Gated CO2 Uptake of N -Protected Dipeptide Crystal as Disclosed by an In Situ X-ray Crystallographic Approach

Gate-opening gas sorption is characteristic behavior observed when the crystal lattice is flexible enough to spontaneously change its structure upon guest uptake. To clarify its gas sorption mechanism, it is crucial to disclose the crystal structures of both saturated and unsaturated gas sorption states. Herein, we report the selective gate-opening CO2 sorption behavior of crystalline Boc-glycyl-l-phenylalanine (1). Single-crystal X-ray diffraction analyses of 1 in the absence and presence of CO2 unveiled its atomic-level mechanism, where the single crystal of 1 created discrete voids amenable to expansion or contraction to gradually welcome CO2 molecules into the expanded voids in a stepwise manner, thereby giving rise to the observed gate-opening CO2 sorption behavior of 1. The present experimental findings provide the second example of clearly elucidating both the saturated and unsaturated gas sorption states of purely organic crystals exhibiting a gated gas uptake.