Micellar electrokinetic chromatography of charged and neutral drugs in acidic running buffers containing a zwitterionic surfactant, sulfonic acids or sodium dodecyl sulphate separation of heroin, basic by-products and adulterants

A procedure for the separation of charged and neutral solutes in acidic micellar running buffers has been developed. The procedure is based on a zwitterionic surfactant 3-N,N-dimethylmyristylammoniopropanesulfonate (MAPS) and alkylsulfonates added to the running buffer at pH 4.0. The alkylsulfonates increase the migration-time window for elution of neutral substances by increasing electro-osmotic mobility and by creating a negative micellar electrophoretic mobility. The test solution contained opiates and adulterants found in heroin seizures. Both the test solution and actual heroin seizures were successfully separated using a running buffer containing 50 mM 6-aminocaproic acid adjusted to pH 4.0 with 50 mM MAPS, 5 mM 1-heptanesulfonic acid and 10% acetonitrile. The procedure offers an alternative to micellar electrokinetic chromatographic separations based on charged surfactants in alkaline buffers.     

Membrane-bound conformation of peptaibols with methyl-deuterated alpha-amino isobutyric acids by 2H magic angle spinning solid-state NMR spectroscopy

We present the use of 2H magic-angle spinning (MAS) NMR on methyl-deuterated alpha-amino isobutyric acid (Aib) as a new method to obtain fast and accurate structural constraints on peptaibols in membrane-bound environments. Using nonoriented vesicle-reconstituted samples we avoid the delicate preparation of oriented samples, and the use of MAS ensures high sensitivity and thereby very fast acquisition of experimental spectra. Furthermore, given the high content ( approximately 40%) of Aib in peptaibols and the fact that the amino acid Aib may be synthesized from cheap starting materials, even in the case of 2H, 13C, or 15N labeling, this method is ideally suited for studies of the membrane-bound conformation of peptaibols.     

Supported liquid membranes in hollow fiber liquid-phase microextraction (LPME)--practical considerations in the three-phase mode

In this work, three-phase liquid-phase microextraction (LPME) based on a supported liquid membrane (SLM) sustained in the wall of a hollow fiber was investigated with special focus on optimization of the experimental procedures in terms of recovery and repeatability. Recovery data for doxepin, amitriptyline, clomipramine, and mianserin were in the range of 67.8-79.8%. Within-day repeatability data for the four basic drugs were in the range of 4.1-7.7%. No single factor was found to be responsible for these variations, and the variability was caused by several factors related to the LPME extractions as well as to the final HPLC determination. Although the volume of the SLM varied within 0.4-3.1% RSD depending on the preparation procedure, and the volume of the acceptor solution varied within 4.8% RSD, both recoveries and repeatability were found to be relative insensitive to these variations. Thus, the handling of microliters of liquid in LPME was not a very critical factor, and the preparation of the SLM was accomplished in several different ways with comparable performance. Reuse of hollow fibers was found to suffer from matrix effects due to built-up of analytes in the SLM, whereas washing of the hollow fibers in acetone was beneficial in terms of recovery, especially for the extraction of the most hydrophobic substances. Several of the organic solvents used in the literature as SLM suffered from poor long-term stability, but silicone oil AR 20 (polyphenylmethylsiloxane), 2-nitrophenyl octyl ether (NPOE), and dodecyl acetate (DDA) all extracted with unaltered performance even after 60 days of storage at room temperature.     

Bridging coarse-grained models by jump-in-sample simulations

We present an efficient method to construct coarse-grained (CG) models from models of finer resolution. The method estimates the free energies in a generated sample of the CG conformational space and then fits the entire effective potential surface in the high-dimensional CG conformational space. A jump-in-sample algorithm that uses a random jumping walk in the CG sample is used to iteratively estimate the free energies. We test the method in a tetrahedral molecular fluid where we construct the intermolecular effective potential and evaluate the CG molecular model. Our algorithm for calculating the free energy involves an improved Wang-Landau (WL) algorithm, which not only works more efficiently than the standard WL algorithm, but also can work in high-dimensional spaces.     

Ketene as a Reaction Intermediate in the Carbonylation of Dimethyl Ether to Methyl Acetate over Mordenite

Unprecedented insight into the carbonylation of dimethyl ether over Mordenite is provided through the identification of ketene (CH₂CO) as a reaction intermediate. The formation of ketene is predicted by detailed DFT calculations and verified experimentally by the observation of doubly deuterated acetic acid (CH₂DCOOD), when D₂O is introduced in the feed during the carbonylation reaction.     

Methodological considerations for using thermal analysis in the characterization of soil organic matter

Thermal analysis is primarily used in the field of materials science, but has a long history in the geosciences. Soil organic matter (SOM) has received a great deal of recent scientific interest because of its role in the global carbon cycle. Conventional methods of characterizing SOM quality are unsatisfactory because they do not adequately capture the complete quality continuum that SOM comprises or the various mechanisms that act to stabilize it in the soil matrix. Thermal analysis techniques have the potential to capture this quality continuum, but are dependent on numerous experimental conditions that limit the comparability of results among different studies. Published methodology on thermal analysis of soils and sediments has largely focused on the characterization of the mineral component, while the organic component has received little attention. We tested several experimental conditions for their effects on the exothermic region of curves generated by thermal analysis of easily dispersed soil clay fractions and non-protected light-density particulate organic matter fractions isolated from the surface horizon of a forest soil. Results were found to be highly repeatable but strongly sensitive to crucible material, heating rate, and sample amount, and relatively insensitive to the use of a reference material. Thermal analysis is an important addition to the set of analytical tools used to characterize SOM quality because it provides direct, quantitative information of the energy potentially available for microbial metabolism. However, users will need to balance the needs of specific scientific objectives with the need for standardized methods and comparability between studies.     

Semi‐quantitative and structural metabolic phenotyping by direct infusion ion trap mass spectrometry and its application in genetical metabolomics

The identification of quantitative trait loci (QTL) for plant metabolites requires the quantitation of these metabolites across a large range of progeny. We developed a rapid metabolic profiling method using both untargeted and targeted direct infusion tandem mass spectrometry (DIMSMS) with a linear ion trap mass spectrometer yielding sufficient precision and accuracy for the quantification of a large number of metabolites in a high‐throughput environment. The untargeted DIMSMS method uses top‐down data‐dependent fragmentation yielding MS² and MS³ spectra. We have developed software tools to assess the structural homogeneity of the MS² and MS³ spectra hence their utility for phenotyping and genetical metabolomics. In addition we used a targeted DIMS(MS) method for rapid quantitation of specific compounds. This method was compared with targeted LC/MS/MS methods for these compounds. The DIMSMS methods showed sufficient precision and accuracy for QTL discovery. We phenotyped 200 individual Lolium perenne genotypes from a mapping population harvested in two consecutive years. Computational and statistical analyses identified 246 nominal m/z bins with sufficient precision and homogeneity for QTL discovery. Comparison of the data for specific metabolites obtained by DIMSMS with the results from targeted LC/MS/MS analysis showed that quantitation by this metabolic profiling method is reasonably accurate. Of the top 100 MS¹ bins, 22 ions gave one or more reproducible QTL across the 2 years. Copyright © 2009 John Wiley & Sons, Ltd.     

Highly fluorescent oligothiophenes through the incorporation of central dithieno[3,2-b:2',3'-d]pyrrole units

[structures: see text] Dithieno[3,2-b:2',3'-d]pyrrole-based terthiophene (2a-c) and quaterthiophene (3a-c) analogues have been prepared from dithieno[3,2-b:2',3'-d]pyrrole (1) via Stille coupling utilizing a one-pot method. In comparison to the parent oligothiophenes (T(n), where n = 2-4), the resulting dithieno[3,2-b:2',3'-d]pyrrole-based systems exhibit enhanced fluorescence efficiencies in solution (up to 53%). These new oligomeric systems also allow the incorporation of solubilizing side chains without the negative steric interactions that typically reduce backbone planarity.