Study on the reversible changes of the surface properties of an L-cysteine self-assembled monolayer on gold as a function of pH

A stimuli-response biological surface of L-cysteine was prepared on a polycrystalline gold surface from aqueous solution. The effect of the pH value of the rinsing solution on the surface composition was studied with X-ray photoelectron spectroscopy (XPS). Qualitative and quantitative analysis of the amino, carboxyl, and thiol functional groups of these self-assembled monolayers indicate that L-cysteine molecules exist in the neutral and zwitterionic forms and that they are sensitive to the pH of the rinsing solution. In addition, the wetting properties of the functionalized surface were studied by contact angle (CA) analysis: they were also dependent on the pH of the rinsing solution. Furthermore, it was shown that this functionalization process was reversible.     

Stacey Crossed Products Associated to Exel Systems

There are many different crossed products by an endomorphism of a C*-algebra, and constructions by Exel and Stacey have proved particularly useful. Here we consider Exel crossed products associated to transfer operators which extend to be unital on the multiplier algebra. We show that every Exel crossed product is isomorphic to a Stacey crossed product, though by a different endomorphism of a different C*-algebra. We apply this result to a variety of Exel systems, including those associated to shifts on the path spaces of directed graphs.     

Stable polymethacrylate nanocapsules from ultraviolet light-induced template radical polymerization of unilamellar liposomes

We employed UV-induced template polymerization to create hollow nanometer-sized polymer capsules. Homogeneous, unilamellar liposomes served as a two-dimensional template for the cross-linking of either butyl methacrylate or hydroxyethyl methacrylate with the bifunctional ethyleneglycol dimethacrylate. Different molar ratios of lipid/hydrophobic monomer/bifunctional monomer/photoinitiator were tested and dynamic light scattering revealed negligible changes of size at a defined molar ratio of 2/1/10/20, respectively. Cryo-transmission electron microscopy provided clear evidence that incorporation of the methacrylate monomers into and polymerization in the hydrophobic bilayer phase does not disrupt vesicle integrity. Moreover, after solubilization of the lipids, the polymethacrylate nanocapsules were stable at conditions needed for negative staining and could be visualized by atomic force microscopy. In contrast to previous findings, the nanocapsule size and shape did not change considerably after removal of the template phase, and the size distribution remained strictly monomodal. The employed method is not only an advance to fortify liposomes, but the nanocapsules themselves can be functionalized.     

Photochemically driven shape changes of crystalline organic nanorods

Nanorods composed of 9-tert-butylanthroate (9-TBAE) are synthesized using an Al2O3 template and solvent annealing. The rods consist of micron-scale crystalline domains, and UV light induces a [4 + 4] photodimerization that results in a uniform 15% expansion along the rod axis. This is in contrast to random 9-TBAE crystals, which disintegrate under the same conditions. Transmission electron microscopy, atomic force microscopy, and comparison of the X-ray crystal structures of the monomer and photodimer all provide evidence for a mechanism based on a crystal-to-crystal photoreaction leading to an increase in molecular volume. It is likely that the high surface-to-volume ratio in the nanorods provides a strain relief pathway that is absent in larger crystals. Preliminary attempts to reverse the reaction using shorter wavelength light to photodissociate the dimers were only partly successful. These results suggest that crystalline organic nanostructures may provide an efficient way to transform photochemical energy into mechanical motion on the nanometer scale.     

A key step in the formation of acrylic acid from CO2 and ethylene: the transformation of a nickelalactone into a nickel-acrylate complex

The reaction of a nickelalactone with dppm, resulting in the formation of a stable binuclear Ni(I) complex with an acrylate, a Ph2P- and a dppm bridge, models a key step in the formation of acrylic acid from CO2 and ethylene.     

Model order reduction for nonlinear problems in circuit simulation

Electrical circuits usually contain nonlinear components. Hence we are interested in MOR methods that can be applied to a system of nonlinear Differential-Algebraic Equations (DAEs). In particular we consider the TPWL (Trajectory PieceWise Linear) and POD (Proper Orthogonal Decomposition) methods. While the first one fully exploits linearity, the last method needs modifications to become efficient in evaluation. We describe a particular technique based on Missing Point Estimation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bimetallic assemblies, [Ni(en)2]3[M(CN)6]2·3H2O (en = H2NCH2CH2NH2; M = Fe,Co)

The reaction between tris(ethyl­enedi­amine)­nickel(II) cations and hexa­cyanometallate(III) anions (M = Fe, Co) yields ordered bimetallic assemblies, catena‐poly­[[tris­(ethyl­enedi­amine)­nickel‐bis(μ‐hexa­cyano­iron‐N,N′)] trihydrate] and catena‐poly­[[tris­(ethyl­enedi­amine)­nickel‐bis(μ‐hexa­cyano­cobalt‐N,N′)] trihydrate], [{Ni(C₂H₈N₂)₂}₃{M(CN)₆}₂]·3H₂O, in which both cis and trans [Ni(en)₂] and [M(CN)₆] moieties are linked to give S‐shaped Ni–NC–M–CN–Ni–NC–M–CN–Ni units which are cross­linked to give ribbons parallel to the b axis. The two compounds are isomorphous with mean metal–ligand distances Fe—C = 1.940 (3), Co—C = 1.844 (3) and Ni—N = 2.102 (2) Å for the iron, and 2.105 (3) Å for the cobalt compound. These compounds appear to be identical with those formulated as [Ni(en)₂]₃[M(CN)₆]₂·2H₂O [Ohba, Maruona, Okawa, Enoki & Latour (1994). J. Am. Chem. Soc. 116 , 11566–11567; Ohba, Fukita & Okawa (1997). J. Chem. Soc. Dalton Trans. pp. 1733–1737] which were indexed on a smaller unit cell and described as disordered.     

Single-electron quantum dots in silicon MOS structures

We present experimental results for two types of quantum dots, which are embedded within a silicon metal-oxide-semiconductor structure. Evidence is found for single-electron charging at low temperature, and for an asymmetric shape of the dot. First results of simulations of these dots are presented. Received: 14 April 2000 / Accepted: 17 April 2000 / Published online: 6 September 2000