Application of Cyclam-Capped β-Cyclodextrin-Bonded Silica Particles as a Chiral Stationary Phase in Capillary Electrochromatography for Enantiomeric Separations

Abstract

Two novel types of substituted cyclam-capped beta-cyclodextrin (beta-CD)-bonded silica particles have been prepared and used as chiral stationary phases in capillary electrochromatography (CEC). The two stationary phases have a chiral selector with three recognition sites: beta-CD, cyclam, and the latter's sidearm. They exhibit excellent enantioselectivities in CEC for a wide range of compounds as a result of the cooperative functioning of the anchored beta-CD and cyclam. After inclusion of the metal ion (Ni2+) from the running buffer into the substituted cyclams and their sidearm ligands, the bonded stationary phases become positively charged and can provide extra electrostatic interactions with ionizable solutes and enhance the dipolar interactions with some polar neutral solutes. This enhances the host-guest interaction with some solutes and improves chiral recognition and enantioselectivity. These new types of stationary phases exhibit great potential for fast chiral separations in CEC.

Recent accomplishments in the field of enantiomer separation by CEC

“…6a) or with 1,8-di-(2-hydroxymethylpyridine-6-ylmethyl)-substituted cyclam (Fig. 6b) [52]. With these novel CSPs all 28 tested analyte substances could be separated with enantioresolution between 0.9 and 12.9 and enantioselectivity in the range of 1.1-2.8.…”

“…This was obviously the focus of a few CEC studies on CD-based CSPs lately. Thus, Gong and Lee [52] employed cyclam-capped bCDs (note, cyclam is synonymous for 1,4,8,11-tetra-azacyclotetradecane) for the enantiomer separation of a series of chiral compounds including basic pharmaceuticals such as b-blockers as well as acids, esters, ketones and alcohols. Two different CSPs were fabricated [53]: first, sodium hydride activated b-CD was derivatised with 3-glycidoxypropyltrimethylsilane at the C(2) secondary hydroxyl position and the product was covalently immobilized onto silica particles by a silylation reaction.…”

Pharmaceutical and biomedical applications of chiral capillary electrophoresis and capillary electrochromatography: An update

“…Other new chiral selectors in CEC included crown ether and cyclam-capped b-CD derivatives covalently bound to silica gel [131][132][133]. These stationary phases exhibited better enantioselectivity than either b-CD or crown ether or cylam-bonded phases indicating a synergistic effect of the selectors.…”

Preparation and application of methylcalix[4]resorcinarene‐bonded silica particles as chiral stationary phase in high‐performance liquid chromatography

“…Development and application of new chiral stationary phases (CSPs) with high enantioselectivities to separate chiral molecules is one of the most active areas of liquid chromatography (LC). 1 Many chiral separations have been successfully accomplished using b-cyclodextrin (CD)-based [2][3][4][5] and crown ether-based 6 silica particles as CSPs in LC. This is possible due to the cavity structure of b-cyclodextrins and crown ethers which can form host-guest complex by including chiral solutes.…”