LOW-FREQUENCY RAMAN-SPECTRA OF LYSOZYME CRYSTALS AND ORIENTED DNA FILMS - DYNAMICS OF CRYSTAL WATER

We observed low-frequency Raman spectra of tetragonal lysozyme crystal s and DNA films, with varying water content of the samples. The spectr a are fitted well by sums of relaxation modes and damped harmonic osci llators in the region from similar to 1 cm(-1) to 250 cm(-1). The rela xation modes are due to crystal water, and the distribution of relaxat ion times is determined. In wet samples, the relaxation time of a smal l part of the water molecules is a little longer than that of bulk wat er. The relaxation time of a considerable part of the crystal water, w hich belongs mainly to the secondary hydration shell, is an order of m agnitude longer than that of bulk water. Furthermore, the relaxation t ime of some water molecules in the primary hydration shell of semidry samples is shorter than we expected. Thus we have shown that low-frequ ency Raman measurements combined with properly oriented samples can gi ve specific information on the dynamics of hydration water in the ps r ange. On the other hand, we concluded, based on polarized Raman spectr a of lysozyme crystals, that the damped oscillators correspond to esse ntially intramolecular vibrational modes.