H-1 NMR relaxivity of aqueous suspensions of titanium dioxide nanoparticles coated with a gadolinium(III) chelate of a DOTA-monoamide with a phenylphosphonate pendant arm

A new efficient and easy method to anchor Gd(III) chelates onto a TiO2 surface in order to prepare a nanoparticulate T-1 MRI contrast agent is reported. For this purpose, a new ligand, DOTAPP, a DOTA-monoamide derivative containing a phenylphosphonic acid function in the amide side chain, was synthesized. As expected, its Ln(III) complexes exhibit structure analogy to the Ln(III) complexes of DOTA with one water molecule bound in the apical position. The Gd(III)-DOTAPP complex shows similar relaxometric properties as Gd(III) complexes of other DOTA-monoamides. Gd(III)-DOTAPP was anchored onto the surface of nanocrystalline TiO2 via its phosphonate moiety. The oxide surface is completely covered by the complexes and a strong interaction between the TiO2 surface and the phosphonate group results in stable chemisorption. The millimolar relaxivity (r(1)) of the Gd(III)DOTAPP complex adsorbed on the surface is substantially higher than that of the free (non-anchored) complex.