Association of chlorophyll with inverted micelles of dodecylpyridinium iodide in toluene

Dodecylpyridinium iodide forms inverted micelles in water-containing toluene at concentrations higher than 10^-4 M, as it reportedly does in other nonpolar solvents. Micelle formation is characterized by changes in the charge-transfer absorption band, and in the chemical shifts of protons, especially those on or near the pyridinium group. The micelles associate with chlorophyll a, also dissolved in the toluene, as evidenced by large changes in the chemical shift of some of the surfactant and the chlorophyll resonances. Temperature effects are small and are consistent with a loosening of the association at higher temperatures (to 345 K). The fluorescence quantum yield of chlorophyll is little reduced by the presence of 10^-3 M 2,2′-dithiobis(5-nitropyridine), a quencher which is soluble in toluene and probably associates weakly with the micelles, but is strongly reduced by the presence of the bis(tetramethylammonium) salt of 5,5′-dithiobis(2-nitrobenzoic acid), which is solubilized only in the presence of the inverted micelles, and furthermore forms a complex with chlorophyll. These cationic inverted micelles constitute a new environment for the pursuit of chlorophyll model system investigations.