Application of fast amplitude-modulated pulse trains for signal enhancement in static and magic-angle-spinning -NMR spectra

Fast amplitude-modulated pulse trains with frequency sweep (SW-FAM) in solid-state NMR of spin-7/2 nuclei

“…A similar picture as described for enhancement of 45 Sc spectra was obtained for 43 Ca. Numerical simulations were carried out for the quadrupolar parameters of CaTiO 3 , v = 2.13 MHz and g = 0.7 [48].…”

“…Recently, a number of solidstate NMR studies has been published involving nuclei with spin I = 7/2, such as 43 Ca [4][5][6], 45 Sc [7][8][9], 49 Ti [10][11][12], 51 V [13][14][15], 139 La [16,17], or a combination of these isotopes [18]. The purpose of such studies is to determine the chemical shift and the quadrupolar interaction parameters, and to correlate them to structure and properties of the compounds under investigation.…”

“…Since the reintroduction of this principle by Vega and Naor in 1981 [25], and by Haase et al [26][27][28] in a series of detailed papers, several experimental techniques have been put forward to effect the necessary manipulations of the ST's [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. Among these techniques are double frequency sweeps (DFS) [29][30][31][32][33], the application of hyperbolic secant pulses (HS) [45] to quadrupolar nuclei [34][35][36], and the use of pulse trains with alternating phases, designated either ''rotor assisted population transfer" (RAPT/FSG-RAPT) [37][38][39] or ''fast amplitude-modulated" (FAM) pulse trains [40][41][42][43][44]. (More details about these methods and their development may be found in the introductions of Refs.…”

“…In this paper, we focus on sensitivity enhancement of both MAS and 7QMAS spectra of spin-7/2 nuclei by using fast amplitudemodulated (FAM) pulse trains, in particular the use of FAM pulse trains with swept modulation frequency (SW-FAM) [42][43][44]. It is demonstrated that application of SW-FAM sequences results in considerable improvement of the signal-to-noise ratio, which directly translates into time saving when acquisition of NMR spectra of spin-7/2 nuclei is required, as in the studies in Refs.…”

Sensitivity enhancement of the central-transition signal of half-integer spin quadrupolar nuclei in solid-state NMR: Features of multiple fast amplitude-modulated pulse transfer

“…Although it is true that the FAM pulses are most effective under MAS, certain enhancement could be obtained in static cases as well [24]. Variants of FAM which generate a frequency sweep by modulating the pulse duration in either a linear or non-linear way, notated as SW(s)-FAM and SW(1/s)-FAM, were found to give good signal enhancement in the case of static samples [25,26].…”