Comparative spectroscopic studies on liposomes containing chlorophyll a and chlorophyllide a

Chlorophyll a (Chla) and chlorophyllyde a (Chlida) - a derivative of Chla, have been incorporated in the lipid bilayers of two types of liposomes, small unilamellar vesicles (SUV) and multilamelar vesicles (MLV). The objective of the present work was to compare the spectral behaviour of Chla and Chlida incorporated in the lipid bilayers and their sensing behaviour at molecular level. The VIS absorption and fluorescence emission presented differences depending on the type of liposomes and inserted pigment, reflecting the different localization of porphyrin macrocycle in the lipid moieties. The temperature dependence of emission anisotropy and fluorescence intensity, for both Chla and Chlida incorporated in DPPC SUV, revealed the presence of different lipid phases. The degree of incorporation of quercetin (QCT) in liposome membrane was studied by using Chla and Chlida as molecular sensors. The fluorescence polarisation data and the fluorescence quenching process provided arguments for the insertion of the QCT at the interface lipid/water, in the vicinity of lipid polar heads and porphyrin macrocycle. The phytyl chain of Chla penetrating in the hydrophobic core of the lipid bilayers is responsible for the observed differences among Chla and Chlida in sensing the lipid phase transition and the fluorescence quenching process induced by QCT.