INTERACTION OF THE FUNGAL METABOLITE HARZIANIC ACID WITH RAREEARTH CATIONS

Harzanic acid is a secondary metabolite belonging to the subgroup of dienoyl tetramic acids, essentially produced by fungi of Trichoderma genera (Figure 1). 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 (H2L) toward some rareearth elements (La3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Ho3+ and Tm3+) have been studied because these elements are emerging contaminants of soil and water bodies which destiny in the environment and effects on organisms is modulated by their interactions with natural ligands produced by bacteria, fungi and plants. Preliminary to chelating properties has been studying the acidbase behaviour of ligand conducted by UVVis spectrophotometry titrations. The measures 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 (< 106 M), The data collected and processed by numerical methods2 agree with the following protolysis constants: H2L + H2O ⇆ HL + H3O+ log KA1 = 4.08  0.02 HL + H2O ⇆ L2 + H3O+ log KA2 = 5.63  0.04 The study of coordination properties has been investigated using mass spectrometry, circular dichroism, UV–Vis spectrophotometry, and pH measurements. In particular, the experimental data obtained by UVVis titrations and elaborated by numerical procedure2, can be satisfactorily explained by assuming, for all investigated cations, the formation of a monocomplex (LnL+) as well as with a biscomplex (LnL2−). Since Gadolinium is the element that raises the most concern among lanthanide elements, its effects on organisms at different levels of biological organization were explored, in the presence and absence of harzianic acid. Results of ecotoxicological tests suggest that harzianic acid can decrease gadolinium biotoxicity, presumably because of complex formation with Gd3+.