Selective effect of guest molecule length and hydrogen bonding on the supramolecular host structure

A host supramolecular structure consisting of bis-(2,2':6',2' '-terpyridine)-4'-oxyhexadecane (BT-O-C16) is shown to respond to guest molecules in dramatic ways, as observed by using scanning tunneling microscopy (STM) on a highly oriented pyrolytic graphite surface under ambient conditions. It is observed that small linear molecules can be encapsulated within the host supramolecular lattice. The characteristics of the host structure were nearly unaffected by the encapsulated guest molecules of terphthalic acid (TPA) dimers, whereas appreciable changes in cavity dimension can be observed with azobenzene-4,4'-dicarboxylic acid. The STM study and density functional theory (DFT) analysis reveal that intermolecular hydrogen bonding interaction plays an essential role in forming the assembling structures. The difference in guest molecule length is considered the important cause for the different guest-host complexes.     

Toward well-organised ionic discotic liquid crystals via versatile supramolecular approach

Various ordered structures of crystalline three-dimensional (3D) cubic, 2D columnar or 1D lamellar mesophases have been facilely achieved through host–guest interactions of electrically neutral host tris(18-crown-6)triphenylene and guest potassium sulfonates with alkyl tails of variant number and length. The convenient construction of functionalised ionic complexes and the flexibility of such a supramolecular approach offer a wide variety of possibilities to prepare various ordered functional soft materials, especially those in their 2D ordered columnar liquid crystalline mesophases may serve as promising electron and ion dual-channel transport organic electronic materials.     

Fluorescent Linear Supramolecular Polymer Based on Host‐Guest Interactions

Construction of supramolecular polymers, in which functional monomer components are held together by noncovalent interactions, is considered as a promising design principle for functional materials. Linear fluorescent supramolecular polymer assembled on account of electrostatic attractions based host‐guest interaction is synthesized and illustrated here. ¹H NMR was involved to ensure the structure of guest and polymer, UV –vis and fluorescent spectra were recorded to be a readout signal to investigate the assemble process of polymer. TEM and AFM measurements were carried out to confirm the homogeneous nanometer‐sized molecular assembly. It shows the way to be used as remote readout fluorescent functional material in the future.     

Constructing Adaptive Photosensitizers via Supramolecular Modification Based on Pillararene Host–Guest Interactions

In order to promote the development of photodynamic therapy (PDT), undesired side effects like low tumor specificity and the “always‐on” phenomenon should be avoided. An effective solution is to construct an adaptive photosensitizer that can be activated to generate reactive oxygen species (ROS) in the tumor microenvironment. Herein, we design and synthesize a supramolecular switch based on a host–guest complex containing a water‐soluble pillar[5]arene ( WP5 ) and an AIEgen photosensitizer ( G ). The formation of the host–guest complex WP5 ? G quenches the fluorescence and inhibits ROS generation of G . Benefitting from the pH‐responsiveness of WP5 , the binding site between G and WP5 changes in an acidic environment through a shuttle movement. Consequently, fluorescence and ROS generation of the host–guest complex can be switched on at pH 5.0. This work offers a new paradigm for the construction of adaptive photosensitizers by using a supramolecular method.     

Constructing Adaptive Photosensitizers via Supramolecular Modification Based on Pillararene Host–Guest Interactions

In order to promote the development of photodynamic therapy (PDT), undesired side effects like low tumor specificity and the “always-on” phenomenon should be avoided. An effective solution is to construct an adaptive photosensitizer that can be activated to generate reactive oxygen species (ROS) in the tumor microenvironment. Herein, we design and synthesize a supramolecular switch based on a host–guest complex containing a water-soluble pillar[5]arene ( WP5 ) and an AIEgen photosensitizer ( G ). The formation of the host–guest complex WP5 ⊃ G quenches the fluorescence and inhibits ROS generation of G . Benefitting from the pH-responsiveness of WP5 , the binding site between G and WP5 changes in an acidic environment through a shuttle movement. Consequently, fluorescence and ROS generation of the host–guest complex can be switched on at pH 5.0. This work offers a new paradigm for the construction of adaptive photosensitizers by using a supramolecular method.     

Macrocycle-Based Crystalline Supramolecular Assemblies Built with Intermolecular Charge-Transfer Interactions

Synthetic macrocycles have served as principal tools for supramolecular chemistry, have greatly extended the scope of organic charge transfer (CT) complexes, and have proved to be of great practical value in the solid state during the past few years. In this Minireview, we summarize the research progress on the macrocycle-based crystalline supramolecular assemblies primarily driven by intermolecular CT interactions (a.k.a. macrocycle-based crystalline CT assemblies, MCCAs for short), which are classified by their donor–acceptor (D-A) constituent elements, including simplex macrocyclic hosts, heterogeneous macrocyclic hosts, and host–guest D-A pairs. Particular attention will be focused on their diverse functions and applications, as well as the underlying CT mechanisms from the perspective of crystal engineering. Finally, the remaining challenges and prospects are outlined.     

Supramolecular Inorganic Chemistry: Small Guests in Small and Large Hosts

A key reaction in the biological and material world is the controlled linking of simple (molecular) building blocks, a reaction with which one can create mesoscopic structures, which, for example, contain cavities and display specifically desired properties, but also compounds that exhibit typical solid-state structures. The best example in this context is the chemistry of host–guest interactions, which spans the entire range from three- and two-dimensional to one- and “zero-dimensional”, discrete host structures. Members of the class of multidimensional compounds have been classified as such for a long time, for example, clathrates and intercalation compounds. Thus far, however, there are no classifications for discrete inorganic host–guest compounds. The first systematic approach can be applied to novel polyoxometalates, a class of compounds which has only recently become known. Molecular recognition; tailor-made, molecular engineering; control of fragment linkage of spin organization and crystallization; cryptands and coronands as “cages” for cations, anions or anion–cation aggregates as sections of ionic lattices; anions within anions, receptors; host–guest interactions; complementarity, as well as the dialectic terms reduction and emergence are important terms and concepts of supramolecular inorganic chemistry. Of particular importance for future research is the comprehension of the mesoscopic area (molècular assemblies)—that between individual molecules and solids (“substances”)—which acts in the biological world as carrier of function and information and for which interesting material properties are expected. This area is accessible through certain variations of “controlled” self-organization processes, which can be demonstrated by using examples from the chemistry of polyoxometalates. The comprehension of the laws that rule the linking of simple polyhedra to give complex systems enables one to deal with numerous interdisciplinary areas of research: crystal physics and chemistry, heterogeneous catalysis, bioinorganic chemistry (biomineralization), and materials science. In addition, conservative self-organization processes, for example template-directed syntheses, are of importance for natural philosophy in the context of the question about the inherent properties of material systems.     

Design, synthesis, and application of a library of supramolecular structures formed by N-lipidated peptides immobilized on cellulose. Artificial receptors

An array of supramolecular structures formed from N-lipidated peptides attached to cellulose via aminophenylamino-1,3,5-triazine was synthesized. The structures thus prepared were prone to self-organization and to formation of monolayer of "holes" and "pockets" in dynamic equilibrium, structures which were capable of binding small guest molecules very efficiently recognizing the shape, size, and polarity of ligands, thus resembling artificial receptors. Because of the high flexibility of N-lipidated peptides, it is expected that the host adjusts its shape to wrap guest molecules most efficiently. The selectivity and rate of binding was studied by using triphenylmethyl dyes. It was found that the selectivity of binding depends on the structure of the peptide and the N-lipidic fragment of the receptor and varies with the structure of the analyte. Even tiny structural changes in guest molecules were detected by monitoring the alteration of the binding pattern.     

超分子体系中轴－轮状D.D.主体分子的立体异构现象

组装了轴一轮状主体分子1,1,6,6-四基乙－2,4－二炔-1,6二醇(1)与天然主物异补骨脂素(2)。茴香醚(3)形成的两种超分子异构体的包结物晶体,它们的主客体分子摩尔比分别为1：2和2：1单晶X射线衍射分析了游离主体分子以及超分子包结物晶体的结构,结果表明在主客体分子摩尔比1：2的晶体中,主体分子与异补骨脂素形成氢键,主体分子采取对位交叉式构象;在主客体分子摩尔比为2：1的晶体中,主体分子这间形成氢键,主体分子采取邻位交叉式构,主体分子所取的构象取决于客体分子的性质,当客体分子为氢键好的受体时,可与主体分子生成1：2的包结物;当客体分子为氢键差的受体时,生成2：1有包结物,本文还对三种晶体是的主体分子的立体构苯环两面角,C(1)和C(6)所连基团的夹角和能量变化规律进行了比较和分析。     

Tandem mass spectrometry for the analysis of self‐sorted pseudorotaxanes: the effects of Coulomb interactions

The increasing complexity of self‐assembled supramolecules generates the need for analytical techniques that can accurately elucidate their structures. Here, we explore the ability of tandem mass spectrometry to deliver structural information on a series of self‐sorted crown ether/ammonium pseudorotaxanes. Of these intertwined molecules, different charge states are accessible and the effects of Coulomb interactions on the fragmentation pattern can be examined. Three different cases can be distinguished: (1) one or more counterions are present in the complex and compete with the crown for binding to the ammonium ion. This destabilizes the supramolecular bond. (2) In multiply charged complexes, charge repulsion significantly alters the fragmentation behavior as compared with singly charged ions. (3) If guest and host are both charged, the supramolecular bond becomes very weak. The different charge states provide different pieces of information about the supramolecules under study. Although singly charged complexes provide data on the building block connectivity, the doubly charged analogs are more reliable with respect to complex stoichiometry. As there are several factors which may cause differences in the gas phase and solution behavior of supramolecules (the presence and absence of solvation, changes in the strength of non‐covalent interactions upon ionization), it is important to establish well understood correlations between the complexes' gas‐phase behavior and their solution structures. A more detailed understanding will help to characterize the structures of even more complex supramolecular architectures by mass spectrometry. Copyright © 2010 John Wiley & Sons, Ltd.     

Cooperatively Enhanced Receptors for Biomimetic Molecular Recognition

The concept of preorganization suggests that organizing a receptor around its guest during binding is detrimental, because the cost of conformational change is assumed to be paid out of the binding energy. Although this concept has historically guided the synthesis of a great many synthetic hosts, in recent years, chemists have begun to synthesize receptors that resemble proteins in their cooperative conformational changes. Such changes could enhance the host–guest interactions, in particular if the binding of the guest triggers previously unengaged noncovalent interactions within the host. These hosts, referred to as cooperatively enhanced receptors, corroborate with their biological counterparts to support the approach of creating high‐affinity receptors through the combined strategies of cooperativity and preorganization. Solvents, often the invisible participants of any solution‐based supramolecular process, should be properly considered in the design of synthetic receptors, whether preorganized or cooperatively enhanced.     

Thermoresponsive Supramolecular Dendronized Polymers

Combining the concepts of supramolecular polymers and dendronized polymers provides the opportunity to create bulky polymers with easy structural modification and tunable properties. In the present work, a novel class of side‐chain supramolecular dendronized polymethacrylates is prepared through the host–guest interaction. The host is a linear polymethacrylate (as the backbone) attached in each repeat unit with a β‐cyclodextrin (β‐CD) moiety, and the guest is constituted with three‐fold branched oligoethylene glycol (OEG)‐based first‐ (G1) and second‐generation (G2) dendrons with an adamantyl group core. The host and guest interaction in aqueous solution leads to the formation of the supramolecular polymers, which is supported with ¹H NMR spectroscopy and dynamic light scattering measurements. The supramolecular formation was also examined at different host/guest ratios. The water solubility of hosts and guests increases upon supramolecular formation. The supramolecular polymers show good solubility in water at room temperature, but exhibit thermoresponsive behavior at elevated temperatures. Their thermoresponsiveness is thus investigated with UV/Vis and ¹H NMR spectroscopy, and compared with their counterparts formed from individual β‐CD and the OEG dendritic guest. The effect of polymer concentration and molar ratio of host/guest was examined. It is found that the polar interior of the supramolecules contribute significantly to the thermally‐induced phase transitions for the G1 polymer, but this effect is negligible for the G2 polymer. Based on the temperature‐varied proton NMR spectra, it is found that the host–guest complex starts to decompose during the aggregation process upon heating to its dehydration temperature, and this decomposition is enhanced with an increase of solution temperature.     

Supramolecular Polymerization Engineered with Molecular Recognition

Supramolecular polymeric assemblies represent an emerging, promising class of molecular assemblies with enormous versatility compared with their covalent polymeric counterparts. Although a large number of host–guest motifs have been produced over the history of supramolecular chemistry, only a limited number of recognition motifs have been utilized as supramolecular connections in polymeric assemblies. This account describes the molecular recognition of host molecules based on calix[5]arene and bisporphyrin that demonstrate unique guest encapsulations; subsequently, these host–guest motifs are applied to the synthesis of supramolecular polymers that display polymer‐like properties in solution and solid states. In addition, new bisresorcinarenes are developed to form supramolecular polymers that are connected via a rim‐to‐rim hydrogen‐bonded dimeric structure, which is composed of two resorcinarene moieties.

     

Pillararene‐Based Assemblies: Design Principle,Preparation and Applications

In this review, we highlight recent advancements on pillararene‐based assemblies. The driving forces for the formation of the pillararene‐based assemblies are discussed first. The host–guest interactions are deemed as not only general strategy for constructing assemblies but also essential components for preventing the assemblies from the dissociation. Solvent effect is also important in the assembling process, since it could influence the host–guest interactions and provide solvophobic effect on pillararenes for the assembly. Then, several pillararene‐based assembly architectures are introduced, including pillararene‐based interlocked structures, such as (poly)pseudorotaxanes, (poly)rotaxanes, and daisy chains, classified by their topological structures and synthetic strategy. The morphologies of the supramolecular assemblies are divided into several types, for example, nanospheres, nanotubes and supramolecular polymers. Furthermore, the functions and potential applications are summarized accompanied with related assembly structures. The review not only provides fundamental findings, but also foresights future research directions in the research area of pillararene‐based assemblies.     

The Crystalline Sponge Method in Water

The crystalline sponge method entails the elucidation of the (absolute) structure of molecules from a solution phase using single-crystal X-ray diffraction and eliminates the need for crystals of the target compound. An important limitation for the application of the crystalline sponge method is the instability of the available crystalline sponges that can act as host crystals. The host crystal that is most often used decomposes in protic or nucleophilic solvents, or when guest molecules with Lewis basic substituents are introduced. Here a new class of (water) stable host crystals based on f-block metals is disclosed. It can be shown that these hosts not only increase the scope of the crystalline sponge method to a wider array of solvents and guests, but that they can even be applied to aqueous solutions containing hydrophilic guest molecules, thereby extending the crystalline sponge method to the important field of water-based chemistry.     

Control of release properties of guest molecules by the type of benzoheterocyclic ring in supramolecular host complexes

Three types of supramolecular benzoheterocyclic host complexes were successfully prepared using (1R,2S)-2-amino-1,2-diphenylethanol and three types of benzoheterocyclic (benzothiophene, benzofuran, and benzopyrrole) acid derivatives. The host complexes had one-dimensional (1D) channel-like cavities that were formed by the assembly of two-component 2₁-helical columnar network structures, which included guest alcohol molecules. The release behavior of the guest molecules could be tuned by the type of heterocyclic ring in the supramolecular host complex.     

Cucurbituril‐mediated immobilization of fluorescent proteins on supramolecular biomaterials

The reversible introduction of functionality at material surfaces is of interest for the development of functional biomaterials. In particular, the use of supramolecular immobilization strategies facilitates mild reaction and processing conditions, as compared to other covalent analogues. Here, the engineering of multicomponent supramolecular materials, beyond the use of a single supramolecular entity is proposed. Cucurbit[8]uril (Q8) mediated host–guest chemistry is combined with hydrogen bonding supramolecular 2‐ureido‐4‐pyrimidinone (UPy)‐based materials. The modular incorporation of a UPy‐additive that presents one guest to incorporate into the Q8 host allows for selective supramolecular functionalization at the water–polymer material interface. Supramolecular ternary complex formation at the material surface was studied by X‐ray photoelectron spectroscopy, which as a result of large overlap in atomic composition of the different components showed minor changes is surface composition upon complex formation. Surface MALDI‐ToF MS measurements revealed useful insights in the formation of complexes. Protein immobilization was monitored using both fluorescence spectroscopy and quartz crystal microbalance with dissipation monitoring, which successfully demonstrated ternary complex formation. Although proteins could selectively be immobilized onto the surfaces, control of the system's stability remains a challenge as a result of the dynamicity of the host–guest assembly. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3607–3616     

Unbiased Rotational Motions of an Ellipsoidal Guest in a Tight Yet Pliable Host

In the design of machinery such as steel bearings, a fundamental understanding of material characteristics provides an indispensable basis for the design. Although hydrocarbon cycloarylenes have started to be used for providing unique supramolecular bearings with anomalous dynamic behaviors, their fundamental understanding is immature. A unique property of the cycloarylene host is now reported: the cyclic host is so pliable that it tracks the orientational changes of the ellipsoidal guest, that is, C₇₀ fullerene. Unique structures of the complex were revealed by spectroscopic and crystallographic analyses, and additional theoretical investigations deepened our understanding by revealing the structural changes associated with unbiased rotational motions.     

A Hybrid Supramolecular Polymeric Hydrogel with Rapid Self‐Healing Property

A hybrid supramolecular polymeric hydrogel is conveniently constructed via host–guest interaction of a host cyclodextrin polymer (poly‐CD) with a guest α‐bromonaphthalene polymer (poly‐BrNp) and mixing with 6‐thio‐β‐cyclodextrin (β‐SH‐CD) modified gold nanoparticles (GPCDs) in aqueous solution. According to the dynamic oscillatory data, the hydrogel exhibits markedly enhanced stiffness compared with the GPCD‐free one (both G′ and G“ values are almost twice as high as those of the original GPCD‐free hydrogel) due to the introduction of the inorganic gold nanoparticles. This hybrid supramolecular polymeric hydrogel has a rapid and excellent self‐healing property (only about 1 min, and the G′ and G” of the self‐healed hydrogel almost turned back to their original levels after 1 hour) in air (without adding any solvent or additive).     

Stepwise Evolution of Molecular Nanoaggregates Inside the Pores of a Highly Flexible Metal–Organic Framework

The crystalline sponge method (CSM) is primarily used for structural determination by single‐crystal X‐ray diffraction of a single analyte encapsulated inside a porous MOF. As the host–guest systems often show severe disorder, reliable crystallographic determination is demanding; thus the dynamics of the guest entering and the formation of nanoconfined molecular aggregates has not been in the spotlight. Now, the concept is investigated of the CSM for monitoring the structural evolution of nanoconfined supramolecular aggregates of eugenol guests with displacement of DMF inside the cavities of the flexible MOF, PUM168. The interpretation of the electron density provides a series of unique detailed snapshots depicting the supramolecular guest aggregation, thus showing the tight interplay between the host flexible skeleton and the molecular guests through the DMF‐to‐eugenol exchange process.