Excess Free Energies of Interaction of Chlorophyll a with a-Tocopherylquinone and Plastoquinone 3 and 9: A Mixed-Monolayer Study

The surface pressure-area isotherms of chlorophyll a, alpha -tocopherylquinone, and plastoquinone 3 and 9 were studied at the air-water interface. Mixtures of chlorophyll a with those molecules were also measured. Results for mixed monolayers were analyzed in terms of the additivity rule. For the chlorophyll a/ alpha -tocopherylquinone and chlorophyll a/plastoquinone 3 mixtures, negative deviations from ideality were observed independent of surface pressure. The chlorophyll a/plastoquinone 9 mixtures were shown to be miscible. Excess free energies of mixing were calculated for the chlorophyll a/ alpha -tocopherylquinone and chlorophyll a/ plastoquinone 3 mixtures at four different surface pressures. They are similar to those found for the chlorophyll a/vitamin K//1 system.