Some applications of RF-gradients and excitation sculpting in NMR spectroscopy

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>RF-gradients produced utilizing RF-field inhomogenity of conventional receiver/transmitter coil of NMR-probe can be used to mimic the effects of B₀-gradients. This is done by placing long inhomogenous pulse in between two 90° pulses of appropriate phases (z-rotation cluster). B0-gradient based excitation sculpting can be converted into RF-gradient version. Selective one-dimensional TOCSY and NOESY using RF-gradient based excitation sculpting are described. In addition, non-selective two-dimensional experiments, TOCSY and NOESY, with RF-gradient based coherence selection are presented. Excitation sculpting using BIRD or BIRD_R as inversion element results in isotope filter. Pre-suppression of non-¹³C-bound protons using RF-gradient BIRD prior to HSQC enables recording of spectrum of comparable quality to B₀-gradient selected HSQC. This is beneficial for spectrometers lacking B₀-gradient capabilities. Excitation sculpting using BIRD_R can be used efficiently as low-pass filter in HMBC experiment. Furthermore, simultaneous elimination of protons bound to ¹⁵N and ¹³C can be accomplished with BIRD_R based method.</p></div>