Increasing the Hole Transfer Rate Through DNA by Chemical Modification

Abstract

The self-assembly of hundreds of well-designed oligonucleotides, the so-called DNA origami method, recently enabled the creation of a variety of two- and three-dimensional nanostructures of defined size. Thus, if the DNA can efficiently conduct an electrical current, DNA can serve as an interesting bottom-up material for the construction of nano-electronic sensors and devices. However, experimental and theoretical efforts of the last two decades have demonstrated that DNA itself does not serve as a molecular wire. In this chapter, we showed that hole transfer rate through DNA can be increased by tuning its physicochemical properties by proper chemical modification. By using various natural and artificial nucleobases with different HOMO energy levels, we demonstrate that hole transfer rate strongly depends on HOMO energy gap between nucleobases (ΔHOMO). The change in the ΔHOMO value from 0.78 to 0 eV resulted in an increase in the hole transfer rate by more than three orders of magnitude. We also demonstrated that hole transfer rate through DNA is affected by the rigidity or the flexibility of DNA. 5-Me-2′-deoxyzebularine (B), which is supposed to increase the flexibility of DNA by weakening the base-pair association, increased hole transfer rate by more than 20-fold, thus demonstrating that hole transfer rate through DNA can be increased by making it more flexible. This was consistent with the fact that locked nucleic acid (LNA), which is known to reduce the flexibility of DNA making it more rigid, caused a decrease of more than two orders of magnitude in hole transfer rate. These results presented in this chapter may help in the future development of programmable DNA-based nano-electronics, which would require higher hole transport properties than that consists of natural nucleobases.