Electron spin resonance methods

ESR methods unambiguously establishes the presence of species bearing unpaired electrons (ion-radicals and radicals). The ESR spectrum quantitatively characterizes the distribution of electron density within the paramagnetic particle by a hyperfine structure of ESR spectra. This establishes the nature and electronic configuration of the particle. A review by Davies (2001) is highly recommended as a guide to current practice for ESR spectroscopic studies (this quotation is from the title of the review). The ESR method dominates in ion-radical studies. Its modern modifications, namely, ENDOR and electron-nuclear-nuclear triple resonance (TRIPLE) and special methods to observe ion-radicals by swiftness or stealth are described in special literatures (Moebius and Biehl 1979, Kurreck et al. 1988, Werst and Trifunac 1998). 

To investigate multispin systems, the so-called electron spin transient nutation (ESTN) spectroscopy is recently elaborated. This is a version of pulsed ESR. Nutation is the precessional motion of spin. The method and its applications are detailed in the paper of Itoh et al. (1997). Chapters 1 and 8 describes that the determination of spin multiplicity becomes a very important problem in organic chemistry of ion-radicals. 

---

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]. 

Nuclear Magnetic Resonance and Electron Spin Resonance Methods X-ray Spectrometry Vol. 2D Coulometric Analysis... 

Nuclear Magnetic Resonance and Electron Spin Resonance Methods... 

The sign of the dominant charge photocarriers in most of the polymers investigated has been found to be positive. The photosensitivity increase under ultraviolet irradiation might be connected with the photoionization of polymer molecules and the creation of local, positively charged centers acting as photoelectron traps. This mechanism seems to be confirmed by the electron spin resonance method. 

Alkali metal aryl ketyls have been known for many years and have been studied by electron-spin resonance methods (Adam and Weissman, 1958 Hirota and Weissman, 1960). Only recently, however, have the isoelectronic neutral radicals R2NO been discovered (Baird and Thomas, 1961 Thomas, 1960). Results for a series of these radicals are summarized in Table 8. 

Results for C02 and N02 are important in that they illustrate one of the major successes of the electron spin resonance method. This is that, provided the ratio of p- to s-character is smaller than about ten, the results from the isotropic coupling (giving the s-character) and the anisotropic coupling (giving the p-character) yield a good estimate of the 8+p hybridization of the molecular orbital on the atom concerned. As shown by the squares of the coefficients of the wave function (a2) given in Table 16, both C02- and N02 have appreciable 2s-character for the orbital of the impaired electron, showing that these radicals are bent. The structure of C02 has been discussed in detail by Ovenall and Whiffen (1961) and that of N02 by Atkins et al. (1962). 

Spectroscopic observation within the UV-visible range is the main detection method, but recently have also been successfully applied the IR and ESR (electron spin resonance) methods [13-16]. 

The traditional fluorescence and electron-spin resonance methods for recording molecular collisions do not allow the study of translational diffusion and rare encounters of molecules in a viscous media because of the short characteristic times of these methods. To measure the rate constants of rare encounters between macromolecules and to investigate the translation diffusion of labelled proteins and probes in a medium of high viscosity (like biomembranes), a new triplet-photochrome labeling technique has been developed (Mekler and Likhtenshtein, 1986 Mekler and Umarova, 1988 Likhtenshtein, 1993 Papper and Likhtenshtein, 2001). 

Swartz, H. M., and S. M. Swartz. Biochemical and biophysical applications of electron-spin resonance. Methods Biochem. Anal. 29 (1983), 207-323. 

In polymers, the oxidative degradation is caused by the free radical reactions that lead to the formation of the peroxy radicals, viz. (R-22). The role of the peroxy radicals has been elucidated by several groups, e.g., by the luminescence and electron spin resonance methods, ESR [Partridge, 1972 Dole, 1973b Kadir et al., 1989 Kashiwabara and Seguchi, 1992 Williams, 1992 Jipa et al.,... 

Jiang et al. reported that Ginsenosides-Re, -Rgi, -Rg2 and-Rh had both calcium channel blockade and anti-ffee-radical actions, -Rf had blockade action on L type channel in cultured myocardiocytes of rats with the cell attached configuration of patch-clamp technique and electron spin resonance method[21]. Ginsenoside-Re could coordinately promote the colony formation and increase H-TdR incorporation of bone marrow cell[22]. 

In the oxidation of organic species, terminal oxidation products are CO2, HCOOH (formic acid) and H2O. As Ce(lV) is typically the hmiting reagent, intermediate products are often identified to confirm reaction pathways. Since cerium(IV) is a one-electron oxidant and the organic substrates are two-electron donors, the chemistry of the oxidized substrate involves subsequent reactions of free radical species. The presence of free radicals is verified experimentally by the initiation of polymerization upon addition of methacrylic acid, or other easily polymerized organic species. In some cases the radicals are stable enough to have been studied by ESR (electron spin resonance) methods. There are a few examples of reactions which exhibit an inverse dependence on [Ce(III)], which can be interpreted in terms of hydrolytic dimers or reversible reactions of the type... 

Zhurkov, S. N. and Tomashevskii, E. E. (1966) Investigation of the fracture process by the electron spin resonance method, in Proceedings of a Conference on the Physical Basis of Yield and Fracture, edited by Strickland, A. C. and Cook, R. A., London Physical Society, pp. 200 08. 

In nuclear magnetic resonance and electron-spin resonance methods, the reaction competes with spin relaxation. In the various electrochemical methods, reaction competes w ith diffusion towards an electrode. 

Here the H is bound, moving in a double-minimum potential well the theory is therefore somewhat modified, but leads to broadly similar conclusions. Such a case is described elsewhere in this volume (T)> and is representative of the special contribution of nuclear magnetic resonance measurements to this subject (cf. below). Electron-spin resonance methods also give special information, on radical reactions (see below, and ref. 9). 

Sierra GA. 1997. Two-dimensional pulse electron spin resonance methods for spectral resolution enhancement in solids. PhD thesis. No. 12241, ETH Zurich. 

---