Infrared (600-4000 cm-1) and Raman (100-4000 cm-1) spectra of four phospholipid-water mixtures (20% water) have been measured as a function of temperature. The infrared spectra are insensitive to phase transitions, except for a methylene deformation vibration of the fatty acid chains, at 1470 cm-1. A plot of its intensity, relative to that of another band in the spectrum, as a function of temperature, provides a sensitive method for detecting the phase transitions. In the Raman spectrum, a change in relative intensity of symmetric and asymmetric C-H stretches is observed. In the C-C stretching region a collapse of the symmetric and asymmetric stretch into a broad, central maximum is observed. The spectral changes are discussed with reference to the polyethylene system.
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