Surprising flexibility-the entatic state principle and its recent interpretations and applications.

The concept of the entatic state has been a staple in bio-inorganic chemistry for over half a century, explaining the effect of structural distortion and rigidity on the reactivity of metalloproteins and their model systems. This perspective gives an overview of recent applications of the concept in bio-inorganic chemistry but also aims to shed light on how the application of the concept has shifted towards more bio-inspired topics that also include conventional and photo-redox catalysis. As illustrated in this review, the concept of entasis, despite originating in the middle of the 20th century, still impacts modern chemistry and provides a constructive framework to improve the efficacy of molecular system via targeted ligand design.