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231.
A new method for the determination of the enrichment of [6,6-2H2]-D-glucose in human plasma by gas chromatography-mass spectrometry (GC-MS) is described. (2,3,4,5,6)-Pentakis-O-trimethylsilyl-O-methyloxime-D-glucose is used as a derivative for the GC measurement. Using GC-MS with electron-impact ionization, the enrichment is measured in the single-ion monitoring mode observing the masses m/z 319 and 321. In contrast to other methods the use of this glucose derivative reduced the amount of plasma needed from 200 to 10 microliters and no chemical ionization equipment is needed for the mass spectrometer. 相似文献
232.
Summary Calmagite [1-(1-hydroxy-4-methyl-2-phenyl azo)-2-naphthol sulphonic acid], dissociates in two steps. It forms violet complexes with Al3+, Ga3+ and In3+. The stepwise proton-ligand stability constants of calmagite and stepwise metal-ligand stability constants of these complexes were evaluated by potentiometric titration technique ofBjerrum andIrving andRossotti. The order of the stabilities of complexes is In3+ > Ga3+ > > Al3+.
Zusammenfassung Camalgit [1-(1-Hydroxy-4-methyl-2-phenylazo)-2-naphtholsulfonsäure] dissoziiert in zwei Stufen und bildet violette Komplexe mit Al(III), Ga(III) und In(III). Die Konstanten der Dissoziationsstufen der freien Säure und die der Metallkomplexe wurden potentiometrisch nachBjerrum bzw.Irving undRossotti ermittelt. Die Stabilität der Komplexe nimmt in der Reihe In(III) > Ga(III) > Al(III) ab.相似文献
233.
The values of ΔG, ΔH and ΔS for the formation of the mixed 1:1:1 lanthanide EDTA complexes with the anions of 8-hydroxyquinoline-5-sulfonic acid, iminodiacetic acid and nitrilotriacetic acid were determined by pH-titrations and a direct calorimetric method. These thermodynamic data are discussed and compared with those for the formation of the Ln(III)EDTA complexes. Contrary to current opinion it is concluded that all trivalent lanthanide aquoions have the same coordination number in dilute solution. However, in the series of the lanthanide EDTA complexes the coordination number changes between Sm and Tb. In this region, equilibria occur between two types of EDTA complexes with different numbers of coordinated water molecules: The corresponding equilibrium constants could be evaluated. The coordination number changes also in many other Ln complexes along the lanthanide series, and similar equilibria occur. 相似文献
234.
Rate constants, k(ArOH/dpph*)(S), for hydrogen atom abstraction from 13 hindered and nonhindered phenols by the diphenylpicrylhydrazyl radical, dpph*, have been determined in n-heptane and a number of alcoholic and nonalcoholic, hydrogen-bond accepting solvents. Abnormally enhanced k(ArOH/dpph*)(S) values of have been observed in alcohols. It is proposed that this is due to partial ionization of the phenols and a very fast electron transfer from phenoxide anion to dpph*. The popular assessment of the antioxidant activities of phenols with dpph* in alcohol solvents will generally lead to an overestimation of their activities. 相似文献
235.
Vrouwe EX Gysler J Tjaden UR van der Greef J 《Rapid communications in mass spectrometry : RCM》2000,14(18):1682-1688
A sheathless and electrodeless nanospray interface has been used to interface a polycarbonate capillary electrophoresis (CE) chip to a mass spectrometer (MS). The chip was made of two flat polycarbonate plates which were bolted together. Channels were imprinted in one of the plates with metal wires, using a hydraulic press. A short tapered capillary connected to the chip was used as the nanospray emitter. The advantage of this electrodeless interface is that it was not necessary to apply a electrospray voltage to the chip or the nanospray emitter. Instead, the CE voltage already applied to the buffer compartment on the chip, to drive the electrophoresis, was used to generate the spray also. A low conductivity buffer of 1.25 mmol/L ammonium acetate in 80% methanol was used to obtain a large electric field across the buffer channel. The performance of the device was evaluated by analyzing a mixture of three beta-agonists Relative standard deviation (RSD) values obtained were between 4.8 and 5.0%. A sample concentration of 40 nmol/L resulted in a signal-to-noise ratio of 2 to 5 for the different components. Compared to a conventional CE analysis in a fused silica capillary with UV detection, only a minor loss of resolution was observed, which can be attributed to the design of the chip. 相似文献
236.
α-Methyl and α-phenyl substituted 2 and 4-styrylpyridines were prepared by classical routes. The geometrical isomers were separated and characterized on the basis of their U.V. absorption spectra and/or of their behaviour under U.V. irradiation which led to photoisomerization and photocyclization products. The last photoreaction, in the case of α-phenyl derivatives, gave pyridyl-substituted phenanthrenes and phenyl-substituted azaphenanthrenes which were isolated and characterized. Spectral, chromatographic and physical properties of trans and cis derivatives and related photocyclization products are given as well as some kinetic data for the photochemical reactions. 相似文献
237.
The stereoselectivity of the α-alkylation of chiral β-hydroxy ester is discussed. The configuration of the alkylated product was proved chemically (Scheme 2). A one pot aldol-alkylation reaction was developed leading stereoselectively to racemic (s*,s*)-α-alkyl-β-hydroxy ester (Scheme 3,4). Baker's yeast reduction of 2-alkyl-3-keto ester led to valuable chiral (2RS,3S)-intermediates, which were converted via the corresponding dianion to compounds with a chiral quaternary C atom (Scheme 6). Synthetic applications of the above findings are shown in the synthesis of various chiral compounds (Scheme 8 and 9). 相似文献
238.
U. Burkert 《Tetrahedron》1977,33(17):2237-2242
The treatment of oxygen lone pairs in force field calculations is discussed. The geometries of 1,3-dioxanes can be calculated well without explicit account of lone pairs. For the calculation of conformational energies in 5-alkyl-1,3-dioxanes electrostatic interactions between point charges taken from quantum mechanical calculations must be included. Addition of van der Waals interactions of lone pairs as weak potentials further improves the calculated conformational energies. 相似文献
239.
240.
U. K. Chakrabarti S. J. Pearton W. S. Hobson C. R. Abernathy 《Plasma Chemistry and Plasma Processing》1993,13(2):333-350
Vinyl iodide (C2H3I) microwave discharges with additions of H2 and Ar are found to provide faster etch rates than conventional CH4/H2/Ar discharges for InP, InGaAs, GaAs, and AlGaAs. This is a result of the relatively high volatilities of indium, gallium, and aluminum iodide species. The etched features are smooth and anisotropic over a wide range of do self-biases (–150 to –350 V), process pressures (1–20mTorr), and microwave powers (150–500 W). The polymer that forms on the mask during the plasma exposure can be readily removed in O2 discharges. Electron spectroscopy for chemical analysis (ESCA) showed that the etched surfaces are slightly deficient in the group V elements under most conditions, but changes to the optical properties of the semiconductors are minimal. No defects are visible by transmission electron microscopy (TEM) in GaAs or InP samples etched at dc biases –250 V. 相似文献