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The E3 subunit, called the dihydrolipoyl dehydrogenase enzyme, is characterized as a homodimer protein wherein two cysteine residues, engaged in disulfide bonding, and the FAD cofactor in the active site facilitate its main purpose as an oxidizing catalyst. One example of E3 structure, found in Pseudomonas putida, is formed such that each individual homodimer subunit contains two binding domains responsible for FAD binding and NAD binding, as well as a central domain and an interface domain. | 1 | Biochemistry |
* [http://www.eanet.asia/ Acid Deposition Monitoring Program in East Asia (EANET)]
* [https://www.canada.ca/en/environment-climate-change/services/air-pollution/monitoring-networks-data/canadian-air-precipitation.html Canadian Air and Precipitation Monitoring Network (CAPMoN)]
* [https://www.epa.gov/castnet Clean Air Status and Trends Network (CASTNET)]
* [https://www.epa.gov/great-lakes-monitoring Great Lakes National Program Office (GLNPO)]
* [http://apmmn.org/About/ Asia-Pacific Mercury Monitoring Network (APMMN)] | 2 | Environmental Chemistry |
Metallurgy only appears in Mesoamerica in 800 CE with the best evidence from West Mexico. Much like in South America, fine metals were seen as a material for the elite. Metal's special qualities of colour and resonance seemed to have appealed most and then led to the particular technological developments seen in the region.
Exchange of ideas and goods with peoples from the Ecuador and Colombia region (likely via a maritime route) seems to have fueled early interest and development. Similar metal artifact types are found in West Mexico and the two regions: copper rings, needles, and tweezers being fabricated in the same ways as in Ecuador and also found in similar archaeological contexts. A multitude of bells were also found, but in this case they were cast using the same lost-wax casting method as seen in Colombia. During this period, copper was being used almost exclusively.
Continual contact kept the flow of ideas from that same region and later, coinciding with the development of Andean long distance maritime trade, influence from further south seems to have reached the region and led to a second period (1200–1300 CE to the Spanish arrival). By this time, copper alloys were being explored by West Mexican metallurgists, partly because the different mechanical properties were needed to fashion specific artifacts, particularly axe-monies – further evidence for contact with the Andean region. However, in general the new properties such alloys introduced were developed to meet regional needs, especially wirework bells, which at times had such high tin content in the bronze that it was irrelevant for its mechanical properties but gave the bells a golden colour.
The actual artifacts and then techniques were imported from the south, but west Mexican metallurgists worked ores from the abundant local deposits; the metal was not being imported. Even when the technology spread from West into north-eastern, central and southern Mexico, artifacts that can be traced back to West Mexican ores are abundant, if not exclusive. It is not always clear if the metal reached its final destination as an ingot, an ore or a finished artifact. Provenance studies on metal artifacts from southern Mesoamerica cast with the lost wax technique and dissimilar to west Mexican artifacts have shown that there might have been a second point of emergence of metallurgy into Mesoamerica there since no known source could be identified.
In the Tarascan Empire, copper and bronze was used for chisels, punches, awls, tweezers, needles, axes, discs, and breastplates.
The Aztecs did not initially adopt metal working, even though they had acquired metal objects from other peoples. However, as conquest gained them metal working regions, the technology started to spread. By the time of the Spanish conquest, a bronze-smelting technology had already been developed. Spanish conquistadors used indigenous smelting technology to produce weapons and tools. | 8 | Metallurgy |
The boiling point is an important property because it determines the speed of evaporation. Small amounts of low-boiling-point solvents like diethyl ether, dichloromethane, or acetone will evaporate in seconds at room temperature, while high-boiling-point solvents like water or dimethyl sulfoxide need higher temperatures, an air flow, or the application of vacuum for fast evaporation.
*Low boilers: boiling point below 100 °C (boiling point of water)
*Medium boilers: between 100 °C and 150 °C
*High boilers: above 150 °C | 2 | Environmental Chemistry |
The intercalation compounds graphite bisulfate and graphite perchlorate can be prepared by treating graphite with strong oxidizing agents in the presence of strong acids. In contrast to the potassium and calcium graphites, the carbon layers are oxidized in this process:
:48 C + 0.25 O + 3 HSO → [C][HSO]·2HSO + 0.5 HO
In graphite perchlorate, planar layers of carbon atoms are 794 picometers apart, separated by ions. Cathodic reduction of graphite perchlorate is analogous to heating , which leads to a sequential elimination of .
Both graphite bisulfate and graphite perchlorate are better conductors as compared to graphite, as predicted by using a positive-hole mechanism.
Reaction of graphite with affords the salt . | 6 | Supramolecular Chemistry |
Many metabolites are chemically reactive and unstable, and thus prone to chemical damage. In general, any reaction that occurs in vitro under physiological conditions can also occur in vivo. Some metabolites are so reactive that their half-life in a cell is measured in minutes. For example, the glycolytic intermediate 1,3-bisphosphoglyceric acid has a half-life of 27 minutes in vivo. Typical types of chemical damage reactions that can occur to metabolites are racemization, rearrangement, elimination, photodissociation, addition, and condensation. | 1 | Biochemistry |
Various magnetic particles (magnetic carrier) coated with silica are often used as silica coated beads
Maghemite particle (γ-FeO) and magnetite particle (FeO),
as well as an intermediate iron oxide particle thereof, are most suitable as magnetic carriers.
Generally, the quality of the magnetic beads is characterized by
following parameters:
* saturation magnetization (～10-80 A m2/kg (emu/g):Superparamagnetic),
* coercive force (～ 0.80-15.92 kA/m),
* size diameter (～ 0.1-0.5 μm),
* mass of each particle (～ 2.7 ng),
* ease of collection (to be mentioned later),
* capture ability (to be mentioned later),
* Sedimentation rate (～4% in 30 min),
* Area ratio (> 100 m/g),
* Effective density (～ 2.5 g/cm), and
* Particle counts (～ 1 x 10 particles/mg).
Here, "ease of collection" is defined and compared by while capture ability are defined and compared by | 1 | Biochemistry |
CeCoIn is a member of a rich family of heavy-fermion compounds. CeIn is heavy-fermion metal with cubic crystal structure that orders antiferromagnetically below 10K. With applying external pressure, antiferromagnetism in CeIn is continuously suppressed, and a superconducting dome emerges in the phase diagram near the antiferromagnetic quantum critical point. CeCoIn has a tetragonal crystal structure, and the unit cell of CeCoIn can be considered as CeIn with an additional CoIn layer per unit cell.
Closely related to CeCoIn is the heavy-fermion material CeRhIn, which has the same crystal structure and which orders antiferromagnetically below 4K, but does not become superconducting at ambient pressure. At high pressure CeRhIn becomes superconducting with a maximum T slightly above 2 K at a pressure around 2 GPa, and at the same pressure the Fermi surface of CeRhIn changes suggesting so-called local quantum criticality.
Also the compound PuCoGa, which is a superconductor with T approximately 18.5 K and which can be considered an intermediate between heavy-fermion and cuprate superconductors, has the same crystal structure.
Growth of single-crystalline CeCoIn has been very successful soon after the discovery of the material, and large single crystals of CeCoIn, such as required for inelastic neutron scattering, have been prepared. (In contrast to some other heavy-fermion compounds where single-crystal growth is more challenging.) | 8 | Metallurgy |
The term Schiff base is normally applied to these compounds when they are being used as ligands to form coordination complexes with metal ions. One example is Jacobsen's catalyst. The imine nitrogen is basic and exhibits pi-acceptor properties. Several, especially the diiminopyridines are noninnocent ligands. Many Schiff base ligands are derived from alkyl diamines and aromatic aldehydes.
Chiral Schiff bases were one of the first ligands used for asymmetric catalysis. In 1968 Ryōji Noyori developed a copper-Schiff base complex for the metal-carbenoid cyclopropanation of styrene. Schiff bases have also been incorporated into metal–organic frameworks (MOF). | 0 | Organic Chemistry |
Diazo compounds may be explosive and should be handled with care. Very often, the diazocarbonyl compound is prepared and immediately used via treatment of the corresponding acid chloride with an excess of diazomethane (see Eq. (18) below for an example). Reactions mediated by copper are typically on the order of hours, and in some cases, slow addition of the diazocarbonyl compound is necessary. Reactions should be carried out under an inert atmosphere in anhydrous conditions. | 0 | Organic Chemistry |
The first form of crucible steel was wootz, developed in India some time around 300 BCE. In its production the iron was mixed with glass and then slowly heated and then cooled. As the mixture cooled the glass would bond to impurities in the steel and then float to the surface, leaving the steel considerably purer. Carbon could enter the iron by diffusing in through the porous walls of the crucibles. Carbon dioxide would not react with the iron, but the small amounts of carbon monoxide could, adding carbon to the mix with some level of control. Wootz was widely exported throughout the Middle East, where it was combined with a local production technique around 1000 CE to produce Damascus steel, famed throughout the world. Wootz derives from the Tamil term for steel urukku. Indian wootz steel was the first high quality steel that was produced.
Henry Yule quoted the 12th-century Arab Edrizi who wrote: "The South Indians excel in the manufacture of iron, and in the preparations of those ingredients along with which it is fused to obtain that kind of soft iron which is usually styled Indian steel. They also have workshops wherein are forged the most famous sabres in the world. ...It is not possible to find anything to surpass the edge that you get from Indian steel (al-hadid al-Hindi).
As early as the 17th century, Europeans knew of India's ability to make crucible steel from reports brought back by travelers who had observed the process at several places in southern India. Several attempts were made to import the process, but failed because the exact technique remained a mystery. Studies of wootz were made in an attempt to understand its secrets, including a major effort by the famous scientist, Michael Faraday, son of a blacksmith. Working with a local cutlery manufacturer he wrongly concluded that it was the addition of aluminium oxide and silica from the glass that gave wootz its unique properties.
After the Indian Rebellion of 1857, many Indian wootz steel swords were ordered to be destroyed by the East India Company. The metalworking industry in India went into decline during the period of British Crown control due to various colonial policies, but steel production was revived in India by Jamsetji Tata. | 8 | Metallurgy |
Cyanobacteria are challenged by environmental stresses and internally generated reactive oxygen species that cause DNA damage. Cyanobacteria possess numerous E. coli-like DNA repair genes. Several DNA repair genes are highly conserved in cyanobacteria, even in small genomes, suggesting that core DNA repair processes such as recombinational repair, nucleotide excision repair and methyl-directed DNA mismatch repair are common among cyanobacteria. | 5 | Photochemistry |
Self-renewal and differentiation abilities are exceptional properties of stem cells. These cells can be classified by their differentiation capacity, which progressively decrease with development, in totipotents, pluripotents, multipotents and unipotents.
Self-renewal process is highly regulated from cell cycle and genetic transcription control. There are some signaling pathways, such as LIF/JAK/STAT3 (Leukemia inhibitory factor/Janus kinase/Signal transducer and activator of transcription 3) and BMP/SMADs/Id (Bone morphogenetic proteins/ Mothers against decapentaplegic/ Inhibitor of differentiation), mediated by transcription factors, epigenetic regulators and others components, and they are responsible for self-renewal genes expression and inhibition of differentiation genes expression, respectively.
At cell cycle level there is an increase of complexity of the mechanisms in somatic stem cells. However, it is observed a decrease of self-renewal potential with age. These mechanisms are regulated by p16-CDK4/6-Rb and p19-p53-P21 signaling pathways. Embryonic stem cells have constitutive cyclin E-CDK2 activity, which hyperphosphorylates and inactivates Rb. This leads to a short G1 phase of the cell cycle with rapid G1-S transition and little dependence on mitogenic signals or D cyclins for S phase entry. In fetal stem cells, mitogens promote a relatively rapid G1-S transition through cooperative action of cyclin D-CDK4/6 and cyclin E-CDK2 to inactivate Rb family proteins. p16 and p19 expression are inhibited by Hmga2-dependent chromatin regulation. Many young adult stem cells are quiescent most of the time. In the absence of mitogenic signals, cyclin-CDKs and the G1-S transition are suppressed by cell cycle inhibitors including Ink4 and Cip/Kip family proteins. As a result, Rb is hypophosphorylated and inhibits E2F, promoting quiescence in G0-phase of the cell cycle. Mitogen stimulation mobilizes these cells into cycle by activating cyclin D expression. In old adult stem cells, let-7 microRNA expression increases, reducing Hmga2 levels and increasing p16 and p19 levels. This reduces the sensitivity of stem cells to mitogenic signals by inhibiting cyclin-CDK complexes. As a result, either stem cells cannot enter the cell cycle, or cell division slows in many tissues.
Extrinsic regulation is made by signals from the niche, where stem cells are found, which is able to promote quiescent state and cell cycle activation in somatic stem cells. Asymmetric division is characteristic of somatic stem cells, maintaining the reservoir of stem cells in the tissue and production of specialized cells of the same.
Stem cells show an elevated therapeutic potential, mainly in hemato-oncologic pathologies, such as leukemia and lymphomas. Little groups of stem cells were found into tumours, calling cancer stem cells. There are evidences that these cells promote tumor growth and metastasis. | 7 | Physical Chemistry |
Today, the process of fermentation is used for a multitude of everyday applications including medication, beverages and food. Currently, companies like Genencor International uses the production of enzymes involved in fermentation to build a revenue of over $400 million a year. Many medications such as antibiotics are produced by the fermentation process. An example is the important drug cortisone, which can be prepared by the fermentation of a plant steroid known as diosgenin.
The enzymes used in the reaction are provided by the mold Rhizopus nigricans. Just as it is commonly known, alcohol of all types and brands are also produced by way of fermentation and distillation. Moonshine is a classic example of how this is carried out. Finally, foods such as yogurt are made by fermentation processes as well. Yogurt is a fermented milk product that contains the characteristic bacterial cultures Lactobacillus bulgaricus and Streptococcus thermopiles. | 1 | Biochemistry |
Other industrial uses of thiourea include production of flame retardant resins, and vulcanization accelerators.
Thiourea is building blocks to pyrimidine derivatives. Thus, thioureas condense with β-dicarbonyl compounds. The amino group on the thiourea initially condenses with a carbonyl, followed by cyclization and tautomerization. Desulfurization delivers the pyrimidine. The pharmaceuticals thiobarbituric acid and sulfathiazole are prepared using thiourea. 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea and hydrazine.
Thiourea is used as an auxiliary agent in diazo paper, light-sensitive photocopy paper and almost all other types of copy paper.
It is also used to tone silver-gelatin photographic prints (see Sepia Toning).
Thiourea is used in the Clifton-Phillips and Beaver bright and semi-bright electroplating processes. It is also used in a solution with tin(II) chloride as an electroless tin plating solution for copper printed circuit boards.
Thioureas are used (usually as hydrogen-bond donor catalysts) in a research theme called thiourea organocatalysis. Thioureas are often found to be stronger hydrogen-bond donors (i.e., more acidic) than ureas. | 0 | Organic Chemistry |
Because the light energy recorded by the detector array is proportional to the volume of the particles, laser diffraction results are intrinsically volume-weighted. This means that the particle size distribution represents the volume of particle material in the different size classes. This is in contrast to counting-based optical methods such as microscopy or dynamic image analysis, which report the number of particles in the different size classes. That the diffracted light is proportional to the particle’s volume also implies that results are assuming particle sphericity, i.e. that the particle size result is an equivalent spherical diameter. Hence particle shape cannot be determined by the technique.
The main graphical representation of laser diffraction results is the volume-weighted particle size distribution, either represented as density distribution (which highlights the different modes) or as cumulative undersize distribution. | 7 | Physical Chemistry |
Uroporphyrinogens are cyclic tetrapyrroles with four propionic acid groups ("P" groups) and four acetic acid groups ("A" groups).
There are four forms, which vary based upon the arrangements of the "P" and "A" groups (in clockwise order):
* In the "I" variety (i.e. uroporphyrinogen I), the order repeats four times: AP-AP-AP-AP.
* In the "III" variety (i.e. uroporphyrinogen III), the fourth is reversed: AP-AP-AP-PA.
*:This is the most common form. In the synthesis of porphyrin, it is created from the linear tetrapyrrole hydroxymethylbilane by the enzyme uroporphyrinogen III synthase, and is further converted into coproporphyrinogen III by the enzyme uroporphyrinogen III decarboxylase.
* The "II" and "IV" varieties can be created synthetically, but do not appear in nature. | 1 | Biochemistry |
*[http://www.acadsoft.co.uk/scdbase/scdbase.htm IUPAC SC-Database] A comprehensive database of published data on equilibrium constants of metal complexes and ligands
*[https://www.nist.gov/ts/msd/srd/nist46.cfm NIST Standard Reference Database 46] : Critically selected stability constants of metal complexes
*[https://web.archive.org/web/20081009060809/http://www.chem.wisc.edu/areas/reich/pkatable/ Inorganic and organic acids and bases] pK data in water and DMSO
*[https://web.archive.org/web/20060928231137/http://www.grc.nasa.gov/WWW/CEAWeb/ceaHome.htm NASA Glenn Thermodynamic Database webpage with links to (self-consistent) temperature-dependent specific heat, enthalpy, and entropy for elements and molecules] | 7 | Physical Chemistry |
Specific characters may be used to create a suitable (ambigraphic) nucleic acid notation for complementary bases (i.e. guanine = b, cytosine = q, adenine = n, and thymine = u), which makes it is possible to complement entire DNA sequences by simply rotating the text "upside down". For instance, with the previous alphabet, (GTCA) would read as (TGAC, reverse complement) if turned upside down.
Ambigraphic notations readily visualize complementary nucleic acid stretches such as palindromic sequences. This feature is enhanced when utilizing custom fonts or symbols rather than ordinary ASCII or even Unicode characters. | 1 | Biochemistry |
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with water (hydrolysis) using amylase enzymes as catalyst, which produces constituent sugars (monosaccharides, or oligosaccharides). They range in structure from linear to highly branched. Examples include storage polysaccharides such as starch, glycogen and galactogen and structural polysaccharides such as cellulose and chitin.
Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure, these macromolecules can have distinct properties from their monosaccharide building blocks. They may be amorphous or even insoluble in water.
When all the monosaccharides in a polysaccharide are the same type, the polysaccharide is called a homopolysaccharide or homoglycan, but when more than one type of monosaccharide is present, they are called heteropolysaccharides or heteroglycans.
Natural saccharides are generally composed of simple carbohydrates called monosaccharides with general formula (CHO) where n is three or more. Examples of monosaccharides are glucose, fructose, and glyceraldehyde. Polysaccharides, meanwhile, have a general formula of C(HO) where x and y are usually large numbers between 200 and 2500. When the repeating units in the polymer backbone are six-carbon monosaccharides, as is often the case, the general formula simplifies to (CHO), where typically .
As a rule of thumb, polysaccharides contain more than ten monosaccharide units, whereas oligosaccharides contain three to ten monosaccharide units, but the precise cutoff varies somewhat according to the convention. Polysaccharides are an important class of biological polymers. Their function in living organisms is usually either structure- or storage-related. Starch (a polymer of glucose) is used as a storage polysaccharide in plants, being found in the form of both amylose and the branched amylopectin. In animals, the structurally similar glucose polymer is the more densely branched glycogen, sometimes called "animal starch". Glycogen's properties allow it to be metabolized more quickly, which suits the active lives of moving animals. In bacteria, they play an important role in bacterial multicellularity.
Cellulose and chitin are examples of structural polysaccharides. Cellulose is used in the cell walls of plants and other organisms and is said to be the most abundant organic molecule on Earth. It has many uses such as a significant role in the paper and textile industries and is used as a feedstock for the production of rayon (via the viscose process), cellulose acetate, celluloid, and nitrocellulose. Chitin has a similar structure but has nitrogen-containing side branches, increasing its strength. It is found in arthropod exoskeletons and in the cell walls of some fungi. It also has multiple uses, including surgical threads. Polysaccharides also include callose or laminarin, chrysolaminarin, xylan, arabinoxylan, mannan, fucoidan and galactomannan. | 0 | Organic Chemistry |
The photostationary state of a reversible photochemical reaction is the equilibrium chemical composition under a specific kind of electromagnetic irradiation (usually a single wavelength of visible or UV radiation).
It is a property of particular importance in photochromic compounds, often used as a measure of their practical efficiency and usually quoted as a ratio or percentage.
The position of the photostationary state is primarily a function of the irradiation parameters, the absorbance spectra of the chemical species, and the quantum yields of the reactions. The photostationary state can be very different from the composition of a mixture at thermodynamic equilibrium. As a consequence, photochemistry can be used to produce compositions that are "contra-thermodynamic".
For instance, although cis-stilbene is "uphill" from trans-stilbene in a thermodynamic sense, irradiation of trans-stilbene results in a mixture that is predominantly the cis isomer. As an extreme example, irradiation of benzene at 237 to 254 nm results in formation of benzvalene, an isomer of benzene that is 71 kcal/mol higher in energy than benzene itself. | 5 | Photochemistry |
Hundreds of such cycles have been proposed and investigated. This task has been eased by the availability of computers, allowing a systematic screening of chemical reactions sequences based on thermodynamic databases. Only the main "families" will be described in this article. | 7 | Physical Chemistry |
A Knudsen gas is a gas in a state of such low density that the average distance travelled by the gas molecules between collisions (mean free path) is greater than the diameter of the receptacle that contains it. If the mean free path is much greater than the diameter, the flow regime is dominated by collisions between the gas molecules and the walls of the receptacle, rather than intermolecular collisions with each other. It is named after Martin Knudsen. | 7 | Physical Chemistry |
An enamine is an unsaturated compound derived by the condensation of an aldehyde or ketone with a secondary amine. Enamines are versatile intermediates.
The word "enamine" is derived from the affix en-, used as the suffix of alkene, and the root amine. This can be compared with enol, which is a functional group containing both alkene (en-) and alcohol (-ol). Enamines are considered to be nitrogen analogs of enols.
If one or both of the nitrogen substituents is a hydrogen atom it is the tautomeric form of an imine. This usually will rearrange to the imine; however there are several exceptions (such as aniline). The enamine-imine tautomerism may be considered analogous to the keto-enol tautomerism. In both cases, a hydrogen atom switches its location between the heteroatom (oxygen or nitrogen) and the second carbon atom.
Enamines are both good nucleophiles and good bases. Their behavior as carbon-based nucleophiles is explained with reference to the following resonance structures. | 0 | Organic Chemistry |
The rate of hormone biosynthesis and secretion is often regulated by a homeostatic negative feedback control mechanism. Such a mechanism depends on factors that influence the metabolism and excretion of hormones. Thus, higher hormone concentration alone cannot trigger the negative feedback mechanism. Negative feedback must be triggered by overproduction of an "effect" of the hormone.
Hormone secretion can be stimulated and inhibited by:
* Other hormones (stimulating- or releasing -hormones)
* Plasma concentrations of ions or nutrients, as well as binding globulins
* Neurons and mental activity
* Environmental changes, e.g., of light or temperature
One special group of hormones is the tropic hormones that stimulate the hormone production of other endocrine glands. For example, thyroid-stimulating hormone (TSH) causes growth and increased activity of another endocrine gland, the thyroid, which increases output of thyroid hormones.
To release active hormones quickly into the circulation, hormone biosynthetic cells may produce and store biologically inactive hormones in the form of pre- or prohormones. These can then be quickly converted into their active hormone form in response to a particular stimulus.
Eicosanoids are considered to act as local hormones. They are considered to be "local" because they possess specific effects on target cells close to their site of formation. They also have a rapid degradation cycle, making sure they do not reach distant sites within the body.
Hormones are also regulated by receptor agonists. Hormones are ligands, which are any kinds of molecules that produce a signal by binding to a receptor site on a protein. Hormone effects can be inhibited, thus regulated, by competing ligands that bind to the same target receptor as the hormone in question. When a competing ligand is bound to the receptor site, the hormone is unable to bind to that site and is unable to elicit a response from the target cell. These competing ligands are called antagonists of the hormone. | 1 | Biochemistry |
Hydrastine is an isoquinoline alkaloid which was discovered in 1851 by Alfred P. Durand. Hydrolysis of hydrastine yields hydrastinine, which was patented by Bayer as a haemostatic drug during the 1910s. It is present in Hydrastis canadensis (thus the name) and other plants of the family Ranunculaceae. | 0 | Organic Chemistry |
The most notable effects of eutrophication are vegetal blooms, sometimes toxic, loss of biodiversity and anoxia, which can lead to the massive death of aquatic organisms.
Due to the hypoxic conditions present in dead zones, marine life within these areas tends to be scarce. Most fish and motile organisms tend to emigrate out of the zone as oxygen concentrations fall, and benthic populations may experience severe losses when oxygen concentrations are below 0.5 mg l O. In severe anoxic conditions, microbial life may experience dramatic shifts in community identity as well, resulting in an increased abundance of anaerobic organisms as aerobic microbes decrease in number and switch energy sources for oxidation such as nitrate, sulfate, or iron reduction. Sulfur reduction is a particular concern as Hydrogen sulfide is toxic and stresses most organisms within the zone further, exacerbating mortality risks.
Low oxygen levels can have severe effects on survivability of organisms inside the area while above lethal anoxic conditions. Studies conducted along the Gulf Coast of North America have shown hypoxic conditions lead to reduction of reproductive rates and growth rates in a variety of organisms including fish and benthic invertebrates. Organisms able to leave the area typically do so when oxygen concentrations decrease to less than 2 mg l. At these oxygen concentrations and below, organisms that survive inside the oxygen deficient environment and are unable to escape the area will often exhibit progressively worsening stress behavior and die. Surviving organisms tolerant of hypoxic conditions often exhibit physiological adaptations appropriate for persisting within hypoxic environments. Examples of such adaptations include increased efficiency of oxygen intake and use, lowering required amount of oxygen intake through reduced growth rates or dormancy, and increasing the usage of anaerobic metabolic pathways.
Community composition in benthic communities is dramatically disrupted by periodic oxygen depletion events, such as those of seasonal dead zones and occurring as a result of Diel cycles. The longterm effects of such hypoxic conditions result in a shift in communities, most commonly manifest as a decrease in species diversity through mass mortality events. Reestablishment of benthic communities depend upon composition of adjacent communities for larval recruitment. This results in a shift towards faster establishing colonizers with shorter and more opportunistic life strategies, potentially disrupting historic benthic compositions. | 9 | Geochemistry |
BC200 RNA has been found to be a factor in numerous types of cancer. Although this type of RNA is normally expressed in neurons, it has been detected in cancers of the breast, cervix, esophagus, lungs, ovaries, parotid glands, tongue, and the colon. In certain cancers, expression of BC200 RNA is upregulated. This occurs in esophageal squamous cell carcinoma (ESCC) and higher expression is considered to be a predictor of poor prognosis and may serve as a predictive biomarker for the disease. It was also discovered to be overexpressed in tumor cells of colorectal cancer where the transcript is located just next to a known oncogene, epithelial cell adhesion molecule (EpCAM). Here, expression of BC200 RNA and EpCAM are believed to be correlated as they both play a role in cell migration and invasion. Conversely, research has indicated that BC200 RNA is downregulated in ovarian cancer, as it is a tumor suppressor in normal ovarian cells controlling proliferative ability. | 1 | Biochemistry |
The plasma used in an ICP-MS is made by partially ionizing argon gas (Ar → Ar + e). The energy required for this reaction is obtained by pulsing an alternating electric current in load coil that surrounds the plasma torch with a flow of argon gas.
After the sample is injected, the plasma's extreme temperature causes the sample to separate into individual atoms (atomization). Next, the plasma ionizes these atoms (M → M + e) so that they can be detected by the mass spectrometer.
An inductively coupled plasma (ICP) for spectrometry is sustained in a torch that consists of three concentric tubes, usually made of quartz. The two major designs are the Fassel and Greenfield torches. The end of this torch is placed inside an induction coil supplied with a radio-frequency electric current. A flow of argon gas (usually 14 to 18 liters per minute) is introduced between the two outermost tubes of the torch and an electrical spark is applied for a short time to introduce free electrons into the gas stream. These electrons interact with the radio-frequency magnetic field of the induction coil and are accelerated first in one direction, then the other, as the field changes at high frequency (usually 27.12 MHz or 40 MHz). The accelerated electrons collide with argon atoms, and sometimes a collision causes an argon atom to part with one of its electrons. The released electron is in turn accelerated by the rapidly changing magnetic field. The process continues until the rate of release of new electrons in collisions is balanced by the rate of recombination of electrons with argon ions (atoms that have lost an electron). This produces a ‘fireball’ that consists mostly of argon atoms with a rather small fraction of free electrons and argon ions. | 3 | Analytical Chemistry |
Specific mutations in different splice sites in various genes that cause inherited disorders, including, for example, Type 1 diabetes (e.g., PTPN22, TCF1 (HCF-1A)), hypertension (e.g., LDL, LDLR, LPL), Marfan syndrome (e.g., FBN1, TGFBR2, FBN2), cardiac diseases (e.g., COL1A2, MYBPC3, ACTC1), eye disorders (e.g., EVC, VSX1) have been uncovered. A few example mutations in the donor and acceptor splice sites in different genes causing a variety of inherited disorders identified using S&S are shown in Table 2. | 1 | Biochemistry |
A chemical analysis of a sample of methyl acetate provides the following elemental data: 48.64% carbon (C), 8.16% hydrogen (H), and 43.20% oxygen (O). For the purposes of determining empirical formulas, it's assumed that we have 100 grams of the compound. If this is the case, the percentages will be equal to the mass of each element in grams.
:Step 1: Change each percentage to an expression of the mass of each element in grams. That is, 48.64% C becomes 48.64 g C, 8.16% H becomes 8.16 g H, and 43.20% O becomes 43.20 g O.
:Step 2: Convert the amount of each element in grams to its amount in moles
:Step 3: Divide each of the resulting values by the smallest of these values (2.7)
:Step 4: If necessary, multiply these numbers by integers in order to get whole numbers; if an operation is done to one of the numbers, it must be done to all of them.
Thus, the empirical formula of methyl acetate is . This formula also happens to be methyl acetate's molecular formula. | 3 | Analytical Chemistry |
Many other methods have been developed to treat the contamination of dyes in a solution, including electrochemical degradation, ion exchange, laser degradation, and absorption onto various solids such as activated charcoal. | 3 | Analytical Chemistry |
Many experiments have suggested that leaf tissues of living plants emit methane. Other research has indicated that the plants are not actually generating methane; they are just absorbing methane from the soil and then emitting it through their leaf tissues. | 1 | Biochemistry |
In 1995, Robert Conry demonstrated that intramuscular injection of naked RNA encoding carcinoembryonic antigen elicited antigen-specific antibody responses. Then, it was elaborated by demonstrating that dendritic cells(DCs) exposed to mRNA coding for specific antigens or to total mRNA extracted from tumor cells and injected into tumor-bearing mice induced T cell immune responses and inhibited the growth of tumors. Then, researchers started to approach mRNA transfected DCs using vaccines based on ex vivo IVT mRNA-transfected DCs. Meanwhile, Argos Therapeutics had initiated a Phase III clinical trial using DCs with advanced renal cell carcinoma in 2015 (NCT01582672) but it was terminated due to the lack of efficacy.
For further application, IVT mRNA was optimized for in situ transfections of DCs in vivo. It improved the translation efficiency and stability of IVT mRNA and enhanced the presentation of the mRNA-encoded antigen on MHC class I and II molecules. Then, they found out that the direct injection of naked IVT mRNA into lymph nodes was the most effective way to induce T cell responses. Based on this discovery, first-in-human testing of the injection of naked IVT mRNA encoding cancer antigens by BioNTech has started with patients with melanoma (NCT01684241).
Recently, the new cancer immunotherapy, the combining of self-delivering RNA(sd-rxRNA) and adoptive cell transfer(ACT) therapy, was invented by RXi Pharmaceuticals and the Karolinska Institute. In this therapy, the sd-rxRNA eliminated the expression of immunosuppressive receptors and proteins in therapeutic immune cells so it improved the ability of immune cells to destroy the tumor cells. Then, the PD-1 targeted sd-rxRNA helped increasing the anti-tumor activity of tumor-infiltrating lymphocytes (TIL) against melanoma cells. Based on this idea, the mRNA-4157 has been tested and passed phase I clinical trial.
Cytosolic nucleic acid-sensing pathways can enhance immune response to cancer. RIG-I agonist, stem loop RNA (SLR) 14. Tumor growth was significantly delayed and extended survival in mice. SLR14 improved antitumor efficacy of anti-PD1 antibody over single-agent treatment. SLR14 was absorbed by CD11b+ myeloid cells in the tumor microenvironment. Genes associated with immune defense were significantly up-regulated, along with increased CD8+ T lymphocytes, NK cells, and CD11b+ cells. SLR14 inhibited nonimmunogenic B16 tumor growth, leaving immune memory. | 1 | Biochemistry |
Bacterial recombination is a type of genetic recombination in bacteria characterized by DNA transfer from one organism called donor to another organism as recipient. This process occurs in three main ways:
* Transformation, the uptake of exogenous DNA from the surrounding environment.
* Transduction, the virus-mediated transfer of DNA between bacteria.
* Conjugation, the transfer of DNA from one bacterium to another via cell-to-cell contact.
The final result of conjugation, transduction, and/or transformation is the production of genetic recombinants, individuals that carry not only the genes they inherited from their parent cells but also the genes introduced to their genomes by conjugation, transduction, and/or transformation.
Recombination in bacteria is ordinarily catalyzed by a RecA type of recombinase. These recombinases promote repair of DNA damages by homologous recombination.
The ability to undergo natural transformation is present in at least 67 bacterial species. Natural transformation is common among pathogenic bacterial species. In some cases, the DNA repair capability provided by recombination during transformation facilitates survival of the infecting bacterial pathogen. Bacterial transformation is carried out by numerous interacting bacterial gene products. | 1 | Biochemistry |
The properties molar internal energy, , and entropy, , defined by the first and second laws of thermodynamics, hence all thermodynamic properties of a simple compressible substance, can be specified, up to a constant of integration, by two measurable functions, a mechanical equation of state, , and a constant volume specific heat, . | 7 | Physical Chemistry |
In synaptic vesicle fusion, the vesicle must be within a few nanometers of the target membrane for the fusion process to begin. This closeness allows the cell membrane and the vesicle to exchange lipids which is mediated by certain proteins which remove water that comes between the forming junction. Once the vesicle is in position it must wait until Ca enters the cell by the propagation of an action potential to the presynaptic membrane. Ca binds to specific proteins, one of which is Synaptotagmin, in neurons which triggers the complete fusion of the vesicle with the target membrane.
SNARE proteins are also thought to help mediate which membrane is the target of which vesicle. | 1 | Biochemistry |
Five basic modes of alternative splicing are generally recognized.
* Exon skipping or cassette exon: in this case, an exon may be spliced out of the primary transcript or retained. This is the most common mode in mammalian pre-mRNAs.
* Mutually exclusive exons: One of two exons is retained in mRNAs after splicing, but not both.
* Alternative donor site: An alternative 5 splice junction (donor site) is used, changing the 3 boundary of the upstream exon.
* Alternative acceptor site: An alternative 3 splice junction (acceptor site) is used, changing the 5 boundary of the downstream exon.
* Intron retention: A sequence may be spliced out as an intron or simply retained. This is distinguished from exon skipping because the retained sequence is not flanked by introns. If the retained intron is in the coding region, the intron must encode amino acids in frame with the neighboring exons, or a stop codon or a shift in the reading frame will cause the protein to be non-functional. This is the rarest mode in mammals but the most common in plants.
In addition to these primary modes of alternative splicing, there are two other main mechanisms by which different mRNAs may be generated from the same gene; multiple promoters and multiple polyadenylation sites. Use of multiple promoters is properly described as a transcriptional regulation mechanism rather than alternative splicing; by starting transcription at different points, transcripts with different 5-most exons can be generated. At the other end, multiple polyadenylation sites provide different 3 end points for the transcript. Both of these mechanisms are found in combination with alternative splicing and provide additional variety in mRNAs derived from a gene.
<br>These modes describe basic splicing mechanisms, but may be inadequate to describe complex splicing events. For instance, the figure to the right shows 3 spliceforms from the mouse hyaluronidase 3 gene. Comparing the exonic structure shown in the first line (green) with the one in the second line (yellow) shows intron retention, whereas the comparison between the second and the third spliceform (yellow vs. blue) exhibits exon skipping. A model nomenclature to uniquely designate all possible splicing patterns has recently been proposed. | 1 | Biochemistry |
In larger urban centres, studies have noted that lesbian, gay, bisexual, transgender and queer (LGBTQ+) populations are among the fastest-growing users of fertility care. IVF is increasingly being used to allow lesbian and other LGBT couples to share in the reproductive process through a technique called reciprocal IVF. The eggs of one partner are used to create embryos which the other partner carries through pregnancy. For gay male couples, many elect to use IVF through gestational surrogacy, where one partners sperm is used to fertilise a donor ovum, and the resulting embryo is transplanted into a surrogate carriers womb. There are various IVF options available for same-sex couples including, but not limited to, IVF with donor sperm, IVF with a partners oocytes, reciprocal IVF, IVF with donor eggs, and IVF with gestational surrogate. IVF with donor sperm can be considered traditional IVF for lesbian couples, but reciprocal IVF or using a partners oocytes are other options for lesbian couples trying to conceive to include both partners in the biological process. Using a partners oocytes is an option for partners who are unsuccessful in conceiving with their own, and reciprocal IVF involves undergoing reproduction with a donor egg and sperm that is then transferred to a partner who will gestate. Donor IVF involves conceiving with a third partys eggs. Typically, for gay male couples hoping to use IVF, the common techniques are using IVF with donor eggs and gestational surrogates. | 1 | Biochemistry |
Affinity capillary electrophoresis (ACE) refers to a number of techniques which rely on specific and nonspecific binding interactions to facilitate separation and detection through a formulary approach in accordance with the theory of electromigration. Using the intermolecular interactions between molecules occurring in free solution or mobilized onto a solid support, ACE allows for the separation and quantitation of analyte concentrations and binding and dissociation constants between molecules. As affinity probes in CAE, fluorophore-labeled compounds with affinities for the target molecules are employed. With ACE, scientists hope to develop strong binding drug candidates, understand and measure enzymatic activity, and characterize the charges on proteins. Affinity capillary electrophoresis can be divided into three distinct techniques: non-equilibrium electrophoresis of equilibrated sample mixtures, dynamic equilibrium ACE, and affinity-based ACE.
Nonequilibrium electrophoresis of equilibrated sample mixtures is generally used in the separation and study of binding interactions of large proteins and involves combining both the analyte and its receptor molecule in a premixed sample.
These receptor molecules often take the form of affinity probes consisting of fluorophore-labeled molecules that will bind to target molecules that are mixed with the sample being tested. This mixture, and its subsequent complexes, are then separated through capillary electrophoresis. Because the original mixture of analyte and receptor molecule were bound together in an equilibrium, the slow dissociation of these two bound molecules during the electrophoretic experiment will result in their separation and a subsequent shift in equilibrium towards further dissociation. The characteristic smear pattern produced by the slow release of the analyte from the complex during the experiment can be used to calculate the dissociation constant of the complex.
Dynamic equilibrium ACE involves the combination of the analyte found in the sample and its receptor molecule found in the buffered solution in the capillary tube so that binding and separation only occur in the instrument. It is assumed for dynamic equilibrium affinity capillary electrophoresis that ligand-receptor binding occurs rapidly when the analyte and buffer are mixed. Binding constants are generally derived from this technique based upon the peak migration shift of the receptor which is dependent upon the concentration of the analyte in the sample.
Affinity-based capillary electrophoresis, also known as capillary electroaffinity chromatography (CEC), involves the binding of analyte in sample to an immobilized receptor molecule on the capillary wall, microbeads, or microchannels. CEC offers the highest separation efficacy of all three ACE techniques as non-matrixed sample components are washed away and the ligand then be released and analyzed.
Affinity capillary electrophoresis takes the advantages of capillary electrophoresis and applies them to the study of protein interactions. ACE is advantageous because it has a high separation efficiency, has a shorter analysis time, can be run at physiological pH, and involves low consumption of ligand/molecules. In addition, the composition of the protein of interest does not have to be known in order to run ACE studies. The main disadvantage, though, is that it does not give much stoichiometric information about the reaction being studied. | 1 | Biochemistry |
Redox gradients are commonly found in the environment as functions of both space and time, particularly in soils and aquatic environments. Gradients are caused by varying physiochemical properties including availability of oxygen, soil hydrology, chemical species present, and microbial processes. Specific environments that are commonly characterized by redox gradients include waterlogged soils, wetlands, contaminant plumes, and marine pelagic and hemipelagic sediments.
The following is a list of common reactions that occur in the environment in order from oxidizing to reducing (organisms performing the reaction in parentheses):
# Aerobic respiration (aerobes: aerobic organisms)
# Denitrification (denitrifiers: denitrifying bacteria)
# Manganese reduction (Manganese reducers)
# Iron reduction (iron reducers: iron-reducing bacteria)
# Sulfate reduction (sulfate reducers: Sulfur-reducing bacteria)
# Methanogenesis (methanogens) | 7 | Physical Chemistry |
Many cancers can raise LDH levels, so LDH may be used as a tumor marker, but at the same time, it is not useful in identifying a specific kind of cancer. Measuring LDH levels can be helpful in monitoring treatment for cancer. Noncancerous conditions that can raise LDH levels include heart failure, hypothyroidism, anemia, pre-eclampsia, meningitis, encephalitis, acute pancreatitis, HIV and lung or liver disease.
Tissue breakdown releases LDH, and therefore, LDH can be measured as a surrogate for tissue breakdown (e.g., hemolysis). LDH is measured by the lactate dehydrogenase (LDH) test (also known as the LDH test or lactic acid dehydrogenase test). Comparison of the measured LDH values with the normal range help guide diagnosis. | 1 | Biochemistry |
Cyclic AMP-dependent protein kinases (protein kinase A) are activated by the signal cascade originated by the activation of the G protein Gs by the LHCG-receptor. Activated Gs binds the enzyme adenylate cyclase and this leads to the production of cyclic AMP (cAMP). Cyclin AMP-dependent protein kinases are present as tetramers with two regulatory subunits and two catalytic subunits. Upon binding of cAMP to the regulatory subunits, the catalytic units are released and initiate the phosphorylation of proteins leading to the physiologic action. Cyclic AMP is degraded by phosphodiesterase and release 5’AMP. One of the targets of protein kinase A is the Cyclic AMP Response Element Binding Protein, CREB, which binds DNA in the cell nucleus via direct interactions with specific DNA sequences called cyclic AMP response elements (CRE); this process results in the activation or inactivation of gene transcription.
The signal is amplified by the involvement of cAMP and the resulting phosphorylation. The process is modified by prostaglandins. Other cellular regulators that participate are the intracellular calcium concentration regulated by phospholipase C activation, nitric oxide, and other growth factors.
Other pathways of signaling exist for the LHCGR. | 1 | Biochemistry |
* NSD1 ()
* PELP-1 (proline, glutamic acid and leucine rich protein 1)
* RIP140 (receptor-interacting protein 140)
* YAP
* WWTR1 (TAZ) | 1 | Biochemistry |
DEPBT (3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one) is a peptide coupling reagent used in peptide synthesis. It shows remarkable resistance to racemization.
Fmoc-Dab(Mtt)-OH, a commercially available amino acid building block for solid-phase peptide synthesis (SPPS), was proven to undergo rapid lactamization, instead of reacting with the N-terminal end of the peptide. Compared with other commercially available coupling reagents, DEPBT has shown superior performance in coupling Fmoc-Dab(Mtt)-OH to the N-terminal end of peptide during SPPS, though the approach was regarded as costly and tedious. | 1 | Biochemistry |
A powerful demonstration of stacking is found in the buckycatcher. This molecular tweezer is based on two concave buckybowls with a perfect fit for one convex fullerene molecule. Complexation takes place simply by evaporating a toluene solution containing both compounds. In solution an association constant of 8600 M is measured based on changes in NMR chemical shifts.
Pi stacking is prevalent in protein crystal structures, and also contributes to the interactions between small molecules and proteins. As a result, pi–pi and cation–pi interactions are important factors in rational drug design. One example is the FDA-approved acetylcholinesterase (AChE) inhibitor tacrine which is used in the treatment of Alzheimer's disease. Tacrine is proposed to have a pi stacking interaction with the indolic ring of Trp84, and this interaction has been exploited in the rational design of novel AChE inhibitors. | 6 | Supramolecular Chemistry |
The citric acid cycle is regulated mainly by the availability of key substrates, particularly the ratio of NAD to NADH and the concentrations of calcium, inorganic phosphate, ATP, ADP, and AMP. Citrate – the ion that gives its name to the cycle – is a feedback inhibitor of citrate synthase and also inhibits PFK, providing a direct link between the regulation of the citric acid cycle and glycolysis. | 1 | Biochemistry |
Another widely used application of the immobilization approach together with enzymes has been the enzymatic reactions on immobilized substrates. This approach facilitates the analysis of enzyme activities and mimics the performance of enzymes on e.g. cell walls. | 4 | Stereochemistry |
The Geochemical Ocean Sections Study (GEOSECS) was a global survey of the three-dimensional distributions of chemical, isotopic, and radiochemical tracers in the ocean. A key objective was to investigate the deep thermohaline circulation of the ocean, using chemical tracers, including radiotracers, to establish the pathways taken by this.
Expeditions undertaken during GEOSECS took place in the Atlantic Ocean from July 1972 to May 1973, in the Pacific Ocean from August 1973 to June 1974, and in the Indian Ocean from December 1977 to March 1978.
Measurements included those of physical oceanographic quantities such as temperature, salinity, pressure and density, chemical / biological quantities such as total inorganic carbon, alkalinity, nitrate, phosphate, silicic acid, oxygen and apparent oxygen utilisation (AOU), and radiochemical / isotopic quantities such as carbon-13, carbon-14 and tritium. | 9 | Geochemistry |
Glycine encephalopathy, also known as non-ketotic hyperglycinemia (NKH), is a primary disorder of the glycine cleavage system, resulting from lowered function of the glycine cleavage system causing increased levels of glycine in body fluids. The disease was first clinically linked to the glycine cleavage system in 1969. Early studies showed high levels of glycine in blood, urine and cerebrospinal fluid. Initial research using carbon labeling showed decreased levels of CO and serine production in the liver, pointing directly to deficiencies glycine cleavage reaction. Further research has shown that deletions and mutations in the 5' region of the P-protein are the major genetic causes of nonketotic hyperglycinemia. . In more rare cases, a missense mutation in the genetic code of the T-protein, causing the histidine in position 42 to be mutated to arginine, was also found to result in nonketotic hypergycinemia. This specific mutation directly affected the active site of the T-protein, causing lowered efficiency of the glycine cleavage system. | 1 | Biochemistry |
A number of different classification systems of the patterns of leaf veins (venation or veination) have been described, starting with Ettingshausen (1861), together with many different descriptive terms, and the terminology has been described as "formidable". One of the commonest among these is the Hickey system, originally developed for "dicotyledons" and using a number of Ettingshausens terms derived from Greek (1973–1979): (see also': Simpson Figure 9.12, p. 468) | 5 | Photochemistry |
Some sulfate-reducing bacteria produce hydrogen sulfide, which can cause sulfide stress cracking. Acidithiobacillus bacteria produce sulfuric acid; Acidothiobacillus thiooxidans frequently damages sewer pipes. Ferrobacillus ferrooxidans directly oxidizes iron to iron oxides and iron hydroxides; the rusticles forming on the RMS Titanic wreck are caused by bacterial activity. Other bacteria produce various acids, both organic and mineral, or ammonia.
In presence of oxygen, aerobic bacteria like Acidithiobacillus thiooxidans, Thiobacillus thioparus, and Thiobacillus concretivorus, all three widely present in the environment, are the common corrosion-causing factors resulting in biogenic sulfide corrosion.
Without presence of oxygen, anaerobic bacteria, especially Desulfovibrio and Desulfotomaculum, are common. Desulfovibrio salixigens requires at least 2.5% concentration of sodium chloride, but D. vulgaris and D. desulfuricans can grow in both fresh and salt water. D. africanus is another common corrosion-causing microorganism. The genus Desulfotomaculum comprises sulfate-reducing spore-forming bacteria; Dtm. orientis and Dtm. nigrificans are involved in corrosion processes. Sulfate-reducers require a reducing environment; an electrode potential lower than -100 mV is required for them to thrive. However, even a small amount of produced hydrogen sulfide can achieve this shift, so the growth, once started, tends to accelerate.
Layers of anaerobic bacteria can exist in the inner parts of the corrosion deposits, while the outer parts are inhabited by aerobic bacteria.
Some bacteria are able to utilize hydrogen formed during cathodic corrosion processes.
Bacterial colonies and deposits can form concentration cells, causing and enhancing galvanic corrosion. [https://web.archive.org/web/20060504072637/http://httd.njuct.edu.cn/MatWeb/corrosie/c_bio.htm].
Bacterial corrosion may appear in form of pitting corrosion, for example in pipelines of the oil and gas industry. Anaerobic corrosion is evident as layers of metal sulfides and hydrogen sulfide smell. On cast iron, a graphitic corrosion selective leaching may be the result, with iron being consumed by the bacteria, leaving graphite matrix with low mechanical strength in place.
Various corrosion inhibitors can be used to combat microbial corrosion. Formulae based on benzalkonium chloride are common in oilfield industry.
Microbial corrosion can also apply to plastics, concrete, and many other materials. Two examples are Nylon-eating bacteria and Plastic-eating bacteria. | 8 | Metallurgy |
Electrochemical reactions in water are better analyzed by using the ion-electron method, where H, OH ion, HO and electrons (to compensate the oxidation changes) are added to the cell's half-reactions for oxidation and reduction. | 7 | Physical Chemistry |
Molecules interact at close range through intermolecular forces (the "van der Waals
forces"), which cause minute shifts of the electron density distributions (relative
the distributions of electrons when the molecules are not interacting).
Intermolecular forces are repulsive at near range, where electron exchange
forces dominate the interaction, and attractive at somewhat greater separations,
where the dispersion forces are active. (If separations are further increased, all
intermolecular forces fall off rapidly and may be totally neglected.)
Repulsion and attraction are due, respectively, to the small defects or
excesses of electron densities of molecular complexes in the space
between the interacting molecules, which often result in interaction-induced
electric dipole moments that contribute some to interaction-induced emission and
absorption intensities. The resulting dipoles are referred to as exchange
force-induced dipole and dispersion force-induced dipoles, respectively.
Other dipole induction mechanisms also exist in molecular (as opposed to
monatomic) gases and in mixtures of gases, when molecular gases are present.
Molecules have centers of positive charge (the nuclei), which are surrounded by
a cloud of electrons. Molecules thus may be thought of being surrounded by various
electric multipolar fields which will polarize any collisional partner
momentarily in a fly-by encounter, generating the so-called multipole-induced
dipoles. In diatomic molecules such as H and N, the lowest-order
multipole moment is the quadrupole, followed by a hexadecapole, etc., hence the
quadrupole-induced, hexadecapole-induced,... dipoles. Especially the former is often
the strongest, most significant of the induced dipoles contributing to CIA and CIE.
Other induced dipole mechanisms exist. In collisional systems involving
molecules of three or more atoms (CO, CH...), collisional frame
distortion may be an important induction mechanism. Collision-induced
emission and absorption by simultaneous collisions of three or more particles
generally do involve pairwise-additive dipole components, as well as important
irreducible dipole contributions and their spectra. | 7 | Physical Chemistry |
The genome size, and the number of genes it encodes varies widely between organisms. The smallest genomes occur in viruses, and viroids (which act as a single non-coding RNA gene). Conversely, plants can have extremely large genomes, with rice containing >46,000 protein-coding genes. The total number of protein-coding genes (the Earth's proteome) is estimated to be 5 million sequences.
Although the number of base-pairs of DNA in the human genome has been known since the 1950s, the estimated number of genes has changed over time as definitions of genes, and methods of detecting them have been refined. Initial theoretical predictions of the number of human genes in the 1960s and 1970s were based on mutation load estimates and the numbers of mRNAs and these estimates tended to be about 30,000 protein-coding genes. During the 1990s there were guesstimates of up to 100,000 genes and early data on detection of mRNAs (expressed sequence tags) suggested more than the traditional value of 30,000 genes that had been reported in the textbooks during the 1980s.
The initial draft sequences of the human genome confirmed the earlier predictions of about 30,000 protein-coding genes however that estimate has fallen to about 19,000 with the ongoing GENCODE annotation project . The number of noncoding genes is not known with certainty but the latest estimates from Ensembl suggest 26,000 noncoding genes. | 1 | Biochemistry |
Halonium ylides can be prepared from allyl halides and metal carbenoids. After a [2,3]-rearrangement, a homoallylhalide is obtained.
The active form of Tebbe's reagent is often considered a titanium ylide. Like the Wittig reagent, it is able to replace the oxygen atom on carbonyl groups with a methylene group. Compared with the Wittig reagent, it has more functional group tolerance. | 0 | Organic Chemistry |
Classical dyes and pigments produce color by the absorption and reflection of light; these are the materials that make a major impact on the color of our daily lives. In 2000, world production of organic dyes was 800,000 tonnes and of organic pigments, 250,000 tonnes and the volume has grown at a steady rate throughout the early years of this century. In 2019 the value of the organic dyes/pigments market is forecast to be $19.5bn. Their value is exceeded by the very large production of inorganic pigments. Organic dyes are used mainly to color textile fibers, paper, hair, leather, while pigments are used largely in inks, paints, plastic and cosmetics. Both are used in the growth area of the digital printing of textiles, paper and other surfaces.
Dyes are also made using the properties of chromic substances: Examples being
Photochromic dyes and
Thermochromic dyes | 5 | Photochemistry |
Example values of activity coefficients of sodium chloride in aqueous solution are given in the table. In an ideal solution, these values would all be unity. The deviations tend to become larger with increasing molality and temperature, but with some exceptions. | 7 | Physical Chemistry |
There are several ways to approach the topic of premelting, the most figurative way might be thermodynamically. A more detailed or abstract view on what physics is important for premelting is given by the Lifshitz and the Landau theories.
One always starts with looking at a crystalline solid phase (fig. 1: (1) solid) and another phase. This second phase (fig. 1: (2)) can either be vapour, liquid or solid. Further it can consist of the same chemical material or another. In the case of the second phase being a solid of the same chemical material one speaks of grain boundaries. This case is very important when looking at polycrystalline materials. | 7 | Physical Chemistry |
If a beam of particles enters a thin layer of material of thickness , the flux of the beam will decrease by according to
where is the total cross section of all events, including scattering, absorption, or transformation to another species. The volumetric number density of scattering centers is designated by . Solving this equation exhibits the exponential attenuation of the beam intensity:
where is the initial flux, and is the total thickness of the material. For light, this is called the Beer–Lambert law. | 7 | Physical Chemistry |
Fluorescent biomaterials are a possible way of using external factors to observe a pathway more visibly. The method involves fluorescently labeling peptide molecules that would alter an organisms natural pathway. When this peptide is inserted into the organisms cell, it can induce a different reaction. This method can be used, for example to treat a patient and then visibly see the treatment's outcome. | 1 | Biochemistry |
GTPases are a large family of hydrolase enzymes that bind to the nucleotide guanosine triphosphate (GTP) and hydrolyze it to guanosine diphosphate (GDP). The GTP binding and hydrolysis takes place in the highly conserved P-loop "G domain", a protein domain common to many GTPases. | 1 | Biochemistry |
Biosurvey protocols have been published for use in different waterbody types and ecoregions. One such publication is the Rapid Bioassessment Protocol for streams and rivers, issued by the U.S. Environmental Protection Agency (EPA). Such protocols provide a structure for developing an IBI, which may include measures such as richness of taxa (species, genera, etc.) and proportion of pollution-tolerant or intolerant taxa. | 2 | Environmental Chemistry |
Ribosome profiling is a method that can reveal pausing sites through sequencing the ribosome protected fragments (RPFs or footprints) to map ribosome occupancy on the mRNA. Ribosome profiling has the ability to reveal the ribosome pause sites in the whole transcriptome. When the kinetics layer is added, it discloses the time of the pause, and the translation takes place. Ribosome profiling is however still in early stages and has biases that need to be explored further. Ribosome profiling allows for translation to be measured more accurately and precisely. During this process, translation needs to be stopped in order for ribosome profiling to be performed. This may cause a problem with ribosome profiling because the methods that are used to stop translation in an experiment can impact the outcome, which causes incorrect results. Ribosome profiling is useful for getting specific information on translation and the process of protein synthesis. | 1 | Biochemistry |
The ICBM carries out fundamental and applied research in marine and environmental sciences. Interdisciplinary research will provide understanding of the various interactions of marine environmental systems.
The research focuses on marine biogeochemical cycles and energy fluxes, as well as on the functional role of marine biodiversity, especially in coastal zones worldwide, and in the oceans.
The mathematic modelling of different environmental systems is complemented by modern, high-resolution analytics and in-house marine sensor developments.
The institute is composed of three sections covering altogether 18 research groups:
*Section Geochemistry and Analytics
*Section Biology and Ecology
*Section Physics and Modelling
For a better understanding of the complex relations the ICBM aims to foster interdisciplinary research. | 9 | Geochemistry |
When carbon dioxide diffuses as a dissolved gas from the tissue capillaries, it binds to the α-amino terminus of the globulin chain, forming Carbaminohemoglobin. Carbaminohemoglobin is able to directly stabilise the T conformation as part of the carbon dioxide Bohr effect. Deoxyhemoglobin in turn subsequently increases the uptake of carbon dioxide in the form of favouring the formation of Bicarbonate as well as Carbaminohemoglobin through the Haldane effect. | 1 | Biochemistry |
Cellulose, fibre starch that is indigestible to humans, and a filler in some low calorie foods, can be and is made from sawdust, as well as from other plant sources. While there is no documentation for the persistent rumor, based upon Upton Sinclairs novel The Jungle', that sawdust was used as a filler in sausage, cellulose derived from sawdust was and is used for sausage casings. Sawdust-derived cellulose has also been used as a filler in bread.
When cereals were scarce, sawdust was sometimes an ingredient in kommissbrot. Auschwitz concentration camp survivor, Dr. Miklós Nyiszli, reports in Auschwitz: A Doctors Eyewitness Account' that the subaltern medical staff, who served Dr. Josef Mengele, subsisted on "bread made from wild chestnuts sprinkled with sawdust".
Sawdust is a primary ingredient in many types of processed chicken. | 2 | Environmental Chemistry |
Atmospheric pressure (AP) matrix-assisted laser desorption/ionization (MALDI) is an ionization technique (ion source) that in contrast to vacuum MALDI operates at normal atmospheric environment. The main difference between vacuum MALDI and AP-MALDI is the pressure in which the ions are created. In vacuum MALDI, ions are typically produced at 10 mTorr or less while in AP-MALDI ions are formed in atmospheric pressure. In the past, the main disadvantage of the AP-MALDI technique compared to the conventional vacuum MALDI has been its limited sensitivity; however, ions can be transferred into the mass spectrometer with high efficiency and attomole detection limits have been reported. AP-MALDI is used in mass spectrometry (MS) in a variety of applications ranging from proteomics to drug discovery. Popular topics that are addressed by AP-MALDI mass spectrometry include: proteomics; mass analysis of DNA, RNA, PNA, lipids, oligosaccharides, phosphopeptides, bacteria, small molecules and synthetic polymers, similar applications as available also for vacuum MALDI instruments. The AP-MALDI ion source is easily coupled to an ion trap mass spectrometer or any other MS system equipped with electrospray ionization (ESI) or nanoESI source.
MALDI with ionization at reduced pressure is known to produce mainly singly-charged ions (see "Ionization mechanism" below). In contrast, ionization at atmopsheric pressure can generate highly-charged analytes as was first shown for infrared and later also for nitrogen lasers. Multiple charging of analytes is of great importance, because it allows to measure high-molecular-weight compounds like proteins in instruments, which provide only smaller m/z detection ranges such as quadrupoles. Besides the pressure, the composition of the matrix is important to achieve this effect. | 1 | Biochemistry |
The Viking missions to Mars in the 1970s conducted the first experiments which were explicitly designed to look for biosignatures on another planet. Each of the two Viking landers carried three life-detection experiments which looked for signs of metabolism; however, the results were declared inconclusive. | 2 | Environmental Chemistry |
# Agriculture and Resource Management Council of Australia and New Zealand, “Prediction of Food Intake” In Feeding Standards for Australian Livestock; Ruminants (CSIRO Publishing, 1990) 261.
# Bentley, David, Hegarty, Rodger and Alford, Andrew, “Managing Livestock Enterprises in Australia’s Extensive Rangelands for Greenhouse Gas and Environmental Outcomes: A Pastoral Company Perspective,” Australian Journal of Experimental Agriculture 2, no. 48, (January 2008) 60–64.
# Brightling, Anthony, Brightling, Tony and Fowler, Diane, "Issues with Cattle" In Livestock Diseases in Australia; Diseases of Cattle, Sheep, Goats and Farm Dogs (C.H. Jerram & Associates, 2006) 21.
# Buckley, David, The Cattle Parasite Atlas; A Regional Guide to Cattle Parasite Control in Australia (CSIRO publishing, 2005) 32.
# Cranston, Michael, “Leading Cattle Company The North Australian Pastoral” The North Queensland Register, 13 September 2012, 5.
# Commonwealth Scientific and Industrial Research Organization for the Australian Agricultural Council, Australian Journal of Experimental Agriculture and Animal Husbandry, (Cornell University Publishers, 1979) 261.
# Denniss, Siobhan, A Critique of Environmental Management Systems and their Relevance in the North Australian Pastoral Industry (Melbourne: MTEM Publishers, 2002) 28.
# Derner, Justin D, “Livestock Production Systems,” in Rangeland Systems: Processes, Management and Challenges, ed. David D. Briske, (Springer International Publishing: 2017) 347.
# Dundon, Peter, "Feedlots" In The Australian Feedlot Directory, (Elders Press Ltd, 1994) 12; Quevedo Martin Morgan, “The Beef Cattle Industry” In Australia's Livestock and Meat Industry, (Urbana-Champaign: University of Illinois Press, 1971) 2.
# Eldridge, David J, Poore, Alistair G. B, Ruiz-Colmenero, Marta, Letnic, Mike and Soliveres, Santiago, “Ecosystem structure, function, and composition in rangelands are negatively affected by livestock grazing” In Ecological Applications, Vol. 26 No. 4 (Ecological Society of America, 2016) 1273–1283.
# Gerber, Pierre, Mooney, Harold A. and Dijkman, Jeroen “Livestock in a Changing Landscape” In Experiences and Regional Perspectives, Vol. 2 (Stanford: Island Press, 2010) 23.
# Gerrard, Marjorie A and O’Leary, Patrick, “Union-Avoidance Strategies in the Meat Industry in Australia and the United States” In Frontiers of Labor: Comparative Histories of the United States and Australia, ed. Greg Patmore, (Illinois: University of Illinois Press, 2018), 129.
# Kahn, Lewis and Cottle, David John, “Beef Composition of the Northern Beef Herd” In Beef Cattle Production and Trade (CSIRO publishing, 2014) 180.
# Lesslie, Rob and Mewett, Jodie, “Land Use and Management - The Australian Context” in Land Use in Australia: Past, Present and Future, ed. Richard Trackway (Australian National University Press, 2018) 31.
# Meat and Livestock Australia, “Composite Breeds in the Northern Rangelands” In Beef Cattle Nutrition; An Introduction to the Essentials, (Meat and Livestock Australia, 2006) 76.
# Millard, Steve “Experiences with Composites: North Australia Pastoral Company (NAPCO)” Armidale Feeder Steer School; Conference Proceedings and Support Material no.1 (August 2003): 131–133.
# M. Moore, Raymond, “Proceedings” In Australian Grasslands, (Australian National University Press, 1970) 22.
# Pearson, Michael, “Exploring in the 1860s and 1870s,” in Pastoral Australia: Fortunes, Failures and Hard Yakka: A Historical Overview 1788-1967 ed Jane Lennon, (Collingwood: CSIRO publishing, 2010) 103–106.
# Phillips, Amy, “NAPCO for sale; The North Australian Pastoral Company, One of the Largest Cattle Producers and Landholders in Northern Australia, is for Sale” ABC Regional News NSW, 13 May 2013, 3.
# Reid, Robert L, "Agriculture and the Economy" from The Manual of Australian Agriculture (Butterworths publishers, 1990) 1.
# Velado-Alonso, Elena, Morales-Castilla, Ignacio, Rebollo, Salvador and Gómez-Sal, Antonio, “Relationships between the distribution of wildlife and livestock diversity” In Diversity and Distributions, Vol. 26 No. 10, (Wiley Publishers, 2010) 1264. | 2 | Environmental Chemistry |
The salt spray test (or salt fog test) is a standardized and popular corrosion test method, used to check corrosion resistance of materials and surface coatings. Usually, the materials to be tested are metallic (although stone, ceramics, and polymers may also be tested) and finished with a surface coating which is intended to provide a degree of corrosion protection to the underlying metal.
Salt spray testing is an accelerated corrosion test that produces a corrosive attack to coated samples in order to evaluate (mostly comparatively) the suitability of the coating for use as a protective finish. The appearance of corrosion products (rust or other oxides) is evaluated after a pre-determined period of time. Test duration depends on the corrosion resistance of the coating; generally, the more corrosion resistant the coating is, the longer the period of testing before the appearance of corrosion or rust.
The salt spray test is one of the most widespread and long-established corrosion tests. ASTMB117 was the first internationally recognized salt spray standard, originally published in 1939. Other important relevant standards are ISO9227, JISZ2371 and ASTMG85. | 8 | Metallurgy |
In the physical realm, many irreversible processes are present to which the inability to achieve 100% efficiency in energy transfer can be attributed. The following is a list of spontaneous events which contribute to the irreversibility of processes.
* Ageing (this claim is disputed, as aging has been demonstrated to be reversed in mice. NAD+ and telomerase have also been demonstrated to reverse ageing.)
* Death
* Time
* Heat transfer through a finite temperature difference
* Friction
* Plastic deformation
* Flow of electric current through a resistance
* Magnetization or polarization with a hysteresis
* Unrestrained expansion of fluids
* Spontaneous chemical reactions
* Spontaneous mixing of matter of varying composition/states
A Joule expansion is an example of classical thermodynamics, as it is easy to work out the resulting increase in entropy. It occurs where a volume of gas is kept in one side of a thermally isolated container (via a small partition), with the other side of the container being evacuated; the partition between the two parts of the container is then opened, and the gas fills the whole container. The internal energy of the gas remains the same, while the volume increases. The original state cannot be recovered by simply compressing the gas to its original volume, since the internal energy will be increased by this compression. The original state can only be recovered by then cooling the re-compressed system, and thereby irreversibly heating the environment. The diagram to the right applies only if the first expansion is "free" (Joule expansion), i.e. there can be no atmospheric pressure outside the cylinder and no weight lifted. | 7 | Physical Chemistry |
Murexide test is a color test for uric acid and some other purines. The (solid) sample is first treated with small volume of a concentrated acid such as hydrochloric acid, nitric acid, which is slowly evaporated away; subsequent addition of ammonia (NH) gives a purple color if uric acid was present, due to formation of murexide, or a yellow color that turns to red on heating if xanthine or its derivatives are present. | 3 | Analytical Chemistry |
The unit of osmotic concentration is the osmole. This is a non-SI unit of measurement that defines the number of moles of solute that contribute to the osmotic pressure of a solution. A milliosmole (mOsm) is 1/1,000 of an osmole. A microosmole (μOsm) (also spelled micro-osmole) is 1/1,000,000 of an osmole. | 3 | Analytical Chemistry |
Born in Feilding on 23 April 1931, Malcolm was educated at Feilding Agricultural High School. He then studied at Canterbury University College, graduating Master of Science with first-class honours in 1954. He was awarded an 1851 Exhibition Memorial Scholarship, and completed doctoral studies at the University of Manchester in 1956.
In 1958, Malcolm married Sheila Mary Wilson, and the couple went on to have four children.
After a short period as an assistant lecturer at the University of Manchester in 1956–57, Malcolm returned to New Zealand. He was appointed as a lecturer in chemistry at the University of Otago in 1958, rising to the rank of reader. In 1969, he was appointed as professor of physical chemistry at Massey University, and was the first professor of chemistry at that institution. He later served as dean of science from 1984 to 1994. Following his retirement in 1995, he was conferred the title of professor emeritus. Malcolm was elected a Fellow of the New Zealand Institute of Chemistry (NZIC) in 1966, and served as president of the NZIC in 1977.
Malcolm died in Palmerston North on 11 August 2019. | 7 | Physical Chemistry |
There are five UCP homologs known in mammals. While each of these performs unique functions, certain functions are performed by several of the homologs. The homologs are as follows:
*UCP1, also known as thermogenin or SLC25A7
*UCP2, also known as SLC25A8
*UCP3, also known as SLC25A9
*UCP4, also known as SLC25A27
*UCP5, also known as SLC25A14 | 1 | Biochemistry |
Dimer fatty acids are produced from different fatty acids by heating. Necessary are a fatty acid with conjugated double bonds or other unsaturated fatty acids. Examples of such fatty acids are conjugated linoleic acids. The reaction is carried out via Diels-Alder addition, whereby a partially unsaturated C6 ring is formed. Besides the dimer, trimers as well as (unreacted) monomers of the fatty acids may be present in the mixture. | 0 | Organic Chemistry |
The Analytical Scientist named Barbas to their 2016 Power List in recognition of her contributions to chemistry. In 2017, she was honored by Acta Sanitaria for her chemical research linking diabetes and obesity. In 2018, she received the International Award of the Belgian Society of Pharmaceutical Sciences. | 3 | Analytical Chemistry |
The principle behind fluorescence is that the fluorescent moiety contains electrons which can absorb a photon and briefly enter an excited state before either dispersing the energy non-radiatively or emitting it as a photon, but with a lower energy, i.e., at a longer wavelength (wavelength and energy are inversely proportional).
The difference in the excitation and emission wavelengths is called the Stokes shift, and the time that an excited electron takes to emit the photon is called a lifetime. The quantum yield is an indicator of the efficiency of the dye (it is the ratio of emitted photons per absorbed photon), and the extinction coefficient is the amount of light that can be absorbed by a fluorophore. Both the quantum yield and extinction coefficient are specific for each fluorophore and multiplied together calculates the brightness of the fluorescent molecule. | 1 | Biochemistry |
A heat engine is a system that converts heat to usable energy, particularly mechanical energy, which can then be used to do mechanical work. While originally conceived in the context of mechanical energy, the concept of the heat engine has been applied to various other kinds of energy, particularly electrical, since at least the late 19th century. The heat engine does this by bringing a working substance from a higher state temperature to a lower state temperature. A heat source generates thermal energy that brings the working substance to the higher temperature state. The working substance generates work in the working body of the engine while transferring heat to the colder sink until it reaches a lower temperature state. During this process some of the thermal energy is converted into work by exploiting the properties of the working substance. The working substance can be any system with a non-zero heat capacity, but it usually is a gas or liquid. During this process, some heat is normally lost to the surroundings and is not converted to work. Also, some energy is unusable because of friction and drag.
In general, an engine is any machine that converts energy to mechanical work. Heat engines distinguish themselves from other types of engines by the fact that their efficiency is fundamentally limited by Carnot's theorem of thermodynamics. Although this efficiency limitation can be a drawback, an advantage of heat engines is that most forms of energy can be easily converted to heat by processes like exothermic reactions (such as combustion), nuclear fission, absorption of light or energetic particles, friction, dissipation and resistance. Since the heat source that supplies thermal energy to the engine can thus be powered by virtually any kind of energy, heat engines cover a wide range of applications.
Heat engines are often confused with the cycles they attempt to implement. Typically, the term "engine" is used for a physical device and "cycle" for the models. | 7 | Physical Chemistry |
Prime editing was developed in the lab of David R. Liu at the Broad Institute and disclosed in Anzalone et al. (2019). Since then prime editing and the research that produced it have received widespread scientific acclaim, being called "revolutionary" and an important part of the future of editing. | 1 | Biochemistry |
This could happen in two different ways: ammonia itself might simply diffuse (as NH3) or be transported (as NH4+) across the cell membranes in and out of the extracellular space, or a shuttle system involving carrier molecules (amino acids) might be employed. Certainly, ammonia can diffuse across lipid membranes, and it has been shown that ammonia can be transported by K+/Cl− co-transporters. | 1 | Biochemistry |
Carbonate ions (CO) are essential in marine calcifying organisms, like plankton and shellfish, as they are required to produce their calcium carbonate () shells and skeletons. As the ocean acidifies, the increased uptake of CO by seawater increases the concentration of hydrogen ions, which lowers the pH of the water. This change in the chemical equilibrium of the inorganic carbon system reduces the concentration of these carbonate ions. This reduces the ability of these organisms to create their shells and skeletons.
The two polymorphs of calcium carbonate that are produced by marine organisms are aragonite and calcite. These are the materials that makes up most of the shells and skeletons of these calcifying organisms. Aragonite, for example, makes up nearly all mollusc shells, as well as the exoskeleton of corals. The formation of these materials is dependent on the saturation state of CaCO in ocean water. Waters which are saturated in are favorable to precipitation and formation of shells and skeletons, but waters which are undersaturated are corrosive to shells. In the absence of protective mechanisms, dissolution of calcium carbonate will occur. As colder arctic water absorbs more , the concentration of CO is reduced, therefore the saturation of calcium carbonate is lower in high-latitude oceans than it is in tropical or temperate oceans.
The undersaturation of CaCO causes the shells of calcifying organisms to dissolve, which can have devastating consequences to the ecosystem. As the shells dissolve, the organisms struggle to maintain proper health, which can lead to mass mortality. The loss of many of these species can lead to intense consequences on the marine food web in the Arctic Ocean, as many of these marine calcifying organisms are keystone species. Laboratory experiments on various marine biota in an elevated environment show that changes in aragonite saturation cause substantial changes in overall calcification rates for many species of marine organisms, including coccolithophore, foraminifera, pteropods, mussels, and clams.
Although the undersaturation of arctic water has been proven to have an effect on the ability of organisms to precipitate their shells, recent studies have shown that the calcification rate of calcifiers, such as corals, coccolithophores, foraminiferans and bivalves, decrease with increasing p, even in seawater supersaturated with respect to . Additionally, increased p has been found to have complex effects on the physiology, growth and reproductive success of various marine calcifiers. | 9 | Geochemistry |
Although enzymes are generally specific towards their substrate, enzymatic side activities (enzyme promiscuity) can lead to toxic or useless products. These side reactions proceed at much lower rates than their normal physiological reactions, but build-up of damaged metabolites can still be significant over time. For example, the mitochondrial malate dehydrogenase reduces alpha-ketoglutarate to L-2-hydroxyglutarate 10 times less efficiently than its regular substrate oxaloacetate, but L-2-hydroxyglutarate can still accumulate to several grams per day in a human adult. | 1 | Biochemistry |
SSCP used to be a way to discover new DNA polymorphisms apart from DNA sequencing but is now being supplanted by sequencing techniques on account of efficiency and accuracy. These days, SSCP is most applicable as a diagnostic tool in molecular biology. It can be used in genotyping to detect homozygous individuals of different allelic states, as well as heterozygous individuals that should each demonstrate distinct patterns in an electrophoresis experiment. SSCP is also widely used in virology to detect variations in different strains of a virus, the idea being that a particular virus particle present in both strains will have undergone changes due to mutation, and that these changes will cause the two particles to assume different conformations and, thus, be differentiable on an SSCP gel. | 1 | Biochemistry |
For an elementary step, there is a relationship between stoichiometry and rate law, as determined by the law of mass action. Almost all elementary steps are either unimolecular or bimolecular. For a unimolecular step
the reaction rate is described by , where is a unimolecular rate constant. Since a reaction requires a change in molecular geometry, unimolecular rate constants cannot be larger than the frequency of a molecular vibration. Thus, in general, a unimolecular rate constant has an upper limit of k ≤ ~10 s.
For a bimolecular step
the reaction rate is described by , where is a bimolecular rate constant. Bimolecular rate constants have an upper limit that is determined by how frequently molecules can collide, and the fastest such processes are limited by diffusion. Thus, in general, a bimolecular rate constant has an upper limit of k ≤ ~10 Ms.
For a termolecular step
the reaction rate is described by , where is a termolecular rate constant.
There are few examples of elementary steps that are termolecular or higher order, due to the low probability of three or more molecules colliding in their reactive conformations and in the right orientation relative to each other to reach a particular transition state. There are, however, some termolecular examples in the gas phase. Most involve the recombination of two atoms or small radicals or molecules in the presence of an inert third body which carries off excess energy, such as O + + → + . One well-established example is the termolecular step 2 I + → 2 HI in the hydrogen-iodine reaction. In cases where a termolecular step might plausibly be proposed, one of the reactants is generally present in high concentration (e.g., as a solvent or diluent gas). | 7 | Physical Chemistry |
Fungal cells usually die when they travel through the atmosphere due to the desiccating effects of higher altitudes. However, some particularly resilient fungal bioaerosols have been shown to survive in atmospheric transport despite exposure to severe UV light conditions. Although bioaerosol levels of fungal spores increase in higher humidity conditions, they can also be active in low humidity conditions and in most temperature ranges. Certain fungal bioaerosols even increase at relatively low levels of humidity. | 7 | Physical Chemistry |
In 1979 teams at Harvard and Caltech extended the basic idea of making DNA copies of mRNAs in vitro to amplifying a library of such in bacterial plasmids. In 1982–1983, the idea of selecting random or semi-random clones from such a cDNA library for sequencing was explored by Greg Sutcliffe and coworkers. and Putney et al. who sequenced 178 clones from a rabbit muscle cDNA library. In 1991 Adams and co-workers coined the term expressed sequence tag (EST) and initiated more systematic sequencing of cDNAs as a project (starting with 600 brain cDNAs). The identification of ESTs proceeded rapidly, millions of ESTs now available in public databases (e.g. GenBank).
In 1995, the idea of reducing the tag length from 100 to 800 bp down to tag length of 10 to 22 bp helped reduce the cost of mRNA surveys. In this year, the original SAGE protocol was published by Victor Velculescu at the Oncology Center of Johns Hopkins University. Although SAGE was originally conceived for use in cancer studies, it has been successfully used to describe the transcriptome of other diseases and in a wide variety of organisms. | 1 | Biochemistry |
Polysaccharides (sugar polymers) can be linear or branched and are typically joined with glycosidic bonds. The exact placement of the linkage can vary, and the orientation of the linking functional groups is also important, resulting in α- and β-glycosidic bonds with numbering definitive of the linking carbons' location in the ring. In addition, many saccharide units can undergo various chemical modifications, such as amination, and can even form parts of other molecules, such as glycoproteins. | 1 | Biochemistry |
The residual sodium carbonate (RSC) index of irrigation water or soil water is used to indicate the alkalinity hazard for soil. The RSC index is used to find the suitability of the water for irrigation in clay soils which have a high cation exchange capacity. When dissolved sodium in comparison with dissolved calcium and magnesium is high in water, clay soil swells or undergoes dispersion which drastically reduces its infiltration capacity.
In the dispersed soil structure, the plant roots are unable to spread deeper into the soil due to lack of moisture. However, high RSC index water does not enhance the osmotic pressure to impede the off take of water by the plant roots unlike high salinity water. Clay soils irrigation with high RSC index water leads to fallow alkali soils formation. | 9 | Geochemistry |
With the discovery of the dual-membrane nature of mitochondria, the pioneers of mitochondrial ultrastructural research proposed different models for the organization of the mitochondrial inner membrane. Three models proposed were:
*Baffle model – According to Palade (1953), the mitochondrial inner membrane is convoluted in a baffle-like manner with broad openings towards the intra-cristal space. This model entered most textbooks and was widely believed for a long time.
*Septa model – Sjöstrand (1953) suggested that sheets of inner membrane are spanned like septa (plural of septum) through the matrix, separating it into several distinct compartments.
*Crista junction model – Daems and Wisse (1966) proposed that cristae are connected to the inner boundary membrane via tubular structures characterized by rather small diameters, termed crista junctions (CJs). In the middle of 1990s these structures were rediscovered by EM tomography, leading to the establishment of this currently widely accepted model.
More recent research (2019) finds rows of ATP synthase dimers (formerly known as "elementary particles" or "oxysomes") forming at the cristae. These membrane-curving dimers have a bent shape, and may be the first step to cristae formation. They are situated at the base of the crista. A mitochondrial contact site cristae organizing system (MICOS) protein complex occupies the crista junction. Proteins like OPA1 are involved in cristae remodeling.
Crista are traditionally sorted by shapes into lamellar, tubular, and vesicular cristae. They appear in different cell types. It is debated whether these shapes arise by different pathways. | 1 | Biochemistry |
When looking at what affects SVA, one of the main things that come up first is the solvent that is used, and what nanostructure is wanted to be obtained. For example, if a hierarchical structure is desired, a solvent that has a vapor that can selectively mobilize the amorphous polymer chains of a semi-crystalline polymer is ideal because it can also keep the integrity of the crystals, allowing for the secondary structure to form.
Looking more at BCP itself, they make ordered nanostructures because of thermodynamic differences between different blocks of the polymer. The sample morphology at equilibrium can be predicted using the molar mass of the blocks, the degree of polymerization of the chains (N), and the Flory-Huggins interaction parameter (χ) which is a magnitude of exactly how incompatible the different blocks are. These factors, along with the composition of the BCP, allow microphase separation of chains and the rearrangement into the desired product. The composition provides an especially important part of the process as knowing the ordering, such as alternating AB monomers, gives light on how to section the polymer in the desired manner.
Along with this, the selection of a specific type of block polymer is important for the process and its effectiveness. The main thing to consider is the original structure of the block at room temperature, as well as, temperatures in which each block will begin to change phase. Knowing these temperatures is critical in determining when each will begin to react and take in solvent and at what rate this will happen, which is critical in pushing to a desired morphology of the given block polymer through annealing.
Other factors that affect SVA are parameters such as vapor pressure, solvent concertation in the film, and evaporation rate of the solvent. Each of these factors contributes to the volatility and imprecision at times of this method, not possessing a set mechanism for the construction of structures that are desired, such as nanocylinders. Getting perfect success of the desired morphology of a polymer has yet to be achieved with these plethoras of factors dictating formation. | 7 | Physical Chemistry |
The more assumptions that are made, the more uncertain estimates of risk related to pathogens will be. However, even with considerable uncertainty, QMRAs are a good way to compare different risk scenarios. In a study comparing estimated health risks from exposures to recreational waters impacted by human and non-human sources of fecal contamination, QMRA determined that the risk of gastrointestinal illness from exposure to waters impacted by cattle were similar to those impacted by human waste, and these were higher than for waters impacted by gull, chicken, or pig faeces. Such studies could be useful to risk managers for determining how best to focus their limited resources, however, risk managers must be aware of the limitations of data used in these calculations. For example, this study used data describing concentrations of Salmonella in chicken feces published in 1969. Methods for quantifying bacteria, changes in animal housing practices and sanitation, and many other factors may have changed the prevalence of Salmonella since that time. Also, such an approach often ignores the complicated fate and transport processes that determine bacteria concentrations from the source to the point of exposure. | 3 | Analytical Chemistry |
Gerard ONeill, noting the problem of high launch costs in the early 1970s, proposed building the SPSs in orbit with materials from the Moon. Launch costs from the Moon are potentially much lower than from Earth because of the lower gravity and lack of atmospheric drag. This 1970s proposal assumed the then-advertised future launch costing of NASAs space shuttle. This approach would require substantial upfront capital investment to establish mass drivers on the Moon. Nevertheless, on 30 April 1979, the Final Report ("Lunar Resources Utilization for Space Construction") by General Dynamics Convair Division, under NASA contract NAS9-15560, concluded that use of lunar resources would be cheaper than Earth-based materials for a system of as few as thirty solar power satellites of 10 GW capacity each.
In 1980, when it became obvious NASAs launch cost estimates for the space shuttle were grossly optimistic, ONeill et al. published another route to manufacturing using lunar materials with much lower startup costs. This 1980s SPS concept relied less on human presence in space and more on partially self-replicating systems on the lunar surface under remote control of workers stationed on Earth. The high net energy gain of this proposal derives from the Moon's much shallower gravitational well.
Having a relatively cheap per pound source of raw materials from space would lessen the concern for low mass designs and result in a different sort of SPS being built. The low cost per pound of lunar materials in ONeills vision would be supported by using lunar material to manufacture more facilities in orbit than just solar power satellites. Advanced techniques for launching from the Moon may reduce the cost of building a solar power satellite from lunar materials. Some proposed techniques include the lunar mass driver and the lunar space elevator, first described by Jerome Pearson. It would require establishing silicon mining and solar cell manufacturing facilities on the Moon. | 7 | Physical Chemistry |
The development of the Ferrier carbocyclization has been useful for the synthesis of numerous natural products that contain the carbocycle group. In 1991, Bender and co-workers reported a synthetic route to pure enantiomers of myo-inositol derivatives using this reaction. It has also been applied to the synthesis of aminocyclitols in work done by Barton and co-workers. Finally, Amano et al. used the Ferrier conditions to synthesise complex conjugated cyclohexanones in 1998. | 0 | Organic Chemistry |
* If it takes more than five minutes to form 1/8 in. cake thicknesses, continuous filtration should not be attempted.
* For negligible cake build up in clarification, cartridges, pre-coat drums, or sand filters are used for filtration
*When the filtering surface is expected to be more than a few square meters, it is advisable to do laboratory tests to determine whether cake washing is critical. If there is a problem with the cake drying, filter precoating might be needed.
* For finely ground ores and minerals, rotary drum filtration rates may be 1500 lb/(day)(sqft), at 20 rev/h and 18-25 inch Hg vacuum
* Coarse solids and crystals may be filtered at rates of 6000 lb/ (day) (sqft) at 20 rev/h, 2-6 inch Hg vacuum.
* Surface areas in porous ceramics: Porous ceramics processed by a sol-gel technique have extremely large surface areas, ranging from 200 to 500 square meters per gram | 3 | Analytical Chemistry |
There are state laws on DNA profiling in all 50 states of the United States. Detailed information on database laws in each state can be found at the National Conference of State Legislatures website. | 1 | Biochemistry |
The most common adverse effects of cefalexin, like other oral cephalosporins, are gastrointestinal (stomach area) disturbances and hypersensitivity reactions. Gastrointestinal disturbances include nausea, vomiting, and diarrhea, the latter being the most common. Hypersensitivity reactions include skin rashes, urticaria, fever, and anaphylaxis. Pseudomembranous colitis and Clostridium difficile have been reported with use of cefalexin. Less common and more serious side effects include bruising of the skin and yellowing of the skin or eye whites.
Signs and symptoms of an allergic reaction include rash, itching, swelling, trouble breathing, or red, blistered, swollen, or peeling skin. Overall, cefalexin allergy occurs in less than 0.1% of patients. Evidence suggests that it is seen in 1% to 10% of patients with a penicillin allergy. | 4 | Stereochemistry |
Zn isotopes may be useful as a tracer for breast cancer. Relative to non-cancerous patients, breast cancer patients are known to have significantly higher concentrations of Zn in their breast tissue, but lower concentrations in their blood serum and erythrocytes, due to overexpression of Zn transporters in breast cancer cells. Consistent with these body-wide shifts in Zn homeostasis, δZn values in breast cancer tumors of 5 patients were found to be anomalously light (varying from -0.9 to -0.6‰) relative to healthy tissue in 3 breast cancer patients and 1 healthy control (δZn = -0.5 to -0.3‰). In this study, δZn values of blood and serum were not found to be significantly different between cancerous and non-cancerous patients, suggesting an unknown isotopically heavy pool of Zn must exist in cancer patients. Though results from this study are promising regarding the use of Zn isotope ratios as a biomarker for breast cancer, a mechanistic understanding of how Zn isotopes fractionate during tumor formation in breast cancer is still lacking. Fortunately, increasing attention is being devoted to the use of stable metal isotopes as tracers of cancer and other diseases, and the usefulness of these isotope systems in medical applications will become more apparent in the next few decades. | 9 | Geochemistry |
There are also reports of antihomoaromatic compounds. Just as aromatic compounds exhibit exceptional stability, antiaromatic compounds, which deviate from Huckel's rule and contain a closed loop of 4n π electrons, are relatively unstable. The bridged bicyclo[3.2.1]octa-3,6-dien-2-yl cation contains only 4 π electrons, and is therefore "bishomoantiaromatic." A series of theoretical calculations confirm that it is indeed less stable than the corresponding allyl cation.
Similarly, a substituted bicyclo[3.2.1]octa-3,6-dien-2-yl cation (the 2-(4'-Fluorophenyl) bicyclo[3.2.1]oct-3,6-dien-2-yl cation) was also shown to be an antiaromate when compared to its corresponding allyl cation, corroborated by theoretical calculations as well as by NMR analysis. | 7 | Physical Chemistry |
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