are binding free energy and binding affinty physically equivilant and interchangeable

No, binding free energy and binding affinity are not physically equivalent or interchangeable terms.

Binding affinity refers to the strength of the interaction between a ligand (such as a drug or molecule) and its target (such as a receptor or enzyme). It represents the ability of the ligand to bind to the target and form a stable complex.

On the other hand, binding free energy is a thermodynamic quantity that measures the change in free energy when a ligand binds to its target. It takes into account factors such as enthalpy (heat) and entropy (disorder) changes during the binding process.

While both binding affinity and binding free energy are related to the strength of the ligand-target interaction, they represent different aspects of this interaction. Binding affinity is a measure of the strength of the interaction, while binding free energy is a measure of the thermodynamic stability of the ligand-target complex.