As alluded to the introduction, both the macroscopic and microscopic pK values are of interest. A partition function approach can account for coupling between residues and the microscopic pK values between individual states. Note that the (de)protonation of the sidechain of an amino acid can be described using a standard equilibrium binding formalism. Specifically, the "binding" of protons can be fully described by the proton concentration (c) and the binding constant (K), from which it follows that the grand partition