Preparation of imprinted membranes by photograft polymerisation

Molecular imprinting has entered in different fields with particular attention in chemistry, biochemistry, biotechnology and medicine. This technology, firstly proposed by Wulff in 1972 [1], is a method to introduce molecular recognition sites for a given interesting molecule into a polymeric material during its preparation. The process needs of three fundamental components: 1) functional monomer (that will polymerise in order to form polymer matrix); 2) cross-linker (that favourites the formation of a network in a polymeric matrix); 3) template (analyte that will be imprinted in the polymer). An organic solvent (porogen) is added in order to induce a porous structure inside the imprinted polymer. The preparation procedure consists of mixing the template (target) molecule with the monomers having functional moieties, which form covalent or non-covalent bonds with the template in solution [1]. In the following step the cross-linker is added to the complex solution with the mixture being polymerised to form highly cross-linked polymer. After the following extraction of the template molecule from the polymer, the shape of the template and the alignment of the functional moieties are retained in the polymer matrix and optimally set for future specific recognition. The molecular imprinting technique is used nowadays in order to prepare imprinted membranes in the field of the separation techniques. In the present work composite molecularly imprinted polymeric (MIP) membranes with recognition properties toward (S)-naproxen and flavonoid naringin have been prepared. The used method was the surface photograft polymerisation [2] of the monomer 4-vinylpyridine (4-VPY) on commercial polyvinylidene fluoride (PVDF) microfiltration membranes. This technique offers the advantage to combine the mechanical integrity of the membrane support with the selectivity of the imprinted polymer. In the presence of a template molecule, binding sites are introduced into the membrane support without damaging its pore structure. . Results and Discussion The membrane preparation procedure has been carried out by immersing firstly the membrane to be modified (PVDF 0.2 µm) in the photoinitiator solution (Benzoin ethyl ether) and successively in the functional monomer solution (4-VPY) containing ethyleneglycol dimethacrylate (EDMA) as cross-linker and the template molecule (S-naproxen or flavonoid naringin). Finally, the membrane has been exposed to UV irradiation and the photo co-polymerisation process has been accomplished in nitrogen atmosphere and controlling the temperature by using a thermostated sample holder. Blank membrane samples (without template in the monomer solution) have been also prepared under identical conditions. The modified membrane consists of a non selective porous support (PVDF) coated with a thin imprinted layer of 4-VPY. In figure 1, the SEM surface micrographs of commercial PVDF support (a) and naringin imprinted membrane (b) are reported. a b Figure1. Surface SEM micrographs of the commercial PVDF membrane (a) and the composite membrane imprinted with flavonoid naringin (b). The membrane recognition properties have been investigated by permeation experiments using a cross-flow filtration cell [3]. The concentration of the template molecule has been determined calculating in time the quantities (?mol) of naproxen enantiomers and naringin in the permeate and retentate side while the concentration ((?g/ml) has been evaluated by HPLC analysis. Preliminary experimental results show that the imprinted membrane are able to resolve racemic naproxen (selectivity factor = 1.7) by means a specific recognition of (S)-naproxen enantiomer (template). Furthermore, imprinted membrane prepared using naringin also exhibit specific recognition properties for the template. Conclusions In this work, novel composite molecularly imprinted membranes have been prepared via photograft polymerisation of the monomer 4-vinylpyridine on the commercial polyvinylidene fluoride support membrane. (S)-naproxen and naringin have been used as template molecule. Permeation studies in a cross-flow filtration set-up have been shown that the imprinted membranes are able to separate naproxen enantiomers and selectively recognize flavonoid naringin. On the opposite, the non-modified PVDF membrane and the membrane modified in the absence of the template molecule do not show any recognition property toward the molecules of our interest. References [1] M. Yoshikawa, Molecularly imprinted polymeric membranes, Bioseparations 10 (2002) 277-286 [2] S. A. Piletsky, H. Matuschewski, U. Schedler, A. Wilpert, E. V. Piletska, T. Thiele, M. Ulbricht, Surface functionalisation of porous polypropylene membranes with molecularly imprinted polymers by photograft copolymerisation in water, Macromolecules 33 (2000) 3092-3098 [3] L. Donato, A. Figoli, E. Drioli, Novel composite poly(4-vinylpyridine)/polypropylene membranes with recognition properties for (S)-naproxen, Journal of Pharmaceutical and Biomedical Analysis 37 (2''5) 1003-1008