The WURST kind of pulses in solid-state NMR

WURST pulses (wideband, uniform rate, smooth truncation) were first introduced two decades ago by Kupce and Freeman as a means of achieving broadband adiabatic inversion of magnetisation for solution-state C-13 decoupling at high magnetic field strengths. In more recent years these pulses have found use in an increasingly diverse range of applications in solid-state NMR. This article reviews a number of recent developments that take advantage of WURST pulses, including broadband excitation, refocusing and cross polarisation for the acquisition of ultra-wideline powder patterns, signal enhancement for half-integer and integer spin quadrupolar nuclei, spectral editing, direct and indirectly observed N-14 overtone MAS, and symmetry-based homonuclear recoupling. Simple mathematical descriptions of WURST pulses and some brief theory behind their operation in the adiabatic and non-adiabatic regimes are provided, and various practical considerations for their use are also discussed. (C) 2013 Elsevier Inc. All rights reserved.