An ultrahigh chiral covalent organic framework, preparation method and application

Abstract

This invention provides an ultra-chiral covalent organic framework, its preparation method, and its applications, belonging to the field of chiral covalent organic framework materials. It aims to solve the technical problem of racemization of chiral signals caused by existing high-temperature synthesis methods. First, a C3-symmetric aldehyde monomer is reacted with a chiral monoamine in an alcohol solvent to generate a 1:1 precursor molecule. Then, an achiral diamine is added, and ligand exchange and chiral transfer are performed at room temperature to form a trilobal propeller-structured macromolecule with pure uniform chirality. Finally, long-range conjugation and crystallization are completed via a water bath or air bath, followed by washing and drying to obtain the target product. The obtained material exhibits ultra-high chiral signal, with a circular dichroism spectral signal intensity CD≈±2,000 mdeg and an asymmetry factor g. abs The chiral stability reached ±0.085, and a cascade chiral amplification effect of up to 200-fold was observed. Furthermore, the material exhibited excellent chiral stability, maintaining its stability for at least 5 years. In addition, it can be used as a recognition reagent, capable of distinguishing at least seven pairs of amino acid enantiomers and five other small molecule enantiomers.

Description

Technical Field

[0001] This invention relates to the field of chiral covalent organic framework materials and chiral molecule recognition technology, specifically to an ultra-chiral covalent organic framework, its preparation method, and its applications. Background Technology

[0002] Chirality is a fundamental law of the universe and life, determined by its inherent energy and information. Major human diseases, such as malignant tumors, can be considered deviations from the correct path of life, requiring effective correction using chiral substances and energy. Therefore, it can be inferred that certain ultra-high signal chiral materials should possess the ability to correct these deviations. Currently, significant progress has been made in the preparation and application of chiral nanomaterials. However, methods for manufacturing ultra-high signal chiral materials, especially simple, environmentally friendly, and room-temperature synthesis methods, still face enormous challenges.

[0003] Biomolecules are typically chiral. The asymmetric nature of biochemical reactions is ensured by chiral biological systems, which contrasts sharply with the scarcity of spontaneously generated asymmetric chemical reactions. Biological systems offer two important insights into obtaining materials with pure, uniform chirality: chiral driving forces and room-temperature operation. Therefore, without the chiral influence of nearby “seeds” or templates, the products of a reaction would be a racemic mixture. Take covalent organic frameworks (COFs) as an example; many COFs have asymmetric structures within their frameworks; however, they invariably form racemates in bulk solids with a 1:1 ratio of left-handed to right-handed components. Therefore, ultra-high signal chiral materials should exhibit at least two fundamental characteristics: (1) globally uniform chirality, i.e., uniform chirality between different individuals or different parts of the structure; and (2) massive chiral amplification.

[0004] In 2018, Han et al. pioneered the combination of chiral induction and solvothermal methods to synthesize a series of chiral COFs (CCOFs) characterized by their unique three-bladed propeller structure. This process involves imine condensation, specifically by linking a C3-symmetric 1,3,5-trialdehyde phloroglucinol (Tp) to an achiral diamine or triamine linker, using R- or S-1-phenylethylamine (1-PEA) as a chiral inducing agent (Han X, Zhang J, Huang J, et al. Chiralinduction in covalent organic frameworks[J]. Nat. Commun. 2018, 9: 1294.). Although chiral induction can skew this equivalent probabilistic process, thereby increasing the number of single-chiral structures, the degree of global chirality remains quite limited. This can be illustrated by the low intensity of the circular dichroism spectrum (CD signal approximately 10–40 mdeg), and especially by the obvious circular dichroism spectral asymmetry (Dong J, Liu Y, Cui Y. Emerging chiral two-dimensional materials[J]. Nat. Chem. 2024, 16: 1398-1407.). Therefore, obtaining porous materials with ultra-large chiral signals is a problem we must face and solve. Inspired by chiral biological systems, we hypothesize that the reduction in global chirality is due to the increase in solvothermal operating temperature during synthesis. Generally, the temperature-dependent bond rotation speed between molecules in the precursor plays an important role in the substitution of the achiral monomer for the 1-PEA enantiomer, thereby reducing the degree of "global" chirality.

[0005] How can we overcome this bottleneck and achieve globally consistent chirality? Theoretically, we first synthesize the precursor molecule R-1-PEA-Tp or S-1-PEA-Tp, then add an achiral diamine linker. Under ideal and extreme conditions, such as ultra-low temperatures under liquid nitrogen (assuming the chemical reaction proceeds as planned), a rigid glassy medium ensures that the planes of the two linkers in the precursor are at optimal fixed angles determined by intrinsic stereochemistry. Using R-1-PEA or S-1-PEA as a template, the other two sites of Tp are covalently bonded to the achiral linker. Finally, 1-PEA is replaced to generate an enantiomeric pure triblade propeller. Crystallization yields pure chiral COF enantiomers. Of course, this is an ideal scenario, as all chemical reactions would cease at such low temperatures. Considering the complex influence of temperature on the chemical reaction rate, solubility, and bond rotation speed during synthesis, room temperature is determined to be the optimal condition for obtaining a pure, consistent chiral triblade propeller. In this invention, circular dichroism spectroscopy and ultraviolet-visible absorption spectroscopy were used to continuously monitor the entire synthesis process and optimize the temperature. The chiral and achiral spectra of the prepared ultra-chiral covalent organic framework enantiomers were also characterized.

[0006] How chiral life systems sense, distinguish, and transmit enantiomer information is a core question that the field of chiral science has long strived to answer. For example, aminoacyl-tRNA synthetase, an enzyme involved in amino acid selection during protein synthesis, preferentially binds to L-amino acids through steric hindrance of D-amino acids. Due to the large distance between reaction sites, the peptide elongation of D-amino acids at the ribosome is slow, limiting the production of polypeptides incorporating D-amino acids.

[0007] In recent years, the enantioselective recognition of amino acids has attracted widespread research and attention from scientists. However, reports on enantioselective recognition using chiral covalent organic frameworks are extremely rare, especially the recognition of amino acid enantioselections. Summary of the Invention

[0008] This invention aims to provide a simple, environmentally friendly, and versatile room temperature synthesis method to solve the core problem of chiral racemization of products caused by high temperature in the existing high-temperature solvothermal method for preparing chiral covalent organic frameworks (COFs). This method will obtain materials with ultra-high chiral signal and long-term stability, and apply them to the efficient spectral recognition of various amino acids and small molecule enantiomers.

[0009] To achieve the above-mentioned technical objectives of this invention, the following technical solution is adopted: A method for preparing a highly chiral covalent organic framework includes the following steps: (1) In a reaction vessel, a C3 symmetrical aldehyde monomer and a chiral monoamine are reacted in an alcohol solvent to generate a precursor molecule solution; (2) Dissolve the non-chiral diamine monomer and catalyst in a solvent, and then add them to the precursor molecule solution obtained in step (1), and carry out the chiral transfer reaction at room temperature of 20℃~30℃. (3) Evaporate the solvent after the reaction in step (2) until the system is viscous; (4) Transfer the viscous system obtained in step (3) to an air bath or water bath and carry out conjugation and crystallization reaction at 80℃~100℃; (5) The solid obtained in step (4) is washed and dried to obtain the ultra-chiral covalent organic framework.

[0010] Preferably, the C3 symmetric aldehyde monomer is trialdehyde phloroglucinol (Tp), the chiral monoamine is S-1-phenylethylamine (S-1-PEA) or R-1-phenylethylamine (R-1-PEA), and the molar ratio of trialdehyde phloroglucinol to the chiral monoamine is 1:1.

[0011] Preferably, the achiral diamine monomer is any one of p-phenylenediamine (Pa-1), 3,3′-dimethylbenzidine (BD-Me2), or 3,3′-dimethoxybenzidine (BD-(OMe)2), and the molar ratio of trialdehyde phloroglucinol to the achiral diamine monomer is 1:1.5 to 3.

[0012] Preferably, the catalyst is p-toluenesulfonic acid or acetic acid; when the catalyst is p-toluenesulfonic acid, the molar ratio of the non-chiral diamine monomer to p-toluenesulfonic acid (PTSA) is 1:4; when the catalyst is acetic acid, the concentration of acetic acid in the reaction system is 3 mol / L to 8 mol / L.

[0013] Preferably, in step (2), the solvent for dissolving the non-chiral diamine monomer and the catalyst is deionized water, methanol, or a mixture of deionized water and methanol.

[0014] Preferably, in step (2), the chiral transfer reaction is carried out at room temperature for 3 to 6 hours; when the operating temperature of chiral transfer is higher than room temperature, for example, when it reaches 40°C or 50°C, the efficiency of pure uniform chiral transfer is greatly reduced (taking the S system as an example, the measured asymmetry factor g abs The values ​​were 0.042 and 0.017 respectively, which is consistent with g at room temperature. abs Compared to a value of 0.085, this represents only about 50% and 20% (the difference is only about 20%). This fully demonstrates the indispensability of "room temperature operation" for achieving "ultra-high chirality signals".

[0015] Preferably, in step (4), the time for the conjugation long-range formation and crystallization reaction is 4 to 12 hours.

[0016] To achieve the technical objective of this invention, another technical solution is adopted: a highly chiral covalent organic framework prepared by the method described above, wherein the highly chiral covalent organic framework is of S-configuration or R-configuration, and the absolute value of the maximum signal intensity CD of its circular dichroism spectrum is approximately 2000 mdeg, and the asymmetry factor g abs The absolute value reaches 0.085.

[0017] Preferably, its BET specific surface area is 1,300 to 1,600 m². 2 / g, with a thermal decomposition temperature above 400℃ under a nitrogen atmosphere.

[0018] To achieve the technical objective of this invention, another technical solution is adopted: an application of the aforementioned highly chiral covalent organic framework in enantiomeric molecule recognition, wherein the highly chiral covalent organic framework is prepared into a solution, and the changes in its circular dichroism spectral signal are used to identify amino acid enantiomeric molecules; the amino acid enantiomeric molecules include proline, histidine, tyrosine, glutamic acid, aspartic acid, glutamine, and asparagine.

[0019] Preferably, the ultra-chiral covalent organic framework is prepared into a solution, and the small molecule enantiomers are identified by utilizing the changes in its circular dichroism spectral signal; the small molecule enantiomers include lactic acid, mandelic acid, α-pinene, carvone, and ibuprofen.

[0020] Compared with the prior art, the present invention achieves the following technical effects: This invention, through an innovative "room-temperature chiral transfer" process, fundamentally avoids the problem of chiral racemization caused by high temperatures, successfully achieving the precise construction of purely uniform chiral trilobal propeller macromolecules. Based on this, a series of enantiomeric covalent organic frameworks with ultra-high chiral signals were obtained through conjugation long-range formation and crystallization reactions. This method possesses good versatility; by flexibly replacing achiral diamine linkers with different structures, it can be extended to synthesize a variety of high-performance COF materials with high asymmetric responses.

[0021] The obtained product not only clearly exhibited spectral characteristic absorptions corresponding to the three-bladed propeller configuration, but also achieved a cascaded chiral amplification effect of up to 200 times. The prepared material displayed excellent chiral response intensity, with a circular dichroism (CD) signal value of approximately ±2,000 mdeg and an asymmetry factor g. abs With a value of ±0.085, this is the highest record reported so far in the field of chiral covalent organic frameworks.

[0022] The prepared ultra-chiral COFs exhibit superior performance in molecular recognition and sensing, particularly in enantiomeric spectral recognition. They achieve efficient resolution of seven amino acid enantiomeric compounds (proline, histidine, tyrosine, glutamic acid, aspartic acid, glutamine, and asparagine), with corresponding spectral selectivity ratios (ΔID / ΔIL, ER) of 5.64, 1.50, 1.85, 8.38, 26.86, 7.09, and 2.66, respectively. Furthermore, they also demonstrate good recognition ability for small molecule enantiomeric compounds such as lactic acid, mandelic acid, α-pinene, carvone, and ibuprofen, with enantiomeric selectivity ratios consistently ranging from 1.3 to 2.3. These results indicate that the materials prepared by this method have significant application potential in enantiomeric recognition, chiral sensing, and separation analysis. Attached Figure Description

[0023] For ease of explanation, the present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0024] Figure 1 A schematic diagram of the key chemical reactions involved in the entire process of preparing a covalent organic framework with ultra-high chirality. (a) is the reaction for generating the precursor molecule: the C3-symmetric aldehyde monomer Tp reacts with a chiral monoamine R-1-PEA or S-1-PEA to generate the precursor molecule; (b) is the room-temperature chiral transfer reaction: the precursor molecule reacts with an achiral diamine to generate a trilobed propeller molecule with an R- or S-configuration; (c) is the conjugation long-range formation and crystallization reaction: the trilobed propeller molecule further reacts to generate an ultra-high chiral covalent organic framework with an R- or S-configuration.

[0025] Figure 2 The figures show the UV-Vis absorption spectra of the R and S experimental systems after chiral transfer and subsequent crystallization at room temperature. S or R in the figures represent the experimental systems with chiral templates S-1-PEA or R-1-PEA.

[0026] Figure 3 The circular dichroism spectra of the R and S experimental systems are shown after chiral transfer and subsequent crystallization at room temperature. In the figure, S or R represents the experimental system with the chiral template S-1-PEA or R-1-PEA.

[0027] Figure 4 The asymmetry factor (g) of the chiral inducer, the pure uniform chiral trilobal propeller, and the finally obtained chiral covalent organic framework. abs (and quantitative comparison graphs. In the graph, S or R represents the experimental system with chiral template S-1-PEA or R-1-PEA.)

[0028] Figure 5Experimental diagram showing the dependence of the circular dichroism signal on reaction temperature during the chiral transfer process from precursor molecules to the formation of a pure, uniform chiral three-bladed propeller.

[0029] Figure 6 The Fourier transform infrared spectra of the enantiomers of R-COF and S-COF are shown.

[0030] Figure 7 Powder X-ray diffraction patterns of the R-COF and S-COF enantiomers.

[0031] Figure 8 Images are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the enantiomers of R-COF and S-COF. (a) and (b) are SEM and TEM images of R-COF, respectively; (c) and (d) are SEM and TEM images of S-COF, respectively.

[0032] Figure 9 Thermogravimetric analysis curves of the R-COF and S-COF enantiomers under nitrogen atmosphere.

[0033] Figure 10 The N2 adsorption isotherms are for the enantiomers of R-COF and S-COF.

[0034] Figure 11 The images show the spectral resolution results of lactate enantiomers using ultra-chiral covalent organic frameworks. (a) and (b) show the resolution results of lactate enantiomers using R-COF combined with circular dichroism and UV-Vis spectroscopy; (c) and (d) show the resolution results of lactate enantiomers using S-COF combined with circular dichroism and UV-Vis spectroscopy.

[0035] Figure 12 The images show the spectroscopic resolution results of mandelic acid enantiomers using ultra-chiral covalent organic frameworks. (a) and (b) show the resolution results using R-COF; (c) and (d) show the resolution results using S-COF.

[0036] Figure 13 The images show the spectroscopic resolution results of α-pinene enantiomers using ultra-chiral covalent organic frameworks. (a) and (b) show the resolution results using R-COF; (c) and (d) show the resolution results using S-COF.

[0037] Figure 14 The images show the spectroscopic resolution results of carvone enantiomers using ultra-chiral covalent organic frameworks. (a) and (b) show the resolution results using R-COF; (c) and (d) show the resolution results using S-COF.

[0038] Figure 15The images show the spectroscopic resolution results of ibuprofen enantiomers using ultra-chiral covalent organic frameworks. (a) and (b) show the resolution results using R-COF; (c) and (d) show the resolution results using S-COF.

[0039] Figure 16 The images show the UV-Vis absorption spectra of the R and S experimental systems after chiral transfer and crystallization at room temperature in Example 2. In the figures, S or R represents the experimental system containing the chiral template S-1-PEA or R-1-PEA.

[0040] Figure 17 The image shows the circular dichroism spectra of the R and S experimental systems after chiral transfer and crystallization at room temperature in Example 2. In the figure, S or R represents the experimental system containing the chiral template S-1-PEA or R-1-PEA.

[0041] Figure 18 The images show the spectral resolution results of proline and histidine enantiomers using ultra-chiral covalent organic frameworks. (a)-(d) show the circular dichroism and UV-Vis spectra of the proline enantiomers using R-COF and S-COF, respectively; (e)-(h) show the circular dichroism and UV-Vis spectra of the histidine enantiomers using R-COF and S-COF, respectively.

[0042] Figure 19 The images show the spectral resolution results of five amino acid enantiomers using S-COF. (a) and (b) show the resolution results for the tyrosine enantiomer; (c) and (d) show the resolution results for the glutamic acid enantiomer; (e) and (f) show the resolution results for the aspartic acid enantiomer; (g) and (h) show the resolution results for the glutamine enantiomer; and (i) and (j) show the resolution results for the asparagine enantiomer.

[0043] Figure 20 The images shown are from Example 3, illustrating the continuous monitoring of the entire synthesis process (after room temperature chiral template replacement and after crystallization) using UV-Vis and circular dichroism spectroscopy. (a) is the UV-Vis spectrum, and (b) is the circular dichroism spectrum. In the figures, S or R represents the experimental system containing the chiral template S-1-PEA or R-1-PEA.

[0044] Figure 21The images show the achiral spectra of the chiral COFs (R-COF and S-COF) prepared in Example 3. (a) shows the Fourier transform infrared spectra of R-COF, S-COF, Tp, and Pa⁻¹; (b) and (c) are the powder X-ray diffraction patterns of the synthesized R-COF and S-COF enantiomers, respectively; (d) and (e) are the scanning electron microscope (SEM) and transmission electron microscope (TEM) images of R-COF, respectively; and (f) and (g) are the SEM and TEM images of S-COF, respectively. Detailed Implementation

[0045] The following are specific embodiments of the present invention, in conjunction with the appendix. Figure 1-21 The technical solutions of the present invention will be further described below, but the present invention is not limited to these embodiments; in the following description, specific details such as specific configurations are provided only to help to fully understand the embodiments of the present invention. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention.

[0046] Unless otherwise specified, the materials, practices, and experimental equipment involved in the embodiments of this invention are all commercially available products in the relevant chemical and biotechnology fields.

[0047] Example 1 (where the non-chiral diamine is 3,3′-dimethoxybenzidine) Throughout the experiment, the molar ratio of the four reagents Tp, 1-PEA, 3,3′-dimethoxybenzidine, and PTSA was maintained at 1:1:1.5:6. A mixture of Tp (210 mg, 1 mmol) and S- or R-1-PEA (120 mg, 1 mmol) was refluxed overnight in methanol solution to prepare solutions of the precursors R-1-PEA-Tp or S-1-PEA-Tp (chemical reactions are shown in [link to chemical reaction description]). Figure 1 (a) Subsequently, a solution containing a non-chiral diamine salt of PTSA was added. After stirring at room temperature for 4 hours (see chemical reaction section a) Figure 1 (b) Evaporate the solvent until it becomes viscous, then transfer it to an oven at 80°C–100°C and heat for 6 hours. Wash repeatedly with distilled water, dimethylacetamide, and acetone to remove PTSA, unreacted reagents, and oligomeric fragments. Dry under vacuum at 60°C to obtain ultra-chiral COFs, named R-COF and S-COF (chemical reactions are shown in [reference]). Figure 1 (c) The spectral characteristics of the products at each stage of the entire preparation process were monitored using circular dichroism spectroscopy and UV-Vis absorption spectroscopy. Figures 2-3 ), chiral asymmetry factor (g) abs ) quantitatively described the huge chiral cascade amplification effect throughout the preparation process ( Figure 4 ), and optimized the suitable temperature range for room temperature chiral transfer (). Figure 5 The structural properties of the prepared product were characterized using several non-chiral spectroscopic techniques. Figures 6-10 Finally, R-COF or S-COF was used to perform spectral resolution on five small molecule enantiomers: lactic acid, mandelic acid, α-pinene, carvone, and ibuprofen. Figures 11-15 The specific results are listed below in order: Figure 2 The two green lines represent the absorption spectra of the chiral templates in R-1-PEA-Tp or S-1-PEA-Tp after being replaced by achiral diammonium at room temperature. The main absorption peak at 430 nm corresponds to the characteristic absorption of the generated trilobed propeller molecules, while the absorption above 450 nm is due to the conjugation of multiple trilobed propeller molecules. In the two spectra after crystallization at 90 °C (the two magenta lines), the main absorption peak at 550 nm shows the long-range conjugation of COFs and the characteristic absorption of the crystal framework.

[0048] Figure 3 As shown in Figures a and b, the CD spectra of the R- and S- experimental systems after room-temperature chiral transfer and after crystallization of chiral COFs exhibit excellent mirror symmetry. Both the R- and S- experimental systems show significant differences in circular dichroism (CD) spectra before and after crystallization, namely, different peak positions and intensities. The CD spectral peaks are located at 510 nm and 550 nm before and after crystallization, respectively. Most importantly, the maximum CD spectral intensity of the enantiomers of the crystallized COFs is close to ±2,000 mdeg, and the maximum CD value can reach 30-40 times that of the corresponding trilobed propeller molecule before crystallization. This demonstrates that the long-range conjugation and highly ordered structure of the crystallized COFs not only redshifts the absorption peak wavelength but also exhibits a significant chiral amplification effect.

[0049] Figure 4 In this study, the asymmetry factors of S-1-PEA, R-1-PEA, the corresponding trilobed propeller molecules, and the enantiomers of chiral COFs were calculated in detail and quantitatively compared. Throughout the synthesis, a large cascade amplification effect based on globally consistent chirality was observed. The first-order chiral amplification from the chiral inducer to the purely consistent chiral trilobed propeller was approximately 3.5 times, while the second-order amplification from the trilobed propeller to the chiral covalent organic framework formed through crystallization was 57 times, resulting in an overall amplification of 200 times. Particularly noteworthy is the complete correspondence between the CD spectra of the chiral inducer R- or S-1-PEA and the CD spectra of the corresponding trilobed propeller molecules and chiral COFs (R- or S-COF) generated by chiral transfer. The main peaks of the R enantiomers all showed negative values, while the main peaks of the S enantiomers showed positive values, indicating the existence of an inherent chiral transfer effect.

[0050] Asymmetric factor (g) abs The calculation formula for ) is as follows: g abs = Circular dichroism value (unit: mdeg) / (32,982 × absorbance) The circular dichroism value comes from the circular dichroism spectrum, while the absorbance value comes from the ultraviolet-visible spectrum.

[0051] Figure 5 This paper presents an experiment demonstrating the temperature dependence of the circular dichroism signal during the chiral transfer process from precursor molecules to the generation of a pure, uniform chiral three-bladed propeller. We optimized the temperature range during the template chiral transfer process to generate the three-bladed propeller, designing the experiment to a range of 20-50 °C, while the optimal temperature for COF crystallization was 90 °C. Figure 5 The changes in the CD spectrum with temperature during the chiral transfer of non-chiral diammonium via the template S-1-PEA are shown. Notably, the CD peak intensity is highest and remains essentially stable within the 20-30 °C temperature range. However, at higher temperatures, such as 40 °C and 50 °C, a significant decrease in peak intensity is observed. This indicates that increasing temperature significantly accelerates the rotational speed of the bond between Tp and 1-PEA in the precursor, thereby greatly reducing the chiral purity of the three-bladed propeller and leading to a decrease in the degree of globally consistent chirality, resulting in a significant decrease in the CD spectral intensity of the final chiral COFs. Therefore, the 20-30 °C temperature range is determined to be the most favorable operating temperature.

[0052] Figure 6 The infrared spectra of the R-COF and S-COF enantiomers are shown, exhibiting almost identical spectral characteristics. The Fourier transform infrared spectra of both the R-COF and S-COF samples show complete consumption of the initial reactants, as evidenced by the absence of the NH stretching band of the diamine (3100-3300 cm⁻¹). -1 ) and the carbonyl extension band of Tp (1639 cm) -1 Furthermore, the Fourier transform infrared spectra of the COF enantiomers at 1578 cm⁻¹ -1 A C=C stretching band is shown at 1267 cm. -1 A CN extension band is shown at the point, and since both bands originate from the enol-ketone isomerized form, this indicates that enol-ketone isomerization has occurred.

[0053] Figure 7The image shows the crystallinity characteristics of the synthesized R- and S-COF enantiomers detected using X-ray powder diffraction analysis. The initial sharp diffraction peaks observed in the PXRD patterns are attributed to 100-plane reflections, with a 2θ angle of 3.4° for both R-COF and S-COF. The broad peak at 2θ ≈ 26.0° can be attributed to the π-π stacking plane (001) of the COF enantiomers.

[0054] Figure 8 The image shows scanning electron microscope (SEM) and transmission electron microscope (TEM) images of R-COF and S-COF, revealing that they have almost identical microstructures, both composed of submicron fibers with a size of 0.1*1 μm.

[0055] Figure 9 Thermogravimetric analysis (TGA) of the R- and S-COF enantiomers is presented. Thermogravimetric analysis (TGA) performed under N2 atmosphere shows that the synthesized R- and S-COF enantiomers have thermal stability up to 400 °C.

[0056] Figure 10 The N2 adsorption isotherms of R-COF and S-COF are shown in the figure, and the surface areas calculated using the BET method are 1,398.64 and 1,589.12 m², respectively. 2 g -1 .

[0057] like Figure 11 The spectral resolution of lactate enantiomers by ultra-chiral COFs is demonstrated. As can be seen from the figure, both R-COF and S-COF synthesized ultra-chiral covalent organic frameworks can achieve good resolution of lactate enantiomers by CD spectroscopy or absorption spectroscopy.

[0058] Example 2 (where the non-chiral diamine is 3,3′-dimethylbenzidine) Throughout the experiment, the molar ratio of the four reagents Tp, 1-PEA, 3,3′-dimethylbenzidine, and PTSA was maintained at 1:1:1.5:6. A mixture of Tp (210 mg, 1 mmol) and S- or R-1-PEA (120 mg, 1 mmol) was refluxed overnight in 10 mL of methanol to prepare the precursors R-1-PEA-Tp or S-1-PEA-Tp (chemical reaction details are provided in the original text). Figure 1 (a) Subsequently, a solution containing PTSA diamine salt was added. After stirring at room temperature for 4 hours (see chemical reaction section a) Figure 1(b) Evaporate the solvent to a viscous state, then transfer to an oven at 80°C–100°C and heat for 6 hours. Wash repeatedly with distilled water, dimethylacetamide, and acetone to remove PTSA, unreacted reagents, and oligomeric fragments. Obtain ultra-chiral COFs by vacuum drying at 60°C, named R-COF and S-COF (chemical reactions are described in [reference]). Figure 1 (c) The spectral characteristics and trends of the products at each stage of the entire preparation process were monitored using circular dichroism spectroscopy and UV-Vis absorption spectroscopy. Figures 16-17 The structural characteristics of the prepared products were characterized using several achiral spectroscopic techniques, and the enantiomers of seven amino acids were spectrally resolved using R-COF or S-COF. Figures 18-19 The specific results are listed below in order: Figure 16 The image shows the UV-Vis absorption spectra of the R and S experimental systems after chiral transfer and crystallization at room temperature. In the figure, S or R represents the experimental system containing the chiral template S-1-PEA or R-1-PEA. From... Figure 16 It can be observed that the spectra of the R- and S- experimental systems after chiral transfer at room temperature show significant consistency (green and blue lines in the figure). Furthermore, after crystallization, their UV-Vis spectra are almost identical. This indicates that almost the same molecular change process occurred in both the R- and S- experimental systems. Figure 16 Of the four spectra, the absorption peak observed near 300 nm is attributed to the absorption of residual reactants. In the absorption spectrum after the chiral template is substituted with diammonium at room temperature, the absorption peak near 430 nm corresponds to the characteristic absorption of the generated trilobed propeller molecules, while the absorption above 450 nm is due to the conjugation of multiple trilobed propeller molecules. In the two spectra after crystallization, the main absorption peak near 550 nm shows the characteristic absorption of long-range conjugation and the crystal framework of COFs. The significant redshift of the absorption peaks from 430 nm to 550 nm before and after crystallization fully demonstrates that COFs form a highly ordered periodic array and long-range conjugation effect after crystallization, simultaneously leading to a decrease in the HOMO-LUMO band gap.

[0059] Figure 17 The image shows the circular dichroism spectra of the R and S experimental systems after chiral transfer at room temperature and after crystallization. In the figure, S or R represents the experimental system containing the chiral template S-1-PEA or R-1-PEA. From... Figure 17It can be observed that the CD spectra of the R- and S- experimental systems after room-temperature chiral transfer and after crystallization of chiral COFs exhibit excellent mirror symmetry. Both the R- and S- experimental systems show significant differences in circular dichroism (CD) spectra before and after crystallization: different peak positions and intensities. The CD spectral peaks before and after crystallization are located around 510 nm and 550 nm, respectively. Most importantly, the maximum CD spectral intensity of the enantiomers of the crystallized COFs can approach ±1,600 mdeg, and the maximum CD value can reach 30 times that of the corresponding trilobed propeller molecule before crystallization. This demonstrates that the long-range conjugation and highly ordered structure of the crystallized COFs not only causes a redshift in wavelength but also exhibits a significant chiral amplification effect.

[0060] Figure 18 The paper demonstrates the spectral resolution of ultra-chiral COFs for proline and histidine enantiomers. From... Figure 18 It is evident that the enantiomers of proline and histidine can be obtained through S-COF or R-COF ( Figure 18 (Ah) to achieve effective resolution of circular dichroism and absorption spectra.

[0061] Figure 19 The circular dichroism and absorption spectra of S-COF for tyrosine, glutamic acid, aspartic acid, glutamine, and asparagine are shown in the figure.

[0062] Example 3 (where the linker diamine is p-phenylenediamine) Throughout the experiment, the molar ratio of the four reagents TP, 1-PEA, diamine, and PTSA was maintained at 1:1:1.5:6. A mixture of Tp (210 mg, 1 mmol) and S- or R-1-PEA (120 mg, 1 mmol) was refluxed in methanol solution to prepare the precursors R-1-PEA-Tp or S-1-PEA-Tp (chemical reaction details are provided in the original text). Figure 1 (a) Subsequently, a mixture containing PTSA diamine salt is added. The reactants undergo a chiral transfer reaction at room temperature (see chemical reaction diagram). Figure 1 (b) After evaporation to near dryness, the product was transferred to an oven at 80℃~100℃ and heated for 4 hours. The precipitate was collected by centrifugation and washed repeatedly with distilled water, dimethylacetamide, and acetone to remove PTSA, unreacted reagents, and oligomeric fragments. Chiral COFs, named R-COF and S-COF, were obtained by vacuum drying at 60℃. The spectral characteristics of the products at each stage of the preparation process were monitored using circular dichroism spectroscopy and UV-Vis absorption spectroscopy. Figure 20 The structural characteristics of the prepared product were characterized using several achiral spectroscopic techniques. Figure 21 ).

[0063] Figure 20The image demonstrates continuous monitoring of the entire synthesis process using ultraviolet-visible spectroscopy and circular dichroism spectroscopy. From... Figure 20 As can be seen from a, the spectra of the R- and S- experimental systems after chiral transfer at room temperature show significant consistency. Figure 20 (The green and blue lines in the middle). After crystallization, their UV-Vis spectra are almost identical. This indicates that almost the same molecular changes occurred in both the R- and S- experimental systems. Figure 20 In the four spectra of α, the absorption peak observed near 300 nm is attributed to the absorption of residual reactants. In the absorption spectrum of the chiral template substituted with diammonium at room temperature, the absorption peak near 430 nm corresponds to the characteristic absorption of the generated tri-propeller molecules, while the absorption above 450 nm is due to the conjugation of multiple tri-propeller molecules. The achiral linker in this experimental system is p-phenylenediamine. Compared to the linkers in the previous two experimental systems, the absorption peak at 430 nm is lower and transforms into a shoulder peak, indicating that the concentration of the tri-propeller in this system is relatively low or the absorption coefficient is low. In the two spectra after crystallization at 90℃, the main absorption peak near 550 nm still shows the characteristic absorption of long-range conjugation of COFs and the crystal framework. The significant red shift of the absorption spectrum peaks from 430 nm to 550 nm before and after crystallization fully demonstrates that COFs form a highly ordered periodic array and long-range conjugation after crystallization, simultaneously leading to a decrease in the HOMO-LUMO band gap.

[0064] Figure 21 The paper presents various achiral spectral characterization features of chiral COFs. Figure 21 Figure a shows the infrared spectra of the R-COF and S-COF enantiomers, which exhibit identical characteristic peaks. The Fourier transform infrared spectra of both the R-COF and S-COF samples show complete consumption of the initial reactants, as evidenced by the NH stretching band of the diamine (3100-3300 cm⁻¹). -1 ) and the carbonyl extension band of Tp (1639 cm) -1 The complete disappearance of ) and the Fourier transform infrared spectrum of the enantiomers of COFs at 1582 cm⁻¹. -1 A C=C stretching band is shown at 1257 cm. -1 A CN-stretched band is shown at [location missing]. Since both bands originate from the enol-ketone isomerized form, this indicates that enol-ketone isomerization has occurred. It is particularly noteworthy that none of the chiral COFs exhibit a 1-PEA methyl group at 1370 cm⁻¹ in their infrared spectra. -1 The characteristic CH bend at this point indicates that 1-PEA molecules were not incorporated into the final COF product. Furthermore, due to the 1605 cm⁻¹... -1 and 815 cm-1 The absence of peak values ​​indicates that the molecular organization agent PTSA has been completely removed from COFs.

[0065] The crystallinity of the synthesized R- and S-COF enantiomers was investigated using X-ray powder diffraction analysis (Figure 21, b, c). The initial sharp diffraction peaks observed in the PXRD patterns are attributed to 100-plane reflections, with a 2θ angle of 4.7° for both R-COF and S-COF. The broad peak at 2θ ≈ 27.0° can be attributed to the π-π stacking plane (001) of the COF enantiomers.

[0066] SEM and TEM images of R-COF and S-COF ( Figure 21 The data (dg) show that they have almost identical microstructures, both composed of submicron fibers with a size of 0.1*1 μm.

[0067] Finally, it should be noted that the above examples are merely illustrative of this application and are not intended to limit the implementation. For example, according to the strategy of this invention, the use of any other chiral monoamine in the precursor molecule preparation reaction, any non-chiral diamine in the room-temperature chiral transfer reaction, and various inorganic and organic acid catalysts are all within the scope of protection. Those skilled in the art can make variations based on the above description. It is neither necessary nor possible to exhaustively list all embodiments here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method for preparing a highly chiral covalent organic framework, characterized in that, Includes the following steps: (1) In a reaction vessel, a C3 symmetrical aldehyde monomer and a chiral monoamine are reacted in an alcohol solvent to generate a precursor molecule solution; (2) Dissolve the non-chiral diamine monomer and catalyst in a solvent, and then add them to the precursor molecule solution obtained in step (1). Carry out the chiral transfer reaction at room temperature of 20℃~30℃. (3) Evaporate the solvent after the reaction in step (2) until the system is viscous; (4) Transfer the viscous system obtained in step (3) to an air bath or water bath and carry out conjugation and crystallization reaction at 80℃~100℃; (5) The solid obtained in step (4) is washed and dried to obtain the ultra-chiral covalent organic framework.

2. The method according to claim 1, characterized in that, The C3 symmetric aldehyde monomer is trialdehyde phloroglucinol, the chiral monoamine is S-1-phenylethylamine or R-1-phenylethylamine, and the molar ratio of trialdehyde phloroglucinol to the chiral monoamine is 1:

1.

3. The method according to claim 1, characterized in that, The achiral diamine monomer is any one of p-phenylenediamine, 3,3′-dimethylbenzidine, or 3,3′-dimethoxybenzidine, and the molar ratio of trialdehyde phloroglucinol to the achiral diamine monomer is 1:1.5 to 3.

4. The method according to claim 1 or 3, characterized in that, The catalyst is p-toluenesulfonic acid or acetic acid; when the catalyst is p-toluenesulfonic acid, the molar ratio of the non-chiral diamine monomer to p-toluenesulfonic acid is 1:4; when the catalyst is acetic acid, the concentration of acetic acid in the reaction system is 3 mol / L to 8 mol / L.

5. The method according to claim 1, characterized in that, In step (2), the solvent for dissolving the non-chiral diamine monomer and the catalyst is deionized water, methanol, or a mixture of deionized water and methanol.

6. The method according to claim 1, characterized in that, In step (2), the chiral transfer reaction is carried out at room temperature for 3 to 6 hours; in step (4), the conjugation long-range formation and crystallization reaction is carried out for 4 to 12 hours.

7. A highly chiral covalent organic framework prepared by the method according to any one of claims 1-6, characterized in that, The ultra-chiral covalent organic framework is of S- or R-configuration, and the absolute value of the maximum signal intensity CD in its circular dichroism spectrum is approximately 2000 mdeg, with an asymmetry factor g. abs The absolute value reaches 0.

085.

8. The application of a highly chiral covalent organic framework as described in claim 7 in enantiomeric molecule recognition, characterized in that, The ultra-chiral covalent organic framework was prepared into a solution, and the changes in its circular dichroism spectral signal were used to identify the enantiomers of amino acids; the enantiomers of amino acids included proline, histidine, tyrosine, glutamic acid, aspartic acid, glutamine, and asparagine.

9. The application of a highly chiral covalent organic framework as described in claim 7 in enantiomeric molecule recognition, characterized in that, The ultra-chiral covalent organic framework was prepared into a solution, and small molecule enantiomers were identified by utilizing changes in its circular dichroism spectral signal; the small molecule enantiomers included lactic acid, mandelic acid, α-pinene, carvone, and ibuprofen.

10. A highly chiral covalent organic framework as described in claim 7, characterized in that, Its BET specific surface area is 1,300–1,600 m². 2 / g, with a thermal decomposition temperature above 400℃ under a nitrogen atmosphere.

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