Hwang T L, Shaka A J
Chemistry Department, University of California, Irvine, California, 92697-2025, USA.
J Magn Reson. 1998 Dec;135(2):280-7. doi: 10.1006/jmre.1998.1598.
Rotating-frame NMR experiments which either emphasize or suppress cross relaxation, and which simultaneously suppress TOCSY, COSY, and zero-quantum peaks in NMR spectra, are presented and analyzed. The new experiments rely on mixing sequences which follow naturally from the transverse-ROESY (Tr-ROESY) sequence of Hwang and Shaka, and which are applicable to larger molecules in solution (spin diffusion limit). In the first variant a modified Tr-ROESY sequence, called multiple-pulse ROESY (MP-ROESY), is used to enhance cross-relaxation peak intensity compared to Tr-ROESY; in the second, called phase-modulated CLEAN chemical exchange (CLEANEX-PM), cross-relaxation peaks are greatly attenuated. The two methods are thus complementary: MP-ROESY is used to observe Overhauser peaks, and CLEANEX-PM is used to eliminate them, permitting clear observation of chemical exchange peaks alone. The new techniques are examined by theory and experiment. Practical guidelines that will result in high-quality spectra are given, including the judicious use of continuous weak static magnetic field gradients.
本文介绍并分析了旋转框架核磁共振实验，这些实验要么强调要么抑制交叉弛豫，同时抑制核磁共振谱中的TOCSY、COSY和零量子峰。新实验依赖于混合序列，这些序列自然源自Hwang和Shaka的横向旋转Overhauser效应光谱学（Tr-ROESY）序列，并且适用于溶液中的大分子（自旋扩散极限）。在第一个变体中，一种称为多脉冲旋转Overhauser效应光谱学（MP-ROESY）的改良Tr-ROESY序列用于增强与Tr-ROESY相比的交叉弛豫峰强度；在第二个变体中，称为相位调制的CLEAN化学交换（CLEANEX-PM），交叉弛豫峰被大大衰减。因此，这两种方法是互补的：MP-ROESY用于观察Overhauser峰，而CLEANEX-PM用于消除它们，从而仅允许清晰观察化学交换峰。通过理论和实验对新技术进行了研究。给出了将产生高质量光谱的实用指南，包括明智地使用连续弱静磁场梯度。
