IMMOBILIZATION OF ENZYMES ONTO MODIFIED POLYACRYLONITRILE MEMBRANES -APPLICATION OF THE ACYL AZIDE METHOD

Chemical reactions toward acyl azide activated polyacrylonitrile (PAN) and conditions for membrane surface modifications are described. Ultr afiltration (UF) membranes were prepared from PAN homopolymer and copo lymer with methyl acrylate. Besides hydrazide formation and nitrosatio n, a new method to introduce acyl azide groups into carboxyl modified PAN, using azido transfer with diphenyl phosphoryl azide, was develope d. Chemical conversions were characterized, especially with Fourier tr ansform infrared spectroscopy. The heterogeneous modifications are not chemically selective due to side reactions and/or incomplete conversi on. The pore structure is altered predominately via modified polymer s welling causing changed UF fluxes and selectivities. However, for the modification via PAN reaction with hydroxyl amine, acid hydrolysis, an d azido transfer, the initial membrane separations performance is qual itatively preserved. Using the acyl azide method, amyloglucosidase (AG ) (EC 3.2.1.3) was immobilized onto the modified PAN UF membranes, ena bling hydrolysis of starch or maltose to glucose. Enzyme activity was assayed depending on previous chemical modification (azide content) an d immobilization (pH) conditions as well as hydrolysis parameters (sub strate, conversion during diffusion or UF). The best results (up to 60 0 mU/cm(2) at 40 degrees C and pH 5.0) were obtained after modificatio n of PAN membranes via carboxyl creation and azido transfer. AG covale ntly bound to PAN is not influenced much in its catalytic properties ( K-m = 3.48 and 3.1 mmol/L for free and bound AG, respectively, with ma ltose at 40 degrees C and pH 5.0). Under UF conditions, AG effective a ctivity can be improved by the convective flow through the membrane. U F selectivity for the polymer starch determines effective substrate co ncentrations in the membrane, thus affecting observed activities and p roduct purities in the filtrate. (C) 1996 John Wiley & Sons, Inc.