Molecular imprinting | EPFL Graph Search

Molecular imprinting is a technique to create template-shaped cavities in polymer matrices with predetermined selectivity and high affinity. This technique is based on the system used by enzymes for substrate recognition, which is called the "lock and key" model. The active binding site of an enzyme has a shape specific to a substrate. Substrates with a complementary shape to the binding site selectively bind to the enzyme; alternative shapes that do not fit the binding site are not recognized. Molecularly imprinted materials are prepared using a template molecule and functional monomers that assemble around the template and subsequently get cross-linked to each other. The monomers, which are self-assembled around the template molecule by interaction between functional groups on both the template and monomers, are polymerized to form an imprinted matrix (commonly known in the scientific community as a molecular imprinted polymer (MIP)). The template is subsequently removed in part or entirely, leaving behind a cavity complementary in size and shape to the template. The obtained cavity can work as a selective binding site for the templated molecule. In recent decades, the molecular imprinting technique has been developed for use in drug delivery, separations, biological and chemical sensing, and more. Taking advantage of the shape selectivity of the cavity, use in catalysis for certain reactions has also been facilitated. The first example of molecular imprinting is attributed to M. V. Polyakov in 1931 with his studies in the polymerization of sodium silicate with ammonium carbonate. When the polymerization process was accompanied by an additive such as benzene, the resulting silica showed a higher uptake of this additive. By 1949, the concept of instructional theory molecular imprinting was used by Dickey; his research precipitated silica gels in the presence of organic dyes and showed imprinted silica had high selectivity towards the template dye.

Biomimetic catalysis with immobilized transition metal complexes

Alexander Schiller

The tetradentate chelate ligand tris[(1-vinylimidazol-2-yl)methyl]amine (10) was synthesized in five steps from commercially available starting materials. Upon reaction with MCl2 (M = Zn, Cu, Ni, Co) in the presence of NH4PF6, the complexes [M(10)Cl]PF6 (M = Zn (11), Cu (12), Co (14)) and [Ni(10)Cl]2(PF6)2 (13) were obtained. The structure of all complexes was determined by single crystal X-ray crystallography. Immobilization of 11 and 12 was achieved by copolymerization with ethyleneglycol dimethacrylate (EGDMA) to obtain P11-Zn and P12-Cu. Immobilized versions of 13 and 14 have been generated by cleavage the metal from P12-Cu and subsequent assembly of MCl2 (M = Ni (P12-Ni), Co (P12-Co)). The supported complexes P11-Zn, P12-Cu, P12-Ni, and P12-Co were found to be efficient catalysts for the hydrolysis of bis(ρ-nitrophenyl)phosphate (BNPP) at 50 °C. At pH 9.5, the heterogeneous catalyst P12-Cu was 56 times more active than the homogeneous catalyst 12. Partitioning effects, which increase the local concentration of BNPP in the polymer, are shown to contribute to the enhanced activity of the immobilized catalyst. The tridentate N,N',N''-chelate ligand tris(1-vinylimidazol-2-yl)phosphine (20) was synthesized from commercially available starting materials. Three immobilized Cu(II) complexes were generated by the following: (a) homopolymerization of 20 and subsequent metalation with CuCl2; (b) copolymerization of 20 with EGDMA and subsequent metalation with CuCl2; or (c) molecular imprinting with the organometallic Mo-complex Mo(η3-C4H7)(CO)2(20) (28) and EGDMA and subsequent replacement of Mo(II) by Cu(II). All three polymeric Cu complexes were found to very efficiently promote the hydrolysis of activated phosphoesters with the relative activity being dependent on the nature of the polymer and the substrate. The complex Fe2O(CH3COO)(10)23 (42) was synthesized and structurally investigated by single crystal X-ray crystallography. After copolymerization with EGDMA and subsequent replacement of Fe(III) by Cu(II), Zn(II) or Mn(III), hydrolysis and oxidation reactions were investigated. A higher activity compared to the corresponding monometallic immobilized complexes was observed. This increase in activity is most likely caused by cooperative effects.

EPFL2006

Highly cross-linked polymers containing N,N ',N ''-chelate ligands for the Cu(II)-mediated hydrolysis of phosphoesters

Kay Severin, Alexander Schiller

Three immobilized Cu(II) complexes were generated by the following: (a) homopolymerization of the N,N',N '' chelate ligand tris[2-(1-vinylimidazolyl)]phosphine (1) and subsequent metalation with CuCl2; (b) copolymerization of 1 with ethyleneglycol dimethacrylate (EGDMA) und subsequent metalation with CuCl2; or (c) molecular imprinting with the organometallic Mo-complex (Mo(eta(3)-C4H7)(CO)(2)(1)](TsO) (5) and EGDMA and subsequent replacement of Mo(II) by Cu(II). All three polymeric Cu complexes were found to efficiently promote the hydrolysis of activated phosphoesters with the relative activity being dependent on the nature of the polymer and the substrate.

2005

Biomimetic catalysis with immobilized transition metal complexes

Alexander Schiller

EPFL2006