某些分析化学实验教材中均相沉淀概念的误区

目前,均相沉淀法在大学分析化学实验中已很少采用。高锰酸钾间接滴定法测定钙含量是大学分析化学实验中的经典实验之一,历史上存在均相沉淀法和传统沉淀法2种不同的沉淀操作。虽然我国现有大学分析化学实验中已不采用均相沉淀法进行该实验,但在某些分析化学实验教材中,却存在概念混乱的现象,即把传统沉淀法称作均相沉淀法。对这种现象进行了探讨和总结。     

Sandwich教学法在物理化学教学中的应用——以化学势表达式的推导为例

以化学势表达式的推导为例,探究了Sandwich教学法在物理化学教学中的应用。详细介绍了Sandwich教学法实施过程中教师如何提出问题以呈现教学目标,学生如何通过自主学习与全班交流来探究与解决问题,以及最后又如何通过总结与反馈回归教学目标。通过以学生为主体的Sandwich教学过程的实施,学生对化学势概念、热力学基本方程及状态函数法等重要的物理化学基本概念、公式及方法有了更深入的理解和掌握。Sandwich教学方法相较于传统教学模式更能激发学生学习的主动性和积极性,从而提高学生学习物理化学的兴趣与效果。     

表面增强拉曼光谱法分析软饮料中的阿斯巴甜

应用超声技术辅助预处理,以纳米银为活性基底,在溶液pH 5.0、纳米银与阿斯巴甜(APM)混合比例1∶1、混合温度30℃、加热时间6 min的条件下,利用表面增强拉曼光谱(SERS)结合化学计量法对纯品及软饮料中APM进行定量检测。结果表明:APM在0.5～100 mg/L范围内线性关系较好,其中水标准溶液的相关系数为0.993 3,检出限(LOD)为0.41 mg/L,苏打水、雪碧、可乐、芬达等标准溶液的相关系数为0.974 7～0.984 8,加标平均回收率为88.4%～121%,相对标准偏差小于7%。运用SERS检测软饮料中APM具有分析速度快、无损、环境污染小等优点,适用于食品中阿斯巴甜的定量分析,为食品添加剂的进一步表征和检测建立了依据,显示了SERS技术在化学物质检测领域具有巨大潜力。     

柱前衍生毛细管电泳-电致化学发光法测定瓜瓤组织中的瓜氨酸含量

以甲醛和硼氢化钠为主要衍生反应试剂,对瓜氨酸分子中的α-氨基进行N-甲基化得到具有强电致化学发光信号的单一衍生产物。据此建立了一种用毛细管电泳-电致化学发光法(CE-ECL)高选择性测定瓜瓤组织中瓜氨酸含量的新方法。在优化的实验条件下,瓜氨酸的衍生物可在5 min内达到电泳分离,且瓜氨酸浓度在9.0～250μmol/L范围内时,其衍生物的电泳峰强度值与待测浓度间呈良好的线性关系(r~2=0.999 6),检出限(S/N=3)为3.2μmol/L。对同一标准样品平行进样6次,测得其电泳峰强度值和迁移时间值的相对标准偏差分别为2.6%和0.92%。此外,采用标准加入法对4种鲜瓜瓤组织中的瓜氨酸进行了定量测定,结果表明西瓜、甜瓜、籽瓜、哈密瓜的鲜瓜瓤组织中瓜氨酸的含量分别为2.75、0.95、1.26、1.19 mg/g,对实际样品的加标回收率为91.4%～106%。     

Chiral DMAP‐N‐oxides as Acyl Transfer Catalysts: Design,Synthesis, and Application in Asymmetric Steglich Rearrangement

A DMAP‐N‐oxide, featuring an α‐amino acid as the chiral source, was developed, synthesized and applied in asymmetric Steglich rearrangement. A series of O‐acylated azlactones afforded C‐acylated azlactones possessing a quaternary stereocenter in high yields (up to 97 % yield) and excellent enantioselectivities (up to 97 % ee). Compared to the widespread use of pyridine nitrogen, which serves as the nucleophilic site in the asymmetric acyl transfer reaction, we discovered that chiral DMAP‐N‐oxides, in which the oxygen now acts as the nucleophilic site, are efficient acyl transfer catalysts. Our finding might open a new door for the development of chiral DMAP‐N‐oxides for asymmetric acyl transfer reactions.     

Four new dammarane-type triterpenes derivatives from hydrolyzate of total Gynostemma pentaphyllum saponins and their bioactivities

Phytochemical investigation of hydrolysate of total G. pentaphyllum saponins led to the isolation of four novel triterpenes, Gypensapogenin U (1), Gypensapogenin V (2), Gypensapogenin W (3) and Gypensapogenin X (4). The structures of these compounds were identified by 1D, 2D-NMR and HR-ESI-MS evidences. Additionally, the protective activity of these new compounds against cardiomyocytes injury induced by H₂O₂ and their cytotoxic activity against t-HSC/Cl-6 cells were evaluated.     

Lab-in-cell based on spontaneous amino-yne click polymerization

Unnatural reaction in the living cells is a powerful tool for biological research. However, the polymerization inside cells is rarely reported. In this work, a lab-in-cell is illustrated based on our developed spontaneous amino-yne click polymerization. Carbonyl group activated terminal diyne can spontaneously polymerize with tetraphenylethene(TPE)-containing primary diamine inside cells, and polymer with weight-average molecular weight of 7,300 was yielded. By utilizing this in vivo amino-yne click polymerization and taking advantage of the aggregation-induced emission feature of TPE, a "turn-on" cell imaging was realized,and in-situ killing of cells was also acquired by destroying the structures of actin and tubulin, which cannot be realized by preprepared polymer. This strategy provides a useful platform and holds great promise in biochemistry and therapy applications.     

常用制冷工质稠密流体的黏度推算方法

本文通过关联无量纲化剩余黏度与对比密度的关系,提出了一种推算常用制冷工质稠密流体黏度的维里型黏度状态方程.应用该方程只需已知该工质的临界参数、分子量和偏心因子即可完成计算,使得迁移性质的计算在热力学面上和平衡性质的计算保持了完整的一致性.本文通过上述方法计算了9种常用制冷工质的液相黏度,与实验数据比较显示,总平均偏差为2.36%,最大偏差为27.6%.     

Synthesis and Structural Study of Sr2CuO3+δ Superconductor under High Pressure

A single-phase Sr₂CuO_3+δ superconductor is synthesized under high temperature and high pressure, in which oxygen atoms only partially occupy the apical sites next to the CuO₂ planes and act as hole-dopants. Thesuperconducting transition temperature with T_c^max=75K is achieved in the material. Structure analysis from x-ray powder diffraction data show that this material crystallizes into a K₂NiF₄ structure with tetragonal unit cell of a=3.795(3)AAand c= 12.507(1)AA. Energy-dispersive synchrotron x-ray-diffraction studies at ambient are performed on powder samples of Sr₂CuO_3+δ in a diamond-anvil cell at pressure up to 35GPa. Anisotropic compressibility is found. Pressure-induced isostructural phase transition might exist as revealed by the discontinuous change of crystal cell volume V withpressure.     

Effects of degree correlation on the controllability of networks

In this paper, we investigate the effects of degree correlation on the controllability of undirected networks with different degree-mixing patterns based on simulation analysis. Considering random pinning, max-degree pinning and mix-degree pinning, some relevance factors on controllability such as the control gain and the number of pinned nodes are discussed in detail. It is found that disassortative mixing enhances the network controllability contrast to assortative mixing, to which the network controllability is sensible. Furthermore, too large or too low value of the feedback gain can reduce the controllability. From the viewpoint of practical application, mix-degree pinning strategy is suggested in assortative network, while in disassortative network, max-degree pinning scheme is better than random pinning.