ascorbic-acid and phenyl-2-aminoethylselenide

Peroxynitrite, a reactive cytotoxic species generated by the reaction of superoxide with nitric oxide, rapidly oxidizes phenylaminoethyl selenide (PAESe) and its para-substituted derivatives with second-order rate constants ranging from 900 to 3000 M(-1) s(-1) at neutral pH (pH 7.0) and 25 degrees C. These values are approximately 3 x 10(4) times greater than the corresponding rate constants for the reactions of selenides with hydrogen peroxide. The peroxynitrite reaction was also studied at alkaline pH. HPLC analysis confirms that both the peroxynitrite and hydrogen peroxide reactions produced the corresponding phenylaminoethyl selenoxide (PAESeO) as the sole selenium-containing product, with a stoichiometry of 1 mol of PAESe oxidized per 1 mol of PAESeO formed per 1 mol of oxidant reacted. The influence of para-substituents on the rate constants was investigated using Hammett plots; in both cases the data are consistent with an S(N)2-type mechanism, wherein the selenium atom acts as the nucleophile. Our results provide further evidence that organoselenium compounds may play a protective role in the defense against the many reactive oxidizing species produced in cellular metabolism.

Topics: Antihypertensive Agents; Antioxidants; Ascorbic Acid; Chromatography, High Pressure Liquid; Ethylamines; Hydrogen Peroxide; Hydrogen-Ion Concentration; Kinetics; Molecular Structure; Nitrates; Organoselenium Compounds; Oxidants; Oxidation-Reduction; Oxides; Oxidoreductases; Phenethylamines; Reactive Oxygen Species; Sulfur Compounds; Thermodynamics

Topics: Animals; Antihypertensive Agents; Ascorbic Acid; Blood Pressure; Chromaffin Granules; Dopamine beta-Hydroxylase; Ethylamines; Male; Organoselenium Compounds; Rats; Rats, Inbred SHR