Confocal laser scanning microscope analysis of antimony porphyrin chromophore immobilized on silica-gel beads

Article abstract of DOI:10.1246/cl.2005.1484

Dihydroxoantimony(V) tetraphenylporphyrin chromophore (SbTPP) was immobilized on 3-aminopropyl-silica gel (NH₂-SiO₂) by the reaction of dihydroxoantimony [4-(N-succinimidyloxycarbonyl)phenyl] triphenylporphyrin with NH₂-Si

Full text of DOI:10.1246/cl.2005.1484

1484
Chemistry Letters Vol.34, No.11 (2005)
Confocal Laser Scanning Microscope Analysis of Antimony Porphyrin Chromophore
Immobilized on Silica-gel Beads
Jin Matsumoto,ꢀ Tomokazu Fuchikawa, Yasuhiro Komiya, Yoshiyuki Fueda,y Tomoko Matsumoto,
Tsutomu Shiragami, and Masahide Yasuda
Department of Applied Chemistry, Faculty of Engineering, University of Miyazaki, Gakuen-Kibanadai, Miyazaki 889-2192
yFuji Silysia Chemical Ltd., 16303-3, Kihara, Hichiya, Hyuga, Miyazaki 883-0062
(Received July 25, 2005; CL-050957)
Dihydroxoantimony(V) tetraphenylporphyrin chromophore
(SbTPP) was immobilized on 3-aminopropyl-silica gel (NH2–
SiO2) by the reaction of dihydroxoantimony [4-(N-succinimi-
dyloxycarbonyl)phenyl]triphenylporphyrin with NH2–SiO2.
Spectroscopic analysis of the complex by confocal laser scan-
ning microscope suggested the interaction of SbTPP with the re-
sidual amino group on SiO2. The photoreaction of the complex
with Et2NH induced the demetallation.
equivalent (a; 2–20 meq) of 1a to the amino group of the
NH2–SiO2 in the presence of imidazole to give the immobilized
complex (SbTPPCONH–SiO2; 2). The bond formation was
confirmed by FT-IR spectra that showed the appearance of
amide bond at 1630 and 1580 cmꢁ1
.
Absorption spectra of a bead of 2 were measured by micro-
scopic analysis on confocal laser scanning microscope (CLSM;
Olympus FV-300) equipped with a multi-spectrophotometer
(Seki Technotron, STFL-250). The Q band of porphyrins ap-
peared at 550 and 590 nm, which were very similar to that of di-
hydroxoantimony [4-(n-propylcarbamoyl)phenyl]triphenylpor-
phyrin (SbTPPCONHPr; 1b) in solution (552 and 595 nm, re-
spectively). The diameters (b cm) of a bead of 2 were measured
by CLSM. The values (A=b), which were obtained by the divi-
sion of the observed absorbances (A) at 552 nm by b, were plot-
ted against the value a, giving a good linear correlation until a
value reached to 12 meq, as shown in Figure 1. From the slope
(5:52 ꢂ 103 eqꢁ1ꢃcmꢁ1) of the plots, the immobilization yield
(ꢀ) of 1a on NH2–SiO2 was estimated to be 23.8%.7 Thus, the
loading amount (x mol/g) of SbTPP chromophore in 1 g of SiO2
can be calculated using x ¼ 2:53 ꢂ 10ꢁ3ꢀ ꢃ a.
Metalloporphyrin chromophores play important roles as en-
ergy-harvest pigments in natural photosynthesis1 and the photo-
sensitizer operating under visible light irradiation.2,3 It is well
known that dihydroxoantimony tetraphenylporphyrin halide
(SbTPP) has strong oxidation ability among the metalloporphy-
rin complexes prepared so far. On the other hand, silica-gel
(SiO2) has high transparency of visible light and binding ability
of the cationic chromophore by a Coulombic force and hydrogen
bonding. Therefore, we have prepared the photocatalysts by the
fixation of SbTPP on SiO2 to apply to the dechlorination,2 the
epoxidation,3 and sterilization.4 However, the binding force of
SbTPP chromophore to SiO2 was not so strong, since a Coulom-
bic force and hydrogen bonding were weak. So, we here immo-
bilized SbTPP chromophore on SiO2 beads through a covalent
bond.5
at 552 nm
80
60
40
20
0
80
60
40
20
0
19.8 meq
11.9
7.90
Ph
OH
5.93
Ph
HO
Ph
N
+
Ph
O
N
0
10
a / meq
20
Ph
HO
3.95
N
N
N
1.98
Sb
N
Sb
Ph
C
O
O
N
N
Sb
OH
Ph
N
N
N
N
OH
Ph
N
O
-
Ph
Br
OH
SbTPPCO2NSu (1a)
O
C
C
O
N
H
NH
2
N
H
SiO2
H2N
OH
( NH2 SiO2
)
OH
O
O
O
O
O
O
O
O
O
500
550
600
Wavelength / nm
650
Si
n
Si
Si
Si
Si
n
Si
Si
Imidazole
O
O
O
O
(2) n = 2 ~ 3
SbTPPCONH SiO2
Figure 1. Absorption spectra of a bead of 2 in various a values.
Inset shows the plots of A=b vs the a value.
Scheme 1. Synthetic route to SbTPPCONH–SiO2 (2).
Micrometer size of 3-aminopropyl-silica gel (NH2–SiO2, di-
The fluorescence spectra of a bead of 2 were remarkably dif-
ferent from that of 1b in solution; new broad emission appeared
near 630 nm (Figure 2a). It is deduced that the SbTPP chromo-
phores in the excited state interacted with other chromophores.
When the residual amino group on a bead of 2 was protected
by an acetylation with Ac2O, the new emission at 630 nm disap-
peared (Figure 2b). Therefore, the SbTPP chromophore interact-
ed with the residual amino moieties through hydrogen bonds. Ir-
respective of the acetylation, however, the spectral shape was
changed when more than 19.8 meq of SbTPP chromophore
ameter = 56.7 mm)6 with a sharp size distribution was selected
as a support of a chromophore. As the chromophore being
capable of linking with NH2–SiO2, we used an active ester,
SbTPPCO2NSu (1a) (Scheme 1). The 1a was prepared by the
reaction of N-hydroxysuccinimide with dihydroxoantimony(V)
(4-carboxyphenyl)triphenylporphyrin, which was prepared by
the reaction of SbBr3 with meso-(4-carboxyphenyl)triphenylpor-
phyrin followed by the treatment with Br2 and the subsequent
hydrolysis. The NH2–SiO2 was reacted with a given molar
Copyright ꢀ 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.11 (2005)
1485
a
1
b
c
19.8 meq
11.9
5 min
4
3
2
1
0
7.90
3.95
1.98
H2O
0.5
0
600
650
600
650
600
650
Wavelength / nm
700
Wavelength / nm
Wavelength / nm
Figure 2. Fluorescence spectra of a bead of 2 (a) before and (b) after acetylation. (c) Fluorescence spectral change of a bead of the
acetylated 2 in MeCN solution of 5 mmol/dm3 Et2NH under irradiation of a laser light at 543 nm.
was loaded. In this case, it is attributable to the interaction
between SbTPP chromophores.
ful tool for the analysis and photochemical reaction in micro-
region on beads.
The distance between aminopropyl groups was estimated as
follows. When 2.53 mmol/g of the amino groups were contained
on the NH2–SiO2, the composition ratio, SiO2:HO–Si–
C3H6NH2, is calculated to be 6.9:1. If the SiO2 moieties were ar-
ranged in two dimensions, the aminopropyl groups presumed to
be apart from 2–3 units of SiO2 each other. Therefore, the SbTPP
chromophores located at the distance enough to interact with the
residual amino moiety (Scheme 1).
This work was supported by a Grand-in-Aid for Scientific
Research on Priority Areas (417) from Ministry of Education,
Culture, Sports, Science and Technology (MEXT) of the Japan
Government.
References and Notes
1
D. Gust and T. A. Moore, in ‘‘The Porphyrin Handbook,’’ ed.
by K. M. Kadish, K. M. Smith, and R. Guilard, Academic
Press, New York (2000), Vol. 8, p 153.
For the photoreaction of microbeads, we used a microchan-
nel reactor (MCR)8,9 that consisted of a narrow channel (width
190 mm, depth 85 mm, length 6 cm) and a neck (width and depth
20 mm) located at the middle point of the channel. An MeCN
solution of Et2NH (5 mmol/dm3) was introduced with micro-
syringe pump into the MCR, where beads of the acetylated 2
(x ¼ 7:17 mmol/g) was packed (Figure 3). He–Ne laser irradia-
tion at 543 nm was performed on CLSM at the area of 30 mm
squares, which was the comparable size of the beads. As increase
of the irradiation time, the emissions from the surface of the cat-
alyst at 600 nm decreased and new emission at 630 nm increased
(Figure 2c). However, no spectral change was observed in
non-irradiated beads. New emission can be assigned to be
metal-free porphyrin chromophore (H2TPPCONH–SiO2) by
the comparison of the absorption and fluorescence spectra with
authentic sample. The immobilization through covalent bond
makes the metal exchange of the SbTPP on beads possible.
Free energy change for the electron transfer from Et2NH to
the excited singlet state of a bead of 2 was calculated to be neg-
ative (ꢁ0:34 eV) by a Rehm–Weller equation using the oxida-
tion potential of Et2NH (E1/2 ox ¼ 1:01 V vs Ag/Agþ)10 and
the reduction potentials and the excitation energy of SbTPP
chromophore.11 Therefore, the photoinduced electron transfer
from Et2NH to SbTPP chromophore caused the reduction from
SbV to SbIV to induce the demetallation from SbTPP chromo-
phore. Thus, a combination of CLSM with MCR will be power-
2
T. Shiragami, Y. Shimizu, K. Hinoue, Y. Fueta, K.
Nobuhara, I. Akazaki, and M. Yauda, J. Photochem. Photo-
biol., A, 156, 115 (2003).
3
4
T. Shiragami, R. Makise, Y. Inokuchi, J. Matsumoto, H.
Inoue, and M. Yasuda, Chem. Lett., 33, 736 (2004).
H. Yokoi, T. Shiragami, J. Hirose, T. Kawauchi, K. Hinoue,
Y. Fueda, K. Nobuhara, I. Akazaki, and M. Yasuda, World J.
Microbiol. Biotechnol., 19, 559 (2003).
5
6
C. E. Kibbey and M. E. Meyerhoff, Anal. Chem., 65, 2189
(1993).
Aminopropyl silica gel (NH2–SiO2): Fuji Silysia, Average
diameter (mm): 56.7, Area (m2/g): 272, Density (g/mL):
0.62, Content of NH2 (mmol/g): 2.53.
7
According to Lambert–Beer’s law (Eq 1) where A and b are
absorbance and light path-length in cm, respectively, the A=b
values are equal to the immobilized SbTPP concentration (c)
that was related to the mol number (x) of SbTPP chromo-
phore in 1 g of SiO2. If the mol absorptivity (") of a bead
of 2 is equal to that of 1b (1:48 ꢂ 104 dm3ꢃmolꢁ1ꢃcmꢁ1),
the value of A=b can be related to equivalent (a) to the
aminopropyl moiety by Eq 2 using the immobilization yield
(ꢀ) of 1a on NH2–SiO2. Therefore, the slope of Figure 1
can be represented by Eq 3, resulting that ꢀ is 23.8%. A ¼
"bc (Eq 1), A=b ¼ "c ¼ 1:57"ꢀa (Eq 2) where c ¼
1000Wx=V ¼ 2:53Wꢀa=V ¼ 1:57ꢀa, x ¼ 2:53 ꢂ 10ꢁ3ꢀa,
and W ¼ 0:62V. Slope ¼ 1:57"ꢀ (Eq 3), and ꢀ ¼
slope=ð1:57"Þ.
8
9
K. Sato, M. Tokeshi, H. Kimura, and T. Kitamori, Anal.
Chem., 73, 1213 (2001).
G. H. Seong and R. M. Crooks, J. Am. Chem. Soc., 124,
13360 (2002).
10 C. K. Mann, Anal. Chem., 36, 2424 (1964).
11 Y. Andou, T. Shiragami, K. Shima, and M. Yasuda, J.
Photochem. Photobiol., A, 147, 191 (2001). E1/2 red vs.
Ag/Agþ ¼ ꢁ0:73 V for [Sb(OH)2TPP]PF6 and E0{0
¼
Figure 3. Microscopic image of the acetylated 2 in a MCR
(left) and its CLSM fluorescence image (right).
2:08 V for 1b.
Published on the web (Advance View) September 28, 2005; DOI 10.1246/cl.2005.1484