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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Determination of the g Tensors for the Dominant Stable Radicals in X-Irradiated _-n-Fructose Single Crystals
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Determination of the g Tensors for the Dominant Stable Radicals in X-Irradiated _-n-Fructose Single Crystals

机译：X射线辐照的_-n-果糖单晶中主要稳定自由基的g张量的确定

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摘要

In spite of recent successful identifications of radicals produced after X-ray irradiation at 10 and 77 K in _-D-fructose, the structure of the two stable radicals dominating the electron paramagnetic resonance (EPR) spectrum after room temperature irradiation is still unclear. Based on the agreement between proton hyperfine (HF) tensors obtained in electron nuclear double resonance (ENDOR) experiments and the results of single molecule density functional calculations, a model for these radicals, involving OH abstraction at the C2 ring position, had previously been proposed, but this assignment could not be confirmed when the radical was embedded in a crystal environment. In this paper, we therefore provide additional experimental information for these radicals. First, their g tensors are determined from angular dependent ENDOR-induced EPR experiments. The relatively large anisotropy of these tensors is indicative of delocalization of the unpaired electron onto a neighboring oxygen atom. Second, EPR spectra of fructose powders, selectively enriched in 13C on various ring positions, are presented, demonstrating that the HF interaction with the carbon atom C3 is larger than with the C2. Combining the g tensor, proton and ~(13)C HF data, we conclude that Ohe structure of the stable radicals differs strongly from that of intact molecules and that further advanced quantum chemical modeling will be required to fully identify them.
机译：尽管最近成功地鉴定了在10 D和77 K的D-果糖中进行X射线辐照后产生的自由基，但在室温辐照后，两个稳定的自由基支配电子顺磁共振（EPR）光谱的结构仍然不清楚。基于电子核双共振（ENDOR）实验中获得的质子超细（HF）张量与单分子密度泛函计算结果之间的一致性，以前已经提出了这些自由基的模型，其中涉及C2环位置的OH抽象，但是当自由基嵌入晶体环境中时无法确认此分配。因此，在本文中，我们提供了这些自由基的其他实验信息。首先，它们的g张量是由依赖于角度的ENDOR诱导的EPR实验确定的。这些张量的相对较大的各向异性表明未成对的电子离域到邻近的氧原子上。其次，呈现了果糖粉末的EPR光谱，该果糖粉末在13 C的各个环位置上选择性富集，表明HF与碳原子C3的相互作用大于与C2的相互作用。结合g张量，质子和〜（13）C HF数据，我们得出结论，稳定基团的Ohe结构与完整分子的结构大不相同，并且需要进一步的先进量子化学建模才能完全识别它们。

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