ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Deuterium quadrupole echo spectroscopy is used to study the dynamics of the CD3 group in polycrystalline L-alanine-d3. Temperature-dependent quadrupole echo line shapes, their spectral intensities and τ dependence, and the anisotropy of the 2H spin-lattice relaxation were employed to determine the rate and mechanism of the –CD3 group motion. The rigid lattice Pake pattern observed at low temperature (T〈−120 °C) transforms to a triplet spectrum characteristic of threefold jumps in the intermediate exchange regime (−120 to −70 °C) and this in turn to a Pake pattern of reduced breadth at higher temperatures (T〉−70 °C). The quadrupole echo line shapes and their τ dependence, which are especially sensitive to the rate and mechanism of the motion, can be simulated quantitatively with the threefold jump model. We find Ea=20.0 kJ/mol for this process which is higher than is observed for most methyl groups, probably because of steric crowding in the L-Ala molecule. Finally, we observe a line shape due to the presence of multiple crystallographic forms which suggests that this technique can be extended to studies of the dynamics of more complex systems.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.452693
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