Cyclodextrin-Driven Movement of Cucurbit[7]uril

Abstract

The movement of cucurbit[7]uril (CB[7]) driven by α-cyclodextrin (α-CD) is investigated by various experimental techniques including NMR, ESI-MS, UV−vis, and ITC. CB[7] can form stable pseudorotaxanes with N-methyl-N‘-octyl-4,4‘-bipyridinium (MVO²⁺) and N,N‘-dioctyl-4,4‘-bipyridinium (OV²⁺) dication in aqueous solution. CB[7] shuttles between the octyl and bipyridinium moieties in MVO²⁺, but docks at one of the octyl moieties in OV²⁺. The addition of α-CD pushes CB[7] from the octyl moiety of MVO²⁺ or OV²⁺ to the bipyridinium moiety. Thermodynamically, the movement of CB[7] is mainly driven by exothermic enthalpy changes coming from the complexation of the octyl moiety of MVO²⁺ or OV²⁺ with α-CD.