Surface chemistry and nonadecanoic acid adsorbate layers on TiO2(100) surfaces prepared at ambient conditions

The surface and adsorbate chemistry of the TiO₂(100) surface prepared at high temperatures and ambient conditions were studied by means of angle resolved X-ray photoelectron spectroscopy (AR-XPS), Low Energy Electron Diffraction (LEED) and Atomic Force Microscopy (AFM) based nanoshaving studies. The TiO₂(100) surface shows a 1 × 1 structure with a 1 × 3 superstructure assigned to surface defects. A significant hydroxide surface concentration was revealed by means of AR-XPS measurements. The adsorbate formation of nonadecanoic acid (NDCA) from ethanolic solution led to disordered sub-monolayer surface coverage. The weak interaction between the carboxylic acid group and the TiO₂ surface is assumed to be a combination of the neutral to acid behavior of the TiO₂ surface and the stable hydroxide surface layer created under ambient conditions.     

Scaling Up DNA Origami Lattice Assembly

The surface-assisted hierarchical assembly of DNA origami nanostructures is a promising route to fabricate regular nanoscale lattices. In this work, the scalability of this approach is explored and the formation of a homogeneous polycrystalline DNA origami lattice at the mica-electrolyte interface over a total surface area of 18.75 cm² is demonstrated. The topological analysis of more than 50 individual AFM images recorded at random locations over the sample surface showed only minuscule and random variations in the quality and order of the assembled lattice. The analysis of more than 450 fluorescence microscopy images of a quantum dot-decorated DNA origami lattice further revealed a very homogeneous surface coverage over cm² areas with only minor boundary effects at the substrate edges. At total DNA costs of € 0.12 per cm², this large-scale nanopatterning technique holds great promise for the fabrication of functional surfaces.     

Quantitative Assessment of Tip Effects in Single‐Molecule High‐Speed Atomic Force Microscopy Using DNA Origami Substrates

High‐speed atomic force microscopy (HS‐AFM) is widely employed in the investigation of dynamic biomolecular processes at a single‐molecule level. However, it remains an open and somewhat controversial question, how these processes are affected by the rapidly scanned AFM tip. While tip effects are commonly believed to be of minor importance in strongly binding systems, weaker interactions may significantly be disturbed. Herein, we quantitatively assess the role of tip effects in a strongly binding system using a DNA origami‐based single‐molecule assay. Despite its femtomolar dissociation constant, we find that HS‐AFM imaging can disrupt monodentate binding of streptavidin (SAv) to biotin (Bt) even under gentle scanning conditions. To a lesser extent, this is also observed for the much stronger bidentate SAv–Bt complex. The presented DNA origami‐based assay can be universally employed to quantify tip effects in strongly and weakly binding systems and to optimize the experimental settings for their reliable HS‐AFM imaging.     

In situ PM‐IRRAS studies of organothiols and organosilane monolayers–ZnO interfaces at high water activities

In situ photoelastic‐modulated Fourier transform infrared reflection absorption spectroscopy has been applied for the investigation of interfacial stability of organothiol and organosilane monolayer films on nanocrystalline zinc oxide thin films. It has been shown that for octadecyltriethoxysilane films, exposure to high water activities results in physisorption of water in the cross‐linked film. This high water activity at the interface leads to a reversible wet de‐adhesion of the interfacial silanol groups from the ZnO surface. However, the organothiol seems to form a denser monolayer and a stable by S–Zn bond that is resistant to the competition with adsorbed water. The reversible attachment for cross‐linked organosilanol films has been demonstrated for the first time by means of an in situ spectroscopic method on model ZnO surfaces. Copyright © 2016 John Wiley & Sons, Ltd.     

Interface chemistry and molecular interactions of phosphonic acid self-assembled monolayers on oxyhydroxide-covered aluminum in humid environments

Barrier properties of self-assembled octadecylphosphonic acid (ODPA) monolayers on plasma-modified oxyhydroxide-covered aluminum surfaces were analyzed by means of in situ photoelastic modulated infrared reflection absorption spectroscopy (PM-IRRAS). The surface hydroxyl density prior to ODPA adsorption was increased by means of a low-temperature H(2)O-plasma treatment. Adsorption isotherms of H(2)O on ODPA self-assembled monolayer (SAM) modified surfaces in comparison to bare oxide covered aluminum surfaces showed that the ODPA SAM leads to a strongly reduced amount of adsorbed water based on the inability of water to form hydrogen bonds to the low-energy aliphatic surface. However, the ODPA SAM covered surfaces did not show a significant inhibition of the H(2)O/D(2)O isotope exchange reaction between the D(2)O gas phase and the hydroxyl groups of the aluminum oxyhydroxide film, as the interfacial layer between the ODPA SAM and the metal substrate, while the interfacial phosphonate group as well as the orientation of the SAM is not affected by the adsorption of water. It can be followed that the strong adhesion promoting and high corrosion resistances of organophosphonate monolayers on oxyhydroxide-covered aluminum is a result of the strong acid-base interaction of the phosphonate headgroup with the Al ions in the oxyhydroxide film, even in the presence of high interfacial water activity and the molecular interactions of the aliphatic chains. However, the barrier effect of such monolayers on the transport of water is negligible.     

Adsorption kinetics of organophosphonic acids on plasma-modified oxide-covered aluminum surfaces

Tailoring of oxide chemistry on aluminum by means of low-pressure water and argon plasma surface modification was performed to influence the kinetics of the self-assembly process of octadecylphosphonic acid monolayers. The plasma-induced surface chemistry was studied by in situ FTIR reflection-absorption spectroscopy (IRRAS). Ex situ IRRAS and X-ray photoelectron spectroscopy were applied for the analysis of the adsorbed self-assembled monolayers. The plasma-induced variation of the hydroxide to oxide ratio led to different adsorption kinetics of the phosphonic acid from dilute ethanol solutions as measured by means of a quartz crystal microbalance. Water plasma treatment caused a significant increase in the density of surface hydroxyl groups in comparison to that of the argon-plasma-treated surface. The hydroxyl-rich surface led to significantly accelerated adsorption kinetics of the phosphonic acid with a time of monolayer formation of less than 1 min. On the contrary, decreasing the surface hydroxyl density slowed the adsorption kinetics.     

Thin Organic-Inorganic Anti-Fouling Hybrid-Films for Microreactor Components

Deposit formation and fouling in reactors for polymer production and processing especially in microreactors is a well-known phenomenon. Despite the flow and pressure loss optimized static mixers, fouling occurs on the surfaces of the mixer elements. To improve the performance of such parts even further, stainless steel substrates are coated with ultra-thin films which have low surface energy, good adhesion, and high durability. Perfluorinated organosilane (FOTS) films deposited via chemical vapor deposition (CVD) are compared with FOTS containing zirconium oxide sol-gel films regarding the prevention of deposit formation and fouling during polymerization processes in microreactors. Both film structures led to anti-adhesive properties of microreactor component surfaces during aqueous poly(vinylpyrrolidone) (PVP) synthesis. To determine the morphology and surface chemistry of the coatings, different characterization methods such as X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy as well as microscopic methods such as field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) are applied. The surface free energy and wetting properties are analyzed by means of contact angle measurements. The application of thin film-coated mixing elements in a microreactor demonstrates a significant lowering in pressure increase caused by a reduced deposit formation.     

Magnesium-Free Immobilization of DNA Origami Nanostructures at Mica Surfaces for Atomic Force Microscopy

DNA origami nanostructures (DONs) are promising substrates for the single-molecule investigation of biomolecular reactions and dynamics by in situ atomic force microscopy (AFM). For this, they are typically immobilized on mica substrates by adding millimolar concentrations of Mg²⁺ ions to the sample solution, which enable the adsorption of the negatively charged DONs at the like-charged mica surface. These non-physiological Mg²⁺ concentrations, however, present a serious limitation in such experiments as they may interfere with the reactions and processes under investigation. Therefore, we here evaluate three approaches to efficiently immobilize DONs at mica surfaces under essentially Mg²⁺-free conditions. These approaches rely on the pre-adsorption of different multivalent cations, i.e., Ni²⁺, poly-l-lysine (PLL), and spermidine (Spdn). DON adsorption is studied in phosphate-buffered saline (PBS) and pure water. In general, Ni²⁺ shows the worst performance with heavily deformed DONs. For 2D DON triangles, adsorption at PLL- and in particular Spdn-modified mica may outperform even Mg²⁺-mediated adsorption in terms of surface coverage, depending on the employed solution. For 3D six-helix bundles, less pronounced differences between the individual strategies are observed. Our results provide some general guidance for the immobilization of DONs at mica surfaces under Mg²⁺-free conditions and may aid future in situ AFM studies.     

On the Stability of DNA Origami Nanostructures in Low‐Magnesium Buffers

DNA origami structures have great potential as functional platforms in various biomedical applications. Many applications, however, are incompatible with the high Mg²⁺ concentrations commonly believed to be a prerequisite for maintaining DNA origami integrity. Herein, we investigate DNA origami stability in low‐Mg²⁺ buffers. DNA origami stability is found to crucially depend on the availability of residual Mg²⁺ ions for screening electrostatic repulsion. The presence of EDTA and phosphate ions may thus facilitate DNA origami denaturation by displacing Mg²⁺ ions from the DNA backbone and reducing the strength of the Mg²⁺–DNA interaction, respectively. Most remarkably, these buffer dependencies are affected by DNA origami superstructure. However, by rationally selecting buffer components and considering superstructure‐dependent effects, the structural integrity of a given DNA origami nanostructure can be maintained in conventional buffers even at Mg²⁺ concentrations in the low‐micromolar range.     

Zur Polymorphie von Sm2Se3

Polymorphism of Sm₂Se₃ Two modifications of Sm₂Se₃ could be obtained in form of single crystals by chemical transport reaction. We prepared starting from Sm₂Se₃ powders red brown crystals of Sm₂Se₃ in the defective Th₃P₄ type structure with the space group I4 3d and a = 878.2 pm as well as starting from SmSe_1.9 and samarium metal black, prismatic crystals of Sm₂Se₃ in the U₂S₃ type structure with the space group Pnma and a = 1 127.3 pm, b = 409.1 pm and c = 1103.2 pm.