Gadolinium nicotinate clusters as potential MRI contrast agents

Abstract

Three multinuclear gadolinium(III) clusters containing the nicotinate (nic) ligand, [Gd₂(nic)₆(H₂O)₄] (1), [Gd₄(μ₃-OH)₄(Hnic)₅(H₂O)₁₂](ClO₄)₈·7H₂O (2), and [Gd₄(μ₃-OH)₄(nic)₆(H₂O)₆]₂(ClO₄)₄·4H₂O (3) were synthesized and characterized. Potential applications of these Gd(III) clusters as high-field magnetic resonance imaging (MRI) contrast agents were evaluated. The longitudinal relaxivities (r₁) of 1–3 in water at 7 T were determined to be 10.45 ± 0.16, 9.28 ± 0.06, and 2.04 ± 0.29 mM⁻¹ s⁻¹ on a per Gd ion basis, respectively. In 1% agarose solution, the r₁ values increased slightly to 10.37 ± 0.31, 10.74 ± 0.11, and 4.60 ± 0.29 mM⁻¹ s⁻¹ for 1–3, respectively. The ability to tune the number of inner-sphere water molecules, cluster sizes, organic ligands, and Gd coordination modes in such Gd(III) clusters provide interesting opportunities to further enhance the MR relaxivities for potential MRI applications.