Host-Guest Photosensitizer of a Cationic BODIPY Derivative and Cucurbit[7]uril for High-Efficiency Visible Light-Induced Photooxidation Reactions

In recent years, there has been a notable surge of interest in the fields of organic and pharmaceutical research about photocatalysts (PCs) and photosensitizers (PSs). In this study, a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) molecule adorned with quaternary ammonium (TMB) functionality was meticulously designed and synthesized. This compound has remarkable characteristics such as exceptional water solubility, great optical qualities, and commendable photostability. It can form a 1:1 complex (TMB-CB[7]) with cucurbit[7]uril (CB[7]) through host-guest interactions in the aqueous solution and shows obvious fluorescence enhancement. The reactive oxygen species (ROS) including superoxide anion radical (O2·-) and singlet oxygen (1O2) generation ability of TMB-CB[7] were promoted compared with that of TMB in the aqueous solution. More interestingly, the ROS generated from TMB-CB[7] can be used as PCs for aerobic cross dehydrogenation coupling reactions and photooxidation reactions in water with high yields of 89 and 95%, respectively. Therefore, the utilization of a host-guest PS presents a novel and environmentally friendly approach for conducting photocatalyzed organic processes under ambient conditions using visible light.

A Closed Cavity Strategy for Selective Dipeptide Binding by a Polyaromatic Receptor in Water

Precise recognition of peptides is a daunting task owing to the substantial number of available amino acids and their combination into various oligo/polymeric structures in addition to the high hydration of their flexible frameworks. Here, we report the selective recognition of a dipeptide through a closed cavity strategy, in contrast to previous synthetic receptors with open cavities. A polyaromatic receptor with a virtually isolated, hydrophobic cavity exclusively binds one molecule of phenylalanine dipeptide from a mixture with its amino acid and tripeptide in water via multiple CH-π and hydrogen-bonding interactions in the complementary cavity. The binding selectivity persists even in the presence of other dipeptides, such as leucine-leucine, leucine-phenylalanine, tyrosine-phenylalanine, tryptophan-tryptophan, and aspartame, revealed by NMR/MS-based competitive binding experiments. ITC studies reveal that the selective binding of the phenylalanine dipeptide is relatively strong (Ka = 1.1 × 105 M-1) and an enthalpically and entropically favorable process (ΔH = -11.7 kJ mol-1 and TΔS = 17.0 kJ mol-1). In addition, the present receptor can be used for the emission detection of the dipeptide through a combination with a fluorescent dye in water.

Stimuli-Responsive Codelivery System Self-Assembled from in Situ Dynamic Covalent Reaction of Macrocyclic Disulfides for Cancer Magnetic Resonance Imaging and Chemotherapy

Supramolecular self-assembly has gained increasing attention to construct multicomponent drug delivery systems for cancer diagnosis and therapy. Despite that these self-assembled nanosystems present surprising properties beyond that of each subcomponent, the spontaneous nature of co-self-assembly causes significant difficulties in control of the synthesis process and consequently leads to unsatisfactory influences in downstream applications. Hence, we utlized an in situ dynamic covalent reaction based on thiol-disulfide exchange to slowly produce disulfide macrocycles, which subsequently triggered the co-self-assembly of an anticancer drug (doxorubicin, DOX) and a magnetic resonance imaging (MRI) contrast agent of ultrasmall iron oxide nanoparticles (IO NPs). It showed concentration regulation of macrocyclic disulfides, DOX, and IO NPs by a dynamic covalent self-assembly (DCS) strategy, resulting in a stable codelivery nanosystem with high drug loading efficiency of 37.36%. More importantly, disulfide macrocycles in the codelivery system could be reduced and broken by glutathione (GSH) in tumor cells, thus leading to disassembly of nanostructures and intellgent release of drugs. These stimuli-responsive performances have been investigated via morphologies and molecular structures, revealing greatly enhanced dual-modal MRI abilities and smart drug release under the trigger of GSH. Moreover, the codelivery system conjugated with a targeting molecule of cyclic Arg-Gly-Asp (cRGD) exhibited significant biocompatibility, MR imaging, and chemotherapeutic anticancer effect in vitro and in vivo. These results indicated that in situ dynamic covalent chemistry enhanced the control over co-self-assembly and paved the way to develop more potential drug delivery systems.

Host-Guest Interaction-Based Supramolecular Self-Assemblies for H2O2 Upregulation Augmented Chemiluminescence Resonance Energy Transfer-Induced Cancer Therapy

Given that light is hard to reach deep tumor tissue, how to enhance photodynamic therapy (PDT) efficacy is a big challenge. Herein, we proposed the supramolecular polymer self-assemblies (HACP) with bis[2,4,5-trichloro-6 (pentyloxycar-bonyl) phenyl] oxalate as the cargos (HACP@CPPO) to realize the chemiluminescence resonance energy transfer (CRET)-induced generation of 1O2 in situ. HACP was prepared by cinnamaldehyde-modified hyaluronic acid (HA-CA) and β-cyclodextrin-modified protoporphyrin IX (β-CD-PPIX) via host-guest interactions. The CA moiety could elevate H2O2 levels for the enhanced production of chemical energy and macrocyclic CD could enhance the stacking distance of PPIX for enhanced 1O2 yield. Thus, HACP@CPPO exhibited excellent antitumor performance without light irradiation.

Building a Poly(amino acid)/Chitosan-Based Self-Healing Hydrogel via Host-Guest Interaction for Cartilage Regeneration

Cartilage injury is a very common joint disease, and cartilage repair is a great challenge in clinical treatment due to the specific structure of cartilage tissue and its microenvironment in vivo. The injectable self-healing hydrogel is a very promising candidate as a cartilage repair material because of its special network structure, high water retention and self-healing properties. In this work, a self-healing hydrogel cross-linked by host-guest interaction between cyclodextrin and cholic acid was developed. The host material was composed of β-cyclodextrin and 2-hydroxyethyl methacrylate-modified poly(l-glutamic acid) (P(LGA-co-GM-co-GC)), while the guest material was chitosan modified by cholic acid, glycidyl methacrylate, and (2,3-epoxypropyl)trimethylammonium chloride (EPTAC) (QCSG-CA). The host-guest interaction self-healing hydrogels, named as HG hydrogels (HG gel), exhibited excellent injectability and self-healable property, and the self-healing efficiency was greater than 90%. Furthermore, in order to enhance the mechanical properties and slow down the degradation of the HG gel in vivo, the second network was constructed by photo-cross-linking in situ. Biocompatibility tests showed that the enhanced multi-interaction hydrogel (MI gel) was extremely suitable for cartilage tissue engineering both in vitro and in vivo. In addition, the adipose derived stem cells (ASCs) in MI gel were able to differentiate cartilage effectively in vitro in the presence of inducing agents. Subsequently, the MI gel without ASCs was transplanted into rat cartilage defects in vivo for the regeneration of cartilage. After 3 months postimplantation, new cartilage tissue was successfully regenerated in a rat cartilage defect. All results indicated that the injectable self-healing host-guest hydrogels have important potential applications in cartilage injury repair.

Bacteria-Induced Colloidal Encapsulation for Probiotic Oral Delivery

Probiotic oral delivery has crucial implications in biomedical engineering, but its oral bioavailability remains unsatisfactory because of the limited survival and colonization of probiotics in the harsh gastrointestinal tract. Here, a bacteria-induced encapsulation strategy is achieved by assembling metastable colloids to enhance the oral bioavailability of probiotics. The colloids (NTc) composed of amino-modified poly-β-cyclodextrin and tannic acid are formed based on the balance of host-guest interaction-driven attraction and electrostatic repulsion between colloids. Negatively charged probiotics electrostatically attract positively charged NTc to break the balance and induce further assembly surrounding the probiotics. Through a facile one-step mixing, 97% of bacteria are rapidly encapsulated into NTc shells within 10 s, with a high utilization rate of feeding colloids of 91%. More importantly, we show that the compact, thick, and positively charged NTc shells synergistically endow the encapsulated probiotics with strong resistance against simulated gastric fluid with an excellent survival rate of up to 19%, 7500 times superior to the commercial enteric material L100. Moreover, owing to the dynamically noncovalent and self-adaptive nature of host-guest interactions, NTc shells support the proliferation of the encapsulated EcN comparable with that of the naked EcN. In vitro and in vivo experiments also confirm that the NTc-encapsulated probiotics possess durable intestinal adhesion, continuous proliferation activity, enhanced oral bioavailability, good oral biosafety, and excellent therapeutic efficacy in a colitis mouse model. This facile bacteria-induced colloidal encapsulation strategy may extend to various microbes as oral bioagents for treating various diseases.

Spin-Resolved Band Structure of Hoffman Clathrate [Fe(pz)2Pt(CN)4] as an Essential Tool to Predict Optical Spectra of Metal-Organic Frameworks

Paramount spin-crossover properties of the 3D-Hoffman metalorganic framework (MOF) [Fe(pz)₂Pt(CN)₄] are generally described on the basis of the ligand field theory, which provides adequate insight into theoretical and simulation analysis of spintronic complexes. However, the ligand field approximation does not take into account the 3D periodicity of the actual complex lattice and surface effects and therefore cannot predict a full-scale periodic structure without utilizing more advanced methods. Therefore, in this paper, the electronic properties of the exemplar MOF were analyzed from the band structure perspective in low-spin (LS) and high-spin (HS) states. The density-of-states spectra determined for both spin-up and spin-down electrons of Fe d⁶ orbitals indicate spin-orbital splitting and delocalization for HS due to spin polarization in the iron atom ligand field. Presence of the surface states in the real crystal causes a red shift of the metal-metal charge transfer (MMCT) and metal-ligand charge transfer (MLCT) peaks for both HS and LS states. The addition of residual water molecules and disorder among the pyrazine rings reveal additional influences on the positions of the pyrazine band and, therefore, on the absorption spectra of the crystal. The results show a magnification of the peak correlated with the MLCT in the HS state and a significant red shift of the LS characteristic absorption band. The presented approach involving band structure analysis delivers a more complete image of the electronic properties of the [Fe(pz)₂Pt(CN)₄] crystalline network and can be a landmark for insightful studies of other MOFs.

Conjugation of Macrophage-Mimetic Microalgae and Liposome for Antitumor Sonodynamic Immunotherapy via Hypoxia Alleviation and Autophagy Inhibition

Sonodynamic therapy (SDT) is a noninvasive technique for local antitumor treatment; however, its clinical application is often limited by the low tumor accumulation of SDT agents, tumor's hypoxic microenvironment, and cytoprotective effects of autophagy. To address these issues, herein we developed surface-engineered chlorella (Chl, a green algae) as a targeted drug carrier and sustainable oxygen supplier (via photosynthesis) for significantly improved SDT via hypoxia alleviation as well as autophagy inhibition of chloroquine phosphate. In this design, the macrophage membrane was coated onto Chl to form macrophage-mimetic Chl (MChl) to increase its biocompatibility and targeted tumor accumulation driven by the inflammatory-homing effects of macrophage membranes. In addition, the membrane coating on Chl allowed lipid insertion to yield β-cyclodextrin (β-CD) modified MChl (CD-MChl). Subsequently, supramolecular conjugates of MChl-NP were constructed via host-guest interactions between CD-MChl and adamantane (ADA)-modified liposome (ADA-NP), and the anchored liposome went with CD-MChl hand-in-hand to the tumor tissues for co-delivery of Chl, hematoporphyrin, and chloroquine phosphate (loaded in ADA-NP). The synergistic therapy achieved via local oxygenation, SDT, and autophagy inhibition maximally improved the therapeutic efficacy of MChl-CQ-HP-NP against melanoma. Tumor rechallenging results revealed that the changes of tumor microenvironment including hypoxia alleviation, SDT induced immunogenic cell death, and autophagy inhibition collectively induced a strong antitumor immune response and memory.

Stability and pKa Modulation of Aminophenoxazinones and Their Disulfide Mimics by Host-Guest Interaction with Cucurbit[7]uril. Direct Applications in Agrochemical Wheat Models

Aqueous solubility and stability often limit the application of aminophenoxazinones and their sulfur mimics as promising agrochemicals in a sustainable agriculture inspired by allelopathy. This paper presents a solution to the problem using host-guest complexation with cucurbiturils (CBn). Computational studies show that CB7 is the most suitably sized homologue due to its strong affinity for guest molecules and its high water solubility. Complex formation has been studied by direct titrations monitored using UV-vis spectroscopy, finding a preferential interaction with protonated aminophenoxazinone species with high binding affinities (CB7·APOH⁺, K_a = (1.85 ± 0.37) × 10⁶ M^-1; CB7·DiS-NH₃⁺, K_a = (3.91 ± 0.53) × 10⁴ M^-1; and DiS-(NH₃⁺)₂, K_a= (1.27 ± 0.42) × 10⁵ M^-1). NMR characterization and stability analysis were also performed and revealed an interesting pK_a modulation and stabilization by cucurbiturils (2-amino-3H-phenoxazin-3-one (APO), pK_a = 2.94 ± 0.30, and CB7·APO, pK_a = 4.12 ± 0.15; 2,2'-disulfanediyldianiline (DiS-NH₂), pK_a = 2.14 ± 0.09, and CB7·DiS-NH₂, pK_a = 3.26 ± 0.09), thus favoring applications in different kinds of crop soils. Kinetic studies have demonstrated the stability of the CB7·APO complex at different pH media for more than 90 min. An in vitro bioassay with etiolated wheat coleoptiles showed that the bioactivity of APO and DiS-NH₂ is enhanced upon complexation.

Novel Strategy of Constructing Artificial Light-Harvesting System with Two-Step Sequential Energy Transfer for Efficient Photocatalysis in Water

An efficient artificial light-harvesting system with a two-step sequential energy transfer was fabricated in the aqueous solution based on the host-guest interactions between cyano-substituted p-phenylenevinylene derivative (PPTA) and a water-soluble pillar[5]arene (WP5). PPTA-WP5 complex could self-assemble into nanoparticles, and two fluorescent dyes eosin Y (EY) and Nile Red (NIR) are employed as acceptors to realize sequential energy transfer. The PPTA-WP5-EY-NIR system could achieve efficient two-step sequential energy transfer process from PPTA-WP5 to EY and then to NIR (67% for the first step and 66% for the second step). Moreover, to make full use of the harvested energy, the hydrophobic microenvironment in the assembled nanoparticles is used to promote the aerobic cross-dehydrogenative coupling (CDC) reaction in aqueous medium with 88% yield after 12 h of irradiation. To our knowledge, this is the first example of artificial LHS with two-step energy transfer used to catalyze the CDC reaction in aqueous medium. This work directly mimics the function of photosynthesis in nature of converting solar energy into chemical energy in aqueous solution.

Supramolecular Self-Assemblies with Self-Supplying H2O2 and Self-Consuming GSH Property for Amplified Chemodynamic Therapy

Fe-based chemodynamic therapy (CDT) has become one potential method for cancer therapy due to its lower side effect and tumor-specific property. During the process of CDT, the lack of active targeting and biodegradable ability, insufficient endogenous H₂O₂, and overexpressed GSH in the tumor were responsible for the unsatisfactory therapeutic performance. Hence, we report host-guest interaction-based supramolecular polymers (HGSPs) that were constructed with the biomacromolecule β-cyclodextrin-grafted hyaluronic acid (HA-CD) as the active targeting host unit and hydrophobic ROS-responsive ferrocene-(phenylboronic acid pinacol ester) (Fc-BE) as the guest unit. HGSPs can further self-assemble into self-assemblies (HGSAs) and encapsulate PA as the prooxidant. After CD44-receptor-mediated cellular internalization, HGSAs could disassemble and release PA to elevate the H₂O₂ level for the production of higher cytotoxic hydroxyl radicals (^•OH) through the Fc-induced Fenton reaction. Moreover, quinone methide (QM) was generated to downregulate antioxidant GSH. The enhancement of H₂O₂ and consumption of GSH were favorable for CDT due to the amplified oxidative stress. In vivo experimental results indicated that HGSAs@PA might be used as an active targeting amplified CDT agent.

Recent Applications of Pillar[n]arene-Based Host-Guest Recognition in Chemosensing and Imaging

Pillar[n]arene is a novel kind of synthetic supramolecular macrocyclic host characterized by its particular pillar-shaped structure consisting of an electron-rich cavity and two finely adjustable rims. Benefiting from its rigid structure, facile synthesis, ease of functionalization, and outstanding host-guest chemistry, pillar[n]arene shows great potential for diverse applications. Significantly, the host-guest recognition of pillar[n]arene provides a novel approach for chemosensing and imaging. Herein, this Review critically and comprehensively reviews the applications of pillar[n]arene-based host-guest recognition in chemosensing and imaging. The sensing and imaging mechanisms as well as the unique roles and advantages of pillar[n]arene-based host-guest recognition are summarized. In addition, preparations of hybrid materials based on pillar[n]arene and inorganic materials are also introduced comprehensively in the light of chemosensing and imaging. Finally, current challenges and perspectives on pillar[n]arene-based host-guest recognition in chemosensing and imaging are outlined.

Insights into Paraben Adsorption by Metal-Organic Frameworks for Analytical Applications

Metal-organic frameworks (MOFs) are attractive materials used as sorbents in analytical microextraction applications for contaminants of emerging concern (CECs) from environmental liquid matrices. The demanding specs for a sorbent in the analytical application can be comprehensively studied by considering the interactions of the target analytes with the frameworks by the use of single-crystal X-ray diffraction, computational analysis, and adsorption studies, including the kinetic ones. The current study intends a better understanding of the interactions of target CECs (particularly, propylparaben (PPB) as a model) and three Zn-based layered pillared MOFs: CIM-81 [Zn₂(tz)₂(bdc)] (Htz = 1,2,4-triazole and H₂bdc = 1,4-benzenedicarboxylic acid) and their amino derivatives [Zn₂(NH₂-tz)₂(bdc)] CIM-82 and [Zn₂(tz)₂(NH₂-bdc)] CIM-83 (NH₂-Htz = 3-amino-1,2,4-triazole and NH₂-H₂bdc = 2-amino-1,4-benzenedicarboxylic acid). The crystal structures of the two solvate compounds (dma@CIM-81 (dma = dimethylacetamide) and acetone@CIM-81) were solved by single-crystal X-ray diffraction to determine the points of interaction between the framework and the guest molecules. They also served as a starting point for the computational modeling of the PPB@CIM-81 compound, showing that up to two PPB molecules can be hosted in one of the pores, while only one can be trapped in the second pore type, leading to a maximum theoretical capacity of 291.9 mg g^-1. This value is close to the value obtained by the adsorption isotherm experiment for CIM-81 (283 mg g^-1). This value is, by far, higher than those previously reported for other materials for the removal of PPB from water, and also higher than the experimental values obtained for CIM-82 (54 mg g^-1) and CIM-83 (153 mg g^-1). The kinetics of adsorption is not very fast, with uptake of about 40% in 3 h, although a 70% release in methanol is achieved in 1 h. In addition, a further comparison of performance in analytical microextraction (requiring only 10 mg of CIM-81) was carried out together with chromatographic analysis to support all insights attained, with the method being able to monitor CECs as low as μg L^-1 levels in complex environmental water samples, thus performing successfully for water monitoring even in multicomponent scenarios.

Design of Fluorescent and Robust Covalent Organic Framework Host Matrices for Illuminating Mechanistic Insight into Solvatochromic Decoding

Two functional covalent organic frameworks (COFs), constructed from 3-connected triazine-based amine or hydrazine with linear dialdehyde, are decorated with molecular docking sites to showcase their solvatochromic decoding behavior toward volatile solvent molecules (VSMs). These luminescent and crystalline COFs, namely, COF-N and COF-NN, are characterized by numerous analytical techniques. After accommodation of different VSMs as guests, the inclusion compounds of COF-N and COF-NN display solvatochromism. More fascinatingly, the singlet energy, band gaps, and lifetime of these VSM-accommodated COF-N and COF-NN are linearly correlated with the properties of VSMs. Density functional theory (DFT) and Monte Carlo simulation studies further support the interaction of VSMs with COF-N and COF-NN. The presence of an extra amine functionality in COF-NN leads to the better interaction with VSMs and, therefore, results in different modes of interaction and correlation. Considering their inestimable chemical diversity, this study introduces a new path for finely tuned solvatochromic properties by COFs.

Antifouling Nanofiltration Membrane Fabrication via Surface Assembling Light-Responsive and Regenerable Functional Layer

Membrane fouling, caused by aggregation of organics and microorganisms from filtrate on the membrane surface, seriously reduces the service life of a nanofiltration (NF) membrane. Developing facile and renewable antifouling modification methods without sacrificing separation properties of the membrane remain an imperative requirement. Herein, a thin-film composite (TFC) NF membrane with a light-responsive and regenerable functional layer (P-TFC) was fabricated via host-guest interactions between the azobenzene (guest) labeled functional polymers and the β-cyclodextrin (host) bonded membrane surface (H-TFC). The P-TFC-3 not only showed outstanding antifouling ability and high flux recovery ratio (FRR > 90% at the fourth antiadhesive test) but also exhibited enhanced water permeability (17.9 L m^-2 h^-1 bar^-1) and high selectivity (α_MgSO4^NaCl = 33.4 and fast antibiotics enrichment capacity) compared with the pristine membrane. Furthermore, when the functional layer was contaminated, it can be removed by ultraviolet light irradiation and a new functional layer can be rebuilt by adding fresh azobenzene labeled functional polymers. After several regeneration processes, the membranes still showed constant separation properties and high flux recovery ability (FRR > 90%). This work proposes an easy-to-assemble and regenerable surface modification strategy to endow TFC NF membranes with excellent fouling resistance and sustainable utilization ability while maintaining high separation properties.

Discrete Supracrystalline Heterostructures from Integrative Assembly of Nanocrystals and Porous Organic Cages

Although self-assembly across multiple length scales has been well recognized and intensively investigated in natural biological system, the design of artificial heterostructures enabled by integrative self-assembly is still in its infancy. Here we report a strategy toward the growth of discrete supracrystalline heterostructures from inorganic nanocrystals and porous organic cages (CC3-R), which in principle relies on the host-guest interactions between alkyl chains coated on nanocrystals and the cavity of cage molecules. Density functional theory calculation indicates that an attractive energy of ∼-2 k_BT is present between an alkyl chain and the cavity of a CC3-R molecule, which is responsible for the assembly of nanocrystal superlattices on the CC3-R octahedral crystals. Of particular interest is that, determined by the shape of the nanocrystals, two distinct assembly modes can be controlled at the mesoscale level, which eventually produce either a core/shell or heterodimer supracrystalline structure. Our results highlight opportunities for the development of such a noncovalent integrative self-assembly not limited to a particular length scale and that could be generally applicable for flexible integration of supramolecular systems.

Supramolecular Chemotherapy Based on the Host-Guest Complex of Lobaplatin-Cucurbit[7]uril

This work aimed to develop a supramolecular chemotherapy-based strategy to reduce the cytotoxicity of the antitumor drug lobaplatin (LbPt) toward normal human intestinal cells and recover its antitumor bioactivity toward human intestinal tumor cells. Through host-guest interactions, cucurbit[7]uril (CB[7])-encapsulated LbPt decreased the cytotoxicity of LbPt toward normal human intestinal cells, and even at a concentration of 100.0 μM, LbPt-CB[7] exhibited 77.4% higher safety over a 24 h period compared with LbPt. At pH 6.0, the binding affinity constant (K_a) of CB[7] and spermine was (1.18 ± 0.12) × 10⁶ M^-1, which is an order of magnitude higher than that of CB[7] with LbPt [K_a = (2.09 ± 0.07) × 10⁵ M^-1]; thus, the encapsulated LbPt can be released from its host-guest complex of LbPt-CB[7] through competitive replacement with spermine solution. The LbPt-CB[7] complex exhibited good in vitro performance for spermine as a biomarker tumor, as demonstrated with human intestinal tumor cells. These results indicate that LbPt is released from its host-guest complex by spermine in the tumor microenvironment, and supramolecular strategies will likely be extended to other clinical antitumor drugs to decrease their severe side effects in normal tissues and recover their antitumor bioactivity in tumors, which will enrich the field of safe supramolecular chemotherapy.

Molecular recognition-directed site-specific release of stem cell differentiation inducers for enhanced joint repair

The remarkable difference in cell type and matrix composition between two connected parts of a joint (cartilage and subchondral bone) makes it challenging to simultaneously regenerate both parts for joint repair. Thus we chemically designed a biphasic hydrogel made of two well-bonded shape-tunable hydrogel phases, termed bone-regenerating hydrogel (BRH) and cartilage-regenerating hydrogel (CRH). The BRH and CRH, encapsulating stem cells, were produced by photo-crosslinking bone and cartilage matrix-mimicking biopolymers and a nanobox (β-cyclodextrin) in situ in the subchondral bone defect and cartilage defect, respectively. The nanoboxes in BRH and CRH were loaded with osteogenic and chondrogenic differentiation inducers (melatonin and kartogenin) by host-guest interactions, respectively. Such interactions directed the sustained phase- and defect site-specific release of the inducers and subsequent site-specific stem cell differentiation into cartilage and bone forming cells for joint repair. The strategy opens up a new chemical approach to biomaterials with phase-specific drug release for tissue repair.

Calixarene-Functionalized Porous Carbon Aerogels for Polysulfide Capture: Cathodes for High Performance Lithium-Sulfur Batteries

A cage-type composite was successfully prepared by attaching p-sulfonatocalix[4]arene to a porous activated carbon aerogel (ACA). The resulting composite showed a high specific surface area of 1620.7 m²  g^-1 and a high sulfur loading of 2.5 mg cm^-2 . The calixarene is uniformly dispersed on the carbon spheres and efficiently captures polysulfides by interaction with the sulfonate groups. Meanwhile, the cross-linked porous structure of the composite restricts the migration of polysulfides. The cathode delivers an outstanding electrochemical performance with an initial capacity of 1304.7 mAh g^-1 at 0.2 C. Furthermore, it displays excellent long-term cycling stability, maintaining 884.7 mAh g^-1 after 300 cycles at 0.5 C. Density functional theory (DFT) adsorption calculations support the strong interaction between the calixarenes and polysulfides and reveal the capture mechanism.

Tough Self-Healing Elastomers Based on the Host-Guest Interaction of Polycyclodextrin

Inspired by animal muscles, we developed a kind of tough elastomers combining high strength and high stretchability with autonomous self-healing capability. A key structural feature is the construction of a double network (DN) connected by the hydrogen bond and host-guest interactions. The first network is the classic elastomer polyacrylate matrix cross-linked by strong hydrogen bonding. The second network is formed through the host-guest interactions between polycyclodextrin and the adamantane (Ad) groups on the side of the polyacrylate chain. Supramolecular interactions between two networks make them miscible and interpenetrate in the molecular level and then can share the load as the sample was stretched. The host-guest interactions act not only as sacrificial bonds for energy dissipation but also as self-healing driving forces. The tensile strength of the DN elastomer reaches about 6.7 MPa and the strain is as high as about 950%. The DN elastomer can be easy to repair by touching the damaged surface together at ambient conditions when broken or cut. The recovered tensile strength can reach over 4.5 MPa, which is better than the most pristine strength of existing spontaneous self-healing elastomers.

Measuring Binding Constants of Cucurbituril-Based Host-Guest Interactions at the Single-Molecule Level with Nanopores

Cucurbiturils are one type of widely used macrocyclic host compound in supramolecular chemistry. Their peculiar properties have led to applications in a wide variety of research areas such as fluorescence spectroscopy, drug delivery, catalysis, and nanotechnology. However, the solubilities of cucurbiturils are rather poor in water and many organic solvents, which may cause accuracy problems when measuring binding constants with traditional methods. In this report, we aim to develop an approach to measure the binding constants of cucurbituril-based host-guest interactions at the single-molecule level. First, we covalently attach different guest compounds to the side-chain of DNA molecules. Then, excess cucurbiturils are incubated with DNA probes to form the host-guest complexes. Next, the modified DNA hybrids are threaded through α-hemolysin nanopore to generate highly characteristic current events. Finally, statistical analyses of the obtained events afford the binding constants of cucurbiturils with various molecules. This new approach provides a simple and straightforward method to compare binding strength of different host-guest complexes and may find applications for quantifying other macrocycle-based host-guest interactions.

Brighter, More Stable, and Less Toxic: A Host-Guest Interaction-Aided Strategy for Fabricating Fluorescent Silica Nanoparticles and Applying Them in Bioimaging and Biosensing at the Cellular Level

The exploration of fluorescent tools with distinguished optical properties and favorable biocompatibility is significant for biosensing and bioimaging. We herein present a host-guest interactions aided strategy for fabricating fluorescent silica nanoparticles (FSNPs), which is enabled by cyclodextrin (CD) supermolecules. Compared with conventional FSNPs, the modified products (are named as fluorophore@CD@SNPs) possess several advantages. First, the incorporated fluorophores can thoroughly get rid of their intrinsic aggregation due to CD's inclusion effect, and the fluorescence intensity of the obtained fluorophore@CD@SNPs can enhance 48-67%. The fluorophores can then be well-fixed by the host CD molecules. As a result, the leak rates of the incorporated fluorophores are only 15-17%, which is about 3 times lower than that of conventional ones (42-48%). Notably, the as-prepared fluorophore@CD@SNPs show observable less cytotoxicity as compared with their conventional counterparts, probably due to the substantially decreased leakage of the incorporated fluorophores. Because of prominent properties and versatile fabrication, the proposed fluorophore@CD@SNPs not only possess better performances for cell-imaging but are competent for ratiometric sensing of pH value at living cell using (indicator-reference) integrative silica NPs.

Theranostic Prodrug Vesicles for Imaging Guided Codelivery of Camptothecin and siRNA in Synergetic Cancer Therapy

The construction of prodrugs has been a popular strategy to overcome the limitations of chemotherapeutic drugs. However, complicated synthesis procedures and laborious purification steps make the fabrication of amphiphilic prodrugs rather difficult. By harnessing the concept of host-guest interaction, we designed and prepared a supra-amphiphile consisting of a dendritic cyclodextrin host and an adamantane/naphthalimide-modified camptothecin guest through glutathione-responsive disulfide linkage. This host-guest complex could self-assemble in aqueous solution to give nanosized vesicles. When the disulfide bond in adamantane/naphthalimide-modified camptothecin was cleaved by glutathione, the fluorescence of the freed adamantane/naphthalimide unit showed a significant red shift with enhanced intensity. Such glutathione-responsive fluorescence change allows for intracellular imaging and simultaneous monitoring of drug release in real time. On account of abundant positively charged amine groups on the supramolecular vesicle surface, siRNA (siPlK1) could be efficiently loaded on the vesicle. The gel retardation and fluorescence experiments proved that the siPlK1 was successfully bonded to the supramolecular vesicle. The vesicle with dendritic cyclodextrin ring exhibited negligible cytotoxicity even at high concentrations, avoiding the shortcoming of cytotoxicity from commonly used gene vectors. In vitro studies demonstrated that the loaded siRNA was transported into cancer cells to improve cancer therapeutic efficacy. Thus, we developed a prodrug-based supramolecular amphiphile via the host-guest interaction with better therapeutic performance than free camptothecin. The assembled system was utilized as a drug/gene vector to achieve combinational gene therapy and chemotherapy with a synergistic effect, providing an alternative strategy to deliver both prodrug and therapeutic gene.

Supramolecular Porphyrin Photosensitizers: Controllable Disguise and Photoinduced Activation of Antibacterial Behavior

A series of supramolecular photosensitizers were fabricated from porphyrin derivatives (Por) containing quaternary ammonium groups with cucurbit[7]uril (CB[7]) based on host-guest interactions. The antibacterial activity of Por in the dark could be turned off upon binding with CB[7], whereas the antibacterial activity under white-light illumination could be turned on. In addition, its antibacterial efficiency could be greatly enhanced by introducing metal ions. When Pd(II) was introduced into porphyrin, its antibacterial efficiency was enhanced from 40 to 100%. It should be noted that these small molecules showed little to no cytotoxicity toward mammalian cells even at concentrations higher than those under the antibacterial condition studied. This line of research will provide a strategy for germicides consisting of quaternary ammonium groups to fight against bacterial accumulation in the long term and holds huge potential for application in the real world.

Microfluidic Reactors Based on Rechargeable Catalytic Porous Supports: Heterogeneous Enzymatic Catalysis via Reversible Host-Guest Interactions

We report on the fabrication of a microfluidic device in which the reservoir contains a porous surface with enzymatic catalytic activity provided by the reversible immobilization of horseradish peroxidase onto micrometer size pores. The porous functional reservoir was obtained by the Breath Figures approach by casting in a moist environment a solution containing a mixture of high molecular weight polystyrene (HPS) and a poly(styrene-co-cyclodextrin based styrene) (P(S-co-SCD)) statistical copolymer. The pores enriched in CD were employed to immobilize horseradish peroxidase (previously modified with adamantane) by host-guest interactions (HRP-Ada). These surfaces exhibit catalytic activity that remains stable during several reaction cycles. Moreover, the porous platforms could be recovered by using free water-soluble β-CD with detergents. An excess of β-CD/TritonX100 in solution disrupts the interactions between HRP-Ada and the CD-modified substrate thus allowing us to recover the employed enzyme and reuse the platform.

Supramolecular Aggregate as a High-Efficiency Gene Carrier Mediated with Optimized Assembly Structure

For cancer gene therapy, a safe and high-efficient gene carrier is a must. To resolve the contradiction between gene transfection efficiency and cytotoxicity, many polymers with complex topological structures have been synthesized, although their synthesis processes and structure control are difficult as well as the high molecular weight also bring high cytotoxicity. We proposed an alternative strategy that uses supramolecular inclusion to construct the aggregate from the small molecules for gene delivery, and to further explore the relationship between the topological assembly structure and their ability to deliver gene. Herein, PEI-1.8k-conjugating β-CD through 6-hydroxyl (PEI-6-CD) and 2-hydroxyl (PEI-2-CD) have been synthesized respectively and then assembled with diferrocene (Fc)-ended polyethylene glycol (PEG-Fc). The obtained aggregates were then used to deliver MMP-9 shRNA plasmid for MCF-7 cancer therapy. It was found that the higher gene transfection efficiency can be obtained by selecting PEI-2-CD as the host and tuning the host/guest molar ratios. With the rational modulation of supramolecular architectures, the aggregate played the functions similar to macromolecules which exhibit higher transfection efficiency than PEI-25k, but show much lower cytotoxicity because of the nature of small/low molecules. In vitro and in vivo assays confirmed that the aggregate could deliver MMP-9 shRNA plasmid effectively into MCF-7 cells and then downregulate MMP-9 expression, which induced the significant MCF-7 cell apoptosis, as well inhibit MCF-7 tumor growth with low toxicity. The supramolecular aggregates maybe become a promising carrier for cancer gene therapy and also provided an alternative strategy for designing new gene carriers.

Enantioselective Liquid-Solid Extraction (ELSE)--An Unexplored, Fast, and Precise Analytical Method

A novel method of evaluating the enantioselectivity of chiral receptors is investigated. It involves extraction of an ionic guest in racemic form from an ion-exchange resin to the organic solvent, where it is bound by a chiral receptor. The enantioselectivity of the examined receptor is determined simply by measuring the enantiomeric excess of the extracted guest. We show that the concept is viable for neutral receptors binding chiral organic anions extracted into acetonitile. This method was determined to be more accurate and far less time-consuming than the classical titrations. Multiple racemic guests can be applied to a resin in a single experiment, giving the method a very high throughput.