: Temperature-responsive N-isopropylacrylamide (NIPAAm) polymer (PNIPAAm) with a free carboxyl functional end group and a copolymer (NIPNAS) of NIPAAm and N-acryloxysuccinimide (NAS) were synthesized and used for immobilization of a-amylase. The enzyme forms covalent bonds with the former polymer by single point attachment and with the latter polymer by multiple point attachment. Such a di †erence inÑuences the enzyme activity and properties of the immobilized enzymes. The polymers are temperature-sensitive with lower critical solution temperatures (LCST) of 34É7 and 36É0¡C for NIPNAS and PNIPAAm, respectively. The immobilized enzyme exhibited an LCST of 35É5¡C for NIPNAS-amylase and 37É1¡C for PNIPAAm-amylase. They precipitated and Ñocculated in aqueous solution above the LCST and redissolved when cooled below that temperature. The activity of the immobilized enzyme depended on the pH of the coupling bu †er, with 8É0 being the optimum value. The speciÐc activities of the immobilized enzymes were 87% and 108% compared with that of free enzyme with soluble starch as the substrate for NIPNASamylase and PNIPAAm-amylase, respectively. By characterizing the properties of the immobilized enzymes and comparing with those of free enzyme, no di †u-sion limitation of substrate was found for the immobilized enzymes and they are more thermal stable than the free enzyme. Within the two immobilized enzymes, NIPNAS-amylase showed better thermal stability and reusability. Repeated batch hydrolysis of soluble starch can be carried out efficiently with the immobilized enzymes by intermittent thermal precipitation and recycle of the enzyme.

A composite membrane was made by casting hydrogel onto a nonwoven polyester support and used for enzyme immobilization. The hydrogel consists of N-isopropylacrylamide, cross-linker N, N'-methylenebis(acrylamide), 2-hydroxyethyl methacrylate, soluble starch, and N-(acryloxy)succinimide (NAS). The composite membrane is temperature-sensitive with a lower critical solution temperature (LCST) around 35 degreesC. It responds to temperature change by swelling below the LCST and shrinking above the LCST, corresponding to opening and closing of the membrane pores. alpha-Amylase was immobilized to the membrane by covalent bonds through reacting with the high reactive ester groups in NAS. The membrane-immobilized enzyme retained 32% of specific activity toward soluble starch when compared with that of free enzyme, and its properties were characterized and compared with those of the free enzyme. The immobilized enzyme was more thermally stable than the free enzyme. Kinetic constants, (Km) and the activation energy of the immobilized enzyme were both larger than those of the free enzyme. Starch hydrolysis with the immobilized enzyme was investigated in two-compartment permeation cells with a composite membrane between the cells. Reaction was carried out by hydrolyzing soluble starch in the donor side and collecting the hydrolyzed products in the receptor side. This reactor could be operated with temperature cycling to enhance the reaction and facilitate separation of products from the substrate. The best operating condition is cycling the temperature between 50 and 20 degrees C every 5 min. The membrane reactor was operated up to eight times for successive starch hydrolysis.

Composite hydrogel membranes of crosslinked poly(N-isopropylacrylamide-co-N-acryloxysuccinimide-co-2-hydroxyet hyl methacrylate) [P(NIPAAm-NAS-HEMA)] with starch, as a macropore forming agent, on nonwoven polyester was prepared. The membranes could swell and de-swell around the characteristic lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAAm). It was demonstrated that the presence of macropores in the membranes could improve the immobilization efficiency as well as lead to a short responding time upon temperature change across the LCST. Immobilized alpha-amylase could retain as high as 33% of the activity of the free enzyme with a loading level of 0.60-0.65 mg/cm2 when the membrane preparation and enzyme immobilization conditions were optimized. The half time (T0.5) for the swelling or de-swelling response of the gel phase within the membranes was less than 2 min, and the 90% time (T0.9) was less than 6 min. The permeability for maltose through the membranes could change as much as 4.9-fold when the temperature was raised above or reduced below the LCST.