Double-quantum homonuclear NMR correlation spectroscopy of quadrupolar nuclei subjected to magic-angle spinning and high magnetic field.
We present a new application of the R2(2)(1) symmetry-based dipolar recoupling scheme, for exciting directly double-quantum (2Q) coherences between the central transition of homonuclear half-integer quadrupolar nuclei. With respect to previously published 2Q-recoupling methods (M. Eden, D. Zhou, J. Yu, Chem. Phys. Lett. 431 (2006) 397), the R2(2)(1) sequence is used without pi/2 bracketing pulses and with an original super-cycling. This leads to an improved efficiency (a factor of two for spin-5/2) and to a much higher robustness to radio-frequency field inhomogeneity and resonance offset. The 2Q-coherence excitation performances are demonstrated experimentally by (27)Al NMR experiments on the aluminophosphates berlinite, VPI5, AlPO(4)-14, and AlPO(4)-CJ3. The two-dimensional 2Q-1Q correlation experiments incorporating these recoupling sequences allow the observation of 2Q cross-peaks between central transitions, even at high magnetic field where the difference in offset between octahedral and tetrahedral (27)Al sites exceeds 10 kHz.
Wang
Q
Q
UCCS, CNRS-8181, Lille University, Fr-59652, Villeneuve d'Ascq, France.
Hu
B
B
Lafon
O
O
Trébosc
J
J
Deng
F
F
Amoureux
J P
JP
D000465:Algorithms; D017607:Aluminum Compounds / Q000032:analysis*; D003198:Computer Simulation; D004574:Electromagnetic Fields; D008956:Models, Chemical; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D010710:Phosphates / Q000032:analysis*; D012680:Sensitivity and Specificity; D013113:Spin Labels
D017607:Aluminum Compounds; D010710:Phosphates; D013113:Spin Labels