Binding Free Energy and Binding Affinity: Understanding the Equation

The relationship between binding free energy (ΔG) and binding affinity (K) can be described using the following equation:

ΔG = -RT ln(K)

where:

• ΔG is the binding free energy (measured in energy units, such as Joules or calories),
• R is the gas constant (8.314 J/(mol·K) or 1.987 cal/(mol·K)),
• T is the temperature in Kelvin, and
• ln denotes the natural logarithm.

This equation is known as the Gibbs free energy equation and is derived from thermodynamics principles. It relates the equilibrium constant (K) of a reaction to the change in Gibbs free energy (ΔG) associated with that reaction. In the context of binding affinity, the equation quantifies the relationship between the strength of the interaction between a ligand and a receptor (binding affinity) and the corresponding change in free energy.