Investigation of the interaction of iron(iii) complexes with dAMP by ESI-MS, MALDI-MS and potentiometric titration: insights into synthetic nuclease behavior

Abstract

We report herein the characterization by electrospray ionization (ESI) mass spectrometry (MS), matrix assisted laser desorption ionization (MALDI-MS) and potentiometric titration of three iron(III) compounds: [Fe^III(HPClNOL)Cl₂]·NO₃ (1), [Cl(HPClNOL)Fe^III-(μ-O)-Fe^III(HPClNOL)Cl]·Cl₂·H₂O (2) and [(SO₄)(HPClNOL)Fe^III-(μ-O)-Fe^III(HPClNOL)(SO₄)]·6H₂O (3), where HPClNOL= 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol). Despite the fact that the compounds have distinct structures in solid state and non-buffered solution, all compounds present similar ESI and MALDI mass spectra in a buffered medium (pH 7.0). At this pH, the species [(PClNOL)Fe^III-(μ-O)-Fe^III(PClNOL)]²⁺ (m/z 354) was observed for all the compounds under investigation. Potentiometric titration confirms a similar behavior for all compounds, indicating that the dihydroxo form [(OH)(HPClNOL)Fe^III-(μ-O)-Fe^III(HPClNOL)(OH)]²⁺ is the major species at pH 7.0, for all the compounds. The products of the interaction between compounds (1), (2) and (3) and dAMP (2′-deoxyadenosine-5′-monophosphate) in a buffered medium (pH 7.0) were identified by MALDI-MS/MS. The fragmentation data obtained by MS/MS allow one to identify the nature of the interaction between the iron(III) compounds and dAMP, revealing the direct interaction between the iron center and phosphate groups.