Ayşe Dinçer

Biosensing approach for glutathione detection using glutathione reductase and sulfhydryl oxidase bienzymatic system

Chitosan membrane with glutathione reductase and sulfhydryl oxidase (SOX) was subsequently integrated onto the surface of spectrographic graphite rods for obtaining a glutathione biosensor. The working principle was based on the monitoring of O(2) consumption that correlates the concentration of glutathione during the enzymatic reaction. A linear relationship between sensor response and concentration was obtained between 0.5 and 2.0 mM for oxidized glutathione (GSSG), and 0.2-1.0 mM for reduced glutathione (GSH) in the presence of 2 microM nicotinamide adenine dinucleotide phosphate (NADPH) under the optimum working conditions. Also, reduced/oxidized glutathione were separated by HPLC and utility of bienzymatic system was investigated as an electrochemical detector for the analysis of these compounds. All data were given as a comparison of two systems: biosensor and diode array detector (DAD).

Immobilization of tyrosinase on chitosan–clay composite beads

Tyrosinase was immobilized on glutaraldehyde crosslinked chitosan-clay composite beads and used for phenol removal. Immobilization yield, loading efficiency and activity of tyrosinase immobilized beads were found as 67%, 25% and 1400 U/g beads respectively. Optimum pH of the free and immobilized enzyme was found as pH 7.0. Optimum temperature of the free and immobilized enzyme was determined as 25-30 °C and 25 °C respectively. The kinetic parameters of free and immobilized tyrosinase were calculated using l-catechol as a substrate and K(m) value for free and immobilized tyrosinase were found as 0.93 mM and 1.7 mM respectively. After seven times of repeated tests, each over 150 min, the efficiency of phenol removal using same immobilized tyrosinase beads were decreased to 43%.

Removal of lead (II) ions from aqueous solution by using crosslinked chitosan-clay beads

Abstract A simple and effective biodegradable material known as chitosan-clay composite beads were prepared to remove Pb(II) ions from aqueous solution. For this purpose, various important parameters such as contact time, pH and temperature were examined on the adsorption of Pb(II) ions onto crosslinked chitosan-clay composite beads. Maximum adsorption capacity of Pb(II) was observed at pH 4.5 and 25°C and calculated as 7.93 mg/g according to Langmuir isotherm model. Thermodynamic parameters namely ΔG°, ΔH° and ΔS° of the Pb(II) adsorption process have been calculated as 7.889 kJ/mol, −15.131 kJ/mol and −0.0785 kJ/molK respectively. EDTA was the best eluent for the desorption of Pb(II) ions from the crosslinked chitosan-clay beads. Scanning electron microscope (SEM) was used to characterize the surface morphology of the crosslinked chitosan-clay beads.

Characterization of β-glucosidase immobilized on chitosan-multiwalled carbon nanotubes (MWCNTS) and their application on tea extracts for aroma enhancement

β-Glucosidase was covalently immobilized on chitosan-MWCNTs carrier and its aroma enhancement effect in different tea samples was investigated. Chitosan-MWCNTs carrier was prepared by mixing chitosan with MWCNTs (5:1w/w) and characterization of prepared composite carrier was done by FTIR, TGA and SEM analysis. β-Glucosidase was covalently immobilized on the composite carrier after glutaraldeyde activation. After optimization of the immobilization conditions, immobilization yield was achieved as 95.22%. Optimum pH was found as pH 6.0 and pH 5.0 for free and immobilized enzyme, respectively. Optimum temperature of the enzyme was shifted from 35°C to 45°C after immobilization. The Km and Vmax values for immobilized β-glucosidase calculated as 5.55mM and 7.14U/mg protein respectively. Immobilized β-glucosidase showed better pH and storage stability than free enzyme. After storage at +4°C for 50days, the immobilized enzyme retained its 68.4% of the initial activity. The calculated half-life (t1/2) of immobilized enzyme was 115.8min. After 10 cycles of reuse, immobilized β-glucosidase showed 72.83% of its initial activity.

Immobilization of α‐Glucosidase in Chitosan Coated Polygalacturonic Acid

Abstract Crude α‐glucosidase from Bakers yeast was immobilized in polygalacturonic acid beads and coated with chitosan. Chemical and physical characterization were performed by using p‐nitrophenyl‐α‐D‐glucopyranoside (pNPG) as an artificial substrate. Operation, thermal, pH, and strorage stabilities of the free and immobilized enzyme were also examined. The stabilities of immobilized enzyme were found to be better than that of the free enzyme. Furthermore, the hydrolysis rate of the chitosan coated α‐glucosidase polygalacturonic acid beads were studied. In conclusion, the enzyme beads appear to have good characteristics and offer the prospect that this system may find application in enzyme immobilization, in addition to controlled drug release studies.

Caffeic Acid Detection Using an Inhibition-Based Lipoxygenase Sensor

An inhibition based biosensing system was developed for the caffeic acid as lipoxygenase (LOX) inhibitor. LOX was immobilized in carbon paste electrode and the amperometric detection of hydroperoxy linoleic acid due to the enzymatic reaction using linoleic acid as a substrate was monitored at +0.9 V versus Ag/AgCl. The decrease in biosensor response in the presence of caffeic acid was found to be correlated with the inhibitor concentration. Diode array detector and LOX biosensor was used as an electrochemical detector for the analysis of this compound. All data were given as a comparison of two systems.

Preparation of glutathione imprinted polymer.

Glutathione imprinted polymer was prepared using 1-vinyl imidazole and ethylene glycol dimethacrylate as the functional monomer and crosslinker, respectively, in dimethyl sulfoxide. The adsorption selectivity of glutathione-imprinted polymer was tested by reduced glutathione, oxidized glutathione, and L-Gly-Leu-Tyr in 30% phosphate buffer (0.01 M, pH 5.0)–70% acetonitrile and binding affinity values were compared. Reusability of molecularly imprinted polymer particles was also investigated. Molecularly imprinted polymer particles were found to be stable and to maintain glutathione adsorption capacity at 95% when washed with methanol–acetic acid (10%) after seven usages. Functional monomer 1-vinyl imidazole and cross linker ethylene glycol dimethacrylate-based glutathione imprinted polymer could be used as solid phase extraction material for recognition of glutathione in biological samples.

Differentially displayed proteins as a tool for the development of type 2 diabetes

Background Type 2 diabetes is a complex disease that still requires a great deal of work to be carried out to understand the pathophysiology. Recently, researchers have focused on studying the organs and tissues known to be involved in the development of the type 2 phenotype using a proteomic approach. Little work has been reported on plasma of type 2 diabetics in whom the clinical status has been well characterized. In this study, changes in plasma proteins of type 2 diabetics were investigated by proteomic analysis in well-characterized individuals with type 2 diabetes (early and late stage) and control groups (with or without a family history of diabetes). Methods Samples were analysed by two-dimensional gel electrophoresis and significantly differentiated proteins were identified by nano-LC-ESI-MS. Results A total of 12 protein signatures that were differentially displayed with high significance compared with controls were selected. Four of the differentially displayed proteins were identified as haptoglobin alpha2, haptoglobin Hp2(fragment) and transthyretin and Chain A (formerly prealbumin), and all were up-regulated. Thiol-specific antioxidant protein, Chain A, tertiary structures of three amyloidogenic transthretin variants and haptoglobin-related protein precursor were all down-regulated in controls with a family history of diabetes, early and late diabetic patients in comparison with the control. Conclusion A proteomic-based approach was used to discover and identify the differentially expressed proteins in various states of type 2 diabetes.

Poly(methyl methacrylate-ethylene glycol dimethacrylate) copolymer for adsorptive removal of erythrosine dye from aqueous solution

AbstractThe preparation and characterization of poly(methyl methacrylate-ethylene glycol dimethacrylate), (poly(MMA-EGDMA)) polymer for erythrosine adsorption has been investigated. Erythrosine is a synthetic red dye used to color food. Water-soluble acid dyes have caused serious water pollution. Poly(MMA-EGDMA) polymer showed better adsorption performance for erythrosine at acidic region and at 30°C. The adsorption process had also been verified by Langmuir and Freundlich adsorption isotherms at 30, 40, and 50°C. Free energy of adsorption (∆G°), enthalpy (∆H°), and entropy (∆S°) changes were calculated to predict the nature of adsorption. The estimated value for ∆G° was calculated as −125.6 kJ/mol at 303 K (30°C). The estimated value for ∆H° was found as −60.69 kJ/mol at 303 K. The negative value for ∆H° indicated that the adsorption of erythrosine on poly(MMA-EGDMA) polymer was an exothermic process.

Epichlorohydrin crosslinked chitosan–clay composite beads for on-line preconcentration and determination of chromium(III) by flow injection flame atomic absorption spectrometry

An on-line flow injection preconcentration-flame atomic absorption spectrometry (FI-AAS) method is developed for trace determination of chromium(III) by sorption on a mini-column packed with epichlorohydrin (ECH) crosslinked chitosan–clay composite beads. The factors affecting preconcentration of Cr(III) ions such as sample and eluent flow rate, loading time, sample and eluent pH, and eluent type and concentration were investigated. The Cr(III) ions were eluted from the mini-column with 0.1 M EDTA. Under the optimized parameters, the calibration graph using the preconcentration system for Cr(III) was linear with a correlation coefficient of 0.9982. Detection and quantification limits of the method were obtained to be 0.0162 and 0.0929 μg mL−1 respectively, with an enrichment factor of 13.4.