Indirect detection via spin-1/2 nuclei in solid state NMR spectroscopy: application to the observation of proximities between protons and quadrupolar nuclei.
We present a comprehensive comparison of through-space heteronuclear correlation techniques for solid state NMR, combining indirect detection and single-channel recoupling method. These techniques, named D-HMQC and D-HSQC, do not suffer from dipolar truncation and can be employed to correlate quadrupolar nuclei with spin-1/2 nuclei. The heteronuclear dipolar couplings are restored under magic-angle spinning by applying supercycled symmetry-based pulse sequences (SR412) or simultaneous frequency and amplitude modulation (SFAM). The average Hamiltonian theory (AHT) of these recoupling methods is developed. These results are applied to analyze the performances of D-HMQC and D-HSQC sequences. It is shown that, whatever the magnitude of spin interations, D-HMQC experiment offers larger efficiency and higher robustness than D-HSQC. Furthermore, the spectral resolution in both dimensions of proton detected two-dimensional D-HMQC and D-HSQC spectra can be enhanced by applying recently introduced symmetry-based homonuclear dipolar decoupling schemes that cause a z-rotation of the spins. This is demonstrated by 1H-13C and 1H-23Na correlation experiments on l-histidine and NaH2PO4, respectively. The two-dimensional heteronuclear 1H-23Na correlation spectrum yields the assignment of 23Na resonances of NaH2PO4. This assignment is corroborated by first-principles calculations.
Lafon
Olivier
O
Unité de Catalyse et de Chimie du Solide (UCCS), UMR CNRS 8181, Ecole Nationale Supérieure de Chimie de Lille, Université de Lille 1, Batiment C7, B.P. 90108, 59652 Villeneuve d'Ascq Cedex, France.
Wang
Qiang
Q
Hu
Bingwen
B
Vasconcelos
Filipe
F
Trébosc
Julien
J
Cristol
Sylvain
S
Deng
Feng
F
Amoureux
Jean-Paul
JP
D003198:Computer Simulation; D006639:Histidine / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000592:standards; D008956:Models, Chemical; D010710:Phosphates / Q000737:chemistry*; D011522:Protons; D012015:Reference Standards; D012964:Sodium / Q000737:chemistry
D010710:Phosphates; D011522:Protons; D006639:Histidine; D012964:Sodium; C018279:sodium phosphate