AB-initio studies of N-O-F compounds. Internal rotation in hydroxylamine and its fluorinated derivatives

Ab-initio molecular orbital theory at both the minimal and extended basis set levels have been applied to the study of internal rotation in hydroxylamine and its fluorinated derivatives. The computed energies are analyzed in terms of a Fourier-type expansion of the potential function. The total potential function V(φ)can be dissected into onefold (V₁), twofold (V₂) and threefold (V₃) components and plots of these components together with V(φ) are given for each of the molecules studied herein. Additionally geometry optimizations have been carried out as a function of the internal rotation angle φ (φ = : NOX dihedral angle) for H₂NOH and F₂NOF. For H₂NOH geometry optimizations are found to be less important than for F₂NOF. In general the fluorinated hydroxylamines prefer a $\text{trans}$-conformation (φ = 180°) while hydroxylamine itself adopts the $\text{cis}$-conformation (φ = 0°) largely as a result of a lower dipole interaction (V₁ term) in the $\text{cis}$-conformation.     

Linear functionalized polyethylene prepared with highly active neutral Ni(II) complexes

Neutral Ni(II) salicylaldimine catalysts (pendant ligand = NCMe or PPh₃) were used to copolymerize ethylene with monomers containing esters, alcohols, anhydrides, and amides and yielded linear functionalized polyethylene in a single step. α‐Olefins and polycyclic olefin comonomers carrying functionality were directly incorporated into the polyethylene backbone by the catalysts without any cocatalyst, catalyst initiator, or other disturber compounds. The degree of comonomer incorporation was related to the monomer structure: tricyclononenes > norbornenes > α‐olefins. A wide range of comonomer incorporation, up to 30 mol %, was achieved while a linear polyethylene structure was maintained under mild conditions (40 °C, 100 psi ethylene). Results from the characterization of the copolymers by solution and solid‐state NMR techniques, thermal analysis, and molecular weight demonstrated that the materials contained a relatively pure microstructure for a functionalized polyethylene that was prepared in one step with no catalyst additive. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2842–2854, 2002     

Two-dimensional correlation gel permeation chromatography (2D GPC) study of the CH<Subscript>3</Subscript>SO<Subscript>3</Subscript>H-catalyzed polymerization of triethoxysilyl-terminated polystyrene. Molecular weight effect on the aggregate–aggregate interactions

The two-step polymerization process of two well-defined polymeric silane coupling agents, triethoxysilyl-terminated polystyrene with molecular weights equal to 2400 [TESi-PS (2400)] and 8000 [TESi-PS (8000)], catalyzed by 0.1 mol/kg CH₃SO₃H, was traced as a function of reaction time using gel-permeation chromatography (GPC). Two sets of GPC traces, collected during the condensation, were then converted to two-dimensional (2D) correlation spectra by using generalized 2D correlation theory. The 2D correlation spectra elucidated details of the aggregate–aggregate correlations [in particular, the difference between the correlations of TESi-PS (2400) and TESi-PS (8000)], thus demonstrating the effect of aggregation on the polymerization.     

Silicone-grease-based immobilisation method for the preparation of enzyme electrodes

An approach to the construction of amperometric biosensors based on the incorporation of an enzyme in silicone grease and using the grease to fill micropores on a graphite surface is described. The enzyme-grease electrode concept, illustrated with the enzyme tyrosinase, offers a very simple, rapid and inexpensive approach to the fabrication of enzyme electrodes. The tyrosinase electrode responds very rapidly to dynamic changes in the concentration of phenolic compounds. A response time (t95%) as low as 5 s has been determined. With flow injection, 120 samples per hour can be processed with a relative standard deviation of 2.4%. The electrode remains active for about 12 d. The detection limit for dopamine is 6 x 10(-6) M. This method of biosensor construction should be applicable to other enzyme-substrate systems.     

Determination of Michaelis-Menten parameters obtained from isothermal flow calorimetric data

Recent papers have reported [Thermochim. Acta 399 (2003) 63; Thermochim. Acta, in press] the results of a preliminary inter/intra laboratory study into the suitability of the base-catalysed hydrolysis of methyl paraben as a test and reference reaction for isothermal flow-through calorimeters. It was shown that this reaction can be used to investigate the flow characteristics of the instrument being used. It has also allowed, for the first time, the calculation of accurate values for the rate constant and for the enthalpy change, ΔH (hereafter H (enthalpy) for simplicity) of reaction directly from the calorimetric data, free from assumption. These findings have been extended to permit the direct determination of Michaelis-Menten based kinetic parameters from calorimetric data again free from assumption (except that the system conforms to Michaelis-Menten kinetic theory). This paper describes the method used for such an analysis and reports the results of a preliminary study on the urea/urease enzymatic system.     

Condensations of aryl trifluoromethyl ketones with arenes in acidic media

The chemistry of trifluoromethyl ketones has been studied. The work examines the condensation reactions of trifluoromethyl ketones with arenes in the superacid, including both synthetic and mechanistic aspects.     

Theory and numerical evaluation of oddoids and evenoids: Oscillatory cuspoid integrals with odd and even polynomial phase functions

The properties of oscillating cuspoid integrals whose phase functions are odd and even polynomials are investigated. These integrals are called oddoids and evenoids, respectively (and collectively, oddenoids). We have studied in detail oddenoids whose phase functions contain up to three real parameters. For each oddenoid, we have obtained its Maclaurin series representation and investigated its relation to Airy–Hardy integrals and Bessel functions of fractional orders. We have used techniques from singularity theory to characterise the caustic (or bifurcation set) associated with each oddenoid, including the occurrence of complex whiskers. Plots and short tables of numerical values for the oddenoids are presented. The numerical calculations used the software package CUSPINT [N.P. Kirk, J.N.L. Connor, C.A. Hobbs, An adaptive contour code for the numerical evaluation of the oscillatory cuspoid canonical integrals and their derivatives, Comput. Phys. Commun. 132 (2000) 142–165].     

High pressure matrix-assisted laser desorption/ionization Fourier transform mass spectrometry for minimization of ganglioside fragmentation

Transiently elevating pressure in a matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) source into the 1-10 mbar range during ionization decreases the metastable fragmentation of gangliosides. This allows detection of the molecular ion species without loss of the highly labile sialic acid residues. In these experiments, gangliosides with up to five sialic acids were ionized by MALDI and detected with the FTMS. In each case, when the high pressure collisional cooling was used, the singly charged molecular ion was the base peak in the spectra, both in the positive and negative ion modes, and minimal metastable fragmentation was observed. This result is promising, as the previously developed TLC separation methods can be coupled to MALDI-FTMS.