Dispersion dominated halogen-pi interactions: energies and locations of minima

The interactions of halogen atoms with aromatic pi-systems can be crucial for structural stability and ligand binding. However, many aspects of the nature and energetics of these interactions remain elusive. Therefore, we designed model systems mimicking the T-shaped complex of chloro- and bromobenzene with tyrosine as found, e.g., in serine protease-inhibitor complexes. Three dimensional potential energy surfaces (3D-PES) were calculated at a high level of theory, up to CCSD(T). On these 3D-PES the exact location of the minima and, even more important, the shape of favorable interaction regions were determined. We show that the height of the halogen atom above the tyrosine-ring is decisive, while the lateral position is of minor influence. Finally, a truncated harmonic potential is developed to modify the Amber/GAFF force field to shift the locations of the minima to the correct regions.