Molecular motions of alpha-L-rhamnopyranose and methyl alpha-L-rhamnopyranoside in the glassy and crystalline states: A proton NMR study

作者：Tang HR; Wang YL; Belton PS^*

来源：Physical Chemistry Chemical Physics, 2004, 6(13): 3694-3701.

DOI：10.1039/b402812k

Molecular motions of two saccharides, alpha-L-rhamnopyranose monohydrate (Rha) and methyl alpha-L-rhamnopyranoside (Me-Rha) in the crystalline and glassy states have been investigated using proton spin lattice relaxation times, T-1 and T-1rho, and transverse relaxation measurements over the temperature range 110-360 K. The results showed that, in all cases, threefold rotational motion of the methoxyl and methyl groups dominate their proton spin-lattice (T-1 and T-1rho) relaxation processes at low temperatures. In the crystalline solids the only other process observed to affect T-1rho was water rotation. In the glasses both water rotation and anisotropic rotation of whole sugar molecules was observed. The anisotropic rotation, which was responsible for T-1rho relaxation, gave way to a more isotropic rotation at about 50 K above T-g that was responsible for T-1 relaxation. In general the dynamics of the systems could be described by a model which used discrete correlation times and an Arrhenius temperature dependence for motion. There was no need for recourse to a distribution of correlation times model. The results obtained suggest that both the motion of methyl groups and water are not coupled to the motion of the whole sugar molecules and that a correlation time diagram for the motions of whole molecules above T-g and for water and methyl groups below T-g can be prepared.

• 出版日期2004-7-7
• 单位陕西科技大学