Phonon dispersion in poly(L-tryptophan)

The normal modes and their dispersions for poly(L-tryptophan) (PLTR) in the alpha-helical form have been obtained in a reduced zone scheme with Wilson's GF matrix method as modified by Higgs. Dynamic studies of the alpha form are of special significance as it is the predominant secondary structure for protein molecules. X-ray and circular dichroism (CD) studies by Peggion et al. have confirmed the alpha-helical conformation of PLTR. The side group of PLTR is more complicated than that of other natural polypeptides. It consists of both a pyrrole and a benzene ring along with a CH2 group. Optically active frequencies corresponding to the zone center and zone boundary are identified and discussed. Some of the characteristic features of the dispersion curves are repulsion accompanied by an exchange of character and von Hove singularities. The heat capacity has been calculated via densities of state with Debye's equation in the temperature range of 220-390 K and has been compared with experimental measurements. (C) 2003 Wiley Periodicals, Inc.