EPR Spectra from “EPR-Silent” Species:  High-Field EPR Spectroscopy of Aqueous Chromium(II)

1998 ◽  
Vol 37 (22) ◽  
pp. 5769-5775 ◽  
Author(s):  
Joshua Telser ◽  
Luca A. Pardi ◽  
J. Krzystek ◽  
Louis-Claude Brunel
Keyword(s):  
Epr Spectroscopy ◽  
High Field ◽  
Epr Spectra

EPR Spectra from “EPR-Silent” Species:  High-Frequency and High-Field EPR Spectroscopy of Pseudotetrahedral Complexes of Nickel(II)

2002 ◽  
Vol 41 (17) ◽  
pp. 4478-4487 ◽  
Author(s):  
J. Krzystek ◽  
Ju-Hyun Park ◽  
Mark W. Meisel ◽  
Michael A. Hitchman ◽  
Horst Stratemeier ◽  
...  
Keyword(s):  
Epr Spectroscopy ◽  
High Frequency ◽  
High Field ◽  
Epr Spectra

scholarly journals EPR Spectra from “EPR-Silent” Species:  High-Field EPR Spectroscopy of Aqueous Chromium(II).

2000 ◽  
Vol 39 (8) ◽  
pp. 1834-1834 ◽  
Author(s):  
Joshua Telser ◽  
Luca A. Pardi ◽  
J. Krzystek ◽  
Louis-Claude Brunel
Keyword(s):  
Epr Spectroscopy ◽  
High Field ◽  
Epr Spectra

EPR Spectra from “EPR-Silent” Species:  High-Field EPR Spectroscopy of Manganese(III) Porphyrins

1997 ◽  
Vol 119 (37) ◽  
pp. 8722-8723 ◽  
Author(s):  
David P. Goldberg ◽  
Joshua Telser ◽  
J. Krzystek ◽  
Antonio Garrido Montalban ◽  
Louis-Claude Brunel ◽  
...  
Keyword(s):  
Epr Spectroscopy ◽  
High Field ◽  
Epr Spectra

Properties of electrochemically generated primary cationradicals of phenyl- and 2-(4-tolyl)-1,3,4,7-tetramethylisoindoles

1980 ◽  
Vol 45 (6) ◽  
pp. 1669-1676 ◽  
Author(s):  
Pavel Kubáček
Keyword(s):  
Electrochemical Oxidation ◽  
Spin Polarization ◽  
High Spin ◽  
Epr Spectroscopy ◽  
Half Life ◽  
Electrochemical Behaviour ◽  
Epr Spectra ◽  
Electrochemical Generation ◽  
Splitting Constant ◽  
Reduced Temperature

The first step of electrochemical oxidation of 2-phenyl- and 2-(4-tolyl)-1,3,4,7-tetramethylisoindoles in anhydrous acetonitrile produces relatively stable cationradicals which have been studied by means of EPR spectroscopy using the method of internal electrochemical generation of radicals under reduced temperature. The same electrochemical behaviour of the both studied derivatives and identical EPR spectra of their cationradicals can be explained within the Huckel MO method. The largest contribution to the magnitude of splitting constant of nitrogen nucleus is due to π-σ-spin polarization of C-N bonds caused by high spin abundance of pz-AO of carbon atoms. Half-life of decomposition of the studied cationradicals is 4 min at -30°C.

scholarly journals EPR Spectroscopy as a Tool to Characterize the Maturity Degree of Humic Acids

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3410
Author(s):  
Bozena Debska ◽  
Ewa Spychaj-Fabisiak ◽  
Wiesław Szulc ◽  
Renata Gaj ◽  
Magdalena Banach-Szott
Keyword(s):  
Humic Acids ◽  
Epr Spectroscopy ◽  
Plant Material ◽  
Crop Residues ◽  
Triticum Aestivum L ◽  
Epr Spectra ◽  
Thuja Plicata ◽  
Anthropogenic Factors ◽  
Paramagnetic Resonance ◽  
Spin Concentration

The major indicator of soil fertility and productivity are humic acids (HAs) arising from decomposition of organic matter. The structure and properties of HAs depend, among others climate factors, on soil and anthropogenic factors, i.e., methods of soil management. The purpose of the research undertaken in this paper is to study humic acids resulting from the decomposition of crop residues of wheat (Triticum aestivum L.) and plant material of thuja (Thuja plicata D.Don.ex. Lamb) using electron paramagnetic resonance (EPR) spectroscopy. In the present paper, we report EPR studies carried out on two types of HAs extracted from forest soil and incubated samples of plant material (mixture of wheat straw and roots), both without soil and mixed with soil. EPR signals obtained from these samples were subjected to numerical analysis, which showed that the EPR spectra of each sample could be deconvoluted into Lorentzian and Gaussian components. It can be shown that the origin of HAs has a significant impact on the parameters of their EPR spectra. The parameters of EPR spectra of humic acids depend strongly on their origin. The HA samples isolated from forest soils are characterized by higher spin concentration and lower peak-to-peak width of EPR spectra in comparison to those of HAs incubated from plant material.

scholarly journals Biomolecular EPR Meets NMR at High Magnetic Fields

2018 ◽  
Vol 4 (4) ◽  
pp. 50 ◽  
Author(s):  
Klaus Möbius ◽  
Wolfgang Lubitz ◽  
Nicholas Cox ◽  
Anton Savitsky
Keyword(s):  
Solid State ◽  
Transition Metal ◽  
Epr Spectroscopy ◽  
High Field ◽  
Double Resonance ◽  
Reaction Centers ◽  
Photosynthetic Reaction Centers ◽  
Reaction Intermediates ◽  
Frozen Solution ◽  
Epr Experiments

In this review on advanced biomolecular EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR regarding the measurement of interactions and dynamics of large molecules embedded in fluid-solution or solid-state environments. Our focus is on the characterization of protein structure, dynamics and interactions, using sophisticated EPR spectroscopy methods. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy to new horizons reaching millimeter and sub-millimeter wavelengths and 15 T Zeeman fields. Expanding traditional applications to paramagnetic systems, spin-labeling of biomolecules has become a mainstream multifrequency approach in EPR spectroscopy. In the high-frequency/high-field EPR region, sub-micromolar concentrations of nitroxide spin-labeled molecules are now sufficient to characterize reaction intermediates of complex biomolecular processes. This offers promising analytical applications in biochemistry and molecular biology where sample material is often difficult to prepare in sufficient concentration for NMR characterization. For multifrequency EPR experiments on frozen solutions typical sample volumes are of the order of 250 μL (S-band), 150 μL (X-band), 10 μL (Q-band) and 1 μL (W-band). These are orders of magnitude smaller than the sample volumes required for modern liquid- or solid-state NMR spectroscopy. An important additional advantage of EPR over NMR is the ability to detect and characterize even short-lived paramagnetic reaction intermediates (down to a lifetime of a few ns). Electron–nuclear and electron–electron double-resonance techniques such as electron–nuclear double resonance (ENDOR), ELDOR-detected NMR, PELDOR (DEER) further improve the spectroscopic selectivity for the various magnetic interactions and their evolution in the frequency and time domains. PELDOR techniques applied to frozen-solution samples of doubly spin-labeled proteins allow for molecular distance measurements ranging up to about 100 Å. For disordered frozen-solution samples high-field EPR spectroscopy allows greatly improved orientational selection of the molecules within the laboratory axes reference system by means of the anisotropic electron Zeeman interaction. Single-crystal resolution is approached at the canonical g-tensor orientations—even for molecules with very small g-anisotropies. Unique structural, functional, and dynamic information about molecular systems is thus revealed that can hardly be obtained by other analytical techniques. On the other hand, the limitation to systems with unpaired electrons means that EPR is less widely used than NMR. However, this limitation also means that EPR offers greater specificity, since ordinary chemical solvents and matrices do not give rise to EPR in contrast to NMR spectra. Thus, multifrequency EPR spectroscopy plays an important role in better understanding paramagnetic species such as organic and inorganic radicals, transition metal complexes as found in many catalysts or metalloenzymes, transient species such as light-generated spin-correlated radical pairs and triplets occurring in protein complexes of photosynthetic reaction centers, electron-transfer relays, etc. Special attention is drawn to high-field EPR experiments on photosynthetic reaction centers embedded in specific sugar matrices that enable organisms to survive extreme dryness and heat stress by adopting an anhydrobiotic state. After a more general overview on methods and applications of advanced multifrequency EPR spectroscopy, a few representative examples are reviewed to some detail in two Case Studies: (I) High-field ELDOR-detected NMR (EDNMR) as a general method for electron–nuclear hyperfine spectroscopy of nitroxide radical and transition metal containing systems; (II) High-field ENDOR and EDNMR studies of the Oxygen Evolving Complex (OEC) in Photosystem II, which performs water oxidation in photosynthesis, i.e., the light-driven splitting of water into its elemental constituents, which is one of the most important chemical reactions on Earth.

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