Explosions of large Xe clusters ( ~ 11,000) irradiated by femtosecond pulses of 850 eV x-ray photons focused to an intensity of up to 10(17) W/cm(2) from the Linac Coherent Light Source were ...investigated experimentally. Measurements of ion charge-state distributions and energy spectra exhibit strong evidence for the formation of a Xe nanoplasma in the intense x-ray pulse. This x-ray produced Xe nanoplasma is accompanied by a three-body recombination and hydrodynamic expansion. These experimental results appear to be consistent with a model in which a spherically exploding nanoplasma is formed inside the Xe cluster and where the plasma temperature is determined by photoionization heating.
We reconstructed the 3D Fourier intensity distribution of monodisperse prolate nanoparticles using single-shot 2D coherent diffraction patterns collected at DESY's FLASH facility when a bright, ...coherent, ultrafast x-ray pulse intercepted individual particles of random, unmeasured orientations. This first experimental demonstration of cryptotomography extended the expansion-maximization-compression framework to accommodate unmeasured fluctuations in photon fluence and loss of data due to saturation or background scatter. This work is an important step towards realizing single-shot diffraction imaging of single biomolecules.
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 for achieving subnanometer X-ray imaging of single particles and that X-ray pulses need to be as short as possible. Based on the 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 high-resolution 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.
We have focused a beam (BL3) of FLASH (Free-electron LASer in Hamburg: lambda = 13.5 nm, pulse length 15 fs, pulse energy 10-40 microJ, 5 Hz) using a fine polished off-axis parabola having a focal ...length of 270 mm and coated with a Mo/Si multilayer with an initial reflectivity of 67% at 13.5 nm. The OAP was mounted and aligned with a picomotor controlled six-axis gimbal. Beam imprints on poly(methyl methacrylate) - PMMA were used to measure focus and the focused beam was used to create isochoric heating of various slab targets. Results show the focal spot has a diameter of < or =1 microm. Observations were correlated with simulations of best focus to provide further relevant information.
Coherent diffractive imaging of single particles using the single-shot “diffract and destroy” approach with an x-ray free electron laser (FEL) was recently demonstrated. A high-resolution low-noise ...coherent diffraction pattern, representative of the object before it turns into a plasma and explodes, results from the interaction of the FEL with the particle. Iterative phase retrieval algorithms are used to reconstruct two-dimensional projection images of the object from the recorded intensities alone. Here we describe the first single-shot diffraction data set that mimics the data proposed for obtaining 3D structure from identical particles. Ellipsoidal iron oxide nanoparticles (250nm×50nm ) were aerosolized and injected through an aerodynamic lens stack into a soft x-ray FEL. Particle orientation was not controlled with this injection method. We observed that, at the instant the x-ray pulse interacts with the particle, a snapshot of the particle’s orientation is encoded in the diffraction pattern. The results give credence to one of the technical concepts of imaging individual nanometer and subnanometer-sized objects such as single molecules or larger clusters of molecules using hard x-ray FELs and will be used to help develop robust algorithms for determining particle orientations and 3D structure.
The thermodynamics of hydrogen bond breaking and formation was studied in solutions of alcohol (methanol, ethanol, 1-propanol) molecules. An extensive series of over 400 molecular dynamics ...simulations with an aggregate length of over 900 ns was analyzed using an analysis technique in which hydrogen bond (HB) breaking is interpreted as an Eyring process, for which the Gibbs energy of activation ΔG⧧ can be determined from the HB lifetime. By performing simulations at different temperatures, we were able to determine the enthalpy of activation ΔH ⧧ and the entropy of activation TΔS ⧧ for this process from the Van't Hoff relation. The equilibrium thermodynamics was determined separately, based on the number of donor hydrogens that are involved in hydrogen bonds. Results (ΔH) are compared to experimental data from Raman spectroscopy and found to be in good agreement for pure water and methanol. The ΔG as well as the ΔG ⧧ are smooth functions of the composition of the mixtures. The main result of the calculations is that ΔG is essentially independent of the environment (around 5 kJ/mol), suggesting that buried hydrogen bonds (e.g., in proteins) do not contribute significantly to protein stability. Enthalpically HB formation is a downhill process in all substances; however, for the alcohols there is an entropic barrier of 6−7 kJ/mol, at 298.15 K, which cannot be detected in pure water.
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