Self-assembling cyclic D,L-peptide nanotubes are electronically insulating and possess wide band gaps (E(g) > 4 eV). Our ab initio electronic structure calculations indicate that the presence of aromatic rings in the side chain of peptide nanotubes significantly reduces the band gap. We investigate the conductivity of the modified peptide nanotubes through calculations of the electron tunneling probability. The electron tunneling probability through a molecule depends on the length of the molecule, L, as e-beta(E)L, where the tunneling beta(E)-factor is strongly energy-dependent. We have calculated beta(E) in three types of peptide nanotubes that have different sequences of amino acid residue, (L-Gln, D-Ala)(4), (L-Gln, D-Leu)(4) and (L-Gln, D-Phe)(4), using the complex band structure approach. We find large beta values near midgap, making these peptide nanotubes a poor tunneling conductor.
The question of whether DNA conducts electric charges is intriguing to physicists and biologists alike. The suggestion that electron transfer/transport in DNA might be biologically important has triggered a series of experimental and theoretical investigations. Here, we review recent theoretical progress by concentrating on quantum-chemical, molecular dynamics-based approaches to short DNA strands and physics-motivated tight-binding transport studies of long or even complete DNA sequences. In both cases, we observe small, but significant differences between specific DNA sequences such as periodic repetitions and aperiodic sequences of AT bases, λ-DNA, centromeric DNA, promoter sequences as well as random-ATGC DNA. (Revision : 1.15)
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