金属和非金属元素的甲基化行为其在环境化学研究中的意义

甲基化过程是许多金属元素与生物地球化学循环的重要途径,目前已知多种金属,非金属元素在自然界中均匀甲在化反应过程,在前人工作的基础上,本文对甲基化供体以及甲化反应的机理进行了论述,并对其在环境化学研究中的意义进行了讨论。     

Transition Metal Thiometalates: Properties and Significance in Complex and Bioinorganic Chemistry

In their highest oxidation states the early transition metals V, Nb, Ta, Mo, W, and Re form tetrahedral, strongly colored thioanions endowed with some remarkable properties. Thiometalates can be formed by solid-state reactions or in solution from the oxometalates. Poly-thiometalates with mixed valences can be produced by new types of intramolecular condensation-redox reactions from thioanions. The metal-sulfur bonds can react either nucleophilically or electrophilically, and in the case of the Mo–S bonds this is of biochemical interest. It is important to mention the applications of thiometalates as ligands in complex chemistry (generation of multi-metal complexes, versatile coordination behavior, unique electronic properties of the ligands), in which thiometalato complexes with a variety of electron populations can exist because of the marked electron delocalization. Apart from this, MoS has a significance in bioinorganic problems, e.g. the nitrogenase problem and Cu? Mo antagonism.     

Improvements of Speciation Analyses in Environmental Matrices

The release of some organometallic compounds and other chemical forms of elements in the environment has led to great international concern because of their high toxicity. The validation of the analytical techniques became of paramount importance which led the Community Bureau of Reference (BCR) to decide on the organisation of a series of projects for the improvement of the quality of speciation analyses. In addition, it was found useful to discuss thoroughly the different sources of error likely occurring in speciation analyses and a workshop was organized for this purpose; the aim of this workshop was to discuss the state of the art of speciation determinations, to define use, applicability and necessity of determinations of element species, to investigate where limitations exist and discuss the work necessary to overcome these and to detect where techniques have sufficiently been developed to produce reliable and valuable results. This paper presents the organization of the workshop, its main issue and describe the state of the current BCR projects on speciation.Abbreviations AAS Atomic absorption spectrometry - CVAAS Cold vapour AAS - DPP Differential pulse polarography - ECD Electron capture detector - ETAAS Electrothermal AAS - FIA Flow injection analysis - FID Flame ionisation detector - FLUOR Spectrofluorimetry - FPD Flame photometric detector - GC Gas chromatography - HG Hydride generation - HPLC High performance liquid chromatography - HPLC-AES HPLC atomic emission spectrometry - INAA Instrumental neutron activation analysis - ICPAES Inductively coupled plasma AES - MS Mass spectrometry - QFAAS Quartz furnace AAS - RNAA Neutron activation analysis with radiochemical separation     

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.     

Speciation of Arsenic in Environmental and Biological Samples

A novel arsine generator glass assembly is constructed and reported for the spectrophotometric determination and speciation of arsenic in real samples. In an arsine generator, sodium borohydride is added dropwise to the acidic sample solution and arsine thus formed is reacted with silver diethyldithiocarbamate (Ag‐DDTC) ‐ Tritron‐X (TX‐100) solution in pyridine to form a red coloured complex. The complex showed the absorption maximum at λ_max 540 nm. The molar absorptivity of the method was found to be (1.55) × 10⁴ L mole^?1 cm^?1 at this wavelength. The presence of non‐ionic surfactant, i.e. TX‐100 in the Ag‐DDTC solution, makes the method ≈ 3 times more sensitive than the conventional Ag‐DDTC method. Beer's law is obeyed in the concentration range of 0.05–2.80 mg L^?1 of arsenic. The detection limit of the method was calculated to be 20 μg L^?1 As. Speciation of arsenite from other forms of arsenic in sample solutions was carried out by extraction of arsenite with Pb‐DDTC in chloroform, followed by spectrophotometric determination. After arsenite separation the sample is used for the arsenate determination. Total arsenic was determined by acid decomposition of the same sample. The speciation data were found to be comparable (±2%) with ICP‐MS, with better precision (< 1%). The method has been successfully applied for the speciation of arsenic in drinking water and dust samples of arsenic affecting the Rajnandgaon district of Chhattisgarh, India, and urine and blood samples of patients with arsenical diseases. Concentration of total arsenic in tube‐well water of this area was 3–6 times more than the permissible limit. Dust samples contained less amounts of arsenic than the ground water.     

The Significance of the Secondary Reactions Regularity for the Chemistry of Condensed Metal Phosphates

Abstract

One of the fundamental methods for the synthesis of condensed phosphates (CP) is their isolation from the aqueous systems containing condensed metal phosphates and polyvalent cations by the method of residual concentrations. The CP regularity was found to show the behaviour in aqueous solutions, conventionally called the secondary reactions. The secondary transformations (ST) or secondary reactions (SR) are expressed in self-deposition of stable crystalline phases through metastable (primary) compounds after a definite induction period from the aqueous systems containing AMCP (ammonium, thallium) and multicharged cations. Various types of secondary reactions, their mechanism, causal relationship, and significance have been investigated. They are typical for simple and complex CP compounds with the chain as well as the cyclic structure of the phosphate ligands containing 2,3,4 phosphorous atom despite the polyvalent cation nature. More than 400 compounds have been obtained by means of the rational methods based on SR. SR contribute significantly to the complexation theory. SR of complex compounds are in their character contrary to the complexation reactions of the known inorganic salt systems. This opposition is realized by isolation of these complex compounds in the form of little-soluble salts. They are the products of a stepwise complex dissociation or of the primary complexation compounds. The isolated compounds are of great purity.     

冲积平原区土壤中重金属元素的存在形态分析

采用0.1mol／L氢氧化钠浸提腐殖酸的方法,将土壤中的腐殖酸及与腐殖酸结合的重金属元素分离出来;分别用分光光度法、原子荧光光谱法、等离子质谱法测定样品中腐殖酸及重金属元素的含量;初步测定结果显示：与腐殖酸结合的重金属元素是冲积平原区表层土壤中重金属元素的1种重要存在形态,而且可能是土壤中重金属污染元素主要的存在形式。     

Metal Speciation - General Concepts and Applications

Abstract

Several aspects of metal speciation in sediments are reviewed: (1) Due to the instability of polluted solid materials, sample handling and storage prior to analysis is problematic. In particular, changes from reducing to oxidizing conditions, which involve transformations of sulfides and a shift to more acid conditions, increase the mobility of critical metals. (2) Simple “standard” leaching tests can be used for easily soluble components such as halides or sulfates, but in most cases are not adequate for assessing mobility of trace metals. With sequential extraction procedures rearrangements of specific solid “phases” can be evaluated prior to their actual remobilisation. (3) Estimation of long-term release of metals from solids can be made using a test procedure, which combines data from column experiments applying controlled intensivation of parameters such as pH-value, redox potential and temperature with results from sequential extraction of the contaminated solids before and after exposure. (4) Partitioning studies on materials from core profiles are particularly useful, since they provide information on relative variations of elemental phases irrespective of the method applied, and thereby an insight into diagenetic processes taking place after deposition of the sediment components. (5) The leachable fraction does not necessarily correspond to the amount available to biota. Studies on the prediction of the trace metal levels in benthic organisms have shown, that the prognostic value of sequential extraction data is improved, when the trace metal concentrations are normalized with respect to the iron (hydrous oxide) and/or organic content of the sediments.     

Speciation in the environmental field – trends in Analytical Chemistry

The need for speciation-related information in environmental chemistry is critically evaluated. Recent advances in the analysis for volatile or volatizable organometallic compounds and redox states are presented. They include microwave-assisted extraction for the leaching of analytes and the solubilization of tissues, multicapillary gas chromatography, and integration of the sample preparation and separation steps in a single speciation-dedicated instrument. Particular attention is given to the needs for speciation analysis in environmental biota: plant and animal tissues. The areas discussed include speciation of selenium and arsenic, analytical chemistry of metal complexes with phytochelatins and metallothioneins, the need for the identification of metal enzymes and co-enzymes and their role in the biosynthesis of metal complexes. The status of the rapidly emerging field of bioinorganic analytical chemistry is discussed.     

环境电分析化学

介绍了环境电分析化学的基础、应用和发展，并与其它分析技术进行了比较。     

生物和环境样品中硒元素的形态分析研究

金属组学是继基因组学/蛋白质组学和代谢组学后提出的一种新的组学,其研究重点在于对所研究的金属和类金属元素的各种存在形态进行分析。硒是生物环境中存在的一种重要的类金属元素。形态与浓度不同的硒化合物可能是生物体的必需元素,同时也可能导致中毒。本文对目前存在的硒元素形态分析方法的研究现状进行了总结,并对前景进行了展望。     

金属氟化物在富勒烯化学中的应用

综述了金属氟化物的制备方法及其在富勒烯化学中的应用。参考文献19篇。     

Recovery of Metal Ions by Chitosan: Sorption Mechanisms and Influence of Metal Speciation

Chitosan is characterized by a high affinity for metal ions due to its high content of amine groups. The sorption mechanism depends on both the protonation of these amine groups and the speciation of metal ions. Metal cations may be adsorbed at pH close to neutrality by chelation mechanism while metal anions can be adsorbed in acidic solutions through ionic interactions with protonated amine groups. Several examples are considered. The first example focuses on Cd sorption, which proceeds by a chelation mechanism on free non‐protonated amine groups in neutral media. In acidic solutions the protonation of amine groups limits the ability of amine groups to complex Cd. The cross‐linking of chitosan with glutaraldehyde also results in a dramatic decrease of sorption properties due to the decrease in the density of complexation sites available for sorption. The sorption of vanadium(V) and molybdenum(VI) illustrates the high capacity of chitosan for the sorption of oxo‐anions. They are very efficiently sorbed in acidic solutions by ionic interactions. The correlation of sorption capacities with the distribution of metal species shows that the sorbent has a greater affinity for highly charged anionic species. The sorption of complex anionic species such as chloro‐complexes of Pd and Pt; and that of copper complexed with organic ligands have also been studied. The optimum conditions for sorption are obtained when anionic complexes predominate in the solution. The chemical modification of chitosan, obtained by grafting of sulfur compounds, allows modifying the sorption mechanism: the ion‐exchange polymer is transformed to a dual ion‐exchange and chelating polymer.

Copper sorption isotherm in presence of sodium citrate (0.004 M ) (? RNH: fraction of protonated amine groups; ACuC: total fraction of anionic copper complexes; Cu‐FAL: total fraction of copper‐free anionic ligands).     

色谱法分析环境中铝形态的进展

综述了色谱法在环境体系铝形态研究中的应用进展,比较了离子交换色谱、体积排阻色谱、反相高效液相色谱、快速蛋白质液相色谱、毛细管电泳以及流路中嵌入色谱小柱的流动注射分析法的优缺点。引用文献55篇。     

Computational Chemistry in Environmental Toxicology QSAR

Abstract

Computational chemistry provides a means for the calculation or estimation of three-dimensional chemical structure, organization and analysis of chemical data, classification of industrial chemicals by structure and properties, prediction of toxicity, and identification of chemical structure. The development of the EPA National Environmental Supercomputer Center (NESC) in Bay City, Michigan, makes available to scientists in EPA Headquarters, the ability to perform advanced QSAR modeling. This provides the means to develop and apply QSAR models for chemicals acting by a variety of molecular mechanisms. The work makes possible improved programmatic support to the Office of Pollution Prevention and Toxics under the Toxic Substances Control Act and the Pollution Prevention Act.     

环境污染是化学惹的祸吗

人们总是将环境污染与化学连在一起,并认为化学是环境污染的根源。本文在分析环境污染的产生、化学在环境保护方面的作为的基础上认为,产生环境问题的根源主要是人类对自然无节制的索取和向环境超量排放废弃物以及没有充分利用化学科学的力量根治源头。