Radical oxidatively induced

Direct conversion of methane to ethane and ethylene (C2 hydrocarbons) has a large implication towards the utilization of natural gas in the gas-based petrochemical and liquid fuels industries [ 1 ]. CO2 OCM process provides an alternative route to produce useful chemicals and materials where the process utilizes CO2 as the feedstock in an environmentally-benefiting chemical process. Carbon dioxide rather than oxygen seems to be an alternative oxidant as methyl radicals are induced in the presence of oxygen. Basicity, reducibility, and ability of catalyst to form oxygen vacancies are some of the physico-chemical criteria that are essential in designing a suitable catalyst for the CO2 OCM process [2]. The synergism between catalyst reducibility and basicity was reported to play an important role in the activation of the carbon dioxide and methane reaction [2]. 

Evans, P.H., Campbell, A.K., Yano, E. and Goodman, B. (1987). Phagocytic oxidant stress and antioxidant interactions in the pneumoconioses and dust-induced tumourigenic lung disease. In Free Radicals, Oxidant Stress and Drug Action (ed. C. Rice-Evans) pp. 213-235. Richelieu, London. 

PAH radical cations are also involved in the metabolic conversion of PAH to PAH diones. Carcinogenicity studies of PAH in rat mammary gland indicate that only PAH with ionization potential low enough for activation by one-electron oxidation induce tumors in this target organ. These results and others indicate that one-electron oxidation of PAH is involved in their tumor initiation process. 

There are various pathways for free radical-mediated processes in microsomes. Microsomes can stimulate free radical oxidation of various substrates through the formation of superoxide and hydroxyl radicals (the latter in the presence of iron) or by the direct interaction of chain electron carriers with these compounds. One-electron reduction of numerous electron acceptors has been extensively studied in connection with the conversion of quinone drugs and xenobiotics in microsomes into reactive semiquinones, capable of inducing damaging effects in humans. (In 1980s, the microsomal reduction of anticancer anthracycline antibiotics and related compounds were studied in detail due to possible mechanism of their cardiotoxic activity and was discussed by us earlier [37], It has been shown that semiquinones of... 

FIGURE 9 Oxidative degradation of dictyotene by TPPMn/Ph-I==0. Compounds 1-14 are isolated products of an oxidative degradation of dictyotene by a radical pathway induced by the system TPPMn/Ph-I=0. Most of these compounds are present among the oxygenated derivatives of dictyotene from natural sources (cf. Figure 8). 

As exemplified in Figure 2, Type 1 mechanism, electron transfer from L to sens yields two radicals, the substrate radical, L", and the sensitizer radical anion (sens ). In the next step, the lipid radical may induce a chain peroxidation cascade involving propagation reactions -The sensitizer radical anion may also start a sequential one-electron reduction of 2 generating HO in the presence of reduced transition metals. As a result, this may lead to abstraction of a lipid allylic hydrogen with subsequent generation of a carbon-centered lipid radical, L, that is rapidly oxidized to a peroxyl radical (vide supra). 

Copper is part of several essential enzymes including tyrosinase (melanin production), dopamine beta-hydroxylase (catecholamine prodnction), copper-zinc superoxide dismutase (free radical detoxihcation), and cytochrome oxidase and ceruloplasmin (iron conversion) (Aaseth and Norseth 1986). All terrestrial animals contain copper as a constituent of cytochrome c oxidase, monophenol oxidase, plasma monoamine oxidase, and copper protein complexes (Schroeder et al. 1966). Excess copper causes a variety of toxic effects, including altered permeability of cellular membranes. The primary target for free cupric ions in the cellular membranes are thiol groups that reduce cupric (Cu+ ) to cuprous (Cu+ ) upon simultaneous oxidation to disulfides in the membrane. Cuprous ions are reoxidized to Cu+ in the presence of molecular oxygen molecular oxygen is thereby converted to the toxic superoxide radical which induces lipoperoxidation (Aaseth and Norseth 1986). 

The changes in the protein composition and flavor of "cooked" and "cooked- -stored" beef seemed to be related to degradation by free radical species induced during lipid oxidation 1-10, 16, 22, 23), Based on the information presented in the aforementioned publication, it seemed reasonable to suggest that the appearance of "bitter" and "sour" tastes and the disappearance of "meaty" and "beefy" flavors were a result of the activity of the free radicals derived from lipid oxidation on flavor proteins (2, 24-28),... 

The formation of free radicals after lipid oxidation is known to play a key role in the deterioration of meat flavor 8, 23), Since proteins constitute a major portion of the muscle s composition, the relationship between chemically active radical species and decomposition of food flavor proteins and peptides needs to be studied in detail. Data has been presented showing the correlation of proteins with flavor (Figures 5 and 6). Data is now presented showing how soluble meat proteins change in an environment where free radicals are induced by a free-radical oxidation generating system or FROG (Figure 10). 

A complicating feature proved to be the fact that some alkyl radicals also induced the blue color, although it appeared possible to allow for this by varying the distance of the molybdenum oxide layer from the front face of the reaction cell. The silica surfaces were at first thought to be perfect reflectors for H atoms, but corrections were applied subsequently by Allen et al. (2) when this was found not to be strictly correct. 

A kinetic model for the UV/H202 process based on UV/H202-induced OH radical oxidation of butylchloride in the presence of humic acid was developed (Liao and Gurol, 1995). 

Ozone molecules can also react with chlorine radicals to induce the chain reaction and generate oxygen molecules and chlorine oxide radicals. The reaction mechanism is very much the same as that for ozone layer depletion by CFC compounds ... 

Erlejman AG, Fraga CG, Oteiza PI. 2006. Procyanidins protect Caco-2 cells from bile acid- and oxidant-induced damage. Free Radic Biol Med 41 1247-1256. 

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