Illustration of all species and all microspecies involved in full protonation steps of spermine and determination of corresponding most abundant and most stable conformers, a gas phase theoretical study

In this research a theoretical study on the successive proton macroaffinities of a linear aliphatic tetraamine, spermine, via density functional theory (DFT) is carried out. DFT (B3LYP) calculations employing standard 6-31G∗ basis set are used to determine the gas phase protonation energies. We studied all possible microspecies for all L, HL+, H2L2+, H3L3+ and H4L4+ species that differ in the location of proton/charge and all possible conformers for all microspecies that differ in the number and/or the location of intramolecular hydrogen bonding. Then the most stable conformers as well as the most abundant conformers were determined in each case. Two different schemes were considered for full protonation steps of spermine according to latter conformers. Then the proton micro-, macro- and for both schemes were determined according to our published method.