Search results for "free radicals"
showing 10 items of 154 documents
Effects of static and dynamic perturbations on isotropic hyperfine coupling constants in some quinone radicals.
2004
The effects of solvent dielectric response on the isotropic hyperfine coupling constants of the 1,4-benzoquinone, 1,4-naphthoquinone and 9,10-anthraquinone anions and 1,4-naphthalenediol cation radicals were studied by electron spin resonance (ESR) spectroscopy and by the theoretical density functional method within the polarizable continuum model. Experimental results demonstrate that the isotropic hyperfine coupling constants can be obtained with high accuracy and that the effects of solvent impurities can be minimized by careful sample preparation. The results obtained correlate well with theoretical predictions from density functional theory calculations. For 1,4-naphthalenediol both th…
Heptacoordinated Molybdenum(VI) Complexes of Phenylenediamine Bis(phenolate): A Stable Molybdenum Amidophenoxide Radical
2013
The syntheses, crystallographic structures, magnetic properties, and theoretical studies of two heptacoordinated molybdenum complexes with N,N′-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-1,2-phenylenediamine (H4N2O2) are reported. A formally molybdenum(VI) complex [Mo(N2O2)Cl2(dmf)] (1) was synthesized by the reaction between [MoO2Cl2(dmf)2] and H4N2O2, whereas the other molybdenum(VI) complex [Mo(N2O2)(HN2O2)] (2) was formed when [MoO2(acac)2] was used as a molybdenum source. Both complexes represent a rare case of the MoVI ion without any multiply bonded terminal ligands. In addition, molecular structures, magnetic measurements, ESR spectroscopy, and density functional theory calculations ind…
Integrated experimental and computational spectroscopy study on the protonation of the α-nitronyl nitroxide radical unit
2011
The stability of the α-nitronyl nitroxide radical unit under acidic conditions is investigated by an integrated experimental UV/Vis spectroscopy and TDDFT study. In the field of molecular magnetism, α-nitronyl nitroxide radicals are important as purely organic spin carriers due to their synthetic versatility. Here, the existence of an intermediate of the protonated α-nitronyl nitroxide radical unit is demonstrated for the first time and a proposed disproportionation reaction is confirmed.
Single-molecule magnetic behavior in a neutral terbium(III) complex of a picolinate-based nitronyl nitroxide free radical
2011
The terdentate anionic picolinate-based nitronyl nitroxide (picNN) free radical forms neutral and robust homoleptic complexes with rare earth-metal ions. The nonacoordinated Tb3+ complex Tb(picNN)3• 6H2O is a single-molecule magnet with an activation energy barrier Δ = 22.8 ± 0.5 K and preexponential factor τ0 = (5.5 ± 1.1) × 10-9 s. It shows magnetic hysteresis below 1 K. © 2011 American Chemical Society.
Photoreaction Between Benzoylthiophenes and N-BOC-Tryptophan Methyl Ester‡
2005
Drug-induced photoallergy requires as the first step formation of covalent drug-protein photoadducts. One of the key amino acids involved in this process is tryptophan (Trp). In this context, several diaryl ketones, including 2-benzoylthiophene (BT), [2-(5-benzoyl-5-thienyl)]-2-methylpropanoic methyl ester (TPA methyl ester) and 4-(2-thienylcarbonyl)phenyl]-2-methylpropanoic methyl ester (SUP methyl ester) have been irradiated in the presence of N-BOC-(L)-tryptophan methyl ester. Laser flash photolysis has allowed to detect three neutral radicals (ketyl, indolyl and skatolyl radicals) resulting from formal hydrogen-atom abstraction. This correlates well with the isolation of homodimers, as …
l-Carnitine l-tartrate supplementation favorably affects biochemical markers of recovery from physical exertion in middle-aged men and women.
2009
The purpose of this study was to examine the effects of Carnipure tartrate (Lonza, Allendale, NJ) supplementation (total dose of 2 g/d of l-carnitine) on markers of performance and recovery from physical exertion in middle-aged men and women. Normally active and healthy men (n = 9, 45.4 +/- 5.3 years old) and women (n = 9, 51.9 +/- 5.0 years old) volunteered to participate in the investigation. Double-blind, placebo, balanced treatment presentation and crossover design were used with 3 weeks and 3 days of supplementation followed by a 1-week washout period before the other counterbalanced treatment was initiated. After 3 weeks of each supplementation protocol, each participant then performe…
Nitric oxide synthase inhibition and oxidative stress in cardiovascular diseases: Possible therapeutic targets?
2013
International audience; Nitric oxide (• NO) is synthetized enzymatically from L-arginine (L-Arg) by three NO synthase isoforms, iNOS, eNOS and nNOS. The synthesis of NO is selectively inhibited by guanidino-substituted analogs of L-Arg or methylarginines such as asymmetric dimethylarginine (ADMA), which results from protein degradation in cells. Many disease states, including cardiovascular diseases and diabetes, are associated with increased plasma levels of ADMA. The N-terminal catalytic domain of these NOS isoforms binds the heme prosthetic group as well as the redox cofactor, tetrahydrobiopterin (BH 4) associated with a regulatory protein, calmodulin (CaM). The enzymatic activity of NOS…
Radical Polymerization of Styrene Controlled by Half-Sandwich Mo(III)/Mo(IV) Couples: All Basic Mechanisms Are Possible
2001
Density functional calculations of bond dissociation energies (BDEs) have been used as a guide to the choice of metal system suitable for controlling styrene polymerization by either the stable free radical polymerization (SFRP) or the atom transfer radical polymerization (ATRP) mechanism. In accord with the theoretical prediction, CpMo(eta(4)-C(4)H(6))(CH(2)SiMe(3))(2), 2, is not capable of yielding SFRP of styrene. Still in accord with theoretical prediction, CpMo(eta(4)-C(4)H(6))Cl(2), 1, CpMo(PMe(3))(2)Cl(2), 3, and CpMo(dppe)Cl(2) (dppe = 1,2-bis(diphenylphosphino)ethane), 4, yield controlled styrene polymerization by the SFRP mechanism in the presence of 2,2'-azobisisobutyronitrile (A…
Restricting Magnetic Interaction Pathways in Polyoxometalate Salts of Cationic Nitronyl Nitroxide Free Radicals
2004
Abstract : Salts 1 and 2 that combine the [W 6 O 19 ] 2- Lindqvist anion with the cationic nitronyl nitroxide (NN) free radicals p -MepyNN + and n Bu 3 NCH 2 NN + , respectively, have been synthesized and their structural and magnetic properties have been studied. Keywords: Nitroxide radicals, polyoxometalates, magnetism. Introduction Ferromagnetism based on purely organic materials has raised a lot of interest during the last decade [1]. Most of the studies have been performed with nitronyl nitroxide (NN) radicals due to their persistence, stability and ease of functionalization [2]. Bulk ferromagnetism in these compounds arises from ferromagnetic interactions between open-shell molecules …
Molecular and electronic structure of square-planar nickel(ii), nickel(iii) and nickel(iii)π-cation radical complexes with a tetradentate o-phenylene…
2005
The molecular and electronic structures of the electron transfer series of four-coordinate square-planar nickel complexes with the ligand o-phenylenebis(N'-methyloxamidate), [NiL]z (z = 2-, 1-, 0), have been evaluated by DFT and TDDFT calculations, and most of their experimentally available structural and spectroscopic properties (X. Ottenwaelder et al., Dalton Trans., 2005, DOI: 10.1039/b502478a) have been reasonably reproduced at the B3LYP level of theory. The anionic species [NiL]2- and [NiL]- are genuine low-spin nickel II and nickel III complexes with diamagnetic singlet (S = 0) and paramagnetic doublet (S = 1/2) states, respectively. The nickel III complex presents shorter Ni-N(amidat…