A number of liposomal preparations of norfloxacin (NF) containing variable concentrations of phosphatidylcholine (PC) (10.8–16.2 mM) have been formulated and an entrapment of NF to the extent of 41.7–56.2% was achieved. The values of apparent first-order rate constants (kobs) for the photodegradation of NF in liposomes (pH 7.4) lie in the range of 1.05–2.40 × 10−3 min−1 compared to a value of 8.13 × 10−3 min−1 for the photodegradation of NF in aqueous solution (pH 7.4). The values of kobs are a linear function of PC concentration indicating an interaction of PC and NF during the reaction. The second-order rate constant for the photochemical interaction of PC and NF has been determined as 8.92 × 10−2 M−1 min−1. Fluorescence measurements on NF in liposomes indicate a decrease in fluorescence with an increase in PC concentration as a result of formation of NF− species which exhibits poor fluorescence. Dynamic light scattering has shown an increase in the size of NF encapsulated liposomes with an increase in PC concentration. The stabilization of NF in liposomes is achieved by the formation of a charge-transfer complex between NF and PC.GRAPHICAL ABSTRACT
The photochemical interaction of NF and PC leads to the formation of charge-transfer complex to give the photoresistant NF− species resulting in the stabilization of NF in liposomes.