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Iron speciation at physiological pH in media containing ascorbate and oxygen

Published online by Cambridge University Press:  09 March 2007

Clare Dorey ,
Chris Cooper ,
Dominic P. E. Dickson ,
John F. Gibson ,
Robert J. Simpson  and
Timothy J. Peters
Clare Dorey
Affiliation:
Division of Clinical Cell Biology, MRC Clinical Research Centre, Watford Rd, Harrow, Middlesex
Chris Cooper
Affiliation:
Division of Biomolecular Sciences, King's College, University of London, Campden Hill Rd, London W8 7AH
Dominic P. E. Dickson
Affiliation:
Department of Physics, University of Liverpool, Liverpool L69 3BX
John F. Gibson
Affiliation:
Department of Chemistry, Imperial College, London SW7 2AY
Robert J. Simpson
Affiliation:
Department of Clinical Biochemistry, King's College School of Medicine and Dentistry, Bessemer Rd, London SE5 9PJ
Timothy J. Peters
Affiliation:
Department of Clinical Biochemistry, King's College School of Medicine and Dentistry, Bessemer Rd, London SE5 9PJ
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Abstract

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The stability of iron ascorbate solutions was investigated, under both anaerobic and aerobic conditions, with the Fe2+ and Fe3+ indicators, respectively ferrozine and mimosine, at different pH values. The species present under the differing conditions were investigated by electron paramagnetic resonance (EPR) and Mössbauer spectroscopy and by gel-filtration chromatography. At physiological pH (6·8–7·4) iron ascorbate solutions rapidly form mononuclear chelatable Fe3+ species as reflected by indicator studies and EPR. Mössbauer spectroscopy fails to detect any Fe2+ species. EPR studies show a time-dependent decrease in rhombic Fe3+, particularly in oxygenated buffers, consistent with a conversion to polynuclear Fe. O2 uptake studies show that the conversion of Fe2+ to Fe3+ in Fe–ascorbate solutions at pH > 7·0 was accompanied by rapid O2 consumption but preceded depletion of ascorbate. Addition of high concentrations of mannitol (50–200 mM) reduces the O2 consumption and partly stabilizes the rapidly chelatable Fe form. Gel filtration studies show that the oxidation of Fe–ascorbate solutions at pH 7·4 is accompanied by an increase in the apparent relative molecular mass of the Fe, presumably due to Fe polymer formation. These studies indicate the inherent instability of Fe–ascorbate solutions above neutral pH and clearly have important implications in the use of ascorbate in studies of Fe physiology.

Keywords

IronAscorbate solutionsSpeciation of iron
Type
Iron Intake and Status
Information
British Journal of Nutrition , Volume 70 , Issue 1 , July 1993 , pp. 157 - 169
Copyright
Copyright © The Nutrition Society 1993

References

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