Kinetic Study of the Degradation of PAC-1 and Identification of a Degradation Product in Alkaline Condition

A selective and validated stability-indicating LC method was developed for the kinetic study of the degradation of PAC-1, which was carried out in aqueous solutions at 37, 60, 80 and 100 °C with pH 1.5–9.0. Separation was performed on a Kromasil C₁₈ column with acetonitrile–water–fomic acid (30:70:0.1, v/v/v) as mobile phase with a flow rate of 1.0 mL min^?1 at 281 nm. The degradation rate obtained indicated a first-order reaction law and the activation energy (E _a) was calculated. The results showed that temperature and pH values were significant factors affecting the degradation of PAC-1. An unknown degradation product in alkaline condition was isolated using a reverse-phase semi-preparative LC system. The structure of the degradation product is identified as 2-hydroxy-3-(2-propenyl)-[[2-hydroxy-3-(2-propenyl)phenyl]methylene]hydrazone utilizing the ¹H NMR, ¹³C NMR, IR and Q-TOF-MS techniques.     

合成文拉法星的2-氮杂-1,3-丁二烯杂Diels-Alder反应与其 单分子环合竞争反应的研究

研究了不同的Lewis酸催化剂、温度、微波等条件下, 4-(4-甲氧苯基)-1-苯基-3-三甲基硅氧基-2-氮杂-1,3-丁二烯(2-ABDE)和亲二烯体环己酮发生杂Diels-Alder反应生成[4＋2]的六元环合产物噁嗪酮衍生物, 伴随的2-ABDE的 [2＋2]单分子环合, 生成单环β-内酰胺衍生物. 结果表明: 在低温条件下如(－78 ℃)[4＋2]反应占主导; 而在高温条件下(如135 ℃)仅进行[2＋2]反应. 微波加热方式可显著提高[2＋2]反应的速率和产率. 不同的Lewis酸催化剂对[2＋2]反应和[4＋2]反应的催化效率不同. Lewis酸的酸性强弱、软硬对2-ABDE的[2＋2]反应的催化能力起决定性作用.     

The geometry of optimal partitions in location problems

Given the position of some facilities, we study the shape of optimal partitions of the customers’ area in a general planar demand region minimizing total average cost that depends on a set up cost plus some function of the travelling distances. By taking into account different norms, according to the considered situation of the location problem, we characterize optimal consumers’ partitions and describe their geometry. The case of dimensional facilities is also investigated.     

Bifurcations of traveling wave solutions for the nonlinear schrodinger equation with fourth-order dispersion and cubic-quintic nonlinearity

For the nonlinear schrodinger equation with fourth-order dispersion and cubic-quintic nonlinearity, by using the method of dynamical systems, the dynamics and bifurcations of the corresponding traveling wave system are studied. Under different parametric conditions, twenty exact parametric representations of the traveling wave solutions are obtained.     

Structure and chemical bond characteristics of LaB6

The structure and chemical bond characteristics of LaB₆ have been achieved by means of the density functional theory using the state-of-the-art full-potential linearized augmented plane wave (FPLAPW) method, which are implemented within the EXCITING code. The results show our optimized lattice constant a (4.158 Å), parameter z (0.1981) and bulk modulus B (170.4 GPa) are in good agreement with the corresponding experimental data. Electron localization function (ELF) shows the La–La bond mainly is ionic bond, La–B bond is between ionic and covalent bond while the covalent bond between the nearest neighbor B atoms (B2 and B3) is a little stronger than that between the nearer neighbor B atoms (B1 and B4).     

Sulfur substitution and pressure effect on superconductivity of α-FeSe

In this paper, sulfur substitution and pressure effect on superconductivity of α-FeSe has been investigated in Fe(Se_1 ? xS_x)_0.88 (x = 0.1, 0.2). For x = 0.1, the critical temperature T_c is slightly larger than that of non-substituted sample, in consistent with the pressure effect on the superconductivity of α-FeSe. However, with further increasing S content to x = 0.2, T_c decreases. Temperature dependent of specific heat showed that the structural transition seems to be suppressed. T_c for x = 0.2 can be further decreased by applying pressure of 5 kbar, in contrary to the pressure effect on α-FeSe. We suggest that, in addition to the suppression of structural transition, other factors like the increase of carrier concentration should be considered for understanding the pressure effect on the superconductivity of α-FeSe.     

Unravelling the Synergy between Oxygen Vacancies and Oxygen Substitution in BiO2−x for Efficient Molecular‐Oxygen Activation

Defects in nanomaterials often lead to properties that are absent in their pristine counterparts. To date, most studies have focused on the effect of single defects, while ignoring the synergy of multiple defects. In this study, a model of photocatalytic O₂ activation was selected to unravel the role of dual defects by decorating bismuth oxide with surface O vacancies and bulk O substitution simultaneously. The introduction of dual defects led to a spatial and electronic synergistic process: i) O substitution induced a local electric field in the bulk of BiO_2?x, which promoted bulk separation of electrons and holes immediately after their generation; ii) O vacancies efficiently lowered the conduction band, served as the capture center for electrons, and thus facilitated the adsorption and activation of O₂. This effect was greatly promoted by the coexistence of bulk O substitution, and DFT calculations showed that only O substitution near an O vacancy could have this effect.