Common Photo-oxidative Decarboxylation Mechanism in Iron Hydroxy Carboxylate Complexes

Photochemical oxidation of dissolved organic matter isa crucialcomponent of carbon cycling in surface waters. Photo-oxidation ofiron(III)-carboxylate complexes is of particular interest becausecomplexation with iron(III) can sensitize this functional group tophotodecarboxylation. The photo-oxidation mechanism of ferrioxalatehas been extensively characterized, but it is unclear whether themechanism or timing is similar for other more complex carboxylates.In this study, we use time-resolved infrared spectroscopy to demonstratethat Fe(III)-citrate, an aliphatic carboxylate, and Fe(III)-salicylate,an aromatic carboxylate, follow the same photo-oxidation kineticsas ferrioxalate. Hence the data suggest a common mechanism for decarboxylationof iron hydroxy carbonates. Differences in the CO2 yieldwithin 50 ps are qualitatively similar to the long-time-scale quantumyield for Fe(II) production.

Automated summary

The photochemical oxidation of dissolved organic matter plays an important role in the carbon cycling in surface waters. The photo-oxidation of iron(III)-carboxylate complexes is of interest due to its sensitization to photodecarboxylation. This study demonstrates that Fe(III)-citrate and Fe(III)-salicylate follow the same photo-oxidation kinetics as ferrioxalate, suggesting a common mechanism for decarboxylation of iron hydroxy carbonates. The differences in CO2 yield within 50 ps are similar to the long-time-scale quantum yield for Fe(II) production.