Spectroscopic Determination of Metal-Ligand Coordination by Biologically Active 2-Picolinehydroxamic Acid With Iron(III) and Oxidovanadium(IV) in Aqueous Solutions

The complexing properties of 2-picolinehydroxamic acid towards iron(III) as well as oxidovanadium(IV) were characterized in aqueous solutions by the UV-Vis spectrophotometric method. The speciation models have been confirmed and even extended by electrospray-ionization mass spectrometry (ESI-MS) studies. For both systems, mononuclear complexes were formed below a pH of 1 and coordination by {O,O-} chelation mode leading to the formation of five-membered rings was confirmed. The overall stability constant values were determined and compared with other similar systems, indicating more effective binding of the ligand by Fe(III) than VO(IV). The acidic medium of the reaction in the VO(IV) -2-picolinehydroxamic acid system prevented the oxidation of VO(IV) to V(V). 2-Picolinehydroxamic acid was chosen because of its previously evidenced biological properties. As a result of acidification, reversible dissociation of the complexes in both systems was observed, indicating the action of 2-picolinehydroxamic acid as a potential siderophore.