Mechanism of the radiolytic transformations of cellulose 1. Formation and transformation of radicals

The formation (77K) and transformation (300K) of radicals in celluloses with various degrees of crystallinity under -radiation have been studied by the ESR method. The radical products of the low-temperature -radiolysis of cellulose formed in the polymer chain are macroradicals the unshared electrons of which are localized on C₍₁₎ C₍₄₎, O_(O), and C₍₅₎. With a rise in the temperature to 300K they undergo substantial changes, which shows the dominating role of secondary reactions of macroradicals in the radiation-chemical transformation of cellulose.A. S. Sadykov Institute of Organic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 62 70 71. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 587–595, July–August, 1996. Original article submitted February 26, 1996.     

High-performance liquid chromatography – atmospheric pressure negative chemical ionisation – mass spectrometry of 2,4-dinitrophenyl derivatives of amines

High-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) is used to detect 2,4-dinitrophenyl (DNP) derivatives of amines by means of negative chemical ionisation at atmospheric pressure. The high sensitivity and good comparability of UV- and MS-detection of DNP-derivatives of amines is shown by several examples. The high selectivity of the derivatisation and the detection method (UV and MS) is used for the analysis of unknown amines in aqueous phases after hydrolytic degradation of polyamide-amine- or polyamine-epoxide-adducts as well as for the characterisation of commercial products.     

Theoretical approach and the practice to the evaluation of structural parameters characterizing concentration polarization alongside ion-exchange membranes by means of dielectric measurement

As the application of a dielectric theory proposed previously (J Membrane Sci 64:153–161 (1991)), theoretical formulation and the practical procedure of dielectric analysis are developed to calculate the structural parameters such as the conductivity gradient and the thickness of the concentration polarization layer, the capacitances and the conductances of the two adjoining aqueous phases from the observed dielectric parameters. The procedure of calculation consequent upon the theoretical formulation was applied to double relaxation data observed for cation-exchange membrane systems under application of d.c. bias voltage. As a consequence, the structural parameters of concentration polarization were readily obtained with accuracy.     

Solid state properties and catalytic behavior of the α- and β-vanadium bronzes

Decomposition of isopropanol (IPA) on V₂O₅, Li_0.02V₂O₅, Na_0.02V₂O₅, Na_0.06V₂O₅, Li_0.33V₂O₅, and Na_0.33V₂O₅ has been studied in the temperature range 186–300°C. The first four catalysts (α-phase) show predominately dehydration, whereas the last two (β-phase) have comparable dehydration and dehydrogenation activity. Dehydration activity increases with alkali metal concentration within the α-phase, but falls sharply on the β-phase catalysts. This difference is attributed to the different rate determining steps for the reaction on the α- and β-phase catalysts. X-ray and ir spectral data show that the β-phase catalysts are much more stable than the α-phase. A mechanism for the dehydration of IPA based on the electrical resistivity, ESR spectra, and kinetic data has been proposed.     

Vibronic intensity borrowing. Deuterium effect and emission—absorption asymmetry of the S1---S0 transition in pyrene

The intensities of the vibrationally induced bands in the S₁---S₀ emission and absorption spectra of pyrene-h₁₀ and -d₁₀ are measured and analysed. Several new expressions are reported which relate the deuterium effect and emission—absorption asymmetry of induced spectra to the vibronic coupling mechanism.     

Étude thermodynamique de la complexation de `l'argent par la pipérazine et quelques-uns de ses dérivés en milieu aqueux

The stability constants of the complexes formed by Ag⁺ ion with piperazine and its 2-methyl-, N-methyl-, and N-phenyl-derivatives were determined in aqueous 0.1 M KNO₃ solution at 25°C, by means of the corresponding metal—complex electrodes.The direct calorimetric study of these reactions in the same conditions of temperature and medium made it possible to calculate the standard enthalpies and standard entropies of formation of the complexes.On the basis of a comparison of all the thermodynamic functions of these systems, the ability of each ligand to coordinate is discussed.     

Vilsmeier formylation of 2-methyl-3 -carbethoxy-5-methoxy- and 2-methyl-5-methoxyindoles

The corresponding 6- and 3-formyl derivatives were obtained by formylation of 2-methyl-3-carbethoxy-5-methoxy- and 2-methyl-5-methoxyindole derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 339–341, March, 1971.     

Adsorption indicators in the titrations of hexacyanoferrate(II) and oxalate with thorium ions

Alizarin Red S, Pyrocatechol Violet and Xylenol Orange are shown to be effective adsorption indicators for the titrations of hexacyanoferrate(II) and oxalate with Thorium(IV) solution. The action of the indicators can be explained by the theory of surface compound formation.     

Radiometrische schnellbestimmungen mit ädte durch rückmessung

The principle of back-titration with EDTA is applied to rapid radiometric methods. A suitable vessel for performing the reaction, filtration and count-rate measurement is described. The optimal conditions for the use of solid ^110mAgIO₃ as indicator were studied: the time for solubility-equilibrium of solid silver iodate, the reaction time of EDTA with silver iodate, and the pH-dependence of the silver-EDTA reaction rate. Procedures are given for calibration curves and for rapid radiometric determinations of copper(II). nickel(II), lead(II) and zinc(II). The method is suitable for the range 1–100μg.