Electron paramagnetic resonance spectroscopy, detection

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. 

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. 

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]. 

Langrehr, J. M., Muller, A. R., Bergonia, H. A., Jacob, T. D., Lee, T. K., Schraut, W. H., Lancaster, J. R., Jr., Hoffman, R. A., and Simmons, R. L. (1992). Detection of nitric oxide by electron paramagnetic resonance spectroscopy during rejection and graft-versus host disease after small-bowel transplantation in the rat. Surgery 112, 395-401 discussion. 

Electron paramagnetic resonance spectroscopy, also known as electron spin resonance (ESR) spectroscopy, detects the excitation of electron spins in an applied external magnetic field.13 Conventional continuous-wave (CW) EPR is based on resonance of a fixed-frequency standing microwave to excite some of the electrons in Zeeman-split spin multiplets to undergo a transition from a lower Ms level to a higher... 

Kozlov AV, Bini A, Gallesi D, Giovannini F, lannone A, Masini A, Meletti E and Tomasi A, Free iron, as detected by electron paramagnetic resonance spectroscopy, increases unequally in different tissues during dietary iron overload in the rat. Biometals 9(1) 98-103, 1996. 

For example, McIntosh et al. [8] have detected a charge-separated species by electron paramagnetic resonance spectroscopy of a number of covalently linked P-Q compounds. 

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 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... 

Cantilena, L. R., Jr., Smith, R. P., Frasur, S., Kruszyna, H., Kruszyna, R., and Wilcox, D. E. (1992). Nitric oxide hemoglobin in patients receiving nitroglycerin as detected by electron paramagnetic resonance spectroscopy [see comments]. J. Lab. Clin. Med. 120, 902-907. 

There are five main techniques of analysis that have been used to determine dissolved manganese inductively coupled plasma (ICP) (using both emission spectroscopy and mass spectrometry detection), atomic absorption spectroscopy (AAS) (using both flame and furnace atomization), electronic spectroscopy (colorimetry), electron paramagnetic resonance spectroscopy (EPR), and anodic stripping voltammetry (ASV). 

Electron paramagnetic resonance spectroscopy has also been used as a probe of radical formation in the photoreactions between UO and carboxylic acids. In the photolysis of acetic acid and propionic acid with UOi at ambient temperature the respective radicals CH2C02H and CH3CHCO2H have been detected by their multiplicities. ... 

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