Solvent effect on the rate of decomposition of peroxy compounds

Solvent effect on the rate of decomposition of peroxy compounds was described by multiparameter equations based on the linear Gibbs energy relationship. In the decomposition of dialkyl peroxides, the determining factors are the cohesion energy density of solvents and their ability to electrophilic solvation, which accelerate the process. In the case of hydroperoxides, the nonspecific solvation factor should additionally be taken into account.Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 10, 2004, pp. 1459–1463.Original Russian Text Copyright © 2004 by Midyana, Makitra, Palchikova.     

Molecular dynamics simulation of aqueous NaF and NaI solutions near a hydrophobic surface

We present results from molecular dynamics simulation of aqueous solutions of alkali halide salts (NaI and NaF) at the interface with hydrophobic objects. The primary objective of this study is to investigate the structural properties of the salt solutions at the hydrophobic surface. An alkane crystal has been taken as the parent model for a hydrophobic surface. A hexagonal hole was created on it, which was half a nm deep and 2.5 nm wide. The density distributions of different species (water, anions, and cations) are studied as a function of distance from the surface. While iodide prefers the interface, the fluoride ions stay inside the bulk water region. The higher concentration of iodide ions at the interface drags sodium counterions to the interface. It also decreases the water density at the interface because of steric effects of the iodide ions. The number of contacts between the surface carbons and water decreases in the case of NaI solutions but is unchanged for NaF solutions. The orientation of the water-ion and the water-water hydrogen bond vector orientations near the interface is discussed in detail.     

New conducting polymers, 3. Doping,stability, electrical,and optical characteristics of poly-(P-phenylphosphoethynediyl)

Studies on direct-current electrical conductivity and optical properties of a new solution of processable conducting polymer are reported. Electrical conductivity of thin films of the polymer on glass plate at room temperature was 6×10⁻⁶ S/cm. Study of conductivity with variation of temperature does not provide any definite thermal activation energy, which is in accordance with the amorphous nature of polymer. Optical absorption data adopting the Bardeen equation showed that maximum ‘optical gap’ (E _g ) is 3.30 eV. Doping with Br₂-vapor was found to be only partially effective in decreasingE _g by 0.43 eV. The polymer was found to be quite stable under normal atmospheric conditions. Environmental stability of both undoped and doped polymer has been discussed. Part 2: [5]     

Hydrogenation of schiff bases with group 6 metal carbonyls and sodium methoxide as catalyst precursors

Summary Schiff bases are hydrogenated to secondary amines by H₂ in the presence of [M(CO)₆](M=Cr, Mo or W) and NaOMe in methanol solution at 60–160 °C andca. 100 bar H₂ pressure. The reaction is significantly slower in the absence of NaOMe. In a stoichiometric reaction, [HCr(CO)₅]^– hydrogenatesN- benzylidene-aniline at 75 °C toN-benzylaniline forming [Cr₂(CO)₁₀]^2–.     

Magnetic Anisotropy in CoIIX4 (X=O,S, Se) Single‐Ion Magnets: Role of Structural Distortions versus Heavy Atom Effect

Mononuclear four coordinate Co^II complexes have drawn a great deal of attention as they often exhibit excellent single‐ion magnet (SIM) properties. Among the reported complexes, the axial zero‐field splitting parameter (D) was found to vary drastically both in terms of the sign as well as strength. There are various proposals in this respect such as structural distortions, heavier atom substitution, metal‐ligand covalency, tuning secondary coordination sphere, etc. that are expected to control the D values. To assess the importance of structural distortions vs. heavier atom substitution effect, here we have undertaken detailed theoretical studies based on the ab initio CASSCF/NEVPT2 method to estimate zero‐field splitting parameters for twelve complexes reported in the literature. Our test set includes the {Co^IIX₄} (where X=O, S, Se) core structure where the D value was found to vary from +19 to ?118 cm^?1. Based on the structural variation, we have classified the complexes into three types (I–III) where type I complexes were found to exhibit the largest negative D value as desired for SIMs. The other two types (II and III) of complexes have been found to be inferior with respect to type I. The secondary coordination sphere was also found to influence D, as substitution on the secondary coordination sphere atom was found to significantly alter the magnitude of D values. Particularly, two structural parameters, namely, the dihedral angle between the two ligand planes and the X‐Co‐X polar angle were found to heavily influence the sign and strength of D values. Our analysis clearly reveals that these structural factors are much more important than the heavier atom substitution, or metal‐ligand covalency. A large variation in the D and E/D values among these complexes despite possessing a very close structural similarity offers an exquisite playground for a chemist to design and develop new‐generation Co^II‐based SIMs.     

Size-dependent properties of Zn(m)S(n) clusters: a density-functional tight-binding study

We present the results of our theoretical calculations on structural and electronic properties of ligand-free Zn(n)S(n) [with n ranging from 4 to 104 (0.8-2.0-nm diameter)] clusters as a function of size of the clusters. We have optimized the structure whereby our initial structures are spherical parts of either zinc-blende or wurtzite structure. We have also considered some hollow bubblelike structures. The calculations are performed by using a parametrized linear combination of atomic orbitals-density-functional theory-local-density approximation-tight-binding method. We have focused on the variation of radial distribution function, Mulliken populations, electronic energy levels, band gap, and stability as a function of size for both zinc-blende and wurtzite-derived ZnS clusters. We have also reported the results of some nonstoichiometric Zn(m)S(n) (with m+n=47, 99, 177) clusters of zinc-blende modification.     

Oxanorbornenes: promising new single addition monomers for the metathesis polymerization

Higher ring-opening metathesis propagation rates of exo-norbornene derivatives over endo derivatives are well established in the literature. Here, we report for the first time that endo-isomers of oxanorbornene derivatives show higher reactivity towards ring-opening metathesis with Grubbs'' 3rd generation catalyst (G3) than the corresponding exo-isomers. A very high selectivity for the reaction of G3 with endo over the exo-isomers could be shown. Furthermore, single molecular addition of the endo-isomers with G3 was observed. On the other hand, pure exo-monomers could successfully be homopolymerized. Mixtures of exo- and endo- monomers, however, prevented the homopolymerization of the exo-monomer. Such mixtures could successfully be copolymerized with cycloalkenes, resulting in alternating copolymers. An oxanorbornadiene derivative could be shown to undergo single addition reactions, exploited in the preparation of mono-end functional ROMP polymers. These could be selectively derivatized via endgroup selective thiol-ene click reactions. A thiol and alcohol end functional ROMP polymer was synthesized, and the efficient end functionalization was confirmed by ¹H NMR spectroscopy and MALDI-ToF spectrometry.

Bridgehead revisited: endo-7-oxa norborneneimide derivatives (green) initiate faster but propagate more slowly than the analogous exo-derivatives (red) in ring-opening metathesis allowing the synthesis of alternating and end functional polymers.     

Improved separation of metallothionein isoforms by the presence of cyclodextrin in capillary zone electrophoresis

Capillary zone electrophoresis (CZE) with cyclodextrin (CD) in the polyacrylamide-coated capillary was used to study metallothionein (MT) forms in the horse kidney preparation produced commercially by Sigma. It is known that CDs form complexes with hydrophobic amino acids. The results show that the presence of CD improves the separability of the various MT forms, including the MT-IA and the MT-IB forms, metallothionein aggregates, as well as the so far unidentified a and b forms. This was true both below and above the isoelectric points (pIs), although the migration times were somewhat longer at increasing CD concentrations for runs at constant voltage than with constant current.     

Solubility and distribution of radon in organic solvents

The influence of physicochemical properties of solvents on the solubility of radon in them can be described by multiparameter linear equations taking into account various solvent characteristics; the decisive (and negative) effect on the radon solubility is exerted by the cohesion energy density and polarity of the solvent. This approach is efficient for summarizing data on the distribution ratios of radon between organic and aqueous phases.     

Kinetics and mechanism of the oxidation of neutralized α-hydroxy acids by tris(pyridine-2-carboxylato)manganese(III)

The kinetics of oxidation of the neutralized -hydroxy acids: lactic, -hydroxyisobutyric, mandelic, benzilic and atrolactic acids by tris(pyridine-2-carboxylato)manganese(III) have been studied. The reactions were carried out in a Na(pic)-picH [Na(pic) = sodium salt of pyridine-2-carboxylic acid and picH = pyridine-2-carboxylic acid] buffer medium in the 4.89–6.10pH range. The oxidation rate was found to be independent of pH, and rate follows the order: benzilate > mandelate >atrolactate>lactate > -hydroxy isobutyrate. The oxidation products are MeCHO, Me2CO, PhCHO, Ph2CO and PhCOMe for the respective reactions. A mechanism is proposed involving intermediate formation of hepta-coordinated MnIII complexes in a fast step. The complexes then decompose to give free radicals and MnII in the rate determining step. The free radicals subsequently react with another molecule of the MnIII species to give the respective carbonyl compounds in a fast step.