Bacterial siderophores promote dissolution of UO2 under reducing conditions

Tetravalent actinides are often considered environmentally immobile due to their strong hydrolysis and formation of sparingly soluble oxide phases. However, biogenic ligands commonly found in the soil environment may increase their solubility and mobility. We studied the adsorption and dissolution kinetics of UO2 in the presence of a microbial siderophore, desferrioxamine-B (DFO-B), under reducing conditions. Using batch and continuous flow stirred tank reactors (CFSTR),we found that DFO-B increases the solubility of UIV and accelerates UO2 dissolution rates through a ligand-promoted dissolution mechanism. DFO-B adsorption to UO2 followed a Langmuir-type isotherm. The maximum adsorbed DFO-B concentrations were 3.3 micromol m(-2) between pH 3 and 8 and declined above pH 8. DFO-B dissolved UO2 at a DFO-B surface-saturated net rate of 64 nmol h(-1) m(-2) (pH 7.5, l = 0.01 M) according to the first-order rate equation R = kL[Lads], with a rate coefficient kL of 0.019 h(-1). Even at very low siderophore concentrations (e.g. 1 microM), net dissolution rates (16 nmol h(-1) m(-2), pH 7.5, l = 0.01 M) were substantially greater than net proton-promoted dissolution rates (3 nmol h(-1) m(-2), pH 7-7.5, l = 0.01 M). Interestingly, adding dissolved FeIII had negligible effects on DFO-B-promoted UO2 dissolution rates, despite its potential as a competitor for DFO-B and as an oxidant of UIV. Our results suggest that strong organic ligands could influence the environmental mobility of tetravalent actinides and should be considered in predictions for nuclear waste storage and remediation strategies.     

Effects of Ca2+ and Mg2+ on defluoridation in the electrocoagulation process

Because aqueous ions can influence the defluoridation of the electrocoagulation (EC) process, the effects of Ca(2+) and Mg(2+) were investigated. The behaviors and mechanisms of EC defluoridation in Ca(2+)-containing systems were different from those in Mg(2+)-containing systems. An increase in Ca(2+) concentration improved the defluoridation efficiency (ε(F)), but it could not change the optimal molar ratio of OH(-) and F(-) to Al(3+) (r(OH+F)). The highest ε(F) can usually be obtained at r(OH+F) = 3 for defluoridation. Only a small portion of Ca(2+) entered into the flocs, and Ca(2+) could not influence the mechanism of EC defluoridation. For the Mg(2+)-containing system, the optimal r(OH+F) increased with increasing Mg(2+) concentration. The optimal r(OH+F) was maintained at 3 after the Mg(2+) concentration was corrected using the obtained correction coefficient of 0.3435. About 50% to 70% of the total Mg(2+) entered into the flocs. From the XRD analysis, it was found that some Mg-Al-F layered double hydroxides (LDHs) were formed by Mg(2+), F(-), and Al(3+) during electrolysis. It is proposed for the first time that the formation of Mg-Al-F LDH is one of the mechanisms for EC defluoridation in systems containing both F(-) and Mg(2+).     

Formation of studtite during the oxidative dissolution of UO2 by hydrogen peroxide: a SFM study

Understanding the formation of alteration phases on the surface of spent nuclear fuel, such as those observed during leaching experiments, is necessary in order to predict the concentration of radionuclides in the near-field of a final repository. Hydrogen peroxide has been identified as one of the oxidants formed by the radiolysis of water in the presence of spent nuclear fuel; especially due to alpha activity. The presence of this species in solution can contribute to the formation of uranium peroxide secondary phases. In this work, we have studied the oxidative dissolution of synthetic UO2 disks in hydrogen peroxide solutions of two different concentrations (5 x 10(-4) and 5 x 10(-6) mol dm(-3)), both at pH 5.8 +/- 0.1. The solid surface evolution of the disks has been followed by means of ex-situ scanning force microscope (SFM) measurements, and uranium concentration in solution has been determined by inductively coupled plasma mass spectrometry. During the first stage of the experiment, SFM images indicate that only UO2 dissolution is occurring. After 142 h, a secondary phase is observed on the surface of the solid at 5 x 10(-4) mol dm(-3) hydrogen peroxide concentration. This secondary phase has been identified by X-ray diffraction as studtite (UO4 x 4H2O). From the analysis of SFM topographic profiles at different elapsed times, a precipitation rate for the studtite has been estimated to be in the range of (8-32) x 10(-10) mol m(-2) s(-1).     

Sorption and desorption of Cd2+ and Zn2+ ions in apatite-aqueous systems

As a low-soluble phosphate mineral capable of binding various metal ions, apatite can be used to immobilize toxic metals in soils and waters. In the present research the factors affecting sorption and desorption of Cd2+ and Zn2+ ions on/from apatites are investigated. Batch experiments were carried out using synthetic hydroxy-, fluoride-, and carbonate-substituted apatites having various specific surface area (SSA). Apatite sorption capacity was found to depend mainly on its SSA, ranging from 16 to 78 and from 11 to 79 mmol per 100 g of apatite for Cd2+ and Zn2+, respectively. The solution composition (pH, and presence of Cl- and NO3- ions) had no essential impact on sorption. Desorption of bound cations depended both on the sorption level and solution composition. The amount of desorbed Cd2+ and Zn2+ increased proportionally to the amount of sorbed cations. However, apatites having higher sorption capacity release relatively less sorbed cations. Desorption increases with increasing Ca2+ concentration in the solution, reaching 8-20% of sorbed Cd2+ in 0.002 M, 10-35% in 0.01 M, and 33-45% in 0.05 M Ca(NO3)2 solution. Compared to nitrate solutions, the presence of Cl- ions in the solution promotes the release of bound cations. Desorption of Zn2+ is slightly higher than that of Cd2+. The desorption mechanism was assumed to include both ion-exchange and adsorption of Ca2+ ions on apatite surface.     

Ca2+、Mg2+及食盐对浸酸铬鞣的影响

研究了水中Ca2+、Mg2+和NaCl的含量对猪皮浸酸铬鞣的影响.通过正交试验和扩大试验研究发现,Ca2+、Mg2+和NaCl对浸酸铬鞣的影响趋势为Mg2+＞NaCl＞Ca2+.当水中Ca2+、Mg2+含量分别达到质量浓度为80 mg/L和30 mg/L时,铬吸收率大于95%,坯革的Ts均达到100℃以上.坯革粒面平细、染色均匀,物理机械性能达到同类产品指标.NaCl质量浓度高于65 g/L时,不利于铬的吸收和结合.试验结果表明水中Ca2+、Mg2+含量分别达到质量浓度为80 mg/L和30 mg/L时,对猪皮浸酸铬鞣无不良影响.     

Effect of Zn Concentration, Ca Source, Percent Milkfat and Homogenization on Ca, Fe and Zn Solubility in Wheat Cereal Systems under Simulated Gastrointestinal pH

An in vitro sequential pH treatment, simulating the gastrointestinal tract, was used to evaluate effects of Zn fortification, source of Ca and milk type (skim, 1 and 2% fat, homogenized and unhomogenized whole) on Ca, Fe and Zn solubility in moderately (MF) and highly fortified (HF) whole wheat cereals. In both cereals, soluble Zn significantly increased in response to fortification level. While CaCO₃-supplemented skim milk promoted mineral solubility in all MF systems, whole milk was most effective in the HF systems. This effect was apparently related to % milkfat and the homogenization process.     

植酸酶作用对米糠中钙、铁、锌生物利用率的影响

米糠含有丰富的矿物质,但植酸等抗营养因子的存在,使其消化吸收率很低.以米糠为原料,通过植酸酶处理以降解其中的植酸,并采用体外消化方法分析处理后的米糠的钙、铁、锌的吸收率.研究结果表明植酸酶能够有效地降低米糠中的植酸含量,添加量2.5 U/g米糠时,经2 h植酸的降解率达95%以上.同时,钙、铁、锌的可利用率均显著提高,相关性分析的结果显示,米糠的植酸含量与钙、锌的利用率之间存在显著负相关,铁的相关性不显著.     

麦汁中锌离子的控制与测定

0　前言锌离子对啤酒酵母菌体的生长繁殖 ,各种酶的活性及代谢副产物的形成都有着重要的作用。锌是乙醇脱氢酶和乳酸脱氢酶的活性基 ,如果麦汁中的锌含量低于 0 15～ 0 18ｍｇ/Ｌ就会导致酵母细胞的增殖变弱 ,主发酵和后发酵迟缓、双乙酰及其前驱体α -乙酰乳酸不能完全还原 ,有时还可能使酵母在发酵结束后沉淀困难 ,影响过滤 ,因此酿酒师们都在努力探讨如何通过工艺手法 ,保证麦汁中锌离子的含量。1　麦汁中锌离子含量的控制据资料介绍锌主要存在于麦粒的皮层和糊粉层中 ,在干麦芽中的含量为 3 0～ 3 5ｍｇ/ 10 0ｇ,糖化中仅能使 2 0 %的…     

Competitive binding of CU2+ and Zn2+ to live cells of shewanella putrefaciens

Binding of Cu2+ and Zn2+ to live cells of Shewanella putrefaciens was measured at pH 4, 5.5, and 7 for dissolved metal concentrations ranging from 0.1 to 100 microM. Release of organic compounds by the cells resulted in concentrations of dissolved organic carbon (DOC) between 0.5 and 1.6 mM. A discrete site, nonelectrostatic model was used to describe Cu2+ and Zn2+ binding to the cells. Binding of Zn2+, which increased with increasing pH over the entire range of dissolved Zn2+ concentration, could be explained by invoking two types of cell wall binding sites: acidic and neutral functional groups. Binding of Cu2+ exhibited a more complex pH dependence: at dissolved metal concentrations below 1 microM, binding to the cells actually increased with decreasing pH. This behavior could be reproduced by (1) assuming the existence of a small fraction of high-affinity binding sites in the cell wall (approximately 5%) and (2) including metal complexation by dissolved organic ligands. The latter compete with the neutral cell wall groups and decrease Zn2+ and Cu2+ binding at pH 5.5 and 7. The observed isotherms implied that binding of the metals was only weakly affected by cell wall charging. Model parameters derived from the single-metal binding isotherms were able to account for the observed competition of Zn2+ and Cu2+ for cell wall sites when both metals were present.     

Ca2+对菠萝蛋白酶热稳定性和二级结构的影响

研究了Ca2+对菠萝蛋白酶活性及远紫外圆二色谱的变化.在37℃下,Ca2+与酶作用1h后,5～10mmol/L Ca2+对酶的活性均有促进作用,其中当Ca2+浓度为2mmoL/L时.促进作用最明显.在60℃下,Ca2+浓度为3mmol/L时,对菠萝蛋白酶的热稳定化效果最好,处理100min后仍然能保留68%的活性;菠萝蛋白酶在60℃下活性的半衰期为86min,除Ca2+浓度为1mmoVL外,其他浓度(2、3、4、5mmol/L)的Ca2+与菠萝蛋白酶作用后,酶的半衰期均有所延长.由圆二色谱曲线发现,菠萝蛋白酶在波长209nm与221am处有明显的负峰.与Ca2+作用后菠萝蛋白酶的α-螺旋、β-转角和无规则卷曲均有所变化,其中,在37℃下加入Ca2+后,菠萝蛋白酶的α-螺旋均减少,而β-转角有所增加.在70℃下处理1h,Ca2+对菠萝蛋白酶二级结构也有所影响.无Ca2+处理的菠萝蛋白酶和加入4mmol/L Ca2+的菠萝蛋白酶的α-螺旋分别减少为34.90%和35.60%,而β-转角则有所增加,分别为26.30%和25.10%.圆二色谱结果表明,α-螺旋结构对菠萝蛋白酶的稳定性起关键作用.     

The dissolution rates of SiO2 nanoparticles as a function of particle size

There is a critical need to better define the relationship among particle size, surface area, and dissolution rate for nanoscale materials to determine their role in the environment, their toxicity, and their technological utility. Although some previous studies concluded that nanoparticles dissolve faster than their bulk analogs, contradictory evidence suggests that nanoparticles dissolve more slowly. Furthermore, insufficient characterization of the nanoparticulate samples and the solution chemistry in past studies obscures the relationship between particle size, surface area, and dissolution rate. Here we report amorphous SiO(2) dissolution rates in aqueous solutions determined from complementary mixed-flow and closed reactor experiments at 6.9 ≥ pH ≥ 11.2 and 25 °C as a function of particle diameter from 25 to 177 nm. Experiments were performed at far-from-equilibrium conditions to isolate kinetic effects from those of changing the reaction driving force on overall dissolution rates. Measured far-from-equilibrium mass normalized dissolution rates are nearly independent of particle size, but corresponding BET surface area normalized rates decrease substantially with decreasing particle size. Combining these observations with existing established kinetic rate equations allows the prediction of nanoparticle dissolution rates as a function of both particle size and aqueous fluid saturation state.     

Matrix metalloproteinase-2 inhibition and Zn2+-chelating activities of pyoverdine-type siderophores

Pyoverdine-type siderophores from fluorescent Pseudomonas species were purified by Zn2+-chelate chromatography, and their matrix metalloproteinase-2 (MMP-2) inhibition and metal-ion-chelating activities were studied. Structurally different pyoverdines showed different MMP-2 inhibition activities, and the inhibition activity was correlated with Zn2+-chelating activity. The IC50 value of a pyoverdine ((P113A1)-2, MW 1187) for MMP-2 was 0.27 microg/ml (0.23 microM).     

胰岛素原C肽对2型糖尿病患者离体红细胞膜Na+-K+-ATP酶活性及红细胞内Ca2+浓度的影响

目的研究外源性胰岛素原C肽对2型糖尿病患者离体红细胞膜Na -K -ATP酶活性及红细胞内Ca2 浓度的影响。方法取2型糖尿病患者空腹血,肝素抗凝,分离红细胞,生理盐水重新悬浮,加外源性C肽,分别测定细胞膜上的Na -K -ATP酶活性和细胞内Ca2 浓度。结果外源性C肽的加入可升高2型糖尿病患者红细胞膜的Na -K -ATP酶活性,并降低红细胞内的Ca2 浓度。结论胰岛素原C肽可以改善2型糖尿病患者降低的红细胞膜Na -K -ATP酶活性。     

Ca2+激活生物酶对苎麻纤维脱胶的工艺参数优化

利用Ca2+对生物酶进行有效激活,以提高苎麻生物酶脱胶效果,优化脱胶工艺中Ca2+浓度、pH值、通气量等工艺参数,经过Box-Behnken试验设计和SAS软件分析,得出最优工艺条件为:果胶酶、半纤维素酶浓度分别为12、4 mg/mL,酶处理时间5 h,酶处理温度50°C,Ca2+浓度4.23 mg/mL,pH值4.8,通气量9.2 dm3/min.利用最优工艺处理后的精干麻的残胶率为1.96%,断裂强力为64.5 cN,纤维平均细度为0.457 tex.     

Effect of phytate on the in-vitro solubility of Al+, Ca2+, Hg2+ and Pb2+ as a function of pH at 37°C

The effect of phytate on the solubility of Al³⁺ and Pb^{2 +} has been investigated in vitro at 37°C across the pH ranges 3–7 (Pb²⁺) and 2–5 (Al³⁺). For both ions minimum solubility was found when the initial metal ion: phytate ratio was in the range 5:1–3:1 across the whole pH range. For Al³⁺ the solubility rose sharply either side of these ratios whereas for Pb^{2 +} solubility rose only slowly as the metal ion: phytate ratio was reduced. Hg²⁺ was totally soluble under all conditions tested. At pH 7 Ca²⁺ solubility was found to be at a minimum when the initial Ca : phytate ratio was 5 :1 irrespective of the initial Ca²⁺ concentration.     

采后Ca2+处理对小油菜衰老进程的影响

以白菜型油菜(Brassica campestris L,品种五月慢,俗称小油菜)为实验材料,以不同浓度的CaCl2溶液作为ca2 来源,研究Ca2 处理对小油菜衰老进程的影响.结果表明:0.25%～0.35%的CaCl2溶液能在一定程度上延长小油菜的贮藏期;用0.3%的CaCl2溶液处理小油菜,测定其细胞膜渗透率,说明在贮藏后期钙能够有效降低膜透性,延缓细胞衰老.     

Zn2+-SiO2-TiO2三元复合催化剂的制备及其光催化降解性能

采用溶胶-凝胶法制备了Zn2+-SiO2-TiO2三元复合纳米催化剂,并用DRS、FT-IR、XRD和SEM等对样品的形态和结构进行了表征,并以罗丹明B和刚果红染料的印染废水做探针反应,分别在紫外光和可见光照射下评价了其光催化性能.与TiO2一元纳米催化剂和Zn2+-TiO2、SiO2-TiO2二元纳米催化剂进行对比,Zn2+-SiO2-TiO2三元复合纳米催化剂对罗丹明B溶液(5 mg/L)和刚果红溶液(10 mg/L)都表现出较高的光催化降解性能,可见光下的降解率分别达到90%和83%.     

Ca^2＋和聚乙二醇对菠萝蛋白酶活性和热稳定性的影响

研究了Ca2 和聚乙二醇对菠萝蛋白酶活性及热稳定性的影响.在37℃下,Ca2 与酶作用1 h后,5～10mmol/LCa2 对酶的活性均有促进作用,其中当Ca2 浓度为2 mmol/L时,促进作用最明显.在60℃下,Ca2 浓度为3 mmol/L时对菠萝蛋白酶的热稳定性效果最好,处理100 min后仍然能保留68％的活性;菠萝蛋白酶在60℃下活性的半衰期为86min,除Ca2 浓度为1 mmol/L外,其他浓度(2 mmol/L、3 mmol/L、4 mmoFL和5 mmol/L)Ca2 与菠萝蛋白酶作用后,酶的半衰期均有所延长,未经修饰的聚乙二醇6000加入酶反应体系中,其对酶活性起很大的抑制作用,且酶的热稳定性也未得到改善.     

荧光分析法检测金藻对Zn2+的利用

研究球等鞭金藻3011(Isochrysis Galbana 3011)对Zn2+的利用。采用FDA-PI双色荧光分析法对处理藻液进行流式细胞技术检测和荧光显微镜镜检,评价4 h和24 h的细胞活性,通过单因素对比试验设计,试验数据使用spss17.0统计软件进行方差分析。结果在活性浓度作用域中,未发现致毒现象,藻细胞长势良好,Zn2+处理Isochrysis Galbana 30114 h、24 h时,FDA-PI荧光检测显示Zn2+浓度为80μg/L时流式检测结果与对照组比较具统计学意义,藻细胞膜的完整性几乎没有受到影响,而FDA荧光检测则表明藻细胞的脂酶活性受到刺激。这一趋势在处理24 h时依然存在,并获得最大活度。研究表明80μg/L是Zn2+利用的最佳浓度域,说明Zn2+的摄入加速了细胞膜上磷脂代谢。     

The effect of Ca2+ and cellular structure on apple firmness and acoustic emission

This study presents the influence of calcium lactate treatment (0?C6?%) and cellular composition on two mechanical attributes: firmness and total acoustic emission (AE) events registered in the puncture test of apple tissue. The experiment was performed on five apple cultivars stored for nine months in a normal or controlled atmosphere. The microstructure was characterized quantitatively on control samples by confocal scanning laser microscope followed by image analysis. The mean area and perimeter of detected objects, which were either cells or spaces, and estimated cell wall fraction were used for the characterization of the tissue microstructure. Treatment with increased Ca²⁺ concentration caused a significant increase in firmness and total AE events. The increase was more pronounced in the case of total AE events which better reflected an increase in brittleness of apple tissue than firmness parameter. The effect was particularly positive in the case of very soft apples (stored in a normal atmosphere) due to greater extent of de-esterification of homogalacturonan. Analysis of the results, together with a review of the literature, suggests that calcium importantly changes the cracking mode of tissue, from intercellular debonding to cell wall rupturing. Firmness and the total AE events significantly relate negatively to the object??s size and positively to estimated cell wall fraction. A rough accordance of the number of split cells open across cell walls by puncture probe and the total AE events registered in the test, which was saturated in high Ca²⁺ concentrations, was noticed.