Derivative des borols : II. Pentaphenylborol: Synthese,reduktion zum dianion und komplexe von kobalt und platin

Analytically pure, dark blue pentaphenylborole (PPB) can be synthesized from 1,1-dibutyl-2,3,4,5-tetraphenylstannole and C₆H₅BCl₂ in toluene in 95% yield. Reduction of PPB with elemental potassium in THF produces brownish red K₂[PPB] which is derived from the new 6π-electron anion [PPB]^2?. The new complexes (C₅H₅)Co(PPB) and (COD)Pt(PPB) (COD = 1,5-cyclooctadiene) are obtained by irradiation of a toluene solution of (C₅H₅)Co(CO)₂ and PPB and by ligand substitution reaction from Pt(COD)₂ and PPB respectively.     

Effect of monovalent and divalent cations on the photoinactivation of bacteria with meso-substituted cationic porphyrins

It is well established that for successful photoinactivation (PI) of gram-negative bacteria a cationic photosensitizer is required. This requirement suggests a charge-dependent interaction between the photosensitizer and the gram-negative bacterium, which may be influenced by the presence of ions in the suspending medium. The aim of the present study was to investigate the effect of cations Na+ and Ca2+ on the efficacy of the PI of the gram-negative Pseudomonas aeruginosa and the gram-positive Staphylococcus aureus. The bacteria were suspended in buffer containing either meso-tetra(N-methyl-4-pyridyl)-porphyrin or meso-mono-phenyl-tri(N-methyl-4-pyridyl)-porphyrin as photosensitizer and various concentrations of Na+ or Ca2+. The cell suspensions were exposed to a broadband light dose of 9 J/cm2. In buffer without added cations, P. aeruginosa and S. aureus were equally sensitive to PI. Addition of cations strongly decreased the sensitivity of both bacteria to PI, with the PI of P. aeruginosa being much more decreased than that of S. aureus, and Ca2+ being more effective than Na+. The decreased sensitivity was accompanied by a reduced binding of the photosensitizers to the bacteria.     

Versatile route to centro-substituted triquinacene derivatives: synthesis of 10-phenyltriquinacene

[reaction: see text] A versatile route to prepare centro-substituted triquinacene derivatives (1, R = various substituents), as exemplified by the preparation of 10-phenyltriquinacene (1, R = Ph), is reported. The quaternary, centro substituent (C-10) was installed by a trimethylsilyl chloride-promoted conjugate addition reaction of an organocuprate, derived from phenylmagnesium bromide, and the protected bicyclic enone (11). The resultant trimethylsilyl enol ether was then converted regioselectively to the C-2-allylated conjugate addition products (13, R = Ph). The allyl moiety, following oxidative cleavage of the carbon-carbon double bond, was used to elaborate the tricyclic ring system by an intramolecular aldol/acetal deprotection reaction. The product of this reaction was then converted to the target compound using a standard series of functional group transformation reactions.     

Nanomaterialien zum Anfassen. Do‐it‐yourself !

Eight selected experiments intend at demonstrating synthesis, properties, function and application of nanomaterials. The reader should be stimulated to “Do‐it‐yourself” experiments at schools as well as at universities. In detail the experiments are: (1) Light scattering of suspensions, (2) Self‐made opals, (3) Quantum‐Size effects and red gold, (4) Surfaces and surface functionalization, (5) Pyrophoric iron, (6) Superparamagnetism and magnetic liquids, (7) TiO₂ and dye‐sensitized solar cells as well as (8) Phosphors and luminescent biomarkers. All experiments are organized to allow for simple and fast implementation, although this implies a certain limitation regarding the quality of the material properties in detail. Altogether, the interest in nanosciences and nanotechnology should be aroused as well as the curiosity to learn even more.     

Reliability of stable carbon and oxygen isotope compositions of pedogenic needle fibre calcite as environmental indicators: examples from Western Europe

Stable carbon and oxygen isotope analyses were conducted on pedogenic needle fibre calcite (NFC) from seven sites in areas with roughly similar temperate climates in Western Europe, including the Swiss Jura Mountains, eastern and southern France, northern Wales, and north-eastern Spain. The δ¹³C values (?12.5 to?6.8 ‰ Vienna Pee Dee Belemnite (VPDB)) record the predominant C₃ vegetation cover at the sites. A good correlation was found between mean monthly climatic parameters (air temperature, number of frost days, humidity, and precipitation) and δ¹⁸O values (?7.8 to?3.4‰ VPDB) of all the NFC. Similar seasonal variations of δ¹⁸O values for monthly NFC samples from the Swiss sites and those of mean monthly δ¹⁸O values of local precipitation and meteorological data point out precipitation and preferential growth/or recrystallisation of the pedogenic needle calcite during dry seasons. These covariations indicate the potential of stable isotope compositions of preserved NFC in fossil soil horizons as a promising tool for palaeoenvironmental reconstructions.     

Vortex Generation in a Liquid Metal Duct Flow near a Magnetic Dipole

The generation of vortical structures by a strong magnetic dipole field in a liquid metal duct flow is studied by means of three-dimensional direct numerical simulations. The dipole is considered as the paradigm for a magnetic obstacle which will deviate the streamlines due to Lorentz forces which act on the fluid elements. Our model uses the quasi-static approximation applicable in the limit of small magnetic Reynolds numbers. The analysis covers the stationary flow regime at smaller flow Reynolds numbers Re as well as the fully time-dependent regimes at higher values with a turbulent flow in the wake of the magnetic obstacle. We present a systematic study of these two basic flow regimes on Re and the Hartmann number Ha, a measure of the strength of the magnetic dipole field. Furthermore, three orientations of the dipole are compared, the streamwise, spanwise and wall-normal ones. The most efficient generation of turbulence at a fixed distance above the duct occurs for the spanwise orientation in which we can observe the formation of Hartmann layers at the top plate. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Measurement of the Mutual Coherence Function of an Incoherent Infrared Field with a Gold Nano-wire Dipole Antenna Array

The first direct measurement of the mutual coherence function of a spatially incoherent infrared beam was performed at 10.6 μm using a pair of infrared dipole nano-wire antennas that were connected to a common bolometer in the center of the pair by short lengths of coplanar strip transmission line. A spatially incoherent source was constructed by dithering a BaF2 diffuser near the focus of a CO2 laser beam. The distance from the diffuser to the nano-wire antenna pair was held constant while the distance from the focus of the laser beam to the diffuser was varied to control the effective diameter of the source. The measured bolometer signal was proportional to the magnitude of the mutual coherence function at the plane of the antennas. The experimental results were found to match the predicted performance closely. If this technology can be extended to large arrays, a form of synthetic aperture optical imaging based on the Van Cittert-Zernike theorem is possible, similar to that performed at microwave frequencies now by astronomers. This has the potential to greatly increase the angular resolution attainable with optical instruments.     

Two precatalysts for application in propargylic CH activation

The complexes {bis[(2‐diphenylphosphanyl)phenyl] ether‐κ²P,P′}(η⁴‐norbornadiene)rhodium(I) tetrafluoridoborate, [Rh(C₇H₈)(C₃₆H₂₈OP₂)]BF₄, and {bis[(2‐diphenylphosphanyl)phenyl] ether‐κ²P,P′}[η⁴‐(Z,Z)‐cycloocta‐1,5‐diene]rhodium(I) tetrafluoridoborate dichloromethane monosolvate, [Rh(C₈H₁₂)(C₃₆H₂₈OP₂)]BF₄·CH₂Cl₂, are applied as precatalysts in redox‐neutral atomic‐economic propargylic CH activation [Lumbroso et al. (2013). Angew. Chem. Int. Ed. 52 , 1890–1932]. In addition, the catalytically inactive pentacoordinated 18‐electron complex {bis[(2‐diphenylphosphanyl)phenyl] ether‐κ²P,P′}chlorido(η⁴‐norbornadiene)rhodium(I), [RhCl(C₇H₈)(C₃₆H₂₈OP₂)], was synthesized, which can form in the presence of chloride in the reaction system.