Values in brackets indicate the microstate (e.g., [11] : doubly protonated, [10] : first residue protonated, etc.) and four corresponding dissociation constants. In the fully uncoupled case, K 1 = K 4 and K 2 = K 3 , and each (de)protonation event can be considered separately; this is not true when K 1 K 4 and K 2 K 3 . In this case, we have a more complex partition function given by ξ