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Yazar "Bayramoğlu, Gülay" seçeneğine göre listele

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    Adsorption of IgG on spacer-arm and L-arginine ligand attached poly(GMA/MMA/EGDMA) beads
    (Wiley, 2007) Bayramoğlu, Gülay; Şenel, Ayşegül U.; Arica, M. Yakup
    This work presents data on human imrnunoglobulin G (HlgG) adsorption onto L-arginine ligand attached poly(GMA/MMA/EGDMA)-based affinity beads which were synthesized from methyl methacrylate (NUVIA) and glycidiyl methacrylate (GMA) in the presence of a crosslinker (i.e., ethylene glycol dimethacrylate; EGDMA) by suspension polymerization. The epoxy groups of the poly(GMA/NMA/ EGDMA) beads were converted into amino groups after reaction with ammonia or 1,6-diaminohexane (i.e., spacer-arm). With L-arginine as a ligand, it was covalently immobilized on the an-dnated (poly(GMA/MMA/EGDMA)AA) and/or the spacer-arm attached (poly(GMA/NMA/ EGDM.A)-SA) beads, using glutaric dialdehyde as a coupling agent. Both affinity poly(GMA/MMA/EGDMA)-based beads were used in HlgG adsorption/desorption studies under defined pH, ionic strength, or temperature conditions in a batch reactor, using acid-treated poly(GMA/MMA/EGDMA) beads as a control system. The poly(GMA/MMA/EGDMA)-SA affinity beads resulted in an increase in the adsorption capacity to HlgG compared with the aminated counterpart (i.e., poly(GMA/MMA/EGDMA)-AA). The maximum adsorption capacities of the poly(GMA/MMA/EGDMA)-AA and poly(GMA/MNA/EGDMA)-SA affinity beads were found to be 112.36 and 142 mg g(-1), and the affinity constants (K-d), evaluated by the Langmuir model, were 2.48 x 10(-7) and 6.98 x 10(-7) M, respectively. Adsorption capacities of the poly(GMA/MMA/EGDMA)-AA and poly(GMA/MMA/EGDMA)-SA were decreased with HIgG by increasing the ionic strength adjusted with NaCl. Adsorption kinetic of HIgG onto both affinity adsorbents was analyzed with first- and second-order kinetic equations. The first-order equation fitted well with the experimental data. (c) 2007 Wiley Periodicals, Inc.
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    Adsorption of serum albumin and γ-globulin from single and binary mixture and characterization of pHEMA-based affinity membrane surface by contact angle measurements
    (Elsevier Science Bv, 2005) Bayramoğlu, Gülay; Yalçın, Emine; Arıca, M. Yakup
    In this study, an affinity membrane was synthesized using 2-hydroxyethylmethacrylate (HEMA) via UV-initiated photopolymerization. A dye-ligand (i.e., Procion Red HE-3B; Red-120) was covalently immobilized onto membrane. Human serum albumin (HSA) and human gamma-globulin (HIgG) adsorption onto pHEMA-Red-120 membrane were studied using bare poly(hydroxyethylmethacrylate) (pHEMA) membrane as a control system. The information about surface energy, hydrophobicity and chemical heterogeneity of the affinity membrane was obtained by contact angle measurements. The contact angle values of the affinity membrane were determined by sessile drop method using water, glycerol and diiodomethane as test liquids. Component and parameters of the surface free energy of all the investigated samples were calculated from measured contact angle values using the acid-base method of the van Oss. The adsorption of HSA and HIgG significantly changed both the contact angles and component of surface free energies of the affinity membrane. The reversible HSA and HIgG adsorption on the pHEMA-Red-120 followed the Freundlich and Langmuir-Freundlich isotherm models. Selectivity of the affinity membrane was tested at different pH values to HSA and HIgG and the protein concentration of in the binary system was determined by HPLC. The affinity membrane was stable when subjected to sanitization with sodium hydroxide after repeated adsorption-elution cycles. (c) 2005 Elsevier B.V. All rights reserved.
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    Biosorption of benzidine based textile dyes "Direct Blue 1 and Direct Red 128" using native and heat-treated biomass of Trametes versicolor
    (Elsevier, 2007) Bayramoğlu, Gülay; Arica, M. Yakup
    The capacities and mechanisms of native and heat-treated white rot fungus "Trametes versicolor" biomass in removing of two different benzidine based dyes (i.e., Direct Blue 1, DB-1 and Direct Red 128, DR-128) from aqueous solution was investigated with different parameters, such as molecular weight of dye, adsorbent dosage, pH, temperature and ionic strength. In the batch system, the biosorption equilibrium time for both dyes was about 6 h. The maximum biosorption was observed at pH 6.0 for DB-1 and at pH 3.0 for DR-128 on the native and heat-treated fungal biomass. The biosorption capacities of the native and heat-treated fungal biomass (at 800 mg/L dye concentration) were found to be 101.1 and 152.3 mg/g for DB-1 and these were 189.7 and 225.4 mg dye/g biomass for DR-128, respectively. The Freundlih and Temkin adsorption isotherm models were used for the mathematical description of the biosorption equilibrium. The Freundlich and Temkin models were able to describe the biosorption equilibrium of DB-1 and DR-128 on the native and heat-treated fungal preparations. The Freundlich model also showed that the small molecular weight dye (i.e., DR-128) had a higher affinity of adsorption that than of the higher molecular weight dye (i.e., DB-1). The dye biosorption on the fungal biomass preparations followed the second order kinetics model. (C) 2006 Elsevier B.V. All rights reserved.
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    Biosorption of mercury(II), cadmium(II) and lead(II) ions from aqueous system by microalgae Chlamydomonas reinhardtii immobilized in alginate beads
    (Elsevier, 2006) Bayramoğlu, Gülay; Tüzün, İlhami; Çelik, Gökçe; Yilmaz, Meltem; Arica, M. Yakup
    The potential use of the immobilized microalgae (in Ca-alginate) of Chlamydomonas reinhardtii to remove Hg(II), Cd(II) and Pb(II) ions from aqueous solutions was evaluated using bare Ca-alginate bead as a control system. Ca-alginate beads containing immobilized microalgae were incubated for the uniform growth at 22 degrees C for 5 days. Effects of pH, temperature, initial concentration of metal ions and biosorbent dosages on the adsorption of Hg(II), Cd(II) and Pb(II) ions were studied. Adsorption of Hg(II), Cd(II) and Pb(II) ions on the immobilized microalgae showed highest values at around pH 5.0 to 6.0. The adsorption equilibrium was represented with Langnmir and Freundlich adsorption isotherms. The adsorption of these ions on the immobilized microalgae followed second-order kinetics and equilibrium was established in about 60 min. The temperature change in the range of 5-40 degrees C did not affect the adsorption capacities of the immobilized microalgae. The immobilized-algal systems can be regenerated using 2 M NaCl for Hg(II), Cd(II) and Pb(II) ions. (c) 2006 Elsevier B.V. All rights reserved.
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    Biosorption of Reactive Blue 4 dye by native and treated fungus Phanerocheate chrysosporium: Batch and continuous flow system studies
    (Elsevier, 2006) Bayramoğlu, Gülay; Çelik, Gökçe; Arıca, M. Yakup
    The native and treated fungal biomass of Phanerocheate chrysosporium was used for the biosorption of a textile dye (i.e., Reactive Blue 4). In the batch system, the biosorption equilibrium time was about 4 h and the maximum dye uptake on all the tested fungal biomass preparations was observed at pH 3.0. The dye uptake capacities of the biosorbents at 600 mg L-1 dye concentration were found to be 132.5, 156.9, 147.6 and 81.1 mg g(-1) for native and heat-, acid- and base-treated dry fungal preparations, respectively. The dye uptake capacity order of the fungal preparations was found as heat-treated > acid-treated > native > base-treated. The Langmuir, Freundlich and Temkin adsorption models were used for the mathematical description of the biosorption equilibrium. The Freundlich and Temkin models were able to describe the biosorption equilibrium of Reactive Blue 4 on native and treated fungal preparations. The dye biosorption on the fungal biomass preparations followed Ritchie kinetic model. Biosorption of the dye from aqueous solution was also investigated in a continuous flow system. The maximum biosorption capacity of the heat-treated fungal biomass P chrysosporium was 211.6 mg (g dry biomass)(-1) at an initial dye concentration of 600 mg L-1 and at a flow rate of 20 mL h(-1). (c) 2006 Elsevier B.V. All rights reserved.
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    Biosorption of Reactive Red-120 dye from aqueous solution by native and modified fungus biomass preparations of Lentinus sajor-caju
    (Elsevier, 2007) Arıca, M. Yakup; Bayramoğlu, Gülay
    The capacities and mechanisms of native and treated white-rot fungus "Lentinus sajur-caju" biomass preparations in removing of textile dye (i.e. Reactive Red-120) from aqueous solution was investigated with different parameters, such as adsorbent dosage, pH, temperature and ionic strength. In the batch system, the maximum dye uptake on all the tested fungal biomass preparations was observed at pH 3.0, and the dye uptake capacities of the biosorbents (at 800 mg/l dye concentration) were found to be 117.8, 182.9, 138.6 and 57.2 mg/g for native and heat-, acid- and base-treated dry fungal preparations, respectively. The uptake capacities order of the fungal preparations for the dye were found as heat-treated > acid-treated > native > base-treated. The Langmuir, Freundlih and Temkin adsorption models were used for the mathematical description of the biosorption equilibrium. The Freundlich and Temkin models were able to describe the biosorption equilibrium of Reactive Red-120 on the fungal biomass preparations. The dye biosorption on the fungal biomass preparations followed second-order kinetic model and equation. (c) 2007 Elsevier B.V. All rights reserved.
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    Characterization of polyethylenimine grafted and Cibacron Blue F3GA immobilized poly (hydroxyethylmethacrylate-co-glycydylmethacrylate) membranes and application to bilirubin removal from human serum
    (Elsevier Science Bv, 2005) Bayramoğlu, Gülay; Yalçın, Emine; Arıca, M. Yakup
    In this study, acrylic hydrogel copolymer membrane was synthesized from 2-hydroxyethylmethacrylate (HEMA) and glycidyl methacrylate (GMA) monomers. The pol ethylenimine polymer was then grafted onto membrane surface (poly(HEMA-co-GMA)-PEI). A dye-ligand (i.e., Cibacron Blue F3GA) was then covalently immobilized on the membrane through the amino groups of the polyethylenimine molecules (poly(HEMA-co-GMA)-PEI-CB). Both affinity membranes were used for the removal of bilirubin (BR) from aqueous solutions and human serum. The effects of pH, ionic strength, temperature and initial BR concentration on the adsorption capacity of both affinity membranes were investigated in a batch system. Separation of BR from human serum was also investigated in a batch system. Experimental data indicate that poly(HEMA-co-GMA)-PEI affinity membrane shows more adsorption capacity to BR than that of the poly(HEMA-co-GMA)-PEI-CB membrane, which may be explained on the basis of opposite charge on both PEI and BR. The BR adsorption on the poly(HEMA-co-GMA)-PEI and poly(HEMA-co-GMA)-PEI-CB affinity membrane did not well described by the Langmuir model, but obeyed the Freundlich isotherm model. The poly(HEMA-co-GMA)-PEI and poly(HEMA-co-GMA)-PEI-CB affinity membranes are stable when subjected to sanitization with sodium hydroxide after repeated adsorption-desorption cycles. (c) 2005 Elsevier B.V. All rights reserved.
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    Chitosan-grafted poly(hydroxyethyl methacrylate-co-glycidyl methacrylate) membranes for reversible enzyme immobilization
    (Wiley, 2007) Arıca, M. Yakup; Yılmaz, Meltem; Bayramoğlu, Gülay
    Epoxy group-contain g poly(hydroxyethyl methacrylate/glycidyl methacrylate), p(HEMA/GMA), membrane was prepared by UV initiated photopolymerization. The membrane was grafted with chitosan (CH) and some of them were chelated with Fe(III) ions. The CH grafted, p(HEMA/GMA), and Fe(III) ions incorporated p(HEMA/ GMA)-CH-Fe(III) membranes were used for glucose oxidase (GOD) immobilization via adsorption. The maximum enzyme immobilization capacity of the p(HEMA/GMA)-CH and p(HEMA/GMA)-CH-Fe(HI) membranes were 0.89 and 1.36 mg/mL, respectively. The optimal PH value for the immobilized GOD preparations is found to have shifted 0.5 units to more acidic PH 5.0. Optimum temperature for both immobilized preparations was 10 degrees C higher than that of the free enzyme and was significantly broader at higher temperatures. The apparent K-m values were found to be 6.9 and 5.8 mM for the adsorbed GOD on p(HEMA/GMA)-CH and p(HEMA/GMA)-CH-Fe(HI) membranes, respectively. In addition, all the membranes surfaces were characterized by contact angle measurements. (c) 2006 Wiley Periodicals, Inc.
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    Cr(VI) biosorption from aqueous solutions using free and immobilized biomass of Lentinus sajor-caju: preparation and kinetic characterization
    (Elsevier Science Bv, 2005) Arıca, M. Yakup; Bayramoğlu, Gülay
    The potential use of the free and immobilized mycelia (in carboxymethylcellulose (CMC)) of Lentinus sajor-caju to remove hexavalent form of chromium ions, Cr(VI), from aqueous solutions was evaluated using CMC bead as a control system for immobilised form of fungus. The CMC beads containing immobilized fungus mycelia were incubated for the uniform growth on the beads surface at 30degreesC for 3 days. Effects of pH, biosorption time, initial concentration and biosorbent dosages on the biosorption of Cr(VI) ions were studied. The biosorption of Cr(VI) ions on the biosorbents showed a highest value at around pH 2.0. The biosorption of Cr(VI) ions on both free and immobilized L. sajor-caju biomass (mg/g) was increased as the initial concentration of Cr(VI) ions increased in the medium. Biosorption equilibrium was established in about 2.0 h. The determined maximum biosorption capacities of the free and immobilized fungus were 18.9 and 32.2 mg/g dry weight, respectively. The biosorption equilibrium was also represented with Langmuir and Freundlich adsorption isotherms. The biosorption of Cr(VI) on these biomasses follows pseudo-second-order kinetics. The temperature change in the range of 5-40degreesC affected the biosorption capacities of the biosorbents. The biosorbent systems can be regenerated using 0.1 M NaOH, with more than 95% recovery, the biosorbents reused in five biosorption-desorption cycles without any considerable loss in the biosorption capacity. (C) 2004 Elsevier B.V. All rights reserved.
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    Cytochrome c adsorption on glutamic acid ligand immobilized magnetic poly(methylmethacrylate-co-glycidylmethacrylate) beads
    (Elsevier, 2007) Bayramoğlu, Gülay; Loğoğlu, Elif; Arıca, M. Yakup
    This work presents data on cytochrome c adsorption onto glutamic acid immobilized magnetic poly(methylmethacrylate-coglycidylmethacrylate), mp(GMA-MMA) beads which were synthesized from glycidylmethacrylate (GMA) and methylmethacrylate (MMA) in the presence of a cross-linker (i.e., ethyleneglycol dimethacrylate; EGDMA) via suspension polymerization. The epoxy groups of the mp(GMA-MMA) beads were converted into amino groups after reaction with ammonia and the aminated magnetic beads was activated with glutaric dialdhyde. It was then glutamic acid as an amino acid ligand covalently immobilized on the activated beads. The affinity mp(GMA-MMA)-A-GA beads were used in cytochrome c (Cytc) adsorption studies under defined pH, ionic strength or temperature conditions in a batch system using plain mp(GMA-MMA)-A beads as a control system. The maximum adsorption capacity of the mp(GMA-MMA)-A-GA affinity beads was found to be 140.3 mg g(-1) beads and the affinity constant (K-d), evaluated by the Langmuir model, was 5.42 x 10(-6) M. Adsorption capacity of the mp(GMA-MMA)-A-GA were decreased to Cytc by increasing the ionic strength adjusted with NaCl. Adsorption kinetic of Cytc onto magnetic affinity beads was analyzed with first-order and second-order kinetic equations. The first-order equation fitted well with the experimental data. (c) 2006 Elsevier B.V. All rights reserved.
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    A dye-ligand immobilized poly(2-hydroxyethylmethacrylate) membrane used for adsorption and isolation of immunoglobulin G
    (Elsevier, 2007) Bayramoğlu, Gülay; Öktem, H. Avni; Arıca, M. Yakup
    Poly(2-hydroxyethylmethaerylate) (pHEMA) membrane was prepared by photo-polymerization and a dye ligand (i.e., Reactive Green 5) was immobilised on the membrane surface (pHEMA-RG-5). Surface wettability and hydrophilicity of the dye-ligand immobilised membranes were investigated by static contact angle measurements. The chromatographic properties of the dye-ligand immobilized membrane for adsorption and purification of IgG are discussed using bare membrane as a control system. The non-specific adsorption of IgG was low (0.45 mg protein ml(-1) membrane). The attachment of dye ligand onto the membrane significantly increased the IgG adsorption (33.75 mg protein ml(-1) membrane). The maximum IgG adsorption was observed at pH 6.0. The reversible IgG adsorption on the membrane obeyed both the Freundlich and the Langmuir-Freundlich isotherm models. To test the efficiency of IgG isolation from human serum with the pHEMA-RG-5 membrane, the purity of the eluted IgG, as determined by HPLC, was 81% with a recovery of 67%. (c) 2006 Elsevier B.V. All rights reserved.
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    Effect of spacer-arm and Cu(II) ions on performance of L-histidine immobilized on poly(GMA/MMA) beads as an affinity ligand for separation and purification of IgG
    (Elsevier, 2006) Bayramoğlu, Gülay; Şenel, Aysegül Ülkü; Arıca, M. Yakup
    In this study, the beads were prepared from glycidiyl methacrylate (GMA) and methyl methacrylate (MMA) via suspension polymerization and, the used beads fractions were between 75 and 150 mu m. The epoxy groups of the beads were converted into amino groups by the reaction of ammonia or 1,6-diaminohexane as a spacer-arm. L-Histidine ligand was immobilized onto both beads. Cu(II) ions were chelated onto spacer-arm attached and L-histidine immobilized beads. The IgG adsorption capacity of the spacer-arm attached and Cu(II) chelated affinity beads led to higher adsorption capacities about 1.64- and 2.94-fold, respectively. The adsorption equilibrium studies showed that the adsorption isotherm of IgG obeyed the Langmuir isotherm model. The experimental data was well described by the second-order equations. Purification data of IgG with spacer-arm attached and Cu(II) ions chelated (i.e. poly(GMA/MMA)-SAH-Cu(II)) beads indicated that 87.5% of IgG was removed from human serum with a purity of 90%. (C) 2005 Elsevier B.V. All rights reserved.
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    Equilibrium and kinetic studies on biosorption of Hg(II), Cd(II) and Pb(II) ions onto microalgae Chlamydomonas reinhardtii
    (Academic Press Ltd- Elsevier Science Ltd, 2005) Tüzün, İlhami; Bayramoğlu, Gülay; Yalçın, Emine; Başaran, Gökben; Çelik, Gökçe; Arıca, M. Yakup
    The microalgae Chlamydomonas reinhardtii was used for the biosorption of Hg(II), Cd(II) and Pb(II) ions. The maximum adsorption of Hg(II) and Cd(II) ions on Chlamydomonas reinhardtii biomass was observed at pH 6.0 and the corresponding value for Pb(II) ions was 5.0. The biosorption of Hg(II), Cd(II) and Pb(II) ions by microalgae biomass increased as the initial concentration of Hg(II), Cd(II) and Pb(II) ions increased in the biosorption medium. The maximum biosorption capacities of microalgae for Hg(II), Cd(II) and Pb(II) ions were 72.2 +/- 0.67, 42.6 +/- 0.54 and 96.3 +/- 0.86 mg/g dry biomass, respectively. The affinity order for algal biomass was Pb(II) > Hg(II) > Cd(II). FT-IR analysis of algal biomass revealed the presence of amino, carboxyl, hydroxyl and carbonyl groups, which were responsible for biosorption of metal ions. Biosorption equilibrium was established in about 60 min and the equilibrium was well described by the Freundlich biosorption isotherms. Temperature change in the range of 5 - 35 degrees C did not affect the biosorption capacity. The microalgae could be regenerated using 0.1 M HCl, with up to 98% recovery, which allowed the reuse of the biomass in six biosorption-desorption cycles without any considerable loss of biosorption capacity. (c) 2005 Elsevier Ltd. All rights reserved.
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    Ethylenediamine grafted poly(glycidylmethacrylate-co-methylmethacrylate) adsorbent for removal of chromate anions
    (Elsevier Science Bv, 2005) Bayramoğlu, Gülay; Arıca, M. Yakup
    The removal of chromate anions (CrO42-) from aqueous solutions under different experimental conditions using cross-linked poly(glycidylmethacrylate-co-methylmethacrylate), poly(GMA-co-MMA), adsorbent was investigated in this study. The epoxy group containing adsorbent in the beads form was prepared from glycidylmethacrylate and methylmethacrylate via suspension polymerization. The epoxy groups of the poly (GMA-co-MMA) beads were used for grafting with ethylenediamine to prepare specific adsorbent (poly(GMA-co-MMA)-ED) for CrO42- anions removal from aqueous solutions. Adsorption equilibrium was achieved in approximately 120 min. The removal was favored at low pH, with a maximum adsorption at pH 2.0. Isotherm studies showed that CrO42- anions could be effectively removed by poly(GMA-co-MMA)-ED beads. The maximum adsorption capacities of the poly(GMA-co-MMA) and poly(GMA-co-MMA)-ED beads were 0.044 and 0.441 mmol CrO42- anions/g of dry adsorbents, respectively. The experimental data of the adsorption equilibrium from CrO42- anions aqueous solution correlated well with the Langmuir-Freundlich isotherm model. The experimental data were analyzed using the first- and the second-order kinetic models. The rate constants of adsorption for both kinetics models have been calculated. The second-order model provides the best correlation of the data. Desorption experiments show that the process of adsorption of CrO42- anions was reversible and the adsorbent was easily regenerated with 0.1 M NaOH up to 96% recovery. (C) 2005 Elsevier B.V. All rights reserved.
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    Heparin ve albumin tutuklanmış pHEMA bazlı biyoprotez geliştirilmesi
    (2003) Arıca, Yakup; Yılmaz, Meltem; Kaya, Bülent; Bayramoğlu, Gülay
    Bu çalışmanın başlıca amacı, biyolojik olarak uyumlu olan poli(hidroksietil metakrilat), pHEMA, hidrojel kökenli dolaşım sisteminde kullanılabilir yapay bir damar geliştirmekdi. Bu amaç doğrultusunda farklı miktarlarda heparin ve albumin tutuklanmış pHEMA-AL-HEP tüpleri hazırlandı. Proje kapsamının birinci aşamasında uygun çap ve boyutlara sahip ve farklı miktarlarda insan serum albumini içeren pHEMA-AL tüpleri 6 mm iç çapta yapay damar olarak fotopolimerizasyon yöntemi ile benzoil peroksit başlatıcısı varlığında sentezlendi. Albumin içeren pHEMA-AL yapıların kan uyumluluğunu artırmak ve yüzeyininde thrombus oluşumunu engellemek için karbodiimid ile aktive edildi ve yüzeye düşük molekül ağırlıklı heparin kovalent olarak bağlandı. Heparin bağlanma miktarları farklı albumin ve heparin başlangıç konsantrasyonlarında ayrıntılı olarak incelendi. pHEMA'nın biyolojik ve kan uyumluluğunu artırmak işin sentez sırasında insan serum albumini matriks içi tutuklama yöntemi ile yerleştirildi ve sonrasında yüzey modifikasyonu ile heparin, pHEMA-AL yapının yüzeyine kovalent olarak bağlandı Yapay damar olarak kullanıması planlanan yeni geliştirilen biyomateryalin, kan uyumluluk testleri kanda hemolitik aktivite, rekalsifikasyon zamanı, kan hücrelerinin kaybı ve kan pıhtılaşma zamanı gibi parametrelerle incelendi. Ayrıca rutin analizler dışında, geliştirilen biyomateryalin, yüzey özellikleri SEM, yüzey temas açıları, ve mekanik özellikleri ve kan serum proteinlerinin adsorpsiyonları detaylı olarak çalışıldı. Son olarak, optimize edilmiş koşullarda üretilen pHEMA-AL-HEP-3 polimerik yapay damar modeli sürekli sistemde 60 saat süre ile dayanıklılık testleri yapıldı.
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    Human serum albumin adsorption on poly[(glycidyl methacrylate)-co-(methyl methacrylate)] beads modified with a spacer-arm-attached L-histidine ligand
    (Wiley, 2006) Bayramoğlu, Gülay; Şenel, Ayşegül Ülkü; Yalçın, Emine; Arıca, M. Yakup
    Poly(GMA/MMA) beads were synthesized from glycidyl methacrylate (GMA) and methyl methacrylate (MMA) in the presence of a cross-linker (i.e. ethyleneglycol dimethacrylate) (EGDMA) via suspension polymerization. The epoxy groups of the poly(GMA/MMA) beads were converted into amino groups with either ammonia or 1,6-diaminohexane (i.e. spacer-arm). An L-histidine ligand was then covalently immobilized on the aminated (poly(GMA/MMA)-AH) and/or the spacer-arm attached (poly(GMA/MMA)-SAH) beads using glutaric dialdehyde as a coupling agent. Both affinity adsorbents were used in human serum albumin (HSA) adsorption/desorption studies under defined pH, ionic strength or temperature conditions in a batch reactor. The spacer-arm attached affinity adsorbent resulted in an increase in the adsorption capacity to HSA when compared to the aminated counterpart (i.e. poly(GMA/MMA)-AH). The maximum adsorption capacities of the affinity adsorbents were found to be significantly high, i.e. 43.7 and 80.2 mg g(-1) (of the beads), while the affinity constants, evaluated by the Langmuir model, were 3.96 x 10(-7) and 9.53 x 10(-7) molL(-1) for poly(GMA/MMA) -AH and poly(GMA/MMA)-SAH, respectively. The adsorption capacities of the affinity adsorbents were decreased for HSA by increasing the ionic strength, adjusted with NaCl. The adsorption kinetics of HSA were analysed by using pseudo-first and pseudo-second-order equations. The second-order equation fitted well with the experimental data. (c) 2005 Society of Chemical Industry.
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    Immobilization of Candida rugosa lipase onto spacer-arm attached poly(GMA-HEMA-EGDMA) microspheres
    (Elsevier Sci Ltd, 2005) Bayramoğlu, Gülay; Kaya, Bülent; Arıca, M. Yakup
    Epoxy group-containing poly(GMA-HEMA-EGDMA) microspheres were prepared by suspension polymerisation. The epoxy groups of the poly(GMA-HEMA-EGDMA) microspheres were used for the covalent attachment of Candida rugosa lipase and 1,6-diaminohexane (i.e., spacer-arm). C rugosa lipase was also covalently immobilised onto the spacer-arm-attached poly(GMA-HEMA-EGDMA) microspheres using glutaric dialdehyde as a coupling agent. The maximum lipase immobilization capacities of the poly(GMA-HEMA-EGDMA) and poly(GMA-HEMA-EGDMA)-spacer-arm attached microspheres were 16.1 and 28.3 mg g(-1), respectively. The attachment of the spacer-arm resulted in an increase in the apparent activity of the immobilised lipase with respect to the enzyme immobilised via the epoxy groups of the microspheres. The activity yield of the lipase immobilised on the spacer-arm attached microspheres was up to 45%, and this was 9% for the enzyme immobilized through epoxy groups. Therefore, the rest of the immobilization study was carried out using only spacer-arm attached microspheres. The optimum temperature for lipase immobilised on the spacer-arm attached microspheres was 5 degrees C higher than that of the free enzyme and was also significantly broader. The immobilised lipase had better resistance to temperature inactivation than did the free form. (c) 2004 Elsevier Ltd. All rights reserved.
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    Immobilization of urease via adsorption onto L-histidine-Ni(II) complexed poly(HEMA-MAH) microspheres: Preparation and characterization
    (Elsevier Sci Ltd, 2005) Bayramoğlu, Gülay; Yalçın, Emin; Arıca, M. Yakup
    Poly(2-hydroxyethyl methacrylate-co-N-methacryloly-L-histidinemethylester) poly(HEMA-MAH) microspheres was prepared via suspension polymerization. L-Histidine groups of the poly(HEMA-MAH) microspheres were then chelated with Ni(II) ions (poly(HEMA-MAH)-Ni(II)). Urease immobilization onto the poly(HEMA-MAH) and poly(HEMA-MAH)-Ni(II) microspheres from aqueous solutions was investigated in a batch system. The amount of immobilized urease on the poly(HEMA-MAH) and poly(REMA-MAH)-Ni(II) was 47.8 and 66.1 mg/g support, respectively. The values of Michaelis constants K-m for both immobilized urease preparations were significant higher than free enzyme, indicating decreased affinity by the enzyme for its substrate, whereas V-max values were smaller for both immobilized urease preparations compared to free enzyme. However, the urease-immobilized onto the poly(HEMA-MAH)-Ni(II) resulted in an increase in enzyme stability with time. Optimum operational temperature for both immobilized preparations was 5.0 degrees C higher than that of the free enzyme and the temperature profiles of the immobilized preparations were significantly broader. It was observed that enzyme could be repeatedly adsorbed and desorbed on the poly(HEMA-MAH) and poly(HEMA-MAH)-Ni(II) microspheres without loss of adsorption capacity or enzymic activity. Finally, a packed bed enzyme-reactor with/urease-immobilized poly(HEMA-MAH)-Ni(II) microspheres, were used for degradation of urea in the continuous operation mode. The enzyme-reactor operated continuously at 35 degrees C for 40 h without significant loss of performance. (c) 2005 Elsevier Ltd. All rights reserved.
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    Immunoglobulin G adsorption behavior of L-histidine ligand attached and Lewis metal ions chelated affinity membranes
    (Elsevier Science Bv, 2006) Bayramoğlu, Gülay; Çelik, Gökçe; Arica, M. Yakup
    Immobilized metal affinity membranes were prepared by chelating Cu(II) and Fe(III) ions on poly(2-hydroxyethyl methacrylate-glycidyl methacrylate), poly(HEMA-GMA) membranes using L-histidine as a chelating ligand. To achieve this goal, the poly(HEMA-GMA) membrane was prepared via UV initiated photopolymerization. A spacer-arm (i.e., 1,6-diaminohexane) was introduced through the epoxy groups of the membrane (poly(HEMA-GMA)-SA). A chelating ligand (i.e., L-histidine amino acid) was covalently attached on the poly(HEMA-GMA) and/or poly(HEMAGMA)-SA using glutaric dialdehyde as a coupling agent, poly(HEMA-GMA)-H and poly(HEMA-GMA)-SAH membranes, respectively. Then, Cu(II) and Fe(III) ions were chelated through poly(HEMA-GMA)-SAH membrane. The binding characteristics of human immunoglobulin G (IgG) to IMAC membranes and the selectivity of Cu(II) and Fe(III) ions to the IgG have been investigated from aqueous solution using L-histidine attached membrane (poly(HEMA-GMA)-SAH) as a control system. The experimental data was analyzed using two adsorption kinetic models, the pseudo-first-order and the pseudo-second-order, to determine the best-fit equation for the adsorption of IgG onto L-histidine incorporated and/or different metals ion immobilized affinity membranes. The first-order equation in the affinity membrane systems is the most appropriate equation to predict the adsorption capacity for all the tested adsorbents. Moreover, the effect of spacer-arm on the adsorption capacity was evaluated using poly(HEMA-GMA)-H membrane as a control system. The IgG binding order on the affinity membranes was poly(HEMA-GMA)-SAHCu(II) > poly(HEMA-GMA)-SAH-Fe(III) > poly(HEMA-GMA)-SAH > poly(HEMA-GMA)-H. Finally, the polarities and the surface free energies of the affinity membranes were determined by contact angle studies. (c) 2006 Elsevier B.V. All rights reserved.
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    Invertase reversibly immobilized onto polyethylenimine-grafted poly(GMA-MMA) beads for sucrose hydrolysis
    (Elsevier Science Bv, 2006) Arıca, M. Yakup; Bayramoğlu, Gülay
    The epoxy group containing poly(glycidyl methacrylate-co-methyl methacrylate) poly(GMA-MMA) beads were prepared by suspension polymerisation and the beads surface were grafted with polyethylenimine (PEI). The PEI-grafted beads were then used for invertase immobilization via adsorption. The immobilization of enzyme onto the poly(GMA-MMA)-PEI beads from aqueous solutions containing different amounts of invertase at different pH was investigated in a batch system. The maximum invertase immobilization capacity of the poly(GMA-MMA)-PEI beads was about 52 mg/g. It was shown that the relative activity of immobilized invertase was higher then that of the free enzyme over broader pH and temperature ranges. The Michaelis constant (K-m) and the maximum rate of reaction (V-max) were calculated from the Lineweaver-Burk plot. The K-m and V-max values of the immobilized invertase were larger than those of the free enzyme. The immobilized enzyme had a long-storage stability (only 6% activity decrease in 2 months) when the immobilized enzyme preparation was dried and stored at 4 degrees C while under wet condition 43% activity decrease was observed in the same period. After inactivation of enzyme, the poly(GMA-MMA)-PEI beads can be easily regenerated and reloaded with the enzyme for repeated use. (c) 2005 Elsevier B.V. All rights reserved.
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