Extraction methods in soil phosphorus characterisation : Limitations and applications

The quantification and characterisation of soil phosphorus (P) is of agricultural and environmental importance and different extraction methods are widely used to asses the bioavailability of P and to characterize soil P reserves. However, the large variety of extractants, pre-treatments and sample preparation procedures complicate the comparison of published results. In order to improve our understanding of the behaviour and cycling of P in soil, it is crucial to know the scientific relevance of the methods used for various purposes. The knowledge of the factors affecting the analytical outcome is a prerequisite for justified interpretation of the results. The aim of this thesis was to study the effects of sample preparation procedures on soil P and to determine the dependence of the recovered P pool on the chemical nature of extractants. Sampling is a critical step in soil testing and sampling strategy is dependent on the land-use history and the purpose of sampling. This study revealed that pre-treatments changed soil properties and air-drying was found to affect soil P, particularly extractable organic P, by disrupting organic matter. This was evidenced by an increase in the water-extractable small-sized (<0.2 µm) P that, at least partly, took place at the expense of the large-sized (>0.2 µm) P. However, freezing induced only insignificant changes and thus, freezing can be taken to be a suitable method for storing soils from the boreal zone that naturally undergo periodic freezing. The results demonstrated that chemical nature of the extractant affects its sensitivity to detect changes in soil P solubility. Buffered extractants obscured the alterations in P solubility induced by pH changes; however, water extraction, though sensitive to physicochemical changes, can be used to reveal short term changes in soil P solubility. As for the organic P, the analysis was found to be sensitive to the sample preparation procedures: filtering may leave a large proportion of extractable organic P undetected, whereas the outcome of centrifugation was found to be affected by the ionic strength of the extractant. Widely used sequential fractionation procedures proved to be able to detect land-use -derived differences in the distribution of P among fractions of different solubilities. However, interpretation of the results from extraction experiments requires better understanding of the biogeochemical function of the recovered P fraction in the P cycle in differently managed soils under dissimilar climatic conditions.

Properties of acetylcholinesterase from Pisum sativum

Acetylcholinesterase (AChE) from Pisum sativum purified 28 fold showed two closely moving protein bands on polyacrylamide gel electrophoresis, both of which have AChE activity. AChE activity occurs in roots, stem and leaves, that in roots varying with age. Activity is optimal at pH 9 and at 30”. The energy of activation is 9.82 x lo3 J per mol and MW is greater than 200000. Although the enzyme can hydrolyze both choline and non-choline esters, it has greater affinity for acetylthiocholine (ATCh) and acetylcholine (ACh). ATCh inhibits the enzyme at higher concentrations and the K, is 0.2 mM with this as substrate. The enzyme is not as sensitive to Eserine as it is to Neostigmine. It is also inhibited by organophosphorus pesticides such as Fensulfothion, Parathion and Dimethoate. Treatment of the seeds with Fensulfothion [O, O-diethyl (p-methylsulfinylphenyl) phosphorothioate] affects growth and secondary root development. This might be explained by its inhibition of AChE and the consequent increase of endogenous levels of ACh.

Synthesis, Structure, and Magnetic Properties of Amine-Templated Transition-Metal Phosphites

Transition-metal phosphites of cobalt and vanadium, [C4N2H12][Co(HPO3)(2)] (I), [C4N2H14][Co(HPO3)(2)] (II), [Co[C4H8N12)(H2PO3)(2)] (III),[C4N2H14][(VF)-F-III(HPO3)(2)]center dot H2O (IV), and[C3N2H5](2)[V-4(III)(H2O)(3)(HPO3)(4)(HPO4)(3)] (V), have been synthesized and characterized. Organophosphorus esters were employed to stabilize cobalt in tetrahedral coordination and also to prepare the low-dimensional structures, which are otherwise difficult to synthesize. The structures have one- (I, II, IV), two- (III) and three-dimensionally (V) extended networks built up by the linking of metal polyhedra and phosphite units. Another vanadyl phosphite, [C2N2H10][((VO)-O-IV)(3)(H2O) (HPO3)(4)]center dot H2O,([15]) was also prepared and investigated extensively by ESR, magnetic susceptibility, and other studies. All the compounds in the present study exhibit antiferromagnetic interactions. Well-established magnetic models have been used to fit the experimental data. The compounds havealso been characterized in detail by using UV/Vis spectroscopic studies.

Vacancy-Engineered Nanoceria: Enzyme Mimetic Hotspots for the Degradation of Nerve Agents

Organophosphorus-based nerve agents, such as paraoxon, parathion, and malathion, inhibit acetylcholinesterase, which results in paralysis, respiratory failure, and death. Bacteria are known to use the enzyme phosphotriesterase (PTE) to break down these compounds. In this work, we designed vacancy-engineered nanoceria (VE CeO2 NPs) as PTE mimetic hotspots for the rapid degradation of nerve agents. We observed that the hydrolytic effect of the nano-material is due to the synergistic activity between both Ce3+ and Ce4+ ions located in the active site-like hotspots. Furthermore, the catalysis by nanoceria overcomes the product inhibition generally observed for PTE and small molecule-based PTE mimetics.

Vacancy-Engineered Nanoceria: Enzyme Mimetic Hotspots for the Degradation of Nerve Agents

Organophosphorus-based nerve agents, such as paraoxon, parathion, and malathion, inhibit acetylcholinesterase, which results in paralysis, respiratory failure, and death. Bacteria are known to use the enzyme phosphotriesterase (PTE) to break down these compounds. In this work, we designed vacancy-engineered nanoceria (VE CeO2 NPs) as PTE mimetic hotspots for the rapid degradation of nerve agents. We observed that the hydrolytic effect of the nano-material is due to the synergistic activity between both Ce3+ and Ce4+ ions located in the active site-like hotspots. Furthermore, the catalysis by nanoceria overcomes the product inhibition generally observed for PTE and small molecule-based PTE mimetics.

Impact of phosphamidon and its metabolites on histopathology of the liver, gill and intestine of Labeo rohita

Impact of phosphamidon, an organophosphorus pesticide and its metabolites viz. dimethyl phosphoric acid and 2-chloro 2-diethyl carbamoylmethyl vinyl acid on histopathology of a common teleost, Labeo rohita was studied by exposing the fish to sub-lethal concentrations which were taken as 1/3rd of LC50 and were equal to 0.0123 ppm for phosphamidon, 0.0160 ppm for dimethyl phosphoric acid and 0.0167 ppm for 2-chloro 2-diethyl carbamoylmethyl vinyl acid respectively. The results revealed that hepatocytes in the liver were markedly swollen and exhibited hydropic degeneration. Fusion of primary lamellae and moderate congestion of blood vessels were evident in the gill. Intestine showed degeneration of mucosa and cellular infiltration in sub-mucosa. LC50 values and histopathological photomicrographs suggest that phosphamidon is more toxic as compared to dimethyl phosphoric and 2-chloro 2-diethyl carbamoylmethyl vinyl acid.

The residue measurment of pesticide in water and biota of the Sorkhrood River in the south of the Caspian Sea

Pesticide residue is considered as a crucial factor in the fresh water ecosystem pollution of north Iran (Esp. Gillan and Mazandaran provinces). It is also regarded dangerous to the health of human being and animals. In this research , pesticide residue in 3 species of fish was gauged in stations of the Haraz river , the Sorkhrood river , and the Caspian sea. The sampeles were taken during 27 mounths (started in April 97 and ended to June 99). The maximum level of pesticide in water was found in July 98 for lindine at 12.4 ppb. The level of chlorinated pesticide residue recorded at 63 ppb in April 98. The level of. organophosphorus pesticides residue in water was at 1.75 ppb in Aug 97. The toxicity of the mentioned pesticide and bioaccomulation were taken into account in conducting this researched.

An improved method for the extraction of low molecular weight organic acids in variable charge soils

Due to specific adsorption to variable charge soils, low molecular weight organic acids (LMWOAs) have not been sufficiently extracted, even if common extractants, such as water and 0.1 M sodium hydroxide (NaOH), were employed. In this work, the method for extracting LMWOAs in soils with 0.1 M NaOH was improved for variable charge soils; e.g. 1.0 M potassium fluoride (KF) with pH 4.0 was applied as an extractant jointed with 0.1 M NaOH based on its stronger ability to change the electrochemical properties of variable charge soils by specific adsorption. With the proposed method, the recoveries of oxalic, tartaric, malic, citric and fumaric acids were increased from 83 4, 93 1, 22 2, 63 +/- 5 and 84 +/- 3% to 98 +/- 2, 100 +/- 2, 85 +/- 2, 90 +/- 2 and 89 +/- 2%, respectively, compared with NaOH alone. Simultaneously, the LMWOAs in Agri-Udic Ferrosol with field moisture were measured with a satisfactory result.

Growth of Chlorella vulgaris in cultures with low concentration dimethoate as source of phosphorus

The growth response of Chlorella vulgaris to low concentration of dimethoate, an organophosphorus pesticide, was studied. Results show that cell density, protein content, chlorophyll pigment and alkaline phosphatase activity were all increased, which indicates that low concentration dimethoate can accelerate growth of Chlorella vulgaris. (C) 1997 Elsevier Science Ltd.

稀土萃取数据库和稀土萃取剂的构效关系研究

随着计算方法和计算机技术的不断发展。计算机在各个领域的应用越来越广泛．计算机在化学上的应用就是在这种形式下产生的一种新兴学科．本论文工作着重于稀土萃取数据库和稀土萃取剂的构效关系研究．在研究中，取得了一些有意义的结果．主要工作如下：I．稀土萃取数据库将原来位于Micro VAXII上的数据库移植到微机上，并利用ACCESS数据库重建稀土萃取数据库．完成数据库的主页建设，同时应用ASP技术构造数据库的网上检索程序，使其能够很方便地对外服务．II.稀土萃取剂的构效关系研究建立了有机化合物pKa值的数据库，并由此，进行了脂肪酸类、苯甲酸类、苯胺类、苯酚类和毗咤类化合物的结构与其pKa值之间的相关性研究．针对不同类的化合物，我们提取了能表征其特点的参数来表征它们的结构．如在进行脂肪酸类和苯甲酸类化合物的构效关系研究时，着重计算了化合物的量子化学参数；对于苯胺类和苯酚类化合物则应用了分子在三维空间的投影和扩展的引力指数等参数；而对吡啶类化合物则应用了连接树的方法．同时最佳变量子集算法和正交化方法用来进行变量的选择．利用多元回归分析和人工神经网法进行二维QSPR研究，用CoMFA方法进行三维空间的研究，并取得较好的结果．另外，对核磁共振成像造影剂的结构与其稳定性的相关性也进行了探讨．通过只考虑配体的结构而简化了特征的提取，进而应用量子化学参数和拓扑指数获得了比较满意的结果．本论文还应用QSPR方法研究了手性化合物的色谱分离，并有较好的进展．

酸性磷（膦）酸酯萃取稀土、相关元素的机理及萃合物结构研究

本文研究了酸性磷（膦）酸酯对稀土及相关元素的萃取（包括协同萃取）机理，利用核磁共振（NMR）测试手段对HEH/EHP(III)、BTMPPA－Yb(III)的萃合物结构进行了~1H、~(13)C、~31P NMR谱的测定，获得了一些新的结构信息。

有机磷降解菌的分离鉴定及其降解特性研究

从沈阳苏家屯地区长期受有机磷污染的土壤中分离到10株以敌敌畏（DDVP）为唯一碳源生长的细菌，其中降解活性最高的菌株经生理生化鉴定和16SrDNA同源性比较,鉴定为甲基杆菌属(Methylobacterium sp.)，将其命名为DDV-1(GenBank Accession NO. FJ225120)。该菌株最适生长条件： pH 7.0，温度 30℃。 对菌株DDV-1降解性能的研究表明，该菌株降解敌敌畏的最适条件为：pH 7.0，30℃，在此条件下，500 mg/L敌敌畏经过DDV-1菌株代谢5天后，降解率可达74.9%。装液量对菌株生长及降解率影响不大。DDV-1对敌敌畏有较高的耐受度，在初始量浓度为 1 500 mg/L敌敌畏的高浓度下同样能进行降解。敌敌畏的降解速率与起始接种量呈正比。正交设计实验结果表明6个因素对敌敌畏降解率影响的程度依次为C(pH)、D（温度）>B(N源)>E（接种量）>A（C源）>F（DDVP浓度）。 除了敌敌畏，菌株DDV-1还能以甲基异硫磷、辛硫磷、敌百虫、甲胺磷、对硫磷为唯一碳源，对有机磷类农药有广谱降解性。 酶学方面，酶的定位试验表明，菌株DDV-1的有机磷水解酶为胞内酶。该水解酶最适反应条件为：pH 7.0，温度30℃；粗酶液在20-40℃稳定性良好，在pH6.0-9.0都能保持活力，最适产酶碳、氮源分别为葡萄糖和蛋白胨。 在分子生物学方面，通过功能基因扩增，扩增到有机磷水解酶基因（mpd基因）。该片段为818碱基，其与已知的有机磷水解酶基因不具有同源性。 实验室条件下模拟有机磷污染土壤修复的研究表明，农药的初始浓度和接种量对敌敌畏降解影响较大，最适接种量为1000000个细胞/g土壤。

Solvent extraction study of protactinium(V) with methyl-iso-butyl carbinol and methyl-iso-butyl ketone

In order to study the extraction pattern of protactinium in different types of extracting agents and compare the similarity of patterns of extraction with dubnium and thereby unraveling its chemistry, solvent extraction of protactinium(V) with methyl-iso-butyl carbinol (MIBC) and methyl-iso-butyl ketone (MIBK) was studied using Pa-233 as a radiotracer. The extraction efficiencies of Pa were determined as a function of shaking time, concentrations of mineral acids, and extractant concentrations using the two extractants. The results show that MIBK is more suitable for the extraction of protactinium than MIBC in benzene. Furthermore, the effect of the F anion is also discussed.

Solvent extraction of americium and europium ions by amide-derivatized polyethers from picric acid aqueous solution

The extraction of Am3+ and Eu3+ from picric acid aqueous solution by N,N-1,2-ethanediyl-bis[2-(N,N-diphenyl-carbamoyl-methoxy)-benzamide] was investigated by a radioactive tracer technique. The composition of the extracted species has been determined as ML(Pic)(3) (M = Eu, Am). The effect of various parameters such as pH, organic diluents, different extractants, picric acid concentration and extractants concentration on the extraction of Am3+ and Eu3+ has been studied. The extraction equilibrium mechanism has been also evaluated and discussed.

Preparation of stir bars for sorptive extraction using sol-gel technology

A sol-gel coating method for the preparation of extractive phase on bars used in sorptive microextraction is described. The extraction phase of poly(dimethylsiloxane) is partially crosslinked with the sol-gel network, and the most part is physically incorporated in the network. Three aging steps at different temperatures are applied to complete the crosslinking process. Thirty-micrometer-thick coating layer is obtained by one coating process. The improved coating shows good thermal stability up to 300degreesC. Spiked aqueous samples containing n-alkanes, polycyclic aromatic hydrocarbons and organophosphorus pesticides were analyzed by using the sorptive bars and GC. The results demonstrate that it is suitable for both aploar and polar analytes. The detection limit for chrysene is 7.44 ng/L, 0.74 ng/L for C-19 and 0.9 ng/L for phorate. The extraction equilibration can be reached in less than 15 min by supersonic extraction with the bars of 30 mum coating layer. (C) 2004 Elsevier B.V. All rights reserved.