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

Abstract

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-tetraaza-1,4,7,10-tetrakis(carboxymethyl)cyclododecane] for the purpose of identifying properties of the transition states of geometrical isomer interconversions, which have been the object of numerous NMR studies. An analogous study has been carried out on model complexes of the same trications formed by the DOTA-like ligand 1,7-bis(1-methylimidazol-2-ylmethyl)-4,10-bis(carboxymethyl)-1,4,7,10-tetraazacyclododecane, LH₂. Features of the transition states for the two types of systems are compared.