Folding encapsulation toward Lindqvist polyoxometalates within adaptive coordination cages for catalysis

Abstract

In nature, enzymes at specific folded conformations exhibit high substrate complementarity, enabling them to efficiently and selectively catalyze biochemical reactions. Inspired by enzymes, coordination cages with conformational dynamics have been designed and are receiving increasing attention due to their versatile applications in allosteric guest binding and catalysis. We present here two enzyme-mimicking adaptive macrocycle-based coordination cages, Pd₂L¹₂ and Pd₂L²₂, from macrocycle-based ligands (L¹ and L²) and the encapsulation and stabilization of Lindqvist polyoxometalates anions M₆O₁₉²⁻ (M = W or Mo) in neutral aqueous solution. X-ray crystallographic studies have verified the formation of 1:1 host-guest complexes of two Pd₂L₂ cages and the W₆O₁₉²⁻. anion, via an induced-fit folding mechanism. Compared with the free host, Pd₂L¹₂ exhibited an induced-fit semi-folded conformation in the inclusion complex, while Pd₂L²₂ adopted an induced-fit fully-folded conformation. Moreover, the Mo₆O₁₉⊂Pd₂L₂ host-guest complexes demonstrate high yield and selectivity in the oxidative decontamination reaction of the sulfur mustard simulant, 2-chloroethyl ethyl sulfide. This work not only sheds light on the importance of conformational adaptability in enzyme-like systems but also paves the way for protecting labile POM clusters via host-guest encapsulation toward enhanced catalytic performance in aqueous solution.