Magnetic chitosan composite particles: Evaluation of thorium and uranyl ion adsorption from aqueous solutions

Magnetic chitosan composite particles with 40 μm average size and 24 emu/g saturation magnetization obtained by an in situ procedure were evaluated as a new low-cost adsorbent for radioactive wastewater decontamination. Sorbent characterization by SEM, EDX, FTIR and magnetization measurements proved that the target ions were bound and their surface distribution was uniform. The 18 emu/g magnetization of the metal loaded particles was high enough to ensure their easy magnetic field separation and recovery. The parameters influencing the sorption process were optimized with respect to sorbent mass, target ion concentration and contact time. The material under study had superior adsorption capacity both for uranyl (666.67 mg/g) and thorium (312.50 mg/g) ions when compared to other low-cost adsorbents reported in literature. The adsorption process is spontaneous and endothermic. The material may be regenerated and re-used.     

Biosorption of uranium and thorium

Selected samples of waste microbial biomass originating from various industrial fermentation processes and biological treatment plants have been screened for biosorbent properties in conjunction with uranium and thorium in aqueous solutions. Biosorption isotherms have been used for the evaluation of biosorptive uptake capacity of the biomass which was also compared to an activated carbon and the ion exchange resin currently used in uranium production processes. Determined uranium and thorium biosorption isotherms were independent of the initial U or Th solution concentration. Solution pH affected the exhibited uptake. In general, lower biosorptive uptake was exhibited at pH 2 than at pH 4. No discernible difference in uptake was observed between pH 4 and pH 5 where the optimum pH for biosorption lies. The biomass of Rhizopus arrhizus at pH 4 exhibited the highest uranium and thorium biosorptive uptake capacity (g) in excess of 180 mg/g. At an equilibrium uranium concentration of 30 mg/liter, R. arrhizus removed approximately 2.5 and 3.3 times more uranium than the ion exchange resin and activated carbon, respectively. Under the same conditions, R. arrhizus removed 20 times more thorium than the ion exchange resin and 2.3 times more than the activated carbon. R. arrhizus also exhibited higher uptake and a generally more favorable isotherm for both uranium and thorium than all other biomass types examined.     

INFLUENCE OF IONIC CONDITIONS ON CELL DIFFERENTIATION AND MORPHOGENESIS OF THE CELLULAR SLIME MOLDS

Effects of various ionic conditions on the development of the cellular slime molds D. discoideum and D. mucoroides were studied. A certain concentration of lithium ions (7 mM) promoted differentiation of the stalk cells and conversely inhibited formation of the spores. The presence of calcium and magnesium ions was needed for Li to manifest its specific effect. A high concentration of Ca (100-120 mM) also facilitated differentiation of the stalk cells. On the other hand, fluoride ions stimulated considerable formation of spores at 15 mM. In the absence of divalent cations, sodium ions inhibited morphogenesis and cell differentiation proportionately with its concentration, and complete inhibition was obtained at 20 mM. The inhibitory effect of Na was nullified by addition of small amounts of Ca. Possible mechanisms by which these ions exert their influences on development of this organism were discussed.     

Studies on Uranium Removal by the Extracellular Polysaccharide of a Pseudomonas aeruginosa Strain

Extracellular polysaccharide (EPS) produced by a Pseudomonas aeruginosa strain BU2 was characterized for its ability to remove uranium from aqueous solution. The EPS was acidic in nature and found as a potent biosorbent for uranium (U), showing pH dependence and fast saturating metal sorption, being maximum (985 mg U g^{? 1} EPS) at pH 5.0. The polymer showed enhanced uranium sorption capacity and affinity with increasing solution pH, suggesting a preferential sorption of monovalent uranyl hydroxide ions over the nonhydroxylated divalent species. Pseudo-first-order and pseudo-second-order kinetic models were applied to the experimental data, assuming that the external mass transfer limitations in the system can be neglected and biosorption is sorption controlled. Equilibrium metal binding showing conformity to the Freundlich model suggested a multilayer sorption involving specific binding sites with affinity distribution. The presence of two types of metal binding sites corresponding to strong and weak binding affinity was interpreted from the Scatchard model equation. Uranium sorption by EPS was unaffected or only slightly affected in the presence of several interfering cations and anions, except iron and thorium. Fourier transform infrared (FTIR) spectroscopy ascertained the strong binding of uranium with the carboxylic groups of uronic acids of bacterial EPS at pH 5.0, whereas at lower pH, amino and hydroxyl groups played a major role in metal binding.     

Zum chemischen Status der Deoxyribonucleinsäure im Bakteriennucleoid

Zusammenfassung Der in einer früheren Mitteilung beschriebene Effekt der Uranylsalze auf die Struktur des Bakteriennucleoids tritt bereits bei wesentlich niedrigeren Uranylionenkonzentrationen ein, wenn die Zellen bereits mit Uranylacetat und ÄDTE (successiv) vorbehandelt wurden. ÄDTE allein verursacht eine geringere Senkung der Grenzkonzentration. Durch Anwendung eines Gemisches von Calcium-und Magnesiumionen und Polyaminen wird diese Erscheinung größtenteil wieder rückgängig gemacht.Außerdem wurde versucht, die Bindungsverhältnisse der Uranylionen an DNS in vitro genauer zu charakterisieren.Alle Befunde sprechen dafür, daß die Uranylionen natürliche Liganden von den Phosphatgruppen der DNS zu verdrängen vermögen. Diese Liganden sind, soweit sie mit Hilfe von ÄDTE allein ausgetauscht werden können, Metallionen, im übrigen sind sie organischer Natur. Die Experimente sind als erster Schritt zu einer indirekten Charakterisierung dieser Liganden aufzufassen.Der Struktureffekt der Uranylionen am Nucleoid tritt ein, wenn etwa die Hälfte der DNS-Phosphatgruppen durch Uranylionen neutralisiert ist.

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Summary The limiting concentration of uranyl ions which is necessary to induce a fibrillar appearance in bacterial nucleoids as observed in ultrathin section, was decreased markedly by pretreatment of the cells with solutions of uranyl salt and subsequent removal of uranyl ions by EDTA, in a lesser extent by pretreatment with EDTA alone. If the pretreatment was followed by application of a mixture of calcium and magnesium ions and polyamines, its effect was reversed to a great extent.In in vitro experiments the association of uranyl ions to DNA was studied in some detail.All observations are in accordance with the view that uranyl ions displace ligands from the phosphate groups of intracellular DNA which are partly (as far as they are removed by EDTA alone) divalent metal ions, the remainder being of organic nature and possibly of low molecular weight.The experiments may be considered as a first step to an indirect characterization of these ligands.The effect of uranylions on nucleoid structure is induced as soon as about 50% of the phosphate groups of DNA are neutralized by uranyl ions.

     

Cadmium biosorption by a cadmium resistant strain of Bacillus thuringiensis: regulation and optimization of cell surface affinity for metal cations

A marine bacterial strain putatively identified asBacillus thuringiensis strain DM55, showed multiple heavy metal resistance and biosorption phenotypes. Electron microscopic studies revealed that DM55 cells are encased in anionic cell wall polymers that can immobilize discrete aggregates of cations. Factors affecting cell surface affinity for metal cations, monitored by means of Cd²⁺ binding capability, are investigated. The mechanisms of cadmium resistance and Cd²⁺ biosorption by the bacterium appeared to be inducible and coincident. Medium components affecting metal removal under cadmium-stressed growth conditions were explored based on the application of two sequential multi-factorial statistical designs. Concentrations of potassium phosphates and peptone were the most significant variables. Optimized culture conditions allowed DM55 cells grown in the presence of 0.25 mM CdCl₂ to remove about 79% of the metal ions within 24 h with a specific biosorption capacity of 21.57 mg g^–1 of biomass. Both fresh and dry cells of DM55 prepared under cadmium-free optimal nutrient condition were also able to biosorb Cd²⁺. In addition to the concentration of phosphate in the medium, KinA, a major phosphate provider in the phosphorelay of Bacillus cells, was also demonstrated to regulate the magnitude of cell surface affinity for cadmium ions.     

Surface charge near the cardiac inward-rectifier channel measured from single-channel conductance

Summary The conductance of a channel to permeable ions depends on the number of ions near the mouth of the pore. Surface charge controls the local concentration, and impermeable cations can modify this charge. Correlating channel conductance with the concentration of impermeable cations therefore determines the local charge near the open pore. This paper presents data from cell-attached patches on embryonic chick ventricle cells, and it uses the conductance of inward-rectifier channels in the patch (in 100mm K, with various concentrations of Na, Ca, Ba, and Mg) to estimate the local surface potential. The results indicate the presence of ionized residues near the mouth of the channel. Using the Boltzmann equation and the Gouy-Chapman relation, the surface potential due to these residues (in 100K/33Na/0Ca/0Ba/0Mg) is –40 mV, and the charge density is –0.25e/nm².     

Refractive index of uranyl-treated bacterial cytoplasm as related to ribonucleic-acid content and growth rate

After fixation and treatment with uranyl acetate solutions, the refractive index (n _D) of the cytoplasm ofCorynebacterium bovis varies with substrate-dependent growth rate and RNA content. The effect, which presumably is due to quantitative binding of uranyl ions by RNA, permits a measurement of the growth rate of single cells in a single-species system by interference microscopy. Temperature-induced changes in growth rate are not reflected in changes ofn _D or RNA content.     

Ion exchange/complexation of the uranyl ion by Rhizopus biosorbent

Nonliving biomass of nine Rhizopus species effectively sequestered the uranyl ion from solution, taking up 150-250 mg U/g dry cells at 300 ppm U equilibrium concentration in solution, and 100-160 mg U/g dry cells with 100 ppm U in solution. The affinity of this biosorbent for the uranyl ion was found to be affected by timing of harvesting and medium composition. Uptake of the uranyl ion by nonliving biomass of Rhizopus oligosporus was due to ion exchange or complexation, since binding was reversed by the addition of complexing ligands or the reduction of pH to a value less than 2. Uptake isotherms were interpreted in terms of a model of multiple equilibria. At pH 相似文献   

Study on the diuretic activity of Strychnos potatorum Linn. seed extract in albino rats

Methanol extract of Strychnos potatorum Linn. seeds (SPSE) was evaluated for its diuretic activity in Wistar albino rats. The SPSE was administered at the graded doses of 200, 400, and 600 mg/kg body weight. The parameters which were taken into account during the experimental on each rat were: total urine volume (corrected for water intake during the test period), body weight before and after the experiment, and the concentration of sodium, potassium, and chloride ions in urine. The total urine volumes of the SPSE (600 mg/kg)-treated rats were evaluated nearly two and half fold then compared with the control (saline treated) group. Excretion of cations (sodium and potassium ions) and anions (chloride ions) also increased significantly with respect to the control group. The diuretic effect was comparable with that of the standard drug Furosemide. The increase of cations in the urine on treatment with Strychnos potatorum seed extract (SPSE) was dose-dependent. This effect supports the use of the Strychnos potatorum seeds as a diuretic in folk remedies.     

Biosorption of uranium and lead by Streptomyces longwoodensis

Biosorption of uranium and lead by lyophilized cells of Streptomyces longwoodensis was examined as a function of metal concentration, pH, cell concentration, and culture age. Cells harvested from the stationary growth phase exhibited an exceptionally high capacity for uranium (0.44 g U/g dry weight) at pH 5. Calculated values of the distribution coefficient and separation factor indicated a strong preference of the cell mass for uranyl ions over lead ions. The specific uranium uptake was similar for the cell wall and the cytoplasmic fraction. Uranium uptake was associated with an increase in hydrogen ion concentration, and phosphorus analysis of whole cells indicated a simple stoichiometric ratio between uranium uptake and phosphorus content. It is proposed that metal ions are bound to phosphodiester residues present both in the cell wall and cytoplasmic fractions. Based on this model, it was shown that uranium accumulation exhibits a maximum at pH 4.6 that is supported by experimental data from previous investigations.     

Extremophilic Bacillus cereus MVK04 Isolated from Thorium Ore Sample Possesses Self-Assembled Surface Layer Protein on Cell Wall to Resist Extreme Environments

The present study investigates the extremophilic nature of bacteria present in thorium rich mine ore samples collected from Manavalakuruchi, Tamilnadu, India. Six different bacteria strains were isolated from these ore samples and screened for its resistance against varying pH, uranium and gamma radiation. Deinococcus radiodurans ATCC 13939 and Escherichia coli MTCC 1687 was used as positive and negative control respectively. Among the six different bacterial strains, MVK04 strain was found to resist higher pH, uranium concentration and gamma radiation. The organism was identified as Bacillus cereus based on biochemical, 16S rRNA and MALDI TOF fingerprinting studies. The interaction of uranium ions with MVK04 bacterial cell wall was investigated using high resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS). The bacterial MVK04 was further investigated for the presence of surface layer protein (S-layer protein) on the bacterial cell wall. The S-layer protein was isolated, partially purified and self-assembled onto TEM copper grids and the self-assembled protein nanostructures were characterized using HRTEM. The presence of surface layer protein on bacterial cell wall may be the possible reason for its extremophilic characteristics and its escape from lethal effect of higher concentration of uranium, lower pH and increased gamma radiation.     

Biosorption of thorium (IV) by a Pseudomonas biomass

Lyophilized biomass of a Pseudomonas soilisolate adsorbed thorium (IV) (430 mg g^–1 dry wt) optimally at pH 4, with 91% of equilibrium loading being reached in 1 min. Equilibrium metal sorption showing conformity to Langmuir isotherm model suggested a monolayered thorium binding. Thorium binding remained unaffected or slightly affected (< 20% inhibition) in presence of equimolar (430 M) concentration of several interfering ions except Fe³⁺ (40% inhibition). More than 90% of loaded thorium could be recovered using 1 M CaCO₃, though mineral acids and Na₂CO₃ were also effective.     

ELECTRON STAINS : I. Chemical Studies on the Interaction of DNA with Uranyl Salts

Chemical studies have been carried out on the interaction of DNA with uranyl salts. The effect of variations in pH, salt concentration, and structural integrity of the DNA on the stoichiometry of the salt-substrate complex have been investigated. At pH 3.5 DNA interacts with uranyl ions in low concentration yielding a substrate metal ion complex with a UO₂⁺⁺/P mole ratio of about ½ and having a large association constant. At low pH's (about 2.3) the mole ratio decreases to about ⅓. Destruction of the structural integrity of the DNA by heating in HCHO solutions leads to a similar drop in the amount of metal ion bound. Raising the pH above 3.5 leads to an apparent increase in binding as does increasing the concentration of the salt solution. This additional binding has a lower association constant. Under similar conditions DNA binds about seven times more uranyl ion than bovine serum albumin, indicating useful selectivity in staining for electron microscopy.     

Interaction between chitosan and uranyl ions: Part 1. Role of physicochemical parameters

This work is devoted to the comprehension of the sorption mechanism of uranyl ions on chitosan particle dispersions. The uranyl concentration measurements were obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) and we considered the role of various physicochemical parameters (pH; nature and concentration of added salts; degree of acetylation, DA). The use of appropriate calculation software allowed us to determine the chemical nature of uranyl species in solution in relation to these different parameters. The optimal pH of fixation has been found to be within 6.5–7.5 and can be related to the necessity of having both deprotonated amino groups and no carbonate ions, which are a strong complexant of uranyl ions, thus inhibiting their interaction with chitosan. The decrease of metal uptake with an increase of DA and the lack of influence of ionic strength, confirm the results obtained with pH and allowed us to suppose the formation of a complex with chitosan amino groups rather than interactions of an electrostatic nature.     

Formation of effective channels in alginate gel for immobilization of anchorage-dependent animal cells

Summary The conditions for formation of effective channels in alginate gels for growth of anchorage-dependent animal cells were examined. Many channels were formed in the gels by adding a low concentration solution of a high molecular weight polymer of alginate to a high concentration solution of divalent cations. It is recommended that an alginate with a high molecular weight and a low mannuronic acid/guluronic acid ratio be gelled by contact with strontium ions for the cultivation of immobilized anchorage-dependent cells because the gels produced have many channels and are mechanically strong.     

The glucose-dependent transport of l-malate in Zygosaccharomyces bailii

Zygosaccharomyces bailii possesses a constitutive malic enzyme, but only small amounts of malate are decomposed when the cells ferment fructose. Cells growing anaerobically on glucose (glucose cells) decompose malate, whereas fructose cells do not. Only glucose cells show an increase in the intracellular concentration of malate when suspended in a malate-containing solution. The transport system for malate is induced by glucose, but it is repressed by fructose. The synthesis of this transport system is inhibited by cycloheximide. Of the two enantiomers l-malate is transported preferentially. The transport of malate by induced cells is not only inhibited by addition of fructose but also inactivated. This inactivation is independent of the presence of cycloheximide. The transport of malate is inhibited by uranyl ions; various other inhibitors of transport and phosphorylation were of little influence. It is assumed that the inducible protein carrier for malate operates by facilitated diffusion. Fructose cells of Z. bailii and cells of Saccharomyces cerevisiae do not contain a transport system for malate.This research was supported in part by a grant from the Forschungsring des Deutschen Weinbaus.     

Inorganic polyphosphates and sensitivity of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> cells to membrane-damaging agents

The leakage of ATP and potassium ions from the cells of Saccharomyces cerevisiae with different levels of inorganic polyphosphate was studied under the action of two detergents (natural cellobiose lipid 16-[6-O-acetyl-2′-O-(3-hydroxyhexanoyl)-β-cellobiosyloxy)-2,15-dihydroxyhexadecanoic acid and sodium dodecyl sulfate) and silver cations. Cellobiose lipid had practically the same membrane-damaging activity against the cells grown in phosphate-containing medium, under phosphate starvation, and under polyphosphate hypercompensation. The cells grown under the latter conditions were less sensitive to sodium dodecyl sulfate and silver cations. The possible protective action of polyphosphates against the membrane-damaging agents under study is discussed.     

Effect of the essential oil fromAchillea fragrantissima onEscherichia coli cells

Escherichia coli cells treated with the essential oil from the plantAchillea fragrantissima released five polypeptides as well as K⁺ ions into the incubation medium. The oil also inhibited the respiration ofE. coli cells and reduced their ATP content. Electron micrographs showed that oil-treated cells were permeable to uranyl acetate. The effect of the essential oil on the cell membrane is discussed.     

Potential use of Cu2+, K+ and Na+ for the destruction of Caulerpa taxifolia: differential effects on photosynthetic parameters

Chemical techniques were investigated in order to eradicate Caulerpa taxifolia, a green alga spreading at a remarkable rate in the Mediterranean Sea. The action of copper, potassium and sodium ions on survival rates and photosynthetic parameters was compared, in order to optimise the conditions of further in situ treatments. The lethal doses were determined and the impact of the studied cations on photosynthesis and respiration rates and PSII photochemistry was analysed from measurements of net oxygen exchanges and chlorophyll fluorescence. The Cu²⁺ concentrations required to obtain 100% mortality were 15 × 10² to 10⁴ times lower than those of K⁺ and Na⁺. Respiration was slightly affected whatever the salt concentration,while photosynthesis could be totally inhibited depending on the applied treatment. Changes in the structure of the Ribulose-1,5-biphosphate carboxylase/oxygenase (RubisCO, EC: 4.1.1.39) were also detected when C. taxifolia under went cation treatments (10 mg L^-1 Cu²⁺, 1h; 20 gL^-1 K⁺, 3 h; 20 g L^-1 Na⁺, 1 h). Given the high concentration and long incubation periods required with K⁺ and Na⁺ ions, these cations are not suitable to be used in situ. Our results make possible the utilisation of copper cations following technical approaches such asion-exchange textile covers, which allows a controlled release of cupric ions without dissemination in the marine environment. This revised version was published online in August 2006 with corrections to the Cover Date.