Browsing by Author "Aydemir T."
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Item Effects of antioxidant vitamins A, C, E and trace elements Cu, Se on CuZnSOD, GSH-Px, CAT and LPO levels in chicken erythrocytes(2000) Aydemir T.; Öztürk R.; Bozkaya L.A.; Tarhan L.The biologically damaging effects of reactive oxygen species are controlled in vivo by a wide spectrum of antioxidant defence mechanisms. Dietary constituents of antioxidant vitamins and trace elements may play an important role in protecting against oxidant damage. The effects of supplementation of vitamins A, C, E and trace elements Cu and Se on the activities of antioxidant enzymes and lipid peroxide levels in chicken erythrocytes were investigated depend on the time. CuZnSOD activity and plasma Cu levels in the Cu group were increased by 39 and 37 per cent respectively. CuZnSOD activity in vitamin C groups was also increased by 20 per cent. The GSH-Px activity in Se, Se + E and Se + Cu groups was raised by 35, 46 and 69 per cent respectively. Also, the GSH-Px activity in the vitamin C group was increased by 33 per cent. Catalase activity in all of these groups was not significantly different when compared with controls (p < 0.01). The maximum decrease in LPO levels of 42 per cent was obtained for the Se + E group. Copyright (C) 2000 John Wiley and Sons, Ltd.Item Purification and characterization of catalase from chard (Beta vulgaris var. cicla)(Harwood Academic Publishers GmbH, 2001) Dinçer A.; Aydemir T.Catalase is a major primary antioxidant defence component that primarily catalyses the decomposition of H2O2 to H2O. Here we report the purification and characterization of catalase from chard (Beta vulgaris var. cicla). Following a procedure that involved chloroform treatment, ammonium sulfate precipitation and three chromatographic steps (CM-cellulose, Sephadex G-25, and Sephadex G-200), catalase was purified about 250-fold to a final specific activity of 56947 U/mg of protein. The molecular weight of the purified catalase and its subunit were determined to be 235 000 and 58 500 daltons, indicating that the chard catalase is a tetramer. The absorption spectra showed a soret peak at 406 nm, and there was slightly reduction by dithionite. The ratio of absorption at 406 and 275 nanometers was 1.5, the value being similar to that obtained for catalase from other plant sources. In the catalytic reaction, the apparent Km value for chard catalase was 50 mM. The purified protein has a broad pH optimum for catalase activity between 6.0 and 8.0. The enzyme had an optimum reaction temperature at 30°C. Heme catalase inhibitors, such as azide and cyanide, inhibited the enzyme activity markedly and the enzyme was also inactivated by β-mercaptoethanol, dithiothreitol and iodoacetamide.Item Voltammetric determination of timolol maleate: A β-adrenergic blocking agent(Maik Nauka-Interperiodica Publishing, 2001) Türkdemir M.H.; Erdögdu G.; Aydemir T.; Karagözler A.A.; Karagözler A.E.Timolol as a β-adrenoceptor antagonist is a potent antihypertensive and antianginal drug, which was also proved to be effective for the secondary prevention of myocardial infarction. The analysis of timolol, as with other oxprenolols, in ophthalmic solutions and biological liquids using sensitive instrumental methods has gained importance. Investigation of the electrochemical behavior of timolol maleate on a mercury drop electrode reveals the presence of a specific reduction peak of analytical significance. Analysis conditions affecting the properties of this peak were optimized by a systematic study. The limit of detection of about 2.5 ppb, obtained for the DPV technique using SMDE, is comparable with the most sensitive techniques. This method is suitable for routine analysis in that it is simpler and requires no preconcentration step for the analysis of therapeutic doses of the drug. © 2001 MAIK "Nauka/Interperiodica".Item Purification and partial characterisation of superoxide dismutase from chicken erythrocytes(2001) Aydemir T.; Tarhan L.Superoxide dismutase (SOD), which plays a very important role in protecting organisms from oxygen toxicity, was purified from chicken erythrocyte and partially characterised. Erythrocyte membranes were disintegrated via freeze-thaw methods in the presence of Triton X-100. Following ethanol precipitation, SOD-containing solution was applied to DEAE-cellulose and then Sephadex G-100 gel columns. Chicken erythrocyte SOD was purified 508-fold with a specific activity of 8,480 units per mg. The molecular weight was estimated to be 30.6 kDa ± 0.4 by gel filtration. The enzyme was composed of two subunits of equal size and contained one atom of copper and one atom of zinc per molecule. Maximum SOD activity was observed between pH 7.0 to 9.0 at 25°C. The enzyme has high thermal stability.Item Partial purification and characterization of polyphenoloxidase from peppermint (Mentha piperita)(2001) Kavrayan D.; Aydemir T.Polyphenoloxidase (PPO) of peppermint leaves ( Mentha piperita) was isolated by (NH4)2SO4 precipitation and dialysis. Its pH and temperature optima were 7.0 and 30°C, respectively. On heat-inactivation, half of the activity was lost after 6.5 and 1.5 min of treatment at 70 and 80°C, respectively. Sucrose, (NH4)2SO4, NaCl and KCl appeared to be protective agents of peppermint PPO against thermal denaturation. Km of this enzyme ranged from 6.25×10-3 M with catechol to 9.00×10-3 M with L-dopa. The I50 values of inhibitors studied on PPO were determined by means of activity percentage (I) diagrams. Values were 1.4×10-4 M, 1.7×10-4 M, 9.7×10-5 M, 2.45×10-4 M, 2.16×10-1 M, 1.83×10-5 M, 6.5×10-5 M, 1.4×10-2 M, 7.5×10-5 M, for potassium cyanide, glutathione, ascorbic acid, thiourea, sodium azide, sodium metabisulfite, dithioerythritol, β-mercaptoethanol and sodium diethyl dithiocarbamate respectively. Therefore, sodium metabisulfite was the most effective inhibitor. Copyright © 2001 Elsevier Science Ltd.Item Effects of Se, Cu and Se + vitamin E deficiency on the activities of CuZnSOD, GSH-Px, CAT and LPO levels in chicken erythrocytes(2001) Bozkaya L.A.; Oand̈ztuand̈rk-Uand̈rek R.; Aydemir T.; Tarhan L.Antioxidant enzymes and vitamins provide a defence against the damage of cells by reactive oxygen species in living systems. The effect of Cu, Se and vitamin E deficiencies on the antioxidant enzyme activities and lipid peroxide levels of chicken erythrocytes were investigated during 6 weeks of a depletion diet. CuZnSOD activity and the plasma Cu level of the Cu-deficient group which was fed a diet containing 0.2 mg Cu kg -1 were reduced to 62 and 71% respectively. GSH-Px activity of the Se-deficient group was decreased by 46% but by 21% in the Cu-deficient group. CAT activity values of Se- and Cu-deficient groups were increased by 28 and 10% respectively. The maximum increase of LPO levels in erythrocyte membranes was observed as 32% for the Se + E-deficient group. The LPO level of the Cu-deficient group which had decreased CuZnSOD and GSH-Px activity, was also observed to be significantly increased when compared with the controls (p < 0.05). Copyright © 2001 John Wiley & Sons, Ltd.Item Purification and partial characterization of catalase from chicken erythrocytes and the effect of various inhibitors on enzyme activity(2003) Aydemir T.; Kuru K.Catalase plays a major role in the protection of tissues from the toxic effects of H2O2 and partially reduced oxygen species. A nearly 136-fold enzyme purification was obtained from chicken erythrocyte by acetone precipitation, ethanol-chloroform treatment, CM-cellulose and Sephadex G-200 chromatography. The specific activity of purified enzyme was 42,556 U/mg. The molecular weight of the native chicken erythrocyte catalase was estimated at 240 kDa by gel filtration. SDS-gel electrophoresis results indicated that chicken erythrocyte catalase consists of four apparently identical subunits, with a molecular weight of around 57.5 kDa. The optical spectrum of the purified enzyme shows a Soret band at 406 nm, which is the characteristic for the heme group. Dithionite treatment of the enzyme resulted in the reduction of enzyme. The Km of chicken erythrocyte catalase was 33 mM H2O2. The maximal activity of catalase was observed between pH 6.0 and 8.0. Enzyme activity was stable at temperatures between 10 and 30°C. The activity of purified catalase was inhibited by azide, cyanide, β-mercaptoethanol, dithiotreitol (DTT) and iodoacetamide.Item Partial purification and characterization of polyphenol oxidase from artichoke (Cynara scolymus L.) heads(2004) Aydemir T.Partial characterization of polyphenol oxidase activity in artichoke heads is described. Stable and highly active PPO extracts were obtained using 1.0% (w/v) polyethylene glycol (PEG), 1.5% (w/v) Triton X-100 and 0.1% NaCl in 0.2 M potassium phosphate buffer, pH 6.0. Three isoenzymes of the artichoke PPO were detected by polyacrylamide gel electrophoresis. The pH optimum for artichoke PPO was found to be a very broad (5.0-7.0) and the enzyme activity was stable in the range 6.0-7.0 at 25°C for 60 min. The optimum temperature was 25°C. The enzyme was heat-stable between 20 and 30°C and completely inactivated at 80°C after 5 min. The activation energy (Ea) with catechol was 15.8 kJ/mol at pH 6.0. PPO showed activity to catechol, pyrogallol and 4-methylcatechol, DL-dopa, L-dopa and gallic acid. (Km and V max values were 10.2 mM and 19,662 U/ml min for catechol, 12.4 mM and 12,500 U/ml min for 4-methylcatechol, 14.3 mM and 8065 U/ml min for pyrogallol, 37.7 mM and 5865 U/ml min for L-dopa 36.3 mM and 6060 U/ml min for DL-dopa, 43.6 mM and 4620 U/ml min for gallic acid, respectively). L-tyrosine was also tested but was not oxidized by artichoke PPO. The I50 values of inhibitors studied on PPO were determined by means of activity percentage (I50) diagrams. The values were 6.17×10-5 M, 6.32×10-5 M, 9.11×10-5 M, 1.76×10 -5 M, 1.47×10-5 M, 8.33×10-5 M, 4.12×10-5 M, 1.94×10-4 M and 1.83×10-5 M for glutathione, thiourea, sodium azide, sodium metabisulfite, dithiothreitol, β-mercaptoethanol, sodium diethyl dithiocarbamate, oxalic acid and ascorbic acid, respectively. Therefore, the most effective inhibitor was dithiothreitol, followed in decreasing order by sodium metabisulphide and ascorbic acid. Metal ions (Zn++, Ba ++, Cu++) were poor inhibitors of the enzyme at 10 mM. © 2003 Elsevier Ltd. All rights reserved.Item Glucose sensing employing fluorescent pH indicator: 4-[(p-N,N-dimethylamino)benzylidene]-2-phenyloxazole-5-one(2005) Ertekin K.; Cinar S.; Aydemir T.; Alp S.The proton sensitive azlactone derivative; 4-[(p-N,N-dimethylamino) benzylidene]-2-phenyloxazole-5-one (DPO) exhibits high quantum yield, excellent photostability, and high molar absorptivity in a sol - gel matrix. In this work, two different DPO containing constructions were tested and evaluated as glucose sensors. In the first, both glucose oxidase (GOx) and azlactone derivative were incorporated into a single tetraethylorthosilicate (TEOS) based sol - gel phase. In the second, TEOS and 3-aminopropyltriethoxysilane (APTEOS) containing dye-doped sol - gel layer was covered with GOx entrapped sol - gel (the two-layer configuration). The monolayer configuration has the fastest response time (τ90 = 20 s) but suffers from leaching upon prolonged use. Response time and dynamic working range of the cross-linking agent containing two-layer configuration are 40 s and 0.1-15 mM glucose, respectively. The resulting glucose sensor was characterized by high sensitivity, low interference from acidogenic species, and a working lifetime of at least 90 days. © 2004 Elsevier Ltd. All rights reserved.Item Partial purification and some properties of polyphenol oxidase from Laurus nobilis L.(Industrie Grafiche V. Lischi e Figli, 2006) Aydemir T.; Çinar S.Polyphenol oxidase from laurel leaves tissue (Laurus nobilis L.) was isolated by (NH4)2SO4 precipitation and dialysis. Stable and highly active PPO extracts were obtained using 1.5% (w/v) Triton X-100 and 1.0% (w/v) polyethylene glycol (PEG) in 0.05 M potassium phosphate buffer pH 7.0. The optimum pH values were found to be 7.0 for catechol, DL-dopa and L-dopa, 6.5 for 4-methylcatechol, 6.0 for pyrogallol and 5.0 for gallic acid. Laurus nobilis PPO is more stable at basic pH than acidic pH values. The optimum temperature was found to be 40°C for catechol, 35°C for 4-methylcatechol, 30°C for pyrogallol and gallic acid, 25°C for DL-dopa and L-dopa. Half lives of PPO activity were 28 min. at 60°C and 7 min. at 70°C with catechol. Ea value was calculated from the Arhenius equation 16.628 kj/mol for catechol as substrate. Polyphenol oxidase showed activity toward catechol, 4-methylcatechol, gallic acid, pyrogallol, L-dopa and DL-dopa (KM and Vmax values were 8.3 mM and 15538 U/ml for catechol. 14.8 mM and 11300 U/ml for 4-methylcatechol, 15.6 mM and 9153 U/ml for gallic acid, 28.0 mM and 8835 U/ml for pyrogallol, 66.7 mM and 7142 U/ml for L-dopa, 70.9 mM and 5000 U/ml for DL-dopa). L-tyrosine was also tested but was not oxidized by Laurus nobilis PPO. The I50 value was found to be 7.60×10-6 M for dithiothreitol, 1.60×10-5 M for β-mercaptoethanol, 2.40×10-5 M for glutathione, 3.00×10-5 M for sodium thiosulphate, 0.76×10-4 M for sodium azide, 0.80×10-4 M for thiourea, 0.84×10-4 M for sodium metabisulfite, 1.45×10 -4 M for L-csyteine, 5.00 ×10-4 for ascorbic acid, 6,00×10-4 M for oxalic acid, 1.11×10-2 M for citric acid and 4.40×10-2 M for EDTA. Various amino acids such as L-csyteine, L-glycine, L-arginine, L-phenyl alanin, L-glutamic acid and L-aspartic acid have been investigated and the results showed that L-cysteine was the most effective inhibitors. NaCl, CoCl2, CaCl2, were poor inhibitors of enzyme at 1 mM. Fe++, Mg++, Mn++, Zn++ ions did not show away significant effect on partially purified enzyme activity.Item Partial purification and characterisation of polyphenol oxidase from celery root (Apium graveolens L.) and the investigation of the effects on the enzyme activity of some inhibitors(Blackwell Publishing Ltd, 2006) Aydemir T.; Akkanli G.Polyphenol oxidase (PPO) of celery root was extracted and partially purified by (NH4)2SO4 fractionation and dialysis. Optimum pH and temperature were found at pH 7.0 and 30°C, and Km and Vmax values were 29 mM and 5560 U mL-1 min-1 with catechol, respectively. The activation energy of the enzyme with catechol was 17.9 kJ mol-1 at pH 7.0. In electrophoretic seperation, six isoenzymes were detected with DL-dopa substrate. PPO showed activity to catechol, 4-methylcatechol, pyrogallol, gallic acid, DL-dopa. L-Tyrosine was also tested but was not oxidised by celery root PPO. β-Mercaptoethanol was found to be the most effective inhibitor. (NH 4)2SO4, NaCl, KCl and sucrose appeared to be protective agents of celery root PPO against thermal denaturation. Metal ions (Cu2+, Zn2+, Mn2+) were poor inhibitors of the celery root PPO at 1 mm. PPO activity was also inhibited by CaCl2, NaCl, BaCl2, FeSO4 and NiCl2. © 2006 Institute of Food Science and Technology Trust Fund.Item Purification and characterization of glutathione-S-transferase from chicken erythrocyte(2009) Aydemir T.; Kavrayan D.The glutathione-s-transferases are a family of multifunctional enzymes involved in the detoxification of electrophilic xenobiotics primarily through conjugation to reduce glutathione. A form of the enzyme, designated GSH-S transferase ρ, was purified chicken erythrocyte by acetone precipitation, ethanol-chloroform treatment, DEAE-Cellulose, Q-Sepharose, Sephadex G-100 chromatography. The molecular weight of GST purified from chicken erythrocyte was estimated as 47,500 Da by gel filtration. The subunit molecular weight of chicken erythrocyte GST as determined by electrophoresis in the presence of sodium dodecyl sulfate was predicted as 24,000 Da. The specific activity was found to be 20.39 U/mg. The km for CDNB calculated from Lineweaver-Burk plot was 0.71 mM. Optimum temperature of maximum GST activity was 28°C for CDNB. The maximal activity of the enzyme was observed at pH 7.5. The activity of purified GST is inhibited by DDT, urea, CDNB, Triton X-100, DTNB. Copyright © 2009 Informa UK Ltd.Item Selected kinetic properties of polyphenol oxidase extracted from rosmarinus officinalis l(2010) Aydemir T.Polyphenol oxidase from Rosmarinus officinalis L. (PPO, EC 1:14:18.1) was extracted and partially purified by using (NH4)2SO 4 precipitation and dialysis. Stable and highly active PPO extracts were obtained using 0.5% (w/v) PEG and 0.5% (w/v) Triton X-100 in 0.1 M phosphate buffer 7.0. KM values were found to be as 14.3 mM for catechol. Four isoenzymes of Rosemary PPO were detected by PAGE with DL-dopa substrate. The enzyme was strongly inhibited by dithiotreitol, sodium metasulfite, sodium thiosulfate, ascorbic acid, and L-cysteine. Metal ions Ca++, Mg++, and Mn++ were poor inhibitors of rosemary PPO at 10 Mm. Copyright © Taylor & Francis Group, LLC.Item Phenolic content and antioxidant activity of different extracts from ocimum basilicum, apium graveolens and lepidium sativum seeds(2011) Aydemir T.; Becerik S.The antioxidative properties and total phenolic contents of methanol, ethanol and water extracts from Ocimum basilicum, Apium graveolens and Lepidium sativum seeds were investigated and the results were compared with standards. The methanol extracts of the seeds had significantly higher (P<0.05) superoxide radical scavenging activity with the concentration for 50% inhibition (IC50) value of 98.73μg/mL for O. basilicum, 121.57μg/mL for A. graveolens and 166.16μg/mL for L. sativum. The results indicated that all the seed extracts showed excellent H2O2 scavenging activities. IC50 values for H2O2 scavenging activity by methanol extract of O. basilicum, A. graveolens, L. sativum and butylated hydroxyanisole were found to be as 49.9, 52.3, 65.2 and 49.6μg/mL, respectively. O. basilicum methanol extract had significantly (P<0.05) higher 1,1-diphenyl-2-picryl-hydrazyl scavenging effect than the other two seeds. The methanol extracts of three seeds were better in Fe+2 chelating activity, reducing power and higher in the content of total phenol as compared with ethanol and water extracts. +PRACTICAL APPLICATIONS: Recent epidemiological studies have strongly suggested that consumption of certain plant materials such as seeds, leaves, fruits and roots may reduce the risk of chronic diseases related to oxidative stress on account of their antioxidant activity and promote general health benefits. In this study, all seeds extracts exhibited good antioxidant activity (78.3-96.9%) at concentration 500μg/mL. Total phenolic content in the seed extracts ranged from 51 to 92mg GAE/100g extract. In addition, there was a statistically significant correlation between the amount of phenolic compounds and antioxidant activity (R2=0.9058, P<0.05) in all the seed extracts. Therefore, O. basilicum, A. greveolens and L. sativum seed extracts have the potential to be developed into dietary supplements and nutraceuticals. © 2010 Wiley Periodicals, Inc.Item Antioxidant responses of lentil and barley plants to boron toxicity under different nitrogen sources(Academic Journals, 2011) Tepe M.; Aydemir T.In this study, the effects of different nitrogen sources on lentil (Lens clunaris) and barley (Hordeum vulgare) plants, exposed to 5 and 10 mM boron stress previously, were studied. After ten-day germination, the lentil (native) and barley (Tokak157/37) were incubated 16 h light and 8 h dark per day for 7-day growth cycle under the conditions of boron stress via different nitrogen sources (10 mM nitrogen in NH4 Cl, KNO3 and urea). As a result of the changes in the nitrogen sources of the plants, there were determined decreases in the relative growth rate (%) and total chlorophyll content related to boron stress, (p < 0.05) and (p < 0.01), respectively. The changes in the lentil were obtained much more than those in the barley. In addition, the changes in the groups in which NH4 + was used as nitrogen source were obtained at lowest levels. The concentrations of MDA, H2O2 and proline showed increases under boron stress (p < 0.05). The effect of boron toxicity on the activities of SOD, GPX and LOX was similar in the two species but the levels of CAT and APX activities were different in both species under 5 and 10 mM boron stress (p < 0.01). SOD, GPX and LOX activities increased in the roots and shoots of boron treated plants as compared with the controls (p < 0.01). Although, lentil CAT and APX, activities decreased; in barley, CAT and APX, activities increased under boron toxicity. In conclusion, the fertilizers which contain NH4 + should be used in the boron stressed farmlands. © 2011 Academic Journals.Item Removal of nickel(II) ions by histidine modified chitosan beads(2012) Eser A.; Nüket Tirtom V.; Aydemir T.; Becerik S.; Dinçer A.In order to increase the nickel adsorption capacity of raw chitosan beads (CB), they were chemically modified with histidine (HIS-ECH-CB) by using crosslinking agent, epichlorohydrine (ECH). The nature and morphology of the sorbent were characterized using FTIR, TGA and SEM analysis. For optimization of adsorption conditions, sorption experiments were performed by varying contact time, pH, temperature and initial nickel concentration. Based on the adsorption experiment, the HIS-ECH-CB showed the significant adsorption capacity of 55.6mg/g under the optimal adsorption condition. Nickel adsorption isotherms data were fitted to Freundlich isotherm. Thermodynamic parameters namely ΔG°, ΔH° and ΔS° of the Ni(II) adsorption process were calculated. The negative values of Gibbs free energy of adsorption (ΔG°) indicated the spontaneity of the adsorption of Ni(II) ions on the histidine modified chitosan. Desorption of Ni(II) ions from HIS-ECH-CB could be done rapidly by using 0.1M HCl, HNO 3 and EDTA solutions and the beads could be used again to adsorb Ni(II) ions. © 2012 Elsevier B.V..Item Comparative adsorption of Ni(II) and Cd(II) ions on epichlorohydrin crosslinked chitosan-clay composite beads in aqueous solution(2012) Tirtom V.N.; Dinçer A.; Becerik S.; Aydemir T.; Çelik A.Removal of Ni(II) and Cd(II) by adsorption on epichlorohydrin crosslinked chitosan-clay composite beads was examined in solutions representative of contaminated solutions containing heavy metals. Several important parameters influencing the adsorption of Ni(II) and Cd(II) ions such as contact time, pH, temperature and effect of metal concentration were investigated systematically by batch experiments. Langmuir and Freundlich adsorption models were used to describe adsorption isotherms and constants. The obtained results showed that the equilibrium adsorption behavior of Ni (II) and Cd (II) on epichlorohydrin crosslinked chitosan-clay composite beads could be applied to Langmuir and Freundlich models respectively. Maximum adsorption capacities for Ni(II) and Cd(II) ions were found as 32.36mgg-1 and 72.31mgg-1 respectively. The recovery of the metal ions after adsorption and the regeneration of the adsorbent was carried out by treatment of the loaded beads with either 0.1M HNO3, or 0.01M EDTA. The adsorbents were characterized by FTIR, SEM and TGA analysis. © 2012 Elsevier B.V.Item Removal of lead (II) ions from aqueous solution by using crosslinked chitosan-clay beads(Elsevier B.V., 2012) Tirtom V.N.; Dinçer A.; Becerik S.; Aydemir T.; Çelik A.Faculty of Arts and Sciences, Department of Chemistry, Celal Bayar University, 45140, Manisa Turkey Tel. +90 2362412151; Fax: +90 2362412128, +90 2362412158;A simple and effective biodegradable material known as chitosan-clay composite beads wereprepared to remove Pb(II) ions from aqueous solution. For this purpose, various importantparameters such as contact time, pH and temperature were examined on the adsorption ofPb(II) ions onto crosslinked chitosan-clay composite beads. Maximum adsorption capacity ofPb(II) was observed at pH 4.5 and 25°C and calculated as 7.93 mg/g according to Langmuirisotherm model. Thermodynamic parameters namely ΔG°, ΔH° and ΔS° of the Pb(II) adsorptionprocess have been calculated as 7.889 kJ/mol, -15.131 kJ/mol and -0.0785 kJ/molK respectively.EDTA was the best eluent for the desorption of Pb(II) ions from the crosslinked chitosan-claybeads. Scanning electron microscope (SEM) was used to characterize the surface morphologyof the crosslinked chitosan-clay beads. © 2012 Elsevier Inc.Item Removal of lead (II) ions from aqueous solution by using crosslinked chitosan-clay beads(Taylor and Francis Inc., 2012) Tirtom V.N.; Dinçer A.; Becerik S.; Aydemir T.; Çelik A.A simple and effective biodegradable material known as chitosan-clay composite beads were prepared to remove Pb(II) ions from aqueous solution. For this purpose, various important parameters such as contact time, pH and temperature were examined on the adsorption of Pb(II) ions onto crosslinked chitosan-clay composite beads. Maximum adsorption capacity of Pb(II) was observed at pH 4.5 and 25°C and calculated as 7.93 mg/g according to Langmuir isotherm model. Thermodynamic parameters namely ΔG°, ΔH° and ΔS° of the Pb(II) adsorption process have been calculated as 7.889 kJ/mol, -15.131 kJ/mol and -0.0785 kJ/molK respectively. EDTA was the best eluent for the desorption of Pb(II) ions from the crosslinked chitosan-clay beads. Scanning electron microscope (SEM) was used to characterize the surface morphology of the crosslinked chitosan-clay beads. © 2012 Desalination Publications.Item Immobilization of tyrosinase on chitosan-clay composite beads(Elsevier B.V., 2012) Dinçer A.; Becerik S.; Aydemir T.Tyrosinase was immobilized on glutaraldehyde crosslinked chitosan-clay composite beads and used for phenol removal. Immobilization yield, loading efficiency and activity of tyrosinase immobilized beads were found as 67%, 25% and 1400U/g beads respectively. Optimum pH of the free and immobilized enzyme was found as pH 7.0. Optimum temperature of the free and immobilized enzyme was determined as 25-30°C and 25°C respectively. The kinetic parameters of free and immobilized tyrosinase were calculated using l-catechol as a substrate and Km value for free and immobilized tyrosinase were found as 0.93mM and 1.7mM respectively. After seven times of repeated tests, each over 150min, the efficiency of phenol removal using same immobilized tyrosinase beads were decreased to 43%. © 2011 Elsevier B.V.