Induced antiferroelectric smectic- C(*)(A) phase by doping ferroelectric- C* phase with bent-shaped molecules

Doping of the ferroelectric Sm-C(*) phase with bent-shaped molecules induces the antiferroelectric Sm-C(*)(A) phase. The effect was observed by means of electro-optic and dielectric measurements in systems with weak interlayer interactions in which the relative strength of anticlinic-synclinic order between molecules in adjacent layers is easily controlled by external factors. Fourier-transform infrared spectroscopy studies suggest that the bent-shaped molecules are not flat. They reorient upon the electric field-induced antiferroelectric-ferroelectric transition to adopt a position in which the average direction of the carbonyl groups is in the smectic plane and a bending tip along the C2 symmetry axis.     

Sandwich compounds of cyanotrispyrazolylborates: complexation-induced ligand isomerization

Reaction of the new cyanoscorpionate ligand, hydrotris(4-cyano-3-phenyl)pyrazolylborate (Tp(Ph),(4CN)) with Co(II), Mn(II), and Fe(II) unexpectedly results in the isolation only of crystals containing sandwich complexes in which the ligands have been isomerized to produce the heterocyanoscorpionate hydrobis(4-cyano-3-phenylpyrazolyl)(4-cyano-5-phenylpyrazolyl)borate (Tp(Ph),(4CN*)). The three complexes have been characterized crystallographically and are isostructural, with each ligand acting in a tridentate manner toward the metal. The isomerization of the ligand appears to be more facile than that of the analogous non-cyano ligand, Tp(Ph), with which crystals of the unisomerized sandwich compound have been isolated for Mn(II) and Fe(II).     

Cluster growth and fragmentation in the highly fluxional platinum derivatives of Sn9 4-: synthesis, characterization, and solution dynamics of Pt2@Sn17 4- and Pt@Sn9H 3-

Sn94- reacts with Pt(PPh3)4 in ethylenediamine/toluene solvent mixtures in the presence of 2,2,2-cryptand to give four different complexes: "Rudolph's complex" of proposed formula [Sn9Pt(PPh3)x]4- (2), the previously reported [Pt@Sn9Pt(PPh3)]2- ion (3), and the title complexes Pt2@Sn174- (4) and Pt@Sn9H3- (5). The use of Pt(norbornene)3 instead of Pt(PPh3)4 gives complex 4 exclusively. The structure of 4 contains two Pt atoms centered in a capsule-shaped Sn17 cage. The complex is highly dynamic in solution showing single, mutually coupled 119Sn and 195Pt NMR resonances indicative of an intramolecular liquidlike dynamic exchange process. Complex 5 has been characterized by selectively decoupled 1H, 119Sn, and 195Pt NMR experiments and shows similar liquidlike fluxionality. In addition, the H atom scrambles across the cage showing small couplings to both Sn and Pt atoms. Neither 3 nor 4 obeys Wades rules; they adopt structures more akin to the subunits in alloys such as PtSn4. The structural and chemical relevance to supported PtSn4 heterogeneous catalysts is discussed.     

Surface modification of expanded poly(tetrafluoroethylene) by means of microwave plasma treatment for improvement of adhesion and growth of human endothelial cells

Surface modification of expanded poly(tetrafluoroethylene) (ePTFE) vascular prostheses was carried out by means of low pressure microwave plasma treatment. Hydrogen/ water vapour mixtures (containing excess of hydrogen) were shown to be efficient with respect to functionalization of PTFE. The results of treatments in dependence on various gas pressures and treatment times were detected by physicochemical techniques (zeta potential, wetting measurements) and by surface spectroscopy (XPS, ATR-FTIR). Furthermore, adhesion and proliferation of human endothelial cells from umbilical cord (HUVEC) onto modified ePTFE were observed in vitro in culture media. The results of this biological test of plasma treated materials correlate well with physicochemical surface parameters.     

Surface properties and swelling behaviour of hyperbranched polyester films in aqueous media

Thin films of hydroxyl (POH) and carboxyl (PCOOH) terminated aromatic hyperbranched polyesters (HBPs) were prepared by spin coating on silicon wafers and subsequently annealed above their glass transition temperature (T_g). The surface properties and the swelling behaviour of these films in aqueous buffer solutions were studied as a function of annealing time using contact angle measurements and ellipsometry. Non-annealed films were hydrophilic with surface free energies of 51 mJ/m² for POH and 49 mJ/m² for PCOOH, respectively. The swelling behaviour of the polymer films in buffer solution with pH 7.4 was described in terms of changes of the thickness and effective refractive index of the swollen layer. Under identical conditions a lower water uptake was found for hydroxyl terminated HBPs (POH) which were annealed more then 2 h. The lower water uptake correlates with the surface properties of the films. The annealed films were less hydrophilic. Their surface free energy was 38 mJ/m² independent of the annealing. Films of carboxyl terminated HBPs (PCOOH) showed similar surface properties after annealing. However, these films were unstable under the same conditions in aqueous solutions. Stable PCOOH films were obtained by additional covalent binding to the substrate using an epoxy silane as a coupling agent.     

Spectroscopic and thermodynamic characterization of the adsorption of plasma proteins onto cellulosic substrates

The sorption of the plasma proteins human serum albumin (HSA) and human fibrinogen (FIB) onto hemodialytic cellulosic substrates was investigated by the surface sensitive ATR-FTIR-spectroscopy. By means of this method we monitored the protein sorption kinetics onto acetylated and unmodified cellulose (AKZO-NOBEL). Furthermore, secondary structure alterations of the adsorbed proteins as well as changes of the composition in sorbed layers consisting of two proteins were detected. These findings were compared with results of the zeta potential and contact angle measurements on comparable sorption experiments.