Reaction of Hydroxyurea with Iron(III): Formation of Mono- and Bis(hydoxyureato)-iron(III) Complexes

Nikola Kujundžić*, Biljana Nigović and Maja Bival

Faculty of Pharmacy and Biochemistry, University of Zagreb, 10 000 Zagreb, Croatia
* Corresponding author: E-mail: nkujundzic@pharma.hr,
fax: +385-1-4856-201

Abstract
Complex formation reaction between iron(III) and hydroxyurea in acidic aqueous and dimethylformamide solutions were studied by UV/VIS spectroscopy, cyclic voltammetry and EPR spectroscopy. Under conditions of an excess of hydroxyurea over iron(III, mono- and bis(hydoxyureato)iron(III) complexes are formed. The complexes quickly decompose in aqueous solutions, but are relatively stable in dimethylformamide. Equilibrium quotients for the formation of the mono- and bis- complexes in acidic aqueous solution at 25 °C and I = 2.0 mol dm^–3 (maintained by NaClO₄) are found to be 0.91 and 0.15, respectively. The kinetic results suggest that the formation of bis complex is much faster process. The cyclic voltammogram exhibits one well-defined quasi-reversible cathodic peak at +0.29 V in dimethylformamide. The redox potential was shifted to less positive values by 140 mV compared to the solvated iron(III) ion due to electron donating effect of ligand molecule. EPR spectra of the radical formed in the solution show presence of the radical species H₂N–CO–NHO^• suggesting the same degradation pathway found in the mono(hydoxyureato)iron(III) complex.

Keywords: Hydroxyurea; Mono- and Bis(hydroxyureato)iron(III) complex; Complex stability; Hydroxyurea radical