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  • Küçük Resim
    Öğe
    Covalent immobilization of invertase on chemically activated poly (styrene-2-hydroxyethyl methacrylate) microbeads
    (Wiley, 2008) Altinok, Haydar; Aksoy, Serpil; Tumturk, Hayrettin; Hasirci, Nesrin
    A carrier for invertase enzyme was synthesized from styrene (S) and 2- hydroxyethyl methacrylate (HEMA) in the form of microbeads. These poly (styrene-2-hydroxyethyl methacrylate), P(S-HEMA) microbeads were activated by epichlorohydrin (ECH) treatment for covalent immobilization. The free and immobilized invertase were assayed in the hydrolysis of sucrose to glucose, and the obtained results were compared. The optimum pH was 4.5 for free and 5.5 for immobilized invertase. The optimum temperature of invertase shifted from 45C to 55C upon immobilization. For free and immobilized enzymes, kinetic parameters were calculated as 4.1 x 10(-3) mol L(-1)and 9.2 x 10(-3) mol L(-1)for K-m, and 6.6 x 10(-2) mol L-1 min(-1)and 4.1 x 10(-1) mol L-1 min(-1)for V-max, respectively. After 1 month of storage at 4C, free enzyme retained 36% of its initial activity, while for the ECH-activated P(S-HEMA) immobilized enzyme, P(S-HEMA)-E, this value was observed as 67%. In repeated batch use, i.e., 20 times in 3 days, 78% retention of the initial activity was observed for P(S-HEMA)-E system.
  • Küçük Resim
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    Effect of polycondensation reaction conditions on the properties of thermotropic liquid-crystalline copolyester
    (Taylor & Francis Inc, 2008) Yikici, Meryem; Yerlikaya, Zekeriya; Aksoy, Serpil; Altinok, Haydar
    In this study a range of wholly aromatic copolyesters based on kink m-acetoxybenzoic acid (m-ABA) monomer (33 mol%) and equimolar-linear p-acetoxybenzoic acid (p-ABA), hydroquinone diacetate (HQDA) and terephthalic acid (TPA) monomers (67 mol%) have been synthesized by melt polycondensation reaction process at 280 degrees C and 260 degrees C for different time intervals. Characterization of copolyesters were performed by solution viscosity measurement, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), hot-stage polarized light microscopy, proton-nuclear magnetic resonance analysis ((1)H-NMR). According to the results obtained, copolyesters showed thermotropic liquid crystalline behavior in an appropriate temperature range. The copolyesters were prepared in high yields. It was observed that the intrinsic viscosities of the copolyesters are increased regularly with increasing polymerization time and temperature. All the copolyesters were soluble in a trifluoroacetic acid/dichloromethane (30:70 v/v) except the copolyesters which were synthesized at 280 degrees C in 5h. According to the WAXD results; the degree of crystallinity of copolyesters were found to be between 5-15%. DSC and hot stage polarized light microscopy results showed that all the copolyesters are melt processable and a significant molecular interaction exist in a very broad temperature range (160 degrees C and 165 degrees C) in the nematic mesophase. The Tg values are increased with an increasing polycondensation reaction time and temperature and they were observed between 93-126 degrees C. Fibers prepared by a hand-spinning technique from the polymer melt exhibit well-developed fibrillar structure parallel to the fiber axis.
  • Küçük Resim
    Öğe
    Immobilization of glucose isomerase in surface-modified alginate gel beads
    (Wiley, 2008) Tumturk, Hayrettin; Demirel, Gokhan; Altinok, Haydar; Aksoy, Serpil; Hasirci, Nesrin
    In this study, glucose isomerase enzyme was entrapped into modified and nonmodified calcium alginate gel beads. Various characteristics of free and immobilized enzymes such as the optimum pH, temperature and dependence of activity on storage and operational stability were evaluated. The optimum pH and temperature of free and immobilized glucose isomerase were found to be the same values as 7.5 and 60C, respectively. For free and immobilized enzymes, kinetic parameters were calculated as 1.79 x 10(-2) and 8.27 x 10(-3) mol/L for Km, and 2.39 x 10(-3) and 6.03 x 10(-3) mol/L min for V-max, respectively. After 42 days of storage at 4C, free enzyme retained 56% of its initial activity, while for the immobilized enzyme, this value was observed as 86%. The immobilized samples were used repeatedly 22 times by retaining more than 85% of their initial activity.