Chiral separations of five -adrenergic antagonists (propranolol, esmolol, atenolol,\r\nmetoprolol, and bisoprolol) were studied by capillary electrophoresis using six cyclodextrins\r\n(CDs) as the chiral selectors. Carboxymethylated--cyclodextrin (CM--CD) exhibited a\r\nhigher enantioselectivity power compared to the other tested CDs. The influences of the\r\nconcentration of CM--CD, buffer pH, buffer concentration, temperature, and applied\r\nvoltage were investigated. The good chiral separation of five -adrenergic antagonists was\r\nachieved using 50 mM Tris buffer at pH 4.0 containing 8 mM CM--CD with an applied\r\nvoltage of 24 kV at 20 Ã?°C. In order to understand possible chiral recognition mechanisms\r\nof these racemates with CM--CD, host-guest binding procedures of CM--CD and these\r\nracemates were studied using the molecular docking software Autodock. The binding free\r\nenergy was calculated using the Autodock semi-empirical binding free energy function.\r\nThe results showed that the phenyl or naphthyl ring inserted in the hydrophobic cavity\r\nof CM--CD and the side chain was found to point out of the cyclodextrin rim. Hydrogen\r\nbonding between CM--CD and these racemates played an important role in the process of\r\nenantionseparation and a model of the hydrogen bonding interaction positions was\r\nconstructed. The difference in hydrogen bonding formed with the ââ?¬â??OH next to the chiral center of the analytes may help to increase chiral discrimination and gave rise to a bigger\r\nseparation factor. In addition, the longer side chain in the hydrophobic phenyl ring of the\r\nenantiomer was not beneficial for enantioseparation and the chiral selectivity factor was\r\nfound to correspond to the difference in binding free energy.
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