分子陀螺的设计、合成与组装

近来,科学家设计和合成了系列分子水平的陀螺。类似于儿童的玩具陀螺仪,这种分子陀螺由一个转子、一个定子框架和连接定子和转子的轴组成。定子框架通过自身的刚性结构为中心转子的转动提供足够的内在自由度,得以对内部的转子实施保护。并使得分子陀螺成为一个理想的分子转子。当转子上有偶极距时,则可能在外来电、磁、光的刺激下进行定向转动,成为分子马达。化学家们通过X射线晶体衍射技术、动态核磁技术、理论计算化学、热力学分析等方法表征了分子陀螺的各种特征,并积极探索其潜在的应用价值。本文着重介绍分子陀螺,以及超分子陀螺仪的发展历史以及研究进展。     

从分子构造到分子构型和分子构象（下）

范特霍夫和列贝尔分别各自提出碳原子的四个价键指向一个正四面体的四个顶点概念确立后,1885年德国化学家拜尔(Baeyer,Adolphvon 1835-1917)发表价键的张力学说。他根据碳原子四个价键的正四面体模型,任何两个价键之间的正常角度应当是109o28',如图I所示。     

从分子构造到分子构型和分子构象（中）

我们从(上)文看到,化学家们最初认为物质的性质只决定于物质的分子组成,后来逐渐认识到物质的性质除决定于物质的分子组成外,还决定于分子构造.     

从分子构造到分子构型和分子构象（上）

分子构造(constitution)是指分子中原子相互联结的方式和次序,过去长期以来称为分子结构((structure),根据国际纯粹和应用化学联合会的建议,改为“构造”。“结构”一词应用在广泛的范围,例如物质结构、原子的电子结构等等。     

基于C=O…HN分子间氢键的超分子液晶研究进展

基于C=O…HN的分子间氢键能够自组装形成具有精确分子排列和很好稳定性的有序结构,在设计构造液晶功能材料方面具有重要的不可替代的地位.分子形状是设计小分子热致液晶的一个主要考虑因素,它对液晶态的结构有至关重要的影响.以分子形状与液晶态相互关系为主线,重点介绍了目前文献报道的基于C=O…HN分子间氢键的盘状和楔形分子形成液晶的研究进展,以期为新型液晶材料的分子设计提供一些借鉴.     

卟啉超分子化合物在分子器件中的应用

分子电子器件已成为近年来的一个研究热点，卟啉类化合物因为光敏性好、性能稳定、易于修饰等优点成为分子器件研究的理想模型化合物。本文着重介绍了它在分子器件中的最新应用进展。     

分子调控的概念及其意义

在分子识别的基础之上提出了分子调控的新概念，指出分子调控是外界因素对分子某些性质的指令性干预，是超分子体系所持有的功能，通过这种调控作用，可以有意识、有目的地控制分子的行为，并列举若干实例加以说明。     

分子识别在分析化学中的应用

本文概述了分子模板理论的产生和发展，总结了分子模板技术在分析化学领域中的应用和发展趋势，同时对分子印渍技术的理论进行概述，并指出分子印渍技术在分析化学领域中的应用和发展情况，阐述了分子模板和分子印渍技在分子识别分析方面的应用前景，其将为各种物质的超微量分析提供更加讯捷，准确，方便的分析方法。     

分子逻辑器件研究进展

分子器件具有尺寸小、设计合成可控、存储量大、反应速度快、人工智能等诸多优点,是当今化学、物理和材料等领域研究最为重要的一个交叉领域.综述了近些年来分子逻辑器件领域的研究进展.介绍了各种类型的分子逻辑门、半(加)减法器、分子逻辑线路以及DNA分子和固态分子计算.最后提出了分子器件存在的问题并展望了其应用前景.     

药物头孢氨苄分子模板聚合物水中结合性质的研究

采用分子模板技术合成了以头孢氨苄为模板分子以三氟甲基丙烯酸和４－乙烯基吡啶同时为功能单体的分子模板聚合物。将得到的棒状聚合物研磨过筛后,运用平衡结合实验研究了头孢氨苄分子模板聚合物的结合性质,Ｓｃａｔｃｈａｒｄ分析表明,在所研究的浓度范围内,在聚合物中形成了两类不同的结合位点。头孢氨苄分子模板聚合物与其化学组成相同的非模板聚合物相比,有很高的结合容量。底物选择性实验表明,与其它结构相似的药物相比,     

Synthesis and Surface‐Spectroscopic Characterization of Photoisomerizable glyco‐SAMs on Au(111)

Photoisomerizable glyco‐SAMs (self‐assembled monolayers), utilizing synthetic azobenzene glycoside derivatives were fabricated. The ultimate goal of this project is to assay the influence of the 3D arrangement of sugar ligands on cell adhesion, and eventually make cell adhesion photoswitchable. However, it is a prerequisite for any biological study on the spatial conditions of carbohydrate recognition, that photoisomerization of the surface molecules can be verified. Here, we employed IRRAS and XPS to spectroscopically characterize glyco‐SAMs. In particular and unprecedented to date, we prove reversible E→Z→E isomerization of azobenzene glycoside‐terminated SAMs.     

偶氮苯衍生物自组装单分子膜中的分子取响

利用反射红外光谱研究了金表面一系列具有不同碳链长度的偶氮苯巯基衍生物的自组装单分子膜.通过对比各向同性样品的透射谱和单分子膜的反射谱中各个吸收峰强度,定量地研究了分子中各部分的取向与分子结构的关系.我们分别提出了烷基链和偶氮基团取向计算的方法,利用该方法成功地求得了分子中各部分在膜的倾角.结果显示,当分子中烷基链长度增大时,碳链和偶氮苯基团相对于法线的倾斜逐渐加剧.这种倾角的变化归因于分子中碳链间范德华引力增大时,引起分子逐渐倾斜以达到最佳的范德华接触.同时研究发现,烷基链和偶氮基团受碳长度变化的影响并不相同.当分子中亚甲基数目增多时,烷基链的倾角迅速增大而偶氮苯倾角的增大则相对缓慢,这反映了它们在空间需求和本身刚性上的不同。     

Improving the Switching Capacity of Glyco-Self-Assembled Monolayers on Au(111)

Self-assembled monolayers (SAMs) decorated with photoisomerizable azobenzene glycosides are useful tools for investigating the effect of ligand orientation on carbohydrate recognition. However, photoswitching of SAMs between two specific states is characterized by a limited capacity. The goal of this study is the improvement of photoswitchable azobenzene glyco-SAMs. Different concepts, in particular self-dilution and rigid biaryl backbones, have been investigated. The required SH-functionalized azobenzene glycoconjugates were synthesized through a modular approach, and the respective glyco-SAMs were fabricated on Au(111). Their photoswitching properties have been extensively investigated by applying a powerful set of methods (IRRAS, XPS, and NEXAFS). Indeed, the combination of tailor-made biaryl-azobenzene glycosides and suitable diluent molecules led to photoswitchable glyco-SAMs with a significantly enhanced and unprecedented switching capacity.     

Reversible wettability of optothermal responsively perfluoroalkyl azobenzene self-assembled monolayers

In this study, two perfluoroalkyl azobenzene trichlorosilanes were synthesized and then characterized by Fourier transform infrared spectroscopy (FT-IR), ¹H NMR, and ¹⁹F NMR. Subsequently, these fluorine containing trichlorosilanes were applied to form self-assembled monolayers (SAMs) on silicon substrates by the method of chemical deposition in liquid phase. The optothermal responsively isomerization of the azobenzene was achieved via UV irradiation and heat treatment. The surface structures of the SAMs were investigated by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). The results showed that the thermal migration of the terminal fluoroalkyl groups promoted the isomerization of the azo-groups. Moreover, the reversible contact angles of the SAMs demonstrated a good reversibility of surface wettability, which was consistent with the optothermal responsive isomerization of the azo-groups.     

Rational construction of self-assembly azobenzene derivative monolayers with photoswitchable surface properties

hoto-responsive azobenzene (ABZ) derivatives with different end groups (R) were employed to construct selfassembled monolayers (SAMs) on silicon substrates. The SAMs based on hydrophilic (4-(4'-aminophenylazo) benzoic acid, ABZ-COOH) show excellent reversible photoswitching performance with a large contact angle change of 35° under optimized process.     

新型偶氮苯硫醇衍生物自组装膜的制备与结构表征

Self Assembled Monolayers(SAMs) of a series of mercapto contained azobenzene derivatives with the structure of CnH2n+1AzoO(CH 2)mSH (where n =4,6,8,10,12; with m =3,5 respectively) were prepared and characterized. Wettability measurement of water on the SAMs demonstrates that molecular packing density in the monolayers increases while the alkyl chain in the molecules is lengthened. Both the n and m values have similar contribution to the wetting property of SAMs. The RA IR spectra reveal that the alkyl chains in the SAMs tilt away dramatically from the surface normal direction with the increase in their length. However, the orientation of azobenzene moiety is found to be influenced slightly by the alkyl chain length, which is due to the tenderness of the molecule.     

Study on self-assembled monolayers of functionalized azobenzene thiols on gold: XPS,electrochemical properties,and surface-enhanced Raman spectroscopy

Self-assembled monolayers (SAMs) of 4-acetamino-4'-(4-mercaptobutoxy)azobenzene (CH3)CONH-ph-N=N-ph-O(CH2)(4)SH, abbr. aaAzoC4SH) and 4-mercaptobutoxy azobenzene (ph-N=N-ph-O(CH2)(4)SH, abbr. AzoC4SH) on a gold surface have been studied by X-ray photoelectron spectroscopy (XPS), FT Raman spectroscopy, and electrochemistry. A surface-enhanced Raman scattering (SERS)-active system with a "sandwiched" structure of Ag/R-Azo-C4S-/Au was conveniently obtained by the method of Tollen's test. The relationship between the SERS effect and the structural nature of the system indicates that the enhancement correlates to both the silver islands above and the gold substrate underneath. The redox behaviors of the self-assembly on gold electrodes showed that the SAMs of the two compounds exhibit well-behaved voltammetric responses in a Britton-Robinson buffer corresponding to the irreversible two-electron, two-proton reduction-oxidation of azobenzene. The apparent electron-transfer rate kinetics is very sluggish, and the rate constant k(app) of aaAzoC4SH/Au (1.34 x 10(-6) s(-1)) is lower than that of AzoC4SH/Au (1.63 x 10(-4) s(-1)), which may be attributed to the different spatial restriction of close-packing structures on the conformational change accompanied by electron and proton transfer in the SAMs.     

The Intermolecular Interaction in Self-Assembled Monolayers on Gold Electrode

Theunderstandingoftheinteractionamongmoleculesisoffundamentalinterest.Selfassembledmonolayers(SAMs)havebeenusedasapowerfijlmethodtoanchorredoxactivespeciesontoelectrodeswithadesireddistanceandacontrolledmicroenvironment,whichpresentsanidealmodelforthestudyofintermolecularinteractionandlongrangeelectrontransfer(ET)kinetics'.Theazobenzenealkanethiol(HS-CH=CH,NHC(O)-adN=N-4,denotedasAzoCZSH)westudied,containsalargers-conjugatedsystem(azobenzene)andanamidegroup,whichcanformstrongintermolec…     

O?+?C2H4 potential energy surface: lowest-lying singlet at the multireference level

Extensive density functional theory (DFT) calculations have been performed to develop a force field for the classical molecular dynamics (MD) simulations of various azobenzene derivatives. Besides azobenzene, we focused on a thiolated azobenzene’s molecular rod (4′-{[(1,1′-biphenyl)-4-yl]diazenyl}-(1,1′-biphenyl)-4-thiol) that has been previously demonstrated to photoisomerize from trans to cis with high yields on surfaces. The developed force field is an extension of OPLS All Atoms, and key bonding parameters are parameterized to reproduce the potential energy profiles calculated by DFT. For each of the parameterized molecule, we propose three sets of parameters: one best suited for the trans configuration, one for the cis configuration, and finally, a set able to describe both at a satisfactory degree. The quality of the derived parameters is evaluated by comparing with structural and vibrational experimental data. The developed force field opens the way to the classical MD simulations of self-assembled monolayers (SAMs) of azobenzene’s molecular rods, as well as to the quantum mechanics/molecular mechanics study of photoisomerization in SAMs.     

Preparation and electrochemistry of azobenzene self-assembled monolayers on gold--long range tunneling and end-group hydrogen bonding effect

A series of thiol-functionalied azobenzene derivatives (RAzoCnSH: R=H for n=3-6, abbreviated as AzoCnSH; R=CH(3)CONH for n=4, abbreviated as aaAzoC4SH) on gold electrodes were prepared and their self-assembly and electrochemical properties were studied by cyclic voltammetry. They all formed uniform and reproducible self-assembled monolayers (SAMs) on gold and showed well-behaved voltammetric responses in aqueous solution. Both the length of the alkyl chain spacer and the H-bonding of the end acetamino group had effects on the stability and the electrochemical kinetics of the SAMs, and the effect of the H-bonding was dominant. The surface coverage of the SAMs (AzoCnSH) is gradually increased with an increase of the alkyl chain spacer length, whereas the presence of the terminal acetamino group leads to a greater increase of the surface coverage. At a low scan rate, voltammetric responses corresponding to an irreversible two-electron, two-proton reduction/oxidation of the trans-azobenzene redox center were obtained in the range of +300 mV and -800 mV, which exhibited very large peak-to-peak splitting. At a high scan rate of 500 mV/s, two steps of reversible one-electron, one-proton reduction/oxidation corresponding to the cis-isomer in azobenzene-thiol SAMs (n is odd) was clearly observed between +300 and -200 mV. The apparent electron-transfer rate is decreased with increasing distance between the azobenzene redox center and the gold electrode. The existence of the end acetamino group which restricted the conformational change during the redox process also led to a decrease of the standard rate constant, and this restriction effect is more predominant than the distance effect.