Metal Ion Mediation of Interfacial Chiral Supramolecular Formation of Amphiphilic Schiff Bases Studied by In Situ Second Harmonic Generation
2020
Xue, Man | Zhang, Li | Liu, Minghua | Bai, Yu | Guo, Yuan | Zhang, Zhen
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.
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