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31.
Test‐Strip‐Based Fluorometric Detection of Fluoride in Aqueous Media with a BODIPY‐Linked Hydrogen‐Bonding Receptor
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Dr. Pichandi Ashokkumar Dr. Hardy Weißhoff Dr. Werner Kraus Dr. Knut Rurack 《Angewandte Chemie (International ed. in English)》2014,53(8):2225-2229
The measurement of biologically relevant anions, such as fluoride, is an important task in analytical chemistry, in particular, for dental health and osteoporosis. Although a large number of fluoride probes are known, the applicability under relevant conditions is limited to a few examples. To improve this situation, BODIPY‐amidothiourea dyes with varying hydrogen‐bond donating strengths were developed, the most H‐acidic of which ( 1 c ) could detect F? from an inorganic source (NaF) in 50 % aqueous solution (DMSO/water 1:1, v/v) with 0.01 ppm sensitivity through selective fluorescence quenching by a photoinduced electron‐transfer (PET) process. Use of the probe and a reference dye with a test‐strip assay and a portable and rapidly recording lateral‐flow fluorescence reader made determination of F? in neat aqueous solutions, such as spiked water samples and toothpaste extracts, possible in a self‐referenced manner, achieving a detection limit of 0.2 ppm. 相似文献
32.
Knut Bakke Claudio Furtado J. R. Nascimento 《The European Physical Journal C - Particles and Fields》2009,60(3):501-507
We investigate the relativistic and non-relativistic quantum dynamics of a neutral spin-1/2 particle subject to an external
electromagnetic field in the presence of a cosmic dislocation. We analyze the explicit contribution of the torsion in the
geometric phase acquired in the dynamics of this neutral spinorial particle. We discuss the influence of the torsion in the
relativistic geometric phase. Using the Foldy–Wouthuysen approximation, the non-relativistic quantum dynamics is studied and
the influence of the torsion on the Aharonov–Casher and He–McKellar–Wilkens effects are discussed.
An erratum to this article can be found at 相似文献
33.
34.
Theodore R. Lundquist 《Surface science》1979,90(2):548-556
Despite its great sensitivity, the usefulness of secondary ion mass spectrometry (SIMS) for many applications has been limited by an inadequate understanding of the probability of sputtering an atom in an ionized state. To determine this ionization probability for clean Cu and Ni surfaces, I have measured the energy distribution of sputtered neutrals and ions by quadrupole mass filtering and retarding potential analysis using potential modulation differentiation. Analysis of sputtered neutrals was accomplished by electron impact ionization. Because the neutrals outnumber the ions by at least two orders of magnitude, the ratio of sputtered ions to neutrals is an accurate measure of the ionization probability. For energies below 20 eV the dependence of the ionization probability on energy goes as P(E) α En, where n = 0.65 for clean Cu. The absorption of oxygen on the Cu surface increases the total ion yield while causing a reduction in the value of the exponent n. Similar results are found for nickel, where n = 0.54 for the clean surface. 相似文献
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37.
Michael J. Cook Ghoabad Ghaem-Maghami Festus Kaberia Knut Bergesen 《Magnetic resonance in chemistry : MRC》1983,21(5):339-343
1H NMR Parameters are reported for five 1,4-dithiepan-6-ones. 1,4-Dithiepan-6-one 1-oxide exists in solution as an equilibrium involving two different twist-chair conformations, which contrasts with its conformational behaviour in the solid state. Twist-chair conformers are also adopted by other members of the series, the favoured form varying with ring substitution. The S?O bond in 1,4-dithiepan-6-one 1-oxide and in its 5,5-dimethyl analogue exhibit a preference for the pseudoaxial site. 相似文献
38.
For three target proteins with different binding pocket characteristics (size and shape, hydrophobicity, hydrogen-bonding) a structure-based validation of the translationally and rotationally invariant 3D-QSAR technique MaP is performed (MaP: Mapping Property distributions of molecular surfaces). The structure-based validation procedure comprises two steps: first, QSAR models are derived without using the information of the target protein. Second, the models are back-projected into the crystal structure of the binding pockets and interpreted. It is demonstrated that MaP is able to identify characteristics important for ligand binding in the cases studied here. Moreover, it is demonstrated that MaP is a versatile 3D-QSAR technique since good, predictive models could be obtained for all three data sets showing distinct characteristics. 相似文献
39.
The use of custom-made solid-phase microextraction (SPME) fibers coated with a perfluorosulfonated ionomer, Nafion, was investigated for nitrogen isotopic analysis of ammonium in aqueous solutions. Aqueous ammonium was converted to ammonia by addition of a base, followed by absorption from the headspace, desorption in the injection port of a gas chromatograph, and analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Fibers coated with a Nafion tubing were chosen due to a higher fiber-gas distribution constant and a higher Nafion thickness than fibers coated with Nafion solution, both leading to a higher amount of ammonia absorbed at equilibrium. The Nafion membrane-coated fiber absorbed approximately 20 times more than a commercial polydimethylsiloxane (PDMS) fiber. The isotopic fractionation between fiber and gas was 1.0117 +/- 0.0009 (standard deviation, SD, of all measurements) at an initial ammonia gas concentration of 21-210 microM. At 390 microM initial gas concentration it was slightly lower. When sampling from liquid samples, an ammonium concentration of 10 mM was needed to obtain a sufficient amount of ammonia absorbed. Modeling of the absorption at different temperatures showed that the absorption was approximately constant in the temperature range suitable for SPME experiments. Absorption at room temperature was therefore used for simplicity. A pilot study was conducted in which absorption was achieved from a single 9 microL droplet of sample. The preliminary results showed that delta(15)N analysis was possible for only 0.4-0.5 micromol of ammonium with a SD of 0.8 per thousand (n = 5). 相似文献
40.
Rolf Stomberg Shiming Li Knut Lundquist Ulf Norinder 《Journal of chemical crystallography》2001,31(6):321-328
The conformations of stereoisomers of -arylcinnamic acids and their esters are discussed based on crystal structures of the E and Z forms of 2,3-bis(3,4-dimethoxyphenyl)propenoic acid and its methyl ester. In the E forms of the cinnamic acid and the cinnamic acid ester, the plane of the -aryl substituent is approximately perpendicular to that of the rest of the molecule. In the Z forms the plane of the carboxyl or methoxycarbonyl group is approximately perpendicular to that of the ethylenic group, and both the aromatic group planes are significantly twisted out of the ethylenic group plane. Crystal structures of methyl (E)-2,3-bis(3,4-dimethoxyphenyl)propenoate (space group P21/n with a = 8.1697(5), b = 11.3882(9), c = 19.7766(9) Å, = 90.058(4)°, V = 1840.0(2) Å3, and Z = 4), monoclinic methyl (Z)-2,3-bis(3,4-dimethoxyphenyl)propenoate (space group P21/n with a = 11.183(2), b = 5.640(2), c = 29.737(7) Å, = 99.19(2)°, V = 1851.4(9) Å3, and Z = 4), and orthorhombic methyl (Z)-2,3-bis(3,4-dimethoxyphenyl)propenoate (space group P212121 with a = 8.849(4), b = 24.288(9), c = 8.734(3) Å, V = 1877(1) Å3, and Z = 4) are reported. 相似文献