Atmospheric reactions influence seasonal PAH and nitro-PAH concentrations in the Los Angeles basin

Ambient measurements of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs were carried out during August 2002 and January 2003 in Los Angeles, CA, a source site and in Riverside, CA, a downwind receptor site approximately 90 km to the east of Los Angeles. Atmospheric concentrations of PAHs and nitro-PAHs are of interest because both of these compound classes include potent mutagens and carcinogens. To augment our current understanding of atmospheric formation of nitro-PAHs, four sampling periods were employed to study the diurnal variations of these compounds. The PAH concentrations were highest in Los Angeles during January, as a result of traffic input at this source site undertightwintertime atmospheric inversions. In contrast, nitro-PAH levels were highest in Riverside during August, as a result of enhanced summertime photochemistry. Hydroxyl radical-initiated reactions produced nitro-PAHs in both seasons, while in winter little evidence for nitrate radical chemistry was seen. For the August samples, nitrate radical-initiated formation of nitro-PAHs is suggested by nitro-PAH isomer profiles not only at the downwind location as anticipated, but also atthe source site. In southern California, the contribution of atmospheric formation through gas-phase radical-initiated PAH reactions to the ambient burden of nitro-PAHs is dominant, with the semi-volatile nitro-PAHs being the most abundant and 2-nitrofluoranthene being the major particle-associated nitro-PAH.     

Increased biological activity of a recombinant factor IX variant carrying alanine at position +1

In attempts to improve the post-translational modification andprocessing of recombinant factor IX (FIX) we have altered thecDNA sequence encoding pre-pro-FIX using site-directed mutagenesisand have expressed the variant cDNAs in BHK21 cells using avaccinia-virus-derived vector. We find that substitution ofthe tyrosine residue at +1 for an alanine increases the biologicalactivity of the recombinant molecules 2–fold. On the otherhand, substitution of the proline at –3 for a valine resultsin no significant change to the specific activity of the protein.Other alterations to the N-terminus of the FIX proteins, inattempts to mimic other vitamin-K-dependent proteins, resultin the failure to produce a secreted polypeptide. N-terminalsequence analysis of purified recombinant molecules revealsa correlation between specific activity and the efficiency ofcorrect pro-sequence cleavage. -Carboxylation analysis of purifiedrecombinant proteins indicates that each molecule includingunmutated FIX is completely -carboxylated in this system. Thusthe observed increase in biological activity of FIX variantscontaining an alanine at position +1 is not due to increased-carboxylation but, at least in part, to more efficient pro-peptidecleavage.     

Photo-Fenton-peroxide process using FE (II)-embedded composites based on activated carbon: Characterization of catalytic tests

Cost-efficient Fenton-like catalysts for the removal of organic molecules in aqueous solutions were elaborated by a simple process. Porous activated carbons (ACs) were directly impregnated with a precursor solution using the wet impregnation method. Their efficiency as Fenton-like catalysts was studied. Photo-Fenton tests were performed to establish the performance of the prepared Fe-impregnated activated carbons in relation to the degradation of an organic pollutant (Indigo Carmine) model in aqueous solution, under different conditions. Photo-catalytic tests were carried out by means of a laboratory photo-reactor (UV-Consulting Peschl). The influence of several parameters such as solution pH value, initial concentration of the model pollutant, and hydrogen peroxide dose on the process performance was investigated. The ACs and prepared catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, SEM, and thermogravimetric analyses. The total Fe content of the synthesized composites was estimated by the phenanthroline method using UV-vis spectrophotometry. The results show an increase in the degradation rate when the heterogeneous photo-Fenton process is conducted with an ozone generating UV lamp.     

Influence of the anionic part of the stabilizer on electroless nickel-boron plating

Selectivity and smooth operation of electroless nickel plating require that a stabilizing agent is used. It operates by blocking catalytic activity on unwanted germination sites and regulating the activity of the substrate. In the case of alkaline electroless nickel-boron plating systems, which use sodium (or potassium) borohydride as reducing agent, lead and thallium salts are the most popular stabilizers. However, there is little knowledge about the way the stabilizer acts. In this study, 4 different lead-based stabilizers (tungstate, sulphate, nitrate and chloride) have been used, all other things left constant, in electroless nickel-boron plating baths. The thickness, composition, roughness, morphology, hardness and structure of all the obtained coatings have been investigated. Chloride led to thinner deposits and the boron content varied between 5.5?wt.% for lead tungstate and 6.5?wt.% for lead nitrate and lead sulphate, with a lead content between 0.2 and 0.25?wt.%. Coatings obtained with a lead tungstate stabilized bath were thicker, harder and contained less boron and lead than the others. This shows the influence of the anionic part of the stabilizing agent on the plating process.     

Adhesion of resin cement to contemporary hybrid ceramic and polymeric CAD/CAM materials: effect of conditioning methods and ageing

This study assessed the effect of different surface conditioning methods and ageing protocols on adhesion of resin cement to hybrid ceramic and polymeric CAD/CAM materials. CAD/CAM materials (n?=?360, n?=?30 per group), namely (a) Lithium disilicate (IPS e.max CAD-LIS), (b) Zirconia (IPS e.max ZirCAD-ZIR), (c) Polymer (Lava Ultimate-LAV), (d) Polymer infiltrated ceramic network (Enamic-ENA), (e) Polymer infiltrated ceramic (Experimental-1-CS1), (f) Polymer infiltrated ceramic (Experimental-2-CS2), (g) Lithium disilicate reinforced alumina (n!ce-NIC) were cut into slices (3?×?6 × 8?mm³) and conditioned: (a) Method 1: 5% hydrofluoric acid etching (H)+silane and (b) Method 2: Silica coating (CoJet (A)+silane). Group LIS was conditioned with only Method 1 and Group ZIR only with Method 2 (control). Resin cement (Variolink Esthetic II) was bonded onto the conditioned specimens and photopolymerized. One-half of the specimens was subjected to ageing (thermocycling 5–55°, 5000 cycles) and the other half was stored in distilled water (37?°C, 24?h). The resin-substrate interface was loaded under shear forces in a Universal Testing Machine (1?mm/min). Data (MPa) were analyzed using two-way ANOVA and Tukey`s tests (α?=?0.05). Substrate type, conditioning method and ageing had a significant effect on adhesion values (p?<?.05). In aged conditions, ENA-H, ENA-A, LAV-H, LAV-A, CS2-A (15?±?4 – 11.6?±?5) showed no significant difference (p?>?.05), with the CS2-A (15?±?4) showing the least reduction (5.5%) compared to all other groups (5.8–62.6%). CS1-A (100%) followed by ENA-H, ENA-A (93%), CS2-A (80%) presented the highest incidence of cohesive failures after ageing.     

Partitioning of metal species during an enriched fuel combustion experiment. speciation in the gaseous and particulate phases

Combustion processes are the most important source of metal in the atmosphere and need to be better understood to improve flue gas treatment and health impact studies. This combustion experiment was designed to study metal partitioning and metal speciation in the gaseous and particulate phases. A light fuel oil was enriched with 15 organometallic compounds of the following elements: Pb, Hg, As, Cu, Zn, Cd, Se, Sn, Mn, V, Tl, Ni, Co, Cr, and Sb. The resulting mixture was burnt in a pilot-scale fuel combustion boiler under controlled conditions. After filtration of the particles, the gaseous species were sampled in the stack through a heated sampling tube simultaneously by standardized washing bottles-based sampling techniques and cryogenically. The cryogenic samples were collected at -80 degrees C for further speciation analysis by LT/GC-ICPMS. Three species of selenium and two of mercury were evidenced as volatile species in the flue gas. Thermodynamic predictions and experiments suggest the following volatile metal species to be present in the flue gas: H2Se, CSSe, CSe2, SeCl2, Hg(0), and HgCl2. Quantification of volatile metal species in comparison between cryogenic techniques and the washing bottles-based sampling method is also discussed. Concerning metal partitioning, the results indicated that under these conditions, at least 60% (by weight) of the elements Pb, Sn, Cu, Co, Tl, Mn, V, Cr, Ni, Zn, Cd, and Sb mixed to the fuel were found in the particulate matter. For As and Se, 37 and 17%, respectively, were detected in the particles, and no particulate mercury was found. Direct metal speciation in particles was performed by XPS allowing the determination of the oxidation state of the following elements: Sb(V), Tl(III), Mn(IV), Cd(II), Zn(II), Cr(III), Ni(II), Co(II), V(V), and Cu(II). Water soluble species of inorganic Cr, As, and Se in particulate matter were determined by HPLC/ICP-MS and identified in the oxidation state Cr(III), As(V), and Se(IV).