Chen Zhong, Cai Shuhui, Chen Zhiwei, Zhong Jianhui
Department of Physics, Fujan Key Laboratory of Plasma and Magnetic Resonance, State Key Laboratory of Physical Chemistry of Solid Surface, Xiamen University, Xiamen 361005, China.
J Chem Phys. 2009 Feb 28;130(8):084504. doi: 10.1063/1.3076046.
A pulse sequence, IDEAL-II, is proposed based on the concept of intermolecular dipolar-interaction enhanced all lines [Z. Chen et al., J. Am. Chem. Soc. 126, 446 (2004)] for obtaining one-dimensional (1D) high-resolution liquid NMR spectra in inhomogeneous fields via two-dimensional acquisitions. With the new acquisition scheme, the range of magnetic field inhomogeneity rather than chemical shift is sampled in the indirect dimension. This enables a great reduction in acquisition time and amount of data, much improved over the original IDEAL implementation. It is applicable to both isolated and J-coupled spin systems in liquid. For the latter, apparent J coupling constants are magnified threefold in spectra obtained with this sequence. This allows a more accurate measurement of J coupling constants in the cases of small J coupling constants or large inhomogeneous fields. Analytical expression was derived based on intermolecular multiple-quantum coherence treatments. Solution samples that were purposely deshimmed and biological samples with intrinsic field inhomogeneities were tested. Experimental results demonstrate that this sequence retains useful structural information including chemical shifts, relative peak areas, and multiplet patterns of J coupling even when the field inhomogeneity is severe enough to almost erase all spectroscopic information with conventional 1D single-quantum coherence techniques. This sequence is more applicable to weakly coupled and uncoupled spin systems, potentially useful for studying metabolites in in vivo NMR spectroscopy and for characterizing technologically important new materials in combinatorial chemistry.
基于分子间偶极相互作用增强所有谱线的概念[Z. Chen等人，《美国化学会志》126, 446 (2004)]，提出了一种脉冲序列IDEAL-II，用于通过二维采集在非均匀场中获得一维(1D)高分辨率液体核磁共振谱。采用新的采集方案，在间接维度中对磁场不均匀性范围而非化学位移进行采样。这使得采集时间和数据量大幅减少，比原始的IDEAL实现有了很大改进。它适用于液体中的孤立自旋系统和J耦合自旋系统。对于后者，在使用该序列获得的谱图中，表观J耦合常数放大了三倍。这使得在小J耦合常数或大不均匀场的情况下能够更准确地测量J耦合常数。基于分子间多量子相干处理推导了解析表达式。对故意去匀场的溶液样品和具有固有场不均匀性的生物样品进行了测试。实验结果表明，即使场不均匀性严重到几乎用传统的一维单量子相干技术消除所有光谱信息时，该序列仍保留有用的结构信息，包括化学位移、相对峰面积和J耦合的多重峰模式。该序列更适用于弱耦合和非耦合自旋系统，可能有助于研究体内核磁共振波谱中的代谢物以及表征组合化学中技术上重要的新材料。
