Thermotropic state transition in isolated platelet membranes studied by Raman spectroscopy

The thermotropic state transition of the lipids in isolated platelet membranes has been studied by Raman spectroscopy in the temperature range from -3 degrees C to +45 degrees C using the (C-H) stretching vibrations, carotenoid(s) vibrations at 1530 cm-1 and 1160 cm-1, as well as the skeletal optical vibrations. 1. The increase of temperature causes a decrease in intensity of the 2885 cm-1 band relative to the 2855 cm-1 one. The evaluation of the ratio I2885/I2855 as a function of temperature indicates a double thermotropic state transition of platelet membrane lipids: the first one near 5 degrees C and the second near 17.5 degrees C. 2. The ratio I1530/I1160 shows that the intensity variations in the carotenoid(s) peaks follow the second lipid transition. Thus, it seems that the platelet membrane carotenoid(s) might be linked to the lipids which undergo transition near 17.5 degrees C. 3. The spectral changes in the skeletal optical range suggest a considerable proportion of all trans chains in the membrane lipids at lower temperatures whereas gauche structures seem to be introduced at higher temperatures.