| Summary: | Harzianic acid is a secondary metabolite of <i>Trichoderma</i>, structurally belonging to the dienyltetramic acid subgroup of the tetramic acids. Biological activities of harzianic acid are of great interest for its antimicrobial and plant growth-promoting activities, which might be related to its chelating properties. In the present work harzianic acid, isolated from cultures of a strain of <i>Trichoderma pleuroticola</i> associated to the gastropod <i>Melarhaphe neritoides</i>, was studied as a complexant agent of a number of biologically relevant transition metals (i.e., Zn<sup>2+</sup>, Fe<sup>2+</sup>, Cu<sup>2+</sup>, and Mn<sup>2+</sup>), using UV-VIS, potentiometry, MS and NMR techniques. Our findings show the coordination capacity of harzianic acid toward the above cations through the formation of neutral or charged complexes in a variable ratio depending on the metal and pH conditions.
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