The recognition of n-alkyl phosphonic or carboxylic acid by mono-squaramide-functionalised pillar[5]arenes
摘要:
Abstract: The synthesis of a novel mono-squaramide-functionalised pillar[5]arene 1a is reported, by which n-hexylphosphonic acid (HPA) or n-heptanoic acid (HA) could be recognised. The results of H-1 NMR titration, Job Plot, ESI-MS and 2D NMR experiments reveal that 1a forms a 1:1 stoichiometric complex with HPA and HA, respectively, and its association constants (log K/M-1) with HPA and HA are determined to be 3.83 +/- 0.05 and 1.98 +/- 0.04, respectively, suggesting much stronger binding ability of 1a with HPA over HA. To compare with 1a, 1b with the electron-withdrawing group (CF3) on the phenyl ring of squaramide moiety is synthesised as well, which shows the similar selective binding ability for HPA and HA but with a little stronger binding ability than 1a.