CN114752099B - Magnetic hollow molecularly imprinted polymer and application thereof in separation of ferulic acid - Google Patents
Magnetic hollow molecularly imprinted polymer and application thereof in separation of ferulic acid Download PDFInfo
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Abstract
The invention relates to the field of ferulic acid extraction, in particular to a magnetic hollow molecularly imprinted polymer and application thereof in separation of ferulic acid. According to the invention, nano ferroferric oxide is used as a substrate, amination modification is carried out on the nano ferroferric oxide, imidazole-4, 5-dicarboxylic acid is grafted through an amide reaction, zinc chloride is used for treatment, and finally 2-chloroethylamine hydrochloride is used for quaternization, so that a magnetic hollow molecularly imprinted polymer is prepared, and the magnetic hollow molecularly imprinted polymer has the adsorption capacity and selectivity on ferulic acid and is beneficial to improvement of efficiency and purity of the ferulic acid directly extracted from plants.
Description
Technical Field
The invention relates to the field of ferulic acid extraction, in particular to a magnetic hollow molecularly imprinted polymer and application thereof in separation of ferulic acid.
Background
Ferulic Acid (FA), a phenolic acid ubiquitous in the plant world, is a cinnamic (3-phenyl-2-propenoic acid) type phenolic acid (also known as styrene type) that forms a binding state with mainly oligomeric glycolipids and polysaccharides, and binds with polysaccharides and proteins in the cell wall to form the skeleton of the cell wall. Researches find that the ferulic acid is one of the effective components of various traditional Chinese medicines such as asafetida, ligusticum wallichii, angelica sinensis, rhizoma cimicifugae, horsetail and the like. Ferulic acid has multiple pharmacological functions of resisting oxidation, resisting thrombus, reducing blood fat, preventing and treating coronary heart disease, resisting bacteria, diminishing inflammation, resisting mutation, resisting cancer and the like. In recent years, ferulic acid has attracted more and more attention, and its extraction has become a focus of research. Besides being widely used in medicine, ferulic acid has been approved as a food additive in some countries. Some countries in japan, the united states and europe have allowed the use of ferulic acid as an antioxidant for food, and some coffee, herbs, vanilla beans, etc., which contain a high amount of ferulic acid, have been allowed to be used as an antioxidant. At present, ferulic acid is mainly used as an antiseptic preservative, a food cross-linking agent and a sports food additive in the food industry.
The method for directly extracting ferulic acid from plants is more economical and practical than the synthetic method, and greatly reduces the pollution to the nature. Ferulic acid mainly forms a part of cell walls by crosslinking with cell wall polysaccharide and lignin in plants, generally adopts an enzymatic method and an alkaline method to break ester bonds to release ferulic acid, and then uses a solvent to extract to obtain a crude extract. The crude extract has very complicated components, and the separation and purification of ferulic acid are difficult. Common solid adsorbents such as activated carbon, macroporous resin, anion exchange resin, biomass and the like have been used to separate ferulic acid from crude extract, but the common adsorbents have a common disadvantage of lack of selectivity of adsorption, so that the separation efficiency is poor.
Molecular imprinting is a technique in which recognition sites are carefully placed in a polymer matrix. A large number of cavities which are highly matched with template molecules in size, spatial configuration and action sites are distributed in the molecularly imprinted polymer, so that the MIPs have excellent binding performance and identification selectivity on the template molecules, are called Artificial receptors and Artificial receptors (Artificial antibodies or receptors), and can specifically identify, select and bind the template molecules from a mixed system at the molecular level. Currently, scientists and researchers in at least tens of countries are engaged in the research and development of molecular imprinting polymerization throughout the world. The development of molecular imprinting technology can be so rapid, mainly because molecular imprinting materials have three major characteristics: structure effect presetting property, specific identification property and wide applicability. The molecularly imprinted polymer prepared based on the technology has the characteristics of high associativity and selectivity, strong severe environment resistance, good stability, long service life, wide application range and the like, and the molecularly imprinted technology is increasingly widely researched and developed in various fields such as solid phase extraction, chromatographic separation, membrane separation, clinical drug analysis, biomimetic sensing and the like, and is widely researched and applied in the industries such as bioengineering, natural drug separation, clinical medicine, environmental monitoring, food industry and the like.
If the molecular surface imprinting technology (MISPE) technology is introduced into the separation and extraction of ferulic acid, the method has a development prospect. However, as described above, the ferulic acid molecule structure contains polymerizable double bonds, and is not suitable for preparing Molecularly Imprinted Polymers (MIPs) by a general polymerization method, so ferulic acid imprinted polymers are rarely reported. In order to overcome the above difficulties, researchers have prepared ferulic acid imprinted polymers by using their analogs hydrogenated ferulic acid as "pseudo-templates", and obviously, imprinting effects are affected.
CN 113087842A discloses a preparation method and an application of a ferulic acid molecularly imprinted polymer, wherein the magnetic carbon nanotube is further prepared into the molecularly imprinted polymer by taking magnetic carbon nanotube as a carrier, ferulic acid as a template molecule, alpha-methacrylic acid as a functional monomer, azodiisobutyronitrile as an initiator and ethylene glycol dimethacrylate as a cross-linking agent. It has poor adsorption capacity to ferulic acid and low selectivity.
Disclosure of Invention
Aiming at the defects in the prior art, the invention prepares a magnetic hollow molecularly imprinted polymer and applies the magnetic hollow molecularly imprinted polymer to ferulic acid separation.
A preparation method of a magnetic hollow molecularly imprinted polymer comprises the following steps:
(1) Adding 10-15 parts by mass of ferric chloride hexahydrate, 35-40 parts by mass of ammonium citrate and 35-45 parts by mass of sodium citrate into 650-750 parts by mass of ethylene glycol, stirring at the rotating speed of 100-200r/min for 5-15min, then reacting at 160-180 ℃ for 0.5-1.5h, then reacting at 180-210 ℃ for 10-15h, filtering to obtain a filter cake, washing and drying to obtain nano ferroferric oxide;
(2) Mixing 9-11 parts by mass of (3-aminopropyl) trimethoxysilane, 2-3 parts by mass of ammonia water with the concentration of 18-22wt%, 9-11 parts by mass of the nano ferroferric oxide prepared in the step (1), 70-90 parts by mass of water and 15-25 parts by mass of ethylene glycol, performing ultrasonic treatment for 4-6min, stirring at the rotating speed of 100-200r/min, reacting at the temperature of 45-55 ℃ for 20-30h, filtering to obtain a filter cake, washing and drying to obtain amino modified nano ferroferric oxide;
(3) Mixing 4-6 parts by mass of amino modified nano ferroferric oxide prepared in the step (2), 1-3 parts by mass of imidazole-4, 5-dicarboxylic acid, 0.5-1 part by mass of thionyl chloride and 90-100 parts by mass of absolute ethyl alcohol, stirring and reacting for 3-5 hours at the temperature of 75-85 ℃ at the rotating speed of 100-200r/min, filtering, taking a filter cake, washing and drying to obtain imidazole grafted nano ferroferric oxide;
(4) Adding 2-3 parts of zinc chloride into 9-11 parts of water by mass, stirring for 5-10min at the rotating speed of 100-200r/min, adding 1-2 parts of imidazole-grafted nano ferroferric oxide prepared in the step (3), stirring for 20-30h at the rotating speed of 100-200r/min at room temperature, filtering to obtain a filter cake, washing and drying to obtain imidazole-zinc-grafted nano ferroferric oxide;
(5) Mixing 0.7-0.8 part of 2-chloroethylamine hydrochloride and 15-30 parts of water by mass, stirring at the rotating speed of 100-200r/min for 5-8min, adding 1-2 parts of imidazole zinc grafted nano ferroferric oxide prepared in the step (4) and 75-85 parts of water, stirring at the rotating speed of 100-200r/min at the temperature of 55-65 ℃ for reaction for 3-5h, filtering to obtain a filter cake, washing and drying to obtain quaternized imidazole zinc grafted nano ferroferric oxide;
(6) Mixing 0.3-0.5 part of ferulic acid, 3-5 parts of methacrylic acid and 25-35 parts of acetonitrile by mass, stirring at the rotating speed of 100-200r/min for 10-20min, then adding 1-2 parts of quaternized imidazole zinc grafted nano ferroferric oxide prepared in the step (5), 1-2 parts of crosslinked polyvinylpyrrolidone and 0.3-0.5 part of surfactant, continuously stirring at the rotating speed of 100-200r/min for 1.5-3h, finally adding 0.1-0.3 part of azodiisobutyronitrile, and refluxing at the temperature of 65-75 ℃ for 10-14h to obtain a polymerization solution; filtering the polymerization solution to obtain a filter cake, washing the filter cake with an anhydrous methanol/acetic acid solution for 4-6 times, and drying in vacuum to obtain the magnetic hollow molecularly imprinted polymer.
The power of the ultrasonic wave in the step (2) is 50-70W, and the frequency is 70-90kHz.
The solvent is one of acetonitrile, absolute ethyl alcohol and absolute methyl alcohol; preferably, the solvent is acetonitrile.
The surfactant is one of sodium dodecyl sulfate, sodium stearate and tween 80; preferably, the surfactant is sodium dodecyl sulfate.
The mass ratio of the anhydrous methanol to the acetic acid in the anhydrous methanol/acetic acid solution is (8-10): 1.
aiming at the problems that the ferulic acid molecular structure contains polymerizable double bonds, the general polymerization method for preparing the molecularly imprinted polymer has poor adsorption capacity and low selectivity. The invention takes nano ferroferric oxide as a substrate, and the ferroferric oxide is magnetic and is easy to separate through a magnetic field, so that the adsorbed ferulic acid can be directly separated from the plant body conveniently. Secondly, in order to enhance the adsorption capacity and selectivity of the magnetic hollow molecularly imprinted polymer prepared by the invention to ferulic acid. The invention further modifies the prepared nano ferroferric oxide. Firstly, (3-aminopropyl) trimethoxy silane is adopted to graft nano ferroferric oxide, amino groups on the nano ferroferric oxide have certain adsorption effect on ferulic acid, but the adsorption effect of the ferulic acid is realized by the hydrogen bond effect between the amino groups and hydroxyl groups, the adsorption capacity is weak, and the nano ferroferric oxide has no selectivity. Therefore, the imidazole group is grafted on the basis of the amino modified nano ferroferric oxide. The invention selects imidazole-4, 5-dicarboxylic acid, performs acyl chlorination on carboxyl on the dicarboxylic acid, and then performs amide reaction with amino to realize the grafting of imidazole groups. Because the imidazole-4, 5-dicarboxylic acid is a five-membered aromatic heterocyclic compound containing two meta nitrogen atoms, the adsorption capacity of the prepared magnetic hollow molecularly imprinted polymer on ferulic acid can be further enhanced. Furthermore, according to the strong chelation of imidazole on zinc ions, the imidazole-grafted nano ferroferric oxide is treated by a zinc chloride solution to obtain the imidazole-zinc-grafted nano ferroferric oxide, and isothermal adsorption experiments show that the imidazole-zinc-grafted nano ferroferric oxide has stronger ferulic acid adsorption capacity and selectivity. The invention speculates that the two nitrogen atoms show the property of quaternary ammonium ions due to the chelation of the zinc ions and the meta nitrogen on the imidazole, while the molecular structure of the ferulic acid contains benzene ring conjugated pi bonds, and the ferulic acid and the quaternary ammonium ions generate cation-pi interaction to realize strong chelation and have certain selectivity. Furthermore, the invention discovers that imidazole-4, 5-dicarboxylic acid generates a plurality of amido bonds when being grafted, wherein the amido groups are tertiary amido groups, and the tertiary amido groups can be quaternized by 2-chloroethylamine hydrochloride to generate more quaternary ammonium ions. Isothermal adsorption experiments show that the generated quaternary ammonium ions also have strong adsorption capacity and selectivity on ferulic acid, and zinc imidazole and 2-chloroethylamine hydrochloride are synergistic, so that the adsorption capacity and selectivity of the prepared magnetic hollow molecularly imprinted polymer on ferulic acid are greatly enhanced, and the efficiency and purity of directly extracting ferulic acid from plants are improved.
The invention has the beneficial effects that:
according to the invention, nano ferroferric oxide is used as a substrate, is subjected to amination modification, is grafted with imidazole-4, 5-dicarboxylic acid through an amide reaction, is treated with zinc chloride, and is quaternized with 2-chloroethylamine hydrochloride, so that the magnetic hollow molecularly imprinted polymer is prepared, has adsorption capacity and selectivity on ferulic acid, and is beneficial to improvement of efficiency and purity of directly extracting ferulic acid from plants.
Detailed Description
(3-aminopropyl) trimethoxysilane, cat No.: F-A11284, shanghai Ji to Biochemical technology, inc.
Imidazole-4, 5-dicarboxylic acid, CAS No.: 570-22-9, cargo number: s48501, shanghai-derived leaf Biotech, inc.
2-chloroethylamine hydrochloride, CAS No.: 870-24-6, cat No.: c79140, shanghai Ji to Biochemical technologies, inc.
Ferulic acid, cat No.: b20007, shanghai-derived leaf Biotechnology, inc.
Methacrylic acid, cat No.: m82070, shanghai Ji to Biochemical technology, inc.
Crosslinked polyvinylpyrrolidone, cat No.: r002142, shanghai yi chemical technology limited.
Example 1
A preparation method of a magnetic hollow molecularly imprinted polymer comprises the following steps:
(1) Adding 13 parts by mass of ferric chloride hexahydrate, 38 parts by mass of ammonium citrate and 4 parts by mass of sodium citrate into 700 parts by mass of ethylene glycol, stirring at a rotating speed of 180r/min for 10min, then placing at 170 ℃ for reaction for 1h, then turning to 200 ℃ for reaction for 12h, filtering to obtain a filter cake, washing and drying to obtain nano ferroferric oxide;
(2) Mixing 0.4 part of ferulic acid, 4 parts of methacrylic acid and 30 parts of solvent by mass, stirring at the rotating speed of 180r/min for 15min, then adding 1 part of nano ferroferric oxide prepared in the step (1), 1.2 parts of crosslinked polyvinylpyrrolidone and 0.4 part of surfactant, continuously stirring at the rotating speed of 180r/min for 2h, finally adding 0.2 part of azobisisobutyronitrile, and refluxing at 70 ℃ for 12h to obtain a polymerization solution; and filtering the polymerization solution to obtain a filter cake, washing the filter cake for 5 times by using an anhydrous methanol/acetic acid solution, and drying in vacuum to obtain the magnetic hollow molecularly imprinted polymer.
The solvent is acetonitrile.
The surfactant is sodium dodecyl sulfate.
The mass ratio of the anhydrous methanol to the acetic acid in the anhydrous methanol/acetic acid solution is 9:1.
example 2
A preparation method of a magnetic hollow molecularly imprinted polymer comprises the following steps:
(1) Adding 13 parts by mass of ferric chloride hexahydrate, 38 parts by mass of ammonium citrate and 4 parts by mass of sodium citrate into 700 parts by mass of ethylene glycol, stirring at a rotating speed of 180r/min for 10min, then placing at 170 ℃ for reaction for 1h, then turning to 200 ℃ for reaction for 12h, filtering to obtain a filter cake, washing and drying to obtain nano ferroferric oxide;
(2) Mixing 10 parts by mass of (3-aminopropyl) trimethoxysilane, 3 parts by mass of ammonia water with the concentration of 20wt%, 10 parts by mass of the nano ferroferric oxide prepared in the step (1), 80 parts by mass of water and 20 parts by mass of ethylene glycol, carrying out ultrasonic treatment for 5min, stirring at the rotating speed of 180r/min, reacting at the temperature of 50 ℃ for 24h, filtering to obtain a filter cake, washing and drying to obtain amino-modified nano ferroferric oxide;
(3) Mixing 0.4 part of ferulic acid, 4 parts of methacrylic acid and 30 parts of solvent by mass, stirring at the rotating speed of 180r/min for 15min, then adding 1 part of amino modified nano ferroferric oxide prepared in the step (2), 1.2 parts of crosslinked polyvinylpyrrolidone and 0.4 part of surfactant, continuously stirring at the rotating speed of 180r/min for 2h, finally adding 0.2 part of azobisisobutyronitrile, and refluxing at 70 ℃ for 12h to obtain a polymerization solution; and filtering the polymerization solution to obtain a filter cake, washing the filter cake for 5 times by using an anhydrous methanol/acetic acid solution, and drying in vacuum to obtain the magnetic hollow molecularly imprinted polymer.
The power of the ultrasound in the step (2) is 60W, and the frequency is 80kHz.
The solvent is acetonitrile.
The surfactant is sodium dodecyl sulfate.
The mass ratio of the anhydrous methanol to the acetic acid in the anhydrous methanol/acetic acid solution is 9:1.
example 3
A preparation method of a magnetic hollow molecularly imprinted polymer comprises the following steps:
(1) Adding 13 parts by mass of ferric chloride hexahydrate, 38 parts by mass of ammonium citrate and 4 parts by mass of sodium citrate into 700 parts by mass of ethylene glycol, stirring at a rotating speed of 180r/min for 10min, then placing at 170 ℃ for reaction for 1h, then turning to 200 ℃ for reaction for 12h, filtering to obtain a filter cake, washing and drying to obtain nano ferroferric oxide;
(2) Mixing 10 parts by mass of (3-aminopropyl) trimethoxysilane, 3 parts by mass of ammonia water with the concentration of 20wt%, 10 parts by mass of the nano ferroferric oxide prepared in the step (1), 80 parts by mass of water and 20 parts by mass of ethylene glycol, carrying out ultrasonic treatment for 5min, stirring at the rotating speed of 180r/min, reacting at the temperature of 50 ℃ for 24h, filtering to obtain a filter cake, washing and drying to obtain amino-modified nano ferroferric oxide;
(3) Mixing 5 parts by mass of amino modified nano ferroferric oxide prepared in the step (2), 2 parts by mass of imidazole-4, 5-dicarboxylic acid, 0.8 part by mass of thionyl chloride and 100 parts by mass of absolute ethyl alcohol, stirring and reacting for 4 hours at 80 ℃ and a rotating speed of 180r/min, filtering, taking a filter cake, washing and drying to obtain imidazole grafted nano ferroferric oxide;
(4) Mixing 0.4 part of ferulic acid, 4 parts of methacrylic acid and 30 parts of solvent by mass, stirring at the rotating speed of 180r/min for 15min, then adding 1 part of imidazole-grafted nano ferroferric oxide prepared in the step (3), 1.2 parts of crosslinked polyvinylpyrrolidone and 0.4 part of surfactant, continuously stirring at the rotating speed of 180r/min for 2h, finally adding 0.2 part of azobisisobutyronitrile, and refluxing at 70 ℃ for 12h to obtain a polymerization solution; filtering the polymerization solution to obtain a filter cake, washing the filter cake for 5 times by using an anhydrous methanol/acetic acid solution, and drying in vacuum to obtain the magnetic hollow molecularly imprinted polymer.
The power of the ultrasound in the step (2) is 60W, and the frequency is 80kHz.
The solvent is acetonitrile.
The surfactant is sodium dodecyl sulfate.
The mass ratio of the anhydrous methanol to the acetic acid in the anhydrous methanol/acetic acid solution is 9:1.
example 4
A preparation method of a magnetic hollow molecularly imprinted polymer comprises the following steps:
(1) Adding 13 parts by mass of ferric chloride hexahydrate, 38 parts by mass of ammonium citrate and 4 parts by mass of sodium citrate into 700 parts by mass of ethylene glycol, stirring at a rotating speed of 180r/min for 10min, then placing at 170 ℃ for reaction for 1h, then turning to 200 ℃ for reaction for 12h, filtering to obtain a filter cake, washing and drying to obtain nano ferroferric oxide;
(2) Mixing 10 parts of (3-aminopropyl) trimethoxy silane, 3 parts of ammonia water with the concentration of 20wt%, 10 parts of the nano ferroferric oxide prepared in the step (1), 80 parts of water and 20 parts of ethylene glycol, carrying out ultrasonic treatment for 5min, stirring at the rotating speed of 180r/min, reacting at the temperature of 50 ℃ for 24h, filtering to obtain a filter cake, washing and drying to obtain amino modified nano ferroferric oxide;
(3) Mixing 5 parts by mass of amino modified nano ferroferric oxide prepared in the step (2), 2 parts by mass of imidazole-4, 5-dicarboxylic acid, 0.8 part by mass of thionyl chloride and 100 parts by mass of absolute ethyl alcohol, stirring and reacting for 4 hours at 80 ℃ and a rotating speed of 180r/min, filtering, taking a filter cake, washing and drying to obtain imidazole grafted nano ferroferric oxide;
(4) Adding 2.5 parts by mass of zinc chloride into 10 parts by mass of water, stirring at a rotating speed of 180r/min for 8min, adding 1.2 parts by mass of the imidazole-grafted nano ferroferric oxide prepared in the step (3), stirring at a rotating speed of 180r/min for 24h at room temperature, filtering to obtain a filter cake, washing and drying to obtain imidazole-zinc-grafted nano ferroferric oxide;
(5) Mixing 0.4 part of ferulic acid, 4 parts of methacrylic acid and 30 parts of solvent by mass, stirring at the rotating speed of 180r/min for 15min, then adding 1 part of zinc imidazole grafted nano ferroferric oxide prepared in the step (4), 1.2 parts of crosslinked polyvinylpyrrolidone and 0.4 part of surfactant, continuously stirring at the rotating speed of 180r/min for 2h, finally adding 0.2 part of azobisisobutyronitrile, and refluxing at 70 ℃ for 12h to obtain a polymerization solution; filtering the polymerization solution to obtain a filter cake, washing the filter cake for 5 times by using an anhydrous methanol/acetic acid solution, and drying in vacuum to obtain the magnetic hollow molecularly imprinted polymer.
The power of the ultrasound in the step (2) is 60W, and the frequency is 80kHz.
The solvent is acetonitrile.
The surfactant is sodium dodecyl sulfate.
The mass ratio of the anhydrous methanol to the acetic acid in the anhydrous methanol/acetic acid solution is 9:1.
example 5
A preparation method of a magnetic hollow molecularly imprinted polymer comprises the following steps:
(1) Adding 13 parts by mass of ferric chloride hexahydrate, 38 parts by mass of ammonium citrate and 4 parts by mass of sodium citrate into 700 parts by mass of ethylene glycol, stirring at the rotating speed of 180r/min for 10min, then placing at 170 ℃ for reacting for 1h, then turning to 200 ℃ for reacting for 12h, filtering to obtain a filter cake, washing and drying to obtain nano ferroferric oxide;
(2) Mixing 10 parts of (3-aminopropyl) trimethoxy silane, 3 parts of ammonia water with the concentration of 20wt%, 10 parts of the nano ferroferric oxide prepared in the step (1), 80 parts of water and 20 parts of ethylene glycol, carrying out ultrasonic treatment for 5min, stirring at the rotating speed of 180r/min, reacting at the temperature of 50 ℃ for 24h, filtering to obtain a filter cake, washing and drying to obtain amino modified nano ferroferric oxide;
(3) Mixing 5 parts by mass of amino modified nano ferroferric oxide prepared in the step (2), 2 parts by mass of imidazole-4, 5-dicarboxylic acid, 0.8 part by mass of thionyl chloride and 100 parts by mass of absolute ethyl alcohol, stirring and reacting at 80 ℃ at a rotating speed of 180r/min for 4 hours, filtering to obtain a filter cake, washing and drying to obtain imidazole grafted nano ferroferric oxide;
(4) Adding 2.5 parts by mass of zinc chloride into 10 parts by mass of water, stirring at a rotating speed of 180r/min for 8min, adding 1.2 parts by mass of the imidazole-grafted nano ferroferric oxide prepared in the step (3), stirring at a rotating speed of 180r/min for 24h at room temperature, filtering to obtain a filter cake, washing and drying to obtain imidazole-zinc-grafted nano ferroferric oxide;
(5) Mixing 0.74 part of 2-chloroethylamine hydrochloride and 20 parts of water by mass, stirring at the rotating speed of 180r/min for 6min, adding 1 part of the imidazole zinc grafted nano ferroferric oxide prepared in the step (4) and 80 parts of water, stirring at the rotating speed of 180r/min at 60 ℃ for reaction for 4h, filtering to obtain a filter cake, washing and drying to obtain quaternized imidazole zinc grafted nano ferroferric oxide;
(6) Mixing 0.4 part of ferulic acid, 4 parts of methacrylic acid and 30 parts of solvent by mass, stirring at the rotating speed of 180r/min for 15min, then adding 1 part of quaternized imidazole zinc grafted nano ferroferric oxide prepared in the step (5), 1.2 parts of crosslinked polyvinylpyrrolidone and 0.4 part of surfactant, continuously stirring at the rotating speed of 180r/min for 2h, finally adding 0.2 part of azobisisobutyronitrile, and refluxing at 70 ℃ for 12h to obtain a polymerization solution; filtering the polymerization solution to obtain a filter cake, washing the filter cake for 5 times by using an anhydrous methanol/acetic acid solution, and drying in vacuum to obtain the magnetic hollow molecularly imprinted polymer.
The power of the ultrasound in the step (2) is 60W, and the frequency is 80kHz.
The solvent is acetonitrile.
The surfactant is sodium dodecyl sulfate.
The mass ratio of the anhydrous methanol to the acetic acid in the anhydrous methanol/acetic acid solution is 9:1.
example 6
A preparation method of a magnetic hollow molecularly imprinted polymer comprises the following steps:
(1) Adding 13 parts by mass of ferric chloride hexahydrate, 38 parts by mass of ammonium citrate and 4 parts by mass of sodium citrate into 700 parts by mass of ethylene glycol, stirring at a rotating speed of 180r/min for 10min, then placing at 170 ℃ for reaction for 1h, then turning to 200 ℃ for reaction for 12h, filtering to obtain a filter cake, washing and drying to obtain nano ferroferric oxide;
(2) Mixing 10 parts of (3-aminopropyl) trimethoxy silane, 3 parts of ammonia water with the concentration of 20wt%, 10 parts of the nano ferroferric oxide prepared in the step (1), 80 parts of water and 20 parts of ethylene glycol, carrying out ultrasonic treatment for 5min, stirring at the rotating speed of 180r/min, reacting at the temperature of 50 ℃ for 24h, filtering to obtain a filter cake, washing and drying to obtain amino modified nano ferroferric oxide;
(3) Mixing 5 parts by mass of amino modified nano ferroferric oxide prepared in the step (2), 2 parts by mass of imidazole-4, 5-dicarboxylic acid, 0.8 part by mass of thionyl chloride and 100 parts by mass of absolute ethyl alcohol, stirring and reacting at 80 ℃ at a rotating speed of 180r/min for 4 hours, filtering to obtain a filter cake, washing and drying to obtain imidazole grafted nano ferroferric oxide;
(4) Mixing 0.74 parts of 2-chloroethylamine hydrochloride and 20 parts of water by mass, stirring at the rotating speed of 180r/min for 6min, adding 1 part of imidazole grafted nano ferroferric oxide prepared in the step (3) and 80 parts of water, and stirring at the rotating speed of 180r/min at 60 ℃ for reaction for 4h to obtain quaternized imidazole zinc grafted nano ferroferric oxide;
(5) Mixing 0.4 part of ferulic acid, 4 parts of methacrylic acid and 30 parts of solvent by mass, stirring at the rotating speed of 180r/min for 15min, then adding 1 part of quaternized imidazole grafted nano ferroferric oxide prepared in the step (5), 1.2 parts of crosslinked polyvinylpyrrolidone and 0.4 part of surfactant, continuously stirring at the rotating speed of 180r/min for 2h, finally adding 0.2 part of azobisisobutyronitrile, and refluxing at 70 ℃ for 12h to obtain a polymerization solution; and filtering the polymerization solution to obtain a filter cake, washing the filter cake for 5 times by using an anhydrous methanol/acetic acid solution, and drying in vacuum to obtain the magnetic hollow molecularly imprinted polymer.
The power of the ultrasound in the step (2) is 60W, and the frequency is 80kHz.
The solvent is acetonitrile.
The surfactant is sodium dodecyl sulfate.
The mass ratio of the anhydrous methanol to the acetic acid in the anhydrous methanol/acetic acid solution is 9:1.
test example 1
The experiment temperature of the ferulic acid isothermal adsorption experiment is 25 ℃.
Preparing 2mmol/L ferulic acid aqueous solution.
An isothermal adsorption experiment was performed: weighing 0.02g of the magnetic hollow molecularly imprinted polymer prepared in each example, respectively placing the magnetic hollow molecularly imprinted polymer into a plurality of 50mL conical flasks with stoppers, respectively adding 15mL of 2mmol/L ferulic acid aqueous solution, oscillating and adsorbing for 4h in a water bath oscillator at 25 ℃, standing and separating, measuring the concentration of ferulic acid in a supernatant by using an ultraviolet spectrophotometry, and calculating the equilibrium adsorption quantity Qe (mmol/g) of the magnetic hollow molecularly imprinted polymer prepared in each example on ferulic acid according to the following formula.
Co (mmol/L) is the initial concentration of ferulic acid;
ce (mmol/L) is the equilibrium concentration of ferulic acid;
v (mL) is the volume of the solution;
m (g) is the mass of the magnetic hollow molecularly imprinted polymer prepared in each example. The test results are shown in Table 1.
Table 1: equilibrium adsorption amount of ferulic acid
| Qe（mmol/g） | |
| Example 1 | 0.06 |
| Example 2 | 0.19 |
| Example 3 | 0.42 |
| Example 4 | 0.69 |
| Example 5 | 0.78 |
| Example 6 | 0.71 |
It can be seen from table 1 that the magnetic hollow molecularly imprinted polymer prepared in example 1 has the worst adsorption performance to ferulic acid, because example 1 uses nano ferroferric oxide as a substrate, the adsorption performance to ferulic acid is poor, but because ferroferric oxide has magnetism, the adsorbed ferulic acid can be easily separated by a magnetic field, and the adsorbed ferulic acid can be conveniently and directly separated from a plant body. The adsorption capacity of the magnetic hollow molecularly imprinted polymer prepared in example 2 to ferulic acid is slightly better than that of example 1, but is far worse than that of example 3, because the adsorption capacity and selectivity of the magnetic hollow molecularly imprinted polymer prepared in the invention to ferulic acid are enhanced. The invention further modifies the prepared nano ferroferric oxide. In the embodiment 2, (3-aminopropyl) trimethoxy silane is adopted to graft nano ferroferric oxide, amino groups on the nano ferroferric oxide have certain adsorption effect on ferulic acid, but the adsorption effect of ferulic acid is realized by means of hydrogen bond effect between amino groups and hydroxyl groups, the adsorption capacity is weak, and selectivity is unavailable. Therefore, in example 3, imidazole groups are grafted on the basis of the amino-modified nano ferroferric oxide. The invention selects imidazole-4, 5-dicarboxylic acid, performs acyl chlorination on carboxyl on the dicarboxylic acid, and then performs amide reaction with amino to realize the grafting of imidazole groups. Since the imidazole-4, 5-dicarboxylic acid is a five-membered heteroaromatic compound containing two meta nitrogen atoms, the adsorption capacity of the prepared magnetic hollow molecularly imprinted polymer on ferulic acid can be further enhanced. Still further, in example 4, according to the strong chelating effect of imidazole on zinc ions, the imidazole-grafted nano ferroferric oxide is treated by a zinc chloride solution to obtain imidazole-zinc-grafted nano ferroferric oxide, which shows a stronger adsorption capacity than that in example 3. The invention speculates that the two nitrogen atoms show the property of quaternary ammonium ions due to the chelation of the zinc ions and the meta nitrogen on the imidazole, while the molecular structure of the ferulic acid contains benzene ring conjugated pi bonds, and the ferulic acid and the quaternary ammonium ions generate cation-pi interaction to realize strong chelation and have certain selectivity, thereby showing stronger absorption capacity and selectivity of the ferulic acid. Furthermore, the invention discovers that imidazole-4, 5-dicarboxylic acid generates a plurality of amido bonds when being grafted, wherein the amino is tertiary amino, and the tertiary amino can be quaternized by 2-chloroethylamine hydrochloride to generate more quaternary ammonium ions. Therefore, in example 5, the imidazole zinc grafted nano ferroferric oxide is further treated by 2-chloroethyl amine hydrochloride, so that the generated quaternary ammonium ions also have strong adsorption capacity and selectivity on ferulic acid, and therefore, example 5 shows the best ferulic acid adsorption performance. Example 6 the prepared imidazole grafted nano ferroferric oxide is not subjected to zinc chloride treatment, and the adsorption performance of the prepared imidazole grafted nano ferroferric oxide on ferulic acid is slightly reduced. The imidazole zinc and the 2-chloroethyl amine hydrochloride are synergistic, so that the adsorption capacity and selectivity of the prepared magnetic hollow molecularly imprinted polymer to ferulic acid are greatly enhanced, and the efficiency and purity of directly extracting ferulic acid from plants are improved.
Test example 2
Selective isothermal adsorption experiment, the experimental temperature is 25 ℃.
Preparing 4mmol/L ferulic acid aqueous solution and 4mmol/L chlorogenic acid, and mixing the two solutions according to a mass ratio of 1:1 to obtain a mixed acid aqueous solution.
An isothermal adsorption experiment was performed: weighing 0.02g of the magnetic hollow molecularly imprinted polymer prepared in each example, respectively placing the weighed magnetic hollow molecularly imprinted polymer into a plurality of 50mL conical flasks with stoppers, respectively adding 15mL of mixed acid aqueous solution, oscillating and adsorbing for 4h in a water bath oscillator at 25 ℃, standing and separating, measuring the concentration of ferulic acid in a supernatant by using an ultraviolet spectrophotometry, and calculating the equilibrium adsorption quantity Qe (mmol/g) of the magnetic hollow molecularly imprinted polymer prepared in each example to the ferulic acid according to the following formula.
Co (mmol/L) is the initial concentration of ferulic acid;
ce (mmol/L) is the equilibrium concentration of ferulic acid;
v (mL) is the volume of the solution;
m (g) is the mass of the magnetic hollow molecularly imprinted polymer prepared in each example. The test results are shown in Table 2.
Table 2: equilibrium adsorption capacity of ferulic acid
| Qe Ferulic acid (mmol/g) | Qe chlorogenic acid (mmol/g) | |
| Example 2 | 0.08 | 0.09 |
| Example 3 | 0.27 | 0.22 |
| Example 4 | 0.61 | 0.04 |
| Example 5 | 0.76 | 0.01 |
| Example 6 | 0.69 | 0.02 |
As can be seen from Table 2, the selective adsorption capacity of the magnetic hollow molecularly imprinted polymer prepared in example 2 on ferulic acid is slightly inferior to that of example 3, because the amino group on the nano ferroferric oxide grafted by (3-aminopropyl) trimethoxy silane in example 2 is not selective. And in the embodiment 3, imidazole groups are grafted on the basis of amino modified nano ferroferric oxide. The invention selects imidazole-4, 5-dicarboxylic acid, performs acyl chlorination on carboxyl on the dicarboxylic acid, and performs amide reaction with amino to realize the grafting of imidazole groups. Because the imidazole-4, 5-dicarboxylic acid is a five-membered aromatic heterocyclic compound containing two meta-nitrogen atoms, the imidazole-4, 5-dicarboxylic acid has stronger adsorption capacity on ferulic acid, and the formed molecular imprinting is not easy to deform and has stronger selectivity. Example 4 according to the strong chelating effect of imidazole on zinc ions, the imidazole-grafted nano ferroferric oxide is treated by a zinc chloride solution to obtain the imidazole-zinc-grafted nano ferroferric oxide. The invention speculates that two nitrogen atoms show the property of quaternary ammonium ions due to the chelation of zinc ions and meta nitrogen on imidazole, and the molecular structure of ferulic acid contains benzene ring conjugated pi bonds, so that cation-pi interaction is generated between the ferulic acid and the quaternary ammonium ions, strong chelation is realized, and the generated molecular imprinting is more accurate, so that the ferulic acid has stronger selectivity. Example 5 the imidazole zinc grafted nano ferroferric oxide is further treated by 2-chloroethyl amine hydrochloride, so that the generated quaternary ammonium ions also have strong selectivity on ferulic acid, and therefore, example 5 shows the best ferulic acid selectivity. Example 6 the prepared imidazole grafted nano ferroferric oxide is not subjected to zinc chloride treatment, and the selectivity of the prepared imidazole grafted nano ferroferric oxide to ferulic acid is slightly reduced. The imidazole zinc and the 2-chloroethyl amine hydrochloride are synergistic, so that the adsorption capacity and selectivity of the prepared magnetic hollow molecularly imprinted polymer to ferulic acid are greatly enhanced, and the efficiency and purity of directly extracting ferulic acid from plants are improved.
Claims (3)
1. A preparation method of a magnetic hollow molecularly imprinted polymer is characterized by comprising the following steps:
(1) Adding 10-15 parts by mass of ferric chloride hexahydrate, 35-40 parts by mass of ammonium citrate and 35-45 parts by mass of sodium citrate into 650-750 parts by mass of ethylene glycol, stirring at the rotating speed of 100-200r/min for 5-15min, then reacting at 160-180 ℃ for 0.5-1.5h, then reacting at 180-210 ℃ for 10-15h, filtering to obtain a filter cake, washing and drying to obtain nano ferroferric oxide;
(2) Mixing 9-11 parts by mass of (3-aminopropyl) trimethoxysilane, 2-3 parts by mass of ammonia water with the concentration of 18-22wt%, 9-11 parts by mass of nano ferroferric oxide, 70-90 parts by mass of water and 15-25 parts by mass of ethylene glycol, carrying out ultrasonic treatment for 4-6min, stirring at the rotating speed of 100-200r/min, reacting at the temperature of 45-55 ℃ for 20-30h, filtering to obtain a filter cake, washing and drying to obtain amino modified nano ferroferric oxide;
(3) Mixing 4-6 parts by mass of amino-modified nano ferroferric oxide, 1-3 parts by mass of imidazole-4, 5-dicarboxylic acid, 0.5-1 part by mass of thionyl chloride and 90-100 parts by mass of absolute ethyl alcohol, stirring and reacting at 75-85 ℃ at a rotating speed of 100-200r/min for 3-5 hours, filtering to obtain a filter cake, washing and drying to obtain imidazole-grafted nano ferroferric oxide;
(4) Adding 2-3 parts of zinc chloride into 9-11 parts of water by mass, stirring for 5-10min at the rotating speed of 100-200r/min, adding 1-2 parts of imidazole grafted nano ferroferric oxide, stirring for 20-30h at the rotating speed of 100-200r/min at room temperature, filtering to obtain a filter cake, washing and drying to obtain imidazole zinc grafted nano ferroferric oxide;
(5) Mixing 0.7-0.8 part of 2-chloroethylamine hydrochloride and 15-30 parts of water by mass, stirring at the rotating speed of 100-200r/min for 5-8min, adding 1-2 parts of imidazole zinc grafted nano ferroferric oxide and 75-85 parts of water, stirring and reacting at the rotating speed of 100-200r/min for 3-5h at 55-65 ℃, filtering to obtain a filter cake, washing and drying to obtain quaternized imidazole zinc grafted nano ferroferric oxide;
(6) Mixing 0.3-0.5 part of ferulic acid, 3-5 parts of methacrylic acid and 25-35 parts of acetonitrile by mass, stirring at the rotating speed of 100-200r/min for 10-20min, then adding 1-2 parts of quaternized imidazole zinc grafted nano ferroferric oxide, 1-2 parts of crosslinked polyvinylpyrrolidone and 0.3-0.5 part of surfactant, continuously stirring at the rotating speed of 100-200r/min for 1.5-3h, finally adding 0.1-0.3 part of azobisisobutyronitrile, and refluxing at the temperature of 65-75 ℃ for 10-14h to obtain a polymerization solution; filtering the polymerization solution to obtain a filter cake, washing the filter cake with an anhydrous methanol/acetic acid solution for 4-6 times, and drying in vacuum to obtain the magnetic hollow molecularly imprinted polymer;
the mass ratio of the anhydrous methanol to the acetic acid in the anhydrous methanol/acetic acid solution is (8-10): 1;
the surfactant is one of sodium dodecyl sulfate, sodium stearate and tween 80.
2. A magnetic hollow molecularly imprinted polymer characterized by being prepared by the method for preparing a magnetic hollow molecularly imprinted polymer according to claim 1.
3. Use of the magnetic hollow molecularly imprinted polymer of claim 2 for the isolation of ferulic acid.
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