Molecular interactions of penetration enhancers within ceramides organization: a Raman spectroscopy approach

Skin penetration enhancers (PEs) are present in a large number of dermatological and cosmetic products to aid absorption of curatives and aesthetics. They penetrate into skin to reversibly decrease the barrier resistance. Their mode of action on the stratum corneum lipids involves interactions at the level of the polar heads of the lipids and at the level of apolar hydrophobic alkyl chains. Vibrational spectroscopies have been widely used for the study of intra- and intermolecular structures of long chain compounds. In this work we employ Raman spectroscopy to probe the local activities on ceramides and to monitor the dependence of this activity on the ceramide structure, i.e. the presence of double bonds in the alkyl chains, the length of these chains and the nature of the polar heads. The action of three PEs, limonene, DMSO and ethanol, is studied. For intra- chain monitoring, the Raman features associated with CH3 rocking (450-890 cm(-1)) and CC stretching (1050-1140 cm(-1)) are used while the lateral packing is observed with the CH2 stretching band evolution (2840-2900 cm(-1)). Finally, polar interactions are probed using the Amide I band (1600-1650 cm(-1)).