Contrast agents for magnetic resonance angiographic applications: 1H and 17O NMR relaxometric investigations of two gadulinium(III) DTPA-like chelates endowed with high binding affinity to human serum albumin

The relaxometric properties of two Gd(III)DTPA-like complexes (DTPA = diethylenetriamine-N,N,N,N--pentaacetic acid) bearing different substituents for binding to human serum albumin (HSA) are compared. In spite of the structural differences of the recognition synthon and of the residual electric charge, the two chelates display an analogous binding affinity for the serum protein. Upon formation of the adducts with HSA, the exchange rates of the coordinated water appear slowed down by an amount corresponding to ca. 50% of the rates found for the free complexes. The relaxivity of [Gd(BOM)3DTPA (H2O)]2 - is significantly higher than that of MS-325 either in the free complex or in the macromolecular adduct. Finally, the effect of pH on the stability of the HSA adducts and on the values of their relaxivities has been investigated.