Complexation of indole-3-acetic acid with iron(III): Influence of coordination on the pi-electronic system of the ligand

摘要

The iron(III) complex of indole-3-acetic acid (1) was prepared, and its physicochemical properties, mode of iron(III) coordination, and electronic structure were studied using UV/Vis, diffuse reflectance infrared Fourier transform I:DRIFT), and transmission Fe-57 Mossbauer spectroscopic techniques. The data obtained provide evidence that iron(III) is not only coordinated by the carboxylic O-donor atom, but also via the conjugated rr-electronic system of the pyrrole moiety involving both the non-shared electronic pair of the heteroatom and the C(2)-(:(3) double bond. Considering the well-known increased sensitivity of the pyrrole residue in indole derivatives to oxidation as compared to the benzene ring, as well as the formation of a triple complex (peroxidase-1-O-2) proposed for the enzymatic 1 oxidative degradation mechanism involving as a key step the Fe3+ --> Fe2+ transition in the enzyme form as discussed in literature, it is concluded that iron(III) coordination with 1 can influence the redox properties of the pyrrole ring by affecting its pi -electronic system. [References: 33]