Interfacial Assembly of Diethyl Ester Glutamic Acid Terminated Bolaamphiphile at the Air/Water Interface: Chiral Interaction and Morphology

We investigated the self. assembly behavior of bolaamphiphilic tetraethyl ester-di-L-glutamicacid-N,N'-hexadecanedioic amide (L-HDGE) and its enantiomer D-HDGE at the air/water interface. The self. assembled structures of the HDGE (L-HDGE or D-HDGE) molecule at the air/water interface and some other factors that affect the assembled structures, such as the chirality of the hydrophilic head group, surface tension, and ionic liquid subphase were studied. Atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy were employed to investigate the morphology and assembly mechanism of the transferred film. The HDGE molecule was found to form parallel nanowires on the surface of water with widths from 50 to 120 nm and heights from 1 to 5 nm while only a thin film was obtained when the racemic mixture was used under the same conditions. The FTIR spectra show that the heterochiral interaction of the HDGE molecule is stronger than the homochiral interaction. With an increase in surface tension, the parallel nanowires aggregate. Trace amounts of ionic liquid added to the subphase remarkably accelerated the aggregation of the nanowires to yield nanostrips, and some helical structures were observed when the surface tension was increased. The handedness of the helical structures was determined by the molecular chirality of the head group.