The complex structures of proteins enable their many biological functions, most of which include selective interactions with other molecules, i.e., molecular recognition. The variety of recognition motifs, the range of binding affinities, and the fidelity of recognition displayed by proteins are truly remarkable and enable biological processes as diverse as cellular respiration, transport, signaling, metabolism, and the immune response, to name a few. In parallel with the efforts to characterize biomolecular recognition mechanisms, chemists have attempted to mimic them using designed small molecules and selected biological molecules (e.g., monoclonal antibodies, nucleic acid aptamers, display peptides). Indeed, the...