A photolysis study on superoxide quenching at water/oil interface of Aerosol OT reversed micelle

The quenching kinetics of superoxide (O2−) in water/oil (w/o) interface region of Aerosol OT reversed micelle has been investigated with a transient absorption method. Photodecomposition of α-tocopherol by 266 nm laser light in the presence of O2 produced O2− together with the tocopheroxyl radical (Toc). The subsequent reaction between Toc and O2− occurred in the time region of 1-150 μs after the photoexcitation. There, O2− kinetics could be traced by monitoring the Toc absorption. In an Aerosol OT reversed micelle solution containing vitamin C (VC), VC would be located in water droplets inside the reversed micelle and would react with both Toc and O2− at the w/o interface around the reversed micelle. The Toc decay in the time region of 1-150 μs was accelerated by addition of VC, suggesting that the O2− quenching by VC progressed as well as the Toc quenching by VC. From a numerical simulation with treating the simultaneous rate equations for Toc concentration by Runge-Kutta method, the rate constant for the O2− quenching by VC could be estimated to be 6.9 × 107 M−1 s−1. This value is much larger than the corresponding value reported in homogeneous water solution, suggesting that the O2− quenching by VC indeed occurred at the w/o interface of the reversed micelle.