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

Tang, H. R., Wang, Y. L. and Belton, Peter (2004) Molecular motions of α-L-rhamnopyranose and methyl α-L-rhamnopyranoside in the glassy and crystalline states: A proton NMR study. Physical Chemistry Chemical Physics, 6 (13). p. 3694. ISSN 1463-9084

Full text not available from this repository. (Request a copy)

Abstract

Molecular motions of two saccharides, a-L-rhamnopyranose monohydrate (Rha) and methyl a-L-rhamnopyranoside (Me–Rha) in the crystalline and glassy states have been investigated using proton spin lattice relaxation times, T1 and T1?, 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 (T1 and T1?) relaxation processes at low temperatures. In the crystalline solids the only other process observed to affect T1? 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 T1? relaxation, gave way to a more isotropic rotation at about 50 K above Tg that was responsible for T1 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 Tg and for water and methyl groups below Tg can be prepared.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
Related URLs:
Depositing User: Rachel Smith
Date Deposited: 07 Mar 2011 16:38
Last Modified: 24 Jul 2019 16:49
URI: https://ueaeprints.uea.ac.uk/id/eprint/21267
DOI: 10.1039/b402812k

Actions (login required)

View Item View Item