Relationship between hydration energy of zeolites and cation distribution in their crystals

A method is proposed for calculating the heat of immersion of zeolites in water from data on the composition and density of the zeolite framework. The phenomenon of localization of some of the zeolite cations in the unhydrated crystallographic positions is explained. For ferrisilicates with the ZSM-5 structure, the fraction of iron atoms in the framework has been estimated from data on the energy of hydration.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 2, pp. 174–179, March–April, 1993.     

Physicochemical aspects of the development of new functional materials based on heterosubstituted titanates of rare-earth elements with the Perovskite structure

In the example of titanates of rare-earth elements with the perovskite structure, relationships have been established for the influence of heterovalent substitution in the cation sublattices, through which the electrophysical properties within a single structural type can be controlled over a broad range, from microwave dielectrics to cationic conductors and semiconductors. V. I. Vernadskii Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine, 32/34 Akademika Palladina Prospekt, Kiev-142 252680, Ukraine. Translated from Teoretischeskaya i éksperimental'naya Khimiya, Vol. 34, No. 6, pp. 331–346, November–December, 1998.     

Photosensitization of electronic transitions by dye molecules in systems consisting of a semiconductor and adsorbed molecules of p-benzoquinone

Electrophysical methods and ESR measurements have been used to investigate the changes, photosensitized by molecules of rhodamine B (RB), in the charge states of electron traps created by molecules of p-benzoquinone (pBQ) in the Ge/GeO₂ system. The results obtained in studying the quenching of fluorescence of RB molecules indicate that the photodestruction of electron traps is due to transfer of electronic excitation energy traps is due to transfer of electronic oxidation energy from the RB molecules to charged complexes formed upon adsorption of the pBQ. In order to select optimal conditions for recharging of such complexes, a study has been made of the relationship between the relative change in ESR signal and the concentration of adsorbed RB molecules.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 545–550, September–October, 1989.     

Kinetics of p-cumylphenol alkylation by isobutylene in the presence of p-toluenesulfonic acid

Kinetics of p-cumylphenol alkylation by isobutylene in the presence of 0.1–2 wt.% p-toluenesulfonic acid has been studied and a reaction scheme is suggested. The rate constants have been determined.

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- 0,1–2 % . -. .

     

Diels-Alder versus heterodiene reaction: The effect of acid catalysis.

The difference between thermal, AlCl₃- and CF₃ COOH-catalyzed reaction of (E)-4-benzal-1-phenyl-5-pyrazolone and 2,3-dimethylbutadiene is discussed in terms of Diels-Alder $\text{versus}$ heterodiene reactivity.     

A new method for the direct calculation of resonance parameters with application to the quasibound states of the H2X1Σ g + system

A new method for the direct calculation of resonance parameters is presented. It is based upon searching for poles of the scattering matrix at complex energies. This search is expedited by the use of analytic derivatives of the scattering matrix with respect to the total energy. This procedure is applied initially to a single channel problem, but is generalizable to more complicated systems. Using the most accurate available potential energy data, we calculate resonance parameters for all of the physically important quasibound states of the ground electronic state of the hydrogen molecule. Corrections to the Born-Oppenheimer potential are included and assessed. The new method has no difficulty locating resonances with widths greater than about 1×10^–7 cm^–1. It is easier to find narrow resonances by monitoring the dependence of the imaginary part of the reactance matrix on the real part of a complex energy than to monitor the dependence of the eigenphase sum on energy at real energies.     

Surface reaction dynamics and the harmonic oscillator

One of the fundamental steps in chemical reaction dynamics involves breaking reactant bonds. This is facilitated by placement of energy into the vibrational degrees of freedom associated with the bond. Here we present a model for vibrational excitation in molecule-surface collisions in which the equilibrium geometry of the (diatomic) molecule varies with distance from the surface. The special feature of this model is that the potential energy surfaces for bound nuclear motion are constructed from quadratic potentials, thus enabling analytic solutions. Comparisons are made between exact results obtained from a purely classical trajectory model and various hybrid models in which the internal vibrational modes are treated quantum mechanically in the harmonic limit.     

Depolarization and fine structure effects in half collisions of sodium-noble gas systems

Population ratios and polarization of the Na3P _J fine structure states following far wing photon excitation of Na-noble gas collision pairs are studied with respect to the underlying interaction potentials and molecular coupling schemes. For this purpose spectral profiles of these quantities, i.e. its dependencies on excitation frequency, have been measured up to ±200 cm^?1 detuning from the NaD lines for NaAr and NaHe under nearly single collision conditions. Comparing the measured population ratios with quantummechanical coupled channels calculations the Σ potential well depths differ considerably from results of model potential calculations. Large residualJ=3/2 alignment observed in the far wings disagrees with simple models assuming incoherent excitation and/or full adiabatic reorientation of the radiating dipole along straight trajectories. By comparison with Lewis model calculations, using realistic trajectories and decoupling radius, it is found instead, that realistic trajectories are constitutive for alignment after Σ-excitation (blue wing), whereas coherence between the²Π_1/2 and²Π_3/2 states determine primarily alignment after Π-excitation (red wing).     

BINDING, EXCITATION ENERGY TRANSFER AND PHOTOSENSITIZATION IN GRISEOFULVIN-DNA MIXTURES

Abstract— The weak and reversible binding of the antifungal drug, griseofulvin (GF), to calf thymus DNA has been demonstrated by difference spectroscopy and the quenching of the fluorescence of GF by DNA observed. The value of K _n was determined to be 800 M ^-1by fluorescence quenching titration. Adenosine and guanosine also exhibit difference spectra with GF and quench GF fluorescence indicating that they may be the site of both binding and energy transfer. The in vitro photosensitization of DNA by griseofulvin is shown to occur. It is proposed that the clinically observed in vivo photosensitizing action of griseofulvin may result from binding followed by excitation energy transfer and that this may also be important in the antifungal activity of the drug.     

Thermodynamic properties of solutions of water-soluble mixed cellulose esters

The thermodynamics of the mixing of water-soluble mixed cellulose esters with water has been studied. A dependence of the affinity of a water-soluble cellulose acetate for water on the nature of a new radical introduced into the macromolecule and the competing interaction of molecules of the same and different types has been shown. Thermodynamic analysis has demonstrated the dominating role of solvation among the various factors determining the interaction of cellulose acetomaleate and acetophthalate with a solvent. A fall in affinity in the cellulose aminoacetate-water system is due to the contribution of entropy effects, leading to an increase in the Flory-Huggins parameter.Tashkent Institute of Chemical Technology. Translated from Khimiya Prirodnykh Soedinenii, Vol. 33, No. 1, pp. 97–101, January–February, 1997.