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1.
Nat Commun ; 11(1): 2131, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32358505

RESUMO

OLED technology beyond small or expensive devices requires light-emitters, luminophores, based on earth-abundant elements. Understanding and experimental verification of charge transfer in luminophores are needed for this development. An organometallic multicore Cu complex comprising Cu-C and Cu-P bonds represents an underexplored type of luminophore. To investigate the charge transfer and structural rearrangements in this material, we apply complementary pump-probe X-ray techniques: absorption, emission, and scattering including pump-probe measurements at the X-ray free-electron laser SwissFEL. We find that the excitation leads to charge movement from C- and P- coordinated Cu sites and from the phosphorus atoms to phenyl rings; the Cu core slightly rearranges with 0.05 Å increase of the shortest Cu-Cu distance. The use of a Cu cluster bonded to the ligands through C and P atoms is an efficient way to keep structural rigidity of luminophores. Obtained data can be used to verify computational methods for the development of luminophores.

2.
Nat Commun ; 10(1): 3606, 2019 Aug 09.
Artigo em Inglês | MEDLINE | ID: mdl-31399565

RESUMO

Disentangling the strong interplay between electronic and nuclear degrees of freedom is essential to achieve a full understanding of excited state processes during ultrafast nonadiabatic chemical reactions. However, the complexity of multi-dimensional potential energy surfaces means that this remains challenging. The energy flow during vibrational and electronic relaxation processes can be explored with structural sensitivity by probing a nuclear wavepacket using femtosecond time-resolved X-ray Absorption Near Edge Structure (TR-XANES). However, it remains unknown to what level of detail vibrational motions are observable in this X-ray technique. Herein we track the wavepacket dynamics of a prototypical [Cu(2,9-dimethyl-1,10-phenanthroline)2]+ complex using TR-XANES. We demonstrate that sensitivity to individual wavepacket components can be modulated by the probe energy and that the bond length change associated with molecular breathing mode can be tracked with a sub-Angstrom resolution beyond optical-domain observables. Importantly, our results reveal how state-of-the-art TR-XANES provides deeper insights of ultrafast nonadiabatic chemical reactions.

4.
Struct Dyn ; 5(5): 054303, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30364211

RESUMO

The development of X-ray free-electron lasers (XFELs) has opened the possibility to investigate the ultrafast dynamics of biomacromolecules using X-ray diffraction. Whereas an increasing number of structures solved by means of serial femtosecond crystallography at XFELs is available, the effect of radiation damage on protein crystals during ultrafast exposures has remained an open question. We used a split-and-delay line based on diffractive X-ray optics at the Linac Coherent Light Source XFEL to investigate the time dependence of X-ray radiation damage to lysozyme crystals. For these tests, crystals were delivered to the X-ray beam using a fixed-target approach. The presented experiments provide probe signals at eight different delay times between 19 and 213 femtoseconds after a single pump event, thereby covering the time-scales relevant for femtosecond serial crystallography. Even though significant impact on the crystals was observed at long time scales after exposure with a single X-ray pulse, the collected diffraction data did not show significant signal reduction that could be assigned to beam damage on the crystals in the sampled time window and resolution range. This observation is in agreement with estimations of the applied radiation dose, which in our experiment was clearly below the values expected to cause damage on the femtosecond time scale. The experiments presented here demonstrate the feasibility of time-resolved pump-multiprobe X-ray diffraction experiments on protein crystals.

5.
J Synchrotron Radiat ; 25(Pt 4): 1238-1248, 2018 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-29979187

RESUMO

The SwissFEL Aramis beamline, covering the photon energies between 1.77 keV and 12.7 keV, features a suite of online photon diagnostics tools to help both users and FEL operators in analysing data and optimizing experimental and beamline performance. Scientists will be able to obtain information about the flux, spectrum, position, pulse length, and arrival time jitter versus the experimental laser for every photon pulse, with further information about beam shape and size available through the use of destructive screens. This manuscript is an overview of the diagnostics tools available at SwissFEL and presents their design, working principles and capabilities. It also features new developments like the first implementation of a THz-streaking based temporal diagnostics for a hard X-ray FEL, capable of measuring pulse lengths to 5 fs r.m.s. or better.

6.
Nat Commun ; 9(1): 478, 2018 02 02.
Artigo em Inglês | MEDLINE | ID: mdl-29396396

RESUMO

Nanostructures of transition metal oxides, such as zinc oxide, have attracted considerable interest for solar-energy conversion and photocatalysis. Both applications are sensitive to the transport and trapping of photoexcited charge carriers. The probing of electron trapping has recently become possible using time-resolved element-sensitive methods, such as X-ray spectroscopy. However, valence-band-trapped holes have so far escaped observation. Herein we use X-ray absorption spectroscopy combined with a dispersive X-ray emission spectrometer to probe the charge carrier relaxation and trapping processes in zinc oxide nanoparticles after above band-gap photoexcitation. Our results, supported by simulations, demonstrate that within 80 ps, photoexcited holes are trapped at singly charged oxygen vacancies, which causes an outward displacement by ~15% of the four surrounding zinc atoms away from the doubly charged vacancy. This identification of the hole traps provides insight for future developments of transition metal oxide-based nanodevices.

7.
J Synchrotron Radiat ; 25(Pt 1): 16-19, 2018 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-29271745

RESUMO

One of the remaining challenges for accurate photon diagnostics at X-ray free-electron lasers (FELs) is the shot-to-shot, non-destructive, high-resolution characterization of the FEL pulse spectrum at photon energies between 2 keV and 4 keV, the so-called tender X-ray range. Here, a spectrometer setup is reported, based on the von Hamos geometry and using elastic scattering as a fingerprint of the FEL-generated spectrum. It is capable of pulse-to-pulse measurement of the spectrum with an energy resolution (ΔE/E) of 10-4, within a bandwidth of 2%. The Tender X-ray Single-Shot Spectrometer (TXS) will grant to experimental scientists the freedom to measure the spectrum in a single-shot measurement, keeping the transmitted beam undisturbed. It will enable single-shot reconstructions for easier and faster data analysis.

8.
Chimia (Aarau) ; 71(5): 299-307, 2017 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-28576157

RESUMO

X-ray techniques have long been applied to chemical research, ranging from powder diffraction tools to analyse material structure to X-ray fluorescence measurements for sample composition. The development of high-brightness, accelerator-based X-ray sources has allowed chemists to use similar techniques but on more demanding samples and using more photon-hungry methods. X-ray Free Electron Lasers (XFELs) are the latest in the development of these large-scale user facilities, opening up new avenues of research and the possibility of more advanced applications for a range of research. The SwissFEL XFEL project at the Paul Scherrer Institute will begin user operation in the hard X-ray (2.1-12.4 keV) photon energy range in 2018 with soft X-ray (240-1930 eV) user operation to follow and here we will present the details of this project, it's operating capabilities, and some aspects of the experimental stations that will be particularly attractive for chemistry research. SwissFEL is a revolutionary new machine that will complement and extend the time-resolved chemistry efforts in the Swiss research community.

9.
Environ Sci Technol ; 51(11): 6063-6070, 2017 Jun 06.
Artigo em Inglês | MEDLINE | ID: mdl-28436657

RESUMO

Stability and temporal changes in size distributions have been observed for citrate- (cit) and polyvinylpyrrolidone- (PVP) capped silver nanoparticles (AgNPs), in the presence or absence of sulfide and natural organic matter (NOM, as humic acid), while under suboxic conditions. There were substantial differences in the influence of the two capping agents, with PVP-AgNPs showing few or no significant changes in apparent stability or particle size distribution under the conditions examined, while the apparent size distributions of citrate-capped AgNPs changed rapidly. Sulfide and humic acid each individually caused immediate increases in cit-AgNP size distributions, which were then relatively stable over 60-145 days. This may be due to sulfide bridging and cation bridging, respectively. However, in competition, it was the influence of the humic acid that dominated that of the sulfide. These observations have implications for environmental fate and toxicity of AgNP. The increased stability in the presence of even low concentrations of NOM may limit the rapidity of Ag dispersal but may also concentrate the dose received by organisms, which subsequently ingest the stabilized particles.


Assuntos
Substâncias Húmicas , Nanopartículas Metálicas , Tamanho da Partícula , Prata
10.
Sci Rep ; 6: 33292, 2016 09 13.
Artigo em Inglês | MEDLINE | ID: mdl-27620067

RESUMO

X-ray techniques have evolved over decades to become highly refined tools for a broad range of investigations. Importantly, these approaches rely on X-ray measurements that depend linearly on the number of incident X-ray photons. The advent of X-ray free electron lasers (XFELs) is opening the ability to reach extremely high photon numbers within ultrashort X-ray pulse durations and is leading to a paradigm shift in our ability to explore nonlinear X-ray signals. However, the enormous increase in X-ray peak power is a double-edged sword with new and exciting methods being developed but at the same time well-established techniques proving unreliable. Consequently, accurate knowledge about the threshold for nonlinear X-ray signals is essential. Herein we report an X-ray spectroscopic study that reveals important details on the thresholds for nonlinear X-ray interactions. By varying both the incident X-ray intensity and photon energy, we establish the regimes at which the simplest nonlinear process, two-photon X-ray absorption (TPA), can be observed. From these measurements we can extract the probability of this process as a function of photon energy and confirm both the nature and sub-femtosecond lifetime of the virtual intermediate electronic state.

11.
Biophys J ; 110(6): 1304-11, 2016 Mar 29.
Artigo em Inglês | MEDLINE | ID: mdl-27028640

RESUMO

The biological influence of radiation on living matter has been studied for years; however, several questions about the detailed mechanism of radiation damage formation remain largely unanswered. Among all biomolecules exposed to radiation, DNA plays an important role because any damage to its molecular structure can affect the whole cell and may lead to chromosomal rearrangements resulting in genomic instability or cell death. To identify and characterize damage induced in the DNA sugar-phosphate backbone, in this work we performed x-ray absorption spectroscopy at the P K-edge on DNA irradiated with either UVA light or protons. By combining the experimental results with theoretical calculations, we were able to establish the types and relative ratio of lesions produced by both UVA and protons around the phosphorus atoms in DNA.


Assuntos
Dano ao DNA , DNA/efeitos da radiação , Espectroscopia por Absorção de Raios X/métodos , Animais , Bovinos , Prótons , Raios Ultravioleta
12.
Proc Natl Acad Sci U S A ; 112(42): 12922-7, 2015 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-26438842

RESUMO

Diatomic ligands in hemoproteins and the way they bind to the active center are central to the protein's function. Using picosecond Fe K-edge X-ray absorption spectroscopy, we probe the NO-heme recombination kinetics with direct sensitivity to the Fe-NO binding after 532-nm photoexcitation of nitrosylmyoglobin (MbNO) in physiological solutions. The transients at 70 and 300 ps are identical, but they deviate from the difference between the static spectra of deoxymyoglobin and MbNO, showing the formation of an intermediate species. We propose the latter to be a six-coordinated domed species that is populated on a timescale of ∼ 200 ps by recombination with NO ligands. This work shows the feasibility of ultrafast pump-probe X-ray spectroscopic studies of proteins in physiological media, delivering insight into the electronic and geometric structure of the active center.


Assuntos
Mioglobina/metabolismo , Óxido Nítrico/metabolismo , Análise Espectral/métodos , Cinética , Ligantes
13.
Phys Chem Chem Phys ; 17(36): 23298-302, 2015 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-26300122

RESUMO

Identifying the intermediate species along a reaction pathway is a first step towards a complete understanding of the reaction mechanism, but often this task is not trivial. There has been a strong on-going debate: which of the three intermediates, the CHI2 radical, the CHI2-I isomer, and the CHI2(+) ion, is the dominant intermediate species formed in the photolysis of iodoform (CHI3)? Herein, by combining time-resolved X-ray liquidography (TRXL) and time-resolved X-ray absorption spectroscopy (TR-XAS), we present strong evidence that the CHI2 radical is dominantly formed from the photolysis of CHI3 in methanol at 267 nm within the available time resolution of the techniques (∼20 ps for TRXL and ∼100 ps for TR-XAS). The TRXL measurement, conducted using the time-slicing scheme, detected no CHI2-I isomer within our signal-to-noise ratio, indicating that, if formed, the CHI2-I isomer must be a minor intermediate. The TR-XAS transient spectra measured at the iodine L1 and L3 edges support the same conclusion. The present work demonstrates that the application of these two complementary time-resolved X-ray methods to the same system can provide a detailed understanding of the reaction mechanism.

14.
Phys Chem Chem Phys ; 16(17): 7692-6, 2014 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-24425065

RESUMO

The electronic structure of nano-NiO was determined using resonant inelastic X-ray scattering (RIXS) spectroscopy. The nanosized NiO particles were reduced in situ, leading to the formation of metallic Ni in a single step. Time-resolved RIXS elucidated in real time the changes on the occupied and unoccupied electronic structure of the material, which are dramatically affected by the reduction process.

15.
Phys Chem Chem Phys ; 16(4): 1617-31, 2014 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-24317683

RESUMO

We present an iron K-edge X-ray absorption study of carboxymyoglobin (MbCO), nitrosylmyoglobin (MbNO), oxymyoglobin (MbO2), cyanomyoglobin (MbCN), aquomet myoglobin (metMb) and unligated myoglobin (deoxyMb) in physiological media. The analysis of the XANES region is performed using the full-multiple scattering formalism, implemented within the MXAN package. This reveals trends within the heme structure, absent from previous crystallographic and X-ray absorption analysis. In particular, the iron-nitrogen bond lengths in the porphyrin ring converge to a common value of about 2 Å, except for deoxyMb whose bigger value is due to the doming of the heme. The trends of the Fe-Nε (His93) bond length is found to be consistent with the effect of ligand binding to the iron, with the exception of MbNO, which is explained in terms of the repulsive trans effect. We derive a high resolution description of the relative geometry of the ligands with respect to the heme and quantify the magnitude of the heme doming in the deoxyMb form. Finally, time-dependent density functional theory is used to simulate the pre-edge spectra and is found to be in good agreement with the experiment. The XAS spectra typically exhibit one pre-edge feature which arises from transitions into the unoccupied dσ and dπ - πligand* orbitals. 1s → dπ transitions contribute weakly for MbO2, metMb and deoxyMb. However, despite this strong Fe d contribution these transitions are found to be dominated by the dipole (1s → 4p) moment due to the low symmetry of the heme environment.


Assuntos
Compostos Férricos/química , Compostos Ferrosos/química , Mioglobina/química , Elétrons , Modelos Moleculares , Estrutura Molecular , Soluções , Espectroscopia por Absorção de Raios X
16.
J Am Chem Soc ; 135(51): 19071-4, 2013 Dec 26.
Artigo em Inglês | MEDLINE | ID: mdl-24328233

RESUMO

We report an in situ time-resolved high-energy resolution off-resonant spectroscopy study with subsecond resolution providing insight into the oxidation and reduction steps of a Pt catalyst during CO oxidation. The study shows that the slow oxidation step is composed of two characteristic stages, namely, dissociative adsorption of oxygen followed by partial oxidation of Pt subsurface. By comparing the experimental spectra with theoretical calculations, we found that the intermediate chemisorbed O on Pt is adsorbed on atop position, which suggests surface poisoning by CO or surface reconstruction.

17.
Analyst ; 138(7): 1966-70, 2013 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-23431560

RESUMO

The dynamics of TiO2 conduction band electrons were followed with a novel broadband synchrotron-based transient mid-IR spectroscopy setup. The lifetime of conduction band electrons was found to be dependent on the injection method used. Direct band gap excitation results in a lifetime of 2.5 ns, whereas indirect excitation at 532 nm via Ru-N719 dye followed by injection from the dye into TiO2 results in a lifetime of 5.9 ns.

19.
Chimia (Aarau) ; 65(5): 308-12, 2011.
Artigo em Inglês | MEDLINE | ID: mdl-21744681

RESUMO

We review our recent activity in the field of photo-induced structural dynamics in crystalline solids studied using femtosecond X-ray diffraction techniques.


Assuntos
Teoria Quântica , Cristalização , Estrutura Molecular , Fatores de Tempo , Difração de Raios X
20.
Rev Sci Instrum ; 82(6): 063111, 2011 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-21721678

RESUMO

We present the extension of time-resolved optical pump/x-ray absorption spectroscopy (XAS) probe experiments towards data collection at MHz repetition rates. The use of a high-power picosecond laser operating at an integer fraction of the repetition rate of the storage ring allows exploitation of up to two orders of magnitude more x-ray photons than in previous schemes based on the use of kHz lasers. Consequently, we demonstrate an order of magnitude increase in the signal-to-noise of time-resolved XAS of molecular systems in solution. This makes it possible to investigate highly dilute samples at concentrations approaching physiological conditions for biological systems. The simplicity and compactness of the scheme allows for straightforward implementation at any synchrotron beamline and for a wide range of x-ray probe techniques, such as time-resolved diffraction or x-ray emission studies.


Assuntos
Lasers , Síncrotrons , Espectroscopia por Absorção de Raios X/instrumentação , 2,2'-Dipiridil/análogos & derivados , 2,2'-Dipiridil/química , Absorção , Animais , Complexos de Coordenação , Ferro/química , Mioglobina/química , Oxirredução , Espalhamento de Radiação , Soluções , Fatores de Tempo
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