Binding Free Energy vs. Binding Affinity: Are They the Same?

No, binding free energy and binding affinity are not physically equivalent terms. They represent different concepts in the context of molecular interactions.

Binding affinity refers to the strength of the interaction between a ligand (small molecule) and a target molecule (e.g., protein). It quantifies how tightly the ligand binds to the target molecule. Higher binding affinity indicates a stronger interaction.

On the other hand, binding free energy is a thermodynamic concept that measures the change in free energy associated with the formation of a complex between a ligand and a target molecule. It takes into account various factors such as enthalpy (heat) and entropy (disorder) changes. Binding free energy provides information about the stability and feasibility of the ligand-target complex formation.

While binding affinity and binding free energy are related, they are not synonymous. Binding affinity is a measure of the strength of interaction, whereas binding free energy takes into account the thermodynamic aspects of the binding process.