Laser flash photolysis studies on the first superoxide thermal source. First direct measurements of the rates of solvent-assisted 1,2-hydrogen atom shifts and a proposed new mechanism for this unusual rearrangement

The thermal decomposition of bis(4-carboxybenzyl)hyponitrite (SOTS-1) in ae rated water under physiological conditions has previously been shown to giv e the superoxide radical anion in a yield of 40 mol % (Ingold, K. U.; et al . J. Am. Chem. Sec. 1997, 119, 12364). The absolute kinetics of the element ary reactions involved in the cascade of events leading from the first-form ed water-soluble benzyloxyl radical to superoxide have been determined by l aser flash photolysis. On the basis of these kinetics it is concluded that SOTS-1 will be suitable for studies of superoxide-induced oxidative stress in most biological systems. A water-assisted 1,2-H shift converting benzylo xyl into the benzyl ketyl radical is an important step in the above reactio n cascade. The kinetics of the 1,2-H shift assisted by H2O, D2O, and a numb er of nucleophilic alcohols have been measured for the first time. These da ta have led to a proposed new mechanism involving the initial formation of a ketyl radical anion and an oxonium cation which generally collapse to giv e the neutral ketyl radical as the first observable product on the time sca le of our experiments (ca. 80 ns).