Magnetic susceptibility of Mn(III) complexes of hydroxamate siderophores

• Hydroxamate siderophore complexation promotes oxidation of Mn(II) to Mn(III) by O2.
• Magnetic susceptibility establishes Mn(III) in the Mn(III)-siderophore complexes.
• Multiple Mn(III) putrebactin complexes are formed.

The hydroxamate siderophores putrebactin, desferrioxamine B, and desferrioxamine E bind Mn(II) and promote the air oxidation of Mn(II) to Mn(III) at pH > 7.1. The magnetic susceptibility of the manganese complexes were determined by the Evans method and the stoichiometry was probed with electrospray ionization mass spectrometry (ESIMS). The room temperature magnetic moments (μeff) for the manganese complexes of desferrioxamines B and E were 4.85 BM and 4.84 BM, respectively, consistent with a high spin, d4, Mn(III) electronic configuration. The manganese complex of putrebactin had a magnetic moment of 4.98 BM, consistent with incomplete oxidation of Mn(II), as confirmed by X band EPR spectroscopy. Mass spectra of the Mn(III) desferrioxamine B and E complexes showed complexes at m/z 613.26 and 653.26, respectively, consistent with 1:1 complexation. Mass spectral peaks for manganese putrebactin at m/z 797.31 and 1221.41 corresponds to 1:2 and 2:3 Mn:putrebactin complexation. This study directly confirms the Mn(III) oxidation state in hydroxamate siderophore complexes.

The hydroxamate siderophores putrebactin, desferrioxamine B, and desferrioxamine E bind Mn(II) and promote the air oxidation of Mn(II) to Mn(III) at pH > 7.1. The magnetic susceptibility of these green manganese complexes establishes the Mn(III) oxidation state in a high spin, d4, electronic configuration.Figure optionsDownload as PowerPoint slide