Theoretical Studies on Electronic Structures of Polypeptide Chains

Electronic structures of polypeptide chains are theoretically studied. To extract the electronic tendency and/or electronic functions of individual amino acids, twelve kinds of homopolypeptide chains, which are formed by a single kind of amino acids, are considered, and their electronic structures are investigated by the first-principle band calculation. Polypeptide chains have the potential to be a semiconductor having a wide band gap of 3 ∼5 eV. Their band-edge states are basically the π electronic states and can delocalize along the peptide backbone. The degree of the delocalization depends on the kind of constituent amino acids and also the orientation of the amino acid side chains against the peptide backbone. We also investigate how the random alignment of amino acids affects the band-edge electronic structures by using the coherent potential approximation approach. In accordance with the kind of aligned amino acids, the aperiodicity in the alignment produces amalgamated electronic states so as to annihilate the individual amino acid's electronic identity, or produces persistent states in order to maintain their electronic characteristics.