elucidate the origin of this high catalytic activity experimentally, but they speculated
that the Pd NPs could benefit from being near the bacteria’s membrane proteins
with their multiple electronic centers and electron transfer systems. Apart from the
high catalytic activity, this BWCS also exhibited an excellent substrate selectivity
for formate, and no electrocatalysis could be observed in the presence of other
related compounds such as MeOH, EtOH, or acetate. In contrast, current responses
were observed in the presence of all of these compounds when electrodeposited
Pd was used as the catalyst.
Kimber et al. also showed that it is possible to prepare Cu-based BWCSs through
the use of S. oneidensis, and additionally, they demonstrated that this BWCS could
be used as a catalyst for “Click reactions” [133]. The biosynthesis of the Cu NPs was
achieved by supplying the bacteria with a solution containing 50 Â 10
À6 M CuSO 4
and 30 Â 10
À3 M lactate, from which they were capable of extracting and reducing
all Cu(II) within 96 h. Analysis by TEM revealed that the majority of the Cu NPs
were in the size range of 20–50 nm, and furthermore it was found that they
were primarily located intracellularly. From X-ray absorption near edge structure
(XANES) spectroscopy, the authors were able to determine that the Cu NPs
were mainly composed of Cu(0), although they were covered with a surface layer
of Cu 2 O. In the catalytic evaluations of this Cu-based BWCS, it was tested as
a catalyst for the cycloaddition of benzyl azide with various alkynes. By using
BWCS quantities that corresponded to a Cu loading of 1.1 mol%, the authors were
able to prepare a number of triazoles in good to high yields (51–79%) within 12 h
at room temperature (Scheme 6a).
Although much of the focus of this part of the chapter has so far been dedicated
to S. oneidensis and its rather remarkable ability to reduce different transition
metal ions, it is important to point out that other microorganisms have also
been employed for the preparation of BWCS-based catalysts. For example,
in 2009, the group of Skrydstrup reported on the design of two different
Pd-based BWCSs involving the Gram-negative bacteria Cupriavidus necator and
Pseudomonas putida [134]. By TEM characterization of these BWCSs, the authors
could establish that the morphology of the biosorbed Pd differed significantly
between the two bacteria species. Cupriavidus necator was found to give rise to
very small and well-dispersed Pd NPs, while the Pd formed large aggregates on the
cell surface of Pseudomonas putida. Because of the more desirable Pd morphology
generated by the Cupriavidus necator, the authors chose to focus most of their
catalytic study on this BWCS, and here they could show that it was a highly
competent catalyst for both Suzuki-Miyaura and Mizoroki-Heck reactions (Scheme
6b,c). For the Suzuki-Miyaura reaction between p-iodotoluene and phenylboronic
acid, they were also able to demonstrate the recyclability of this BWCS catalyst by
showing that it could be reused four times without any signs of activity loss. The
Pd(0)-Pseudomonas putida BWCS was also briefly tested in their study, and
despite its non-ideal Pd morphology, it still showed good catalytic activity for
both transformations.
The group of Macaskie has also reported on the preparation of Pd
NP-based BWCSs involving a variety of Gram-negative and Gram-positive
Nanocatalysis Meets Biology
265
that the Pd NPs could benefit from being near the bacteria’s membrane proteins
with their multiple electronic centers and electron transfer systems. Apart from the
high catalytic activity, this BWCS also exhibited an excellent substrate selectivity
for formate, and no electrocatalysis could be observed in the presence of other
related compounds such as MeOH, EtOH, or acetate. In contrast, current responses
were observed in the presence of all of these compounds when electrodeposited
Pd was used as the catalyst.
Kimber et al. also showed that it is possible to prepare Cu-based BWCSs through
the use of S. oneidensis, and additionally, they demonstrated that this BWCS could
be used as a catalyst for “Click reactions” [133]. The biosynthesis of the Cu NPs was
achieved by supplying the bacteria with a solution containing 50 Â 10
À6 M CuSO 4
and 30 Â 10
À3 M lactate, from which they were capable of extracting and reducing
all Cu(II) within 96 h. Analysis by TEM revealed that the majority of the Cu NPs
were in the size range of 20–50 nm, and furthermore it was found that they
were primarily located intracellularly. From X-ray absorption near edge structure
(XANES) spectroscopy, the authors were able to determine that the Cu NPs
were mainly composed of Cu(0), although they were covered with a surface layer
of Cu 2 O. In the catalytic evaluations of this Cu-based BWCS, it was tested as
a catalyst for the cycloaddition of benzyl azide with various alkynes. By using
BWCS quantities that corresponded to a Cu loading of 1.1 mol%, the authors were
able to prepare a number of triazoles in good to high yields (51–79%) within 12 h
at room temperature (Scheme 6a).
Although much of the focus of this part of the chapter has so far been dedicated
to S. oneidensis and its rather remarkable ability to reduce different transition
metal ions, it is important to point out that other microorganisms have also
been employed for the preparation of BWCS-based catalysts. For example,
in 2009, the group of Skrydstrup reported on the design of two different
Pd-based BWCSs involving the Gram-negative bacteria Cupriavidus necator and
Pseudomonas putida [134]. By TEM characterization of these BWCSs, the authors
could establish that the morphology of the biosorbed Pd differed significantly
between the two bacteria species. Cupriavidus necator was found to give rise to
very small and well-dispersed Pd NPs, while the Pd formed large aggregates on the
cell surface of Pseudomonas putida. Because of the more desirable Pd morphology
generated by the Cupriavidus necator, the authors chose to focus most of their
catalytic study on this BWCS, and here they could show that it was a highly
competent catalyst for both Suzuki-Miyaura and Mizoroki-Heck reactions (Scheme
6b,c). For the Suzuki-Miyaura reaction between p-iodotoluene and phenylboronic
acid, they were also able to demonstrate the recyclability of this BWCS catalyst by
showing that it could be reused four times without any signs of activity loss. The
Pd(0)-Pseudomonas putida BWCS was also briefly tested in their study, and
despite its non-ideal Pd morphology, it still showed good catalytic activity for
both transformations.
The group of Macaskie has also reported on the preparation of Pd
NP-based BWCSs involving a variety of Gram-negative and Gram-positive
Nanocatalysis Meets Biology
265