Molecular Imprinting of Polymeric Core-Shell Nanoparticles
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MOLECULAR IMPRINTING OF POLYMERIC CORE-SHELL NANOPARTICLES Natalia Pérez Moral and Andrew G. Mayes School of Chemical Sciences, University of East Anglia, Norwich, NR4 7TJ, U.K. ABSTRACT In order to evaluate the compatibility of structured nanoparticles produced by aqueous emulsion polymerisation with the non-covalent imprinting procedure, a number of imprinted polymeric nanoparticles have been synthesised by seeded emulsion polymerisation in the presence and absence of a porogenic solvent. Propranolol was chosen as the template molecule using methacrylic acid (MAA) and ethylene glycol dimethacrylate (EDMA) as functional monomer and crosslinker respectively. The influence of the porogen and the amount of template added was studied by measuring the capacity of the polymeric particles to rebind template both in organic and aqueous buffers by radioligand binding assay. By increasing the amount of template from 0.5 to 6% (mol/mol with respect to monomers) the specific rebinding was increased from 2% to 24% in aqueous buffer and to 31% in a toluene based assay. The influence of the porosity was also established when the rebinding was performed in an organic solvent. INTRODUCTION Molecularly imprinted polymers (MIPs) address the need for robust, simple, fast and efficient methods to detect and separate specific molecules of interest such as drugs and pesticides. They are prepared easily and rapidly, and can be used in pre-concentration techniques, analysis, extraction, catalysis or separation. The imprinting technology consists basically of the synthesis of a highly crosslinked polymer in the presence of a template molecule. After removal of the template, the polymer is left with imprinted sites “fixed” in its structure that are complementary in shape, size and functionality to the targeted molecule, and therefore will selectively distinguish and bind such molecules when present in the medium to be processed or analysed. Specific recognition in the imprinted polymer depends on the type of interaction established between the template and the monomer(s) prior to polymerisation, which could be covalent, non-covalent or a combination of the two. Covalent interactions are strong and more selective but there are few types sufficiently labile to be made and broken under the mild conditions required for dynamic rebinding, limiting this approach to only a few specific functional groups. The use of a combination of covalent interactions in the creation of the imprinted step and non-covalent interactions in the rebinding of the ligand has also proved to be useful in some cases, but its use is restricted by the synthetic steps required to modify the template molecule prior to polymerisation. There are numerous examples of imprinted polymers based on non-covalent interactions, a more adaptable methodology that can be used with a large number of template molecules and allows fast kinetics in the rebinding of ligands. So far, molecules have been successfully imprinted based on hydrogen bonds, electrostatic and hydrophobic interactions,
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