Spectroscopy electron paramagnetic resonance

Although most lanthanide ions are paramagnetic, because of rapid relaxation effects, spectra can be obtained only at low temperatures (often 4.2 K) in most cases. From the point of view of the chemist, EPR spectra are readily obtained (at room temperature) only from the f Gd +, with its 87/2 ground state. The sublevels of this state are degenerate in the absence of a crystal field (in a free Gd + ion), but are split into four Kramers doublets, with M/-values of 1/2, 3/2, 5/2 and 7/2. The application of a magnetic field removes the degeneracy of each doublet, and transitions can occur on irradiation with microwave radiation, subject to the usual selection rule of AM/ = 1. 

In the absence of a zero-field splitting (z.f.s.), all transitions occur at the same field (corresponding to a -value of 2.00), but as the z.f.s. increases, transitions occur at higher 

The EPR spectra of the radical cations derived from pyrrole solutions can all be simulated by electronic structures in which the unpaired electron is located in an orbital with the nodal plane on the nitrogen and (2) showing large coupling constant values at the 2- and 5-positions and small values at the 3- and 4-positions 2000J(P2)905 . The EPR parameters of the radical cations from 2,5-dimethyl-l-phenylpyrroles and 3,4-bis(alkylthio)-2,5-dimethyl-l-phenylpyrroles (Table 30) denote a marked stabilization of the radical cations by the sulfanyl groups through mesomeric effects. 

The application of RPR in the detection and quantification of species formed by spin-trapping the products of radical-monomer reactions is described in Section 3.5.2.1, The application of time-resolved F.PR spectroscopy to study intermolecular radical-alkene reactions in solution is mentioned in Section 3.5.1. 

The application of RPR in the detection and quantification of species formed by spin-trapping the products of radical-monomer reactions is described in Section 

The application of time-resolved RPR spectroscopy to study intermolecular radical-alkene reactions in solution is mentioned in Section 3.5.1. 

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Pont A and Schwelger A 1994 Echo phenomena in electron paramagnetic resonance spectroscopy Appl. Magn. Reson. 7 363-403... 

Luciferase is irreversibly inactivated by H2O2, and strongly inhibited by KCN, diethyldithiocarbamate and o-phenanthroline. Electron paramagnetic resonance spectroscopy (EPR) of luciferase showed a... 

Electron paramagnetic resonance spectroscopy (HER), also called electron spin resonance spectroscopy (ESR), may be used for direct detection and conformational and structural characterization of paramagnetic species. Good introductions to F.PR have been provided by Fischer8 and I.effler9 and most books on radical chemistry have a section on EPR. EPR detection limits arc dependent on radical structure and the signal complexity. However, with modern instrumentation, radical concentrations > 1 O 9 M can be detected and concentrations > I0"7 M can be reliably quantified. 

Green, M.R., Allen, FI., Hill, O., Okolowzubkowska, M.J. and Segal, A.W. (1979). The production of OH and OJ by stimulated human neutrophils - measurements by electron paramagnetic resonance spectroscopy. FEBS Lett. 100, 23-26. 

Schreckenbach, G., Ziegler, T., 1997b, Calculation of the g-Tensor of Electron Paramagnetic Resonance Spectroscopy Using Gauge-Including Atomic Orbitals and Density Functional Theory , J. Phys. Chem. A, 101, 3388. 

The crystallographic structure of rubredoxin from Clostridium pasteurianum at 2.5 A, a resolution sufficient to reveal the sequence of several of the bulky amino acid side chains, shows the iron coordinated to two pairs of cysteine residues located rather near the termini of the polypeptide chain (Fig. 1). A related rubredoxin, with a three times larger molecular weight, from Pseudomonas oleovorans is believed to bind iron in a similar fashion. This conclusion is based on physical probes, especially electron paramagnetic resonance spectroscopy, all of which indicate that the iron is in each case situated in a highly similar environment however, the proteins display some specificity in catalytic function. 

Tshisuaka, B. Kappl, R. Huttermann, J., and Lingens, F., Quinoline Oxidoreductase From Pseudomonas-Putida-86 - an Improved Purification Procedure and Electron-Paramagnetic-Resonance Spectroscopy. Biochemistry-US, 1993. 32 (47) pp. 12928-12934. 

Bramley, R. and Strach, S.J. 1983. Electron paramagnetic resonance spectroscopy at zero magnetic field. Chemical Reviews 83 49-82. 

Lagerstedt, J.O., Budamagunta, M.S., Oda, M.N., and Voss, J.C. 2007. Electron paramagnetic resonance spectroscopy of site-directed spin labels reveals the structural heterogeneity in the N-terminal domain of ApoA-I in solution. The Journal of Biological Chemistry 282 9143-9149. 

Venable, J.H. 1967. Electron paramagnetic resonance spectroscopy of protein single crystals II. Computational methods. In Magnetic Resonance in Biological Systems, eds. A. Ehrenberg, B.G. Malmstrom and T. Vanngard Elmsford. New York Pergamon Press, 373-381. 

Electron paramagnetic resonance (EPR) and NMR spectroscopy are quite similar in their basic principles and in experimental techniques. They detect different phenomena and thus yield different information. The major use of EPR spectroscopy is in the detection of free radicals which are uniquely characterised by their magnetic moment that arises from the presence of an unpaired electron. Measurement of a magnetic property of a material containing free radicals, like its magnetic susceptibility, provides the concentration of free radicals, but it lacks sensitivity and cannot reveal the structure of the radicals. Electron paramagnetic resonance spectroscopy is essentially free from these defects. 

NMR X-ray EPR = = Characterization by NMR spectroscopy. = Characterization by X-ray diffraction. = Characterization by electron paramagnetic resonance spectroscopy. ... 

Second law studies by Lucarini, Pedulli, and Cipollone, using electron paramagnetic resonance spectroscopy, have shown that the entropy of this reaction in... 

Based on our current understanding of ribosomal protein synthesis, several strategies have been developed to incorporate amino acids other than the 20 standard proteinogenic amino acids into a peptide using the ribosomal machinery . This allows for the design of peptides with novel properties. On the one hand, such a system can be used to synthesize nonstandard peptides that are important pharmaceuticals. In nature, such peptides are produced by nonribosomal peptide synthetases, which operate in complex pathways. On the other hand, non-natural residues are a useful tool in biochemistry and biophysics to study proteins. For example, incorporation of non-natural residues by the ribosome allows for site-specific labeling of proteins with spin labels for electron paramagnetic resonance spectroscopy, with... 

Chapman A, Cammack R, Linstead DJ, Lloyd D. 1986. Respiration of Trichomonas vaginalis components detected by electron paramagnetic resonance spectroscopy. Eur J Biochem 156 193-8. 

One of the earliest reports of LO inhibition concerned the effects of ortho-dihydroxybenzene (catechol) derivatives on soybean 15-LO [58]. Lipophilic catechols, notably nordihydroguaiaretic acid (NDGA) (19), were more potent (10 /zM) than pyrocatechol itself. The inactivation was, under some conditions, irreversible, and was accompanied by oxidation of the phenolic compound. The orfAo-dihydroxyphenyl moiety was required for the best potency, and potency also correlated with overall lipophilicity of the inhibitor [61]. NDGA and other phenolic compounds have been shown by electron paramagnetic resonance spectroscopy to reduce the active-site iron from Fe(III) to Fe(II) [62] one-electron oxidation of the phenols occurs to yield detectable free radicals [63]. Electron-poor, less easily oxidized catechols form stable complexes with the active-site iron atom [64]. 

Ecker DJ, Lancaster JR Jr., Emery T (1982) Siderophore Iron Transport Followed by Electron Paramagnetic Resonance Spectroscopy. J Biol Chem 257 8623... 

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