Type II porous ionic liquid based on metal-organic cages that enables l-tryptophan identification
Zhuxiu Zhang, Baolin Yang, Bingjie Zhang, Mifen Cui, Jihai Tang, Xu Qiao
Abstract
Abstract Porous liquids with chemical separation properties are quite well-studied in general, but there is only a handful of reports in the context of identification and separation of non-gaseous molecules. Herein, we report a Type II porous ionic liquid composed of coordination cages that exhibits exceptional selectivity towards l -tryptophan ( l -Trp) over other aromatic amino acids. A previously known class of anionic organic–inorganic hybrid doughnut-like cage (HD) is dissolved in trihexyltetradecylphosphonium chloride (THTP_Cl). The resulting liquid, HD/THTP_Cl, is thereby composed of common components, facile to prepare, and exhibit room temperature fluidity. The permanent porosity is manifested by the high-pressure isotherm for CH 4 and modeling studies. With evidence from time-dependent amino acid uptake, competitive extraction studies and molecular dynamic simulations, HD/THTP_Cl exhibit better selectivity towards l -Trp than other solid state sorbents, and we attribute it to not only the intrinsic porosity of HD but also the host-guest interactions between HD and l -Trp. Specifically, each HD unit is filled with nearly 5 l -Trp molecules, which is higher than the l -Trp occupation in the structure unit of other benchmark metal-organic frameworks.