Molecularly imprinted polymers (MIPs) display intriguing recognition properties and can be used as sensor recognition elements or in separation. In this work, we investigated the formation of hierarchical porosity of compositionally varied MIPs using 129Xe Nuclear Magnetic Resonance (NMR) and 1H Time Domain Nuclear Magnetic Resonance (TD-NMR). Variable temperature 129Xe NMR established the morphological variation with respect to the degree of cross-linking, supported by 1H TDNMR determination of polymer chain mobility. Together, the results indicate that a high degree of cross-linking stabilizes the porous structure: highly cross-linked samples display a significant amount of accessible mesopores that instead collapse in less structured polymers. No significant differences can be detected due to the presence of templated pores in molecularly imprinted polymers: in the dry state, these specific shapes are too small to accommodate xenon atoms, which, instead, probe higher levels in the porous structure, allowing their study in detail. Additional resonances at a high chemical shift are detected in the 129Xe NMR spectra. Even though their chemical shifts are compatible with xenon dissolved in bulk polymers, variable temperature experiments rule out this possibility. The combination of 129Xe and TDNMR data allows attribution of these resonances to softer superficial regions probed by xenon in the NMR time scale. This can contribute to the understanding of the surface dynamics of polymers.

A series of 172 molecular structures that block the hERG K+ channel were used to develop a classification model where, initially, eight types of PaDEL fingerprints were used for k-nearest neighbor model development. A consensus model constructed using Extended-CDK, PubChem and Substructure count fingerprint-based models was found to be a robust predictor of hERG activity. This consensus model demonstrated sensitivity and specificity values of 0.78 and 0.61 for the internal dataset compounds and 0.63 and 0.54 for the external (PubChem) dataset compounds, respectively. This model has identified the highest number of true positives (i.e. 140) from the PubChem dataset so far, as compared to other published models, and can potentially serve as a basis for the prediction of hERG active compounds. Validating this model against FDA-withdrawn substances indicated that it may even be useful for differentiating between mechanisms underlying QT prolongation.

The regiochemical outcome of a cobalt(ii) catalysed C-H activation reaction of aminoquinoline benzamides with unsymmetrical 1,3-diynes under relatively mild reaction conditions can be steered through the choice of diyne. The choice of diyne provides access to either 3- or 4-hydroxyalkyl isoquinolinones, paving the way for the synthesis of more highly elaborate isoquinolines.

Background: The interaction between biotin and avidin is utilized in a wide range of assay and diagnostic systems. A robust material capable of binding biotin should offer scope in the development of reusable assay materials and biosensor recognition elements. Results: Biotin-selective thin (3-5 nm) films have been fabricated on hexadecanethiol self assembled monolayer (SAM) coated Au/quartz resonators. The films were prepared based upon a molecular imprinting strategy where N, N'-methylenebisacrylamide and 2-acrylamido-2-methylpropanesulfonic acid were copolymerized and grafted to the SAM-coated surface in the presence of biotin methyl ester using photoinitiation with physisorbed benzophenone. The biotinyl moiety selectivity of the resonators efficiently differentiated biotinylated peptidic or carbohydrate structures from their native counterparts. Conclusions: Molecularly imprinted ultra thin films can be used for the selective recognition of biotinylated structures in a quartz crystal microbalance sensing platform. These films are stable for periods of at least a month. This strategy should prove of interest for use in other sensing and assay systems.

This report demonstrates that the diversity of hydrogen bond interactions present in molecularly imprinted polymer pre-polymerization mixtures, typically associated with binding-site heterogeneity, can also contribute to morphological characteristics that may influence polymer–template recognition. Comparisons have been made between a series of bupivacaine molecularly imprinted methacrylic acid (MAA)–ethylene glycol dimethacrylate (EGDMA) copolymers and a series of analogous methyl methacrylate (MMA)–EGDMA copolymers using comprehensive molecular dynamics studies of the respective pre-polymerization mixtures, template–polymer binding studies and detailed BET surface area and BJH porosity analyses. The role of the carboxylic acid functionality of MAA, and in particular the acidic proton, in generating morphological features conducive to analyte access (slit-like rather than ink bottle-like structures) and recognition is discussed.

We here present the first simulation of a complete molecularly imprinted polymer prepolymerization system. Molecular dynamics studies were performed for a system comprising a total of 1199 discrete molecules, replicating the components and concentrations employed in the corresponding polymer synthesis. The observed interactions correlate well with results obtained from (1)H NMR spectroscopic studies. Comparison with simulations performed in the absence of cross-linking agent (ethylene dimethacrylate) demonstrated its significance in the formation of ligand recognition sites. Moreover, the influence of events such as template-template (bupivacaine) and monomer-monomer (methacrylic acid) self-association, porogen-template interactions, and template conformational variability was revealed. The template recognition capacity of the modeled polymer system was verified by synthesis of imprinted and reference polymers and subsequent radioligand binding Analysis. Collectively, through a series of statistical analyses of molecular trajectories in conjunction with spectroscopic data it was demonstrated that an ensemble of complex structures is present in the prepolymerization mixture and that this diversity is the basis for the binding site heterogeneity observed in molecularly imprinted polymers (MIPs) prepared using the noncovalent strategy.

Oxytocin imprinted polymer nanoparticles were synthesized by glass bead supported solid phase synthesis, with NMR and molecular dynamics studies used to investigate monomer-template interactions. The nanoparticles were characterized by dynamic light scattering, scanning- and transmission electron microscopy and X-ray photoelectron spectroscopy. Investigation of nanoparticle-template recognition using quartz crystal microbalance-based studies revealed sub-nanomolar affinity, k(d) approximate to 0.3 +/- 0.02 nM (standard error of the mean), comparable to that of commercial polyclonal antibodies, k(d) approximate to 0.02-0.2 nM.

Glycosylation plays an important role in various pathological processes such as cancer. One key alteration in the glycosylation pattern correlated with cancer progression is an increased level as well as changes in the type of sialylation. Developing molecularly-imprinted polymers (MIPs) with high affinity for sialic acid able to distinguish different glycoforms such as sialic acid linkages is an important task which can help in early cancer diagnosis. Sialyllactose with alpha 2,6 ' vs. alpha 2,3 ' sialic acid linkage served as a model trisaccharide template. Boronate chemistry was employed in combination with a library of imidazolium-based monomers targeting the carboxylate group of sialic acid. The influence of counterions of the cationic monomers and template on their interactions was investigated by means of H-1 NMR titration studies. The highest affinities were afforded using a combination of Br- and Na+ counterions of the monomers and template, respectively. The boronate ester formation was confirmed by MS and H-1/B-11 NMR, indicating 1 : 2 stoichiometries between sialyllactoses and boronic acid monomer. Polymers were synthesized in the form of microparticles using boronate and imidazolium monomers. This combinatorial approach afforded MIPs selective for the sialic acid linkages and compatible with an aqueous environment. The molecular recognition properties with respect to saccharide templates and glycosylated targets were reported.

The further evolution of molecularly imprinted polymer science and technology necessitates the development of robust predictive tools capable of handling the complexity of molecular imprinting systems. A combination of the rapid growth in computer power over the past decade and significant software developments have opened new possibilities for simulating aspects of the complex molecular imprinting process. We present here a survey of the current status of the use of in silico-based approaches to aspects of molecular imprinting. Finally, we highlight areas where ongoing and future efforts should yield information critical to our understanding of the underlying mechanisms sufficient to permit the rational design of molecularly imprinted polymers. 

In principle, molecularly imprinted polymer science and technology provides a means for ready access to nano-structured polymeric materials of predetermined selectivity. The versatility of the technique has brought it to the attention of many working with the development of nanomaterials with biological or biomimetic properties for use as therapeutics or in medical devices. Nonetheless, the further evolution of the field necessitates the development of robust predictive tools capable of handling the complexity of molecular imprinting systems. The rapid growth in computer power and software over the past decade has opened new possibilities for simulating aspects of the complex molecular imprinting process. We present here a survey of the current status of the use of in silico-based approaches to aspects of molecular imprinting. Finally, we highlight areas where ongoing and future efforts should yield information critical to our understanding of the underlying mechanisms sufficient to permit the rational design of molecularly imprinted polymers.

The development of in silico strategies for the study of the molecular imprinting process and the properties of molecularly imprinted materials has been driven by a growing awareness of the inherent complexity of these systems and even by an increased awareness of the potential of these materials for use in a range of application areas. Here we highlight the development of theoretical and computational strategies that are contributing to an improved understanding of the mechanisms underlying molecularly imprinted material synthesis and performance, and even their rational design.

Recent years have witnessed a dramatic increase in the use of theoretical and computational approaches in the study and development of molecular imprinting systems. These tools are being used to either improve understanding of the mechanisms underlying the function of molecular imprinting systems or for the design of new systems. Here, we present an overview of the literature describing the application of theoretical and computational techniques to the different stages of the molecular imprinting process (pre-polymerization mixture, polymerization process and ligand-molecularly imprinted polymer rebinding), along with an analysis of trends within and the current status of this aspect of the molecular imprinting field.

Theoretical and computational studies of molecular imprinting have helped provide valuable insights concerning the nature of the molecular-level events underlying the recognition characteristics of molecularly imprinted materials. Here, we first present an overview of a thermodynamic treatment of factors governing the behaviour of these functional materials, and then a summary of the development and current status of the use of computational strategies for studying aspects of molecular imprinting and the resulting material properties.

Antibody–peptide/protein interactions are instrumental for many processes in the pharmaceutical and biotechnology industries and as tools for biomedical and biochemical research. The recent development of molecularly imprinted polymer nanoparticles displaying antibody-like recognition of peptides and proteins offers the possibility for substituting antibodies with these robust materials for applications where the structural integrity and function of antibodies is compromised by temperature, pH, solvent, etc. The background to the development of this class of antibody-mimicking material and the state-of-the-art in their synthesis and application is presented in this review.

A series of molecular dynamics simulations of prepolymerization mixtures for phenylalanine anilide imprinted co-(ethylene glycol dimethacrylate-methacrylic acid) molecularly imprinted polymers have been employed to investigate the mechanistic basis for template selective recognition in these systems. This has provided new insights on the mechanisms underlying template recognition, in particular the significant role played by the crosslinking agent. Importantly, the study supports the occurrence of template self-association events that allows us to resolve debate between the two previously proposed models used to explain this system's underlying recognition mechanisms. Moreover, the complexity of the molecular level events underlying template complexation is highlighted by this study, a factor that should be considered in rational molecularly imprinted polymer design, especially with respect to recognition site heterogeneity.

It is now widely accepted that the recognition properties of a MIP are derived from molecular level events present during the prepolymerization stage.¹ Studies regarding the nature and extent of template complexation during this stage should therefore yield valuable information regarding the template recognition properties of the final MIP. One method of great potential for illuminating molecular level details in this area of MIP research is molecular dynamics (MD).² MD simulations enable studies of molecular-level events in MIP prepolymerization mixtures.

Phenylalanine anilide (PA) is a molecule that has been extensively used as a template in a series of seminal molecular imprinting studies.^3-5 In an effort to elucidate the origin to the imprinting effect, Sellergren, Lepistö and Mosbach proposed that selective high-affinity sites in the PA-MIP were based on functional monomer-template complexation of a 2:1 stoichiometry.³ In a follow-up study, Katz and Davis presented results that revealed further information regarding the origin of recognition in PA-MIPs.⁵ It was suggested that the template recognition sites were based on functional monomer-template complexes of 1:1 stoichiometry, and also that the formation of higher order template-template complexes has important effects on the final PA-MIP recognition properties. In light of this conjecture and several more recent studies highlighting the diversity of template complexation mechanisms in prepolymerization mixtures, have pointed at the complexity and diversity in the ensemble of complexes leading to the final “molecular memory”.

Here we present the novel insights into the molecular basis for PA-MIP template recognition derived from a series of MD simulations of the PA-MIP prepolymerisation systems. Data support the presence of PA-PA complexes and that the most statistically prevalent stoichiometry functional monomer-PA complexes was 1:1. The role of cross-linker is also discussed. This study highlights the potential of all component MD studies for rational MIP design.

(1)      Alexander, C.; Andersson, H.S.; Andersson, L.I.; Ansell, R.J.; Kirsch, N.; Nicholls, I.A.; O'Mahony, J.; Whitcombe, M.J.  Molecular imprinting science and technology: A survey of the literature for the years up to and including 2003. Journal of Molecular Recognition 2006, 19, 106-180.

(2)      Nicholls, I.A.; Andersson, H.S.; Charlton, C; Henschel, H.; Karlsson, B.C.G.; Karlsson, J.G.; O’Mahony, J.; Rosengren, A.M.; Rosengren, J.K.; Wikman, S. Theoretical and computational stratgies for rational molecularly imprinted polymer design. Biosensors and Bioelectronics 2009, 25, 543-552

(3)      Sellergren, B.; Lepistoe, M.; Mosbach, K.. Highly enantioselective and substrate-selective polymers obtained by molecular imprinting utilizing noncovalent interactions. NMR and chromatographic studies on the nature of recognition. Journal of American Chemical Society 1988, 110, 5853-5860

(4)      Sellergren, B.. Molecular imprinting by noncovalent interactions: Tailor-made chiral stationary phases of high selectivity and sample load capacity. Chirality 1989, 1, 63-68

(5)      Katz, A.; Davis, M.E. Investigations into the mechanism of molecular recognition with imprinted polymers. Macromolecules 1999, 32, 4113-4121

In this work, classical molecular dynamics (MD) simulations have been used to provide unique insights on the nature and extent of intermolecular interactions present in a phenylalanine anilide (PA) molecularly imprinted polymers (MIP) prepolymerization mixture.

Molecular Imprinting is a technique for producing highly selective synthetic receptors for a predetermined molecular structure, and involves the formation of cavities in a synthetic polymer matrix that are of complementary functional and structural character to a template molecule.¹ It is generally accepted that the recognition properties of a MIP is a product of the interactions between monomers and template during the prepolymerization stage. Accordingly, studies of the nature and extent of the interactions present in prepolymerization mixtures, in patricular those involving template, should yield information which can be related to the observed recognition properties of the final MIP.

Phenylalanine anilide MIPs have been the subject of a significant number of studies aimed at producing an understanding of the mechanisms underlying the recognition processes. Interestingly, two different models have been proposed to explain the behaviour of PA-MIPs. Studies by Sellergren et al. proposed that template selectivity, was a consequence of  the presence of a functional monomer-template complexes of 2:1 stoichiometry.² Later, however, Katz and Davis proposed an alternative model,³ where the template (PA) recognition sites in the MIP were suggested to arise from functional monomer-template complexes of 1:1 stoichiometry in combination with the presence of higher order template-template complexes.

To resolve this conjecture, we performed a series of MD studies, the results of which demonstrated both the presence of PA-PA self association complexes, and that the most statistically prevalent monomer-PA complex stoichiometry was of a 1:1 nature, though differetn in character from that proposed by Katz and Davis.  Moreover, the role of cross-linker in forming recognition sites was apparnet in these studies, a fact not previously considered.

References

1. Alexander C, Andersson HS, Andersson LI, Ansell RJ, Kirsh N, Nicholls IA, O’Mahony J, Whitcombe MJ. Molecular imprinting science and technology: A survey of the literature for the years up to and including 2003. Journal of Molecular Recognition 2006;19:106-180
2. Sellergren B, Lepistö M, Mosbach K. Highly enantioselective and substrate selective polymers obtained by molecular imprinting utilizing noncovalent interactions. NMR and chromatographic studies on the nature of recognition. Journal of the American Chemical Society 1988;110:5853-5860
3. Katz A, Davis ME. Investigations into the mechanisms of molecular recognition with imprinted polymers. Macromolecules 1999;32:4113-4121

The molecular imprinting technique has received significant attention due to its utility in the production of synthetic polymeric materials with predetermined ligand recognition properties [1].

It is generally accepted that the recognition properties of a molecularly imprinted polymer (MIP) is established during the prepolymerization stage. Previous investigations on the nature and extent of template prepolymerization complexation in a phenylalanine anilide (PA) MIP pointed at the complexity and diversity in the ensemble of complexes leading to the final “molecular memory”. In particular, conflicting models have been used to explain the observed molecular memory. Sellergren, Lepistö and Mosbach [2] proposed that selective, high-affinity sites in the final MIP were based on functional monomer-PA complexation of a 2:1 stoichiometry. Later, Katz and Davis [3] proposed that the template recognition sites arose due to a 1:1 functional monomer-template complex stoichiometry and that the effect of template dimerization is critical for the observed PA-MIP recognition properties.

In this study, we have attempted to shed new light on this as yet unresolved conflict using a series of molecular dynamics (MD) simulations. Results demonstrated the presence of PA-PA complexes and that the most statistically prevalent stoichiometry of functional monomer-PA complexes was of 1:1.

[1]             Alexander C, Andersson HS, Andersson LI, Ansell R, Kirsch N, Nicholls IA et al. Molecular imprinting science and technology: a survey of the literature for the years up to and including 2003, Journal of Molecular Recognition, 19, 106-180 (2006).

[2]            Sellergren B, Lepistö M, Mosbach K. Highly enantioselective and substrate selective polymers obtained by molecular imprinting utilizing noncovalent interactions. NMR and chromatographic studies on the nature of recognition, Journal of the American Chemical Society, 110, 5853-5860 (1988).

[3]             Katz A, Davis ME. Investigations into the mechanisms of molecular recognition with imprinted polymers, Macromolecules, 32, 4113-4121 (1999).

Molecular dynamics (MD) simulations of prepolymerization mixtures can provide detailed insights concerning the molecular-level mechanisms underlying the performance of molecularly imprinted polymers (MIPs) and can be used for the in silico screening of candidate polymer systems. Here, we describe the use of MD simulations of all-atom, all-component MIP prepolymerization mixtures and procedures for the evaluation of the simulation data using the Amber simulation software suite.

A series of polymers molecularly imprinted with the general anaesthetic propofol were synthesized using both semi- and non-covalent approaches. The polymers were evaluated with respect to template rebinding in both aqueous and organic media. In aqueous media, the observed propofol binding in these polymer systems was largely hydrophobic and non-specific in nature. In non-polar solvents such as hexane, electrostatic (hydrogen bonding) interactions dominate resulting in some selectivity. The implication of these results, in conjunction with those obtained using structures of similar size in other studies, is that propofol, a template possessing limited functionality and size, appears to define the lower limit for template size and degree of functionalization that can be used for the creation of ligand-selective recognition sites in molecularly imprinted polymers. Furthermore, studies with alternative ligands indicate that the steric crowding of a ligand's functionality to the polymer contributes to the extent of polymer-ligand recognition.

Materials that can mimic the molecular recognition-based functions found in biology are a significant goal for science and technology. Molecular imprinting is a technology that addresses this challenge by providing polymeric materials with antibody-like recognition characteristics. Recently, significant progress has been achieved in solving many of the practical problems traditionally associated with molecularly imprinted polymers (MIPs), such as difficulties with imprinting of proteins, poor compatibility with aqueous environments, template leakage, and the presence of heterogeneous populations of binding sites in the polymers that contribute to high levels of non-specific binding. This success is closely related to the technology-driven shift in MIP research from traditional bulk polymer formats into the nanomaterial domain. The aim of this article is to throw light on recent developments in this field and to present a critical discussion of the current state of molecular imprinting and its potential in real world applications.

The influence of the physical properties of incubation medium on the rebinding of template to bupivacaine molecularly imprinted and non-imprinted methacrylic acid–ethylene dimethacrylate co-polymers has been studied. Principal component analysis (PCA) was employed to identify the factors with the greatest influence on binding. While the dielectric constant (D) made a significant contribution to describing the observed binding, the influence of polarity as reflected in the Snyder polarity index (SPI) was also demonstrated to make a significant contribution. The use of solvents containing hydroxyl functionality in particular was observed to exert unique effects on recognition. The variation in solvent influence on binding at constant D motivates more complex analyses when studying MIP–ligand recognition.

In order to examine the physical mechanisms underlying molecularly imprinted polymer¹ (MIP)–ligand recognition, polymers with selectivity for the local anaesthetic bupivacaine have been synthesised and their ligand-recognition characteristics examined. As several previous studies have pointed at the complexity of the rebinding characteristics and the dependence on rebinding media,^2-4 we used chemometric strategies for the analysis of ligand-MIP binding in various media.⁵

In a previous study we presented results from a chemometric analysis showing that rebinding of bupivacaine to the MIP in different solvent mixtures and at different temperatures follow a complicated non-linear relationship.⁶ The results from that analysis, motivated an investigation into the significance of the solvent physical characteristics (molecular and bulk) on rebinding properties. In this work,⁷ principal component analysis was employed to identify the factors with the greatest influence on binding. While the dielectric constant made a significant contribution to describing the observed binding, the influence of polarity as reflected in the Snyder polarity index was also demonstrated to also make a significant contribution. The use of solvents containing hydroxyl functionality was observed to exert unique effects on recognition. The variation in solvent influence on binding at constant dielectricity motivates more complex analyses when studying MIP-ligand recognition.

(1)      Alexander, C.; Andersson, H.S.; Andersson, L.I.; Ansell, R.J.; Kirsch, N.; Nicholls, I.A.; O'Mahony, J.; Whitcombe, M.J. Molecular imprinting science and technology: A survey of the literature for the years up to and including 2003. Journal of Molecular Recognition 2006, 19, 106-180.

(2)      Andersson, L.I. Efficient sample pre-concentration of bupivacaine from human plasma by solid-phase extraction on molecularly imprinted polymers. Analyst 2000, 125, 1515-1517.

(3)      Karlsson, J.G.; Andersson, L.I.; Nicholls, I.A. Probing the molecular basis for ligand-selective recognition in molecularly imprinted polymers selective for the local anaesthetic bupivacaine. Analytica Chimica Acta 2001, 435, 57-64.

(4)      Karlsson, J.G.; Karlsson, B.; Andersson, L.I.; Nicholls, I.A. The roles of template complexation and ligand binding conditions on recognition in bupivacaine molecularly imprinted polymers. Analyst 2004, 129, 456-462.

(5)      Nicholls, I.A.; Andersson, H.S.; Charlton, C.; Henschel, H.; Karlsson, B.C.G.; Karlsson, J.G.; O’Mahony, J.; Rosengren, A.M.; Rosengren, K.J.; Wikman, S. Theoretical and computational strategies for rational molecularly imprinted polymer design. Biosensors and Bioelectronics 2009, 25, 543-552.

(6)      Rosengren, A.M.; Karlsson, J.G.; Andersson, P.O.; Nicholls, I.A. Chemometric models of template-molecularly imprinted polymer binding. Analytical Chemistry 2005, 77, 5700-5705.

(7)      Rosengren, A.M; Golker, K.; Wiklander, J.G.; Nicholls, I.A. Dielectric constants are not enough: Principal component analysis of the influence of solvent properties on molecularly imprinted polymer–ligand rebinding. Biosensors and Bioelectronics 2009, 25, 553-557.

Molecular imprinting is a technique for creating polymeric recognition materials with predetermined ligand selectivities.¹ A molecularly imprinted polymer (MIP) with selectivity for the local anaesthetic bupivacaine has been synthesised in order to examine the physical mechanisms underlying MIP–ligand recognition characteristics. As rebinding characteristics has shown to be complex, we use chemometric strategies for the analysis of ligand-MIP binding in various media.^2-4 The use of chemometrics simplify the selection of optimal experimental parameters as well as the extraction of significant information generated from multivariate data analysis.⁵

Previously we have presented results from a chemometric analysis pointing at a complex non-linear relationship when studying binding of bupivacaine to the MIP in different solvent mixtures and at different temperatures.⁶ The results motivated an investigation into the significance of the solvent physical characteristics (molecular and bulk) on rebinding properties. In this work, principal component analysis was employed to identify the factors with the greatest influence on binding. While the dielectric constant made a significant contribution to describing the observed binding, the influence of polarity as reflected in the Snyder polarity index was also demonstrated to make a significant contribution. The use of solvents containing hydroxyl functionality was observed to exert unique effects on recognition. The variation in solvent influence on binding at constant dielectricity motivates more complex analyses when studying MIP-ligand recognition. Collectively, the results provided general insights concerning the complex interplay between the mechanisms controlling ligand recognition in MIPs.

References

1. Alexander, C.; Andersson, H.S.; Andersson, L.I.; Ansell, R.J.; Kirsch, N.; Nicholls, I.A.; O’Mahony, J.; Whitcombe, M.J. Journal of Molecular Recognition 2006, 19, 106-180.
2. Andersson, L.I. Analyst 2000, 125, 1515-1517.
3. Karlsson, J.G.; Andersson, L.I.; Nicholls, I.A. Analytica Chimica Acta 2001, 435, 57-64.
4. Karlsson, J.G.; Karlsson, B.; Andersson, L.I.; Nicholls, I.A. Analyst 2004, 129, 456-462.
5. Nicholls, I.A.; Andersson, H.S.; Charlton, C.; Henschel, H.; Karlsson, B.C.G.; Karlsson, J.G.; O’Mahony, J.; Rosengren, A.M.; Rosengren, K.J.; Wikman, S. Biosensors and Bioelectronics 2009, 25, 543-552.
6. Rosengren, A.M.; Karlsson, J.G.; Andersson, P.O.; Nicholls, I.A. Analytical Chemistry 2005, 77, 5700-5705.

A molecularly imprinted polymer (MIP) is a polymeric material with selective recognition for an analyte.¹ In order to examine the physical mechanisms underlying MIP–ligand recognition, polymers with selectivity for the local anaesthetic bupivacaine have been synthesised and their ligand-recognition characteristics examined. As several previous studies have pointed at the complexity of the rebinding characteristics and the dependence on rebinding media,^2-4 we used chemometric strategies for the analysis of ligand-MIP binding in various media.⁵

In a previous study we presented results from a chemometric analysis showing that rebinding of bupivacaine to the MIP in different solvent mixtures and at different temperatures follow a complicated non-linear relationship.⁶ The results from that analysis, motivated an investigation into the significance of the solvent physical characteristics (molecular and bulk) on rebinding properties. In this work, principal component analysis was employed to identify the factors with the greatest influence on binding. While the dielectric constant made a significant contribution to describing the observed binding, the influence of polarity as reflected in the Snyder polarity index was also demonstrated to also make a significant contribution. The use of solvents containing hydroxyl functionality was observed to exert unique effects on recognition. The variation in solvent influence on binding at constant dielectricity motivates more complex analyses when studying MIP-ligand recognition.

References

1. Alexander, C.; Andersson, H.S.; Andersson, L.I.; Ansell, R.J.; Kirsch, N.; Nicholls, I.A.; O’Mahony, J.; Whitcombe, M.J. Journal of Molecular Recognition 2006, 19, 106-180.
2. Andersson, L.I. Analyst 2000, 125, 1515-1517.
3. Karlsson, J.G.; Andersson, L.I.; Nicholls, I.A. Analytica Chimica Acta 2001, 435, 57-64.
4. Karlsson, J.G.; Karlsson, B.; Andersson, L.I.; Nicholls, I.A. Analyst 2004, 129, 456-462.
5. Nicholls, I.A.; Andersson, H.S.; Charlton, C.; Henschel, H.; Karlsson, B.C.G.; Karlsson, J.G.; O’Mahony, J.; Rosengren, A.M.; Rosengren, K.J.; Wikman, S. Biosensors and Bioelectronics 2009, 25, 543-552.
6. Rosengren, A.M.; Karlsson, J.G.; Andersson, P.O.; Nicholls, I.A. Analytical Chemistry 2005, 77, 5700-5705.

Three molecular imprinting strategies, each based upon a series of ethylene glycol dimethacrylate (EGDMA) cross-linked co-polymers, have been used to produce materials selective for the commonly used analgesic and antipyretic agent paracetamol (p-acetaminophen or 4-acetamidophenol) (1). The polymers were synthesised using either a semi-covalent imprinting strategy based upon 4-acetamidophenyl-(4-vinylphenyl) carbonate (4) or a non-covalent strategy based on methacrylic acid (MAA) as the functional monomer, or by employing a combination of these strategies. Radioligand binding studies demonstrated low template affinity in polymers offering only a single electrostatic interaction point for recognition via the phenolic residue in the template, whereas binding was substantially increased upon the introduction of a second binding mode, namely interaction at the acetamide moiety. HPLC analyses revealed no imprinting effect in the purely semi-covalent system, and only a minor effect in the purely non-covalent systems. However, a pronounced imprinting effect was demonstrated for polymers prepared by a combination of semi-covalent and non-covalent imprinting. This study illustrates a limitation of both the non-covalent and the semi-covalent strategies when it comes to achieving imprinted selectivity for small and poorly functionalised templates such as paracetamol. Parallels with conclusions from studies with antibodies are discussed.