RNA-Mediated Synthesis of Particles from Organometallic Palladium and Platinum Precursors

Abstract

RNA sequences have been discovered that mediate the growth of hexagonal, cubic and spherical palladium and platinum containing particles. In vitro selection techniques were used to evolve an initial library of ˜ 3 x 10¹³ unique RNA sequences through six to ten cycles of selection to yield several active sequence families. The particle growth occurred in aqueous solution at ambient temperature, without any endogenous reducing agent, and at low concentrations of metal precursor (10 μM — 400 μM). Relative to the metal precursor the RNA concentration was significantly lower (1 μM).

RNA sequences that utilize the organometallic complex tris(dibenzylideneacetone) dipalladium(0) ([Pd₂(DBA)₃]) to form palladium containing particles were further characterized for their ability to control particle growth. These RNA sequences (Pdases) were found to form hexagonal and cubic palladium containing particles with a high degree of shape specificity. Replacing the pyridyl-modified RNA sequence with native RNA resulted in a complete loss of RNA function. Removing the 3′-fixed sequence region from the Pdase had little effect on particle growth; however, further truncations into the variable region resulted in a significant loss of activity and particle shape control. Changing the metal center and ligand of the group VIII organometallic precursor complex revealed a strong dependence of particle growth and shape on the DBA ligands.

The Pdases were covalently immobilized on gold surfaces and evaluated for their activity toward particle synthesis. When coupled to gold via oligoethylene glycol linkers, both RNA isolates 17 and 34 were able to mediate the formation of Pd containing particles with the same shape control previously observed in solution. Finally, the use of surface-bound RNA as a tool for directing the orthogonal synthesis of materials on surfaces was demonstrated. Patterning the RNA sequence for hexagons next to the sequence for cubes, followed by incubation in a solution containing [Pd₂(DBA)₃], resulted in the spontaneous formation of spatially distinct spots of Pd containing hexagonal and cubic particles.