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

Supramolecular Porous Materials for Biomedical Applications

Supramolecular porous materials have been used to tackle some major challenges in modern biomedical science, including disease therapy and diagnosis. Their inherent dynamicity, stimuli-responsiveness, and tunable architectures enable precise control over molecular recognition, cargo encapsulation, and release kinetics. This perspective explores their potential in diagnostics and therapeutics, highlighting adaptability to physiological stimuli and precise control over structure via bottom-up assembly. A visionary framework is proposed for programmable self-assembly, where supramolecular building blocks form porous architectures with customized channels and responsive behavior, facilitating applications in tissue engineering, biosensing, soft robotics, and cargo recognition. Addressing challenges related to building block design, assembly conditions, and scalability will be crucial for translating these materials from bench to bedside. This perspective underscores the transformative potential of supramolecular porous materials in advancing personalized medicine and smart diagnostics.

Design, Synthesis, and Application of Immobilized Enzymes on Artificial Porous Materials

Enzymes have been recognized as highly efficient biocatalysts, whereas characteristics such as poor stability and single reaction type greatly significantly limit their wide application. Hence, the exploitation of suitable carriers for immobilized enzymes enables the provision of a protective layer for the enzyme, with the capability of chemical and biological cascade catalysis. Among the various immobilization carriers, metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and hydrogen-bonded organic frameworks (HOFs) have been emerging as a promising strategy to surpass the inherent instability and other limitations of free enzymes. Specifically, the integration of such artificial porous materials as carriers improves the stability and reusability of enzymes, while simultaneously affording a platform for multifunctional applications. Herein, this review systematically discusses the various preparation strategies and advantages of artificial porous materials, while elucidating the effects of different immobilization methods on enzyme activity. Furthermore, the innovative applications of artificial porous materials as multifunctional carriers in the field of enzyme immobilization fields such as enzyme carriers, photocatalysts, chemical catalysts and sensing are also comprehensively summarized here, thus demonstrating their multifunctional characteristics and promising applications in addressing complex biotransformation challenges.

From Guest-Induced Crystallization to Molecular Imprinting: Calculation-Guided Discovery of Hydrogen-Bonded Tetrazole Frameworks for p-Xylene Separation

Exploring host-guest interactions to regulate hydrogen-bonding assembly offers a promising approach for developing advanced porous crystal materials (PCMs). However, screening compatible guests with appropriate geometries and host-guest interactions that could inhibit the dense packing of building blocks remains a primary challenge. This study presents a novel guest-induced crystallization (GIC) strategy, guided by thermodynamic calculations, to develop porous hydrogen-bonded organic frameworks (HOFs) using structurally challenging tetrazole building units. Thermodynamic principles are established from the crystal structure data and the density functional theory calculation of the formation energy (ΔE). This provides criteria to identify available guests in GIC, enabling the successful discovery of a hidden HOF that is kinetically challenging to crystallize. Furthermore, the potential application for p-xylene (PX) separation is predicted by analyzing the ΔE of guest-induced HOFs. A high PX selectivity (PX/m-xylene=6.1, PX/o-xylene=7.2, and PX/ethylbenzene=4.1) is achieved through selective inclusion of PX from C8 aromatic isomers within the guest-induced HOFs. Significantly, the guest-free HOF (HOF-PX-a), bearing PX-templated cavities derived from molecular imprinting, shows a record-high PX/ethylbenzene selectivity (21.7) in liquid adsorption. This work elucidates the underpinning self-assembly rules of GIC for HOF construction, providing exciting new opportunities for the predictable assembly of PCMs for molecular recognition and target-specific separations.

Construction of a hydrogen-bonded organic framework-based therapeutic platform by one-pot method

The anticancer drug camptothecin (CPT) was successfully in situ loaded into a hydrogen-bonded organic framework (HOF) by one-pot method with a high loading efficiency of 42 wt%. The resultant HOF based therapeutic platform could suppress the tumor growth effectively.

Comparison of Hydrogen Bonded Organic Framework with Reduced Graphene Oxide-Pd Based Nanocatalyst: Which One Is More Efficient for Entrapment of Nitrophenol Pollutants?

In this study, a Pd nanoparticles@hydrogen-bonded organic framework (Pd NPs@HOF) thin film was fabricated at the toluene-water interface. The HOF was formed through the interaction of trimesic acid (TMA) and melamine (Mel) in the water phase, while Pd(0) was produced from the reduction of [PdCl2(cod)] in the organic phase. The as-synthesized Pd NPs@HOF thin film was demonstrated to be an effective catalyst for the selective reduction of p-nitrophenol and o-nitrophenol to p-aminophenol and o-aminophenol. The porous network of the Pd NPs@HOF introduced strong active sites between Mel, TMA, and Pd(0). Kinetic studies showed that the Pd NPs@HOF catalyst exhibited an enhanced rate of p-nitrophenol and o-nitrophenol reduction in comparison with Pd@reduced-graphene oxide (r-GO) with rates that were 1.7 times faster for p-nitrophenol and 1.5 times faster for o-nitrophenol or even 10 times faster than some Pd-based catalysts, with a maximum conversion of 97.1% which was attributed to the higher porosity and greater surface-to-volume ratio of the Pd NPs@HOF material. Furthermore, π-π stacking interactions enhance the catalytic activity of the Pd NPs@HOF catalyst by increasing the active sites, stabilizing the NPs and trapping the nitrophenols, facilitating the electron transfer, and providing the synergistic effect. Also, contributions of hydrogen bonding, van der Waals forces, electrostatic interactions, and π-σ noncovalent interactions are reasons for better performance of Pd NPs@HOF than Pd/r-GO catalyst with the reduced functional groups.

A Grafting Hydrogen-bonded Organic Framework for Benchmark Selectivity of C2H2/CO2 Separation under Ambient Conditions

Reticular chemistry and pore engineering have garnered significant advancements in metal-organic frameworks and covalent organic frameworks, leveraging robust metal-coordination and covalent bonds. However, these achievements remain elusive in hydrogen-bonded organic frameworks, hindered by their inherent weakness in hydrogen bonding. Herein, we strategically manipulate the porosity of hydrogen-bonded frameworks through a grafting approach, culminating in the synthesis of two isomorphic HOFs, HOF-FJU-99 and HOF-FJU-100, with distinct pore environments. Remarkably, HOF-FJU-100, with its microporous architecture, not only showcases exceptional stability but also achieves unparalleled separation efficiency and ultrahigh selectivity for C2H2/CO2 mixtures (50/50, v/v) under ambient conditions. Its IAST selectivity value of 201 stands as a benchmark, towering over all previously reported HOFs. The pore of HOF-FJU-100 boasts an electrostatic potential highly favourable for C2H2 adsorption, as evidenced by single crystal X-ray diffraction analysis revealing multiple hydrogen bonding interactions between C2H2 molecules and the framework. In situ gas-carrier powder X-ray diffraction analysis underscores the adaptability of pore structure, dynamically adjusting its orientation in response to C2H2, thereby enabling a highly efficient and specific separation of C2H2/CO2 mixtures through specific adsorptive interactions.

Synthetic Nanocapsules with Tailored Surface Chemistry for Lung-Specific Protein Delivery and Cancer Immunotherapy

Efficient delivery of therapeutic proteins remains a major challenge in developing effective immunotherapies and treatments for genetic disorders due to the limited tissue targeting capability of native proteins. In this study, the design and synthesis of protein nanocapsules (NCs) that achieve lung-specific delivery of therapeutic proteins are reported. These NCs are synthesized through a surface modification process that involves coating protein with functional monomers and cross-linkers, followed by in situ polymerization to create a protective shell on the protein surface with tailored surface chemistry. This approach preserves protein integrity and significantly enhances delivery efficiency and tissue specificity. Notably, it is shown that protein@NC with guanidine-rich surfaces exhibit exceptional lung-targeting capabilities. This is likely attributed to the formation of a vitronectin-rich protein corona, which facilitates receptor-mediated endocytosis by lung cells. The platform effectively delivers various proteins, such as ovalbumin, to antigen-presenting cells (APCs) in the lung, thereby enhancing antigen presentation and offering a promising strategy for cancer immunotherapy. These findings provide a significant advancement in tissue-specific protein delivery and hold the potential for targeted cancer immunotherapy.

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.

Polyphenol-Assisted Biomineralization of Metal-Organic Framework Nanoparticles for Precision Delivery of Therapeutic Proteins to Cancer Cells

The delivery of proteins into the cytosol holds great promise for cell signaling manipulation and the development of precision medicine. However, this potency is challenged by achieving targeted and controlled delivery, specifically within diseased cells. In this study, we introduce a versatile and effective method for the precision delivery of therapeutic proteins to cancer cells by designing polyphenol-assisted biomineralization of zeolite imidazole framework-8 (ZIF-8). We demonstrate that by leveraging the strong noncovalent binding affinity of epigallocatechin gallate (EGCG) with both proteins and ZIF-8, our approach significantly enhances the biomineralization of ZIF-8, which in turn improves the efficiency of protein encapsulation and intracellular delivery. Moreover, the incorporation of EGCG within ZIF-8 enables controlled degradation of the nanoparticles and the selective release of the encapsulated proteins in cancer cells. This selective release is triggered by the oxidation of EGCG in response to the high levels of reactive oxygen species (ROS) found within cancer cells that destabilize the EGCG/ZIF-8 nanoparticles. We have further demonstrated the ability of EGCG/ZIF-8 to deliver a wide range of proteins into cancer cells, including bacterial virulence protein, to rewire cell signaling and prohibit tumor cell growth in a mouse xenograft model. Our strategy and findings underscore the potential of designing the EGCG/ZIF-8 interface for specific and controlled protein delivery for targeted cancer therapy.