Imprinting of amino acid derivatives in macroporous polymers

Enantioseparations by high-performance liquid chromatography using molecularly imprinted polymers

Molecularly imprinted polymers (MIPs) are becoming increasingly useful as chromatographic adsorbents for molecular separations, especially chiral separations, because they can be tailored to specifically recognize the target molecule including its stereochemistry. Traditionally formed MIPs (as described here) are stable under ambient conditions for years, take only days to make, and use relatively inexpensive components, with the possible exception of the template in some cases which can be reused after it is removed from the polymer to keep costs down. In addition to providing experimental details for typical synthetic methods to fabricate MIPs and pack them into HPLC columns, this chapter also gives an overview of the concepts of molecular imprinting method and discusses important factors for designing an effective imprinted polymer.

Study on the Weakest Interaction Model for Chiral Resolution Using Molecularly Imprinted Polymer

Molecularly imprinted polymers (MIPs) of L-phenylalanine ethyl ester were synthesized in this study. Then, the prepared MIPs were packed in a stainless column and evaluated as the chiral stationary phases of high performance liquid chromatography (HPLC). The MIPs exhibited a considerable capability of chiral separation between template molecule and its enantiomer with the separation factor of 1.69. Furthermore, the weakest interaction model was introduced to study the chiral recognition mechanism of MIPs. The results suggested that the weakest interaction between the template molecule and the imprinted cavity played crucial role in chiral separation, and the molecular tension should be taken into consideration during the separation procedure. The separation factor of 2.07 was calculated by the theoretical model, which was very close to the value obtained from chromatographic experiment.

Microgels and nanogels with catalytic activity

Molecular imprinting has grown considerably over the last decade with more and more applications being developed. The use of this approach for the generation of enzyme-mimics is here reviewed with a particular focus on the most recent achievements using different polymer formats such as microgels and nanogels, beads, membranes and also silica nanoparticles.

Mimicking Biological Delivery Through Feedback-Controlled Drug Release Systems Based on Molecular Imprinting

Intelligent drug delivery systems (DDS) are able to rapidly detect a biological event and respond appropriately by releasing a therapeutic agent; thus, they are advantageous over their conventional counterparts. Molecular imprinting is a promising area that generates a polymeric network which can selectively recognize a desired analyte. This field has been studied for a variety of applications over a long period of time, but only recently has it been investigated for biomedical and pharmaceutical applications. Recent work in the area of molecularly imprinted polymers in drug delivery highlights the potential of these recognitive networks as environmentally responsive DDS that can ultimately lead to feedback controlled recognitive release systems.

Chiral recognition applications of molecularly imprinted polymers: a critical review

Molecular imprinting technology offers the unique opportunity to tailor chiral stationary phases with predefined chiral recognition properties by employing the enantiomers of interest as binding-site-forming templates. Added advantages, such as ease of preparation, chemical robustness, low-cost production, and the possibility of shaping molecularly imprinted polymers (MIPs) in various self-supporting formats, render them attractive materials for a broad range of chiral recognition applications. In this review a critical overview on recent developments in the field of MIP-based chiral recognition applications is given, focusing on separation techniques and molecular sensing. Inherent limitations associated with the use of enantioselective MIP materials in high-performance separation techniques are outlined, including binding site heterogeneity and slow mass transfer characteristics. The prospects of MIP materials as versatile recognition elements for the design of enantioselective sensor systems are highlighted.

Protein-imprinted polymer with immobilized assistant recognition polymer chains

Here we introduce a new method for preparing a protein-imprinted polymer with immobilized assistant recognition polymer chains as an additional element of monomer to create effective recognition sites. In this work the bovine serum albumin was used as template and the template protein was selectively assembled with immobilized assistant recognition polymer chains from their library, numerous limited length polymer chains with randomly distributed recognition sites and immobilizing sites. These assemblies of protein and immobilized assistant recognition polymer chains would be adsorbed by the macro porous adsorbent spheres and immobilized by cross-linking polymerization. After removing the template, binding sites that were complementary to the target protein in size, shape and position of recognition groups were exposed, and their confirmation was preserved by the cross-linked structure. The synthesized imprinted polymer was used to adsorb BSA from protein mixtures, and showed a high selectivity.

Non-covalent molecular imprinting with emphasis on its application in separation and drug development

The molecular imprinting technique can be defined as the formation of specific nano-sized cavities by means of template-directed synthesis. The resulting molecularly imprinted polymers (MIPs), which often have an affinity and a selectivity approaching those of antibody-antigen systems, have thus been coined "artificial antibodies." MIPs are characterized by their high specificity, ease of preparation, and their thermal and chemical stability. They have been widely studied in connection with many potential applications, including their use for separation and isolation purposes, as antibody mimics (biomimetic assays and sensors), as enzyme mimics, in organic synthesis, and in drug delivery. The non-covalent imprinting approach, developed mainly in Lund, has proven to be more versatile than the alternative covalent approach because of its preparation being less complicated and of the broad selection of functional monomers and possible target molecules that are available. The paper presents a review of studies of this versatile technique in the areas of separation and drug development, with emphasis being placed on work carried out in our laboratory.

Molecular imprinted polymer with cloned bacterial protein template enriches authentic target in cell extract

Here we describe a new method for preparing a protein-imprinted polymer with a cloned bacterial protein template, which recognizes/adsorbs authentic target protein present at a relatively low level in cell extract. In this work, cloned pig cyclophilin 18 (pCyP18) was used as a template. The template protein was selectively assembled with memory molecules from their library, which consists of numerous limited length polymer chains with randomly distributed recognition sites and immobilizing sites. These assemblies of protein and memory molecules were adsorbed by porous polymeric beads and immobilized by cross-linking polymerization. After removing the template, binding sites that were complementary to the target protein in size, shape and the position of recognition groups were exposed, and their confirmation was preserved by the cross-linked structure. The synthesized imprinted polymer was used to adsorb authentic pCyP18 from cell extract, and its proportional content was enriched 300 times.

Molecular imprinting science and technology: a survey of the literature for the years up to and including 2003

Over 1450 references to original papers, reviews and monographs have herein been collected to document the development of molecular imprinting science and technology from the serendipitous discovery of Polyakov in 1931 to recent attempts to implement and understand the principles underlying the technique and its use in a range of application areas. In the presentation of the assembled references, a section presenting reviews and monographs covering the area is followed by papers dealing with fundamental aspects of molecular imprinting and the development of novel polymer formats. Thereafter, literature describing attempts to apply these polymeric materials to a range of application areas is presented.

Replica Ornstein-Zernike theory of adsorption in a templated porous material: Interaction site systems

Molecular templating offers the possibility of porous materials whose selectivity rivals the molecular recognition observed in nature. The design of templated materials requires a molecular understanding of the templating effect on the material structure and performance. We present here a theoretical description of adsorption in a model templated porous material. Our model material is a quenched, equilibrated mixture of template and matrix molecular species where the template component has been subsequently removed. We propose a set of site-site [i.e., reference interaction site model (RISM)] replica Ornstein-Zernike equations relating the correlation functions of template, matrix, and adsorbing fluid molecules. To test this approach, we focus here on systems interacting via hard-sphere site-site potentials and employ a Percus-Yevick closure. We consider chain and cluster species composed of up to five spheres and observe a range of effects associated with template structure, including higher affinity toward, and enhanced templating by, compact cluster molecules. We assess these effects by grand canonical Monte Carlo simulation and discuss their implication to the design of templated molecular recognition materials.

Chitosan beads as molecularly imprinted polymer matrix for selective separation of proteins

Two kinds of molecularly imprinted polymers were prepared using hemoglobin as the imprinting molecule, acrylamide as the functional monomer, chitosan beads and maleic anhydride-modified chitosan beads as matrixes, respectively. Static adsorbing experimental results showed that an equal class of adsorption was formed in the imprinted polymers and the adsorption equilibrium constant and the maximum adsorption capacity were evaluated. Chromatographic characteristics showed that the column bedded with the hemoglobin imprinted beads could separate hemoglobin and bovine serum albumin effectively from their mixture, which indicates that the imprinted beads have very higher selectivity for hemoglobin than the non-imprinted with the same chemical composition.

Towards the rational development of molecularly imprinted polymers: 1H NMR studies on hydrophobicity and ion-pair interactions as driving forces for selectivity

The preparation of molecularly imprinted polymers (MIP) based on non-covalent interactions has become a widely used technique for creating highly specific sorbent materials predominantly used in separation chemistry. A crucial factor in a successful imprinting protocol is the optimisation of the template/functional monomer interaction in the pre-polymerisation mixture, eventually leading to a maximum of high-affinity binding sites in the resulting polymer matrix. In order to develop more efficient preparation technologies for imprinted polymers, two separate pre-polymerisation complexes were investigated by NMR spectroscopic techniques in order to identify the types of interactions occurring in the pre-polymerisation mixture, and their implications for the subsequently formed imprinted polymer. In particular, hydrophobic effects have been followed by NMR spectroscopy and their contribution to the selectivity of the resulting MIP has been investigated. The 2,4-D imprint system is used as an example to fundamentally study whether observations at the pre-polymerisation stage correlate with properties of the finally prepared MIP, and which parameters govern success of an imprinting protocol.

An insight into molecularly imprinted polymers for capillary electrochromatography

Molecularly imprinted polymers (MIPs) are actively being developed as a practical tool for affinity chromatographic supports. From the viewpoint of separation science, capillary electrochromatography (CEC) might be one of the more promising chromatographic techniques to be used in combination with the MIPs. However, up to the present, very little MIP work has involved CEC. This review gives a full overview of MIP including current trends in MIP, methods for the characterization of MIP, and methods for the preparation of MIP with particular emphasis on application of the resulting materials in CEC. To prepare MIPs with selectivity predetermined for a particular substance or group of structural analogues is an important factor for the development of a new format of CEC. From the fundamental research with the batch method, a better knowledge of imprint formation and imprint recognition will be helpful for expanding the application area of the combination of MIPs with CEC.

Adsorptive separation of hemoglobin by molecularly imprinted chitosan beads

A simply hemoglobin (Hb) molecularly imprinted polymer (MIP) was prepared using Hb as the imprinted molecule, acrylamide as the functional monomer and cross-linked chitosan beads as the supporting matrix. The MIP was achieved by entrapment of the selective soft polyacrylamide gel in the pores of the cross-linked chitosan beads by letting acrylamide monomer and the protein diffuse into the pores of chitosan beads before starting the polymerization. The chitosan beads were freed from the surrounding polyacrylamide gel by washing. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. Langmuir analysis showed that an equal class of adsorption was formed in the MIP and the adsorption equilibrium constant and the maximum adsorption capacity were evaluated. The MIP has much higher adsorption capacity for Hb than the non-imprinted polymer with the same chemical composition, and the MIP also has a higher selectivity for the imprinted molecule. The MIP can be reused in an easy way and the reproduction coefficient was approximately 100% at low concentration.

Performance analysis of molecularly imprinted polymers for carboxylate and aminophosphate templates using commercially available basic functional monomers

A survey of commercially available amine-based monomers for binding and selectivity of carboxylate and phosphonic acid templates has revealed that the best selectivity is found for the pyridine-based monomers, while the highest affinity was found for 2-(dimethylamino)ethyl methacrylate (2-DEMA, 1). In fact, a more general finding is that selectivity is higher for aromatic amine-based monomers even though affinity remains higher for aliphatic amine-based monomers. An attempt to combine the optimal properties of these two classes of amine monomers, i.e. 2-vinylpyridine (2-VPY, 2), and 2-DEMA by using both simultaneously in a single imprinted polymer resulted in an MIP whose properties were dominated by the aliphatic amine-based monomer 2-DEMA. A controversy between the two commercially available vinylpyridine monomers, 2-VPY and 4-vinylpyridine (4-VPY, 3), was investigated, revealing that neither monomer is generally better for molecular imprinting; rather, the choice of 2-VPY or 4-VPY is template specific (although the preponderance of data tends to frequently favor 4-VPY). Phosphonic acid templates proved to be less successful as templates for molecular imprinting versus carboxylate functionalized templates, although binding was obtained and shown to be controllable via an ion-exchange process.

Synthetic hosts via molecular imprinting—are universal synthetic antibodies realistically possible?

Of the many ways to make synthetic hosts, one of the most appealing involves molecular imprinting. In the commonest approach monomer units assemble around or are attached to a template (imprint) molecule and then linked together using a cross-linking agent. Template removal ideally leaves cavities within the molecularly imprinted polymer (MIP) that possess a shape and functional group complementarity to the imprint molecule allowing its tight and selective uptake. This review highlights some recent advances in the synthesis of MIPs (often called "synthetic antibodies") and enumerates a "wish list" of properties for the perfect MIP that may guide future studies.

Improving methods of analysis for mycotoxins: molecularly imprinted polymers for deoxynivalenol and zearalenone

Selective polymeric phases intended for future use in separation/extraction of deoxynivalenol and zearalenone from beverages have been prepared. Using crystalline deoxynivalenol, zearalenone and quercetin, molecularly imprinted polymers were obtained by a non-covalent imprinting approach via a photo-initiated addition polymerization. Prepared polymers were based on 4-vinylpyridine, methacrylic acid or 2-trifluoromethylacrylic acid as the functional monomer and on ethyleneglycol dimethacrylate, trimethyltrimethacrylate or divinylbenzene as the cross-linking monomer. Selectivity of the generated molecularly imprinted polymers has been investigated by application of the prepared molecularly imprinted polymers as stationary phases in high-pressure liquid chromatography experiments. The retention and elution behaviours of the template compounds and structurally related substances were determined and compared. The results promise future application of molecularly imprinted polymers as alternative selective matrices for clean-up and enrichment of deoxynivalenol and zearalenone.

Synthetic hosts by monomolecular imprinting inside dendrimers

Synthetic host systems capable of selectively binding guest molecules are of interest for applications ranging from separations and chemical or biological sensing to the development of biomedical materials. Such host systems can be efficiently prepared by 'imprinting' polymers or inorganic materials with template molecules, which, upon removal, leave behind spatially arranged functional groups that act as recognition sites. However, molecularly imprinted polymers have limitations, including incomplete template removal, broad guest affinities and selectivities, and slow mass transfer. An alternative strategy for moulding desired recognition sites uses combinatorial libraries of assemblies that are made of a relatively small number of molecules, interconverting in dynamic equilibrium; upon addition of a target molecule, the library equilibrium shifts towards the best hosts. Here we describe the dynamic imprinting of dendritic macromolecules with porphyrin templates to yield synthetic host molecules containing one binding site each. The process is based on our general strategy to prepare cored dendrimers, and involves covalent attachment of dendrons to a porphyrin core, cross-linking of the end-groups of the dendrons, and removal of the porphyrin template by hydrolysis. In contrast to more traditional polymer imprinting, our approach ensures nearly homogeneous binding sites and quantitative template removal. Moreover, the hosts are soluble in common organic solvents and amenable to the incorporation of other functional groups, which should facilitate further development of this system for novel applications.