Adsorption of Sr by immobilized microorganisms

Wastewaters from numerous industrial and laboratory operations can contain toxic or undesirable components such as metal ions, which must be removed before discharge to surface waters. Adsorption processes that have high removal efficiencies are attractive methods for removing such contaminants. For economic operations, it is desirable to have an adsorbent that is selective for the metal contaminant of interest, has high capacity for the contaminant, has rapid adsorption kinetics, can be economically produced, and can be regenerated to a concentrated waste product or decomposed to a low-volume waste. Selected microorganisms are potentially useful adsorbents for these applications because they can be inexpensive, have high selectivities, and have high capacities for adsorption of many heavy metals, which are often problems in a variety of industries.     

Use of radiochemical methods as tools for speciation purposes in environmental and biological sciences.

Chemical speciation for a few elements can be facilitated to a great extent by incorporating a suitable radioisotope into the system and measuring the radiation of the isolated species. This radiospiking can be applied to in vitro and in vivo labelled experiments. Radionuclides are, however, also present as an anthropogenic contaminant from various nuclear fission activities. The radiotracer should be added under such conditions that it behaves in exactly the same way as the isotopes it represents. It should possess an adequate radioactive half-life, and preferably be a gamma-emitter because of the ease of detection. Radiotracer labelling is now widely used to study speciation problems of many essential and toxic elements in body fluids and tissues. It can be used to trace the different locations where the element is metabolized and stored, and subsequently to detect the element in the isolated biocomponents. The determination of the location of a radiotracer in a cell by autoradiography proved to be impractical because of the lack of resolution. Radiochemistry is similarly very useful for investigating particular aspects of the speciation of heavy metals as they occur in the ecosystem, and to follow the fate and effects of fission nuclides in the environment as they are carried around by the water and air masses. However, in certain circumstances the behaviour of fission products appears to be different from that of their stable analogues. For the actinides they simply do not exist. Radiochemical methods are a major tool for identifying and quantifying the nuclides in the different species.     

Stability and Mobility of Metal-Humic Complexes Isolated from Different Soils

The contamination of potable water aquifers by heavy metals is one of the most severe environmental threats. For the transport of heavy metals from various types of contaminated sites into the ground water and also into surface water aquifers, humic substances (HS) are recognized to be of main importance. Dissolved in natural waters humic substances are readily complexed with a variety of metal ions. Therefore, humic substances are of cardinal importance for the migration and, consequently, the pollution of ground waters with heavy metals. Our paper presents the results of a comprehensive comparison of several isolated humic acids of soils of different origin (different geochemical milieu) and their metal complexes. Two polluted sites in Germany, which differ in their geochemical milieu (pH-value) were selected. The aim of our experiments was to describe the properties of terrestrial humic substances depending on their origin and genesis as well as the effects of the transport of humic substance-bound metals into the water-unsaturated soil zone. After determination of heavy metals in the soils by photon activation analysis the activated soil was used as an inherent tracer in batch experiments with the isolated humic acid. After adsorption of the loaded humic acid on an XAD-8 resin column, the partition of metals mobilized by humic acids could be quantified. There are correlations of the formation of metal-humic complexes with the soil pedogenes, with the pH-value as well as with the humic acid concentration.     

Speciation analysis of heavy metals in natural waters: a review.

Metal speciation in natural waters is of increasing interest and importance because toxicity, bioavailability, environmental mobility, biogeochemical behavior, and potential risk in general are strongly dependent on the chemical species of metals. This paper provides an overview of the need for speciation of heavy metals in natural waters, the chemical and toxicological aspects of speciation, and the analytical procedures for separation and the different techniques for final determination that are used today. The trends and developments of speciation are also discussed. Finally, the case of chromium (Cr) was selected for a detailed presentation because the speciation of this metal has attracted a great deal of interest in view of the toxic properties of Cr(VI).     

Determination of trace metals in cow's milk from waste water irrigated areas in Central Mexico by chemical treatment coupled to PIXE

The Mezquital valley is an area near Mexico City that has been irrigated since 1890 with wastewater. The use of such waters in agriculture increases soil fertility but at the same time provokes the accumulation of heavy and toxic metals in soils and plants. Cows grazing in these conditions could accumulate heavy and toxic metals in their milk. In this work, a coprecipitation method with APDC is coupled to PIXE for the analysis of Fe, Ni, Cu, Zn, Se and Pb in bovine milk from the Mixquiahuala area in the Mezquital valley. Milk samples were analyzed from cows with supervised and unsupervised feedings finding significant differences between the milks in the Cu, Pb and Zn content. However, no correlation between the type of milk and the metal content could be established. Lead does not represent a health risk for humans in its current concentration and other metals do not seem to be toxic. The transfer ratio from soil and plants to the milk is apparently low.     

Determination of chemical species of selected trace elements in fly ash

Complex analytical methods have been developed for determining the chemical composition of fly ashes. Samples were collected at coal-fired power plants and municipal waste incinerators. Morphological investigations and single particle analysis were performed by SEM/EDAX method. A survey of mineralogical phases was made by X-ray powder diffraction and infrared spectrometry. Solvent-leaching experiments were carried out for the information on the mobility of metal pollutants under real environmental conditions. Copper, Ni, Co, Cr, Pb and Cd have been studied, and of the toxic metals, Cd has been found in exchangeable forms in a great amount. Mobile species of toxic metals may have an impact on the quality of receiving waters or on organisms in soils.     

Solution extraction of transition and post-transition heavy and precious metals by chelate and macrocyclic ligands

This review focuses on compounds and methods that can be used for the extraction and separation from solution of two classes of elements that we define as heavy metals and precious metals. These elements are often targeted because they are toxic, costly, and their coordination chemistry has already been well studied, and because there is a need to develop methods of economically extracting, separating and recovering them from waste sites. This review outlines possible strategies that can be used, and reviews the present literature regarding the available methods for their extraction.     

The importance of stereochemically active lone pairs for influencing Pb(II) and As(III) protein binding

The toxicity of heavy metals, which is associated with the high affinity of the metals for thiolate rich proteins, constitutes a problem worldwide. However, despite this tremendous toxicity concern, the binding mode of As(III) and Pb(II) to proteins is poorly understood. To clarify the requirements for toxic metal binding to metalloregulatory sensor proteins such as As(III) in ArsR/ArsD and Pb(II) in PbrR or replacing Zn(II) in δ-aminolevulinc acid dehydratase (ALAD), we have employed computational and experimental methods examining the binding of these heavy metals to designed peptide models. The computational results show that the mode of coordination of As(III) and Pb(II) is greatly influenced by the steric bulk within the second coordination environment of the metal. The proposed basis of this selectivity is the large size of the ion and, most important, the influence of the stereochemically active lone pair in hemidirected complexes of the metal ion as being crucial. The experimental data show that switching a bulky leucine layer above the metal binding site by a smaller alanine residue enhances the Pb(II) binding affinity by a factor of five, thus supporting experimentally the hypothesis of lone pair steric hindrance. These complementary approaches demonstrate the potential importance of a stereochemically active lone pair as a metal recognition mode in proteins and, specifically, how the second coordination sphere environment affects the affinity and selectivity of protein targets by certain toxic ions.     

Trace Metal Speciation and Research in Marine Geochemistry

Abstract

In order to precise the origin and behaviour of trace metals associated with coastal marine sediments, marine geochemists frequently utilize various methods of sequential extraction. The main objective is to test the potential mobility / stability of particulate metals in the natural environments. Several examples are presented in the article, namely: i/ Exchangeable Pb from podzolic soils of the drainage basin of a lagoon which sediments and phreatic waters are for a large part inherited from the surrounding soils; ii/ Evolution of particulate metals in an estuary; iii/ Mobility of metals at the sea bottom interface; iv/ Role of amorphous components of estuarine sediments and suspended matter; v/ Effects of dredging activities on solubility of metals in an estuary; vi/ Behaviour of heavy metals in lagoons.

Main results obtained from the extraction procedures are described, as well as particular difficulties encountered when applying some classical methods.     

Hydrogen bonding versus coordination of adsorbate molecules on Ti-silicalites: a density functional theory study

The present study discusses the results of theoretical calculations obtained at the B3LYP/ 6-31G level on the structural, electronic, and energetic properties of Ti-silicalites. Particularly, the relevance of 5T cluster models, either H- or OH-terminated, in large-scale calculations has been critically considered. It was shown that an open surface structure with one OH group and a closed-bulk structure with no bonded OH group at the Ti site are responsible for the observed UV-vis properties of Ti-silicalite materials. Both water and methanol can preferably interact with Ti-silicalites through the H-bonding mechanism, while ammonia can form either H-bonded or coordination complexes. The calculations support the existence of highly dispersed Ti sites in a tetrahedral environment only in Ti-silicalites because an increase in the coordination number of the Ti site by next-neighbor lattice oxygens is the energetically less favorable process.     

In silico analysis of metal coordination geometry in arsenic,beryllium, and lead bound structures

Metal toxicity is a potential hazard to health and toxic effects of metals have been implicated in many diseases. Understanding the interaction of toxic metals becomes vital to prevent hazards following its association in living systems. Coordination chemistry helps in predicting the metal environments like coordinating residues, coordination space, metal coordination geometry, etc. Our work aimed at predicting the coordination of toxic metals arsenic, lead, and beryllium. In this work, we analyzed coordination for each metal from a set of arsenic, beryllium and lead bound structures which were retrieved from the Protein Data Bank. The structures were validated using B-factor and occupancy of the coordinating residues towards the metals. Coordination patterns such as chelate residues, chelate length, geometry, coordination number and structural architecture were predicted. Coordination geometry of the metals was exposed beyond the coordination space with their coordination number ranging from 2 to 11. Analysis of metal environment revealed the acidic amino acids aspartic acid, glutamic acid, and the basic amino acids lysine, histidine, and cysteine to be predominant in coordinating with the metals. Chelate patterns like DDVMITAK, DWNVTVK, ESGKNSS for beryllium, CCCSK, DSDWD for lead and FLICVI and LKHHKEE for arsenic were predicted to be common through extended coordination space. The distinct molecular geometries such as pentagonal bipyramid and square planar were observed only in lead bound structures but not in beryllium and arsenic bound structures. Beryllium had a larger influence than arsenic and lead, based on conformational changes owing to the presence of the metals. Our coordination study puts forth several propositions based on the metal environment that would help in designing chelation strategies.     

Reactivity at the mineral-water interface: dissolution and inhibition

The reactivity of the mineral-water interface is often interpreted with the help of models used in electrochemistry, in solution coordination chemistry and in crystallography. Progress in understanding mechanisms of growth and dissolution of crystals and the inhibition of these processes depends on a better integration of these models. It is shown that dissolution can be explained in terms of a ligand exchange process; simplified rate laws for proton- and ligand-protonated dissolution rates, being related to surface bound protons and ligands, respectively, can be derived. Further refinement in interpreting surface reactivity comes from an appreciation of the molecular structures at the mineral water interface; here significant advances have been made by X-ray absorption spectroscopy, especially EXAFS (Extended X-ray Absorption Fine Structure spectroscopy), which permit distinction to be made between outer-sphere and inner-sphere surface complexes, and in many cases to determine the structure of the surface species at different crystallographic planes (e.g., bi-nuclear or mono-nuclear linkage of ligands on metal ions to surface metal centers). Such information coupled with solution-chemical studies on the extent of adsorption can provide new insight into the mechanisms of dissolution reactions and their inhibition and surface poisoning. A few experimental results are given to exemplify the factors that enhance and inhibit the non-reductive (EDTA) and reductive dissolution (by H₂S) of Fe(III)(hydr)oxides. Binuclear surface complexes by multivalent cations and by oxoanions, such as phosphate, arsenate and borate, are believed to be efficient inhibitors for oxide dissolution because they form bi- or multinuclear innersphere surface complexes that can bridge two or more metal centers in the surface lattice; the simultaneous removal of such bi- or multinuclear surface complexes from the surface is energetically unfavorable. Proton and ligand promoted dissolution reactions and their inhibition by oxoanions and bi- or multinuclear surface complexes are not only relevant in geochemistry (weathering, soil-formation, transfer of elements and pollutants) but also in metallic corrosion, formation and breakdown of passive oxide films.     

Trace elements in soil: Their determination and speciation

Summary The different types of soil analysis are reviewed in-outline and some recent developments and methodologies are discussed.For the determination of the total trace element content of soils, conventional, multi-element, solid sample methods including d.c. arc optical emission and spark source mass spectrometric procedures are briefly considered together with the potential of current X-ray fluorescence, solid sample graphite furnace atomic absorption and glow discharge mass spectrometry.The use of strong acid digestion, with for example aqua regia, for the determination of pseudo-total concentrations of heavy or toxic metal accumulations in soil is described.The limitations of solution methods for multi-element analysis of soils are outlined together with the prospects for the use of soil slurries to eliminate the sample preparation and dilution problems associated with the dissolution of soils. The difficulties in taking reproducible and representative samples of inhomogeneous materials such as soils are highlighted.Trace element speciation can be defined as the identification and quantification of the different forms or phases in which they occur in soils. Some examples of such procedures and extractants for both essential and toxic elements in soils are presented. The difficulties of trace element speciation in soils as distinct from soil extracts or soil solutions are illustrated briefly.     

NMR and EPR structural delineation of copper(II) complexes formed by kanamycin A in water

The complexes formed by kanamycin A at three different pH values (5.5, 7.4 and 12.0) were investigated by NMR and EPR spectroscopy. Paramagnetic relaxation contributions to proton relaxation rates were measured using a combination of the TOCSY sequence with the inversion recovery experiment in order to gain signal resolution in the bulk region. Measured contributions were converted into distances and used for structural determination by restrained simulated annealing where all possible chair and boat conformations of the rings were taken into account. The interaction of the Cu(II) ion with the nitrogen of the C ring is apparent at all pH values. At higher pH also the amino group of ring A starts to be involved in the metal coordination sphere. This is accompanied by a switch in conformation of ring C. Structures are consistent with the involvement in the coordination sphere either of the 2' or 4' hydroxyl oxygens at pH 5.5 and the 5 and the 6' hydroxyl oxygens (or the ring oxygen) at pH 12.0.     

Two distinct anion-binding modes and their relative stabilities

Two distinct hydrogen-bonding modes, end-on and end-to-end coordination, have been observed in the complexation between macrocycles and polyatomic anions such as azide and oxoanions.     

极谱催化波的研究

本文综述北京大学化学系电化学分析小组二十多年来极谱催化波的研究工作。将已研究的二十五个元素的催化体系、灵敏度、催化波的性质和应用列于表1.催化波有足够的灵敏度和选择性,适用于半导体材料、高纯金属、合金、矿物、矿石、水、土壤等各方面的痕量分析。关于催化波的机理,用测量催化电流、悬汞电极、i～t曲线、循环伏安、电流积分、放射性示踪诸方法研究了反应历程、电极活性络合物的组成、稳定常数、化学反应的速率常数和吸附现象。介绍了现正着重研究稀土元素的极谱催化波的情况。     

Removal,recovery and enrichment of metals from aqueous solutions using carbon nanotubes

Environmental pollution caused by toxic metals (heavy metals, radioactive metals, etc.) is one of the major global issues, thus removal of toxic metals from contaminated water seems to be particularly important. On the other hand, the recovery and enrichment of metals, especially noble metals, from waste water is also crucial. To address these issues, nanotechnology plays an essential role in environmental monitoring and pollution control. To remove metals from contaminated water, or enrich metals from waste water, carbon nanotubes (CNTs) and their composites have attracted great attention due to their excellent adsorption performance. The removal efficiency for metal ions by CNTs was observed aroud 10–80 %, which could be improved to approach 100 % by selectively functionalizing CNTs with organic ligands. Herein, we review the applications of CNTs in treatment of toxic metal-containing wastewater for environmental monitoring and metals recovery. Due to their higher sensitivity and selectivity towards the enrichment of metals or detection of toxic metal pollution of the environment, and the latest research progress of using CNT composites for metal treatment is also discussed.     

脲类受体对阴离子的结合、识别和分离

在阴离子受体中,脲基因其作为双氧键给予体,能与许多阴离子结合,成为一类重要的、有效的受体单元,同时该类受体的功能化为阴离子结合行为的检测提供了方便.本文综述了近年来单脲、二脲、多脲及金属辅助的脲类受体的设计合成及对阴离子的结合、识别和分离方面的研究进展.     

Simulating GTP:Mg and GDP:Mg with a simple force field: A structural and thermodynamic analysis

Di‐ and tri‐phosphate nucleotides are essential cofactors for many proteins, usually in an Mg²⁺‐bound form. Proteins like GTPases often detect the difference between NDP and NTP and respond by changing conformations. To study such complexes, simple, fixed charge force fields have been used, which allow long simulations and precise free energy calculations. The preference for NTP or NDP binding depends on many factors, including ligand structure and Mg²⁺ coordination and the changes they undergo upon binding. Here, we use a simple force field to examine two Mg²⁺ coordination modes for the unbound GDP and GTP: direct, or “Inner Sphere” (IS) coordination by one or more phosphate oxygens and indirect, “Outer Sphere” (OS) coordination involving one or more bridging waters. We compare GTP: and GDP:Mg binding with OS and IS coordination; combining the results with experimental data then indicates that GTP prefers the latter. We also examine different kinds of IS coordination and their sensitivity to a key force field parameter: the optimal Mg:oxygen van der Waals distance R_min. Increasing R_min improves the Mg:oxygen distances, the GTP: and GDP:Mg binding affinities, and the fraction of GTP:Mg with β + γ phosphate coordination, but does not improve or change the GTP/GDP affinity difference, which remains much larger than experiment. It has no effect on the free energy of GDP binding to a GTPase. © 2012 Wiley Periodicals, Inc.