Hydrogen-bonded organic frameworks: new horizons in biomedical applications

Developing porous electrocatalysts to minimize overpotential for the oxygen evolution reaction

The development of electrocatalysts for the oxygen evolution reaction (OER) is one of the most critical issues for improving the efficiency of electrochemical water-splitting, which can produce green hydrogen energy without CO2 emissions. This review outlines the advances in the precise design of inorganic- and organic-based porous electrocatalysts, which are designed by various strategies, to catalyze the OER in the electrolytic cycle for efficient water-splitting. For developing high-performance electrocatalysts with low overpotentials, it is important to design a chemical composition that optimizes binding energy for an intermediate in the OER and allows the easy access of reactants to active sites depending on the porosity of electrocatalysts. Porous structures give us the positive opportunity to increase the accessible surface of active sites and effective diffusion of targeting molecules, which is potentially one of the guidelines for developing active electrocatalysts. Further modification of the frameworks is also powerful for tailoring the function of pore surfaces and the environment of inner spaces. Designable organic molecules can also be embedded inside inorganic- and organic-based frameworks. According to chemical composition (inorganic and organic), nanostructure (crystalline and amorphous) and additional modification (metal doping and organic design) of porous electrocatalysts, the current status of resultant OER performance is surveyed with some problems that should be solved for improving the OER activity. The remarkable progress in OER electrocatalysts is also introduced for demonstrating the bifunctional hydrogen evolution reaction (HER) and for utilizing seawater.

Employing conductive porous hydrogen-bonded organic framework for ultrasensitive detection of peanut allergen Ara h1

Peanut allergy has garnered worldwide attention due to its high incidence rate and severe symptoms, stimulating the demand for the ultrasensitive detection method of peanut allergen. Herein, we successfully developed a novel electrochemical aptasensor for ultrasensitive detection Ara h1, a major allergenic protein present in peanuts. A conductive nickel atoms Anchored Hydrogen-Bonded Organic Frameworks (PFC-73-Ni) were utilized as excellent electrocatalysts toward hydroquinone (HQ) oxidation to generate a readable current signal. The developed electrochemical aptasensor offers wide linear range (1-120 nM) and low detection limit (0.26 nM) for Ara h1. This method demonstrated a recovery rate ranging from 95.00% to 107.42% in standard addition detection of non-peanut food samples. Additionally, the developed electrochemical method was validated with actual samples and demonstrated good consistency with the results obtained from a commercial ELISA kit. This indicates that the established Ara h1 detection method is a promising tool for peanut allergy prevention.

Stable Porous Organic Cage Nanocapsules for pH-Responsive Anticancer Drug Delivery for Precise Tumor Therapy

The search for drug nanocarriers with stimuli-responsive properties and high payloads for targeted drug delivery and precision medicine is currently a focal point of biomedical research, but this endeavor still encounters various challenges. Herein, a porous organic cage (POC) is applied to paclitaxel (PTX) drug delivery for cancer therapy for the first time. Specifically, water-soluble, stable, and biocompatible POC-based nanocapsules (PTX@POC@RH40) with PTX encapsulation efficiency over 98% can be synthesized by simply grafting nonionic surfactant (Polyoxyl 40 hydrogenated castor oil, RH40) on the POC surface. These PTX@POC@RH40 nanocapsules demonstrate remarkable stability for more than a week without aggregation and exhibit pH-responsive behavior under acidic conditions (pH 5.5) and display sustained release behavior at both pH 7.4 and pH 5.5. Intravenous administration of PTX@POC@RH40 led to a 3.5-fold increase in PTX bioavailability compared with the free PTX group in rats. Moreover, in vivo mouse model experiments involving 4T1 subcutaneous breast cancer tumors revealed that PTX@POC@RH40 exhibited enhanced anticancer efficacy with minimal toxicity compared with free PTX. These findings underscore the potential of POCs as promising nanocarriers for stimuli-responsive drug delivery in therapeutic applications.

Anthracene-Based Endoperoxides as Self-Sensitized Singlet Oxygen Carriers for Hypoxic-Tumor Photodynamic Therapy

Singlet oxygen is a crucial reactive oxygen species (ROS) in photodynamic therapy (PDT). However, the hypoxic tumor microenvironment limits the production of cytotoxic singlet oxygen through the light irradiation of PDT photosensitizers (PSs). This restriction poses a major challenge in improving the effectiveness of PDT. To overcome this challenge, researchers have explored the development of singlet oxygen carriers that can capture and release singlet oxygen in physiological conditions. Among these developments, anthracene-based endoperoxides, initially discovered almost 100 years ago, have shown the ability to generate singlet oxygen controllably under thermal or photo stimuli. Recent advancements have led to the development of a new class of self-sensitized anthracene-endoperoxides, with potential applications in enhancing PDT effects for hypoxic tumors. This review discusses the current research progress in utilizing self-sensitized anthracene-endoperoxides as singlet oxygen carriers for improved PDT. It covers anthracene-conjugated small organic molecules, metal-organic complexes, polymeric structures, and other self-sensitized nano-structures. The molecular structural designs, mechanisms, and characteristics of these systems will be discussed. This review aims to provide valuable insights for developing high-performance singlet oxygen carriers for hypoxic-tumor PDT.

Freestanding Hydrogen-Bonded Organic Framework Membrane for Efficient Wound Healing

Hydrogen-bonded organic frameworks (HOFs) are emerging as multifunctional materials with exceptional biocompatibility, abundant active sites, and tunable porosity, which are highly beneficial for advanced wound care. However, a significant challenge involves transforming pristine HOFs powders into lightweight, ultrathin, freestanding membranes compatible with soft biological systems. Herein, the study successfully develops shape-adaptive HOF-based matrix membranes (HMMs) using a polymer-assisted liquid-air interface technique. The HMMs conform seamlessly to tissues of different sizes and shapes, effectively stopping bleeding, and provide high water-vapor permeability. Notably, both in vitro and in vivo studies with mice wound models demonstrated that these tissue-conformable HMMs significantly accelerate wound healing by modulating the inflammatory environment of the injured tissue and promoting rapid re-epithelialization. Furthermore, RNA-seq analysis and mechanistic studies revealed that HMMs effectively reduce inflammation and facilitate the tissue transition from the proliferative stage to the remodeling stage of skin development. This work not only opens up new avenues for advanced wound care materials but also establishes a foundation for hybridizing HOFs with polymers for a wide range of potential applications.

Smart Bioorthogonal Nanozymes: From Rational Design to Appropriate Bioapplications

Bioorthogonal chemistry has provided an elaborate arsenal to manipulate native biological processes in living systems. As the great advancement of nanotechnology in recent years, bioorthogonal nanozymes are innovated to tackle the challenges that emerged in practical biomedical applications. Bioorthogonal nanozymes are uniquely positioned owing to their advantages of high customizability and tunability, as well as good adaptability to biological systems, which bring exciting opportunities for biomedical applications. More intriguingly, the great advancement in nanotechnology offers an exciting opportunity for innovating bioorthogonal catalytic materials. In this comprehensive review, the significant progresses of bioorthogonal nanozymes are discussed with both spatiotemporal controllability and high performance in living systems, and highlight their design principles and recent rapid applications. The remaining challenges and future perspectives are then outlined along this thriving field. It is expected that this review will inspire and promote the design of novel bioorthogonal nanozymes, and facilitate their clinical translation.

Hypoxia-Responsive Hydrogen-Bonded Organic Framework-Mediated Protein Delivery for Cancer Therapy

The efficient delivery of therapeutic proteins to tumor sites is a promising cancer treatment modality. Hydrogen-bonded organic frameworks (HOFs) are successfully used for the protective encapsulation of proteins; however, easy precipitation and lack of controlled release of existing HOFs limit their further application for protein delivery in vivo. Here, a hypoxia-responsive HOF, self-assembled from azobenzenedicarboxylate/polyethylene glycol-conjugated azobenzenedicarboxylate and tetrakis(4-amidiniumphenyl)methane through charge-assisted hydrogen-bonding, is developed for systemic protein delivery to tumor cells. The newly generated HOF platform efficiently encapsulates representative cytochrome C, demonstrating good dispersibility under physiological conditions. Moreover, it can respond to overexpressed reductases in the cytoplasm under hypoxic conditions, inducing fast intracellular protein release to exert therapeutic effects. The strategy presented herein can be applied to other therapeutic proteins and can be expanded to encompass more intrinsic tumor microenvironment stimuli. This offers a novel avenue for utilizing HOFs in protein-based cancer therapy.

Facile and scale-up syntheses of high-performance enzyme@meso-HOF biocatalysts

Facile immobilization is essential for the wide application of enzymes in large-scale catalytic processes. However, exploration of suitable enzyme supports poses an unmet challenge, particularly in the context of scale-up biocatalyst fabrication. In this study, we present facile and scale-up syntheses of high-performance enzyme biocatalysts via in situ encapsulation of cytochrome c (Cyt-c) as mono-enzyme and glucose oxidase (GOx)-horseradish peroxidase (HRP) as dual-enzyme cascade (GOx&HRP) systems, respectively, into a stable mesoporous hydrogen-bonded organic framework (meso-HOF) matrix. In situ encapsulation reactions occur under ambient conditions, and facilitate scale up (∼3 g per reaction) of enzyme@meso-HOF within a very short period (5-10 min). The resultant biocatalysts not only exhibit high enzyme loading (37.9 wt% for mono-enzyme and 22.8 wt% for dual-enzyme) with minimal leaching, but also demonstrate high catalytic activity, superior reusability, and durability. This study represents an example of scale-up fabrication of enzyme@meso-HOF biocatalysts on the gram level and highlights superior meso-HOFs as suitable host matrices for biomolecular entities.

Self-correcting mismatches in metastable hydrogen-bonded organic frameworks with an 11-fold interpenetrated array

The polymorphic self-correction from a metastable phase to a stable one often occurs and plays crucial roles in synthesizing robust hydrogen-bonded organic frameworks (HOFs). However, identifying metastable phases and understanding the self-correcting mechanisms is a challenging venture due to their intrinsic instability. Here, we for the first time introduce 1,8-naphtholactam (Np) as a hydrogen-bonding synthon positioned on the periphery of a bicarbazole to create a versatile molecular unit for 3D HOFs. The as-synthesized NCU-HOF1, analyzed by single-crystal X-ray diffraction (SCXRD), is found to be metastable. It exhibits an 11-fold interpenetrated dia topology with a quarter of the Np units exhibiting monomeric N-H⋯O interactions between adjacent Np link sites, which readily self-correct upon desolvation to form fully dimeric ones. Consequently, the resultant NCU-HOF1a becomes highly robust in polar solvents, strong acid or alkaline aqueous solutions, and has permanent porosity with contracted cavities for selective adsorption and efficient "turn-up" fluorescent sensing of C2H4 gas. This work not only debuts a new hydrogen-bonding synthon but offers more insights into investigating solid-state dynamics in metastable HOFs.

Microporous Materials in Polymer Electrolytes: The Merit of Order

Solid-state batteries (SSBs) have garnered significant attention in the critical field of sustainable energy storage due to their potential benefits in safety, energy density, and cycle life. The large-scale, cost-effective production of SSBs necessitates the development of high-performance solid-state electrolytes. However, the manufacturing of SSBs relies heavily on the advancement of suitable solid-state electrolytes. Composite polymer electrolytes (CPEs), which combine the advantages of ordered microporous materials (OMMs) and polymer electrolytes, meet the requirements for high ionic conductivity/transference number, stability with respect to electrodes, compatibility with established manufacturing processes, and cost-effectiveness, making them particularly well-suited for mass production of SSBs. This review delineates how structural ordering dictates the fundamental physicochemical properties of OMMs, including ion transport, thermal transfer, and mechanical stability. The applications of prominent OMMs are critically examined, such as metal-organic frameworks, covalent organic frameworks, and zeolites, in CPEs, highlighting how structural ordering facilitates the fulfillment of property requirements. Finally, an outlook on the field is provided, exploring how the properties of CPEs can be enhanced through the dimensional design of OMMs, and the importance of uncovering the underlying "feature-function" mechanisms of various CPE types is underscored.

Postsynthetic Modification of Hydrogen-Bonded Frameworks

Hydrogen-bonded frameworks have garnered significant attention due to their flexible structures with tailored porosity, making them a promising class of porous framework materials. However, the direct synthesis of hydrogen-bonded frameworks with specific functions is highly challenging due to the unpredictable formation of hydrogen-bonded frameworks. In response, postsynthetic modification has emerged as a potent strategy to imbue desired functions into hydrogen-bonded frameworks. Recent advances have demonstrated the effectiveness of postsynthetic modification in hydrogen-bonded frameworks for studying their mechanical, luminescent, electrochemical, and chiral properties. In this concept, we comprehensively summarize the methodologies and outcomes of postsynthetic modification to hydrogen-bonded frameworks, providing a highlight of this exciting research area.

Flexible hydrogen-bonded organic frameworks (HOFs): opportunities and challenges

Flexible behavior is one of the most fascinating features of hydrogen-bonded organic frameworks (HOFs), which represent an emerging class of porous materials that are self-assembled via H-bonding between organic building units. Due to their unique flexibility, HOFs can undergo structural changes or transformations in response to various stimuli (physical or chemical). Taking advantage of this unique structural feature, flexible HOFs show potential in multifunctional applications such as gas storage/separation, molecular recognition, sensing, proton conductivity, biomedicine, etc. While some other flexible porous materials have been extensively studied, the dynamic behavior of HOFs remains relatively less explored. This perspective highlights the inherent flexible properties of HOFs, discusses their different flexible behaviors, including pore size/shape changes, interpenetration/stacking manner, H-bond breaking/reconstruction, and local dynamic behavior, and highlights their potential applications. We believe that this perspective will not only contribute to HOF chemistry and materials science, but will also facilitate the ongoing extensive research on dynamic porous materials.

Single-atom nanozymes shines diagnostics of gastrointestinal diseases

Various clinical symptoms of digestive system, such as infectious, inflammatory, and malignant disorders, have a profound impact on the quality of life and overall health of patients. Therefore, the chase for more potent medicines is both highly significant and urgent. Nanozymes, a novel class of nanomaterials, amalgamate the biological properties of nanomaterials with the catalytic activity of enzymes, and have been engineered for various biomedical applications, including complex gastrointestinal diseases (GI). Particularly, because of their distinctive metal coordination structure and ability to maximize atom use efficiency, single-atom nanozymes (SAzymes) with atomically scattered metal centers are becoming a more viable substitute for natural enzymes. Traditional nanozyme design strategies are no longer able to meet the current requirements for efficient and diverse SAzymes design due to the diversification and complexity of preparation processes. As a result, this review emphasizes the design concept and the synthesis strategy of SAzymes, and corresponding bioenzyme-like activities, such as superoxide dismutase (SOD), peroxidase (POD), oxidase (OXD), catalase (CAT), and glutathione peroxidase (GPx). Then the various application of SAzymes in GI illnesses are summarized, which should encourage further research into nanozymes to achieve better application characteristics.

Protein-Integrated Hydrogen-Bonded Organic Frameworks: Chemistry and Biomedical Applications

Hydrogen-bonded organic frameworks (HOFs) are porous nanomaterials that offer exceptional biocompatibility and versatility for integrating proteins for biomedical applications. This minireview concisely discusses recent advancements in the chemistry and functionality of protein-HOF interfaces. It particularly focuses on strategic methodologies, such as the careful selection of building blocks and the genetic engineering of proteins, to facilitate protein-HOF interactions. We examine the role of enzyme encapsulation within HOFs, highlighting its capability to preserve enzyme function, a crucial aspect for applications in biosensing and disease diagnosis. Moreover, we discuss the emerging utility of nanoscale HOFs for intracellular protein delivery, illustrating their applicability as nanoreactors for intracellular catalysis and neuroprotective biorthogonal catalysis within cellular compartments. We highlight the significant advancement of designing biodegradable HOFs tailored for cytosolic protein delivery, underscoring their promising application in targeted cancer therapies. Finally, we provide a perspective viewpoint on the design of biocompatible protein-HOF assemblies, underlining their promising prospects in drug delivery, disease diagnosis, and broader biomedical applications.

Hybrid 2D Supramolecular Organic Frameworks (SOFs) Assembled by the Cooperative Action of Hydrogen and Halogen Bonding and π⋯π Stacking Interactions

The cis- and trans-isomers of 6-(3-(3,4-dichlorophenyl)-1,2,4-oxadiazol-5-yl)cyclohex-3-ene-1-carboxylic acid (cis-A and trans-A) were obtained by the reaction of 3,4-dichloro-N'-hydroxybenzimidamide and cis-1,2,3,6-tetrahydrophthalic anhydride. Cocrystals of cis-A with appropriate solvents (cis-A‧½(1,2-DCE), cis-A‧½(1,2-DBE), and cis-A‧½C6H14) were grown from 1,2-dichloroethane (1,2-DCE), 1,2-dibromoethane (1,2-DBE), and a n-hexane/CHCl3 mixture and then characterized by X-ray crystallography. In their structures, cis-A is self-assembled to give a hybrid 2D supramolecular organic framework (SOF) formed by the cooperative action of O-H⋯O hydrogen bonding, Cl⋯O halogen bonding, and π⋯π stacking. The self-assembled cis-A divides the space between the 2D SOF layers into infinite hollow tunnels incorporating solvent molecules. The energy contribution of each noncovalent interaction to the occurrence of the 2D SOF was verified by several theoretical approaches, including MEP and combined QTAIM and NCIplot analyses. The consideration of the theoretical data proved that hydrogen bonding (approx. -15.2 kcal/mol) is the most important interaction, followed by π⋯π stacking (approx. -11.1 kcal/mol); meanwhile, the contribution of halogen bonding (approx. -3.6 kcal/mol) is the smallest among these interactions. The structure of the isomeric compound trans-A does not exhibit a 2D SOF architecture. It is assembled by the combined action of hydrogen bonding and π⋯π stacking, without the involvement of halogen bonds. A comparison of the cis-A structures with that of trans-A indicated that halogen bonding, although it has the lowest energy in cis-A-based cocrystals, plays a significant role in the crystal design of the hybrid 2D SOF. The majority of the reported porous halogen-bonded organic frameworks were assembled via iodine and bromine-based contacts, while chlorine-based systems-which, in our case, are structure-directing-were unknown before this study.