REACTIONS OF OH AND E(AQ)(-) ADDUCTS OF CYTOSINE AND ITS NUCLEOSIDES OR NUCLEOTIDES WITH CU(II) IONS IN DILUTE AQUEOUS-SOLUTIONS - A STEADY-STATE AND PULSE-RADIOLYSIS STUDY

The reactions of OH and e(aq)(-) adducts of cytosine, cytidine and deo xycytidine in the presence of Cu(II) ions have been studied by product analysis and pulse radiolysis. The product analysis studies show that the degradation of the base is enhanced in N2O-saturated conditions i n the presence of Cu(II) ions and the major radiolytic products are Cu (I), cytosine glycols and 5(6)-hydroxy-cytosine. It is also interestin g to note that the yields of Cu(I) are equivalent to cytosine degradat ion yields, which suggests that the interaction of the OH adducts with Cu(II) ions restricts the radical recombination reactions (known to b e the major physicochemical repair process) which partly regenerate th e parent cytosine. The rate constants of the reactions of cytosine OH adducts with Cu(II) ions determined by pulse radiolysis lie between 10 (7) and 10(8) dm(3) mol(-1) s(-1). The growth in the transient absorpt ion spectra of cytosine OH adducts in the range 330-400 mm, observed i n the presence of copper(II) ions in free and complexed state, suggest s formation of copper radical adduct which decays by water insertion a t the copper-carbon bond to give glycol as the major product. Such cop per radical adduct formation was also observed in the case of cytidine and deoxycytidine. The protonated electron adducts (at the hetero ato ms) of cytosine, cytidine and deoxycytidine transfer electrons to the Cu(II) ions with rate constants of 10(8) and 10(9) dm(3) mol(-1) s(-1) . Here no adduct formation is observed. The steady-state results show that such electron transfer reactions regenerate the parent molecules themselves. Hence such electron transfer reactions do not contribute t o enhanced base degradation in the presence of copper ions. (C) 1996 b y Radiation Research Society