Institute of Environmental Science and Technology, Zhejiang University, Hangzhou 310029, PR China.
Anal Chem. 2011 Oct 15;83(20):7856-62. doi: 10.1021/ac201622g. Epub 2011 Aug 1.
Photoreduction is a major obstacle for using the X-ray absorption near-edge structure (XANES) fingerprint to perform metal speciation at the molecular level in biological and environmental samples, especially for metalloproteins. In this study, soft X-ray induced photoreduction was observed in organic Cu(II) compounds during XANES measurements in a third-generation synchrotron source. Next Cu L(3)-edge, O K-edge, and C K-edge XANES spectroscopy, together with the scanning transmission X-ray microscopy (STXM), were used to probe the specific radiation damage processes of Cu acetate with similar local structures to Cu metalloproteins. Breakup of the Cu-Cu bond was hypothesized for the initial photoreduction of Cu acetate. The following radiation damage of Cu acetate produced CuO and an organic Cu(I) compound with a C═C bond, and the further photoreduction of the resulting CuO to Cu metal was also demonstrated. Our results indicated the importance of consideration of photoreduction during soft XANES measurements for the solid state compounds with high valence metals. Reducing the radiation dose to ~0.1 MGy effectively prevented the photoreduction of organic Cu(II) compounds during these measurements. This proposed radiation damage mechanism in Cu acetate may be generally useful in explaining the photoreduction process in Cu metalloproteins.
光还原是在生物和环境样品中进行分子水平金属形态分析时使用 X 射线吸收近边结构（XANES）指纹的主要障碍，特别是对于金属蛋白。在这项研究中，在第三代同步加速器源中的 XANES 测量过程中观察到有机 Cu(II) 化合物中的软 X 射线诱导光还原。接下来的 Cu L(3)-边、O K-边和 C K-边 XANES 光谱，以及扫描透射 X 射线显微镜（STXM），用于探测具有与 Cu 金属蛋白相似局部结构的 Cu 醋酸盐的特定辐射损伤过程。假设 Cu 醋酸盐的初始光还原会导致 Cu-Cu 键的断裂。随后的 Cu 醋酸盐辐射损伤产生了 CuO 和具有 C=C 键的有机 Cu(I) 化合物，并且还证明了由此产生的 CuO 进一步光还原为 Cu 金属。我们的结果表明，在具有高价金属的固态化合物的软 XANES 测量中，考虑光还原的重要性。将辐射剂量降低到约 0.1 MGy 可有效防止在这些测量过程中有机 Cu(II) 化合物的光还原。在 Cu 醋酸盐中提出的这种辐射损伤机制可能在解释 Cu 金属蛋白的光还原过程中普遍有用。
