Phonon Dispersion in ω Helical Poly N^ε (p-Bromobenzoyl-L-Ornithine)

Abstract

Poly N^ε(p-bromo benzoyl-L-ornithine) is one of the few biopolymers existing in rare ω helical (four-fold) conformation which can be obtained from α form through an irreversible heat treatment. A study of its normal modes and dispersive behaviour shows several interesting features such as \lsquo crossing over\ squo, \lsquo repulsion with character exchange\ squo and Von Hove type \lq singularities\ q which lead to a fuller interpretation of infrared (i.r.) spectra. The existence of alternately different side chain conformations which makes the phonon problem too large has been taken into account by considering the vibrations of the PBrBO chains with two independent conformations. Detailed study of skeletal, amide and side chain modes has been reported.