Propyl paraben-induced changes in dipalmitoyl phosphatidylethanolamine vesicles

This article reports the influence of the preservative, propyl paraben (PPB), on the phase transition and dynamics of dipalmitoyl phosphatidylethanolamine (DPPE) vesicles both in multilamellar vesicular (MLV) and unilamellar vesicular (ULV) forms using DSC and (¹H and ³¹P) NMR. DSC results indicate that the mechanism by which PPB interacts with DPPE vesicles is similar in both forms. Addition of PPB to DPPE dispersion results in lowering of the gel to liquid crystalline phase transition temperature (T _m) and consequently increases DPPE headgroup fluidity. At high PPB concentration, additional transitions are observed whose intensity increases with increasing PPB concentration. DSC and NMR data indicate that the PPB molecules get intercalated between the DPPE headgroups as the polar group of the PPB molecules interacts with the polar group of PE, and the alkyl chain of PPB penetrates into the acyl chain region. The interesting finding with MLV is that the gel phase of DPPE in the presence of PPB, on equilibration at 25 °C, transforms to a stable crystalline subgel phases and whose intensity increases with increasing PPB concentration. The effect of inclusion of cholesterol in the PPB-free and PPB-doped DPPE dispersion was also studied.