π–Cation Interactions in Molecular Recognition: Perspectives on Pharmaceuticals and Pesticides

The π–cation interaction that differs from the cation−π interaction is a valuable concept in molecular design of pharmaceuticals and pesticides. In this Perspective we present an up-to-date review (from 1995 to 2017) on bioactive molecules involving π–cation interactions with the recognition site, and categorize into systems of inhibitor–enzyme, ligand–receptor, ligand–transporter, and hapten–antibody. The concept of π–cation interactions offers use of π systems in a small molecule to enhance the binding affinity, specificity, selectivity, lipophilicity, bioavailability, and metabolic stability, which are physiochemical features desired for drugs and pesticides.