Two-dimensional crystalline structures and photochemical behavior of cinnamate monolayers on water surfaces

Abstract

A direct relationship between the structures of two-dimensional (2-D) crystallites of 4-octadecyloxy-E-cinnamic acid and 4-octadecyloxy-E-cinnamamide amphiphiles at the air-water interface and their photochemical behavior, is presented. The detailed packing arrangements of the monolayers were determined, close to the atomic level, from the diffraction pattern measured, in situ on the water surface, by the grazing incidence X-ray diffraction (GID) technique using synchrotron radiation. The products of the photochemical reaction, performed by irradiating the monolayer films directly on the water surface, were collected and analyzed. While the acid crystallites yield a β-truxinic acid product together with the cis-isomer, the amide undergoes only trans-cis isomerisation, in full agreement with the 2-D crystalline packing arrangements of the two amphiphiles on the water surface. Chirality 10:60–65, 1998. © 1998 Wiley-Liss,Inc.