Interpretation of inorganic arsenic metabolism in humans in the light of observations made in vitro and in vivo in the rat

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 (As_i). In order to document the methylation process in humans, the kinetics of As_i, MMA and DMA elimination were studied in volunteers given a single dose of one of these three arsenicals or repeated doses of As_i. 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 As_i 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 As_i 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.     

ICP-AES测定铀污染土壤植物中铀的研究

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.     

测定血清中Na 含量不确定度的评定

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。     

茶叶中高氯酸盐检测方法研究进展

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.     

Formation of disperse ferromagnetic nanoparticles in zeolites in the course of thermal activation in oxygen

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.     

Assessment of performance of laboratories in determining acrylamide in crispbread

A proficiency testing round was undertaken to assess the performance of laboratories to measure acrylamide in a sample of crispbread. Retail samples of crispbread were ground to a fine powder and after thorough mixing were packed in 40 g units for distribution. Ten samples were selected at random and analyzed in duplicate for acrylamide by liquid chromatography/mass spectrometry (LC/MS). Standard statistical tests showed that the material was homogeneous for the purposes of proficiency testing. Test samples were distributed to 55 laboratories in 16 countries in Europe, North America, Australia, and the Middle East. The results were analyzed by standard proficiency testing statistical procedures, and laboratories were awarded z-scores on the basis of their reported results. Based on a target standard deviation (sigmap value) taken from the Horwitz equation, for a robust mean value of 1.2 mg/kg acrylamide, satisfactory results (z-score within +/- 2 for those between 0.8 and 1.6 mg/kg) were obtained by 86% of the 37 laboratories that returned results. Only 1 laboratory was unsatisfactory and 4 had questionable results. About equal numbers of laboratories used gas chromatography (GC)/MS and LC/MS procedures with about 25% using MS/MS and one using GC with electron capture detection. There was no evident trend in performance or bias in results. GC/MS and LC/MS data were evenly distributed across the population of laboratories reporting results.     

Variation in the accumulation levels of N,N-dimethyltryptamine in micropropagated trees and in in vitro cultures of Mimosa tenuiflora

The present article reports the accumulation of N,N-dimethyltryptamine and its metabolic precursors (tryptophan, tryptamine) in different organs of micropropagated Mimosa tenuiflora trees (leaves, flowers and bark) subjected to seasonal variations (January and June), as well as in in vitro cultures (plantlets and calluses) of this plant species. The accumulation of all the tested compounds varied according to the organ, the month of collection, and age of the plant material. In all cases, the neurotoxic compound N,N-dimethyltryptamine (DMT) was detected with the lowest concentration 0.01% dry weight (DW) in flowers, and the highest 0.33% DW in bark. For the in vitro cultures, DMT was present in high yields in plantlets (0.1-0.2% DW), while in calluses this compound was initially detected but its concentration decreased significantly in the subsequent subcultures.     

Assessment of recent trends in concentrations of alkyl-lead compounds in rainwater

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.     

锅炉水总碱度测量不确定度的评估

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。     

Interpretation of spin relaxation in polyisobutylene in terms of specific motions

Porton and carbon spin-lattice relaxation times T₁ and nuclear Overhauser enhancements are interpreted in terms of motions likely in linear polyisobutylene. Most of the interpretation is based on relaxation data in the literature, but some additional ¹H and ¹³C pulse Fourier transform experiments were conducted to resolve a disagreement in the literature concerning cross relaxation between the two types of protons present in polyisobutylene. Spin relaxation in solution and the bulk is accounted for by three specific motions considered as independent sources of motional modulation of the dipole–dipole interaction. The first motion is overall isotropic rotatory diffusion which has a known dependence on molecular weight, intrinsic viscosity, and solvent viscosity for polymers in solution, and a known dependence on molecular weight and viscosity for bulk polymers. The effects of overall tumbling account for a decrease of T₁ for the methylene and methyl carbons with increasing molecular weight in solution and increase of T₁ of methylene carbons with molecular weight in bulk. The second motion considered is backbone rearrangements caused by the three-bond jump. This motion dominates relaxation of the methylene carbons either in solution or in the bulk allowing for the determination of the associated correlation time. The correlation time characterizing the occurrence of the three-bond jump in a 5% (wt/vol) solution in CCI₄ at 45°C is 58 psec, and in the bulk at 45°C it is 11 nsec. The last motion included in the model is methyl-group rotation about the threefold symmetry axis. The methyl-group rotational correlation time is 0.20 nsec in a 5% (wt/vol) solution in CCI₄ at 45°C and 0.33 nsec in the bulk at 45°C. The concentration dependence of the backbone motion contrasts strongly with the corresponding dependence of methyl-group rotation.     

The in situ determination of iron and of copper in wine

The improved determination of both iron and copper in red and white wines has been developed which avoids the preliminary process of ashing the sample before processing the ash for the actual evaluation of these two troublesome impurities. The new procedure employs bathocuproine and bathophcnanthroline as completing ligands with spectrophotometric determination of the Cu and the Fe in situ. The new method is economical in required analysis time, manipulative details and in quantity of sample involved. It has been shown that the new method is comparable in accuracy to previous published procedures, and as control analyses substitute wet ashing technique, the HNO₃-HCIO₄ destruction of organic matter, was applied.     

水环境中铜的光化学研究进展

水环境中的铜主要以配合物形式存在,大多具有光化学活性.由于铜在光化学过程中的氧化还原循环可以导致其配体以及水体中有机污染物的降解,所以铜及其配合物在污染修复技术中的应用逐渐受到关注.本文综述了水环境中铜的光化学研究进展以及在多相和均相光催化体系中铜对污染修复的影响.     

Radiochemical investigation of the consequence of isomeric transition in telluric acid in solid and in solution

The chemical states of tellurium ground state isomers formed as a result of isomeric transition from the meta state isomers of tellurium-121, 127, 129 and 131 isotopes have been studied in solid telluric acid and solution. The fraction of tetra-valent tellurium obtained for the above isotopes differed from isotope to isotope and also from solid to solution. More tetra-valent form was found in solution than in solid. The observed results were interpreted in terms of the partial decay constant of the parent meta state isomers. Anion exchange chromatography was applied to separate the tetra-valent and hexa-valent forms of tellurium.     

Variation in entropy in the course of combination of fractions in units of a separating cascade and losses of accomplished work

The summary variation in entropy in the course of combining the fractions in units of a symmetrical cascade is calculated. The thermodynamic interpretation of the difference between the work of separation, determined using the separating potential, and the thermodynamically evaluated work of isobaric-isothermal process of mixing is given.     

Photodimerisation of glycothymidines in solution and in micelles

Glycothymidines were designed and synthesized as a new class of functional glycomimetics in which a photochemical [2+2] cycloaddition of the thymine moiety induces structural changes of carbohydrate presentation. To test if photodimerisation of these glycothymidines is feasible within an array of molecules, the photochemical reaction was investigated using NMR and NMR diffusion experiments in solution as well as in the supramolecular context of detergent micelles that mimic cellular membranes.     

HPLC-ICP-MS联用技术在富硒金针菇硒的形态分析中的应用

从富硒培养的金针菇中分离得到含硒化合物, 并采用SE-HPLC-ICP-MS联机技术对浸提液中的含硒化合物进行分离分析; 同时对样品中的硒蛋白在特定条件下水解, 采用RP-HPLC-ICP-MS联机技术对水解液中硒代氨基酸进行确认, 并测定其中硒的含量. 结果表明, 可溶态硒是富硒金针菇中硒的主要存在形式, 其中小分子含硒有机化合物中的含硒量占浸提液中硒的71.87%; 而含硒蛋白所占比例为4.88%; 进一步确定富硒金针菇中含有硒代胱氨酸、硒代蛋氨酸和由二者组成的含硒多肽等, 各形态硒的含量为总硒量的12.3%, 17.6%和36.8%. 本方法将具有高效分离能力的色谱技术与高灵敏度的元素检测技术成功结合, 用于含硒生物分子中硒的在线分析, 具有快速、灵敏及准确等特点.     

Production of radicals in the ozonolysis of propene in air

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...     

Beneficial role of surfactants in electrochemistry and in the modification of electrodes

This review deals with the beneficial use of surfactants in various fields of electrochemistry, in general and in the modification of electrodes with immobilized electroactive species, in particular. Special emphasis is laid on the modification of electrodes with metal hexacyanoferrates (MHCFs). After an introduction and brief notes on fundamentals of surfactants, and their applications in electrochemistry, covering some of the very important works in the past two decades involving beneficial use of surfactants, the article gives a brief account on metal hexacyanoferrate modified electrodes and the salient features of our published results on the beneficial role of cetyltrimethylammonium bromide (CTAB), a cationic surfactant, in the modification of electrodes with MHCFs and their derivatized oxides, and with titanium dioxide.     

Spectroscopic properties of protochlorophyllide analyzed in situ in the course of etiolation and in illuminated leaves

The spectroscopic properties of photoactive (i.e. flash-transformable) and nonphotoactive protochlorophyll(ide)s (Pchl(ide)) were reinvestigated during the development of bean leaves in darkness. Two phases in the process of Pchl(ide) accumulation were apparent from quantitative measurements of pigment content: a lag phase (first week) during which photoactive Pchl(ide) accumulated faster than nonphotoactive Pchl(ide); and a fast phase (second week), showing parallel accumulation of both types of Pchl(ide). 'Flashed-minus-dark' absorbance difference spectra recorded in situ at 77 K showed that P650-655 was the predominant form of photoactive protochlorophyllide regardless of developmental stage. Quantitative analysis of energy migration processes between the Pchl(ide) forms showed the existence of energy transfer units containing a 1:8 ratio of nonphotoactive and photoactive Pchl(ide)s during development. Gaussian deconvolution of in situ 77 K fluorescence spectra indicated that the 633 nm band of nonphotoactive Pchl(ide) was made of four bands, at 625, 631, 637 and 643 nm, whose relative amplitudes only slightly changed during development. The emission band of photoactive Pchlide was also analyzed using the same method. Three components were found at 644, 652 and 657 nm. The emission band of P650-655 included the last two components, which become predominant only in fully etiolated plants. Photoactive Pchlide with an emission maximum at 653 nm was detected in the light during development of leaves of photoperiodically grown plants.     

Theoretical study of the stability of myrsinone in vacuo and in solution

The stability of various conformers of myrsinone (2,3-dihydroxy-5-undecyl-1,4-benzoquinone) and its tautomer [2,3-dihydroxy-5-(undec-1-ene)-cyclohex-2-ene-1,4-dione] has been studied in vacuo and in solution on model systems with the long alkyl side chains replaced with ethyl and eth-1-ene groups, respectively. Ab initio Hartree–Fock (HF) calculations in vacuo and free-energy calculations either in chloroform or in water solution, in the framework of the polarizable continuum model, have been carried out on the 6-31G* optimized geometries obtained in vacuo and in solution (water or chloroform). The nature of the stationary points found was investigated using normal mode analysis. The energy gap between the two tautomeric forms turns out to be about 1.3 kcal/mol in vacuo and becomes about 0.3 kcal/mol in chloroform solution, whereas in water the second tautomer is favored by about 1.2 kcal/mol. The effect of second-order M?ller–Plesset (MP2) correlation corrections has been considered on both the energy and the geometry of the tautomers in vacuo, whereas in solution only their effect on the energy was taken into account. The contribution to the stability in the gas phase and in solution of the intramolecular hydrogen bonds between the hydroxy hydrogen and the quinonoid oxygen is larger at the MP2 level than at the HF one. The directionality of the hydrogen bonds between the hydroxy groups affects considerably only the stability of the isomer with the exocyclic double bond. The computed chemical shifts for the two tautomers were compared to the experimental ones. In addition the solvation properties of 2,5-dihydroxy-3-ethyl-1,4-benzoquinone and of an ortho-quinonoid system were considered in order to evaluate the effect of the repulsion between vicinal hydroxy or quinonoid groups. Received: 14 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000