In this study, the effects of counterion type and surfactant-to-counterion ratio on the selectivity of several binaphthyl derivatives with L,L- undecanoyl leucine-valinate was examined by use of Micellar Electrokinetic Chromatography (MEKC). The chiral separations of [1,1'-bi-2-naphthyl-2,2'-diyl hydrogen (BNP) 1,1′-bi-2-naphthyl-2,2′-diamine (BNA) and 1,1′-bi-2-naphthol (BOH)] by the dipeptide surfactant varied widely in the presence of three counterions, 1,2 diaminoethyl, 1,2 diaminopropyl, and 1,3 diaminopropyl and with surfactant-to-counterion ratios of 1-to-1 and 1-to-0.5. The results of this study have shown that the selection of 1,2 diaminoethyl in a 1:1 surfactant-counterion-ratio provides enhanced baseline separation for enantiomers of BOH in comparison to its 1-to-0.5 counterpart, though no significant difference in separation can be observed for enantiomers of BNP under the same conditions. Despite the observation that every one of the three included counterions engendered some degree of separation for each analyte, enantiomers of BNP exhibited heightened separation in the presence of 1,2 diaminoethyl and 1,2 diaminopropyl at a pH level of 8. Conversely, the comparative Na counterion separates enantiomers of BOH and BNA significantly better than the counterions examined.

Comparison of diamine and sodium counterions on chiral selectivity of dipeptide-based surfactants

ACS Spring 2022

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