Insights into the molecular organization of lipids in the skin barrier from infrared spectroscopy studies of stratum corneum lipid models.

In order to gain some insight into the molecular organization of lipids in the skin barrier we used Fourier transform infrared (FTIR) spectroscopy to investigate models of the stratum corneum (SC) containing deuterated hexadecanoic acid, cholesterol, and ceramide 2 or ceramide 5. In both models there is clear evidence of separate conformationally ordered domains of ceramide and fatty acids. In addition, these chains are packed in orthorhombic subcells at physiological temperatures. The ceramide headgroup behavior indicates distinct hydrogen bonding patterns between the ceramide 2 and ceramide 5 models. In the ceramide 2 model the amide I mode is split into two components suggesting strong transverse intermolecular hydrogen bonding between headgroups. In contrast, no amide splitting is observed for ceramide 5 although the amide frequencies are indicative of strong hydrogen bonding. These observations on the molecular organization of SC lipids are discussed in terms of skin barrier function.