Tognetti, Jacqueline, Franks, W. Trent, Lewandowski, Józef Romuald and Brown, Steven P. (2022) Optimisation of 1H PMLG homonuclear decoupling at 60 kHz MAS to enable 15N-1H through-bond heteronuclear correlation solid-state NMR spectroscopy. Physical Chemistry Chemical Physics, 24 (34). pp. 20258-20273. doi:10.1039/D2CP01041K ISSN 1463-9076.

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Abstract

The Lee-Goldburg condition for homonuclear decoupling in 1H magic-angle spinning (MAS) solid-state NMR sets the angle θ corresponding to arctan of the ratio of the rf nutation frequency, ν1, to the rf offset, to be the magic angle, θm, equal to tan-1(√2) = 54.7⁰. At 60 kHz MAS, we report enhanced decoupling compared to MAS alone in a 1H spectrum of 15N-glycine with PMLG5 at θ = 30⁰ for a ν1 of ~100 kHz at a 1H Larmor frequency, ν0, of 500 MHz and 1 GHz, corresponding to a high chemical shift scaling factor (CS) of 0.82. At 1 GHz, we also demonstrate enhanced decoupling compared to 60 kHz MAS alone for a lower ν1 of 51 kHz, i.e., a case where the nutation frequency is less than the MAS frequency, with θ = 18⁰, λCS = 0.92. The ratio of the rotor period to the decoupling cycle time, Ψ = τr/ τc, is in the range 0.53 to 0.61. Windowed PMLG5 decoupling using the optimised parameters for a ν1 of ~100 kHz also gives good performance in a 1H spin-echo experiment, enabling implementation in a 1H-detected 15N-1H cross polarisation (CP)-refocused INEPT heteronuclear correlation NMR experiment. Specifically, initial 15N transverse magnetisation as generated by 1H-15N CP is transferred back to 1H using a refocused INEPT pulse sequence employing windowed 1H decoupling. Such an approach ensures the observation of through-bond N-H connectivities. For 15N-glycine, while the CP-refocused INEPT experiment has a lower sensitivity (~50%) as compared to a double CP experiment (with a 200 μs 15N to 1H CP contact time), there is selectivity for the directly bonded NH3+ moiety, while intensity is observed for the CH2 1H resonances in the double CP experiment. Two-dimensional 15N-1H correlation MAS NMR spectra are presented for the dipeptide β-AspAla and the pharmaceutical cimetidine at 60 kHz MAS, both at natural isotopic abundance. For the dipeptide β-AspAla, different build-up dependence on the first spin-echo duration is observed for the NH and NH3+ moieties demonstrating that the experiment could be used to distinguish resonances for different NHx groups.

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry
Divisions:	Faculty of Science, Engineering and Medicine > Science > Chemistry Faculty of Science, Engineering and Medicine > Science > Physics
Library of Congress Subject Headings (LCSH):	Nuclear magnetic resonance spectroscopy, Solid state chemistry
Journal or Publication Title:	Physical Chemistry Chemical Physics
Publisher:	Royal Society of Chemistry
ISSN:	1463-9076
Official Date:	14 September 2022
Dates:	Date Event 14 September 2022 Published 15 July 2022 Accepted 3 March 2022 Submitted
Volume:	24
Number:	34
Page Range:	pp. 20258-20273
DOI:	10.1039/D2CP01041K
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Open Access (Creative Commons)
Date of first compliant deposit:	26 July 2022
Date of first compliant Open Access:	27 July 2022
RIOXX Funder/Project Grant:	Project/Grant ID RIOXX Funder Name Funder ID EP/L015307/1 [EPSRC] Engineering and Physical Sciences Research Council http://dx.doi.org/10.13039/501100000266
Related URLs:	Related dataset

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