Metal ion promoted hydrogels for bovine serum albumin adsorption: Cu(II) and Co(II) chelated poly[(N-vinylimidazole)-maleic acid].

Poly[(N-vinylimidazole)-maleic acid] (poly(VIm-MA)), copolymeric hydrogels were prepared by gamma-irradiating ternary mixtures of N-vinylimidazole-maleic acid-water in a (60)Co-gamma source. Cu(II) and Co(II) ions were chelated within the gels at pH=5.0. The maximum adsorption capacity of the gels were 3.71 mmol/g dry gel for Cu(II) and 1.25 mmol/g dry gel for Co(II) at pH=5.0. The swelling ratios of the gels were 1200% for poly(VIm-MA), 60 and 45% for Cu(II) and Co(II)-chelated poly(VIm-MA) gels at pH=5.0 in acetate buffer solution. These affinity gels with different swelling ratios for plain poly(VIm-MA), Cu(II)-, and Co(II)-chelated poly(VIm-MA), in acetate and phosphate buffers were used in the bovine serum albumin (BSA) adsorption/desorption studies in batch reactor. The maximum BSA adsorption capacities of the gels were 0.38 g/g dry gel for plain, 0.88 g/g dry gel for Cu(II)-chelated poly(VIm-MA) and 1.05 g/g dry gel for Co(II)-chelated poly(VIm-MA) gels. Adsorption capacity of BSA by the gels was reduced dramatically by increasing the ionic strength adjusted with NaCl. More than 95% of BSA were desorbed in 10 h in desorption medium containing 0.1M of EDTA for metal ion-chelated gels at pH=4.7.

Enhancement of stability of glucose oxidase by immobilization onto metal ion-chelated poly(N-vinyl imidazole) hydrogels.

Poly(N-vinylimidazole), PVIm, gels were prepared by gamma-irradiation polymerization of N-vinylimidazole in aqueous solutions as an affinity gel for glucose oxidase (GOx). These affinity gels with a water swelling ratio of 1800% for plain polymeric gel and between 30-80% for Cu(II) and Co(II)-chelated gels at pH 6.0 in phosphate buffer were used in the GOx adsorption studies. Maximum metal ion adsorption capacity of these hydrogels was found to be 3.64 mmol/g dry gel for Cu(II) and 1.72 mmol/g dry gel for Co(II) leading to GOx adsorption capacities of 343 and 528 mg enzyme/g dry gel, respectively, as compared to 228 mg for the plain dry PVIm gel. Activity studies were carried out using plain and the metal ion-chelated form of this hydrogel to investigate the stability and retained activity of the GOx in different buffer solutions and at different temperatures. Activity of the enzyme, either in free or immobilized form on the gel, decreased dramatically in acetate buffer solutions. In phosphate buffer solution, however, stability of enzyme has been found to be significantly high reaching 90% retained activity at the end of a 40-day period at 4 degrees C for Co(II) chelated systems. After immobilization of the enzyme onto metal-chelated hydrogel, the thermal stability of enzyme was enhanced significantly showing 23% activity, even at 75 degrees C.

Complex formation of linear poly(methacrylic acid) with uranyl ions in aqueous solutions.

The complex formation of uranyl ions (UO(2+)2) with poly(methacrylic acid) (PMAA) was investigated by potentiometric, conductometric, UV-visible, luminescence and FTIR spectroscopic, and thermal analysis methods. The stoichiometric ratio at complexation between polymer and uranyl ions was found to be equal to 2 polymer base units per uranyl ion. FTIR spectra of the PMAA-UO(2+)2 complex confirmed incorporation of metal ions into the polymer and showed that the electrostatic interactions play a major role in complexation. An increase of emission intensity in luminescence spectra of uranyl ions suggests influence of conformation peculiarity of the poly(methacrylic acid) chain. The thermal degradation of polycomplex starts at lower temperature as compared to pristine PMAA that is due to the lower thermal stability of PMAA-UO(2+)2 complex.