Hole wave functions and transport with deazaadenines replacing adenines in DNA.

Transport of a hole along the base stack of DNA is relatively facile for a series of adenines (As) paired with thymines (Ts) or for a series of guanines (Gs) paired with cytosines (Cs). However, the speed at which a hole was found to travel was much too small to make useful semiconductor-type devices. Quite recently it was found that replacing one of the electronegative nitrogens (N3 or N7) with a carbon and a hydrogen, thus turning A into deazaadenine, increased the hole speed in what was A/T by a factor 30.

Effect of negative differential conductance in carbon nanotubes.

Measurements of transport at high electric fields in metallic single-walled carbon nanotubes (CNTs) have shown either saturation of the current or a region of negative differential conductance (NDC) characterized by the current, after reaching a maximum, decreasing with further increase in voltage. We point out that both types of behavior are characteristic of NDC, but the NDC is masked in samples showing current saturation due to generation of space charge, leading to a nonuniform electric field. We derive the relation between the carrier concentration, the electric field at which the drift velocity peaks, and the length of the sample that is required for the NDC to be manifest as saturation.

Duplex polarons in DNA.

In earlier work we calculated the wavefunction and energy of the solvated polaron in DNA with a simple model in which the charge was taken to be on a single chain of bases at the center of the double helix. To better approximate the actual situation, we have now extended the calculations to the case in which the charge is distributed on two chains of bases, complementary to each other, one on each side of the center. The binding energy of the resulting polaron is somewhat larger than that obtained for the single-chain polaron, the result of each chain of the polaron being closer to some of the polarization charge it induces.

Base sequence effects on transport in DNA.

Given the success of the polaron model based on solvation in accounting for the width of a hole polaron on an all-adenine (A) sequence on DNA, we extend the calculations to other sequences. We find excellent agreement with the free energy differences measured by Lewis et al. (J.

Charge transport in DNA in solution: the role of polarons.

Since the discovery a decade ago of rapid photoinduced electron transfer in DNA over a distance >4 nm, a large number of experiments and theories have been advanced in the attempt to characterize the transfer, mainly of a radical cation or hole. Particularly influential experiments were carried out by Giese [Giese, B. (2000) Acc.