Abstract
The radio-frequency-driven recoupling (RFDR) pulse sequence is used in magic-angle spinning (MAS) NMR to recouple homonuclear dipolar interactions. Here we show simultaneous recoupling of both the heteronuclear and homonuclear dipolar interactions by applying RFDR pulses on two channels. We demonstrate the method, called HETeronuclear RFDR (HET-RFDR), on microcrystalline SH3 samples at 10 and 55.555 kHz MAS. Numerical simulations of both HET-RFDR and standard RFDR sequences allow for better understanding of the influence of offsets and paths of magnetization transfers for both HET-RFDR and RFDR experiments, as well as the crucial role of XY phase cycling.
Highlights
Magic-angle spinning (MAS) NMR spectroscopy is used to obtain atomic resolution spectra of materials and biological molecules in the solid state, by removal of the broadening associated with anisotropic dipolar couplings and other interactions
The radio-frequencydriven recoupling (RFDR) pulses are applied according to a variety of XY phase cycling schemes, which have been analyzed with the intent to suppress imperfections associated with offset differences, radio frequency-field inhomogeneity, and second-order average Hamiltonian terms between different anisotropic interactions (Zhang et al, 2015)
In order to understand via which operators the polarization transfer occurs, we considered the evolution of two systems – I2 homonuclear and IS heteronuclear spin systems – under RFDR and HET-RFDR sequences with 10 kHz MAS
Summary
Magic-angle spinning (MAS) NMR spectroscopy is used to obtain atomic resolution spectra of materials and biological molecules in the solid state, by removal of the broadening associated with anisotropic dipolar couplings and other interactions. The RFDR pulses are applied according to a variety of XY phase cycling schemes, which have been analyzed with the intent to suppress imperfections associated with offset differences, radio frequency (rf)-field inhomogeneity, and second-order average Hamiltonian terms between different anisotropic interactions (Zhang et al, 2015). We perform and compare a numerical operator analysis of both RFDR and HET-RFDR experiments under different simulated conditions This numerical analysis allows us to define the conditions under which homonuclear and heteronuclear RFDR polarization transfers have similar behaviors, to understand the paths through which the signals are transferred between operators, and to understand the crucial role of 90◦ phase alternation (XY-4, XY-8, etc.) (Ishii, 2001; Nishiyama et al, 2014b; Zhang et al, 2015; Hellwagner et al, 2018) for both RFDR and HET-RFDR recoupling
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