Microcapsule Structure with a Tunable Textured Surface via the Assembly of Polyoxomolybdate Clusters: A Bioinspired Strategy and Enhanced Activities in Alkene Oxidation.

A polyamine-mediated bioinspired strategy to assemble Keggin-type phosphomolybdic acid (PMA) clusters is demonstrated for the fabrication of microcapsule (MC) structures with unique surface textures. It involves supramolecular aggregation of polyamines with multivalent anions, which then allows the assembly of negatively charged PMA into MCs in an aqueous medium under ambient conditions. Resembling the role of polyamines in biosilicification of diatoms, the polyamine-anion interaction is shown to be the key for the assembly process. It not only provides structural stability but also facilitates an interesting transition from a smooth to a wrinkled surface alongside a change in the Keggin form to its lacunary form depending on the pH of the medium. Moreover, the presence of isolated PMA units in the hybrid structure enables them to be active in catalyzing the aerobic oxidation of alkenes under solvent-free conditions with better selectivity and reusability. Hence, the assembly approach represents an effective way for heterogenization of PMA-based materials and is expected to find considerable application in the wider hybrid-cluster field.