Depth of penetration of binaphthyl derivatives into the micellar core of sodium undecenoyl leucyl-leucinate surfactants

Two different diastereomeric forms of sodium N-undecanoyl leucyl-leucinate (SULL) (both l,l and l,d) are used to examine the role of depth of penetration of chiral analytes into the micellar core of polymeric and monomeric surfactants on enantioselectivity. In this study, chiral separation of three binaphthyl derivatives, i.e. (±)-1,1′-bi-naphthyl-2,2′-diamine (BNA), (±)-1,1′-bi-2-naphthol (BOH), and (±)-1,1′-binaphthyl-2,2′-dihydrogen phosphate (BNP), are studied. Chromatographic results suggest that BNP interacts approximately the same with both the C- and N-terminal amino acid of poly SULL, while the preferential site of interaction of this analyte with the monomeric form of SULL (mono SULL) is at the C-terminal amino acid. This indicates that BNP enantiomers penetrate deeper into the micellar core of the poly SULL than that of the mono SULL. Varying the temperature resulted in a change in the depth of penetration of BNP into the micellar core of the poly SULL. However, the enantiomers of BNA and BOH always interact preferentially with the N-terminal amino acid of SULL surfactants (both polymer and monomer), independent of the temperatures studied.