JP4457555B2 - Water-soluble polyuronic acid - Google Patents

Description

【００１７】
（式中、Ｘは水素又はアルカリ金属を示す）
【００１８】
さらに本発明の水溶性ポリウロン酸は、その重量平均分子量が３０，０００以上、より好ましくは５０，０００以上であることを特徴とし、上記したように、化学構造が明確・均一であり、且つ高分子量である点が大きな特徴である。そのため、本発明のポリウロン酸水溶液をコーティング材料として用いる場合には、塗工性が向上し、コーティング膜の耐湿性や膜物性の向上に寄与できる。さらに本発明のポリウロン酸を原料に化学修飾する場合も、生成物の物性向上、及び物性の安定化が期待できる。
【００１９】
ここに記載した重量平均分子量とは、標準物質としてプルランを用いて、サイズ排除クロマトグラフィー法により測定した、プルラン換算重量平均分子量である。
【００２０】
さらに本発明の水溶性ポリウロン酸は、α−（１，４）−Ｄ−グルコースを主鎖とする多糖類を原料として、Ｎ−オキシル化合物触媒による酸化手法を用いることにより得られるが、本発明の特徴である均一な構造を有して且つ高分子量のポリウロン酸を得るためには、穏やかな反応条件下で、選択的な反応の進行に必要な薬剤が必要量だけ随時供給され、かつ出来るだけ短時間で酸化することが重要となる。つまり、Ｎ−オキシル化合物の触媒の存在下、臭化アルカリ金属と酸化剤を用いて、５℃以下の低温、水系で、ｐＨを１０〜１１．５の範囲で一定に保ちながら酸化することにより、本発明のポリウロン酸が得られる。ここでＮ−オキシル化合物としては、２，２，６，６−テトラメチル−１−ピペリジン−Ｎ−オキシル（ＴＥＭＰＯ）が、臭化アルカリ金属としては臭化ナトリウムが、酸化剤としては次亜塩素酸ナトリウムが特に好ましい。
【００２１】
ここで上記酸化手法は、例えば、水に原料を溶解或いは均一に分散させて、ＴＥＭＰＯと臭化ナトリウムを溶解した水溶液を加え、系内を５℃以下に冷却、ｐＨを１０に調整する。ここに先ず少量の次亜塩素酸ナトリウム溶液を加えると、一時ｐＨは上昇するが、攪拌を続けると、系内のｐＨは徐々に低下してくるので、水酸化ナトリウム水溶液を滴下して、系内のｐＨを１０〜１１．５の範囲で一定に保つ。さらに酸化剤である次亜塩素酸ナトリウム溶液を反応の進行具合に応じて調整しながら滴下することで、余剰の酸化剤が系内に存在し、副反応に作用することを抑える。また反応中は系内の温度を５℃以下に維持する。反応の進行に伴い、系内は均一な溶液となる。この反応条件においては、添加される水酸化ナトリウムの量は、ほぼ酸化により導入されたカルボキシル基の量に対応しており、原料のグルコース残基量と当モルの添加量に達した時点で、エタノールを添加して過剰の酸化剤を失活させ、過剰量のエタノール中で再沈させる。生成物はアセトンと水の混合溶液を用いて十分洗浄後、アセトンで脱水してから減圧乾燥することにより、本発明のポリウロン酸のナトリウム塩が得られる。
【００２２】
なお上記により得られたポリウロン酸のナトリウム塩を水溶後酸処理し、上記のエタノールで再沈、洗浄、乾燥の操作を繰り返すことで、脱塩したポリウロン酸を得ることができる。
【００２３】
この酸化反応の原料としては、α−（１，４）−Ｄ−グルコースからなるアミロースが好ましく用いられるが、１，６結合を含むアミロペクチン部分も含有するでんぷんを原料としても、同様にα−（１，４）−ポリグルクロン酸を得ることができる。つまり本酸化反応では、ピラノース環のＣ６位を選択的に酸化するだけではなく、機構はまだ明確ではないが、でんぷんの１，６結合部分を切断して、均一な構造のα−（１，４）−ポリグルクロン酸を生成することができる。この点も本発明の特徴の一つであり、原料として、でんぷんは極めて安価なため、工業的に利用する上では非常に好ましい。
【００２４】
さらに、本発明のポリウロン酸は、構造が均一な、β−（１、４）−ポリウロン酸であるため、重水に溶解させて¹³Ｃ−ＮＭＲを測定すると、ピラノース環Ｃ６位の水酸基を持つ炭素に由来するピーク（δ＝６０〜６５ｐｐｍ付近）は見られず、カルボキシル基に由来するピーク（δ＝１７０〜１８０ｐｐｍ付近）を有し、さらに、Ｃ３位の２級水酸基の酸化により生じるケトンなどのピーク（δ＝２００〜２１０ｐｐｍ付近）は検出されないことを特徴とする。
【００２５】
【実施例】
以下実施例により、本発明についてさらに詳しく説明する。
【００２６】
＜実施例１＞
とうもろこしでんぷん由来のアミロース（関東化学（株）製）１．０ｇを、５％濃度で蒸留水に均一に分散させた。ここに、ＴＥＭＰＯ １９ｍｇ、臭化ナトリウム ０．２５ｇを溶解させた水溶液を加え、アミロースの固形分濃度が約２ｗｔ％になるよう調製した。反応系を冷却し、１１％次亜塩素酸ナトリウム水溶液３．０ｇを添加し、酸化反応を開始する。反応温度は常に５℃以下に維持した。反応中は系内のｐＨが低下するが、０．５Ｎ−ＮａＯＨ水溶液を逐次添加し、ｐＨ１０．８付近に調整するとともに、さらに１１％次亜塩素酸ナトリウム水溶液８．０ｇを反応の進行に応じて調整しながら滴下した。グルコース残基の全モル数に対し、１００％のモル数に対応するアルカリ添加量に近づくと、次亜塩素酸ナトリウム水溶液の滴下に関係なく、アルカリの添加速度は遅くなり、系内は完全に溶解して、黄色の均一な溶液となる。アルカリ添加量が前記の１００％（１２．３４ｍｌ）に達した時点で、エタノールを添加して反応を停止させた。反応時間は２時間であった。この反応溶液は、濾過により不溶の不純物を除いてから、過剰量のエタノール中に投入して、生成物を再沈させた。さらに水：アセトン＝１：７の溶液により充分洗浄した後、アセトンで脱水して、４０℃減圧乾燥して、白色粉末状のポリウロン酸のナトリウム塩１．１ｇを得た。
【００２７】
＜実施例２＞
水溶性でんぷん（ＡＣＲＯＳ社製）５．０ｇを、５％濃度で蒸留水に加熱溶解してから、溶液を冷却した。ここに、ＴＥＭＰＯ ９６ｍｇ、臭化ナトリウム １．２７ｇを溶解させた水溶液を加え、でんぷんの固形分濃度が約２ｗｔ％になるよう調製した。反応系を冷却し、１１％次亜塩素酸ナトリウム水溶液１７ｇを添加し、酸化反応を開始する。反応温度は常に５℃以下に維持した。反応中は系内のｐＨが低下するが、０．５Ｎ−ＮａＯＨ水溶液を逐次添加し、ｐＨ１０．８付近に調整するとともに、さらに１１％次亜塩素酸ナトリウム水溶液４０ｇを反応の進行に応じて調整しながら滴下した。グルコース残基の全モル数に対し、１００％のモル数に対応するアルカリ添加量に近づくと、次亜塩素酸ナトリウム水溶液の滴下に関係なく、アルカリの添加速度は遅くなった。アルカリ添加量が前記の１００％（６１．６８ｍｌ）に達した時点で、エタノールを添加して反応を停止させた。反応時間は１時間４０分であった。この反応溶液は、濾過により不溶の不純物を除いてから、過剰量のエタノール中に投入して、生成物を再沈させた。さらに水：アセトン＝１：７の溶液により充分洗浄した後、アセトンで脱水して、４０℃減圧乾燥して、白色粉末状のポリウロン酸のナトリウム塩５．７ｇを得た。
【００２８】
＜実施例３＞
実施例１の原料をとうもろこしでんぷん（関東化学（株）製）に代えた以外、実施例１と同様に酸化処理を行い、白色粉末状のポリウロン酸のナトリウム塩１．１ｇを得た。反応時間は２時間であった。
【００２９】
＜実施例４＞
実施例２のポリウロン酸のナトリウム塩２．０ｇを８０ｍｌの蒸留水に溶解し、攪拌しながら、ｐＨ１になるまで２Ｎ−塩酸を添加した。溶液は透明な溶液のままであった。この溶液を過剰量のエタノール中に投入し、生成物を再沈させた。さらに水：アセトン＝１：７の溶液により充分洗浄した後、アセトンで脱水して、４０℃減圧乾燥して、白色粉末状の脱塩したポリウロン酸１．６ｇを得た。
【００３０】
＜比較例１＞
水溶性でんぷん（ＡＣＲＯＳ社製）５．０ｇを、５％濃度で蒸留水に加熱溶解してから、溶液を冷却した。ここに、ＴＥＭＰＯ ９６ｍｇ、臭化ナトリウム １．２７ｇを溶解させた水溶液を加え、でんぷんの固形分濃度が約２ｗｔ％になるよう調製した。反応系を冷却し、１１％次亜塩素酸ナトリウム水溶液４５ｇを添加し、酸化反応を開始する。反応温度は常に５℃以下に維持した。反応中は系内のｐＨが低下するが、０．５Ｎ−ＮａＯＨ水溶液を逐次添加し、ｐＨ１０．８付近に調整した。アルカリ添加量が、グルコース残基の全モル数に対し、８０％のモル数に対応する添加量（４９．３４ｍｌ）に達した時点で、エタノールを添加して反応を停止させた。反応時間は５０分であった。この反応溶液は、濾過により不溶の不純物を除いてから、過剰量のエタノール中に投入して、生成物を再沈させた。さらに水：アセトン＝１：７の溶液により充分洗浄した後、アセトンで脱水して、４０℃減圧乾燥して、比較例１の白色粉末状のポリウロン酸ナトリウム塩５．５ｇを得た。
【００３１】
＜比較例２＞
水溶性でんぷん（ＡＣＲＯＳ社製）５．０ｇを、５％濃度で蒸留水に加熱溶解してから、溶液を冷却した。ここに、ＴＥＭＰＯ ９６ｍｇ、臭化ナトリウム １．２７ｇを溶解させた水溶液を加え、でんぷんの固形分濃度が約２ｗｔ％になるよう調製した。１１％次亜塩素酸ナトリウム水溶液５７ｇを添加し、酸化反応を開始する。反応温度は常に１０℃〜２０℃に維持した。反応中は系内のｐＨが低下するが、０．５Ｎ−ＮａＯＨ水溶液を逐次添加し、ｐＨ１０．８付近に調整した。アルカリ添加量が、グルコース残基の全モル数に対し、１００％のモル数に対応する添加量（６１．６８ｍｌ）に達した時点で、エタノールを添加して反応を停止させた。反応時間は４５分であった。この反応溶液は、濾過により不溶の不純物を除いてから、過剰量のエタノール中に投入して、生成物を再沈させた。さらに水：アセトン＝１：７の溶液により充分洗浄した後、アセトンで脱水して、４０℃減圧乾燥して、比較例２の白色粉末状のポリウロン酸ナトリウム塩５．６ｇを得た。
【００３２】
＜比較例３＞
未酸化の水溶性でんぷん（ＡＣＲＯＳ社製）を比較例３として用いた。
【００３３】
＜評価＞
（水溶性）
実施例１〜４、比較例１〜３のポリウロン酸（或いはでんぷん）１．０ｇを、２５℃の蒸留水１０ｍｌに溶解させた。比較例３以外は、全て完全に溶解し、さらに高濃度での溶解も可能であった。
【００３４】
（ＮＭＲによる構造分析）
実施例１、２、４、比較例１、３のサンプルを重水に溶解させ、１３Ｃ−ＮＭＲを測定した。その結果を図１に示す。ＮＭＲスペクトルから、実施例のポリウロン酸は、ピラノース環Ｃ６位の水酸基をもつ炭素に由来するピーク（δ＝６０〜６５ｐｐｍ付近）が完全に消えて、カルボキシル基（δ＝１７０〜１８０ｐｐｍ付近）に変換しており、２位、３位の炭素に由来するピークは変化せず、ケトンなどのピーク（δ＝２００〜２１０ｐｐｍ付近）は確認されなかった。従って、本発明のポリウロン酸は、ほぼ構造が均一な、α−（１，４）−ポリグルクロン酸であると言える。一方で、比較例１のポリウロン酸では、δ＝１７０〜１８０ｐｐｍ付近にカルボキシル基の炭素由来のピークが確認されているが、δ＝６０〜６５ｐｐｍ付近にピラノース環Ｃ６位の水酸基をもつ炭素に由来するピークが残存しており、均一なα−（１，４）−ポリグルクロン酸とはなっていない。
【００３５】
（重量平均分子量の測定）
実施例１〜４、比較例１〜３のポリウロン酸（或いはでんぷん）の重量平均分子量（Ｍｗ）を、ＧＰＣ法により測定した。カラムはＴＳＫ−ｇｅｌＧ６０００ＰＷＸＬ、ＴＳＫ−ｇｅｌＧ３０００ＰＷＸＬを用い、０．１Ｍ−ＮａＣｌを溶離液とし、ＲＩ検出器を用い測定した。分子量既知の標準プルランから検量線を作成し、プルラン換算の重量平均分子量を算出した。その結果、実施例のポリウロン酸は、実施例１から順にＭｗ＝４２，０００、６５，０００、５８，０００、６６，０００といずれも分子量３０，０００以上のポリウロン酸であった。なお比較例のサンプルについては、比較例１から順にＭｗ＝９２，０００、２２，０００、１３４，０００であった。
【００３６】
（ガスバリア性の測定）
ウレタン系のアンカーコート層を設けた厚さ２０μｍの二軸延伸ポリプロピレンフィルムを基材として、実施例１、２、３、及び比較例１、２、３のポリウロン酸（或いはでんぷん）の５％水溶液を、それぞれバーコーターによりコーティングして、８０℃オーブン中で乾燥し、乾燥膜厚１．５μｍの被膜を形成した。これらポリウロン酸類のコーティングフィルムの酸素透過度を以下の様にして測定した。なお、４０℃９０％ＲＨ雰囲気下に１ヶ月保存後にも同様の測定を行った。結果を表１に示す。
（酸素透過度の測定方法）
酸素透過度測定装置（モダンコントロール社製、ＯＸＴＲＡＮ １０／４０Ａ）を用いて３０℃７０％ＲＨ雰囲気下、及び、３０℃１００％ＲＨ雰囲気下で測定した。
【００３７】
【表１】

【００３８】
【発明の効果】
以上より、本発明の水溶性ポリウロン酸は、構造が明確、均一かつ高分子量で水溶性が良好なことから、水系の反応原料として、及び水系のコーティング材料として好ましく用いることができる。特にガスバリア性コーティング剤とした場合には、高いガスバリア性とともに、耐湿性や保存安定性が向上する。さらに、食品、医療・医薬、化粧品等、様々な機能性材料としての応用も期待できる。
【００３９】
【図面の簡単な説明】
【図１】実施例１、２のポリウロン酸ナトリウム塩、及び実施例４のポリウロン酸、及び比較例１のポリウロン酸ナトリウム塩、及び比較例３のでんぷんを重水に溶解して測定した１３Ｃ−ＮＭＲスペクトルである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the provision of water-soluble polyuronic acid having a high molecular weight and a uniform structure.
[0002]
[Prior art]
Naturally occurring uronic acids are mainly glucuronic acid, mannuronic acid, and galacturonic acid, and are present as plant structural polysaccharides such as pectin and alginic acid, etc. It also plays a function. The aforementioned pectin is a polyuronic acid mainly composed of α-D-galacturonic acid, and alginic acid is a polyuronic composed of β- (1,4) -D-mannuronic acid and α- (1,4) -L-guluronic acid. It is an acid. These are used industrially as food additives, thickeners, stabilizers and the like.
[0003]
In recent years, taking advantage of the functionality of polyuronic acid, such as safety, biodegradability, biocompatibility, and its physiological functions, chemical and physical modification, derivatization, compounding with other materials, etc. Studies are also underway to develop new high-performance materials by secondary modification. However, most of the naturally occurring polyuronic acids are heteropolysaccharides, and because of their heterogeneous structure, it is difficult to analyze the chemical structure affecting the function, design the material, and control the material properties. Such a raw material is not preferable.
[0004]
On the other hand, attempts have been made to obtain polyuronic acids by oxidizing inexpensive polysaccharides such as starch and cellulose. There are few methods for selectively oxidizing only the primary hydroxyl group at the C6 position of the pyranose ring, and effective oxidation methods currently proposed include oxidation with nitrogen dioxide and 2,2,6,6-tetramethyl-1 Examples include oxidation with an N-oxyl compound catalyst such as -piperidine-N-oxyl (hereinafter sometimes referred to as TEMPO). However, it has been reported that in the oxidation with nitrogen dioxide, if all the primary hydroxyl groups at the C6 position of the pyranose ring are oxidized, the secondary hydroxyl groups at the C2 position and the C3 position are also oxidized, and the degree of polymerization is greatly reduced. Yes.
[0005]
Further, in the oxidation with a TEMPO catalyst, if the raw material is starch, amylose, amylopectin or the like, almost all primary hydroxyl groups at the C6 position can be selectively oxidized (see Non-Patent Document 1), but about tens of thousands or more. Oxidation while maintaining the high molecular weight is not clear.
On the other hand, TEMPO oxidation of polysaccharides has also been reported to obtain a high molecular weight superabsorbent material, but in this case, not all the primary hydroxyl groups at the C6 position are oxidized, Polyuronic acid having a uniform structure has not been obtained (see Patent Document 1). Further, it is difficult to selectively oxidize all primary hydroxyl groups at the C6 position and maintain a high molecular weight.
[0006]
Furthermore, as described above, when chemically modifying water-soluble polyuronic acids to synthesize new highly functional materials, the raw polyuronic acids have a clear and uniform chemical structure for analysis and material design. In addition, it is important to reduce the molecular weight in the modification reaction, and the molecular weight is required to be as high as possible. An aqueous solution of polyuronic acid can also be used as a gas barrier coating agent. However, even in this case, the uniformity of the chemical structure of the material greatly affects the gas barrier property of the coating film, and the degree of polymerization (molecular weight) of the material greatly affects the moisture resistance and storage stability of the coating film (for example, patents). Reference 2).
[0007]
[Non-Patent Document 1]
Carbohydrate Polymers 39 (1999) 361-367.
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-226502.
[Patent Document 2]
JP 2001-334600 A.
[0008]
[Problems to be solved by the invention]
The object of the present invention is excellent in safety such as biocompatibility and biodegradability, and also excellent in physical properties as a functional material, and further as a raw material for synthesizing various functional materials such as foods, medical / pharmaceuticals and cosmetics. The object is to provide a water-soluble polyuronic acid that is useful and has a clear and uniform structure and a high molecular weight.
[0009]
[Means for Solving the Problems]
The invention of claim 1 includes a step of preparing a solution containing amylose or starch, an N-oxyl compound, and water, the temperature of the solution is 5 ° C. or less, and the pH of the solution is 10 to 11.5. Water-soluble polyuronic acid used in a gas barrier coating agent by adding an oxidizing agent dropwise to the solution while adjusting the amount according to the progress of the oxidation reaction. This is a method for producing polyuronic acid.
[0010]
According to a second aspect of the present invention, the solution contains an alkali metal bromide, the N-oxyl compound is 2,2,6,6-tetramethyl-1-piperidine-N-oxyl, and the oxidizing agent is hypochlorous acid. It is sodium chlorate, The manufacturing method of the water-soluble polyuronic acid of Claim 1 characterized by the above-mentioned.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The water-soluble polyuronic acid in the present invention has a structure represented by the following chemical formula (1), and a large number of α- (1,4) -bonded D-glucuronic acids (or alkali metal salts of D-glucuronic acid). However, the chemical structure is clear and uniform, and is particularly preferable as a synthetic raw material in the case of secondary modification. Further, when X in the chemical formula (1) is hydrogen or sodium, it exhibits a solubility of 10% or more in distilled water at 25 ° C., so that it is used as an aqueous reaction material and as an aqueous coating material. Useful, the coating film has a high gas barrier property.
[0016]
[Chemical 3]

[0017]
(Wherein X represents hydrogen or an alkali metal)
[0018]
Furthermore, the water-soluble polyuronic acid of the present invention is characterized in that its weight average molecular weight is 30,000 or more, more preferably 50,000 or more, and as described above, the chemical structure is clear and uniform, and high A major feature is the molecular weight. Therefore, when the polyuronic acid aqueous solution of the present invention is used as a coating material, the coating property is improved, which can contribute to the improvement of moisture resistance and film properties of the coating film. In addition, when the polyuronic acid of the present invention is chemically modified as a raw material, improvement in physical properties and stabilization of physical properties can be expected.
[0019]
The weight average molecular weight described here is a weight average molecular weight in terms of pullulan measured by size exclusion chromatography using pullulan as a standard substance.
[0020]
Furthermore, the water-soluble polyuronic acid of the present invention can be obtained by using a polysaccharide having α- (1,4) -D-glucose as the main chain and using an oxidation method using an N-oxyl compound catalyst. In order to obtain a high molecular weight polyuronic acid having a uniform structure, which is characteristic of the present invention, a necessary amount of a drug necessary for the progress of a selective reaction can be supplied as needed under mild reaction conditions. It is important to oxidize in only a short time. That is, by using an alkali metal bromide and an oxidizing agent in the presence of an N-oxyl compound catalyst and oxidizing at a low temperature of 5 ° C. or lower and in an aqueous system while keeping the pH constant within a range of 10 to 11.5. The polyuronic acid of the present invention is obtained. Here, the N-oxyl compound is 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO), the alkali metal bromide is sodium bromide, and the oxidizing agent is hypochlorous acid. Sodium acid is particularly preferred.
[0021]
In this oxidation method, for example, a raw material is dissolved or uniformly dispersed in water, an aqueous solution in which TEMPO and sodium bromide are dissolved is added, the system is cooled to 5 ° C. or lower, and the pH is adjusted to 10. When a small amount of sodium hypochlorite solution is added here, the pH temporarily rises, but if the stirring is continued, the pH in the system gradually decreases. The pH is kept constant in the range of 10 to 11.5. Further, by dropping the sodium hypochlorite solution, which is an oxidizing agent, while adjusting according to the progress of the reaction, it is possible to suppress the presence of excess oxidizing agent in the system and acting on the side reaction. During the reaction, the temperature in the system is maintained at 5 ° C. or lower. As the reaction proceeds, the system becomes a homogeneous solution. Under these reaction conditions, the amount of sodium hydroxide added corresponds approximately to the amount of carboxyl groups introduced by oxidation, and when the amount of glucose residues in the raw material and the amount added in an equimolar amount are reached, Ethanol is added to quench excess oxidant and reprecipitate in excess ethanol. The product is sufficiently washed with a mixed solution of acetone and water, dehydrated with acetone, and then dried under reduced pressure to obtain the sodium salt of polyuronic acid of the present invention.
[0022]
The sodium salt of polyuronic acid obtained as described above is subjected to acid treatment after water treatment, and the desalted polyuronic acid can be obtained by repeating the reprecipitation, washing and drying operations with the above ethanol.
[0023]
As a raw material for this oxidation reaction, amylose composed of α- (1,4) -D-glucose is preferably used. Similarly, a starch that also contains an amylopectin part containing 1,6 bonds may be α- ( 1,4) -polyglucuronic acid can be obtained. That is, in this oxidation reaction, not only the C6 position of the pyranose ring is selectively oxidized, but the mechanism is not yet clear, but the 1,6-bonded portion of starch is cleaved to form α- (1,1 having a uniform structure. 4)-Polyglucuronic acid can be produced. This point is also one of the features of the present invention. As a raw material, starch is extremely inexpensive, and is very preferable for industrial use.
[0024]
Furthermore, since the polyuronic acid of the present invention is β- (1,4) -polyuronic acid having a uniform structure, it is a carbon having a hydroxyl group at the C6-position of the pyranose ring when ¹³ C-NMR is measured by dissolving in heavy water. There is no peak derived from (δ = 60 to 65 ppm), there is a peak derived from a carboxyl group (δ = 170 to 180 ppm), and a ketone produced by oxidation of the secondary hydroxyl group at the C3 position A peak (around δ = 200 to 210 ppm) is not detected.
[0025]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[0026]
<Example 1>
1.0 g of amylose derived from corn starch (manufactured by Kanto Chemical Co., Ltd.) was uniformly dispersed in distilled water at a concentration of 5%. To this, an aqueous solution in which 19 mg of TEMPO and 0.25 g of sodium bromide were dissolved was added to prepare a solid content concentration of amylose of about 2 wt%. The reaction system is cooled, and 3.0 g of 11% aqueous sodium hypochlorite solution is added to start the oxidation reaction. The reaction temperature was always kept below 5 ° C. During the reaction, the pH in the system decreases, but 0.5N-NaOH aqueous solution is sequentially added to adjust the pH to around 10.8, and 8.0 g of 11% sodium hypochlorite aqueous solution is further added according to the progress of the reaction. It was added dropwise while adjusting. When approaching the amount of alkali added corresponding to 100% of the total number of moles of glucose residues, the rate of alkali addition becomes slow regardless of the dropping of the sodium hypochlorite aqueous solution, and the system is completely removed. Dissolves to a yellow uniform solution. When the amount of alkali added reached 100% (12.34 ml), ethanol was added to stop the reaction. The reaction time was 2 hours. This reaction solution was filtered to remove insoluble impurities, and then poured into an excess amount of ethanol to reprecipitate the product. Furthermore, after thoroughly washing with a solution of water: acetone = 1: 7, dehydration with acetone and drying under reduced pressure at 40 ° C., 1.1 g of sodium salt of polyuronic acid in the form of white powder was obtained.
[0027]
<Example 2>
After dissolving 5.0 g of water-soluble starch (manufactured by ACROS) in distilled water at a concentration of 5%, the solution was cooled. To this, an aqueous solution in which 96 mg of TEMPO and 1.27 g of sodium bromide were dissolved was added to prepare a solid content concentration of starch of about 2 wt%. The reaction system is cooled, 17 g of 11% sodium hypochlorite aqueous solution is added, and the oxidation reaction is started. The reaction temperature was always kept below 5 ° C. During the reaction, the pH in the system decreases, but 0.5N-NaOH aqueous solution is sequentially added to adjust the pH to around 10.8, and further, 40 g of 11% sodium hypochlorite aqueous solution is adjusted according to the progress of the reaction. While dripping. When approaching the amount of alkali added corresponding to 100% of the total number of moles of glucose residues, the rate of alkali addition slowed regardless of the dropping of the aqueous sodium hypochlorite solution. When the amount of alkali added reached 100% (61.68 ml), ethanol was added to stop the reaction. The reaction time was 1 hour 40 minutes. This reaction solution was filtered to remove insoluble impurities, and then poured into an excess amount of ethanol to reprecipitate the product. Further, after sufficiently washing with a solution of water: acetone = 1: 7, dehydration with acetone and drying under reduced pressure at 40 ° C., a white powdery sodium salt of polyuronic acid 5.7 g was obtained.
[0028]
<Example 3>
Oxidation treatment was carried out in the same manner as in Example 1 except that corn starch (manufactured by Kanto Chemical Co., Ltd.) was used as the raw material of Example 1, and 1.1 g of sodium salt of polyuronic acid in the form of white powder was obtained. The reaction time was 2 hours.
[0029]
<Example 4>
2.0 g of sodium polyuronic acid of Example 2 was dissolved in 80 ml of distilled water, and 2N hydrochloric acid was added to pH 1 while stirring. The solution remained a clear solution. This solution was poured into an excess amount of ethanol to reprecipitate the product. Further, it was sufficiently washed with a solution of water: acetone = 1: 7, dehydrated with acetone, and dried under reduced pressure at 40 ° C. to obtain 1.6 g of desalted polyuronic acid as a white powder.
[0030]
<Comparative Example 1>
After dissolving 5.0 g of water-soluble starch (manufactured by ACROS) in distilled water at a concentration of 5%, the solution was cooled. To this, an aqueous solution in which 96 mg of TEMPO and 1.27 g of sodium bromide were dissolved was added to prepare a solid content concentration of starch of about 2 wt%. The reaction system is cooled, 45 g of 11% aqueous sodium hypochlorite solution is added, and the oxidation reaction is started. The reaction temperature was always kept below 5 ° C. During the reaction, the pH in the system was lowered, but 0.5N-NaOH aqueous solution was sequentially added to adjust the pH to around 10.8. When the alkali addition amount reached the addition amount (49.34 ml) corresponding to the number of moles of 80% with respect to the total number of moles of glucose residues, ethanol was added to stop the reaction. The reaction time was 50 minutes. This reaction solution was filtered to remove insoluble impurities, and then poured into an excess amount of ethanol to reprecipitate the product. Furthermore, after thoroughly washing with a solution of water: acetone = 1: 7, dehydration with acetone and drying under reduced pressure at 40 ° C., 5.5 g of sodium polyuronic acid salt in the form of white powder of Comparative Example 1 was obtained.
[0031]
<Comparative example 2>
After dissolving 5.0 g of water-soluble starch (manufactured by ACROS) in distilled water at a concentration of 5%, the solution was cooled. To this, an aqueous solution in which 96 mg of TEMPO and 1.27 g of sodium bromide were dissolved was added to prepare a solid content concentration of starch of about 2 wt%. Add 57 g of 11% sodium hypochlorite aqueous solution and start the oxidation reaction. The reaction temperature was always maintained between 10 ° C and 20 ° C. During the reaction, the pH in the system was lowered, but 0.5N-NaOH aqueous solution was sequentially added to adjust the pH to around 10.8. When the alkali addition amount reached the addition amount (61.68 ml) corresponding to 100% of the total number of moles of glucose residues, ethanol was added to stop the reaction. The reaction time was 45 minutes. This reaction solution was filtered to remove insoluble impurities, and then poured into an excess amount of ethanol to reprecipitate the product. Furthermore, after sufficiently washing with a solution of water: acetone = 1: 7, it was dehydrated with acetone and dried under reduced pressure at 40 ° C. to obtain 5.6 g of sodium polyuronic acid salt in the form of white powder of Comparative Example 2.
[0032]
<Comparative Example 3>
Unoxidized water-soluble starch (manufactured by ACROS) was used as Comparative Example 3.
[0033]
<Evaluation>
(Water soluble)
1.0 g of polyuronic acid (or starch) of Examples 1 to 4 and Comparative Examples 1 to 3 was dissolved in 10 ml of distilled water at 25 ° C. Except for Comparative Example 3, all dissolved completely, and dissolution at a higher concentration was possible.
[0034]
(Structural analysis by NMR)
The samples of Examples 1, 2, and 4 and Comparative Examples 1 and 3 were dissolved in heavy water, and 13C-NMR was measured. The result is shown in FIG. From the NMR spectrum, in the polyuronic acid of the example, the peak derived from carbon having a hydroxyl group at the C6-position of the pyranose ring (δ = 60 to 65 ppm) completely disappears and converted to a carboxyl group (δ = 170 to 180 ppm). The peaks derived from the carbons at the 2nd and 3rd positions were not changed, and the peaks of ketone and the like (around δ = 200 to 210 ppm) were not confirmed. Therefore, it can be said that the polyuronic acid of the present invention is α- (1,4) -polyglucuronic acid having a substantially uniform structure. On the other hand, in the polyuronic acid of Comparative Example 1, a peak derived from the carbon of the carboxyl group was confirmed in the vicinity of δ = 170 to 180 ppm, but derived from the carbon having a hydroxyl group at the C6-position of the pyranose ring in the vicinity of δ = 60 to 65 ppm. Peak remains and is not uniform α- (1,4) -polyglucuronic acid.
[0035]
(Measurement of weight average molecular weight)
The weight average molecular weight (Mw) of the polyuronic acid (or starch) of Examples 1-4 and Comparative Examples 1-3 was measured by GPC method. TSK-gelG6000PWXL and TSK-gelG3000PWXL were used as columns, and 0.1M NaCl was used as an eluent, and measurement was performed using an RI detector. A calibration curve was prepared from a standard pullulan having a known molecular weight, and a weight average molecular weight in terms of pullulan was calculated. As a result, the polyuronic acids of the examples were polyuronic acids having Mw = 42,000, 65,000, 58,000, 66,000 in order from Example 1 and molecular weights of 30,000 or more. In addition, about the sample of the comparative example, they were Mw = 92,000, 22,000, 134,000 in order from the comparative example 1.
[0036]
(Measurement of gas barrier properties)
5% aqueous solution of polyuronic acid (or starch) of Examples 1, 2, 3 and Comparative Examples 1, 2, 3 using a biaxially stretched polypropylene film having a thickness of 20 μm provided with a urethane anchor coat layer as a base material Each was coated with a bar coater and dried in an oven at 80 ° C. to form a film having a dry film thickness of 1.5 μm. The oxygen permeability of these polyuronic acid coating films was measured as follows. The same measurement was performed after storage for 1 month in an atmosphere of 40 ° C. and 90% RH. The results are shown in Table 1.
(Measurement method of oxygen permeability)
It measured in 30 degreeC70% RH atmosphere and 30 degreeC100% RH atmosphere using the oxygen permeability measuring apparatus (The Modern Control company make, OXTRAN 10 / 40A).
[0037]
[Table 1]

[0038]
【The invention's effect】
As described above, the water-soluble polyuronic acid of the present invention has a clear structure, is uniform, has a high molecular weight, and has good water solubility. Therefore, it can be preferably used as an aqueous reaction raw material and an aqueous coating material. In particular, when a gas barrier coating agent is used, moisture resistance and storage stability are improved as well as high gas barrier properties. Furthermore, application as various functional materials such as food, medicine / medicine and cosmetics can be expected.
[0039]
[Brief description of the drawings]
1 is a 13C-NMR measured by dissolving the polyuronic acid sodium salt of Examples 1 and 2, the polyuronic acid of Example 4, the sodium polyuronic acid salt of Comparative Example 1, and the starch of Comparative Example 3 in heavy water. Spectrum.

Claims (2)

Preparing a solution comprising amylose or starch, an N-oxyl compound, and water;
The temperature of the solution is 5 ° C. or less, the pH of the solution is in the range of 10 to 11.5, an oxidizing agent is dropped into the solution while adjusting the amount according to the progress of the oxidation reaction , and a coating agent for gas barrier And a step of obtaining a water-soluble polyuronic acid used in the method.   The solution contains an alkali metal bromide, the N-oxyl compound is 2,2,6,6-tetramethyl-1-piperidine-N-oxyl, and the oxidizing agent is sodium hypochlorite. The method for producing a water-soluble polyuronic acid according to claim 1, wherein

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