Gentisate-1,2-dioxygenase activity by an iron(II)-phenanthroline complex

Abstract

In this work, we have synthesised and crystallographically characterized a mononuclear iron(II) complex, [ $$\hbox {Fe}(\hbox {phen})_{3}$$ ]( $$\hbox {NO}_{3})_{2}\cdot 2\hbox {H}_{2}\hbox {O}$$ (1) (phen = 1,10-phenanthroline). Single crystal X-ray diffraction (SXRD) analysis revealed that 1 crystallizes in monoclinic system with P $$1^{-}$$ space group. The lattice water molecules in 1 form a water-nitrate cluster, $$(\hbox {H}_{2}\hbox {O})_{2}^{\ldots }(\hbox {NO}_{3})_{2}$$ through strong H-bonding interaction mediated via iron(II) complex in a unique binding motif and provide additional stability to the compound in the solid state. This iron(II) complex is able to catalyze the cleavage of aromatic C-C linkage of 2,5-dihydroxybenzoic acid (Gentisic acid, GA) in oxygen environment. The iron(II) complex in the presence of two equivalent of triethylamine $$(\hbox {Et}_{3}\hbox {N})$$ binds with GA stoichiometrically in acetonitrile medium at $$25\,{^{\circ }}\hbox {C}$$ . Observation of GA-to-iron LMCT optical bands at 521 and 609 nm supports in situ generated iron-GA adduct in solution. This in situ generated iron-GA adduct reacts with molecular oxygen at the rate, $$k_{\mathrm{obs}} = 6.58 \times 10^{-3}\,\mathrm{min}^{-1}$$ in acetonitrile and affords exclusively 2-oxo-4-hydroxy-hepta-3,5-dienedioic acid. The incorporation of both the oxygen atoms of molecular oxygen in the bio-mimicking activity of gentisate-1,2-dioxygenase by this iron(II)-phenanthroline complex remain a rare example in scientific literature. A mononuclear iron(II) phenanthroline complex exhibits significant catalytic activity towards oxidative cleavage of 2,5-dihydroxy benzoic acid at a rate, $$\hbox {k}_{\mathrm{obs}}(\mathrm{min}^{-1}) = 6.58\times 10^{-3}$$ which predominantly produced 2-oxo-4-hydroxy-hepta-3,5-dienedioic acid upon addition of 2,5-dihydroxybenzoic acid in the presence of molecular oxygen.