Asynchronising five-fold symmetry sequence for better homonuclear polarisation transfer in magic-angle-spinning solid-state NMR

Vaishali Arunachalam; Kshama Sharma; Kaustubh R Mote; P K Madhu

doi:10.1016/j.ssnmr.2023.101858

Asynchronising five-fold symmetry sequence for better homonuclear polarisation transfer in magic-angle-spinning solid-state NMR

Solid State Nucl Magn Reson. 2023 Feb 11;124:101858. doi: 10.1016/j.ssnmr.2023.101858. Online ahead of print.

Authors

Vaishali Arunachalam¹, Kshama Sharma², Kaustubh R Mote³, P K Madhu⁴

Affiliations

¹ Tata Institute of Fundamental Research Hyderabad, 36/P Gopanpally Village, Ranga Reddy District, Hyderabad, 500046, India. Electronic address: vaishalia@tifrh.res.in.
² Tata Institute of Fundamental Research Hyderabad, 36/P Gopanpally Village, Ranga Reddy District, Hyderabad, 500046, India. Electronic address: kshamasharma35@gmail.com.
³ Tata Institute of Fundamental Research Hyderabad, 36/P Gopanpally Village, Ranga Reddy District, Hyderabad, 500046, India. Electronic address: krmote@tifrh.res.in.
⁴ Tata Institute of Fundamental Research Hyderabad, 36/P Gopanpally Village, Ranga Reddy District, Hyderabad, 500046, India. Electronic address: madhu@tifrh.res.in.

PMID: 36796278
DOI: 10.1016/j.ssnmr.2023.101858

Abstract

Recoupling, decoupling, and multidimensional correlation experiments in magic-angle-spinning (MAS) solid-state NMR can be designed by exploiting the symmetry of internal spin interactions. One such scheme, namely, C5₂¹, and its supercycled version SPC5₂¹, notated as a five-fold symmetry sequence, is widely used for double-quantum dipole-dipole recoupling. Such schemes are generally rotor synchronised by design. We demonstrate an asynchronous implementation of the SPC5₂¹ sequence leading to higher double-quantum homonuclear polarisation transfer efficiency compared to the normal synchronous implementation. Rotor-synchronisation is broken in two different ways: lengthening the duration of one of the pulses, denoted as pulse-width variation (PWV), and mismatching the MAS frequency denoted as MAS variation (MASV). The application of this asynchronous sequence is shown on three different samples, namely, U-¹³C-alanine and 1,4-¹³C-labelled ammonium phthalate which include ¹³C_α-¹³C_β, ¹³C_α-¹³C_o, and ¹³C_o-¹³C_o spin systems, and adenosine 5'- triphosphate disodium salt trihydrate (ATP⋅3H₂O). We show that the asynchronous version performs better for spin pairs with small dipole-dipole couplings and large chemical-shift anisotropies, for example, ¹³C_o-¹³C_o. Simulations and experiments are shown to corroborate the results.

Keywords: Asynchronous implementation; Double-quantum recoupling; Magic-angle spinning; Solid-state NMR; Symmetry sequence.