We report the first demonstration of the coherent diffraction imaging analysis of nanoparticles using focused hard X-ray free-electron laser pulses, allowing us to analyze the size distribution of ...particles as well as the electron density projection of individual particles. We measured 1000 single-shot coherent X-ray diffraction patterns of shape-controlled Ag nanocubes and Au/Ag nanoboxes and estimated the edge length from the speckle size of the coherent diffraction patterns. We then reconstructed the two-dimensional electron density projection with sub-10 nm resolution from selected coherent diffraction patterns. This method enables the simultaneous analysis of the size distribution of synthesized nanoparticles and the structures of particles at nanoscale resolution to address correlations between individual structures of components and the statistical properties in heterogeneous systems such as nanoparticles and cells.
Fluctuation X-ray scattering (FXS) is an emerging experimental technique in which X-ray solution scattering data are collected from particles in solution using ultrashort X-ray exposures generated by ...a free-electron laser (FEL). FXS experiments overcome the low data-to-parameter ratios associated with traditional solution scattering measurements by providing several orders of magnitude more information in the final processed data. Here we demonstrate the practical feasibility of FEL-based FXS on a biological multiple-particle system and describe data-processing techniques required to extract robust FXS data and significantly reduce the required number of snapshots needed by introducing an iterative noise-filtering technique. We showcase a successful ab initio electron density reconstruction from such an experiment, studying the Paramecium bursaria Chlorella virus (PBCV-1).
We present the characterization of a Zero-bias Schottky diode-based Terahertz (THz) detector up to 5.56 THz. The detector was operated with both a table-top system until 1.2 THz and at a ...Free-Electron Laser (FEL) facility at singular frequencies from 1.9 to 5.56 THz. We used two measurement techniques in order to discriminate the sub-ns-scale (via a 20 GHz oscilloscope) and the ms-scale (using the lock-in technique) responsivity. While the lock-in measurements basically contain all rectification effects, the sub-ns-scale detection with the oscilloscope is not sensitive to slow bolometric effects caused by changes of the IV characteristic due to temperature. The noise equivalent power (NEP) is 10 pW/Hz in the frequency range from 0.2 to 0.6 THz and 17 pW/Hz at 1.2 THz and increases to 0.9 μW/Hz at 5.56 THz, which is at the state of the art for room temperature zero-bias Schottky diode-based THz detectors with non-resonant antennas. The voltage and current responsivity of ∼500 kV/W and ∼100 mA/W, respectively, is demonstrated over a frequency range of 0.2 to 1.2 THz with the table-top system.
The non‐monochromatic beamline BL1 at the FLASH free‐electron laser facility at DESY was upgraded with new transport and focusing optics, and a new permanent end‐station, CAMP, was installed. This ...multi‐purpose instrument is optimized for electron‐ and ion‐spectroscopy, imaging and pump–probe experiments at free‐electron lasers. It can be equipped with various electron‐ and ion‐spectrometers, along with large‐area single‐photon‐counting pnCCD X‐ray detectors, thus enabling a wide range of experiments from atomic, molecular, and cluster physics to material and energy science, chemistry and biology. Here, an overview of the layout, the beam transport and focusing capabilities, and the experimental possibilities of this new end‐station are presented, as well as results from its commissioning.
Beamline BL1 at the FLASH free‐electron laser facility at DESY was upgraded with new transport and focusing optics for the installation of the new permanent CAMP end‐station, a multi‐purpose instrument optimized for electron‐ and ion‐spectroscopy, imaging and pump–probe experiments. An overview of the layout, beam transport, focusing capabilities, and experimental possibilities of this new end‐station, as well as results from its commissioning and first experiments, are presented.
The long‐anticipated high‐resolution structures of the human melatonin G protein‐coupled receptors MT1 and MT2, involved in establishing and maintaining circadian rhythm, were obtained in complex ...with two melatonin analogs and two approved anti‐insomnia and antidepression drugs using X‐ray free‐electron laser serial femtosecond crystallography. The structures shed light on the overall conformation and unusual structural features of melatonin receptors, as well as their ligand binding sites and the melatonergic pharmacophore, thereby providing insights into receptor subtype selectivity. The structures revealed an occluded orthosteric ligand binding site with a membrane‐buried channel for ligand entry in both receptors, and an additional putative ligand entry path in MT2 from the extracellular side. This unexpected ligand entry mode contributes to facilitating the high specificity with which melatonin receptors bind their cognate ligand and exclude structurally similar molecules such as serotonin, the biosynthetic precursor of melatonin. Finally, the MT2 structure allowed accurate mapping of type 2 diabetes‐related single‐nucleotide polymorphisms, where a clustering of residues in helices I and II on the protein–membrane interface was observed which could potentially influence receptor oligomerization. The role of receptor oligomerization is further discussed in light of the differential interaction of MT1 and MT2 with GPR50, a regulatory melatonin coreceptor. The melatonin receptor structures will facilitate design of selective tool compounds to further dissect the specific physiological function of each receptor subtype as well as provide a structural basis for next‐generation sleeping aids and other drugs targeting these receptors with higher specificity and fewer side effects.
The two melatonin G protein‐coupled receptors, MT1 and MT2, are involved in the implementation and maintenance of circadian rhythms and are implicated in sleeping disorders, depression, cancer, and diabetes. Recent crystallographic studies provided the structural basis of ligand recognition and subtype selectivity at these receptors and revealed an occluded binding site with a highly unusual ligand access mode via a narrow membrane‐buried channel.
Ever since the discovery that Mn was required for oxygen evolution in plants by Pirson in 1937 and the period‐four oscillation in flash‐induced oxygen evolution by Joliot and Kok in the 1970s, ...understanding of this process has advanced enormously using state‐of‐the‐art methods. The most recent in this series of innovative techniques was the introduction of X‐ray free‐electron lasers (XFELs) a decade ago, which led to another quantum leap in the understanding in this field, by enabling operando X‐ray structural and X‐ray spectroscopy studies at room temperature. This review summarizes the current understanding of the structure of Photosystem II (PS II) and its catalytic centre, the Mn4CaO5 complex, in the intermediate Si (i = 0–4)‐states of the Kok cycle, obtained using XFELs.
Water oxidation reaction in nature is catalysed by the Mn4CaO5 cluster in Photosystem II. We have developed operando X‐ray crystallography and X‐ray spectroscopy methods at the X‐ray free‐electron laser facilities and applied them to understand the catalytic mechanism and associated protein dynamics in Photosystem II.
A theoretical study of the spontaneous and stimulated undulator radiation (UR) from electrons in undulators with multiple periods in both transversal directions is presented. Exact expressions are ...derived for the UR intensities in terms of the generalized Bessel and Airy functions, accounting for undulator field harmonics of arbitrary strength and for real parameters of the beams and installations. Theoretical results are verified with numerical and experimental data for SWISS‐XFEL, PAL‐XFEL, LEUTL, LCLS etc. The spectrum, UR line shape and width, and the harmonic evolution along the undulators are analyzed and compared with the available data for these experiments. Moreover, the effect of the field harmonics is elucidated. It is demonstrated that the third field harmonic can cause distinct odd UR harmonics. The asymmetric undulator field configuration is identified, which allows intense radiation of these harmonics. The power evolution in a free‐electron laser (FEL) with such an undulator is studied by means of an analytical FEL model. The latter is enhanced by a true description of the gradual power saturation of harmonics. A FEL with elliptic undulator and electron–photon phase‐shifting is proposed and modeled. It is shown that the resulting harmonic power from the phase‐shifted elliptic undulator can be significantly higher than from a planar undulator with the same phase‐shifting.
A comparative theoretical analysis of the free‐electron laser (FEL) radiation in main FEL experiments is given. It is shown that an elliptic undulator with field harmonics and electron–photon phase‐shifting yields significantly higher harmonic power than that from a planar undulator with phase‐shifting.
Proteins that contain metal cofactors are expected to be highly radiation sensitive since the degree of X‐ray absorption correlates with the presence of high‐atomic‐number elements and X‐ray energy. ...To explore the effects of local damage in serial femtosecond crystallography (SFX), Clostridium ferredoxin was used as a model system. The protein contains two 4Fe–4S clusters that serve as sensitive probes for radiation‐induced electronic and structural changes. High‐dose room‐temperature SFX datasets were collected at the Linac Coherent Light Source of ferredoxin microcrystals. Difference electron density maps calculated from high‐dose SFX and synchrotron data show peaks at the iron positions of the clusters, indicative of decrease of atomic scattering factors due to ionization. The electron density of the two 4Fe–4S clusters differs in the FEL data, but not in the synchrotron data. Since the clusters differ in their detailed architecture, this observation is suggestive of an influence of the molecular bonding and geometry on the atomic displacement dynamics following initial photoionization. The experiments are complemented by plasma code calculations.
The European X‐ray Free Electron Laser (EuXFEL) offers intense, coherent femtosecond pulses, resulting in characteristic peak brilliance values a billion times higher than that of conventional ...synchrotron facilities. Such pulses result in extreme peak radiation levels of the order of terawatts cm−2 for any optical component in the beam and can exceed the ablation threshold of many materials. Diamond is considered the optimal material for such applications due to its high thermal conductivity (2052 W mK−1 at 300 K) and low absorption for hard X‐rays. Grating structures were fabricated on free‐standing CVD diamond of 10 µm thickness with 500 µm silicon substrate support. The grating structures were produced by electron‐beam lithography at the Laboratory for Micro‐ and Nanotechnology, Paul Scherrer Institut, Switzerland. The grating lines were etched to a depth of 1.2 µm, resulting in an aspect ratio of 16. The characterization measurements with X‐rays were performed on transmissive diamond gratings of 150 nm pitch at the P10 beamline of PETRA III, DESY. In this paper, the gratings are briefly described, and a measured diffraction efficiency of 0.75% at 6 keV in the first‐order diffraction is shown; the variation of the diffraction efficiency across the grating surface is presented.
Grating structures with 150 nm pitches were fabricated on free‐standing CVD diamond membranes supported by a silicon frame. The efficiencies and structural homogeneity of the gratings were measured with synchrotron X‐rays at different photon energies.
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