Synthesis and characterization of poly(urethane-urea) microparticles from poly(vinyl alcohol) and binary blends of diisocyanates and their application for immobilization of maltogenic α-amylase

Novel poly(urethane-urea) (PUU) microparticles were synthesized from poly(vinyl alcohol) (PVA) and a blend of 1,6-hexamethylene diisocyanate (HMDI) and 2,4-toluene diisocyanate (TDI) in a dimethyl sulfoxide/water (99/1 vol.%) solution. Influence of the initial molar ratio of PVA and the blend of HMDI and TDI, reaction time and temperature on the yield of PUU and contents of functional groups have been studied. The structure of PUU was verified by chemical analysis and infrared spectrometry. Thermal stability of PUU in an inert atmosphere was studied by simultaneous thermal analysis. The size of PUU microparticles was evaluated by optical microscopy. Maltogenic alpha-amylase (EC 3.2.1.133) from Bacillus stearothermophilus was immobilized onto PUU microparticles. The effect of synthesis parameters of PUU on the efficiency of immobilization (EI) of maltogenic alpha-amylase and the yield of immobilization of protein (YP) were studied. The high yield of PUU microparticles (72%) and EI of maltogenic a-amylase (96%) was obtained when the initial molar ratio of PVA : (HMDI:TDI) was 1 : (0.75 : 0.25). The residual activity of immobilized maltogenic alpha-amylase onto PUU microparticles after storage for 28 days remained 95%. Repeated batch starch hydrolysis by maltogenic alpha-amylase, immobilized onto PUU microparticles, allowed at least seven cycles without a sensible activity decrease in starch saccharification. Immobilized maltogenic alpha-amylase maintained all initial catalytic activity after seven cycles.