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Öğe Covalent immobilization of invertase on chemically activated poly (styrene-2-hydroxyethyl methacrylate) microbeads(Wiley, 2008) Altinok, Haydar; Aksoy, Serpil; Tumturk, Hayrettin; Hasirci, NesrinA 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.Öğe Effect of polycondensation reaction conditions on the properties of thermotropic liquid-crystalline copolyester(Taylor & Francis Inc, 2008) Yikici, Meryem; Yerlikaya, Zekeriya; Aksoy, Serpil; Altinok, HaydarIn 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.Öğe Immobilization of glucose isomerase in surface-modified alginate gel beads(Wiley, 2008) Tumturk, Hayrettin; Demirel, Gokhan; Altinok, Haydar; Aksoy, Serpil; Hasirci, NesrinIn 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.Öğe Immobilization of laccase in κ-carrageenan based semi-interpenetrating polymer networks(Elsevier Science Bv, 2010) Makas, Y. Gizem; Kalkan, N. Ayça; Aksoy, Serpil; Altınok, Haydar; Hasırcı, NesrinLaccase enzyme (L) was immobilized by entrapment into semi-interpenetrating polymer networks (semi-IPNs) prepared from kappa-carrageenan with either poly(acrylamide-acrylic acid) [P(AAm-AA)/kappa-car] or poly(acrylamide-itaconic acid) [P(AAm-IA)/kappa-car]. For both systems, immobilized enzymes achieved the same optimum values observed for free enzyme (pH = 5.0 and T = 40 degrees C), except for P(AAm-IA)/kappa-car system there was a shift to 5.5 in optimum pH value. At the end of 42 days of storage immobilized enzymes retained more than 80% of their original activities while the retained activities of both systems after 10 uses in batch type application were found to be higher than 50%. K-m values were calculated as 2.52 x 10(-2) mM and 1.08 x 10(-2) mM and V-max values were found as 6.8 x 10(-3) mM min(-1) and 4.4 x 10(-3) mM min(-1), for P(AAm-AA)/kappa-car-L and P(AAm-IA)/kappa-car-L, respectively. When methyl orange containing solutions (10 mg/L) were treated with the immobilized laccases (68.2 U), enzymatic decolorization of methyl orange in 6 h was achieved to the level of 35% for both systems. Supplementing the reaction medium with ABTS as the redox mediator increased this value to about 70%. These initial results show that, laccase containing semi-IPNs can find some applications in decolorization of the industrial wastes. (C) 2010 Elsevier B.V. All rights reserved.Öğe Semi-interpenetrating polymer networks (semi-IPNs) for entrapment of laccase and their use in Acid Orange 52 decolorization(Elsevier Sci Ltd, 2009) Yamak, Özgür; Kalkan, N. Ayça; Aksoy, Serpil; Altınok, Haydar; Hasırcı, NesrinLaccase enzyme (L) from Trametes versicolor was entrapped in three hydrogel structures namely poly(acrylamide-N-isopropylacrylamide), P(AAm-NIPA), and semi-interpenetrating networks of poly(-acrylamide)/alginate, P(AAm)/Alg, and poly(acrylamide-N-isopropylacrylamide)/alginate, P(AAm-NIPA)/Alg. The optimum temperatures for free and all immobilized systems were found to be 40 degrees C. For free and immobilized laccase systems of P(AAm-NIPA)-L, P(AAm)/Alg-L and P(AAm-NIPA)/Alg-L, K-m values were found to be 6.7 x 10(-3), 8.8 x 10(-2), 5.5 x 10(-2) and 1,8 x 10(-2) mM: V-max values were calculated as 1.8 x 10(-3). 2.5 x 10(-2), 1.5 x 10(-2) and 6.1 x 10(-3) mM min(-1), respectively. For free and the same immobilized systems, the enzymes retained 42%, 91%. 79% and 86% of their initial activities at the end of 56 days of storage. After using the mentioned immobilized systems repeatedly 10 times, they retained 77%, 71% and 84% of their original activities, respectively. For free and the same immobilized systems, decolorization of Acid Orange 52 (AO52) in 6 h were found to be 63%, 50%, 48% and 66%, respectively. Addition of 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid), ABTS, into the assay medium increased these values LIP to 73%, 73%, 74% and 75%, respectively. (C) 2008 Elsevier Ltd. All rights reserved.Öğe Thermal and morphological properties of thermotropic liquid-crystalline copolyesters containing poly(ethylene terephthalate), 4-hydroxyphenylacetic acid and main-chain rigid aromatic units(Wiley, 2010) Babacan, Volkan; Aksoy, Serpil; Yerlikaya, Zekeriya; Altınok, HaydarThermotropic liquid-crystalline polymers (TLCPs) have aroused considerable interest due to their attractive properties as high-performance materials. Significant research attention has been devoted to investigating the relationship among monomer structures, syntheses and end-use properties of TLCPs. The study reported here concerns the preparation, characterization and melt spinning of novel copolyesters containing two different flexible units together with two different aromatic units in the polymer chains. A range of copolyesters based on p-hydroxybenzoic acid (p-HBA), m-hydroxybenzoic acid, p-hydroxyphenylacetic acid and poly(ethylene terephthalate) were synthesized. The liquid crystallinity, thermal properties and degrees of crystallinity of these copolyesters were investigated using hot-stage polarized light microscopy, differential scanning calorimetry, thermogravimetry and wide-angle X-ray diffraction. Copolyester fibres were characterized using scanning electron microscopy. The copolyesters were melt-processable, thermally stable and could be processed above their melting temperatures without degradation. The degree of crystal structure was found to depend upon the content of p-HBA. The fibres prepared showed that polymer chains had a well-developed fibrillar structure. Novel TLCPs containing flexible units in the main chain were synthesized and characterized. Copolyesters containing p-HBA units ranging from 55 to 70 mol% exhibited phase-separated liquid-crystalline morphology, appropriate melting temperatures and high thermal stability for melt processing. (C) 2010 Society of Chemical IndustryÖğe Thermal properties and crystallinity of thermotropic liquid crystalline copolyesters prepared from poly(ethylene terephtalate) (PET) and rigid aromatic units(Taylor & Francis Inc, 2007) Tan, Abdullah; Altinok, Eaydar; Yerlikaya, Zekeriya; Aksoy, SerpilA series of copolyesters were synthesized by rnelt-polycondensation reaction of poly(ethylene terephtalate) (PET) with various proportions of equimolar compositions of p-acetoxybenzoic acid (p-ABA), hydroquinone diacetate (HQDA) and terephtalic acid (TPA). Viscosity, liquid crystallinity, thermal properties, degree of crystallinity and thermal stabilitiy of these copolyesters were investigated by Ubbelohde viscometer, hot-stage polarized light microscopy (PLM), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and thermogravimetric analysis,TGA), respectively. On the basis of viscosity measurement, it was observed that intrinsic viscosity values of the copolyesters are increased regularly with increasing amounts of aromatic units (p-ABA, HQDA and TPA) in the polymer chain. Thermotropic liquid crystalline behavior was observed in the copolyesters containing over 50 mol% of rigid p-ABA/HQDA/TPA aromatic units. DSC analysis of the anisotropic copolyesters revealed broad and weak endotherms associated with the nematic phases, and the melting temperatures were found to be in the processable region. As the mol% of PET in the polymer chain increased, the specific enthalpies of fusion and the degree of crystallinity of the copolyesters were also increased regularly.
