Deciphering the Metal Speciation in Low-Molecular-Weight Complexes by IMS-MS: Application to the Detection of Manganese Superoxide Dismutase Mimics in Cell Lysates

The detection and quantification of exogenous metal complexes are crucial to understanding their activity in intricate biological media. Mn-II complexes are difficult to detect and quantify because of low association constants, and high lability. The superoxide dismutase (SOD) mimic (or mimetic) labelled Mn1 is based on a 1,2-di-aminoethane functionalized with imidazole and phenolate and has good intrinsic anti-superoxide, antioxidant and anti-inflammatory activities in lipopolysaccharide (LPS)-activated intestinal epithelial HT29-MD2 cells, similar to that of its propylated analogue labelled Mn1P. Ion mobility spectrometry-mass spectrometry (IMS-MS) is a powerful technique for separating low molecular weight (LMW) metal complexes and can even separate complexes with the same ligand but bound to different divalent metal cations with similar ionic radii. We demonstrated the intracellular presence of the Mn1 and Mn1P complexes, at least partly intact, in lysates of cells incubated with the complexes and estimated the intracellular Mn1P concentration using a Co-C-13(6) analogue.