New cationic group 4 metal alkyl complexes

Cationic group 4 metal alkyl complexes containing tetradentate Schiff base ligands, (acen) Zr(R)⁺ and (F6-acen) Zr(R)⁺, are prepared by protonolysis of suitable neutral dialkyl precursors. These complexes display electrophilic behavior and are moderately active ethylene polymerization catalysts in the presence of 1 molar equivalent of AlR₃.     

Molecular dynamics simulations of the thermal conductivity of methane hydrate

Nonequilibrium molecular dynamics simulations with the nonpolarizable SPC/E (Berendsen et al., J. Phys. Chem. 1987, 91, 6269) and the polarizable COS/G2 (Yu and van Gunsteren, J. Chem. Phys. 2004, 121, 9549) force fields have been employed to calculate the thermal conductivity and other associated properties of methane hydrate over a temperature range from 30 to 260 K. The calculated results are compared to experimental data over this same range. The values of the thermal conductivity calculated with the COS/G2 model are closer to the experimental values than are those calculated with the nonpolarizable SPC/E model. The calculations match the temperature trend in the experimental data at temperatures below 50 K; however, they exhibit a slight decrease in thermal conductivity at higher temperatures in comparison to an opposite trend in the experimental data. The calculated thermal conductivity values are found to be relatively insensitive to the occupancy of the cages except at low (T相似文献   

Association phenomena in a ferromagnetic colloid

We discuss the equation of state and the static correlations in a system of spherical ferromagnetic grains suspended in a magnetically passive fluid. In the domain where dipole-dipole interactions between the grains are large (low temperature) we show that the variation of the small-angle X-ray scattering with magnetic field provides a sensitive test of the model proposed to treat this system. We discuss the condensation of the grains into linear chains at low density, high magnetic field, and low temperature. The possibility of resonances in the small-angle X-ray scattering is demonstrated and certain other consequences of chain formation are indicated.     

Enzymatic oxidation of para-substituted arenes: access to new non-racemic chiral metabolites for synthesis

A series of para-substituted benzene derivatives were subjected to whole-cell fermentation with Escherichia coli JM109 (pDTG601), an organism expressing toluene dioxygenase (TDO). Several compounds proved to be excellent substrates for TDO, including 4-bromo-phenylacetylene, 4-bromobenzaldehyde, 4-bromobenzyl alcohol and 4-bromo-allylbenzene. Some of the first para-functionalized diene diols produced using TDO, are useful substrates for further synthetic manipulations, including their use in the potential synthesis of complex natural products.     

Exact Formula for Currents in Strongly Pumped Diffusive Systems

We analyze a generic model of mesoscopic machines driven by the nonadiabatic variation of external parameters. We derive a formula for the probability current; as a consequence we obtain a no-pumping theorem for cyclic processes satisfying detailed balance and demonstrate that the rectification of current requires broken spatial symmetry.     

Formation constants of copper(I)-olefin complexes in aqueous solution

A simple kinetic method has been applied to measure the formation constants of aqueous copper(I) with fumaronitrile, dimethyl fumarate, and fumaric and maleic acids. At 0.14 M ionic strength, the values of beta(1) are (0.85 +/- 0.02) x 10(3), (6.1 +/- 0.1) x 10(3), (7.3 +/- 0.1) x 10(3), and (2.2 +/- 0.4) x 10(3) M(-1), respectively. The values for the last two olefins are compared to previous results. Values of beta(1) for hydrogen maleate and beta(2) for fumaronitrile also have been determined. A reanalysis of much earlier work has been done, and all the results are discussed in terms of the effect of substituents on the olefin on the beta(1) values. The structure of bis(fumaronitrile)copper(I) nitrate also is reported. The nitrile is N-coordinated to copper(I), which has a distorted tetrahedral geometry, while the overall structure consists of macrocyclic Cu(6)(fumaronitrile)(6) rings which extend in three dimensions.     

Halophilic reactions of a stable silylene with chloro and bromocarbons

A number of disilanes have been synthesized from a stable silylene, 1 (N,N'-di-tert-butyl-1,3-diaza-2-silacyclopent-4-en-2-ylidene), and a variety of halocarbons. It is proposed that disilane formation is a result of an initial halophilic interaction between the silylene and halocarbon. Formation of disilanes from 1 and CCl4, 2a, CHCl3, 2b, CH2Cl2, 2c, benzyl chloride, 2d, and bromobenzene, 5, are described here. An X-ray crystal structure of 2b was determined.     

An investigation of the voltammetric characteristics of the osazone of dihydroxytartaric acid

Differential pulse polarography (d.p.p.), supplemented by other voltammetric techniques, is used to elucidate the tautomeric structures associated with buffered aqueous solutions of the osazone of dihydroxytartaric acid. In particular, d.p.p. is used to evaluate the number of electrons and protons associated with each of seven reduction processes, at pH values ranging from 2.5–11.5. The reversibility of the electrode processes is demonstrated by cyclic voltammetry and d.p.p. All the reduction processes studied are diffusion-controlled. Mechanisms for these reductions are proposed on the basis of the tautomeric equilibrium associated with the osazone in solution.     

An extension of moments calculations for optical absorption bands

In this paper the developments of Henry, Schnatterly and Slichter are extended by using a more general formulation of the principle of spectroscopic stability (for a site of symmetry O_h). The linear effects for any type of stress are obtained next. The expressions indicate how one can test the theory experimentally in a critical manner. This has not been done. The theory shows that one cannot expect to get more information on KCl from stress experiments than is now available. Finally, it is indicated how one may define the irreducible stresses and strains in an unambiguous manner by using the differential strain-energy function.