Desorption electrospray ionisation mass spectrometry reveals in situ modification of a hindered amine light stabiliser resulting from direct N-OR bond cleavage

Detection and characterisation of structural modifications of a hindered amine light stabiliser (HALS) directly from a polyester-based coil coating have been achieved by desorption electrospray ionisation mass spectrometry (DESI-MS) for the first time. In situ detection is made possible by exposing the coating to an acetone vapour atmosphere prior to analysis. This is a gentle and non-destructive treatment that allows diffusion of analyte to the surface without promoting lateral migration. Using this approach a major structural modification of the HALS TINUVIN?123 (bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate) was discovered where one N-ether piperidine moiety (N-OC(8)H(17)) is converted to a secondary piperidine (N-H). With the use of 2-dimensional DESI-MS imaging the modification was observed to arise during high curing temperatures (ca. 260 °C) and under simulated physiological conditions (80 °C, full solar spectrum). It is proposed that the secondary piperidine derivative is a result of a highly reactive aminyl radical intermediate produced by N-O homolytic bond cleavage. The nature of the bond cleavage is also suggested by ESR spin-trapping experiments employing α-phenyl-N-tert-butyl nitrone (PBN) in toluene at 80 °C. The presence of a secondary piperidine derivative in situ and the implication of N-OR competing with NO-R bond cleavage suggest an alternative pathway for generation of the nitroxyl radical-an essential requirement in anti-oxidant activity that has not previously been described for the N-ether sub-class of HALS.     

Use of a Single Capillary Electrophoresis Method as a Routine Identity Test for Batch Release of a Range of Pharmaceutical Products

Two independent and orthogonal analytical methods are required when performing identity testing of pharmaceutical products during routine release testing. A microemulsion electrokinetic chromatography method has been developed and validated for routine use as an identity test to release various pharmaceutical products including tablets, capsules and creams. Implementation of the method involved optimisation of parameters to achieve reliable routine operation. Rinsing procedures, in particular, were found to be essential to obtain consistent profiles and migration times. The method has replaced, and offers the potential to replace, a number of methods including HPLC and IR due to the considerable cost and time savings obtained through its use. This method has been successfully approved by the US FDA as a part of 2 New Drug Applications, is registered in Japan, and is in routine QA use within a factory environment.     

Asymmetric synthesis of (+)-galbelgin, (-)-kadangustin J, (-)-cyclogalgravin and (-)-pycnanthulignenes A and B, three structurally distinct lignan classes, using a common chiral precursor

The enantioselective synthesis of three structurally distinct classes of lignan from a single, aza-Claisen-derived, chiral morpholine amide is reported. The class of lignan formed is dependent on the substitution pattern in the aryl rings and choice of protecting group on a key benzylic hydroxyl group. The methodology has been used to asymmetrically synthesize and determine the absolute stereochemistry of lignans (+)-cyclogalgravin 3, (-)-pycnanthulignene A 4, (-)-pycnanthulignene B 5, and (-)-kadangustin J 8.     

Fortran codes for the correlation functions of hard sphere fluids

Our Fortran codes for hard sphere fluids and their mixtures for the correlation functions that arise from the Percus–Yevick theory and the Verlet–Weis semi-empirical correction have proven useful during a period of nearly four decades and continue to be useful. In order to make these codes even more widely available, a brief summary is presented here and listings of these codes are given in the electronically accessible Supplementary Material to this paper.     

The effect of pressure on halothane binding to hydrated DMPC bilayers

Halothane binding to hydrated dimyristoylphosphatidylcholine (DMPC) bilayer membranes has been examined over a wide range of pressures from 10⁵ to 4?×?10⁸?Pa. We show that the solvation of halothane by the membrane and bulk water are both pressure dependent, with an increased pressure driving halothane into the membrane. Analysis of these results shows that this pressure dependence is not the cause of pressure reversal, the process whereby general anaesthetics lose their efficacy at pressures of about 8?×?10⁶ to about 2.5?×?10⁷?Pa.     

Supersonic velocimetry in a shock tube using laser enhanced ionisation and planar laser induced fluorescence

 A novel flow-tagging technique is presented which was employed to measure gas velocities in the free stream of a shock tube. This method is based on the laser spectroscopic techniques of Laser-Enhanced Ionisation (LEI) and Laser-Induced Fluorescence (LIF). The flow in the shock tube is seeded with small amounts of sodium, and LEI is used to produce a substantial depletion of neutral sodium atom concentration in a well-defined region of the flow, by using two wavelength-resonance excitation and subsequent collisional ionisation. At a specific time delay, single-laser-pulse planar LIF is utilised to produce a two-dimensional (2-D) inverse image of the depleted tagged region downstream of the flow. By measuring the displacement of the tagged region, free stream velocities in a shock tube were determined. Large variations in the concentration of sodium seeded into the flow were observed and even in the presence of these large variations accurate free-stream velocity measurements were obtained. The experimentally determined value for velocity compares very well with the predicted velocity. Received: 25 March 1996/Revised version: 8 July 1996     

H + HOONO2 → products: Temperature-dependent rate constant

The absolute reaction rate constant of the title reaction was measured in a stirred-flow reactor under H-atom-rich conditions at seven temperatures from 226 to 315 K. Carbon monoxide was added to convert any OH radicals produced back to H atom by way of the reaction OH + CO → H + CO₂. The reaction rate constants were essentially constant between 248 and 315 K: (k ± 2σ) = (2.46 ± 0.35) × 10^?14 cm³/s. At temperatures lower than 248 K, the measured rate constant became larger at lower temperatures, possibly due to heterogeneous effects. An hypothesis is advanced that may explain the surprisingly slow rate constant that is virtually independent of temperature, but more experiments are required to determine the dynamical reaction pathway.