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21.
U. Ströle 《Fresenius' Journal of Analytical Chemistry》1955,144(4):256-264
Zusammenfassung Bei der Chromatographie auf Carboxylpapier herrschen definierte Ionenaustauschvorgänge vor, die sich theoretisch näherungsweise ableiten lassen. Durch Variation von Carboxylgehalt und austauschfähigem Kation im Papier, sowie vonph-Wert, Pufferkapazität und Kationenstärke in der entwickelnden Lösung ist es möglich, die für die chromatographische Trennung der drei basischen Aminosäuren günstigsten Bedingungen festzustellen. Es ist zu erwarten, daß sich auf Carboxylpapier weitere, kationenbildende Stoffe trennen lassen, die sich entweder in ihrer Affinität zur Oxycellulose oder in ihrer Basizität oder in beidem voneinander unterscheiden.Die Arbeit wurde durch wertvolle Kritik von Herrn Professor Dr. Th. Wieland gefördert. Wesentliche Anregungen stammen auch von Herrn Dr. W. Vollmer. Im Labor wurden die Chromatogramme sämtlich von Frau E. v. Dungen ausgeführt. 相似文献
22.
Michèle Decouzon Jean-Fraçois Gal Jérôme Gayraud Pierre-Charles Maria Gian-Angelo Vaglio Paolo Volpe 《Journal of the American Society for Mass Spectrometry》1993,4(1):54-57
An accurate gas-phase acidity for germane (enthalpy scale, equivalent to the proton affinity of GeH3 ?), ΔH acid o(GeH4) = 1502.0 ± 5.1 kJ mol?1, is obtained by constructing a consistent acidity ladder between GeH4, and H2S by using Fourier transform-ion cyclotron resonance spectrometry, and 0 and 298.15 K values for the first bond dissociation energy of GeH4 are proposed: D0 o(H3Ge-H) = 352 ± 9 kJ mol?1; D o(H3Ge-H) = 358 ± 9 kJ mol?1, respectively. These results are compared with experimental and theoretical data reported in the literature. Methylgermane was found to be a weaker acid than germane by approximately 35 kJ mol?1: ΔH acid o = 1536.6 kJ mol?1. 相似文献
23.
Hureau C Blondin G Charlot MF Philouze C Nierlich M Césario M Anxolabéhère-Mallart E 《Inorganic chemistry》2005,44(10):3669-3683
Two Mn(II) complexes are isolated and X-ray characterized, namely, cis-[(L(2))Mn(II)(Cl)(2)] (1) and [(L(3))Mn(II)Cl(OH(2))](ClO(4)) (2(ClO(4))), where L(2) and L(3) are the well-known tetradentate N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine and N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)propane-1,3-diamine ligands, respectively. The crystal structure reveals that whereas the ligand L(2) is in the cis-alpha conformation in complex 1, the ligand L(3) is in the more unusual cis-beta conformation in 2. EPR spectra are recorded on frozen solutions for both complexes and are characteristic of Mn(II) species. Electrochemical behaviors are investigated on acetonitrile solution for both complexes and show that cation 2 exists as closely related Mn(II) species in equilibrium. For both complexes exhaustive bulk electrolyses of acetonitrile solution are performed at oxidative potential in various experimental conditions. In the presence of 2,6-lutidine and after elimination of chloride ligands, the formation of the di-mu-oxo mixed-valent complexes [(L(2))Mn(III)(mu-O)(2)Mn(IV)(L(2))](3+) (3a) and [(L(3))Mn(III)(mu-O)(2)Mn(IV)(L(3))](3+) (4) is confirmed by UV-vis and EPR spectroscopies and cyclic voltammetry. In addition crystals of 4(ClO(4))(3) were isolated, and the X-ray structure reveals the cis-alphaconformation of L(3). In the absence of 2,6-lutidine and without elimination of the exogenous chloride ions, the electrochemical oxidation of 1 leads to the formation of the mononuclear Mn(III) complex, namely, [(L(2))Mn(III)(Cl)(2)](+) (5), as confirmed by UV-vis as well as parallel mode EPR spectroscopy and cyclic voltammetry. In the same conditions, the electrochemical oxidation of complex 2 is more intricate, and a thorough analysis of EPR spectra establishes the formation of the binuclear mono-mu-oxo mixed-valent [(L(3))ClMn(III)(mu-O)Mn(IV)Cl(L(3))](3+) (6) complexes. Electrochemical conversion of Mn(II) complexes into mixed-valent Mn(2)(III,IV) oxo-bridged complexes in the presence of 2,6-lutidine is discussed. The role of the chloride ligands as well as that of L(3) in the building of oxo bridges is discussed. Differences in behavior between L(2) and L(3) are commented on. 相似文献
24.
Svetlana Kneevi R. Milai Marjan Veber 《Fresenius' Journal of Analytical Chemistry》1998,362(1):162-166
A procedure was developed for the preconcentration and determination of aluminium and copper in dialysis concentrates at
the ng cm–3 level. The preconcentration was achieved on microcolumns filled with Chelex-100 resin adjusted to a pH of 4.0. Five repetitive
cycles of the sample through the column ensured a sufficient contact time for quantitative retention of aluminium and copper
ions. The retained ions were eluted with HNO3 (0.5 mol dm–3). Aluminium and copper were determined in the eluate by Zeeman ETAAS using the standard addition technique. The procedure
was performed under clean room conditions (class 10,000), The reliability of the results was evaluated by recovery tests,
using dialysis concentrates spiked with aluminium and copper. The recoveries obtained ranged from 86 to 106% for aluminium
and from 92 to 97% for copper. Using the recommended procedure, the LOD of aluminium and copper in dialysis concentrates (preconcentration
factor 2) was found to be 0.5 ng cm–3 and 0.2 ng cm–3, respectively.
Received: 19 December 1997 / Revised: 10 March 1998 / Accepted: 28 March 1998 相似文献
25.
Michle Philoche-Levisalles Claudette Bois Jean-Pierre Clrier Grard Lhommet 《Journal of heterocyclic chemistry》1982,19(3):481-484
The structure of ethyl α-(tetrahydro-2-pyrrolidinylidene) and α-(hexahydro-2-azepinylidene) acetates has been determined from the X-ray crystallographic analysis. The results show that, in a solid state, these compounds exist as β-enaminoesters which have a Z configuration. They also show the presence of intra and intermolecular hydrogen bonding. 相似文献
26.
Z and E N,N,N-trimethylhydrazonium iodides from α,β-unsaturated cyclohexenones are reduced in good yields into saturated aziridines or α,β-unsaturated aziridines by sodium bis (2-methoxy ethoxy) aluminium hydride. Partly hydrolysed hydride leads to reverse proportions of saturated and α,β-unsaturated aziridines. 相似文献
27.
Najiba Douja Raluca Malacea Michle Besson Catherine Pinel 《Journal of molecular catalysis. A, Chemical》2004,210(1-2):205-209
The diastereoselective hydrogenation of 2-methyl nicotinic acid covalently bound to pantolactone was studied over supported metallic catalysts. With this chiral auxiliary, a two-steps reaction was observed with formation of tetrahydropyridine intermediate. The influence of different reaction parameters on the diastereoselectivity of the hydrogenation of pyridine and enamine substrates was studied. 相似文献
28.
Trifluoromethyl aldimines reacted with acetylides in toluene at −78 °C to provide propargyl amines in good yields. From a chiral trifluoromethyl aldimine, the propargyl amines were obtained with excellent diastereoselectivities (de >98%). Trifluoromethyl propargyl amines could be further converted into difluoromethyl imines under basic conditions. 相似文献
29.
Sylviane Sabo Bruno Chaudret Danièle Gervais 《Journal of organometallic chemistry》1985,292(3):411-418
The possibility of making metal—metal bonded heterobimetallic species by metathesis of ruthenium dichlorides with anionic carbonylates is demonstrated by the isolation of MoRu(μ-Cl)(μ-CO)(CO)2(PPh3)2(η-C5H5) (1) and MnRuCl(μ-CO)2(CO)3(μ-dppm)2 (2), obtained by action of [Mo(CO)3(η-C5H5]? on RuCl2(PPh3)3 and of Mn(CO)5? on RuCl2(dppm)2, respectively. In contrast, reaction of Mn(CO)5? with RuCl2(PMe3)4 yielded an ionic species 3 containing the diruthenium cation Ru2Cl3(PMe3)6+. More interestingly, the action of Mn(CO)5? on RuCl2(PPh3)3 resulted in the formation of the unexpected complex MnRu(μ-PPh2)(CO)6(PPh3)2 (4) in which the phosphido group PPh2 bridges the two metals; this process is shown to involve a hydride intermediate, and elimination of a molecule of benzene, both identified in the reaction mixture. 相似文献
30.
Various palladium catalysts promote the addition of hypophosphorous derivatives ROP(O)H(2) to alkenes and alkynes in good yields and under mild conditions. Particularly, Cl(2)Pd(PPh(3))(2)/2 MeLi, and Pd(2)dba(3)/xantphos allow for phosphorus-carbon bond formation instead of transfer hydrogenation. Commercial aqueous solutions of hypophosphorous acid can be employed successfully at ambient temperature. With styrene and terminal alkynes, the regioselectivity (linear versus branched products) can be controlled to some extent with the catalytic system employed. The methodology considerably extends upon previous routes for the preparation of H-phosphinic acids and other organophosphorus compounds. 相似文献