Emerging Complex Behavior Driven by Self-Organization: Dynamic Covalent Libraries of Acylhydrazones in Water

Overview & Synopsis

The generation of self-organized phases drives the emergence of states of matter of higher complexity. Herein, we study in situ generated self-assembled systems based on the condensation between different aldehydes and hydrazides in water. The resulting acylhydrazones can self-organize into turbid hydrogels or bigger micro-crystals depending on the component substituents. The generation of the organized phases was investigated by NMR and UV-Vis spectroscopy as well as by microscopy, rheology and solid-state X-ray analyses. Polar substituents like imidazole rings, carboxylic acids and alcohols still lead to hydrogels due to the high propensity of the hydrophobic aromatic cores to self-assemble. The micro-crystalline gels containing acidic and basic groups displayed pH-responsiveness. Such behaviour allowed for adaptive scrambling-sorting transitions and sorting selectivity switching within 1x2 dynamic covalent libraries driven by self-organization in response to environmental conditions. Moreover, the generation of hydrophobic microenvironments in the self-assembled 3D-network promoted selective imine formation made of apolar components as a result of the stabilization and protection of the reversible covalent bond from hydrolysis. Thus, the dynamic systems described here exhibit up to five levels of adaptive behaviours governed by self-organization (see conclusions).