High Resolution Thz Spectroscopy of Crystalline Trialanine: Extreme Sensitivity to Secondary Structure and Co-Crystallized Water

Published

May 3, 2006

Author(s)

David F. Plusquellic

Abstract

High resolution THz absorption spectra have been obtained at 4.2 K for three well-defined crystalline forms of trialanine [NH3+-(Ala)3-CO2-]. The crystal structures differ in their secondary structures (parallel (p) vs anti-parallel (ap) sheet) and in their water composition (hydrated vs dehydrated anti-parallel sheet). The spectra are nearly vibrationally resolved showing little absorption below 1 THz. The spectral patterns are, however, vastly different illustrating the extreme sensitivity to the intermolecular H-bonding environments and in sharp contrast to observations made in the mid-IR region. Predictions obtained from a classical force field model (CHARMM) and density functional theory (PW91 functional) for periodic solids are compared with the known X-ray structures and the THz absorption spectra. In general, the spectral predictions are in remarkably good agreement with experiment. The hydrogen bond distances are, however, under-estimated at both levels of theory and for the two ap-sheets, the absorption features are significantly red-shifted. Correlations are found between the H-bond distances and [C=]O---H-N angles when compared with the X-ray data suggesting inclusion of an angular dependent energy term to describe the H-bonding interactions may lead to improvements in the classical force field predictions.

Citation

Journal of Physical Chemistry

Volume

128

Issue

17

Pub Type

Journals

Keywords

biosystems and health, CHARMM, co-crystallized water, DMOL, peptide crystals, THz absorption spectra

Citation

Plusquellic, D. (2006), High Resolution Thz Spectroscopy of Crystalline Trialanine: Extreme Sensitivity to Secondary Structure and Co-Crystallized Water, Journal of Physical Chemistry (Accessed October 11, 2025)