JP4953860B2 - Nanostructures using ionic curdlan derivatives - Google Patents

Description

  The present invention relates to a novel technique for orienting functional polymers such as carbon nanotubes and conductive polymers into a regular structure such as a sheet.

For various functional polymers, in order to exert their useful functions, it is important to embody regular shapes according to the respective characteristics.
For example, single-walled carbon nanotubes (SWNT) have a cylindrical structure in which graphene sheets are rolled up, and have very interesting characteristics such as becoming metallic or semiconducting depending on the winding method. Furthermore, although it is a substance composed of a single element called carbon, (1) its anisotropy is large and the physical properties differ greatly between the length direction and the thickness direction of the tube (Fig. 3). (2) It has many unrivaled features such as the energy gap size changing almost continuously depending on the thickness of the tube, and it is highly expected as an excellent functional material. (Non-Patent Document 1).
Riichiro Saito, Hissunori Shinohara; “Basics and Applications of Carbon Nanotubes”, Baifukan

  However, although SWNT has excellent optical and electrical functions, it aggregates and bundles due to the strong interaction between tubes, and SWNT's inherent semiconductor functions, especially light emission and photoelectric conversion functions There is a big problem that can not be demonstrated. In order to use SWNT as a functional material, processing into a thin film is one of the important processes. It is considered important to orient SWNTs.

Kazaoui et al. Used SDS as a dispersion medium and formed a thin film in which SWNTs were isolated and dispersed by using the thin film forming ability of gelatin, a kind of biopolymer. Furthermore, it has succeeded in producing a thin film in which isolated SWNTs are oriented in a certain direction by a stretching process (Non-patent Document 2). When this thin film was irradiated with visible light, near-infrared emission strongly polarized in the SWNT orientation direction was observed. This is the first reported example of a light-emitting SWNT thin film having polarization characteristics. However, in this system, since SWNTs are oriented by physical stretching treatment, strict orientation control has not yet been achieved.
Y. Kim, N. Minami, S. Kazaoui, Appl. Physic. Lett., 86, 073103 (2005).

  The object of the present invention is to develop a simple method for self-organizing a hydrophobic functional polymer such as a single-walled carbon nanotube or a conductive polymer into a sheet-like structure at the nano level, and based on that method. The object is to provide a novel nanometer scale structure (nanostructure).

The present inventors have reported that the interior of β-1,3-glucan such as schizophyllan (SPG) and curdlan (CUR) functions as a one-dimensional host and takes in single-walled carbon nanotubes (SWNT) and solubilizes them. (Non-Patent Document 3). On the other hand, various substituents can be freely introduced selectively through the 6-position of the curdlan by click chemistry (Non-patent Document 4). Conventionally, SPG and CUR have a triple helix structure that is stable in water, so it is necessary to perform a rewinding operation from the random coil state to the triple helix state to include polymers such as SWNT. there were. That is, after SPG or CUR is made into a single chain in a polar solvent, a polymer such as SWNT is taken in when water is added again for rewinding. Recently, we conducted a ORD measurement of a curdlan (CUR-N ⁺ ) with an ammonium group introduced at the 6-position of the curdlan. This curdlan has already taken a random coil structure in water due to the repulsion of the 6-position substituent. (FIG. 1). It has also been clarified that such a curdlan can take in SWNT and the like in water without performing a Renature operation, and can solubilize SWNT more easily (FIG. 2; Non-Patent Document 5).
M. Numata, M. Asai, K. Kaneko, A. Bae, T Hasegawa, K. Sakurai, S. Shinkai, J. Am. Chem. Soc., 127. 5875 (2005). T. Hasegawa etal., Carbohydr. Res., 341, 35 (2006). M. Ikeda etal., J. Am. Chem. Soc., In press

As a result of intensive studies based on the above findings, the present invention succeeded in the construction of a novel structure derived from an ionic curdlan derivative.
Thus, the present invention provides a nanostructure formed by mixing a cationic curdlan derivative / hydrophobic polymer complex and an anionic curdlan derivative / hydrophobic polymer complex in an aqueous solution. .

  As the cationic curdlan derivative in the present invention, any cationic functional group or atomic group introduced into the side chain of the curdlan can be used. A preferred example is represented by the following chemical formula 1. And those consisting of repeating units.

In chemical formula 1, R represents a cationic substituent. A preferred example of the cationic substituent is a quaternary ammonium group (for example, trimethylammonium group), but is not limited thereto.
The anionic curdlan derivative used in the present invention can be used as long as a cationic functional group or atomic group is introduced into the side chain of the curdlan. The thing consisting of the repeating unit represented by 2 is mentioned.

In chemical formula 2, R represents an anionic substituent. Preferable examples of the anionic substituent include —SO ₃ ^—, but are not limited thereto.
The above ionic curdlan derivatives used in the present invention can be easily synthesized by devising a known reaction (see Examples described later).

  Examples of the hydrophobic polymer to which the present invention is applied include conductive polymers such as polysilane, polyaniline, polythiophene, and polyacetylene, and carbon nanotubes (particularly single-walled carbon nanotubes). In addition, nucleic acids that are biopolymers include poly (C) that forms a similar complex with an ionic curdlan.

According to the present invention, a desired cationic curdlan derivative can be obtained by mixing the above-described cationic curdlan derivative or anionic curdlan derivative with a predetermined hydrophobic polymer in water while performing ultrasonic treatment as necessary. / Hydrophobic polymer complex (complex composed of cationic curdlan derivative and hydrophobic polymer) or anionic curdlan derivative / hydrophobic polymer complex (from anionic curdlan derivative and hydrophobic polymer) A complex). In general, the hydrophobic polymer in the cationic curdlan derivative / hydrophobic polymer complex and the hydrophobic polymer in the anionic curdlan derivative / hydrophobic polymer complex are the same type of polymer. However, it may be a different polymer.
When the aqueous solutions of both composites as described above are mixed in an equal ratio, a desired nanostructure can be obtained by electrostatic interaction.

  Thus, according to the present invention, as shown in Chemical Formula 1 and Chemical Formula 2, two kinds of 6-position modified curdlan derivatives into which 6-position selective substituents are introduced are synthesized, and hydrophobic such as SWNTs are synthesized. By combining with a functional polymer, a structure (nanostructure) in which the polymer is more regularly oriented in an aqueous medium is formed by the interaction between substituents (see FIG. 4). The formation of such a structure has been confirmed by measurement of TEM or EDX spectrum. In the structure of the present invention, the SWNT-incorporated complex is considered to have a hierarchical structure in which structures having a basic arrangement in a two-dimensional direction as a basic unit overlap each other.

  As described above, for example, when higher-precision orientation of SWNT is realized, it is expected to lead to development of various optical / electronic functional elements. As an example, if a near-infrared light-emitting element capable of controlling the emission wavelength or a near-infrared photoelectric conversion element having a wide wavelength region is realized, there is a possibility that it can be used in the field of optical communication.

Hereinafter, examples will be described in order to more specifically show the characteristics of the present invention. In the following examples, a cationic curdlan having a quaternary ammonium group (CUR-N ⁺ ) and an anionic curdlan having a sulfone group (CUR-SO ₃ ⁻ ) are used for uncleaved SWNT (Ag-SWNT). It describes examples of solubilization, and examples of attempts to regularly arrange complexes by electrostatic interaction by mixing SWNTs coated with cationic and anionic curdlan.

Synthesis of Quaternary Ammonium Curdlan (CUR-N ⁺ ) Raw material azide curdlan 187 synthesized in a conventional method (Non-patent Document 4) in a 50 ml sample bottle
mg (1.0 mM (monomer unit)) was added and dissolved in 10 ml of DMSO. To this was added 1.0 ml of distilled water, 1.0 ml of propylamine, 11.2 mg (5 mol%) of CuBr _{2 and} 44 mg (25 mol%) of ascorbic acid, and then 668 mg (5 mmol) of 1-propynyl-trimethylammonium chloride was added at room temperature. Stir for 12 hours. Thereafter, this solution was dialyzed, and the resulting aqueous solution was freeze-dried to obtain a milky white solid.

Synthesis of sulfated curdlan (CUR-SO ₃ ⁻ ) Synthesis was performed in the same manner as CUR-N ^{+ in} Example 1. A 50-ml sample bottle was charged with 100 mg (0.53 mM (monomer unit)) of azido curdlan synthesized by a conventional method and dissolved in 10 ml of DMSO. Distilled water (1.0 ml), propylamine (5.2 ml), CuBr (210 mg, 8.4 mol%) and ascorbic acid (50 mg, 54 mol%) were added thereto, and then sodium 1-propynylsulfonate (800 mg, 5.3 mmol) was added, and the mixture was stirred at room temperature for 60 hours. Stir. Thereafter, this solution was dialyzed, and the resulting aqueous solution was freeze-dried to obtain a milky white solid.

CUR-N ⁺ and CUR-SO ₃ ^- a Ag-SWNT sample tube according to solubilize Table 1 Ag-SWNT by ^{adding, CUR-N + (5mg /} mL) was prepared there in Example 1 and 2 or CUR -SO ₃ ^- (5mg / mL) was added, respectively, was solubilized in SWNT by ultrasonic (50min) process. NIR absorption spectrum of the obtained aqueous solution
The path length was 0.1 cm, measured at room temperature, and the result of FIG. 5 was obtained. In all samples, the SWNT-derived peak sharply appears at 400 to 900 nm, indicating that SWNT is solubilized. The SWNT concentration determined from the absorbance at 500 nm was CUR-SO ₃ ⁻ / SWNT 5.6 mg / L and CUR-N ⁺ / SWNT 4.7 mg / L. As can be seen from this spectrum, SWNT is CUR-N ⁺ or CUR-SO ₃ ^- are isolated distributed almost single state by.

Next, in order to completely remove free sugars that were not involved in conjugation, the resulting aqueous solution was subjected to gel filtration chromatography (Amersham Biosciences, Sephadex ^™ G-100) to isolate the complex. . Table 2 shows the purification conditions of the CUR-N ⁺ / SWNT complex and the CUR-SO3 ⁻ / SWNT complex. In addition, FIG. 6 shows an AFM image of each complex after purification. In the obtained AFM image, an isolated and dispersed complex having a height of about 1.8 nm and a length of about several hundred nm to several μm was confirmed. Judging from the height, it can be seen that almost one SWNT is a composite coated with a curdlan derivative. On the other hand, the image considered to be an uncombined curdlan derivative could not be confirmed from the AFM image, and it is considered that all could be removed by gel filtration chromatography.

Alignment of SWNTs with CUR-N ⁺ / SWNT complex and CUR-SO ₃ ⁻ / SWNT complex The aqueous solution of both complexes isolated in Example 3 had the same concentration of SWNT in each solution (4.4 × 10 ⁻² mg / L) and diluted with water. The concentration of each solution was adjusted by the absorbance of SWNT at 500 nm. Thereafter, both aqueous solutions of the composites were mixed at an equal ratio to organize the composite. Although no precipitation or the like was observed after mixing, the solution was cast on a TEM grid and subjected to TEM observation. Similarly, a sample in which CUR-N ⁺ / SWNT and CUR-SO ₃ ⁻ / SWNT were mixed at a ratio of 1:10 was prepared, and the difference in the association form was observed. As a result, in the TEM observation of the mixed sample of the equal ratio, a sheet-like stripe pattern was seen. Further, an image in which fibers are oriented at equal intervals is confirmed in the sheet structure (FIG. 7). Such a striped pattern is not seen in the 1:10 mixed sample, and it is confirmed that the SWNTs are partly bundled fibers. Furthermore, no stripe pattern was observed when only curdlan derivatives not containing SWNTs were mixed. From these results, it can be seen that this stripe pattern is due to the orientation of SWNTs. In addition, since the ratio of SWNTs that are oriented is clarified by the change in the charge ratio between the ammonium group and the sulfonic acid group, neutralization of the charge on the surface of the curdlan derivative, that is, electrostatic interaction between the ammonium group and the sulfonic acid group. The action is considered to be the main driving force for SWNT orientation.

HR-TEM by structure observation and EDX spectroscopy Furthermore, CUR-N ⁺ / SWNT composites and CUR-SO ₃ ^- / demand structure obtained by mixing SWNT complex, high-resolution TEM (HR-TEM ). A solution mixed so that N ⁺ : SO ₃ ⁻ = 1: 1 and N ⁺ : SO ₃ ⁻ = 1: 3 was cast on an A type grid and dried under reduced pressure to obtain a sample. As a result of HR-TEM observation, a sheet-like aggregate of several μm square was observed from the solution in which CUR-N ⁺ / SWNT complex and CUR-SO ₃ ⁻ / SWNT complex were mixed at 1: 1 ( FIG. 8). In the dark field image (FIGS. 8A, 8B, and 8C) at the diffraction spot in FIG. 8, since a striped pattern was observed in a wide area, it is considered that several sheets are overlapped. Moreover, it was found from this electron beam diffraction image and bright field image fringe spacing that this aggregate had a periodicity of about 3.0 nm. This period does not coincide with the diameter of the CUR-N ⁺ / SWNT complex or the CUR-SO ₃ ⁻ / SWNT complex. This is thought to be due to the fact that such narrow cycles occur due to the overlapping of SWNT-oriented sheets.

Furthermore, from the result of the EDX analysis of the sheet shown in FIG. 9, peaks of nitrogen (N) and sulfur (S) can be confirmed although they are weak. This indicates that this sheet structure is formed by CUR-N ⁺ / SWNT complex and CUR-SO ₃ ⁻ / SWNT. CUR-N ⁺ / SWNT composites and CUR-SO ₃ ^- / SWNT composite mixture ratio of 1: In the third sample, a sheet-shaped image is obtained, the mixing ratio of 1: observed when the 1 A striped pattern was not seen, and an image in which bundled fibers and SWNTs were irregularly arranged was obtained (FIG. 10). This result almost coincides with the result obtained when the mixing ratio is 1:10. This is thought to be due to the extraordinary presence of the CUR-SO ₃ ⁻ / SWNT complex, which excluded the regular association of the complex. Further, from the EDX analysis of FIG. 11, the peaks of both N atoms and S atoms were larger than those of the 1: 1 sample, and the presence of each element could be confirmed. From the above results, it was shown that by using chemically modified curdlan as a one-dimensional host, guest polymer (in this case SWNT) can be organized and hierarchized using electrostatic interaction between curdlan as driving force.

  The present invention makes it possible to prepare a sheet-like material in which hydrophobic polymers such as carbon nanotubes and various functional polymers are dispersed and oriented one by one, and therefore is expected to be applied in the nanotechnology field such as electronic devices. Is done.

The OPD spectrum of SPG and CUR-N ⁺ is shown. The composite image of an ionic curdlan derivative and a single-walled carbon nanotube (SWNT) is shown. The optical anisotropy of SWNT. An image of sheet-like layering of SWNT mixtures coated with curdlan derivatives (CUR) with different ionic substituents is shown. CUR-N ⁺ / SWNT and CUR-SO ₃ ^- / indicates a NIR spectrum of SWNT composites (Example 3). An AFM image (Example 3) of CUR-N ⁺ / SWNT and CUR-SO ₃ ⁻ / SWNT complex is shown. N ⁺ : SO ₃ ⁻ = 1: 1 shows a TEM image of Sample C (Example 4). _{^{N +: SO 3 - = 1}} : shows 1 HR-TEM image of the sample (Example 5). _{^{N +: SO 3 - = 1}} : shows 1 sample EDX spectrum (Example 5). HR-TEM image (Example 5) of N ⁺ : SO ₃ ⁻ = 1: 3 sample is shown. N ⁺ : SO ₃ ⁻ = 1: 3 shows an EDX spectrum (Example 5) of the sample.

Claims (1)

A nanostructure formed by mixing a cationic curdlan derivative / hydrophobic polymer complex and an anionic curdlan derivative / hydrophobic polymer complex in an aqueous solution, wherein the hydrophobic polymer is a single-layer carbon A cationic curdlan derivative comprising a repeating unit represented by the following chemical formula 1 (wherein R represents a quaternary ammonium group which is a cationic substituent): A nanostructure comprising a repeating unit represented by the following chemical formula 2 (wherein R represents —SO ₃ ^— which is an anionic substituent).