Chemically Responsive Supramolecular Assemblies of Pyrene-β

Nov 9, 2009 - Pyrene-β-Cyclodextrin Dimer. Tomoki Ogoshi,* Masayoshi Hashizume, Tada-aki Yamagishi, and Yoshiaki Nakamoto*. Graduate School of ...
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Chemically Responsive Supramolecular Assemblies of Pyrene-β-Cyclodextrin Dimer Tomoki Ogoshi,* Masayoshi Hashizume, Tada-aki Yamagishi, and Yoshiaki Nakamoto* Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan Received August 20, 2009. Revised Manuscript Received October 25, 2009 We report supramolecular assemblies of a β-cyclodextrin dimer linked at both ends of a fluorescent phenylethynylpyrene moiety (Py-β-CD dimer). The Py-β-CD dimer formed supramolecular associations in aqueous media due to the π-π stacking of the hydrophobic phenylethynylpyrene moiety. From tapping mode atomic force microscopy measurements, the Py-β-CD dimer formed wire-shaped assemblies in aqueous media. By adding sodium adamantane carboxylate to the supramolecular assemblies, the structural change to J-type assemblies was observed. In contrast, upon addition of the electron-deficient guest, the electron transfer from the electron rich phenylethynylpyrene moiety of the supramolecular assemblies to the electron-deficient guest took place.

Introduction The construction of self-assembly architectures of synthetic molecules using principles of supramolecular chemistry is currently a subject of great interest in various fields such as chemistry, biology, physics, and material science. For the construction of the supramolecular assemblies, noncovalent interactions such as *Corresponding Author. Mailing address: Department of Chemistry and Chemical Engineering, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan. Telephone: þ81-76-234-4775. Fax: þ81-76-234-4800. E-mail: [email protected]. (1) Brunsveld, L.; Folmer, B. J. B.; Meijer, E. W.; Sijbesma, R. P. Chem. Rev. 2001, 101, 4071–4098. (2) Hoeben, F. J. M.; Jonkheijm, P.; Meijer, E. W.; Schenning, A. P. H. J. Chem. Rev. 2005, 105, 1491–1546. (3) Roosma, J.; Mes, T.; Leclere, P.; Palmans, A. R. A.; Meijer, E. W. J. Am. Chem. Soc. 2008, 130, 1120–1121. (4) Wilson, A. J.; Nasuda, M.; Sijbesma, R. P.; Meijer, E. W. Angew. Chem., Int. Ed. 2005, 44, 2275–2279. (5) Prins, L. J.; Timmerman, P.; Reinhoudt, D. N. J. Am. Chem. Soc. 2001, 123, 10153–10163. (6) Barbera, J.; Puig, L.; Romero, P.; Serrano, J. L.; Sierra, T. J. Am. Chem. Soc. 2005, 127, 458–464. (7) Yamauchi, K.; Takashima, Y.; Hashidzume, A.; Yamaguchi, H.; Harada, A. J. Am. Chem. Soc. 2008, 130, 5024–5025. (8) Ogoshi, T.; Takashima, Y.; Yamaguchi, H.; Harada, A. J. Am. Chem. Soc. 2007, 129, 4878–4879. (9) Kuad, P.; Miyawaki, A.; Takashima, Y.; Yamaguchi, H.; Harada, A. J. Am. Chem. Soc. 2007, 129, 12630–12631. (10) Miyauchi, M.; Takashima, Y.; Yamaguchi, H.; Harada, A. J. Am. Chem. Soc. 2005, 127, 2984–2989. (11) Ogoshi, T.; Takashima, Y.; Yamaguchi, H.; Harada, A. Chem. Commun. 2006, 3702–3704. (12) Harada, A. Acc. Chem. Res. 2001, 34, 456–464. (13) Liu, Y.; Wang, K. R.; Guo, D. S.; Jiang, B. P. Adv. Funct. Mater. 2009, 19, 2230–2235. (14) Liu, Y.; Chen, Y. Acc. Chem. Res. 2001, 34, 681–691. (15) Ghosh, S.; Ramakrishnan, S. Macromolecules 2005, 38, 676–686. (16) Ghosh, S.; Ramakrishnan, S. Angew. Chem., Int. Ed. 2005, 44, 5441–5447. (17) Ghosh, S.; Ramakrishnan, S. Angew. Chem., Int. Ed. 2004, 43, 3264–3268. (18) Gallivan, J. P.; Schuster, G. B. J. Org. Chem. 1995, 60, 2423–2429. (19) Xiao, J.; Xu, J.; Cui, S.; Liu, H.; Wang, S.; Li, Y. Org. Lett. 2008, 10, 645– 648. (20) van Herrikhuyzen, J.; George, S. J.; Vos, M. R. J.; Sommerdijk, N. A. J. M.; Ajayaghosh, A.; Meskers, S. C. J.; Schenning, A. P. H. J. Angew. Chem., Int. Ed. 2006, 46, 230–233. (21) Ogoshi, T.; Hiramitsu, S.; Yamagishi, T.; Nakamoto, Y. Macromolecules 2009, 42, 3042–3047. (22) Kim, Y.; Mayer, M. F.; Zimmerman, S. C. Angew. Chem., Int. Ed. 2003, 42, 1121–1126.

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hydrogen bonding,1-6 host-guest,7-14 charge transfer,15-18 and π-π stacking19-27 interactions play critical roles. The supramolecular assemblies produced by these noncovalent interactions have the potential to dynamically change their supramolecular architectures. The dynamic change in supramolecular structures of micelles, vesicles, gels, and supramolecular polymers induced by stimuli such as pH, temperature, redox state, light, and chemicals has been reported.7-9,11,16,17,19,23-29 Among them, the construction of the stimuli-responsive supramolecular assemblies containing chromophore moieties is also a challenge and opens the way for new optoelectronic applications such as optoelectronic devices, sensors, and photosynthesis because the orientation and/or the associated state of the chromophores have an extreme influence on optical and electrical properties. Ajayaghosh and co-workers reported successful chemically responsive supramolecules containing π-conjugated molecules.23-27 Hierarchical amplification of the chirality information using dynamic structural changes of helical polyacetylene has been constructed by Yashima and co-workers.29 Fluorescent detection of the chemicals based on association/dissociation of the π-conjugated polymer has also been reported.11 Herein, we describe chemically responsive supramolecular assemblies from a β-cyclodextrin (β-CD) dimer linked at both ends of a fluorescent phenylethynylpyrene moiety (Py-β-CD dimer, Figure 1). Since the pyrene displays interesting optical and electrochemical properties, we employed a pyrene derivative as a chromophore linker. In this study, we investigated the supramolecular association property of the Py-β-CD dimer in aqueous media. Furthermore, CD forms host-guest complexes (23) Ajayaghosh, A.; Varghese, R.; Mahesh, S.; Praveen, V. K. Angew. Chem., Int. Ed. 2006, 45, 7729–7732. (24) Srinivasan, S.; Babu, S. S.; Praveen, V. K.; Ajayaghosh, A. Angew. Chem., Int. Ed. 2008, 47, 5746–5749. (25) Ajayaghosh, A.; Praveen, V. K. Acc. Chem. Res. 2007, 40, 644–656. (26) Yagai, S.; Kubota, S.; Saito, H.; Unoike, K.; Karatsu, T.; Kitamura, A.; Ajayaghosh, A.; Kanesato, M.; Kikkawa, Y. J. Am. Chem. Soc. 2009, 131, 5408–5410. (27) Praveen, V. K.; Babu, S. S.; Vijayakumar, C.; Varghese, R.; Ajayaghosh, A. Bull. Chem. Soc. Jpn. 2008, 81, 1196–1211. (28) Wang, Y.; Ma, N.; Wang, Z.; Zhang, X. Angew. Chem., Int. Ed. 2007, 46, 2823–2826. (29) Maeda, K.; Mochizuki, H.; Watanabe, M.; Yashima, E. J. Am. Chem. Soc. 2006, 128, 7639–7650.

Published on Web 11/09/2009

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Figure 1. Py-β-CD dimer.

with various kinds of guest compounds,30 and thus, vacant CD cavities of the supramolecular assemblies should capture guest molecules. In this study, we revealed the chemically responsive property of the supramolecular assemblies. Fluorescent quenching of the supramolecular assemblies upon addition of the electron-deficient guest was also studied.

Results and Discussion Association of Py-β-CD Dimer in Aqueous Media. The association behavior of the Py-β-CD dimer was investigated by 1 H NMR, UV-vis absorption, circular dichroism (CD), fluorescence, and tapping mode atomic force microscopy (TM-AFM) measurements. We measured 1H NMR spectra of the Py-β-CD dimer in DMSO-d6 and D2O (Supporting Information). In DMSO-d6, proton signals from aromatic and β-CD groups were clearly found. On the other hand, in D2O, the aromatic proton resonances of the Py-β-CD dimer were largely broadened. These data indicate that the molecular motion of the hydrophobic aromatic moieties in the Py-β-CD dimer was suppressed at room temperature due to their transition to the interior of the associates in aqueous media. Furthermore, we measured variable temperature 1H NMR spectra of the Py-β-CD dimer in D2O (Supporting Information). As the measurement temperature was increased, the aromatic proton resonances started to appear, indicating that the supramolecular assemblies were dissociated by heating. UV-vis absorption spectra of the Py-β-CD dimer dissolved in a series of CH3OH/H2O mixed solvents are shown in Figure 2a. In CH3OH/H2O (80/20) mixed solvent, the maximum absorbance of the Py-β-CD dimer was found at 400 nm. Since the absorption of (30) Rekharsky, M. V.; Inoue, Y. Chem. Rev. 1998, 98, 1875–1918.

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Figure 2. (a) UV-vis absorption and (b) CD spectra of Py-β-CD dimer in H2O/methanol mixed solvents. The concentration of the Py-β-CD dimer was 30 μM.

the Py-β-CD dimer is the same as that of the bis(1,6-phenylethynyl)pyrene derivatives previously reported,19 no association occurred in the mixed solvent. In contrast, by decreasing the ratio of CH3OH to H2O, the peak intensity at 400 nm was decreased and a new shoulder around 430-470 nm was observed. Moreover, at the elevated temperatures, the shoulder was decreased through an isosbestic point at 430 nm (Supporting Information). Because the supramolecular assemblies are dissociated by heating as shown in variable temperature 1H NMR measurements, the shoulder derives from the supramolecular assemblies formed in aqueous media. Figure 2b shows CD spectra of the Py-β-CD dimer in CH3OH/H2O mixed solvents. No CD signal was detected in the CH3OH/H2O (80/20) mixed solvent. As the ratio of CH3OH to H2O decreased, the exciton-coupled negative (440 nm, 418 nm) and positive (382 nm) CD signals were observed in the region of the π-π* transition of the phenylethynylpyrene. Since the same split-type CD spectra were found in the supramolecular helix composed of bis(1,6-phenylethynyl)pyrene derivatives,19 the Py-β-CD dimer formed the supramolecular helical assemblies in aqueous media. Optical activity of the β-CD moiety in the Py-βCD dimer led to the formation of the helical assemblies. We measured the emission spectra of the Py-β-CD dimer in CH3OH/H2O mixed solvents (Figure 3). When the Py-β-CD dimer in CH3OH/H2O (80/20) mixed solvent was excited at 340 nm, the emission peak was observed at 442 nm, which is the monomeric emission peak of the phenylethynylpyrene moiety of the Py-β-CD dimer.19 As the ratio of CH3OH to H2O decreased, the peak was largely red-shifted from 442 to 514 nm. The Langmuir 2010, 26(5), 3169–3173

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Figure 4. TM-AFM height images (2.0 μm  2.0 μm) of Py-β-CD dimer from (a) methanol and (b) water.

Figure 3. Emission spectra of Py-β-CD dimer in solutions of H2O/ methanol mixed solvents (excited at 340 nm). The concentration of the Py-β-CD dimer was 30 μM.

quantum yields of the Py-β-CD dimer in CH3OH and water were measured as 0.102 and 0.065, respectively, with quinine sulfate in an aqueous 0.10 M H2SO4 solution at a standard of 25 °C. These data also support the association of the phenylethynylpyrene segments in aqueous media at 25 °C. We measured the concentration dependence on fluorescence spectra of the Py-β-CD dimer in aqueous media (Supporting Information). In high concentrations, the emission peak at 514 nm from the association of the phenylethynylpyrene segments was observed. However, in low concentrations, the intensity of the peak at 514 nm was clearly decreased, indicating the dissociation of the phenylethynylpyrene segments in dilute concentrations. From the concentration dependence on the emission intensity ratio (I461/I514), the critical association concentration (cac) was found to be 8 μM (Supporting Information). Therefore, the Py-β-CD dimer formed supramolecular assemblies even at extremely dilute concentration levels. Nanostructures of the supramolecular architectures in aqueous media were investigated by TM-AFM measurements (Figure 4). For the preparation of the samples, one drop of Py-β-CD dimer solution was deposited onto a freshly cleaved mica surface. Py-βCD dimer from methanol showed heterogeneous spherical aggregates (Figure 4a), and the size of the aggregates was ca. 3.0 nm. Therefore, the Py-β-CD dimer did not form characteristic supramolecular assemblies in methanol. On the other hand, in the case of the Py-β-CD dimer from water, wire assemblies were mainly observed (Figure 4b) and distributed with uniformity (overall images are shown in the Supporting Information). The average size of the wires was found to be 1.0-1.2 nm. π-π stacking of the planar phenylethynylpyrene moiety resulted in the formation of the wire-shaped assemblies in aqueous media. Chemically Induced J-Type Supramolecular Assemblies of Py-β-CD Dimer in Aqueous Media. CD forms host-guest complexes with various kinds of guest compounds;30 thus, vacant β-CD cavities around the supramolecular assemblies in aqueous media are able to capture the guest molecules. In this study, by employing sodium adamantane carboxylate (AdCNa) as a guest, we investigated the change in the supramolecular assemblies in aqueous media. We measured 1H NMR spectra of the Py-β-CD Langmuir 2010, 26(5), 3169–3173

Figure 5. (a) UV-vis absorption and (b) CD spectra of Py-β-CD dimer in 0.1 N NaOH aqueous media upon addition of AdCNa. The concentration of the Py-β-CD dimer was 30 μM.

dimer in D2O in the absence and presence of AdCNa (Supporting Information). In the absence of AdCNa, proton resonances of the phenylethynylpyrene segments were expanding at 25 °C. The DOI: 10.1021/la903103w

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Figure 6. (a) Transition of the supramolecular structure to J-type associations induced by AdCNa and (b) electron transfer from supramolecular assemblies of Py-β-CD dimer to AdPy.

observation should result from strong facial π-π stacking of the phenylethynylpyrene moieties in aqueous media at 25 °C. In contrast, upon addition of AdCNa, the proton signals from the phenylethynylpyrene segments were observed, indicating loose π-π stacking of the phenylethynylpyrene segments even at 25 °C. From these observations, it was found that addition of AdCNa induced changes in the supramolecular assemblies. Figure 5a shows UV-vis absorption spectra of the Py-β-CD dimer in aqueous media upon addition of AdCNa. When AdCNa was added to the aqueous Py-β-CD dimer solution, a new sharp peak at 432 nm was observed. Since the absorption in the region resulted from the supramolecular assemblies of the phenylethynylpyrene segments of the Py-β-CD dimer as shown in Figure 2a, the dynamic change in the supramolecular structures was induced by AdCNa. The peak at 432 nm corresponded to the J-type assemblies of the phenylethynylpyrene moieties;19 thus, complexation between β-CD of the supramolecular assemblies and AdCNa induced transition of the supramolecular structure to the J-type associations (Figure 6a). Furthermore, upon addition of AdCNa, the monomeric peak at 400 nm was also increasing. The foundation indicates that the complexation of AdCNa with the supramolecular assemblies weakened the π-π stacking of the phenylethynylpyrene segments. Electrostatic repulsive forces and/ or steric hindrance between complexed anions of AdCNa may displace the facial π-π stacking. The peak from the J-type supramolecular assemblies was decreased by heating (Supporting Information), indicating that dissociation of the J-type assemblies took place at elevated temperature. Figure 5b shows CD spectra of aqueous Py-β-CD dimer solutions by adding AdCNa. By adding AdCNa, the intensities of the split-type CD signals started to increase, indicating change in the helical pitch of the supramolecular assemblies by the inclusion of AdCNa. Even though AdCNa is an achiral guest, the inclusion of AdCNa into the β-CD cavity around the supramolecular assemblies induced change in the helical pitch of the supramolecular assemblies. The change in helical pitch should result from the transition of the supramolecular structure to J-type associations. Emission spectra of the Py-β-CD dimer upon addition of AdCNa in aqueous solutions were measured (Figure 7). By adding AdCNa, the fluorescent intensities were increased and the peak was red-shifted. Since the observations are typical (31) Hoeben, F. J. M.; Wolffs, M.; Zhang, J.; De Feyter, S. D.; Leclere, P.; Schenning, A. P. H. J.; Meijer, E. W. J. Am. Chem. Soc. 2007, 129, 9819–9828.

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Figure 7. Emission spectra of Py-β-CD dimer in 0.1 N NaOH aqueous media upon addition of AdCNa (excited at 340 nm). The concentration of the Py-β-CD dimer was 30 μM.

phenomena in the formation of the J-type assemblies,31 construction of the J-type assemblies upon addition of AdCNa was confirmed. Fluorescent Quenching of the Supramolecular Assemblies upon the Addition of the Electron-Deficient Guest. It was demonstrated that the fluorescence of pyrene was quenched by electron accepting pyridinium derivatives.32,33 Therefore, by employing an adamantane derivative having pyridinium salt (AdPy) as an electron accepting guest, we investigated the fluorescent quenching of the supramolecular assemblies in aqueous media. Upon addition of AdPy, large fluorescent quenching was observed (Figure 8, solid line). Holding pyridinium groups around the supramolecular assemblies via the host-guest formation results in efficient electron transfer from the phenylethynylpyrene moieties to the pyridinium moiety (Figure 6b). When excess sodium adamantane carboxylate (AdCNa, 100 equiv to Py-β-CD dimer) was added to the mixture as a competitive guest, the fluorescence completely recovered (Figure 8, dashed line). (32) Tao, C.; Pinto, M. R.; Schanze, K. S. Chem. Commun. 2002, 446–447. (33) Chen, L.; Xu, S.; McBranch, D.; Whitten, D. J. Am. Chem. Soc. 2000, 122, 9302–9303.

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Measurements. The 1H NMR spectra were recorded at 270

Figure 8. Emission spectra (excited at 340 nm) of Py-β-CD dimer with AdPy (0-2 equiv to Py-β-CD dimer, solid line) and with AdPy (2 equiv) and AdCNa (100 equiv, dashed line). The concentration of the Py-β-CD dimer was 30 μM in 0.1 N NaOH aqueous media.

This result indicates the dissociation of the host-guest complexes between β-CD of the supramolecular assemblies and AdPy. Because β-CD forms the complexes with AdCNa more favorably than with AdPy,34 guest exchange from AdPy to AdCNa takes place.

Conclusions We synthesized a new β-CD dimer linked at both ends of the fluorescent phenylethynylpyrene moiety (Py-β-CD dimer). In aqueous media, the Py-β-CD dimer formed the wire-shaped supramolecular assemblies. The supramolecular assemblies showed the structural transition to the J-type assemblies by adding AdCNa. It is interesting to note that addition of the achiral guest induced change in the pitch of the supramolecular assemblies. On the other hand, upon addition of the electrondeficient guest AdPy, the fluorescent quenching was observed. This is due to the electron transfer from the phenylethynylpyrene to the pyridinium salt of AdPy. The chemically responsive structural changes and fluorescent quenching system depending on the kinds of guest molecules are not well-known but will be applied for fluorescent chemical sensors.

and 400 MHz and 13C NMR spectra were recorded at 67.5 and 100 MHz with JEOL-JNM EX270 and EL400 spectrometers. Fluorescence spectra were recorded on a Hitachi F-2500 fluorescent spectrometer at room temperature. UV-vis absorption spectra were recorded with a JASCO V-630 spectrometer. For fluorescence and UV-vis measurements, 1 cm quartz cuvettes were used. Tapping mode atomic force microscopy (TM-AFM) was conducted on a multimode SPA 400 instrument (SEIKO Instruments). Nanoprobe cantilevers (SI-DF20, SEIKO Instruments) were utilized. 1,6-Diethynylpyrene and 6-O-(4-Iodophenyl)-β-CD. 1,6Diethynylpyrene and 6-O-(4-iodophenyl)-β-CD were synthesized according to procedures in the literature.35,36 Pyrene-β-CD Dimer (Py-β-CD). To a solution of 1,6diethynylpyrene (200 mg, 0.84 mmol) in DMF (20 mL), 6-O-(4iodophenyl)-β-CD (2.81 g, 2.10 mmol), Pd(PPh)2Cl2 (70 mg, 0.11 mmol), CuI (26 mg, 0.134 mmol), PPh3 (60 mg, 0.211 mmol), and diethylamine (20 mL) were added under a nitrogen atmosphere. The mixture was stirred at 60 °C for 48 h. After evaporation of diethylamine, the solution was poured into acetone and the precipitate was collected by filtration. The crude product was purified by column chromatography on DIAION HP-20 (eluted with water/methanol = 100/0 to 40/60). The 30/70 (water/ methanol) eluent was concentrated to produce a yellow solid (Py-β-CD dimer, 2.32 g, yield = 29.6%). 1H NMR (DMSO-d6, 400 MHz, ppm): δ 8.68 (d, 2H, pyrene), 8.45-8.20 (m, 6H, pyrene), 7.72 (d, 4H, phenyl), 7.10 (d, 4H, phenyl), 5.90-5.65 (m, 28H, O2,3H of β-CD), 5.00-4.80 (m, 14H, C1H of β-CD), 4.60-4.40 (m, 10H, O6H of β-CD), 4.35-4.20, 3.80-3.50 (m, CH of β-CD). 13C NMR (DMSO-d6, 100 MHz, ppm): δ 159.1 (phenyl), 133.2 (phenyl), 131.0, 130.6, 129.9, 128.6 (pyrene), 125.7 (phenyl), 115.0 (phenyl), 102.0 (C1 of β-CD), 92.9, 92.4 (CtC), 81.5 (C4 of β-CD), 73.0 (C6 of β-CD), 72.4 (C2 of β-CD), 72.0 (C5 of β-CD), 59.9 (C3 of β-CD). Positive ion MALDI-TOF mass m/z = 2693 [(M þ Na)]þ. UV-vis (water/methanol = 20/ 80): ε = 3.89  104 M-1 cm-1 (400 nm).

Acknowledgment. We thank Prof. A. Harada, Dr. Y. Takashima (Osaka Univ.), Prof. K. Takahashi, and Dr. T. Kuwabara (Kanazawa Univ.) for MALDI-TOF mass and TM-AFM measurements. This work was supported by the Ishikawa Foundation for Carbon Science & Technology and a Grant-in-Aid (KIBAN C-20550120 and WAKATE B-21750140) from the Ministry of Education, Culture, Sports, Science and Technology, Japan. Supporting Information Available: 1H and 13C NMR spectra

Materials. All solvents and reagents were used as supplied except the following. Anhydrous N,N-dimethylformamide (DMF) was purchased from Kanto Reagents, Chemicals & Biologicals. Milli-Q water was used for preparation of aqueous solutions.

of Py-β-CD dimer, variable temperature 1H NMR, UV-vis spectra of Py-β-CD dimer, and concentration dependent fluorescent spectra of Py-β-CD dimer, overall TM-AFM images of Py-βCD dimer from water and methanol, 1H NMR spectrum of Py-βCD dimer with AdCNa in D2O, and variable temperature UV-vis spectra of Py-β-CD dimer/AdCNa complex. This material is available free of charge via the Internet at http://pubs.acs.org.

(34) Ohga, K.; Takashima, Y.; Takahashi, H.; Kawaguchi, Y.; Yamaguchi, H.; Harada, A. Macromolecules 2005, 38, 5897–5904. The association constants for 1:1 complexation of β-CD with AdCNa and AdPy are 39 000 M-1 and 1900 M-1, respectively.

(35) Venkataramana, G.; Sankararaman, S. Eur. J. Org. Chem. 2005, 4162– 4166. (36) Sakamoto, K.; Takashima, Y.; Yamaguchi, H.; Harada, A. J. Org. Chem. 2007, 72, 459–465.

Experimental Section

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