Glycine phases formed when aqueous solutions were frozen and subsequently heated under different conditions were studied by Raman scattering, x-ray diffraction, and differential scanning calorimetry (DSC) techniques. Crystallization of ice I(h) was observed in all the cases. On cooling at the rates of 0.5 K∕min and 5 K∕min, glassy glycine was formed as an intermediate phase which lived about 1 min or less only, and then transformed into β-polymorph of glycine. Quench cooling of glycine solutions (15% w∕w) in liquid nitrogen resulted in the formation of a mixture of crystalline water ice I(h) and a glassy glycine, which could be preserved at cryogenic temperatures (80 K) for an indefinitely long time. This mixture remained also quite stable for some time after heating above the cryogenic temperature. Subsequent heating under various conditions resulted in the transformation of the glycine glass into an unknown crystalline phase (glycine "X-phase") at 209-216 K, which at 218-226 K transformed into β-polymorph of glycine. The "X-phase" was characterized by Raman spectroscopy; it could be obtained in noticeable amounts using a special preparation technique and tentatively characterized by x-ray powder diffraction (P2, a = 6.648 Å, b = 25.867 Å, c = 5.610 Å, β = 113.12[ordinal indicator, masculine]); the formation of "X-phase" from the glycine glassy phase and its transformation into β-polymorph were followed by DSC. Raman scattering technique with its power for unambiguous identification of the crystalline and glassy polymorphs without limitation on the crystallite size helped us to follow the phase transformations during quenching, heating, and annealing. The experimental findings are considered in relation to the problem of control of glycine polymorphism on crystallization.

For dipalmitoylphosphatidylcholine (DPPC) lipid/water bilayers, a detailed temperature dependence of the Raman scattering spectra at the spectral range of the CH 2-stretching modes was investigated. Below 150 K the ratio of intensities of the 2880 cm (-1) antisymmetric vibration line and the 2850 cm (-1) symmetric one was found to be nearly temperature-independent. Between 150 and 230 K it decreases slightly as temperature increases; and above 230 K it decreases remarkably. This decrease is accompanied with broadening of the antisymmetric line, from 4.2 cm (-1) at 100 K to 5.7 cm (-1) at 296 K. According to literature, the decrease of the antisymmetric line may be interpreted in two ways: (i) the appearance of a static conformational disorder (or of a disorder fluctuating at the time scale larger than picoseconds) and (ii) relaxation at the ps time scale, which is induced by coupling with temperature-activated librational-torsional motion of the lipid chain. Both these interpretations imply that obtained data evidence the appearance of molecular flexibility of lipids around approximately 200 K. The observed effect is to be compared with low-temperature dynamical transition found in disordered media with neutron scattering, Mossbauer absorption, molecular dynamics simulations and other techniques. This transition implies that with temperature increase harmonic atomic motions are transformed to large-amplitude anharmonic (or stochastic) ones. The characteristic times of these motions lay at the ps time scale. The closeness of the temperature of the transition and of the time scale of motions with those found in this work by Raman scattering for lipid bilayers supports the dynamic nature of the 2880 cm (-1) antisymmetric vibration line decrease (i.e., that it is induced by coupling with libration-torsion). To prove that the observed onset of flexibility is a property of a disordered state, Langmuir-Blodgett films of behenic acid were studied. These films contain, like lipids, long CH 2-tails, but, in opposite to bilayers, they have a well-ordered crystalline-like structure. The relative intensity of the antisymmetric/symmetric CH 2-stretching lines was found in these films to be temperature-independent in the whole temperature range studied, between 60 and 296 K.

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.

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