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991.
JPC – Journal of Planar Chromatography – Modern TLC - A new bonded RP-18 sintered silica gel plate for use in reversed-phase planar electrochromatography has been prepared in our... 相似文献
992.
Wang M Wang BM Shi L Tu YQ Fan CA Wang SH Hu XD Zhang SY 《Chemical communications (Cambridge, England)》2005,(44):5580-5582
A quinine/Selectfluor combination inducing rearrangement reaction of allylic alcohols was discovered, which involved a moderate yield with good enantioselective construction of alpha-quaternary carbon center and beta-fluoro aldehyde under base condition. 相似文献
993.
The use of reduced overlap population (ROP) analysis from EHMO calculations as a means to gauge the presence of metal–metal
bonds in triosmium clusters is examined. A number of triosmium clusters containing bridging ligands have been used as test
cases, including the bis-ethoxy bridged cluster Os3(μ-OEt)2(CO)10, 1b, and some of its group 15 derivatives Os3(μ-OEt)2(CO)9(EPh3), 2. These latter clusters are newly synthesized and have been characterized completely, including by single-crystal X-ray crystallographic
studies.
In honour of Professor Dieter Fenske on his 65th birthday. 相似文献
994.
The evidence for the stabilizing nature of the H–H bonding in planar biphenyl is succinctly reviewed. The stabilizing nature
of the H–H bonding is revealed through a comparison of the atomic energy of every atom in planar biphenyl with the same atom
in the twisted equilibrium structure. It is shown that the barrier to rotation via the planar transition state is the net
resultant of a stabilisation of the four ortho-hydrogen atoms (by 8 kcal/mol each), a stabilisation of the two para-carbon atoms (by 3 kcal/mol each) and by the dominant destabilisation of the two carbon atoms joining the two rings—the two
junction carbon atoms—(by 22 kcal/mol each). The energetic stabilisation of the four ortho-hydrogen atoms is further shown to be in large proportion due to the formation of the hydrogen–hydrogen interatomic surface.
Furthermore, neither the “bond order” between the two junction carbon atoms nor the total electron delocalisation between
the two rings exhibit a significant change in going from the planar to the twisted equilibrium geometry. These findings are
in contrast with the classical view of a balance between “steric non-bonded repulsion” and better electron delocalisation
as a function of the twist dihedral angle. Similar conclusions have been recently reached by Pacios and Gómez through a study
of the electrostatic potential at the position of the hydrogen nuclei.
We dedicate this article to Professor TM Krygowski on the occasion of his 70th birthday wishing him a long and productive
life. 相似文献
995.
Wei-ping Gao Yu Bai Er-qiang Chen~ 《高分子科学》2005,(3):275-284
Small fixed aggregates of a poly(ethylene oxide)-block-polybutadiene diblock copolymer(PEO-b-PB)in THFsolution were obtained by adding a selective solvent for PB blocks,followed by cross-linking the PB shells.Themorphologies of the nanostructured particles with a cross-linked shell were investigated by atomic force microscopy andtransmission electron microscopy.The average behaviors of the PEO crystallization and melting confined within thenanostructured particles were studied by using differential scanning calorimetry experiments.For the deeply cross-linkedsample(SCL-1),the crystallization of the PEO blocks was fully confined.The individual nanoparticles only crystallized atvery low crystallization temperatures(T_cs),wherein the homogenous primary nucleation determined the overallcrystallization rate.For the lightly cross-linked sample(SCL-2),the confinement effect was T_c dependent.At T_c(?)42℃,thecrystallization and melting behaviors of SCL-2 were similar to those of the pure PEO-b-PB diblock copolymer.At T_c>42℃,SCL-2 could form PEO lamellae thicker than those of the pure PEO-b-PB crystallized at the same T_c. 相似文献
996.
The equilibrium geometries, electronic structures, as well as one- and two-photon absorption cross sections of a series of octupolar chromophores with Zn(2+) or Cu(+) as coordinate centers and 4,4'-bis(dibutylaminostyryl)-[2,2']-bis(bipyridyl) as ligands have been determined by using B3LYP/6-31G and ZINDO methods. These molecules are designed by controlled combination of two or three bipyridyl ligands with the metal centers. The results show that Zn(2+) is an effective template for the design of octupolar structures which enable it to form tetrahedral and octahedral coordinated complexes; while Cu(+) only exists in a tetrahedral coordinated complex, comparing the tetrahedral complex with Zn(2+) as the center with that of Cu(+) as the center, it is found that the complex with the Cu(+) center is a better two-photon absorption material than the former as far as the transparency/nonlinearity is concerned. Furthermore, for the same metal center of Zn(2+), both one- and two-photon absorptions of the tetrahedral complex are redshifted relative to those of the octahedral complex, is attributed to the spiroconjugation effect in the tetrahedral complex. Our theoretical findings are consistent with recent experimental observations and provide an important foundation for the design of improved transparency-nonlinearity two-photon absorption materials. 相似文献
997.
A multi-wall carbon nanotube (MWNT)/cetyl pyridine bromine (CPB) composite film modified glassy carbon electrode (GCE) was
developed for the electrochemical determination of hymecromone in phosphonate buffer. Electrochemical behaviour of hymecromone
at the composite film electrode was investigated with voltammetry. Compared with an irreversible oxidation of hymecromone
at the bare GCE, the oxidation peak current was enhanced greatly at the film electrode. Some parameters such as pH, scan rate,
accumulation potential and accumulation time were optimized. Under optimal conditions, an oxidation peak at 0.82 V was employed
to determine hymecromone electrochemically. A linearity between the oxidation peak current and the hymecromone concentration
was obtained in the range of 3.0 × 10−7 − 2.0 × 10−5 mol 1−1 with a detection limit of 8.0 × 10−8 mol 1−1. The proposed procedure was successfully applied to assay hymecromone in pharmaceutical formulation with satisfactory results.
The text was submitted by the authors in English. 相似文献
998.
Zhang De-Qing Wang Shao-Jun Sun Hong-Shan Wang Xiu-Li Cao Mao-Sheng 《Journal of Sol-Gel Science and Technology》2007,41(2):157-161
Lead zirconate titanate nanopowders Pb(Zr0.52Ti0.48)O3 (PZT) were prepared by modified sol-gel process in ethylene glycol system with zirconium nitrate as the zirconium source.
The research showed that it was critical to add lead acetate after the reaction of zirconium nitrate and tetrabutyl titanate
in ethylene glycol system for preparing PZT of exact titanium content. The reaction mechanisms of the sol synthesis, preparation
of xerogel and agglutinating process were characterized through using FT-IR, NMR, TG-FTIR, and GC-MS. The experiment proved
that ethylene glycol system did not rely on hydrolysis and condensation reactions in the process of the sol formation, but
on the formation of chain or network large molecules from complexation of ethylene glycol and all Ti and minor Pd, Zr. In
the preparation of xerogel, the complexation reaction was so completed that it formed large molecules network composed of
metal and dioxyethyl. Bulk weight loss happened before 350°C in the process of sintering xerogel to prepare PZT nanopowders.
Volatile matters and vapor phase decomposition resultants were primarily oxy-compounds including ethylene glycol, aldehyde-ketone
compounds, carbon dioxide and nitrate radical conversion matters. After 350°C, primary vapor phase decomposition resultants
were carbon dioxide and minor carbonyl compound. 相似文献
999.
Jian-yun Du 《Transition Metal Chemistry》2004,29(7):699-702
Two novel complexes, [Zn(dmatrz)2]Cl2
(1) and [Zn(dmatrz)2(SCN)2] (2), have been prepared and characterized by X-ray crystallography, absorption and luminescence spectrometries (dmatrz=3,5-dimethy-4-amino-1,2,4-triazole). The coordination environment of the zinc(II) ions in (1) and (2) has a distorted tetrahedral geometry completed via two independent nitrogen atoms of two triazole ligands and two anions, respectively. Both (1) and (2) show strong blue luminescence properties. Furthermore, (1) displays stronger blue photoluminescence than (2) as the result of different anions (Cl- and SCN-) coordinated to the zinc(II) ions. 相似文献
1000.
六氰合铁酸铜钴在蜡浸石墨电极表面的电化学沉积 总被引:3,自引:0,他引:3
首次报道了电化学沉积的混合金属六氰合铁酸盐修饰电极作为电流型传感器的研究。针对六氰合铁酸盐修饰电极在中性和碱性条件下的不稳定性,采用混合金属电沉积的方法,成功地提高了电极的稳定性,所得到的修饰电极在 pH 4~10之间均表现出良好的稳定性。该电极的响应时间(t95%)为 0.5s,并对Fe3+/Fe2+电对表现出良好的电催化作用。催化氧化峰电流与Fe2+的浓度在1.0×10-4~6.5×10-2mol/L范围内呈很好的线性关系,检测下限为 1.4×10-6mol/L。 相似文献