Angewandte
Chemie
Graphene Quantum Dots
Deciphering a Nanocarbon-Based Artificial Peroxidase: Chemical
Identification of the Catalytically Active and Substrate-Binding Sites
on Graphene Quantum Dots**
Hanjun Sun, Andong Zhao, Nan Gao, Kai Li, Jinsong Ren, and Xiaogang Qu*
Abstract: The design and construction of efficient artificial
enzymes is highly desirable. Recent studies have demonstrated
that a series of carbon nanomaterials possess intrinsic perox-
idase activity. Among them, graphene quantum dots (GQDs)
have a high enzymatic activity. However, the catalytic mech-
anism remains unclear. Therefore, in this report, we chose to
decipher their peroxidase activity. By selectively deactivating
the ketonic carbonyl, carboxylic, or hydroxy groups and
investigating the catalytic activities of these GQD derivatives,
we obtained evidence that the ÀC=O groups were the catalyti-
cally active sites, whereas the O=CÀOÀ groups acted as
substrate-binding sites, and ÀCÀOH groups can inhibit the
diagnostics and therapeutic applications, compared with
natural peroxidase, the low efficiency of the carbon nano-
materials has unfortunately restricted their further applica-
[
2b,c]
tions.
Understanding their catalytic mechanism should
facilitate the design and synthesis of more effective carbon
[
2c,3,4]
nanozymes.
GQDs, which can be regarded as small pieces of graphene,
are a type of zero-dimensional material with characteristics
[5]
derived from both graphene and CDs. Aside from some
superior fluorescence properties, such as higher photostability
against photobleaching and blinking than organic dyes and
semiconductor quantum dots, GQDs exhibit a higher perox-
[
4,6]
activity. These results were corroborated by theoretical studies.
This work should not only enhance our understanding of
nanocarbon-based artificial enzymes, but also facilitate the
design and construction of other types of target-specific
artificial enzymes.
idase-like activity than GO.
Furthermore, GQDs display
no apparent toxicity in vitro and in vivo, which should render
[
7]
them applicable in the area of biomedicine. For these
reasons, GQDs have attracted significant attention from
researchers in both material and biological science. Recently,
we have found that the peroxidase-like activity of GQDs
stems from their ability to catalyze the decomposition of
N
anomaterials with similar functions to those of proteins
[4]
are regarded as an important class of protein mimics and
expected to substitute natural proteins in practical applica-
H O , generating HOC. However, the catalytic and substrate-
2
2
binding sites of GQDs acting as nano-peroxidases are
[
1]
tions. Carbon nanomaterials have shown excellent catalytic
activity in several important chemical and biochemical
reactions. Interestingly, they are even regarded as nano-
zymes because they possess intrinsic enzymatic activity. As
nanozymes, carbon nanomaterials have advantages over
natural enzymes, such as low costs, facile production on
large scale, the possibility of long-term storage, and high
unknown. Herein, through selectively deactivating these
[
8]
specific oxygen-containing functional groups and investi-
gating the catalytic activity of different GQD derivatives as
peroxidase mimics, we obtained evidence that the ketonic
carbonyl groups (ÀC=O) are the catalytically active sites,
whereas the carboxylic groups (O=CÀOÀ) act as substrate-
binding sites, and the hydroxy groups (ÀCÀOH) can even
[
2]
[2c]
[
2c]
stability in harsh environments. Our group was the first to
report the peroxidase-like activity of graphene oxide (GO),
inhibit the catalytic reaction. For the first time, we clarify the
different functions of these three kinds of typical oxygen
functional groups on the surface of GQDs in catalytic
peroxidase-like reactions, which reflects the intrinsic catalytic
activity of GQDs as a peroxidase mimic.
[3]
and has since focused on expanding the applications of GO,
graphene nanocomposites, carbon nanotubes (CNTs), carbon
dots (CDs), and graphene quantum dots (GQDs) as perox-
[2c,4]
idase-like catalysts.
Although the above-mentioned
The GQDs were synthesized according to previous
[
4,9]
carbon nanozymes have exhibited enzymatic activity in
reports.
with carbonyl, carboxylic, and hydroxy groups on their
The as-prepared GQDs were mainly covered
[
4,9]
surface.
Phenylhydrazine (PH), benzoic anhydride (BA),
[
*] H. Sun, A. Zhao, Dr. N. Gao, Dr. K. Li, Prof. J. Ren, Prof. X. Qu
Laboratory of Chemical Biology and State Key Laboratory of Rare
Earth Resource Utilization, Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences
and 2-bromo-1-phenylethanone (BrPE) were chosen as the
titrants to specifically react with the ketonic carbonyl,
hydroxy, and carboxylic groups on the GQDs, respectively
Changchun, Jilin 130022 (China)
E-mail: xqu@ciac.ac.cn
(
Scheme 1), because these reactions have been shown to be
[8]
highly specific under gentle reaction conditions. The typical
transmission electron microscopy (TEM) and atomic force
microscopy (AFM) images of GQDs and the as-prepared
GQD derivatives (referred to as GQDs-PH, GQDs-BA, and
GQDs-BrPE) demonstrated that the reactions with PH, BA,
and BrPE did not change the average sizes and heights as well
as the relative size and height distributions of the GQD
derivatives compared with the unmodified GQDs (Support-
H. Sun, A. Zhao
University of Chinese Academy of Science
Beijing, 100039 (China)
[
**] This work was supported by the 973 Project (2011CB936004,
2
2
012CB720602), and the NSFC (21210002, 21431007, 91413111,
1402183).
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
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