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The Salvinia effect defines surfaces which are able to permanently keep relatively thick air layers as a result of their hydrophobic chemistry, in combination with a complex architecture in nano- and microscopic dimensions.
This phenomenon was discovered during a systematic research on aquatic plants and animals by Wilhelm Barthlott and his colleagues at the University of Bonn between 2002 and 2007. Five criteria have been defined, they enable the existence of stable air layers under water and as of 2009 define the Salvinia effect: (1) hydrophobic surfaces chemistry in combination with (2) nanoscalic structures generate superhydrophobicity, (3) microscopic hierarchical structures ranging from a few mirco- to several millimeters with (4) undercuts and (5) elastic properties. Elasticity appears to be important for the compression of the air-layer in dynamic hydrostatic conditions. An additional optimizing criterion is the chemical heterogeneity of the hydrophilic tips (Salvinia Paradox). This is a prime example of a hierarchical structuring on several levels.
In plants and animals, air retaining salvinia effect surfaces are always fragmented in small compartments with a length of 0.5 to 8 cm and the borders are sealed against loss of air by particular microstructures. Compartments with sealed edges are also important for technical applications.
The working principle is illustrated in for the Giant Salvinia. The leaves of S. molesta are capable of keeping an air layer on its surfaces for a long time when submerged in water. If a leaf is pulled under water, the leaf surface shows a silvery shine. The distinctive feature of S. molesta lies in the long term stability. While the air layer on most hydrophobic surfaces vanishes shortly after submerging, S. molesta is able to stabilize the air for several days to several weeks. The time span is thereby just limited by the lifetime of the leaf.
The high stability is a consequence of a seemingly paradoxical combination of a superhydrophobic (extremely water repellent) surface with hydrophilic (water attractive) patches on the tips of the structures.
When submerged under water, no water can penetrate the room between the hairs due to the hydrophobic character of the surfaces. However, the water is pinned to the tip of each hair by the four wax free (hydrophilic) end cells. This fixation results in a stabilization of the air layer under water. The principle is shown in the figure.
Two submerged, air retaining surfaces are schematically shown: on the left hand side: a hydrophobic surface. On the right hand side: a hydrophobic surface with hydrophilic tips.
If negative pressure is applied, a bubble is quickly formed on the purely hydrophobic surfaces (left) stretching over several structures. With increasing negative pressure the bubble grows and can detach from the surface. The air bubble rises to the surface and the air layer decreases until it vanishes completely.
In case of the surface with hydrophilic anchor cells (right) the water is pinned to the tips of every structure by the hydrophilic patch on top. These linkages allow the formation of a bubble stretching over several structures; bubble release is suppressed because several links have to be broken first. This results in a higher energy input for the bubble formation. Therefore, an increased negative pressure is needed to form a bubble able to detach from the surface and rise upwards. | 7 | Physical Chemistry |
Anhydrous aluminium chloride is a powerful Lewis acid, capable of forming Lewis acid-base adducts with even weak Lewis bases such as benzophenone and mesitylene. It forms tetrachloroaluminate () in the presence of chloride ions.
Aluminium chloride reacts with calcium and magnesium hydrides in tetrahydrofuran forming tetrahydroaluminates. | 0 | Organic Chemistry |
The surface of any liquid is an interface between that liquid and some other medium. The top surface of a pond, for example, is an interface between the pond water and the air. Surface tension, then, is not a property of the liquid alone, but a property of the liquid's interface with another medium. If a liquid is in a container, then besides the liquid/air interface at its top surface, there is also an interface between the liquid and the walls of the container. The surface tension between the liquid and air is usually different (greater) than its surface tension with the walls of a container. And where the two surfaces meet, their geometry must be such that all forces balance.
Where the two surfaces meet, they form a contact angle, , which is the angle the tangent to the surface makes with the solid surface. Note that the angle is measured through the liquid, as shown in the diagrams above. The diagram to the right shows two examples. Tension forces are shown for the liquid–air interface, the liquid–solid interface, and the solid–air interface. The example on the left is where the difference between the liquid–solid and solid–air surface tension, , is less than the liquid–air surface tension, , but is nevertheless positive, that is
In the diagram, both the vertical and horizontal forces must cancel exactly at the contact point, known as equilibrium. The horizontal component of is canceled by the adhesive force, .
The more telling balance of forces, though, is in the vertical direction. The vertical component of must exactly cancel the difference of the forces along the solid surface, .
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| style="text-align:center;"|90°
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| style="text-align:center;"|29°
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Since the forces are in direct proportion to their respective surface tensions, we also have:
where
* is the liquid–solid surface tension,
* is the liquid–air surface tension,
* is the solid–air surface tension,
* is the contact angle, where a concave meniscus has contact angle less than 90° and a convex meniscus has contact angle of greater than 90°.
This means that although the difference between the liquid–solid and solid–air surface tension, , is difficult to measure directly, it can be inferred from the liquid–air surface tension, , and the equilibrium contact angle, , which is a function of the easily measurable advancing and receding contact angles (see main article contact angle).
This same relationship exists in the diagram on the right. But in this case we see that because the contact angle is less than 90°, the liquid–solid/solid–air surface tension difference must be negative: | 6 | Supramolecular Chemistry |
A similar-looking kind of damage is called false brinelling and is caused by fretting wear. Fretting wear occurs when localized wear-marks develop in evenly spaced patterns, with raised or unworn portions in between, like frets on a guitar. False brinelling occurs in two types: stationary and by precession.
Stationary false-brinelling occurs without any rotational motion in the bearing. This occurs when contacting bodies vibrate against each other in the presence of very small loads, which pushes lubricant out of the contact surface area, all while the bearing assembly cannot move far enough (or rotate far enough) to redistribute the displaced lubricant. The result is a finely polished surface that resembles a brinell mark, but has not permanently deformed either contacting surface. This type of false brinelling usually occurs in bearings during transportation, between the time of manufacture and installation. The polished surfaces are often mistaken for brinelling, although no actual damage to the bearing exists. The false brinelling will disappear after a short break-in period of operation.
Fretting wear can also occur during operation, causing deep indentations. This occurs when small vibrations form in the rotating shaft and become harmonically in sync with the speed of rotation, causing circular oscillations in the shaft. The oscillation causes the shaft to move in precession, and the timing of the rotation speed causes the balls or rollers to contact the races only when they are in similar positions. This forms wear marks caused by contact with the bearings and the races in specific areas, but not in others, leaving an uneven wear-pattern that can become quite deep before failure occurs, resembling brinelling. However, the marks are usually too wide, due to the motion of the bearing, and do not exactly match the shape of the rolling elements, and therefore this type of wear can be differentiated from true brinelling. | 8 | Metallurgy |
The goal of combining fluorescence and nucleic acids has been to provide a non-isotopic tag that is detectable to study DNA or RNA. This type of labeling allows scientists to study DNA or RNA in their structure, function, or formation with other nucleic acids. The first base modification for fluorescent labeling occurred in 1971 with a 4-thiouridine and 4-thiouracil. This research along with others, which included various types of direct and non-direct labeling via: analogs, addition via enzymes, or other methods made labeling of nucleotides much safer for scientist to study DNA.
As instrumentation and technologies become more advanced in the field of DNA microarray, better reagents and techniques will be needed to further scientific studies. Fluorescent labeling with Cy3 was shown to be more insufficient and skew results; the method of aminoallyl nucleotide incorporation was opted instead. Using aminoallyl nucleotides as indirect fluorescent labeling seemed to nullify the sensitivity issues seen in cyanine-labeling. | 1 | Biochemistry |
Over 90% of the dry weight of hair comprises proteins called keratins, which have a high disulfide content, from the amino acid cysteine. The robustness conferred in part by disulfide linkages is illustrated by the recovery of virtually intact hair from ancient Egyptian tombs. Feathers have similar keratins and are extremely resistant to protein digestive enzymes. The stiffness of hair and feather is determined by the disulfide content. Manipulating disulfide bonds in hair is the basis for the permanent wave in hairstyling. Reagents that affect the making and breaking of S−S bonds are key, e.g., ammonium thioglycolate. The high disulfide content of feathers dictates the high sulfur content of bird eggs. The high sulfur content of hair and feathers contributes to the disagreeable odor that results when they are burned. | 0 | Organic Chemistry |
Two salt metathesis reactions are popular for laboratory scale reactions. In the Kolbe nitrile synthesis, alkyl halides undergo nucleophilic aliphatic substitution with alkali metal cyanides. Aryl nitriles are prepared in the Rosenmund-von Braun synthesis.
In general, metal cyanides combine with alkyl halides to give a mixture of the nitrile and the isonitrile, although appropriate choice of counterion and temperature can minimize the latter. An alkyl sulfate obviates the problem entirely, particularly in nonaqueous conditions (the Pelouze synthesis). | 0 | Organic Chemistry |
Gestonorone caproate has been available widely in Europe, including in the United Kingdom, and has also been marketed in Japan, China, Mexico, and certain other countries. However, it has been discontinued in most countries and its availability is more limited today; it appears to remain marketed only in the Czech Republic, Japan, Mexico, and Russia. It has not been marketed in the United States, Canada, and many other countries. | 4 | Stereochemistry |
In double knockout STAT2 mice, an increased proliferation of M1, M2, and M1/M2 coexpressing macrophages during influenza-bacterial super-infection is observed. The bacterial clearance was also impaired by neutralization of IFN-γ (M1) and Arginase-1 (M2) what suggests that pulmonary macrophages expressing a mixed M1/M2 phenotype promote bacterial control during influenza-bacterial super-infection. Therefore the STAT2 signaling is associated with suppressing macrophage activation and bacterial control during influenza-bacterial super-infection. These mice demonstrate no developmental defects. The knockout STAT2 and double knockout STAT mice in Vesicular stromatitis Indiana virus (VSV) model produce at least 10 times more virus plaque-forming units than the wild type (WT). IFN-α pretreatment supplied protection in WT and STAT2 cells but not in double knockout STAT2 cells. IFN-γ pretreatment did not provide any antiviral response during infection of VSV. This finding could be explained by the reduced level of STAT1 in cells of STAT2 knockout mice. Additionally, the double knockout STAT2 mice are more sensitive to mouse cytomegalovirus (MCMV), severe fever thrombocytopenia syndrome virus, influenza virus, dengue virus (DNV) and Zika virus than control mice, which suggests that STAT2 plays a critical role in the suppression of virus replication in mice. | 1 | Biochemistry |
Tests for antibiotic effectiveness against E. coli, A. fecalis, B. subtilis, S. aureus, and P. aeruginosa were negative. Also, no inhibitory action was shown against A. niger, A. flavis, P. crustosum, F. graminearum, F. moniliforme, Alternara sp., and Cladosporium sp. However, some insecticidal activity has been shown in one study, possibly showing some use as an insecticide for food crops. In mammalian (mice lung cell) studies, brevianamide A has shown to induce cytoxicity in cells. Furthermore, ELISA assays showed elevated levels of tumor necrosis factor-alpha (TNF-A), macrophage inflammatory protein-2 (MIP-2), and interleukin 6 (IL-6). Therefore, brevianamide A may not be a suitable insecticide in food crops. | 0 | Organic Chemistry |
Carbon dioxide () from air and bicarbonate () or carbonate () anions dissolved in water react with the calcium hydroxide (, portlandite) produced by Portland cement hydration in concrete to form calcium carbonate () while releasing a water molecule in the following reaction:
Exception made of the water molecule, the carbonation reaction is essentially the reverse of the process of calcination of limestone taking place in a cement kiln:
Carbonation of concrete is a slow and continuous process of atmospheric diffusing from the outer surface of concrete exposed to air into its mass and chemically reacting with the mineral phases of the hydrated cement paste. Carbonation slows down with increasing diffusion depth.
Carbonation has two antagonist effects for (1) the concrete strength, and (2) its durability:
# The precipitation of calcite filling the microscopic voids in the concrete pore space decreases the concrete matrix porosity: so, it increases the mechanical strength of concrete;
# At the same time carbonation consumes portlandite and therefore decreases the concrete alkalinity reserve buffer. Hyper-alkaline conditions (i.e., basic chemical conditions) characterized by a high pH (typically 12.5 – 13.5) are needed to passivate the steel surface of the reinforcement bars (rebar) and to protect them from corrosion. Below a pH of 10, the solubility of the iron oxides forming a protective thin coating at the surface of carbon steel increases. The thin protective oxide layer starts to dissolve, and corrosion is then promoted. As the volumetric mass of iron oxides can be as high as 6 – 7 times that of metallic iron (Fe), a detrimental consequence is the expansion of the corrosion products around the rebar. This causes the development of a tensile stress in the concrete matrix around the rebar. When the tensile strength of concrete is exceeded in the concrete cover above the rebar, concrete starts to spall. Cracks appear in the concrete cover protecting the rebar against corrosion and constitute preferential pathways for direct ingress towards the rebar. This accelerates the carbonation reaction and in turn the corrosion process speeds up.
This explain why the carbonation reaction of reinforced concrete is an undesirable process in concrete chemistry. Concrete carbonation can be visually revealed by applying a phenolphthalein solution over the fresh surface of a concrete samples (concrete core, prism, freshly fractured bar). Phenolphthalein is a pH indicator, whose color turns from colorless at pH < 8.5 to pink-fuchsia at pH > 9.5. A violet color indicates still alkaline areas and thus non-carbonated concrete. Carbonated zones favorable for steel corrosion and concrete degradation are colorless.
The presence of water in carbonated concrete is necessary to lower the pH of concrete pore water around rebar and to depassivate the carbon steel surface at low pH. Water is central to corrosion processes. Without water, the steel corrosion is very limited and rebar present in dry carbonated concrete structures, or components, not affected by water infiltration do not suffer from significant corrosion. | 8 | Metallurgy |
The NURF complex in Drosophila contains four subunits: NURF301, NURF140, NURF55, and NURF38. NURF140 is an ISWI ATPase, distinguishable by its HAND, SANT, and SLIDE domains (SANT-like but with several insertions). The NURF complex in Homo sapiens has three subunits, BPTF, SNF2L, and pRBAP46/48, homologous to NURF301, NURF140, and NURF55, respectively. There is no human homolog for NURF38. | 1 | Biochemistry |
ppGpp inhibits IF2-mediated fMet-Phe initiation dipeptide formation, probably by interfering with 30S and 50S subunit interactions. E. coli accumulates more ppGpp than pppGpp during amino acid starvation, and ppGpp has about 8-fold greater efficiency than that of pppGpp. While B. subtilis accumulates more pppGpp than ppGpp. | 1 | Biochemistry |
He left the semiconductor industry in 1972, and began a new career as an entrepreneur in data security and cryptography. In 1972, he founded Atalla Technovation, later called Atalla Corporation, which dealt with safety problems of banking and financial institutions. | 7 | Physical Chemistry |
After escaping the promoter and shedding most of the transcription factors for initiation, the polymerase acquires new factors for the next phase of transcription: elongation. Transcription elongation is a processive process. Double stranded DNA that enters from the front of the enzyme is unzipped to avail the template strand for RNA synthesis. For every DNA base pair separated by the advancing polymerase, one hybrid RNA:DNA base pair is immediately formed. DNA strands and nascent RNA chain exit from separate channels; the two DNA strands reunite at the trailing end of the transcription bubble while the single strand RNA emerges alone. | 1 | Biochemistry |
Earlier converters, with a false bottom that can be detached and repaired, are still in use. Modern converters have a fixed bottom with plugs for argon purging. The energy optimization furnace (EOF) is a BOF variant associated with a scrap preheater where the sensible heat in the off-gas is used for preheating scrap, located above the furnace roof.
The lance used for blowing has undergone changes. Slagless lances, with a long tapering copper tip, have been employed to avoid jamming of the lance during blowing. Post-combustion lance tips burn the CO generated during blowing into carbon dioxide| and provide additional heat. For slag-free tapping, darts, refractory balls, and slag detectors are employed. Modern converters are fully automated with automatic blowing patterns and sophisticated control systems. | 8 | Metallurgy |
In a solar photoelectrochemical process, hydrogen can be produced by electrolysis. To use sunlight in this process, a photoelectrochemical cell can be used, where one photosensitized electrode converts light into an electric current that is then used for water splitting. One such type of cell is the dye-sensitized solar cell. This is an indirect process, since it produces electricity that then is used to form hydrogen. Another indirect process using sunlight is conversion of biomass to biofuel using photosynthetic organisms; however, most of the energy harvested by photosynthesis is used in life-sustaining processes and therefore lost for energy use.
A semiconductor can also be used as the photosensitizer. When a semiconductor is hit by a photon with an energy higher than the bandgap, an electron is excited to the conduction band and a hole is created in the valence band. Due to band bending, the electrons and holes move to the surface, where these charges are used to split the water molecules. Many different materials have been tested, but none so far have shown the requirements for practical application. | 5 | Photochemistry |
Upregulation refers to the increase in the number of receptor sites on the membrane. Estrogen and FSH upregulate LHCGR sites in preparation for ovulation. After ovulation, the luteinized ovary maintains LHCGR s that allow activation in case there is an implantation. Upregulation in males requires gene transcription to synthesize LH receptors within the cell cytoplasm. Some reasons as to why downregulated LH receptors are not upregulated are: lack of gene transcription, lack of RNA to protein conversion and lack of cell membrane targeted shipments from Golgi. | 1 | Biochemistry |
The majority of transition metal dioxides (MO) have the rutile structure, seen to the right. Materials of this stoichiometry exist for Ti, Cr, V and Mn in the first row transition metal and for Zr to Pd in the second. The rutile structure is generated by filling half of the octahedral sites with cations of the hcp oxygen anion array. | 7 | Physical Chemistry |
In the hybridization-ligation assay a template probe replaces the capture probe in the sandwich assay for immobilization to the solid support. The template probe is fully complementary to the oligonucleotide analyte and is intended to serve as a substrate for T4 DNA ligase-mediated ligation. The template probe has in addition an additional stretch complementary to a ligation probe so that the ligation probe will ligate onto the 3'-end of the analyte. Albeit generic, the ligation probe is similar to a detection probe in that it is labelled with, for example, digoxigenin for downstream signalling. Stringent, low/no salt wash will remove un-ligated products.
The ligation of the analyte to the ligation probe makes the method specific for the 3-end of the analyte, ligation by T4 DNA ligase being much less efficient over a bulge loop, which would happen for a 3 metabolite N-1 version of the analyte, for example. The specificity of the hybridization-ligation assay for ligation at the 3-end is particularly relevant because the predominant nucleases in blood are 3 to 5' exonucleases.
One limitation of the method is that it requires a free 3-end hydroxyl which may not be available when targeting moieties are attached to the 3-end, for example. Further, more exotic nucleic acid chemistries with oligonucleotide drugs may impact upon the activity of the ligase, which needs to be determined on a case-by-case basis. | 1 | Biochemistry |
The mitochondrial permeability transition pore (mPTP or MPTP; also referred to as PTP, mTP or MTP) is a protein that is formed in the inner membrane of the mitochondria under certain pathological conditions such as traumatic brain injury and stroke. Opening allows increase in the permeability of the mitochondrial membranes to molecules of less than 1500 daltons in molecular weight. Induction of the permeability transition pore, mitochondrial membrane permeability transition (mPT or MPT), can lead to mitochondrial swelling and cell death through apoptosis or necrosis depending on the particular biological setting. | 1 | Biochemistry |
Photocatalyst radical generation species allow for the degradation of organic pollutants into non-toxic compounds at a high efficiency. Use of CuO nanosheets to breakdown azo bonds in food dyes is one such example, with 96.99% degradation after only 6 minutes. Degradation of organic matter is a highly applicable property, particularly in waste processing.
The use of photocatalyst TiO as a support system for filtration membranes shows promise in improving membrane bioreactors in the treatment of wastewater. Polymer-based membranes have shown reduced fouling and self-cleaning properties in both blended and coated TiO membranes. Photocatalyst-coated membranes show the most promise, as the increased surface exposure of the photocatalyst increases its organic degradation activity.
Photocatalysts are also highly effective reducers of toxic heavy metals like hexavalent chromium from water systems. Under visible light the reduction of Cr(VI) by a Ce-ZrO sol-gel on a silicon carbide was 97% effective at reducing the heavy metal to trivalent chromium. | 5 | Photochemistry |
Substitutions can occur on the level of both the DNA and RNA. RNA editing-dependent amino acid substitutions can produce missense mRNA's of which occur through hydrolytic deaminase reactions. Two of the most prevalent deaminase reactions occur through the Apolipoprotein B mRNA editing enzyme (APOBEC) and the adenosine deaminase acting on RNA enzyme (ADAR) which are responsible for the conversion of cytidine to uridine (C-to-U), and the deamination of adenosine to inosine (A-to-I), respectively. Such selective substitutions of uridine for cytidine, and inosine for adenosine in RNA editing can produce differential isoforms of missense mRNA transcripts, and confer transcriptome diversity and enhanced protein function in response to selective pressures. | 1 | Biochemistry |
Alclad is a corrosion-resistant aluminium sheet formed from high-purity aluminium surface layers metallurgically bonded (rolled onto) to high-strength aluminium alloy core material. It has a melting point of about . Alclad is a trademark of Alcoa but the term is also used generically.
Since the late 1920s, Alclad has been produced as an aviation-grade material, being first used by the sector in the construction of the ZMC-2 airship. The material has significantly more resistance to corrosion than most aluminium-based alloys, for only a modest increase in weight, making Alclad attractive for building various elements of aircraft, such as the fuselage, structural members, skin, and cowling. Accordingly, it became a relatively popular material for aircraft manufacturing. | 8 | Metallurgy |
Overdoses of eszopiclone up to 90 times the recommended dose have been reported in which the patient fully recovered. Fatalities have been reported only in cases in which eszopiclone was combined with other drugs or alcohol. Overdose may be successfully treated with flumazenil, a GABA receptor antagonist used also for benzodiazepine overdose.
Poison control centers reported that between 2005 and 2006 there were 525 total eszopiclone overdoses recorded in the state of Texas, the majority of which were intentional suicide attempts.
If consumed within the last hour, eszopiclone overdose can be treated with the administration of activated charcoal or via gastric lavage. | 4 | Stereochemistry |
Particulate matter (PM), particularly PM2.5, was found to be harmful to aquatic invertebrates. These aquatic invertebrates include fish, crustaceans, and Mollusca. In a study by Han et al, the effects of PM<2.5 micrometers on life history traits and oxidative stress were observed in Tigriopus japonicus. Exposure to particulate matter of less than 2.5 micrometers in diameter led to significant changes in ROS levels, indicating that particulate matter exposure was a causative agent of oxidative stress in Tigriopus japonicus. In addition to aquatic invertebrates, negative effects of particulate matter have been noted in mammals as well. Following acute exposure to ambient particulate matter, rats showed a significant increase in neutrophils and a significant decrease in lymphocytes, indicating that particulate matter exposure can result in activation of the sympathetic stress response. | 2 | Environmental Chemistry |
Solar energy conversion has the potential for many positive social impacts, especially in rural areas that did not previously have grid-based energy access. In many off-grid areas, the solar-electric conversion is the fastest growing form of energy procurement. This is especially true at latitudes within 45° north or south of the Equator, where solar irradiance is more constant throughout the year and where the bulk of the developing world's population lives. From a health perspective, solar home systems can replace kerosene lamps (frequently found in rural areas), which can cause fires and emit pollutants like carbon monoxide (CO), nitric oxides (NOx), and sulfur dioxide (SO2) that adversely affect air quality and can cause impair lung function and increase tuberculosis, asthma, and cancer risks. In such areas, solar energy access has been shown to save rural residents the time and money needed to purchase and transport kerosene, thereby increasing productivity and lengthening business hours.
In addition to energy access, these communities gain energy independence, meaning they are not reliant on a third-party electricity provider. The concept of energy independence is relatively new; for the vast majority of the 20th century, energy analyses were purely technical or financial and did not include social impact analysis. A 1980 study concluded that access to renewable energy would promote values conducive to larger societal benefit as opposed to personal promotion. While some academics argue that historically the parties in control of energy sources are those that create social hierarchies, this type of analysis became less “radical” and more mainstream after the introduction of technologies that enabled solar energy conversion. | 7 | Physical Chemistry |
Diffusion hardening is a process used in manufacturing that increases the hardness of steels. In diffusion hardening, diffusion occurs between a steel with a low carbon content and a carbon-rich environment to increase the carbon content of the steel and ultimately harden the workpiece. Diffusion only happens through a small thickness of a piece of steel (about 2.5 μm to 1.5 mm), so only the surface is hardened while the core maintains its original mechanical properties. Heat treating may be performed on a diffusion hardened part to increase the hardness of the core as desired, but in most cases in which diffusion hardening is performed, it is desirable to have parts with a hard outer shell and a more ductile inside. Heat treating and quenching is a more efficient process if hardness is desired throughout the whole part. In the case of manufacturing parts subject to large amounts of wear, such as gears, the non-uniform properties acquired through diffusion hardening are desired. Through this process, gears obtain a hard wear-resistant outer shell but maintain their softer and more impact-resistant core. | 8 | Metallurgy |
The major steps in the Sulfo-TK pathway are:
* isomerization of sulfoquinovose to sulfofructose (catalyzed by sulfoquinovose isomerase);
* transketol reaction of sulfofructose to release erythrose (catalyzed by sulfofructose transketolase, a thiamine diphosphate dependent enzyme), and transfer of the C2-moiety to glyceraldehyde phosphate, yielding xylulose-5-phosphate (Xu5P).
* 4-Sulfoerythrose is isomerized to 4-sulfoerythrulose (SEu), whereupon a second round of transketolase catalyzed reaction cleaves SE to sulfoacetaldehyde, while the C2-moiety is again transferred to an acceptor molecule, glyceraldehyde phosphate (GAP), yielding a second molecule of xylulose-5-phosphate (Xu5P).
* Finally, the sulfoacetaldehyde is reduced to isethionate and excreted.
The sulfoacetaldehyde may be oxidized to sulfoacetate. | 1 | Biochemistry |
Positive-sense (5′-to-3′) viral RNA signifies that a particular viral RNA sequence may be directly translated into viral proteins (e.g., those needed for viral replication). Therefore, in positive-sense RNA viruses, the viral RNA genome can be considered viral mRNA, and can be immediately translated by the host cell. Unlike negative-sense RNA, positive-sense RNA is of the same sense as mRNA. Some viruses (e.g. Coronaviridae) have positive-sense genomes that can act as mRNA and be used directly to synthesize proteins without the help of a complementary RNA intermediate. Because of this, these viruses do not need to have an RNA polymerase packaged into the virion—the RNA polymerase will be one of the first proteins produced by the host cell, since it is needed in order for the virus's genome to be replicated. | 1 | Biochemistry |
Geneticist Dean Hamer has suggested that a particular allele of the SLC18A2 gene correlates with spirituality using data from a smoking survey, which included questions intended to measure "self-transcendence". Hamer performed the spirituality study on the side, independently of the National Cancer Institute smoking study. His findings were published in the mass-market book The God Gene: How Faith Is Hard-Wired into Our Genes. Hamer himself notes that SLC18A2 plays at most a minor role in influencing spirituality. Furthermore, Hamers claim that the SLC18A2 gene contributes to spirituality is controversial. Hamers study has not been published in a peer-reviewed journal and a reanalysis of the correlation demonstrates that it is not statistically significant. | 1 | Biochemistry |
Loss of SFRP1 protein expression is associated with poor overall survival (OS) in patients with early breast cancer (pT1 tumours); this indicates that SFRP1 may be a putative tumor suppressor gene. SFRP1 methylation has been shown to be an independent risk factor for OS. Veeck and colleagues demonstrate, via Kaplan-Meier analysis, that clear SFRP1 promoter methylation is associated with unfavourable prognosis. Furthermore, a correlation between SFRP1 methylation and OS in breast cancer is dependent on a gene dose effect. In order for the OS to be affected, a sufficient amount of tumour cells may be required to lose SFRP1 expression due to promoter methylation. | 1 | Biochemistry |
The main improvements to immunofluorescence lie in the development of fluorophores and fluorescent microscopes. Fluorophores can be structurally modified to improve brightness and photostability, while preserving spectral properties and cell permeability.
Super-resolution fluorescence microscopy methods can produce images with a higher resolution than those microscopes imposed by the diffraction limit. This enables the determination of structural details within the cell. Super-resolution in fluorescence, more specifically, refers to the ability of a microscope to prevent the simultaneous fluorescence of adjacent spectrally identical fluorophores (spectral overlap). Some of the recently developed super-resolution fluorescent microscope methods include stimulated emission depletion (STED) microscopy, saturated structured-illumination microscopy (SSIM), fluorescence photoactivation localization microscopy (FPALM), and stochastic optical reconstruction microscopy (STORM). | 1 | Biochemistry |
In vivo gene electrotransfer was first described in 1991 and today there are many preclinical studies of gene electrotransfer. The method is used to deliver large variety of therapeutic genes for potential treatment of several diseases, such as: disorders in immune system, tumors, metabolic disorders, monogenetic diseases, cardiovascular diseases, analgesia....
With regards to irreversible electroporation, the first successful treatment of malignant cutaneous tumors implanted in mice was completed in 2007 by a group of scientists who achieved complete tumor ablation in 12 out of 13 mice. They accomplished this by sending 80 pulses of 100 microseconds at 0.3 Hz with an electrical field magnitude of 2500 V/cm to treat the cutaneous tumors. Currently, a number of companies, including AngioDynamics, Inc. and VoltMed, Inc., are continuing to develop and deploy irreversible electroporation-based technologies within clinical environments.
The first group to look at electroporation for medical applications was led by Lluis M Mir at the Institute Gustave Roussy. In this case, they looked at the use of reversible electroporation in conjunction with impermeable macromolecules. The first research looking at how nanosecond pulses might be used on human cells was conducted by researchers at Eastern Virginia Medical School and Old Dominion University, and published in 2003. | 1 | Biochemistry |
In microorganisms and plants TPP results from coupling of pyrimidine fragment HMP-PP with thiazole fragment HET-P to give thiamine monophosphate, followed by conversion to the pyrophosphate.
Biogenesis of HMP-P and HET-P vary with types of organism. | 1 | Biochemistry |
In immunology, a conformational epitope is a sequence of sub-units (usually amino acids) composing an antigen that come in direct contact with a receptor of the immune system.
An antigen is any substance that the immune system can recognize as foreign. Antigens are usually proteins that are too large to bind as a whole to any receptor so only specific segments, that form the antigen, bind with a specific receptor. Such segments are called epitopes. Likewise, it is only the paratope of the receptor that comes in contact with the epitope.
Proteins are composed of repeating nitrogen-containing subunits called amino acids that in nature do not exist as straight chains but as folded whorls with complex loops. The latter is known as the tertiary structure of a protein. So, whenever a receptor interacts with an undigested antigen, the surface amino acids that come in contact may not be continuous with each other if the protein is unwound. Such discontinuous amino acids that come together in three-dimensional conformation and interact with the receptor's paratope are called conformational epitopes. In contrast, if the antigen is digested, small segments called peptides are formed, which bind with major histocompatibility complex molecules, and then later with T cell receptors through amino acids that are continuous in a line. These are known as linear epitopes. | 1 | Biochemistry |
Stereoisomerism about double bonds arises because rotation about the double bond is restricted, keeping the substituents fixed relative to each other. If the two substituents on at least one end of a double bond are the same, then there is no stereoisomer and the double bond is not a stereocenter, e.g. propene, CHCH=CH where the two substituents at one end are both H.
Traditionally, double bond stereochemistry was described as either cis (Latin, on this side) or trans (Latin, across), in reference to the relative position of substituents on either side of a double bond. A simple example of cis-trans isomerism is the 1,2-disubstituted ethenes, like the dichloroethene (CHCl) isomers shown below.
Molecule I is cis-1,2-dichloroethene and molecule II is trans-1,2-dichloroethene. Due to occasional ambiguity, IUPAC adopted a more rigorous system wherein the substituents at each end of the double bond are assigned priority based on their atomic number. If the high-priority substituents are on the same side of the bond, it is assigned Z (Ger. zusammen, together). If they are on opposite sides, it is E (Ger. entgegen, opposite). Since chlorine has a larger atomic number than hydrogen, it is the highest-priority group. Using this notation to name the above pictured molecules, molecule I is (Z)-1,2-dichloroethene and molecule II is (E)-1,2-dichloroethene. It is not the case that Z and cis or E and trans are always interchangeable. Consider the following fluoromethylpentene:
The proper name for this molecule is either trans-2-fluoro-3-methylpent-2-ene because the alkyl groups that form the backbone chain (i.e., methyl and ethyl) reside across the double bond from each other, or (Z)-2-fluoro-3-methylpent-2-ene because the highest-priority groups on each side of the double bond are on the same side of the double bond. Fluoro is the highest-priority group on the left side of the double bond, and ethyl is the highest-priority group on the right side of the molecule.
The terms cis and trans are also used to describe the relative position of two substituents on a ring; cis if on the same side, otherwise trans. | 4 | Stereochemistry |
J.W. Gibbs developed the thermodynamic theory of capillarity based
on the idea of surfaces of discontinuity. Gibbs considered the case of a sharp mathematical surface being placed somewhere within the microscopically fuzzy physical interface that exists between two homogeneous substances. Realizing that the exact choice of the surface's location was somewhat arbitrary, he left it flexible. Since the interface exists in thermal and chemical equilibrium with the substances around it (having temperature and chemical potentials ), Gibbs considered the case where the surface may have excess energy, excess entropy, and excess particles, finding the natural free energy function in this case to be , a quantity later named as the grand potential and given the symbol .
Considering a given subvolume containing a surface of discontinuity, the volume is divided by the mathematical surface into two parts A and B, with volumes and , with exactly. Now, if the two parts A and B were homogeneous fluids (with pressures , ) and remained perfectly homogeneous right up to the mathematical boundary, without any surface effects, the total grand potential of this volume would be simply . The surface effects of interest are a modification to this, and they can be all collected into a surface free energy term so the total grand potential of the volume becomes:
For sufficiently macroscopic and gently curved surfaces, the surface free energy must simply be proportional to the surface area:
for surface tension and surface area .
As stated above, this implies the mechanical work needed to increase a surface area A is , assuming the volumes on each side do not change. Thermodynamics requires that for systems held at constant chemical potential and temperature, all spontaneous changes of state are accompanied by a decrease in this free energy , that is, an increase in total entropy taking into account the possible movement of energy and particles from the surface into the surrounding fluids. From this it is easy to understand why decreasing the surface area of a mass of liquid is always spontaneous, provided it is not coupled to any other energy changes. It follows that in order to increase surface area, a certain amount of energy must be added.
Gibbs and other scientists have wrestled with the arbitrariness in the exact microscopic placement of the surface. For microscopic surfaces with very tight curvatures, it is not correct to assume the surface tension is independent of size, and topics like the Tolman length come into play. For a macroscopic-sized surface (and planar surfaces), the surface placement does not have a significant effect on ; however, it does have a very strong effect on the values of the surface entropy, surface excess mass densities, and surface internal energy, which are the partial derivatives of the surface tension function .
Gibbs emphasized that for solids, the surface free energy may be completely different from surface stress (what he called surface tension): the surface free energy is the work required to form the surface, while surface stress is the work required to stretch the surface. In the case of a two-fluid interface, there is no distinction between forming and stretching because the fluids and the surface completely replenish their nature when the surface is stretched. For a solid, stretching the surface, even elastically, results in a fundamentally changed surface. Further, the surface stress on a solid is a directional quantity (a stress tensor) while surface energy is scalar.
Fifteen years after Gibbs, J.D. van der Waals developed the theory of capillarity effects based on the hypothesis of a continuous variation of density. He added to the energy density the term where c is the capillarity coefficient and ρ is the density. For the multiphase equilibria, the results of the van der Waals approach practically coincide with the Gibbs formulae, but for modelling of the dynamics of phase transitions the van der Waals approach is much more convenient. The van der Waals capillarity energy is now widely used in the phase field models of multiphase flows. Such terms are also discovered in the dynamics of non-equilibrium gases. | 6 | Supramolecular Chemistry |
For most substrates, in the absence of an oxidant, the dihydrophenanthrene intermediate may reversibly open to the corresponding cis-stilbene. However, suitably substituted stilbenes cyclize irreversibly if an aromatizing elimination or hydrogen shift process can take place. Examples of these transformations are provided below. | 5 | Photochemistry |
Some alternatives to IVF are:
*Artificial insemination, including intracervical insemination and intrauterine insemination of semen. It requires that a woman ovulates, but is a relatively simple procedure, and can be used in the home for self-insemination without medical practitioner assistance. The beneficiaries of artificial insemination are people who desire to give birth to their own child who may be single, people who are in a lesbian relationship or females who are in a heterosexual relationship but with a male partner who is infertile or who has a physical impairment which prevents full intercourse from taking place.
*Ovulation induction (in the sense of medical treatment aiming for the development of one or two ovulatory follicles) is an alternative for people with anovulation or oligoovulation, since it is less expensive and more easy to control. It generally involves antiestrogens such as clomifene citrate or letrozole, and is followed by natural or artificial insemination.
*Surrogacy, the process in which a surrogate agrees to bear a child for another person or persons, who will become the child's parent(s) after birth. People may seek a surrogacy arrangement when pregnancy is medically impossible, when pregnancy risks are too dangerous for the intended gestational carrier, or when a single man or a male couple wish to have a child.
*Adoption whereby a person assumes the parenting of another, usually a child, from that person's biological or legal parent or parents. | 1 | Biochemistry |
Surface water can be affected by local geology, as minerals leached from sub-surface rocks can enter surface water bodies and influence water chemistry. Examples of this are the Werii River (Tigray, Ethiopia), where elevated concentrations of heavy metals have been linked to the underlying slate, and drinking wells in Indigenous communities near Anchorage, Alaska, where high concentrations of arsenic have been linked to the underlying McHugh Complex rock formation. | 2 | Environmental Chemistry |
Regulatory elements that responds to other signals are known; examples include photomodulated conductances as well as "thermal switches" constructed by isomerization of the carbamate group. To date, no mechanosensitive synthetic ion channels have been reported. | 6 | Supramolecular Chemistry |
In molecular biology, the Btk-type zinc finger or Btk motif (BM) is a conserved zinc-binding motif containing conserved cysteines and a histidine that is present in certain eukaryotic signalling proteins. The motif is named after Bruton's tyrosine kinase (Btk), an enzyme which is essential for B cell maturation in humans and mice. Btk is a member of the Tec family of protein tyrosine kinases (PTK). These kinases contain a conserved Tec homology (TH) domain between the N-terminal pleckstrin homology (PH) domain and the Src homology 3 (SH3) domain. The N-terminal of the TH domain is highly conserved and known as the Btf motif, while the C-terminal region of the TH domain contains a proline-rich region (PRR). The Btk motif contains a conserved His and three Cys residues that form a zinc finger (although these differ from known zinc finger topologies), while PRRs are commonly involved in protein-protein interactions, including interactions with G proteins. The TH domain may be of functional importance in various signalling pathways in different species. A complete TH domain, containing both the Btk and PRR regions, has not been found outside the Tec family; however, the Btk motif on its own does occur in other proteins, usually C-terminal to a PH domain (note that although a Btk motif always occurs C-terminal to a PH domain, not all PH domains are followed by a Btk motif).
The crystal structures of Btk show that the Btk-type zinc finger has a globular core, formed by a long loop which is held together by a zinc ion, and that the Btk motif is packed against the PH domain. The zinc-binding residues are a histidine and three cysteines, which are fully conserved in the Btk motif.
Proteins known to contain a Btk-type zinc finger include:
* Mammalian Bruton's tyrosine kinase (Btk), a protein tyrosine kinase involved in modulation of diverse cellular processes. Mutations affecting Btk are the cause of X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency in mice.
*Mammalian Tec, Bmx, and Itk proteins, which are tyrosine protein kinases of the Tec subfamily.
*Drosophila tyrosine-protein kinase Btk29A, which is required for the development of proper ring canals and of male genitalia and required for adult survival.
*Mammalian Ras GTPase-activating proteins (RasGAP), which regulate the activation of inactive GDP-bound Ras by converting GDP to GTP. | 1 | Biochemistry |
In geology, silicification is a petrification process in which silica-rich fluids seep into the voids of Earth materials, e.g., rocks, wood, bones, shells, and replace the original materials with silica (SiO). Silica is a naturally existing and abundant compound found in organic and inorganic materials, including Earth's crust and mantle. There are a variety of silicification mechanisms. In silicification of wood, silica permeates into and occupies cracks and voids in wood such as vessels and cell walls. The original organic matter is retained throughout the process and will gradually decay through time. In the silicification of carbonates, silica replaces carbonates by the same volume. Replacement is accomplished through the dissolution of original rock minerals and the precipitation of silica. This leads to a removal of original materials out of the system. Depending on the structures and composition of the original rock, silica might replace only specific mineral components of the rock. Silicic acid (HSiO) in the silica-enriched fluids forms lenticular, nodular, fibrous, or aggregated quartz, opal, or chalcedony that grows within the rock. Silicification happens when rocks or organic materials are in contact with silica-rich surface water, buried under sediments and susceptible to groundwater flow, or buried under volcanic ashes. Silicification is often associated with hydrothermal processes. Temperature for silicification ranges in various conditions: in burial or surface water conditions, temperature for silicification can be around 25°−50°; whereas temperatures for siliceous fluid inclusions can be up to 150°−190°. Silicification could occur during a syn-depositional or a post-depositional stage, commonly along layers marking changes in sedimentation such as unconformities or bedding planes. | 9 | Geochemistry |
The Two-dimensional (2-D) polymers formed by topochemical polymerization are popular topics in material chemistry. By synthesizing and polymerizing monomers with functionality greater than 2, the 2-D networks instead of linear polymers can be obtained. [4+4] and [4+2] involving anthracene units are popular choices for 2D-polymer synthesis. 2-D covalent networks with high crystallinity can be produced in this way in high conversion. Recently, schluter et al. synthesized a 2D polymer via 2+2 topochemical cycloaddition reaction.[https://pubs.acs.org/doi/10.1021/jacs.6b11857] | 7 | Physical Chemistry |
Downregulation refers to the decrease in the number of receptor molecules. This is usually the result of receptor endocytosis. In this process, the bound LCGR-hormone complex binds arrestin and concentrates in clathrin coated pits. Clathrin coated pits recruit dynamin and pinch off from the cell surface, becoming clathrin-coated vesicles. Clathrin-coated vesicles are processed into endosomes, some of which are recycled to the cell surface while others are targeted to lysosomes. Receptors targeted to lysosomes are degraded. Use of long-acting agonists will downregulate the receptor population by promoting their endocytosis. | 1 | Biochemistry |
The remains of diatoms and other silica-utilizing organisms are found, as opal sediments within pelagic deep-sea deposits. Pelagic sediments, containing significant quantities of siliceous biogenic remains, are commonly referred to as siliceous ooze. Siliceous ooze are particularly abundant in the modern ocean at high latitudes in the northern and southern hemispheres. A striking feature of siliceous ooze distribution is a ca. 200 km wide belt stretching across the Southern Ocean. Some equatorial regions of upwelling, where nutrients are abundant and productivity is high, are also characterized by local siliceous ooze.
Siliceous oozes are composed primarily of the remains of diatoms and radiolarians, but may also include other siliceous organisms, such as silicoflagellates and sponge spicules. Diatom ooze occurs mainly in high-latitude areas and along some continental margins, whereas radiolarian ooze are more characteristic of equatorial areas. Siliceous ooze are modified and transformed during burial into bedded cherts. | 1 | Biochemistry |
The industrial processes vary depending on the chain length of the olefin to be hydroformylated, the catalyst metal and ligands, and the recovery of the catalyst. The original Ruhrchemie process produced propanal from ethene and syngas using cobalt tetracarbonyl hydride. Today, industrial processes based on cobalt catalysts are mainly used for the production of medium- to long-chain olefins, whereas the rhodium-based catalysts are usually used for the hydroformylation of propene. The rhodium catalysts are significantly more expensive than cobalt catalysts. In the hydroformylation of higher molecular weight olefins the separation of the catalyst from the produced aldehydes is difficult. | 0 | Organic Chemistry |
Cytoplasmic transfer was originally developed in the 1980s in the course of basic research conducted with mice to study the role that parts of the cell outside of the nucleus played in embryonic development. In this technique, cytoplasm, including proteins, messenger RNA (mRNA), mitochondria and other organelles, is taken from a donor egg and injected into the recipient egg, resulting in a mixture of mitochondrial genetic material. This technique started to be used in the late 1990s to "boost" the eggs of older women who were having problems conceiving and led to the birth of about 30 babies. Concerns were raised that the mixture of genetic material and proteins could cause problems with respect to epigenetic clashes, or differences in the ability of the recipient and donor materials to effect the development process, or due to the injection of the donor material. After three children born through the technique were found to have developmental disorders (two cases of Turner's syndrome and one case of pervasive developmental disorder (an autism spectrum disorder), the FDA banned the procedure until a clinical trial could prove its safety. As of 2015 that study had not been conducted, but the procedure was in use in other countries.
A related approach uses autologous mitochondria taken from healthy tissue to replace the mitochondria in damaged tissue. Transfer techniques include direct injection into damaged tissue and injection into vessels that supply blood to the tissue. | 1 | Biochemistry |
CRISPR-associated transposons have been harnessed for in vitro and in vivo gene editing at different targets, in different hosts, and with different payloads. All CAST components of the Tn6677 system from Vibrio cholerae have been combined into a single plasmid and confirmed to deliver up to 10kb transposons at near 100% efficiency. This has also been shown in a community context with conjugative delivery of suicide vectors to provide antibiotic resistance or enhanced metabolic function to only a single microbe. Much of the initial characterization of these systems has been done in E. coli, but functionality has been confirmed in beta- and gammaproteobacteria with high efficiency, and in alphaproteobacteria at somewhat lower efficiency. A single plasmid Tn677 has also been shown to function in human HEK293T cells showing potential therapeutic use in the future. | 1 | Biochemistry |
Each chemical species (for example, "water molecules", "sodium ions", "electrons", etc.) has an electrochemical potential (a quantity with units of energy) at any given point in space, which represents how easy or difficult it is to add more of that species to that location. If possible, a species will move from areas with higher electrochemical potential to areas with lower electrochemical potential; in equilibrium, the electrochemical potential will be constant everywhere for each species (it may have a different value for different species). For example, if a glass of water has sodium ions (Na) dissolved uniformly in it, and an electric field is applied across the water, then the sodium ions will tend to get pulled by the electric field towards one side. We say the ions have electric potential energy, and are moving to lower their potential energy. Likewise, if a glass of water has a lot of dissolved sugar on one side and none on the other side, each sugar molecule will randomly diffuse around the water, until there is equal concentration of sugar everywhere. We say that the sugar molecules have a "chemical potential", which is higher in the high-concentration areas, and the molecules move to lower their chemical potential. These two examples show that an electrical potential and a chemical potential can both give the same result: A redistribution of the chemical species. Therefore, it makes sense to combine them into a single "potential", the electrochemical potential, which can directly give the net redistribution taking both into account.
It is (in principle) easy to measure whether or not two regions (for example, two glasses of water) have the same electrochemical potential for a certain chemical species (for example, a solute molecule): Allow the species to freely move back and forth between the two regions (for example, connect them with a semi-permeable membrane that lets only that species through). If the chemical potential is the same in the two regions, the species will occasionally move back and forth between the two regions, but on average there is just as much movement in one direction as the other, and there is zero net migration (this is called "diffusive equilibrium"). If the chemical potentials of the two regions are different, more molecules will move to the lower chemical potential than the other direction.
Moreover, when there is not diffusive equilibrium, i.e., when there is a tendency for molecules to diffuse from one region to another, then there is a certain free energy released by each net-diffusing molecule. This energy, which can sometimes be harnessed (a simple example is a concentration cell), and the free-energy per mole is exactly equal to the electrochemical potential difference between the two regions. | 7 | Physical Chemistry |
Cellular noise is often investigated in the framework of intrinsic and extrinsic noise. Intrinsic noise refers to variation in identically regulated quantities within a single cell: for example, the intra-cell variation in expression levels of two identically controlled genes. Extrinsic noise refers to variation in identically regulated quantities between different cells: for example, the cell-to-cell variation in expression of a given gene.
Intrinsic and extrinsic noise levels are often compared in dual reporter studies, in which the expression levels of two identically regulated genes (often fluorescent reporters like GFP and YFP) are plotted for each cell in a population.
An issue with the general depiction of extrinsic noise as a spread along the main diagonal in dual-reporter studies is the assumption that extrinsic factors cause positive expression correlations between the two reporters. In fact, when the two reporters compete for binding of a low-copy regulator, the two reporters become anomalously anticorrelated, and the spread is perpendicular to the main diagonal. In fact, any deviation of the dual-reporter scatter plot from circular symmetry indicates extrinsic noise. Information theory offers a way to avoid this anomaly. | 1 | Biochemistry |
The crystal structure was solved to 3.0 Å resolution in 2000, as shown in the figure in the reference. In (A), notice that the separate subunits appear to be anchored through interactions between an alpha helix and an adjacent subunit. In (B), there are six sets of three loops. The red loop, known as loop II, contains three lysine residues and is thought to be involved in binding the ssDNA that is fed through the center of the enzyme. | 1 | Biochemistry |
Accelerated testing of adhesives is used to predict long term performance of adhesive exposed to a variety of environmental factors. Adhesives are sometimes used as load bearing and sealing joints, which points great stress on them. In accelerated testing, factors like the temperature, moisture, vibrations, voltage, and UV light are greatly increased over a short period so long term predictions can be made about the effect of the aforementioned factors. | 3 | Analytical Chemistry |
Nickel tetracarbonyl and iron pentacarbonyl can be prepared according to the following equations by reaction of finely divided metal with carbon monoxide:
:Ni + 4 CO → Ni(CO) (1 bar, 55 °C)
:Fe + 5 CO → Fe(CO) (100 bar, 175 °C)
Nickel tetracarbonyl is formed with carbon monoxide already at 80 °C and atmospheric pressure, finely divided iron reacts at temperatures between 150 and 200 °C and a carbon monoxide pressure of 50–200 bar. Other metal carbonyls are prepared by less direct methods. | 0 | Organic Chemistry |
IPNs have been used in automotive parts (including modern automotive paint), damping materials, medical devices, molding compounds, and in engineering plastics. While many benefits come from the enhanced mechanical properties of the IPN materials, other characteristics such as resistance to solvent swelling can also make IPNs a material of commercial interest. More recent applications and areas of research for IPNs include uses in drug delivery systems, energy storage materials, and tissue engineering. | 7 | Physical Chemistry |
The starting material for this route is a norbornane derivative with a good leaving group in position 2. If the leaving group is on the exo- face, electron density from the σ bond between carbons 1 and 6 is donated into the σ* antibond between carbon 2 and the leaving group (see Figure 8b).
If the leaving group is on the endo- face, the leaving group first leaves on its own. Then electron density from the σ bond between carbons 1 and 6 is donated into the resulting empty atomic orbital on carbon 2. However, this formation route is much slower than that of the exo- isomer because the σ bond cannot provide anchimeric assistance for the first step, making the activation energy to the first transition state much higher. Additionally, if there is a high concentration of reactive electrophiles in the reaction mixture, formation of a newly substituted norbornane derivative may preclude non-classical ion formation.
An example of this formation route is the reaction that led Winstein and Trifan to propose the delocalized structure of the 2-norbornyl cation. 2-norbornyl tosylates and brosylates form the 2-norbornyl cation through this route as an intermediate towards solvolysis. | 7 | Physical Chemistry |
The most common method of measuring amino acid hydrophobicity is partitioning between two immiscible liquid phases. Different organic solvents are most widely used to mimic the protein interior. However, organic solvents are slightly miscible with water and the characteristics of both phases change making it difficult to obtain pure hydrophobicity scale. Nozaki and Tanford proposed the first major hydrophobicity scale for nine amino acids. Ethanol and dioxane are used as the organic solvents and the free energy of transfer of each amino acid was calculated. Non liquid phases can also be used with partitioning methods such as micellar phases and vapor phases. Two scales have been developed using micellar phases. Fendler et al. measured the partitioning of 14 radiolabeled amino acids using sodium dodecyl sulfate (SDS) micelles. Also, amino acid side chain affinity for water was measured using vapor phases. Vapor phases represent the simplest non polar phases, because it has no interaction with the solute. The hydration potential and its correlation to the appearance of amino acids on the surface of proteins was studied by Wolfenden. Aqueous and polymer phases were used in the development of a novel partitioning scale. Partitioning methods have many drawbacks. First, it is difficult to mimic the protein interior. In addition, the role of self solvation makes using free amino acids very difficult. Moreover, hydrogen bonds that are lost in the transfer to organic solvents are not reformed but often in the interior of protein. | 6 | Supramolecular Chemistry |
In chemistry, a triol is an organic compound containing three hydroxyl groups ( functional groups), such as glycerol. | 0 | Organic Chemistry |
Its isotope fractionation is linked to water temperature and its isotope ratios from a variety of sources have been widely used to reconstruct paleoclimate. Oxygen isotope in calcium carbonates has become the most widely applied as geothermometer for estimating ancient ocean temperatures. The most successful applications of isotope paleoclimatology have been the study of foraminifera from deep-sea sediments. For instance, Shackleton and Kennett (1975) have established the Cenozoic paleotemperature history based on analyzing oxygen isotope composition of both planktonic and benthic foraminifera in the Antarctic region. Since the variations in the 18O/16O ratio in marine fossil records are global, the oxygen isotope stratigraphy has been used for chronological correlation. | 9 | Geochemistry |
For example, a new radiolabelled compound is injected intravenously into a group of 16-20 rodents (typically mice or rats). At intervals of 1, 2, 4, and 24 hours, smaller groups (4-5) of the animals are euthanized, then dissected. The organs of interest (usually: blood, liver, spleen, kidney, muscle, fat, adrenals, pancreas, brain, bone, stomach, small intestine, and upper and lower large intestine, a tumor if present) are placed in pre-weighed containers and weighed, then placed into a device that measures radioactivity (e.g. gamma radiation). Normalizing the tissue radioactivity concentrations to the injected dose gives values in units of percent of the injected dose per gram of organ or biological tissue. The results give a dynamic view of how the compound moves through the animal and where it is retained. | 1 | Biochemistry |
Favipiravir, as an antiviral drug, has been authorized for treating COVID-19 in several countries including Japan, Russia, Serbia, Turkey, India, and Thailand, under emergency provisions. A rapid meta-review in September 2020 (analyzing four studies) noted that the drug led to clinical and radiological improvements; however, no reduction in mortality or differences in oxygen-support requirement were observed and more rigorous studies were sought. A Cochrane Systematic review published in Feb 2024, noted that there is actually no real benefit with Favipiravir in treating Covid-19 in terms of mortality benefits, or admission to mechanical ventillation, or hospitalisation, and it may not make any difference in adverse effects or serious adverse effects.
, large-cohort clinical trials are underway. | 4 | Stereochemistry |
Recent studies focus on the integration of nanofluidic devices into microsystems. An interface should be created for the connection between two length-scales. A system with solely nanofluidic devices standalone is impractical because it would requires a large driving pressure to make fluids flow into the nano-channel.
Nanofluidic devices are powerful in their high sensitivity and accurate manipulation of sample materials even down to a single molecule. Nevertheless, the drawback of nanofuidic separation systems is the relatively low sample throughput and its result in detection. One possible approach to deal with the problem is to use parallel separation channels with parallel detection in each channel. In addition, a better approach for detection needs to be created in view of the very small quantities of molecules present.
One of the biggest challenges in this research area are due to the peculiar size-effect. Researchers try to solve the problems caused by the extremely high surface-to-volume ratios. Under this condition, adsorption of molecules can lead to large losses and can also change the surface properties.
Another issue arises when the sample for detection is a relatively large molecule, such as DNA or protein. In the application for large molecule, clogging is a concern because the small size of the nanochannel makes it easy to happen. A low friction coating at inner surface of the channel is desired to avoid blocking of fluid channels in this application. | 7 | Physical Chemistry |
Oil-eating bacteria biodegrade oil that has escaped to the surface. Oil sands are reservoirs of partially biodegraded oil still in the process of escaping and being biodegraded, but they contain so much migrating oil that, although most of it has escaped, vast amounts are still present—more than can be found in conventional oil reservoirs. The lighter fractions of the crude oil are destroyed first, resulting in reservoirs containing an extremely heavy form of crude oil, called crude bitumen in Canada, or extra-heavy crude oil in Venezuela. These two countries have the world's largest deposits of oil sands.
On the other hand, oil shales are source rocks that have not been exposed to heat or pressure long enough to convert their trapped hydrocarbons into crude oil. Technically speaking, oil shales are not always shales and do not contain oil, but are fined-grain sedimentary rocks containing an insoluble organic solid called kerogen. The kerogen in the rock can be converted into crude oil using heat and pressure to simulate natural processes. The method has been known for centuries and was patented in 1694 under British Crown Patent No. 330 covering, "A way to extract and make great quantities of pitch, tar, and oil out of a sort of stone." Although oil shales are found in many countries, the United States has the world's largest deposits. | 7 | Physical Chemistry |
Agmatine biosynthesis by arginine decarboxylation is well-positioned to compete with the principal arginine-dependent pathways, namely: nitrogen metabolism (urea cycle), and polyamine and nitric oxide (NO) synthesis (see illustration Agmatine Metabolic Pathways). Agmatine degradation occurs mainly by hydrolysis, catalyzed by agmatinase into urea and putrescine, the diamine precursor of polyamine biosynthesis. An alternative pathway, mainly in peripheral tissues, is by diamine oxidase-catalyzed oxidation into agmatine-aldehyde, which is in turn converted by aldehyde dehydrogenase into guanidinobutyrate and secreted by the kidneys. | 1 | Biochemistry |
Many approaches can potentially quantify radiation absorption, with key examples following.
* The absorption coefficient along with some closely related derived quantities
* The attenuation coefficient (NB used infrequently with meaning synonymous with "absorption coefficient")
* The Molar attenuation coefficient (also called "molar absorptivity"), which is the absorption coefficient divided by molarity (see also Beer–Lambert law)
* The mass attenuation coefficient (also called "mass extinction coefficient"), which is the absorption coefficient divided by density
* The absorption cross section and scattering cross-section, related closely to the absorption and attenuation coefficients, respectively
* "Extinction" in astronomy, which is equivalent to the attenuation coefficient
* Other measures of radiation absorption, including penetration depth and skin effect, propagation constant, attenuation constant, phase constant, and complex wavenumber, complex refractive index and extinction coefficient, complex dielectric constant, electrical resistivity and conductivity.
* Related measures, including absorbance (also called "optical density") and optical depth (also called "optical thickness")
All these quantities measure, at least to some extent, how well a medium absorbs radiation. Which among them practitioners use varies by field and technique, often due simply to the convention. | 7 | Physical Chemistry |
Many low-valent and electron-rich transition metals effect stoichiometric dehalogenation. The reaction achieves practical interest in the context of organic synthesis, e.g. Cu-promoted Ullmann coupling.
The reaction is mainly conducted as stoichiometrically. Some metalloenzymes Vitamin B12 and coenzyme F430 are capable of dehalogenations catalytically. Of great interest are hydrodehalogenations, especially for chlorinated precursors: | 0 | Organic Chemistry |
A cosmid is a type of hybrid plasmid that contains a Lambda phage cos sequence. Often used as cloning vectors in genetic engineering, cosmids can be used to build genomic libraries. They were first described by Collins and Hohn in 1978.
Cosmids can contain 37 to 52 (normally 45) kb of DNA, limits based on the normal bacteriophage packaging size. They can replicate as plasmids if they have a suitable origin of replication (ori): for example SV40 ori in mammalian cells, ColE1 ori for double-stranded DNA replication, or f1 ori for single-stranded DNA replication in prokaryotes. They frequently also contain a gene for selection such as antibiotic resistance, so that the transformed cells can be identified by plating on a medium containing the antibiotic. Those cells which did not take up the cosmid would be unable to grow.
Unlike plasmids, they can also be packaged in vitro into phage capsids, a step which requires cohesive ends, also known as cos sites also used in cloning with a lambda phage as a vector, however nearly all the lambda genes have been deleted with the exception of the cos sequence. The hybrid cosmid DNA in the capsids can then be transferred into bacterial cells by transduction. Since there is a requirement for in vitro packaging whereby at least 38 kb of DNA is required between the cos sites, the vector without insert DNA will not be packaged (plasmids instability is increased if the novel inserted DNA contains many direct repeats or palindromic (inverted repeats) DNA. This instability can largely be counteracted by using a host bacterium with specific mutations affecting DNA recombination (N.B. Absence of inverted repeats was noted in the first Hohn & Collins publication cited above; see also). | 1 | Biochemistry |
Another variety of transposons, discovered in 2001, which can also potentially capture host DNA. Helitrons are thought to replicate via a "rolling circle", in which transposase links the helitron to two distinct regions of the genome at once, using a helicase, ligase, and nuclease in the process to unravel the strands involved, replicate the helitron, and subsequently ligate the replicated material into the new site. During this process, it is thought that the helitrons often encode for the surrounding DNA and integrate this into their own material. Non-autuonomous helitrons may lack a transposase, a helicase, a ligase, or a nuclease. All are thought to be necessary for this complex process of transposition. | 1 | Biochemistry |
The most common and most important cryptand is ; the systematic IUPAC name for this compound is 1,10-diaza-4,7,13,16,21,24-hexaoxabicyclo[8.8.8]hexacosane. This compound is termed [[2.2.2-Cryptand|[2.2.2]cryptand]], where the numbers indicate the number of ether oxygen atoms (and hence binding sites) in each of the three bridges between the amine nitrogen caps. Many cryptands are commercially available under the tradename Kryptofix. All-amine cryptands exhibit particularly high affinity for alkali metal cations, which has allowed the isolation of salts of K. | 6 | Supramolecular Chemistry |
The English word lichen derives from the Greek ("tree moss, lichen, lichen-like eruption on skin") via Latin . The Greek noun, which literally means "licker", derives from the verb , "to lick". In American English, "lichen" is pronounced the same as the verb "liken" (). In British English, both this pronunciation and one rhyming with "kitchen" () are used. | 2 | Environmental Chemistry |
The primary amine on the aminoallyl nucleotide reacts with amino-reactive dyes such as a cyanine and patented dyes which contain a reactive leaving group, such as a succinimidyl ester (NHS).The amine groups directly attached to the ring of the base are not affected. These nucleotides are used for labeling DNA. | 1 | Biochemistry |
Effects of oral dosing of PEA has been explored in humans, and include clinical trials for a variety of pain states, for inflammatory and pain syndromes. Daily doses range from 300 to 1200 mg per day. In a 2017 systematic meta-analysis involving 10 studies including data from 786 patients receiving PEA for pain-related indications and 512 controls, PEA was found to be associated with pain reduction significantly greater than observed in controls (P < 0.001). Positive influences have also been observed in dermal applications, specifically atopic eczema, which may be linked to PPAR alpha activation.
In a 2015 analysis of a double blind placebo controlled study of PEA in sciatic pain, the Numbers Needed to Treat was 1.5. Its positive influence in chronic pain, and inflammatory states such as atopic eczema, seems to originate mainly from PPAR alpha activation. Since 2012 a number of new trials have been published, among which studies in glaucoma. PEA also seems to be one of the factors responsible for the decrease in pain sensitivity during and after sport, comparable to the endogenous opiates (endorphines).
From a clinical perspective the most important and promising indications for PEA are linked to neuropathic and chronic pain states, such as diabetic neuropathic pain, sciatic pain, CRPS, pelvic pain and entrapment neuropathic pain states. In a blind trial reported in a conference proceeding, patients affected by pain from synovitis or TMJ osteoarthritis (N=25, in total) were randomly assigned to PEA or ibuprofen groups for two weeks; the decrease in pain reported after two weeks was significantly higher for the PEA-treated group, likewise for improved masticatory function. In 2012, 20 patients with thalidomide and bortezomib induced neuropathy were reported to have improved nerve functions and less pain after a two-month treatment with PEA. The authors pointed out that although a placebo effect might play a role in the reported pain relief, the changes in neurophysiological measures clearly indicated that PEA exerted a positive action on the myelinated fibre groups. Sixteen men and fourteen women with two major types of neuropathic pain refractory to analgesic treatment—peripheral diabetic neuropathy (4 men, 7 women) or post-herpetic neuralgia (12 men, 7 women)—whose symptoms spanned eight pain categories ("burning", "osteoarticular", "piercing", etc.) who were under prior treatment with pregabalin were transferred to PEA, after which pregabalin treatment was gradually reintroduced; all were responding well after 45 days, and presented significant decreases in pain scores (without drug-drug interactions).
In 2013, a metareview was published on the clinical efficacy and safety of PEA in the treatment of the common cold and influenza, based on reports from six double-blind, placebo, randomized controlled trials, addressing PEA's proposed anti-inflammatory and retinoprotectant effects.
In 2019, significant increases in fatty acid amides including PEA, arachidonoylethanolamide, and oleoylethanolamide were noted in a Scottish woman with a previously undocumented variant of congenital insensitivity to pain. This was found to be a result of a combination of a hypomorphic single nucleotide polymorphism of fatty acid amide hydrolase (FAAH), alongside a mutation of the pseudogene, FAAH-OUT. The pseudogene was previously considered to be non-coding DNA, FAAH-OUT was found to be capable of modulating the expression of FAAH, making it a possible future target for novel analgesia/anxiolytic drug development.
In 2020, PEA has been suggested as a drug that may prove beneficial for the treatment of lung inflammation caused by SARS-CoV-2 infection. A pharmaceutical company called FSD Pharma have entered PEA into a Phase 1 clinical trial under the name FSD-201, and has approval from the FDA for progressing to Phase 2a for this indication. | 1 | Biochemistry |
Recent studies have confirmed that TEs can contribute to the generation of transcription factors. However, how this process of contribution can have an impact on the participation of genome control networks. TEs are more common in many regions of the DNA and it makes up 45% of total human DNA. Also, TEs contributed to 16% of transcription factor binding sites. A larger number of motifs are also found in non-TE-derived DNA, and the number is larger than TE-derived DNA. All these factors correlate to the direct participation of TEs in many ways of gene control networks. | 1 | Biochemistry |
Organic geochemists also have an interest in studying the diagenesis of biogenic substances in petroleum and how they are transformed in sediment and fossils. While 90% of this organic material is insoluble in common organic solvents – called kerogen – 10% is in a form that is soluble and can be extracted, from where biogenic compounds can then be isolated. Saturated linear fatty acids and pigments have the most stable chemical structures and are therefore suited to withstanding degradation from the diagenesis process and being detected in their original forms. However, macromolecules have also been found in protected geological regions. Typical sedimentation conditions involve enzymatic, microbial and physicochemical processes as well as increased temperature and pressure, which lead to transformations of biogenic substances. For example, pigments that arise from dehydrogenation of chlorophyll or hemin can be found in many sediments as nickel or vanadyl complexes. A large proportion of the isoprenoids in sediments are also derived from chlorophyll. Similarly, linear saturated fatty acids discovered in the Messel oil shale of the Messel Pit in Germany arise from organic material of vascular plants.
Additionally, alkanes and isoprenoids are found in soluble extracts of Precambrian rock, indicating the probable existence of biological material more than three billion years ago. However, there is the potential that these organic compounds are abiogenic in nature, especially in Precambrian sediments. While Studier et al.’s (1968) simulations of the synthesis of isoprenoids in abiogenic conditions did not produce the long-chain isoprenoids used as biomarkers in fossils and sediments, traces of C-C isoprenoids were detected. It is also possible for polyisoprenoid chains to be stereoselectively synthesised using catalysts such as Al(CH) – VCl. However, the probability of these compounds being available in the natural environment is unlikely. | 0 | Organic Chemistry |
Hypophosphorous acid was first prepared in 1816 by the French chemist Pierre Louis Dulong (1785–1838).
The acid is prepared industrially via a two step process: Firstly, elemental white phosphorus reacts with alkali and alkaline earth hydroxides to give an aqueous solution of hypophosphites:
:P + 4 OH + 4 HO → 4 + 2 H
Any phosphites produced in this step can be selectively precipitated out by treatment with calcium salts. The purified material is then treated with a strong, non-oxidizing acid (often sulfuric acid) to give the free hypophosphorous acid:
: + H → HPO
HPA is usually supplied as a 50% aqueous solution. Anhydrous acid cannot be obtained by simple evaporation of the water, as the acid readily oxidises to phosphorous acid and phosphoric acid and also disproportionates to phosphorous acid and phosphine. Pure anhydrous hypophosphorous acid can be formed by the continuous extraction of aqueous solutions with diethyl ether. | 0 | Organic Chemistry |
A transition metal carbene complex is an organometallic compound featuring a divalent carbon ligand, itself also called a carbene. Carbene complexes have been synthesized from most transition metals and f-block metals, using many different synthetic routes such as nucleophilic addition and alpha-hydrogen abstraction. The term carbene ligand is a formalism since many are not directly derived from carbenes and most are much less reactive than lone carbenes. Described often as , carbene ligands are intermediate between alkyls and carbynes . Many different carbene-based reagents such as Tebbe's reagent are used in synthesis. They also feature in catalytic reactions, especially alkene metathesis, and are of value in both industrial heterogeneous and in homogeneous catalysis for laboratory- and industrial-scale preparation of fine chemicals. | 0 | Organic Chemistry |
Dioxane has affected groundwater supplies in several areas. Dioxane at the level of 1 μg/L (~1 ppb) has been detected in many locations in the US. In the U.S. state of New Hampshire, it had been found at 67 sites in 2010, ranging in concentration from 2 ppb to over 11,000 ppb. Thirty of these sites are solid waste landfills, most of which have been closed for years. In 2019, the Southern Environmental Law Center successfully sued Greensboro, North Carolina's Wastewater treatment after 1,4-Dioxane was found at 20 times above EPA safe levels in the Haw River. | 6 | Supramolecular Chemistry |
Consider a freely jointed chain of N bonds of length subject to a constant elongational force f applied to its ends along the z axis and an environment temperature . An example could be a chain with two opposite charges +q and -q at its ends in a constant electric field applied along the axis as sketched in the figure on the right. If the direct Coulomb interaction between the charges is ignored, then there is a constant force at the two ends.
Different chain conformations are not equally likely, because they correspond to different energy of the chain in the external electric field.
Thus, different chain conformation have different statistical Boltzmann factors .
The partition function is:
Every monomer connection in the chain is characterized by a vector of length and angles in the spherical coordinate system. The end-to-end vector can be represented as: . Therefore:
The Gibbs free energy G can be directly calculated from the partition function:
The Gibbs free energy is used here because the ensemble of chains corresponds to constant temperature and constant force (analogous to the isothermal-isobaric ensemble, which has constant temperature and pressure).
The average end-to-end distance corresponding to a given force can be obtained as the derivative of the free energy:
This expression is the Langevin function , also mentioned in previous paragraphs:
where, .
For small relative elongations () the dependence is approximately linear,
and follows Hooke's law as shown in previous paragraphs: | 7 | Physical Chemistry |
Transmission Kikuchi Diffraction (TKD), also sometimes called transmission-electron backscatter diffraction (t-EBSD), is a method for orientation mapping at the nanoscale. It’s used for analysing the microstructures of thin transmission electron microscopy (TEM) specimens in the scanning electron microscope (SEM). This technique has been widely utilised in the characterization of nano-crystalline materials, including oxides, superconductors, and metallic alloys.
TKD offers improved spatial resolution, enabling effective characterization of nanocrystalline materials and heavily deformed samples where high dislocation densities can prevent successful characterization using conventional Electron backscatter diffraction. Many studies have reported sub-10 nm resolution using TKD.
The main difference between diffraction spots and Kikuchi bands is that in TEM, discrete diffraction spots arise from coherent scattering of the incident beam, while the formation of Kikuchi bands is described as a two-step process consisting of incoherent scattering of the primary beam followed by coherent scattering of these forward biased electrons. TKD has also been applied to analyse fine-grained ultramylonite peridotite samples in a scanning electron microscope. The preparation of TKD samples can be done with standard methods used for transmission electron microscopy (TEM). | 7 | Physical Chemistry |
The model calculates the ground water levels and the incoming and outgoing ground water flows between the polygons by a numerical solution of the well-known Boussinesq equation. The levels and flows influence each other mutually.
The ground water situation is further determined by the vertical groundwater recharge that is calculated from the agronomic water balance. These depend again on the levels of the ground water.
When semi-confined aquifers are present, the resistance to vertical flow in the slowly permeable top-layer and the overpressure in the aquifer, if any, are taken into account.
Hydraulic boundary conditions are given as hydraulic heads in the external nodes in combination with the hydraulic conductivity between internal and external nodes. If one wishes to impose a zero flow condition at the external nodes, the conductivity can be set at zero.
Further, aquifer flow conditions can be given for the internal nodes. These are required when a geological fault is present at the bottom of the aquifer or when flow occurs between the main aquifer and a deeper aquifer separated by a semi-confining layer.
The depth of the water table, the rainfall and salt concentrations of the deeper layers are assumed to be the same over the whole polygon. Other parameters can very within the polygons according to type of crops and cropping rotation schedule. | 9 | Geochemistry |
The pair of trigonometric functions can be thought of as parametrizing the unit circle. The stereographic projection gives an alternative parametrization of the unit circle:
Under this reparametrization, the length element of the unit circle goes over to
This substitution can sometimes simplify integrals involving trigonometric functions. | 3 | Analytical Chemistry |
E74-like factor 1 (ets domain transcription factor) is a protein that in humans is encoded by the ELF1 gene. | 1 | Biochemistry |
The CTCF insulator appears to have enhancer blocking activity via its 3D structure and have no direct connection with barrier activity. Vertebrates in particular appear to rely heavily on the CTCF insulator, however there are many different insulator sequences identified. Insulated neighborhoods formed by physical interaction between two CTCF-bound DNA loci contain the interactions between enhancers and their target genes. | 1 | Biochemistry |
* The process may not remove sufficient organic matter from the wastewater.
* The sludge age may be too low to enable nitrification.
The typical control band for the concentration of MLSS is 2 to 4 g/L for conventional activated sludge, or up to 15 g/L for membrane bioreactors.
One of the easiest control procedures for activated sludge systems is the Constant Mixed Liquor Suspended Solids method. In this method, the operator selects a certain MLSS concentration or range of mix liquor concentrations that produces the best effluent and the highest removal efficiencies. This specific value or range must be calculated depending on COD or BOD load [kg/d]. When the operator finds the optimum MLSS concentration for each plant, they attempt to maintain this value by adjusting the sludge wasting or sludge excess rate. One rule of thumb for activated sludge systems is that for every pound of BOD removed in the secondary system a half a pound of new solids is generated through reproduction of the organisms and addition of new organisms from the influent wastes. So, the operator tries to waste the proper amount of solids to keep their selected optimum mix liquor concentration constant. If the MLSS concentration is above the desired concentration, the wasting of the excess solids will have to be started or increased. If the MLSS concentration is below the desired concentration level, wasting should be decreased or stopped. | 3 | Analytical Chemistry |
The stereochemical term enantiotopic refers to the relationship between two groups in a molecule which, if one or the other were replaced, would generate a chiral compound. The two possible compounds resulting from that replacement would be enantiomers.
For example, the two hydrogen atoms attached to the second carbon in butane are enantiotopic. Replacement of one hydrogen atom (colored blue) with a bromine atom will produce (R)-2-bromobutane. Replacement of the other hydrogen atom (colored red) with a bromine atom will produce the enantiomer (S)-2-bromobutane.
Enantiotopic groups are identical and indistinguishable except in chiral environments. For instance, the CH hydrogens in ethanol (CHCHOH) are normally enantiotopic, but can be made different (diastereotopic) if combined with a chiral center, for instance by conversion to an ester of a chiral carboxylic acid such as lactic acid, or if coordinated to a chiral metal center, or if associated with an enzyme active site, since enzymes are constituted of chiral amino acids. Indeed, in the presence of the enzyme LADH, one specific hydrogen is removed from the CH group during the oxidation of ethanol to acetaldehyde, and it gets replaced in the same place during the reverse reaction. The chiral environment needs not be optically pure for this effect.
Enantiotopic groups are mirror images of each other about an internal plane of symmetry. A chiral environment removes that symmetry. Enantiotopic pairs of NMR-active nuclei are also indistinguishable by NMR and produce a single signal.
Enantiotopic groups need not be attached to the same atom. For example, two hydrogen atoms adjacent to the carbonyl group in cis-2,6-dimethylcyclohexanone are enantiotopic; they are related by an internal plane of symmetry passing through the carbonyl group, but deprotonation on one side of the carbonyl group or on the other will generate compounds that are enantiomers. Similarly, the replacement of one or the other with deuterium will generate enantiomers. | 4 | Stereochemistry |
Methanogens are observed in anoxic soil environments, contributing to the degradation of organic matter. This organic matter may be placed by humans through landfill, buried as sediment on the bottom of lakes or oceans as sediments, and as residual organic matter from sediments that have formed into sedimentary rocks. | 1 | Biochemistry |
PI-3K is one of the important components in the regulation of the insulin signaling pathway. It maintains the insulin sensitivity in the liver. PI-3K is composed of a regulatory subunit (P85) and a catalytic subunit (P110). P85 regulates the activation of PI-3K enzyme. In the PI-3K heterodimer (P85-p110), P85 is responsible for the PI-3K activity, by binding to the binding site on the insulin receptor substrates (IRS). It was noted that an increase of P85 a (isoform of P85) results in a competition between the later and the P85-P110 complex to the IRS binding site, reducing the PI-3k activity and leading to insulin resistance. Insulin resistance refers also to Type 2 diabetes.
It was also noted that increased serine phosphorylation of IRS is involved in the insulin resistance by reducing their ability to attract PI3K. The serine phosphorylation can also lead to degradation of IRS-1. | 1 | Biochemistry |
Generally the goal of this type of sample cell is to improve detection sensitivity by increasing the total optical path length that travels through a small, constant sample volume. In principle, a longer path length results in greater detection sensitivity. Focusing mirrors must be used to redirect the beam at each reflection point, resulting in the beam being restricted to a predefined space along a controlled path until it exits the optical cavity. The output of the cell is the input of an optical detector (a specialized type of transducer), which senses specific changes in the properties of the beam that occur during interaction with the test sample. For instance, the sample may absorb energy from the beam, resulting in an attenuation of the output that is detectable by the transducer. Two conventional multipass cells are called the White cell and Herriott cell. | 7 | Physical Chemistry |
Metallic parts produced by casting are comparatively inexpensive, but are often subject to metallurgical flaws like porosity and microstructural defects. Friction stir processing can be used to introduce a wrought microstructure into a cast component and eliminate many of the defects. By vigorously stirring a cast metal part to homogenize it and reduce the grain size, the ductility and strength are increased. | 8 | Metallurgy |
The Bionic Leaf is a biomimetic system that gathers solar energy via photovoltaic cells that can be stored or used in a number of different functions. Bionic leaves can be composed of both synthetic (metals, ceramics, polymers, etc.) and organic materials (bacteria), or solely made of synthetic materials. The Bionic Leaf has the potential to be implemented in communities, such as urbanized areas to provide clean air as well as providing needed clean energy. | 5 | Photochemistry |
The indenyl effect refers to an explanation for the enhanced rates of substitution exhibited by η-indenyl complexes vs the related η-cyclopentadienyl complexes.
Associative substitution occurs by the addition of a ligand to a metal complex followed by dissociation of an original ligand. Associative pathways are not typically seen in 18-electron complexes due to the requisite intermediates having more than 18 electrons associated with the metal atom. 18 electron indenyl complexes; however, have been shown to undergo substitution via associative pathways quite readily. This is attributed to the relative ease of η to η rearrangement due to stabilization by the arene. This stabilization is responsible for substitution rate enhancements of about 10 for the substitution of indenyl complexes compared to the corresponding cyclopentadienyl complex.
Kinetic data support two proposed mechanisms for associative ligand substitution. The first mechanism, proposed by Hart-Davis and Mawby, is a concerted attack by the nucleophile and η to η transition followed by loss of a ligand and a η to η transition.
In a mechanism proposed by Basolo, η and η isomers exist in rapid chemical equilibrium. The rate-limiting step occurs with the attack of the nucleophile on a η isomer. The nature of the substituents of the allyl group can strongly affect the kinetics and regiochemistry of the nucleophilic attack. | 0 | Organic Chemistry |
Photorespiration (also known as the oxidative photosynthetic carbon cycle or C cycle) refers to a process in plant metabolism where the enzyme RuBisCO oxygenates RuBP, wasting some of the energy produced by photosynthesis. The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvin–Benson cycle, but approximately 25% of reactions by RuBisCO instead add oxygen to RuBP (oxygenation), creating a product that cannot be used within the Calvin–Benson cycle. This process lowers the efficiency of photosynthesis, potentially lowering photosynthetic output by 25% in plants. Photorespiration involves a complex network of enzyme reactions that exchange metabolites between chloroplasts, leaf peroxisomes and mitochondria.
The oxygenation reaction of RuBisCO is a wasteful process because 3-phosphoglycerate is created at a lower rate and higher metabolic cost compared with RuBP carboxylase activity. While photorespiratory carbon cycling results in the formation of G3P eventually, around 25% of carbon fixed by photorespiration is re-released as and nitrogen, as ammonia. Ammonia must then be detoxified at a substantial cost to the cell. Photorespiration also incurs a direct cost of one ATP and one NAD(P)H.
While it is common to refer to the entire process as photorespiration, technically the term refers only to the metabolic network which acts to rescue the products of the oxygenation reaction (phosphoglycolate). | 5 | Photochemistry |
Atomic polarization is observed when the nucleus of the atom reorients in response to the electric field. This is a resonant process. Atomic polarization is intrinsic to the nature of the atom and is a consequence of an applied field. Electronic polarization refers to the electron density and is a consequence of an applied field. Atomic polarization is usually small compared to electronic polarization. | 7 | Physical Chemistry |
The minor spliceosome is a ribonucleoprotein complex that catalyses the removal (splicing) of an atypical class of spliceosomal introns (U12-type) from messenger RNAs in some clades of eukaryotes. This process is called noncanonical splicing, as opposed to U2-dependent canonical splicing. U12-type introns represent less than 1% of all introns in human cells. However they are found in genes performing essential cellular functions. | 1 | Biochemistry |
Twin helical strands form the DNA backbone. Another double helix may be found by tracing the spaces, or grooves, between the strands. These voids are adjacent to the base pairs and may provide a binding site. As the strands are not directly opposite each other, the grooves are unequally sized. One groove, the major groove, is 22 Å wide and the other, the minor groove, is 12 Å wide. The narrowness of the minor groove means that the edges of the bases are more accessible in the major groove. As a result, proteins like transcription factors that can bind to specific sequences in double-stranded DNA usually make contacts to the sides of the bases exposed in the major groove. This situation varies in unusual conformations of DNA within the cell (see below), but the major and minor grooves are always named to reflect the differences in size that would be seen if the DNA is twisted back into the ordinary B form. | 4 | Stereochemistry |
* During energy transformations in living systems, order and organization must be compensated by releasing energy which will increase entropy of the surrounding.
* Organisms are open systems that exchange materials and energy with the environment. They are never at equilibrium with the surrounding.
* Energy is spent to create and maintain order in the cells, and surplus energy and other simpler by-products are released to create disorder such that there is an increase in entropy of the surrounding.
* In a reversible process, entropy remains constant where as in an irreversible process (more common to real-world scenarios), entropy tends to increase.
* During phase changes (from solid to liquid, or to gas), entropy increases because the number of possible arrangements of particles increases.
* If ∆G<0, the chemical reaction is spontaneous and favourable in that direction.
* If ∆G=0, the reactants and products of chemical reaction are at equilibrium.
* If ∆G>0, the chemical reaction is non-spontaneous and unfavorable in that direction.
* ∆G is not an indicator for velocity or rate of chemical reaction at which equilibrium is reached. It depends on amount of enzyme and energy activation. | 1 | Biochemistry |
Tungsten(VI) oxide (WO), which exhibits several different polymorphs at various temperatures, is of interest due to its high conductivity but has a relatively wide, indirect band gap (~2.7 eV) which means it cannot absorb most of the solar spectrum. Though many attempts have been made to increase absorption, they result in poor conductivity and thus WO does not appear to be a viable material for PEC water splitting. | 5 | Photochemistry |
There are three main phases of biofilm development and rhamnolipids are implicated in each phase. Rhamnolipids are reported to promote motility, thereby inhibiting attachment by preventing cells from adhering tightly to the substratum. During biofilm development, rhamnolipids are reported to create and maintain fluid channels for water and oxygen flow around the base of the biofilm. Furthermore, they are important for forming structure in biofilms; a rhlA mutant forms a flat biofilm. Biofilm dispersal is dependent on Rhammnolipids, however other factors such as degradation of the matrix and activation of motility are also likely to be necessary. It has been shown using fluorescence microscopy that the rhlAB operon is induced in the centre of the mushroom cap, followed by dispersal of cells from the polysaccharide matrix from the centre of these caps causing a cavity to form. A mutation in rhlA causes a failure in formation of mushroom caps at all. | 0 | Organic Chemistry |
Heterogeneous cross-coupling catalysts typically lose some portion of activity to metal leaching between different runs as a result of the solution-phase catalytic cycle (see above), and hence can only be recycled a finite number of times.
Multiple groups have pointed out that the need for recycling is obviated at extremely high turnover and low catalyst loading, since in these cases the catalyst cost is negligible relative to the cost of other reaction components. As a result, for most cross-coupling reactions, in which heterogeneous catalysts generally require higher loadings than equivalent homogeneous ones, the benefits of heterogeneous catalysts afforded by the greater ease of recycling may be outweighed by the disadvantages – higher catalyst loadings, and the additional process costs. Additionally, when catalyst loadings are lower than 10 ppm – the regulatory limit for several metals including Pd in pharmaceutical APIs – separation of the metal following the reaction does not even need to be performed. This nullifies another of the commonly perceived advantages of heterogeneous catalysts over their homogeneous counterparts. | 0 | Organic Chemistry |
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