Vapor-particle partitioning of hydrocarbons in Western Mediterranean urban and marine atmospheres

An analytical procedure is described for a comprehensive determination of the composition of hydrocarbons in the atmosphere, based on: (a) aerosol filtration and subsequent adsorption of the vapor phase onto active charcoal and polyurethane foam; (b) GPC and HPLC fractionation of the extracts, and (c) analysis of the fractions by GC-MS under EI and NICI modes. Special emphasis is placed onn-alkanes, PAHs and their oxygenated derivatives.The characterization of samples collected in a coastal urban area (Barcelona city), and far away over the Western Mediterranean, at sea level and at 1100 m of altitude, revealed significant changes in the aerosol composition, mainly attributed to initial vapor-particle partitioning processes, influenced by ambient temperature variations, and to others taking place during long-range atmospheric transport, related with the different compound photoreactivities and with an unexplained source-decoupling phenomenon.     

电子探针定量分析的标准样品——几种多元氧化物单晶

在很高的温度和适宜的生长条件下,分别采用熔盐籽晶法和高温引上法生长了高质量的YAP、NAB、KTP、LN、BBO、SBN等多元氧化物单晶,它们具有优良的物理化学性能,严格的化学比,固定的组成与结构以及较好的化学均匀性和电子束轰击下的稳定性。广泛地用于激光和非线性光学领域。我们选用这些晶体为原材料研制电子探针定量分析的标准样品。经过测量和标定,这些单晶标样符合中华人民共和国国家标准GB 4930-85(电子探针显微分析标准样品通用技术条件)的规定。含有稀土元素的标样如NAB和YAP能发出绿色荧光,是电子显微术中理想的阴极发光材料。     

CHIP-mediated hyperubiquitylation of tau promotes its self-assembly into the insoluble tau filaments

The tau protein is a highly soluble and natively unfolded protein. Under pathological conditions, tau undergoes multiple post-translational modifications (PTMs) and conformational changes to form insoluble filaments, which are the proteinaceous signatures of tauopathies. To dissect the crosstalk among tau PTMs during the aggregation process, we phosphorylated and ubiquitylated recombinant tau in vitro using GSK3β and CHIP, respectively. The resulting phospho–ub-tau contained conventional polyubiquitin chains with lysine 48 linkages, sufficient for proteasomal degradation, whereas unphosphorylated ub-tau species retained only one–three ubiquitin moieties. Mass-spectrometric analysis of in vitro reconstituted phospho–ub-tau revealed seven additional ubiquitylation sites, some of which are known to stabilize tau protofilament stacking in the human brain with tauopathy. When the ubiquitylation reaction was prolonged, phospho–ub-tau transformed into insoluble hyperubiquitylated tau species featuring fibrillar morphology and in vitro seeding activity. We developed a small-molecule inhibitor of CHIP through biophysical screening; this effectively suppressed tau ubiquitylation in vitro and delayed its aggregation in cultured cells including primary cultured neurons. Our biochemical findings point to a “multiple-hit model,” where sequential events of tau phosphorylation and hyperubiquitylation function as a key driver of the fibrillization process, thus indicating that targeting tau ubiquitylation may be an effective strategy to alleviate the course of tauopathies.

Multiple-hit model for tau aggregation, where sequential events of tau phosphorylation and hyperubiquitylation function as a key driver of the fibrillization process.     

Selective binding of the cyano group in acrylonitrile adsorption on Si(100)-2 x 1

The covalent binding of acrylonitrile (CH(2)=CH-C triple bond N) and the formation of a C=C-C=N structure on Si(100) have been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and density functional theory (DFT) calculations. For chemisorbed acrylonitrile, the absence of nu(C triple bond N) at 2245 cm(-1) and the appearance of nu(C=N) at 1669 cm(-1) demonstrate that the cyano group directly participates in the interaction with Si(100), which is further supported by XPS and UPS observations. Our experimental results and DFT calculations unambiguously demonstrate a [2 + 2] cycloaddition mechanism for acrylonitrile chemisorption on Si(100) through the binding of C triple bond N to Si dimers. The resulting chemisorbed monolayer with a C=C-C=N skeleton can serve as a precursor for further chemical syntheses of multilayer organic thin films in a vacuum and surface functionalization for in situ device fabrication.     

Large-volume stacking in capillary electrophoresis using pH hysteresis of the electroosmotic flow in a bare fused-silica capillary

For large-volume stacking with the electroosmotic flow pump (LVSEP) in capillary electrophoresis of anionic analytes it is required that the electroosmotic mobility (EOM) should be smaller than the magnitudes of the effective mobilities of the analytes. When a fused-silica capillary is treated with an acidic solution, the silanoate group on the silica surface is neutralized to silanol and the EOM is suppressed. Due to the slow deprotonation equilibrium of the silanol group at an intermediate pH, this reduced EOM can be retained during a number of electrophoresis runs. Using a bare fused-silica capillary preconditioned with 0.01 M HCl, successful LVSEP at pH 6.0 was achieved for weakly acidic compounds with two orders of magnitude enhancements in the concentration sensitivity. The repeatability in migration times of ten analytes stacked by LVSEP in a single day was excellent with the relative standard deviation (RSD) less than 1% (n = 6). The day-to-day repeatability was also excellent with RSD less than 3% (n = 3 x 6) when the capillary was preconditioned each day.     

Structural determination of hexadecanoic lysophosphatidylcholine regioisomers by fast atom bombardment tandem mass spectrometry

The structural determination of sn-1 and sn-2 hexadecanoic lysophosphatidylcholine (LPC) regioisomers was carried out using fast atom bombardment tandem mass spectrometry (FAB-MS/MS). The collision-induced dissociation (CID) of protonated and sodiated molecules produced diverse product ions due mainly to charge remote fragmentations. Based on the information obtained from the CID spectra of protonated and sodiated molecules, sn-1 and sn-2 hexadecanoic LPC isomers could be discriminated. Especially, the abundance ratio of the diagnostic ion pair [m/z 224/226] in the CID spectra of [M + H](+) ions was shown to be greatly different. Moreover, the CID-MS/MS spectra of sodium-adducted molecules for hexadecanoic LPC isomers showed characteristic product ions such as [M + Na - 103](+), [M + Na - 85](+), and [M + Na - 59](+), by which their regio-specificity can be differentiated.     

ZIP8 exacerbates collagen-induced arthritis by increasing pathogenic T cell responses

Zinc is a trace element that is essential for immune responses. Therefore, changes in cellular zinc levels in specific immune cells may influence inflammatory autoimmune diseases, such as rheumatoid arthritis (RA). However, the regulation of zinc mobilization in immune cells and its role in the pathogenesis of RA are not fully understood. Thus, we investigated the roles of zinc transporters in RA pathogenesis. We demonstrated that ZIP8 was specifically upregulated in CD4⁺ T cells that infiltrated the inflamed joint and that ZIP8 deficiency in CD4⁺ T cells abrogated collagen-induced arthritis. ZIP8 deficiency dramatically affected zinc influx in effector T cells and profoundly reduced T cell receptor (TCR)-mediated signaling, including NF-κB and MAPK signaling, which are pathways that are involved in T helper (Th) 17 cell differentiation. Taken together, our findings suggest that ZIP8 depletion in CD4⁺ T cells attenuates TCR signaling due to insufficient cellular zinc, thereby reducing the function of effector CD4⁺ T cells, including Th17 cells. Our results also suggest that targeting ZIP8 may be a useful strategy to inhibit RA development and pathogenesis.Subject terms: Autoimmunity, Immunological disorders     

The accurate calculation of dipole moments and dipole polarizabilities using Gaussian-based density functional methods

Dipole moments and static dipole polarizabilities have been calculated for a number of small molecules using the linear combination of Gaussian-type orbitals–local spin density method. The effect of augmenting standard orbital basis sets with polarization functions has been investigated. A set of optimum ζ_d, for use in calculating polarizabilities, has been derived for the first-row atoms C, N, O, and F. The results of this optimized doubly polarized double-zeta basis set compare well with results obtained using a double-zeta basis set augmented by four even-tempered ζ_d polarization functions. The results of the optimized basis set, and a basis set augmented with only a single ζ_d polarization function derived from it, compare very favorably with those obtained from Møller–Plesset perturbation theory and with experimental data. They show a marked improvement on results obtained using standard Hartree–Fock self-consistent-field molecular orbital methods where no treatment of electron-correlation is included.     

XPS analysis of the effect of Pt addition to Pd catalysts for complete benzene oxidation

Pt-Pd bimetallic catalysts were prepared in order to develop and investigate catalysts having excellent activity and stability for benzene destruction. The effect of Pt addition to Pd catalysts is studied by XPS analysis. This revised version was published online in August 2006 with corrections to the Cover Date.