HETERONUCLEAR SPIN DECOUPLING IN SOLID STATE NMR

由于增加的化学位移抵消了 大量的自旋（通常为1H），去耦在高 领域 此外，MAS的高比率，需要平均 各向异性相互作用，使质子自旋库 不均匀的 在这种情况下， 脱钩变得戏剧性。 两点调相（TPPM） 我们开发的解耦序列显示出显著的 非均匀自旋中连续波（CW）解耦改进 系统，如13 C-甲酸钙，以及更均匀的情况 例如~-13C。 5 N-甘氨酸。 在非均匀系统中， 由于1H内的homophilic耦合而产生的自解耦效应 水库是最小的，因此CW去耦特别重要。 无效。 二阶耦合的减少描述 Ernst et al.的结果与TPPM显著相关。 在u-13 C中，15 N-甘氨酸， 附加的CW去耦功率提高了分辨率和灵敏度。 然而，即使使用改进的探针技术， 由于大量的1H核， 单独使用CW去耦就可以有效地消除。 从75 kHz开始 到125 kHz CW去耦提供了从66 kHz到125 kHz的线宽改善 到25 Hz，并额外增加到t50 kHz， 信号强度虽然没有变窄。 更戏剧性的 当切换到TPPM方法时，观察到改进;这里， 在变窄方面为六倍，在灵敏度方面为十倍（峰值 在比较75 kHz CW去耦和12 S去耦时， kHz TPPM去耦结果。 改进的探头组合 技术和脱钩方法有可能提供 显着增加的灵敏度和分辨率的直接和 间接化学位移维数 这些方面的改进 已经实现了在更高磁场下预期的类别。

Due to increased chemical shift offsets from resonance among abundant spins (usually 1H), decoupling becomes more demanding at high field. In addition, the high rates of MAS, required to average the anisotropic interactions, render the proton spin reservoir inhomogeneous. Under these conditions, the effects of insufficient decoupling become dramatic. The two-point phase-modulated (TPPM) decoupling sequence which we have developed demonstrates significant improvement over continuous-wave (CW) decoupling in inhomogeneous spin systems such as calcium 13C-formate, as well as more homogeneous cases such as ~-'3C. 5N-glycine. In inhomogeneous systems, the self-decoupling effect due to homonuclear couplings within the 1H reservoir is minimal, and so CW decoupling is particularly ineffective. The reduction of the second-order recoupling described by Ernst et al. is significant with TPPM. In u- 13C,1 5N-glycine, additional CW decoupling power improves resolution and sensitivity. However, even with improved probe technology, the contribution of strong dipolar couplings due to abundant 1H nuclei cannot be effectively removed with CW decoupling alone. Increasing from 75 kHz to 125 kHz CW decoupling provides an improvement in linewidth from 66 to 25 Hz, and an additional increase to tSO kHz provides additional signal intensity albeit without narrowing. The more dramatic improvement is observed when switching to the TPPM method; here a factor of six in narrowing and a factor of ten in sensitivity (peak height) is observed when comparing the 75 kHz CW decoupling and 12S kHz TPPM decoupling results. The combination of improved probe technology and decoupling methodology has potential to provide significant increases in the sensitivity and resolution of direct and indirect chemical shift dimensions. and the improvements in these categories expected at higher magnetic fields have been realized.