Silver(I) arylsulfonates: a systematic study of "softer" hybrid inorganic-organic solids

The present study represents the first systematic examination of the effects on the layered structure of simple silver aryl-monosulfonates as the breadth of the pendant aryl group is increased beyond that where a simple "phosphonate-like" motif is sustainable. Five new silver arenesulfonates are reported. On the basis of comparison with Ag benzenesulfonate, a threshold of approximately 6.4 A is proposed and confirmed as the critical breadth of an aryl group for a simple layered motif to be observed in silver sulfonates. Ag 1,1'-biphenyl-4-sulfonate (1) and Ag 2-naphthalenesulfonate (2) are below this threshold and so form simple layered networks, termed type 1 solids. When the pendant group is broadened to a 1-naphthyl group, the layer incorporates coordinated water to maintain a layered structure giving Ag 1-naphthalenesulfonate hemihydrate (3a). This more diffuse structure is termed a type 2 solid. For anhydrous Ag 1-naphthalenesulfonate (3) and Ag 1-pyrenesulfonate (4), the additional breadth is compensated for by the formation of Ag-pi interactions and the formation of type 3 solids. Interactions between the pendant groups are observed to play a significant role in the packing of the solid. All frameworks are characterized by single crystal and powder X-ray diffraction, IR, DSC-TGA, and elemental analysis. The significance of this adaptable framework is discussed along with implications for design of stacked arene arrays.     

On the convergence for kinetic variational inequality to quasi-static variational inequality with application to elastic-plastic systems with hardening

In this note, a priori estimates for the kinetic problem are obtained that imply, that the kinetic solutions converge to the quasi-static ones, when the size of initial perturbations and the rate of application of the forces tend to 0. An application to three-dimensional elastic-plastic systems with hardening is given. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interactions underpinning the plasticization of a polymer matrix: a dynamic and structural analysis of DMP-plasticized cellulose acetate

This work establishes that the plasticization effect of a classical petrochemical plasticizer, dimethyl phthalate (DMP), on a polymer matrix, cellulose acetate (CA), is due to the development of intermolecular interactions of dipolar type. Plasticized cellulose acetate films are studied with regard to the interactions between the polymer and plasticizer at the macroscopic scale by thermogravimetric analysis and differential scanning calorimetry. At the molecular level, Fourier transform infrared spectroscopy and dielectric relaxation spectroscopy are used to elucidate the nature of interactions that are responsible for the plasticizing effects. These static and dynamic complementary analyses evidenced that DMP does not establish H-bonding interactions with the polymer chains of cellulose acetate but rather weaker interactions of dipolar type. These dipole–dipole interactions that develop between acetyl side groups of CA and the ester phthalate moieties of DMP increase the overall mobility of CA chains and also locally influence the molecular mobility and the water uptake tendency.     

Analysis and Artifact Correction for Volume Correlation Measurements Using Tomographic Images from a Laboratory X-ray Source

The effects of three artifacts (reconstruction, beam hardening and temperature of the X-ray tube) associated with the use of a lab tomograph are analyzed in terms of their induced biases for Digital Volume Correlation (DVC) from a series of reconstructed volumes acquired successively. The most detrimental effect is due to spurious dilatational strains induced by temperature variations in the tomograph. If they are not accounted for, any quantitative kinematic measurement is impossible for strain levels below 0.5%.     

Origin of the Enantioselectivity in Organocatalytic Michael Additions of β‐Ketoamides to α,β‐Unsaturated Carbonyls: A Combined Experimental,Spectroscopic and Theoretical Study

The organocatalytic enantioselective conjugate addition of secondary β‐ketoamides to α,β‐unsaturated carbonyl compounds is reported. Use of bifunctional Takemoto’s thiourea catalyst allows enantiocontrol of the reaction leading either to simple Michael adducts or spirocyclic aminals in up to 99 % ee. The origin of the enantioselectivity has been rationalised based on combined DFT calculations and kinetic analysis. This study provides a deeper understanding of the reaction mechanism, which involves a predominant role of the secondary amide proton, and clarifies the complex interactions occurring between substrates and the catalyst.     

Fluorescent π‐Conjugated Polymer Dots versus Self‐Assembled Small‐Molecule Nanoparticles: What’s the Difference?

Fluorescent nanoparticles based on π‐conjugated small molecules and polymers are two different classes of π‐conjugated systems that have attracted much interest. To date, both emerging classes have only been studied separately and showed no clear differences in their properties. Herein these nanoparticles are compared on the basis of a fluorene co‐polymer and its corresponding small molecule. Both systems formed nanoparticles with the same diameter, whereas the fluorescence properties clearly differed. In case of the polymer the fluorescence diminished, whereas for the small molecules the fluorescence increased. In addition, the capability of encapsulation and release of a hydrophobic dye from the fluorescent nanoparticles was studied. For the polymer system, encapsulation was highly efficient and no release was observed, whereas for the small molecule system encapsulation was less efficient and release of the dye was observed. These studies show a clear difference between small molecules and polymers which has important implications for the design of fluorescent nanoparticles.