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    ADSORPTION OF Fe2+ IONS WITH Saccharomyces cerevisiae IMMOBILIZED PUMICE STONE
    (Gazi Univ, 2005) Lale, Mustafa; Sahin, Nazan; Temocin, Zulfikar
    In this study, the adsorption conditions of Fe2+ ions on Saccharomyces cerevisae immobilized pumice stone were investigated by column method. In order to perform this aim, the effect of solution pH value, initial concentration of ions and suitable solution and concentration for recovery of adsorbed ions were investigated. At pH 5, the maximum adsorption was obtained. At optimal pH value, adsorption capacity of sorbent for metal was obtained as 1,81 mg.g(-1), when initial concentration was 60 mg.ml(-1). Influence of HCl, NaCl, NH4Cl and EDTA solutions on desorption were investigated and maximum recovery was achieved by 0,2M EDTA solution. Desorption were 98% level provided by 0,2 M EDTA solution.
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    The Analgesic Acetaminophen and the Antipsychotic Clozapine Can Each Redox-Cycle with Melanin
    (Amer Chemical Soc, 2017) Temocin, Zulfikar; Kim, Eunkyoung; Li, Jinyang; Panzella, Lucia; Alfieri, Maria Laura; Napolitano, Alessandra; Payne, Gregory F.
    Melanins are ubiquitous but their complexity and insolubility has hindered characterization of their structures and functions. We are developing electrochemical reverse engineering methodologies that focus on properties and especially on redox properties. Previous studies have shown that melanins (i) are redox-active and can rapidly and repeatedly exchange electrons with diffusible oxidants and reductants, and (ii) have redox potentials in midregion of the physiological range. These properties suggest the functional activities of melanins will depend on their redox context. The brain has a complex redox context with steep local gradients in O-2 that can promote redox-cycling between melanin and diffusible redox-active chemical species. Here, we performed in vitro reverse engineering studies and report that melanins can redox-cyde with two common redox-active drugs. Experimentally, we used two melanin models: a convenient natural melanin derived from cuttlefish (Sepia melanin) and a synthetic cysteinyldopamine-dopamine core-shell model of neuromelanin. One drug, acetaminophen (APAP), has been used clinically for over a century, and recent studies suggest that low doses of APAP can protect the brain from oxidative-stress-induced toxicity and neurodegeneration, while higher doses can have toxic effects in the brain. The second drug, clozapine (CLZ), is a second generation antipsychotic with polypharmacological activities that remain incompletely understood. These in vitro observations suggest that the redox activities of drugs may be relevant to their modes of-action, and that melanins may interact with drugs in ways that affect their activities, metabolism, and toxicities.
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    Conversion of Phenolic Compound in Aqueous Solution Using Immobilized Peroxidase onto Blend Nanofiber
    (Mehmet Sinan Bilgili, 2020) Temocin, Zulfikar; Kutluer, Serdar
    Phenolic compounds from various man-made activities pose threats to public health and aquatic ecosystems. The conversion of phenolic compound by immobilized peroxidase onto poly(vinyl alcohol)-poly(acrylic acid) blend nanofiber in aqueous solutions was studied by a batch equilibration technique. Pyrogallol was used as a model phenolic compound. Maximum conversion of pyrogallol was occurred at pH 8 value. The effect of temperature and the initial concentration of pyrogallol on the conversion of pyrogallol were also investigated. Reuse studies indicated that the immobilized peroxidase preserved its pyrogallol conversion efficiency by 50% despite15 reuse.
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    Covalent immobilization of Candida rugosa lipase on aldehyde functionalized hydrophobic support and the application for synthesis of oleic acid ester
    (Taylor & Francis Ltd, 2013) Temocin, Zulfikar
    This study focuses on Candida rugosa lipase (CRL) immobilization by covalent attachment on poly(ethylene terephthalate)-grafted glycidyl methacrylate (PET-g-GMA) fiber. The immobilization yielded a protein loading of 2.38mgg(-1) of PET-g-GMA fiber. The performances of the immobilized and free CRLs were evaluated with regard to hydrolysis of olive oil and esterification of oleic acid. The optimum activity pH of the CRL was changed by immobilization to neutral range. The maximum activity of the free and immobilized CRLs occurred at 40 and 45 degrees C respectively. The immobilized lipase retained 65% of its original activity at 50 degrees C for 2h. It was found that the immobilized lipase stored at 4 degrees C retained 90% of its original activity after 35days, whereas the free lipase stored at 4 degrees C retained 69% of its original activity after the same period. In the esterification experiments, the immobilized CRL could maintain a high activity at a water content range from 1.5 to 6% (v/v), while the activity of free CRL showed a clear dependence on water content and decreased rapidly at above 3% (v/v) water content. In addition, after five reuses, the esterification percent yield of the immobilized CRL slightly decreased from 29 to 27%.
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    Designing of a stable and selective glucose biosensor by glucose oxidase immobilization on glassy carbon electrode sensitive to H2O2 via nanofiber interface
    (SPRINGER, 2020) Temocin, Zulfikar
    The integration of the enzymes on the solid electrode surfaces is an indispensable step for the construction of the bioelectrochemical electrode. In the current work, the blend nanofibers consisting of poly (vinyl alcohol) and poly(ethyleneimine) were deposited by the electrospinning method on an H2O2-sensitive modified glassy carbon electrode. Glucose oxidase was immobilized on the glutaraldehyde-activated blend nanofibers. Bioelectrochemical electrode displayed a good linear response to the glucose concentration ranges with two separate calibration curves, from 2 to 8 mmol L-1 and from 10 to 30 mmol L-1. Besides, it showed a high anti-interference performance against ascorbic and uric acids as well as long-term storage stability over 63 days. Moreover, analysis results in a diluted human serum sample showed that the prepared bioelectrochemical electrode has the ability to measure glucose in real samples.
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    Modification of glassy carbon electrode in basic medium by electrochemical treatment for simultaneous determination of dopamine, ascorbic acid and uric acid
    (Elsevier Science Sa, 2013) Temocin, Zulfikar
    In this paper, a modified glassy carbon electrode was prepared by electrochemical method in basic media (0.5 M NaOH solutions) and was used to electrochemically detect dopamine (DA), ascorbic acid (AA), uric acid (UA) and their mixture by a differential pulse voltammetry (DPV) technique. In this simultaneous detection, the electrochemical potential difference between AA and DA was measured to be 165 mV, while between DA and UA it was 135 mV, and between AA and UA 300 mV. The potential differences were large enough to determine AA, DA, and UA individually and simultaneously. The DPV oxidation peak current was linearly dependent on DA, AA, and UA concentration in the range 3-30 mu M, 25-300 mu M, and 5-70 mu M, with correlation coefficients of 0.994, 0.998, and 0.996, respectively. The limit of detection (S/N = 3) was found to be 2.67, 23.38 and 4.70 mu M for DA, AA and UA. The modified electrode was applied to the determination of DA, AA, and UA in real samples. These results and interference studies showed that the modified electrode possesses the potential for simultaneous determination of DA, AA, and UA. (C) 2012 Elsevier B. V. All rights reserved.
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    Removal of Toxic Cr(VI) Ion from Aqueous Solution Using Amine-Functionalized Poly(Ethylene Terephthalate) Fiber
    (Mehmet Sinan Bilgili, 2020) Temocin, Zulfikar; Kutluer, Serdar
    The adsorption of toxic Cr(VI) ion on to aminated-poly(ethylene terephthalate) fiber in aqueous solutions was studied by a batch equilibration technique. Maximum adsorption of Cr(VI) ion was occurred at pH 4 value as 3.26 mg g(-1). The effect of mixing time and the initial concentration of the ion on the adsorption of Cr(VI) ion were also investigated. Desorption studies indicated that the maximum percent recovery of Cr(VI) was 98.2% with 0.1 M KOH solution.