Dear Dhirar Ben Salem, let me cite, please: "For n > 1,

Eq. (3) may be identified as describing a cooperative reaction

between a sorption site and n sorbate molecules, such that b is

the equilibrium constant of this reaction. In this case, Eq. (3) coincides

with the Hill model characterizing cooperative interactions

of ligand molecules with a macromolecule (Cantor and Schimmel,

1980)."Article Sorption Interactions of Organic Compounds with Soils Affect...