13C-CP/MAS NMR studies of the cyclomalto-oligosaccharide (cyclodextrin) hydrates

The 13C-CP/MAS NMR spectra of cyclomaltohexaose (alpha-cyclodextrin) hexahydrate, cyclomaltoheptaose (beta-cyclodextrin) "undecahydrate", cyclomalto-octaose (gamma-cyclodextrin) "octadecahydrate", and of the same materials at lower levels of hydration are compared with solution NMR data, structures obtained from single crystal diffraction studies, and with previous reports of the 13C-CP/MAS NMR spectra. The chemical shifts of the C-1 and C-4 resonances can be correlated with the conformation about the (1----4) linkage. The chemical shifts of the C-6 resonances are also sensitive to hydrogen-bonding interactions, as shown by the spectral changes on loss of water from the structures. The results suggest that, for resonances of carbon atoms close to a centre of significant conformational change, chemical shifts may be predicted on the basis of conformation alone, but for the resonances of more distant atoms, changes in chemical shift due to conformational change may be masked by the effects of alterations in the local environment.