Synchronous helical pulse sequences in magicangle
spinning nuclear magnetic resonance: Double quantum
recoupling of multiplespin systems,
A. Brinkmann, M. Edén,
and M. H. Levitt,
J. Chem. Phys.
112,
85398554,
(2000).
Full text (PDF)
Some general principles of radiofrequency pulse sequence design
in magicangle spinning NMR are discussed. Sequences with favourable dipolar
recoupling properties may be designed using synchronous helical modulations
of the space and spin parts of the spin Hamiltonian. The selection rules
for the average Hamiltonian may be written in terms of three symmetry numbers,
two defining the winding numbers of the space and spin helices, and one
indicating the number of phase rotation steps in the radiofrequency modulation.
A diagrammatic technique is used to visualize the spacespin symmetry selection.
A pulse sequence C14_{4}^{5} is designed which accomplishes
doublequantum recoupling using a low ratio of radio frequency field to spinning
frequency. The pulse sequence uses 14 radio frequency modulation steps with space
and spin winding numbers of 4 and 5 respectively. The pulse sequence is
applied to the doublequantum spectroscopy of ^{13}C_{3}labelled
Lalanine. Good agreement is obtained between the experimental peak intensities,
analytical results, and numerically exact simulations based on the known molecular
geometry. The general symmetry properties of double quantum peaks in recoupled
multiplespin systems are discussed. A supercycle scheme which compensates
homonuclear recoupling sequences for chemical shifts is introduced. We
show an experimental doublequantum ^{13}C spectrum of
[U^{13}C]Ltyrosine at a spinning frequency of 20.000 kHz.
