Association of Cycloalkanes with Cyclodextrins in Aqueous Medium

The complex formation of α-, β-, and γ-cyclodextrins (CyDs, hosts) with five cycloalkanes (guests), cyclo(pentane, hexane, heptane, octane, and decane), has been studied in aqueous media at 25°C by making use of the volatilization rate of guest molecules from the aqueous into gas phase. In the excess of the host, α-CyD forms both 1 : 1 and 2 : 1 (host: guest) complexes, while β- and γ-CyDs form 1 : 1 complexes with an exception that β-CyD forms a 2 : 1 complex with cylodecane. The 2 : 1 complex formation constants of α-CyD with cyclo(hexane, heptane, octane, and decane), particularly with cyclooctane, are extremely large compared with their 1 : 1 formation constants. The host–guest spatial fitting models are proposed.