Homonuclear NMR Correlations between Half-Integer Quadrupolar Nuclei Undergoing Magic-Angle Spinning

2003 ◽  
Vol 107 (51) ◽  
pp. 14598-14611 ◽  
Author(s):  
Mattias Edén ◽  
Lucio Frydman
Keyword(s):  
Magic Angle Spinning ◽  
Magic Angle ◽  
Quadrupolar Nuclei ◽  
Half Integer ◽  
Angle Spinning

Sensitivity enhancement in MAS NMR of half-integer quadrupolar nuclei using sideband selective double-frequency sweeps

2011 ◽  
Vol 89 (9) ◽  
pp. 1130-1137 ◽  
Author(s):  
M. Goswami ◽  
P.J.M. van Bentum ◽  
A.P.M. Kentgens
Keyword(s):  
Sensitivity Enhancement ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Quadrupolar Nuclei ◽  
Double Frequency ◽  
Half Integer ◽  
Large Bandwidth ◽  
Amplitude Profile ◽  
Frequency Sweeps ◽  
Angle Spinning

Sensitivity enhancement of the NMR signal of the half-integer spin quadrupolar nuclei under magic angle spinning (MAS) conditions is demonstrated using the DFS (Double Frequency Sweep) enhancement scheme. It has been shown, both through numerical simulations and by experiments, that with a sinusoidal amplitude profile a narrow band DFS scheme performs much better than a DFS scheme with a large bandwidth. The total enhancement compares favorably to the hyperbolic secant (HS) pulse scheme under MAS. Finally, we report the robustness of this DFS scheme with respect to variation of different experimental parameters, making it a very attractive choice for acquiring sensitivity-enhanced NMR experiments of half-integer quadrupolar nuclei.

scholarly journals Improved NMR transfer of magnetization from protons to half-integer spin quadrupolar nuclei at moderate and high magic-angle spinning frequencies

2021 ◽  
Vol 2 (1) ◽  
pp. 447-464
Author(s):  
Jennifer S. Gómez ◽  
Andrew G. M. Rankin ◽  
Julien Trébosc ◽  
Frédérique Pourpoint ◽  
Yu Tsutsumi ◽  
...  
Keyword(s):  
Continuous Wave ◽  
Chemical Elements ◽  
Magic Angle Spinning ◽  
Polarization Transfer ◽  
Magic Angle ◽  
Quadrupolar Nuclei ◽  
Adiabatic Pulses ◽  
Integer Spin ◽  
Half Integer ◽  
Angle Spinning

Abstract. Half-integer spin quadrupolar nuclei are the only magnetic isotopes for the majority of the chemical elements. Therefore, the transfer of polarization from protons to these isotopes under magic-angle spinning (MAS) can provide precious insights into the interatomic proximities in hydrogen-containing solids, including organic, hybrid, nanostructured and biological solids. This transfer has recently been combined with dynamic nuclear polarization (DNP) in order to enhance the NMR signal of half-integer quadrupolar isotopes. However, the cross-polarization transfer lacks robustness in the case of quadrupolar nuclei, and we have recently introduced as an alternative technique a D-RINEPT (through-space refocused insensitive nuclei enhancement by polarization transfer) scheme combining a heteronuclear dipolar recoupling built from adiabatic pulses and a continuous-wave decoupling. This technique has been demonstrated at 9.4 T with moderate MAS frequencies, νR≈10–15 kHz, in order to transfer the DNP-enhanced 1H polarization to quadrupolar nuclei. Nevertheless, polarization transfers from protons to quadrupolar nuclei are also required at higher MAS frequencies in order to improve the 1H resolution. We investigate here how this transfer can be achieved at νR≈20 and 60 kHz. We demonstrate that the D-RINEPT sequence using adiabatic pulses still produces efficient and robust transfers but requires large radio-frequency (rf) fields, which may not be compatible with the specifications of most MAS probes. As an alternative, we introduce robust and efficient variants of the D-RINEPT and PRESTO (phase-shifted recoupling effects a smooth transfer of order) sequences using symmetry-based recoupling schemes built from single and composite π pulses. Their performances are compared using the average Hamiltonian theory and experiments at B0=18.8 T on γ-alumina and isopropylamine-templated microporous aluminophosphate (AlPO4-14), featuring low and significant 1H–1H dipolar interactions, respectively. These experiments demonstrate that the 1H magnetization can be efficiently transferred to 27Al nuclei using D-RINEPT with SR412(270090180) recoupling and using PRESTO with R2227(1800) or R1676(270090180) schemes at νR=20 or 62.5 kHz, respectively. The D-RINEPT and PRESTO recoupling schemes complement each other since the latter is affected by dipolar truncation, whereas the former is not. We also analyze the losses during these recoupling schemes, and we show how these magnetization transfers can be used at νR=62.5 kHz to acquire in 72 min 2D HETCOR (heteronuclear correlation) spectra between 1H and quadrupolar nuclei, with a non-uniform sampling (NUS).

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