Gas‐phase basicities and proton affinities of lysine and histidine measured from the dissociation of proton‐bound dimers

Gas‐phase basicities and proton affinities of lysine and histidine were measured by the kinetic method. Using low‐energy collisional activation to change the effective temperature in the dissociation of proton‐bound dimer, proton affinities of lysine and histidine were determined to be 235.3 and 234.0 kcal/mol respectively. A large entropy effect was found for lysine, and thus at temperatures above 300 K, histidine is slightly more basic than lysine. Peptides that contain lysine or histidine are more basic than lysine or histidine. The basicities of these peptides depend on their structures and the internal hydrogen bonding.