The interaction term between the solute and solvent in Eqn. 2 encompasses the classical van der Waals interactions between solute and solvent atoms. The potential of the combined protein and solvent, 𝑉 ss , is characterized by the ENZYMIX force field. This includes the polarization constraints from the Surface Constrained All-Atom Solvent (SCAAS) model and the Local Reaction Field (LRF) approach for long-range interactions. The reference system was immersed in a SCAAS sphere with a 18 Å radius to solvate the system. The surface-constrained water sphere was surrounded by a 2 Å surface of Langevin dipoles and then by a bulk. The nitrogen atom in the chromophore's amide functional group was taken as center of the water sphere.