Directed self-assembly of inorganic redox complexes with artificial peptide scaffolds

An ongoing challenge in the construction of supramolecular systems is controlling the relative geometry of functional redox species for molecular electronics devices, including wires, switches, and gates. This review focuses on the use of artificial peptide strands to assemble inorganic complexes that are redox active. These approaches toward macromolecular assembly use varying oligoamide backbones and assembly motifs that grew from earlier reports of single oligolysine or proline chains containing pendant redox species that undergo photoinduced charge separation. Recently, peptide nucleic acid chains that form double-stranded duplexes analogous to DNA by hydrogen bonding of complementary base pairs have been modified to contain metal complexes. In these structures, hydrogen bonding and metal coordination combine to form crosslinks between the PNA strands. Finally, a family of structures is described that is based on an aminoethylglycine scaffold with pendant metal coordination sites, but without intervening nucleic acid base pairs. These structures form multimetallic complexes that are either single- or double-stranded, or that form hairpin loop structures. These motifs for using artificial peptide strands for self-assembly hold electron donors and acceptors in relative positions that provide structural connectivity and permit electron transfers between linked metal complexes. This is a new approach for creating polyfunctional redox architectures that could ultimately enable the construction of potentially large and complex molecular electronics devices.