LAMELLAR STRUCTURES FORMED BY STRATUM-CORNEUM LIPIDS INVITRO - A DEUTERIUM NUCLEAR-MAGNETIC-RESONANCE (NMR) STUDY

Hydrated lipid mixtures consisting of stratum corneum ceramides, cholesterol, specifically deuterated palmitic acid, and cholesteryl sulfate were investigated by solid-state H-2 NMR spectroscopy at different temperatures. The mole ratio of cholesterol to ceramides was varied from 1 to 0. H-2 NMR spectra from these mixtures showed powder patterns with quadrupolar splittings smaller than those obtained from control mixtures containing dipalmitoylphosphatidylcholine (DPPC) instead of the ceramides. This result is attributed to the rigid amide group of the ceramides, with a planar configuration, which could prevent close packing of the alpha-methylenes of the acyl chains. There was a gradual loss of symmetry in the powder patterns the amount of cholesterol was decreased and the amount of ceramides (or DPPC) was increased concomitantly. The loss was more pronounced in the ceramide-containing samples. This phenomenon is interpreted as a decrease in the axial reorientation rate of the alpha-deuterated palmitic acid in the bilayers, presumably caused by the increased hydrogen bonding resulting from the high amount of hydroxyl-bearing ceramides. Spectra obtained at temperatures above 60-degrees-C indicated the formation of a hexagonal phase (H(II)) by the ceramide-containing mixtures. Spectra of the omega-deuterated palmitic acid in the mixture containing 76 mol% ceramides and no cholesterol indicated phase separation into a more rigid phase and a more mobile phase in the temperature range of 25 to 60-degrees-C. The bilayer configuration of lipids at 25-degrees-C was confirmed by thin-section electron microscopy.