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The retinoblastoma protein (protein name abbreviated Rb; gene name abbreviated Rb, RB or RB1) is a tumor suppressor protein that is dysfunctional in several major cancers. One function of pRb is to prevent excessive cell growth by inhibiting cell cycle progression until a cell is ready to divide. When the cell is ready to divide, pRb is phosphorylated, inactivating it, and the cell cycle is allowed to progress. It is also a recruiter of several chromatin remodeling enzymes such as methylases and acetylases.
pRb belongs to the pocket protein family, whose members have a pocket for the functional binding of other proteins. Should an oncogenic protein, such as those produced by cells infected by high-risk types of human papillomavirus, bind and inactivate pRb, this can lead to cancer. The RB gene may have been responsible for the evolution of multicellularity in several lineages of life including animals. | 1 | Applied and Interdisciplinary Chemistry |
Regular achiral organocatalysts are based on nitrogen such as piperidine used in the Knoevenagel condensation. DMAP used in esterifications and DABCO used in the Baylis-Hillman reaction. Thiazolium salts are employed in the Stetter reaction. These catalysts and reactions have a long history but current interest in organocatalysis is focused on asymmetric catalysis with chiral catalysts, called asymmetric organocatalysis or enantioselective organocatalysis. A pioneering reaction developed in the 1970s is called the Hajos–Parrish–Eder–Sauer–Wiechert reaction. Between 1968 and 1997, there were only a few reports of the use of small organic molecules as catalysts for asymmetric reactions (the Hajos–Parrish reaction probably being the most famous), but these chemical studies were viewed more as unique chemical reactions than as integral parts of a larger, interconnected field.
In this reaction, naturally occurring chiral proline is the chiral catalyst in an Aldol reaction. The starting material is an achiral triketone and it requires just 3% of proline to obtain the reaction product, a ketol in 93% enantiomeric excess. This is the first example of an amino acid-catalyzed asymmetric aldol reaction.
The asymmetric synthesis of the Wieland-Miescher ketone (1985) is also based on proline and another early application was one of the transformations in the total synthesis of Erythromycin by Robert B. Woodward (1981). A mini-review digest article focuses on selected recent examples of total synthesis of natural and pharmaceutical products using organocatalytic reactions.
Many chiral organocatalysts are an adaptation of chiral ligands (which together with a metal center also catalyze asymmetric reactions) and both concepts overlap to some degree.
A breakthrough in the field of organocatalysis came in 1997 when Yian Shi reported the first general, highly enantioselective organocatalytic reaction with the catalytic asymmetric epoxidation of trans- and trisubstituted olefins with chiral dioxiranes. Since that time, several different types of reactions have been developed. | 0 | Theoretical and Fundamental Chemistry |
One of the important factors in determining the dentinal bonding is collagen. When dentin is etched, smear layer and minerals from dentinal structure will be removed, hence exposing the collagen fibres. The areas where the minerals are removed are filled with water which functions as plasticizer for collagen and keeps it at expanded soft state. This means that the spaces for resin-dentin bonding are preserved. However, these collagen fibres can collapse in dry condition and if the organic layer of matrix is denatured, this will obstruct the resin to bond with dentin and form a hybrid layer.
Because of this, the presence of moist or wet dentin is required to achieve successful dentin bonding. This is due to presence of water miscible organic solvents like ethanol or acetone in the primers. The acetone trails water and hence improves the penetration of the monomers into the dentin for better micromechanical bonding. Also, water will prevent collagen fibres from collapsing, thus making better penetration and bonding between resin and dentin.
In order to get a moist dentin, it is advisable to not dry dentin with compressed air after rinsing away the etchant. Instead, high volume evacuation suction can be used to remove excess water and then blot the remaining water present on dentin using gauze or cotton. The dentin surface should appear glistening.
If the dentin surface is too wet, water will dilute the resin primer and compete for the sites in collagen network, which will prevent hybrid layer formation.
If the dentin surface is too dry, collapse of collagen fibres and demineralized dentin can occur, leading to low bond strength. | 0 | Theoretical and Fundamental Chemistry |
A use of ion chromatography can be seen in argentation chromatography. Usually, silver and compounds containing acetylenic and ethylenic bonds have very weak interactions. This phenomenon has been widely tested on olefin compounds. The ion complexes the olefins make with silver ions are weak and made based on the overlapping of pi, sigma, and d orbitals and available electrons therefore cause no real changes in the double bond. This behavior was manipulated to separate lipids, mainly fatty acids from mixtures in to fractions with differing number of double bonds using silver ions. The ion resins were impregnated with silver ions, which were then exposed to various acids (silicic acid) to elute fatty acids of different characteristics.
Detection limits as low as 1 μM can be obtained for alkali metal ions.
It may be used for measurement of HbA1c, porphyrin and with water purification. Ion Exchange Resins(IER) have been widely used especially in medicines due to its high capacity and the uncomplicated system of the separation process. One of the synthetic uses is to use Ion Exchange Resins for kidney dialysis. This method is used to separate the blood elements by using the cellulose membraned artificial kidney.
Another clinical application of ion chromatography is in the rapid anion exchange chromatography technique used to separate creatine kinase (CK) isoenzymes from human serum and tissue sourced in autopsy material (mostly CK rich tissues were used such as cardiac muscle and brain). These isoenzymes include MM, MB, and BB, which all carry out the same function given different amino acid sequences. The functions of these isoenzymes are to convert creatine, using ATP, into phosphocreatine expelling ADP. Mini columns were filled with DEAE-Sephadex A-50 and further eluted with tris- buffer sodium chloride at various concentrations (each concentration was chosen advantageously to manipulate elution). Human tissue extract was inserted in columns for separation. All fractions were analyzed to see total CK activity and it was found that each source of CK isoenzymes had characteristic isoenzymes found within. Firstly, CK- MM was eluted, then CK-MB, followed by CK-BB. Therefore, the isoenzymes found in each sample could be used to identify the source, as they were tissue specific.
Using the information from results, correlation could be made about the diagnosis of patients and the kind of CK isoenzymes found in most abundant activity. From the finding, about 35 out of 71 patients studied suffered from heart attack (myocardial infarction) also contained an abundant amount of the CK-MM and CK-MB isoenzymes. Findings further show that many other diagnosis including renal failure, cerebrovascular disease, and pulmonary disease were only found to have the CK-MM isoenzyme and no other isoenzyme. The results from this study indicate correlations between various diseases and the CK isoenzymes found which confirms previous test results using various techniques. Studies about CK-MB found in heart attack victims have expanded since this study and application of ion chromatography. | 0 | Theoretical and Fundamental Chemistry |
The endogenous steroids dehydroepiandrosterone (DHEA) and its sulfate ester, DHEA sulfate (DHEA-S), have been identified as small-molecule agonists of the TrkA and p75 with high affinity (around 5 nM), and hence as so-called "microneurotrophins". DHEA has also been found to bind to the TrkB and TrkC, though while it activated the TrkC, it was unable to activate the TrkB. It has been proposed that DHEA may have been the ancestral ligand of the Trk receptors early on in the evolution of the nervous system, eventually being superseded by the polypeptide neurotrophins. | 1 | Applied and Interdisciplinary Chemistry |
We start with a three-state Λ-type system, where and are dipole-allowed transitions and is forbidden. In the rotating wave approximation, the semi-classical Hamiltonian is given by
with
where and are the Rabi frequencies of the probe field (of frequency ) and the coupling field (of frequency ) in resonance with the transition frequencies and , respectively, and H.c. stands for the Hermitian conjugate of the entire expression. We will write the atomic wave function as
Solving the Schrödinger equation , we obtain the solutions
Using the initial condition
we can solve these equations to obtain
with . We observe that we can choose the initial conditions
which gives a time-independent solution to these equations with no probability of the system being in state . This state can also be expressed in terms of a mixing angle as
with
This means that when the atoms are in this state, they will stay in this state indefinitely. This is a dark state, because it can not absorb or emit any photons from the applied fields. It is, therefore, effectively transparent to the probe laser, even when the laser is exactly resonant with the transition. Spontaneous emission from can result in an atom being in this dark state or another coherent state, known as a bright state. Therefore, in a collection of atoms, over time, decay into the dark state will inevitably result in the system being "trapped" coherently in that state, a phenomenon known as coherent population trapping. | 0 | Theoretical and Fundamental Chemistry |
The genes required for the synthesis of cysteine are coded for on the cys regulon. The integration of sulfur is positively regulated by CysB. Effective inducers of this regulon are N-acetyl-serine (NAS) and very small amounts of reduced sulfur. CysB functions by binding to DNA half sites on the cys regulon. These half sites differ in quantity and arrangement depending on the promoter of interest. There is however one half site that is conserved. It lies just upstream of the -35 site of the promoter. There are also multiple accessory sites depending on the promoter. In the absence of the inducer, NAS, CysB will bind the DNA and cover many of the accessory half sites. Without the accessory half sites the regulon cannot be transcribed and cysteine will not be produced. It is believed that the presence of NAS causes CysB to undergo a conformational change. This conformational change allows CysB to bind properly to all the half sites and causes the recruitment of the RNA polymerase. The RNA polymerase will then transcribe the cys regulon and cysteine will be produced.
Further regulation is required for this pathway, however. CysB can down regulate its own transcription by binding to its own DNA sequence and blocking the RNA polymerase. In this case NAS will act to disallow the binding of CysB to its own DNA sequence. OAS is a precursor of NAS, cysteine itself can inhibit CysE which functions to create OAS. Without the necessary OAS, NAS will not be produced and cysteine will not be produced. There are two other negative regulators of cysteine. These are the molecules sulfide and thiosulfate, they act to bind to CysB and they compete with NAS for the binding of CysB. | 1 | Applied and Interdisciplinary Chemistry |
The law itself can be stated as follows:
Boyle's law is a gas law, stating that the pressure and volume of a gas have an inverse relationship. If volume increases, then pressure decreases and vice versa, when the temperature is held constant.
Therefore, when the volume is halved, the pressure is doubled; and if the volume is doubled, the pressure is halved. | 0 | Theoretical and Fundamental Chemistry |
In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which succinctly summarizes much of the atomic-level structure of the sequenced molecule. | 1 | Applied and Interdisciplinary Chemistry |
The list shown below enlists some common ligands (showing increasing nephelauxetic effect):
:F O ]] ]]
Although parts of this series may seem quite similar to the spectrochemical series of ligands - for example, cyanide, ethylenediamine, and fluoride seem to occupy similar positions in the two - others such as chloride, iodide and bromide (amongst others), occupy very different positions. The ordering roughly reflects the ability of the ligands to form good covalent bonds with metals - those that have a small effect are at the start of the series, whereas those that have a large effect are at the end of the series. | 0 | Theoretical and Fundamental Chemistry |
In metal base-pairing, the Watson-Crick hydrogen bonds are replaced by the interaction between a metal ion with nucleosides acting as ligands. The possible geometries of the metal that would allow for duplex formation with two bidentate nucleosides around a central metal atom are tetrahedral, dodecahedral, and square planar. Metal-complexing with DNA can occur by the formation of non-canonical base pairs from natural nucleobases with participation by metal ions and also by the exchanging the hydrogen atoms that are part of the Watson-Crick base pairing by metal ions. Introduction of metal ions into a DNA duplex has shown to have potential magnetic or conducting properties, as well as increased stability.
Metal complexing has been shown to occur between natural nucleobases. A well-documented example is the formation of T-Hg-T, which involves two deprotonated thymine nucleobases that are brought together by Hg and forms a connected metal-base pair. This motif does not accommodate stacked Hg in a duplex due to an intrastrand hairpin formation process that is favored over duplex formation. Two thymines across from each other do not form a Watson-Crick base pair in a duplex; this is an example where a Watson-Crick basepair mismatch is stabilized by the formation of the metal-base pair. Another example of a metal complexing to natural nucleobases is the formation of A-Zn-T and G-Zn-C at high pH; Co and Ni also form these complexes. These are Watson-Crick base pairs where the divalent cation in coordinated to the nucleobases. The exact binding is debated.
A large variety of artificial nucleobases have been developed for use as metal base pairs. These modified nucleobases exhibit tunable electronic properties, sizes, and binding affinities that can be optimized for a specific metal. For example, a nucleoside modified with a pyridine-2,6-dicarboxylate has shown to bind tightly to Cu, whereas other divalent ions are only loosely bound. The tridentate character contributes to this selectivity. The fourth coordination site on the copper is saturated by an oppositely arranged pyridine nucleobase. The asymmetric metal base pairing system is orthogonal to the Watson-Crick base pairs. Another example of an artificial nucleobase is that with hydroxypyridone nucleobases, which are able to bind Cu inside the DNA duplex. Five consecutive copper-hydroxypyridone base pairs were incorporated into a double strand, which were flanked by only one natural nucleobase on both ends. EPR data showed that the distance between copper centers was estimated to be 3.7 ± 0.1 Å, while a natural B-type DNA duplex is only slightly larger (3.4 Å). The appeal for stacking metal ions inside a DNA duplex is the hope to obtain nanoscopic self-assembling metal wires, though this has not been realized yet. | 1 | Applied and Interdisciplinary Chemistry |
In the chromatography of a glow stick solution, a piece of chalk, a highly polar substance, is used as the stationary phase while comparatively less-polar solvents like acetone and 91% isopropyl alcohol can be used as the mobile phase. Chalk is made up of calcium carbonate (CaCO) or calcium sulfate (CaSO), and therefore contains ions. This allows it to attract other ions and polar molecules, but not nonpolar molecules. As a result, ionic and more-polar dyes would be attracted to the stationary phase and move relatively slowly or a fairly small distance, while less polar dyes would migrate further as the mobile phase wicks up the chalk. This then allows for the separation of dyes. | 1 | Applied and Interdisciplinary Chemistry |
* Novel treatments for autoimmune disorders: Edward Roberts and his team designed and synthesized a selective and bitopic S1P1 agonist, RPC1063. This compound showed promise as a safe treatment for autoimmune diseases such as multiple sclerosis, ulcerative colitis, and Crohn's disease. Ozanimod (RPC1063), now marketed as Zeposia, has been approved for use in relapsing multiple sclerosis and inflammatory bowel disease.
* Novel treatments for neuropsychiatric and behavioral Disorders: Roberts' lab designed and developed a series of kappa opioid antagonists for stress-related mood disorders, migraine, and other neuropsychiatric conditions. One such antagonist, Navacaprant (formerly CYM-53093, BTRX-335140), exhibited robust efficacy in early clinical trials and is currently in multiple phase 3 trials for major depressive diseases.
* Compounds for use in the treatment of autistic spectrum disorders and/or post-traumatic stress disorders: Roberts' team designed and synthesized novel and improved V1a antagonists for potential therapeutic use in various neuropsychological disorders. One representative molecule NMRA-511 is currently in phase 2 clinical trials.
* Novel compounds for use in fibrotic diseases: Roberts' research explored the therapeutic potential of subtype 3 of the sphingosine-1-phosphate receptors as targets for cardiovascular and pulmonary diseases, fibrosis, and other related conditions.
* Novel compounds for use in seizures; Roberts and colleagues explored the use of Galanin receptor agonists to delay and prevent seizures in animals displaying excellent activity and better mortality outcomes than current first line treatment. | 0 | Theoretical and Fundamental Chemistry |
Vancomycin is recommended to be administered in a dilute solution slowly, over at least 60 min (maximum rate of 10 mg/min for doses >500 mg) due to the high incidence of pain and thrombophlebitis and to avoid an infusion reaction known as vancomycin flushing reaction. This phenomenon has been often clinically referred to as "red man syndrome". The reaction usually appears within 4 to 10 min after the commencement or soon after the completion of an infusion and is characterized by flushing and/or an erythematous rash that affects the face, neck, and upper torso, attributed to the release of histamine from mast cells. This reaction is caused by the interaction of vancomycin with MRGPRX2, a GPCR mediating IgE-independent mast cell degranulation. Less frequently, hypotension and angioedema may also occur. Symptoms may be treated or prevented with antihistamines, including diphenhydramine, and are less likely to occur with slow infusion. | 0 | Theoretical and Fundamental Chemistry |
Because of the H gradient across the thylakoid membrane, the interior of the thylakoid is acidic, with a pH around 4, while the stroma is slightly basic, with a pH of around 8.
The optimal stroma pH for the Calvin cycle is 8.1, with the reaction nearly stopping when the pH falls below 7.3.
CO in water can form carbonic acid, which can disturb the pH of isolated chloroplasts, interfering with photosynthesis, even though CO is used in photosynthesis. However, chloroplasts in living plant cells are not affected by this as much.
Chloroplasts can pump K and H ions in and out of themselves using a poorly understood light-driven transport system.
In the presence of light, the pH of the thylakoid lumen can drop up to 1.5 pH units, while the pH of the stroma can rise by nearly one pH unit. | 0 | Theoretical and Fundamental Chemistry |
:La yielded the highest water splitting rate of photocatalysts without using sacrificial reagents. This ultraviolet-based photocatalyst was reported to show water splitting rates of 9.7 mmol/h and a quantum yield of 56%. The nanostep structure of the material promotes water splitting as edges functioned as production sites and the grooves functioned as production sites. Addition of NiO particles as co-catalysts assisted in production; this step used an impregnation method with an aqueous solution of •6 and evaporated the solution in the presence of the photocatalyst. has a conduction band higher than that of NiO, so photo-generated electrons are more easily transferred to the conduction band of NiO for evolution. | 0 | Theoretical and Fundamental Chemistry |
Almost all the information available on the structure of the Earths deep interior is derived from observations of the travel times, reflections, refractions and phase transitions of seismic body waves, or normal modes. P waves travel through the fluid layers of the Earths interior, and yet they are refracted slightly when they pass through the transition between the semisolid mantle and the liquid outer core. As a result, there is a P wave "shadow zone" between 103° and 142° from the earthquake's focus, where the initial P waves are not registered on seismometers. In contrast, S waves do not travel through liquids. | 1 | Applied and Interdisciplinary Chemistry |
Plant viruses can be used to engineer viral vectors, tools commonly used by molecular biologists to deliver genetic material into plant cells; they are also sources of biomaterials and nanotechnology devices. Knowledge of plant viruses and their components has been instrumental for the development of modern plant biotechnology. The use of plant viruses to enhance the beauty of ornamental plants can be considered the first recorded application of plant viruses. Tulip breaking virus is famous for its dramatic effects on the color of the tulip perianth, an effect highly sought after during the 17th-century Dutch "tulip mania." Tobacco mosaic virus (TMV) and cauliflower mosaic virus (CaMV) are frequently used in plant molecular biology. Of special interest is the CaMV 35S promoter, which is a very strong promoter most frequently used in plant transformations. Viral vectors based on tobacco mosaic virus include those of the [https://www.icongenetics.com/technology/ magnICON®] and TRBO plant expression technologies.
Representative applications of plant viruses are listed below. | 1 | Applied and Interdisciplinary Chemistry |
*Hyrcania, ancient state in the north of Iran
*Sari, Mazandaran Province of Iran
*Anzali, Gilan Province of Iran
*Astara, Gilan Province of Iran
*Astarabad, Golestan Province of Iran
*Tamisheh, Golestan Province of Iran
*Atil, Khazaria
*Khazaran
*Baku, Azerbaijan
*Derbent, Dagestan, Russia
*Xacitarxan, modern-day Astrakhan | 1 | Applied and Interdisciplinary Chemistry |
Nuclease Prime Editor uses Cas9 nuclease instead of Cas9(H840A) nickase. Unlike prime editor 3 (PE3) that requires dual-nick at both DNA strands to induce efficient prime editing, Nuclease Prime Editor requires only a single pegRNA since the single-gRNA already creates double-strand break instead of single-strand nick. | 1 | Applied and Interdisciplinary Chemistry |
A recent report on the Sava river in Serbia suggests that many of the river silts contain about 100 Bq kg of natural radioisotopes (Ra, Th, and U). According to the United Nations the normal concentration of uranium in soil ranges between 300 μg kg and 11.7 mg kg. It is well known that some plants, called hyperaccumulators, are able to absorb and concentrate metals within their tissues; iodine was first isolated from seaweed in France, which suggests that seaweed is an iodine hyperaccumulator.
Synthetic radioisotopes also can be detected in silt. Busby quotes a report on the plutonium activity in Welsh intertidal sediments by Garland et al. (1989), which suggests that the closer a site is to Sellafield, the higher is the concentration of plutonium in the silt. Some relationship between distance and activity can be seen in their data, when fitted to an exponential curve, but the scatter of the points is large (R = 0.3683). | 0 | Theoretical and Fundamental Chemistry |
In crystallography, the term polysome is used to describe overall mineral structures which have structurally and compositionally different framework structures.
A general example is amphiboles, in which cutting along the {010} plane yields alternating layers of pyroxene and trioctahedral mica. | 0 | Theoretical and Fundamental Chemistry |
When drained, soils containing Reduced Inorganic Sulfides such as pyrite may become extremely acidic (pH SO):
The product Fe(OH), iron(III) hydroxide (orange), precipitates as a solid, insoluble mineral by which the alkalinity component is immobilized, while the acidity remains active in the sulfuric acid. The process of acidification is accompanied by the formation of high amounts of aluminium (Al, released from clay minerals under influence of the acidity), which are harmful to vegetation. Other products of the chemical reaction are:
# Hydrogen sulfide (HS), a foul-smelling gas
# Sulfur (S), a yellow solid
# Iron(II) sulfide (FeS), a black/gray/blue solid
# Hematite (FeO), a red solid
# Goethite (), a brown mineral
# Iron sulfate compounds (e.g., jarosite, schwertmannite, gypsum, and epsomite)
# H-Clay (hydrogen clay, with a large fraction of adsorbed H ions, a stable mineral, but poor in nutrients)
The iron can be present in bivalent and trivalent forms (Fe, the ferrous ion, and Fe, the ferric ion respectively). The ferrous form is soluble in a relatively wide range of pH conditions whereas the ferric form is not soluble except in an extremely acidic environment such as muriatic acid rust remover. The more oxidized the soil becomes, the more the ferric forms dominate. Acid sulfate soils exhibit an array of colors ranging from black, brown, blue-gray, red, orange and yellow. The hydrogen clay can be improved by admitting sea water: the magnesium (Mg) and sodium (Na) in the sea water replaces the adsorbed hydrogen and other exchangeable acidic cations such as aluminium (Al). However this can create additional risks when the hydrogen ions and exchangeable metals are mobilised. | 0 | Theoretical and Fundamental Chemistry |
Carbon is one of the few elements that can form long chains of its own atoms, a property called catenation. This coupled with the strength of the carbon–carbon bond gives rise to an enormous number of molecular forms, many of which are important structural elements of life, so carbon compounds have their own field of study: organic chemistry.
Branching is also common in C−C skeletons. Carbon atoms in a molecule are categorized by the number of carbon neighbors they have:
* A primary carbon has one carbon neighbor.
* A secondary carbon has two carbon neighbors.
* A tertiary carbon has three carbon neighbors.
* A quaternary carbon has four carbon neighbors.
In "structurally complex organic molecules", it is the three-dimensional orientation of the carbon–carbon bonds at quaternary loci which dictates the shape of the molecule. Further, quaternary loci are found in many biologically active small molecules, such as cortisone and morphine. | 0 | Theoretical and Fundamental Chemistry |
According to crystal field theory, the interaction between a transition metal and ligands arises from the attraction between the positively charged metal cation and the negative charge on the non-bonding electrons of the ligand. The theory is developed by considering energy changes of the five degenerate d-orbitals upon being surrounded by an array of point charges consisting of the ligands. As a ligand approaches the metal ion, the electrons from the ligand will be closer to some of the d-orbitals and farther away from others, causing a loss of degeneracy. The electrons in the d-orbitals and those in the ligand repel each other due to repulsion between like charges. Thus the d-electrons closer to the ligands will have a higher energy than those further away which results in the d-orbitals splitting in energy. This splitting is affected by the following factors:
* the nature of the metal ion.
* the metal's oxidation state. A higher oxidation state leads to a larger splitting relative to the spherical field.
* the arrangement of the ligands around the metal ion.
* the coordination number of the metal (i.e. tetrahedral, octahedral...)
* the nature of the ligands surrounding the metal ion. The stronger the effect of the ligands then the greater the difference between the high and low energy d groups.
The most common type of complex is octahedral, in which six ligands form the vertices of an octahedron around the metal ion. In octahedral symmetry the d-orbitals split into two sets with an energy difference, Δ (the crystal-field splitting parameter, also commonly denoted by 10Dq for ten times the "differential of quanta") where the d, d and d orbitals will be lower in energy than the d-y, and the two higher-energy orbitals as e. These labels are based on the theory of molecular symmetry: they are the names of irreducible representations of the octahedral point group, O.(see the O character table) Typical orbital energy diagrams are given below in the section High-spin and low-spin.
Tetrahedral complexes are the second most common type; here four ligands form a tetrahedron around the metal ion. In a tetrahedral crystal field splitting, the d-orbitals again split into two groups, with an energy difference of Δ. The lower energy orbitals will be d-y, d and d - opposite to the octahedral case. Furthermore, since the ligand electrons in tetrahedral symmetry are not oriented directly towards the d-orbitals, the energy splitting will be lower than in the octahedral case. Square planar and other complex geometries can also be described by CFT.
The size of the gap Δ between the two or more sets of orbitals depends on several factors, including the ligands and geometry of the complex. Some ligands always produce a small value of Δ, while others always give a large splitting. The reasons behind this can be explained by ligand field theory. The spectrochemical series is an empirically-derived list of ligands ordered by the size of the splitting Δ that they produce (small Δ to large Δ; see also this table):
I (S–bonded) O O (N–bonded) CN < CO.
It is useful to note that the ligands producing the most splitting are those that can engage in metal to ligand back-bonding.
The oxidation state of the metal also contributes to the size of Δ between the high and low energy levels. As the oxidation state increases for a given metal, the magnitude of Δ increases. A V complex will have a larger Δ than a V complex for a given set of ligands, as the difference in charge density allows the ligands to be closer to a V ion than to a V ion. The smaller distance between the ligand and the metal ion results in a larger Δ, because the ligand and metal electrons are closer together and therefore repel more. | 0 | Theoretical and Fundamental Chemistry |
The cost of sequencing has dropped dramatically while the cost of construction of jumping libraries has not. Therefore, as new sequencing technologies and bioinformatic tools are developed, jumping libraries may become redundant. | 1 | Applied and Interdisciplinary Chemistry |
Reactants of the photoreactions can be both gaseous and liquids. In general, it is necessary to bring the reactants close to the light source in order to obtain the highest possible luminous efficacy. For this purpose, the reaction mixture can be irradiated either directly or in a flow-through side arm of a reactor with a suitable light source.
A disadvantage of photochemical processes is the low efficiency of the conversion of electrical energy in the radiation energy of the required wavelength. In addition to the radiation, light sources generate plenty of heat, which in turn requires cooling energy. In addition, most light sources emit polychromatic light, even though only monochromatic light is needed. A high quantum yield, however, compensates for these disadvantages.
Working at low temperatures is advantageous since side reactions are avoided (as the selectivity is increased) and the yield is increased (since gaseous reactants are driven out less from the solvent).
The starting materials can sometimes be cooled before the reaction to such an extent that the reaction heat is absorbed without further cooling of the mixture. In the case of gaseous or low-boiling starting materials, work under overpressure is necessary. Due to the large number of possible raw materials, a large number of processes have been described. Large scale reactions are usually carried out in a stirred tank reactor, a bubble column reactor or a tube reactor, followed by further processing depending on the target product. In case of a stirred tank reactor, the lamp (generally shaped as an elongated cylinder) is provided with a cooling jacket and placed in the reaction solution. Tube reactors are made from quartz or glass tubes, which are irradiated from the outside. Using a stirred tank reactor has the advantage that no light is lost to the environment. However, the intensity of light drops rapidly with the distance to the light source due to adsorption by the reactants.
The influence of the radiation on the reaction rate can often be represented by a power law based on the quantum flow density, i.e. the mole light quantum (previously measured in the unit einstein) per area and time. One objective in the design of reactors is therefore to determine the economically most favorable dimensioning with regard to an optimization of the quantum current density. | 0 | Theoretical and Fundamental Chemistry |
The three most important roles that PEP carboxylase plays in plants and bacteria metabolism are in the cycle, the CAM cycle, and the citric acid cycle biosynthesis flux.
The primary mechanism of carbon dioxide assimilation in plants is through the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (also known as RuBisCO), that adds CO to ribulose-1,5-bisphosphate (a 5 carbon sugar), to form two molecules of 3-phosphoglycerate (2x3 carbon sugars). However, at higher temperatures and lower CO concentrations, RuBisCO adds oxygen instead of carbon dioxide, to form the unusable product glycolate in a process called photorespiration. To prevent this wasteful process, plants increase the local CO concentration in a process called the cycle. PEP carboxylase plays the key role of binding CO in the form of bicarbonate with PEP to create oxaloacetate in the mesophyll tissue. This is then converted back to pyruvate (through a malate intermediate), to release the CO in the deeper layer of bundle sheath cells for carbon fixation by RuBisCO and the Calvin cycle. Pyruvate is converted back to PEP in the mesophyll cells, and the cycle begins again, thus actively pumping CO.
The second important and very similar biological significance of PEP carboxylase is in the CAM cycle. This cycle is common in organisms living in arid habitats. Plants cannot afford to open stomata during the day to take in CO, as they would lose too much water by transpiration. Instead, stomata open at night, when water evaporation is minimal, and take in CO by fixing with PEP to form oxaloacetate though PEP carboxylase. Oxaloacetate is converted to malate by malate dehydrogenase, and stored for use during the day when the light dependent reaction generates energy (mainly in the form of ATP) and reducing equivalents such as NADPH to run the Calvin cycle.
Third, PEP carboxylase is significant in non-photosynthetic metabolic pathways. Figure 3 shows this metabolic flow (and its regulation). Similar to pyruvate carboxylase, PEP carboxylase replenishes oxaloacetate in the citric acid cycle. At the end of glycolysis, PEP is converted to pyruvate, which is converted to acetyl-coenzyme-A (acetyl-CoA), which enters the citric acid cycle by reacting with oxaloacetate to form citrate. To increase flux through the cycle, some of the PEP is converted to oxaloacetate by PEP carboxylase. Since the citric acid cycle intermediates provide a hub for metabolism, increasing flux is important for the biosynthesis of many molecules, such as for example amino acids. | 0 | Theoretical and Fundamental Chemistry |
Many sulfate reducers are organotrophic, using carbon compounds such as lactate and pyruvate (among many others) as electron donors, while others are lithotrophic, using hydrogen gas () as an electron donor. Some unusual autotrophic sulfate-reducing bacteria (e.g. Desulfotignum phosphitoxidans) can use phosphite () as an electron donor whereas others (e.g. Desulfovibrio sulfodismutans, Desulfocapsa thiozymogenes, Desulfocapsa sulfoexigens) are capable of sulfur disproportionation (splitting one compound into two different compounds, in this case an electron donor and an electron acceptor) using elemental sulfur (S), sulfite (), and thiosulfate () to produce both hydrogen sulfide () and sulfate (). | 1 | Applied and Interdisciplinary Chemistry |
Chloramphenicol is a rare example of a naturally occurring nitro compound. At least some naturally occurring nitro groups arose by the oxidation of amino groups. 2-Nitrophenol is an aggregation pheromone of ticks.
Examples of nitro compounds are rare in nature. 3-Nitropropionic acid found in fungi and plants (Indigofera). Nitropentadecene is a defense compound found in termites. Aristolochic acids are found in the flowering plant family Aristolochiaceae. Nitrophenylethane is found in Aniba canelilla. Nitrophenylethane is also found in members of the Annonaceae, Lauraceae and Papaveraceae. | 0 | Theoretical and Fundamental Chemistry |
Research efforts have been focused on determining how thalidomide causes birth defects and its other activities in the human body, efforts to develop safer analogs, and efforts to find further uses for thalidomide. | 0 | Theoretical and Fundamental Chemistry |
When the nasal decongestant is taken in excess, levomethamphetamine has potential side effects. These would be similar to those of other decongestants. | 0 | Theoretical and Fundamental Chemistry |
Up-regulated expression of genes in mammals is initiated when signals are transmitted to the promoters associated with the genes. Promoter DNA sequences may include different elements such as CpG islands (present in about 70% of promoters), a TATA box (present in about 24% of promoters), initiator (Inr) (present in about 49% of promoters), upstream and downstream TFIIB recognition elements (BREu and BREd) (present in about 22% of promoters), and downstream core promoter element (DPE) (present in about 12% of promoters). The presence of multiple methylated CpG sites in CpG islands of promoters causes stable silencing of genes. However, the presence or absence of the other elements have relatively small effects on gene expression in experiments. Two sequences, the TATA box and Inr, caused small but significant increases in expression (45% and 28% increases, respectively). The BREu and the BREd elements significantly decreased expression by 35% and 20%, respectively, and the DPE element had no detected effect on expression.
Cis-regulatory modules that are localized in DNA regions distant from the promoters of genes can have very large effects on gene expression, with some genes undergoing up to 100-fold increased expression due to such a cis-regulatory module. These cis-regulatory modules include enhancers, silencers, insulators and tethering elements. Among this constellation of elements, enhancers and their associated transcription factors have a leading role in the regulation of gene expression.
Enhancers are regions of the genome that are major gene-regulatory elements. Enhancers control cell-type-specific gene expression programs, most often by looping through long distances to come in physical proximity with the promoters of their target genes. In a study of brain cortical neurons, 24,937 loops were found, bringing enhancers to promoters. Multiple enhancers, each often at tens or hundred of thousands of nucleotides distant from their target genes, loop to their target gene promoters and coordinate with each other to control expression of their common target gene.
The schematic illustration in this section shows an enhancer looping around to come into close physical proximity with the promoter of a target gene. The loop is stabilized by a dimer of a connector protein (e.g. dimer of CTCF or YY1), with one member of the dimer anchored to its binding motif on the enhancer and the other member anchored to its binding motif on the promoter (represented by the red zigzags in the illustration). Several cell function specific transcription factors (there are about 1,600 transcription factors in a human cell) generally bind to specific motifs on an enhancer and a small combination of these enhancer-bound transcription factors, when brought close to a promoter by a DNA loop, govern the level of transcription of the target gene. Mediator (coactivator) (a complex usually consisting of about 26 proteins in an interacting structure) communicates regulatory signals from enhancer DNA-bound transcription factors directly to the RNA polymerase II (pol II) enzyme bound to the promoter.
Enhancers, when active, are generally transcribed from both strands of DNA with RNA polymerases acting in two different directions, producing two eRNAs as illustrated in the Figure. An inactive enhancer may be bound by an inactive transcription factor. Phosphorylation of the transcription factor may activate it and that activated transcription factor may then activate the enhancer to which it is bound (see small red star representing phosphorylation of transcription factor bound to enhancer in the illustration). An activated enhancer begins transcription of its RNA before activating a promoter to initiate transcription of messenger RNA from its target gene. | 1 | Applied and Interdisciplinary Chemistry |
Epoxidation of a substituted cyclohexene affords a product where the R group resides in the pseudo-equatorial position. Nucleophilic ring-opening of this class of epoxides can occur by an attack at either the C1 or C2-position. It is well known that nucleophilic ring-opening reactions of these substrates can proceed with excellent regioselectivity. The Fürst-Plattner rule attributes this regiochemical control to a large preference for the reaction pathway that follows the more stable chair-like transition state (attack at the C1-position) compared to the one proceeding through the unfavored twist boat-like transition state (attack at the C2-position). The attack at the C1-position follows a substantially lower reaction barrier of around 5 kcal mol depending on the specific conditions. Similarly, the Fürst-Plattner rule applies to nucleophilic additions to imines and halonium ions. | 0 | Theoretical and Fundamental Chemistry |
Phosphoramidites derived from protected nucleosides are referred to as nucleoside phosphoramidites and are widely used in chemical synthesis of DNA, RNA, and other nucleic acids and their analogs. | 0 | Theoretical and Fundamental Chemistry |
Charles James was born on 27 April 1880 to William James and Mary Diana Shatford-James at Earls Barton near Broughton, Northamptonshire. His father died when he was six and he was brought up by his mother. He attended school in
Wellinborough, taking classes through Cambridge University. His father's chemistry books sparked his interest in chemistry, and he built himself a home laboratory when he was 15. He also began a correspondence with renowned chemist William Ramsay, who encouraged his interest and became a life-long mentor to James.
Oxford and Cambridge did not teach chemistry at that time. His family opposed his choice of chemistry as a career, but finally gave way. In 1899, James went to University College London where he studied under William Ramsay. James won the Ramsay silver medal in 1901. He passed examinations to become an associate of the Institute of Chemistry in 1904, and a fellow in 1907. | 1 | Applied and Interdisciplinary Chemistry |
Medical organizations recommend that patients protect themselves from UV radiation by using sunscreen. Five sunscreen ingredients have been shown to protect mice against skin tumors. However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells. The amount of sunscreen that penetrates into the lower layers of the skin may be large enough to cause damage.
Sunscreen reduces the direct DNA damage that causes sunburn, by blocking UV‑B, and the usual SPF rating indicates how effectively this radiation is blocked. SPF is, therefore, also called UVB-PF, for "UV‑B protection factor". This rating, however, offers no data about important protection against UVA, which does not primarily cause sunburn but is still harmful, since it causes indirect DNA damage and is also considered carcinogenic. Several studies suggest that the absence of UV‑A filters may be the cause of the higher incidence of melanoma found in sunscreen users compared to non-users. Some sunscreen lotions contain titanium dioxide, zinc oxide, and avobenzone, which help protect against UV‑A rays.
The photochemical properties of melanin make it an excellent photoprotectant. However, sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin and therefore, if sunscreen ingredients penetrate into the lower layers of the skin, the amount of reactive oxygen species may be increased. The amount of sunscreen that penetrates through the stratum corneum may or may not be large enough to cause damage.
In an experiment by Hanson et al. that was published in 2006, the amount of harmful reactive oxygen species (ROS) was measured in untreated and in sunscreen treated skin. In the first 20 minutes, the film of sunscreen had a protective effect and the number of ROS species was smaller. After 60 minutes, however, the amount of absorbed sunscreen was so high that the amount of ROS was higher in the sunscreen-treated skin than in the untreated skin. The study indicates that sunscreen must be reapplied within 2 hours in order to prevent UV light from penetrating to sunscreen-infused live skin cells. | 0 | Theoretical and Fundamental Chemistry |
Langmuir films are formed when amphiphilic (surfactants) molecules or nanoparticles are spread on the water at an air–water interface. Surfactants (or surface-acting agents) are molecules with hydrophobic tails and hydrophilic heads. When surfactant concentration is less than the minimum surface concentration of collapse and it is completely insoluble in water, the surfactant molecules arrange themselves as shown in Figure 1 below. This tendency can be explained by surface-energy considerations. Since the tails are hydrophobic, their exposure to air is favoured over that to water. Similarly, since the heads are hydrophilic, the head–water interaction is more favourable than head-air interaction. The overall effect is reduction in the surface energy (or equivalently, surface tension of water).
For very small concentrations, far from the surface density compatible with the collapse of the monolayer (which leads to polylayers structures) the surfactant molecules execute a random motion on the water–air interface. This motion can be thought to be similar to the motion of ideal-gas molecules enclosed in a container. The corresponding thermodynamic variables for the surfactant system are, surface pressure (), surface area (A) and number of surfactant molecules (N). This system behaves similar to a gas in a container. The density of surfactant molecules as well as the surface pressure increases upon reducing the surface area A (compression of the gas). Further compression of the surfactant molecules on the surface shows behavior similar to phase transitions. The ‘gas’ gets compressed into ‘liquid’ and ultimately into a perfectly closed packed array of the surfactant molecules on the surface corresponding to a ‘solid’ state. The liquid state is usually separated in the liquid-expanded and liquid-condensed states. All the Langmuir film states are classified according to the compressionality factor of the films, defined as , usually related to the in-plane elasticity of the monolayer.
The condensed Langmuir films (in surface pressures usually higher than 15 mN/m – typically 30 mN/m) can be subsequently transferred onto a solid substrate to create highly organized thin film coatings. Langmuir–Blodgett troughs
Besides LB film from surfactants depicted in Figure 1, similar monolayers can also be made from inorganic nanoparticles. | 0 | Theoretical and Fundamental Chemistry |
The creation of a complete organ often requires incorporation of a variety of different cell types, arranged in distinct and patterned ways. One advantage of 3D-printed organs, compared to traditional transplants, is the potential to use cells derived from the patient to make the new organ. This significantly decreases the likelihood of transplant rejection, and may remove the need for immunosuppressive drugs after transplant, which would reduce the health risks of transplants. However, since it may not always be possible to collect all the needed cell types, it may be necessary to collect adult stem cells or induce pluripotency in collected tissue. This involves resource-intensive cell growth and differentiation and comes with its own set of potential health risks, since cell proliferation in a printed organ occurs outside the body and requires external application of growth factors. However, the ability of some tissues to self-organize into differentiated structures may provide a way to simultaneously construct the tissues and form distinct cell populations, improving the efficacy and functionality of organ printing. | 1 | Applied and Interdisciplinary Chemistry |
Urethane (ethyl carbamate) was once produced commercially in the United States as a chemotherapy agent and for other medicinal purposes. It was found to be toxic and largely ineffective. It is occasionally used in veterinary medicine in combination with other drugs to produce anesthesia. | 0 | Theoretical and Fundamental Chemistry |
In 2012, the first two methods for m6A sequencing came out that enabled transcriptome-wide profile of m6A in mammalian cells. These two techniques, called m6A-seq and MeRIP-seq (m6A-specific methylated RNA immunoprecipitation), are also the first methods to allow for any type of RNA modification sequencing. These methods were able to detect 10,000 m6A peaks in the mammalian transcriptome; the peaks were found to be enriched in 3’UTR regions, near STOP codons, and within long exons.
The two methods were optimized to detect methylation peaks in poly(A)+ mRNA, but the protocol could be adapted to profile any type of RNA. Collected RNA sample is fragmented into ~100-nucleotide-long oligonucleotides using a fragmentation buffer, immunoprecipitation with purified anti-m6A antibody, elution and collection of antibody-tagged RNA molecules. The immunoprecipitation procedure in MeRIP-Seq is able to produce >130fold enrichment of m6A sequences. Random primed cDNA library generation was performed, followed by adaptor ligation and Illumina sequencing. Since the RNA strands are randomly chopped up, the m6A site should, in principle, lie somewhere in the center of the regions to which sequence reads align. At extremes, the region would be roughly 200nt wide (100nt up- and downstream of the m6A site).
When the first nucleotide of a transcript is an adenosine, in addition to the ribose 2’-O-methylation, this base can be further methylated at the N6 position.
m6A-seq was confirmed to be able to detect m6Am peaks at transcription start sites. Adapter ligation at both ends of RNA fragment results in reads tending to pileup at the 5’ terminus of the transcript. Schwartz et al. (2015) leveraged this knowledge to detect mTSS sites by picking out sites with a high ratio of the size of pileups in the IP samples compared to input sample. As confirmation, >80% of the highly enriched pileup sites contained adenosine.
The resolution of these methods is 100-200nt, which was the range of the fragment size.
These two methods had several drawbacks: (1) required substantial input material, (2) low resolution which made pinpointing the actual site with the m6A mark difficult, and (3) cannot directly assess false positives.
Especially in MeRIP-Seq, the bioinformatics tools that are currently available are only able to call 1 site per ~100-200nt wide peak, so a substantial portion of clustered m6As (~64nt between each individual site within a cluster) are missed. Each cluster can contain up to 15 m6A residues.
In 2013, a modified version of m6A-seq based on the previous two methods m6A-seq and MeRIP-seq came out which aimed to increase resolution, and demonstrated this in the yeast transcriptome. They achieved this by decreasing fragment size and employing a ligation-based strand-specific library preparation protocol capturing both ends of the fragmented RNA, ensuring that the methylated position is within the sequenced fragment. By additionally referencing the m6A consensus motif and eliminating false positive m6A peaks using negative control samples, the m6A profiling in yeast was able to be done at single-base resolution. | 1 | Applied and Interdisciplinary Chemistry |
Until 2007, in the United States, Lugol's solution was unregulated and available over the counter as a general reagent, an antiseptic, a preservative, or as a medicament for human or veterinary application.
Since 1 August 2007, the DEA regulates all iodine solutions containing greater than 2.2% elemental iodine as a List I precursor because they may potentially be used in the illicit production of methamphetamine. Transactions of up to one fluid ounce (30 ml) of Lugol's solution are exempt from this regulation. | 0 | Theoretical and Fundamental Chemistry |
Self-splicing occurs for rare introns that form a ribozyme, performing the functions of the spliceosome by RNA alone. There are three kinds of self-splicing introns, Group I, Group II and Group III. Group I and II introns perform splicing similar to the spliceosome without requiring any protein. This similarity suggests that Group I and II introns may be evolutionarily related to the spliceosome. Self-splicing may also be very ancient, and may have existed in an RNA world present before protein.
Two transesterifications characterize the mechanism in which group I introns are spliced:
# 3OH of a free guanine nucleoside (or one located in the intron) or a nucleotide cofactor (GMP, GDP, GTP) attacks phosphate at the 5 splice site.
# 3OH of the 5 exon becomes a nucleophile and the second transesterification results in the joining of the two exons.
The mechanism in which group II introns are spliced (two transesterification reaction like group I introns) is as follows:
# The 2OH of a specific adenosine in the intron attacks the 5 splice site, thereby forming the lariat
# The 3OH of the 5 exon triggers the second transesterification at the 3' splice site, thereby joining the exons together. | 1 | Applied and Interdisciplinary Chemistry |
Most living things have predators and therefore are in a constant evolutionary arms race to develop antipredator adaptations, while the predator adapts to become more efficient at defeating the prey's adaptations. Some organisms have evolved to make detection less likely, for example by nocturnality and camouflage. Others have developed chemical defences such as the deadly toxins of certain snakes and wasps, or the noxious scent of the skunk. Such prey often send clear and honest warning signals to their attackers with conspicuous aposematic (warning) patterns. The brightness of such warning signs is correlated with the level of toxicity of the organism.
In Batesian mimicry, the mimic effectively copies the coloration of an aposematic animal, known as the model, to deceive predators into behaving as if it were distasteful. The success of this dishonest display depends on the level of toxicity of the model and the abundance of the model in the geographical area. The more toxic the model is, the more likely it is that the predator will avoid the mimic. The abundance of the model species is also important for the success of the mimic because of frequency-dependent selection. When the model is abundant, mimics with imperfect model patterns or slightly different coloration from the model are still avoided by predators. This is because the predator has a strong incentive to avoid potentially lethal organisms, given the likelihood of encountering one. However, in areas where the model is scarce or locally extinct, mimics are driven to accurate aposematic coloration. This is because predators attack imperfect mimics more readily where there is little chance that they are the model species. Frequency-dependent selection may also have driven Batesian mimics to become polymorphic in rare cases where a single genetic switch controls appearance, as in the swallowtail butterflies (the Papilionidae) such as the pipevine swallowtail, and in the New Zealand stonefly Zelandoperla fenestrata. | 1 | Applied and Interdisciplinary Chemistry |
Phonons can scatter through several mechanisms as they travel through the material. These scattering mechanisms are: Umklapp phonon-phonon scattering, phonon-impurity scattering, phonon-electron scattering, and phonon-boundary scattering. Each scattering mechanism can be characterised by a relaxation rate 1/ which is the inverse of the corresponding relaxation time.
All scattering processes can be taken into account using Matthiessen's rule. Then the combined relaxation time can be written as:
The parameters , , , are due to Umklapp scattering, mass-difference impurity scattering, boundary scattering and phonon-electron scattering, respectively. | 0 | Theoretical and Fundamental Chemistry |
A typical sublimation apparatus separates a mix of appropriate solid materials in a vessel in which it applies heat under a controllable atmosphere (air, vacuum or inert gas). If the material is not at first solid, then it may freeze under reduced pressure. Conditions are so chosen that the solid volatilizes and condenses as a purified compound on a cooled surface, leaving the non-volatile residual impurities or solid products behind.
The form of the cooled surface often is a so-called cold finger which for very low-temperature sublimation may actually be cryogenically cooled. If the operation is a batch process, then the sublimed material can be collected from the cooled surface once heating ceases and the vacuum is released. Although this may be quite convenient for small quantities, adapting sublimation processes to large volume is generally not practical with the apparatus becoming extremely large and generally needing to be disassembled to recover products and remove residue.
Among the advantages of applying the principle to certain materials are the comparatively low working temperatures, reduced exposure to gases such as oxygen that might harm certain products, and the ease with which it can be performed on extremely small quantities. The same apparatus may also be used for conventional distillation of extremely small quantities due to the very small volume and surface area between evaporating and condensing regions, although this is generally only useful if the cold finger can be cold enough to solidify the condensate. | 0 | Theoretical and Fundamental Chemistry |
DKPs are synthesized by a wide range of organisms, including bacteria, fungi, more complex marine microorganisms, and even mammals. However, 90% of gram-negative bacteria synthesize these molecules, making them the target of most studies. | 0 | Theoretical and Fundamental Chemistry |
Nickel-cobalt lateritic ores can be treated by either hydrometallurgical processes or pyrometallurgical processes, such as matte or ferronickel smelting, which require the entire ore to be melted and the metal values to be separated from the residual components of the ore. The hydrometallurgical process for laterite ore can use sulfuric acid or ammonia leach solutions. | 1 | Applied and Interdisciplinary Chemistry |
Several transition metal dithiocarbamate complexes are useful in industry. Zinc dithiocarbamates are used to modify the crosslinking of certain polyolefins with sulfur, a process called vulcanization. They are used as ligands for chelating metals.
Some dithiocarbamates, specifically ethylene bisdithiocarbamates (), in the form of complexes with manganese (maneb), zinc (zineb) or a combination of manganese and zinc (mancozeb), have been used extensively as fungicides in agriculture since the 1940s. In the United States they began to be registered for use in the late 1950s and early 1960s and were quickly put to work on sooty blotch and flyspeck. Many growers switched from captan to EBDCs for the longer residual period. Both captan and EBDCs were the primary treatments for SBFS in that country until the early 1990s when the US Environmental Protection Agency banned EBDCs within 77 days to harvest. This effectively made summer use impossible, reduced EBDC use overall, and radically increased SBFS. | 0 | Theoretical and Fundamental Chemistry |
A biosurvey, or biological survey, is a scientific study of organisms to assess the condition of an ecological resource, such as a water body. | 1 | Applied and Interdisciplinary Chemistry |
In sizing, the strength and printability of paper is increased. Sizing also improves the hydrophilic character, liquid spreading, and affinity for ink. Starch is the most common sizing agent. Cationic starch and hydrophilic agents are also applied, including alkenyl succinic anhydride (ASA) and alkyl ketene dimers (AKD).
Cationic starch increases strength because it binds to the anionic paper fibers. The amount added is usually between ten and thirty pounds per ton. When starch exceeds the amount the fibers can bind to, it causes foaming in the production process as well as decreased retention and drainage. | 0 | Theoretical and Fundamental Chemistry |
The U.S. "Secondary Treatment Regulation" is the national standard for municipal sewage treatment plants. | 1 | Applied and Interdisciplinary Chemistry |
LeDock is a molecular docking software designed for protein-ligand interactions, compatible with Linux, macOS, and Windows. It supports the [http://www.csb.yale.edu/userguides/datamanip/dock/DOCK_4.0.1/html/Manual.41.html Tripos Mol2] file format and employs a simulated annealing and genetic algorithm approach for docking. Utilizing a knowledge-based scoring scheme, it is categorized as a flexible docking method. | 1 | Applied and Interdisciplinary Chemistry |
In bioinformatics, the BLOSUM (BLOcks SUbstitution Matrix) matrix is a substitution matrix used for sequence alignment of proteins. BLOSUM matrices are used to score alignments between evolutionarily divergent protein sequences. They are based on local alignments. BLOSUM matrices were first introduced in a paper by Steven Henikoff and Jorja Henikoff. They scanned the BLOCKS database for very conserved regions of protein families (that do not have gaps in the sequence alignment) and then counted the relative frequencies of amino acids and their substitution probabilities. Then, they calculated a log-odds score for each of the 210 possible substitution pairs of the 20 standard amino acids. All BLOSUM matrices are based on observed alignments; they are not extrapolated from comparisons of closely related proteins like the PAM Matrices. | 1 | Applied and Interdisciplinary Chemistry |
Since its adoption into the International System of Units in 1971, numerous criticisms of the concept of the mole as a unit like the metre or the second have arisen:
* the number of molecules, etc. in a given amount of material is a fixed dimensionless quantity that can be expressed simply as a number, not requiring a distinct base unit;
* The SI thermodynamic mole is irrelevant to analytical chemistry and could cause avoidable costs to advanced economies
* The mole is not a true metric (i.e. measuring) unit, rather it is a parametric unit, and amount of substance is a parametric base quantity
* the SI defines numbers of entities as quantities of dimension one, and thus ignores the ontological distinction between entities and units of continuous quantities
In chemistry, it has been known since Prousts law of definite proportions (1794) that knowledge of the mass of each of the components in a chemical system is not sufficient to define the system. Amount of substance can be described as mass divided by Prousts "definite proportions", and contains information that is missing from the measurement of mass alone. As demonstrated by Dalton's law of partial pressures (1803), a measurement of mass is not even necessary to measure the amount of substance (although in practice it is usual). There are many physical relationships between amount of substance and other physical quantities, the most notable one being the ideal gas law (where the relationship was first demonstrated in 1857). The term "mole" was first used in a textbook describing these colligative properties. | 0 | Theoretical and Fundamental Chemistry |
Harry Julius Emeléus CBE, FRS (22 June 1903 – 2 December 1993) was an English inorganic chemist and a professor in the department of chemistry, Cambridge University. | 0 | Theoretical and Fundamental Chemistry |
There are three basic methodologies: gel-clot, turbidimetric, and chromogenic. The primary application for LAL is the testing of parenteral pharmaceuticals and medical devices that contact blood or cerebrospinal fluid. In the United States, the FDA has published a guideline for validation of the LAL test as an endotoxin test for such products.
The LAL cascade is also triggered by (1,3)-β-D-glucan, via a different Factor G. Both bacterial endotoxins and (1,3)-β-D-glucan are considered pathogen-associated molecular patterns, or PAMPs, substances which elicit inflammatory responses in mammals. | 0 | Theoretical and Fundamental Chemistry |
Its use as an analgesic during labor is not advised due to its long onset of action (1 hour). The ratio of the mean concentration of the drug in the fetus compared to that of the mother when it is given intramuscularly for labor pains has been estimated to be 1:94. | 0 | Theoretical and Fundamental Chemistry |
The Randle cycle is a biochemical mechanism involving the competition between glucose and fatty acids for their oxidation and uptake in muscle and adipose tissue. The cycle controls fuel selection and adapts the substrate supply and demand in normal tissues. This cycle adds a nutrient-mediated fine tuning on top of the more coarse hormonal control on fuel metabolism. This adaptation to nutrient availability applies to the interaction between adipose tissue and muscle. Hormones that control adipose tissue lipolysis affect circulating concentrations of fatty acids, these in turn control the fuel selection in muscle. Mechanisms involved in the Randle Cycle include allosteric control, reversible phosphorylation and the expression of key enzymes. The energy balance from meals composed of differing macronutrient composition is identical, but the glucose and fat balances that contribute to the overall energy balance change reciprocally with meal composition. | 1 | Applied and Interdisciplinary Chemistry |
Promoters reside at the beginning of the gene and serve as the site where the transcription machinery assembles and transcription of the gene begins. Enhancers turn on the promoters at specific locations, times, and levels and can be simply defined as the “promoters of the promoter.” Silencers are thought to turn off gene expression at specific time points and locations. Insulators, also called boundary elements, are DNA sequences that create cis-regulatory boundaries that prevent the regulatory elements of one gene from affecting neighboring genes. The general dogma is that these regulatory elements get activated by the binding of transcription factors, proteins that bind to specific DNA sequences, and control mRNA transcription. There could be several transcription factors that need to bind to one regulatory element in order to activate it. In addition, several other proteins, called transcription cofactors, bind to the transcription factors themselves to control transcription. | 1 | Applied and Interdisciplinary Chemistry |
There are two main classes of chemoreceptor: direct and distance.
* Examples of distance chemoreceptors are:
**olfactory receptor neurons in the olfactory system: Olfaction involves the ability to detect chemicals in the gaseous state. In vertebrates, the olfactory system detects odors and pheromones in the nasal cavity. Within the olfactory system there are two anatomically distinct organs: the main olfactory epithelium (MOE) and the vomeronasal organ (VNO). It was initially thought that the MOE is responsible for the detection of odorants, while the VNO detects pheromones. The current view, however, is that both systems can detect odorants and pheromones. Olfaction in invertebrates differs from olfaction in vertebrates. For example, in insects, olfactory sensilla are present on their antennae.
* Examples of direct chemoreceptors include:
** Taste receptors in the gustatory system: The primary use of gustation as a type of chemoreception is for the detection of tasteants. Aqueous chemical compounds come into contact with chemoreceptors in the mouth, such as taste buds on the tongue, and trigger responses. These chemical compounds can either trigger an appetitive response for nutrients, or a defensive response against toxins depending on which receptors fire. Fish and crustaceans, who are constantly in an aqueous environment, use their gustatory system to identify certain chemicals in the mixture for the purpose of localization and ingestion of food.
**Insects use contact chemoreception to recognize certain chemicals such as cuticular hydrocarbons and chemicals specific to host plants. Contact chemoreception is more commonly seen in insects but is also involved in the mating behavior of some vertebrates. The contact chemoreceptor is specific to one type of chemical. | 0 | Theoretical and Fundamental Chemistry |
For the first time Kirschner's group in Max Planck institute of Microstructure Physics showed that the signature of the large wave vector spin waves can be detected by spin polarized electron energy loss spectroscopy (SPEELS). Later, with a better momentum resolution, the spin wave dispersion was fully measured in 8 monolayer (ML) fcc cobalt film on Cu(001) and 8 ML hcp cobalt on W(110), respectively. Those spin waves were obtained up to the surface Brillouin zone (SBZ) at the energy range about few hundreds of meV. Another recent example is the investigation of 1 and 2 monolayer iron films grown on W(110) measured at 120 K and 300 K, respectively. | 0 | Theoretical and Fundamental Chemistry |
This process was patented and sold to Hoffmann-La Roche in 1934. The first commercially sold vitamin C product was either Cebion from Merck or Redoxon from Hoffmann-La Roche.
Even today industrial methods for the production of ascorbic acid can be based on the Reichstein process. In modern methods however, sorbose is directly oxidized with a platinum catalyst (developed by Kurt Heyns (1908–2005) in 1942). This method avoids the use of protective groups. A side product with particular modification is 5-Keto-D-gluconic acid.
A shorter biotechnological synthesis of ascorbic acid was announced in 1988 by Genencor International and Eastman Chemical. Glucose is converted to 2-keto-L-gulonic acid in two steps (via 2,4-diketo-L-gulonic acid intermediate) as compared to five steps in the traditional process.
Though many organisms synthesize their own vitamin C, the steps can be different in plants and mammals. Smirnoff concluded that “..little is known about many of the enzymes involved in ascorbate biosynthesis or about the factors controlling flux through the pathways". There is interest in finding alternatives to the Reichstein process. Experiments suggest that genetically modified bacteria might be commercially usable. | 0 | Theoretical and Fundamental Chemistry |
Indicator bacteria can be cultured on media which are specifically formulated to allow the growth of the species of interest and inhibit growth of other organisms. Typically, environmental water samples are filtered through membranes with small pore sizes and then the membrane is placed onto a selective agar. It is often necessary to vary the volume of water sample filtered in order to prevent too few or too many colonies from forming on a plate. Bacterial colonies can be counted after 24 to 48 hours depending on the type of bacteria. Counts are reported as colony forming units per 100 mL (cfu/100 mL). | 0 | Theoretical and Fundamental Chemistry |
In an attempt to improve the predictions of druglikeness, the rules have spawned many extensions, for example the Ghose filter:
* Partition coefficient log P in −0.4 to +5.6 range
* Molar refractivity from 40 to 130
* Molecular weight from 180 to 480
* Number of atoms from 20 to 70 (includes H-bond donors [e.g. OHs and NHs] and H-bond acceptors [e.g. Ns and Os])
Veber's Rule further questions a 500 molecular weight cutoff. The polar surface area and the number of rotatable bonds has been found to better discriminate between compounds that are orally active and those that are not for a large data set of compounds. In particular, compounds which meet only the two criteria of:
* 10 or fewer rotatable bonds and
* Polar surface area no greater than 140 Å
are predicted to have good oral bioavailability. | 1 | Applied and Interdisciplinary Chemistry |
In humans, the major route of excretion of most arsenic compounds is via the urine. The biological half-life of inorganic arsenic is about 4 days, but is slightly shorter following exposure to arsenate than to arsenite. The main metabolites excreted in the urine of humans exposed to inorganic arsenic are mono- and dimethylated arsenic acids, together with some unmetabolized inorganic arsenic.
The biotransformation of arsenic for excretion is primarily done through the nuclear factor erythroid 2 related factor 2 (Nrf2) pathway. Under normal conditions the Nrf2 is bound to Kelch-like ECH associated protein 1 (Keap1) in its inactive form. With the uptake of arsenic within cells and the subsequent reactions that result in the production of reactive oxygen species (ROS), the Nrf2 unbinds and becomes active. Keap1 has reactive thiol moieties that bind ROS or electrophilic arsenic species such as monomethylted arsenic (III) and induces the release of Nrf2 which then travels through the cytoplasm to the nucleus. The Nrf2 then activates antioxidant responsive element (ARE) as well as electrophilic responsive element (EpRE) both of which contribute in the increase of antioxidant proteins. Of particular note in these antioxidant proteins is heme oxygenase 1 ([HO-1]), NAD(P)H-quinone oxidoreductase 1 (NQO1), and γ-glutamylcysteine synthase (γGCS) which work in conjunction to reduce the oxidative species such as hydrogen peroxide to decrease the oxidative stress upon the cell. The increase in γGCS causes an increased production of arsenite triglutathionine (As(SG)) an important adduct that is taken up by either multidrug associated protein 1 or 2 (MRP1 or MRP2) which removes the arsenic out of the cell and into bile for excretion. This adduct can also decompose back into inorganic arsenic.
Of particular note in the excretion of arsenic is the multiple methylation steps that take place which may increase the toxicity of arsenic due to MMeAsIII being a potent inhibitor of glutathione peroxidase, glutathione reductase, pyruvate dehydrogenase, and thioredoxin reductase. | 1 | Applied and Interdisciplinary Chemistry |
When separating zeotropic mixtures with three or greater liquid components, each distillation column removes only the lowest-boiling point component and the highest boiling point component. In other words, each column separates two components purely. If three substances are separated with a single column, the substance with the intermediate boiling point will not be purely separated, and a second column would be needed. To separate mixtures consisting of multiple substances, a sequence of distillation columns must be used. This multi-step distillation process is also called rectification.
In each distillation column, pure components form at the top (rectifying section) and bottom (stripping section) of the column when the starting liquid (called feed composition) is released in the middle of the column. This is shown in Figure 2. At a certain temperature, the component with the lowest boiling point (called distillate or overhead fraction) vaporizes and collects at the top of the column, whereas the component with the highest boiling point (called bottoms or bottom fraction) collects at the bottom of the column. In a zeotropic mixture, where more than one component exists, individual components move relative to each other as vapor flows up and liquid falls down.
The separation of mixtures can be seen in a concentration profile. In a concentration profile, the position of a vapor in the distillation column is plotted against the concentration of the vapor. The component with the highest boiling point has a max concentration at the bottom of the column, where the component with the lowest boiling point has a max concentration at the top of the column. The component with the intermediate boiling point has a max concentration in the middle of the distillation column. Because of how these mixtures separate, mixtures with greater than three substances require more than one distillation column to separate the components. | 1 | Applied and Interdisciplinary Chemistry |
Kissing hairpins are formed when a single strand of nucleic acid complements with itself creating loops of RNA in the form of a hairpin. When two hairpins come into contact with each other in vivo, the complementary bases of the two strands form up and begin to unwind the hairpins until a double-stranded RNA (dsRNA) complex is formed or the complex unwinds back to two separate strands due to mismatches in the hairpins. The secondary structure of the hairpin prior to kissing allows for a stable structure with a relatively fixed change in energy. The purpose of these structures is a balancing of stability of the hairpin loop vs binding strength with a complementary strand. Too strong an initial binding to a bad location and the strands will not unwind quickly enough; too weak an initial binding and the strands will never fully form the desired complex. These hairpin structures allow for the exposure of enough bases to provide a strong enough check on the initial binding and a weak enough internal binding to allow the unfolding once a favorable match has been found.
</div> | 1 | Applied and Interdisciplinary Chemistry |
In 2005, Oladipo achieved the rank of Research Professor at the Centre for Energy Research and Development (CERD) at Obafemi Awolowo University. He began his career as a Senior Research Fellow in CERD in 1993. He is also a member of Nigerian Association of Medical Physicists. | 0 | Theoretical and Fundamental Chemistry |
Diphosphines are a class of chelating ligands that contain two phosphine groups connected by a bridge (also referred to as a backbone). The bridge, for instance, might consist of one or more methylene groups or multiple aromatic rings with heteroatoms attached. Examples of common diphosphines are dppe, dcpm (Figure 1), and DPEphos (Figure 2). The structure of the backbone and the substituents attached to the phosphorus atoms influence the chemical reactivity of the diphosphine ligand in metal complexes through steric and electronic effects. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, an alcohol is a type of organic compound that carries at least one hydroxyl () functional group bound to a saturated carbon atom. Alcohols range from the simple, like methanol and ethanol, to complex, like sugar alcohols and cholesterol. The presence of an OH group strongly modifies the properties of hydrocarbons, conferring hydrophilic (water-loving) properties. The OH group provides a site at which many reactions can occur. | 0 | Theoretical and Fundamental Chemistry |
Oganessian relocated to Russia, where he graduated from the Moscow Engineering Physics Institute (MEPhI) in 1956. He thereafter sought to join the Kurchatov Institute of Atomic Energy in Moscow, but as there were no vacancies left in Gersh Budker's team, he was instead recruited by Georgy Flyorov and began working at the Joint Institute for Nuclear Research (JINR) in Dubna, near Moscow.
He became director of the Flyorov Laboratory of Nuclear Reactions at JINR in 1989, after Flyorov retired, and had the job until 1996, when he was named the scientific director of the Flyorov laboratory. | 1 | Applied and Interdisciplinary Chemistry |
Bioretention is the process in which contaminants and sedimentation are removed from stormwater runoff. The main objective of the bioretention cell is to attenuate peak runoff as well as to remove stormwater runoff pollutants. | 1 | Applied and Interdisciplinary Chemistry |
Bi-metallic coins and medals have been issued for a long time. The Roman Empire issued special-occasion, large medallions with a center of bronze or copper and an outer ring of orichalcum, starting with the reign of Hadrian. Meanwhile, circulating bi-metallic coins are known from the 17th century. English farthings from 1684 through 1693 were made of tin with a central plug of copper for value. The silver-center cent pattern produced by the United States in 1792 is another example.
In the 1830s and 1840s, British medalist Joseph Moore produced large numbers of bi-metallic "penny model" and less common "halfpenny model" tokens, as a proposal to replace the relatively large penny and halfpenny coins. Though not legal tender, Moore's tokens were circulated widely and accepted at face value by many merchants. Despite their popularity, the Royal Mint rejected the proposal, and did not reduce the size of the penny and halfpenny until decimalization.
The first modern circulating bi-metallic coin was the Italian 500 lire, first issued in 1982. Based on the minting process of the lire coin, the following issued bi-metallic coins for circulation were issued:
* Morocco, with its 5-dirhams coin in 1987;
* France, with a 10-francs coin in 1988;
* Monaco, with a 10 francs;
* Thailand, with a 10 baht, in 1988;
* Czech Republic, with a 50 Kč coin in 1993;
* Hong Kong, with a $10 coin, in 1993;
* Indonesia, with a Rp1,000 coin, in 1993;
* Israel, with a ₪10 coin in 1995;
* Canada, with a $2 coin (nicknamed "toonie") in 1996;
* Hungary, with a 100-forint coin in 1996 and a 200 forint coin in 2009;
* Brazil with the 1 real coin, in 1998;
* The United Kingdom has issued a bi-metallic £2 coin since 1997, and a bi-metallic £1 coin since March 2017;
* The Philippines has minted a bi-metallic 10-peso coin from 2000 to 2017 and a 20-peso coin since 2019.
* The Eurozone circulated the €1 and €2 coins on 1 January 2002;
* India has issued a bi-metallic ₹10 coin since 2009 and a bi-metallic ₹20 coin since 2019;
* Singapore has issued a bi-metallic 1-dollar coin since 2013.
* Japan has issued a bi-metallic 500 yen coin since 2021.
* Costa Rica announced a bi-metallic 500-colones coin that will start to circulate in November 2021.
The first ever tri-metallic circulating coins were 20-francs coins introduced in France and Monaco in 1992. These were similar to the corresponding bi-metallic 10-francs coins, but had two rings instead of one. | 1 | Applied and Interdisciplinary Chemistry |
Under high pressure, solubility of increases. On opening the bottle to atmospheric pressure, solubility decreases and the gas bubbles are released from the liquid. | 0 | Theoretical and Fundamental Chemistry |
The isotopic composition of the components in a biochemical system can be defined in different ways depending on the definition of isotopic ratio. Three definitions are described here: | 0 | Theoretical and Fundamental Chemistry |
HDPE pipe is a type of flexible plastic pipe used to transfer fluids and gases. It is often employed for replacing aging concrete or steel main pipelines. Constructed from the thermoplastic HDPE (high-density polyethylene), it has low permeability and robust molecular bonding, making it suitable for high-pressure pipelines. HDPE pipe is often used for water mains, gas mains, sewer mains, slurry transfer lines, rural irrigation, fire-suppression system supply lines, electrical and communication conduits, and stormwater and drainage pipes. | 1 | Applied and Interdisciplinary Chemistry |
A fermionic condensate (or Fermi–Dirac condensate) is a superfluid phase formed by fermionic particles at low temperatures. It is closely related to the Bose–Einstein condensate, a superfluid phase formed by bosonic atoms under similar conditions. The earliest recognized fermionic condensate described the state of electrons in a superconductor; the physics of other examples including recent work with fermionic atoms is analogous. The first atomic fermionic condensate was created by a team led by Deborah S. Jin using potassium-40 atoms at the University of Colorado Boulder in 2003. | 0 | Theoretical and Fundamental Chemistry |
In the European Union, metreleptin is indicated in addition to diet to treat lipodystrophy, where people have a loss of fatty tissue under the skin and a build-up of fat elsewhere in the body such as in the liver and muscles. It is used in adults and children above the age of two years with generalised lipodystrophy (Berardinelli-Seip syndrome and Lawrence syndrome); and in adults and children above the age of twelve years with partial lipodystrophy (including Barraquer-Simons syndrome), when standard treatments have failed.
In the United States, it is indicated as an adjunct to diet as replacement therapy to treat the complications of leptin deficiency in people with congenital or acquired generalized lipodystrophy. | 1 | Applied and Interdisciplinary Chemistry |
An MFT with a glucose tail of n units is termed MFT-n; MFT-nH in the reduced form. An MFT with a 2-O-methylglucose is termed a methylmycofactocin (MMFT), with analogous numbering. | 1 | Applied and Interdisciplinary Chemistry |
Ligand efficacy refers to the ability of the ligand to produce a biological response upon binding to the target receptor and the quantitative magnitude of this response. This response may be as an agonist, antagonist, or inverse agonist, depending on the physiological response produced. | 1 | Applied and Interdisciplinary Chemistry |
In 1934, Frédéric and Irène Joliot-Curie bombarded aluminium with alpha particles to effect the nuclear reaction + → + , and observed that the product isotope emits a positron identical to those found in cosmic rays (discovered by Carl David Anderson in 1932). This was the first example of decay (positron emission), which they termed artificial radioactivity since is a short-lived nuclide which does not exist in nature. In recognition of their discovery, the couple were awarded the Nobel Prize in Chemistry in 1935.
The theory of electron capture was first discussed by Gian-Carlo Wick in a 1934 paper, and then developed by Hideki Yukawa and others. K-electron capture was first observed in 1937 by Luis Alvarez, in the nuclide V. Alvarez went on to study electron capture in Ga and other nuclides. | 0 | Theoretical and Fundamental Chemistry |
According to pharmacokinetic and pharmacodynamic data of the drugs, the pharmacological action is integrated in the model. By means of specific electrical stimuli protocols, the pharmacological effect of a new drug can be investigated in a completely safe, and controlled computational environment, providing preliminary important considerations concerning the cardiotoxicity of new pharmacological compounds.
According to the outcome of the simulations, several aspects can be investigated to identify the pro-arrhythmicity of a new pharmacological compound. The typical changes, called repolarization abnormalities, in the action potential morphology that are considered pro-arrhythmic are:
* Early afterdepolarization
* Electrical alternans
* Repolarization failures | 1 | Applied and Interdisciplinary Chemistry |
In March 2014, NASA's Jet Propulsion Laboratory demonstrated a unique way to study the origins of life: fuel cells. Fuel cells are similar to biological cells in that electrons are also transferred to and from molecules. In both cases, this results in electricity and power. The study of fuel cells suggest that an important factor in protocell development was that the Earth provides electrical energy at the seafloor. "This energy could have kick-started life and could have sustained life after it arose. Now, we have a way of testing different materials and environments that could have helped life arise not just on Earth, but possibly on Mars, Europa and other places in the Solar System." | 0 | Theoretical and Fundamental Chemistry |
The ARC gene, located on chromosome 15 in the mouse, chromosome 7 in the rat, and chromosome 8 in the human, is conserved across vertebrate species and has low sequence homology to spectrin, a cytoskeletal protein involved in forming the actin cellular cortex. A number of promoter and enhancer regions have been identified that mediate activity-dependent Arc transcription: a serum response element (SRE; see serum response factor) at ~1.5 kb upstream of the initiation site. a second SRE at ~6.5 kb; and a synaptic activity response element (SARE) sequence at ~7 kb upstream that contains binding sites for cyclic AMP response element-binding protein (CREB), myocyte enhancer factor 2 (MEF2), and SRF.
The 3' UTR of the mRNA contains a cis-acting element required for the localization of Arc to neuronal dendrites, as well as sites for two exon junction complexes (EJCs) that make Arc a natural target for nonsense mediated decay (NMD). Also important for translocation of cytoplasmic Arc mRNA to activated synapses is an 11 nucleotide binding site for heterogeneous nuclear ribonucleoprotein A2 (hnRNP A2).
It is suspected that the ARC gene originated from the gag gene of a Ty3/gypsy retrotransposon and was repurposed for mediating neuron-neuron communication. | 1 | Applied and Interdisciplinary Chemistry |
Nearly all materials could be seen as hierarchically structured, since the changes in spatial scale bring about different mechanisms of deformation and damage. However, in biological materials, this hierarchical organization is inherent to the microstructure. One of the first examples of this, in the history of structural biology, is the early X-ray scattering work on the hierarchical structure of hair and wool by Astbury and Woods. In bone, for example, collagen is the building block of the organic matrix, a triple helix with diameter of 1.5 nm. These tropocollagen molecules are intercalated with the mineral phase (hydroxyapatite, calcium phosphate) forming fibrils that curl into helicoids of alternating directions. These "osteons" are the basic building blocks of bones, with the volume fraction distribution between organic and mineral phase being about 60/40.
In another level of complexity, the hydroxyapatite crystals are mineral platelets that have a diameter of approximately 70 to 100 nm and thickness of 1 nm. They originally nucleate at the gaps between collagen fibrils.
Similarly, the hierarchy of abalone shell begins at the nanolevel, with an organic layer having a thickness of 20 to 30 nm. This layer proceeds with single crystals of aragonite (a polymorph of CaCO) consisting of "bricks" with dimensions of 0.5 and finishing with layers approximately 0.3 mm (mesostructure).
Crabs are arthropods, whose carapace is made of a mineralized hard component (exhibits brittle fracture) and a softer organic component composed primarily of chitin. The brittle component is arranged in a helical pattern. Each of these mineral "rods" (1 μm diameter) contains chitin–protein fibrils with approximately 60 nm diameter. These fibrils are made of 3 nm diameter canals that link the interior and exterior of the shell. | 1 | Applied and Interdisciplinary Chemistry |
According to DLVO theory, particles are held in suspension by a balance of attractive and repulsive forces. This theory can be applied to the adsorption of small molecules like mucoadhesive polymers, on surfaces, like mucus layers. Particles in general experience attractive van der Waals forces that promote coagulation; in the context of adsorption, the particle and mucus layers are naturally attracted. The attractive forces between particles increases with decreasing particle size due to increasing surface-area-to-volume ratio. This increases the strength of van der Waals interactions, so smaller particles should be easier to adsorb onto mucous membranes.
DLVO theory also explains some of the challenges in establishing contact between particles and mucus layers in mucoadhesion due to their repulsive forces. Surfaces will develop an electrical double layer if they are in a solution containing ions, as is the case with many bodily systems, creating electrostatic repulsive forces between the adhesive and surface. Steric effects can also hinder particle adsorption to surfaces. Entropy or disorder of a system will decrease as polymeric mucoadhesives adsorb to surfaces, which makes establishing contact between the adhesive and membrane more difficult. Adhesives with large surface groups will also experience a decrease in entropy as they approach the surface, creating repulsion. | 1 | Applied and Interdisciplinary Chemistry |
The North Australian Pastoral Company (NAPCO) is a large, privately owned, Australian cattle company which operates 13 cattle stations (as well as the Wainui farm and feedlot) covering over 60,000 km, managing about 200,000 cattle, in Queensland and the Northern Territory. It produces beef cattle which are grass fed and grain finished before sale to Australian meat processors who onsell beef to domestic and international customers. | 1 | Applied and Interdisciplinary Chemistry |
MALDI techniques typically employ the use of UV lasers such as nitrogen lasers (337 nm) and frequency-tripled and quadrupled Nd:YAG lasers (355 nm and 266 nm respectively).
Infrared laser wavelengths used for infrared MALDI include the 2.94 μm Er:YAG laser, mid-IR optical parametric oscillator, and 10.6 μm carbon dioxide laser. Although not as common, infrared lasers are used due to their softer mode of ionization. IR-MALDI also has the advantage of greater material removal (useful for biological samples), less low-mass interference, and compatibility with other matrix-free laser desorption mass spectrometry methods. | 1 | Applied and Interdisciplinary Chemistry |
Cleaving relies on planar weaknesses of the chemical bonds in the crystal structure of a mineral. If a sharp blow is applied at the correct angle, the stone may split cleanly apart. While cleaving is sometimes used to split uncut gemstones into smaller pieces, it is never used to produce facets. Cleaving of diamonds was once common, but as the risk of damaging a stone is too high, undesirable diamond pieces often resulted. The preferred method of splitting diamonds into smaller pieces is now sawing.
An older and more primitive style of faceting machine called a jamb peg machine used wooden dop sticks of precise length and a "mast" system consisting of a plate with holes carefully placed in it. By placing the back end of the dop into one of the many holes, the stone could be introduced to the lap at precise angles. These machines took considerable skill to operate effectively.
Another method of facet cutting involves the use of cylinders to produce curved, concave facets. This technique can produce many unusual and artistic variations of the traditional faceting process. | 0 | Theoretical and Fundamental Chemistry |
In 1891, approximately ten years after Pockels first surface tension measurements, through her brother Friedrich Pockels, she became aware that John William Strutt, 3rd Baron Rayleigh [Lord Rayleigh] was publishing studies of the effect of small amounts of oils on the surface of water. It was clear to her that Lord Rayleighs research was closely related to her own. At the encouragement of her brother, Agnes Pockels wrote to Lord Rayleigh to describe her apparatus, her findings, and the fact that she was unable to publish her findings in the scientific journals of the time. Pockels original correspondence with Rayleigh was in the German language and was translated for Rayleigh by his wife. In an act of generosity and unthreatened by correspondence from an unknown amateur, Rayleigh forwarded Pockels findings to the journal Nature with a suitable cover letter to enable Pockels' findings to be published. Her first paper was "Surface Tension," describing her measurements and findings with her sliding trough.
The letter to Lord Rayleigh was described in a 1971 journal article on the origin of the surface film balance as being "a landmark in the history of surface chemistry." Lord Rayleigh retained his correspondence, and Pockels’s letter to him dated 10 January 1891 began:
The body of Pockels's letter to Rayleigh then described her sliding trough method, her initial findings, and her assessment of the limitations of her experimental methods. The closing of her letter stated:
Lord Rayleigh forwarded Pockelss correspondence to the editor of the journal Nature', with a covering letter dated 2 March 1891. The editor at the time was Sir Joseph Norman Lockyer who chose to publish the correspondence from Rayleigh and Pockels. The covering letter stated:
Ostwald's biography of Pockels reports that Pockels had initially approached physicists at the University of Göttingen about her findings and received no expression of interest. | 0 | Theoretical and Fundamental Chemistry |
The mold, protozoan, and coelenterate mitochondrial code and the mycoplasma/spiroplasma code (translation table 4) is the genetic code used by various organisms, in some cases with slight variations, notably the use of UGA as a tryptophan codon rather than a stop codon. | 1 | Applied and Interdisciplinary Chemistry |
Green vegetables such as spinach provide magnesium because of the abundance of chlorophyll molecules, which contain the ion. Nuts (especially Brazil nuts, cashews and almonds), seeds (e.g., pumpkin seeds), dark chocolate, roasted soybeans, bran, and some whole grains are also good sources of magnesium.
Although many foods contain magnesium, it is usually found in low levels. As with most nutrients, daily needs for magnesium are unlikely to be met by one serving of any single food. Eating a wide variety of fruits, vegetables, and grains will help ensure adequate intake of magnesium.
Because magnesium readily dissolves in water, refined foods, which are often processed or cooked in water and dried, in general, are poor sources of the nutrient. For example, whole-wheat bread has twice as much magnesium as white bread because the magnesium-rich germ and bran are removed when white flour is processed. The table of food sources of magnesium suggests many dietary sources of magnesium.
"Hard" water can also provide magnesium, but "soft" water contains less of the ion. Dietary surveys do not assess magnesium intake from water, which may lead to underestimating total magnesium intake and its variability.
Too much magnesium may make it difficult for the body to absorb calcium. Not enough magnesium can lead to hypomagnesemia as described above, with irregular heartbeats, high blood pressure (a sign in humans but not some experimental animals such as rodents), insomnia, and muscle spasms (fasciculation). However, as noted, symptoms of low magnesium from pure dietary deficiency are thought to be rarely encountered.
Following are some foods and the amount of magnesium in them:
* Pumpkin seeds, no hulls ( cup) = 303 mg
*Chia seeds, ( cup) = 162 mg
* Buckwheat flour ( cup) = 151 mg
* Brazil nuts ( cup) = 125 mg
* Oat bran, raw ( cup) = 110 mg
* Cocoa powder ( cup) = 107 mg
* Halibut (3 oz) = 103 mg
* Almonds ( cup) = 99 mg
* Cashews ( cup) = 89 mg
* Whole wheat flour ( cup) = 83 mg
* Spinach, boiled ( cup) = 79 mg
* Swiss chard, boiled ( cup) = 75 mg
* Chocolate, 70% cocoa (1 oz) = 73 mg
* Tofu, firm ( cup) = 73 mg
* Black beans, boiled ( cup) = 60 mg
* Quinoa, cooked ( cup) = 59 mg
* Peanut butter (2 tablespoons) = 50 mg
* Walnuts ( cup) = 46 mg
* Sunflower seeds, hulled ( cup) = 41 mg
* Chickpeas, boiled ( cup) = 39 mg
* Kale, boiled ( cup) = 37 mg
* Lentils, boiled ( cup) = 36 mg
* Oatmeal, cooked ( cup) = 32 mg
* Fish sauce (1 Tbsp) = 32 mg
* Milk, non fat (1 cup) = 27 mg
* Coffee, espresso (1 oz) = 24 mg
* Whole wheat bread (1 slice) = 23 mg | 1 | Applied and Interdisciplinary Chemistry |
BUN is an indication of kidney health. The normal range is 2.1–7.1 mmol/L or 6–20 mg/dL.
The main causes of an increase in BUN are: high-protein diet, decrease in glomerular filtration rate (GFR) (suggestive of kidney failure), decrease in blood volume (hypovolemia), congestive heart failure, gastrointestinal hemorrhage, fever, rapid cell destruction from infections, athletic activity, excessive muscle breakdown, and increased catabolism.
Hypothyroidism can cause both decreased GFR and hypovolemia, but BUN-to-creatinine ratio has been found to be lowered in hypothyroidism and raised in hyperthyroidism.
The main causes of a decrease in BUN are malnutrition (low-protein diet), severe liver disease, anabolic state, and syndrome of inappropriate antidiuretic hormone.
Another rare cause of a decreased BUN is ornithine transcarbamylase deficiency, which is a genetic disorder inherited in an X-linked recessive pattern. OTC deficiency is also accompanied by hyperammonemia and high orotic acid levels. | 1 | Applied and Interdisciplinary Chemistry |
Melt inclusions can be used to determine the composition, compositional evolution and volatile components of magmas that existed in the history of magma systems. This is because melt inclusions act as a tiny pressure vessel that isolates and preserves the ambient melt surrounding the crystal before they are modified by later processes, such as post-entrapment crystallization. Given that melt inclusions form at varying pressures (P) and temperatures (T), they can also provide important information about the entrapping conditions (P-T) at depth and their volatile contents (HO, CO, S, Cl and F) that drive volcanic eruptions. | 0 | Theoretical and Fundamental Chemistry |
Enzyme inhibitors are a chemically diverse set of substances that range in size from organic small molecules to macromolecular proteins.
Small molecule inhibitors include essential primary metabolites that inhibit upstream enzymes that produce those metabolites. This provides a negative feedback loop that prevents over production of metabolites and thus maintains cellular homeostasis (steady internal conditions). Small molecule enzyme inhibitors also include secondary metabolites, which are not essential to the organism that produces them, but provide the organism with an evolutionary advantage, in that they can be used to repel predators or competing organisms or immobilize prey. In addition, many drugs are small molecule enzyme inhibitors that target either disease-modifying enzymes in the patient or enzymes in pathogens which are required for the growth and reproduction of the pathogen.
In addition to small molecules, some proteins act as enzyme inhibitors. The most prominent example are serpins (serine protease inhibitors) which are produced by animals to protect against inappropriate enzyme activation and by plants to prevent predation. Another class of inhibitor proteins is the ribonuclease inhibitors, which bind to ribonucleases in one of the tightest known protein–protein interactions. A special case of protein enzyme inhibitors are zymogens that contain an autoinhibitory N-terminal peptide that binds to the active site of enzyme that intramolecularly blocks its activity as a protective mechanism against uncontrolled catalysis. The Nterminal peptide is cleaved (split) from the zymogen enzyme precursor by another enzyme to release an active enzyme.
The binding site of inhibitors on enzymes is most commonly the same site that binds the substrate of the enzyme. These active site inhibitors are known as orthosteric ("regular" orientation) inhibitors. The mechanism of orthosteric inhibition is simply to prevent substrate binding to the enzyme through direct competition which in turn prevents the enzyme from catalysing the conversion of substrates into products. Alternatively, the inhibitor can bind to a site remote from the enzyme active site. These are known as allosteric ("alternative" orientation) inhibitors. The mechanisms of allosteric inhibition are varied and include changing the conformation (shape) of the enzyme such that it can no longer bind substrate (kinetically indistinguishable from competitive orthosteric inhibition) or alternatively stabilise binding of substrate to the enzyme but lock the enzyme in a conformation which is no longer catalytically active. | 1 | Applied and Interdisciplinary Chemistry |
Turbulent mixing in stratified flows is described by mixing efficiency. This mixing efficiency compares the energy used in irreversible mixing, enlarging the minimum gravitational potential energy that can be kept in the density field, to the
entire change in mechanical energy during the mixing process. It can be defined either as an integral quantity, calculated between inert initial and final conditions or as a fraction of the energy flux to mixing and the power into the system. These two definitions can give different values if the system is not in steady state. Mixing efficiency is especially important in oceanography as mixing is required to keep the overall stratification in a steady-state ocean. The entire amount of mixing in the oceans is equal to the product of the power input to the ocean and the mean mixing efficiency. | 1 | Applied and Interdisciplinary Chemistry |
Steroid sulfates are endogenous sulfate esters of steroids. They are formed by steroid sulfotransferases via sulfation of endogenous steroids like cholesterol and steroid hormones. Although steroid sulfates do not bind to steroid hormone receptors and hence are hormonally inert, they can be desulfated by steroid sulfatase and in this way serve as precursors and circulating reservoirs for their active unsulfated counterparts. In addition, some steroid sulfates have biological activity in their own right, for instance acting as neurosteroids and modulating ligand-gated ion channels such as the GABA and NMDA receptors among other biological targets. | 1 | Applied and Interdisciplinary Chemistry |
The Hamiltonian describing a spinor condensate is most frequently written using the language of
second quantization. Here the field operator
creates a boson in Zeeman level at position . These
operators satisfy bosonic commutation relations:
The free (non-interacting) part of the Hamiltonian is
where denotes the mass of the constituent particles and
is an external potential.
For a spin-one spinor condensate, the interaction Hamiltonian is
In this expression,
is the operator corresponding to the density,
is the local spin operator (
is a vector composed of the spin-one matrices),
and :: denotes normal ordering. The parameters
can be expressed in terms of the s-wave scattering lengths of the constituent particles.
Higher spin versions of the
interaction Hamiltonian are slightly more involved, but
can generally be expressed by using Clebsch–Gordan coefficients.
The full Hamiltonian then is . | 0 | Theoretical and Fundamental Chemistry |
Nitrogen is an element required for growth by all biological systems. While extremely common (80% by volume) in the atmosphere, dinitrogen gas () is generally biologically inaccessible due to its high activation energy. Throughout all of nature, only specialized bacteria and Archaea are capable of nitrogen fixation, converting dinitrogen gas into ammonia (), which is easily assimilated by all organisms. These prokaryotes, therefore, are very important ecologically and are often essential for the survival of entire ecosystems. This is especially true in the ocean, where nitrogen-fixing cyanobacteria are often the only sources of fixed nitrogen, and in soils, where specialized symbioses exist between legumes and their nitrogen-fixing partners to provide the nitrogen needed by these plants for growth.
Nitrogen fixation can be found distributed throughout nearly all bacterial lineages and physiological classes but is not a universal property. Because the enzyme nitrogenase, responsible for nitrogen fixation, is very sensitive to oxygen which will inhibit it irreversibly, all nitrogen-fixing organisms must possess some mechanism to keep the concentration of oxygen low. Examples include:
* heterocyst formation (cyanobacteria e.g. Anabaena) where one cell does not photosynthesize but instead fixes nitrogen for its neighbors which in turn provide it with energy
* root nodule symbioses (e.g. Rhizobium) with plants that supply oxygen to the bacteria bound to molecules of leghaemoglobin
* anaerobic lifestyle (e.g. Clostridium pasteurianum)
* very fast metabolism (e.g. Azotobacter vinelandii)
The production and activity of nitrogenases is very highly regulated, both because nitrogen fixation is an extremely energetically expensive process (16–24 ATP are used per fixed) and due to the extreme sensitivity of the nitrogenase to oxygen. | 1 | Applied and Interdisciplinary Chemistry |
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