The First Example of Molecularly Imprinted Nanogels with Aldolase Type I Activity

Abstract

The molecular-imprinting approach was used to obtain a nanogel preparation capable of catalysing the cross-aldol reaction between 4-nitrobenzaldehyde and acetone. A polymerisable proline derivative was used as the functional monomer to mimic the enamine-based mechanism of aldolase type I enzymes. The diketone template used to create the cavity was designed to imitate the intermediate of the aldol reaction and was bound to the functional monomer using a reversible covalent interaction prior to polymerisation. By using a high-dilution polymerisation method, soluble imprinted nanogels were prepared with dimensions similar to those of an enzyme and with the advantage of solubility and flexibility previously unattainable with monolithic polymers. Following template removal and estimation of active-site concentrations, the kinetic characterisation of both imprinted and non-imprinted nanogels was carried out with catalyst concentrations between 0.7 and 3.5 mol %. Imprinted nanogel AS147 was found to have a k(cat) value of 0.25 x 10(-2) min(-1), the highest value ever achieved with imprinted polymers catalysing C--C bond formation. Comparison of the catalytic constants for both imprinted nanogel AS147 and non-imprinted nanogel AS133 gave a ratio of k(cat 147)/k(cat 133)=18.8, which is indicative of good imprinting efficiency and highlights the significance of the template during the imprinting process. This work represents a significant demonstration of the superiority of nanogels, when the molecular-imprinting approach is used, over "bulk" polymers for the generation of catalysts.