Topics in Current Chemistry (2020) 378:43
1 3
1 Introduction
Proteins are well-designed nanosized machines that can dynamically catalyze myriad catalytic reactions with molecular-level accuracy [1–4]. As an example of heterogeneous catalysis, electrocatalysis, which explores the relationship between the
physicochemical properties of electrode materials and both their underlying mechanism and rate of the electrode reactions, have been widely investigated. Particularly,
the development of bio-based advanced energy conversion nanosystems has recently
emerged as an important and attractive topic. Water-splitting reactions represent a
promising and sustainable way to obtain hydrogen and oxygen through the development of renewable energy fuel devices, which fulfill a crucial role in solving the
global energy crisis. The mechanistic principles that proteins use to acts as efficient
catalysts towards the generation of fuels have been intensively investigated [5]. As
a result, bio-inspired synthetic catalysts have been generated to deeply study the
biological activity of different kinds of enzymes for the production of added-value
chemical compounds. Additional efforts have been performed to unravel the connection between the structure and the catalytic performances of active enzymes for
water-splitting reactions [6–9]. It has been established that there is a good relationship between the structural or conformational changes of enzymes and their catalytic activity on the ms–μs timescale. [10–15] In this sense, small conformational
variations or motions of just a few residues in the three-dimensional (3D) protein
frameworks can also improve the efficiency of the electrochemical reaction that
occurs at the electrode–electrolyte interface and, in turn, the overall electrocatalytic
process. The impressive abilities of proteins to adopt catalytically competent configurations via efficient conformational changes on specific domains of their tertiary
structures towards environmental changes such as pH, temperature or even ionic
strength then become promising candidates for the development of high-performance electrocatalysts.
Although several enzymes exhibit high catalytic performances, electronic conductivity through the amino acids of the tertiary structure is still being low, which
represents a drawback to obtaining effective electrocatalytic nanosystems [16–19].
To address this limitation, several strategies have been attempted in the past years.
Among them, the engineering of nanobiointerfaces at the molecular level using
different immobilization approaches to optimize the efficiency of electrocatalytic
reactions has become one of the most effective strategies [20]. To develop the latter strategy, a couple of key factors have been fairly well determined. Firstly, the
enzyme immobilization process should be optimized to reach a high coverage of
active molecules on the electrode surface. Secondly, the electronic wiring between
the active sites of the immobilized enzyme molecules and the electrodes plays a
crucial role in generating advanced electrocatalysts. Consequently, they have been
integrated via covalent or non-covalent functionalization to a large number of conductive nanomaterials (i.e., gold nanoparticles, graphene sheets, and nanotubes) to
generate the most electroactive orientations of active centers assuring faster electron
transfer (ET) processes and enhancing the conductive wiring and, in turn, the catalytic efficiency of the resulting biomaterials [21–26].
238
Reprinted from the journal
1 3
1 Introduction
Proteins are well-designed nanosized machines that can dynamically catalyze myriad catalytic reactions with molecular-level accuracy [1–4]. As an example of heterogeneous catalysis, electrocatalysis, which explores the relationship between the
physicochemical properties of electrode materials and both their underlying mechanism and rate of the electrode reactions, have been widely investigated. Particularly,
the development of bio-based advanced energy conversion nanosystems has recently
emerged as an important and attractive topic. Water-splitting reactions represent a
promising and sustainable way to obtain hydrogen and oxygen through the development of renewable energy fuel devices, which fulfill a crucial role in solving the
global energy crisis. The mechanistic principles that proteins use to acts as efficient
catalysts towards the generation of fuels have been intensively investigated [5]. As
a result, bio-inspired synthetic catalysts have been generated to deeply study the
biological activity of different kinds of enzymes for the production of added-value
chemical compounds. Additional efforts have been performed to unravel the connection between the structure and the catalytic performances of active enzymes for
water-splitting reactions [6–9]. It has been established that there is a good relationship between the structural or conformational changes of enzymes and their catalytic activity on the ms–μs timescale. [10–15] In this sense, small conformational
variations or motions of just a few residues in the three-dimensional (3D) protein
frameworks can also improve the efficiency of the electrochemical reaction that
occurs at the electrode–electrolyte interface and, in turn, the overall electrocatalytic
process. The impressive abilities of proteins to adopt catalytically competent configurations via efficient conformational changes on specific domains of their tertiary
structures towards environmental changes such as pH, temperature or even ionic
strength then become promising candidates for the development of high-performance electrocatalysts.
Although several enzymes exhibit high catalytic performances, electronic conductivity through the amino acids of the tertiary structure is still being low, which
represents a drawback to obtaining effective electrocatalytic nanosystems [16–19].
To address this limitation, several strategies have been attempted in the past years.
Among them, the engineering of nanobiointerfaces at the molecular level using
different immobilization approaches to optimize the efficiency of electrocatalytic
reactions has become one of the most effective strategies [20]. To develop the latter strategy, a couple of key factors have been fairly well determined. Firstly, the
enzyme immobilization process should be optimized to reach a high coverage of
active molecules on the electrode surface. Secondly, the electronic wiring between
the active sites of the immobilized enzyme molecules and the electrodes plays a
crucial role in generating advanced electrocatalysts. Consequently, they have been
integrated via covalent or non-covalent functionalization to a large number of conductive nanomaterials (i.e., gold nanoparticles, graphene sheets, and nanotubes) to
generate the most electroactive orientations of active centers assuring faster electron
transfer (ET) processes and enhancing the conductive wiring and, in turn, the catalytic efficiency of the resulting biomaterials [21–26].
238
Reprinted from the journal