Chapter 2
MET-Type Bioelectrocatalysis
Abstract This chapter deals with theoretical features of MET-type bioelectrocatalysis with emphasis of steady-state serial reactions. The fundamental concept
in the selection of mediators is described based on linear free energy relationship and diffusion-controlled kinetics. Basic features of redox potential tuning and
immobilization of mediators including redox polymers are also introduced.
Keywords Steady-state current · Serial resistance model · Linear free energy
relationship · Diffusion-controlled kinetics · Ligand parameter · Bifunctional
reagents · Redox polymers
2.1 Reaction-Layer Approximation in a Homogeneous
System
The simplest situation of MET-type bioelectrocatalysis is that a redox enzyme (E)
and a mediator (M) exist homogenously in a quiescent solution. In such situations, the
system essentially provides a steady-state sigmoidal wave of the catalytic reaction.
For the oxidation of the substrate (S), the reaction proceeds as follows:
S +
n S
n M
M ox Enzyme
−−−−→
P +
n S
n M
M red ,
(2.1)
M red Electrode
−−−−−→
M ox + n M e
−
,
(2.2)
where M ox and M red denote the oxidized and reduced forms of M, respectively; P
denotes the product, whereas n S and n M denote the number of electrons in S and M,
respectively.
The enzymatic reaction (2.1) proceeds only in the diffusion layer of the oxidized
mediator (M ox ) regenerated by the electrode reaction (2.2). The current (i) corresponds to the concentration gradient of M ox at the electrode surface (x = 0) as
follows:
© 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_2
23
MET-Type Bioelectrocatalysis
Abstract This chapter deals with theoretical features of MET-type bioelectrocatalysis with emphasis of steady-state serial reactions. The fundamental concept
in the selection of mediators is described based on linear free energy relationship and diffusion-controlled kinetics. Basic features of redox potential tuning and
immobilization of mediators including redox polymers are also introduced.
Keywords Steady-state current · Serial resistance model · Linear free energy
relationship · Diffusion-controlled kinetics · Ligand parameter · Bifunctional
reagents · Redox polymers
2.1 Reaction-Layer Approximation in a Homogeneous
System
The simplest situation of MET-type bioelectrocatalysis is that a redox enzyme (E)
and a mediator (M) exist homogenously in a quiescent solution. In such situations, the
system essentially provides a steady-state sigmoidal wave of the catalytic reaction.
For the oxidation of the substrate (S), the reaction proceeds as follows:
S +
n S
n M
M ox Enzyme
−−−−→
P +
n S
n M
M red ,
(2.1)
M red Electrode
−−−−−→
M ox + n M e
−
,
(2.2)
where M ox and M red denote the oxidized and reduced forms of M, respectively; P
denotes the product, whereas n S and n M denote the number of electrons in S and M,
respectively.
The enzymatic reaction (2.1) proceeds only in the diffusion layer of the oxidized
mediator (M ox ) regenerated by the electrode reaction (2.2). The current (i) corresponds to the concentration gradient of M ox at the electrode surface (x = 0) as
follows:
© 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_2
23