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X-ray free electron lasers are increasingly available for use in macromolecular structure determination. Here, the authors describe the successful use of selenium single-wavelength anomalous diffraction data to calculate experimentally derived phases.

Metal carbonyl complexes show photoreactivity interesting for catalytic and biological applications. Here the authors capture the structural dynamics of the photodissociation of iron pentacarbonyl in real space and time using ultrafast X-ray scattering.

Femtosecond crystallography with an X-ray free-electron laser is used to analyse micrometre-sized protein crystals, generating a high-resolution structure of the protein without previous knowledge of what it looks like.

The local X-ray-induced dynamics that occur in protein crystals during serial femtosecond crystallography (SFX) measurements at XFELs are not well understood. Here the authors performed a time-resolved X-ray pump X-ray probe SFX experiment, and they observe distinct structural changes in the disulfide bridges and peptide backbone of proteins; complementing theoretical approaches allow them to further characterize the details of the X-ray induced ionization and local structural dynamics.

Bacteriorhodopsin (bR) is a light-driven proton pump. Here the authors combine time-resolved crystallography at a free-electron laser, ultrafast spectroscopy and quantum chemistry to study the structural changes following multiphoton photoexcitation of bR and find that they occur within 300 fs not only in the light-absorbing chromophore but also in the surrounding protein.

X-ray fee-electron lasers (XFELs) enable time-resolved crystallography experiments and the structure determination of proteins with little or no radiation damage. However currently it is unknown whether the designated 4.5 MHz maximum pulse rate for the European XFEL could lead to sample damage caused by shock waves from preceding pulses. Here, the authors address this question by performing a X-ray pump X-ray probe experiment on haemoglobin microcrystals at the Stanford XFEL facility that mimics the 4.5 MHz data collection mode and observe structural changes and a drop in diffraction data quality of the crystals.

Optical microscopy and X-ray diffraction are used to study the freezing of water droplets in vacuum, leading to the development of a seven-stage model of freezing and the mapping of ice structures and crystal order.

Photosystem II is the biosynthetic machinery that allows the conversion of water to oxygen using light. Here, the authors combine X-ray emission and diffraction data to probe the structural changes that take place during photosystem II catalysis.

Serial femtosecond X-ray crystallography permits the use of very small protein crystals; however, a continuous flow of sample is required. Weierstall et al. design and demonstrate an injector system that can supply microcrystals in the lipidic cubic phase, dramatically reducing the quantities of protein required.

The structure of the bacterial toxin BinAB, which is used to combat mosquito-borne diseases, reveals pH-sensitive switches and carbohydrate-binding modules that may contribute to the larvicidal function of the toxin.

Availability of intense hard X-ray pulses allows exploration of multiple ionization effects in heavier elements. Here, the authors measure the complex charge state distributions of xenon and found a reasonable agreement by comparing with the model including the relativistic and resonance effects.

X-ray-induced explosions in water drops, examined using time-resolved imaging, show interacting high-speed liquid and vapour flows. This type of X-ray absorption dynamics is predictable and may be used for inducing particular dynamical liquid states.

A robust acoustic droplet ejection–drop-on-tape method delivers samples to an X-ray free-electron laser source for combined serial femtosecond crystallography and X-ray emission spectroscopy analysis, providing detailed insights into macromolecular reaction dynamics.

Providing detailed structural descriptions of the ultrafast photochemical events that occur in light-sensitive proteins is key to their understanding. Now, excited-state structures in the reversibly switchable fluorescent protein rsEGFP2 have been solved by time-resolved crystallography using an X-ray laser. These structures enabled the design of a mutant with improved photoswitching quantum yields.

Serial femtosecond crystallography using X-ray free-electron lasers has huge potential for time-resolved structural experiments. Here, the authors present a structure of the light-driven proton pump bacteriorhodopsin using these techniques.

The structures of amyloid fibres are currently primarily studied through solid state NMR and cryo-EM. Here the authors present a free-standing graphene support device that allows diffraction imaging of non-crystalline amyloid fibrils with single X-ray pulses from an X-ray free-electron laser.

Photoabsorption is a fundamental process that leads to changes in the electron density in matter. Here, the authors show a direct measurement of the distribution of electron density when a cyclohexadine molecule is excited by pulsed UV radiation and probed by a time delayed X-ray pulse generated at LCLS.

Quantum coherence and dephasing in molecular motions determine the behaviour of many chemical reactions and are the fundamental basis for the concept of coherent control. Now, ultrafast X-ray scattering combined with a detailed structural determination analysis precisely measures the coherent vibrational motions of a polyatomic organic molecule following photoexcitation.

The crystal structure of the complement receptor C5aR1 bound to a small-molecule antagonist provides insights into this receptor class and how they could be better targeted therapeutically.

The structures of three intermediate states of photosystem II, which is crucial for photosynthesis, have been solved at room temperature, shedding new light on this process.

A computational approach and software tool, cctbx.xfel, enables the determination of accurate macromolecular structure factors using a relatively small number of serial femtosecond crystallography diffraction snapshots.

Crystallography and spectroscopy are used to solve high-resolution structures of the intermediates of Kok’s S-state clock in photosystem II.

Crystal lattice disorder, which gives rise to a continuous diffraction pattern, is exploited to determine the structure of the integral membrane protein complex photosystem II to a higher resolution than could be achieved using Bragg diffraction alone.

A concentric-flow microfluidic electrokinetic sample injector enables efficient delivery of microcrystals in their mother liquor for serial femtosecond X-ray crystallography with minimal sample consumption.