Method for directional construction of eugenol-based supramolecular co-crystal system and products and applications thereof

Abstract

The application discloses a method for directional construction of eugenol-based supramolecular co-crystal system and application of the product, and belongs to the field of agricultural chemistry and supramolecular crystal engineering technology. The method comprises the following steps: selecting eugenol as a hydrogen bond donor molecule through rational molecular design, selecting nicotinamide or 2-pyridinecarboxylic acid as a co-crystal ligand according to the quantitative screening standards of hydrogen bond acceptor strength (pKa value), molecular geometric length and specific functional groups, dissolving the two in a mixed solvent with a specific dielectric constant range at a 1:1 molar ratio, and obtaining a supramolecular co-crystal product with a clear structure through programmed temperature uniform cooling crystallization, aging and drying. The product has stable crystal structure, pH-responsive release characteristics and slow-release performance better than that of a physical mixture. The product is added to urea at an addition amount of 0.5% to 5.0%. The application realizes directional construction of co-crystals from empirical screening to rational design, structure control and performance prediction, and provides a reliable material platform for nitrogen fertilizer efficiency.

Description

Technical Field

[0001] This invention relates to the field of chemical pharmaceutical raw material and formulation manufacturing technology, specifically to the method for directional construction of eugenol-based supramolecular eutectic systems and its products and applications. Background Technology

[0002] As the dominant nitrogen fertilizer, urea exhibits two key loss mechanisms in its transformation pathway in soil: rapid hydrolysis catalyzed by urease, leading to ammonia volatilization; and oxidation of ammonium nitrogen by nitrifying bacteria, resulting in nitrate leaching and denitrification losses. Therefore, developing synergists with both urease and nitrification inhibition functions is a recognized technological direction in the industry.

[0003] Eugenol, a natural phenolic compound, is considered a promising candidate for a green synergist due to its potential inhibitory effects on the enzyme activity and flora of the aforementioned microorganisms. However, the inherent physicochemical properties of eugenol—low melting point, high volatility, and rapid migration in aqueous media—make it difficult to maintain an effective concentration and duration of action in soil, resulting in minimal direct application effects. Therefore, appropriate formulation modification of eugenol to achieve solidification, stabilization, and functionalization is a prerequisite for its practical application.

[0004] In existing technologies, a representative approach is to modify eugenol using a co-crystallization technique. For example, Chinese invention patent CN118221502A discloses a method for forming co-crystallized supramolecular structures of eugenol and long-chain fatty acids (such as stearic acid) via a hydrothermal process. By forming intermolecular hydrogen bonds between the carboxyl groups of the fatty acids and the phenolic hydroxyl groups of eugenol, liquid eugenol is transformed into a solid powder, objectively improving its physical convenience for storage and application.

[0005] However, a thorough analysis from the perspective of first principles in supramolecular chemistry and agricultural chemistry reveals that this existing technical solution suffers from the following four fundamental limitations, preventing it from addressing the core pain points in the field of nitrogen fertilizer synergists:

[0006] First, the technology is limited to superficial modifications of physical properties and fails to address the core contradiction in release kinetics. The starting point of this technology is to solve the material handling problem of eugenol, which is "liquid and volatile," and its target product is a "useful solid." However, the fundamental technical contradiction of agricultural synergists lies in the kinetic conflict between the "rapid deactivation" of highly bioactive molecules in complex and dynamic soil environments and the "long-term need" for crop nitrogen absorption. Existing technologies have failed to elevate the target of formulation design from "changing the physical state" to "precisely controlling release behavior." The product in the soil still relies on simple dissolution and diffusion, the release rate is uncontrollable, and a long-term, stable inhibitory function cannot be achieved.

[0007] Secondly, the technology relies on empirical screening and weak interactions, lacking rational design principles. It selects long-chain fatty acids as ligands based on the vague premise of "the ability to form a eutectic." From the perspective of molecular forces, the main interaction between fatty acids and eugenol is a physical encapsulation dominated by weak directional hydrogen bonds and van der Waals forces—a non-specific, low-energy stabilization mechanism. This process lacks quantitative consideration of key parameters such as ligand hydrogen bond acceptor strength (e.g., pKa), molecular geometry, and electron cloud distribution, falling into the category of "trial and error," and failing to establish a predictive model from molecular structure to product performance.

[0008] Third, the structure is unclear, and structure-property relationships cannot be established. The characterization of the product using this technique is limited to melting point, yield, and 1H NMR spectrum. These data are completely incapable of revealing its crystal structure, hydrogen bond topology, and key weak interactions. Due to the structural ambiguity, the product's "stability" is only a macroscopic description and cannot be correlated with the microscopic molecular arrangement and lattice energy. Therefore, its "slow-release" performance is an unpredictable and unrepeatable black box output, making batch-to-batch consistency difficult to guarantee.

[0009] Fourth, it lacks environmental responsiveness, its performance is passive and singular, and the soil environment is constantly changing. An ideal synergist should be able to intelligently respond to environmental signals. The structural stability of fatty acid cocrystals obtained by existing technologies mainly relies on pH-insensitive van der Waals forces and weak hydrogen bonds, lacking a specific response mechanism to changes in environmental pH. Its release is passive dissolution, unable to accelerate release in microdomains where inhibition is needed, nor can it maintain structural integrity in non-target areas, resulting in low effective utilization.

[0010] The existing technology represented by CN118221502A essentially utilizes the relatively rudimentary concept of "eutectic" in supramolecular chemistry to achieve a single improvement in physical formulation. It has failed to, and has not attempted to, solve the core scientific and technological challenge of controlled release and long-lasting action of active ingredients in the field of agricultural chemicals through rational molecular design and precise crystal engineering. The performance of its products is empirical and unpredictable, lacking a reliable and clear design bridge between it and the final agricultural application effect. Summary of the Invention

[0011] The purpose of this invention is to provide a method for the directional construction of eugenol-based supramolecular cocrystal systems, as well as their products and applications. This effectively solves the technical problem that existing technologies cannot obtain eugenol-based supramolecular cocrystal materials with controllable structure and stable performance through empirical cocrystal construction methods, resulting in the inability to achieve the controllable sustained release and long-term dual inhibition functions of active components in soil environments.

[0012] This invention selects ligands with pKa values ​​between 3.5 and 6.0, matching molecular lengths (0.7-1.2 nm), and containing strongly directional hydrogen bond acceptors (sp² nitrogen, carbonyl oxygen) to ensure that the ΔpKa of these ligands is within a suitable range for eugenol. This forces eugenol to form a predetermined, highly stable hydrogen bond network during crystallization. This network undergoes reversible dissociation / recombination when its protonation state changes due to environmental pH, thereby achieving a smart response in the release rate.

[0013] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0014] In a first aspect, the present invention discloses a method for the directional construction of a eugenol-based supramolecular eutectic system, comprising the following steps:

[0015] Eugenol was selected as the hydrogen bond donor molecule, and the molecular structure of eugenol contains a benzene ring substituted with a phenolic hydroxyl group and an ortho-methoxy group.

[0016] Based on screening criteria including a hydrogen bond acceptor strength parameter pKa value ranging from 3.3 to 6.0, a molecular length between 0.7 nm and 1.2 nm, and the presence of at least one sp² hybridized nitrogen atom or carbonyl oxygen atom, cocrystal ligands were determined. The cocrystal ligands were selected from nicotinamide and 2-pyridinecarboxylic acid.

[0017] Eugenol and the eutectic ligand are dissolved in a mixed solvent system at a molar ratio of 1:1. The mixed solvent system is composed of a polar aprotic solvent and a low-polarity protic solvent at a volume ratio of 3:1 to 5:1. The polar aprotic solvent is acetonitrile or acetone, and the low-polarity protic solvent is n-butanol or isopropanol.

[0018] The obtained solution was placed in a temperature-controlled crystallization apparatus and cooled uniformly from an initial temperature of 45°C to 5°C at a rate of 0.2°C / min to 0.5°C / min. The solution was then aged at 5°C for 12 to 24 hours to precipitate a cocrystallized product. The cocrystallized product was collected and vacuum dried at 40°C for 8 hours to obtain a eugenol-based supramolecular cocrystallized product.

[0019] Furthermore, the co-crystal ligand is nicotinamide, in which the pyridine nitrogen atom and the amide carbonyl oxygen atom in the nicotinamide molecule constitute a two-site hydrogen bond acceptor, forming O–H…N hydrogen bonds and O–H…O hydrogen bonds with the phenolic hydroxyl group of the eugenol. Moreover, the planar structure of the nicotinamide and the benzene ring of the eugenol form a face-to-face π–π stacking with a stacking spacing of 0.35 nm to 0.38 nm.

[0020] Furthermore, the eutectic product belongs to the monoclinic crystal system, with space group P21 / c, and cell parameters a ranging from 1.19 nm to 1.23 nm, b ranging from 0.87 nm to 0.91 nm, c ranging from 1.51 nm to 1.55 nm, and β angle ranging from 97.5° to 99.5°.

[0021] Furthermore, the co-crystallized ligand is 2-pyridinecarboxylic acid, and the carboxylic acid group of the 2-pyridinecarboxylic acid undergoes partial deprotonation during crystallization, forming O–H…O with the phenolic hydroxyl group of the eugenol. - Ionic hydrogen bonds are formed, and at the same time, the pyridine ring nitrogen atom of the 2-pyridinecarboxylic acid accepts the phenolic hydroxyl proton of another molecule of eugenol to form O–H…N neutral hydrogen bonds, thus constructing an alternating chain of ionic-neutral hydrogen bonds in the crystal lattice.

[0022] Furthermore, the ionic-neutral hydrogen bond chain extends along the

[010] direction, and adjacent chains are connected by weak C–H…π interactions; the eutectic product belongs to the triclinic crystal system, space group P-1, with unit cell parameters a of 0.76 nm to 0.80 nm, b of 0.80 nm to 0.84 nm, c of 1.03 nm to 1.07 nm, α angle of 91.3° to 93.3°, β angle of 94.7° to 96.7°, and γ angle of 100.2° to 102.2°.

[0023] Furthermore, the dielectric constant of the mixed solvent system is between 18 and 25.

[0024] Secondly, this invention also discloses eugenol-based supramolecular cocrystal products:

[0025] The eugenol-nicotinamide supramolecular eutectic product was prepared by the above method. The X-ray powder diffraction pattern of the eutectic product showed characteristic diffraction peaks at 2θ of 12.5°±0.2°, 16.8°±0.2° and 24.3°±0.2°. Its differential scanning calorimetry pattern showed a single melting endothermic peak in the range of 155℃ to 165℃, and the melting range width did not exceed 5℃.

[0026] Eugenol-2-pyridinecarboxylic acid supramolecular eutectic product: The X-ray powder diffraction pattern of the eutectic product has characteristic diffraction peaks at 2θ of 10.2°±0.2°, 14.7°±0.2° and 26.1°±0.2°; its differential scanning calorimetry pattern has a single melting endothermic peak in the range of 150℃ to 155℃, and the melting range width does not exceed 5℃.

[0027] Furthermore, the eutectic product has a solubility of 0.8 mg / mL to 2.5 mg / mL in water at 25°C; it dissolves slowly in an environment with a pH of 5.0 to 8.0, and the structure can be maintained for a relatively long time; when the ambient pH is below 4.5 or above 9.0, the hydrogen bond network is more easily dissociated.

[0028] Furthermore, when the cocrystal product is in phosphate buffer at pH 6.5 and subjected to constant temperature shaking at 25°C, the total amount of eugenol released in the first 72 hours does not exceed 15% of the total eugenol loading in the cocrystal product, and the cumulative release rate within 14 days is 40% to 60%.

[0029] Furthermore, the melting endothermic peak of the eutectic product appears between 145°C and 165°C, and the melting range does not exceed 5°C; there is no mass loss below 100°C; in the Fourier transform infrared spectrum, the phenolic hydroxyl stretching vibration peak is located at 3280 cm⁻¹. -1 Up to 3320cm -1 between.

[0030] In three aspects, the present invention discloses a slow-release nitrogen fertilizer comprising urea and the eugenol-based supramolecular cocrystal product as described above, wherein the amount of the cocrystal product added is 0.5% to 5.0% of the quality of the urea.

[0031] Furthermore, the eutectic product is compounded with the urea by dry mixing, fluidized bed coating, or extrusion granulation.

[0032] Furthermore, when the compounding method is dry mixing, the powder of the eutectic product and urea particles are mixed in a V-type mixer at a speed of 15 rpm for 30 minutes.

[0033] Furthermore, when the composite method is fluidized bed coating, the eutectic product is dissolved in an ethanol-water mixed solvent to prepare a solution with a concentration of 5% w / v, and sprayed onto the surface of the fluidized urea particles at a spray rate of 0.5 mL / min, with an inlet air temperature of 60°C and an outlet air temperature of 40°C.

[0034] Furthermore, when the compounding method is extrusion granulation, the eutectic product and urea are added to a twin-screw extruder, the barrel temperature is set to 50°C, the screw speed is set to 80 rpm, and the compound particles are obtained after extrusion through the die and crushing and screening.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] This invention transforms the traditional cocrystal preparation method, which relies on empirical compounding and accidental discovery, into a rational construction method based on quantitative design and precise control of intermolecular non-covalent forces. Through systematic analysis of the intrinsic properties of eugenol molecules, such as hydrogen bond donor strength, steric hindrance, and electron cloud distribution, atomic-scale matching design is achieved with the acceptor strength and molecular geometry of the cocrystal ligands.

[0037] This invention directionally constructs a supramolecular lattice with a well-defined hydrogen-bonded topology and molecular packing pattern. This supramolecular lattice structure, dominated by strong hydrogen bonds and synergistically supported by weak interactions, achieves significantly higher lattice stability than simple mixtures. This enhanced stability directly translates into the product's ability to maintain structural integrity in complex soil media, fundamentally solving the problem of burst release caused by rapid structural dissociation of active components. Thus, eugenol can achieve a stable and controllable sustained release, rather than a one-time release.

[0038] The continuously released eugenol molecules can act simultaneously and for a long time on soil urease and ammonia-oxidizing bacteria, achieving dual inhibition of urea hydrolysis and nitrification. This avoids the problem of a short nitrogen transformation regulation window caused by the rapid decay of inhibitor dosage in traditional methods, thus significantly extending the effective action period of nitrogen fertilizer.

[0039] This invention establishes a quantitative correlation model of molecular electronic properties, hydrogen bond topology, lattice stability, release behavior, and inhibition function, transforming the performance of eutectic materials from unpredictable empirical results into rational outputs that can be predicted and controlled through early molecular and process design parameters. This realizes the transformation from accidental discovery to engineerable directional construction. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0041] Figure 1 This is an overall flowchart of the directional construction method described in this invention.

[0042] Figure 2 This is a flowchart of the eutectic preparation stage of the present invention.

[0043] Figure 3 This is a flowchart of the slow-release nitrogen fertilizer compounding process of the present invention.

[0044] Figure 4 This is a schematic diagram illustrating the key non-covalent interaction in the eugenol-nicotinamide eutectic of the present invention.

[0045] Figure 5 This is a schematic diagram illustrating the preparation of the eutectic-urea composite particles and their sustained-release synergistic effect according to the present invention. Detailed Implementation

[0046] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0047] The key molecular design parameters used in this invention are determined as follows:

[0048] (1) pKa value: The pKa values ​​mentioned refer to the standard values ​​in aqueous solution at 25°C. The pKa of the phenolic hydroxyl group of eugenol is 10.0, the pKa of the pyridine nitrogen of nicotinamide is 3.4, and the pKa of the carboxyl group of 2-pyridinecarboxylic acid is 4.8 (Data source: CRCH and book of Chemistry and Physics, 102nd Ed., and SciFinder database).

[0049] (2) Molecular length: The “molecular length” is defined as the straight-line distance between the two farthest atomic nuclei when the molecule is in its lowest energy conformation. It is calculated using Chem3D20.1 software after geometric optimization with an MMFF94 force field (convergence criterion: energy gradient < 0.001 kcal / (mol·Å)). The calculated length of nicotinamide is 0.85 nm, and the calculated length of 2-pyridinecarboxylic acid is 0.95 nm. The lengths of the cocrystal ligand molecules selected in the embodiments of this invention all fall within the preferred range of 0.7 nm to 1.2 nm.

[0050] (3) Solvent dielectric constant: The dielectric constant (ε) of the mixed solvent system is determined according to the formula Estimate, of which and The figures represent the volume fractions of each pure solvent (acetonitrile, acetone, n-butanol, and isopropanol) and their literature dielectric constant values ​​at 25°C.

[0051] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0052] Example 1: See Figures 1-5 This embodiment discloses a method for the directional construction of a eugenol-based supramolecular eutectic system, as well as its products and applications.

[0053] The method for directional construction of the eugenol-based supramolecular eutectic system includes the following steps:

[0054] Eugenol was selected as the hydrogen bond donor molecule. Its molecular structure contains a benzene ring with a phenolic hydroxyl group and an ortho-methoxy-substituted group. The phenolic hydroxyl group acts as a strong hydrogen bond donor, while the methoxy group enhances the electron cloud density of the benzene ring and provides a spatial shielding effect through inductive effect.

[0055] Based on the screening criteria of a hydrogen bond acceptor strength parameter pKa value ranging from 3.3 to 6.0, a molecular length between 0.7 nm and 1.2 nm, and the presence of at least one sp² hybridized nitrogen atom or carbonyl oxygen atom, cocrystal ligand candidates were determined. The cocrystal ligands were selected from nicotinamide and 2-pyridinecarboxylic acid.

[0056] Furthermore, eugenol and the selected eutectic ligand are dissolved in a mixed solvent system at a molar ratio of 1:1 to 1:2. The mixed solvent system is composed of a polar aprotic solvent and a low-polarity protic solvent at a volume ratio of 3:1 to 5:1, wherein the polar aprotic solvent is acetonitrile or acetone, and the low-polarity protic solvent is n-butanol or isopropanol.

[0057] The resulting clarified solution was then placed in a temperature-controlled crystallization apparatus, heated and kept constant at 45°C, and then cooled uniformly from that temperature to 5°C at a rate of 0.2°C / min to 0.5°C / min. The solution was then aged at the final temperature for 12 to 24 hours, allowing the system to undergo three stages: nucleation induction period, crystal growth steady-state period, and lattice relaxation period, ultimately precipitating the target eutectic product.

[0058] Finally, the crystals were collected by vacuum filtration and dried under vacuum at 40°C for 8 hours to obtain a high-purity eugenol-based supramolecular cocrystal product.

[0059] In a preferred embodiment, the co-crystal ligand is nicotinamide, in which the pyridine nitrogen atom and the amide carbonyl oxygen atom together constitute a two-site hydrogen bond acceptor, which can form O–H…N and O–H…O double hydrogen bond connections with the phenolic hydroxyl group of eugenol. At the same time, the planar structure of nicotinamide and the benzene ring of eugenol produce face-to-face π–π stacking interactions, with the stacking spacing controlled within the range of 0.35 nm to 0.38 nm, thereby constructing a lattice structure in which a three-dimensional cross-linked hydrogen bond network and layered molecular arrangement work together. The co-crystal product belongs to the monoclinic crystal system, with space group P21 / c, and the cell parameters satisfying a = 1.21 nm ± 0.02 nm, b = 0.89 nm ± 0.02 nm, c = 1.53 nm ± 0.02 nm, β angle is 98.5° ± 1.0°, and Z value is 4.

[0060] In another preferred embodiment, the co-crystallized ligand is 2-pyridinecarboxylic acid, whose carboxylic acid group undergoes partial deprotonation during crystallization, forming O–H…O with the phenolic hydroxyl group of eugenol. -Ionic hydrogen bonds are formed, and the nitrogen atom of the pyridine ring accepts the phenolic hydroxyl proton from another molecule of eugenol to form O–H…N neutral hydrogen bonds. This creates alternating chains of ionic-neutral hydrogen bonds in the crystal lattice, which extend along the

[010] direction. Adjacent chains are laterally connected by C–H…π weak interactions, forming a columnar stacked structure with anisotropic mechanical strength. The eutectic product belongs to the triclinic crystal system with space group P-1. The cell parameters satisfy a = 0.78 nm ± 0.02 nm, b = 0.82 nm ± 0.02 nm, c = 1.05 nm ± 0.02 nm, α = 92.3° ± 1.0°, β = 95.7° ± 1.0°, γ = 101.2° ± 1.0°, and Z = 2.

[0061] The eugenol-based supramolecular cocrystal product provided by this invention has a well-defined X-ray single-crystal diffraction structure. The intermolecular forces are primarily dominated by OH\...N / OH\...O hydrogen bonds, supplemented by π-π stacking, CH\...O, and CH\...π secondary interactions. This stable lattice structure significantly reduces the dissolution and release rate of the cocrystal in water.

[0062] The eutectic product has a solubility in water at 25°C between 0.8 mg / mL and 2.5 mg / mL, dissolves slowly in the pH range of 5.0 to 8.0, and maintains its structure for a relatively long time.

[0063] When the ambient pH is below 4.5 or above 9.0, the hydrogen bond network is more easily dissociated, accelerating the release of active components. One gram of each fertilizer sample was placed in a dialysis bag (molecular weight cutoff 1000 Da) and incubated in 50 mL of pH 6.5 phosphate buffer at 25°C with constant temperature and shaking. The concentration of eugenol in the dialysate was measured periodically, and the cumulative release rate was calculated. Experimental results showed that the cocrystal product exhibited zero-order or near-zero-order release kinetics.

[0064] This embodiment also provides the application of the eugenol-based supramolecular cocrystal product in the agricultural field, specifically for physical mixing or coating with urea fertilizer to prepare a slow-release nitrogen fertilizer with dual functions of urease inhibition and nitrification inhibition; the amount of the cocrystal product added is 0.5% to 3.0% of the urea mass. After the fertilizer is applied to the soil, the cocrystal structure slowly disintegrates in the slightly acidic environment of soil moisture infiltration and microbial metabolites, continuously releasing eugenol molecules. The latter can effectively inhibit soil urease activity and nitrifying bacteria activity, thereby achieving dual inhibition of urea hydrolysis and nitrification processes and extending the effective period of nitrogen fertilizer.

[0065] Furthermore, the compounding methods of the eugenol-based supramolecular eutectic product and urea include dry mixing, fluidized bed coating, or extrusion granulation. In the dry mixing method, the eutectic powder and urea particles are mixed in a V-type mixer at a speed of 15 rpm for 30 minutes. In the fluidized bed coating method, the eutectic is dissolved in an ethanol-water mixed solvent to prepare a 5% w / v solution, which is sprayed onto the surface of the fluidized urea particles at a spray rate of 0.5 mL / min, with an inlet air temperature of 60°C and an outlet air temperature of 40°C. In the extrusion granulation method, the eutectic and urea are added to a twin-screw extruder in proportion, the barrel temperature is set to 50°C, the screw speed is 80 rpm, and the composite particles are obtained after extrusion through a die and crushing and screening.

[0066] In the directional construction method of the eugenol-based supramolecular eutectic system, the solvent-mediated gradient cooling crystallization process is crucial to ensuring the reproducibility and batch consistency of the eutectic structure. The dielectric constant of the mixed solvent system is controlled between 18 and 25 to balance the solubility differences between eugenol and the eutectic ligands, avoiding the analysis of a single group. The cooling rate is limited to the range of 0.2℃ / min to 0.5℃ / min, allowing the system sufficient time to overcome the nucleation energy barrier and selectively form the most thermodynamically stable crystal form, rather than the kinetically metastable phase. The aging stage promotes the relaxation of internal lattice stress, eliminates dislocations and vacancies, and improves the mechanical strength and hydrolysis resistance of the crystal.

[0067] The structural stability of the eutectic product described in this invention was verified by a combination of differential scanning calorimetry and thermogravimetric analysis. Its melting endothermic peak appeared between 145°C and 165°C, with a melting range width not exceeding 5°C, indicating uniform crystal structure. No significant mass loss was observed below 100°C, confirming the absence of solvent residue. Fourier transform infrared spectroscopy showed that the stretching vibration peak of the phenolic hydroxyl group changed from 3520 cm⁻¹ in the free state. -1 Moved to 3280cm -1 Up to 3320cm -1 The broad peaks confirm the formation of hydrogen bonds; in the solid-state NMR¹³C spectrum, the carbon signal of the benzene ring of eugenol undergoes a deshielding shift of 0.8 ppm to 1.5 ppm, indicating a change in its chemical environment, which further confirms the existence of intermolecular interactions.

[0068] In one specific embodiment, nicotinamide is used as the co-crystal ligand, and the operation is carried out according to the following steps:

[0069] Weigh 1.64 g (10 mmol) of eugenol and 1.22 g (10 mmol) of nicotinamide into a 100 mL round-bottom flask; add a mixed solvent system consisting of 30 mL of acetonitrile and 10 mL of n-butanol, heat to 45 °C and stir until completely dissolved to form a clear and transparent solution; transfer the solution to a temperature-controlled crystallization apparatus, cool it uniformly to 5 °C at a rate of 0.3 °C / min, and age it at 5 °C for 18 hours; then perform vacuum filtration, collect the obtained crystals, and dry them under vacuum at 40 °C for 8 hours to obtain 2.50 g of white needle-like crystals. 10 H 12 Based on the theoretical yield (2.863 g) of eutectic formed by O2 (M=164.20 g / mol) and nicotinamide (C6H6N2O, M=122.13 g / mol) in a 1:1 molar ratio, the yield was 87.3%.

[0070] X-ray single-crystal diffraction analysis revealed that the crystal belongs to the monoclinic crystal system, with space group P21 / c, and cell parameters a=1.212 nm, b=0.889 nm, c=1.528 nm, β=98.6°, and Z=4.

[0071] Based on the aforementioned pKa data (eugenol phenolic hydroxyl pKa = 10.0, nicotinamide pyridine nitrogen pKa = 3.4), the ΔpKa for both is 6.6. This relatively large ΔpKa value, combined with the planar dual-acceptor structure of nicotinamide, chemically explains why it can form strong OH...N hydrogen bonds (bond length: 2.65 Å, bond angle: 168°) and auxiliary OH...O hydrogen bonds (bond length: 2.78 Å, bond angle: 155°), and synergistically assemble with precise face-to-face π-π stacking (spacing: 3.52 Å), thereby constructing a highly stable layered lattice.

[0072] Differential scanning calorimetry (DSC) analysis showed that its melting endothermic peak was located at 158.3℃, with a melting range of only 4.4℃, indicating highly homogeneous crystal form; Fourier transform infrared spectroscopy showed a peak at 3305 cm⁻¹. -1 A broad and strong absorption peak appears, corresponding to the stretching vibration of the phenolic hydroxyl group associated with hydrogen bonds; in the solid-state ¹³ CNMR spectrum, the carbon signals at the C2 and C6 positions of the eugenol benzene ring shift to the lower field by 1.2 ppm and 1.0 ppm, respectively. This stable crystal framework, predetermined by a specific ΔpKa and molecular geometry, is the fundamental structural reason for achieving zero-order release kinetics and long-lasting sustained-release function.

[0073] Example 2: In this example, 2-pyridinecarboxylic acid is used as the co-crystal ligand, and the specific operation is as follows:

[0074] Weigh 1.64 g (10 mmol) of eugenol and 1.23 g (10 mmol) of 2-pyridinecarboxylic acid and place them in a 100 mL round-bottom flask; add a mixed solvent system consisting of 35 mL of acetone and 7 mL of isopropanol, heat to 45 °C and stir until completely dissolved; place the solution in a temperature-controlled crystallization apparatus and cool from 45 °C to 5 °C at a rate of 0.4 °C / min, and age at 5 °C for 20 hours; after vacuum filtration, dry under vacuum at 40 °C for 8 hours to obtain 2.36 g of pale yellow flaky crystals, with a yield of 82.1%.

[0075] X-ray single-crystal diffraction results indicate that the crystal belongs to the triclinic system, space group P-1, with cell parameters a = 0.781 nm, b = 0.823 nm, c = 1.049 nm, α = 92.4°, β = 95.8°, γ = 101.3°, and Z = 2. Based on the aforementioned pKa data (2-pyridinecarboxylic acid carboxyl group pKa = 4.8), its ΔpKa with eugenol is 5.2. This ΔpKa value falls within the range where partial proton transfer is likely to occur, which is consistent with the observed unique OH...O - The formation of ionic hydrogen bonds (bond length: 2.59 Å) alternates with the formation of a chain-like structure of OH…N neutral hydrogen bonds (bond length: 2.70 Å). Differential scanning calorimetry (DSC) shows a single melting peak at 152.7 °C with a melting range of 3.9 °C; the infrared spectrum is at 3290 cm⁻¹. -1 A broad peak was observed, confirming hydrogen bond formation; in the solid-state ¹³C NMR spectrum, the carbon signals at the C3 and C5 positions of the eugenol benzene ring shifted to the lower field by 1.3 ppm and 1.1 ppm, respectively. This ionic component has a significant impact on the H+ in the environment. + Its concentration is extremely sensitive, forming a molecular switch for pH-responsive release, which is the basis for a clear structure-activity relationship to achieve intelligent release function.

[0076] Comparative Example 1: A simple mixture of eugenol and nicotinamide was prepared using a conventional physical mixing method: 1.64 g of eugenol and 1.22 g of nicotinamide were thoroughly ground and mixed in a mortar for 30 minutes to obtain a uniform powder; the mixture was not subjected to any crystallization treatment and did not have an ordered supramolecular structure; it was mixed with urea at a mass ratio of 1:99 and applied to a simulated soil system to monitor the eugenol release behavior and nitrogen conversion inhibition effect.

[0077] The phase structure, lattice stability, release kinetic mechanism and final biological function of the products were systematically quantitatively compared, and the results are shown in Tables 1 and 2.

[0078] Table 1: Quantitative comparison of the structure and properties of eutectic products and physical mixtures;

[0079]

[0080] Table 2: Correlation data between pH-responsive release and structural integrity of eutectic products;

[0081]

[0082] * A first-order dynamic model was used for fitting.

[0083] Table 1 shows that the present invention successfully constructed a novel stable crystal phase (single melting point, novel XRPD pattern, high lattice energy), and its release mechanism changed from diffusion-controlled burst release of physical mixtures (first-order kinetics) to constant-rate or framework dissolution-type release dominated by crystal framework stability (zero-order / Higuchi kinetics). This fundamental mechanism change directly led to a significant extension of the inhibition function half-life.

[0084] Table 2 further quantifies the pH response threshold of the eutectic product, confirming its structural stability and slow release within a pH range of 5.0-8.0 (covering most soil environments); however, when the ambient pH deviates from this range, the crystal structure rapidly dissociates, accelerating the release. This demonstrates that the present invention can pre-program the intelligent response behavior of materials in complex environments through crystal engineering.

[0085] Furthermore, the long-term stability of the eutectic product obtained in Example 1 was tested: the sample was placed in an accelerated aging chamber with a relative humidity of 75% and a temperature of 40°C for 30 days, and samples were taken periodically for X-ray powder diffraction analysis; the results showed that the diffraction patterns at all time points were highly consistent with the initial sample, and no new peaks or peak shifts appeared, indicating that the eutectic still maintained crystal stability under high temperature and high humidity conditions; thermogravimetric analysis also showed that the aged sample had no mass loss below 100°C, confirming that there was no moisture absorption or solvent adsorption phenomenon.

[0086] In practical applications, a fluidized bed coating method is used to prepare eutectic-urea composite particles:

[0087] 5g of the eutectic product obtained in Example 1 was dissolved in an appropriate amount of ethanol-water (volume ratio 4:1) mixed solvent and diluted to 100mL to prepare a 5% (w / v) solution. 100g of urea granules (particle size 1-2 mm) were added to a fluidized bed coating machine. The inlet air temperature was set to 60℃ and the outlet air temperature to 40℃, and the fan was turned on to ensure the granules were in a good fluidized state. The eutectic solution was uniformly sprayed onto the surface of the urea granules at a rate of 0.5mL / min. After coating, the granules were dried at 50℃ for 2 hours. The resulting composite granules had a smooth surface, a uniform eutectic coating, and an eugenol loading of 2.4%. The composite granules were applied to potted rice in an experiment. A blank control (pure urea), a control with the same content of synergistic components (a physically mixed mixture of eugenol and nicotinamide, with the same amount added as the eugenol treatment group), and a commercially available synergist control (NBPT, added at the recommended dosage) were set up. The results showed that, under the same active ingredient (eugenol) dosage, the soil ammonium nitrogen concentration in the treatment group was consistently significantly higher than that in the control groups within 30 days after fertilization (p<0.05), nitrate nitrogen accumulation was reduced by approximately 42%, and nitrogen use efficiency of rice plants was increased by approximately 28% compared to the blank control group. No phytotoxicity symptoms were observed. Nitrogen use efficiency was calculated using the difference method: (nitrogen uptake by the plant - nitrogen uptake by the control plant) / nitrogen application rate × 100%.

[0088] In the preparation of composite particles by extrusion granulation, 2.9g of the eutectic product obtained in Example 2 and 97g of urea powder were added to a twin-screw extruder. The temperature of each section of the barrel was set to 50℃, and the screw speed was 80rpm. After the material was extruded through the die, it was cooled, crushed, and passed through a 1.0-2.0 mm sieve to obtain cylindrical composite particles. The particles have high mechanical strength and an average crushing force of 8.5N, which meets the requirements of mechanized fertilization. In a leaching simulation experiment in sandy soil, the results showed that under continuous rainfall simulation conditions (the cumulative leaching water volume is equivalent to 200 mm of precipitation), the cumulative leaching amount of eugenol to its initial total load (i.e., the loss rate) was only 11.3%, while the loss rate of the physical mixture under the same conditions reached 63.7%, which fully demonstrated the protective effect of the eutectic structure on the active ingredients.

[0089] The environmental response characteristics of the eutectic product described in this invention were also verified through a pH-triggered release experiment:

[0090] The eugenol product of Example 1 was dispersed in a series of buffer solutions with different pH values ​​(3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0), and the release of eugenol was measured after standing at 25°C for 24 hours. The results showed that the release rate was less than 20% in the pH range of 5.0 to 8.0. When the pH dropped to 4.0 or rose to 9.0, the release rate increased to 58.2% and 61.7%, respectively. Under the conditions of pH 3.0 and 10.0, the release rate exceeded 90% in 24 hours. This result confirms that the eugenol system has pH responsiveness and can accelerate release in slightly acidic soil environments (such as rhizosphere or microbial metabolic zones), while releasing slowly in neutral to weakly alkaline regions, thus achieving intelligent responsive release.

[0091] The comparative experiments are as follows: a comparison of the performance of the eutectic of the present invention with that of the prior art (CN118221502A scheme) and physical mixtures.

[0092] To demonstrate the outstanding substantive features and significant progress of the directional construction method and its products provided by this invention, the following systematic comparative experiments were conducted.

[0093] 1. Sample preparation:

[0094] Sample A (the present invention - nicotinamide cocrystal): prepared according to the method of Example 1.

[0095] Sample B (2-pyridinecarboxylic acid eutectic of the present invention): prepared according to the method of Example 2.

[0096] Sample C (Prior Art - Fatty Acid Cocrystal): Eugenol-stearic acid cocrystal was prepared strictly in accordance with the specific steps and all conditions (reactant molar ratio, hydrothermal temperature and time, etc.) disclosed in Example 2 of the prior art CN118221502A specification to ensure the objectivity of the comparison.

[0097] Sample D (physical mixture): an equimolar physical mixture of eugenol and nicotinamide, prepared according to Comparative Example 1.

[0098] 2. Comparison of structural definition and thermal stability:

[0099] X-ray powder diffraction (XRPD): Samples A and B both exhibit a set of sharp, novel characteristic diffraction peaks, confirming the formation of a single, long-range ordered novel crystalline phase. The spectrum of sample C mainly shows the superposition of the characteristic strong crystalline peaks of stearic acid and the diffuse peaks of eugenol, indicating that it may be a complex of simple coexistence of component crystals or a low degree of order, rather than a structurally defined novel eutectic phase. Sample D is a simple superposition of the spectra of the two components.

[0100] Differential scanning calorimetry (DSC): Samples A and B both show a single, sharp melting peak (melting range <5℃). The DSC curve of sample C shows a broad endothermic peak near the melting point of stearic acid, accompanied by volatilization weight loss, indicating poor thermal stability and phase purity. Sample D shows two independent endothermic peaks.

[0101] 3. Comparison of release kinetics and pH-responsive intelligence:

[0102] Sustained-release performance (pH 6.8 buffer): Eugenol release from sample A followed a near-zero order kinetic model, with a cumulative release rate of ~55% after 14 days. Release from sample B followed a Higuchi model, with a cumulative release rate of ~50% after 14 days. Release from samples C and D both followed a first-order kinetic model, with significant initial burst release, and cumulative release rates exceeding 85% and 95% after 14 days, respectively.

[0103] pH responsiveness: In pH 4.0 buffer, the release rates of samples A and B increased sharply to approximately 60% within 24 hours, exhibiting a clear "on / off" response. The release rate of sample C did not change significantly at different pH values ​​(<15%), indicating that its structure lacks a proton transfer-based intelligent response mechanism. Sample D was rapidly released at all pH values.

[0104] 4. Comparison of agricultural functional durability (soil incubation simulation):

[0105] Samples A, C, and D with equal eugenol content were combined with urea and then subjected to soil culture experiments.

[0106] Urease inhibition half-life: Based on the soil urease activity recovery curve, the inhibition half-life of treatment group A exceeded 14 days, treatment group C was about 5-7 days, and treatment group D was less than 3 days.

[0107] The above comparative data fully demonstrates that the cocrystal constructed by the present invention based on rational molecular design (specific pKa, length, functional group screening) and directional crystallization process has achieved unexpected technical effects that are significantly superior to existing technologies (fatty acid cocrystals) and physical mixtures in terms of structural clarity, thermal stability, controllable release behavior (slow release and intelligent response), and ultimately long-term inhibitory function.

[0108] This invention establishes a quantitative correlation model between the macroscopic sustained-release performance of cocrystals and microscopic molecular parameters such as the ΔpKa value, molecular geometry, and receptor site characteristics between ligands and active molecules. This transforms performance from "experimental screening discovery" to "computationally guided targeted acquisition," overcoming the blindness of empirical design. Simultaneously, by selecting ligands with different ΔpKa and topological structures (such as nicotinamide or 2-pyridinecarboxylic acid), the release triggering mechanism (such as a specific pH response threshold) and release kinetic mode (such as zero-order or Higuchi release) of the cocrystal product can be pre-encoded, achieving rational design of the material's environmental response behavior. Products obtained based on the above principles exhibit a synergistic enhancement effect in structural stability (manifested as a single melting peak and melting range <5℃), intelligent environmental response (pH-triggered release), and long-lasting agricultural functionality (significantly prolonged half-life of the inhibitory function). Their overall performance far surpasses that of cocrystals (such as fatty acid cocrystals) or physical mixtures obtained based on empirical screening, solving the core application problems of uncontrollable release of active components and short-lasting inhibitory effects.

[0109] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0110] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the directional construction of eugenol-based supramolecular eutectic systems, characterized in that, Includes the following steps: Eugenol was selected as the hydrogen bond donor molecule, and the molecular structure of eugenol contained a benzene ring substituted with a phenolic hydroxyl group and an ortho-methoxy group. Based on the screening criteria of a hydrogen bond acceptor strength parameter pKa value ranging from 3.3 to 6.0, a molecular length between 0.7 nm and 1.2 nm, and the presence of at least one sp² hybridized nitrogen atom or carbonyl oxygen atom, cocrystal ligands were determined. The cocrystal ligands were selected from nicotinamide and 2-pyridinecarboxylic acid. Eugenol and the cocrystal ligand are dissolved in a mixed solvent system at a molar ratio of 1:

1. The mixed solvent system is composed of a polar aprotic solvent and a low polar protic solvent at a volume ratio of 3:1 to 5:

1. The polar aprotic solvent is acetonitrile or acetone, and the low polar protic solvent is n-butanol or isopropanol. The obtained solution was placed in a temperature-controlled crystallization apparatus and cooled uniformly from an initial temperature of 45°C to 5°C at a rate of 0.2°C / min to 0.5°C / min. The solution was then aged at 5°C for 12 to 24 hours to precipitate a cocrystallized product. The cocrystallized product was collected and vacuum dried to obtain a eugenol-based supramolecular cocrystallized product.

2. The method for directional construction of the eugenol-based supramolecular eutectic system according to claim 1, characterized in that, The co-crystal ligand is nicotinamide. The pyridine nitrogen atom in the nicotinamide molecule and the amide carbonyl oxygen atom form a two-site hydrogen bond acceptor, which forms O–H…N hydrogen bonds and O–H…O hydrogen bonds with the phenolic hydroxyl group of the eugenol. The planar structure of the nicotinamide and the benzene ring of the eugenol form a face-to-face π–π stacking with a stacking spacing of 0.35 nm to 0.38 nm.

3. The method for directional construction of the eugenol-based supramolecular eutectic system according to claim 2, characterized in that, The eutectic product belongs to the monoclinic crystal system, with space group P21 / c, and cell parameters a ranging from 1.19 nm to 1.23 nm, b ranging from 0.87 nm to 0.91 nm, c ranging from 1.51 nm to 1.55 nm, and β angle ranging from 97.5° to 99.5°.

4. The method for directional construction of the eugenol-based supramolecular eutectic system according to claim 1, characterized in that, The co-crystallized ligand is 2-pyridinecarboxylic acid, and the carboxylic acid group undergoes partial deprotonation during crystallization, forming O–H…O with the phenolic hydroxyl group of the eugenol. - Ionic hydrogen bonds are formed, and at the same time, the pyridine ring nitrogen atom of the 2-pyridinecarboxylic acid accepts the phenolic hydroxyl proton of another molecule of eugenol to form O–H…N neutral hydrogen bonds, thus constructing an alternating chain of ionic-neutral hydrogen bonds in the crystal lattice.

5. The method for directional construction of the eugenol-based supramolecular eutectic system according to claim 4, characterized in that, The ionic-neutral hydrogen bond chain extends along the [010] direction, and adjacent chains are connected by weak C–H…π interactions; the eutectic product belongs to the triclinic crystal system, space group P-1, with unit cell parameters a of 0.76 nm to 0.80 nm, b of 0.80 nm to 0.84 nm, c of 1.03 nm to 1.07 nm, α angle of 91.3° to 93.3°, β angle of 94.7° to 96.7°, and γ angle of 100.2° to 102.2°.

6. The method for directional construction of the eugenol-based supramolecular eutectic system according to claim 1, characterized in that, The dielectric constant of the mixed solvent system is between 18 and 25.

7. An eugenol-nicotinamide supramolecular cocrystal product prepared by the method according to any one of claims 1, 2, 3, and 6, characterized in that, The X-ray powder diffraction pattern of the eutectic product has characteristic diffraction peaks at 2θ of 12.5°±0.2°, 16.8°±0.2° and 24.3°±0.2°; its differential scanning calorimetry pattern has a single melting endothermic peak in the range of 155°C to 165°C, and the melting range width does not exceed 5°C.

8. A supramolecular cocrystal product of eugenol-2-pyridinecarboxylic acid prepared by the method according to any one of claims 1, 4, 5, and 6, characterized in that, The X-ray powder diffraction pattern of the eutectic product has characteristic diffraction peaks at 2θ of 10.2°±0.2°, 14.7°±0.2° and 26.1°±0.2°; its differential scanning calorimetry pattern has a single melting endothermic peak in the range of 150°C to 155°C, and the melting range width does not exceed 5°C.

9. The eugenol-based supramolecular eutectic product according to claim 7, characterized in that, The eutectic product has a solubility of 0.8 mg / mL to 2.5 mg / mL in water at 25°C; it dissolves slowly in environments with a pH of 5.0 to 8.0, and its structure can be maintained for a relatively long time; when the ambient pH is below 4.5 or above 9.0, the hydrogen bond network is more easily dissociated.

10. A slow-release nitrogen fertilizer, characterized in that, The product comprises urea and the eugenol-based supramolecular cocrystal product according to any one of claims 7 to 9, wherein the amount of the cocrystal product added is 0.5% to 5.0% of the quality of the urea.

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