Chiral Discrimination in Langmuir Monolayers of N-Acyl Glutamic Acids Inferred from π−A Measurements and Atomic Force Microscopy

Abstract

A kind of amino acid amphiphile (N-stearoyl-glutamic acid) was synthesized and used to investigate chiral discrimination at the interface by surface pressure−area (π−A) isotherm measurements and atomic force microscopy (AFM). On the acidified water and aqueous CdCl2 solution subphase at pH = 2, monolayers were built up from the l enantiomer and the racemate of N-stearoyl-glutamic acid. The π−A isotherms indicated that chiral discrimination could be observed on the aqueous CdCl2 solution more obviously than on acidified water. The monolayers of the racemate were transferred onto newly cleaved mica surfaces for AFM investigation. Molecular images obtained on the monolayer prepared from the acidified water subphase gave a two-molecule rectangular unit cell that accommodates only racemates, whereas the mirror images could be obtained on the monolayer prepared from aqueous CdCl2 solution, which indicates chiral discrimination in two dimensions.