The kinetics and mechanisms of the reactions of iron(III) with naringenin, hesperetin, 3-hydroxychromone and 3-hydroxyflavone. A comparison of the coordination power of 3-hydroxychromone and 5-hydroxychromone

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.

Keywords:

• Kinetics
• Mechanisms
• Flavonoids
• Electron transfer
• Hydroxychromone
• Iron

Acknowledgements

PR thanks the National University of Ireland, Galway, for a Fellowship and Galway County Council for a grant.