Bülent Zeybek

Electrochemical DNA biosensor based on poly(2,6-pyridinedicarboxylic acid) modified glassy carbon electrode for the determination of anticancer drug gemcitabine

In this study, a simple methodology was used to develop a new electrochemical DNA biosensor based on poly(2,6-pyridinedicarboxylic acid) (P(PDCA)) modified glassy carbon electrode (GCE). This modified electrode was used to monitor for the electrochemical interaction between the dsDNA and gemcitabine (GEM) for the first time. A decrease in oxidation signals of guanine after the interaction of the dsDNA with the GEM was used as an indicator for the selective determination of the GEM via differential pulse voltammetry (DPV). The guanine oxidation peak currents were linearly proportional to the concentrations of the GEM in the range of 1-30mgL(‒1). Limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.276mgL(‒1) and 0.922mgL(‒1), respectively. The reproducibility, repeatability, and applicability of the analysis to pharmaceutical dosage forms and human serum samples were also examined. In addition to DPV method, UV-vis and viscosity measurements were utilized to propose the interaction mechanism between the GEM and the dsDNA. The novel DNA biosensor could serve for sensitive, accurate and rapid determination of the GEM.

A sensitive electrochemical DNA biosensor for antineoplastic drug 5-fluorouracil based on glassy carbon electrode modified with poly(bromocresol purple)

This paper describes an electrochemical sensor for the first time based on poly(bromocresol purple) (P(BCP)) developed to observe the interaction between 5-fluorouracil (5-FU) and fish sperm double strand DNA (dsDNA). The P(BCP) film was electrosynthesized by cyclic voltammetry method on the glassy carbon electrode (GCE). The dsDNA was electrochemically immobilized on the surface of P(BCP) modified GCE and the DNA biosensor was prepared. The interaction mechanism of dsDNA with 5-FU was investigated by differential pulse voltammetry using this biosensor. A decrease in the guanine oxidation peak current of the biosensor was observed after the interaction of dsDNA and 5-FU in 0.5 mol L(-1) acetate buffer (pH 4.8) containing 0.02 mol L(-1) NaCl. The accumulation time and dsDNA concentration were optimized to obtain the best peak current response. Under optimum conditions, the linear response on the guanine signal decreasing curve was observed in the 5-FU concentration range of 1.0-50 mg L(-1). The interaction mechanism between dsDNA and 5-FU was further investigated by UV-vis spectroscopy and viscometer. The results reveal that intercalation is the primary mode of interaction between 5-FU and dsDNA.

Electrochemical glucose biosensor based on nickel oxide nanoparticle-modified carbon paste electrode

Abstract In the present work, we designed an amperometric glucose biosensor based on nickel oxide nanoparticles (NiONPs)-modified carbon paste electrode. The biosensor was prepared by incorporation of glucose oxidase and NiONPs into a carbon paste matrix. It showed good analytical performances such as high sensitivity (367 μA mmolL–1) and a wide linear response from 1.9 × 10–3 mmolL–1 to 15.0 mmolL–1 with a limit of detection (0.11 μmolL–1). The biosensor was used for the determination of glucose in human serum samples. The results illustrate that NiONPs have enormous potential in the construction of biosensor for determination of glucose.

Amperometric carbon paste enzyme electrodes with Fe(3)O(4) nanoparticles and 1,4-benzoquinone for glucose determination.

Abstract Two new amperometric carbon paste enzyme electrodes including Fe3O4 nanoparticles with and without 1,4-benzoquinone were developed for glucose determination. Electron transfer properties of unmodified and Fe3O4 nanoparticles and/or 1,4-benzoquinone modified carbon paste electrodes were investigated in 0.1 M KCl support electrolyte containing Fe(CN)63−/4− as redox probe by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. Fe3O4 nanoparticles increased electron transfer at solution/electrode interface. The parameters affecting the analytical performance of the enzyme electrode have been investigated in detail and optimized for Fe3O4 nanoparticle modified enzyme electrode (Fe3O4–CPEE). Fe3O4 nanoparticles and 1,4-benzoquinone modified enzyme electrode (BQ‐Fe3O4‐CPEE) exhibited linear response from 1.9 × 10‐7 M to 3.7 × 10‐6 M, from 7.2 × 10‐6 M to 1.5 × 10‐4 M and from 1.3 × 10‐3 M to 1.2 × 10‐2 M with an excellent detection limit of 1.9 × 10‐8 M. BQ‐Fe3O4‐CPEE was used for determination of glucose in serum samples and results were in good agreement with those obtained by spectrophotometric method.

Determination of the Ionization Constants of Some Benzoyl Thiourea Derivatives in Dioxane-Water Mixture

The stoichiometric ionization constants of N,N-dialkyl--(4-substituted benzoyl) thiourea (Substitutes: H, Cl, and Br; alkyl groups: ethyl, n-propyl, n-butyl, and phenyl) derivatives have been determined potentiometrically in dioxane-water (v:v, 50:50) mixture at ionic strength of 0.1 M and °C. The ionization constants were calculated with the BEST computer program and the formation curves using the data obtained from the potentiometric titrations. The effects of substituents and alkyl groups on the ionization constants of the benzoyl thiourea derivatives have been investigated. A comparison of the basicities of ethyl, n-propyl, and n-butyl thiourea derivatives shows that the n-butyl group is a more powerful electron-releasing group than the other groups in 50% dioxane-50% water mixture (v:v). So, the acidity of benzoyl thiourea derivative compounds decreases, while the length of alkyl chain increases. The orders of values for all thiourea derivatives are as expected in the light of steric, resonance and inductive effects of substituents. Furthermore, when the basicities of halogen derivatives of the same substitution pattern are compared, orders obtained (4-Br -Cl -H) can be explained by considering the total electronic substituent effect (electron-withdrawing and electron-donating effects) except the 4-Br_Ph derivative.

Electrochemical Behaviors and Determinations of Some 2,5-Disubstituted Benzoxazole Compounds at the Hanging Mercury Drop Electrode

The electrochemical behaviors of N-(2-benzylbenzoxazol-5-yl)benzamide (B1), N-(2-benzylbenzoxazol-5-yl)4-nitrobenzamide (B2) and N-(2-(4-chlorobenzyl)benzoxazol-5-yl)-4-nitrobenzamide (B3) were investigated by cyclic voltammetry (CV), square wave voltammetry (SWV), differential puls voltammetry (DPV), chronoamperometry (CA) and bulk electrolysis (BE) techniques in dimethylsulfoxide (DMSO) containing 0.1 M tetrabutylammonium tetrafluoroborate (TBATFB). The number of electrons transferred and diffusion coefficients were calculated by using chronoamperometry and bulk electrolysis techniques. Standard heterogeneous rate constants for the electrochemical reduction were calculated by Klingler-Kochi technique. The data obtained showed that the quantitative determination of benzoxazoles could be done by using DPV and SWV rapidly and sensitively. For the DPV technique, linear working ranges for B2 and B3 were found to be (6.0 10-4.0 10) M and (1.0 10-2.0 10) M respectively. The corresponding ranges for these compounds found by SWV were (6.0 10-4.0 10) M and (1.0 10-2.0 10) M. The detection limits for B2 obtained from DPV and SWV were calculated to be 1.33 10 M and 1.76 10 M respectively. The detection limits with B3 deplicted to be almost the same.

Fenolik Bileşiklerin Tayini için Polifenol Oksidaz Temelli Amperometrik Enzim Elektrot Hazırlanması

In this study, amperometric enzyme electrodes based on polymer film for determination phenolic compounds were prepared. For this purpose platin electrodes were modified by electropolymerization using asetonitril-water mixture containing o-phenylenediamine (o-PD) or o-phenylenediamine C and -0.20 V (vs. Ag/AgCl) respectively. The linear working range of 1.96×10-6-3.5×10-5 M. Response time, reusability, life time, and amperometric responses to other phenolic compounds were also investigated.and 3-methylthiophene (3MT). Polyphenol oxidase was immobilized onto Pt/PoPD and Pt/PoPD-3MT electrodes and amperomeric responses to pyrocatechol were investigated. Pt/PoPD-3MT/POx electrode that obtained higher sensitivity was used for determination of working conditions and performance factors. Optimum type of buffer, buffer concentration, pH, temperature and working potential were determinated as phos