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951.
Wang GC Zhou YH Morikawa Y Nakamura J Cai ZS Zhao XZ 《The journal of physical chemistry. B》2005,109(25):12431-12442
The decomposition of methanol on the Ni(111) surface has been studied with the pseudopotential method of density functional theory-generalized gradient approximation (DFT-GGA) and with the repeated slab models. The adsorption energies of possible species and the activation energy barriers of the possible elementary reactions involved are obtained in the present work. The major reaction path on Ni surfaces involves the O-H bond breaking in CH(3)OH and the further decomposition of the resulting methoxy species to CO and H via stepwise hydrogen abstractions from CH(3)O. The abstraction of hydrogen from methoxy itself is the rate-limiting step. We also confirm that the C-O and C-H bond-breaking paths, which lead to the formation of surface methyl and hydroxyl and hydroxymethyl and atom hydrogen, respectively, have higher energy barriers. Therefore, the final products are the adsorbed CO and H atom. 相似文献
952.
Y. Zhao 《Chromatographia》1993,37(5-6):284-286
Summary The composition of 3,5-diBr-PADAP metal chelates was determined by liquid chromatography employing appropriate eluents and non-polar bonded stationary phase. The metal-to-ligand ratios were 12, 12 and 12 for Cu(II), Co(III) and Cr(III) respectively, and the V(V)-to-ligand ratio found to be 111 in V(V)-3,5-diBr-PADAP-H2O2 in the presence of H2O2. The results are in agreement with literature data. 相似文献
953.
Paul C. Kline Bruce C. Noll Hongqiu Zhao Anthony S. Serianni 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(2):o137-o140
1‐(β‐d ‐Erythrofuranosyl)cytidine, C8H11N3O4, (I), a derivative of β‐cytidine, (II), lacks an exocyclic hydroxymethyl (–CH2OH) substituent at C4′ and crystallizes in a global conformation different from that observed for (II). In (I), the β‐d ‐erythrofuranosyl ring assumes an E3 conformation (C3′‐exo; S, i.e. south), and the N‐glycoside bond conformation is syn. In contrast, (II) contains a β‐d ‐ribofuranosyl ring in a 3T2 conformation (N, i.e. north) and an anti‐N‐glycoside linkage. These crystallographic properties mimic those found in aqueous solution by NMR with respect to furanose conformation. Removal of the –CH2OH group thus affects the global conformation of the aldofuranosyl ring. These results provide further support for S/syn–anti and N/anti correlations in pyrimidine nucleosides. The crystal structure of (I) was determined at 200 K. 相似文献
954.
Liping Zhao Shengfu Ji Fengxiang Yin Zexiang Lu Hui Liu Chengyue Li 《天然气化学杂志》2006,15(4):287-296
A series of CoxMgxO/Al2O3/FeCrAl catalysts (x=0-1) were prepared. The structures of the catalysts were characterized using XRD, SEM, and TPR analyses. The catalytic activity of the catalysts for methane combustion was evaluated in a continuous flow microreactor. The results indicated that the active washcoats adhered well on the FeCrAl foils. The phases in the catalysts were Co--xMgxO solid solutions, α-Al2O3, and γ-Al2O3. The surface particle size of the catalysts varied with variations in the molar ratios of Co to Mg. The Co component of the Co1_xMgxO/Al2O3/FeCrAl catalysts played an important role in the catalytic activity for methane combustion. In the Co1-xMgxO/AluO3/FeCrAl series catalyst (x=0.2-0.8), the catalytic activity in terms of x was in the order of 0.5〉0.2〉0.8 under the experimental conditions. The presence of Mg in these catalysts could promote the thermal stability to a large extent. There were strong interactions between the Co1-xMgxO oxides and the AluO3/FeCrAl supports. 相似文献
955.
X. Li Y. Zhao X. Jing F. Liu F. Hao 《International journal of quantum chemistry》2006,106(5):1086-1092
The equilibrium geometries, vibrational frequencies, and dissociation energies of rare gas iodine clusters Rg2I?(Rg = Ar, Kr, Xe) were calculated at the Hartree–Fock (HF), second‐order Møller–Plesset (MP2), the coupled cluster method with single and double excitation and a noniterative correction for triple excitations method [CCSD(T)] levels. The title species have bent C2v structure of about 60° angle. The electron correlation effects and relativistic effects on the geometry and stability were investigated at CCSD(T) level. Both effects stabilize title species. The calculated electron affinities are in good agreement with the experimental results available. The effect of high angular momentum functions (g and h) was studied. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
956.
Recently,theconformationofthecalixarenehasbeenshowntobeimportantincontrollingtheseIectivityofthereceptor.Forexample,sodiumioncouldbeboundverystronglybyesterderivativesofcalix[4]areneintheconeconformationl.Wehavefoundthatinthepresenceofcertainamountofsodiumion,microamountofReO4-canbequantitativelyextractedintol,2-dichloroethanebytheligandtetraethylp-tert-butylcalix[4]arenetetraacetate(L).ItshowsthatthepresenceofNa inaqueoussolutioncanpromotetheformationofhydrophobiccomplex[NaL] .ReO'-whichc… 相似文献
957.
A structure and kinetic stability study on some complexes with the general formula MN5, where M are the alkali-metal atoms, Li, Na, K, and Rb, has been carried by using hybrid density functional methods. Complex B (C2v) with two points of attachment to the N5 ring is the most energetically favored for all metals considered here. Pyramidal structures A (C5v) are kinetically unstable and they rapidly rearrange to the most stable planar structures B. At the QCISD(T)/6-311 + G*//B3LYP/6-311 + G* + ZPE (B3LYP/6-311 + G*) level, the decomposition barrier heights of LiN5-B, NaN5–B, KN5-B, and RbN5-B are predicted to be 19.9, 22.0, 22.5, and 23.0 kcal/mol, respectively. In addition, the rate constants of the decomposition reaction MN5-B MN3 + N2 (M + Li, Na, K, and Rb) are also predicted using conventional transition state theory and canonical variational transition state theory, respectively. 相似文献
958.
A novel microwave dielectric powder with composition of Ca2Zn4Ti16O38 was synthesized through a citrate sol-gel process. The development of crystalline phases with heat-treating temperature for the gel derived powders was evaluated by using thermo-gravimetric analysis and X-ray powder diffraction analysis techniques. The pure phase of Ca2Zn4Ti16O38 with crichtonite crystal structure was obtained at relatively low temperature of 1000 °C. The synthesized powder has high reactivity and the dense ceramics with single crystalline phase were obtained at low sintering temperature of 1100 °C. Impedance spectroscopy and microwave dielectric measurements on sintered samples showed the present compound to be a modest dielectric insulator with excellent dielectric properties of εr∼47-49, Qf value ∼27,800-31,600 GHz and τf∼+45 to +50 ppm/°C. It shows comparable microwave dielectric properties to other moderate-permittivity microwave dielectrics, but much lower sintering temperature of 1100 °C. 相似文献
959.
稀土元素对人肝癌细胞SMMC-7721增殖的影响 总被引:7,自引:3,他引:7
用MTT法研究了14种稀土元素(La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb和Lu)对人肝癌细胞SMMC-7721增殖的影响。他们对肝癌细胞的生长作用可分为3类。其中La^3 、Ce^3 和Eu^3 对肝癌细胞的增殖有剂量依赖性正效应,能够在一定浓度范围内刺激细胞生长;Sm^3 ,Gd^3 ,Ho^3 ,Er^3 ,Yb^3 对肝癌细胞生长的刺激作用没有剂量依赖性特征;而Pr^3 ,Nd^3 ,Tb^3 ,Dy^3 ,Tm^3 和Lu^3 则表现出对肝癌细胞的增殖具有不用程度的抑制。推测14种稀土元素作用方式的不同与他们的原子结构有一定的关系,它们对肝癌细胞的相对增殖率随着原子序数的增加呈现出一定的规律性。 相似文献
960.
Shuhui Yu Kui Yao Francis Eng Hock Tay 《Journal of Sol-Gel Science and Technology》2007,42(3):357-364
The preferential formation of a pyrochlore structure is a knotty problem in the preparation of Pb(Zn1/3Nb2/3)O3 (PZN)-based thin film materials and its presence is significantly detrimental to the dielectric and piezoelectric properties.
In this study, 40 mol% of PZN was replaced with Pb(Mg1/3Nb2/3)O3 (PMN) for obtaining a perovskite composition around a morphotropic phase boundary (MPB), (1−x)(0.6PZN-0.4PMN)-xPT ((1−x)PZMN-xPT, PT: PbTiO3) where x = 0.23. The thin films with this composition were prepared with a polyethylene glycol (PEG) modi-fied sol-gel method on LaAlO3 substrates. The microstructural evolution of the films on heat treatment was examined with X-ray diffraction. With the aid
of PEG, the formation of the pyrochlore phase was suppressed and the perovskite phase formed directly from the amorphous gel
film. The multilayer films with a thickness around 0.25 μm showed a single perovskite phase without any detectable pyrochlore
structure. Microscopic images showed uniform grain size of a few tens of nanometers. The role of the polymer dramatically
promoting the perovskite phase was investigated with the aid of X-ray photoelectron spectroscopy and thermal analysis. The
dielectric constant of the obtained film was 4160 at 1 kHz. The film demonstrated typical ferroelectric hysteresis loops and
exhibited excellent piezoelectric performance. 相似文献