Mass spectrometric studies on cyclo- and poly-phosphazenes: 4—Attempts at mass spectrometrically induced polymerization of cyclotriphosphazenes substituted with primary and secondary amines

In this paper, the mass spectrometric behaviour of cyclophosphazenes substituted with primary and secondary amines is investigated, together with the mass spectrometric polymerization pattern of these compounds. While it is not possible to achieve the mass spectrometric polymerization of hexa(anilino)cyclotriphosphazene, ion–molecule reactions take place in the case of hexa(piperidino)- and hexa(morpholino)cyclotriphosphazenes, which lead to the formation of hexameric species. Evidence is given that pentasubstituted cyclophosphazenephosphorus cations are the species responsible for the oligomerization process.     

The Morita-Baylis-Hillman reaction in aqueous-organic solvent system

We have found that water and organic solvents mixed at different proportions can give good to excellent yields and short reaction times for the Morita-Baylis-Hillman reaction. The present Letter details our findings in the Morita-Baylis-Hillman reaction between several aromatic aldehydes and methyl acrylate or acrylonitrile. The selection of the catalyst was also evaluated and DABCO affored the best results when compared to DBU, DMAP, HMT, Imidazole and Triethylamine.     

Thermal oxidation of metallocene ethylene-1-olefin copolymer films during one year oven aging

Metallocene ethylene homopolymer, ethylene-1-hexene and ethylene-1-octadecene copolymer films were characterized and analysed during their aging in a forced draft oven at 60 °C and compared to commercial polymers (HDPE and LDPE). Each polymer is essentially different in its structure, and the variables used in the present study are comonomer size and content in the main linear backbone polymer. The polymers were characterized initially using GPC, DSC, FTIR, and tensile tests. Later, at different time intervals, samples were removed from the oven and characterized using FTIR and GPC in order to detect changes in chemical structure, size, and molecular weight distribution due to thermo-oxidative aging. At the end of aging, films were subjected to tensile tests to quantify the effect of time on their useful life. As a qualitative reference parameter, the carbonyl index, the ratio of the infrared absorbance of the CO stretching band at 1715 cm⁻¹ and the absorbance of a reference band at 718 cm⁻¹, was determined. Kinetic thermo-oxidation is related to comonomer size and content in the main backbone polymer. As comonomer size decreases or comonomer content increases, degradation rate increases. The scission factor (S) and carbonyl index (CI) graphs of each material show a slope increase which is related to the autocatalytic rate of oxidation.     

A novel derivative for the assessment of urinary and salivary nitrate using gas chromatography/mass spectrometry

Previous gas chromatography/mass spectrometry (GC/MS) methods for determining nitrate in biological samples involve either hazardous chemicals or produce multiple isomers that can be difficult to quantitate. Modification of these methods, by the nitration of mesitylene instead of benzene and in the presence of trifluoroacetic anhydride rather than sulphuric acid, should enable simple isotopic quantitation for use in tracer studies, for example, in the measurement of nitric oxide production. Desiccated urine and saliva samples, in addition to aqueous labelled and unlabelled nitrate standards, were treated with trifluoroacetic anhydride and mesitylene at 70°C for 1 h, cooled, then sequentially washed with deionised water and aqueous sodium bicarbonate. The solution of nitromesitylene in mesitylene was separated, dried and analysed by GC/MS. The full mass spectra exhibited abundant ions at m/z 165 and 166 corresponding to the unlabelled and labelled molecular species of nitromesitylene, respectively. Selected ion monitoring of these masses for a series of gravimetrically prepared standards indicated good agreement with isotopic enrichments in the range 0.0625–5 mole % excess, and at nitrate concentrations within the physiological range of 0.078–2 mmol/L. Derivatised samples were stable with respect to isotopic enrichments and nitrate concentrations at −20°C for up to 21 days and exhibited excellent repeatability. Nitration of mesitylene proved to be a simple and rapid method for the measurement of isotope ratios in aqueous nitrates by GC/MS, which has applications in tracer studies and in concentration determinations by isotope dilution techniques for nitric oxide production. Copyright © 2008 John Wiley & Sons, Ltd.     

Spectral residual method without gradient information for solving large-scale nonlinear systems of equations

A fully derivative-free spectral residual method for solving large-scale nonlinear systems of equations is presented. It uses in a systematic way the residual vector as a search direction, a spectral steplength that produces a nonmonotone process and a globalization strategy that allows for this nonmonotone behavior. The global convergence analysis of the combined scheme is presented. An extensive set of numerical experiments that indicate that the new combination is competitive and frequently better than well-known Newton-Krylov methods for large-scale problems is also presented.

     

On the sequence of partial maxima of some random sequences

Let {X_n, n ? 1} be a sequence of identically distributed random variables, Z_n = max {X₁,…, X_n} and {u_n, n ? 1 } an increasing sequence of real numbers. Under certain additional requirements, necessary and sufficient conditions are given to have, with probability one, an infinite number of crossings of {Z_n} with respect to {u_n}, in two cases: (1) The X_n's are independent, (2) {X_n} is stationary Gaussian and satisfies a mixing condition.