Broadband homonuclear TOCSY with amplitude and phase-modulated RF mixing schemes
Anika Kirschstein, Christian Herbst, Kerstin Riedel, Michela Carella, Jörg Leppert, Oliver Ohlenschläger, Matthias Görlach and Ramadurai Ramachandran
Journal of Biomolecular NMR; 2008; 40(4); pp 227-237
Abstract:
We have explored the design of broadband scalar coupling mediated 13C–13C and cross-relaxation suppressed 1H–1H TOCSY sequences employing phase/amplitude modulated inversion pulses. Considering a variety of supercycles, pulsewidths and a RF field strength of 10 kHz, the Fourier coefficients defining the amplitude and phase modulation profiles of the 180° pulses were optimised numerically so as to obtain efficient magnetisation transfer within the desired range of resonance offsets. The coherence transfer characteristics of the mixing schemes were assessed via numerical simulations and experimental measurements and were compared with commonly used sequences based on rectangular RF pulses. The efficacies of the clean 1H–1H TOCSY sequences were also examined via numerical simulations for application to weakly oriented systems and sequences with efficient, broadband and clean dipolar transfer characteristics were identified. In general, the amplitude and phase modulated TOCSY sequences presented here have moderately better performance characteristics than the sequences currently employed in biomolecular NMR spectroscopy.