http://journals.iucr.org/a/issues/2010/02/00/isscontsbdy.html Acta Crystallographica Section A: Foundations of Crystallography publishes papers reporting fundamental advances in all areas of crystallography in the broadest sense. The central themes are, on the one hand, experimental and theoretical studies of the properties and arrangements of atoms, ions and molecules in condensed matter, ideal or real, and of their symmetry and, on the other, the theoretical and experimental aspects of the various methods to determine these arrangements. en Copyright (c) 2010 International Union of Crystallography 2010-03-01 International Union of Crystallography International Union of Crystallography http://journals.iucr.org urn:issn:0108-7673 Acta Crystallographica Section A: Foundations of Crystallography publishes papers reporting fundamental advances in all areas of crystallography in the broadest sense. The central themes are, on the one hand, experimental and theoretical studies of the properties and arrangements of atoms, ions and molecules in condensed matter, ideal or real, and of their symmetry and, on the other, the theoretical and experimental aspects of the various methods to determine these arrangements. text/html Acta Crystallographica Section A: Foundations of Crystallography, Volume 66, Part 2, 2010 text yearly 6 2002-01-01T00:00+00:00 2 66 2010-03-01 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography 133 urn:issn:0108-7673 med@iucr.org March 2010 2010-03-01 http://journals.iucr.org/logos/rss10a.gif http://journals.iucr.org/a/issues/2010/02/00/isscontsbdy.html Still image http://scripts.iucr.org/cgi-bin/paper?me0417 Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Collet, E. 2010-02-18 doi:10.1107/S0108767310004551 International Union of Crystallography en editorial dynamical structural science text/html Dynamical structural science text 2 66 2010-02-18 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography editorial 133 134 http://scripts.iucr.org/cgi-bin/paper?xd5030 A perspective on the new developments of structural dynamics is presented. The scope of applications and advances, from microscopy to diffraction and spectroscopy, defines the new age of endeavour. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Zewail, A.H. 2010-02-09 doi:10.1107/S0108767309047801 International Union of Crystallography A perspective on the new developments of structural dynamics is presented. The scope of applications and advances, from microscopy to diffraction and spectroscopy, defines the new age of endeavour. en structural dynamics electron diffraction electron microscopy spectroscopy A perspective on the new developments of structural dynamics is presented. The scope of applications and advances, from microscopy to diffraction and spectroscopy, defines the new age of endeavour. text/html The new age of structural dynamics text 2 66 2010-02-09 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 135 136 http://scripts.iucr.org/cgi-bin/paper?xd5029 Recent advances in high-intensity electron and X-ray pulsed sources now make it possible to directly observe atomic motions as they occur in barrier-crossing processes. These rare events require the structural dynamics to be triggered by femtosecond excitation pulses that prepare the system above the barrier or access new potential energy surfaces that drive the structural changes. In general, the sampling process modifies the system such that the structural probes should ideally have sufficient intensity to fully resolve structures near the single-shot limit for a given time point. New developments in both source intensity and temporal characterization of the pulsed sampling mode have made it possible to make so-called `molecular movies', i.e. measure relative atomic motions faster than collisions can blur information on correlations. Strongly driven phase transitions from thermally propagated melting to optically modified potential energy surfaces leading to ballistic phase transitions and bond stiffening are given as examples of the new insights that can be gained from an atomic level perspective of structural dynamics. The most important impact will likely be made in the fields of chemistry and biology where the central unifying concept of the transition state will come under direct observation and enable a reduction of high-dimensional complex reaction surfaces to the key reactive modes, as long mastered by Mother Nature. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Miller, R.J.D. Ernstorfer, R. Harb, M. Gao, M. Hebeisen, C.T. Jean-Ruel, H. Lu, C. Moriena, G. Sciaini, G. 2010-02-09 doi:10.1107/S0108767309053926 International Union of Crystallography The long-held dream of directly observing atomic motions during the primary events governing structural dynamics has been realized using high-number-density electron pulses, and soon ultrabright X-ray pulses from fourth-generation light sources, to light up the atomic motions on 100 fs timescales. There are many surprises in store for us as we attain the fundamental limits to observe dynamical phenomena at the atomic level – as they occur. en femtosecond electron diffraction pulsed electron sources ponderomotive scattering structural phase transitions homogeneous nucleation nonthermal melting warm dense matter molecular movies atomically resolved structural dynamics Recent advances in high-intensity electron and X-ray pulsed sources now make it possible to directly observe atomic motions as they occur in barrier-crossing processes. These rare events require the structural dynamics to be triggered by femtosecond excitation pulses that prepare the system above the barrier or access new potential energy surfaces that drive the structural changes. In general, the sampling process modifies the system such that the structural probes should ideally have sufficient intensity to fully resolve structures near the single-shot limit for a given time point. New developments in both source intensity and temporal characterization of the pulsed sampling mode have made it possible to make so-called `molecular movies', i.e. measure relative atomic motions faster than collisions can blur information on correlations. Strongly driven phase transitions from thermally propagated melting to optically modified potential energy surfaces leading to ballistic phase transitions and bond stiffening are given as examples of the new insights that can be gained from an atomic level perspective of structural dynamics. The most important impact will likely be made in the fields of chemistry and biology where the central unifying concept of the transition state will come under direct observation and enable a reduction of high-dimensional complex reaction surfaces to the key reactive modes, as long mastered by Mother Nature. text/html `Making the molecular movie': first frames text 2 66 2010-02-09 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 137 156 http://scripts.iucr.org/cgi-bin/paper?xd5018 The timescales for structural changes in a single crystal of bismuth after excitation with an intense near-infrared laser pulse are studied with femtosecond pump-probe X-ray diffraction. Changes in the intensity and reciprocal-lattice vector of several reflections give quantitative information on the structure factor and lattice strain as a function of time, with a resolution of 200 fs. The results indicate that the majority of excess carrier energy that remains near the surface is transferred to vibrational modes on a timescale of about 10 ps, and that the resultant increase in the variance of the atomic positions at these times is consistent with the overall magnitude of lattice strain that develops. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Johnson, S.L. Beaud, P. Vorobeva, E. Milne, C.J. Murray, É.D. Fahy, S. Ingold, G. 2010-02-09 doi:10.1107/S0108767309053859 International Union of Crystallography Grazing-incidence femtosecond X-ray diffraction is used to study the non-equilibrium structural dynamics in bismuth after intense near-infrared laser excitation on timescales ranging from 200 fs to 400 ps. The data indicate that at times earlier than 10 ps there are significant deviations from local thermal equilibrium due to incomplete electronic relaxation. en phonon dynamics grazing-incidence femtosecond X-ray diffraction bismuth lattice strain The timescales for structural changes in a single crystal of bismuth after excitation with an intense near-infrared laser pulse are studied with femtosecond pump-probe X-ray diffraction. Changes in the intensity and reciprocal-lattice vector of several reflections give quantitative information on the structure factor and lattice strain as a function of time, with a resolution of 200 fs. The results indicate that the majority of excess carrier energy that remains near the surface is transferred to vibrational modes on a timescale of about 10 ps, and that the resultant increase in the variance of the atomic positions at these times is consistent with the overall magnitude of lattice strain that develops. text/html Non-equilibrium phonon dynamics studied by grazing-incidence femtosecond X-ray crystallography text 2 66 2010-02-09 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 157 167 http://scripts.iucr.org/cgi-bin/paper?xd5020 Femtosecond X-ray diffraction allows for real-time mapping of structural changes in condensed matter on atomic length and timescales. Sequences of diffraction patterns provide both transient geometries and charge-density maps of crystalline materials. This article reviews recent progress in this field, the main emphasis being on experimental work done with laser-driven hard X-ray sources. Both Bragg diffraction techniques for bulk and nanostructured single crystals as well as the recently implemented powder diffraction from polycrystalline samples are discussed. In ferroelectric superlattice structures, coherent phonon motions and the driving stress mechanisms are observed in real time. In molecular crystals charge-transfer processes and the concomitant changes of the lattice geometry are analyzed. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Elsaesser, T. Woerner, M. 2010-02-09 doi:10.1107/S0108767309048181 International Union of Crystallography Real-time studies of structural dynamics by femtosecond X-ray diffraction are reviewed, discussing results for single-crystal and polycrystalline polar materials. en structural dynamics femtosecond X-ray diffraction charge-density maps superlattice structures charge-transfer processes Femtosecond X-ray diffraction allows for real-time mapping of structural changes in condensed matter on atomic length and timescales. Sequences of diffraction patterns provide both transient geometries and charge-density maps of crystalline materials. This article reviews recent progress in this field, the main emphasis being on experimental work done with laser-driven hard X-ray sources. Both Bragg diffraction techniques for bulk and nanostructured single crystals as well as the recently implemented powder diffraction from polycrystalline samples are discussed. In ferroelectric superlattice structures, coherent phonon motions and the driving stress mechanisms are observed in real time. In molecular crystals charge-transfer processes and the concomitant changes of the lattice geometry are analyzed. text/html Photoinduced structural dynamics of polar solids studied by femtosecond X-ray diffraction text 2 66 2010-02-09 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 168 178 http://scripts.iucr.org/cgi-bin/paper?xd5023 Definitive experimental results on the geometry of fleeting species are at the time of writing still limited to monochromatic data collection, but methods for modifications of the polychromatic Laue data to increase their accuracy and their suitability for pump–probe experiments have been implemented and are reviewed. In the monochromatic experiments summarized, excited-state conversion percentages are small when neat crystals are used, but are higher when photoactive species are embedded in an inert framework in supramolecular crystals. With polychromatic techniques and increasing source brightness, smaller samples down to tenths of a micrometre or less can be used, increasing homogeneity of exposure and the fractional population of the excited species. Experiments described include a series of transition metal complexes and a fully organic example involving excimer formation. In the final section, experimental findings are compared with those from theoretical calculations on the isolated species. Qualitative agreement is generally obtained, but the theoretical results are strongly dependent on the details of the calculation, indicating the need for further systematic analysis. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Coppens, P. Benedict, J. Messerschmidt, M. Novozhilova, I. Graber, T. Chen, Y.-S. Vorontsov, I. Scheins, S. Zheng, S.-L. 2010-02-18 doi:10.1107/S0108767309055342 International Union of Crystallography Excited-state geometries determined by time-resolved synchrotron diffraction are summarized with emphasis on their comparison with a series of theoretical results. The relative merits of monochromatic and polychromatic (Laue) techniques are discussed. en pump–probe experiments time-resolved diffraction excited-state molecular geometries excimers Definitive experimental results on the geometry of fleeting species are at the time of writing still limited to monochromatic data collection, but methods for modifications of the polychromatic Laue data to increase their accuracy and their suitability for pump–probe experiments have been implemented and are reviewed. In the monochromatic experiments summarized, excited-state conversion percentages are small when neat crystals are used, but are higher when photoactive species are embedded in an inert framework in supramolecular crystals. With polychromatic techniques and increasing source brightness, smaller samples down to tenths of a micrometre or less can be used, increasing homogeneity of exposure and the fractional population of the excited species. Experiments described include a series of transition metal complexes and a fully organic example involving excimer formation. In the final section, experimental findings are compared with those from theoretical calculations on the isolated species. Qualitative agreement is generally obtained, but the theoretical results are strongly dependent on the details of the calculation, indicating the need for further systematic analysis. text/html Time-resolved synchrotron diffraction and theoretical studies of very short-lived photo-induced molecular species text 2 66 2010-02-18 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 179 188 http://scripts.iucr.org/cgi-bin/paper?xd5027 Fast and ultra-fast time-resolved diffraction is a fantastic tool for directly observing the structural dynamics of a material rearrangement during the transformation induced by an ultra-short laser pulse. The paper illustrates this ability using the dynamics of photoinduced molecular switching in the solid state probed by 100 ps X-ray diffraction. This structural information is crucial for establishing the physical foundations of how to direct macroscopic photoswitching in materials. A key feature is that dynamics follow a complex pathway from molecular to material scales through a sequence of processes. Not only is the pathway indirect, the nature of the dynamical processes along the pathway depends on the timescale. This dictates which types of degrees of freedom are involved in the subsequent dynamics or kinetics and which are frozen or statistically averaged. We present a recent investigation of the structural dynamics in multifunctional spin-crossover materials, which are prototypes of molecular bistability in the solid state. The time-resolved X-ray diffraction results show that the dynamics span from subpicosecond molecular photoswitching followed by volume expansion (on a nanosecond timescale) and additional thermoswitching (on a microsecond timescale). Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Cailleau, H. Lorenc, M. Guérin, L. Servol, M. Collet, E. Buron-Le Cointe, M. 2010-02-18 doi:10.1107/S0108767309051046 International Union of Crystallography A recent investigation by 100 ps X-ray diffraction of the structural dynamics in multifunctional spin-crossover materials, which are prototypes of molecular bistability, is presented. This illustrates how the dynamics of molecular photoswitching between low-spin and high-spin states follows a complex pathway from molecular to material scales through a sequence of processes. en molecular switching photoinduced transformation time-resolved diffraction Fast and ultra-fast time-resolved diffraction is a fantastic tool for directly observing the structural dynamics of a material rearrangement during the transformation induced by an ultra-short laser pulse. The paper illustrates this ability using the dynamics of photoinduced molecular switching in the solid state probed by 100 ps X-ray diffraction. This structural information is crucial for establishing the physical foundations of how to direct macroscopic photoswitching in materials. A key feature is that dynamics follow a complex pathway from molecular to material scales through a sequence of processes. Not only is the pathway indirect, the nature of the dynamical processes along the pathway depends on the timescale. This dictates which types of degrees of freedom are involved in the subsequent dynamics or kinetics and which are frozen or statistically averaged. We present a recent investigation of the structural dynamics in multifunctional spin-crossover materials, which are prototypes of molecular bistability in the solid state. The time-resolved X-ray diffraction results show that the dynamics span from subpicosecond molecular photoswitching followed by volume expansion (on a nanosecond timescale) and additional thermoswitching (on a microsecond timescale). text/html Structural dynamics of photoinduced molecular switching in the solid state text 2 66 2010-02-18 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 189 197 http://scripts.iucr.org/cgi-bin/paper?xd5019 A method for determining a comprehensive chemical kinetic mechanism in macromolecular reactions is presented. The method is based on five-dimensional crystallography, where, in addition to space and time, temperature is also taken into consideration and an analysis based on singular value decomposition is applied. First results of such a time-resolved crystallographic study are presented. Temperature-dependent time-resolved X-ray diffraction measurements were conducted on the newly upgraded BioCARS 14-ID-B beamline at the Advanced Photon Source and aimed at elucidating a comprehensive kinetic mechanism of the photoactive yellow protein photocycle. Extensive time series of crystallographic data were collected at two temperatures, 293 K and 303 K. Relaxation times of the reaction extracted from these time series exhibit measurable differences for the two temperatures, hence demonstrating that five-dimensional crystallography is feasible. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Schmidt, M. Graber, T. Henning, R. Srajer, V. 2010-02-18 doi:10.1107/S0108767309054166 International Union of Crystallography Here it is demonstrated how five-dimensional crystallography can be used to determine a comprehensive chemical kinetic mechanism in concert with the atomic structures of transient intermediates that form and decay during the course of the reaction. en time-resolved crystallography chemical kinetics protein structure temperature dependence A method for determining a comprehensive chemical kinetic mechanism in macromolecular reactions is presented. The method is based on five-dimensional crystallography, where, in addition to space and time, temperature is also taken into consideration and an analysis based on singular value decomposition is applied. First results of such a time-resolved crystallographic study are presented. Temperature-dependent time-resolved X-ray diffraction measurements were conducted on the newly upgraded BioCARS 14-ID-B beamline at the Advanced Photon Source and aimed at elucidating a comprehensive kinetic mechanism of the photoactive yellow protein photocycle. Extensive time series of crystallographic data were collected at two temperatures, 293 K and 303 K. Relaxation times of the reaction extracted from these time series exhibit measurable differences for the two temperatures, hence demonstrating that five-dimensional crystallography is feasible. text/html Five-dimensional crystallography text 2 66 2010-02-18 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 198 206 http://scripts.iucr.org/cgi-bin/paper?xd5026 Proteins undergo conformational changes during their biological function. As such, a high-resolution structure of a protein's resting conformation provides a starting point for elucidating its reaction mechanism, but provides no direct information concerning the protein's conformational dynamics. Several X-ray methods have been developed to elucidate those conformational changes that occur during a protein's reaction, including time-resolved Laue diffraction and intermediate trapping studies on three-dimensional protein crystals, and time-resolved wide-angle X-ray scattering and X-ray absorption studies on proteins in the solution phase. This review emphasizes the scope and limitations of these complementary experimental approaches when seeking to understand protein conformational dynamics. These methods are illustrated using a limited set of examples including myoglobin and haemoglobin in complex with carbon monoxide, the simple light-driven proton pump bacteriorhodopsin, and the superoxide scavenger superoxide reductase. In conclusion, likely future developments of these methods at synchrotron X-ray sources and the potential impact of emerging X-ray free-electron laser facilities are speculated upon. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Westenhoff, S. Nazarenko, E. Malmerberg, E. Davidsson, J. Katona, G. Neutze, R. 2010-02-18 doi:10.1107/S0108767309054361 International Union of Crystallography Time-resolved structural studies of proteins have undergone several significant developments during the last decade. Recent developments using time-resolved X-ray methods, such as time-resolved Laue diffraction, low-temperature intermediate trapping, time-resolved wide-angle X-ray scattering and time-resolved X-ray absorption spectroscopy, are reviewed. en time-resolved diffraction structural biology protein structural dynamics Laue diffraction kinetic crystallography WAXS XAS Proteins undergo conformational changes during their biological function. As such, a high-resolution structure of a protein's resting conformation provides a starting point for elucidating its reaction mechanism, but provides no direct information concerning the protein's conformational dynamics. Several X-ray methods have been developed to elucidate those conformational changes that occur during a protein's reaction, including time-resolved Laue diffraction and intermediate trapping studies on three-dimensional protein crystals, and time-resolved wide-angle X-ray scattering and X-ray absorption studies on proteins in the solution phase. This review emphasizes the scope and limitations of these complementary experimental approaches when seeking to understand protein conformational dynamics. These methods are illustrated using a limited set of examples including myoglobin and haemoglobin in complex with carbon monoxide, the simple light-driven proton pump bacteriorhodopsin, and the superoxide scavenger superoxide reductase. In conclusion, likely future developments of these methods at synchrotron X-ray sources and the potential impact of emerging X-ray free-electron laser facilities are speculated upon. text/html Time-resolved structural studies of protein reaction dynamics: a smorgasbord of X-ray approaches text 2 66 2010-02-18 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 207 219 http://scripts.iucr.org/cgi-bin/paper?xd5025 In order to explore the ligand-migration dynamics in myoglobin induced by photodissociation, cryogenic X-ray crystallographic investigations of carbonmonoxy myoglobin crystals illuminated by continuous wave and pulsed lasers at 1–15 kHz repetition rate have been carried out. Here it is shown that this novel method, extended pulsed-laser pumping of carbonmonoxy myoglobin, promotes ligand migration in the protein matrix by crossing the glass transition temperature repeatedly, and enables the visualization of the migration pathway of the photodissociated ligands in native Mb at cryogenic temperatures. It has revealed that the migration of the CO molecule into each cavity induces structural changes of the amino-acid residues around the cavity which result in the expansion of the cavity. The sequential motion of the ligand and the cavity suggests a self-opening mechanism of the ligand-migration channel arising by induced fit. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Tomita, A. Sato, T. Nozawa, S. Koshihara, S. Adachi, S. 2010-02-09 doi:10.1107/S0108767309050752 International Union of Crystallography The ligand migration dynamics in myoglobin are visualized by cryogenic X-ray crystallography under continuous or pulsed laser illumination. en ligand-migration dynamics myoglobin amino acids In order to explore the ligand-migration dynamics in myoglobin induced by photodissociation, cryogenic X-ray crystallographic investigations of carbonmonoxy myoglobin crystals illuminated by continuous wave and pulsed lasers at 1–15 kHz repetition rate have been carried out. Here it is shown that this novel method, extended pulsed-laser pumping of carbonmonoxy myoglobin, promotes ligand migration in the protein matrix by crossing the glass transition temperature repeatedly, and enables the visualization of the migration pathway of the photodissociated ligands in native Mb at cryogenic temperatures. It has revealed that the migration of the CO molecule into each cavity induces structural changes of the amino-acid residues around the cavity which result in the expansion of the cavity. The sequential motion of the ligand and the cavity suggests a self-opening mechanism of the ligand-migration channel arising by induced fit. text/html Tracking ligand-migration pathways of carbonmonoxy myoglobin in crystals at cryogenic temperatures text 2 66 2010-02-09 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 220 228 http://scripts.iucr.org/cgi-bin/paper?xd5024 The need to visualize molecular structure in the course of a chemical reaction, a phase transformation or a biological function has been a dream of scientists for decades. The development of time-resolved X-ray and electron-based methods is making this true. X-ray absorption spectroscopy is ideal for the study of structural dynamics in liquids, because it can be implemented in amorphous media. Furthermore, it is chemically selective. 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 the local geometric structure of the system under study, but also the underlying photoinduced electronic structure changes that drive the structural dynamics. Recent developments in picosecond and femtosecond X-ray absorption spectroscopy applied to molecular systems in solution are reviewed: examples on ultrafast photoinduced processes such as intramolecular electron transfer, low-to-high spin change, and bond formation are presented. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Chergui, M. 2010-02-09 doi:10.1107/S010876730904968X International Union of Crystallography Picosecond and femtosecond X-ray absorption spectroscopic studies of photoinduced molecular processes in solution are presented, with examples of intramolecular electron transfer, low-to-high spin conversion and bond formation in metal-based molecular complexes. en structural dynamics ultrafast phenomena molecules EXAFS XANES The need to visualize molecular structure in the course of a chemical reaction, a phase transformation or a biological function has been a dream of scientists for decades. The development of time-resolved X-ray and electron-based methods is making this true. X-ray absorption spectroscopy is ideal for the study of structural dynamics in liquids, because it can be implemented in amorphous media. Furthermore, it is chemically selective. 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 the local geometric structure of the system under study, but also the underlying photoinduced electronic structure changes that drive the structural dynamics. Recent developments in picosecond and femtosecond X-ray absorption spectroscopy applied to molecular systems in solution are reviewed: examples on ultrafast photoinduced processes such as intramolecular electron transfer, low-to-high spin change, and bond formation are presented. text/html Picosecond and femtosecond X-ray absorption spectroscopy of molecular systems text 2 66 2010-02-09 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 229 239 http://scripts.iucr.org/cgi-bin/paper?xd5022 Transient molecular structures along chemical reaction pathways are important for predicting molecular reactivity, understanding reaction mechanisms, as well as controlling reaction pathways. During the past decade, X-ray transient absorption spectroscopy (XTA, or LITR-XAS, laser-initiated X-ray absorption spectroscopy), analogous to the commonly used optical transient absorption spectroscopy, has been developed. XTA uses a laser pulse to trigger a fundamental chemical process, and an X-ray pulse(s) to probe transient structures as a function of the time delay between the pump and probe pulses. Using X-ray pulses with high photon flux from synchrotron sources, transient electronic and molecular structures of metal complexes have been studied in disordered media from homogeneous solutions to heterogeneous solution–solid interfaces. Several examples from the studies at the Advanced Photon Source in Argonne National Laboratory are summarized, including excited-state metalloporphyrins, metal-to-ligand charge transfer (MLCT) states of transition metal complexes, and charge transfer states of metal complexes at the interface with semiconductor nanoparticles. Recent developments of the method are briefly described followed by a future prospective of XTA. It is envisioned that concurrent developments in X-ray free-electron lasers and synchrotron X-ray facilities as well as other table-top laser-driven femtosecond X-ray sources will make many breakthroughs and realise dreams of visualizing molecular movies and snapshots, which ultimately enable chemical reaction pathways to be controlled. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Chen, L.X. Zhang, X. Lockard, J.V. Stickrath, A.B. Attenkofer, K. Jennings, G. Liu, D.-J. 2010-02-18 doi:10.1107/S0108767309051496 International Union of Crystallography A decade of development in X-ray transient absorption spectroscopy of metal complexes and interfacial systems for light-activated processes in the authors' institution is summarized through several examples and future prospective. en X-ray transient absorption spectroscopy LITR-XAS MLCT state structures excited-state metalloporphyrins ultrafast X-ray sciences XTA Transient molecular structures along chemical reaction pathways are important for predicting molecular reactivity, understanding reaction mechanisms, as well as controlling reaction pathways. During the past decade, X-ray transient absorption spectroscopy (XTA, or LITR-XAS, laser-initiated X-ray absorption spectroscopy), analogous to the commonly used optical transient absorption spectroscopy, has been developed. XTA uses a laser pulse to trigger a fundamental chemical process, and an X-ray pulse(s) to probe transient structures as a function of the time delay between the pump and probe pulses. Using X-ray pulses with high photon flux from synchrotron sources, transient electronic and molecular structures of metal complexes have been studied in disordered media from homogeneous solutions to heterogeneous solution–solid interfaces. Several examples from the studies at the Advanced Photon Source in Argonne National Laboratory are summarized, including excited-state metalloporphyrins, metal-to-ligand charge transfer (MLCT) states of transition metal complexes, and charge transfer states of metal complexes at the interface with semiconductor nanoparticles. Recent developments of the method are briefly described followed by a future prospective of XTA. It is envisioned that concurrent developments in X-ray free-electron lasers and synchrotron X-ray facilities as well as other table-top laser-driven femtosecond X-ray sources will make many breakthroughs and realise dreams of visualizing molecular movies and snapshots, which ultimately enable chemical reaction pathways to be controlled. text/html Excited-state molecular structures captured by X-ray transient absorption spectroscopy: a decade and beyond text 2 66 2010-02-18 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 240 251 http://scripts.iucr.org/cgi-bin/paper?xd5028 A time-resolved X-ray solution scattering study of bromine molecules in CCl4 is presented as an example of how to track atomic motions in a simple chemical reaction. The structures of the photoproducts are tracked during the recombination process, geminate and non-geminate, from 100 ps to 10 µs after dissociation. The relaxation of hot Br2* molecules heats the solvent. At early times, from 0.1 to 10 ns, an adiabatic temperature rise is observed, which leads to a pressure gradient that forces the sample to expand. The expansion starts after about 10 ns with the laser beam sizes used here. When thermal artefacts are removed by suitable scaling of the transient solvent response, the excited-state solute structures can be obtained with high fidelity. The analysis shows that 30% of Br2* molecules recombine directly along the X potential, 60% are trapped in the A/A′ state with a lifetime of 5.5 ns, and 10% recombine non-geminately via diffusive motion in about 25 ns. The Br—Br distance distribution in the A/A′ state peaks at 3.0 Å. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Kong, Q. Lee, J.H. Lo Russo, M. Kim, T.K. Lorenc, M. Cammarata, M. Bratos, S. Buslaps, T. Honkimaki, V. Ihee, H. Wulff, M. 2010-02-09 doi:10.1107/S0108767309054993 International Union of Crystallography The reaction dynamics of molecular bromine in CCl4 are studied by time-resolved X-ray scattering with 100 ps pulses from a synchrotron. en time-resolved X-ray scattering laser pump and X-ray probe bromine recombination dynamics geminate recombination non-geminate recombination transient-state structure A time-resolved X-ray solution scattering study of bromine molecules in CCl4 is presented as an example of how to track atomic motions in a simple chemical reaction. The structures of the photoproducts are tracked during the recombination process, geminate and non-geminate, from 100 ps to 10 µs after dissociation. The relaxation of hot Br2* molecules heats the solvent. At early times, from 0.1 to 10 ns, an adiabatic temperature rise is observed, which leads to a pressure gradient that forces the sample to expand. The expansion starts after about 10 ns with the laser beam sizes used here. When thermal artefacts are removed by suitable scaling of the transient solvent response, the excited-state solute structures can be obtained with high fidelity. The analysis shows that 30% of Br2* molecules recombine directly along the X potential, 60% are trapped in the A/A′ state with a lifetime of 5.5 ns, and 10% recombine non-geminately via diffusive motion in about 25 ns. The Br—Br distance distribution in the A/A′ state peaks at 3.0 Å. text/html Photolysis of Br2 in CCl4 studied by time-resolved X-ray scattering text 2 66 2010-02-09 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 252 260 http://scripts.iucr.org/cgi-bin/paper?xd5021 As ultrafast time-resolved studies of liquid systems with the laser pump/X-ray scattering probe method have come of age over the past decade, several groups have developed methods for the analysis of such X-ray scattering data. The present article describes a method developed primarily with a focus on determining structural parameters in the excited states of medium-sized molecules (~30 atoms) in solution. The general methodology is set in a maximum-likelihood framework and is introduced through the analysis of the photoactive platinum compound PtPOP, in particular the structure of its lowest triplet excited state (3A2u). Emphasis is put on structure determination in terms of model comparisons and on the information content of difference scattering signals as well as the related experimental variables. Several suggestions for improving the accuracy of these types of measurements are presented. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Haldrup, K. Christensen, M. Meedom Nielsen, M. 2010-02-18 doi:10.1107/S0108767309054233 International Union of Crystallography This article describes a robust analysis methodology developed primarily with a focus on determining structural parameters for the excited states of medium-sized molecules in solution using time-resolved X-ray scattering. Emphasis is given to structure determination in terms of model comparisons and to the information content of difference scattering signals as well as the related experimental variables. en liquids photochemistry structural dynamics time-resolved X-ray scattering data analysis As ultrafast time-resolved studies of liquid systems with the laser pump/X-ray scattering probe method have come of age over the past decade, several groups have developed methods for the analysis of such X-ray scattering data. The present article describes a method developed primarily with a focus on determining structural parameters in the excited states of medium-sized molecules (~30 atoms) in solution. The general methodology is set in a maximum-likelihood framework and is introduced through the analysis of the photoactive platinum compound PtPOP, in particular the structure of its lowest triplet excited state (3A2u). Emphasis is put on structure determination in terms of model comparisons and on the information content of difference scattering signals as well as the related experimental variables. Several suggestions for improving the accuracy of these types of measurements are presented. text/html Analysis of time-resolved X-ray scattering data from solution-state systems text 2 66 2010-02-18 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 261 269 http://scripts.iucr.org/cgi-bin/paper?xd5017 In recent years, the time-resolved X-ray diffraction technique has been established as an excellent tool for studying reaction dynamics and protein structural transitions with the aid of 100 ps X-ray pulses generated from third-generation synchrotrons. The forthcoming advent of the X-ray free-electron laser (XFEL) will bring a substantial improvement in pulse duration, photon flux and coherence of X-ray pulses, making time-resolved X-ray diffraction even more powerful. This technical breakthrough is envisioned to revolutionize the field of reaction dynamics associated with time-resolved diffraction methods. Examples of candidates for the first femtosecond X-ray diffraction experiments using highly coherent sub-100 fs pulses generated from XFELs are presented in this paper. They include the chemical reactions of small molecules in the gas and solution phases, solvation dynamics and protein structural transitions. In these potential experiments, ultrafast reaction dynamics and motions of coherent rovibrational wave packets will be monitored in real time. In addition, high photon flux and coherence of XFEL-generated X-ray pulses give the prospect of single-molecule diffraction experiments. Copyright (c) 2010 International Union of Crystallography urn:issn:0108-7673 Kim, J. Kim, K.H. Lee, J.H. Ihee, H. 2010-02-18 doi:10.1107/S0108767309052052 International Union of Crystallography The present status of reaction dynamics studies using the time-resolved X-ray diffraction technique and the future prospects combining the X-ray free-electron laser with the technique are discussed. Examples of femtosecond X-ray diffraction experiments that can be implemented using sub-100 fs X-ray pulses from the free-electron laser are presented with the prospect of directly probing ultrafast structural dynamics of chemical reactions and coherent wave packet motions. en time-resolved X-ray diffraction X-ray free-electron laser reaction dynamics ultrafast structural dynamics time-resolved electron diffraction In recent years, the time-resolved X-ray diffraction technique has been established as an excellent tool for studying reaction dynamics and protein structural transitions with the aid of 100 ps X-ray pulses generated from third-generation synchrotrons. The forthcoming advent of the X-ray free-electron laser (XFEL) will bring a substantial improvement in pulse duration, photon flux and coherence of X-ray pulses, making time-resolved X-ray diffraction even more powerful. This technical breakthrough is envisioned to revolutionize the field of reaction dynamics associated with time-resolved diffraction methods. Examples of candidates for the first femtosecond X-ray diffraction experiments using highly coherent sub-100 fs pulses generated from XFELs are presented in this paper. They include the chemical reactions of small molecules in the gas and solution phases, solvation dynamics and protein structural transitions. In these potential experiments, ultrafast reaction dynamics and motions of coherent rovibrational wave packets will be monitored in real time. In addition, high photon flux and coherence of XFEL-generated X-ray pulses give the prospect of single-molecule diffraction experiments. text/html Ultrafast X-ray diffraction in liquid, solution and gas: present status and future prospects text 2 66 2010-02-18 Copyright (c) 2010 International Union of Crystallography Acta Crystallographica Section A: Foundations of Crystallography research papers 270 280