N‐Methyl‐2, 2'‐Dipicolylamine Complexes as Potential Models for Metal‐Mediated Base Pairs

Metal‐mediated base pairs can be used to insert metal ions into nucleic acids at precisely defined positions. As structural data on the resulting metal‐modified DNA are scarce, appropriate model complexes need to be synthesized and structurally characterized. Accordingly, the molecular structures of nine transition metal complexes of N‐methyl‐2, 2'‐dipicolylamine (dipic) are reported. In combination with an azole‐containing artificial nucleoside, this tridentate ligand had recently been used to generate metal‐mediated base pairs (Chem. Commun. 2011 , 47, 11041–11043). The Pd^II and Pt^II complexes reported here confirm that the formation of planar complexes (as required for a metal‐mediated base pair) comprising N‐methyl‐2, 2'‐dipicolylamine is possible. Two Hg^II complexes with differing stoichiometry indicate that a planar structure might also be formed with this metal ion, even though it is not favored. In the complex [Ag₂(dipic)₂](ClO₄)₂, the two Ag^I ions are located close to one another with an Ag ··· Ag distance of 2.9152(3) Å, suggesting the presence of a strong argentophilic interaction.     

Incorporation of β-(1,6)-linked glucooligosaccharides (pustulooligosaccharides) into plant cell wall structures

Protein extract of germinating nasturtium (Tropaeolum majus) seeds containing xyloglucan endotransglycosylase (xyloglucan xyloglucosyl transferase, EC 2.4.1.207, abbreviated XET) exhibited the heterotransglycosylating activity with donor/acceptor substrate pair xyloglucan/sulphorhodamine labelled pustulooligosaccharides (XG/PUOS-SR) in a dot blot assay. The heterotransglycosylating activity was confirmed by the substrate-product changes during transglycosylation by HPLC size-exclusion chromatography. Another donor substrate capable of being coupled with PUOS-SR was cellulose, probably owing to its structural similarity to xyloglucan. Surprisingly, microscopic comparison of the incorporation of the labelled xyloglucan nonasaccharide XGO9-SR (specific substrate for XET) and PUOS-SR into the cell wall structures clearly showed differences in their binding to specific cell structures: the primary cell wall and the plasma membrane. These findings indicate the existence in nasturtium of XETs with different localisation, substrate specificity and, probably, function.     

Capillary and gel electromigration techniques and MALDI-TOF MS – Suitable tools for identification of filamentous fungi

Microbial strains are now spreading out of their original geographical areas of incidence and previously adequate morphological identification methods often must be accompanied by a phenotypic characterization for the successful microbial identification. The fungal genus Monilinia represents a suitable example. Monilinia species represent important fruit pathogens responsible for major losses in fruit production. Four closely related spp. of Monilinia: Monilinia laxa, Monilinia fructigena, Monilinia fructicola and Monilia polystroma have been yet identified. However, the classical characterization methods are not sufficient for current requirements, especially for phytosanitary purposes.     

Synthesis,adsorption and adhesive properties of a cationic amphiphilic block copolymer for use as compatibilizer in composites

In this work, the objective was to synthesize a compatibilizer that can electrostatically adsorb onto cellulose fibers, in fiber-based composites, to enhance the interaction between the fibers and non-polar polymer matrices. This physical route to attach the compatibilizer onto and thereby modify a fiber surface is convenient since it can be performed in water under mild conditions. Polystyrene (PS) was used for the high molecular weight, non-polar, block and poly(dimethylamino)ethyl methacrylate (PDMAEMA) was used as the polar block, which was subsequently quaternized to obtain cationic charges. The block copolymer self-assembles in water into cationic micelles and the adsorption to both silicon oxide surfaces and cellulose model surfaces was studied. The micelles spread out on the surface after heat treatment and contact angle measurements showed that the contact angles against water increased significantly after this treatment. AFM force measurements were performed with a PS probe to study the adhesive properties. The adhesion increased with increasing contact time for the treated surfaces, probably due to entanglements between the polystyrene blocks at the treated surface and the probe. This demonstrates that the use of this type of amphiphilic block copolymer is a promising route to improve the compatibility between charged reinforcing materials, such as cellulose-based fibers/fibrils, and hydrophobic matrices in composite materials.     

Self-organised microdots formed by dewetting in a highly volatile liquid

Dewetting induced self-organisation was used to prepare an ordered microstructure from a highly volatile liquid. Dewetting of an evaporating iron oxide precursor solute on silicon substrate resulted in arrays of microdots with nearly hexagonal and tetragonal symmetries. Ordered structures form either by stick-slip motion or fingering instability at the receding contact line of evaporating droplets. Subsequent thermal treatment at 550 °C yields crystalline Fe(2)O(3) microdots with a diameter range of 1-4 μm. The size, density and shape of the microdots can be changed by using patterned substrates with different surface energies.     

Predicting the Limit of Control in the ATRP Process: Results from Kinetic Simulations

Kinetic simulations are reported, where the ATRP equilibrium constant K_ATRP is varied and the rates and degree of control in different ATRP systems are evaluated. The apparent rate constant k_app increases with increasing K_ATRP, but a maximum is reached. The limit of control is passed before the maximum, i.e. when K_ATRP is increased further, apparent first‐order kinetics and well‐controlled molecular weights will no longer be obtained. The equilibrium constant at which the limit of control is reached varies linearly with the propagation rate constant. This enables the design of well controlled ATRP systems. The influence of the conversion and chain length dependence of the termination rate constant on the simulation results is discussed.

     

Characterization of a Transformation Function of a Photochromic Adaptive Filter

Simple, fast and accurate procedure is developed for measuring a Transformation Function (TF) of a Photochromic Adaptive Filter (PAF). Photochromic filters, whose spectral transmittance depends on previous and immediate radiant exposure and other environmental conditions, require special methods of spectro-photometry to determine their properties. This article describes methodology of characterizing the luminous transmittance as a function of light intensity using easy to implement method. Transformation functions of sample filters for different sources of radiation and varied light intensity are evaluated. The measuring system can also be used for fast determination of spatially and spectrally uniform light sources with UV spectral component.