scholarly journals Use of Electron Paramagnetic Resonance Spectroscopy to Study Dielectric Properties of Liquids

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Daniel T. Glatzhofer ◽  
Rahul S. Kadam
Keyword(s):  
Dielectric Constant ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Mixed Solvents ◽  
Active Species ◽  
Dielectric Constants ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Epr Signal ◽  
Signal Response ◽  
High Dielectric

The signal response of an EPR active species is attenuated by the medium it is in. Keeping all other parameters the same, the higher the dielectric constant of the medium, the lower the EPR signal response. This behavior is problematic in studying EPR active species in high dielectric media but can be capitalized upon to monitor changes in the dielectric constant or estimate the dielectric constant of the medium. Using a coaxial EPR cell design, the EPR signal of a stable nitroxyl radical compound (2,2,6,6-tetramethyl-piperidin-1-oxyl radical) in a low dielectric constant solvent in an inner tube is attenuated by the solvent present between the inner and outer tubes (jacket medium). The attenuation increases monotonically with an increase in the dielectric constant of the jacket medium. Calibration curves can be constructed using jacket media of known dielectric constants ranging from 2 to 80 and the dielectric constant of a sample used as the jacket medium can be estimated by interpolation. This technique is applied to estimate the dielectric constants and/or composition of mixed solvents and to monitor the rate of a reaction.

The behaviour of a synthetic 57Fe-doped kaolin: Mössbauer and electron paramagnetic resonance studies

Clay Minerals ◽  
1980 ◽  
Vol 15 (4) ◽  
pp. 429-444 ◽  
Author(s):  
A. H. Cuttler
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Ferric Oxide ◽  
Ferrous Iron ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
X Irradiation ◽  
Epr Signal ◽  
Signal Changes ◽  
Electron Paramagnetic

AbstractThe thermal behaviour of a ferrous doped kaolin has been studied by Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy. From the observations it is concluded that the iron substitutes trioctahedrally as Fe2+ in the ‘gibbsite-like’ sheet in place of dioctahedral aluminium. The g = 2 EPR signal is shown to be associated with these ferrous ‘cells’ which appear to occur in clusters. It is suggested that these ferrous cells are trapped within the normal dioctahedral aluminium structure. Dehydroxylation of the ferrous iron cells takes place between 623 and 673 K leading to the formation of an iron-rich pyroxene and, by 723 K, a ferric oxide. At temperatures > 723 K the pyroxene itself oxidizes to a second ferric oxide. The EPR signal changes at 623 K and disappears at 723 K. The signal is attributed to a trapped hole induced by X-irradiation, located near a silicon atom on the boundary between normal dioctahedral cells and trioctahedral Fe2+ cells. It is possible to extend the model to explain some puzzling features concerning the g = 2 EPR signals reported by other authors and to propose other effects which might result from the presence of these cells.

Activation of Mg acceptors in GaN:Mg monitored by electron paramagnetic resonance spectroscopy.

2002 ◽  
Vol 743 ◽  
Author(s):  
D. Matlock ◽  
M. E. Zvanut ◽  
Jeffrey R. DiMaio ◽  
R. F. Davis ◽  
R. L. Henry ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Chemical Process ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Epr Signal ◽  
P Type ◽  
Electron Paramagnetic ◽  
Deposited Films ◽  
Mg Doped

ABSTRACTHydrogen removal from Mg-doped GaN is necessary to activate p-type conductivity, but the exact chemical process is not yet clear. We have investigated this issue by monitoring the intensity of an electron paramagnetic resonance (EPR) signal attributed to Mg through a series of isochronal and isothermal anneals between 600 and 1000 °C. Measurements made on GaN:Mg epitaxial layers deposited on SiC and annealed between 700 and 850 °C indicate that the Mg-related EPR signal increases with temperature as expected for depassivation of a Mg complex by removal of hydrogen. However, data obtained outside this temperature range suggest that additional processes may occur. For example, as-deposited films contain a signal resembling the Mg acceptor that is quenched by a 650 °C N2 anneal. Also, for all samples, N2 annealing at T>850 °C irreversibly decreases the signal thought to be due to Mg. Although the presence of the signal in the as-grown films is not fully understood, the effects observed at T>850 °C may be attributed to preferential N-desorption from Mg-N-H complexes.

scholarly journals EPR Study of Paramagnetic Defects in Clay Minerals

Mineralogia ◽  
2007 ◽  
Vol 38 (2) ◽  
pp. 125-138
Author(s):  
Joanna Babińska ◽  
Krystyna Dyrek ◽  
Piotr Wyszomirski
Keyword(s):  
Clay Minerals ◽  
Metal Ion ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Radioactive Elements ◽  
Paramagnetic Resonance ◽  
Radiation Induced ◽  
Epr Signal ◽  
Induced Defects ◽  
Electron Paramagnetic

EPR Study of Paramagnetic Defects in Clay MineralsRadiation induced defects (RID-s) and transition metal ion impurities were revealed by EPR (Electron Paramagnetic Resonance) spectroscopy in kaolinites from a number of Polish deposits. Arelationship between the intensity of the EPR signals of the RID-s and quantity of radioactive elements was defined in these minerals. In one of the deposits of kaolinites (Wyszonowice) the EPR signal intensity depends on grain size. Other clay minerals studied (illites, montmorillonites) only show weak signals of the RID type.

scholarly journals Tauroursodeoxycholic Acid (TUDCA)—Lipid Interactions and Antioxidant Properties of TUDCA Studied in Model of Photoreceptor Membranes

Membranes ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 327
Author(s):  
Michał J. Sabat ◽  
Anna M. Wiśniewska-Becker ◽  
Michał Markiewicz ◽  
Katarzyna M. Marzec ◽  
Jakub Dybas ◽  
...  
Keyword(s):  
Antioxidant Activity ◽  
Plasma Membranes ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Protective Action ◽  
Antioxidant Properties ◽  
Model Membranes ◽  
Dynamics Simulation ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Tauroursodeoxycholic Acid

Tauroursodeoxycholic acid (TUDCA), a hydrophilic bile acid containing taurine conjugated with the ursodeoxycholic acid (UDCA), has been known and used from ancient times as a therapeutic compound in traditional Chinese medicine. TUDCA has recently been gaining significant interest as a neuroprotective agent, also exploited in the visual disorders. Among several mechanisms of TUDCA’s protective action, its antioxidant activity and stabilizing effect on mitochondrial and plasma membranes are considered. In this work we investigated antioxidant activity of TUDCA and its impact on structural properties of model membranes of different composition using electron paramagnetic resonance spectroscopy and the spin labeling technique. Localization of TUDCA molecules in a pure POPC bilayer has been studied using a molecular dynamics simulation (MD). The obtained results indicate that TUDCA is not an efficient singlet oxygen (1O2 (1Δg)) quencher, and the determined rate constant of its interaction with 1O2 (1Δg) is only 1.9 × 105 M−1s−1. However, in lipid oxidation process induced by a Fenton reaction, TUDCA reveals substantial antioxidant activity significantly decreasing the rate of oxygen consumption in the system studied. In addition, TUDCA induces slight, but noticeable changes in the polarity and fluidity of the investigated model membranes. The results of performed MD simulation correspond very well with the experimental results.

scholarly journals Ambient base-free glycerol oxidation over bimetallic PdFe/SiO2 by in situ generated active oxygen species

2021 ◽  
Author(s):  
Ricci Underhill ◽  
Mark Douthwaite ◽  
Richard J. Lewis ◽  
Peter J. Miedziak ◽  
Robert D. Armstrong ◽  
...  
Keyword(s):  
Heterogeneous Catalysts ◽  
Bimetallic Catalyst ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Active Oxygen Species ◽  
Catalytic Performance ◽  
Resonance Spectroscopy ◽  
Oxygen Species ◽  
Paramagnetic Resonance ◽  
Temperature Oxidation

AbstractLow temperature oxidation of alcohols over heterogeneous catalysts is exceptionally challenging, particularly under neutral conditions. Herein, we report on an efficient, base-free method to oxidise glycerol over a 0.5%Pd-0.5%Fe/SiO2 catalyst at ambient temperature in the presence of gaseous H2 and O2. The exceptional catalytic performance was attributed to the in situ formation of highly reactive surface-bound oxygenated species, which promote the dehydrogenation on the alcohol. The PdFe bimetallic catalyst was determined to be significantly more active than corresponding monometallic analogues, highlighting the important role both metals have in this oxidative transformation. Fe leaching was confirmed to occur over the course of the reaction but sequestering experiments, involving the addition of bare carbon to the reactions, confirmed that the reaction was predominantly heterogeneous in nature. Investigations with electron paramagnetic resonance spectroscopy suggested that the reactivity in the early stages was mediated by surface-bound reactive oxygen species; no homogeneous radical species were observed in solution. This theory was further evidenced by a direct H2O2 synthesis study, which confirmed that the presence of Fe in the bimetallic catalyst neither improved the synthesis of H2O2 nor promoted its decomposition over the PdFe/SiO2 catalyst.

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