Origin of the regioselectivity in an intramolecular nucleophilic addition to arene chromium tricarbonyl complexes

The source of the regioselectivity in the intramolecular nucleophilic addition of nitrile-stabilized carbanions to arene chromium tricarbonyl complexes was investigated for seven different substitution patterns on the arenes. All of the arenes are 1,4-dioxygenated and the substitution varies in the oxygen substituent and in the substituents of the arene carbons (hydrogen and alkyl). The regioselectivity is correlated with the preferred conformations of the chromium tricarbonyl group which in turn was determined by solution and solid-state ¹³C NMR spectroscopy, ¹H NMR spectroscopy in solution as well as X-ray diffraction. In the four complexes analyzed by X-ray diffraction and the three complexes analyzed by solid-state ¹³C NMR spectroscopy, there was only one complex where it was found that the preferred conformation of the -Cr(CO)₃ is different in solution than it is in the solid-state.     

Cytopathic Action of Naegleria fowleri Amoebae on Rat Neuroblastoma Target Cells

The axenically cultured, weakly pathogenic Naegleria fowleri LEE and the highly pathogenic, mouse passaged N. fowleri LEEmp are cytopathic for B103 rat nerve cells in culture. Cytopathogenicity was measured by release of radiolabeled rubidium or radiolabeled chromium from B103 target cells. Cytopathogenicity was time-dependent for up to 18 h and dependent upon amoebae effector to nerve cell target ratios of less than 1:1. Release of⁵¹ Cr from B103 cells by either LEE or LEEmp amoebae was enhanced by addition of calcium or magnesium to medium free of these divalent cations but the ion-channel inhibitor, verapamil, or the ionophore A23187 and phorbol myristate acetate did not alter release of ⁵¹ Cr from B103 cells cocultured with the amoebae. Cycloheximide or actinomycin D impaired release of ⁵¹ Cr from B103 target cells injured by either LEE or LEEmp amoebae. Both strains of amoebae were fractionated by glass bead disruption and high speed centrifugation into membrane and soluble fractions. Each fraction was incubated with either ⁸⁶Rb or ⁵¹ Cr labeled nerve cells. The membrane fraction from LEEmp was more active than the soluble fraction in facilitating rubidium and chromium release. In contrast, the soluble fraction from LEE was more active than the membrane fraction in facilitating rubidium release from radiolabeled target cells. The sequential release of ⁸⁶Rb and ⁵¹ Cr from target cells rather than the simultaneous release of the two isotopes indicates that target cell death is due to the release of ions followed later by the release of large macromolecules. The results indicate that N. fowleri amoebae injure nerve cells by two alternate mechanisms, trogocytosis or contact-dependent lysis.     

Dietary and metabolite effects on trivalent chromium retention and distribution in rats

The purpose of this study was to determine if diet or various metabolites alter chromium (Cr) uptake and distribution in rats. Radioactively labeled Cr was detected within 15 min of oral administration to rats, and the total amount retained remained relatively constant from 1 to 24 h. Dietary Cr intake did not alter Cr retention or distribution. The majority of the Cr was retained in the carcass. However, when the amount of labeled Cr was expressed per gram of tissue, the highest amounts of Cr were found in the kidneys, spleen, and pancreas. Pharmacological doses of insulin, epinephrine, glucagon, and dibutyryladenosine-3’ −5’ cyclic monophosphate, prostaglandins A₁, A₂, B₁, B₂, E₁, E₂, F_1α, and F_2α did not significantly influence Cr retention. Glucose, sucrose, nicotinic acid, glutathione, and other metabolites administered orally in conjunction with labeled Cr also did not significantly alter Cr retention. These data indicate that most nutrients and metabolites do not alter Cr retention and distribution. The regulation of Cr homeostasis appears to be at the level of excretion.     

Influence of Cr3+ on microbial cluster formation in biofilm and on steel corrosion

Pit corrosion of mild steel in seawater increased with Cr³⁺ concentration. SEM observations showed that increasing Cr³⁺ concentration caused microbes in biofilm on the steel surface to aggregate forming clusters. AFM images suggested that pit corrosion occurred largely on the mild steel surface between clusters, and only little corrosion on the surface covered by microbes.     

A sensitive method for determination of trace amounts of chromate (III) with terbium (III) sodium hexametaphosphate chelate as fluorescent probe

Based on the fluorescence quenching of Terbium (III)‐sodium hexametaphosphate (Tb/SHMP) chelates in the presence chromate (III), a sensitive fluorimetric method was developed for the determination of trace amounts of chromium (III) in aqueous solutions. Under the optimum conditions, the linear calibration graph was obtained (R = 0.996). The linear range and detection limit of Cr (III) were 7.69 × 10^?7 to 1.15 × 10^?4 mol L^?1 and 4.50 × 10^?7 mol L^?1, respectively. The proposed method had a wider linear range and was proved to be very sensitive, rapid and simple. The method was applied successfully to the determination of chromium (III) in the synthetic samples and real water samples. Moreover, the reaction mechanism was discussed through the fluorescence lifetime and proved to be dynamic quenching behavior. Copyright © 2010 John Wiley & Sons, Ltd.     

谷子幼苗对土壤铅、铬的生长响应及吸收积累的差异性

采用盆栽土培试验,研究了谷子幼苗对土壤中不同含量铅（Pb）、铬（Cr）的生长响应和吸收积累的差异性。结果表明,在所试浓度（50～800 mg·kg^-1）范围内,Pb、Cr在谷子幼苗地上部和地下部的积累量存在较大差异,幼苗重金属的吸收富集和转运系数均为Pb大于Cr、Pb、Cr胁迫对幼苗生物量的影响表现为低浓度的促进和高浓度的抑制作用,但Cr对生物量的影响比Pb更强。相同处理条件下,幼苗茎叶中可溶性蛋白质、DNA含量和增色效应对Pb、Cr的响应也有明显差别,Cr对幼苗的生理毒性和DNA损伤效应的作用强度大于Pb。     

Phytoremediation of Water Using Phragmites karka and Veteveria nigritana in Constructed Wetland

Constructed wetland is an innovative and emerging ecological technology for wastewater treatment. This study was conducted to investigate the effectiveness of a Vegetated Submerged Bed Constructed Wetland (VSBCW) for removal of heavy metals from industrial wastewater in a steel manufacturing company. A pilot Effluent Treatment Plant (ETP) consisting of equalization basin, two VSBCW basins and a storage tank was constructed. The VSBCW was constructed using 10–30 mm round granite for the different zones. This was overlaid by 200 mm deep granite and 150 mm washed sand with Phragmites karka, Vetiveria nigritana and Cana lilies as macrophytes. Irrigation of macrophytes using effluent from the industry was done after 3 months of planting and ETP monitored. Industrial wastewater samples were collected and analyzed for heavy metals such as zinc (Zn), lead (Pb), iron (Fe), manganese (Mn), magnesium (Mg) and chromium (Cr) to know the treatment efficiency of the ETP. Results indicated that the removal efficiencies of the VSBCW for Pb, Mg and Cr were 15.4%, 79.7% and 97.9% respectively. Fe and Mn were seen to increase by 1.8% and 33% respectively. The ETP using locally available macrophytes is effective in the phytoremediation of heavy metals, particularly Cr from the wastewater.     

Lithium,Vanadium and Chromium Uptake Ability of Brassica juncea from Lithium Mine Tailings

The potential for phytoremediation and phytostabilization of lithium in lieu with vanadium and chromium on a formulated acidic heterogeneous growth media engineered around lithium mine tailings, was investigated in four phases: (1) overall efficiency of the removal of the three metals, (2) bioaccumulation ratios of the three metals, (3) overall relative growth rate, and (4) translocation index of the three metals in the physiology of the hyperaccumulator plant. A pot study was conducted to assess the suitability of Brassica juncea (Indian mustard) in a phytoremediation process whereby it was lingered for eighty-six days under homogeneous growth conditions and irrigated bidaily with organic fertilizer amended with LiCl. A post harvest data analysis was achieved through ashing and the implementation of cold digestion procedure in a concentrated hydrochloric acidic matrix. In physiological efficiency parameters, the hyperaccumulator plant was twice as able to phytostabilize chromium and four times was able to phytostabilize vanadium in comparison to lithium. Moreover, it was extremely efficient in translocating and accumulating lithium inside its upper physiological sites, more so than chromium and vanadium, thereby demonstrating Indian mustard, as a hyperaccumulator plant, for phytoextraction and phytostabilization in an acidic heterogeneous rhizosphere, with an extremely low relative growth rate.     

Evaluation of Cr(VI) Exposed and Unexposed Plant Parts of Tradescantia pallida (Rose) D. R. Hunt. for Cr Removal from Wastewater by Biosorption

Phytoremediation is an efficient method for the removal of heavy metals from contaminated systems. A productive disposal of metal accumulating plants is a major concern in current scenario. In this work, Cr(VI) accumulating Tradescantia pallida plant parts were investigated for its reuse as a biosorbent for the removal of Cr(VI) ions. The effect of pH, contact time, sorbent dosage, Cr(VI) concentration and temperature was examined to optimize these process parameters. Results showed that Cr(VI) exposed/unexposed T. pallida leaf biomass could remove 94% of chromium with a sorption capacity of 64.672 mg g^?1. Whereas the kinetics of Cr(VI) biosorption was well explained by the pseudo second-order kinetic model, the Langmuir model better described the data on Cr(VI) sorption isotherm compared with the Freundlich model. The changes in the free energy (ΔG°), entropy (ΔS°) and enthalpy (ΔH°) were found to be ?5.276 kJ mol^?1, 0.391 kJ mol^?1 K^?1 and 11.346 kJ mol^?1, respectively, which indicated the process to be spontaneous, feasible and endothermic in nature. FTIR spectra of T. pallida leaf biomass revealed the active participation of ligands, such as ?NH, amide, hydroxyl and sulphonate groups present in the biomass for Cr(VI) binding, SEM analysis revealed a porous structure of the biosorbent for an easy uptake of Cr(VI).     

水环境中Cr(Ⅵ)对鱼类毒性机理研究进展

随着工业,特别是不锈钢产业的迅速发展,环境中的铬污染问题日益严重,Cr(Ⅵ)能够很容易地透过细胞膜进入细胞和生物体内,其毒性远高于Cr(Ⅲ).铬作为变价金属,其在鱼类体内能够产生活性氧自由基(ROS),对机体产生氧化胁迫效应;此外,Cr(Ⅵ)在细胞还原作用下生成的中间产物\[Cr(Ⅴ)、Cr(Ⅳ)等\]会进一步和DNA结合,导致基因的损伤和突变,从而危害鱼类的生长发育和种群结构.本文在不同水平上,系统总结了Cr(Ⅵ)对鱼类的毒性效应,从多个层次(分子、细胞、组织、器官、个体）阐述了Cr(Ⅵ)的毒性作用机制和鱼类相应的毒性解毒机制,并对于Cr(Ⅵ)的毒性研究中尚不完全清楚、需要深入考察的方面进行了探讨.