Quantum-chemical estimates of geometric parameters of free radicals

Experimental geometries of the HCO^· and H₂CO^·+ -electron radicals were compared with those obtained from calculations with the total energy optimization carried out in the framework of widely used ab initio and semiempirical computational procedures. For each structural form of the radicals, the magnetic resonance parameters calculated in the MNDO approximation were correlated with experimental values determined by ESR spectroscopy. Comparative analysis of the results obtained indicates the possibility of systematic correction of the optimized geometric parameters of free radicals using the results of ESR measurements. A simple computational procedure for automatic geometry correction in the MNDO approximation is developed and evaluated.     

The properties of water in solutions of hydrophilic polymers

The properties of water in solutions of hydrophilic polymers were compared with those in solutions of their monomeric analogues. The properties of polar groups grafted to polymeric molecules were known to remain unchanged. A comparison of the properties of water in solutions of polymers and the corresponding monomers under equal conditions therefore allowed us to obtain information about the influence of polymeric bonds on the properties of water in solutions of polymers. Proceeding from this, we analyzed the influence of polymeric chains and three-dimensional polymeric network on the activity and concentration of water in solutions of polymers.     

A study of the applicability of a method for successive determination of the kinetic coefficients of sorption on the basis of mathematical modeling

This paper presents the results of mathematical modeling and experimental studies of ion-exchange process between a weakly concentrated uranium solution and sorbent grains. On the basis of mathematical modeling, we analyze the method of successive determination of the kinetic coefficients of sorption, determining its practicality.     

High-sensitivity X-ray fluorescence analysis of solutions with the use of a sorption accumulation microsystem

A mass-transfer kinetic model is proposed for an embedded sorption accumulation microsystem based on polycapillary structures to be used in the developed X-ray fluorescence analyzer with preconcentration. The model is used to substantiate a kinetic method for high-sensitivity X-ray fluorescence determination of elements in multicomponent solutions. With the use of this model, experimental data on X-ray fluorescence spectra are analyzed and kinetic and equilibrium parameters are found for the sorption of copper, nickel, manganese, iron, and zinc on the selective DETATA sorbent.     

Correlations between magnetic resonance parameters of ESR and NMR spectra

Empirically established correlations between magnetic resonance parameters of free radicals (g-factors, isotropic hyperfine coupling constans) and isostructural molecules (chemical shifts, isotropic spin-spin coupling constants) or structurally similar ligands in paramagnetic transition metal complexes (isotropic chemical shifts) are systematized and critically discussed. Quantum-chemical analysis of the suggested spin distribution damping coefficients in model systems and structurally similar chemical compounds is performed. Based on the results obtained, physicochemical interpretation of the observed correlations between the parameters of ESR and NMR spectra is given. Dedicated to the memory of Academician V. V. Voevodskii (to the 80th anniversary). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1575–1583, September, 1997     

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.     

Evaluation of a new procedure for quantum-chemical estimates of constants of isotropic hyperfine coupling with protons in free radicals

A new procedure for quantum-chemical estimates of the constants of isotropic hyperfine coupling (IHFC) with protons using the orbital spin populations calculated in the basis set of symmetrically orthogonalized (according to Löwdin) atomic orbitals is tested taking 16 well-studied simplest π-electron and σ-electron radicals as examples. The most probable reasons for and possible ways of correcting large deviations of calculated IHFC constants from experimental values are considered. The efficiency of the semiempirical MNDORU scheme, which makes it possible to consistently estimate the delocalization and spin-polarization contributions to the constants of IHFC with protons in free radicals, is demonstrated.     

The properties of water in swollen cross-linked polystyrene sulfo acids

The properties of water in polystyrene sulfo acid gels with various cross-linking degrees were studied by optical volumetry and dynamic desorption porosimetry. The isotherms of water desorption obtained by dynamic desorption porosimetry coincided with isopiestic isotherms, which allowed this method to be recommended for the determination of the amount of water in polymer gels. Joint optical volumetry and dynamic desorption porosimetry studies showed that the interphase boundary in the cross-liked hydrophilic polymer-water system did not coincide with the visible gel boundary, because gels were two-phase systems, which contained water of two types, “free” and “bound.” The influence of the degree of polymer cross-linking on the amounts and properties of water of the two types was studied. It was shown that constants of water distribution in the polymer could be calculated from the dynamic desorption porosimetry data.     

Dynamics of Heavy Carriers in the Ferromagnetic Superconductor UGe<Subscript>2</Subscript>

Superconductivity and ferromagnetism in a number of uranium-based materials come from the same f-electrons with a relatively large effective mass, suggesting the presence of a band of heavy quasiparticles, whose nature is still a mystery. Here, UGe₂ dynamics in both ferromagnetic and paramagnetic phases is studied employing high-field μ⁺SR spectroscopy. The spectra exhibit a doublet structure characteristic to formation of subnanometer-sized magnetic polarons. This model is thoroughly explored here and correlated with the unconventional physics of UGe₂. The heavy-fermion behavior is ascribed to magnetic polarons; when coherent they form a narrow band, thus reconciling heavy carriers with superconductivity and itinerant ferromagnetism.