Butyl paraben induced changes in the biophysical properties of dipalmitoyl phosphatidic acid vesicles

The perturbation in the biophysical properties of multilamellar vesicular (MLV) and unilamellar vesicular (ULV) of dipalmitoyl phosphatidic acid (DPPA) by the preservative butyl paraben(BPB) has been studied using DSC and (¹H and ³¹P) NMR. DSC results indicate that the mechanism by which BPB interacts with the DPPA vesicles is similar in MLV and ULV. BPB affected the thermotropic phase transition and the molecular mobility of the DPPA vesicles. For all concentrations, the BPB molecules seem to get intercalated between the polar groups of the phospholipids with its alkyl chain penetrating into the co-operative region. The gel to liquid crystalline phase transition temperature(Tm) of the DPPA vesicles was decreased in the presence of BPB. This suggests increased headgroup fluidity due to reduced headgroup-headgroup interaction. In the presence of BBP additional transitions are observed whose intensity increases with increasing BPB concentration. The large enthalpy values obtained in the presence of BPB suggest that presence of BPB makes the DPPA bilayer more ordered (rigid). The effect of inclusion of cholesterol in the BPB-free and BPB-doped DPPA dispersion was also studied.