The kinetics of polymerization of cyclopentene by WCl6/AliBu3 catalyst

The kinetics of the polymerization of cyclopentene by WCl₆/AliBu₃ catalysts have been studied and the factors controlling the reproducibility of the rate of polymerization have been ascertained. A significant dependence of the rate of polymerization on the time between the additions of WCl₆ and AliBu₃ was observed. The dependence of the catalyst activity r,i this time delay suggested that WCl₆ reacted with cyclopentene to produce an unstable species (W₁) that could react with AliBu₃ to produce a catalytically active species (W₁¹) or that could react further with cyclopentene to produce another species W₂ that in turn would react with AliBu₃ to produce a much less active catalyst W₂¹. The detailed study of the kinetics of polymerization under controlled conditions suggested a kinetic chain mechanism initiated by two catalyst species; mechanism of polymerization based on the carbene system is suggested.     

Electron-Transfer Processes in Indium(II) Iodide-o-Quinone Systems

Indium(II) iodide reacts with various substituted o-quinones in nonaqueous solution by successive one-electron-transfer reactions to give (SQ)InI(2) products (SQ = semiquinonate radical anion). Electron spin resonance spectroscopy demonstrates the presence of both mono- and diradical species in the reaction mixture. Addition of 4-picoline to a mixture of In(2)I(4) and TBQ (=3,5-di-tert-butyl-o-quinone) in toluene causes the precipitation of the indium(III)-semiquinonate complex (TBSQ)InI(2)(pic)(2) whose structure has been established by X-ray crystallography: space group P&onemacr;, with a = 13.013(3) ?, b = 13.317(3) ?, c = 10.828(5) ?, alpha = 97.71(3) degrees, beta = 107.98(3) degrees, gamma = 103.92(3) degrees, V = 1684.8(1.2) ?(3), Z = 2. Refinement converged at R = 0.051 and R(w) = 0.064 for 5918 reflections at 23 degrees C. The InO(2)N(2)I(2) kernel is pseudooctahedral, and the structure confirms the presence of the semiquinonate ligand. A reaction scheme which incorporates these results is proposed.     

Sulphur diffusion in GaAs-AlAs superlattices

Diffusion and heat treatment experiments in closed ampoules were carried out on two different molecular beam epitaxy-grown GaAs-AlAs superlattice wafers. All of the diffusion experiments were undertaken at 1000° C. The effects of varying the As and S vapour pressures as well as the diffusion time were investigated. Angle-lapping, transmission electron microscopy, X-ray photoelectron spectroscopy and secondary-ion mass spectroscopy were the techniques employed to analyse the samples. It was demonstrated that the diffusion of S enhances the group III interdiffusion or intermixing compared with the effect of plain heat treatment. It was also shown that S-induced intermixing has two origins, one being the diffusion of S and its effects on the concentration of native defects and the other being a mechanism related to the formation of a coating on the semiconductor surface during the diffusion.     

On the scope of radical reactions in aqueous media utilizing quaternary ammonium salts of phosphinic acids as chiral and achiral hydrogen donors

A broad range of fundamental free radical reactions such as hydrogen atom transfer, radical deoxygenations, and radical cyclizations utilizing quaternary ammonium salts of phosphinic acids as chiral and achiral hydrogen donors at room temperature are investigated. The reactions proceed in good to excellent yields with some degree of enantioselectivity.     

The preparation of samples for α-counting by the direct evaporation of organic solutions

A method is described for the preparation of thin deposits of α-emitting elements by evaporation of solutions in organic solvents. By heating the periphery of the tray, a suitable temperature gradient is maintained across the tray, giving smooth evaporation of the solvent to leave a deposit which is suitable for α-counting. It has been shown that on a semi-routine basis, the method is rapid and gives good precision.     

Adhesion force studies using a dangling optical lever with variable sensitivity

Adhesion force sensed using tips on microcantilevers via an optical lever requires care to ensure that the tip alone contacts the liquid; is sensitive to high degrees of measurement error from departure from the laser spot; requires specialized optics and careful arrangement to produce a small laser probing spot; and limits the distance between cantilever and photodiode for increased force sensitivity. An alternative scheme, using microimaging electronic speckle pattern interferometry to monitor the deformation of a tipless microcantilever, necessitates that the beam be rigid enough to be independent of the drop location; is not amenable to very low adhesion force measurement; and requires more complicated instrumentation. All these limitations can be effectively circumvented by a variable sensitivity scheme described here that harnesses the geometric properties of a dangling cantilever operating as an optical lever.     

Fit-for-Purpose Synthesis of CDK2 Inhibitor GNE-140

A six-step, stereoselective synthesis of cyclin-dependent kinase 2 (CDK2) inhibitor GNE-140 was developed. The key bonds were assembled through palladium-catalyzed Negishi cross-coupling and Buchwald–Hartwig C−N coupling steps. The stereodiad was established through a single-step, CuH-catalyzed enone reduction proceeding in >99 : 1 er and 89 : 11 dr. GNE-140 was obtained in 25 % overall yield with 98.6 A% HPLC purity.     

On <Emphasis Type="Italic">g</Emphasis>-functions for Laguerre function expansions of Hermite type

We examine weighted L ^p boundedness of g-functions based on semigroups related to multi-dimensional Laguerre function expansions of Hermite type. A technique of vector-valued Calderón–Zygmund operators is used.