Vibrational dynamics and phonon dispersion in poly(β-benzyl-l-aspartate) (β-sheet)

Poly(β-benzyl- l -aspartate) (PBLA) shows unusual conformational variety and under varying conditions of preparation it is capable of adopting four different conformations, namely left-handed α helix (αl), right-handed α helix (αr), ω helix and β pleated sheet. We present here a complete phonon dispersion and heat capacity study on the β form of PBLA. A comparison of the characteristic features and the conformational dependence of modes for α, β and ω forms of PBLA are made. It is observed that the dispersion of modes in the β form is in general larger than in the α form. Crossing over and repulsion of various dispersion branches are discussed.