JP2013028562A - Nanofiber forming compound, method for forming nanofiber, and method for forming nanofiber assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nanofiber forming compound capable of forming nanofiber of which the fiber diameter is in the range of 10 to 1,000 nm and the length is 10 μm or more by a simple method, and to provide a method for forming the nanofiber and a method for forming a nanofiber assembly using the nanofiber forming compound.SOLUTION: The nanofiber forming compound is represented by general formula I. In the formula, Rrepresents a 6-29C hydrocarbon group and Rrepresents a hydrogen atom or methyl group. Mrepresents an alkali metal ion.

Description

  The present invention relates to a nanofiber-forming compound that spontaneously forms nanofibers, and a method for forming nanofibers and nanofiber aggregates thereby. More specifically, by drying from a uniformly dissolved solution state or by cooling from a uniformly dissolved solution state, nanofibers having a fiber diameter in the range of 10 to 1000 nm and a length of 10 μm or more are obtained. The present invention relates to a nanofiber-forming compound that can be formed, a method for forming a nanofiber using the compound, and a method for forming a nanofiber aggregate.

  It is known that a compound with a structure in which a long-chain alkyl group is bonded to an amino acid derivative or glycoside derivative forms a kind of nanofiber called an organic nanotube having a hollow cylindrical structure by self-assembling from a solution. (Patent Documents 1 to 5 and Non-Patent Document 1). In addition to the characteristics as a fiber that is a nanofiber, these materials have been proposed for use in which a functional material is sealed in the hollow portion, particularly focusing on the hollow portion inside the fiber structure. For example, in the field of pharmaceuticals and chemical products, the diameter and fiber length of the hollow part can be controlled by controlling the structure with the aim of functions such as inclusion, separation, and sustained release.

  When paying attention to the form as a fiber that is a nanofiber, the fiber diameters and lengths of the organic nanotubes shown in these prior arts are in the range of 10 to several 100 nm and roughly 1 μm to several mm, respectively. It is characterized by extremely fine fibers compared to the general-purpose fibers that are used. Regardless of whether it is a hollow structure or not, there is a possibility that it is extremely useful as a compound that forms fine nanofibers, and various fields such as fiber products, nonwoven fabric products, paper products, film products, etc. that use this Application to is expected.

  Non-Patent Document 1 describes nanofibers formed when the position of an unsaturated double bond group contained in an acyl group is changed for glycolipids having various long-chain acyl groups introduced as 1-glucosamide compounds. However, the formation of nanofibers was confirmed only when an unsaturated double bond was included at a specific position of the acyl group, but when the unsaturated double bond was not included, the nanofiber Even when nanofibers are formed, disordered aggregates may be included in other cases, and nanofibers are not always stably formed.

  In Patent Document 1, similarly, a long-chain alkyl group is bonded to a sugar residue via an amide bond, and the other end is an asymmetric bihead lipid compound having a carboxyl group and a nanofiber formed using the same Nanotubes are disclosed. As a method for forming nanofibers from the compound disclosed herein, nanofibers are formed from the solution by dissolving the compound in hot water and slowly cooling the resulting aqueous solution. However, in addition to the formed nanofibers, there may be cases where components of microtubes and other forms are included, and there are cases where crystalline solids and vesicles (spherical vesicles) are generated when rapidly cooled from a heated solution, It was not always possible to stably form nanofibers.

  Patent Document 2 discloses an N-glycoside glycolipid in which a long-chain unsaturated hydrocarbon group is bonded to the sugar terminal via an amide group, and an organic nanotube which is a nanofiber formed therefrom. Also in this case, the glycolipid is dissolved in hot water, and the resulting aqueous solution is slowly cooled and allowed to stand at room temperature, whereby nanofibers are formed in the form of aggregates from the solution. In this case, since the solubility of the glycolipid in hot water is extremely low, there is no particular problem when obtaining a small amount of nanofibers, but there is a problem when trying to produce a large amount at a time on an industrial scale. was there. In addition, a step of gradually cooling after dissolving in hot water and then allowing to stand at room temperature for a long time is required, and this is also a major problem for obtaining an efficient and stable production.

  Patent Document 3 discloses the N-glycoside type glycolipid described in Patent Document 2 and a peptide lipid in which an acyl group having a long alkyl group is bonded to the N-terminal of an oligopeptide such as glycylglycine. And a method for producing organic nanotubes, which are nanofibers formed therefrom. In this case, unlike the previous patent document, a method of forming nanofibers in a system that does not contain water is disclosed. In one method, these compounds are dissolved using an organic solvent, the solution dissolved by heating is slowly cooled (10 to several hours to several days), and left at room temperature to leave nanofibers from the solution. Is used in the form of aggregates. As another method, a method is used in which nanofibers are formed in the form of aggregates in the process of dissolving these compounds using an organic solvent and concentrating the solution using an evaporator or the like. As another method, nanofibers in a dispersed form are prepared by dissolving these compounds using an organic solvent and adding a poor solvent for N-glycoside type glycolipid or peptide lipid to this solution. A method is disclosed. In the case of the last-mentioned method, the dispersion state is maintained because the length of the nanofiber is as short as 1 μm or less. However, when the length is 1 to 10 μm or more, the nanofibers are intertwined with each other. There was a problem of agglomeration.

  Patent Document 4 discloses an organic nanotube composed of the above peptide lipid and a transition metal. In this case, a solution in which peptide lipid is dissolved in water by adding an alkali metal hydroxide such as sodium hydroxide is used, and transition metal ions such as manganese, iron, cobalt, nickel, copper, zinc and silver are added to the solution. Thus, nanofibers are instantly formed in the form of aggregates from the aqueous solution.

  Patent Document 5 discloses an organic nanotube in which an aromatic compound having a photoisomerization function such as azobenzene is bonded to the carboxylic acid terminal of an oligoglycine such as glycylglycine via an ethylenediamino group. In this case as well, the disclosed compound is dissolved in hot water, and the resulting aqueous solution is slowly cooled and allowed to stand at room temperature, whereby nanofibers are formed in the form of aggregates from the solution.

  In any of the above examples, in the formation of organic nanotubes, which are examples of nanofibers, they are formed in the process of being gradually formed in water, or in the process of being concentrated from a solution using an organic solvent. In particular, there are cases where it is obtained in a dry powder form. These are assumed to be used in a state where the nanofiber is used as a powder in a solid state or in a state where the nanofiber is dispersed in a liquid. However, in other applications, for example, when an assembly of nanofibers to be formed is to be formed on the surface of a substrate such as a film or paper, a method by coating is preferable. It is preferable that the components contained in the solution are uniformly dissolved or dispersed, and the aggregate of nanofibers formed by the above method is in an agglomerated state, and it is difficult to perform uniform coating when used as a coating solution was there. Furthermore, when a compound that forms nanofibers is dissolved and used, for example, it is possible to fix the compound to a substrate surface such as a film or paper by applying a solution dissolved using hot water. In many cases, after coating, the coating solution is usually quickly dried and the substrate is wound up, and in such a short drying process, the nanofibers are formed from the compound in the coating solution over time. Since there is no allowance, it was usually formed on the substrate surface as an aggregate of aggregates that does not form crystals or nanofibers of the compound.

  Alternatively, a solution in which nanofibers are dispersed can also be used as a coating solution by a method of concentrating a solution dissolved using an organic solvent as shown in Patent Document 3, but in this case also, the dispersion state is uniform. In addition, it is difficult to uniformly apply to the surface of a substrate such as a film or paper, and the drying time is short, and not only nanofibers but also part of the compound is formed on the substrate surface as crystals or aggregates. Was normal.

  Furthermore, in the method of Patent Document 4, nanofibers are not formed on the surface of a substrate such as a film or paper even when a solution of a compound dissolved uniformly using sodium hydroxide or the like is applied and dried. When transition metal ions are added, nanofiber aggregates are formed immediately, and in this case as well, it is difficult to use them as a coating solution. As described above, there is no method for uniformly forming nanofiber aggregates on the surface of a substrate such as a film or paper, and there is no compound used therefor. That is, in order to form nanofibers having a fiber diameter in the range of 10 to 1000 nm and a length of 10 μm or more, drying from a uniformly dissolved solution state or cooling from a uniformly dissolved solution state is performed. Therefore, there is a demand for a nanofiber forming compound capable of forming nanofibers having a fiber diameter in the range of 10 to 1000 nm and a length of 10 μm or more, and a method for forming a nanofiber aggregate using the same. It was.

JP 2002-322190 A JP 2004-224717 A JP 2008-30185 A JP 2004-250797 A JP 2011-46669 A

Langmuir, 2005, 21, 743.

  The present invention provides nanofibers having a fiber diameter in the range of 10 to 1000 nm and a length of 10 μm or more by drying from a uniformly dissolved solution state or by cooling from a uniformly dissolved solution state. It is an object to provide a nanofiber-forming compound that can be formed, a method for forming a nanofiber using the compound, and a method for forming a nanofiber aggregate.

  An object of the present invention is to form a nanofiber-forming compound represented by the following general formula I, a method for forming nanofibers for drying or cooling a solution in which the nanofiber-forming compound is dissolved, and further applying a solution in which the nanofiber-forming compound is dissolved on a substrate. Then, it is solved by a method for forming a nanofiber assembly in which the applied liquid is cooled and the gelated coating liquid is dried prior to drying or drying.

In the formula, R ₁ represents a hydrocarbon group having 6 to 29 carbon atoms, and R ₂ represents a hydrogen atom or a methyl group. M ⁺ represents an alkali metal ion.

  According to the present invention, by drying from a uniformly dissolved solution state or cooling from a uniformly dissolved solution state, nanofibers having a fiber diameter in the range of 10 to 1000 nm and a length of 10 μm or more are obtained. A nanofiber-forming compound that can be formed, a method of forming a nanofiber using the compound, and a method of forming a nanofiber aggregate are provided.

The observation image by the scanning electron microscope of the nanofiber obtained in Example 1. FIG. The observation image by the scanning electron microscope of the nanofiber obtained in Example 3. FIG. The observation image by the transmission electron microscope of the nanofiber obtained in Example 3. FIG. The observation image by the scanning electron microscope of the nanofiber obtained in Example 4. FIG. The observation image by the confocal laser scanning microscope of the nanofiber obtained in Example 4. FIG. The observation image by the confocal laser scanning microscope of the nanofiber obtained in Example 5. FIG.

  The nanofiber-forming compound represented by the general formula I given in the present invention is easily soluble in hot water, and the nanofiber is spontaneously produced when a uniformly dissolved solution is applied on a film, paper or other substrate and dried. Is characterized by being formed on the substrate. Alternatively, when the solution is cooled, nanofibers are formed immediately from the solution.

  The nanofiber-forming compound of the present invention dissolves uniformly in the solution. However, the nanofiber-forming compound spontaneously assembles from the solution to form nanofibers by drying the solution or cooling the solution. The produced nanofibers are further formed in a solution or on a substrate such as a film or paper in the form of an intertwined nanofiber assembly.

  First, the nanofiber-forming compound represented by the general formula I given in the present invention will be described.

In the formula, R ₁ represents a hydrocarbon group having 6 to 29 carbon atoms, and R ₂ represents a hydrogen atom or a methyl group. M ⁺ represents an alkali metal ion. The hydrocarbon group for R ₁ is an optionally branched alkyl group or a hydrocarbon group containing an unsaturated bond group, preferably a straight-chain alkyl group having 6 to 29 carbon atoms or a carbon group having 6 to 29 carbon atoms. The case where it is a hydrocarbon group containing 1-4 saturated bond groups is preferable. Further, it is most preferable that the alkali metal ion of M ⁺ is sodium ion, potassium ion or lithium ion.

  Regarding the synthesis of the nanofiber-forming compound represented by the general formula I, it can be synthesized by various known synthetic methods such as reacting a carboxylic acid and an amine in the presence of a condensing agent. Is a so-called Schotten-Baumann reaction (for example, literature) in which water is used as a reaction solvent and acid chloride and glycosamine (guanidinoacetic acid) or creatine are reacted in water in the presence of a base such as sodium hydroxide or various organic amines. As “March's Advanced Organic Chemistry, Fifth Ed., John Wiley & Sons, Inc., (2001) P.506), it is the most convenient, inexpensive, high yield and high purity. As shown in the examples described later, an acid chloride of a fatty acid having 7 to 30 carbon atoms is used as the acid chloride, In an aqueous solution obtained by dissolving suspending or dissolved glycocyamine or creatine a base such as sodium hydroxide, it is preferably added to the acid chloride gradually.

Examples of the acid chloride that can be preferably used in the above include heptanoyl chloride, octanoyl chloride, nonanoyl chloride, decanoyl chloride, undecanoyl chloride, lauroyl chloride, tridecanoyl chloride, myristoyl chloride, pentadecanoyl chloride, Saturated fatty acid chlorides such as palmitoyl chloride, stearoyl chloride, nonadecanoyl chloride, eicosanoyl chloride, docosanoyl chloride, tetracosanoyl chloride, hexacosanoyl chloride, heptacosanoyl chloride, octacosanoyl chloride, triacosanoyl chloride Or examples of unsaturated fatty acid chlorides include 6-heptenoyl chloride, 2-octenoyl chloride, Silenoyl chloride, oleoyl chloride, elidoyl chloride, cis-11-eicosenoyl chloride, linoleoyl chloride, linolenoyl chloride, arachidonoyl chloride, 2-heptinoyl chloride, 2-octinoyl chloride, etc. are preferred As an example. Among these, lauroyl chloride, myristoyl chloride, palmitoyl chloride, stearoyl chloride, oleoyl chloride and the like having 12 to 18 carbon atoms are easily available and inexpensive, and the nanofiber formation of the present invention obtained therefrom is provided. It can be most preferably used for reasons such as good solubility of the compound. Therefore, as R ₁ represented by the general formula I, a case where it is a saturated or unsaturated hydrocarbon group having 11 to 17 carbon atoms can be most preferably used.

  The above various acid chlorides can be used in the reaction alone or diluted in an organic solvent that does not react with acid chlorides such as acetone, tetrahydrofuran, and 1,4-dioxane. As the method of adding acid chloride, a method of gradually adding it into an aqueous solution over a period of several tens of minutes to several hours using a dropping funnel or the like with respect to an aqueous solution in which glycosylamine or creatine is dissolved or suspended is preferably performed. .

  In the above reaction, the reaction is carried out using equimolar amounts of acid chloride, glycosamine or creatine and a base such as sodium hydroxide, and the pH of the system shifts from neutral to weakly acidic as the reaction proceeds. The product is precipitated in the form of a carboxylic acid derivative by adding an acid if necessary, and separated from the reaction system by a method such as filtration, and then an equimolar amount of a base is added to obtain the desired general formula I The method of synthesizing the nanofiber-forming compound represented by is most preferable. In this case, if necessary, purification is performed by recrystallization from a solvent such as alcohol in the state of a carboxylic acid derivative in the middle, and then an equimolar amount of a base is added to obtain a target nano-formula represented by the general formula I. A method for obtaining a fiber-forming compound can also be preferably used.

  As side reactions that occur in the above reaction, hydrolysis of the acid chloride with an alkali or by-product formation of an acid anhydride that occurs when the acid chloride reacts with a carboxylic acid moiety of glycosylamine or creatine occurs. In particular, when the reaction system is not sufficiently stirred due to a product precipitated in the middle of the reaction, the hydrochloric acid produced by the reaction is not neutralized by the base in the aqueous solution, and a large amount of acid anhydride is produced. There is a case.

  In order to suppress the side reaction as described above and obtain the target carboxylic acid derivative in a high yield, in the present invention, the reaction temperature for reacting acid chloride with glycosylamine or creatine is 0-10. The reaction may be carried out at a relatively low temperature of 0 ° C., but more preferably when the reaction is carried out in the range of 40 ° C. to 80 ° C., the carboxylic acid derivative can be obtained with the highest yield and high purity. It has been found that this is one of the features of the present invention. That is, normally, in order to avoid hydrolysis of the acid chloride to be used by alkali, when performing the Schotten-Baumann reaction, the reaction is usually performed at a low temperature of about 0 to 10 ° C. In the invention as well, the reaction can be carried out in the range of 0 ° C. to 10 ° C. to obtain the desired carboxylic acid derivative. In this case, it is preferable to sufficiently slow down the addition rate of the acid chloride to be added, and it is usually preferable to add the acid chloride over a period of about 2 to 6 hours. When the reaction is carried out by adding acid chloride at a faster rate than this, a side reaction giving an acid anhydride may occur remarkably. This is considered to be due to the fact that the solubility of glucosylamine or creatine in water is low at low temperatures and the reaction proceeds in a heterogeneous state in which glycosylamine or creatine is suspended. On the other hand, when the reaction temperature is in the range of 40 ° C. to 80 ° C., the solubility of glycosylamine or creatine in water is remarkably increased, and the reaction is carried out in a homogeneous system in the form of dissolved glycosylamine or creatine salt. Therefore, it is considered that the acylation reaction with respect to the nitrogen atom occurs preferentially. In this case, the acid chloride may be added at a rate of about 30 minutes to 2 hours, or over a longer time for the purpose of avoiding an excessive increase in the reaction temperature. May be performed.

The compound of the general formula I obtained in the present invention is soluble in hot water, and the temperature for dissolving in water gradually increases as the number of carbons contained in the substituent R ₁ increases. As shown in the examples described later, for example, in the case of an alkyl group having 11 carbon atoms in the substituent R ₁ , it dissolves uniformly at a temperature around 40 ° C., but in the case of an alkyl group having 17 carbon atoms. In this case, a uniform solution can be obtained by heating to a temperature around 80 ° C. When the aqueous solution that has been dissolved and becomes uniform is cooled, nanofibers are deposited. In this case, the cooling rate may be arbitrary, and in either case, the same nanofibers and the nanofiber aggregates in which these are assembled are used in either case of rapid cooling or slow cooling over a long period of time. Forming is one of the features of the present invention. Since the solution is gelled by the nanofibers formed in the solution, this system change is a sol-gel transition. At this time, the concentration of the nanofiber-forming compound in the solution is preferably 0.1% or more. When the concentration is higher than this concentration, a sol-gel transition is observed, and the nanofiber-forming compound solution is dried or cooled. It was observed that the nanofiber aggregate was formed without problems.

  As described in Examples below, the nanofibers and nanofiber aggregates formed by the sol-gel transition described above, or a solution in which the nanofiber-forming compound of the general formula I is dissolved, are immediately formed by drying. The shapes of the nanofibers and the nanofiber aggregates are the same, and when observed with an optical microscope and an electron microscope, the nanofibers having a diameter in the range of 10 to 1000 nm and a length of 10 μm or more and from these It was found to be a nanofiber aggregate formed. Furthermore, when each nanofiber was observed in detail with a transmission electron microscope, no particular change was observed in the electron beam transmission density in the outline of the nanofiber. If the hollow structure is used, the transparency of the electron beam is reduced in the contour portion. Therefore, the nanofiber obtained in the present invention is not recognized as having a hollow structure, and has a uniform density, possibly a β-sheet structure. It is estimated that

  In order to form nanofibers on a substrate, a solution in which a nanofiber-forming compound of the general formula I is uniformly dissolved is used as a coating solution, applied to the surface of a substrate such as a film or paper, and further dried. Nanofibers formed from the nanofiber-forming compound of general formula I and nanofiber aggregates formed from these can be formed on the substrate surface. At this time, the concentration of the nanofiber-forming compound used in the coating in the solution is preferably 0.1% by mass or more, and it was confirmed that the nanofiber aggregate can be formed without any problems when the concentration is higher than this concentration. .

  In this case, when the coating solution is applied to the substrate surface, the coating solution is cooled to a temperature between −20 ° C. and 20 ° C. before the coating solution is dried. A fiber assembly may be formed and then dried. Alternatively, a coating solution may be applied and dried immediately to form a dried nanofiber aggregate on the substrate surface. The drying temperature is preferably in the range of 0 ° C. to 120 ° C., and any drying temperature can be set as long as the temperature is in this range. Regarding the drying speed, the air may be blown as quickly as possible, or the drying may be slowly performed over a long time depending on the case.

  As one of the features of the present invention, as described above, the coating solution in which the nanofiber-forming compound of the general formula I is uniformly dissolved is a uniform solution when applied to the substrate surface. Although it can be applied uniformly, it is also characterized in that nanofibers and nanofiber aggregates can be similarly formed on the substrate surface regardless of the drying speed after application. is there. In addition, when the coating liquid immediately after coating is cooled, an aggregate of nanofibers is formed in the solution, and the coated liquid is gelated by a sol-gel transition. Examples of such a coating method using the sol-gel transition include, for example, “Basics of Photographic Engineering, Silver Salt Photo Edition” (Japan Photographic Society, Corona, published in 1979, Chapter 3) and JP-A-8. Example of multi-layer simultaneous coating using sol-gel transition of gelatin aqueous solution used in a method for producing a silver halide photographic light-sensitive material using a slide hopper type coating device as described in Japanese Patent No. 243462 In the present invention, multilayer simultaneous coating can also be performed by a known method. By using such a method, for example, as shown in the examples described later, a gelatin aqueous solution and an aqueous solution of a nanofiber forming compound used for coating obtained by the present invention are sequentially used in this order by using a slide hopper type coating device. Apply to the surface of the substrate and immediately pass through a cooled zone called a chill zone to set the above two aqueous solutions without intermixing, and then in the drying zone usually between 30-80 ° C By drying at a temperature, a film having a nanofiber aggregate layer formed adjacent to the gelatin layer is obtained. As shown in these examples, a layer composed of nanofiber aggregates and another layer can be fabricated in a single coating process so that they are adjacent to each other. This is an extremely useful method because it can be formed on the surface of the substrate in a very simple manner and can be formed on the substrate surface in a form in which the nanofiber assembly layer and another layer are functionally separated.

  EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In addition, the percentage in an Example is a mass reference | standard unless there is a notice.

Example 1
In a 500 ml round bottom flask equipped with a nitrogen introduction tube, a thermometer, a reflux condenser, and a dropping funnel, 23.4 g of glucosamine (Tokyo Chemical Industry reagent) was weighed, and 300 ml of water was added and stirred. To this was added 13.2 g of potassium hydroxide (purity 85%), and the internal temperature was lowered to 5 ° C. on an ice-cooled water bath. A solution in which 30 g of acetone was added to 55 g of palmitoyl chloride (manufactured by Tokyo Chemical Industry Co., Ltd.) was introduced into the dropping funnel and placed under a nitrogen stream. The palmitoyl chloride solution was dropped from the dropping funnel over 4 hours. Stirring was continued at room temperature for another hour after the completion of the dropwise addition. The pH of the reaction system changed from neutral to weakly acidic, and then the precipitated product was separated by suction filtration, sufficiently washed with water and dried. The product was analyzed by HPLC under the following conditions. That is, two columns TSK-GEL G2500HXL for Tosoh Co., Ltd. GPC were used as a column, THF was used as a solvent, a flow rate was 0.5 ml / min, and a differential refractometer was used as a detector. Analysis. As a result, a peak of the main product was observed at an elution time of 40 minutes, and a peak due to a by-product was observed at an elution time of 37 minutes. From the peak area ratio, it was found that the by-product was contained by 7% with respect to the main product. The reaction yield was 80% excluding by-products. The entire product was recrystallized from ethanol and analyzed again by HPLC. As a result, by-products were completely removed, and only a peak due to the main product was observed. As a result of analyzing the recrystallized sample by ¹ H-NMR, 0.854 ppm (3H, tr), 1.238 ppm (24H, m), 1.477 ppm (2H, m), 2.176 ppm (2H, tr ) Was found to be a carboxylic acid derivative represented by the following chemical formula.

Further, the by-product is performed separately ^separation, 1 H-NMR and FT-IR result of the analysis of the structure, the particular characteristic 1798Cm ^-1 and 1740 cm ^-1 to the acid anhydride structure at the FT-IR measurement From the presence of two absorption peaks, it was clarified that the acid anhydride was represented by the following chemical formula.

  The nanofiber-forming compound of the present invention was synthesized by using the carboxylic acid derivative purified through recrystallization as described above and neutralizing it by adding an equimolar amount of a base thereto. That is, when the above carboxylic acid derivative is dispersed in water so as to have a concentration of 20%, an equimolar amount of sodium hydroxide is added thereto and heated, and the solution is completely dissolved at about 70 ° C. and becomes a transparent aqueous solution. was gotten. The aqueous solution was applied to a slide glass, the liquid was spread to a uniform thickness using a glass rod, and immediately dried using a dryer. When the sample was observed with a scanning electron microscope (SEM), as shown in FIG. 1, it showed a structure in which a large number of nanofibers having an average fiber diameter of 75 (± 25) nm and a length of 10 μm or more were intertwined. It became clear that Furthermore, when the glass beaker containing the heated solution was separately transferred onto ice-cold water and rapidly cooled, the whole gelled. A portion of the gelled sample was taken out and transferred onto a slide glass, dried by blowing cold air using a dryer, and the obtained sample was similarly observed by SEM. As a result, nanofibers similar to those in FIG. 1 were assembled. It was found to show the structure.

(Example 2)
In a 500 ml round bottom flask equipped with a nitrogen introduction tube, a thermometer, a reflux condenser, and a dropping funnel, 23.4 g of glucosamine (Tokyo Chemical Industry reagent) was weighed, and 300 ml of water was added and stirred. To this was added 13.2 g of potassium hydroxide (purity 85%), and the internal temperature was raised to 50 ° C. on a water bath. A solution in which 30 g of acetone was added to 55 g of palmitoyl chloride (manufactured by Tokyo Chemical Industry Co., Ltd.) was introduced into the dropping funnel and placed under a nitrogen stream. The palmitoyl chloride solution was added dropwise from the dropping funnel over 1 hour. After completion of the dropwise addition, the internal temperature was kept at 50 ° C. for 1 hour and stirring was continued. The pH of the reaction system changed from neutral to weakly acidic, and then the precipitated product was separated by suction filtration, sufficiently washed with water and dried. The product was analyzed by HPLC under the same conditions as in the previous examples. As a result, only the main product peak was observed at an elution time of 40 minutes. As a result of analyzing the obtained product by ¹ H-NMR, it was clarified that it was the same as the carboxylic acid derivative obtained after recrystallization in Example 1. The reaction yield was 90%. By raising the reaction temperature to 50 ° C., only a carboxylic acid derivative, which is a precursor for producing a nanofiber-forming compound, could be selectively obtained in a high yield.

(Example 3)
The reaction was performed in exactly the same manner as in Example 2 except that 0.2 mol of lauroyl chloride was used in place of palmitoyl chloride in Example 2 as the acid chloride to obtain a carboxylic acid derivative having a structure represented by the following chemical formula. As a result of analysis by HPLC and ¹ H-NMR, the purity was 99% or more and the reaction yield was 90%.

  The nanofiber-forming compound of the present invention was synthesized by using the carboxylic acid derivative obtained above and neutralizing it by adding an equimolar amount of a base thereto. That is, when the above carboxylic acid derivative is dispersed in water to a concentration of 10%, and equimolar sodium hydroxide is added thereto and heated, the solution is completely dissolved at about 40 ° C. and a transparent aqueous solution is formed. Obtained. The solution was applied to a glass slide, spread using a glass rod to a uniform thickness, and immediately dried using a dryer. When the sample was observed with a scanning electron microscope (SEM), as shown in FIG. 2, it showed a structure in which a large number of nanofibers having an average fiber diameter of 85 (± 25) nm and a length of 10 μm or more were intertwined. It became clear that When observed using a transmission electron microscope, as shown in FIG. 3, the transmittance of the electron beam with respect to the cross section of each nanofiber is almost uniform, and a result suggesting a hollow structure cannot be obtained. -Results suggesting a sheet-like structure.

Example 4
The reaction was performed in exactly the same manner as in Example 2 except that 0.2 mol of oleoyl chloride was used instead of palmitoyl chloride in Example 2 as the acid chloride to obtain a carboxylic acid derivative having a structure represented by the following chemical formula. As a result of analysis by HPLC and ¹ H-NMR, the purity was 99% or more and the reaction yield was 90%.

  The nanofiber-forming compound of the present invention was synthesized by using the carboxylic acid derivative obtained above and neutralizing it by adding an equimolar amount of a base thereto. That is, when the above carboxylic acid derivative is dispersed in water so as to have a concentration of 10%, and equimolar sodium hydroxide is added thereto and heated, a completely aqueous solution that is completely dissolved at room temperature is obtained. It was. The solution was applied to a glass slide, spread using a glass rod to a uniform thickness, and immediately dried using a dryer. As a result of observing the sample using a scanning electron microscope (SEM) and a confocal laser microscope, it was confirmed that nanofibers as shown in FIGS. 4 and 5 were formed, respectively. A structure in which a large number of nanofibers having an average fiber diameter of 90 (± 25) nm and a fiber length of 10 μm or more were intertwined was observed.

(Example 5)
27 g of creatine (Aldrich reagent, anhydride) was weighed into a 500 ml round bottom flask equipped with a nitrogen inlet tube, thermometer, reflux condenser, and dropping funnel, and 300 ml of water was added and stirred. To this was added 8 g of sodium hydroxide, and the internal temperature was raised to 45 ° C. on a water bath. A solution obtained by adding 30 g of acetone to 61 g of stearoyl chloride (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was introduced into the dropping funnel and placed under a nitrogen stream. The stearoyl chloride solution was added dropwise from the dropping funnel in 1.5 hours. After completion of the dropwise addition, the internal temperature was kept at 45 ° C. for 1 hour, and stirring was continued. The pH of the reaction system changed from neutral to weakly acidic, and then the precipitated product was separated by suction filtration, sufficiently washed with water and dried. The product was analyzed by HPLC under the same conditions as in Example 1 above. As a result, only the main product peak was observed at an elution time of 39 minutes. As a result of analyzing the obtained product by ¹ H-NMR, it became clear that a carboxylic acid derivative represented by the following chemical formula was obtained. The reaction yield was 85%.

  The nanofiber-forming compound of the present invention was synthesized by using the carboxylic acid derivative obtained above and neutralizing it by adding an equimolar amount of a base thereto. That is, when the above carboxylic acid derivative is dispersed in water to a concentration of 10%, an equimolar amount of sodium hydroxide is added thereto and heated, and then completely dissolved at about 85 ° C. to obtain a transparent aqueous solution. It was. The solution was applied to a glass slide, spread using a glass rod to a uniform thickness, and immediately dried using a dryer. As a result of observing the sample using a confocal laser microscope, it was confirmed that nanofibers as shown in FIG. 6 were formed. A structure in which a large number of nanofibers having an average fiber diameter of 90 (± 25) nm and a fiber length of 10 μm or more were intertwined was observed.

(Example 6) Example of multi-layer simultaneous application utilizing sol-gel transition The heating aqueous solution obtained by neutralizing the carboxylic acid derivative obtained in Example 3 with sodium hydroxide has a solid content concentration of 5%. The solution temperature was kept at 40 ° C. Separately, a solution in which commercially available gelatin was dissolved so as to have a solid content concentration of 5% was prepared, and kept at 40 ° C. in the same manner. Using the slide hopper type coating apparatus as described in JP-A-8-243462, the above two types of solutions are simultaneously applied from two parallel slits provided on the sliding plane of the coating apparatus. The liquid was passed over the polyester film with two layers forming on the slide surface. At this time, coating was performed so that a gelatin solution layer and a layer in which nanofibers were dissolved were laminated in this order on the polyester film. The two layers of liquid formed on the polyester film immediately moved to the cooling zone (adjusted to a temperature of 5 ° C.) and rapidly cooled. The surface temperature of the coating layer was measured using a radiation thermometer (THI-500 manufactured by TASCO Japan Co., Ltd.), and it was confirmed that the coating layer surface temperature was actually cooled to 5 ° C. Furthermore, it was confirmed from the sampled samples that the coating layer immediately after cooling was set without mixing the two layers. After passing through the cooling zone, the coating layer was dried at a drying temperature of 40 ° C. and wound up in the drying zone. As a result of observing the thus prepared coated sample using a confocal laser microscope, it was confirmed that the nanofiber aggregate layer was uniformly formed on the gelatin layer.

  Since nanofibers and aggregates thereof can be formed in layers on a substrate such as a film or paper by coating, application to various filters, separation membranes, adsorbents, pharmaceuticals, and medical uses can be considered.

Claims (5)

A nanofiber-forming compound represented by the following general formula I:
(In the formula, R ₁ represents a hydrocarbon group having 6 to 29 carbon atoms, R ₂ represents a hydrogen atom or a methyl group, and M ⁺ represents an alkali metal ion.)   A method for forming a nanofiber, comprising drying a solution in which the nanofiber-forming compound according to claim 1 is dissolved.   A method for forming nanofibers, comprising cooling a solution in which the nanofiber-forming compound according to claim 1 is dissolved.   A method for forming a nanofiber assembly, wherein a solution in which the nanofiber-forming compound according to claim 1 is dissolved is applied onto a substrate and dried.   The method for forming a nanofiber aggregate according to claim 4, wherein the applied liquid is cooled and gelled prior to drying.