Superficial chiral etching on an achiral metal‐organic framework for high‐performance liquid chromatography enantioseparations

Abstract

Chiral metal-organic frameworks have shown great potential in enantioselective separation and asymmetric catalysis due to their diverse and adjustable structures with abundant chiral recognition sites. Herein, a new chiral post-synthetic modification was used for preparing an achiral@chiral metal-organic frameworks core-shell composite [Cu 3 (Btc) 2 ]@[Cu 2 ((+)-Cam) 2 Dabco] by a superficial chiral etching method. The [Cu 3 (Btc) 2 ]@[Cu 2 ((+)-Cam) 2 Dabco] composite was utilized as a novel chiral stationary phase for HPLC enantioseparation. Various racemates were separated on the [Cu 3 (Btc) 2 ]@[Cu 2 ((+)-Cam) 2 Dabco]-packed column (column A). It exhibited good chiral resolving ability toward many different kinds of racemates, especially chiral drugs. Among them, the highest resolution value for 1,2-diphenyl-1,2-ethanediol reaches 2.70. The relative standard deviations of retention time and peak area for repeated separation of 1,2-diphenyl-1,2-ethanol were 0.45% and 0.81%, respectively. Compared with the resolution ability of [Cu 2 ((+)-Cam) 2 Dabco]-packed column (column B), column A shows higher column efficiency and better separation performance than those of column B. The results indicated that the [Cu 3 (Btc) 2 ]@[Cu 2 ((+)-Cam) 2 Dabco] as a stationary phase can greatly improve the column efficiency and chiral resolution ability of chiral metal-organic frameworks, which demonstrated that the superficial chiral etching as an economic and efficient strategy opens up a new way for the application of metal-organic frameworks.

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

“…Chiral etching process (SCEP) is an effective post-modification method, [30,31] which does not change the original structure of the MOFs on the basis of developing new functions. The principle of SCEP is to modify chiral ligands onto achiral MOFs to form core-shell structures.…”

Recent progress for chiral stationary phases based on chiral porous materials in high‐performance liquid chromatography and gas chromatography separation

“…Subsequently, the Yuan group reported core‐shell MOFs@chiral MOFs ([Cu 3 (Btc) 2 ] @ [Cu 2 ((+)‐Cam) 2 Dabco]) as CSPs synthesized by surface chiral etching method [106]. The [Cu 3 (Btc) 2 ]@[Cu 2 ((+)‐Cam) 2 Dabco] column showed lower back pressure (17–20 bar), higher column efficiency and better chiral separation performance compared to the pure [Cu 2 ((+)‐Cam) 2 Dabco] column (48–53 bar) and showed good chiral separation performance for 15 racemates, especially achieved baseline separation for 1‐phenyl‐1‐pentanol and 1,2‐diphenyl‐1,2‐ethanediol that the two commercial columns cannot (Table S4), which suggesting that the surface chiral etching is an effective strategy to prepare novel HPLC CSPs.…”

Chiral covalent triazine framework CC-DMP CCTF@SiO2 core–shell microspheres used for HPLC enantioseparation

“…The separation performance and thermodynamic parameters of CC-DMP CCTF@SiO 2 -packed column were evaluated by retention factor ( k ), separation factor ( α ), resolution (Rs), Gibbs free energy change (Δ G ), enthalpy change (Δ H ), and entropy change (Δ S ), all of which were calculated based on previously published literature reports. 19,40–43…”