Aerobic oxidation of thioglycol catalysed by metallophthalocyanine in an organic-inorganic hybrid vesicle “cerasome”

Article abstract of DOI:10.1016/j.inoche.2020.107866

A molecular assembly of a hydrophobized metallophthalocyanine derivative embedded in a cerasome, an organic–inorganic hybrid vesicle with a lipid bilayer and silica surface, was a potent catalyst for aerobic oxidation of thioglycol. The catalytic activity was higher than those in hexadecyl 2-hydroxy-3-chloropropyl phosphate vesicles, sodium dodecylsulfate micelles, ethanol, and benzene.

Full text of DOI:10.1016/j.inoche.2020.107866

Inorganic Chemistry Communications 115 (2020) 107866
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Aerobic oxidation of thioglycol catalysed by metallophthalocyanine in an
organic-inorganic hybrid vesicle “cerasome”
a
a
a
a
b
c
Guolin Zhang , Li Zhang , Dan Zhang , Qiuhua Wu , Yoshihiro Sasaki , Yoshio Hisaeda ,
d
d,⁎
a,⁎
Kazuma Yasuhara , Jun-ichi Kikuchi , Xi-Ming Song
a
b
c
Liaoning Key Laboratory for Green Synthesis and Preparative Chemistry of Advanced Materials, College of Chemistry, Liaoning University, Shenyang 110036, China
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
d
G R A P H I C A L A B S T R A C T
A graphical and textural abstract for the Table of contents entry.
A molecular assembly of a hydrophobized metallophthalocyanine derivative embedded in a cerasome, an organic-inorganic hybrid vesicle with a lipid bilayer and
silica surface, was a potent catalyst for aerobic oxidation of thioglycol.
A R T I C L E I N F O
A B S T R A C T
Keywords:
A molecular assembly of a hydrophobized metallophthalocyanine derivative embedded in a cerasome, an or-
ganic–inorganic hybrid vesicle with a lipid bilayer and silica surface, was a potent catalyst for aerobic oxidation
of thioglycol. The catalytic activity was higher than those in hexadecyl 2-hydroxy-3-chloropropyl phosphate
vesicles, sodium dodecylsulfate micelles, ethanol, and benzene.
Cerasome
Organic-inorganic hybrid vesicle
Aerobic oxidation of thioglycol
Catalytic activity
1
. Introduction
reactions for material and energy conversion and information proces-
sing. Until now, much effort has been paid to the development of in-
A lipid bilayer membrane is a basic structural component of bio-
telligent reaction fields inspired by self-assembled biological systems
using phospholipid liposomes and synthetic lipid vesicles as a
membranes, which provide
a platform for systematic chemical
⁎
Corresponding authors.
E-mail addresses: sasaki.yoshihiro.8s@kyoto-u.ac.jp (Y. Sasaki), yhisatcm@mail.cstm.kyushu-u.ac.jp (Y. Hisaeda), jkikuchi@ms.naist.jp (J.-i. Kikuchi),
songlab@lnu.edu.cn (X.-M. Song).
https://doi.org/10.1016/j.inoche.2020.107866
Received 25 December 2019; Received in revised form 1 March 2020; Accepted 1 March 2020
Available online 03 March 2020
1387-7003/ © 2020 Elsevier B.V. All rights reserved.

G. Zhang, et al.
Inorganic Chemistry Communications 115 (2020) 107866
Scheme 1. Synthesis of (2,9,16,23-tetrakis(dodecoxycarbonyl)phthalocyanato) zinc(II) (ZnPc) or cobalt(II) (CoPc).
membrane matrix in aqueous media [1–6]. As for the material con-
version in artificial lipid membranes, a membrane matrix that has
morphological stability should be employed. We have previously re-
ported that bilayer vesicles formed with a synthetic peptide lipid and a
were placed in a 500 mL round-bottomed flask and refluxed at 100 °C
for 12 h under stirring. The reaction mixture was diluted with 500 mL
distilled water and filtered through a glass sand funnel. The pH of the
filtrate was regulated to 2 with a 12 mol/L HCl aqueous solution to give
a dark blue cotton-shaped precipitate. The mixture allowed to stand
overnight and was then filtered through a glass sand funnel. The solid
was washed with 0.1 mol/L HCl, distilled water, acetone, and diethyl
ether, and then dried under vacuum to give Zn(II)-tcPc (or Co(II)-tcPc).
Zn(I1)-tcPc (4): yield: 23%. Co(I1)-tcPc (5): yield: 49%.
hydrophobized coenzyme derivative of vitamin B or B12 exhibited
6
significant morphological stability and effective catalytic performance
as artificial enzymes [7]. To further enhance the morphological stabi-
lity, we have recently developed cerasomes, lipid bilayer vesicles with a
silica surface, by introducing the concept of organic–inorganic hybrid
nanomaterials [8]. Although various unique characteristics of cera-
somes as compared with conventional lipid bilayer vesicles have been
identified, the potential of using cerasomes as catalytic reactors is un-
certain. In this communication, we report the preparation of a hybrid
cerasome with metallophthalocyanine reaction sites and its catalytic
performance for aerobic oxidation of thioglycol.
2.3. Synthesis of Zn(II)- or Co(II)-tcPc tetraacid chloride
A solution containing 1.13 g (0.0015 mol) of Zn(II)-tcPc (or 1.12 g
(0.0015 mol) of Co(I1)-tcPc), 5.5 mL (0.07 mol) of thionyl chloride, a
few drops of pyridine, and 50 mL of benzene was refluxed for 10 h
under stirring. The product was filtered off, washed with benzene, and
dried at 70 °C under vacuum to give Zn(II)-tcPc tetraacid chloride (or
Co(II)-tcPc tetraacid chloride). Zn(I1)-tcPc tetraacid chloride (6): yield:
93%. Co(I1)-tcPc tetraacid chloride (7): yield: 96%.
2
. Experimental
2
.1. Synthesis of Zn(II) or Co(II)-4,4′,4″,4″′-tetraamide phthalocyanine
(
Zn(II)-taPc or Co(II)-taPc)
2
.4. Synthesis of (2,9,16,23-tetrakis(dodecoxycarbonyl) phthalocyanato)
The metallophthalocyanines were synthesized according to a lit-
zinc(II) (ZnPc) or cobalt(II) (CoPc)
erature method [9]. 5.0 g (0.025 mol) of trimellitic anhydride (1),
1
0
5.0 g (0.25 mol) of urea, 0.015 mol of the metal salt (ZnCl
2
or CoCl
2
),
A solution containing 1.0 g (0.0012 mol) of Zn(II)-tcPc tetraacid
chloride (or 0.98 g (0.0012 mol) Co(II)-tcPc tetraacid chloride), 2.3 g
(0.012 mol) of dodecanol, a few drops of pyridine, and 50 mL of an-
hydrous benzene was refluxed for 15 h under stirring. The mixture was
filtered through a glass sand funnel. The precipitate was washed with
chloroform until the filtrate was colourless. The filtrate was combined
and concentrated by rotary evaporator to obtain a blue-black solid,
which was dried under vacuum. The product was purified by column
chromatography with silica gel (CH CH OH/CHCl = 3:1 v/v). ZnPc
−
4
.5 g (4.0 × 10
mol) of ammonium molybdate, and 75 mL of ni-
trobenzene were placed in a 200 mL round-bottomed flask and main-
tained at 150–170 °C for 3 h under stirring. The reaction mixture was
filtered to give a blue-black solid, which was washed with 100 mL of
methanol. The crude product was soaked in 100 mL of 6 mol/L HCl
aqueous solution under stirring for 1 h and then filtered. The procedure
was repeated three times. The product was washed with distilled water,
methanol, and diethyl ether and then dried under vacuum to give the
product as a blue-black solid. Zn(I1)-taPc (2): yield: 82%. Co(I1)-taPc
3
2
3
(8): yield: 5.1%. CoPc (9): yield: 15.3%. The reaction route is shown in
(
3): yield: 86%.
Scheme 1.
2
.2. Synthesis of Zn(II)-4,4′,4″,4″′-tetracarboxy phthalocyanine (Zn(II)-
2.5. Preparetion of hybrid cerasome
tcPc or Co(II)-tcPc)
The hybrid cerasome was prepared from a cerasome-forming lipid,
α
5
.0 g of Zn(II)-taPc (or Co(II)-taPc) and 200 mL of 50% KOH(aq)
N,N-dihexadecyl-N -(6-((3-triethoxysilyl)propyldimeth-ylammonio)
2

G. Zhang, et al.
Inorganic Chemistry Communications 115 (2020) 107866
2
.53%; N, 14.75%.
3.3. Synthesis of Zn(II)- or Co(II)-tcPc tetraacid chloride
In the IR spectrum of Zn(I1)-tcPc tetraacid chloride (6), the peak at
−1
1
716 cm
comes from the C]O stretching vibration of -COCl seg-
−1
ment. The peaks at 1637, 1506, 1471, 1082, 777, 678 cm
are as-
signed to the characteristic absorption of phthalocyanine macrocycle.
Anal. calcd for C36 Cl Zn: C, 52.23%; H, 1.46%; N, 13.54%.
H
12
N
8
O
4
4
Found: C, 52.59%; H, 1.27%; N, 13.29%. In the IR spectrum of Co(I1)-
−1
tcPc tetraacid chloride (7), the peak at 1701 cm comes from the C]
O stretching vibration of eCOOH segment. The peaks at 1636, 1521,
−
1
1
476, 1088, 744, 678 cm
are assigned to the characteristic absorp-
tion of phthalocyanine macrocycle. Anal. calcd for C36
H
12
N
8
O
4
Cl Co:
4
C, 52.65%; H, 1.47%; N, 13.64%. Found: C, 52.43%; H, 1.51%; N,
1
3.35%.
3.4. Synthesis of ZnPc or CoPc
−1
In the IR spectrum of ZnPc (8), the peak at 1700 cm comes from
the C]O stretching vibration of eCOOC12H25 segment. The peaks at
−
1
1
625, 1577, 1387, 1090, 737 cm
are assigned to the characteristic
1
absorption of phthalocyanine macrocycle. The H NMR spectrum of
ZnPc (8) is shown in Fig. 2A. The peak at 0.87 ppm is assigned to
Fig. 1. Structures of cerasome-forming lipid (CL) and metallophthalocyanine
protons a in the eCH segments. The peaks at 1.26–1.91 ppm are as-
3
(
MPc) derivatives and a schematic image of a hybrid cerasome.
signed to protons b in the e(CH
2
)
10CH
3
2
segments. The peak at
4
7
.03 ppm is assigned to protons c in the eCH
Oe segments. The peak at
hexanoyl)glycinamide bromide (CL) [10] and a hydrophobized me-
tallophthalocyanine derivative (MPc), (2,9,16,23-tetrakis(dodecox-
ycarbonyl)phthalocyanato)cobalt(II) (CoPc) or (2,9,16,23-tetrakis(do-
decoxycarbonyl)phthalocya-nato) zinc(II) (ZnPc) (Fig. 1). In a glass
vessel, appropriate amounts of CL and MPc were dissolved in chloro-
form and evaporated to give a homogeneous mixture. This mixture was
.26 ppm is assigned to protons d in the Ph-H segments. Anal. calcd for
C
84
H
112
N
8
O Zn: C, 70.69%; H, 7.91%; N, 7.85%. Found: C, 70.51%; H,
8
7
1
.64%; N, 7.71%. In the IR spectrum of CoPc (9), the peak at
−1
716 cm comes from the C]O stretching vibration of eCOOC12
H
25
−1
segment. The peaks at 1626, 1491, 1365, 1094, 729 cm are assigned
1
to the characteristic absorption of phthalocyanine macrocycle. The H
dispersed
in
2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonate
NMR spectrum of CoPc (9) is shown in Fig. 2B. The peak at 0.88 ppm is
(
HEPES) buffer (25 mM, pH 7.0) by vortex mixing and followed by
assigned to protons
a
in the eCH
3
segments. The peaks at
sonication with a groove-type sonicator at 100 W power for 10 min to
give a translucent cerasome solution.
1
.26–1.95 ppm are assigned to protons b in the e(CH
2
)
10CH segments.
3
The peak at 3.64 ppm is assigned to protons c in the eCH Oe segments.
2
The peak at 7.26 ppm is assigned to protons d in the Ph-H segments.
Anal. calcd for C84 Co: C, 71.01%; H, 7.94%; N, 7.89%. Found:
C, 71.18%; H, 7.72%; N, 7.67%.
3
. Results and discussion
.1. Synthesis of Zn(II)-taPc or Co(II)-taPc
In the IR spectrum of Zn(I1)-taPc (2), the peak at 1668 cm comes
H
112 8 8
N O
3
3.5. Preparetion of hybrid cerasome
−1
from the C]O stretching vibration of eCOeNH segment. The peaks at
are assigned to the char-
acteristic absorption of phthalocyanine macrocycle. Anal. calcd for
Zn: C, 57.65%; H, 2.69%; N, 22.41%. Found: C, 57.35%;
2
The hydrodynamic diameter of the hybrid cerasome evaluated by
−
1
1
615, 1525, 1351, 1092, 767, 713 cm
dynamic light scattering measurements was 500 ± 25 nm. Optical
microscopy images of hybrid cerasomes formed with CL and ZnPc are
shown in Fig. 3. The cerasome particles were observed in both phase
contrast mode and fluorescence mode using an optical light filter U-
MWU2 (λex, 330–380 nm; λem, > 450 nm). A similar particle image
was also observed in phase contrast mode for the hybrid cerasomes
containing 1–5 mol% of non-fluorescent CoPc. Although the image of
MPc-free cerasomes was also confirmed by phase contrast microscopy,
no particles were detected in the fluorescence mode. Because the MPc
derivatives were insoluble in water, the results indicated that CL and
MPc formed the corresponding hybrid cerasomes.
C
36
H
20
N
O
12 4
H, 2.74%; N, 21.86%. In the IR spectrum of Co(I1)-taPc (3), the peak at
−
1
1
659 cm
comes from the C]O stretching vibration of eCOeNH
2
are
−1
segment. The peaks at 1618, 1516, 1324, 1083, 771, 738 cm
assigned to the characteristic absorption of phthalocyanine macrocycle.
Anal. calcd for C36
H
20
N
12
4
O Co: C, 58.15%; H, 2.71%; N, 22.61%.
Found: C, 58.42%; H, 2.89%; N, 22.38%.
3.2. Synthesis of Zn(II)-tcPc or Co(II)-tcPc
The microenvironment around the MPc in the cerasomes was
evaluated by electronic spectroscopy. The UV–vis absorption spectrum
of hybrid cerasomes formed with CL and CoPc is shown in Fig. 4A. The
absorption maximum at 675 nm was assigned to the monomeric CoPc
species, based on our previous report that a MPc, (2,9,16,23-tetrakis
(propoxy-carbonyl) phthalocyanato) cobalt(II), is present as a monomer
with a maximum absorption at 680 nm in benzene and the aqueous
vesicle formed with hexadecyl 2-hydroxy-3-chloropropyl phosphate
(HHP) or as a dimer with broad absorption at 620 nm in ethanol and a
aqueous micelle of sodium dodecyl sulfate (SDS) [11].
In the IR spectrum of Zn(I1)-tcPc (4), the peak at 1705 cm−1 comes
from the C]O stretching vibration of eCOOH group. The peaks at
−
1
1
610, 1332, 1086, 765, 737 cm
are assigned to the characteristic
Zn: C, 57.34%; H, 2.14%; N, 14.86%. Found: C, 57.25%; H,
absorption of phthalocyanine macrocycle. Anal. calcd for
C
36
H
16
N
O
8 8
2
.42%; N, 14.37%. In the IR spectrum of Co(I1)-tcPc (5), the peak at
−1
1
705 cm comes from the C]O stretching vibration of eCOOH group.
−1
The peaks at 1613, 1383, 1094, 785, 744 cm
are assigned to the
characteristic absorption of phthalocyanine macrocycle. Anal. calcd for
C
36
H
16
N
8
O
8
Co: C, 57.84%; H, 2.16%; N, 14.99%. Found: C, 57.56%; H,
The ZnPc in the cerasomes showed fluorescence with an emission
3

G. Zhang, et al.
Inorganic Chemistry Communications 115 (2020) 107866
Fig. 2. 1H NMR spectra of ZnPc (A) and CoPc (B) in CDCl
.
3
maximum at 704 nm (Fig. 4B). Since the maximum emission wave-
length of ZnPc depends on the solvent polarity, we can evaluate the
microenvironmental polarity around ZnPc in the cerasomes. Thus, it
became apparent that the cerasomes provided a hydrophobic micro-
environment similar to that in dioxane for ZnPc. This is comparable to
the HHP vesicular system in which ZnPc was placed in a polar micro-
environment similar to that in benzene and the emission maximum was
680 nm. The results indicated that MPc molecules were distributed
homogeneously in a hydrophobic region of the cerasomes without the
formation of aggregates.
3.6. Catalytic properties of hybrid cerasome
MPc compounds are synthetic aromatic metal complexes that
Fig. 3. Optical microscopy images of hybrid cerasomes formed with CL (1.0 mmol dm−3) and ZnPc (0.05 mmol dm−3) in HEPES buffer (25 mmol dm−3, pH 7.0) at
2
5 °C: (A) phase contrast mode, (B) fluorescence mode.
4

G. Zhang, et al.
Inorganic Chemistry Communications 115 (2020) 107866
Fig. 4. UV–vis spectra of CoPc hybrid cerasome (A) and fluorescence spectra of ZnPc hybrid cerasome (B) in HEPES buffer (25 mmol dm−3, pH 7.0) at 25 °C: [CL],
−
3
−3
1
.0 mmol dm ; [MPc], 0.01 mmol dm
.
possess catalytic performance towards a wide variety of reactions
12,13]. Mercapto compound can be oxided to produce disulfides as:
RSH + O → 2RSSR + 2H O. The oxidation can be catalysed by MPc
To study the catalytic activity of CoPc hybrid cerasomes further, we
evaluated the reactivity of CoPc for the aerobic oxidation of thioglycol
in various media. As shown in Fig. 5B, the catalytic activities increased
in the following order: ethanol, benzene, SDS micelle, HHP vesicle, and
cerasomes; the CoPc hybrid cerasomes exhibited the highest activity
among CoPc in various reaction media. As mentioned above, the CoPc
molecules were embedded as monomer species in a hydrophobic region
of the cerasome. It is well known that solubility of oxygen is higher in
apolar solvents than in polar solvents. Thus, the higher catalytic activity
of the CoPc hybrid cerasomes is probably because of the increase in the
local concentration of catalytically active monomeric CoPc and oxygen
in the microenvironment provided by the cerasomes.
[
4
2
2
complexes. The reaction has significance not only to clarify the cata-
bolic mechanism of sulfhydryl compounds in biological system but also
to develop novel active deodorant catalysts in industrial fields. On these
grounds, we evaluated the catalytic activity of hybrid cerasomes formed
with CL and CoPc for the aerobic oxidation of a sulfhydryl compound.
Thioglycol was the select sulfhydryl compound and the oxidation pro-
duct was diethyl disulfide. The oxidation reaction was followed by
oxygen consumption with a Warburg respirometer [9,11].
Fig. 5A shows time courses of oxygen consumption for the aerobic
oxidation of thioglycol in cerasome, as prepared or after incubation
overnight at room temperature, in the presence and absence of CoPc.
Although the non-catalytic oxidation of thioglycol by dissolved oxygen
proceeded gradually in CoPc-free cerasomes, we observed extremely
high catalytic activity of hybrid cerasomes containing CoPc. We have
previously clarified that the development of a siloxane network on the
cerasome surface depends on the incubation time after the preparation
of the cerasomes; that is, the siloxane network is not well developed in
freshly prepared cerasomes but developed well, although not com-
pletely, after incubation overnight at room temperature, based on the
surfactant resistance behaviour of the cerasomes [10]. The degree of
development of the siloxane network on the cerasome surface only had
a small effect on the catalytic activity of CoPc hybrid cerasomes. The
results suggest that morphologically stable cerasomes can provide an
effective reaction field similar to that provided by conventional lipid
bilayer vesicles, even if the membrane surface of the cerasomes is
covered with an inorganic siloxane network.
4. Conclusion
In summary, organic-inorganic hybrid vesicles were prepared by the
combination of a cerasome-forming lipid and a metallophthalocyanine
derivative. The hybrid cerasomes containing CoPc showed a marked
improvement in catalytic activity for the aerobic oxidation of thioglycol
compared with those in other reaction media, such as conventional
aqueous molecular assemblies and organic solvents. Thus, morpholo-
gically stable cerasomes have the potential to provide an effective re-
action field for various catalytic conversions.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Fig. 5. Time courses of oxygen consumption for the
aerobic oxidation of thioglycol in cerasomes in the
presence and absence of CoPc (A) and in various
reaction media containing CoPc (B) in HEPES
−3
buffer (25 mmol dm , pH 7.0) at 25 °C: [thio-
−
3
glycol],
570
mmol
dm
;
[CoPc],
−
3
−3
−3
0
1
.01 mmol dm ; [CL], 1.0 mmol dm ; [HHP],
−3
.0 mmol dm ; [SDS], 10 mmol dm . CoPc hy-
brid cerasome as prepared (○) and after incubation
overnight (●), freshly prepared CoPc-free cera-
somes (□) and after incubation overnight (■), HHP
vesicle (▴), SDS micelle (△), benzene (♦), and
ethanol (♢).
5

G. Zhang, et al.
Inorganic Chemistry Communications 115 (2020) 107866
Acknowledgements
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This research was financially supported by the National Natural
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