Metal-organic frameworks (MOFs) based separation columns: fundamental study for molecular recognitions and potential for separation of linear polymers with close terminal structure

Abstract

We report stationary phases using metal-organic frameworks (MOFs) composed of metal ions and organic ligands in HPLC. We mainly applied [Zn2(1,4-ndc)2ted]n (ZnJAST4) (ndc: naphthalenedicarboxylate, ted: triethylenediamine) for the stationary phase. To inspect how metal ions and organic ligands affect retention behavior, three different types of MOF, [Cu2(1,4-ndc)2ted]n (CuJAST4) substituted from zinc ions of ZnJAST4 to copper ions, [Zn2(1,4-bdc)2ted]n (ZnJAST1) (bdc: benzenedicarboxylate) substituted from a part of naphthalene of ZnJAST4 to benzene, and ZnJAST4 were packed to columns, and then HPLC using benzene derivatives was conducted to evaluate the recognition ability toward functional groups and shapes of molecules using hexane as the mobile phase. The result revealed that the retention behavior depended on various factors such as halogen bonding, π stacking, molecular shapes, and molecular sizes. Furthermore, to evaluate retention selectivity toward functional groups, HPLC analyses were conducted with a ZnJAST4 packed column in a mobile phase, N,N-dimethylformamide (DMF), using poly(ethylene glycol) (PEG) derivatives, which have different polar terminal groups, as analytes. The result showed that when the polarity was low, the retention to ZnJAST4 decreased, and the retention behavior was affected by the molecular weight of the PEG.