Tetrahedral intermediates 3: The kinetics and mechanism of the breakdown of some hemiorthoesters

The kinetics of the breakdown of hemiorthoesters generated from dialkoxyalkyl acetates or ketene acetals have been investigated. The following compounds were studied: dimethyl hemiorthoformate (1b), diethyl hemiorthoformate (2b), 2-hydroxy-1,3-dioxolane (3b), 2-hydroxy-4,4,5,5-tetramethyl-1, 3-dioxolane, (4b), 2-hydroxy-2-methyl-1,3-dioxolane (5b),and 2-hydroxy-2,4,4,5,5-pentamethyl-1,3-dioxolane (6b).The whole series was studied in aqueous acetonitrile (c_H2O= 8.33 M); 4b, 5b, and 6b were studied in aqueous acetonitrile (c_H2O = 2.22 M) and 4b and 6b in water. Complete pc_H-rate or pH-rate profiles were obtained for each reaction. The mechanisms of the hydronium-ion, hydroxide-ion and “water” catalysed reactions are discussed and compared to those for the breakdown of hemiacetals and the hydrolysis of orthoesters.     

Spectrofluorimetric determination of beryllium based on the inclusion complex of 1-amino-4-hydroxyanthraquinone with β-cyclodextrin as ligand

The use of the inclusion complex of 1-amino-4-hydroxyanthraquinone (AHA) in the internal cavity of β-cyclodextrin is compared with AHA alone as a ligand for the spectrofluorimetric determination of beryllium. The organizing ability of the cyclodextrin medium and the protection of the ligand from the micro-environment confers increased sensitivity, selectivity and detection limit, and allows the determination of 10–70 ng ml^?1 beryllium, compared to 60–500 ng ml^?1 in the absence of the cyclodextrin.     

Influence of ion pairs on the dynamical behaviour of Er3+-doped fibre lasers

We demonstrate experimentally the influence of ion-pair concentration on the dynamical behaviour of erbium-doped fibre lasers. At low pair densities, the laser has a CW output, while at higher densities it exhibits a self-pulsing behaviour. For intermediate pair concentrations, the output intensity evolves continuously from an infinite train of pulses to a CW steady state as the pumping ratio is increased.     

Investigation of CdTe films with Fe,in and Sb impurities produced by R.F. sputtering technique

We report here the preliminary results on CdFeTe with indium and antimonium thin films. The population of Fe²⁺ increases linerly with the alitimonium content in FeCdTe thin films and this results in a less crystallized material. Indium, on the other hand, has a less pronounced effect on the Fe²⁺/Fe³⁺ population.     

Nonlinear Wave Interactions in Nonlinear Nonintegrable Systems

The main goal of this article is to understand the qualitative appearances of regular arrays of pulses that come up in nonintegrable systems in a variety of contexts, particularly in fluid dynamics. It is shown that even nonintegrable systems have a kind of particle dynamics made up of solitary waves. But the interaction of these solitary waves is not absolutely “clean” as in the case of the KdV and other integrable equations.     

MRI of inflammatory synovial processes

MRI was used to evaluate inflammatory synovial processes in 53 patients over a 4-year period. Multiple disease processes were imaged, including: rheumatoid arthritis [n = 12], osteochondromatosis [n = 6], bursal abnormalities [n = 17], ganglion cyst [n = 1], meniscal cyst [n = 5], hemophilia [n = 1], and septic arthritis [n = 11]. The soft tissue contrast resolution of MRI and its multiplanar capability makes it particularly suitable for evaluating masslike or fluid inflammatory processes for diagnostic purposes, to determine extent of disease, and in some cases, to determine the composition of the inflammatory processes.     

Vinylarenetricarbonyl complexes of chromium as chain propagation regulators for polymerization of acrylic monomers

The polymerization of methyl methacrylate and butyl acrylate initiated by azo‐bis‐isobutyronitrile in the presence of metal‐containing monomers (p‐methylstyrene‐, stilbene‐ and α‐methylstyrene‐chromiumtricarbonyl) was studied. Kinetic parameters (i.e. the decrease in the autoacceleration during the polymerization of acrylic monomers, its shift towards a high conversion region in the presence of α‐methylstyrenechromiumtricarbonyl, a linear dependence of the molecular weight of a polymethyl methacrylate and the shift of molecular‐weight distribution curves to a high molecular weight region with conversion) demonstrate the influence of vinylarenetricarbonyl complexes of chromium on basic steps of polymerization. It is important to note that the above organometallic compounds enable the controlled synthesis of polymers under temperature conditions (50–70 °C) corresponding to those of the industrial polymer production. Copyright © 2003 John Wiley & Sons, Ltd.