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991.
Romain Heck 《Tetrahedron letters》2004,45(2):281-284
A new tripodal α-cyclodextrin having three ureido-bipyridyl tethers symmetrically distributed on its upper rim was prepared in one step by the polymer supported ‘phosphine imide’ reaction in a medium yield. As expected, the highly selective complexation properties towards ‘hard’ and ‘soft’ cations were maintained with regards to the URFT-Cd (upper rim fully tethered) family previously investigated. Its EuIII and TbIII lanthanide complex fluorescence behaviour clearly indicates that a limited number of tethers allow a better bis-heterocyclic antenna self-organisation around the cation leading to enhanced fluorescence properties. 相似文献
992.
1 INTRODUCTION Recently, the low-spin square-planar nickel(II) complexes and high-spin octahedral nickel(II) complexes with Schiff base ligands have received much attention in optical materials[1~3]. Some nic- kel(II) complexes are widely used as lubricating oil, rubber industry additives, a fire-resistant additive and fungicide for leather[4~7]. Also, their adducts with nitrogen have attracted broad attention due to their potential applications as organic conductors and magnetic mate… 相似文献
993.
Gong WT Li XC Ning GL Zhu L Wang L Lin Y 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(4-5):835-839
Two novel phenylated pyrylium compounds, silver (I)-bridged 2,3,4,5-tetraphenylpyrylium perchlorate (P1) and its silver (I)-free pyrylium ligand (P2) were prepared from 1,2,3,4-tetraphenylcyclopentadiene to examine their spectroscopic behaviors. The UV/vis absorption and fluorescent emission spectra of P1 and P2, measured in three solvents (acetonitrile, dichloromethane and toluene), reveal that the photophysical behaviors are closely related to silver (I) fragment, and strongly dependent on solvent polarity. In polar acetonitrile, P1 displays longer absorption wavelength and much lower fluorescent emission intensity than P2, although they exhibit much similarity in shape. In contrast, in nonpolar toluene, while P2 shows an apparent absorption band at 338 nm, P1 displays a tail-like line without absorption band observed. All the spectra obtained indicate a better coplanarity and a stronger intra-molecular charge transfer in P1 due to the effect of silver (I) fragment. Additionally, the 1H NMR spectra of P1 and P2, which were recorded under the same conditions, indicate that the silver (I) fragment reinforces pyrylium ring's capacity to localize the formal positive charge within the heterocyclic ring. 相似文献
994.
The selectivity of a column system, S, defined by equation 28, includes a variation coefficient (β) of plate number with capacity ratio which has a large influence on the peak capacity, as shown in Fig. 18. Some typical chromatograms are given. In order to predict S for a column system from Kovat's Index, equations 40 and 41 are given to calculate the constant of the carbon number rule for squalane at different temperatures or for different stationary phases. The specific retention value of heptane on squalane at different temperatures can be calculated from equation 42. The nonpolarity index, defined by equation 43, was used to calculate the retention value of heptane on various stationary phases. In liquid chromatography, the order of elution may be reversed by changing the composition of the eluent on the same chemically bonded silica (manufactured in China). The linear relations between the log retention values of different kinds of solutes or of a single solute on the silicas of different surface areas when using the same eluent are given. 相似文献
995.
Jihong Cheng 《Journal of solid state chemistry》2004,177(1):126-133
LaGaO3 perovskites doped with Sr or Ba at the La site and Mg at the Ga site were prepared by solid-state reaction or sol-gel method and characterized. Enthalpies of formation from constituent oxides at 298 K were determined by high-temperature oxide melt solution calorimetry. Energetic trends are discussed in terms of defect chemistry. As oxygen deficiency increases, formation enthalpies define three trends, LaGa1−yMgyO3−δ (LGM), La1−xSrxGa1−yMgyO3−δ (LSGM), and La1−xBaxGa1−yMgyO3−δ (LBGM). They become less exothermic with increasing doping, suggesting a dominant destabilization effect from oxygen vacancies. The endothermic enthalpy of vacancy formation is 275±37, 166±18 and 138±12 kJ/mol of VO·· for LGM, LBGM and LSGM, respectively. Tolerance factor and ion size mismatch also affect enthalpies. In terms of energetics, Sr is the best dopant for the La site and Mg for the Ga site, supporting earlier studies, including oxygen ion conductivity and computer modeling. 相似文献
996.
Yuri N. Belokon’Devayani Bhave Daniela D'AddarioElizabetta Groaz Viktor MaleevMichael North Armine Pertrosyan 《Tetrahedron letters》2003,44(10):2045-2048
Copper(salen) complex 1 has been found to catalyse the asymmetric alkylation of enolates derived from a variety of amino acids. There is a clear relationship between the size of the side chain in the substrate and the enantioselectivity of the process, so that the enantioselectivity decreases in the order alanine>aminobutyric acid>allylglycine>leucine>phenylalanine>valine. A transition state model which accounts for the influence of the size of the side chain on the enantioselectivity of the reactions is presented. 相似文献
997.
Summary A novel method of separating and detecting trace aluminum by capillary zone electrophoresis is described. Aluminum is reacted with lumogallion [4-chloro-3-(2,4-dihydroxyphenylazo)-2-hydroxybenzen-1-sulphonic acid] so that the complex can be selectively and sensitively detected by a laser-induced fluorescence detector after capillary electrophoretic separation. Using the proposed method, limits of detection in the sub parts per billion range are achieved. The technique is applied to the determination of aluminum in human serum. 相似文献
998.
A radical mechanism of the reaction of molybdenum carbonyl complexes with bis(triethylgermyl)mercury
M. I. Sykhrannova A. N. Tatarnikov S. Ya. Khorshev E. N. Gladyshev 《Russian Chemical Bulletin》1993,42(9):1585-1587
The reaction of [Cp(CO)3Mo]2 with (Et3Ge)2Hg occurs in toluene and THF by a radical mechanism. The interaction between [Cp(CO)3Mo]2Hg and (Et3Ge)2Hg has a radical character only in THF. The formation of Cp(CO)3MoH at the first stage of these reactions substantially affects the further course of the process.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1648–1650, September, 1993. 相似文献
999.
钪—铋—三溴偶氮胂混合多核络合物显色反应及其在钪光度分析中应用研究 总被引:3,自引:0,他引:3
本文研究了钪-铋-三溴偶氮胂络合物的共显色反应。实验表明,共显色反应是由于形成混合多核络合物所致。钪络合物最大吸收峰在635nm,表观摩尔吸光系数为7.1×10~4L·mol~(-1)·cm~(-1)。钪在0~5μg/25ml遵守比尔定律。 相似文献
1000.
The polarographic behaviour of dithiodiacetic acid and that of U(VI) in a solution containing dithiodiacetic acid as complexing agent have been investigated. For the dithiodiacetic acid system, two waves appear over the pH range studied. The prewave is kinetic in nature and the mainwave is diffusion-controlled. However, as U(VI) is added into the dithiodiacetic acid system, the polarogram changes due to the existence of a complex. The current-potential curve of the first wave is not the normal S shape. This is due to the superposition of the first wave of the ligand and the wave due to the reduction of the U(VI) in the complex to U(V). The second wave is due to the reduction of the complex The first wave is an adsorption-controlled current and the second wave is partly diffusion-controlled and partly adsorption-controlled. We propose an electrode reaction mechanism for both systems and the complex species. The dissociation constant of the complex HASSAUO+2 is found to be of the order of 10?4. 相似文献