t 1 -Noise eliminated dipolar heteronuclear multiple-quantum coherence solid-state NMR spectroscopy

Heteronuclear multiple‐quantum coherence (HMQC) pulse sequences for establishing heteronuclear correlation in solid‐state nuclear magnetic resonance (NMR) between 35Cl and 1H nuclei in chloride salts under fast (60 kHz) magic‐angle spinning (MAS) and at high magnetic field (a 1H Larmor frequency of 850 MHz) are investigated. Specifically, recoupling of the 35Cl–1H dipolar interaction using rotary resonance recoupling with phase inversion every rotor period or the symmetry‐based SR421 pulse sequences are compared. In our implementation of the population transfer (PT) dipolar (D) HMQC experiment, the satellite transitions of the 35Cl nuclei are saturated with an off‐resonance WURST sweep, at a low nutation frequency, over the second spinning sideband, whereby the WURST pulse must be of the same duration as the recoupling time. Numerical simulations of the 35Cl–1H MAS D‐HMQC experiment performed separately for each crystallite orientation in a powder provide insight into the orientation dependence of changes in the second‐order quadrupolar‐broadened 35Cl MAS NMR lineshape under the application of dipolar recoupling. Two‐dimensional 35Cl–1H PT‐D‐HMQC MAS NMR spectra are presented for the amino acids glycine·HCl and l‐tyrosine·HCl and the pharmaceuticals cimetidine·HCl, amitriptyline·HCl and lidocaine·HCl·H2O. Experimentally observed 35Cl lineshapes are compared with those simulated for 35Cl chemical shift and quadrupolar parameters as calculated using the gauge‐including projector‐augmented wave (GIPAW) method: the calculated quadrupolar product (PQ) values exceed those measured experimentally by a factor of between 1.3 and 1.9.

Section: Discussionmentioning

confidence: 99%

Section: Evaluation Of 35 CL  1 H D-hmqc Mas Nmr Pulse Sequencesmentioning

confidence: 91%

³⁵Cl–¹H Heteronuclear correlation magic‐angle spinning nuclear magnetic resonance experiments for probing pharmaceutical salts

Iuga

Corlett

Brown

2021

“…The partial refocusing of the CSA 1H as well as the shorter delay between the CT-selective π/2 pulse and the maximum intensity of the spin echo, which is equal to τ 2 for PRESTO-III instead of 2jτ R (≥2τ 2 ) for PRESTO-II, can compensate for the magnetization loss due to the additional CT-selective π pulse applied to the S isotope in the case of the PRESTO-III variant. [38] It must be noted that using a phase inversion super cycle (e.g., R18 5 2 :R18 − 5 2 ) to increase the PRESTO robustness leads to a non γ-encoded sequence.…”

Section: Phase-shifted Recoupling Effects a Smooth Transfer Of Ordermentioning

confidence: 99%

“…This approach has already been employed to improve the efficiency of through-bond and through-space heteronuclear multiple-quantum coherence (HMQC) experiments involving half-integer quadrupolar isotopes in solids. [38,[58][59][60] 3 | NUMERICAL SIMULATIONS…”

Section: Refocused Ineptmentioning

confidence: 99%

“…17 O PRESTO and RINEPT spectra of isotopically unmodified Mg(OH) 2 acquired with the variants of these sequences, in which two and three pulses are applied to the quadrupolar isotope. For both PRESTO and RINEPT techniques, the variants with two pulses are approximately 50% more efficient than those with three pulses because (i) 17 O CTselective π pulse produces losses [38] and (ii) the CSA 1H is fivefold smaller than the 1 H- 17 O dipolar interactions and hence weakly interferes with the polarization transfer. [37,63,64] Furthermore, the RINEPT-II-CW-SR4 2 1 tt ð Þ transfer is more efficient than the PRESTO-II-R18 5 2 π ð Þ scheme owing to its larger scaling factor, leading to shorter recoupling time, as well as its higher robustness to 1 H-1 H dipolar couplings and rf-field inhomogeneity.…”

Section: Large Heteronuclear Dipolar Interactionsmentioning

confidence: 99%

See 1 more Smart Citation

Efficient transfer of DNP‐enhanced ¹H magnetization to half‐integer quadrupolar nuclei in solids at moderate spinning rate

Nagashima

Trébosc

Kon

et al. 2021

We show herein how the proton magnetization enhanced by dynamic nuclear polarization (DNP) can be efficiently transferred at moderate magic-angle spinning (MAS) frequencies to half-integer quadrupolar nuclei, S ≥ 3/2, using the Dipolar-mediated Refocused Insensitive Nuclei Enhanced by Polarization Transfer (D-RINEPT) technique, in which a symmetry-based SR4 2 1 recoupling scheme built from adiabatic inversion 1 H pulses reintroduces the 1 H-S dipolar couplings, while suppressing the 1 H-1 H ones. The use of adiabatic pulses also improves the robustness to offsets and radiofrequency (rf)-field inhomogeneity. Furthermore, the efficiency of the polarization transfer is further improved by using 1 H composite pulses and continuous-wave irradiations between the recoupling blocks, as well as by manipulating the S satellite transitions during the first recoupling block. Furthermore, in the case of large 1 H-S dipolar couplings, the D-RINEPT variant with two pulses on the quadrupolar channel results in an improved transfer efficiency. We compare here the performances of this new adiabatic scheme with those of its parent version with single π pulses, as well as with those of PRESTO and CPMAS transfers. This comparison is performed using simulations as well as DNP-enhanced 27 Al, 95 Mo, and 17 O NMR experiments on isotopically unmodified γ-alumina, hydrated titaniasupported MoO 3 , Mg(OH) 2 , and L-histidineÁHClÁH 2 O. The introduced RINEPT method outperforms the existing methods, both in terms of efficiency and robustness to rf-field inhomogeneity and offset.

Through‐space ¹¹B–²⁷Al correlation: Influence of the recoupling channel

Zheng

Xin

Wang

et al. 2021

Through-space heteronuclear correlation (D-HETCOR) experiments based on heteronuclear multiple-quantum correlation (D-HMQC) and refocused insensitive nuclei enhanced by polarization transfer (D-RINEPT) sequences have been proven to be useful approaches for the detection of the spatial proximity between half-integer quadrupolar nuclei in solids under magic-angle spinning (MAS) conditions. The corresponding pulse sequences employ coherence transfers mediated by heteronuclear dipolar interactions, which are reintroduced under MAS by radiofrequency irradiation of only one of the two correlated nuclei. We investigate herein using numerical simulations of spin dynamics and solid-state NMR experiments on magnesium aluminoborate glass how the choice of the channel to which the heteronuclear dipolar recoupling is applied affects the transfer efficiency of D-HMQC and D-RINEPT sequences between 11 B and 27 Al nuclei. Experimental results show that maximum transfer efficiency is achieved when the recoupling scheme is applied to the channel, for which the spin magnetization is parallel to the B 0 axis in average. K E Y W O R D Sdipolar recoupling, half-integer quadrupolar nuclei, heteronuclear correlation, solid-state NMR, spatial proximity Mingji Zheng and Shaohui Xin with equal contributions.