In this case, we focus on the overall ∆pK a for the deprotonation of residue A by explicitly considering all possible protonation states of residue B. When considering the free energy difference between protonation in a folded protein and protonation in a capped peptide, one can resolve ∆∆G 30 = ∆G 0 -∆G 3 (note that this is equal to ∆∆G 0 ); however, we can also resolve ∆G 1 and ∆G 2 from ∆∆G 41 and ∆∆G 52 , respectively.