Kinetics of reduction of ferrichrome and ferrichrome A by chromium(II), europium(II), vanadium(II), and dithionite

Kazmi, Syed Jamil Hasan; Shorter, Andrew L.; McArdle, James V.

doi:10.1021/ic00193a045

Cited by 10 publications

(7 citation statements)

References 3 publications

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“…These authors argue that the inner sphere mechanism is limited by slow water exchange rates on V(II) and Eu(II), but not for Cr(II), which has rapid solvent exchange rates due to JahnTeller effects. Similar observations were made in the case of ferrichrome (Kazmi et al 1984). In the case of ferrichrome A, the reduction of the iron(III) complex by Cr(II) proceeds by an outer-sphere mechanism due to the steric influence of the bulkier pendant arms.…”

Section: Siderophore Electron Transfer Reactions: Kinetics and Mechanismsupporting

confidence: 77%

The redox hypothesis in siderophore-mediated iron uptake

Harrington

Crumbliss

2009

Biometals

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Section: Siderophore Electron Transfer Reactions: Kinetics and Mechanismsupporting

confidence: 77%

The redox hypothesis in siderophore-mediated iron uptake

Harrington

Crumbliss

2009

Biometals

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“…is the effective reducing species rather than the dithionite ion [25]. Similar observations were made earlier for reductions of ferrioxamine B [26], ferrichrome, and ferrichrome A [24]. The proposed mechanism for the reduction of ferrioxamine E by dithionite is similar, i.e., …”

Section: Kinetics Of Reduction Reduction By M Iisupporting

confidence: 77%

“…. This is the same rate law as derived for reduction of other hexadentate siderophore complexes and for other Fe III -trihydroxamate complexes by the same reductant [24] [26]. However, for the tris(acetohydroxamato) complex of Fe III , Fe(AHA) 3 , a twoterm rate law is obtained wherein one term has a first-order dependence on dithionite concentration and the other term has a half-order dependence on dithionite concentration.…”

Section: Kinetics Of Reduction Reduction By M Iisupporting

confidence: 71%

“…Results for reduction by M II ¼ V II , Cr II , and Eu II are summarized in Tables 2, 3, and 4, respectively. In all cases, the intercepts of plots of k obs vs. reductant concentration had nearly zero intercept and no saturation kinetics features as seen in the earlier study with ferrichrome [24]. Under similar conditions, the rates of reduction by V II were the slowest among the three divalent metal-ion reductants used in this study, while the rates of reduction by Eu II were the fastest.…”

Section: Kinetics Of Reduction Reduction By M Iisupporting

confidence: 69%

“…Stopped-Flow Measurements. Methods applied were similar to those described in earlier studies used for ferrioxamine B [26], and ferrichrome and ferrichrome A [24]. Initial studies on the reduction of ferrioxamine E by Cr II , V II , and Eu II were studied on a stopped-flow instrument (DURRAM) assembled inside an inert atmosphere chamber.…”

Section: Experimental Partmentioning

confidence: 99%

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Studies on the Redox Characteristics of Ferrioxamine E

Kazmi

Shorter

McArdle³

et al. 2010

Chemistry & Biodiversity

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Thermodynamic parameters for the reduction of ferrioxamine E as calculated from redox potentials determined at four different temperatures were found to be DeltaH( not equal)=7.1+/-3.4 kJ mol(-1) and DeltaS( not equal)=-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 degrees of 1.37x10(4) and 1.23x10(5) M(-1) s(-1), respectively. For the V(II) reduction, the corresponding rate constant was 1.89x10(3) M(-1) s(-1). The activation parameters for the V(II) reduction were DeltaH( not equal) = 8.3 kJ mol(-1); DeltaS( not equal) =-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(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.

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