The research groups, led by Prof. Susumu Kitagawa at Kyoto University in Japan and Prof. Fengting Li at Tongji University in China, have been collaborating on efficient molecule recognition and environmentally friendly separation processes using selective adsorption technologies and porous materials. In this collaboration, we have developed two strategies so far: the structural-deformation-energy-modulation strategy in soft PCPs for controllable molecular recognition (published in Angew. Chem. Int. Ed. in 2020) and the host-guest interaction modulation strategy in PCPs for inverse gas separation (published in Angew. Chem. Int. Ed. in 2021). In our recent publication in Nature Communications in 2023, we discuss the latest progress of our research on exclusive molecular recognition in a soft porous coordination network.

Incorporating precise molecule recognition properties into porous materials is crucial for various applications^1,2. Porous coordination polymers (PCPs) or metal-organic frameworks (MOFs) provide an excellent platform for molecular recognition and separation due to their inherent porous properties^3-5. PCPs with rigid channels can sort molecules of different sizes based on the molecular sieving mechanism^6,7. The interaction sites within PCPs also contribute to their recognition properties through specific host-guest interactions^8,9. Recently, flexible PCPs that exhibit guest-triggered structural transformations have gained significant attention in recognition applications^10-12. However, achieving selective uptake of only one target guest from multicomponent mixtures, regardless of the sizes and affinities of other competing species, remains a challenge¹³.

Fig. 1 | Flexible framework with restricted narrow-corrugated channel for Exclusive CO₂ Recognition.

We envisioned that by synergistically utilizing all available recognition mechanisms through the manipulation of the energetic and stereochemical features of PCPs, we could achieve superior recognition performance. As proof of this concept, we have designed a flexible porous coordination polymer (PCP) with a corrugated-channel system (Fig. 1) that exhibits an exclusive discrimination gating (EDG) effect for CO₂ over nine similar gas molecules, including N₂, CH₄, CO, O₂, H₂, Ar, C₂H₆, and even higher-affinity gases such as C₂H₂ and C₂H₄ (Fig. 2). Mechanistic investigations indicate that the optimal cooperation of stereochemical shape, location of binding sites, and structural softness, achieved by designing narrow-corrugated channel structures in soft porous materials, leads to such unprecedented recognition efficiency.

Fig. 2 | Adsorption isotherms of N₂, CO₂, CH₄, CO, O₂, H₂, Ar, C₂H₂, C₂H₄, and C₂H₆ at low temperatures.

For more details on this work, please refer to our publication titled "Soft Corrugated Channel with Synergistic Exclusive Discrimination Gating for CO₂ Recognition in Gas Mixture" in Nature Communications.

Reference

1. Tashiro, S. & Shionoya, M. Novel Porous Crystals with Macrocycle-Based Well-Defined Molecular Recognition Sites. Acc. Chem. Res. 53, 632-643 (2020).
2. Yuan, Y., Yang, Y. & Zhu, G. Molecularly Imprinted Porous Aromatic Frameworks for Molecular Recognition. ACS. Central. Sci. 6, 1082-1094 (2020).
3. Chen, B., Xiang, S. & Qian, G. Metal-organic frameworks with functional pores for recognition of small molecules. Acc. Chem. Res. 43, 1115-1124 (2010).
4. Li, J.-R., Kuppler, R.J. & Zhou, H.-C. Selective gas adsorption and separation in metal-organic frameworks. Chem. Soc. Rev. 38, 1477-1504 (2009).
5. Li, J., Bhatt, P.M., Li, J., Eddaoudi, M. & Liu, Y. Recent progress on microfine design of metal-organic frameworks: Structure regulation and gas sorption and separation. Adv. Mater. 32, 2002563 (2020).
6. Lin, R.-B. et al. Molecular sieving of ethylene from ethane using a rigid metal-organic framework. Nat. Mater. 17, 1128-1133 (2018).
7. Ma, S., Sun, D., Yuan, D., Wang, X.-S. & Zhou, H.-C. Preparation and Gas Adsorption Studies of Three Mesh-Adjustable Molecular Sieves with a Common Structure. J. Am. Chem. Soc. 131, 6445-6451 (2009).
8. Yoon, J.W. et al. Selective nitrogen capture by porous hybrid materials containing accessible transition metal ion sites. Nat. Mater. 16, 526-531 (2017).
9. Kim, E.J. et al. Cooperative carbon capture and steam regeneration with tetraamine-appended metal–organic frameworks. Science 369, 392-396 (2020).
10. Chang, Z., Yang, D.-H., Xu, J., Hu, T.-L. & Bu, X.-H. Flexible Metal-Organic Frameworks: Recent Advances and Potential Applications. Adv. Mater. 27, 5432-5441 (2015).
11. Schneemann, A. et al. Flexible metal–organic frameworks. Chem. Soc. Rev. 43, 6062-6096 (2014).
12. Horike, S., Shimomura, S. & Kitagawa, S. Soft porous crystals. Nat. Chem., 1, 695-704 (2009).
13. Zhou, D.-D. et al. Intermediate-sized molecular sieving of styrene from larger and smaller analogs. Nat. Mater., 18, 994-998 (2019).