Designing Hierarchical Organic-Inorganic Hybrid Materials with High-Information-Content Building Blocks

Abstract

Hierarchical hybrid materials are attractive for catalytic, opto-electronic and sensing applications due to the collective and emergent properties that originate from the precise organization and interplay of organic and inorganic units. However, intimate integration of disparate components remains difficult. To overcome this challenge, we propose a strategy to design organic-inorganic hybrid hierarchical nanostructures through the binding or mineralization of inorganic building blocks onto sequence-defined organic scaffolds. Our approach makes use of self-assembling synthetic peptoids as the foundational building blocks, solid-binding proteins as the functional building blocks, and inorganic nanoparticles as the block that is captured or synthesized by solid-binding proteins. By conjugating solid-binding proteins to 2D or 1D peptoid scaffolds co-assembled from unmodified and maleimide-terminated oligomers, and by exploiting the adhesive or morphogenetic functions of the materials-binding segments engineered within each protein unit we demonstrate: (i) the spontaneous self-assembly of 3D architectures consisting of alternating layers of peptoids, proteins, and silica upon addition of SiO2 nanoparticles to peptoid nanosheets derivatized with silica-binding proteins; (ii) exquisite control over the size of TiO2 anatase crystallites in the 1.4 to 4.4 nm range using peptoid nanotubes derivatized with proteins displaying one or more titania-binding segment to the solvent; (iii) synthesis of Au nanoparticles and TiO2/Au nanocomposites on peptoid nanotubes decorated, respectively, with proteins displaying a gold-binding segment or both a titania and gold-binding segment to the solvent; and (iv) close integration of the two materials on the nanotube surface, as evidenced by the ability of the composite structures to support rhodamine photodegradation under visible light illumination. In another proof-of-concept study, we constructed thermo-responsive gold-binding proteins and showed their potential to produce protein functionalized gold nanoparticles (AuNPs) with temperature-dependent dynamic assembly by binding pre-synthesized AuNPs or mineralization. This example demonstrated that the protein framework can be also engineered to introduce additional functionalities. Considering the outstanding programmability of peptoids, the diversity of natural and de novo designed protein frameworks, and the abundance of solid-binding peptides interacting with a variety of inorganic compounds, the simple and modular strategies described here should prove useful for the fabrication of a broad range of advanced functional materials.