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Difference in the Dynamic Properties of Chiral and Racemic Crystals of Serine Studied by Raman Spectroscopy at 3−295 K

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journal contribution
posted on 27.12.2007, 00:00 by B. A. Kolesov, E. V. Boldyreva
Single-crystal polarized Raman spectra (60−4000 cm-1 at 3 ≤ T ≤ 295 K) were measured for chiral l- and racemic dl-serine, α-amino-β-hydroxypropionic acid, (NH3)+CH(CH2OH)(COO)-. The Raman spectra of dl-serine do not show any striking changes with temperature or on storage. In contrast to that, the dynamical properties of l-serine change at about 140 K. These changes can be interpreted as the reorientation of the side chain −CH2OH fragments of the zwitterions with respect to the backbone C−C bonds, resulting in the positional disorder of the O−H···O intermolecular H-bonds. The redistribution in the intensities of the Raman spectra of the crystals of l-serine stored for a long time (about a year) indicates the changes in the orientation of the molecular fragments in the direction normal to the axes of the head-to-tail chains. The difference in the thermodynamic functions of l- and dl-serine reported previously [Drebushchak, V. A.; Kovalevskaya, Yu. A.; Paukov, I. E.; Boldyreva, E. V. J. Therm. Anal. Calorim. 2007, 89 (2), 649−654] is explained by the difference in the spectra of external vibrations of the crystals.