Access to Paullone Analogues by Intramolecular Heck Reaction

The syntheses of paullone ( 1a ) and three paullone derivatives, including a sulfur analogue ( 2a ), a tricyclic derivative ( 2b ), and a ring‐enlarged variant ( 2c ), are described, Pd‐catalyzed intramolecular Heck reaction being the key step. The kinase‐inhibitory properties of the novel paullone analogues were investigated.     

A Modular Approach to Introduce Function into Single‐Chain Polymeric Nanoparticles

Here, a modular approach is reported to introduce a specific function into single‐chain polymeric nanoparticles (SCPNs). Hereto, an amphiphilic polymer with pendant benzene‐1,3,5‐tricarboxamide (BTA) units is mixed with a “free” BTA that contains a functional group, either a fluorescent naphthalimide or a catalytically active l ‐proline. Taking advantage of hydrophobic interactions and self‐recognition properties of the BTA units, the “free” BTAs are captured into the interior of the SCPN in water as evidenced by fluorescence studies. To illustrate that function can be readily introduced using a modular approach, l ‐proline‐based BTAs are incorporated to procure a catalytically active SCPN in water. The aldol reaction between p‐nitrobenzaldehyde and cyclohexanone shows good conversions at low catalyst loadings and substrate concentrations, and high stereoselectivities are obtained (de = 91% and ee = 98%).

     

First principles and experimental 1H NMR signatures of solvated ions: The case of HCl(aq).

A combined experimental and ab initio study is presented of the 1H NMR chemical shift distribution of aqueous hydrogen chloride solution as a function of acid concentration, based on Car-Parrinello molecular dynamics simulations and fully periodic NMR chemical-shift calculations. The agreement of computed and experimental spectra is very good. From first-principles calculations, we can show that the individual contributions of Eigen and Zundel ions, regular water molecules, and the chlorine solvation shell to the NMR line are very distinct and almost independent of the acid concentration. From the computed instantaneous NMR distributions, it is further possible to characterize the average variation in hydrogen-bond strength of the different complexes.     

Highly fluorescent crystalline and liquid crystalline columnar phases of pyrene-based structures

A concept for highly ordered solid-state structures with bright fluorescence is proposed: liquid crystals based on tetraethynylpyrene chromophores, where the rigid core is functionalized with flexible, promesogenic alkoxy chains. The synthesis of this novel material is presented. The thermotropic properties are studied by means of differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM), and X-ray diffraction. The mesogen possesses an enantiotropic Col(h) phase over a large temperature range before clearing. The material is highly fluorescent in solution and, most remarkably, in the condensed state, with a broad, strongly red shifted emission. Fluorescence quantum yields (Phi(F)) have been determined to be 70% in dichloromethane solution and 62% in the solid state. Concentration- and temperature-dependent absorption and emission studies as well as quantum-chemical calculations on isolated molecules and dimers are used to clarify the type of intermolecular interactions present as well as their influence on the fluorescence quantum yield and spectral properties of the material. The high luminescence efficiency in the solid state is ascribed to rotated chromophores, leading to an optically allowed lowest optical transition.     

Calculation of the auto-bias voltage for RF frequencies well abovethe ion-plasma frequency

A model is presented which describes the coupling of the two RF sheaths in the high-frequency regime for a reactor with different electrodes. The sheaths are coupled by the current-balance equation and the assumption of a harmonic potential difference between the two electrodes. In contrast with most existing models, no assumption is made for either the displacement current or the potential drops across the sheaths. The sheath dynamics are due to an oscillating, step-like electron density profile. The calculations show that the sheaths react nonlinearly to the applied potential. The auto-bias voltage and averaged ion-impact energy coincide reasonably well with experimental data for different reactor types only if one demands that the time-averaged conduction currents flowing towards the electrodes vanish     

Photochemistry of solid C60 with tunable infrared radiation

60 with trains of picosecond infrared (IR) pulses, tuned over the 8–15 μm range, is studied. At some specific wavelengths, white-light emission as well as ejection of ionic species from the solid is observed. The spectral characteristics of the white-light emission resemble those of a black body. The mass distribution of the ejected ionic species shows substantial amounts of C₆₀ coalescence products. Unexpectedly, all these processes only occur at wavelengths where solid C₆₀ is relatively transparent. No white-light emission nor ejection of ionic species is observed when being resonant with an IR-allowed transition of C₆₀. It is concluded that regular C₆₀ is not the chromophore for the observed processes, and that sequential absorption of single photons by a strong absorber that is dilute in the crystal takes place. Plausible chromophores are sites that are intercalated with alkali metals. Accumulation of energy at these sites leads to fullerene coalescence in the solid, ion ejection, and white-light emission, ultimately resulting in the destruction of the C₆₀ molecules. Received: 14 April 1998/Accepted: 22 April 1998     

Inter-laboratory comparison of methods used for analysing polycyclic aromatic hydrocarbons (PAHs) in soil samples

Summary In view of the investigation of contaminated model sites in Baden-Württemberg an inter-laboratory comparison was organized for the methods used for analysing polycyclic aromatic hydrocarbons (PAHs). The laboratories performing chemical and physical analyses at the model sites participated at the request of the Landesanstalt für Umweltschutz, Baden-Württemberg. This inter-laboratory comparison was meant as a first laboratory evaluation, and not as the search for the best method available. Furthermore, it was to show the difficulties in comparing results from different laboratories, which have analysed identical samples. The results of the inter-laboratory comparison between the nine laboratories showed a reproducibility coefficient of variation, for the total of the 16 PAHs according to the EPA, between 48.8 and 61.1% in the concentration range of 5 to 55 mg/kg in the soil samples. One of the laboratories reported significantly lower values compared with the true value. This was probably due to an ill-suited (sample) preparation method. Although the results of the inter-laboratory comparison are, in general, satisfactory, the reproducibility can be improved by standardizing the analytical method for the determination of PAHs in solid environmental samples.