Local Distortions in a Prototypical Zeolite Framework Containing Double Four-Ring Cages: The Role of Framework Composition and Organic Guests**

Cube-like double four-ring (d4r) cages are among the most frequent building units of zeolites and zeotypes. In materials synthesised in fluoride-containing media, the fluoride anions are preferentially incorporated in these cages. In order to study the impact of framework composition and organic structure-directing agents (OSDAs) on the possible occurrence of local distortions of fluoride-containing d4r cages, density functional theory (DFT) calculations and DFT-based molecular dynamics simulations were performed for AST-type zeotypes, considering four different compositions (SiO₂, GeO₂, AlPO₄, GaPO₄) and two different OSDA cations (tetramethylammonium [TMA] and quinuclidinium [QNU]). All systems except SiO₂-AST show significant deformations, with a pyritohedron-like distortion of the d4r cages occurring in GeO₂- and GaPO₄-AST, and a displacement of the fluoride anions towards one of the corners of the cage in AlPO₄- and GaPO₄-AST. While the distortions occur at random in TMA-containing zeotypes, they exhibit a preferential orientation in systems that incorporate QNU cations. In addition to providing detailed understanding of the local structure of a complex host-guest system on the picosecond timescale, this work indicates the possibility to stabilise ordered distortions through a judicious choice of the OSDA, which might enable a tuning of the material's properties.     

Loop Groups and Twin Buildings

In these notes we describe some buildings related to complex Kac–Moody groups. First we describe the spherical building of SL_n() (i.e. the projective geometry PG(ⁿ)) and its Veronese representation. Next we recall the construction of the affine building associated to a discrete valuation on the rational function field (z). Then we describe the same building in terms of complex Laurent polynomials, and introduce the Veronese representation, which is an equivariant embedding of the building into an affine Kac–Moody algebra. Next, we introduce topological twin buildings. These buildings can be used for a proof which is a variant of the proof by Quillen and Mitchell, of Bott periodicity which uses only topological geometry. At the end we indicate very briefly that the whole process works also for affine real almost split Kac–Moody groups.Supported by a Heisenberg fellowship by the Deutsche Forschungsgemeinschaft.     

PAH metabolism in the earthworm Eisenia fetida – identification of phase II metabolites of phenanthrene and pyrene

Polycyclic aromatic hydrocarbons (PAHs) are soil contaminants. Because of their high lipophilicity, PAHs are associated with the organic matter in the soil. Transformation of PAHs generates polar metabolites and the interaction with organic matter in the soil changes. The polar PAH metabolites are persistent, highly water-soluble and potentially leachable from the soil; the understanding of transformation of PAHs to polar metabolites in the responsible organisms is of great importance. Here, we present a study of transformation of the PAHs pyrene and phenanthrene, by the common earthworm Eisenia fetida. The study showed that E. fetida in hydroponic culture was able to transform PAHs to conjugated phase II metabolites. We detected phenanthrene and pyrene metabolites with single- and multiple-phase II-conjugated groups. Sulphate conjugates were excreted to experiment water, and glucuronide and glucoside conjugates and metabolites with several hydroxylations and multiple conjugations were detected in worm tissue. The results demonstrate that earthworms are able to transform PAHs to water-soluble phase II metabolites, which can be excreted to the surrounding environment.     

An elastic network model to identify characteristic stress response genes

Exposing eukaryotic cells to a toxic compound and subsequent gene expression profiling may allow the prediction of selected toxic effects based on changes in gene expression. This objective is complicated by the observation that compounds with different modes of toxicity cause similar changes in gene expression and that a global stress response affects many genes. We developed an elastic network model of global stress response with nodes representing genes which are connected by edges of graded coexpression. The expression of only few genes have to be known to model the global stress response of all but a few atypical responder genes. Those required genes and the atypical response genes are shown to be good biomarker for tox predictions. In total, 138 experiments and 13 different compounds were used to train models for different toxicity classes. The deduced biomarkers were shown to be biologically plausible. A neural network was trained to predict the toxic effects of compounds from profiling experiments. On a validation data set of 189 experiments with 16 different compounds the accuracy of the predictions was assessed: 14 out of 16 compounds have been classified correctly. Derivation of model based biomarkers through the elastic network approach can naturally be extended to other areas beyond toxicology since subtle signals against a broad response background are common in biological studies.     

Luminescence Enhancement from Silica-Coated Gold Nanoparticle Agglomerates Following Multi-photon Excitation

Multi-photon absorption induced luminescence (MAIL) from bare gold nanoparticles, silica-coated particles, as well as silica-coated agglomerated gold nanoparticles suspended in aqueous solution was studied by using time-resolved and steady-state luminescence spectroscopy. The nanoparticles were excited by femtosecond pulses of wavelengths ranging from 630 nm to 900 nm. The luminescence from the particles exhibits a broad spectrum in the UV and VIS region. The time-resolved measurements indicate a luminescence lifetime of a few ps, limited by the response of the experimental system. The studied dependence of the MAIL efficiency on the excitation wavelength showed that the luminescence from silica-coated agglomerates was enhanced over the whole range of excitation wavelengths, when compared to the luminescence from individual gold nanoparticles. The agglomerates show an almost excitation wavelength independent efficiency of the MAIL, while for individual nanoparticles a rapid decrease of the MAIL efficiency was observed with increasing excitation wavelength. The observed enhancement of the MAIL from the agglomerated nanostructures can be attributed to the presence of localized surface plasmon resonances in the spectral region corresponding to the excitation wavelengths. The high MAIL efficiency from the agglomerated nanoparticle structures in the near-infrared could be an advantage in the expanding field of luminescence-based-imaging, as well as in biosensor technology.     

Coarse equivalences of Euclidean buildings

We prove the following rigidity results. Coarse equivalences between metrically complete Euclidean buildings preserve spherical buildings at infinity. If all irreducible factors have dimension at least two, then coarsely equivalent Euclidean buildings are isometric (up to scaling factors); if in addition none of the irreducible factors is a Euclidean cone, then the isometry is unique and has finite distance from the coarse equivalence.     

A spectroscopic method to estimate the binding potency of amphiphile assemblies

A fast and convenient spectroscopic methodology to determine the water uptake capacity of amphiphile assemblies studied in multilayer films is presented. This method was developed to provide a reliable but relatively simple tool for estimating the binding potency of such complex systems. The water-binding potency represents a general propensity of higher-order systems to bind or embed relevant ligands, such as various non-lipid effectors in the case of artificial lipid membranes. In this sense, the binding potency might contribute to a specific functional role of certain lipids. The essence of the new method is that the calibration of data measured by infrared (IR) spectroscopy against those directly obtained by Karl–Fischer titration (KFT) enables one to replace the expensive chemical–analytical technique by a more comfortable and efficient IR-spectroscopic protocol. This approach combines the easy handling, versatility, and availability of IR spectroscopy with the high accuracy of KFT. The usefulness of the procedure is demonstrated on an example set of six amphiphiles with a common chain length of 18 carbon atoms. Despite this similarity, the binding potency data differ tremendously in a way which can be correlated with the systematic variations introduced into the amphiphile structure. Going further beyond the methodical aspect, the scientific relevance of the data is comprehensively discussed especially in terms of the structural factors that govern the binding potency of amphiphiles. That is favored mainly by fluidity and disfavored mainly by inter-amphiphile binding networks. For phosphatidylcholine, our data are strongly in favor of a particular hydration model that involves primary water binding to phosphate as well as the formation of water semi-clathrates hosting the trimethylammonium moiety. Interestingly, stearylamine and diolein assemblies did not take up any water at all. This unexpected hydrophobicity is due to the unusual structures formed in these latter cases: rigid ammonium amide with a strong hydrogen-bonding/salt bridge network in stearylamine, and patches of inverted micelles in diolein, as revealed by molecular dynamics simulations.