Complete gas-phase proton microaffinity analysis of five linear tetraamines containing two ethylenediamine residues

Density functional theory (DFT) and ab initio (Hartree-Fock) calculations employing the 6-31G∗∗ basis set were used to determine gas-phase proton microaffinities (PAn,i) of five linear tetraamines with general formula NH2(CH2)2NH(CH2)nNH(CH2)2NH2 (where n = 2, 3, 4, 5 and 6). The corresponding proton macroaffinities (PA¯n) were calculated according to our recently established method with and without considering Boltzmann distribution of microspecies. The results showed that there are good correlations between the calculated proton macroaffinities, PA¯n, and proton overallaffinities, log PA¯ov, of these tetraamines in the gas phase with corresponding protonation macroconstants, log Kn, and overall protonation constants, logβ4, in solution, respectively.