Alkaline metal oxoantimonates(III), A3[SbO3] (A = K or Cs)

The two title trialkaline trioxoantimonates(III), tripotassium trioxoantimonate(III), K₃[SbO₃], (I), and tricaesium trioxo­antimonate(III), Cs₃[SbO₃], (II), crystallize in the cubic Na₃[AsS₃] structure type in space group P2₁3. The structures show discrete Ψ-tetrahedral [SbO₃]³⁻ anions with C_3v point-group symmetry. The Sb—O distances are 1.923 (4) Å in (I) and 1.928 (2) Å in (II), and the O—Sb—O bond angles are 99.5 (2)° in (I) and 100.4 (1)° in (II).     

Polyelectrolyte complex formation between poly(diallyldimethyl-ammonium chloride) and copolymers of acrylamide and sodium-acrylate

 The interaction between oppositely charged polyelectrolytes, in this study poly(diallyldimethylammonium chloride) (PDADMAC) and copolymers of acrylamide and sodium-acrylate differing in their chain length and charge density parameter (ξ) was investigated in relation to the molar charge ratio of anionic to cationic charges (n ₋/n ₊). The molecular weights of the polyelectrolytes used were 2.9·10⁵g/mol for PDADMAC and for the polyacrylamide copolymers 14 ·10⁶g/mol as well as 5·10⁵g/mol obtained by ultrasonic degradation of the high molecular weight copolymers. The charge density parameters of the polyanions used (ξ ^PR ) varied between 0.14 and 0.64. Complexation between PDADMAC and high molecular weight polyanions leads mainly to macroscopic phase separation whereas the degraded polyanions and PDADMAC formed soluble complexes as well as stable dispersions, if charge excess was available. Precipitates and dispersions were characterized by several methods such as element analysis, thermogravimetry, pyrolysis-GC/MS, PEL titration, ζ-potential measurements, determination of turbidity, particle size measurements and determination of carbon content (TOC).  All precipitated complexes include about 20% water and are of 1:1 stoichiometry concerning ionic binding. Investigations of dispersions confirm 1:1 stoichiometry of complex particles stabilized by excess polyelectrolyte and soluble complexes. It was also found that the particle size can be varied via the charge density parameter of the polyanions used in the range of negative charge excess. Received: 21 June 2001 Accepted: 9 October 2001     

Steviosid aus Süßkraut

The diterpene glycoside stevioside is the most abundant among a group of sweet steviol glycosides, present in sweetleaf (Stevia rebaudiana), which is naturally occurring in Paraguay. It has already been used by the Guarani Indians as a sweetener. Since 2011 such “steviosides” have an EU approval as sweeteners E 960. They taste ca. 250 times sweeter than sucrose. Meanwhile, they have got a significant recognition, not least due to their use in Coca Cola life®. We describe the isolation of stevioside and rebaudioside A from dried leaves of the sweetleaf plant. The complete set of spectra for stevioside is reported. Based on students' laboratory work this project is a follow up of the book “Classics in Spectroscopy” by S. Berger und D. Sicker (Wiley‐VCH 2009).     

Cationic,Methylene‐Bridged,Intramolecular Donor‐Acceptor Systems Based on Zirconium and Hafnium and Phosphino‐methanides

A new access to cationic zirconium and hafnium compounds [L₂MCH₂PR₂][MeB(C₆F₅)₃] (L = Cp, Ind; R = iso‐Pr, tert‐Bu; M = Zr, Hf) exhibiting an intramolecular donor‐acceptor system was established by treating the precursors L₂M(Me)CH₂PR₂ with B(C₆F₅)₃ (BCF). Precursors 1 – 6 [L₂M(Me)CH₂PR₂ with L = Cp, Ind; R = iso‐Pr, tert‐Bu; M = Zr, Hf] were fully characterized. The crystal structures of these compounds revealed large M–CH₂–P bond angles with values of about 134° indicating the absence of interactions between the Lewis‐acid and Lewis‐base. The cationic compounds [L₂MCH₂PR₂][MeB(C₆F₅)₃] ( 7 – 12 ) were obtained by treatment of 1 – 6 with BCF. They were characterized by NMR spectroscopy, mass spectrometry, and elemental analyses; in H/D‐scrambling experiments with H₂/D₂ mixtures 7 – 12 disclosed their reactivity towards cleavage of hydrogen.     

Structure‐Directing Forces in Intercluster Compounds of Cationic [Ag14(CCtBu)12Cl]+ Building Blocks and Polyoxometalates: Long‐Range versus Short‐Range Bonding Interactions

Crystallization of [Ag₁₄(C?CtBu)₁₂Cl][BF₄] and different polyoxometalates in organic solvents yields a series of new intercluster compounds: [Ag₁₄(C?CtBu)₁₂Cl(CH₃CN)]₂[W₆O₁₉] ( 1 ), (nBu₄N)[Ag₁₄(C?CtBu)₁₂Cl(CH₃CN)]₂[PW₁₂O₄₀] ( 2 ), and [Ag₁₄(C?CtBu)₁₂Cl]₂[Ag₁₄(C?CtBu)₁₂Cl(CH₃CN)]₂[SiMo₁₂O₄₀] ( 3 ). Applying the same technique to a system starting from polymeric {[Ag₃(C?CtBu)₂][BF₄]?0.6 H₂O}_n and the polyoxometalate (nBu₄N)₂[W₆O₁₉] results in the formation of [Ag₁₄(C?CtBu)₁₂(CH₃CN)₂][W₆O₁₉] ( 4 ). Here, the Ag₁₄ cluster is generated from polymeric {[Ag₃(C?CtBu)₂][BF₄]?0.6 H₂O}_n during crystallization. In a similar way, [Ag₁₅(C?CtBu)₁₂(CH₃CN)₅][PW₁₂O₄₀] ( 5 ) has been obtained from {[Ag₃(C?CtBu)₂][BF₄]?0.6 H₂O}_n and (nBu₄N)₃[PW₁₂O₄₀]. The use of charged building blocks was intentional, because at these conditions the contribution of long‐range Coulomb interactions would benefit most from full periodicity of the intercluster compound, thus favoring formation of well‐crystalline materials. The latter has been achieved, indeed. However, as a most conspicuous feature, equally charged species aggregate, which demonstrates that the short‐range interactions between the “surfaces” of the clusters represent the more powerful structure direction forces than the long‐range Coulomb bonding. This observation is of significant importance for understanding the mechanisms underlying self‐organization of monodisperse and structurally well‐defined particles of nanometer size.     

SAXS in combination with a free liquid jet for improved time-resolved in situ studies of the nucleation and growth of nanoparticles

A new setup for fast in situ SAXS studies of early stages in the nucleation and growth of colloidal nanoparticles is presented. Evading the disturbing influence of container walls and minimizing the possibility of beam-induced reactions, the benefits of the setup are demonstrated exemplarily for the well-known synthesis of gold nanoparticles via the Turkevich method. Analysis with the new experimental setup reveals the initial rate of particle formation, and enables analysis of particle growth rates.     

Nanoassemblies with light‐responsive size and density from linear flexible polyelectrolytes

This study presents electrostatically self‐assembled nanoparticles from linear flexible polyelectrolytes (poly(diallyldimethylammonium chloride or quarternized poly(4‐vinylpyridine)) and an ionic photo‐isomerizable azo dye (Acid Yellow 38) that can change their size upon UV‐light irradiation. Assemblies with narrow size distribution are stable in aqueous solution. For samples with under‐stoichiometric dye load, UV‐light exposure triggers a size decrease, e.g. from a hydrodynamic radius of R_h = 94 nm to R_h = 62 nm for an Ay38‐PDADMAC sample with a charge ratio of l_charge = 0.7. Size changes are caused by trans‐cis isomerization of the dye, accompanied by a change in hydrophilicity, binding enthalpy and entropy. Assemblies are characterized by static and dynamic light scattering, atomic force microscopy, UV–vis spectroscopy and isothermal titration calorimetry. Zeta potential measurements give insight into the electrostatic stabilization and size‐control of the ionic nano‐assemblies, revealing a master curve of effective surface charge density versus hydrodynamic radius. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys., 2013     

Approaches to mathematical design of ballistic experiment: Part I

Mathematical expedients used in designing ground tests of aerodynamic object models with the aim of finding experimental conditions optimal in terms of the body and accuracy of extracted information are described. In the first part of this paper, the method used in designing ballistic experiment is demonstrated with processing of single-experiment data. In the second part, the validity of the design approach is illustrated by simultaneously processing trajectory data obtained in several experiments.     

Design of plasmonic nanoantennae for enhancing spontaneous emission

We apply two- and three-dimensional numerical calculations to study optical nanoantennae made of two coupled gold nanostructures, enclosing a single emitter in their gap. We show that, using structures manufacturable with today's nanotechnology, it is possible to increase the radiative decay rate by three orders of magnitude while keeping a quantum efficiency larger than 80% in the near-infrared regime. We examine the competition between the radiative and nonradiative processes in the presence of the antennae as a function of wavelength and antenna geometry. Our results hold great promise for improving the quantum efficiency of poor emitters such as silicon nanocrystals or carbon nanotubes.