Metal ion size profoundly affects H3glyox chelate chemistry

The bisoxine hexadentate chelating ligand, H(3)glyox was investigated for its affinity for Mn2+, Cu2+ and Lu3+ ions; all three metal ions are relevant with applications in nuclear medicine and medicinal inorganic chemistry. The aqueous coordination chemistry and thermodynamic stability of all three metal complexes were thoroughly investigated by detailed DFT structure calculations and stability constant determination, by employing UV in-batch spectrophotometric titrations, giving pM values (pM = -log[Mn+](free) when [Mn+] = 1 mu M, [L] = 10 mu M at pH 7.4 and 25 degrees C) - pCu (25.2) > pLu (18.1) > pMn (12.0). DFT calculated structures revealed different geometries and coordination preferences of the three metal ions; notable was an inner sphere water molecule in the Mn2+ complex. H(3)glyox labels [Mn-52g]Mn2+, [Cu-64]Cu2+ and [Lu-177]Lu3+ at ambient conditions with apparent molar activities of 40 MBq mu mol(-1), 500 MBq mu mol(-1) and 25 GBq mu mol(-1), respectively. Collectively, these initial investigations provide insight into the effects of metal ion size and charge on the chelation with the hexadentate H(3)glyox and indicate that further investigations of the Mn2+-H(3)glyox complex in Mn-52g/55-based bimodal imaging might be worthwhile.

Automated summary

The study investigated the affinity of the bisoxine hexadentate chelating ligand H(3)glyox for Mn2+, Cu2+, and Lu3+ ions, revealing different thermodynamic stabilities of the three metal complexes with Cu2+ being the highest and Mn2+ the lowest. DFT calculations showed distinct geometries and coordination preferences of these metal ions in the complexes, with potential implications for further investigations in Mn-52g/55-based bimodal imaging.