The external region of a cell membrane, known as the glycocalyx, is dominated by glycosylated molecules, which direct specific interactions such as cell-cell recognition and contribute to the steric repulsion that prevents undesirable non-specific adhesion of other molecules and cells. Mimicking the non-adhesive properties of a glycocalyx provides a potential solution to the clinical problems, such as thrombosis, that are associated with implantable devices owing to non-specific adsorption of plasma proteins. Here we describe a biomimetic surface modification of graphite using oligosaccharide surfactant polymers, which, like a glycocalyx, provides a dense and confluent layer of oligosaccharides. The surfactant polymers consist of a flexible poly(vinyl amine) with dextran and alkanoyl side chains. We show that alkanoyl side chains assemble on graphite through hydrophobic interaction and epitaxial adsorption. This constrains the polymer backbone to lie parallel to the substrate, with solvated dextran side chains protruding into the aqueous phase, creating a glycocalyx-like coating. The resulting biomimetic surface is effective in suppressing protein adsorption from human plasma protein solution.

A series of novel surfactant polymers: poly(N-vinyldextran aldonamide-co-N-vinylhexanamide) (PNVDA-co-PNVH), in which hydrophilic dextran oligosaccharides and hydrophobic hexanoyl groups were incorporated simultaneously on to poly(vinylamine) (PVAm), were synthesized, and characterized by FTIR and 1 H NMR spectroscopy. Structurally well-defined poly(vinylamine) was prepared by hydrolysis of poly(N-vinylformamide), which was obtained by free radical polymerization of N-vinylformamide. Dextran molecules (Mw ) 1600) were attached to poly(vinylamine) by reacting amine groups with dextran lactone, while hexanoyl groups were attached by reacting amine groups with N-(hexanoyloxy)succinimide. By adjustment of the feed ratio, surfactant polymers with different hydrophilic/hydrophobic balances were prepared. Surface activity of the surfactants at an air/water interface was demonstrated by significant reductions in water surface tension. Surface activity at a solid surface/water interface was demonstrated by atomic force microscopy of surfactant molecules adsorbed onto a highly oriented pyrolytic graphite. The synthetic approach described in this report provides a route to prepare a variety of oligosaccharide surfactant polymers with well-defined structures and hydrophilic/hydrophobic balances, by selecting different combinations of oligosaccharide and alkanoyl groups or by adjusting feed ratio of the oligosaccharide to alkanoyl groups.

Quite different meanings are attached by chemists to the words element, atom, orbital, order of orbitals or configurations. This causes conceptual inconsistencies, in particular with respect to the transition-metal elements and their atoms or ions. The different meanings will here be distinguished carefully. They are analyzed on the basis of empirical atomic spectral data and quasi-relativistic density functional calculations. The latter are quite reliable for different average configuration energies of transition-metal atoms. The so-called "configurations of the chemical elements", traditionally displayed in periodic tables, are the dominant configurations of the lowest spin-orbit levels of the free atoms. They are chemically rather irrelevant. In many-electron systems the ns and np AOs are significantly below the more hydrogen-like nd ones. Even (n+1)s is below nd for all light neutral atoms from C onwards, but only up to the first elements of the respective long rows! The most common orbital order in transition-metal atoms is 3p << 3d < 4s etc. The chemically relevant configuration in group g is always d(g) instead of d(g-2) s(2). Conceptually clear reasoning eliminates apparent textbook inconsistencies between simple quantum-chemical models and the empirical facts. The empirically and theoretically well-founded Rydberg (n-deltal) rule is to be preferred instead of the historical Madelung (n+l) rule with its large number of exceptions.

No abstract

The use of a GaAsSb metamorphic buffer layer (MBL) is demonstrated to significantly enhance the room-temperature photoluminescence intensity for 1.55μm metamorphic InAs∕GaAs quantum dots (QDs) in comparison with a conventional InGaAs MBL. A dramatic reduction of QD photoluminescence emission efficiency above 1.5μm has been observed at room temperature when the indium composition in the InxGa1−xAs MBL is increased over x=0.25. By using a GaAsSb buffer instead of InGaAs, we demonstrate a strong enhancement of photoluminescence intensity of InAs∕GaAs QDs. The effects of the GaAsSb MBL can be understood in terms of smoothing the surface morphology of the buffer layer and, hence, suppressing the formation of dislocations in the QD region. These results suggest an alternative approach to developing GaAs-based light sources in the telecommunication-wavelength range near 1.55μm.

The trends in the series of lanthanoid (lanthanide) trifluoride molecules LnF3 (Ln = La to Lu) are governed by the valence-active Ln(4f,5d,5p,6s) shells. The series is investigated by quasi-relativistic density functional theory at both the scalar and spin-orbit-coupled levels. Integrating many of the previous experimental and theoretical deductions, we obtain the following comprehensive picture: (1) The comparatively small Ln-F bond length contraction of 14 pm from La to Lu is rather smooth but weakly modulated by spin-orbit coupling. (2) From La to Lu the floppy structure becomes more quasi-planar. (3) The heterolytic LnF bond energies (⅓LnF3→⅓Ln(3+) + F(-)) at the spin-orbit averaged level increase smoothly from 15.3 to 16.3 eV for La to Lu, only the 'divalent' lanthanoids Eu and Yb are outliers with 0.2 eV higher bond energies. (4) The homolytic LnF bond energies (⅓LnF3→⅓Ln + F) however show an overall W-shaped double-periodicity with maxima for LaF3, GdF3 and LuF3, decreasing from La to Eu and from Gd to Yb, the large individual variations being caused by different spin-orbit coupling and Coulomb interaction effects in Ln(0) and LnF3. (5) The Ln-F interaction is basically ionic (increasing with decreasing ionic radii) with some dative Ln(3+)← F(-) bonding. (6) The latter is of the Ln(5d)-F(2p) type with a rather constant bond order from La to Lu, with small Ln(5p) and very small Ln(4f) semi-core contributions decreasing from La to Lu. All these trends are rationalized.

Modified poly 2,4-dichlorostyrene microspheres were designed and synthesized, and were proved to be an effective carrier to synthesize supported manganese dioxide nanoparticles.

No abstract