Molecular recognition-based affinity chromatography strategy for selective separation of cucurbit[5]uril and cucurbit[7]uril on hybrid monolithic materials

Background As a class of star macrocyclic molecules, cucurbit [n]urils (CB[n]) have gained extensive applications across multiple fields, including perovskite batteries, adsorption separation, room-temperature phosphorescence and biomolecular science and so on. The acquisition of high-purity CB[n] presents a significant challenge, especially for researchers without a dedicated background in organic synthesis and purification. The separation of individual CB[n] homologues is notoriously difficult, especially in the case of CB[7] and CB[5] due to their similar solubility and chemical properties. Therefore, development of specific and selective chromatographic methods is necessary for efficient separation of CB[n] homologues. Results In this work, three types of bipyridine-containing hybrid monolithic materials were designed and fabricated through “one-pot” approach, and then employed as an adsorption platform for the separation of CB[5] and CB[7] via supramolecular affinity chromatography strategy. This novel method offers efficient separation based on the differential molecular recognition mechanism of CB[5] and CB[7] toward the guest bipyridine moiety. Compared with the guests within the polymer chains, exposing the guests at the terminal ends of the adsorbent surface would benefit the specific adsorption capability of CB[7]. After optimizing the chromatographic conditions, the separation of CB[5] and CB[7] was successfully achieved on hybrid monolithic materials modified with 4,4′-bipyridine (Monolith-Ⅱ-Bp), enabling the isolation of 12 mg CB[5] and 10 mg CB[7] with high-purity from 40 mg of the crude product, corresponding to yields of 30.0% and 25.0%, respectively. Significance This work is the first to introduce hybrid monolithic materials and a separation strategy based on specific and reversible host-guest interactions, enabling simplified purification of CB[5] and CB[7] and accurate determination of their purity by MALDI-TOF MS. This approach is expected to serve as a reliable laboratory-scale method for the preparation of high-purity CB[n] homologues.