Analytical chemistry of nonlinear systems

Analytical methods for characterizing complex, nonlinear chemical systems are reviewed. Emphasis is on those aspects of systems which make their characterization more difficult than just measuring concentrations or simple reaction rates. Examples include phase transitions, oscillating chemical reactions, laser fluctuations, and electrochemical oscillations. Data reduction algorithms specific to such systems are described.     

The current state of analytical control in Lithuania

In Lithuania research and development in chemical analysis are concentrated in scientific institutes and universities. The main fields of interest focus on biosensors, electrochemical sensors, sampling techniques and methods, study of atomization processes in spectrochemical analysis and noise evaluation in analytical measurements. Some laboratories also take part in international environmental monitoring programmes. There are about 50 researchers at the Ph.D. level engaged in analytical chemistry and several hundred technicians specialized in the field of analytical control. About one hundred chemical laboratories are active in scientific institutes, universities and factories. Specialized laboratories of chemical analysis are at the disposal of Environmental Control and Health Protection Departments and forensic investigation organizations. So far no laboratories are accredited according to the ISO 9000 norms. Special courses on analytical chemistry are offered at a few schools of higher education in the country. Only at the Department of Analytical Chemistry of the University of Vilnius specialized programmes are available to postgraduate students working towards a Ph.D. to improve their skills in current techniques of analytical chemistry. Recently the Technical Committee TC-16 for Chemical Analysis was formed within the standardization system of Lithuania. Its main activities are centered on issues such as national terminology, certified reference materials (CRMs), analytical methods and analytical quality assurance. There are numerous problems related to national terminology, the preparation of special documents in the field of analytical control and the production of regional environmental CRMs. Problems, also arise in obtaining and using CRMs for analytical instrument calibration and validation.     

Evaluation of the Chemical Exergy of Fuels and Petroleum Fractions

A correlation formula to estimate chemical exergies of oil fractions and fuel mixtures from enthalpy of combustion and atomic composition is developed. Heat capacity ofa mixture of 10 hydrocarbons was measured in the range 5–290 K. It was shown that contribution of entropy of mixing to exergy of typical oil fractions is about –0.11% in the approximation of ideal solution, and about –0.18% for a real solution. This revised version was published online in July 2006 with corrections to the Cover Date.     

美国AP课程中化学概念的引导式探究教学*——以“化学方程式”为例

在美国《AP化学课堂中的引导式探究活动》中,明确了概念性知识采用探究式教学方式的必要性,并根据学习圈理论依次划分出概念探究、概念形成、概念应用及概念评估4个连续的教学活动阶段,使学生能够全程参与到科学概念的形成过程中。以“化学方程式”教学内容为例,介绍了相关教学理论及在此基础上形成的探究式教学闭环,以期对国内中学有关化学概念的探究式教学改革起到一定的借鉴与参考作用。     

Design of thiol-containing amino acids for native chemical ligation at non-Cys sites

<正>Protein chemical synthesis usually relies on the use of native chemical ligation that couples peptide thioester with a Cys-peptide.A limitation of this method is the difficulty of finding an appropriate Cys ligation site in many synthetic targets.To overcome this problem,the ligation-desulfurization approach has been developed.This approach involves the use of a thiol-containing amino acid as the ligation partner.After the sequence assembly is completed,the thiol group is removed through a desulfurization reaction to generate the standard amino acids.Currently this strategy has been applied to the ligations at a number of amino acids including Ala,Phe,Val,Lys,Thr,Leu,Pro and Gln.The present article reviews the design and synthesis of these thiol-containing amino acids for native chemical ligation at non-Cys sites.     

Kinetic study of depolymerization of polyurethanes: A experimental and computational insight for chemical recycling

This work reports experimental and computational studies of polyurethanes depolymerization from industrial waste through a reaction with potassium hydroxide. A computational study was performed to identify the chemical reaction mechanism, which is more difficult to determine experimentally. Kinetic and thermodynamic parameters of activation process were also obtained by theoretical calculations. An experimental procedure led to products identified by ¹³C solid-state NMR analysis, which agree to the computational study. A small variation of less than 5% in the activation energy values found between the data obtained through theoretical calculations and experimental methods suggests that the described computational procedure is enough to describe the process in a satisfactory manner.     

高中学生化学概念掌握和问题表征程度关系的实证研究

本研究结合国内外有关化学概念教学的研究情况,对高中学生化学概念掌握和问题表征程度的关系进行了实证性的探索和研究。设计并在江苏省7所不同类型的学校进行了有关化学概念掌握的研究测试,同时选取优差学生进行有关化学问题的口语报告作业。研究结果表明：学生化学概念理解水平显著地影响着其解题时的表征程度。     

化学计量在产品质量保证中的重要作用

阐述在化学分析中,由于增强了化学计量意识,满意地解决了粘胶基碳布质量问题,显示出化学计量在产品质量保证中的重要作用。     

基于核心素养的化学实验社团活动*

通过问卷的形式调查了赣州市高中化学实验教学开展的情况,结合赣州中学化学实验社团开发与运行的实际,研究了化学实验社团的创建与运行、开展趣味化学实验社团活动、社员参加化学研学活动、拍摄社团原创趣味实验视频、创办化学实验社团公众号、创新改进教材实验等等。实践结果表明:在高中开发化学实验社团具有可行性和操作性,通过开展化学实验社团活动,可以锻炼学生多方面的能力、促进学生化学核心素养的发展。     

Statistics of the Popularity of Chemical Compounds in Relation to the Non-Target Analysis

The idea of popularity/abundance of chemical compounds is widely used in non-target chemical analysis involving environmental studies. To have a clear quantitative basis for this idea, frequency distributions of chemical compounds over indicators of their popularity/abundance are obtained and discussed. Popularity indicators are the number of information sources, the number of chemical vendors, counts of data records, and other variables assessed from two large databases, namely ChemSpider and PubChem. Distributions are approximated by power functions, special cases of Zipf distributions, which are characteristic of the results of human/social activity. Relatively small group of the most popular compounds has been denoted, conventionally accounting for a few percent (several million) of compounds. These compounds are most often explored in scientific research and are practically used. Accordingly, popular compounds have been taken into account as first analyte candidates for identification in non-target analysis.     

Temperature-dependent approach to chemical reactivity concepts in density functional theory

The chemical reactivity concepts of density functional theory are studied through a unified view in the temperature-dependent approach provided by the grand canonical ensemble. This procedure leads to a more general perspective that enriches our understanding of the behavior of the average energy and its derivatives with respect to the average number of electrons, provides alternative definitions for those quantities that are “ill defined” at zero temperature, and allows one to determine the relationships among reactivity concepts at any temperature. In particular, it has been found that at high temperatures the parabolic model for reactivity indicators may be justified through the electronic entropy term in the Helmholtz free energy, and that at nonzero temperatures there is an electronic heat capacity contribution to the average energy. In summary, the unified view of the temperature-dependent approach is an important complement to the zero-temperature formulation that clarifies fundamental issues therein.     

中学化学实验教学发展历程回顾及启示(中)

按照时间脉络将我国中学化学实验教学划分为4个主要阶段。第3个阶段是“拨乱反正”、快速发展期,伴随着“文革”结束和中国共产党十一届三中全会的召开,我国的教育事业迎来了发展的新时代。在这一历史时期,中学化学实验教学围绕国家的中心工作,育人功能不断拓展,教学质量不断提升,在教学实践中产生了一些新的教学理念和教学方法,教师素质不断提高,实验教学理论也得到了发展。     

简析化学文化与化学教育

从文化的角度看待化学,分析了化学文化的内涵,阐明了化学文化的教育功能,并根据化学文化的研究,论述了化学文化观下的化学教育,以及在化学教育中体现化学文化的途径。     

化学生物学新前沿——化学蛋白质组学

随着包括人类在内的主要模式生物的基因组计划的完成,生命科学的研究重心转向蛋白质组的研究--在对应基因组的整体蛋白质水平上系统研究调控细胞生命活动的蛋白质.化学蛋白质组学是化学生物学在后基因组时代的最新发展:化学蛋白质组学利用化学小分子为工具和手段,以基于靶蛋白质功能的新战略探测体内蛋白质组,是新一代的功能蛋白质组学.本文综述了化学蛋白质组学的最新进展、有关技术及其在生物医学和药物研发等方面的应用,并对化学蛋白质组学的发展趋势和前景进行了讨论.     

Total Chemical Synthesis and Biological Activities of Glycosylated and Non‐Glycosylated Forms of the Chemokines CCL1 and Ser‐CCL1

CCL1 is a naturally glycosylated chemokine protein that is secreted by activated T‐cells and acts as a chemoattractant for monocytes. 1 Originally, CCL1 was identified as a 73 amino acid protein having one N‐glycosylation site, 1 and a variant 74 residue non‐glycosylated form, Ser‐CCL1, has also been described. 2 There are no systematic studies of the effect of glycosylation on the biological activities of either CCL1 or Ser‐CCL1. Here we report the total chemical syntheses of both N‐glycosylated and non‐glycosylated forms of (Ser‐)CCL1, by convergent native chemical ligation. We used an N‐glycan isolated from hen egg yolk together with the Nbz linker for Fmoc chemistry solid phase synthesis of the glycopeptide‐^αthioester building block. 3 Chemotaxis assays of these glycoproteins and the corresponding non‐glycosylated proteins were carried out. The results were correlated with the chemical structures of the (glyco)protein molecules. To the best of our knowledge, these are the first investigations of the effect of glycosylation on the chemotactic activity of the chemokine (Ser‐)CCL1 using homogeneous N‐glycosylated protein molecules of defined covalent structure.     

中学化学教学中的追求简便

以化学用语、化学计算的发展为例,论述了追求简便是化学学科发展的重要推动力。如果教师给予正确的引导,合理追求简便将成为学生创新的不竭动力。以化学教学中2个简化不当的例子说明,过度追求简便会束缚学生的思维,阻碍教学研究的发展与兴盛。     

Chemical network algorithms for the risk assessment and management of chemical threats

A network of chemical threats: Current regulatory protocols are insufficient to monitor and block many short-route syntheses of chemical weapons, including those that start from household products. Network searches combined with game-theory algorithms provide an effective means of identifying and eliminating chemical threats. (Picture: an algorithm-detected pathway that yields sarin (bright red node) in three steps from unregulated substances.).     

Structure of irradiated polytetrafluoroethylene according to DFT calculations of NMR chemical shifts

Methods of density functional theory were used to calculate ¹H, ¹³C, and ¹⁹F magnetic shielding tensors for C₇F_nH_mO_l model molecules, which can arise as fragments from radiation exposure of polytetrafluoroethylene.     

基于化学史和实验数据的化学键概念教学

沿循化学键发展史、创设实验和文献情境、分析实验数据,引导学生自主建构化学键的概念及其表征方式。研究结果表明:基于化学史和实验数据的教学不仅能帮助学生充分理解概念的含义,在学生构建概念并解释真实问题的过程中,还能发展学生宏微结合、证据推理、科学探究与社会责任的化学学科核心素养,认识化学研究的创新方法和研究结论的相对合理性。