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Unusual specific heat of almost dry L-cysteine and L-cystine amino acids
Journal article

Unusual specific heat of almost dry L-cysteine and L-cystine amino acids

M. S. Ishikawa, T. A. Lima, F. F. Ferreira and H. S. Martinho
Physical review. E, Statistical, nonlinear, and soft matter physics, v 91(3), pp 032709-032709
23 Mar 2015
DOI: https://doi.org/10.1103/PhysRevE.91.032709
PMID: 25871146

Abstract

Physical Sciences Physics Physics, Fluids & Plasmas Physics, Mathematical Science & Technology
A detailed quantitative analysis of the specific heat in the 0.5- to 200-K temperature range for almost dry L-cysteine and its dimer, L-cystine, amino acids is presented. We report the occurrence of a sharp first-order transition at similar to 76 K for L-cysteine associated with the thiol group ordering which was successfully modeled with the two-dimensional Ising model. We demonstrated that quantum rotors, two-level systems (TLS), Einstein oscillators, and acoustic phonons (the Debye model) are essential ingredients to correctly describe the overall experimental data. Our analysis pointed out the absence of the TLS contribution to the low temperature specific heat of L-cysteine. This result was similar to that found in other noncrystalline amorphous materials, e.g., amorphous silicon, low density amorphous water, and ultrastable glasses. L-cystine presented an unusual nonlinear acoustic dispersion relation omega(q) = vq(0.95) and a Maxwell-Boltzmann-type distribution of tunneling barriers. The presence of Einstein oscillators with Theta(E) similar to 70 K was common in both systems and adequately modeled the boson peak contributions.

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Physics, Fluids & Plasmas
Physics, Mathematical
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