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

Abstract

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 ω₀ (ω₀ = [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 ω₀, 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 ω₀ to be extrapolated and indicate an increase in η_w values with water content, reflecting changes in the shape of Trx-100 microemulsions, which occur at ω₀ = 8.