PROBING BILE-SALT AGGREGATES BY FLUORESCENCE QUENCHING

The combination of steady-state and time-resolved quenching experiment s was employed to study the aggregation behavior of sodium cholate at concentrations below 50 mM. Naphthalene, anthracene and pyrene were us ed as fluorescent probe molecules, and protection by the aggregates fr om aqueous quenchers, as well as the onset of aggregation at low sodiu m cholate concentrations, was dependent on the shape of the probes. Pr otection from aqueous quenchers was inferred by comparing the efficien cy for dynamic quenching in the absence and presence of sodium cholate and was best for naphthalene followed by pyrene and anthracene. Stati c quenching was observed, suggesting that probe molecules are located in an aggregate environment that also contains iodide. The incorporati on of pyrene at low sodium cholate concentrations, as well as the smal l degree of static quenching observed, suggest that the shape compleme ntarity, i.e. hydrophobic surface and packing, between pyrene and sodi um cholate is optimum for aggregate formation.