An efficient and practical chemoenzymatic preparation of optically active secondary amines

[reaction: see text] An efficient and practical chemoenzymatic method was developed for the preparation of a variety of chiral secondary amines. Here, oxalamic esters were identified as unique derivatives amenable to the enzyme-catalyzed kinetic resolution of racemic secondary amines. Both enantiomers of the amines were produced in high optical purity and yields after the cleavage of the oxalamic groups.     

Characterisation of derivatised monomeric and prepolymeric isocyanates by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry and structural elucidation by tandem mass spectrometry

Isocyanates are an important class of compounds in occupational hygiene monitoring due mainly to their behaviour as respiratory sensitisers. Here, we demonstrate the application of matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) and MALDI tandem mass spectrometry (MS-MS) to the analysis of derivatised isocyanate monomers and prepolymers. The aim of the work has been to gauge the selectivity obtainable from the direct analysis of isocyanate mixtures without prior separation. Monomeric and prepolymeric isocyanate mixtures were analysed as their 1-(2-methoxyphenyl) piperazine derivatives and the potential of MALDI time-of-flight (ToF)-MS for an NCO monitoring program was assessed. The results obtained demonstrated the possibility of direct mixture analysis by this method. MALDI-MS-MS was used for the elucidation of fragment structures in the prepolymer samples. The developed methodology was then applied to the analysis of swabs from an occupational hygiene monitoring scheme and enabled the identification of the isocyanate species detected.     

Nonradiative and radiative deactivation of singlet molecular oxygen (O2(a1deltag)) in micellar media and microemulsions

The effects of microheterogeneous media (micelles and microemulsions) on the lifetime and, to our knowledge for the first time, on the emission of singlet molecular oxygen (O2 (a1Ag), denoted as 1O2) were investigated. Micellar media and various types of microemulsions based on anionic (sodiumdodecyl sulfate), cationic (cetyltrimethylammonium chloride) or nonionic (Triton X-100) surfactants were formulated for this purpose. The nonradiative and radiative deactivation rate constants (k(d) and k(e), respectively) were determined in selected microheterogeneous media and in the pure solvents used for their formulation, by combining steady-state and time-resolved 1O2, luminescence detection techniques. We have shown that a simple additive model, as used in homogeneous mixtures of solvents, was inadequate for predicting values of k(d) and k(e) in organized media. In contrast, both 1O2 lifetimes (taudelta = 1/k(d)) and k(e) in the microheterogeneous systems investigated could be predicted with good precision from the composition of the media and the taudelta and k(e) values in the pure solvents, using a two-pseudophase kinetic model for the 1O2 distribution. Such a model takes into account the average times spent by 1O2 in the aqueous and lipophilic pseudo-phases of the organized media, the corresponding equilibrium constant (Keq) depending on the nature of the system.     

A multirate scan conversion method

B-mode ultrasonic imaging requires that the acquired polar coordinate ultrasound data be converted to the Cartesian format used by digital monitors. Image quality depends on the interpolation algorithm used to this purpose. In this work a selective sampling technique, based on acquiring data at specific points of the scanned area together with a straightforward linear interpolation step, is proposed. Hardware complexity is avoided, because the interpolation task can be carried out by software in real time, concurrently with data acquisition. The performances of the proposed approach are analysed with regard to those provided by other algorithms and some implementation issues are addressed.     

Preliminary application of a DGV system using a single intensified camera in a supersonic wind tunnel

A DGV system using a continuous wave Argon laser and an optical arrangement with a single intensified camera has been set up at the ISL blow-down supersonic wind tunnel. The first tests have been performed over a 12.5° 2D wedge at a freestream Mach number of 2. A mean velocity field has been calculated from 28 individual measurements. When compared to the theoretical velocity distribution, deviations of 8 % to 15 % have been obtained. Preliminary tests have also been performed on a missile-like model equipped with a lateral jet system. Individual as well as mean velocity fields are presented.