Search results for "radical"
showing 10 items of 1401 documents
Reaction of melatonin with hemoglobin-derived oxoferryl radicals and inhibition of the hydroperoxide-induced hemoglobin denaturation in red blood cel…
2001
Melatonin has been shown to act as a radical scavenger in various chemical and biological model systems in vitro. Kinetic evidence is now provided showing that melatonin inhibits the irreversible degradation of hemoglobin (Hb), when incubated with red blood cells exposed to the oxidant activity of cumene hydroperoxide (cumOOH). A decrease of heme loss and accumulation of soluble methemoglobin (met-Hb) are explained in terms of the interaction of the indoleamine with perferryl Hb ( . Hb[Fe IV = O]), a highly reactive Hb-derived radical species responsible for the irreversible Hb degradation. A kinetic study, in pure chemical solution, showed that melatonin can effectively reduce the oxoferry…
Consequences of the One-Electron Reduction and Photoexcitation of Unsymmetric Bis-imidazolium Salts
2012
Coupling of uronium salts with in situ generated N-heterocyclic carbenes provides straightforward access to symmetrical [4](2+) and unsymmetrical bis-imidazolium salts [6](2+) and [9](2+) . As indicated by cyclic and square-wave voltammetry, [6](2+) and [9](2+) can be (irreversibly) reduced by one electron. The initially formed radicals [6](.+) and [9](.+) undergo further reactions, which were probed by EPR spectroscopy and density functional calculations. The final products of the two-electron reduction are the two carbenes. Upon irradiation with UV light both [6](2+) and [9](2+) emit at room temperature in solution but with dramatically different characteristics. The different fluorescenc…
Structures and EPR spectra of binary sulfur–nitrogen radicals from DFT calculations
2007
Abstract The scattered electron paramagnetic resonance (EPR) spectroscopic data for binary sulfur–nitrogen (S,N) radicals have been compiled and critically assessed.Many of these are inorganic rings or cages.For each species, possible equilibrium structures in the gas phase and the EPR hyperfine coupling (hfc) constants have been calculated with DFT using the B3LYP functional and basis sets of triple-ζ (or better) quality.Good agreement is obtained between calculated and measured values for the well characterized [S3N2]+ , a planar π-radical for which the s-component of the orbitals is likely to be reasonably independent of minor geometrical changes between gas-phase and condensed-phase sta…
Diffusion and reactions of interstitial oxygen species in amorphous SiO2: A review
2008
This article briefly summarizes the diffusion and reactions of interstitial oxygen species in amorphous SiO 2 (a-SiO 2 ). The most common form of interstitial oxygen species is oxygen molecule (O 2 ), which is sensitively detectable via its characteristic infrared photoluminescence (PL) at 1272 nm. The PL observation of interstitial 0 2 provides key data to verify various processes related to interstitial oxygen species: the dominant role of interstitial O 2 in long-range oxygen transport in a-SiO 2 ; formation of the Frenkel defect pair (Si-Si bond and interstitial oxygen atom, 0°) by dense electronic excitation; efficient photolysis of interstitial O 2 into O° with F 2 laser light (λ= 157…
Modellbetrachtung zur Radikalausbeute bei der radikalischen Polymerisation
1974
Die kinetisch wirksame Radikalausbeute ist eine chemisch und diffusionskontrollierte Grose. Der Grad der jeweiligen Kontrolle ist systemspezifisch. Die chemische Kontrolle geht hauptsachlich von der Kettenstartreaktion, die Diffusionskontrolle von der Primarradikalrekombination aus. Die entwickelte Modellvorstellung erfast diese konkurrierenden Einflusse. Mittlere Diffusionswege der Primarradikale bis zu ihrer Rekombination werden abgeschatzt. The kinetically effective radical efficiency is chemically and diffusion controlled. The proportion of each control mechanism characterizes the polymerizing system. The chemical control can be deduced from the chain initiation reaction, the diffusion …
Studies in organic mass spectrometry. Part 9—mass spectra of 9,10-disubstituted 2,3,6,7-tetraalkoxy-9,10-dihydroanthracenes: A remarkable loss of rad…
1991
The electron impact-induced fragmentations of 23 9,10-disubstituted 2,3,6,7-tetraalkoxy-9,10-dihydroanthracenes, including six stereoisomeric pairs, were studied. The loss of the 9-(or 10-)substituent constitutes the main fragmentation route. The resulting ions give rise to a remarkable violation of the so-called even-electron rule as they eject the second substituent at the 10-(or 9-)position as a radical. The latter aspect was particularly investigated with the aid of low-energy (nominal value 15 eV) and mass-analysed ion kinetic energy spectra
A Superoxovanadium(V) Complex Linking the Peroxide and Dioxygen Chemistry of Vanadium.
2001
A missing link: A superoxovanadium(V) complex is the first reaction intermediate in the oxidative conversion of a peroxovanadium(V) complex into a vanadyl(IV) complex and molecular oxygen. The superoxo species appears also to play an essential role in the formation of the peroxovanadium(V) complex from the vanadyl(IV) complex and molecular oxygen.
Formation of HXeO in a xenon matrix: Indirect evidence of production, trapping, and mobility of XeO (1 1Σ+) in solid Xe
2004
IR spectroscopy, laser induced fluorescence (LIF), and thermoluminescence (TL) measurements have been combined to monitor trapping, thermal mobility, and reactions of oxygen atoms in solid xenon. HXeO and O(3) have been used as IR active species that probe the reactions of oxygen atoms. N(2)O and H(2)O have been used as precursors for oxygen atoms by photolysis at 193 nm. Upon annealing of matrices after photolysis, ozone forms at two different temperatures: at 18-24 K from close O ...O(2) pairs and at approximately 27 K due to global mobility of oxygen atoms. HXeO forms at approximately 30 K reliably at higher temperature than ozone. Both LIF and TL show activation of oxygen atoms around 3…
Synthesis, structure and biological properties of several binary and ternary complexes of copper(II) with ciprofloxacin and 1,10 phenanthroline
2009
In this study, a new binary complex [Cu(HCip) 2 ](NO 3 ) 2 · 6H 2 O ( 1 ) has been synthesized and then characterized by X-ray structure analyses. In this compound, each ciprofloxacin acts as a bidentate ligand resulting in a crystallographically planar configuration; the nitrate anions are located in apical positions with an axial distance significantly larger than the equatorial distances, which would be consistent with a very weak metal ion interaction due to the Jahn–Teller effect. In addition, both the synthesis and characterization of two new ternary complexes of ciprofloxacin–copper(II)–1,10-phenanthroline, [Cu(phen)(Cip)](NO 3 ) · 4H 2 O ( 2 ) and Cu(phen)(HCip)(NO 3 ) 2 · H 2 O (…