Electron Paramagnetic Resonance Absorption Spectra Research Articles

Electron spin resonance absorption spectrum of CO2-molecule-ions in single crystal calcite

An electron spin resonance absorption spectrum due to CO2 - molecule-ions has been observed at 3 cm wavelength in single crystals of optical grade calcite. The spectrum exhibits orthorhombic symmetry with both the 12C and 13C isotopically substituted CO2 - molecule-ions having the same g-tensor components given by gzz = 2·00161, gxx = 2·00320 and gyy = 1·99727, where z refers to the carbonate-ion C-O bond direction, x the crystal [111] direction and y the direction perpendicular to these two. The CO2 - molecule-ions are located at carbonate-ion sites with their planes parallel to those of carbonate-ions and with their two-fold symmetry axes parallel to the z direction. The hyperfine structure tensor components associated with the 13C isotope are Azz = 177·28 oe, Axx = 134·62 oe, and Ayy = 131·69 oe.

UV-INDUCED ELECTRON SPIN RESONANCES IN DNA AND THYMINE.

The electron spin resonance absorption spectra of uv irradiated DNA and thymine was observed. The principal free radical formed in both cases as determined by analysis of the resonance data, consisted of an unpaired electron on the 5-carbon of thymine. (P.C.H.)

Paramagnetic Resonance Absorption Spectrum of Trivalent Iron in Single-Crystal Calcite

The electron paramagnetic resonance absorption spectrum of trace amounts of trivalent iron in single crystals of natural calcite has been observed at 9.6 kMc/sec. The spectrum is symmetric about the crystal [111] direction which, together with the doublet character of each spectral component, suggests that the trivalent iron ions occupy sites closely approximating those of the calcium ions. At 77\ifmmode^\circ\else\textdegree\fi{}K, the best-fit parameters to the spin Hamiltonian are found to be ${g}_{\mathrm{II}}={g}_{\ensuremath{\perp}}=2.0030$, ${{B}_{2}}^{0}=343.23$ Oe, ${{B}_{4}}^{0}=\ensuremath{-}0.69102$ Oe, and $|{{B}_{4}}^{3}|=15.6$ Oe. The signs of the zero-field splitting parameters, determined by comparing relative line intensity ratios at 1.5 and at 77\ifmmode^\circ\else\textdegree\fi{}K, are such that the \ifmmode\pm\else\textpm\fi{}\textonehalf{} doublet spin state lies lowest. From this, it is concluded that the sign of the cubic-field splitting parameter is positive. The spectrum is found to exhibit a strong linewidth anisotropy. From the dependence of this broadening on the polar angle $\ensuremath{\theta}$, it is concluded that the sites occupied by this ion have a mosaic structure whose width is given by $\ensuremath{\delta}\ensuremath{\theta}=0.04$ deg. An x-ray diffraction analysis of the calcite single crystal yields a mosaic angle of $\ensuremath{\delta}\ensuremath{\theta}=0.011$ deg.

Paramagnetic resonance and optical absorption of trapped holes and electrons in irradiated KCI: Ag

The electron spin resonance and optical absorption spectra of crystals of KCl containing silver impurity ions were examined after the crystals had been X -irradiated at 77 °K. It is shown that the silver impurity ions act as traps for both electrons and positive holes. A description is given of the annealing behaviour of the crystals after low-temperature irradiation.

Spectrophotometric and electron-spin resonance studies of complexes of catecholamines with Cu(II) ions and the interaction of ceruloplasmin with catecholamines

The complex formation of catecholamines with Cu(II) ions, and their interaction with the copper-containing enzyme ceruloplasmin, have been investigated, with special emphasis on complex formation in the absence of oxygen. In argon, stable 1:2 copper(II)ion-catecholamine complexes with definite optical properties have been observed. The electron-spin resonance (ESR) absorption spectra of these complexes in solution have been recorded. They exert the same characteristics as described for Cu(II) complexes with small molecules in general. Introduction of oxygen initiates the transformation of the catecholamines to the corresponding indolic structures, the adrenochrome, and the noradrenochrome, with characteristic optical properties. The ESR absorption spectra of the complexes are retained in the oxygen-containing solution, but the hyperfine structure is diminished. The interaction of catecholamines with ceruloplasmin in the absence of oxygen is characterized by the disappearance of the 605 mμ absorption band. At the same time the ESR signal of ceruloplasmin completely disappears. Introduction of oxygen reactivates the enzyme and promotes oxidation of the ligand. Simultaneously the ESR absorption spectrum of the enzyme partly reappears. A cupric-cuprous couple has been indicated for the mechanism of enzyme action. The mechanism of electron transfer during oxidation of catecholamines by the model complexes and by ceruloplasmin has been discussed.

Detailed Hyperfine Structure in the Electron Paramagnetic Resonance Absorption Spectrum of the Phenazine Semiquinone Ion

Detailed Hyperfine Structure in the Electron Paramagnetic Resonance Absorption Spectrum of the Phenazine Semiquinone Ion

Studies on the Gamma Ray Irradiation on the Protein

Co/sup 60/ irradiation of proteins was carried out at a rate of 3000 r/ min in vacuo or in an atmosphere of oxygen or nitrogen. The electron spin resonance (ESR) absorption spectra of irradiated bovine and human serum albumin, fibrin, and silk fibroin were determined. It was shown that the free radicals in the irradiated proteins are associated with their cystine or cysteine content. The higher the content of these sulfur-containing amino acids in irradiated proteins, the more their ESR patterns resemble those of cystine and cysteine. Irradiated silk fiber provided a doublet similar to that of glycyl-glycyl-glycine. Such an orientation-dependent pattern could be explained as an unpaired electron localized on the oxygen atom hydrogenbonded to the NH group of the adjacent polypeptide chain. When irradiation was done in the presence of oxygen, the ESR signals of proteins were markedly different from those irradiated in vacuo, the former being attributable to peroxide radicals. Proteins irradiated in the presence of water barely provided a detectable ESR signal. When irradiated albuim or cysteine were dissolved into the solution of native albumin, the titrable SH group decreased, probably due to reaction of sulfhydryl radicals with the SH group. It is concluded that themore » effect of radiation on protein solutions is chiefly, if not entirely, attributable to radicals from the irradiated water, and that the decrease in the SH group of irradiated protein solution can be partly ascribed to free radical reactions. (H.H.D.)« less

Exchange Effects and Anisotropy Broadening of the Hyperfine Spin Resonance Spectrum of the Biphenyl Negative Ion in Solution

The electron spin resonance absorption spectrum of the biphenyl negative ion has been measured at 9.5 mm wavelength in solution in tetra-hydrofuran and in diethylene glycol dimethyl ether (DGDE) over the temperature range -90°C to + 70°C and for concentrations from 1.94 x 10-3 to 4.35 x 10-3M The normal nine line hyperfine spectrum loses its structure with falling temperature for solution in DGDE at about -70°C independent of concentration It is thought that this is due to a decrease in motional narrowing of an anisotropic hyperfine interaction comparable in magnitude with the isotropic hyperfine interaction. With rising temperature the hyperfine structure again disappears. This occurs at -34°C for a concentration 4.35 x 10-3 M and increases with falling concentration to +37°C at 1.94x10-3 M. After loss of structure the line continues to narrow with increasing temperature. Similar but less extensive measurements have been possible for solution in tetrahydrofuran. This effect is thought to be due to exchange, i.e. perturbation of the electron spins at encounters between the radicals which are diffusing through the solvent. An analysis is carried out using a theory proposed by Pake and Tuttle in 1959 in which a quantity related to the ratio of exchange frequency to collision frequency is derived and which should be constant and of order unity. We find this quantity to be indeed of order unity over a wide range of temperature and for the two solvents but that it varies significantly nevertheless. These variations have not been explained and show that a more elaborate theory even than that proposed by Kivelson in 1960 is required.

THE ELECTRON SPIN RESONANCE ABSORPTION SPECTRA OF SEMIQUINONE IONS: PART I. THE HYPERFINE SPLITTING DUE TO ALKOXY GROUPS

The electron spin resonance absorption spectra of semiquinone ions with alkoxy groups have been examined and compared with those with substituted alkyl groups. The splitting constant for the alkoxy protons has been found to be about one-half that of alkyl protons in the corresponding free radical. Hyperfine splittings due to methoxy, ethoxy, and isopropoxy protons have been demonstrated using the semiquinone ions formed by oxidation of alkyl gallates. The available evidence suggests that, in accounting for the hyperfine splitting due to alkyl protons, spin polarization is as important as electron delocalization.

THE ELECTRON SPIN RESONANCE ABSORPTION SPECTRA OF SEMIQUINONE IONS: PART II. THE HYPERFINE SPLITTING DUE TO AMINO GROUPS

The electron spin resonance absorption spectra of amino-substituted p-benzosemiquinone ions have been examined. The hyperfine splittings due to the amino protons and the amino nitrogen atom have been demonstrated. It has been found that the magnitude of the hyper fine splitting constants due to these two kinds of nuclei depends very much on the nature of the free radical.

Electron Spin Resonance Absorption Spectra of Some Organic Free Radicals

Electron Spin Resonance Absorption Spectra of Some Organic Free Radicals