133 research outputs found
a view from modern soft X-ray spectroscopies
Soft X-ray spectroscopies are powerful tools for probing the local electronic
and molecular orbital structures of materials in different phases and various
environments. While modern spectroscopic tools using soft X-ray synchrotron
photons perspicuously reveal the molecular orbital (MO) structure in detail,
structures remain widely unknown in the liquid phase since many of these
techniques could only be applied to solutions very recently. Furthermore, the
interactions and dynamics of molecules in the liquid phase are especially
complicated compared to those in gas and solid phases and thereby impede the
understanding of functional materials in solution. This review presents recent
developments using soft X-ray radiation for probing the electronic structure
of ions and molecules in solution. The presented X-ray absorption, emission,
and photo-electron spectroscopy studies exhibit the powerful contributions of
soft X-ray liquid spectroscopies in the last few years
recent techniques and applications using soft X-ray spectroscopy
The aim of a more precise knowledge about molecular structures and the nature
of chemical bonds is the driving force behind the development of numerous
experimental methods and theories. Recent soft X-ray based techniques provide
novel opportunities for tackling the structure and the dynamics of chemical
and biochemical systems in solution. In our research group we are developing
experimental methods for mapping the electronic structure and dynamics of
molecular systems in solution during bond-building and breaking using soft
X-ray absorption and emission spectroscopy. The combination of such recent
developments with conventional spectroscopy as well as theoretical modeling
allows us to address open questions about hydrogen bonds, thermodynamics and
active centers of biological systems. Based on the core-hole clock and
pump–probe spectroscopy dynamics on the time scale from sub-femtoseconds up to
picoseconds can be revealed
an iron L-edge X-ray absorption study of the active centre
Iron L-edge X-ray absorption spectra of the active centre of myoglobin in the
met-form, in the reduced form and upon ligation to O2, CO, NO and CN are
presented. The strength of ligation with the iron centre is finger-printed
through the variation of the L3 : L2 intensity ratio. Charge Transfer
Multiplet calculations are performed and give qualitative information about
oxidation states as well as charge transfer
One-Pot Synthesis of nickel-modified carbon nitride layers toward efficient photoelectrochemical cells
[EN] A new method to significantly enhance the photoelectrochemical properties of phenyl-modified carbon nitride layers via the insertion of nickel ions into carbon nitride layers is reported. The nickel ions: are embedded within the carbon nitride layers by manipulating the interaction of Ni ions and molten organic molecules at elevated temperature prior to their condensation. A detailed analysis of the chemical and photophysical properties suggests that the nickel ions dissolve in the molten molecules, leading to the homogeneous distribution of nickel atoms within the carbon nitride layers. We found that the nickel atoms can alter the growth mechanism of carbon nitride layers, resulting in extended light absorption, charge transfer properties, and the total photoelectrochemical performance. For the most photoactive electrode, the Ni ions have an oxidation state of 2.8, as confirmed by soft X-ray absorption spectroscopy. Furthermore, important parameters such as absorption coefficient, exciton lifetime, and diffusion length were studied in depth, providing substantial progress in our understanding of the photoelectrochemical properties of carbon nitride films. This work opens new opportunities for the growth of carbon nitride layers and similar materials on different surfaces and provides important progress in our understanding of the photophysical and photoelectrochemical properties of carbon nitride layers toward their implantation in photoelectronic and other devices.We thank the use Katz Institute for Nanoscale Science & Technology Ben Gurion University for HR-TEM measurements. M.S. thanks Dr. Laurent Chabanne for fruitful discussion. K.M.L. is grateful for the support by the Helmholtz Association (VH-NG-1140).Zhang, W.; Albero-Sancho, J.; Xi, L.; Lange, KM.; García Gómez, H.; Wang, X.; Shalom, M. (2017). One-Pot Synthesis of nickel-modified carbon nitride layers toward efficient photoelectrochemical cells. ACS Applied Materials & Interfaces. 9(38):32667-32677. https://doi.org/10.1021/acsami.7b08022S326673267793
Hydrophilic nanoparticles stabilising mesophase curvature at low concentration but disrupting mesophase order at higher concentrations
Silica nanoparticles form aggregates at mesophase domain boundaries, which may suppress or promote curvatures depending on the nanoparticle concentration.</p
hydrogen bonds and nuclear dynamics
Knowledge about the hydrogen bond network of water is essential for
understanding its anomalies as well as its special role for biochemical
systems. Different types of x-ray spectroscopy allow probing of the molecular
orbitals of water, revealing the electronic structure which reflects the
hydrogen bond conformations. In this work a recently developed high-resolution
x-ray emission spectrometer was used in combination with the microjet
technique for recording spectra of liquid H2O and D2O and their mixtures with
acetonitrile. Variation of the nuclear dynamics via isotope substitution and
variation of the hydrogen bond conformation via dissolution in acetonitrile
was investigated. These two effects have two clearly distinguishable spectral
fingerprints
oxygen K-edge X-ray absorption and emission spectroscopy on micro-jets
Oxygen K-edge X-ray absorption, emission, and resonant inelastic X-ray
scattering spectra were measured to site selectively gain insights into the
electronic structure of aqueous zinc acetate solution. The character of the
acetate ion and the influence of zinc and water on its local electronic
structure are discussed
Ion pairing versus water structure modifications
The effect of monovalent cations (Li+, K+, NH4 +, Na +) on the water structure
in aqueous chloride and acetate solutions was characterized by oxygen K-edge
X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy, and resonant
inelastic X-ray scattering (RIXS) of a liquid microjet. We show ion- and
counterion dependent effects on the emission spectra of the oxygen K-edge,
which we attribute to modifications of the hydrogen bond network of water. For
acetates, ion pairing with carboxylates was also probed selectively by XAS and
RIXS. We correlate our experimental results to speciation data and to the
salting-out properties of the cations
Polymersomes at the solid-liquid interface:Dynamic morphological transformation and lubrication
Polymersomes are hollow spheres self-assembled from amphiphilic block copolymers of certain molecular architecture. Whilst they have been widely studied for biomedical applications, relatively few studies have reported their interfacial properties. In particular, lubrication by polymersomes has not been previously reported. Here, interfacial properties of polymersomes self-assembled from poly(butadiene)-poly(ethylene oxide) (PBD-PEO; molecular weight 10,400 g mol−1) have been studied at both hydrophilic and hydrophobic surfaces. Their morphology at silica and mica surfaces was imaged with quantitative nanomechanical property mapping atomic force microscopy (QNM AFM), and friction and surface forces they mediate under confinement between two surfaces were studied using colloidal probe AFM (CP-AFM). We find that the polymersomes remained intact but adopted flattened conformation once adsorbed to mica, with a relatively low coverage. However, on silica these polymersomes were unstable, rupturing to form donut shaped residues or patchy bilayers. On a silica surface hydrophobized with a 19 nm polystyrene (PS) film, the polymer vesicles formed a more stable layer with a higher surface coverage as compared to the hydrophilic surface, and the interfacial structure also evolved over time. Moreover, friction was greatly reduced on hydrophobized silica surfaces in the presence of polymersomes, suggesting their potential as effective aqueous lubricants.</p
On the enzymatic activity of catalase: an iron L-edge X-ray absorption study of the active centre
Catalase and methaemoglobin have very similar haem groups, which are both ferric, yet catalase decomposes hydrogen peroxide to water and oxygen very efficiently, while methaemoglobin does not. Structural studies have attributed this behaviour to their different distal environments. Here we present Fe L-2,L-3-edge X-ray absorption spectra of these proteins in physiological solutions, which reveal clear differences in their electronic structures, in that pi back-donation of the Fe atom occurs in catalase, which confers on it a partial ferryl (Fe4+) character, while this is not the case in methaemoglobin. The origin of the Fe4+ character stems from the proximal tyrosine residue. We also find that both systems are in a high spin state. Temperature effects influence the spectra of catalase only weakly, in agreement with previous studies of its chemical activity. We conclude that the high activity of catalase is not only determined by its distal environment but also by its partial ferryl character
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