X ‐Ray Emission Spectroscopic Techniques in Bioinorganic Applications

Abstract

Hard X‐ray core hole spectroscopy plays an important role in countless areas of research including chemistry, physics, biology, materials science, medicine, geoscience, and even natural and cultural heritage. The main attraction of these methods lies in the atomic level structural and chemical information, the elemental selectivity, and the practical advantages related to the penetration power of hard X‐rays, allowing for a wide range of samples and sample environments. Powerful synchrotron sources with intense, tunable, and highly collimated X‐ray beams have pushed the detection limit for X‐ray spectroscopy to minute elemental concentrations, including the active sites in dilute metalloproteins. Much of the focus over the past 40 years has been on X‐ray absorption spectroscopy (XAS) methods including X‐ray absorption near edge structure (XANES) and extended range X‐ray absorption fine structure (EXAFS) spectroscopy. More recently, there has been an increasing activity in X‐ray emission spectroscopy (XES) and other high‐resolution photon‐out techniques such as X‐ray Raman scattering. These efforts have been aided by the development of efficient, dedicated, high‐resolution photon‐out X‐ray spectrometers that are now routinely used at many synchrotron facilities. XES provides information on the local atomic and electronic structure that is complementary to X‐ray scattering and diffraction methods and XAS. We will discuss various XES techniques and their specific benefits and limitations regarding studies in bioinorganic chemistry and describe examples of recent results. We will present the basic information regarding the required instrumentation, discuss the various approaches, and give a comprehensive instrumentation literature review. With the advent of X‐ray free electron lasers (XFELs), fourth‐generation synchrotron light sources that are many orders of magnitude brighter than storage rings, revolutionary new capabilities for the studies of many materials on times scales down to femtoseconds have become available. Owing to the stochastic nature of the XFEL pulses, XES techniques, where the whole spectrum is collected in a shot‐by‐shot manner, are specifically attractive and have been the predominant choice of the early XFEL‐based X‐ray spectroscopy work. We will discuss this work and the related instrumentation from the perspective of the bioinorganic field. We conclude with a few thoughts on potential future XES techniques, which take advantage of nonlinear processes that result from the interaction of very intense XFEL pulses with matter.

High‐Energy Resolution Fluorescence Detected X‐Ray Absorption Spectroscopy: A Powerful New Structural Tool in Environmental Biogeochemistry Sciences

“…Detailed explanations of the XAS and XES theories fall outside the scope of this paper and can be found in numerous recent reviews, on core‐level spectroscopy generality (de Groot and Kotani, 2008), XANES (Henderson et al, 2014; Joly and Grenier, 2016), EXAFS (Newville, 2014), XAS (Rehr and Albers, 2000; Ortega et al, 2012; Milne et al, 2014), XES (DeBeer and Bergmann, 2016), and HERFD (Bauer, 2014; Kowalska et al, 2016) applied to bioionorganic chemistry, and applications in environmental sciences (Gräfe et al, 2014). We will briefly recall the main principles of the core‐level spectroscopy techniques with special attention to effects that can be better analyzed with CAS.…”

TEXS: in-vacuum tender X-ray emission spectrometer with 11 Johansson crystal analyzers

“…The spectroscopic techniques with such an instrument include nonresonant x-ray emission spectroscopy (XES), that does not require a monochromatic incoming beam to excite the analyte atom, as well as resonant inelastic x-ray scattering (RIXS) and high energy resolution fluorescence detected (HERFD) x-ray absorption near edge structure (XANES) spectroscopy. A series of books and review papers describes the applications of XES, RIXS and HERFD-XANES in solid state physics, materials science, coordination chemistry and biology [1][2][3][4][5][6][7][8][9] . High performance and user-friendly x-ray emission spectrometers at synchrotron radiation facilities and in the laboratory, combined with tools for theoretical interpretation of the data, have greatly helped the adoption of the techniques by a large community.…”

Persistent Octahedral Coordination in Amorphous GeO2 Up to 100 GPa by Kβ′′Spiekermann1, Harder2, Gilmore3 et al. 2019Phys. Rev. X202250View full textAdd to dashboardCite

“…In this study, we address the ambiguity in the average germanium CN in compressed amorphous GeO 2 by a new approach on the basis of measured and computed valenceto-core x-ray emission spectroscopy (VTC XES) spectra of compressed GeO 2 . VTC XES has been mostly applied to 3d transition metal molecular complexes, where it is known to provide insight into the spin state and the type of the bonding ligand [25][26][27][28][29][30][31][32][33][34]. There have been only a few studies on nonmolecular crystalline compounds [35][36][37][38][39].…”