Enantioseparation of single layer native cyclodextrin chiral stationary phases: Effect of cyclodextrin orientation and a modeling study

- Two native β-CD CSPs with similar surface concentration were prepared at CD's C2 and C6 positions via click chemistry.
- The surface CD orientation plays an essential role in CSP's enantio-differentiation ability.
- Elution order of specific racemates can be reversed by tuning the surface CD orientation.
- MD simulation provides a robust tool for investigation of the CD's discrimination mechanism under “real” mobile phase.

A novel native cyclodextrin (CD) chiral stationary phase (CSP) with single triazole-bridge at CD C2 position (CSP1) was prepared by anchoring mono(2A-azido-2A-deoxy)-β-CD onto alkynyl silica via click chemistry. The effect of CD orientation on single layer CD-CSP's enantioseparation was comprehensively investigated using CSP1 (reversed orientation) and our previously reported CSP2 (C6 single triazole-bridge, normal orientation) as well as a commercial CD-CSP (Cyclobond I 2000, hybrid orientation) by separating several groups of analytes in chiral high performance liquid chromatography. It is found that the CD orientation on silica surface plays an important role in separating different racemates. CSP2 with normal CD orientation affords best separation for isoxazolines while CSP1 with reversed CD orientation better separates naringenin, hesperetin and Tröger's base. CSP2 and Cyclobond I 2000 show comparable separation ability for dansyl amino acids while poor separation was found on CSP1. Besides, molecular dynamics simulation was performed under “real” separation conditions using flavanone as model analyte to reveal the essential factors for CD's chiral discrimination behaviors.

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