The electronic structures of protein nanotubes (PNTB), which are formed by the periodical stacking of cyclo-peptide-ring (CPR) rings, are theoretically investigated in terms of the ab initio calculations. The inter-ring H bonds among the CPRs cause the electronic interaction when CPRs are periodically stacked. This interaction has a potential to delocalize electrons and holes along the tube axis as if the band conduction occurs through the bridging H bonds. The protonation of this system is also investigated. The migrated proton (charged H* species) is expected to create the impurity (acceptor) level in the band gap of the PNTB.
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