Reaction rate of OH radicals with phi X174 DNA: influence of salt and scavenger.

A derivation is given for the dependence of the rate constant of the reaction of OH radicals with a spherical macromolecule on the rate by which such radicals are scavenged by the medium. Experiments were carried out with oxygenated solutions of dilute single-stranded phi X174 DNA at 10(-4)M NaCl (large reaction radius of DNA) or at 10(-4)M NaCl + MgCl2 (small reaction radius) with t-butanol as a scavenger. The results of these experiments cannot be described by simple second-order competition, but can be explained by the predicted dependence of the rate constant of the reaction OH + DNA on the concentration of t-butanol. Furthermore, the results show that only part of the reactions of OH radicals with phi X174 DNA leads to DNA inactivation, and that even at zero scavenger concentration OH radicals are scavenged by other molecules than DNA, presumably impurities remaining even after careful purification of the DNA.