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Studies on the Redox Characteristics of Ferrioxamine E
Author(s) -
Kazmi S. Arif,
Shorter A. Lee,
McArdle James V.,
Ashiq Uzma,
Jamal Rifat Ara
Publication year - 2010
Publication title -
chemistry and biodiversity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.427
H-Index - 70
eISSN - 1612-1880
pISSN - 1612-1872
DOI - 10.1002/cbdv.200900031
Subject(s) - chemistry , dithionite , reaction rate constant , redox , ionic strength , metal , gibbs free energy , inner sphere electron transfer , kinetics , solvent , ionic bonding , ionic radius , sodium dithionite , medicinal chemistry , inorganic chemistry , aqueous solution , thermodynamics , ion , organic chemistry , physics , quantum mechanics , enzyme
Thermodynamic parameters for the reduction of ferrioxamine E as calculated from redox potentials determined at four different temperatures were found to be Δ H ≠ =7.1±3.4 kJ mol −1 and Δ S ≠ =−146 J mol −1 K −1 . The negative entropy value is large, because the decrease in the charge at the metal center and an increase in its ionic radius force the structure of the complex to become less rigid and resemble the desferrisiderophore. The hydrophilic groups of the system are now (relatively more) available for solvent interaction. Thus, a large negative entropy change accompanies the reduction of the complex. Kinetics of reduction of ferrioxamine by V II , Cr II , Eu II , and dithionite were measured at different temperatures and by dithionite at different pH values. The Cr II and Eu II reactions proceed by an inner‐sphere mechanism and have second‐order rate constants at 25° of 1.37×10 4 and 1.23×10 5 M −1 s −1 , respectively. For the V II reduction, the corresponding rate constant was 1.89×10 3 M −1 s −1 . The activation parameters for the V II reduction were Δ H ≠ = 8.3 kJ mol −1 ; Δ S ≠ = −154 J mol −1 K −1 . These values are indicative of an outer‐sphere mechanism for V II reduction. The reduction by dithionite is half order in dithionite concentration indicating that SO $\rm{{_{2}^{-}}}$ . is the sole reducing species. log of reduction rate constants of different trihydroxamates by this reductant were correlated with their respective redox potentials, and the variation was found to be in approximate correspondence with the expectations of Marcus relationship.