Bispicolyamine-Based Supramolecular Polymeric Gels Induced by Distinct Different Driving Forces with and Without Zn2+
Department of Chemistry and Research Institute of Natural Sciences, Gyeongsang National University, Jinju 52828, Korea
Chemical Engineering Program, Graduate School of Advanced Science and Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527, Japan
Authors to whom correspondence should be addressed.
These authors contributed equally in this work.
Int. J. Mol. Sci. 2020, 21(13), 4617; https://doi.org/10.3390/ijms21134617
Received: 2 June 2020 / Revised: 24 June 2020 / Accepted: 26 June 2020 / Published: 29 June 2020
(This article belongs to the Special Issue The Self-Assembly and Design of Polyfunctional Nanosystems)
Metal-coordination polymeric gels are interesting areas as organic/inorganic hybrid supramolecular materials. The bispicolylamine (BPA) based gelator (1) showed excellent gelation with typical fibrillar morphology in acetonitrile. Upon complexing 1 with Zn2+, complexes ([1 + Zn + ACN]2+ and [1 + zinc trifluoromethanesulfonate (ZnOTf)]+) with four coordination numbers were formed, which determine the gel structure significantly. A gel-sol transition was induced, driven by the ratio of the two metal complexes produced. Through nuclear magnetic resonance analysis, the driving forces in the gel formation (i.e., hydrogen-bonding and π–π stacking) were observed in detail. In the absence and the presence of Zn2+, the intermolecular hydrogen-bonds and π–π stacking were the primary driving forces in the gel formation, respectively. In addition, the supramolecular gels exhibited a monolayer lamellar structure irrespective of Zn2+. Conclusively, the gels’ elasticity and viscosity reduced in the presence of Zn2+.