Understanding the charging mechanism of dissociable AAs has a long history, starting with Linderstrøm-Lang of the Carlsberg Laboratory and followed by the early general studies of the acid-base equilibria in polyelectrolytes by Lifson and Marcus . Protonisation/deprotonisation dissociation equilibria were introduced into protein electrostatics in the seminal works of Kirkwood and Shumaker and Tanford and Kirkwood , and later developed further through detailed simulation models of protein behaviour in biomolecular solutions . The connection between the protonisation/deprotonisation dissociation equilibria and Poisson-Boltzmann electrostatics was developed by Ninham and Parsegian , who introduced the CR mechanism as a self-consistent relationship between the local electrostatic potential and the dissociated state of chargeable surface groups described by the Langmuir isotherm, which has been recently extended to any adsorption isotherm . CR in the context of proteins and its development was authoritatively reviewed by Borkovec et al. .