Theoretical investigation on the geometries of DOTA and DOTA-like complexes and on the transition states of their conformational equilibria

Computations, mostly at the RHF level, have been performed on La3+ and Y3+ model complexes of the widely used DOTA ligand [DOTA 1,4,7,10-tetra-aza-1,4,7,10-tetrakis(carboxy-methyl)cyclo-dodecane] for the purpose of identifying properties of the transition states of geometrical isomer inter-conversions, which have been the object of numerous NMR studies. An analogous study has been carried out on model complexes of the same tri-cations formed by the DOTA-like ligand 1,7-bis(1-methyl-imidazole-2-ylmethyl)-4,10-bis(carboxy-methyl)-1 4,7,10-tetra-aza-cyclo-dodecane, LH2. Features of the transition states for the two types of systems are compared. (authors)