Electrocatalytic oxidation of l-tyrosine by a nitroxide

The electrochemistry of l-tyrosine was studied by cyclic voltammetry at a glassy carbon electrode. Although l-tyrosine itself showed very poor electrochemical response, the response could be greatly enhanced by using 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy (HO-TEMPO) as a mediator that enables a sensitive determination of the substrate. An electrocatalytic EC’ mechanism with the oxoammonium ion of HO-TEMPO as the active oxidant is proposed. The catalytic rate constant was determined to be 2.0×104 M−1 s−1 by using chronoamperometry.