Room temperature synthesis of a chiral covalent organic framework core-shell composite for high-performance liquid chromatography enantioseparation.

In this article, chiral covalent organic framework core-shell composite CCOF-TpPa-Py@SiO2 was facilely synthesized by induction at room temperature. The CCOF-TpPa-Py@SiO2 core-shell composite was used as a chiral stationary phase for the separation of the racemates by high-performance liquid chromatography, which exhibits good separation performance for chiral compounds including ketones, alcohols, esters, epoxides, carboxylic acids, amides, and amines. The effects of analyte injection mass on the enantioseparation were studied. The reproducibility and stability of the CCOF-TpPa-Py@SiO2 chiral column were explored. The intra-day (n = 5), inter-day (n = 5), and inter-column (n = 3) relative standard deviations for the migration times and resolution of benzoin were 0.32%-0.54%, 0.45%-0.61%, and 1.21%-1.53%, respectively. In addition, the chiral separation ability of the CCOF-TpPa-Py@SiO2 chiral column (column A) was compared with that of the MDI-ß-CD-Modified COF@SiO2 (column B) as well as a commercial chiral column (Chiralpak AD-H). The chiral recognition ability of column A is complementary to that of column B and AD-H column. The resolution mechanism of CCOF-TpPa-Py@SiO2 stationary phase towards chiral analyte was explored. Hence, the synthesis of CCOF-TpPa-Py@SiO2 core-shell composite by induction at room temperature as chiral stationary phases for chromatographic separation has important research potential and application prospects.

In situ growth preparation of a new chiral covalent triazine framework core-shell microspheres used for HPLC enantioseparation.

The manufacturing of chiral covalent triazine framework core-shell microspheres CC-MP CCTF@SiO2 composite is reported as stationary phase for HPLC enantioseparation. The CC-MP CCTF@SiO2 core-shell microspheres were prepared by immobilizing chiral COF CC-MP CCTF constructed using cyanuric chloride and (S)-2-methylpiperazine on the surface of activated SiO2 through an in-situ growth approach. Various racemates as analytes were separated on the CC-MP CCTF@SiO2-packed column. The experimental results indicate that 19 pairs of enantiomers were well separated on the CC-MP CCTF@SiO2-packed column, including alcohols, phenols, amines, ketones, and organic acids. Among them, there are 17 pairs of enantiomers that can achieve baseline separation with good peak shapes. Their resolution values on this chiral column are between 0.4 and 5.61. The influences of analyte mass, column temperature, and composition of the mobile phase on the resolution of enantiomers were studied. In addition, the chiral resolution ability of CC-MP CCTF@SiO2-packed column was compared with the commercial chiral chromatographic columns (Chiralpak AD-H and Chiralcel OD-H columns) and some CCOF@SiO2 chiral columns (ß-CD-COF@SiO2, CTpBD@SiO2, and MDI-ß-CD-modified COF@SiO2). The CC-MP CCTF@SiO2-packed column exhibited some unique advantages and can complement these chiral columns in chiral separations. The research results show that the CC-MP CCTF@SiO2 chiral column offered high column efficiency (e.g., 17680 plates m-1 for ethyl mandelate), low column backpressure (5-9 bar), high enantioselectivity, and excellent chiral resolution ability for HPLC enantioseparation with good stability and reproducibility. The relative standard deviations (RSD) (n = 5) of the retention time, and peak areas by repeated separation of ethyl mandelate are 0.23% and 0.67%, respectively. It demonstrates that the CC-MP CCTF@SiO2 core-shell microsphere composite has great potential in enantiomeric separation by HPLC.

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

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 [Cu3 (Btc)2 ]@[Cu2 ((+)-Cam)2 Dabco] by a superficial chiral etching method. The [Cu3 (Btc)2 ]@[Cu2 ((+)-Cam)2 Dabco] composite was utilized as a novel chiral stationary phase for HPLC enantioseparation. Various racemates were separated on the [Cu3 (Btc)2 ]@[Cu2 ((+)-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 [Cu2 ((+)-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 [Cu3 (Btc)2 ]@[Cu2 ((+)-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.

A chiral porous organic polymer COP-1 used as stationary phase for HPLC enantioseparation under normal-phase and reversed-phase conditions.

A spherical chiral porous organic polymer (POPs) COP-1 is synthesized by the Friedel-Crafts alkylation reaction of Boc-3-(4-biphenyl)-L-alanine (BBLA) and 4,4'-bis(chloromethyl)-1,1'-biphenyl (BCMBP), which was used as a novel chiral stationary phase (CSPs) for mixed-mode high-performance liquid chromatography (HPLC) enantioseparation. The racemic compounds were resolved in normal-phase liquid chromatography (NPLC) using n-hexane/isopropanol as mobile phase and reversed-phase liquid chromatography (RPLC) using methanol/water as mobile phase. The COP-1-packed column exhibited excellent separation performance toward various racemic compounds including alcohols, amines, ketones, esters, epoxy compounds, organic acids, and amino acids in NPLC and RPLC modes. The effects of analyte mass and column temperature on the separation efficiency of racemic compounds were investigated. In addition, the chiral resolution ability of the COP-1-packed column not only can be complementary in RPLC/NPLC modes but also exhibit a good chiral recognition complementarity with Chiralpak AD-H column and chiral porous organic cage (POC) NC1-R column. The relative standard deviations (RSD) (n = 5) of the retention time, resolution value, and peak area by repeated separation of 1-(4-chiorophenyl)ethanol are all below 3.0%. The COP-1 column shows high column efficiency (e.g., 17,320 plates m-1 for 1-(4-chlorophenyl)ethanol on COP-1 column in NPLC), high enantioselectivity, and good reproducibility toward various racemates. This work demonstrates that chiral POPs microspheres are promising chiral materials for HPLC enantioseparation.

A chiral metal-organic cage [Fe4L6](ClO4)8 used for capillary gas chromatographic separations.

Metal-organic cages (MOCs), as a promising class of crystalline porous materials with well-defined cavities, have attracted wide attention due to their multifarious potential applications in gas storage, host-guest chemistry, molecular recognition, separation, catalysis, sensing, and drug delivery and so on. Herein, we report that a chiral MOC [Fe4L6](ClO4)8 coated capillary column was fabricated for high-resolution gas chromatographic separation of various analytes, including n-alkanes, n-alcohols, positional isomers, aromatic hydrocarbon mixture, especially for racemic compounds. A series of racemic compounds such as alcohols, epoxides, aldehydes, ketones, ethers, esters, alkenes, sulfoxides and amino acid derivatives could be well separated on the [Fe4L6](ClO4)8 coated capillary column with high enantioselectivity and good reproducibility. Comparing the chiral resolution ability of the MOC [Fe4L6](ClO4)8 coated column with the commercial ß-DEX 120 column and the porous organic cage (POC) CC10 coated column, the chiral MOC column can be complementary to the two different types of columns. The results show that the chiral MOC [Fe4L6](ClO4)8 exhibited excellent separation performance toward a wide range of organic compounds, which will be very attractive as a new chiral separation media and has potential application prospects in separation science.