Diffusion of Gold Nanoparticles in Inverse Opals Probed by Heterodyne Dynamic Light Scattering

The diffusive behavior of nanoparticles inside porous materials is attracting a lot of interest in the context of understanding, modeling, and optimization of many technical processes. A very powerful technique for characterizing the diffusive behavior of particles in free media is dynamic light scattering (DLS). The applicability of the method in porous media is considered, however, to be rather difficult due to the presence of multiple sources of scattering. In contrast to most of the previous approaches, the DLS method was applied without ensuring matching refractive indices of solvent and porous matrix in the present study. To test the capabilities of the method, the diffusion of spherical gold nanoparticles within the interconnected, periodic nanopores of inverse opals was analyzed. Despite the complexity of this system, which involves many interfaces and different refractive indices, a clear signal related to the motion of particles inside the porous media was obtained. As expected, the diffusive process inside the porous sample slowed down compared to the particle diffusion in free media. The obtained effective diffusion coefficients were found to be wave vector-dependent. They increased linearly with increasing spatial extension of the probed particle concentration fluctuations. On average, the slowing-down factor measured in this work agrees within combined uncertainties with literature data.

     

Pathways to Triplet or Singlet Oxygen during the Dissociation of Alkali Metal Superoxides: Insights by Multireference Calculations of Molecular Model Systems

Recent experimental investigations demonstrated the generation of singlet oxygen during charging at high potentials in lithium/oxygen batteries. To contribute to the understanding of the underlying chemical reactions a key step in the mechanism of the charging process, namely, the dissociation of the intermediate lithium superoxide to oxygen and lithium, was investigated. Therefore, the corresponding dissociation paths of the molecular model system lithium superoxide (LiO₂) were studied by CASSCF/CASPT2 calculations. The obtained results indicate the presence of different dissociation paths over crossing points of different electronic states, which lead either to the energetically preferred generation of triplet oxygen or the energetically higher lying formation of singlet oxygen. The dissociation to the corresponding superoxide anion is energetically less preferred. The understanding of the detailed reaction mechanism allows the design of strategies to avoid the formation of singlet oxygen and thus to potentially minimize the degradation of materials in alkali metal/oxygen batteries. The calculations demonstrate a qualitatively similar but energetically shifted behavior for the homologous alkali metals sodium and potassium and their superoxide species. Fundamental differences were found for the covalently bound hydroperoxyl radical.     

A Metallic Room‐Temperature Oxide Ion Conductor

Nanoparticles of Bi₃Ir, obtained from a microwave‐assisted polyol process, activate molecular oxygen from air at room temperature and reversibly intercalate it as oxide ions. The closely related structures of Bi₃Ir and Bi₃IrO_x (x≤2) were investigated by X‐ray diffraction, electron microscopy, and quantum‐chemical modeling. In the topochemically formed metallic suboxide, the intermetallic building units are fully preserved. Time‐ and temperature‐dependent monitoring of the oxygen uptake in an oxygen‐filled chamber shows that the activation energy for oxide diffusion (84 meV) is one order of magnitude smaller than that in any known material. Bi₃IrO_x is the first metallic oxide ion conductor and also the first that operates at room temperature.     

Detection equipment for investigating dp elastic scattering at internal target of nuclotron in the framework of DSS project

A complex of detection equipment based on scintillation detectors for investigating dp elastic scattering at the internal target of the Nuclotron developed in the framework of the Deuteron Spin Structure (DSS) project is presented. The results of optimizing scintillation detectors and the results of test measurements of a deuteron beam of the Nuclotron are given.     

Die Kerze

In this paper we discuss the physical chemistry of the candle light, which has shown to encompass thermodynamics, chemical kinetics, transport processes and quantum chemistry and physics. In a candle light all states of matter (solid, liquid, gas and plasma) are present. Solid wax is molten by the heat radiation of the flame and subsequently pumped through the wick by capillary forces to the interior of the flame, where the liquid wax is evaporated and ignited. Oxygen cannot penetrate deeply into the flame so that inside the flame reducing reaction conditions prevail. In the flame the wax molecules are pyrolized to small molecule fragments (including ions: plasma), which are the starting point for building up poly‐aromatic rings and finally soot particles. The almond‐shape of the candle light is the result of convection of the hot air around the flame. The candle light serves as a flow reactor with luminous effect where molecular oxygen from the atmosphere oxidized ultimately the wax molecules to CO₂ and water. Only a very small percentage (0.5 %) of the released heat in the combustion reaction is transformed into visible light, rendering the candle light an incredibly inefficient albeit romantic light source.     

Thermodynamics,structure and kinetics in the system Ga–O–N

Within the ternary system Ga–O–N we performed experimental and theoretical investigations on the thermodynamics, structure and kinetics of new stable and metastable compounds.We studied the ammonolysis of β-Ga₂O₃ at elevated temperatures by means of ex situ X-ray diffraction, ex situ neutron diffraction, and in situ X-ray absorption spectroscopy (XAS). From total diffraction pattern refinement with the Rietveld method we analyzed the anionic occupancy factors and the lattice parameters of β-Ga₂O₃ during the reaction. Within the detection limits of these methods, we can rule out the existence of a crystalline oxynitride phase that is not derived from wurtzite-type GaN. The nitrogen solubility in β-Ga₂O₃ was found to be below the detection limit of about 2–3 at.% in the anionic sublattice. The kinetics of the ammonolysis of β-Ga₂O₃ to α-GaN and of the oxidation of α-GaN to β-Ga₂O₃ was studied by means of in situ X-ray absorption spectroscopy. In both cases the reaction kinetics could be described well by fitting linear combinations of β-Ga₂O₃ and α-GaN spectra only, excluding that other crystalline or amorphous phases appear during these reactions. The kinetics of the ammonolysis can be described well by an extended Johnson–Mehl–Avrami–Kolmogorow model with nucleation and growth of GaN nuclei, while the oxidation kinetics can be modeled by a shrinking core model where Ga₂O₃ grows as a layer. Investigations by means of TEM and SEM support the assumptions in both models.To investigate the structure and energetics of spinel-type gallium oxynitrides (γ-galons) we performed first-principles calculations using density-functional theory. In addition to the ideal cubic γ-Ga₃O₃N we studied gallium deficient γ-galons within the Constant-Anion-Model.In highly non-stoichiometric, amorphous gallium oxide of approximate composition GaO_1.2 we found at a temperature around 670 K an insulator–metal transition, with a conductivity jump of seven orders of magnitude. We demonstrate through experimental studies and density-functional theory calculations that the conductivity jump takes place at a critical gallium concentration and is induced by crystallization of stoichiometric β-Ga₂O₃ within the metastable oxide matrix. By doping with nitrogen the critical temperature and the conductivity in the highly conducting state can be tuned.     

Phosphopeptide analysis by positive and negative ion matrix-assisted laser desorption/ionization mass spectrometry.

This article describes a simple procedure for the detection of phosphorylated peptides by comparable positive and negative ion mode matrix-assisted laser desorption/ionization mass spectrometry measurements. Based on studies with phosphorylated peptides (EAIXAAPFAK, X = pS, pT, pY) and their corresponding non-phosphorylated analogs, it was found that phosphopeptides, which are characterized by a low ionization efficiency in the positive ion mode, exhibit drastically increased signal intensities in the negative ion mode compared to their non-phosphorylated analogs. The effect was successfully used to identify phosphorylated sequences of the commonly used phosphoprotein standards, protein kinase A and beta-casein, by peptide mass fingerprint analyses of the corresponding Lys C and trypsin digests using both (positive and negative) ion modes. The comparison of positive and negative ion spectra of a given protein digest (relative intensity([M - H]-)/relative intensity([M + H]+)) can be used to identify any phosphopeptides present which may then be separated and analyzed further.