Efficient Preparation of Hybrid Linear‐Branched Esters of PEG‐PEE Derivatives

A simple and efficient preparation of a number of hybrid linear‐branched PEG esters are described. The polymers are generated by direct coupling of PEG–carboxylic acids and a variety of pentaerythritol ethoxylates using carbon tetrabromide catalyst.     

Etching Characteristics and Mechanisms of Mo and Al2O3 Thin Films in O2/Cl2/Ar Inductively Coupled Plasmas: Effect of Gas Mixing Ratios

An investigation of etching behaviors for Mo and Al₂O₃ thin films in O₂/Cl₂/Ar inductively coupled plasmas at constant gas pressure (6 mTorr), input power (700 W) and bias power (200 W) was carried out. It was found that an increase in Ar mixing ratio for Cl₂/Ar plasma results in non-monotonic etching rates with the maximums of 160 nm/min at 60 % Ar for Mo and 27 nm/min at 20 % Ar for Al₂O₃. The addition of O₂ in the Cl₂/Ar plasma causes the non-monotonic Mo etching rate (max. 320 nm/min at 40–45 % O₂) while the Al₂O₃ etching rate decreases monotonically. The model-based analysis of etching kinetics allows one to relate the non-monotonic etching rates in Cl₂/Ar plasma to the change in the etching regime from the ion-flux-limited mode (at low Ar mixing ratios) to the neutral-flux-limited mode (for high Ar mixing ratios). In the Cl₂/O₂/Ar plasma, the non-monotonic Mo etching rate is probably due to the change in reaction probability.     

A sensitive chromatographic determination of hydrazines by naphthalene-2,3-dialdehyde derivatization

A new high-performance liquid chromatography (HPLC) method for the sensitive simultaneous determination of hydrazine (Hy), monomethylhydrazine (MMH) and 1,1-dimethylhydrazine (UDMH) based upon the derivatization of hydrazines with naphthalene-2,3-dialdehyde and the separation of the derivatives on Zorbax Eclipse AAA column in a single chromatographic run under acidic conditions (pH 2.4) was developed. Hydrazine and monomethylhydrazine derivatives were found to be strongly fluorescent at λ_ex?=?273?nm, λ_em?=?500?nm. It was shown that UDMH derivative can be detected as non-fluorescent hydrazone at 290?nm by UV-detection. Limits of detection were 0.05?µg?·?L^?1 for Hy and MMH, and 1?µg?·?L^?1 for UDMH for the injection volume of 100?µL. The method was validated for water sample analysis. It proved to be selective, accurate and precise with the supplementary advantage of the simple and rapid sample preparation.     

Conformational Isomerism in Monomeric,Low‐Coordinate Group 12 Complexes Stabilized by a Naphthyl‐Substituted m‐Terphenyl Ligand

The synthesis and characterization of the first series of low‐coordinate bis(terphenyl) complexes of the Group 12 metals, [Zn(2,6‐Naph₂C₆H₃)₂] ( 1 ), [Cd(OEt₂)(2,6‐Naph₂C₆H₃)₂] ( 2 ) and [Hg(OEt₂)(2,6‐Naph₂C₆H₃)₂] ( 3 ) (Naph=1‐C₁₀H₇) are described. The naphthyl substituents of the terphenyl ligands confer considerable steric bulk, and as a result of limited flexibility introduce multiple conformations to these unusual systems. In the solid state, complex 1 features a two‐coordinate Zn centre with the ligands oriented in a syn/anti conformation, whereas the three‐coordinate distorted T‐shaped complexes 2 and 3 feature the ligands in the syn/syn configurations. The results of DFT calculations are in good agreement with the solid‐state configurations for these complexes and support the spectroscopic measurements, which indicate several conformers in solution.     

Functionalization of Metal–Organic Frameworks through the Postsynthetic Transformation of Olefin Side Groups

For the first time, the adaptability of the C?C double bond as a versatile precursor for the postsynthetic modification (PSM) of microporous materials was extensively investigated and evaluated. Therefore, an olefin‐tagged 4,4′‐bipyridine linker was synthesized and successfully introduced as pillar linker within a 9,10‐triptycenedicarboxylate (TDC) zinc paddle‐wheel metal–organic framework (MOF) through microwave‐assisted synthesis. Different reactions, predominately used in organic chemistry, were tested, leading to the development of new postsynthetic reactions for the functionalization of solid materials. The postsynthetic oxidation of the olefin side groups applying osmium tetroxide (OsO₄) as a catalyst led to the formation of a microporous material with free vicinal diol functionalities. The epoxidation with dimethyldioxirane (DMDO) enabled the synthesis of epoxy‐functionalized MOFs. In addition to that, reaction procedures for a postsynthetic hydroboration with borane dimethyl sulfide as well as a photoinduced thiol–ene click reaction with ethyl mercaptan were developed. For all of these PSMs, yields of more than 90 % were obtained, entirely maintaining the crystallinity of the MOFs. Since the direct introduction of the corresponding groups by means of pre‐synthetic approaches is hardly possible, these new PSMs are useful tools for the functionalization of porous solids towards applications such as selective adsorption, separation, and catalysis.     

Padé approximants for functions with branch points — strong asymptotics of Nuttall–Stahl polynomials

Let f be a germ of an analytic function at infinity that can be analytically continued along any path in the complex plane deprived of a finite set of points, \({f \in \mathcal{A}(\bar{\mathbb{C}} \setminus A)}\), \({\# A< \infty}\). J. Nuttall has put forward the important relation between the maximal domain of f where the function has a single-valued branch and the domain of convergence of the diagonal Padé approximants for f. The Padé approximants, which are rational functions and thus single-valued, approximate a holomorphic branch of f in the domain of their convergence. At the same time most of their poles tend to the boundary of the domain of convergence and the support of their limiting distribution models the system of cuts that makes the function f single-valued. Nuttall has conjectured (and proved for many important special cases) that this system of cuts has minimal logarithmic capacity among all other systems converting the function f to a single-valued branch. Thus the domain of convergence corresponds to the maximal (in the sense of minimal boundary) domain of single-valued holomorphy for the analytic function \({f\in\mathcal{A}(\bar{\mathbb{C}} \setminus A)}\). The complete proof of Nuttall’s conjecture (even in a more general setting where the set A has logarithmic capacity 0) was obtained by H. Stahl. In this work, we derive strong asymptotics for the denominators of the diagonal Padé approximants for this problem in a rather general setting. We assume that A is a finite set of branch points of f which have the algebro-logarithmic character and which are placed in a generic position. The last restriction means that we exclude from our consideration some degenerated “constellations” of the branch points.     

Enumeration of non-labile oxygen atoms in dissolved organic matter by use of 16O/18O exchange and Fourier transform ion-cyclotron resonance mass spectrometry

We report a simple approach for enumeration of non-labile oxygen atoms in individual molecules of dissolved organic matter (DOM), using acid-catalyzed ¹⁶O/¹⁸O exchange and ultrahigh-resolution Fourier-transform ion-cyclotron-resonance mass spectrometry (FTICR-MS). We found that by dissolving DOM in H₂ ¹⁸O at 95 °C for 20 days it is possible to replace all oxygen atoms of DOM molecules (excluding oxygen from ether groups) with ¹⁸O. The number of exchanges in each molecule can be determined using high-resolution FTICR. Using the proposed method we identified the number of non-labile oxygen atoms in 231 molecules composing DOM. Also, using a previously developed hydrogen–deuterium (H/D)-exchange approach we identified the number of labile hydrogen atoms in 450 individual molecular formulas. In addition, we observed that several backbone hydrogen atoms can be exchanged for deuterium under acidic conditions. The method can be used for structural and chemical characterization of individual DOM molecules, comparing different DOM samples, and investigation of biological pathways of DOM in the environment.     

Energy-momentum conserving discretization of mixed shell elements for large deformation problems

In the present paper we consider structure-preserving integration methods in the context of mixed finite elements. The used low-order mixed finite elements typically exhibit improved coarse mesh accuracy. On the other hand energy-momentum (EM) consistent time-stepping schemes have been developed in the realm of nonlinear structural dynamics to enhance the numerical stability properties. EM schemes typically exhibit superior robustness and thus offer the possibility to use large time steps while still producing physically meaningful results. Accordingly, combining mixed finite element discretizations in space with EM consistent discretizations in time shows great promise for the design of numerical methods with superior coarse mesh accuracy in space and time. Starting with a general Hu-Washizu-type variational formulation we develop a second-order accurate structure-preserving integration scheme. The present approach is applicable to a large number of mixed finite element formulations. As sample application we deal with a specific mixed shell element. Numerical examples dealing with large deformations will show the improved coarse mesh accuracy in space and time of the advocated approach. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison of a mixed least-squares formulation using different approximation spaces

The main goal of the present work is the comparison of the performance of a least-squares mixed finite element formulation where the solution variables (displacements and stresses) are interpolated using different approximation spaces. Basis for the formulation is a weak form resulting from the minimization of a least-squares functional, compare e.g. [1]. As suitable functions for standard interpolation polynomials of Lagrangian type are chosen. For the conforming discretization of the Sobolev space vector-valued Raviart-Thomas interpolation functions, see also [2], are used. The resulting elements are named as P_mP_k and RT_mP_k. Here m (stresses) and k (displacements) denote the approximation order of the particular interpolation function. For the comparison we consider a two-dimensional cantilever beam under plain strain conditions and small strain assumptions. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)