Molecular dynamics of polycrystalline cellobiose studied by solid-state NMR

Molecular motions of polycrystalline cellobiose have been investigated by measuring proton spin-lattice relaxation times, T(1) and T(1rho), and the second moment, M(2), in both protonated and D(2)O exchanged forms over the temperature range 120-380 K. T(1) relaxation is dominated by the motions of hydroxyl groups between 150 and 380 K, characterised by an activation energy of about 8.74 kJ/mol, whereas T(1rho) relaxation is driven by the motions of the same groups between 120 and 300 K. T(1rho) results suggest that hydroxyl groups have a distribution of dynamics. Motion of methylene groups was detected in the second-moment experiments at about 350 K, characterised by activation energy of about 40 kJ/mol. Consideration of the calculated and observed rigid-lattice second moments suggests that the reported X-ray data are incorrect for the inter-proton distance on C6'. (13)C CPMAS spectra of both protonated and deuterated cellobiose have also been measured. Spectra of the deuterated material showed the existence of a second crystalline form in addition to the normal form. (C) 2002 Elsevier Science (USA).