Problematic Attributions of Entropic and Hydrophobic Effects in Drug Interactions

The ΔG affinity of drugs with biopolymers and the underling noncovalent interactions play an essential role in drug discovery. Supramolecular complexes can be designed for the identification and quantification of specific interactions, including their dependence on the medium; they also secure the additivity of ΔΔG increments. Such analyses have helped to clarify hydrophobic effects in intermolecular associations, which are barely measurable with small alkyl groups, but large in the presence of curved surfaces in which the replacement of hydrogen bond-deficient water molecules by a ligand leads to sizable enthalpy gain. Difficult to predict entropy contributions TΔS to ΔG vary between 5% and over 90%, particularly in drug associations, as is obvious from literature data. As illustrated with several drug complexes, many so-called hydrophobic effects involve in fact van der Waals or dispersive interactions. Measurements with supramolecular porphyrin complexes allowed us to derive dispersive binding contributions for many groups, which exhibit a correlation with polarizability. In consequence, heteroatoms or π-systems always lead to enhanced van der Waals contributions, while for hydrophobic effects the opposite is expected. Binding contributions from supramolecular complexes can in the future also help artificial intelligence approaches in drug discovery, by expansion of hybrid databases with potential ligands containing groups with desired binding contributions.