Structure-related variable responses of calcium sensitive MRI probes

Abstract

A new series of Gd³⁺ complexes based on DO3A (GdL¹–GdL⁴) was synthesized and investigated. They possess side chains with different structures which determine their varying binding properties and response towards endogenous metal ions, measured by changes in the longitudinal relaxivity (r₁). GdL⁴ exhibits the highest selectivity toward Ca²⁺ in comparison to the other complexes, with up to a 63% increase of the r₁. GdL² and GdL³ also respond to different Ca²⁺ concentration ranges, however with a lower selectivity since the r₁ changes are also observed in the presence of other cations such as Mg²⁺, Zn²⁺ or Cu²⁺. Assessment of the hydration number (q) via luminescence lifetime measurements confirmed that the change in q is responsible for the r₁ response for all the complexes.