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    Biosorption of Hg(II) and Cd(II) from aqueous solutions: Comparison of biosorptive capacity of alginate and immobilized live and heat inactivated Phanerochaete chrysosporium
    (Elsevier Sci Ltd, 2002) Kacar, Y.; Arpa, C.; Tan, S.; Denizli, A.; Genc, O.; Arica, M.Y.
    Basidiospores of P. chryosporium were immobilized into Ca-alginate beads via entrapment, and the beads incubated for vegetation at 30 degreesC for 5 days. The alginate beads and both entrapped live and heat inactivated fungal mycelia of Phanerochaete chryosporium were used for the removal of Hg(II) and Cd(II) ions from aqueous solution in the concentrations range of 30-500 mg l (-1). The biosorption of Hg(II) and Cd(II) ions by the biosorbents increased as the initial concentration of Hg(II) and Cd(11) ions increased in the medium. A biosorption equilibrium was established in about 1 h and the adsorbed heavy metal ions did not change further with time. The effect of pH was also investigated and the maximum biosorption of Hg(11) and Cd(II) ions on all the tested biosorbents were obtained between pH 5.0 and 6.0. Temperature over the range 15-45 degreesC had no significant effect on the biosorption capacity. The equilibrium was well described by Langmuir and Freundlich biosorption isotherms. The alginate-fungus beads could be regenerated using 10 mM HCl, up to 97% recovery. The biosorbents were reused in three biosorption-desorption cycles with negligible decrease in biosorption capacity. (C) 2002 Elsevier Science Ltd. All rights reserved.
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    Covalent immobilization of lipase onto hydrophobic group incorporated poly(2-hydroxyethyl methacrylate) based hydrophilic membrane matrix
    (Elsevier Sci Ltd, 2002) Bayramoğlu, G.; Kacar, Y.; Denizli, A.; Arica, M.Y.
    In this study, a hydrophobic group containing monomer, 2-methacrylamidophenyalanine (MAPA) was prepared by using methacrylochloride and phenylalanine. Then, poly(2-hydroxyethyl methacrylate-co-methacrylamido-phenlyalanine) (pHEMA-MAPA) membranes were prepared by UV-initiated photopolymerization of HEMA and MAPA in the presence of an initiator alpha-alpha'-azobisisobutyronitrile (AIBN). The lipase was immobilized onto these membranes by covalent bonding through carbodiimide activation. The amount of enzyme loading on the membranes was increased as the MAPA ratio increased in the membrane structure. Immobilization improved the pH stability of the enzyme as well as its temperature stability. Thermal stability was found to increase with immobilization and at 60 degreesC the thermal stability constants were 1.1 x 10(-1) min for free enzyme and 1.2 x 10(-2) min for the immobilized enzyme. The immobilized enzyme activity was found to be quite stable in repeated experiments. (C) 2002 Elsevier Science Ltd. All rights reserved.
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    Immobilization of catalase via adsorption onto L-histidine grafted functional pHEMA based membrane
    (Elsevier Science Bv, 2001) Akgöl, S.; Kacar, Y.; Özkara, S.; Yavuz, H.; Denizli, A.; Arica, M.Y.
    Poly(2-hydroxyethylmethacrylate) (pHEMA) based flat sheet membrane was prepared by UV-initiated photopolymerization technique. The membrane was then grafted with L-histidine. Catalase immobilization onto the membrane from aqueous solutions containing different amounts of catalase at different pH was investigated in a batch system. The maximum catalase immobilization capacity of the pHEMA-histidine membrane was 86 mug cm(-2). The activity yield was decreased with the increase of the enzyme loading. It was observed that there was a significant change between V-max value of the free catalase and V-max value of the adsorbed catalase on the pHEMA-histidine membrane. The K-m value of the immobilized enzyme was higher 1.5 times than that of the free enzyme. Optimum operational temperature was 5 degreesC higher than that of the free enzyme and was significantly broader. It was observed that enzyme could be repeatedly adsorbed and desorbed without loss of adsorption capacity or enzyme activity. (C) 2001 Elsevier Science B.V. All rights reserved.