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, C₂H₂. The resulting phase change affords exceptionally strong C₂H₂ binding that in turn enables highly selective C₂H₂/C₂H₄ and C₂H₂/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 C₂H₂ induced phases (β' and γ). sql-SIFSIX-bpe-Zn-β exhibited strong affinity for C₂H₂ at ambient conditions as demonstrated by benchmark isosteric heat of adsorption (Qst ) 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 C₂H₂ induced fit transformation, binding positions and the nature of host-guest and guest-guest interactions.