Preparation of molecularly imprinted polymers (MIPs) using chiral and non-chiral templates and the application of these MIPs in separation and catalysis

In der modernen Reaktionstechnik werden hohe Anforderungen insbesondere an katalytisch aktive Materialien hinsichtlich Selektivität und Effizienz, aber auch Stabilität und Langlebigkeit gestellt. Derzeit werden entweder teure Edelmetallkatalysatoren eingesetzt oder es wird vielfach mit biologischen Katalysatoren gearbeitet, hauptsächlich mit immobilisierten Enzymen, deren Haltbarkeiten in der Regel nur kurz sind. Als Alternative bieten sich biomimetische Katalysatoren an, wie z.B. molekular geprägte Polymere. Unter molekularem Prägen ("molecular imprinting") versteht man die Erzeugung künstlicher Rezeptoren bzw. Antikörper ("plastibodies") durch die Polymerisation von funktionellen Monomeren und Quervernetzern in Anwesenheit von Templatmolekülen. Nach dem Eluieren des Templats entstehen spezifische molekulare Abdrücke so genannte MIPs ("molecularly imprinted polymers"), die in der Lage sind, das Templat auf molekularer Ebene zu erkennen, und somit zur Separation des Templats aus Analytgemischen verwendet werden können. Wählt man das Templat nach besti ten Kriterien, so können die Abdrücke als katalytisch aktive Zentren agieren ("plastizymes"). Ziel dieser Arbeit war es, molekular geprägte Polymere zu generieren und deren Verwendbarkeit in der Separation und Katalyse zu untersuchen. Dazu wurden MIPs in der Chromatographie auf ihre Affinität zum verwendeten Templat getestet und in Reaktoren hinsichtlich ihrer katalytischen Aktivitäten und ihres Materialverhaltens charakterisiert. Ein weiterer Schwerpunkt wurde in die Herstellung und Anwendung enantioselektiver MIPs gesetzt

Catalyzing a cycloaddition with molecularly imprinted polymers obtained via immobilized templates

Polymeric catalysts to be applied in the Diels-Alder cycloaddition of hexachlorocyclopentadiene and maleic acid have been prepared via molecular imprinting with template molecules immobilized on silica particles. These enzyme mimicking polymers exhibit specific catalytic effects compared to non-imprinted control polymers or polymer-free solutions. It could be demonstrated that the activity of the molecularly imprinted material rises when increasing the temperature. By this means, the reduction of the activation energy (as expected for catalysts) from 63 to 55 kJ mol(-1) could be observed. Furthermore, the reaction was characterized based on the Michaelis-Menten model. For the diene compound a Michaelis constant of K-M = 5.8 mmol l(-1) and an effective reaction rate of r(max,eff) = 0.41 mumol l(-1) s(-1), leading to a reaction rate constant k(eff) = 1.1 x 10(-3) s(-1), were determined. (C) 2003 Elsevier B.V. All rights reserved

Preparation and characterization of imprinted porous materials with high selectivity for luteolin

In order to selectively separate luteolin from its crude solution, we synthesized imprinted porous materials with high recognition specificity for luteolin, using an imprinting technique. Modified luteolin was used as template, vinyltriethoxysilane as the functional monomer, and tetraethyl orthosilicate (TEOS) as the cross-linking agent. The results showed the following optimum reaction conditions: The reaction ratio between luteolin and acryloyl chloride was 1:2 (0.10 g/0.20 g), adding 1.0 g precursor; the feasible elution time was 12 h; when the molar quantity of modified template molecule was 0.01 mol and ethenyltriethyloxy-silane (VTEO) was 0.04 mol, the maximum yield reached 91.6 %. All samples were tested by Brunauer-Emmett-Teller method, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy, equilibrium adsorption experiments and selective adsorption experiments. It was found that the imprinted porous materials showed excellent selectivity for luteolin in aqueous solution. Characterization by FTIR suggested that an addition reaction had occurred between the modified template molecule and VTEO while forming ester bonds in the functional precursor. Results from pore structure analysis indicated that the imprinted porous materials had good channels, and the average pore size of the prepared porous materials was between 35.85 and 95.82 Å. Adsorption dynamics analysis suggested that, when the adsorption time reached 3 h, the adsorption process had reached balance and the adsorption capacity was at steady state. These porous materials had highly selective recognition properties and high equilibrium adsorption capacity for the template molecule. The equilibrium adsorption capacity of the imprinted porous materials to the template molecule was 11.4 times that of the blank porous materials