N-OCTADECANOYL-L-ALANINE AMPHIPHILE MONOLAYER AT THE AIR WATER INTERFACE AND LB FILM STUDIED BY FTIR SPECTROSCOPY/

Surface pressure (pi)-molecular area (A) compression/expansion isother ms of N-octadecanoyl-L-alanine reflect homochiral discrimination behav ior of the enantiomeric monolayer. FTIR studies indicate that carboxyl ic acid groups form out-of-plane ring dimers between two adjacent N-oc tadecanoyl-L-alanine molecules in monolayer LB films and that the long hydrocarbon chains in the film matrix take a biaxial orientation. The enantiomeric molecules assemble regularly and twist from neighbor to neighbor, thus giving rise to chirality of the aggregate in the two-di mensional condensed phase. Prior to the phase transition, the transfor mation of the triclinic subcell packing of the hydrocarbon chains into a hexagonal packing occurs. The variable-temperature infrared spectra of LB films provide powerful evidence for the formation of a hydrogen -bonded structure between chiral headgroups.