A density functional study on the formation of charge transfer complexes between alkaloids and iodine monochloride

The formation of charge-transfer (CT) complexes between N-methyl-6,7-methylenedioxy-tetrahydro-4-isoquinolone (MMDTIQ, the model molecule of alkaloids) and iodine monochloride has been studied with the density functional B3LYP method. The competition for ICl between n-donor(s) and π-donor in the same molecule has been compared for the first time. The results indicate that the electron-donating ability of various donor sites decreases in the following order: amino nitrogen>carbonyl oxygen>etheric oxygen≈aromatic ring. Complexes with a stoichiometry of 1:1 to 1:5 (MMDTIQ–ICl) might form. Among complexes with a given stoichiometry, the one in which the phenyl ring is involved in the binding is always the least stable. According to these results, in order to ensure an alkaloid iodinated, the amount of ICl should be far beyond that of alkaloids and a low polar solvent should be used, which is quite in agreement with our recent experimental results.     

The microstructure and Ruppeiner geometry of charged anti-de Sitter black holes in Gauss–Bonnet gravity: from the critical point to the triple point

Ruppeiner geometry has been successfully applied in the study of the black hole microstructure by combining with the small–large black hole phase transition, and the potential interactions among the molecular-like constituent degrees of freedom are uncovered. In this paper, we will extend the study to the triple point, where three black hole phases coexist acting as a typical feature of black hole systems quite different from the small–large black hole phase transition. For the six-dimensional charged Gauss–Bonnet anti-de Sitter black hole, we thoroughly investigate the swallow tail behaviors of the Gibbs free energy and the equal area laws. After obtaining the black hole triple point in a complete parameter space, we exhibit its phase structures both in the pressure–temperature and temperature–horizon radius diagrams. Quite different from the liquid–vapor phase transition, a double peak behavior is present in the temperature–horizon radius phase diagram. Then we construct the Ruppeiner geometry and calculate the corresponding normalized curvature scalar. Near the triple point, we observe multiple negatively divergent behaviors. Positive curvature scalar is observed for the small black hole with high temperature, which indicates that the repulsive interaction dominates among the microstructure. Furthermore, we consider the variation of the curvature scalar along the coexisting intermediate and large black hole curves. Combining with the observation for different fluids, the result suggests that this black hole system behaves more like the argon or methane. Our study provides a first and preliminary step towards understanding black hole microstructure near the triple point, as well as uncovering the particular properties of the Gauss–Bonnet gravity.     

Dehydration characteristics of struvite-K pertaining to magnesium potassium phosphate cement system in non-isothermal condition

Struvite-K (KMgPO₄·6H₂O) is the main hydration product of magnesium potassium phosphate cement. Its thermal stability is critical to the properties of magnesium potassium phosphate cement. Therefore, in this study, the dehydration behavior of struvite-K was investigated at N₂ atmosphere in non-isothermal condition. The process was conducted and controlled in a simultaneous TG/DTA analyzer, at heating rates of 2, 5, 10, 15, and 20 K min^?1. The residual mass was always around 58.5% of the initial one, regardless of the heating rate, which corresponds to the dehydration reaction through one step, KMgPO₄·6H₂O → KMgPO₄. The activation energy (E _a) corresponding to the dehydration of struvite-K was evaluated by non-isothermal kinetic analysis based on the application of isoconversional methods (Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods). The calculated results show that Flynn–Wall–Ozawa has slightly higher values of activation energy (E _a) and correlation coefficients (R ²). Both methods have been proved to be suitable for analyzing dehydration behavior of struvite-K.     

量子化学和统计热力学结合的实验:确定过氧化氢二面角

介绍一个面向高年级本科生的计算化学实验。通过量子化学计算与统计热力学方法相结合,预测了298 K时过氧化氢的二面角,并与实验值进行比较。通过这一应用实例,使学生能够深入理解结构化学和物理化学的相关理论知识,尤其是对统计热力学的本质有一个直观认识,提升学生利用统计热力学处理科学问题的能力。     

附面层吸除对带间隙的高负荷压气机叶栅流动特性影响的实验研究

将附面层吸除技术应用于带间隙的高负荷压气机叶栅中,并在低速平面叶栅风洞里,实验研究了附面层吸除对带间隙的高负荷压气机叶栅流动特性的影响。实验采用五孔气动探针测量了叶栅出口截面参数,得到了该截面的二次流速度矢量分布,并对叶栅壁面进行了墨迹流动显示。结果表明,采用恰当的附面层吸除设置可以大幅改善流动,降低损失;在吸力面附近和间隙内采用附面层吸除(本文的方案1、2和4)都将削弱间隙泄漏流动的动能,从而影响吸力面再附线和端壁分离线的长度和位置,达到对相应区域三维流动分离的控制,并大幅降低总损失,其中方案1的损失下降达到20.8%。     

磷灰石结构荧光粉Ba10(PO4)6F2:Ce3+,Tb3+的合成、发光和能量传递

采用高温固相法合成了系列Ce~(3+)和Ce~(3+)/Tb~(3+)激活的具有磷灰石结构荧光粉Ba_(10)(PO_4)_6F_2。用X射线衍射(XRD)、扫描电镜(SEM)、激发和发射(PLE和PL)光谱对样品进行了表征分析。研究结果表明:所合成的荧光粉Ba_(10)(PO_4)_6F_2∶Ce~(3+),Tb~(3+)具有氟磷灰石结构,样品微观呈现不规则形貌。荧光粉Ba10-x(PO4)6F2∶x Ce~(3+)的相对发射强度随着x增加而增强,当x=0.09时,荧光强度达到最大。荧光粉Ba_(10)(PO_4)_6F_2∶Ce~(3+),Tb~(3+)的激发光谱为240～330 nm的宽带,发射光谱呈现出Ce~(3+)的5d→4f跃迁紫外光(335和358 nm)发射和Tb~(3+)的4f→4f跃迁绿光(542 nm)发射。光谱特性表明,发光过程中存在Ce~(3+)→Tb~(3+)能量传递,能量传递效率可以达到60%。计算Ce~(3+)和Tb~(3+)的临界距离为0.79 nm,能量传递机理是偶极-偶极交互作用。此外,详细论述了Ce~(3+)和Tb~(3+)之间的能量传递和发光的过程。通过调节Tb~(3+)的掺杂浓度,对荧光粉发光色坐标与Tb~(3+)的掺杂浓度之间的关系也进行了研究,随着Tb~(3+)的掺杂量从0增加0.52,荧光粉Ba_(10)(PO_4)_6F_2∶Ce~(3+),Tb~(3+)的发射光谱色坐标可以从(0.149 4,0.045 1)蓝色区变化到(0.280 1,0.585 3)绿色区。     

Topological Vortices in a Spin-Triplet Superconductor

Based on the complex three-component order parameter model of a spin-triplet superconductor, by using the C-mapping theory, we derive a new equation describing the distribution of the magnetic field for vortices, which can be reduced to the modified London equation in the case of ｜ψ^2｜^2 ~- ｜ψ^3｜^2 = 0 and Wl^1= 1. A magnetic flux quantization condition for vortices in a spin-triplet superconductor is also derived, which is topological-invariant. Fhrthermore, the branch processes during the evolution of the vortices in a spin-triplet superconductor are discussed. We also point out that the sum of the magnetic flux quantization that those vortices carried is 2nФo （Фo is the unit magnetic flux）, that is to say, the sum of winding number is even, which needs to be proved by experiment.     

Theoretical mechanism study of UF6 hydrolysis in the gas phase

The mechanism of the gas-phase reaction UF 6 + H 2O --> UOF 4 + 2HF is explored using relativistic density functional theory calculations. Initially, H 2O coordinates with UF 6 to form a 1:1 complex UF 6.H 2O. Over an activation energy barrier of about 19 kcal/mol, H 2O transfers a H atom to a nearby ligand F, resulting in UF 5OH + HF. The eliminated HF or another H 2O molecule may form a hydrogen bond with UF 5OH. Starting from UF 5OH, the second HF elimination results in UOF 4. If UF 5OH is in the isolated form, UF 5OH --> UOF 4 + HF takes place over a barrier of 24 kcal/mol. If UF 5OH is hydrogen-bonded with H 2O or HF, the conversion barrier is less than 10 kcal/mol. Once formed, the unstable UOF 4 tends to associate with additional ligands and hydrogen-bonding donors. The calculated binding energies indicate the significance of such interactions, which may have profound impact on further HF eliminating reactions. The IR spectra features can be used to indicate the formation and interaction type of the intermediates and products.     

Theoretical study on reaction mechanism of fulminic acid HCNO with CN radical

The HCNO + CN reaction is one potentially important process during the NO-reburning process for the reduction of NOx pollutants from fossil fuel combustion emissions. To compare with the recent experimental study, we performed the first theoretical potential energy surface investigation on the mechanism of HCNO + CN at the G3B3 and CCSD(T)/aug-cc-pVTZ levels based on the B3LYP/6-311++G(d,p) structures, covering various entrance, isomerization, and decomposition channels. The results indicate that the most favorable channel is to barrierlessly form the entrance isomer L1c NCCHNO followed by successive ring closure and concerted CC and NO bond rupture to generate the product P1 HCN + NCO. However, the formation of P4 (3)HCCN + NO, predicted as the only major product in the recent experiment, is kinetically much less competitive. This conclusion is further supported by the master equation rate constant calculation. Future experimental reinvestigations are strongly desired to test the newly predicted mechanism for the CN + HCNO reaction. Implications of the present results are discussed.     

Physical states and BRST operators for higher-spin <Emphasis Type="Italic">W</Emphasis> strings

In this paper, we mainly investigate the W _2,s ^M ⊗ W _2,s ^L system, in which the matter and the Liouville subsystems generate the W _2,s ^M and W _2,s ^L algebras, respectively. We first give a brief discussion of the physical states for the corresponding W strings. The lower states are given by freezing the spin-2 and spin-s currents. Then, introducing two pairs of ghost-like fields, we give the realizations of the W _1,2,s algebras. Based on these linear realizations, the BRST operators for the W _2,s algebras are obtained. Finally, we construct new BRST charges of the Liouville system for the W _2,s ^L strings at the specific values of the central charges c: for the W _2,3^L algebra, c=−24 for the W _2,4^L algebra and for the W _2,6^L algebra, at which the corresponding W _2,s ^L algebras are singular.