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An amperometric biosensor for uric acid determination prepared from uricase immobilized in polypyrrole film.

In order to prepare a biosensor for the determination of uric acid, electropolymerization of pyrrole on Pt surface was carried out with an electrochemical cell containing pyrrole, ferrocene (as a electron mediator) and tetrabutylammonium tetrafluoroborat in acetonitrile by cyclic voltammetry between 0.0 and 1.0 V (vs. Ag/AgCl) at a scan rate of 50 mV/s upon Pt electrode. Uricase was immobilized by a glutaraldehyde/gelatine croslinking procedure on to polypyrrole film after the electropolymerization processes. The response of the biosensor against uric acid was measured after 330 seconds following the application of a constant potential of +0.7 V (vs. Ag/AgCl). The resulting biosensor exhibits excellent electrocatalysis for the uric acid. The amperometric determination is based on the electrochemical detection of H2O2, which is generated in enzymatic reaction of uric acid. The sensor responds to uric acid with a detection limit of 5.0 × 10−7 M. The sensor remains relatively stable for 5 weeks. Interference effect were investigated on the amperometric response of the biosensor. Determination of uric acid was carried out in the biological fluids by biosensor.

Synthesis, characterization, electrochemical behavior, and antimicrobial activities of aromatic/heteroaromatic sulfonylhydrazone derivatives

The aromatic/heteroaromatic sulfonylhydrazone derivatives as indole-3-carboxaldehyde methanesulfonylhydrazone (1), indole-3-carboxaldehydeethanesulfonyl hydrazone (2), thiophene-2-carboxaldehydeethanesulfonylhydrazone (3), 2-hydroxybenzaldehydeethanesulfonyl hydrazone (4), 2-hydroxyacetophenoneethanesulfonylhydrazone (5) and 2-hydroxy-1-naphth aldehydeethane sulfonylhydrazone (6) were synthesized by the reaction of sulfonic acids with aromatic/heteroaromatic aldehydes and characterized by using elemental analysis, 1H–13C NMR, LC–MS and IR spectra. The electrochemical behavior of the sulfonylhydrazones in DMSO at glassy carbon electrode was investigated using cyclic voltammetry, controlled potential electrolysis and chronoamperometry techniques. The number of electrons transferred, diffusion coefficient and standard heterogeneous rate constants were determined using electrochemical methods. Antimicrobial activities of the compounds 1–6 were tested against some microorganisms. The biological activity screening showed that compound 6 exhibited better activity than the others. Structure–activity relationship analysis of the sulfonylhydrazone derivatives was performed to explain the trend of activity with molecular descriptors. The indicator descriptors for compound 6 having naphtyl ring are the most important descriptos that are sensitive both to the size and electrophility of the molecules.

Synthesis, potentiometric and antimicrobial activity studies on DL-amino acids-Schiff bases and their complexes

A relationship between antimicrobial activities and the formation constants of amino acid-Schiff bases and their Cu(II) and Ni(II) complexes was studied. For this purpose, a series of Schiff bases were prepared from DL-amino acids (DL-glycine, DL-alanine) and halo aldehydes (5-chloro-2-hydroxybenzaldehyde, 5-bromo-2-hydroxybenzaldehyde). Schiff bases and their Cu(II) and Ni(II) complexes were characterized by the elemental analysis, spectral analysis, magnetic moment (at ca. 25°C), molar conductivity, and thermal analysis data. The complexes were found to have general compositions [ML(H2O)]. The protonation constants of the Schiff bases and stability constants of the complexes were determined potentiometrically in a dioxane-water (1: 1) solution at 25°C and 0.1 M KCl ionic strength. Antimicrobial activities of the Schiff bases and their complexes were estimated for six bacteria, such as Bacillus cereus RSKK 863, Staphylococcus aureus ATCC 259231, Micrococcus luteus NRLL B-4375, Escherichia coli ATCC 11230, Aeromonas hydrophila 106, Pseudomonas aeroginosa ATCC 29212, and the yeast Candida albicans ATCC 10239. The role of halogen substitution on the ligands, effect of the metal ion, and stabilities of the complexes are discussed on antimicrobial activities.

Glucose biosensor based on the immobilization of glucose oxidase on electrochemically synthesized polypyrrole-poly(vinyl sulphonate) composite film by cross-linking with glutaraldehyde

Abstract In this study, a novel amperometric glucose biosensor was developed by immobilizing glucose oxidase (GOX) by cross-linking via glutaraldehyde on electrochemically polymerized polypyrrole-poly(vinyl sulphonate) (PPy–PVS) films on the surface of a platinum (Pt) electrode. Electropolymerization of pyrrole and poly(vinyl sulphonate) on the Pt surface was carried out with an electrochemical cell containing pyrrole and poly(vinyl sulphonate) by cyclic voltammetry between −1.0 and + 2.0 V (vs.Ag/AgCl) at a scan rate of 50 mV/s upon the Pt electrode. The amperometric determination was based on the electrochemical detection of H2O2 generated in enzymatic reaction of glucose. Determination of glucose was carried out by the oxidation of enzymatically produced H2O2 at 0.4 V vs. Ag/AgCl. The effects of pH and temperature were investigated and optimum parameters were found to be 7.5 and 65°C, respectively. The effect of working potential was investigated and optimum potential was determined to be 0.4 V. The operational stability of the enzyme electrode was also studied. The response of the PPy/PVS-GOX glucose biosensor exhibited good reproducibility with a relative standard deviation (RSD) of 2.48%. The glucose biosensor retained 63% of initial activity after 93 days when stored in 0.1 M phosphate buffer solution of pH 7.5 at 4°C. With the low operating potential, the biosensor demonstrated little interference from the possible interferants.

Preparation of a Polypyrrole-Polyvinylsulphonate Composite Film Biosensor for Determination of Cholesterol Based on Entrapment of Cholesterol Oxidase

In this paper, a novel amperometric cholesterol biosensor with immobilization of cholesterol oxidase on electrochemically polymerized polypyrrole-polyvinylsulphonate (PPy-PVS) films has been accomplished via the entrapment technique on the surface of a platinum electrode. Electropolymerization of pyrrole and polyvinylsulphonate on the Pt surface was carried out by cyclic voltammetry between -1.0 and +2.0 V (vs. Ag/AgCl) at a scan rate of 100 mV upon the Pt electrode with an electrochemical cell containing pyrrole and polyvinylsulphonate. The amperometric determination is based on the electrochemical detection of H(2)O(2) generated in the enzymatic reaction of cholesterol. Determination of cholesterol was carried out by the oxidation of enzymatically produced H(2)O(2) at 0.4 V vs. Ag/AgCl. The effects of pH and temperature were investigated and optimum parameters were found to be 7.25 and 35 °C, respectively. The storage stability and operational stability of the enzyme electrode were also studied. The results show that 32% of the response current was retained after 19 activity assays. The prepared cholesterol biosensor retained 43% of initial activity after 45 days when stored in 0.1 M phosphate buffer solution at 4 °C.

Immobilization of Uricase Upon Polypyrrole-Ferrocenium Film

In this study, uricase was immobilized by a glutaraldehyde/gelatine crosslinking procedure onto polypyrrole film. The Km value for immobilized enzyme 0.44 mM was much higher than that of the free enzyme 0.39 mM. Vmax values were 8.4 × 10−2 mM/dak and 7.1 × 10−2 mM/dak for free and immobilized enzyme, respectively. The optimal pH values for free and immobilized enzymes were 8.5 and 8.0, respectively. The optimum temperature for both free and immobilized uricase was 35°C and 55°C. The enzyme activity after storage for 7 weeks was found to be 42% and 49% of the initial activity values for free and immobilized enzymes, respectively. The amperometric current obtained after 30 measurements at a constant uric acid concentration of 5.0 × 10−5 M was found to be 77.7% of initial activity.

An amperometric biosensor for fish freshness detection from xanthine oxidase immobilized in polypyrrole-polyvinylsulphonate film

Abstract A new amperometric biosensor was developed for determining hypoxanthine in fish meat. Xanthine oxidase with pyrrole and polyvinylsulphonate was immobilized on the surface of a platinum electrode by electropolymerization. The determination of xanthine-hypoxanthine was performed by means of oxidation of uric acid liberated during the enzyme reaction on the surface of the enzyme electrode at + 0.30V (SCE). The effects of pH, substrate concentration, and temperature on the response of the xanthine-hypoxanthine biosensor were investigated. The linear working range of the enzyme electrode was 1.0 × 10−7 –1.0 × 10−3 M of the hypoxanthine concentration, and the detection limit was 1.0 × 10−7M. The apparent Km(app) and Imax of the immobilized xanthine oxidase were found to be 0.0154 mM and 1.203 μA/mM, respectively. The best pH and temperature value for xanthine oxidase were selected as 7.75 and 25°C, respectively. The sensor was used for the determination of hypoxhantine in fish meat. Results show that the fish degraded very rapidly after seven days and the hypoxanthine amount was found to increase over days of storage.

Tetradentate asymmetric Schiff bases and their Ni(II) and Fe(III) complexes

Three asymmetric Schiff-base tetradentate diimines H2L1, H2L2, and H2L3 [(2-OH)C6H4N=CHC6H42-N=CHC6H3(2-OH)(5-X), X = H, CH3, Cl respectively] have been synthesized by a two step process. The reaction of 2-hydroxy aniline with 2-nitro-benzaldehyde in EtOH gave the starting Schiff base, 2-hydroxy-N-(2-nitrobenzylidene)aniline (SB-NO2), which was reduced into the amino derivative (SB-NH2) in solution. Reacting SB-NH2 with 2-hydroxybenzaldehyde, 2-hydroxy-5-methylbenzaldehyde and 2-hydroxy-5-chlorobenzaldehyde gave the three new ligands H2L1, H2L2, and H2L3 respectively. Their dimeric, binuclear metal complexes with Ni(II) and Fe(III) have also been synthesized. The ligands and their complexes were characterized by elemental analyses, LC–MS, IR, electronic, 1H and 13C-NMR spectra, TGA, conductivity and magnetic measurements. All of the spectroscopic, analytical and other data indicate octahedral geometry M2L2(H2O)X2 (M: Ni,Co;X: Cl or H2O), except for NiL2 which is monomeric. Antimicrobial activities of the ligands and the complexes were evaluated against five bacteria. While the ligands and the Ni complexes are inactive towards Pseudomonas aeruginosa and Staphylococcus aureus, Fe complexes are active; only Fe complexes are inactive against Escherichia coli. All of the compounds have antimicrobial activities against Bacillus subtilis, and Yersinia enterecolitica.

The effects of smoking on antioxidant defence system and membrane free fatty acid content of erythrocytes and plasma lipid parameters : Protective role of antioxidant vitamins

Abstract Activities of antioxidant enzymes were measured in the erythrocytes from 15 smokers and 15 non-smokers. Superoxide dismutase (SOD) and catalase (CAT) activities were found lower but, glutathione peroxidase (GSH-Px) activity unchanged in the erythrocytes from smokers compared with non-smokers. Levels of thiobarbituric acid-reactive substances (TBARS) were however higher both in erythrocytes and plasma from smokers. Antioxidant vitamin (vitamins E and C) supplementation for the period of 15 days caused significant increases in the activities of all antioxidant enzymes and decreases in the TBARS levels of erythrocytes and of blood plasma in smoker group. It has been observed that smoking caused significant changes in the concentrations of plasma lipid fractions as well. In this regard, total cholesterol level (TC) was found unchanged, LDL cholesterol and triglyceride (TG) levels increased and HDL cholesterol decreased in the plasma from smokers compared with non-smokers. Vitamin supplementation caused a significant increase in HDL cholesterol and a decrease in LDL cholesterol in plasma from smokers. The vitamins normalised the HDL HDL ratio in smokers. Fatty acid composition of erythrocyte membranes from smokers also presented significant changes. In particular, oleic acid (18:1) was almost in the erythrocyte membranes of smokers. In contrast, the relative amount of stearic acid (18:0) was found to be significantly increased but, those of some fatty acids (12:0, 14:0, 14:1 and 16:0) decreased in the erythrocyte membranes of smokers. Results suggested that enzymatic antioxidant defence system of erythrocytes was depressed and the erythrocytes were exposed to oxidant stress due to smoking. Increased plasma TBARS levels indicated that not only erythrocytes but also some other tissues and cells might be exposed to the radical stress by cigarette smoke. Smoking also caused significant changes in the levels of plasma lipid parameters and antioxidant vitamins partly protected erythrocytes against such harmful effects of smoking by scavenging free radical species and by activating and/or inducing antioxidant enzymes.

Synthesis and antimicrobial activity studies of some novel substituted phenylhydrazono-1H-tetrazol-5-yl-acetonitriles

AbstractIn this study, some substituted phenylhydrazono-1H-tetrazol-5-yl-acetonitriles have been synthesized (2a–o, 2a and 2k are known compounds). The synthesized compounds were characterized by spectroscopic methods [Fourier-transform infrared (FTIR), nuclear magnetic resonance (NMR), mass spectroscopy (MS)]. In addition, antimicrobial activities of synthesized compounds were investigated against Bacillus cereus RSKK 863, Escherichia coli ATCC 3521, Pseudomonas aeruginosa ATCC 2921, and Staphylococcus aureus TP32. These compounds had antimicrobial effect against these bacteria (except for 2l).Graphical AbstractIn this study, some substituted phenylhydrazono-1H-tetrazol-5-yl-acetonitriles have been synthesized (2a-o, 2a and 2k are known compounds, but others are novel). The synthesized compounds were characterized by spectroscopic methods (FTIR, NMR, MS).In addition, antimicrobial activities of synthesized compounds were investigated against Bacillus cereus RSKK 863, Escherichia coli ATCC 3521, Pseudomonas aeruginosa ATCC 2921, and Staphylococcus aureus TP32. These compounds (except for 2l) have antimicrobial effect against these bacteria. Antimicrobial activities of these compounds were compared with antimicrobial activities of some antibiotics.Scheme 1: Protocol for the synthesis substituted phenylhydrazono-1H-tetrazol-5-yl-acetonitriles. (a) R1: H, R2: H; (b) R1: F, R2: H; (c) R1: H, R2: F; (d) R1: Cl, R2: H; (e) R1: H, R2: Cl; (f) R1: Br, R2: H; (g) R1: H, R2: Br; (h) R1: I, R2: H; (i) R1: H, R2: I; (j) R1: CH3, R2: H; (k) R1: H, R2: CH3; (l) R1: OCH3, R2: H; (m) R1: H, R2: OCH3; (n) R1: NO2, R2: H; (o) R1: H, R2: NO2.