Metal Ion Mediation of Interfacial Chiral Supramolecular Formation of Amphiphilic Schiff Bases Studied by In Situ Second Harmonic Generation

• DOI: 10.1021/acs.jpcb.0c05545
• Publication Date: 2020-07-27T16:38:47Z
• Authors: Man Xue; Li Zhang; Minghua Liu; Yu Bai; Yuan Guo; Zhen Zhang
• Keywords: 01 natural sciences; 0104 chemical sciences

The coordination effects between chiral Schiff bases and metal ions can provide an effective strategy for fabricating chiral supramolecular self-assemblies. We studied the supramolecular self-assembly of the amphiphilic Schiff base enantiomer, 2-hydroxy-1-naphthylmethylamino-N,N'-bis(octadecyl)-l/d-glutamic diamide (l/dGJ), at the air/water interfaces by using in situ second harmonic generation linear dichroism (SHG-LD) technique combined with UV-vis spectroscopy and atom force microscopy. lGJ and dGJ monolayers can form mirror-image structures of each other at different interfaces, which can be mediated by metal ions. When Mg2+ and Zn2+ ions were added into the subphases, the l/dGJ monolayers self-assembled into a nanofiber-like structure and showed significant chirality similar to that at the pure water interface. However, when Cu2+ ions were added into the subphase, the chirality of the l/dGJ monolayer was destroyed because of the Cu2+ coordination effect. The degree of the chirality excess (DCE) value decreased with the increment of the concentration of Cu2+ in the subphase. Furthermore, when the surface pressure increased, the DCE value of Cu2+-l/dGJ complexes increased gradually, which indicated that the Cu2+-l/dGJ complex aggregated into a chiral supramolecular structure through lateral molecular packing.