¹³C NMR Spectroscopy on the Complexation of α-Cyclodextrin with 1-Alkanols and 1-Alkanoate Ions

Abstract

Binding constants for α -cyclodextrin (α -CD) complexes with 1- alkanols and 1- alkanoate ions were determined by analyzing changes (Δ δ) in chemical shifts of guest ¹³C NMR signals with α -CD concentration. The guests gave well-separated ¹³C NMR signals. The curve-fitting analyses of Δ δ for individual carbons upon assumption of a simple 1:1 complexation gave virtually the same binding constants (K₁) in the cases of guests with relatively short alkyl chains, such as 1-propanol, 1-butanol, 1- pentanol , 1- butanoate , 1- pentanoate , and 1-hexanoate. However, thus obtained individual K₁ values were significantly different from one another, when the guests had relatively long alkyl chains such as 1- hexanol , 1- heptanol , and 1-octanoate. In these guests, satisfactorily consistent K₁ values were obtained by the curve-fitting analyses of Δ δ for individual carbons upon an assumption that not only 1:1 but also 2:1 (host:guest) complexation occurs.