Unexpectedly large change of water exchange rate and mechanism on Ln(DTPA-BMA)(H2O) complexes along the lanthanide(III) series

The water exchange rate and the relaxivity of the complex (Ln{DTPA-BMA}{H2O}) where Ln = Nd, Eu, Tb, Dy and Ho and DTPA-BMA = 1,7-bis(N-methylcarbamoyl methyl)-1,4,7-triazaheptane-1,4,7-triacetate or diethylenetriaminepentaacetate-bis(methylamide), depend on the lanthanide size. The rate and mechanism of the water exchange is characterized by the steric crowding of the water binding site.