Towards a novel 3D covalent organic framework with record large pores for efficient drug delivery

Materials science is constantly evolving research area as researchers strive to discover and synthesize novel functional materials with desirable properties suited to a variety of applications. One example on this front is furnished by covalent organic frameworks (COFs), a class of materials characterized by crystalline porous polymers connected in the form of a network via covalent bonds.

Owing to their structural diversity, high porosity, and easily accessible active sites, COFs can be designed for a range of applications such as gas storage and separation, catalysis, and drug delivery. Despite such vast potential, however, most reported COFs suffer from small pore size due to the formation of interpenetrated frameworks during the construction process, which results in closely knit interwoven structures with restricted pore sizes. Moreover, most research so far has focused on 2D COFs given the difficulty of constructing a 3D, non-interpenetrated COF with large pore sizes.

Now, in a new study published in Angewandte Chemie on 23 January 2023, researchers from Zhejiang Normal University, China and Tokyo University of Science (TUS), Japan have reported a novel 3D COF with the largest pore size and lowest density ever recorded. The team, led by Professor Yuichi Negishi from TUS and including contributions from Dr. Saikat Das from TUS and Professor Teng Ben from Zhejiang Normal University, has achieved this feat by reticulating a 6-linked triptycene linker and a 4-linked porphyrin linker to form a non-interpenetrated network, resulting in the unprecedented pore size and density.

The material, which the team named TUS-64, was constructed by linking two specific building units: a 2,3,6,7,14,15-hexakis(4’-formylphenyl)-triptycene (HFPTP) as a 6-linked linker and a 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) as a 4-linked linker. The team used a method known as solvothermal condensation, which involved combining the two linkers in a solvent at a high pressure and temperature.

TUS-64 showed a honeycomb-like structure with a pore size of 4.7 nm, and a record low density of 0.106 g/cm³ (the density of water is 1 g/cm³).  Despite its seemingly delicate structure, the material was shown to be resilient, withstanding decomposition in both organic and inorganic solvents, as well as temperatures up to 400°C.

The material’s highly interconnected mesoporous structure along with its high stability make it ideal to hold and transport guest molecules. To explore the potential of TUS-64 as a drug delivery system, the team loaded five different drugs within the pores of the material and monitored their release in a phosphate buffer solution simulating human body fluid. The drugs included captopril (for hypertension and heart failure), ibuprofen (for fever and pain), isoniazid (for tuberculosis), 5-fluorouracil (for cancer), and brimonidine (for glaucoma).

In all instances, TUS-64 displayed a high capacity to hold the drugs along with a sustained release rate, making it suitable for delivering drugs over extended periods.

“TUS-64 shows all the desirable qualities of a drug delivery vehicle, such as controlled release kinetics, sustained delivery, and site-specific targeting,” highlights Prof. Negishi, excited.

With TUS-64 as a potential game changer for many applications, new methods and techniques for developing 3D COFs with desirable characteristics – such as the one described in this study – could transform a wide range of industries and even people’s lives.

“By making use of these characteristics of COFs, we could create new materials that will be required in the next generation society, such as drug delivery vehicles, energy and environmental materials, and separation materials,” concludes Prof. Negishi.

And we sure hope his visions are realized soon!

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Reference                     

DOI: https://doi.org/10.1002/anie.202300172

About The Tokyo University of Science
Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan’s development in science through inculcating the love for science in researchers, technicians, and educators.

With a mission of “Creating science and technology for the harmonious development of nature, human beings, and society”, TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today’s most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.

Website: https://www.tus.ac.jp/en/mediarelations/

About Professor Yuichi Negishi from Tokyo University of Science
Dr. Yuichi Negishi is a Professor in the Department of Applied Chemistry at Tokyo University of Science, Japan with over 200 publications to his credit. His research expertise includes physical chemistry, cluster chemistry, and nanomaterial chemistry. His notable achievements include The Chemical Society of Japan Award for Young Chemists (Japan Chemical Society, 2008), the Japan Society for Molecular Science Award for Young Scientists (Japan Society for Molecular Science, 2012), Yagami Prize (Keio University, 2017), Distinguished Award 2018 for Novel Materials and Their Synthesis (IUPAC etc., 2018), International Investigator Awards of the Japan Society for Molecular Science (Japan Society for Molecular Science, 2020), and The Chemical Society of Japan Award for Creative Work (Japan Chemical Society, 2021).

Funding information
This study was supported by the National Key R&D Program of China (2021YFA1200400), the National Natural Science Foundation of China (No. 91956108, 21871103, 22201256), and the Natural Science Foundation of Zhejiang Province (No. LZ22B010001). Funding provided by the Japan Society for the Promotion of Science (JSPS) KAKENHI (grant nos. 20H02698, 20H02552), Scientific Research on Innovative Areas “Aquatic Functional Materials” (grant no. 22H04562), Yazaki Memorial Foundation for Science and Technology, and the Ogasawara Foundation for the Promotion of Science and Engineering is also gratefully acknowledged.