Synthesis of an anionically chargeable, high-molar-mass, second-generation dendronized polymer and the observation of branching by scanning force microscopy

An efficient synthesis of a methacrylate-based, second-generation (G2) dendronized macromonomer and its free radical polymerization to the corresponding high-molar-mass G2 dendronized polymer are described. The molar mass is determined by gel permeation chromatography (GPC), light-scattering, and analytical ultracentrifugation and compared with values estimated from a scanning force microscopy (SFM) contour lengths analysis of individualized polymer strands on mica. The polymer carries terminal tert-butyl-protected carboxyl groups, the degree of deprotection of which with trifluoroacetic acid is quantified by NMR spectroscopy using the highest molar mass sample. SFM imaging of both protected (noncharged) and unprotected (charged) dendronized polymers on solid substrates reveals mostly linear chains but also some with main-chain branches. The nature of these branches is investigated and the degree roughly estimated to which they are formed. Finally, a synthetic model experiment is described which sheds some light on the aspect of whether chain transfer, a process that could lead to covalent branching, is of importance in the synthesis of the present dendronized polymers.     

Sulphur diagenesis in the sediments of the Kiel Bight, SW Baltic Sea, as reflected by multiple stable sulphur isotopes

In this work, the biogeochemistry of marine sediments from the Kiel Bight, coastal SW Baltic Sea, is studied based on the abundance and isotopic composition of organic carbon and different forms of sedimentary sulphur. Active bacterial sulphate reduction, partly under sulphate-limiting conditions, is evident from paired δ(34)S and δ(18)O values of pore water sulphate. The resulting pore water sulphide is partly precipitated as acid-volatile iron sulphide and subsequently forms sedimentary pyrite, partly serves in later diagenetic sulphurisation of organic matter, or remains dissolved in the pore water, all evident from the respective δ(34)S values. Microbial sulphate turnover is associated with an apparent isotopic fractionation between dissolved sulphate and dissolved sulphide (Δ(34)S) that varies between 46 and 66‰.     

Semantics of OpenMath and MathML3

Even though OpenMath has been around for more than 10?years, there is still confusion about the ??semantics of OpenMath??. As the recent MathML3 recommendation semantically bases Content MathML on OpenMath Objects, this question becomes more pressing. One source of confusions about OpenMath semantics is that it is given on two levels: a very weak algebraic semantics for expression trees, which is extended by considering mathematical properties in content dictionaries that interpret the meaning of (constant) symbols. While this two-leveled way to interpret objects is well-understood in logic, it has not been spelt out rigorously for OpenMath. We present two denotational semantics for OpenMath: a construction-oriented semantics that achieves full coverage of all legal OpenMath expressions at the cost of great conceptual complexity, and a symbol-oriented one for a subset of OpenMath expressions. This subset is given by a variant of the OpenMath 2 role system, which??we claim??does not exclude any representations of meaningful mathematical objects.     

Synthesis with Single Macromolecules: Covalent Connection between a Neutral Dendronized Polymer and Polyelectrolyte Chains as well as Graphene Edges

Single chains of a neutral, dendronized polymer with peripheral azide groups ( PG3A ) are co‐deposited onto molecularly modified graphite substrates with a positively charged dendronized polymer ( PG2 ) as well as with negatively charged plasmid dsDNA. PG3A is also prepared near graphite step‐edges. Single PG3A chains are moved with a scanning force microscope tip, into close contact with either of the two polyelectrolytes, as well as the step‐edge at predetermined positions. Treating these structures in situ with UV light leads to photochemically induced cross‐linking between the PG3A chains carrying azide groups and PG2 , dsDNA, and graphite step‐edges, respectively, which is proven by mechanically challenging the “welding” points by pulling on the molecules with the SFM‐tip.

     

Magnetic and electric phase control in epitaxial EuTiO(3) from first principles

We propose a design strategy--based on the coupling of spins, optical phonons, and strain--for systems in which magnetic (electric) phase control can be achieved by an applied electric (magnetic) field. Using first-principles density-functional theory calculations, we present a realization of this strategy for the magnetic perovskite EuTiO(3).     

Multiferroic domain dynamics in strained strontium titanate

Multiferroicity can be induced in strontium titanate by applying biaxial strain. Using optical second harmonic generation, we report a transition from 4/mmm to the ferroelectric mm2 phase, followed by a transition to a ferroelastic-ferroelectric mm2 phase in a strontium titanate thin film. Piezoelectric force microscopy is used to study ferroelectric domain switching. Second harmonic generation, combined with phase-field modeling, is used to reveal the mechanism of coupled ferroelectric-ferroelastic domain wall motion. These studies have relevance to multiferroics with coupled polar and axial phenomena.     

Catalytic partial oxidation of methane to synthesis gas over a ruthenium catalyst: the role of the oxidation state

The catalytic partial oxidation of methane to synthesis gas over ruthenium catalysts was investigated by thermogravimetry coupled with infrared spectroscopy (TGA-FTIR) and in situ X-ray absorption spectroscopy (XAS). It was found that the oxidation state of the catalyst influences the product formation. On oxidized ruthenium sites, carbon dioxide was formed. The reduced catalyst yielded carbon monoxide as a product. The influence of the temperature was also investigated. At temperatures below the ignition point of the reaction, the catalyst was in an oxidized state. At temperatures above the ignition point, the catalyst was reduced. This was also confirmed by the in situ XAS spectroscopy. The results indicate that both a direct reaction mechanism as well as a combustion-reforming mechanism can occur. The importance of knowing the oxidation state of the surface is discussed and a method to determine it under reaction conditions is presented.