Compositional analysis of multi-element magnetic nanoparticles with a combined NMR and TEM approach

The increasing interest in nanoscale materials goes hand in hand with the challenge to reliably characterize the chemical compositions and structural features of nanosized objects in order to relate those to their physical properties. Despite efforts, the analysis of the chemical composition of individual multi-element nanoparticles remains challenging—from the technical point of view as well as from the point of view of measurement statistics. Here, we demonstrate that zero-field solid-state nuclear magnetic resonance (NMR) complements local, single particle transmission electron microscopy (TEM) studies with information on a large assembly of chemically complex nanoparticles. The combination of both experimental techniques gives information on the local composition and structure and provides an excellent measurement statistic through the corresponding NMR ensemble measurement. This analytical approach is applicable to many kinds of magnetic materials and therefore may prove very versatile in the future research of particulate magnetic nanomaterials.     

Isotope selective photoionization of NaK by optimal control: theory and experiment

We present a joint theoretical and experimental study of the maximization of the isotopomer ratio (23)Na(39)K(23)Na(41)K using tailored phase-only as well as amplitude and phase modulated femtosecond laser fields obtained in the framework of optimal control theory and closed loop learning (CLL) technique. A good agreement between theoretically and experimentally optimized pulse shapes is achieved which allows to assign the optimized processes directly to the pulse shapes obtained by the experimental isotopomer selective CLL approach. By analyzing the dynamics induced by the optimized pulses we show that the mechanism involving the dephasing of the wave packets between the isotopomers (23)Na (39)K and (23)Na (41)K on the first excited state is responsible for high isotope selective ionization. Amplitude and phase modulated pulses, moreover, allow to establish the connection between the spectral components of the pulse and corresponding occupied vibronic states. It will be also shown that the leading features of the theoretically shaped pulses are independent from the initial conditions. Since the underlying processes can be assigned to the individual features of the shaped pulses, we show that optimal control can be used as a tool for analysis.     

On the origin of ionic liquid‐induced variations in hydroxypropyl methacrylate propagation rate coefficients

Pulsed laser polymerizations were used to study the propagation kinetics of hydroxypropyl methacrylate (HPMA) in ionic liquids (ILs) and common organic solvents. The functional monomer was chosen to investigate the complex interplay of all interactions between monomer molecules and between monomer and solvent molecules and to obtain a deeper understanding of the impact of these interactions. The solvent effect on the HPMA propagation rate coefficient (k_p) was examined using a linear solvation energy relationship (LSER) based on Kamlet‐Taft solvatochromic parameters π*, α, and β. The results suggest that dipolarity/polarizability, associated with π*, and hydrogen bond–donating ability of the solvents, accounted for by α, majorly contribute to variations in k_p. Hydrogen bond–accepting (electron pair donating) ability of the solvents (β parameter) is of much lesser importance. In addition, LSER enables the prediction of HPMA k_p based on solvatochromic parameters of the solvents. The results suggest that interactions between the hydroxyl group of the monomer and the anion are dominant compared with classical hydrogen bonding between carbonyl and hydroxyl groups of the monomer units. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3188–3199, 2010     

Membrantrennschichten aus monomolekularen Filmen von synthetischen Glycolipiden

The different steps for the preparation of a new type of membranes are presented. The separation layer of these membranes consists of a well-ordered monolayer comparable to the structure of biological membranes. Several preparative methods are described for the production of synthetic glycolipids. They allow a wide variation with respect to the aliphatic chain and to the sugar head group as well. Most of these surfactants are able to form stable monolayers, a necessary condition for the next steps. Effective cross-linking of the spread monolayers via the hydrophilic head group is demonstrated by qualitative tests. As a supporting carrier for the monolayers suitable membranes are prepared by covering commercial filter paper with a cross-linked layer of poly(oxypropylene) of variable pore size. The material allows the glycolipid monolayer to be transferred quantitatively by the Langmuir-Blodgett technique and has also free functional groups necessary for a chemical fixation.     

Regio- and diastereoselective reactions of chiral secondary alkylcopper reagents with propargylic phosphates: preparation of chiral allenes

The diastereoselective S_N2′-substitution of secondary alkylcopper reagents with propargylic phosphates enables the preparation of stereodefined alkylallenes. By using enantiomerically enriched alkylcopper reagents and enantioenriched propargylic phosphates as electrophiles anti-S_N2′-substitutions were performend leading to α-chiral allenes in good yields with excellent regioselectivity and retention of configuration. DFT-calculations were performed to rationalize the structure of these alkylcopper reagents in various solvents, emphasizing their configurational stability in THF.

The diastereoselective S_N2′-substitution of secondary alkylcopper reagents with propargylic phosphates enables the preparation of stereodefined alkylallenes.     

Two mononuclear Tc complexes: [2,2′‐(3‐phenylpropylimino)‐ and [2,2′‐(propylimino)bis(ethanethiolato)](4‐methoxybenzenethiolato)oxidotechnate(V)

The molecular structures of the two mononuclear title complexes, namely (4‐methoxybenzenethiolato‐κS)oxido[2,2′‐(3‐phenylpropylimino)bis(ethanethiolato)‐κ³S,N,S′]technetium(V), [Tc(C₁₄H₂₁NS₂)(C₇H₇OS)O], (I), and (4‐methoxybenzenethiolato‐κS)oxido[2,2′‐(propylimino)bis(ethanethiolato)‐κ³S,N,S′]technetium(V), [Tc(C₇H₁₅NS₂)(C₇H₇OS)O], (II), exhibit the same coordination environment for the central Tc atoms. The atoms are five‐coordinated (TcNOS₃) with a square‐pyramidal geometry comprising a tridentate 2,2′‐(3‐phenylpropylimino)bis(ethanethiolate) or 2,2′‐(propylimino)bis(ethanethiolate) ligand, a 4‐methoxybenzenethiolate ligand and an additional oxide O atom. Intermolecular C—H...O and C—H...S hydrogen bonds between the monomeric units result in two‐dimensional layers with a parallel arrangement.     

Helium atom scattering from oxide surfaces.

Many experimental methods of surface science employ electrons or photons of considerable incident energy as probe particles. However, insulating surfaces or delicate physisorbed layers may be damaged by these particles and should, therefore, be analyzed with a gentler probe: He atom scattering allows to determine the symmetry of the unit cell and the detection of phase transitions from diffraction measurements as well as the determination of surface and adsorbate vibrations by time-of-flight resolved detection. Herein, the application of He atom scattering to oxide surfaces is demonstrated on the basis of the examples of MgO and ZnO. MgO(001) is a very inert and stable surface, whereas hydrogen atoms are chemisorbed on the mixed-terminated ZnO(1010) and on both polar faces: ZnO(0001) and ZnO(0001). He atom scattering is very sensitive to the presence of hydrogen on surfaces. In addition ZnO reacts with molecules such as water, CO and CO(2). It is demonstrated that in combination with photoelectron spectroscopy and thermal desorption spectroscopy He atom scattering can also contribute to studies of surface chemistry.     

Die Oxoantimonate(III) Rb2Sb8O13 und Cs8Sb22O37: Neue Schicht‐ und Gerüststrukturen mit ‘Lone‐Pair’ ‐Kationen

The Oxoantimonates(III) Rb₂Sb₈O₁₃ and Cs₈Sb₂₂O₃₇: New Framework and Layer Structures with ‘Lone‐Pair’ Cations The oxoantimonates(III) Rb₂Sb₈O₁₃ and Cs₈Sb₂₂O₃₇ were synthezised from Sb₂O₃, the elemental alkali metals (A) and the hyperoxides (AO₂) at 500 °C. The crystal structures of Rb₂Sb₈O₁₃ (monoclinic, P2₁/m, a=743.7(12)pm, b=1724(3)pm, c=1380(2)pm, β=90.44(4) °, Z=4) and Cs₈Sb₂₂O₃₇ (monoclinic, Cc, a=1299.93(11)pm, b=719.87(6)pm, c=3089.9(3)pm, β=96.00(2) °, Z=2) exhibit complex layer (Rb) and framework oxoantimonate ions (Cs), with the Sb^III cation, due to its stereochemically active ‘lone‐pair’, in ψ‐tetrahedral (CN=3) to ψ‐trigonal‐bipyramidal (CN=4) coordination by O.