Chiral discrimination in langmuir monolayers of N-acyl glutamic acids inferred from pi-A measurements and atomic force microscopy

A kind of amino acid amphiphile (N-stearoyl-glutamic acid) was synthesized and used to investigate chiral discrimination at the interface by surface p ressure-area (pi -A) isotherm measurements and atomic force microscopy (AFM ). On the acidified water and aqueous CdCl2 solution subphase at pH = 2, mo nolayers were built up from the L enantiomer and the racemate of N-stearoyl -glutamic acid. The pi -A isotherms indicated that chiral discrimination co uld be observed on the aqueous CdCl2 solution more obviously than on acidif ied water. The monolayers of the racemate were transferred onto newly cleav ed mica surfaces for AFM investigation. Molecular images obtained on the mo nolayer prepared from the acidified water subphase gave a two-molecule rect angular unit cell that accommodates only racemates, whereas the mirror imag es could be obtained on the monolayer prepared from aqueous CdCl2 solution, which indicates chiral discrimination in two dimensions.