The effects of the natural antioxidant quercetin and anions of the Hofmeister series on liposomes marked with chlorophyll a.

The unilamellar liposomes of dimyristoylphosphatidylcholine (DMPC), marked with chlorophyll a (Chla), have been chosen as suitable models in studies aimed at determining the effects of natural antioxidant quercetin (QCT) and Hofmeister series anions on lipid bilayers. The variations of steady state fluorescence emission intensity of Chla have been recorded and the values of Chla fluorescence anisotropy, under constant temperature and viscosity, at pH = 7.3-7.4 have been measured. Two types of experiments have been performed. In the first type of experiment, the concentration of anions was maintained constant and the concentration of QCT was varied (from 0 to 100 micromol/l). In the second type of experiment, the concentration of QCT was constant (30 micromol/l) and the concentration of anions was varied (from 0 to 152 mmol/l). The quenching of Chla fluorescence by QCT pleads in favor of QCT insertion at interface water-lipid, in the vicinity of the polar heads of lipids from liposomal bilayer at physiological pH and temperature. Fluorescence anisotropy of Chla in liposomes brought more evidences for QCT localizations at lipid/water interface. Chla is sensing a more rigid microenvironment when QCT is added to the lipid bilayer and specific effects of the Hofmeister series anions.