A. A. Dubinskii

Pulsed EPR in 2-mm band

A pulsed 2-mm band EPR spectrometer is described. The perspectives of 2-mm band EPR are comprehensively discussed.

Magnetic properties of metal–quinone high-spin complexes prepared by solid-state mechano-activation and by chemical synthesis in solution. Comparative study with very high-field and low-temperature EPR and ENDOR

EPR spectroscopy at high frequencies and low temperatures and ENDOR spectroscopy at X- and W-bands have been applied to investigate two- and three-spin complexes of the type MQ2˙ and MQ3˙ generated by mechanochemical treatment (by grinding or by the action of elastic waves) of solid mixtures of quinones and metals (M = Al, Ga, In, Cd, Sn, Zn). In addition, complexes obtained in liquid-phase reactions of metal amalgams with quinones were investigated. The magnetic-resonance parameters and the observed thermal spin polarization provide evidence for the identity of the magnetic complexes produced in solutions and by solid-state mechanochemical treatment. In particular, the presence of ground-state triplet and quartet species has been demonstrated in both cases. In addition, the exchange and the dipole–dipole interaction parameters were evaluated, their comparison providing information about the electronic intramolecular interaction.

Mechanism of formation ofo-semiquinone metal complexes under mechanical pulse action on metal oxide-quinone-pyrocatechol systems

The possibility of the mechanochemical synthesis of metal-containing mono-, bi-, and triradicals under mechanical pulse action on mixtures of metal oxides (CuO, ZnO, CdO, PbO, Al2O3, Ga2O3, Sb2O3, Bi2O3, Cr2O3, TiO2, GeO2, ZrO2, or SnO2) with quinone and pyrocatechol was examined. The reaction products are formed both on the surface of metal oxides and as individual solid phases. The mechanism of chemical processes that occur under the action of a single elastic wave pulse is proposed.

Models for spin-label macromolecule motion in the 3 cm and 2 mm ESR ranges

A study is presented on models for the motion of spin-label macromolecules indicated by 3 cm and 2 mm ESR spectra. Theoretical calculations are employed to simulate combination of the relative motion with transport motion (in conjunction with a macromolecule segment) for various temperature-viscosity relationships in the anisotropic Brownian diffusion of nitroxyl radicals. In that approach, one cannot match the relaxation effects in the two sets of spectra. It is concluded that there are fast relative label oscillations that do not average the g and A tensors to axisymmetric ones.

Sequential coordination of orthosemiquinone radical ligands by surface centers on γ-Al2O3

The kinetics of sequential generation of mono-, bi-, and triradical centers in heterogeneous reactions of toluene solutions of orthoquinones, catechols, and their mixtures with γ-Al2O3 was studied. The localization of mono- and biradical centers on the solid oxide surface and the transfer of triradical Al3+ (Q−)3 complexes (Q− is the corresponding 3,6-di-tert-butylsemiquinone radical) to a solution (extraction of Al from the solid phase) were proved. The number of the triradical complexes extracted is considerably higher than that of active surface centers accessible for coordination with radical ligands. The conditions favoring the formation of the radical complexes on the Al ions were established. Possible mechanisms of these processes were proposed.

FORMATION AND STABILIZATION OF RADICAL PAIRS IN THE QUINONE-PYROCATECHOL-POLYMER SYSTEM

The formation of radical pairs (RP) in solid mixtures of 3,6-di-tert-butyl-o-quinones (Q) and 3,6-di-tert-butylpyrocatechol (QH2) under the action of shock-wave (SW) pulses was studied by ESR and IR spectroscopy. The radical pairs are formed only when a threshold value of SW power is achieved. The generation of RP is preceded by the formation of hydrogen-bonded associates QH2…Q upon intimate mixing and fine dispergation of the reagents in a SW field. The incorporation of the reagents into a polymeric matrix favors the formation of associates and stabilization of the pairs, which leads to a decrease in the SW power threshold.

An ESR study of the effect of the medium on the kinetics of the destruction of tert-butyl peroxide radicals

1. Study has been made of the destruction of tert-butyl peroxide radicals in water, methanol, acetic acid, and their binary mixtures. 2. The effect of the medium on the rates of the radical reactions studied here is largely the result of nonspecific radical solvation. 3. Reaction between tert-butyl peroxide radicals can proceed along parallel paths which differ in the conformation of the intermediate state. The effective constant for RO2 destruction is the sum of two constants, one predominating in media of high dielectric constant and the other predominating in media of low dielectric constant.