TANDEM MASS-SPECTROMETRIC INVESTIGATION OF THE PHYTOSIDEROPHORES MUGINEIC ACID, DEOXYMUGINEIC ACID AND NICOTIANAMINE

Phytosiderophores are low molecular mass iron chelating compounds that are secreted from the roots of graminaceous plants to allow iron solubilization and transport. To date no mass spectrometric investigation has been carried out on these novel structures or their metal complexes. This report describes a detailed analysis of the collision-induced dissociation (CID) spectra of mugineic acid, deoxymugineic acid, and nicotianamine in both positive and negative ion modes obtained using fast atom bombardment mass spectrometry in conjunction with tandem mass spectrometry. The CID spectra in the positive ion mode are dominated by loss of neutral fragments in the higher mass region, whereas in the lower mass region, charge retention on the azetidine ring is especially prominent. The negative ion CID spectra are more complicated than the positive ion spectra, but as the three structures are closely related this simplifies the interpretation. Mass spectrometric analysis of the Fe-III complex of mugineic acid showed that the complex underwent a one-electron reduction under the fast atom bombardment measurement conditions.