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.

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.

In this report, principal component analysis (PCA) has been used to explore the influence of template complexation in the pre-polymerization phase on template molecularly imprinted polymer (MIP) recognition and polymer morphology. A series of 16 bupivacaine MIPs were studied. The ethylene glycol dimethacrylate (EGDMA)-crosslinked polymers had either methacrylic acid (MAA) or methyl methacrylate (MMA) as the functional monomer, and the stoichiometry between template, functional monomer and crosslinker was varied. The polymers were characterized using radioligand equilibrium binding experiments, gas sorption measurements, swelling studies and data extracted from molecular dynamics (MD) simulations of all-component pre-polymerization mixtures. The molar fraction of the functional monomer in the MAA-polymers contributed to describing both the binding, surface area and pore volume. Interestingly, weak positive correlations between the swelling behavior and the rebinding characteristics of the MAA-MIPs were exposed. Polymers prepared with MMA as a functional monomer and a polymer prepared with only EGDMA were found to share the same characteristics, such as poor rebinding capacities, as well as similar surface area and pore volume, independent of the molar fraction MMA used in synthesis. The use of PCA for interpreting relationships between MD-derived descriptions of events in the pre-polymerization mixture, recognition properties and morphologies of the corresponding polymers illustrates the potential of PCA as a tool for better understanding these complex materials and for their rational design.

A series of 436 Munro database chemicals were studied with respect to their corresponding experimental LD50 values to investigate the possibility of establishing a global QSAR model for acute toxicity. Dragon molecular descriptors were used for the QSAR model development and genetic algorithms were used to select descriptors better correlated with toxicity data. Toxic values were discretized in a qualitative class on the basis of the Globally Harmonized Scheme: the 436 chemicals were divided into 3 classes based on their experimental LD50 values: highly toxic, intermediate toxic and low to non-toxic. The k-nearest neighbor (k-NN) classification method was calibrated on 25 molecular descriptors and gave a non-error rate (NER) equal to 0.66 and 0.57 for internal and external prediction sets, respectively. Even if the classification performances are not optimal, the subsequent analysis of the selected descriptors and their relationship with toxicity levels constitute a step towards the development of a global QSAR model for acute toxicity.

The need for materials with predetermined ligand-selectivities for use in sensing and separation technologies, e.g. membranes and chromatography, has driven the development of molecularly imprinted polymer science and technology. Over recent years, the need to develop robust predictive tools capable of handling the complexity of molecular imprinting systems has become apparent The current status of the use of in silica techniques in molecular imprinting is here presented, and we highlight areas where new developments are contributing to improvements in the rational design of molecularly imprinted polymers.

The relationship between molecularly imprinted polymer (MIP) morphology and template-rebinding over a series of warfarin-imprinted methacrylic acid co(ethylene dimethacrylate) polymers has been explored. Detailed investigations of the nature of template recognition revealed that an optimal template binding was obtained with polymers possessing a narrow population of pores (~3–4 nm) in the mesopore size range. Importantly, the warfarin-polymer rebinding analyses suggest strategies for regulating ligand binding capacity and specificity through variation of the degree of cross-linking, where polymers prepared with a lower degree of cross-linking afford higher capacity though non-specific in character. In contrast, the co-existence of specific and non-specific binding was found in conjunction with higher degrees of cross-linking and resultant meso- and macropore size distributions.

The role of the structural diversity of the widely used anticoagulant drug warfarin on its distribution in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayer membranes was investigated using a series of both restrained (umbrella sampling) and unrestrained molecular dynamics simulations. Data collected from unrestrained simulations revealed favorable positions for neutral isomers of warfarin, the open side chain form (OCO), and the cyclic hemiketal (CCO), along the bilayer normal close to the polar headgroup region and even in the relatively distant nonpolar lipid tails. The deprotonated open side chain form (DCO) was found to have lower affinity for the DOPC bilayer membrane relative to the neutral forms, with only a small fraction interacting with the membrane, typically within the polar headgroup region. The conformation of OCO inside the lipid bilayer was found to be stabilized by intramolecular hydrogen bonding thereby mimicking the structure of CCO. Differences in free energies, for positions of OCO and CCO inside the bilayer membrane, as compared to positions in the aqueous phase, were −97 and −146 kJ·mol^–1. Kinetic analysis based on the computed free energy barriers reveal that warfarin will diffuse through the membranes within hours, in agreement with experimental results on warfarin’s accumulation in the plasma, thus suggesting a passive diffusion mechanism. We propose that this membrane transport may be an isomerization-driven process where warfarin adapts to the various local molecular environments encountered under its journey through the membrane. Collectively, these results improve our understanding of the influence of warfarin’s structural diversity on the drug’s distribution and bioavailability, which in turn may provide insights for developing new formulations of this important pharmaceutical to better address its narrow therapeutic window.

A combination of theoretical and experimental studies has provided correlations between molecularly imprinted polymer composition, morphology, and recognition behavior obtained using a series of bupivacaine-imprinted methacrylic acid (MAA)–ethylene glycol dimethacrylate copolymers differing in molar ratios of the respective monomers. Results extracted from analysis of molecular dynamics (MD) trajectory data demonstrated that stability and frequency of interactions between bupivacaine and the monomers in the prepolymerization phase were strongly affected by minor changes in polymer composition, which in turn affected binding site affinity and heterogeneity of the imprinted polymers. Moreover, through the characterization of polymer morphology, we show that higher molar fractions of MAA resulted in polymeric materials with increased pore size, a feature that enhanced the binding capacity of the polymers. Furthermore, the results presented point at the strength of MD for predicting MIP-template binding capacity and affinity.