Frantsuzov Ilya, Vasa Suresh K, Ernst Matthias, Brown Steven P, Zorin Vadim, Kentgens Arno P M, Hodgkinson Paul
Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, United Kingdom.
Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 ED, Nijmegen, The Netherlands.
Chemphyschem. 2017 Feb 17;18(4):394-405. doi: 10.1002/cphc.201601003. Epub 2017 Jan 23.
Factors affecting the performance of H heteronuclear decoupling sequences for magic-angle spinning (MAS) NMR spectroscopy of organic solids are explored, as observed by time constants for the decay of nuclear magnetisation under a spin-echo (T2' ). By using a common protocol over a wide range of experimental conditions, including very high magnetic fields and very high radio-frequency (RF) nutation rates, decoupling performance is observed to degrade consistently with increasing magnetic field. Inhomogeneity of the RF field is found to have a significant impact on T2' values, with differences of about 20 % observed between probes with different coil geometries. Increasing RF nutation rates dramatically improve robustness with respect to RF offset, but the performance of phase-modulated sequences degrades at the very high nutation rates achievable in microcoils as a result of RF transients. The insights gained provide better understanding of the factors limiting decoupling performance under different conditions, and the high values of T2' observed (which generally exceed previous literature values) provide reference points for experiments involving spin magnetisation refocussing, such as 2D correlation spectra and measuring small spin couplings.
研究了影响用于有机固体魔角旋转（MAS）核磁共振波谱的H异核去耦序列性能的因素，通过自旋回波（T2'）下核磁化强度衰减的时间常数进行观察。通过在广泛的实验条件下使用通用协议，包括非常高的磁场和非常高的射频（RF）章动速率，观察到去耦性能随着磁场增加而持续下降。发现RF场的不均匀性对T2'值有显著影响，不同线圈几何形状的探头之间观察到约20%的差异。增加RF章动速率显著提高了对RF偏移的鲁棒性，但由于RF瞬变，在微线圈中可实现的非常高章动速率下，相位调制序列的性能会下降。所获得的见解有助于更好地理解不同条件下限制去耦性能的因素，并且观察到的高T2'值（通常超过先前文献值）为涉及自旋磁化重聚焦的实验提供了参考点，例如二维相关光谱和测量小的自旋耦合。
