Synthesis of crown ether and cyclam-capped beta-cyclodextrin bonded silica particles and their application as chiral stationary phases in liquid chromatography

Abstract

Several new types of beta-cyclodextrin-bonded, crown ether-bonded, and crown ether/cyclam-capped beta-cyclodextrin-bonded silica particles have been synthesized using a successive multiple-step liquid-solid phase reaction on the silica gel surface. These bonded silica particles have shown to have excellent separation selectivities when used as stationary phases in HPLC, UHPLC and CEC. The crown ether/cyclam-capped beta-cyclodextrin-bonded stationary phases have a chiral selector with several recognition sites: beta-cyclodextrin, crown ether/cyclam, and the lattera??s side arm. They exhibit excellent enantioselectivities for a wide range of compounds due to the cooperative functioning of the anchored crown ether/cyclam and beta-cyclodextrin. After inclusion of the metal ion from the mobile phase into the crown ether/cyclam unit, the chiral stationary phases become positively charged and can provide extra electrostatic interactions with ionisable solutes and enhance the dipolar interactions with polar neutral solutes. This enhances host-guest interaction with some solutes and improves chiral recognition and selectivity.