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Öğe Catalase adsorption onto cibacron blue F3GA and Fe(III)derivatized poly(hydroxyethyl methacrylate) membranes and application to a continuous system(Elsevier Science Bv, 1997) Arica, MY; Denizli, A; Salih, B; Piskin, E; Hasirci, VPoly(2-hydroxyethyl methacrylate) (poly(HEMA)) membranes were prepared by W-initiated photopolymerization of HEMA in the presence of an initiator (a-a'-azobisisobutyronitrile, AIBN). An affinity dye, i.e. Cibacron Blue F3GA (CB) was incorporated covalently and then complexed with Fe(III) ions. The polyHEMA-CB and polyHEMA-CB-Fe(III) derivatized membranes were used in the adsorption of catalase (CAT). The enzyme-loading capability of the Fe(III)-containing membrane (23.6 mu g/cm(2)) was greater than that of the poly(HEMA)-CB derivatized membrane (17.1 mu g/cm(2)). The adsorption phenomena appeared to follow a typical Langmuir isotherm. The K-m values for both immobilized catalases (poly(HEMA)-CB-CAT (22.4 mM) and poly(HEMA)-CB-Fe(III)-CAT (19.3 mM)) were higher than that of free enzyme (16.5 mM). Optimum operational temperature was 5 degrees C higher than that of the free enzyme and was significantly broader. A similar observation was made for the optimum pH. Operational, thermal and storage stabilities were found to increase with immobilization, especially in the presence of Fe(III). It was observed that enzyme could be repeatedly adsorbed and desorbed without significant loss in adsorption capacity or enzyme activity.Öğe Cibacron Blue F3GA-incorporated macroporous poly(2-hydroxyethyl methacrylate) affinity membranes for heavy metal removal(Elsevier Science Bv, 1997) Denizli, A; Salih, B; Arica, MY; Kesenci, K; Hasirci, V; Piskin, EMacroporous poly(2-hydroxyethyl methacrylate), poly(HEMA), membranes were prepared by UV-initiated photo-polymerization of HEMA in the presence of an initiator (azobisisobutyronitrile, AIBN). An affinity dye, i.e., Cibacron Blue F3GA was then incorporated covalently. These affinity membranes with a swelling ratio of 58%, and carrying 10.67 mmol Cibacron Blue F3GA/m(2) membrane were used in the adsorption/desorption of some selected heavy metal ions [i.e., As(III), Cd(II) and Pb(II)] from aqueous media. Very high adsorption rates were observed and adsorption equilibria were reached in about 30 min. The maximum adsorptions of heavy metal ions onto the dye-incorporated affinity membranes from their single solutions were 12.6 mmol/m(2) for As(III), 61.0 mol/m(2) for Cd(II) and 79.0 mol/m(2) for Pb(II), However, when the heavy metal ions competed (in the case of the adsorption from their mixture) the amounts of adsorption for As(III), Cd(II) and Pb(II) were quite close. Desorption of heavy metal ions was carried out by using 0.1 M HNO3 (pH 1.0). Up to 95% of the adsorbed heavy metal ions were desorbed in 60 min. Repeated adsorption/desorption cycles showed the feasibility of this novel affinity membrane for heavy metal removal.Öğe Comparison of β-galactosidase immobilization by entrapment in and adsorption on poly(2-hydroxyethylmethacrylate) membranes(John Wiley & Sons Ltd, 1997) Baran, T; Arica, MY; Denizli, A; Hasirci, Vbeta-Galactosidase was immobilized in/on poly(2-hydroxyethyl methacrylate) (pHEMA) membranes by two different methods: adsorption on Cibacron F3GA derivatized pHEMA membranes (pHEMA-CB), and entrapment in the bulk of the pHEMA membranes. The maximum beta-galactosidase adsorption on pHEMA-CB membranes was obtained as 95.6 mu g cm(-2) in 2.0 mg cm(-3) enzyme solution. The adsorption phenomena appeared to follow a typical Langmuir isotherm. In the entrapment, an increase in beta-galactosidase loading resulted in a consistent increase in membrane activity from 3.3 x 10(-2) to 17.8 x 10(-2) U cm(-2) pHEMA membranes. The K-m values for both immobilized beta-galactosidase (adsorbed 0.32 mM and entrapped 0.81 mM) were higher than that of the free enzyme (0.26 mM). The optimum reaction temperature of the adsorbed enzyme was 5 degrees C higher than that of both the free and the entrapped enzyme. The optimum reaction pH was 7.5 for free and both immobilized preparations. After 15 successive uses the retained activity of the adsorbed and the entrapped enzymes was 80% and 95%, respectively. The storage stability of the enzyme was found to increase upon immobilization.Öğe Controlled release of aldicarb from carboxymethyl cellulose microspheres: in vitro and field applications(John Wiley & Sons Ltd, 1999) Kok, FN; Arica, MY; Gencer, O; Abak, K; Hasirci, VAldicarb is a carbamate pesticide that is widely used throughout the world in the protection Of crops (eg cotton, nuts, potatoes, onion, tobacco, sugar beet and sugar cane). In Turkey, especially in the Cukurova region, it is used for the control of the cotton white fly (Bemisia tabaci) which attacks cotton plants cultivated in this region. Aldicarb contamination in surface and ground water is a serious problem in several countries, partly due to its high water solubility. It is also highly toxic to mammals. In order to overcome these problems, microspheres of aldicarb were prepared using carboxymethyl cellulose (CMC) as the biodegradable support material cross-linked with aluminium chloride. A strong hysteresis behaviour was observed upon drying and reswelling. Encapsulation efficiency was in the range 12-23% and aldicarb contents of 5.7-10.3 mg per 100mg of microspheres was achieved. In vitro release was distinctly Fickian, and Higuchi constants were very close to 0.5. Release in pots revealed that only one sample had a release capability for more than four weeks. In the cotton plot much longer durations of release (more than seven weeks) were observed while a commercial granular formulation released its content immediately. It was thus possible to construct a controlled pesticide release system that prolonged the bioavailability to about eight weeks. (C) 1999 Society of Chemical Industry.Öğe Controlled release of Aldicarb from carboxymethylcellulose microcapsules(Scientific Technical Research Council Turkey, 1997) Arica, MY; Yigitoglu, M; Lale, M; Kok, FN; Hasirci, VSodium carboxymethyl cellulose was converted into microspheres by crosslinking with aluminum chloride. Various microsheres with different amounts of crosslinker, biopolymer of various concentrations and molecular weights, and with different pesticide (Aldicarb) contents and pesticide to polymer ratios were prepared. The pesticide encapsulation efficiencies and aldicarb release kinetics of the resultant microcapsules were investigated. It was possible to modify the release behaviour by varying the above parameters and to have drug release with half-lives longer than 100 hours in aqueous media. The release kinetics were described by first order and zero order kinetics.Öğe Controlled release of aldicarb from lignin loaded ionotropic hydrogel microspheres(Taylor & Francis Ltd, 1999) Kok, FN; Wilkins, RM; Cain, RB; Arica, MY; Alaeddinoglu, G; Hasirci, VAldicarb loaded microspheres of carboxymethyl cellulose, CMC, of various compositions were prepared with the crosslinking action of AI(III). Into these microspheres, lignin was introduced as a filler to further regulate the rate of release. The encapsulation efficiency was low (4.15-13.00%) due to the high water solubility of aldicarb. Release into aqueous media was quite rapid and almost complete within 24h. Initial stages of the release (60% of AS released) was investigated to determine the release mechanism and it was found that release from the microspheres was governed by Fickian diffusion. Among the various parameters, the ratio of lignin to CMC and aldicarb to CMC were found to be influential on the rate of release from the crosslinked CMC-lignin microspheres. The soil behaviour confirmed the delayed release effect of the controlled release formulation compared to Temik (a commercial preparation of aldicarb), especially when lignin was incorporated.Öğe Dye derived and metal incorporated affinity poly(2-hydroxyethyl methacrylate) membranes for use in enzyme immobilization(John Wiley & Sons Ltd, 1998) Arica, MY; Denizli, A; Baran, T; Hasirci, VMicroporous poly(2-hydroxyethyl methacrylate) (PHEMA) membranes were prepared by W-initiated photopolymerization of HEMA in the presence of an initiator (alpha,alpha'-azobisisobutyronitrile, AIBN). An affinity dye Cibacron Blue F3GA (CB) was attached covalently and then Fe3+ ions incorporated. The PHEMA-CB and PHEMA-CB-Fe3+ membranes derived were used for adsorption of glucose oxidase (GOD). The adsorption capacities of these membranes were determined under conditions of different pH and with different concentrations of the adsorbate in the medium. The adsorption phenomena appeared to follow a typical Langmuir isotherm. The glucose oxidase adsorption capacity of the Fe3+ incorporated membrane (87 mu g cm(-2)) was greater than that of the dye-derived membrane (66 mu g cm(-2)). Non-specific adsorption of the glucose oxidase on the PHEMA membranes was negligible. The K-m values for both immobilized glucose oxidase PHEMA-CB-GOD (8.3) and PHEMA-CB-Fe3+-GOD (7.6) were higher than that of the free enzyme (6.2 mM). Optimum reaction pH was 5.5 for the free and 6.0 for both immobilized preparations. The optimum reaction temperature of the adsorbed enzymes was 5 degrees C higher than that of the free enzyme and was significantly broader. After 15 successive uses the retained activity of the adsorbed enzyme was 87%. It was observed that enzymes could be repeatedly adsorbed and desorbed on the derived PHEMA membranes without significant loss in adsorption capacity or enzymic activity. (C) 1998 SCI.Öğe Immobilization of glucoamylase onto activated pHEMA/EGDMA microspheres: properties and application to a packed-bed reactor(Elsevier Science Inc, 1998) Arica, MY; Alaeddinoglu, NG; Hasirci, VGlucoamylase was covalently immobilized onto pHEMA/EGDMA microspheres of two different sizes: 50-100 mu m and 100-200 mu m in diameter. The activity of the enzyme on smaller microspheres was found to be almost twice that of the larger microspheres. A higher enzyme lending was observed on small microspheres (0.64 mg g(-1) support) as compared to large spheres (0.40 mg g(-1) support). The K-m of glucoamylase was significantly increased (approximately five times) upon immobilization, indicating decreased affinity by the enzyme for its substrate. V-max of the enzyme was, however, not as significantly altered upon immobilization as the K-m. More significantly, the V-max was much higher with the large substrate (dextrin) than it was with the small substrate (maltose). Activity of the immobilized enzyme was quite stable. In 120 h, only 9.0% of the immobilized glucoamylase activity was lost. (C) 1998 Elsevier Science Inc.Öğe Immobilization of glucose oxidase and urease in hydrogel matrices(Scientific Technical Research Council Turkey, 1997) Gurel, I; Arica, MY; Hasirci, VImmobilization of glucose oxidase and urease in hydrogels of 2-hydroxyethyl methacrylae, and N-vinyl pyrrolidone (NVP) was achieved by irradiation (using UV kand gamma-rays). The effect of radiation on entrapment efficiencies, retention of activities and swelling rates was obtained. To optimize the system, duration of exposure, reaction temperature, co-monomer concentrations, initiator and cross linker compositions were varied. The repeated reusability of the generated products was also tested. It was found that gamma-irradiation at very low temperatures did not have a detrimental effect on the enzyme activity. Incorporation of more hydrophilic monomer (NVP), influenced matrix morphology and entrapment efficiencies and retained enzyme activities positively Repeated use studies revealed that there is a gradual loss (higher in the NVPL incorporated group) of activity following 10 runs. With the use of the present approach it is believed that the construction of biosensors using hydrogels of arious forms is possible.Öğe In-vitro studies of enteric coated diclofenac sodium-carboxymethylcellulose microspheres(Taylor & Francis Ltd, 1996) Arica, B; Arica, MY; Kas, HS; Hincal, AA; Hasirci, VMicrospheres containing diclofenac sodium (DS) were prepared using carboxymethylcellulose (CMC) as the main support material (1.0, 2.0, 3.0% (w/v)) and aluminium chloride as the crosslinker. Drug to polymer ratios of 1:1, 1:2 and 1:4 were used to obtain a range of microspheres. The microspheres were then coated with an enteric coating material, Eudragit(R)S-100, with aqueous solution concentrations of 10 and 20% (w/v). Encapsulation efficiency, % yield value, particle sizes and in-vitro dissolution behaviour were investigated. The surface of the enteric coated microspheres seemed to be all covered with Eudragit(R)S-100 from scanning electron microscopy observation. It was also observed that increasing the CMC concentration led to an increase in the encapsulation efficiency, % yield value and particle size and decreased the release rate. Eudragit(R)S-100 coating did not significantly alter the size but the release rate was significantly lower even when the lower concentration solution was used.Öğe Novel dye-attached macroporous films for cadmium, zinc and lead sorption: Alkali Blue 6B-attached macroporous poly(2-hydroxyethyl methacrylate)(Elsevier Science Bv, 1998) Denizli, A; Kesenci, K; Arica, MY; Salih, B; Hasirci, V; Piskin, EAlkali Blue GB-attached poly(2-hydroxyethyl methacrylate) (poly(HEMA)) microporous films were investigated as chelate forming sorbents for heavy metal removal. Poly(HEMA) microporous films were prepared by UV-initiated photo-polymerization of HEMA in the presence of an initiator (azobisisobutyronitrile (AIBN)). Alkali Blue 6E was attached covalently. These films with a swelling ratio of 58%, and carrying 14.8 mmol Alkali Blue 6E m(-2) which were then used in the removal of Cd(II), Zn(II) and Pb(II) from aqueous media. Adsorption rates were very high, equilibrium was achieved in about 30 min. The maximum adsorption of heavy metal ions onto the Alkali Blue BE-attached films were 41.4 mmol m(-2) for Cd(II), 52.4 mmol m(-2) for Zn(II), and 64.5 mmol m(-2) for Pb(II). When the heavy metal ions competed during the adsorption from a mixture the adsorption values for Cd(II), Zn(II) and Pb(II) were quite close. Heavy metal ions were desorbed by using 0.1 M HNO3. A significant amount of the adsorbed heavy metal ions (up to 95%) could be desorbed in 30 min. Repeated adsorption/desorption cycles showed the feasibility of these novel dye-attached microporous films for heavy metal removal. (C) 1998 Elsevier Science B.V. All rights reserved.Öğe Synthesis and mechanical properties of interpenetrating networks of polyhydroxybutyrate-co-hydroxyvalerate and polyhydroxyethyl methacrylate(Elsevier Sci Ltd, 1998) Gursel, I; Balcik, C; Arica, Y; Akkus, O; Akkas, N; Hasirci, VNaturally occurring, biocompatible, and biodegradable polyhydroxybutyrate-co-hydroxyvalerate (PHBV), and synthetic, non-degrading polyhydroxyethylmethacrylate (PHEMA) membranes were prepared and their mechanical properties were studied. Their performances were compared with the interpenetrating networks (IPN) prepared by photopolymerization of HEMA in the presence of PHBV. The modulus of elasticity, failure stress and failure strain indicated that the IPNs are viscoelastic with properties closer to PHEMA but much stronger than PHEMA homopolymers. Incorporation of PHBV (7, 14 and 22% I-IV) affected the mechanical properties positively. Increasing the PHBV content increased the modulus of elasticity and failure stress nearly in all samples tested. PHBV (7, 14, and 22% HV, 300 mg) samples showed an approximately 17-30 fold increase in terms of modulus of elasticity and 7-10 fold increase in terms of failure stress. The scanning electron micrographs of the membranes showed that the PHEMA membranes are more porous than the PHBV membranes but the IPN structure displayed channels on the membrane surface indicating that HEMA polymerization was achieved by using the PHBV as a scaffold. With the use of the present technique, it is possible to synthesize supramolecular structures from molecules that are not compatible and miscible with each other. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.
