摘要：

The interaction between the sunscreen agent, phenylbenzimidazole sulphonic acid (PBSA) and hydrophilic α-, β-, and γ-cyclodextrin derivatives was investigated under acidic conditions (pH 4.0) by phase-solubility analysis. Among the available cyclodextrins, hydroxypropyl-β-cyclodextrin (HP-β-CD) and random methyl-β-cyclodextrin (RM-β-CD) had the greatest solubilizing activity. The complexation of the sunscreen agent with HP-β-CD and RM-β-CD was confirmed by nuclear magnetic resonance spectroscopy. Solid-phase characterization of the PBSA/cyclodextrin systems by X-ray diffractometry defined the most appropriate method (co-evaporation) and cyclodextrin concentration (10-fold molar excess) for the preparation of a stable complexed form of PBSA. Long-term stability studies demonstrated that the decrease of the sunscreen level in emulsion preparations (pH 4.0) was almost completely suppressed by HP-β-CD, RM-β-CD being less effective. Moreover, the irradiation-induced decomposition of PBSA in the emulsion vehicle was markedly reduced by complexation with HP-β-CD (the extent of degradation was 3.9% for the complex compared to 9.1% for uncomplexed PBSA), whereas RM-β-CD had no significant influence. In addition, electron paramagnetic resonance (EPR) spin-trapping studies showed that the inclusion of the sunscreen agent into the HP-β-CD cavity completely inhibited the formation of free-radicals generated by PBSA on exposure to simulated sunlight, thereby suppressing its photosensitising potential.

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