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Synthesis and aggregation properties of amphiphilic mono and bisadducts of fullerene in aqueous solution
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Chinese Chemical Letters 19 (2008) 1039–1042 www.elsevier.com/locate/cclet
Synthesis and aggregation properties of amphiphilic mono and bisadducts of fullerene in aqueous solution Pu Zhang a,*, Zhi Xin Guo a, Shuang Lv b a b
Department of Chemistry, Renmin University of China, Beijing 100872, China Department of Chemistry, Beijing Institute of Technology, Beijing 100081, China Received 10 March 2008
Abstract New amphiphilic[60]fullerene monoadduct TPF and bisadducts BTPF were synthesized and well-characterized. Their aggregation properties in aqueous solution was investigated by UV–vis and TEM methods. In aqueous solution, monoadduct TPF forms irregularly shaped and some rod-like aggregates, whereas bisadducts BTPF gives spherical aggregates with diameters of 50–150 nm. It indicated that the aggregation properties of amphiphilic fullerene derivatives depend on the number of hydrophilic appendage on the C60 cage. # 2008 Pu Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Fullerene; Aggregation; Amphiphilic
Fullerene has attracted much attention and generated a great deal of research interest due to its unique structure and interesting properties [1]. Amphiphilic fullerene derivatives containing polar functions, such as hydroxyl, carboxyl and amino groups, hold promise for potential biological applications and have a propensity to aggregate into morphologically different nanostructure in aqueous solution [2–4]. It is important to understand the facts that regulate the morphologies of the aggregates since the aggregation cause a significant change in photophysical and photochemical properties. Morphologies of fullerene aggregates in solution could be affected by concentration [5,6], pH [7,8], counter anion [9,10] and nature of the appendage [4,11]. However, the influence of the number of the hydrophilic appendages on the morphology was rarely reported. In this work, we synthesized amphiphilic monoadduct TPF bearing two hydrophilic appendage and bisadducts BTPF bearing four hydrophilic appendage and report their aggregation behavior in aqueous solution. Our findings indicated that the increase in the number of hydrophilic appendages on the C60 cage could offer stronger hydrophilicity and thus, induce different structures of fullerene aggregates. 1. Experimental All reagents were purchased from commercial suppliers and used without further purification. All the solvents were purified according to standard methods before use. * Corresponding author. E-mail address: [email protected] (P. Zhang). 1001-8417/$ – see front matter # 2008 Pu Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.06.017
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P. Zhang et al. / Chinese Chemical Letters 19 (2008) 1039–1042
New fullerene monoadduct TPF and bisadducts BTPF were synthesized, purified and characterized. 1 H and 13C NMR spectra were recorded on Bruker AV400 spectrometers. MALDI–TOF–MS spectra were obtained on a Bruker BIFLEX III machine. The UV–vis absorption spectra were measured on a computer-controlled Shimadzu UV2501-PC spectrophotometer. A Hitachi H-600 transmission electron microscope (TEM) was used. To prepare fullerene aggregates, a tetrahydrofuran (THF) solution of fullerene derivatives (1 mL) was injected into deionized water (3 mL) in a test tube with vigorous stirring, gaseous nitrogen was purged through the solution to remove THF. This cycle was repeated three times. In the final stage, a part of water was added up to the original volume in order to compensate the evaporated water during the nitrogen purge process. 2. Results and discussion Scheme 1 showed the synthesis routes of TPF and BTPF. Compound 1 was synthesized according to literatures. TPF was separated with column chromatography (SiO2, toluene/methanol 30/1, v/v), brownish solid, yield: 25%. BTPF was separated with column chromatography (SiO2, toluene/methanol 40/1, v/v), brownish solid, yield: 5%. Both TPF and BTPF had good solubility in common organic solvents, such as CH2Cl2, CHCl3 and THF. The solubility of TPF and BTPF in CHCl3 is higher than 20 mg/mL. Characterization of TPF: 1H NMR (CDCl3, d ppm): 7.41 (s, 1H, ArH), 7.31 (d, 1H, ArH), 6.94 (d, 1H, ArH), 5.73 (s, 1H, ArCHN), 5.08 (d, 1H, C60CH2N), 4.86 (d, 1H, C60CH2N), 4.18–4.15 (m, 4H, OCH2), 3.86–3.83 (m, 4H, OCH2), 3.71–3.58 (m, 16H, OCH2), 3.50 (q, 4H, OCH2Me), 1.19 (t, 6H, CH3); 13C NMR (CDCl3, d ppm): 156.22, 153.97, 153.64, 149.02 148.86, 147.20, 147.17, 146.31, 146.24, 146.19, 146.12, 146.06, 145.93, 145.48, 145.46, 145.41, 145.32, 145.29, 145.25, 145.18, 144.55, 144.37, 142.71, 142.62, 142.57, 142.52, 142.33, 142.22, 142.15, 142.04, 140.17, 140.14, 130.71, 121.42, 114.74, 114.24, 77.94, 77.25, 76.88, 72.70, 70.86, 70.70, 70.68, 69.83, 69.74, 69.64, 68.93, 68.69, 66.64, 61.63, 15.20; MALDI–TOF–MS: 1215.7 (C84H41O8N + Na+) calculated value:1215.2. Characterization of BTPF: 1H NMR (CDCl3, d ppm): 7.42–7.02 (m, 6H, ArH), 5.60–4.65 (m, 6H, C60CH2N and ArCHN), 4.23–3.47 (m, 56H, OCH2), 1.18 (t, 12H, CH3); MALDI–TOF–MS: 1686.3 (C108H82O16N2 + Na+) calculated value: 1686.8. The aggregation behavior of amphiphilic TPF and BTPF in aqueous solution was investigated at a concentration of 0.2 mmol/L. The aggregation of TPF and BTPF in water can be evidenced from UV–vis absorption spectroscopic method (Fig. 1). The UV–vis absorptions of TPF in THF are located at 256, 310 and 430 nm, showing typical absorption features characteristic of a mono-fulleropyrrolidine derivative in form of monomer. The TPF aqueous solution gives a featureless spectrum, with a maximum absorption peak at 264 nm and a shoulder peak at 320 nm, which is similar to those absorption spectra of aggregates of C60 derivatives [12], indicating the aggregation of TPF in water. UV–vis absorption spectroscopy is a routine and reliable tool to determine the bisaddition patterns of C60 bissadducts [13]. The UV–vis spectrum of BTPF in THF is identical with that of a known trans-4 fulleropyrrolidine
Scheme 1. Synthetic routes of monoadduct TPF and bisadducts BTPF. Reagents and conditions: (a) 3,4-dihydroxy benzaldehyde, K2CO3, N,Ndimethylformamide; (b) C60:2:glycine (molar ratio 1:1:5), toluene; (c) C60:2:glycine (molar ratio 1:2:10), o-dichlorobenzene.
P. Zhang et al. / Chinese Chemical Letters 19 (2008) 1039–1042
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Fig. 1. UV–vis absorption spectra of TPF and BTPF in THF and in water.
bisadduct in the fingerprint region of 400–750 nm, with two major absorption peaks at 415 and 460 nm (Fig. 1). Therefore, bisadducts BTPF was assigned as trans-4 structure. Considering the reaction mechanism of Prato reaction, the benzene ring in compound 2 can be attached on the a or a0 -carbon of the pyrrolidine ring, thus, BTPF is a mixture of trans-4 bisadducts. The absorption features of BTPF in the visible region also disappeared in the aqueous solution, indicating the formation of BTPF aggregates. To examine the size and morphology of TPF and BTPF aggregates in aqueous solution, TEM experiments were performed. As shown in Fig. 2, TPF aqueous solution gives irregularly shaped and rod-like aggregates. In case of bisadducts BTPF, the aggregates have a smaller size and are uniformly distributed in size and shape, only spherical aggregates with diameters of 50–150 nm can be seen. It is clearly indicated that the introduction of more hydrophilic chain on C60 cage induces morphologically different nanostructure. This observation is confirmed when we investigated the aggregation of TPF and BTPF at a lower concentration of 0.02 mmol/L. TPF aqueous solution shows irregularly shaped aggregates again, while BTPF aqueous solution gives perfectly spherical aggregates with diameters of 50–100 nm throughout the sample. These experimental results seems to indicated that the size and shape difference of BTPF aggregates relative to that of TPF aggregates might be attributed to the additional hydrophilic appendage on the C60 cage in BTPF molecule. For bisadducts BTPF, the increase in the number of hydrophilic appendage on the C60 cage could offer stronger
Fig. 2. TEM images of TPF and BTPF self-aggregates formed in aqueous solution.
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hydrophilicity and steric repulsion to counterbalance the [60]fullerene moiety and thus, BTPF is more suited for selforganization and form spherical aggregates with a variety of different sizes but well-defined shape. In summary, we have synthesized new amphiphilic fullerene derivatives and investigated their aggregation properties in water. It seems that the aggregation properties of amphiphilic fullerene derivatives depend on the number of hydrophilic appendage on the C60 cage. An extended series of derivatives is under consideration in our laboratories for better understanding these aspects and will be reported in due time. Acknowledgments This research was sponsored by the National Natural Science Foundation of China (No. 20503039) and the Scientific Research Starting Foundation of Department of Chemistry, Renmin University of China. References [1] A.F. Hebard, M.J. Rosseninsky, R.C. Haddon, et al. Nature 350 (1991) 600. [2] L.J. Wilson, Interface 8 (1999) 24. [3] S.R. Wilson, in: K.M. Kadish, R.S. Ruoff (Eds.), Fullerenes: Chemistry, Physics and Technology, John Wiley and Sons, New York, 2000, p. 437. [4] V. Georgakilas, F. Pellarini, M. Prato, et al. Proc. Natl. Acad. Sci. U.S.A. 99 (2002) 5075. [5] S.S. Gayathri, A. Patnaik, J. Chem. Phys. 124 (2006) 131104–131111. [6] M. Sano, K. Oishi, T. Ishi-i, et al. Langmuir 16 (2000) 3773. [7] M. Brettreich, S. Burghardt, C. Bottcher, et al. Angew. Chem., Int. Ed. 39 (2000) 1845. [8] M. Braun, U. Hartnagel, E. Ravanelli, et al. Eur. J. Org. Chem. (2004) 1983. [9] A.M. Cassell, C.L. Asplund, J.M. Tour, Angew. Chem., Int. Ed. 38 (1999) 2403. [10] P. Brough, D. Bonifazi, M. Prato, Tetrahedron 62 (2006) 2110. [11] C. Burger, J.C. Hao, Q.C. Ying, et al. J. Colloid Inter. Sci. 275 (2004) 632. [12] G. Angelini, P. De Maria, A. Fontana, et al. Langmuir 17 (2001) 6404. [13] K. Kordatos, S. Bosi, M. Proto, et al. J. Org. Chem. 66 (2001) 2802.
Chinese Chemical Letters 19 (2008) 1039–1042 www.elsevier.com/locate/cclet
Synthesis and aggregation properties of amphiphilic mono and bisadducts of fullerene in aqueous solution Pu Zhang a,*, Zhi Xin Guo a, Shuang Lv b a b
Department of Chemistry, Renmin University of China, Beijing 100872, China Department of Chemistry, Beijing Institute of Technology, Beijing 100081, China Received 10 March 2008
Abstract New amphiphilic[60]fullerene monoadduct TPF and bisadducts BTPF were synthesized and well-characterized. Their aggregation properties in aqueous solution was investigated by UV–vis and TEM methods. In aqueous solution, monoadduct TPF forms irregularly shaped and some rod-like aggregates, whereas bisadducts BTPF gives spherical aggregates with diameters of 50–150 nm. It indicated that the aggregation properties of amphiphilic fullerene derivatives depend on the number of hydrophilic appendage on the C60 cage. # 2008 Pu Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Fullerene; Aggregation; Amphiphilic
Fullerene has attracted much attention and generated a great deal of research interest due to its unique structure and interesting properties [1]. Amphiphilic fullerene derivatives containing polar functions, such as hydroxyl, carboxyl and amino groups, hold promise for potential biological applications and have a propensity to aggregate into morphologically different nanostructure in aqueous solution [2–4]. It is important to understand the facts that regulate the morphologies of the aggregates since the aggregation cause a significant change in photophysical and photochemical properties. Morphologies of fullerene aggregates in solution could be affected by concentration [5,6], pH [7,8], counter anion [9,10] and nature of the appendage [4,11]. However, the influence of the number of the hydrophilic appendages on the morphology was rarely reported. In this work, we synthesized amphiphilic monoadduct TPF bearing two hydrophilic appendage and bisadducts BTPF bearing four hydrophilic appendage and report their aggregation behavior in aqueous solution. Our findings indicated that the increase in the number of hydrophilic appendages on the C60 cage could offer stronger hydrophilicity and thus, induce different structures of fullerene aggregates. 1. Experimental All reagents were purchased from commercial suppliers and used without further purification. All the solvents were purified according to standard methods before use. * Corresponding author. E-mail address: [email protected] (P. Zhang). 1001-8417/$ – see front matter # 2008 Pu Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.06.017
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P. Zhang et al. / Chinese Chemical Letters 19 (2008) 1039–1042
New fullerene monoadduct TPF and bisadducts BTPF were synthesized, purified and characterized. 1 H and 13C NMR spectra were recorded on Bruker AV400 spectrometers. MALDI–TOF–MS spectra were obtained on a Bruker BIFLEX III machine. The UV–vis absorption spectra were measured on a computer-controlled Shimadzu UV2501-PC spectrophotometer. A Hitachi H-600 transmission electron microscope (TEM) was used. To prepare fullerene aggregates, a tetrahydrofuran (THF) solution of fullerene derivatives (1 mL) was injected into deionized water (3 mL) in a test tube with vigorous stirring, gaseous nitrogen was purged through the solution to remove THF. This cycle was repeated three times. In the final stage, a part of water was added up to the original volume in order to compensate the evaporated water during the nitrogen purge process. 2. Results and discussion Scheme 1 showed the synthesis routes of TPF and BTPF. Compound 1 was synthesized according to literatures. TPF was separated with column chromatography (SiO2, toluene/methanol 30/1, v/v), brownish solid, yield: 25%. BTPF was separated with column chromatography (SiO2, toluene/methanol 40/1, v/v), brownish solid, yield: 5%. Both TPF and BTPF had good solubility in common organic solvents, such as CH2Cl2, CHCl3 and THF. The solubility of TPF and BTPF in CHCl3 is higher than 20 mg/mL. Characterization of TPF: 1H NMR (CDCl3, d ppm): 7.41 (s, 1H, ArH), 7.31 (d, 1H, ArH), 6.94 (d, 1H, ArH), 5.73 (s, 1H, ArCHN), 5.08 (d, 1H, C60CH2N), 4.86 (d, 1H, C60CH2N), 4.18–4.15 (m, 4H, OCH2), 3.86–3.83 (m, 4H, OCH2), 3.71–3.58 (m, 16H, OCH2), 3.50 (q, 4H, OCH2Me), 1.19 (t, 6H, CH3); 13C NMR (CDCl3, d ppm): 156.22, 153.97, 153.64, 149.02 148.86, 147.20, 147.17, 146.31, 146.24, 146.19, 146.12, 146.06, 145.93, 145.48, 145.46, 145.41, 145.32, 145.29, 145.25, 145.18, 144.55, 144.37, 142.71, 142.62, 142.57, 142.52, 142.33, 142.22, 142.15, 142.04, 140.17, 140.14, 130.71, 121.42, 114.74, 114.24, 77.94, 77.25, 76.88, 72.70, 70.86, 70.70, 70.68, 69.83, 69.74, 69.64, 68.93, 68.69, 66.64, 61.63, 15.20; MALDI–TOF–MS: 1215.7 (C84H41O8N + Na+) calculated value:1215.2. Characterization of BTPF: 1H NMR (CDCl3, d ppm): 7.42–7.02 (m, 6H, ArH), 5.60–4.65 (m, 6H, C60CH2N and ArCHN), 4.23–3.47 (m, 56H, OCH2), 1.18 (t, 12H, CH3); MALDI–TOF–MS: 1686.3 (C108H82O16N2 + Na+) calculated value: 1686.8. The aggregation behavior of amphiphilic TPF and BTPF in aqueous solution was investigated at a concentration of 0.2 mmol/L. The aggregation of TPF and BTPF in water can be evidenced from UV–vis absorption spectroscopic method (Fig. 1). The UV–vis absorptions of TPF in THF are located at 256, 310 and 430 nm, showing typical absorption features characteristic of a mono-fulleropyrrolidine derivative in form of monomer. The TPF aqueous solution gives a featureless spectrum, with a maximum absorption peak at 264 nm and a shoulder peak at 320 nm, which is similar to those absorption spectra of aggregates of C60 derivatives [12], indicating the aggregation of TPF in water. UV–vis absorption spectroscopy is a routine and reliable tool to determine the bisaddition patterns of C60 bissadducts [13]. The UV–vis spectrum of BTPF in THF is identical with that of a known trans-4 fulleropyrrolidine
Scheme 1. Synthetic routes of monoadduct TPF and bisadducts BTPF. Reagents and conditions: (a) 3,4-dihydroxy benzaldehyde, K2CO3, N,Ndimethylformamide; (b) C60:2:glycine (molar ratio 1:1:5), toluene; (c) C60:2:glycine (molar ratio 1:2:10), o-dichlorobenzene.
P. Zhang et al. / Chinese Chemical Letters 19 (2008) 1039–1042
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Fig. 1. UV–vis absorption spectra of TPF and BTPF in THF and in water.
bisadduct in the fingerprint region of 400–750 nm, with two major absorption peaks at 415 and 460 nm (Fig. 1). Therefore, bisadducts BTPF was assigned as trans-4 structure. Considering the reaction mechanism of Prato reaction, the benzene ring in compound 2 can be attached on the a or a0 -carbon of the pyrrolidine ring, thus, BTPF is a mixture of trans-4 bisadducts. The absorption features of BTPF in the visible region also disappeared in the aqueous solution, indicating the formation of BTPF aggregates. To examine the size and morphology of TPF and BTPF aggregates in aqueous solution, TEM experiments were performed. As shown in Fig. 2, TPF aqueous solution gives irregularly shaped and rod-like aggregates. In case of bisadducts BTPF, the aggregates have a smaller size and are uniformly distributed in size and shape, only spherical aggregates with diameters of 50–150 nm can be seen. It is clearly indicated that the introduction of more hydrophilic chain on C60 cage induces morphologically different nanostructure. This observation is confirmed when we investigated the aggregation of TPF and BTPF at a lower concentration of 0.02 mmol/L. TPF aqueous solution shows irregularly shaped aggregates again, while BTPF aqueous solution gives perfectly spherical aggregates with diameters of 50–100 nm throughout the sample. These experimental results seems to indicated that the size and shape difference of BTPF aggregates relative to that of TPF aggregates might be attributed to the additional hydrophilic appendage on the C60 cage in BTPF molecule. For bisadducts BTPF, the increase in the number of hydrophilic appendage on the C60 cage could offer stronger
Fig. 2. TEM images of TPF and BTPF self-aggregates formed in aqueous solution.
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hydrophilicity and steric repulsion to counterbalance the [60]fullerene moiety and thus, BTPF is more suited for selforganization and form spherical aggregates with a variety of different sizes but well-defined shape. In summary, we have synthesized new amphiphilic fullerene derivatives and investigated their aggregation properties in water. It seems that the aggregation properties of amphiphilic fullerene derivatives depend on the number of hydrophilic appendage on the C60 cage. An extended series of derivatives is under consideration in our laboratories for better understanding these aspects and will be reported in due time. Acknowledgments This research was sponsored by the National Natural Science Foundation of China (No. 20503039) and the Scientific Research Starting Foundation of Department of Chemistry, Renmin University of China. References [1] A.F. Hebard, M.J. Rosseninsky, R.C. Haddon, et al. Nature 350 (1991) 600. [2] L.J. Wilson, Interface 8 (1999) 24. [3] S.R. Wilson, in: K.M. Kadish, R.S. Ruoff (Eds.), Fullerenes: Chemistry, Physics and Technology, John Wiley and Sons, New York, 2000, p. 437. [4] V. Georgakilas, F. Pellarini, M. Prato, et al. Proc. Natl. Acad. Sci. U.S.A. 99 (2002) 5075. [5] S.S. Gayathri, A. Patnaik, J. Chem. Phys. 124 (2006) 131104–131111. [6] M. Sano, K. Oishi, T. Ishi-i, et al. Langmuir 16 (2000) 3773. [7] M. Brettreich, S. Burghardt, C. Bottcher, et al. Angew. Chem., Int. Ed. 39 (2000) 1845. [8] M. Braun, U. Hartnagel, E. Ravanelli, et al. Eur. J. Org. Chem. (2004) 1983. [9] A.M. Cassell, C.L. Asplund, J.M. Tour, Angew. Chem., Int. Ed. 38 (1999) 2403. [10] P. Brough, D. Bonifazi, M. Prato, Tetrahedron 62 (2006) 2110. [11] C. Burger, J.C. Hao, Q.C. Ying, et al. J. Colloid Inter. Sci. 275 (2004) 632. [12] G. Angelini, P. De Maria, A. Fontana, et al. Langmuir 17 (2001) 6404. [13] K. Kordatos, S. Bosi, M. Proto, et al. J. Org. Chem. 66 (2001) 2802.