Development of a model for the rational design of molecular imprinted polymer: Computational approach for combined molecular dynamics/quantum mechanics calculations

A new rational approach for the preparation of molecularly imprinted polymer (MIP) based on the combination of molecular dynamics (MD) simulations and quantum mechanics (QM) calculations is described in this work. Before performing molecular modeling, a virtual library of functional monomers was created containing forty frequently used monomers. The MD simulations were first conducted to screen the top three monomers from virtual library in each porogen-acetonitrile, chloroform and carbon tetrachloride. QM simulations were then performed with an aim to select the optimum monomer and progen solvent in which the QM simulations were carried out; the monomers giving the highest binding energies were chosen as the candidate to prepare MIP in its corresponding solvent. The acetochlor, a widely used herbicide, was chosen as the target analyte. According to the theoretical calculation results, the MIP with acetochlor as template was prepared by emulsion polymerization method using N,N-methylene bisacrylamide (MBAAM) as functional monomer and divinylbenzene (DVB) as cross-linker in chloroform. The synthesized MIP was then tested by equilibrium-adsorption method, and the MIP demonstrated high removal efficiency to the acetochlor. Mulliken charge distribution and ¹H NMR spectroscopy of the synthesized MIP provided insight on the nature of recognition during the imprinting process probing the governing interactions for selective binding site formation at a molecular level. We think the computer simulation method first proposed in this paper is a novel and reliable method for the design and synthesis of MIP.     

Investigating the mechanisms of 17<Emphasis Type="Italic">β</Emphasis>-estradiol imprinting by computational prediction and spectroscopic analysis

Molecular dynamics simulations combined with spectroscopic analysis were applied to understand the nature of recognition in molecularly imprinted polymers (MIPs), and for optimizing the MIP formulation. The best monomers for synthesizing imprinted materials for 17β-estradiol (BE2) were selected by evaluating the strength of the template–monomer interaction derived from molecular dynamics simulations. A number of potential functional monomers for BE2 were screened for hydrogen-bonding strength in order to analyze template–monomer interactions favorable for synthesizing noncovalent MIPs, with the simulations revealing that methacrylic acid, 2-(diethylamino)ethyl methacrylate, and methacrylamide provided the highest binding affinity to BE2. These theoretical predictions agree with previously reported results on batch rebinding studies using the corresponding functional monomers for synthesizing a series of MIPs. Molecular analysis such as ¹H NMR was used for experimentally confirming the prevalent template–monomer interactions derived from the modeling results. Molecular dynamics simulations indicating monomer dimerization in the prepolymerization solution correlated with the nature of the porogenic solvent, which was confirmed by NMR studies on hydrogen-bonding interactions of methacrylic acid in different solvents. Furthermore, batch rebinding studies revealed that the specific functionalities of the monomers essential to rebinding are retained after polymerization, which proves that the application of computational methods for modeling the prepolymerization solution provides useful information for optimizing real MIP systems.     

Molecular recognition properties of salicylic acid-imprinted polymers

Summary Two molecularly imprinted polymers (MIP) have been prepared using the acidic drug salicylic acid, which can form intramolecular hydrogen bond, as the template and acrylamide or 4-vinylpyridine as the functional monomer. HPLC was used to evaluate the binding performance of the MIP for the template and for several analogues. The results showed that the MIP (P₂) prepared using acrylamide as the functional monomer had no molecular imprinting effect whereas that (P₁) prepared using 4-vinylpyridine as the functional monomer had a significant molecular imprinting effect. The reason the molecular imprinting effect was different for the two MIP was elucidated and the molecular recognition properties of P₁ were studied in detail. It was confirmed that electrostatic interaction played an important role in the molecular recognition of P₁. Scatchard analysis showed that two types of binding site with distinctly different affinity were formed in P₁. Their dissociation constants were estimated to be 7.6×10⁻⁵ mol L⁻¹ and 3.2×10⁻³ mol L⁻¹, respectively. Because P₁ has high affinity and selectivity for salicylic acid not only in organic systems but also in water-containing systems, it gives P₁ the potential for use in the enrichment, separation, and detection of salicylic acid in biological fluids.     

Investigation of enantiomer recognition of molecularly imprinted polymeric monoliths in pressurized capillary electrochromatography screening the amino acids and their derivatives

Molecularly imprinted monolithic columns were prepared for chiral separation of tyrosine and its amino acid derivatives by in situ therm-initiated copolymerization of methacrylic acid, 4-vinylpyridine and ethylene glycol dimethacrylate. The enantiomers were rapidly separated on monolithic columns in less than 10 min by pressurized capillary electrochromatography (pCEC). The influences of several parameters such as the content of cross-linking monomer on the composition of the pre-polymerization mixture were systematically investigated. The influence of the pCEC conditions including the composition of the mobile phase was also optimized to obtain the good enantioseparation. It was found that in addition to molecularly imprinted recognition, chromatographic retention and electrophoretic migration play important roles in the retention and chiral recognition of molecularly imprinted polymer (MIP) columns. The cross-selectivity for similar amino acids and its derivatives were systematical investigated for understanding the recognition mechanism on the MIP monolithic columns. The results indicated that molecularly imprinted polymer recognizes the template molecule by its molecular shape defined binding cavity.     

Examining ligand-protein interactions with binding-energy landscapes

Binding-energy landscapes are used to investigate the thermodynamics of molecular recognition for the pteridine ring, a recognition anchor in binding with dihydrofolate reductase, and two molecules with the same shape but different heteroatom substitutions. The relative importance of hydrogen bonding and hydrophobic interactions in this system is analyzed by comparing these three different decorations of the pteridine scaffold. Received: 5 May 1998 / Accepted: 3 September 1998 / Published online: 17 December 1998     

Novel polymer system for molecular imprinting polymer against amino acid derivatives

Molecular imprinting polymers (MIPs) against N-Cbz-L-Tyr were prepared utilizing different polymer systems and evaluated in HPLC mode. It was found that MEP utilizing cocktail functional monomers, acrylamide 2-vinylpyridine showed better molecular recognition and better separation ability for the template molecule than those utilizing other functional monomers. MIP utilizing trimethylolpropane trimethacrylate as cross-linker showed higher load capacity and separation factor than those utilizing ethylene glycol dimethacrylate as cross-linker. Increasing the concentration of competing solvent, acetic acid weakened the ionic interaction and hydrogen bonding between the analyte and the functional monomers, 2-vinylpyridine and acrylamide, when the template enantiomer was separated by HPLC. Therefore increasing of the concentration of acetic acid leads to decreasing of capacity factor, separation factor and resolution.     

Capturing molecules with templated materials--analysis and rational design of molecularly imprinted polymers

The creation of synthetic tailor-made receptors capable of recognizing desired molecular targets with high affinity and selectivity is a persistent long-term goal for researchers in the fields of chemical, biological, and pharmaceutical research. Compared to biomacromolecular receptors, these synthetic receptors promise simplified production and processing, less costs, and more robust receptor architectures. During recent decades, molecularly imprinted polymers (MIPs) are widely considered mimics of natural molecular receptors suitable for a diversity of applications ranging from biomimetic sensors, to separations and biocatalysis.A remaining challenge for the next generation of MIPs is the synthesis of deliberately designed and highly efficient receptor architectures suitable for recognizing biologically relevant molecules, for which natural receptors are either not prevalent, or difficult to isolate and utilize. Hence, this review discusses recent advances in synthetic receptor technology for biomolecules (e.g. drugs, amino acids, steroids, proteins, entire cells, etc.) via molecular imprinting techniques. Surface imprinting methods and epitope imprinting approaches have been introduced for protein recognition at imprinted surfaces. Imprinting techniques in aqueous solution or organic-water co-solvents have been introduced avoiding denaturation of biomolecules during MIP synthesis. In addition, improved bioreactivity of entire enzyme or active site mimics generated by molecular imprinting will be highlighted. Finally, the emerging importance of molecular modeling and molecular dynamics studies detailing the intermolecular interactions between the template species, the porogenic solvent molecules, and the involved monomer and cross-linker in the pre-polymerization solution will be addressed yielding a rational approach toward next-generation MIP technology.     

A selective molecularly imprinted polymer-solid phase extraction for the determination of fenitrothion in tomatoes

A new and selective sorbent for molecularly imprinted solid-phase extraction (MISPE) was developed and applied for the determination of residues of fenitrothion (FNT) in tomatoes, using HPLC coupled to photodiode array detection (HPLC-DAD). Using FNT as the template molecule, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, toluene as the porogenic solvent, and bulk polymerization as the synthetic method, a molecularly imprinted polymer (MIP) was synthesized. In order to choose the medium which promotes the best molecular recognition of FNT by the MIP, the adsorption of FNT by the MIP was studied in different media containing acetonitrile and toluene. Besides FNT, three structurally related compounds were used to evaluate the selectivity of the FNT-molecularly imprinted polymer. The MIP exhibited the highest selective rebinding to FNT. The method developed was validated, using fortified blank tomato samples. The extraction efficiency was 96%. The limits of detection and quantitation were 0.050 and 0.130 μg g⁻¹, respectively. The intra-day precision was 5.9% and the inter-day precision 8.1%. The accuracy was higher than 89% for a concentration level around the maximum residue limit of 0.5 μg g⁻¹.     

Synthesis,Application, and Molecular Recognition Mechanism Study of Phenylalanine Molecularly Imprinted Polymer

Abstract

Phenylalanine molecularly imprinted polymer was synthesized in the presence of triflouroacetic acid. HPLC‐MS evaluation showed it had good affinity toward its template among 16 amino acid mixtures. It was used for quantification of phenylalanine in protein hydrolysis solution and in serum without sample pre‐treatment. Further study revealed the molecular recognition mechanism involved size exclusion, hydrophobic interaction, and hydrogen bonding interaction. The molecularly imprinted polymer presented here can be used for actual sample analysis and the well characterized recognition mechanism can benefit the design, synthesis, and application of MIP.     

A comparative study of the potential of acrylic and sol-gel polymers for molecular imprinting

The successful molecular imprinting of 2-aminopyridine (2-apy) in bulk polymerisations of acrylic and sol-gel based polymers has been achieved. Both polymeric systems reveal varying degrees of affinity in rebinding the original template as well as a number of structural analogues. Rebinding was conducted in chloroform, acetonitrile and methanol in order to assess the role of hydrogen bonding in imprinting. The acrylic imprinted polymer retained approximately 50% of the template in rebinding studies in chloroform compared to 100% for the sol-gel. However, this higher affinity for the sol-gel was accompanied by a higher degree of non-specific binding. While the acrylic polymer performed poorly in acetonitrile, the sol-gel maintained a high degree of discrimination.The acrylic polymer exhibited little discrimination between imprinted and reference polymers for 3-aminopyridine (3-apy) indicating the high selectivity of the MIP polymer for 2-apy relative to 3-apy. This selectivity was reduced in acetonitrile. Selectivity of the sol-gel for 2-apy in chloroform was poor as 3-apy was retained to a similar degree. Comparable results were obtained in acetonitrile. 4-Aminopyridine (4-apy) bound strongly to all polymers in all solvents and proved very difficult to remove due to the high degree of non-specific binding for both polymeric matrices.     

Chromatographic evaluation of polymers imprinted with analogs of chloramphenicol and application to selective solid-phase extraction

To obtain a highly selective material for the antibiotic chloramphenicol, which has several harmful side effects in humans, different molecularly imprinted polymers (MIPs) were prepared. In order to avoid a major traditional drawback associated with MIPs of residual template bleeding, molecules that are structurally related to chloramphenicol were used as templates for polymer synthesis. Chromatographic evaluation indicated that the employed template imparted a significant influence on the recognition properties of the corresponding polymer. A strong retention of chloramphenicol under nonpolar elution conditions (k = 68.03, IF = 17.72) and under aqueous elution conditions (k = 92.44, IF = 1.35) was achieved. After chromatographic evaluation, the MIP was utilized as the recognition sorbent in a solid-phase extraction to determine chloramphenicol using either an organic or aqueous washing solvent. Recoveries of nearly 100% from the chloramphenicol standard solution and nearly 90% from honey samples spiked with chloramphenicol were attained. Furthermore, the applicability of the MIP for sample cleanup was demonstrated.     

Preparation and characterization of molecularly imprinted organic–inorganic hybrid materials by sol–gel processing for selective recognition of ibuprofen

This work adopted semi-covalent imprinting to prepare molecularly imprinted polymers (MIP) with ibuprofen, a non-steroidal anti-inflammatory drug, as template by sol–gel processing, which is characterized by both the high affinity of covalent binding and the mild operation conditions of non-covalent rebinding. A functional monomer, which was used to synthesize the monomer-imprinted molecule complex, was prepared by multi-step synthesis for the first time. MIP was characterized by Fourier transform IR spectrum and nitrogen adsorption. Thin-layer chromatography separation was used to evaluate the specific molecular recognition ability of MIP. In addition, dynamic and thermodynamic studies on MIP imprinting ibuprofen were undertaken. The results of equilibrium rebinding experiments showed that MIP exhibited good adsorption capacity for ibuprofen. Scatchard analysis illustrated that the template-polymer system shows only one-site binding behavior with a dissociation constant of 1.84 mmol L^?1. Dynamic adsorption exhibited pseudo-second-order kinetics. The positive value of ΔH^θ and the negative values of ΔG^θ demonstrated that the binding system for MIP is endothermic and spontaneous.     

Probing cavity versus surface preference of fluorescent template molecules in molecularly imprinted polystyrene microspheres

Functional polystyrene (PS) crosslinked microbeads were developed by dispersion polymerization as fluorescent molecularly imprinted polymers (MIPs) having cavities with specific recognition sites. The functional azobenzene molecule modified with pyridine was self‐assembled with Pyrenebutyric acid (template molecules), and introduced during the second stage of dispersion polymerization of polystyrene. The template molecule was removed from MIP by Soxhlet using acetonitrile as solvent. Non imprinted polymer (NIP) having no template was also synthesized for comparative study. Fluorescence spectroscopy could be used as a tool to derive insight into the location of the template molecules on the MIP or NIP. The template molecules were adsorbed on the surface of the NIPs during binding studies, which was evidenced from the pyrene excimeric emission observed at 440 nm. The template binding efficiency of the NIPs were much lower compared to MIPs. Pyrene emission from MIP upon rebinding showed typical monomeric emission in the 375–395 nm range, confirming its location in isolated cavities. In rebinding studies of the template molecules, the MIPs selectively took up the template for which the cavity was designed, which demonstrated their selectivity towards template molecules. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1558–1565     

Sulfonamide imprinted polymers using co-functional monomers

Molecular imprinted polymers (MIPs) prepared using combination of acrylamide (ACM) and 4-vinylpyridine (4-Vpy) as co-functional monomers exhibited efficient recognition properties in both organic and aqueous media as HPLC stationary phase. The results indicate that amide and pyridine groups in functional monomers formed strong hydrogen-bonding interaction with the template molecule, and specific recognition sites were created within the polymer matrix during the imprinting process. When sulfamethoxazole (SMO) was used as template, a MIP prepared in a polar organic solvent (acetonitrile) using the combination of ACM and 4-Vpy showed better recognition of template than the polymer prepared in the same solvent using the combination of acidic monomer (methacrylic acid) and basic monomer 4-Vpy. On the contrary, when sulfamethazine (SMZ) was used as template, a MIP prepared using the combination of methacrylic acid (MAA) and 4-Vpy showed better recognition of template than the polymer prepared using the combination of ACM and 4-Vpy. Our results indicate that in organic media the degree of retention of the sample molecules on the imprinted polymers was controlled by the hydrogen-bonding interaction between the sample molecules and the polymer, while in aqueous media it was determined to a considerable extent by hydrophobic interactions. In both media the shape, size and the electronic structure of the template molecule were all-important factors in the recognition process.     

Development of a selective molecularly imprinted polymer-based solid-phase extraction for indomethacin from water samples

A selective molecularly imprinted solid-phase extraction (MISPE) for indomethacin (IDM) from water samples was developed. Using IDM as template molecule, acrylamide (AM) or methacrylic acid (MAA) as functional monomer, ethylene dimethacrylate (EDMA) as crosslinker, and bulk or suspension polymerization as the synthetic method, three molecularly imprinted polymers (MIPs) were synthesized and characterized with a rebinding experiment. It was found that the MIP of AM-EDMA produced by bulk polymerization showed the highest binding capacity for IDM, and so it was chosen for subsequent experiments, such as those testing the selectivity and recognition binding sites. Scatchard analysis revealed that at least two kinds of binding sites formed in the MIP, with the dissociation constants of 7.8 μmol L⁻¹ and 127.2 μmol L⁻¹, respectively. Besides IDM, three structurally related compounds — acemetacin, oxaprozin and ibuprofen — were employed for selectivity tests. It was observed that the MIP exhibited the highest selective rebinding to IDM. Accordingly, the MIP was used as a solid-phase extraction sorbent for the extraction and enrichment of IDM in water samples. The extraction conditions of the MISPE column for IDM were optimized to be: chloroform or water as loading solvent, chloroform with 20% acetonitrile as washing solution, and methanol as eluting solvent. Water samples with or without spiking were extracted by the MISPE column and analyzed by HPLC. No detectable IDM was observed in tap water and the content of IDM in a river water sample was found to be 1.8 ng mL⁻¹. The extraction efficiencies of the MISPE column for IDM in spiked tap and river water were acceptable (87.2% and 83.5%, respectively), demonstrating the feasibility of the prepared MIP for IDM extraction. Figure Molecularly imprinted polymer-based solid-phase extraction for indomethacin     

Selectivity features of molecularly imprinted polymers recognising the carbamate group

The molecular recognition properties of molecular imprinted polymers which bind the carbamate function were studied. Functional monomers potentially able to form non-covalent interactions with the model molecule N,O-dibenzylcarbamate were selected on the basis of a computational approach describing possible interactions between the template and a small library of vinylic monomers. These results were in accordance with N,O-dibenzylcarbamate batch-rebinding measurements performed on several miniMIPs prepared with the same library. From these preliminary results, four polymers were prepared by thermoinduced radical polymerization, using ethylene dimethacrylate as a cross-linker, chloroform (MIP1, MIP3) or acetonitrile (MIP2, MIP4) as porogens and methacrylic acid (MIP1, MIP2) or acrylamide (MIP3, MIP4) as functional monomers. Molecular recognition features of these materials were studied by high-performance liquid chromatography. In this manner selectivity was evaluated by considering the column retention of a library of sixteen structural analogues of dibenzylcarbamate, characterized by the transformation of the carbamate into a related function, or by the alteration of the molecular structure.The experimental results show that methacrylic acid is more efficient than acrylamide as a functional monomer (imprinting factors: MIP1 = 24.1, MIP2 = 25.6, MIP3 = 13.3, MIP4 = 2.44), and that chloroform enhances polymer selectivity. As regards structural motifs which conditionate the selectivity, the carbamate function strictly controls the presence/absence of molecular recognition, while shape and dimension of the substituents modulate the recognition itself. In particular, a marked recognition for analogs which were slightly bigger than the template was observed (N-benzyl-O-phenethylcarbamate: MIP1 α = 1.13, MIP2 α = 1.41, MIP3 α = 0.97; N-phenethyl-N-benzylcarbamate: MIP1 α = 1.61, MIP2 α = 1.17, MIP3 α = 0.81; N,O-diphenethylcarbamate: MIP1 α = 0.89, MIP2 α = 1.20, MIP3 α = 0.55).     

Shape selectivity versus functional group pre-organization in molecularly imprinted polymers

A systematic survey of related molecular probes differing in shape or functional group orientation was used to compare the effects of shape selectivity versus pre-organization of functional monomers on imprinting and rebinding performance of molecularly imprinted polymers (MIPs). These studies revealed that templates with two functional group interactions with the MIPs are influenced to a larger degree by shape selective interactions than templates with three functional group interactions. For example, with two functional group interactions, increasing side chain size of compounds 1-5 increased selectivity 5-fold; while the same size change for compounds with three functional group interactions leads to a maximum 2-fold increase. Thus, the effects of shape selectivity and pre-organization of functional groups do not appear to work in concert with each other during the imprinting process or in the rebinding behavior. Furthermore, greater selectivity is generally found for templates with two functional groups, where the dominant mode of molecular recognition is shape selectivity. For example, the α value for the MIP elicited toward template compound 5 with two hydrogen bonding groups was 5-12-fold higher than equivalently shaped compounds 6-8 that have three non-covalent binding interactions (Table 3). On the other hand, pre-organization of functional groups dominated the performance of MIPs elicited toward templates with three template-functional group interactions. This is observed in Tables 6-8, where compounds with identical positioning of three functional groups all show less than an order of magnitude change in α values despite changes in shape.     

Preparation, characterization and properties studies of quinine-imprinted polymer in the aqueous phase

The uniform-sized spherical molecularly imprinted polymers were successfully prepared through molecular imprinting technology by two-step seed swelling and mini-emulsion polymerization in the aqueous condition using quinine as template molecules and methacrylic acid (MAA) as functional monomer. The polymers were characterized by IR spectra, thermal-weight analysis, scanning electron microscope and laser particle size analysis. The properties of imprinted polymers were investigated in different organic phases and aqueous media. In the organic media, results suggested that polar interactions (hydrogen bonding, ionic interactions) between acidic monomer/polymer and template molecules are mainly responsible for the binding and recognition; whereas in the aqueous medium, a considerable recognition effect was also obtained where the ionic (electrostatic) interaction and hydrophobic interaction play an important role. The experiments of binding different substrates indicated that the MIPs possessed an excellent rebinding ability and inherent selectivity to quinine. __________ Translated from Zhongshan Dcocue Xuebao/Acta Scientianum Natralium University Sunyatseni, 2005, 44(3)(in Chinese)     

Factors Affecting Preparation of Molecularly Imprinted Polymer and Methods on Finding Template-Monomer Interaction as the Key of Selective Properties of the Materials

Molecular imprinting is a technique for creating artificial recognition sites on polymer matrices that complement the template in terms of size, shape, and spatial arrangement of functional groups. The main advantage of Molecularly Imprinted Polymers (MIP) as the polymer for use with a molecular imprinting technique is that they have high selectivity and affinity for the target molecules used in the molding process. The components of a Molecularly Imprinted Polymer are template, functional monomer, cross-linker, solvent, and initiator. Many things determine the success of a Molecularly Imprinted Polymer, but the Molecularly Imprinted Polymer component and the interaction between template-monomers are the most critical factors. This review will discuss how to find the interaction between template and monomer in Molecularly Imprinted Polymer before polymerization and after polymerization and choose the suitable component for MIP development. Computer simulation, UV-Vis spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Proton-Nuclear Magnetic Resonance (¹H-NMR) are generally used to determine the type and strength of intermolecular interaction on pre-polymerization stage. In turn, Suspended State Saturation Transfer Difference High Resolution/Magic Angle Spinning (STD HR/MAS) NMR, Raman Spectroscopy, and Surface-Enhanced Raman Scattering (SERS) and Fluorescence Spectroscopy are used to detect chemical interaction after polymerization. Hydrogen bonding is the type of interaction that is becoming a focus to find on all methods as this interaction strongly contributes to the affinity of molecularly imprinted polymers (MIPs).     

Desulfurization of Gasoline using Molecularly Imprinted Chitosan as Selective Adsorbents

For desulfurization of gasoline, novel chitosan-based molecularly imprinted polymer (MIP) was prepared by cross-linking chitosan with epichlorohydrin in the presence of dibenzothiophene (DBT) as the template. The influence of cross-linking ratio on the specific adsorption was evaluated. The effects of the types and the amounts of porogen on selectivity of the chitosan MIP were also examined. Results showed that MIP has a higher recognition property to DBT. The maximum rebinding capacities of the MIP reached 22.69 mg g⁻¹ in the model solution. The adsorption behaviors of the MIP including adsorption kinetics, isotherms, and thermodynamic parameters were investigated and the experimental data agreed well with the Langmuir model. The dynamical adsorption behaved in first-order kinetics. Negative values for the Gibbs free energy showed that the adsorptions were spontaneous processes. The MIP was further used to selectively adsorb organosulfur from gasoline.