Nitroxide biradicals have been prepared with electron-electron spin-spin exchange interaction, J, ranging from weak to very strong. EPR spectra of these biradicals in fluid solution depend on the ratio of J to the nitrogen hyperfine coupling, AN, and the rates of interconversion between conformations with different values of J. For relatively rigid biradicals EPR spectra can be simulated as the superposition of AB splitting patterns arising from different combinations of nitrogen nuclear spin states. For more flexible biradicals spectra can be simulated with a Liouville representation of the dynamics that interconvert conformations with different values of J on the EPR timescale. Analysis of spectra, factors that impact J, and examples of applications to chemical and biophysical problems are discussed.

中文翻译：

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溶液中氮自由基的连续波电子顺磁共振

制备的一氧化二氮自由基具有电子-电子自旋-自旋交换相互作用J，范围从弱到非常强。这些双自由基在流体溶液中的EPR谱取决于J与氮超细偶合的比率AN和不同J值的构象之间的相互转化率。对于相对刚性的双自由基，EPR谱可以模拟为AB分裂的叠加氮核自旋态不同组合产生的模式。为了更灵活地生成双自由基，可以使用动力学的Liouville表示来模拟光谱，该动力学在EPR时标上将具有不同J值的构象相互转换。讨论了光谱分析，影响J的因素以及化学和生物物理问题的应用实例。