Sequence-dependent charge transfer in donor-DNA-acceptor systems: A theoretical study

We have theoretically studied charge transfer in donor-DNA-acceptor systems by using a quantum mechanical model based on the tight-binding approach an d by applying the Miller-Abrahams model of incoherent hopping model. Accord ing to the quantum mechanical model, the rate for charge transfer through D NA bridges consisting of adenine-thymine (AT) base pairs decreases with the bridge length almost exponentially with a falloff parameter beta. The valu e of beta was found to increase with the energy difference between the dono r and the AT base pairs on the bridge. This behavior allows us to reproduce both weak and strong variations of the transfer rate with the bridge lengt h as found in different experiments. The quantum mechanical model also repr oduces the observed increase of the charge-transfer rate due to exchange of AT base pairs on the DNA bridge by guanine-cytosine (GC) base pairs. In co ntrast, the Miller-Abrahams model of hopping is unable to reproduce the exp erimentally observed trends. Therefore we conclude that the latter model is not applicable to the description of charge transfer in the systems invest igated. (C) 1999 John Wiley & Sons, Inc.