Metal organic framework and application thereof, and purification method of scutellarin

Abstract

The invention provides a metal organic framework which is prepared from zinc nitrate and ligands as raw materials, and the ligands are terephthalic acid (PTA) and phenylenediboronic acid (BDBA); the molar ratio of zinc to the ligand (PTA + BDBA) is (1: 4)-(5: 4), and the molar percentage of BDBA in the ligand is 0-50%. The invention also provides a preparation method of the metal organic framework and a purification method of scutellarin. According to the method, firstly, the scutellarin in the traditional Chinese medicinal material water extract is efficiently adsorbed through the boric acid group-MOF, then the MOF material is eluted by adopting DES as an eluent, the volume of the eluent is small, the content of the scutellarin is high, the amount of water added during water precipitation is small, and the content of the scutellarin is high. The practical application of the preparation of the scutellarin in the traditional Chinese medicine erigeron breviscapus is facilitated.

Description

Technical Field

[0001] The present invention relates to a metal-organic framework and its use, and a method for purifying scutellarin. Background Art

[0002] Scutellarin, also known as scutellarin, is a flavonoid component that plays a major biological activity in Erigeron breviscapus. Scutellarin has multiple effects such as antioxidant, anti-inflammatory, vasodilating, antiplatelet, anticoagulant, and myocardial protection, and has been clinically used to treat stroke, myocardial infarction, and diabetic complications. Therefore, it is necessary to establish a green and efficient method for purifying and preparing scutellarin from Erigeron breviscapus.

[0003] Among various types of solid-phase extraction methods currently, dispersive solid-phase extraction (DSPE) has been widely used in the purification and enrichment of samples due to its advantages such as simple operation, less adsorbent consumption, less solvent consumption, and high efficiency. DSPE mainly directly mixes the sample with the solid-phase adsorbent, makes the adsorbent and the target compound fully contact during the mixing process, then separates the solid-phase extractant by means of centrifugation and other separation methods, and then desorbs with a certain solvent to achieve the separation or enrichment of the target compound. In DSPE, the type and properties of the adsorbent play a very important role in the extraction efficiency of the target compound. In recent years, metal-organic frameworks (MOFs) have been applied in DSPE to a certain extent. One advantage of MOFs is that the properties of MOFs can be adjusted according to the structural characteristics of the target compound by the types of metal ions and ligands to achieve more efficient purification. However, the pore size and surface properties of MOFs need to be precisely regulated to achieve efficient adsorption of specific compounds. Different target compounds may require different pore structures and surface modifications, which increases the difficulty of material design and optimization.

[0004] Deep eutectic solvents (DESs) are a new type of green solvent, which have the advantages of simple synthesis method, biodegradability, adjustable properties, etc., and have been widely used in the extraction and purification of flavonoid components in traditional Chinese medicine. Ultrasonic extraction and purification of scutellarin from Erigeron breviscapus DOI:

[0005] 10.1016 / j.ultsonch.2023.106560. Use DESs as the extraction solvent to extract scutellarin from the Chinese medicinal material Erigeron breviscapus, and then precipitate the DESs extract with water. Although this method has the advantages of high extraction efficiency and greenness compared with traditional solvents, due to the relatively high viscosity of DESs, it will cause inconvenience during operation; in addition, when precipitating the DESs extract by adding water, because the volume of the DESs extract is relatively large, the volume of water added is also relatively large, causing inconvenience to the actual purification operation. Summary of the Invention

[0006] The present invention uses DESs to replace organic solvents as the eluent of DSPE. An efficient adsorption DSPE method for scutellarin with Zn-PTA-BDBA MOF as the adsorbent and DESs as the eluent is established and used for the purification of scutellarin in the Chinese medicinal material Erigeron breviscapus and the pretreatment of scutellarin in urine samples.

[0007] The present invention provides a metal-organic framework, which is prepared from zinc nitrate and ligands as raw materials. The ligands are terephthalic acid PTA and 4,4'-boronic acid biphenyl BDBA; the molar ratio of zinc to ligands (PTA + BDBA) is 1:4 to 5:4, and the molar percentage of BDBA in the ligands is 0 to 50%.

[0008] Further, the molar ratio of zinc to ligands (PTA + BDBA) is 1:2, and the molar percentage of BDBA in the ligands is 25%.

[0009] Specifically, the molar ratio of zinc nitrate, terephthalic acid, and 4,4'-boronic acid biphenyl is: 2:3:1.

[0010] The present invention provides a preparation method of the metal-organic framework, which includes the following steps:

[0011] a. Weigh three raw materials: zinc nitrate, terephthalic acid PTA, and 4,4'-boronic acid biphenyl BDBA;

[0012] b. Disperse in DMF, place the mixture in a polytetrafluoroethylene reaction kettle and heat at 120 °C for 10 h to obtain the metal-organic framework.

[0013] The present invention provides the application of the metal-organic framework in the purification of scutellarin.

[0014] The present invention provides a purification method for scutellarin, which includes the following steps:

[0015] a. Take the scutellarin mother liquor, adjust the pH, weigh the metal-organic framework described above, add it to the mother liquor, vortex until adsorption equilibrium is reached, and then centrifuge;

[0016] b. After centrifugation to obtain a precipitate, add a DESs solution for elution, vortex until desorption equilibrium is reached, centrifuge, add water to the supernatant, let stand overnight, centrifuge to collect the precipitate, wash with water until neutral, and freeze-dry to obtain the pure compound of Erigeron breviscapus.

[0017] Among them, the pH value in step a is 7.0 - 9.0, the concentration of the scutellarin mother liquor is 100 - 1000 μg / mL; the vortex time is 5 - 120 min.

[0018] Among them, in step b, the type of DES is a mixture of PEG200 and lactic acid, hexanoic acid, levulinic acid, malic acid, and citric acid, and the molar ratio is 1:4 - 8:1; the desorption time in step b is 1 - 5 min; the volume ratio of the amount of the DESs solution to the mass of the precipitate is 1:1. Preferably, in step b, the type of DESs is PEG200 / lactic acid LA, and the molar ratio is 4:1; the desorption time in step b is 5 min.

[0019] In the adsorbent of the present invention, the boric acid group has high adsorption performance for vicinal diol hydroxyl groups. The structure of scutellarin has a vicinal diol hydroxyl group structure. The present invention synthesized a MOF material Zn-PTA-BDBA with zinc nitrate as the metal ion and terephthalic acid (PTA) and 1,4-benzenediboronic acid (BDBA) as mixed ligands, combined with DSPE, for the efficient adsorption of erigeronanthin.

[0020] The present invention first efficiently adsorbs scutellarin in the aqueous extract of traditional Chinese medicine through boric acid-based MOF, and then uses DESs as the eluent to elute the MOF material. The volume of the eluent is small, and the content of scutellarin in it is high. The amount of water added during water precipitation is small, which is beneficial to the practical application of the preparation of scutellarin in Erigeron breviscapus.

[0021] The beneficial effects of the present invention are:

[0022] (1) The synthesized Zn-PTA-BDBA MOF material has not been reported at present and is synthesized for the first time; and Zn-PTA-BDBA has a high adsorption efficiency for scutellarin, which can be as high as 570 mg / g;

[0023] (2) The established preparation method of scutellarin in Erigeron breviscapus mainly includes three steps: water extraction, MOF purification, and water precipitation with DESs eluent. Compared with traditional methods (such as the methods included in the Chinese Pharmacopoeia), it is simple, efficient, does not use organic solvents, and is green and safe;

[0024] (3) Compared with the direct extraction of DESs - water precipitation method, the volume of water added during water precipitation is small, which is more conducive to industrial actual operation. Description of the Drawings

[0025] Figure 1 . SEM of Zn-PTA (A: 50 μm, C: 1 μm) and Zn-PTA-BDBA (B: 50 μm, D: 1 μm);

[0026] Figure 2 . (A) Infrared spectra of Zn-PTA and Zn-PTA-BDBA, (B) EDS elemental analysis of Zn-PTA-BDBA (carbon / oxygen / zinc / boron), (C) Thermogravimetric analysis of Zn-PTA and Zn-PTA-BDBA, (D) BET specific surface area and nitrogen adsorption-desorption analysis of Zn-PTA and Zn-PTA-BDBA;

[0027] Figure 3 . Mechanism of action of Zn-PTA-BDBA;

[0028] Figure 4 . Structure of Zn-PTA-BDBA;

[0029] Figure 5 . (A) Proportion diagram of boric acid in the ligand, (B) Proportion diagram of zinc source and ligand, (C) Influence of different pH values on extraction capacity;

[0030] Figure 6 . (A) Adsorption isotherm investigation diagram, (B) Adsorption kinetics investigation;

[0031] Figure 7 . (A) First-order kinetics, (B) Second-order kinetics, (C) Langmuir model, (D) Freundlich model;

[0032] Figure 8 . (A) Desorption rate diagram of different desorbents, (B) Different PEG200 / lactic acid molar ratios, (C) Different desorption time diagrams, (D) Different desorption volumes;

[0033] Figure 9 . Chromatogram of the extraction process of scutellarin in the extract;

[0034] Figure 10 . Standard curve of scutellarin. Detailed implementation mode

[0035] Example 1 Preparation of metal-organic framework

[0036] The synthesis methods of Zn-PTA and Zn-PTA-BA are as follows: Zinc nitrate and terephthalic acid with a molar ratio of 1:2 are dispersed in DMF and dissolved by ultrasonic treatment (the ratio of Zn-PTA-BA is zinc nitrate: terephthalic acid: terephthalic diboric acid = 2:3:1), reacted at 120 °C for 10 h, cooled to room temperature, washed several times with DMF and ethanol, and vacuum dried at 60 °C for 2 h.

[0037] Example 2 Purification Method of Scutellarin

[0038] Weigh 1 g of Erigeron breviscapus, and perform ultrasonic extraction with 100 mL of sodium hydroxide solution with pH = 9 for 60 min; filter the extract, adjust the pH of the filtrate to 2 with hydrochloric acid, then place it in a refrigerator at 4 °C overnight to precipitate Erigeron breviscapus from the solution, collect the precipitate by centrifugation, wash it with water until neutral, and freeze-dry to obtain the crude extract of Erigeron breviscapus.

[0039] Precisely weigh an appropriate amount of the crude extract, dissolve and dilute it to a crude extract solution of 1 mg / mL with an appropriate amount of Tris solution (pH = 9) at 0.5 mg / mL (i.e., equivalent to containing 0.42 mg / mL of scutellarin), and adjust to pH = 8 with sodium hydroxide. Weigh 5 mg of Zn-PTA-BDBA prepared in Example 1 into an EP tube, add 5 mL of the crude extract solution, vortex for 1 h until adsorption equilibrium is reached, then centrifuge at 3000 rpm for 5 min, and discard the supernatant; then add 5 mL of DES solution of PEG200 / lactic acid (4:1) to the EP tube, vortex for desorption for 5 min, then centrifuge at 3000 rpm for 5 min, separate the supernatant and add 100 mL of water to it, place it in a refrigerator at 4 °C overnight, centrifuge to collect the precipitate, wash it with water until neutral, and freeze-dry to obtain the purified product of Erigeron breviscapus.

[0040] Dissolve the purified product with Tris solution and determine its purity by HPLC. The content of Erigeron breviscapus in the purified product of Erigeron breviscapus is 70.21 ± 4.00%.

[0041] Table 1 Purification of 5 Batches of Scutellarin

[0042]

[0043] Example 3 Characterization and Condition Optimization of the Metal-Organic Framework of the Present Invention

[0044] 1. Apply techniques such as SEM, XRD, and EDS to characterize the synthesized MOF material and determine the property characteristics of the material.

[0045] 2. Solid Phase Extraction Procedure

[0046] Prepare a 1 mg / mL scutellarin stock solution using a Tris buffer solution with a concentration of 0.5 mg / mL, and adjust the pH to 8. Weigh 5 mg of the packing material precisely, add 5 mL of the scutellarin stock solution, vortex for 1 h until adsorption equilibrium is reached, centrifuge at 3000 rpm for 5 min, aspirate a small amount of the supernatant for high-performance liquid chromatography analysis, and calculate the adsorption capacity using the external standard single-point method and Equation (1). Discard the supernatant after centrifugation, add different volumes of DESs to an EP tube, vortex until desorption equilibrium is reached, centrifuge at 3000 rpm for 5 min, aspirate the DESs desorption solution, conduct high-performance liquid chromatography analysis, and calculate the desorption rate using the external standard single-point method and Equation (2).

[0047] The adsorption capacity Q (mg / g) = (C 0 ×V 0 -C S ×V S )×10 / (m×10 3 ) (1)

[0048] The desorption rate (%) = (C 0 ×V 0 -C S ×V S ) / (Cd×Vd×)×10×100% (2)

[0049] In the formula, C 0 and C S are the concentrations of the stock solution and the supernatant respectively, V 0 and V S are the volumes of the stock solution and the supernatant respectively, m is the volume of the weighed packing material, C d and V d are the concentration and volume of scutellarin in the desorption solution, and 10 is the dilution factor

[0050] 3. The HPLC chromatographic conditions are as follows:

[0051] The mobile phase is methanol: water = 40:60, the detection wavelength is 315 nm, the flow rate is 1 mL / min, the column temperature of the chromatographic column is 30 °C, the injection volume is 10 μL, and the Thermo C18 chromatographic column (Thermo, 5 μm, 4.6 × 250 nm)

[0052] 4. Experimental results

[0053] 4.1 Zn-PTA-BDBA characterization

[0054] Scanning electron microscopy ( Figure 1 ), infrared ( Figure 2 .A), EDS elemental energy spectrum ( Figure 2 .B), thermogravimetry ( Figure 2 .C) and nitrogen adsorption / desorption ( Figure 2. D), etc., characterized Zn-PTA-BDBA. The mechanism of action of Zn-PTA-BDBA is shown in Figure 3 ; The structure of Zn-PTA-BDBA is shown in Figure 4 .

[0055] Figure 1 . A are the SEM images of Zn-PTA and Zn-PTA-BDBA at 50 μm and 1 μm respectively. As can be seen from Figure 1 . A, Zn-PTA is a regular and thick block on the surface, with a size of about 50 μm. Compared with Zn-PTA, although the overall size of Zn-PTA-BDBA has not changed, its morphology has changed greatly, which may be due to the introduction of BDBA. In addition, it is worth noting that at an observation magnification of 1 μm, the surface of Zn-PTA is wavy and no obvious pores are observed, while the introduction of BDBA brings more mesopores to the structure. The change in structure and the introduction of mesopores bring more binding sites, which is beneficial to its application in the adsorption of components.

[0056] The functional groups of the material were further investigated by FT-IR analysis, and the results are as shown in Figure 2 . A. In the infrared spectrum, the characteristic peaks at 1605, 1504, and 1437 cm -1 come from the unique skeletal vibration of the benzene ring. The symmetric and asymmetric stretching vibration peaks of ―COO appear between 1620–1390 cm -1 . The displacement of this characteristic peak proves that the metal zinc ion forms a coordination bond with ―COO, proving the successful synthesis of Zn-PTA. Then, in the infrared spectrum of Zn-PTA-BDBA, due to the introduction of boric acid, the broad absorption peak at 3700 - 2500 cm -1 becomes sharp. At the same time, the absorption bands observed at 1159 and 1015 cm -1 prove the existence of B-H bonds. In addition, as shown in Figure 2 . B, the energy-dispersive X-ray spectroscopy (EDS) element mapping shows obvious element signals such as B and Zn, all of which indicate that BA has been successfully modified on Zn-PTA.

[0057] The thermal stability of the material was determined by thermogravimetric analysis (TGA), and the test results are as shown in Figure 2 . C. It can be seen from the figure that there is a continuous weight loss process at 25–350 °C, corresponding to the residual organic solvents and small molecules. The mass is relatively stable at 350 °C–450 °C; at 450–500 °C, the mass drops sharply, the skeleton collapses, and the organic ligand PTA is lost. After 500 °C, it is basically constant in weight, and the remaining substances are inorganic salts.

[0058] Using N 2The specific surface area and pore size of the material were analyzed by isothermal adsorption / desorption experiments. From Figure 2 .D N2 adsorption / desorption isotherm analysis, it can be seen that the introduction of BDBA significantly improved the pore structure and specific surface area of Zn-PTA. The average pore size was 68.75 nm, and the specific surface area increased from 5.23 to 87.28 (m 2 / g -K ), enabling the adsorbent to have more borate affinity sites. The hysteresis loop of Zn-PTA-BDBA conforms to the H3 type hysteresis loop. The pores reflected by the H3 type hysteresis loop include flat slit structures, crack pores, and wedge structures, etc., and no adsorption saturation was shown in the higher relative pressure region. These characteristics are consistent with the phenomena observed by SEM.

[0059] 4.2. Optimization of the solid-phase extraction process

[0060] Investigation of the proportion of boric acid in the ligand: Keeping the total ratio of zinc to the ligand unchanged, the ratio of terephthalic acid to terephthalic diborate in the ligand structure was changed (the molar ratio of terephthalic diborate in the ligand increased from 0 to 50%).

[0061] Investigation of the zinc dosage: Keeping the molar ratio of boric acid to the ligand (terephthalic acid + terephthalic diborate) at 25%, different molar ratios of zinc to the ligand were changed during the synthesis process.

[0062] The introduction of the boric acid ligand enables the MOF to specifically form five- or six-membered cyclic lactones with compounds having an ortho-dihydroxy structure in a basic environment (the reaction mechanism is as Figure 3 shown). Therefore, pH is an important investigation index. Standard solutions of scutellarin with concentrations of 1 mg / mL and pH values of 7, 7.5, 8, 8.5, and 9 were respectively prepared. 5 mg of the material obtained under the above optimal synthesis conditions was precisely weighed for extraction, and the adsorption capacity was calculated. The results are shown in Figure 5 .

[0063] Table 2. Influence of Zn-PTA-BDBA on the adsorption capacity of scutellarin under different adsorption conditions

[0064]

[0065] As Figure 5 shown in A, with the addition of the boric acid dosage, the adsorption capacity of Zn-PTA-BDBA increased. When the molar ratio of boric acid to the total ligand was 25%, the adsorption capacity could reach 517 mg / g. However, when the boric acid dosage continued to increase, the basic structure of Zn-PTA-BDBA was difficult to exist stably, resulting in a decrease in the adsorption capacity.

[0066] As Figure 5As can be seen from B, if the amount of zinc used is too low, there will be insufficient metal binding sites and the MOFs cannot be synthesized to the optimal state. On the contrary, if the amount of zinc source used is too high, there will be insufficient ligand fragments, and the excessive zinc may cover the surface of the formed MOFs, thus affecting their binding to cis-diol compounds. Therefore, the optimal molar ratio of zinc source to ligand is 1:2.

[0067] pH is the most crucial factor affecting the specific binding of boric acid to vicinal dihydroxy groups. As can be seen from Figure 5 C, when the pH is 8.0, the specific adsorption capacity of Zn-PTA-BDBA for scutellarin is the largest, up to 570.97 mg / g.

[0068] Therefore, under the optimal conditions (the proportion of boric acid in the ligand is 25%, the molar ratio of zinc to ligand is 1:2, pH = 8, vortex for 30 min), repeated extraction is carried out multiple times (n = 6), and the adsorption capacity of this adsorbent for scutellarin is 570.19 ± 14.44.

[0069] 4.3. Adsorption Isotherm and Adsorption Kinetics Analysis

[0070] Investigation of adsorption isotherm: A series of scutellarin standard solutions (100 - 1000 μg / mL) were prepared. After adding 5 mL of the scutellarin standard solution to 5 mg of the packing and vortexing for 30 min, the maximum equilibrium adsorption capacity was calculated after HPLC analysis.

[0071] Investigation of adsorption kinetics: In order to further investigate the properties of the adsorbent, a scutellarin standard solution with a concentration of 1 mg / mL was prepared. 5 mL of the mother liquor was added to 5 mg and vortexed for 5, 10, 15, 20, 30, 60, and 120 min respectively. The adsorption capacity was calculated after high-performance liquid phase analysis. According to the scatter plot of the adsorption capacity, the scatter plot was fitted with the pseudo-first-order adsorption kinetics and the pseudo-second-order kinetics, as well as the Langmuir model and the Freundlich model for analysis to determine the adsorption mode of this material for scutellarin. The results are shown in Figure 6 .

[0072] The pseudo-first-order adsorption kinetics equation and the pseudo-second-order adsorption kinetics equation were further analyzed according to formula (3) and formula (4).

[0073] ln(Q - Q t ) = lnQ - k 1 t (3)

[0074]

[0075] h = k 2 Q 2 (5)

[0076]

[0077] Wherein, Q (mg / g) is the equilibrium adsorption capacity, and Q t (mg / g) is the adsorption capacity at time t, and k 1 (min -1 ) and k 2 (g / mg / min) are the adsorption rate constants of the pseudo-first-order adsorption kinetic equation and the pseudo-second-order adsorption kinetic equation, respectively. The fitting effects of the pseudo-first-order kinetic equation and the pseudo-second-order adsorption kinetic equation are as shown in Figure 7 .A and Figure 7 .B. Table 3 shows the relevant data calculated according to formulas (3) and (4), where Q exp represents the equilibrium adsorption capacity of scutellarin actually measured, and Q tf and Q ts represent the equilibrium adsorption capacities of scutellarin calculated according to the pseudo-first-order adsorption kinetic equation and the pseudo-second-order adsorption kinetic equation, respectively. By comparing Q exp with Qtf and Qts, and the linear correlation coefficient (R 2 ) after fitting, it can be found that the adsorption behavior of Zn-PTA-BDBA for scutellarin better conforms to the pseudo-second-order kinetic model. In addition, according to formulas (5) and (6), the initial adsorption rate h (mg / g / min) and the half-equilibrium time t 1 / 2 (min) of the pseudo-second-order kinetic model were calculated respectively.

[0078] In addition, according to formulas (6) and (7), the binding mode of the adsorbent and scutellarin was further described by the Langmuir adsorption model and the Freundlich adsorption model (Table 4).

[0079]

[0080] Q = K F C 1 / n (8)

[0081] Wherein, Q (mg / g) is the equilibrium adsorption capacity, Q m (mg / g) is the maximum adsorption capacity, K L and K F are the equilibrium adsorption constants of the two equilibrium adsorption models respectively, C (mg / L) is the concentration at equilibrium, and n is a dimensionless fitting value.

[0082] Table 3. Data parameters of pseudo-first-order and pseudo-second-order adsorption kinetic models

[0083]

[0084] Q exp 、Q tf 、Q tsThe unit is (mg / g), k 1 The unit is (1 / min), k 2 The unit of is (g / mg / min), the unit of h is (mg / mL / min), and the unit of t 1 / 2 The unit is

[0085] Table 4. Data parameters of Langmuir model and Freundlich model

[0086]

[0087] According to the kinetic experiments (Table 3), by comparing the correlation coefficients of pseudo-first-order and pseudo-second-order kinetics of the two adsorbents, it can be found that the pseudo-second-order kinetics (R 2 =0.9984) can better fit the adsorption of scutellarin by the metal organic framework. Therefore, it can be inferred that the main rate-controlling step in the adsorption of scutellarin by Zn-PTA-BDBA is the boron affinity between scutellarin and the boronic acid ligand fragment.

[0088] According to the adsorption equilibrium test, Figure 6 A), the adsorption equilibrium curves of Zn-PTA-BDBA show that the adsorption capacity of both increases sharply in the initial stage, and then slowly reaches adsorption equilibrium. From Table 4 and comparison Figure 7 It can be observed from C and D that the Langumir isotherm model can fit the experimental data well, and the adsorption of scutellariae by Zn-PTA-BDBA is a monolayer adsorption.

[0089] 4.4. Investigation of desorption process

[0090] Boronic acid ligands can release adsorbed compounds when exposed to acid. Therefore, acidic DESs were synthesized by heating and stirring at 60°C to act as desorbents. The desorption rate was used as an evaluation index to compare the desorption performance of different DESs as desorbents.

[0091] The specific steps are as follows: discard the supernatant after centrifugation, add 5 mL of DESs desorption solution into the EP tube, vortex at 2500 rpm for 5 min to desorption equilibrium, centrifuge at 3000 rpm for 5 min, aspirate the supernatant and dilute it 10 times, perform HPLC analysis, and calculate the adsorption capacity using the external standard one-point method.

[0092] Desorption rate (%) = m a / (C d ×V d ×10)×100%

[0093] In the formula, C d is the concentration of scutellarin in the desorption solution, V d is the volume of desorbent, m ais the mass of scutellarin adsorbed, 10 is the dilution factor. Methanol, methanol / acetic acid (50%), methyl-β-cyclodextrin / lactic acid, hydroxypropyl-β-cyclodextrin / lactic acid, PEG200 / citric acid, PEG200 / malic acid, PEG200 / lactic acid, PEG200 / caproic acid, and PEG200 / levulinic acid (with a molar ratio of 4:1 for all) were used to select the best desorbent type. PEG200 / lactic acid was selected as the desorbent, and the desorption rates at different molar ratios were investigated. PEG200 / lactic acid was selected as the desorbent, and the effects of vortex times of 1, 2, 3, 4, and 5 min on the desorption rate were investigated. PEG / lactic acid was selected as the desorbent, and the effects of 1, 2, 3, 4, and 5 mL of desorbent solution on the desorption rate were investigated (see Figure 8 ).

[0094] Table 5. Effects of different desorption conditions on the desorption rate of scutellarin

[0095]

[0096] Under the optimal conditions (desorbent: PEG200 / lactic acid, molar ratio 4:1, desorption volume 5 mL, desorption time 5 min), multiple desorptions (n = 6) were carried out. The desorption rate of PEG200 / lactic acid (4:1) for scutellarin was 97.77 ± 2.06%.

[0097] 4.5. Investigation of reproducibility and reusability

[0098] Six batches of adsorbents were synthesized for the adsorption of scutellarin to evaluate the batch reproducibility of Zn-PTA-BDBA. The results are shown in Table 6. The measured adsorption capacities were in the range of 542.5 - 581.7 (mg / g), and the relative standard deviations (RSDs) were between 0.80 - 2.79%. Therefore, the Zn-PTA-BDBA adsorbent has good stability and reproducibility. In addition, the reusability of Zn-PTA-BDBA was also studied. After cycling through adsorption, separation, elution, and HPLC analysis, the adsorbent was centrifuged from the solution, washed twice with ethanol respectively, and this operation process was repeated after recovery. The results are shown in Table 7. After 5 cycles, the adsorption capacity decreased by 18.12% compared to the original adsorption capacity, which may be due to the reduction of selective binding sites during the regeneration process.

[0099] Table 6. Changes in the adsorption capacity of the material after 5 cycles of use.

[0100]

[0101] Table 7. Changes in the adsorption capacity of the material after 5 cycles of use

[0102]

[0103] 5. Actual sample analysis

[0104] 5.1 Preparation of scutellarin in Chinese medicinal materials

[0105] (1) Preparation method: Weigh 1 g of Erigeron breviscapus, and perform ultrasonic extraction with 100 mL of sodium hydroxide solution with pH = 9 for 60 min; filter the extract, adjust the pH of the filtrate to 2 with hydrochloric acid, then place it in a refrigerator at 4 °C overnight to precipitate Erigeron breviscapus from the solution, centrifuge to collect the precipitate, wash it with water until neutral, and freeze-dry to obtain the crude extract of Erigeron breviscapus.

[0106] Accurately weigh an appropriate amount of the crude extract, dissolve and dilute it with an appropriate amount of 0.5 mg / mL Tris solution (pH = 9) to a crude extract solution of 1 mg / mL (i.e., equivalent to containing 0.42 mg / mL of scutellarin), and adjust the pH to 8 with sodium hydroxide. Weigh 5 mg of Zn-PTA-BDBA prepared in Example 1 into an EP tube, add 5 mL of the crude extract solution, vortex for 1 h until adsorption equilibrium is reached, then centrifuge at 3000 rpm for 5 min, and discard the supernatant; then add 5 mL of DES solution of PEG200 / lactic acid (4:1) to the EP tube, vortex for desorption for 5 min, then centrifuge at 3000 rpm for 5 min, take the supernatant and add 100 mL of water to it, place it in a refrigerator at 4 °C overnight, centrifuge to collect the precipitate, wash it with water until neutral, and freeze-dry to obtain the purified product of Erigeron breviscapus.

[0107] After material adsorption, desorption, and water precipitation, its purity is increased to 70.21 ± 4.00%, and the chromatogram is as Figure 9 shown.

[0108] 5.2 Methodology investigation

[0109] Preparation of standard curve and investigation of linear relationship

[0110] Weigh 10 mg of scutellarin standard product, accurately weigh it, transfer it to a 100 mL volumetric flask, dissolve and dilute it with an appropriate amount of 0.5 mg / mL Tris buffer solution to the scale, to obtain a scutellarin reference stock solution of 0.1001 mg / mL. Accurately pipette 50, 100, 200, 300, 500, 750 μL of the scutellarin reference stock solution into 10 mL volumetric flasks respectively, add Tris buffer solution to dilute to the scale, shake well, to obtain reference solutions with concentrations of 5.0, 10.0, 20.0, 30.0, 50.1, 75.1 μg·mL -1 respectively. Accurately pipette 10 μL of each scutellarin reference solution into a high-performance liquid chromatograph, and record the peak area. Taking the concentration of the scutellarin reference solution as the abscissa and the peak area as the ordinate, plot the standard curve and calculate the regression equation. The results show that the linear regression equation of scutellarin is y = 29721x + 7963.6, R2 = 0.9999( Figure 10 ), the concentration of scutellarin showed a good linear relationship in the range of 5.0 - 75.1 μg·mL -1 .

[0111] Instrument precision test

[0112] Precisely pipette 10 μL of the same reference solution (50.1 μg·mL -1 ), inject it into the high performance liquid chromatograph continuously for 6 times, measure the peak area of the reference substance, and calculate the RSD value. The RSD of the chromatographic peak area was 1.1%, indicating good instrument precision.

[0113] Stability test

[0114] Take the same PEG200 / lactic acid (4:1) desorbing solution, inject samples at 0, 2, 4, 8, 12, and 24 h respectively. The RSD of the peak area was 1.43%. It shows that the stability of scutellarin in PEG200 / lactic acid (4:1) was good within 24 h.

[0115] Table 8. Analytical characteristics of the determination method of scutellarin in Erigeron breviscapus samples

[0116]

[0117] Spiked recovery test

[0118] Add standard solutions of scutellarin at three concentration levels to the crude product of the third batch as sample solutions. Then add 5 mg of Zn-PTA-BDBA to 5 mL of the sample solution, perform adsorption and desorption under the optimal extraction conditions, and calculate the spiked recovery according to formula (9). The actual sample chromatograms before and after extraction are as Figure 9 shown. It can be seen that as the concentration of the scutellarin standard solution increases, the eluted scutellarin content increases almost proportionally, and Zn-PTA-BDBA has good adsorption performance for scutellarin in real samples.

[0119] P(%) = (C 2 - C 1 ) / C 0 × 100% (9)

[0120] In the formula, P is the spiked recovery, C 2 is the concentration after adding the standard solution, C 1 is the concentration before adding the standard solution, and C 0 is the concentration of the added standard solution. According to Table 9, the obtained spiked recoveries were between 87.67 - 109.02%.

[0121] Table 9. Spike recovery rate of scutellarin in the crude product (n = 3)

[0122]

Claims

1. A metal organic framework, characterized in that: It is prepared from zinc nitrate and ligands as raw materials. The ligands are terephthalic acid PTA and terephthalic diboric acid BDBA. The molar ratio of zinc to ligands (PTA+BDBA) is 1:4-5:4, and the molar percentage of BDBA in the ligands is 0-50%.

2. The metal organic framework according to claim 1, characterized in that: The molar ratio of zinc to ligand (PTA+BDBA) is 1:2, and the molar percentage of BDBA in the ligand is 25%.

3. The method for preparing a metal organic framework according to claim 1 or 2, characterized in that: It includes the following steps: a. Weigh three raw materials: zinc nitrate, phthalic acid PTA, terephthalic acid BDBA; b. Disperse in DMF, place the mixture in a polytetrafluoroethylene reactor and heat at 120°C for 10 h to obtain a metal organic framework.

4. Use of the metal organic framework according to claim 1 or 2 in purifying scutellariae.

5. A method for purifying scutellarin, characterized in that: It includes the following steps: a. Take a mother solution of scutellarin, adjust the pH, weigh the metal organic framework according to claim 1 or 2, add it to the mother solution, vortex until adsorption equilibrium, and centrifuge; b. After centrifugation, add DES solution to elute the precipitate, vortex and shake until desorption equilibrium, centrifuge, add water to the supernatant, let it stand overnight, collect the precipitate by centrifugation, wash with water until neutral, and freeze-dry to obtain the purified product of Erigeron chinensis.

6. The method for purifying scutellarin according to claim 5, characterized in that: The pH value of step a is 7.0-9.0, the concentration of scutellaria baicalenol mother solution is 100-1000 μg / mL; and the vortex time is 5-120 min.

7. The method for purifying scutellarin according to claim 5, characterized in that: In step b, the type of DES is a mixture of PEG200 and lactic acid, caproic acid, levulinic acid, malic acid and citric acid in a molar ratio of 1:4 to 8:1; the desorption time in step b is 1 to 5 minutes; the mass volume ratio of the amount of DES solution to the precipitate is 1:

1.

8. The method for purifying scutellarin according to claim 7, characterized in that: In step b, the type of DES is PEG200 / lactic acid LA, and the molar ratio is 4:1; the desorption time in step b is 5 minutes.

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