Theoretical analysis of the three-dimensional structure of tetrathiolato iron complexes

The three-dimensional structures of a number of [M(SR)(4)](n-) complexes, where M is a 3d transition metal and R is an alkyl or aryl group, have been analyzed using density functional theory (DFT). Special attention is paid to the Fe(II)/Fe(III) mimics of rubredoxin. The Fe(II) model complex [Fe(SCH(3))(4)](2-) has an equilibrium conformation with D2d symmetry. The DFT energy has been decomposed into contributions for ligand-ligand and metal-ligand interactions. The latter contribution is analyzed with the angular overlap model (AOM) and constitutes the dominant stereospecific interaction in the Fe(II) complex. The sulfur lone-pair electrons exert anisotropic pi interactions on the 3d(6) shell of Fe(II), which are controlled by the torsion angles, omega(i), for the rotations of the S(i)-C(beta) bonds around the Fe-S(i) axes. In contrast, the pi interactions acting on the high-spin 3d(5) shell of Fe(III) are isotropic. As a consequence, the stereochemistry of the Fe(III) complexes is determined by the Coulomb repulsions between the ligands and has S(4) symmetry. The electrostatic repulsions between the lone pairs of the sulfurs are an essential component of the ligand-ligand interaction. The lone-pair repulsions distort the 90 degree angle SFeS' angles (delta + delta(t)) and give rise to a correlation between delta and omega, which is confirmed by crystallographic data. Both the Fe(II) and Fe(III) complexes exhibit structural bistability due to the presence of low-lying equilibrium conformations with S(4) symmetry in which the complex can be trapped by the crystalline host.     

Assemblies from metallic and semiconducting nanocrystals

Optical properties of nanomaterials such as semiconductor and metal quantum dots are important for sensors and photovoltaic applications. We report on optical, microscopic, and AFM investigations on bulk and single nanoobjects such as metal and semiconducting nanoparticles. Firstly, of special interest is the investigation of Ag metal nanoaggregates formed in zeolites. Here, the defined structure of the zeolite serves both as size directing and a stabilizing agent. The size selected Ag aggregates fluoresce in the zeolite cages even after storage under ambient conditions for almost one year. In addition, single Ag particles escape the cages and can be investigated by fluorescence microscopy also with respect to sensor applications. Secondly, with respect to photovoltaic applications, energy transfer among organic dye molecules and semiconductor quantum dots is of great importance. We report on the extension of the optical absorption of ZnSe quantum dots into the UV regime and investigate excitation energy transfer within self-assembled nanoaggregates of surface functionalized QDs and fluorescent styrylpyridine dyes.     

Syntheses of chiral fused 4,5-diazafluorene–bis(nopinane) derivatives

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The impact of blood on liver metabolite profiling – a combined metabolomic and proteomic approach

Metabolomics has entered the well‐established omic sciences as it is an indispensable information resource to achieve a global picture of biological systems. The aim of the present study was to estimate the influence of blood removal from mice liver as part of sample preparation for metabolomic and proteomic studies. For this purpose, perfused mice liver tissue (i.e. with blood removed) and unperfused mice liver tissue (i.e. containing blood) were compared by two‐dimensional gas chromatography time of flight mass spectrometry (GC × GC‐TOFMS) for the metabolomic part, and by liquid chromatography tandem mass spectrometry (LC‐MS/MS) for the proteomic part. Our data showed significant differences between the unperfused and perfused liver tissue samples. Furthermore, we also observed an overlap of blood and tissue metabolite profiles in our data, suggesting that the perfusion of liver tissue prior to analysis is beneficial for an accurate metabolic profile of this organ. Copyright © 2013 John Wiley & Sons, Ltd.     

Efficient entry into hydrazinopeptide-like structures via sequential Ugi reactions

Novel types of hydrazinopeptide-like units containing five elements of diversity have been prepared in two steps using sequential Ugi reactions.     

Simulation of a mixed-conducting membrane-based gas turbine power plant for CO<Subscript>2</Subscript> capture: system level analysis of operation stability and individual process unit degradation

A gas turbine power plant for CO₂ capture, based on oxygen-permeable membranes with mixed ionic-electronic conductivity, was analysed with respect to long-term stability by means of numerical simulation. Due to the attractive transport and physicochemical properties of mixed-conducting La₂NiO_4+δ, this nickelate was selected as a prototype membrane material for this application. Experiments showed very slow degradation of La₂NiO_4+δ membranes at oxygen chemical potentials close to atmospheric conditions, which are associated with kinetic demixing and other microstructure-related factors. Interaction with CO₂ in the intermediate temperature range also leads to lower oxygen permeation, whilst increasing oxygen pressure may cause partial phase decomposition and microstructural changes, thus again limiting the range of possible operation conditions. The relevant operational constraints were included in a detailed membrane-based gas turbine power plant model. The membrane performance degradation with time was approximated by a linear function with average rate of 3.3% per 1,000 operation hours. Furthermore, performance deterioration of the gas turbine compressor and turbine were also considered. Simulations revealed that the power plant is substantially affected by degradation of the ceramic membranes and turbomachinery components. The already rather small operating window was further narrowed when compared with a conventional gas turbine power plant. Two different designs of the membrane-based power plant were analysed: (1) with and (2) without additional combustors (afterburners) between the membrane reactor and the gas turbine. Afterburners increase thermal efficiency as well as power output, but also lead to non-negligible CO₂ emissions. In order to have a frame of comparison, results for a conventional gas turbine power plant with degradation of turbomachinery components are also presented. Simulations representing changes in ambient temperature and fuel composition as well as failure incidents were executed to analyse the susceptibility of the gas turbine power plant to external and internal changes.     

Synthesis of polyampholyte microgels from colloidal salts of pectinic acid and their application as pH-responsive emulsifiers

A novel method for obtaining cross-linked microgels of apple pectin has been introduced. This method is based on the Ugi four-component condensation in colloidal suspensions of pectinic acid and amines. Using various processing parameters (the polysaccharide concentration, the type and density of crosslink, and the optimal pH range), particles with controlled colloidal properties have been obtained. Lightly cross-linked polysaccharide chains acquire anionic character due to deprotonation of the carboxyl groups at pH?9–10. Increasing the degree of cross-linking leads to a polyampholyte microgel, which can be protonated in acidic medium or deprotonated in basic medium. Polyampholyte microgels derived from apple pectin have proved to be an effective Pickering emulsifier at low concentrations and pH?2–3, forming stable oil-in-water emulsions. These Pickering emulsions exhibited pH-responsive behavior: raising the solution pH to 10 resulted in immediate demulsification due to the destabilization of microgel network at the oil–water interface.     

A new approach to constant term identities and Selberg-type integrals

Selberg-type integrals that can be turned into constant term identities for Laurent polynomials arise naturally in conjunction with random matrix models in statistical mechanics. Built on a recent idea of Karasev and Petrov we develop a general interpolation based method that is powerful enough to establish many such identities in a simple manner. The main consequence is the proof of a conjecture of Forrester related to the Calogero–Sutherland model. In fact we prove a more general theorem, which includes Aomoto's constant term identity at the same time. We also demonstrate the relevance of the method in additive combinatorics.     

Combined Crossed Molecular Beams and Ab Initio Study of the Bimolecular Reaction of Ground State Atomic Silicon (Si; 3P) with Germane (GeH4; X1A1)

The chemical dynamics of the elementary reaction of ground state atomic silicon (Si; ³P) with germane (GeH₄; X¹A₁) were unraveled in the gas phase under single collision condition at a collision energy of 11.8±0.3 kJ mol⁻¹ exploiting the crossed molecular beams technique contemplated with electronic structure calculations. The reaction follows indirect scattering dynamics and is initiated through an initial barrierless insertion of the silicon atom into one of the four chemically equivalent germanium-hydrogen bonds forming a triplet collision complex (HSiGeH₃; ³ i1 ). This intermediate underwent facile intersystem crossing (ISC) to the singlet surface (HSiGeH₃; ¹ i1 ). The latter isomerized via at least three hydrogen atom migrations involving exotic, hydrogen bridged reaction intermediates eventually leading to the H₃SiGeH isomer i5 . This intermediate could undergo unimolecular decomposition yielding the dibridged butterfly-structured isomer ¹ p1 (Si(μ-H₂)Ge) plus molecular hydrogen through a tight exit transition state. Alternatively, up to two subsequent hydrogen shifts to i6 and i7 , followed by fragmentation of each of these intermediates, could also form ¹ p1 (Si(μ-H₂)Ge) along with molecular hydrogen. The overall non-adiabatic reaction dynamics provide evidence on the existence of exotic dinuclear hydrides of main group XIV elements, whose carbon analog structures do not exist.