All-component molecular dynamics studies were used to probe a library of oseltamivir molecularly imprinted polymer prepolymerization mixtures. Polymers included one of five functional monomers (acrylamide, hydroxyethylmethacrylate, methacrylic acid, 2-(triflouromethyl)acrylic acid, 4-vinylpyridine) and one of three porogens (acetonitrile, chloroform, methanol) combined with the crosslinking agent ethylene glycol dimethacrylate and initiator 2,2'-azobis(2-methylpropionitrile). Polymers were characterized by nitrogen gas sorption measurements and SEM, and affinity studies performed using radioligand binding in various media. In agreement with the predictions made from the simulations, polymers prepared in acetonitrile using either methacrylic or trifluoromethacrylic acid demonstrated the highest affinities for oseltamivir. Further, the ensemble of interactions observed in the methanol system provided an explanation for the morphology of polymers prepared in this solvent. The materials developed here offer potential for use in solid-phase extraction or for catalysis. The results illustrate the strength of this in silico strategy as a potential prognostic tool in molecularly imprinted polymer design.

Aspects of the molecular-level basis for the function of ethylene glycol dimethacrylate and trimethylolproprane trimethacrylate crosslinked methacrylic acid copolymers molecularly imprinted with (S)-propranolol have been studied using a series of all-component and all-atom molecular dynamics studies of the corresponding prepolymerization systems. The crosslinking agents were observed to contribute to template complexation, and the results were contrasted with previously reported template-recognition behavior of the corresponding polymers. Differences in the extent to which the two crosslinkers interacted with the functional monomer were identified, and correlations were made to polymer-ligand recognition behavior and the results of nuclear magnetic resonance spectroscopic studies studies. This study demonstrates the importance of considering the functional monomer-crosslinker interaction when designing molecularly imprinted polymers, and highlights the often neglected general contribution of crosslinker to determining the nature of molecularly imprinted polymer-template selectivity.

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.

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 risks to society associated with the spread of new strains of influenza with human pathogenicity, or with impact on agricultureare significant. Our capacity to challenge the threat of the virus is dependent upon our ability to develop new vaccines, and upon ouraccess to effective virus-targeted small molecule pharmaceuticals. The current primary small molecule weapons oseltamivir(Tamiflu) and zanamivir (Relenza) currently form our last line of defence against this virus. More recently, the identification ofstrains resistant to (in particular) drugs targeting neuraminidase has awoken serious concern. Equally as worrying is the clearevidence of the presence of these substances in the World’s water systems which has now come forth. Collectively, this makes thedevelopment of techniques giving us better insight into the virus and antiviral agents a priority. Robust methods for the rapid andsensitive determination of these substances are required, especially as the monitoring methods should be able to withstand therigours of environments not normally conducive to biomacromolecules (temperature, toxic substances etc) e.g. antibodies.Advanced materials fulfilling these requirements can be obtained by Molecular Imprinting, which is a technique forproducing highly selective synthetic receptors for biochemical and chemical structures in synthetic polymers. The polymerscontain nano-structured cavities that are of complementary functional and structural character to predetermined target.The technique entails the judicious selection of a monomer or monomer mixture with chemical functionality comple-mentary to that of the imprint species (template). The complementary interacting functionalities (reversible covalent ornon-covalent) form predictable solution structures, which after polymerisation in the presence of a suitable cross linkingagent and removal of the template lead to the defining of recognition sites of complementary steric and functionaltopography to the template molecule. These sites give selective recognition of the template. Furthermore, by analogy tocatalytic antibody production, using transition state analogues as templates yields synthetic enzymes.Synthetic polymers with neuraminidase-like behaviour have been designed through the screening of candidate polymersystems using a combination of molecular dynamics and NMR studies. The characterisation of the resulting materials hasdemonstrated systems with selectivity for the targeted antiviral agents. Our studies illustrate the potential of these uniquenanostructured materials for the monitoring of these antiviral agents in the environment, which is an important aspect inefforts aimed at limiting the development of resistant strains, and as a tool for policy makers.

Fundamental studies of molecularly imprinted polymer¹ (MIP) systems are necessary in order to facilitate the development of the field in general, in particular through the development of rational MIP design strategies.² Recent efforts using molecular dynamics studies of all-component molecular imprinting systems have demonstrated the unique insights that can be obtained regarding the massive diversity of interactions present in a given system.³

One of the most widely used templates in molecular imprinting is the beta-blocker propranolol.^4-8 Its use in fundamental studies and for providing proof-of-principle cases has been motivated by a number of factors including its clinical relevance, its inherent chirality, and availability in enantiomerically pure and radio-labelled forms. Significant efforts have been made to map the molecular basis for propranolol-MIP ligand recognition, though never through the simultaneous study of all components present during polymerization.

Here we present the first all component MD study of this system which has provided unique insights concerning, in particular the role of cross-linking agent on template complexation. Through correlations with recognition data, consequences for MIP design are proposed.

(1)      Alexander, C.; Andersson, H.S.; Andersson, L.I.; Ansell, R.J.; Kirsch, N.; Nicholls, I.A.; O'Mahony, J.; Whitcombe, M.J. J. Mol. Recognit. 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, K. J.; Wikman, S. Biosens. Bioelectron. 2009, 25, 543-552.

(3)      Karlsson, B. C. G.; O´Mahony, J.; Karlsson, J. G.; Bengtsson, H.; Eriksson, L. A.; Nicholls, I. A. J. Am. Chem. Soc., 2009, 131, 13297-13304.

(4)      Andersson, L.I. Anal. Chem. 1996, 68, 111-117.

(5)      Schweitz, L.; Andersson, L.I.; Nilsson, S. Anal. Chem. 1997, 69, 1179-1183.

(6)      Haupt, K.; Noworyta, K.; Kutner, W. Anal. Commun. 1999, 36, 391-393.

(7)      Philip, J.Y.N.; Buchweishaija, J.; Mkayula, L.L.; Ye, L. J. Agric Food Sci. 2007, 55, 8870-8876.

(8)      Nguyen, T.H.; Ansell, R.J. Org. Biomol. Chem. 2009, 7, 1211-1220.

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).