A kind of high polymerization degree water-soluble polyampholyte chitosan and preparation method thereof

Abstract

The invention discloses a polyampholyte chitosan with high polymerization degree and water solubility and a preparation method thereof, and belongs to the field of natural polymer material preparation. The polyampholyte chitosan is prepared by mixing aminosulfonic acid and one or more of glycerol, urea, lactic acid or choline chloride as a low eutectic solvent, and then adding chitosan for modification, and contains a polyampholyte of cationic groups and anionic groups. The chitosan sulfate product prepared by the invention has a small molecular weight loss, controllable modification sites, and can obtain a polyampholyte chitosan with high polymerization degree; the sulfation reaction has high efficiency, few side reactions, high product purity, good product water solubility, and extremely high application value.

Description

Technical Field

[0001] The invention relates to a high-polymerization-degree water-soluble polyampholyte chitosan and a preparation method thereof, belonging to the field of natural polymer material preparation. Background Art

[0002] Chitosan is very abundant in nature. It is the second largest natural polymer after cellulose in terms of reserves and the only cationic polysaccharide in nature. Chitosan has multiple physiological functions such as antibacterial, antioxidant, and antiviral properties. It has good biodegradability and biocompatibility and is widely used in various fields such as medicine, food, and agriculture. However, due to its relatively dense crystal structure, chitosan is only soluble in some acidic solutions and is almost insoluble in neutral and alkaline solutions. This low solubility limits its further development. The preparation of chitosan sulfate by chemical modification is an effective method to improve the solubility of chitosan. Among various chitosan sulfates, chitosan sulfate has attracted much attention from researchers because of its multiple physiological activities such as immunomodulation, antioxidant, neuroprotection, antiproliferation, and anticoagulant effects.

[0003] The traditional preparation method of chitosan sulfate is to modify it with different sulfonating agents such as chlorosulfonamide, concentrated sulfuric acid, SO3, etc. These methods involve toxic and irritating raw materials and produce a large amount of reaction waste liquid. There are many problems such as cumbersome operation, serious environmental pollution, and serious molecular degradation. The green preparation of soluble chitosan sulfate is an important way to achieve efficient utilization of chitosan. Low eutectic solvent refers to a solvent that has a significant decrease in melting point temperature relative to the starting compound after mixing multi-component compounds. It is usually composed of a certain stoichiometric ratio of hydrogen bond acceptors and hydrogen bond donors. Compared with the volatility, flammability and toxicity of traditional molecular solvents, low eutectic solvents have good solvent potential, recyclability, and environmental friendliness. Summary of the invention

[0004] The purpose of the present invention is to provide a polyampholyte chitosan and a preparation method thereof, so as to solve the problems of low water solubility and serious pollution in the preparation process in the prior art.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A water-soluble polyampholyte chitosan with a high degree of polymerization is prepared by mixing aminosulfonic acid and one or more of glycerol, urea, lactic acid or choline chloride as a low eutectic solvent, and then adding chitosan for modification. The polyampholyte contains both cationic groups and anionic groups.

[0007] A method for preparing a highly polymerized water-soluble polyampholyte chitosan comprises the following steps:

[0008] (1) Weighing aminosulfonic acid and one or more of glycerol, urea, lactic acid or choline chloride separately, mixing, heating and stirring until a clear liquid is obtained, to prepare a deep eutectic solvent;

[0009] (2) adding chitosan to the low eutectic solvent, heating and stirring for a period of time to carry out sulfation modification of chitosan;

[0010] (3) After the reaction is completed, cool it, add excess water, wash it until it is neutral, remove the precipitate by centrifugation or filtration, and take the supernatant;

[0011] (4) The supernatant is placed in a dialysis bag and dialyzed in distilled water;

[0012] (5) The dialysate is concentrated by rotary evaporation and then freeze-dried to obtain chitosan sulfate.

[0013] Furthermore, in the step (1), the mixture of aminosulfonic acid: glycerol or urea or lactic acid or choline chloride is in a molar ratio of 1:1-1:5, and heated and stirred at 70-150° C. until a clear liquid is obtained.

[0014] Furthermore, in the step (2), a certain amount of chitosan is added, the mass of the added chitosan is less than or equal to half the mass of the low eutectic solvent, and the mixture is heated and stirred at 70-150° C. for a period of time to carry out sulfation modification of the chitosan.

[0015] Furthermore, in step (4), the dialysis bag (molecular weight cut-off 100-3500 Da) is dialyzed in distilled water for 10-72 h.

[0016] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0017] The reaction process of the invention is simple, the solvent and the reaction reagent are combined into one, and the preparation conditions are easy to operate and control; the reaction process conforms to the concept of green chemistry, and a low eutectic solvent is used as a sulfation reagent, which has mild properties and low toxicity, thereby reducing environmental pollution.

[0018] The chitosan sulfate product prepared by the invention has small molecular weight loss, controllable modification sites, and can obtain polyampholyte chitosan with high polymerization degree; the sulfation reaction efficiency is high, the side reaction is small, the product purity is high, and the product has good water solubility. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a process flow chart of the preparation method of water-soluble chitosan.

[0020] Figure 2 It is the dissolved state of chitosan sulfate in water.

[0021] Figure 3This is the Fourier infrared spectrum of chitosan sulfate.

[0022] Figure 4 Zeta potential diagram of chitosan and its derivatives.

[0023] Figure 5 Fluorescence spectra of chitosan (CS) and its derivatives (SCS).

[0024] Figure 6 The carbon NMR spectra of chitosan and chitosan sulfate. DETAILED DESCRIPTION

[0025] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0026] Embodiment 1:

[0027] like Figure 1 As shown, the preparation method of polyampholyte chitosan involved in this embodiment comprises the following steps:

[0028] (1) Weigh 7.01 g and 4.34 g of aminosulfonic acid and urea (molar ratio of 1:1), respectively, and heat and stir at 80°C until a clear liquid is obtained to prepare a deep eutectic solvent;

[0029] (2) Add 0.57 g chitosan (weight average molecular weight 3.4*10 5 Da), heating and stirring at 100 °C for 1 h to carry out chitosan sulfation modification;

[0030] (3) After the reaction is completed, cool for a few minutes, add 150 mL of water, wash with water until neutral, remove the precipitate by centrifugation at 8000 r / min for 20 min, and take the supernatant;

[0031] (4) The supernatant was placed in a dialysis bag (molecular weight cutoff 3500 Da) and dialyzed in distilled water for 60 h.

[0032] (5) The dialysate is concentrated by rotary evaporation and then freeze-dried to obtain chitosan sulfate.

[0033] The weight average molecular weight of chitosan sulfate obtained in this example is 3.2*10 5 Da, sulfur content is 15.1%. The product was tested for water solubility, such as Figure 2As shown in the figure, after 2% (w / w) chitosan sulfate is dissolved in water, no insoluble matter is visible to the naked eye, and its viscosity is much lower than chitosan with the same mass concentration and the same molecular weight.

[0034] Further increase the amount of chitosan sulfate added to a mass concentration of 28%, at which point the solution is already very viscous, and no insoluble matter can be seen in the system with the naked eye, that is, the solubility of chitosan sulfate in water is greater than 28%. In the prior art, the solubility of ionic chitosan synthesized by chemical modification is only 1.6% in water; the solubility of chitosan sulfate prepared by chemical modification of chitosan is 5.3% under neutral conditions. This shows that this product has the characteristics of high molecular weight, low viscosity, and high solubility.

[0035] Figure 3 The Fourier transform infrared spectra of chitosan and chitosan sulfate are shown in Figure 2. Compared with the raw chitosan, the chitosan sulfate has a -1 and 813 cm -1 The characteristic spectral bands of stretching vibration of S=O and COS appeared respectively, which indicated that the SO3 group was successfully introduced, that is, the Fourier infrared spectroscopy characterization results confirmed the structure of the target product.

[0036] Due to the presence of -NH2 at the C2 position of chitosan, the chitosan sulfate molecular chain obtained after modification is a polyampholyte containing both cationic groups and anionic groups. Figure 4 This is the Zeta potential diagram of chitosan and its derivatives. The original chitosan has a positive charge on its surface in acetic acid, and the potential of the modified chitosan sulfate in pure water is close to 0, which is presumably due to the offset of positive and negative charges.

[0037] Figure 5 Figure 3 is the fluorescence spectrum of chitosan and its derivatives. Chitosan and its derivatives are excited at 350 nm. The chemical modification of chitosan causes the maximum emission peak of CS to blue-shift from 416 nm to 409 nm, and the peak fluorescence intensity increases by 65%. This change may be due to the increase in the number of sulfate groups in the structure.

[0038] Embodiment 2:

[0039] The preparation method of polyampholyte chitosan involved in this embodiment comprises the following steps:

[0040] (1) Weigh 5.17 g and 9.59 g of aminosulfonic acid and urea (molar ratio of 1:3), respectively, and heat and stir at 80°C until a clear liquid is obtained to prepare a deep eutectic solvent;

[0041] (2) Add 0.074 g chitosan (weight average molecular weight 3.4*10 5 Da), heating and stirring at 80 °C for 2 h to carry out chitosan sulfation modification;

[0042] (3) After the reaction is completed, cool for a few minutes, add 150 mL of water, wash with water until neutral, remove the precipitate by filtration, and take the supernatant;

[0043] (4) The supernatant was placed in a dialysis bag (molecular weight cutoff 3500 Da) and dialyzed in distilled water for 60 h.

[0044] (5) The dialysate is concentrated by rotary evaporation and then freeze-dried to obtain chitosan sulfate.

[0045] The weight average molecular weight of chitosan sulfate obtained in this example is 1.8*10 5 Da, sulfur content is 8.16%.

[0046] Embodiment 3:

[0047] The preparation method of polyampholyte chitosan involved in this embodiment comprises the following steps:

[0048] (1) Weigh 5.17 g and 9.59 g of aminosulfonic acid and urea (molar ratio of 1:3), respectively, and heat and stir at 100°C until a clear liquid is obtained to prepare a deep eutectic solvent;

[0049] (2) Add 0.148 g chitosan and heat and stir at 100 °C for 5 h to carry out sulfation modification of chitosan;

[0050] (3) After the reaction is completed, cool for a few minutes, add 150 mL of water, centrifuge at 10,000 r / min for 20 min, remove the precipitate, and take the supernatant;

[0051] (4) The supernatant was placed in a dialysis bag (molecular weight cutoff 3500 Da) and dialyzed in distilled water for 90 h.

[0052] (5) The dialysate is concentrated by rotary evaporation and then freeze-dried to obtain chitosan sulfate.

[0053] The chitosan sulfate obtained in this example has a sulfate content of 29.5%.

[0054] Embodiment 4:

[0055] The preparation method of polyampholyte chitosan involved in this embodiment comprises the following steps:

[0056] (1) Weigh 5.07 g and 6.27 g of aminosulfonic acid and urea (molar ratio of 1:2), respectively, and heat and stir at 80°C until a clear liquid is obtained to prepare a deep eutectic solvent;

[0057] (2) Add 0.567 g chitosan (weight average molecular weight 3.4*10 5Da), heating and stirring at 140 °C for 1 h to carry out sulfation modification of chitosan;

[0058] (3) After the reaction is completed, cool for a few minutes, add 120 mL of water, wash with water until neutral, remove the precipitate by filtration, and take the supernatant;

[0059] (4) The supernatant was placed in a dialysis bag (molecular weight cutoff 3500 Da) and dialyzed in distilled water for 60 h.

[0060] (5) The dialysate is concentrated by rotary evaporation and then freeze-dried to obtain chitosan sulfate.

[0061] The weight average molecular weight of chitosan sulfate obtained in this example is 5.2*10 4 Da, containing 36% sulfate. Figure 6 The C NMR spectra of chitosan and chitosan sulfate show that the 59.9 ppm signal of C6 (OH) in chitosan is transferred to 66.5 ppm in sulfated chitosan, which represents the C6 (SO3) signal in chitosan sulfate. 13 C signal. Different from the traditional chitosan sulfation modification method, this method can control the chitosan modification site by controlling the temperature. By increasing the temperature, SO3 groups can be introduced at the C6 and C3-(OH) sites respectively.

[0062] Embodiment 5:

[0063] The preparation method of polyampholyte chitosan involved in this embodiment comprises the following steps:

[0064] (1) Weigh 7.01 g and 4.34 g of aminosulfonic acid and urea (molar ratio of 1:1), respectively, and heat and stir at 80°C until a clear liquid is obtained to prepare a deep eutectic solvent;

[0065] (2) Add 0.57 g chitosan (weight average molecular weight 3.4*10 5 Da), heating and stirring at 80 °C for 1 h to carry out sulfation modification of chitosan;

[0066] (3) After the reaction is completed, cool for a few minutes, add 150 mL of water, wash with water until neutral, remove the precipitate by centrifugation at 8000 r / min for 20 min, and take the supernatant;

[0067] (4) The supernatant was placed in a dialysis bag (molecular weight cutoff 3500 Da) and dialyzed in distilled water for 60 h.

[0068] (5) The dialysate is concentrated by rotary evaporation and then freeze-dried to obtain chitosan sulfate.

[0069] The weight average molecular weight of the chitosan sulfate obtained in this example is 1.1*10 5 Da, sulfur content is 13.6%.

[0070] Compared with the traditional chitosan sulfation modification method, the outstanding feature of the method of the present invention is that the reaction conforms to the concept of green chemistry, the product has less molecular weight loss than the initial chitosan, and the directional site modification can be achieved by simply adjusting the reaction time and temperature to generate polyampholyte chitosan with a high degree of polymerization. The solubility of the product in water is greatly improved compared with the solubility of chitosan sulfate reported in the literature, providing unique macromolecular materials for the fields of food, biology, materials, medicine, etc., which can meet the application needs in different scenarios.

[0071] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A highly polymerized water-soluble polyampholyte chitosan, characterized in that: The polyampholyte chitosan is prepared by mixing aminosulfonic acid and urea as a low eutectic solvent, and then adding chitosan for modification, and contains cationic groups and anionic groups. The polyampholyte comprises the following steps: (1) Weigh 7.01 g and 4.34 g of aminosulfonic acid and urea, respectively, at a molar ratio of 1:1, and heat and stir at 80°C until the mixture becomes a clear liquid to prepare a deep eutectic solvent; (2) Add 0.57 g chitosan, with a weight average molecular weight of 3.4*10 5 Da, heating and stirring at 100 °C for 1 h to carry out chitosan sulfation modification; (3) After the reaction is completed, cool for a few minutes, add 150 mL of water, wash with water until neutral, remove the precipitate by centrifugation at 8000 r / min for 20 min, and take the supernatant; (4) The supernatant was placed in a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed in distilled water for 60 h; (5) The dialysate is concentrated by rotary evaporation and then freeze-dried to obtain chitosan sulfate.

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