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971.
Hanne?Heiberg Odd?GropenEmail author Jon K.?Laerdahl Ole?Swang Ulf?Wahlgren 《Theoretical chemistry accounts》2003,110(3):118-125
Different density functional theory (DFT) functionals have been evaluated by studying geometries and bond strengths of YbH, YbF, EuF, GdF, and NdF and compared with accurate CCSD(T) results and, when available, experiment. The agreement between the CCSD(T) results and experiment, when available, is good. The agreement is also good between bond strengths calculated at the DFT level using relativistic effective core potentials and the CCSD(T) results. However, the all-electron ADF calculations systematically overestimate binding energies. The geometries obtained by both the all-electron and the effective-core-potential-based DFT calculations are generally in good agreement with the CCSD(T) results.Contribution to the Björn Roos Honorary Issue 相似文献
972.
The π-π stacking interactions between maleimide's and nitrone's aromatic rings during the 1,3-dipolar cycloaddition were assumed to control the exo-endo selectivity of the reaction. The exo-endo ratios change during the reactions until they reach a constant value, which depends on the substituent. Electron-withdrawing groups favour the exo adduct while electron-donating groups favour the endo adduct. The nitrone ZnBr2 complexes react much more slowly than the free nitrone and the cycloaddition is exo selective in all cases independent of the substituents on the maleimide's aromatic ring. Thermal retrocycloaddition of the cycloadducts produce the corresponding nitrones. The ring opening in the presence of secondary amines did not induce imine formation. endo Adducts were shown for the first time to be the stable paramagnetic compounds. 相似文献
973.
Andreas?HeintzEmail author Dagmar?Klasen Jochen?K.?Lehmann Christiane?Wertz 《Journal of solution chemistry》2005,34(10):1135-1144
Experimental densities were measured for the system 1-methyl-3-octyl-imidazolium tetrafluoroborate [OMIM][BF4] + butan-1-ol, + pentan-1-ol at 298.15 K and ambient pressure using a vibrating tube densimeter, taking into account the
influence of the viscosity correction. Excess molar volumes VE have been determined. VE is quite small and negative in the alcohol-rich range of the mixture composition and positive in the alcohol-poor range.
LLE data of [OMIM][BF4] + pentan-1-ol have been measured using a laser light scattering cell for detecting cloud points at different compositions
in the temperature range of 282–292 K. A miscibility gap with an upper critical solution temperature (UCST) of 292 K has been
found. 相似文献
974.
Vítězslav Zima Jan Svoboda Klára Melánová Ji?í Dybal 《Journal of solid state chemistry》2007,180(3):929-939
Several new strontium 4-carboxyphenylphosphonates, i.e., two modifications of Sr(HOOCC6H4PO3H)2, SrH(OOCC6H4PO3)·H2O, Sr3(OOCC6H4PO3)2·4H2O and Sr3(OOCC6H4PO3)2·5.7H2O were prepared and characterized by elemental analysis, thermogravimetry, X-ray powder diffraction and infrared spectroscopy. It was found that the compositions of these compounds depend on the acidity of the reaction medium. In addition, the presented compounds are interconvertible in dependence on pH. The position of the acid hydrogen atom in SrH(OOCC6H4PO3)·H2O was determined from the IR spectra of the studied compounds.The structure of the β modification of Sr(HOOCC6H4PO3H)2 was solved from its X-ray powder diffraction pattern using an ab initio method (the FOX program) with subsequent Rietveld refinement in the FULLPROF program. The compound is monoclinic, with the space group P21/c (No. 14), a=49.88(2), b=7.867(2), c=5.602(3) Å, β=128.68(2)°, and Z=4. It has a one-dimensional structure with an inorganic part built of SrO8 distorted tetragonal antiprisms. 相似文献
975.
Barro R Ares S Garcia-Jares C Llompart M Cela R 《Analytical and bioanalytical chemistry》2005,381(1):255-260
A combination of sorbent enrichment and ultrasound-assisted solvent extraction has been used to determine polychlorinated biphenyls in air. Analytes were sampled by pumping a known volume of air through a porous polymer (Tenax TA). The enriched adsorbent was transferred into a glass vial, and ultrasound-assisted extraction of the analytes was then performed in n-hexane. Quantification was carried out by using gas chromatography coupled to tandem mass spectrometry. Breakthrough volume of the sampling step was studied, indicating that 10 m3 of air could be processed without losses of the most volatile compounds. Good recoveries (75–96%) were obtained, and limits of detection at the sub ng m–3 were achieved for all the analytes. The proposed method is very simple and fast, avoiding the use of large solvent volumes and time-consuming preconcentration steps. 相似文献
976.
Stereoselective synthesis of cruciferous indole phytoalexin (R)-(+)-1-methoxyspirobrassinin and its unnatural (S)-(−)-enantiomer was achieved by spirocyclization of 1-methoxybrassinin in the presence of (+)- and (−)-menthol and subsequent oxidation of the obtained menthyl ethers. Methanolysis of menthyl ethers in the presence of TFA afforded (2R,3R)-(−)-1-methoxyspirobrassinol methyl ether as well its unnatural (2S,3S)-, (2R,3S)-, and (2S,3R)-isomers. 相似文献
977.
Rodrigues e Silva AA da Silva Góes AJ de Lima WT de Souza Maia MB 《Chemical & pharmaceutical bulletin》2003,51(12):1351-1355
The search for new anti-inflammatory drugs has been constant in several research centers. The use of the Bioisostery concept allows the elaboration of new bioactive compounds with different properties through the introduction of substitute groups in one or more positions of a main molecule with known biological activity. Preliminary works accomplished at our laboratory with 2,4-thiazolidinedione isosters demonstrated inhibitory activity on edema formation for N-tryptophyl-5-(3,5-di-tert-butyl-4-hydroxybenzylidene)-2,4-thiazolidinedione (GS28) and N-tryptophyl-5-(3,5-di-tert-butyl-4-hydroxybenzylidene) rhodanine (GS26). We verified the antiedematogenic and ulcerogenic activity of these two compounds in Wistar rats. The carrageenan induced paw edema suffered significant (p<0.05) inhibition (28.36% on average) for GS28 (100 mg/kg; v.o.) during the entire time of the experiment. GS26 (50 and 100 mg/kg; v.o.) significantly inhibited (p<0.05) the paw edema dextran induced (22.1 and 27.8%, for the respective doses) after 180 min. The compounds GS26 and GS28 did not show ulcerogenic activity on gastric mucous. The results suggest antiedematogenic action for both compounds without the appearance of gastric lesions. 相似文献
978.
A reversed-phase LC–MS method with quadrupole-time of flight (QTOF) detection has been developed for the determination of four dinitro-toluenesulfonic acids and two amino-nitro-toluenesulfonic acids in groundwater. The analytes were separated by HPLC with 0.1% (v/v) formic acid as mobile phase modifier compatible with mass spectrometric detection. QTOF-MS analysis with negative ion electrospray ionization afforded good selectivity and sensitivity for analysis of the dinitro- and amino-nitro-toluenesulfonic acids. Structure elucidation and confirmation were accomplished by tandem mass spectrometry. Characteristic ions resulting from the loss of NO, NO2, and SO2 from the [M–H]– ions were detected. An intense fragment ion at m/z 80 representing the [SO3]– ion was detected for all dinitro- and amino-nitro-toluenesulfonic acids. Solid-phase extraction using a co-polymer cartridge was developed for preconcentration of the analytes from water. Good recovery (>85%) was achieved when 0.1% formic acid was added into the water samples before extraction. Method detection limits ranged from 10 to 76 ng L–1 for the targeted compounds when 10 mL water was analyzed. Groundwater samples collected from wells close to a former ammunition plant in Stadtallendorf, Germany, were analyzed for the dinitro- and amino-nitro-toluenesulfonic acids. 相似文献
979.
This work utilizes on-column ligand synthesis and affinity capillary electrophoresis (ACE) to determine binding constants (Kb) of 9-flourenylmethyloxy carbonyl (Fmoc)-amino acid derivatives to the glycopeptide antibiotics ristocetin (Rist) and teicoplanin (Teic). In this technique, two separate plugs of sample are injected on to the capillary column and electrophoresed. The initial sample plug contains a d-Ala-d-Ala terminus peptide and either one or two non-interacting standard(s). The second plug contains a Fmoc-amino acid-N-hydroxysuccinimide (NHS) ester. The electrophoresis is then carried out with an increasing concentration of Rist or Teic in the running buffer. Upon electrophoresis the initial d-Ala-d-Ala peptide reacts with the Fmoc-amino acid yielding a new Fmoc-amino acid-d-Ala-d-Ala peptide derivative. Continued electrophoresis results in the binding of Rist or Teic to the Fmoc-amino acid-d-Ala-d-Ala peptide derivatives. Analysis of the change in the relative migration time ratio (RMTR) or electrophoretic mobility () of the Fmoc-amino acid-d-Ala-d-Ala peptide derivatives relative to the non-interacting standards, as a function of the concentration of Rist and Teic, yields a value for
Kb. These findings demonstrate the advantage of coupling on-column ligand synthesis to ACE for estimating binding parameters between antibiotics and ligands.Abbreviations Rist
Ristocetin
- Teic
Teicoplanin
- ACE
Affinity capillary electrophoresis
- RMTR
Relative migration time ratio 相似文献
980.
Tuncer??aykaraEmail author Recai??nam Zülfiye??ztürk Olgun?Güven 《Colloid and polymer science》2004,282(11):1282-1285
The formation of metal complexes between water-soluble polymers, poly(vinyl alcohol) [PVA], poly(N-vinylpyrrolidone) [PVP], poly(acrylamide) [PAAm] and poly(ethylene oxide) [PEO] with trivalent metal ions, Fe3+, Cr3+, and V3+ were studied by using differential pulse polarography (DPP). The general experimental observation is the shift of totally reversible reduction peaks (M3++Hg+e–M2++Hg) towards more negative potentials when the complexing water-soluble polymers are added to the solution of trivalent metal ions. The negative shift in potential permitted the determination of complex formation constants (Kf) between trivalent metal ions and water soluble polymers. The complex formation constants for Fe3+, Cr3+, and V3+ ions with these polymers increased in the order of V3+>Cr3+>Fe3+. 相似文献