Phonon dispersion in poly(L-arginine)

Poly(L-arginine) is a basic polypeptide, which undergoes dramatic conformational changes as a consequence of variation in its water content. Complete normal mode calculations and their dispersion are reported for the P-sheet conformation of this biopolymer using the Urey-Bradley force field and the Higgs method for infinite systems. The results indicate that the modes below 1350 cm(-1) show appreciable dispersion. A study of its normal modes and their dispersive behavior shows repulsion with character exchange. Amide modes, side-chain modes, and mixed modes are reported. The heat capacity calculated from the dispersion curves via density-of-states using Debye's relation is compared with the experimental data in the temperature range 220-390K.