Alkylammonium Cation Affinities of Nitrogenated Organobases: The Roles of Hydrogen Bonding and Proton Transfer.

Alkylammonium cation affinities of 64 nitrogen-containing organobases, as well as the respective proton transfer processes from the alkylammonium cations to the base, have been computed in the gas phase by using DFT methods. The guanidine bases show the highest proton transfer values (191.9-233 kJ mol-1 ) whereas the cis-2,2'-biimidazole presents the largest affinity towards the alkylammonium cations (>200 kJ mol-1 ) values. The resulting data have been compared with the experimentally reported proton affinities of the studied nitrogen-containing organobases revealing that the propensity of an organobase for the proton transfer process increases linearly with its proton affinity. This work can provide a tool for designing senors for bioactive compounds containing amino groups that are protonated at physiological pH.