Influence of ligand-bridged substitution on the exchange coupling constant of chromium-wheels host complexes: a density functional theory study

Designing and introducing novel wheel-shaped supramolecular as host complexes with new magnetic properties is the theme of the day. So in this study, new eight binuclear chromium (III) complexes, as models of real chromium-wheel host complexes, were designed based on changing of bridged-ligands and exchange coupling constants (J) of them were calculated using the broken symmetry density functional theory approach. Substitution of fluorine ligand in fluoro-bridged model [Cr₂F(tBuCO₂)₂(H₂O)₂(OH)₄]^?1 by halogen anions (Cl^?, Br^? and I^? ) decreased the antiferromagnetic exchange coupling between Cr(III) centres such that by going from F^? to I^? the J values became more positive. In the case of hydroxo-bridged model [Cr₂OH(tBuCO₂)₂(H₂O)₂(OH)₄]^?1, replacement of hydroxyl by methoxy anion (OMe^?) strengthened the antiferromagnetic property of the complex but substitution by sulfanide (SH^?) and amide (NH₂^?) anions weakened it and changed the nature of complexes to ferromagnetic. Because of their different magnetic properties, these new investigated complexes can be suggested as interesting synthetic targets. Also, the J value changes due to ligand substitution were evaluated and it was found that the Cr–X bond strength and partial charges of involved atoms were the most effective factors on it.     

硅酸铜色谱分离中性氨基酸研究

本文合成了一种新型无机离子交换剂—硅酸铜,对其进行了中性氨基酸(Gly,Ala)的色谱分离研究,并与硅酸锌的分离性能进行了比较,显现出较好的特性。     

Study on cytotoxicity and photocatalytic properties of different titania/hydroxyapatite nanocomposites prepared with a combination of sol–gel and precipitation methods

Research on Chemical Intermediates - In the present study different titania/hydroxyapatite nanocomposites were successfully synthesized via a combination of sol–gel and precipitation methods....     

强度理论百年总结

自从1900年著名的Mohr-Coulomb强度理论建立以来,已有100年的历史.在20世纪,关于材料在复杂应力状态下的强度理论进行了大量的理论研究和实验研究工作.本文对材料(包括金属材料、岩石、土、混凝土、冰、铁、聚合物、含能材料等)在复杂应力状态下强度理论(屈服准则、破坏准则等)的百年发展进行了总结,讨论了各种准则之间的关系,为研究和工程应用中的合理选择破坏准则提供了一种方法.文中还总结了三大系列强度理论、统一屈服准则、统一强度理论和其他各种强度理论,并简述了强度理论的计算机实施,以及多轴疲劳等问题.     

一类具有Logistic增长和HollingⅡ类功能反应的免疫模型

研究了一类具有Logistic增长和HollingⅡ类功能反应的免疫模型.以时滞为分支参数,分析了系统正平衡点的稳定性和Hopf分支的存在性;然后利用中心流形定理和规范型方法,给出了分支周期解的分支方向与稳定性的计算公式,利用数值模拟验证了所得结论.     

Electrodeposition iron target for the cyclotron production of 55Co in labeling proteins

Natural iron electrodeposition on copper substrate was studied with the aim of production of cobalt-55 radionuclide. ⁵⁵Co seems well suited for PET imaging due to its high abundance of positron decay (I _β+ = 76%), its relatively long half-life (T _1/2 = 17.5 h) and its mean positron energy (E _avg = 570 keV). The electrodeposition experiments were carried out by chloride bath. Operating parameters such as pH, temperature, current density and amount of the electrolyte components are also optimized. The optimum conditions of the iron electrodeposition were follows: 8 g/L FeCl₂, 2 g/L CaCl₂, pH = 1, DC current density of 21.3 A/dm² with a bath temperature of 75 °C temperature and 20% current efficiency. SEM photomicrographs demonstrated fine-grained structure of the deposit obtained from the optimum bath. The electroplated iron-target was irradiated with 29.5 MeV protons at current of 100 μA for 1 h and yields of about 31.25 MBq/μAh were experimentally obtained.     

Theoretical study of the mechanism of stable phosphorus ylides derived from 2-aminothiophenol in the presence of different dialkyl acetyelenedicarboxylates

A stepwise reaction mechanism between triphenylphosphine 1 and dialkyl acetylenedicarboxylates 2 in the presence of a SH-acid, such as 2-aminothiophenol 3, has been investigated theoretically with B3LYP method using 6-311++G(d,p) basis set. Potential energies of all structures participating along the reaction path have been evaluated. For all the reactions investigated, the first step was recognized to be the rate-determining step. Quantum mechanical calculations clarified the existence of reaction product as a mixture of two E- or Z-geometrical isomers, and indicate which one of them represents the major form. The effect of subsituated alkyl groups on the potential energy surfaces was investigated. Also, the natural bond orbital method was applied for better understanding the molecular interactions.     

Further Insight into the Mechanism of the Novel Multicomponent Reactions Involving Isoquinoline and Dimethyl Acetylenedicarboxylate in the Presence of 3‐Methylindole: Theoretical and Experimental Approach

The kinetics of the reactions among isoquinoline, dimethyl acetylenedicarboxylate, and 3‐methyl indole (as NH‐acid) was studied using UV spectrophotometry. The overall rate constant (k_ov) was evaluated from the slope of the plot of k_obs versus reactant concentration. A large deal of useful information was obtained from the study of the effects of solvent, temperature, and reactants and concentration on the reaction rates. Based on experimental data and theoretical concepts, the reaction's first step (k₁) was recognized as the rate‐determining step. Theoretical studies were performed to evaluate potential energy surfaces of all components participated in the reaction mechanism. Furthermore, the proposed mechanism was confirmed by the obtained results. The probable reaction path and product configuration were suggested based upon the theoretical results.     

Theoretical study on mechanism of reaction between tert-butyl isocyanide and dimethyl acetylenedicarboxylate in presence of ethanethiol or thiophenol

Research on Chemical Intermediates - The mechanism of the multicomponent reaction between tert-butyl isocyanide and dimethyl acetylenedicarboxylate in presence of ethanethiol and thiophenol (as...