Double-quantum-filtered nuclear magnetic resonance spectroscopy applied to quadrupolar nuclei in solids

Abstract

A double-quantum filtered nuclear magnetic resonance experiment is applied to half-integer quadrupolar nuclei in solids. Filtering through a double-quantum coherence excited in a dipolar-coupled two-spin system allows spatial correlations between spins to be determined. Theoretical and experimental investigations have been carried out to optimize the excitation of double-quantum coherence between the central transitions of two neighboring nuclei while minimizing double-quantum excitation on each individual spin. The presence of the large quadrupolar coupling in the systems under study allows multiple-quantum excitation via the dipolar coupling between two spins even under conditions of magic-angle spinning, without the need for a recoupling sequence. Two-dimensional double-quantum-filtered correlation spectra have been recorded on Na23 (I=32) for Na2ZrO3 which contains three distinct Na23 sites.

Supercycled symmetry-based double-quantum dipolar recoupling of quadrupolar spins in MAS NMR: I. Theory

“…(5)], the first-order quadrupolar interaction has no direct influence on the CT 2Q-dynamics [13]. This has been the underlying assumption made in all theoretical studies of half-integer spin-recoupling presented thus far [15][16][17][18]29]. Some consequences of this approximation were explored numerically in Ref.…”

“…Such options have been proposed for the purposes of either driving magnetization transfers between the CT of the recoupled half-integer spins [15,16], or for exciting two-spin CT double quantum coherence (2QC) [17][18][19][20]. As will be examined further in this article, the latter category of dipolar recoupling schemes may be viewed as supercycles of 2Q-HORROR irradiation [22] and generalizations thereof [23,24], meaning that the rf amplitude matches 1/2 of the MAS frequency.…”

“…The main obstacle with such approaches is their dependence of the dipolar recoupling on the particular spin system parameters and on the choice of spinning frequency. Consequently, more recent progress in this area has focussed on rf-driven homonuclear recoupling methodology [14][15][16][17][18][19][20], as reviewed in Ref. [21].…”

“…Following the successful introduction of techniques for restoring and utilizing homonuclear through-space dipolar interactions among spin-1/2 nuclei under magic-angle-spinning (MAS) conditions [1][2][3], increasing efforts have in recent years been made for designing analogous dipolar recoupling tools for half-integer spin quadrupolar nuclei [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. To minimize losses of the central-transition (CT) signals, the first generation of homonuclear recoupling techniques avoided application of radio-frequency (rf) pulses and relied on the non-commutation between homonuclear couplings and other anisotropic interactions, such as heteronuclear couplings to 1 H or first-order quadrupolar interactions [4][5][6][7][8][9][10][11][12][13].…”

Double-quantum homonuclear NMR correlation spectroscopy of quadrupolar nuclei subjected to magic-angle spinning and high magnetic field

“…Even if the fictitious spin-1/2 approximation may not be fulfilled at all times for all crystallite orientations in a powder, the dipolar recoupling techniques employing rf fields that were originally introduced for spins-1/2 were transposed to the case of half-integer quadrupolar nuclei. Rotary resonance recoupling (R 3 ) techniques and especially the HORROR condition [17,18] have been demonstrated for recoupling of quadrupolar nuclei [19][20][21][22][23]. The HORROR condition, which selectively reintroduces the homonuclear dipolar interaction, is obtained for a spin-S when the rf amplitude m 1 fulfills:…”