Unusual Difference in Enantioselectivity of Two Chiral Stationary Phases with Grafted Antibiotic Ristocetin A

Retention and separation factors of enantiomers of several dipeptides were measured on chiral stationary phases with grafted macrocyclic antibiotic ristocetin A from different manufacturers, Chirobiotic R and Nautilus-R, using buffered and unbuffered methanol–water mixtures with 0 to 90% (v/v) of methanol as mobile phases. A remarkable difference in enantioselectivity toward both hydrophilic and hydrophobic dipeptides was observed between these two stationary phases that were explained by different configurations of the binding sites of the selectors resulted from different anchoring reactions applied to graft the antibiotic moiety to the silica support and also by different number of ionizable amino groups of the grafted selectors.