Mixed proton complexes of aminoacids and carboxylic ligands in aqueous solution

Formation and stability of proton-mixed ligand complexes have been studied for the systems H(+)-lysine-aspartic acid, H(+)-lysine-succinic acid and H(+)-glycine malonic acid, in aqueous solution at 25 degrees , by potentiometric technique using the (H(+))-glass electrode. For all these systems it has been found that the species ABH(j) (A and B, first and second ligand, respectively; j = 1, 2, ... m + n - 1; m and n are the maximum protonation degrees of the two ligands, respectively) are formed. The stability of these species is discussed with respect to various factors and, in particular, as a function of speciation problems.