Question

EDTA is a widely used food preservative. One reason that food spoils is that proteases begin to break down proteins within the food. Often proteases rely on metal ions to function properly. Hypothesize why EDTA is used as a preservative instead of another ligand such as a monodentate ligand.

Answer 1

Experimentally, it is observed that metal complexes of polydentate ligands(like EDTA) are significantly more stable than the corresponding complexes of chemically similar monodentate ligands; this increase in stability is called the chelate effect.The stability of a chelate complex depends on the size of the chelate rings. For ligands with a flexible organic backbone like ethylenediamine, complexes that contain five-membered chelate rings, which have almost no strain, are significantly more stable than complexes with six-membered chelate rings, which are in turn much more stable than complexes with four- or seven-membered rings.The complex resulting from coordination with the chelating ligand is much more thermodynamically stable.