Abstract
The 19F-13C heteronuclear single quantum coherence (HSQC) experiment is vital for the structural elucidation of polyfluorinated organic species, yet its sensitivity and phaseability are limited by difficulties in uniform excitation of the widely disperse 19F spectral window. Adiabatic pulses of different types have previously been employed to generate effective π pulses for inversion and refocussing, but a systematic comparison of various adiabatic and other inversion pulses has not been published. In this work, it was observed that the use of a broadband inversion pulse (BIP) during the t 1 evolution period resulted in properly phaseable spectra for experiments optimized to detect 1 J CF, in contrast to CHIRP or WURST adiabatic pulses. For the INEPT and reverse-INEPT transfer segments of the HSQC, optimal sensitivity for resonances distant from the transmitter frequency was afforded by optimized universal rotation (BURBOP) or CHIRP pulses. In HSQC experiments with delays optimized for two-bond correlations, only the use of BURBOP pulses in INEPT and reverse-INEPT sequences afforded spectra cleanly phaseable across the F 2 and F 1 spectral windows. This observation is supported by off-resonance pulsed field gradient spin-echo experiments.
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Acknowledgements
We gratefully acknowledge Dr. Clemens Anklin of Bruker-Biospin for the 150 kHz CHIRP pulse and a coded version of the double-echo HSQC, Dr. J. Michael Geckle of Bruker-Biospin for rendering the main HSQC sequence used here compatible with Icon automation, and Ms. Rebecca Dooley for helpful discussions of the manuscript.
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723_2017_876_MOESM1_ESM.pdf
HSQC and spin-echo pulse sequences used in this study, coded for compatibility with Bruker TopSpin v3.2 and Varian VnmrJ v3.2A software, and the analogue of Fig. 5 with echo delay of 1.82 ms (PDF 315 kb)
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Marchione, A.A., Conklin, B. Comparison of the Effects of Different 19F π Pulses on the Sensitivity and Phaseability of the 19F-13C HSQC. Appl Magn Reson 48, 485–499 (2017). https://doi.org/10.1007/s00723-017-0876-y
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DOI: https://doi.org/10.1007/s00723-017-0876-y