pH dependent binding of chlorin-p6 with phosphatidyl choline liposomes

The pH dependent binding of the photosensitizer chlorin-p6 with phosphatidyl choline liposomes was investigated at varying lipid:drug molar ratio. At pH 5.0, substantial changes in the absorption and emission spectra of the drug were observed when liposomes were added. At higher pH these changes became progressively smaller and observable only at higher liposomes concentrations. Studies carried out on fluorescence emission lifetimes as well as quenching of fluorescence with KI suggest that at pH 5.0 the drug localizes in the central region of lipid bilayer and for pH 6.0 and higher the drug binds closer to the liposome interface.