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H2O2 System (h2o2 + system)

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Chemistry100%

Selected Abstracts

Mössbauer Investigation of Peroxo Species in the Iron(III),EDTA,H2O2 System

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2005
Virender K. Sharma
Abstract The reaction of a diiron(III),EDTA complex with H2O2 in alkaline medium is studied by Mössbauer spectroscopy in conjunction with the rapid-freeze/quench technique in order to identify possible intermediate species during the formation and decomposition of the purple (EDTA)FeIII(,2 -O2)3, complex ion. Starting from the six-coordinate [FeIIIEDTA], species at acidic pH, it is demonstrated that mononuclear complexes formed at a pH of about 1 are convert into the diiron(III),EDTA complex [(EDTA)FeIII -O-FeIII(EDTA)]4, upon raising the pH to around 10.4. H2O2 reacts with the diiron(III) complex to give peroxide/hydroperoxide related adducts. Initially, the reaction tears apart the dimers to form a peroxo adduct, namely the seven-coordinate mononuclear [(EDTA)FeIII(,2 -O2)]3,, which is stable only at very high pH. The decomposition of this peroxo adduct gives two new species, which are reported for the first time. The Mössbauer parameters of these species suggest a six-coordinate ,-peroxodiiron(III) complex [(EDTA)FeIII -(OO)-FeIII(EDTA)]4, and a seven-coordinate ,-hydroxo-,-peroxodiiron(III) complex [(EDTA)FeIII -(OO)(OH)-FeIII(EDTA)]5,. A badly resolved, extremely broad component is observed in the Mössbauer spectra during the conversion of the monomer to dimeric peroxo species, which may be attributed to the short-lived [(EDTA)FeIII -OO]3, or [(EDTA)FeIII -OOH]2, intermediate species. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Luminol chemiluminescence catalysed by colloidal platinum nanoparticles

LUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 2 2007
Sheng-Liang Xu
Abstract Platinum colloids prepared by the reduction of hexachloroplatinic acid with citrate in the presence of different stabilizers were found to enhance the chemiluminescence (CL) of the luminol,H2O2 system, and the most intensive CL signals were obtained with citrate-protected Pt colloids synthesized with citrate as both a reductant and a stabilizer. Light emission was intense and reproducible. Transmission electron microscopy and X-ray photoelectron spectroscopy studies were conducted before and after the CL reaction to investigate the possible CL enhancement mechanism. It is suggested that this CL enhancement is attributed to the catalysis of platinum nanoparticles, which could accelerate the electron-transfer process and facilitate the CL radical generation in aqueous solution. The effects of Pt colloids prepared by the hydroborate reduction were also investigated. The application of the luminol,H2O2,Pt colloids system was exploited for the determination of compounds such as uric acid, ascorbic acid, phenols and amino acids. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Scavenging of reactive oxygen species by the plant phenols genistein and oleuropein

LUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 2 2005
Irena Kruk
Abstract The plant-derived phenolic compounds genistein and oleuropein are known to exhibit several biological properties, many of which may result from their antioxidant and free radical scavenger activity. In this paper we report the results of a complex study of antioxidant activity of genistein and oleuropein, using electron spin resonance (ESR), chemiluminescence, fluorescence and spectrophotometric techniques. Different reaction systems were applied to study the inhibitory effect of the phenolic compounds studied: (a) the potassium superoxide[sol ]18- crown -6 dissolved in DMSO system, which generates superoxide radical (O2·,) and hydrogen peroxide (H2O2); (b) the Co(II),EDTA,H2O2 system (the Fenton-like reaction), which generates hydroxyl radical (HO·); (c) 2,2,-azobis(2-amidino-propane)dichloride (AAPH) as the peroxyl radical (ROO·) generator, and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical test. Results showed that genistein and oleuropein decreased the chemiluminescence sum from the O2·, generating system, an inhibitory effect that was dependent on their concentration. These compounds also reacted with ROO radicals and they showed activity about two-fold greater than the standard Trolox. The antioxidant effects were studied at different concentrations and reflected in protection against the fluorescence decay of , -phycoerythrin (, -PE), due to ROO· attack on this protein. Using the Fenton-like reaction and the spin trap agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), the phenolic compounds examined were found to inhibit DMPO,·OH radical formation in the range 10,90% at concentrations of 0.1 mmol[sol ]L to 2 mmol[sol ]L. Furthermore, these compounds also inhibited HO· -dependent deoxyribose degradation; about 20% and 60% inhibitions were observed in the presence of 0.5 mmol[sol ]L genistein and oleuropein, respectively. It was also demonstrated that genistein had a weaker DPPH radical scavenging activity than oleuropein. Our results confirm good scavenging activity towards O2·,, HO· and ROO· and the antioxidant effect of genistein and oleuropein. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Analysis of oxidation process of cholecystokinin octapeptide with reactive oxygen species by high-performance liquid chromatography and subsequent electrospray ionization mass spectrometry

BIOMEDICAL CHROMATOGRAPHY, Issue 2 2010
Hideaki Ichiba
Abstract The C -terminal octapeptide of cholecystokinin (CCK8) includes some easily oxidizable amino acids. The oxidation of CCK8 by reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) and hydroxyl radicals (OH,) was investigated using reversed-phase high performance liquid chromatography (RP-HPLC) and subsequent electrospray ionization mass spectrometry. The mechanism of oxidation of CCK8 in the H2O2 system differed from that of CCK8 in the Fenton system, in which OH, are produced. In the H2O2 system, 28Met and 31Met were oxidized to methionine sulfoxide, and no further oxidation or degradation/hydrolysis occurred. On the other hand, in the Fenton system, 28Met and 31Met residues were oxidized to methionine sulfone via the formation of methionine sulfoxide. In addition, the oxidized product was observed at the Trp residue but not at the Tyr residue, and small peptide fragments from CCK8 were observed in the Fenton system. From these results, it was concluded that 28Met and 31Met residues of CCK8 are susceptible to oxidation by ROS. Copyright © 2009 John Wiley & Sons, Ltd. [source]