Pillar[5]arene based water-soluble [3]pseudorotaxane with enhanced fluorescence emission for cell imaging and both type I and II photodynamic cancer therapy

Preparation of water-soluble imidazole-functionalized pillar[5]arenes: The activities of antibacterial and antioxidant, catalytic reduction of 4-nitrophenol

Macrocyclic supramolecular materials such as pillar[n]arenes play a prominent role in enhancing antibacterial activity through host-guest interactions. Herein, the water-soluble pillar[5]arene imidazole-1 and pillar[5]arene imidazole-2 were prepared, and their structure and chemical compositions were analyzed through multiple characterization methods. Afterward, the prepared imidazole-functionalized pillar[5]arenes were examined for antibacterial activity against Escherichia coli, Enterococcus faecalis, Staphylococcus aureus, and Salmonella typhimurium bacteria. Also, the antioxidant activities of the prepared imidazole-functionalized pillar[5]arenes were investigated using 2,2-Diphenyl-1-picrylhydrazyl. In addition, the catalytic activities of pillar[5]arene imidazole-1 and pillar[5]arene imidazole-2 by reduction of 4-nitrophenol were studied, indicating the catalytic reduction of 4-nitrophenol was 93.0 % for the pillar[5]arene imidazole-1 catalyst at 18 min. Comparison of the reactivity of pillar[5]arene imidazole-1 with that of pillar[5]arene imidazole-2 shows an increase in antibacterial and catalytic activity. This study summarized that using suitable catalysts, catalytic reduction aims to convert the most harmful and toxic organic compound 4-nitrophenol into non-toxic 4-aminophenol and popularize it in industry.

Pillar[n]arene-Based Supramolecular Nanodrug Delivery Systems for Cancer Therapy

Macrocyclic supramolecular materials play an important role in encapsulating anticancer drugs to improve the anticancer efficiency and reduce the toxicity to normal tissues through host-guest interactions. Among them, pillar[n]arenes, as an emerging class of supramolecular macrocyclic compounds, have attracted increasing attention in drug delivery and drug-controlled release due to their high biocompatibility, excellent host-guest chemistry, and simplicity of modification. In this review, we summarize the research progress of pillar[n]arene-based supramolecular nanodrug delivery systems (SNDs) in recent years in the field of tumor therapy, including drug-controlled release, imaging diagnostics and therapeutic modalities. Furthermore, the opportunities and major limitations of pillar[n]arene-based SNDs for tumor therapy are discussed.

In Situ NADH-Activated BODIPY-Based Macrocyclic Supramolecular Photosensitizer for Chemo-Photodynamic Synergistic Tumor Therapy

Photodynamic therapy (PDT) based on supramolecular assembly has been receiving wide attention due to its great potential application in clinical treatment. Herein, we report a supramolecular photoelectron "reservoir" (SPR) constructed by tetracationic boron dipyrromethene (BODIPY)-based macrocycle (BBox·4Cl), doxorubicin (Dox), and tumor-targeted β-cyclodextrin-grafted hyaluronic acid (HACD). Upon irradiation, BBox·4Cl can in situ catalyze nicotinamide adenine dinucleotide (NADH) to continuously generate electrons to inject into SPR, which further transfers electrons to oxygen, inducing highly efficient hydroxyl radical generation even under hypoxia. Synergistically, Dox in SPR as "pump" can be encapsulated by BBox·4Cl and transport photoelectrons between two BODIPY units, while HACD as "sponge" can enrich BBox·4Cl by the electrostatic interaction to concentrate them closer in space, which facilitates intramolecular and intermolecular photoelectron transfer, respectively, and significantly enhances the generation of hydroxyl radicals. Meanwhile, electron replenishment in SPR causes NADH depletion and redox dysfunction, thereby accelerating the apoptosis and achieving highly effective synergistic tumor therapy.

Resveratrol-loaded metal-organic framework for mitochondria-targeted amplified CO gas therapy

Carbon monoxide (CO) based gas therapy has recently garnered significant attention due to its remarkable therapeutic effects for various major diseases. However, the primary challenge in gas therapy is the effective delivery of gas prodrug to targeted sites, as well as achieving precise spatial-temporal control over their release behavior. In this work, we provide a facile method to design ROS-responsive and mitochondrial targeting CO-delivery nanoplatform, based on the thiol-functionalized metal-organic framework (MOF), abbreviated as UiO-66-SH, incorporating the drug resveratrol (RES) for combined tumor therapy. After endocytosis by tumor cells and localization within the mitochondria, UiO@FeCO@RES was decomposed by ATP to release RES and generate CO gas via a Fenton-like reaction between hydroxyl radicals (·OH) and FeCO. RES acts as an ATPase inhibitor, disrupting the metabolism of the respiratory chain in tumor cell and thereby facilitating ATP-blocked metabolic therapy. In vitro experimental results demonstrate that the combination therapy, involving both RES drug and CO gas therapy, exhibits a synergistic effect against cancer cells. This synergistic strategy has endowed UiO@FeCO@RES as a promising material for biomedical applications.

Supramolecular Porphyrin Photosensitizers Based on Host-Guest Recognition for In Situ Bacteria-Responsive Near-Infrared Photothermal Therapy

Antibiotic resistance resulting from the overuse of antibiotics sets a high challenge for brutal antimicrobial treatment. Although photothermal therapy (PTT) overcomes the awkward situation of antibiotic resistance, it usually mistakenly kills the beneficial bacteria strains when eliminating pernicious bacteria. Specifically recognizing and damaging the target pathogens is urgently required for PTT-mediated sterilization strategy. Based on the host-guest recognition between cucurbit[10]uril (CB[10]) and porphyrins, two water-soluble supramolecular porphyrins are designed and implement selective bactericidal effect via in situ bacteria-responsive near-infrared (NIR) PTT. With the help of CB[10], the π-π stacking and hydrophobic interactions of porphyrins are efficiently inhibited, thus contributing to a good photostability and a high photothermal conversion efficiency. Attributing to the matching reduction potential between facultative anaerobic Escherichia coli (E. coli) and porphyrins, they are selectively in situ reduced into supramolecular phlorin and supramolecular chlorin by E. coli, successfully achieving a selective sterilization against E. coli. In vivo, the in situ bacteria-responsive NIR PTT systems also promote the quick recovery of E. coli-infected abscesses and trauma on mice without inducing obvious systemic toxicity, providing a new alternative to the current antibiotics and helping relieve the global public health crisis of abusive antibiotics.

Acid/base responsive pseudo[3]rotaxanes from amine naphthotubes and bis-pyridinium/isoquinolinium guests

A novel cooperative pseudo[3]rotaxane system was successfully constructed by the inclusion complexation of two identical amine naphthotubes with a bis-pyridinium/isoquinolinium guest. Single crystal structure analysis revealed that weak Csp3-H⋯O hydrogen bonds between the two hosts are responsible for the positive cooperativity during the formation of pseudo[3]rotaxanes. Moreover, intermolecular charge-transfer interactions between the electron-rich host and the electron-poor guests were observed. The pseudo[3]rotaxanes showed pH-controllable association/dissociation processes with naked-eye color changes in solution.

Perphenazine modified pillar[5]arene based nano-assemblies for synergistic photothermal and photodynamic cancer therapy

Nano-assemblies based on perphenazine modified pillar[5]arene were constructed successfully for synergistic photothermal and photodynamic (I&II) cancer therapy.

Fluorescence-enhanced supra-amphiphiles based on pillar[5]arene: construction, controllable self-assembly and application in cell imaging

Fluorescence-enhanced supra-amphiphiles based on (WP5)2⊃ENDTn were constructed successfully. When n = 9, they can self-assemble into uniform micelles with an average diameter of about 90 nm and be further applied in cell imaging.

A type I and type II chemical biology toolbox to overcome the hypoxic tumour microenvironment for photodynamic therapy

Photodynamic therapy (PDT) is a minimally invasive therapeutic modality employed for the treatment of various types of cancers, localized infections, and other diseases. Upon illumination, the photo-excited photosensitizer generates singlet oxygen and other reactive species, thereby inducing cytotoxicity in the target cells. The hypoxic tumour microenvironment (TME), however, poses a limitation on the supply of oxygen in tumour tissues. Moreover, under such conditions, tumour metastasis and drug resistance frequently occur, further compromising the efficacy of PDT in combating tumours. Traditionally, type I photosensitizers with lower oxygen consumption demonstrate significant potential in overcoming hypoxic environments and play a crucial role in determining the therapeutic efficacy of PDT because type I photosensitizers can generate highly cytotoxic free radicals. In comparison, type II photosensitizers exhibit high oxygen dependence. The rate of reactive oxygen species (ROS) generation in the type II process is significantly higher than that in the type I process. Thus, the efficiency and selectivity of PDT depend on the properties of the photosensitizer. Here, the recent development and application of type I and type II photosensitizers, mainly in the past year, are summarized. The design methods, electronic structures, photophysical properties, lipophilic properties, electric charge, and other molecular characteristics of these photosensitizers are discussed in detail. These modifications alter the microstructure of photosensitizers and directly impact the results of PDT. The main content of this paper will have a positive promoting and inspiring effect on the future development of PDT.

Regulation of Fluorescence and Self-assembly of a Salicylaldehyde Azine-Containing Amphiphile by Pillararene

Regulation of fluorescence and self-assembly of a salicylaldehyde azine-containing amphiphile by a water-soluble pillar[5]arene via host-guest recognition in water was realized. The fluorescence and the self-assembled aggregates of the bola-type amphiphile G can be tailored by adding different amounts of water-soluble pillar[5]arene (WP5). In addition, the emission property and self-assembly behavior of G and WP5 are responsive to pH conditions. Furthermore, the fluorescence emission property of G and the regulation by WP5 or pH conditions was applied as information encryption material, rewritable paper, and erasable ink. We believe that this fluorescence regulation strategy is promising for the construction of advanced fluorescent organic materials.

Pillararene-Based Stimuli-Responsive Supramolecular Delivery Systems for Cancer Therapy

Cancer poses a significant challenge to global public health, seriously threatening human health and life. Although various therapeutic strategies, such as chemotherapy (CT), radiotherapy, phototherapy, and starvation therapy, are applied to cancer treatment, their limited therapeutic effect, severe side effects, and unsatisfactory drug release behavior need to be carefully considered. Thus, there is an urgent need to develop efficient drug delivery strategies for improving cancer treatment efficacy and realizing on-demand drug delivery. Notably, pillararenes, as an emerging class of supramolecular macrocycles, possess unique properties of highly tunable structures, superior host-guest chemistry, facile modification, and good biocompatibility, which are widely used in cancer therapy to achieve controllable drug release and reduce the toxic side effects on normal tissues under various internal/external stimuli conditions. This review summarizes the recent advance of stimuli-responsive supramolecular delivery systems (SDSs) based on pillararenes for tumor therapy from the perspectives of different assembly methods and hybrid materials, including molecular-scale SDSs, supramolecular nano self-assembly delivery systems, and nanohybrid SDSs. Moreover, the prospects and critical challenges of stimuli-responsive SDSs based on pillararenes for cancer therapy are also discussed.

Switchable Metal-Ion Selectivity in Sulfur-Functionalised Pillar[5]arenes and Their Host-Guest Complexes

Nucleophilic substitution of pertosylated pillar[5]arene (P-OTs) with commercially available sulfur containing nucleophiles (KSCN, KSAc, and thiophenol), yields a series of sulfur-functionalised pillar[5]arenes. DLS results and SEM images imply that these pillararene macrocycles self-assemble in acetonitrile solution, while X-ray crystallographic evidence suggests solvent-dependent assembly in the solid state. The nature of the sulfur substituents decorating the rim of the pillararene controls binding affinities towards organic guest encapsulations within the cavity and dictates metal-ion binding properties through the formation of favorable S-M2+ coordination bonds outside the cavity, as determined by 1 H NMR and fluorescence spectroscopic experiments. Addition of a dinitrile guest containing a bis-triazole benzene spacer (btn) induced formation of pseudorotaxane host-guest complexes. Fluorescence emission signals from these discrete macrocycles were significantly attenuated in the presence of either Hg2+ or Cu2+ in solution. Analogous titrations utilizing the corresponding pseudorotaxanes alter the binding selectivity and improve fluorescence sensing sensitivity. In addition, preliminary liquid-liquid extraction studies indicate that the macrocycles facilitate the transfer of Cu2+ from the aqueous to the organic phase in comparison to extraction without pillar[5]arene ligands.