JP2003212903A - Manufacturing process for oxidized chitosan - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-purity oxidized chitosan provided with a high hydrophilicity and a water-solubility in a wide pH region, which are useful in various fields such as medical fields and cosmetic fields, and a manufacturing process which can produce the oxidized chitosan readily at low costs by a simple refining process. <P>SOLUTION: There is provided a manufacturing process for oxidized chitosan, which comprises dissolving or swelling chitosan in an aqueous acidic solution, neutralizing the resultant solution to obtain a chitosan solution, and oxidatively treating the chitosan solution to selectively oxidize carbon at 6-position in the pyranose ring of N-acetylglucosamine or glucosamine, which is a constituent monosaccharide of chitosan, to convert it to a carboxy group or a salt thereof. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an oxide of chitosan. Particularly, the present invention relates to a method for producing oxidized chitosan having a structure having both a carboxyl group and an amino group in the molecule of chitosan and easily swelling or dissolving in water in a wide pH range by a simple method in an aqueous system. It is a thing.

[0002]

Chitin is a skeletal substance of crustaceans such as crabs and shrimps, insects such as beetles and crickets, and also present in fungi and cell walls, and contains many N-acetyl D-glucosamine residues, β- ( 1,4) -linked polysaccharide. It is an aminopolysaccharide (mucopolysaccharide) that has a structure similar to cellulose, which is the most abundant organic compound on the earth, and has an acetamide group added instead of the hydroxyl group bonded to the carbon at the 2-position. . Chitosan is a polysaccharide obtained by deacetylating chitin, in which glucosamine residue or N-acetylglucosamine residue is β- (1,4).
A linked polysaccharide, having a cationic amino group derived from a glucosamine residue. Although chitin and chitosan have a structure similar to that of cellulose, they are generally insoluble in water and have not been used effectively because they contain few proper solvents.

On the other hand, in recent years, these natural polysaccharides have attracted attention as a new type of biodegradable polymer material and as a biocompatible material, and many studies have been conducted on their use, and many findings have been obtained. There is. In particular, chitin and chitosan have been extensively studied in this field, and various biological activity effects such as a wound healing promoting effect, an anticoagulant effect, an immunostimulating activity, and a bacteriostatic / antibacterial activity have been reported. Furthermore, it is becoming clear that sugar chains play an important role as key substances in the expression of biological functions such as cell recognition and associated information transmission mechanism.

Even when it is used as such a medical material, it is water-soluble in a wide pH range from the viewpoints of handling convenience, compatibility with various chemicals and drugs, uniformity of drug effect, processability, etc. It is desirable to be sex. Chitosan is known to be sparingly soluble in water. Various derivatization methods are known as water-solubilizing methods for chitin and chitosan, but most of them have a different distribution of substituents and a non-uniform structure. There was a problem that it is likely to have an impact.

[0005]

DISCLOSURE OF THE INVENTION The object of the present invention is useful in various fields such as the pharmaceutical field or the cosmetic field.
It is an object of the present invention to provide high-purity oxidized chitosan having high hydrophilicity and water solubility in a wide pH range, and a method for producing these oxidized chitosan easily and inexpensively by a simple purification step. Another object of the present invention is to provide an oxidized chitosan having a uronic acid residue in which a primary hydroxyl group of glucosamine or an N-acetylglucosamine residue, which is a constituent monosaccharide of chitosan, is selectively oxidized, and a method for producing the same. It is in. Still another object of the present invention is to provide a method capable of uniformly and efficiently oxidizing chitosan as described above under mild reaction conditions using a safer reagent and imparting high water solubility.

[0006]

The invention according to claim 1 is
The chitosan solution obtained by dissolving or swelling chitosan in an acidic aqueous solution and then neutralizing is subjected to an oxidation treatment, and N-acetylglucosamine which is a constituent monosaccharide of chitosan, or the 6th carbon is selected from the pyranose ring of glucosamine. It is a method for producing oxidized chitosan, which comprises chemically oxidizing and converting to carboxyl groups or salts thereof.

According to the second aspect of the present invention, the method for the oxidation treatment for selectively oxidizing the 6-position carbon to convert it to a carboxyl group or a salt thereof is carried out in the presence of a catalyst such as an N-oxyl compound. The method for producing oxidized chitosan according to claim 1, which is characterized in that.

According to a third aspect of the present invention, the N-oxyl compound is 2,2,6,6-tetramethyl-1-piperidine-N-oxyl and the alkali metal bromide or alkali metal iodide in water is used. In the presence of, at least one oxidizing agent selected from the group consisting of hypohalous acid, halogenous acid, perhalogenic acid and salts thereof, and adding an alkali to pH.
The oxidation is carried out while keeping a constant value.
Alternatively, it is the method for producing oxidized chitosan according to the item 2.

The invention according to claim 4 is the method for producing chitosan oxide according to claim 3, characterized in that the degree of oxidation of the chitosan can be controlled by the amount of alkali metal halide added.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The details of the present invention will be described below.
The chitosan that is the raw material of the present invention is not particularly limited, but for example, it may be obtained by deacetylating chitin. Further, the purification method, the degree of polymerization, etc. are not particularly limited. Moreover, the shape of chitosan such as powder, flakes, gel, fiber, film, and non-woven fabric is not particularly limited.

Generally, chitin is represented by the following chemical formula (1)
It is a compound containing what is represented by (Y: NHCOCH ₃ ) as a constituent monosaccharide. Chitosan is a compound containing as a constituent monosaccharide a compound obtained by converting NHCOCH ₃ in a portion represented by Y in the following chemical formula (1) into NH ₂ by generally deacetylating chitin. . The chitosan of the present invention only has a deacetylation degree of 100%,
As a portion represented by Y in the following chemical formula (1), NHC
It also includes a mixture of OCH ₃ and NH ₂ .

[0012]

[Chemical 1]

In the present invention, before the carboxyl group is selectively introduced into the N-acetylglucosamine of chitosan or the 6-position carbon portion of the pyranose ring of glucosamine, the distribution of the introduced carboxyl group is made more uniform. In order to do so, it is characterized by swelling or dissolving with an acid, neutralizing a solution of chitosan in which intermolecular forces such as hydrogen bonds have collapsed, removing the produced salt, or using the solution as it is. In this case, the treated chitosan is usually directly subjected to the oxidation reaction without being dried. In the case of drying, it is desirable that the product is subjected to oxidation in a state where formation of hydrogen bond is suppressed again, for example, by freeze-drying or completely substituting water with acetone or the like and then drying.

Further, the oxidation method of the present invention is characterized in that chitosan dissolved or dispersed in water is treated in an aqueous system in the presence of a catalyst such as an N-oxyl compound.

The oxidized chitosan of the present invention can be obtained by oxidizing the starting chitosan with an oxidizing agent in the presence of an N-oxyl compound (oxoammonium salt). N-oxyl compounds include 2,2,6,6-tetramethyl-1-piperidine N-oxyl (hereinafter TEMP.
Referred to as O), and the like. In this oxidation method, the carboxyl group can be introduced uniformly and efficiently depending on the degree of oxidation. It is advantageous to carry out the main oxidation reaction in the presence of the N-oxyl compound and bromide or iodide. As the bromide or iodide, a compound capable of dissociating in water to be ionized, such as alkali metal bromide or alkali metal iodide, can be used. As the oxidant, halogen, hypohalous acid, halohalous acid, perhalogenic acid or salts thereof, halogen oxides, nitrogen oxides, peroxides, and the like can be used as long as they can promote the desired oxidation reaction. Any oxidizing agent can be used.

The oxidation of the present invention selectively oxidizes the hydroxyl group at the 6-position of glucosamine or N-acetylglucosamine residue, which is a constituent monosaccharide of chitosan. The N-oxyl compound may be used in a catalytic amount, for example, 10 ppm to 5% is sufficient with respect to the number of moles of the constituent monosaccharide of chitosan, but 0.05% to 3% is preferable.

The oxidation reaction conditions and the like of the present invention are not particularly limited and should be optimized depending on the properties of the raw materials and the equipment used, but when the oxidation reaction is carried out in the coexistence with bromide or iodide, it is mild. The oxidation reaction can proceed smoothly under various conditions, and the introduction efficiency of the carboxyl group can be greatly improved.

The amount of bromide and / or iodide used can be selected within a range that can accelerate the oxidation reaction, and is, for example, 0 to 100% based on the number of moles of the monosaccharide constituting chitosan. However, from the viewpoint of reaction efficiency, 10 to 50% is preferable.

In the oxidation reaction system of chitosan oxide in the present invention, it is preferable to use TEMPO as the N-oxyl compound and sodium hypochlorite as an oxidizing agent in the presence of sodium bromide.

In the oxidation reaction of oxidized chitosan in the present invention, the reaction temperature is room temperature or lower, more preferably 5 ° C. or lower in the system for the purpose of increasing the selectivity of the oxidation to the C6-position primary hydroxyl group and suppressing side reactions. It is desirable to react.

In the method for producing oxidized chitosan of the present invention, it is preferable to keep the system alkaline during the reaction in order to increase the reaction efficiency. At this time, the pH is preferably maintained at 9 to 13, more preferably 10 to 11.5. Furthermore,
The present invention is characterized in that the degree of oxidation can be controlled by the amount of alkali added when keeping the pH constant.
With respect to 1 mol of glucosamine or N-acetylglucosamine residue, which is a constituent monosaccharide of chitosan, the degree of oxidation becomes 100% when 1 mol of alkali is added, and all glucosamine or N-acetylglucosamine residues are oxidized to form C6. Almost 100% of the primary hydroxyl groups are carboxyl groups.

The oxidized chitosan thus oxidized has a structure represented by the following chemical formula (2) as a constituent monosaccharide, and only the primary hydroxyl group and the reducing end are oxidized with a very high selectivity, and the secondary secondary No hydroxyl or amine oxidation is observed. Oxidized chitosan has a uronic acid structure in which the C6 position of glucosamine or N-acetylglucosamine residue, which is a constituent monosaccharide of chitosan, is oxidized, and therefore, both anionic and cationic functional groups are present in one molecule and one unit. It has a group and can be expected to be used as an amphoteric polymer. Furthermore, oxidized chitosan is a polymer derived from a natural product, and the produced uronic acid is also highly safe, and it can be expected to be used not only in the fields of foods, cosmetics, etc., but also in the medical and pharmaceutical fields as a biomaterial.

[0023]

[Chemical 2]

(R: CH ₂ OH or COOX (X: H or alkali metal or alkaline earth metal), Y: NHCO
CH ₃ or NH ₂ )

[0025]

EXAMPLES The present invention will be specifically described below based on examples. Example 1 Flake-shaped commercially available chitosan (deacetylation degree: about 75%) was used as the raw material chitosan. Neutralize 2% aqueous chitosan hydrochloride with sodium hydroxide,
After washing with water for desalination, 100 g of 5% chitosan suspension
An aqueous solution in which 0.1 g of TEMPO and 1.25 g of sodium bromide were dissolved was added to (5 g of chitosan), and the concentration was adjusted to about 2 wt% of the total solid weight of chitosan. The reaction system was cooled, and 35 g of an aqueous solution of sodium hypochlorite (Cl = 5%) was added to start the oxidation reaction. The reaction temperature was always kept below 5 ° C. Although the pH in the system was lowered during the reaction, 0.5N-NaOH aqueous solution was sequentially added to adjust the pH to 10.75. Ethanol was added to stop the reaction when the amount of alkali added reached 18.63 mL corresponding to the number of moles of 30% with respect to the total number of moles of the primary hydroxyl group at the 6-position. Water: alcohol = 2: 8 After being sufficiently washed with, the product was dehydrated with acetone and dried at 40 ° C. to obtain chitosan oxide having an oxidation degree of 30%.

The infrared spectrum of the obtained chitosan oxide was measured by the KBr tablet method, and the structure was analyzed. As a result, from the IR spectrum, 1620, 1420 cm
A peak derived from a carboxyl group (sodium salt) was observed near ^-1 . From these results, it was confirmed that the carboxyl group was introduced by the oxidation of chitosan, and it was also confirmed that the oxidized chitosan was obtained by the deacetylation reaction from the oxidized chitin. Further, the obtained chitosan oxide was completely dissolved in water. This oxidized chitosan was dissolved in heavy water and 13 C-NMR was measured. From the 13 C-NMR spectrum, the peak at the C6 position having a primary hydroxyl group decreases, and in addition to the carbonyl peak of the acetyl group originally possessed by chitosan at 175 to 178 ppm, the carbonyl peak of the introduced carboxyl group (sodium salt) (glucosamine). Those attached to the residue and those attached to the N-acetylglucosamine residue (2) were observed, and formation of a ketone due to oxidation at the 3-position was not observed.

Example 2 Flake-shaped commercially available chitosan (deacetylation degree: about 75%) was used as the raw material chitosan. A 2% aqueous solution of chitosan hydrochloride was neutralized with sodium hydroxide, washed with water for desalting, and then an aqueous solution prepared by dissolving 0.1 g of TEMPO and 1.25 g of sodium bromide in 100 g of a 5% chitosan suspension. Was added so that the concentration of chitosan with respect to the total solid weight was adjusted to about 2 wt%. The reaction system was cooled, and 35 g of an aqueous solution of sodium hypochlorite (Cl = 5%) was added to start the oxidation reaction.
The reaction temperature was always kept below 5 ° C. P during the reaction
Although H decreased, 0.5N-NaOH aqueous solution was added successively to adjust the pH to 10.75. When the amount of alkali added corresponding to 100% of the total number of primary hydroxyl groups at the 6-position is reached, ethanol is added to stop the reaction, and the mixture is thoroughly washed with water: alcohol = 2: 8. After doing
It was dehydrated with acetone and dried at 40 ° C. to obtain powdery chitosan oxide having an oxidation degree of 100%.

The infrared spectroscopy spectrum of the obtained chitosan oxide was measured by the KBr tablet method, and the structure was analyzed. As a result, from the IR spectrum, 1620, 1420 cm
A peak derived from a carboxyl group (sodium salt) was observed near ^-1 . From these results, it was confirmed that the carboxyl group was introduced by the oxidation of chitosan, and it was also confirmed that the oxidized chitosan was obtained by the deacetylation reaction from the oxidized chitin. Further, the obtained chitosan oxide was completely dissolved in water. This oxidized chitosan was dissolved in heavy water and 13 C-NMR was measured. From the 13 C-NMR spectrum, the peak at the C6 position having a primary hydroxyl group decreases, and in addition to the carbonyl peak of the acetyl group originally possessed by chitosan at 175 to 178 ppm, the carbonyl peak of the introduced carboxyl group (sodium salt) (glucosamine). Those attached to the residue and those attached to the N-acetylglucosamine residue (2) were observed, and formation of a ketone due to oxidation at the 3-position was not observed.

[0029]

INDUSTRIAL APPLICABILITY According to the present invention, chitosan is uniformly and efficiently oxidized under mild reaction conditions at the 2- and 3-position carbons of its constituent monosaccharides, glucosamine or N-acetylglucosamine. High-purity oxidation with high hydrophilicity and water solubility in a wide pH range, which can oxidize only the 6-position carbon and convert it to a carboxyl group without being used, and is useful in various fields such as the pharmaceutical field or cosmetic field. You can get Chitosan. Further, these water-solubilized chitosan oxides are excellent not only in impregnation and coating but also in moldability, and can be processed into arbitrary shapes such as fibers and membranes. Moreover, since the oxidized chitosan of the present invention has both functional groups of a cationic amine and an anionic carboxyl group in the molecule, it can be expected to be used as an amphoteric polymer. Furthermore, oxidized chitosan is a polymer derived from a natural product, and the produced uronic acid is also highly safe, and it can be expected to be used not only in the fields of foods, cosmetics, etc., but also in the medical and pharmaceutical fields as a biomaterial.

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Claims (4)

[Claims] 1. A chitosan solution obtained by dissolving or swelling chitosan in an acidic aqueous solution and then neutralizing the solution, and oxidizing the solution.
N-acetylglucosamine, which is a constituent monosaccharide of chitosan,
Alternatively, a method for producing oxidized chitosan, which comprises selectively oxidizing the 6-position carbon in the pyranose ring of glucosamine and converting it into a carboxyl group or a salt thereof. 2. A method of oxidation treatment for selectively oxidizing the 6-position carbon to convert it to a carboxyl group or a salt thereof is N-
The method for producing oxidized chitosan according to claim 1, wherein the treatment is performed in the presence of a catalyst such as an oxyl compound. 3. The N-oxyl compound is 2, 2, 6,
6-tetramethyl-1-piperidine-N-oxyl in the presence of an alkali metal bromide or an alkali metal iodide in water, at least one of hypohalous acid, halogenous acid, perhalogenic acid and salts thereof. The method for producing oxidized chitosan according to claim 1 or 2, wherein an alkali is added using a kind of oxidizing agent to perform oxidation while keeping the pH constant. 4. The method for producing chitosan oxide according to claim 3, wherein the degree of oxidation of the chitosan can be controlled by the amount of alkali metal halide added.