1,721,074 research outputs found
The distribution of paramagnetic centers in glass and lavas from eruptive activity at Mt. Etna: implications for magmatic processes during basaltic eruptions
No full textAntioxidant potential in lipophilic and hydrophilic extracts from medicinal herbs (Salvia officinalis and Echinacea angustifolia). A comparison between assays based on electron paramagnetic resonance and spectrophotometry
No full textThe role of dietary chlorophylls: an EPR study on the antioxidant activities of tomato lipid extracts
No full textIdentification of the components responsible for the antioxidant activity of lipid extracts from tomato with some lipid antioxidants was obtained by EPR using the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH). Lipid extracts were obtained from leaves, roots and berries of tomato grown in hydroponics. Both fast lipophilic antioxidants (FLA) and slow lipophilic antioxidants (SLA) were present in leaves and berries whereas only SLA could be identified in the root lipid extract. Simulation of the decay kinetic of DPPH by leaves was obtained with a chlorophyll b/β-carotene mixture whereas lycopene, which reduced DPPH with a stoichiometry 1:1, behaved as a SLA. Antioxidant activity of lipid extract from leaves showed values 56-and 45-fold higher than the antioxidant activity of lipid extract from root and berries, respectively and it was mainly due to the presence of chlorophyll, representing in the leaf 38% of FLA
Spin labeling study of human serum albumin in reverse micelles
No full textHuman serum albumin (HSA), spin labeled at the sulfhydryl group by the reagent 3-maleimidoproxyl
(3MAL), was studied in reverse micelles formed by sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in
isooctane. The electron spin resonance spectra were recorded at different water contents and analyzed
by computer simulations. In order to obtain agreement between experimental and calculated spectra, the
use of an anisotropic model of reorientational diffusion for 3MAL-HSA in reverse micelles was necessary.
An isotropic reorientational motion was suitable to simulate the 3MAL-HSA spectrum in aqueous solution.
This result suggests that conformational changes of the protein which modify the label environment occur
in reverse micelles. The rotational correlation times for 3MAL-HSA in reverse micelles were strongly
dependent on the water content: the protein experienced a more hindered environment for rotational
diffusion as the water pool size decreased
Some New Results on the Fischer-Hafner Synthesis of Vanadium Arenes
No full textThe biphasic liquid system formed in the Fisher-Hafner reduction of VCl3 in toluene contains the [V(η6-MeC6H5)2]+ cation which has been isolated in the solid state as the tetraphenylborato- (from aqueous solution) or as the [Al2Cl7]-, [Al4O2Cl10]2- and [catena-Al4O2Cl9]- salt (directly from the biphasic liquid system). The crystal structures of [V(η6-MeC6H5)2]2[Al4O2Cl10] (2), and [V(η6-MeC6H5)2][catena-Al4O2Cl9] (3), have been solved representing the first structural report of the [V(η6-MeC6H5)2]+ cation (compounds 2 and 3) and of the polymeric nonachlorodioxoaluminate anion [Al4O2Cl9]- (compound 3)
Room Temperature Long-Lived [Nb2F11]- Salts of Radical Cations of Simple Arenes: EPR, UV-VIS and DFT Results
No full textThe computed structures of the long-lived radical cation salts [Arene][Nb2F(11)] [Arene 1,4-F-2-2,5-(OMe)(2)C6H2, 2; 1,4-(OMe)(2)C6H4, 3; 2,5-(OEt)(2)(Me)C(6)H3(,) 4; C6H6, 5] and that of the transient [1,3-(OMe)(2)C6H4][Nb2F11], 6, obtained for the gas-phase by DFT at the B3LYP/6-31G** level, are presented. The degree of inertness observed in chloroform solution seems to increase on decreasing the steric demand of the ring substituents, and may be correlated to the calculated distance between the cation-centroid and the niobium atoms. The room-temperature EPR spectra of 2e4, in CHCl3, are described in detail; the spectrum of 3 is compared to those of analogous 1,4-dimethoxybenzene radical species reported previously. The EPR spectra display a hyperfine structure due to coupling of the unpaired electron with nuclei belonging to both the cation (H and F in the case of 2) and the anion (F and eventually Nb). The UV-Vis spectra of 2e4 exhibit one strong absorption attributed to the cation and one anion-to-cation charge-transfer band (e.g. for 3 at 398 and 589 nm, respectively). Thermodynamic calculations indicate that the low yield formation of the benzene radical salt 5 occurs with Gibbs free energy variation significantly higher than those involved in the synthesis of 2e4 and 6
Nb(V) and Ta(V) Haloanions as Effective Counterions for the Room Temperature Isolation of Salts of Uncommon Organic Cations
No full textIn the framework of our recent studies on the direct interaction of MX5 (M = Nb, Ta; X = F, Cl, Br) with oxygen compounds, we have been aware that M(V) haloanions possess outstanding capability of stabilizing uncommon organic cations. Reactions involving ketones or polyethers may be accompanied by CH bond activation, thus the salts [(MePhCO)2(-H)][TaCl6], 1 (Fig. A) [1], and [diglyme(H)][NbCl6], 2 [2], have been isolated in the respective cases. Otherwise the reaction of NbCl5 with CMe2(OMe)2 proceeds with CO cleavage and leads to selective formation of the methylated mesityl oxide species [Me2C=CHC(=OMe)Me][NbCl5(OMe)], 3 (Fig. B) [3]. A series of [Nb2F11] radical cation salts of monocyclic arenes have been prepared according to unexpected redox reaction including metal reduction [4]. These salts are surprisingly long-lived at room-temperature or above, due to stabilizing cation-anion interactions; the [C6H6]+ radical has been identified for the first time by EPR as a non-transient species in solution at room temperature. The same redox pathway has been exploited for the straightforward synthesis of thermally stable [M2F11] salts of protonated 1,3-dimethoxybenzene (Fig. C) [5]
structure of volcanic glasses from the NMR-EPR perspective: a preliminary application to the Neapolitan Yellow Tuff
No full textBULL. VOLCANOL
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