Differential incorporation of L- and D-N-acyl-1-phenyl-d(5)-2-aminopropanein a cesium N-dodecanoyl-L-alaninate cholesteric nematic lyomesophase

Deuterium quadrupole splittings from two series of optical isomers, L- and D-N-acyl-l-phenyl-d(5)-2-aminopropane, with linear acyl chains ranging from I to 10 carbon atoms, were measured using H-2 NMR spectroscopy. Both serie s of molecules were dissolved in anionic nematic cholesteric lyotropic liqu id crystals prepared with cesium N-dodecanoyl-L-alaninate. With these value s, the two order parameters that completely characterize the average alignm ent of the aromatic ring were calculated. Differential incorporation of bot h series of isomers into the aggregate is observed for intermediate size mo lecules, as evidenced by the values of the order parameters of the ring. Ou r results indicate that the first two derivatives in both series, Land D-C, and L- and D-C-2, are located near the interface, possibly forming a H bon d between the NH and/or CO groups and the interstitial water molecules. Inc reasing the hydrophobicity of the chain by adding one carbon atom induces a decrease in the overall alignment. Intermediate acyl chain length molecule s progressively incorporate sufficiently into the aggregate for both asymme tric carbons, from the surface and the guest molecule, to approach each oth er, introducing differences in the average alignment of the aromatic ring b etween both series of isomers. Longer acyl chain derivatives incorporate de eper into the micelle and do not show this differentiation, possibly becaus e the asymmetric carbons are located far away from each other.