Guest Moieties Research Articles

Noninnocent Role of Na+ Ions in the Binding of the N-Phenyl-2-naphthylammonium Cation as a Ditopic Guest with Cucurbit[7]uril

Na+ ions influence the mechanism for the binding of the ditopic guest N-phenyl-2-naphthylammonium cation (Ph-AH+-Np) to cucurbit[7]uril (CB[7]) by facilitating, at increased Na+ concentrations, the formation of a higher-order complex. Binding of the larger naphthyl moiety of Ph-AH+-Np forms the Ph-AH+-Np@CB[7] 1:1 complex (where "@" represents an inclusion complex) at low Na+ ion concentrations (≤5 mM), whereas the inclusion of the smaller phenyl moiety in CB[7] (CB[7]@Ph-AH+-Np) is transient. Ph-AH+-Np@CB[7] is formed by reactions with free CB[7] and CB[7]·Na+ (where "·" represents an exclusion complex) with displacement of the Na+ cation. Because of the latter reaction, the dissociation of Ph-AH+-Np@CB[7] is faster at higher Na+ concentrations. At high Na+ concentrations (≥25 mM), the Na+ ion stabilizes the inclusion of the phenyl moiety in CB[7] by capping the portal of CB[7]. The dynamics of the capped Na+·CB[7]@Ph-AH+-Np 1:1 complex is slower than in the absence of Na+ capping. This stabilization of the phenyl moiety inclusion in CB[7] by Na+ leads to the formation of the Na+·CB[7]@Ph-AH+-Np@CB[7] 2:1 host-guest complex, where each moiety of the ditopic guest is included in a different CB[7]. The opposing roles of Na+ cations in the formation of the two 1:1 complexes are essential for the switch in mechanism with changes in Na+ concentration and provide an example of systems chemistry, where new properties arise in the form of an increased diversity of complexes and altered complexation dynamics that depend on the system's composition.

Photochromism of three supramolecular assemblies derived from benzenecarboxylate donors and viologen acceptors

Based on 1,2,4,5-benzenetetracarboxylic acid (H4BTEC) and different viologen cations (MQ+ = 1-methyl-4,4′-bipyridinium cation; MV2+ = 1,1′-bis(methyl)-4,4′-bipyridinium dication; EV2+ = 1,1′-bis(ethyl)-4,4′-bipyridinium dication), three novel supramolecular assemblies [(H3O)(MQ)(H4BTEC)(H2BTEC)]·H2O (1), (H3O)(MV)0.5(BTEC)0.5 (2), (H3O)(EV)0.5(H2BTEC) (3), have been synthesized and structurally characterized with viologen cations as the guest and acid moieties acting as the host. The crystal structures and photochromic properties of three compounds have been explored. Similar to other viologen-based materials, compounds 2 and 3 are found to exhibit electron-transfer (ET) photochromism, while compound 1 has no photochromism observed. The photosensitivity of the compounds should be due to the rational modulation of electron acceptors and donors. Controllably fabricating appropriate donor and acceptor units at the molecular level in photosensitive materials is critical to the development of new photochromic host–guest materials.

Supramolecular redox-responsive substrate carrier activity of a ferrocenyl Janus device

Supramolecular Janus compounds have recently attracted increasing attention owing to their dynamic reversible properties, distinct topological structures, and remarkable physicochemical characteristics, e.g., amphiphilicity, heterofunctionality, and high-density of terminal groups. Herein, a new redox-responsive supramolecular Janus device was designed and synthesized involving β-cyclodextrin and 2-fold ferrocene host-guest interactions. The complex formation was analyzed via one-dimensional 1H NMR and two-dimensional Nuclear Overhauser Enhancement Spectroscopy. FeCl3 and ascorbic acid were used as oxidation and reduction triggers, respectively, to modulate the self-assembly behavior in water through complexation/dissociation of β-cyclodextrin inclusion compounds resulting from redox-conversion of the ferrocenyl guest moieties. The redox-responsiveness of the obtained supramolecular micelles was studied via scanning electron microscopy and dynamic light scattering. Substrate-loading ability of the supramolecular micelles was confirmed with Rhodamine B, and the oxidation of ferrocenyl groups led to the release of the loaded cargos. The present work illustrates a valuable design example of supramolecular Janus systems using the host-guest complexation between β-cyclodextrin and ferrocenyl structures. The present supramolecular micelle may be used as a promising molecular vehicle for application in the field of stimuli-responsive drug delivery.

Equilibrium, structural and antibacterial characterization of moxifloxacin-β-cyclodextrin complex

Moxifloxacin (MOX), a novel fourth-generation fluoroquinolone antibacterial was characterized in terms of β-cyclodextrin (β-CD) complexation in order to improve its antibacterial activity. The inclusion complexation has been examined with a wide variety of state-of-the-art analytical techniques, such as nuclear magnetic resonance spectroscopy (NMR), affinity capillary electrophoresis (ACE), mass spectrometry (MS), infrared spectroscopy (IR) and differential scanning calorimetry (DSC). The stoichiometry of the complex was investigated by two different techniques. NMR Job plot method indicated 1:1 stoichiometry in liquid state, however MS study revealed that a complex with 2:1 (MOX:β-CD) stoichiometry can also be formed in gas phase. The stability constants were determined by 1H NMR titration and ACE at different pH values, where MOX exists predominantly in monocationic, neutral and monoanionic form, respectively, indicating that the neutral macrospecies forms the most stable complex with the host (logK = 2.51 ± 0.03). Geometric aspects of the inclusion complex were assessed by 2D ROESY NMR and proved that the tricyclic moiety of guest can enter the host cavity. To understand the interaction of different protonation forms of MOX with β-CD at atomic level molecular modeling studies were also performed. Solid state complexation in 1:1 M ratio was carried out by lyophilization and investigated by DSC and IR, which also confirmed the inclusion complex formation in solid state. The antibacterial activity of the complex was tested against Gram-negative and Gram-positive bacteria by determination of minimum inhibitory concentrations, which revealed that supramolecular interactions do not affect significantly the antibacterial activity of the drug.

Dramatically shrinking of hydrogels controlled by pillar[5]arene-based synergetic effect of host-guest recognition and electrostatic effect

Polyacrylamide-based polymer networks were constructed as a hydrogel, and the novel and simple method was demonstrated to create dramatically shrinking hydrogels triggered by water-soluble pillar[5]arene (WP5)-based synergetic effect of host-guest recognition and electrostatic effect. The shrinking behavior of hydrogels was studied, which significantly exhibited an equilibrium shrinking percentage of approximately 89.2% in weight. More importantly, the WP5 controlled shrinking behavior of hydrogels was further investigated by the encapsulation and release of two types of small molecular drug models (anionic calcein and cationic rhodamine B), which displayed a much better selective release of anionic calcein than that of cationic rhodamine B, due to the host-guest interaction of WP5 and guest moiety of polymer networks in hydrogel as well as the electrostatic effect of anionic host molecule WP5.

Essential oil–cyclodextrin complexes: an updated review

Cyclodextrins, degradation product of carbohydrates, have been extensively exploited by food, pharmaceutical and cosmetic industry by virtue of their ease of availability and their ability to entrap guest moieties. Various cyclodextrin derivatives have been granted generally recognized as safe (GRAS) status by several countries. The most noteworthy characteristic of cyclodextrins is their ability to form inclusion complexes with variety of molecules, imparting protection and enabling solubility, bioavailability and safety enhancement of challenging bioactives. In the last few decades, investigations have revealed anti-microbial, anti-inflammatory, insecticidal, analgesic and sedative properties of essential oils. However, their poor solubility, volatility and sensitivity to environmental factors pose challenge for the formulation scientists. Inclusion complexes of essential oils with cyclodextrins have proved a useful strategy to circumvent these challenges. The success of this approach for essential oils is examplified by the commercial garlic oil/β-cyclodextrin products, available under the trade names Xund, Tegra, Allidex and Garlessence. Here, we present an in-depth account of essential oil loaded cyclodextrin inclusion complexes.

Shear-thinning and self-healing hydrogels as injectable therapeutics and for 3D-printing.

The design of injectable hydrogel systems addresses the growing demand for minimally invasive approaches for local and sustained delivery of therapeutics. We developed a class of hyaluronic acid (HA) hydrogels that form through noncovalent guest-host interactions, undergo disassembly (shear-thinning) when injected through a syringe and then reassemble within seconds (self-healing) when shear forces are removed. Its unique properties enable the use of this hydrogel system for numerous applications, such as injection in vivo (including with cells and therapeutic molecules) or as a 'bioink' in 3D-printing applications. Here, we describe the functionalization of HA either with adamantanes (guest moieties) via controlled esterification or with β-cyclodextrins (host moieties) through amidation. We also describe how to modify the HA derivatives with methacrylates for secondary covalent cross-linking and for reaction with fluorophores for in vitro and in vivo imaging. HA polymers are rationally designed from relatively low-molecular-weight starting materials, with the degree of modification controlled, and have matched guest-to-host stoichiometry, allowing the preparation of hydrogels with tailored properties. This procedure takes 3-4 weeks to complete. We detail the preparation and characterization of the guest-host hydrogels, including assessment of their rheological properties, erosion and biomolecule release in vitro. We furthermore demonstrate how to encapsulate cells in vitro and provide procedures for quantitative assessment of in vivo hydrogel degradation by imaging of fluorescently derivatized materials.

Dynamic Macromolecular Material Design-The Versatility of Cyclodextrin-Based Host-Guest Chemistry.

Dynamic and adaptive materials are powerful constructs in macromolecular and polymer chemistry with a wide array of applications in drug delivery, bioactive systems, and self-healing materials. Very often, dynamic materials are based on carefully tailored cyclodextrin host-guest interactions. The precise incorporation of these host and guest moieties into macromolecular building blocks allows the formation of complex macromolecular structures with predefined functions. Thus, dynamic materials with extraordinary adaptive property profiles-responsive to thermal, chemical, and photonic fields-become accessible. This Review explores the hierarchical formation of dynamic materials and complex macromolecular structures from the molecular via the macromolecular to the colloidal and macroscopic level, with a specific emphasis on the functionality and responsiveness of the assemblies, specifically in biological contexts.

Free-energy landscapes of the coupled conformational transition and inclusion processes of altro-cyclodextrins

Mono-altro-cyclodextrin (altro-CD) may undergo a conformational change of its altropyranose unit when encapsulating guest molecules of different sizes. This conformational transition is found to be coupled to the inclusion processes. In the present contribution, the possible conformational transition pathways in the four (self-)inclusion processes of altro-α and -β-CDs with moieties of variant shapes are explored from the insights of free-energy calculations. The two-dimensional free-energy landscapes characterising the coupled (self-)inclusion and isomerisation processes are determined, and the lowest free-energy pathways (LFEP) connecting the minima of the landscapes are located. The conformational statistics of the altropyranose units along the LFEPs reveal different transition pathways in the four (self-)inclusion processes. It can be concluded that when accommodating a free bulky guest molecule, the altropyranose unit will adjust its conformation to match the guest. However, such induced fit effect in the self-complexation of altro-CD derivatives will be weakened. The conformation of the altropyranose unit changes accompanying the self-complexation, but always adopts the 4C1 one in the self-inclusion complex, irrespective of the shape of the guest moieties. The present results help determine the transition states of the (self-)inclusion processes of CDs and further improve the understanding of the mechanical properties of CD-based molecular shuttles.

Secondary Interactions in Halogenated Werner Clathrates

Halogenated Werner clathrates which contain Cl, Br, and I as part of the host and guest moieties have been synthesized and characterized by single X-ray diffraction, thermal analysis, and solid–vapor kinetics of formation. The compounds derived from NiI2 are ionic, forming I– salts and which yielded tri-iodide anions by the addition of I2. Secondary interactions involving halogen···halogen and hydrogen bonds have been fully characterized and the structures were correlated with the thermal decomposition results.

Construction of supramolecular polymer gels cross-linked by two types of discrete well-defined metallacycles through self-sorting

A dipyridyl donor D1 decorated with pillar[5] arene unit and a dipyridyl donor D2 containing neutral guest moiety were successfully synthesized. Through the X-ray single crystal analysis, it was found that the angle between the two pyridine unit in D1 was about 128 degrees and the distance between two nitrogen atoms was about 1.48 nm, while the angle between the two pyridine units of D2 was about 118 degrees and the distance between the two nitrogen atoms was about 0.98 nm, much shorter than that in D1. Thus, a metallacycle containing three pillar[5] arene units (H) and a metallacycle possessing three neutral guest units (G) were successfully constructed in one pot coordination-driven self-assembly from dipyridyl donors (D1 and D2) and 120 degrees di-Pt(II) acceptor through size-control self-sorting strategy. Moreover, driven by the host-guest interaction between metallacycles H and G, a new family of supramolecular polymer, cross-linked by these two kinds of discrete well-defined metllacycles H and G, was gradually constructed with the increase of concentration. By concentration-dependent H-1-NMR measurement, it was found that the typical signals of metllacycle G were gradually disappeared with the increase of concentration, indicating the enhanced host-guest interaction between metallacycles H and G. Meanwhile, the analysis of 2-D diffusion ordered spectroscopy (DOSY) tests of H superset of G showed that the diffusion coefficient D gradually decreased with the increase of concentration, and D-1 mmol/(L)/D-16 mmol/(L) value was ca. 31.6, also demonstrating the formation of supramolecular polymer. Scanning electron microscope (SEM) was also used to investigate the morphology change during the concentration increasing process. More intuitionally, cross-linked networks were observed with the increase of concentration of H. G. Interestingly, the resultant supramolecular polymer could transforme into supramolecular polymer gels when the concentration was increased to a relatively high value (9.9 wt%). Moreover, due to the existence of discrete well-defined metallacycles and the dynamic nature of host-guest hierarchical self-assembly, reversible gel-sol transitions were successfully realized through the disassembly and reassembly of such cross-linked supramolecular polymer networks stimulated by various external stimuli such as temperature, competitive guest, and halide, etc.

Thermal and other analytical studies on bifenthrin urea co-inclusion complex

In current study, thermal and other analytical techniques have been successfully utilized in characterization of bifenthrin urea co-inclusion complex (BNUCIC)—a human-guarded insecticide formulation. Bifenthrin (BN)—a widely used pyrethroid insecticide was successfully engulfed in the cavities of hexagonal urea lattice in the presence of a suitable rapidly complexing agent (RCA). Resulting formulation shields human beings from insecticides through direct inhalation, ingestion or dermal contact. Insects will be exposed to insecticide only after BNUCIC comes in contact with water in soil/crops following switching on of water sprinkling/distribution system in the fields. Formation of BNUCIC was characterized by DSC, FTIR, XRD and 1H-NMR studies. Thermal analysis played a key role in characterization, in estimation of the minimum proportion of RCA needed for complexation and to study the influence of relative proportion of RCA on heat of decomposition of complexes. Thermal analysis depicted gradual increase in heat of decomposition of BNUCIC and excellent r2 value with increasing molar fraction of linear chain RCA. Increased heat of decomposition ensures improved physical stability of complexes. Overlay of DSC curves of BNUCIC complexes revealed absence of melting endotherm of insecticide indicating amorphous nature of BN. FTIR spectrum and XRD diffractogram depicted characteristic peaks and interplanar spacings of hexagonal urea. 1H-NMR spectrum revealed presence of exposed protons of guest moieties in hexagonal urea. BNUCIC exhibited uniform formulation composition and improved dissolution profile. Studies reveal insecticide–fertilizer amalgamation to be a useful technique for formulation of an effective human-guarded insecticide formulation with improved characteristics.

A highly controllable protein self-assembly system with morphological versatility induced by reengineered host-guest interactions.

Manipulating proteins to self-assemble into highly ordered nanostructures not only provides insights into the natural protein assembly process but also allows access to advanced biomaterials. Host-guest interactions have been widely used in the construction of artificial protein assemblies in recent years. CB[8] can selectively associate with two tripeptide Phe-Gly-Gly (FGG) tags with an extraordinarily high binding affinity (Kter = 1.5 × 1011 M-2). However, the FGG tags utilized before are all fixed to the N-termini via genetic fusion; this spatial limitation greatly confined the availability of the CB[8]/FGG pair in the construction of more sophisticated protein nanostructures. Here we first designed and synthesized a maleimide-functionalized Phe-Gly-Gly tag as a versatile site-specific protein modification tool; this designed tag can site-selectively introduce desired guest moieties onto protein surfaces for host-guest driven protein assembly. When regulating the self-assembly process of proteins and CB[8], the constructed protein nanosystem can exhibit distinctive morphological diversities ranging from nanorings, nanospirals, nanowires to superwires. This work developed a new strategy for site-specific protein modification of the CB[8] binding tag and provides a possible direction for the construction of 'smart', dynamic self-assembly systems.

Controlled Supramolecular Architecture Transformation from Homopolymer to Copolymer through Competitive Self-Sorting Method.

Supramolecular copolymers can not only enrich the diversity of the polymer backbone but also exhibit certain special and improved properties compared with supramolecular homopolymers. However, the synthesis procedure of supramolecular copolymers is relatively complicated and time-consuming. Herein, a simple transformation from an AB2 -based supramolecular hyperbranched homopolymer to an AB2 +CD2 -based supramolecular hyperbranched alternating copolymer by the "competitive self-sorting" strategy is reported. After adding CD2 monomer, which bears a competitive neutral guest moiety (TAPN) and two receptive benzo-21-crown-7 host moieties (B21C7), to the as-prepared AB2 -type supramolecular hyperbranched homopolymer constructed by the self-assembly of dialkylammonium salt (DAAS, A group)-functionalized pillar[5]arene (MeP5, B groups) monomers, the initial homopolymer structure is disrupted and then reassemble into a new supramolecular hyperbranched alternating copolymer based on the competitive self-sorting interaction between MeP5-TAPN and B21C7-DAAS. This study supplies a convenient approach to directly transform supramolecular homopolymers into supramolecular copolymers.

ChemInform Abstract: Recent Advances in Molecular Recognition with Tetrathiafulvalene‐Based Receptors

AbstractReview: [46 refs.

Multifunctional and Regenerable Antibacterial Surfaces Fabricated by a Universal Strategy.

Development of a versatile strategy for antibacterial surfaces is of great scientific interest and practical significance. However, few methods can be used to fabricate antibacterial surfaces on substrates of different chemistries and structures. In addition, traditional antibacterial surfaces may suffer problems related to the attached dead bacteria. Herein, antibacterial surfaces with multifunctionality and regenerability are fabricated by a universal strategy. Various substrates are first deposited with multilayered films containing guest moieties, which can be further used to incorporate biocidal host molecules, β-cyclodextrin (β-CD) derivatives modified with quaternary ammonium salt groups (CD-QAS). The resulting surfaces exhibit strong biocidal activity to kill more than 95% of attached pathogenic bacteria. Notably, almost all the dead bacteria can be easily removed from the surfaces by simple immersion in sodium dodecyl sulfate, and the regenerated surfaces can be treated with new CD-QAS for continued use. Moreover, when another functional β-CD derivative molecule is co-incorporated together with CD-QAS, the surfaces exhibit both functions simultaneously, and neither specific biofunction and antibacterial activity is compromised by the presence of the other. These results thus present a promising way to fabricate multifunctional and regenerable antibacterial surfaces on diverse materials and devices in the biomedical fields.

Removal of SDS from biological protein digests for proteomic analysis by mass spectrometry

BackgroundMetal-organic frameworks (MOFs - MIL-101) are the most exciting, high profiled developments in nanotechnology in the last ten years, and it attracted considerable attention owing to their uniform nanoporosity, large surface area, outer-surface modification and in-pore functionality for tailoring the chemical properties of the material for anchoring specific guest moieties. MOF’s have been particularly highlighted for their excellent gas storage and separation properties. Recently biomolecules-based MOF’s were used as nanoencapsulators for antitumor and antiretroviral controlled drug delivery studies. However, usage of MOF material for removal of ionic detergent-SDS from biological samples has not been reported to date. Here, first time we demonstrate its novel applications in biological sample preparation for mass spectrometry analysis.MethodsSDS removal using MIL-101 was assessed for proteomic analysis by mass spectrometry. We analysed removal of SDS from 0.5 % SDS solution alone, BSA mixture and HMEC cells lysate protein mixture. The removal of SDS by MIL-101 was confirmed by MALDI-TOF-MS and LC-MS techniques.ResultsIn an initial demonstration, SDS has removed effectively from 0.5 % SDS solution by MIL-101via its binding attraction with SDS. Further, the experiment also confirmed that MIL-101 strongly removed the SDS from BSA and cell lysate mixtures.ConclusionsThese results suggest that SDS removal by the MIL-101 method is a practical, simple and broad applicable in proteomic sample processing for MALDI-TOF-MS and LC-MS analysis.

A Universal and Versatile Approach for Surface Biofunctionalization: Layer‐by‐Layer Assembly Meets Host–Guest Chemistry

A universal and versatile approach is developed using noncovalent interactions as driving forces to build bioactive surfaces with desired biofunctions. A polyanion containing guest moieties is designed as a building block to form a polyelectrolyte multilayered film via electrostatic interactions by layer-by-layer assembly technique, and as a matrix to provide binding sites for incorporation of biofunctional host molecules via host–guest interactions. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Coupling of a single active nanoparticle to a polymer-based photonic structure

Abstract The engineered coupling between a guest moiety (molecule, nanoparticle) and the host photonic nanostructure may provide a great enhancement of the guest optical response, leading to many attractive applications. In this article, we describe briefly the basic concept and some recent progress considering the coupling of a single nanoparticle into a photonic structure. Different kinds of nanoparticles of great interest including quantum dots and nitrogen-vacancy centers in nanodiamond for single photon source, nonlinear nanoparticles for efficient nonlinear effect and sensors, magnetic nanoparticles for Kerr magneto-optical effect, and plasmonic nanoparticles for ultrafast optical switching and sensors, are briefly reviewed. We focus further on the coupling of plasmonic gold nanoparticles and polymeric photonic structures by optimizing theoretically the photonic structures and developing efficient way to realize desired hybrid structures. The simple and low-cost fabrication technique, the optical enhancement of the fluorescent nanoparticles induced by the photonic structure, as well as the limitations, challenges and appealing prospects are discussed in details.

Rotaxane‐type hyperbranched polymers from a crown ether host and paraquat guests containing blocking groups

ABSTRACTRotaxane‐type hyperbranched polymers are synthesized for the first time from A2B type semi‐rotaxane monomers formed in situ via complexation of bis(m‐phenylene)‐32‐crown‐10 dimethanol (1) and two paraquat ω‐n‐alkylenecarboxylic acid derivatives with tris(p‐t‐butylphenyl)methylphenylalkylene stoppers (8 and 9). Rotaxane and taco complexes exist in solutions of the hyperbranched polyesters in CD3CN/CDCl3 as confirmed by NMR spectroscopy, but the taco complexes, which derive from non‐rotaxanated paraquat units, disappear in DMSO‐d6. NMR spectroscopy indicates the portion of rotaxanes strongly interlocked by the environment (inner rotaxanes) is larger in HP1•9, which has longer alkylene spacers, perhaps indicating a higher degree of polymerization. The molecular size increases upon formation of the hyperbranched polymers are confirmed by dynamic light scattering and by viscometry. As with covalent hyperbranched polymers a number of potential applications exist; the unique mechanically linked character and the presence of uncomplexed host and guest moieties foreshadow the use of such systems for their responses to external stimuli with the added benefit of providing molecular recognition sites useful as delivery vehicles. Use of other host‐guest motifs to form the semirotaxane A2B monomers is possible and complementary systems with higher binding constants will enable efficient syntheses of high molecular weight, mechanically linked hyperbranched polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1647–1658