74 research outputs found
Estimating signal and noise of time-resolved X-ray solution scattering data at synchrotrons and XFELs
No full text© 2020. J. Synchrotron Rad. Elucidating the structural dynamics of small molecules and proteins in the liquid solution phase is essential to ensure a fundamental understanding of their reaction mechanisms. In this regard, time-resolved X-ray solution scattering (TRXSS), also known as time-resolved X-ray liquidography (TRXL), has been established as a powerful technique for obtaining the structural information of reaction intermediates and products in the liquid solution phase and is expected to be applied to a wider range of molecules in the future. A TRXL experiment is generally performed at the beamline of a synchrotron or an X-ray free-electron laser (XFEL) to provide intense and short X-ray pulses. Considering the limited opportunities to use these facilities, it is necessary to verify the plausibility of a target experiment prior to the actual experiment. For this purpose, a program has been developed, referred to as S-cube, which is short for a Solution Scattering Simulator. This code allows the routine estimation of the shape and signal-to-noise ratio (SNR) of TRXL data from known experimental parameters. Specifically, S-cube calculates the difference scattering curve and the associated quantum noise on the basis of the molecular structure of the target reactant and product, the target solvent, the energy of the pump laser pulse and the specifications of the beamline to be used. Employing a simplified form for the pair-distribution function required to calculate the solute-solvent cross term greatly increases the calculation speed as compared with a typical TRXL data analysis. Demonstrative applications of S-cube are presented, including the estimation of the expected TRXL data and SNR level for the future LCLS-II HE beamlines11Nsciescopu
Sub-nanosecond secondary geminate recombination in mercury halides HgX2 (X = I, Br) investigated by time-resolved x-ray scattering
No full text© 2019 Author(s).In this work, we present a detailed investigation on the recombination dynamics of mercury halides HgX2 (X = I, Br) in acetonitrile solution after UV-induced photodissociation. The study is performed by combining time-resolved wide-angle x-ray scattering (TRWAXS) and optical transient absorption spectroscopy. Up to 68% of the UV (266 nm) photodissociated HgX and X radicals that escape the solvent cage surrounding parent HgX2 recombine within a nanosecond after photodissociation. In contrast to classical primary geminate recombination, occurring on much faster time scales, we interpret the sub-nanosecond recombination channel as secondary geminate recombination (SGR), also referred to as diffusion-limited geminate recombination. The family of triatomic mercury halides therefore represents an important class of molecules to study chemical mechanisms of solvent-dependent SGR by TRWAXS. The methodology described here allows for direct mapping of the time-dependent inter-radical distance distribution function, a critical parameter for the assessment of the SGR dynamics in solution phase and solvation in genera
Direct Observation of a Transiently Formed Isomer During Iodoform Photolysis in Solution by Time-Resolved X-ray Liquidography
No full textPhotolysis of iodoform (CHI3) in solution has been extensively studied, but its reaction mechanism remains elusive. In particular, iso-iodoform (iso-CHI2-I) is formed as a product of the photolysis reaction, but its detailed structure is not known, and whether it is a major intermediate species has been controversial. Here, by using time-resolved X-ray liquidography, we determined the reaction mechanism of CHI3 photodissociation in cyclohexane as well as the structure of iso-CHI2-I. Both iso-CHI2-I and CHI2 radical were found to be formed within 100 ps with a branching ratio of 40:60. Iodine radicals (I), formed during the course of CHI3 photolysis, recombine nongeminately with either CHI2 or I. Based on our structural analysis, the I-I distance and the C-I-I angle of iso-CHI2-I were determined to be 2.922 +/- 0.004 angstrom and 133.9 +/- 0.8 degrees, respectively.111sciescopu
Tumor metastasis to lymph nodes requires YAP-dependent metabolic adaptation
No full textIn cancer patients, metastasis of tumors to sentinel lymph nodes (LNs) predicts disease progression and often guides treatment decisions. The mechanisms underlying tumor LN metastasis are poorly understood. By using comparative transcriptomics and metabolomics analyses of primary and LN-metastatic tumors in mice, we found that LN metastasis requires that tumor cells undergo a metabolic shift toward fatty acid oxidation (FAO). Transcriptional coactivator yes-associated protein (YAP) is selectively activated in LN-metastatic tumors, leading to the up-regulation of genes in the FAO signaling pathway. Pharmacological inhibition of FAO or genetic ablation of YAP suppressed LN metastasis in mice. Several bioactive bile acids accumulated to high levels in the metastatic LNs, and these bile acids activated YAP in tumor cells, likely through the nuclear vitamin D receptor. Inhibition of FAO or YAP may merit exploration as a potential therapeutic strategy for mitigating tumor metastasis to LNs. 2017 © The Author
Optical Kerr Effect of Liquid Acetonitrile Probed by Femtosecond Time-Resolved X-ray Liquidography
No full text© Optical Kerr effect (OKE) spectroscopy is a method that measures the time-dependent change of the birefringence induced by an optical laser pulse using another optical laser pulse and has been used often to study the ultrafast dynamics of molecular liquids. Here we demonstrate an alternative method, femtosecond time-resolved X-ray liquidography (fs-TRXL), where the microscopic structural motions related to the OKE response can be monitored using a different type of probe, i.e., X-ray solution scattering. By applying fs-TRXL to acetonitrile and a dye solution in acetonitrile, we demonstrate that different types of molecular motions around photoaligned molecules can be resolved selectively, even without any theoretical modeling, based on the anisotropy of two-dimensional scattering patterns and extra structural information contained in the q-space scattering data. Specifically, the dynamics of reorientational (libration and orientational diffusion) and translational (interaction-induced motion) motions are captured separately by anisotropic and isotropic scattering signals, respectively. Furthermore, the two different types of reorientational motions are distinguished from each other by their own characteristic scattering patterns and time scales. The measured time-resolved scattering signals are in excellent agreement with the simulated scattering signals based on a molecular dynamics simulation for plausible molecular configurations, providing the detailed structural description of the OKE response in liquid acetonitrile.11Nsciescopu
Ultrafast excited state relaxation dynamics in a heteroleptic Ir(iii) complex,: Fac -Ir(ppy)2(ppz), revealed by femtosecond X-ray transient absorption spectroscopy
No full text© 2021 the Partner Organisations.A typical metal complex has a central metal surrounded by multiple ligands, which greatly affect the properties of the whole complex. Although heteroleptic complexes often exhibit substantially different behaviors from homoleptic complexes, systematic studies to explain their origins have been rare. Of special importance is to understand why the heteroleptic metal complex shows a more complicated excited state relaxation dynamics than the homoleptic metal complex. To address this issue, we investigated the excited state relaxation dynamics of a heteroleptic Ir(iii) complex, fac-Ir(ppy)2(ppz), and two homoleptic Ir(iii) complexes, fac-Ir(ppy)3 and fac-Ir(ppz)3, using femtosecond X-ray transient absorption (fs-XTA) spectroscopy, ultrafast optical transient absorption (TA) spectroscopy, and DFT/TDDFT calculation. The data show that the ultrafast relaxation dynamics of ∼450 fs, which is significantly faster than those of previous Ir(iii) complexes with other ligands, is observed only in fac-Ir(ppy)2(ppz) but not in the homoleptic Ir(iii) complexes. Such dynamics observed for only heteroleptic Ir(iii) complexes must originate from the heteroleptic character, and naturally, the inter-ligand energy transfer between two different types of ligands has been suggested to explain the fast dynamics. Both fs-XTA and TA data, however, favor the assignment of the ultrafast dynamics of ∼450 fs to the internal conversion (IC) process from the ppz-localized 3MLCT to the ppy-localized 3MLCT. The DFT/TDDFT calculations support that the abnormally fast IC for fac-Ir(ppy)2(ppz) is due to a large nonadiabatic coupling and the small energy gap between the two states.11Nsciescopu
Gold nanoparticle formation via x-ray radiolysis investigated with time-resolved x-ray liquidography
Get PDF© 2020 by the authors. We report the generation of gold nanoparticles (AuNPs) from the aqueous solution of chloro(2,2′,2′′-terpyridine)gold(III) ion ([Au(tpy)Cl]2+ ) through X-ray radiolysis and optical excitation at a synchrotron. The original purpose of the experiment was to investigate the photoinduced structural changes of [Au(tpy)Cl]2+ upon 400 nm excitation using time-resolved X-ray liquidography (TRXL). Initially, the TRXL data did not show any signal that would suggest structural changes of the solute molecule, but after an induction time, the TRXL data started to show sharp peaks and valleys. In the early phase, AuNPs with two types of morphology, dendrites, and spheres, were formed by the reducing action of hydrated electrons generated by the X-ray radiolysis of water, thereby allowing the detection of TRXL data due to the laser-induced lattice expansion and relaxation of AuNPs. Along with the lattice expansion, the dendritic and spherical AuNPs were transformed into smaller, raspberry-shaped AuNPs of a relatively uniform size via ablation by the optical femtosecond laser pulse used for the TRXL experiment. Density functional theory calculations confirm that the reduction potential of the metal complex relative to the hydration potential of X-ray-generated electrons determines the facile AuNP formation observed for [Au(tpy)Cl]2+11sciescopu
Angiopoietin-2-integrin alpha 5 beta 1 signaling enhances vascular fatty acid transport and prevents ectopic lipid-induced insulin resistance
Get PDF© 2020, The Author(s). Proper storage of excessive dietary fat into subcutaneous adipose tissue (SAT) prevents ectopic lipid deposition-induced insulin resistance, yet the underlying mechanism remains unclear. Here, we identify angiopoietin-2 (Angpt2)–integrin α5β1 signaling as an inducer of fat uptake specifically in SAT. Adipocyte-specific deletion of Angpt2 markedly reduced fatty acid uptake and storage in SAT, leading to ectopic lipid accumulation in glucose-consuming organs including skeletal muscle and liver and to systemic insulin resistance. Mechanistically, Angpt2 activated integrin α5β1 signaling in the endothelium and triggered fatty acid transport via CD36 and FATP3 into SAT. Genetic or pharmacological inhibition of the endothelial integrin α5β1 recapitulated adipocyte-specific Angpt2 knockout phenotypes. Our findings demonstrate the critical roles of Angpt2–integrin α5β1 signaling in SAT endothelium in regulating whole-body fat distribution for metabolic health and highlight adipocyte–endothelial crosstalk as a potential target for prevention of ectopic lipid deposition-induced lipotoxicity and insulin resistance11sci
Impact localization on a composite plate based on error outliers with Pugh’s concept selection
No full textImpacts of Learning Orientation on the Modeling of Programming Using Feature Selection and XGBOOST: A Gender-Focused Analysis
No full textIn programming, modeling is a generalized explanatory system that organizes key characteristics of a specific matter or object of interest using computer science concepts. Modeling is integral for both automation design in programming education and communication in the collaborative process. This study investigates the effect of learning orientation on the modeling stage based on gender. The study includes 756 male and 688 female elementary-school students. We analyzed the results of XGBOOST by extracting the influential characteristics from feature selection along with the basic statistics. As a result of the study, it was confirmed that learners, regardless of gender, had the largest gap in modeling and that this was the stage at which differences occurred in programming education. For male students, the process of collecting data for modeling or devising a solution was found to be an important learning method. This shows that it is necessary to create an environment to focus on activities that derive solutions from the collected data along with strengthening information retrieval education. Although female students showed a similar tendency to male students, the process of cooperating with friends as a differentiating factor was found to be an important learning method. It seems necessary to apply teaching and learning methods that can strengthen team projects that can collaborate with friends. The findings could serve as a reference for teaching and learning design and operation for effective programming education
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