The Experts below are selected from a list of 285141 Experts worldwide ranked by ideXlab platform
Ahmed H. Zewail - One of the best experts on this subject based on the ideXlab platform.
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Structural Dynamics of surfaces by ultrafast electron crystallography experimental and multiple scattering theory
Journal of Chemical Physics, 2011Co-Authors: Sascha Schäfer, Wenxi Liang, Ahmed H. ZewailAbstract:Recent studies in ultrafast electron crystallography (UEC) using a reflection diffraction geometry have enabled the investigation of a wide range of phenomena on the femtosecond and picosecond time scales. In all these studies, the analysis of the diffraction patterns and their temporal change after excitation was performed within the kinematical scattering theory. In this contribution, we address the question, to what extent dynamical scattering effects have to be included in order to obtain quantitative information about Structural Dynamics. We discuss different scattering regimes and provide diffraction maps that describe all essential features of scatterings and observables. The effects are quantified by dynamical scattering simulations and examined by direct comparison to the results of ultrafast electron diffraction experiments on an in situ prepared Ni(100) surface, for which Structural Dynamics can be well described by a two-temperature model. We also report calculations for graphite surfaces. The theoretical framework provided here allows for further UEC studies of surfaces especially at larger penetration depths and for those of heavy-atom materials.
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Structural Dynamics of nanoscale gold by ultrafast electron crystallography
Chemical Physics Letters, 2011Co-Authors: Sascha Schäfer, Wenxi Liang, Ahmed H. ZewailAbstract:By employing ultrafast electron crystallography in a transmission geometry for ultra-thin (2–3 nm) gold, here we show that Structural Dynamics of the transverse atomic motions and the atomic displacements around the equilibrium position can be separated from the measured change in Bragg diffraction, the positions and intensities of the peaks, respectively. The rate of intensity change provides the electron-lattice equilibration time whereas the observed lattice expansion, which occurs on a slower time scale, maps the delayed response of transverse lattice strain. These textbook-type results provide the microscopic stress–strain profile that is critical for understanding dynamical deformations and the effect of morphological structures at surfaces.
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ultrafast electron crystallography of surface Structural Dynamics with atomic scale resolution
Angewandte Chemie, 2004Co-Authors: Franco Vigliotti, Songye Chen, Chongyu Ruan, Vladimir A Lobastov, Ahmed H. ZewailAbstract:A formidable contender to X-ray diffraction is ultrafast electron crystallography. Whereas the former is more suited to investigate the bulk of the substrate, the time, length, and sensitivity scales of electron crystallography provide powerful and complementary information on atomic-scale Structural Dynamics at the surface (see diffraction image of GaAs crystal).
Majed Chergui - One of the best experts on this subject based on the ideXlab platform.
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excited state x ray absorption spectroscopy probing both electronic and Structural Dynamics
Journal of Chemical Physics, 2016Co-Authors: Majed Chergui, Simon P Neville, Vitali Averbukh, M Ruberti, Renjie Yun, Serguei Patchkovskii, Albert Stolow, Michael S SchuurmanAbstract:We investigate the sensitivity of X-ray absorption spectra, simulated using a general method, to properties of molecular excited states. Recently, Averbukh and co-workers [M. Ruberti et al., J. Chem. Phys. 140, 184107 (2014)] introduced an efficient and accurate L2 method for the calculation of excited state valence photoionization cross-sections based on the application of Stieltjes imaging to the Lanczos pseudo-spectrum of the algebraic diagrammatic construction (ADC) representation of the electronic Hamiltonian. In this paper, we report an extension of this method to the calculation of excited state core photoionization cross-sections. We demonstrate that, at the ADC(2)x level of theory, ground state X-ray absorption spectra may be accurately reproduced, validating the method. Significantly, the calculated X-ray absorption spectra of the excited states are found to be sensitive to both geometric distortions (Structural Dynamics) and the electronic character (electronic Dynamics) of the initial state, s...
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molecular Structural Dynamics probed by ultrafast x ray absorption spectroscopy
Annual Review of Physical Chemistry, 2010Co-Authors: Christian Bressler, Majed CherguiAbstract:The ability to visualize molecular structure in the course of a chemical reaction or a biological function has been a dream of scientists for decades. X-ray absorption spectroscopy (XAS) is ideal in this respect because it is chemically selective and can be implemented in any type of medium. Furthermore, using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) in laser pump/X-ray probe experiments allows the retrieval of not only the local geometric structure of the system under study, but also the underlying electronic structure changes that drive the Structural Dynamics. We review recent developments in picosecond and femtosecond XAS applied to molecular systems in solution. Examples on ultrafast photoinduced processes such as intramolecular electron transfer, low-to-high spin change, and bond formation are presented.
C V Shank - One of the best experts on this subject based on the ideXlab platform.
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ultrafast Structural Dynamics in insb probed by time resolved x ray diffraction
Physical Review Letters, 1999Co-Authors: A H Chin, R W Schoenlein, T E Glover, Peter Balling, W P Leemans, C V ShankAbstract:Ultrafast Structural Dynamics in InSb are studied using time-resolved x-ray diffraction. A delayed onset of significant lattice expansion and an indication of subpicosecond disordering are observed.
Hyotcherl Ihee - One of the best experts on this subject based on the ideXlab platform.
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Protein Structural Dynamics Revealed by Time-Resolved X-ray Solution Scattering
AMER CHEMICAL SOC, 2018Co-Authors: Jong Goo Kim, Tae Wu Kim, Kim J., Hyotcherl IheeAbstract:Conspectus One of the most important questions in biological science is how a protein functions. When a protein performs its function, it undergoes regulated Structural transitions. In this regard, to better understand the underlying principle of a protein function, it is desirable to monitor the dynamic evolution of the protein structure in real time. To probe fast and subtle motions of a protein in physiological conditions demands an experimental tool that is not only equipped with superb spatiotemporal resolution but also applicable to samples in solution phase. Time-resolved X-ray solution scattering (TRXSS), discussed in this Account, fits all of those requirements needed for probing the movements of proteins in aqueous solution. The technique utilizes a pump-probe scheme employing an optical pump pulse to initiate photoreactions of proteins and an X-ray probe pulse to monitor ensuing Structural changes. The technical advances in ultrafast lasers and X-ray sources allow us to achieve superb temporal resolution down to femtoseconds. Because X-rays scatter off all atomic pairs in a protein, an X-ray scattering pattern provides information on the global structure of the protein with subangstrom spatial resolution. Importantly, TRXSS is readily applicable to aqueous solution samples of proteins with the aid of theoretical models and therefore is well suited for investigating Structural Dynamics of protein transitions in physiological conditions. In this Account, we demonstrate that TRXSS can be used to probe real-time Structural Dynamics of proteins in solution ranging from subtle helix movement to global conformational change. Specifically, we discuss the photoreactions of photoactive yellow protein (PYP) and homodimeric hemoglobin (HbI). For PYP, we revealed the kinetics of Structural transitions among four transient intermediates comprising a photocycle and, by applying Structural analysis based on ab initio shape reconstruction, showed that the signaling of PYP involves the protrusion of the N-terminus with significant increase of the overall protein size. For HbI, we elucidated the Dynamics of complex allosteric transitions among transient intermediates. In particular, by applying Structural refinement analysis based on rigid-body modeling, we found that the allosteric transition of HbI accompanies the rotation of quaternary structure and the contraction between two heme domains. By making use of the experimental and analysis methods presented in this Account, we envision that the TRXSS can be used to probe the Structural Dynamics of various proteins, allowing us to decipher the working mechanisms of their functions. Furthermore, when combined with femtosecond X-ray pulses generated from X-ray free electron lasers, TRXSS will gain access to ultrafast protein Dynamics on sub-picosecond time scales. © 2015 American Chemical Society141
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ultrafast x ray scattering Structural Dynamics from diatomic to protein molecules
International Reviews in Physical Chemistry, 2010Co-Authors: Hyotcherl Ihee, Michael Wulff, Jeongho Kim, Shinichi AdachiAbstract:Recent years have witnessed the birth of picosecond pump-probe X-ray diffraction and scattering techniques, thanks to the technological developments in the third generation synchrotron beamlines and advances in theory and data analysis by combining quantum calculations, molecular Dynamics simulations and global fitting analysis. Our laboratories have employed this technique to study Structural Dynamics and spatiotemporal kinetics of many molecular systems in solution including diatomic molecules, haloalkanes, organometallic complexes and protein molecules over timescales from picoseconds (ps) to milliseconds. The visualising power and unbiased sensitivity of X-ray scattering proved to be instrumental in identifying global reaction pathways and in some cases capturing detailed three-dimensional structures of reaction intermediates. Many results have accumulated from which we have selected some interesting examples to be reviewed here. The Structural Dynamics of Br2 and I2 are compared and the reaction path...
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Tracking the Structural Dynamics of proteins in solution using time-resolved wide-angle X-ray scattering.
Nature methods, 2008Co-Authors: Marco Cammarata, Matteo Levantino, Friedrich Schotte, Philip A. Anfinrud, Friederike Ewald, Jungkweon Choi, Antonio Cupane, Michael Wulff, Hyotcherl IheeAbstract:We demonstrate tracking of protein Structural changes with time-resolved wide-angle X-ray scattering (TR-WAXS) with nanosecond time resolution. We investigated the tertiary and quaternary conformational changes of human hemoglobin under nearly physiological conditions triggered by laser-induced ligand photolysis. We also report data on optically induced tertiary relaxations of myoglobin and refolding of cytochrome c to illustrate the wide applicability of the technique. By providing insights into the Structural Dynamics of proteins functioning
Sascha Schäfer - One of the best experts on this subject based on the ideXlab platform.
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Structural Dynamics of surfaces by ultrafast electron crystallography experimental and multiple scattering theory
Journal of Chemical Physics, 2011Co-Authors: Sascha Schäfer, Wenxi Liang, Ahmed H. ZewailAbstract:Recent studies in ultrafast electron crystallography (UEC) using a reflection diffraction geometry have enabled the investigation of a wide range of phenomena on the femtosecond and picosecond time scales. In all these studies, the analysis of the diffraction patterns and their temporal change after excitation was performed within the kinematical scattering theory. In this contribution, we address the question, to what extent dynamical scattering effects have to be included in order to obtain quantitative information about Structural Dynamics. We discuss different scattering regimes and provide diffraction maps that describe all essential features of scatterings and observables. The effects are quantified by dynamical scattering simulations and examined by direct comparison to the results of ultrafast electron diffraction experiments on an in situ prepared Ni(100) surface, for which Structural Dynamics can be well described by a two-temperature model. We also report calculations for graphite surfaces. The theoretical framework provided here allows for further UEC studies of surfaces especially at larger penetration depths and for those of heavy-atom materials.
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Structural Dynamics of nanoscale gold by ultrafast electron crystallography
Chemical Physics Letters, 2011Co-Authors: Sascha Schäfer, Wenxi Liang, Ahmed H. ZewailAbstract:By employing ultrafast electron crystallography in a transmission geometry for ultra-thin (2–3 nm) gold, here we show that Structural Dynamics of the transverse atomic motions and the atomic displacements around the equilibrium position can be separated from the measured change in Bragg diffraction, the positions and intensities of the peaks, respectively. The rate of intensity change provides the electron-lattice equilibration time whereas the observed lattice expansion, which occurs on a slower time scale, maps the delayed response of transverse lattice strain. These textbook-type results provide the microscopic stress–strain profile that is critical for understanding dynamical deformations and the effect of morphological structures at surfaces.
