HETERONUCLEAR SPIN DECOUPLING IN SOLID STATE NMR

我们已经演示了TPPM在500和750 MHz下的去耦， 观察到了理论预测的急剧缩小。 其他研究 已在以前的摘要中描述，如下所述：由于 增加的化学位移抵消了大量自旋之间的共振 （通常为“H”），去耦在高场变得更加苛刻。 在 此外，平均各向异性所需的MAS的高速率 相互作用使质子自旋库不均匀。 下 在这些条件下，不充分解耦的影响变得 戏剧化 两点相位调制（TPPM）去耦序列 我们已经开发出的技术， 非均匀自旋系统中的连续波（CW）去耦， 13 C-甲酸钙，以及更均匀的情况， (x-C，N-甘氨酸。 在非齐次系统中，由于自解耦 由于在'H水库内的homopolymer耦合的影响， 最小，CW去耦特别无效。 减少 Ernst等人描述的二阶再耦合是重要的 关于TPPM 在α_13 C，1 ′ N-甘氨酸中，额外的CW去耦功率 提高分辨率和灵敏度。 然而，即使改进了 探针技术，强偶极耦合的贡献，由于 CW去偶不能有效地去除大量的H核 一个人 从75 kHz增加到125 kHz CW去耦， 线宽从66 Hz提高到25 Hz， 至150 kHz提供了额外的信号强度，尽管没有 缩小 当切换到 TPPM方法;这里，缩小系数为6，缩小系数为10 当比较75 kHz CW时，观察到灵敏度（峰高） 去耦和125 kHz TPPM去耦结果。 的组合 改进的探针技术和解耦方法有可能 提供了显着增加的灵敏度和分辨率， 直接和间接化学位移的尺寸，以及改进， 这些类别预计在较高的磁场已经 实现了

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.