Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 7Citation - Scopus: 6Thickness Gradient in Polymer Coating by Reactive Layer-By Assembly on Solid Substrate(Amer Chemical Soc, 2023) Özenler, Sezer; Alkan, Ali Ata; Gunay, Ufuk Saim; Dağlar, Özgün; Durmaz, Hakan; Yıldız, Ümit HakanThe study describes a simple yet robust methodology for forming gradients in polymer coatings with nanometer-thickness precision. The thickness gradients of 0-20 nm in the coating are obtained by a reactive layer-by-layer assembly of polyester and polyethylenimine on gold substrates. Three parameters are important in forming thickness gradients: (i) the incubation time, (ii) the incubation concentration of the polymer solutions, and (iii) the tilt angle of the gold substrate during the dipping process. After examining these parameters, the characterization of the anisotropic surface obtained under the best conditions is presented in the manuscript. The thickness profile and nanomechanical characterization of the polymer gradients are characterized by atomic force microscopy. The roughness analysis has demonstrated that the coating exhibited decreasing roughness with increasing thickness. On the other hand, Young's moduli of the thin and thick coatings are 0.50 and 1.4 MPa, respectively, which assured an increase in mechanical stability with increasing coating thickness. Angle-dependent infrared spectroscopy reveals that the C-O-C ester groups of the polyesters exhibit a perpendicular orientation to the surface, while the C=C groups are parallel to the surface. The surface properties of the polymer gradients are explored by fluorescence microscopy, proving that the dye's fluorescence intensity increases as the coating thickness increases. The significant benefit of the suggested methodology is that it promises thickness control of gradients in the coating as a consequence of the fast reaction kinetics between layers and the reaction time.Article Citation - WoS: 4Citation - Scopus: 5Continuous Treatment of Diethyl Hexyl and Dibutyl Phthalates by Fixed-Bed Reactor: Comparison of Two Esterase Bionanocomposites(Elsevier, 2022) Sanroman, Maria Angeles; Balcı, Esin; Rosales, Emilio; Pazos, Marta; Sofuoğlu, AysunThe removal of Diethyl hexyl phthalate (DEHP) and Dibutyl phthalate (DBP) is of great importance due to their potential adverse effects on the environment and human health. In this study, two bionanocomposites prepared by immobilization of Bacillus subtilis esterase by crosslinking to halloysite and supported in chitosan and alginate beads were studied and proposed as a green approach. The esterase immobilization was confirmed by physical-chemical characterization. Bionanocomposite using chitosan showed the best degradation levels in batch tests attaining complete degradation of DBP and around 90% of DEHP. To determine the operational stability and efficiency of the system, two fixed bed reactors filled with both bionanocomposites were carried out operating in continuous mode. Chitosan based bionanocomposite showed the best performance being able to completely remove DBP and more than 85% of DEHP at the different flowrates. These results proved the potential of these synthesized bionanocomposites to effectively remove Phthalic Acid Esters.Article Citation - WoS: 3Citation - Scopus: 4Enhanced Thermostability of the Immobilized Thermoalkalophilic Esterase Onto Magnetic-Cornstarch Nanoparticle(Wiley, 2022) Öz, Yasin; Sürmeli, Yusuf; Şanlı Mohamed, GülşahThe immobilization of the biocatalysts onto magnetic nanoparticles has been extensively applied as the external magnetic field facilitates the enzyme recovery from the reaction mixture. In the present study, glutaraldehyde-modified magnetite-cornstarch nanoparticles (MCNs) were successfully synthesized, elaborately characterized by ZetaSizer and surface-enhanced Raman spectroscopy, and used for the immobilization of a thermoalkalophilic esterase from Geobacillus sp. The optimal immobilization conditions were obtained at 65 degrees C, 2:3 molar ratios of Fe2+:Fe3+, and 1 g cornstarch resulted in approximately 90 nm magnetic particles in size. Also, immobilization yield and immobilization efficiency of the esterase were found as 74% and 82%, respectively. Scanning electron microscopy micrographs showed that MCNs were uniform, spherical in shape, and well dispersed and esterase immobilized MCNs displayed similar morphology as free MCNs. The maximum activity of free and immobilized esterase was obtained at 65 degrees C and pH 9. Immobilization onto glutaraldehyde-modified MCNs significantly enhanced the esterase thermostability. Additionally, the immobilized esterase kept its residual activity of 75% after three sequential cycles, suggesting that it has favorable operational stability.Article Citation - WoS: 7Citation - Scopus: 8Thermoalkalophilic Recombinant Esterase Entrapment in Chitosan/Calcium Beads and Its Characterization(Wiley, 2021) Tercan, Cisem; Sürmeli, Yusuf; Şanlı Mohamed, GülşahBACKGROUND Esterases (EC 3.1.1.1), a class of hydrolases, degrade the ester bonds of lipids into alcohol and carboxylic acids and synthesize carboxylic ester bonds. They are used in a variety of biotechnological, industrial, environmental, and pharmaceutical applications due to their many valuable properties. Particularly, extremophilic esterases with many superior properties are of great interest for various reactions. Immobilization of enzymes may provide some advantages over free enzymes not only to improve the properties of enzymes but also to increase the reusability of biocatalyst in industrial applications. Therefore, many different immobilization applications for enzymes have been reported in various studies. To our knowledge, a thermophilic esterase has not so far been immobilized by entrapment using chitosan/calcium/alginate-blended beads. Here, we reported the immobilization of thermoalkalophilic recombinant esterase by entrapment using chitosan/calcium/alginate-blended beads, and then the entrapped esterase was characterized biochemically in details. RESULTS In the present study, a thermophilic recombinant esterase was immobilized by entrapment in chitosan/calcium/alginate-blended beads for the first time. The 0.5 mg mL(-1) purified recombinant esterase was entrapped in 1% chitosan, 2% alginate, and 0.7 M CaCl2 blended beads. The results showed that immobilization yield and entrapment efficiency of the entrapped esterase were 69.5% and 80.4%, respectively. SEM micrograph showed that the surface of the beads resembled a mesh and very compact structures. Chitosan/calcium/alginate-blended beads exhibited an 18.8% swelling ratio and had a moderate porous structure. The entrapment technique highly enhanced the thermostability of the esterase and shifted its optimum temperature from 65 to 80 degrees C. The immobilized esterase was very stable in a wide range of pH (8.5-11) displaying maximum activity at pH 9. ZnCl2 slightly increased the activity of immobilized esterase whereas several metal ions reduced the enzyme activity. When the enzyme was immobilized in chitosan/calcium/alginate-blended beads, its K-m increased about 2 times and V-max value decreased almost 1.5 times. Immobilization allowed repeated uses of the esterase having good operational stability in a continuous process. CONCLUSION The results revealed that the immobilization of a thermophilic recombinant esterase by entrapment in chitosan/calcium/alginate-blended beads exhibited considerably better compared to other immobilization processes with various entrapment strategies. (c) 2021 Society of Chemical Industry (SCI).Article Citation - WoS: 49Citation - Scopus: 55Immobilization of Thermoalkalophilic Recombinant Esterase Enzyme by Entrapment in Silicate Coated Ca-Alginate Beads and Its Hydrolytic Properties(Elsevier Ltd., 2012) Gülay, Seçkin; Şanlı Mohamed, GülşahThermoalkalophilic esterase enzyme from Balçova (Agamemnon) geothermal site were aimed to be immobilized effectively via a simple and cost-effective protocol in silicate coated Calcium alginate (Ca-alginate) beads by entrapment. The optimal immobilization conditions of enzyme in Ca-alginate beads were investigated and obtained with 2% alginate using 0.5mg/ml enzyme and 0.7M CaCl 2 solution. In order to prevent enzyme from leaking out of the gel beads, Ca-alginate beads were then coated with silicate. Enzyme loading efficiency and immobilization yield for silicate coated beads was determined as 98.1% and 71.27%, respectively and compared with non-coated ones which were 68.5% and 45.80%, respectively. Surface morphologies, structure and elemental analysis of both silicate coated and non-coated alginate beads were also compared using Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscope (SEM) equipped with Energy-dispersive X-ray spectroscopy (EDX). Moreover, silicate coated alginate beads enhanced reusability of esterase in continuous processes compared to non-coated beads. The hydrolytic properties of free and immobilized enzyme in terms of storage and thermal stability as well as the effects of the temperature and pH were determined. It was observed that operational, thermal and storage stabilities of the esterase were increased with immobilization.Article Citation - WoS: 15Citation - Scopus: 21Preparation, Characterization and Optimization of Chitosan Nanoparticles as Carrier for Immobilization of Thermophilic Recombinant Esterase(Taylor and Francis Ltd., 2011) İlgü, Hüseyin; Turan, Taylan; Şanlı Mohamed, GülşahImmobilization of biologically important molecules on myriad nano-sized materials has attracted great attention. Through this study, thermophilic esterase enzyme was obtained using recombinant DNA technology and purified applying one-step His-Select HF nickel affinity gel. The synthesis of chitosan was achieved from chitin by deacetylation process and degree of deacetylation was calculated as 89% by elemental analysis. Chitosan nanoparticles were prepared based on the ionic gelation of chitosan with tripolyphosphate anions. The physicochemical properties of the chitosan and chitosan nanoparticles were determined by several methods including SEM (Scanning Electron Microscopy), FT-IR (Fourier Transform Infrared Spectroscopy) and DLS (Dynamic Light Scattering). The morphology of chitosan nanoparticles was spherical and the nanospheres' average diameter was 75.3 nm. The purified recombinant esterase was immobilized efficiently by physical adsorption onto chitosan nanoparticles and effects of various immobilization conditions were investigated in details to develope highly cost-effective esterase as a biocatalyst to be utilized in biotechnological purposes. The optimal conditions of immobilization were determined as follows; 1.0 mg/mL of recombinant esterase was immobilized on 1.5 mg chitosan nanoparticles for 30 min at 60C, pH 7.0 under 100 rpm stirring speed. Under optimized conditions, immobilized recombinant esterase activity yield was 88.5%. The physicochemical characterization of enzyme immobilized chitosan nanoparticles was analyzed by SEM, FT-IR and AFM (Atomic Force Microscopy).Article Citation - WoS: 62Citation - Scopus: 67Thermal Stability of Carbonic Anhydrase Immobilized Within Polyurethane Foam(John Wiley and Sons Inc., 2010) Kanbar, Bora; Özdemir, EkremThermal stability of carbonic anhydrase (CA) immobilized within polyurethane (PU) foam was investigated. The catalytic activity of the enzyme was estimated by using p-nitrophenyl acetate (p-NPA) as the substrate in tris buffer containing 10% acetonitrile. The immobilized CA was stable during the repeatable washings and stability tests over 45 days stored in tris buffer at ambient conditions indicating that the CA was covalently attached to the polyurethane (PU) foam by crosslinking. The immobilized CA was found to be 98% stable below 50°C, whereas a drastic decrease was seen at temperatures between 50 and 60°C. The optimum temperature for the immobilized CA was found to be 45°C and it lost its activity completely at 60°C. Thermal deactivation energies for the free and immobilized CA were estimated to be 29 and 86 kcal/mol, respectively. The association of unfolded CA with the polymeric backbone chains of the PU foam was also addressed. It was concluded that the immobilized CA was highly stable at temperatures less than 50°C and could be used in biomimetic CO sequestration processes. © 2010 American Institute of Chemical EngineersArticle Citation - WoS: 23Citation - Scopus: 26Partial Purification and Preparation of Bovine Lactoperoxidase and Characterization of Kinetic Properties of Its Immobilized Form Incorporated Into Cross-Linked Alginate Films(Elsevier Ltd., 2007) Mecitoğlu, Çiğdem; Yemenicioğlu, AhmetLactoperoxidase (LPS), purified directly from bovine rennet whey by Toyopearl-SP cation-exchange chromatography and lyophilized by using dextran as supporting material, maintained almost 70 and 60% of its activity after almost 2 and 5 months storage at -18 °C, respectively. Incorporation of the prepared LPS into alginate films between 0.08 and 0.69 mg/cm2 (516-4325 U/cm2) caused the immobilization of most of the enzyme and gave films with LPS activity between 0.05 and 2.8 U/cm2, determined in the presence of 8 μM H2O2. Between 2 and 24 μM H2O2 concentrations, a two-fold increase in H2O2 concentration caused 1.5-2.5-fold increase in LPS activity of films incorporated with 0.24-0.28 mg/cm2 (1200 U/cm2) LPS. The Q10 and Ea of immobilized enzyme activity between 4 and 16 °C were 1.69 and 34.6 kJ/mol, respectively. However, in the 16-30 °C range, the temperature change had almost no effect on LPS activity of films. The optimal activity of immobilized LPS was observed at pH 6.0, but the enzyme maintained 30-85% of its activity between pH 3.0 and 7.0. The immobilized LPS also had a high stability between pH 4.0 and 6.0. The results of this study showed the good potential of LPS-incorporated alginate films in forming a natural antimicrobial mechanism in different foods.