Cucurbit[7]uril complexations of Good's buffers

The cucurbit[7]uril (CB[7]) host–guest complexations of a series of zwitterionic “Good's” biological pH buffers have been investigated in aqueous solution by means of 1H NMR spectroscopy. The cyclohexylammonium buffers bind very strongly (KCB[7] = 107 to 108 dm3 mol−1), while the morpholinium (102 to 103 dm3 mol−1) and piperazinium (103 to 104 dm3 mol−1) buffers have binding constants several orders of magnitude smaller. The binding constants increase as the distance between the ammonium and sulfonate groups increases. The pKa of 2-(cyclohexylammonio)ethanesulfonate (CHES) increases by 3.1 units upon complexation by CB[7].