Abstract
Kinetics and mechanisms of the reactions of naringenin, hesperetin, 3-hydroxychromone and 3-hydroxyflavone with a pseudo first order excess of iron(III) have been investigated in aqueous solution at 25°C and an ionic strength of 0.5 M. Mechanisms have been proposed which account satisfactorily for the kinetic data. These are consistent with a mechanism in which a 1 : 1 metal : ligand complex is formed in each case. For naringenin and hesperetin, the main reaction path involves reaction of the ligand with the monohydroxy species Fe(OH)2+, however the iron hydroxo dimer proved to be most reactive in the reactions with 3-hydroxyflavone and 3-hydroxychromone. The 1 : 1 iron(III) : naringenin and iron(III) : hesperetin complexes did not undergo subsequent electron-transfer based decomposition while both the iron(III) : 3-hydroxyflavone and iron(III) : 3-hydroxychromone complexes decompose rather slowly in an electron-transfer step. The reactions were monitored using UV–visible spectrophotometry. The suggested mechanisms and calculated rate constants are supported by calculations carried out using global analysis of time dependant spectra.
Acknowledgements
PR thanks the National University of Ireland, Galway, for a Fellowship and Galway County Council for a grant.