CN116371466A - Molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst and preparation method and application thereof - Google Patents

Molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst and preparation method and application thereof Download PDF

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CN116371466A
CN116371466A CN202310178702.8A CN202310178702A CN116371466A CN 116371466 A CN116371466 A CN 116371466A CN 202310178702 A CN202310178702 A CN 202310178702A CN 116371466 A CN116371466 A CN 116371466A
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tryptophan
catalyst
magnetic
imprinted polymer
molecularly imprinted
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CN116371466B (en
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高瑞霞
刘亚
李远航
李静
郝旖
李洋
徐四龙
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Xian Jiaotong University
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    • B01J35/00Catalysts, in general, characterised by their form or physical properties
    • B01J35/50Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
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    • B01J37/00Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/0009Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
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Abstract

The invention discloses a magnetic immobilized tryptophan catalyst modified by a molecularly imprinted polymer, a preparation method and application thereof, wherein the method uses magnetic Fe 3 O 4 The nanospheres are used as carriers, tryptophan catalysts are fixed on the surfaces of the nanospheres, and then a sol-gel technology is adopted, and phenyl trimethoxy silane (PTMOS) andn-octyl trimethoxy silane (OTMS) is used as a functional monomer, and Tetraethoxysilane (TEOS) is used as a cross-linking agent to modify a molecularly imprinted polymer with substrate selectivity on the surface of the molecularly imprinted polymer. The modification of the molecularly imprinted polymer enables the catalyst to have substrate selectivity, can selectively catalyze substrate molecules matched with templates in a complex reaction system, solves the problem of insufficient selectivity of the catalyst in organic synthesis to a certain extent, and has wide application prospect.

Description

Molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst and preparation method and application thereof
Technical Field
The invention belongs to the technical field of nano material preparation and organic catalysis, and particularly relates to a magnetic immobilized tryptophan catalyst modified by a molecularly imprinted polymer, and a preparation method and application thereof.
Background
In recent years, asymmetric organocatalysis has made remarkable progress, established as one of the most promising and practical methods in asymmetric synthesis and catalysis. Among them, the asymmetric aldol reaction is considered as one of the most important carbon-carbon bond formation reactions, and the hydroxycarbonyl compound produced by the reaction is a very valuable intermediate in organic synthesis, and thus attracts great attention in the synthesis world. Proline and its various structural derivatives have proven to be organic catalysts for intermolecular aldol reactions, with tryptophan as one of them, and good yields and enantioselectivities can be obtained in both the aqueous and organic phases, widening the range of applications to some extent. However, the organic micromolecule catalytic system such as tryptophan has the problems of insufficient selectivity of target products and the like, so that additional energy is required for separation and treatment of byproducts, and the synthesis cost is greatly increased.
Although the small molecular catalyst is fixed to form a supported heterogeneous catalyst, the catalyst and the product can be rapidly separated by centrifugation and the like, so that the difficulty of separation and purification in organic synthesis is reduced to a certain extent, and the limited selectivity is still a key factor for restricting the development of the catalyst. In the past, it was thought that low specificity of the interaction between the active site and the reagent may lead to limited selectivity, resulting in increased by-products, and therefore the development of various strategies to improve selectivity of heterogeneous catalysts has become a major focus of synthesis.
Among them, the molecular imprinting technique is a technique for synthesizing a molecularly imprinted polymer that is perfectly matched with a target molecule in size, dimension, and site of action. The magnetic molecularly imprinted polymer formed by modifying the molecularly imprinted polymer on the surface of the magnetic particle has the advantages of good superparamagnetism of the magnetic particle, high selectivity, high specificity and presettiness of the molecularly imprinted polymer. Combining it with an organic catalyst is expected to solve the problems of difficult separation and insufficient selectivity of a small molecule catalyst, but at present, no related report on the preparation of tryptophan catalyst by adopting a molecular imprinting technology exists.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a magnetic immobilized tryptophan catalyst modified by a molecularly imprinted polymer, and a preparation method and application thereof, and solve the problems of difficult separation and insufficient selectivity of a small molecular catalyst.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme:
the invention discloses a preparation method of a magnetic immobilized tryptophan catalyst modified by a molecularly imprinted polymer, which comprises the following steps:
1) Fixing L-tryptophan on the surface of the boric acid functionalized magnetic nano-particles to prepare a tryptophan immobilized magnetic catalyst;
2) Taking an aldol condensation product of 4-nitrobenzaldehyde and cyclohexanone catalyzed by tryptophan as a template molecule, and fixing the template on the surface of a tryptophan immobilized magnetic catalyst under the action of polyvinylpyrrolidone to form a template-carrier compound;
3) Sequentially adding ammonia water, phenyl trimethoxy silane, n-octyl trimethoxy silane functional monomer and tetraethoxysilane into the template-carrier compound by adopting a sol-gel method to prepare a polymer layer containing template molecules;
4) And removing the template molecules in the polymer layer containing the template molecules, and cleaning and drying to obtain the magnetic immobilized tryptophan catalyst modified by the molecular imprinted polymer, namely the magnetic molecular imprinted polymer loaded by tryptophan.
Preferably, in the step 1), the tryptophan-immobilized magnetic catalyst is prepared from boric acid functionalized magnetic nano-particles and L-5-bromotryptophan as raw materials and Na 2 Cl 4 Pd is a palladium source, tris (3-sodium sulfonate phenyl) phosphine is a ligand, K 2 CO 3 Providing an alkaline environment at N 2 Reflux at 85 ℃ under protection;
wherein, boric acid modified magnetic nano particles, L-5-bromotryptophan and Na 2 Cl 4 Pd, tri (3-sodium sulfonate phenyl) phosphine as ligand and K 2 CO 3 The dosage ratio of (1) is (100-300) mg, (200-800) mg, (150-500) mg, (300-1200) mg and (500-2000) mg.
Preferably, in the step 2), the dosage ratio of the template molecule, the tryptophan immobilized magnetic catalyst, the polyvinylpyrrolidone and the solvent is (25-125) mg (100-500) mg (5-25) g (50-250) mL, and the reaction time is 15-100 min; wherein the solvent is a mixture of water and ethanol, and the volume ratio of water to ethanol is 1:3-1:6.
Preferably, in the step 3), the polymer layer containing the template molecule is prepared by adding ammonia water, phenyl trimethoxysilane, n-octyl trimethoxysilane functional monomer and tetraethoxysilane into (100-1000) mg template-carrier compound according to the dosage ratio of (1-5) mL (0.5-3) mL (0.5-5) mL (50-500) mu L in sequence and reacting for 3-12 h.
Preferably, in the step 4), the template molecules are removed by adopting an elution solution prepared by mixing absolute methanol and glacial acetic acid in a volume ratio of (80-95) to (20-5).
Further preferably, in step 1), the preparation method of the boric acid functionalized magnetic nanoparticle is as follows:
first, amino Fe is prepared 3 O 4 Magnetic nanoparticles and amino Fe 3 O 4 Surface modification of magnetic nano particle with polyethylenimine to prepare Fe 3 O 4 -PEI; then at Fe 3 O 4 Grafting phenylboronic acid on the surface of PEI to prepare boric acid functionalizationIs a magnetic nanoparticle of (a).
Still more preferably, amino Fe 3 O 4 The magnetic nano-particles are prepared by a solvothermal method; the molecular weight of the polyethyleneimine used is 1800; the grafted phenylboronic acid takes 4-formylphenylboronic acid as a boric acid reagent.
The invention also discloses a magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer and prepared by the preparation method, wherein the magnetic immobilized tryptophan catalyst is spherical and has the particle size of 100-200 nm.
The invention also discloses application of the magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer in catalyzing aldol reaction of 4-nitrobenzaldehyde and cyclohexanone.
Preferably, in the catalytic reaction, the molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst can selectively adsorb a substrate 4-nitrobenzaldehyde matched with a template structure;
the catalytic reaction conditions are as follows: the dosage of the magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer is 50-300 mg for every 10mg of 4-nitrobenzaldehyde; the molar ratio of cyclohexanone to 2-nitrobenzaldehyde/3-nitrobenzaldehyde/4-nitrobenzaldehyde is (2-15): 1, a step of; the solvent is H 2 O; the temperature is 25-40 ℃.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a preparation method of a molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst, which comprises the steps of firstly synthesizing a chiral tryptophan immobilized magnetic catalyst (Fe 3 O 4 -Trp), then adding tryptophan catalyzed reaction product of 4-nitrobenzaldehyde and cyclohexanone [ 2- (hydroxy (4-nitrophenyl) methyl) cyclohexanone ] as template, and forming a template-carrier compound in a solvent with an alcohol-water volume ratio of 6:1 by a fixed template method; then the compound is reacted with difunctional monomers of Phenyl Trimethoxysilane (PTMOS) and n-Octyl Trimethoxysilane (OTMS) to form a polymer network under the crosslinking of Tetraethoxysilane (TEOS) by sol-gel technology; washing and drying the template after eluting under the assistance of an external magnetic field to obtain the molecular imprinting polymerA compound modified immobilized tryptophan heterogeneous catalyst.
The heterogeneous catalyst synthesized by the invention has the following advantages: (1) By magnetic Fe 3 O 4 As a substrate material, the catalyst can be rapidly separated from a reaction system under an external magnetic field, so that the purification difficulty in organic synthesis is reduced to a certain extent; (2) The chiral tryptophan catalyst is grafted on the surface of the magnetic carrier through the covalent action of C-C, so that the chiral tryptophan catalyst maintains relative stability in the subsequent reaction process, is beneficial to the repeated recycling of the catalyst, and reduces the cost of organic synthesis; (3) PTMOS and OTMS are adopted as difunctional monomers, so that the interaction between a target object and the monomers is enhanced, and the stability and the selectivity of a molecular imprinting hole are improved; (4) The two functional monomers are cheap and easy to obtain, and the synthesis method is simple and easy to realize; (5) The prepared magnetic tryptophan heterogeneous catalyst modified by the molecularly imprinted polymer has good catalytic performance and can be used for catalyzing specific aldol reaction.
The magnetic sphere-supported tryptophan solid catalyst modified by the molecularly imprinted polymer has excellent selectivity, can selectively adsorb a target substrate matched with a template molecule in catalyzing the aldol reaction of a specific benzaldehyde substrate and cyclohexanone, and can selectively catalyze the reaction of 4-nitrobenzaldehyde matched with the template and cyclohexanone even in a mixed substrate of 2-nitrobenzaldehyde, 3-nitrobenzaldehyde and 4-nitrobenzaldehyde with similar structure and reactivity, so that the difficult problem of limited selectivity in organic synthesis is solved to a great extent, and the magnetic sphere-supported tryptophan solid catalyst has wide application prospect.
Drawings
FIG. 1 is a transmission electron microscope image of a magnetic immobilized tryptophan catalyst modified by a molecularly imprinted polymer prepared in example 1 of the invention;
FIG. 2 is an adsorption curve of the magnetic immobilized tryptophan catalyst modified by molecular imprinting/non-imprinting, prepared in invention example 1, to a 4-nitrobenzaldehyde substrate;
FIG. 3 is a selective adsorption drawing of the molecular imprinting/non-imprinting modified magnetic immobilized tryptophan catalyst prepared in invention example 1 on different reaction substrates.
Detailed Description
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention is described in further detail below with reference to the attached drawing figures:
1. preparation of magnetic immobilized tryptophan catalyst modified by molecularly imprinted polymer
Example 1
Step one: preparation of amino Fe 3 O 4 Magnetic nanoparticles
1.0g FeCl 3 ·6H 2 O, 3.6g of anhydrous sodium acetate and 6.3g of 1, 6-hexamethylenediamine are placed in a 100mL beaker, 30mL of ethylene glycol is added, after being fully mixed, the clear liquid is transferred into a reaction kettle, and the reaction is finished at 200 ℃ for 7 hours. The obtained product is separated by an external magnetic field, washed by ethanol and water, and dried overnight in an oven at 50 ℃.
Step two: preparation of Polyethylenimine (PEI) grafted magnetic nanoparticles (denoted Fe 3 O 4 -PEI)
1mg/mL of PEI solution and 1% glutaraldehyde solution were prepared in methanol, and 200mg of Fe was weighed 3 O 4 -NH 2 In a three-necked flask, 30mL of PEI and glutaraldehyde solution were sequentially added, dispersed by sonication, and 90mg of NaBH was added under mechanical stirring 4 After reacting for 1h, removing the supernatant by magnetic separation; 30mL of PEI solution and 90mg of NaBH were again added 4 After 2h, the reaction was completed. And magnetically separating, cleaning and drying the material for later use.
Step two: preparation of boric acid functionalized magnetic nanoparticles (denoted Fe 3 O 4 -HPBA)
200mg Fe 3 O 4 -PEI, 300mg 4-formylphenylboronic acid and 225mg NaBH 4 Placing the mixture into a three-necked flask, adding 30mL of methanol solution, reacting for 24 hours at room temperature, magnetically separating, cleaning and drying to obtain Fe 3 O 4 -
HPBA is ready for use.
Step three: preparation of Tryptophan immobilized magnetic catalyst (denoted Fe 3 O 4 -Trp)
200mg Fe 3 O 4 HPBA, 400mg L-5-bromotryptophan, 284mg Na 2 Cl 4 Pd, 710mg tris (3-sodium sulfonate phenyl) phosphine (TPPTS) and 970mg K 2 CO 3 Placed in a three-necked flask, 60mL of deaerated water was added thereto, and the flask was filled with N 2 And (3) refluxing for 24 hours at 85 ℃ under the atmosphere, and cleaning and drying the material for later use.
Step four: preparation of molecularly imprinted Polymer-modified Tryptophan-immobilized magnetic catalyst (designated as P-
MMIP)
200mg of Fe is weighed 3 O 4 Trp, 10.0g polyvinylpyrrolidone (PVP) in a 250mL three-necked flask, 20mL ultrapure water and 120mL absolute ethanol were added and sonicated. Then 100mg of template molecule was added to the above mixture and stirred for 30 minutes to form a template-carrier complex. Then adding 3.0mL of ammonia water, 130. Mu.L of Phenyl Trimethoxysilane (PTMOS), 670. Mu.L of n-octyl trimethoxy siliconAlkane (OTMS) and 250 μl of tetraethyl orthosilicate (TEOS) were reacted for 6h. The reaction product was washed with ultrapure water to neutrality and dried overnight at 50 ℃ for further use.
Eluting the template by using a mixed solution of methanol and acetic acid with the volume ratio of 90:10, washing the eluted polymer material to be neutral by using ultrapure water, and drying overnight at 50 ℃ to obtain the molecular engram polymer modified tryptophan immobilized magnetic catalyst (P-MMIP).
The non-imprinted material (P-MNIP) was prepared using the same synthetic strategy as the molecularly imprinted material, except that no template molecule was added.
As shown in FIG. 1, the prepared magnetic catalyst modified by the molecularly imprinted polymer and immobilized by tryptophan is uniform and spherical and has a size of about 160nm.
Example 2
Step one: preparation of amino Fe 3 O 4 Magnetic nanoparticles
1.0g FeCl 3 ·6H 2 O, 3.6g of anhydrous sodium acetate and 6.3g of 1, 6-hexamethylenediamine are placed in a 100mL beaker, 30mL of ethylene glycol is added, after being fully mixed, the clear liquid is transferred into a reaction kettle, and the reaction is finished at 200 ℃ for 7 hours. The obtained product is separated by an external magnetic field, washed by ethanol and water, and dried overnight in an oven at 50 ℃.
Step two: preparation of Polyethylenimine (PEI) grafted magnetic nanoparticles (denoted Fe 3 O 4 -PEI)
1mg/mL of PEI solution and 1% glutaraldehyde solution were prepared in methanol, and 200mg of Fe was weighed 3 O 4 -NH 2 In a three-necked flask, 30mL of PEI and glutaraldehyde solution were sequentially added, dispersed by sonication, and 90mg of NaBH was added under mechanical stirring 4 After reacting for 1h, removing the supernatant by magnetic separation; 30mL of PEI solution and 90mg of NaBH were again added 4 After 2h, the reaction was completed. And magnetically separating, cleaning and drying the material for later use.
Step two: preparation of boric acid functionalized magnetic nanoparticles (denoted Fe 3 O 4 -HPBA)
200mg Fe 3 O 4 -PEI, 300mg 4-formylPhenylboronic acid and 225mgNaBH 4 Placing the mixture into a three-necked flask, adding 30mL of methanol solution, reacting for 24 hours at room temperature, magnetically separating, cleaning and drying to obtain Fe 3 O 4 -
HPBA is ready for use.
Step three: preparation of Tryptophan immobilized magnetic catalyst (denoted Fe 3 O 4 -Trp)
100mg Fe 3 O 4 HPBA, 200mg L-5-bromotryptophan, 150mg Na 2 Cl 4 Pd, 300mg tris (3-sodium sulfonate phenyl) phosphine (TPPTS) and 500mg K 2 CO 3 Put in a three-necked flask, 10mL of deaerated water was added thereto, and the mixture was stirred under N conditions 2 And (3) refluxing for 24 hours at 85 ℃ under the atmosphere, and cleaning and drying the material for later use.
Step four: preparation of molecularly imprinted Polymer-modified Tryptophan-immobilized magnetic catalyst (designated as P-
MMIP)
100mg of Fe is weighed 3 O 4 Trp, 5.0g polyvinylpyrrolidone (PVP) in a 250mL three-necked flask, 20mL ultrapure water and 60mL absolute ethanol were added and sonicated. Then 25mg of template molecule was added to the above mixture and stirred for 30 minutes to form a template-carrier complex. Then 1.0mL of ammonia was added and 500. Mu.L of Phenyltrimethoxysilane (PTMOS), 500. Mu.L of n-Octyltrimethoxysilane (OTMS) and 50. Mu.L of Tetraethylorthosilicate (TEOS) were reacted for 6 hours. The reaction product was washed with ultrapure water to neutrality and dried overnight at 50 ℃ for further use.
Eluting the template by using a mixed solution of methanol and acetic acid with the volume ratio of 95:5, washing the eluted polymer material to be neutral by using ultrapure water, and drying overnight at 50 ℃ to obtain the molecular engram polymer modified tryptophan immobilized magnetic catalyst (P-MMIP).
The non-imprinted material (P-MNIP) was prepared using the same synthetic strategy as the molecularly imprinted material, except that no template molecule was added.
The prepared magnetic catalyst modified by the molecularly imprinted polymer and immobilized by tryptophan is uniform and spherical, and the size of the magnetic catalyst is about 120nm.
Example 3
Step one: preparation of amino Fe 3 O 4 Magnetic nanoparticles
1.0g FeCl 3 ·6H 2 O, 3.6g of anhydrous sodium acetate and 6.3g of 1, 6-hexamethylenediamine are placed in a 100mL beaker, 30mL of ethylene glycol is added, after being fully mixed, the clear liquid is transferred into a reaction kettle, and the reaction is finished at 200 ℃ for 7 hours. The obtained product is separated by an external magnetic field, washed by ethanol and water, and dried overnight in an oven at 50 ℃.
Step two: preparation of Polyethylenimine (PEI) grafted magnetic nanoparticles (denoted Fe 3 O 4 -PEI)
1mg/mL of PEI solution and 1% glutaraldehyde solution were prepared in methanol, and 600mg of Fe was weighed 3 O 4 -NH 2 In a three-necked flask, 60mL of PEI and glutaraldehyde solution were sequentially added, dispersed by sonication, and 270mg of NaBH was added with mechanical stirring 4 After reacting for 1h, removing the supernatant by magnetic separation; 60mL of PEI solution and 2700mg of NaBH were again added 4 After 2h, the reaction was completed. And magnetically separating, cleaning and drying the material for later use.
Step two: preparation of boric acid functionalized magnetic nanoparticles (denoted Fe 3 O 4 -HPBA)
600mg Fe 3 O 4 -PEI, 900mg 4-formylphenylboronic acid and 675mg NaBH 4 Placing the mixture into a three-necked flask, adding 90mL of methanol solution, reacting for 24 hours at room temperature, magnetically separating, cleaning and drying to obtain Fe 3 O 4 -
HPBA is ready for use.
Step three: preparation of Tryptophan immobilized magnetic catalyst (denoted Fe 3 O 4 -Trp)
600mg Fe 3 O 4 HPBA, 800mg L-5-bromotryptophan, 500mg Na 2 Cl 4 Pd, 1.2g tris (3-sodium sulfonate phenyl) phosphine (TPPTS) and 2.0. 2.0g K 2 CO 3 Placed in a three-necked flask, 80mL of deaerated water was added thereto, and the flask was filled with N 2 And (3) refluxing for 24 hours at 85 ℃ under the atmosphere, and cleaning and drying the material for later use.
Step four: preparation of molecularly imprinted Polymer-modified Tryptophan-immobilized magnetic catalyst (designated as P-
MMIP)
500mg Fe is weighed 3 O 4 Trp, 25.0g polyvinylpyrrolidone (PVP) in a 250mL three-necked flask, 40mL ultrapure water and 160mL absolute ethanol were added and sonicated. 125mg of template molecule was then added to the above mixture and stirred for 30 minutes to form a template-carrier complex. Then 5.0mL of ammonia water, 3.0mL of Phenyltrimethoxysilane (PTMOS), 5.0mL of n-Octyltrimethoxysilane (OTMS) and 500. Mu.L of Tetraethylorthosilicate (TEOS) were added and reacted for 6 hours. The reaction product was washed with ultrapure water to neutrality and dried overnight at 50 ℃ for further use.
Eluting the template by using a mixed solution of methanol and acetic acid with the volume ratio of 80:20, washing the eluted polymer material to be neutral by using ultrapure water, and drying overnight at 50 ℃ to obtain the molecular engram polymer modified tryptophan immobilized magnetic catalyst (P-MMIP).
The non-imprinted material (P-MNIP) was prepared using the same synthetic strategy as the molecularly imprinted material, except that no template molecule was added.
The prepared magnetic catalyst modified by the molecularly imprinted polymer and immobilized by tryptophan is uniform and spherical, and the size is about 180nm.
Example 4
Step one: preparation of amino Fe 3 O 4 Magnetic nanoparticles
1.0g FeCl 3 ·6H 2 O, 3.6g of anhydrous sodium acetate and 6.3g of 1, 6-hexamethylenediamine are placed in a 100mL beaker, 30mL of ethylene glycol is added, after being fully mixed, the clear liquid is transferred into a reaction kettle, and the reaction is finished at 200 ℃ for 7 hours. The obtained product is separated by an external magnetic field, washed by ethanol and water, and dried overnight in an oven at 50 ℃.
Step two: preparation of Polyethylenimine (PEI) grafted magnetic nanoparticles (denoted Fe 3 O 4 -PEI)
1mg/mL of PEI solution and 1% glutaraldehyde solution were prepared in methanol, respectively, and 200 was weighed
mg Fe 3 O 4 -NH 2 In a three-necked flask, 30mL of PEI and glutaraldehyde solution were sequentially added, followed by superDispersing by sound, adding 90mg NaBH under mechanical stirring 4 After reacting for 1h, removing the supernatant by magnetic separation; 30mL of PEI solution and 90mg of NaBH were again added 4 After 2h, the reaction was completed. And magnetically separating, cleaning and drying the material for later use.
Step two: preparation of boric acid functionalized magnetic nanoparticles (denoted Fe 3 O 4 -HPBA)
200mg Fe 3 O 4 -PEI, 300mg 4-formylphenylboronic acid and 225mg NaBH 4 Placing the mixture into a three-necked flask, adding 30mL of methanol solution, reacting for 24 hours at room temperature, magnetically separating, cleaning and drying to obtain Fe 3 O 4 -
HPBA is ready for use.
Step three: preparation of Tryptophan immobilized magnetic catalyst (denoted Fe 3 O 4 -Trp)
150mg Fe 3 O 4 HPBA, 350mg L-5-bromotryptophan, 200mg Na 2 Cl 4 Pd, 600mg tris (3-sodium sulfonate phenyl) phosphine (TPPTS) and 850mg K 2 CO 3 In a three-necked flask, 50mL of deaerated water was added to the flask, followed by N 2 And (3) refluxing for 24 hours at 85 ℃ under the atmosphere, and cleaning and drying the material for later use.
Step four: preparation of molecularly imprinted Polymer-modified Tryptophan-immobilized magnetic catalyst (designated as P-
MMIP)
150mg Fe is weighed 3 O 4 Trp, 7.0g polyvinylpyrrolidone (PVP) in a 250mL three-necked flask, 10mL ultrapure water and 50mL absolute ethanol were added and sonicated. Then 75mg of template molecule was added to the above mixture and stirred for 30 minutes to form a template-carrier complex. Then, 2.0mL of ammonia water and 150. Mu.L of Phenyltrimethoxysilane (PTMOS), 750. Mu.L of n-Octyltrimethoxysilane (OTMS) and 300. Mu.L of Tetraethylorthosilicate (TEOS) were added and reacted for 6 hours. The reaction product was washed with ultrapure water to neutrality and dried overnight at 50 ℃ for further use.
Eluting the template by using a mixed solution of methanol and acetic acid with the volume ratio of 85:15, washing the eluted polymer material to be neutral by using ultrapure water, and drying overnight at 50 ℃ to obtain the molecular engram polymer modified tryptophan immobilized magnetic catalyst (P-MMIP).
The non-imprinted material (P-MNIP) was prepared using the same synthetic strategy as the molecularly imprinted material, except that no template molecule was added.
The prepared magnetic catalyst modified by the molecularly imprinted polymer and immobilized by tryptophan is uniform and spherical, and the size of the magnetic catalyst is about 170nm.
2. Evaluation of adsorption Performance of molecularly imprinted Polymer-modified magnetic immobilized tryptophan catalyst on substrate adsorption Performance detection of molecularly imprinted Polymer-modified magnetic immobilized tryptophan catalyst prepared in example 1 is performed as follows:
(1) 5mg of the molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst is added into 12mL of 4-nitrobenzaldehyde solution with the concentration of 90 mug/mL, and after shaking for 6 hours at room temperature, the supernatant is separated by an external magnetic field.
(2) Measuring the concentration of 4-nitrobenzaldehyde in the supernatant obtained in the step (1) by using an ultraviolet-visible spectrum, and then calculating the adsorption quantity of the molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst to the 4-nitrobenzaldehyde;
the concentration of 4-nitrobenzaldehyde in the supernatant was measured to be 11.95. Mu.g/mL.
The calculation formula of the adsorption quantity of the molecular imprinting polymer modified tryptophan immobilized magnetic nano catalyst to 4-nitrobenzaldehyde is as follows:
Figure SMS_1
c in the formula e The concentration of 4-nitrobenzaldehyde in the supernatant;
by calculation, the adsorption amount of the molecular engram polymer modified tryptophan immobilized magnetic nano catalyst to the 4-nitrobenzaldehyde substrate is as follows: 187.33mg/g.
And carrying out isothermal adsorption experiment verification on the prepared magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer. As shown in FIG. 2, the adsorption capacity of the imprinted magnetic nano catalyst gradually tends to be balanced after increasing along with the change of the concentration of the 4-nitrobenzaldehyde substrate, and the adsorption capacity of the imprinted polymer modified material is far higher than that of the non-imprinted material; meanwhile, selectivity experiments show that the selectivity of the material modified by the imprinted polymer is far higher than that of the material not imprinted (figure 3), and the excellent adsorption performance and selectivity of the polymer modified layer of the imprinted layer are proved.
In addition, the selectivity of the prepared magnetic nano catalyst modified by the molecularly imprinted polymer and immobilized by tryptophan is researched, and the result is as follows:
the magnetic nano catalyst prepared by taking substrates 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, 4-cyanobenzaldehyde, 2-cyanobenzaldehyde and 3-cyanobenzaldehyde which have similar structures and reactivity with 4-nitrobenzaldehyde as competitors is studied to selectively adsorb the 4-nitrobenzaldehyde. Adding 5mg of the molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst into 12mL of aqueous solution of 4-nitrobenzaldehyde and a competitor thereof with the concentration of 90 mu g/mL respectively, oscillating for 6 hours at room temperature, and separating out supernatant by an external magnetic field; the concentration of 4-nitrobenzaldehyde and its competing reactants in the resulting supernatant was determined by UV-vis, and the adsorption amount of each reaction substrate by the molecularly imprinted polymer-modified magnetically immobilized tryptophan catalyst was calculated by the following formula.
Figure SMS_2
C in the formula e The concentration of the different reaction substrates in the supernatant.
Through calculation, the prepared magnetic nano catalyst has the following adsorption amounts of 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, 4-cyanobenzaldehyde, 2-cyanobenzaldehyde and 3-cyanobenzaldehyde respectively: 68.04, 50.13, 73.20, 44.67 and 32.33mg/g, it was found that the prepared magnetic nanospheres adsorbed testosterone in an amount much higher than its competitor (fig. 3). Therefore, the prepared magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer has higher selective adsorption capacity on 4-nitrobenzaldehyde matched with a template structure.
3. Evaluation of catalytic performance of molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst
The synthesized magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer is used for catalyzing aldol reaction of benzaldehyde and cyclohexanone, and the specific operation is as follows:
50mg of P-MMIP and 75.5mg of 4-nitrobenzaldehyde are placed in a reaction vessel, 9.0mL of ultrapure water is added, and after stirring uniformly, 12.5mL of cyclohexanone is added and reacted at 30℃for 48 hours. After the reaction, saturated aqueous ammonium chloride solution is added for quenching, and dichloromethane is used for extracting for multiple times. After combining, the organic layers were concentrated and purified by column chromatography on silica gel (ethyl acetate: petroleum ether=1:3) to give the product as pale yellow 2-hydroxy (4-nitrophenyl) methylcyclohexanone.
As shown in Table 1, the prepared magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer still maintains higher catalytic activity of the tryptophan catalyst, successfully catalyzes the reaction of 4-nitrobenzaldehyde substrate cyclohexanone, and has higher yield (80%).
In addition, the catalytic selectivity of the prepared magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer is studied, and the operation is as follows:
the reaction substrates 2-nitrobenzaldehyde and 3-nitrobenzaldehyde which have similar structures and reactivity to 4-nitrobenzaldehyde are taken as competitors, 50mg of P-MMIP is taken as a catalyst, and the competitors are respectively added into the reaction vessels of 75.5mg of 4-nitrobenzaldehyde, 2-nitrobenzaldehyde and 3-nitrobenzaldehyde, and then 9.0mL of ultrapure water and 12.5mL of cyclohexanone are respectively added for reaction for 48 hours at 30 ℃. After the completion, saturated aqueous ammonium chloride solution was added to quench the mixture, and the mixture was extracted with methylene chloride several times. After combining, the organic layers were concentrated and purified by column chromatography on silica gel (ethyl acetate: petroleum ether=1:3) to give the final product.
As controls, 50mg of L-Trp and 50mg of P-MNIP were selected as catalysts, and the above-described catalytic selectivity experiment was performed. The reaction equation and conditions are shown in table 1 below:
TABLE 1 catalytic selectivity experiments
Figure SMS_3
As can be seen from Table 1, when the reactions of 4-nitrobenzaldehyde, 2-nitrobenzaldehyde and 3-nitrobenzaldehyde with cyclohexanone are catalyzed by using L-Trp as a catalyst, the yields of the 4-nitrobenzaldehyde, 2-nitrobenzaldehyde and 3-nitrobenzaldehyde are not obviously different, and the reactivity difference is not great; when P-MNIP is used as a catalyst, the yield and the selectivity are low because of the lack of imprinting holes, so that Fe is loaded 3 O 4 The catalytic sites of the tryptophan are partially buried, so that the catalytic activity is lost, and the selectivity is not greatly improved; when the magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer is selected, the magnetic immobilized tryptophan catalyst can selectively adsorb 4-nitrobenzaldehyde matched with a template and catalyze the reaction of the 4-nitrobenzaldehyde and cyclohexanone due to the existence of the selective imprinting cavity, so that the yield (80%) of the 4-nitrobenzaldehyde is greatly improved compared with that of 2-nitrobenzaldehyde (15%) and 3-nitrobenzaldehyde (10%), and the excellent catalytic selectivity of the magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer is fully demonstrated.
Particularly, the catalytic selectivity of the prepared magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer in a complex reaction system is researched, and the preparation method comprises the following operations:
(1) 75.5mg of each of 4-nitrobenzaldehyde, 2-nitrobenzaldehyde and 3-nitrobenzaldehyde are fully mixed and taken as complex substrates, the complex substrates are placed in a reaction vessel, 50mg of P-MMIP and 9.0mL of ultrapure water are added, 12.5mL of cyclohexanone are added after uniform stirring, the reaction is finished at 30 ℃ for 48 hours, then the complex substrates are quenched with saturated ammonium chloride aqueous solution, the complex substrates are extracted with dichloromethane for multiple times, and the organic layers are combined and purified by silica gel column chromatography (ethyl acetate: petroleum ether=1:3), so that a pale yellow product is obtained.
(2) The reaction products of 4-nitrobenzaldehyde, the products of 2-nitrobenzaldehyde and the products of 3-nitrobenzaldehyde in the mixture were confirmed by HPLC, and the yields of the 4-nitro-substituted products, the 2-nitro-substituted products and the 3-nitro-substituted products were confirmed.
As a control, 50mg of L-Trp and 50mg of P-MNIP were selected as catalysts, respectively, and the above-mentioned experiments of catalytic selectivity of complex reaction substrates were performed. The reaction equation and conditions are shown in table 2 below:
TABLE 2 catalytic selectivity experiments
Figure SMS_4
As can be seen from Table 2, the prepared molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst still has higher catalytic activity in a mixed reaction system, and the total yield (75%) is equivalent to that of the prepared molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst alone (84%). In addition, when the P-MMIP is used as a catalyst, the P-MMIP has higher catalytic selectivity in the mixed reaction of o-, m-and P-nitro substituted benzaldehyde compared with L-Trp and P-MNIP, the yield of the catalyzed 4-nitrobenzaldehyde reaction is about 2 times of that of the 2-nitrobenzaldehyde reaction, and about 10 times of that of the 2-nitrobenzaldehyde reaction, which indicates that the catalyst has stronger anti-interference capability and can keep good catalytic selectivity in a complex reaction system by modifying molecular imprinting.
In summary, the invention discloses a preparation method of a molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst, which comprises the steps of covalently loading an organic small molecule catalyst (L-Trp) on magnetic Fe 3 O 4 On a carrier, a reaction product of 4-nitrobenzaldehyde and cyclohexanone catalyzed by the carrier is selected as a template, two silanization reagents PTMS and OTMS are used as difunctional monomers, and a molecular engram polymer modified immobilized tryptophan catalyst (P-MMIP) is synthesized under the crosslinking of TEOS by a sol-gel technology. By magnetic Fe 3 O 4 The nano particles are used as carriers, so that the rapid separation of the catalyst can be realized under the action of an external magnetic field, the difficulty of separation and purification in synthesis is reduced, the consumption of organic reagents is reduced, and the cost is correspondingly reduced; in addition, the tryptophan catalyst acts on the carrier in a covalent loading manner, so that the stability of the material is greatly increased, and the catalytic performance of the tryptophan catalyst is ensured; two silanization reagents are selected as functional monomers, so that the surface functional groups of the molecularly imprinted polymer are enriched, the adsorption capacity of the material to a reaction substrate is improved, and the adsorption selection is improvedSelectivity of the method. The immobilized tryptophan catalyst prepared by the method has the advantages of high stability, high adsorption capacity, good selectivity, easiness in separation and the like, and can be used for catalyzing specific aldol reaction.
The magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer synthesized by the invention maintains the excellent catalytic performance of the tryptophan small molecule catalyst, and good yield is obtained when the magnetic immobilized tryptophan catalyst is used for the reaction of benzaldehyde and cyclohexanone. In addition, due to the successful modification of the surface molecular imprinting, the catalyst has substrate selectivity, and can selectively catalyze the reaction of the 4-nitrobenzaldehyde substrate matched with the template.
Particularly, the synthesized magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer is used in a complex reaction system of mixing various substrates (2-nitrobenzaldehyde, 3-nitrobenzaldehyde and 4-nitrobenzaldehyde), good selective catalytic performance is still reserved, the reactivity distinction of the substrates is realized, the generation of byproducts is reduced, the difficulty of limited selectivity in organic synthesis is solved to a certain extent, and the application prospect is wide.
The above is only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited by this, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims (10)

1. The preparation method of the magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer is characterized by comprising the following steps of:
1) Fixing L-tryptophan on the surface of the boric acid functionalized magnetic nano-particles to prepare a tryptophan immobilized magnetic catalyst;
2) Taking an aldol condensation product of 4-nitrobenzaldehyde and cyclohexanone catalyzed by tryptophan as a template molecule, and fixing the template on the surface of a tryptophan immobilized magnetic catalyst under the action of polyvinylpyrrolidone to form a template-carrier compound;
3) Sequentially adding ammonia water, phenyl trimethoxy silane, n-octyl trimethoxy silane functional monomer and tetraethoxysilane into the template-carrier compound by adopting a sol-gel method to prepare a polymer layer containing template molecules;
4) And removing the template molecules in the polymer layer containing the template molecules, and cleaning and drying to obtain the magnetic immobilized tryptophan catalyst modified by the molecular imprinted polymer, namely the magnetic molecular imprinted polymer loaded by tryptophan.
2. The method for preparing a magnetic immobilized tryptophan catalyst modified by a molecularly imprinted polymer according to claim 1, wherein in the step 1), the tryptophan immobilized magnetic catalyst is prepared from boric acid functionalized magnetic nano-particles and L-5-bromotryptophan as raw materials and Na 2 Cl 4 Pd is a palladium source, tris (3-sodium sulfonate phenyl) phosphine is a ligand, K 2 CO 3 Providing an alkaline environment at N 2 Reflux at 85 ℃ under protection;
wherein, boric acid modified magnetic nano particles, L-5-bromotryptophan and Na 2 Cl 4 Pd, tri (3-sodium sulfonate phenyl) phosphine as ligand and K 2 CO 3 The dosage ratio of (1) is (100-300) mg, (200-800) mg, (150-500) mg, (300-1200) mg and (500-2000) mg.
3. The preparation method of the molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst according to claim 1, wherein in the step 2), the dosage ratio of the template molecule, the tryptophan immobilized magnetic catalyst, the polyvinylpyrrolidone and the solvent is (25-125) mg (100-500) mg (5-25) g (50-250) mL, and the reaction time is 15-100 min; wherein the solvent is a mixture of water and ethanol, and the volume ratio of water to ethanol is 1:3-1:6.
4. The method for preparing a molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst according to claim 1, wherein in the step 3), the polymer layer containing the template molecule is prepared by adding ammonia water, phenyl trimethoxysilane, n-octyl trimethoxysilane functional monomer and tetraethoxysilane into (100-1000) mg template-carrier compound according to the dosage ratio of (1-5) mL (0.5-3) mL (0.5-5) and (50-500) mu L in sequence, and reacting for 3-12 h.
5. The preparation method of the molecularly imprinted polymer modified magnetic immobilized tryptophan catalyst according to claim 1, wherein in the step 4), the template molecule is removed by adopting an elution solution prepared by mixing absolute methanol and glacial acetic acid in a volume ratio of (80-95): 20-5.
6. The method for preparing a molecularly imprinted polymer modified magnetic immobilization tryptophan catalyst according to any one of claims 1 to 5, wherein in the step 1), the preparation method of the boric acid functionalized magnetic nanoparticle is as follows:
first, amino Fe is prepared 3 O 4 Magnetic nanoparticles and amino Fe 3 O 4 Surface modification of magnetic nano particle with polyethylenimine to prepare Fe 3 O 4 -PEI; then at Fe 3 O 4 And grafting phenylboronic acid on the PEI surface to prepare the magnetic nano particle with boric acid functionalization.
7. The method for preparing the molecularly imprinted polymer modified magnetic immobilization tryptophan catalyst according to claim 6, wherein the amino Fe 3 O 4 The magnetic nano-particles are prepared by a solvothermal method; the molecular weight of the polyethyleneimine used is 1800; the grafted phenylboronic acid takes 4-formylphenylboronic acid as a boric acid reagent.
8. The magnetically immobilized tryptophan catalyst modified by the molecularly imprinted polymer and prepared by the preparation method of any one of claims 1 to 7, wherein the magnetically immobilized tryptophan catalyst is spherical and has a particle size of 100 to 200nm.
9. The use of the molecularly imprinted polymer modified magnetic immobilization tryptophan catalyst of claim 8 for catalyzing aldol reaction of 4-nitrobenzaldehyde and cyclohexanone.
10. The use according to claim 9, wherein in the catalytic reaction, the molecularly imprinted polymer modified magnetically immobilized tryptophan catalyst is capable of selectively adsorbing a substrate 4-nitrobenzaldehyde matched with a template structure;
the catalytic reaction conditions are as follows: the dosage of the magnetic immobilized tryptophan catalyst modified by the molecularly imprinted polymer is 50-300 mg for every 10mg of 4-nitrobenzaldehyde; the molar ratio of cyclohexanone to 2-nitrobenzaldehyde/3-nitrobenzaldehyde/4-nitrobenzaldehyde is (2-15): 1, a step of; the solvent is H 2 O; the temperature is 25-40 ℃.
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