Dynamic Self‐Assembly Adhesion of a Paraquat Droplet on a Pillar[5]arene Surface

The adhesion of herbicide droplets on leaf surfaces plays an important role in the herbicide's adsorption by crops. How to control the adhesive binding which occurs through dynamic self‐assembly between the macroscopic droplet and the surface is a challenging task. We introduce a host onto surfaces that controls the binding of guests in the paraquat droplets. The pillar[5]arene‐functional surface showed the selective binding of paraquat droplets via the host–guest interaction. The work is promising for improving the efficiency of herbicides.     

A Study of the Interaction Between Cucurbit[8]uril and Alkyl‐Substituted 4‐Pyrrolidinopyridinium Salts

The interaction between cucuribit[8]uril (Q[8]) and a series of 4‐pyrrolidinopyridinium salts bearing aliphatic substituents at the pyridinium nitrogen, namely 4‐(C₄H₈N)C₅H₅NRBr, where R=Et (g1), n‐butyl (g2), n‐pentyl (g3), n‐hexyl (g4), n‐octyl (g5), n‐dodecyl (g6), has been studied in aqueous solution by ¹H NMR spectroscopy, electronic absorption spectroscopy, isothermal titration calorimetry and mass spectrometry. Single crystal X‐ray diffraction revealed the structure of the host–guest complexes for g1, g2, g3, and g5. In each case, the Q[8] contains two guest molecules in a centrosymmetric dimer. The orientation of the guest molecule changes as the alkyl chain increases in length. Interestingly, in the solid state, the inclusion complexes identified are different from those observed in solution, and furthermore, in the case of g3, Q[8] exhibits two different interactions with the guest. In solution, the length of the alkyl chain plays a significant role in determining the type of host–guest interaction present.     

Supramolecular chirogenesis in zinc porphyrins: interaction with bidentate ligands,formation of tweezer structures,and the origin of enhanced optical activity

The complexation behavior, binding properties, and spectral parameters of supramolecular chirality induction in the achiral host molecule, syn (face-to-face conformation) ethane-bridged bis(zinc porphyrin), upon interaction with chiral bidentate guests (diamines and amino alcohols) have been studied by means of UV-vis, CD, fluorescence, (1)H NMR, and ESI MS techniques. It was found that the guest structure plays a decisive role in the chirogenesis pathway. The majority of bidentate ligands (except those geometrically unsuitable) exhibit two major equilibria steps: the first guest ligation leading to formation of the 1:1 host-guest tweezer structure (K(1)) and the second guest molecule ligation (K(2)) forming the anti bis-ligated species (1:2). The second ligation is much weaker (K(1) > K(2)) due to the optimal geometry and stability of the 1:1 tweezer complex. The enhanced conformational stability of the tweezer complex ensures an efficient chirality transfer from the chiral guest to the achiral host, consequently inducing a remarkably high optical activity in the bis-porphyrin.     

Biomimetic Taste Receptors with Chiral Recognition by Photoluminescent Metal–Organic Frameworks Chelated with Polyaniline Helices

The adsorption of phenylaniline (Phe) enantiomers on (+)‐polyaniline (PAN)‐chelated [In(OH)(bdc)]_n microcrystals was carefully designed and studied by using the Job titration, circular dichroism, X‐ray photoelectron spectroscopy, and photoluminescence to mimic heterotrimeric guanine nucleotide‐binding protein (G protein)‐coupled receptors in selective, but not specific, ligand binding with chiral recognition and signal transduction. Six essential working principles across different length scales are unraveled: 1) a chiral (+)‐PAN (host), 2) specific sites for Phe‐(+)/PAN (guest–host) binding, 3) a conformational change of (+)‐PAN after binding with Phe enantiomers, 4) different degrees of packing for (+)‐PAN, 5) interactions between (+)‐PAN and the underlying signal‐generating framework (i.e., [In(OH)(bdc)]_n microcrystals), and 6) a systematic photoluminescent signal combination by using principal‐component analysis from the other three polymer‐chelated metal–organic frameworkds (MOFs), such as poly(acrylic acid) (PAA), sodium alginate (SA), and polyvinylpyrrolidone (PVP) to enhance the selectivity and discrimination capabilities.     

Functional biointerface materials inspired from nature

Controlling the interfacial chemical and physical properties, and thus modulating the behaviours of cells and biomolecules on material surfaces, form an important foundation for the development of high-performance biomaterials and devices. Biological systems in nature exhibit unique features in this aspect. The first one is that the superior properties of natural biomaterials are normally not determined by their bulk properties, but more related to the multi-scale micro- and nanostructures on the surface; the second is that biological systems usually utilize highly specific weak interactions (e.g. hydrogen bonding interaction, hydrophobic interaction, etc.) to solve the problems of biomolecule interactions; the third is that the biomolecules in nature are often chiral molecules and show high preference for one specific enantiomorphous configuration, suggesting a distinctive chiral recognition mechanism in biological systems. These features bring much inspiration to design novel biointerface materials with special functionalities, e.g. structural biointerface materials, smart biointerface materials and chiral biointerface materials. The purpose of this critical review is to give a brief introduction of recent advances in these aspects (90 references).     

Chiral polymer-based biointerface materials

Chirality is a unique phenomenon in nature. Chiral interactions play an important role in biological and physiological processes, which provides much inspiration for scientists to develop chiral materials. As a breakthrough from traditional materials, biointerface materials based on chiral polymers have attracted increasing interest over the past few years. Such materials elegantly combine the advantages of chiral surfaces and traditional polymers, and provide a novel solution not only for the investigation of chiral interaction mechanisms but also for the design of biomaterials with diverse applications, such as in tissue engineering and biocompatible materials, bioregulation, chiral separation and chiral sensors. Herein, we summarize recent advances in the study of chiral effects and applications of chiral polymer-based biointerface materials, and also present some challenges and perspectives.     

Theoretical analyses of the host–guest interaction within chlorine hydrate

The host–guest interaction is necessary for the stabilization of hydrates. Using Density Function Theory methods, the host–guest interaction within an unconventional chlorine hydrate was investigated, in combination with typical noncovalent analyses. The host–guest interaction energy was predicted to be as high as 17.51 kcal/mol, which was stronger than the typical van der Waals (vdW) interaction, due to an involvement of up to 20 Cl…O interactions. Polarization and dispersion energies made up the main contribution to the total interaction energy. Further visualization of the host–guest interaction validated, together with the general Cl…O interaction, another vdW interaction between the guest‐Cl atom and the five‐membered H₂O cluster. Isosurfaces associated with two patterns of vdW interactions yielded a better “fit” in shape, suggesting their cooperativity in stabilizing the steric configuration. The σ‐region on the guest‐Cl atom was verified to regulate the electron redistribution over the molecular space. These results are useful for understanding specific halogen behavior, and the origin and nature of host–guest interaction in hydrates. © 2013 Wiley Periodicals, Inc.     

Chiral biointerface materials

Chiral phenomena are ubiquitous in nature from macroscopic to microscopic, including the high chirality preference of small biomolecules, special steric conformations of biomacromolecules induced by it, as well as chirality-triggered biological and physiological processes. The introduction of chirality into the study of interface interactions between materials and biological systems leads to the generation of chiral biointerface materials, which provides a new platform for understanding the chiral phenomena in biological system, as well as the development of novel biomaterials and devices. This critical review gives a brief introduction to the recent advances in this field. We start from the fabrication of chiral biointerface materials, and further investigate the stereo-selective interaction between biological systems and chiral interface materials to find out key factors governing the performance of such materials in given conditions, then introduce some special functionalities and potential applications of chiral biointerface materials, and finally present our own thinking about the future development of this area (108 references).     

Water-Stable Metal Azolate Frameworks Showing Interesting Flexibilities for Highly Effective Bioethanol Dehydration

The ethanol/water separation challenge highlights the adsorption capacity/selectivity trade-off problem. We show that the target guest can serve as a gating component of the host to block the undesired guest, giving molecular sieving effect for the adsorbent possessing large pores. Two hydrophilic/water-stable metal azolate frameworks were designed to compare the effects of gating and pore-opening flexibility. Large amounts (up to 28.7 mmol g⁻¹) of ethanol with fuel-grade (99.5 %+) and even higher purities (99.9999 %+) can be produced in a single adsorption process from not only 95 : 5 but also 10 : 90 ethanol/water mixtures. More interestingly, the pore-opening adsorbent possessing large pore apertures showed not only high water adsorption capacity but also exceptionally high water/ethanol selectivity characteristic of molecular sieving. Computational simulations demonstrated the critical role of guest-anchoring aperture for the guest-dominated gating process.     

Enantioselective Light Harvesting with Perylenediimide Guests on Self‐Assembled Chiral Naphthalenediimide Nanofibers

Self‐assembling molecular systems often display amplified chirality compared to the monomeric state, which makes the molecular recognition more sensitive to chiral analytes. Herein, we report the almost absolute enantioselective recognition of a chiral perylenediimide (PDI) molecule by chiral supramolecular nanofibers of a bichromophoric naphthalenediimide (NDI) derivative. The chiral recognition was evaluated through the Förster resonance energy transfer (FRET) from the NDI‐based host nanofibers to the guest PDI molecules. The excitation energy was successfully transferred to the guest molecule through efficient energy migration along the host nanofiber, thus demonstrating the light‐harvesting capability of these hybrid systems. Furthermore, circularly polarized luminescence (CPL) was enantioselectively sensitized by the guest molecule as the wavelength band and sign of the CPL signal were switched in response to the chiral guest molecule.     

Protein Adsorption Switch Constructed by a Pillar[5]arene‐Based Host–Guest Interaction

The interfacial properties of solid substrates are of importance for protein adsorption. Herein, we report a reversible protein adsorption switch based on the host–guest interaction of the butoxy pillar[5]arene and adipic acid. By the detector of the contact angle (CA), atomic force microscopy (AFM), and luminoscope on the silicon substrate, the intelligent protein switch exhibits excellent adsorptivity for BSA and switch performance by pH regulation.     

Elucidation of Adsorbate Structures and Interactions on Brønsted Acid Sites in H‐ZSM‐5 by Synchrotron X‐ray Powder Diffraction

Microporous H‐ZSM‐5 containing one Brønsted acid site per asymmetric unit is deliberately chosen to host pyridine, methanol, and ammonia as guest molecules. By using new‐generation in situ synchrotron X‐ray powder diffraction combined with Rietveld refinement, the slight but significant alteration in scattering parameters of framework atoms modified by the guest molecules enables the user to elucidate their adsorption geometries and interactions with the Brønsted acid sites in H‐ZSM‐5 in terms of atomic distances and angles within experimental errors. The conclusion, although demonstrated in the H‐ZSM‐5, is expected to be transferable to other zeolites. This approach provides a stepping stone towards the rational engineering of molecular interaction(s) with acid sites in zeolitic catalysis.     

Pillararene Host–Guest Complexation Induced Chirality Amplification: A New Way to Detect Cryptochiral Compounds

The contradiction between the rising demands of optical chirality sensing and the failure in chiral detection of cryptochiral compounds encourages researchers to find new methods for chirality amplification. Inspired by planar chirality and the host–guest recognition of pillararenes, we establish a new concept for amplifying CD signals of cryptochiral molecules by pillararene host–guest complexation induced chirality amplification. The planar chirality of pillararenes is induced and stabilized in the presence of the chiral guest, which makes the cryptochiral molecule detectable by CD spectroscopy. Several chiral guests are selected in these experiments and the mechanism of chiral amplification is studied with a non‐rotatable pillararene derivative and density functional theory calculations. We believe this work affords deeper understanding of chirality and provides a new perspective for chiral sensing.     

Semiconducting Clathrates Meet Gas Hydrates: Xe24[Sn136]

Semiconducting Group 14 clathrates are inorganic host–guest materials with a close structural relationship to gas hydrates. Here we utilize this inherent structural relationship to derive a new class of porous semiconductor materials: noble gas filled Group 14 clathrates (Ng_x[M₁₃₆], Ng=Ar, Kr, Xe and M=Si, Ge, Sn). We have carried out high‐level quantum chemical studies using periodic Local‐MP2 (LMP2) and dispersion‐corrected density functional methods (DFT‐B3LYP‐D3) to properly describe the dispersive host–guest interactions. The adsorption of noble gas atoms within clathrate‐II framework turned out to be energetically clearly favorable for several host–guest systems. For the energetically most favorable noble gas filled clathrate, Xe₂₄[Sn₁₃₆], the adsorption energy is ?52 kJ mol^?1 per guest atom at the LMP2/TZVPP level of theory, corresponding to ?9.2 kJ mol^?1 per framework Sn atom. Considering that a hypothetical guest‐free Sn clathrate‐II host framework is only 2.6 kJ mol^?1 per Sn atom less stable than diamond‐like α‐Sn, the stabilization resulting from the noble gas adsorption is very significant.     

Sulfonated Hollow Covalent Organic Polymer: Highly‐Selective Adsorption toward Cationic Organic Dyes over Anionic Ones in Aqueous Solution

A sulfonated hollow covalent organic polymer (sh‐COP‐P) was prepared by post sulfonation of hollow covalent organic polymer (h‐COP‐P) synthesized through poly‐condensation of tetrabiphenylporphyrin (TBPP). In comparison with h‐COP‐P, sh‐COP‐P exhibits significantly enhanced adsorption capacity of organic cationic dyes in aqueous solutions accompanied with notably reduced adsorption capacity of anionic dyes. This gives sh‐COP‐P a satisfactory performance in selectively separating cationic organic dyes from anionic ones, mainly attributed to the electrostatic interaction between polymer backbone and the guest molecules.     

Macroscopic Responsive Liquid Quantum Dots Constructed via Pillar[5]arene‐Based Host‐Guest Interactions

Liquid quantum dots (QDs) have been used as a fluorescent films sensor. Constructing a macroscopic, responsive, liquid QD system for lysine (Lys) is a challenging task. To achieve a selective macroscopic response towards Lys, herein we present a new strategy for integrating host–guest chemistry into a liquid QD system. Water‐soluble pillar[5]arene WP5 was designed and synthesized as a host. WP5 was introduced onto the surface of PEG1810‐modified QDs by host–guest interactions to obtain liquid WP5‐1810‐QDs. The interaction between WP5 and Lys is stronger than that between WP5 and PEG‐1810, causing WP5 to be released from the 1810‐QDs surface in the presence of Lys, resulting in macroscopic fluorescence quenching. This smart material shows promise in amino acid sensing and separation.     

Emerging Cubic Chirality in γCD‐MOF for Fabricating Circularly Polarized Luminescent Crystalline Materials and the Size Effect

The chiral feature of γCD‐MOF, and especially the emergent cubic void, was not unveiled so far. Now, through the host–guest interaction between γCD‐MOF and achiral luminophores with different charges and sizes, the unique cubic chirality of the emerging void in γCD‐MOF as well as a size effect on CPL induction are revealed for the first time. Numerous achiral luminophores could be integrated into γCD‐MOF and emitted significantly boosted circularly polarized luminescence. While the small sized luminophores preferred to be loaded into the intrinsic void of γCD, large ones were selectively encapsulated into the cubic void. Interestingly, when the size of the guest luminophores was close to the cube size, it showed strong negative CPL. Otherwise, either positive or negative CPL was induced.     

Controlling the Host–Guest Interaction Mode through a Redox Stimulus

A proof‐of‐concept related to the redox‐control of the binding/releasing process in a host–guest system is achieved by designing a neutral and robust Pt‐based redox‐active metallacage involving two extended‐tetrathiafulvalene (exTTF) ligands. When neutral, the cage is able to bind a planar polyaromatic guest (coronene). Remarkably, the chemical or electrochemical oxidation of the host–guest complex leads to the reversible expulsion of the guest outside the cavity, which is assigned to a drastic change of the host–guest interaction mode, illustrating the key role of counteranions along the exchange process. The reversible process is supported by various experimental data (¹H NMR spectroscopy, ESI‐FTICR, and spectroelectrochemistry) as well as by in‐depth theoretical calculations performed at the density functional theory (DFT) level.     

A Rapidly Self‐Healing Host–Guest Supramolecular Hydrogel with High Mechanical Strength and Excellent Biocompatibility

It is still a challenge to achieve both excellent mechanical strength and biocompatibility in hydrogels. In this study, we exploited two interactions to form a novel biocompatible, slicing‐resistant, and self‐healing hydrogel. The first was molecular host–guest recognition between a host (isocyanatoethyl acrylate modified β‐cyclodextrin) and a guest (2‐(2‐(2‐(2‐(adamantyl‐1‐oxy)ethoxy)ethoxy)ethoxy)ethanol acrylate) to form “three‐arm” host–guest supramolecules (HGSMs), and the second was covalent bonding between HGSMs (achieved by UV‐initiated polymerization) to form strong cross‐links in the hydrogel. The host–guest interaction enabled the hydrogel to rapidly self‐heal. When it was cut, fresh surfaces were formed with dangling host and guest molecules (due to the breaking of host–guest recognition), which rapidly recognized each other again to heal the hydrogel by recombination of the cut surfaces. The smart hydrogels hold promise for use as biomaterials for soft‐tissue repair.     

Smart Materials Based on Synthetic Host Molecules: The Role of Host–Guest Chemistry in the Fabrication and Application

Stimuli-responsive or smart materials have recently shown a significant impact on the frontier of material science and engineering. The exponential development of synthetic host molecules (SHMs) over the last decades and their corresponding host–guest chemistry, have empowered researchers with new opportunities to design and construct tailored or guest-specific smart materials. In this Minireview, we present the recent advancements in synthetic host based smart materials, ranging from the fabrication strategies to the state-of-art applications including adsorption, separation, luminescence, self-healing and actuation. The role that the host–guest chemistry plays in these systems is highlighted throughout to give a better prospective of the available possibilities for emerging materials of future economies.