Convenient scaffold for forming heteroporphyrin arrays in aqueous media

Article abstract of DOI:10.1021/ja035055q

A new methodology for preparing heteroporphyrin arrays in aqueous solution has been presented. The present method is based on the extremely strong ability of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TMe-β-CD) to include 5,10,15,20-tetrakis(p-substitut

Full text of DOI:10.1021/ja035055q

Published on Web 08/08/2003
Convenient Scaffold for Forming Heteroporphyrin Arrays in
Aqueous Media
Koji Kano,*,† Ryuhei Nishiyabu,† Tomoko Yamazaki,‡ and Iwao Yamazaki‡
Contribution from the Department of Molecular Science and Technology, Faculty of
Engineering, Doshisha UniVersity, Kyotanabe, Kyoto 610-0321, Japan, and Department of
Chemical Process Engineering, Graduate School of Engineering, Hokkaido UniVersity,
Kita-13-Nishi-8, Kita-ku, Sapporo 060-8628, Japan
Received March 7, 2003; E-mail: kkano@mail.doshisha.ac.jp.
Abstract: A new methodology for preparing heteroporphyrin arrays in aqueous solution has been presented.
The present method is based on the extremely strong ability of heptakis(2,3,6-tri-O-methyl)-â-cyclodextrin
(TMe-â-CD) to include 5,10,15,20-tetrakis(p-substituted-phenyl)porphyrins (Por) affording trans-type 1:2
complexes of the porphyrins and TMe-â-CD. Two different Por-per-O-methylated â-CD (per-Me-â-CD)
conjugates were synthesized. Conjugate 2 was prepared by an SN2 reaction of 5,10,15,20-tetrakis(p-
hydroxyphenyl)porphyrin and per-O-methylated â-cyclodextrin having one primary OTs group. Four per-
Me-â-CD moieties are attached to the meso positions of 2. Conjugate 3, synthesized from 5-(p-
hydroxyphenyl)-10,15,20-tris(3,5-dicarboxyphenyl)porphyrin and monotosylated per-O-methylated â-cyclodextrin,
has one per-Me-â-CD moiety at the periphery of the porphyrin. Conjugate 2 yields a stable 1:4 complex
with the zinc complex of 5-phenyl-10,15,20-tris(3,5-dicarboxyphenyl)porphyrin (8) in the dissociated form.
In this system, the energy transfer from photoexcited Zn-8 to free base 2 occurs with 85% efficiency.
Conjugate 3 forms a very stable 1:1 complex with Zn-8 (K ) (7.0 ( 0.3) × 105 dm3 mol-1) with an energy
transfer efficiency (93%) larger than that obtained in the case of 2. The structure of the 3-Zn-8 complex,
which can account for the efficient energy transfer, was deduced from 1H NMR spectroscopy. Intramolecular
fluorescence quenching of 2 and 3 by Fe(III)-8 also occurred through an electron-transfer process as the
main quenching mechanism. The present method is a very simple and convenient means to construct
various heteroporphyrin arrays in aqueous solution.
Introduction
an ortho position of a phenyl group catalyzed the enantiose-
lective photooxidation of R-pinene in organic media.7 Breslow
A porphyrin (Por)-â-cyclodextrin (â-CD) conjugate, where
the cyclodextrin (CD) moiety is attached to the para position
of the peripheral phenyl group of a tetraarylporphyrin, was
synthesized for the first time by Gonzalez et al.1 The Por-CD
conjugate is a very attractive supramolecular system, since it
possesses simple functions closely mimicking those of biological
materials. In particular, the Por and CD parts of a conjugate
are regarded as representing artificial coenzyme or active sites
and apoenzyme or binding sites, respectively. From this
viewpoint, several Por-â-CD conjugate systems were prepared
to mimic the process of photosynthesis.2-5 A cyclodextrin-
sandwiched porphyrin and its ferric complex were also synthe-
sized in an effort to reproduce the function of oxygenases.6 A
tetraphenylporphyrin having a di-O-methylated CD moiety at
et al. modeled cytochrome P-450 in the Por-â-CD conjugate 1
having four â-CD moieties at the meso positions of the
tetraarylporphyrin (Figure 1).8 The metal complexes of 1 can
bind stilbene derivatives with hydrophobic substituents at the
4,4′-positions of the substrates by incorporating the hydrophobic
tails into the â-CD cavities at the 5- and 15-positions of
porphyrin 1. Substrate-selective oxidation of stilbenes by iodosyl
benzene has been achieved using 1 as an artificial enzyme.8a
A
carotene dioxygenase model composed of a metalloporphyrin
and two â-CD moieties was also prepared.9 Most of these Por-
CD conjugates carry an unmodified â-CD moiety or moieties.
(6) (a) Kuroda, Y.; Hiroshige, T.; Sera, T.; Shiroiwa, Y.; Tanaka, H.; Ogoshi,
H. J. Am. Chem. Soc. 1989, 111, 347-350. (b) Kuroda, Y.; Ito, M.; Sera,
T.; Ogoshi, H. J. Am. Chem. Soc. 1993, 115, 7003-7004.
(7) Weber, L.; Imiolczyk, I.; Haufer, G.; Rehorek, D.; Henning, H. J. Chem.
Soc., Chem. Commun. 1992, 301-303.
† Doshisha University.
‡ Hokkaido University.
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Soc. 1996, 118, 11678-11679. (b) Breslow, R.; Huang, Y.; Zhang, X.;
Yang, J. Proc. Natl. Acad. Sci. U. S. A. 1977, 94, 11 156-11 158. (c)
Breslow, R.; Zhang, X.; Huang, Y. J. Am. Chem. Soc. 1997, 119, 4535-
4536. (d) Breslow, D.; Gabriele, B.; Yang, J. Tetrahedron Lett. 1998, 39,
2887-2890. (e) Yang, J.; Breslow, R. Angew. Chem., Int. Ed. 2000, 39,
2692-2694. (f) Yang, J.; Gabriele, B.; Belvedere, S.; Huang, Y.; Breslow,
R. J. Org. Chem. 2002, 67, 5057-5067.
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J. AM. CHEM. SOC. 2003, 125, 10625-10634
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A R T I C L E S
Kano et al.
Figure 1. Structures of Por-CD conjugates and guest porphyrins.
Recent studies revealed that heptakis(2,3,6-tri-O-methyl)-â-
cyclodextrin (TMe-â-CD) forms extraordinarily stable 1:2
complexes with water-soluble porphyrins (Por: TMe-â-CD )
1:2), while the complexes with native â-CD are very un-
stable.10,11 These findings led us to design the Por-CD conjugate
2 (Figure 1), which is a tetraphenylporphyrin derivative where
the para-positions of the phenyl groups are substituted by per-
O-methylated â-CD (per-Me-â-CD) moieties. Conjugate 2 was
expected to easily form various heteroporphyrin arrays through
noncovalent bonding simply by mixing 2 with another water-
soluble porphyrin in aqueous solution.
Developing and refining methods for the preparation of
heteroporphyrin arrays are very important in areas relating to
the study of energy transfer and/or electron transfer in artificial
photosynthetic systems. To date, the organization of heteropor-
phyrin molecules has been achieved by using covalent bonds,12,13
coordination bonds to metal ions,14-27 complementary hydrogen
bonds between nucleo bases,28 and Coulomb interactions.29,30
Porphyrin arrays constructed by covalent bonds between the
porphyrin moieties require great effort to synthesize each array.
Although the use of coordination bonds is rather sophisticated,
the systems employed require, in some cases, the inclusion of
additional heavy atom(s), which quenches the fluorescence of
the porphyrin. To the best of our knowledge, there is no example
of porphyrin architecture that has been prepared through the
use of coordination bonds in aqueous solution. The employment
of complementary hydrogen bonding is a clever approach used
in the preparation of heteroporphyrin arrays. However, this
approach can only be used in organic solvents. Although
Coulomb interactions between oppositely charged porphyrins
are very convenient for forming heteroporphyrin aggregates in
aqueous solution,29 this concept is hardly applied for a general
method to prepare the porphyrin arrays having well-defined
stoichiometry. An interesting method for forming cationic
heteroporphyrin pile blocks has been developed by using a
polyanionic calix[4]arene as a connector of the cationic por-
phyrin molecules.30 We prepared a new strategy for the
construction of heteroporphyrin arrays just by mixing two types
of porphyrins in aqueous solution. We took advantage of the
extraordinarily strong ability of TMe-â-CD to include aryl
moieties at the meso positions of the porphyrins.10,11 For
example, TMe-â-CD quantitatively yields a 1:2 complex of
tetrakis(p-sulfonatophenyl)porphyrin (TPPS4) in aqueous solu-
tion even when the concentration of TPPS4 is below 10-6 mol
dm-3, although the ability of â-CD to complex with TPPS4 is
much weaker.11 Conjugates 2 and 3 (Figure 1) were designed
as the building blocks of heteroporphyrin arrays that are soluble
in aqueous solution.
(10) Carofiglio, T.; Fornasier, R.; Lucchini, Y.; Rosso, C.; Tonellato, U.
Tetrahedron Lett. 1996, 37, 8019-8022.
(11) (a) Kano, K.; Tanaka, N.; Minamizono, H.; Kawakita, Y. Chem. Lett. 1996,
925-926. (b) Kano, K.; Nishiyabu, R.; Asada, T.; Kuroda, Y. J. Am. Chem.
Soc., 2002, 124, 9937-9944.
(12) (a) Prathapan, S.; Johnson, T. E.; Lindsey, J. S. J. Am. Chem. Soc. 1993,
115, 7519-7520. (b) Hsiao, J.-S.; Krueger, B. P.; Wagner, R. W.; Johnson,
J. E.; Delaney, J. K.; Mauzerall, D. C.; Fleming, G. R.; Lindsey, J. S.;
Bocian, D. F.; Donohoe, R. J. J. Am. Chem. Soc. 1996, 118, 11 181-
11 193. (c) Li, J.; Diers, J. R.; Seth, J.; Yang, S. I.; Bocian, D. F.; Holten,
D.; Lindsey, J. S. J. Org. Chem. 1999, 64, 9090-9100. (d) Kuciauskas,
D.; Liddell, P. A.; Lin, S.; Jphnson, T. E.; Weghorn, S. J.; Lindsey, J. S.;
Moore, A. L. Moore, T. A.; Gust, D. J. Am. Chem. Soc. 1999, 121, 8604-
8614.
(13) (a) Choi, M.-S.; Aida, T.; Yamazaki, T.; Yamazaki, I. Angew. Chem., Int.
Ed. 2001, 40, 3194-3198. (b) Choi, M.-S.; Aida, T.; Yamazaki, T.;
Yamazaki, I. Chem.sEur. J. 2002, 8, 2668-2678.
(14) (a) Brum, A. M.; Atherton, S. J.; Harriman, A.; Heitz, V.; Sauvage, J.-P.
J. Am. Chem. Soc. 1992, 114, 4632-4639. (b) Chambron, J.-C.; Harriman,
A.; Heitz, V.; Sauvage, J.-P. J. Am. Chem. Soc. 1993, 115, 6109-6114.
(c) Andersson, M.; Linke, M.; Chambron, J.-C.; Davidsson, J.; Heitz, V.;
Sauvage, J.-P.; Hammarstro¨m, L. J. Am. Chem. Soc. 2000, 122, 3526-
3527.
Results
Synthesis of Porphyrins. Por-CD conjugate 2 was synthe-
sized via a route shown in Scheme 1. Monohydroxy per-O-
(15) (a) Chi, X.; Guerin, A. J.; Haycock, R. A.; Hunter, C. A.; Sarson, L. J.
Chem. Soc., Chem. Commun. 1995, 2567-2569. (b) Hunter, C. A.; Hyde,
R. K. Angew. Chem. Int. Ed. Engl. 1996, 35, 1936-1939. (c) Haycock, R.
A.; Yartsev, A.; Michelsen, U.; Sundstro¨m, V.; Hunter, C. A. Angew. Chem.,
Int. Ed. 2000, 39, 3616-3619.
(23) Lo Schiavo, S.; Pocsfalvi, G.; Serroni, S.; Cardiano, P.; Piraino, P. Eur. J.
Inorg. Chem. 2000, 1371-1375.
(24) (a) Iengo, E.; Milani, B.; Zangrando, E.; Geremia, S.; Alessio, E. Angew.
Chem., Int. Ed. 2000, 39, 1096-1099. (b) Prodi, A.; Kleverlaan, C. J.;
Indelli, M. T.; Scandola, F.; Alessio, E.; Iengo, E. Inorg. Chem. 2001, 40,
3498-3504.
(16) Yuan, H.; Thomas, L.; Woo, L. K. Inorg. Chem. 1996, 35, 2808-2817.
(17) Slone, R. V.; Hupp, J. T. Inorg. Chem. 1997, 36, 5422-5423.
(18) Burrell, A. K.; Officer, D. L.; Reid, D. C. W.; Wild, K. Y.Angew. Chem.,
Int. Ed. 1998, 37, 114-116.
(25) Ogawa, K.; Kobuke, T. Angew. Chem., Int. Ed. 2000, 39, 4070-4073.
(26) Rucareanu, S.; Mongin, O.; Schuwey, A.; Hpyler, N.; Gossauer, A.; Amrein,
W.; Hediger, H.-U. J. Org. Chem. 2001, 66, 4973-4988.
(27) Splan, K. E.; Keefer, M. H.; Massari, A. M.; Walters, K. A.; Hupp, J. T.
Inorg. Chem. 2002, 41, 619-621.
(28) Sessler, J. L.; Wang, B.; Harriman, A. J. Am. Chem. Soc. 1995, 117, 704-
714.
(29) Endisch, C.; Fuhrhop, J.-H.; Buschmann, J.; Luger, P.; Siggel, U. J. Am.
Chem. Soc. 1996, 118, 6671-6680.
(30) Moschetto, G.; Lauceri, R.; Gulino, F. G.; Sciotto, D.; Purrello, R. J. Am.
Chem. Soc. 2002, 124, 14536-14537.
(19) Fan, J.; Whiteford, J. A.; Olenyuk, B.; Levin, M. D.; Stang, P. J.; Fleischer,
E. B. J. Am. Chem. Soc. 1999, 121, 2741-2752.
(20) Kim, H.-J.; Bampos, N.; Sanders, J. K. M. J. Am. Chem. Soc. 1999, 121,
8120-8121.
(21) Prodi, A.; Indelli, M. T.; Kleverlaan, C. J.; Scandola, F.; Alessio, E.;
Gianferrara, T.; Marzilli, L. G. Chem.sEur. J. 1999, 5, 2668-2679.
(22) (a) Kuroda, Y.; Sugou, K.; Sasaki, K. J. Am. Chem. Soc. 2000, 122, 7833-
7834. (b) Sugou, K.; Sasaki, K.; Kitajima, K.; Iwaki, T.; Kuroda, Y. J.
Am. Chem. Soc. 2002, 124, 1182-1183.
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A R T I C L E S
Scheme 1
Scheme 2
methylated â-CD (4) was obtained according to the procedures
previously described.31 Compound 4 was tosylated affording
5, which yielded 2 (36%) upon reaction with 5,10,15,20-tetrakis-
(4-hydroxyphenyl)porphyrin in dry DMF containing K2CO3.
Spectroscopic data indicated that 2 in aqueous media aggregates
spontaneously at higher concentrations (∼5 × 10-4 mol dm-3
for 1H NMR measurements) but exists as the monomer at lower
concentrations (∼1 × 10-6 mol dm-3 for fluorescence measure-
ments).
The porphyrin having one per-Me-â-CD moiety (3) was
prepared via the route outlined in Scheme 2. The six carboxy
groups of 3 are necessary in an effort to prevent self-inclusion
and to solvate the Por-CD conjugate in water. Additionally, the
carboxylate groups are expected to check self-aggregation of
the porphyrin in aqueous solution. Six singlet signals due to
the primary OCH3 groups were observed with 3 at 0.99-2.90
ppm (vide infra). The signals of the secondary OCH3 groups
were observed at 3.3-3.7 ppm. The primary OCH3 group
signals of 3 shifted to higher magnetic fields due to ring current
effects of the porphyrin ring. It is quite reasonable to assume
that the per-Me-â-CD moiety of 3 sits on the porphyrin ring,
where the primary OCH3 groups face the porphyrin ring.
In an effort to prepare heteroporphyrin arrays, the Zn(II) and
Fe(III) complexes of tetraphenylporphyrinhexacarboxylic acid
(8) were synthesized (Scheme 3). The Lindsey’s method32
afforded both 9 and 10. Porphyrins 9 (12% yield) and 10 (10%),
separated by silica gel column chromatography, were hydrolyzed
to afford 8 and 11, respectively. The Zn(II) complex of 8 (Zn-
8) was prepared by reacting 8 with zinc oxide in water and
purified by means of gel filtration and ion-exchange column
chromatography (75%). The Fe(III) complex of 8 (Fe-8) was
prepared by reaction of the ester 10 with FeCl2 in DMF-
dichloromethane yielding Fe-10 (81%), which was hydrolyzed
in aqueous methanol containing KOH.
Complexation of Zn-8 and Fe-8 with TMe-â-CD. The
interactions of Zn-8 and Fe-8 with TMe-â-CD in aqueous
solution were initially investigated in an effort to foresee the
structure and stability of the porphyrin arrays. The absorption
spectrum of Zn-8 changed continuously upon addition of TMe-
â-CD (supporting information). In particular, addition of TMe-
â-CD caused a decrease in the optical densities (OD) at 422
nm and a simultaneous increase in the ODs at 424 nm. A Job’s
plot corroborated the formation of a 1:1 complex. The UV-
vis titration curves fitted well with the formation of a 1:1
complex and yielded a binding constant (K) of (1.5 ( 0.1) ×
107 dm3 mol-1 in 0.1 mol dm-3 phosphate buffer at pH 7.0 and
1
25 °C. H NMR data including ROESY clearly revealed the
presence of the phenyl moiety and the absence of any carboxy-
late groups of Zn-8 being incorporated into the TMe-â-CD
cavity from the secondary OCH3 group side (supporting
-
information). The two CO2 groups of each dicarboxyphenyl
group of Zn-8 prevent the incorporation of this substituent into
the TMe-â-CD cavity. We reported that the anionic porphyrin,
TPPS4, formed an extraordinarily stable 1:2 complex with TMe-
â-CD (TPPS4: TMe-â-CD ) 1:2) in aqueous solution and that
the K value (K1K2) was too large to be determined.11 Although
the complex of Zn-8 and TMe-â-CD is rather less stable than
that of TPPS4, the K value for the Zn-8-TMe-â-CD complex
is still large. A K value of (1.8 ( 0.3) × 106 dm3 mol-1 was
also determined from the UV-vis absorption spectroscopic
titration for the 1:1 complex of Fe-8 and TMe-â-CD in 0.01
mol dm-3 succinic acid buffer at pH 5.5 and 25 °C. These data
suggest that the Por-CD conjugates 2 and 3 produced stable
heteroporphyrin arrays by incorporating Zn-8 and Fe-8.
(31) Chen, Z.; Bradshaw, J. S.; Lee, M. L. Tetrahedron Lett. 1996, 37 (38),
6831-6834.
(32) (a) Lindsey, J. S. In The Porphyrin Handbook; Kadish, K. M.; Smith, K.
M.; Guilard, R., Eds.; Academic Press: San Diego, 2000; Vol. I, pp 45-
118. (b) Fudickar, W.; Zimmerman, J.; Ruhlmann, L.; Scheider, J.; Ro¨der,
B.; Siggel, U.; Fuhrhop, J.-H. J. Am. Chem. Soc. 1999, 121, 9539-9545.
Complexation of 2 and 3 with Zn-8 and Fe-8. The
employment of UV-vis absorption spectroscopy in the inves-
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A R T I C L E S
Scheme 3
Kano et al.
tigation of complexation of 2 and 3 with Zn-8 and Fe-8 is very
difficult due to the overlap of the absorption bands. A micro-
calorimetric method was applied to determine the stability of
the heteroporphyrin arrays. The sigmoidal calorimetric titration
curve obtained for the 3-Zn-8 system fitted well with the
theoretical curve for 1:1 complexation (supporting information).
The K value and the enthalpy (∆H) and entropy changes (∆S)
for complexation of 3 with Zn-8 in 0.1 mol dm-3 phosphate
buffer at pH 7.0 and 25 °C were determined to be (7.02 ( 0.33)
× 105 dm3 mol-1, -47.1 ( 0.4 kJ mol-1, and -46.1 ( 2.1 J
mol-1 K-1, respectively. The K value for the 3-Zn-8 system
was considerably smaller than that for the TMe-â-CD-Zn-8
system. This could be ascribed to electrostatic repulsion between
-
the CO2 groups of 3 and Zn-8. The result of the calorimetric
titration for the 2-Zn-8 system is shown in Figure 2. As with
the case of the 3-Zn-8 system, a sigmoidal titration curve was
obtained. The midpoint of the titration curve corresponds to a
molar ratio of ca. 3.3, suggesting the formation of 1:3 and/or
Figure 2. Titration of 1.0 × 10-5 mol dm-3 of 2 with 25 aliquots (10 mL
each) of Zn-8 (4.0 × 10-4 mol dm-3) in 0.1 mol dm-3 phosphate buffer
solution at pH 7.0 and 25 °C. The top panel shows the raw data, denoting
the amount of generated heat after each injection of Zn-8. The bottom panel
shows the plot of amount of heat generated per injection as a function of
the molar ratio of Zn-8 to 2.
-
1:4 complexes of 2 and Zn-8. Since there are no CO2 groups
in 2, Zn-8 should be more strongly bound to 2 than in the case
of 3. The formation of a 1:4 complex of 2 and Zn-8 was
supported by UV-vis absorption spectroscopy. Figure 3 shows
the differential absorption spectral changes of Zn-8 upon
addition of 2. Since the absorption bands of 2 and Zn-8 overlap,
analysis of the data is considerably difficult; however, the change
in the absorbance at 604 nm is characteristic. As shown in Figure
3, the difference in the absorbances (∆A) at 604 nm decreased
as the molar ratio of 2:Zn-8 approached 1:4 and then increased
above this molar ratio. This result confirms the formation of a
stable 1:4 complex of 2 and Zn-8.
the formation of a multi-porphyrin array, further detailed
analysis could not be done.
Energy Transfer from Photoexcited Zn-8 to 2 and 3.
Figure 4 shows the fluorescence spectra of 2, Zn-8, and an
equimolar mixture of 2 and Zn-8 in 0.1 mol dm-3 phosphate
buffer at pH 7.0. Each sample was excited at 556 nm, at which
point the extinction coefficients of 2 and Zn-8 are 7715 and
18 860 dm3 mol-1 cm-1, respectively. Therefore Zn-8 is
preferentially excited at 556 nm. The fluorescence intensity of
2 in the presence of equimolar amounts of Zn-8 is ca. 3 times
larger than that in the absence of Zn-8, indicating that energy
transfer from photoexcited Zn-8 (donor) to 2 (acceptor) had
occurred. It is well-known that the singlet energies of photo-
excited Zn(II) complexes of porphyrins are transferred to the
porphyrin-free bases through the Fo¨rster’s mechanism.12,13,15c,22,27,28
Figure 5 shows the decrease in fluorescence intensity of Zn-8
at 605 nm and the increase in fluorescence intensity of 2 at
The interactions of 2 and 3 with Fe-8 were also investigated
by means of microcalorimetry. The data for the 3-Fe-8 system
indicated the formation of a 1:1 complex, with K, ∆H, and ∆S
being (2.56 ( 0.17) × 105 dm3 mol-1, -60.4 ( 0.8 kJ mol-1
,
and -99.0 ( 3.2 J mol-1 K-1, respectively. In comparison to
the data for the 3-Zn-8 system, the complexation is enthalpi-
cally more favorable and entropically less favorable. Although
the calorimetric titration curve for the 2-Fe-8 system suggested
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Scaffold for Forming Heteroporphyrin Arrays
A R T I C L E S
Figure 3. (a) Differential absorption spectral changes of Zn-8 (2.0 × 10-5
mol dm-3) upon addition of 2 in 0.1 mol dm-3 phosphate buffer at pH 7.0
and 25 °C and (b) changes in absorbances (∆A) at 604 nm.
Figure 5. Changes in fluorescence intensities at (a) 605 nm and (b) 712
nm upon addition of 2 (1) and 3 (m) to the solution of Zn-8 (1.0 × 10-5
mol dm-3) in 0.1 mol dm-3 phosphate buffer at pH 7.0 and 25 °C and
differences in the fluorescence intensities (∆If) between the systems of 2
and 3 (n).
Figure 4. Fluorescence spectra of 2, Zn-8, and equimolar mixture of Zn-8
and 2 in 0.1 mol dm-3 phosphate buffer at pH 7.0 and 25 °C. The
concentration of each porphyrin was 1 × 10-6 mol dm-3 and each sample
was excited at 556 nm.
Figure 6. Fluorescence decay profiles of (a) Zn-8 (1 × 10-5 mol dm-3),
(b) Zn-8 in the presence of equimolar amounts of 2 (1 × 10-5 mol dm-3),
and (c) Zn-8 in the presence of equimolar amounts of 3 (1 × 10-5 mol
dm-3). The decays were monitored at 600 nm in 0.1 mol dm-3 phosphate
buffer at pH 7.0 upon exciting Zn-8 at 415 nm.
712 nm upon addition of 2 into the 1 × 10-5 mol dm-3 Zn-8
solution. Up to [2]/[Zn-8] ) 0.25, both Zn-8 and 2 fluorescence
intensities changed abruptly. At [2]/[Zn-8] > 0.25, the changes
in fluorescence intensities were less abrupt. Since the fluores-
cence lifetime of Zn-8 is 1750 ps in the absence of acceptor
(vide infra), intermolecular energy transfer via a dynamic
process would be negligible under the present conditions. It can
be concluded, therefore, that the very efficient energy transfer
from Zn-8 to 2 proceeds intramolecularly through the formation
of the 2-Zn-8 inclusion complex(es). No energy transfer
occurred when the Zn complex (Zn-11) of 11, which does not
interact with 2 at all, was used in place of Zn-8.
As in the case of 2, the energy transfer occurred from
photoexcited Zn-8 to 3 possessing one per Me-â-CD moiety.
The results are shown in Figure 5. Both the decrease in
fluorescence intensity of the donor (Zn-8) and the increase in
fluorescence intensity of the acceptor (3) are less abrupt than
in the case of 2. The photoenergy is gathered more efficiently
by 2 than by 3. At [acceptor]/[donor] < 1, donor molecules are
captured by 2 more effectively than by 3 due to the greater
number of donor binding sites present in 2. The largest
difference in photon-gathering efficiency between 2 and 3
(∆If ) |If2 - If3|) should be observed at [acceptor]/[donor] )
0.25 if the binding constants for complexation of 2 and 3 with
Zn-8 are satisfactorily large. Indeed, the maximum ∆If was
found at [acceptor]/ [donor] ) 0.25 (Figure 5). In other words,
the acceptor molecule 2 gathers four Zn-8 molecules even at
low Zn-8 concentrations.
The fluorescence decay curves of Zn-8 (1 × 10-5 mol dm-3
)
in 0.1 mol dm-3 phosphate buffer at pH 7.0 in the absence and
presence of equimolar amounts of 2 and 3 are shown in Figure
6. Zn-8 was excited at 415 nm and the time course of the
fluorescence of Zn-8 was monitored at 600 nm. The fluorescence
lifetime of Zn-8 in the absence of an energy acceptor is 1750
ps, while the decay in the presence of 2 was apparently
composed of three components: 128 ps (34%), 494 ps (22%),
and 2237 ps (44%). The longest component is due to the Zn-8
molecule, which does not participate in energy transfer. The
two shorter components can be ascribed to the excited Zn-8
molecules whose energies were transferred to 2. The geometry
9
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A R T I C L E S
Kano et al.
is higher than that of the 1:1 complex.34 We failed to determine
the stoichiometry of the 2-Fe-8 complex by means of absorp-
tion spectroscopy. However, it is reasonable to assume that the
1:4 complex is predominant at higher Fe-8 concentrations as in
the case of the 2-Zn-8 system. Meanwhile, the fluorescence
quenching of 3 by Fe-8 hardly occurred and was saturated at
much lower I0/I (Figure 7).
Discussion
Water-soluble porphyrins tend to form self-aggregates in
aqueous solutions.35 Well-ordered porphyrin aggregates are
J-aggregates which consist of edge-to-edge aggregates having
large association numbers.36 However, it is difficult to control
the molecular architecture of the self-aggregates at will. To
arrange the porphyrin moieties intentionally, the linking of
moieties through covalent bonds and/or noncovalent bonds such
as coordination and hydrogen bonds is required. van der Waals
interactions have been recognized to be inadequate for this
purpose. As mentioned above, porphyrin arrays can be prepared
by connecting more than one porphyrin through covalent
bonds.12,13,37 With this methodology, however, each porphyrin
array has to be synthesized by individual processes. The
preparation of many porphyrin arrays might be troublesome.
Coordination bonds are useful and convenient in the construction
of both homo- and heteroporphyrin arrays in organic solvents.14-27
To the best of our knowledge, however, no successful examples
of porphyrin architectures prepared by coordination bonds or
covalent bonds in aqueous solution have been reported. The
use of hydrogen bonding is also an unfavorable approach in
the formation of porphyrin arrays in aqueous media.28 There
are very few examples of porphyrin arrays known to have been
Figure 7. Stern-Volmer plots for fluorescence quenching of 2 (1.0 × 10-5
mol dm-3, l) and 3 (1.0 × 10-5 mol dm-3, m) by Fe-8 in 0.01 mol dm-3
succinic buffer solutions (pH 5.5) containing 0.1 mol dm-3 NaClO4. The
porphyrin free bases were excited at 590 nm and the fluorescence intensities
were monitored at 700 nm.
between the donor and acceptor parts of the 2-Zn-8 complex
is anticipated to be rather complicated since the acceptor 2 has
four binding sites. Four shorter components might exist in the
fluorescence decay of Zn-8. Presumably, two components were
apparently observed. The mean rate constant (kEnT) and the
efficiency of the energy transfer (Φ ) kEnTτDA ) 1 - τDA/τD,
where τD and τDA represent the fluorescence lifetimes of donor
in the absence and presence of acceptor) in the 2-Zn-8 system
was calculated to be 3.1 × 109 s-1 and 85%, respectively.
The fluorescence decay of Zn-8 in the presence of equimolar
amounts of 3 was composed of 122 ps (73%) and 1800 ps
(27%). In this case only one binding site exists in 3, and so,
the fluorescence decay was relatively simple. The rate constant
and the energy transfer efficiency were 7.6 × 109 s-1 and 93%,
respectively. Very efficient energy transfer took place in the
3-Zn-8 system.
Fluorescence Quenching of 2 and 3 by Fe-8. The interac-
tions of 2 and 3 with Fe-8 were also studied. The fluorescence
spectral changes of 2 and 3 were monitored in 0.01 mol dm-3
succinic acid buffer at pH 5.5 as a function of [Fe-8].
Measurements were carried out at pH 5.5 to completely
eliminate the contribution of the µ-oxo dimers. UV-vis
spectroscopy indicated that Fe-11 did not form the µ-oxo dimer
even in alkaline solution. The Ka value for the equilibrium
between the diaqua and monohydroxo-monoaqua forms of Fe-
11 was determined to be 8.0. Meanwhile, formation of the µ-oxo
dimer was detected with Fe-8 in aqueous alkaline solution when
[Fe-8] > 1 × 10-5 mol dm-3. At lower concentrations of Fe-8,
the pKa value for the equilibrium between the diaqua and
monohydroxo-monoaqua forms of Fe-8 was determined to be
7.7. Therefore no µ-oxo-dimer of Fe-8 was formed at pH 5.5 at
any concentrations of Fe-8. These results (Stern-Volmer plots)
are shown in Figure 7. Very efficient fluorescence quenching
occurred with 2. The Stern-Volmer plot for 2 shows a
sigmoidal shape. The Stern-Volmer plot should be linear if
only static quenching through formation of a 1:1 nonfluorescent
complex proceeds.33 The sigmoidal Stern-Volmer plot for 2
can be interpreted in terms of the formation of a complex(es)
having stoichiometry other than 1:1, where the quenching
efficiency of the complex carrying more than one Fe-8 molecule
(34) David, E.; Born, R.; Kaganer, E.; Joselevich, E.; Du¨rr, H.; Willner, I. J.
Am. Chem. Soc. 1997, 119, 7778-7790.
(35) (a) Pasternack, R. F.; Huber, P. R.; Boyd, P.; Engasser, G.; Francesconi,
L.; Gibbs, E.; Fasella, P.; Venturo, G. C.; Hinds, L. deC. J. Am. Chem.
Soc. 1972, 94, 4511-4517. (b) Krishnamurthy, M.; Sutter, J. R.; Hambright,
P. J. Chem. Soc., Chem. Commun. 1975, 13-14. (c) Chandrashekar, T.
K.; Van Willigen, H.; Ebersole, M. H. J. Phys. Chem. 1984, 88, 4326-
4332. (d) Kano, K.; Minamizono, H.; Kitae, T.; Negi, S. J. Phys. Chem. A
1997, 101, 6118-6124. (e) Kano, K.; Fukuda, K.; Wakami, H.; Nishiyabu,
R.; Pasternack, R. F. J. Am. Chem. Soc. 2000, 122, 7494-7502.
(36) (a) Stone, A.; Fleischer, E. B. J. Am. Chem. Soc. 1968, 90, 2735-2748.
(b) Chandrashekar, T. K.; van Willigen H. J. Am. Chem. Soc. 1983, 105,
6323-6324. (c) Ohno, O.; Kaizu, Y.; Kobayashi, H. J. Chem. Phys. 1993,
99, 4128-4139. (d) Ribo, J. M.; Crusats, J.; Farrera, J.-A.; Valero, M. L.
J. Chem. Soc., Chem. Commun. 1994, 681-682. (e) Pasternack, R. F.; (f)
Maiti, N. C.; Ravikanth, M.; Mazumdar, S.; Periasamy, N. J. Phys. Chem.
1995, 99, 17192-17197. (g) Akins, D. L.; Zhu, H.-R.; Guo, C. J. Phys.
Chem. 1996, 100, 5420-5425. (h) Jin, R.-H.; Aoki, S.; Shima, K. J. Chem.
Soc., Faraday Trans. 1997, 93, 3945-3953. (i) Huang, C. Z.; Li, Y. F.;
Li, N.; Li, K. A.; Tong, S. Y. Bull. Chem. Soc. Jpn. 1998, 71, 1791-1797.
(j) Parkash, J.; Robblee, J. H.; Agnew, J.; Gibbs, E.; Collings, P.; Pasternack,
R. F.; de Paula, J. C. Biophys. J. 1998, 74, 2089-2099. (k) Purrello, R.;
Monsu Scolaro, L.; Bellacchio, E.; Gurrieri, S.; Romeo, A. Inorg. Chem.
1998, 37, 3647-3648. (l) Micali, N.; Mallamace, F.; Romeo, A.; Purrello,
R.; Monsu Scolaro, L. J. Phys. Chem. B 2000, 104, 5897-5904. (m) Micali,
N.; Romeo, A.; Lauceri, R.; Purrello, R.; Mallamace, F.; Monsu Scolaro,
L. J. Phys. Chem. B 2000, 104, 9416-9420. (n) Ribo, J. M.; Crusats, J.;
Sagues, F.; Claret, J.; Rubires, R. Science 2001, 292, 2063-2066. (o) Ribo,
J. M.; Bofill, J. M.; Crusats, J.; Rubires, R. Chem.sEur. J. 2001, 7, 2733-
2737. (p) Castriciano, M. A.; Romeo, A.; Monsu Scolaro, L. J. Porphyrins
Phthalocyanines 2002, 6, 431-438.
(37) (a) Sessler, J. L.; Capuran, V. L.; Harriman, A. J. Am. Chem. Soc. 1993,
115, 4816-4628, (b) Biemans, H. A. M.; Rowan, A. E.; Verhoeven, A.;
Vanoppen, P.; Latterini, L.; Foekema, J.; Schenning, R. J. M.; Meijer, E.
W.; de Schryver, F. C.; Nolte, R. J. M. J. Am. Chem. Soc. 1998, 120,
11 054-11 060. (c) Aratani, N.; Osuka, A.; Kim, Y. H.; Jeong, D. H.; Kim,
D. Angew. Chem., Int. Ed. Engl 2000, 39, 1458-1462. (d) Tsuda, A.; Osuka,
A. J. Inclusion Phenom. Macrocyclic Chem. 2001, 41, 77-81. (e) Nakano,
A.; Osuka, A.; Yamazaki, T.; Nishimura, Y.; Akimoto, S.; Yamazaki, I.;
Itaya, A.; Murakami, M.; Miyasaka, H. Chem. sEur. J. 2001, 7, 3134-
3151. (f) Aratani, N.; Osuka, A. Org. Lett. 2001, 3, 4213-4216. (g) Aratani,
N.; Osuka, A. Bull. Chem. Soc. Jpn. 2001, 74, 1361-1379. (h) Aratani,
N.; Tsuda, A.; Osuka, A. Synlett 2001, 1663-1674.
(33) Nemzek, T.; Ware, W. R. J. Chem. Phys. 1975, 62, 477-489.
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A R T I C L E S
prepared in aqueous solution.29,30 For the first case, we suc-
ceeded in making water-soluble heteroporphyrin arrays utilizing
the inclusion capacity of per-Me-â-CD, which can function as
an intramolecular energy and electron-transfer system. The
present methodology is based on the extraordinarily strong
ability of TMe-â-CD to incorporate aryl substituents at the meso
positions of water-soluble porphyrins.10,11 We designed the Por-
per-Me-â-CD conjugates 2 and 3. Breslow et al. synthesized
the porphyrin-â-CD conjugate 1, whose structure is similar to
2.8a However, conjugate 1 has four native â-CD moieties whose
ability to include tetraarylporphyrins is much weaker than the
per-Me-â-CD moiety.11 In contrast, conjugate 2 was expected
to strongly bind with other types of tetraarylporphyrins through
van der Waals interactions. Conjugate 3 was designed to form
a porphyrin dyad. A characteristic feature of conjugate 3 is
ascribed to the three dicarboxyphenyl groups at the meso
positions of 3. The dissociated dicarboxyphenyl groups pre-
vented self-inclusion of conjugate 3. Therefore 3 can exclusively
incorporate another porphyrin component to form the hetero-
porphyrin dimer.
In the present study, the design of the guest porphyrin was
also very important. We used porphyrin 8 and its Zn(II) and
Fe(III) complexes as the guests. The guest porphyrin 8 has only
one site for binding, which facilitates the formation of porphyrin
arrays having maximum stoichiometries of 1:4 for 2 and 1:1
for 3.
Figure 8. 1H NMR spectra of 3 (1.0 × 10-3 mol dm-3) in the presence of
various amounts of Zn-8 ([Zn-8] ) 0, 0.5, and 1.0 × 10-3 mol dm-3) at 25
°C in 0.1 mol dm-3 phosphate buffer (D2O, pD ) 7.0) and plausible
structure of 3-Zn-8 complex in D2O (the corboxylato groups of 3 and Zn-8
are omitted for clarity).
Microcalorimetric measurements confirmed the formation of
the very stable 1:1 complexes of 3 and Zn-8 (K ) (7.02 ( 0.33)
× 105 dm3 mol-1, ∆H ) -47.1 ( 0.4 kJ mol-1, ∆S ) -46.1
( 2.1 J mol-1 K-1) and 3 and Fe-8 (K ) (2.56 ( 0.17) × 105
dm3 mol-1, ∆H ) -60.4 ( 0.8 kJ mol-1, ∆S ) -99.0 ( 3.2
J mol-1 K-1). The K values for the complexes of 3 are
significantly smaller than those for the complexation of TMe-
â-CD with Zn-8 (K ) (1.5 ( 0.1) × 107 dm3 mol-1) and Fe-8
(K ) (1.8 ( 0.3) × 106 dm3 mol-1). The smaller K values for
the host 3 can be accounted for in terms of the electrostatic
repulsion between the carboxylate anion groups of the host 3
and of the guest Zn-8 or Fe-8. As indicated by the thermo-
dynamic parameters, the complexation of 3 with Zn-8 and Fe-8
represents an enthalpically favorable and entropically unfavor-
able process. The main binding force seems to be van der Waals
interactions. Absorption spectroscopy suggested the formation
of a 1:4 complex of 2 and Zn-8 (Figure 3). Calorimetric titration
also supported the formation of the 1:4 complex.
bonds for linking a Zn-porphyrin moiety with a tetraphenylpor-
phyrin free base.12b This porphyrin conjugate is similar to the
3-Zn-8 conjugate. The energy transfer efficiency of their
covalently linked heteroporphyrin dimer was estimated to be
98% in toluene, which is comparable to that obtained for the
3-Zn-8 system (93%). Aida et al. also reported the energy
transfer from Zn-porphyrin to free-base porphyrin in the
heteroporphyrin dimer where the two porphyrin components are
connected by a -C6H4-OCH2-C6H4- linkage.13 The energy
transfer efficiency of their system is 86% in THF.13b On the
basis of these findings, it can be concluded that the 3-Zn-8
heteroporphyrin dimer prepared through a noncovalent bond in
aqueous solution displays characteristics similar to or better than
those of the covalently linked heteroporphyrin dimers in organic
solvents.
Efficient Fo¨rster-type energy transfer occurred in the het-
eroporphyrin dimer system composed of 3 and Zn-8. The energy
transfer efficiency obtained from the fluorescence decay was
93%. Sessler et al. reported an energy transfer efficiency of 57%
for the heteroporphyrin dimer prepared by complementary
hydrogen bonding between a guanosine-bearing Zn-porphyrin
and a cytidine-bearing porphyrin free base in dichloromethane.28
They calculated a critical distance (Rc) for the Fo¨rster-type
energy transfer from the photoexcited Zn-porphyrin to the
porphyrin free base of ca. 2.4 nm. An energy transfer efficiency
of 57% suggests that the mean distance between the energy
donor and the acceptor of the nucleo base pair is close to Rc.
Indeed the estimated distance was ca. 2.25 nm.28 It might be
assumed, therefore, that the mean distance of the 3-Zn-8 system
is much shorter than that of the nucleo base pair. Lindsey and
co-workers prepared a heteroporphyrin dimer using C-C triple
Figure 8 shows the 1H NMR spectra of 3 in the absence and
presence of Zn-8. In the absence of Zn-8, six singlet signals
due to the CH3 groups at the primary OCH3 side of per-Me-
â-CD were clearly observed at ca. 1-3 ppm. The signals of
the OCH3 groups at the 2-, 3-, and 6-positions of TMe-â-CD
appeared at 3.568, 3.659, and 3.435 ppm in D2O,38 and shifted
to 2.967, 2.475, and 3.489 ppm, respectively, upon addition of
equimolar amounts of Zn-8. It is noteworthy that the signal due
to the OCH3 groups at the 6-positions shifted to lower magnetic
field resulting from a deshielding effect due to the ring current
of the porphyrin ring. Large upfield shifts of the CH3 protons
at the 6-positions of 3 in the absence of Zn-8 indicate that the
per-Me-â-CD moiety of 3 is placed on the porphyrin ring, which
(38) Botsi, A.; Yannakopoulou, K.; Hadjoudis, E. Magn. Reson. Chem. 1996,
34, 419-423.
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A R T I C L E S
Kano et al.
hangs over the primary OCH3 group side of the CD cavity. In
the presence of half-equivalent amounts of Zn-8, the signal
intensities of the primary OCH3 groups were diminished without
any shifts. New singlet signals appeared at ca. 1.8-3.0 ppm
upon addition of Zn-8. Since the signals of the secondary OCH3
groups of the per-Me-â-CD moiety are expected to shift to ca.
2.5-3 ppm upon inclusion of Zn-8 (vide supra), the singlet
signals that appeared at least in the 1.8-2.5 ppm range should
be assigned to the primary OCH3 groups. In other words, the
folding structure of 3 is maintained even after incorporating
Zn-8 (Figure 8).
The kET value for the 3-Fe-8 system was determined to be 2.6
× 108 s-1. In the case of the 2-Fe-8 system, the experimentally
determined value of (I/I0)sat was 0.11, which leads to a kET value
of 7.9 × 108 s-1 (τ0 ) 10.0 ns for 2). Heiler et al. prepared a
heteroporphyrin dimer composed of free-base porphyrin and Fe-
(III) porphyrin that are linked to each other by a phenyl group.40
The fluorescence quenching rate of this dyad was reported to
be 2 × 1011 s-1. The kET values in the present systems are much
smaller than that in the covalently bonded heteroporphyrin
dimer. This could be ascribed to a barrier effect of the
cyclodextrin cavity impeding electron transfer. We found that
the very stable 1:2 complex of TPPS4 and TMe-â-CD was
completely inactive toward fluorescence quenching by 9,10-
anthraquinone-2-sulfonate (AQS) via electron transfer, though
AQS quenched the fluorescence of TPPS4 in the absence of
TMe-â-CD. The per-Me-â-CD cavity in 2 or 3 seems to act as
a barrier toward electron transfer from 2 or 3 to Fe-8
incorporated in the per-Me-â-CD cavities or cavity of 2 or 3.
The difference in efficiency of the fluorescence quenching by
Fe-8 between 2 and 3 can be accounted for in terms of the
diversity in spatial relationship between the donor and the
acceptor in the 2-Fe-8 system.
As shown in Figure 5, the energy transfer from photoexcited
Zn-8 to 2 apparently occurred more efficiently than that from
Zn-8 to 3. However, the energy transfer efficiency of the
2-Zn-8 system (85%) was considerably lower than that of the
3-Zn-8 system (93%). Assuming the formation of a 1:4
complex of 2 and Zn-8, four types of geometrical orientations
should be assumed for the four donor-acceptor pairs in the
2-Zn-8 system. Each pair has independent energy transfer
efficiency. The probability of photon absorption of 2 is 4 times
higher than that of 3. Since the energy transfer efficiency
evaluated from fluorescence decay represents the mean, it should
be lower than that of the 3-Zn-8 system where the orientation
between the donor and the acceptor is opportune for energy
transfer due to its holding conformation. This situation is the
same as that observed for the energy transfer in dendritic
multiporphyrin arrays.13 The efficiency of the energy transfer
from the surrounding Zn(II) porphyrin moiety to a central free-
base porphyrin decreases as the generation of dendrimer
increases.13 The heteroporphyrin array composed of a tet-
raarylporphyrin free base and four zinc tetraarylporphyrins was
synthesized by linking each zinc porphyrin with the free-base
porphyrin by a C-C triple bond.12a This heteroporphyrin array
is similar to the 2-Zn-8 array. In this covalently linked
heteroporphyrin array, the orientations of the four donor-
acceptor pairs are almost the same since each donor is bound
to the acceptor by a C-C triple bond. The energy transfer
efficiency of the covalently linked pentad in dichloromethane
was reported to be ca. 90%, which is slightly higher than that
of the 2-Zn-8 system. A detailed 1H NMR study could not be
We would like to emphasize that the present systems provide
a very convenient means to prepare heteroporphyrin arrays in
aqueous solution. Simply mixing 2 or 3 with other water-soluble
porphyrins can yield a variety of heteroporphyrin arrays whose
character is almost the same as covalently linked heteropor-
phyrin arrays.
Experimental Section
Syntheses of Porphyrin-Cyclodextrin Conjugates. Conjugates 2
and 3 were synthesized via routes shown in Schemes 1 and 2,
respectively.
Mono-6-O-tosyl Permethylated â-Cyclodextrin (5). p-Toluene-
sulfonyl chloride (0.36 g, 1.91 mmol) was added to a solution of 431
(1.8 g, 1.27 mmol) in 50 mL of dry pyridine at 0 °C under N2. The
mixture was warmed to 50 °C and stirred for 12 h. The solvent was
removed and the residue was dissolved in CHCl3 (50 mL). The
chloroform solution was washed with water (50 mL) and saturated
aqueous NaCl (2 × 50 mL) and dried over Na2SO4. The solvent was
evaporated and the solid residue was purified by silica gel column
chromatography with CHCl3/CH3OH (1/50). Yield 90%. 1H NMR (δ/
ppm, CDCl3, 400 MHz, 25 °C): 2.47 (s, 3 H, tosyl-CH3), 3.05-4.52
(m, 102 H), 5.01-5.20 (m, 7 H), 7.38 (d, 2 H, phenyl), 7.78 (d, 2 H,
phenyl). MS (FAB, m-NBA) m/z 1592 (M + Na)+.
carried out due to self-aggregation of 2 (5 × 10-4 mol dm-3
)
in D2O, which resulted in the broadening of all NMR signals.
1
However, it was confirmed that no H NMR signals due to a
folded conformation appeared at 1.5-2.5 ppm with 2 in the
absence or presence of 8 (supporting information).
Conjugate 2. A mixture of 5 (600 mg, 3.8 × 10-4 mol), 5,10,15,-
20-tetrakis(4-hydroxyphenyl)porphyrin (45 mg, 6.6 × 10-5 mol), and
K2CO3 (100 mg) in dry DMF (10 mL) was stirred at 80 °C for 60 h
under N2. The solvent was removed and the residue was dissolved in
CHCl3 (50 mL). The chloroform solution was washed with water (50
mL) and saturated aqueous NaCl (2 × 50 mL) and then dried over
Na2SO4. The purple solid obtained by evaporating the solvent was
purified by silica gel column chromatography with CHCl3 and CHCl3/
Efficient fluorescence quenching of 2 by Fe-8 took place,
while that of 3 by Fe-8 was leveled off at lower I0/I (Figure 7).
Two mechanisms can be considered to account for the fluores-
cence quenching: electron transfer for a short donor-acceptor
distance and energy transfer for a long distance.39 A linear
relationship was observed between I/I0 (not I0/I) and the
percentage of 3-Fe-8 complex formed under certain conditions
for the 3-Fe-8 system. From this relationship, the I/I0 value
for the conditions where 100% of 3 forms the complex can be
evaluated to be 0.34. The rate constant for quenching of the
photoexcited singlet state of donor (kET) can be estimated from
1
CH3OH (50/1). Yield 36%. H NMR (δ/ppm, CDCl3, 400 MHz, 25
°C): -2.79 (s, 2 H, NH), 3.11-4.76 (m, 408 H), 5.02-5.35 (m, 7 H),
7.34 (d, 8 H, phenyl), 8.09 (d, 8 H, phenyl), 8.84 (s, 8 H, â-pyrrole).
MS (MALDI-TOF, dithranol): m/z 6264.9 (calcd for M+: 6268.9).
UV- vis (CH2Cl2, 25 °C): 422 (ꢀ 493 400 dm3 mol-1 cm-1), 518
(17 600), 555 (12 650), 594 (5800), 649 nm (6300). Anal. Calcd for
kET ) [(I0/I)sat - 1]/τ0
(39) Kilsa, K.; Kajanus, J.; Larsson, S.; Macpherson, A. N.; Mårtensson, J.;
Albinsson, B. Chem.sEur. J. 2001, 7, 2122-2133.
(40) Heiler, D.; McLendon, G. L.; Rogalsky, P. J. Am. Chem. Soc. 1987, 109,
604-606.
where τ0 is the fluorescence lifetime of the donor. The τ0 values
were determined to be 10.0 and 7.4 ns for 2 and 3, respectively.
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A R T I C L E S
C
292H462N4O140: C, 55.95; H, 7.43; N, 0.89; O, 35.75. Found: C, 55.26;
O, 18.05. 10. 1H NMR (δ/ppm, CDCl3, 400 MHz, 25 °C): -2.78 (s, 2
H, NH), 1.43 (t, 24 H, CO2CH2CH3), 4.50 (q, 16 H, CO2CH2CH3),
8.78 (d, 8 H, â-pyrrole), 9.06 (s, 8 H, diethoxycarbonylphenyl), 9.15
(s, 4 H, diethoxycarbonylphenyl). MS (FAB, m-NBA): m/z 1190 (M+),
1191(M + H)+. UV-vis (CH2Cl2): 420 (ꢀ 580 500 dm3 mol-1 cm-1),
514 (24 200), 549 (7600), 589 (7220), 644 nm (3150). Anal. Calcd for
C68H62N4O16: C, 68.56; H, 5.25; N, 4.70; O, 21.49. Found: C, 68.57;
H, 5.17; N, 4.60; O, 21.49.
H, 7.35; N, 0.70; O, 36.02.
Porphyrin 6. 5-Formyldiethylisophthalate (1.56 g, 6.19 mmol),
p-hydroxybenzaldehyde (0.46 g, 3.77 mmol), and pyrrole (0.69 mL,
10 mmol) were dissolved in 1 L of CH2Cl2 under N2 atmosphere and
then BF3 etherate (190 µL) was added into this solution. After the
solution was stirred at room temperature for 1 h, 2,3-dichloro-5,6-
dicyanobenzoquinone (2.5 g) was added into the reaction mixture and
the resulting solution was refluxed for 1 h. The solvent was evaporated
and the residue was purified twice by silica gel column chromatography
with CH2Cl2/CH3OH (20/1) and CH2Cl2/ethyl acetate (100/1). Yield
5%. 1H NMR (δ/ppm, CDCl3, 400 MHz, 25 °C): -2.78 (s, 2 H, NH),
1.42 (t, 18 H, CO2CH2CH3), 4.49 (q, 12 H, CO2CH2CH3), 5.25 (s, 1
H, OH), 7.24 (d, 2 H, phenyl), 8.09 (d, 2 H, phenyl), 8.73 (m, 6 H,
â-pyrrole), 8.93 (d, 2 H, â-pyrrole), 9.06 (s, 6 H, diethoxycarbonylphe-
nyl), 9.14 (s, 3 H, diethoxycarbonylphenyl). MS (FAB, m-NBA): m/z
1063 (M+), 1064 (M + H)+. UV-vis (CH2Cl2): 422 (ꢀ 462 650 dm3
mol-1 cm-1), 517 (21 200), 552 (8450), 591 (6400), 646 nm (4050).
Conjugate 7. A mixture of 5 (92 mg, 5.8 × 10-5 mol), 6 (50 mg,
4.7 × 10-5 mol), and K2CO3 (100 mg) in dry DMF (10 mL) was stirred
at 60 °C for 48 h under N2 atmosphere. After the solvent was removed,
the residue was dissolved in CHCl3 (50 mL). The chloroform solution
was washed with water (50 mL) and saturated aqueous NaCl (2 × 50
mL) and then dried over Na2SO4. The purple solid obtained by
evaporating CHCl3 was purified by silica gel column chromatography
with CHCl3 to CHCl3/ethyl acetate/CH3OH (100/0.75/0.25). Yield 83%.
1H NMR (δ/ppm, CDCl3, 400 MHz, 25 °C): -2.80 (s, 2 H, NH), 1.40
(t, 18 H, CO2CH2CH3), 3.16-4.68 (m, 102 H), 4.47 (q, 12 H, CO2CH2-
CH3), 5.09-5.29 (m, 7 H), 7.33 (d, 2 H, phenyl), 8.11 (d, 2 H, phenyl),
8.70 (d, 2 H, â-pyrrole), 8.73 (s, 4 H, â-pyrrole), 8.90 (d, 2 H,
â-pyrrole), 9.02 (s, 6 H, diethoxycarbonylphenyl), 9.12 (s, 3 H,
diethoxycarbonylphenyl). MS (MALDI-TOF, dithranol): m/z 2459.0
(calcd for M+: 2460.7). UV-vis (CH2Cl2): 422 (ꢀ 442 500 dm3 mol-1
cm-1), 517 (19 850), 552 (7900), 593 (5800), 646 nm (3350).
Conjugate 3. A solution of 7 (50 mg) and KOH (0.4 g) in a mixed
solvent of water (10 mL), methanol (30 mL), and dioxane (10 mL)
was refluxed for 12 h. The organic solvents were evaporated and the
aqueous residue was acidified to pH 1 with hydrochloric acid. The
green precipitate was extracted using CHCl3 (100 mL) and the organic
layer was washed with water (3 × 100 mL) and dried over Na2SO4.
Carboxylic Acids 8 and 11. An aqueous methanol solution (H2O/
MeOH ) 10 mL/60 mL) of a mixture of 9 (200 mg) and KOH (1.6 g)
was refluxed for 12 h. After the reaction, methanol was evaporated.
The aqueous residue was acidified to pH 1 with aqueous HCl and cooled
by ice. The precipitate of 8 was collected by filtration. Compound 1132b
1
was prepared by the same procedure. Yield: 8, 84%; 11, 94%. 8. H
NMR (δ/ppm, 0.1 mol dm-3 phosphate buffer (D2O), pD ) 7, 400
MHz, 25 °C): 7.79 (t, 2 H, phenyl), 7.85 (d, 1 H, phenyl), 8.16 (d, 2
H, phenyl), 8.78 (m, 3 H, diethoxycarbonylpheny), 8.83 (m, 6 H,
diethoxycarbonylphenyl), 9.10 (br, 8 H, â-pyrrole). MS (FAB, glyc-
erol): m/z 878 (M - H)-, 879 (M-). UV-vis (0.1 mol dm-3 phosphate
buffer, pH ) 7.0): 414 (ꢀ 526 900 dm3 mol-1 cm-1), 514 (17 125),
549 (7045), 589 (6535), 645 nm (3845).
Zn-8. An aqueous solution (30 mL) of the free-base porphyrin 8
(50 mg) and zinc oxide (50 mg) was refluxed for 2 days in the dark.
After the reaction, excess zinc oxide was removed by filtration. The
reaction mixture was concentrated and passed through DOWEX HCR-
W2 (Na form) ion-exchange resin and Sephadex G-25 columns. The
purple solid was obtained by evaporating the solvent. Yield: 75%. 1H
NMR (δ/ppm, D2O, 400 MHz, 25 °C): 7.87 (m, 3 H, phenyl), 8.32 (d,
2 H, phenyl), 8.74 (s, 3 H, dicarboxylatophenyl), 8.81 (s, 6 H,
dicarboxylatophenyl), 8.99-9.07 (m, 8 H, â-pyrrole). MS (MULDI-
TOF, 1,5-naphthalenediamine): m/z 941.0 (M - 6Na + 5H)-. UV-
vis (0.1 mol dm-3 phosphate buffer, pH ) 7.0): 422 (ꢀ 601 400 dm3
mol-1 cm-1), 556 (18 860), 595 nm (8405).
Zn-11. The procedure used was the same as that for Zn-8. Yield
76%. 1H NMR (δ/ppm, D2O, 400 MHz, 25 °C): 8.76 (s, 4 H,
dicarboxylatophenyl), 8.83 (s, 8 H, dicarboxylatophenyl), 9.03 (br s, 8
H, â-pyrrole). MS (MULDI-TOF, 1,5-naphthalenediamine): m/z 1028.7
(M - 8Na + 7H)-. UV-vis (0.1 mol dm-3 phosphate buffer, pH )
7.0): 422 (ꢀ 597 000 dm3 mol-1 cm-1), 557 (18 350), 596 nm (7475).
Fe-9. A solution of free-base porphyrin 9 (100 mg) in FeCl2‚nH2O-
saturated DMF (10 mL) was added to CH2Cl2 (60 mL) and stirred for
12 h at 50 °C in the dark under N2 atmosphere. The progress of the
reaction was monitored by fluorescence spectroscopy and TLC (SiO2;
CH2Cl2/ethyl acetate (20/1); Rf value, 0.59 (9) and 0.24 (Fe-9)). The
solvent was removed under reduced pressure and the residue was
dissolved in CHCl3 (100 mL). The chloroform solution was washed
with water (200 mL) and saturated aqueous NaCl (2 × 200 mL) and
then dried over Na2SO4. A dark purple solid was obtained after
evaporating the solvent. Yield: 81%. MS (FAB, m-NBA): m/z 1101
(M+).
1
Evaporation of CHCl3 afforded 3 as a purple solid. Yield: 87%. H
NMR (δ/ppm, 0.1 mol dm-3 phosphate buffer (D2O), pD ) 7.0, 400
MHz, 25 °C): 0.96-5.56 (m, 109 H), 7.45 (d, 2 H, phenyl), 8.40 (d,
2 H, phenyl), 8.70-8.84 (m, 9 H, dicarboxylatophenyl), 8.90-9.10
(br, â-pyrrole). MS (MALDI-TOF, dithranol): m/z 2313.4 (calcd for
(M + Na)+: 2315.3). UV-vis (0.1 mol dm-3 phosphate buffer, pH )
7.0): 417 (ꢀ 370 950 dm3mol-1cm-1), 516 (14 250), 551 (5600), 584
(5450), 636 nm (3100).
Esters 9 and 10. BF3 etherate (190 µL) was added to a mixture of
5-formyldiethylisophthalate (1.8 g, 7.1 mmol), benzaldehyde (0.32 g,
3.0 mmol), and pyrrole (0.69 mL, 10 mmol) in 1 L of CH2Cl2 under
the N2 atmosphere. After stirring the solution at room temperature for
1 h, 2,3-dichloro-5,6-dicyanobenzoquinone (2.5 g) was added and the
reaction mixture was refluxed for 1 h. TLC (SiO2; CH2Cl2/ethyl
acetate: 20/1 (v/v)) suggested two major products with Rf values of
0.59 (9) and 0.38 (10). The solvent was evaporated and the residue
was purified by silica gel column chromatography with CH2Cl2/ethyl
Fe-10. The procedure used was the same as that for Fe-9. Yield:
86%. MS (FAB, m-NBA): m/z 1245 (M+).
Fe-8. An aqueous methanol solution (H2O/MeOH ) 10 mL/60 mL)
of a mixture of Fe-9 (85 mg) and KOH (1.5 g) was refluxed for 12 h.
Methanol was evaporated and the aqueous residue was acidified to pH
1 with aqueous HCl. The resulting solution was cooled by ice and the
Fe-8 precipitate was collected by filtration. Yield: 84%. MS (MULDI-
TOF, 1,5-naphthalenediamine): m/z 931.6 (M - H)-. UV-vis (aqueous
NaOH solution containing 0.1 mol dm-3 NaClO4 at pH ) 9.9) 333 (ꢀ
41 650 dm3mol-1cm-1), 416 nm (148 225). UV-vis (0.01 mol dm-3
succinic acid buffer containing 0.1 mol dm-3 NaClO4 at pH ) 5.5):
395 (ꢀ 153 200 dm3 mol-1 cm-1), 529 nm (14 875).
Fe-11. Similar treatment afforded Fe-11. Yield 94%. UV-vis
(aqueous NaOH solution containing 0.1 mol dm-3 NaClO4 at pH )
9.5): 333 (ꢀ 37 175 dm3 mol-1 cm-1), 415 nm (141 375). MS (MULDI-
TOF, 1,5-naphthalenediamine): m/z 1020.2 (M - H)-. UV-vis (0.01
1
acetate (50/1). Yield: 9, 12%; 10, 10%. 9. H NMR (δ/ppm, CDCl3,
400 MHz, 25 °C): -2.78 (s, 2 H, NH), 1.42 (t, 18 H, CO2CH2CH3),
4.50 (q, 12 H, CO2CH2CH3), 7.79 (m, 3 H, phenyl), 8.22 (d, 2 H,
phenyl), 8.74-8.76 (m, 6 H, â-pyrrole), 8.90 (d, 2 H, â-pyrrole), 9.05
(m, 6 H, diethoxycarbonylphenyl), 9.15 (m, 3 H, diethoxycarbonyl-
phenyl). MS (FAB, m-NBA): m/z 1046 (M+), 1047 (M + H)+. UV-
vis (CH2Cl2): 420 (ꢀ 569 000 dm3 mol-1 cm-1), 514 (23 300), 549
(7870), 589 (6935), 645 nm (3455). Anal. Calcd for C62H54N4O12: C,
71.12; H, 5.20; N, 5.35; O, 18.33. Found: C, 71.12; H, 5.50; N, 5.11;
9
J. AM. CHEM. SOC. VOL. 125, NO. 35, 2003 10633

A R T I C L E S
Kano et al.
mol dm-3 succinic acid buffer containing 0.1 mol dm-3 NaClO4 at pH
) 5.5): 395 (ꢀ 144 275 dm3 mol-1 cm-1), 529 nm (13 825).
Other Materials. TMe-â-CD (Nacalai) was purchased and used
without further purification. â-CD (Nacalai) was washed with THF
using a Soxhlet extractor and dried. D2O (CEA, 99.8%) and CDCl3
(CEA, 99.8%) were used as received.
emitted were collected by a Hamamatsu model R2809U-01 micro-
channel-plate photomultiplier. The fluorescence decay curves were
analyzed by using the IGOR software program. Energy transfer
efficiencies were calculated from fluorescence lifetimes of the donor
in the absence or presence of the acceptor by an ordinary method.13a
The determination of K values from UV-vis spectroscopic titrations
were carried out by the method previously described.11
Measurements. Absorption and fluorescence spectra were recorded
on a Shimadzu UV-2100 spectrometer and a Shimadzu RF-5300PC
The reproducibility of all data shown herein was confirmed by
repeated experiments.
1
spectrofluorometer, respectively. H NMR spectra were taken using a
JEOL JNM-A400 spectrometer (400 MHz). TMS (Nacalai) and sodium
3-trimethylsilyl[2,2,3,3-2H4]propionate (TSP, Aldrich) were used as
internal (for organic solvents) and external (for D2O) standards,
respectively. FAB MS and MALDI-TOF MS spectra were recorded
on a JEOL JMS-700 spectrometer and a Shimadzu/Kratos KOMPACT
MALDI IV spectrometer, respectively. Microcalorimetric measurements
were carried out with an Isothermal Titration Calorimeter VP-ITC and
the titration data were analyzed with the ORIGIN software program.
Fluorescence decay curves were recorded by exciting the samples at
415 nm using a picosecond pulse laser (a Coherent model Mira 900
mode-locked Ti-sapphire laser pumped by Coherent model Innova 300
Ar-ion laser combined with a Coherent model 9200 pulse picker) and
counting the photons with a single photon timing apparatus. The photons
Acknowledgment. This work was supported by a Grant-in-
Aid for Scientific Research B (KAKENHI 14340224) from the
Ministry of Education, Culture, Sports, Science and Technology,
Japan.
Supporting Information Available: Absorption and 1H NMR
spectra of Zn-8 in the absence or presence of TMe-â-CD,
calorimetric titration data for the 3-Zn-8 system, and 1H NMR
spectra of 2 in the absence or presence of 8 and 11. This material
is available free of charge via the Internet at http://pubs.acs.org.
JA035055Q
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10634 J. AM. CHEM. SOC. VOL. 125, NO. 35, 2003