Effect of reaction conditions on the rearrangement of radicals in solution

Russian Chemical Bulletin -     

Calculations of the isotropic hyperfine coupling constants in free radicals

For a number of free radicals the results of non-empirical (ab initio) and semi-empirical (INDO, DEPAC, CNDO/SP) calculations of the isotropic hyperfine coupling constants are compared.     

Effect of a weak magnetic field on hematite sol in stationary and flowing systems

The effect of a weak magnetic field on the aggregation state and electrophoretic mobility of hematite sol was studied in flowing (dynamic) systems as a function of time and electrolyte concentration (0–60 mmol/dm³ KCl) and compared with the effect of the field in stationary (static) systems and flow in the absence of the field. During the entire treatment period, the pH remained almost constant (4.06–4.24). Conductance varied with KCl concentration, but except for minor fluctuations appeared to be unaffected by any form of treatment. While aggregation of hematite was observed during dynamic magnetic treatment (change in turbidity, scattered light intensity, and photon correlation spectroscopy), little effect on aggregation state was observed for the static systems or for the flowing systems in the absence of the field. Mobility also increased during the first 30 min of static and dynamic magnetic treatment. After longer treatment periods (90–120 min), the mobility decreased, but in almost all cases remained larger than in the case of untreated systems. Changes in both mobility and particle aggregation state also showed a significant dependence on electrolyte concentration. These effects are discussed in terms of a magnetohydrodynamic interaction between the magnetic field and the charged colloidal particles, which results only when the particles are made to pass rapidly through the field.     

Electron spin relaxation of radicals in weak magnetic fields

The review summarizes the results of studies on specific features of spin relaxation of radicals in liquids in weak magnetic fields. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1642–1654, October, 2006.     

Orientation of benzothiophene by a magnetic field in the isotropic liquid phase

The¹H NMR spectra of benzothiophene (a 2M solution in acetone), recorded on spectrometers with magnetic field intensities of 4.7, 9.39, and 11.74 T, were analyzed with high accuracy. By the use of the method of many spectrometers the spin-spin and dipole-diople coupling constants were obtained for all the pairs of protons, and the orientation parameters for the investigated molecule and , characterizing the anisotropy and asymmetry of the magnetic susceptibility, were obtained.M. V. Lomonosov Moscow State University, Moscow. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 318–323, March, 1997.     

Rate constants for the combination of trichloromethyl radicals and the electron-transfer reaction between hydroxymethyl radicals and carbon tetrachloride in solution

The rate constant for the bimolecular combination of trichloromethyl radicals in methanol is determined as a function of temperature by steady-state kinetics and electron-spin resonance with modulated radical initiation. The rate constant is in accord with the Smoluchowski equation and indicates a diffusion-controlled radical termination. The temperature dependence of the rate constant for the electron-transfer reaction between hydroxymethyl radicals and carbon tetrachloride in methanol is determined, and is found to disagree with predictions of the Marcus theory. This disagreement is tentatively ascribed to the structure of the transition state.     

Effect of magnetic field on enthalpy of solution of KCl in water

The enthalpies of solution of potassium chloride (KCl) in water and magnetically treated water (magnetized water) have been measured at 298.15 K using a LKB-8700 precision solution calorimeter. From the experimental results, it was observed that the effect of magnetic field on the enthalpy of solution is measurable. This is probably due to the distortion of the hydrogen bond of water resulting from magnetic treatment.     

Orientation of benzofuran by a magnetic field in an isotropic liquid phase

¹H NMR spectra of solutions of benzofuran in acetone, registered in NMR spectrometers with low (2.35 T) and high (9.36 T) strength of the magnetic field, have been analyzed with high precision. The orientation parameters of benzofuran have been evaluated. The two-spectrometer method gives an adequate accounting for orientation effects in low-symmetry aromatic polycycles in strong magnetic fields.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1214–1219, September, 1995.     

Reactions with dye free radicals reveal weak redox properties of drugs

The calcium release channel (CRC) of the skeletal sarcoplasmic reticulum is rich in thiol groups and is strongly regulated by covalent modification of these thiols. Oxidizing reagents activate the release channel, whereas reducing reagents inhibit the channel. However, most CRC regulators are not thiol reagents. Here, we propose that reversible redox interactions are involved in regulation of the CRC by nonthiol reagents. This hypothesis was tested with several CRC regulators. The local anesthetics tetracaine, procaine and QX-314, which block the CRC, behaved as electron donors in reactions with dye free radicals. In contrast, ryanodine, caffeine, doxorubicin and daunorubicin, compounds known to activate the release channel, all accepted electrons from dye anion radicals. Moreover, release of Ca2+ from SR initiated by doxorubicin (acceptor) was antagonized by local anesthetics (donors). Based on the redox characterization of CRC modulators, we propose a functional model in which channel inhibitors and activators act as weak electron donors and acceptors, respectively, and shift the thiol-disulfide balance within the release protein. The consequence of this model is that, in spite of the chemical diversity of CRC modulators, a common mechanism of channel regulation involves the transient exchange of electrons between the activator/inhibitor and the CRC.     

On quantum-chemical estimates of constants of isotropic hyperfine coupling with protons in free radicals

A scheme of consitent quantum-chemical calculations of constants of isotropic hyperfine coupling (IHFC) with protons (a _H ^iso ) in free radicals is considered for the case where the spin populations ρ_s ^H are determined in the basic set of symmetrically orthogonalized atomic orbitals taking model σ-and π-electron fragments as an example. The competence of using two coefficients of proportionalityK(H) when estimating the proton IHFC constants by semiempirical quantum-chemical methods was demonstrated. Theoretical substantiation of empirical values of the above coefficients previously used is revealed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 245–249, February, 1999.     

Acid-catalyzed formation of free radicals in the reaction of hydroperoxides with ketones

The kinetics of formation of free radicals in the cyclohexanone (CH)-tert-butylhydroperoxide (TBHP)-para-toluenesulfonic acid (PTSA) system in acetonitrile was studied. The stoichiometry of the reaction corresponds to the consumption of two TBHP molecules per ketone molecule, whereas the yield of free radicals is -20 % based on the TBHP reacted.     

The role of free radicals in the reaction of dimethyldioxirane with adamantane

The products and the kinetics of the reaction of dimethyldioxirane with adamantane in CCl₄ were studied. It was found that the reaction simultaneously occurred via molecular and radical paths. The contribution of the radical process was 65% at 30.6°C. The activation parameters of the reaction of dimethyldioxirane with adamantane in the presence of an inhibitor were determined: logk = (7.33 ± 0.14)-(58.5 ± 0.8)/, = 2.3RT(kJ/mol) (10.3–69.3°C).Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 859–862.Original Russian Text Copyright © 2004 by Grabovskiy, Antipin, Kabalnova.