Structural Dynamics-Us最新文献

Transmission electron microscopy (TEM) has significantly advanced fields such as materials science, nanotechnology, and structural biology by providing detailed structural and analytical information at picometer resolutions. To further enhance TEM's capabilities, time-resolved electron microscopy introduces the temporal domain, using ultrafast electron pulses to capture dynamic processes. Traditional methods generate these pulses via photocathode illumination by femtosecond lasers and face challenges like complex alignment and limited repetition rates. An alternative approach employing electronic devices as beam choppers, specifically resonant RF cavities in combination with electrostatic beam blankers, simplifies alignment and increases repetition rates, achieving picosecond and sub-picosecond pulses. Additionally, these devices do not compromise the performance of the microscope in any other imaging mode. The microscope can be rapidly toggled between continuous and pulsed imaging, providing flexibility of operation in modern research labs. This study integrates these beam choppers into high-end TEMs and demonstrates their effectiveness in achieving high temporal resolution for pump-probe experiments. Results show that these methods maintain high spatial resolution and coherence, making them a promising solution for ultrafast electron microscopy.

Time-resolved (TR) Raman spectroscopy is a unique tool for studying the dynamic properties of quantum matter and can become a key element of the multi-messenger research in the time domain. We present here the features and results of a novel setup for TR Raman, designed to expand the NFFA-SPRINT facility by integrating it with TR optical, transient grating and electron spectroscopy and spin polarization techniques. The TR Raman setup is characterized by a wide energy tunability of the pump and probe pulses, owing to the presence of a laser system providing ultrashort (50 fs to 2 ps) light pulses from the near ultraviolet to the infrared spectral regions. The ultra-high vacuum sample environment allows for the measurement of air-sensitive samples and ensures the full compatibility with photoelectron spectroscopies, as well as a wide sample temperature range. The functionalities of the setup and the multi-messenger research approach are here demonstrated by presenting studies of the relaxation dynamics in photoexcited semiconductor systems, namely, Si and MoS₂. In addition, the pump-probe response of magnetite across the Verwey transition is presented, highlighting the capability of TR spontaneous Raman spectroscopy to be a valuable tool for probing photoinduced phase transitions in the time domain.

Interfacial thermal and acoustic phenomena have an important role in quantum science and technology, including in spintronic and spincaloritronic materials and devices. Simultaneous measurements of the low-temperature thermal and acoustic properties of a metal/insulator heterostructure reveal distinct dynamics in the characteristic phonon frequency ranges of acoustic and thermal transport. The measurements probed a heterostructure consisting of a thin film of Pt on the ferrimagnetic insulator gadolinium iron garnet (Gd₃Fe₅O₁₂, GdIG) grown epitaxially on a gadolinium gallium garnet substrate. Ultrafast structural dynamics within the Pt layer were tracked using time-resolved ultrafast x-ray diffraction and analyzed to probe interfacial acoustic and thermal properties. The rapid heating of the Pt layer by a 400 nm wavelength femtosecond-duration optical pulse produced transient structural changes that provided the stimulus for these measurements. Rapid heating produced a broadband acoustic pulse that was partially reflected by the Pt/GdIG interface. Temporal frequencies up to 740 GHz, corresponding to angular frequencies of several THz, were detected in a wavelet analysis of the acoustic oscillations of the strain in the Pt layer. The structural results were analyzed to determine (i) the acoustic damping coefficient and phonon mean free path in Pt at frequencies of hundreds of GHz and (ii) the Grüneisen anharmonicity parameter. The thermal conductance of the Pt/GdIG interface was tracked using the slower, tens-of-picosecond-scale, dynamics of the initial cooling of the heated Pt layer. Analysis using a model based on the Boltzmann transport equation shows that the phonon transmission is lower at the phonon frequencies relevant to thermal transport than for subterahertz regime acoustics.

Given proteins' fundamental importance in human health and catalysis, the relationships between protein sequence, structure, dynamics, and function have become a topic of great interest. One way to extract information from proteins is to compute the local energetic frustration of their native state. Traditionally, energetic frustration calculations require protein structures as a starting point. However, using a single protein structure to evaluate the energetic frustration for a given amino acid sequence does not always fully represent the protein's structural ensemble. Therefore, we have developed a sequence-based method to evaluate energetic frustration in proteins using direct coupling analysis and statistical potentials. Our approach exhibits significant agreement with established structure-based frustration methods in terms of their mutual agreement with crystallographic B-factor. Moreover, our sequence-based method shows elevated precision in classifying high B-factor residues, suggesting that it has some robustness to unstructured regions of proteins.

About 100 years ago, the field of structural biology was born, led by James B. Sumner who recognized that enzymes were molecules with specific functions. In its contemporary form structural biology is used to interpret and understand molecular and cellular function, to design drugs, and to advance biotechnology in general.

Molybdenum oxides have attracted considerable attention in heterogeneous catalysis and energy storage applications owing to the unusual chemical flexibility of the Mo center. Unlike many transition metals, molybdenum can shift between several oxidation states without losing structural integrity, largely due to the stabilizing role of oxo-bridged linkages. This versatility gives rise to an extraordinary diversity of structural motifs that can be tailored for specific catalytic and electrochemical functions. In this study, we investigate the elusive structure and nuclear dynamics of the monohydrate (MoO₃ $·$ H₂O) and dihydrate (MoO₃ $·$  2H₂O) phases of $\beta$ -MoO₃, an important family of precursors for molybdenum oxide-based hybrid materials. We employ a combined experimental and computational approach to explore the local environment and nuclear dynamics of protons in water confined within the interlamellar space of the $\beta$ -MoO₃ layers. High-resolution neutron diffraction confirms the established structure of the dihydrate phase while revealing hydrogen-sublattice disorder in the metastable monohydrate. Complementary computational analysis, including harmonic lattice dynamics and ab initio Born-Oppenheimer molecular dynamics simulations, provides deeper insight into proton confinement in these systems, yielding plausible models of their local structure. These findings further validated through temperature-dependent inelastic neutron scattering and neutron Compton scattering, which probe the vibrational response and proton momentum distributions, respectively. The joint analysis of experimental data and molecular dynamics simulations identifies rotationally bound, orientationally disordered water molecules as the mechanism underlying proton disorder in $\beta$ -MoO₃ $·$ H₂O. Overall, the results reveal pronounced differences in water ordering and proton dynamics between the mono- and dihydrate forms, offering a detailed quantum-mechanical description of the hydrogen behavior in hydrated molybdenum trioxides and highlighting the interplay between the thermal effect and the confinement-induced local proton dynamics.

Here, we describe recently developed upgrades to our experimental scheme for obtaining the photoelectron spectrum, the anisotropy parameter, and the photoelectron circular dichroism (PECD) of jet-cooled flexible molecules with conformer selectivity. The one-color resonance-enhanced multiphoton ionization process used allows ionizing selectively the different conformers present in the supersonic expansion by selecting their S₀-S₁ transition. We first describe the experimental setup with emphasis on the data acquisition and processing. Then, we apply this ionization scheme to a flexible molecule, 1,2,3,4-tetrahydro-3-isoquinoline methanol (THIQM). This molecule shows two stereogenic centers, namely, an asymmetric carbon and a nitrogen atom. It exists in two conformers, THIQM_I and THIQM_II, which differ by the direction of the intramolecular hydrogen bond and the absolute configuration of the nitrogen atom. Therefore, these two conformers are also diastereomers, endowed with slightly different ionization energies. The ionization energy of THIQM_I, which shows an OH…N hydrogen bond, is slightly higher than that of THIQM_II. Their PECD spectra, although of identical signs, differ in shape and magnitude. Surprisingly, the anisotropy parameter is more sensitive than the PECD to the conformational isomerism at play in this system.

Time-resolved serial femtosecond crystallography (TR-SFX) is a technique designed to reveal the molecular dynamics underlying chemical reactions, thereby providing insights into the relationship between structure and function. By capturing a series of conformational changes in intermediate states, TR-SFX enables the visualization of dynamic structural transitions. In this study, we have presented a new approach for modeling reaction state conformations using molecular dynamics (MD) simulations. In this approach, MD simulations were first performed to generate a large number of conformational samples, which were then used as initial models for refinement against diffraction data from the triggered states, thereby facilitating the construction of accurate dynamic structure models. The derived models were evaluated using tools such as Edstats and MolProbity to identify models with high-quality geometries and local electron density metrics. This procedure provides a semi-automated approach for building dynamic structural models from TR-SFX data, ensuring their robustness for further exploration and understanding of macromolecular dynamics.

The high-temperature phase of the hexagonal halide perovskite KNiCl₃ is investigated using time-of-flight single crystal neutron diffraction at 633 K (360 °C). Phonons are captured through thermal diffuse scattering, integrated in energy but resolved in momentum. Harmonic phonon calculations based on density functional theory yield imaginary phonon frequencies for this phase, indicating the presence of structural instabilities at this level of theory. It is shown that the inclusion of anharmonic phonon-phonon interactions removes these instabilities, leading to good qualitative agreement with the experimental diffuse scattering. These results demonstrate that the high-temperature phase of KNiCl₃ is stabilized by anharmonic phonon-phonon interactions.