Syntheses and characterization of porphyrins and their zinc complexes appending a multi-dentate ligand

Article abstract of DOI:10.1016/S0020-1693(01)00630-2

Porphyrins with a multi-dentate ligand have been prepared by a covalent binding of nitrilotriacetic acid (NTA) to meso-mono (ortho- or para-aminophenyl)-triphenylporphyrin. The equilibrium between the porphyrins and Zn²⁺ has been analyzed by ultra violet-visible (UV-Vis) and ¹H NMR spectroscopies and the porphyrins are found to form complexes with porphyrin/zinc ratios of 1:1 and 1:2. The zinc complexes with the porphyrin/zinc ratios of 1:1 and 1:2 have been prepared and characterized by UV-Vis, infrared (IR) and ¹H NMR spectroscopies. An accelerated zinc incorporation reaction into the porphyrin appending NTA at its ortho-phenyl group is reported.

Full text of DOI:10.1016/S0020-1693(01)00630-2

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Inorganica Chimica Acta 325 (2001) 29–35
Syntheses and characterization of porphyrins and their zinc
complexes appending a multi-dentate ligand
Yoshio Uemori *, Atsuko Kitamura, Hiroki Munakata, Hiroyasu Imai,
Shigeo Nakagawa
Faculty of Pharmaceutical Sciences, Hokuriku Uni6ersity, 3-Ho Kanagawa-machi, Kanazawa 920-1181, Japan
Received 30 May 2001; accepted 26 July 2001
Abstract
Porphyrins with a multi-dentate ligand have been prepared by a covalent binding of nitrilotriacetic acid (NTA) to meso-mono
(ortho- or para-aminophenyl)-triphenylporphyrin. The equilibrium between the porphyrins and Zn2+ has been analyzed by ultra
1
violet–visible (UV–Vis) and H NMR spectroscopies and the porphyrins are found to form complexes with porphyrin/zinc ratios
of 1:1 and 1:2. The zinc complexes with the porphyrin/zinc ratios of 1:1 and 1:2 have been prepared and characterized by UV–Vis,
1
infrared (IR) and H NMR spectroscopies. An accelerated zinc incorporation reaction into the porphyrin appending NTA at its
ortho-phenyl group is reported. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Porphyrins; Zinc complexes; Zinc incorporation reaction
techniques, zinc was selected as the metal because of its
diamagnetism.
1. Introduction
Studies on the model complexes with a binuclear
metal/heme center have received much attention in
relation to their biological interests. Among these,
meso-teraphenylporphyrin derivatives with a tri-dentate
ligand attached to the ortho-position of a meso-phenyl
group have been synthesized as models for cytochrome
c oxidase [1–12]. These studies have focused on the
properties of the binuclear complexes synthesized, how-
ever, there are few reports on the properties of the
porphyrin ligands. As model complexes with a binu-
clear metal/heme center, we have prepared the model
compounds by a covalent binding of a multi-dentate
ligand (nitrilotriacetic acid (NTA), H3nta) to meso-
mono(o- or p-aminophenyl)-triphenylporphyrin (Fig.
1). In our model porphyrins, the none-heme site is
tri-dentate ligand and is suitable for metals favoring
four coordination such as Zn2+ and Cu2+. To gain
structural information for the metal complexes of the
porphyrins using nuclear magnetic resonance (NMR)
* Corresponding author.
E-mail address: y-uemori@hokuriku-u.ac.jp (Y. Uemori).
Fig. 1. Structure of the porphyrins and their zinc complexes.
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00630-2

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Y. Uemori et al. / Inorganica Chimica Acta 325 (2001) 29–35
Here, we report the synthesis and characterization of
phenyl)-triphenylporphyrin [16] were prepared by the
published methods.
porphyrins appending a multi-dentate ligand; equilibria
between the porphyrins and zinc acetate; the synthesis
of zinc complexes with porphyrin/zinc ratios of 1:1 and
1:2; the preliminary kinetic studies of zinc incorpora-
tion reaction into the porphyrins.
2.3. HntaEt2
A solution of triethyl nitrilotriacetate (25.5 g, 0.0926
mol) in EtOH (70 ml) was added to a water (30 ml)
containing KOH (0.0926 mol). The solution was
refluxed for 1 h and the solvent was removed by
evaporation. The residue was dissolved in water and
pH of the solution was adjusted to approximately 9
with NaHCO3, then unreacted triethyester of NTA was
extracted with ether. After adjusting pH of the aqueous
layer to approximately 3 by dilute HCl, the aqueous
layer was extracted with ether. The extract was distilled
under reduced pressure. Pale yellow oil (6.0 g, 26%) was
2. Experimental
2.1. Measurements
Infrared (IR) spectra were recorded on a Perkin–
Elmer spectrum GX Fourier transform-infrared (FT-
IR) spectrophotometer. Ultra violet–visible (UV–Vis)
spectra were recorded on a Hitachi 340 spectrophoto-
meter. Temperatures of the solutions were maintained
by the use of a constant-temperature circulation pump
(Neslab Model RTE-8) and a variable-temperature cell
holder (Hitachi).
1
obtained, b.p. 205 °C (6 mmHg). H NMR (CDCl3):
l=8.7 (br, 1H, ꢀCOOH), 4.22 (q, J=7.3 Hz, 4H,
ꢀCH2ꢀ), 3.62 (s, 4H, ꢀNCH2COOꢀ), 3.56 (s, 2H,
ꢀNCH2ꢀ), 1.29 (t, J=7.3 Hz, 6H, ꢀCH3).
Job’s experiments were conducted in methanol at
20 °C by mixing different volumes of equimolar solu-
tions (ca. 50 mM) of zinc acetate and porphyrins. The
mixtures were allowed to equilibrate for up to a week
prior to recording the spectrum. The absorbances mea-
sured at a given wavelength for mixtures containing
various ratios of porphyrins and Zn2+ with a constant
total concentration (c=[Zn2+]+[porphyrin]) have
been used to calculate the expression
2.4. H2-1a
A solution of meso-mono(o-aminophenyl)-triphenyl-
porphyrin (300 mg, 0.476 mmol) in CH2Cl2 (100 ml),
HntaEt2 (354 mg, 1.431 mmol) in CH2Cl2 (30 ml), and
1,3-dicyclohexylcarbodiimide (DCC, 354 mg, 1.716
mmol) in CH2Cl2 (30 ml) was mixed and the solution
was stirred at room temperature for 3 h. The solvent
was removed by evaporation. The residue was dissolved
in CHCl3, the resulting mixture was purified on silica
gel (3×25 cm) using CHCl3 as eluent. The product was
recrystallized from benzene–hexane. The yield was 367
mg (89%). UV–Vis [umax nm in CHCl3 (log m)]: 419
(5.64), 516 (4.26), 550 (3.84), 590 (3.77), 647 (3.72).
F(x)=Aobs/c−AporX(1−x)/c−AZn2+X(x)/c
where x=[Zn2+]/([Zn2+]+[porphyrin]), and Apor and
AZn
are the absorbance for porphyrin and Zn2+
,
2+
respectively. In practice, selecting the wavelength at
which AZn is zero, the following expression has been
2+
used:
2.5. H2-2a
F(x)=Aobs/c−AporX(1−x)/c
This porphyrin was prepared from meso-mono(p-
aminophenyl)-triphenylporphyrin in a similar manner
as described for H2-1a. Yield was 80%. UV–Vis [umax
nm in CHCl3 (log m)]: 420 (5.67), 516 (4.26), 552 (3.94),
591 (3.74), 647 (3.64).
Proton NMR spectra were recorded on a JOEL
GSX-400 spectrometer. The samples for the spectra of
H2-1b at various concentration of zinc acetate were
prepared by adding each aliquot of zinc acetate to 2.1
mM porphyrin solution. The samples were allowed to
equilibrate for up to 1 h prior to recording the spectra.
2.6. H2-3a
2.2. Materials
A portion of meso-mono(o-propenoylaminophenyl)-
triphenylporphyrin (1.10 g, 1.27 mmol) was dissolved in
pyridine (80 ml), and to the solution, diethylester of
iminodiacetic acid (2.1 g, 11 mmol) was added. The
solution was stirred at 120 °C for 10 days under N2
atmosphere. The solvent was removed under vacuum.
The residue was dissolved in benzene, the resulting
mixture was purified on silica gel (4×30 cm) using
benzene–ether (4:1 v/v) as eluent. The product was
recrystallized from MeOH. The yield was 0.138 g
All chemicals were reagent grade and were used
without further purification. For the measurements of
UV–Vis spectra, methanol (Wako, HPLC grade) or
chloroform (Wako, HPLC grade) was used without
purification. Silica gel (Wakogel C-200) was used for
column chromatography. Meso-mono(o- or p-amino-
phenyl)-triphenylporphyrin [13,14], meso-tetraphenyl-
porphyrin [15] and meso-mono(o-propenoylamino-

Y. Uemori et al. / Inorganica Chimica Acta 325 (2001) 29–35
31
(9.83%). UV–Vis [umax nm in CHCl3 (log m)]: 419 (5.66),
515 (4.28), 549 (3.85), 589 (3.77), 645 (3.56).
temperature. After 2 weeks, the solution was filtered,
the solid was washed with methanol. The yield was 42
mg (79%). UV–Vis [umax nm in CH3OH (log m)]: 422
(5.81), 556 (4.32), 596 (3.83).
2.7. H2-1b
A portion of H2-1a (200 mg, 0.233 mmol) was dis-
solved in CH2Cl2 (40 ml)–ethanol (100 ml), and to the
solution, 2 ml of 0.475 M NaOH in water was added.
The solution was stirred at 60 °C for 3 h. The solution
was filtered, the solid was recrystallized from
methanol–ethanol. The yield was 140 mg (65%). UV–
Vis [umax nm in CH3OH (log m)]: 414 (5.63), 512 (4.27),
546 (3.85), 588 (3.73), 646 (3.57).
2.13. Zn-2a
This complex was prepared from H2-2a in a similar
manner as described for Zn-1a. The yield was 80%.
UV–Vis [umax nm in CH3OH (log m)]: 422 (5.86), 556
(4.33), 596 (3.94).
2.14. Zn-2b
2.8. H2-2b
This complex was prepared from H2-2b in a similar
manner as described for Zn-1b. The yield was 71%.
UV–Vis [umax nm in CH3OH (log m)]: 421 (5.81), 556
(4.32), 596 (3.95).
This porphyrin was prepared from H2-2a in a similar
manner as described for H2-1b. The yield was 89%.
UV–Vis [umax nm in CH3OH (log m)]: 414 (5.68), 512
(4.29), 547 (3.99), 588 (3.81), 645 (3.70).
2.15. Zn-2b-Zn
2.9. H2-3b
This complex was prepared from H2-2b in a similar
manner as described for Zn-1b-Zn. The yield was 46%.
UV–Vis [umax nm in DMF (log m)]: 427 (5.75), 559
(4.32), 600 (4.07).
This porphyrin was prepared from H2-3a in a similar
manner as described for H2-1b. The yield was 57%.
UV–Vis [umax nm in CH3OH (log m)]: 414 (5.66), 512
(4.28), 547 (3.85), 588 (3.75), 645 (3.51).
3. Results and discussion
2.10. Zn-1a
3.1. Synthesis
A portion of zinc acetate (76 mg, 0.35 mmol) was
added to a solution of H2-1a (100 mg, 0.116 mmol) in
CH2Cl2 (20 ml), and the solution was stirred overnight
at room temperature. The solvent was removed on a
rotary evaporator. The resulting mixture was purified
on silica gel (2×20 cm) using CHCl3–methanol as
eluent. The product was recrystallized from ether–hex-
ane. The yield was 104 mg (97%). UV–Vis [umax nm in
CH3OH (log m)]: 422 (5.82), 556 (4.32), 595 (3.82).
Fig. 1 represents the porphyrins and their zinc com-
plexes together with the abbreviations used in this
paper. Diethylester of H3nta, HntaEt2, was prepared by
partial hydrolysis of triethyl nitrilotriacetate with KOH.
Coupling of HntaEt2 with meso-mono (o- or p-
aminophenyl)-triphenylporphyrin in dichloromethane
using DCC gave the corresponding protected por-
phyrins (H2-1a, H2-2a) in 85–95% yield after chromato-
graphic purification. H2-3a was prepared from
meso-mono(o-propenoylaminophenyl)
2.11. Zn-1b
A portion of Zn-1a (50 mg, 0.054 mmol) was dis-
solved in CH2Cl2 (5 ml)–ethanol (20 ml), and 2 ml of
0.475 M NaOH was added to the solution. The solution
was stirred at 60 °C for 3 h. The solution was concen-
trated, filtered, and then the solid was recrystallized
from methanol–ethanol. The yield was 40 mg (76%).
UV–Vis [umax nm in CH3OH (log m)]: 422 (5.76), 556
(4.27), 596 (3.81).
-triphenylporphyrin and diethyl iminodiacetate. The
protected porphyrins (H2-1a, H2-2a and H2-3a) were
hydrolyzed with NaOH to give porphyrins H2-1b, H2-
2b and H2-3b. One of the carboxyl groups in NTA
binds to aminophenylporphyrin, where the appended
NTA in both H2-1b and H2-2b can act as a tridentate
ligand [17,18].
The zinc complexes were prepared by the reaction of
zinc acetate with porphyrins in acetic acid. Zn-1a and
Zn-2a were hydrolyzed with NaOH in 50% ethanol–
water to give Zn-1b and Zn-2b, respectively. The binu-
clear zinc complexes, Zn-1b-Zn and Zn-2b-Zn, were
prepared by the reaction of zinc acetate with H2-1b and
H2-2b in methanol, respectively.
2.12. Zn-1b-Zn
A portion of zinc acetate (35 mg, 0.16 mmol) was
added to a solution of H2-1b (100 mg, 0.116 mmol) in
methanol (60 ml), and the solution was stirred at room

32
Y. Uemori et al. / Inorganica Chimica Acta 325 (2001) 29–35
Table 1
Selected 1H NMR data for appended groups
ꢀCH3
ꢀCH2ꢀ
ꢀNCH2COOꢀ
ꢀNCH2ꢀ
a
H2-1a
0.33 (t, J=7.2 Hz)
1.35 (t, J=7.1 Hz)
0.47 (t, J=7.0 Hz)
2.67 (q, J=7.2 Hz)
4.30 (q, J=7.2 Hz)
3.06 (q, J=7.1 Hz)
1.54 (s)
3.74 (s)
0.29 (s)
2.75 (s)
3.70 (s)
1.81 (t, J=5.8 Hz);
1.99 (t, J=5.8 Hz)
2.49 (s)
H2-2a a
H2-3a a
H2-1b b
H2-2b b
H2-3b b
–
–
–
–
–
–
2.27 (s)
3.70 (s)
2.50 (s)
3.48 (s)
1.57 (t, J=6.8 Hz);
2.20 (t, J=6.8 Hz)
2.73 (s)
Zn-1a c
0.37 (t, J=7.3 Hz)
–
–
1.33 (t, J=7.3 Hz)
–
–
2.83 (q, J=6.8 Hz)
–
–
4.27 (q, J=7.3 Hz)
–
–
1.35 (s)
2.12 (s)
2.64 (d, J=16.6 Hz)
3.62 (s)
3.40 (s)
Zn-1b b
2.51 (s)
Zn-1b-Zn b
Zn-2a a
2.62 (s); 2.86 (d, J=16.6 Hz)
3.28 (s)
2.92 (s)
Zn-2b c
Zn-2b-Zn c
3.20 (d, J=16.6 Hz);
3.34 (d, J=16.6 Hz)
3.81 (s)
a Solvent: CDCl3.
b Solvent: CD3OD.
c Solvent: (CD3)2SO.
3.2. Characterization of porphyrins
K[Pt(ida)Cl]·2H2O [21,22], where ida represents
iminodiacetate ion. From the evidence, the tri-dentate
binding of the appended NTA to Zn is confirmed.
Further, the appended NTA proton signals for Zn-1b-
Zn appear at a lower field than those for Zn-1b by 0.35
and 0.52 ppm, respectively. Therefore, it is suggested
that the appended NTA in Zn-1b-Zn is situated slightly
away from the porphyrin plane upon binding to zinc
(conformation C in Scheme 1).
The UV–Vis spectra for Zn-1a, Zn-1b and Zn-1b-Zn
in methanol show characteristic spectra for methanol
adduct of porphyrinatozinc complexes [23]. The tem-
perature dependence of the spectra for Zn-1b and Zn-
1b-Zn in methanol was measured in the temperature
range between 10 and 50 °C, and these spectra did not
show significant temperature dependence. From these
results, we conclude that the appended NTA moieties
do not cause any intra- or intermolecular interaction.
1
The H NMR signals for the appended NTA protons
in both H2-1a and H2-3a shift to a higher field com-
pared with those in H2-2a (Table 1). Similar to this, the
appended NTA proton signals in both H2-1b and H2-3b
appear at a higher field than those in H2-2b. These
observed high-field shifts are due to the ring current of
porphyrin. Because the signals for ꢀNCH2COOꢀ in
H2-1b and H2-3b shift to a lower field compared with
those in H2-1a and H2-3a, respectively, it is suggested
that the appended NTA in the former two and the
latter two is situated over the porphyrin plane as shown
in conformation A and B of Scheme 1, respectively.
3.3. Characterization of zinc complexes
Coordination of the appended NTA to zinc was
1
confirmed in terms of IR and H NMR spectral data.
3.4. Equilibria between porphyrins and zinc acetate
The ꢀCOO− band of the appended NTA in Zn-1b-Zn
and Zn-2b-Zn appears at 1623 and 1616 cm−1, respec-
tively. These wave numbers are similar to that for
Na[Zn(nta)]·3.5H2O (1624 cm−1) [19]. On the other
hand, the wave numbers of the ꢀCOO− band of Zn-1b
(1597 cm−1) and Zn-2b (1598 cm−1) are similar to that
of H2-1b (1596 cm−1). From these results, the coordi-
nation of the carboxyl groups in appended NTA in
Zn-1b-Zn and Zn-2b-Zn is confirmed. Furthermore, the
1H NMR signals for ꢀNCH2COOꢀ in the appended
NTA appear as two doublets for Zn-1b-Zn and Zn-1b-
Zn, whereas those appear as a singlet for the corre-
sponding sodium salts (Zn-1b and Zn-2b). Similar
spectral data were observed for H[Co(ida)2] [20] and
To determine the composition of complexes in solu-
tion, Job’s experiments were conducted in methanol at
20 °C. Job plots for H2-1a with Zn2+ show a simple
Scheme 1.

Y. Uemori et al. / Inorganica Chimica Acta 325 (2001) 29–35
33
{x=[Zn2+]/([Zn2+]+[porphyrin])}, F(x) varies lin-
early with x; for x\0.5, it exhibits a maximum at
x=0.67. A similar diagram is obtained for H2-2b ex-
cept that F(x) is virtually unchanged for xB0.5 and
exhibits a maximum at 0.67. These diagrams indicate
that different complexes are formed in solution, one
with 1:1 stoichiometry and one with 1:2 stoichiometry
and therefore the appended NTA in both H2-2b and
H2-1b are suggested to act as a ligand for Zn2+
.
Binding of Zn2+ to porphyrin center induces large
UV–Vis spectral changes, but binding of Zn2+ to the
appended NTA induces little UV–Vis spectral change.
Therefore, to know the complexes formed in the solu-
tion, 1H NMR spectra of H2-1b were measured at
various concentrations of zinc acetate in CD3OD (Fig.
3). Both the spectra for the [zinc acetate]/[H2-1b] ratios
of 2.2:1 and 10:1 are similar to that of Zn-1b-Zn. We
conclude that the main product is Zn-1b-Zn for x\
0.68. In the spectrum measured for the [zinc acetate]/
[H2-1b] ratio of 0.7:1 (x=0.4), broadening of the
signals for the appended NTA is large compared with
that for pyrrole protons, hence binding of Zn2+ to the
appended NTA is speculated.
Because pyrrole NH proton signal was generally not
observed in CD3OD, a spectrum was recorded using
(CD3)2SO as the solvent to elucidate the complexes
formed in the solution containing H2-1b and Zn2+ for
xB0.5. The preparation of the sample was as follows.
A methanol solution containing zinc acetate and H2-1b
(x=0.41) was equilibrated over night, the solvent was
removed under reduced pressure, and the residue was
dissolved in 0.6 ml of (CD3)2SO. The signals at −2.84
and −2.94 ppm are assigned to the pyrrole NꢀH (Fig.
4). Comparing the signal area between the pyrrole NꢀH
signals and the phenyl signals, 85% of the total pyrrole
NꢀH protons are estimated to have appeared, e.g. 85%
of the porphyrin are in the form of H2-1b and H2-1b-
Zn, 15% of the porphyrin are in the form of Zn-1b
and/or Zn-1b-Zn. Among the two signals, the signal at
−2.84 ppm is assigned to that of pyrrole NꢀH in H2-1b
Fig. 2. Job diagram for H2-1b (ꢀ, at 557 nm; ꢁ, at 515 nm) or H2-2b
(ꢂ, at 557 nm, ꢃ, at 515 nm) with zinc acetate in methanol at 20 °C.
Fig. 3. 1H NMR spectra of H2-1b (2.1 mM) in methanol-d4 with (a)
no zinc acetate; (b) 1.5 mM; (c) 3.1 mM; (d) 4.6 mM zinc acetate.
diagram (not shown) indicating the formation of 1:1
complex, whereas those for both H2-1b and H2-2b show
complicated diagrams (Fig. 2). The diagram obtained
for H2-1b presents two inflection points: for xB0.5
Fig. 4. 1H NMR spectrum of H2-1b (2.11 mmol) in DMSO-d6
containing zinc acetate (1.49 mmol).

34
Y. Uemori et al. / Inorganica Chimica Acta 325 (2001) 29–35
The kobs values obtained for H2-1a, H2-1b, H2-2b,
H2-3a, H2-3b and H2TPP are 0.00029, 0.017, 0.0019,
0.00033, 0.0024 and 0.0020 s−1, respectively. Consider-
ing that the incorporation reaction of zinc into por-
phyrins occurs at both sides of the porphyrin plane, the
reaction occurring at the side of the porphyrin plane
appending an NTA derivative in H2-1a, b and H2-3a, b
is responsible for the change in reactivity. Because
H2-1b, H2-2b and H2-3b form binuclear zinc complexes,
while H2TPP, H2-1a and H2-3a form mono zinc com-
plexes, comparison can be made among the former three
and the latter three.
The obtained kobs values are in the order H2TPP\
H2-3a\H2-1a. The decreased reactivity for H2-1a and
H2-3a should be due to the appended NTA diester
decelerating incorporation of zinc into the porphyrin
center spatially [27,28] because the appended NTA
diester in H2-1a or H2-3a is found to be located above
the porphyrin center. Following this argument, the
increased reactivity for H2-1b compared with that for
H2-2b is due to another effect that overcomes the spatial
obstruction. It has been found that the ortho-phenyl
substituted porphyrins are less basic and less reactive
with metal ions than the para-isomers [29], but the
present results can not be explained by this. The ap-
pended NTA locates near the porphyrin center in H2-1b,
whereas that locates on the periphery of the porphyrin
plane in H2-2b. Therefore, location of the appended
NTA near the porphyrin center should be responsible
for the increased reactivity for H2-1b.
To know the effects of the location of the appending
NTA on the reactivity, H2-3a and H2-3b were prepared
and examined. Similar reactivity for H2-3a compared
with that for H2-1a may be due to spatial obstruction by
the appended NTA diester. Contrary to this, the reactiv-
ity for H2-3b is decreased compared with that for H2-1b.
We speculate that this results from the appended NTA
group moving away from the ‘preferred’ position for
zinc incorporation into the porphyrin. Further, we also
speculate that our results can be interpreted in terms of
a mechanism featuring intramolecular transfer of the
metal ion from the appended groups to the porphyrin
[25]. Because of the limited data available, further work
should be done to obtain the details.
Fig. 5. Changes in absorption spectra during the reaction of H2-2b (1
mM) with zinc acetate (1.0 mM) in methanol at 20 °C.
(−2.86 ppm in (CD3)2SO). Comparing the area of the
two signals, the ratio of [H2-1b]/[H2-1b-Zn] is estimated
to be 1:2. Thus, the breakdowns of 85% of the total
porphyrin are H2-1b (28%) and H2-1b-Zn (57%). On the
other hand, the amount of zinc added is 71% of the
total porphyrin where the amount of zinc remaining is
equal to 14% (=71–57%) of the total porphyrin. Be-
cause this value is comparable to that for the rest of
porphyrin (100−85=15%), the rest of zinc is in the
form of Zn-1b, and Zn-1b-Zn would be negligible.
Therefore, it is estimated that the complexes existing in
the solution are H2-1b (28%), H2-1b-Zn (57%) and
Zn-1b (15%).
3.5. Zinc incorporation reaction to porphyrins
There are many reports on the incorporation reaction
of metal into porphyrins [24], however, few reports on
that of the porphyrins appended ligands have appeared
[25,26]. To know the effects of the appended ligands on
the reaction, the experiments have been carried out in
MeOH at 20 °C containing the porphyrins (1 mM) and
large excess of zinc acetate (1.0 mM). The reaction was
monitored by a UV–Vis spectrophotometer as a func-
tion of time and the spectra obtained exhibit isosbestic
points (Fig. 5). Under our experimental conditions, the
reaction was first-order in porphyrin and the pseudo-
first order rate constants (kobs) were determined by
fitting the absorbance changes to the rate equation (Eq.
(1)).
4. Supplementary material
The NMR, FAB mass data, melting points and the
microanalysis data for the new porphyrins are available
from the authors upon request.
Acknowledgements
This work was supported partly by the Grants-in-Aid
from the foundation of Hokuriku University.
−d[porphyrin]/dt=kobs[porphyrin]
(1)

Y. Uemori et al. / Inorganica Chimica Acta 325 (2001) 29–35
35
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