A new metal chelate sorbent for glucose oxidase: Cu(II)and Co(II)-chelatedpoly(N-vinylimidazole) gels

Poly(N-vinylimidazole) (PVIm) gels were pre-pared by irradiating a binary m ixture of N-vinylimidazole (VIm)-water in a Co-60-gamma source having 4.5 k Gy/h dose rate. In the glucose oxidase (GOx) adsorption studies, affinity g els with a swelling ratio of 1100% for PVIm and 40 and 55% for Cu(II)- and CO(II)-chelated PVIm gels, respectively, at pH 6.5 in phosphate buffer were used. FTIR spectra were taken for PVIm and Cu(II)- and Co(II)-chelated PVI m, and glucose oxidase adsorption on these gels, to characterize the nature of the interactions in each species. The results show that PVIm- glucose o xidase interaction is mainly electrostatic and metal ion-chelated PVIm gel- glucose oxidase interaction is of coordinate covalent nature. Cu(II) and C o(II) ions were chelated within the gels via amine groups on the imidazole ring of the gel. Different amounts of Cu(II) and Co(II) ions [maximum 3.64 mmol/g dry gel for Cu(II) and 1.72 mmol/g dry gel for Co(II)] were loaded o n the gels by changing the initial concentration of Cu(II) and Co(II) ions at pH 7.0. GOx adsorption on these gels from aqueous solutions containing d ifferent amounts of GOx at different pH was investigated in batch reactors. GOx adsorption capacity was further increased when Cu(II) and Co(II) ions were attached [up to 0.53 g GOx/g dry Co(II)-chelated PVIm gels]. More than 90% of the adsorbed GOx was desorbed in 5 h in desorption medium containin g 1.0M KSCN at pH 7.0 for plain gel and 0.05M EDTA at pH 4.9 for metal-chel ated gel. Nonspecific glucose oxidase adsorption on/in the metal ion-chelat ed PVIm gel was investigated using 0.02M of phosphate buffer solution. The nonspecific GOx adsorption was determined to be about 18% for PVIm and 8% f or the metal ion-chelated PVIm gels. The ionic strength effect was investig ated both on PVIm and on the metal ion-chelated PVIm gels for the glucose o xidase adsorption. It was found that ionic strength was more effective on t he PVIm gel because of the electrostatic interaction between protonated gel and the deprotonated glucose oxidase side chain. (C) 2001 John Wiley & Son s, Inc.