The paramagnetic germanium–sodium impurity centres and in α-quartz

1991 ◽  
Vol 69 (7) ◽  
pp. 761-779 ◽  
Author(s):  
R. S. Dickson ◽  
J. A Weil ◽  
P. H. Davis
Keyword(s):  
Bond Angle ◽  
Resonance Spectroscopy ◽  
Crystallographic Axis ◽  
Paramagnetic Resonance ◽  
Angle Bisector ◽  
X Band ◽  
Ca 50 ◽  
X Irradiation ◽  
Na Ions ◽  
Sodium Impurity

Centres [Formula: see text] formed in α-quartz by 77 K x irradiation and warming above ca. 165 K, both exhibit a reversible change in symmetry of the centres from C1 at 75 K to C2 at 295 K, as observed by X-band electronic paramagnetic resonance spectroscopy. Each centre contains a Ge3+ ion (S = 1/2) substituted for a Si4+ ion, with a nearby Na+ interstitial ion. Spin-Hamiltonian electronic Zeeman, 73Ge and 23Na nuclear hyperfine and quadrupole parameter matrices for these centres were measured at temperatures 75, 190, and 295 K. They show that the change is associated with the defect reorienting between sites related by a two-fold crystallographic axis a, with energy barrier 0.223(6) eV for A and 0.178(14) eV for C. In both centres, ca. 50% of the spin density is located in a Ge sp orbital; in A, the sp orbital is oriented close to a, while in C it is nearly parallel to an O–Si–O bond-angle bisector that is nearly normal to a. Theoretical hyperfine matrices indicate that the Na ions are located near a, in a c-axis channel near the Ge site. Above ca. 270 K, A and C are observably in equilibrium, and are thus deemed to be isomeric species.

Paramagnetic Ge–Li centres in alpha quartz revisited: The DLi([GeO4/Li]0D) centre

2008 ◽  
Vol 86 (11) ◽  
pp. 1303-1311
Author(s):  
R F.C. Claridge ◽  
O M Kryliouk ◽  
J A Weil ◽  
J A.S. Williams
Keyword(s):  
Electron Paramagnetic Resonance Spectroscopy ◽  
Spin Hamiltonian Parameter ◽  
Resonance Spectroscopy ◽  
Paramagnetic Defect ◽  
Paramagnetic Resonance ◽  
Hamiltonian Parameter ◽  
X Band ◽  
X Irradiation ◽  
And Storage ◽  
Electron Paramagnetic

A previously unreported stable paramagnetic defect centre in single-crystal alpha-quartz has been studied by quantitative X-band electron paramagnetic resonance spectroscopy at 15, 100, and 296 K, and is shown to contain a Ge3+ ion, presumably located substitutional for Si4+, with a nearby interstitial Li+ ion. The centre, called DLi herein, grows in slowly (months) after room-temperature x-irradiation and storage. Hyperfine structure arising from 73Ge, 7Li, and 29Si has been observed. The spin-Hamiltonian parameter matrices g, A(7Li), A(73Ge), and P(73Ge) are reported, also for centre CLi. A thermal dynamic process, probably involving Li+ hopping, begins to be appreciable above 100 K. Discussion of DLi, its apparent growth from another paramagnetic centre (not yet fully characterized), and comparison with other similar defects is included.PACS Nos.: 42.70.Ce, 61.72.Hh, 61.72–y, 61.72S–, 61.72uf, 61.80–x, 76.30–v, 76.30.Mi

scholarly journals Effect of temperature on liposome structures studied using EPR spectroscopy

2005 ◽  
Vol 19 (1) ◽  
pp. 37-42 ◽  
Author(s):  
W.W. Sulkowski ◽  
D. Pentak ◽  
W. Korus ◽  
A. Sulkowska
Keyword(s):  
Structural Changes ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Rotational Correlation Time ◽  
Effect Of Temperature ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Liposome Membrane ◽  
X Band ◽  
Increasing Temperature ◽  
Parameter Values

The effect of temperature on liposome structures has been investigated by means of electron paramagnetic resonance spectroscopy with the use of the spin labelling technique. The EPR spectra were recorded on a Bruker EMX spectrometer at the X band in the temperature range 300–340 K. Liposomes were prepared from L?a?phosphatidylcholine dipalmitoyl (1,2?dihexadecanoyl?sn?glycerol?3?phosphocholine) 99% (DPPC), DL?a?phosphatidylcholine dimyristoyl (1,2?ditetradecanoyl?rac?glycerol?3?phosphocholine) 99% (DMPC) and cholesterol (5?cholesten?3ß?ol) 99+% to constitute the membrane. The spin marker, 2?(3carboxypropyl)?4,4?dimethyl?2?tridecyl?3?oxazolidinyloxyl free radical (5?DOXYL), placed in a liposome membrane, allows for observation of structural changes in liposomes with temperature increase. The changes of rotational correlation time and order parameter values with increasing temperature result from the motion rise of the spin probe. The intensity of the EPR signal of 5?DOXYL gives us information about membrane fluidity.

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.

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.

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