Aggregation Kinetics of Diesel Soot Nanoparticles in Wet Environments

Soot produced during incomplete combustion consists mainly of carbonaceous nanoparticles (NPs) with severe adverse environmental and health effects, and its environmental fate and transport are largely controlled by aggregation. In this study, we examined the aggregation behavior for diesel soot NPs under aqueous condition in an effort to elucidate the fundamental processes that govern soot particle–particle interactions in wet environments such as rain droplets or surface aquatic systems. The influence of electrolytes and aqueous pH on colloidal stability of these NPs was investigated by measuring their aggregation kinetics in different aqueous solution chemistries. The results showed that the NPs had negatively charged surfaces and exhibited both reaction- and diffusion-limited aggregation regimes with rates depended upon solution chemistry. The aggregation kinetics data were in good agreement with the classic Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The critical coagulation concentrations (CCC) were quantified and the Hamaker constant was derived for the soot (1.4 × 10^–20 J) using the colloidal chemistry approach. The study indicated that, depending upon local aqueous chemistry, single soot NPs could remain stable against self-aggregation in typical freshwater environments and in neutral cloud droplets but are likely to aggregate under salty (e.g., estuaries) or acidic (e.g., acid rain droplets) aquatic conditions or both

In-vitro hydrolytic metabolism of lambda–cyhalothrin by crude homogenates of <i>H</i>. <i>armigera</i> larvae midguts.

<p>Asterisks (*) indicate significantly different between treatment and the control (untreated) group at the 0.05 level.</p

The influences of quercetin intake and synergism effect of DEF on the lambda–cyhalothrin toxicity to <i>H</i>. <i>armigera</i> larvae.

<p>The influences of quercetin intake and synergism effect of DEF on the lambda–cyhalothrin toxicity to <i>H</i>. <i>armigera</i> larvae.</p

The effect of quercetin intake on carboxylesterases activity at different treatment time.

<p>Data in the figure are the mean ± <i>SE</i>. Asterisks (*) indicate significant differences within same treatment time at the 0.05 level.</p

HPLC chromatograms of in-vitro hydrolytic metabolism of lambda–cyhalothrin by the crude homogenates of <i>H</i>. <i>armigera</i> larvae midguts.

<p>Metabolite 3-PBA of lambda–cyhalothrin is pointed out with arrow. (A) Indicates metabolism of lambda–cyhalothrin catalyzed by midguts homogenates from the treatment group of <i>H</i>. <i>armigera</i> larvae with 0.1% quercetin for 72 h, (B) indicates metabolism of lambda–cyhalothrin catalyzed by midguts homogenates from the control group of <i>H</i>. <i>armigera</i> larvae.</p

The metabolic pathways of lambda–cyhalothrin.

<p>The metabolic pathways of lambda–cyhalothrin.</p

Elevated carboxylesterase activity contributes to the lambda-cyhalothrin insensitivity in quercetin fed <i>Helicoverpa armigera</i> (Hübner)

<div><p>Quercetin as one of the key plant secondary metabolite flavonol is ubiquitous in terrestrial plants. In this study, the decrease in sensitivity to lambda-cyhalothrin was observed in quercetin<i>-</i>fed <i>Helicoverpa armigera</i> larvae. In order to figure out the mechanisms underlying the decreased sensitivity of <i>H</i>. <i>armigera</i> larvae to lambda-cyhalothrin by quercetin induction, the changes in carboxylesterase activity and in-vitro hydrolytic metabolic capacity to lambda-cyhalothrin were examined. The LC₅₀ value of quercetin-fed <i>H</i>. <i>armigera</i> larvae to lambda-cyhalothrin showed 2.41-fold higher than that of the control. S, S, S-Tributyl phosphorotrithioate (DEF) treatment showed a synergism effect on lambda-cyhalothrin toxicity to quercetin-fed <i>H</i>. <i>armigera</i>. Moreover, the activity of carboxylesterase was significantly higher in quercetin-fed <i>H</i>. <i>armigera</i> larvae after fed on quercetin for 48 h. The in-vitro hydrolytic metabolic capacity to lambda-cyhalothrin in quercetin-fed <i>H</i>. <i>armigera</i> larvae midgut was 289.82 nmol 3-PBA/mg protein/min, which is significant higher than that in the control group (149.60 nmol 3-PBA/mg protein/min). The elevated CarE enzyme activity and corresponding increased hydrolytic metabolic capacity to lambda-cyhalothrin in quercetin-fed <i>H</i>. <i>armigera</i> contributed to the enhanced tolerance to lambda-cyhalothrin.</p></div

Characterization of the individual domains of the Bacillus thuringiensis Cry2Aa implicates Domain I as a possible binding site to Helicoverpa armigera

Bacillus thuringiensis (Bt) Cry2Aa is a member of the Cry pore-forming, 3-domain, toxin family with activity against both lepidopteran and dipteran insects. Although domains II and III of the Cry toxins are believed to represent the primary specificity determinant through specific binding to cell receptors, it has been proposed that the pore-forming domain I of Cry2Aa also has such a role. Thus, a greater understanding of the functions of Cry2Aa's different domains could potentially be helpful in the rational design of improved toxins. In this work, cry2Aa and its domain fragments (DI, DII, DIII, DI-II and DII-DIII) were subcloned into the vector pGEX-6P-1 and expressed in Escherichia coli. Each protein was recognized by anti-Cry2Aa antibodies and, except for the DII fragment, could block binding of the antibody to Cry2Aa. Cry2Aa and its DI and DI-II fragments bound to brush border membrane vesicles (BBMV) from H. armigera and also to a ca 150 kDa BBMV protein on a far western (ligand) blot. In contrast the DII, DIII and DII-III fragments bound to neither of these. None of the fragments were stable in H. armigera gut juice nor showed any toxicity towards this insect. Our results indicate that contrary to the general model of Cry toxin activity domain I plays a role in the binding of the toxin to the insect midgut.</p