Synthesis and organogelating behaviour of urea- and Fmoc-containing diphenylalanine based hexaamide

A new low molecular mass organic gelator based on tri-tert-butylates Glu-Urea-Lys and Fmoc-capped di-L-Phe-containing hexaamide (tri-tert-butyl (10S,13S,31S,35S)-10,13-dibenzyl-1-(9H-fluoren-9-yl)-3,9,12,15,18,25,33-heptaoxo-2-oxa-4,8,11,14,19,26,32,34-octaazaheptatriacontane-31,35,37-tricarboxylate, 9) was synthesized and examined for the ability to gelate various organic solvents (dichloromethane (DCM), chlorophorm, methanol, acetonitrile and acetonitrile/water mixtures, ethyl acetate). The microstructure of the obtained gels was studied using scanning electron microscopy (SEM). It was shown that the morphologies of the xerogels, formed by the slow drying of the corresponding organogels, differ for different solvents. For example, xerogels from DCM showed the layered slab structures with widths and lengths to hundreds of micrometers, but xerogels in ethanol exhibit networks composed of entwined fibers. Based on FTIR, 1H NMR and UV-vis data, the gelator molecules are aggregate via N–H/O hydrogen bonding, hydrophobic interaction and π-π-staking.