Introduction to the dynamic theory of the (H+, e−) couple insertion in γ-MnO2

This paper presents a phenomenological theory of coupled H⁺ and e⁻ diffusion in γ/ɛ-MnO₂. A set of five dynamic regimes governs the (H⁺, e⁻) insertion during the entire reduction (0.08 < r < 1) of the dioxide. It is imposed by a global balance of several physical quantities which depend on the reduction level r. The principal potential factor for the diffusion in a given direction is the difference between the components, along this direction, of the self velocities V _e− and V _H+. The longitudinal component E _ld of the internal electric field vector E _d plays, with respect to electrons and protons, the velocity regulator role. The transversal component E _td allows some homogenisation of (H⁺,e⁻) concentration during the first half of the reaction and trapping of electrons in the second half. Towards r≈ 0.50, V _e− and V _H+ are equal, the internal electric field reverses its orientation after taking a null value and the first Mn³⁺ ions appear. This introduction to the dynamic theory of γ/ɛ-MnO₂ is a new finding and can interpret most of its physical/chemical properties, especially the behaviour change around r≈ 0.50. Received: 11 November 1998 / Accepted: 25 March 1999     

Improvement of the crystal rotation method to measure the flexoelectric difference (e1–e3) in achiral materials using AC electric fields

We show that the crystal rotation method for measuring the difference between splay and bend flexoelectric coefficients (e₁–e₃) [Outram and Elston, Liq. Cryst. 39, 149 (2012)] can be improved by using AC instead of DC fields. The field frequency is small (~0.05 Hz), yet sufficient to get rid of the difficulties connected with the migration of charge carriers. The method is sensitive enough so as to use fields with amplitudes as small as 1 V/mm. This has the advantage of avoiding the consideration of the interaction due to the dielectric anisotropy, and greatly simplifies the analysis of data. The results are extracted from a simple fitting scheme, which involves two parameters. In particular (e₁–e₃) is obtained from a scale factor in a one-parameter fit. Measurements of the temperature dependence of (e₁–e₃) are presented for two classical nematic materials.     

Chronopotentiometric Study of the Reaction Am (III) + 3e → Am(o) in Molten Licl-KCl Eutectic

Abstract

A chronopotentiometric study of the reaction Am(III) + 3e → Am(O) in molten LiCl-KCL is reported. The diffusion coefficient ^DAm(III) increases from 3.5 to 26.0 10^?6 cm² sec^?1 when the temperature was raised from 400 to 650°C. The mechanism of the diffusion is discussed on the base of the hole theory for molten salts.     

（e, 2e） Investigations of the Simultaneous Ionization and Excitation of Helium to He＋（n=2）

Three-Coulomb-wave method is employed to treat the process of （e, 2e） simultaneous ion- ization and excitation to the n=2 state of helium, with radial and angular correlated wave-function of He target. The triple differential cross sections are calculated and analyzed in very asymmetric coplanar geometry at incident energies of 5.50, 1.50 and 0.57 keV. Results are compared with the absolute measurements and the theoretical first and second Born approximation. The present triply differential cross section （TDCS） is found to be in good agreement with experimental data qualitatively. The distinguishing feature noted in TDCS structure is the presence of intense recoil peak that for certain parameters is even larger than the binary peak, an unusual feature for the single-ionization process at high and intermediate energies.     

Radiation stability tests of the SMELS materials in the LVR-15 experimental reactor at Řež

Radiation stability of a set of three synthetic multielement standards (SMELS) designed for validation of k ₀-standardization in neutron activation analysis was tested by monitoring mass and element content changes following irradiation at a high neutron fluence rate (up to 9^.10¹³ n^.cm^-2.s^-1) for stepwise increased periods of time. No mass changes were detected and for all the 26 elements investigated only a chlorine content loss was observed. Thus, radiation stability of the SMELS materials for the given purpose and their suitability for use also in high-power reactors was demonstrated.     

Effect of the Composition of the Water–Dimethyl Sulfoxide Solvent on the Thermodynamics of the Formation of the [Ag(18-Crown-6)]+Complex

The effect of a water–dimethyl sulfoxide solvent (X _DMSO= 0–0.97, where X _DMSOis the mole fraction of DMSO) on the thermodynamics of complexation between Ag⁺and 18-crown-6 and the solvation of all reagents involved in this equilibrium were studied. In aqueous solutions, the complex is stable mainly because of the enthalpy contribution to _r G°. For X _DMSO> 0.3, the contributions from entropy and enthalpy become comparable in magnitude, but they are opposite in sign. In the binary solvent, the complex is most stable at X _DMSO= 0.2 to 0.3. Analysis of the enthalpy characteristics of reagent solvation showed that this solvent effect was due to the superposition of two opposite solvation contributions occurring with an increase in the DMSO concentration in the binary solvent, namely, the destabilization of the ligand solvate sphere and the formation of stable Ag⁺complexes with DMSO.     

Method of the selection of the g(α) function based on the reduced-time plot

A method for the selection of the g(α) function describing the thermal decomposition of solids based on the reduced-time plot is proposed. This method allows more objective selection of the g(α) function best describing the experimental results from a mathematical point of view, when compared to the graphical method applied up to the present. With the use of variously defined values of reduced time, this method was applied to the investigation of the kinetics of the isothermal decomposition of CaCO₃ under nitrogen. The listing of a computer program enabling the carrying out of calculations and the making of plots is given.     

Effects of Thermal Activation on the Electrocatalysis of the Ru(0001) Surface

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｅｌｅｃｔｒｏｃｈｅｍｉｃａｌｏｘｉｄａｔｉｏｎｏｆｓｍａｌｌ,ｏｘｙ ｇｅｎａｔｅｄｏｒｇａｎｉｃｍｏｌｅｃｕｌｅｓｏｎ ｐｌａｔｉｎｕｍａｎｄｒｅｌａｔｅｄｅｌｅｃｔｒｏｄｅｍａｔｅｒｉａｌｓｈａｓｂｅｅｎｅｘｔｅｎｓｉｖｅｌｙｓｔｕｄｉｅｄｏｖｅｒｔｈｅｐａｓｔｔｈｒｅｅｄｅｃａｄｅｓ ,ｍａｉｎｌｙｉｎｓｕｐｐｏｒｔｏｆｆｕｅｌｃｅｌｌｒｅｓｅａｒｃｈｅｓ[1— 4 ] .Ｔｈｅｓｅｒｅａｃｔｉｏｎｓａｒｅｃｏｍｐｌｉｃａｔｅｄ ,ａｓｓｅｖｅｒａｌｅｌｅｍｅｎｔａｒｙｓ…     

Mechanism of the Deaquation of Aquopentaaminocobalt(III) Bromide

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｓｏｌｉｄ ｐｈａｓｅｄｅａｑｕａｔｉｏｎ ａｎａｔｉｏｎｒｅａｃｔｉｏｎ[Ｍ(ＮＨ3 ) 5(Ｈ2 Ｏ) ]Ｘ3 → [Ｍ(ＮＨ3 ) 5Ｘ]Ｘ2 +Ｈ2 Ｏ(Ｍ =Ｃｏ3 + ,Ｃｒ3 + ｏｒＲｕ3 + ａｎｄＸ =Ｃｌ- ,Ｂｒ- ｏｒＮＣＳ- )ｈａｓｂｅｅｎｗｉｄｅｌｙｓｔｕｄｉｅｄｓｉｎｃｅｔｈｅｎｉｎｅｔｅｅｎｓｉｘｔｉｅｓ .Ｔｈｅｔｈｅｒｍａｌａｎｄｋｉｎｅｔｉｃｐａｒａｍｅｔｅｒｓｈａｖｅｂｅｅｎｃａｌｃｕｌａｔｅｄａｎｄｔｈｅｄｉｆｆｅｒｅｎｔｍｅｃｈａｎｉｓｍｈａｓｂｅｅｎｐｒｏｐｏｓｅｄａｎｄｄ…     

Synthesis of the D-Galactopyranoside Derivative of C_(60)

ThefascinatingsbocturesandpropertiesoffullereneshaveoPeneduPanewfieldofchendstry.Inparticular,F.Wudletal.l'2haveshownthatwatersofubleC6ocomPoundsinhibittheHITVen-zymesprotease(HIVP)andreversetranscriPtase(HIVRT).IthasbeenafocusofstUdytoinvestigatethebiologicalactivitiesofthesenovelsubstances.Fortheirpossiblemedicaluses,tolinkC6omoleculetonaturalProductssuchassugars,pephdes,amioacides,andsoonisanimPortantmethodinthisfield.Vasella3reportedthefirstglucosidederivativeofC6o'InthispaPer,w…     

Effect of the Nature of the Polymer Matrix on the Luminescence of Tb(III) Complexes with β-Diketone Copolymers

The formation conditions and luminescence of Tb(III) complexes with synthesized copolymers of unsaturated acetylacetone derivatives with styrene and methyl methacrylate were studied. The luminescence intensity of these Tb(III) complexes was found to depend on the β-diketone substituent nature (CH₃, CF₃, C₆H₅) and structure (linear, branched) and the β-diketone to monomer ratio in the polymerizing mixture.     

A study of the quenching of PCl(b1∑+) by the E-V model

Using the reaction of Ar(3Po,2) + PCl3 as a source of PCl(b1 +), we have measured the quenching rate constants of PCl(b,v'=0) for more than 20 quenchers. The E-V model is used to calculate the rate constants. The comparison of the calculated values with the experimental ones shows that the quenching of PCl(b) by the reagent molecules results from the electronic to vi-brational energy near resonance transfer and has been related to the Franck-Condon factors for the PCl(b,v'=0-a,v"=m) transition and to the anharmonicities of the terminal bonds of the quenchers. In addition, the influence of the polarizability of the reagent molecule on the quenching rate constant is discussed.     

Determination of the Absolute Configuration of the (−)-Me(EtO)(HO)P-Mo(CO)5 Coordination Complex by Decomplexation of the Organophosphorus Ligand

Abstract

The resolution of a chiral coordination complex (1) was recently carried out in our laboratory, and some stereochemical transformations of the resolved specie have been reported (L. P. Reiff, L. J. Szafraniec, D. I. Rossman and H. S. Aaron, Inorg. Chem. 1986, 25, 0000). Decomplexation studies of its organophosphorus ligand have now been carried out. Thus, treatment of the (?)-1 complex with two molar equivalents of triphenylphosphine yields (+)-ethyl methylphosphinate (2), considerably racemized, however, due to the 120°C temperature required to achieve decomplexation. To determine its optical purity and its absolute configuration, the latter was converted into the known S-(?)-3 thioic acid and S-(?)-4 methyl ester, respectively. While the method does not appear to be of synthetic utility for the preparation of optically active (decomplexed) organophosphorus species, the absolute configuration of the S-(?)-1 coordination complex is established on the basis of these stereochemical relationships.     

A new version of the conversion of plant polyprenols into (±)-terpenols of the dolichol series

A two-step method for the chemoselective reduction of the trisubstituted double bond of an α-isoprene unit in plant polyprenols was developed for the preparation of racemic terpenols of the dolichol series of mammals. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1491–1492, August, 2000.     

The influence of the nature of the solvent on the crystal structure and the character of formation of hydrogen bonds inN′-(5-nitrofurfurylidene)isonicotinehydrazide

N(5-Nitrofurfurylidene)isonicotinehydrazide (1) was synthesized in the reaction of nicotinic acid hydrazide with 5-nitrofurfurol in anhydrous or aqueous ethanol. Crystals of different shape and color were obtained depending on the conditions of synthesis and the nature of the solvent. As was established by IR spectroscopy, compound1 in the crystalline state forms solvates of various types. An X-ray study of two different crystals, one obtained by recrystallization from methanol (1a), and the other obtained from aqueous acetic acid (1b), was performed. In the crystal structure of1a intermolecular hydrogen bonds (IMHB) of the NH...N(Py) type occur; the crystals1b are built of solvates with one molecule of acetic acid in which the components are bonded by the IMHB (Ac)O-H..N(Py). The solvates are linked in an infinite chain by the amidohydrate IMHB C=O...W...H-N.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2263–2268, September, 1996.     

Theoretical Study of the Thermal Decomposition of Chlorofluoromethanol (CHClFOH)

Introduction Hydrochlorofluorocarbons (HCFCs) have been widely used as replacements of chlorofluorcarbons (CFCs). The insertion of O (1D) into the CH bond of HCFC forms the activated alcohol. It has been shown that these hot alcohols play an important role in the degradation mechanism of atmospheric compounds1.Chlorofluoromethanol (CHClFOH) appears in the reaction of O (1D) with CH2ClF (HCFC-31)2. Neither experimental nor theoretical study of this species was available to date. U…     

Studies of the Interaction of the Salicylideneserinatecopper(II) Complex with β-Cyclodextrin: Characterization and Reactivity of the Inclusion Compound

The compound formed by the copper-Schiff base complex salicylideneserinatecopper(II), [Cu(sal-ser)(H2O)], interacting with -cyclodextrin was prepared, and characterized in the solid state by infrared, UV-visible and EPR spectroscopies, X- ray diffraction, and thermoanalytical techniques. The catalytic activity of this compound, [Cu(sal-ser)CD], in the decomposition of hydrogen peroxide, and in the dismutation of superoxide radicals was also verified, in comparison with the reactivity of the free complex, in aqueous solution. In both cases, a decreasing in the reaction rate was observed for the CD-containing compound. The results of structural characterization, in addition to the substantial differences observed in the catalytic activities of the compounds, are indicative of partial insertion of the copper complex in the cavity of the oligosaccharide.     

Role of the molecular weight and the composition on the hydrolysis kinetics of monolayers of poly(α-hydroxy acid)s

The hydrolysis kinetics of spread insoluble monolayers of poly(α-hydroxy acid)s with various molecular weights and lactic acid–glycolic acid molar ratios was followed by measuring simultaneously the decrease in the surface area at constant surface pressure and the evolution of the surface potential. The interfacial hydrolysis at alkaline pH leads to the progressive fragmentation of the polymer molecules and the appearance of charged insoluble products (detected by measuring the surface potential) and small soluble fragments (detected by measuring the decrease in the surface area). The data obtained by both approaches were interpreted in the framework of the random scission model. The rates of hydrolysis are larger for polymers with smaller initial polymerization numbers and increase with the decrease in the molar ratio of lactic acid units. Received: 7 December 1998 Accepted in revised form: 8 March 1999     

Electrochemistry of bis(indenyl)dimethylzirconium complex—the precursor of the olefin polymerization catalyst

The reduction in THF and oxidation in CH₂Cl₂ of the bent-sandwich complex (η⁵-lnd)₂ZrMe₂ (1) (Ind=C₉H₇, indenyl) were studied by cyclic voltammetry. Complex1 in THF undergoes one-electron reduction to radical anion1 ⁻, which partially decomposes with the liberation of the Ind⁻ anion. Even at −45°C the one-electron oxidation leads to the formation of an unstable 15-electron radical cation undergoing fast heterolytic decomposition to the Me^• radical and (η⁵-lnd)₂ZrMe² cation, which is the key reaction center in the catalytic polymerization of olefins. Comparative analysis of electron-transfer-induced transformations of bent-sandwich dimethyl and dichloride zirconocenes of the general formula L₂ZrX₂ (L=η⁵-lnd, η⁵-Cp: X=Xl, Me) was performed. The material of the paper was first reported at the 195th Meeting of the Electrochemical Society (see Ref. 1). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 59–62, January, 2000.