pH-Responsive Relaxometric Behaviour of Coordination Polymer Nanoparticles Made of a Stable Macrocyclic Gadolinium Chelate

Graphical Abstract

An act of Gd: A coordination polymer has been synthesised by using a stable Gd^III chelate in order to prevent any fortuitous release of free lanthanide ion. The use of this chelate as a linker in the coordination polymer allows the enhancement of the relaxometric properties (maximum r₁=16.4 mm⁻¹ s⁻¹ at 10 MHz) and the pH responsiveness (Δr₁=108 % between pH 4 and 6.5), beyond the values obtained for the Gd^III chelate itself.

Abstract

Lanthanide-containing nanoscale particles have been widely explored for various biomedical purposes, however, they are often prone to metal leaching. Here we have created a new coordination polymer (CP) by applying, for the first time, a stable Gd^III chelate as building block in order to prevent any fortuitous release of free lanthanide(III) ion. The use of the Gd-DOTA-4AmP complex as a design element in the CP allows not only for enhanced relaxometric properties (maximum r₁=16.4 mm⁻¹ s⁻¹ at 10 MHz), but also for a pH responsiveness (Δr₁=108 % between pH 4 and 6.5), beyond the values obtained for the low molecular weight Gd-DOTA-4AmP itself. The CP can be miniaturised to the nanoscale to form colloids that are stable in physiological saline solution and in cell culture media and does not show cytotoxicity.