Heat capacity and phonons in ω-helical poly-l-phenylalanine

Although several polypeptides are known to exist in omega-helical (fourfold) form, no work has yet been reported on phonon dispersion in these important biomacromolecules. As a consequence, study of the thermodynamical behavior also remains incomplete. Poly-L-phenylalanine is the simplest polypeptide which goes into this rare form. In the present communication we report a comprehensive study of the normal mode analysis, phonon dispersion, density of states, and heat capacity of omega-poly-L-phenylalanine derived from the dispersion curves. One of the characteristic features of the dispersion curves is the repulsion between pairs of modes, viz. (1300 and 1289 cm(-1)), (1082 and 1053 cm(-1)), and (948 and 915 cm(-1)). In the low-frequency region the dispersion curves have regions of high density of states at multiples of half-helix angle. Such regions where (partial derivative omega partial derivative k) --> 0 are akin to critical points known as Von Hove singularities.