NMR study of AOT microemulsion with acetone in the presence of chlorophyll a: distribution of acetone and role of chlorophyll

Reverse micelles or water-in-oil microemulsions with proteins or molecules involved in photosynthesis such as Chlorophyll a (Chl a) are interesting as membrane mimetic systems. The multicomponent AOT/iso-octane/water-acetone system has been proposed as a carrier of photoactive Chl a. We have focused our attention on this system to characterize its microstructure through NMR techniques. We noted a considerable structural modification in the AOT/iso-octane/water system caused by acetone addition. The acetone partition between the organic bulk and the micellar phase was determined. Furthermore, a competition between Chl a and acetone to penetrate into the outer surfactant palisade was suggested. The solubilizate penetration controls the redistribution of the components between the bulk and the surfactant layers. The aggregation state of the photoactive Chl a dihydrate dimer, proposed as a model for the hypothesized primary donor of the PSII (photosystem II of higher plants) reaction center, is strongly modified when such a microemulsion is used.