Novel application of liquid chromatography/mass spectrometry for the characterization of drying oils in art: Elucidation on the composition of original paint materials used by Edvard Munch (1863–1944)

Modern oil paints, introduced at the beginning of the 20th century, differ from those classically used in antiquity in their chemical and compositional features. The main ingredients were still traditional drying oils, often used in mixtures with less expensive oils and added with several classes of additives. Consequently, detailed lipid profiling, together with the study of lipid degradation processes, is essential for the knowledge and the conservation of paint materials used in modern and contemporary art.     

Reduced molybenum-oxide-based core-shell hybrids: "blue" electrons are delocalized on the shell

The present study refers to a variety of reduced metal-oxide core-shell hybrids, which are unique with regard to their electronic structure, their geometry, and their formation. They contain spherical {Mo72Fe30} Keplerate-type shells encapsulating Keggin-type polyoxomolybdates based on very weak interactions. Studies on the encapsulation of molybdosilicate as well as on the earlier reported molybdophosphate, coupled with the use of several physical methods for the characterization led to unprecedented results (see title). Upon standing in air at room temperature, acidified aqueous solutions obtained by dissolving sodium molybdate, iron(II) chloride, acetic acid, and molybdosilicic acid led to the precipitation of monoclinic greenish crystals (1). A rhombohedral variant (2) has also been observed. Upon drying at room temperature, compound 3 with a layer structure was obtained from 1 in a solid-state reaction based on cross-linking of the shells. The compounds 1, 2, and 3 have been characterized by a combination of methods including single-crystal X-ray crystallography, magnetic studies, as well as IR, M?ssbauer, (resonance) Raman, and electronic absorption spectroscopy. In connection with detailed studies of the guest-free two-electron-reduced {Mo72Fe30}-type Keplerate (4) and of the previously reported molybdophosphate-based hybrids (including 31P NMR spectroscopy results), it is unambiguously proved that 1, 2, and 3 contain non-reduced Keggin ion cores and reduced {Mo72Fe30}-type shells. The results are discussed in terms of redox considerations (the shell as well as the core can be reduced) including those related to the reduction of "molybdates" by FeII being of interdisciplinary including catalytic interest (the MoVI/MoV and FeIII/FeII couples have very close redox potentials!), while also referring to the special formation of the hybrids based on chemical Darwinism.     

Depletion at solid/liquid interfaces: flowing hexadecane on functionalized surfaces

We present a neutron reflectivity study on interfaces in contact with flowing hexadecane, which is known to exhibit surface slip on functionalized solid surfaces. The single crystalline silicon substrates were either chemically cleaned Si(100) or Si(100) coated by octadecyl-trichlorosilane (OTS), which resulted in different interfacial energies. The liquid was sheared in situ and changes in reflectivity profiles were compared to the static case. For the OTS surface, the temperature dependence was also recorded. For both types of interfaces, density depletion of the liquid at the interface was observed. In the case of the bare Si substrate, shear load altered the structure of the depletion layer, whereas for the OTS covered surface no effect of shear was observed. Possible links between the depletion layer and surface slip are discussed. The results show that, in contrast to water, for hexadecane the enhancement of the depletion layer with temperature and interfacial energy reduces the amount of slip. Thus a density depletion cannot be the origin of surface slip in this system.     

Neurotoxin II bound to acetylcholine receptors in native membranes studied by dynamic nuclear polarization NMR

Methods enabling structural studies of membrane-integrated receptor systems without the necessity of purification provide an attractive perspective in membrane protein structural and molecular biology. This has become feasible in principle since the advent of dynamic nuclear polarization (DNP) magic-angle-spinning NMR spectroscopy, which delivers the required sensitivity. In this pilot study, we observed well-resolved solid-state NMR spectra of extensively (13)C-labeled neurotoxin II bound to the nicotinic acetylcholine receptor (nAChR) in native membranes. We show that TOTAPOL, a biradical required for DNP, is localized at membrane and protein surfaces. The concentration of active, membrane-attached biradical decreases with time, probably because of reactive components of the membrane preparation. An optimal distribution of active biradical has strong effects on the NMR data. The presence of inactive TOTAPOL in membrane-proximal situations but active biradical in the surrounding water/glycerol "glass" leads to well-resolved spectra, yet a considerable enhancement (ε = 12) is observed. The resulting spectra of a protein ligand bound to its receptor are paving the way for further DNP investigations of proteins embedded in native membrane patches.     

Inhomogeneous fluids of colloidal hard dumbbells: fundamental measure theory and Monte Carlo simulations

Recently, a density functional theory for hard particles with shape anisotropy was developed, the extended deconvolution fundamental measure theory (edFMT). We apply edFMT to hard dumbbells, arguably the simplest non-convex shape and readily available experimentally in the form of colloids. We obtain good agreement between edFMT and Monte Carlo simulations for fluids of dumbbells in a slit and for the same system under gravity. This indicates that edFMT can be successfully applied to nearly all colloidal shapes, not just for the convex shapes for which edFMT was originally derived. A theory, such as edFMT, that allows a fast and general way of mapping the phase behavior of anisotropic colloids, can act as a useful guide for the design of colloidal shapes for various applications.     

Low-temperature H2 sensing in self-assembled organotin thin films

Self-assembled nanoporous tin-based hybrid thin films prepared by the sol-gel method from organically-bridged ditin hexaalkynides detect hydrogen gas from 50 to 200 °C at the 200-10,000 ppm level. This finding opens a fully new class of gas-sensing materials as well as a new opportunity to integrate organic functionality in gas sensing metal oxides.     

Bioactive isocoumarins from a terrestrial Streptomyces sp. ANK302

Four isocoumarins have been isolated from the terrestrial Streptomyces sp. ANK302, namely 6,8-dimethoxy-3-methylisocoumarin (1), 6,8-dihydroxy-3-methylisocoumarin (2), 6,8-dihydroxy-7-methoxy-3-methylisocoumarin (3), and 6,7,8-trimethoxy-3-methylisocoumarin (4). Compound 1 is a new naturally-occurring isocoumarin, and 2 was isolated as a new bacterial product. The structures 1-4 were deduced from high resolution mass, 1D and 2D NMR spectra and by comparison with related compounds from the literature. Compound 2 showed a strong zoosporicidal activity at a concentration of 5 microg/mL against a phytopathogenic oomycete, Plasmopara viticola, and 1 was active against     

Two-Phase Flow in Heterogeneous Porous Media with Non-Wetting Phase Trapping

This article presents a mathematical model describing flow of two fluid phases in a heterogeneous porous medium. The medium contains disconnected inclusions embedded in the background material. The background material is characterized by higher value of the non-wetting-phase entry pressure than the inclusions, which causes non-standard behavior of the medium at the macroscopic scale. During the displacement of the non-wetting fluid by the wetting one, some portions of the non-wetting fluid become trapped in the inclusions. On the other hand, if the medium is initially saturated with the wetting phase, it starts to drain only after the capillary pressure exceeds the entry pressure of the background material. These effects cannot be represented by standard upscaling approaches based on the assumption of local equilibrium of the capillary pressure. We propose a relevant modification of the upscaled model obtained by asymptotic homogenization. The modification concerns the form of flow equations and the calculation of the effective hydraulic functions. This approach is illustrated with two numerical examples concerning oil–water and CO₂–brine flow, respectively.     

Correlations of two-dimensional super-paramagnetic colloids in tilted external magnetic fields

We outline the formalism of liquid integral equation theory for anisotropic interactions in two dimensions and subsequently apply this theory to one-component super-paramagnetic particles exposed to a tilted magnetic field. Inhomogeneous local ordering of the particles is observed for different in-plane directions. The anisotropy of the interaction as well as of the liquid structure is increased by increasing the tilt angle. Furthermore, the particles favour an alignment in the direction of the in-plane component of the magnetic field. For increasing tilt angle, the anisotropy of the structural correlations is qualitatively similar to that of the corresponding solid lattice which is stable at lower temperatures. However, the mean-square displacements behave qualitatively different in the solid and fluid phases as a function of the tilt angle.