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Journal ArticleDOI

Reversible Electrochemical Modulation of a Catalytic Nanosystem.

26 Aug 2016-Angewandte Chemie (John Wiley & Sons Ltd)-Vol. 55, Iss: 36, pp 10737-10740

TL;DR: A catalytic system based on monolayer-functionalized gold nanoparticles (Au NPs) that can be electrochemically modulated and reversibly activated is reported and the activity of this supramolecular nanosystem can be reversibly switched on or off by oxidizing/reducing Cu/Cu(2+) ions under controlled conditions.
Abstract: A catalytic system based on monolayer-functionalized gold nanoparticles (Au NPs) that can be electrochemically modulated and reversibly activated is reported. The catalytic activity relies on the presence of metal ions (Cd2+ and Cu2+), which can be complexed by the nanoparticle-bound monolayer. This activates the system towards the catalytic cleavage of 2-hydroxypropyl-p-nitrophenyl phosphate (HPNPP), which can be monitored by UV/Vis spectroscopy. It is shown that Cu2+ metal ions can be delivered to the system by applying an oxidative potential to an electrode on which Cu0 was deposited. By exploiting the different affinity of Cd2+ and Cu2+ ions for the monolayer, it was also possible to upregulate the catalytic activity after releasing Cu2+ from an electrode into a solution containing Cd2+. Finally, it is shown that the activity of this supramolecular nanosystem can be reversibly switched on or off by oxidizing/reducing Cu/Cu2+ ions under controlled conditions.

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German Edition: DOI: 10.1002/ange.201605309
Supramolecular Catalysis
International Edition: DOI: 10.1002/anie.201605309
Reversible Electrochemical Modulation of a Catalytic Nanosystem
Flavio della Sala, Jack L.-Y. Chen, Simona Ranallo, Denis Badocco, Paolo Pastore,
Francesco Ricci,* and Leonard J. Prins*
Abstract: A catalytic system based on monolayer-functional-
ized gold nanoparticles (Au NPs) that can be electrochemically
modulated and reversibly activated is reported. The catalytic
activity relies on the presence of metal ions (Cd
2+
and Cu
2+
),
which can be complexed by the nanoparticle-bound mono-
layer. This activates the system towards the catalytic cleavage of
2-hydroxypropyl-p-nitrophenyl phosphate (HPNPP), which
can be monitored by UV/Vis spectroscopy. It is shown that
Cu
2+
metal ions can be delivered to the system by applying an
oxidative potential to an electrode on which Cu
0
was deposited.
By exploiting the different affinity of Cd
2+
and Cu
2+
ions for
the monolayer, it was also possible to upregulate the catalytic
activity after releasing Cu
2+
from an electrode into a solution
containing Cd
2+
. Finally, it is shown that the activity of this
supramolecular nanosystem can be reversibly switched on or
off by oxidizing/reducing Cu/Cu
2+
ions under controlled
conditions.
Complexity is emerging as a major theme in chemistry.
[1]
Not
only does it mark a shift from the study of relatively simple
molecules to complex molecular structures similar to those
found in nature, but it also marks a shift from the study of
single molecules to networks of molecules.
[2–4]
Within the
subfield of catalysis,
[5]
the emergence of nanozymes, defined
as nanomaterials with enzyme-like activity, nicely illustrates
this development.
[6]
Nanozymes are prepared following
a bottom-up strategy relying on the use of simple synthetic
components for the formation of structures with a size and
structural complexity similar to that of enzymes.
[7,8]
Their high
stability, uniformity, and ease of modification is favoring
applications in the fields of sensing,
[9]
materials science,
[10]
and
systems chemistry.
[11]
The observation that nanozymes can
exhibit an emerging property such as cooperativity is indeed
a sign that significant progress has been made in the design of
functional complex systems.
[12]
However, whereas nature has
gained exquisite control over the complex biological machi-
nery by using specific triggers to up- and down-regulate
catalytic processes, similar regulatory pathways are still
largely inexistent for nanozymes. Herein, we present
a simple setup for the reversible activation and modulation
of nanozymes using an electronic input. The electrochemical
activation is highly attractive because of its ease of imple-
mentation, cleanliness, precision, and rapid response.
[13–16]
The availability of this kind of regulatory mechanism will
strongly determine the success of chemists in constructing
synthetic networks for studying complexity on the systems
level.
The main component of our system is Au NP 1, which are
gold nanoparticles (d = 1.5 0.3 nm) covered with C9-thiols
terminating with a 1,4,7-triazacyclononane (TACN) head
group (Figure 1 a).
[11]
Such nanoparticle-bound TACN moi-
eties are able to coordinate Zn
2+
-metal ions forming a supra-
Figure 1. a) Representation of the activation of Au NP 1 through the
electrochemically activated release of metal ions from an electrode.
b) Initial rate (v
init
) of HPNPP transphosphorylation as a function of
the concentration of Cu
2+
(red) or Cd
2+
(green). The gray bar marks
the difference in reactivity of Au NP 1 (v
init
= 8.6(1.9)10
10
ms
1
,
background), Au NP 1·Cu
2+
(v
init
= 7.7(0.9)10
9
ms
1
), Au NP
1·Cd
2+
(v
init
= 2.0(0.3)10
9
ms
1
) when [TACN]/[M
2+
] ratio is 1:1.
Conditions: [TACN]= 20 m m, [HPNPP]= 1mm, [HEPES] = 10 mm,
pH 7.0, 25
8
C.
[*] Dr. F. della Sala, Dr. J. L.-Y. Chen, Dr. D. Badocco, Prof. Dr. P. Pastore,
Prof. Dr. L. J. Prins
Department of Chemical Sciences, University of Padova
Via Marzolo 1, 35131 Padova (Italy)
E-mail: leonard.prins@unipd.it
S. Ranallo, Prof. Dr. F. Ricci
Chemistry Department, University of Rome Tor Vergata
Via della Ricerca Scientifica, 00133 Rome (Italy)
E-mail: francesco.ricci@uniroma2.it
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
http://dx.doi.org/10.1002/anie.201605309.
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molecular catalyst that very efficiently promotes the trans-
phosphorylation of 2-hydroxypropyl-p-nitrophenyl phos-
phate (HPNPP), a common substrate used for mimicking
RNA-hydrolysis.
[12]
The role of the nanoparticle support is critical, as the
observed rate acceleration is due to the cooperative effect
between TACN head groups in close proximity. Limited
activity is observed for unbound TACN analogues.
[12]
Exten-
sive previous studies have shown that the system displays
Michaelis–Menten-like catalytic activity, resulting from the
formation of catalytic pockets between two neighboring NP-
bound TACN·Zn
2+
-complexes.
[17]
For this reason, these sys-
tems have also been referred to as nanozymes.
[12]
The
numerous analogous multivalent systems (both molecular
and NP-based) that have been reported require the presence
of Zn
2+
or other metal ions (for example, Cu
2+
,Co
3+
,Ce
4+
,
Fe
3+
) for catalytic activity.
[18]
The observation that Au NP
1 and related systems are poorly active in the absence of metal
ions implies that the controlled association and dissociation of
metal ions can be used as a regulatory mechanism for
catalysis. The low residual activity of non-metalated Au NP
1 presumably originates from the presence of protonated
TACN-ligands, at neutral or acidic pH.
[19]
In this study, Cu
2+
and Cd
2+
metal ions were deliberately
chosen for a number of reasons. Firstly, measurement of the
catalytic activity as a function of the amount of Cu
2+
and Cd
2+
added to Au NP 1 showed that both metal ions activated the
system for catalysis, reaching a maximum when a stoichiom-
etry of 1:1 between the TACN head group and the metal ion
was obtained ([TACN] = [Cu
2+
or Cd
2+
] = 20 mm, Figure 1b).
The sharp transition to the plateau-level at this ratio indicates
that metal binding occurs under saturation conditions.
Importantly, for a 1:1 ratio of [TACN]:[M
2+
], the rate
acceleration was significantly higher for Au NP 1·Cu
2+
(9
times, red squares) than for Au NP 1·Cd
2+
(2.5 times, green
squares) when compared to the background (Figure 1b,
dashed line). It is pointed out that the absolute activities of
the Cu
2+
and Cd
2+
systems are much lower compared to that
of the analogous Zn
2+
system that we have studied previ-
ously.
[12,17,18]
Yet, the more accessible redox-chemistry of Cu
and Cd made us focus on these metals, despite the lower
catalytic activity. Second, the difference in terms of binding
affinity for the TACN group is about six orders of magnitude
in favor of Cu
2+
(logK
TACNCu
2þ
= 15.4 and logK
TACNCd
2þ
=
9.3),
[20]
resulting in complete displacement of Cd
2+
ions from
the NP-bound TACN head groups upon the addition of just an
equimolar amount of Cu
2+
ions. The difference in the activity
of the Cu
2+
and Cd
2+
systems provides a means to upregulate
the catalysis by exchanging Cd
2+
for Cu
2+
.
[21]
Finally, Cu
2+
and
Cd
2+
metal ions were chosen for their different standard
reduction potentials (respectively 0.40 and + 0.34 V for
Cd
2+
and Cu
2+
, relative to the standard hydrogen elec-
trode).
[22]
We focused our initial investigations on the electrochem-
ical generation of metal ions from a source in order to switch
on catalytic activity. To that purpose, we used a carbon chip
[23]
previously coated with a film of Cu
0
. The deposition was
carried out by dipping the electrode into an aqueous solution
of Cu(NO
3
)
2
and by applying a fixed reductive potential of
1.0 V vs. Ag/AgCl.
[22]
Cu
2+
ions were released from the
electrode into a buffered solution containing Au NP 1 and
HPNPP by applying a potential oxidative ramp from 0.3 to
0.5 V vs. Ag/AgCl for 60 seconds. We employed square wave
voltammetry (SWV; Supporting Information, Figure S4),
which quantitatively suggested that about 20 mm of Cu
2+
was
electrochemically released from the electrode.
[22]
The absence
of NP precipitation and/or aggregation was proven by
a combination of UV/Vis spectroscopy, DLS and TEM
analyses, confirming that Au NP 1 is stable under the release
conditions (Supporting Information, Figures S6–S8). Kinetic
measurements (Figure 2) of the initial rate of HPNPP trans-
phosphorylation confirmed that the catalytic system achieved
the same activity after the electrochemical release of Cu
2+
(v
init
= 7.4(1.2) 10
9
m s
1
) as compared to manual addition
(v
init
= 7.7(1.2) 10
9
m s
1
). Control experiments confirmed
that, without application of the potential, the HPNPP trans-
phosphorylation occurred at a low rate, which is comparable
to Au NP 1 in the absence of metal ions (Supporting
Information, Figure S5). Quantitative ICP-MS analysis con-
firmed that the concentration of electrochemically released
Cu
2+
was consistently above the concentration of the NP-
bound TACN head groups (20 mm; Supporting Information,
Table S1), confirming the results initially suggested by SWV
(Supporting Information, Figure S4). It is noted that an excess
of Cu
2+
, with regards to the concentration of head groups,
does not affect the catalytic activity of the system, as the metal
Figure 2. a) Comparison of the efficacy of electrochemical delivery of
metal ions as compared to manual addition. b) Example of PNP-
formation upon the electrochemical (red) or manual (blue) delivery of
Cu
2+
metal ions to a solution of Au NP 1 ([TACN]= 20 mm) and
HPNPP (1 mm). For comparison also the traces for only Au NP 1 and
Cu
2+
are given. c) Averaged initial rates (v
init
, three independent
measurements for each trace) for the HPNPP transphosphorylation
obtained from the experiments shown in (a). Error bars: 1 s.d.
Experimental conditions: [HEPES]= 10 mm, pH 7.0, 25
8
C. Electro-
chemical release of Cu
2+
: ramp of potential from 0.3 to 0.5 V vs. Ag/
AgCl for 60 s.
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ion by itself is not active at these concentrations (see also
Figure 1b). The study was then repeated using Cd instead of
Cu. In this case, because of the low oxidation potential of Cd
0
,
controlled release of Cd
2+
from the electrode was not
possible. ICP-MS (Supporting Information, Table S1) and
kinetic experiments confirmed that Cd
2+
is spontaneously
released from the electrode upon exposure to the solution
containing Au NP 1 and HPNPP (Supporting Information,
Figure S5). For this reason, the electrode initially covered
with Cd was used as a spatially confined metal source in
a displacement experiment (Figure 3a). More specifically,
a solution containing Au NP 1 (20 mm) and HPNPP (1 mm)
was deposited onto the Cd-loaded electrode, which allowed
spontaneous Cd
2+
release. HPNPP transphosphorylation was
then monitored for 30 min by UV/Vis spectroscopy (Fig-
ure 3b, trace I, green). The efficient delivery of Cd
2+
was
evidenced by the observed rate (v
init
= 2.1 10
9
m s
1
), which
corresponded to that of Au NP 1·Cd
2+
(v
init
= 2.0(0.3)
10
9
m s
1
upon manual addition of Cd
2+
). Next, the same
solution was re-deposited on a Cu-loaded electrode and
a potential ramp from 0.3 to 0.5 V vs. Ag/AgCl was applied,
after which the kinetic measurements were continued for an
additional 30 minutes. A clear increase in the rate of PNP-
formation was observed (v
init
from 2.1 10
9
to 1.1 10
8
m s
1
,
Figure 3b, trace I, red), which is in full agreement with the
value obtained when Cu
2+
was manually added or electro-
chemically released in the presence of Au NP 1. This
demonstrates the effective displacement of Cd
2+
by Cu
2+
from the monolayer resulting in upregulation of catalytic
activity. It was important to observe that the rate of PNP-
formation did not change at all when Cd
2+
was released in
a solution containing Au NP 1·Cu
2+
and HPNPP, confirming
that Cd
2+
does not displace Cu
2+
from the monolayer
(Figure 3b, trace II, empty squares).
The described experiments demonstrate that Cu
2+
ions
can be efficiently delivered through an electrochemical input
for the activation of a pre-catalyst. However, full electro-
chemical control over catalytic activity is achieved only when
catalyst activation is a reversible process.
[24,25]
The reversi-
bility of the electrochemical activation of the system was
investigated using Cu
2+
(Figure 4a). As before, Cu
2+
was
released from a prepared electrode into a buffered solution
containing Au NP 1 and HPNPP after which the rate of PNP-
Figure 3. a) Representation of the electrochemical upregulation of
catalytic activity. Exposure of Au NP 1 to a Cd
0
-coated electrode results
in a weak increase in catalytic activity. Application of an electrochem-
ical trigger to the same solution with a Cu
0
-coated electrode causes
the release of Cu
2+
. The released Cu
2+
displaces Cd
2+
from the TACN-
head groups. b) Representative example of a displacement experiment
(all experiments were performed in triplicate; see the Supporting
Information, Figure S9). Trace I: initial exposure of Au NP 1 to a Cd-
coated electrode followed by exposure (after 30 min) to a Cu-coated
electrode to which an oxidative potential was applied. Trace II: initial
exposure of Au NP 1 to a Cu-coated electrode with application of an
oxidative potential and subsequent exposure (after 30 min) to a Cd-
coated carbon chip. PNP-concentration was measured by UV/Vis
spectroscopy at 405 nm. Electrochemical release of Cu
2+
: ramp of
potential from 0.3 to 0.5 V vs. Ag/AgCl for 60 s. c) Averaged rates of
HPNPP transphosphorylation after exposure of Au NP 1 to the differ-
ent carbon electrodes described in (b). Experimental conditions:
[TACN]= 20 mm, [HPNPP] = 1mm, [HEPES]= 10 mm, pH 7.0, 25
8
C.
Error bars: 1 s.d. calculated from three independent measurements.
Figure 4. a) Representation of the reversible activation of Au NP
1 driven by the electrochemically controlled release and deposition of
Cu
2+
-ions on the electrode. b) Rate of HPNPP transphosphorylation
after two cycles of activation/deactivation of Au NP 1. The control
experiment indicates the observed rate when Au NP 1 was just
activated once by the electrochemical release of Cu
2+
at the start of
the experiment. Experimental conditions: [TACN]= 20 mm,
[HPNPP]= 1mm, [HEPES] = 10 mm, pH 7.0, 25
8
C. Error bars: 1 s.d.
calculated from three independent measurements. Electrochemical
release of Cu
2+
: ramp of potential from 0.3 to 0.5 V vs. Ag/AgCl for
60 s. Electrochemical deposition of Cu
2+
: fixed potential of 1.0 V vs.
Ag/AgCl for 10 min.
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formation was measured for 30 minutes. Next, the same
solution was deposited on a clean electrode and a fixed
reductive potential of 1.0 V vs. Ag/AgCl was applied for
10 min to re-deposit Cu
2+
as Cu
0
onto the electrode surface.
Control experiments performed by UV/Vis spectroscopy,
DLS and TEM analyses confirmed that the monolayer-
protected Au nanoparticles were stable under these condi-
tions (Supporting Information, Figures S10–S12). Further-
more, UV/Vis titration experiments of Cu
2+
to a solution of
Au NP 1 after application of the reducing conditions con-
firmed no changes in the ability of TACN to complex Cu
2+
(Supporting Information, Figure S13).
[17]
Importantly, contin-
uation of the reaction monitoring by UV/Vis revealed that the
rate of PNP-formation (v
init
= 1.2(0.4) 10
9
m s
1
) had
dropped to the background rate observed for Au NP 1,
demonstrating that Cu
2+
was sufficiently depleted from the
system to inhibit catalytic activity. To fully demonstrate
reversibility, a second cycle of activation (using a new
electrode with freshly deposited Cu) and deactivation was
performed with the same solution. Notably, when the system
was electrochemically re-activated (from Au NP 1 to Au NP
1·Cu
2+
), the PNP rate of formation was strictly comparable,
within experimental error, to that measured for a control
experiment monitored for the same length of time where the
oxidative potential was applied only at the beginning of the
analysis (Figure 4, dashed line).
In conclusion, we have shown the reversible electro-
chemical regulation of a supramolecular nanocatalyst. Metal
ions have been electrochemically released from a pre-coated
electrode and complexed by the pre-catalytic system resulting
in its activation. This mechanism of catalyst activation
permitted the upregulation of catalytic activity through the
electrochemical release of Cu
2+
-metal ions possessing
a higher affinity for the macrocyclic ligands compared to
Cd
2+
. Finally, the reversibility of the process was demon-
strated by showing that the re-deposition of Cu
2+
on the
electrode resulted in a loss of catalytic activity. These results
show that electrochemistry is a very effective and clean tool
for the regulation of the catalytic activity of a supramolecular
catalyst. The release of metal ions from a well-defined solid
support also opens up the possibility for spatial and temporal
control over catalyst activation in systems of higher complex-
ity.
Acknowledgements
Financial support from the University of Padova
(CPDA138148) is acknowledged.
Keywords: gold nanoparticles · nanocatalysis · nanozymes ·
supramolecular catalysis · supramolecular chemistry
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Received: May 31, 2016
Published online: && &&, &&&&
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Communications
Supramolecular Catalysis
F. della Sala, J. L.-Y. Chen, S. Ranallo,
D. Badocco, P. Pastore, F. Ricci,*
L. J. Prins*
&&&& &&&&
Reversible Electrochemical Modulation of
a Catalytic Nanosystem
Hop on, hop off: Metal ions are reversibly
released from an electrode to regulate the
activity of a gold nanoparticle catalyst
(see picture). The system catalyzes the
cleavage of 2-hydroxypropyl-p-nitrophenyl
phosphate and the formation of p-nitro-
phenolate can be monitored by UV/Vis
spectroscopy.
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e
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Qi Zhang1, Wen-Zhi Wang1, Jing-Jing Yu1, Da-Hui Qu1  +1 moreInstitutions (1)
TL;DR: A tri-stable switchable catalyst is encoded by pH-controlled dynamic self-assembly of gold and TiO2 nanoparticles by precise adjustment of the integrated dynamic covalent and noncovalent self- assembly process.
Abstract: A tri-stable switchable catalyst is encoded by pH-controlled dynamic self-assembly of gold and TiO2 nanoparticles (NPs). Through precise adjustment of the integrated dynamic covalent and noncovalent self-assembly process of the two types of nanoparticles, the photocatalytic activity of the hybrid system is modulated by switching pH conditions between tri-stable "highly active", "active", and "inactive" states.

45 citations


Journal ArticleDOI
Shrivats Semwal1, Joyanta Choudhury1Institutions (1)
TL;DR: A molecular switch which responds to acid-base stimuli and serves as a bi-state catalyst for two different reactions, used in an assisted tandem catalysis set up involving dehydrogenative coupling of an amine and then hydrogenation of the resulting imine product by switching between the respective states of the catalyst.
Abstract: Disclosed here is a molecular switch which responds to acid-base stimuli and serves as a bi-state catalyst for two different reactions. The two states of the switch serve as a highly active and poorly active catalyst for two catalytic reactions (namely a hydrogenation and a dehydrogenative coupling) but in a complementary manner. The system was used in an assisted tandem catalysis set-up involving dehydrogenative coupling of an amine and then hydrogenation of the resulting imine product by switching between the respective states of the catalyst.

37 citations


Journal ArticleDOI
Joyanta Choudhury1Institutions (1)
Abstract: This Digest letter aims to stimulate the readers with some recent developments in the field of artificial switchable catalysis achieved during the last couple of years. The significance of this young but burgeoning field was emphasized with the help of these latest examples.

35 citations


References
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Matthew W. Kanan1, Daniel G. Nocera1Institutions (1)
22 Aug 2008-Science
TL;DR: A catalyst that forms upon the oxidative polarization of an inert indium tin oxide electrode in phosphate-buffered water containing cobalt (II) ions is reported that not only forms in situ from earth-abundant materials but also operates in neutral water under ambient conditions.
Abstract: The utilization of solar energy on a large scale requires its storage. In natural photosynthesis, energy from sunlight is used to rearrange the bonds of water to oxygen and hydrogen equivalents. The realization of artificial systems that perform "water splitting" requires catalysts that produce oxygen from water without the need for excessive driving potentials. Here we report such a catalyst that forms upon the oxidative polarization of an inert indium tin oxide electrode in phosphate-buffered water containing cobalt (II) ions. A variety of analytical techniques indicates the presence of phosphate in an approximate 1:2 ratio with cobalt in this material. The pH dependence of the catalytic activity also implicates the hydrogen phosphate ion as the proton acceptor in the oxygen-producing reaction. This catalyst not only forms in situ from earth-abundant materials but also operates in neutral water under ambient conditions.

3,351 citations


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Hui Wei1, Erkang Wang1Institutions (1)
TL;DR: This review discusses various nanomaterials that have been explored to mimic different kinds of enzymes and covers their kinetics, mechanisms and applications in numerous fields, from biosensing and immunoassays, to stem cell growth and pollutant removal.
Abstract: Over the past few decades, researchers have established artificial enzymes as highly stable and low-cost alternatives to natural enzymes in a wide range of applications. A variety of materials including cyclodextrins, metal complexes, porphyrins, polymers, dendrimers and biomolecules have been extensively explored to mimic the structures and functions of naturally occurring enzymes. Recently, some nanomaterials have been found to exhibit unexpected enzyme-like activities, and great advances have been made in this area due to the tremendous progress in nano-research and the unique characteristics of nanomaterials. To highlight the progress in the field of nanomaterial-based artificial enzymes (nanozymes), this review discusses various nanomaterials that have been explored to mimic different kinds of enzymes. We cover their kinetics, mechanisms and applications in numerous fields, from biosensing and immunoassays, to stem cell growth and pollutant removal. We also summarize several approaches to tune the activities of nanozymes. Finally, we make comparisons between nanozymes and other catalytic materials (other artificial enzymes, natural enzymes, organic catalysts and nanomaterial-based catalysts) and address the current challenges and future directions (302 references).

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Journal ArticleDOI
Youhui Lin1, Jinsong Ren1, Xiaogang Qu1Institutions (1)
TL;DR: Graphene oxide could serve as a modulator to greatly improve the catalytic activity of lysozyme-stabilized gold nanoclusters at neutral pH, which will have great potential for applications in biological systems and the incorporation of modulator into artificial enzymes can offer a facile but highly effective way to improve their overall catalytic performance.
Abstract: ConspectusNatural enzymes, exquisite biocatalysts mediating every biological process in living organisms, are able to accelerate the rate of chemical reactions up to 1019 times for specific substrates and reactions. However, the practical application of enzymes is often hampered by their intrinsic drawbacks, such as low operational stability, sensitivity of catalytic activity to environmental conditions, and high costs in preparation and purification. Therefore, the discovery and development of artificial enzymes is highly desired. Recently, the merging of nanotechnology with biology has ignited extensive research efforts for designing functional nanomaterials that exhibit various properties intrinsic to enzymes. As a promising candidate for artificial enzymes, catalytically active nanomaterials (nanozymes) show several advantages over natural enzymes, such as controlled synthesis in low cost, tunability in catalytic activities, as well as high stability against stringent conditions.In this Account, we fo...

771 citations


Journal ArticleDOI
Zhi-You Zhou1, Na Tian1, Jun-Tao Li1, Ian Broadwell1  +1 moreInstitutions (1)
TL;DR: This critical review presents a review of the progress made for producing shape-controlled synthesis of nanomaterials of high surface energy using electrochemical and wet chemistry techniques and discusses important nanommaterials such as nanocrystal catalysts based on Pt, Pd, Au and Fe, metal oxides TiO(2) and SnO( 2), as well as lithium Mn-richMetal oxides.
Abstract: The properties of nanomaterials for use in catalytic and energy storage applications strongly depends on the nature of their surfaces. Nanocrystals with high surface energy have an open surface structure and possess a high density of low-coordinated step and kink atoms. Possession of such features can lead to exceptional catalytic properties. The current barrier for widespread industrial use is found in the difficulty to synthesise nanocrystals with high-energy surfaces. In this critical review we present a review of the progress made for producing shape-controlled synthesis of nanomaterials of high surface energy using electrochemical and wet chemistry techniques. Important nanomaterials such as nanocrystal catalysts based on Pt, Pd, Au and Fe, metal oxides TiO2 and SnO2, as well as lithium Mn-rich metal oxides are covered. Emphasis of current applications in electrocatalysis, photocatalysis, gas sensor and lithium ion batteries are extensively discussed. Finally, a future synopsis about emerging applications is given (139 references).

637 citations


PatentDOI
16 Dec 2011-Science
Abstract: Electrochemical reduction of an exemplary ATRP catalyst, C 11 Br 2 /Me 6 TREN, is shown to be an efficient process to mediate and execute an ATRP. The onset of polymerization occurs only through passage of a cathodic current achieved under a reductive potential to form Cu 1 Br 2 /Me 6 TREN, within the reaction medium. Unprecedented control over the polymerization kinetics can be attained through electrochemical methods by modulating the magnitude of the applied potential allowing polymerization rate enhancement or retardation. Additional polymerization control is gained through electrochemical “dials” allowing polymerization rate enhancements achieved by larger applied potentials and the ability to successfully switch a polymerization “on” and “off between dormant and active states by application of multistep intermittent potentials.

599 citations


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