Equilibrium Fe isotope fractionation between inorganic aqueous Fe(III) and the siderophore complex, Fe(III)-desferrioxamine B

摘要: Abstract In oxic oceans, most of the dissolved iron (Fe) exists as complexes with siderophore-like, strongly coordinating organic ligands. Thus, isotope composition little amount free inorganic Fe that is available for precipitation and preservation in geological record may largely be controlled by fractionation between complexed iron. We have determined equilibrium induced ligand activity experiments solutions having co-existing Fe(III) species siderophore complexes, Fe-desferrioxamine B (at pH 2). The two differently pools were separated addition Na 2 CO 3 , which led to immediate without causing significant dissociation complexes. Experiments using enriched 57 tracer showed isotopic equilibration Fe-labelled isotopically “normal” siderophore-bound was rapid during first few seconds then became slower. Consequently, data fitted poorly second order reaction equations. However, a two-stage reaction, fit perfectly equation slower stage, indicating approximately 40% re-equilibration take place separation pools. To further test if leads experimental artefacts, determined. Assuming Rayleigh-type precipitation, this experiment yielded an factor α 56 solution-solid  = 1.00027. Calculations based on these results indicate unlikely significantly affect our inorganically organically Fe. determine bound Fe(III), variable proportions carried out at 25 °C. Irrespective proportion Fe, factors within uncertainty, yielding average factor, Δ DFOB-inorg 0.60 ± 0.15‰. ligands fractionate isotopes nature. likely important oxic, Fe(III)-bearing environments, such soils rivers, may, example, control marine Fe–Mn crusts.