AGGREGATION NUMBER FOR SODIUM DEOXYCHOLATE FROM STEADY-STATE AND TIME-RESOLVED FLUORESCENCE

Steady-state fluorescence and time-resolved fluorescence have been use d to study sodium deoxycholate aggregates at basic pH. Pyrene was used as a probe, and dimethylaniline, as a quencher. It is concluded that dynamic quenching with partially micellized quenchers and not static q uenching with the quencher totally micellized, as has been often quote d in the literature, must be considered to interpret the experimental results. Fluorescence lifetimes for pyrene in the absence of quencher and the kinetic constants involved in quenching by dimethylaniline are given and compared to those for similar systems. The derived aggregat ion number, equal to 8 +/- 2, is close to the ones determined by other authors from freezing point depression and static light scattering. T he possible distortion of these small aggregates by probes is also dis cussed.