| 1. |
- Caleman, Carl, et al.
(författare)
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Ultrafast dynamics of water exposed to XFEL pulses
- 2019
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Ingår i: OPTICS DAMAGE AND MATERIALS PROCESSING BY EUV/X-RAY RADIATION VII. - : SPIE-INT SOC OPTICAL ENGINEERING. - 9781510627376 - 9781510627369
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Konferensbidrag (refereegranskat)abstract
- These proceedings investigate the ionization and temperature dynamics of water samples exposed to intense ultrashort X-ray free-electron laser pulses ranging from 10(4) - 10(7) J/cm(2), based on simulations using a non-local thermodynamic plasma code. In comparison to earlier work combining simulations and experiments, a regime where a hybrid simulations approach should be applicable is presented.
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| 2. |
- Jönsson, H. Olof, et al.
(författare)
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Simulations of Radiation Damage as a Function of the Temporal Pulse Profile in Femtosecond X-ray Protein Crystallography
- 2015
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495 .- 1600-5775. ; 22:2, s. 256-266
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Tidskriftsartikel (refereegranskat)abstract
- Serial femtosecond X-ray crystallography of protein nanocrystals using ultrashort and intense pulses from an X-ray free-electron laser has proved to be a successful method for structural determination. However, due to significant variations in diffraction pattern quality from pulse to pulse only a fraction of the collected frames can be used. Experimentally, the X-ray temporal pulse profile is not known and can vary with every shot. This simulation study describes how the pulse shape affects the damage dynamics, which ultimately affects the biological interpretation of electron density. The instantaneously detected signal varies during the pulse exposure due to the pulse properties, as well as the structural and electronic changes in the sample. Here ionization and atomic motion are simulated using a radiation transfer plasma code. Pulses with parameters typical for X-ray free-electron lasers are considered: pulse energies ranging from 10$\sp 4$ to 10$\sp 7$Jcm$\sp $-$2$ with photon energies from 2 to 12keV, up to 100fs long. Radiation damage in the form of sample heating that will lead to a loss of crystalline periodicity and changes in scattering factor due to electronic reconfigurations of ionized atoms are considered here. The simulations show differences in the dynamics of the radiation damage processes for different temporal pulse profiles and intensities, where ionization or atomic motion could be predominant. The different dynamics influence the recorded diffracted signal in any given resolution and will affect the subsequent structure determination.
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| 3. |
- Jönsson, Olof, et al.
(författare)
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FreeDam – A Webtool for Free-Electron Laser-Induced Damage in Femtosecond X-ray Crystallography
- 2018
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Ingår i: High Energy Density Physics. - : Elsevier. - 1574-1818. ; 26, s. 93-98
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Tidskriftsartikel (refereegranskat)abstract
- Over the last decade X-ray free-electron laser (XFEL) sources have been made available to the scientific community. One of the most successful uses of these new machines has been protein crystallography. When samples are exposed to the intense short X-ray pulses provided by the XFELs, the sample quickly becomes highly ionized and the atomic structure is affected. Here we present a webtool dubbed FreeDam based on non-thermal plasma simulations, for estimation of radiation damage in free-electron laser experiments in terms of ionization, temperatures and atomic displacements. The aim is to make this tool easily accessible to scientists who are planning and performing experiments at XFELs.
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| 4. |
- Mandl, Thomas, et al.
(författare)
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Structural Heterogeneity in Single Particle Imaging Using X-ray Lasers
- 2020
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 11:15, s. 6077-6083
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Tidskriftsartikel (refereegranskat)abstract
- One of the challenges facing single particle imaging with ultrafast X-ray pulses is the structural heterogeneity of the sample to be imaged. For the method to succeed with weakly scattering samples, the diffracted images from a large number of individual proteins need to be averaged. The more the individual proteins differ in structure, the lower the achievable resolution in the final reconstructed image. We use molecular dynamics to simulate two globular proteins in vacuum, fully desolvated as well as with two different solvation layers, at various temperatures. We calculate the diffraction patterns based on the simulations and evaluate the noise in the averaged patterns arising from the structural differences and the surrounding water. Our simulations show that the presence of a minimal water coverage with an average 3 Å thickness will stabilize the protein, reducing the noise associated with structural heterogeneity, whereas additional water will generate more background noise.
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| 5. |
- Sanchez-Gonzalez, A., et al.
(författare)
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Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen K-edge measured with an X-FEL
- 2015
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Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 48:23
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Tidskriftsartikel (refereegranskat)abstract
- We report the first measurement of the near oxygen K-edge auger spectrum of the glycine molecule. Our work employed an x-ray free electron laser as the photon source operated with input photon energies tunable between 527 and 547 eV. Complete electron spectra were recorded at each photon energy in the tuning range, revealing resonant and non-resonant auger structures. Finally ab initio theoretical predictions are compared with the measured above the edge auger spectrum and an assignment of auger decay channels is performed.
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| 6. |
- Sinelnikova, Anna, et al.
(författare)
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Reproducibility in the unfolding process of protein induced by an external electric field
- 2021
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 12:6, s. 2030-2038
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of proteins are crucial for their function. However, commonly used techniques for studying protein structures are limited in monitoring time-resolved dynamics at high resolution. Combining electric fields with existing techniques to study gas phase proteins, such as Single Particle Imaging using Free-electron Lasers and gas phase Small Angle X-ray Scattering, has the potential to open up a new era in time-resolved studies of gas phase protein dynamics. Using molecular dynamics simulations, we identify well-defined unfolding pathways of a protein, induced by experimentally achievable external electric fields. Our simulations show that strong electric fields in conjunction with short pulsed X-ray sources such as Free-electron Lasers can be a new path for imaging dynamics of gas-phase proteins at high spatial and temporal resolution.
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| 7. |
- Östlin, Christofer
(författare)
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Advances in Biomolecular Imaging with X-ray Free-Electron Lasers
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Utilizing X-rays to solve molecular structures has proven to be an immensely powerful and im- portant scientific technique. The invention of X-ray crystallography has allowed for countless breakthroughs in chemistry, biology and material science and remains the number one method used for structural determination today. Of particular interest is the structures of biomolecules, such as proteins, due to their medical relevance. Unfortunately, the need for crystals of sufficient size constitutes the biggest drawback to this approach. This is troubling since many of the im- portant biomolecules, in particular membrane proteins, have proven to be difficult or sometimes even impossible to crystalize. When limited to a small nanocrystal or even a single particle, con- ventional crystallography is no longer adequate to probe the structure at high enough resolution. Recent developments, most notably the introduction of X-ray free-electron lasers (XFELs), have opened up new possibilities for circumventing these limitations. The high intensities and ultra- short pulse lengths provided by XFELs allows for diffractive imaging of smaller crystals through Serial Femtosecond Crystallography (SFX) and can even be extended to single molecules, Single Particle Imaging (SPI). These methods are still in their infancies, and much research and refine- ment is needed before they can be properly established.The current work covers fundamental studies of X-ray interaction with biomatter carried out to aid and improve upon SFX and SPI. Three papers based on computer simulation studies are presented, related to mainly two central aspects faced when imaging molecules with XFELs. Pa- per I explores a novel approach using explosion mapping to facilitate spatial orientation of single particles, which is necessary to reconstruct the three dimensional structure from two dimensional diffraction patterns. Paper II concerns radiation damage of the sample in SFX experiments using a plasma model and studies the impact of different pulse profiles on these processes. Lastly, pa- per III outlines the details of an online database available to researchers worldwide that contains simulated data on damage development in samples exposed to an XFEL pulse.In the first study, molecular dynamics was adopted to map the XFEL-induced Coulomb explo- sions in SPI for biomolecules. Four proteins were investigated, each with three different levels of hydration, and it was found that explosion patterns for both carbon and sulfur ions are re- producible for all twelve systems. However, water bound to the protein surface seems to have a shielding effect on carbons, causing their trajectories to be favored toward the exposed parts of the sample. This complicates the adoption for orientation determination as the water content would have to be known. Sulfurs, on the other hand, showed no signs of water dependence and consistently produced similar explosion patterns regardless of hydration level. We speculate that this is because of their higher mass and ionization cross section and conclude that mapping of heavier ions could provide valuable information for spatial orientation.In the second study, radiation damage in terms of ionization and atomic displacement within a nanometer-sized crystal illuminated by an XFEL pulse was explored with a non-local thermody- namic equilibrium plasma code. Different temporal distributions of the same number of photons was employed to assess its impact of damage dynamics. The results show that the pulse profile is substantially important. A front-loaded pulse is more beneficial for imaging purposes since the bulk of the photons encounters an undamaged sample. If the majority of photons instead arrive late, early photons will already have initiated the crystal decay causing further contribution to the diffraction pattern to be degraded.In the third study, the free-electron laser damage simulation database (FreeDam) was estab- lished. It presents simulated time-resolved data for average ionization, ion and electron temper- atures and atomic displacement for various materials and XFEL parameters. Simulations were carried out using the same code as in paper II, and the data is freely available online.This thesis is aimed to provide one of the stepping stones toward atomic resolution imaging of nanocrystals and single particles with free-electron lasers. If realized, these techniques could well turn out to be one of the greatest scientific achievements of the 21th century.
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| 8. |
- Östlin, Christofer, 1988-, et al.
(författare)
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Is Radiation Damage the Limiting Factor in Single Particle Imaging with X-ray Free-Electron Lasers?
- 2019
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- The prospect of single particle imaging with atomic resolution is one of the scientific drivers for the development of X-ray free-electron lasers. The assumption since the beginning has been that damage to the sample caused by intense X-ray pulses is one of the limiting factors of coherent diffractive imaging of single particles and that X-ray pulses need to be as short as possible. Based on molecular dynamics simulations of proteins in X-ray fields of various durations (5 fs, 25 fs and 50 fs), we show that the noise in the diffracted signal caused by radiation damage is less than what can be expected from other sources, such as sample inhomogeneity and X-ray shot-to-shot variations. These findings show a different aspect of the feasibility of single particle imaging using free-electron lasers, where employing X-ray pulses of longer durations could still provide a useful diffraction signal above the noise due to the Coulomb explosion.
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| 9. |
- Östlin, Christofer, et al.
(författare)
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Reproducibility of Single Protein Explosions Induced by X-ray Lasers
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 20:18, s. 12381-12389
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Tidskriftsartikel (refereegranskat)abstract
- Single particle imaging (SPI) using X-ray pulses has become increasingly attainable with the advent of high-intensity free electron lasers. Eliminating the need for crystallized samples enables structural studies of molecules previously inaccessible by conventional crystallography. While this emerging technique already demonstrates substantial promise, some obstacles need to be overcome before SPI can reach its full potential. One such problem is determining the spatial orientation of the sample at the time of X-ray interaction. Existing solutions rely on diffraction data and are computationally demanding and sensitive to noise. In this in silico study, we explore the possibility of aiding these methods by mapping the ion distribution as the sample undergoes a Coulomb explosion following the intense ionization. By detecting the ions ejected from the fragmented sample, the orientation of the original sample should be possible to determine. Knowledge of the orientation has been shown earlier to be of substantial advantage in the reconstruction of the original structure. 150 explosions of each of twelve separate systems – four polypeptides with different amounts of surface bound water – were simulated with molecular dynamics (MD) and the average angular distribution of carbon and sulfur ions was investigated independently. The results show that the explosion maps are reproducible in both cases, supporting the idea that orientation information is preserved. Additional water seems to restrict the carbon ion trajectories further through a shielding mechanism, making the maps more distinct. For sulfurs, water has no significant impact on the trajectories, likely due to their higher mass and greater ionization cross section, indicating that they could be of particular interest. Based on these findings, we conclude that explosion data can aid spatial orientation in SPI experiments and could substantially improve the capabilities of the novel technique.
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| 10. |
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| 11. |
- Östlin, Christofer, 1988-
(författare)
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Simulations of Biomolecular Fragmentation and Diffraction with Ultrafast X-ray Lasers
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Studies of biomolecules have recently seen substantial developments. New X-ray lasers allow for high-resolution imaging of protein crystals too small for conventional X-ray crystallography. Even structures of single particles have been determined at lower resolutions with these new sources. The secret lies in the ultrashort high-intensity pulses, which allow for diffraction and retrieval of structural information before the sample gets fragmented. However, the attainable resolution is still limited, in particular when imaging non-crystalline samples, making further advancements highly desired. In this thesis, some of the resolution-limiting obstacles facing single particle imaging (SPI) of proteins are studied in silico.As the X-ray pulse interacts with injected single molecules, their spatial orientation is generally unknown. Recovering the orientation is essential to the structure determination process, and currently nontrivial. Molecular dynamics simulations show that the Coulomb explosion due to intense X-ray ionization could provide information pertaining to the original orientation. Used in conjunction with current methods, this would lead to an enhanced three-dimensional reconstruction of the protein.Radiation damage and sample heterogeneity constitute considerable sources of noise in SPI. Pulse durations are presently not brief enough to circumvent damage, causing the sample to deteriorate during imaging, and the accuracy of the averaged diffraction pattern is impaired by structural variations. The extent of these effects were studied by molecular dynamics. Our findings suggest that radiation damage in terms of ionization and atomic displacement promotes a gating mechanism, benefiting imaging with longer pulses. Because of this, sample heterogeneity poses a greater challenge and efforts should be made to minimize its impact.X-ray lasers generate pulses with a stochastic temporal distribution of photons, affecting the achievable resolution on a pulse-to-pulse basis. Plasma simulations were performed to investigate how these fluctuations influence the damage dynamics and the diffraction signal. The results reveal that structural information is particularly well-preserved if the temporal distribution is skewed such that most photons are concentrated at the beginning.While many obstacles remain, the prospect of atomic-resolution SPI is drawing ever closer. This thesis is but one of the stepping stones necessary to get us there. Once we do, the possibilities are limitless.
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