Interactions of p-coumaric, caffeic and ferulic acids and their styrenes with model lipid membranes

The influence of the p-coumaric, caffeic and ferulic phenolic acids, and their corresponding styrenes, on structural properties of a model lipid membrane was investigated by differential scanning calorimetry and fluorimetry. The phenolic acids were seen to have smaller effects, compared to their styrenes, on the temperature and enthalpy of the main phase transition (gel-to-liquid) of extruded large unilamellar liposomes prepared from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine lipids. A slight thermal and enthalpy destabilisation of the liposomes was seen with the phenolic acids at a lipid:acid molar ratio of 1:1. In contrast, their styrenes had higher destabilisation effects on the enthalpy of the phase transition. For fluorescence spectroscopy with 1,6-diphenyl-1,3,5-hexatriene as the membrane probe, the polarisation measurements showed that the styrenes, which are less polar than their corresponding acids, had greater effects on lipid membrane structure. The correlations between the structural properties of these compounds and their effects on membrane structure are discussed.