Reactions of hydroxyl radical ((OH)-O-center dot) and oxide radical anion (O center dot-) with 2-aminopurine in aqueous medium

摘要

Pulse radiolysis has been used to investigate the reaction of hydroxyl radical ((OH)-O-center dot) and oxide radical anion (O center dot-) with 2-aminopurine (2AP), a fluorescent analogue of adenine, in aqueous medium. The second-order rate constant for the reaction of (OH)-O-center dot with 2AP was determined to be 3 x 10(9) dm(3) mol(-1) s(-1) and for the reaction of O center dot- it was 7.1 x 10(8) dm(3) mol(-1) s(-1). The transient absorption spectrum obtained in the reaction of (OH)-O-center dot at pH 7 has absorption maxima at 370 and 470 nm. The spectrum undergoes a time-dependent transformation at higher time-scale. The intermediate species was found to react with N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD). The yield of TMPD center dot+ was calculated in terms of G(TMPD center dot+) to be 3.3 x 10(-7) mol J(-1) at pH 7. The (OH)-O-center dot reactions were also carried out at pH 10 and the transient absorption spectra have lambda(max) at 400 and 480 nm. The transient spectra obtained in the reaction of O center dot- at pH approximate to 14 have maxima at 400 and 480 nm. The transient intermediate species at pH 7 are assigned to the formation of 2AP-4-OH center dot (54%), 2AP-5-OH center dot (7%) and 2AP-8-OH center dot (39%) based on the spectral evidence and TMPD center dot+ build-up. Both 2AP-4-OH center dot and 2AP-5-OH center dot undergo OH- elimination to form a radical cation. At higher pH (pH 10), the dehydration reaction of these OH-adducts leads to a N-centered radical (2AP-N(9)(center dot), 71%). Formation of 2AP-8-OH center dot (29%) is also proposed at this pH. In the reaction of O center dot- with 2AP, it is proposed that a similar nitrogen centered 2AP-N(9)(center dot) radical is formed by an electron-transfer reaction at N(9).