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101.
Acid-catalyzed isomerization of the petrosterol side chain () proceeds stereospecifically to yield the naturally occurring 26-dehydro-25-epiaplysterol side chain (); in addition, a 1.5-hydride shift leading to 22-dehydro-25-epiaplysteryl acetate () has also been observed. 相似文献
102.
We have investigated two-photon resonant up conversion of 375 to 159 nm coherent radiation using the four-frequency process 159=2375+1040 in cadmium vapour, where the ir component (1040 nm) is internally generated by the 375 nm pump tuned to the Cd two-photon transition 5s
2
1
S
05s6s
1
S
0. Scaling laws and tuning behaviour of both the 159 and 1040 nm output power were measured up to 1×108 W cm–2 pump intensity and 2×1017 cm–3 Cd number density. The results are compared to numerical calculations based on semiclassical theory in a stationary perturbation approximation up to third order. Here, in accordance with experimental results, the ir component was assumed to originate from a superposition of stimulated emission and parametric generation. The observed saturation effects turned out to be mainly due to population changes of the atomic levels involved and are qualitatively reproduced by calculations. Discrepancies with respect to absolute output levels are discussed in terms of the approximations in the theoretical formalism. 相似文献
103.
Li HX Ren ZG Zhang Y Zhang WH Lang JP Shen Q 《Journal of the American Chemical Society》2005,127(4):1122-1123
The complex [{(TMS)2N}4(mu4-Cl)Sm4(mu-SPh)4(mu3-Cl)Li(THF)] has been formed by protonolysis of [(Me3Si)2N]3Sm(mu-Cl)Li(THF)3 with 1 equiv of HSPh, which contains a square array of Sm(III) ions connected by a central mu4-Cl ligand. The edges of the square Sm4 array are bridged by four mu3-Cl and four mu-SPh ligands. The four Sm atoms and Li atom are connected by four mu3-Cl ligands. 相似文献
104.
Griesbeck AG Heinrich T Oelgemöller M Lex J Molis A 《Journal of the American Chemical Society》2002,124(37):10972-10973
An elaborated protocol is described which allows the efficient transformation of di-, tri-, and tetrapeptides into cyclopeptides with a minimum of protection and activation chemistry using the photoinduced electron transfer initiated decarboxylation of N-phthaloyl peptides resulting in C-C coupling between the initially formed carbon radicals. 相似文献
105.
The synthesis and characterization of the anionic mononuclear and homobinuclear osmium complexes [AsPh4][OsCl5L].xEtOH [L = H2O, x = 2 (9); L = EtOH, x = 1 (10a); L = py, x = 0 (10b)] and [AsPh4]2[Cl5Os(pyz)OsCl5] (12) (pyz = pyrazine) are described. Upon reduction in a chloride-containing medium, OsO4 (1) affords the osmium(IV) species [OsCl5(H2O)]- (2), which could be isolated by extraction with n-tributyl phosphate (TBP). Complex 9 is the first fully characterized chloroaquo complex of Os(IV). This complex is an effective starting material for the preparation of novel species, such as 10a, 10b, and 12. The X-ray structures of 9 and 10a were determined. Both compounds crystallize in the monoclinic space group P2(1)/n. 9: C28H34AsCl5O3Os, a = 10.910(4) A, b = 17.127(5) A, c = 17.555(7) A, beta = 103.77(2) degrees, V = 3186(2) A3, and Z = 4. 10a: C28H32AsCl5O2Os, a = 10.7762(2) A, b = 17.3939(1) A, c = 17.1477(3) A, beta = 103.645(1) degrees, V = 3123.45(8) A, and Z = 4. Complexes 9 and 10a crystallize with two and one molecule of EtOH and are bonded via hydrogen bridges to the H2O and EtOH ligand in 9 and 10a, respectively. 相似文献
106.
Two methods based on gel permeation chromatography (GPC) [size exclusion chromatography] for the analysis of traces (ng/kg)
of nitrogen and phosphorus containing pesticides (like triazines or phosphothionates) from marine sediment samples are compared:
A macro GPC with Biobeads SX-3 and a chromatography on a high-performance (HP-GPC) column with UV-detection. Results for eight
triazine herbicides, two triazine metabolites, the phenylurea derivative linuron, two acetanilides and two organophosphorus
compounds are given. Concentrations obtained with the HP-GPC are compared with those obtained with a macro GPC approach in
an earlier study.
Received: 4 October 1996/Revised: 20 December 1996/Accepted: 24 December 1996 相似文献
107.
Lenice de Loureno Marques Ernesto Schulz Lang Herton Fenner Eduardo Ernesto Castellano 《无机化学与普通化学杂志》2005,631(4):745-748
[Hg(sulfamethoxazolato)2]·2DMSO ( 1 ) and [Cu2(CH3COO)4(sulfa‐methoxazole)2] ( 2 ) can be obtained by the reaction of sulfamethoxazole with mercury acetate or copper acetate in methanol. The structures of the two complexes were characterized by single crystal X—ray diffractometry. Compound 1 consists of sulfamethoxazolato ligands bridging the metal ions building an unidimensional chain. Two solvent dimethylsulfoxide molecules are involved via N‐H···O hydrogen bridges. The mercury atom shows a linear primary coordination arrangement formed by two trans deprotonated sulfonamidic nitrogen atoms. The overall coordination around the metal atom may be regarded as a strongly distorted octahedron when the interactions of mercury with four sulfonamidic oxygen atoms [bond distances of 2.761(4) Å—2.971(4) Å] are also considered to build an equatorial plane and the N1 and N1′ atoms [bond distance of 2.037(5) Å] occupy the apical positions. Compound 2 is a dinuclear complex in which the copper ions are bridged by four syn‐syn acetate ligands which are related by a symmetry centre located in the centre of the complex. Each copper atom presents a nearly octahedral coordination where the equatorial plane is formed by four oxygen atoms and an isoxazolic nitrogen atom and the second copper atom occupy the apical positions. 相似文献
108.
Heinrich Wefelscheid 《Journal of Geometry》1977,9(1-2):127-133
A characterisation of those (B*G)-Geometries (in the sense of Benz) is given, which can be constructed with the help of nearfields F, char F 2, in which the multiplicative group F*(·) has a subgroup A with index [F*:A]=2.
Werner Burau zum 70. Geburtstag gewidmet 相似文献
Werner Burau zum 70. Geburtstag gewidmet 相似文献
109.
An on-line two-stage column chromatographic technique is described which combines reversed-phase and anion-exchange chromatography for the separation of purine nucleic acid components. The elution program applied, consisting of two gradient programmes, provides a separation of bases and nucleosides on the octadecyl silica column and a separation of the nucleotides on the anion-exchange column to which they have been switched at the beginning of the elution. This method is easy to modify for special problems and can be used when establishing a complete profile of purines. 相似文献
110.