A highly stable l-alanine-based mono(aquated) Mn(ii) complex as a T1-weighted MRI contrast agent

Abstract

The synthesized lithium (S)-6,6′-(1-carboxyethylazanediyl)bis(methylene)dipicolinate (Li₃cbda) is a new chiral, alanine-based ligand bearing two picolinate functionalities. The trianionic form of the ligand [(cbda)³⁻] constitutes a seven-coordinate, water-soluble, pentagonal bipyramidal Mn(II) complex (1). The structural analysis reveals the presence of a water coordinating site in the complex. The complex is thermodynamically very stable, and the stability is not affected by the presence of physiological anions (HCO₃⁻, PO₄³⁻, and F⁻). The pH of the medium exerts a small effect on the stability of the complex. The r₁ relaxivity of 3.02 mM⁻¹ s⁻¹ is exhibited by the complex at 1.41 T, pH ∼7.4, and 25 °C. Phantom images obtained via a clinical MRI BRIVO MR355 system established concentration-dependent signal enhancement by the complex. The cytotoxicity test confirmed complex 1 as a biocompatible potential T₁-weighted MRI contrast agent.