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Magnetochemistry 2018, 4(3), 33; https://doi.org/10.3390/magnetochemistry4030033

Analysis of Artifacts Caused by Pulse Imperfections in CPMG Pulse Trains in NMR Relaxation Dispersion Experiments

1
Graduate School of Medical Life Science, Yokohama City University, 1-7-29 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
2
Bruker Japan K.K., Osaka Office, 1-8-29 Nishimiyahara, Yodogawa-ku, Osaka-shi, Osaka 532-0004, Japan
*
Author to whom correspondence should be addressed.
Received: 28 June 2018 / Revised: 25 July 2018 / Accepted: 26 July 2018 / Published: 30 July 2018
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Abstract

Nuclear magnetic resonance relaxation dispersion (rd) experiments provide kinetics and thermodynamics information of molecules undergoing conformational exchange. Rd experiments often use a Carr-Purcell-Meiboom-Gill (CPMG) pulse train equally separated by a spin-state selective inversion element (U-element). Even with measurement parameters carefully set, however, parts of 1H–15N correlations sometimes exhibit large artifacts that may hamper the subsequent analyses. We analyzed such artifacts with a combination of NMR measurements and simulation. We found that particularly the lowest CPMG frequency (νcpmg) can also introduce large artifacts into amide 1H–15N and aromatic 1H–13C correlations whose 15N/13C resonances are very close to the carrier frequencies. The simulation showed that the off-resonance effects and miscalibration of the CPMG π pulses generate artifact maxima at resonance offsets of even and odd multiples of νcpmg, respectively. We demonstrate that a method once introduced into the rd experiments for molecules having residual dipolar coupling significantly reduces artifacts. In the method the 15N/13C π pulse phase in the U-element is chosen between x and y. We show that the correctly adjusted sequence is tolerant to miscalibration of the CPMG π pulse power as large as ±10% for most amide 15N and aromatic 13C resonances of proteins. View Full-Text
Keywords: nuclear magnetic resonance (NMR); Carr-Purcell-Meiboom-Gill (CPMG) pulse train; relaxation dispersion; off-resonance effect; pulse imperfection nuclear magnetic resonance (NMR); Carr-Purcell-Meiboom-Gill (CPMG) pulse train; relaxation dispersion; off-resonance effect; pulse imperfection
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Konuma, T.; Nagadoi, A.; Kurita, J.-I.; Ikegami, T. Analysis of Artifacts Caused by Pulse Imperfections in CPMG Pulse Trains in NMR Relaxation Dispersion Experiments. Magnetochemistry 2018, 4, 33.

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