Complexation of gallium(III) nitrate with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylenephosphonic acid)

Eight dissociation constants of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis (methylene phosphonic acid) (DOTMP, H8L) were determined for the first time by potentiometric titration in water using the CHEMEQUI program. The stability constants of Ga3+ complexes with deprotonated forms of DOTMP were determined. The stability constant of the Ga3+ complex with the fully deprotonated DOTMP ligand, lg KML equal to 27.8, is higher than the corresponding constant for the Ga3+ complex with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), the ligand most widely used in radiopharmacy; it is also higher than the constant for the Ga3+ complex with plasma protein transferrin, which makes the DOTMP ligand very promising for the use in radiopharmacy.