Benchmark Acetylene Binding Affinity and Separation through Induced Fit in a Flexible Hybrid Ultramicroporous Material

Abstract

Structural changes at the active site of an enzyme induced by binding to a substrate molecule can result in enhanced activity in biological systems. Herein, we report that the new hybrid ultramicroporous material sql-SIFSIX-bpe-Zn exhibits an induced fit binding mechanism when exposed to acetylene, C₂ H₂ . The resulting phase change affords exceptionally strong C₂ H₂ binding that in turn enables highly selective C₂ H₂ /C₂ H₄ and C₂ H₂ /CO₂ separation demonstrated by dynamic breakthrough experiments. sql-SIFSIX-bpe-Zn was observed to exhibit at least four phases: as-synthesised (α); activated (β); and C₂ H₂ induced phases (β' and γ). sql-SIFSIX-bpe-Zn-β exhibited strong affinity for C₂ H₂ at ambient conditions as demonstrated by benchmark isosteric heat of adsorption (Q_st ) of 67.5 kJ mol^-1 validated through in situ pressure gradient differential scanning calorimetry (PG-DSC). Further, in situ characterisation and DFT calculations provide insight into the mechanism of the C₂ H₂ induced fit transformation, binding positions and the nature of host-guest and guest-guest interactions.