Dielectric studies on glass transitions in biological systems

Despite several reports on glass transitions in different biological systems, their existence is still controversial. The method of thermally stimulated depolarization currents, which is very sensitive to transitions, is used to investigate this question. The thermograms obtained with different systems (plant tissue, proteins, saccharides) show, at high water contents, transitions in the temperature range 170 to 200 K, which shift to higher temperatures with decreasing water content. Three features of the transitions, namely the dependence of their dynamics on water content, the dependence of their activation energies on temperature, and the validity of compensation effects, reveal, in analogy to synthetic polymeric systems, the existence of two glass transitions, probably due to the hydration water and the matrix structure, respectively.<
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