Fundamental and applied aspects of bioelectrochemistry have been considered by placing emphasis on bioelectrocatalysis, a key reaction allowing electrochemical measurements and controls of oxidoreductase reactions. Recent investigations in the authors’ laboratory on this subject will be reviewed. Mediated bioelectrocatalysis is the enzyme-electrochemical reaction with an electrochemical regeneration of an electron acceptor (or donor) of the enzyme. We developed new methods of kinetic and redox potential measurements in oxidoreductase reactions based on mediated bioelectrocatalysis, which proved to be powerful tools in fundamental research on biochemistry. Physicochemical properties of a new enzyme discovered by us are studied using these techniques. Bacterial catalytic activity has also been measured by the present methods. In applied aspects, mediated bioelectrocatalysis is the working principle of a variety of amperometric biosensors, some of which are now in practical use and are commercially available. We discuss fundamental aspects of the amperometric biosensor and mention its novel applications in the fields of microbiology and food science. Studies of biofuel cells are a rapidly growing field and have received great attention very recently. A biofuel cell relying upon mediated bioelectrocatalysis is described, which operates under ambient temperature and at neutral pH.

Participation of Glu-194 and Glu-204 in the photo-induced proton releasing reaction at the extracellular surface of bacteriorhodopsin molecule was examined by a photoelectrochemical means in which films of bacteriorhodopsin and its site-displacement mutants are immobilized at the electrode-electrolyte interface. Displacement of glutamate with aspartate at the residue site 194 and 204 suppressed the rate of proton release with distinct pH dependence characteristics, indicating that pKa’s of these acidic residues are crucial for activating the proton release. In pH dependence, the mutant of Glu-194 to Asp-194 displacement showed a pKa of proton release much increased from that of the wild type. Laser pulse excitation of the mutant showed large retardation in proton release rate. Glu-194 is thus regarded to participate in the pKa-controlled proton transfer relay from Schiff base to Asp-85 in the reaction center core and work as a terminal proton releaser at the extracellular surface.

Self-ordering behavior of anodic porous alumina formed in sulfuric acid, oxalic acid and phosphoric acid solutions was investigated. Domains of ordered cell array appeared following an exponential current increase with the increase in anodizing voltage. Concurrently, the ratio of pore diameter to cell diameter lowered to approximately 0.3, that was corresponding to a porosity of 0.1, regardless of electrolyte type when the voltage approached to the established individual self-ordering voltage. Mechanism of self-ordering is assumed to be closely related to the electric field strength at the porous film growth.

We have already measured the performance and the physical property by some methods to evaluate some gas diffusion electrodes for chlor-alkali electrolysis. In this paper, we studied about the ability to evaluate the gas diffusion electrodes by thermal analysis. We prepared the powder and the seat before hot-press and after hot-press. These were made from polytetrafluoroethylene (PTFE) and from the material (GSP) of the gas-supplying layer that was mixed carbon black and PTFE. We prepared some samples of GSP that had difference of PTFE dispersion. We used the differential scanning calorimetry (DSC) and measured the heat change of fusion of PTFE in all samples. The heat change of fusion of PTFE powder was 70 J/g. On the other hand, that of PTFE sheet after hot-press was smaller than 25 J/g, may be due to the combination of PTFE by hot-press at 350°C. In a case of GSP, the heat change of fusion of the GSP sheet after hot-press was the smallest, probably because this one had much interaction between carbon black and PTFE. The heat change of fusion of GSP 1 that prepared by no flocculation process of PTFE and that PTFE was distributed homogeneous in sheet was the lowest 5.65 J g, may be due to the higher interaction between carbon black and PTFE. Consequently, it was possible to evaluate the inner structure of the electrode by DSC.

In the near field of an illuminated scanning probe tip with a dimension much smaller than a wavelength of the incident light a field enhancement is possible. This effect is similar to the field enhancement on small metal particles investigated in SERS (Surface Enhanced Raman Spectroscopy). In this article a formerly developed and successfully applied BEM (Boundary Element Method) calculation of the electric potential and field is used to compute respective values of an experimental setup arranged by Pettinger et al. which is similar to our experiments focussing on single molecule Raman spectroscopy. The calculated field enhancement factors are compared with the experimentally determined. The results show high electric field enhancement factors in the vicinity of the metallic tip.