L-Edge X-ray Absorption Spectroscopy of Dilute Systems Relevant to Metalloproteins Using an X-ray Free-Electron Laser

Abstract

L-edge spectroscopy of 3d transition metals provides important electronic structure information and has been used in many fields. However, the use of this method for studying dilute aqueous systems, such as metalloenzymes, has not been prevalent because of severe radiation damage and the lack of suitable detection systems. Here we present spectra from a dilute Mn aqueous solution using a high-transmission zone-plate spectrometer at the Linac Coherent Light Source (LCLS). The spectrometer has been optimized for discriminating the Mn L-edge signal from the overwhelming O K-edge background that arises from water and protein itself, and the ultrashort LCLS X-ray pulses can outrun X-ray induced damage. We show that the deviations of the partial-fluorescence yield-detected spectra from the true absorption can be well modeled using the state-dependence of the fluorescence yield, and discuss implications for the application of our concept to biological samples.

High energy resolution off-resonant spectroscopy: A review

“…Hence this technique found applications in many research fields like physics, chemistry, medicine, biology and material sciences (see, e.g., Refs. [6][7][8][9][10][11][12]). …”

A new compact soft x-ray spectrometer for resonant inelastic x-ray scattering studies at PETRA III

“…3,4 Therefore, XES and RIXS have been a popular method to study the electronic structure of chemical systems, 3d transition metal etc. [5][6][7][8][9][10][11][12][13][14][15] While XES and RIXS in the hard X-ray regime are detectable with crystal spectrometers using the Bragg law, 16,17 in the soft X-rays the needed lattice constant of crystals is too high and the quality of the planes of these crystals is not sufficient for high energy resolution. Early pioneering work by Callcott et al 18 and Nordgren et al 19 introduced a grating spectrometer based on the Rowland circle principle as the answer to perform high resolution XES and RIXS measurements in the soft X-ray regime, opening the possibility to study the K lines of systems containing vital elements like C, N and O and L lines of 3d metals.…”

“…Early pioneering work by Callcott et al 18 and Nordgren et al 19 introduced a grating spectrometer based on the Rowland circle principle as the answer to perform high resolution XES and RIXS measurements in the soft X-ray regime, opening the possibility to study the K lines of systems containing vital elements like C, N and O and L lines of 3d metals. [5][6][7][8][9][10][11][12][13] In recent years, new high resolution soft X-ray spectrometers based on varied line spacing gratings have been build. [20][21][22][23][24][25] Some are even able to resolve vibrational states in the spectrum.…”

Methods development for diffraction and spectroscopy studies of metalloenzymes at X-ray free-electron lasers

“…The highest occupied orbitals are of special interest as they are involved in the actual chemistry during a reaction. XES has also some advantages over XAS for experiments at XFELS: (i) there is no requirement to have a monochromatic excitation pulse, as long as the [25]). In the inset, Mn-L-edge spectra of Mn II Cl 2 obtained either at the synchrotron in transmission mode (trans.…”