Iron topochemistry and surface reactivity of amphibole asbestos: relations with in vitro toxicity

Chemical reactivity of asbestos tremolite from Italy and USA localities and Union Internationale Contre le Cancer (UICC) crocidolite was studied in relation to Fe content, oxidation state, and structural coordination. Direct correlation between amount of Fe²⁺ at the exposed M(1) and M(2) sites of the amphibole structure and fiber chemical reactivity was established. The in vitro toxicity of the same samples was investigated on human alveolar A549 cell line. Relationship between crystal-chemical features and cell toxicity is not straightforward. UICC crocidolite has Fe content and chemical reactivity largely higher than that of tremolite samples, but all show comparable in vitro toxic potential. Results obtained evidenced that Fe topochemistry is not a primary factor for induced cell toxicity, though it accounts for asbestos chemical reactivity (and possibly genotoxicity).     

Desorption electrospray ionization ‐ orbitrap mass spectrometry of synthetic polymers and copolymers

Desorption ElectroSpray Ionization (DESI) ‐ Orbitrap Mass Spectrometry (MS) was evaluated as a new tool for the characterization of various industrial synthetic polymers (poly(ethylene glycol), poly(propylene glycol), poly(methylmethacrylate), poly(dimethylsiloxane)) and copolymers, with masses ranging from 500 g.mol⁻¹ up to more than 20 000 g.mol⁻¹. Satisfying results in terms of signal stability and sensitivity were obtained from hydrophobic surfaces (HTC Prosolia) with a mixture water/methanol (10/90) as spray solvent in the presence of sodium salt. Taking into account the formation of multiplied charged species by DESI‐MS, a strategy based on the use of a deconvolution software followed by the automatic assignment of the ions was described allowing the rapid determination of M_n, M_w and PDI values. DESI‐Orbitrap MS results were compared to those obtained from matrix‐assisted laser desorption/ionization‐ time‐of‐flight MS and gel permeation chromatography. An application of DESI‐Orbitrap MS for the detection and identification of polymers directly from cosmetics was described. Copyright © 2012 John Wiley & Sons, Ltd.     

Size-exclusion chromatography using deuterated mobile phases

The effect of deuterated solvents in size-exclusion chromatography (SEC) was studied by comparing intrinsic viscosity measurements, SEC calibration curves, and column efficiency using water-soluble polymers. For aqueous SEC, the use of deuterium oxide slightly increases the SEC elution volume. To verify that adsorption onto the packing was absent, data from exclusion experiments were compared at 35 and 50 degrees C. Our results indicate that adsorption is not occurring for pullulan or polyethylene glycol (PEG)/poly(ethylene oxide) (PEO); for the latter, however, the elution volume increased using both D2O and H2O, indicative of slight hydrodynamic volume contraction of PEG/PEO at higher temperatures. A moderate increase in band broadening (moderate decrease in column efficiency) was observed using D2O. Finally, the effects of chloroform versus deuterated chloroform were evaluated, but no hydrodynamic volume changes were observed.     

Precision and accuracy of the subjective haptic vertical in the roll plane

Background

Autophagy, an intracellular response to stress, is characterized by double membrane cytosolic vesicles called autophagosomes. Prolonged autophagy is known to result in autophagic (Type II) cell death. This study examined the potential role of an autophagic response in cultured cerebellar granule neurons challenged with excitotoxin N-methyl-D-aspartate (NMDA).

Results

NMDA exposure induced light chain-3 (LC-3)-immunopositive and monodansylcadaverine (MDC) fluorescent dye-labeled autophagosome formation in both cell bodies and neurites as early as 3 hours post-treatment. Elevated levels of Beclin-1 and the autophagosome-targeting LC3-II were also observed following NMDA exposure. Prolonged exposure of the cultures to NMDA (8-24 h) generated MDC-, LC3-positive autophagosomal bodies, concomitant with the neurodegenerative phase of NMDA challenge. Lysosomal inhibition studies also suggest that NMDA-treatment diverted the autophagosome-associated LC3-II from the normal lysosomal degradation pathway. Autophagy inhibitor 3-methyladenine significantly reduced NMDA-induced LC3-II/LC3-I ratio increase, accumulation of autophagosomes, and suppressed NMDA-mediated neuronal death. ATG7 siRNA studies also showed neuroprotective effects following NMDA treatment.

Conclusions

Collectively, this study shows that autophagy machinery is robustly induced in cultured neurons subjected to prolonged exposure to excitotoxin, while autophagosome clearance by lysosomal pathway might be impaired. Our data further show that prolonged autophagy contributes to cell death in NMDA-mediated excitotoxicity.     

Gas‐Phase Interactions between Lead(II) Ions and Cytosine: Tandem Mass Spectrometry and Infrared Multiple‐Photon Dissociation Spectroscopy Study

Gas‐phase interactions between Pb²⁺ ions and cytosine (C) were studied by combining tandem mass spectrometry, infrared multiple photon dissociation spectroscopy, and density functional theory (DFT) calculations. Both singly and doubly charged complexes were generated by electrospray. The [Pb(C)?H]⁺ complex was extensively studied, and this study shows that two structures, involving the interaction of the metal with the deprotonated canonical keto‐amino tautomer of cytosine, are generated in the gas phase; the prominent structure is the bidentate form involving both the N1 and O2 electronegative centers. The DFT study also points out a significant charge transfer from the nucleobase to the low‐lying p orbitals of the metal and a strong polarization of the base upon complexation. The various potential energy surfaces explored to account for the fragmentation observed are consistent with the high abundance of the [PbNH₂]⁺ fragment ion.     

Particle Sizing by Photon Correlation Spectroscopy. Part IV: Resolution of bimodals and comparison with other particle sizing methods

The practical performances of single and multi-angle photon correlation spectroscopy (PCS) for resolving bimodal distributions of industrial poly (methyl methacrylate) samples was investigated in a comparative study by several users affiliated to academic and industrial groups and by two suppliers of commercial equipment. The results for the harmonic intensity averaged diameters obtained by cumulants analysis reported by the different laboratories are in agreement, in addition to the results for the normalized second cumulants. The uncertainty on the latter quantities is large, however. For the bimodal samples with two populations with average diameters in a ratio of about 2.5 : 1, not all users were able to resolve the distribution in its components by single-angle PCS. Some slight improvement was obtained by multi-angle PCS. Other indirect techniques (polarization intensity differential scattering, static light scattering data and disc photosedimentometer) appeared to be superior for resolving the bimodal distributions.     

Assignment strategy for proteins with known structure

In protein NMR the assignment of nuclear spin resonances is a prerequisite for all subsequent applications, such as studies of ligand binding, protein-DNA interactions, and dynamics. Resonance assignment is a time consuming step even when the 3D x-ray structure of the protein is available. A new strategy is presented to solve the "inverse" assignment problem, which is the determination of the NMR resonance assignment from a known 3D protein structure. The protocol employs NMR data in the form of residual dipolar couplings and chemical shifts, while it does not require any sequential NMR connectivity information. The assignment problem is mathematically formulated in terms of a weighted matching problem that can be computationally efficiently solved by a combinatorial optimization algorithm. The protocol is applied to ubiquitin using two or three residual dipolar couplings per amino acid measured in Pfl phage medium together with chemical shift information. The algorithm yields for more than 90% of the protein backbone resonances the correct assignment.     

Synthése totale d'α-disaccharidyles de tridésoxy-2,5,6-streptamine apparentés aux aminosides à partir du maltose et du lactose

Total synthesis of α-disaccharidyl-2,5,6-trideoxy-streptamines related to aminoglycoside antibiotics derived from maltose and lactose The synthesis of the hitherto unknown 4-O-substituted α-linked pseudo-tri-saccharides 1,2 and 3 is described. The key intermediates required in the reaction sequence are the glycals 12, 13 and 14 , prepared from maltose, lactose and the chiral ditosyloxy-cyclohexanol 15 , readily accessible from quinic acid. The pivotal step in the reaction's scheme - a stereospecific α-glycosylution procedure -, is an acid-catalyzed addition of the alcohol 15 to the glycals 12, 13 and 14 leading to the corresponding 2,3-unsaturated trisaccharides. The latter compounds were transformed to the target α-glycosides of 2,5,6-trideoxystreptamine 1, 2 and 3 which were devoid of significant antibacterial activity. These results indicate that the presence of an ether linkage at the position 4′ is probably critical for antibacterial activity.