Vinyl imidazole carrying metal-chelated beads for reversible use in yeast invertase adsorption

Abstract

Poly(ethylene glycol dimethacrylate- n-vinyl imidazole) [poly(EGDMA–VIM)] hydrogel (average diameter 150–200 μm) was prepared copolymerizing ethylene glycol dimethacrylate (EGDMA) with n-vinyl imidazole (VIM). Poly(EGDMA–VIM) beads had a specific surface area of 59.8 m 2/g. Poly(EGDMA–VIM) beads were characterized by swelling studies and scanning electron microscope (SEM). Cu 2+ ions were chelated on the poly(EGDMA–VIM) beads (452 μmol Cu 2+/g), then the metal-chelated beads were used in the adsorption of yeast invertase in a batch system. The maximum invertase adsorption capacity of the poly(EGDMA–VIM)–Cu 2+ beads was observed as 35.2 mg/g at pH 4.5. The adsorption isotherm of the poly(EGDMA–VIM)–Cu 2+ beads can be well fitted to the Langmuir model. Adsorption kinetics data were tested using pseudo-first- and -second-order models. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The value of the Michaelis constant K m of invertase was significantly larger upon adsorption, indicating decreased affinity by the enzyme for its substrate, whereas V max was smaller for the adsorbed invertase. The optimum temperature for the adsorbed preparation of poly(EGDMA–VIM)–Cu 2+-invertase at 50 °C, 10 °C higher than that of the free enzyme at 40 °C. Storage stability was found to increase with adsorption. Adsorbed invertase retains an activity of 82% after 10 batch successive reactions, demonstrating the usefulness of the enzyme-loaded beads in biocatalytic applications.