A molecular recognition method based on nuclear magnetic resonance using cyclodextrin

Abstract

The present invention discloses a method for cyclodextrin molecular recognition based on nuclear magnetic resonance. The method comprises: modifying cyclodextrin with imidazole groups, using nuclear magnetic resonance to identify guest molecules with carboxyl or sulfonic acid groups using the modified cyclodextrin, and obtaining nuclear magnetic resonance spectra before and after cyclodextrin inclusion. If the peak of the monomer in the mixture spectrum shows a chemical shift and peak shape change compared to the spectrum of the cyclodextrin, it indicates that there is an interaction between the host and the guest. The present invention provides a method for the specific recognition of cyclodextrin by guest molecules based on nuclear magnetic resonance detection. The method is simple to operate and has good recognition effect, which is of great significance for the development of new molecular recognition systems.

Description

Technical Field

[0001] The present invention relates to a molecular recognition method, in particular to a method for identifying objects containing carboxyl groups or sulfonic acid groups by using positively charged modified cyclodextrin based on nuclear magnetic resonance. Background Art

[0002] Molecular recognition is a key concept in supramolecular chemistry. It works by selecting the guest molecule based on the varying strengths of interactions between the host and guest molecules, driven by factors such as size, charge, hydrogen bonding, and hydrophobic interactions. In addition to these direct interactions, the solvent also plays a significant role in molecular recognition. The host and guest molecules involved in molecular recognition exhibit molecular complementarity.

[0003] Cyclodextrins, as supramolecules, have been extensively studied due to their unique cavity structure. The primary hydroxyl group at position C6 (primary hydroxyl group) is located at the edge of the smaller opening of the cavity, while the secondary hydroxyl groups at positions C2 and C3 are located at the edges of the larger opening. The hydrogen atoms at positions C3 and C5 and the oxygen atoms in the glycosidic bond are located within the cavity. This unique structure gives the cyclodextrin cavity a hydrophilic exterior and a hydrophobic interior, allowing it to selectively incorporate a variety of guest molecules to form supramolecular complexes. Due to its propensity to form reversible inclusion complexes and selectively recognize analytes, cyclodextrins are widely used in various fields.

[0004] As a tool for characterizing the structure of organic molecules, nuclear magnetic resonance (NMR) has been used in practice for decades, achieving significant breakthroughs. Over the decades of development, NMR technology has seen continuous theoretical refinement, instrumentation, and methodological innovation, enhancing our ability to explore the essence of molecular structure. NMR spectroscopy provides information related to the molecular structure of compounds and is used to study chemical dynamics. For example, intramolecular rotation and chemical exchange, which affect the chemical environment outside the nucleus, should be reflected in the spectrum. Summary of the Invention

[0005] Using nuclear magnetic resonance technology to study the interactions of cyclodextrins with guest molecules, thereby identifying these molecules, is of great significance for the development of novel molecular recognition systems. This study designed a positively charged modified cyclodextrin as a host, explored the interactions between this positively charged modified cyclodextrin and guest molecules containing carboxyl or sulfonic acid groups, and explored the molecular recognition interaction mechanism, which is of great significance for the development of novel molecular recognition systems.

[0006] In order to achieve the above object, the present invention provides a molecular recognition method based on nuclear magnetic resonance using cyclodextrin, which comprises:

[0007] Using nuclear magnetic resonance spectroscopy, measuring a first nuclear magnetic resonance hydrogen spectrum of the positively charged imidazole-modified cyclodextrin, a second nuclear magnetic resonance hydrogen spectrum of the molecule to be identified, and a third nuclear magnetic resonance hydrogen spectrum of the complex of the positively charged imidazole-modified cyclodextrin and the molecule to be identified;

[0008] The third H NMR spectrum is compared and analyzed with the first H NMR spectrum and the second H NMR spectrum, and the type of the molecule to be identified is determined based on the chemical shift and peak shape changes of the peaks in each H NMR spectrum.

[0009] Optionally, the positively charged imidazole-modified cyclodextrin can be a monosubstituted allyl imidazole cyclodextrin or a polysubstituted allyl imidazole cyclodextrin. The cyclodextrin can be one of α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin. The allyl imidazole can be a substituent with an imidazole ring. The molecule to be identified can be a molecule that matches the size of the cyclodextrin cavity and contains a carboxyl or sulfonic acid structure.

[0010] Alternatively, the structural formula of the positively charged imidazole-modified cyclodextrin may be:

[0011] ;

[0012] Wherein, n1+n2=n, n is selected from 6, 7 or 8, n1 and n2 are both natural numbers; R is selected from hydrogen, alkyl, alkenyl, or alkynyl.

[0013] Alternatively, when R is an alkenyl group, the structural formula of the positively charged imidazole-modified cyclodextrin may be:

[0014] ;

[0015] Among them, n1+n2=n, n is selected from 6, 7 or 8, n1 and n2 are both natural numbers; n3 is selected from 0, 1 or 2.

[0016] In practical applications, the cyclodextrin in the positively charged imidazole-modified cyclodextrin can be α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin, and the imidazole group can replace one or more sugar rings in α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin.

[0017] Alternatively, the molecule to be identified may include a molecule having a carboxyl group or a sulfonic acid group.

[0018] Alternatively, the molecule having a carboxyl group or a sulfonic acid group may include adamantane acid, 2-naphthoic acid, 2-naphthylsulfonic acid, lithocholic acid, ferrocenecarboxylic acid, acetic acid or deuterated acetic acid.

[0019] Optionally, when measuring the first hydrogen nuclear magnetic resonance spectrum, the second hydrogen nuclear magnetic resonance spectrum and the third hydrogen nuclear magnetic resonance spectrum by nuclear magnetic resonance spectroscopy, a polar deuterated solvent is used to prepare the solution.

[0020] Specifically, the positively charged imidazole-modified cyclodextrin can be dissolved in a deuterated reagent to obtain a first sample solution, the molecule to be identified can be dissolved in the same deuterated reagent to obtain a second sample solution, and the complex of the positively charged imidazole-modified cyclodextrin and the molecule to be identified can be dissolved in the same deuterated reagent to obtain a third sample solution; then, one-dimensional nuclear magnetic spectra of the first sample solution, the second sample solution, and the third sample solution can be performed. 1 H NMR measurement; then compare the NMR spectra of the first to third sample solutions, analyze the changes in the chemical shift and peak shape of the peaks in the NMR spectra, and examine whether the positively charged imidazole-modified cyclodextrin has a specific recognition function for the guest molecule.

[0021] Optionally, in the third sample solution, the molar ratio of the positively charged imidazole-modified cyclodextrin to the molecule to be identified can be 1:1. The third sample solution can be prepared by dissolving the imidazole-modified cyclodextrin and the molecule to be identified in a deuterated reagent and then sonicating for a period of time (e.g., 30 minutes) to obtain a complex solution (or inclusion complex solution).

[0022] Optionally, the polar deuterated solvent is deuterated water, or the polar deuterated solvent is a mixed deuterated solvent of deuterated methanol and deuterated water.

[0023] Optionally, when the polar deuterated solvent is a mixed deuterated solvent of deuterated methanol and deuterated water, the volume ratio of deuterated water in the mixed deuterated solvent is greater than 60%.

[0024] In practical applications, the deuterated solvent is CD3OD:D2O=40%-0%:60%-100%, preferably CD3OD:D2O=40%:60%.

[0025] Optionally, determining the type of the molecule to be identified based on the chemical shift and peak shape changes of the peaks in each hydrogen nuclear magnetic resonance spectrum may specifically include: if, in the third hydrogen nuclear magnetic resonance spectrum compared with the first hydrogen nuclear magnetic resonance spectrum, the peak shape of the hydrogen atoms on the imidazole ring of the positively charged imidazole-modified cyclodextrin changes, then determining that the molecule to be identified is an acidic molecule.

[0026] Optionally, if, compared with the first hydrogen nuclear magnetic resonance spectrum, in the third hydrogen nuclear magnetic resonance spectrum, the peak shape of the hydrogen atoms on the imidazole ring of the positively charged imidazole-modified cyclodextrin changes, then determining that the molecule to be identified is an acidic molecule may specifically include: if, compared with the first hydrogen nuclear magnetic resonance spectrum, in the third hydrogen nuclear magnetic resonance spectrum, the peaks of H-7 and H-8 on the imidazole ring of the imidazole-modified cyclodextrin merge and the peak of H-9 appears, then determining that the molecule to be identified is an acidic molecule;

[0027] Wherein, H-7, H-8 and H-9 on the imidazole ring of the positively charged imidazole-modified cyclodextrin can be as shown in the following figure:

[0028] ;

[0029] Wherein, R1 is selected from α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin; R2 is selected from hydrogen, alkyl, alkenyl or alkynyl.

[0030] Optionally, determining that the molecule to be identified is an acidic molecule may specifically include: determining that the molecule to be identified is a molecule with a carboxyl group or a sulfonic acid group.

[0031] Alternatively, in order to explore the specific recognition of guest molecules by cyclodextrin based on nuclear magnetic resonance, 1-allyl-3-methylimidazolium chloride can be dissolved in a mixed solution of CD3OD:D2O for testing, where the ratio of CD3OD to D2O is 40%:60%.

[0032] Alternatively, taking mono-6-(1-allylimidazole)-β-cyclodextrin as an example, the positively charged imidazole-modified cyclodextrin can be prepared by the following steps:

[0033] 5.24 g of p-Toluenesulfonyl chloride-β-cyclodextrin and 1-allylimidazole (1.3 mL) were added to 10 mL of DMF and stirred at 95°C under a nitrogen atmosphere for 48 hours. The reaction solution was poured into 30 mL of acetone and stirred for 1 hour. The solid was filtered to obtain a solid. The solid was washed twice with acetone (2 × 20 mL) and filtered. The product was vacuum dried at 60°C for 5 hours, the toluenesulfonyl groups were replaced with chloride ions using chloride ion exchange resin, and then vacuum dried at 80°C for 24 hours to obtain mono-6-(1-allylimidazole)-β-CD.

[0034] Compared with the existing technology, the present invention provides a method for specifically identifying guest molecules substituted with carboxyl or sulfonic acid groups using cyclodextrin based on nuclear magnetic resonance. The identification of guest molecules with carboxyl or sulfonic acid groups is achieved in a mixed solution of CD3OD and D2O, providing a new method for developing new molecular recognition systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0036] Figure 1 Schematic diagram of the method for cyclodextrin to recognize guest molecules of the present invention;

[0037] Figure 2 This is the nuclear magnetic resonance image of adamantane acid identified by allyl imidazole cyclodextrin prepared in Example 1 of the present invention based on nuclear magnetic resonance;

[0038] Figure 3 This is the NMR image of allyl imidazole cyclodextrin prepared in Example 2 of the present invention identifying 1-naphthalenesulfonic acid based on NMR;

[0039] Figure 4 This is the nuclear magnetic resonance image of amantadine identified by allyl imidazole cyclodextrin prepared in Example 3 of the present invention based on nuclear magnetic resonance. DETAILED DESCRIPTION

[0040] To make the purpose, technical solutions, and advantages of one or more embodiments of this specification more clear, the technical solutions of one or more embodiments of this specification will be clearly and completely described below in conjunction with the specific embodiments of this specification and the corresponding drawings. Obviously, the embodiments described are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of one or more embodiments of this specification.

[0041] As a supramolecular host, cyclodextrin exhibits excellent host-guest inclusion ability for hydrophobic guest molecules due to its special cavity structure. The modified allyl imidazole cyclodextrin has strong electrostatic interaction and has specific recognition ability for guest molecules containing carboxyl or sulfonic acid groups.

[0042] The present invention provides a method for identifying cyclodextrin molecules based on nuclear magnetic resonance. Cyclodextrin is modified with allyl imidazole to obtain modified allyl imidazole cyclodextrin (the allyl imidazole can be monosubstituted or polysubstituted). A mixed solution of CD3OD and D2O is used as the solvent, and nuclear magnetic resonance is used to detect the allyl imidazole cyclodextrin alone and the complex of allyl imidazole cyclodextrin and a guest molecule. The solvent is prepared in a ratio of CD3OD:D2O = 40%-0%:60%-100%, preferably CD3OD:D2O = 40%:60%. Guest molecules are identified using allyl imidazole cyclodextrin based on nuclear magnetic resonance.

[0043] Methods for allyl imidazole cyclodextrin to recognize guest molecules Figure 1 As shown, the steps are as follows:

[0044] 5.24 g of p-Toluenesulfonyl chloride-β-cyclodextrin and 1-allylimidazole (1.3 mL) were added to 10 mL of DMF and stirred at 95°C under a nitrogen atmosphere for 48 hours. The reaction solution was poured into 30 mL of acetone and stirred for 1 hour. The solid was filtered to obtain a solid. The solid was washed twice with acetone (2 × 20 mL) and filtered. The product was vacuum dried at 60°C for 5 hours, the toluenesulfonyl groups were replaced with chloride ions using chloride ion exchange resin, and then vacuum dried at 80°C for 24 hours to obtain mono-6-(1-allylimidazole)-β-CD.

[0045] The guest molecule, allyl imidazole cyclodextrin molecule and the inclusion complex of the guest and allyl imidazole cyclodextrin were dissolved in a mixed solvent of CD3OD and D2O and subjected to one-dimensional NMR spectroscopy. 1 H NMR experiments, the ratio of CD3OD to D2O was 40%:60% to 0%:100%;

[0046] The following examples illustrate the molecular recognition of carboxyl or sulfonic acid group-containing objects using cyclodextrin based on nuclear magnetic resonance provided by the present invention.

[0047] Example 1

[0048] 20 mg of allyl imidazole cyclodextrin, 2 mg of guest molecule and their mixture were weighed and dissolved in a mixed solvent of CD3OD and D2O = 40%:60% to obtain a sample solution. The sample solution was tested using 400M NMR and the obtained NMR spectrum was analyzed. It was found that H-9 of allyl imidazole cyclodextrin did not appear in CD3OD and D2O = 40%:60%. When allyl imidazole cyclodextrin was mixed with adamantane acid, H-7 and H-8 merged into one peak, and the peak of H-9 reappeared.

[0049] The reappearance of H-9 on allyl imidazole cyclodextrin is due to the change in the acidity and alkalinity of the solution. There are two inferences about the specific reasons for the reappearance of H-9: one is that the acidic environment inhibits the hydrogen-deuterium exchange between H-9 and the deuterated reagent; the other is that the added molecule contains a carboxyl group, and the active hydrogen on the carboxyl group and the fully deuterated H-9 are exchanged again.

[0050] The special changes in the H-7 and H-8 peaks in allyl imidazole cyclodextrin and adamantane acid are inferred to be because adamantane acid enters the cyclodextrin cavity with the carboxyl group facing downward, resulting in close contact between the positively charged imidazole and the carboxyl ion of adamantane acid, weakening the electrostatic induction effect on the imidazole ring, causing high-field shifts of H-7 and H-8. The different distances between the carboxyl group and H-7 and H-8 lead to different degrees of displacement, resulting in changes in peak fusion.

[0051] According to the above conditions, nuclear magnetic resonance detection was carried out, and the nuclear magnetic spectrum was as follows Figure 2 shown.

[0052] Example 2

[0053] 20 mg of allyl imidazole cyclodextrin, 5 mg of guest molecule and their mixture were weighed and dissolved in a mixed solvent of CD3OD and D2O=40%:60% to obtain a sample solution. The sample solution was tested using 400M NMR and the obtained NMR spectrum was analyzed. It was found that H-9 of allyl imidazole cyclodextrin did not appear in CD3OD and D2O=40%:60%. When allyl imidazole cyclodextrin was mixed with 1-naphthalenesulfonic acid, H-7 and H-8 merged into one peak, and the peak of H-9 reappeared.

[0054] The reappearance of H-9 on cyclodextrin is due to the change in the acidity and alkalinity of the solution. It is also believed that this change occurs because: first, the acidic environment inhibits the hydrogen-deuterium exchange between H-9 and the deuterated reagent; second, the added molecule contains a sulfonic acid group, and the active hydrogen on the sulfonic acid group and the fully deuterated H-9 are exchanged again.

[0055] The special changes in the H-7 and H-8 peaks in allyl imidazole cyclodextrin and 1-naphthalenesulfonic acid are inferred to be because 1-naphthalenesulfonic acid enters the cyclodextrin cavity with the sulfonic acid group facing downward, resulting in close contact between the positively charged imidazole and the sulfonic acid ions of 1-naphthalenesulfonic acid, weakening the electrostatic induction effect on the imidazole ring, resulting in high-field shifts of H-7 and H-8. Due to the different distances of the carboxyl group from H-7 and H-8, the degree of displacement is different, resulting in changes in peak fusion.

[0056] According to the above conditions, nuclear magnetic resonance detection was carried out, and the nuclear magnetic spectrum was as follows Figure 3 shown.

[0057] Example 3

[0058] 20 mg of allyl imidazole cyclodextrin, 4 mg of guest molecule and their mixture were weighed and dissolved in a mixed solvent of CD3OD and D2O = 40%:60% to obtain a sample solution. The sample solution was tested using 400M NMR and the obtained NMR spectrum was analyzed. It was found that H-9 of allyl imidazole-β-cyclodextrin did not appear in CD3OD and D2O = 40%:60%. When allyl imidazole cyclodextrin was mixed with adamantane amine, the peak shapes of H-7 and H-8 did not change, and the peak of H-9 still did not appear.

[0059] The distinct effects of adamantane acid, adamantane amine and allyl imidazole cyclodextrin on H-7, H-8 and H-9 indicate different host-guest inclusion modes, indicating the specific recognition of allyl imidazole cyclodextrin for guests containing carboxyl or sulfonic acid groups.

[0060] According to the above conditions, nuclear magnetic resonance detection was carried out, and the nuclear magnetic spectrum was as follows Figure 4 shown.

[0061] In summary, combined with the above multiple embodiments, it can be seen that the present invention provides a method for the specific recognition of carboxyl or sulfonic acid group-containing guest molecules by cyclodextrin based on nuclear magnetic resonance. The method is simple to operate and has good recognition effect, providing a new method for developing new molecular recognition systems.

[0062] It should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0063] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A molecular recognition method based on nuclear magnetic resonance using cyclodextrin, characterized in that: The method comprises: Using nuclear magnetic resonance spectroscopy, measuring a first nuclear magnetic resonance hydrogen spectrum of the positively charged imidazole-modified cyclodextrin, a second nuclear magnetic resonance hydrogen spectrum of the molecule to be identified, and a third nuclear magnetic resonance hydrogen spectrum of the complex of the positively charged imidazole-modified cyclodextrin and the molecule to be identified; Comparing and analyzing the third H NMR spectrum with the first H NMR spectrum and the second H NMR spectrum, and determining the type of the molecule to be identified based on the chemical shift and peak shape changes of the peaks in each H NMR spectrum; The determining the type of the molecule to be identified based on the chemical shift and peak shape changes of the peaks in each hydrogen nuclear magnetic resonance spectrum specifically includes: if, in the third hydrogen nuclear magnetic resonance spectrum compared with the first hydrogen nuclear magnetic resonance spectrum, the peak shape of the hydrogen atoms on the imidazole ring of the positively charged imidazole-modified cyclodextrin changes, then determining that the molecule to be identified is an acidic molecule; the acidic molecule is a molecule with a carboxyl group or a sulfonic acid group.

2. The method according to claim 1, wherein The structural formula of the positively charged imidazole-modified cyclodextrin is: Wherein, n1+n2=n, n is selected from 6, 7 or 8, n1 and n2 are both natural numbers; R is selected from hydrogen, alkyl, alkenyl or alkynyl.

3. The method according to claim 1, wherein The molecules to be identified include molecules with carboxyl groups or sulfonic acid groups.

4. The method according to claim 3, wherein The molecules with carboxyl or sulfonic acid groups include adamantane acid, 2-naphthoic acid, 2-naphthosulfonic acid, lithocholic acid, ferrocenecarboxylic acid, acetic acid or deuterated acetic acid.

5. The method according to claim 1, wherein When the first nuclear magnetic resonance hydrogen spectrum, the second nuclear magnetic resonance hydrogen spectrum and the third nuclear magnetic resonance hydrogen spectrum are measured by nuclear magnetic resonance spectroscopy, a polar deuterated solvent is used to prepare the solution.

6. The method according to claim 5, wherein The polar deuterated solvent is deuterated water, or the polar deuterated solvent is a mixed deuterated solvent of deuterated methanol and deuterated water.

7. The method according to claim 6, wherein When the polar deuterated solvent is a mixed deuterated solvent of deuterated methanol and deuterated water, the volume ratio of the deuterated water in the mixed deuterated solvent is greater than 60%.

8. The method according to claim 1, wherein The method further comprises: determining that the molecule to be identified is an acidic molecule if, in the third hydrogen nuclear magnetic resonance spectrum, the peak shape of the hydrogen atoms on the imidazole ring of the positively charged imidazole-modified cyclodextrin changes compared to the first hydrogen nuclear magnetic resonance spectrum, the method further comprises: Compared with the first hydrogen nuclear magnetic resonance spectrum, in the third hydrogen nuclear magnetic resonance spectrum, if the peaks of H-7 and H-8 on the imidazole ring of the positively charged imidazole-modified cyclodextrin are fused and the peak of H-9 appears, then the molecule to be identified is determined to be an acidic molecule; Wherein, H-7, H-8 and H-9 on the imidazole ring of the positively charged imidazole-modified cyclodextrin are shown in the figure below: Wherein, R1 is selected from α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin; R2 is selected from hydrogen, alkyl, alkenyl or alkynyl.

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