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991.
Dr. J. Grant Hill Xiaojun Hu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(11):3620-3628
Benchmark quality geometries and interaction energies for the prereactive halogen‐bonded complexes of dihalogens and ammonia, including hypothetical astatine containing dihalogens, have been produced via explicitly correlated coupled cluster methods. The application of local electron correlation partitioning reveals dispersion, electrostatics and ionic substitutions all contribute significantly to the interaction energy, with a linear relationship between the ionic substitutions and the degree of charge transfer. Potential energy curves for H3N???ClF show that as the relative orientations of the two subunits are manipulated appreciable interactions can be found at considerably angular displaced geometries, signifying lower directionality in halogen bonding than previously supposed. 相似文献
992.
Dr. Weiyi Li Zhishan Su Prof. Dr. Changwei Hu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(1):124-134
The mechanism of the allylation reaction between 4‐chloroacetophenone and pinacol allylboronates catalyzed by ZnEt2 with alcohols was investigated using density functional theory (DFT) at the M05‐2X/6‐311++G(d,p) level. The calculations reveal that the reaction prefers to proceed through a double γ‐addition stepwise reaction mechanism rather than a Lewis acid‐catalyzed concerted one. The intermediate with a four‐coordinated boron center, which is formed through proton transfer from EtOH to the ethyl group of ZnEt2 mediated by the boron center, is the active species and an entrance for the catalytic cycle. The latter is composed of three elementary steps: 1) boron to zinc transmetalation leading to the formation of allylzincate species, 2) electrophilic addition of ketone to allylzincate species, and 3) generation of the final product with recovery of the catalyst. The boron to zinc transmetalation step has the largest energy barrier of 61.0 kJ mol?1 and is predicted to be the rate‐determining step. The calculations indicate that the additive EtOH plays important roles both in lowering the activation free energy for the formation of the four‐coordinated boron active intermediate and in transforming the low catalytic activity ZnEt2 into high activity zinc alkoxide species. The alcohols with a less sterically encumbering R group might be the effective additives. The substituted groups on the allylboronates might primarily affect the boron to zinc transmetalation, and the allylboronates with substituents on the Cγ atom is poor in reactivity. The comparison of the catalytic effect between the zinc compounds investigated suggest that Zn(OEt)2, Zn(OH)2, and ZnF2 exhibit higher catalytic efficiency for the boron to zinc transmetalation due to the activation of the B? Cα bond through orbital interactions between the p orbitals of the EtO, OH, F groups and the empty p orbital of the boron center. 相似文献
993.
Feng Zou Prof. Xianluo Hu Dr. Yongming Sun Dr. Wei Luo Fangfang Xia Long Qie Yan Jiang Prof. Yunhui Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(19):6027-6033
Zn2GeO4/N‐doped graphene nanocomposites have been synthesized through a fast microwave‐assisted route on a large scale. The resulting nanohybrids are comprised of Zn2GeO4 nanorods that are well‐embedded in N‐doped graphene sheets by in situ reducing and doping. Importantly, the N‐doped graphene sheets serve as elastic networks to disperse and electrically wire together the Zn2GeO4 nanorods, thereby effectively relieving the volume‐expansion/contraction and aggregation of the nanoparticles during charge and discharge processes. We demonstrate that an electrode that is made of the as‐formed Zn2GeO4/N‐doped graphene nanocomposite exhibits high capacity (1463 mAh g?1 at a current density of 100 mA g?1), good cyclability, and excellent rate capability (531 mAh g?1 at a current density of 3200 mA g?1). Its superior lithium‐storage performance could be related to a synergistic effect of the unique nanostructured hybrid, in which the Zn2GeO4 nanorods are well‐stabilized by the high electronic conduction and flexibility of N‐doped graphene sheets. This work offers an effective strategy for the fabrication of functionalized ternary‐oxide‐based composites as high‐performance electrode materials that involve structural conversion and transformation. 相似文献
994.
Dr. Qingsong Dong Prof. Xiao‐Juan Yang Shida Gong Dr. Qiong Luo Prof. Qian‐Shu Li Prof. Ji‐Hu Su Dr. Yanxia Zhao Prof. Biao Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(45):15240-15247
A nickel? nickel‐bonded complex, [{Ni(μ‐L.?)}2] ( 1 ; L=[(2,6‐iPr2C6H3)NC(Me)]2), was synthesized from reduction of the LNiBr2 precursor by sodium metal. Further controllable reduction of 1 with 1.0, 2.0 and 3.0 equiv of Na, respectively, afforded the singly, doubly, and triply reduced compounds [Na(DME)3] ? [{Ni(μ‐L.?)}2] ( 2 ; DME=1,2‐dimethoxyethane), [Na(Et2O)]Na[(L.?)Ni? NiL2?] ( 3 ), and [Na(Et2O)]2Na[L2?Ni? NiL2?] ( 4 ). Here L represents the neutral ligand, L.? denotes its radical monoanion, and L2? is the dianion. All of the four compounds feature a short Ni? Ni bond from 2.2957(6) to 2.4649(8) Å. Interestingly, they display two different structures: the perpendicular ( 1 and 2 ) and the coaxial ( 3 and 4 ) structure, in which the metal? metal bond axis is perpendicular to or collinear with the axes of the α‐diimine ligands, respectively. The electronic structures, Ni? Ni bonding nature, and energetic comparisons of the two structure types were investigated by DFT computations. 相似文献
995.
Composite hydrogels were prepared from pineapple peel cellulose with the combinations of polyethylene glycol (PEG), polyvinyl alcohol (PVA), к-carrageenan (CN), or soluble starch (SH) in 1-allyl-3-methylimidazolium chloride solvent. Impacts of these macromolecules on the texture profile analysis (TPA) parameters, equilibrium swelling ratio (ESR), and sodium salicylate (NaSA) load of the prepared hydrogels were studied. The NaSA release kinetics of the composite hydrogels were also compared. The composite hydrogels exhibited differences in Fourier transform infrared spectroscopy (FTIR), TPA parameters, ESR, NaSA load ratio, and release kinetics. CN addition increased the hardness of the hydrogels, while PEG played an opposite role. SH and PVA could decrease hardness, gumminess, and resilience, and SH could increase the springiness and cohesiveness of the hydrogels. Most of the composite hydrogels exhibited the same basic FTIR features as the simple hydrogel. Freeze-dried composite hydrogels exhibited a markedly higher ESR than the oven-dried ones, and additions of PEG, PVA, CN, and SH showed the same effect. Addition of the PEG and PVA combination could lower the ESR of the hydrogels, whereas additions of the PEG and CN combination or PEG and SH combination could markedly increase the ESR of the hydrogels. Addition of PEG, PVA, CN, and SH respectively could increase the NaSA load ratio of the hydrogels. Oven-drying treatment, additions of the PEG and PVA combination or PEG and CN combination were propitious for extending the NaSA fast-release phase of the hydrogels. 相似文献
996.
997.
Tao Cai Zhen Yang Haijiang Li Hu Yang Aimin Li Rongshi Cheng 《Cellulose (London, England)》2013,20(5):2605-2614
In this present work, a series of hydrolyzed polyacrylamide grafted carboxymethyl cellulose (CMC-g-HPAM) was prepared. The structure and solution properties of CMC-g-HPAM were characterized by FTIR, 1H-NMR, elemental analysis and zeta potential measurements. The graft copolymers were applied as flocculants to remove methylene blue (MB), a cationic dye, from aqueous solutions. In comparison with its precursors, carboxymethyl cellulose (CMC) and polyacrylamide CMC-g-PAM, CMC-g-HPAM exhibited higher removal efficiencies. Furthermore, the flocculation performance of the copolymers was significantly improved with the increase of the hydrolysis degree, and the MB removal efficiency was more than 90 % when the hydrolysis degree of CMC-g-HPAM was higher than 80 %. More importantly, image analysis in combination with fractal theory demonstrated that the graft copolymers could produce notably denser and larger flocs, which was of great significance in practical water treatment. The improved flocculation performance was ascribed to both charge neutralization and bridging effects. 相似文献
998.
采用软模板法制备了氮化钨-钨/掺氮有序介孔碳复合材料(WN-W/NOMC),作为一种高比表面积且价格低廉的阴极氧还原反应催化剂。通过适量添加尿素来改变复合材料中的氮含量,在掺氮量为7%(w/w)时,实验发现材料能够保持完整有序介孔结构,测试其比表面积高达835 m2·g-1,透射电子显微镜(TEM)测试结果显示其催化颗粒均匀地分散在氮掺杂有序介孔碳载体上。在O2饱和的0.1 mol·L-1 KOH溶液中测试了材料的氧还原催化性能(ORR),显示其起始电位为0.87 V(vs RHE),极限电流密度为4.49 mA·cm-2,氧还原反应的转移电子数为3.4,接近于20%(w/w)商业Pt/C的3.8,说明该材料表现出近似4电子的氧还原反应途径。研究结果表明,WN-W/NOMC的催化性能虽然稍弱于商业铂碳(0.99 V,5.1 mA·cm-2),但其具有远超铂碳的循环稳定性和耐甲醇毒化能力。 相似文献
999.
1000.