Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances. Experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined

Atrasentan and renal events in patients with type 2 diabetes and chronic kidney disease (SONAR): a double-blind, randomised, placebo-controlled trial

Background: Short-term treatment for people with type 2 diabetes using a low dose of the selective endothelin A receptor antagonist atrasentan reduces albuminuria without causing significant sodium retention. We report the long-term effects of treatment with atrasentan on major renal outcomes. Methods: We did this double-blind, randomised, placebo-controlled trial at 689 sites in 41 countries. We enrolled adults aged 18–85 years with type 2 diabetes, estimated glomerular filtration rate (eGFR)25–75 mL/min per 1·73 m 2 of body surface area, and a urine albumin-to-creatinine ratio (UACR)of 300–5000 mg/g who had received maximum labelled or tolerated renin–angiotensin system inhibition for at least 4 weeks. Participants were given atrasentan 0·75 mg orally daily during an enrichment period before random group assignment. Those with a UACR decrease of at least 30% with no substantial fluid retention during the enrichment period (responders)were included in the double-blind treatment period. Responders were randomly assigned to receive either atrasentan 0·75 mg orally daily or placebo. All patients and investigators were masked to treatment assignment. The primary endpoint was a composite of doubling of serum creatinine (sustained for ≥30 days)or end-stage kidney disease (eGFR <15 mL/min per 1·73 m 2 sustained for ≥90 days, chronic dialysis for ≥90 days, kidney transplantation, or death from kidney failure)in the intention-to-treat population of all responders. Safety was assessed in all patients who received at least one dose of their assigned study treatment. The study is registered with ClinicalTrials.gov, number NCT01858532. Findings: Between May 17, 2013, and July 13, 2017, 11 087 patients were screened; 5117 entered the enrichment period, and 4711 completed the enrichment period. Of these, 2648 patients were responders and were randomly assigned to the atrasentan group (n=1325)or placebo group (n=1323). Median follow-up was 2·2 years (IQR 1·4–2·9). 79 (6·0%)of 1325 patients in the atrasentan group and 105 (7·9%)of 1323 in the placebo group had a primary composite renal endpoint event (hazard ratio [HR]0·65 [95% CI 0·49–0·88]; p=0·0047). Fluid retention and anaemia adverse events, which have been previously attributed to endothelin receptor antagonists, were more frequent in the atrasentan group than in the placebo group. Hospital admission for heart failure occurred in 47 (3·5%)of 1325 patients in the atrasentan group and 34 (2·6%)of 1323 patients in the placebo group (HR 1·33 [95% CI 0·85–2·07]; p=0·208). 58 (4·4%)patients in the atrasentan group and 52 (3·9%)in the placebo group died (HR 1·09 [95% CI 0·75–1·59]; p=0·65). Interpretation: Atrasentan reduced the risk of renal events in patients with diabetes and chronic kidney disease who were selected to optimise efficacy and safety. These data support a potential role for selective endothelin receptor antagonists in protecting renal function in patients with type 2 diabetes at high risk of developing end-stage kidney disease. Funding: AbbVie

Synthesis, spectroscopic characterization and catalytic activity of platinum(II) carbene complexes

A novel platinum complex with 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidenyl ligand has been synthesized and characterized on the basis of elemental analysis, MS, 1H and 13C NMR spectroscopy, X-ray Absorption Spectroscopy and single crystal X-ray diffraction studies. The XRD determination of the complex (monoclinic, C2/c) revealed a structure in which the platinum (II) centre coordinates two chlorides, a carbon atom of the N-heterocyclic carbene (NHC) and is stabilized by coordinating the nitrogen atom of a 3-chloropyridine molecule, forming an over-all square planar geometry. By prolonging the time of the reaction, it was possible to obtain the trans-dichloridobis(3-chloropyridine) platinum(II) complex under the same reaction conditions. The electronic and molecular properties of both complexes were investigated and compared by means of Near Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS), supported by numerical simulations. The platinum carbene complex obtained was tested in a series of C-H activation and hydrosilylation reactions

Electrochemical and XAS investigation of oxygen reduction reaction on Pt-TiO2-C catalysts

Pt-TiO2-C composites with different titanium oxide loading were synthesized by photo-deposition and chemical vapor deposition methods. The changes in their electronic properties improve the electrochemical activity toward the oxygen reduction reaction (ORR) compared to the Pt-C catalyst synthesized at the same conditions. The platinum samples were physically characterized by means of Transmission Electron Microscopy (TEM), Small Angle X-ray Scattering (SAXS), X-ray Absorption Spectroscopy (XAS) and X-ray Photo-electron Spectroscopy (XPS). Their electrochemical activity was also investigated by cyclic and linear voltammetry techniques. TEM analysis shows homogeneously dispersed platinum nanoparticles with an average particle size of 2 nm in all the synthesized samples. Form factor (morphology model) and particle size were determined by SAXS, the data adjusted to spherical Pt nanoparticles in both synthesis methods. XAS studies at the Pt L-3-edge shows a close interaction of Pt with the support material, i.e. C or TiO2. XPS analysis reveals surface modifications that induce electronic changes on Pt-TiO2-C. Significant differences in the ORR electrochemical activity were correlated to the TiO2 loading and the synthesis procedure. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Resolving the Ultrafast Changes of Chemically Inequivalent Metal–Ligand Bonds in Photoexcited Molecular Complexes with Transient X‑ray Absorption Spectroscopy

Photoactive transition-metal complexes that incorporate heteroleptic ligands present a first coordination shell, which is asymmetric. Although it is generally expected that the metal–ligand bond lengths respond differently to photoexcitation, resolving these fine structural changes remains experimentally challenging, especially for flexible multidentate ligands. In this work, ultrafast X-ray absorption spectroscopy is employed to capture directly the asymmetric elongations of chemically inequivalent metal–ligand bonds in the photoexcited spin-switching FeII complex [FeII(tpen)]2+ solvated in acetonitrile, where tpen denotes N,N,N′,N′-tetrakis­(2-pyridylmethyl)-1,2-ethylenediamine. The possibility to correlate precisely the nature of the donor/acceptor coordinating atoms to specific photoinduced structural changes within a binding motif will provide advanced diagnostics for optimizing numerous photoactive chemical and biological building blocks

Characterization of metal hydrides by in-situ XRD

In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) technique is a powerful tool to gain a deeper understanding of reaction mechanisms in crystalline materials. In this paper, the implementation of a new in-situ SR-PXD cell for solid–gas reactions is described in detail. The cell allows performing measurements in a range of pressure which goes from light vacuum (10−2 bar) up to 200 bar and temperatures from room temperature up to 550 °C. The high precision, with which pressure and temperature are measured, enables to estimate the thermodynamic properties of the observed changes in the crystal structure and phase transformations

SEM and XAS characterization at beginning of life of Pd-based cathode electrocatalysts in PEM fuel cells

The fuel cell performance of membrane electrode assemblies with a Pt anode and Pd, PdCu or Pd5Cu4Pt cathodes has been tested during 116 h (beginning of life). The incorporation of Cu to Pd increases the fuel cell performance. Incorporation of Pt leads to further improvement. SEM micrographs of the as-prepared and the fuel cell-tested assemblies show the effects of the 116 h of continuous operation. Nafion membranes were characterized by small angle X-ray scattering. The results show a reduction of the size of the lamellar domains in the perfluorinated matrix after fuel cell testing, but no correlation with the cathode electrocatalyst material. The cathode electrocatalysts were characterized by ex-situ synchrotron radiation X-ray diffraction and X-ray absorption spectroscopy at the Pd L-3, Cu K and Pt L-3 edges. Re-organization of Pd5Cu4Pt electrocatalyst after fuel cell testing was observed. The Cu in the electrocatalyst can be described as a nano-mixture of metallic Cu, alloyed Cu and CuO. The CuO acts as a promoter of the ORR. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Synchrotron-based structural and spectroscopic studies of ball milled RuSeMo and RuSnMo particles as oxygen reduction electrocatalyst for PEM fuel cells

Particles of RuSeMo and RuSnMo have been produced by ball milling; they present catalytic activity towards the oxygen reduction reaction (ORR) in acid media. A Tafel slope close to 120 mV/dec was found for both materials. Their morphology was first characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM images reveal particles in the sub-micrometer range. The structure of the materials was further probed with synchrotron radiation powder X-ray diffraction (SR-PXD) and X-ray absorption spectroscopy (XAS). SR-PXD reveals the existence of metallic Ru as the main phase and the formation of phases such as RuSe2 in RuSeMo and Ru3Sn7 in RuSnMo. Mo was found to form solid solution into the RuSe2 phase in ball milled RuSeMo. Finally, The Ru L-3-edge and Mo L-3-edge XAS fingerprints were correlated with the catalytic activity towards ORR. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Towards longer-lived metal-to-ligand charge transfer states of iron(ii) complexes: an N-heterocyclic carbene approach.

A 9 ps (3)MLCT lifetime was achieved by a Fe(II) complex based on C(NHC)⁁N(py)⁁C(NHC) pincer ligands. This is the longest known so far for any kind of complexes of this abundant metal, and increased by almost two orders of magnitude compared to the reference Fe(II) bis-terpyridine complex