Photochemistry of nabumetone in aqueous solution of sodium dodecyl sulfate (SDS) micelles

The photochemistry, solubility and distribution between two phases of nabumetone (NB) in aqueous solution of sodium dodecyl sulfate (SDS) micelles were studied. The solubility (SNB) of NB was monitored using steady-state UV–Vis absorption spectroscopy. The linear relationship of SNB to SDS concentration ([SDS]) gave the large value of partition coefficient, P (logP = 3.5), for NB distribution between the aggregate and the water phase showing the localization of NB in the micellar phase. NB fluorescence (FL) quantum yield increases with [SDS] from 0.03 in water to 0.056 at 0.2 M [SDS]. The dependence of FL intensity at 355 nm (F335) on [SDS] is bell-shaped. The plot of initial F335 increase with [SDS] in the range 0–0.05 M gave the expected value of the critical micelle concentration (cmc = 7.9 mM). Further increase of [SDS] resulted in 10% decrease of F335 demonstrating the variation of the micellar structure. Small-Angle Neutron Scattering (SANS) and refractometry confirmed this variation. The NB in SDS was protected against photodegradation. High Performance Liquid Chromatography/Mass Spectrometry (HPLC/MS) detected 2-(but-2-en-1-yl)-6-methoxynaphthalene as NB final photoproducts in SDS solution which was not found in homogeneous media. The hydrated electron localized in water phase, NB radical cation and NB triplet excited state both localized in the micellar phase were observed by laser flash photolysis of NB in micellar solution. The decay kinetics of these intermediates was different with respect to that in the homogeneous media. The reactivity of NB in SDS micellar environment compared to the homogeneous media is under the discussion.