Some Applications of Rf- Gradients and Excitation Sculpting in Nmr Spectroscopy

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). B0gradient based excitation sculpting can be converted into RF-gradient version. Selective onedimensional 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 BIRDR as inversion element results in isotope filter. Pre-suppression of non-C-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 BIRDR can be used efficiently as low-pass filter in HMBC experiment. Furthermore, simultaneous elimination of protons bound to N and C can be accomplished with BIRDR based method.