Phonon Spectra of Helical Biopolymers

Abstract

Petticolas and Dowley have reported an approximate calculation of the acoustical phonon spectrum of a simplified helical model in the harmonic approximation¹. The purpose of the present communication is to report that the normal modes of motion have already been obtained for a number of polymeric molecules of greater complexity than the model considered by the authors and the corresponding phonon spectra have been measured by the inelastic neutron scattering technique². Moreover, Petticolas and Dowley's model involves only intrachain hydrogen bonded helix and is quite inapplicable to the polyglycine molecule which they discuss because in this molecule only interchain hydrogen bonds are present³. In other polypeptides, which exist in the helix form, the-presence of bulky side groups is expected to change-appreciably the dispersion of the low frequency modes, of vibration.