Phonon dispersion in poly(l-arginine)

Abstract

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 β-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.

Keywords:

• Phonons
• Dispersion curves
• Density-of-states
• Heat capacity

Acknowledgments

Financial assistance from Council of Scientific and Industrial Research to N.K.M. under the Senior Research Fellowship scheme is gratefully acknowledged. We are grateful to Mr. Rajesh Khanna, Central Drug Research Institute, Lucknow, for running the spectra.