Acoustic phonon quantization and low-frequency Raman spectra of spherical viruses.

Low-frequency vibrational modes are calculated using elastic continuum approximation model for spherical viruses immersed in a medium. The blueshift in the vibrational modes is observed with decrease in the virus particle size. To incorporate the effect of surrounding environment, the anisotropic and finite medium is taken into account. The presence of medium significantly affects the Raman peaks representing acoustic modes and results into the linewidth broadening accompanied by damping of modes. The estimated damping constant and quality factor suggest less loss of energy of the fundamental breathing mode in the virus-glycerol configuration. The temperature effect on the virus results into the redshift of the low-frequency Raman peaks with increase in temperature. Significant differences in Raman spectra of wet and dry lysozyme are observed. The conformational changes are more prominent at low temperature for virus-water configuration suggesting that water works as a low energy barrier for conformational changes of spherical virus.