Investigation of a cylindrical chemosorptive denuder for sampling and phase separation of toluene diisocyanate aerosols

A cylindrical chemosorptive denuder in series with a glass fibre filter has been evaluated for sampling toluene diisocyanate (TDI) aerosols. The sampler is designed for measuring personal exposure to diisocyanates. Several denuder coatings and derivatising reagents were investigated. Dimethylpolysiloxane (SE-30) and 5% phenyl dimethylpolysiloxane (SE-54) with either dibutylamine (DBA) or dipentylamine (DPeA) as derivatising reagents yielded the lowest vapour breakthrough (the amount (%) of the vapour that passes through the denuder), close to values predicted by theory. Immobilisation of the SE-30 denuder coating by in-situ cross-linking yielded comparable results. With an SE-30/DBA-coated denuder operating within an airflow range of 100–500 mL min^–1, the phase separation was shown to be consistent with theoretical predictions derived by use of the Gormley–Kennedy equation. This provides a means of calculating the vapour breakthrough and correcting experimentally obtained values with regard to vapour–particulate phase distribution, suggesting that the denuder can provide accurate phase-distribution measurements. The SE-30/DBA denuder can be used over a concentration range spanning nearly six orders of magnitude. Its capacity is sufficient to perform 15-min exposure measurements of a TDI aerosol with air concentrations as high as 1,700 g m^–3, 40 times higher than the Swedish occupational exposure limit (OEL). At the other end of the range, the estimated limit of detection (LOD) was less than 2 ng m^–3 for both the vapour and the aerosol phases when LC–ESI–MS–MS was used for chemical analysis.Electronic Supplementary Material Supplementary material for this article is available at     

Heterobimetallic Cuprates Consisting of a Redox‐Switchable,Silicon‐Based Metalloligand: Synthesis,Structures, and Electronic Properties

A series of bimetallic silyl halido cuprates consisting of the new tripodal silicon‐based metalloligand [κ³N‐Si(3,5‐Me₂pz)₃Mo(CO)₃]^? is presented (pz=pyrazolyl). This metalloligand is straightforwardly accessible by reacting the ambidentate ligand tris(3,5‐dimethylpyrazolyl)silanide ({Si(3,5‐Me₂pz)₃}^?) with [Mo(CO)₃(η⁶‐toluene)]. The compound features a fac‐coordinated tripodal chelating ligand and an outward pointing, “free” pyramidal silyl donor, which is easily accessible for a secondary coordination to other metal centers. Several bimetallic silyl halido cuprates of the general formula [CuX{μ‐κ¹Si:κ³N‐Si(3,5‐Me₂pz)₃Mo(CO)₃}]^? (X=Cl, Br, I) have been synthesized. The electronic and structural properties of these complexes were probed in detail by X‐ray diffraction analysis, electrospray mass spectrometry, infrared‐induced multiphoton dissociation studies, cyclic voltammetry, spectroelectrochemistry, gas‐phase photoelectron spectroscopy, as well as UV/Vis and fluorescence spectroscopy. The heterobimetallic complexes contain linear two‐coordinate copper(I) entities with the shortest silicon–copper distances reported so far. Oxidation of the anionic complexes in methylene chloride and acetonitrile solutions at ${E{{0\hfill \atop 1/2\hfill}}}$ =?0.60 and ?0.44 V (vs. ferrocene/ferrocenium (Fc/Fc⁺)), respectively, shows substantial reversibility. Based on various results obtained from different characterization methods, as well as density functional theory calculations, these oxidation events were attributed to the Mo⁰/Mo^I redox couple.     

Neuronal expression of muskelin in the rodent central nervous system

Background  

The kelch repeat protein muskelin mediates cytoskeletal responses to the extracellular matrix protein thrombospondin 1, (TSP1), that is known to promote synaptogenesis in the central nervous system (CNS). Muskelin displays intracellular localization and affects cytoskeletal organization in adherent cells. Muskelin is expressed in adult brain and has been reported to bind the Cdk5 activator p39, which also facilitates the formation of functional synapses. Since little is known about muskelin in neuronal tissues, we here analysed the tissue distribution of muskelin in rodent brain and analysed its subcellular localization using cultured neurons from multiple life stages.     

Efficient synthesis of branched poly(acrylic acid) derivatives via postpolymerization modification

The utility of pentafluorophenyl esters for the selective introduction of functional units and branch points in well-defined poly(acrylic acid) (PAA) derivatives is demonstrated using a combination of controlled radical polymerization and postpolymerization modification. Reversible addition-fragmentation chain transfer enables the synthesis of well-defined copolymers—poly(pentafluorophenyl acrylate-co-tert-butyl acrylate)—with the active ester repeat units serving as attachment points for reaction with primary amines, specifically tris(2-(t-butoxycarbonyl)ethyl)methyl amine (Behera's amine). Deprotection using trifluoroacetic acid removes both the backbone and side chain t-butyl esters to give a series of branched PAA derivatives containing novel tricarboxylic acid side chains that are well suited to complexation and multidentate interactions. Surprisingly, the active ester homopolymer is shown to have the highest reactivity with Behera's amine when compared to copolymers with lower incorporation of pentafluorophenyl esters, suggesting an intriguing interplay of neighboring group effects and steric interactions. The ability to tune the efficiency of postpolymerization modification gives a library of PAA derivatives.     

Controlled,one-pot synthesis of recyclable poly(1,3-diene)-polyester block copolymers,catalyzed by yttrium β-diketiminate complexes

The one-pot synthesis of well-defined block copolymers of olefins/1,3-dienes and polar monomers, such as cyclic esters and acrylates has long been the focus of intense research. Cationic alkyl rare earth metal catalysts, activated by organoborates, have shown to be promising for the polymerization of isoprene or styrene and ε-caprolactone. In this study, we synthesize a series of yttrium bis(alkyl) complexes supported by simple β-diketiminate ancillary ligands. Subtle changes have been made to the β-diketiminate ligand framework to elucidate the effect of ligand structure on the rate and selectivity of olefin/1,3-diene and cyclic ester polymerization, with small ligand changes having a large impact on the resulting polymerizations. Generation of the active cationic species was easily streamlined by identification of appropriate catalyst : organoborate ratios, allowing for high catalyst efficiencies. Notably, we demonstrate the first cationic rare earth metal alkyl-initiated polymerization of δ-valerolactone and ε-decalactone as well as introduced five new block copolymer morphologies. In addition, selective degradation of the ester block in poly(isoprene-b-caprolactone) enabled recovery of the polyisoprene block with identical spectroscopic and thermal properties. Significantly, recopolymerization of the recovered poly(1,3-diene) with fresh ε-caprolactone reproduced the desired diblocks with nearly identical thermal and physical properties to those of virgin copolymer, illustrating a plausible recycling scheme for these materials.

Ligand features that promote one-pot block copolymerization of 1,3-dienes and cyclic esters were realized with yttrium β-diketiminate complexes. Depolymerization and repolymerization of the polyester block introduced a plausible recycling strategy.     

Metal-salen-base-pair complexes inside DNA: complexation overrides sequence information

Two isomeric salicylic aldehyde nucleobases have been prepared and incorporated into various DNA duplexes. Reaction with ethylenediamine leads to formation of the well-known salen ligand inside the DNA double helix. Addition of transition-metal ions such as Cu(2+), Mn(2+), Ni(2+), Fe(2+), or VO(2+) results in the formation of metal-salen-base-pair complexes, which were studied by using UV and circular dichroism (CD) spectroscopy. HPLC and ESI mass spectrometric measurements reveal an unusually high stability of the DNA-metal system. These metal-salen complexes act as interstrand cross-links and thereby lead to a strong stabilization of the DNA duplexes, as studied by thermal de- and renaturing experiments. Complex formation is strong enough to override sequence information even when the preorganization of the ligand precursors is unfavorable and the DNA duplex is distorted by the metal complexation. Furthermore, melting-point studies show that the salen complex derived from ligand 2 fits better into the DNA duplex, in accordance with results obtained from the crystal structure of the corresponding copper-salen complex 8.     

Microwave-assisted "libraries from libraries" approach toward the synthesis of allyl- and C-cyclopropylalkylamides

Cascade reactions of internal and terminal alkynes, zirconocene hydrochloride, dimethylzinc, and phosphinoyl imines (prepared in one step from aldehydes and diphenylphosphinoyl amide) lead to allylic phosphinoyl amides after aqueous workup. Microwave acceleration allows the completion of this one-pot reaction sequence in 10 min. These allylic amides can be converted into a variety of derivatives, including carbamates and sulfonamides, or reacted prior to workup with diiodomethane to give novel C-cyclopropylalkylamides. A solution-phase "libraries from libraries" approach was used to generate an intermediate 20-member library which was subsequently expanded to a 100-member library by a series of N-functionalizations. The biological activity was evaluated in an assay for competitive binding to the estrogen receptor (ERalpha), revealing three potent lead compounds of a new structural type.     

Cyclometalated Iridium(III) Complexes Containing Semicarbazone Ligands: Synthesis,Characterization, Photophysical and Biological Studies

The synthesis, crystal structure, photophysical properties, and biological activity of the novel bis‐cyclometalated complexes [Ir(ptpy)₂(vnsc)] ( 2 ) and [Ir(ptpy)₂(acsc)] ( 3 ) [ptpy = 2‐(p‐tolyl)pyridinato, vnsc = vanillin semicarbazone, acsc = acetone semicarbazone] are described. The new compounds were prepared by the reaction of [{Ir(μ‐Cl)(ptpy)₂}₂] ( 1 ) with the corresponding semicarbazone ligands under basic conditions. The molecular structure of compound 3 was confirmed by a single‐crystal X‐ray diffraction study. The complex crystallized from chloroform as a mono‐ solvate in the orthorhombic space group Pcab with eight molecules in the unit cell.     

Mobile phase selection for the combined use of liquid chromatography–inductively coupled plasma mass spectrometry and electrospray ionisation mass spectrometry

Four different organic solvents: dimethylformamide, 1,4-dioxane, n-propanol and ethanol were evaluated as alternative organic modifiers to acetonitrile for liquid chromatography (LC) separations. The aim was to establish common sets of chromatographic conditions that could be applied for LC hyphenation to inductively coupled plasma mass spectrometry (ICPMS) as well as to electrospray ionization MS (ESIMS). The approach was to evaluate candidate solvents that, compared to acetonitrile, potentially could give improved analytical performance (low solvent vapor loading, maximized analyte sensitivity and minimized carbon depositions on instrumental parts) in ICPMS analysis while retaining chromatographic and ESIMS performances. The study showed that dimethylformamide, 1,4-dioxane, n-propanol and ethanol all can be advantageous chromatographic modifiers for LC–ICPMS analysis, giving superior performance compared to acetonitrile. For the combined use of LC–ICPMS and LC–ESIMS with a common set of chromatographic conditions, n-propanol gave the best overall performance. The ¹⁹⁵Pt⁺ signal in ICPMS was continuously monitored during a 0–60% organic solvent gradient and at 25% of organic modifier, 100% of the signal obtained at the gradient start was preserved for n-propanol compared to only 35% of the signal when using acetonitrile. Platinum detection limits were 5–8 times lower using n-propanol compared with acetonitrile. Signal-to-noise ratio in continuous ESIMS signal measurements was 100, 90 and 110 for a 100 μg/ml solution of leucine–enkephaline using acetonitrile, ethanol and n-propanol, respectively. Chromatographic efficiency in reversed phase separations was preserved for n-propanol compared to acetonitrile for the analysis of the whole protein cytochrome C and the peptide bacitracin on a column with particle and pore sizes of 5 μm and 300 Å, but slightly deteriorated for the separation of the peptides leucine–enkephaline and bacitracin on a 3 μm and 90 Å column as the peak width at half height for both peptides increased by a factor of two. The performance on the smaller dimensioned column could however be improved by running the separations at 40 °C.