1 3
supplies, and in the manufacture of plastics, explosives, textiles, pesticides, dyes,
and other chemicals.
2 Proteins as Efficient Building Blocks to Construct Advanced
Electrocatalytic Materials
Currently, many researchers, motivated by the high efficiency observed in nature,
have directed their studies towards the design of bioinspired materials. In this sense,
enzymes are highly efficient and selective biological catalysts. The presence of redox
groups in this type of biomolecule has led to different electrochemical applications.
Enzymes can catalyze a series of redox reactions with great technological importance, which generally require high overpotentials [35]. It is worth highlighting that
the use of enzymes provides many advantages, such as high electrocatalytic currents
and the possibility of carrying out electrocatalytic processes in a reversible way.
For instance, hydrogenases are metalloenzymes, which catalyze the reversible
conversion of hydrogen [36]. Depending on the metal content in the active sites of
the protein, three main classes of hydrogenases can be highlighted: [FeFe], which
contains two iron atoms and is a faster biological catalyst for hydrogen oxidation/
reduction reactions; [NiFe], which possesses an active heterobimetallic site; and
[Fe], which contains only one iron atom in its structure. Due to their ability to efficiently electrocatalyze hydrogen production, a series of hydrogen fuel cells has been
designed using these enzymes, representing a valuable alternative in the design of
biodegradable energy devices [37–39].
Hemoglobin, in particular, is a protein that contains iron atoms in its structure,
and that has been widely characterized due to its importance for living beings [40].
Hemoglobin comprises a redox, globular, and tetrameric structure. Each subunit is
formed by polypeptide chains, mostly in alpha-helix conformation, that encompass
in their structure a heme group containing an atom of Fe. This Fe
2+
ion is in the
center of an organic heterocycle called porphyrin, which is responsible for reacting
with oxygen and carrying out blood oxygen transport. These characteristics allow
these types of proteins to act as smart catalytic platforms in the oxygen evolution
reaction, as well as in other types of oxidation reactions. Moreover, peroxidases are
another class of enzymes that have been used as sustainable electrocatalysts. These
proteins catalyze the oxidation of organic molecules using H 2 O 2 , thanks to the presence of the Fe-porphyrin group [41].
In particular, enzymes known as multicopper oxidases (MCOs) show excellent
properties towards electroreduction of O 2 at high potentials [42]. MCOs are a family of metalloenzymes that possess three different copper sites: Cu types 1, 2 and 3.
In this case, oxidation of the reducing substrate occurs at the Cu type 1 site (T1),
while the reduction of O 2 occurs in the trinuclear group T2/T3 [43]. A wide range
of strategies has been used to immobilize these enzymes, from covalent bonding to
carbon nanotubes and graphene conductive nanomaterials to encapsulation in silica
structures [44, 45].
Furthermore, it is known that specific enzymes exhibit excellent ability to reduce
CO 2 –CO and formic acid, behaving as reversible electrocatalysts. For example, the
240
Reprinted from the journal
Topics in Current Chemistry (2020) 378:43
supplies, and in the manufacture of plastics, explosives, textiles, pesticides, dyes,
and other chemicals.
2 Proteins as Efficient Building Blocks to Construct Advanced
Electrocatalytic Materials
Currently, many researchers, motivated by the high efficiency observed in nature,
have directed their studies towards the design of bioinspired materials. In this sense,
enzymes are highly efficient and selective biological catalysts. The presence of redox
groups in this type of biomolecule has led to different electrochemical applications.
Enzymes can catalyze a series of redox reactions with great technological importance, which generally require high overpotentials [35]. It is worth highlighting that
the use of enzymes provides many advantages, such as high electrocatalytic currents
and the possibility of carrying out electrocatalytic processes in a reversible way.
For instance, hydrogenases are metalloenzymes, which catalyze the reversible
conversion of hydrogen [36]. Depending on the metal content in the active sites of
the protein, three main classes of hydrogenases can be highlighted: [FeFe], which
contains two iron atoms and is a faster biological catalyst for hydrogen oxidation/
reduction reactions; [NiFe], which possesses an active heterobimetallic site; and
[Fe], which contains only one iron atom in its structure. Due to their ability to efficiently electrocatalyze hydrogen production, a series of hydrogen fuel cells has been
designed using these enzymes, representing a valuable alternative in the design of
biodegradable energy devices [37–39].
Hemoglobin, in particular, is a protein that contains iron atoms in its structure,
and that has been widely characterized due to its importance for living beings [40].
Hemoglobin comprises a redox, globular, and tetrameric structure. Each subunit is
formed by polypeptide chains, mostly in alpha-helix conformation, that encompass
in their structure a heme group containing an atom of Fe. This Fe
2+
ion is in the
center of an organic heterocycle called porphyrin, which is responsible for reacting
with oxygen and carrying out blood oxygen transport. These characteristics allow
these types of proteins to act as smart catalytic platforms in the oxygen evolution
reaction, as well as in other types of oxidation reactions. Moreover, peroxidases are
another class of enzymes that have been used as sustainable electrocatalysts. These
proteins catalyze the oxidation of organic molecules using H 2 O 2 , thanks to the presence of the Fe-porphyrin group [41].
In particular, enzymes known as multicopper oxidases (MCOs) show excellent
properties towards electroreduction of O 2 at high potentials [42]. MCOs are a family of metalloenzymes that possess three different copper sites: Cu types 1, 2 and 3.
In this case, oxidation of the reducing substrate occurs at the Cu type 1 site (T1),
while the reduction of O 2 occurs in the trinuclear group T2/T3 [43]. A wide range
of strategies has been used to immobilize these enzymes, from covalent bonding to
carbon nanotubes and graphene conductive nanomaterials to encapsulation in silica
structures [44, 45].
Furthermore, it is known that specific enzymes exhibit excellent ability to reduce
CO 2 –CO and formic acid, behaving as reversible electrocatalysts. For example, the
240
Reprinted from the journal
Topics in Current Chemistry (2020) 378:43