<i>Theory and Applications of Electron Spin Resonance</i> and <i>Spin Exchange: Principles and Applications in Chemistry and Biology</i>

Gordy, Walter; Molin, Yu. N.; Salikhov, K. M.; Zamaraev, K. I.; Hyde, James S.

doi:10.1063/1.2914770

Cited by 43 publications

(94 citation statements)

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“…If the radical is tumbling rapidly in solution, the three components are ofequal intensity, are separated by the isotropic hyperfine coupling, Ai.0, and are centered -at the isotropic g value, giso0 However, if the motion is slowed, then the lines broaden as the anisotropy of the magnetic parameters of the radical is no longer averaged. r4N hyperfine couplings in Xr radicals are generally axial (AX = AY = A±, AZ = All) and strongly anisotropic (All >» AL); g values also are axial (gx = gy = g, gZ = g11) (19). The result of this is that the spectrum of the immobilized radical is dominated by z components, giving a characteristic spectrum of the kind observed here.…”

Section: Resultssupporting

confidence: 52%

Novel free radicals in synthetic and natural pheomelanins: distinction between dopa melanins and cysteinyldopa melanins by ESR spectroscopy.

Sealy¹,

Hyde²,

Felix³

et al. 1982

Proc. Natl. Acad. Sci. U.S.A.

126

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Synthetic pheomelanins from enzymic oxidation of the 3,4-dihydroxyphenylalanine (dopa) derivative 5-S-cysteinyldopa have been examined by ESR spectroscopy. These alkalisoluble polymers contain a novel kind of free radical that is spectroscopically distinct from that found in eumelanins. Delocalization of the unpaired electron onto a nitrogen atom and the ability of the radical to chelate complexing metal ions strongly suggest an o-semiquinonimine structure. The synthetic pheomelanin was compared with natural red pigments extracted from human red hair and from red chicken feathers. Spectroscopically, the chicken feather pheomelanin is almost identical to synthetic cysteinyldopa pheomelanin. In contrast, the pigment from red hair has a major spectral component very similar to that found in dopa melanin, with a smaller component corresponding to that found in cysteinyldopa melanin.Melanin pigmentation ofhair, skin, and eye is thought to result from two separate but biogenetically interrelated classes ofpigments: eumelanins (black-brown, insoluble in dilute alkali) and pheomelanins (yellow to reddish-brown, alkali soluble) (1). Eumelanins are generally considered to be derived from the enzymic oxidation of tyrosine through 3,4-dihydroxyphenylalanine (dopa) (structure I) (2), whereas pheomelanins arise by a diversion of the eumelanin pathway through the intervention of cysteine or related sulfhydryl compounds (3). A major intermediate in the biosynthesis of pheomelanins is the dopa metabolite 5-S-cysteinyldopa (structure II).

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Section: Resultssupporting

confidence: 52%

Novel free radicals in synthetic and natural pheomelanins: distinction between dopa melanins and cysteinyldopa melanins by ESR spectroscopy.

Sealy¹,

Hyde²,

Felix³

et al. 1982

Proc. Natl. Acad. Sci. U.S.A.

126

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“…Furthermore, we have found that the shift of the centroid of the 42 mT with respect to the main position of the E' γ central line is ∆g=0.0071±0.0005, and that of the 49 mT with respect to the E' α is ∆g=0.0096±0.0005. Second order hyperfine interaction corrections [20] predict a shift of ∆g≅0.0072 for the 42 mT and of ∆g≅0.0099 for the 49 mT doublets, in quite good agreements with the experimental values. The different shift observed for the two hyperfine doublets being due to the dependence of the second order corrections on the square of the hyperfine splitting.…”

supporting

confidence: 72%

Si29Hyperfine Structure of theE′αCenter in Amorphous Silicon Dioxide

Buscarino

Agnello²,

Gelardi³

2006

Phys. Rev. Lett.

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We report a study by electron paramagnetic resonance (EPR) on the E' α point defect in amorphous silicon dioxide (a-SiO 2 ). Our experiments were performed on γ-ray irradiated oxygen-deficient materials and pointed out that the 29 Si hyperfine structure of the E' α consists in a pair of lines split by ~49 mT. On the basis of the experimental results a microscopic model is proposed for the E' α center, consisting in a hole trapped in an oxygen vacancy with the unpaired electron sp 3 orbital pointing away from the vacancy in a back-projected configuration and interacting with an extra oxygen atom of the a-SiO 2 matrix.

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“…The corresponding ESR frequencies are collected in (4) From the transition probabilities for the allowed (Ia) and forbidden (I,) ESR transitions, which are given by the expressions in (6) with sin ' p, = B/w, and sin 'pg = B/wg, it follows that the "forbidden" transitions can only take place if the quantity B [see (3)] differs from zero.…”

Section: Conventional Esr Spectroscopymentioning

confidence: 99%

“…[1][2][3][4] The electronic Zeeman operator PEz includes the interaction of the electron spin with the external field B,. As the Zeeman energy can also be affected by orbital magnetic moments, the term PEz often yields information about excited electronic states and about the symmetry of the environment of a paramagnetic center.…”

Section: Conventional Esr Spectroscopymentioning

confidence: 99%

Pulsed Electron Spin Resonance Spectroscopy: Basic Principles, Techniques, and Examples of Applications [New Analytical Methods (43)]

Schweiger

1991

Angew. Chem. Int. Ed. Engl.

192

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Electron spin resonance (ESR) spectroscopy has recently undergone a major innovative advance, which is described by the magical phrase pulsed ESR. To the spectroscopist who rubs this Aladdin's lamp there now opens up the mysterious world of spin acrobatics with its many novel and surprising phenomena. The use of pulse techniques makes it possible to reduce measurement times, increase sensitivity, improve resolution and simplify spectra. This article describes the most important pulse techniques used in ESR spectroscopy. Mathematical descriptions are kept to a minimum, space being devoted instead to examples of applications in various areas of chemical research.

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Theory and Applications of Electron Spin Resonance and Spin Exchange: Principles and Applications in Chemistry and Biology

Cited by 43 publications

References 0 publications

Novel free radicals in synthetic and natural pheomelanins: distinction between dopa melanins and cysteinyldopa melanins by ESR spectroscopy.

Novel free radicals in synthetic and natural pheomelanins: distinction between dopa melanins and cysteinyldopa melanins by ESR spectroscopy.

Si29Hyperfine Structure of theE′αCenter in Amorphous Silicon Dioxide

Pulsed Electron Spin Resonance Spectroscopy: Basic Principles, Techniques, and Examples of Applications [New Analytical Methods (43)]

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