Internally coordinated organozinc-transition metal compounds. Crystal structure of (CH3)2N(CH2)3ZnW(ν-C5H5)(CO)3

The stabilities of simple and internally coordinated organozinc-transition metal compounds towards disproportionation have been investigated by the microwave titration technique. Simple alkyl- and aryl-derivatives disproportionate to such an extent as to preclude isolation. Internal coordination was found to stabilize the asymmetric compounds, and several derivatives containing the dimethylaminopropyl group were isolated. The crystal structure of one of them, Me₂N(CH₂)₃-ZnW(Cp)(CO)₃, was determined by a single-crystal X-ray study. The crystals are orthorhombic, space group P2₁2₁2₁, with four molecular units in a cell with parameters a 8.406(1), b 12.179(2) and c 16.642(2) Å. The structure was solved by standard Patterson and Fourier techniques. The refinement, with anisotropic temperature factors for the two heavy atoms, converged at R_F = 0.092 (R_wF = 0.089) for 1536 observed reflections with I>2.5σ(I). The molecule consists of a central tungsten atom, surrounded in a tetragonal pyramidal fashion by a cyclopentadienyl group in the apical position and three carbon monoxyde molecules and a zinc atom occupying the basal positions. The zinc atom is three-coordinate, being surrounded by the tungsten atom and the chelating dimethylaminopropyl group; there is, however, a short intermolecular contact between zinc and a carbonyl oxygen atom at 2.61(3) Å.     

Systematic computer-aided interpretation of infrared and raman vibrational spectra based on the crise program

The CRISE computer program is used to correlate wavenumber regions and 6 structural elements containing carbon, hydrogen and oxygen on the basis of 2 standard files with 549 infrared and Raman spectra. The degree of correlation, including score percentages and interfering percentages, is established for different types of intervals in relation to various intensity thresholds. Specific regions (score 100%, interference 0%) proved to be rare, whereas pseudo-specific regions (score < 100%, interference 0%) are normally present. The usefulness of selective regions (score 100%, interference > 0%) is doubtful. The infrared and Raman results for a structural element can differ appreciably, yet neither technique is clearly superior for interpretative purposes.     

The application of chromatography to the analysis of pharmaceutical creams

Summary The application of GLC, HPLC and TLC to the analysis of pharmaceutical creams is discussed with special attention to sample clean-up. The results of the determination of hydrocortisone acetate, salicylic acid, benzoic acid, diethyl stilbestrol, chloramphenicol, diphenhydramine HCl, tretinoin and some cream base components by reversed phase HPLC are given.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Dynamic imaging of single DNA-protein interactions using atomic force microscopy

Atomic force microscopy (AFM) imaging of static DNA-protein complexes, in air and in liquid, can be used to directly obtain quantitative and qualitative information on the structure of different complexes. For example, DNA length, the location of preferential binding sites for proteins and bending of DNA as a result of the complexation can all be measured. Recording consecutive AFM images of DNA and protein molecules under conditions that they are still able to move and interact, or dynamic AFM imaging, however, can reveal information on the dynamic aspects of the interactions between these molecules. Here, an overview is given of the technical challenges that need to be considered for successful dynamic AFM imaging studies of individual DNA-protein interactions. Necessary technical improvements to the AFM set-up and the development of new sample preparation methods are described in this paper.     

Glutathione Synthesis Is Not Involved in Protection by N-Acetyl cysteine Against UVB-lnduced Systemic Immunosuppression in Mice

The photophysics of 5,10,15,20-tetraarylethynylporphyrinatozinc(II) complexes, 1 and 2, are reported. Compared to 5,10,15,20-tetraphenylporphyrinatozinc(II) (ZnTPP), the UV/visible spectra of 1 and 2 have red-shifted B and Q bands, with the Q bands of increased intensity relative to the B band. FIuorescence quantum yields and lifetimes and triplet quantum yields and lifetimes are similar to ZnTPP. However, quantum yields for in vitro singlet-oxygen generation are much larger than for ZnTPP and for 2 the quantum yield is near unity. These findings suggest that the title compounds could be potential lead compounds as sensitizers for photodynamic therapy.     

Study on the electroreduction of In(III) ions at gold from acidic bromide solutions by the rotating ring-disc electrode technique

The mechanism of the indium electrodeposition on gold from acidic KBr solutions has been investigated by means of the rotating ring-disc electrode technique. The measurements showed that the overall electrode reaction In(III) + 3 e In consists of two successive charge transfer steps, i.e. In(III) + 2 e In(I) and In(I) + e In, with soluble monovalent indium as an intermediate. The current efficiency for In(I) generation under steady-state conditions is 100% in the case of low disc current densities. The disproportionation of In(I) in the bulk of solution occurs in slightly acidified solutions,pH=2, in addition to the In(I) electrochemical reduction. Based on the ring current transients, it was established that the two-electron transfer step is preceded by the formation of a thin passive film of indium metal.

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Untersuchung der elektrochemischen Reduktion von In(III)-Ionen an Gold in sauren Bromidlösungen mit der rotierenden Ring-Scheiben-Elektrode

Zusammenfassung Mit Hilfe der rotierenden Ring-Scheiben-Elektrode wurde der Mechanismus der kathodischen Abscheidung von Indium auf Gold in sauren KBr-Lösungen untersucht. Aus den Messungen folgt, daß die Bruttoreaktion In(III) + 3e In über zwei aufeinanderfolgende Durchtrittsreaktionen, In(III) + 2 e In(I) und In(I) + e In, mit löslichem einwertigem Indium als Zwischenprodukt abläuft. Bei kleinen Stromdichten werden die In(I)-Ionen mit 100%iger Stromausbeute erzeugt. In schwächer sauren Lösungen (pH=2) konnte außer der elektrochemischen Reduktion von In(I) zusätzlich dessen Disproportionierung innerhalb der Lösung ermittelt werden. Auf Grund der Ringstrom-Zeit-Kurven wurde auch festgestellt, daß die Bildung von einer dünnen In-Metallschicht, die ein passives Verhalten aufweist, dem Zweielektronenübergang vorangegangen ist.

     

Disposable ionic liquid coating for headspace solid-phase microextraction of benzene, toluene, ethylbenzene, and xylenes in paints followed by gas chromatography-flame ionization detection

Solid-phase microextraction (SPME) with a disposable ionic liquid (IL) coating was developed for headspace extraction of benzene, toluene, ethylbenzene, and xylenes (BTEX) in paints. The SPME fiber was coated with IL prior to every extraction, then the analytes were extracted and desorbed on the injection port of gas chromatography, and finally the IL coating on the fiber was washed out with solvents. The coating and washing out of IL from the fiber can be finished in a few minutes. This disposable IL-coated fiber was applied to determine BTEX in water-soluble paints with results in good agreement with that obtained by using commercially available SPME fibers. For all the four studied paints samples, the benzene contents were under the detection limits, but relatively high contents of toluene, ethylbenzene and xylenes (56-271 microg g(-1)) were detected with spiked recoveries in the range of 70-114%. Compared to the widely used commercially available SPME fibers, this proposed disposable IL-coated fiber has much lower cost per determination, comparable reproducibility (RSD < 11%), and no carryover between each determination. Considering that IL possess good extractability for various organic compounds and metals ions, and that task-specific IL can be designed and synthesized for selective extraction of target analytes, this disposable IL coating SPME might has great potential in sample preparation.