Laser-Induced Strand Break Formation of Polyuridylic Acid in the Presence and Absence of Tris(2,2’-Bipyridyl)Ruthenium Chloride and K2S2O8

The effect of light (steady state and laser pulse) on the system poly(U), Ru(bpy)2 3 + (Ru(II)) and S2O8 2- has been studied and the following mechanism for the formation of single-strand breaks (ssb) is proposed: Electronically excited Ru(bpy)2+ 3 ions, bound to poly(U), react with S2O2- 8 by electron transfer resulting in Ru(bpy)3 3+ (Ru(III)) and SO4 -. Both the ruthenium(III) complex and SO4 react with the bases of poly(U) leading to base radicals which in turn leads to ssb formation by H abstraction from position 2’ of the sugar moiety. The reaction scheme is complicated by reactions of the base radicals with Ru(III) or with S2O8 2-,reactions which compete with ssb formation. The rate and yield of ssb formation was measured by transient conductivity.