CHELATING PROPERTIES OF THE FUNGAL METABOLITE HARZIANIC ACID TOWARD TOXIC HEAVY DIPOSITIVE CATIONS (Cd2+, Co2+, Ni2+, Pb2+)

Harzanic acid is a secondary metabolite belonging to the subgroup of dienoyl tetramic acids, essentially produced by fungi of Trichoderma genera. This metabolite is particular regarded for its valuable biological activities (e.g. antimicrobial, plant growth-promoting1) which are also related to its chelating properties. In this work, the complexing properties of harzianic acid toward some dipositive toxic heavy metals (Cd2+, Co2+, Ni2+ and Pb2+) have been studied because they might have a crucial role in the tolerance of plants growing in metalcontaminated soil. The measurements have been investigated at 25 °C in CH3OH/0.1 M NaClO4 (50/50 w/w) as ionic medium, in according to the low solubility of this metabolite in water (less than 106 M), using techniques as UV-Vis, potentiometry, CDUV as well as MS and NMR. In particular, the elaboration of UV-Vis data by numerical procedure2 has shown the presence of neutral and negatively charged coordination complexes where metal/harzianic acid ratio is 1:1 or 1:2 confirmed also by MS and NMR measures. In addiction by 1HNMR spectra analysis has been established the involvement in the coordination complexes of the C=O group of the amide and the external carbonyl groups of the ligand.