Energy Transfer and Fluorescence Quenching in Chlorophyll Containing Vesicles

Fluorescence spectroscopic experiments are reported on dimyristoyllecithin (DML) vesicles containing pheophytin a, chlorophyll a or chlorophyll b. From the temperature as well as from the concentration dependence of the fluorescence intensity a phase separation at low temperatures is observed: The chlorophylls are solubilized by the DML phase only up to concentrations of the order of 1 mole‐%. the excess molecules being precipitated in domains containing almost exclusively the chlorophylls. – Whereas at high temperatures (30°C) for chlorophyll a containing vesicles a phase separation could not be established, this was possible in the pheophytin case. The pheophytin solubility in the liquid DML phase amounts to about 10 mole‐%, which is consistent with monolayer studies of the system. – The efficiency of energy transfer from chlorophyll b to chlorophyll a increases with decreasing temperature for small chlorophyll concentrations (< 1 mol‐%). This is due to the decrease in intermolecular distance on solidification of the lipid. The temperature dependence of the transfer efficiency is reversed at high chlorophyll concentrations (≤ 20 mole‐%). This is interpreted as a consequence of the decrease of the chlorophyll solubility in the DML phase that causes a decrease in the chlorophyll‐chlorophyll distance.