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991.
GONG Da-chun ZHOU Hua WEI Ping OUYANG Ping-kai 《高等学校化学研究》2007,23(5):544-548
New ligand 1,2-bis{di[(R,R)-1,3,2-oxzaphosphlidine]phosphino}ethane [(R,R)-BDOPPEs 1,2,3 and 4] with C2-symmetric axis and bearing nitrogen and oxygen were synthesized from readily available optically active amino alcohols.Rh complexes with these ligands were highly enantioselective catalysts for asymmetric hydrogenation of N-benzoyldehydroamino acid derivatives and α-functionalized ketones in 99%e.e.and 98%e.e.,respectively.This new class of(R,R)-BDOPPEs 1,2,3 and 4 gave much more effectivity and enantionselectivity than their corresponding non-C2-asymmetric aminophosphine phosphinite. 相似文献
992.
Hassan Rabaâ Bernd Engels Thomas Hupp A. Stephen K. Hashmi 《International journal of quantum chemistry》2007,107(2):359-365
A general scheme for the endo‐ and exo‐cyclization of furan reactivity with [L ‐AuIII, IClx] with (x = 3, 1 and L ‐acetylene and vinylidene) complexes is investigated using density functional theory (DFT) code. Two conceivable mechanisms via a [4 + 2] Diels–Alder process or carbene complex are analyzed. According to the activation energy values of the gold (III and I) catalyst, the first mechanism, which implies the Diels–Alder reaction of AuIII, is thermodynamically favored and gives more evidence of the intramolecular addition of the furan with the alkynes. The second mechanism, presumably assisted by the spontaneous formation of the exo‐vinylidene complexes and intermediates of gold (III, I) by forming the carbene complex, is kinetically favored. Additionally, we compare our results with other structures with intramolecular additions that exhibit the quasi‐similarity of gold analogue structures. Differences in activation energies are observed, according to the functional used. Finally, we probe the solvent effects, which decrease the energy barrier in the path. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
993.
Mechanical properties decay and morphological behaviour of biodegradable films for agricultural mulching in real scale experiment 总被引:1,自引:0,他引:1
Giacomo Scarascia-Mugnozza Giuliano Vox Barbara Immirzi 《Polymer Degradation and Stability》2006,91(11):2801-2808
The use of plastic materials in agriculture causes the serious drawback of huge quantities of waste. The introduction of biodegradable materials, which can be disposed directly into the soil, can be one possible solution to this problem. Biodegradable materials are actually innovative materials; therefore, their physical properties must be evaluated in relation to their functionality during the use in field. In the present research results of experimental tests carried out on biodegradable films used in strawberries protected cultivation are presented. The decay of some relevant physical parameters of biodegradable films during the cultivation period was monitored by laboratory tests (SEM analysis, mechanical tensile tests and infrared reflectance spectroscopy). Infrared spectroscopy clearly indicated that the mechanical degradation starts from the starch component of the material. Tensile tests showed that the value of elongation at break of biodegradable materials decreased in some cases by 300% after 10 days of field application. 相似文献
994.
O. Yu. Slabko N. V. Ageenko D. V Kuklev V. A. Kaminski 《Chemistry of Heterocyclic Compounds》2002,38(3):354-358
Oxidative coupling of derivatives of 4a,9-diaza-1,2,4a,9a-tetrahydro-9H-fluorene with 2-ethyl-, 2,2-dimethyl-, and 2-hydroxymethyl-2-methylaminoethanol in the presence of MnO2 led to the selective formation of the corresponding mono- and di(hydroxymethyl)quinonediimines, subsequent cyclization of which gave the products of 6,7-annelation. Coupling with 2,2-di(hydroxymethyl)aminoethanol gave the annelation products directly. 相似文献
995.
Three acyclic polythioethers containing 2-thienyl units at both ends were synthesized and the effect of substituent on the extraction of copper(II) was studied. The methyl groups in the terminal thiophene ring have imparted an appreciable degree of increase in the percent extraction of copper(II), while the introduction of chlorine atoms into the 2-thienyl unit resulted in the reverse effect. Among the counter dye anions examined, tetrabromophenolphthalein ethylester was the best one for copper(II) extraction. The composition of extracted species was evaluated to be 122 (Cu(II)/polythioether/dye anion). Quantitative extraction of copper(I) was attained as complexes with various triphenylmethane dyes, i.e., bromocresol green, bromothymol blue, bromo-phenol blue and pyrogallol red. Copper(I) in organic phase was completely back-extracted with 2 mole/l sulfuric acid containing 10% hydrogen peroxide. 相似文献
996.
J. Díaz-Ferrero M.C. Rodríguez-Larena L. Comellas B. Jiménez 《Trends in analytical chemistry : TRAC》1997,16(10):1865-573
The usual methods for determining polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF) and polychlorinated biphenyls (PCB) are generally expensive and time consuming. This fact has favored the development of faster and cheaper techniques, based on immunoassays and bioassays. This paper reviews these bioanalytical methods and their analytical importance at the present moment. 相似文献
997.
998.
Pb8FeIIFeF24 is triclinic: a = 20.118(3) Å, b = 5.597(1) Å, c = 9.440(2) Å, α = 89.75(2)°, β = 105.79(2)°, α = 89.38(2)°, Z = 2. The structure is solved in the unconventional space group C1 , from X-ray single crystal data using 1 641 independent reflections (R = 0.048, Rw = 0.051). It is built up from the stacking of two subnetworks along the a axis: fluorite-like [Pb8F10]n6n+ layers and infinite dimetallic [FeIIFeF14]n6n? double-chains of corner-sharing octahedra running along the b axis. 相似文献
999.
P. Torline G. du Plessis N. Schnautz J. C. Thompson 《Journal of separation science》1979,2(10):613-616
A detailed method for the routine preparation of glass capillary columns is presented. The method consists of coating a glass tube with quartz powder prior to pulling the tube into a capillary. The inner surface of the capillary consists of an even distribution of quartz particles fused to the walls. This surface has been found readily deactivated by standard procedures and ideal for the preparation of thick-film glass capillary columns. The method has been thoroughly tested in two independent laboratories to ensure that the procedures described are reproducible. 相似文献
1000.
By a procedure of successive projections, the authors decompose a coupled system of wave equations into a sequence of sub-systems. Then, they can clarify the indirect controls and the total number of controls. Moreover, the authors give a uniqueness theorem of solution to the system of wave equations under Kalman’s rank condition. 相似文献