Thermodynamic parameters of dilute solutions of a polymer in benzene at varying temperatures and concentrations

Dilatometric studies of solutions of four different mole fractions of poly(ethylene glycol) of average molecular mass 400 g mol^?1 dissolved in benzene have been performed to estimate molar volumes (V) and volume expansion coefficients (α) at different temperatures. From these, thermodynamic parameters appropriate to these solutions have been evaluated at different temperatures ranging from 299 to 328 K. These parameters have been employed to collect and discuss the information on molecular structure, molecular order, molecular packing, polymer segment extension, and molecular interactions.     

分子信标的构建及其应用研究进展

分子信标（molecular beacon,MB）是一种寡聚核苷酸荧光探针,其具有灵敏度高、特异性强、操作简单以及不必与未反应的探针分离即可实时检测等优点,在分子生物学和基因组学及分子医学等领域具有十分重要的应用价值。 本文介绍了近年来出现的各种新型分子信标的结构及工作原理,概述了分子信标技术在生命科学领域中的应用,展望了分子信标技术的发展趋势。     

干湿循环中水对13X分子筛机械强度劣化和晶格畸变

本文选用化工过程中常用的13X分子筛为模型,详细研究了在不同湿度下以及在干湿循环后分子筛机械强度的变化,发现经历干湿循环后分子筛的强度明显下降。经过干湿循环处理后的分子筛结构分析和表征结果显示,13X分子筛X射线衍射特征峰向高角度发生较显著的位移,这种位移与强度劣化有明显的正相关。干湿循环后分子筛的吸附-脱附特征也发生明显变化,对应的红外、核磁等表征结果也与强度下降、吸脱附特征变化、结构畸变有明显的对应关系。本文的结果表明,干湿循环过程中水分子可能诱发了13X分子筛晶格畸变,导致或者诱导了分子筛体相晶格有序度破坏,致使其机械强度大幅度降低。本文的结果对于改进分子筛载体的强度和理解分子筛载体失效有一定的指导意义。     

UV-vis, IR and 1H NMR spectroscopic studies of some mono- and bis-azo-compounds based on 2,7-dihydroxynaphthalene and aniline derivatives

The absorption spectra of mono- and bis-azo-derivatives obtained by coupling the diazonium salts of aromatic amines and 2,7-dihydroxynaphthalene have been studied in six organic solvents. The different absorption bands have been assigned and the effect of solvents on the charge transfer band is also discussed. The diagnostic IR spectral bands and 1H NMR signals are assigned and discussed in relation to molecular structure. Also, semi-empirical molecular orbital calculations using the atom superposition and electron delocalization molecular orbital (ASED-MO) theory have been performed to investigate the molecular and electronic structures of these compounds. According to these calculations, an intramolecular hydrogen bonding is essential for stabilization of such molecules.     

Gel permeation chromatography: calibration procedures for chains containing p-phenylene units

Experimental gel permeation chromatography calibrations have been obtained for polystyrene standards, polysulphone fractions, and polycarbonate fractions in chloroform at 30°. Chloroform is a good solvent for all three polymers which have similar polymer solvent interactions. The fractions have narrow molecular weight distributions, so that viscosity average molecular weight can be taken as the peak molecular weight of a chromatogram. The experimental polysulphone and polycarbonate calibrations are compared with curves calculated from the polystyrene calibration using equations which assume that the unperturbed mean-square end-to-end distance and hydrodynamic volume are universal calibration parameters. For molecular weights between 20,000 and 100,000 both universal calibration procedures were found to be acceptable. For polycarbonate extended chain length was also found to be satisfactory for universal calibration. For polycarbonate molecular weights below 20,000, the predicted molecular weight calibration deviated from the experimental data. Possible reasons for this difference are discussed.     

从分子水平研究电子传递

有机分子中电子传递受到诸多因素的影响, 纳米电极、界面、环境和分子本身都是必须要系统考察的因素. 本文从理论模拟和实验研究两个方面总结了在分子尺度上电子传递研究的最新进展. 着重讨论了分子动力学方法模拟纳米电极的制备, 量子化学方法研究电场作用下的分子构象及分子电导, 另外还讨论了扫描隧道显微术和电化学方法研究单分子结的电子传递. 分子电子传递的研究不仅涉及微观的实验测量, 从宏观的实验结果通过合理的分析推导, 也可以得到微观的信息.     

羧酸系混凝土超塑化剂的作用机理及分子结构模型设计

简要讨论了羧酸系混凝土超塑化剂的作用机理和分子设计原理,并详细分析了各种不同超塑化剂分子结构模型与分散和保坍性能之间的关系,提出了新型超塑化剂的分子设计原则,设计了一种集大减水、高保坍、低掺量的分子结构模型,对模型进行了试验验证,结果证实了其分子设计原则的可行性。     

Fast molecular mass and size characterization of polysaccharides using asymmetrical flow field-flow fractionation-multiangle light scattering

Asymmetrical flow field-flow fractionation (asymmetrical flow FFF), connected on-line to multi-angle light scattering detection (MALS) was shown here to be an efficient method for size characterization of pullulan standards and dextrans ranging from 20 000 up to 2 000 000 in molecular mass. The characterization of molecular mass and the molecular mass distribution of these polysaccharides is often complex and may require different methods. Using asymmetrical flow FFF-MALS, information was obtained not only about molecular mass and molecular mass distribution but also about hydrodynamic size as well as radius of gyration and conformation. The analysis time was very short, often below 5 min. It was shown that the pullulan standards have a narrow molecular mass distribution compared to the more polydisperse dextrans. Obtained molecular masses and distributions were in good agreement with data from the manufacturer. The dextrans, especially at high molecular mass, were found to have a more compact structure than the pullulans in both water and 0.1 M NaCl.     

改进的分子连接性方法

通过用Mulliken键级来加权分子连接性指数中的点价,使分子轨道理论与分子连接性指数有机地结合起来,将分子连接性指数改进成为一种量子拓扑指数。对比发现,分子连接性指数的点价与Mulliken键级具有相近的物理意义,而Mulliken键级更具有独特的优越性。利用改进的分子连接性指数对几种具有代表性的烃类与其体积、疏水常数以及热力学性质进行了关联,得到了满意的结果。     

Electronic,mechanistic, and structural factors that influence the performance of molecular water oxidation catalysts anchored on electrode surfaces

To harness solar energy to generate fuels powerful anodes for the water oxidation reaction need to be developed. During the last decade, an extensive number of molecular water oxidation catalysts based on transition metals have been reported, and in some cases, these molecular catalysts have been anchored on conductive surfaces generating molecular anodes. In this review, we analyze the factors that influence the performance of these molecular anodes, which are largely related to their mechanism of O–O bond formation and the nature of the anchoring functionality.     

分子力场进展

分子力学（简称ＭＭ）是近年来化学家常用的一种计算方法。与量子力学从头计算和半经验方法相比，用分子力学处理大分子可以大大节省计算时间，而且，在大多数情况下，用分子力学方法计算得到的分子几何构型参数与实验值之间的差值可在实验误差范围之内。所以，分子力学是研究生物化学体系的有效和可行的手段。分子力学的核心是分子力场。本文介绍了分子力场的量子力学背景、分子力场和光谱力场之间的关系。分子力场的一般形式、分力     

On the efficient calculation of the quantum properties (dipolar moments) of the molecular heteroatomic (nitrogen) polycyclic aromatic hydrocarbons

In this work, we have developed an efficient (very fast) theoretical methodology able to calculate the quantum properties of any molecular heteroatomic PAH. If all the heteroatoms are Nitrogens, we can obtain these results directly from its chemical formula. We have obtained and analyzed the electric dipolar moment of 43 small Nitrogen PAHs (NPAHs). We have obtained the atomic spin densities of several large (5,000 atoms) molecular Nitrogen Graphene Nanoribbons (GNRs), which have the Nitrogen atoms in the same zig-zag edge. According to our computational results, this kind of molecular Nitrogen GNRs should have significant ferroelectric and ferromagnetic properties.     

基于PET过程的分子开关型荧光传感器研究进展

基于PET过程的分子开关型荧光传感器研究进展;光诱导电子转移;给体;受体;分子开关;光物理技术     

芳杂环类多重氢键分子钳人工受体对中性分子的识别性能研究

根据多点氢键识别原理,设计合成了新的分子钳受体1～6。研究了其对巴比妥 、尿素、二苯甲酮、戊二酰亚胺等中性分子的识别性能。用差紫外光谱法测定了结 合常数和自由能变化（ΔG）。结果表明,所有分子钳受体与所考察的客体分子均 形成1：1型超分子配合物,识别作用的推动力主要为多重氢键的协同作用。讨论了 主客体间尺寸/形状、几何互补等因素对形成超分子配合物的影响。并利用~1H NMR、计算机模拟作辅助手段对实验结果和现象进行了解释。     

Application of preparative gel-permeation chromatography to studies of low molecular weight carboxy-polybutadienes

Low molecular weight carboxy-polybutadiene liquid polymers are used as the binderfuel fraction in solid composite propellants. Analytical GPC determinations of low molecular weight materials (100 through 500 molecular weight range) were previously found to correlate significantly with final propellant properties. These low molecular weight materials are being characterized, and studies of their role in determining propellant physical properties are being conducted. Sufficient quantities of material in the 100–500 molecular weight range have been isolated by using preparative scale GPC to establish the chemical nature of these materials. Infrared and chemical analysis of fractions collected by using preparative GPC also has permitted the construction of functional group distribution profiles. In addition, narrow fractions isolated over the molecular weight range of the whole polymer were analyzed for average molecular weight by vapor pressure osmometry and have been used as calibration standards for analytical GPC.     

Functional nanomachines: Recent advances in synthetic molecular machinery

A mini-review: As the top-down approach for miniaturisation of technology reaches its inherent limitations, robust strategies to build nanoscale machinery components, which have the ability to convert an input energy into motion, from the molecular level up, become increasingly important. Nature is certainly the most proficient in the control of molecular level motion; nevertheless, many successes have been enjoyed in the pursuit of mimicking key aspects of nature’s molecular machines, including two state switches, ion pumps, unidirectional rotary motors and molecular robots that can move molecular cargo. This mini-review outlines of some of the most impressive recent examples towards this end.     

On measurement of molecular and thermal diffusion coefficients in multicomponent mixtures

We have developed the theory for using the deflection of laser beams of various wavelengths to determine molecular and thermal diffusion coefficients in multicomponent mixtures. In the past, simultaneous determination of molecular and thermal diffusion coefficients have only been achieved for binaries. Our procedure is faster and more accurate than the current techniques to determine molecular diffusion coefficients. The analysis for an N-component mixture requires deflections from (N - 1) beams of different wavelengths. We show in an example that the molecular and thermal diffusion coefficients can be determined reliably in a ternary mixture.     

A mini review of the crossed molecular beam apparatus in molecular reaction dynamics

This review has introduced some experimental techniques of crossed molecular beam apparatus in chemical reaction dynamics. First of all, the history of crossed molecular beam equipment is retrospected in this paper. The detectors of both the universal crossed molecular beam machine and Hydrogen-atom Rydberg-tagging apparatus have been discussed. Other types of crossed molecular beam instruments have also been reviewed. Each experimental apparatus makes a compromise among the resolution, sensibility and universality. As a matter of fact, it is these equipments that make many breakthroughs happen in chemical reaction dynamics. This review aims to provide the readers and researchers with some information about the experiments in molecular reaction dynamics. We believe that new types of experimental techniques can emerge and contribute to the development of molecular reaction dynamics and relevant research fields.     

Recent advances in new-type molecular switches

Molecular switches that can undergo reversible switching between two or more different states in response to external stimuli have been used in the fabrication of various optoelectronic devices and smart materials for many decades, and also found many applications in sensing, molecular self-assembly and photo-controlled biological systems. Recently, mechanically interlocked molecules, such as rotaxanes and catenanes, and molecular rotary motors based on overcrowded alkenes have emerged as two new kinds of molecular switches. Some novel applications of above-mentioned molecular switches have been discovered. In this mini review, we mainly highlight noticeable achievements over the past decade in this field, and summarize the applications of new types of molecular switches, for instance, controlling the chiral space to regulate catalytic reaction as organocatalysts, controlling molecular motions, synthesizing a peptide in a sequence-specific manner and modulating the wettability of the self-assembled monolayers.     

Theoretical study of molecular conduction: I. Effective Green's function based on perturbation theory

There have been many experimental and theoretical studies on molecular conduction, as it is a fundamental parameter in the study of molecular‐scale electronics. We have investigated the features of molecular conduction using a Green's function method, which has often been used to solve problems in quantum transport and is also effective in elucidating electron transport in molecules. We have obtained the novel effective Green's functions, including the first‐order energy corrections, by accommodating the self‐energy of the electrodes as perturbation terms. Although these approximate Green's functions only provide information on the first‐order energy corrections, they can involve the elementary properties of molecular conduction. We propose a scheme for the analysis of the relations between molecular orbitals and their roles in molecular conduction and present analytical calculations for normal and cyclic polyenes. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006