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Although N-terminus arginylation was originally thought to be the only site for targeting by ATE1 enzymes, it has recently been discovered that arginylation may also occur in the middle of the peptide chain of a protein. The first discovery of this unprecedented modification occurred when neurotensin, a biological peptide found in the central nervous system, was isolated from cells and it was discovered that arginine was attached to a mid-chain glutamine residue. This discovery changed the view of how arginylation occurs, as this meant that there may be ways to modify and arginylate intact proteins.
In an effort to determine the prevalence of mid-chain arginylation, a mass spectrometry screen of various peptides was performed. The results from this experiment revealed a plethora of various proteins which contained modified asparagine and glutamine residues present in the middle of their peptide chain, and further studies determined that ATE1 could also be mediating this reaction. Indeed, this discovery changed the biological scope of arginylation by suggesting that arginylation can also occur on fully intact proteins, not just on the N-terminus of protein fragments or pre-processed proteins. | 1 | Applied and Interdisciplinary Chemistry |
Over 350,000 residents in the Veneto region are estimated to have been exposed to contamination through tap water, and it is thought to be Europes biggest PFAS-related environmental disaster. While Italys National Health Institute (ISS, Istituto Superiore di Sanità) set the threshold limit of PFOA in the bloodstream at 8 nanograms per milliliter (ng/mL), some residents had reached 262 and some industrial employees reach 91,900 ng/mL. In 2021 some data was disclosed by Greenpeace and local citizens after a long legal battle against the Veneto Region and ISS, which for years has denied access to data, despite values known since or even before 2017. The Veneto region has not carried out further monitoring or taken resolutive actions to eliminate pollution and reduce, at least gradually, the contamination of non-potable water. Although in 2020 the European Food Safety Agency (EFSA) has reduced by more than four times the maximum tolerable limit of PSAS that can be taken through the diet, the region has not carried out new assessments or implemented concrete actions to protect the population and the agri-food and livestock sectors. Some limits were added to monitoring the geographical area, which does not include the orange zone and other areas affected by contamination, as well as the insufficiency of analysis on important productions widespread in the areas concerned: eggs (up to 37,100 ng/kg), fish (18,600 ng/kg) spinach and radicchio (only one sampling carried out), kiwis, melons, watermelons, cereals (only one sample was analyzed), soy, wines and apples. | 0 | Theoretical and Fundamental Chemistry |
The synthesis of the pyrimidines CTP and UTP occurs in the cytoplasm and starts with the formation of carbamoyl phosphate from glutamine and CO. Next, aspartate carbamoyltransferase catalyzes a condensation reaction between aspartate and carbamoyl phosphate to form carbamoyl aspartic acid, which is cyclized into 4,5-dihydroorotic acid by dihydroorotase. The latter is converted to orotate by dihydroorotate oxidase. The net reaction is:
:(S)-Dihydroorotate + O → Orotate + HO
Orotate is covalently linked with a phosphorylated ribosyl unit. The covalent linkage between the ribose and pyrimidine occurs at position C of the ribose unit, which contains a pyrophosphate, and N of the pyrimidine ring. Orotate phosphoribosyltransferase (PRPP transferase) catalyzes the net reaction yielding orotidine monophosphate (OMP):
:Orotate + 5-Phospho-α-D-ribose 1-diphosphate (PRPP) → Orotidine 5'-phosphate + Pyrophosphate
Orotidine 5-monophosphate is decarboxylated by orotidine-5-phosphate decarboxylase to form uridine monophosphate (UMP). PRPP transferase catalyzes both the ribosylation and decarboxylation reactions, forming UMP from orotic acid in the presence of PRPP. It is from UMP that other pyrimidine nucleotides are derived. UMP is phosphorylated by two kinases to uridine triphosphate (UTP) via two sequential reactions with ATP. First, the diphosphate from UDP is produced, which in turn is phosphorylated to UTP. Both steps are fueled by ATP hydrolysis:
:ATP + UMP → ADP + UDP
:UDP + ATP → UTP + ADP
CTP is subsequently formed by the amination of UTP by the catalytic activity of CTP synthetase. Glutamine is the NH donor and the reaction is fueled by ATP hydrolysis, too:
:UTP + Glutamine + ATP + HO → CTP + ADP + P
Cytidine monophosphate (CMP) is derived from cytidine triphosphate (CTP) with subsequent loss of two phosphates. | 1 | Applied and Interdisciplinary Chemistry |
In most stability studies, real-time or accelerated, a few units of the reference material are tested at intervals. If the measurement system used for testing the materials is not perfectly stable, this can generate imprecise data or can be mistaken for instability of the material. To overcome these difficulties, it is often possible to move RM units, at intervals, to some reference temperature where they remain stable, and then test all the accumulated units - which have undergone different exposure times - at the same time. This is referred to as an isochronous study. This strategy has the advantage of improving the precision of data used in assessing stability at the cost of delaying results until the end of the stability study period. | 0 | Theoretical and Fundamental Chemistry |
Due to their high photoluminescence quantum efficiencies, perovskites may find use in light-emitting diodes (LEDs). Although the stability of perovskite LEDs is not yet as good as III-V or organic LEDs, there is ongoing research to solve this problem, such as incorporating organic molecules or potassium dopants in perovskite LEDs. Perovskite-based printing ink can be used to produce OLED display and quantum dot display panels. | 0 | Theoretical and Fundamental Chemistry |
Platinum Metals Review was abstracted and indexed by:
* Chemical Abstracts
* Chemical Engineering and Biotechnology Abstracts
* Compendex
* Corrosion Abstracts
* Current Contents/Physical, Chemical & Earth Sciences
* Environment Abstracts
* Metals Abstracts/METADEX
* Metal Finishing Abstracts
* Science Citation Index Expanded
* Scopus
* World Textile Abstracts | 1 | Applied and Interdisciplinary Chemistry |
In atomic, molecular and optical physics, the Araki–Sucher correction is a leading-order correction to the energy levels of atoms and molecules due to effects of quantum electrodynamics (QED). It is named after Huzihiro Araki and Joseph Sucher, who first calculated it for the helium atom in 1957. The method is based on a perturbative expansion of the energy in the Bethe–Salpeter equation, and have since been used to calculate corrections for atoms other than helium (e.g. beryllium and lithium), and for systems with more than two electrons. The correction typically involves the fine-structure constant and may sometimes include terms of third order and higher . | 0 | Theoretical and Fundamental Chemistry |
One short inscription on the pillar is associated with the Tomara king Anangpal, although it is hard to decipher.. Alexander Cunningham (1862–63) read the inscription as follows:
Based on this reading, Cunningham theorized that Anangpal had moved the pillar to its current location while establishing the city of Delhi. However, his reading has been contested by the later scholars. Buddha Rashmi Mani (1997) read it as follows: | 1 | Applied and Interdisciplinary Chemistry |
Focusing his research on photochemistry, Natarajan studied various areas of the discipline such as polymer dynamics using fluorescence, flash photolysis studies using picosecond and femtosecond lasers and solar energy conversion. He demonstrated that micromolecular dye coatings of electrodes used in photoelectrochemical cells returned high current density. This led to his subsequent studies of solar energy conversion using chemically modified electrodes. He published his research in peer-reviewed journals including Nature, Journal of the American Chemical Society, Journal of Physical Chemistry A, Inorganic Chemistry and Chemical Communications for a total of 107 articles. He was granted patents for four of his findings. He mentored over 30 doctoral scholars and was associated with a number of journals as their editorial board member. He also was on a number of government committees including those of the Department of Science and Technology and the Council of Scientific and Industrial Research and delivered several featured talks and orations. | 0 | Theoretical and Fundamental Chemistry |
Some wastes contain chemicals capable of suppressing microbiological growth or activity. Potential sources include industrial wastes, antibiotics in pharmaceutical or medical wastes, sanitizers in food processing or commercial cleaning facilities, chlorination disinfection used following conventional sewage treatment, and odor-control formulations used in sanitary waste holding tanks in passenger vehicles or portable toilets. Suppression of the microbial community oxidizing the waste will lower the test result. | 0 | Theoretical and Fundamental Chemistry |
(AD 900–1500)
Utilitarian and ceremonial objects; objects of personal adornment
#Coatlán, Oaxaca
#Coixtlahuaca, Oaxaca
#Ejutla, Oaxaca
#Guiengola, Oaxaca
#Huajuapan, Oaxaca
#Huitzo, Oaxaca
#Juquila, Oaxaca
#Mitla, Oaxaca
#Monte Albán Oaxaca
#Sola de Vega, Oaxaca
#Tehuantepec, Oaxaca
#Teotitlán del Camino, Oaxaca
#Teotitlán del Valle, Oaxaca
#Tlacolula, Oaxaca
#Tlaxiaco, Oaxaca
#Tututepec, Oaxaca
#Xaaga, Oaxaca
#Yanhuitlán, Oaxaca
#Zachila, Oaxaca | 1 | Applied and Interdisciplinary Chemistry |
Sustainable development requires the promotion of environmental management and a constant search for new technologies to treat vast quantities of wastes generated by increasing anthropogenic activities. Biotreatment, the processing of wastes using living organisms, is an environmentally friendly, relatively simple and cost-effective alternative to physico-chemical clean-up options. Confined environments, such as bioreactors, have been engineered to overcome the physical, chemical and biological limiting factors of biotreatment processes in highly controlled systems. The great versatility in the design of confined environments allows the treatment of a wide range of wastes under optimized conditions. To perform a correct assessment, it is necessary to consider various microorganisms having a variety of genomes and expressed transcripts and proteins. A great number of analyses are often required. Using traditional genomic techniques, such assessments are limited and time-consuming. However, several high-throughput techniques originally developed for medical studies can be applied to assess biotreatment in confined environments. | 1 | Applied and Interdisciplinary Chemistry |
The formation of thienamycin is thought to occur through a different pathway from classic β-lactams (penicillins, cephalosporins). Production of classic β-lactams in both fungi and bacteria occur through two steps: First, the condensation of -cysteine, -valine, and -α-aminoadipic acid by ACV synthetase (ACVS, a nonribosomal peptide synthetase) and then cyclization of this formed tripeptide by isopenicillin N synthetase (IPNS).
The gene cluster (thn) for the biosynthesis of thienamycin of S. cattleya was identified and sequenced in 2003, lending insight into the biosynthetic mechanism for thienamycin formation. The biosynthesis is thought to share features with the biosynthesis of the simple carbapenems, beginning with the condensation of malonyl-CoA with glutamate-5-semialdehyde to form the pyrroline ring. The β-lactam is then formed by a β-lactam synthetase, which makes use of ATP, providing a carbapenam. At some later point, oxidation to the carbapenem and ring inversions must occur.
The hydroxyethyl side chain of thienamycin is thought to be a result of two separate methyl transfers from S-adenosyl methionine. According to the proposed gene functions, ThnK, ThnL, and ThnP could catalyze these methyl-transfer steps. A β-lactam synthetase (ThnM) is thought to catalyze the formation of the β-lactam ring fused to the five-membered ring. How the cysteaminyl side-chain is incorporated is largely unknown, although ThnT, ThnR, and ThnH are involved in the processing of CoA to cysteamine for use in the pathway. Various oxidations complete the biosynthesis. | 0 | Theoretical and Fundamental Chemistry |
Simultaneous use of the one- and two-hybrid methods (that is, simultaneous protein–protein and protein–DNA interaction) is known as a one-two-hybrid approach and expected to increase the stringency of the screen. | 1 | Applied and Interdisciplinary Chemistry |
The unique interaction between the oligosaccharide chains have different applications. First, it aids in quality control by identifying misfolded proteins. The oligosaccharide chains also change the solubility and polarity of the proteins that they are bonded to. For example, if the oligosaccharide chains are negatively charged, with enough density around the protein, they can repulse proteolytic enzymes away from the bonded protein. The diversity in interactions lends itself to different types of glycoproteins with different structures and functions.
One example of glycoproteins found in the body is mucins, which are secreted in the mucus of the respiratory and digestive tracts. The sugars when attached to mucins give them considerable water-holding capacity and also make them resistant to proteolysis by digestive enzymes.
Glycoproteins are important for white blood cell recognition. Examples of glycoproteins in the immune system are:
* molecules such as antibodies (immunoglobulins), which interact directly with antigens.
* molecules of the major histocompatibility complex (or MHC), which are expressed on the surface of cells and interact with T cells as part of the adaptive immune response.
*sialyl Lewis X antigen on the surface of leukocytes.
H antigen of the ABO blood compatibility antigens.
Other examples of glycoproteins include:
* gonadotropins (luteinizing hormone and follicle-stimulating hormone)
* glycoprotein IIb/IIIa, an integrin found on platelets that is required for normal platelet aggregation and adherence to the endothelium.
* components of the zona pellucida, which surrounds the oocyte, and is important for sperm-egg interaction.
* structural glycoproteins, which occur in connective tissue. These help bind together the fibers, cells, and ground substance of connective tissue. They may also help components of the tissue bind to inorganic substances, such as calcium in bone.
* Glycoprotein-41 (gp41) and glycoprotein-120 (gp120) are HIV viral coat proteins.
Soluble glycoproteins often show a high viscosity, for example, in egg white and blood plasma.
* Miraculin, is a glycoprotein extracted from Synsepalum dulcificum a berry which alters human tongue receptors to recognize sour foods as sweet.
Variable surface glycoproteins allow the sleeping sickness Trypanosoma parasite to escape the immune response of the host.
The viral spike of the human immunodeficiency virus is heavily glycosylated. Approximately half the mass of the spike is glycosylation and the glycans act to limit antibody recognition as the glycans are assembled by the host cell and so are largely self. Over time, some patients can evolve antibodies to recognise the HIV glycans and almost all so-called 'broadly neutralising antibodies (bnAbs) recognise some glycans. This is possible mainly because the unusually high density of glycans hinders normal glycan maturation and they are therefore trapped in the premature, high-mannose, state. This provides a window for immune recognition. In addition, as these glycans are much less variable than the underlying protein, they have emerged as promising targets for vaccine design.
P-glycoproteins are critical for antitumor research due to its ability block the effects of antitumor drugs. P-glycoprotein, or multidrug transporter (MDR1), is a type of ABC transporter that transports compounds out of cells. This transportation of compounds out of cells includes drugs made to be delivered to the cell, causing a decrease in drug effectiveness. Therefore, being able to inhibit this behavior would decrease P-glycoprotein interference in drug delivery, making this an important topic in drug discovery. For example, P-Glycoprotein causes a decrease in anti-cancer drug accumulation within tumor cells, limiting the effectiveness of chemotherapies used to treat cancer. | 0 | Theoretical and Fundamental Chemistry |
A dentine conditioning agent is used initially, to remove the smear layer resulting from the preparation of a cavity and, to alter the dentine surface by partially demineralising the intertubulary dentine. This partially demineralised dentine acts as a hollow scaffolding which can be perfused with the primer. Over-etching (as well as over-drying) of the dentine can lead to collapse of the collagen network, making infiltration of the primer more challenging. However, sclerosed dentine requires a longer time of exposure to the dentine conditioner compared to healthy dentine. Some dentine conditioners contain a chemical called glutaraldehyde, which reinforces the collagen matrix, preventing its collapse.
Some common dentine conditioners include:
* phosphoric acid
* nitric acid
* maleic acid
* citric acid
* ethylene diamine tetra-acetic acid (EDTA) | 0 | Theoretical and Fundamental Chemistry |
The early work of the scientists J. Arthur Harris and Francis G. Benedict showed that approximate values for BMR could be derived using body surface area (computed from height and weight), age, and sex, along with the oxygen and carbon dioxide measures taken from calorimetry. Studies also showed that by eliminating the sex differences that occur with the accumulation of adipose tissue by expressing metabolic rate per unit of "fat-free" or lean body mass, the values between sexes for basal metabolism are essentially the same. Exercise physiology textbooks have tables to show the conversion of height and body surface area as they relate to weight and basal metabolic values.
The primary organ responsible for regulating metabolism is the hypothalamus. The hypothalamus is located on the diencephalon and forms the floor and part of the lateral walls of the third ventricle of the cerebrum. The chief functions of the hypothalamus are:
# control and integration of activities of the autonomic nervous system (ANS)
#* The ANS regulates contraction of smooth muscle and cardiac muscle, along with secretions of many endocrine organs such as the thyroid gland (associated with many metabolic disorders).
#* Through the ANS, the hypothalamus is the main regulator of visceral activities, such as heart rate, movement of food through the gastrointestinal tract, and contraction of the urinary bladder.
# production and regulation of feelings of rage and aggression
# regulation of body temperature
# regulation of food intake, through two centers:
#* The feeding center or hunger center is responsible for the sensations that cause us to seek food. When sufficient food or substrates have been received and leptin is high, then the satiety center is stimulated and sends impulses that inhibit the feeding center. When insufficient food is present in the stomach and ghrelin levels are high, receptors in the hypothalamus initiate the sense of hunger.
#* The thirst center operates similarly when certain cells in the hypothalamus are stimulated by the rising osmotic pressure of the extracellular fluid. If thirst is satisfied, osmotic pressure decreases.
All of these functions taken together form a survival mechanism that causes us to sustain the body processes that BMR measures. | 1 | Applied and Interdisciplinary Chemistry |
Similar to foraminifera shells, the isotopic composition of coral skeletons is used to reconstruct past temperature, CO concentrations, and pH. Vital effects arise from algal symbionts and biological responses to changes in conditions such as pH. Again, culture experiments are used to quantify vital effects and calibrate the use of coral isotopic composition as a proxy. | 0 | Theoretical and Fundamental Chemistry |
The PI (or photosynthesis-irradiance) curve is a graphical representation of the empirical relationship between solar irradiance and photosynthesis. A derivation of the Michaelis–Menten curve, it shows the generally positive correlation between light intensity and photosynthetic rate. It is a plot of photosynthetic rate as a function of light intensity (irradiance). | 0 | Theoretical and Fundamental Chemistry |
In chemical thermodynamics, an exergonic reaction is a chemical reaction where the change in the free energy is negative (there is a net release of free energy). This indicates a spontaneous reaction if the system is closed and initial and final temperatures are the same. For processes that take place in a closed system at constant pressure and temperature, the Gibbs free energy is used, whereas the Helmholtz energy is relevant for processes that take place at constant volume and temperature. Any reaction occurring at constant temperature without input of electrical or photon energy is exergonic, according to the second law of thermodynamics. An example is cellular respiration.
Symbolically, the release of free energy, , in an exergonic reaction (at constant pressure and temperature) is denoted as
Although exergonic reactions are said to occur spontaneously, this does not imply that the reaction will take place at an observable rate. For instance, the disproportionation of hydrogen peroxide releases free energy but is very slow in the absence of a suitable catalyst. It has been suggested that eager would be a more intuitive term in this context.
More generally, the terms exergonic and endergonic relate to the free energy change in any process, not just chemical reactions. By contrast, the terms exothermic and endothermic relate to an enthalpy change in a closed system during a process, usually associated with the exchange of heat. | 0 | Theoretical and Fundamental Chemistry |
Over time, there has been increasing recognition of the importance of drinking water quality and its impact on public health. This has led to increasing protection and management of water quality.
The understanding of the links between water quality and health continues to grow and highlight new potential health crises: from the chronic impacts of infectious diseases on child development through stunting to new evidence on the harms from known contaminants, such as manganese with growing evidence of neurotoxicity in children. In addition, there are many emerging water quality issues—such as microplastics, perfluorinated compounds, and antimicrobial resistance. | 0 | Theoretical and Fundamental Chemistry |
One design brings the water in the top of a container through a "header" which distributes the water evenly. The filter "media" start with fine sand on the top and then becomes gradually coarser sand in a number of layers followed by gravel on the bottom, in gradually larger sizes. The top sand physically removes particles from the water. The job of the subsequent layers is to support the finer layer above and provide efficient drainage.
As particles become trapped in the media, the differential pressure across the bed increases. Periodically, a backwash may be initiated to remove the solids trapped in the bed. During backwash, flow is directed in the opposite direction from normal flow. In multi-media filters, the layers in the media re-stratify due to density differences prior to resuming normal filtration. Multimedia filter can remove particles down to 10-25 microns. | 1 | Applied and Interdisciplinary Chemistry |
As examples, the dimension of the physical quantity speed is
The dimension of the physical quantity acceleration is
The dimension of the physical quantity force is
The dimension of the physical quantity pressure is
The dimension of the physical quantity energy is
The dimension of the physical quantity power is
The dimension of the physical quantity electric charge is
The dimension of the physical quantity electric potential difference is
The dimension of the physical quantity capacitance is | 1 | Applied and Interdisciplinary Chemistry |
* ASTM B374-06(2011) — Standard Terminology Relating to Electroplating
* ASTM B542-13 — Standard Terminology Relating to Electrical Contacts and Their Use
* ASTM B735-16 — Standard Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor
* ASTM B765-03(2018) — Standard Guide for Selection of Porosity and Gross Defect Tests for Electrodeposits and Related Metallic Coatings
* ASTM B798-95(2014) — Standard Test Method for Porosity in Gold or Palladium Coatings on Metal Substrates by Gel-Bulk Electrography
* ASTM B799-95(2014) — Standard Test Method for Porosity in Gold and Palladium Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
* ASTM B809-95(2018) — Standard Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor ("Flowers-of-Sulfur")
* ASTM B810-01a (Reapproved 2017) —Standard Method for Calibration of Atmospheric Corrosion Test Chambers by Change in Mass of Copper Coupons
* ANSI/ISA-71.04-2013 Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants, The International Society of Automation, Research Triangle Park, NC. | 1 | Applied and Interdisciplinary Chemistry |
This method relies on the idea that deoxidation of slag will lead to the deoxidation of steel.
The chemical equilibrium equation used for this process is:
where a is the activity of the oxygen in the slag, and a is the activity of oxygen in the steel.
Reducing the activity in the slag (a) will lower the oxygen levels in the slag. Afterwards, oxygen will diffuse from the steel into the lesser concentrated slag. This method is done by using deoxidizing agents on the slag, such as coke or silicon. As these agents do not come into direct contact with the steel, non-metallic inclusions will not form in the steel itself. | 1 | Applied and Interdisciplinary Chemistry |
The earliest complex trace fossils, not including microbial traces such as stromatolites, date to . This is far too early for them to have an animal origin, and they are thought to have been formed by amoebae.
Putative "burrows" dating as far back as may have been made by animals which fed on the undersides of microbial mats, which would have shielded them from a chemically unpleasant ocean; however their uneven width and tapering ends make a biological origin so difficult to defend that even the original author no longer believes they are authentic.
The first evidence of burrowing which is widely accepted dates to the Ediacaran (Vendian) period, around . During this period the traces and burrows basically are horizontal on or just below the seafloor surface. Such traces must have been made by motile organisms with heads, which would probably have been bilateran animals. The traces observed imply simple behaviour, and point to organisms feeding above the surface and burrowing for protection from predators. Contrary to widely circulated opinion that Ediacaran burrows are only horizontal the vertical burrows Skolithos are also known. The producers of burrows Skolithos declinatus from the Vendian (Ediacaran) beds in Russia with date have not been identified; they might have been filter feeders subsisting on the nutrients from the suspension. The density of these burrows is up to 245 burrows/dm. Some Ediacaran trace fossils have been found directly associated with body fossils. Yorgia and Dickinsonia are often found at the end of long pathways of trace fossils matching their shape. The feeding was performed in a mechanical way, supposedly the ventral side of body these organisms was covered with cilia. The potential mollusc related Kimberella is associated with scratch marks, perhaps formed by a radula, further traces from appear to imply active crawling or burrowing activity.
As the Cambrian got underway, new forms of trace fossil appeared, including vertical burrows (e.g. Diplocraterion) and traces normally attributed to arthropods. These represent a "widening of the behavioural repertoire", both in terms of abundance and complexity.
Trace fossils are a particularly significant source of data from this period because they represent a data source that is not directly connected to the presence of easily fossilized hard parts, which are rare during the Cambrian. Whilst exact assignment of trace fossils to their makers is difficult, the trace fossil record seems to indicate that at the very least, large, bottom-dwelling, bilaterally symmetrical organisms were rapidly diversifying during the early Cambrian.
Further, less rapid diversification occurred since, and many traces have been converged upon independently by unrelated groups of organisms.
Trace fossils also provide our earliest evidence of animal life on land. Evidence of the first animals that appear to have been fully terrestrial dates to the Cambro-Ordovician and is in the form of trackways. Trackways from the Ordovician Tumblagooda sandstone allow the behaviour of other terrestrial organisms to be determined. The trackway Protichnites represents traces from an amphibious or terrestrial arthropod going back to the Cambrian. | 1 | Applied and Interdisciplinary Chemistry |
The fact that the binding motif appears as a "triplet" of the conserved TxT repeat, as well as the observation that blastp queries have returned no viable matches, has led some researchers to suggest that RiAFP represents a new type of AFP – one that differs from the heavily studied TmAFP (from T. molitor), DcAFP (from D. canadensis), and CfAFP (from C. fumiferana). On the basis of these observations, it has been predicted that the need for insect AFPs came about after insect evolutionary divergence, much like the evolution of fish AFPs; thus, different AFPs most likely evolved in parallel from adaptations to cold (environmental) stress. As a result, homology modelling with TmAFP, DcAFP, or CfAFP would prove to be fruitless.
Secondary structure modelling algorithms have determined that the internal repeats are spaced sufficiently to tend towards β-strand configuration; no helical regions include the conserved repeats; and all turn regions are located at the ends of β-strand regions. These data suggest that RiAFP is a well-folded β-helical protein, having six β-strand regions consisting of 13-amino acids (including one TxTxTxT binding motif) per strand.
Primary crystallographic studies, have been published on a RiAFP crystal (which diffracted to 1.3Å resolution) in the trigonal space group P321 (or P321), with unit-cell parameters a = b = 46.46, c = 193.21Å. | 1 | Applied and Interdisciplinary Chemistry |
Several nucleoside analogues are used as antiviral or anticancer agents. The viral polymerase incorporates these compounds with non-canonical bases. These compounds are activated in the cells by being converted into nucleotides, they are administered as nucleosides since charged nucleotides cannot easily cross cell membranes. | 1 | Applied and Interdisciplinary Chemistry |
In intrinsic termination, the RNA transcript doubles back and base pairs with itself, creating an RNA stem-loop, or hairpin, structure. This structure is critical for the release of both the transcript and polymerase at the end of transcription. In living cells, the key components are the stable stem-loop itself, as well as the sequence of 6-8 uracil residues that follow it. The stem usually consists of 8-9 mostly guanine and cytosine (G-C) base pairs, and the loop consists of 4-8 residues. It is thought that the stem portion of the structure is essential for transcription termination, while the loop is not. This is suggested by the fact that termination can be achieved in non-native structures that do not include the loop.
The stem portion of the hairpin is usually rich in G-C base pairs. G-C base pairs have significant base-stacking interactions, and can form three hydrogen bonds with each other, which makes them very thermodynamically favorable. Conversely, while the uracil-rich sequence that follows the hairpin is not always necessary for termination, it is hypothesized that the uracil-rich sequence aids in intrinsic termination because the U-A bond is not as strong as G-C bonds. This inherent instability acts to kinetically favor the dissociation of the RNA transcript. | 1 | Applied and Interdisciplinary Chemistry |
Sulfones are typically prepared by organic oxidation of thioethers, often referred to as sulfides. Sulfoxides are intermediates in this route. For example, dimethyl sulfide oxidizes to dimethyl sulfoxide and then to dimethyl sulfone. | 0 | Theoretical and Fundamental Chemistry |
Like other fuel cells, biological photovoltaic systems are divided into anodic and cathodic half-cells.
Oxygenic photosynthetic biological material, such as purified photosystems or whole algal or cyanobacterial cells, are employed in the anodic half-cell. These organisms are able to use light energy to drive the oxidation of water, and a fraction of the electrons produced by this reaction are transferred to the extracellular environment, where they can be used to reduce an anode. No heterotrophic organisms are included in the anodic chamber - electrode reduction is performed directly by the photosynthetic material.
The higher electrode potential of the cathodic reaction relative to the reduction of the anode drives current through an external circuit. In the illustration, oxygen is being reduced to water at the cathode, though other electron acceptors can be used. If water is regenerated there is a closed loop in terms of electron flow (similar to a conventional photovoltaic system), i.e. light energy is the only net input required for production of electrical power. Alternatively, electrons can be used at the cathode for electrosynthetic reactions that produce useful compounds, such as the reduction of protons to hydrogen gas. | 0 | Theoretical and Fundamental Chemistry |
The most common pipe trace heating applications include:
* Freeze protection
* Temperature maintenance
* Snow Melting On Driveways
Other uses of trace heating cables include:
* Ramp and stair snow / ice protection
* Gulley and roof snow / ice protection
* Underfloor heating
* Door / frame interface ice protection
* Window de-misting
* Anti-condensation
* Pond freeze protection
* Soil warming
* Preventing cavitation
* Reducing Condensation On Windows | 1 | Applied and Interdisciplinary Chemistry |
The word detergent is derived from the Latin adjective detergens, from the verb detergere, meaning to wipe or polish off. Detergent can be defined as a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. However, conventionally, detergent is used to mean synthetic cleaning compounds as opposed to soap (a salt of the natural fatty acid), even though soap is also a detergent in the true sense. In domestic contexts, the term detergent refers to household cleaning products such as laundry detergent or dish detergent, which are in fact complex mixtures of different compounds, not all of which are by themselves detergents.
Detergency is the ability to remove unwanted substances termed soils from a substrate (e.g., clothing). | 0 | Theoretical and Fundamental Chemistry |
Protein was studied using a protein nanoprobe (that enables cross-linking) that introduced photo-methionine within the protein (during the recombinant expression) which lead to the protein keeping its reserved structure while having the ability to be mapped out for its interactions. The model was used as a region of contact surface that is involved in a well-known interaction (homodimerization) between two molecules of 14-3-3ζ protein. Once the photo-methionine is introduced and has become activated using UV-light, it can cross-link with no specificity (meaning no group) and the links have zero-length. High resolution mass spectrometry or MS can (even MS/MS) be used then to determine the cross-linked residues and the reaction radius; allowing the researchers to characterize and research the homodimerization of the protein. The usage of the high-resolution MS with photo-methionine has its advantages as it again allows the protein to be in its native state, there are reasonable time scales while using small quantities of the protein. There are also fewer limitations on the reaction specificity and restrictions using a photo-active cross-linker (photo-methionine) compared to chemical cross-linking. This method of combined photo-initiated cross-linking from the protein nanoprobe in tandem with MS could be useful to characterize not only homodimer formation but also oligomers and in theory; heteromers (such as the composition of the protein-protein mixture and its functionality). | 0 | Theoretical and Fundamental Chemistry |
Chemical mimicry exists in many forms and for a variety of uses. It may be classified by the function it performs for the mimicking species and the effect that the mimic will have on the species that is deceived. It can be used for such functions as deterring predators, drawing prey, to allow a parasite to deceive a host species, or to help assist in the reproduction of an organism. | 1 | Applied and Interdisciplinary Chemistry |
Polysialic acid is an unusual posttranslational modification that occurs on neural cell adhesion molecules (NCAM). Polysialic acid is considerably anionic. This strong negative charge gives this modification the ability to change the protein's surface charge and binding ability. In the synapse, polysialation of NCAM prevents its ability to bind to NCAMs on the adjacent membrane. | 1 | Applied and Interdisciplinary Chemistry |
This can be visualized with an ellipsoid, which is defined by the eigenvectors and eigenvalues of D. The FA of a sphere is 0 since the diffusion is isotropic, and there is equal probability of diffusion in all directions. The eigenvectors and eigenvalues of the Diffusion Tensor give a complete representation of the diffusion process. FA quantifies the pointedness of the ellipsoid, but does not give information about which direction it is pointing to.
Note that the FA of most liquids, including water, is unless the diffusion process is being constrained by structures such as network of fibers. The measured FA may depend on the effective length scale of the diffusion measurement. If the diffusion process is not constrained on the scale being measured (the constraints are too far apart) or the constraints switch direction on a smaller scale than the measured one, then the measured FA will be attenuated. For example, the brain can be thought of as a fluid permeated by many fibers (nerve axons). However, in most parts the fibers go in all directions, and thus although they constrain the diffusion the FA is . In some regions, such as the corpus callosum the fibers are aligned over a large enough scale (on the order of a mm) for their directions to mostly agree within the resolution element of a magnetic resonance image, and it is these regions that stand out in an FA image. Liquid crystals can also exhibit anisotropic diffusion because the needle or plate-like shapes of their molecules affect how they slide over one another. When the FA is 0 the tensor nature of D is often ignored, and it is called the diffusion constant.
One drawback of the Diffusion Tensor model is that it can account only for Gaussian diffusion processes, which has been found to be inadequate in accurately representing the true diffusion process in the human brain. Due to this, higher order models using spherical harmonics and Orientation Distribution Functions (ODF) have been used to define newer and richer estimates of the anisotropy, called Generalized Fractional Anisotropy. GFA computations use samples of the ODF to evaluate the anisotropy in diffusion. They can also be easily calculated by using the Spherical Harmonic coefficients of the ODF model. | 1 | Applied and Interdisciplinary Chemistry |
Ion funnels are frequently used in mass spectroscopy devices to collect ions from an ionization source. Previous devices lacking an ion funnel often lost ions during the transition from ionization source to the detector of the mass spectrometer. This loss was due to the increasing number of collisions undergone by ions with other gas molecules present in the atmosphere. The introduction of the ion funnel greatly reduced the amount of ions lost during experiments by guiding ions towards a desired destination, and through modification of the number of inlets is also able to increases sensitivity of measurements taken by the mass spectrometer. Multiple inlets allow multiple electrospray emitters, reducing the flow through each individual emitter. This creates many highly efficient electrosprays at low flow rates. Multiple inlets also improve sensitivity, with a linearly arranged 19 electrospray emitter coupled to 19 inlets operating at 18 Torr giving a nine-fold increase compared to a single inlet. | 0 | Theoretical and Fundamental Chemistry |
In engineering and science, dimensional analysis is the analysis of the relationships between different physical quantities by identifying their base quantities (such as length, mass, time, and electric current) and units of measurement (such as meters and grams) and tracking these dimensions as calculations or comparisons are performed. The term dimensional analysis is also used to refer to conversion of units from one dimensional unit to another, which can be used to evaluate scientific formulae.
Commensurable physical quantities are of the same kind and have the same dimension, and can be directly compared to each other, even if they are expressed in differing units of measurement; e.g., meters and feet, gallons and liters, seconds and years. Incommensurable physical quantities are of different kinds and have different dimensions, and can not be directly compared to each other, no matter what units they are expressed in, e.g. metres and grams, seconds and grams, metres and seconds. For example, asking whether a gram is larger than an hour is meaningless.
Any physically meaningful equation, or inequality, must have the same dimensions on its left and right sides, a property known as dimensional homogeneity. Checking for dimensional homogeneity is a common application of dimensional analysis, serving as a plausibility check on derived equations and computations. It also serves as a guide and constraint in deriving equations that may describe a physical system in the absence of a more rigorous derivation.
The concept of physical dimension, and of dimensional analysis, was introduced by Joseph Fourier in 1822. | 1 | Applied and Interdisciplinary Chemistry |
The book begins by describing how the Atchafalaya River drains 30 percent of the Mississippi River at its source 300 miles upriver from New Orleans. Thanks to its steeper gradient and more direct route, the Atchafalaya seeks to change the course of the Mississippi as has happened in its long geological history. Due to the Mississippis vital importance to industry, the Army Corps of Engineers constructed a control structure at the Atchafalayas source to prevent this from occurring and to maintain the 30 percent drainage. McPhee explains how Morgan City, Louisiana would be destroyed if the river's banks increase. Three million cubic feet of water would inundate the town in the case of a hundred-year flood, though the Corps of Engineers has been trying its hardest to build a more stable flood structure. | 1 | Applied and Interdisciplinary Chemistry |
Not all non-stick pans use Teflon; other non-stick coatings have become available. For example, a mixture of titanium and ceramic can be sandblasted onto the pan surface, and then fired at to produce a non-stick ceramic coating.
Ceramic nonstick pans use a finish of silica (silicon dioxide) to prevent sticking. It is applied using a sol-gel process without the use of PFAS. The coating layer of Ceramic nonstick pans starts to break down at about 370 °C (700 °F). The coating layer of PTFE cookware starts to break down when heated to 426 °C (800 °F).
With the EPA imposing stricter limits on the use of PFAS, some companies are voluntarily replacing their PTFE cookware with ceramic options. | 0 | Theoretical and Fundamental Chemistry |
The fugacity capacity constant (Z) is used to help describe the concentration of a chemical in a system (usually in mol/mPa). Hemond and Hechner-Levy (2000) describe how to utilize the fugacity capacity to calculate the concentration of a chemical in a system. Depending on the chemical, fugacity capacity varies. The concentration in media m equals the fugacity capacity in media m multiplied by the fugacity of the chemical.
For a chemical system at equilibrium, the fugacity of the chemical will be the same in each media/phase/compartment. Therefore equilibrium is sometimes called "equifugacity" in the context of these calculations.
where Z is a proportional constant, termed fugacity capacity. This equation does not necessarily imply that C and f are always linearly related. Non-linearity can be accommodated by allowing Z to vary as a function of C or f.
For a better understanding of the fugacity capacity concept, heat capacity may provide a precedent for introducing Z as a capacity of a phase to absorb particular quantity of chemical. However, phases with high fugacity capacity do not necessarily retain high fugacity.
In calculations of fugacity capacity key factors would be (a) the nature of the solute (chemical), (b) the nature of the medium or compartment, (c) temperature. | 0 | Theoretical and Fundamental Chemistry |
The domains in the polyketide synthase type I:
* ACP: acyl carrier protein (serves as chaperone)
* AT: acyl transferase (transfers acyl group form CoA to ACP)
* KS: keto synthase (forms the new carbon-carbon bond)
* KR: keto reductase (NADPH-dependent reduces beta-ketone to beta-hydroxyl)
* DH: dehydratase (eliminates beta-OH to anpha/beta-unsaturation)
* ER: enoyl reductase (NADPH-dependent reduces anpha/beta-unsaturation)
* TE: thioesterase (hydrolyses / cyclizes) | 1 | Applied and Interdisciplinary Chemistry |
Coding regions are composed of codons, which are decoded and translated into proteins by the ribosome; in eukaryotes usually into one and in prokaryotes usually into several. Coding regions begin with the start codon and end with a stop codon. In general, the start codon is an AUG triplet and the stop codon is UAG ("amber"), UAA ("ochre"), or UGA ("opal"). The coding regions tend to be stabilised by internal base pairs; this impedes degradation. In addition to being protein-coding, portions of coding regions may serve as regulatory sequences in the pre-mRNA as exonic splicing enhancers or exonic splicing silencers. | 1 | Applied and Interdisciplinary Chemistry |
Some situations may call for the use of degenerate primers. These are mixtures of primers that are similar, but not identical. These may be convenient when amplifying the same gene from different organisms, as the sequences are probably similar but not identical. This technique is useful because the genetic code itself is degenerate, meaning several different codons can code for the same amino acid. This allows different organisms to have a significantly different genetic sequence that code for a highly similar protein. For this reason, degenerate primers are also used when primer design is based on protein sequence, as the specific sequence of codons are not known. Therefore, primer sequence corresponding to the amino acid isoleucine might be "ATH", where A stands for adenine, T for thymine, and H for adenine, thymine, or cytosine, according to the genetic code for each codon, using the IUPAC symbols for degenerate bases. Degenerate primers may not perfectly hybridize with a target sequence, which can greatly reduce the specificity of the PCR amplification.
Degenerate primers are widely used and extremely useful in the field of microbial ecology. They allow for the amplification of genes from thus far uncultivated microorganisms or allow the recovery of genes from organisms where genomic information is not available. Usually, degenerate primers are designed by aligning gene sequencing found in GenBank. Differences among sequences are accounted for by using IUPAC degeneracies for individual bases. PCR primers are then synthesized as a mixture of primers corresponding to all permutations of the codon sequence. | 1 | Applied and Interdisciplinary Chemistry |
The typical FCS setup consists of a laser line (wavelengths ranging typically from 405–633 nm (cw), and from 690–1100 nm (pulsed)), which is reflected into a microscope objective by a dichroic mirror. The laser beam is focused in the sample, which contains fluorescent particles (molecules) in such high dilution, that only a few are within the focal spot (usually 1–100 molecules in one fL). When the particles cross the focal volume, they fluoresce. This light is collected by the same objective and, because it is red-shifted with respect to the excitation light it passes the dichroic mirror reaching a detector, typically a photomultiplier tube, an avalanche photodiode detector or a superconducting nanowire single-photon detector. The resulting electronic signal can be stored either directly as an intensity versus time trace to be analyzed at a later point, or computed to generate the autocorrelation directly (which requires special acquisition cards). The FCS curve by itself only represents a time-spectrum. Conclusions on physical phenomena have to be extracted from there with appropriate models. The parameters of interest are found after fitting the autocorrelation curve to modeled functional forms. | 0 | Theoretical and Fundamental Chemistry |
Some reasons why plastic piping systems may fail are poor product bonding/gluing during installation and naturally-occurring physical damage, such as from tree root infiltration.
Plastic pipes were also found to fail more often during dry, hot summers. | 1 | Applied and Interdisciplinary Chemistry |
When the constituent components of silicone foam are mixed together, they evolve hydrogen gas, which causes bubbles to form within the rubber, as it changes from liquid to solid. This results in an outward pressure. Temperature and humidity can influence the rate of expansion. | 0 | Theoretical and Fundamental Chemistry |
The idea of double beta decay was first proposed by Maria Goeppert Mayer in 1935.
In 1937, Ettore Majorana demonstrated that all results of beta decay theory remain unchanged if the neutrino were its own antiparticle, now known as a Majorana particle.
In 1939, Wendell H. Furry proposed that if neutrinos are Majorana particles, then double beta decay can proceed without the emission of any neutrinos, via the process now called neutrinoless double beta decay.
It is not yet known whether the neutrino is a Majorana particle, and, relatedly, whether neutrinoless double beta decay exists in nature.
As parity violation in weak interactions would not be discovered until 1956, earlier calculations showed that neutrinoless double beta decay should be much more likely to occur than ordinary double beta decay, if neutrinos were Majorana particles. The predicted half-lives were on the order of ~ years. Efforts to observe the process in laboratory date back to at least 1948 when E.L. Fireman made the first attempt to directly measure the half-life of the isotope with a Geiger counter.
Radiometric experiments through about 1960 produced negative results or false positives, not confirmed by later experiments. In 1950, for the first time the double beta decay half-life of was measured by geochemical methods to be 1.4× years,
reasonably close to the modern value. This involved detecting the concentration in minerals of the xenon produced by the decay.
In 1956, after the V − A nature of weak interactions was established, it became clear that the half-life of neutrinoless double beta decay would significantly exceed that of ordinary double beta decay. Despite significant progress in experimental techniques in 1960–1970s, double beta decay was not observed in a laboratory until the 1980s. Experiments had only been able to establish the lower bound for the half-life – about years. At the same time, geochemical experiments detected the double beta decay of and .
Double beta decay was first observed in a laboratory in 1987 by the group of Michael Moe at UC Irvine in .
Since then, many experiments have observed ordinary double beta decay in other isotopes. None of those experiments have produced positive results for the neutrinoless process, raising the half-life lower bound to approximately years. Geochemical experiments continued through the 1990s, producing positive results for several isotopes. Double beta decay is the rarest known kind of radioactive decay; as of 2019 it has been observed in only 14 isotopes (including double electron capture in observed in 2001, observed in 2013, and observed in 2019), and all have a mean lifetime over yr (table below). | 0 | Theoretical and Fundamental Chemistry |
One of the first societies for chemists was the Society of Chemical Industry, founded in London in 1881. This inspired a number of other groups, including the Société de Chimie Industrielle in Paris, France. The French Société was modeled on the British organization in 1917.
A number of those active in forming the French Société were elected to its first set of officers, which included industrialist Paul Kestner as president,
vice-presidents Albin Haller and Henry Louis Le Châtelier, and
Jean Gérard as general secretary.
Creation of the French Société in turn inspired creation of a related American association in New York in 1918. This was part of an effort to rebuild international connections between individuals and institutions that had been disrupted during the First World War.
René Laurent Engel encouraged the re-establishment of ties between chemists in the two countries in his position as the scientific representative in a French Mission to the United States.
Victor Grignard of the University of Nancy also encouraged the creation of an American organization. A circular appealed to the Chemists and Manufacturers of America to "extend to our French fellow chemists and manufacturers our moral and financial support and the right hand of good fellowship."
The American section of the Société de Chimie Industrielle was formed on January 18, 1918, following the presentation of the Perkin Medal by the Society of Chemical Industry (American Section) at The Chemists Club in New York. Engel, as secretary of the parent organization, addressed the meeting. Officers of the newly created American section of the Société de Chimie Industrielle included Leo Baekeland as president, Jerome Alexander as vice-president, Charles Avery Doremus as secretary, and George Frederick Kunz as treasurer. A report describes the Sociétés purpose as follows:
The first official meeting of the American section of the Société de Chimie Industrielle was held on April 4, 1918 at The Chemists' Club in New York. William H. Nichols, president of the American Chemical Society, welcomed the new organization. Frederick J. LeMaistre reported on "Conditions in the French chemical industries during 1916". | 1 | Applied and Interdisciplinary Chemistry |
The first chapter of Omega Chi Epsilon was formed at the University of Illinois in 1931 by a group of chemical engineering students. These Founders were:
* F. C. Howard
* A. Garrell Deem
* Ethan M. Stifle
* John W. Bertetti
Professors D.B. Keyes and Norman Krase supported the students in their efforts. The Beta chapter was formed in the Iowa State University 1932.
The society grew slowly at first. Bairds Manual' indicates there were six chapters by 1957, of which three were inactive. However, interest was revived in the 1960s, allowing a sustained growth that has continued to the present day. There are approximately eighty active chapters of the society as of 2021.
Omega Chi Epsilon amended its constitution to permit women to become members as of 1966. The organization became a member of the Association of College Honor Societies in 1967. | 1 | Applied and Interdisciplinary Chemistry |
An adsorption isotherm depicts the relation between the quantity adsorbate and the bulk phase pressure (or density) at equilibrium for a constant temperature. It is a dataset of specified adsorption equilibrium. Such equilibrium data are required for optimal design of process relying on adsorption and are considered fundamental information for theoretical studies. | 0 | Theoretical and Fundamental Chemistry |
#Motilin
#Neurotensin
#Substance P
#Somatostatin
#Bombesin
#Serotonin
#Angiotensin
#Nitric Oxide
#Kinins
#Histamine | 1 | Applied and Interdisciplinary Chemistry |
The Annual Review of Chemical and Biomolecular Engineering was first published in 2010 by nonprofit publisher Annual Reviews. Its founding editor was John Prausnitz. In 2018, Prausnitz was succeeded by Michael F. Doherty and Rachel A. Segalman as co-editors. Though it was initially published in print, as of 2021 it is only published electronically.
As of 2023, it is being published as open access, under the Subscribe to Open model. | 1 | Applied and Interdisciplinary Chemistry |
The Noyori asymmetric hydrogenation of ketones is an excellent example of dynamic kinetic resolution at work. The enantiomeric β-ketoesters can undergo epimerization, and the choice of chiral catalyst, typically of the form Ru[(R)-BINAP]X, where X is a halogen, leads to one of the enantiomers reacting preferentially faster. The relative free energy for a representative reaction is shown below. As can be seen, the epimerization intermediate is lower in free energy than the transition states for hydrogenation, resulting in rapid racemization and high yields of a single enantiomer of the product.
The enantiomers interconvert through their common enol, which is the energetic minimum located between the enantiomers. The shown reaction yields a 93% ee sample of the anti product shown above. Solvent choice appears to have a major influence on the diastereoselectivity, as dichloromethane and methanol both show effectiveness for certain substrates. Noyori and others have also developed newer catalysts which have improved on both ee and diastereomeric ratio (dr).
Genêt and coworkers developed SYNPHOS, a BINAP analogue which forms ruthenium complexes, which perform highly selective asymmetric hydrogenations. Enantiopure Ru[SYNPHOS]Br was shown to selectively hydrogenate racemic α-amino-β-ketoesters to enantiopure aminoalcohols, as shown below utilizing (R)-SYNPHOS. 1,2-syn amino alcohols were prepared from benzoyl protected amino compounds, whereas anti products were prepared from hydrochloride salts of the amine. | 0 | Theoretical and Fundamental Chemistry |
MIKE 21C can be used for designing protection schemes against bank erosion, evaluating measures to reduce or manage shoaling, analyzing alignments and dimensions of navigation channels for minimizing capital and maintenance dredging, predicting the impact of bridge, tunnel and pipeline crossings on river channel hydraulics and morphology, optimizing restoration plans for habitat environment in channel floodplain systems, designing monitoring networks based on morphological forecasting.
Due to its accurate descriptions of the physical processes, MIKE 21C can simulate a braided river developing from a plane bed, which was illustrated by Enggrob & Tjerry (1998). | 1 | Applied and Interdisciplinary Chemistry |
In biochemistry, naturally occurring phenols are natural products containing at least one phenol functional group. Phenolic compounds are produced by plants and microorganisms. Organisms sometimes synthesize phenolic compounds in response to ecological pressures such as pathogen and insect attack, UV radiation and wounding. As they are present in food consumed in human diets and in plants used in traditional medicine of several cultures, their role in human health and disease is a subject of research. Some phenols are germicidal and are used in formulating disinfectants. | 0 | Theoretical and Fundamental Chemistry |
Metalation was first observed in the laboratory by Edward Frankland during a synthesis of diethylzinc in 1849. While this development eventually led to the development of organometallic compounds of other metals, these compounds saw little use in the laboratory because of their expense and (in the case of organozinc compounds) their highly pyrophoric nature. Metalation reactions (particularly in the form of transmetalation) only began to see more widespread use in synthetic laboratories after François Auguste Victor Grignard’s synthesized organomagnesium halides directly from metallic magnesium and organic halides. These newfound organomagnesium reagents extreme versatility in organic synthesis caused metalation to see widespread use in laboratory science. Organolithium reagents were synthesized for the first time in 1917 by Schlenk and Holtz, though these reagents did not see widespread use as metallating agents or reagents in organic synthesis until Karl Ziegler, Henry Gilman, and Georg Wittig — among others — developed synthetic methods that improved upon this initial synthesis. After these improvements in synthesis came to be known, interest in the compounds increased significantly, as they are generally more reactive than organomagnesium compounds. The first use of an organolithium reagent as a metalation reagent occurred in 1928, with Schlenk and Bergmanns metalation of fluorene with ethyllithium. | 0 | Theoretical and Fundamental Chemistry |
* There is a monument of Zelinsky in Elektrostal city. It was opened in July 2013 in front of the entrance of the Elektrostal Chemical and Mechanical Plant OJSC. | 0 | Theoretical and Fundamental Chemistry |
The SCO phenomenon has potential uses as switches, data storage devices, and optical displays. These potential applications would exploit the bistability (HS and LS) which leads to changes in the colour and magnetism of samples. Molecular switches, like electrical switches, require a mechanism that for turning ON and OFF, as is achieved with the abrupt spin transitions with hysteresis. In order for the size of data storage devices to be reduced while the capacity of them increase, smaller units (such as molecules) that exhibit a bistability and thermal hysteresis are required. One research goal is to develop new materials where the SCO response time can be decreased from nanoseconds, as we know it, to femtoseconds. One of the advantages of SCO phenomena is the absence of fatigue, because there is an intraelectronic transition instead of an electron displacement through space. | 0 | Theoretical and Fundamental Chemistry |
Stereocenters can exist on chiral or achiral molecules. They are defined as a location (point) within a molecule, rather than a particular atom, in which the interchanging of two groups creates a stereoisomer. A stereocenter can have either four different attachment groups, or three different attachment groups where one group is connected by a double bond. Since stereocenters can exist on achiral molecules, stereocenters can have either sp or sp hybridization. | 0 | Theoretical and Fundamental Chemistry |
In addition to fatty acid synthesis in the cytosol, mitochondria also have their own fatty acid synthesis (mtFASII). Mitochondrial fatty acid synthesis is essential for cellular respiration and mitochondrial biogenesis. A role as a mediator in intracellular signal transduction is also assumed, as the levels of bioactive lipids, such as lysophospholipids and sphingolipids, correlate with mtFASII.
In the first step of mtFASII, malonyl-CoA is formed from malonic acid by ACSF3. This occurs in tandem with a mitochondrial isoform of ACC1 (mtACC1), which can still provide malonyl-CoA from acetyl-CoA. The fatty acids, such as octanoyl-ACP (C8), which forms the starting substrate of lipoic acid biosynthesis, are formed via further intermediate steps and chain extensions. Through lipoic acid as a cofactor respectively the degree of lipoylation, mtFASII has an influence on mitochondrial enzyme complexes in energy metabolism, such as the pyruvate dehydrogenase complex, the α-ketoglutarate dehydrogenase complex, the BCKDH complex and the glycine cleavage system (GCS), among others. | 1 | Applied and Interdisciplinary Chemistry |
Methanesulfonyl chloride (mesyl chloride) is an organosulfur compound with the formula . Using the organic pseudoelement symbol Ms for the methanesulfonyl (or mesyl) group –, it is frequently abbreviated MsCl in reaction schemes or equations. It is a colourless liquid that dissolves in polar organic solvents but is reactive toward water, alcohols, and many amines. The simplest organic sulfonyl chloride, it is used to make methanesulfonates and to generate the elusive molecule sulfene (methylenedioxosulfur(VI)). | 0 | Theoretical and Fundamental Chemistry |
β-Glycerophosphate is an inhibitor of the enzyme serine-threonine phosphatase. It is often used in combination with other phosphatase/protease inhibitors for broad spectrum inhibition.
β-Glycerophosphate is also used to drive osteogenic differentiation of bone marrow stem cells in vitro.
β-Glycerophosphate is used to buffer M17 media for Lactococcus culture in recombinant protein expression. | 1 | Applied and Interdisciplinary Chemistry |
Non-B DNA refers to DNA conformations that differ from the canonical B-DNA conformation, the most common form of DNA found in nature at neutral pH and physiological salt concentrations. Non-B DNA structures can arise due to various factors, including DNA sequence, length, supercoiling, and environmental conditions. Non-B DNA structures can have important biological roles, but they can also cause problems, such as genomic instability and disease. | 1 | Applied and Interdisciplinary Chemistry |
In December 2021, the first direct measurement of a quantum spin liquid of the toric code type was reported, it was achieved by two teams: one exploring ground state and anyonic excitations on a quantum processor and the other implementing a theoretical blueprint of atoms on a ruby lattice held with optical tweezers on a quantum simulator. | 0 | Theoretical and Fundamental Chemistry |
Within the six sections of the Jain literary corpus belonging to the Svetambara school, it is classed as one of the Cheda Sūtras. This Sutra contains detailed life histories and, from the mid-15th century, was frequently illustrated with miniature painting. The oldest surviving copies are written on paper in western India in the 14th century.
The Kalpa Sutra is ascribed to Bhadrabahu, traditionally said to have composed it some 150 years after the Nirvāṇa (samadhi) of Mahavira. It was compiled probably during the reign of Dhruvasena, 980 or 993 years after Mahavira's death. | 1 | Applied and Interdisciplinary Chemistry |
Peroxisomal disorders are a class of medical conditions that typically affect the human nervous system as well as many other organ systems. Two common examples are X-linked adrenoleukodystrophy and the peroxisome biogenesis disorders. | 1 | Applied and Interdisciplinary Chemistry |
The Energine Corporation was a South Korean company that claimed to deliver fully assembled cars running on a hybrid compressed air and electric engine. The compressed-air engine is used to activate an alternator, which extends the autonomous operating capacity of the car. The CEO was arrested for fraudulently promoting air motors with false claims. | 1 | Applied and Interdisciplinary Chemistry |
Where, the index 1 refers to upstream properties, and the index 2 refers to down stream properties. The subscript 0 refers to total or stagnation properties. T is temperature, M is the mach number, P is pressure, ρ is density, and γ is the ratio of specific heats. | 1 | Applied and Interdisciplinary Chemistry |
Typically, the work-piece is immersed in a temperature-controlled bath of electrolyte and serves as the anode; it is connected to the positive terminal of a DC power supply, the negative terminal being attached to the cathode. A current passes from the anode, where metal on the surface is oxidised and dissolved in the electrolyte, to the cathode. At the cathode, a reduction reaction occurs, which normally produces hydrogen. Electrolytes used for electropolishing are most often concentrated acid solutions such as mixtures of sulfuric acid and phosphoric acid. Other electropolishing electrolytes reported in the literature include mixtures of perchloric acid with acetic anhydride (which has caused fatal explosions), and methanolic solutions of sulfuric acid.
To electropolish a rough surface, the protruding parts of a surface profile must dissolve faster than the recesses. This process, referred to as anodic leveling, can be subject to incorrect analysis when measuring the surface topography. Anodic dissolution under electropolishing conditions deburrs metal objects due to increased current density on corners and burrs.
Most importantly, successful electropolishing should operate under diffusion limited constant current plateau, achieved by following current dependence on voltage (polarisation curve), under constant temperature and stirring conditions. | 1 | Applied and Interdisciplinary Chemistry |
Hydrogel modifications, as with other coatings, are designed to improve the body's response to the implant and thereby improve their consistency and long-term performance. Hydrogel surface modifications achieve this by significantly altering the hydrophilicity of the neural implant surface to one that is less favorable for protein adsorption. In general, protein adsorption increases with increasing hydrophobicity as a result of the decreased Gibbs energy from the energetically favorable reaction (as seen in the equation below)
Water molecules are bonded to both the proteins and to the surface of the implant; as the protein binds to the implant, water molecules are liberated, resulting in an entropy gain, decreasing the overall energy in the system. For hydrophilic surfaces, this reaction is energetically unfavorable due to the strong attachment of water to the surface, hence the decreased protein adsorption. The decrease in protein adsorption is beneficial for the implant as it limits the body's ability to both recognize the implant as a foreign material as well as attach potentially deleterious cells such as astrocytes and fibroblasts that can create fibrous glial scars around the implant and hinder stimulating and recording processes. Increasing the hydrophilicity can also enhance the electrical signal transfer by creating a stable ionic conductance layer. However, increasing the water content of the hydrogel too much can cause swelling and eventually mechanical instability. An appropriate water balance must be created to optimize the efficacy of the implant coating. | 0 | Theoretical and Fundamental Chemistry |
Due to the very low temperatures required, varying levels of stress are put on the DNA samples. Spermatozoa, in particular, are stressed by temperature shock, osmotic stress, and oxidative stress with the latter being the most detrimental. When temperature shock occurs, the membrane is damaged through freezing and thawing of the sperm. Osmotic stress occurs when ice crystals form inside the nucleus during the freezing process, causing differing osmotic pressures within the cell. Oxidative stress is the result of too many reactive oxygen species (ROS), which is highly reactive and damaging to all parts of the cell. Although these stressors are present within the cell, there are solutions to each. By introducing cholesterol to the samples, temperature shock can be reduced. The use of antifreeze proteins provides one solution for osmotic stress. Oxidative stress is the most difficult to combat because of the highly reactive components of ROS, but some measures like adding certain proteins to limit freeze-thaw damage and increase the survival rate of the DNA. | 1 | Applied and Interdisciplinary Chemistry |
An on-line method of measuring hydrogen in aluminum is then required to characterize and optimize the process, which helps ensure the quality of outgoing products and monitors the performance of these degassing processes. Traditional laboratory methods, such as hot extraction, are too expensive for routine quality assurance, and too slow for effective process control. The Reduced Pressure Test (RPT) is often used on the foundry floor. The RPT is a semi-quantitative method with limited accuracy that provides an indication of the hydrogen level. | 1 | Applied and Interdisciplinary Chemistry |
A gradation test is performed on a sample of aggregate in a laboratory. A typical sieve analysis uses a column of sieves with wire mesh screens of graded mesh size.
A representative weighed sample is poured into the top sieve which has the largest screen openings. Each lower sieve in the column has smaller openings than the one above. At the base is a pan, called the receiver.
The column is typically placed in a mechanical shaker, which shakes the column, usually for a set period, to facilitate exposing all of the material to the screen openings so that particles small enough to fit through the holes can fall through to the next layer. After the shaking is complete the material on each sieve is weighed. The mass of the sample of each sieve is then divided by the total mass to give a percentage retained on each sieve.
The size of the average particle on each sieve is then analysed to get a cut-off point or specific size range, which is then captured on a screen.
The results of this test are used to describe the properties of the aggregate and to see if it is appropriate for various civil engineering purposes such as selecting the appropriate aggregate for concrete mixes and asphalt mixes as well as sizing of water production well screens.
The results of this test are provided in graphical form to identify the type of gradation of the aggregate. The complete procedure for this test is outlined in the American Society for Testing and Materials (ASTM) C 136 and the American Association of State Highway and Transportation Officials (AASHTO) T 27
A suitable sieve size for the aggregate underneath the nest of sieves to collect the aggregate that passes through the smallest. The entire nest is then agitated, and the material whose diameter is smaller than the mesh opening pass through the sieves. After the aggregate reaches the pan, the amount of material retained in each sieve is then weighed. | 1 | Applied and Interdisciplinary Chemistry |
Undesirable effects of a drug include:
*Increased probability of cell mutation (carcinogenic activity)
*A multitude of simultaneous assorted actions which may be deleterious
*Interaction (additive, multiplicative, or metabolic)
*Induced physiological damage, or abnormal chronic conditions | 1 | Applied and Interdisciplinary Chemistry |
Hypothetically, it should be possible to recreate an entire ecosystem from the bottom up, in mirror form.
Advances in synthetic biology, like synthesizing viruses since 2002, partially synthetic bacteria in 2010, or synthetic ribosomes in 2013, may lead to the possibility of fully synthesizing a living cell from small molecules, where we could use mirror-image versions (enantiomers) of life's building-block molecules, in place of the standard ones. Some proteins have been synthesized in mirror-image versions, including polymerase in 2016.
Reconstructing regular lifeforms in mirror-image form, using the mirror-image (chiral) reflection of their cellular components, could be achieved by substituting left-handed amino acids with right-handed ones, in order to create mirror reflections of all regular proteins. Analogously, we could get reflected sugars, DNA, etc., on which reflected enzymes would work perfectly. Finally we would get a normally functioning mirror reflection of a natural organism—a chiral counterpart organism.
Electromagnetic force (chemistry) is unchanged under such molecular reflection transformation (P-symmetry). There is a small alteration of weak interactions under reflection, which can produce very small corrections, but these corrections are many orders of magnitude lower than thermal noise—almost certainly too tiny to alter any biochemistry. However, there are also theories that weak interactions can have a greater effect on longer nucleic acids or protein chains, resulting in much less efficient conversion of mirror ribozymes or enzymes than normal ribozymes or enzymes.
Mirror animals would need to feed on reflected food, produced by reflected plants. Mirror viruses would not be able to attack natural cells, just as natural viruses would not be able to attack mirror cells.
Mirror life presents potential dangers. For example, a chiral-mirror version of cyanobacteria, which only needs achiral nutrients and light for photosynthesis, could take over Earth's ecosystem due to lack of natural enemies, disturbing the bottom of the food chain by producing mirror versions of the required sugars. Some bacteria can digest L-glucose; exceptions like this would give some rare lifeforms an unanticipated advantage. | 0 | Theoretical and Fundamental Chemistry |
In 2010, the FDA approved the combination drug dextromethorphan/quinidine under the brand name Nuedexta for the treatment of pseudobulbar affect (uncontrollable laughing/crying). Dextromethorphan is the actual therapeutic agent in the combination; quinidine merely serves to inhibit the enzymatic degradation of dextromethorphan and thereby increase its circulating concentrations via inhibition of CYP2D6. | 0 | Theoretical and Fundamental Chemistry |
Thymolphthalein is a phthalein dye used as an acid–base (pH) indicator. Its transition range is around pH 9.3–10.5. Below this pH, it is colorless; above, it is blue. The molar extinction coefficient for the blue thymolphthalein dianion is 38,000 M cm at 595 nm.
Thymolphthalein is also known to have use as a laxative and for disappearing ink. | 0 | Theoretical and Fundamental Chemistry |
Mitochondria may have a number of different shapes. A mitochondrion contains outer and inner membranes composed of phospholipid bilayers and proteins. The two membranes have different properties. Because of this double-membraned organization, there are five distinct parts to a mitochondrion:
# The outer mitochondrial membrane,
# The intermembrane space (the space between the outer and inner membranes),
# The inner mitochondrial membrane,
# The cristae space (formed by infoldings of the inner membrane), and
# The matrix (space within the inner membrane), which is a fluid.
Mitochondria have folding to increase surface area, which in turn increases ATP (adenosine triphosphate) production.
Mitochondria stripped of their outer membrane are called mitoplasts. | 1 | Applied and Interdisciplinary Chemistry |
There are four major pools of phosphorus in freshwater ecosystems: dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP), particulate inorganic phosphorus (PIP) and particulate organic phosphorus (POP). Dissolved material is defined as substances that pass through a 0.45 μm filter. DIP consists mainly of orthophosphate (PO) and polyphosphate, while DOP consists of DNA and phosphoproteins. Particulate matter are the substances that get caught on a 0.45 μm filter and do not pass through. POP consists of both living and dead organisms, while PIP mainly consists of hydroxyapatite, Ca(PO)OH . Inorganic phosphorus comes in the form of readily soluble orthophosphate. Particulate organic phosphorus occurs in suspension in living and dead protoplasm and is insoluble. Dissolved organic phosphorus is derived from the particulate organic phosphorus by excretion and decomposition and is soluble. | 0 | Theoretical and Fundamental Chemistry |
Elisabeth Karamichailova was born in 1897 in Vienna, to Ivan Mikhaylov and Mary Slade. Both her parents had studied at the University of Vienna - Ivan, born in Shumen, was studying medicine, while Mary, a native of Minster Lovell in Oxfordshire, studied music. After her father graduated in 1907, the family remained in Vienna for two years before moving to Bulgaria in 1909 where they acquired a spacious house in central Sofia.
Karamichailova grew up in both an artistic and scientific environment. Her father turned the upper floor of his house into a Red Cross Hospital where he treated his patients without requiring payment. She enrolled in the Sofia Girls' College and graduated there in 1917, after which she departed to study at the University of Vienna. | 0 | Theoretical and Fundamental Chemistry |
Several new nonpeptide ARBs are undergoing clinical trials or are at pre-clinical stages of development. Among these are embusartan (BAY 10-6734 or BAY 10-6734), KRH-594, fonsartan (HR 720) and pratosartan (KT3-671). Pratosartan, for example, has a novel structure: a seven-membered ring that bears an oxo moiety (C=O) fused to the imidazole ring (figure 4), and its affinity for the AT receptor is about 7 times higher than losartan's. The purpose of the oxo group is similar to that of the carboxylic acid groups on other ARBs.<br />
Other attributes of ARBs are also under investigation, such as the positive effects of telmisartan on lipid and glucose metabolism and losartan's effects of lowering uric acid levels. Such effects might lead to new indications for these drugs but further research is needed. | 1 | Applied and Interdisciplinary Chemistry |
Most of the existing hydrophobicity scales are derived from the properties of amino acids in their free forms or as a part of a short peptide. Bandyopadhyay-Mehler hydrophobicity scale was based on partitioning of amino acids in the context of protein structure. Protein structure is a complex mosaic of various dielectric medium generated by arrangement of different amino acids. Hence, different parts of the protein structure most likely would behave as solvents with different dielectric values. For simplicity, each protein structure was considered as an immiscible mixture of two solvents, protein interior and protein exterior. The local environment around individual amino acid (termed as "micro-environment") was computed for both protein interior and protein exterior. The ratio gives the relative hydrophobicity scale for individual amino acids. Computation was trained on high resolution protein crystal structures. This quantitative descriptor for microenvironment was derived from the octanol-water partition coefficient, (known as Rekker's Fragmental Constants) widely used for pharmacophores. This scale well correlate with the existing methods, based on partitioning and free energy computations. Advantage of this scale is it is more realistic, as it is in the context of real protein structures. | 0 | Theoretical and Fundamental Chemistry |
Perfluorocarbon tracers (PFTs) are a range of perfluorocarbons used in flow tracers and other tracing applications. They are used by releasing the PFT at a certain point, and determining the concentration of that PFT at another set of points, allowing the flow from the source to the points to be determined. | 1 | Applied and Interdisciplinary Chemistry |
A variety of signals can be obtained by NICE-OHMS. First, due to the presence of high intensity counter-propagating beams in the cavity, both Doppler-broadened and Doppler-free signals can be obtained. The former have the advantage of being present at high intracavity pressures, which is suitable when atmospheric pressure samples are analyzed, whereas the latter provide narrow frequency features, which is of importance for frequency standard applications, but also opens up possibilities for interference-free detection. Second, due to the use of FMS, both absorption and dispersion signals can be detected (or a combination thereof). Third, to reduce the influence of low frequency noise, wavelength modulation (wm) can additionally be applied, which implies that the technique can be operated in either fm or wm mode.
The mode of operation to be preferred depends on the particular application of the technique and on the prevailing experimental conditions, mainly the type of noise or background signal that limits the detectability. | 0 | Theoretical and Fundamental Chemistry |
Take the simplest CHX–CH system as an example; the donor orbital is σ(C–H) orbital and the acceptor is σ*(C–X). When moving from fluorine to chlorine, then to bromine, the electronegativity of the halogen and the energy level of the σ*(C–X) orbitals decreases. Consequently, the general trend of acceptors can be summarized as: π*(C=O)>σ*(C–Hal)>σ*(C–O)>σ*(C–N)>σ*(C–C), σ*(C–H). For donating orbitals, the nonbonding orbitals, or the lone pairs, are generally more effective than bonding orbitals due to the high energy levels. Also, different from acceptors, donor orbitals require less polarized bonds. Thus, the general trends for donor orbitals would be: n(N)>n(O)>σ(C–C), σ(C–H)>σ(C–N)>σ(C–O)>σ(C–S)>σ(C–Hal).
Stereoelectronic effect can be directional in specific cases. The radius of sulfur is much larger than the radius of carbon and oxygen. Thus the differences in C–S bond distances generate a much-amplified difference in the two stereoelectronic effects in 1,3-dithiane (σ(C–H) → σ*(C–S)) than in 1,3-dioxane(σ(C–H) → σ*(C–O)). The differences between C–C and C–S bonds shown below causes a significant difference in the distances between C–S and two C–H bonds. The shorter the difference is, the better the interaction and the stronger the stereoelectronic effect. | 0 | Theoretical and Fundamental Chemistry |
IUBMB organizes a triennial Congress of Biochemistry and Molecular Biology and sponsors three annual focussed meetings. In addition, it supports symposia, educational activities (including the Tang Fellowships), award lectures (including Jubilee Lectures), and travel grants for students around the world. | 1 | Applied and Interdisciplinary Chemistry |
In the United Kingdom, the Hallmarking Act 1973 makes it an offence to describe as platinum, gold or silver an item which is not hallmarked as appropriate or exempt from hallmarking. In July 2009, following a proposal by the British Hallmarking Council, an amendment to the Act also brought palladium under the hallmarking regime.
The first UK assay office was Goldsmiths Hall, founded around 1300, and where the term "hallmarking" originates, meaning "marked in Goldsmiths Hall". Since then, there have been ten assay offices in the UK.
There are four remaining assay offices in the UK: | 0 | Theoretical and Fundamental Chemistry |
The title complex is one of several platinum ammine complexes.
*Hexaammineplatinum(IV) chloride
*Trichlorotriammineplatinum(IV) chloride
*cis-Tetrachlorodiammineplatinum(IV)
*trans-Tetrachlorodiammineplatinum(IV) (RN 16986-23-5) | 0 | Theoretical and Fundamental Chemistry |
The yeast Saccharomyces cerevisiae is a simple single-celled eukaryote with both a diploid and haploid mode of existence. The mating of yeast only occurs between haploids, which can be either the a or α (alpha) mating type and thus display simple sexual differentiation. Mating type is determined by a single locus, MAT, which in turn governs the sexual behaviour of both haploid and diploid cells. Through a form of genetic recombination, haploid yeast can switch mating type as often as every cell cycle. | 1 | Applied and Interdisciplinary Chemistry |
Since members of the type I and type II cytokine receptor families possess no catalytic kinase activity, they rely on the JAK family of tyrosine kinases to phosphorylate and activate downstream proteins involved in their signal transduction pathways. The receptors exist as paired polypeptides, thus exhibiting two intracellular signal-transducing domains.
JAKs associate with a proline-rich region in each intracellular domain that is adjacent to the cell membrane and called a box1/box2 region. After the receptor associates with its respective cytokine/ligand, it goes through a conformational change, bringing the two JAKs close enough to phosphorylate each other. The JAK autophosphorylation induces a conformational change within itself, enabling it to transduce the intracellular signal by further phosphorylating and activating transcription factors called STATs (Signal Transducer and Activator of Transcription, or Signal Transduction And Transcription). The activated STATs dissociate from the receptor and form dimers before translocating to the cell nucleus, where they regulate transcription of selected genes.
Some examples of the molecules that use the JAK/STAT signaling pathway are colony-stimulating factor, prolactin, growth hormone, and many cytokines. Janus Kinases have also been reported to have a role in the maintenance of X chromosome inactivation. | 1 | Applied and Interdisciplinary Chemistry |
Space debris describes particulates in the vacuum of outer space, specifically particles originating from human activity that remain in geocentric orbit around the Earth. The International Association of Astronauts define space debris as "any man-made Earth orbiting object which is non-functional with no reasonable expectation of assuming or resuming its intended function or any other function for which it is or can be expected to be authorized, including fragments and parts thereof".
Space debris is classified by size and operational purpose, and divided into four main subsets: inactive payloads, operational debris, fragmentation debris and microparticulate matter. Inactive payloads refer to any launched space objects that have lost the capability to reconnect to its corresponding space operator; thus, preventing a return to Earth. In contrast, operational debris describes the matter associated with the propulsion of a larger entity into space, which may include upper rocket stages and ejected nose cones. Fragmentation debris refers to any object in space that has become dissociated from a larger entity by means of explosion, collision or deterioration. Microparticulate matter describes space matter that typically cannot be seen singly with the naked eye, including particles, gases, and spaceglow.
In response to research that concluded that impacts from Earth orbital debris could lead to greater hazards to spacecraft than the natural meteoroid environment, NASA began the orbital debris program in 1979, initiated by the Space Sciences branch at Johnson Space Center (JSC). Beginning with an initial budget of $70,000, the NASA orbital debris program began with the initial goals of characterizing hazards induced by space debris and creating mitigation standards that would minimize the growth of the orbital debris environment. By 1990, the NASA orbital debris program created a debris monitoring program, which included mechanisms to sample the low Earth orbit (LEO) environment for debris as small as 6mm using the Haystack X-band ground radar. | 1 | Applied and Interdisciplinary Chemistry |
The sharing of edges and particularly faces by two anion polyhedra decreases the stability of an ionic structure. Sharing of corners does not decrease stability as much, so (for example) octahedra may share corners with one another.
The decrease in stability is due to the fact that sharing edges and faces places cations in closer proximity to each other, so that cation-cation electrostatic repulsion is increased. The effect is largest for cations with high charge and low C.N. (especially when r+/r- approaches the lower limit of the polyhedral stability). Generally, smaller elements fulfill the rule better.
As one example, Pauling considered the three mineral forms of titanium dioxide, each with a coordination number of 6 for the cations. The most stable (and most abundant) form is rutile, in which the coordination octahedra are arranged so that each one shares only two edges (and no faces) with adjoining octahedra. The other two, less stable, forms are brookite and anatase, in which each octahedron shares three and four edges respectively with adjoining octahedra. | 0 | Theoretical and Fundamental Chemistry |
In an electrochemical cell the faradaic impedance of an electrolyte-electrode interface is the joint electrical resistance and capacitance at that interface.
Let us suppose that the Butler-Volmer relationship correctly describes the dynamic behavior of the redox reaction:
Dynamic behavior of the redox reaction is characterized by the so-called charge transfer resistance defined by:
The value of the charge transfer resistance changes with the overpotential. For this simplest example the faradaic impedance is reduced to a resistance. It is worthwhile to notice that:
for . | 0 | Theoretical and Fundamental Chemistry |
When a melt undergoes cooling along the liquid line of descent, the results are limited to the production of a homogeneous solid body of intrusive rock, with uniform mineralogy and composition, or a partially differentiated cumulate mass with layers, compositional zones and so on. This behaviour is fairly predictable and easy enough to prove with geochemical investigations. In such cases, a magma chamber will form a close approximation of the ideal Bowen's reaction series. However, most magmatic systems are polyphase events, with several pulses of magmatism. In such a case, the liquid line of descent is interrupted by the injection of a fresh batch of hot, undifferentiated magma. This can cause extreme fractional crystallisation because of three main effects:
* Additional heat provides additional energy to allow more vigorous convection, allows resorption of existing mineral phases back into the melt, and can cause a higher-temperature form of a mineral or other higher-temperature minerals to begin precipitating
* Fresh magma changes the composition of the melt, changing the chemistry of the phases which are being precipitated. For instance, plagioclase conforms to the liquid line of descent by forming initial anorthite which, if removed, changes the equilibrium mineral composition to oligoclase or albite. Replenishment of the magma can see this trend reversed, so that more anorthite is precipitated atop cumulate layers of albite.
* Fresh magma destabilises minerals which are precipitating as solid solution series or on a eutectic; a change in composition and temperature can cause extremely rapid crystallisation of certain mineral phases which are undergoing a eutectic crystallisation phase. | 0 | Theoretical and Fundamental Chemistry |
For example, different sources and sinks of methane have different affinity for the C and C isotopes, which allows distinguishing between different sources by the C/C ratio in methane in the air. In geochemistry, paleoclimatology and paleoceanography this ratio is called δC. The ratio is calculated with respect to Pee Dee Belemnite (PDB) standard:
Similarly, carbon in inorganic carbonates shows little isotopic fractionation, while carbon in materials originated by photosynthesis is depleted of the heavier isotopes. In addition, there are two types of plants with different biochemical pathways; the C3 carbon fixation, where the isotope separation effect is more pronounced, C4 carbon fixation, where the heavier C is less depleted, and Crassulacean Acid Metabolism (CAM) plants, where the effect is similar but less pronounced than with C plants. Isotopic fractionation in plants is caused by physical (slower diffusion of C in plant tissues due to increased atomic weight) and biochemical (preference of C by two enzymes: RuBisCO and phosphoenolpyruvate carboxylase) factors. The different isotope ratios for the two kinds of plants propagate through the food chain, thus it is possible to determine if the principal diet of a human or an animal consists primarily of C plants (rice, wheat, soybeans, potatoes) or C plants (corn, or corn-fed beef) by isotope analysis of their flesh and bone collagen (however, to obtain more accurate determinations, carbon isotopic fractionation must be also taken into account, since several studies have reported significant C discrimination during biodegradation of simple and complex substrates).
Within C3 plants processes regulating changes in δC are well understood, particularly at the leaf level, but also during wood formation. Many recent studies combine leaf level isotopic fractionation with annual patterns of wood formation (i.e. tree ring δC) to quantify the impacts of climatic variations and atmospheric composition on physiological processes of individual trees and forest stands. The next phase of understanding, in terrestrial ecosystems at least, seems to be the combination of multiple isotopic proxies to decipher interactions between plants, soils and the atmosphere, and predict how changes in land use will affect climate change.
Similarly, marine fish contain more C than freshwater fish, with values approximating the C and C plants respectively.
The ratio of carbon-13 and carbon-12 isotopes in these types of plants is as follows:
* C plants: -16 to -10 ‰
* CAM plants: -20 to -10 ‰
* C plants: -33 to -24 ‰
Limestones formed by precipitation in seas from the atmospheric carbon dioxide contain normal proportion of C. Conversely, calcite found in salt domes originates from carbon dioxide formed by oxidation of petroleum, which due to its plant origin is C-depleted. The layer of limestone deposited at the Permian extinction 252 Mya can be identified by the 1% drop in C/C.
The C isotope is important in distinguishing biosynthetized materials from man-made ones. Biogenic chemicals are derived from biospheric carbon, which contains C. Carbon in artificially made chemicals is usually derived from fossil fuels like coal or petroleum, where the C originally present has decayed below detectable limits. The amount of C currently present in a sample therefore indicates the proportion of carbon of biogenic origin. | 0 | Theoretical and Fundamental Chemistry |
Since both shearing and stretching are as low as possible along a parabolic LCS, one may seek initial positions of such material surfaces as trenches of the FTLE field . A geophysical example of a parabolic LCS (generalized jet core) revealed as a trench of the FTLE field is shown in Fig. 14a. | 1 | Applied and Interdisciplinary Chemistry |
In biochemistry, activation, specifically called bioactivation, is where enzymes or other biologically active molecules acquire the ability to perform their biological function, such as inactive proenzymes being converted into active enzymes that are able to catalyze their substrates reactions into products. Bioactivation may also refer to the process where inactive prodrugs are converted into their active metabolites, or the toxication' of protoxins into actual toxins.
An enzyme may be reversibly or irreversibly bioactivated. A major mechanism of irreversible bioactivation is where a piece of a protein is cut off by cleavage, producing an enzyme that will then stay active. A major mechanism of reversible bioactivation is substrate presentation where an enzyme translocates near its substrate. Another reversible reaction is where a cofactor binds to an enzyme, which then remains active while the cofactor is bound, and stops being active when the cofactor is removed.
In protein synthesis, amino acids are carried by transfer RNA (tRNA) molecules and added to a growing polypeptide chain on the ribosome. In order to transfer the amino acids to the ribosome, tRNAs must first be covalently bonded to the amino acid through their 3' CCA terminal. This binding is catalyzed by aminoacyl-tRNA synthetase, and requires a molecule of ATP. The amino acid bound to the tRNA is called an aminoacyl-tRNA, and is considered the activated molecule in protein translation. Once activated, the aminoacyl-tRNA may move to the ribosome and add the amino acid to the growing polypeptide chain. | 0 | Theoretical and Fundamental Chemistry |
The symbol used to represent pressure in equations is "p" or "P" with SI units of pascals.
When describing a container of gas, the term pressure (or absolute pressure) refers to the average force per unit area that the gas exerts on the surface of the container. Within this volume, it is sometimes easier to visualize the gas particles moving in straight lines until they collide with the container (see diagram at top of the article). The force imparted by a gas particle into the container during this collision is the change in momentum of the particle. During a collision only the normal component of velocity changes. A particle traveling parallel to the wall does not change its momentum. Therefore, the average force on a surface must be the average change in linear momentum from all of these gas particle collisions.
Pressure is the sum of all the normal components of force exerted by the particles impacting the walls of the container divided by the surface area of the wall. | 0 | Theoretical and Fundamental Chemistry |
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