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排序方式: 共有392条查询结果,搜索用时 15 毫秒
31.
Giuseppe Gattuso Sebastiano Pappalardo Melchiorre F. Parisi Ilenia Pisagatti 《Supramolecular chemistry》2014,26(7-8):597-600
The molecular recognition in water of neurotransmitter monoamine and trace amine hydrochlorides by p-tert-butylcalix[5]-arene 1 – bearing 4-sulphonatobutoxy groups at the lower rim – has been investigated. According to 1H NMR measurements, the hydrophobic cavity of receptor 1 best binds tyramine hydrochloride, Ka = 5370 ± 870 M? 1. 相似文献
32.
33.
Giuseppe Ronsisvalle Francesco Bottino Sebastiano Pappalardo 《Magnetic resonance in chemistry : MRC》1980,14(5):344-348
The stereochemistry in solution of three octathia[2.2.2.2]metacyclophanes has been investigated by means of 1H NMR spectroscopy. The results lead to the conclusion that the saddle or crown conformation is preferred for these compounds, depending on the substitution pattern of the constituent aromatic rings. 相似文献
34.
Bianco A Guiso M Ballero M Foddai S Nicoletti M Piccin A Serafini M Tomassini L 《Natural product research》2004,18(3):241-246
During our systematic study on the species of genus Linaria (Scrophulariaceae) present in Italy, we examined the glycosidic fraction of Linaria capraria Moris et De Not., a species endemic of Tuscany archipelago. This fraction is particularly complex and we considered in this article only the medium polarity components. In accordance with previous studies, L. capraria shows acyl derivatives of antirrhinoside 1 as specific chemotaxonomic iridoidic markers. L. capraria exhibits a complex composition, with regard to iridoidic constituents, with several chromatographic problems to be resolved. We then isolated, besides the known antirrhinoside 1, two acyl derivatives of antirrhinoside, the 6'-O-senecioyl derivative, 2, and the 6'-O-angeloyl derivative, 3. In addition a glucoside of an acyclic monoterpene, 4, was also isolated, which may be correlated to the other monoterpenic glycosides isolated from other species of Scrophulariaceae. 相似文献
35.
Leveque J Moucheron C Kirsch-De Mesmaeker A Loiseau F Serroni S Puntoriero F Campagna S Nierengarten H Van Dorsselaer A 《Chemical communications (Cambridge, England)》2004,(7):878-879
The first ligand-cored dendrimer based on branching Ru(II) centers and containing mixed polypyridine bridging ligands has been prepared; redox experiments suggest that the redox-active core is not reduced at the expected potential, probably as a consequence of shielding induced by the rigid dendritic array. 相似文献
36.
We address the problem of observables in generally invariant spacetime theories such as Einstein’s general relativity. Using
the refined notion of an event as a “point-coincidence” between scalar fields that completely characterise a spacetime model,
we propose a generalisation of the relational local observables that does not require the existence of four everywhere invertible
scalar fields. The collection of all point-coincidences forms in generic situations a four-dimensional manifold, that is naturally
identified with the physical spacetime. 相似文献
37.
Let ℱ be a local net of von Neumann algebras in four spacetime dimensions satisfying certain natural structural assumptions.
We prove that if ℱ has trivial superselection structure then every covariant, Haag-dual subsystem ℬ is of the form ℱ1
G
⊗I for a suitable decomposition ℱ=ℱ1⊗ℱ2 and a compact group action. Then we discuss some application of our result, including free field models and certain theories
with at most countably many sectors.
Received: 26 January 2000 / Accepted: 28 September 2000 相似文献
38.
Magno Aparecido Gonçalves Trindade Maria Valnice Boldrin Zanoni Frank‐Michael Matysik 《Electroanalysis》2010,22(9):955-962
This paper describes an analytical method using high‐performance liquid chromatographic (HPLC) separation coupled with electrochemical detection to detect three dyes, Solvent Blue 14 (SB‐14), Solvent Blue 35 (SB‐35) and Solvent Red 24 (SR‐24). The dyes were eluted and separated using a reversed‐phase column (C‐8) under isocratic elution with the mobile phase containing a mixture of acetonitrile/ammonium acetate (5.0 mmol L?1) at the ratio of 75 : 25 (v/v). Two sample pretreatment methods were tested and successfully applied to quantify SB14, SB‐35 and SR‐24 dyes in gasoline samples. The proposed method was simple, fast and suitable to detect and quantify marker dyes in gasoline sample at low concentration. 相似文献
39.
A calix[4]arene derivative has been anchored to carboxyl CPG and TentaGel supports by an easily cleavable ester bond and DMT groups allow a simple loading evaluation via UV-vis spectroscopy. The loading of the calixarene on TentaGel resin has also been estimated by HR-MAS NMR experiments. The potential of the polymer supported calixarenes (9 and 10) in solid phase synthesis has been tested by condensation of four thymine nucleotide units onto the upper rim of the calix[4]arene skeleton. 相似文献
40.
Commercial preparations of S‐adenosylmethionine (SAM) when analyzed in uncoated capillaries show a minute impurity believed to be decarboxylated (dc) SAM. By using two types of cationic coatings, thus reducing the electro‐endo‐osmotic flow (EOF), it was possible to separate this impurity into two diastereoisomers of dcSAM. The coatings evaluated for this purpose were: (i) N‐methylpolyvinylpyridinium, used under reversed EOF at acidic conditions (pH 4.0) and (ii) deposition of divalent barium at alkaline pH values (pH 9.4), providing reduced EOF. Under these conditions, it was possible to separate this impurity into two diastereoisomers, which by chemical synthesis were indeed proven to be dcSAM. It was further demonstrated that, in the alkylation of 5′‐methylthioadenosine by 3‐bromopropylamine in bromidric acid to dcSAM, another minute impurity was present, proven, via mass spectrometry, to consist of S‐(5′‐adenosyl)‐3‐thiopropylamine (decarboxylated and demethylated (dc‐SAH)). The LOD for the two dcSAM diastereoisomers was assessed as 17.5 μg/mL and their LOQ as 25.5 μg/mL. By the barium‐based protocol it was possible to quantify the dcSAM, present in a commercial sample of SAM, as a 0.1% impurity. 相似文献