Detection of changes in the environment of hydrocarbon chains by raman spectroscopy and its application to lipid-protein systems

It is shown that changes in the environment of hydrocarbon chains of lipid molecules give strong effects on the C-H stretching vibration region of the Raman spectra. Different liquid-crystalline lipid-water phases can thus be identified according to the intensity ratio of the 2850 and 2885 cm−1 peaks, i.e. the symmetric stretching vibrations of the CH2 and CH3 groups, respectively. More important is the possibility of studying lipid-protein interaction from the relative intensities of the different C-H stretching vibrations, which is demonstrated by aqueous precipitates of insulin and long-chain phosphate esters. The results indicate that if is possible to detect whether the hydrocarbon chains of the lipid molecules are associated into separate lipid regions or located in a protein environment.