Raman study of low-frequency modes in three glycine polymorphs

The temperature dependence of selected low-wavenumber (< 200 cm(-1)) Raman bands was studied for the different crystalline phases (α-, β-, γ-) of glycine--the simplest possible "building block" of a biomolecule. The temperature dependence of the frequencies of vibrational modes deviates from the theoretical expectation based on the assumption of cubic anharmonicity. Although relatively small, this deviation was observed above 250 K for all the three polymorphs. This finding was discussed in relation to the "dynamical transition" phenomenon, observed in variety of biomolecules in the range 200-250 K. The similarity of the temperatures suggests, that the origin of the dynamical transition phenomenon can be related to intrinsic conformational states of biomolecules, while water serves rather as a plasticizer or a structure organizer.