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

The relaxometric properties of two Gd(III) DTPA-like complexes (DTPA = diet hylenetriamine-N, N', N, N"'-pentaacetic acid) bearing different substituen ts for binding to human serum albumin (HSA) are compared. In spite of the s tructural differences of the recognition synthon and of the residual electr ic charge, the two chelates display an analogous binding affinity for the s erum 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)( 3)DTPA (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 h as been investigated.