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    Newly Synthesized Multifunctional Biopolymer Coated Magnetic Core/Shell Fe3O4@Au Nanoparticles for Evaluation of L-asparaginase Immobilization
    (Springer/Plenum Publishers, 2023) Tarhan, Tuba; Dik, Gamze; Ulu, Ahmet; Tural, Bilsen; Tural, Servet; Ates, Burhan
    The immobilization strategy can promote greater enzyme utilization in applications by improving the overall stability and reusability of the enzyme. In this work, the L-asparaginase (L-ASNase) obtained from Escherichia coli was chosen as a model enzyme and immobilized onto the Fe3O4@Au-carboxymethyl chitosan (CMC) magnetic nanoparticles (MNPs) through adsorption. TEM, SEM, FT-IR, XRD, EDS, and TGA analyses were performed to examine the structure with and without L-ASNase. The yield of immobilized L-ASNase on Fe3O4@Au-CMC was found to be 68%. The biochemical properties such as optimum pH, optimum temperature, reusability, and thermal stability of the Fe3O4@Au-CMC/L-ASNase were comprehensively investigated. For instance, Fe3O4@Au-CMC/L-ASNase reached maximum activity at pH 7.0 and the optimum temperature was found to be 50 degrees C. The noticeably lower Ea value of the Fe3O4@Au-CMC/L-ASNase revealed the enhanced catalytic activity of this enzyme after immobilization. The Km and Vmax values were 3.27 +/- 0.48 mM, and 51.54 +/- 0.51 mu mol min(-1) for Fe3O4@Au-CMC/L-ASNase, respectively, which means good substrate affinity. The Fe3O4@Au-CMC/L-ASNase retained 65% of its initial activity even after 90 min at 60 degrees C. Moreover, it maintained more than 75% of its original activity after 10 cycles, indicating its excellent reusability. The results obtained suggested that this investigation highlights the use of MNPs as a support for the development of more economical and sustainable immobilized enzyme systems.
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    Rapid synthesis and characterization of maghemite nanoparticles
    (Amer Scientific Publishers, 2008) Tural, Bilsen; Oezenbas, Macit; Atalay, Selcuk; Volkan, Muervet
    Fe2O3-SiO2 nanocomposites were prepared by a sol-gel method using various evaporation surface to volume (S/V) ratios ranging from 0.03 to 0.2. The Fe2O3-SiO2 sols were gelated at various temperatures ranging from 50 degrees C to 70 degrees C, and subsequently they were calcined in air at 400 degrees C for 4 hours. The structure and the magnetic properties of the prepared Fe2O3-SiO2, nanocomposites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), and vibrating sample magnetometer (VSM) measurements. The gelation temperature of the Fe2O3-SiO2 sols influenced strongly the particle size and crystallinity of the maghemite nanoparticles. It was observed that the particle size of maghemite nanoparticles increased with the increasing of the gelation temperature of the sols, which may be due to the agglomeration of the maghemite particles at elevated temperatures inside the microporosity of the silica matrix during the gelation process, and the subsequent calcination of these gels at 400 degrees C resulted in the formation of large size iron oxide particles. Magnetization studies at temperatures of 10, 195, and 300 K showed superparamagnetic behavior for all the nanocomposites prepared using the evaporation surface to volume ratio (S/V) of 0.1, 0.2, 0.09, and 0.08. The saturation magnetization, Ms, values measured at 10 K were 5.5, 8.5, and 9.5 emu/g, for the samples gelated at 50, 60, and 70 degrees C, respectively. At the gelation temperature of 70 degrees C, gamma-Fe2O3 crystalline superparamagnetic nanoparticles with the particle size of 9 +/- 2 nm were formed in 12 hours for the samples prepared at the S/V ratio of 0.2.