Electrophilic substances

Whether or not the intermediate is a diradical, its reactions with organic bases are those appropriate for an electron deficient or electrophilic substance.80... 

Both the monomers and the catalyst influence the mechanism of cationic polymerisation. Electrophilic substances which under certain conditions are capable of inducing cationic polymerisation can be classified as under ... 

Phenol is catabolized by liver microsomal monooxygenases to hydroxylated products (e.g., 1,4-dihydroxybenzene) that can undergo further conversion to a variety of electrophilic substances (e.g., benzoquinones). Such reactions may be involved in generating reactive toxic intermediates in the liver (Eastmond et al. 1986 Lunte and Kissinger 1983 Subrahmanyam and O Brien 1985). Based on the available data, hepatic effects are unlikely to occur at the exposure levels found in the environment or near hazardous waste sites. 

Certain substances may need special consideration, such as highly electrophilic substances, which give positive results in vitro, particularly in the absence of metabolic activation. Although these substances may react with proteins and water in vivo and thus be rendered inactive toward many tissues, they may be able to express their mutagenic potential at the first site of contact with the body. Consequently, the use of test methods that can be applied to the respiratory tract, upper gastrointestinal tract, and skin may be appropriate. 

Highly electrophilic substances may react with proteins and water in vivo and thus be rendered inactive toward many tissues however, they may be able to express their mutagenic potential at the initial site of contact with the body. 

Isocyanates are a very important commercial class of electrophilic substances. They are widely used for a variety of purposes, including adhesive formulations,... 

Skin cancer is the most common type of cancer. Damage to skin DNA from sunlight is the most common cause of skin cancer. This causes mutations that result in formation of cancer cells and that suppress the immune responses that normally prevent replication of such cells. The class of chemicals most commonly associated with causing skin cancer are the polycyclic aromatic hydrocarbons from sources such as coal tar. These can be metabolized to electrophilic substances that bind with DNA to initiate cancer (see Figures 7.3 and 8.3). Arsenic in drinking water has been established as a cause of precancerous lesions, called arsenical keratoses, and squamous cell carcinoma of skin. 

Living polymers can only exist in aprotic solvents. They are killed by water, oxygen and a high number of electrophilic substances. Operating in absence of killing impurities one obtains stable living species they are ionic species whose exact form (free ion, contact ion-pair, solvent separated ion-pair1417 depends upon the concentration and the nature of the monomer, the counterion and the solvent polar... 

Acids now are atoms or groups which can accept an electron pair (acceptors or electrophilic substances), for example, molecules with a sextet configuration (p. 164) such as BF3 and SOs (and the proton which aims at the helium configuration). Thus the formation of BF3.NH3 or of H2S04 from S03 and water is an acid-base reaction. 

In some cases. Phase I metabolites may not be detected, owing to their instability or high chemical reactivity. The latter type are often electrophilic substances, called reactive intermediates, which frequently react non-enzymically as well as enzymically with conjugating nucleophiles to produce a Phase II metabolite. A common example of this type is the oxidative biotransformation of an aromatic ring and conjugation of the resulting arene oxide (epoxide) with the tripeptide glutathione. Detection of metabolites derived from this pathway often points to the formation of precursor reactive electrophilic Phase I metabolites, whose existence is nonetheless only inferred. 

While four domains of methionine synthase bind reaction components (HCY, SAM, cobalamin, and methylfolate), the fifth domain, known as the Cap domain, hovers above cobalamin while it is in its readily oxidized Cob(I) state, limiting access of reactive oxygen species or electrophilic substances. As such, the Cap domain restricts inactivation of methionine synthase and consequently promotes methylation over transsulfuration. In rt-PCR smdies using RNA from cultured human neuroblastoma cells, we found that the Cap sequence, corresponding to... 

Caustic substances like strong acids, strong alkalis, bromine, chlorine gas, etc., are toxic because they dissolve and destroy tissue. Many accidents happen because of carelessness with such substances, but in ecotoxicology they are perhaps not so important. More interest is focused on electrophilic substances that may react with DNA and induce cancer. Such substances are very often formed by transformation of harmless substances within the body. Their production, occurrence, and protection mechanisms will be described in some detail later. 

These electrophilic substances can react with nucleophilic compounds, for example, of the microbial cell, by way of an elimination reaction in the case of micro-bicides with an activated halogen in the a-position to an electronegative group, whereas microbicides with vinyl-activated halogen combine with nucleophiles by way of an addition-elimination reaction (Fig. 3). 

Triphenylsilylpotassium was intensively studied by Gilman before he made the silyllithium reagent, and he showed that it reacted with a variety of electrophilic substances in addition to carbonyl compounds and epoxides, such as silyl halides, pyridine, azo- and azoxybenzene, thiocyanates, and benzonitrile, as well as with far less electrophilic substances like stilbene, anthracene, diphenyl sulfide, and diphenyl sulfone. ... 

We have investigated the behavior of thiocystine in its transfer of persulfide sulfur (sulfane) in order to better understand its biochemical properties. When thiocystine was dissolved in a glycine phosphate buffer, pH 7.4, the solution was stable for at least 6 hours. However, when a trace of an electrophilic substance, such as cyanide, was added, the solution quickly became turbid and deposited free sulfur. The other product was cystine. 

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