Intermolecular zero-quantum coherence NMR spectroscopy in the presence of local dipole fields.
Intermolecular zero-quantum coherence NMR spectroscopy in the presence of local dipole fields.
复制标题
DOI：
10.1063/1.2904564
复制
发表时间：
2008-04
期刊：
影响因子：
--
通讯作者：
Dávid Z. Balla;C. Faber
中科院分区：
文献类型：
--
作者：
Dávid Z. Balla;C. Faber
探测分子间零量子相干（izqc）的核磁共振实验允许在不均匀磁场下观察均匀的线形。局部偶极子场削弱了这类实验的重聚焦能力，使现有的信号演化理论描述失效。在本文中，通过进行广泛的数值模拟，评估了局部偶极子场对二维iZQC光谱实验的影响，该模拟解决了64(3)个空间点磁化阵列中二元解的非线性Bloch方程。采用不同磁化率值的球形体（分别对应于直径为100微米的玻璃球或空气夹杂物）模拟局部偶极子场。局域场导致局域相互作用的自旋差频分布变宽，导致溶质峰幅度减小的主导效应，然后在光谱中观察到谱线展宽。通过使用17.6 T磁场强度的模拟，确定了玻璃和空气包裹体中仍然允许观察溶质峰的样品与包裹体体积的最小比值分别为eta（极限）=215和eta（极限）=392。将直径为100微米的玻璃球包埋在琼脂凝胶中获得的实验数据得出eta（极限）=252，与模拟得到的数量级一致。从这些数据可以得出结论，只要空气夹杂物的相对体积不超过样品体积的0.1%数量级，iZQC光谱是可能的。与先前的推测相反，这一限制强烈地排除了iZQC光谱研究中具有高密度强不均匀性的材料或组织。
NMR experiments detecting intermolecular zero-quantum coherences (iZQCs) allow for observation of homogeneous line shapes under inhomogeneous magnetic fields. Local dipole fields impair the refocusing capacity of such experiments and render the available theoretical description of signal evolution invalid. In this article, the impact of local dipole fields on two-dimensional iZQC spectroscopy experiments was assessed by performing extensive numerical simulations, which solved the nonlinear Bloch equations for a binary solution in a magnetization array of 64(3) spatial points. Local dipole fields were simulated using spherical volumes with different magnetic susceptibility values corresponding to either a glass sphere or an air inclusion with a diameter of 100 microm. The local field resulted in a broadened distribution of difference frequencies between locally interacting spins and led to the dominating effect of decreasing the amplitude of the solute peak, before line broadening was observed in the spectra. From simulations using a magnetic field strength of 17.6 T, the smallest ratio of sample to inclusion volume that still allowed for observation of the solute peak was determined to be eta(limit)=215 and eta(limit)=392 for glass and air inclusions, respectively. Experimental data acquired with a 100 microm diameter glass sphere embedded in agar gel yielded a value of eta(limit)=252 and confirmed the order of magnitude obtained from the simulations. From these data, it was concluded that iZQC spectroscopy is possible as long as the relative volume occupied by air inclusions does not exceed the order of 0.1% of the sample volume. This limit, in contrast to the previous speculations, strongly excludes materials or tissues with high density of strong inhomogeneities from the investigation by iZQC spectroscopy.