Person: DEMİR, SERAP
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DEMİR
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SERAP
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Publication Metadata only Immobilization of pectinase on polyethyleneimine based support via spontaneous amino-yne click reaction(ELSEVIER, 2020) OKTAY, BURCU; Oktay, Burcu; Demir, Serap; Kayaman-Apohan, NilhanThe immobilization of an enzyme can improve catalytic activity, stability, and reusability of its. In this study, we investigated a new method for enzyme immobilization. Alkyne-pectinase was first immobilized on the polyethyleneimine-based cryogel via a spontaneous amino-yne click reaction under very mild conditions and then the apple juice was clarified. Amino-yne click reactions do not need any photoinitiator or catalyst, unlike other click reactions. The immobilization efficiency of the alkyne pectinase was 90%. The immobilized enzyme continued to retain 70% of its initial activity after 60 days. An improvement observed in the pH tolerance in the range of 6.5-8.0. The higher thermal tolerance of the immobilized pectinase was increased above 50 degrees C. Immobilized pectinase showed 100% activity at 55 degrees C and pH 6.5. The clarification rate of apple juice was achieved about 50% by the pectinase immobilized support. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.Publication Metadata only Nonhydrolytic sol-gel synthesized oligosiloxane resin reinforced thiol-ene photocured coatings for the immobilization of acetylcholinesterase(SPRINGER, 2019) ÇAKMAKÇI, EMRAH; Cakmakci, Emrah; Demir, SerapAcetylcholinesterase (AChE), which is responsible for the hydrolysis of neurotransmitter acetylcholine, is a critical enzyme for the nervous system and also a biomarker for organophosphorous pesticide detection. The immobilization of AChE is an active area of research and recently the use of sol-gel-derived materials for enzyme immobilization has gained a lot of attraction. In this work, AChE was covalently immobilized onto a photocured substrate which was reinforced with an oligosiloxane resin. The oligosiloxane resin was designed to have both vinyl and epoxide groups and prepared via nonhydrolytic sol-gel technique. The strategy employed in this study offered a platform that has good mechanical and thermal properties and also suitable for modification. Thus, AChE was also immobilized onto these substrates after amine modification of the epoxy groups and followed by glutaraldehyde activation. Over 80% enzyme immobilization yield was achieved. At certain pH values (5.5 and 8.5) and under relatively higher temperatures (above 40 degrees C) the immobilized enzymes were found to have higher catalytic activity than the free enzyme. Furthermore, by immobilization the reuse and the storage stability of the enzyme was improved and the stability of the immobilized enzyme against the inhibitory effects of certain metal cations was enhanced [GRAPHICS] . Nonhydrolytic sol-gel synthesized oligosiloxane resin reinforced thiol-ene photocured coatings for the immobilization of acetylcholinesterase. Emrah CAKMAKCI, Serap DEMIR. HighlightsAn oligosiloxane resin was prepared via nonhydrolytic sol-gel technique.The oligosiloxane resin was used to reinforce thiol-ene photocured coatings.Acetylcholinesterase was immobilized onto the photocured coatings.By immobilization, storage stability, reuse and metal ion resistance were improved.Publication Metadata only Physical and Covalent Immobilization of Lipase onto Amine Groups Bearing Thiol-Ene Photocured Coatings(HUMANA PRESS INC, 2017) ÇAKMAKÇI, EMRAH; Cakmakci, Emrah; Muhsir, Pelin; Demir, SerapIn this study, amine groups containing thiol-ene photocurable coating material for lipase immobilization were prepared. Lipase (EC 3.1.1.3) from Candida rugosa was immobilized onto the photocured coatings by physical adsorption and glutaraldehyde-activated covalent bonding methods, respectively. The catalytic efficiency of the immobilized and free enzymes was determined for the hydrolysis of p-nitrophenyl palmitate and also for the synthesis of p-nitrophenyl linoleate. The storage stability and the reusability of the immobilized enzyme and the effect of temperature and pH on the catalytic activities were also investigated. The optimum pH for free lipase and physically immobilized lipase was determined as 7.0, while it was found as 7.5 for the covalent immobilization. After immobilization, the optimum temperature increased from 37 A degrees C (free lipase) to 50-55 A degrees C. In the end of 15 repeated cycles, covalently bounded enzyme retained 60 and 70 % of its initial activities for hydrolytic and synthetic assays, respectively. While the physically bounded enzyme retained only 56 % of its hydrolytic activity and 67 % of its synthetic activity in the same cycle period. In the case of hydrolysis V (max) values slightly decreased after immobilization. For synthetic assay, the V (max) value for the covalently immobilized lipase was found as same as free lipase while it decreased dramatically for the physically immobilized lipase. Physically immobilized enzyme was found to be superior over covalent bonding in terms of enzyme loading capacity and optimum temperature and exhibited comparable re-use values and storage stability. Thus, a fast, easy, and less laborious method for lipase immobilization was developed.Publication Metadata only Preparation of a Poly(ethylene glycol)-Based Cross-Linked Network from a Click Reaction for Enzyme Immobilization(WILEY-V C H VERLAG GMBH, 2019) OKTAY, BURCU; Oktay, Burcu; Demir, Serap; Kayaman-Apohan, NilhanIn this study, a polyethylene glycol (PEG)-maleimide film was prepared by a thiol-ene click reaction. The covalent immobilization of amylase was carried out onto the PEG-maleimide based photo-curable network via epoxy and C=O groups without any linker. The epoxy and carbonyl groups on the PEG backbone improved the affinity of the enzyme. The immobilization yield of amylase onto the film was 72.46%. The immobilization capacity was also determined as 313 mg/g. The thermal stability of amylase improved via covalent attachment. Immobilized amylase showed maximum activity at 40 degrees C and pH 6.5. The immobilized amylase continued to retain 66% of its initial activity after 30 days.Publication Metadata only Xylanase immobilization on functionalized polyaniline support by covalent attachment(WILEY-V C H VERLAG GMBH, 2013) KAHRAMAN, MEMET VEZİR; Madakbas, Seyfullah; Danis, Ozkan; Demir, Serap; Kahraman, Memet VezirChemically synthesized polyaniline (PANI) was used as polymeric support for xylanase immobilization. The polymer was first activated with glutaraldehyde and then xylanase was successfully immobilized. Xylanase bound polymer was characterized using FTIR. The optimum pH of the immobilized enzyme was at pH 5, which was shifted 1.0?pH unit to the acidic region when compared to the free enzyme. Thermal stability of the xylanase was improved with the immobilization. The characteristic properties of the immobilized and native enzyme, such as kinetic activity, reusability and storage stability were also studied at optimum pH and temperature. Immobilized enzyme exhibited better reusability and storage stability than the free one. Vmax values for the free and immobilized enzymes were calculated as 1.44 and 0.44?mg/mL/min, respectively. The Km values for the immobilized xylanase were found to be lower.Publication Metadata only Covalent immobilization of a-amylase onto thermally crosslinked electrospun PVA/PAA nanofibrous hybrid membranes(WILEY, 2013) KAHRAMAN, MEMET VEZİR; Basturk, Emre; Demir, Serap; Danis, Ozkan; Kahraman, Memet VezirPoly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) nanofibers with the fiber diameter of 100150 nanometers were fabricated by electrospinning. PVA/PAA nanofibers were crosslinked by heat-induced esterification and resulting nanofiber mats insoluble in water. a-Amylase was covalently immobilized onto the PVA/PAA nanofiber surfaces via the activation of amine groups in the presence of 1,1'-carbonyldiimidazole. The immobilized a-amylase has more resistance to temperature inactivation than that of the free form and showed maximum activity at 50 degrees C. pH-dependent activities of the free and immobilized enzymes were also investigated, and it was found that the pH of maximum activity for the free enzyme was 6.5, while for the optimal pH of the immobilized enzyme was 6.0. Reuse studies demonstrated that the immobilized enzyme could reuse 15 times while retaining 81.7% of its activity. Free enzyme lost its activity completely within 15 days. Immobilized enzyme lost only 17.1% of its activity in 30 days. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012