The magnetic structure of clinopyroxene-type LiFeGe2O6 and revised data on multiferroic LiFeSi2O6

The clinopyroxene compounds LiFeSi₂O₆ and LiFeGe₂O₆ have been investigated by constant wavelength neutron diffraction at low temperatures and by bulk magnetic measurements. Both compounds are monoclinic, space group P2₁/c and do not exhibit a change in nuclear symmetry down to 1.4 and 5 K respective. However, they transform to a magnetically ordered state below 20 K. LiFeSi₂O₆ shows a simple magnetic structure with no indication of an incommensurate modulation. The magnetic space group is P2₁/c′ and the structure is described by a ferromagnetic coupling of spins within the infinite M1 chains of edge-sharing octahedra, while the coupling between these M1 chains is antiferromagnetic. The magnetic phase transition is accompanied by magnetostriction of the lattice when passing through the magnetic phase transition. The magnetic structure of LiFeGe₂O₆ is different to the silicate: the space group is and the magnetic unit cell doubled along the a-direction. Within the M1 chains spins are coupled antiferromagnetically, while the chain to chain coupling is antiferromagnetic when coupling goes via the GeB tetrahedron and ferromagnetic when it goes via the GeA tetrahedron.     

Capillary electrophoresis of ANTS labelled oligosaccharide ladders and complex carbohydrates

The detection limits of the ANTS (8-aminonaphthalene-1,3,6-trisulfonic acid) label and ANTS maltose as a model carbohydrate conjugate were investigated with on-column UV and laser induced fluorescence detection. Under capillary electrophoresis conditions, the concentration and mass detection limits were found to be 5×10^–7 mol/l or 8 femtomole with UV and 5×10^–8 mol/l or 400 attomole with laser induced fluorescence detection, respectively. Including the derivatization reaction, the best concentration detection limit increases to 1×10^–6 mol/l carbohydrate. A model calculation shows that these detection levels are still insufficient to match those of current protein sequencing protocols.Derivatization conditions for dextran and polygalacturonic acid ladders are described with subsequent fast separation in a capillary electrophoresis system under acidic pH buffer conditions. Up to 30 oligomers could be separated in less than 10 min. The application of ANTS labelled carbohydrate analysis in the food industry is demonstrated with the carbohydrate fraction of sweets and the kinetic monitoring of the hydrolysis of polygalacturonic acid.The described ANTS derivitization protocol works with as little as 5 g carbohydrate as demonstrated with a complex oligosaccharide labelled in a reaction volume as little as 2 l. To demonstrate the applicability of this approach to complex carbohydrate analysis, an oligosaccharide mixture derived from human Immunoglobuline G was labelled and separated within 5 min. Separation efficiency and speed are superior to state-of-the-art chromatographic methods. Both electrophoretic and chromatographic methods are complementary because of their different separation mechanism. The implications of using capillary electrophoresis with laser induced fluorescence and appropriate labelling strategies for structural and compositional analysis of complex carbohydrates are discussed.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Self‐assembled silane monolayers: an efficient step‐by‐step recipe for high‐quality,low energy surfaces

Organosilane self‐assembled monolayers (SAMs) are commonly used for modifying a wide range of substrates. Depending on the end group, highly hydrophobic or hydrophilic surfaces can be achieved. Silanization bases on the adsorption, self‐assembly and covalent binding of silane molecules onto surfaces and results in a densely packed, SAM. Following wet chemical routines, the quality of the monolayer is often variable and, therefore, unsatisfactory. The process of self‐assembly is not only affected by the chemicals involved and their purity but is also extremely sensitive to ambient parameters such as humidity or temperature and to contaminants. Here, a reliable and efficient wet‐chemical recipe is presented for the preparation of ultra‐smooth, highly ordered alkyl‐terminated silane SAMs on Si wafers. The resulting surfaces are characterized by means of atomic force microscopy, X‐ray reflectometry and contact angle measurements. Copyright © 2015 John Wiley & Sons, Ltd.     

Adsorption of multivalent alkylthiols on Au(111) surface: Insights from DFT

The adsorption of multivalent thiols on gold (111) surface was investigated using density functional theory applying the Perdew–Burke–Ernzerhof functional. Through the comparison of differences in energetics, structure and charge density distribution of a set of monodentate and polydentate thiols, we have described in detail the factors affecting the adsorption energy and the role played by the multivalence, which causes a decreasing of adsorption energy because of both electronic and steric hindrance effects. Finally, the comparison between the adsorption of 1,2‐ and 1,3‐disulfides revealed how the chain length may affect the cleavage of the S? S bond when they adsorb on Au(111) surface. © 2013 Wiley Periodicals, Inc.     

Thermal Properties of Oligo(2-ethyl-2-oxazoline) Containing Comb and Graft Copolymers and their Aqueous Solutions

Summary: The cationic ring opening polymerization of 2-ethyl-2-oxazoline (EtOx) was applied for the synthesis of methacrylate end-functionalized well-defined macromonomers that could be polymerized in a controlled manner using reversible addition-fragmentation chain transfer polymerization. The obtained comb polymers revealed lower critical solution temperature behavior in aqueous solution. The cloud points of these solutions could be tuned in a range from 35 °C to 85 °C by the incorporation of hydrophobic methyl methacrylate comonomer in varying amounts into the graft copolymers whereas copolymerization with methacrylic acid rendered temperature and pH sensitive copolymers. Thermo-gravimetric analysis showed a two-step decomposition of the graft copolymers and differential scanning calorimetry revealed glass transition temperatures that are significantly lowered in comparison to linear PEtOx.     

On the physisorption of water on graphene: a CCSD(T) study

The electronic structure of the zero-gap two-dimensional graphene has a charge neutrality point exactly at the Fermi level that limits the practical application of this material. There are several ways to modify the Fermi-level-region of graphene, e.g. adsorption of graphene on different substrates or different molecules on its surface. In all cases the so-called dispersion or van der Waals interactions can play a crucial role in the mechanism, which describes the modification of electronic structure of graphene. The adsorption of water on graphene is not very accurately reproduced in the standard density functional theory (DFT) calculations and highly-accurate quantum-chemical treatments are required. A possibility to apply wavefunction-based methods to extended systems is the use of local correlation schemes. The adsorption energies obtained in the present work by means of CCSD(T) are much higher in magnitude than the values calculated with standard DFT functional although they agree that physisorption is observed. The obtained results are compared with the values available in the literature for binding of water on the graphene-like substrates.     

New Scabimycins A-C Isolated from Streptomyces acidiscabies (Lu19992)

Peptide natural products displaying a wide range of biological activities have become important drug candidates over the years. Microorganisms have been a powerful source of such bioactive peptides, and Streptomyces have yielded many novel natural products thus far. In an effort to uncover such new, meaningful compounds, the metabolome of Streptomyces acidiscabies was analyzed thoroughly. Three new compounds, scabimycins A–C (1–3), were discovered, and their chemical structures were elucidated by NMR spectroscopy. The relative and absolute configurations were determined using ROESY NMR experiments and advanced Marfey’s method.