Reactivity of Nucleosides Toward Hydroxyl Radicals in Aqueous Solution

Rate constants for reactions of hydroxyl radicals with nucleosides and related compounds were determined by a p-nitrosodimethylaniline method. The obtained rate constants of nucleosides were found to be generally smaller than the sum of those for free bases and ribose, of which the nucleosides are composed. An attempt was made to explain the reduced reactivity of nucleoside in terms of steric hindrance of reaction sites due to other part of the same molecule. The steric hindrance was estimated by solid angle admitted to the radical attack. The observed reactivity was found to be well interpreted by the calculated reactivity according to the following equation, knucleoside =ƒ1kbase + ƒ2kribose where ƒ1 and ƒ2 are steric factors estimated from the solid angles.