Effect of penetration enhancers on the phase transition of multilamellar liposomes of dipalmitoylphosphatidylcholine. A study by differential scanning calorimetry

Multilamellar liposomes of dipalmitoylphosphatidylcholine were used as a simple model of lipid bilayers representing the intercellular lipid arrangement of the stratum corneum. The effect of skin penetration enhancers such as 1-dodecylazacycloheptan-2-one (Azone), oleic acid (OA), dimethyl sulphoxide (DMSO), thiamorpholine-3-one and N-dodecylthiamorpholine-3-one (C12-thiamorpholine-3-one) on the liposomal bilayer was assessed using differential scanning calorimetry. Azone, OA and C12-thia-morpholine-3-one dramatically modified the thermotropic behaviour of the phospholipid. The pretransition peak vanished at low penetration enhancer concentrations and an increase in the penetration enhancer: lipid molar ratio broadened the gel-to-liquid crystalline transition peak and shifted it to lower temperatures. For the tested concentrations, neither DMSO nor thiamorpholine-3-one changed the phase transition temperature of the liposomes.