High‐Temperature Stable Zirconia Particles Doped with Yttrium,Lanthanum, and Gadolinium

Zirconia microspheres synthesized by a wet‐chemical sol–gel process are promising building blocks for various photonic applications considered for heat management and energy systems, including highly efficient reflective thermal barrier coatings and absorbers/emitters used in thermophotovoltaic systems. As previously shown, pure zirconia microparticles deteriorate at working temperatures of ≥1000 °C. While the addition of yttrium as a dopant has been shown to improve their phase stability, pronounced grain growth at temperatures of ≥1000 °C compromises the photonic structure of the assembled microspheres. Here, a new approach for the fabrication of highly stable ceramic microparticles by doping with lanthanum, gadolinium, and a combination of those with yttrium is introduced. The morphological changes of the particles are monitored by scanning electron microscopy, ex situ X‐ray diffraction (XRD), and in situ high‐energy XRD as a function of dopant concentration up to 1500 °C. While the addition of lanthanum or gadolinium has a strong grain growth attenuating effect, it alone is insufficient to avoid a destructive tetragonal‐to‐monoclinic phase transformation occurring after heating to >850 °C. However, combining lanthanum or gadolinium with yttrium leads to particles with both efficient phase stabilization and attenuated grain growth. Thus, ceramic microspheres are yielded that remain extremely stable after heating to 1200 °C.     

Microscopic Li self-diffusion parameters in the lithiated anode material Li4 + xTi5O12 (0 < or = x < or = 3) measured by 7Li solid state NMR

The microscopic Li diffusion parameters in the lithiated spinel Li4 + xTi5O12, which is on its way to become a commercially used anode material in Li ion batteries, are probed for the first time via nuclear magnetic resonance spectroscopy.     

Stereoselective preparation of six diastereomeric quatercyclopropanes from bicyclopropylidene and some derivatives

Diastereomeric meso- and d,l-bis(bicyclopropylidenyl) (5) were obtained upon oxidation with oxygen of a higher-order cuprate generated from lithiobicyclopropylidene (4) in 50 and 31 % yield, respectively. Their perdeuterated analogues meso-[D(14)]- and d,l-[D(14)]-5 were obtained along the same route from perdeuterated bicyclopropylidene [D(8)]-3 (synthesized in six steps in 7.4 % overall yield from [D(8)]-THF) in 20.5 % yield each. Dehalogenative coupling of 1,1-dibromo-2-cyclopropylcyclopropane (6) gave a mixture of all possible stereoisomers of 1,5-dicyclopropylbicyclopropylidene 16 in 69 % yield, from which (Z)-cis-16 was separated by preparative gas chromatography (26 % yield). The crystal structure of meso-5 looks like a superposition of the crystal structures of two outer bicyclopropylidene units (3) and one inner s-trans-bicyclopropyl unit, whereas the two outer cyclopropyl moieties adopt a gauche orientation with respect to the cyclopropane rings at the inner bicyclopropylidene units in (Z)-cis-16. Birch reduction with lithium in liquid ammonia of meso-5 and d,l-5 gave two pairs of diastereomeric quatercyclopropanes trans,trans-(R*,S*,R*, S*)-17/cis,trans-(R*,S*,R*,R*)-18 and trans,trans-(R*,S*,S*,R*)-19/cis,trans-(R*,S*,S*,S*)-20 in 97 and 76 % yield, respectively, in a ratio 9:1 for every pair. The latter diastereomer was also obtained as the sole product by Birch reduction of (Z)-cis-16 in 96 % yield. Under the same conditions, tetradecadeuterio analogues trans,trans-[D(14)]-(R*,S*,R*,S*)-17/cis,trans-[D(14)]-(R*, S*,R*,R*)-18 (8:1) and trans,trans-[D(14)]-(R*,S*,S*,R*)-19/cis,trans-[D(14)]-(R*,S*,S*,S*)-20 (12:1) were prepared from meso-[D(14)]-5 and d,l-[D(14)]-5 in 37 and 63 % yield, respectively. Reduction of meso-5 with diimine gave the cis,cis-quatercyclopropane (S*,S*,R*,R*)-21 as the main product (58 % yield) along with the cis,trans-diastereomer (S*,S*,R*,S*)-18 (29 % yield). Thus, five of the six possible diastereomeric quatercyclopropanes were obtained from meso-5, d,l-5, and (Z)-cis-16. The X-ray crystal structure analyses of trans,trans-(R*,S*,R*,S*)-17 and cis,cis-(S*,S*,R*,R*)-21 revealed for the both an unusual conformation in which the central bicyclopropyl unit adopts an s-trans-(antiperiplanar) orientation with phi=180.0 degrees , and the two terminal bicyclopropyl moieties adopt a synclinal conformation with phi=49.8 and 72.0 degrees , respectively. In solution the vicinal coupling constants (3)J(H,H) in trans,trans-(R*,S*,R*,S*)-[D(14)]-17, trans,trans-(R*,S*,S*,R*)-[D(14)]-19, trans,cis-(R*,S*,R*,R*)-[D(14)]-18 and trans,cis-(R*,S*,S*,S*)-[D(14)]-20 were found to be 4.1, 4.7, 5.9 and 5.9 Hz, respectively. This indicates a predominance of the all-gauche conformer in (R*,S*,R*,S*)-17 and a decreasing fraction of it in this sequence of the other diastereomers.     

Four distinctively different decomposition pathways of metastable Supermesityltellurium(IV) trichloride

Chlorination of bis(supermesityl)ditelluride RTeTeR (R = 2,4,6-t-Bu3C6H2) with 3 equiv of sulfuryl chloride SO2Cl2 provided the intrinsically unstable supermesityltellurium(IV) trichloride RTeCl3 (1) as bright yellow crystals. Severe repulsion between the equatorial Cl atom and one tert-butyl group in an ortho position in the supermesityl ligand is the reason for the extreme reactivity of 1, which is in contrast to that of all previously known monoorganotellurium trihalides. In the solid state at room temperature, (the triclinic modification of) 1 reacts slowly under HCl elimination and intramolecular Te-C bond formation to give the bicyclic 5,7-di-tert-butyl-2-hydro-3,3-dimethylbenzo[b]tellurophene-1,1-dichloride (2), which was originally obtained as a colorless amorphous solid. On one occasion, when the solid-state reaction was allowed to occur under air conditions, compound 2 and a colorless crystalline byproduct, namely, trans-supermesityltellurium hydroxide dichloride (3), had formed, from which a few crystals were hand-selected. The formation of 3 has been tentatively rationalized by a solid-state hydrolysis of a second (monoclinic?) modification present in the bulk material of 1. In diethyl ether, THF, or carbon disulfide, a redox equilibrium exists between yellow supermesityltellurium(IV) trichloride RTeCl3 (1), deep blue supermesityltellurenyl(II) chloride RTeCl (4), and chlorine gas, which can be shifted to 4 when the reaction vessel is purged with argon to remove the chlorine gas. Compound 4 was also obtained by the reaction of RTeTeR (R = 2,4,6-t-Bu3C6H2) with 1 equiv of SO2Cl2. When a solution of 1 was stored with an excess of SO2Cl2 for a prolonged amount of time, Te-C bond cleavage occurred and [(Et2OH)2Te2Cl10].2Et2O (5) was formed. Compounds 1-5 have been characterized by X-ray crystallography.     

Synthetic 6-O-methylglucose-containing polysaccharides (sMGPs): design and synthesis

With the hope of mimicking the chemical and biological properties of natural 6-O-methyl-D-glucose-containing polysaccharides (MGPs), synthetic 6-O-methyl-D-glucose-containing polysaccharides (sMGPs) were designed and synthesized from alpha-, beta-, and gamma-cyclodextrins (CDs). The synthetic route proved to be flexible and general, to furnish a series of sMGPs ranging from 6-mer to 20-mer. A practical and scalable method was discovered selectively to cleave the CD derivatives and furnish the linear precursors to the glycosyl donors and acceptors. The Mukaiyama glycosidation was adopted to couple the glycosyl donors with the glycosyl acceptors. Unlike in the 3-O-methyl-D-mannose-containing polysaccharide (sMMP) series, the amount of the Mukaiyama acid required in the sMGP series increased with an increase of substrate size; that is, for large oligomers, more than one equivalent of the acid was required.     

Evaluation of light scattering data from bimodal turbid suspensions: a simple fit procedure

Whereas correlation spectroscopy gives reliable information on the size of immersed particles in those cases where the size distribution is narrow, large problems arise for more complex particle distributions. For instance, samples containing distinctly different particles of rather similar size lead to correlation functions which are very close to those of monodisperse samples. We present a measurement technique which is based on angle dependent measurements of 3D cross correlation functions and an evaluation scheme which uses the results of the Mie theory. The experimental technique warrants applications to strongly scattering samples. Having tested this procedure with mixtures containing standard latex particles we applied it to a sample of skimmed, homogenized milk.     

Cover Picture: Photoprogrammable Organic Light‐Emitting Diodes (Angew. Chem. Int. Ed. 22/2009)

Programmable organic light‐emitting diodes: UV irradiation converts an oxetane‐functionalized dithienylethene derivative from its colorless open form into a dark blue closed form, while visible light reverses the reaction. In the Communication on page 4038 ff., K. Meerholz and co‐workers describe a reversibly switchable organic light‐emitting diode based on this principle.

     

Structural characterization of ß-amyloid oligomer-aggregates by ion mobility mass spectrometry and electron spin resonance spectroscopy

Formation and accumulation of fibrillar plaques and aggregates of ß-amyloid peptide (Aß) in brain have been recognized as characteristics of Alzheimer’s disease (AD). Oligomeric aggregates of Aß are considered critical intermediates leading to progressive neurodegeneration; however, molecular details of the oligomerization and aggregation pathway and the structures of Aß-oligomers are hitherto unclear. Using an in vitro fibril formation procedure of Aß(1–40), ß-amyloid aggregates were prepared and insoluble aggregates separated from soluble products by centrifugation. In this study, ion mobility mass spectrometry (IM-MS) was applied in combination with electron paramagnetic resonance spectroscopy (EPR) to the identification of the components of Aß-oligomers, and to their structural and topographical characterization. The formation of Aß-oligomers and aggregates was monitored by gel electrophoresis, and Aß-oligomer bands were identified by in-gel tryptic digestion and matrix-assisted laser desorption ionization–mass spectrometry (MALDI-MS) to consist predominantly of Aß(1–40) peptide. First, ion mobility-MS studies of soluble Aß-aggregates prepared by incubation for 5 days were performed on a quadrupole time-of-flight mass spectrometer and revealed (1) the presence of at least two different conformational states, and (2), the formation of Met-35 oxidized products. For estimation of the size of Aß-aggregates using EPR spectroscopy, a modified Aß(1–40) peptide containing an additional N-terminal cysteine residue was prepared, and a 3-(2-iodoacetamido)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy radical spin label derivative (IPSL) was coupled by S-alkylation. The EPR spectra of the spin-labeled Cys-Aß(1–40) oligomers were matched with spectra simulations using a multi-component simulation strategy, resulting in complete agreement with the gel electrophoresis results.     

FINITE ELEMENTS WITH LOCAL PROJECTION STABILIZATION FOR INCOMPRESSIBLE FLOW PROBLEMS

In this paper we review recent developments in the analysis of finite element methods for incompressible flow problems with local projection stabilization （LPS）. These methods preserve the favourable stability and approximation properties of classical residual-based stabilization （RBS） techniques but avoid the strong coupling of velocity and pressure in the stabilization terms. LPS-methods belong to the class of symmetric stabilization techniques and may be characterized as variational multiscale methods. In this work we summarize the most important a priori estimates of this class of stabilization schemes developed in the past 6 years. We consider the Stokes equations, the Oseen linearization and the NavierStokes equations. Furthermore, we apply it to optimal control problems with linear（ized） flow problems, since the symmetry of the stabilization leads to the nice feature that the operations ＂discretize＂ and ＂optimize＂ commute.