Effects of Cyclodextrins on the Riboflavin-Sensitized Photooxidation of Phenothiazine Derivatives

Abstract

The effects of three cyclodextrins (α-, β, and γ-CyDs) on the riboflavin (RF)-sensitized photooxidation of phenothiazine derivatives (PTZ) were examined in an acidic solution (pH 4.0). The photoirradiation (400 nm<) of PTZ in the presence of RF gave the corresponding sulfoxides under aerobic conditions. The RF-sensitized photooxidation of PTZ was inhibited by the addition of RF triplet quencher or singlet oxygen quenchers. Since the charge transfer interaction between RF and PTZ was of minor importance, singlet oxygen generated by the RF triplet could be primarily responsible for the RF-sensitized photooxidation of PTZ. Under these experimental conditions, the RF-sensitized photooxidation of PTZ was significantly retarded by β-CyD, while α- and γ-CyDs affected no noticeable changes in this reaction. The deceleration effect of β-CyD seems to be attributed to the decrease in the susceptibility to oxidation of PTZ rather than the reduction in the photoche mical reactivity of RF through inclusion complexation.