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, T1 and T1rho, and the second moment, M2, in both protonated and D2O exchanged forms over the temperature range 120-380 K. T1 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 T1rho relaxation is driven by the motions of the same groups between 120 and 300 K. T1rho 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'. 13C 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.
Institute of Food Research, Norwich Research Park, Colney, UK. huiru.tang@ic.ac.uk
H R
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Tang
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Belton
D002475:Cellobiose / Q000737:chemistry*; D002482:Cellulose / Q000737:chemistry; D003460:Crystallization; D009682:Magnetic Resonance Spectroscopy
D002475:Cellobiose; D002482:Cellulose