Magnetic Co(II) porphyrin nanospheres appending different substituent groups showing higher catalytic activities in cyclohexane

Article abstract of DOI:10.1166/jnn.2016.12615

Magnetic polymer nanospheres immobilizing Co(II) porphyrins with different substituents were prepared and exhibited satisfying size, morphology and magnetic responsiveness. These core/shell structured nanospheres showed much higher catalytic activities in hydroxylating cyclohexane than the non-supported Co(II) porphyrin analogues. Moreover, these magnetic nanospheres could be easily recovered and reused for up to five times with maintaining their high catalytic efficiencies, and thus are good candidates for high-efficient, environmental-friendly catalysts.

Full text of DOI:10.1166/jnn.2016.12615

Article
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Nanoscience and Nanotechnology
Vol. 16, 9843–9850, 2016
Copyright © 2016 American Scientific Publishers
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Printed in the United States of America
Magnetic Co(II) Porphyrin Nanospheres Appending
Different Substituent Groups Showing Higher
Catalytic Activities in Cyclohexane
Ping Zhao1ꢀ∗, Min-Chao Liu1, Min Zheng2, Shu-Fang Jin1, Ding-Tong Tang1,
Jia-Qi Lin1, Yan-Na Ma1, Jiong Chen1, and Hong-Jian Liu1
1School of Chemistry and Chemical Engineering, Guangdong Pharmaceutical University,
Zhongshan 528458, P. R. China
2School of Basic Courses, Guangdong Pharmaceutical University, Education Mega Centre,
Guangzhou 510006, P. R. China
Magnetic polymer nanospheres immobilizing Co(II) porphyrins with different substituents were pre-
pared and exhibited satisfying size, morphology and magnetic responsiveness. These core/shell
structured nanospheres showed much higher catalytic activities in hydroxylating cyclohexane than
the non-supported Co(II) porphyrin analogues. Moreover, these magnetic nanospheres could be
easily recovered and reused for up to five times with maintaining their high catalytic efficiencies,
and thus are good candidates for high-efficient, environmental-friendly catalysts.
IP: 193.93.193.77 On: Mon, 08 Oct 2018 15:05:15
Copyright: American Scientific Publishers
Keywords: Nanostructures, Chemical Synthesis, Electron Microscopy, Magnetic Properties.
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1. INTRODUCTION
and reused, etc. Among the supports that can be used
to immobilize metalloporphyrins, polystyrene derivatives
are often employed for their cheapness, ready avail-
ability, mechanical robustness, chemical inertness and
facile functionalization. Moreover, they can also pro-
vide suitable microenvironment for the “accommoda-
tion” of porphyrin catalytic centers.5–10 However, as for
polystyrene supported catalysts, troublesome centrifuga-
tion or filtration is needed to recycle them, which often
causes decreases in catalytic efficiency for the reused
catalysts.12ꢁ13 In overcoming such problems, magnetic
polymer microspheres arouse our attention due to their
specific surface properties, and relatively rapid and effort-
less magnetic separation.14–18 In this field, nanometer-
sized catalyst supports have recently attracted a great deal
of interest because of their high specific surface area
and outstanding stability as well as activity in the liquid
phase.19–24 The combination of the easy separation of mag-
netic polymer microspheres and the special properties of
nanometer-sized catalyst supports provides a good oppor-
tunity to design and synthesize novel polystyrene sup-
ported metalloporphyrins to mimic the function of P450
enzymes.
Interests in the field of synthetic metalloporphyrins to
mimic cytochrome P-450 monooxygenase (P-450) have
mushroomed since the pioneering work of Groves et al.
in 1979.1 The design, synthesis, structure, and catalytic
activity research of new catalysts as the analogues of the
active sites in metalloenzymes constitute a new research
area currently named “biomimetic catalysis.” In special,
studies involving catalytic oxidation mediated by metallo-
porphyrins have been increased in many areas such as in
the conversion of both saturated and unsaturated hydrocar-
bons to valuable fine chemicals and oxidation of drugs and
pollutants.2–4
Previous studies concluded that the catalysis in homo-
geneous systems is limited by the following drawbacks:
the porphyrin ring is liable to oxidative self-destruction
and the metalloporphyrins are subject to aggregation
through ꢀ–ꢀ interaction.3ꢁ5 Immobilization of metallo-
porphyrins on solid supports can offer several advantages
over traditional solution-phase chemistry, such as higher
stability, increased selectivity, being easily recovered
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2016, Vol. 16, No. 9
1533-4880/2016/16/9843/008
doi:10.1166/jnn.2016.12615
9843

Magnetic Co(II) Porphyrin Nanospheres Appending Different Substituent Groups Showing Higher Catalytic Activities
Zhao et al.
Meanwhile, comparative studies of catalytic efficiency
in the biomimetic oxidations of hydrocarbons using
metalloporphyrins as catalysts take us to conclude that
the efficiency is significantly affected by the factors such
as steric, metal centre and substituents on porphyrin ring
structures.5–8 However, so far research on the influential
factors has been mostly focused on the symmetric catal-
ysis while that on the asymmetric catalysis is relatively
rare.
In this paper, a series of magnetic polymer nanospheres
immobilizing Co(II) porphyrins appending p-OCH3,
p-H and p-Cl phenyl substituents (designated as
MPNSs(CoMP), MPNSs(CoPP) and MPNSs(CoCP),
respectively) were synthesized and characterized. The
magnetic polymer nanospheres are of core/shell struc-
ture in which the core is composed of numerous Fe3O4
particles and the shell is composed of a copolymer of
styrene and Co(II) porphyrin acrylates. The catalytic per-
formance of these nanospheres for cyclohexane hydroxy-
lation with molecular oxygen was compared with that of
non-supported Co(II) porphyrin acrylates. The effects of
peripheral subtituents to the catalytic efficiency using dif-
ferent oxidants were also discussed.
products were detected by Gas Chromatography (GC-
7890II) of Tianmei Co. Ltd.
2.3. Synthesis of Porphyrin Acrylates
Porphyrin acrylates including 5-(4-acryloxy)phenyl-
10,15,20-trimethoxyphenylporphyrin (APTMPP), 5-(4-acryl-
oxy)phenyl-10,15,20-triphenylporphyrin (APTPP) and
5-(4-acryloxy)phenyl-10,15,20-trichlorophenylporphyrin
(APTCPP) were similarly synthesized. A typical reaction
was conducted as follows. A mixture of 50 mL CHCl3
ꢀ
and 0.2500 g HPTMPP was stirred at 60 C. 2.0 g acrylyl
chloride dissolved in 5 mL CHCl3 was added dropwise.
After 2 h, the mixture was washed with 5% K2CO3 several
times and then evaporated to dryness. The crude material
was purified on a silica gel chromatograph using CHCl3
and petroleum ether as eluent. APTMPP was obtained as
a purple powder. Yield: 0.2128 g (79.2 wt%). ESI-MS
[CHCl3, m/z]: 775 ([APTMPP]+). 1H NMR (CDCl3,
500 MHz): ꢂ 8.86 (m, 8H, pyrrole ring), 8.20–8.22
(d, J = 8ꢃ5 Hz, 2H), 8.08–8.10 (d, J = 8ꢃ6 Hz, 6H),
7.51–7.52 (d, J = 8ꢃ5 Hz, 2H), 7.22–7.24 (d, J = 8ꢃ6 Hz,
6H), 6.74–6.78 (m, 1H), 6.45–6.51 (m, 1H), 6.10–6.12
(m, 1H), 4.03 (s, 9H), −2.73 (s, 2H, Pyrrole N–H).
APTPP was similarly prepared by replacing HPTMPP
by HPTPP. Yield: 76.5 wt%. ESI-MS [CHCl3, m/z]: 684
([APTPP]+). 1H NMR(CDCl3, 500 MHz): ꢂ 8.84–8.88
(m, 8H, pyrrole ring), 8.24–8.26 (d, J = 8ꢃ5 Hz, 2H),
8.20–8.22 (d, J = 8ꢃ3 Hz, 6H), 7.75 (m, 6H), 7.73 (m, 3H,
p), 7.53–7.54 (d, J = 8ꢃ5 Hz, 2H), 6.75–6.78 (m, 1H),
6.46–6.52 (m, 1H), 6.11–6.13 (m, 1H), −2.76 (s, 2H, Pyr-
role N–H).
2. EXPERIMENTAL DETAILS
2.1. Materials
The precursors, 5-(4-hydroxyl)phenyl-10,15,20-trimeth-
oxyphenylporphyrin (HPTMPP), 5-(4-hydroxyl) phenyl-
10,15,20-triphenylporphyrin (HPTPP) and 5-(4-hydroxyl)
phenyl-10,15,20-trichlorophenylporphyrin (HPTCPP) were
synthesized according to the literature [10]. All other
reagents were commercially available.
IP: 193.93.193.77 On: Mon, 08 Oct 2018 15:05:15
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APTCPP was also similarly prepared by replacing
HPTMPP by HPTCPP. Yield: 74.3 wt%. ESI-MS [CHCl3,
1
m/z]: 788 ([APTCPP]+). H NMR(CDCl3, 500 MHz): ꢂ
2.2. Physical Measurements
8.81–8.88 (m, 8H, pyrrole ring), 8.18–8.20 (d, J = 8ꢃ6 Hz,
2H), 8.09–8.10 (d, J = 8ꢃ5 Hz, 6H), 7.69–7.71 (d, J =
8ꢃ0 Hz, 6H), 7.52–7.53 (d, J = 8ꢃ6 Hz, 2H), 6.75–6.79
(m, 1H), 6.46–6.52 (m, 1H), 6.12–6.14 (m, 1H), −2.84 (s,
2H, Pyrrole N–H).
Elemental analysis (C, H and N) was carried out on a
Perkin-Elmer 240 Q elemental analyzer. ESI-MS was mea-
sured on a Thermo Finnigan LCQ DECA XP spectrometer.
1H NMR spectra were recorded on a Varian INOVA500NB
superconducting Fourier transform nuclear magnetic reso-
nance spectrometry with CDCl3 as solvent at room temper-
ature and TMS as internal standard. UV-Vis and IR spectra
were recorded on a Shimadzu UV-3150 spectrophotometer
and an Equinox 55 Fourier transformation infra-red spec-
trometer. The scanning electron microscopy (SEM) anal-
yses were performed with a JSM-6330F field emission
scanning electron microscope. The transmission electron
microscope (TEM) analyses were performed with a JEM-
2010HR transmission electron microscope. The particle
sizes were measured by a Mastersizer 2000 laser parti-
cle size analyzer. An Iris (HR) inductively coupled plasma
(ICP) -atomic emission spectrometer was used to deter-
mine the contents of Co(II) porphyrin acrylates and Fe3O4.
Magnetic measurements were performed by using a XL-
7 magnetic property measurement system. The catalytic
2.4. Synthesis of Metalloporphyrin Acrylates
Co(II) porphyrin acrylates including 5-(4-acryloxy)phenyl-
10,15,20-trimethoxyphenylporphyrin Co(II) (CoAPTMPP),
5-(4-acryloxy)phenyl-10,15,20-triphenylporphyrin Co(II)
(CoAPTPP)
and
5-(4-acryloxy)phenyl-10,15,20-
trichlorophenylporphyrin Co(II) (CoAPTCPP) were syn-
thesized by a reaction of Co(Ac)2 with corresponding
porphyrin acrylates. A typical reaction was conducted as
follows. 0.5 g Co(Ac)2 and 1 g NaCl dissolved in 40 mL
HAc were mixed with 20 mL CHCl3 solution of APTMPP
(0.3180 g). The mixture was stirred at 65 ꢀC for 8 h.
Then, the reaction mixture was washed with H2O and
1 M HCl several times. After washing to neutrality with
H2O, drying over anhydrous Na2SO4 and concentrating
via rotary evaporation, the residue was chromatographed
9844
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Zhao et al.
Magnetic Co(II) Porphyrin Nanospheres Appending Different Substituent Groups Showing Higher Catalytic Activities
on a silica gel coluCo using CHCl3 as eluent. Evaporation
of solvent afforded CoAPTMPP as a green powder. Yield:
93.5 wt%. (Found: C, 67.85; H, 4.71; N, 6.26%. Calc.
For C50H36N4O5Co ·3H2O: C, 67.79; H, 4.78; N, 6.32%).
CoAPTPP, yield: 94.2 wt%. (Found: C, 71.05; H,
4.43; N, 7.11%. Calc. For C47H30N4O2Co · 3H2O: C,
70.94; H, 4.56; N, 7.04%). ESI-MS [CHCl3, m/z]: 741
1
([CoAPTPP]+). H NMR(CDCl3, 500 MHz): ꢂ 8.82–8.88
1
ESI-MS [CHCl3, m/z]: 831 ([CoAPTMPP]+). H NMR
(m, 8H, pyrrole ring), 8.23–8.26 (d, J = 8ꢃ5 Hz, 2H),
8.20–8.22 (d, J = 8ꢃ3 Hz, 6H), 7.75 (m, 6H), 7.71 (m,
3H), 7.53–7.54 (d, J = 8ꢃ5 Hz, 2H), 6.75–6.78 (m, 1H),
6.42–6.52 (m, 1H), 6.11–6.13 (m, 1H).
CoAPTCPP, yield: 95.5 wt%. (Found: C, 62.68; H,
3.65; N, 6.28%. Calc. For C47H27N4O2CoCl3 · 4H2O: C,
(CDCl3, 500 MHz): ꢂ 8.85 (m, 8H, pyrrole ring), 8.18–
8.22 (d, J = 8ꢃ5 Hz, 2H), 8.08–8.10 (d, J = 8ꢃ6 Hz, 6H),
7.51–7.52 (d, J = 8ꢃ5 Hz, 2H), 7.22–7.24 (d, J = 8ꢃ6 Hz,
6H), 6.72–6.78 (m, 1H), 6.45–6.51 (m, 1H), 6.10–6.12
(m, 1H), 4.03 (s, 9H).
IP: 193.93.193.77 On: Mon, 08 Oct 2018 15:05:15
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Scheme 1. The strategy to prepare magnetic Co(II) porphyrin nanospheres.
J. Nanosci. Nanotechnol. 16, 9843–9850, 2016
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Magnetic Co(II) Porphyrin Nanospheres Appending Different Substituent Groups Showing Higher Catalytic Activities
Zhao et al.
Figure 1. SEM (left) and TEM (right) images of MPNSs(CoMP).
ꢀ
62.79; H, 3.70; N, 6.23%). ESI-MS [CHCl3, m/z]: 845
([CoAPTCPP]+). 1H NMR(CDCl3, 500 MHz): ꢂ 8.79–
8.86 (m, 8H, pyrrole ring), 8.16–8.19 (d, J = 8ꢃ6 Hz, 2H),
8.07–8.10 (d, J = 8ꢃ5 Hz, 6H), 7.69–7.71 (d, J = 8ꢃ0 Hz,
6H), 7.52–7.53 (d, J = 8ꢃ6 Hz, 2H), 6.74–6.79 (m, 1H),
6.43–6.51 (m, 1H), 6.12–6.14 (m, 1H).
vessel at 30ꢃ0 0ꢃ1 C.10 Using O2 as the oxidant, the
catalytic system consisted of metalloporphyrin or por-
phyrin nanospheres (the content of porphyrin were 1ꢃ29×
10−3 mmol), coreductant (3.0 mmol ascrobate, 4ꢃ0 ×
10−2 mmol thiosalicylic acid), substrate (5.55 mmol cyclo-
hexane), acetone/water (9:1, 10 mL) and pure oxygenase
(101 kPa). The products were detected after reaction for
3 h by Gas Chromatography using p-Chlorotoluene as an
internal standard.
2.5. Synthesis of MPNSs(CoMP), MPNSs(CoPP) and
MPNSs(CoCP)
The strategy to prepare these nanospheres is shown in
Scheme 1. A total of 10.0 g magnetic fluid, 12.0 g styrene,
The magnetic polymer nanospheres were recovered
from the catalytic system by separating in an external mag-
IP: 193.93.193.77 On: Mon, 08 Oct 2018 15:05:15
30 mg reactive Co(II) porphyrin acrylate, 3.0 g divinyl-
Copyright: American Scientific Publishers
netic field (0.42 T) after the reaction for 3 h. The hydroxy-
lation of cyclohexane catalyzed by recovered nanospheres
was performed under identical conditions.
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benzene (DVB), 1.5 g polyvinylpyrrolidone(K-30) (PVP
K-30), 0.30 g 2,2ꢁ-azo-bis-isobutyronitrile (AIBN) and
100 mL H2O/C2H5OH were mixed in a 250 mL round-
bottomed flask equipped with a reflux condenser. The
mixture was stirred at 70 ꢀC for 20–24 h under a N2 atmo-
sphere. The product was washed with 1 M HCl solution
to remove the unenclosed Fe3O4 and then with acetone to
remove the residual Co(II) porphyrin acrylate. The final
product was separated by applying an additional magnetic
3. RESULTS AND DISCUSSION
3.1. Characterization of Magnetic Microspheres
The morphology of the magnetic metalloporphyrin
nanospheres was obtained by SEM, with satisfying spheri-
cal uniformity and average diameter of ca. 300 nm. Mean-
while, the internal structures of these nanospheres were
given by TEM, from which one can clearly find the Fe3O4
magnetic core embodied in the chitosan shells. Figure 1
gives the SEM and TEM images of MPNSs(CoMP) and
Figure 2 shows the size histograms of these nanospheres.
ꢀ
field (0.42 T) and dried for 24 h at 60 C in vacuum.
2.6. Catalysis
Cyclohexane hydroxylation catalyzed by metallopor-
phyrins was carried out in a specially constructed reaction
(a)
(b)
(c)
Figure 2. Nanosphere size histograms of MPNSs(CoMP) (a), MPNSs(CoPP) (b) and MPNSs(CoCP) (c).
J. Nanosci. Nanotechnol. 16, 9843–9850, 2016
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Zhao et al.
Magnetic Co(II) Porphyrin Nanospheres Appending Different Substituent Groups Showing Higher Catalytic Activities
Table I. Contents of Co(II) porphyrin acrylates and Fe3O4 in the
nanaospheres.
Negligible difference was found between the nanospheres
with different metalloporphyrins.
Co(II) porphyrin acrylate/wt%a (%) Fe3O4/wt% (%)
The presence of metalloporphyrins in the microsphere
support was confirmed by solid state UV-Vis spectra as
well as ICP results of the catalysts. No substantial UV
spectra were observed with the blank magnetic chitosan
nanosperes. However, typical absorption spectra of Co(II)
porphyrin with Soret bands centered at ca. 480 nm and
428 nm, respectively, were observed in the solid state
UV-Vis spectra of MPNSs(CoPP) (Fig. 3). Similar results
were obtained for the other two nanospheres. The solid
state UV-Vis results ambiguously evidenced the exis-
tence of metalloporphyrin on the nanospheres. Further-
more, the contents of metalloporphyrins in the magnetic
nanospheres were calculated from the contents of Co,
which can be obtained using ICP. The contents of met-
alloporphyrins in microsphere were given in Table I. The
ICP results further confirmed the presence of metallopor-
phyrins in the nanospheres. Meanwhile, the contents of
magnetic cores, Fe3O4 in the nanospheres were similarly
calculated.
Catalyst
MPNSs(CoMP)
MPNSs(CoPP)
MPNSs(CoCP)
0.22
0.16
0.23
6.33
7.35
7.69
Note: awt% refers to the content of Co(II) porphyrin acrylates in the nanaospheres.
ꢀ
ꢀ
ꢀ
degrade at 260 C, 258 C and 262 C, respectively. This
demonstrates tꢀhat these catalysts are thermally stable up
to almost 260 C, exhibiting relatively high thermostabili-
ꢀ
ties. ꢀThe organic parts decompose completely at 483 C,
ꢀ
446 C, and 532 C for MPNSs(CoMP), MPNSs(CoPP)
and MPNSs(CoCP), respectively.
These nanospheres are superparamagnetic and have
excellent magnetic responsibility which is the key fac-
tor for their effortless recovery. Magnetic hysteresis loops
(Fig. 5) show that magnetic nanospheres MPNSs(CoMP)
exhibit superparamagnetic behavior with zero coerciv-
ity and remanence because the diameter of the mag-
netic Fe3O4 particles used in the preparation of these
nanospheres is about 9 nm which is smaller than the
critical particle size of Fe3O4 particles.16 Similar results
were obtained for the other two nanospheres. The satu-
ration magnetizations of these magnetic nanospheres are
almost the same, about 3.50 emu/g, which are lower
IR spectra of these nanospheres are given in Figure 4
and are very similar to each other. Characteristic bands of
styrene and Co(II) porphyrin acrylates are shown in the IR
spectra of all these nanospheres. For example, the bands in
the region of 3100–2900 cm−1, three peaks at 1601, 1491
and 1446. cm−1 and double peaks at 758 and 700 cm−1 are
IP: 193.93.193.77 On: Mon, 08 Oct 2018 15:05:15
clearly observed and can be attributed to the benzene rings
than that of Fe O nanoparticles. It could be explained
by the copolymer coating of the Fe O nanoparticles in
Copyright: American Scientific Publish3 er4s
in styrene. Two peaks at 1024 and 1670 cm−1 attributed to
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3
4
the bands of C–O and C O of Co(II) porphyrin acrylate,
respectively, are also observed. All these results suggest
that the shell of the nanospheres is composed of copolymer
of styrene and Co(II) porphyrin acrylates.
nanospheres.18
Furthermore, it was experimentally observed that these
nanospheres dispersed in water are rapidly attracted by
a conventional magnet placed close to the reaction ves-
sel (Fig. 6), demonstrating the efficacy of magnetic
separation.
Thermostabilities of the nanospheres have been
determined by using thermogravimetric analysis
(TGA). The TG curves give us the information that
MPNSs(CoMP), MPNSs(CoPP) and MPNSs(CoCP)
Figure 3. Solid state UV–Vis absorption spectra of MPNSs(CoPP)
(solid lines) and blank magnetic nanosperes (red dotted line) as well as
CoTPP (blue dash lines).
Figure 4. IR spectra of MPNSs(CoMP) (a), MPNSs(CoPP) (b) and
MPNSs(CoCP) (c).
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Magnetic Co(II) Porphyrin Nanospheres Appending Different Substituent Groups Showing Higher Catalytic Activities
Zhao et al.
Figure 7. Changes of the turnover numbers of MPNSs(CoMP) (ꢀ),
MPNSs(CoPP) (•) and MPNSs(CoCP) (ꢁ) calculated from the reaction
products with catalytic time.
Figure 5. Magnetic hysteresis loops of MPNSs(CoMP).
3.2. Hydroxylation of Cyclohexane Catalysis
3.2.1. The Optimum Catalytic Time
Co(II) porphyrin acrylates after reaction for 3 h are listed
in Table II. Controlled experiments using styrene-acrylic
acid copolymer microspheres or nanopheres with free por-
phyrins in the presence of Co(Ac)2 as catalysts were car-
ried out and did not lead to substantial product yields
(data not shown). From Table II, we can easily find that
the three types of nanospheres all have much higher cat-
alytic activities than non-supported Co(II) porphyrin acry-
lates. The total turnover numbers of the nanospheres are
about 200 times larger than those of non-supported Co(II)
The hydroxylation of cyclohexane catalyzed by these
nanospheres was investigated in the Co(II) porphyrin–O2–
ascrobate system. Usually cyclohexanol and cyclohexanone
are the main products of the oxidation of cyclohexane
in the matelloporphyrin–O2–ascrobate system under mild
conditions.10 The kinetic curves of turnover numbers for
MPNSs(CoMP), MPNSs(CoPP) and MPNSs(CoCP) are
shown in Figure 7, from which we can find that the curves
have a similar trend, enhancing rapidly and reaching max-
imum values after about 3 h. The turnover numbers are
porphyrin acrylates. As is well known, the hydrophobic
IP: 193.93.193.77 On: Mon, 08 Oct 2018 15:05:15
unchanged with a further increase in the reaction time.
Copyright: American Scientific Publishers
microenvironment produced by the protein chain folded
around the binding site of cytochrome P450 plays an
important role in the process of hydroxylating substrate.10
However, metalloporphyrins as models of cytochrome
P450 have limited catalytic activities to hydroxylate sub-
strate under mild conditions, which may be caused by the
lack of this hydrophobic microenvironment. It is believed
that the nanospheres provide suitable microenvironment
for the “accommodation” of porphyrin catalytic centers5–10
and thus remarkably enhance the catalytic capability of
Co(II) porphyrins.
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These results further suggest that the by-products which
come from the over-oxidation of cyclohexanol and cyclo-
hexanone in our reaction system are negligible and 3 h may
be the optimum reaction time in the experiments of cyclo-
hexane hydroxylation catalyzed by these catalysts.
3.2.2. The Greatly Enhanced Catalytic Efficiency of
Metalloporphyrin Nanospheres
The results of cyclohexane hydroxylation catalyzed by
the nanospheres (fresh and recovered) and non-supported
Figure 6. (a): Comparison of the magnetic and natural separation of MCSCoTPP from the liquid media; (b) Transmittance of MCSCoTPP monitored
by UV with and without magnetic field.
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Zhao et al.
Magnetic Co(II) Porphyrin Nanospheres Appending Different Substituent Groups Showing Higher Catalytic Activities
Table II. The catalytic performance of MPNSs(CoMP), MPNSs(CoPP),
MPNSs(CoCP) and Co(II) porphyrin acrylates to hydroxylate cyclohex-
ane after reaction for 3 h.
loss of magnetic responsiveness or morphological change
after recycle. Meanwhile, the UV-Vis and IR spectra of
these recovered nanospheres did not show any substantial
change compared with those of the fresh ones. The results
above provide strong evidence for the stable catalytic capa-
bilities and chemical properties of these catalysts.
Irrespective of their substituents, these magnetic
nanospheres immobilizing Co(II) porphyrin are excellent
potential candidates for recoverable and reusable cata-
lysts to model P450 enzymes. Moreover, MPNSs(CoMP)
exhibit the best catalytic activity among this type of
nanospheres.
Product (turnover number)c
Catalystsa
Runb Cyclohexanol Cyclohexanone
Total
MPNSs(CoMP)
1
2
3
4
5
51.7 (646)
50.2 (627)
51.5 (643)
52.4 (655)
51.3 (641)
25.3 (316)
23.6 (295)
23.8 (298)
21.7 (271)
24.0 (300)
77.0 (962)
73.8 (922)
75.3 (941)
74.1 (926)
74.3 (941)
MPNSs(CoPP)
MPNSs(CoCP)
1
2
3
4
5
45.3 (567)
43.0 (538)
44.1 (551)
45.6 (570)
42.9 (536)
23.5 (294)
22.1 (276)
21.2 (265)
20.7 (259)
23.1 (289)
68.8 (861)
65.1 (814)
65.3 (816)
66.3 (829)
66.0 (825)
4. CONCLUSIONS
1
2
3
4
5
35.8 (448)
34.5 (431)
35.1 (439)
35.2 (440)
34.6 (432)
17.5 (219)
16.7 (202)
17.2 (215)
16.9 (211)
17.0 (212)
53.3 (667)
51.1 (633)
52.3 (654)
52.1 (651)
51.6 (644)
We have prepared three types of novel magnetic polymer
nanospheres immobilizing Co(II) porphyrin appending dif-
ferent phenyl substituents and have investigated their
catalysis to hydroxylate cyclohexane. These core/shell
structured nanospheres are of an average diameter of
ca.200 nm and have good magnetic responsiveness. The
turnover numbers of these nanospheres to hydroxylate
cyclohexane are much larger than those of non-supported
Co(II) porphyrin acrylates under identical conditions and
follow the order of MPNSs(CoMP) >MPNSs(CoPP) >
MPNSs(CoCP).
CoAPTMPP
CoAPTPP
1
1
1
3.73 (2.89)
2.98 (2.31)
2.32 (1.79)
0.94 (0.72)
1.15 (0.89)
0.77 (0.59)
4.67 (3.61)
4.13 (3.20)
3.09 (2.38)
CoAPTCPP
Notes: aCo(II) porphyrin in the nanospheres and non-supported Co(II) porphyrin
acrylates is 0.08 ꢄmol and 1.29 ꢄmol, respectively. bThe recovery times of cataly-
sis; the non-supported Co(II) porphyrin cannot be recovered. cThe product (ꢄmol);
Turnover number = product(mol)/catalyst(mol).
Electron-donating groups on the periphery of porphyrins
3.2.3. The Influence of on Porphyrinato
can enhance the catalytic activity of the nanospheres.
IP: 193.93.193.77 On: Mon, 08 Oct 2018 15:05:15
Ring Structures
Copyright: American Scientific Publishers
Moreover, these magnetic nanospheres can be effectively
Interestingly, the turnover numbers of the three Dtyepleivseorefd by Ingenta
recovered and can retain their high catalytic activity after
nanospheres under identical conditions follow the order
of MPNSs(CoMP) > MPNSs(CoPP) > MPNSs(CoCP)
(Table II). It is supposed that the difference in catalytic
activity among these magnetic nanospheres is caused by
the difference of the phenyl substituents on the por-
phyrin core. Usually, existence of electron-donating phenyl
substituents in the meso-position of porphyrin, such as
–OCH3, will increase the electron density of center metal
ions. According to the theory about the catalytic cycle
of cytochrome P-450,6 the increase in electron density
of the center metal ion in metalloporphyrin is in favor
of reduction of the metal ion, and coordination and acti-
vation of dioxygen as well as formation of active inter-
mediate hypervalent metal–oxo species, and thus leads to
high catalytic activity of metalloporphyrin. Apparently, the
substituent effect also exists in the catalytic process of
magnetic nanospheres and the nanospheres with electron-
donating p-OCH3 on porphyrin are more efficient catalysts
than those with electron-withdrawing p-Cl groups.
being recycled five times. These results may facilitate the
design of high-efficient, environmental-friendly metallo-
porphyrin catalysts.
Acknowledgments: This work was financially sup-
ported by the National Nature Science Foundation of
China (21101033).
References and Notes
1. J. T. Groves and W. J. Kruper, J. Am. Chem. Soc. 101, 7613 (1979).
2. S. Ritter, Chem. Eng. News Archive 90, 7 (2012).
3. K. Mittra, S. Chatterjee, S. Samanta, and A. Dey, Inorg. Chem.
52, 14317 (2013).
4. C. Q. Ma, D. Xing, C. W. Zhai, J. W. Che, S. Y. Liu, J. Wang, and
W. H. Hu, Org. Lett. 15, 6140 (2013).
5. C. Monnereau, P. H. Ramos, A. B. C. Deutman, J. A. A. W. Elemans,
R. J. M. Nolte, and A. E. Rowan, J. Am. Chem. Soc. 132, 1529
(2010).
6. G. Huang, L. Q. Mo, J. L. Cai, X. Cao, Y. Peng, Y. A. Guo, and S.
J. Wei, Appl. Catal. B 162, 364 (2015).
7. J. Li, J. P. Lei, Q. B. Wang, P. Wang, and H. X. Ju, Electrochim.
Acta 83, 73 (2012).
3.2.4. The Recovery and Reuse of
8. F. Zadehahmadi, S. Tangestaninejad, M. Moghadam, V. Mirkhani,
I. M. Baltork, A. R. Khosropour, and R. Kardanpour, J. Solid State
Chem. 218, 56 (2014).
9. S. L. H. Rebelo, M. Linhares, M. M. Q. Simões, A. M. S. Silva,
M. G. P. M. S. Neves, J. A. S. Cavaleiro, and C. Freire, J. Catal.
315, 33 (2014).
Metalloporphyrin Nanospheres
It is notable that these catalysts can be completely recov-
ered and effectively reused although they are nano-sized.
As shown in Table II, these catalysts retain their high
turnover numbers after being reused five times. There is no
J. Nanosci. Nanotechnol. 16, 9843–9850, 2016
9849

Magnetic Co(II) Porphyrin Nanospheres Appending Different Substituent Groups Showing Higher Catalytic Activities
Zhao et al.
10. J. W. Huang, W. J. Mei, J. Liu, and L. N. Ji, J. Mol. Catal. A
170, 261 (2001).
17. F. X. Chen, R. Liu, S. W. Xiao, and C. T. Zhang, Mater. Res. Bull.
55, 38 (2014).
11. S. M. G. Pires, M. M. Q. Simões, C. M. S. Santos, S. L. H. Rebelo,
F. A. A. Paz, M. Graça P. M. S. Neves, and J. A. S. Cavaleiro, Appl.
Catal. B 160–161, 80 (2014).
18. J. M. Hong and Y. He, Desalination 332, 67 (2014).
19. A. C. S. Sekhar, K. Sivaranjani, C. S. Gopinath, and C. P. Vinod,
Catal. Today 198, 92 (2012).
12. A. Modak, J. Mondal, and A. Bhaumik, Appl. Catal. A 459, 41
(2013).
20. K. Nishioka, S. Horita, K. Ohdaira, and H. Matsumura, Sol. Energy
Mater. Sol. Cells 92, 919 (2008).
13. C. Eichholz, J. Knoll, D. Lerche, and H. Nirschl, J. Magn. Magn.
Mater. 368, 139 (2014).
21. K. Nishioka, T. Sueto, and N. Saito, Appl. Surface Sci. 255, 9504
(2009).
14. J. Han, Y. Zhuo, Y. Q. Chai, Y. Q. Yu, N. Liao, and R. Yuan, Anal.
Chim. Acta 790, 24 (2013).
22. W. Y. Xie, D. J. West, Y. Y. Sun, and S. B. I. Zhang, Nano. Energy
2, 742 (2013).
15. S. Ghasemi, M. Heidary, M. Faramarzi, and Z. Habibi, J. Mole.
Catal. 100, 121 (2014).
23. K. Rad-Moghadam and N. Dehghan, J. Mol. Catal. A 392, 97
(2014).
16. Y. X. Wang, H. Q. Sun, H. M. Ang, M. O. Tadé, and S. B. Wang,
J. Colloid Interface Sci. 433, 68 (2014).
24. S. Zakavi, A. G. Mojarrad, and S. Rayati, J. Mol. Catal. A
363–364, 153 (2012).
Received: 11 December 2014. Accepted: 21 November 2015.
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