Mechanism and energetics for complexation of 90Y with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), a model for cancer radioimmunotherapy

Ab initio methods were utilized to calculate the structures and energetics of YH2(DOTA)+, YH(DOTA) and YH(DOTA)-. Calculation shows that Y3+ is coordinated only by four equivalent carboxylate oxygens in the doubly protonated intermediate YH2(DOTA). Y3+, which is found away from ring nitrogens, spontaneously moves toward the ring as protons are removed from ring nitrogens. Such movement results in the creation of final complex Y(DOTA)- in which Y3+ is coordinated by all four carboxylate oxygens and all four nitrogens.