Low-wavenumber Raman spectra of multilamellar vesicles are studied for phospholipids differing in the unsaturation degree, the hydrocarbon chain length, and the temperature of the gel-fluid transition. For all phospholipids studied, the low-temperature Raman spectra reveal the peaks attributed to vibrational eigenmodes of the lipid layers. Analysis of the experimental data allows us to identify the lowest eigenmodes of the bilayer, of the monolayer (leaflet), and of the hydrocarbon chain layer. In a continuum approximation, their spectral positions are determined by the ratio of the acoustic velocity and the layer thickness, although their Raman intensities depend on the interleaflet elastic coupling. Temperature dependences of the peak positions, effects of the unsaturation degree, and effects of the saline solution are considered in the work. Parameters of vibrational eigenmodes are determined by mesoscopic properties of bilayers, and the low-wavenumber Raman spectroscopy becomes a powerful method for their description.
- low-wavenumber Raman scattering