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Öğe Investigation of applicability of plant extracts (Euphorbia orientalis L.) instead of chemical disinfectants(Wiley-Blackwell, 2013) Alp Avcı, Gülçin; Avcı, Emre; Köse, Dursun Ali; Geldi, Merve; Uzeli, Sevil[Abstract Not Available]Öğe Electrochemical evaluation and determination of antiretroviral drug fosamprenavir using boron-doped diamond and glassy carbon electrodes(2010) Gümüştaş, Mehmet; Özkan, Sibel AyşılFosamprenavir is a pro-drug of the antiretroviral protease inhibitor amprenavir and is oxidizable at solid electrodes. The anodic oxidation behavior of fosamprenavir was investigated using cyclic and linear sweep voltammetry at boron-doped diamond and glassy carbon electrodes. In cyclic voltammetry, depending on pH values, fosamprenavir showed one sharp irreversible oxidation peak or wave depending on the working electrode. The mechanism of the oxidation process was discussed. The voltammetric study of some model compounds allowed elucidation of the possible oxidation mechanism of fosamprenavir. The aim of this study was to determine fosamprenavir levels in pharmaceutical formulations and biological samples by means of electrochemical methods. Using the sharp oxidation response, two voltammetric methods were described for the determination of fosamprenavir by differential pulse and square-wave voltammetry at the boron-doped diamond and glassy carbon electrodes. These two voltammetric techniques are 0.1 M H2SO4 and phosphate buffer at pH 2.0 which allow quantitation over a 4×10-6 to 8×10 -5 M range using boron-doped diamond and a 1×10-5 to 1×10-4 M range using glassy carbon electrodes, respectively, in supporting electrolyte. All necessary validation parameters were investigated and calculated. These methods were successfully applied for the analysis of fosamprenavir pharmaceutical dosage forms, human serum and urine samples. The standard addition method was used in biological media using boron-doped diamond electrode. No electroactive interferences from the tablet excipients or endogenous substances from biological material were found. The results were statistically compared with those obtained through an established HPLC-UV technique; no significant differences were found between the voltammetric and HPLC methods. © 2009 Springer-Verlag.Öğe Experimental and simulation study on structural characterization and hydrogen storage of metal organic structured compounds(Elsevier Ltd, 2016) Öztürk, Zeynel; Özken, Göksel; Köse, Dursun Ali; Asan, AbdurrahmanOne of the barrier for common usage of hydrogen energy system is storing hydrogen efficiently. Especially for mobile applications, it is very important to store hydrogen in small spaces reversibly. Metal-organic framework (MOF) structured materials step forward with the ability of reversible hydrogen storage which meet the storage targets. The MOF structured compounds were synthesized using Cu(II) and Zn(II) metals, trimesic acid (benzene 1,3,5 tricarboxylic acid) (TMA) and 1,10 phenantroline (Phen) building blocks. The compounds were activated thermally at 398 K for 4 days under a vacuum for sorption experiments. Then, DTA/TGA, FT-IR, powder-XRD, BET surface area and elemental analysis techniques were used to determine the molecular structures of the synthesized compound. Finally, the hydrogen storage properties were measured at 77 K and 1 bar of hydrogen pressure. In addition to experimental investigations, hydrogen adsorption characteristics and performances of the compounds were also determined with the molecular simulation calculations. It is found that the Cu(II) and Zn(II) compounds could uptake 2.652 wt. % (sim. 2.434 wt. %) and 1.383 wt. % (1.187 wt. %) respectively, at 77 K and 1 bar pressure. Consequently, hydrogen adsorption mechanism and capacities of the compounds clarified. And it is found out that the compounds have good storage performance in comparison to the previously reported MOFs. © 2015 Hydrogen Energy Publications LLC.Öğe Inhibition effect of berberine on the corrosion of copper in acidic medium(Editions de l'Academie Republique Populaire, 2013) Karadaş Bakırhan, Nurgül; Akbaş, AhmetInhibition of copper corrosion by berberine in 0.5 M HCl was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The inhibition efficiency of berberine was studied for five concentrations in the range 5.0×10 -5 -5.0×10 -3 M. Potentiodynamic polarization curves indicated that berberine act as mixed type inhibitor. The adsorption of the inhibitor was more suited with the Langmuir adsorption isotherm and kinetic parameters K ads and ?G ads were determined at room temperature. The surface morphology of the copper after its exposure to 0.5 M HCl solution with and without 5.0×10 -3 M berberine was examined by scanning electron microscopy (SEM). The results showed that berberine performed well inhibiting effect for the corrosion of the copper.Öğe Selective and sensitive determination of repaglinide in pharmaceuticals by voltammetric and LC methods(Editions de l'Academie Republique Populaire, 2015) Gümüştaş, Mehmet; Coşkun, Gökçe; Özkan, Sibel AyşılDetailed electrochemical study and novel voltammetric and LC methods are presented for the determination of repaglinide (RPG) in pharmaceuticals. Repaglinide in methanol: buffer solution (20:80; v/v) shows one or two anodic responses on glassy carbon electrode between pH 0.3 and 12.0 depending on the pH values. The HPLC and UPLC methods were developed using core shell columns with mobile phase consisting of 50:50; ACN:Water (0.05 % TFA; at pH: 3.0) (v/v) with UV detection at 215 nm. Finally, the proposed methods were successfully applied for the determination of RPG in pharmaceutical dosage forms. The proposed voltammetric and LC methods allow a number of cost and time saving benefits. RPG was also exposed to thermal, photolytic, oxidative stress, acid-base catalyzed hydrolyses, and the stressed samples were detected by the proposed RP-HPLC method.Öğe Validated electroanalytical and RP-LC assay of ertapenem in its pharmaceutical dosage form(Editions de l'Academie Republique Populaire, 2013) Gümüştaş, Mehmet; Karadaş Bakırhan, Nurgül; Özkan, Sibel AyşılErtapenem is a member of carbapenem group beta-lactam antibiotics. The electrochemical behavior of ertapenem at the surface on a boron-doped diamond electrode is described. It is investigated and determined using cyclic, linear sweep, differential pulse and square wave voltammetric techniques with this electrode. Two responses of ertapenem are irreversible in nature, and diffusion-controlled. A linear voltammetric response for both peaks was obtained in the concentration range of 1.0 to 12.00 µg.mL-1 for differential pulse and square wave voltammetric techniques. Also simple, accurate, precise and fully validated RP-LC assay as a comparison method of this compound in its dosage form has been developed. An X-Select RP-18 column at 25 °C was used with the mobile phase of water: methanol 55:45 (v/v) adjusted to pH 3.0. The RP-LC method allowed quantitation over the 1.0-15.00 µg.mL -1 range for ertapenem. The necessary statistical validation parameters with the system suitability test results revealed that the proposed methods are free from significant systematic errors. Degradation studies were also performed in bulk substance to demonstrate the stability indicating power with using chromatographic technique. The proposed methods successfully applied to the pharmaceutical dosage form.Öğe Electrochemical approach for the sensitive determination of anticancer drug epirubicin in pharmaceuticals in the presence of anionic surfactant(Editions de l'Academie Republique Populaire, 2013) Bozal Palabıyık, Burçin; Kurbanoğlu, Sevinç; Gümüştaş, Mehmet; Uslu, Bengi; Özkan, Sibel AyşılIn this research, sensitive, rapid, different electrochemical methods were developed for the determination of anticancer drug epirubicin. The aim of the study was to fully validated determination of epirubicin in pharmaceuticals, by means of electroanalytical methods. The detailed electrooxidative behavior of epirubicin was investigated using cyclic, differential pulse and square wave voltammetry at boron-doped diamond electrode. The possible oxidation mechanism was discussed. Surfactant effect was also examined using 1×10-3 M sodium dodecyl sulphate. The oxidation process was found nearly irreversible over the pH range studied and exhibited diffusion controlled electrode process. All experimental parameters have been optimized and the following studies were realized under the optimum conditions. The sensor used in this research is suitable for the analysis of the trace amounts of epirubicin in pharmaceuticals. The proposed methods were applied to commercial preparations and average percentage recovery was in good agreement between each other (differential pulse and square wave voltammetry).Öğe Investigation of immobilization and kinetic properties of catalase enzyme on poly(HEMA-GMA) cryogel(Slovak Academy of Sciences Institute of Experimental Physics Department of Biophysics, 2017) Erol, Kadir; Cebeci, Büşra; Köse, Kazım; Köse, Dursun AliCatalase is a metalloenzyme, which is found in almost all aerobic respiratory organisms. This enzyme acts as a detoxification agent for the hydrogen peroxide (H2O2) compound, protecting tissues and cells from oxidative damage [1]. Cryogels are synthetic materials commonly used in adsorption and immobilization studies in recent years. In this study, it is aimed to investigate immobilization conditions of catalase enzyme poly(HEMA-GMA) cryogel for 3, 6, 9, 12, 18 and 24 hours in stationary solution and to determine how the activity of immobilized catalase enzyme will be changed by pesticides. This is very important in determining the effect of antioxidant activity and catalase, which is an important enzyme in organisms, to environmental pollution. For the characterization of cryogels; swelling test, Fourier transform infrared spectroscopy (FT-IR) analysis, scanning electron microscopy (SEM) analysis and elemental analysis.
