Association Constant
The equilibrium constant for the combination of two species into a single associated entity, the reciprocal of the dissociation constant.
Formula / equation
Ka = 1 / Kd
Unit
L/mol
In depth
Association constants are the natural way to express binding strength, with larger values meaning tighter binding. They are used throughout supramolecular chemistry and biochemistry, where they quantify how strongly a host binds a guest or an antibody binds its antigen.
Examples in the real world
The biotin–streptavidin pair has an association constant near 10¹⁵ L/mol, among the strongest known.