Dinitrogen chemistry from trigonally coordinated iron and cobalt platforms

This report establishes that trigonally coordinated "[PhBPiPr3]M" platforms (M = Fe, Co) will support both pi-acidic (N2) and pi-basic (NR) ligands at a fourth binding site. The N2 complexes of iron that are described are the first thoroughly characterized examples to exhibit a 4-coordinate geometry. Methylation of monomeric {Fe0(N2)-} and {Co0(N2)-} species successfully derivatizes the beta-N atom of the coordinated N2 ligand and affords the diazenido products {FeII(N2Me)} and {CoII(N2Me)}, respectively. One-electron oxidation of the mononuclear M0(N2)- species produces dinuclear and synthetically versatile MI(N2)MI complexes. These latter species provide clean access to the chemistry of the "[PhBPiPr3]MI" subunit. For example, addition of RN3 to MI(N2)MI results in oxidative nitrene transfer to generate [PhBPiPr3]MNR with concomitant N2 release.     

A homoleptic phosphine adduct of Tl(I)

A homoleptic phosphine adduct of thallium(I) supported by a tris(phosphino)borate ligand has been isolated and structurally characterized.     

Accumulated programming of a complex spectral grating

A complex spectral grating is accumulated by repeated application of a pair of low-power optical programming pulses to a short-term persistent inhomogeneously broadened transition in Tm:YAG at 4.5 K and then probed to investigate the buildup dynamics. The necessary frequency stability is obtained by locking a cw Ti:sapphire laser to a regenerating transient spectral hole in the same transition. Grating accumulation is demonstrated for both a periodic spectral grating, representing a true-time delay, and a complex spectral grating, permitting correlation-based pattern recognition. This work is a step toward demonstrating an optical coherent transient continuously programmed continuous processor.     

Formation of higher cyclic oligomers in polyamide‐4,6

An example of morphology‐steered chemistry of cyclic oligomers with the example of polyamide‐4,6 (PA46) is discussed in this article. The cyclic oligoamide profiles of solid‐state post condensed PA46 show an unusual maximum for intermediate cycles consisting of 10 and 12 amide groups, which are formed in the initial stage of solid state post condensation. This is explained from the short chain length at the start of the post condensation, the preorganization of linear oligomers in the lamellar crystal structure, and the occurrence of amide units in the PA46 lamellar folds. Further the development of the cyclic oligomers up to the cyclic hexadecamide is followed on heating the base polymer in the melt at 310 °C, where it showed to react back to the theoretical Jacobsen and Stockmayer distribution. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Using rheometry to determine nucleation density in a colored system containing a nucleating agent

A new suspension-based rheological method was applied to experimentally study the crystallization of a nucleating agent (NA) filled isotactic polypropylene. This method allows for determination of point nucleation densities where other methods fail. For example, optical microscopy can fail because nucleation densities become too high to be counted (materials with effective NA) or crystallites are not easily visible (colored materials), while differential scanning calorimetry does not allow the effect of flow to be studied. Both quiescent and mild-shear-induced crystallization were investigated. The results show that the addition of a nucleating agent increases the nucleation density by six decades for quiescent crystallization. The effect of shear on crystallization in the presence of a nucleating agent was assessed, and it is demonstrated that, at least for this system, the effect of shear is much smaller than the effect of the nucleating agent.     

Multi-residue screening of veterinary drugs in egg,fish and meat using high-resolution liquid chromatography accurate mass time-of-flight mass spectrometry

The last 2 years multi-compound methods are gaining ground as screening methods. In this study a high-resolution liquid chromatography combined with time-of-flight mass spectrometry (HRLC–ToF-MS) is tested for the screening of about 100 veterinary drugs in three matrices, meat, fish and egg. While the results are satisfactory for 70–90% of the veterinary drugs, a more efficient sample preparation or extract purification is required for quantitative analysis of all analytes in more difficult matrices like egg. The average mass measurement error of the ToF-MS for the veterinary drugs spiked at concentrations ranging from 4 to 400 μg/kg, is 3.0 ppm (median 2.5 ppm) with little difference between the three matrices, but slightly decreases with increasing concentration. The SigmaFit value, a new feature for isotope pattern matching, also decreases with increasing concentration and, in addition, shows an increase with increasing matrix complexity. While the average SigmaFit value is 0.04, the median is 0.01 indicating some high individual deviations. As with the mass measurement error, the highest deviations are found in those regions of the chromatogram where most compounds elute from the column, be it analytes or matrix compounds. The median repeatability of the method ranges from 8% to 15%, decreasing with increasing concentration, while the median reproducibility ranges from 15% to 20% with little difference between matrices and concentrations. The median accuracy is in between 70% and 100% with a few compounds showing higher values due to matrix interference. The squared regression coefficient is >0.99 for 92% of the compounds showing a good overall linearity for most compounds. The detection capability, CCβ, is within 2 times the associated validation level for >90% of the compounds studied. By changing a few conditions in the analyses protocol and analysing a number of blank samples, it was determined that the method is robust as well as specific. Finally, an alternative validation strategy is proposed and tested for screening methods. While the results calculated for repeatability, within-lab reproducibility and CCβ show a good comparison for the matrices meat and fish, and a reasonable comparison for the matrix egg, only 27 analyses are required to obtain these results versus 63 analysis in the traditional, 2002/657/EC, approach. This alternative is suggested as a cost-effective validation procedure for screening methods.     

Literatur

Ohne Zusammenfassung     

A study of the electron quenching of excimers in a KrF* laser excited by a coaxial electron beam

Measurements of the output energy, the optical pulse length and the build-up time of the laser pulse, obtained with a coaxially e-beam pumped KrF^* laser, were performed varying the total gas fill pressure, the F₂ content and the e-beam current from 1–5 bar, 0.1–0.8% and 13.3–26.6 kA, respectively. The maximum specific extraction energy amounts to 64 J/l. The large range of measurements, especially at low F₂ concentrations, reveals the necessity to extend the kinetics of the F₂ chain in the usual computer model. With the introduction of electron quenching of KrF^* and ArF^* by dissociative attachment the predictions are also for low F₂ concentration in agreement with experiments.