Nanoscale separations combined with electrospray ionization mass spectrometry: Sulfonamide determination

Nanoscale capillary liquid chromatography (nCLC) and capillary zone electrophoresis (CZE) have been combined with quadrupole mass spectrometry via an electrospray ionization (ESI) interface. These methodologies have been applied to the separation and determination of a variety of sulfonamides. CZE/ESI/MS is the more rapid and sensitive technique, but nCLC/ESI/MS shows promise for the analysis of dilute samples. Ultimately, the two techniques provide complementary methods of analysis. The detection limits of these techniques in the full-scan mode are in the low picomole range. Dissociation of the sulfonamides can be induced by increasing the skimmer voltage. This provides a limited means of discriminating between compounds of identical molecular weight but, more important, provides fragments that could be used to confirm the presence of analyte within a sample.     

Determination of non-toxic and potentially toxic elements concentration and antioxidant capacity in selected natural and essential oils with high market values

Natural oils (NOs) and essential oils (EOs) are widely used in the food and beverage, medical, aromatherapy and cosmetic industries, but little is known about their elemental composition or antioxidant ability. Microwave-assisted acid digestion and inductively coupled plasma-optical emission spectroscopy were used to determine the non-toxic elements (Al, Ca, Cu, Fe, K, Mg, Na, Se and Zn) and potentially toxic elements (As, Cr, Cd, Mn, Ni and Pb) concentrations in 13 selected NOs and EOs. The per cent recoveries of laboratory-fortified blanks analysed for quality control were 94–110%. The elemental concentrations varied widely in NO and EO samples, as demonstrated by the large standard deviation obtained for some elements. The average levels of non-toxic elements (Al (14.5 ± 3.7 μg/g); Ca (278 ± 138 μg/g); Cu (7 ± 14 μg/g); Fe (16 ± 5 μg/g); K (36 ± 31 μg/g); Mg (56 ± 27 μg/g); Na (266 ± 277 μg/g); Se (0.7 ± 0.3 μg/g) and Zn (6.1 ± 2.6 μg/g)) were determined in NOs and EOs. Comparatively, low levels of potentially toxic elements (As (0.1 ± 0.2 μg/g); Cd (0.1 ± 0.0 μg/g); Cr (0.2 ± 0.1 μg/g); Mn (0.8 ± 0.1 μg/g); Ni (4.5 ± 2.2 μg/g); and Pb (0.3 ± 0.2 μg/g)) were obtained in the oils. Principal component analysis (PCA) revealed that the first two principal components explained 100% of the variability in the elemental concentrations. Na, Ca, Mg and K were the main contributors to PCA. Non-toxic element pairs were strongly correlated (R² > 0.9440) indicating a common source in these oils, but toxic element pairs were poorly correlated. Although toxic element concentrations were low, routine monitoring in oils is recommended. The antioxidant ability of NOs and EOs to potentially reduce free radicals, which are often involved in several degenerative diseases, such as ageing, stroke, diabetes and cancers was determined by DPPH (2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl) free radical scavenging assay and ultraviolet-visible spectroscopy. Jasmine, castor and tea tree lemon oils were the best antioxidants. The oils in this study have the potential to replace artificial antioxidants used in foods, cosmetics and other products.     

Viscoelasticity and self-diffusion in melts of entangled asymmetric star polymers

The crossover from linear to branched polymer dynamics in highly entangled melts was investigated with a series of asymmetric three-arm stars of poly(ethylene-alt-propylene). Two arms of equal length formed a linear backbone, kept constant through the series, while branches of various length were appended as the third arm. The materials were made by carbanionic polymerization of isoprene and the judicious application of chlorosilane linking chemistry. Subsequent saturation of the polymeric double bonds with deuterium and hydrogen, followed by fractionation, led to a set of structurally matched, nearly monodisperse pairs of deuterium-labeled and fully hydrogenous samples. Dynamic moduli were measured over wide ranges of frequency and temperature. With increasing branch length, the resulting master curves evolve smoothly, but with surprising rapidity, from the relatively narrow terminal spectrum of linear polymers to the much broader spectrum of symmetric stars. The viscosity η_o increases rapidly with branch length, and the diffusion coefficient D, obtained by forward recoil spectrometry, decreases even more rapidly. The product η_oD, however, distinguishes the transition from linear to branched polymer dynamics most clearly: for a backbone with about 38 entanglements, the crossover is already approaching completion for a single mid-backbone branch with only about three entanglements. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1943–1954, 1997     

Triple-Helix Formation by Pyrimidine Oligonucleotides Containing Nonnatural Nucleosides with Extended Aromatic Nucleobases: Intercalation from the major groove as a method for recognizing C·G and T · A base pairs

The sequence-specific recognition of double-helical DNA by oligonucleotide-directed triple helix formation is limited primarily to purine tracts. To identify potential lead compounds which are able to extend the sequence repertoire of triple helical complexes, we designed two carbocyclic nucleosides with nucleobases attached via amide bonds. N⁵-[(1R, 2S, 3R, 4R)-3-hydroxy-4-(hydroxymethyl)-2-methoxycyclopentyl]-2-{[(1H-pyrrol-2-yl)carbonyl]-amino}thiazole-5-carboxamide ( L1 ) and 2-benzamido-N⁵-[(1R, 2S, 3R, 4R)-3-hydroxy-4-(hydroxymethyl)-2-methoxycyclopentyl]thiazole-5-carboxamide ( L2 ) were synthesized and incorporated into pyrimidine oligonucleotides. The 2-(trimethylsilyl)ethoxymethyl (SEM) protecting group for the 1H-pyrrole NH was found to be compatible with DNA solid-phase synthesis of pyrimidine Oligonucleotides. By quantitative DNase I footprinting analysis, both nonnatural nucleosides L1 and L2 showed preferential binding of pyrimidine over purine bases: L1 / 2 ·(C·G) ≈ L1 / 2 ·(T · A) > L1 / 2 ·(G·C) ≈ L1 / 2 ·(A · T). Comparison with the previously reported nonnatural nucleosides with extended aromatic nucleobases 1-(2-deoxy-β-D -ribofuranosyl)-4-(3-benzamidophenyl)-imidazole ( D3 ) and N⁴-[6-(benzamido)pyridin-2-yl]-2′-deoxycytidine (^bz M ) suggests that the observed binding selectivity C · G ≈ T · A > G · C ≈ A · T for the nucleoside analogs L1 , L2 , D3 , and ^bz M is derived from sequence-specific intercalation with preferential stacking of their nucleobases over pyrimidine · purine Watson-Crick base pairs.     

A numerical analysis of two point boundary value problem algorithms

The mathematical modeling of optimal control system problems is a method applied in industry to obtain correct electrical and mechanical design parameters once the system equations have been derived. The algorithms required to implement the control loop for these applications must provide stable, relatively accurate, efficient solutions.The purpose of this paper is to address the computational characteristics which would concern a system designer in the consideration of the selection of an effective algorithm to implement a two-point boundary value problem solution. Three Invariant Imbedding Algorithms are evaluated for a worst case and a best case problem by an adaptation of four methods of analysis. The areas of computer science, numerical analysis and Turing Machine Theory are drawn upon in these methods to implement and compare the computational form of the algorithms. The four analysis techniques indicated consistent results for the three two-point boundary value problem algorithms considered. Applications of two-point boundary value problem algorithms occur in problems of nuclear reactor heat transfer, pollution control, fluidics, vibration and magnetics.     

Orientation of peptides in aqueous monolayer films. Infrared reflection-absorption spectroscopy studies of a synthetic amphipathic beta-sheet

Infrared reflection-absorption spectroscopy (IRRAS) intensities of the Amide I vibration are used to develop a quantitative approach for determining the Euler angles that describe the orientation of protein beta-sheets in aqueous monolayer films. A synthetic amphipathic peptide, Val-Glu-Val-Orn-Val-Glu-Val-Orn-Val-Glu-Val-Orn-Val-OH is used as a test case. The pattern of Amide I frequencies suggests that the molecule is organized as an antiparallel beta-sheet at the air/water interface. The model used to simulate the Amide I intensities reveals that the beta-sheet has a slight preferential alignment parallel to the direction of compression; i.e., deviation from uniaxial symmetry is observed. In addition, the sheet is found to lie flat on the aqueous surface, with (presumably) the polar side chains interacting with the aqueous subphase. Limitations and advantages of the theoretical approach are discussed.