Label-free DNA detection based on modified conducting polypyrrole films at microelectrodes

A label-free electrochemical detection method for DNA hybridization based on electrostatic modulation of the ion-exchange kinetics of a polypyrrole film deposited at microelectrodes is reported. Synthetic single-stranded 27-mer oligonucleotides (probe) have been immobilized at 2,5-bis(2-thienyl)-N-(3-phosphorylpropyl)pyrrole film formed by electropolymerization on the previously formed polypyrrole layer. The 27- or 18-mer target oligonucleotides were monitored via the electrochemically driven anion exchange of the inner polypyrrole film. The performance of the miniaturized DNA biosensor system was studied in respect to selectivity, sensitivity, reproducibility, and regeneration of the sensor. Control experiments were performed with a noncomplementary target of 27-mer DNA and 12 base-pair mismatched 18-mer sequences, respectively, and did not show any unspecific binding. Under optimized experimental conditions, the label-free electrochemical biosensor enabled the detection limits of 0.16 and 3.5 fmol for the 18- and 2 7-mer DNA strand, respectively. Furthermore, we demonstrate reusability of the electrochemical DNA biosensor after successful recovery of up to 100% of the original signal by regenerating the DNA label-free electrode with 50 mM HCl at room temperature.

Electrochemical study of perchlorate reduction at tin electrodes

The electrochemical behaviour of tin in de-aerated sodium perchlorate was studied using potentiodynamic and potentiostatic techniques. Tin behaviour in sodium perchlorate has been complicated unexpectedly by the reduction of the perchlorate anion. It is shown that the reduction process takes place within a potential region comprising the negative side of the double layer region and the positive side of the hydrogen region (-0.7 less than or equal to E less than or equal to -1.3 V). The presence of oxide on the electrode surface favours the reduction reaction, which may occur in two steps: the formation of basic tin(II) chloride followed by its reduction, producing chloride.

The cathodic deprotection of the nitrobenzoyl group from phenyl nitrobenzoates in N,N-dimethylformamide

The reduction of phenyl benzoates with nitro substituents at the 2-,3- and 4-positions of the benzoates in N,N-dimethylformamide is reported. The phenyl 4- and 3-nitrobenzoate are reduced in two cathodic steps. The first one, at about -0.9 V vs. SCE, a reversible one-electron process, gives a rather stable anion radical. The second reduction step at potentials between -1.5 and -2.0 V vs. SCE leads to formation of the dianion, which decomposes giving free phenol in good yields (> 80%). on the other hand, the phenyl 2-nitrobenzoate is reduced in one cathodic step. This step occurs at -0.9 V with formation of an unstable anion radical which decomposes via C-O bond cleavage, giving phenol with a yield of ca. 80%. The mechanisms of the reduction of these compounds are discussed. (C) 1997 Elsevier B.V. S.A.

Toxicity of chronic ethanol ingestion and superoxide radical formation on seminal vesicles of rats

The toxic effects of chronic ethanol ingestion were evaluated in male adult rats for 300 days. The animals were divided into three groups: the controls received only tap water as liquid diet; the chronic ethanol ingestion group received only ethanol solution (30%) in semivoluntary research; and the withdrawal group received the same treatment as chronic ethanol-treated rats until 240 days, after which they reverted to drinking water. Chronic ethanol ingestion induced increased lipoperoxide levels and acid phosphatase activities in seminal vesicles. Cu-Zn superoxide dismutase (SOD) decreased from its basal level 70.8 +/- 3.5 to 50.4 +/- 1.6 U/mg protein at 60 days of chronic ethanol ingestion. As changes in GSH-PX activity were observed in rats after chronic ethanol ingestion, while SOD activities were decreased in these animals, it is assumed that superoxide anion elicits lipoperoxide formation and induces cell damage before being converted to hydrogen peroxide by SOD. Ethanol withdrawal induced increased SOD activity and reduced seminar vesicle damage, indicating that the toxic effects were reversible, since increased SOD activity was adequate to scavenge superoxide radical formation. Superoxide radical is an important intermediate in the toxicity of chronic ethanol ingestion. Copyright (C) 1996 Elsevier B.V. Ltd

Toxicity of ad lib. overfeeding: effects on cardiac tissue

The aim of the present study was to determine the effects of ad lib, overfeeding and of dietary restriction (DR) on oxidative stress in cardiac tissue. Lipoperoxide concentrations ere decreased and antioxidant enzymes ere increased in moderate-DR-fed rats. Severe-DR induced increased lipoperoxide concentrations. Overfeeding increased lipoperoxide levels in cardiac tissue. Total superoxide dismutase (SOD) and Cu-Zn superoxide dismutase (Cu-Zn SOD) activities were decreased in cardiac tissue at 35 days of overfeeding. As no changes in glutathione peroxidase (GSH-Px) ere observed in overfed rats, awhile SOD and Cu-Zn SOD activities were decreased in these animals. it is assumed that superoxide anion is an important intermediate in the toxicity of ad lib, overfeeding. Overfeeding induced alterations in markers of oxidative stress in cardiac tissue. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

Preparation of zinc sodium polyphosphates glasses from coacervates precursors. Characterisation of the obtained glasses, and their applications

A soft chemistry route is described to obtain glasses in the P2O5-Na2O-ZnO-H2O. It is based on the addition of zinc salts to coacervates prepared from sodium polyphosphate. The processing of these coacervates leads to polyphosphate glasses with the same properties as those of glasses prepared in the classical way. So far, little work has been implemented in this system using 'coacervate route'. However, it makes an attractive method for coating and joining processes on the industrial scale. As the anion associated to zinc may take part in the adhesion mechanism, coacervate formation has been studied using zinc chloride, nitrate and sulphate as starting materials. The physical properties of the glasses obtained by this method are reported and potential applications of zinc and silver coacervate are described. (C) 2002 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.

Charge distribution and calcium affinity of sulfated alpha-L-galactans from ascidians. Comparison between linear and highly branched polymers

Calcium binding and charge distribution on highly branched and linear sulfated L-galactans from ascidians have been studied using a metallochromic indicator and conductimetric titrations. The distance between charged groups of the linear and highly branched galactans does not vary despite their marked differences in sulfate/total sugar molar ratios. These results indicate that the sulfated L-galactose units are concentrated in the central polysaccharide core and not intercalated among non-sulfated units. This inference is consistent with the chemical studies of these galactans. Surprisingly, calcium affinity increases with increasing amounts of non-sulfated sugar branches in the molecule. Thus, calcium binding in these polymers is not a simple function of availability of anion binding sites but a more complex calcium-polysaccharide interaction. (C) 1998 Elsevier B.V. Ltd. All rights reserved.

Solid-state chelates of ethylenediamine-tetraacetate with alkali earth metals

Solid-state M-EDTA chelates, where M represents the divalent ions Mg(II), Ca(II), Sr(II) or Ba(II) and EDTA is ethylenediaminetetraacetate anion, were synthesized. Thermogravimetry, derivative thermogravimetry (TG, DTG), differential scanning calorimetry (DSC) and X-ray diffraction powder patterns have been used to characterize and to study the thermal behaviour of these chelates. The results provided information concerning the stoichiometry, crystallinity, thermal stability and thermal decomposition.

Preparation and thermal behavior of mixture of basic carbonate and 4-dimethylaminocinnamylidenepyruvate with lanthanides (III) and yttrium (III) in the solid state

Solid Ln-OKCO3-DMCP compounds, where Ln represents lanthanides (III) and yttrium (III) ions and DMCP is the anion 4-dimethyiaminocinnamylidenepyruvate, have been prepared. Thermogravimetry, derivative thermogravimetry (TG, DTG), differential scanning calorimetry (DSC), X-ray diffraction powder patterns and elemental analysis have been used to characterize the compounds. The thermal stability as well as the thermal decomposition of these compounds were studied using an alumina crucible in an air atmosphere.

Investigations on the new free radical scavenger polynitroxyl-albumin to prevent ischemia and reperfusion injury after orthotopic heart transplantation in the pig model

Objective: Nitroxides have strong antioxidant capacity but their effectiveness is limited by their rapid intracellular inactivation. Poly nitroxyl-Albumin (PNA) is capable of regenerating inactivated nitroxide. We tested the effect of PNA against reperfusion injury in heart transplantation. Methods: Pig hearts were transplanted orthotopically. In the control group (n = 9) reperfusion was performed without reperfusion modifications. In the experimental group (n = 10) 1 ml/kg PNA was given before cross-clamp release. Results: Hemodynamic performance was impaired after transplantation in both groups without significant intergroup differences. Plasma malonedialdehyde levels were significantly diminished in the PNA group as compared to the controls. CK-MB levels in both groups were increased within the first 2 h of reperfusion without significant intergroup differences. In contrast, there were found significant higher values of myocardial specific lactate dehydrogenase (LD1) in the controls versus PNA group. Conclusions: PNA was able to reduce lipid peroxidation and attenuate free radical activity. Contractile dysfunction could no be improved, indicating that (a) the radical scavenging effect was to weak or (b) other mechanisms than free oxygen radicals are responsible for myocardial damage in this experimental model. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Purification and characterization of pectin methylesterase from acerola (Malpighia glabra L.)

The enzyme pectinmethylesterase (PME) from acerola was extracted and purified by gel anion-exchange chromatography (Q Sepharose) and filtration on Sephadex G-100. The results showed two different PME isoforms (PME1 and PME2), with molecular masses of 25.10 and 5.20 kDa, respectively. PMEI specific activity increased by 9.63% after 60 min incubation at 98 degrees C, while PME2 retained 66% of its specific activity under the same conditions. The K-m values of PMEI, PME2 and concentrated PME were 0.94, 0.08 and 0.08mg mL(-1), respectively. The V-max value of PMEI, PME2 and concentrated were 204.08, 2, 158.73 and 2.92 mu mol min(-1) mg(-1) protein, respectively. (c) 2007 Society of Chemical Industry.

Structure characterization of molecular complexes for non-linear optical materials. II. 1 : 1 complexes of 4-methyl-morpholine-N-oxide (1) and 3-picoline-N-oxide (2) with 2,4,6-trinitrophenol, studied by X-ray, AM1 and DFT calculations

(1) C6H2N3O7- center dot C5H12NO2+, Mr = 346.26, P2(1)/c, a = 7.2356(6), b = 10.5765(9), c = 19.593(2) angstrom, 3 beta=95.101(6)degrees, V = 1493.5(2) angstrom(3), Z = 4, R-1 = 0.0414; (2) C6H2N3O7- center dot C6H8NO+, Mr = 38.24, P2(1)/n, a = 7.8713(5), b = 6.1979(7), c = 28.697(3) angstrom, beta = 90.028(7)degrees, V = 1400.0(2) angstrom(3), Z = 4, R-1 = 0.0416. The packing units in both compounds consist of hydrogen bonded cation-anion pairs. The (hyper)polarizabilities have been calculated for the crystallographic and optimized molecules, by AM1 and at the DFT/B3LYP(6-31G**) level.

THERMAL-DECOMPOSITION OF THE HYDRATED BASIC CARBONATES OF LANTHANIDES AND YTTRIUM IN CO2 ATMOSPHERE

The hydrated basis carbonates of lanthanides and yttrium were prepared by precipitation from homogeneous solution via the hydrolysis of urea, without the addition of an auxiliary anion. Thermogravimetry, derivative thermogravimetry (TG-DTG), and differential thermal analysis (DTA) have been used in the study of these compounds in CO2 atmosphere. The results lead to the composition and thermal stability of the studied compounds, and also to a comparative study with reported results in air atmosphere.

The electrochemical cleavage of the nitrobenzoyl group from butyl nitrobenzoates in N,N-dimethylformamide

The applicability of the nitrobenzoyl group [NO2C6H4CO-] to protecting the functional hydroxyl group was investigated through study of the electrochemical behaviour of the butyl 4-, 3- and 2-nitrobenzoate compounds. These isomers are reduced in two cathodic steps. The first, at potentials of ca. -0.9 V vs. SCE, is attributed to the formation of rather stable anion radicals, involving one-electron transfer. The second, at potentials of ca. -1.7 V vs. SCE, occurs with a two-electron transfer in an ECE process, in which the dianion produced undergoes scission of the C-O bond giving n-butanoate ions with high yields (similar to 80%)

Purification and characterization of two beta-glucosidases from the thermophilic fungus Thermoascus aurantiacus

beta-Glucosidase from the fungus Thermoascus aurantiacus grown oil semi-solid fermentation medium (using ground corncob as substrate) was partially purified in 5 steps - ultrafiltration, ethanol precipitation, gel filtration and 2 anion exchange chromatography runs, and characterized. After the first anion exchange chromatography, beta-glucosidase activity was eluted in 3 peaks (Gl-1, Gl-2, Gl-3). Only the Gl-2 and Gl-3 fractions were adsorbed on the gel matrix. Gl-2 and Gl-3 exhibited optimum pH at 4.5 and 4.0, respectively. The temperature optimum of both glucosidases was at 75-80 degreesC. The pH stability of Gl-2 (4.0-9.0) was higher than Gl-3 (5.5-8.5); both enzyme activities showed similar patterns of thermostability. Under conditions of denaturing gel chromatography the molar mass of Gl-2 and Gl-3 was 175 and 157 kDa, respectively. Using 4-nitrophenyl beta-D-glucopyranoside as substrate, K-m, values of 1.17 +/- 0.35 and 1.38 +/- 0.86 mmol/L were determined for Gl-2 and Gl-3, respectively. Both enzymes were inhibited by Ag+ and stimulated by Ca2+.