A calorimetric study of the interaction of synthetic phospholipid liposomes with lipid-soluble small molecules used as dental materials and devices.

The interaction of 22 lipid-soluble small molecules, widely used in dental materials and devices, with synthetic phospholipid liposomes, was investigated by the application of differential scanning calorimetry (DSC), in order to clarify the mechanism of small molecules in biological systems. Dimyristoyl phosphatidyl choline (DMPC) and dipalmitoyl phosphatidyl choline (DPPC) were used as lipids. The interaction of various monomers with liposomes has been reported by us in this journal. In this experiment, various compounds such as redox-initiator, photo-initiator or photo-sensitizer, inhibitor, root-canal disinfectant, cement-base materials (eugenol and 2-ethoxybenzoic acid) etc., were investigated. From changes in the phase transition temperature (T), enthalpy (delta H kcal mol-1) and H/HHW values of both DMPC and DPPC liposomes induced by these molecules, it was concluded that aromatic tertiary amine, benzoyl peroxide and hydroquinone monomethyl ether had a relatively large effect on liposomes, and that in phenol derivatives, m-cresol and p-chlorophenol had a large effect on liposomes compared to phenol. Eugenol used as dental cement also had a large effect on liposomes due to its high hydrophobicity. Changes in the transition properties of liposomes induced by small molecules (characterized by shift of T to a lower temperature, an increase or decrease in cooperativity (H/HHW), and a decrease in delta H of a endothermic peak) seemed to be related to biological activities.