Abstract 

Synchronous helical pulse sequences in magicangle spinning nuclear magnetic resonance: Double quantum recoupling of multiplespin systems,
J. Chem. Phys.
112,
85398554,
(2000).
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. 

Dr. Andreas Brinkmann Measurement Science and Standards National Research Council 1200 Montreal Road, M40 Ottawa, Ontario K1A 0R6 Canada Tel. +16139900319 Fax. +16139901555 Andreas.Brinkmann@nrccnrc.gc.ca 

Dr. Andreas Brinkmann, NRCMSS, 1200 Montreal Road, M40,
Ottawa, ON K1A 0R6, Canada Andreas.Brinkmann@nrccnrc.gc.ca 