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    ?-Amylase Immobilization on P(HEMA-co-PEGMA) Hydrogels: Preparation, Characterization, and Catalytic Investigation
    (Wiley-V C H Verlag Gmbh, 2021) Dogan, Demet; Ulu, Ahmet; Sel, Evren; Koytepe, Suleyman; Ates, Burhan
    The aims of this study are to synthesize and characterize poly (2-hydroxyethyl methacrylate-co-poly (ethylene glycol) methacrylate) (P(HEMA-co-PEG500MA)) structures containing polyethylene glycol (PEG) side groups and to investigate their possible use in alpha-amylase immobilization. For this purpose, P(HEMA-co-PEG500MA) copolymer structures are synthesized by using different monomer ratios. P(HEMA-co-PEG500MA) copolymer structures are confirmed by Fourier transform infrared spectroscopy (FTIR), and elemental analysis techniques. In addition, thermal, and morphological properties of the copolymers are investigated by thermal gravimetric analysis/differential scanning calorimetry, and scanning electron microscopy (SEM). Afterward, alpha-amylase from Aspergillus oryzae is immobilized on synthesized copolymer support by using physical interactions. The success of immobilization is elucidated via FTIR, SEM, and energy dispersive X-ray spectroscopy (EDX) methods. In addition, the influences of temperature, pH, storage time, and repeated uses on the activity of free and immobilized alpha-amylase are investigated. According to the outcomes, the immobilized alpha-amylase possesses a better pH and thermal resistance than the free one. Additionally, the immobilized alpha-amylase maintains about 53% of its original activity after eight reuses and it exhibits about 50% relative activity after 28 days of storage. In conclusion, the immobilized alpha-amylase can be utilized as a potential efficient catalyst to produce maltose from the hydrolysis of starch.
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    Dye removal by dead biomass of newly isolated Pleurotus ostreatus strain
    (Natl Inst Science Communication-Niscair, 2018) Dogan, Demet; Boran, Filiz; Kahraman, Sibel; Akmil-Basar, Canan; Yesilada, Ozfer
    Dead biomass prepared from newly isolated Pleurotus ostreatus strain was tested for their efficiency in removal of indigo carmine. The effects of operational parameters such as contact time, initial dye concentration, amount of biomass, initial pH and agitation rate on removal were examined. The dye removal increased rapidly during the first 60 minutes (87%) and remained nearly constant between 60 - 120 minutes of adsorption (87 - 90%). The removal of dye by dead biomass of newly isolated P. ostreatus was clearly dependent on the initial dye concentration of the solution and dye removal was reduced from 83% to 53% as concentration was increased from 100 to 500 mg/L indigo carmine. Results were analyzed by the Langmiur, Freundlich, Dubinin-Redushkevich (D-R), Temkin, Frumkin, Harkins-Jura, Halsey, Henderson isotherm using linearised correlation coefficient. The kinetics of adsorption of IC have been discussed using six kinetic models, i.e., the pseudo first order model, the pseudo second order model, the Elovich equation, the intraparticle diffusion model, the Bangham equation, the modified Freundlich equation. In order to determine the best fit isotherm and kinetic models, three error analysis methods of residual mean square error (RMSE), chi-square (X-2) statistic and the average percentage error (APE%) were used to evaluate the data.
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    Preparation and Characterization of Amino-Functionalized Zeolite/SiO2 Materials for Trypsin-Chymotrypsin Co-immobilization
    (Springer, 2021) Dogan, Demet; Sezer, Selda; Ulu, Ahmet; Koytepe, Suleyman; Ates, Burhan
    Inorganic supports have attracted increased attention in enzyme immobilization since they not only improve enzyme stability but also reduce the final cost of enzymatic reactions. Herein, we explored the suitability of the amino-functionalized zeolite/SiO2 materials to co-immobilize trypsin-chymotrypsin mixture. For this purpose, the trypsin-chymotrypsin mixture was co-immobilized on the amino-functionalized zeolite/SiO2 materials and the immobilization yield was 80.7 +/- 7.6%. The pre-support and its modification were characterized by several techniques. Besides, the charges of the materials were investigated by zeta potentials at pH 5.0. As expected, the zeta potentials shifted from - 24.4 to - 8.16 mV after amino functionalization. Following immobilization, whereas the optimum pH (9.0) was not changed, the optimum temperature shifted from 50 to 40 degrees C. On the other hand, the immobilized trypsin-chymotrypsin showed comparatively higher thermal stability and storage stability than the soluble trypsin-chymotrypsin. The kinetic parameters were also calculated, however, while no significant change was observed in V-max, K-m value increased, which means that the affinity of enzyme to the substrate decreased after immobilization. Most strikingly, the residual activity of immobilized trypsin-chymotrypsin was 58% after eight repeated cycles. In conclusion, the preliminary experiments inferred that the amino-functionalized zeolite/SiO2 particles can be suitable and helpful support for trypsin-chymotrypsin immobilization. Graphic
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    Preparation and Characterization of Amino-Functionalized Zeolite/SiO2 Materials for Trypsin-Chymotrypsin Co-immobilization (Apr, 10.1007/s10562-021-03636-2, 2021)
    (Springer, 2021) Dogan, Demet; Sezer, Selda; Ulu, Ahmet; Koytepe, Suleyman; Ates, Burhan
    [Abstract Not Available]
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    REMOVAL OF INDIGO CARMINE FROM AN AQUEOUS SOLUTION BY FUNGUS PLEUROTUS OSTREATUS
    (Polish Acad Sciences, Inst Environmental Engineering, 2012) Kahraman, Sibel; Kuru, Filiz; Dogan, Demet; Yesilada, Ozfer
    The role of fungi in the treatment of wastewater has been extensively researched. Many genera of fungi have been employed for the dye decolourization either in living or dead form. In this study, the removal of an acidic dye, Indigo Carmine (IC), from an aqueous solution by biosorption on dead fungus, Pleurotus ostreatus, was investigated. The effects of contact time, initial dye concentration, amount of dead biomass, agitation rate and initial pH on dye removal have been determined. Experimental results show that an increase in the amount of dead biomass positively affected the dye removal. The highest removal was obtained at 150-200 rpm. Slightly lower removing activities were found at lower agitation rates. The dye adsorption efficiency was not affected by pH except minor variation in the pH of 2-8. Color removal was observed to occur rapidly within 60 minutes. The removal of dye by dead biomass of ostreatus was clearly dependent on the initial dye concentration of the solution. Dye removal was reduced from 93% to 64% as concentration was increased from 50 to 500 mg/L Indigo Carmine. This study showed that it was possible to remove textile dyes by dead biomass of P ostreatus.