Three new defined proton affinities for polybasic molecules in the gas-phase: Proton microaffinity, proton macroaffinity and proton overallaffinity

A theoretical study on complete protonation of a series of tetrabasic molecules with general formula N[(CH2)nNH2][(CH2)mNH2][(CH2)pNH2] (tren, pee, ppe, tpt, epb and ppb) is reported. For first time, three kinds of gas-phase proton affinities for each polybasic molecule are defined as: ‘proton microaffinity (PAn,i)’, ‘proton macroaffinity ( PA ¯ n ) ’ and ‘proton overall affinity ( PA ¯ ov )’. The variations of calculated log PA ¯ n in the series of these molecules is very similar to that of their measured log Kn. There is also a good correlation between the calculated gas-phase proton macroaffinities and proton overallaffinities with corresponding equilibrium macroconstants and overall protonation constants in solution.