超分子凝胶的手性功能应用:手性分子识别与不对称催化

超分子凝胶通过形成三维空间网络结构将溶剂液体相固定化,是一类重要的软物质材料。由于超分子凝胶能快速形成,自组装形成的纳米结构均一、可调,且可大规模制备,因此成为超分子化学、纳米技术以及材料科学研究的重要研究方向之一,并在诸多领域得到广泛的功能研究和应用拓展,如在材料模板、光电开关、药物释放、分子识别和超分子催化等方面已有大量研究报道。由于超分子凝胶具有固-液相可逆转变、可控组装等特性,成为了超分子手性和分子手性研究的重要载体。近年来超分子凝胶在超分子手性催化、手性分子识别等方面取得了一系列重要突破,为超分子凝胶功能应用开辟了新的空间,为手性科学研究提供了新的手段和方法。     

手性杯芳烃及其超分子手性

杯芳烃是由苯酚单元通过亚甲基连接而成的空腔型分子,具有衍生位点多,构象丰富等特点,被称为第三代主体分子。在分子层次,依手性因素的结构特点不同,可将手性杯芳烃分为具有手性亚单元的杯芳烃、固有手性杯芳烃和桥手性杯芳烃。在超分子层次,杯芳烃自身或杯芳烃与其他分子或离子在溶液中、晶态中或二维表面可通过非共价键力形成多种拓扑结构的纳米手性聚集体。研究手性杯芳烃和基于杯芳烃的超分子手性组装体的合成、结构和性能,不仅在理解手性起源、手性结构等方面具有理论意义,而且有望获得以分子识别为基础的手性传感器、手性催化剂、手性分离材料、手性载体和手性纳米材料。本文综述近十年来有代表性的分子手性杯芳烃和以杯芳烃为组分的超分子手性聚集体的设计、合成、结构和功能。着重展示杯芳烃骨架在形成新颖分子手性和超分子手性上的优势,以及杯芳烃单元在实现特定功能如手性识别时发挥的作用。相信随着杯芳烃合成技术和杯芳烃超分子设计的发展,必将进一步发挥杯芳烃的结构优势,涌现出更多性能优异的手性杯芳烃功能分子和超分子手性杯芳烃功能材料。     

超分子凝胶中的光化学反应

超分子凝胶中的光化学反应是比较特殊的一类反应,通常是将具有光响应活性的基团或分子引入到超分子凝胶的自组装体系中,因此,能够将超分子凝胶独特的性质与光化学反应的优势有效地结合起来,构筑新型的光功能材料,这使得此类超分子凝胶在光信息存储、光开关及光转换器件等前沿领域具有广阔的应用前景.本文主要总结近年来国内外包括作者课题组对超分子凝胶中光化学反应方面的研究进展,以及其在多重响应凝胶、手性光学开关以及手性合成方面的应用.     

超分子聚合物凝胶

作为非常重要的软物质材料,超分子聚合物凝胶代表了一个全新的概念和更复杂的凝胶体系.这种新型的超分子体系的构建,是基于多种非共价相互作用协同的多层次组装.即小分子构筑基元首先组装成为超分子聚合物,而这些非共价聚合物的多层次组装形成凝胶的纳米结构.超分子聚合物凝胶无论是在结构上,还是在性能上都具有很多崭新的特点.因此,尽管有关超分子聚合物凝胶的研究开展的时间还很短,这一体系所表现出的独特性以及巨大潜力已经引起科学家们越来越广泛的关注.本文简要综述了这一领域的最新进展.主要论述基于多种非共价相互作用的超分子聚合物凝胶的构建以及对其力学性能的调控.     

超分子手性组装体的构建与应用

超分子手性组装体通常由多种非共价相互作用协同驱动形成,是一类具有独特手性限域微环境的软物质,对材料工程、生命科学、光学器件、催化合成等领域的发展具有重要作用.其主要构建方法分为三种;手性基元组装、手性因素诱导非手性基元组装、非手性基元对称性破缺组装.通过分析近年来的研究成果,归纳了利用这三种方法构建超分子手性组装体的一...     

基于芳香分子-糖类手性超分子组装体及功能

手性超分子组装体广泛存在于自然界中,因其在材料、化学和生物学等领域广阔的应用前景,引起了科学家们极大的兴趣。其中以糖类分子作为手性源,经分子自组装构筑手性超分子组装体的研究已成为超分子化学领域的研究热点之一。本文综述了基于糖类修饰的苝酰亚胺分子、偶氮苯分子、联苯类分子和卟啉类分子等芳香分子化合物经自组装构筑的手性超分子组装体,介绍了其在有机溶剂和水的混合溶剂、水中的凝胶性质,超分子手性特征和功能,糖分子类型与超分子组装体手性间的关系等,并对基于糖类的手性超分子组装体的前景进行了展望。     

手性超分子组装研究进展

介绍了超分子手性的基本构筑方式及其特点,分别从手性分子组装、手性分子诱导非手性分子及非手性分子组装等3个方面对最近几年来在手性超分子组装领域内的重要成果及最新进展进行了综述,并对这一领域的发展前景作了展望。     

胆酸超分子凝胶化学

胆酸来源丰富,价格低廉,在生命过程中发挥着重要的作用。与胆固醇不同,胆酸以其结构和修饰途径的多样性,以及独特的双亲结构备受超分子化学工作者关注。近年来以胆酸为基本构筑单元的小分子胶凝剂创制及其相关凝胶的研究取得了重要的进展。本文从胆酸衍生物结构设计到胆酸衍生物凝胶构建,概要介绍了胆酸超分子凝胶及其性能研究进展。在此基础上,简要阐述胆酸超分子凝胶材料的潜在应用。     

基于中性铂炔基元的超分子有机金属凝胶研究进展

作为一类经典的软物质材料,超分子凝胶在催化、化学传感、药物释放等许多领域展示了广泛的应用前景.最近人们研究发现,在基元砌块中引入金属特别是过渡金属之后,所形成的有机金属凝胶在光电材料、催化、磁性等方面具有独特的物理化学性质.近年来,电中性铂炔基元因其独特的线性结构、易合成及丰富的光物理性质在超分子化学及材料科学中被广泛应用.总结了基于中性铂炔基元的超分子有机金属凝胶的构筑及其功能研究进展,主要包括以苯撑共轭结构为核心骨架的铂炔有机金属凝胶以及官能团修饰的铂炔有机金属凝胶.     

基于天然小分子化合物的超分子自组装

天然产物来源广泛、手性结构独特、具有多修饰位点、良好的生物相容性和可控的降解性, 与其他非天然产物的自组装体系相比, 具有更多的优势. 简单修饰的天然产物在溶剂中容易形成氢键、π-π堆积、范德华作用等非共价键作用, 促使分子有序排列形成聚集体, 成为超分子自组装体系的重要构筑基元. 同时, 其独特的手性结构在分子有序排列过程中, 通常会实现手性由分子层次到超分子层次的传递和放大, 因此, 可用于构建螺旋带、纳米管等多种手性组装体. 天然产物良好的生物相容性和生物活性, 也使得基于此类化合物的组装体可应用于组织工程、药物传递、细胞成像等生命科学领域, 显示其广阔的应用前景. 本文介绍了基于氨基酸、糖、核苷碱基、甾体、三萜等天然产物缀合物在超分子自组装特性方面的研究概况及其发展趋势.     

Strong circularly polarized luminescence from the supramolecular gels of an achiral gelator: tunable intensity and handedness

Although the importance of circularly polarized luminescence (CPL) materials has been widely recognized, the CPL responses of supramolecular gels are still rarely studied. Moreover, developing CPL materials based on supramolecular gels is of great significance, due to their special advantages and important applications. Herein, we report the first circularly polarized supramolecular gels self-assembled exclusively from a simple achiral C ₃-symmetric molecule. Most importantly, the excellent tunability of these novel CPL materials, which benefits from achiral molecular building blocks as well as the nature of supramolecular gels, has been investigated. Thus, the CPL intensity of these supramolecular gels is easily enhanced by mechanical stirring or doping chiral amines. The handedness of CPL signals is controlled by the chirality of organic amines.     

Electron-induced switching of the supramolecular chirality of optically active polythiophene aggregates

A chiral regioregular polythiophene (PT), poly[3-[4-((R)-4-ethyl-2-oxazolin-2-yl)phenyl]thiophene] (poly-1), forms chiral aggregates which exhibit a unique induced circular dichroism (ICD) in the pi-pi transition region derived from the supramolecular chirality in the presence of various poor solvents or metal salts in chloroform. We report here that the chirality of such supramolecular aggregates can be switched ("on" and "off") through electron transfer. We have found that upon the addition of copper(II) trifluoromethanesulfonate [Cu(OTf)(2)] to the chiral aggregates of poly-1 in a chloroform-acetonitrile mixture, the ICD disappears because of the oxidative doping of the poly-1 main chain, while a further addition of amines such as triethylenetetramine (TETA) induces undoping of the poly-1 which results in the reappearance of the ICDs. Therefore, the supramolecular chirality of the poly-1 assemblies was reversibly controlled by the addition or removal of an electron from the poly-1 main chain. This may be the first example of a reversible supramolecular chirality switch on chiral PT aggregates. We investigated the mechanism of the chirality switch through the doping and undoping process on the polymer main chain by means of absorption and CD spectroscopies, ESR, cyclic voltammetry, X-ray diffraction, and AFM measurements.     

Molecular basis for water-promoted supramolecular chirality inversion in helical rosette nanotubes

Helical rosette nanotubes (RNTs) are obtained through the self-assembly of the GwedgeC motif, a self-complementary DNA base analogue featuring the complementary hydrogen bonding arrays of both guanine and cytosine. The first step of this process is the formation of a 6-membered supermacrocycle (rosette) maintained by 18 hydrogen bonds, which then self-organizes into a helical stack defining a supramolecular sextuple helix whose chirality and three-dimensional organization arise from the chirality, chemical structure, and conformational organization of the GwedgeC motif. Because a chiral GwedgeC motif is predisposed to express itself asymmetrically upon self-assembly, there is a natural tendency for it to form one chiral RNT over its mirror image. Here we describe the synthesis and characterization of a chiral GwedgeC motif that self-assembles into helical RNTs in methanol, but undergoes mirror image supramolecular chirality inversion upon the addition of very small amounts of water (<1% v/v). Extensive physical and computational studies established that the mirror-image RNTs obtained, referred to as chiromers, result from thermodynamic (in water) and kinetic (in methanol) self-assembly processes involving two conformational isomers of the parent GwedgeC motif. Although derived from conformational states, the chiromers are thermodynamically stable supramolecular species, they display dominant/recessive behavior, they memorize and amplify their chirality in an achiral environment, they change their chirality in response to solvent and temperature, and they catalytically transfer their chirality. On the basis of these studies, a detailed mechanism for supramolecular chirality inversion triggered by specific molecular interactions between water molecules and the GwedgeC motif is proposed.     

Macroscopic Chirality of Supramolecular Gels Formed from Achiral Tris(ethyl cinnamate) Benzene‐1,3,5‐tricarboxamides

A C₃‐symmetric benzene‐1,3,5‐tricarboxamide substituted with ethyl cinnamate was found to self‐assemble into supramolecular gels with macroscopic chirality in a DMF/H₂O mixture. The achiral compound simultaneously formed left‐ and right‐handed twists in an unequal number, thus resulting in the macroscopic chirality of the gels without any chiral additives. Furthermore, ester–amide exchange reactions with chiral amines enabled the control of both the handedness of the twists and the macroscopic chirality of the gels, depending on the structures of the chiral amines. These results provide new prospects for understanding and regulating symmetry breaking in assemblies of supramolecular gels formed from achiral molecular building blocks.     

Self‐Assembled Luminescent Quantum Dots To Generate Full‐Color and White Circularly Polarized Light

The design and fabrication of quantum dots (QDs) with circularly polarized luminescence (CPL) has been a great challenge in developing chiroptical materials. We herein propose an alternative to the use of chiral capping reagents on QDs for the fabrication of CPL‐active QDs that is based on the supramolecular self‐assembly of achiral QDs with chiral gelators. Full‐color‐tunable CPL‐active QDs were obtained by simple mixing or gelation of a chiral gelator and achiral 3‐mercaptopropionic acid capped QDs. In addition, the handedness of the CPL can be controlled by the supramolecular chirality of the gels. Moreover, QDs with circularly polarized white light emission were fabricated for the first time by tuning the blending ratio of colorful QDs in the gel. The chirality transfer in the co‐assembly of the achiral QDs with the gelator and the spacer effect of the capping reagents on the QD surface are also discussed. This work provides new insight into the design of functional chiroptical materials.     

Self-assembly of folic acid derivatives: induction of supramolecular chirality by hierarchical chiral structures

Hierarchical chiral structures made up of dendritic oligo(L- or D-glutamic acid) moieties of folic acid derivatives induce supramolecular chirality in the self-assembled columnar structures of the folic acids. These folic acids self-assemble through the intermolecular hydrogen bonds of the pterin rings to form disklike tetramers. In the neat states, the stacked tetramers form thermotropic hexagonal columnar phases over wide temperature ranges, including room temperature. Addition of alkali metal salts induces chirality in the columnar phases. In dilute solution states in a relatively polar solvent (chloroform), the folic acid derivatives form non-chiral, self-assembled structures. In the presence of sodium triflate, the folic acid forms chiral columnar assemblies through the oligo(L-glutamic acid) moiety, similar to those formed in the liquid-crystalline (LC) states. The enantiomer of the folic acid induces columnar assemblies with reversed helicity. In the case of the diastereomer, no induced helicity is observed. Application of an apolar solvent (dodecane) drives the folic acid derivatives to form chiral assemblies in the absence of ions. In this case, lipophilic interactions promote nanophase segregation, which enhances the formation of chiral columns. Interestingly, the chiral supramolecular structure of the diastereomer induces the most intense circular dichroism. In both cases, the molecular chirality in the oligo(glutamate) moieties yields supramolecular chirality of the folic acids that self-assemble through cooperative molecular interactions.     

Insight into the chiral induction in supramolecular stacks through preferential chiral solvation

Preferred handedness in the supramolecular chirality of self-assembled achiral oligo(p-phenylenevinylene) (OPV) derivatives is induced by chiral solvents and spectroscopic probing provides insight into the mechanistic aspects of this chiral induction through chiral solvation.     

Interfacial assembly of cinnamoyl-terminated bolaamphiphiles through the air/water interface: headgroup-dependent assembly, supramolecular nanotube and photochemical sewing

A series of cinnamoyl-terminated bolaamphiphiles were synthesized and their assemblies at the air/water interface were investigated. It was found that the assembly behaviour depended on the substituted groups on the cinnamoyl unit. The bolaamphiphile with 4-hydroxycinnamoyl head groups (HCDA) was found to assemble into a supramolecular nanotube, while the others formed only layer-structured films. Moreover, the nanotube formed from HCDA showed supramolecular chirality due to the symmetry breaking. Both the layered films and the nanotubes showed photochemical dimerization upon UV irradiation, which were studied from the UV-Vis, FT-IR spectral and MALDI-TOF MS analysis. Interestingly, such dimerization behavior of the cinnamoyl group could be used to stabilize the nanotube of HCDAvia photochemical sewing. During such a process both the supramolecular chirality and the tubular shapes were kept. Remarkably, such a photochemical sewed chiral nanotube could further induce the chirality of an achiral porphyrin derivative assembled on it, and produced the induced chirality without using any chiral molecules.