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

Published: April 2, 2021

Nagashima, Hiroki, Julien Trébosc, Yoshihiro Kon, Olivier Lafon, and Jean‐Paul Amoureux. “Efficient Transfer of DNP‐enhanced 1 H Magnetization to Half‐integer Quadrupolar Nuclei in Solids at Moderate Spinning Rate.” Magnetic Resonance in Chemistry, January 14, 2021, mrc.5121.

https://doi.org/10.1002/mrc.5121.

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 through-space refocused INEPT (D-RINEPT) technique, in which a symmetry-based SR412 recoupling scheme built from adiabatic inversion 1H pulses reintroduces the 1H-S dipolar couplings, while suppressing the 1H-1H ones. The use of adiabatic pulses also improves the robustness to offsets and rf-field inhomogeneity. Furthermore, the efficiency of the polarization transfer is further improved by using 1H 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 1H-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 pulses, as well as with those of PRESTO and CPMAS transfers. This comparison is performed using simulations as well as DNP-enhanced 27Al, 95Mo and 17O experiments on isotopically unmodified γ-alumina, hydrated titania-supported MoO3, Mg(OH)2 and L-histidine·HCl·H2O. The introduced RINEPT method outperforms the existing methods, both in terms of efficiency and robustness to rf-field inhomogeneity and offset.