A WATER-SOLUBLE AMETHYLBENZIDINE-2-HYDROXYPROPYL-BETA-CYCLODEXTRIN INCLUSION COMPLEX AS AN EFFICIENT MEDIATOR FOR OXIDOREDUCTASES

A water soluble amethylbenzidine-2-hydroxypropyl-beta-cyclodextrin (TM B-hp beta CyD) inclusion complex was demonstrated for the first time a s an efficient mediator for glucose oxidase, xanthine oxidase and glut amate dehydrogenase. At pH 5, the cyclic voltammogram of the TMB-hp be ta CyD complex exhibited two reversible oxidation waves with potential peak values (E(pa)) of 384mV (TMB --> TMB(+.)) and 496mV (TMB(+.) --> TMB(2+)) at a glassy carbon electrode (vs. Ag/AgCl). The E(pa) value of the former was pH-independent, whereas that of the latter was stron gly pH dependent. However, at pH 7 the inclusion complex exhibited onl y one reversible oxidation wave with E(pa) of 396mV. Based on cyclic v oltammetric measurements, the second rate constant (k) for the TMB(+.) (glucose oxidase) reaction was determined as 6.7 x 10(5) M(-1)s(-1) w hich compares favorably with that of ferrocene (2.6 x 10(4) M(-1)s(-1) ), one of the most common mediators. The inclusion complex was then in vestigated for bioelectrocatalysis at membrane electrodes of glucose o xidase and xanthine oxidase. The response of the hypoxanthine electrod e was linear up to 40 mu M; its sensitivity was 2.8 mu A mM(-1) and a response time was smaller than 2 min. A similar response time was also observed for the glucose electrode, however, the linear range and sen sitivity of the glucose electrode were 0-3 mM and 0.6 mu A mM(-1), res pectively. The capability of TMB(+.) to oxidize NADH formed from a glu tamate dehydrogenase:NAD/glutamate reaction, was also demonstrated, as illustrated by a well-defined catalytic wave for NADH oxidation.