HYSCORE, a variant of two-dimensional ESEEM spectroscopy, is currently one of the most effective tools in high-resolution solid-state EPR spectroscopy. Our systematic studies of hydrogen bonds with semiquinones in 15 N-labeled proteins have previously provided us with an extensive collection of 15 N HYSCORE spectra produced by N–H…O nitrogen donors. Examination of these spectra has indicated in several cases lineshape distortions not described by available theoretical models. We were able to explain all observed artificial phenomena in the 15 N spectra of semiquinones considering a single mechanism—strain of the isotropic hyperfine interaction. In this review article, we introduce the HYSCORE experiment and the theoretical background for spectra of I = 1/2 nuclei in orientation-disordered samples. We then present a description of the observed lineshape distortions and an explanation of the hyperfine strain’s influence on the experimental spectra. In the final part of the article, we discuss (i) similar lineshape distortions found in previously published spectra from 15 N, 29 Si, 31 P, and 57 Fe nuclei that can be explained using the approach applied for the analysis of the 15 N spectra of semiquinones, and (ii) a recently published analysis of 31 P spectra with a different type of lineshape distortion based on a more sophisticated method, where the strength of anisotropic coupling is correlated with the sign and value of the isotropic constant in different conformations of a Cu(II) complex.

中文翻译：

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超精细耦合应变对来自 I = 1/2 核的二维 ESEEM 光谱的影响

HYSCORE 是二维 ESEEM 光谱的一种变体，是目前高分辨率固态 EPR 光谱中最有效的工具之一。我们对 15 个 N 标记蛋白质中半醌氢键的系统研究以前为我们提供了大量由 N–H…O 氮供体产生的 15 N HYSCORE 光谱。对这些光谱的检查表明在几种情况下存在可用理论模型未描述的线形失真。考虑到单一机制——各向同性超精细相互作用的应变，我们能够解释半醌的 15 N 光谱中所有观察到的人工现象。在这篇评论文章中，我们介绍了 HYSCORE 实验和 I = 1/2 原子核在取向无序样品中的光谱的理论背景。然后，我们描述了观察到的线形失真，并解释了超精细应变对实验光谱的影响。在文章的最后部分，我们讨论了 (i) 在先前发表的 15 N、29 Si、31 P 和 57 Fe 原子核光谱中发现的类似线形畸变，可以使用用于分析 15 N 原子核的方法进行解释半醌的光谱，以及 (ii) 最近发表的基于更复杂方法的具有不同类型线形失真的 31 P 光谱分析，其中各向异性耦合的强度与不同构象中各向同性常数的符号和值相关Cu(II) 络合物。