Molecular and Environmental Sciences Group, Department of Geological Sciences , University of Saskatchewan , Saskatoon , Saskatchewan S7N 5E2 , Canada.
Stanford Synchrotron Radiation Lightsource , SLAC National Accelerator Laboratory, Stanford University , Menlo Park , California 94025 , United States.
Inorg Chem. 2018 Sep 4;57(17):10867-10872. doi: 10.1021/acs.inorgchem.8b01522. Epub 2018 Aug 22.
Selenium-based selenyl free radicals are chemical entities that may be involved in a range of biochemical processes. We report the first X-ray spectroscopic observation of a selenyl radical species generated photochemically by X-ray irradiation of low-temperature solutions of l-selenocysteine. We have employed high energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS) and electron paramagnetic resonance (EPR) spectroscopy, coupled with density functional theory calculations, to characterize and understand the species. The HERFD-XAS spectrum of the selenyl radical is distinguished by a uniquely low-energy transition with a peak energy at 12 659.0 eV, which corresponds to a 1s → 4p transition to the singly occupied molecular orbital of the free radical. The EPR spectrum shows the broad features and highly anisotropic g-values that are expected for a selenium free radical species. The availability of spectroscopic probes for selenyl radicals may assist in understanding why life chooses selenium over sulfur in selected biochemical processes.
基于硒的硒自由基是可能参与一系列生化过程的化学实体。我们报告了首例通过 X 射线辐照低温 l-硒代半胱氨酸溶液产生的硒自由基物种的 X 射线光谱学观察。我们采用高能量分辨荧光探测 X 射线吸收光谱（HERFD-XAS）和电子顺磁共振（EPR）光谱，并结合密度泛函理论计算，对该物种进行了表征和理解。硒自由基的 HERFD-XAS 光谱的特征是具有独特的低能跃迁，其峰值能量为 12659.0 eV，对应于自由基单占据分子轨道的 1s→4p 跃迁。EPR 光谱显示出宽特征和高度各向异性的 g 值，这是硒自由基物种所预期的。硒自由基的光谱探针的可用性可能有助于理解为什么生命在某些生化过程中选择硒而不是硫。
