Electron paramagnetic resonance methods

Pulsed EPR is becoming more widely available. A 90° pulse is typically in the range of 10 to 30 ns. The free induction decay, FID, after such a pulse can be used to measure the electron spin relaxation time or to monitor the decay of radicals that have been produced by some fast method, such as flash photolysis or pulse radiolysis. Electron spin-echo envelope modulation, ESEEM, spectroscopy is a pulse method used primarily for detecting weak hyperfine coulping. 

Most applications use EPR as a detection method for reactants or products. Various flow methods can be coupled with EPR to monitor the time dependence of EPR-active species. It is also possible to use EPR line broadening to measure exchange rates, and in this area the time scale is in the range of 10 to 1(T s. 

Spin trapping can be used to convert radical intermediates into more stable species that can be detected by EPR. For example, fiimarate ion was used to trap the aryl radicals, Ar, formed in the oxidation of Fe(II) by benzenediazonium ions, ArNj , in a stopped-flow EPR study. The 02C(CgHj)CH- CHC02 radical is sufficiently stable relative to dimerization so that its concentration after the 3S-ms mixing time could be used to determine the rate of the initial oxidation reaction. 

The DMPO (OH) radical could be detected at the 5- tM level, and the time dependence of its formation was studied as a function of reagent concentrations. It was concluded from initial rates that the reaction is Hrst-order in [Fe EDTA] and [HjOj], but that only -20% of the expected amount of DMPO (OH) is form with initial concentrations of 100 pM Fe(II), 200 pM EDTA, 600 pM HjOj and 20 mM DMPO at pH 7.4. The amount of DMPO (OH) decreased as the [Fe(II)]/[H202] ratio increased. This indicates that OH is reacting by other pathways, in addition to being trapped by DMPO. One known reaction is that of Fe EDTA with OH.  

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Persson, M., Harbridge, J. R., Hammerstrom, P., Mitri, R., Ma rtenson, L-G., Carlson, U., Eaton, G., and Eaton, S. (2001) Comparison of electron paramagnetic resonance methods to determine distances between spin labels on human carbonic anhydrase II, Biophys. J. 80, 2886-2897. 

Pilhrow JR, Hanson GR. Electron paramagnetic resonance. Methods Enzymol. 1993 227 330-384. 

Drew SC, Bamham KJ (2008) Biophysical investigations of the prion protein using electron paramagnetic resonance. Methods Mol Biol 459 173-196... 

The yIeMa in rodieolt are generally obtained for the liquid state by the interceptor method and, for the solid state, by the electronic paramagnetic resonance method. 

Lakshmi KV, Brudvig GW. 2001. Pulsed electron paramagnetic resonance methods for macromolecular structure determination. Curr Opin Struc Biol 11 523-531. 

Insulin-Enhancing Vanadium Pharmaceuticals The Role of Electron Paramagnetic Resonance Methods in the Evaluation OF Antidiabetic Potential... 

It can be seen from Table 1 that there are no individual steps that are exothermic enough to break carbon—carbon bonds except the termination of step 3a of —407.9 kJ/mol (—97.5 kcal/mol). Consequentiy, procedures or conditions that reduce the atomic fluorine concentration or decrease the mobiUty of hydrocarbon radical intermediates, and/or keep them in the soHd state during reaction, are desirable. It is necessary to reduce the reaction rate to the extent that these hydrocarbon radical intermediates have longer lifetimes permitting the advantages of fluorination in individual steps to be achieved experimentally. It has been demonstrated by electron paramagnetic resonance (epr) methods (26) that, with high fluorine dilution, various radicals do indeed have appreciable lifetimes. 

Nuclear magnetic resonance spectroscopy of the solutes in clathrates and low temperature specific heat measurements are thought to be particularly promising methods for providing more detailed information on the rotational freedom of the solute molecules and their interaction with the host lattice. The absence of electron paramagnetic resonance of the oxygen molecule in a hydroquinone clathrate has already been explained on the basis of weak orientational effects by Meyer, O Brien, and van Vleck.18... 

Porphyrin is a multi-detectable molecule, that is, a number of its properties are detectable by many physical methods. Not only the most popular nuclear magnetic resonance and light absorption and emission spectroscopic methods, but also the electron spin resonance method for paramagnetic metallopor-phyrins and Mossbauer spectroscopy for iron and tin porphyrins are frequently used to estimate the electronic structure of porphyrins. By using these multi-detectable properties of the porphyrins of CPOs, a novel physical phenomenon is expected to be found. In particular, the topology of the cyclic shape is an ideal one-dimensional state of the materials used in quantum physics [ 16]. The concept of aromaticity found in fuUerenes, spherical aromaticity, will be revised using TT-conjugated CPOs [17]. 

Up to date, several experimental techniques have been developed which are capable of detecting some of these particles under ordinary thermodynamic conditions. One can use these methods to keep track of transformations of the particles. For instance, it is relevant to mention here the method of electron paramagnetic resonance (EPR) with sensitivity of about 10 particles per cm [IJ. However, the above sensitivity is not sufficient to study physical and chemical processes developing in gaseous and liquid media (especially at the interface with solids). Moreover, this approach is not suitable if one is faced with detection of particles possessing the highest chemical activity, namely, free radicals and atoms. As for the detection of excited molecular or atom particles... 

Subczynski, W. K., J. Widomska, A. Wisniewska, and A. Kusumi. 2007a. Saturation-recovery electron paramagnetic resonance discrimination by oxygen transport (DOT) method for characterizing membrane domains. In Methods in Molecular Biology Lipid Rafts, ed. T. J. McIntosh, Vol. 398, pp. 145-159, Totowa, NJ Humana Press. 

G. Palmer, Electron paramagnetic resonance of metalloproteins, in Physical Methods in Bioinorganic Chemistry, Spectroscopy and Magnetism, ed. L. Que, Jr, University Science Books, Sausalito, CA, 2000. 

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) spectroscopic methods are used for the detection and identification of species that have a nett electronic spin radicals, radical ions, etc. It is extremely sensitive, capable of detecting species down to concentration levels of 1 x 10 12 moles dm "3, and produces spectra that are distinctive and generally easily interpreted. Consequently, the technique has found extensive application in electrochemistry since the late 1950s. In order to understand epr, it may be helpful to review some fundamental concepts. 

Various other techniques have been used to determine molybdenum, including adsorption voltammetry [510], electron-paramagnetic resonance spectrometry [512], and neutron activation analysis [513,514]. EPR spectrometry is carried out on the isoamyl alcohol soluble Mo(SCN)s complex and is capable of detecting 0.46 mg/1 molybdenum in seawater. Neutron activation is carried out on the /J-naphlhoin oxime [514] complex and the pyrrolidone dithiocar-bamate and diethyldithiocarbamate complex [513]. The neutron activation analysis method [514] was capable of determining down to 0.32 xg/l of molybdenum in seawater. 

The description theoretical study of defects frequently refers to some computation of defect electronic structure i.e., a solution of the Schrodin-ger equation (Pantelides, 1978 Bachelet, 1986). The goal of such calculations is normally to complement or guide the corresponding experimental study so that the defect is either properly identified or otherwise better understood. Frequently, the experimental study suffices to identify the basic structure of the defect this is particularly true when the system is EPR (electron paramagnetic resonance) active. However, if the computational method properly simulates the defect, we are provided with a wealth of additional information that can be used to reveal some of the more basic and general features of many-electron defect systems and defect reactions. 

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