Salen‐Based Coordination Polymers of Manganese and the Rare‐Earth Elements: Synthesis and Catalytic Aerobic Epoxidation of Olefins

Treatment of N,N′‐bis(4carboxysalicylidene)ethylenediamine (H₄L), with MnCl₂ ? (H₂O)₄, and Ln(NO₃)₃ ? (H₂O)_m (Ln=Nd, Eu, Gd, Dy, Tb), in the presence of N,N‐dimethylformamide (DMF)/pyridine at elevated temperature resulted (after work up) in the formation of 1D coordination polymers {[Ln₂(MnLCl)₂(NO₃)₂(dmf)₅] ? 4 DMF}_n ( 1 – 5 ). In these coordination polymers the rare earth ions are connected through carboxylate groups from Mn–salen units in a 1D chain structure. Thus, the Mn–salen complex acts as a “metalloligand” with open coordination sites. All compounds were used as catalysts in the liquid‐phase epoxidation of trans‐stilbene with molecular oxygen, which resulted in the formation of stilbene oxide. Since the choice of the lanthanide had virtually no influence on the performance of the catalyst, only the manganese–gadolinium was studied in detail. The influence of solvent, catalyst concentration, reaction temperature, oxidant, and oxidant flow rate on conversion, yield, and selectivity was analyzed. A conversion of up to 70 %, the formation of 61 % stilbene oxide (88 % selectivity), and a TON of 84 were observed after 24 h. A hot filtration test confirmed that the reaction is mainly catalyzed through a heterogeneous pathway, although a minor contribution of homogeneous species could not be completely excluded. The catalyst could be reused without significant loss of activity.     

Multivalent interaction and selectivities in selectin binding of functionalized gold colloids decorated with carbohydrate mimetics

Colloidal gold particles with functionalized organic shells were applied as novel selectin binders. The ligand shell was terminated with different monocyclic carbohydrate mimetics as simplified analogs of the sLe(x) unit found in biological selectin ligands. The multivalent presentation of the sulfated selectin binding epitopes on the gold particles led to extremely high binding affinities towards L- and P-selectin and IC(50) values in the subnanomolar range. Depending on the ring size of the sulfated carbohydrate mimetic, its substitution pattern and its configuration, different selectivities for either L-selectin or P-selectin were obtained. These selectivities were not found for gold particles with simple acyclic sulfated alcohols, diols and triols in the ligand shell. In addition, the influence of the particle size and the thickness of the hydrophobic organic shell were systematically investigated.     

On the Sensitiveness of Absorption Coefficient to Changes in Material Parameters

An essential property of porous absorbers is the resistance to the incident sound wave, resulting in a damping effect. Damping results from the friction between air molecules and absorber pore-walls. In practice, the known dependencies of the sound absorption coefficient are used in the design of absorbers. But not every material can be characterized by a one-parameter model. The reliability of prediction can be improved by using detailed material models. Hence, additional material parameters, especially the pore geometry are needed. Since in practice the effort for determining material parameters must be minimized, this paper discusses the sensitivity of prediction of absorbers' performance depending on the influence of material parameters that are input for the prediction model chosen. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zwitterionic [(4‐n‐Alkyl‐1,4‐bisazoniacyclohex‐1‐yl)methyl]pentafluorosilicates: A New Class of Surface‐Active Compounds with a Hexacoordinate Silicon Atom

A series of [(4‐n‐alkyl‐1,4‐bisazoniacyclohex‐1‐yl)methyl]pentafluorosilicates (alkyl = hexyl, heptyl, octyl, nonyl, decyl; compounds 14 – 18 ) were synthesized and studied for their surface activity. The zwitterionic pentafluorosilicates with hexacoordinate Si atoms 14 – 18 were prepared by reaction of the respective [(4‐n‐alkylpiperazin‐1‐yl)methyl]trimethoxysilanes [obtained by treatment of (MeO)₃SiCH₂Cl with the respective n‐alkylpiperazine in the presence of NEt₃] with HF in water/ethanol. Surface tension measurements with solutions of 14 – 18 in 0.01 M hydrochloric acid proved that these compounds are surfactants, the increase of the n‐alkyl chain length resulting in an increase of surface activity ( 14 → 18 ). The equilibrium surface tension vs concentration isotherms for 14 – 17 (solutions of “surface‐chemically pure” samples in 0.01 M hydrochloric acid) were analyzed quantitatively.     

Synthesis and Structural Characterization of Cationic Complexes with Hexacoordinate Silicon(IV) and Three Bidentate 1‐Oxopyridine‐2‐olato(1–) Ligands

The cationic complexes with hexacoordinate silicon(IV), tris[1‐oxopyridine‐2‐olato(1–)]silicon(IV) trifluoromethanesulfonate ( 4 ), 4 · ¹/₂ C₅H₅NO₂, tris[1‐oxopyridine‐2‐olato(1–)]silicon(IV) ethyl sulfate–ethanol ( 5 · EtOH), and tris[1‐oxopyridine‐2‐olato(1–)]silicon(IV) isopropyl sulfate ( 6 ), were synthesized. The identities of 4 , 4 · ¹/₂ C₅H₅NO₂, 5 · EtOH, and 6 were established by elemental analyses (C, H, N, S), mass‐spectrometric studies (FAB MS) as well as solid‐state (²⁹Si) and solution (¹H, ¹³C, ¹⁹F, ²⁹Si) NMR experiments. In addition, 4 · ¹/₂ C₅H₅NO₂ was structurally characterized by single‐crystal X‐ray diffraction.     

3D Arrangement of Magnetic Particles in Thin Polymer Films Assisted by Magnetically Patterned Exchange Bias Layer Systems

The possibility to arrange and embed magnetic micro- and nanoparticles in thin polymer film systems using flat magnetically patterned substrate templates is investigated. In contrast to self-organized particle rows forming by applying a homogeneous magnetic field, particles adapt to the magnetic field landscape of the substrate's magnetic pattern prior to polymer crosslinking. Crosslinking then fixes the particle positions in the polymer. The process is tested for composites of hydrophobic polydimethylsiloxane (PDMS) and maghemite nanoparticles as well as for hydrophilic polyvinyl alcohol (PVOH) and hydrophilic functionalized, superparamagnetic core–shell microspheres. The substrate template is an exchange bias layer system magnetically patterned into parallel-stripe domains with in-plane magnetizations and head-to-head/tail-to-tail remanent magnetization orientation in adjacent magnetic domains. A high occupancy percentage of magnetic beads on a domain wall as well as anisotropic actuation of the composite is achieved.     

Polypropylene-Clay Nanocomposites: Comparison of Different Layered Silicates

In former studies of the preparation of polypropylene(PP)-clay nanocomposites, different types of layered silicates were used. However, the obtained results were not comparable due to different preparation conditions and types of silicates. The aim of this work was the investigation of the influence of different layered silicates on the properties of the resulting nanocomposites. FT-IR-spectra, SAXS, TEM micrographs, elemental analysis, mechanical properties and surface tension measurements were used for the comparison of the four different layered silicates under investigation.     

Generation of Supraclusters and Nanoclusters Using Laser Desorption/Ionisation Mass Spectrometry

Laser desorption/ionisation of discrete molecular clusters combined with time-of-flight (TOF) or Fourier-transform ion cyclotron resonance (FTICR) mass spectrometry affords spectra in which extensive higher mass clusters are observed. The size of the largest cluster aggregates (or supraclusters) is of the same order of magnitude as nanoclusters. The spectra obtained using TOF mass spectrometry sometimes exhibit post-source decay fragmentation, depending upon the operational conditions employed during data acquisition, which, although providing useful data on the ligand dissociation dynamics, complicate spectral interpretation. Complementary FTICR mass spectra are free of such features. The identities of the supra/nanoclusters generated from the molecular cluster precursors have not been conclusively established but are mostly coordinatively unsaturated. Density functional molecular orbital calculations have identified the possible structures of the comparatively simple electronically unsaturated system, [Ru₃(CO)₆]^–, that provides a clue to the aggregation mechanism.     

Immobilisation and characterisation of the demineralised, fully hydrated organic matrix of nacre - An atomic force microscopy study

Mimicry of the tough natural composite nacre in future bioengineering requires knowledge of the biomineralisation process. The insoluble organic matrix isolated from the shell of the gastropod Haliotis laevigata was characterised by protein chemistry, topographical and mechanical measurements. Demineralisation of nacre in dilute acetic acid or ethylenediaminetetraacetic acid revealed a set of soluble proteins and the insoluble matrix. The insoluble matrix contains a chitin core and firmly attached proteins, which could be removed by sodium dodecyl sulfate and glycerol indicating a hydrophobic interaction. Atomic force microscopy images of the native insoluble matrix showed a filamentous network with pores or holes, where the filaments showed globular attachments of different sizes, possibly the attached protein molecules. During direct observation of protein degradation imaged by atomic force microscopy the insoluble matrix gets smooth and flat indicating the removal of the attached proteins by proteases. We propose a model of protein coated chitin filaments for the insoluble matrix of nacre. Mechanical measurements by force mapping revealed a Young's modulus depending on the hydration state of the organic layers. The fully hydrated organic matrix has an elastic modulus below 1MPa comparable to some hydrogels.