Kinetics of porphyrin metalation reactions in micellar media. Singlet emission studies

Abstract

The kinetics of Cu²⁺, Zn²⁺, and Cd²⁺ incorporation eactions into meso-tetraphenylporphyrin (H₂TPP) have been studied in neutral and anionic surfactant media. Fluorescence pectroscopy employed in these investigations revealed many advantages in deriving the kinetic data. A general kinetic scheme is proposed that takes into account implicitly the influence of surfactant concentration and interphase effects on the rates of metal incorporation reactions. The enhancement of rates of rphyrin metalation reaction in micellar media relative to those found in homogeneous media is interpreted in terms of distribution of metal ions in the stern region of the icellar media. The relative rates of metal incorporation reactions in SDS micelles for different metal ions are found to follow the order Cu²⁺ > Zn²⁺ > Cd²⁺. On the basis of the magnitude of protonation constant (pK₃) of H₂TPP in SDS micelles, a mechanism similar to that proposed in homogeneous media is advanced for the metal incorporation reaction in the micellar media.