Search results for "Spin Trapping"
showing 8 items of 8 documents
Interplay between spin crossover and proton migration along short strong hydrogen bonds
2021
The iron(ii) salt [Fe(bpp)2](isonicNO)2·HisonicNO·5H2O (1) (bpp = 2,6-bis(pyrazol-3-yl)pyridine; isonicNO = isonicotinate N-oxide anion) undergoes a partial spin crossover (SCO) with symmetry breaking at T1 = 167 K to a mixed-spin phase (50% high-spin (HS), 50% low-spin (LS)) that is metastable below T2 = 116 K. Annealing the compound at lower temperatures results in a 100% LS phase that differs from the initial HS phase in the formation of a hydrogen bond (HB) between two water molecules (O4W and O5W) of crystallisation. Neutron crystallography experiments have also evidenced a proton displacement inside a short strong hydrogen bond (SSHB) between two isonicNO anions. Both phenomena can al…
Electron paramagnetic resonance (EPR) spin trapping of biological nitric oxide
2007
Nitric oxide (NO) is a free radical species with multiple physiological functions. Because of low concentrations and short half-life of NO, its direct measurement in living tissues remains a difficult task. Electron paramagnetic resonance (EPR) spin trapping is probably one of the best suitable platforms for development of new methods for quantification of biological NO. The most reliable EPR-based approaches developed so far are based on the reaction of NO with various iron complexes, both intrinsic and exogenously applied. This review is focused on the current state and perspectives of EPR spin trapping for experimental and clinical NO biology.
Single-Crystal X-Ray Diffraction Study of Pressure and Temperature-Induced Spin Trapping in a Bistable Iron(II) Hofmann Framework.
2020
High-pressure single-crystal X-ray diffraction has been used to trap both the low-spin (LS) and high-spin (HS) states of the iron(II) Hofmann spin crossover framework, [FeII (pdm)(H2 O)[Ag(CN)2 ]2 ⋅H2 O, under identical experimental conditions, allowing the structural changes arising from the spin-transition to be deconvoluted from previously reported thermal effects.
EPR investigations of polymeric and H2O2 -modified C3N4 -based photocatalysts
2019
The C3N4 -based nanopowders prepared by thermal condensation of melamine (MCN) with subsequent thermal etching (MCN-TE) and H2O2 -treatment were investigated by Q- and X-band EPR spectroscopy in dark and upon in situ UVA or visible-light exposure. Lorentzian signal at g = 2.003, more pronounced in the case of the thermally etched material, dominates EPR spectra of MCN and MCN-TE. More complex spectra were found for H2O2 -treated photocatalysts revealing the presence of signals attributed to the radicals produced via H2O2 interaction with C/N sites in the C3N4 polymeric network. The X-band spectra monitored upon in situ irradiation of the C3N4 -based photocatalysts evidenced the intensity gr…
Ultrasound-assisted MnO2 catalyzed homolysis of peracetic acid for phenol degradation: The assessment of process chemistry and kinetics
2013
Abstract The combination of peracetic acid (PAA) and heterogeneous catalyst (MnO 2 ) was used for the degradation of phenol in an aqueous solution in the presence of ultrasound irradiation (US). As a relevant source of free radicals (e.g. OH), peracetic acid was comprehensively studied by means of electron spin resonance (ESR) spin trapping (ST) techniques with the subsequent identification of free radicals by simulation based fitting (SBF) technique. The radical reaction mechanism, where hydroxyl radical was a primary product of O O bond rupture of PAA, was established taking into account radical reactions, occurring during sonolysis. The potential barriers and the reaction heat were deter…
Glycyrrhetinic Acid Reverses the Lipopolysaccharide-Induced Hypocontractility to Noradrenaline in Rat Aorta: Implications to Septic Shock
2014
Abstract.: Septic shock and associated vascular hyporeactivity to vasoconstrictor agonists remain a major problem of critical care medicine. Here we report that glycyrrhetinic acid (GA), the active component of licorice, effectively restores vascular contractility in the model of lipopolysaccharide (LPS)-treated rat aorta. GA was as effective as the NO synthase inhibitor NG-nitroarginine methylester. GA did not affect the vascular NO levels (measured by EPR spin trapping) and relaxations to l-arginine in LPS-treated rings as well as relaxation to S-nitroso-Nacetylpenicillamine in control rings. Thus, GA may represent an interesting alternative to NO synthase inhibitors in sepsis-associated …
ELECTRON SPIN RESONANCE AND ELECTROCHEMICAL STUDIES OF OXIDATION PRODUCTS DERIVATES OF APOMORPHINE IN APROTIC SOLVENTS
2002
Apomorphine acts as contractile muscular agent through an extra cellular calcium mechanism dependent. This activity is accompanied with autoxidación process producing o-quinone derivates. o-Quinone is also obtained by apomorphine oxidation in acid medium; in basic conditions a hydroxi-p-quinone is formed. In order to characterize the apomorphine derivates species generated via metabolism or chemical mechanism, specially free radical forms, electrochemical and Electronic Spin Resonance studies were done to o and p-quinones metabolites in presence or absence of Calcium ions. The electrochemical study of these compounds using cyclic voltametric indicated that the reduction mechanism consists o…
Spin Trapping of Carbon-Centered Ferrocenyl Radicals with Nitrosobenzene
2015
In contrast to metal centered 17 valence electron radicals, such as [Mn(CO)5]•, ferrocenium ions [Fe(C5H5)2]+ (1+), [Fe(C5Me5)2]+ (2+), [Fe(C5H5)(C5H4Et)]+ (3+), [Fe(C5H5)(C5H4NHC(O)Me)]+ (4+), and [Fe(C5H5)(C5H4NHC(S)Me)]+ (5+) do not add to nitrosobenzene PhNO to give metal-coordinated stable nitroxyl radicals. In the presence of the strong and oxidatively stable phosphazene base tert-butylimino-tris(dimethylamino)phosphorane, the quite acidic ferrocenium ions 1+–5+ are deprotonated to give a pool of transient and persistent radicals with different deprotonation sites [1–Hx]•–[5–Hx]•. One rather persistent iron-centered radical [4–HN]•, deprotonated at the nitrogen atom, has been detected…