Reactive oxygen species relative reactivity

In acidic media, the reactivity of ethanol on Au electrodes is much lower than in alkaline media. The main product of the oxidation of ethanol on Au in an acidic electrolyte was found to be acetaldehyde, with small amounts of acetic acid [Tremiliosi-FiUio et al., 1998]. The different reactivities and the product distributions in different media were explained by considering the interactions between the active sites on Au, ethanol, and active oxygen species absorbed on or near the electrode surface. In acidic media, surface hydroxide concentrations are low, leading to relatively slow dehydrogenation of ethanol to form acetaldehyde as the main oxidation pathway. In contrast, in alkaline media, ethanol, adsorbed as an ethoxy species, reacts with a surface hydroxide, forming adsorbed acetate, leading to acetate (acetic acid) as the main reaction product. 

The reactive oxygen species involved with protein oxidation can be generally categorized according to their relative reactivity as follows ... 

The presence of the OH group in alcohols makes alcohol combustion chemistry an interesting variation of the analogous paraffin hydrocarbon. Two fundamental pathways can exist in the initial attack on alcohols. In one, the OH group can be displaced while an alkyl radical also remains as a product. In the other, the alcohol is attacked at a different site and forms an intermediate oxygenated species, typically an aldehyde. The dominant pathway depends on the bond strengths in the particular alcohol molecule and on the overall stoichiometry that determines the relative abundance of the reactive radicals. 

This difference in half-lives in serum and tissues was misinterpreted in the early literature as an accumulation of aminoglycosides in the inner ear and held responsible for their organ-specificity. Such an interpretation is, however, not tenable. Aminoglycoside antibiotics are present in the fluids (perilymph and endolymph) and the tissues of the inner ear at relatively low levels, typically at one-tenth of peak serum levels. The reason for the differential sensitivity of inner ear sensory cells may then be based on the extreme persistence of the drugs or on an intrinsic susceptibility to their actions, notably to the generation of reactive oxygen species as described later. ... 

In addition, such chelators, based on the hydroxamic acid bidentate ligand, may diminish the toxic effect of Reactive Oxygen Species (ROS), such as hydroxyl and superoxide radicals, by generating relatively stable nitroxyl radicals. ... 

Of the different oxygen species, the main interest has been in O-, Oj, and O3. Relatively little attention has been paid to the characterization and reactivity of singlet oxygen, O -, lattice or adsorbed O2- species, and most importantly polynuclear species. The work on dioxygen species is likely to be related to the studies of oxygen carriers. Features of special interest in the future on the characterization side are likely to be the detailed geometry of the adsorption site, how the oxygen species is bonded to the surface, and its mobility. 

A proper description of heterogeneously catalyzed oxidation reactions must treat several difficult problems simultaneously. First is the characterization of the solid surface in its reactive state. What oxygen species exist on this surface and what reactions does each species undergo What other sites for adsorption are present Second is the problem of reaction path. What steps are involved in the reaction What are the structures and relative energy contents of the intermediates Third is the problem of reaction velocity, a general and difficult problem in all chemistry. What are transition states, activation energies, and reaction probabilities for the various steps ... 

Since free radical accumulation was proposed to mediate Ap toxicity,27 we studied the effects of EGCG on intracellular reactive oxygen species (ROS) using DCF assay. As expected, a 24-hour exposure to Ap, 42 resulted in a small but significant increase in DCF fluorescence (+18% relative to control), which was reduced by EGCG (10 xM) and by EC (101xM), a tea catechin that failed to protect cells. 

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