In vivo and in vitro studies on inactivation of selenium containing protein- glutathione peroxidase 3 in mice nephrocytes caused by lead.

Glutathione peroxidases (Gpxs) play vital roles in elimination of hydroperoxide and other reactive oxygen species through catalyzing reduced glutathione to protect from oxidative stress caused by heavy metals such as lead. Among the family of Gpxs, Gpx3 is the only extracellular enzyme synthesized in the kidney and actively secreted into the plasma. This study investigated mechanisms of lead-induced GPx3 inactivation both at the animal and molecular levels. Six-week-old mice were randomly divided into 4 groups, and exposed to different lead concentrations (0, 1, 2 and 4 g/L) in their drinking water for 4 weeks. Contents of GPx3 in blood serum were tested by enzyme-linked immunosorbent assay (ELISA) and the mRNA levels of Gpx3 in mice nephrocytes were determined by quantitative real-time PCR (qPCR), both of which showed significantly inhibited at higher lead concentrations accompanied by the decreased Gpx3 activities and the elevated levels of malondialdehyde (MDA) in nephrocytes, which indicated that lead could induce strongly oxidative stress through affecting Gpx3 function. So we further investigated molecular mechanisms of GPx3 inactivation caused by lead with multiple spectroscopic techniques, isothermal titration calorimetry (ITC) and molecular docking studies in vitro. Results showed that lead statically quenched GPx3 fluorescence by tightly binding to the structural domain of GPx3 in a 3:1 ratio with high binding affinity (K = 3.1(±0.087) × 107 mol-1). Further investigation of the conformation of GPx3 by UV-visible spectroscopy and circular dichroism (CD) spectroscopy indicated that lead changed the secondary structure of GPx3 by loosening the GPx3 skeleton and decreasing the hydrophobicity around tryptophan residues. This work proved in vivo and in vitro experiments that lead could induce oxidative stress in mice nephrocytes by interacting with GPx3.

Mechanism of high temperature induced destabilization of nonpolar organoclay suspension.

HYPOTHESIS: High temperatures can reduce the colloidal stability and rheological properties of nonpolar organoclay suspensions. The desorption of surfactants from organoclay has been proposed to explain this effect, but the mechanism remains unclear. In this work, it was hypothesized that the high-temperature-induced desorption of ion-exchanged surfactants is the main factor affecting the stabilization of suspensions. EXPERIMENTS: Using the cationic surfactant dimethyldioctadecylammonium chloride (DODMAC) and Na-montmorillonite (Na-MMT), the high-temperature-induced reestablishment of the adsorption-desorption equilibrium of DODMAC in organoclay suspensions was studied. Thermogravimetric analysis combined with infrared spectroscopy and gas chromatography/mass spectrometry experiments were performed to determine the thermal decomposition products and, ultimately, infer the adsorption modes and locations of DODMAC on Na-MMT. Thermal analysis and rheology were utilized to demonstrate the high-temperature-induced desorption and transfer of DODMAC in organoclay suspensions. FINDINGS: High temperatures induced the complete desorption of physically adsorbed DODMAC molecules from particle surfaces, the partial desorption of ion-exchanged dimethyldioctadecylammonium ions (DODMA+ ions) from particle surfaces, and the partial transfer of ion-exchanged DODMA+ ions from the surfaces to the interlayers. Importantly, desorption of ion-exchanged DODMA+ ions resulted in destabilization of the organoclay suspensions at high temperatures.

Arsenic accumulation, distribution and source analysis of rice in a typical growing area in north China.

Rice (Oryza sativa) is believed to be a major source of arsenic (As) exposure in humans, especially in Asia. In this study, As accumulation, distribution and source analysis of rice are investigated in five sites (SZ, QH, XZ, WS and JX) in the Nansi Lake area, an important rice-growing region in north China. Findings show that total As average concentrations were 6.3-13.6 mg kg-1 and 5.5-9.9 µg L-1 in paddy soil and irrigation water, respectively. Inorganic arsenic As(III) and dimethylarsinic acid DMAs(V) were the major speciation in polished rice, with a small proportion of As(V) evident. Notably, the percentage of As(III) increased by 63.9-68.5%. Based on survey data, the addition of total As to farm soil due to fertilizer application was 31.5-11,580 mg per hectare per year. According to the results of Spearman's rank correlation analysis and Principal Component Analysis (PCA), As levels in soil and irrigation water may be important factors influencing As concentration in rice.

Reuse of organobentonites with a carbon dioxide responsive solvent.

Synthesized organobentonite (SOB), montmorillonite (MMT), and commercial organobentonite (COB) were used as adsorbents for paraffin oil, a model pollutant in land-based oil spills and oil pipeline rupture. The characterization of clays was carried out with scanning electron microscopy (SEM), thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). After adsorption, oil was separated from adsorbents with a carbon dioxide responsive solvent N,N-dimethylcyclohexylamine (DMCHA), and DMCHA was subsequently separated from paraffin oil upon CO2 bubbling instead of distillation with high energy cost. The adsorption capacity of oil to SOB, MMT, and COB was 0.686, 1.124, and 1.239 g/g, respectively. It was found that the adsorption capacity and rinsed amount of the adsorbents depended on the d-spacing, which is related to surfactant content. Electrical conductivity and pH measurements suggested that the separation process occurred via two steps. Firstly, during the initial 35 min, carbonate ions coexisted with bicarbonate ions. Then, only bicarbonate ions existed after the introduction of CO2 gas for 120 min. Thus, organobentonites were feasible for hydrocarbon adsorption and could be simply reused by an amine-based responsive solvent. This work provided a cost-effective and sustainable method of recycling of organobentonites and the responsive solvent, which can be used to deal with leaked oil and oil spills.

Aqueous foam stabilized by plate-like particles in the presence of sodium butyrate.

The addition of salt promotes the adsorption of layered double hydroxide (LDH) particles onto the air-water interface, but stable foams cannot be prepared from LDH dispersions at all the concentration of NaCl or sodium acetate. We generated stable foams using positively charged plate-like LDH particles in the presence of sodium butyrate. The effects of adding sodium butyrate to LDH on the particle zeta potential, adsorption behavior and the adsorption of modified particles at the air-water interface were studied. At a fixed LDH particle concentration, adding of a trace amount of sodium butyrate maximizes flocculation of the aqueous particle dispersion. Foams prepared under this condition of particle dispersion are most stable to coalescence and halt completely disproportionation. Also, the size of the bubbles is the smallest. The bubbles are stable when drying at 80 degrees C with little change in size. Laser-induced fluorescent confocal micrographs and scanning electron microscopy observations clearly confirm the adsorption of LDH particles on the foam surfaces, and the bubbles are armored by an interfacial particle multilayer.

Phase behavior of mixtures of positively charged colloidal platelets and nonadsorbing polymer.

We investigated the effect of nonadsorbing polymer on the phase behavior of suspensions of positively charged Mg2Al layered double hydroxide (LDH) platelets by birefringence observations and rheological measurements. We show that the depletion attraction, induced by the addition of a high-molecular-weight polyvinyl pyrrolidone (PVP), enriches the phase behavior of these electrostatically stabilized suspensions. At intermediate LDH and polymer concentration, two isotropic phases (I1-I2) coexist, nematic-nematic (N1-N2) demixing occurs, and a sediment phase is observed, with the appearance of two-, three-, four-, and even six-phase coexistence. Upon increasing the polymer concentration, the I-N phase transition and the sol-gel transition shift to lower LDH concentrations; meanwhile, the I-N coexistent samples enter the purely nematic phase. We explain the richness of the phase behavior in such LDH-PVP mixtures by discussing the interactions among PVP-induced depletion attraction, particle polydispersity, and particle sedimentation.

Phase behavior of aqueous suspensions of Mg(2)Al layered double hydroxide: the competition among nematic ordering, sedimentation, and gelation.

Birefringence observations and rheological measurements were used to monitor the phase behavior of Mg/Al (the molar ratio of Mg(2+) to Al(3+) being 2:1) layered double hydroxide (LDH) suspensions. The suspensions of concentration lower than 16% (w/w) appear isotropic (I) between crossed polarizers. In contrast, the suspensions of concentration between 16% and 30% (w/w) showed an isotropic (I)-nematic (N) biphasic coexistence. Detailed observations led us to divide the suspensions in the gap into three groups according to their behaviors: the suspensions with concentration between 16% and 25% (w/w) experienced an I-N phase transition and particle sedimentation simultaneously, while the suspensions of 25% to 27% (w/w) showed I-N transition after particle sedimentation, and in the suspension of 30% (w/w), a critical sol-gel transition appeared with an I-N transition. Above 33% (w/w), the gel network hindered a complete I-N separation in the suspensions. Upon raising the NaCl concentration, the liquid crystalline phase transition and the sol-gel transition shifted to higher particle concentrations. The facts demonstrate that the phase behavior of aqueous LDH suspensions is controlled by the competition among liquid crystal phase transition, sedimentation, and gelation.