Radiolysis of di- and tri-methyl phosphates in oxygenated aqueous solution: a model system for DNA strand breakage

Abstract

In the radiolysis of aqueous solutions of trimethyl phosphate saturated with N₂O–O₂ the major products (G values in parentheses) are dimethyl hydrogen phosphate (6.4), formic acid (3.1), formaldehyde (1.7), hydrogen peroxide (2.1), organic peroxide (0.5), and carbon monoxide (1.0). Oxygen is consumed (G 4.1). In the dimethyl phosphate (sodium salt) system the products and their G values are similar to those of the trimethyl phosphate system. Pulse radiolytic studies have shown that in the trimethyl phosphate system the first formed peroxyl radicals react with each other to give a short lived tetraoxide (2k= 9 × 10⁸ dm³ mol^–1 S^–1). This intermediate decays either by concerted mechanisms or by fragmentation to form O₂ and two oxyl radicals. Among other reactions these oxyl radicals undergo a 1,2-hydrogen shift, followed by a complex series of reactions. There are two processes that yield acids at longer reaction times. The faster process has been identified as the hydrolysis of formic dimethylphosphoric anhydride (k= 0.3 + 2.3 × 10⁴[OH^–]S^–1). The slower process (k= 2600[OH^–] S^–1) is only observed in basic solutions and has not yet been identified with certainly. The present findings are used as a model to assist in the interpretation of some aspects of DNA radiolysis.