Phosphinate selective hosts and importance of C[sbnd]H hydrogen bonding for affinity modulation toward anion guests

Abstract

Even though phosphinate and its analogs are very important guests in nature, the artificial receptors which are capable of selective recognition of phosphinate are rare. Here, we report a series of acetate and phosphinate selective hosts (1, 2 and 3) which utilize amide NH and aliphatic CH groups as hydrogen bonding donors. In this series of receptors, even though the amide NH hydrogen bonding element was found to be the most significant, by varying the polarity of CH group, the magnitude of recognition could be modulated considerably. The affinities of host 3 against all the tested anion guests showed significantly higher affinities compared with those of hosts 1 and 2, and this could be attributed to the difference of CH group polarities among the receptors 1, 2 and 3. Cα-H hydrogen in host 3 is the most highly polarized by the charged pyridinium group. Therefore, it is the strongest host in this series of hosts. From the experiments shown here, we demonstrated the importance of CH hydrogen bonding element as a decisive modulating moiety for anionic recognition.