Determination of conditional stability constants of metal–Trichoderma viride complexes by the potentiometric titration method

In this paper the binding ability of functional groups present in the cell walls of an ubiquitous soil fungus, Trichoderma viride Pers.: Fr., towards some divalent heavy metals, Cd, Co, Cu, Pb and Zn, was studied. Processing the data from potentiometric titrations of T. viride by the McCallum, Midgley and Gran’s combined methods, the surface of the cell wall was characterised in terms of functional group total acidity, distinguishing among strong, weak and very weak acidity. The dissociation constant values of weak and very weak acid, pKa1 and pKa2, respectively, were graphically determined using the Henderson-Hasselbach equation. Titration data of T. viride in the presence of metal were processed with the Bjerrum’s method as adapted by Gregor for determining the conditional stability constants of metal complexes with synthetic polyelectrolytes in terms of log K1 and log K2. Here has been used for 1:1 and 1:2 metal-T. viride complexes, respectively.