Structure of stratum corneum lipids characterized by FT-Raman spectroscopy and DSC .1. Ceramides

Fourier transform Raman spectroscopy and differential scanning calorimetry (DSC) were used to study ceramides type IV as a model substance for the ceramides fraction of stratum corneum lipids. The major part of the Raman spectrum consists of bands owing to the alkyl chain, but there are also bands which belong to the head group of the ceramides. The appearance of the conformationally dependent bands indicates the ordered structure of the hydrocarbon chains. The temperature dependence of the conformationally sensitive bands in the CH2 stretching region (2800-2975 cm-(1)), in the chain C-C stretching region (1050-1150 cm(-1)), and in the low frequency region below 300 cm(-1) is used to estimate the degree of order in terms of the relative population of trans and gauche conformers. The C-C stretching modes at 1063 cm(-1) and 1130 cm(-1) (trans conformation) and the asymmetric CH2 stretching mode at 2880 cm(-1) decrease rapidly near the phase transition temperature and disappear in the liquid state. The temperature and width of the phase transition, derived from Raman data, are similar to these of the DSC study.