Theoretical Investigation of the Cyclic Peptide System Cyclo[(d-Ala-Glu-d-Ala-Gln)m₌₁₋₄]

Using newly developed theoretical methods, we present preliminary results for some calculated properties of the cyclic peptide system cyclo[( d -Ala-Glu- d -Ala-Gln) m = 1 - 4 ]. These calculations are motivated by the fact that the cyclo[( d -Ala-Glu- d -Ala-Gln) 2 ] cyclic peptide structure was the first cyclic peptide structure synthesized by an experimental group through a self-assembly process. In this paper, we calculate the electronic structure and vibrational mode properties of the isolated ring structures for cyclo[( d -Ala-Glu- d -Ala-Gln) m = 1 - 4 ] and of the cyclic peptide nanotube system cyclo[( d -Ala-Glu- d -Ala-Gln) 2 ]. The HOMO−LUMO gap is wide (∼5.0 eV) yielding a transparent material with possibly unique bioelectronic device applications. In addition, we find that the C−O carbonyl stretch modes and the N−H amide-I stretch modes of these isolated ring structures to be highly localized at around 1773 and 3192 cm -1, respectively.