<p>A growing problem in agriculture is the increasing resistance of bacteria to antibiotics used in animal feed. The strong antibacterial activity of tannins, plant polyphenols that can chelate metal ions, makes them one of the potential antibiotic substitutes. The present study investigates the chelation of Fe(II) ions by roburins A and D, ellagitannins isolated from aqueous chestnut wood extract, which is currently used as an antibacterial additive in animal feed. A combination of previously determined stoichiometries and the microscopic protolytic equilibrium of ellagitannins enabled the development of a model describing the contribution of the structural elements NHTP and HHDP to Fe(II) chelation. The parameters obtained from the fit to the experimental Job plots were used to calculate the model Job curves for the roburins. The good agreement between the experimental and model curves confirms the suitability of the model and shows its predictive power in determining the binding stoichiometries and the degree of Fe(II) chelation.</p>