Empirical force fields for complex hydrated calcio-silicate layered materials

The use of empirical force fields is now a standard approach in predicting the properties of hydrated oxides which are omnipresent in both natural and engineering applications. Transferability of force fields to analogous hydrated oxides without rigorous investigations may result in misleading property predictions. Herein, we focus on two common empirical force fields, the simple point charge ClayFF potential and the core-shell potential to study tobermorite minerals, the most prominent family of Calcium-Silicate-Hydrates that are complex hydrated oxides. We benchmark the predictive capabilities of these force fields against first principles results. While the structural information seem to be in close agreement with DFT results, we find that for higher order properties such as elastic constants, the core-shell potential quantitatively improves upon the simple point charge model, and shows a larger degree of transferability to complex materials. In return, to remedy the deficiencies of the simple point charge potential for hydrated calcio-silicates, we suggest using both structural data and elasticity data for potential calibration, a new force field potential, CSH-FF. This re-parameterized version of ClayFF is then applied to simulating an atomistic model of cement (Pellenq et al., PNAS, 2009). We demonstrate that this force field improves the predictive capabilities of ClayFF, being considerably less computational intensive than the core-shell model.     

Structure Determination of New Iridals from Iris pallida and Iris foetidissima

The four novel iridals 8 – 10 and 18 were isolated from rhizome extracts of Iris pallida and Iris foetidissima, and their structures were established by spectroscopic methods and oxidative degradation. The compounds 8 – 10 bearing a conjugated triene moiety are extremely labile and decompose rapidly. Thus, the monocyclic triene 8 was only isolated after its conversion to a Diels-Alder adduct with 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione ( 14 ), The tricyclic iridal 18 is a hitherto unknown precursor of α-irone. The possible biogenesis of these unusual triterpenoids is discussed.     

Damage and Failure of Metal/Fibre-Reinforced Polymer Tensile Specimens with Inelastic Interface

Hybrid specimens of metal and fibre-reinforced polymer are applied in automotive and aerospace industry. The simulation and analysis of damage of such engineering structures is the focus of this research. The investigation includes a computation of the extension of single lap tensile specimen, produced by ultrasonic metal welding. The specimen is manufactured from CF-PA66 - fibre-reinforced polymer and AlMg3 (AA5754), which is used as a metallic joining partner. The aluminium substrate is treated as an elastoplastic material. The polymer composite generally shows an orthotropic elastic behaviour. The interface material has been numerically modeled as an elastoplastic material with linear hardening, coupled with Lemaitre-type damage. The finite element method is used for the investigation of so-called interface elements. The geometry of the interface is a consequence of the welding sonotrode geometry. The behaviour of specimens with square and ring interface geometry are analysed. The influence of the interface geometry on the mechanical properties of the joint is shown. The increase of the damage parameter and the development of failure are described for both cases. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modelling of θ-conditions for bisphenol—A polycarbonate single chains

Assessing conformational dimensions of macromolecules is a topic of long-standing interest. Because of its simplicity, it is attractive to investigate the chain properties in θ-conditions. Under these special conditions, the effects of excluded volume of the segments of the polymer chain vanish. The molecular chain is only subject to local constraints resulting from the bond structure and the hindrance to rotations about bonds. To model θ-conditions a contour length dependent cutoff is introduced ensuring that only nonbonded interactions of atoms of neighbouring monomeric units are taken into account for energy calculations. Using this energy model we will show that it is possible to model θ-conditions of a single bisphenol-A polycarbonate (BPA-PC) chain in vacuum by two different methods: (i) (Pseudo-) Langevin dynamics simulations and (ii) regular reassignment of randomly generated atom velocities during a molecular dynamics simulation. Both methods can be used to avoid oscillative dynamic behaviour of the chain. Calculations of the end-to-end vector and the radius of gyration of the equilibrium ensembles derived from simulations at different temperatures show good agreement with experimental data. Thus our model techniques are well suited to simulate θ-conditions with small computational expense.     

Light scattering and dielectric relaxation studies of glass forming liquids

Extended Abstract: Glass forming organic liquids and polymers exhibit long range density fluctuations with correlation length ξ in the range of 10–300 nm at temperatures above T_g (1 - 6). This follows from dynamic and static light scattering experiments revealing some unexpected features, which cannot be explained on the basis of conventional liquid state theories: (i) In static light scattering the intensity I(q → 0) is no longer proportional to the isothermal compressibility, (ii) This excess scattering I_exc shows a strong q-dependence (q = (4π/Λ.)sin(θ/2)) corresponding to a correlation length ξ in the above mentioned range, (iii) The Landau-Placzek ratio I_Rayleigh/2I_Brillouin is much too high compared with the results of light scattering theories, (iv) In photon correlation spectroscopy a new ultraslow hydrodynamic mode (Γ ˜ q²) is detected with relaxation rates Γ about 10⁻⁶ to 10⁻⁹ lower than those of the α-process at a given temperature. In order to explain these observations, a two-state fluid model is proposed, which starts from the coexistence of “liquid-like” and “aperiodic solid-like” regions within the liquids. Such ideas have been discussed many times before, so for example A.R. Ubbelohde (7) speculates about “anticrystalline” clusters in liquids. Molecular dynamics simulations of atomic liquids showed that long range orientational fluctuations appear upon supercooling (8). A preferred icosahedral ordering is observed (9) and the number of icosahedral clusters increases with decreasing temperature (10). In connection with the interpretation of the dynamics of supercooled liquids different “two-state” models have been proposed (11 - 15). For the explanation of the light scattering results we propose that the molecules in the different dynamic states (“liquid” or “solid”) aggregate during annealing of the liquid at temperatures above T_g. Experiments showed that the equilibration times can be rather long (3 - 5), but nevertheless the liquids exhibiting long range density fluctuations are in the state of lowest free energy. We claim that our observations are the first experimental proof of the existence of such different dynamic states, which have been discussed many times before. The extended secondary clusters can also be detected by ultra small angle X-ray scattering.     

Application of a Viscoelastic Model to simulate the Interface of a Metal/Fibre-Reinforced Polymer Joint

A viscoelastic model with the Lemaitre-type damage is applied to simulate an interfacial adhesive zone in light weight engineering structures, like aluminum/fiber-reinforced polymer specimens. The evolution of irreversible deformation and damage progression are investigated. The joint of aluminium alloy 5754 (AA5754) and carbon fibre reinforced thermoplastic composite CF-PA66 is manufactured by means of an epoxy (1K) adhesive. The adhesive zone is considered as an interface material. The aim of the research is to study the influence of the interface geometry on the mechanical characteristics of the structure. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Non-Hydroxamate Zinc-Binding Groups as Warheads for Histone Deacetylases

Histone deacetylases (HDACs) remove acetyl groups from acetylated lysine residues and have a large variety of substrates and interaction partners. Therefore, it is not surprising that HDACs are involved in many diseases. Most inhibitors of zinc-dependent HDACs (HDACis) including approved drugs contain a hydroxamate as a zinc-binding group (ZBG), which is by far the biggest contributor to affinity, while chemical variation of the residual molecule is exploited to create more or less selectivity against HDAC isozymes or other metalloproteins. Hydroxamates have a propensity for nonspecificity and have recently come under considerable suspicion because of potential mutagenicity. Therefore, there are significant concerns when applying hydroxamate-containing compounds as therapeutics in chronic diseases beyond oncology due to unwanted toxic side effects. In the last years, several alternative ZBGs have been developed, which can replace the critical hydroxamate group in HDACis, while preserving high potency. Moreover, these compounds can be developed into highly selective inhibitors. This review aims at providing an overview of the progress in the field of non-hydroxamic HDACis in the time period from 2015 to present. Formally, ZBGs are clustered according to their binding mode and structural similarity to provide qualitative assessments and predictions based on available structural information.     

Dry friction in the Frenkel-Kontorova-Tomlinson model: dynamical properties

Wearless friction is investigated in a simple mechanical model called Frenkel-Kontorova-Tomlinson model. We have introduced this model in [Phys. Rev. B, 53, 7539 (1996)] where the static friction has already been considered. Here the model is treated for constant sliding speed. The motion of the internal degrees of freedom is regular for small sliding velocities or weak interaction between the sliding surfaces. The regular motion for large velocities is strongly determined by normal and superharmonic resonance of phonons excited by the so-called “washboard wave”. The kinetic friction has maxima near these resonances. For increasing interaction strength the regular motion becomes unstable due to parametric resonance leading to quasistatic and chaotic motion. For sliding velocities beyond first-order parametric resonance bistability occurs between the strongly chaotic motion (fluid sliding state), where friction is large and a regular motion (solid sliding state), where friction is weak. The fluid sliding state is mainly determined by the density of decay channels of m washboard waves into n phonons. This density describes qualitatively the effectiveness of the energy transfer from the uniform sliding motion into the microscopic, irregular motion of the degrees of freedom at the sliding interface. For a narrow interval of the sliding velocities we also found enhanced friction due to coherent motion. In the regime of coherent motion nondestructive interactions of dark envelope solitons occur.     

Über die Reaktion von Trimethylamin mit Antimon(V)-chlorid

Inhaltsübersicht. Trimethylamin und Antimon(V)-chlorid bilden keinen Dornor-Acceptor Komplex. In Abhängigkeit vom Molverhältnis reagieren die Komponenten zu (CH₃)₃NCl⁺SbCl₆^– (I) bzw. zu (CH₃)₃NH+X^– und (CH₃)₂N=CH₃⁺X^– (X^– = SbCl₆^–, SbCI₄^–, Sb₃CI₁₄^3– und CI^–). I kann in (CH₃)₃NH⁺SbCl₆^– und (CH₃)₂N=CH₂+SbCl₆^– zerfallen. The Reaction of Trimethylamine with Antimony (V) Chloride Abstract. Trimethylamine and antimony(V) chloride forms no donor-acceptor-complex. In dependence of the molar ratio the compounds reacts to (CH₃)₃NCl⁺SbCl₆^– (I) resp. to (CH₃)₃NH+X^– and (CH₃)₂N=CH₃⁺X^– (X^– = SbCl₆^–, SbCI₄^–, Sb₃CI₁₄^3– and CI^–). I can decompose into (CH₃)₃NH⁺SbCl₆^– and (CH₃)₂N=CH₂+SbCl₆^–.