X-ray Spectroscopic Study of Solvent Effects on the Ferrous and Ferric Hexacyanide Anions

We present an Fe K alpha resonant inelastic X-ray scattering (RIXS) and X-ray emission (XES) study of ferrous and ferric hexacyanide dissolved in water and ethylene glycol. We observe that transitions below the absorption edge show that the solvent has a distinct effect on the valence electronic structure. In addition, both the RIXS and XES spectra show a stabilization of the 2p levels when dissolved in water. Using molecular dynamics simulations, we propose that this effect arises from the hydrogen-bonding interactions between the complex and nearby solvent molecules. This withdraws electron density from the ligands, stabilizing the complex but also causing a slight increase in pi-backbonding

Renewable energy from Cyanobacteria: energy production optimization by metabolic pathway engineering

The need to develop and improve sustainable energy resources is of eminent importance due to the finite nature of our fossil fuels. This review paper deals with a third generation renewable energy resource which does not compete with our food resources, cyanobacteria. We discuss the current state of the art in developing different types of bioenergy (ethanol, biodiesel, hydrogen, etc.) from cyanobacteria. The major important biochemical pathways in cyanobacteria are highlighted, and the possibility to influence these pathways to improve the production of specific types of energy forms the major part of this review

Characterizing the Structure and Defect Concentration of ZnO Nanoparticles in a Colloidal Solution

The structure and defect concentration of colloidal solutions of ZnO nanoparticles, synthesized by a sol gel procedure (SG-NP), as well as commercially available ZnO nanoparticles (SA-NP) are investigated by UV-vis absorption spectroscopy, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD). The XRD patterns, in agreement with the TEM images, reveal that the SG-NPs are more ellipsoidal than the SA-NPs. XRD and XAS reveal the presence of both zinc and oxygen vacancies. The concentration of the latter is independent of the NP size. This is not the case for the zinc vacancies, whose concentration increases sharply in the SG-NPs compared to the SA-NPs, and an similar to 40% oxygen excess in comparison to the expected stoichiometric ratio is found. Importantly, an extended X-ray absorption fine structure (EXAFS) analysis shows that this large concentration of zinc vacancies does not lead to distortions of the local lattice structure. Finally, the Zn K-edge X-ray absorption near edge structure (XANES) spectra show distinct changes in the rising edge and above edge regions, which supports the presence of zinc vacancies. In all cases, two weak pre-edge features are also observed and assigned to a small concentration of oxygen vacancies

The role of Hartree-Fock exchange in the simulation of X-ray absorption spectra: A study of photoexcited [Fe(bpy)(3)](2+)

We present a theoretical analysis for the K- and L-2/3-edge static and picosecond X-ray absorption spectra of [Fe(bpy)(3)](2+). Simulations of the pre-edge region at the Fe K-edge using time-dependent density functional theory demonstrate the importance of Hartree-Fock exchange within the exchange-correlation functional, especially when describing charge transfer and 1s -> 3d transitions. This becomes particularly relevant for range separated functionals, for which the incorporation of Hartree-Fock exchange at short range decreases the absolute error in the excitation energy usually observed using TD-DFT. Finally, we compute and interpret the L-2/3-edge spectrum using the Restricted Open-Shell Configuration Interaction Singles method. (C) 2013 Elsevier B.V. All rights reserved

Ultrafast X-ray Absorption Studies of the Structural Dynamics of Molecular and Biological Systems in Solution

We review our recent studies of excited state structures and dynamics of chemical and biological systems with pico- and femtosecond X-ray absorption spectroscopy in the liquid phase

X‑ray Spectroscopic Study of Solvent Effects on the Ferrous and Ferric Hexacyanide Anions

We present an Fe Kα resonant inelastic X-ray scattering (RIXS) and X-ray emission (XES) study of ferrous and ferric hexacyanide dissolved in water and ethylene glycol. We observe that transitions below the absorption edge show that the solvent has a distinct effect on the valence electronic structure. In addition, both the RIXS and XES spectra show a stabilization of the 2p levels when dissolved in water. Using molecular dynamics simulations, we propose that this effect arises from the hydrogen-bonding interactions between the complex and nearby solvent molecules. This withdraws electron density from the ligands, stabilizing the complex but also causing a slight increase in π-backbonding

Solvent-Induced Luminescence Quenching: Static and Time-Resolved X‑Ray Absorption Spectroscopy of a Copper(I) Phenanthroline Complex

We present a static and picosecond X-ray absorption study at the Cu K-edge of bis­(2,9-dimethyl-1,10-phenanthroline)­copper­(I) ([Cu­(dmp)₂]⁺; dmp = 2,9-dimethyl-1,10-phenanthroline) dissolved in acetonitrile and dichloromethane. The steady-state photoluminescence spectra in dichloromethane and acetonitrile are also presented and show a shift to longer wavelengths for the latter, which points to a stronger stabilization of the excited complex. The fine structure features of the static and transient X-ray spectra allow an unambiguous assignment of the electronic and geometric structure of the molecule in both its ground and excited ³MLCT states. Importantly, the transient spectra are remarkably similar for both solvents, and the spectral changes can be rationalized using the optimized ground- and excited-state structures of the complex. The proposed assignment of the lifetime shortening of the excited state in donor solvents (acetonitrile) to a metal-centered exciplex is not corroborated here. Molecular dynamics simulations confirm the lack of complexation; however, in both solvents the molecules come close to the metal but undergo rapid exchange with the bulk. The shortening of the lifetime of the title complex and nine additional related complexes can be rationalized by the decrease in the ³MLCT energy. Deviations from this trend may be explained by means of the effects of the dihedral angle between the ligand planes, the solvent, and the ³MLCT-¹MLCT energy gap