Non-bonded interactions for protein-ligand binding

Weak non-bonded interactions are of fundamental importance for molecular recognition in all chemical and biological systems. As the detailed study of non-covalent interactions in biological and complex chemical systems is often complicated by arrays of interactions featuring multiple molecular contacts and solvent molecules, these interactions have been mostly investigated so far by computational and crystallographic studies. In the last two decades, some unimolecular machines called „molecular torsion balances“ have emerged as a reliable model system to study non-covalent interactions, since they exhibit minimal entropic penalty associated with the intermolecular association and no other perturbations influence the overall stability. These molecular balances provide a very accurate and sensitive measure of their intramolecular interactions via their influence on the folded-unfolded conformational equilibrium. The subtle non-bonded interactions can thus be quantified in solution by determining the relative population of each distinct conformation using NMR spectroscopy. In our recent study we successfully quantified a series of halogen-aryl π interactions in solution using molecular balances (Sun et al., Angew. Chem. Int. Ed., 2017). For the first time, we demonstrated the feasibility of employing anisotropic NMR data in studying the geometry of the interaction in solution. The gained knowledge is highly important to understand the impact of halogen-aryl π interactions in biological systems as well as to develop new applications of halogen-aryl π interactions in organic, analytical, and pharmaceutical chemistry.