THE PHOTOPHYSICS OF MEROCYANINE 540. A COMPARATIVE STUDY IN ETHANOL AND IN LIPOSOMES

Abstract— Absorption and fluorescence emission spectra, fluorescence lifetimes, fluorescence quantum yields, photoisomerization quantum yields and triplet quantum yields were measured for Merocyanine 540 (MC540) in ethanol and in large unilamellar dimyristoyl phosphatidylcholine vesicles. The major differences in the photophysics between the two media are the increase of the fluorescence quantum yield from 0.15 in ethanol to 0.6 in vesicles at 25° C, and the appearance of a second fluorescence decay with a lifetime of 1.87 ns in the latter medium. Upper and lower limits for the photoisomerization quantum yields were determined by combining the data from laser flash photolysis and optoacoustic spectroscopy. The decrease in photoisomerization quantum yield upon incorporation of the dye into the lipid bilayer by a factor 2 suggests that this process competes directly with fluorescence. The temperature dependence of the fluorescence and photoisomerization quantum yields in solution supports this model. In both media MC540 has a very low triplet quantum yield with values 0.002 > (> ø_T > 0.02 in ethanol and 0.01 > ø_T- > 0.09 in liposomes Our data are consistent with the model whereby the dye is incorporated into the lipid bilayer as a monomer with two different orientations and this model is adopted on the basis of the biexponential behaviour of the fluorescence and photoisomer decay.     

Thermodynamics of Adsorption ofn-Alkanes on Maleated Wood Fibers by Inverse Gas Chromatography

The adsorption ofn-heptane,n-octane,n-nonane, andn-decane on untreated wood fiber and wood fiber treated with maleated polypropylene was studied by inverse gas chromatography (IGC) at infinite dilution or zero surface coverage. The specific retention volume increased with increasing probe chain length, decreased with increasing column temperature, and increased with increasing maleated polypropylene concentration. The enthalpy of adsorption increased with increasing chain length of the probe vapors. The enthalpy of adsorption remained constant after the treatment of wood fiber. The London dispersive component of the surface free energy decreased with the column temperature and showed no dependency with either the type of wood fiber or the maleated polypropylene concentration.     

Determination of salbutamol enantiomers in human urine using heptakis(2,3-di-O-acetyl-6-O-sulfo)-beta-cyclodextrin in nonaqueous capillary electrophoresis

Nonaqueous capillary electrophoresis (NACE) was successfully applied to the resolution and the determination of salbutamol enantiomers in urine samples using heptakis(2,3-di-O-acetyl-6-O-sulfo)-beta-cyclodextrin (HDAS-beta-CD). After optimization of the electrophoretic parameters, namely the background electrolyte (BGE) composition and the HDAS-beta-CD concentration, salbutamol enantiomers were completely resolved using a BGE made up of 10 mM ammonium formate and 15 mM HDAS-beta-CD in methanol acidified with 0.75 M formic acid. Isoprenaline was selected as internal standard. Solid-phase extraction (SPE) was used for sample cleanup prior to the CE separation. Different sorbents involving polar, nonpolar interactions or dual retention mechanisms were evaluated and extraction cartridges containing both nonpolar and strong cation-exchange functionalities were finally selected. Salbutamol enantiomers recoveries from urine samples were determined. The method was then successfully validated using a new approach based on accuracy profiles over a concentration range from 375 to 7500 ng/mL for each enantiomer.     

The Baire Category Property and Some Notions of Compactness

We work in set theory without the axiom of choice: ZF. We showthat the axiom BC: Compact Hausdorff spaces are Baire, is equivalentto the following axiom: Every tree has a subtree whose levelsare finite, which was introduced by Blass (cf. [4]). This settlesa question raised by Brunner (cf. [9, p. 438]). We also showthat the axiom of Dependent Choices is equivalent to the axiom:In a Hausdorff locally convex topological vector space, convex-compactconvex sets are Baire. Here convex-compact is the notion whichwas introduced by Luxemburg (cf. [16]).     

A second-order accurate material-order-independent interface reconstruction technique for multi-material flow simulations

A new, second-order accurate, volume conservative, material-order-independent interface reconstruction method for multi-material flow simulations is presented. First, materials are located in multi-material computational cells using a piecewise linear reconstruction of the volume fraction function. These material locator points are then used as generators to reconstruct the interface with a weighted Voronoi diagram that matches the volume fractions. The interfaces are then improved by minimizing an objective function that smoothes interface normals while enforcing convexity and volume constraints for the pure material subcells. Convergence tests are shown demonstrating second-order accuracy. Static and dynamic examples are shown illustrating the superior performance of the method over existing material-order-dependent methods.     

A high‐throughput bioanalytical platform using automated infusion for tandem mass spectrometric method optimization and its application in a metabolic stability screen

Liquid chromatography/tandem mass spectrometry (LC/MS/MS) is the bioanalytical method of choice to support plate‐based, in vitro early ADME (Absorption, Distribution, Metabolism and Excretion) screens such as metabolic stability (Metstab) assessment. MS/MS method optimization has historically been the bottleneck in this environment, where samples from thousands of discrete compounds are analyzed on a monthly basis, mainly due to the lack of a high‐quality commercially available platform to handle the necessary MS/MS method optimization steps for sample analysis by selected reaction monitoring (SRM) on triple quadrupole mass spectrometers. To address this challenge, we recently developed a highly automated bioanalytical platform by successfully integrating QuickQuan? 2.0, a unique high‐throughput solution featuring MS/MS method optimization by automated infusion, with a customized in‐house software tool in support of a Metstab screen. In this platform, a dual‐column setup running parallel chromatography was also implemented to reduce the bioanalytical cycle time for LC/MS/MS sample analysis. A set of 45 validation compounds was used to demonstrate the speed, quality and reproducibility of MS/MS method optimization, sample analysis, and data processing using this automated platform. Metstab results for the validation compounds in microsomes from multiple species (human, rat, mouse) showed good consistency within each batch, and also between batches conducted on different days. We have achieved and maintained a monthly throughput of 1300 compound assays representing 500 discrete compounds per instrument per month on this platform, and it has been used to generate metabolic stability data for more than 25 000 compounds to date with an overall success rate of more than 95%. Copyright © 2009 John Wiley & Sons, Ltd.