Method for regulating the motion of polyrotaxane molecules

Abstract

The application discloses a method for regulating the motion of polyrotaxane ring molecules, which is characterized by connecting part of coaxially adjacent ring molecules through chemical bonds to realize the regulation of the activity degree of the ring molecules. The application adds a bridging agent to a polyrotaxane system, and utilizes the bridging agent to bridge the hydroxyl groups of coaxially adjacent ring molecules to regulate the locking degree of the polyrotaxane ring molecules, so as to obtain a locking polyrotaxane. By adjusting the concentration of the bridging agent, the locking degree of coaxially adjacent ring molecules in the polyrotaxane material can be accurately regulated, the structural characteristics at the molecular level are converted into the macroscopic performance of the material, and the precise regulation of the motion of the polyrotaxane ring molecules and the performance of the material is realized. The locking polyrotaxane prepared by the method regulates the motion of the ring molecules by covalent bonds, is more controllable and repeatable than the environmental regulation mode, has obvious advantages in the biomedical field such as drug delivery, controlled release or preparation of tissue and cell scaffolds, and greatly improves the application potential of the polyrotaxane in the biomedical field.

Description

Technical Field

[0001] This invention belongs to the field of polyrotaxane material technology, specifically, it relates to a method for regulating the movement of polyrotaxane ring molecules. Background Technology

[0002] Molecular machines can controllably alter their spatial relative positions through mechanical motion to achieve specific design goals. They possess precise controllability, high selectivity, and flexibility, providing new tools and methods for the biomedical field. The emergence of artificial molecular machines such as rotaxanes, cyclohexanes, and molecular motors has made precise control of molecular motion possible. These breakthroughs enable synthetic materials to mimic the molecular motion mechanisms of living organisms at the molecular level, opening new avenues for designing more flexible and functional materials. Molecular motion is the core link between material structure and properties. By regulating molecular motion, molecular-level structural features can be transformed into macroscopic material properties, thereby achieving precise adjustment of material properties. Polyrotaxanes are another typical example of molecular machines, assembled from a chain molecule (axis) and multiple cyclic molecules through host-guest interactions, with large molecules (end-capping agents) at both ends of the axis preventing the rings from falling off. Unlike traditional polymers, the cyclic units in polyrotaxanes are connected to the axis units by mechanical bonds rather than traditional covalent bonds, allowing the cyclic molecules to slide and rotate relatively freely on the axis, thus possessing molecular dynamics. The unique structural complexity and higher degrees of freedom at the molecular level of polyrotaxane molecules make them more similar to functional biomolecules with complex structures found in nature. Furthermore, the dynamics and mobility of the ring molecules can effectively enhance the interaction between the active structure modified on the ring molecule and the target molecule. Therefore, regulating the dynamics of polyrotaxane ring molecules is of great significance for optimizing their performance and improving their effectiveness in biomedical applications.

[0003] Existing methods for regulating the molecular motion of polyrotaxane ring molecules mainly include temperature, pH, and solvent. These external conditions influence the molecular motion of polyrotaxane ring molecules by affecting the interactions between ring molecules. Temperature changes directly affect the molecular motion of polyrotaxane ring molecules, primarily by altering the kinetic energy of the molecules and the intermolecular forces. As temperature increases, the kinetic energy of the molecules increases, and the thermal motion becomes more intense. For polyrotaxane, the kinetics of the ring molecules may be enhanced, making it easier for the ring molecules to slide or rotate on the axis. Changes in pH alter the interactions between polyrotaxane ring molecules; for example, changes in the acid-base environment may cause the hydrogen bonds on the ring molecules to break or recombine, thus affecting the relative motion of the ring molecules. Similarly, the properties of the solvent also have a significant impact on the molecular motion of polyrotaxane ring molecules, especially the solvent's polarity, solvation effect, and interactions with the polyrotaxane ring molecules. Polar solvents may interact with the polar groups on the polyrotaxane ring molecules, thus affecting the interactions between the ring molecules themselves. These methods of regulating the movement of polyrotaxane ring molecules by altering the external environment all change the non-covalent forces between ring molecules, resulting in poor controllability. Furthermore, due to the special and complex nature of the in vivo environment, they are difficult to be perfectly compatible with the internal environment of organisms. Over-reliance on these external environmental factors may lead to biosafety issues, thus limiting the widespread application of polyrotaxane materials in the biomedical field.

[0004] Therefore, it is of great significance to provide a method for finely controlling the movement of cyclic molecules in polyrotaxane to optimize its properties and improve its application in biomedicine. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned defects and shortcomings in the prior art and provide a method for regulating the molecular motion of polyrotaxane rings. By selecting a suitable bridging agent and adjusting its concentration, this invention can flexibly control the degree of ring-locking between coaxially adjacent ring molecules in polyrotaxane materials, thereby achieving precise regulation of the molecular motion of polyrotaxane ring molecules and the material properties.

[0006] A second objective of this invention is to provide a ring-locked polyrotaxane.

[0007] A third objective of this invention is to provide the application of the above-mentioned ring-locked polyrotaxane in the preparation of biomedical materials.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] This invention provides a method for regulating the movement of polyrotaxane cyclic molecules by connecting some coaxially adjacent cyclic molecules through chemical bonds, thereby achieving regulation of the degree of cyclic molecule activity.

[0010] Current methods for regulating the movement of polyrotaxane ring molecules through external stimuli often fail to achieve perfect compatibility with the internal environment of organisms, limiting the widespread application of polyrotaxane materials in the biomedical field. This invention proposes a method for precisely controlling the movement of polyrotaxane ring molecules through ring-locking. By selecting a suitable bridging agent and adjusting its concentration, the degree of ring-locking between coaxially adjacent ring molecules in the polyrotaxane material can be flexibly controlled, thereby achieving precise regulation of molecular motion and material properties. This method not only makes the movement behavior of polyrotaxane ring molecules more controllable, but more importantly, a series of polyrotaxane materials prepared using this method can achieve different ring molecule movement characteristics without altering the internal environment of the organism, greatly enhancing the biomedical application potential of polyrotaxane materials.

[0011] This invention provides a ring-locked polyrotaxane, the polyrotaxane comprising an axial molecule, a ring molecule, a capped structure, and a linkage structure formed between coaxially adjacent ring molecules through a chemical reaction with hydroxyl groups on adjacent ring molecules; the axial molecule is polyethylene glycol or a polyethylene glycol block copolymer; the ring molecule is cyclodextrin.

[0012] Furthermore, the axial molecule is polyethylene glycol or a polyethylene glycol block copolymer with a molecular weight of 4000 to 35000 Da.

[0013] Preferably, the polyethylene glycol block copolymer is Pluronic L64, Pluronic F127, or Pluronic F68.

[0014] Furthermore, the cyclic molecule is one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

[0015] Furthermore, the end-capping structure is formed by the reaction of adamantane with the terminal carboxyl group of the axial molecule.

[0016] Furthermore, the connecting structure is composed of a bridging agent bridging the hydroxyl groups of coaxially adjacent ring molecules; the bridging agent is one of epichlorohydrin or diisocyanate compounds.

[0017] Furthermore, the concentration of epichlorohydrin used is 0–0.508 mol / L (excluding the case of a concentration of 0, 0 < C ≤ 0.508 mol / L). Different concentrations of bridging agents can regulate the degree of ring-locking of polyrotaxanes. Within a given range of bridging agent concentrations, bridging only occurs between coaxial ring molecules, while non-coaxial ring molecules do not form bridging bonds. This is because coaxial ring molecules are closest to each other and these ring molecules are strung on the same axis. Their diffusion direction in solution is relatively fixed, mainly exhibiting axial sliding. Therefore, bridging is more likely to occur between coaxial cyclodextrin molecules. Only bridging between coaxial ring molecules can effectively regulate the degree of ring-locking of individual polyrotaxane molecules. When the bridging agent concentration exceeds this range, non-coaxial bridging occurs between cyclodextrin molecules, leading to cross-linking between polyrotaxane molecules. Cross-linking between three or more polyrotaxane molecules may even occur, thus failing to effectively control the movement of ring molecules on the polyrotaxane axis. Gel permeation chromatography (GPC) analysis showed that within this bridging agent concentration range, the GPC spectrum exhibited a single peak shape, indicating the absence of cross-linking between polyrotaxane molecules.

[0018] Preferably, when the concentration of the bridging agent epichlorohydrin is ≤0.127 mol / L, after the bridging reaction is completed, the reaction solution is cooled to room temperature and subjected to dialysis to separate the ring-locked polyrotaxane; when the concentration of the bridging agent epichlorohydrin is between 0.127 mol / L and 0.508 mol / L, after the bridging reaction is completed, the reaction solution is cooled to room temperature and subjected to dialysis, followed by lyophilization to obtain the crude product, and then washing and filtration to obtain the ring-locked polyrotaxane.

[0019] Furthermore, the method of using epichlorohydrin involves dissolving polyrotaxane in a solution of sodium hydroxide, potassium hydroxide, or potassium tert-butoxide, and then adding epichlorohydrin. The role of sodium hydroxide is to deprotonate the hydroxyl groups on the polyrotaxane ring molecule, thereby increasing its nucleophilicity. Because polyrotaxane can dissolve in a 1 mol / L sodium hydroxide solution, and acid is generated during the reaction to neutralize some of the sodium hydroxide, the more bridging agent added, the more sodium hydroxide is consumed. Therefore, to ensure that the sodium hydroxide concentration in the reaction system is 1 mol / L after the reaction is complete, the amount of sodium hydroxide used will vary depending on the amount of bridging agent used to avoid precipitation.

[0020] Furthermore, the diisocyanate compound is terephthalic diisocyanate or o-phthalic diisocyanate.

[0021] Preferably, the method for adding the terephthalic diisocyanate is to dissolve polyrotaxane in DMSO and then add the terephthalic diisocyanate.

[0022] Furthermore, the average number of bridging bonds (connection structures) on each polyrotaxane ring molecule in the ring-locked polyrotaxane is 1 to 6.

[0023] As a preferred embodiment, the present invention provides a specific preparation method for ring-locked polyrotaxane, comprising the following steps:

[0024] S1. Polyrotaxane was synthesized via a heterogeneous reaction using polyethylene glycol (molecular weight ranging from 4000 to 35000 Da) as the axial molecule, α-cyclodextrin as the cyclic molecule, and adamantane as the end-capping agent.

[0025] S2. Dissolve polyrotaxane in sodium hydroxide solution, and slowly add epichlorohydrin as a bridging agent. The hydroxyl groups on the bridging ring molecules lock the ring molecules to control the molecular motion of the polyrotaxane ring molecules, thus obtaining ring-locked polyrotaxane.

[0026] Further, step S1 involves first carboxylating the end of polyethylene glycol, then reacting it with α-cyclodextrin to obtain a quasi-polyrotaxane intermediate, and finally reacting the quasi-polyrotaxane intermediate with adamantane to obtain the final product, polyrotaxane.

[0027] Specifically, when the concentration of the bridging agent epichlorohydrin is ≤0.127 mol / L, after the reaction in step S2, the reaction solution is cooled to room temperature and dialyzed to separate the ring-locked polyrotaxane. When the concentration of the bridging agent epichlorohydrin is between 0.127 mol / L and 0.508 mol / L, after the reaction in step S2, the reaction solution is cooled to room temperature and dialyzed, then lyophilized to obtain the crude product, followed by washing and filtration to obtain the ring-locked polyrotaxane. Based on the above steps, polyrotaxanes with different degrees of ring locking can be obtained. The molecular motion rate of the ring molecules can be characterized by variable-temperature NMR, and the polyrotaxane materials prepared by this control method can be used in vivo.

[0028] Polyrotaxane has significant applications in the biomedical field. For example, it can be used as a drug delivery carrier. By utilizing its molecular motion properties, polyrotaxane can slowly deliver drugs to where they are needed in the body. This is particularly beneficial for patients with chronic diseases requiring long-term medication, significantly reducing the frequency of drug administration and improving treatment efficacy. Secondly, polyrotaxane also has important applications in tissue engineering. It can serve as a scaffold material, aiding cell growth and tissue repair. Its molecular motion properties allow for the construction of scaffolds with suitable microenvironments, providing a good growth platform for cells. Furthermore, polyrotaxane can be used to prepare high-performance biomedical composite materials. By mixing it with other materials, polyrotaxane can significantly improve the properties of composite materials, such as toughness and corrosion resistance, thus meeting the high performance requirements of materials in the biomedical field. By precisely controlling the molecular motion of the ring molecules on polyrotaxane through a ring-locking mechanism, polyrotaxane materials with different molecular motion properties can be applied in vivo. Moreover, ring-locked polyrotaxane, through covalent bonds linking the ring molecules on the coaxial axis, can maintain molecular structural stability under a wider range of environmental conditions. By bridging the ring molecules, the degree of ring-locking of polyrotaxanes can be precisely controlled, thereby adjusting their physicochemical properties. This precise control is more controllable and reproducible compared to environmental regulation methods (such as temperature and pH). In certain biological environments, changes in environmental factors can lead to instability in the movement of polyrotaxanes. Ring-locked polyrotaxanes, by regulating the molecular motion of their ring molecules, offer a solution relatively independent of external conditions, making them more advantageous in biomedical applications such as drug delivery.

[0029] Therefore, the present invention provides the application of the above-mentioned ring-locked polyrotaxane in the preparation of biomedical materials.

[0030] Furthermore, the biomedical material is a material used for drug delivery, controlled release, or preparation of tissue and cell scaffolds.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] This invention provides a method for regulating the movement of polyrotaxane ring molecules. The method involves connecting some coaxially adjacent ring molecules through chemical bonds to adjust the degree of ring molecule activity. This invention adds a bridging agent to the polyrotaxane system, utilizing the bridging agent to bridge the hydroxyl groups of coaxially adjacent ring molecules to regulate the ring-locking degree of the polyrotaxane ring molecules, obtaining a ring-locked polyrotaxane. The polyrotaxane includes an axial molecule, ring molecules, end-capped structures, and connection structures formed between coaxially adjacent ring molecules through chemical reactions with the hydroxyl groups on adjacent ring molecules. The axial molecule is polyethylene glycol or a polyethylene glycol block copolymer; the ring molecules are cyclodextrins. By adjusting the concentration of the bridging agent, the ring-locking degree of coaxially adjacent ring molecules in the polyrotaxane material can be precisely controlled, transforming molecular-level structural characteristics into macroscopic material properties, thereby achieving precise regulation of the molecular movement of polyrotaxane ring molecules and material properties. The ring-locked polyrotaxane prepared by this method controls molecular motion by locking the ring molecules with covalent bonds. Compared with environmental regulation, it is more controllable and reproducible, and has significant advantages in biomedical fields such as drug delivery, controlled release, or preparation of tissue and cell scaffolds, greatly enhancing the application potential of polyrotaxane in biomedicine. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the synthesis of ring-locked polyrotaxane.

[0034] Figure 2 The proton NMR spectrum of polyrotaxane PR ( 1 H NMR, DMSO-d6, 298K).

[0035] Figure 3 The 1H NMR spectrum of the ring-locked polyrotaxane PR(1.1) prepared according to Example 1 ( 1 H NMR, DMSO-d6, 298K).

[0036] Figure 4 The 1H NMR spectrum of the ring-locked polyrotaxane PR(2.1) prepared according to Example 2 ( 1 H NMR, DMSO-d6, 298K).

[0037] Figure 5 The 1H NMR spectrum of the ring-locked polyrotaxane PR(3.8) prepared according to Example 3 ( 1 H NMR, DMSO-d6, 298K).

[0038] Figure 6 The 1H NMR spectrum of the ring-locked polyrotaxane PR (5.9) prepared according to Example 4 ( 1 H NMR, DMSO-d6, 298K).

[0039] Figure 7Temperature-dependent nuclear magnetic resonance (VT) spectrum of polyrotaxane PR 1 H NMR, DMSO-d6).

[0040] Figure 8 Temperature-dependent nuclear magnetic resonance (VT) spectrum of the ring-locked polyrotaxane PR(1.1) prepared according to Example 1. 1 H NMR, DMSO-d6).

[0041] Figure 9 Temperature-dependent nuclear magnetic resonance (VT) spectrum of the ring-locked polyrotaxane PR(2.1) prepared according to Example 2. 1 H NMR, DMSO-d6).

[0042] Figure 10 Temperature variable magnetic resonance (VT) spectrum of the ring-locked polyrotaxane PR(3.8) prepared according to Example 3. 1 H NMR, DMSO-d6).

[0043] Figure 11 Temperature-dependent nuclear magnetic resonance (VT) spectrum of the ring-locked polyrotaxane PR (5.9) prepared according to Example 4. 1 H NMR, DMSO-d6).

[0044] Figure 12 Gel permeation chromatograms of the ring-locked polyrotaxanes prepared according to Examples 1-4. Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0046] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0047] Example 1 Synthesis of polyrotaxane and polyrotaxane ring-locking reaction

[0048] I. Synthesis Method

[0049] (1) Synthesis of terminal carboxylated polyethylene glycol

[0050] Weigh 30 g of polyethylene glycol (35k-PEG, 30.0 g, 0.86 mmol, -OH 1.7 mmol) into a reaction flask, add 300 mL of pure water, and stir until the PEG is completely dissolved. Then add 2,2,6,6-tetramethylpiperidine oxide (TEMPO, 300 mg, 1.92 mmol) to the above solution and stir until completely dissolved. Subsequently, add sodium bromide (NaBr, 3.0 g, 30 mmol) and sodium hypochlorite (NaClO, 15 mL, available chlorine >5.0%) solutions sequentially, and stir the reaction at room temperature for 15 minutes. After the reaction is complete, add 10 mL of ethanol to quench the reaction, and then adjust the pH to <2 with hydrochloric acid solution. Extract the reaction solution with dichloromethane, collect the lower organic phase, concentrate it by rotary evaporation, slowly pour the concentrate into diethyl ether to precipitate, collect the precipitate by filtration, and dry it under vacuum to obtain terminal carboxylated polyethylene glycol 35k-PEG-(COOH)2.

[0051] (2) Synthesis of polyrotaxane

[0052] Terminally carboxylated polyethylene glycol (35k-PEG-(COOH)2, 12.0 g, 0.34 mmol) and α-cyclodextrin (α-CD, 48.0 g, 49.4 mmol) were dissolved separately in deionized water, with 35k-PEG-(COOH)2 dissolved in 60 mL of pure water and α-CD dissolved in 300 mL of pure water (heating in a 60°C water bath can promote dissolution). Subsequently, the 35k-PEG-(COOH)2 aqueous solution was slowly added dropwise to the α-CD aqueous solution, with the system being stirred uniformly during the addition. After the addition was complete, the reaction system was continuously stirred at 60°C for 6 hours, allowing the hydrophobic segments of 35k-PEG-(COOH)2 and the cavity of α-CD to self-assemble into a quasi-polyrotaxane structure through host-guest interactions. After the reaction was completed, the resulting white paste was freeze-dried to remove the solvent, yielding the quasi-polyrotaxane (PPR) intermediate product.

[0053] Next, quasi-polyrotaxane (PPR, 15.0 g, 0.09 mmol), 1-adamantaneamine (Ad-NH2, 1.3 g, 8.6 mmol), and Carter's condensing agent (BOP, 0.38 g, 0.86 mmol) were weighed into a reaction vessel and thoroughly mixed by solid shaking or mechanical stirring. Then, approximately 5 mL of anhydrous N,N-dimethylformamide (DMF) was slowly added dropwise to wet the reaction system, followed by dropwise addition of N,N-diisopropylethylamine (DIPEA, 0.15 mL, 0.86 mmol) dispersed in 1 mL of anhydrous DMF. The addition of anhydrous DMF continued until a thick slurry was formed. The amount of DMF used was strictly controlled and the volume added was recorded to ensure the reaction system remained heterogeneous. The reaction mixture was stirred continuously overnight at 4°C to allow the terminal carboxyl groups of 1-adamantaneamine and quasi-polyrotaxane to undergo an amidation reaction catalyzed by BOP and DIPEA. After the reaction was complete, the product was washed twice with a DMF / methanol (1:1, v / v) mixture and twice with methanol, with stirring for 30 minutes each time. The washed product was dissolved in an appropriate amount of DMSO and then added to water for recrystallization. The precipitate was collected by centrifugation (10,000 rpm, 10 minutes), and then washed with excess water to remove excess solvent and impurities. The resulting grayish-white solid was freeze-dried to obtain adamantane-terminated polyrotaxane (PR).

[0054] (3) Polyrotaxane ring-locking reaction

[0055] The end-capped polyrotaxane was dissolved in a 1.01 mol / L, 3 mL sodium hydroxide aqueous solution. After complete dissolution, the reaction solution was heated to 60 °C, and epichlorohydrin (EPI, bridging agent, 15 μL) was slowly added dropwise. At this point, the final concentration of epichlorohydrin was 0.0635 mol / L. The system was reacted at 60 °C for 24 hours. After the reaction was completed, the reaction solution was cooled to room temperature and dialyzed to remove small molecule impurities. The dialysate was centrifuged, and the white precipitate was separated, lyophilized, and the ring-locked polyrotaxane was obtained, denoted as PR(1.1).

[0056] II. Result Verification

[0057] A schematic diagram of the synthesis of ring-locked polyrotaxanes is shown below. Figure 1 As shown, the axial molecule passes through the cavity of the ring molecule through host-guest interactions, and the ends of the axial molecule are sealed with sterically hindered groups to prevent the ring molecule from sliding out. The ring molecule on the polyrotaxane axis can slide and rotate along the axis.

[0058] The proton NMR spectrum of polyrotaxane PR ( 1 H NMR, DMSO-d6, 298K) such as Figure 2As shown, free cyclodextrin molecules have a high diffusion rate, allowing them to move rapidly and freely in solution. This results in a relatively singular and uniform signal distribution, leading to high and sharp characteristic peaks in NMR spectra. However, when cyclodextrin is attached to a polyethylene glycol (PEG) axis to form a polyrotaxane structure, its diffusion rate is affected by the PEG chain. Due to the large molecular weight of the PEG chain, its hydrodynamic volume in solution is large, resulting in more complex forces. Forces in different directions may cancel each other out, making it difficult to form a resultant force driving molecular motion, thus leading to a lower diffusion rate. When cyclodextrin molecules are fixed to the PEG chain, this structural confinement effect reduces the diffusion rate, causing the characteristic peaks to become shorter and wider. The short and wide characteristic peaks of cyclodextrin can be seen in the 1H NMR spectrum of polyrotaxane, indicating that the cyclodextrin molecules have been effectively confined to the PEG axis, proving the successful synthesis of polyrotaxane. Further analysis of the NMR data revealed that the average number of rings per axis in the polyrotaxane molecule was 105, and the ring-crossing rate was 26.5%.

[0059] To achieve precise control over the motion of ring molecules along the polyethylene glycol axis, epichlorohydrin was used as a bridging agent. This bridging strategy utilizes the reaction between epichlorohydrin molecules and the hydroxyl groups on cyclodextrin molecules to form stable covalent bonds, thereby restricting the free rotation of the ring molecules along the polyethylene glycol axis. The 1H NMR spectrum of the prepared ring-locked polyrotaxane PR(1.1) was obtained when the epichlorohydrin concentration was 0.0635 mol / L. 1 H NMR, DMSO-d6, 298K) such as Figure 3 As shown, through integral calculation, the average number of rings per axis of the ring-locked polyrotaxane PR (1.1) is 105, the ring-crossing rate is 26.5%, and the average number of bridging bonds per ring is 1.1.

[0060] Example 2: Polyrotaxane ring-locking reaction

[0061] I. Synthesis Method

[0062] The method for synthesizing polyrotaxane is the same as that in Examples 1 and 1 (2), except that:

[0063] (3) The end-capped polyrotaxane was dissolved in NaOH aqueous solution (1.03 mol / L, 3 mL). After complete dissolution, the reaction solution was heated to 60 °C, and epichlorohydrin (EPI, 30 μL) was slowly added dropwise. At this point, the final concentration of epichlorohydrin was 0.127 mol / L. The system was reacted at 60 °C for 24 hours. After the reaction was completed, the reaction solution was cooled to room temperature and dialyzed to remove small molecule impurities. The dialysate was centrifuged to separate the white precipitate, which was then lyophilized to obtain the ring-locked polyrotaxane, denoted as PR(2.1).

[0064] II. Result Verification

[0065] The 1H NMR spectrum of the prepared ring-locked polyrotaxane PR(2.1) when the concentration of epichlorohydrin used was 0.127 mol / L ( 1 H NMR, DMSO-d6, 298K) such as Figure 4 As shown, through integral calculation, the average number of rings per axis of the ring-locked polyrotaxane PR (2.1) is 105, the ring-crossing rate is 26.5%, and the average number of bridging bonds per ring is 2.1.

[0066] Example 3: Polyrotaxane ring-locking reaction

[0067] I. Synthesis Method

[0068] The method for synthesizing polyrotaxane is the same as that in Examples 1 and 1 (2), except that:

[0069] (3) The end-capped polyrotaxane was dissolved in NaOH aqueous solution (1.05 mol / L, 3 mL). After complete dissolution, the reaction solution was heated to 60 °C, and epichlorohydrin (EPI, 60 μL) was slowly added dropwise. At this time, the final concentration of epichlorohydrin was 0.254 mol / L. The system was reacted at 60 °C for 24 hours. After the reaction was completed, the reaction solution was cooled to room temperature and dialyzed to remove small molecule impurities. Then, it was lyophilized to obtain crude product. The lyophilized crude product was washed with an appropriate amount of anhydrous dichloromethane and stirred at room temperature for 24 hours. A white solid product was obtained by filtration and vacuum drying at room temperature for 24 hours to obtain the ring-locked polyrotaxane, denoted as PR(3.8).

[0070] II. Result Verification

[0071] The 1H NMR spectrum of the prepared ring-locked polyrotaxane PR(3.8) when the concentration of epichlorohydrin used was 0.254 mol / L ( 1 H NMR, DMSO-d6, 298K) such as Figure 5As shown, through integral calculation, the average number of rings per axis of the ring-locked polyrotaxane PR (3.8) is 105, the ring-crossing rate is 26.5%, and the average number of bridging bonds per ring is 3.8.

[0072] Example 4: Polyrotaxane ring-locking reaction

[0073] I. Synthesis Method

[0074] The method for synthesizing polyrotaxane is the same as that in Examples 1 and 1 (2), except that:

[0075] (3) The end-capped polyrotaxane was dissolved in NaOH aqueous solution (1.1 mol / L, 3 mL). After complete dissolution, the reaction solution was heated to 60 °C, and epichlorohydrin (EPI, 120 μL) was slowly added dropwise. At this time, the final concentration of epichlorohydrin was 0.508 mol / L. The system was reacted at 60 °C for 24 hours. After the reaction was completed, the reaction solution was cooled to room temperature and dialyzed to remove small molecule impurities. Then, it was lyophilized to obtain crude product. The lyophilized crude product was washed with an appropriate amount of anhydrous dichloromethane and stirred at room temperature for 24 hours. A white solid product was obtained by filtration and vacuum drying at room temperature for 24 hours to obtain the ring-locked polyrotaxane, denoted as PR(5.9).

[0076] II. Result Verification

[0077] The 1H NMR spectrum of the prepared ring-locked polyrotaxane PR(5.9) when the concentration of epichlorohydrin used was 0.508 mol / L ( 1 H NMR, DMSO-d6, 298K) such as Figure 6 As shown, through integral calculation, the average number of rings per axis of the ring-locked polyrotaxane PR (5.9) is 105, the ring-crossing rate is 26.5%, and the average number of bridging bonds per ring is 5.9.

[0078] By adjusting the amount of bridging agent and reaction conditions, polyrotaxanes with different degrees of ring-locking can be synthesized. Figures 3-6 The proton NMR spectra of the ring-locked polyrotaxanes PR(1.1), PR(2.1), PR(3.8), and PR(5.9) prepared according to Examples 1–4 are shown. 1 The successful synthesis of cyclic polyrotaxane was confirmed by the characteristic peaks of the newly formed bridging bonds (H NMR, DMSO-d6, 298K). Further analysis of the reduced number of cyclodextrin hydroxyl groups in the NMR spectrum can infer the number of bridging bonds on each cyclodextrin molecule.

[0079] Example 5: Investigating the relationship between molecular motion of ring molecules on the polyrotaxane axis and the degree of ring locking.

[0080] To further investigate the relationship between the molecular motion of ring molecules on the polyrotaxane axis and the degree of ring locking, polyrotaxane solutions with different degrees of ring locking were prepared, ensuring that the molar concentration of ring molecules was the same for each sample. Temperature-variable-temperature nuclear magnetic resonance (TMR) spectroscopy was performed in the range of 25–80 °C. 1 The H NMR experiment was used to observe the changes in the cyclic molecular motion of ring-locked polyrotaxane under different temperature conditions.

[0081] The results are as follows Figure 7 The image shows the temperature-dependent NMR spectrum of polyrotaxane PR. Figures 8-11 The following are the temperature-dependent NMR spectra of the ring-locked polyrotaxanes PR (1.1), PR (2.1), PR (3.8), and PR (5.9) prepared according to Examples 1-4, respectively. The differences in cyclic molecular motion are reflected in the changes in the peak shapes of the cyclic molecules -OH-2,3, H-1, and OH-6 with temperature. As the temperature increases from 25℃ to 80℃, the peak shapes become higher and narrower, and the signal becomes stronger, indicating that the molecular motion of the cyclic molecules is faster. Figures 7-11 As can be seen, the cyclic molecular motion of polyrotaxanes with different degrees of ring-locking exhibits significant differences. Specifically, when the temperature is increased from 25℃ to 80℃, the characteristic peaks of -OH-2,3, H-1, and OH-6 in PR and PR(1.1) samples show the most significant changes in peak shape with increasing temperature. The peak shapes become sharper and the signal intensity increases with increasing temperature, indicating that the cyclodextrin molecules in these samples have relatively fast molecular motion. In contrast, the characteristic peak shapes of the cyclic molecules in the ring-locked polyrotaxanes PR(2.1) and PR(3.8) show smaller changes than those in PR(1.1), indicating that the cyclic molecular motion speed in these samples is relatively slow. In comparison, the characteristic peaks of the cyclic molecules in the ring-locked polyrotaxane PR(5.9) show almost no significant changes with increasing temperature, indicating that its cyclic molecular motion speed is the slowest.

[0082] Based on the above experimental data, as the degree of ring locking increases, the bridging effect between ring molecules strengthens, restricting the free rotation of molecules and causing the motion of ring molecules to gradually slow down. This is ultimately manifested as smaller peak changes and weaker signal enhancement in the temperature-dependent NMR spectrum. Therefore, it is possible to... Figures 7-11 Based on temperature-dependent NMR data, it can be inferred that the degree of ring-locking of polyrotaxane directly affects the mobility of its on-axis ring molecules. The higher the degree of ring-locking, the more restricted the molecular motion is, and the molecular motion of the polyrotaxane ring molecules can be controlled to a certain extent.

[0083] Gel permeation chromatography (GPC) spectra of polyrotaxanes and the ring-locked polyrotaxanes prepared according to Examples 1-4 are shown below. Figure 12As shown in the graphs, analysis reveals that the efflux time of polyrotaxane before and after ring locking changes very little, indicating that the molecular weight does not increase significantly. This suggests that, at a given bridging agent concentration, polyrotaxane does not undergo large-scale cross-linking during ring locking; the bridging agent primarily functions to form bridging bonds between coaxially adjacent cyclodextrin molecules.

[0084] Example 6 Synthesis of Ring-locked Polyrotaxane

[0085] The method for synthesizing polyrotaxane (PR) is as described in steps (1) and (2) of Example 1.

[0086] 1 g of polyrotaxane was dissolved in 30 mL of anhydrous dimethyl sulfoxide (DMSO). Under nitrogen protection, dibutyltin dilaurate (DBTDL, 20 μL) was added sequentially as a catalyst, and 2,6-di-tert-butyl-p-cresol (BHT, 1.0 mg, 0.0047 mmol) pre-dissolved in 3 mL of anhydrous DMSO. Subsequently, terephthalic diisocyanate (62 mg, 160 g / mol) dissolved in 3 mL of anhydrous DMSO was slowly added dropwise. After stirring until homogeneous, the reaction was carried out at 40 °C for 12 h. After the reaction was completed, the resulting reaction solution was slowly poured into excess ice-cold acetone to precipitate the product. The precipitate was collected by centrifugation. The precipitate was washed with acetone and then dried under vacuum to obtain the final product.

[0087] Experimental results show that terephthalic diisocyanate can also be used as a bridging agent to regulate the ring-locking degree of polyrotaxane molecules.

Claims

1. A ring-locked polyrotaxane, characterized in that, The polyrotaxane comprises axial molecules, cyclic molecules, end-capped structures, and a linkage structure formed by the chemical reaction of coaxially adjacent cyclic molecules with hydroxyl groups on adjacent cyclic molecules; the axial molecules are polyethylene glycol or polyethylene glycol block copolymers; the cyclic molecules are cyclodextrins; the linkage structure is composed of a bridging agent bridging the hydroxyl groups of coaxially adjacent cyclic molecules; the bridging agent is one of epichlorohydrin or diisocyanate compounds; the concentration of epichlorohydrin used is 0 < c ≤ 0.508 mol / L.

2. The ring-locked polyrotaxane according to claim 1, characterized in that, The cyclic molecule is one of α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin.

3. The ring-locked polyrotaxane according to claim 1, characterized in that, The end-capped structure is formed by the reaction of adamantane with the terminal carboxyl group of the axial molecule.

4. The ring-locked polyrotaxane according to claim 1, characterized in that, The diisocyanate compounds are terephthalic diisocyanate and o-phthalic diisocyanate.

5. The ring-locked polyrotaxane according to claim 1, characterized in that, The average number of linkages on each polyrotaxane ring molecule in the ring-locked polyrotaxane is 1 to 6.

6. The use of the ring-locked polyrotaxane according to any one of claims 1 to 5 in the preparation of biomedical materials.

7. The application according to claim 6, characterized in that, The biomedical material is used for drug delivery, controlled release, or preparation of tissue and cell scaffolds.

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