Description of natural abundance deuterium 2D-NMR experiments in weakly ordered liquid-crystalline solvents using a tailored cartesian spin-operator formalism
Résumé
We report an appropriate cartesian spin-operator formalism which retains all physical insights and provides a
pictorial representation for I=1 spin nuclei subjected to both a chemical shift and a small quadrupolar
moment such as deuterons in liquid crystals with low order-parameters. Using a tree-like pictorial
representation, this approach allows a straightforward description of natural abundance deuterium
autocorrelation 2D-NMR experiments in weakly ordered solvents. As illustrative examples we study the 2D
Q-COSY and Q-resolved NMR sequences which have been recently developed to facilitate the analysis of
overcrowded proton-decoupled deuterium spectra in natural abundance of enantiomers oriented in
liquid-crystalline solutions of poly-gamma-benzyl-L-glutamate (PBLG). These 2D-NMR experiments allow the
correlation between the two components of each quadrupolar doublet in the deuterium spectra to be obtained,
and their assignment on the basis of chemical shifts. Several improvements of the basic sequences are proposed
and discussed. Applications of these sequences in natural abundance deuterium NMR spectroscopy using a 9.4
T magnetic Ðeld and standard NMR equipment are examined.