| Abstract
| - Here we examine the photooxidation of two kinetically fast electron hole traps, N4-cyclopropylcytosine (CPC) and N2-cyclopropylamine-guanosine (CPG), incorporated in DNA duplexes of various sequenceusing different photooxidants. DNA oxidation studies are carried out either with noncovalently bound [Ru(phen)(dppz)(bpy‘)]3+ (dppz = dipyridophenazine) and [Rh(phi)2(bpy)]3+ (phi = phenanthrenequinone diimine)or with anthraquinone tethered to DNA. Because the cyclopropylamine-substituted bases decompose rapidlyupon oxidation, their efficiency of decomposition provides a measure of relative hole localization. Consistentwith a higher oxidation potential for CPC versus CPG in DNA, CPC decomposes with photooxidation by [Rh(phi)2(bpy)]3+, while CPG undergoes ring-opening both with photoexcited [Rh(phi)2(bpy)]3+ and with [Ru(phen)(dppz)(bpy‘)]3+. Anthraquinone-modified DNA assemblies of identical base composition but differentbase sequence are also probed. Single and double base substitutions within adenine tracts modulate CPCdecomposition. In fact, the entire sequence within the DNA assembly is seen to govern CPC oxidation, notsimply the bases intervening between CPC and the tethered photooxidant. These data are reconciled in thecontext of a mechanistic model of conformationally gated charge transport through delocalized DNA domains.Photooxidations of anthraquinone-modified DNA assemblies containing both CPC and CPG, but with varieddistances separating the modified bases, point to a domain size of at least three bases. Our model forDNA charge transport is distinguished from polaron models. In our model, delocalized domains within thebase pair stack form transiently based upon sequence-dependent DNA structure and dynamics. Giventhese results, DNA charge transport is indeed remarkably sensitive to DNA sequence and structure.
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