Patrizia Baravalle

A connection between the binding properties of imprinted and nonimprinted polymers: a change of perspective in molecular imprinting.

In the current paradigm for molecular imprinting, the imprinted binding sites exist as a consequence of the polymerization process around templates, and the properties of nonimprinted polymers (NIPs) have largely been overlooked. Thus, nothing can be affirmed a priori concerning the binding properties of NIPs. We propose an alternative view where the imprinting effect is due to the presence of a template molecule that enhances the pre-existing binding properties of a polymer. If a NIP shows no binding properties toward a target molecule, the corresponding imprinted polymer (MIP) will show a weak imprinting effect. On the other hand, if a NIP shows binding properties toward a target molecule, the corresponding MIP will show a significant imprinting effect. To verify this hypothesis, we prepared a 96-member combinatorial polymeric library in the absence of any template molecule. This library was screened for several potential ligands, and with no exceptions, the composition of the best-binding NIP produced a MIP with excellent binding properties, whereas a low-binding NIP formulation produced a MIP with comparable low binding. To validate these results, the binding properties toward naproxen and ibuprofen were measured for two combinatorial libraries of polymers prepared in the presence (MIP library) and the absence (NIP library) of the template molecule. The experiments results showed a correlation between the apparent affinity constants measured for the NIP and MIP libraries, confirming the proposed hypothesis. Moreover, for closely related molecules, it was shown that binding selectivity is an emergent property derived from the imprinting process and not a property of NIPs.

Determination of banned Sudan dyes in food samples by molecularly imprinted solid phase extraction-high performance liquid chromatography.

A method for molecularly imprinted SPE of banned Sudan azo-dyes from food samples was investigated. The molecularly imprinted polymer was obtained by suspension polymerization using 1-(4-chlorophenyl)azonaphthalen-2-ol as the mimic template. The molecular recognition properties of imprinted beads were evaluated for use as a SPE sorbent, in order to develop a selective extraction protocol for the Sudan class of dyes. The optimized extraction protocol resulted in a reliable molecularly imprinted SPE (MISPE) method suitable for HPLC analysis. It was selective for the main analyte, Sudan I, and the related azo-dyes Sudan II, III, IV, Sudan Red B, and Sudan Red 7B, while the permitted azo-dyes Allura Red AC, Neococcin, and Sunset Yellow FCF were not extracted. The method was tested for Sudan I, II, III, and IV in five different food samples (hot chilli pepper, hot chilli tomato sauce, sausage, tomato sauce, and hard boiled egg yolk) at three concentration levels (15, 100, and 300 microg/g). It demonstrated itself to be insensitive to the presence of different complex matrices, precise, accurate, and with good recovery rates (85-101%). The LOD and LOQ were satisfactory for most analytical determinations.

Molecularly imprinted polymers for corticosteroids: analysis of binding selectivity.

In this work we prepared a library of cortisol-imprinted polymers via a sequential approach by combining 10 different functional monomers, 7 cross-linkers and 5 porogen solvents. The best combinations of functional monomers, cross-linkers and porogen solvents in terms of cortisol binding were used to prepare three imprinted polymers--polyacrylamide-co-ethylene dimethacrylate (porogen: chloroform), poly-4-vinylpyridine-co-ethylene dimethacrylate (porogen: chloroform) and polyacrylamide-co-ethylene dimethacrylate (porogen: acetonitrile)--whose selectivity towards 10 synthetic corticosteroids and 4 natural steroidal hormones was tested. The experimental results obtained show how different combinations of functional monomers, cross-linkers and porogen solvents produce cortisol-imprinted polymers with very different selectivity patterns, and that a careful optimization of the pre-polymerization mixtures makes it possible to increase the number of target steroids recognized by the resulting imprinted polymer. Moreover, through the use of a Free-Wilson analysis of the binding selectivity, it has been possible to obtain insights on the steroidal structural motifs able to increase or decrease the molecular recognition of corticosteroids by the imprinted polymers.

An innovative approach to molecularly imprinted capillaries for polar templates by grafting polymerization

Molecularly imprinted polymers have been successfully used as selective stationary phases in capillary electrophoresis. Notwithstanding, this technique suffers from several drawbacks as the loss of molecular recognition properties in aqueous media and the lack of feasibility for imprinted systems directed towards highly polar templates soluble in aqueous environments only. Thus, the preparation of imprinted polymers for highly polar, water‐soluble analytes, represents a challenge. In this work, we present an innovative approach to overcome these drawbacks. It is based on a surface molecular imprinting technique that uses preformed macromonomers as both functional recognition elements and cross‐linking agents. A poly‐2‐hydroxyethyl‐co‐methacrylic acid linear polymer was grafted from the surface of silica capillaries. The grafted polymer was exhaustively esterified with methacrylic anhydride to obtain polyethylendimethacrylate‐co‐methacrylic acid linear chains. Then, as a proof of concept, an adequate amount of a very polar template like penicillin V was added in a hydro‐organic mixture, and a thin layer of imprinted polymer was obtained by cross‐linking the polymer linear chains. The binding behaviour of the imprinted and non‐imprinted capillaries was evaluated in different separation conditions in order to assess the presence of template selectivity and molecular recognition effects. The experimental results clearly show that this innovative kind of imprinted material can be easily obtained in very polar polymerization environments and that it is characterized by enhanced molecular recognition properties in aqueous buffers and good selectivity towards the template and strictly related molecules. Copyright

Molecular Recognition of the Fungicide Carbendazim by a Molecular Imprinted Polymer Obtained through a Mimic Template Approach

Abstract A molecularly imprinted polymer recognizing the fungicide carbendazim was prepared using a mimicking template approach. Methyl-3-propylcarbamoyl-1H-benzimidazol-2-ylcarbamate was synthesized and used as a mimic template for polymer preparation. Selectivity of this polymer for carbendazim and structurally related substances (the template, fluberidazole, rabenzazole, thiabendazole, and benomyl and its two degradation products) was evaluated by liquid chromatography. Results demonstrate that imprinted polymer shows significant recognition properties for carbendazim, whereas the mimic and other carbendazim-related molecules are not recognized. This peculiar selectivity pattern can be explained as an imprinting effect due to the in situ formation of carbendazim from mimic degradation during the polymerization process.