Thermal behavior and functional group interaction of lipids extracted from the stratum corneum

Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) is a powerful tool for evaluating the functional group interaction of intercellular lipids in the stratum corneum. However, as the large amide I and amide II absorption bands are mainly derived from keratin, which constitutes about 90% of the stratum corneum, it is difficult to investigate the amide bonding interactions of intercellular lipids. In this study, we used extracted lipids from the stratum corneum to investigate the amide bonding derived from lipid interaction. Synchrotron X-ray diffraction studies showed that the extracted lipids formed hexagonal and orthorhombic structures, which play a key role in skin barrier function, as well as high-temperature hexagonal structures. Moreover, in ATR-FTIR measurements, the thermal profiles of stratum corneum lipids and extracted lipids showed similar behavior. The amide absorptions increased with increasing temperature, similar to the observations for the formation of high-temperature hexagonal structures by synchrotron X-ray diffraction. Furthermore, these characteristic changes were disturbed by l-menthol, which fluidizes the polar and hydrophobic regions of intercellular lipids in the stratum corneum. The extracted lipids were useful as an appropriate model of stratum corneum lipid organization for investigation of amide bonding interactions in stratum corneum lipids without interference from keratin.

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