Uniform broadband excitation of crystallites in rotating solids using interleaved sequences of delays alternating with nutation
Publication year: 2012
Source:Journal of Magnetic Resonance
Veronika Vitzthum, Marc A. Caporini, Simone Ulzega, Julien Trébosc, Olivier Lafon, Jean-Paul Amoureux, Geoffrey Bodenhausen
In solids that are spinning about the magic angle, trains of short pulses in the manner of Delays Alternating with Nutations for Tailored Excitation (DANTE) allow one to improve the efficiency of the excitation of magnetization compared to rectangular pulses. By interleaving N pulse trains with N > 1, one obtains ‘DANTE–N’ sequences comprising N pulses per rotor period that extend over K rotor periods. Optimized interleaved DANTE schemes with N > 1 are shorter than basic DANTE-1 sequences with N = 1. Therefore, they are less affected by coherent or incoherent decays, thus leading to higher signal intensities than can be obtained with basic DANTE-1 or with rectangular pulses. Furthermore, the shorter length of DANTE-N with N > 1 increases the width of the spikelets in the excitation profile, allowing one to cover the range of isotropic chemical shifts and second-order quadrupolar effects typical for side-chain and backbone amide 14N sites in peptides at B0 = 18.8 T. In DANTE-N, spinning sidebands only appear at multiples of the spinning frequency ?rot, as if the samples were rotating at N?rot. We show applications to direct detection of nitrogen-14 nuclei with spin I = 1 subject to large quadrupole interactions, using fast magic angle spinning (typically ?rot ? 60 kHz), backed up by simulations that provide insight into the properties of basic and interleaved DANTE sequences. When used for indirect detection, we show by numerical simulations that even basic DANTE-1 sequences can lead to a four-fold boost of efficiency compared to standard rectangular pulses.
Graphical abstract
Graphical abstract Highlights
? N interleaved delays alternating with nutations for tailored excitation. ? (DANTE-N). ? provide efficient broadband excitation of quadrupolar nuclei such as nitrogen-14. ? excite a large number of crystallite orientations in a spinning powder sample. ? can be combined with the indirect detection of 14N for efficient excitation.
Source:
Journal of Magnetic Resonance