induced by applying an AC voltage to a dither piezo-scanner. Also, the fiber tip is fixed to a bimorph piezo-scanner so that the amplitude of the oscillation of the tip can be monitored through the scanner. | 7 | Physical Chemistry |
For molecules adsorbed on surfaces there have been various conventions proposed based on hypothetical standard states. For adsorption that occurs on specific sites (Langmuir adsorption isotherm) the most common standard state is a relative coverage of , as this choice results in a cancellation of the configurational entropy term and is also consistent with neglecting to include the standard state (which is a common error). The advantage of using is that the configurational term cancels and the entropy extracted from thermodynamic analyses is thus reflective of intra-molecular changes between the bulk phase (such as gas or liquid) and the adsorbed state. There may be benefit to tabulating values based on both the relative coverage based standard state and in an additional column the absolute coverage based standard state. For 2D gas states, the complication of discrete states does not arise and an absolute density base standard state has been proposed, similar for the 3D gas phase. | 7 | Physical Chemistry |
As in the case of single molecule fluorescence spectroscopy, the technique known as single channel recording can be used to obtain specific kinetic information—in this case about ion channel function—that is not available when ensemble recording, such as whole-cell recording, is performed. Specifically, ion channels alternate between conducting and non-conducting classes, which differ in conformation. Therefore, the functional state of ion channels can be directly measured with sufficiently sensitive electronics, provided that proper precautions are taken to minimize noise. In turn, each of these classes may be divided into one or more kinetic states with direct bearing on the underlying function of the ion channel. Performing these types of single molecule studies under systematically varying conditions (e.g. agonist concentration and structure, permeant ion and/or channel blocker, mutations in the ion channel amino acids), can provide information regarding the interconversion of various kinetic states of the ion channel. In a minimal model for an ion channel, there are two states: open and closed. However, other states are often needed in order to accurately represent the data, including multiple closed states as well as inactive and/or desensitized states, which are non-conducting states that can occur even in the presence of stimulus. | 7 | Physical Chemistry |
Isopentenyl pyrophosphate (IPP, isopentenyl diphosphate, or IDP) is an isoprenoid precursor. IPP is an intermediate in the classical, HMG-CoA reductase pathway (commonly called the mevalonate pathway) and in the non-mevalonate MEP pathway of isoprenoid precursor biosynthesis. Isoprenoid precursors such as IPP, and its isomer DMAPP, are used by organisms in the biosynthesis of terpenes and terpenoids. | 1 | Biochemistry |
Biomarkers can be classified based on different criteria.
Based on their characteristics they can be classified as imaging biomarkers (CT, PET, MRI) or molecular biomarkers with three subtypes: volatile, like breath, body fluid, or biopsy biomarkers.
Molecular biomarkers refer to non-imaging biomarkers that have biophysical properties, which allow their measurements in biological samples (e.g., plasma, serum, cerebrospinal fluid, bronchoalveolar lavage, biopsy) and include nucleic acids-based biomarkers such as gene mutations or polymorphisms and quantitative gene expression analysis, peptides, proteins, lipids metabolites, and other small molecules.
Biomarkers can also be classified based on their application such as diagnostic biomarkers (i.e., cardiac troponin for the diagnosis of myocardial infarction), staging of disease biomarkers (i.e., brain natriuretic peptide for congestive heart failure), disease prognosis biomarkers (cancer biomarkers), and biomarkers for monitoring the clinical response to an intervention (HbAlc for antidiabetic treatment).
Another category of biomarkers includes those used in decision making in early drug development. For instance, pharmacodynamic (PD) biomarkers are markers of a certain pharmacological response, which are of special interest in dose optimization studies. | 1 | Biochemistry |
Lyotropic liquid crystals result when amphiphiles, which are both hydrophobic and hydrophilic, dissolve into a solution that behaves both like a liquid and a solid crystal. This liquid crystalline mesophase includes everyday mixtures like soap and water.
To break the word down, "lyo" and "tropic" mean, respectively, "dissolve" and "change." Historically, the term was used to describe the common behavior of materials composed of amphiphilic molecules upon the addition of a solvent. Such molecules comprise a water-loving hydrophilic head-group (which may be ionic or non-ionic) attached to a water-hating, hydrophobic group.
The micro-phase segregation of two incompatible components on a nanometer scale results in different type of solvent-induced extended anisotropic arrangement, depending on the volume balances between the hydrophilic part and hydrophobic part. In turn, they generate the long-range order of the phases, with the solvent molecules filling the space around the compounds to provide fluidity to the system.
In contrast to thermotropic liquid crystals, lyotropic liquid crystals have therefore an additional degree of freedom, that is the concentration that enables them to induce a variety of different phases. As the concentration of amphiphilic molecules is increased, several different type of lyotropic liquid crystal structures occur in solution. Each of these different types has a different extent of molecular ordering within the solvent matrix, from spherical micelles to larger cylinders, aligned cylinders and even bilayered and multiwalled aggregates. | 7 | Physical Chemistry |
* Several arthropods translate the codon AGG as lysine instead of serine (as in the Pterobranchia Mitochondrial Code) or arginine (as in the standard genetic code).
* GUG may possibly function as an initiator in Drosophila. AUU is not used as an initiator in Mytilus
* "An exceptional mechanism must operate for initiation of translation of the cytochrome oxidase subunit I mRNA in both D. melanogaster and D. yakuba, since its only plausible initiation codon, AUA, is out of frame with the rest of the gene. Initiation appears to require the "reading" of an AUAA quadruplet, which would be equivalent to initiation at AUA followed immediately by a specific ribosomal frameshift. Another possible mechanism ... is that the mRNA is "edited" to bring the AUA initiation into frame." | 1 | Biochemistry |
In October 2006, Finnish paper and pulp manufacturer UPM announced its plans to produce biodiesel by the Fischer–Tropsch process alongside the manufacturing processes at its European paper and pulp plants, using waste biomass resulting from paper and pulp manufacturing processes as source material. | 0 | Organic Chemistry |
The photocyte of Arachnocampa luminosa was found to contain a circular nucleus, and large amounts of ribosomes, smooth endoplasmic reticulum, mitochondria, and microtubules. Instead of having photocyte granules, the photocytes of the organism were shown to undergo the luciferase reaction in their cytoplasm. The cells do not have a golgi apparatus or rough endoplasmic reticulum and were found to be 250 micrometers by 120 micrometers overall with a depth of 25 to 30 micrometers. | 1 | Biochemistry |
There are three different variations of seipin's amino acid sequence:
* a N → S change in position 88, does not affect protein subcellular location.
* a S → L change in position 90, does not affect the function in lipid storage.
* a A → P change in position 212 that increases localization to nuclear envelope.
All seipin mutations occur within its loop domain. Between some of these, four large deletions can be found which indicate that at least exons 4 and 5 are required for seipin function in humans. In addition, other six mutations have been identified in the loop domain. The majority of these cluster at the single asparagine-linked glycosylation site (NVS) in seipin. The two mutations that cause neuronal seipinopathy, N88S and S90L, are located directly within this site. Apart from suspending the glycosylation process, these mutations engender an aggregation of seipin and, consequently, the initiation of the ER stress response. The seipin protein can also have a modification residue, that can transform the 289’ and 372’ serine into a phosphoserine, an ester of serine and phosphoric acid.
Overexpression of mutated seipin proteins N88S or S90L can also activate autophagy, and substantially altering the sub-cellular distribution of the autophagosome marker GFP-LC3, which leads to a number of large vacuoles appearing in the cytoplasm. The sub-cellular location of GFP-LC3 and mutated seipin proteins highly overlap. Moreover, these seipin proteins can diffuse small lipid droplets to fuse into larger lipid.
Seipin mutations have been associated with congenital generalized lipodystrophy (see below), and mutations in an N-glycosylation motif links seipin to two other disorders, i.e. Silver syndrome and autosomal-dominant distal hereditary motor neuropathy type V. | 1 | Biochemistry |
Exposure limits for UV, particularly the germicidal UV-C range, have evolved over time due to scientific research and changing technology. The American Conference of Governmental Industrial Hygienists (ACGIH) and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) have set exposure limits to safeguard against both immediate and long-term effects of UV exposure. These limits, also referred to as Threshold Limit Values (TLVs), form the basis for emission limits in product safety standards.
The UV-C photobiological spectral band is defined as 100–280 nm, with limits currently applying only from 180 to 280 nm. This reflects concerns about acute damage such as erythema and photokeratitis as well as long-term delayed effects like photocarcinogenesis. However, with the increased safety evidence surrounding UV-C for germicidal applications, the existing ACGIH TLVs were revised in 2022.
The TLVs for the 222 nm UV-C wavelength (peak emissions from KrCl excimer lamps), following the 2022 revision, are now 161 mJ/cm for eye exposure and 479 mJ/cm for skin exposure over an eight-hour period. For the 254 nm UV wavelength, the updated exposure limit is now set at 6 mJ/cm for eyes and 10 mJ/cm for skin. | 5 | Photochemistry |
An example of an isozyme is glucokinase, a variant of hexokinase which is not inhibited by glucose 6-phosphate. Its different regulatory features and lower affinity for glucose (compared to other hexokinases), allow it to serve different functions in cells of specific organs, such as control of insulin release by the beta cells of the pancreas, or initiation of glycogen synthesis by liver cells. Both these processes must only occur when glucose is abundant.
1.) The enzyme lactate dehydrogenase is a tetramer made of two different sub-units, the H-form and the M-form. These combine in different combinations depending on the tissue:
2.) Isoenzymes of creatine phosphokinase: Creatine kinase (CK) or creatine phosphokinase (CPK) catalyses the interconversion of phospho creatine to creatine .
CPK exists in 3 isoenzymes. Each isoenzymes is a dimer of 2 subunits M (muscle), B (brain) or both
3.) Isoenzymes of alkaline phosphatase: Six isoenzymes have been identified. The enzyme is a monomer, the isoenzymes are due to the differences in the carbohydrate content (sialic acid residues). The most important ALP isoenzymes are α-ALP, α-heat labile ALP, α-heat stable ALP, pre-β ALP and γ-ALP. Increase in α-heat labile ALP suggests hepatitis whereas pre-β ALP indicates bone diseases. | 1 | Biochemistry |
When surface charges present at the wall of a channel of micro-scaled width, counterions are attracted and co-ions are repelled by electrostatic force. The counterions form a shielding area near the wall. This region penetrate into solution to a certain distance called Debye length until the electric potential decays to the bulk value of neutrality. The Debye length is ranging typically from 1 nm to 100 nm for aqueous solutions.
In nano-channels, the Debye length is usually comparable with the channel width, therefore solution within the channel is charged. Ions inside the fluid is no longer shielded from surface charge. Instead, surface charge affect the dynamics of ions within a nano-channel. | 7 | Physical Chemistry |
Gaseous mediators are chemicals that are produced in small amounts by some cells of the mammalian body and have a number of biological signalling functions. There are three so-far-identified gaseous mediator molecules: nitric oxide (NO), hydrogen sulfide (HS), and carbon monoxide (CO). | 1 | Biochemistry |
Dally works as a co-receptor of some secreted signaling molecules as fibroblast growth factor, vascular endothelial growth factor, hepatocyte growth factor and members of the Wnt signaling pathway, TGF-b and Hedgehog families. It is also necessary for the cell division patterning during the post-embryonic development of the nervous system.
It is a regulatory component of the Wg receptor and is part of a multiprotein complex together with Frizzled (Fz) transmembrane proteins. Therefore, it regulates two cell growth factors in Drosophila melanogaster, Wingless (Wg) and Decapentaplegic (Dpp). It must be said that in vertebrates the equivalent to Dpp are Bone Morphogenetic Proteins, and the mammalian equal to Wg might be integrin-beta 4. The first one (Wg) controls cell proliferation and differentiation during embryos development, specifically in epidermis, whereas the latter (Dpp) plays a role in the imaginal discs’ growth.
Dpp and Wg are mutually antagonistic in patterning genitalia. Concretely, dally selectively regulates both Wg signalling in epidermis and Dpp in genitalia. This selectivity is supposed to be controlled by the type of Glycosaminoglycan GAG bonded to the dally protein, considering that there is a huge structural variety in GAGs.
Tissue malformations occur in various situations. As said in the introduction, the sgl enzyme is essential for a normal biosynthesis of dally. That is why the absence or malfunction of this enzyme doesn’t allow the correct Wg and Dpp signalling. Also the expression of mutated dally proteins alters Wnt signalling pathways, which leads to anomalies in Drosophila melanogaster’s eye, antennal, genital, wing and neural morphogenesis. | 1 | Biochemistry |
In order to provide a good minigene model, the gene fragment should have all of the necessary elements to ensure it exhibits the same alternative splicing (AS) patterns as the wild type gene, i.e., the length of the fragment must include all upstream and downstream sequences which can affect its splicing. Therefore, most minigene designs begin with a thorough in silico analysis of the requirements of the experiment before any "wet" lab work is conducted. With the advent of Bioinformatics and widespread use of computers, several good programs now exist for the identification of cis-acting control regions that affect the splicing outcomes of a gene and advanced programs can even consider splicing outcomes in various tissue types. Differences in minigenes are usually reflected in the final size of the fragment, which is in turn a reflection of the complexity of the minigene itself. The number of foreign DNA elements (exon and introns) inserted into the constitutive exons and introns of a given fragment varies with the type of experiment and the information being sought. A typical experiment might involve wild type minigenes which are expected to express genes normally in a comparison run against genetically engineered allelic variations which replace the wild-type gene and have been cloned into the same flanking sequences as the original fragment. These types of experiments help to determine the effect of various mutations on pre-mRNA splicing. | 1 | Biochemistry |
Because they form a strong electrophile when treated with Lewis acids, acyl halides are commonly used as acylating agents. For example, Friedel–Crafts acylation uses acetyl chloride () as the agent and aluminum chloride () as a catalyst to add an acetyl group to benzene:
This reaction is an example of electrophilic aromatic substitution.
Acyl halides and acid anhydrides of carboxylic acids are also common acylating agents. In some cases, active esters exhibit comparable reactivity. All react with amines to form amides and with alcohols to form esters by nucleophilic acyl substitution.
Acylation can be used to prevent rearrangement reactions that would normally occur in alkylation. To do this an acylation reaction is performed, then the carbonyl is removed by Clemmensen reduction or a similar process. | 0 | Organic Chemistry |
P-Chiral phosphines are organophosphorus compounds of the formula PRR′R″, where R, R′, R″ = H, alkyl, aryl, etc. They are a subset of chiral phosphines, a broader class of compounds where the stereogenic center can reside at sites other than phosphorus. P-chirality exploits the high barrier for inversion of phosphines, which ensures that enantiomers of PRR'R" do not racemize readily. The inversion barrier is relatively insensitive to substituents for triorganophosphines. By contrast, most amines of the type NRR′R″ undergo rapid pyramidal inversion. | 4 | Stereochemistry |
The use of chlorofluorocarbons as aerosols in medicine, such as USP-approved salbutamol, has been phased out by the U.S. Food and Drug Administration. A different propellant known as hydrofluoroalkane, or HFA, which was not known to harm the environment, was chosen to replace it. | 2 | Environmental Chemistry |
Deriving the Gibbs–Duhem equation from the fundamental thermodynamic equation is straightforward. The total differential of the extensive Gibbs free energy in terms of its natural variables is
Since the Gibbs free energy is the Legendre transformation of the internal energy, the derivatives can be replaced by their definitions, transforming the above equation into:
The chemical potential is simply another name for the partial molar Gibbs free energy (or the partial Gibbs free energy, depending on whether N is in units of moles or particles). Thus the Gibbs free energy of a system can be calculated by collecting moles together carefully at a specified T, P and at a constant molar ratio composition (so that the chemical potential doesn't change as the moles are added together), i.e.
The total differential of this expression is
Combining the two expressions for the total differential of the Gibbs free energy gives
which simplifies to the Gibbs–Duhem relation: | 7 | Physical Chemistry |
Smooth mirror-like surfaces provide specular reflections, allowing easy detection of the acoustic wave. However, as surfaces become rougher the reflections become more diffuse, making detection of the acoustic wave more challenging for two reasons. Firstly, the reflected beam is spread out in a cone, as this cone increases in diameter less light is returned to the system - decreasing detection efficiency. Secondly, the light which is returned to the detector no longer exabits a gaussian intensity, instead the interfering wave fronts create a stochastic speckle pattern. However, many engineering processes impart an optically rough surface, for example additive manufacturing or forging, and there is a desire to make measurements on such components in their as manufactured state. To achieve this, an interferometric technique compatible with rough surfaces is required. For example, a Fabry–Pérot interferometer - which is inherently tolerant to speckle, two-wave mixing - which can adapt to the speckle pattern, or a speckle knife edge detector. With the use of such detection techniques, it is possible to make SRAS measurements on optically rough surfaces. | 7 | Physical Chemistry |
The "strain energy" of a molecule is a quantity that is difficult to precisely define, so the meaning of this term can easily vary depending on one's interpretation. Instead, an objective way to view the allylic strain of a molecule is through its conformational equilibrium. Comparing the heats of formation of the involved conformers, an overall ΔH can be evaluated. This term gives information about the relative stabilities of the involved conformers and the effect allylic strain has one equilibrium. Heats of formation can be determined experimentally though calorimetric studies; however, calculated enthalpies are more commonly used due to the greater ease of acquisition.
Different methods utilized to estimate conformational equilibrium enthalpy include: the Westheimer method, the homomorph method, and more simply—using estimated enthalpies of nonbonded interactions within a molecule. Because all of these methods are approximations, reported strain values for the same molecule can vary and should be used only to give a general idea of the strain energy. | 4 | Stereochemistry |
The standard state for liquids and solids is simply the state of the pure substance subjected to a total pressure of (or 1 bar). For most elements, the reference point of ΔH = 0 is defined for the most stable allotrope of the element, such as graphite in the case of carbon, and the β-phase (white tin) in the case of tin. An exception is white phosphorus, the most common allotrope of phosphorus, which is defined as the standard state despite the fact that it is only metastable. This is because the thermodynamically stable black allotrope is difficult to prepare pure. | 7 | Physical Chemistry |
The structure of the voltage gated K channel is that of six transmembrane helices along the lipid bilayer. The selectivity of this channel to voltage is mediated by four of these transmembrane domains (S1–S4) – the voltage sensing domain. The other two domains (S5, S6) form the pore by which ions traverse. Activation and deactivation of the voltage gated K channel is triggered by conformational changes in the voltage sensing domain. Specifically, the S4 domain moves such that it activates and deactivates the pore. During activation, there is outward S4 motion, causing tighter VSD-pore linkage. Deactivation is characterized by inward S4 motion.
The switch from depolarization into repolarization is dependent on the kinetic mechanisms of both voltage gated K and Na channels. Although both voltage gated Na and K channels activate at roughly the same voltage (−50 mV), Na channels have faster kinetics and activate/deinactivate much more quickly. Repolarization occurs as the influx of Na decreases (channels deinactivate) and the efflux of K ions increases as its channels open. The decreased conductance of sodium ions and increased conductance of potassium ions cause the cell's membrane potential to very quickly return to, and past the resting membrane potential, which causes the hyperpolarization due to the potassium channels closing slowly, allowing more potassium to flow through after the resting membrane potential has been reached. | 7 | Physical Chemistry |
A solution of sulfur tetrafluoride in hydrogen fluoride converts hydroxy-containing amino acids to the fluoro amino acids:
When vicinal diols are combined with SF, difluorination occurs with inversion of configuration at only one of the alcohols. This was demonstrated in the synthesis of meso-difluorosuccinate from (L)-tartrate and the synthesis of (D)- and (L)-difluorosuccinate from meso-tartrate.
Carbonyl compounds generally react with SF to yield geminal difluorides. Reaction times tend to be on the order of hours and yields are moderate. Fluorination of lactones can provide heterocyclic fluorides, although ring opening has been observed for γ-butyrolactone. The six-membered lactide does not experience ring opening.
Fluorination opens epoxides to give either geminal or vicinal difluorides in most cases. Monoarylepoxides give geminal products with migration of the aryl group. Yields are low for sterically hindered di- and trisubstituted epoxides. Epoxides substituted with an ester group give vicinal difluorides via an alkoxysulfur trifluoride intermediate.
Carboxylic acids react with SF to afford trifluoromethyl compounds:
The formation of the trifluoromethyl derivative sometimes competes with formation of tetrafluoroalkyl ethers, which arise from the reaction between difluoromethyl cation and acyl fluoride.
Sulfur tetrafluoride can be used to fluorinate polymers efficiently. This often has a profound effect on polymer properties—fluorination of polyvinyl alcohol, for instance, improves its resistance to strong acids and bases.
A prostaglandin bearing a trifluoromethyl group at C-16 is prepared using sulfur tetrafluoride. | 0 | Organic Chemistry |
A light-harvesting complex consists of a number of chromophores which are complex subunit proteins that may be part of a larger super complex of a photosystem, the functional unit in photosynthesis. It is used by plants and photosynthetic bacteria to collect more of the incoming light than would be captured by the photosynthetic reaction center alone. The light which is captured by the chromophores is capable of exciting molecules from their ground state to a higher energy state, known as the excited state. This excited state does not last very long and is known to be short-lived.
Light-harvesting complexes are found in a wide variety among the different photosynthetic species, with no homology among the major groups. The complexes consist of proteins and photosynthetic pigments and surround a photosynthetic reaction center to focus energy, attained from photons absorbed by the pigment, toward the reaction center using Förster resonance energy transfer. | 5 | Photochemistry |
Protein adsorption is a process that has a fundamental role in the field of biomaterials. Indeed, biomaterial surfaces in contact with biological media, such as blood or serum, are immediately coated by proteins. Therefore, living cells do not interact directly with the biomaterial surface, but with the adsorbed proteins layer. This protein layer mediates the interaction between biomaterials and cells, translating biomaterial physical and chemical properties into a "biological language". In fact, cell membrane receptors bind to protein layer bioactive sites and these receptor-protein binding events are transduced, through the cell membrane, in a manner that stimulates specific intracellular processes that then determine cell adhesion, shape, growth and differentiation. Protein adsorption is influenced by many surface properties such as surface wettability, surface chemical composition and surface nanometre-scale morphology.
Surfactant adsorption is a similar phenomenon, but utilising surfactant molecules in the place of proteins. | 7 | Physical Chemistry |
Siloxanes are a premier example of an inorganic polymer, even though they have extensive organic substituents. Their backbond is composed of alternating silicon and oxygen atoms, i.e. Si-O-Si-O... The silicon atoms bear two substituents, usually methyl as in the case of polydimethylsiloxane. Some uncommon but illustrative inorganic polymers include polythiazyl ((SN)x) with alternating S and N atoms, and polyphosphates ((PO)). | 0 | Organic Chemistry |
Lactones contribute significantly to the flavor of fruit, and of unfermented and fermented dairy products, and are therefore used as flavors and fragrances. Some examples are γ-decalactone (4-decanolide), which has a characteristic peach flavor; δ-decalactone (5-decanolide), which has a creamy coconut/peach flavour; γ-dodecalactone (4-dodecanolide), which also has a coconut/fruity flavor, a description which also fits γ-octalactone (4-octanolide), although it also has a herbaceous character; γ-nonalactone, which has an intense coconut flavor of this series, despite not occurring in coconut, and γ-undecalactone.
Macrocyclic lactones (cyclopentadecanolide, 15-pentadec-11/12-enolide) have odors similar to macrocyclic ketones of animal origin (muscone, civetone), but they can be prepared more easily, for example, by depolymerization of the corresponding linear polyesters. Replacement of a methylene unit by oxygen barely affects the odor of these compounds, and oxalactones with 15 – 17-membered rings are produced in addition to cyclopentadecanolide (e. g., 12-oxa-16-hexadecanolide). | 0 | Organic Chemistry |
An air quality control region is an area, designated by the federal government, where communities share a common air pollution problem. | 2 | Environmental Chemistry |
Retinal gene therapy holds a promise in treating different forms of non-inherited and inherited blindness.
In 2008, three independent research groups reported that patients with the rare genetic retinal disease Leber's congenital amaurosis had been successfully treated using gene therapy with adeno-associated virus (AAV). In all three studies, an AAV vector was used to deliver a functional copy of the RPE65 gene, which restored vision in children suffering from LCA. These results were widely seen as a success in the gene therapy field, and have generated excitement and momentum for AAV-mediated applications in retinal disease.
In retinal gene therapy, the most widely used vectors for ocular gene delivery are based on adeno-associated virus. The great advantage in using adeno-associated virus for the gene therapy is that it poses minimal immune responses and mediates long-term transgene expression in a variety of retinal cell types. For example, tight junctions that form the blood-retina barrier, separate subretinal space from the blood supply, providing protection from microbes and decreasing most immune-mediated damages.
There is still a lot of knowledge missing in regards of retina dystrophies. Detail characterization is needed in order to improve knowledge. To address this issue, creation of Registries is an attempt to grouped and characterize rare diseases. Registries help to localize, and measure all the phenotype of these conditions and therefore to provide easy follow-ups and provide a source of information to scientist community. Registry designs varies from region to region, however localization and characterization of the phenotype are the standard gold.
Examples of Registries are:
RetMxMap<ARVO 2009>. A Mexican and Latin-American registry created since 2009. This registry was created by Dr Adda Lízbeth Villanueva Avilés. She is a clinical-scientist gene mapping inherited retina dystrophies in Mexico and other Latin countries. | 1 | Biochemistry |
In 1997, Sinaÿ and co-workers reported an alternative route to the synthesis (shown below) that did not involve cleavage of the bond at the anomeric position (the glycosidic bond). In this case, the major product formed had maintained its original configuration at the anomeric position.
Sinaÿ proposed this reaction went through the following transition state:
Sinaÿ also discovered that titanium (IV) derivatives such as [TiCl(OiPr)] worked in the same reaction as a milder version of the Lewis acid, i-BuAl, which goes through a similar transition state involving the retention of configuration at the anomeric center.
In 1988, Adam reported a modification of the reaction that used catalytic amounts of palladium (II) salts, which brought about the same conversion of enol ethers into carbosugars in a more environmentally friendly manner. | 0 | Organic Chemistry |
Chemotherapeutics, by design, induce DNA damage and are targeted towards rapidly dividing cancer cells. However, these drugs can not tell the difference between sick and healthy cells, resulting in the damage of normal cells. | 1 | Biochemistry |
Exothermic refers to a transformation in which a closed system releases energy (heat) to the surroundings, expressed by
When the transformation occurs at constant pressure and without exchange of electrical energy, heat is equal to the enthalpy change, i.e.
while at constant volume, according to the first law of thermodynamics it equals internal energy () change, i.e.
In an adiabatic system (i.e. a system that does not exchange heat with the surroundings), an otherwise exothermic process results in an increase in temperature of the system.
In exothermic chemical reactions, the heat that is released by the reaction takes the form of electromagnetic energy or kinetic energy of molecules. The transition of electrons from one quantum energy level to another causes light to be released. This light is equivalent in energy to some of the stabilization energy of the energy for the chemical reaction, i.e. the bond energy. This light that is released can be absorbed by other molecules in solution to give rise to molecular translations and rotations, which gives rise to the classical understanding of heat. In an exothermic reaction, the activation energy (energy needed to start the reaction) is less than the energy that is subsequently released, so there is a net release of energy. | 7 | Physical Chemistry |
TLC is a useful tool for reaction monitoring. For this, the plate normally contains a spot of starting material, a spot from the reaction mixture, and a co-spot (or cross-spot) containing both. The analysis will show if the starting material disappeared and if any new products appeared. This provides a quick and easy way to estimate how far a reaction has proceeded. In one study, TLC has been applied in the screening of organic reactions. The researchers react an alcohol and a catalyst directly in the co-spot of a TLC plate before developing it. This provides quick and easy small-scale testing of different reagents.
Compound characterization with TLC is also possible and is similar to reaction monitoring. However, rather than spotting with starting material and reaction mixture, it is with an unknown and a known compound. They may be the same compound if both spots have the same R and look the same under the chosen visualization method. However, co-elution complicates both reaction monitoring and characterization. This is because different compounds will move to the same spot on the plate. In such cases, different solvent mixtures may provide better separation. | 3 | Analytical Chemistry |
Stochastic thermodynamics can be applied to driven (i.e. open) quantum systems whenever the effects of quantum coherence can be ignored. The dynamics of an open quantum system is then equivalent to a classical stochastic one. However, this is sometimes at the cost of requiring unrealistic measurements at the beginning and end of a process.
Understanding non-equilibrium quantum thermodynamics more broadly is an important and active area of research. The efficiency of some computing and information theory tasks can be greatly enhanced when using quantum correlated states; quantum correlations can be used not only as a valuable resource in quantum computation, but also in the realm of quantum thermodynamics. New types of quantum devices in non-equilibrium states function very differently to their classical counterparts. For example, it has been theoretically shown that non-equilibrium quantum ratchet systems function far more efficiently then that predicted by classical thermodynamics. It has also been shown that quantum coherence can be used to enhance the efficiency of systems beyond the classical Carnot limit. This is because it could be possible to extract work, in the form of photons, from a single heat bath. Quantum coherence can be used in effect to play the role of Maxwell's demon though the broader information theory based interpretation of the second law of thermodynamics is not violated.
Quantum versions of stochastic thermodynamics have been studied for some time and the past few years have seen a surge of interest in this topic. Quantum mechanics involves profound issues around the interpretation of reality (e.g. the Copenhagen interpretation, many-worlds, de Broglie-Bohm theory etc are all competing interpretations that try to explain the unintuitive results of quantum theory) . It is hoped that by trying to specify the quantum-mechanical definition of work, dealing with open quantum systems, analyzing exactly solvable models, or proposing and performing experiments to test non-equilibrium predictions, important insights into the interpretation of quantum mechanics and the true nature of reality will be gained.
Applications of non-equilibrium work relations, like the Jarzynski equality, have recently been proposed for the purposes of detecting quantum entanglement and to improving optimization problems (minimize or maximize a function of multivariables called the cost function) via quantum annealing . | 7 | Physical Chemistry |
In 1761, Benjamin Franklin wrote a letter describing his experiments on the relationship between color and heat absorption. He found that darker color clothes got hotter when exposed to sunlight than lighter color clothes. One experiment he performed consisted of placing square pieces of cloth of various color out in the snow on a sunny day. He waited some time and then measured that the black pieces sank furthest into the snow of all the colors, indicating that they got the hottest and melted the most snow. | 7 | Physical Chemistry |
The concept of pH was defined in 1909 by S. P. L. Sørensen, and electrodes were used for pH measurement in the 1920s.
In October 1934, Arnold Orville Beckman registered the first patent for a complete chemical instrument for the measurement of pH, U.S. Patent No. 2,058,761, for his "acidimeter", later renamed the pH meter. Beckman developed the prototype as an assistant professor of chemistry at the California Institute of Technology, when asked to devise a quick and accurate method for measuring the acidity of lemon juice for the California Fruit Growers Exchange (Sunkist).
On April 8, 1935, Beckman's renamed National Technical Laboratories focused on the manufacture of scientific instruments, with the Arthur H. Thomas Company as a distributor for its pH meter. In its first full year of sales, 1936, the company sold 444 pH meters for $60,000 in sales. In years to come, the company sold millions of the units. In 2004 the Beckman pH meter was designated an ACS National Historic Chemical Landmark in recognition of its significance as the first commercially successful electronic pH meter.
The Radiometer Corporation of Denmark was founded in 1935, and began marketing a pH meter for medical use around 1936, but "the development of automatic pH-meters for industrial purposes was neglected. Instead American instrument makers successfully developed industrial pH-meters with a wide variety of applications, such as in breweries, paper works, alum works, and water treatment systems."
In the 1940s the electrodes for pH meters were often difficult to make, or unreliable due to brittle glass. Dr. Werner Ingold began to industrialize the production of single-rod measuring cells, a combination of measurement and reference electrode in one construction unit, which led to broader acceptance in a wide range of industries including pharmaceutical production.
Beckman marketed a portable "Pocket pH Meter" as early as 1956, but it did not have a digital read-out.
In the 1970s Jenco Electronics of Taiwan designed and manufactured the first portable digital pH meter. This meter was sold under the label of the Cole-Parmer Corporation. | 7 | Physical Chemistry |
Other thermal hydraulic phenomena are subject of interest:
* Critical discharge
* Countercurrent flow limitation
* Condensation
* Flow instability
* Rewetting | 7 | Physical Chemistry |
Tashiro's indicator is a pH indicator (pH value: 4.4–6.2), mixed indicator composed of a solution of methylene blue (0.1%) and methyl red (0.03%) in ethanol or in methanol.
It can be used e.g. for the titration of ammonia in Kjeldahl analysis. | 3 | Analytical Chemistry |
A cis-regulatory element called the GAIT element is involved in the selective translational silencing of the Ceruloplasmin transcript.
The silencing requires binding of a cytosolic inhibitor complex called IFN-gamma-activated inhibitor of translation (GAIT) to the GAIT element. | 1 | Biochemistry |
Another way of storing energy is with the use of hydrazine. This molecule is related to ammonia and has the potential to be equally as useful as ammonia. It can be created from ammonia and hydrogen peroxide or via chlorine based oxidations. This makes it an even denser energy storing fuel. The downside of hydrazine is that it is very toxic and that it will react with oxygen quite violently. This makes it an ideal fuel for oxygen low area's such as space. Recent launched Iridium NEXT satellites have hydrazine as their source of energy. However toxic, this fuel has great potential, because safety measures can be increased sufficiently to safely transport and convert hydrazine back into hydrogen and ammonia. Researchers discovered a way to decompose hydrazine with a photo catalysis system that works over the entire visible-light region. This means that sunlight can not only be used to produce hydrazine, but also to produce hydrogen from this fuel. The decomposition of hydrazine is done with a p-n bilayer consisting of fullerene (C), also known as "buckeyballs" which is a n-type semiconductor and zinc phthalocyanine (ZnPc) which is a p-type semiconductor creating an organic photo catalysis system. This system uses visible light irradiation to excite electrons to the n-type semiconductor creating an electric current. The holes created in the p-type semiconductor are forced in the direction of the so called Nafion part of the device, which oxidizes hydrazine to nitrogen gas and dissolved hydrogen ions. This was done in the first compartment of the fuel cell. The hydrogen ions travel through a salt bridge to another compartment to be reduced to hydrogen gas by the electrons, gained by the interaction with light, from the first compartment. Thus creating hydrogen, which can be used in fuel cells. This promising studies shows that hydrazine is a solar fuel that has great potential to become very useful in the energy transition.
A different approach to hydrazine are the direct fuel cells. The concepts for these cells have been developed since the 1960s. Recent studies provide much better direct hydrazine fuel cells, for example with the use of hydrogen peroxide as an oxidant. Making the anode basic and the cathode acidic increased the power density a lot, showing high peaks of around 1 W/cm at a temperature of 80 degrees Celsius. As mentioned earlier the main weakness of direct hydrazine fuel cells is the high toxicity of hydrazine and its derivatives. However hydrous hydrazine, which is a water-like liquid retains the high hydrogen density and can be stored and transported safely using the existing fuel infrastructure. Researchers also aim for self-powered fuel cells involving hydrazine. These fuel cells make use of hydrazine in two ways, namely as the fuel for a direct fuel cell and as the splitting target. This means that one only needs hydrazine to produce hydrogen with this fuel cell, so no external power is needed. This is done with the use of iron doped cobalt sulfide nanosheets. The doping with iron decreases the free-energy changes of hydrogen adsorption and hydrazine dehydrogenation. This method has a 20 hour stability and 98% Faradaic efficiency, which is comparable with the best reported claims of self-powered hydrogen generating cells. | 5 | Photochemistry |
For a given composition, only certain phases are possible at a given temperature and pressure. The number and type of phases that will form is hard to predict and is usually determined by experiment. The results of such experiments can be plotted in phase diagrams.
The phase diagram shown here is for a single component system. In this simple system, phases that are possible, depend only on pressure and temperature. The markings show points where two or more phases can co-exist in equilibrium. At temperatures and pressures away from the markings, there will be only one phase at equilibrium.
In the diagram, the blue line marking the boundary between liquid and gas does not continue indefinitely, but terminates at a point called the critical point. As the temperature and pressure approach the critical point, the properties of the liquid and gas become progressively more similar. At the critical point, the liquid and gas become indistinguishable. Above the critical point, there are no longer separate liquid and gas phases: there is only a generic fluid phase referred to as a supercritical fluid. In water, the critical point occurs at around 647 K (374 °C or 705 °F) and 22.064 MPa.
An unusual feature of the water phase diagram is that the solid–liquid phase line (illustrated by the dotted green line) has a negative slope. For most substances, the slope is positive as exemplified by the dark green line. This unusual feature of water is related to ice having a lower density than liquid water. Increasing the pressure drives the water into the higher density phase, which causes melting.
Another interesting though not unusual feature of the phase diagram is the point where the solid–liquid phase line meets the liquid–gas phase line. The intersection is referred to as the triple point. At the triple point, all three phases can coexist.
Experimentally, phase lines are relatively easy to map due to the interdependence of temperature and pressure that develops when multiple phases form. Gibbs' phase rule suggests that different phases are completely determined by these variables. Consider a test apparatus consisting of a closed and well-insulated cylinder equipped with a piston. By controlling the temperature and the pressure, the system can be brought to any point on the phase diagram. From a point in the solid stability region (left side of the diagram), increasing the temperature of the system would bring it into the region where a liquid or a gas is the equilibrium phase (depending on the pressure). If the piston is slowly lowered, the system will trace a curve of increasing temperature and pressure within the gas region of the phase diagram. At the point where gas begins to condense to liquid, the direction of the temperature and pressure curve will abruptly change to trace along the phase line until all of the water has condensed. | 7 | Physical Chemistry |
Intermolecular forces are repulsive at short distances and attractive at long distances (see the Lennard-Jones potential). In a gas, the repulsive force chiefly has the effect of keeping two molecules from occupying the same volume. This gives a real gas a tendency to occupy a larger volume than an ideal gas at the same temperature and pressure. The attractive force draws molecules closer together and gives a real gas a tendency to occupy a smaller volume than an ideal gas. Which interaction is more important depends on temperature and pressure (see compressibility factor).
In a gas, the distances between molecules are generally large, so intermolecular forces have only a small effect. The attractive force is not overcome by the repulsive force, but by the thermal energy of the molecules. Temperature is the measure of thermal energy, so increasing temperature reduces the influence of the attractive force. In contrast, the influence of the repulsive force is essentially unaffected by temperature.
When a gas is compressed to increase its density, the influence of the attractive force increases. If the gas is made sufficiently dense, the attractions can become large enough to overcome the tendency of thermal motion to cause the molecules to disperse. Then the gas can condense to form a solid or liquid, i.e., a condensed phase. Lower temperature favors the formation of a condensed phase. In a condensed phase, there is very nearly a balance between the attractive and repulsive forces. | 6 | Supramolecular Chemistry |
A nicking enzyme (or nicking endonuclease) is an enzyme that cuts one strand of a double-stranded DNA at a specific recognition nucleotide sequences known as a restriction site. Such enzymes hydrolyse (cut) only one strand of the DNA duplex, to produce DNA molecules that are “nicked”, rather than cleaved.
They can be used for strand-displacement amplification, Nicking Enzyme Amplification Reaction, exonucleotyic degradation, the creation of small gaps, or nick translation. The latter process has been successfully used to incorporate both radioactively labelled nucleotides and fluorescent nucleotides allowing specific regions on a double stranded DNA to be studied. Over 200 nicking enzymes have been studied, and 13 of these are available commercially and are routinely used for research and in commercial products. | 1 | Biochemistry |
Crevice corrosion refers to corrosion occurring in occluded spaces such as interstices in which a stagnant solution is trapped and not renewed. These spaces are generally called crevices. Examples of crevices are gaps and contact areas between parts, under gaskets or seals, inside cracks and seams, spaces filled with deposits and under sludge piles. | 8 | Metallurgy |
Samarium(II) iodide is an inorganic compound with the formula SmI. When employed as a solution for organic synthesis, it is known as Kagan's reagent. SmI is a green solid and forms a dark blue solution in THF. It is a strong one-electron reducing agent that is used in organic synthesis. | 0 | Organic Chemistry |
Coelenterazine was simultaneously isolated and characterized by two groups studying the luminescent organisms sea pansy (Renilla reniformis) and the cnidarian Aequorea victoria, respectively. Both groups independently discovered that the same compound was used in both luminescent systems. The molecule was named after the now-obsolete phylum coelenterata. Likewise, the two main metabolites – coelenteramide and coelenteramine – were named after their respective functional groups. While coelenterazine was first discovered in Aequorea victoria, it was later shown that they do not synthesize coelenterazine, but obtain it through their diet, largely from crustaceans and copepods. | 1 | Biochemistry |
The extent of adsorption at a liquid interface can be evaluated using the surface tension concentration data and the Gibbs adsorption equation. The microtome blade method is used to determine the weight and molal concentration of an interface. The method involves attaining a one square meter portion of air-liquid interface of binary solutions using a microtome blade.
Another method that is used to determine the extent of adsorption at an air-water interface is the emulsion technique, which can be used to estimate the relative surface excess with respect to water.
Additionally, the Gibbs surface excess of a surface active component for an aqueous solution can be found using the radioactive tracer method. The surface active component is usually labeled with carbon-14 or sulfur-35. | 7 | Physical Chemistry |
The majority of optical tweezers make use of conventional TEM Gaussian beams. However a number of other beam types have been used to trap particles, including high order laser beams i.e. Hermite-Gaussian beams (TEM), Laguerre-Gaussian (LG) beams (TEM) and Bessel beams.
Optical tweezers based on Laguerre-Gaussian beams have the unique capability of trapping particles that are optically reflective and absorptive. Laguerre-Gaussian beams also possess a well-defined orbital angular momentum that can rotate particles. This is accomplished without external mechanical or electrical steering of the beam.
Both zero and higher order Bessel Beams also possess a unique tweezing ability. They can trap and rotate multiple particles that are millimeters apart and even around obstacles.
Micromachines can be driven by these unique optical beams due to their intrinsic rotating mechanism due to the spin and orbital angular momentum of light. | 1 | Biochemistry |
The chiral allylic stannane 1 adds to acrolein to yield the 1,5-syn diastereomer as a single stereoisomer. A subsequent sigmatropic rearrangement increased the distance between the stereocenters even further. This step was carried out en route to (±)-patulolide C.
Repeated use of the allylic stannane addition in an intramolecular sense was used in the synthesis of hemibrevetoxin B (one example is shown below). The pseudoequatorial positions of both "appendages" in the starting material lead to the observed stereoisomer. | 0 | Organic Chemistry |
Cefamandole (INN, also known as cephamandole) is a second-generation broad-spectrum cephalosporin antibiotic. The clinically used form of cefamandole is the formate ester cefamandole nafate, a prodrug which is administered parenterally. Cefamandole is no longer available in the United States.
The chemical structure of cefamandole, like that of several other cephalosporins, contains an N-methylthiotetrazole (NMTT or 1-MTT) side chain. As the antibiotic is broken down in the body, it releases free NMTT, which can cause hypoprothrombinemia (likely due to inhibition of the enzyme vitamin K epoxide reductase)(vitamin K supplement is recommended during therapy) and a reaction with ethanol similar to that produced by disulfiram (Antabuse), due to inhibition of aldehyde dehydrogenase.
Cefamandole has a broad spectrum of activity and can be used to treat bacterial infections of the skin, bones and joints, urinary tract, and lower respiratory tract. The following represents cefamandole MIC susceptibility data for a few medically significant microorganisms.
* Escherichia coli: 0.12 - 400 μg/ml
* Haemophilus influenzae: 0.06 - >16 μg/ml
* Staphylococcus aureus: 0.1 - 12.5 μg/ml
CO is generated during the normal constitution of cefamandole and ceftazidime, potentially resulting in an explosive-like reaction in syringes. | 4 | Stereochemistry |
Spectral and spatial is collected by the detection system. The spatial component catches the position of the particles distribution across the width of the sorting machine, which is then used in case the ejection mechanism is activated for a single particle. Spectral data comprises the features that are used for material discrimination. In a superseding processing step, spectral and spatial can be combined to include patterns into the separation criterion. Huge amount of data is collected in real time multiple processing and filtering steps are bringing the data down to the Yes/no decision – either for ejecting a particle or for keeping the ejection mechanism still for that one. | 3 | Analytical Chemistry |
A metabolic network can be broken down into a stoichiometric matrix where the rows represent the compounds of the reactions, while the columns of the matrix correspond to the reactions themselves. Stoichiometry is a quantitative relationship between substrates of a chemical reaction. In order to deduce what the metabolic network suggests, recent research has centered on a few approaches, such as extreme pathways, elementary mode analysis, flux balance analysis, and a number of other constraint-based modeling methods. | 1 | Biochemistry |
Selectfluor is synthesized by the N-alkylation of [[DABCO|diazabicyclo[2.2.2]octane (DABCO)]] with dichloromethane, followed by ion exchange with sodium tetrafluoroborate (replacing the chloride counterion for the tetrafluoroborate). The resulting salt is treated with elemental fluorine and sodium tetrafluoroborate:
The cation is often depicted with one skewed ethylene ((CH)) group. In fact, these pairs of CH groups are eclipsed so that the cation has idealized C symmetry. | 0 | Organic Chemistry |
The energy efficiency and system capacity of systems designed for R-22 is slightly greater using R-22 than the available substitutes.
R-407A is for use in low- and medium-temp refrigeration. Uses a polyolester (POE) oil.
R-407C is for use in air conditioning. Uses a minimum of 20 percent POE oil.
R-407F and R-407H are for use in medium- and low-temperature refrigeration applications (supermarkets, cold storage, and process refrigeration); direct expansion system design only. They use a POE oil.
R-421A is for use in "air conditioning split systems, heat pumps, supermarket pak systems, dairy chillers, reach-in storage, bakery applications, refrigerated transport, self-contained display cabinets, and walk-in coolers." Uses mineral oil (MO), Alkylbenzene (AB), and POE.
R-422B is for use in low-, medium-, and high-temperature applications. It is not recommended for use in flooded applications.
R-422C is for use in medium- and low-temperature applications. The TXV power element will need to be changed to a 404A/507A element and critical seals (elastomers) may need to be replaced.
R-422D is for use in low-temp applications, and is mineral oil compatible.
R-424A is for use in air conditioning as well as medium-temp refrigeration temperature ranges of 20 to 50˚F. It works with MO, alkylbenzenes (AB), and POE oils.
R-427A is for use in air conditioning and refrigeration applications. It does not require all the mineral oil to be removed. It works with MO, AB, and POE oils.
R-434A is for use in water cooled and process chillers for air conditioning and medium- and low-temperature applications. It works with MO, AB, and POE oils.
R-438A (MO-99) is for use in low-, medium-, and high-temperature applications. It is compatible with all lubricants.
R-458A is for use in air conditioning and refrigeration applications, without capacity or efficiency loss. Works with MO, AB, and POE oils.
R-32 or HFC-32 (difluoromethane) is for use in air conditioning and refrigeration applications. It has zero ozone depletion potential (ODP) [2] and a global warming potential (GWP) index 675 times that of carbon dioxide. | 2 | Environmental Chemistry |
In a chemical analysis, the internal standard method involves adding the same amount of a chemical substance to each sample and calibration solution. The internal standard responds proportionally to changes in the analyte and provides a similar, but not identical, measurement signal. It must also be absent from the sample matrix to ensure there is no other source of the internal standard present. Taking the ratio of analyte signal to internal standard signal and plotting it against the analyte concentrations in the calibration solutions will result in a calibration curve. The calibration curve can then be used to calculate the analyte concentration in an unknown sample.
Selecting an appropriate internal standard accounts for random and systematic sources of uncertainty that arise during sample preparation or instrument fluctuation. This is because the ratio of analyte relative to the amount of internal standard is independent of these variations. If the measured value of the analyte is erroneously shifted above or below the actual value, the internal standard measurements should shift in the same direction.
Ratio plot provides good way of compensation of detector sensitivity variation, but may be biased and should be replaced by Relative concentration/Relative calibration calculations if the reason of response variability is in different mass of analysed sample and traditional (not internal standard) calibration curve of any analyte is not linear through origin. | 3 | Analytical Chemistry |
Hans Thacher Clarke (27 December 1887 – 21 October 1972) was a prominent biochemist during the first half of the twentieth century. He was born in England where he received his university training, but also studied in Germany and Ireland. He spent the remainder of his life in the United States. | 0 | Organic Chemistry |
The redox reactions catalyzed by oxidoreductases are vital in all parts of metabolism, but one particularly important area where these reactions occur is in the release of energy from nutrients. Here, reduced compounds such as glucose and fatty acids are oxidized, thereby releasing energy. This energy is transferred to NAD by reduction to NADH, as part of beta oxidation, glycolysis, and the citric acid cycle. In eukaryotes the electrons carried by the NADH that is produced in the cytoplasm are transferred into the mitochondrion (to reduce mitochondrial NAD) by mitochondrial shuttles, such as the malate-aspartate shuttle. The mitochondrial NADH is then oxidized in turn by the electron transport chain, which pumps protons across a membrane and generates ATP through oxidative phosphorylation. These shuttle systems also have the same transport function in chloroplasts.
Since both the oxidized and reduced forms of nicotinamide adenine dinucleotide are used in these linked sets of reactions, the cell maintains significant concentrations of both NAD and NADH, with the high NAD/NADH ratio allowing this coenzyme to act as both an oxidizing and a reducing agent. In contrast, the main function of NADPH is as a reducing agent in anabolism, with this coenzyme being involved in pathways such as fatty acid synthesis and photosynthesis. Since NADPH is needed to drive redox reactions as a strong reducing agent, the NADP/NADPH ratio is kept very low.
Although it is important in catabolism, NADH is also used in anabolic reactions, such as gluconeogenesis. This need for NADH in anabolism poses a problem for prokaryotes growing on nutrients that release only a small amount of energy. For example, nitrifying bacteria such as Nitrobacter oxidize nitrite to nitrate, which releases sufficient energy to pump protons and generate ATP, but not enough to produce NADH directly. As NADH is still needed for anabolic reactions, these bacteria use a nitrite oxidoreductase to produce enough proton-motive force to run part of the electron transport chain in reverse, generating NADH. | 5 | Photochemistry |
Since the 1940s, the DLVO theory has been used to explain phenomena found in colloidal science, adsorption and many other fields. Due to the more recent popularity of nanoparticle research, DLVO theory has become even more popular because it can be used to explain behavior of both material nanoparticles such as fullerene particles and microorganisms. | 7 | Physical Chemistry |
There are at least three stages involve in the operation of a vacuum disc filter:
Stage 1: Cake formation
The discs rotate in a slurry trough, compartmentalized to reduce the volume held in it at any one time, and therefore to reduce the residence time of slurry in the trough. The time available for this stage depends on two factors, the rotation speed of the disc and the height of the slurry level in the basin. A vacuum is applied inside the discs to promote cake filtration.
Stage 2: Cake dewatering
Washing is largely restricted to the upper portions where the cake surface is nearly horizontal in orientation, which occurs at the temperature of the feed. The ceramic filter uses a sintered alumina disc to dewater slurry under low vacuum. The dewatering occurs by drawing water from the slurry by capillary action. This ensures that no air or particles are drawn into the filter medium to cause blockage. However, if too much wash water is applied then it can cascade down the cake and into the feed trough, where it merely dilutes the slurry.
Stage 3: Cake drying
The final water (moisture) content in the cake is regulated by passing dry (cold or hot) air or gas through the cake. Drying time is dependent on the distribution valve timing, slurry level on the basin, rotation speed, and scraper position.
Stage 4: Cake discharge
These are the typical conditions for the overall operation of the vacuum ceramic filter:
* Slurry level: must be higher than the top of the sectors as they pass through the trough (otherwise air would simply pass through the cloth during cake formation).
* Solids throughput: up to 4,000 kg/mh
* Typical filtration capacity: 200-5,000 L/mh
* Typical air consumption/ flow rate: 50–80 m/h·m at 500 Torr vacuum
* Pressure difference: Typically, the pressure difference with ceramic disc is between 0.90 and 0.95 bar. However, pressure differences across the filter are usually limited to less than 85 kPa making it possible to process a wide range of feed materials in a continuous manner.
* Rotating speed: Higher rotating speeds enable greater solid production rates by formation of thinner cakes. However, this may not be wholly desirable as washing efficiency is likely to be compromised. Moreover, an increased rotating speed requires more electrical power.
* Minimum cake thickness: 3/8-1/2 in or 10–13 mm (for effective discharge)
* Submergence required for cake discharge: 25% of cycle
* Effective maximum submergence of the disk: 28% of cycle. | 3 | Analytical Chemistry |
In his spare time Kowalski enjoyed horse-breeding and riding, sailing, hiking and backpacking, his Harley-Davidison motorcycle and skiing. According to Chemical & Engineering News, "After his retirement in 1999, Kowalski joined the Fort Lewis Mesa fire department in Durango, Colo., where he specialized in the handling of hazardous materials. Kowalski and his companion dog, Chaco-Bob, were a key part of the district’s canine search and rescue program." | 3 | Analytical Chemistry |
The Curtin–Hammett principle applies to systems in which different products are formed from two substrates in equilibrium with one another. The rapidly interconverting reactants can have any relationship between themselves (stereoisomers, constitutional isomers, conformational isomers, etc.). Product formation must be irreversible, and the different products must be unable to interconvert.
For example, given species A and B that equilibrate rapidly while A turns irreversibly into C, and B turns irreversibly into D:
K is the equilibrium constant between A and B, and k and k are the rate constants for the formation of C and D, respectively. When the rate of interconversion between A and B is much faster than either k or k, then the Curtin–Hammett principle tells us that the C:D product ratio is not equal to the equilibrium A:B reactant ratio, but is instead determined by the relative energies of the transition states (i.e., difference in the absolute energies of the transition states). If reactants A and B were at identical energies, the product ratio would depend only on the activation barriers of the reactions leading to each respective product. However, in a real-world scenario, the two reactants are likely at somewhat different energy levels, although the barrier to their interconversion must be low for the Curtin–Hammett scenario to apply. In this case, the product distribution depends both on the equilibrium ratio of A to B and on the relative activation barriers going to the corresponding products C and D. Both factors are taken into account by the difference in the energies of the transition states (ΔΔG in the figure below).
The reaction coordinate free energy profile of a typical reaction under Curtin-Hammett control is represented by the following figure:
The ratio of products only depends on the value labeled ΔΔG in the figure: C will be the major product, because the energy of TS1 is lower than the energy of TS2. A common but false assertion is that the product distribution does not in any way reflect the relative free energies of substrates A and B; in fact, it reflects the relative free energies of the substrates and the relative activation energies. This misunderstanding may stem from failing to appreciate the distinction between "the difference of energies of activation" and "the difference in transition state energies". Although these quantities may at first appear synonymous, the latter takes into account the equilibrium constant for interconversion of A and B, while the former does not.
Mathematically, the product ratio can be expressed as a function of K, k, and k or in terms of the corresponding energies ΔG°, ΔG, and ΔG. By combining terms, the product ratio can be rewritten in terms of the quantity ΔΔG alone, where ΔΔG = (ΔG – ΔG) + ΔG°. Inspection of the energy diagram (shown above) makes it apparent that ΔΔG is precisely the difference in transition state energies. | 7 | Physical Chemistry |
Indirect catalysts may also act through surface sensitization of reactants, by which species sorbed to a surface become more susceptible to photodegradation. | 5 | Photochemistry |
As with many other small mammal species, M. pennsylvanicus plays important ecological roles. The eastern meadow vole is an important food source for many predators, and disperses mycorrhizal fungi. It is a major consumer of grass and disperses grass nutrients in its feces. After disruptive site disturbances such as forest or meadow fires, the meadow vole's activities contribute to habitat restoration. It prefers open, nonforest habitats and colonizes such open areas created by fire or other clearing disturbances. Very few eastern meadow voles are found in forest or woodland areas. In newly opened areas, it is quite abundant. In these new open areas, the vole quickly becomes a food source for predators. | 2 | Environmental Chemistry |
Canadian bitumen does not differ substantially from oils such as Venezuelan extra-heavy and Mexican heavy oil in chemical composition, and the real difficulty is moving the extremely viscous bitumen through oil pipelines to the refinery. Many modern oil refineries are extremely sophisticated and can process non-upgraded bitumen directly into products such as gasoline, diesel fuel, and refined asphalt without any preprocessing. This is particularly common in areas such as the US Gulf coast, where refineries were designed to process Venezuelan and Mexican oil, and in areas such as the US Midwest where refineries were rebuilt to process heavy oil as domestic light oil production declined. Given the choice, such heavy oil refineries usually prefer to buy bitumen rather than synthetic oil because the cost is lower, and in some cases because they prefer to produce more diesel fuel and less gasoline. By 2015 Canadian production and exports of non-upgraded bitumen exceeded that of synthetic crude oil at over per day, of which about 65% was exported to the United States.
Because of the difficulty of moving crude bitumen through pipelines, non-upgraded bitumen is usually diluted with natural-gas condensate in a form called dilbit or with synthetic crude oil, called synbit. However, to meet international competition, much non-upgraded bitumen is now sold as a blend of multiple grades of bitumen, conventional crude oil, synthetic crude oil, and condensate in a standardized benchmark product such as Western Canadian Select. This sour, heavy crude oil blend is designed to have uniform refining characteristics to compete with internationally marketed heavy oils such as Mexican Mayan or Arabian Dubai Crude. | 7 | Physical Chemistry |
Gel permeation chromatography (GPC) is a type of size-exclusion chromatography (SEC), that separates high molecular weight or colloidal analytes on the basis of size or diameter, typically in organic solvents. The technique is often used for the analysis of polymers. As a technique, SEC was first developed in 1955 by Lathe and Ruthven. The term gel permeation chromatography can be traced back to J.C. Moore of the Dow Chemical Company who investigated the technique in 1964. The proprietary column technology was licensed to Waters Corporation, who subsequently commercialized this technology in 1964. GPC systems and consumables are now also available from a number of manufacturers. It is often necessary to separate polymers, both to analyze them as well as to purify the desired product.
When characterizing polymers, it is important to consider their size distribution and dispersity (Đ) as well their molecular weight. Polymers can be characterized by a variety of definitions for molecular weight including the number average molecular weight (M), the weight average molecular weight (M) (see molar mass distribution), the size average molecular weight (M), or the viscosity molecular weight (M). GPC allows for the determination of Đ as well as M and, based on other data, the M, M, and M can be determined. | 3 | Analytical Chemistry |
NADK is highly regulated by the redox state of the cell. Whereas NAD is predominantly found in its oxidized state NAD, the phosphorylated NADP is largely present in its reduced form, as NADPH. Thus, NADK can modulate responses to oxidative stress by controlling NADP synthesis. Bacterial NADK is shown to be inhibited allosterically by both NADPH and NADH. NADK is also reportedly stimulated by calcium/calmodulin binding in certain cell types, such as neutrophils. NAD kinases in plants and sea urchin eggs have also been found to bind calmodulin. | 1 | Biochemistry |
An upper limit on of 4 is usually quoted, corresponding to the precision of the measurements, but it also depends on how intense the effect is. Spectra of contributing species should be clearly distinct from each other | 7 | Physical Chemistry |
Activation refers to the opening of ion channels, i.e. the conformational change that allows ions to pass. | 7 | Physical Chemistry |
Roasting consists of thermal gas–solid reactions, which can include oxidation, reduction, chlorination, sulfation, and pyrohydrolysis.
The most common example of roasting is the oxidation of metal sulfide ores. The metal sulfide is heated in the presence of air to a temperature that allows the oxygen in the air to react with the sulfide to form sulfur dioxide gas and solid metal oxide. The solid product from roasting is often called "calcine". In oxidizing roasting, if the temperature and gas conditions are such that the sulfide feed is completely oxidized, the process is known as "dead roasting". Sometimes, as in the case of pre-treating reverberatory or electric smelting furnace feed, the roasting process is performed with less than the required amount of oxygen to fully oxidize the feed. In this case, the process is called "partial roasting" because the sulfur is only partially removed. Finally, if the temperature and gas conditions are controlled such that the sulfides in the feed react to form metal sulfates instead of metal oxides, the process is known as "sulfation roasting". Sometimes, temperature and gas conditions can be maintained such that a mixed sulfide feed (for instance a feed containing both copper sulfide and iron sulfide) reacts such that one metal forms a sulfate and the other forms an oxide, the process is known as "selective roasting" or "selective sulfation". | 8 | Metallurgy |
The KhAB-500 is the provisional naming of a series of World War II-era aerial bombs developed by the Soviet Air Force to deliver chemical weapons. | 1 | Biochemistry |
* ASTM B374-06(2011) — Standard Terminology Relating to Electroplating
* ASTM B542-13 — Standard Terminology Relating to Electrical Contacts and Their Use
* ASTM B735-16 — Standard Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor
* ASTM B765-03(2018) — Standard Guide for Selection of Porosity and Gross Defect Tests for Electrodeposits and Related Metallic Coatings
* ASTM B798-95(2014) — Standard Test Method for Porosity in Gold or Palladium Coatings on Metal Substrates by Gel-Bulk Electrography
* ASTM B799-95(2014) — Standard Test Method for Porosity in Gold and Palladium Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
* ASTM B809-95(2018) — Standard Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor ("Flowers-of-Sulfur")
* ASTM B810-01a (Reapproved 2017) —Standard Method for Calibration of Atmospheric Corrosion Test Chambers by Change in Mass of Copper Coupons
* ANSI/ISA-71.04-2013 Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants, The International Society of Automation, Research Triangle Park, NC. | 8 | Metallurgy |
As mentioned before, N-acyl-homoserine lactones (AHL) are the quorum sensing signaling molecules of the gram-negative bacteria. However, these molecules may have different functional groups on their acyl chain, and also a different length of acyl chain. Therefore, there exist many different AHL signaling molecules, for example, 3-oxododecanoyl-L-homoserine lactone (3OC12-HSL) or 3-hydroxydodecanoyl-L-homoserine lactone (3OHC12-HSL). The modification of those quorum sensing (QS) signaling molecules is another sort of quorum quenching. This can be carried out by an oxidoreductase activity. As an example, we will discuss the interaction between a host, Hydra vulgaris, and the main colonizer of its epithelial cell surfaces, Curvibacter spp. Those bacteria produce 3-oxo-HSL quorum sensing molecules. However, the oxidoreductase activity of the polyp Hydra is able to modify the 3-oxo-HSL into their 3-hydroxy-HSL counterparts. We can characterize this as quorum quenching since there is an interference with quorum sensing molecules. In this case, the outcomes differ from simple QS inactivation: the host modification results in a phenotypic switch of Curvibacter, which modifies its ability to colonize the epithelial cell surfaces of H. vulgaris. | 1 | Biochemistry |
NeighborNet is an algorithm for constructing phylogenetic networks which is loosely based on the neighbor joining algorithm. Like neighbor joining, the method takes a distance matrix as input, and works by agglomerating clusters. However, the NeighborNet algorithm can lead to collections of clusters which overlap and do not form a hierarchy, and are represented using a type of phylogenetic network called a splits graph. If the distance matrix satisfies the Kalmanson combinatorial conditions then Neighbor-net will return the corresponding circular ordering. The method is implemented in the SplitsTree and R/Phangorn packages.
Examples of the application of Neighbor-net can be found in virology, horticulture, dinosaur genetics, comparative linguistics, and archaeology. | 1 | Biochemistry |
* List of important publications in thermodynamics
* List of textbooks on thermodynamics and statistical mechanics
* List of thermal conductivities
* List of thermodynamic properties
* Table of thermodynamic equations
* Timeline of thermodynamics
* Thermodynamic equations | 7 | Physical Chemistry |
Gene targeting is a biotechnological tool used to change the DNA sequence of an organism (hence it is a form of Genome Editing). It is based on the natural DNA-repair mechanism of Homology Directed Repair (HDR), including Homologous Recombination. Gene targeting can be used to make a range of sizes of DNA edits, from larger DNA edits such as inserting entire new genes into an organism, through to much smaller changes to the existing DNA such as a single base-pair change. Gene targeting relies on the presence of a repair template to introduce the user-defined edits to the DNA. The user (usually a scientist) will design the repair template to contain the desired edit, flanked by DNA sequence corresponding (homologous) to the region of DNA that the user wants to edit; hence the edit is targeted to a particular genomic region. In this way Gene Targeting is distinct from natural homology-directed repair, during which the ‘natural’ DNA repair template of the sister chromatid is used to repair broken DNA (the sister chromatid is the second copy of the gene). The alteration of DNA sequence in an organism can be useful in both a research context – for example to understand the biological role of a gene – and in biotechnology, for example to alter the traits of an organism (e.g. to improve crop plants). | 1 | Biochemistry |
The Kidd Metallurgical Site (or Met Site) is a metallurgical facility in Timmins, Ontario, Canada. It was built in 1980 and owned and operated by Xstrata Copper, following their 2006 takeover of Falconbridge Ltd. The site employs approximately 675 hourly employees.
The plant is southeast of the Kidd Mine, and houses a concentrator, copper smelter and refinery, zinc plant, cadmium plant, indium plant and a sulphuric acid plant. The Met Site was built away from the mine because of the muskeg-like terrain surrounding the mine.
The Met Site processes material from the Kidd Mine and outside sources, and employs 875 people. Of the 875 employees 125 work at the concentrator, 205 in the copper operations and 275 in the zinc facilities. The remainder of the employees are support staff.
Xstrata announced its plans to close the Metallurgical Site in May 2010. Only the concentrator will remain as the ore will now be shipped to Québec. The demolition of the rest of the plant started in February 2011. | 8 | Metallurgy |
The effect is named after James Prescott Joule and William Thomson, 1st Baron Kelvin, who discovered it in 1852. It followed upon earlier work by Joule on Joule expansion, in which a gas undergoes free expansion in a vacuum and the temperature is unchanged, if the gas is ideal. | 7 | Physical Chemistry |
Recently the possibility of study such compounds using molecular modeling assisted by informatic software has opened new possibilities in the study of the redox reaction of biomimetic compounds. For example, using "Density Functional Theory" (DFT) computer modeling made it possible to propose a catalytic pathway of H binding on the catalytic center of hydrogenase (Greco). Other example of the application of computational modeling in the study of hydrogenases is the work done by Breglia et al., whose results shows the chemical pathway of how oxygen inhibited the redox reaction of [NiFe] hydrogenases. | 1 | Biochemistry |
After injury, neurons in the adult peripheral nervous system can switch from a dormant state with little axonal growth to robust axon regeneration. DNA demethylation in mature mammalian neurons removes barriers to axonal regeneration. This demethylation, in regenerating mouse peripheral neurons, depends upon TET3 to generate 5-hydroxymethylcytosine (5hmC) in DNA. 5hmC was altered in a large set of regeneration-associated genes (RAGs), including well-known RAGs such as Atf3, Bdnf, and Smad1, that regulate the axon growth potential of neurons. | 1 | Biochemistry |
Kai Simons is the son of a physics professor. His father convinced him to study medicine, though he originally wanted to study physics. While studying at the University of Helsinki, Simons spent a summer internship in the Stockholm laboratory of Bengt Samuelsson There, he studied mechanisms of vitamin B12 absorption. He worked with other students to organize a campaign to fight taeniasis, a disease common in eastern Finland where eating raw fish is popular.
After completing his MD in 1964, he began a postdoctoral fellowship at Rockefeller University in New York City where he worked between 1966 and 1967 on blood serum protein polymorphism. He returned to Helsinki in 1967, where he began working as a Junior Investigator for the Finnish Medical Research Council at the University of Helsinki. He became a group leader in 1972 and was a biochemistry professor in 1971–79 at the medical faculty of this university At first, he continued his work on serum proteins. Next, together with Leevi Kääriäinen and Ossi Renkonen, he started a research team – later joined by Ari Helenius, his first PhD student and later a post doctoral researcher who became Simons' brother-in-law. After a one-month stay in MRC Laboratory for Molecular Biology in Cambridge, the group started investigating a Semliki Forest virus, introduced to Simons by Kääriäinen.
In 1975 Simons came to Heidelberg (Germany), as one of the EMBL group leaders. Together with Ari Helenius he helped to develop EMBL, headed at this time by John Kendrew. In years 1982–1998 Simons was a coordinator of the Cell Biology Program there. During this time he for the first time presented the concept of lipid rafts.
In 1999 he took part in setting up ELSO (later incorporated into EMBO), which later he presided over.
He was one of the initiators of establishing and building Max Planck Institute of Molecular Cell Biology and Genetics in Dresden (Germany), where he moved. Formally from 1998 (beginning of MPI-CBG construction) and practically from 2000 he was one of five institutes directors and also a group leader there Since 2006 he is a director emeritus'.
In 2012 he started-up a biotech company Lipotype GmbH, where he is a CEO.
He is married to Carola Simons and a father of three: twins – Mikael (neurobiologist) and Katja (sociologist), and the youngest of three, Matias (physician). | 1 | Biochemistry |
The mTORC2 signaling pathway is less defined than the mTORC1 signaling pathway. The functions of the components of the mTORC complexes have been studied using knockdowns and knockouts and were found to produce the following phenotypes:
* NIP7: Knockdown reduced mTORC2 activity that is indicated by decreased phosphorylation of mTORC2 substrates.
* RICTOR: Overexpression leads to metastasis and knockdown inhibits growth factor-induced PKC-phosphorylation. Constitutive deletion of Rictor in mice leads to embryonic lethality, while tissue specific deletion leads to a variety of phenotypes; a common phenotype of Rictor deletion in liver, white adipose tissue, and pancreatic beta cells is systemic glucose intolerance and insulin resistance in one or more tissues. Decreased Rictor expression in mice decreases male, but not female, lifespan.
* mTOR: Inhibition of mTORC1 and mTORC2 by PP242 [2-(4-Amino-1-isopropyl-1H-pyrazolo[3,4-d]pyrimidin-3-yl)-1H-indol-5-ol] leads to autophagy or apoptosis; inhibition of mTORC2 alone by PP242 prevents phosphorylation of Ser-473 site on AKT and arrests the cells in G1 phase of the cell cycle. Genetic reduction of mTOR expression in mice significantly increases lifespan.
* PDK1: Knockout is lethal; hypomorphic allele results in smaller organ volume and organism size but normal AKT activation.
* AKT: Knockout mice experience spontaneous apoptosis (AKT1), severe diabetes (AKT2), small brains (AKT3), and growth deficiency (AKT1/AKT2). Mice heterozygous for AKT1 have increased lifespan.
* TOR1, the S. cerevisiae orthologue of mTORC1, is a regulator of both carbon and nitrogen metabolism; TOR1 KO strains regulate response to nitrogen as well as carbon availability, indicating that it is a key nutritional transducer in yeast. | 1 | Biochemistry |
Some of the oldest known examples of the lost-wax technique are the objects discovered in the Nahal Mishmar hoard in southern Land of Israel, and which belong to the Chalcolithic period (4500–3500 BC). Conservative Carbon-14 estimates date the items to around 3700 BC, making them more than 5700 years old. | 8 | Metallurgy |
The studies of crystalline ionic conductors where excess ions were provided by point defect continued through 1950s, and the specific mechanism of conduction was established for each compound depending on its ionic structure. The emergence of glassy and polymeric electrolytes in the late 1970s provided new ionic conduction mechanisms. A relatively wide range of conductivities was attained in glasses, wherein mobile ions were dynamically decoupled from the matrix. It was found that the conductivity could be increased by doping a glass with certain salts, or by using a glass mixture. The conductivity values could be as high as 0.03 S/cm at room temperature, with activation energies as low as 20 kJ/mol. Compared to crystals, glasses have isotropic properties, continuously tunable composition and good workability; they lack the detrimental grain boundaries and can be molded into any shape, but understanding their ionic transport was complicated by the lack of long-range order.
Historically, an evidence for ionic conductivity was provided back in the 1880s, when German scientists noticed that a well-calibrated thermometer made of Thuringian glass would show −0.5 °C instead of 0 °C when placed in ice shortly after immersion in boiling water, and recover only after several months. In 1883, they reduced this effect 10 times by replacing a mixture of sodium and potassium in the glass by either sodium or potassium. This finding helped Otto Schott develop the first accurate lithium-based thermometer. More systematic studies on ionic conductivity in glass appeared in 1884, but received broad attention only a century later. Several universal laws have been empirically formulated for ionic glasses and extended to other ionic conductors, such as the frequency dependence of electrical conductivity σ(ν) – σ(0) ~ ν, where the exponent p depends on the material, but not on temperature, at least below ~100 K. This behavior is a fingerprint of activated hopping conduction among nearby sites. | 7 | Physical Chemistry |
The solvents are grouped into nonpolar, polar aprotic, and polar protic solvents, with each group ordered by increasing polarity. The properties of solvents which exceed those of water are bolded.
The ACS Green Chemistry Institute maintains a tool for the selection of solvents based on a principal component analysis of solvent properties. | 2 | Environmental Chemistry |
Availability of IVF in England is determined by Clinical Commissioning Groups (CCGs). The National Institute for Health and Care Excellence (NICE) recommends up to 3 cycles of treatment for people under 40 years old with minimal success conceiving after 2 years of unprotected sex. Cycles will not be continued for people who are older than 40 years. CCGs in Essex, Bedfordshire and Somerset have reduced funding to one cycle, or none, and it is expected that reductions will become more widespread. Funding may be available in "exceptional circumstances" – for example if a male partner has a transmittable infection or one partner is affected by cancer treatment. According to the campaign group Fertility Fairness "at the end of 2014 every CCG in England was funding at least one cycle of IVF". Prices paid by the NHS in England varied between under £3,000 to more than £6,000 in 2014/5. In February 2013, the cost of implementing the NICE guidelines for IVF along with other treatments for infertility was projected to be £236,000 per year per 100,000 members of the population.
IVF increasingly appears on NHS treatments blacklists. In August 2017 five of the 208 CCGs had stopped funding IVF completely and others were considering doing so. By October 2017 only 25 CCGs were delivering the three recommended NHS IVF cycles to eligible people under 40. Policies could fall foul of discrimination laws if they treat same sex couples differently from heterosexual ones. In July 2019 Jackie Doyle-Price said that women were registering with surgeries further away from their own home in order to get around CCG rationing policies.
The Human Fertilisation and Embryology Authority said in September 2018 that parents who are limited to one cycle of IVF, or have to fund it themselves, are more likely choose to implant multiple embryos in the hope it increases the chances of pregnancy. This significantly increases the chance of multiple births and the associated poor outcomes, which would increase NHS costs. The president of the Royal College of Obstetricians and Gynaecologists said that funding 3 cycles was "the most important factor in maintaining low rates of multiple pregnancies and reduce(s) associated complications". | 1 | Biochemistry |
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