Electrochemical studies of the anaesthetic agent enflurane (2-chloro-1,1,2-trifluoroethyl difluoromethyl ether) in the presence of oxygen: reaction with electrogenerated superoxide

Abstract

The electrochemical reduction of the anaesthetic agent enflurane was investigated at gold disc microelectrodes in the presence of oxygen in DMSO solvent. The superoxide anion radical, formed from the electro-reduction of dissolved oxygen, is shown to react with enflurane, complicating their simultaneous detection. The kinetics of the enflurane/superoxide reaction are found to be first order with respect to both superoxide and enflurane with a rate constant of 0.25 M −1 s −1 determined by three independent methods: steady-state voltammetry, digital simulation of cyclic voltammetric data and UV–vis spectroscopic analysis. The likely reaction scheme is outlined below (where R=CHFCF 2OCHF 2). R Cl+ O 2 −→ R O 2 + Cl − R O 2 + O 2 −→ R O 2 −+ O 2 R O 2 −+ R Cl→ R OO R+ Cl − or R O 2 + R O 2 →[ R OOOO R]→ R OO R+ O 2 The electro-reduction of oxygen in the presence of enflurane is found to be dependent on electrode size and enflurane concentration. Using small electrode sizes, the reduction is shown to be a single one-electron process, since the homogeneous reaction kinetics are effectively ‘out-run’. At larger electrode sizes, or with higher concentrations of enflurane, the reduction current is enhanced via the catalytic formation of oxygen, formed from the reaction between superoxide and enflurane.