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

Abstract

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 series of molecules were dissolved in anionic nematic cholesteric lyotropic liquid crystals prepared with cesium N-dodecanoyl-L-alaninate. With these values, the two order parameters that completely characterize the average alignment of the aromatic ring were calculated. Differential incorporation of both series of isomers into the aggregate is observed for intermediate size molecules, as evidenced by the values of the order parameters of the ring. Our 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 bond between the NH and/or CO groups and the interstitial water molecules. Increasing the hydrophobicity of the chain by adding one carbon atom induces a decrease in the overall alignment. Intermediate acyl chain length molecules progressively incorporate sufficiently into the aggregate for both asymmetric carbons, from the surface and the guest molecule, to approach each other, introducing differences in the average alignment of the aromatic ring between both series of isomers. Longer acyl chain derivatives incorporate deeper into the micelle and do not show this differentiation, possibly because the asymmetric carbons are located far away from each other.