Electron paramagnetic resonance spectroscopy electronic structure

New Methods in Electron Paramagnetic Resonance Spectroscopy for Structure and Function Determination in Biological Systems... 

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. 

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. 

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. 

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. 

As noted at the beginning of this chapter, radicals are a unique class of organic intermediates because they can be studied using magnetic resonance techniques such as electron paramagnetic resonance spectroscopy (EPR). The EPR technique has proven valuable for ascertaining the local structure about a radical in a supercritical fluid solvent. 

Due to the complexity of DOM fractionation has revealed more detailed information on the structural subunits prior to the application of advanced analytical methods. Most effective is the combination of different spectroscopic methods using UV-vis absorbance, fluorescence, 1H- and 13C-nuclear magnetic resonance, and Fourier transform-infrared (FT-IR) spectroscopy. In some studies, also electron paramagnetic resonance spectroscopy (EPR) is used (e.g., Chen et al., 2002). 

By using non-invasive techniques, it is possible to determine the concentration and oxidation state of vanadium in living cells. In A. ceratodes, EXAFS (X-ray absorption fine structure) techniques showed that 90% of the vanadium is in the form of V(III), 10% is V(IV)84. In A. nigra, EPR (electron paramagnetic resonance) spectroscopy showed that 95% of the vanadium is in the V(III) form, and 5% is V(IV)85. ... 

Guiles (1988) Structure and function of the manganese complex involved in photosynthetic oxygen evolution determined by X-ray absorption spectroscopy and electron paramagnetic resonance spectroscopy. Ph D dissertation, University of California, Berkeley, CA. Lawrence Berkeley Laboratory Report, LBL-25186... 

The 2 -position has been used to attach other functional groups, either for detection or for further modification. The tertiary structure of TAR RNA has been investigated by the incorporation of the uridine analogue (35). " The analogue incorporates a nitroxide spin-label and may be detected using electron paramagnetic resonance spectroscopy (EPR). A similar spin-label has been attached to the of a guanosine residue, where it was used to monitor hybridisation by EPR. " ... 

Electron Paramagnetic Resonance Spectroscopy Studies of Immobilized Monoclonal Antibody Structure and Function... 

Electron paramagnetic resonance spectroscopy is one of the primary tools in studying the electronic structure of polynuclear complexes (341). Whereas magnetic susceptibility studies are capable of detecting electronic interactions as small as a wavenumber (discussed earlier), the EPR spectrum of a polynuclear complex may be sensitive to intramolecular exchange couplings as small as 0.001 cm even at room temperature. Additionally, the °Mn nucleus has a nuclear spin... 

Simaan, A.J., F. Banse, J.-J. Girerd, K. Wieghardt, and E. Bill (2001). The electronic structure of nonheme iron(llI)-hydroperoxo and iron(llI)-peroxo model complexes studied by Moessbauer and electron paramagnetic resonance spectroscopies. Inorg. Chem. 40, 6538-6540. 

Since its discovery by Zavoisky in 1944, electron spin resonance spectroscopy (ESR) (also called electron paramagnetic resonance spectroscopy [EPR]) has become an essential tool for the study of the structure and dynamics of molecular systems containing one or more unpaired electrons. Such paramagnetic systems can frequently be examined using magnetic susceptibility techniques as well, but these do not provide the detailed information that ESR spectroscopy does. ESR spectroscopy and magnetic susceptibility methods each have their strengths and limitations and often provide complementary information. 

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