Critical Behavior of Iron(III) with a Typical Catecholate Siderophore

Siderophores are ligands that serve as iron scavengers or iron chelators, which hinder the absorption of iron in the body; tannic acid is one of them. since a tannic acid molecule has 8 gallic acid groups, it can bind 1-4 fe(lil) ions, depending upon ligan~ concentration. ph 3,.4, 5, 8 and 10 were selected for this study. the xrnax and m:l molar ratio of the complexes vanes with ph, as well as with ligand concentration. for low ligand concentration at ph 3, 4 and 5, the maximum absorbance of the complex was found at 650 nm, while, at ph 8 and 10, 500 nm was the arnax. for high ligand concentration, ph 550 nm was the xrnax. stability constant values of iron(lil) tannic acid complexes were measured spectrophotometrically using the mole ratio method, as well as the slope ratio method, potentiometrically. the experimental results of ph titrations were treated by program best. the f3 values obtained by these methods were compared. stability constant values were found to be 103 , 108 and 1016 for ml, m2l and m4l, respectively.