A perspective into ligand-receptor affinities using complex numbers.

The binding of ligands by a receptor can be expressed in an equation derived by a thermodynamic stoichiometric approach in which the stoichiometric equilibrium constants are all positive and real. An alternative binding equation can be derived algebraically in which the equilibrium constants can have values that are complex numbers. Some consequences of this situation are explored, and numerical values of the ghost equilibrium constants are evaluated for a number of ligand-receptor complexes.