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Synthesis and spectroscopic characterization of single-wall carbon nanotubes wrapped by glycoconjugate polymer with bioactive sugars
Chemical Physics Letters 428 (2006) 98–101 www.elsevier.com/locate/cplett
Synthesis and spectroscopic characterization of single-wall carbon nanotubes wrapped by glycoconjugate polymer with bioactive sugars Hirofumi Dohi, Satoshi Kikuchi, Shota Kuwahara, Toshiki Sugai, Hisanori Shinohara
*
Department of Chemistry and Institute for Advanced Research, Nagoya University, Nagoya 464-8602, Japan Received 6 February 2006; in final form 10 June 2006 Available online 23 June 2006
Abstract A novel multivalent carbohydrate-CNT hybrid has been synthesized from SWNT and glycoconjugate polymer, carrying carbohydrate as pendant groups at side chain. Dispersion of SWNT in aqueous solution by using glycoconjugate polymer is achieved by sonication and ultracentrifugation. The multivalent carbohydrate-CNT hybrid is revealed to be photoluminescence active by near-infrared fluorescence spectroscopy. AFM measurements of the hybrid support not only the wrapping of SWNT by glycoconjugate polymer but also successful carbohydrate attachment of individual SWNT. Ó 2006 Elsevier B.V. All rights reserved.
1. Introduction Since the discovery of carbon nanotubes (CNTs) in 1991 by Iijima [1], there have been numerous efforts to clarify their mechanical and electronic properties. Their wide potential applicability not only for electronic but also for chemical and biological materials are currently spotlighted [2–5]. Individual dispersion of CNTs in solvent is, therefore, of great importance to realize the homogenous chemical modification and biological application of CNTs. In this respect, non-covalent procedures are desirable for dispersion of CNTs because CNTs can maintain their own characteristic structure and electronic properties, which should be free from the presence of extensive covalent type chemical functionalization. Several research groups have succeeded to disperse CNTs in solvents with monomeric and polymeric surfactant and to obtain the photoluminescence (PL) spectra, which is known to be a good indication of the individual isolation of CNTs [6–11]. Recently, dispersion of CNTs wrapped by biomolecules has been reported by several
*
Corresponding author. Fax: +81 52 789 1169. E-mail address: [email protected] (H. Shinohara).
0009-2614/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2006.06.053
research groups. For example, the DNA-assisted dispersion of CNTs in water has been achieved and the successful observation of PL signals were reported [12,13]. Since then, biological applications of CNTs have widely been recognized. Barone et al. reported that the glucose oxidaseSWNT conjugate emits PL and the conjugate serves as a glucose sensor using PL phenomena [14]. Dai and coworkers have found that DNA-wrapped CNTs can serve as a biological transporter and near-infrared agents for selective cancer cell destruction [15]. In the area of glycoscience, various attractive biological activities of sugar chains in animal cells have been reported [16], and many types of artificial glycoconjugates carrying such bioactive carbohydrates have designed to serve cell surface oligosaccharide mimetics [17,18]. Several groups have recently reported multivalent carbohydrate-CNTs conjugates, such as lactose attached schizophyllan [19], lipid-terminated sugar polymers [20], and covalently attached sugars [21,22] as novel multivalent carbohydrate ligands binding to carbohydrate recognition proteins such as bacterial toxins and viral proteins. In this respect, characteristic photoluminescence signals from dispersed multivalent carbohydrate-CNT conjugate will exploit a new sensing approach to detect carbohydrate recognition proteins.
H. Dohi et al. / Chemical Physics Letters 428 (2006) 98–101
Unfortunately, no multivalent carbohydrate-CNT conjugates have so far been reported to emit PL. Here, we report the first synthesis and characterization of photoluminescence-active CNT-based multivalent-carbohydrates, which can be individually well dispersed in pure water. 2. Experimental Reagents and solvents were purchased at the highest commercial quality from Sigma, Aldrich, and Tokyo Kasei, and used without further purification. 1H NMR spectra were recorded with a JEOL A-600 spectrometer. Size exclusion chromatographies were performed with JASCO 800 HPLC on Shodex B804 + B805 columns eluted with PBS. The molecular weights were estimated by using a pullulan standard. As-produced SWNTs synthesized by the HiPco process [23] was purchased from CNI (Lot# HPR 91). UV–Vis–NIR spectra were measured by a JASCO V-570 spectrophotometer. NIR fluorescent spectra (PL) were recorded by using a newly developed Shimadzu CNT-RF photoluminescence spectrophotometer. A mixture of p-N-acryloylamidophenyl a-D-glucopyranoside [24] (500 mg, 1.54 mmol), AIBN (3.3 mg, 0.02 mmol) and dimethylsulfoxide (1 mL) in glass tube was degassed under reduced pressure. After sealing the glass tube under reduced pressure, the tube was incubated at 60 °C for 5 h. The high-viscosity solution was poured into methanol (20 mL), and the mixture was centrifuged (5 °C, 5000 rpm). The precipitate dissolved into water was dialyzed for three days (Mw 3500 cut off) and lyophilized to afford polymer 1 (343 mg, 67%) as a white powder: Mn = 135 000 (estimated by SEC, pullulan standard, PBS eluent). HiPco SWNTs (0.5 mg) was added to a solution of glycoconjugate polymer (5 mg) in D2O (10 mL). The suspension was homogenized by a tip type sonicator at 40 W with a cool bath (5 °C) for 2 h. The black solution was subjected to ultracentrifugation at 100 000g for 1 h, and then the dark green supernatant was corrected. For AFM observations, the sample solution obtained after ultracentrifugation was deposited onto a piece of mica, and rinsed with distilled water and dried before measurement (Digital Instruments Dimension 3100). Tapping mode was used to acquire the topographic images under ambient conditions.
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in water. Furthermore, such glycoconjugate polymers carrying bioactive sugars have shown strong affinities against bacterial toxins [27] and viral proteins [28], and estimated quantitative carbohydrate-carbohydrate interactions [29]. Some types of glycoconjugate polymer form a large helix of main chain and carbohydrate brushes in water [30]. These facts prompt us to disperse CNT in aqueous phase by using glycoconjugate polymer. The dispersion is achieved by the interaction between inner hydrophobic site of the polymer and hydrophobic surface of CNTs together with a suitable orientation of outer sugar part to water, which results in good isolation of CNTs in water. Moreover, the densely oriented sugars as a pendant group on the CNT hybrid become multivalent carbohydrate ligands and show potential biological activities as well as glycoconjugate polymers. Poly(p-N-acryloylamidophenyl a-glucopyranoside, PAP-a-Glc) 1 (Fig. 1) has been chosen as the glycoconjugate polymer. Polymer 1 was synthesized by the reported method [24], and the Mn was estimated as ca. 71 000. Although dispersion of SWNT in polymer solution by bath-type sonicator was not effective, a tip type sonicator (40 W, 2 h) was successfully applied to give black dispersed solution of SWNT. Stability of polymer 1 after 2 h of homogenization was confirmed by following experiments: (i) 1H NMR spectrum of the sonicated polymer solution was almost the same as that of raw polymer; (ii) No spot from carbohydrate part was observed on thin-layer chromatography (TLC) analysis of the sonicated solution. The maximum solubility of SWNT reached to ca. 0.2 mg/ mL in 0.5 mg/mL polymer solution. The dispersed solution of SWNT was obtained after ultracentrifugation as a dark green solution, and kept dispersed clear over 3 month. The vis-NIR spectrum in the range of 400–1500 nm of the solution so produced exhibits the characteristic adsorption of
3. Results and discussion To construct the carbohydrate-CNT conjugate which interacts specifically with carbohydrate recognition proteins, abundant sugar group should be attached along the surface of CNTs as pendant. In this respect, linear polysaccharides such as amylose are not suitable as surfactant for dispersion of CNTs. On the other hand, glycoconjugate polymers [25] carrying bioactive sugars as pendant groups constitute a brand-new class of biological materials owing to their multivalent effect [26] together with high solubility
Fig. 1. Schematic presentation of the formation of the present GCPSWNT.
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H. Dohi et al. / Chemical Physics Letters 428 (2006) 98–101
Fig. 2. Vis–NIR spectrum of SWNT-dispersed solution obtained after ultracentrifugation (100 000g, 1 h) of homogenized solution of HiPcoSWNTs (0.5 mg) and polymer 1 (5 mg) in D2O (10 mL): D2O, 1 cm cell, room temperature.
HiPco-produced SWNT (Fig. 2). The sharp peaks in the range of 900–1100 nm are due to dispersed and non-bundled SWNTs [6] since the observed peaks, originating form M11, S22, and S11 transitions, are almost the same as those previously reported for surfactant- and DNA-wrapped individual HiPco tubes [6,12]. This indicates the presence of dispersed carbon nanotubes in the solvent by the glycoconjugate polymer. In contrast, the peaks around 1000–1300 nm are redshifted of ca. 30 nm as compared with those of SDS-dispersed SWNT [6]. This can be interpreted to an inhomogeneous environment of SWNT caused by wrapping of glycoconjugate polymer 1 as suggested by O’Connell et al. in the SDS-SWNT case [6]. Fig. 3 shows a contour plot of fluorescence intensities for SWNT wrapped by polymer 1 as a function of excitation and resultant emission. The sharp photoluminescence signals indicate the presence of the individual dispersion of SWNT. The chirality of the major peaks shown in Fig. 3 are assigned according to Bachilo et al. [31]. Typical SDS–HiPco–SWNTs have shown strong peaks at chirality of (9,4), (8,6), (10,2), (7,5) and (7,6), whereas the present glycoconjugate poly-
Fig. 4. (a) A typical tapping-mode AFM (height) image of SWNTs wrapped by poly(PAP-a-Glc), obtained with 5 lm scan, (b) a magnified image of white squared area.
Fig. 3. Contour plots of photoluminescence intensities for SWNTdispersed solution obtained from polymer 1 in D2O.
mer-SWNTs exhibit enhanced peaks at (8,6), (12,1) and (11,3) in the contour map. This strongly suggests that SWNTs with larger diameter preferentially are wrapped by polymer 1 when compared with wrapping by SDS. Atomic force microscopy measurements on the sample prepared form the dispersed solutions show that the glyco-
H. Dohi et al. / Chemical Physics Letters 428 (2006) 98–101
conjugate polymer-wrapped SWNT hybrid has a length distribution from 50 to 900 nm with tube diameters ranging from 1.0 to 2.0 nm. The observed diameters are larger than those of intact HiPco–SWNT (0.9–1.3 nm) due to a selforganized wrapping by polymer 1 (which is consistent with the above PL results), again indicating the isolation of SWNT in water. The length of the hybrid ranges from 100 nm to slightly above 1 lm, and the average length is ca. 236 nm. The average length was shorter than that of raw HiPco tubes, implying that a partial fragmentation of HiPco might have been occurred during the homogenization. Most of the observed polymer-coated nanotubes possess striped structures on the surface with a random pitch of ca. 35 nm (Fig. 4). This suggests that the amphiphilic glycoconjugate polymer 1 interacts effectively with SWNTs as expected by forming helical structures which are induced by hydrophobic interaction such as CH–p interaction between alkyl group at the main chain of the polymer and aromatic part of SWNT. The average length of the polymer is estimated to be ca. 60 nm. This is consistent with the idea that one molecule of the polymer constructs one pitch of polymer 1 on the CNT surface as observed by AFM. Consequently, the UV–vis and PL spectra, and AFM observation jointly support that bundle-free dispersions of individual SWNTs in water have been successfully prepared with multivalent carbohydrate-SWNT hybrid. 4. Summary A high level of dispersion of SWNT in water is achieved by non-covalent modification of as-grown SWNT using glycoconjugate polymer 1, giving a novel multivalent carbohydrate-SWNT hybrid. The individual dispersion of the hybrid is supported by the presence of sharp photoluminescence peaks in water. In addition, AFM measurements strongly support a random helical structure of the hybrid as polymer-wrapped SWNTs. The present study is crucial to future studies on biological activities of carbohydrate-SWNT hybrid and polymer-dependent dispersion ability of SWNTs. Acknowledgements H.S. acknowledges the financial support by the JST CREST project on Novel Carbon Nanotube Materials and the Grants-in-Aid Scientific Research B (No.
101
16350071) of MEXT, Japan. HD thanks the Japan Society for the Promotion of Science Research for a research fellowship for young scientists (PD). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
[20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31]
S. Iijima, Nature 354 (1991) 56. Y. Lin et al., J. Mater. Chem. 14 (2004) 527. A. Hirsch, Angew. Chem. Int. Ed. 41 (2002) 1853. D. Tasis, N. Tagmatarchis, V. Georgakilas, M. Prato, Chem. Eur. J. 9 (2003) 4000. M. Holzinger, J. Abraham, P. Whelan, R. Graupner, L. Ley, F. Hennrich, M. Kappes, A. Hirsch, J. Am. Chem. Soc. 125 (2003) 8566. M.J. O’Connell et al., Science 297 (2002) 593. Y. Maeda et al., J. Phys. Chem. B. 108 (2004) 18395. V. Zorbas et al., J. Am. Chem. Soc. 126 (2004) 7222. D.M. Guldi, M. Holzinger, A. Hirsch, V. Georgakilas, M. Prato, Chem. Commun. (2003) 1130. H. Murakami, T. Nomura, N. Nakashima, Chem. Phys. Lett. 378 (2003) 481. Y. Miyauchi, S. Chiashi, Y. Murakami, Y. Hayashida, S. Maruyama, Chem. Phys. Lett. 387 (2004) 198. M. Zheng, A. Jagota, E.D. Semke, B.A. Diner, R.S. Mclean, S.R. Lustig, R.E. Richardson, N.G. Tassi, Nat. Mater. 2 (2003) 338. S.G. Chou et al., Chem. Phys. Lett. 397 (2004) 296. P.W. Barone, S. Baik, D.A. Heller, M.S. Strano, Nat. Mater. 4 (2005) 86. N.W. Kam, M. O’Connell, J.A. Wisdom, H. Dai, Proc. Natl. Acad. Sci. USA 102 (2005) 11600. A. Valki, Glycobiology 3 (1993) 97. M. Mammen, S.K. Choi, G.M. Whitesides, Angew. Chem. Int. Ed. Engl. 37 (1998) 2755. T.K. Lindhorst, Top. Curr. Chem. 218 (2002) 201. H. Hasegawa, T. Fujisaka, M. Numata, M. Umeda, T. Matsumoto, T. Kimura, S. Okumura, K. Sakurai, S. Shinkai, Chem. Commun. (2004) 2150. X. Chen, G.S. Lee, A. Zettl, C.R. Bertozzi, Angew. Chem. Int. Ed. 43 (2004) 6112. K. Matsuura, K. Hayashi, N. Kimizuka, Chem. Lett. 32 (2003) 212. L. Gu et al., Chem. Commun. (2005) 874. P. Nikolaef, M.J. Bronikowski, R.K. Bradley, F. Rohmund, D.T. Colbert, K.A. Smith, R.E. Smalley, Chem. Phys. Lett. 313 (1999) 91. K. Kobayashi, N. Kakishita, M. Okada, T. Akaite, T. Usui, J. Carbohydr. Chem. 13 (1994) 753. K. Kobayashi, H. Sumitomo, Y. Ina, Polymer J. 17 (1985) 567. Y.C. Lee, R.T. Lee, Acc. Chem. Res. 28 (1995) 321. H. Dohi et al., Bioorg. Med. Chem. 7 (1999) 2053. A. Tsuchida, K. Kobayashi, N. Matsubara, T. Suzuki, Y. Suzuki, Glycoconjugate J. 15 (1998) 1047. K. Matsuura, H. Kitakouji, N. Sawada, H. Ishida, M. Kiso, K. Kitajima, K. Kobayashi, J. Am. Chem. Soc. 122 (2000) 7406. I. Wataoka, H. Urakawa, K. Kobayashi, T. Akaike, M. Schmidt, K. Kajiwara, Macromolecules 32 (1999) 1816. S.M. Bachilo, M.S. Strano, C. Kittrell, R.H. Hauge, R.E. Smalley, R.B. Weisman, Science 298 (2002) 2361.
Synthesis and spectroscopic characterization of single-wall carbon nanotubes wrapped by glycoconjugate polymer with bioactive sugars Hirofumi Dohi, Satoshi Kikuchi, Shota Kuwahara, Toshiki Sugai, Hisanori Shinohara
*
Department of Chemistry and Institute for Advanced Research, Nagoya University, Nagoya 464-8602, Japan Received 6 February 2006; in final form 10 June 2006 Available online 23 June 2006
Abstract A novel multivalent carbohydrate-CNT hybrid has been synthesized from SWNT and glycoconjugate polymer, carrying carbohydrate as pendant groups at side chain. Dispersion of SWNT in aqueous solution by using glycoconjugate polymer is achieved by sonication and ultracentrifugation. The multivalent carbohydrate-CNT hybrid is revealed to be photoluminescence active by near-infrared fluorescence spectroscopy. AFM measurements of the hybrid support not only the wrapping of SWNT by glycoconjugate polymer but also successful carbohydrate attachment of individual SWNT. Ó 2006 Elsevier B.V. All rights reserved.
1. Introduction Since the discovery of carbon nanotubes (CNTs) in 1991 by Iijima [1], there have been numerous efforts to clarify their mechanical and electronic properties. Their wide potential applicability not only for electronic but also for chemical and biological materials are currently spotlighted [2–5]. Individual dispersion of CNTs in solvent is, therefore, of great importance to realize the homogenous chemical modification and biological application of CNTs. In this respect, non-covalent procedures are desirable for dispersion of CNTs because CNTs can maintain their own characteristic structure and electronic properties, which should be free from the presence of extensive covalent type chemical functionalization. Several research groups have succeeded to disperse CNTs in solvents with monomeric and polymeric surfactant and to obtain the photoluminescence (PL) spectra, which is known to be a good indication of the individual isolation of CNTs [6–11]. Recently, dispersion of CNTs wrapped by biomolecules has been reported by several
*
Corresponding author. Fax: +81 52 789 1169. E-mail address: [email protected] (H. Shinohara).
0009-2614/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2006.06.053
research groups. For example, the DNA-assisted dispersion of CNTs in water has been achieved and the successful observation of PL signals were reported [12,13]. Since then, biological applications of CNTs have widely been recognized. Barone et al. reported that the glucose oxidaseSWNT conjugate emits PL and the conjugate serves as a glucose sensor using PL phenomena [14]. Dai and coworkers have found that DNA-wrapped CNTs can serve as a biological transporter and near-infrared agents for selective cancer cell destruction [15]. In the area of glycoscience, various attractive biological activities of sugar chains in animal cells have been reported [16], and many types of artificial glycoconjugates carrying such bioactive carbohydrates have designed to serve cell surface oligosaccharide mimetics [17,18]. Several groups have recently reported multivalent carbohydrate-CNTs conjugates, such as lactose attached schizophyllan [19], lipid-terminated sugar polymers [20], and covalently attached sugars [21,22] as novel multivalent carbohydrate ligands binding to carbohydrate recognition proteins such as bacterial toxins and viral proteins. In this respect, characteristic photoluminescence signals from dispersed multivalent carbohydrate-CNT conjugate will exploit a new sensing approach to detect carbohydrate recognition proteins.
H. Dohi et al. / Chemical Physics Letters 428 (2006) 98–101
Unfortunately, no multivalent carbohydrate-CNT conjugates have so far been reported to emit PL. Here, we report the first synthesis and characterization of photoluminescence-active CNT-based multivalent-carbohydrates, which can be individually well dispersed in pure water. 2. Experimental Reagents and solvents were purchased at the highest commercial quality from Sigma, Aldrich, and Tokyo Kasei, and used without further purification. 1H NMR spectra were recorded with a JEOL A-600 spectrometer. Size exclusion chromatographies were performed with JASCO 800 HPLC on Shodex B804 + B805 columns eluted with PBS. The molecular weights were estimated by using a pullulan standard. As-produced SWNTs synthesized by the HiPco process [23] was purchased from CNI (Lot# HPR 91). UV–Vis–NIR spectra were measured by a JASCO V-570 spectrophotometer. NIR fluorescent spectra (PL) were recorded by using a newly developed Shimadzu CNT-RF photoluminescence spectrophotometer. A mixture of p-N-acryloylamidophenyl a-D-glucopyranoside [24] (500 mg, 1.54 mmol), AIBN (3.3 mg, 0.02 mmol) and dimethylsulfoxide (1 mL) in glass tube was degassed under reduced pressure. After sealing the glass tube under reduced pressure, the tube was incubated at 60 °C for 5 h. The high-viscosity solution was poured into methanol (20 mL), and the mixture was centrifuged (5 °C, 5000 rpm). The precipitate dissolved into water was dialyzed for three days (Mw 3500 cut off) and lyophilized to afford polymer 1 (343 mg, 67%) as a white powder: Mn = 135 000 (estimated by SEC, pullulan standard, PBS eluent). HiPco SWNTs (0.5 mg) was added to a solution of glycoconjugate polymer (5 mg) in D2O (10 mL). The suspension was homogenized by a tip type sonicator at 40 W with a cool bath (5 °C) for 2 h. The black solution was subjected to ultracentrifugation at 100 000g for 1 h, and then the dark green supernatant was corrected. For AFM observations, the sample solution obtained after ultracentrifugation was deposited onto a piece of mica, and rinsed with distilled water and dried before measurement (Digital Instruments Dimension 3100). Tapping mode was used to acquire the topographic images under ambient conditions.
99
in water. Furthermore, such glycoconjugate polymers carrying bioactive sugars have shown strong affinities against bacterial toxins [27] and viral proteins [28], and estimated quantitative carbohydrate-carbohydrate interactions [29]. Some types of glycoconjugate polymer form a large helix of main chain and carbohydrate brushes in water [30]. These facts prompt us to disperse CNT in aqueous phase by using glycoconjugate polymer. The dispersion is achieved by the interaction between inner hydrophobic site of the polymer and hydrophobic surface of CNTs together with a suitable orientation of outer sugar part to water, which results in good isolation of CNTs in water. Moreover, the densely oriented sugars as a pendant group on the CNT hybrid become multivalent carbohydrate ligands and show potential biological activities as well as glycoconjugate polymers. Poly(p-N-acryloylamidophenyl a-glucopyranoside, PAP-a-Glc) 1 (Fig. 1) has been chosen as the glycoconjugate polymer. Polymer 1 was synthesized by the reported method [24], and the Mn was estimated as ca. 71 000. Although dispersion of SWNT in polymer solution by bath-type sonicator was not effective, a tip type sonicator (40 W, 2 h) was successfully applied to give black dispersed solution of SWNT. Stability of polymer 1 after 2 h of homogenization was confirmed by following experiments: (i) 1H NMR spectrum of the sonicated polymer solution was almost the same as that of raw polymer; (ii) No spot from carbohydrate part was observed on thin-layer chromatography (TLC) analysis of the sonicated solution. The maximum solubility of SWNT reached to ca. 0.2 mg/ mL in 0.5 mg/mL polymer solution. The dispersed solution of SWNT was obtained after ultracentrifugation as a dark green solution, and kept dispersed clear over 3 month. The vis-NIR spectrum in the range of 400–1500 nm of the solution so produced exhibits the characteristic adsorption of
3. Results and discussion To construct the carbohydrate-CNT conjugate which interacts specifically with carbohydrate recognition proteins, abundant sugar group should be attached along the surface of CNTs as pendant. In this respect, linear polysaccharides such as amylose are not suitable as surfactant for dispersion of CNTs. On the other hand, glycoconjugate polymers [25] carrying bioactive sugars as pendant groups constitute a brand-new class of biological materials owing to their multivalent effect [26] together with high solubility
Fig. 1. Schematic presentation of the formation of the present GCPSWNT.
100
H. Dohi et al. / Chemical Physics Letters 428 (2006) 98–101
Fig. 2. Vis–NIR spectrum of SWNT-dispersed solution obtained after ultracentrifugation (100 000g, 1 h) of homogenized solution of HiPcoSWNTs (0.5 mg) and polymer 1 (5 mg) in D2O (10 mL): D2O, 1 cm cell, room temperature.
HiPco-produced SWNT (Fig. 2). The sharp peaks in the range of 900–1100 nm are due to dispersed and non-bundled SWNTs [6] since the observed peaks, originating form M11, S22, and S11 transitions, are almost the same as those previously reported for surfactant- and DNA-wrapped individual HiPco tubes [6,12]. This indicates the presence of dispersed carbon nanotubes in the solvent by the glycoconjugate polymer. In contrast, the peaks around 1000–1300 nm are redshifted of ca. 30 nm as compared with those of SDS-dispersed SWNT [6]. This can be interpreted to an inhomogeneous environment of SWNT caused by wrapping of glycoconjugate polymer 1 as suggested by O’Connell et al. in the SDS-SWNT case [6]. Fig. 3 shows a contour plot of fluorescence intensities for SWNT wrapped by polymer 1 as a function of excitation and resultant emission. The sharp photoluminescence signals indicate the presence of the individual dispersion of SWNT. The chirality of the major peaks shown in Fig. 3 are assigned according to Bachilo et al. [31]. Typical SDS–HiPco–SWNTs have shown strong peaks at chirality of (9,4), (8,6), (10,2), (7,5) and (7,6), whereas the present glycoconjugate poly-
Fig. 4. (a) A typical tapping-mode AFM (height) image of SWNTs wrapped by poly(PAP-a-Glc), obtained with 5 lm scan, (b) a magnified image of white squared area.
Fig. 3. Contour plots of photoluminescence intensities for SWNTdispersed solution obtained from polymer 1 in D2O.
mer-SWNTs exhibit enhanced peaks at (8,6), (12,1) and (11,3) in the contour map. This strongly suggests that SWNTs with larger diameter preferentially are wrapped by polymer 1 when compared with wrapping by SDS. Atomic force microscopy measurements on the sample prepared form the dispersed solutions show that the glyco-
H. Dohi et al. / Chemical Physics Letters 428 (2006) 98–101
conjugate polymer-wrapped SWNT hybrid has a length distribution from 50 to 900 nm with tube diameters ranging from 1.0 to 2.0 nm. The observed diameters are larger than those of intact HiPco–SWNT (0.9–1.3 nm) due to a selforganized wrapping by polymer 1 (which is consistent with the above PL results), again indicating the isolation of SWNT in water. The length of the hybrid ranges from 100 nm to slightly above 1 lm, and the average length is ca. 236 nm. The average length was shorter than that of raw HiPco tubes, implying that a partial fragmentation of HiPco might have been occurred during the homogenization. Most of the observed polymer-coated nanotubes possess striped structures on the surface with a random pitch of ca. 35 nm (Fig. 4). This suggests that the amphiphilic glycoconjugate polymer 1 interacts effectively with SWNTs as expected by forming helical structures which are induced by hydrophobic interaction such as CH–p interaction between alkyl group at the main chain of the polymer and aromatic part of SWNT. The average length of the polymer is estimated to be ca. 60 nm. This is consistent with the idea that one molecule of the polymer constructs one pitch of polymer 1 on the CNT surface as observed by AFM. Consequently, the UV–vis and PL spectra, and AFM observation jointly support that bundle-free dispersions of individual SWNTs in water have been successfully prepared with multivalent carbohydrate-SWNT hybrid. 4. Summary A high level of dispersion of SWNT in water is achieved by non-covalent modification of as-grown SWNT using glycoconjugate polymer 1, giving a novel multivalent carbohydrate-SWNT hybrid. The individual dispersion of the hybrid is supported by the presence of sharp photoluminescence peaks in water. In addition, AFM measurements strongly support a random helical structure of the hybrid as polymer-wrapped SWNTs. The present study is crucial to future studies on biological activities of carbohydrate-SWNT hybrid and polymer-dependent dispersion ability of SWNTs. Acknowledgements H.S. acknowledges the financial support by the JST CREST project on Novel Carbon Nanotube Materials and the Grants-in-Aid Scientific Research B (No.
101
16350071) of MEXT, Japan. HD thanks the Japan Society for the Promotion of Science Research for a research fellowship for young scientists (PD). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
[20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31]
S. Iijima, Nature 354 (1991) 56. Y. Lin et al., J. Mater. Chem. 14 (2004) 527. A. Hirsch, Angew. Chem. Int. Ed. 41 (2002) 1853. D. Tasis, N. Tagmatarchis, V. Georgakilas, M. Prato, Chem. Eur. J. 9 (2003) 4000. M. Holzinger, J. Abraham, P. Whelan, R. Graupner, L. Ley, F. Hennrich, M. Kappes, A. Hirsch, J. Am. Chem. Soc. 125 (2003) 8566. M.J. O’Connell et al., Science 297 (2002) 593. Y. Maeda et al., J. Phys. Chem. B. 108 (2004) 18395. V. Zorbas et al., J. Am. Chem. Soc. 126 (2004) 7222. D.M. Guldi, M. Holzinger, A. Hirsch, V. Georgakilas, M. Prato, Chem. Commun. (2003) 1130. H. Murakami, T. Nomura, N. Nakashima, Chem. Phys. Lett. 378 (2003) 481. Y. Miyauchi, S. Chiashi, Y. Murakami, Y. Hayashida, S. Maruyama, Chem. Phys. Lett. 387 (2004) 198. M. Zheng, A. Jagota, E.D. Semke, B.A. Diner, R.S. Mclean, S.R. Lustig, R.E. Richardson, N.G. Tassi, Nat. Mater. 2 (2003) 338. S.G. Chou et al., Chem. Phys. Lett. 397 (2004) 296. P.W. Barone, S. Baik, D.A. Heller, M.S. Strano, Nat. Mater. 4 (2005) 86. N.W. Kam, M. O’Connell, J.A. Wisdom, H. Dai, Proc. Natl. Acad. Sci. USA 102 (2005) 11600. A. Valki, Glycobiology 3 (1993) 97. M. Mammen, S.K. Choi, G.M. Whitesides, Angew. Chem. Int. Ed. Engl. 37 (1998) 2755. T.K. Lindhorst, Top. Curr. Chem. 218 (2002) 201. H. Hasegawa, T. Fujisaka, M. Numata, M. Umeda, T. Matsumoto, T. Kimura, S. Okumura, K. Sakurai, S. Shinkai, Chem. Commun. (2004) 2150. X. Chen, G.S. Lee, A. Zettl, C.R. Bertozzi, Angew. Chem. Int. Ed. 43 (2004) 6112. K. Matsuura, K. Hayashi, N. Kimizuka, Chem. Lett. 32 (2003) 212. L. Gu et al., Chem. Commun. (2005) 874. P. Nikolaef, M.J. Bronikowski, R.K. Bradley, F. Rohmund, D.T. Colbert, K.A. Smith, R.E. Smalley, Chem. Phys. Lett. 313 (1999) 91. K. Kobayashi, N. Kakishita, M. Okada, T. Akaite, T. Usui, J. Carbohydr. Chem. 13 (1994) 753. K. Kobayashi, H. Sumitomo, Y. Ina, Polymer J. 17 (1985) 567. Y.C. Lee, R.T. Lee, Acc. Chem. Res. 28 (1995) 321. H. Dohi et al., Bioorg. Med. Chem. 7 (1999) 2053. A. Tsuchida, K. Kobayashi, N. Matsubara, T. Suzuki, Y. Suzuki, Glycoconjugate J. 15 (1998) 1047. K. Matsuura, H. Kitakouji, N. Sawada, H. Ishida, M. Kiso, K. Kitajima, K. Kobayashi, J. Am. Chem. Soc. 122 (2000) 7406. I. Wataoka, H. Urakawa, K. Kobayashi, T. Akaike, M. Schmidt, K. Kajiwara, Macromolecules 32 (1999) 1816. S.M. Bachilo, M.S. Strano, C. Kittrell, R.H. Hauge, R.E. Smalley, R.B. Weisman, Science 298 (2002) 2361.