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    Biosorption of mercury on magnetically modified yeast cells
    (Elsevier Science Bv, 2006) Yavuz, Handan; Denizli, Adil; Güngüneş, Hakan; Safarikova, Mirka; Safarik, Ivo
    Brewer's yeast (bottom yeast, Saccharomyces cerevisiae subsp. uvarum) cells were magnetically modified using water based magnetic fluid stabilized perchloric acid. The magnetically modified yeast cells were characterized by scanning electron microscopy (SEM) and electron spin resonance (ESR). Hg2+ biosorption-desorption properties of magnetically modified yeast cells from synthetic solutions were utilized in batch system. The biosorption process was fast; 80% of biosorption occured within 60 min and equilibrium was achieved at around 90 min. The maximum Hg2+ biosorption capacity was obtained to be 114.6 mg/g at 35 degrees C. The suitability of the Langmuir, Freundlich and Redlich-Peterson adsorption models to the equilibrium data was investigated for mercury-biosorbent system. The results were well fitted to the Langmuir isotherm. The applicability of two kinetic models including pseudo-first order and pseudo-second order model was estimated on the basis of comparative analysis of the corresponding rate parameters, equilibrium capacity and correlation coefficients. Results suggest that chemisorption processes could be the rate-limiting step in the biosorption process. The yeast biomass can be easily regenerated by 0.1 M HNO3 with higher effectiveness. Biosorption of heavy metal ions from artificial wastewater was also studied. The biosorption capacities are 29.9 mg/g for Cu2+, 76.2 mg/g for Hg2+, 14.1 mg/g for Ni2+ and 11.8 mg/g for Zn2+. (c) 2006 Elsevier B.V. All rights reserved.
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    Concanavalin a immobilized affinity adsorbents for reversible use in yeast invertase adsorption
    (Wiley-V C H Verlag Gmbh, 2004) Yavuz, Handan; Akgöl, Sinan; Arıca, Yakup; Denizli, Adil
    Concanavalin A (Con A) immobilized poly(2-hydroxyethyl methacrylate) (PHEMA) beads were investigated for specific adsorption of yeast invertase from aqueous solutions. PHEMA beads were prepared by a suspension polymerization technique with an average size of 150-200 mum, and activated by epichlorohydrin. Con A was then immobilized by covalent binding onto these beads. The maximum Con A immobilization was found to be 10 mg/g. The invertase-loading capability of the PHEMA/Con A beads was observed at pH 5.0. The values of the Michaelis constant K-m of invertase were significanly larger upon adsorption, indicating decreased smaller for the adsorbed invertase. Adsorption improved the pH stability of the enzyme activity was found to be quite stable in repeated experiments.