加热方式及原料配比对介孔CeO2结构及其光催化性能的影响

以P123（聚环氧乙烷-聚环氧丙烷-聚环氧乙烷三嵌段共聚物）为模板剂,Ce（NO₃）₃为反应原料,通过考察加热方式、加热温度、原料配比等因素,合成了结构性能较好、表面羟基含量较高的介孔CeO₂材料。利用XRD,N₂吸附-脱附,TEM,Raman,FT-IR等技术对合成样品的结构性能进行了表征,结果表明,当P123与Ce（NO₃）₃物质的量之比为1：10,在110℃水热下合成的CeO₂结构性能最好。以酸性橙7（AO7）为探针分子,对合成介孔CeO₂的光催化性能进行评价。光催化结果证明,由于表面羟基含量较高、介孔及氧缺位的形成,所合成结构性能较好的CeO₂,利用可见光可彻底催化降解溶液中的AO7。     

Mechanism and Influencing Factors of Wettability Alteration of Water-Wet Sandstone Surface by CTAB

Different experimental methods including ellipsometry, zeta potential measurements, imbibition studies, and contact angle measurements were used to study the mechanism and influencing factors of wettability alteration of water-wet sandstone surface caused by CTAB (hexadecyl trimethyl ammonium bromide). Results show that when the concentration of CTAB reaches a certain level (below CMC), due to the electrostatic attraction between the positively charged head groups of CTAB and the negatively charged sandstone surface, the monolayer of CTAB is formed and hydrophobic chains of CTAB molecules are toward the aqueous phase, making the solid surface oil-wet. When the concentration of CTAB continues to increase (above CMC), due to the hydrophobic interaction, the compact bilayer of CTAB is formed and hydrophilic head groups of CTAB molecules are toward the aqueous phase, rendering the solid surface water-wet. The contact angles between the oil–water interface and the surface treated with CTAB increase with the increase of the concentration of NaCl and CaCl_2. Compared to NaCl, the inorganic salt CaCl₂ has a greater impact on the contact angle. In addition, the contact angles increase with the increase of temperature and decrease with the increase of pH value of the aqueous solution.     

Handling of Environmental and Biological Samples via Pre-Column Technologies

Abstract

Sample handling is still a weak point in chromatography and in analytical chemisty in general. One consideration is the automation potential of new procedures. Solid-liquid extraction techniques in combination with pre-column technology are particularly promising in this regards. The construction and geometry of pre-columns both for conventional and narrow-bore HPLC are of major importance, since band broadening should be kept at a minimum for an optimal functioning of the analytical system. The various operations that can be carried out with such a pre-column are trace-enrichment, clean-up of the sample which depends on the type of adsorbents used in the precolumn, i.e., polar or apolar materials, ion exchangers or metal covered surfaces, etc., protection of the analytical column, field sampling and storage of samples and as a substrate for on-column chemical derivatizations. These various operations are demonstrated with practical examples from the fields of environmental and biological analysis. The selectivity can be further enhanced by coupling precolumn technology with selective detection modes such as diode array UV, electrochemical or fluorescence detection. This enables the construction of optimal and integrated analysis sytems which are fully automated and microprocessor controlled. They can also be made compatible with miniaturized LC-technology.     

Are accurate computations of the 13C′ shielding feasible at the DFT level of theory?

The goal of this study is twofold. First, to investigate the relative influence of the main structural factors affecting the computation of the ¹³C′ shielding, namely, the conformation of the residue itself and the next nearest‐neighbor effects. Second, to determine whether calculation of the ¹³C′ shielding at the density functional level of theory (DFT), with an accuracy similar to that of the ¹³C^α shielding, is feasible with the existing computational resources. The DFT calculations, carried out for a large number of possible conformations of the tripeptide Ac‐G XY ‐NMe, with different combinations of X and Y residues, enable us to conclude that the accurate computation of the ¹³C′ shielding for a given residue X depends on the: (i) (?,ψ) backbone torsional angles of X ; (ii) side‐chain conformation of X ; (iii) (?,ψ) torsional angles of Y ; and (iv) identity of residue Y . Consequently, DFT‐based quantum mechanical calculations of the ¹³C′ shielding, with all these factors taken into account, are two orders of magnitude more CPU demanding than the computation, with similar accuracy, of the ¹³C^α shielding. Despite not considering the effect of the possible hydrogen bond interaction of the carbonyl oxygen, this work contributes to our general understanding of the main structural factors affecting the accurate computation of the ¹³C′ shielding in proteins and may spur significant progress in effort to develop new validation methods for protein structures. © 2013 Wiley Periodicals, Inc.     

Incommensurate Phase in Λ-cobalt (III) Sepulchrate Trinitrate Governed by Highly Competitive N−H⋅⋅⋅O and C−H⋅⋅⋅O Hydrogen Bond Networks**

Phase transitions in molecular crystals are often determined by intermolecular interactions. The cage complex of [Co(C₁₂H₃₀N₈)]³⁺ ⋅ 3 NO₃⁻ is reported to undergo a disorder-order phase transition at T_c1 ≈133 K upon cooling. Temperature-dependent neutron and synchrotron diffraction experiments revealed satellite reflections in addition to main reflections in the diffraction patterns below T_c1. The modulation wave vector varies as function of temperature and locks in at T_c3≈98 K. Here, we demonstrate that the crystal symmetry lowers from hexagonal to monoclinic in the incommensurately modulated phases in T_c1<T<T_c3. Distinctive levels of competitions: trade-off between longer N−H⋅⋅⋅O and shorter C−H⋅⋅⋅O hydrogen bonds; steric constraints to dense C−H⋅⋅⋅O bonds give rise to pronounced modulation of the basic structure. Severely frustrated crystal packing in the incommensurate phase is precursor to optimal balance of intermolecular interactions in the lock-in phase.     

Recent research advances of the biomimetic tumor microenvironment and regulatory factors on microfluidic devices: A systematic review

Tumor microenvironment is a multicomponent system consisting of tumor cells, noncancer cells, extracellular matrix, and signaling molecules, which hosts tumor cells with integrated biophysical and biochemical elements. Because of its critical involvement in tumor genesis, invasion, metastasis, and resistance, the tumor microenvironment is emerging as a hot topic of tumor biology and a prospective therapeutic target. Unfortunately, the complex of microenvironment modeling in vitro is technically challenging and does not effectively generalize the local tumor tissue milieu. Recently, significant advances in microfluidic technologies have provided us with an approach to imitate physiological systems that can be utilized to mimic the characterization of tumor responses with pathophysiological relevance in vitro. In this review, we highlight the recent progress and innovations in microfluidic technology that facilitates the tumor microenvironment study. We also discuss the progress and future perspective of microfluidic bionic approaches with high efficiency for the study of tumor microenvironment and the challenges encountered in cancer research, drug discovery, and personalized therapy.     

基于元素指纹的白术产地溯源及其与土壤的相关性研究

本研究主要采用电感耦合等离子体质谱仪(ICP-MS)等手段测定5个产地白术41种矿质元素含量和土壤41种化学成分指标, 结合聚类分析法、偏最小二乘判别分析(PLS-DA)法和Pearson相关性分析研究了不同产区白术矿质元素特征以及不同产区土壤因子的差异, 并对它们的相关性进行了探讨. 结果表明, 采用无监督的聚类分析和有监督的PLS-DA均能正确判别不同产地的白术和土壤, 其中稀土元素在浙江白术与土壤间呈正相关. 另外, Li、V、Mn、Co、Cu、Rb、Cd、Cs、Ba等微量元素是白术产地溯源的关键因素. 研究发现在白术生产实践中可以通过适量控制种植地的土壤湿度、增施特定肥料等措施调控白术矿质元素含量. 本研究将为解释道地白术的品质形成机制, 保证白术药效质量的有效性提供一定帮助.     

“元素化学实验”中的“异常”现象(一)--Mn元素化学实验中的“异常”现象及其探析

大一学生在“元素化学实验”教学过程中,对反应条件如温度、催化剂、酸度、浓度或试剂用量等因素的影响考虑不周,可能出现某些实验现象和预想的或理论分析的结果不一致的“异常”现象。本文就学生在Mn元素化学实验过程中遇到的一些“异常”现象进行分析和总结,借助生动直观的演示实验,引导学生探究“异常”现象产生的可能原因和直观认识反应条件对反应结果的影响,培养学生的观察、分析、判断、归纳、推理和解决实际问题的能力。     

中学化学教学中的科学思维与逻辑辨析

化学是一门具有创造性的基础科学,是环境、生命、医药、材料等科学的基础,在思维逻辑上彰显和蕴含了丰富的科学思维方法。系统总结化学科学思维方法,可以有效破解中学化学学习中的“繁,难,乱”。在多年的教学实践中,提出了化学科学多向思维方法体系,强调多层次思维过程中对多因素的立体逻辑思维辨析。重点介绍了与中学化学教学相关的零阶、初阶、中阶和高阶逻辑思维辨析的内涵,期望化学教学中重视化学思维逻辑过程,实现化学教与学在思维模式上的深层次发展与提升。