Biomimetic synthesis of catalytic materials

by Varpness, Zachary Bradley.

Supramolecular proteins assemblies have been used as platforms for the synthesis of catalytic nanomaterials. These supramolecular structures are assembled from a limited number of subunits that provide a unique structurally defined platform for the synthesis of catalytic nanomaterials. Small heat shock protein (Hsp) and ferritin (Fn) are 12 nm protein cage-like assemblies of 24 subunits that have been used as platforms for the synthesis of noble metal nanoparticles through the in vitro reduction of corresponding ions. Protein encapsulated metal nanoparticles were used as catalysts for photochemical reduction of protons to H2 gas. The maximum catalytic rates of the protein encapsulated platinum nanoparticles are an order of magnitude better than for similarly sized platinum nanoparticles described in the literature. The protein cage increases the activity of the nanoparticles compared to other passivating layers by only minimally coating the particle. Fn was also used as the platform for the synthesis of catalytic platinum alloys of zinc and nickel. The alloys synthesized in this method showed an increase in the catalytic production of H2 gas per platinum atom. The Hsp protein cage was tested as a potential platform for use as a drug delivery vehicle for the targeted delivery of photodynamic therapy agents (PTA). The PTA, a Ru(bpy)32+ derivative, was attached to the interior and exterior of the protein cage to determine the effect of the protein cage on reactive oxygen species (ROS), specifically singlet oxygen, generation by the PTA. While the Hsp was oxidized by ROS, the PTA production of ROS was not significantly quenched by the protein cage displaying its potential as a delivery vehicle for PTA. Thiocapsa roseopersicina hydrogenase that is a a supramolecular was used in the synthesis nickel metal nanoparticles. The enzymatic oxidation of H2 gas was used as the source of reducing equivalents. The hydrogenase was shown to specifically mineralize nickel metal nanoparticles on the interior surface revealing the reductive active site. 1