Eco-friendly decarboxylative cyclization in water: Practical access to the anti-malarial 4-quinolones

Article abstract of DOI:10.1039/c8gc03570a

An environmentally benign decarboxylative cyclization in water has been developed to synthesize 4-quinolones from readily available isatoic anhydrides and 1,3-dicarbonyl compounds. Isatins are also compatible for the reaction to generate 4-quinolones in the presence of TBHP in DMSO. This protocol provides excellent yields under mild conditions for a broad scope of 4-quinolones, and has good functional group tolerance. Only un-harmful carbon dioxide and water are released in this procedure. Moreover, the newly synthesized products have also been selected for anti-malarial examination against the chloroquine drug-sensitive Plasmodium falciparum 3D7 strain. 3u is found to display excellent anti-malarial activity with an IC₅₀ value of 33 nM.

Full text of DOI:10.1039/c8gc03570a

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COMMUNICATION
A binuclear copper-substituted
phosphomolybdate with reactive oxygen species
catalytic ability and antimicrobial activity†
Cite this: CrystEngComm, 2019, 21,
394
Received 6th September 2018,
Accepted 25th November 2018
a
b
a
Xiang Ma,‡ab Chao Zhang, ‡ Jiai Hua, Pengtao Ma,
Jingping Wang
*
*
a
a
and Jingyang Niu
DOI: 10.1039/c8ce01513a
rsc.li/crystengcomm
A novel 1-D phosphomolybdate based on a dinuclear copper-
substituted Strandberg structure was successfully designed and
synthesized. It not only possesses reactive oxygen species (ROS)
catalytic ability in aqueous solution, by synergizing the Cu clusters
with the building blocks, but also shows good antimicrobial
activity.
soft base such as –SH, but also can catalyze ROS generation
by valence interchange of +1 and +2 in the internal environ-
ment.8 Therefore, seeking a suitable auxiliary to synergize
with Cu+/Cu2+ to maximize its effectiveness becomes the es-
sential step.
Polyoxometalates (POMs) are a class of metal oxygen clus-
ters which have multitudinous structures and fascinating
properties.9–12 Of a variety of building blocks, Strandberg-
type ([P2Mo5O23]6−) fragments (Fig. S1†) have several inherent,
irreplaceable advantages such as nano size, a nucleophilic
oxygen-enriched surface and poly-bond-making sites. These
features endow the clusters with the ability to serve as bulky
polydentate ligands to incorporate into multiple transition-
metal cations with flexible coordination modes.13–15 Further-
more, many researchers have demonstrated that POMs with a
Strandberg-type fragment possess excellent oxidation catalytic
capacity, such as ketalization of cyclohexanone with glycol
and oxidation of styrene.13,16,17 These properties may be ben-
eficial to its synergistic effect with copper in catalyzing the
production of ROS. Hence, combination of Cu ions and
[P2Mo5O23]6− in one hybrid material may not only retain the
desirable properties of all the precursor components, but also
express them in a synergistic manner.
Research into new multifunctional materials, particularly
antimicrobial materials, has received more and more interest
from both academia and industry.1,2 Such materials are in
high demand in the consumer marketplace, for example in
hotel and catering equipment, water filtration systems and
medical supplies.3 Silver has been recognized as an
antibacterial material for decades.4 However, its cost severely
limits its range of applications. Therefore, searching for
inexpensive transition metals to replace noble metals for
synthesizing antibacterial materials has become a research
hotspot.5
Copper and silver belong to the same subfamily in the pe-
riodic table, which may make copper a preferred alternative
to silver. Biochemical research has indicated that the coordi-
nation of silver ions with thiol groups (–SH) may play a key
role in inactivation of bacteria, which inhibit basic cell func-
tions such as oxidative phosphorylation and respiratory chain
enzymes.6 Furthermore, Ag+ is believed to catalyze the pro-
duction of reactive oxygen species (ROS), which destroy the
subcellular structure of the bacteria directly.7 Cu2+ is not only
a Lewis soft acid, which is easy to coordinate with a Lewis
Here we report a newly designed POM, (H2en)ijCuIJen)IJH2O)
CuIJen)IJH2O)3]ijP2Mo5O23]·5.5H2O (Fig. 1, abbreviated as CPM),
which was derived from the pure inorganic structure
[P2Mo5O23]6− linked with a dinuclear Cu complex. Notably,
CPM is able not only to catalyze generation of reactive oxygen
species (ROS), but also to inhibit the proliferation of
Escherichia coli (E. coli). Hitherto, most investigations of anti-
biotic POMs have mainly focused on polyoxotungstates
a Henan Key Laboratory of Polyoxometalate Chemistry, Institute of Molecular and
Crystal Engineering, College of Chemistry and Chemical Engineering, Henan
University, Kaifeng, Henan 475004, P. R. China. E-mail: jyniu@henu.edu.cn,
jpwang@henu.edu.cn; Fax: +86 371 23886876
(POTs),18
especially
on
organoantimonyIJIII)-containing
POTs.19,20 By contrast, antimicrobial activity of poly-
oxomolybdates (POMos) remains largely unexplored, with
only Keggin- and Anderson-type structures having been
tested.18 To our knowledge, CPM represents a novel anti-
bacterial POMo based on a Strandberg-type structure, and
provides a good opportunity to exploit the antibacterial appli-
cations of POMos.
b Chemistry and Chemical Engineering Department, Taiyuan Institute of
Technology, Taiyuan, 030008, P. R. China. E-mail: Jiaihua01660@163.com;
Fax: +86 351 3569476
† Electronic supplementary information (ESI) available: IR spectra, EDX-SEM,
XPS spectra, BVS calculation, crystal details and experimental methods. CCDC
931609 and 1866053. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c8ce01513a
‡ These authors contributed equally.
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[CuIJen)IJH2O)2]ijP2Mo5O23]·3.5H2O (abbreviated as C1), is syn-
thesized. The crystallographic data and selected bond lengths
and angles are summarized in Tables S4–S6.† As shown in
Fig. 2A, C1 can be considered as a 1-D structure formed by al-
ternately connecting [CuIJen)IJH2O)2]2+ with [P2Mo5O23]6−. C1 is
similar to the reported classic 1-D chain Cu-substituted
Strandberg-type POM,21 and the only difference is whether
the Cu atom is in a five-coordinate configuration for the
reported structure (Fig. S2†) or a six-coordinate configuration
for C1 (Fig. 2C).
The remarkable characteristic of CPM is that dinuclear Cu
clusters alternate with [P2Mo5O23]6− clusters in one-
dimensional chains. This distinctive structural feature of
CPM, compared with either the reported structure or that of
C1, is likely to improve its performance. To the best of our
knowledge, Cu ions can catalyze the formation of ROS in
aqueous solution by valence interchange of +1 and +2.8 Since
the copper ions in the cluster can transfer electrons quickly,
the catalytic performance may be much higher than for a sin-
gle copper ion. Moreover, ferromagnetic properties are only
generated when more than two Cu2+ ions are within a certain
distance.22 Hence, CPM may have ferromagnetism, and this
may facilitate post-treatment of CPM after water purification
by using magnetic separation of antimicrobial materials and
purification materials. Furthermore, compared with the
POM-containing copper clusters constructed using other
building blocks, such as the Keggin-type unit (Fig. S1†), CPM
constructed by Strandberg-type fragments has natural struc-
tural advantages for antibacterial activity. In the literature,
the building blocks that can induce the formation of copper
clusters often seal the transition-metal ion clusters inside the
POM structure,16,23 causing the Cu ions to lose coordinated
active sites with –SH. CPM largely preserves the potential co-
ordinated sites of Cu ions (see Fig. 1C), which may enhance
the antibacterial ability.
Fig. 1 (A) Combined polyhedral/ball-and-stick view of the 1-D linear
structure of CPM. (B) Combined polyhedral/ball-and-stick representa-
tion of one CPM subunit in the crystal. (C) Polyhedral view of the coor-
dination mode of the dinuclear Cu cluster in CPM (lattice water mole-
cules and protonated en molecules are omitted).
CPM was synthesized by reacting CuCl2·2H2O, Na2MoO4
·2H2O, Na2HPO4·12H2O and ethylenediamine (en) in the mole
ratio of 3 : 3 : 2 : 1 at 85 °C in an acidic solution.
The mazarine crystals of CPM were obtained by volatilizing
the solution at room temperature over one week. The structure
of CPM was characterized by single-crystal X-ray diffraction anal-
ysis. The crystallographic data, selected bond lengths and angles
are summarized in Tables S1–S3.† X-ray structural analysis re-
veals that the molecular structural unit of CPM consists of a
[P2Mo5O23]6− cluster, a dinuclear Cu complex [CuIJen)IJH2O)Cu-
IJen)IJH2O)3]4+, 5.5 lattice water molecules and one protonated en
molecule as counter cation, and the [P2Mo5O23]6− clusters and
Cu complex construct the backbone of CPM.
The geometry of the [P2Mo5O23]6− cluster can be deemed
as a puckered ring of five nearly coplanar corner-sharing/
edge-sharing distorted MoO6 octahedra [Mo–O: 1.702IJ5)–
2.458IJ4) Å] with two capping PO4 tetrahedra [P–O: 1.527IJ4)–
1.560IJ4) Å] on both poles of the {Mo5O21} ring centers (Fig.
S1†). As shown in Fig. 1A, [CuIJen)]2+ acts as a linker
connected to two adjacent [P2Mo5O23]6− clusters by sharing
the terminal oxygen on the PO4 tetrahedron to form a 1-D lin-
ear structure, in which the angles of P1–O–Cu1 and P2–O–
Cu1 are 123.4IJ2)° and 129.0IJ3)° respectively. As shown in
Fig. 1B, another Cu complex, [CuIJen)IJH2O)3]2+, is connected
to the 1-D chain linker [CuIJen)]2+, forming a dinuclear Cu
cluster by sharing an oxygen atom. Notably, the two Cu
atoms in the dinuclear cluster exhibit different coordination
configurations. As shown in Fig. 1C, Cu1 adopts a five-
coordinated square pyramid configuration. Cu2 is coordi-
nated by two nitrogen atoms from an en (Cu–N: 2.000IJ6)–
2.006IJ5) Å), one O atom shared with Cu1 (Cu–O: 2.596(5) Å)
and three H2O (Cu2–O1/2 W: 1.965IJ5)–1.979IJ5) Å, Cu–O3W:
2.574(9) Å). As a result of Jahn–Teller distortion, Cu2 adopts
a six-coordinated, distorted octahedral configuration, and ex-
poses O1W outside the 1-D linear framework.
The X-ray powder diffraction patterns of samples are con-
sistent with those from the single-crystal structure analyses
(Fig. S3†), indicating the phase purity. The composition of
Fig. 2 (A) Combined polyhedral/ball-and-stick view of the 1-D linear
structure of C1. (B) Combined polyhedral/ball-and-stick representation
of one C1 subunit in the crystal. (C) Polyhedral view of the coordina-
tion mode of Cu ions in C1 (lattice water molecules and protonated en
molecules are omitted).
Interestingly, when the amount of en is doubled, another
linear, copper-substituted, Strandberg-type POM, [H2IJen)]2
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CPM and C1 on the crystal surface was studied by EDX-SEM.
The SEM images (Fig. S4 and S5†) show that several points
are randomly selected for testing on the surface of the CPM
and C1 crystals. EDX data (Fig. S6 and S7†) show that the
abundance of Cu on the surface of CPM is about 70% higher
than that of C1 based on Mo, which indicates that the forma-
tion of dinuclear Cu clusters is beneficial to increasing the
abundance of Cu on the surface of materials. These results
have a positive significance for making antibacterial mate-
rials that are loaded on the immobilization phase.
The IR spectra of CPM and C1 were also investigated (Fig.
S8†). The spectra of CPM and C1 are similar and both exhibit
the characteristic peaks of the Strandberg-type POM in low
wave-number regions, with the bands at about 900 cm−1 and
565–688 cm−1 being assigned to ν(Mo–Ot) and ν(Mo–O–Mo)
bonds, respectively. The characteristic bands between 1010 and
1105 cm−1 are attributed to the ν(P–O) bond.24 In addition, the
occurrence of characteristic vibrations at about 3140–3160
cm−1 and 1405–1630 cm−1 can be attributed to the ν(N–H) bond
and confirm the presence of en ligands.25 A broad feature of
peaks at about 3440 cm−1 can be attributed to absorptions of
coordinated and lattice water molecules.25 The IR spectra of
CPM and C1 show significant differences in intensity in the
range 1405–1630 cm−1, which originates from the differences
between the content of en coordinated with copper and proton-
ated en.26 The TG curve of CPM exhibits three steps of weight
loss (Fig. S9†). The first weight loss step is 7.75% (calc. 7.12%)
in the range 25–85 °C, corresponding to release of lattice water
molecules. The second weight loss step is 4.38% (calc. 4.46%)
in the range 86–200 °C, corresponding to release of an en mole-
cule, which indicates that the framework of CPM is beginning
to collapse. The third weight loss step is 16.22% (calc. 16.64%)
in the range 200–520 °C, corresponding to release of coordi-
nated water and P2O5 molecules. These results indicate that
CPM is stable below 85 °C.
Fig. 3 X-ray photoelectron spectra (XPS) of Cu in CPM (A) and C1 (B).
for CPM to have highly efficient ROS catalytic properties. The
valence states of Mo and P in CPM and C1 were also calcu-
lated by bond valence sum (Tables S7 and S8†). The results
show that all Mo and P are +6 and +5 in both CPM and C1,
which was confirmed by the results of the XPS experiment
(Fig. S12†).29,30
Further investigation using X-ray photoelectron spectra
(XPS) has been carried out to detect the valences of Cu, Mo
and P. As shown in Fig. 3A, there are two broad peaks with a
shoulder peak located at 933 and 953 eV, which were
assigned to Cu2p3/2 and Cu2p1/2, respectively.27 The fitted
ROS are considered to be a major component accounting
for the antimicrobial properties of many compounds.31,32 Re-
cently, it has been reported that transition metal-substituted
POMs possess the ability of catalytic oxidation.33,34 Hence, it
is likely that they synergize with Cu ions to further enhance
antibacterial activity. The effect of CPM on mediated ROS gen-
eration was therefore investigated by a dichlorofluoroscein
(DCF) assay. DCF is a fluorescent marker derived from the re-
action of non-fluorescent 2′,7′-dichlorofluorescein (DCFH)
with ROS in the presence of horseradish peroxidase (HRP),
which can indicate the total output of ROS from the system.35
As shown in Fig. 4, the fluorescence intensity of CPM and C1
are higher than that of the control, indicating that the produc-
tion of ROS with CPM and C1 is greater than without them.
Furthermore, the fluorescence intensity of CPM is 1.5–2 times
higher than that of C1, which confirms that the dinuclear Cu
cluster of CPM has a stronger catalytic capacity than the
single-core Cu of C1. Interestingly, as shown in the inset of
Fig. 4, the experimental group with Cu2+ produced signifi-
cantly less ROS, even lower than that of the control group.
This phenomenon may be attributed to the interaction
curves in Fig. 3A (dashed lines) suggest that Cu2+ (2p3/2
,
,
933.9 eV; 2p1/2, 953.9 eV) and Cu+ (2p3/2, 932.5 eV; 2p1/2
27
952.5 eV) are involved in the peaks of Cu2p
.
These results
indicate that Cu ions in the +2 and +1 valence states coexist
in the Cu clusters of CPM. The peak style of C1 is similar to
that of CPM, as shown in Fig. 3B, indicating that Cu ions also
exist in C1 with mixed valence states of +1 and +2. The va-
lence of Cu in CPM and C1 was further calculated by using
the crystallographic data (Tables S2 and S5†), XPS (Fig. 3),
P
and bond valence sums ( s) (Fig. S10 and Fig. S11†),
according to reported methods.28 The calculation results
show that the average valence of Cu(1) is 1.6216, and that of
Cu(2) is 1.7740 in CPM (Tables S7 and S8†). These calcula-
tions are basically consistent with the data obtained from the
XPS experiments (Fig. 3A). Therefore, the existence of a mixed
valence state in the dinuclear Cu clusters makes it possible
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min, although the instantaneous growth rates of both the
CPM group and C1 group were increasing, the growth rate of
the CPM group was slower than that of C1. Then, from 400
to 800 min, the growth rate of the CPM group reduced, and
the growth rate of C1 continued to rise. From 600 to 800
min, the turbidity of C1 remained higher than that of the
group with CPM. These results reveal that both CPM and C1
can inhibit the growth of E. coli, and that CPM is more
efficient.
Conclusions
In this study, two linear Cu substituted phosphomolybdate
Fig. 4 Fluorescence intensity of DCF (λex = 485 nm, λem = 650 nm) by
CPM, C1, Cu2+, Cu2+ + GSH and blank (inset, the expanded graph of
the fluorescence intensity in the range of 0 to 15) from 0 to 3000 min.
complexes,
(H2en)ijCuIJen)IJH2O)CuIJen)IJH2O)3]ijP2Mo5O23]
·5.5H2O (CPM) and [H2IJen)]2ijCuIJen)IJH2O)2]ijP2Mo5O 23]·3.5H2O
(C1), have been designed and synthesized successfully, with
both possessing Cu+ and Cu2+ ions in their structures. As
expected, both CPM and C1 can catalyze the production of
ROS efficiently and can inhibit the proliferation of E. coli to
some extent. In both cases, the catalytic and inhibitory effects
of CPM are superior, which may be due to the existence of di-
nuclear Cu clusters. Moreover, CPM has a ferromagnetic ef-
fect due to the presence of a certain amount of dinuclear
Cu2+ clusters. To our knowledge, CPM represents the first
magnetic antibacterial POM and may have broad applications
in research into non-Ag antibacterial materials.
Conflicts of interest
There are no conflicts to declare.
Fig. 5 Inhibition effect on the growth of E. coli with CPM or C1 in the
growth media.
Acknowledgements
This work was supported by the Natural Science Foundation
of China (Grants 21573056, 21771053, 21701040, 21771054,
20771034 and 21401042), the National Basic Research Pro-
gram of China (2016YFA0200700), the National Natural Sci-
ence Foundation of China (No. 21472029 and 21773041), the
Research Foundation for Advanced Talents of Shanxi Province
(1800006003) and the Research Innovation program of Tai-
yuan Institute of Technology (GK2018049 and GK2018085).
between Cu2+ and the HRP enzyme, which deactivates it. In
fact, in certain microenvironments, bacteria can secrete a con-
siderable number of proteins, polypeptides and chelators,
which may coordinate with Cu2+ and make it lose its catalytic
position.33 We used glutathione (GSH), a short polypeptide
commonly found in organisms, to coordinate with Cu2+ and
found that the production of ROS was totally suppressed.
Therefore, the combination of a Strandberg-type fragment
and Cu ions not only contributes to the synergistic production
of ROS, but also protects the Cu catalytic centers from the
interference of external proteins and chelators.
The antibacterial activity of CPM was tested by using a ki-
netic growth assay.36 CPM, C1 and control groups were incu-
bated with E. coli in LB broth. Bacterial growth was studied
by visual observation as indicated by turbidity, with lack of
turbidity corresponding to low bacterial growth.37 As shown
in Fig. 5, in the first 250 min, the growth curves of the group
with CPM and C1 are almost the same as the control group.
Afterwards, the turbidity of the control group increased rap-
idly and the intensity was obviously higher than that with
CPM or C1, indicating that the production of E. coli without
CPM or C1 is more than that with them. From 250 to 400
Notes and references
1 J. L. Huang, L. Q. Lin, D. H. Sun, H. M. Chen, D. P. Yang
and Q. B. Li, Chem. Soc. Rev., 2015, 44, 6330–6374.
2 G. J. Mi, D. Shi, M. Wang and T. J. Webster, Adv. Healthcare
Mater., 2018, 7, e1800103.
3 D. M. Aruguete, B. Kim, M. F. Hochella, Y. J. Ma, Y. W.
Cheng, A. Hoegh, J. Liu and A. Pruden, Environ. Sci.:
Processes Impacts, 2013, 15, 93–102.
4 J. W. Alexander, Surg. Infect.: Sel. Antibiot. Ther., 2009, 10,
289–292.
5 B. Peng, X. L. Zhang, D. G. A. L. Aarts and R. P. A. Dullens,
Nat. Nanotechnol., 2018, 13, 478–482.
6 K. Burridge, J. Johnston and T. Borrmann, J. Mater. Chem.,
2011, 21, 734–742.
This journal is © The Royal Society of Chemistry 2019
CrystEngComm, 2019, 21, 394–398 | 397

View Article Online
Communication
CrystEngComm
7 J. Gupta, J. Mohapatra and D. Bahadur, Dalton Trans.,
2017, 46, 685–696.
22 J. Zhao, D. Shi, L. Chen, Y. Li, P. Ma, J. Wang and J. Niu,
Dalton Trans., 2012, 41, 10740–10751.
8 P. Faller, C. Hureau and G. La Penna, Acc. Chem. Res.,
2014, 47, 2252–2259.
23 L. Yang, X. Ma, P. T. Ma, J. A. Hua and J. Y. Niu, Cryst.
Growth Des., 2013, 13, 2982–2989.
9 A. Singh and P. Sen, Phys. Chem. Chem. Phys., 2015, 17,
12708–12716.
24 D. E. J. Packiam and K. Vidyasagar, Dalton Trans., 2017, 46,
16102–16112.
10 S. Stankic, R. Cortes-Huerto, N. Crivat, D. Demaille, J.
Goniakowski and J. Jupille, Nanoscale, 2013, 5, 2448–2453.
11 R. J. Liu, Z. W. Xian, S. S. Zhang, C. H. Chen, Z. H. Yang, H.
Li, W. Q. Zheng, G. J. Zhang and H. B. Cao, RSC Adv.,
2015, 5, 74447–74456.
12 J. M. Granda, L. Donina, V. Dragone, D. L. Long and L.
Cronin, Nature, 2018, 559, 377–381.
13 A. Banerjee, B. S. Bassil, G. V. Roschenthaler and U. Kortz,
Chem. Soc. Rev., 2012, 41, 7590–7604.
25 J. Y. Niu, J. A. Hua, X. Ma and J. P. Wang, CrystEngComm,
2012, 14, 4060–4067.
26 J. Y. Niu, X. Ma, J. W. Zhao, P. T. Ma, C. Zhang and J. P.
Wang, CrystEngComm, 2011, 13, 4834–4837.
27 A. A. Dubale, C. Pan, A. G. Tamirat, H. Chen, W. Su, C.
Chen, J. Rick, D. W. Ayele, B. A. Aragaw, J. Lee, Y. Yang and
B. Hwang, J. Mater. Chem. A, 2015, 3, 12482–12499.
28 S. T. Zheng, J. Zhang, J. M. Juan, D. Q. Yuan and G. Y. Yang,
Angew. Chem., Int. Ed., 2009, 48, 7176–7179.
14 N. Fang, Y. M. Ji, C. Y. Li, Y. Y. Wu, C. G. Ma, H. L. Liu and
M. X. Li, RSC Adv., 2017, 7, 25325–25333.
29 Y. Zhang, L. Li, T. Sun, B. Liu, H. Hu and G. Xue, Inorg.
Chem., 2011, 50, 2613–2618.
15 C. H. Gong, X. H. Zeng, C. F. Zhu, J. H. Shu, P. X. Xiao, H.
Xu, L. C. Liu, J. Y. Zhang, Q. D. Zeng and J. L. Xie, RSC Adv.,
2016, 6, 106248–106259.
16 D. Y. Du, J. S. Qin, S. L. Li, Z. M. Su and Y. Q. Lan, Chem.
Soc. Rev., 2014, 43, 4615–4632.
17 J. L. Huang, L. Q. Lin, D. H. Sun, H. M. Chen, D. P. Yang
and Q. B. Li, Chem. Soc. Rev., 2015, 44, 6330–6374.
18 A. Bijelic, M. Aureliano and A. Rompel, Chem. Commun.,
2018, 54, 1153–1169.
19 M. Barsukova-Stuckart, L. F. Piedra-Garza, B. Gautam, G.
Alfaro-Espinoza, N. V. Izarova, A. Banerjee, B. S. Bassil, M. S.
Ullrich, H. J. Breunig, C. Silvestru and U. Kortz, Inorg.
Chem., 2012, 51, 12015–12022.
30 D. Yang, S. Li, P. Ma, J. Wang and J. Niu, Inorg. Chem.,
2013, 52, 8987–8992.
31 Z. Z. Liu, W. Guo, C. S. Guo and S. Q. Liu, RSC Adv., 2015, 5,
72872–72880.
32 H. Yin and P. S. Casey, RSC Adv., 2014, 4, 26149–26157.
33 J. S. Zhao, Y. Wang, J. W. Zhou, P. F. Qi, S. W. Li, K. X.
Zhang, X. Feng, B. Wang and C. W. Hu, J. Mater. Chem. A,
2016, 4, 7174–7177.
34 J. Fielden, J. M. Sumliner, N. Han, Y. V. Geletii, X. Xiang,
D. G. Musaev, T. Lian and C. L. Hill, Chem. Sci., 2015, 6,
5531–5543.
35 X. H. Wang, X. Y. Wang, C. L. Zhang, Y. Jiao and Z. J. Guo,
Chem. Sci., 2012, 3, 1304–1312.
20 P. Yang, B. S. Bassil, Z. Lin, A. Haider, G. Alfaro-Espinoza,
M. S. Ullrich, C. Silvestru and U. Kortz, Chem. – Eur. J.,
2015, 21, 15600–15606.
21 J. J. Lu, Y. Xu, N. K. Goh and L. S. Chia, Chem. Commn.,
1998, 2733–2734.
36 B. Zartl, K. Silberbauer, R. Loeppert, H. Viernstein, W.
Praznik and M. Mueller, Food Funct., 2018, 9, 1638–1646.
37 M. A. Haque, R. Imamura, G. A. Brown, V. R. Krishnamurthi,
I. I. Niyonshuti, T. Marcelle, L. E. Mathurin, J. Y. Chen and
Y. Wang, RSC Adv., 2017, 7, 56173–56182.
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