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Methyl ¹H DQ-CPMG and TQ-CPMG experiments

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You can get the example files from the GitHub ChemEx page.

This example demonstrates the application of methyl ¹H DQ-CPMG (cpmg_ch3_1h_dq) and TQ-CPMG (cpmg_ch3_1h_tq) experiments for studying ¹³CH₃-labeled methyl groups. Both experiments are carried out on the same sample at single magnetic field. The major advantage of combining these two types of experiments is that accurate exchange parameters can already be obtained at single magnetic field. Typically it is necessary to carry out CPMG experiments at multiple static fields to obtain accurate chemical exchange parameters (pB and kex), while in DQ- and TQ-CPMG experiments the effective field strength behaves as two and three times of the static field, respectively. If datasets from ¹H SQ-CPMG experiment (cpmg_ch3_1h_sq) are available it is also possible to perform joint fits for all of these three types of experiments.

Both DQ-CPMG 1 and TQ-CPMG 2 experiments collect signals from I = 3/2 manifold, the selection of different terms of coherences is mainly achieved by different types of phase cycling. In both experiments CPMG pulses are applied with XY-16 phase cycle to help overcome off-resonance effects, besides, CPMG pulses have the option to be applied as 90x180y90x composite variety, which is indicated by comp180_flg.

Footnotes​

  1. A. Gopalan, T. Yuwen, L. E. Kay, and P. Vallurupalli, A Methyl ¹H Double Quantum CPMG Experiment to Study Protein Conformational Exchange, J Biomol NMR, 72:79-91, 2018. https://doi.org/10.1007/s10858-018-0208-z ↩

  2. T. Yuwen, P. Vallurupalli, and L. E. Kay, Enhancing the Sensitivity of CPMG Relaxation Dispersion to Conformational Exchange Processes by Multiple-Quantum Spectroscopy, Angew. Chem. Int. Ed., 55(38):11490-11494, 2016. https://doi.org/10.1002/anie.201605843 ↩