Bianconi A, Congiu-Castellano A, Durham P J, Hasnain S S, Phillips S
Nature. 1985;318(6047):685-7. doi: 10.1038/318685a0.
Our knowledge of the structure of condensed matter has been based primarily on spectroscopic methods that measure first-order pair correlations of atomic arrangements and thus provide interatomic distances (for example neutron and X-ray scattering). Bond angles are given by higher-order correlation functions, and such information can be provided by X-ray absorption near-edge structure (XANES) spectroscopy, the features of which are determined by multiple scattering of photoelectrons whose paths begin and end at the selected absorbing atom. We report here angular-resolved XANES spectroscopy of a single crystal of carboxymyoglobin (MbCO). The large dichroism of the X-ray absorption of the crystal can be fully interpreted by multiple-scattering theory which allows the determination of Fe-ligand bond angles. The analysis of the identified multiple scattering features due to CO in high signal-to-noise-ratio spectra of protein in solution has allowed the determination of the variation of CO bond angles. This opens the way to the determination of subtle structural features due to bond angle variations in proteins in solution which are relevant to an understanding of the characteristics of proteins at the atomic scale.
我们对凝聚态物质结构的认识主要基于光谱方法，这些方法测量原子排列的一阶对关联，从而提供原子间距离（例如中子和X射线散射）。键角由高阶关联函数给出，此类信息可由X射线吸收近边结构（XANES）光谱提供，其特征由光电子的多次散射决定，光电子的路径始于并终于选定的吸收原子。我们在此报告羧基肌红蛋白（MbCO）单晶的角分辨XANES光谱。晶体X射线吸收的大 dichroism 可由多次散射理论完全解释，该理论允许确定铁 - 配体键角。对溶液中蛋白质高信噪比光谱中由CO引起的已识别多次散射特征的分析，使得能够确定CO键角的变化。这为确定溶液中蛋白质因键角变化而产生的细微结构特征开辟了道路，这些特征与在原子尺度上理解蛋白质的特性相关。
