Yazar "Ozyilmaz, Gul" seçeneğine göre listele
Listeleniyor 1 - 15 / 15
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Characterization of extracellular esterase and lipase activities from five halophilic archaeal strains(Springer Heidelberg, 2009) Ozcan, Birgul; Ozyilmaz, Gul; Cokmus, Cumhur; Caliskan, MahmutA total of 118 halophilic archaeal collection of strains were screened for lipolytic activity and 18 of them were found positive on Rhodamine agar plates. The selected five isolates were further characterized to determine their optimum esterase and lipase activities at various ranges of salt, temperature and pH. The esterase and lipase activities were determined by the hydrolysis of pNPB and pNPP, respectively. The maximum hydrolytic activities were found in the supernatants of the isolates grown at complex medium with 25% NaCl and 1% gum Arabic. The highest esterase activity was obtained at pH 8-8.5, temperature 60-65A degrees C and NaCl 3-4.5 M. The same parameters for the highest lipase activities were found to be pH 8, temperature 45-65A degrees C and NaCl 3.5-4 M. These results indicate the presence of salt-dependent and temperature-tolerant lipolytic enzymes from halophilic archaeal strains. Kinetic parameters were determined according to Lineweaver-Burk plot. The KM and V (max) values were lower for pNPP hydrolysis than those for pNPB hydrolysis. The results point that the isolates have higher esterase activity comparing to lipase activity.Öğe Comparison of the performance of entrapped and covalently immobilized lipase in the synthesis of pear flavor(Walter De Gruyter Gmbh, 2017) Ozyilmaz, Gul; Yagiz, EsraIntroduction: Although aroma esters are produced mostly by a chemical method that requires the use of aggressive chemical catalysts, enzymatic esterification has been very favored during previous two decades. The main aim of this study was to investigate the commercially important pear flavor, hexyl acetate (HAc), by the catalysis of immobilized lipase samples and to optimize the immobilization and operational conditions in detail. Methods: Lipases from Candida rugosa (CRL) and porcine pancreas (PPL) were immobilized using biodegradable polysaccharides, by entrapment in calcium alginate/chitosan composite gel (CRLCa-Alg/Chi and PPLCa-Alg/Chi) and by covalent binding onto the chitosan (CRLChi and PPLChi) carrier. Results: Among the several organic media, the highest esterification activites were observed in heptane. HAc yield decreased when substrate concentrations were higher than 50 or 75 mM. Yield increased with increase in reaction time up to the 5th hour in the batch type reactor while it increased during the 8 h reaction time for fixed bed reactors with lower yields. Discussion and conclusions: As well as synthesis conditions, immobilization parameters also affected HAc productivity. The amount of water in the microenvironment of lipase is so important not only for gaining its active conformation but only for the reaction direction.Öğe Different copolymer films on ZnFeCo particles: Synthesis and anticorrosion properties(Elsevier, 2014) Ozyilmaz, A. Tuncay; Avsar, Busra; Ozyilmaz, Gul; Karahan, I. Hakki; Camurcu, Taskin; Colak, FatmaZinc-iron-cobalt (ZnFeCo) particles were electrochemically deposited on carbon steel (CS) electrode applying current of 3 mA with chronopotentiometry technique. ZnFeCo particles had homogenous, smooth with prismatic structure. It was shown that the ZnFeCo particles exhibited important barrier effect on CS substrate. Poly(aniline-co-o-anisidine), poly(aniline-co-pyrrole), poly(aniline-co-N-methylpyrrole) and poly(o-anisidine-co-pyrrole) copolymer films were obtained on CS/ZnFeCo electrode. Evaluation of anticorrosion performance of copolymer coatings in 3.5% NaCl solution was investigated by using AC impedance spectroscopy (EIS) technique, anodic polarization and the E-OCP-time curves. Copolymer films exhibited significant physical barrier behavior on ZnFeCo plated carbon steel, in longer exposure time. (C) 2014 Elsevier B.V. All rights reserved.Öğe The effect of spacer arm on hydrolytic and synthetic activity of Candida rugosa lipase immobilized on silica gel(Elsevier Science Bv, 2009) Ozyilmaz, GulCandida rugosa lipase was covalently immobilized onto silica gel in two different ways: via glutaraldehyde (L-GAL) and via hydrophobic spacer arm (1,6 diamino hexane) (L-SA). Free lipase, L-GAL and L-SA were used to investigate the hydrolysis of two different substrates, namely p-nitrophenyl palmytate (pNPP) and p-nitrophenyl acetate (pNPA), both in aqueous medium. In addition, these lipase samples were used to synthesize the pNPP from p-nitrophenol (pNP) and palmytic acid (PA) and pNPA from pNP and acetic acid (AA), both in hexane medium. Hydrolytic and synthetic activities of L-SA were higher than those of free lipase and LGAL, Synthetic activities of free lipase, LGAL and LSA for pNPA in the presence of pNP and AA within hexane medium were higher than those of hydrolytic activities for pNPA in aqueous medium. The same tendency was also observed with pNPP. The effects of pH and temperature on hydrolytic and synthetic activities were investigated for all lipase preparations. Operational stability was the highest for L-GAL, and L-SA when these enzymes were used for pNPP synthesis and in hexane medium, after 100 repeated uses, 68% and 51% of initial activities remained, respectively, at the end of 100 repeated cycles. Free lipase lost all of its activity within 15 and 20 days when stored at 25 degrees C and 5 degrees C, respectively. However. L-GAL showed 54% and 70% of initial activity at the end of 60 storage days at 25 degrees C and 5 degrees C, respectively. while these values were observed as 36% and 60% for L-SA. (C) 2008 Elsevier B.V. All rights reserved.Öğe Electrochemical synthesis of polyaniline films on zinc-cobalt alloy deposited carbon steel surface in sodium oxalate(Elsevier Science Sa, 2014) Ozyilmaz, A. Tuncay; Akdag, Abdurrahman; Karahan, I. Hakki; Ozyilmaz, GulPolyaniline (PANI) coatings were electropolymerized on zinc-cobalt alloy deposited carbon steel (CS/ZnCo) electrode from an aqueous sodium oxalate solution using three different scan rates in cyclic voltammetric technique. Scanning electron microscopy (SEM) was used to analyze the surface morphology of the polymer film. The SEM images showed that the increase in scan rate induced an increase in grain size of the PANI film. The corrosion behavior of CS/ZnCo electrodes with and without PANI film in 3.5% NaCl solution were investigated through electrochemical impedance spectroscopy (EIS) and anodic polarization studies. The results of the study showed that the PANI coatings provided significant and effective protection for the CS/ZnCo electrode, in preventing corrosion. In addition, the PANI film that was synthesized at a high scan rate, exhibited the best anti-corrosive performance due to the formation of protective oxide layers through its catalytic efficiency. (C) 2014 Elsevier B.V. All rights reserved.Öğe The Formation of Passive Layers on Zinc Based Platings(Slovensko Kemijsko Drustvo, 2016) Ozyilmaz, Ali Tuncay; Ozyilmaz, Gul; Karahan, Ismail HakkiZinc-iron (ZnFe) and zinc-iron-cobalt (ZnFeCo) platings were achieved on carbon steel applying 3 mA current values. Then, oxalate (OX) and tartrate (Tart) passive layers obtained in sodium oxalate and sodium tartrate medium were formed on carbon steel, ZnFe and ZnFeCo plated carbon steel. SEM images showed that the passive layers on CS, CS/ZnFe and CS/ZnFeCo electrodes exhibited different crystal structures. Corrosion tests revealed that the ZnFeCo particles provided a significant barrier efficiency on CS layer when compared with ZnFe alloy plating. Furthermore, OX layers on ZnFe and ZnFeCo plated carbon steel electrodes exhibited better physical barrier behavior on than those of Tart layers in longer periodsÖğe Heavy metal bioaccumulation, oxidative stress and genotoxicity in African catfishClarias gariepinusfrom Orontes river(Springer, 2020) Turan, Funda; Eken, Meltem; Ozyilmaz, Gul; Karan, Serpil; Uluca, HalukOne of the major problems affecting the ecosystem health is the exposure of heavy metals due to anthropogenic activities. These exposures may induce toxiogenetic damage and carcinogenesis in aquatic organism. DNA damage biomarkers for fish species detect genotoxic parameters for ecological risk assessment. In the present study, the effect of heavy metals (Cr, Cd, Cu, Fe and Mn) on DNA damage and oxidative stress ofClarias gariepinuswas examined by Comet assay at Reference site and two different sampling sites of the Orontes River. Moreover, the relationship between DNA damage and physiological response to oxidative stress caused inC. gariepinuswas investigated by sampling seasonal water and fish samples for one year. In this study, Cr, Cd and Cu in water column of Orontes River and the concentrations of Fe and Mn in liver tissue ofC. gariepinuswere highly exceed the maximum permissible limit set by EPA (1999,2016) WHO (1989) and TEG (2012) that can cause adverse effects on environment health. SOD activities in liver tissues were significantly higher than those in muscle tissues. SOD, CAT activity and MDA levels of both Site 1 and Site 2 at Orontes River were higher than those of the Reference site. In result of the COMET analysis, the highest levels of DNA damage were found at gill and liver tissues in Site 2 (17.746 +/- 1.072% T-DNA; 16.014 +/- 0.710% T-DNA respectively) at Orontes river. A higher level of DNA damage in gill cells compared to liver cells was observed in all regions of the Orontes River. In Principal component analysis (PCA), the heavy metals Cd, Cr and Cu (in the water column) and MDA in liver and muscle revealed strong contribution to the observed DNA damage that were scattered opposite to each other's along the principal components. Moreover, correlations between parameters revealed a positive significant relationship between Cd, Cr and Cu in water and DNA damage levels inC. gariepinus. Pearson correlation analysis detected a positive relationship between MDA, CAT and SOD and DNA damage levels in African catfish. Consequently, this study exposed genotoxic damage and oxidative stress ofC. gariepinusdue to metal pollution in Orontes River and lead to the better understanding of genotoxicty, oxidative stress and heavy metal relationships.Öğe The influence of polyaniline (PANI) coating on corrosion behaviour of zinc-cobalt coated carbon steel electrode(Elsevier Science Sa, 2013) Ozyilmaz, A. Tuncay; Akdag, Abdurrahman; Karahan, I. Hakki; Ozyilmaz, GulZinc-cobalt alloy plating (ZnCo) was successfully deposited on carbon steel (CS) applying current of 2 mA with galvanostatic technique. Polyaniline film (PANI) was synthesized with cyclic voltammetry technique from 0.20 M aniline containing 0.20 M sodium tartrate solution on zinc-cobalt plated carbon steel (CS/ZnCo) electrode. PANI film characterized by scanning electron microscopy (SEM), was covered with a dark green-brown homopolymer film of strongly adherent homogeneous characteristic while the other one was plated with a porous light ZnCo one. The corrosion behaviour of zinc-cobalt deposited carbon steel electrodes with and without polyaniline (PANI) film in 3.5% NaCl solution was investigated with AC impedance spectroscopy (EIS) technique and anodic polarization curves. The results showed that PANI coating led to decrease of the permeability of metallic plating. The PANI homopolymer film provided an effective barrier property on zinc-cobalt coating and a remarkable anodic protection to substrate for longer exposure time. (C) 2012 Elsevier B.V. All rights reserved.Öğe Isoamylacetate production by entrapped and covalently bound Candida rugosa and porcine pancreatic lipases(Elsevier Sci Ltd, 2012) Ozyilmaz, Gul; Yagiz, EsraCandida rugosa lipase (CRL) and porcine pancreatic lipase (PPL) were immobilised by entrapping and also by covalent binding for use in synthesis of isoamyl acetate (IAAc), which has a typical banana flavour. Lipase entrapment was carried out by dripping sodium alginate (Na-Alg)-chitosan (Chi)-lipase mixture into CaCl2-glutaraldehyde (GAL) solution to obtain Ca-Alg/Chi(CRL/PPL). Immobilisation conditions were optimised as 1.5% Na-Alg, 1.5% chitosan and 0.15% GAL Ca-Alg/Chi(CRL/PPL) samples showed the highest activity when they were dried upon reaching 27% of their initial weights. Covalent binding was achived with Chi modified with spacerarm via glutaraldehyde to get Chi(CRL/PPL). The highest IAAc production was observed when 1,3-diaminopropane was used as a spacer arm. The best ester yield was achieved in heptane, at 40 and 45 degrees C reaction temperatures, 50 mM IAA and 50 or 75 mM AA concentrations. The amount of IAAc was nearly 10 times higher for the batch type than for the continuous packed bed column reactor. (C) 2012 Elsevier Ltd. All rights reserved.Öğe Kinetic properties and storage stability of catalase immobilized on to florisil(Natl Inst Science Communication-Niscair, 2007) Ozyilmaz, Gul; Tukel, S. Seyhan; Alptekin, OzlemThe covalent immobilization of bovine liver catalase (CAT) oil to florisil via glutaraldehyde was investigated. Optimum immobilization pH and temperature were determined as pH 6.0, 10 degrees C respectively, while the amount of initial CAT per, of carrier and immobilization time was determined as 5 mg . g(-1) and 120 min, respectively. The V-max values for free and immobilized CAT were found to be 1.7 x 10(5) and 2.0 x 10(4) mu mol H2O2 . min(-1) mg protein(-1), respectively, whereas K-M values were 33.3 mM and 1722.0 mM respectively. Operational stability was determined by using a stirred batch-type column reactor. Immobilized CAT retained about 40% of its initial activity after 50 uses. It showed higher storage stability than free CAT at 4 degrees C and 25 degrees C. Its storage stability increased with increasing relative humidity (RH) from 0 to 20% of the medium. The highest storage stability was obtained in 20% RH, however, further increase in RH from 40 to 100% significantly decreased the storage stability.Öğe Poly(2-chloroaniline) and poly(aniline-co-2-chloroaniline) films on ZnFe alloy plating(Emerald Group Publishing Ltd, 2018) Akdag, Abdurrahman; Ozyilmaz, Gul; Ozyilmaz, Ali TuncayPurpose The purpose of this paper is to evaluate and compare the protective, anticorrosion behaviors and electrochemically synthesis of poly(2-chloroaniline) (PCANI) and poly(2-chloroaniline-co-aniline) P(CANI-co-ANI) films on thin zinc-iron plated carbon steel (CS). Design/methodology/approach Zinc-iron (ZnFe) alloy plating was successfully achieved on CS applying 3 mA constant current value. The PCANI and P(CANI-co-ANI) films on ZnFe-plated CS electrode were synthesized by cyclic voltammetry technique using monomer(s) containing 0.20 M sodium oxalate solution. The CS/ZnFe electrodes with and without PCANI or P(CANI-co-ANI) films were characterized using SEM and anodic linear sweep voltammograms. The anticorrosive behaviors of uncoated and coated electrodes were studied in 3.5 per cent NaCl solution by corrosion techniques which include open circuit potential measurements, the anodic polarization curves and alternative current electrochemical impedance spectroscopy (EIS) technique. Findings The protection efficiency values (E per cent) for CS/ZnFe, ZnCS/ZnFe/PCANI and CS/ZnFe/P(CANI-co-ANI) electrodes were calculated as 71.05, 84.53 and 92.79, respectively, after 168 h of immersion time. The results showed that P(CANI-co-ANI) coating on ZnFe-plated CS electrode exhibited higher corrosion resistance and provided better barrier property in comparison with PCANI coating and ZnFe alloy plating, in longer exposure time. Originality/value A number of reports on the synthesis and characterization of PANI have appeared in the literature during the past decade, but there is no such publication of PCANI. At the same time, the synthesis of PCANI onto the surface of metal alloy coating being the first of this kind, no such proceedings have been reported in the literature so far.Öğe Poly(o-anisidine) on brass(Korean Inst Chem Engineers, 2008) Ozyilmaz, Ali Tuncay; Ozyilmaz, Gul; Yilmaz, Ercan; Colak, NureddinThe electrochemical synthesis of poly(o-anisidine) (POA) was achieved on brass (CuZn) electrode by applying two scan rates (50 and 20 mVs(-1)). The synthesized polymer films were strongly adherent and homogeneous in both cases. Their corrosion performance was investigated by AC impedance spectroscopy (EIS) technique, anodic polarization plots and open circuit potential-time curves, in 3.5% NaCl solution. It was clearly seen that poly(o-anisidine) films provided a significant physical protection for longer exposure time. It was shown that polymer film coated at high scan rate (CuZn/POA-H) exhibited better barrier property against the attack of corrosive agents when compared with polymer film obtained at low scan rate (CuZn/POA-L). It was found out that poly(o-anisidine) film synthesized at high scan rate caused a significant increase in corrosion resistance by its catalytic behavior on formation of protective oxide layers on the surface in longer time.Öğe Production of aroma esters by immobilized Candida rugosa and porcine pancreatic lipase into calcium alginate gel(Elsevier, 2010) Ozyilmaz, Gul; Gezer, EsraCandida rugosa lipase (CRL) and porcine pancreatic lipase (PPL) were immobilized into calcium alginate (Ca-Alg) gel beads by means of entrapment and were used to produce three industrially important flavour esters, namely isoamyl acetate (banana flavour), ethyl valerate (green apple flavour) and butyl acetate (pineapple flavour). Immobilization conditions were optimized in terms of sodium alginate (Na-Alg) and CaCl2 concentrations by determination of the entrapped enzyme amount as well as by esterification of 4-nitrophenol and acetic acid. The best results were obtained at 2.5% Na-Alg and 2.5 M CaCl2 for CRL while at 2.5% Na-Alg and 2.0 M CaCl2 for PPL On carrying out flavour syntheses in solvent-free medium and also in hexane medium, higher ester yields were obtained in hexane medium for all esters and both types of lipases. Ester esterification efficiency increased in parallel with both enzyme concentrations at immobilization medium and the immobilized lipase amount in esterification medium. Maximum ester production was observed between 40 and 50 degrees C for CRL and PPL Besides, the effect of substrate concentrations on ester conversion was remarkable. The best ester yield was obtained for isoamyl acetate when immobilized PPL was used. (C) 2009 Elsevier B.V. All rights reserved.Öğe Protective properties of polyaniline and poly(aniline-co-o-anisidine) films electro synthesized on brass(Elsevier Science Sa, 2007) Oezyilmaz, A. Tuncay; Colak, Nureddin; Ozyilmaz, Gul; Sanguen, A. KemalPolyaniline and poly(aniline-co-o-anisidine) films were deposited on brass (Cu40Zn). The synthesis processes of homo and copolymer film were carried out under cyclic voltammetric condition from 0.12 M aniline and 0.06 M aniline +0.06 M o-anisidine containing 0.2 M sodium oxalate solutions. Homo and copolymer films were characterized by scanning electron microscopy (SEM). SEM images clearly show that one of the brass electrodes was covered with a black copolymer film of strongly adherent homogeneous characteristic while the other one with a porous dark green homo polymer one. The corrosion performances of coated and uncoated electrodes in 3.5% NaCl were evaluated with the help of AC impedance spectroscopy, anodic polarization plots and open circuit potential-time curves. The protective effect of homo and copolymer films formed on brass Grew in parallel with extended exposure time. It was only observed with copolymer-coated electrode that changes in the charge transfer resistance C of copolymer-coated electrode were related to strong adsorption of copolymer film on the brass surface which led to the formation of a protective oxide layer due to its catalytic behaviour. (c) 2007 Elsevier B.V. All rights reserved.Öğe Simultaneous and sequential co-immobilization of glucose oxidase and catalase onto florisil(Korean Soc Microbiology & Biotechnology, 2007) Ozyilmaz, Gul; Tukel, S. SeyhanThe co-immobilization of Aspergillus niger glucose oxidase (GOD) with bovine liver catalase (CAT) onto florisil (magnesium silicate-based porous carrier) was investigated to improve the catalytic efficiency of GOD against H2O2 inactivation. The effect of the amount of bound CAT on the GOD activity was also studied for 12 different initial combinations of GOD and CAT, using simultaneous and sequential coupling. The sequentially co-immobilized GOD-CAT showed a higher efficiency than the simultaneously co-immobilized GOD-CAT in terms of the GOD activity and economic costs. The highest activity was shown by the sequentially co-immobilized GOD-CAT when the initial amounts of GOD and CAT were 10 mg and 5 mg per gram of carrier. The optimum pH, buffer concentration, and temperature for GOD activity for the same co-immobilized GOD-CAT sample were then determined as pH 6.5, 50 mM, and 30 degrees C, respectively. When compared with the individually immobilized GOD, the catalytic activity of the co-immobilized GOD-CAT was 70% higher, plus the reusability was more than two-fold. The storage stability of the co-immobilized GOD-CAT was also found to be higher than that of the free form at both 5 degrees C and 25 degrees C. The increased GOD activity and reusability resulting from the co-immobilization process may have been due to CAT protecting GOD from inactivation by H2O2 and supplying additional O-2 to the reaction system.
