Surface chiroselective assembly of enantiopure crystalline porous films containing bichiral building blocks

Preparation and chromatographic performance of chiral peptide-based stationary phases for enantiomeric separation

This study presents the development of three new chiral stationary phases. They are based on silica modified with peptides containing phenylalanine and proline. Successful analyses and characterizations were conducted using Fourier transform infrared spectra, elemental analysis, and thermogravimetric analysis. After this, the enantioselective performance of the three chiral peptide-based columns was evaluated. The evaluation used 11 racemic compounds under normal-phase high performance liquid chromatography mode. Optimized enantiomeric separation conditions were established. Under these conditions, the enantiomers of flurbiprofen and naproxen were successfully separated on CSP-1 column: the separation factor of these was 1.27 and 1.21, respectively. In addition, the reproducibility of the CSP-1 column was also investigated. The results of the investigation illustrated that the stationary phases have good reproducibility (RSD = 0.73%, n = 5).

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

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 π-binding 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.

Chiral Covalent Organic Framework Packed Nanochannel Membrane for Enantioseparation

A nanochannel membrane has the prospect of large-scale separation. However, selectivity in enantioseparation is a challenge, due to the size difference between nanochannels and enantiomers. Here, we compartmented nanochannels by the in situ synthesis of a L-tyrosine functionalized covalent organic framework (L-Tyr-COF). The L-Tyr-COF decreased the pore size of channels to match with naproxen enantiomers (S/R-NPX) and improved the enantioselective gating. In contrast to the surface-functionalized nanochannels (L-Tyr channel), the L-Tyr-COF packed nanochannels (L-Tyr-COF channel) exhibited high enantioselectivity for S-NPX and realized the enantioseparation with the enantiomer excess value up to 94.2 %. The separation flux through the highly porous L-Tyr-COF channel was 1.33 mmol m^-2  h^-1 . This study provided a size-matching strategy and the chiral covalent organic framework packed nanochannel membrane to realize enantioseparation with high selectivity and flux.