REACTIONS OF OH-CENTER-DOT AND E(AQ)(-) WITH URACIL AND THYMINE IN THE PRESENCE OF CU(II) IONS IN DILUTE AQUEOUS-SOLUTIONS - A PULSE-RADIOLYSIS STUDY

The reactions of OH. and e(aq)(.) adducts of uracil and thymine with C u(II) ions in aqueous solutions were followed by pulse radiolysis. The transient absorption spectra of the OH. adducts of uracil when follow ed in the presence of Cu(II) ions show growth in absorption at wavelen gths 420 and 350 nm at 15 mu s and 65 mu s after the pulse respectivel y. Similar transient absorption spectra of thymine showed growth in ab sorption at wavelengths 390 and 320 nm at 38 mu s and 65 mu s after th e pulse respectively. The rates of electron transfer from the OH. addu cts of uracil and thymine to various Cu(II) compounds when monitored a t 360 nm lie between 10(6) and 10(8) mol(-1) dm(3) s(-1), this implies that the electron transfer process is not an efficient process. Low r ate constants coupled with the spectral changes suggest formation of a radical copper adduct which decays by water insertion to give cis-gly cols as the major product. The electron transfer from the electron add ucts of uracil and thymine to various copper(II) compounds takes place more efficiently (rate constants of the order of 10(8) and 10(9) mol( -1) dm(3) s(-1)) compared with that from the OH. adducts. The t-butano l radicals formed on scavenging the OH. radicals also produce adducts with Cu(I) ions which are formed on oxidation of the electron adducts by Cu(II) ions. This adduct has absorption around 400 nm both in the c ase of uracil and thymine.