We utilized Fourier transform infrared (FTIR) spectroscopy to investigate headgroup and chain interactions in model SC lipid barriers containing equimolar amounts of deuterated hexadecanoic acid, cholesterol, and ceramide 2 (non-hydroxy sphingosine) or ceramide 5 (α-hydroxy sphingosine). In the ceramide 2 model the thermotropic response of the CD2 and CH2 stretching modes indicates that hexadecanoic acid begins to disorder at 42°C while ceramide 2 remains ordered until 52°C. Additionally, splitting of the CD2 bending and CH2 rocking modes provides evidence for separate orthorhombic hexadecanoic acid and ceramide domains. The ceramide amide I mode (1650 cm-1) is split into two components indicating strong intermolecular hydrogen bonding between headgroups. In the ceramide 5 model, the CH2 and CD2 stretching frequencies again reveal highly conformationally ordered ceramide 5 and hexadecanoic acid chains. Splitting of both the CD2 bending and CH2 rocking modes is observed. However, the CH2 rocking frequencies indicate distorted packing of the ceramide. The collapse of these highly ordered phases, and the onset of conformational disorder, occurs at 50°C for both ceramide 5 and hexadecanoic acid. The amide I and II frequencies of ceramide 5 indicate strong H-bonding, although neither mode is split. Our results demonstrate that model SC lipid systems have quite different physical properties depending on whether they contain ceramide 2 or 5. From this we infer that ceramide 2 and 5 make distinct contributions to the structural biophysics of the SC lipid barrier. Our observation of ordered lipid domains is also consistent with the recently proposed domain mosaic model of the skin barrier.
All Science Journal Classification (ASJC) codes
- Chemistry (miscellaneous)
- Pharmaceutical Science
- Drug Discovery
- Colloid and Surface Chemistry
- Skin barrier
- Stratum corneum