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Selective Entrapment of the Cationic Form of Norfloxacin within Anionic Sodium Dodecyl Sulfate Micelles at Physiological pH and its Effect on the Drug Photodecomposition†

Authors

  • Salvatore Sortino

    Corresponding author
    1. Dipartimento di Scienze Chimiche, Università di Catania, Viale Andrea Doria 8 I-95125 Catania, Italy
    • To whom correspondence should be addressed: Dipartimento di Scienze Chimiche, Università di Catania, Viale Andrea Doria 8 I-95125 Catania, Italy. Fax: 39-095-580138; e-mail: ssortino@unict.it

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  • This paper is part of a special issue dedicated to Professor J. C. (Tito) Scaiano on the occasion of his 60th birthday.

ABSTRACT

The binding of the photosensitizing fluoroquinolone (FQ) antibiotic norfloxacin (NX) to sodium dodecyl sulfate (SDS) micelles and the photoreactivity of the NX/SDS complex under physiological pH conditions are investigated by means of ab-sorption and emission spectroscopy, steady-state and laser flash photolysis. It is shown that the photolabile zwitterionic form of NX, which is dominant at physiological pH, is not the most abundant species in the presence of SDS micelles. This medium exhibits a high preference for the cationic form of the drug, which is selectively and successfully entrapped within the micellar cage (Kass= 6 × 104M-1± 3000), becoming the largely dominant species at neutral pH. The effect of this trapping is drastically reflected on both efficiency and nature of the drug photodecomposition. It is observed that the photostability of NX incorporated in the micellar pseudophase increases of more than one order of magnitude if compared to that of the “free” drug. Furthermore, the radical photode-composition mechanism occurring in phosphate buffered solution is suppressed by the micellar medium and the low photodegradation observed seems to take place preferentially through an ionic pathway. Hopefully, the results presented herein may contribute to a better understanding of the bio-distribution of NX in biological systems and provide helpful and stimulating information in order to get the control of FQ photoreactivity under physiological pH conditions.

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