Heat Capacity and Vibrational Dynamics of Poly(L-glutamic acid) (α Helix)

Abstract

ABSTRACT:Poly(L-glutamic acid) is one of the polyamino acids containing a bulky side chain. At the room temperature and at pH < 5 it exists in ex helical conformation but at pH > 7 the ex helix is reduced to the random coil state. Normal mode analysis of poly(L-glutamic acid) has been reported by Sengupta and Krimm but no phonon dispersions have been reported so far. As a consequence both the thermodynamical studies and fuller interpretation of spectra remain incomplete. In the present communication we report complete normal mode analysis and full dispersion curves for poly(L-glutamic acid). A comparative study of ex and /32 forms of poly(L-glutamic acid) has been carried out in order to identify and to understand the spectral features due to two different conformations. Heat capacity has also been calculated by using density-of-states (g(v)). For the calculation of normal modes the Urey Bradley force field has been used. The normal modes for N-deuterated systems have also been studied to check the validity of the assignments and force field. Our results are in good agreement with the observed experimental data.

Vibrational Dynamics and Heat Capacity of Poly(L-lysine)

“…The frequency range agrees well with the scissoring modes of poly(L-leucine) (1449 cm -l ), 14 poly(L-glutamic acid) (1451 cm -l ), 20 and poly(L-phenylalanine) (1461 cm-1 ). 21 The CH 2 wagging mode which has also a contribution of (H,µ-C,-N,) bending is calculated at 1192 cm -l and assigned to observed peak at 1185 cm -l _ The range of this mode agrees well with that of poly(L-leucine) (1172 cm -l) and poly(y-benzyl L-glutamate) (1183cm-1 ).…”

Vibrational dynamics of poly(l-isoleucine)

“…They have been observed at nearly the same value, at 1449 cm −1 in poly(l-leucine) [20], 1453 cm −1 in poly(␥-benzyl-l-glutamate) [21] and at 1450 cm −1 in poly(l-glutamic acid) [3]. Fig.…”

“…In earlier publications we have reported the vibrational dynamics of biopolymeric systems having ␣, ␤, and 3-fold helical conformations [1][2][3][4][5][6][7][8][9][10][11]. In continuation of these studies, we report in the present communication our work on the vibration dynamics and heat capacity of poly(l-isoleucine) (PLIS).…”

“…The assignments have been made on the basis of potential energy distribution, band position, band shape, band intensity, derivative spectra, and absorption/scattering in similar molecules having groups placed in similar environments. Full use has been made of the spectral information available in literature [2,3,11]. Except for a couple of frequencies, most of the frequencies are fitted within less than 1%.…”

“…But other coordinates also contribute significantly, indicating that a combination of main chain conformation, hydrogen bond strength, and side chain structures are involved in determining the frequency of this mode. In poly(l-leucine) [20], the amide V band appears at 587 cm −1 and in poly(l-glutamic acid) [3] it appears at 552 cm −1 . For poly(l-␣-amino acids) [22] it is observed at 450 cm −1 .…”