A theoretical model, based in density functional theory with the B3LYP functional and the DZVP basis set from Salahub, has been applied for the calculation of the binding affinity and cation basicity between the 20 common amino acids and the monovalent cations Li+, Na+, K+, Cu+ and Ag+. These magnitudes have been calculated for every combination of the five cations with the twenty amino acids, thus totalling 100 reactions. The highest binding affinities correspond to copper(I) (302.2-479.8 kJ mol(-1)), while potassium has the lowest values (115.6-192.4 kJ mol(-1)). The results of the calculations have been compared with both experimental and theoretical values from the literature when they are available. Also, an energy partitioning scheme has been used to evaluate the different factors that have an influence on the value of the amino acid-cation binding energy, mainly the preorganization energy of the ligand and the interaction energy between the cation and the different donor atoms and/or pi system of the amino acid. The procedure developed here can be used with a wide range of metal cations, including those pertaining to the first and second transition series.