The stratum corneum, the top layer of the epidermis, is the material that constitutes the membrane enveloping our body. The lipids that are present are responsible for the permeability properties of the skin and, as a consequence, are essential to maintain the hydration of the internal components and to protect our body from external agents. In the present work, the mixing and the structural properties of model mixtures formed by the main lipids of the stratum corneum have been examined by infrared spectroscopy. The model is formed by an equimolar mixture of ceramides (type III), cholesterol, and perdeuterated palmitic acid. Binary mixtures as well as mixtures for which the ceramides were substituted by sphingomyelin, a ceramide precursor, have also been studied. The results indicate that the stratum corneum model mixture exhibits a rich polymorphism, ranging from crystalline domains with heterogeneous lipid composition and orthorhombic chain packing, to a fluid and homogeneous phase. To obtain this particular behaviour, the three components are essential and the specific role of each species is discussed. In addition, the results reveal that the homogeneous lipid distribution observed for temperatures higher than 70°C can be maintained at low temperatures, leading to the formation of a metastable phase. Several weeks are needed to obtain the thermodynamically stable phase if the sample is incubated at 5°C. However, it is rapidly induced by annealing the sample at 40°C.Key words: stratum corneum, lipid, infrared spectroscopy, ceramide.
Probing the Unique Role of Ultralong-Chain Omega-Acylceramide Cer[EOS] in a Stratum Corneum Lipid Model Matrix using 2H NMR