Deprotonation of β-cyclodextrin in alkaline solutions

Variable pH C-13 NMR and H-1 NMR spectroscopic studies of the beta-cyclodextrin (beta-CD) in alkaline aqueous solutions revealed that beta-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 beta-CD glucopyranose units, whereas the deprotonation of OH-groups adjacent to C-6 carbon atoms is expressed less markedly. The pK(a) values for beta-CD OH-groups adjacent to C-2 and C-3 carbon atoms are rather close, pK(a1,2) being 13.5 +/- 0.2 (22.5 degrees C). (C) 2008 Elsevier Ltd. All rights reserved.