Interaction of ATP with a Gd3+ complex employed as paramagnetic contrast agent in NMR imaging

The interaction of adenosine S-triphosphate (ATP) and tripolyphosphate (TPP) with the complex GdBOPTA(2-), a contrast agent for NMR imaging (international nonproprietary name: gadobenate), has been studied by,means of potentiometric (pH metric) titrations in 0.15 mol dm(-3) NaCl at. 298.1 K. Both ATP and TPP interact with,GdBOPTA2- forming mono- to penta-protonated mixed-ligand complexes. The equilibrium constants for the formation of such mixed-ligand complexes, as well as for the formation Gd3+ complexes with ATP and TPP have been determined. The results indicate that around physiological pH (7.4), under the experimental conditions employed ([Gd3+ ] = [BOPTA]:= [ATP] = 1 x 10 (-3) mol dm(-3) , 298.1 K), only a very small amount of GdBOPTA(2) - (< 5%). is bound to the nucleotide. Relaxation experiments demonstrated that the interaction of ATP with GdBOPTA2 - in vitro does not compromise the, effectiveness of this complex as paramagnetic contrast agent for NMR imaging, nor cause degradation of the complex fora long time: (C) 1999 Elsevier Science S.A. All rights reserved.