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1.
The toxicity of inorganic trivalent arsenic for living organisms is reduced by in vivo methylation of the element. In man, this biotransformation leads to the synthesis of monomethylarsonic (MMA) and dimethylarsinic (DMA) acids, which are efficiently eliminated in urine along with the unchanged form (Asi). In order to document the methylation process in humans, the kinetics of Asi, MMA and DMA elimination were studied in volunteers given a single dose of one of these three arsenicals or repeated doses of Asi. The arsenic methylation efficiency was also assessed in subjects acutely intoxicated with arsenic trioxide (As2O3) and in patients with liver diseases. Several observations in humans can be explained by the properties of the enzymic systems involved in the methylation process which we have characterized in vitro and in vivo in rats as follows: (1) production of Asi metabolites is catalyzed by an enzymic system whose activity is highest in liver cytosol; (2) different enzymic activities, using the same methyl group donor (S-adenosylmethionine), lead to the production of mono- and di-methylated derivatives which are excreted in urine as MMA and DMA; (3) dimethylating activity is highly sensitive to inhibition by excess of inorganic arsenic; (4) reduced glutathione concentration in liver moderates the arsenic methylation process through several mechanisms, e.g. stimulation of the first methylation reaction leading to MMA, facilitation of Asi uptake by hepatocytes, stimulation of the biliary excretion of the element, reduction of pentavalent forms before methylation, and protection of a reducing environment in the cells necessary to maintain the activity of the enzymic systems. 相似文献
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QI Bin YANG Bing WANG ZhuQing YANG HongYan & LIU Lu School of Chemistry Material Sciences Shaanxi Normal University Xi’an China 《中国科学B辑(英文版)》2009,52(3):356-361
Radical production in the ozonolysis of propene in air was monitored directly by a peroxy radical chemical amplification (PERCA) instrument at room temperature (298±2 K) and atmospheric pressure (1×105 Pa). The ozonolysis reactions were conducted in a flow tube under pseudo-first-order conditions for ozone. The decay in ozone was calculated based on reaction time tr and effective rate constant keff (keff = k1[C3H6]0)) for the ozone-propene reaction. The total radical yields relative to consumed ozone were d... 相似文献
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茶叶中新型污染物高氯酸盐在近年来受到越来越多的关注,相应的检测技术也在不断加强.参考国内外文献,综述了茶叶中高氯酸盐的检测方法.目前,茶叶中高氯酸盐的检测方法主要有离子色谱法(IC)、离子色谱-质谱法(IC-MS)和高效液相色谱-串联质谱法(LC-MS-MS).比较了不同检测方法的局限性和优越性,重点比较了高效液相色谱-串联质谱法不同前处理方法、净化小柱和检测条件的优劣,对茶叶高氯酸盐检测技术的发展和研究进行了展望,为检测茶叶中高氯酸盐的新材料研发和检测新标准的建立提供理论依据. 相似文献
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对成都平原西部金马镇深层土壤取样分析,研究了具有指示意义的几种微量元素富集情况,揭示了土壤原生地球化学环境质量;通过异常信息的筛选,分析了各元素异常反映的地球化学及地质信息. 相似文献
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超临界流体萃取技术在提取中药挥发油中的应用 总被引:5,自引:0,他引:5
全健 《广东微量元素科学》2001,8(7):13-16
用超监介CO2流体萃取技术对多种中药挥发油的提取进行了综述,并将其与传统的水蒸馏法进行比较。结果表明,用超临界流体法不仅挥发油的收率高,而且提取时间也大大缩短。 相似文献
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Samples of synthetic high-silica zeolites after high-temperature activation in oxygen are studied by ferromagnetic resonance. Observation of the fine structure of ferromagnetic resonance (FMR FS) indicates the formation of magnetic iron oxide nanoparticles in the course of thermal treatment of zeolites in oxygen. Features of the formation of a dispersed ferromagnetic phase in zeolites, geometric and magnetic characteristics of constituent nanoparticles are discussed. 相似文献
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ICP-AES测定铀污染土壤植物中铀的研究 总被引:2,自引:0,他引:2
采用电感耦合等离子体发射光谱(ICP-AES)对铀污染土壤植物中铀的测定方法进行了研究.在λU385.958 nm处,选择了仪器的最佳工作条件,考察了酸度和常见共存元素对测定的干扰情况,并且对比了干灰化消解和湿式消解对测定的影响.研究发现2%硝酸溶液为最佳介质,干扰离子对测定没有显著影响,干灰化消解比湿式消解得彻底.在选定条件下,方法检出限为0.18 mg·L-1,测定下限为0.61 mg·L-1,5.0000 mg·L-1的铀标准溶液的相对标准偏差RSD(n=10)为0.81%,方法回收率为96.2%~106.2%.该方法操作简单,快速.结果表明,用ICP-AES测定铀污染土壤植物样品中的铀是可行的. 相似文献
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对血清中Na离子含量的测量不确定度进行评定。不确定度的来源主要包括Na离子标准工作液的配制过程、血清样品的定容消化制备、标准曲线拟合、钠离子各分量不确定度的合成等引入的不确定度计算出各分量的不确定度,通过合成得到测量结果的合成不确定度、扩展不确定度及测试结果的报告形式。 相似文献
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阳江市幼儿头发中微量元素含量分析 总被引:5,自引:2,他引:3
测定了阳江市4449名1~7岁儿童头发中6种元素含量.结果表明,该市儿童头发中的 Zn为(82.15±19.00)×10-6 ,Ca为(511.56±93.55)×10-6 ,Mn为(1.81±0.86)×10-6 ,均低于国内报道的正常儿童发中元素含量低限值 Zn 87.75×10-6,Ca 603.25×10-6,Mn 2.14×10-6.该市儿童发 Pb平均值为(12.82±7.43)×10-6,显著高于国内报道的正常儿童发 Pb高限值10.43×10-6. 相似文献
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Andrea Schuy Theo Woike Dominik Schaniel 《Journal of Sol-Gel Science and Technology》2009,50(3):403-408
Photoswitchable hybrid materials are successfully prepared by embedding guanidinium nitroprussides (GuNP, (CN3H6)2[Fe(CN)5NO]) into mesopores of transparent xerogel monoliths. The such prepared hybrid materials exhibit a higher photostability than
the corresponding GuNP solutions, whereby the chemical stability of the [Fe(CN)5NO]2−-anion in titania gel is nearly infinite. By irradiation with light in the blue-green spectral range one nitrosyl isomer is
formed by a 180° rotation of the NO ligand changing the Fe–NO into a Fe–ON coordination (SI), which is detected by the shift
of the ν(NO) stretching vibration from 1945 cm−1 (Fe–NO) to 1820 cm−1 (Fe–ON). Consequently there is enough space around the NO-ligand for such movement in xerogel mesopores. The embedding in
silica xerogels increases the achievable population of the isomeric nitrosyl configuration to about 15% with respect to a
single crystalline powder where only 9% are reached. 相似文献
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锅炉水总碱度测量不确定度的评估 总被引:1,自引:0,他引:1
对锅炉水中总碱度测量不确定度的来源进行分析,评定了总碱度测定过程中测量重复性、天平、标准物质纯度、滴定管和移液管等因素对总碱度测量不确定度的影响,计算得到炉水水样总碱度为26.00mmol/L时,扩展不确定度为0.12mmol/L。在总碱度的测量过程中,滴定管和移液管的准确度是影响总碱度测量不确定度的主要因素。 相似文献
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富硒香菇中微量元素硒的含量测定 总被引:5,自引:0,他引:5
以香菇为载体,通过在培养基中加入一定质量浓度的复合硒溶液进行富硒栽培,获得了富硒香菇,并成功提取出香菇硒多糖,应用2,3-二氨基萘荧光分光光度法测定了富硒香菇中的硒含量,方法简单,结果可靠。 相似文献
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以乙炔黑、活性炭、石墨粉与适量的Mn(NO3)2为原料,采用热压法制备氧电极,将其应用于光电催化降解水中苯酚的研究。采用BET、X射线衍射(XRD)及扫描电镜分析(SEM)测试技术对氧电极进行了表征,并考察了氧电极的制备条件对电极光电催化性能的影响,比较了铜片、镍片、氧电极3种不同阴极对苯酚的降解效果,也比较了相同操作条件下吸附、光催化、电催化、光电催化等过程对苯酚降解效果的影响。结果表明,氧电极的比表面积较大,主要晶相为石墨、Mn3O4,电极表面和内部的物料混合及气孔分布比较均匀;电极的较佳制备条件为:石墨、乙炔黑与活性炭的质量比1∶1∶1,烧结温度400℃,电极厚度1.0 mm;在降解水中苯酚的过程中,氧电极与光阳极能产生良好的光电协同效应,提高了水中苯酚的矿化率。 相似文献
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Concentrations of tetra-, tri and di-alkyl-lead compounds in rain have been measured at rural and urban sites in England. The measurements are compared with similar data collected in the early 1980s, prior to a 72% reduction in the emission of lead from combustion of leaded petrol. Whilst concentrations of inorganic lead have fallen broadly in line with emissions of automotive lead, alkyl-lead concentrations in rain have fallen by only 50% or less, and thus the ratio of alkyl-lead to inorganic lead in rain has increased appreciably. The reason for this phenomenon is unclear. The data suggest that lead in rainwater would fall to approximately 2 μg dm?3 if automotive lead emissions fell to zero. 相似文献
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对2004年度我国高分子科学领域的某些重要研究成果和动态进行了简要介绍,包括高分子合成、树状高分子及其组装、光电活性聚合物、纳米复合体系、超双疏聚合物表面、聚合物囊泡、酶模拟和胶体晶体图案化组装等。 相似文献
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Ke Min Wojciech Jakubowski Krzysztof Matyjaszewski 《Macromolecular rapid communications》2006,27(8):594-598
Summary: The recently developed initiation system, activators generated by electron transfer (AGET), is used in atom transfer radical polymerization (ATRP) in the presence of a limited amount of air. Ascorbic acid and tin(II ) 2‐ethylhexanoate are used as reducing agents in miniemulsion and bulk, respectively. An excess of reducing agent consumes the oxygen present in the system and, therefore, provides a deoxygenated environment for ATRP. ATRP of butyl acrylate is successfully carried out in miniemulsion and in the presence of air. During polymerization the radical concentration remains constant. The polymerization reaches over 60% monomer conversion after 6 h, which results in polymers with a predetermined molecular weight = 14 000 g · mol−1 and a low polydispersity ( = 1.23). AGET ATRP of styrene is also successful in bulk in the presence of air, as evidenced by linear semi‐logarithmic kinetics, which leads to polystyrene with an of 13 400 g · mol−1 and a low polydispersity index ( = 1.14).