HETERONUCLEAR SPIN DECOUPLING IN SOLID STATE NMR

我们已经演示了在500 MHz和750 MHz下的TPPM去耦合 观察到了理论上预测的戏剧性的缩小。其他研究 已经在以前的摘要中描述过，如下所述：由于 增加的化学位移抵消了丰富自旋之间的共振 (通常为‘H)，去耦合在高场下变得更加苛刻。 此外，平均各向异性所需的高MAS比率 相互作用使质子自旋库变得不均匀。在……下面 在这些条件下，不充分脱钩的影响将成为 太戏剧化了。两点调相(TPPM)解耦序列 我们开发的产品显示出显著的改进 非均匀自旋系统中的连续波(CW)去耦合 13C-甲酸钙，以及更均匀的情况，如 (X-“C”，N-甘氨酸。在非均匀系统中，由于自解耦 ‘H储存库内同核偶联的影响是 最小限度地，CW脱钩尤其无效。减少了 Ernst等人描述的二阶重耦合。意义重大 使用TPPM。在a_13C中，L的N-甘氨酸，附加的CW去偶合功率 提高分辨率和灵敏度。然而，即使改进了 探头技术，由于强偶极耦合的贡献 连续波去偶合不能有效地去除丰度的~H核 独自一人。从75 kHz增加到125 kHz CW去耦可提供 将线宽从66赫兹改进到25赫兹，并额外增加 到150 kHz提供额外的信号强度，尽管没有 缩小范围。当切换到 TPPM方法；这里是缩小范围的六倍和十倍 当比较75 kHz CW时，可以观察到In灵敏度(峰值高度 解耦和125 kHz TPPM解耦的结果。这两种技术的结合 改进的探测技术和解耦方法有可能 提供显著提高的灵敏度和分辨率 直接和间接化学位移维度，以及在 预计在较高磁场下的这些类别已经 意识到了。

We have demonstrated TPPM decoupling at 500 and 750 MHz and observed dramatic narrowing as predicted by theory. Other studies have been described in previous abstracts, as quoted below: Due to increased chemical shift offsets from resonance among abundant spins (usually 'H), 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 that 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 (x-"C,"N-glycine. In inhomogeneous systems, since the self-decoupling effect due to homonuclear couplings within the 'H reservoir is minimal, CW decoupling is particularly ineffective. The reduction of the second-order recoupling described by Ernst et al. is significant with TPPM. In a_13C,l 'N-glycine, additional CW decoupling power improves resolution and sensitivity. However, even with improved probe technology, the contribution of strong dipolar couplings due to abundant 'H 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 150 kHz provides additional signal intensity, albeit without narrowing. A 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 125 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 ex pected at higher magnetic fields have been realized.