NMR estimation of the activation energy of conformational dynamics in the [Dy(DOTA)]− complex: Energetic manifestation of the gadolinium break

Abstract

The conformational dynamics of the paramagnetic complex [Dy(H2O)n(DOTA)]− has been studied by dynamic 1H NMR within the framework of the signal bandshape analysis technique taking into account the temperature variation of the lanthanide-induced shifts (LIS). The corresponding values of the free energy of activation ΔG≠298 were 68 kJ/mol for the SAP → TSAP transformation process, and 60 kJ/mol for the reverse transition (TSAP → SAP). In the series of [Ln(H2O)n(DOTA)]− complexes from praseodymium to lutetium, there is first a monotonic increase in the free energy of activation ΔG≠298 of the conformational transition up to Dy, then there is a gradual decrease in the activation barrier (as a manifestation of the gadolinium break effect).