Can an Amine Be a Weaker and a Stronger Base at the Same Time? Curious Cases of Chameleonic Ionization

Abstract

We discovered an anomalous basic dissociation in certain multiprotic compounds. An amine group placed in the middle of a given compound is predicted to behave unusually─at certain pH ranges, its averaged degree of protonation actually increases with pH (!) resulting from interactions with other ionizable groups. This chameleonic behavior results in two pK50 values: one corresponding to a weaker base and the other to a stronger base for the same group.