A responsive bio-based nanopesticide based on polyphenol-metal coordination and its preparation method

Abstract

This invention discloses a pH-responsive, dissociative bio-based nanopesticide based on polyphenol-metal coordination and its preparation method. Pre-adsorption is achieved through hydrogen bonding between natural polyphenols and the pesticide technical material, followed by the introduction of iron ions to trigger polyphenol-metal coordination cross-linking, constructing a hydrogen-bonded-metal coordination dual-network encapsulation system. This dual-network structure provides adsorption force through hydrogen bonding of the bio-based polyphenols and forms a cross-linked shell through polyphenol-metal coordination bonds, achieving nanoscale in-situ encapsulation of the pesticide. This invention effectively solves the problems of rapid bulk cross-linking, numerous shell defects, and high initial burst release rates in existing technologies caused by one-step mixing coordination. The prepared nanopesticide exhibits extremely low burst release rates under normal storage and transportation conditions and possesses pH-dependent shell dissociation characteristics, endowing the pesticide with intelligent triggering release capabilities in the alkaline environment of the insect midgut or the acidic pathogen microenvironment. Simultaneously, it significantly improves the pesticide's adhesion performance and resistance to UV photolysis on crop leaves.

Description

Technical Field

[0001] This invention belongs to the field of nanopesticide preparation technology, and in particular relates to a responsive bio-based nanopesticide based on polyphenol-metal coordination and its preparation method. Background Technology

[0002] Pesticides are indispensable agricultural production materials for ensuring food security and controlling crop diseases and pests. With the development of modern agriculture, the utilization rate and environmental impact of pesticides have become a focus. Statistics show that due to rainwater runoff, solar degradation, and evaporation drift, the actual effective utilization rate of traditional pesticide formulations in the field is generally less than 40%. The large amount of pesticides lost not only causes serious resource waste but also poses far-reaching ecological and environmental safety hazards. To solve this problem, various controlled-release pesticide systems have been developed. In recent years, supramolecular coordination self-assembly nanocarriers based on natural bio-based polyphenols (such as tannic acid) and metal ions have received widespread attention due to their wide availability of raw materials and good biodegradability. However, existing polyphenol-metal coordination pesticide encapsulation technologies mostly employ a one-step instantaneous coordination assembly method, which directly mixes polyphenols, metal ions, and pesticide active ingredients in one step.

[0003] Because the coordination reaction between polyphenols and metal ions is extremely rapid (typically on the order of milliseconds at room temperature), the one-step mixing method leads to rapid and disordered cross-linking of polyphenols with metal ions in the bulk solution before the polyphenols have even come into contact with or fully coated the pesticide surface. This results in irregular core-shell structures, loose shells, numerous coating defects, and low encapsulation efficiency in the resulting nanoparticles. Furthermore, the formulation exhibits severe initial "burst release" of pesticides in non-targeted storage and transportation environments (such as neutral water bodies) (the cumulative burst release rate over 24 hours typically exceeds 40%), making it impossible to achieve truly intelligent controlled release and reduced application with increased efficacy.

[0004] Therefore, developing a nanopesticide that is easy to synthesize, stably encapsulated, and has intelligent response controlled release function based on natural bio-based materials is of great significance for reducing pesticide application and increasing efficiency, as well as protecting the agricultural ecological environment. Summary of the Invention

[0005] To address the above problems, this invention provides a responsive bio-based nanopesticide based on polyphenol-metal coordination and its preparation method, aiming to solve the technical problems of uncontrollable shell and high burst release rate caused by the one-step coordination method in the prior art.

[0006] This invention utilizes the hydrogen bonds and hydrophobic interactions between pesticide technical and bio-based polyphenols to achieve pre-assembly, forming a pre-adsorption layer with oriented polyphenol molecules on the technical surface, thus enhancing interfacial adhesion. Subsequently, under pH 7-8.5 conditions, the introduction of iron ions triggers in-situ three-coordinate cross-linking on the technical surface, constructing a hydrogen-bonded-metal-coordinated dual-network shell. This system not only achieves precise nanoscale encapsulation of pesticides but also significantly enhances the adhesion and UV resistance of the pesticide on crop leaves. Furthermore, leveraging the pH-responsive characteristics of polyphenol-metal coordination bonds, the nanopesticides prepared in this invention maintain structural integrity under pH 7-8.5 conditions while undergoing shell dissociation in the alkaline environment of the insect midgut or the acidic pathogen microenvironment, achieving intelligent triggered release of the pesticide.

[0007] To achieve the above-mentioned technical effects, the present invention adopts the following technical solution:

[0008] A method for preparing a responsive bio-based nanopesticide based on polyphenol-metal coordination includes the following steps:

[0009] (1) Disperse the pesticide technical in ethanol to obtain a technical dispersion, and control the concentration of the technical dispersion to be 10-50 mg / mL;

[0010] (2) Mix the tannic acid aqueous solution with the original drug dispersion and stir at room temperature for pre-adsorption, so that the tannic acid molecules spontaneously form a directional pre-adsorption layer on the surface of the pesticide particles through hydrogen bonding and hydrophobic interaction.

[0011] (3) Add ferric salt solution dropwise to the pre-adsorption system at a rate of 0.5-2 mL / min, while using a buffer solution to adjust and maintain the pH value of the coordination cross-linking reaction of the system at 7-8.5, so that the coordination cross-linking reaction occurs in situ until the solution color changes and tends to stabilize.

[0012] (4) After centrifugation and washing with deionized water, the reaction product is dried under vacuum to obtain a responsive bio-based nanopesticide based on polyphenol-metal coordination.

[0013] Further, the mass ratio of the tannic acid aqueous solution to the original drug dispersion in step (2) is 1:(0.5~5).

[0014] Furthermore, the stirring pre-adsorption time in step (2) is 30-60 min.

[0015] Further, the ferric salt solution in step (3) is selected from at least one of ferric chloride solution, ferric sulfate solution or ferric nitrate solution; the concentration of the ferric salt solution is 0.05-0.2 mol / L.

[0016] Further, the centrifugation speed in step (4) is 6000–9000 r / min; the vacuum drying time is 12h.

[0017] The present invention also discloses a responsive bio-based nanopesticide prepared according to any of the above preparation methods.

[0018] Furthermore, the responsive bio-based nanopesticide maintains its core-shell structure integrity under pH 7-8.5 conditions, but undergoes shell disintegration due to coordination bond dissociation under pH < 5.0 or pH > 9.0 conditions.

[0019] Compared with the prior art, the preparation method and the obtained nano-pesticide described in this application have the following advantages:

[0020] (1) Stable and controllable structure: By adopting a stepwise strategy of pre-adsorption followed by cross-linking, the defects of disordered coordination and loose shell in one-step method are overcome, the encapsulation efficiency of pesticides is significantly improved, and the burst release rate in non-targeted environments is reduced to the minimum.

[0021] (2) Intelligent response and precise release: By utilizing the stability difference of coordination bonds under different pH levels, the specific release of the agent is achieved for the feeding environment of pests or the microenvironment of pathogens, thereby improving the bioavailability of the agent.

[0022] (3) Green, efficient and environmentally friendly: Bio-based polyphenols are used as carrier materials. The preparation process is mild and the product has good biodegradability, which effectively avoids the microplastic pollution risks brought about by traditional synthetic materials.

[0023] (4) Excellent weather resistance: The obtained nanoshell can not only effectively shield ultraviolet rays and protect photosensitive drugs, but its rich phenolic hydroxyl structure also greatly enhances the drug's ability to resist rain erosion on the plant surface and prolongs the duration of effectiveness. Attached Figure Description

[0024] Figure 1 This refers to the chemical change process in the material preparation method described in the embodiments of this application.

[0025] Figure 2 This is a scanning electron microscope image of the bio-based smart responsive nanopesticide described in the embodiments of this application.

[0026] Figure 3 This refers to the pesticide release rate in the nano-pesticide described in Example 1 of this application.

[0027] Figure 4 The burst release rate of pesticides in Example 1 and Comparative Example 1 of this application at pH=7.4 is shown.

[0028] Figure 5 The leaf surface retention rate under rainwater erosion in Example 2 of this application and each control group is shown to be different.

[0029] Figure 6 The UV photolysis residual rate is shown in Example 1 of this application and in each control group. Detailed Implementation

[0030] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above content.

[0031] Example 1:

[0032] 1.0 g of avermectin technical grade was thoroughly dispersed in 25 mL of anhydrous ethanol to obtain a technical grade dispersion with a concentration of 40 mg / mL. 100 mL of a 1.5% (w / w) tannic acid aqueous solution was prepared. At room temperature, the tannic acid solution was mixed with the technical grade dispersion, and the mixture was stirred continuously at 800 r / min for 45 min. During this stage, tannic acid molecules spontaneously formed a pre-adsorbed layer with oriented arrangement on the surface of the avermectin particles through hydrogen bonding and hydrophobic interactions. 40 mL of a 0.1 mol / L ferric chloride aqueous solution was added dropwise to the system at a rate of 1.0 mL / min. During the dropwise addition, the pH of the system was adjusted and maintained at 8.0 in real time using a saturated sodium bicarbonate solution. The reaction was continued at room temperature for 1.5 h to allow tannic acid and iron ions to undergo in-situ tri-coordinate cross-linking on the particle surface, constructing a dense shell layer. The product was centrifuged at 9000 r / min for 5 min, washed three times with deionized water, and then vacuum dried to obtain the target nano-pesticide. Figure 3 As shown, under a pH 7.4 environment (simulating normal storage and transportation), the initial burst release rate after 24 hours was only 3.2%; while under a pH 5.0 environment (acidic microenvironment), the release rate after 24 hours reached 91.5%.

[0033] Example 2:

[0034] 0.5 g of imidacloprid technical grade was dispersed in 25 mL of anhydrous ethanol to obtain a technical grade dispersion with a concentration of 20 mg / mL. 100 mL of a 0.8% (w / w) tannic acid aqueous solution was prepared. After mixing at room temperature, the mixture was stirred at 500 r / min for 30 min to complete surface pre-adsorption. Confined coordination cross-linking: 30 mL of 0.05 mol / L ferric sulfate solution was added dropwise at a rate of 0.5 mL / min, maintaining the pH of the system at 7.0. The reaction was allowed to proceed at room temperature for 1.0 h until the solution color changed and tended to stabilize. Post-treatment: After centrifugation and washing three times with deionized water, the mixture was vacuum dried to obtain nanopesticides with a clearly defined core-shell structure.

[0035] Figure 2This is a scanning electron microscope image of the bio-based smart responsive nanopesticide described in the embodiments of this application. According to... Figure 2 The results show that the pesticide was successfully and uniformly encapsulated in the shell structure, which is a spherical structure.

[0036] Comparative Example 1:

[0037] 1.0 g of avermectin technical grade was dispersed in 25 mL of anhydrous ethanol. While stirring, 100 mL of 1.5% tannic acid solution and 40 mL of 0.1 mol / L ferric chloride solution (without pre-adsorption) were simultaneously added to the dispersion. The pH was adjusted to 8.0, and the mixture was stirred at room temperature for 1.5 h, then centrifuged and dried. The product obtained in Comparative Example 1 had an irregular morphology, and its 24-h burst release rate at pH 7.4 was as high as 39.5%. Figure 4 This demonstrates the necessity of a stepwise crosslinking strategy for improving shell compactness.

[0038] Comparative Example 2:

[0039] Except for adjusting and maintaining the pH value of the coordination crosslinking reaction at 4.5 in step (3), the raw materials, step-by-step sequential process, and post-treatment conditions in this comparative example are exactly the same as in Example 1. Under the strongly acidic reaction environment of pH 4.5, the phenolic hydroxyl groups of tannic acid undergo extremely low deprotonation and cannot form a stable three-coordinate network with iron ions, mainly existing in an unstable single-coordinate form. The resulting product has a loose shell, is extremely prone to leakage, and essentially loses its encapsulation and controlled-release capabilities.

[0040] Comparative Example 3:

[0041] Except for adjusting and maintaining the pH value of the coordination crosslinking reaction of the system to 10.0 in step (3), the raw materials, step-by-step sequential process and post-treatment conditions of this comparative example are exactly the same as those of Example 1.

[0042] The results showed that, under a strongly alkaline reaction environment of pH 10.0, although tannic acid was completely deprotonated, Fe... 3+ It readily undergoes intense hydrolysis, directly generating a large amount of reddish-brown Fe(OH)3 colloidal precipitate, which aggregates disorderly within the system. This disrupts the continuity and uniformity of the polyphenol-metal network, leading to severe fractures and large-area defects in the resulting nanoparticle shell, thus preventing effective encapsulation.

[0043] Experiment Example 1: Smart Response Release Performance and Shell Stability Test

[0044] To verify the effects of the stepwise crosslinking strategy and pH golden window of this invention on shell compactness and responsiveness, samples prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were placed in parallel in different pH release media to determine the cumulative release rate of avermectin. The results are as follows: Figure 3 As shown.

[0045] At pH 7.4 (simulating normal storage and transportation / neutral non-targeted environment), the initial burst release rate of Example 1 was only 3.2% after 24 hours; while the existing one-step method (Comparative Example 1) achieved a 24-hour burst release rate as high as 39.5% at pH 7.4. Meanwhile, Comparative Examples 2 (pH 5) and 3 (pH 9.5), which deviated from the cross-linking reaction pH window, exhibited severe drug leakage in neutral media. This conclusively demonstrates the necessity of the "hydrogen bond pre-adsorption-stepwise cross-linking" strategy and the pH 7.5–8.5 reaction window of this invention for improving shell compactness and suppressing non-targeted burst release. Furthermore, when the ambient pH was switched to 5.0 (a bactericidal acidic microenvironment), the nanopesticide shell of Example 1 underwent responsive dissociation, and the cumulative release rate rapidly reached 91.5% after 24 hours, exhibiting excellent intelligent triggering release characteristics.

[0046] Experimental Example 2: Parallel Comparative Test of Rainwater Erosion Resistance (Leaf Retention Rate)

[0047] To fairly verify the technological leap in improving the leaf adhesion performance of the step-by-step strategy of this invention, this experiment selected the same pesticide (imidacloprid) for head-to-head comparison under the same test conditions. The test groups included: the imidacloprid nanopesticide prepared in Example 2, the imidacloprid control formulation prepared using the one-step mixing coordination process described in Comparative Example 1, and the unmodified imidacloprid technical material group.

[0048] The three formulations were applied in parallel to the leaves of the same potted crops at equal doses of active ingredients and allowed to air dry. Two hours after application, the leaves were continuously washed with artificial rainfall at a rate of 50 mm / h (simulating a heavy rainstorm) for 1 hour. After washing, the leaves were collected, and the imidacloprid content remaining on their surface was measured to calculate the leaf retention rate. The test results showed that... Figure 5 As shown, the leaf retention rate in Example 2 (step-by-step method of the present invention) was still as high as 88.2%; the leaf retention rate in the process group of Comparative Example 1 (one-step method control) was 51.3%; and the leaf retention rate in the imidacloprid technical control group was only 15.4%.

[0049] Results Analysis: Experimental results show that, under the premise of identical pesticide varieties (imidacloprid), the stepwise method of this invention exhibits significant technical advantages compared to the existing one-step method. This proves that the dense shell regulated by the stepwise method allows tannic acid molecules to arrange themselves regularly, exposing and retaining a larger amount of free functional phenolic hydroxyl groups, thereby forming a stronger supramolecular interface adhesion with plant leaves.

[0050] Experiment Example 3: Parallel Comparative Test of UV Photodegradation Shielding Performance

[0051] Avermectin is a typical highly photosensitive pesticide, which is easily degraded and ineffective in the field due to sunlight exposure. To verify the UV resistance efficacy of this invention, this experiment selected the same pesticide (avermectin) for head-to-head comparison. The test groups included: the avermectin nanopesticide prepared in Example 1, the avermectin nanopesticide prepared in Comparative Example 1, and the pure avermectin technical material group.

[0052] The three formulations were exposed in parallel to a 500 W high-pressure mercury lamp (main wavelength 365 nm) for 50 h of continuous irradiation. Samples were taken at different time points to determine the content of undegraded avermectin and calculate the degradation residue rate. Figure 6 As shown, the nano-pesticide prepared by the present invention (Example 1) still has a drug residue rate of up to 78.0% after irradiation for 50 hours, while the traditional one-step method has a residue rate of only 45.2%, and the traditional material modification method has a residue rate of only 8.5%.

[0053] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for preparing a pH-responsive dissociative bio-based nanopesticide based on polyphenol-metal coordination, comprising the following steps: (1) Disperse the oil-soluble pesticide technical in ethanol to obtain a technical dispersion with a concentration of 10-50 mg / mL; (2) Mix the tannic acid aqueous solution with the original drug dispersion, stir at room temperature for pre-adsorption, and form a pre-adsorption system; (3) Add ferric salt solution dropwise to the pre-adsorption system at a rate of 0.5-2 mL / min, while using a buffer solution to adjust and maintain the pH value of the coordination crosslinking reaction of the system at 7.0-8.5 until the solution color changes and tends to stabilize. (4) After centrifugation, washing with deionized water and vacuum drying of the solution in step (3), a pH-responsive dissociation bio-based nanopesticide based on polyphenol-metal coordination is obtained.

2. The preparation method according to claim 1, wherein: The mass ratio of the tannic acid aqueous solution to the original drug dispersion in step (2) is 1:(0.5~5).

3. The preparation method according to claim 1, wherein: The stirring and pre-adsorption time in step (2) is 30-60 min.

4. The preparation method according to claim 1, wherein: The ferric salt solution in step (3) is selected from at least one of ferric chloride solution, ferric sulfate solution or ferric nitrate solution; the concentration of the ferric salt solution is 0.05-0.2 mol / L.

5. The preparation method according to claim 1, wherein: The centrifugation speed in step (4) is 6000–9000 r / min; The vacuum drying time is 12 hours.

6. A pH-responsive dissociative bio-based nanopesticide prepared by any one of the preparation methods according to claims 1 to 5.

7. The pH-responsive dissociative bio-based nanopesticide according to claim 6, wherein: The pH-responsive dissociative bio-based nanopesticide maintains its core-shell structure at pH 7-8.5, but its shell disintegrates due to the dissociation of coordination bonds at pH < 5.0 or pH > 9.0.

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