Engineering UiO-68-Typed Homochiral Metal–Organic Frameworks for the Enantiomeric Separation of Fmoc-AAs and Mechanism Study

Abstract

Homochiral metal−organic frameworks (HMOFs) have been widely investigated in the application of enantiomeric separation. Nonetheless, it remains a significant challenge to explore the effect of multiple weak interactions between HMOF adsorbents and chiral adsorbates on enantiomeric separation performance still. In this work, robust chiral amine-alcohol-functionalized UiO-68-typed Zr-HMOFs 1−3 with the same hydrogen-bonding sites but slightly different π-binding sites were prepared for the enantioseparation of amino acid derivatives (Fmoc-AAs) with large πbinding groups. As a consequence of multiple host−guest interactions, these Zr-HMOFs exhibit speedy adsorption and high adsorption capacity for Fmoc-L/D-AAs and dissimilar enantioselectivity for the adsorption of their enantiomers. Materials 1 and 2 exhibit excellent enantioselective separation performance for Fmoc-valine with a single terminal π-binding group, while material 3 displays excellent enantioselective separation performance for Fmoc-phenylalanine and Fmoc-tryptophan with π-binding groups at both ends. As evidently demonstrated by our experimental and density functional theory (DFT) computational results, when the number of π-binding groups preset in the confined chiral space of adsorbents matches the number of π-binding groups of chiral adsorbates, the synergism of π−π or σ−π interactions will increase enantioselectivity; otherwise, the competition interactions from redundant identical binding sites will weaken enantioselectivity. Our case not only provides a tremendously typical system for investigating the collaborative discrimination of multiple weak interactions and exploring the impact of relatively excessive binding sites of HMOF adsorbents or chiral adsorbates on the enantioselective separation performance but also provides guidance for targeted functional modifications of high-performance chiral porous materials.

Polypeptide-inspired supramolecular assemblies for enantioselective sorption of chiral molecules

“…1a, which create a unique asymmetric environment for the recognition and discrimination of the enantiomers. 46–49…”

Synthesis Strategies, Preparation Methods, and Applications of Chiral Metal‐Organic Frameworks

“…This separates the D-ephedrine from the racemate (Figure 9). Wu et al [85] prepared three isochiral UiO-68 type Zr-HMOFs1-3 as adsorbents, which showed rapid adsorption and high adsorption capacity for amino acid derivatives (Fmoc-AAs), but their adsorption of enantiomers showed different enantioselectivity, and materials 1 and 2 showed preferential adsorption for Fmoc-L-Val. Material 3 showed preferential adsorption of Fmoc-L-Phe and Fmoc-D-Try.…”

Highly stable chiral Cr(iii)-based metal–organic frameworks for enantioadsorption separation of aromatic alcohols

“…Homochiral metal–organic frameworks (HMOFs), as an emerging class of chiral crystalline porous materials, have gained widespread attention for their intriguing applications in asymmetric catalysis, 1–3 enantioseparation, 4–8 chiral recognition 9–12 and other areas of asymmetry. Nevertheless, despite the appealing characteristics of HMOFs, such as their controlled synthesis, extraordinary porosity and highly accessible chiral functional sites, the limited chemical stability of most reported highly porous HMOFs has immensely hindered their industrial implementation.…”