This article is about sequestering agents parsley root general. For chemicals used in food processing, see Sequestrant.

Chelation is a type of bonding of ions and molecules to metal ions. Chelation results in the formation of a five-membered CuC2N2 ring. N bonds are approximately the same in the two reactions. The thermodynamic approach to describing the chelate effect considers the equilibrium constant for the reaction: the larger the equilibrium constant, the higher the concentration of the complex. Electrical charges have been omitted for simplicity of notation. The square brackets indicate concentration, and the subscripts to the stability constants, β, indicate the stoichiometry of the complex.

R is the gas constant and T is the temperature in kelvins. Since the enthalpy should be approximately the same for the two reactions, the difference between the two stability constants is due to the effects of entropy. These data confirm that the enthalpy changes are approximately equal for the two reactions and that the main reason for the greater stability of the chelate complex is the entropy term, which is much less unfavorable. In general it is difficult to account precisely for thermodynamic values in terms of changes in solution at the molecular level, but it is clear that the chelate effect is predominantly an effect of entropy. Numerous biomolecules exhibit the ability to dissolve certain metal cations. Thus, proteins, polysaccharides, and polynucleic acids are excellent polydentate ligands for many metal ions. Virtually all metalloenzymes feature metals that are chelated, usually to peptides or cofactors and prosthetic groups.