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

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 microcrystals depending on the component substituents. The generation of the organized phases was investigated by nuclear magnetic resonance (NMR) and ultraviolet-visible (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 microcrystalline gels containing acidic and basic groups displayed pH-responsiveness. Such behavior allowed for adaptive scrambling-sorting transitions and sorting selectivity switching within 1 × 2 dynamic covalent libraries driven by self-organization in response to environmental conditions. Moreover, the generation of hydrophobic microenvironments in the self-assembled three-dimensional (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 behaviors governed by self-organization (see conclusions).