Naproxen sodium salt photochemistry in aqueous sodium dodecyl sulfate (SDS) ellipsoidal micelles

The photochemistry and other properties of the anti-inflammatory drug (NSAID) naproxen (NP) in sodium dodecyl sulfate, SDS, micellar aqueous solutions at pH = 7 (NP is in anionic form) were studied. The large value of the partition coefficient (P) was obtained, logP = 2.7, showing that the most part of NP is localized in the micellar phase. The solubilization in SDS micelles results in NP fluorescence and photodegradation quantum yields decrease. The photoproducts 6-methoxy-2-(1-hydroxyethyl)-naphthalene and 6-methoxy-2-acetyl-naphthalene were found by gas chromatography/mass spectrometry (GC/MS). Both photoproducts were formed in SDS solution in significantly smaller amounts than in water. Small angle neutron scattering (SANS) showed that the presence of NP has small effect on the micellar structure. Only a slight decrease of the ionization degree of the micelle was observed by SANS, suggesting that NP was localized in the vicinity of micellar surface. The NP triplet excited state, hydrated electron, NP radical cation and some other relatively long lived intermediate were observed by laser flash photolysis of NP in micellar solution. The decay kinetics of these intermediates was different with respect to that in the homogeneous media. The reactivity of NP in SDS micellar environment was compared to that in the homogeneous media and the probable nature of the intermediate precursors of the final photoproducts are under the discussion.