The role of amide-amide hydrogen-bonding in chiral recognition in Langmuir monolayers of N-stearoylvaline

The formation of amide-amide hydrogen-bonds has been suggested as a key structural feature in the ordered aggregation of N-acylamino acid amphiphiles at interfaces. Langmuir monolayers of N-stearoyl-L-valine and N-stearoyl-N-methyl-L-valine are compared using surface pressure isotherm measurements and observation by Brewster angle microscopy. Monolayers of N-stearoyl-L-valine exhibit highly regular dendritic domains, while those of N-stearoyl-N-methyl-L-valine monolayers exhibit round domains resembling those of fatty acids. Replacement of the hydrogen on the amide nitrogen with a methyl group reveals the key role of amide-amide hydrogen bonding in determining the structure of these monolayers.