Specific Molecular Interaction and Recognition at Single-Walled

Invited Historical Article pubs.acs.org/Langmuir

Specific Molecular Interaction and Recognition at Single-Walled Carbon Nanotube Surfaces Naotoshi Nakashima*,†,‡ and Tomohiro Shiraki† †

Department of Applied Chemistry, Graduate School of Engineering and ‡International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan ABSTRACT: Carbon nanotubes (CNTs) are carbon clusters (polymers) with huge molecular weight and have been the central material in the field of nanomaterials science and nanotechnology because of their remarkable electronic, thermal, mechanical, optical, and electrical properties. In this review article, we first focus on the formation of self-assembled CNT superstructures and spontaneous conductive CNT-honeycomb structure formation from CNT/long-chain ammonium lipids by simple solvent casting. We also summarized our recent studies on specific molecular interactions and recognition at single-walled carbon nanotube surfaces and CNT chirality recognition using specific polymers. For such studies, the key issue is to develop a methodology to solubilize/disperse them in solvent because assynthesized CNTs form tightly bundled structures as a result of their strong van der Waals interactions and are insoluble in many solvents. For the analysis of molecules and CNT surfaces, the introduction of thermodynamic treatment and an HPLC method using CNT-coated silica as a stationary phase was powerful.

1. INTRODUCTION Carbon nanotubes (CNTs) are made of rolled-up graphene sheets with one-dimensional extended π-conjugated structures.1 They are classified into mainly three types in terms of the number of graphene layers, namely, single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes (DWNTs), and multiwalled carbon nanotubes (MWNTs), which have one, two, and more than three walls, respectively (Figure 1). CNTs are materials with highly crystalline 1D

based on soluble CNTs, (ii) quantitative analysis of molecular interactions between CNTs and small molecules based on thermodynamics and the HPLC technique, (iii) CNT chirality recognition, and (iv) assembled supramolecular superstructure hybrids of CNTs and metal nanoparticles because such topics are of interest in view of the self-assembly and recognition chemistry of CNTs.5−7

2. SELF-ASSEMBLY OF CARBON NANOTUBES The construction of nanoscaled superstructures through the self-assembly of CNTs is a challenge, and soluble carbon nanotubes are suitable materials for this goal. So far, reports describing rings of CNTs;8−10 a theoretical approach to the formation of kinks, rings, and a “racket” structure of carbon nanotubes;11 the observation of a ring of SWNTs with ultrahigh-vacuum scanning tunneling microscopy and spectroscopy;12 a ring closure of CNTs in an organic solution in the presence of dicyclohexylcarbodiimide;13 the electron transport, electrical switching, and rectification behaviors of the SWNT ring;9,10,14 the synthesis of organized networks of helically wound SWNTs;15 and helically coiled structure formation of MWNTs16,17 have been published. The helix structure is one of the most stable structures formed via strong interactions between long strings in which

Figure 1. Structures of SWNTs, DWNTs, and MWNTs.

structure and have been central materials in the field of nanomaterials science and nanotechnology because of their remarkable electronic, thermal, mechanical, optical, and electrical properties. One of the key issues in the utilization of CNTs for basic research together with the material applications is to develop a methodology to solubilize/disperse them in solvents2−4 because as-synthesized CNTs form tightly bundled structures as a result of their strong van der Waals interactions and are insoluble in many solvents. In this review article, we focus on (i) self-assembled superstructure formation © XXXX American Chemical Society

Special Issue: Tribute to Toyoki Kunitake, Pioneer in Molecular Assembly Received: May 27, 2016 Revised: July 15, 2016

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DOI: 10.1021/acs.langmuir.6b02023 Langmuir XXXX, XXX, XXX−XXX

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Invited Historical Article

strong van der Waals interactions between several or more nanotube strings in the solvent are a driving force for such helical aggregated structures. We reported the formation of helical superstructures of rings and lassos from aqueous dispersions of empty SWNTs and of fullerene (C70) peapods (C70@SWNTs) solubilized by using compound PyN (Figures 2−4).18 Use of porphyrin ZnPPIX (Figure 2) in place of PyN provided a similar result.

Figure 4. Typical AFM images of an aqueous dispersion of the C70@ SWNTs-PyN (PyN = 1 mM) and their height profiles. Reprinted with permission from ref 18. Copyright 2005 American Chemical Society. Figure 2. Chemical structures of PyN (left) and ZnPPIX (right).

Figure 5. Conformational evolution of a single stiff polymer chain. The Monte Carlo steps are s = (a) 0, (b) 50, (c) 100, (d) 150, (e) 200 (magnification, ×1.5), (f) 213 (magnification, ×2), (g) 230 (magnification, ×2), and (h) 250 (magnification, ×2), which are denoted by s in units of 104 Monte Carlo steps. Reprinted with permission from ref 18. Copyright 2005 American Chemical Society.

Figure 3. TEM images of C70-peapods solubilized in an aqueous solution of compound 1. Reprinted with permission from ref 18. Copyright 2005 American Chemical Society.

spontaneously selected during the thermal fluctuation on the folding process, resulting in chiral symmetry breaking on the helix.19 It is generally expected that stiff polymer chains exhibit the ability to form helical structures as well as bundles.20 We previously reported the formation of a helical molecular bilayer from an aqueous bilayer of a chiral synthetic lipid, 2C12GluC11N+ (Figures 6 and 7).21

A Monte Carlo simulation on single stiff chains is useful in explaining the formation of such superstructures. The formation of the stranded structure was attributed to a kind of kinetic effect; namely, during the “thermal” fluctuation of the conformation, a double- and/or triple-stranded stem is formed spontaneously in some region along the chain, whereas other parts of the chain form rings. These rings shrink with time by zipping, and this process is relatively slow. The conformational evolution of a single stiff polymer chain is shown in Figure 5. If the chain adsorbs on the solid surface during this process, then kinetically frozen morphologies in the simulations acquire further stability on the solid surface in actual experiments. Another specific feature of the collapsed products in the simulation is as follows. All of the collapsed products exhibit dense packing with a few strands that wind around each other to form a helical structure. The winding direction is

Figure 6. Chemical structure of 2C12GluC11N+. B


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complexes,27 poly(D,L-lactic-co-glycolic acid),28 polysulfone,29 amphiphilic poly(p-phenylenes),30 and a poly(ε-caprolactone)/ amphiphilic copolymer.31 We reported that the self-assembly of SWNTs with a honeycomb structure occurs spontaneously on glass substrates32 and on transparent plastic films such as poly(ethylene terephthalate) (PET)33 are formed by a simple solution casting method using a single-walled CNTs (SWNTs)/lipid conjugate (complex 1 in Figure 8) as the material, which is an ion complex of shortened SWNTs and tridodecylmethylammonium chloride, a molecular-bilayer-forming amphiphile that is available via our previous study. We recognized the formation of conducting SWNT honeycomb structures on glass substrates and polyethyleneterephtalate (PET) films (Figure 9). The sizes

Figure 7. Dark-field optical micrograph of an aqueous dispersion of chiral lipid 2C12-GluC11N. Initially formed spherical vesicles and fibrous molecular bilayers grew to helical superstructures after remaining in the dispersion at temperatures below its phase-transition temperature for ∼1 day. Adapted with permission from ref 21. Copyright 1985 American Chemical Society.

3. SELF-ASSEMBLED CNT-BASED HONEYCOMB STRUCTURE Honeycomb structures from organic (polymer) and organic/ inorganic hybrid materials are of interest because of their unique structures and functions. Since the first report by François et al.22 that self-organized honeycomb structures are formed from star-shaped polystyrene or poly(styrene)-poly(paraphenylene) block copolymers in carbon disulfide under flowing moist gas, many papers have been published describing the formation of similar honeycomb structures using different kinds of molecules including polymers of symmetric diblock copolymers,23 rod−coil diblock copolymers,24 a coil-like polymer,25 ion-complexed polymers,26 lipid-packaged Pt

Figure 9. Typical SEM images of cast films on PET from a chloroform solution of complex 1 (1.0 mgmL−1) at 80% RH before (left) and after (right) ion exchange. Reprinted with permission from ref 33. Copyright 2009 Wiley-Interscience.

of the unit cells are controllable by changing the experimental conditions. The surface resistivity of the cast films with the honeycomb structures was insulating (Rs > 108 Ω/square) due to the coating of the tube surfaces with the ammonium lipid. However, by the removal of the lipid from the films by

Figure 8. Preparation of complex 1. Reprinted with permission from ref 29. Copyright 2007 Wiley-VCH Verlag GmbH & Co. KGaA. C


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polymeric solubilizers and SWNTs quantitatively.56 Thermodynamic analysis approaches have been examined by using DNAs57−60 and flavin derivtives61,62 that are applicable to advanced solubilizers for the selective sorting of SWNTs.63,64 We carried out thermodynamic analysis for the solubilizer exchange reactions from sodium cholate (SC) to singlestranded oligo DNAs by using absorption spectroscopy and obtained Kexchange based on the analysis using the Hill equation,

employing the ion-exchange method, the surface resistivity of the film dramatically decreased. The experimental procedure is very simple; namely, each cast film is immersed overnight in a p-toluenesulfonic acid methanol solution and then rinsed with methanol followed by air-drying. By this procedure, the methylene stretching vibrations in the FT-IR of the film almost disappear. The Raman spectra of complex 1 before and after ion exchange were virtually identical. After ion exchange, the skeletons with the honeycomb structures become thin as a result of the removal of the lipid. Higher -magnification SEM measurements show oriented nanotubes along the honeycomb skeletons. Similar self-assembled conductive honey structures are obtained by using graphene as the material.34 Since the discovery of the first isolated graphene prepared by the mechanical exfoliation of graphite crystals,35 graphene has attracted much attention owing to its novel physical properties,36−38 such as ultrahigh electron mobility,39 electromechanical modulation,40 high elesticity,41 quantum electronic transport,42 and tunable band gaps.43 The preparation of graphene honeycomb structures is very simple. We mixed aqueous solutions of graphite oxide (GO) and tridodecylmethylammonium chloride (TDMAC) to obtain the complex, and then by solvent casting, thin films were fabricated on a glass substrate under high humidity conditions to provide honeycomb-like structures with ordered self-organized macropores. The obtained insulating honeycomb films became conductive when they were treated with p-toluenesulfonic acid and then reduced by chemicals such as hydrazine and HI acid (Figure 10).

absorbance = A1 + A 2 θDNA = A1 + A 2

[DNA]n ⎛ [SC] ⎞n n ⎜ ⎟ + [DNA] ⎝ Kexchange ⎠

(1)

where A1 is the absorbance of the SC-SWNTs, A2 is the difference in the absorbance between the DNA-SWNTs and the SC-SWNTs, and n is the Hill coefficient reflecting the cooperativity of the exchanges. We determined the thermodynamic parameters, ΔG, ΔH, and ΔS, from the plots of ln Kexchange versus 1/T based on eq 2. −RT ln Kexchange = ΔG = ΔH − T ΔS

(2)

From the obtained thermodynamic parameters, we revealed the DNA-length dependence and SWNT-diameter dependence on the parameters. The Kexchange values became larger when using longer DNAs. The exchange reactions were entropy-driven and enthalpy-driven for DNAs longer than dC8 (8 mer of cytosine) and shorter than dC8, respectively, for most of the chiral indices investigated in the study. In addition, larger Kexchange values were obtained when using larger-diameter SWNTs. For example, the Kexchange values of dC20-SWNTs are 1260 ± 140 and 8160 ± 300 for (6,5)SWNT of 0.76 nm diameter and (8,6)SWNT of 0.97 nm diameter, respectively.58 The dispersant concentration is an important factor in solubilizing SWNTs; therefore, the concentration effects were examined on the basis of thermodynamic viewpoints using our method. When the SC concentration was varied below the critical micelle concentration, two distinct equilibrium states were found in the exchange reaction between SC and DNAs on the SWNT surfaces.59 The thermodynamic analysis method was applied to doublestranded DNA (ds-DNA) and SWNT hybrids and revealed characteristic complexation behaviors for ds-DNAs.60 The examined ds-DNAs were d(A)20-d(T)20 and the nuclear factor (NF)-κβ decoy. Similar to the single-stranded DNA (ss-DNA) and SWNT systems, a spectral red shift was observed with isosbestic points in the solubilizer exchange reactions on the dsDNA and SWNT hybrids, from which thermodynamic parameters were determined in the same manner. Interestingly, in the obtained 1/T plots, a drastic slope change was observed for d(A)20-d(T)20 at around Tm, whereas the NF-κβ decoy with no Tm in the measurement condition showed a linear slope based on the single equilibrium. The estimated equilibrium constant Kα for d(A)20-d(T)20 and the SWNT hybrids remarkably increased when the temperature increased, indicating that a different adsorption mode with high affinity could be induced by the partial dissociation of the double-helix structures. Comparison between the ds-DNA and ss-DNA using the KF-κβ decoy showed that the exchange reactions from SC to ds-DNA or ss-DNA are endothermic and entropydriven in all cases, but different trends were found in the estimated Kα that shows a unique SWNT chirality dependence when using ds-DNA and ss-DNA, respectively. Theoretical

Figure 10. Typical SEM images for the films (from a toluene solution of the complex under 80% RH) after (a) ion exchange and (b) hydrazine reduction. Reprinted with permission from ref 34. Copyright 2011 Elsevier.

The conductive honeycomb films of CNTs and graphene on glass substrates and plastic films fabricated by the selforganization from nanotube (or oxidized graphene) solutions would be useful in many areas of nanoscience and technology.

4. INTRODUCTION OF THERMODYNAMICS FOR MOLECULAR INTERACTIONS BETWEEN CARBON NANOTUBES AND MOLECULES The solubilization of SWNTs is a key process in investigating the fundamental properties of individual SWNTs and handling them for the development of applications. So far, many solubilizers have been developed, which are exemplified by surfactants,44−48 aromatic compounds,49 biomolecules,46,47,50 and synthetic and biorelated polymers.51−55 Quantitative analysis of the interactions between solubilizers and SWNTs is crucial to a deep understanding of the solubilization phenomena. Coleman et al. used absorption, fluorescence and Raman scattering spectroscopy to analyze interactions between D


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the NH2-silica are controlled by simply changing the ratios of the SWNTs to NH2-silica as well as the SWNT concentrations. We can use many different kinds of CNTs including metallic SWNTs and MWNTs. CNT-coated silica gels are useful for a wide range of materials, such as the stationary phase for liquid chromatography and catalyst supporting materials. The SWNT-coated NH2-silica column was powerful for evaluating the interactions between the SWNTs and molecules; namely, by HPLC measurements, the binding affinity of polyaromatic hydrocarbons with the SWNTs was readily evaluated. The degree of affinity was in the order of benzene < naphthalene < biphenyl< fluorene < phenanthrene < anthracene ≈ pyrene < triphenylene < p-terphenyl < tetraphene < tetracene. The linear-shaped polyphenyls showed a stronger interaction than did the polyacenes, and the interaction was found to be strongly enhanced because the bond rotation can maximize the adsorbed area on the curved CNT surfaces. For polyacenes, linear-shaped polyacenes showed a much higher affinity than the nonlinear polyacenes because of the effective stacking along with the 1D-SWNT structures.66 In addition, we reported that visible absorption spectroscopy is also useful for evaluating the interactions between aromatic molecules and SWNTs when using the SWNT-coated silica gels.67 Such developed methods provide useful information for systematically understanding the interaction of the SWNTs with many molecules.68

calculations based on molecular mechanics were also examined, and in the calculated hybrid structures, partial deformation of the double-stranded to single-stranded form was suggested, by which the interactions between the nucleobases and SWNT side walls would be enhanced through π−π and hydrophobic interactions. Therefore, the thermodynamic analysis allows us not only to determine thermodynamic parameters in the dsDNA and SWNT systems but also to consider selective complexation between SWTNs and DNAs by the nucleobase sequences and by the double-stranded and single-stranded fashions. The thermodynamic analysis unveils the molecular phenomena that occur on the nanointerfaces of SWNTs, which provides useful information not only for fundamentals on the solubilization of SWNTs but also applications toward semiconducting/metallic SWNT separation and chirality-selective sorting.

5. MOLECULAR INTERACTION BETWEEN CARBON NANOTUBES AND MOLECULES BY THE HPLC TECHNIQUE HPLC is one of the common analytical methods in chemistry. We developed a method to fabricate silica gel particles coated with a monolayer of SWNTs (Figure 11).65 The preparation

6. CARBON NANOTUBE CHIRALITY RECOGNITION Although much attention has focused on SWNTs because of their usefulness in applications in the fields of energy, electronics, and bioscience,2,4,69 the coexistence of various chiral SWNTs has interfered with fundamental research and the fabrication of excellent devices. To solve this drawback, the chirality-selective recognition/extraction of the SWNTs is very important. Recently, various methods for the separation of semiconducting and metallic SWNTs, including wrapping by SWNT solubilizers such as DNAs63 and π-conjugated copolymers, 51,52,70 density gradient ultracentrifugation (DGU),71,72 and gel chromatography techniques,73−77 have been reported. However, for almost all of them, the procedures are not very simple but rather complex. We reported rational materials design enabling us to efficiently extract/solubilize pure SWNTs with the desired chirality.53,78,79 On the basis of the concept shown in Figure 12, we designed and synthesized chiral copolymers by the coupling reaction of 2,7-dibromo-9,9-

Figure 11. SEM images of (A) NH2-silica and (B) SWNT-silica. Scale bars: 1 μm. Adapted with permission from ref 65. Copyright 2011 Elsevier.

method is very simple; namely, SWNTs dissolved in 1-methyl2-pyrrolidinone (NMP) were mixed with amino-functionalized silica gels (NH2-silica). Strong interaction between the amino group and the SWNT surfaces induced the adsorption of the SWNTs on the silica, while the stable solvation in NMP hampers further adsorption of the tubes, resulting in the preparation of monolayer-leveled SWNT-coated NH2-silica particles. The density and bundling degree of the SWNTs on

Figure 12. Schematic drawing for the molecular design of compounds (copolymers) that induce a change in SWNT chirality recognition/extraction. Reprinted with permission from ref 53. Copyright 2011 American Chemical Society. E


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SWNTs. Thus, the development of a simple one-pot separation of semiconducting or metallic SWNT enantiomers from a mixture was required. We presented a rational concept for the design of compounds that enable a simple one-pot separation of semiconducting (+)SWNTs and (−)SWNTs with a specific chirality in which the designed and synthesized molecules were copolymers composed of PFO and chiral binaphthol moieties with different composition ratios.84 Here, the introduction of the bulky (R)- or (S)-chiral binaphtol- and PFO moieties was very important. We revealed that by using the 12 selected copolymers with various composition ratios of PFO and binaphthol moieties the (R)- or (S)-chiral copolymers extract either right- or left-handed SWNT enantiomers. Notably, the compounds enabled a simple one-pot sorting of semiconducting (+)SWNTs and (−)SWNTs with a specific chirality.

di-n-decylfluorene and 2,7-dibromo-9,9-bis-[(S)-(+)-2methylbutyl]fluorene comonomers and found that the selectivity of the SWNT chirality was mainly determined by the relative fraction of the achiral and chiral side groups. In addition, molecular mechanics simulations revealed that the cooperative interaction among the fluorene moiety, alkyl side chain, and graphene wall were responsible for the recognition/ dissolution ability of SWNT chirality. The development of a method that enables one-pot sorting of SWNTs with single (n,m) chirality is very important, and PFO copolymer (PFO-BPy, Figure 13) composed of long-

7. ASSEMBLED SUPRAMOLECULAR HYBRIDS OF CARBON NANOTUBES AND METAL NANOPARTICLES Metal nanoparticles exhibit unique physical, chemical, optical, and catalytic properties based on their sizes and shapes.85 CNTs are good building blocks for the preparation of 1D hybrid materials. We developed a method to prepare a metal nanoparticle/chirality-selective SWNT hybrid.86,87 Our method is very simple. We first synthesized a copolymer (1) (Figure 15) with a double long-chain fluorine and a carbazole carrying a

Figure 13. Chemical structures of PFO-BPy and PFO.

chain-carrying fluorene and bipyridine (BPy) units satisfies this demand, namely, the polymer-extracted ∼97%-enriched semiconducting (6,5)SWNTs not containing metallic SWNTs (Figure 14).79 The obtained one-pot SWNT chirality sorting gives a hint as to the design of a molecule that recognizes and extracts SWNTs with single (n,m) chirality.

Figure 15. Chemical structure of copolymer 1.

thiol group and selectively extracted semiconducting SWNTs. A cast film of the solution was then prepared on a substrate followed by deprotection of the thiol moiety. Finally, gold or silver nanoparticles were covalently bonded to the thiol moiety on the copolymer that wrapped the semiconducting SWNTs with a specific chirality. The obtained hybrid was revealed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The copolymer individually dissolved semiconducting (8,7) and (7,6)SWNTs. We prepared metal nanoparticle/(8,7) and (7,6)SWNT composites using copolymer 1 after the deprotection of the acetyl group on the copolymer via the coordination bond between the thiol group and the metal nanoparticles. AFM and SEM studies revealed aligned gold and silver nanoparticles. The preparation of metal nanoparticles/semiconducting SWNT hybrids is important not only for the fundamental properties of such nanohybrids but also for their applications, especially in the nanoelectronics areas.

Figure 14. 2D-PL mapping of the SWNTs solubilized by PFO-BPy in p-xylene. Only the peak from (6,5)SWNTs is observed. Reprinted with permission from ref 79. Copyright 2011 Chemical Society of Japan.

The next topic is SWNT enantiomer sorting. It is known that synthesized SWNTs are racemic mixtures of SWNTs with many chirality indices (n,m),80 thus separated SWNT enantiomers exhibit corresponding circular dichroism (CD),81,82 as can be seen in many chiral organic and polymer compounds. Several reports describing the separation of the racemic mixtures of SWNTs into each enantiomer have been published,72,83 while sorted right- and left-handed SWNT enantiomers contain both metallic and semiconducting F


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8. SUMMARY CNTs are promising future nanomaterials in nanoscience and nanotechnology, including supramolecular materials chemistry (science), polymer science, bioscience, and nanoelectronics. In this review article, we summarized our studies on the selfassembly of CNTs as well as molecular recognition at CNT surfaces. For such studies, unique 1D structure with very high aspect ratios and specific surface structure play an important role. Computer chemistry is powerful for understanding the specific interactions of molecules that have strong affinity for CNT surfaces, the formation of CNTs in solution, and specific molecular recognition at CNT surfaces. The construction of self-assembled hybrid nanomaterials of soluble CNTs with organic, inorganic, biological, and polymer materials as well as with metal nanoparticles are of interest in nanomaterials science as well as energy and environmental science and technology.

■

Tomohiro Shiraki received his Ph.D. from Kyushu University under the supervision of Prof. Nobuo Kimizuka. He worked as a postdoctoral researcher at the Institute of Systems, Information Technologies and Nanotechnologies (ISIT) in Fukuoka, Japan under the supervision of Prof. Seiji Shinkai and as a JSPS Postdoctoral Fellow for Research Abroad in Prof. Jeffrey S. Moore’s group at the University of Illinois at UrbanaChampaign. Currently, he is an assistant professor in the Department of Applied Chemistry, Kyushu University, Japan. His research interests include nanocarbon materials and supramolecular/ polymer chemistry.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected].

■

Notes

The authors declare no competing financial interest. Biographies

REFERENCES

(1) Iijima, S. Helical microtubules of graphitic carbon. Nature 1991, 354, 56−58. (2) Fujigaya, T.; Nakashima, N. Non-covalent polymer wrapping of carbon nanotubes and the role of wrapped polymers as functional dispersants. Sci. Technol. Adv. Mater. 2015, 16, 024802. (3) Fujigaya, T.; Nakashima, N. Soluble Carbon Nanotubes and Nanotube-Polymer Composites. J. Nanosci. Nanotechnol. 2012, 12, 1717−1738. (4) Fujigaya, T.; Nakashima, N. Fuel Cell Electrocatalyst Using Polybenzimidazole-Modified Carbon Nanotubes As Support Materials. Adv. Mater. 2013, 25, 1666−1681. (5) Eder, D. Carbon Nanotube−Inorganic Hybrids. Chem. Rev. 2010, 110, 1348−1385. (6) Wang, H.; Dai, H. Strongly coupled inorganic-nano-carbon hybrid materials for energy storage. Chem. Soc. Rev. 2013, 42, 3088− 3113. (7) Perez, E. M.; Martin, N. π-π interactions in carbon nanostructures. Chem. Soc. Rev. 2015, 44, 6425−6433. (8) Martel, R.; Shea, H. R.; Avouris, P. Rings of single-walled carbon nanotubes. Nature 1999, 398, 299−299. (9) Watanabe, H.; Manabe, C.; Shigematsu, T.; Shimizu, M. Dualprobe scanning tunneling microscope: Measuring a carbon nanotube ring transistor. Appl. Phys. Lett. 2001, 78, 2928−2930. (10) Cuniberti, G.; Yi, J.; Porto, M. Pure-carbon ring transistor: Role of topology and structure. Appl. Phys. Lett. 2002, 81, 850−852. (11) Cohen, A. E.; Mahadevan, L. Kinks, rings, and rackets in filamentous structures. Proc. Natl. Acad. Sci. U. S. A. 2003, 100, 12141−12146. (12) Zha, F. X.; Bertsche, G.; Croitoru, M.; Kentsch, C.; Roth, S.; Kern, D. P. Observation of single-wall carbon nanotube rings by scanning tunneling microscopy and spectroscopy. Carbon 2004, 42, 893−895. (13) Sano, M.; Kamino, A.; Okamura, J.; Shinkai, S. Ring Closure of Carbon Nanotubes. Science 2001, 293, 1299−1301. (14) Shea, H. R.; Martel, R.; Avouris, P. Electrical Transport in Rings of Single-Wall Nanotubes: One-Dimensional Localization. Phys. Rev. Lett. 2000, 84, 4441−4444. (15) Terranova, M. L.; Sessa, V.; Orlanducci, S.; Rossi, M.; Manno, D.; Micocci, G. Organized networks of helically wound single-walled C-nanotubes. Chem. Phys. Lett. 2004, 388, 36−39.

Naotoshi Nakashima received his Ph.D. in 1981 under the direction of Professor Toyoki Kunitake at Kyushu University. He started to work as an assistant professor in 1980 at Kyushu University and then was promoted to associate professor at the same university in 1982. He moved to Nagasaki University in 1987 and was promoted to professor there in 1993. He moved back to Kyushu University in 2004 as a professor in the Department of Applied Chemistry, Graduate School of Engineering. He has also been a principal investigator (PI) of International Institute for Carbon-Neutral Energy Research, Kyushu University (HP: http://i2cner.kyushu-u.ac.jp/ja/) since 2010. His current research interests are the design and functionalization of carbon nanotubes and supramolecular nanomaterials. He earned The Chemical Society of Japan (CSJ) Award for Young Chemists in 1986, The Award of the Society of Polymer Science, Japan in 2000, a 2007 Thomson Scientific Research Front Award, The Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology in 2016, and the SPSJ Award for Outstanding Achievement in Polymer Science and Technology in 2016. G


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Nanotubes by Agarose Gel Electrophoresis. Appl. Phys. Express 2008, 1, 114001. (76) Liu, H.; Nishide, D.; Tanaka, T.; Kataura, H. Large-scale singlechirality separation of single-wall carbon nanotubes by simple gel chromatography. Nat. Commun. 2011, 2, 309. (77) Hirano, A.; Tanaka, T.; Kataura, H. Thermodynamic Determination of the Metal/Semiconductor Separation of Carbon Nanotubes Using Hydrogels. ACS Nano 2012, 6, 10195−10205. (78) Fukumaru, T.; Toshimitsu, F.; Fujigaya, T.; Nakashima, N. Effects of the chemical structure of polyfluorene on selective extraction of semiconducting single-walled carbon nanotubes. Nanoscale 2014, 6, 5879−5886. (79) Ozawa, H.; Ide, N.; Fujigaya, T.; Niidome, Y.; Nakashima, N. One-pot Separation of Highly Enriched (6,5)-Single-walled Carbon Nanotubes Using a Fluorene-based Copolymer. Chem. Lett. 2011, 40, 239−241. (80) Tasaki, S.; Maekawa, K.; Yamabe, T. π-band contribution to the optical properties of carbon nanotubes: Effects of chirality. Phys. Rev. B: Condens. Matter Mater. Phys. 1998, 57, 9301−9318. (81) Sánchez-Castillo, A.; Román-Velázquez, C. E.; Noguez, C. Optical circular dichroism of single-wall carbon nanotubes. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 73, 045401. (82) Peng, X.; Komatsu, N.; Bhattacharya, S.; Shimawaki, T.; Aonuma, S.; Kimura, T.; Osuka, A. Optically active single-walled carbon nanotubes. Nat. Nanotechnol. 2007, 2, 361−365. (83) Green, A. A.; Duch, M. C.; Hersam, M. C. Isolation of singlewalled carbon nanotube enantiomers by density differentiation. Nano Res. 2009, 2, 69−77. (84) Akazaki, K.; Toshimitsu, F.; Ozawa, H.; Fujigaya, T.; Nakashima, N. Recognition and One-Pot Extraction of Right- and Left-Handed Semiconducting Single-Walled Carbon Nanotube Enantiomers Using Fluorene-Binaphthol Chiral Copolymers. J. Am. Chem. Soc. 2012, 134, 12700−12707. (85) Li, X.; Qin, Y.; Picraux, S. T.; Guo, Z.-X. Noncovalent assembly of carbon nanotube-inorganic hybrids. J. Mater. Chem. 2011, 21, 7527−7547. (86) Ozawa, H.; Ide, N.; Fujigaya, T.; Niidome, Y.; Nakashima, N. Supramolecular Hybrid of Metal Nanoparticles and Semiconducting Single-Walled Carbon Nanotubes Wrapped by a Fluorene−Carbazole Copolymer. Chem. - Eur. J. 2011, 17, 13438−13444. (87) Ozawa, H.; Yi, X.; Fujigaya, T.; Niidome, Y.; Asano, T.; Nakashima, N. Supramolecular Hybrid of Gold Nanoparticles and Semiconducting Single-Walled Carbon Nanotubes Wrapped by a Porphyrin−Fluorene Copolymer. J. Am. Chem. Soc. 2011, 133, 14771− 14777.

(55) Li, Z.; Kameda, T.; Isoshima, T.; Kobatake, E.; Tanaka, T.; Ito, Y.; Kawamoto, M. Solubilization of Single-Walled Carbon Nanotubes Using a Peptide Aptamer in Water below the Critical Micelle Concentration. Langmuir 2015, 31, 3482−3488. (56) Coleman, J. N.; Fleming, A.; Maier, S.; O’Flaherty, S.; Minett, A. I.; Ferreira, M. S.; Hutzler, S.; Blau, W. J. Binding Kinetics and SWNT Bundle Dissociation in Low Concentration Polymer−Nanotube Dispersions. J. Phys. Chem. B 2004, 108, 3446−3450. (57) Kato, Y.; Niidome, Y.; Nakashima, N. Thermodynamics of the Exchange of Solubilizers on Single-walled Carbon Nanotubes. Chem. Lett. 2011, 40, 730−732. (58) Kato, Y.; Inoue, A.; Niidome, Y.; Nakashima, N. Thermodynamics on Soluble Carbon Nanotubes: How Do DNA Molecules Replace Surfactants on Carbon Nanotubes? Sci. Rep. 2012, 2, 733. (59) Kato, Y.; Niidome, Y.; Nakashima, N. Spectroscopic Analysis of Two Distinct Equilibrium States for the Exchange Reaction of Sodium Cholate and Oligo-DNA on Single-Walled Carbon Nanotubes. ChemPhysChem 2013, 14, 1652−1655. (60) Shiraki, T.; Tsuzuki, A.; Toshimitsu, F.; Nakashima, N. Thermodynamics for the Formation of Double-Stranded DNA− Single-Walled Carbon Nanotube Hybrids. Chem. - Eur. J. 2016, 22, 4774−4779. ( 6 1 ) S h a r i f i , R . ; S a m a r a w e e r a , M . ; G a s c ó n , J . A . ; Papadimitrakopoulos, F. Thermodynamics of the Quasi-Epitaxial Flavin Assembly around Various-Chirality Carbon Nanotubes. J. Am. Chem. Soc. 2014, 136, 7452−7463. (62) Oh, H.; Sim, J.; Ju, S.-Y. Binding Affinities and Thermodynamics of Noncovalent Functionalization of Carbon Nanotubes with Surfactants. Langmuir 2013, 29, 11154−11162. (63) Tu, X.; Manohar, S.; Jagota, A.; Zheng, M. DNA sequence motifs for structure-specific recognition and separation of carbon nanotubes. Nature 2009, 460, 250−253. (64) Kato, Y.; Fukuzawa, M.; Toshimitsu, F.; Nakashima, N. Separation of Semiconducting Single-walled Carbon Nanotubes Using a Flavin Compound. Chem. Lett. 2015, 44, 566−567. (65) Fujigaya, T.; Yoo, J.; Nakashima, N. A method for the coating of silica spheres with an ultrathin layer of pristine single-walled carbon nanotubes. Carbon 2011, 49, 468−476. (66) Yoo, J.; Ozawa, H.; Fujigaya, T.; Nakashima, N. Evaluation of affinity of molecules for carbon nanotubes. Nanoscale 2011, 3, 2517− 2522. (67) Yoo, J.; Fujigaya, T.; Nakashima, N. Facile Evaluation of Interactions between Carbon Nanotubes and Phthalocyanines Using Silica Spheres Coated with Ultrathin-layers of Single-walled Carbon Nanotubes. Chem. Lett. 2011, 40, 538−539. (68) Yoo, J.; Fujigaya, T.; Nakashima, N. Molecular recognition at the nanoscale interface within carbon nanotube bundles. Nanoscale 2013, 5, 7419−7424. (69) Nakashima, N.; Fujigaya, T. Fundamentals and Applications of Soluble Carbon Nanotubes. Chem. Lett. 2007, 36, 692−697. (70) Ozawa, H.; Fujigaya, T.; Niidome, Y.; Nakashima, N. Effect of Backbone Chemical Structure of Polymers on Selective (n,m)SingleWalled Carbon Nanotube Recognition/Extraction Behavior. Chem. Asian J. 2011, 6, 3281−3285. (71) Arnold, M. S.; Green, A. A.; Hulvat, J. F.; Stupp, S. I.; Hersam, M. C. Sorting carbon nanotubes by electronic structure using density differentiation. Nat. Nanotechnol. 2006, 1, 60−65. (72) Ghosh, S.; Bachilo, S. M.; Weisman, R. B. Advanced sorting of single-walled carbon nanotubes by nonlinear density-gradient ultracentrifugation. Nat. Nanotechnol. 2010, 5, 443−450. (73) Zhang, J.; Gui, H.; Liu, B.; Liu, J.; Zhou, C. Comparative study of gel-based separated arcdischarge, HiPCO, and CoMoCAT carbon nanotubes for macroelectronic applications. Nano Res. 2013, 6, 906− 920. (74) Tulevski, G. S.; Franklin, A. D.; Afzali, A. High Purity Isolation and Quantification of Semiconducting Carbon Nanotubes via Column Chromatography. ACS Nano 2013, 7, 2971−2976. (75) Tanaka, T.; Jin, H.; Miyata, Y.; Kataura, H. High-Yield Separation of Metallic and Semiconducting Single-Wall Carbon I


Specific Molecular Interaction and Recognition at Single-Walled

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