Electrospray Mass Spectrometry Study of 1:1 Ferric Dihydroxamates

In this communication, we report an early example1-8 of the use of electrospray mass spectrometry (ESMS) to probe the solution structure of transition metal complexes.Iron hydroxamic acid complexes are important due to their relationship to siderophore-mediated iron transport.9Dihydroxamic acids, such as the siderophore rhodotorulic acid and its synthetic models,10-14 form 1:1 complexes with iron(III) at low pH.Since this species is an intermediate in the ligand exchange pathway of natural and model ferric dihydroxamates, the elucidation of the 1:1 complex as monomer a or dimer b is an important mechanistic consid- eration.I n <y 1 a: monomer b: dimer Acid-dependent kinetic studies on the dissociation of the 1:1 complexes (R = methyl, = 2-8) gave strong, though not conclusive, evidence that for < 6, the complex was better formulated as the dimer, b, while the monomer, a, predominates