Steric effect on the self-assembly behaviours of amino acid derivatives

Abstract

To investigate the steric effect of amino acids, N,N′-dialanine-1,4,5,8-naphthalene tetracarboxylic acid diethylamide (ANTA) and N,N′-diphenylalanine-1,4,5,8-naphthalene tetracarboxylic acid diethylamide (PNTA) were synthesized based on naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTA) with alanine and phenylalanine, respectively. These compounds were characterized by infrared spectroscopy (IR), magnetic resonance spectroscopy (¹H NMR, ¹³C NMR) and mass spectrometry (MS). Interestingly, ANTA could self-assemble into spiral nanorings, but PNTA formed nanospheres. In order to reveal the self-assembly driving forces, the two-dimensional (2D) supramolecular self-assembly behaviours were studied on highly oriented pyrolytic graphite (HOPG) by scanning tunneling microscopy (STM) at the solid–liquid interface, which indicated the driving forces could be attributed to intermolecular hydrogen-bonding and π–π stacking interactions. These results represent different self-assembly behaviours due to the steric effect of amino acids.