The boundary between liquidlike and solidlike behavior in magnetic resonance
The boundary between liquidlike and solidlike behavior in magnetic resonance
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DOI：
10.1063/1.475504
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发表时间：
1998-06
影响因子：
4.4
通讯作者：
W. Warren;Sangdoo Ahn
中科院分区：
文献类型：
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作者：
W. Warren;Sangdoo Ahn
最近在二维溶液核磁共振(核磁共振)中的实验工作表明，由于远距离原子核之间的偶极耦合，出现了异常的交叉峰和额外的共振。这些光谱的分析要么是经典的，使用Bloch方程(包括对退磁场的平均场近似)，要么是使用全密度矩阵图，显示峰对应于分子间多量子相干(IMQCs)。在这里，我们使用密度矩阵处理来预测通常在固体中看到的偶极效应在溶液中的强度；我们还详细地探讨了固体和液体中偶极效应之间的根本区别。例如，即使通过溶液中的偶极哈密顿量进行极化转移是不可能的，但具有实质性信号增强的间接检测是可能的。我们发现，即使对于像1H或3He这样的高γ核，类固体偶极效应也是相当小的，除非扩散常数不变。
Recent experimental work in two-dimensional solution NMR (nuclear magnetic resonance) has demonstrated anomalous cross-peaks and additional resonances due to dipolar couplings between distant nuclei. These spectra have been analyzed either classically, using Bloch equations which include a mean-field approximation to the demagnetizing field, or quantum mechanically, using a full density matrix picture which shows that the peaks correspond to intermolecular multiple-quantum coherences (iMQCs). Here we use a density matrix treatment to predict intensities in solution for dipolar effects conventionally seen in solids; we also explore in detail the fundamental differences between dipolar effects in solids and liquids. For example, even though polarization transfer via the dipolar Hamiltonian in solution is not possible, indirect detection with substantial signal enhancement is possible. We find that, even for high-γ nuclei such as 1H or 3He, solidlike dipolar effects are quite small unless the diffusion const...