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181.
Letzel MC Decker B Rozhenko AB Schoeller WW Mattay J 《Journal of the American Chemical Society》2004,126(31):9669-9674
Recently a new type of calix[4]arenes has been synthesized via condensation of 2,6-dihydroxypyridine and a number of aldehydes. This type of pyridine[4]arenes forms capsules consisting of two single pyridine[4]arenes. These capsules can incorporate different guest molecules, like carboxylic acids and amides in this case. We proved that the guest acids really are incorporated inside the cavity of the capsules by electrospray mass spectrometry, NMR spectroscopy, and theoretical calculations. 相似文献
182.
183.
In our former investigations, the phenomenon high temperature corrosion (HTC) was described exemplarily on selected materialcoating combinations for blades of stationary gas turbines, mainly in the temperature region of up to 750° C. To answer the question, in which manner higher gas inlet and/or higher material surface temperature would influence the HTC behaviour, a special analytical technique—the integral layer profile analysis—was introduced to ameliorate concentration profile methods. By examining IN 738 LC specimens with CoCrAlY plasma spray coating, stressed by hot gas at 900° C, the limits of this system are shown by explaining the corrosion mechanism; the method is also used for other systems, e.g. U 520 with NiCrAlY coating at 750° C. 相似文献
184.
185.
Sina Escher Wolfgang Giersch Yvan Niclass Grald Bernardinelli Günther Ohloff 《Helvetica chimica acta》1990,73(7):1935-1947
The four possible A/B cis-fused diastereoisomers of Ambrox® have been synthesized and their configurations and conformations established by X-ray and NMR analysis. Only 5β-ambrox (= 1,2,3a,4,5,5β,6,7,8,9,9a,9bα-dodecahydro-3aβ,6,6,9aβ-tetramethylnaphtho[2,1-b]furan; 5 ) has an odor quality comparable to Ambrox®. The 1,3-synperiplanar/diaxial conformation of the substituents at C(8) ( = C(3a)) and C(10) (= C(9a)) has thus been confirmed to be a compulsory structure element for the particular odor. 相似文献
186.
Baldacci A Theurillat R Caslavska J Pardubská H Brenneisen R Thormann W 《Journal of chromatography. A》2003,990(1-2):99-110
γ-Hydroxybutyric acid (GHB), a minor metabolite or precursor of γ-aminobutyric acid (GABA), acts as a neurotransmitter/neuromodulator via binding to GABA receptors and to specific presynaptic GHB receptors. Based upon the stimulatory effects, GHB is widely abused. Thus, there is great interest in monitoring GHB in body fluids and tissues. We have developed an assay for urinary GHB that is based upon liquid–liquid extraction and capillary zone electrophoresis (CZE) with indirect UV absorption detection. The background electrolyte is composed of 4 mM nicotinic acid (compound for indirect detection), 3 mM spermine (reversal of electroosmosis) and histidine (added to reach a pH of 6.2). Having a 50 μm I.D. capillary of 40 cm effective length, 1-octanesulfonic acid as internal standard, solute detection at 214 nm and a diluted urine with a conductivity of 2.4 mS/cm, GHB concentrations ≥2 μg/ml can be detected. Limit of detection (LOD) and limit of quantitation (LOQ) were determined to be dependent on urine concentration and varied between 2–24 and 5–60 μg/ml, respectively. Data obtained suggest that LOD and LOQ (both in μg/ml) can be estimated with the relationships 0.83 κ and 2.1 κ, respectively, where κ is the conductivity of the urine in mS/cm. The assay was successfully applied to urines collected after administration of 25 mg sodium GHB/kg body mass. Negative electrospray ionization ion-trap tandem mass spectrometry was used to confirm the presence of GHB in the urinary extract via selected reaction monitoring of the m/z 103.1→m/z 85.1 precursor–product ion transition. Independent of urine concentration, this approach meets the urinary cut-off level of 10 μg/ml that is required for recognition of the presence of exogenous GHB. Furthermore, data obtained with injection of plain or diluted urine indicate that CZE could be used to rapidly recognize GHB amounts (in μg/ml) that are ≥ 4 κ. 相似文献
187.
188.
One-bond 13C, 13C-spin-coupling constants have been measured, with natural isotope abundance, in η4-diene, η3-allyl and η2-ene transition-metal carbonyl complexes. Typical values of 1J(C,C) are given for Fe-, Ru- and Os-complexes with the three types of olefinic ligands. The effects of substituents and the structural significance of the C,C-coupling constants are discussed. 相似文献
189.
Pentacarbonyl-rhenate and -manganate react with the cationic complexes [cpMo(CO)2(diene)]+, [cpMo(CO)2(cyclopentadiene]+, [cpMo(CO)2(cyclohexadiene)]+, [cpMo(CO)2(trimethylenemethane]+, [(OC)3Mo(η7-C7H7)]+, [cp(OC)-(Ph3P)Mo(alkyne)]+ to give the corresponding heteronuclear hydrocarbon-bridged complexes. 相似文献
190.
Gadolinium dicyanamide dihydrate Gd[N(CN)2]3 · 2 H2O was prepared by ion exchange in aqueous solution followed by evaporation of the solvent at room temperature. Gd[N(CN)2]3 · 2 H2O was characterized by single‐crystal structure analysis, FTIR spectroscopy and DSC analysis. In the crystal there are three crystallographically independent [N(CN)2]? ions and Gd3+ which are coordinated by six N atoms from six different [N(CN)2]? ions and two O atoms from two water molecules forming an irregular quadratic antiprism. Four H bonds have been identified in the structure of Gd[N(CN)2]3 · 2 H2O, two of them running to terminal N atoms and two to the bridging N atoms of dicyanamide ions (Gd[N(CN)2]3 · 2 H2O: P21/n (no. 14), a = 7.4845(15) Å, b = 11.529(2) Å, c = 13.941(3) Å, β = 93.98(3)°, Z = 4, 1948 reflections, 175 parameters, R1 = 0.0493). The DSC analysis indicates that Gd[N(CN)2]3 · 2 H2O looses the crystal water at temperatures around 130 – 140 °C forming anhydrous Gd[N(CN)2]3, the structure of which has been refined by the Rietveld method based on X‐ray powder diffraction data. Gd[N(CN)2]3 was found to be isotypic with Ln[N(CN)2]3 (Ln = La, Ce, Pr, Nd, Sm and Eu) which previously have been described in the literature. 相似文献