A study of the structure and chiral selectivity of micelles of two isomeric D-glucopyranoside-based surfactants

Abstract

We have synthesised the sodium salts of two isomeric surfactants that differ in the anomeric orientation of the C₁₄ hydrocarbon chain to the D-glucopyranoside fused ring structure, containing a phosphate polar head group. The inclusion of α- and β-anomers in the separation buffer, using micellar electrokinetic capillary chromatography (MECC) shows that the latter is the superior chiral selector. The critical micelle concentration (cmc) for both surfactants was around 0.6 mM, and the mean aggregation number is 65 for both anomers. In an attempt to understand the possible mechanism of chiral discrimination, we have calculated minimum energy conformations of micelles produced by these surfactants, and have established the importance of their chiral head groups and the sodium counter-ions in the discriminating process. We have also investigated the micro-structures of the two surfactants by transmission electron microscopy. This technique shows that the two enantiomers aggregate very differently; whereas the α-anomer shows randomly orientated string-like forms the β-anomer forms ordered ‘whorl’ arrays.