Aza-polycyclic aromatic hydrocarbon organic ligand and preparation method thereof, molecular cage assembled by aza-polycyclic aromatic hydrocarbon and preparation method and application of molecular cage

Abstract

The invention relates to an aza-polycyclic aromatic hydrocarbon organic ligand and a preparation method thereof, an aza-polycyclic aromatic hydrocarbon assembled molecular cage and a preparation method and application thereof, the organic ligand takes dimethyl methylene bridged triphenylamine as a core, a benzene ring is modified by an R group, and the molecular cage is prepared from the organic ligand, the organic ligand and the aza-polycyclic aromatic hydrocarbon. A metal organic caged compound obtained by a coordination reaction with a metal complex; the molecular cage is of a truncated tetrahedral structure of twelve metals and eight ligands; each organic ligand is provided with three equal side arms which are wrapped and stacked together in a curved surface manner to form a pseudo six-section ligand; the organic ligands and the metal nodes are self-assembled to form a molecular cage with a hydrophobic cavity for recognizing guest molecules in the center. Compared with the prior art, the organic ligand has flexibility and is combined with metal to construct a novel water-soluble metal organic double-wall knotted flexible molecular cage, a size-adjustable cavity exists in the molecular cage, and selective recognition of nucleotide negative electricity biomolecules in a water phase is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal organic molecular cage main body design and host-guest recognition in supramolecular chemistry, and relates to an nitrogen-polycyclic aromatic hydrocarbon organic ligand and a preparation method thereof, a molecular cage assembled from nitrogen-polycyclic aromatic hydrocarbons and a preparation method and application thereof. Background Art

[0002] Supramolecular chemistry, also known as "chemistry beyond the molecular concept," aims to study the structure and function of entities formed by the combination of two or more chemical substances. It goes beyond the covalent bond-based molecular construction of traditional chemistry and focuses on weak intermolecular interactions (such as electrostatics, hydrogen bonds, and hydrophobic effects). The core concepts of supramolecular chemistry are "molecular recognition" and "self-assembly," namely, the spontaneous formation of supramolecular systems with specific functions and structures through specific intermolecular interactions.

[0003] Supramolecular self-assembly refers to the process by which basic structural units spontaneously organize or aggregate through non-covalent bonds to form a specific, ordered structure without external interference. Self-assembly is ubiquitous and plays a vital role in living systems. For example, the double helix structure of DNA, the double phospholipid layer of cell membranes, and the folded conformation of proteins are all examples of self-assembly.

[0004] The driving forces for self-assembly mainly include hydrogen bonding, van der Waals forces, π-π stacking, electrostatic interactions, hydrophobic effects, and coordination interactions. Based on the different driving forces in the self-assembly process, self-assembling supramolecular systems can be divided into three categories, namely, directional metal coordination, hydrogen bonding, and other non-covalent force-driven supramolecular systems. Among them, self-assembly systems driven by the coordination interaction between metal ions and ligands have attracted attention due to their controllable geometry, high stability, and broad application prospects, thus giving rise to a branch of supramolecular chemistry called "metal-organic supramolecular molecules." Based on their structural characteristics, metal-organic supramolecular molecules can be divided into two categories: one is discrete species with specific size, shape, and internal cavity, such as metal-organic cages (MOCs); the other is polymeric species with characteristic spatially extended arrays, such as metal-organic frameworks (MOFs).

[0005] A key strategy in the synthesis of organometallic coordination compounds is to utilize ligands with strong electron-donating properties to react with highly coordinating metal ions. Pyridine compounds, when used as ligands, precisely meet this requirement. Pyridine and its derivatives possess both strong σ electron-donating and π electron-accepting abilities. Therefore, they are often used as organic ligands to coordinate metals and are currently among the most widely used chelating ligands in coordination chemistry. The coordination mode of pyridine and its derivatives is structure-dependent and can be categorized as monodentate or polydentate. Currently, pyridine ligands and their complexes have important applications in research fields such as small molecule catalysis, molecular recognition, biomedicine, and superconducting materials.

[0006] The building blocks of pyridyl molecular cages reported so far are mostly highly rigid or flexible, while studies on molecular cages based on basic building blocks with a certain degree of curvature and nearly planar structures are relatively rare. Therefore, the development of molecular cages with moderate flexibility, structural stability, and excellent host-guest recognition properties is of great significance.

[0007] Recognition of anions in water is a key goal for applications in medicine, biology, and environmental science. Anions strongly bind to water, making the design of selective anion receptors that function in aqueous media challenging. Metal-organic cages (MOCs) are typically cationic, but currently used hosts suffer from poor water solubility, fixed internal cavity volumes, and a lack of specific functional bonding sites. Therefore, the development of new supramolecular MOC hosts for anion recognition is highly desirable. Summary of the Invention

[0008] The purpose of the present invention is to overcome at least one of the defects of the above-mentioned prior art and to provide an nitrogen-polycyclic aromatic hydrocarbon organic ligand and its preparation method, a nitrogen-polycyclic aromatic hydrocarbon assembled molecular cage and its preparation method and application. The organic ligand in the present invention is flexible and combines with metal to construct a new type of water-soluble metal-organic double-walled knotted flexible molecular cage. There is a cavity of adjustable size in the molecular cage, which realizes the selective recognition of negatively charged nucleotide biological molecules in the aqueous phase.

[0009] The purpose of the present invention can be achieved by the following technical solutions:

[0010] One of the technical solutions of the present invention is to provide an azapolycyclic aromatic hydrocarbon organic ligand, wherein the organic ligand L is a dimethylmethylene-bridged triphenylamine (DTPA) core and the R group modifies the benzene ring. The structural formula of the organic ligand L is as follows, and the R group is selected from one of the following formulas:

[0011]

[0012] The structural formula of the organic ligand L is selected from one of the following formulae:

[0013]

[0014] As a preferred technical solution, the structural formula of the organic ligand L is selected from one of the following formulae:

[0015]

[0016] One of the technical solutions of the present invention is to provide a method for preparing the nitrogen-polycyclic aromatic hydrocarbon organic ligand, which comprises the following steps:

[0017] S1, mixing an arylamine, an aryl halide, a base, a copper catalyst and an Ullmann coupling solvent, and subjecting the mixture to an Ullmann coupling reaction. After the reaction is complete, the reaction solution is cooled, filtered under reduced pressure, and the filter residue is washed. The filtrate is evaporated under vacuum to remove the solvent, and the crude product is purified to obtain a first intermediate S1;

[0018] S2, mixing the first intermediate S1, a nucleophilic reagent and a nucleophilic addition solvent, and performing a nucleophilic addition reaction. After the reaction is complete, quenching the reaction solution, removing the solvent by rotary evaporation, and purifying the crude product to obtain the second intermediate S2;

[0019] S3, mixing the second intermediate S2 with an acid catalyst, dehydrating the mixture, neutralizing the reaction solution after the reaction is complete, extracting the mixture, collecting the organic layer, and purifying the crude product to obtain a third intermediate S3;

[0020] S4, mixing the third intermediate S3, a brominating agent and a bromination solvent, and performing a bromination reaction. After the reaction is complete, the reaction solution is cooled, washed, extracted, and the organic layer is collected, dried, filtered, and the filtrate is vacuum evaporated to remove the solvent, and the crude product is purified to obtain a fourth intermediate S4;

[0021] S5. The fourth intermediate S4, the R group coupling fragment, the Suzuki coupling solvent, the palladium catalyst and the base are mixed, and the Suzuki coupling reaction is carried out. After the reaction is complete, the reaction solution is cooled, the solvent is removed under reduced pressure, extraction is carried out, the organic layer is collected, dried, filtered, and the solvent is removed from the filtrate by vacuum rotary evaporation. The crude product is purified to obtain the nitrogen-polycyclic aromatic hydrocarbon organic ligand L.

[0022] Furthermore, in step S1, the aromatic amine is methyl anthranilate, the aromatic halide is methyl 2-iodobenzoate, the base is potassium carbonate (K2CO3), the copper catalyst is copper (Cu), and the Ullmann coupling solvent is o-dichlorobenzene. The molar / volume ratio of the aromatic amine, aromatic halide, base, copper catalyst and Ullmann coupling solvent is 1 mol: (1.8-2.6 mol): (0.9-1.3 mol): (0.1-0.3 mol): (10-30 L),

[0023] In step S2, the nucleophilic reagent is methyllithium (CH3Li), the nucleophilic addition solvent is ether, the molar / volume ratio of the first intermediate S1, the nucleophilic reagent and the nucleophilic addition solvent is 1 mol: (6-10 mol): (10-30 L), the nucleophilic reagent is dissolved in the nucleophilic addition solvent, and the concentration of the nucleophilic reagent is 0.5-1.5 mol / L.

[0024] In step S3, phosphoric acid is used as the acid catalyst, the concentration of the acid catalyst is 75-95%, and the mole / volume ratio of the second intermediate S2 to the acid catalyst is 1 mol:(2-6 L).

[0025] In step S4, the brominating agent is N-bromosuccinimide (NBS), the bromination solvent is chloroform, and the molar / volume ratio of the third intermediate S3, the brominating agent and the bromination solvent is 1 mol: (2-4 mol): (5-15 L).

[0026] In step S5, the R group coupling fragment is selected from one of pyridine-4-boric acid, pyridine-3-boric acid, pyrimidine-5-boric acid pinacol ester, 2-chloropyridine-4-boric acid, 2,6-dimethylpyridine-4-boric acid pinacol ester, 4-aminophenylboric acid pinacol ester, and biboric acid pinacol ester, the Suzuki coupling solvent is selected from one or more of toluene and ethanol, the palladium catalyst is tetrakis(triphenylphosphine)palladium (Pd(PPh3)4), the base is potassium carbonate, the molar / volume ratio of the fourth intermediate S4, the R group coupling fragment, the Suzuki coupling solvent, the palladium catalyst and the base is 1 mol:(3-4.2 mol):(10-30 L):(0.05-0.25 mol):(5.5-9.5 mol), the base is dissolved in the base solvent, the base solvent is water, and the concentration of the base is 1-3 mol / L.

[0027] Furthermore, the temperature of the Ullmann coupling reaction in step S1 is 160-200° C. and the time is 48-96 h.

[0028] In step S2, the nucleophilic addition reaction is first carried out at -90 to -70°C for 0.5 to 1.5 hours, and then at 15 to 35°C for 3 to 5 hours.

[0029] The dehydration reaction temperature in step S3 is 15-35°C and the time is 1-3 hours.

[0030] The temperature of the bromination reaction in step S4 is 30-40°C and the time is 9-15 hours.

[0031] The temperature of the Suzuki coupling reaction in step S5 is 100-120° C., and the time is 72-120 h.

[0032] As a preferred technical solution, in step S1, after the reaction is completed under the protection of one or more protective gases selected from nitrogen, helium, and argon, the reaction solution is cooled to room temperature, filtered under reduced pressure, and the filter residue is washed with dichloromethane. The filtrate is vacuum evaporated to remove the solvent, and the crude product is recrystallized using petroleum ether to obtain the first intermediate S1.

[0033] In step S2, after the reaction is completed under the protection of one or more protective gases selected from nitrogen, helium, and argon, the reaction solution is quenched with ethanol under low temperature conditions, the solvent is removed by rotary evaporation, and the crude product is subjected to column chromatography using an eluent of n-hexane / ethyl acetate in a volume ratio of (4 to 6):1 to obtain a second intermediate S2.

[0034] After the reaction is complete in step S3, the reaction solution is neutralized with a sodium hydroxide aqueous solution having a concentration of 1 to 3 mol / L, extracted two to four times with dichloromethane, the organic layer is collected, and the crude product is subjected to column chromatography using n-hexane as an eluent, and recrystallized using n-hexane to obtain a third intermediate S3.

[0035] In step S4, after the reaction is completed under the protection of one or more protective gases selected from nitrogen, helium, and argon, the reaction solution is cooled to room temperature, washed with one or more of water and saturated brine, extracted with dichloromethane, the organic layer is collected, dried with one or more of anhydrous sodium sulfate and anhydrous magnesium sulfate, filtered, and the filtrate is vacuum evaporated to remove the solvent. The crude product is subjected to column chromatography using n-hexane as the eluent, and recrystallized using n-hexane to obtain the fourth intermediate S4.

[0036] In step S5, after the reaction is complete under the protection of one or more protective gases of nitrogen, helium, and argon, the reaction solution is cooled to room temperature, the solvent is removed under reduced pressure, the organic layer is collected by extraction with one or more of dichloromethane and saturated brine, and the organic layer is dried with one or more of anhydrous sodium sulfate and anhydrous magnesium sulfate, filtered, and the solvent is removed from the filtrate by vacuum rotary evaporation. The crude product is separated by thin layer chromatography using an ethyl acetate / methanol developing solution with a volume ratio of (8 to 10): 1, and recrystallized using n-hexane to obtain the nitrogen-polycyclic aromatic hydrocarbon organic ligand L.

[0037] One of the technical solutions of the present invention is to provide a molecular cage assembled from nitrogen-polycyclic aromatic hydrocarbons, wherein the molecular cage H is a metal-organic cage compound obtained by the coordination reaction of the organic ligand L and the metal M complex;

[0038] The molecular cage H is a truncated tetrahedral structure M of twelve metals and eight ligands 12 L8;

[0039] Each organic ligand L has three equal side arms, which are stacked together in a curved pattern to form a pseudo six-membered ligand;

[0040] The molecular cage H has two cavities. The central nitrogen atoms of two adjacent organic ligands L repel each other, and the methyl groups on the inner and outer walls repel each other, forming a narrow cavity.

[0041] The aromatic ring of the organic ligand L is naturally hydrophobic. The coordination number and geometric configuration of the metal ion force the organic ligand L to assemble at a specific angle. The hydrophobic groups tend to aggregate in water to reduce the surface area in contact with water, thereby reducing the free energy of the system. This process drives the organic ligand L and the metal node to self-assemble into a molecular cage with a hydrophobic cavity in the center for recognizing guest molecules.

[0042] One of the technical solutions of the present invention is to provide a method for preparing the molecular cage assembled by nitrogen-polycyclic aromatic hydrocarbons, which comprises the following steps:

[0043] The organic ligand L, the metal M complex and the coordination solvent are mixed and subjected to coordination reaction. After the reaction is complete, the reaction liquid is cooled, filtered, and the solvent is removed from the filtrate by vacuum rotary evaporation. The crude product is purified and vacuum dried to obtain a molecular cage H assembled from nitrogen-polycyclic aromatic hydrocarbons.

[0044] The synthetic route of the molecular cage H is as follows:

[0045] Pd 2+ +L→Pd-L;

[0046] Pt 2+ +L→Pt-L.

[0047] As a preferred technical solution, the R group of the organic ligand L is selected from pyridine or its substituents.

[0048] Furthermore, the metal M complex is selected from one or more of tetramethylethylenediamine palladium (II) salt and tetramethylethylenediamine platinum (II) salt, the coordination solvent is water, and the molar / volume ratio of the organic ligand L, the metal M complex and the coordination solvent is 1 mol: (1.3~1.7 mol): (3~7L).

[0049] Furthermore, the coordination reaction temperature is 70-90° C., and the time is 18-30 hours.

[0050] As a preferred technical solution, after the reaction is completed under the protection of one or more protective gases selected from nitrogen, helium, and argon, the reaction solution is cooled to room temperature, filtered, and the filtrate is vacuum evaporated to remove the solvent. The crude product is recrystallized from ethanol and vacuum dried to obtain a molecular cage H assembled from nitrogen-polycyclic aromatic hydrocarbons.

[0051] One of the technical solutions of the present invention is to provide an application of the molecular cage assembled from nitrogen-polycyclic aromatic hydrocarbons in the selective recognition of negatively charged nucleotide biomolecules.

[0052] Furthermore, the negatively charged nucleotide biomolecule is selected from one or more ribonucleotides or their derivatives among adenosine-5′-triphosphate (ATP), adenosine-5′-diphosphate (ADP), guanosine-5′-triphosphate (GTP), guanosine-5′-diphosphate (GDP).

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] (1) There is a strong electron resonance effect between the central nitrogen atom of the precursor triarylamine of the organic ligand unit module in the present invention and its adjacent benzene ring, indicating that it has certain planar structural characteristics; in addition, the introduction of a bridging unit at the ortho position of the nitrogen atom will significantly change the structure and electrical properties of the molecule; among them, orthogonal bridging can obtain a π framework with stronger rigidity and planar characteristics; when dimethylmethylene bridging is used, the rigid π framework will be given a certain flexibility; at the same time, the central nitrogen atom is locked due to the bridging, which makes the π framework as a whole present a micro-pyramid structure, and its peripheral methyl groups can prevent the dense and highly ordered stacking of the π framework; the unbonded lone pair electrons around the central nitrogen atom retain their electron donor characteristics, and further, they can also coordinate with metals to form a more complex assembly system; therefore, compared with all-carbon molecules or all-planar structures, bridged triarylamines have significant differences in structure, electrical properties and performance;

[0055] (2) The methyl groups protruding from the periphery of the molecular cage body of the present invention can not only reduce its high aggregation and increase the distortion of the internal cavity, but also serve as guest molecules to fill the internal cavity of the body, so that the organic ligand itself acts as a template during the synthesis process; the filling of methyl groups can not only avoid the collapse of the internal cavity of the molecular cage, thereby enhancing the thermal stability of the molecular cage, but also avoid the introduction of other guest molecules into the system, providing convenience for subsequent purification;

[0056] (3) The flexibility of the molecular cage body in the present invention provides more possible dynamic "fine-tuning" space, which provides a prerequisite for the induced bonding of the guest to the host and also provides the possibility for its excellent molecular recognition performance; at the same time, the molecular cage has attracted widespread attention in the field of supramolecular chemistry due to its structural diversity and easy adjustment of function; the special cavity structure and multiple functionalized bonding sites of the molecular cage are of great significance for achieving the separation of compounds with special shapes and special functional groups; since the molecular cage body has a hydrophobic cavity inside and 24 positive charges on the periphery, it can achieve selective recognition of negatively charged nucleotide biomolecules in the aqueous phase through the synergistic effect of hydrophobic effect and electrostatic interaction; therefore, the molecular cage body also shows application prospects in the fields of supramolecular catalysis, biomimetic molecular recognition reaction vessels, etc.

[0057] (4) The present invention uses dimethylmethylene-bridged triphenylamine as a skeleton unit, and sequentially introduces a series of diverse groups through bromination and Suzuki coupling to synthesize nitrogen-containing polycyclic aromatic hydrocarbon organic ligands; subsequently, this type of organic ligand is coordinated with transition metal palladium (II) or platinum (II) nodes to construct a new type of water-soluble metal organic double-walled knotted molecular cage; the double-walled knotted molecular cage is very novel in structure. Unlike interlocking cages or metal cages with large internal cavities, this structure does not have any internal multiple knots and entanglements, but has a certain cavity. At the same time, the organic ligand has a certain potential fine-tuning ability to expand the size of the internal cavity;

[0058] (5) The synthetic route of the present invention is simple, the raw materials are readily available, the reaction conditions are mild, the yield is high, and the reproducibility is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 is the H NMR spectrum of the first intermediate S1 in Example 1 of the present invention ( 1 H-NMR) spectra;

[0060] Figure 2 This is the H NMR spectrum of the second intermediate S2 in Example 1 of the present invention;

[0061] Figure 3 This is the H NMR spectrum of the third intermediate S3 in Example 1 of the present invention;

[0062] Figure 4 This is the H NMR spectrum of the fourth intermediate S4 in Example 1 of the present invention;

[0063] Figure 5 is the H NMR spectrum of the nitrogen-polycyclic aromatic hydrocarbon organic ligand L1 in Example 1 of the present invention;

[0064] Figure 6 is the C NMR spectrum of the nitrogen-polycyclic aromatic hydrocarbon organic ligand L1 in Example 1 of the present invention ( 13 C-NMR) spectra;

[0065] Figure 7 is a mass spectrum (MS) of the nitrogen-polycyclic aromatic hydrocarbon organic ligand L1 in Example 1 of the present invention;

[0066] Figure 8 This is the H NMR spectrum of the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons in Example 2.1 of the present invention;

[0067] Figure 9 This is the C NMR spectrum of the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons in Example 2.1 of the present invention;

[0068] Figure 10 2D COSY hydrogen spectrum of molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons in Example 2.1 of the present invention;

[0069] Figure 11 DOSY hydrogen spectrum of the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons in Example 2.1 of the present invention;

[0070] Figure 12 This is a high-resolution mass spectrometry (HRMS) image of the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons in Example 2.1 of the present invention;

[0071] Figure 13This is the H NMR spectrum of the host-guest complex of the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons dissolved in water and recognized by adenosine ribose and its nucleotide molecules in Example 2.1 of the present invention;

[0072] Figure 14 This is the H NMR spectrum of the host-guest complex formed by the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons in Example 2.1 of the present invention, dissolved in water, and identified with adenosine ribose and its nucleotide molecules after ultrasound.

[0073] Figure 15 This is the H NMR spectrum of the host-guest complex of the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons dissolved in water and recognized by guanosine ribose and its nucleotide molecules in Example 2.1 of the present invention;

[0074] Figure 16 This is the H NMR spectrum of the host-guest complex formed by the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons in Example 2.1 of the present invention, dissolved in water, and identified with guanosine ribose and its nucleotide molecules after ultrasound.

[0075] Figure 17 This is the H NMR spectrum of the host-guest complex of the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons dissolved in water and recognized by cytidine ribose and its nucleotide molecules in Example 2.1 of the present invention;

[0076] Figure 18 This is the H NMR spectrum of the host-guest complex formed by the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons in Example 2.1 of the present invention, dissolved in water, and identified with cytidine ribose and its nucleotide molecules after ultrasound.

[0077] Figure 19 This is the H NMR spectrum of the host-guest complex of the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons dissolved in water and recognized by uridine ribose and its nucleotide molecules in Example 2.1 of the present invention;

[0078] Figure 20 This is the H NMR spectrum of the host-guest complex formed by the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons in Example 2.1 of the present invention, dissolved in water, and identified with uridine ribose and its nucleotide molecules after ultrasound.

[0079] Figure 21 This is a hydrogen spectrum of the host-guest complex of the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons dissolved in water and recognized by adenosine-5′-triphosphate molecules in Example 2.1 of the present invention;

[0080] Figure 22 This is a graph showing the isothermal titration calorimetric experimental results of the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons dissolved in water and recognizing with adenosine-5′-triphosphate molecules in Example 2.1 of the present invention;

[0081] Figure 23is the X-ray single crystal diffraction pattern of the molecular cage H1 assembled from nitrogen-polycyclic aromatic hydrocarbons in Example 2.1 of the present invention;

[0082] Figure 24 The single crystal structure and structural space diagram of the molecular cage H1 assembled by nitrogen-polycyclic aromatic hydrocarbons in Example 2.1 of the present invention. DETAILED DESCRIPTION

[0083] The present invention is described in detail below with reference to specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0084] Unless otherwise specified, the equipment used in the following examples are all conventional equipment in the art; the reagents used are all commercially available products or prepared by conventional methods in the art unless otherwise specified. Anything not described in detail in the following examples can be achieved by conventional experimental means in the art.

[0085] Example 1.1:

[0086] A nitrogen-polycyclic aromatic hydrocarbon organic ligand and a preparation method thereof, the reaction equation is as follows:

[0087]

[0088] The specific steps are as follows:

[0089] S1, methyl o-aminobenzoate (1 mmol), methyl 2-iodobenzoate (2.18 mmol), potassium carbonate (K2CO3, 1.13 mmol), copper (Cu, 0.19 mmol) and o-dichlorobenzene (20 mL) were added to a 250 mL round-bottom flask, and the nitrogen was replaced three times for degassing to use nitrogen protection. The reaction was stirred at 180 ° C for 72 h. After the Ullmann coupling reaction was complete, the reaction solution was cooled to room temperature of 25 ° C, filtered under reduced pressure, and the filter residue was washed with dichloromethane. The filtrate was dried under vacuum to remove the solvent, and the crude product was recrystallized from petroleum ether to obtain the first intermediate S1 as a white crystalline solid with a yield of 40%;

[0090] like Figure 1 As shown, 1 H NMR (600MHz, DMSO-d6, 298K) δ7.51(dd,J=7.7,1.7Hz,1H),7.47-7.43(m,1H),7.15(t,J=7.5Hz,1H),6.94(d,J=8.2Hz,1H),3.26(s,3H);

[0091] S2, the vacuum-dried first intermediate S1 (1 mmol) was added to a 250 mL double-necked flask, and the nitrogen was replaced three times for degassing to use nitrogen protection, and a solution of methyl lithium (CH3Li) in anhydrous ether (1 mol / L, 8 mL) and anhydrous ether (20 mL) were slowly added dropwise at -78 ° C. The reaction was stirred for 1 h at -78 ° C. The temperature was slowly raised to room temperature of 25 ° C. The reaction was continued to stir at room temperature of 25 ° C. for 4 h. After the nucleophilic addition reaction was complete, ethanol was slowly added dropwise in an ice bath to quench the reaction solution. The solvent was removed by spin drying, and the crude product was eluted with n-hexane / ethyl acetate in a volume ratio of 5:1. The second intermediate S2 as a yellow-white solid was obtained with a yield of 30%;

[0092] like Figure 2 As shown, 1 H NMR (600MHz, DMSO-d6, 298K) δ7.30-7.26(m,1H),7.03-7.00(m,2H),6.51-6.48(m,1H),5.63(s,1H),1.54(s,3H),0.82(s,3H);

[0093] S3, the second intermediate S2 (1 mmol) was added to a 250 mL round-bottom flask containing 85% concentrated phosphoric acid (4 mL), and the reaction was stirred at room temperature of 25 ° C for 2 h. After the dehydration reaction was complete, the reaction solution was neutralized with a 2 mol / L sodium hydroxide aqueous solution, extracted three times with dichloromethane, and the lower organic layer was collected. The crude product was chromatographed on silica gel using n-hexane as the eluent, and recrystallized with n-hexane to obtain the third intermediate S3 as a white solid with a yield of 47%;

[0094] like Figure 3 As shown, 1 H NMR (600MHz, DMSO-d6, 298K) δ7.44 (d, J = 7.7Hz, 6H), 7.13 (t, J = 7.7Hz, 3H), 1.56 (s, 18H);

[0095] S4, the third intermediate S3 (1 mmol) and N-bromosuccinimide (NBS, 3 mmol) were added to a 250 mL round-bottom flask, chloroform (10 mL) was added, and the nitrogen was replaced three times for degassing to use nitrogen protection, and the reaction was stirred at 35 ° C overnight for 12 h. After the bromination reaction was complete, the reaction solution was cooled to room temperature of 25 ° C, washed with water and saturated brine, extracted with dichloromethane, and the lower organic layer was collected, dried over anhydrous sodium sulfate, filtered, and the filtrate was dried under vacuum to remove the solvent. The crude product was chromatographed on silica gel with n-hexane as eluent, and recrystallized from n-hexane to obtain the fourth intermediate S4 as a white solid in a yield of 75%;

[0096] like Figure 4 As shown, 1 H NMR (600MHz, DMSO-d6, 298K) δ7.57 (s, 6H), 1.55 (s, 18H);

[0097] S5, the fourth intermediate S4 (1mmol) and pyridine-4-boric acid (3.6mmol) were added to a 250mL round-bottom flask, the nitrogen was replaced three times for degassing with nitrogen protection, ultra-dry toluene / ethanol (2:1, v / v, 21mL) was added, and the mixture was stirred and dissolved at room temperature of 25°C, tetrakis(triphenylphosphine)palladium (Pd(PPh3)4, 0.15mmol) and degassed potassium carbonate aqueous solution (2mol / L, 3.75mL) were added, the nitrogen was replaced three times again for nitrogen protection, and the reaction was stirred at 110°C for 96h. After the Suzuki coupling reaction was complete, the reaction solution was cooled to room temperature of 25°C, the solvent was removed under reduced pressure, and the mixture was extracted with dichloromethane and saturated brine respectively. The lower organic layer was collected, dried over anhydrous magnesium sulfate, filtered, and the filtrate was dried under vacuum to remove the solvent. The crude product (R f =0.04 (EA / MeOH)), and recrystallized from n-hexane to obtain the orange-yellow solid nitrogen-polycyclic aromatic hydrocarbon organic ligand L1 with a yield of 70%;

[0098] like Figures 5 to 7 As shown, 1 H NMR (600MHz, DMSO-d6, 298K) δ7.99 (s, 6H), 7.68 (d, J = 4.0Hz, 3H), 7.38 (s, 3H), 1.69 (s, 18H); 13 C NMR (151MHz, CDCl3, 298K) δ150.28,147.91,132.97,132.15,130.82,122.42,121.06,35.97,33.40; MS(ESI):calcd.for C 42 H 36 N4:596.78,found:597.29.

[0099] Example 2.1:

[0100] A molecular cage assembled from nitrogen-polycyclic aromatic hydrocarbons and a preparation method thereof, the reaction equation is as follows:

[0101]

[0102] The synthetic route is as follows:

[0103] Pd 2+ +L→Pd-L;

[0104] Pt 2+ +L→Pt-L ;

[0105] The specific steps are as follows:

[0106] The pyridine-substituted organic ligand L1 (2 mmol) and the metal M complex cis-tetramethylethylenediamine palladium (II) nitrate (Pd (tmeda) (NO 3 ) 2, 3 mmol) in Example 1 were added to a 25 mL round-bottom flask containing 5 mL of distilled water, and the nitrogen was replaced three times for degassing to use nitrogen protection. The reaction was stirred at 80° C. for 24 h. After the coordination reaction was complete, the reaction solution was cooled to room temperature of 25° C. and filtered. The filtrate was vacuum-dried to remove the solvent. The crude product was recrystallized from ethanol and vacuum-dried to obtain a yellow solid nitrogen-polycyclic aromatic hydrocarbon assembled molecular cage H1 with a yield of 20%;

[0107] A saturated sodium tetrafluoroborate (NaBF4) aqueous solution (9.8 mol / L, 2 mL) was added to a 25 mL round-bottom flask containing an aqueous solution (1 mol / L, 1 mL) of the molecular cage H1, and the nitrogen was replaced three times for degassing to use nitrogen protection. The reaction was stirred at room temperature of 25°C for 2 h. After solid precipitated from the anion exchange reaction, the reaction solution was filtered, the filter cake was collected, recrystallized using acetonitrile, and vacuum dried to obtain a yellow solid nitrogen-polycyclic aromatic hydrocarbon-assembled molecular cage with tetrafluoroborate ions replacing nitrate ions as anions with a yield of 87%.

[0108] like Figures 8 to 12 As shown, 1 H NMR(600MHz,D2O,298K)δ9.57-9.54(m,16H),9.47(d,J=5.5Hz,8H),9.25(d,J=5.8Hz,8H),8.44(d,J=6.2Hz,7H),8.2 9(d,J=6.1Hz,8H),8.15(s,8H),7.63(s,8H),7.54(s,8H),7.32(s,8H),6.73(s,8H),5.85(s,8H),3.35(s,48H),3.14 -2.95(m,144H),1.09(s,25H),0.65(s,24H),0.47(s,24H),-1.18(s,24H); 13C NMR(151MHz,D2O,298K)δ152.82,151.66,150.72,150.24,149.52,149.18,13 3.87,133.43,131.36,130.44,130.17,129.81,128.03,127.80,123.79,123.5 2,121.69,120.52,120.09,119.26,117.86,62.80,50.92,50.84,50.59,50.2 5,35.26,35.16,34.96,33.92,21.94,21.73; DOSY-NMR (D2O, 298K): D=1.23×10 -10 m 2 / s;HR-MS(ESI):calcd.for[(C 42 H 36 N4)8(C6H 16 ) 12 Pd 12 (NO3) 19 +H] 5+ :1723.22,found:1723.36.calcd.for[(C 42 H 36 N4)8(C6H 16 ) 12 Pd 12 (BF4) 19 ] 5+ :1817.57,found:1817.57.

[0109] Example 2.2:

[0110] A molecular cage assembled by nitrogen-polycyclic aromatic hydrocarbons and a preparation method thereof are basically the same as those in Example 2.1, except that the metal M complex is replaced by cis-tetramethylethylenediamine palladium (II) nitrate with cis-tetramethylethylenediamine platinum (II) nitrate (Pt(tmeda)(NO3)2), and a yellow solid nitrogen-polycyclic aromatic hydrocarbon assembled molecular cage H2 is obtained with a yield of 25%.

[0111] The molecular cage is subjected to the following tests or experiments, and the test results are then analyzed.

[0112] Test Example 1:

[0113] The NMR data of the host-guest complex under different guest molecules and different environments were analyzed for the molecular cage. The specific steps are as follows:

[0114] Molecular cage H1 (10 μmol) was added to a 25 mL sample bottle, and heavy water (20 mL) was added. The mixture was sonicated at 30 kHz for 2 min at 25 °C to completely dissolve the cage H1, obtaining a clear, light yellow molecular cage H1 solution (0.5 mmol / L).

[0115] Molecular cage H1 solution (0.5 mmol / L, 500 μL) was added to an NMR tube, and a heavy aqueous solution of nucleotide biomolecules (100 mmol / L, 5 μL) was added. The mixture was stirred at room temperature of 25°C for 1 min, and a parallel experiment was performed with 30 kHz ultrasound for 90 min. The NMR hydrogen spectrum was measured on a Bruker AVANCEⅢHD 600M machine (600 MHz, D2O, 298 K). The spectral width of the scan was set to 25, the center was 5, and the number of scans was 64.

[0116] Nucleotide biomolecules include uridine (U), uridine-5′-monophosphate disodium salt (UMP-2Na + ), uridine-5′-diphosphate disodium salt (UDP-2Na + ), uridine-5′-triphosphate trisodium salt (UTP-3Na + ), cytidine (C), cytidine-5′-monophosphate disodium salt (CMP-2Na + ), cytidine-5′-diphosphate disodium salt (CDP-2Na + ), cytidine-5′-triphosphate disodium salt (CTP-2Na + ), guanosine (G), guanosine-5′-monophosphate disodium salt (GMP-2Na + ), guanosine-5′-diphosphate disodium salt (GDP-2Na + ), guanosine-5′-triphosphate disodium salt (GTP-2Na + ), adenosine (A), adenosine-5′-monophosphate disodium salt (AMP-2Na + ), adenosine-5′-diphosphate disodium salt (ADP-2Na + ), adenosine-5′-triphosphate disodium salt (ATP-2Na + ), the specific structure is as follows:

[0117]

[0118] like Figures 13 to 20 As shown, the NMR of the host molecule of the molecular cage H1 in Example 2.1 has undergone relatively obvious changes. For example, the hydrogen in the aromatic region has shifted to the low field region, and the peak shape has undergone obvious splitting. The hydrogen in the high field region belongs to the methyl group on the organic ligand L1, and has also changed from a single peak s to a d peak. The nucleotide guest molecule has also undergone slight changes, resulting in a minimum chemical shift change of 0.01ppm and a maximum of 0.7ppm.

[0119] Taking the adenosine series as an example of ribonucleotides, the addition of adenosine and adenosine-5'-monophosphate does not lead to splitting and displacement of the host and guest; however, the addition of adenosine-5'-diphosphate and adenosine-5'-triphosphate will clearly produce this host-guest phenomenon.

[0120] To rule out insufficient contact time, another parallel experiment was conducted. External force was applied, followed by ultrasonication at 25°C for 90 minutes and then NMR observation. Compared to the shaking group at 25°C, no changes were observed. This suggests that time and external force do not affect host-guest recognition; host-guest recognition is highly correlated with the number of anionic phosphates.

[0121] Next, we investigated 12 other molecules in the guanosine, cytidine, and uridine ribonucleotide series, and conducted the same shaking and ultrasonic exploration and comparison at 25°C for 90 minutes. We finally found that these conditions of subject and object did not exist in other object molecules, but only appeared clearly in the four ribonucleotide molecules or their derivatives: adenosine-5′-diphosphate, adenosine-5′-triphosphate, guanosine-5′-diphosphate, and guanosine-5′-triphosphate.

[0122] In Example 2.1, the molecular cage H1 host molecule has no significant recognition performance for neutral guest molecules, such as pyrene, adamantane, and long-chain alkanes. This is because the volume of these guest molecules is large and does not match the volume of the molecular cage H1 host molecule.

[0123] Test Example 2:

[0124] The above molecular cage was subjected to nuclear magnetic titration of the host-guest complex of adenosine-5′-triphosphate guest molecule. The specific steps are as follows:

[0125] The molecular cage H1 solution (0.25 mmol / L, 500 μL) was added to an NMR tube, and a deuterated aqueous solution of adenosine-5'-triphosphate disodium salt (50 mmol / L) was added dropwise at room temperature of 25°C according to the equivalent amount. The H NMR spectrum was measured on a Bruker AVANCEⅢHD 600M machine (600 MHz, D2O, 298 K), and the spectral width of the scan was set to 25, the center to 5, and the number of scans to 64.

[0126] like Figure 21As shown in Figure 2, after 0.4 eq of adenosine-5'-triphosphate was added, the peak at 0.45 ppm of the main molecule of the molecular cage H1 in Example 2.1 showed a clear split from a single peak to a double peak. From the perspective of the main molecular structure of the molecular cage H1, this is due to the influence of the methyl peak of the organic ligand L1 on the outer wall side close to the inner wall and the methyl peak of the organic ligand L1 on the inner wall side close to the outer wall. At the same time, the number of peak groups and peak shape of pyridine α-H also changed.

[0127] Next, with the increase in the amount of adenosine-5'-triphosphate titrated, the peak splitting of the methyl peak and the aromatic region gradually became clearer and more obvious. After 1.0 eq, the methyl peak of the organic ligand L1 on the inner wall close to the internal cavity was also disturbed, resulting in an obvious splitting from single peak to double peak. The hydrogen of the benzene ring on the dimethylmethylene-bridged triphenylamine unit in the center of the organic ligand L1 also split due to the host-guest interaction; this trend remained stable until after 2.0 eq; at the same time, during this period, other peaks of the main molecule of the molecular cage H1 in Example 2.1 also underwent a series of changes. For example, the peak on pyridine also produced some drift. From the overall trend, it first shifted to the high field region and then to the low field region.

[0128] Test Example 3:

[0129] The isothermal titration calorimetry experiment of adenosine-5′-triphosphate guest molecule was carried out on the above molecular cage. The specific steps are as follows:

[0130] A deionized water solution of molecular cage H1 (0.5 mmol / L, 0.3 mL) was placed in the sample cell, and a deionized water solution of adenosine-5′-triphosphate disodium salt (5 mmol / L, 50 μL) was placed in the syringe;

[0131] Each titration experiment involved 26 injections of 2 μL each, with a 300-s interval between each injection. The heat of dilution generated by the blank solvent of adenosine-5'-triphosphate disodium salt dripping into the sample cell was deducted from each set of data. The data collected and measured by the MicroCal VP-ITC machine could be fitted by a computer-simulated "Multiple Sites" model.

[0132] like Figure 22As shown, there are two binding modes for the binding of adenosine-5′-triphosphate guest molecules. In the first mode, the enthalpy change ΔH1 = 53.38 kJ / mol, and the entropy change ΔS1 = 2.483E2 J / mol·K, both of which are positive, indicating that the first binding process is an endothermic process with an increase in entropy. In the second mode, the enthalpy change ΔH2 = -148.2 kJ / mol, and the entropy change ΔS2 = -4.094E2 J / mol·K, both of which are negative, indicating that the second binding process is an exothermic process with a decrease in entropy. According to the Gibbs free energy change calculation formula, ΔG = ΔH-TΔS, it is calculated that ΔG1 = -20.41 kJ / mol and ΔG2 = -26.20 kJ / mol, both of which are negative values, indicating that both binding processes occur spontaneously at room temperature of 25°C.

[0133] like Figure 23 and Figure 24 As shown, X-ray crystal structure analysis shows that the molecular cage H1 in Example 2.1 is a truncated tetrahedral structure M of twelve metal eight ligands. 12 L8, consisting of 4 hexagons and 4 triangles, a total of 8 faces;

[0134] Among them, each hexagon is adjacent to three triangles, and each triangle is adjacent to three hexagons, with a side length of

[0135] Each organic ligand L1 has three identical side arms, which are wrapped and stacked together in a curved surface. The inner and outer walls together form a pseudo-hexagonal ligand, and the hexagonal face can be regarded as the cross-section of the inner and outer walls.

[0136] Twelve vertices are occupied by palladium metal ligands, and each palladium center is bound to a pyridine site of an outer-wall organic ligand L1 and an inner-wall organic ligand L1 on another face;

[0137] The molecular cage H1 has a total of 5 cavities, of which 4 cavities are due to the mutual repulsion of the central nitrogen atoms of the two organic ligands L1 on the inner and outer walls, the mutual repulsion of the methyl groups on the inner and outer walls on the sides, and the NN center distance. The resulting narrow space;

[0138] The other cavity is due to the natural hydrophobicity of the aromatic ring of the organic ligand L1. The coordination number and geometric configuration of the metal ion force the organic ligand L1 to assemble at a specific angle. The hydrophobic groups tend to aggregate in water to reduce the surface area in contact with water, thereby reducing the free energy of the system. This process drives the organic ligand L1 and the metal node to self-assemble into the molecular cage H1. A smaller hydrophobic cavity is generated in the center of the molecular cage H1 to recognize the guest molecule. The central volume is calculated by CageCavityCalc:

[0139] From a topological point of view, the topology of the molecular cage H1 is marked as Figure eight knot (41knot), and it forms a high-symmetry space group (R-3c) arrangement. There is no cross and interlocking structure in the entire molecular cage H1.

[0140] In addition, the structure of the molecular cage H1 is very rare, extremely special and novel. Literature research shows that discrete double-walled knotted molecular cages without interlocking structures have not been reported, and this invention is the first report.

[0141] The molecular cage H1 in Example 2.1 is relatively stable to acids and bases, and has a good solubility in water, which can reach above 10 mmol / L. The solubility will increase in hot water, but will not destroy the molecular cage structure.

[0142] In Example 2.1, the molecular cage H1 is a cationic host molecule that can strongly bind to negatively charged nucleotide biomolecules through electrostatic interaction, hydrophobic effect, and non-covalent interactions such as CH-π. The binding constant is K 11 =2.85×10 4 M -1 , K 12 =7.2×10 3 M -1 .

[0143] This study synthesized a uniquely flexible organic ligand, L1, which self-assembled with different metal ligands, ethylenediaminetetramethyl palladium(II) salt and ethylenediaminetetramethyl platinum(II) salt, respectively, using nitrate as an anion, to form a rare metal-organic double-walled molecular knotted cage, H1. A series of screening conditions were conducted to investigate the formation of the molecular cage H1. Single crystal analysis and other methods were used to analyze the structural characteristics and physicochemical properties of the cage compared to the pure organic ligand L1. Finally, the molecular cage H1 was investigated for its recognition of nucleotide anionic guest molecules.

[0144] The double-walled knotted molecular cage H in the present invention is very novel in structure. Unlike interlocking cages or metal cages with large internal cavities, this structure does not have any internal multiple knots and entanglements, while having a certain cavity. At the same time, the organic ligand L has a certain potential fine-tuning ability to expand the size of the internal cavity, which has potential application value for molecular recognition.

[0145] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A nitrogen-polycyclic aromatic hydrocarbon organic ligand, characterized in that The organic ligand has dimethylmethylene bridged triphenylamine as the core and an R group modified benzene ring. The structural formula of the organic ligand is as follows, and the R group is selected from one of the following formulas:

2. A method for preparing the nitrogen-polycyclic aromatic hydrocarbon organic ligand according to claim 1, characterized in that: The method comprises the following steps: S1, mixing an arylamine, an aryl halide, a base, a copper catalyst, and an Ullmann coupling solvent, and performing an Ullmann coupling reaction to obtain a first intermediate; S2, mixing the first intermediate, a nucleophilic reagent, and a nucleophilic addition solvent, and performing a nucleophilic addition reaction to obtain a second intermediate; S3, mixing the second intermediate and an acid catalyst, and performing a dehydration reaction to obtain a third intermediate; S4, mixing the third intermediate, a brominating agent and a bromination solvent, and performing a bromination reaction to obtain a fourth intermediate; S5. Mixing the fourth intermediate, the R group coupling fragment, a Suzuki coupling solvent, a palladium catalyst and a base, and performing a Suzuki coupling reaction to obtain an aza-polycyclic aromatic hydrocarbon organic ligand.

3. The method for preparing a nitrogen-polycyclic aromatic hydrocarbon organic ligand according to claim 2, wherein: In step S1, the aromatic amine is methyl o-aminobenzoate, the aromatic halide is methyl 2-iodobenzoate, the base is potassium carbonate, the copper catalyst is copper, and the Ullmann coupling solvent is o-dichlorobenzene. The molar / volume ratio of the aromatic amine, aromatic halide, base, copper catalyst and Ullmann coupling solvent is 1 mol: (1.8-2.6 mol): (0.9-1.3 mol): (0.1-0.3 mol): (10-30 L), In step S2, the nucleophilic reagent is methyl lithium, the nucleophilic addition solvent is diethyl ether, the molar / volume ratio of the first intermediate, the nucleophilic reagent and the nucleophilic addition solvent is 1 mol: (6-10 mol): (10-30 L), the nucleophilic reagent is dissolved in the nucleophilic addition solvent, and the concentration of the nucleophilic reagent is 0.5-1.5 mol / L. In step S3, phosphoric acid is used as the acid catalyst, the concentration of the acid catalyst is 75-95%, and the molar / volume ratio of the second intermediate to the acid catalyst is 1 mol:(2-6 L). In step S4, the brominating agent is N-bromosuccinimide, the brominating solvent is chloroform, and the molar / volume ratio of the third intermediate, the brominating agent and the brominating solvent is 1 mol: (2-4 mol): (5-15 L). In step S5, the R group coupling fragment is selected from one of pyridine-4-boric acid, pyridine-3-boric acid, pyrimidine-5-boric acid pinacol ester, 2-chloropyridine-4-boric acid, 2,6-dimethylpyridine-4-boric acid pinacol ester, 4-aminophenylboric acid pinacol ester, and biboric acid pinacol ester, the Suzuki coupling solvent is selected from one or more of toluene and ethanol, the palladium catalyst is tetrakis(triphenylphosphine)palladium, the base is potassium carbonate, the molar / volume ratio of the fourth intermediate, the R group coupling fragment, the Suzuki coupling solvent, the palladium catalyst and the base is 1 mol:(3-4.2 mol):(10-30 L):(0.05-0.25 mol):(5.5-9.5 mol), the base is dissolved in the base solvent, the base solvent is water, and the concentration of the base is 1-3 mol / L.

4. The method for preparing a nitrogen-polycyclic aromatic hydrocarbon organic ligand according to claim 2, wherein: The temperature of the Ullmann coupling reaction in step S1 is 160-200°C and the time is 48-96h. In step S2, the nucleophilic addition reaction is first carried out at -90 to -70°C for 0.5 to 1.5 hours, and then at 15 to 35°C for 3 to 5 hours. The dehydration reaction temperature in step S3 is 15-35°C and the time is 1-3 hours. The temperature of the bromination reaction in step S4 is 30-40°C and the time is 9-15 hours. The temperature of the Suzuki coupling reaction in step S5 is 100-120° C., and the time is 72-120 h.

5. A molecular cage assembled from nitrogen-polycyclic aromatic hydrocarbons, characterized in that: The molecular cage is a metal-organic cage compound obtained by the coordination reaction of the organic ligand as claimed in claim 1 with a metal complex; The molecular cage is a truncated tetrahedral structure of twelve metals and eight ligands; Each organic ligand has three equal side arms, which are packed together in a curved pattern to form a pseudo-six-membered ligand; The organic ligands and metal nodes self-assemble into a molecular cage with a hydrophobic cavity in the center that recognizes guest molecules.

6. A method for preparing a molecular cage assembled from nitrogen-polycyclic aromatic hydrocarbons as claimed in claim 5, characterized in that: The method comprises the following steps: The organic ligand, the metal complex and the coordination solvent are mixed and subjected to coordination reaction to obtain a molecular cage assembled by nitrogen-polycyclic aromatic hydrocarbons.

7. The method for preparing a molecular cage assembled from nitrogen-polycyclic aromatic hydrocarbons according to claim 6, characterized in that: The metal complex is selected from one or more of tetramethylethylenediamine palladium (II) salt and tetramethylethylenediamine platinum (II) salt, the coordination solvent is water, and the molar / volume ratio of the organic ligand, the metal complex and the coordination solvent is 1 mol: (1.3 to 1.7 mol): (3 to 7 L).

8. The method for preparing a molecular cage assembled from nitrogen-polycyclic aromatic hydrocarbons according to claim 6, characterized in that: The temperature of the coordination reaction is 70-90° C., and the time is 18-30 hours.

9. Use of the molecular cage assembled from nitrogen-polycyclic aromatic hydrocarbons as claimed in claim 5 in selectively recognizing negatively charged biological molecules such as nucleotides.

10. The use of a molecular cage assembled from nitrogen-polycyclic aromatic hydrocarbons according to claim 9, characterized in that: The negatively charged nucleotide biomolecule is selected from one or more ribonucleotides of adenosine-5'-triphosphate, adenosine-5'-diphosphate, guanosine-5'-triphosphate, guanosine-5'-diphosphate or their derivatives.

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