A Dipeptide-Based Hierarchical Nanoarchitecture with Enhanced Catalytic Activity

Article abstract of DOI:10.1002/anie.202006994

Achieving synthetic architectures with simple structures and robust biomimetic catalytic activities remains a great challenge. Herein, we explore a facile supramolecular assembly approach to construct a dipeptide-based hierarchical nanoarchitecture with enhanced enzyme-like catalytic activity. In this nanoarchitecture, nanospheres are put in a chain-like arrangement through coordination-driven directional self-assembly. The reversible transformation of anisotropic nanochains to isotropic nanospheres switches biomimetic activity. Notably, the assembled nanoarchitecture exhibits a high enzyme-like activity and remarkable long-term stability to promote hydroquinone oxidation, superior to the natural counterpart. This work will pave the way to develop reversible and reusable supramolecular biocatalysts with ordered hierarchical structures for accelerating chemical transformations.

Full text of DOI:10.1002/anie.202006994

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Accepted Article
Title: A Dipeptide-Based Hierarchical Nanoarchitecture with Enhanced
Catalytic Activity
Authors: Junbai Li, Chenlei Wang, Jinbo Fei, and Keqing Wang
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10.1002/anie.202006994
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COMMUNICATION
A Dipeptide-Based Hierarchical Nanoarchitecture with Enhanced
Catalytic Activity
Chenlei Wang,[a],[b] Jinbo Fei, * [a],[b] Keqing Wang,[a],[b] and Junbai Li* [a],[b]
Dedication to Professor Youqi Tang on the occasion of his 100th birthday
[a]
[b]
C. Wang, Prof. Dr. J. Fei, K. Wang, Prof. Dr. J. Li
Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Lab of Colloid, Interface and Thermodynamics, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190
E-mail: jbli@iccas.ac.cn; feijb@iccas.ac.cn
C. Wang, Prof. Dr. J. Fei, K. Wang, Prof. Dr. J. Li
University of Chinese Academy of Sciences, Beijing 100049
Supporting information for this article is given via a link at the end of the document.
Abstract: Achieving synthetic architectures with simple structures
and robust biomimetic catalytic activities remains a great challenge.
Herein, we explore a facile supramolecular assembly approach to
supramolecular catalysts with much simpler structures and
enhanced biomimetic catalytic activities.
construct
a dipeptide-based hierarchical nanoarchitecture with
enhanced enzyme-like catalytic activity. In this nanoarchitecture,
nanospheres are with chain-like arrangement through coordination-
driven directional self-assembly. The reversible transformation of
anisotropic nanochains to isotropic nanospheres switches
biomimetic activity. Notably, such assembled nanoarchitecture
exhibits high enzyme-like activity and remarkable long-term stability
to promote hydroquinone oxidation, superior to the natural
counterpart. This work will pave the way to develop reversible and
reusable supramolecular biocatalysts with ordered hierarchical
structures for accelerating chemical transformations.
Supramolecular assembly offers a promising opportunity to
[1]
design and construct biomimetic architectures.
Through
comprehensive modulation of molecular interactions, such
assembled architectures can be tailored with desirable
[2, 3]
physicochemical and biological properties.
In particular, to
overcome intrinsic obstacles of natural enzymes that are easily
inactivated in extreme environments, tremendous effort has
been made to fabricate robust artificial enzyme-mimicking
catalysts by supramolecular assembly. [4] An attractive goal is to
obtain supramolecular catalysts with enhanced enzyme-like
activities by utilizing bio-derived components with simple
structures as building blocks. [5]
Short peptide-based supramolecular assembly has gained
significant interest due to a wide range of applications in
regenerative medicine, optoelectronic devices and bioimaging. [6-
9]
Short peptides possess unique advantages including easy
Figure 1. (A) Highlighted crystal structure of fungus laccase from Trametes
versicolor (PDB: 1GYC). (B) Chemical structure of CDPGA, schematic
illustration of reversible transformation of nanospheres to nanochains
modulating by Cu2+ and H+, and switchable enzyme-like catalytic oxidation of
hydroquinone into benzoquinone.
modification, low immunogenicity, versatile functionality,
excellent biocompatibility and biodegradability. Among them,
diphenylalanine containing two aromatic amino acids has shown
[10]
outstanding performance.
It contains diverse functional
groups providing hydrogen bonding, electrostatic interactions,
aromatic stacking and van der Waals forces. This short peptide
has been widely used as a versatile building block to construct
functional supramolecular architectures, exhibiting promise in
In this communication, we develop a facile strategy to
construct
a
diphenylalanine-based nanoarchitecture with
ordered hierarchical structures and enhanced enzyme-
mimicking activity. In nature, as a copper-containing enzyme
(Figure 1A), laccase catalyzes oxidation of organic compounds
by using oxygen as the electron acceptor. [12] Inspired by nature,
in our case, a bola-like molecule CDPGA (Figure 1B) is
conceived and synthesized through imine condensation reaction
advanced drug delivery, active optical waveguiding and sensitive
[11]
piezoelectricity.
Nevertheless,
diphenylalanine-based
supramolecular systems with enzyme-like catalytic activities are
fairly unexplored. We envision the exploration of self-assembling
diphenylalanine to accommodate specific metal ions to form
1
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between cationic diphenylalanine (H-Phe-Phe-NH2·HCl) and
glutaraldehyde (Figure S1). The Schiff-base CDPGA self-
assemble into nanospheres via possible combination of
hydrophobic and π–π stacking interactions. Further,
nanospheres assemble into nanochains through Cu2+-directed
self-organization. These dipeptide-based supramolecular
assemblies can complete reversible transformation under
regulation by Cu2+ and H+. Remarkably, nanochains are capable
of efficiently and robustly promoting chemical conversion of
hydroquinone into benzoquinone, and exhibit enhanced catalytic
activity, compared with natural laccase. By contrary,
nanospheres show no enzyme-like activity. To our best
emerges. This suggests the formation of coordination complexes
with higher density. Figure 2B and Figure 2D demonstrate these
complexes are one-dimensional nanochains, which are
composed of several nanospheres with smooth surface. There is
no significant difference in the diameter between nanochains
and nanospheres. It implies Cu2+-mediated oriented assembly of
nanospheres to form nanochains. Roughly, energy dispersive
spectrometry analysis in Figure 2E confirms that the elements of
Cu, C, O and N coexist in a single nanochain. Precisely,
inductively coupled plasma mass spectrometry analysis offers a
quantitative result that the content of Cu in nanochains is 1.13
wt%. These findings verify that Cu2+ induces directed alignment
of isotropic nanospheres into anisotropic nanochains.
knowledge, this is the first report on
a dipeptide-based
hierarchical nanoarchitecture for switchable biomimetic catalysis.
To preliminarily understand the formation mechanism of this
chain-like nanoarchitecture, Fourier transform infrared
spectroscopy (FTIR) was performed. Figure S5 shows great
changes in the spectra of cationic diphenylalanine and
nanospheres. To be specific, there are two merging peaks at
1606 and 1395 cm−1, indicative of a characteristic absorption of
[14]
C=N.
Moreover, the absorption intensity at 2934 cm−1 in
nanospheres increases significantly, which are assigned to C–H
stretching of Schiff base. These results suggest Schiff base
bonds in nanospheres. Compared with the UV-Vis absorption
spectrum of cationic diphenylalanine, a new peak appears at
442 nm in that of CDPGA (Figure S6), further confirming the
formation of imine bonds. Moreover, the findings from Figure S7
verify that the imine-linked peptide building blocks self-assemble
by the possible combination of hydrophobic and π-π stacking
interactions. In addition, the results of UV-Vis-NIR absorption
spectra (Figure S8) demonstrate the coordination of Cu2+ to
CDPGA, the building block of nanospheres.
Figure 2. Representative SEM images of (A) nanospheres and (B)
nanochains.Typical TEM images of (C) nanospheres and (D) nanochains. The
insets are relevant magnified images. (E) Element mapping pattern of a single
nanochain. The scale scale is 200 nm.
Specifically, the introduction of glutaraldehyde as a diimine
linker increases hydrophobicity of cationic diphenylalanine,
which allows it to aggregate into nanospheres in mixed solvents.
In the studied conditions, unlinked cationic diphenylalanine is
completely dissolved in the absence or presence of Cu2+ (Figure
S2 and Figure S3). Transmission electron microscopy (TEM)
images in Figure S4 indicate no assemblies formed in these
solutions. These results prove the formation of imine bonds is
essential to achieve assembly into nanospheres. More
importantly, generated nitrogen-containing Schiff-base bond,
together with the carbonyl moiety, form a coordination motif for
Cu2+ to facilitate the incorporation of active sites. [13] Scanning
electron microscopy (SEM) image in Figure 2A reveals uniform
nanospheres with the mean diameter of 450 nm. Figure 2C
demonstrate the solid nanospheres with smooth surface. After
incubation with CuSO4 aqueous solution, much precipitation
Figure 3. (A) Time-dependent size distribution of the assembly after Cu2+
-
directed aggregation. a) 0, b) 5, c) 10, d) 20, e) 30, f) 60, g) 120 min. After that,
0.01 M HCl aqueous solution was added, triggering structure transformation
from nanochains to nanospheres. The transformation above completed within
10 min (h). (B) The relevant mean size change. Corresponding (C) photo
images and (D) mean sizes of recycled nanospheres and nanochains.
Further, dynamic light scattering (DLS) measurement was
carried out to roughly monitor the evolution process, since it
cannot provide an accurate measurement of isotropic structures
at length scales greater than 1 μm. As revealed in Figure 3A, a
single peak at 500 nm is present before adding Cu2+,
2
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10.1002/anie.202006994
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corresponding to apparent hydrodynamic radius of the original
nanospheres. A relatively broader peak at 1 μm appears at 5
min after adding Cu2+, which is attributed to that of assembled
nanochains. With increasing time, the peak has a shift to 1.5 and
2 μm after 10 and 20 min, respectively, demonstrating a nearly
linear growth process. The further aggregation speed slows
down after 30 min. The final hydrodynamic radius of the
assembly is approximately 3.5 μm and remains unchanged after
120 min. At the moment, dropping HCl aqueous solution allows
apparent hydrodynamic radius of the assembly to return to the
original within 10 min (Figure 3A and Figure 3B). It can be
explained that protonation of the nanosphere surface
decomposes interfacial coordination between CDPGA and Cu2+.
Moreover, the relevant TEM image in Figure S9 demonstrates
the regeneration of nanospheres. In addition, Figure S5 reveals
that there are no variations in FTIR spectra between the original
and regenerated nanospheres, further verifying the imine bonds
are intact in our case. The color change accompanying structure
transformation of two assemblies above is easily discerned by
naked eyes (Figure 3C). Importantly, there are no obvious
changes in mean sizes of regenerated nanospheres or
nanochains after several cycles (Figure 3D). This finding
indicates the structure transformation is reversible. Hence, it is
possible that such dipeptide-based supramolecular assembly
possesses switchable properties.
with benzoquinone through Michael coupling to yield a colorless
product. Thus, the catalytic reaction process can be investigated
by monitoring the decolorization degree after definite time
interval. To be specific, UV-Vis spectroscopy was performed to
record the time-dependent absorbance of 2-nitro-5-thiobenzoic
acid at 412 nm in the systems. Meanwhile, the relevant
processes are recognized by naked eyes (Figure S10).
Obviously, Figure 4B shows that nanospheres, CuSO4 or
cationic diphenylalanine-CuSO4 exhibit no laccase-like catalytic
activity, considering the absorbance at 412 nm in three groups
above has little decrease during a period of 60 min. In contrast,
nanochains are capable of catalyzing the decolorization reaction.
These findings confirm that the catalytic activity for
hydroquinone oxidation is a result of the formation of a highly
regular supramolecular assembly containing Cu2+. Quantitatively,
the apparent catalytic activity of nanochains is about 2 times of
that of natural laccase. Especially, it is exciting to observe a
sharp decrease of absorbance at 412 nm after adding
nanochains. This finding proves that nanochains exhibit a high
catalytic activity. Under the same condition, for natural laccase
with the same content of Cu, it decreases more gently. The
detailed decolorization kinetics of nanochains and natural
laccase are present in Figure 4C. For the former, the
decolorization degrees are 61% (1 min), 88% (10 min), 94% (20
min) and 100% (30 min), respectively. For the latter, they are 9%
(1 min), 27% (10 min), 41% (20 min) and 54% (30 min),
respectively. Remarkably, at the beginning (1 min), the apparent
catalytic activity of nanochains reaches up to 7 times that of
natural laccase.
Further, in order to detect the affinity of each catalyst for the
substrate, different concentrations of hydroquinone solutions
were chosen. Based on the standard curve (Figure S11),
according to Lambert-Beer law, through quantitative analysis in
Figure S12, Michaelis constants of nanochains and natural
laccase are determined as 0.026 and 0.049 mM, respectively. It
means that the affinity of nanochains for the substrate is
stronger. That is, nanochains are more easily accessible for the
substrate.
In addition, the catalytic stability of each catalyst was
assessed. As shown in Figure 4D, nanochains have no
significant loss of catalytic activity in 7 days. Particularly, their
catalytic activity maintains 95% even at the last day. By contrary,
along with a period of stewing, the catalytic activity of natural
laccase has considerable loss. The reason can be ascribed to
the simpler but more stable structure of the supramolecular
catalyst, compared with natural laccase. The finding implies this
supramolecular catalyst with hierarchical nanostructures holds a
much greater potential in practical applications over the natural
counterpart.
Moreover, tests were conducted to investigate the catalytic
activity of the dipeptide-based supramolecular catalyst after
structure transformation. As revealed in Figure 4E, during an
integrated cycle, nanochains promote the decolorization reaction
simultaneously while nanospheres hardly accelerate it.
Importantly, the relative catalytic activity of nanochains
maintains 92% after 5 cycles. These results reveal that such
assembled supramolecular catalyst possesses reliable and
switchable enzyme-like catalytic activity.
Figure 4. (A) The decolorization reaction for testing catalytic activity. (B) Time-
dependent relative absorbance after adding (a) nanospheres, (b) CuSO4, (c)
cationic diphenylalanine-CuSO4, (d) laccase, (e) nanochains, respectively. (C)
Relative catalytic activity of nanochains and natural laccase as a function of
time. (D) Comparison of long-term catalytic stability of nanochains and natural
laccase. (E) Switchable catalytic activity of nanochains and nanospheres.
To evaluate enzyme-like catalytic activity of such assembled
dipeptide-based architecture, hydroquinone is chosen as a
model substrate. [15] The decolorization reaction shown in Figure
4A is used for test. In detail, hydroquinone is converted into
benzoquinone by oxygen in the presence of the catalyst with
laccase-like activity. Instantly, 2-nitro-5-thiobenzoic acid reacts
In summary, we explore a dipeptide-based system with
ordered hierarchical nanostructures and switchable robust
enzyme-like activity via supramolecular assembly. Compared
3
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Winter, Angew. Chem. Int. Ed. 2016, 55, 12412-12416; Angew. Chem.
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with
the
natural
counterpart,
this
dipeptide-based
supramolecular catalyst possesses the apparent catalysis
efficiency up to two times. Moreover, it exhibits much more
considerable stability in the practice. Furthermore, the enzyme-
like activity of such assembled nanoarchitecture can be easily
tuned in a switchable manner. In addition, the hierarchical
nanostructures of this supramolecular catalyst bring easy solid-
liquid separation and have obvious advantages over the natural
enzyme. Considering the facile supramolecular assembly, this
strategy above can be extended to fabricate other artificial
biocatalysts toward robust and efficient chemical transformations.
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Acknowledgements
This work was supported by the National Nature Science
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Conflict of interest
The authors declare no conflict of interest.
Keywords: supramolecular assembly • peptide • hierarchical
nanoartchitecture • biocatalysis
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4
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Entry for the Table of Contents
Insert graphic for Table of Contents here.
A dipeptide-based supramolecular catalyst with ordered hierarchical nanostructure is developed through directional self-assembly. Such assembled
chain-like nanoarchitecture possesses switchable enhanced enzyme-like catalytic activity, compared with the natural counterpart. This work offers
a promise for promoting chemical transformations through constructing robust supramolecular biocatalysts.
5
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