When Non-Covalent Interactions Compete: How to Decode Entropy-Enthalpy Compensation
You spend six months designing a macrocyclic host that binds your substrate with a dissociation constant of 50 nanomolar. You run the catalytic assay. Conversion stalls at 40 percent. Forty. A graduate student repeats it. Same plateau. You try a larger cavity—weaker binding but faster turnover. That is entropy-enthalpy compensation (EEC) in the wild: a thermodynamic seesaw that makes catalysis feel like a rigged carnival game. EEC is not just an academic curiosity. In supramolecular catalysis, non-covalent interactions—hydrogen bonds, π-stacking, dispersion forces—compete with solvent reorganization and conformational flexibility. Every enthalpic gain from a tight interaction often carries an entropic cost from restricted motion or desolvation. This article is a field guide for decoding that trade-off. It will not give you a formula to predict EEC (nobody has one that works). Instead, it will help you recognize when you are fighting entropy and when you should stop.