Electron transfer in DNA: predictions of exponential growth and decay of coupling with donor-acceptor distance

Experimental and theoretical work indicates the importance of protein structure in controlling electron-transfer (ET) reactions. Recently, great interest has been shown in exploring electronic coupling interactions in DNA. We report here that the electronic coupling calculated for a recently synthesized class of DNA oligomers with rigidly attached donors and acceptors displays a remarkable dependence on the nucleic acid structure. Indeed, a reversal in the sign of the exponential decay parameter is found in some cases if the donor-acceptor couplings are fit to a single exponential expression. The sign reversal reflects the inadequacy of single exponential models for describing bridge-mediated electron-transfer reaction rates. These effects in DNA oligomers arise from the three-dimensional structure of the double helix. The couplings do decay monotonically with the tunneling pathway length between donor and acceptor, σl (estimated from tunneling pathway analysis), but not with the direct through-space donor-acceptor separation distance.