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911.
Summary For the separation of mixed rare earth (RE) nitrates by Craig-distribution between nitric acid and tri-n-butylphosphate an improved apparatus was used: 200 elements (tubes) and automatic operation instead of 160 elements and operation by hand. A comparison of the separation was made and the efficiency characterised by the practical separation coefficients
eff
and the effective distribution numbern. The new apparatus yielded a better separation of the same quantity ofRE-nitrates or the same separation of a bigger quantity. The conditions seem especially apted for the separation of the heavier yttrium earths. 相似文献
912.
Hans-Joachim Mai Frank Weller Kurt Dehnicke Ccilia Maichle-mssmer Joachim Strhle 《无机化学与普通化学杂志》1994,620(5):851-855
The Crystal Structures of Triphenylarsin-p-toluene Sulfonylimine and of its Donor-Acceptor Complex [ZrCl4(Ph3AsNSO2Tol)]2 The molecular structures of the title compounds are reported. In the donor-acceptor complex [ZrCl4(Ph3AsNSO2Tol)]2 the zirconium atoms are bridged by the oxygen atoms of the triphenylarsin-p-toluene sulfonylimine molecules, forming a centrosymmetric dimer with a puckered Zr2O4S2 eight-membered ring in the chair conformation. Ph3AsNSO2Tol: Space group P1 , Z = 2, structure determination with 4 010 observed unique reflections, R = 0.036. Lattice dimensions at 19°C: a = 897.52(4), b = 1 071.82(6), c = 1 337,49(5) pm, α = 110.280(4)°, β = 98.814(4)°, γ = 109.872(4)°. [ZrCl4(Ph3AsNSO2Tol)]2: Space group P21/n, Z = 4, structure determination with 3 762 observed unique reflections, R = 0.078. Lattice dimensions at ?60°C: a = 1 387.3(4), b = 1 434.9(2), c = 1 404.7(4) pm, β = 92.71(1)°. 相似文献
913.
Morcombe CR Gaponenko V Byrd RA Zilm KW 《Journal of the American Chemical Society》2004,126(23):7196-7197
A new solid-state NMR method is described for obtaining long-range distance constraints in nanocrystalline samples of 13C-, 15N-, and 2H-enriched protein. The method selects only those 13C or 15N nuclei close to 1Hs for dipolar recoupling. When used with extensive deuteration, the bath of abundant 13C spins is made to appear dilute. Contacts over 4.5 A are readily observed in human ubiquitin. 相似文献
914.
Summary On addition of oxidizable organic substances to molten rare earth nitrates reaction takes place with evolution of nitric oxides and formation of basic nitrates, the two-step hydrolysis of which results in effective enrichment of heavy yttrium earths (YE) from rare earth mixtures in kg-quantities. Using methanol as reducing agent the reaction takes place at 160°C, much lower than using the method of purely thermal decomposition. In both methods after the first hydrolysis step a productYE(OH)1.5(NO3)1.5·H2O can be isolated. 相似文献
915.
Takehiko Nishio Peter Mathies Kurt Job Bruno Frei Oskar Jeger 《Helvetica chimica acta》1989,72(5):943-951
Photo-oxygenation of (E)-7-methyl-β-ionone ((E)? 1 ) and (E)-8-methyl-β-ionone ((E)? 2 ) gave rise to the formation of the hydroperoxy-enones (E)? 10 and (E)? 15 , respectively, which, in part, underwent intramolecular epoxidation to the hydroxy-epoxy-ketones 11 and 16 , respectively, The product distribution of the photo-oxidation of (Z)? 1 shows a marked influence of the skewed ground-state conformation of the dienone chromophore. Thus, singlet oxygen (1O2) was added to C(γ) of the dienone chromophore leading to the spirocyclic peroxy-hemiacetal 12 and to the endoperoxide 13 . In addition, the tricyclic peroxide 14 was formed as a new type of product via primary addition of 1O2 to C(γ) of the dienone chromophore. The structure of 14 was established by X-ray crystal-structure analysis of the hemiacetal 22 . 相似文献
916.
The racemic spirosesquiterpenes β-acorenol ( 1 ), β-acoradiene ( 2 ), acorenone-B ( 3 ) and acorenone ( 4 ) (Scheme 2) have been synthesized in a simple, flexible and highly stereoselective manner from the ester 5 . The key step (Schemes 3 and 4), an intramolecular thermal ene reaction of the 1,6-diene 6 , proceeded with 100% endo-selectivity to give the separable and interconvertible epimers 7a and 7b . Transformation of the ‘trans’-ester 7a to (±)- 1 and (±)- 2 via the enone 9 (Scheme 5) involved either a thermal retro-ene reaction 10 → 12 or, alternatively, an acid-catalysed elimination 11 → 13 + 14 followed by conversion to the 2-propanols 16 and 17 and their reduction with sodium in ammonia into 1 which was then dehydrated to 2 . The conversion of the ‘cis’-ester 7b to either 3 (Scheme 6) or 4 (Scheme 7) was accomplished by transforming firstly the carbethoxy group to an isopropyl group via 7b → 18 → 19 → 20 , oxidation of 20 to 21 , then alkylative 1,2-enone transposition 21 → 22 → 23 → 3 . By regioselective hydroboration and oxidation, the same precursor 20 gave a single ketone 25 which was subjected to the regioselective sulfenylation-alkylation-desulfenylation sequence 25 → 26 → 27 → 4 . 相似文献
917.
Phytochemistry of genus Gentiana, XIX: Identification of new C-glycosylflavones in Gentiana pyrenaica L . Five flavone C-glucosides [6-C-β-D -glucopyranosyl-tricine ( 1 ) or isopyrenine; 7-O-β-D -glucopyranosyl-6-C-β-D -glucopyranosyltricine ( 2 ) or isopyrenine-7-O-glucoside; isoscoparine-7-O-glucoside ( 3 ); 7-O-β-D -glucopyranosyl-6-C-β-D -glucopyranosylacacetine ( 4 ) and isovitexine-7-O-glucoside ( 5 ) or saponarine] as well as the flavonol glucoside isoquercitrine ( 9 ) have been isolated chromatographically, using polyamide and cellulose columns, from the aerial parts of Gentiana pyrenaica L . 1 and 2 are new compounds and the first glycoflavones trisubstituted on cycle B. Compound 4 is also encountered for the first time in nature. 相似文献
918.
Time-dependent photoconductivity and photo-absorption measurements, the latter using probe beams of 0.1 eV and 1.4 eV, were analyzed on the basis of a saturated band tail model. By a best fit procedure of theory to experiment band structure and recombination parameters for a-As2Se3 were obtained. 相似文献
919.
Kurt Hansen 《Nachrichten aus der Chemie》1999,47(8):1036-1039
920.