Electron capture ionization of explosives with a microflow rate particle beam interface

A method for the analysis of four widely used explosives based on reversed-phase liquid chromatography coupled to a quadrupole mass spectrometer is presented. A microflow rate particle beam interface was employed that offers simplified operation procedures and improved interfacing performance. A positive role played by the reduced size of the aerosol droplets generated by the microflow rate interface is outlined in this work. Greater vaporization efficiency and negligible thermal decomposition were observed for the selected compounds in the ion source of the mass spectrometer. Electron capture ionization allowed specific and sensitive determination of the analytes. Detection limits that ranged between 60 and 200 pg and had a signal-to-noise ratio of 5:1 were obtained in selected ion monitoring mode after column elution.     

A truncated Newton method in an augmented Lagrangian framework for nonlinear programming

In this paper we propose a primal-dual algorithm for the solution of general nonlinear programming problems. The core of the method is a local algorithm which relies on a truncated procedure for the computation of a search direction, and is thus suitable for large scale problems. The truncated direction produces a sequence of points which locally converges to a KKT pair with superlinear convergence rate.     

Resin dynamics contributes to the NMR line broadening of organic molecules grafted onto a polystyrene resin

Despite the use of high resolution magic angle spinning NMR, the NMR linewidth of anchored molecules on the commonly used Merrifield solid phase resins remains larger than that of the corresponding molecules in solution. We investigate the different mechanisms that might be at the origin of this line broadening. Experimentally, we use the CPMG method to determine the (15)N relaxation times of a tethered tripeptide and show that the slow resin dynamics significantly contributes to the transverse relaxation.     

A Shifted-Barrier Primal-Dual Algorithm Model for Linearly Constrained Optimization Problems

In this paper we describe a Newton-type algorithm model for solving smooth constrained optimization problems with nonlinear objective function, general linear constraints and bounded variables. The algorithm model is based on the definition of a continuously differentiable exact merit function that follows an exact penalty approach for the box constraints and an exact augmented Lagrangian approach for the general linear constraints. Under very mild assumptions and without requiring the strict complementarity assumption, the algorithm model produces a sequence of pairs converging quadratically to a pair where satisfies the first order necessary conditions and is a KKT multipliers vector associated to the linear constraints. As regards the behaviour of the sequence x ^k alone, it is guaranteed that it converges at least superlinearly. At each iteration, the algorithm requires only the solution of a linear system that can be performed by means of conjugate gradient methods. Numerical experiments and comparison are reported.     

Studies on the synthesis of heterocyclic compounds. III. Synthesis of 1,3,2-benzodioxa- and 1,3,2-benzoxathiarsole derivatives

The preparation and reaction of 1,3,2-benzodioxa- and 1,3,2-benzoxathiarsoles (IIa-b) are described. Spiran derivatives Va-c are obtained by treating IIa-b with Ia-b and triethylamine, while the reaction of IIa-b with sodium hydroxide, ethoxide and p-cresolate gives the compounds VIa-b, VIIa-b and VIIIa-b, that can evolve to Xa-b. Reaction of IIa-b with sodium p-toluenethio-late and n-butyllithium gave the compounds IXa-b and XIa-b respectively. The structure of the prepared compounds has been determined by elemental analysis and spectroscopic data.     

SIMQUADNMR: a program for simulation and interpretation of multiple quantum-filtered NMR spectra of quadrupolar nuclei

In this paper, we present a computer program which simulates NMR multiple quantum-filtered spectra of quadrupolar nuclei as a function of physical parameters, of the type of experiment and experimental conditions. The program works by solving relaxation theory equations for the given system, and it can be useful in order to plan the ideal conditions to set up specific experiments or to give a physical interpretation of experimental results. The program allows to independently follow the dependence of individual coherences and relaxation rates as a function of up to 50 parameters regarding the physical properties of the system under investigation, sample conditions and instrumental setup making it an helpful tool also for teaching purposes.     

NMR and EPR structural delineation of copper(II) complexes formed by kanamycin A in water

The complexes formed by kanamycin A at three different pH values (5.5, 7.4 and 12.0) were investigated by NMR and EPR spectroscopy. Paramagnetic relaxation contributions to proton relaxation rates were measured using a combination of the TOCSY sequence with the inversion recovery experiment in order to gain signal resolution in the bulk region. Measured contributions were converted into distances and used for structural determination by restrained simulated annealing where all possible chair and boat conformations of the rings were taken into account. The interaction of the Cu(II) ion with the nitrogen of the C ring is apparent at all pH values. At higher pH also the amino group of ring A starts to be involved in the metal coordination sphere. This is accompanied by a switch in conformation of ring C. Structures are consistent with the involvement in the coordination sphere either of the 2' or 4' hydroxyl oxygens at pH 5.5 and the 5 and the 6' hydroxyl oxygens (or the ring oxygen) at pH 12.0.     

Newton-Like Iteration Based on a Cubic Polynomial for Structured Matrices

We recall Newtons iteration for computing the inverse or Moore–Penrose generalized inverse of a matrix. Then we specialize this approach to the case of structured matrices where all input, output and intermediate auxiliary matrices are represented in a compressed form, via their short displacement generators. We design a new Newton-like iteration based on a cubic polynomial and show its effectiveness by some numerical experiments for matrices from the Toeplitz-like class and the Cauchy-like class.