Determination of airborne isocyanates

Isocyanates are important in industrial hygiene and workplace monitoring. Owing to their severe acute toxicity and sensitizing properties, analytical methods with high sampling efficiency and sensitivity in the low ppb to ppt range are required. The reactivity of isocyanates necessitates initial derivatization with nucleophilic agents—usually amines—for stabilization and enrichment; this is often followed by chromatographic separation with spectroscopic, electrochemical, or mass spectrometric detection. Sampling strategies for airborne isocyanates comprise active, i.e. pumped, or passive, i.e. diffusive, methods; the method selected depends on the application. Whereas active methods rely mainly on impingers, reagent-coated filters, or sampling tubes, passive samplers make use of reagent-coated filters, the surface of which is connected to the air sample by diffusion channels. Because airborne isocyanates are prone to occur in different forms, i.e. as vapors, as aerosols, or adsorbed on particulate matter, denuder sampling has been introduced, thus enabling simultaneous collection of gaseous and aerosol isocyanates. The first part of this review summarizes chemical methods and reagents which have been introduced for derivatization of airborne isocyanates. The advantages and drawbacks of the individual derivatization procedures and their combination with different detection principles are evaluated. In the second part, the most recent developments in air sampling for isocyanates, with special focus on diffusive sampling, are reviewed and critically discussed.     

Identification, synthesis, and conformation of tri- and tetrathiacycloalkanes from marine bacteria

Seven new cyclic natural polysulfides 1-7 were identified in extracts of two bacterial Cytophaga strains (CFB-phylum) isolated from biofilms from the North Sea. Their structures are based on mono- and dimeric-cyclization products of 2-methylpropane-1,2-dithiol 8, which was also present in the extract in trace amounts. The structures were deduced by analysis of their mass spectra and confirmed by synthesis. The 1H NMR spectra of some these compounds suggested a high flexibility of the trithiepane and tetrathiocane systems. Therefore, their conformation was further analyzed by DFT calculations and dynamic NMR spectroscopy. While thiepane 4 possesses a twist-chair lowest energy conformation, its isomers 2 and 3 adopt a chairlike conformation, as does the tetrathiocane 5. In contrast, tetrathiocane 6 favors again a twisted chair conformation.     

The generation of amplified spontaneous emission in high‐power CPA laser systems

An analytical model is presented describing the temporal intensity contrast determined by amplified spontaneous emission in high‐intensity laser systems which are based on the principle of chirped pulse amplification. The model describes both the generation and the amplification of the amplified spontaneous emission for each type of laser amplifier. This model is applied to different solid state laser materials which can support the amplification of pulse durations . The results are compared to intensity and fluence thresholds, e.g. determined by damage thresholds of a certain target material to be used in high‐intensity applications. This allows determining if additional means for contrast improvement, e.g. plasma mirrors, are required for a certain type of laser system and application. Using this model, the requirements for an optimized high‐contrast front‐end design are derived regarding the necessary contrast improvement and the amplified “clean” output energy for a desired focussed peak intensity. Finally, the model is compared to measurements at three different high‐intensity laser systems based on Ti:Sapphire and Yb:glass. These measurements show an excellent agreement with the model.

     

Synergistic effect of the simultaneous chemometric analysis of H NMR spectroscopic and stable isotope (SNIF-NMR,O, C) data: Application to wine analysis

It is known that ¹H NMR spectroscopy represents a good tool for predicting the grape variety, the geographical origin, and the year of vintage of wine. In the present study we have shown that classification models can be improved when ¹H NMR profiles are fused with stable isotope (SNIF-NMR, ¹⁸O, ¹³C) data. Variable selection based on clustering of latent variables was performed on ¹H NMR data. Afterwards, the combined data of 718 wine samples from Germany were analyzed using linear discriminant analysis (LDA), partial least squares-discriminant analysis (PLS-DA), factorial discriminant analysis (FDA) and independent components analysis (ICA). Moreover, several specialized multiblock methods (common components and specific weights analysis (ComDim), consensus PCA and consensus PLS-DA) were applied to the data.     

A Unique Fluoride Nanocontainer: Porous Molecular Capsules Can Accommodate an Unusually High Number of “Rather Labile” Fluoride Anions

The present work refers to the challenging issue of fluoride anion recognition/binding in water by taking advantage of the unique possibilities offered by the porous molecular nanocontainers of the {Mo₁₃₂} Keplerate type allowing the study of a variety of new phenomena. Reaction of the highly reactive carbonate‐type capsule with aqueous HF results in the release of carbon dioxide and integration of an unprecedentedly large number of fluoride anions—partly as coordinated ligands at both the pentagonal units and the linkers, partly as a disordered water/fluoride assembly inside the cavity. The internal assembly and some of the fluoride ligands are easily released, which provides interesting options for future studies regarding coordination chemistry and catalysis under confined conditions.     

{Bis(N,N-di­methyl­form­amide)[μ-N,N′-bis­(salicyl­idene)-1,3-propane­diaminato]­nickel(II)}dibromozinc(II)

The title compound, [NiZnBr₂(C₃H₇NO)₂(C₁₇H₁₆N₂O₂)], is a heterodinuclear nickel complex. The Ni atom has an irregular octahedral environment involving two O and two N atoms from the bis­(salicyl­idene)-1,3-propane­diaminate ligand in the equatorial plane, and two O atoms from the di­methyl­form­amide groups. The Zn—O—Ni, O—Zn—O, Ni—O—Zn and O—Ni—O angles in the bridged plane are 100.1 (2), 79.9 (2), 100.4 (2) and 78.89 (17)°, respectively. The Ni⃛Zn distance is 3.0738 (19) Å.