Abstract

A voltammetric survey of quinone and ferricinium derivatives showed that several are useful for electrocatalytic thiol oxidation. Those showing the highest rates are the quinone form of dihydroxybenzylamine and the dimethylaminomethylferricinium ion, which oxidize glutathione at rates of 18 $\rm M\sp{-1}s\sp{-1}$ and 111 $\rm M\sp{-1}s\sp{-1}$ at pH 7.0. Synthesis of artificial enzymes by coupling these catalysts with the primary or secondary monotosylate of $\beta$-cyclodextrin yielded unique species based on RP-HPLC, and UV-Visible spectroscopy. After isolation by RP-HPLC, synzymes were examined for thiol oxidation under pseudo-first order conditions, and thiol oxidation rates were determined. Only the secondary ferrocene-$\beta$-cyclodextrin product gave enhanced thiol oxidation rates in comparison with free dimethylaminomethylferricinium. Further tests on this species showed it was a better catalyst for cysteine than for glutathione oxidation as oxidation rates for the cysteine were 1470 $\rm M\sp{-1}s\sp{-1}$ as compared to 260 $\rm M\sp{-1}s\sp{-1}$ for the glutathione. Enhanced thiol oxidation rates were also observed at pH 8.0 $\rm(k\sb{obs} = 4123\ M\sp{-1}s\sp{-1})$ for the secondary ferrocene-$\beta$-cyclodextrin with cysteine, as compared to pH 7.0.