Deprotonation of β-cyclodextrin in alkaline solutions

Variable pH 13C NMR and 1H NMR spectroscopic studies of the β-cyclodextrin (β-CD) in alkaline aqueous solutions revealed that β-CD does not deprotonate at pH < 12.0. Further increase in solution pH results in the deprotonation of OH-groups adjacent to C-2 and C-3 carbon atoms of β-CD glucopyranose units, whereas the deprotonation of OH-groups adjacent to C-6 carbon atoms is expressed less markedly. The pKa values for β-CD OH-groups adjacent to C-2 and C-3 carbon atoms are rather close, pKa1,2 being 13.5 ± 0.2 (22.5 °C).