Decoupling Two-Dimensional NMR Spectroscopy in Both Dimensions: Pure Shift NOESY and COSY
Decoupling Two-Dimensional NMR Spectroscopy in Both Dimensions: Pure Shift NOESY and COSY
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DOI：
10.1002/anie.201108888
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Morris, Gareth A.
中科院分区：
文献类型：
--
作者：
Aguilar, Juan A.;Colbourne, Adam A.;Morris, Gareth A.
谱图归属是核磁共振波谱分析化学结构的关键步骤，但往往受到信号重叠的限制。如果抑制自旋-自旋耦合引起的多重态结构，可以大大提高光谱分辨率，并相应地简化指认过程。可以使用各种方法将多重峰折叠成单一的“纯位移”峰，如在1D核磁共振波谱中已经证明的，以及在几个不同的同核2D实验的一维中。[1-10]最近，已经表明，对在一维解耦的TOCSY数据集应用协方差处理可以得到完全解耦的2D谱。[11]以前的完全解耦2D谱的方法使用了模式识别后处理，应用于传统的、完全耦合的2D数据。[12-14]完全解耦的2D谱的分辨率和简单性的显著提高使得它们对于自动结构解析特别有吸引力。在这里，我们比较了两种不同的去耦合方法，通过将不同的单一去耦合方法应用于NOESY和NQF-COSY实验，通过协方差处理产生双纯移位2D谱，说明了纯移位协方差核磁共振谱的非常一般的性质和分辨率增益的潜力。对一个谱维使用纯移位捕获极大地提高了分辨率，将多重态结构折叠为单重态，而协方差处理的使用通过将相关信息压缩成2D单重态，进一步提高了可解释性。在2D核磁共振波谱中实现宽带同核去偶的方法包括Zangger-Sterk(ZS)实验及其改编；[1-4]Pell-Keeler(PK)458相敏2D-J数据投影；[5]序列元素的“鸟”(双线性旋转去偶)族；[6，7]和“恒定时间”(CT)方法。[8-10]所有这些方法都或多或少地牺牲了灵敏度以换取分辨率。前三种方法适用于产生同相交叉峰值的实验，而CT既可以用于同相信号，也可以用于反相信号。每种方法都有各自的优点；ZS实验允许在灵敏度和去耦合范围之间进行折衷，BIRD方法可以避免强耦合的问题，[6]PK投影允许在第三维测量J耦合，而恒定时间方法对于中等大小的分子具有特别好的灵敏度。
Spectral assignment is a crucial step in the analysis of chemical structure by NMR spectroscopy, but is often limited by signal overlap. If the multiplet structure caused by spin–spin coupling is suppressed, spectral resolution can be greatly increased, and the process of assignment correspondingly simplified. Collapsing a multiplet to a single “pure shift” peak can be achieved using a variety of methods, as has been demonstrated in 1D NMR spectroscopy, and in one dimension of several different homonuclear 2D experiments.[1–10] Recently, it has been shown that applying covariance processing to a TOCSY dataset decoupled in one dimension gives a fully decoupled 2D spectrum.[11] Previous routes to fully decoupled 2D spectra have used pattern recognition postprocessing applied to conventional, fully coupled 2D data.[12–14] The considerably increased resolution in, and simplicity of, fully decoupled 2D spectra makes them particularly attractive for automated structure elucidation. Here we compare two different decoupling methods, illustrating the very general nature, and potential for resolution gain, of pure shift covariance NMR spectroscopy, by applying different single decoupling methods to the NOESY and nQF-COSY experiments, producing doubly pure shift 2D spectra by covariance processing. Using pure shift acquisition for one spectral dimension greatly improves resolution, collapsing multiplet structure to singlets, whereas the use of covariance processing gives a further gain in interpretability by condensing the correlation information into 2D singlets. Methods for achieving broadband homonuclear decoupling in 2D NMR spectroscopy include the Zangger–Sterk (ZS) experiment and its adaptations;[1–4] the Pell–Keeler (PK) 458 projection of phase-sensitive 2D-J data;[5] the “BIRD”(bilinear rotation decoupling) family of sequence elements;[6, 7] and the “constant time”(CT) approach.[8–10] All such methods trade sensitivity for resolution, to a greater or lesser extent. The first three methods are appropriate for experiments that generate in-phase cross-peaks, whereas CT can be used with both in-phase and anti-phase signals. Each has specific advantages; the ZS experiment allows a trade-off between sensitivity and decoupling range, the BIRD method can avoid problems with strong coupling,[6] PK projection allows J couplings to be measured in a third dimension, and constant time methods have particularly good sensitivity for medium-sized molecules.