The cooperative effect of CPC micelles and RuIII on the rate enhancement of L-tyrosine oxidation by N-bromosuccinimide

The impact of cetylpyridinium chloride (CPC) micelles on RuIII-catalysed oxidation kinetics of L-Tyrosine (L-Tyr) by N-bromosuccinimide (NBS) has been investigated in aqueous medium. The reaction’s progression was assessed by quantifying unreacted NBS iodometrically. Throughout the range of concentrations analysed, the L-Tyr oxidation demonstrates fractional-order kinetics concerning both [L-Tyr] and [RuIII], exhibits negative first-order reliance with respect to [HClO4] and shows first-order dependence on [NBS]. The fractional-order reliance on L-Tyr and RuIII suggests that the catalyst and substrate form a complex prior to the rate-determining step. The spectrophotometric kinetic investigation revealed that both RuIII and CPC catalyses the oxidation independently, yet their combined influence is significantly more pronounced. RuIII significantly increases the oxidation rate (2.8 times). Interestingly, the kinetic profile demonstrated a subsequent increase in the observed rate constant values (3.2 fold) corresponding to an increase in surfactant concentration. The combination of RuIII and CPC micelles resulted in a six-fold increase in the oxidation rate of L-Tyr. The electrostatic interaction between the charged micelle and RuIII promotes the proximity of the oxidising species to the substrate (L-Tyr), which is typically solubilised in a micellar environment, thus enhancing the oxidation process. A credible mechanism that corresponds with the kinetic findings has been emphasised, alongside an analysis of the Piszkiewicz model, to elucidate the apparent catalytic influence of CPC micellar environments.