Theory of double quantum two-dimensional electron spin resonance with application to distance measurements
Theory of double quantum two-dimensional electron spin resonance with application to distance measurements
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DOI：
10.1063/1.474490
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发表时间：
1997-08-01
影响因子：
4.4
通讯作者：
Freed, JH
中科院分区：
文献类型：
--
作者：
Saxena, S;Freed, JH
提出了一种计算刚性极限下的双量子二维电子自旋共振 (DQ-2D ESR) 谱的公式，该公式对应于最近从氮氧双自由基获得的实验 DQ-2D ESR 谱。该理论包括硝基氧部分之间的偶极相互作用以及完全不对称的 g 和超精细张量以及双自由基的角几何。通过采用最近引入的分裂哈密顿理论进行数值模拟，可以考虑任意钱包（强但不是真正的非选择性脉冲）的影响。它显示了磁共振中的任意脉冲如何创建“禁止的”相干路径，并描述了它们在 DQ-2D ESR 中的作用。这些 DQ-2D ESR 信号对偶极相互作用强度的高敏感性在“禁止”路径的方向选择性方面得到了证明和合理化。进一步表明，这种选择性还对双自由基的结构几何形状（即硝基氧部分的方向）提供了限制。该理论应用于最近对末端标记的聚脯氨酸肽双自由基的双量子调制（DQM）实验。该双自由基两端之间的距离为 18.5 埃。提出了一种新的双脉冲双量子实验（类似于最近的 NMR 实验），并从理论上探讨了其在 ESR 情况下的可行性。 (C) 1997 年美国物理研究所。
A formulation is presented for calculating double quantum two dimensional electron spin resonance (DQ-2D ESR) spectra in the rigid limit that correspond to recent experimental DQ-2D ESR spectra obtained from a nitroxide biradical. The theory includes the dipolar interaction between the nitroxide moieties as well as the fully asymmetric g and hyperfine tensors and the angular geometry of the biradical. The effects of arbitrary purses (strong but not truly nonselective pulses) are included by adapting the recently introduced split Hamiltonian theory for numerical simulations. It is shown how arbitrary pulses in magnetic resonance create ''forbidden'' coherence pathways, and their role in DQ-2D ESR is delineated. The high sensitivity of these DQ-2D ESR signals to the strength of the dipolar interaction is demonstrated and rationalized in terms of the orientational selectivity of the ''forbidden'' pathways. It is further shown that this selectivity also provides constraints on the structural geometry (i.e., the orientations of the nitroxide moieties) of the biradicals. The theory is applied to the recent double quantum modulation (DQM) experiment on an end-labeled poly-proline peptide biradical. A distance of 18.5 Angstrom between the ends is found for this biradical. A new two pulse double quantum experiment is proposed (by analogy to recent NMR experiments), and its feasibility for the ESR case is theoretically explored. (C) 1997 American Institute of Physics.