Formation Mechanism of a Nano-Ring of Bismuth Cations and Mono-Lacunary Keggin-Type Phosphomolybdate

A new hetero-bimetallic polyoxometalate (POM) nano-ring was synthesized in a one-pot procedure. The structure consists of tetrameric units containing four bismuth-substituted monolacunary Keggin anions including distorted [BiO₈] cubes. The nano-ring is formed via self-assembly from metal precursors in aqueous acidic medium. The compound (NH₄)₁₆[(BiPMo₁₁O₃₉)₄] ⋅ 22 H₂O; (P₄Bi₄Mo₄₄) was characterized by single-crystal X-ray diffraction, extended X-ray absorption fine structure spectroscopy (EXAFS), Raman spectroscopy, matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF), and thermogravimetry/differential scanning calorimetry mass spectrometry (TG-DSC-MS). The formation of the nano-ring in solution was studied by time-resolved in situ small- and wide-angle X-ray scattering (SAXS/WAXS) and in situ EXAFS measurements at the Mo−K and the Bi−L₃ edge indicating a two-step process consisting of condensation of Mo-anions and formation of Bi−Mo-units followed by a rapid self-assembly to yield the final tetrameric ring structure.     

The Structure of the Diatom Silaffin Peptide R5 within Freestanding Two-Dimensional Biosilica Sheets

The silaffin peptide R5 is instrumental to the mineralization of silica cell walls of diatom organisms. The peptide is also widely employed in biotechnology, for example, in the encapsulation of enzymes and for fusion proteins in tissue regeneration. Despite its scientific and technological importance, the interfacial structure of R5 during silica precipitation remains poorly understood. We herein elucidate the conformation of the peptide in its active form within silica sheets by interface-specific vibrational spectroscopy in combination with molecular dynamics simulations. Contrary to previous solution-state NMR studies, our data confirm that R5 maintains a defined structure when interacting with extended silica sheets. We show that the entire amino acid sequence of R5 interacts with silica during silica formation, leading to the intercalation of silica into the assembled peptide film.     

The influence of gas-phase etch removal,deposition temperature and substrate properties on the crystallographic perfection of silicon epitaxial layers

An investigation of the defect structure of silicon homoepitaxial layers, as influenced by gas phase etching, deposition temperature, and substrate properties, is presented. The minimum values of etch removal and deposition temperature necessary for sufficient layer perfection have been determined. The defect and impurity distribution in the substrate, as formed during a preceeding arsenic buried layer processing, have been evaluated and are discussed here with regard to their influence on the epitaxial layer perfection.     

Defect generation on mechanically surface defects before and after the oxidation (II). Dislocation generation at cracks

The generation of crystal defects at residual cracks due to a wet oxidation of chemically mechanically polished silicon wafers at 1100 °C was investigated. It was found that the nucleation of oxidation stacking faults at these elastic cracks is impeded as compared to the regions between the cracks. However, extended dislocations, dislocation dipoles, certain stacking faults, and precipitates are generated at such cracks. These crystal defects and the crack itself impede the nucleation of oxidation stacking faults at the crack, as they locally reduce the excess interstitials at the oxidation front.     

Zur Abbildung von Isolierschichtdefekten im Elektronenspiegelmikroskop

Following the investigations on the imaging behaviour of homogeneous dielectric layers considerations on the possibilities of imaging simple layer inhomogeneities are discussed. These considerations imply a contrast amplification by charging phenomena. By definite variation of the substrate potential a distinction between geometrical layer defects (protrusions, indentations, holes) and electrical inhomogeneities of the insulating layer (regions of increased and decreased conductivity, resp.) is possible as shown by the experimental investigations. Criterions for distinguishing different cases can be given. The sensitivity for detecting inhomogeneities in non-covered dielectric layers is higher than in the case of those being covered with a conductive layer.     

ROP of L-lactide and ε-caprolactone catalyzed by tin(ii) and tin(iv) acetates–switching from COOH terminated linear chains to cycles

The catalytic potential of tin(II)acetate, tin(IV)acetate, dibutyltin-bis-acetate and dioctyl tin-bis-acetate was compared based on polymerizations of L-lactide conducted in bulk at 160 or 130°C. With SnAc₂ low-Lac/Cat ratios (15/1–50/1) were studied and linear chains having one acetate and one carboxyl end group almost free of cyclics were obtained. Higher monomer/catalyst ratios and lower temperatures favored formation of cycles that reached weight average molecular weights (Mw's) between 100,000 and 2,500,000. SnAc₄ yielded mixtures of cycles and linear species under all reaction conditions. Dibutyltin- and dioctyl tin bis-acetate yielded cyclic polylactides under most reaction conditions with Mw's in the range of 20,000–80,000. Ring-opening polymerizations performed with ε-caprolactone showed similar trends, but the formation of COOH-terminated linear chains was significantly more favored compared to analogous experiments with lactide. The reactivity of the acetate catalysts decreased in the following order: SnAc₂ > SnAc₄ > Bu₂SnAc₂ ~ Oct₂SnAc₂.     

Minimization of Gerstewitz functionals extending a scalarization by Pascoletti and Serafini

Scalarization in vector optimization is often closely connected to the minimization of Gerstewitz functionals. In this paper, the minimizer sets of Gerstewitz functionals are investigated. Conditions are given under which such a set is nonempty and compact. Interdependencies between solutions of problems with different parameters or with different feasible point sets are shown. Consequences for the parameter control in scalarization methods are proved. It is pointed out that the minimization of Gerstewitz functionals is equivalent to an optimization problem which generalizes the scalarization by Pascoletti and Serafini. The results contain statements about minimizers of certain Minkowski functionals and norms. Some existence results for solutions of vector optimization problems are derived.     

Novel tripod ligands for prickly self-assembled monolayers

The new tridentate thioether ligands PhSi(CH2SMe)3 (1) and Ph-p-C6H4Si(CH2SMe)3 (2) have been synthesised and used for the preparation of the chelates fac-[W(kappa3-1)(CO)3] and fac-[W(kappa3-2)(CO)3], which were characterised by single-crystal X-ray diffraction. 1 and 2 were used as tripodal adsorbate molecules for the fabrication of self-assembled monolayers (SAMs) on gold. Film formation from solution was investigated in situ by second harmonic generation (SHG) and ellipsometry, which revealed a two-stepped process (fast adsorption, followed by slow film ordering). SAMs of 2 on gold were further investigated by ex situ methods, viz. high-resolution X-ray photoelectron spectroscopy (HRXPS), Fourier transform infrared reflection absorption spectroscopy (FTIRRAS), and scanning tunneling microscopy (STM). The latter two methods indicated dense packing of the tripodal anchor groups on the surface, with a substantially lower density of the biphenyl pricks. HRXPS showed three different binding states of sulfur, including a standard thiolate-type and a coordination-type state.     

Synthesis of cyclic poly(l‐lactide) catalyzed by Bismuth Salicylates—A combination of two drugs

l ‐lactide was polymerized in bulk at 160 or 180°C with mixtures of bismuth subsalicylate (BiSub) and salicylic (SA) as catalysts. The SA/Bi ratio and the monomer/Bi ratio were varied. The highest molecular weights (weight average, Mw) were achieved at a SA/Bi ratio of 1/1 (Mw up to 92 000 g mol^?1). l ‐Lactide was also polymerized with combinations of BiSub and silylated SA, and Mw values up to 120 000 g mol^?1 were achieved at 180°C. MALDI‐TOF mass spectrometry and Mark‐Houwink‐Sakurada measurements proved that under optimized reaction conditions the resulting polylactides consist of cycles. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2056–2063