THERMALLY-INDUCED MOLECULAR DISORDER IN HUMAN STRATUM-CORNEUM LIPIDS COMPARED WITH A MODEL PHOSPHOLIPID SYSTEM - FT-RAMAN SPECTROSCOPY

The molecular basis of lipid packing in human stratum corneum and a mo del phospholipid system has been studied as a function of temperature using Fourier Transform (FT) Raman spectroscopy. Thermally induced mol ecular rearrangements of the model lipid system, dipalmitoylphosphatid yl choline (DPPC), and stratum corneum were investigated using FT Rama n spectroscopy coupled to a heating chamber. Spectra were recorded for a range of sample temperatures and the results for the two systems we re compared, producing previously unreported information of the therma l behaviour for the different systems. Discrete thermal events were re corded for both systems by plotting band separation of the lipid upsil on(CH2) symmetric and asymmetric stretching modes against temperature. The main thermal events observed for DPPC included a 'pre-melting' be tween 37 and 39 degrees C, the main transition observed between 41 and 42 degrees C, a 'post-transition' between 42 and 43 degrees C and thr ee minor transitions at 58-60, 65-70 and 75-80 degrees C. No evidence- was found for the pre-transition of DPPC; previously observed al 34-35 degrees C. The main transitions for human stratum corneum were observ ed at 35-45, 55, 72 and 83 degrees C, measured from lipid CH2 stretchi ng and bending vibrations. The keratin thermal transition at about 100 degrees C exerted little effect on the lipid bands and no characteris able structural changes were reflected in the keratotic bands. (C) 199 8 Elsevier Science B.V. All rights reserved.