(1) Voltammetric study of electron transfer reactions at liquid|liquid interfaces
Recently, increasing attention has been paid to heterogeneous electron transfer at liquid|liquid (or organic solvent|water) interface. However, the experiments have been restricted mainly to the system where hexacyanoferrate as the aqueous redox couple is present in excess. We presented the results of the voltammetric study of the electron transfer at liquid|liquid interface where the redox couple of decamethylferrocene as the organic redox couple was present in excess. In this system, biochemical species such as iron protoporphyrin IX and microperoxidase-11 were able to be examined.
Mechanism of the electron transfer reaction at liquid|liquid interface is also studied. By the use of normal-pulse, cyclic, and ac voltammetry, we showed that the electron transfer reaction between ferrocene or dibutylferrocene in organic solvents and hexacyanoferrate redox couple in water takes place by the ion-transfer (IT)-mechanism, that is, the electron transfer takes place homogeneously in the water phase followed by the ion transfer across the liquid|liquid interface. On the other hand, the electron transfer reaction between bis(phtalocyaninato)lutetium in an organic solvent and hexacyanoferrate redox couple in water was shown to proceed by way of the heterogeneous electron-transfer (ET)-mechanism.

(2) Kinetic study of glucoside hydrolases using amperometric biosensors
Although many reports have appeared on enzymatic hydrolysis of starch and cellulose by glucoside hydrolases, quantitative kinetic analyses of the hydrolysis have rarely been provided. Electrochemical measurements have advantages of being free from the influence of turbidity and coloration of a test solution. We introduced an amperometric biosensor to study the kinetics of enzymatic hydrolysis of starch and cellulose in a thick suspension. The initial rate of the enzymatic hydrolysis in the starch or cellulose suspension increased with increasing concentration of the enzyme to approach a saturation value, and was proportional to the amount of the substrate. Also, the rate was proportional to the specific surface area of the substrate. The experimental results can be explained well by the rate equations derived from a three-step mechanism, which consists of the adsorption of the free enzyme onto the surface of the substrate, the reaction of the adsorbed enzyme with the substrate, and the liberation of the product.