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The Influence of Water on the Photophysical and Photochemical Properties of Piroxicam in AOT/ iso ‐octane/Water Reversed Micelles
Author(s) -
Andrade Suzana M.,
Costa Sílvia M.B.,
Pansu Robert
Publication year - 2000
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2000)0710405tiowot2.0.co2
Subject(s) - chemistry , micelle , piroxicam , aqueous solution , photochemistry , picosecond , tautomer , excited state , octane , intramolecular force , spectroscopy , fluorescence , fluorescence spectroscopy , micellar solutions , analytical chemistry (journal) , organic chemistry , medicine , laser , physics , alternative medicine , pathology , quantum mechanics , nuclear physics , optics
The photophysical properties of Piroxicam , a nonsteroidal anti‐inflammatory drug (NSAID), were investigated at different pH ext values in reversed micelles of Aerosol‐OT (AOT) in iso ‐octane, using both steady‐state and picosecond time‐resolved fluorescence spectroscopy. In contrast with the very complex data obtained in aqueous media, where several prototropic species are in equilibrium, the reversed micellar system essentially favors two species. The absorption spectra shows only one isosbestic point at λ= 348 nm. Excited‐state intramolecular proton transfer (ESIPT), also detected in water, is promoted at low water pool contents measured by ω 0 = [H 2 O]/[AOT]. A strongly shifted (λ em = 470 nm) tautomeric emission is found. Upon the gradual increase of ω 0 , striking differences with pH ext are found. At pH ext = 4, the drug preferentially locates itself in the interfacial region partitioning between a hydrophobic and a hydrophilic domain. Global analysis was applied to the decay data and the results were interpreted by the “two‐state excited‐state” formalism. At pH ext = 7, the anionic species is prevalent and the probe locates itself deeper inside the water core of the reversed micelles. Thus, a strong dependence on water content is detected, approaching a behavior similar to that observed in free aqueous solutions.