Chapter 4
Characteristic Properties of Redox
Enzymes as Electrocatalysts
Abstract This chapter introduces specific features of redox enzymes as electrode
catalysts compared with metallic small catalysts. Large sizes of redox enzymes causes
inconvenient effects of the enzyme orientation on DET-type bioelectrocatalysis. The
significant of mesoporous structures to minimize the orientation effects is emphasized. In addition, this chapter describes peculiar and important effects that can facilitate the interfacial electron transfer kinetics at the top edge of microporous structures.
Some strategies for enzyme orientations to enhance the interfacial electron transfer
are also introduced together with examples for individual enzymes. Bidirectional
redox catalysis as one of the important features of enzyme catalysts is exemplified
and the performance will be discussed in back-to-basic style based of Marcus theory.
Keywords Porous electrode · Curvature effect · Enzyme orientation · Electrostatic
interaction · Electron transfer pathway · Bidirectional bioelectrocatalysis ·
Re-orientation energy
4.1 Introduction
In bioelectrocatalysis, redox enzymes work as electrocatalysts as in the case of metalbased inorganic molecules in view of electrochemistry. Significant advantageous
properties of redox enzymes compared with metal-based catalysts are: (1) extremely
high catalytic activity, (2) low reorganization energy, (3) high specificity, (4) high
identicalness and uniformity (thanks to biological expression), and (5) enormous
chemical versatility. These factors are very convenient from the viewpoint of application. In addition, redox potential of the electrochemically communicating site of
redox enzymes can be definitely defined, which leads to more rigorous discussion on
current–potential curves of catalytic waves. However, redox enzymes have huge size
and are fragile. The size matter causes characteristic features in DET-type bioelectrocatalysis; the orientation of an enzyme is a key factor determining the distance
between the electrode surface and the redox site located near the surface of the
enzyme of a large size, since the interfacial electron transfer rate constant decreases
exponentially with the distance between an electrode surface and the redox site of
an enzyme (Eq. (3.14)). First of all, we will discuss this matter in the following.
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
K. Kano et al., Enzymatic Bioelectrocatalysis,
https://doi.org/10.1007/978-981-15-8960-7_4
79
Characteristic Properties of Redox
Enzymes as Electrocatalysts
Abstract This chapter introduces specific features of redox enzymes as electrode
catalysts compared with metallic small catalysts. Large sizes of redox enzymes causes
inconvenient effects of the enzyme orientation on DET-type bioelectrocatalysis. The
significant of mesoporous structures to minimize the orientation effects is emphasized. In addition, this chapter describes peculiar and important effects that can facilitate the interfacial electron transfer kinetics at the top edge of microporous structures.
Some strategies for enzyme orientations to enhance the interfacial electron transfer
are also introduced together with examples for individual enzymes. Bidirectional
redox catalysis as one of the important features of enzyme catalysts is exemplified
and the performance will be discussed in back-to-basic style based of Marcus theory.
Keywords Porous electrode · Curvature effect · Enzyme orientation · Electrostatic
interaction · Electron transfer pathway · Bidirectional bioelectrocatalysis ·
Re-orientation energy
4.1 Introduction
In bioelectrocatalysis, redox enzymes work as electrocatalysts as in the case of metalbased inorganic molecules in view of electrochemistry. Significant advantageous
properties of redox enzymes compared with metal-based catalysts are: (1) extremely
high catalytic activity, (2) low reorganization energy, (3) high specificity, (4) high
identicalness and uniformity (thanks to biological expression), and (5) enormous
chemical versatility. These factors are very convenient from the viewpoint of application. In addition, redox potential of the electrochemically communicating site of
redox enzymes can be definitely defined, which leads to more rigorous discussion on
current–potential curves of catalytic waves. However, redox enzymes have huge size
and are fragile. The size matter causes characteristic features in DET-type bioelectrocatalysis; the orientation of an enzyme is a key factor determining the distance
between the electrode surface and the redox site located near the surface of the
enzyme of a large size, since the interfacial electron transfer rate constant decreases
exponentially with the distance between an electrode surface and the redox site of
an enzyme (Eq. (3.14)). First of all, we will discuss this matter in the following.
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
K. Kano et al., Enzymatic Bioelectrocatalysis,
https://doi.org/10.1007/978-981-15-8960-7_4
79