Cucurbit[7]uril complexations of Good's buffers

Abstract

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 (K_CB[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 pK_a of 2-(cyclohexylammonio)ethanesulfonate (CHES) increases by 3.1 units upon complexation by CB[7].