Molecularly Imprinted Materials Research Articles

Preparation of 2D molecularly imprinted materials based on mesoporous silicas via click reaction.

The two-dimensional (2D) molecular imprinting approach has attracted extensive research interest in recent years due to its potential advantages such as simple construction, fast template removal and rapid mass transfer. In this study, a new 2D imprinting approach based on the combination of mesoporous silica materials and molecular imprinting technology is reported. 2D molecularly imprinted materials (MIMs) for cholesterol were prepared by using cholesterol as the template, azide modified β-cyclodextrin (azide-β-CD) as the functional monomer and alkynyl-modified SBA-15 (alkyne-SBA-15) as the skeleton. In this method, azide-β-CD molecules were first assembled around the templates by formation of template-monomer complexes, and thus the mutual positions of azide-β-CD molecules were fixed. Then, azide-β-CD molecules were anchored to the walls of the nano-pores of SBA-15 via click chemistry. After removal of the template molecules, the resulting cavities, i.e., recognition sites were formed in the nano-pores of mesoporous silicas. The synthesized MIM was characterized by FT-IR, X-ray diffraction (XRD), elemental analysis (EA), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and so on. Binding kinetic experiments demonstrated that the 2D imprinting approach can improve site accessibility for the template effectively. The 2D MIM exhibited binding affinity and specificity for the template, as revealed by equilibrium binding experiments. When using MIM as a stationary phase for HPLC, baseline separation of cholesterol from other compounds can be achieved. In addition, the use of 2D imprinting significantly reduced the peak broadening and tailing.

Preparation of a surface molecularly imprinted fiber for bisphenol a recognition

Surface molecularly imprinted polypropylene-based fibers for specifically recognizing bisphenol A (BPA-MIF) have been prepared through non-covalent surface molecular imprinting and self-assembly post-polymerization techniques. Acrylic acid (AA) was grafted onto pre-irradiated polypropylene (PP) fiber, and then polyethyleneimine (PEI) was assembled onto the AA grafted fiber surface to introduce amine groups for binding BPA templates from its aqueous solution. The imprinted binding sites were stabilized by cross-linking with glutaraldehyde in the presence of BPA templates. The Scatchard analysis indicated that two classes of amine binding sites were formed in the imprinted fiber BPA-MIF. The maximum adsorption capacity and association constant were 85.9 μmol/g and 56.1 μmol/L, respectively. The selectivity of BPA-MIF fibers for BPA against its analogues was obviously increased by adopting the surface molecular imprinting technique. In this work, a new path was given for the preparation of molecular imprinting materials in water system for other toxics with low solubility in aqueous solution.

Synthesis of glycylglycine-imprinted silica microspheres through different water-in-oil emulsion techniques

Sol–gel molecularly imprinted materials (MIMs) are traditionally obtained by grinding and sieving of a monolith formed by bulk polymerization. However, this process has several drawbacks that can be overcome if these materials are synthesized directly in the spherical format. This work aimed at the development of two efficient methods to prepare spherical glycylglycine-templated silica (“whole-imprinted” and surface-imprinted) through a combination of sol–gel and emulsion techniques. The synthesis of the microspheres was optimized regarding emulsion and sol–gel parameters. Imprinting efficiency of the prepared materials was studied by solid phase extraction and flow microcalorimetry. The particles prepared with glycylglycine and functional monomer, in basic medium (using cyclohexane as non-polar continuous medium) presented the highest imprinting factor – 2.5 – and the respective surface-imprinted material presented an imprinting factor of 1.5. The results of flow microcalorimetry confirmed the action of different mechanisms of glycylglycine adsorption: entropically-controlled interactions were present for the “whole-imprinted” material, indicating adsorption inside small imprinted pores; enthalpically-controlled interactions were observed for the surface-imprinted material, a behaviour more compatible with a template/surface-only interaction. Globally, the two approaches allowed for a successful imprinting effect which was more extensive for the “whole-imprinted” material, whereas the surface-imprinting feature confers to the surface-imprinted xerogel advantages regarding mass transfer kinetics. Overall, the spherical particles obtained by both approaches presented characteristics, such as sphericity, mesoporosity, easy/fast accessibility to imprinted sites, important indicators that these materials may be candidates for stationary phases for efficient, selective chromatographic separation.

Functional monomer free synthesis of molecularly imprinted titania for solid-phase extraction of nicotinic acid

A simple method for preparation of molecularly imprinted materials (MIMs) without the use of traditional functional monomers based on titania is presented. Combining the unique affinity of titania to electron-negative compounds and the high selectivity of MIMs to templates, molecularly imprinted titania can be easily prepared via a sol–gel method and applied to off-line solid-phase extraction (SPE). Nicotinic acid (NA) was added in the synthesis of amorphous titania as the template. The recognition mechanism of the obtained NA imprinted material (NAIM) to the template was investigated by static adsorption. The NAIM showed higher adsorption capacity, faster adsorption kinetics and better selectivity compared to the non-imprinted material. The imprinted material was finally applied to SPE of free NA in dried yeast. The molecularly imprinted SPE-HPLC method presented good linearity (R2 = 0.9972) to NA in the range of 2–100 μmol L−1. The limit of detection (3σ) and limit of quantification (10σ) were 0.5 and 2.0 μmol L−1, respectively, which were equivalent to 24.6 and 98.5 μg g−1 NA in dried yeast. The better clean-up ability of the NAIM demonstrated the capability of molecularly imprinted titania for the isolation of carboxylic compounds in complicated samples. This work not only provides a new strategy for molecular imprinting but also extends the application of titania.

Synthesis and recognition of molecularly imprinted polymers for gastrodin based on surface‐modified silica nanoparticles

AbstractA molecular imprinting material with high performance for recognizing Gastrodin (GAS) was prepared by adopting the novel surface molecular imprinting technique. Silica nanoparticles were first modified with 3‐methacryloxypropyltrimethoxysilane (KH‐570) as a carrier material. Then, GAS surface molecule‐imprinted polymer (GAS‐SMIP) were prepared by polymerization with methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the crosslinker. The equilibrium adsorptive experiments indicated that GAS‐SMIP had significantly higher adsorption capacity for GAS than its nonimprinted polymers. Scatchard analysis revealed that two classes of binding sites were formed in GAS‐SMIP with dissociation constants of 1.019 and 7.278 μmol/mL, and the affinity binding sites of 17.82 and 83.11 μmol/g, respectively. The selectivity coefficient of GAS‐SMIP for GAS in respect to competition species obtained was 3.455, which revealed GAS‐SMIP had excellent selectivity and site accessibility for GAS. Kinetic binding study showed GAS‐SMIP adsorbed quickly in the first 40 min, and reached saturation adsorption at 1 h. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Computationally designed monomers for molecular imprinting of chemical warfare agents – Part V

The main objective of this research is to develop and apply state-of-the-art computational tools to achieve an understanding of intermolecular interactions in molecular imprinting of chemical warfare (CW) agents into complex monomeric systems. Molecular dynamic (MD) simulations were carried out for different monomeric molecular systems in order to predict the interaction energies, the closest approach distances and the active site groups between the simulated molecular systems and different CW agents. The minimized structures of CW agents have been obtained with the use of molecular mechanics approach. NVT MD simulations at room temperature were carried out to obtain equilibrated conformations in all cases. The simulated molecular systems consisted of a ligand (CW agents) and commonly used functional monomers. During this study, it was found that electrostatic interactions play the most significant role in the formation of molecular imprinting materials. The simulated systems indicate that the functional groups of monomers interacting with ligands tend to be either –COOH or CH 2 CH–.

Computationally designed monomers and polymers for molecular imprinting of theophylline—part II

The main objective of this research is to develop and apply state-of-the-art computational tools to achieve an understanding of intermolecular interactions in molecular imprinting of theophylline into complex polymeric systems. Molecular dynamics (MD) simulations were carried out for different molecular systems in order to predict the interaction energies, the closest approach distances and the active site groups between the simulated molecular systems and different bio-ligands. The minimized structures of five ligands, theophylline and its derivatives (theobromine, theophylline-8-butanoic acid, caffeine and theophylline-7-acetic acid) have been obtained with the use of molecular mechanics approach. NVT MD simulations at room temperature were carried out to obtain equilibrated conformations in all cases. The first simulated molecular systems consisted of a ligand and commonly used functional monomers, polymers and a substrate. The second simulated molecular systems consisted of a ligand and a monomer or polymer using a solvent (ethanol). During this study, it was found that electrostatic interactions play the most significant role in the formation of molecular imprinting materials. The simulated functional monomers and polymers with ligands indicate that the functional groups interacting with ligands tends to be either –COOH or CH 2 CH–. It was also found that molecular substrate without functional side groups are recommended for molecular imprinting technology. For both the solvated monomer and polymer systems is that it appears that the presence of the solvent appears to favour the formation of more stable clusters with theophylline than with its derivatives.

Use of an Aromatic Polyimide as a Non-Cross-Linked Molecular Imprinting Material

Use of an Aromatic Polyimide as a Non-Cross-Linked Molecular Imprinting Material

CHARACTERIZATION OF ELECTROSYNTHESIZED POLY- (o-AMINOPHENOL) AS A MOLECULAR IMPRINTING MATERIAL FOR SENSOR PREPARATION BY MEANS OF QUARTZ CRYSTAL IMPEDANCE ANALYSIS

ABSTRACT The preparation and properties of electrosynthesized poly-(o-aminophenol) (iPoAP) as a molecular imprinting material were studied by in situ quartz crystal impedance method. During the polymerization, the changes of Δf 0, ΔR 1 and ΔC 0 were investigated based on the Butterworth-Van Dyke model. The thickness shear mode acoustic sensor modified with this material exhibited molecular recognition ability to the template molecule of 2,4-dichlorophenoxyacetic acid, although the specificity was not as good as that of the molecularly imprinted polymer prepared by traditional imprinting technology. In the range of 4.0 × 10−5 to 2.0 × 10−3 M, a linear relationship between the frequency shift (−Δf 0) and log C was found from calibration curve. The determination limit was 1.0 × 10−5 M. Using this electropolymerization technology, the preparation of sensor was very simple and the reproducibility of preparation was very good.

Development of a thickness shear mode acoustic sensor based on an electrosynthesized molecularly imprinted polymer using an underivatized amino acid as the template.

The preparation and characterization of electrosynthesized poly(o-phenylenediamine) (iPoPD) as a molecular imprinting material were studied by an in situ quartz crystal impedance method. The changes of delta f0, delta R1, delta L1 and delta C0 suggest that the polymer film was compact and rigid. The thickness shear mode (TSM) acoustic sensor modified with this material exhibits molecular recognition ability to the template molecule of DL-phenylalanine. In the range 2-20 mM, a linear relationship between the frequency shift delta f0 and logC was found from the calibration graph. Scatchard analysis of the relevant calibration graph offers information on the equilibrium of the binding interaction and the recognition sites. Using this electropolymerization technology, the preparation of the sensor was very simple and the reproducibility of preparation was very good. In particular, it offers possibilities for sensor miniaturization.

A novel molecularly imprinted thin film applied to a Love wave gas sensor

Novel molecularly imprinted materials (MIMs) have been deposited as thin films on acoustic Love wave devices. MIMs offer high selectivity towards target molecules while Love wave devices offer one of the highest sensitivities with respect to surface mass changes that can be achieved with microacoustic devices. Hence this specific sensor configuration promises high sensitivity and specificity at the same time. In this contribution we outline the device configuration and present experimental results obtained with this sensor.

Generation of porosity in a hybrid organic-inorganic xerogel by chemical treatment

A hybrid xerogel of 1,4-bis(trimethoxysilylethynyl)benzene was prepared by using a sol-gel process. Chemical treatment of this material was performed under mild conditions in order to remove the organic group using fluoride anion as a catalyst. Experimental procedures were carried out using different solvents, acidities and counter-cations in order to modify the nucleophilic power of F-. Characterization of the residues was done by elemental analysis, spectroscopy (29Si NMR), thermal analysis, pycnometry, surface area measurement and SAXS. The efficiency of the chemical treatment is related to the solvation of the F- anion. It was possible to demonstrate that elimination of the organic part occurs at the same time as a reorganization of the silica network. This reorganization is the result of two competitive F--catalyzed chemical reactions: a redistribution and a polycondensation process known in solution and which take place in the solid. These processes account for the textural characteristics of the final material and may efface the organization of the organic spacers in the hybrid xerogel. These results demonstrate the limitations of silica as a molecular imprinting material and open a new approach to porous silica with adjustable pore size.