Fluorescence quenching of Acridine Orange in microemulsions induced by the non-steroidal anti-inflammatory drug Piroxicam.

The singlet excited-state quenching of Acridine Orange (AO) by methyl viologen (MV2+) and the non-steroidal anti-inflammatory drug Piroxicam (Prx), incorporated in sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/isooctane/water and Triton X-100 (Trx-100)/cyclohexane-hexanol/water (w/o) microemulsions, was followed by steady- and transient-state fluorescence. The water content was varied by using different values of omega 0 (omega 0 = [H2O]/[S]) at fixed AOT (0.1 M) and Trx-100 (0.2 M) concentrations. In AOT, MV2+ resides at the interface, while Prx partitions between the interface and bulk water, but considerably biased towards the latter compared to AO. The quenching process efficiency increases with increasing omega 0, but reaches a diffusional value similar to that of free water only for the case of Prx, underlining the electrostatic effect of the AOT interface. The quenching process in Trx-100 microemulsions is more efficient for Prx than for MV2+, pointing to a similar polyoxyethylene intra-chain location for the former and AO. In both cases, data obtained allowed the microviscosity of the aqueous interior at different omega 0 to be extrapolated and indicate an increase in eta w values with water content, reflecting changes in the shape of Trx-100 microemulsions, which occur at omega 0 = 8.