Assessment of new symmetry-based dipolar recoupling schemes for homonuclear magnetization exchange between quadrupolar nuclei in two-dimensional correlation MAS NMR

Yang Yu; Philipp Keil; Baltzar Stevensson; Michael Ryan Hansen; Mattias Edén

doi:10.1016/j.jmr.2020.106734

Assessment of new symmetry-based dipolar recoupling schemes for homonuclear magnetization exchange between quadrupolar nuclei in two-dimensional correlation MAS NMR

J Magn Reson. 2020 Jul:316:106734. doi: 10.1016/j.jmr.2020.106734. Epub 2020 Apr 25.

Authors

Yang Yu¹, Philipp Keil², Baltzar Stevensson¹, Michael Ryan Hansen², Mattias Edén³

Affiliations

¹ Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden.
² Institute for Physical Chemistry, Westfälische Wilhelms-Universität Münster, DE-48 149 Münster, Germany.
³ Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden. Electronic address: mattias.eden@mmk.su.se.

PMID: 32590307
DOI: 10.1016/j.jmr.2020.106734

Abstract

We provide an extensive experimental and numerical evaluation of MQ-phase (S)M supercycles with M={3,4} of three groups of symmetry-based homonuclear dipolar recoupling rf-pulse sequences, [Formula: see text] , for establishing proximities among half-integer spin quadrupolar nuclei under moderately fast magic-angle-spinning (MAS) conditions in single-quantum-single-quantum (1Q-1Q) correlation NMR experiments. The relative merits of the (S)M schemes for variations in resonance offsets and rf-amplitude errors were assessed by numerically simulated magnetization transfers in spin-3/2 pairs with variable isotropic chemical shifts and quadrupolar coupling constants. Experimental demonstrations of ²³Na (spin-3/2) NMR on Na₂MoO₄·2H₂O and ²⁷Al (spin-5/2) NMR on AlPO-CJ19 [(NH₄)₂Al₄(PO₄)₄HPO₄·H₂O] are presented at 14.1 T and 24 kHz MAS. We recommend using the (SR2₂¹)3 or (SR2₂¹)4 supercycles for samples that exhibit small chemical-shift dispersions (<3 kHz), and any (SRN_N^N/2)3 scheme with N⩾10 for larger spreads of isotropic chemical shifts. However, because the (SRN_N^N/2)3 sequences recouple heteronuclear dipolar interactions, their application to proton-bearing samples requires high-power proton decoupling during the mixing period. Alternatively, the (SR2₄¹)3 and (SR2₄¹)4 schemes may be employed in the absence of proton decoupling, but with poorer compensation to resonance-offsets and rf-amplitude errors.

Keywords: (23)Na NMR; (27)Al NMR; Dipolar recoupling; Half-integer spins; Homonuclear correlation NMR spectroscopy; Microporous aluminophosphate.