ELECTROCHEMICAL CATALYSIS AT AN ULTRAMICROELECTRODE MODIFIED WITH REDOX SPECIES

General equations of the electrocatalytic reaction at an ultramicroelectrode modified with redox species have been described according to the Andrieux Saveant model. The electrocatalytic kinetic process has been discussed for the whole set of cases, ie (R), (R + S), (SR) (SR + E), (E), (R + E), (ER), (S), (ER + S) and (S + E) limiting situations. The effect of gamma on the catalytic steady state current shows that the higher the value of gamma, the lower the catalytic current. The kinetic process shifts rapidly from R to E with increasing values of gamma. It is favorable for catalysis only when gamma is very low. Therefore, the redox species modified ultramicroelectrode with thin film is utilized for electrocatalysis, and the larger the radius of ultramicroelectrode, the higher the catalytic efficiency.

APPLICATION OF ULTRAMICROELECTRODES IN STUDIES OF HOMOGENEOUS CATALYTIC REACTIONS .2. A THEORY OF QUASI-1ST AND 2ND-ORDER HOMOGENEOUS CATALYTIC REACTIONS

The analytical expressions of quasi-first and second order homogeneous catalytic reactions with different diffusion coefficients at ultramicrodisk electrodes under steady state conditions are obtained by using the reaction layer concept. The method of treatment is simple and its physical meaning is clear. The relationship between the diffusion layer, reaction layer, the electrode dimension and the kinetic rate constant at an ultramicroelectrode is discussed and the factor effect on the reaction order is described. The order of a catalytic reaction at an ultramicroelectrode under steady state conditions is related not only to C(Z)*/C(O)* but also to the kinetic rate constant and the dimension of the ultramicroelectrode; thus the order of reaction can be controlled by the dimension of the ultramicroelectrode. The steady state voltammetry of the ultramicroelectrode is one of the most simple methods available to study the kinetics of fast catalytic reactions.

MEASUREMENT OF CATALYTIC ACTIVITY VARIATION FOR H2O2 OXIDATION AT A COBALT PORPHYRIN COATED ELECTRODE

A rapid rotation-scan method was used for the electrocatalytic oxidation of H2O2 at a cobalt protoporphyrin modified pyrolytic graphite electrode (CoPP/PG). The rate constant of H2O2 oxidation at the CoPP/PG electrode at different potentials and in different pH solutions was measured. The variation of catalytic activity with reaction charges (Q) passed through the electrode was analyzed. This provided a convenient electrochemical method to study the passivation and poisoning of catalytic sites with time.

ELECTROCATALYSIS AT A MICRODISK ELECTRODE MODIFIED WITH A REDOX SPECIES

The current equation of the electrocatalytic reaction at a microdisk electrode modified with redox species has been described and verified experimentally. There exists a linear relationship between plateau limiting current and the radius of the microdisk electrode for a catalytic process. The influence of the dimensions of the microdisk electrode on catalytic efficiency is discussed. The polyvinylferrocene (PVFc)-modified microdisk electrode prepared by the coating method was taken as a typical example, on which the electrocatalytic oxidation of ascorbic acid could be studied. The catalytic reaction rate constants were determined as an average value of 1.5 X 10(-7) cm3/mol s by this method, and are consistent with those obtained at a conventional electrode.

ELECTRODEPOSITION OF POLYCRYSTALLINE CD-RICH HG1-XCDXTE AND PHOTOELECTRO-CHEMICAL BEHAVIOR OF HG0.09CD0.91TE THIN-FILM

Electrodeposition process of polycrystalline Cd-rich Hg_(1-z)Cd_xTe (x>0.5) in acidic bath of CdSO_4+HTeO_2~+HgCl_2 was investigated. The simultaneous electrodeposition technique of three kinds of ions at the same potential has been achieved. The XRD, SEM and EDAX analysis of the thin film electrodeposited on titanium substrate showed a typical cubic zinc blende polycrystalline structure and homogeneous dispersion. The photoelectrochemical behavior of (1-x)=0.09 polycrystalline thin film in a polysulfide re...

Identification and molecular analysis of a stress-inducible Hsp70 from Sciaenops ocellatus

Hsp70 proteins are a family of molecular chaperones that are involved in many aspects of protein homeostasis. In this study, an Hsp70 homologue (SoHsp70) was identified from red drum Sciaenops ocellatus and analyzed at molecular level. The open reading frame of SoHsp70 is 1920 bp and intronless, with a 5'-untranslated region (UTR) of 399 bp and a 3'-UTR of 241 bp. The deduced amino acid sequence of SoHsp70 shares 84-92% overall identities with the Hsp70s of a number of fish species. In silico analysis identified in SoHsp70 three conserved Hsp70 domains involved in nucleotide and substrate binding. The coding sequence of SoHsp70 was subcloned into Escherichia coli, from which recombinant SoHsp70 was purified and, upon ATPase assay, found to exhibit apparent ATPase activity. Expressional analysis showed that constitutive expression of SoHsp70 was detectable in heart, liver, spleen, kidney, brain, blood, and gill. Experimental challenges with poly(I:C) and bacterial pathogens of Gram-positive and Gram-negative nature induced SoHsp70 expression in kidney to different levels. Stress-responsive analysis of SoHsp70 expression in primary cultures of red drum hepatocytes showed that acute heat shock treatment elicited a rapid induction of SoHsp70 expression which appeared after 10 min and 30 min of treatment. Exposure of hepatocytes separately to iron, copper, mercury, and hydrogen peroxide significantly unregulated SoHsp70 expression in time-dependent manners. Vaccination of red drum with a Streptococcus iniae bacterin was also found to induce SoHsp70 expression. Furthermore, recombinant SoHsp70 enhanced the immunoprotective effect of a subunit vaccine. Taken together, these results suggest that SoHsp70 is a stress-inducible protein that is likely to play a role in immunity and in coping with environmental and biological stresses. (C) 2010 Elsevier Ltd. All rights reserved.

Distribution and their pollution assessment of heavy metals in the sediments of the Yalu River Estuary and its adjacent coastal waters

The present paper deals with the distribution patterns of heavy metals and the associated influencing factors in the Yalu River Estuary and its adjacent coastal waters. Based upon the analysis of the surficial and core sediments measurements, the pollution of heavy metal and potential ecological risk were evaluated. The burial flux and contents of heavy metals (except for copper) have been continuously increasing since the 1920s. Therefore, the gross potential ecological risk for the sediments was high or very high, and the study area was endangered by heavy metals contamination. Heavy metals originated mainly from upstream pollutant input, correlation analysis showed that chromium, nickel, zinc, cadmium, lead, arsenic, and mercury in the sediments of the middle and west channels as well as the sea area of the western Yalu River Estuary concentrations were most probably derived from similar sources. In contrast, the metal of copper most probably originated from sources different from the other metals. Preliminary studies indicate that copper contamination was most likely the result of emission from mining activities situated at the upstream of the river. The contents of heavy metals in the sediments of estuarine turbidity maximum zone of Yalu River were larger than those of any other areas in the middle channel. With large portion of fine sediments, weaker hydrodynamics, and richer sources of heavy metals, the sediments of the west channel, were even more enriched with heavy metals than those of the middle channel.

四角蛤蜊Mactra veneriformis对镉和汞污染胁迫的生理响应

本论文基于对我国沿海重金属污染加剧以及滩涂贝类资源衰退现象的关注，围绕典型滩涂贝类四角蛤蜊生物化学、细胞生物学和免疫学特征开展研究，调查了渤海湾天津近岸海域四角蛤蜊体内重金属含量和分布规律，以及四角蛤蜊对沉积物重金属的富集能力。室内模拟研究了四角蛤蜊对重金属镉和汞的富集能力及同化机制（assimilation mechanism）差异性，四角蛤蜊各组织对镉和汞的解毒机理和负载能力，以及重金属胁迫对四角蛤蜊血细胞结构和功能的损伤效应。研究结果可望为探讨四角蛤蜊受重金属胁迫细胞水平上的响应机制，揭示重金属污染和贝类资源衰退的关系，建立快速可靠的重金属污染生物标志物指标体系，开展生态健康评估和生境修复等提供科学依据。主要研究结果如下： 1．查明了渤海湾天津近岸四角蛤蜊体内和表层沉积物中Cd、Pb、Cu、Zn、Mn、Cr和Ni七种重金属的含量和周年时空分布特征；表层沉积物中Cd具有较强的污染程度和潜在生态风险，四角蛤蜊对重金属元素Cd和Pb具有较高的富集能力，对环境重金属污染具有很好的指示作用。 2．查明了Cd对四角蛤蜊在24h，48h和96h的半致死浓度（LC50）分别为15.96mg/L、5.15mg/L和2.38mg/L，汞的24h，48h和96h LC50分别为3.71mg/L，0.61mg/L和0.21mg/L。镉和汞对四角蛤蜊的安全质量浓度分别为0.0238mg/L和0.0021mg/L。 3．四角蛤蜊软体部对Cd和Hg的富集能力有显著差异。暴露过程中，四角蛤蜊软体部Cd和Hg的增加量分别为0.12-7.7µg/g和0.002-0.024µg/g，富集率分别为0.3-6.2%和0.11-0.68%，吸收率常数分别为0.07-1.10和0.001-0.005。 4．四角蛤蜊受Cd和Hg胁迫后，外套膜、鳃和肝胰腺的金属硫蛋白（MT）含量均在暴露浓度和胁迫时间上都有极显著变化。组织内MT含量的大小关系为：肝胰腺＞鳃＞外套膜。肝胰腺可以作为双壳贝类MT重金属污染指示研究的目标组织。四角蛤蜊对Cd和Hg不同的解毒机制，导致组织中MT的表达含量和Cd胁迫显著相关，而与Hg胁迫无显著相关性。 5．四角蛤蜊肝胰腺和鳃中抗氧化系统酶、脂质过氧化产物、酸性磷酸酶（ACP）和碱性磷酸酶（ALP）在不同Cd胁迫浓度和暴露时间下有显著差异。与对照组相比，超氧化物歧化酶（SOD）、过氧化氢酶（CAT）、谷胱甘肽过氧化物酶（GPx）的活力和丙二醛（MDA）含量均随着暴露时间的增加而增加，达到一个峰值，然后减低。而ACP和ALP活力则表现出先被抑制，然后升高的变化趋势。肝胰腺中CAT和GPx活力高于鳃，鳃中SOD和MDA含量高于肝胰腺，这种差异与两种组织不同的解毒机理有关。 6．重金属胁迫能够造成四角蛤蜊血细胞超微结构的损伤、溶酶体膜稳定性改变、微核和总畸形核生成，各种损伤均表现出明显的浓度依赖效应。2μg/L Hg暴露14天后，血细胞溶酶体膜中性红保持时间（NRR）、微核生成率（MN）和总畸形核生成率（TNA）与对照组相比没有显著差异。相同暴露时间下，25 μg/L Hg处理组血细胞NRR值低于25 μg/L Cd处理组，而MN和TNA值则相反，说明Hg胁迫对四角蛤蜊血细胞溶酶体膜具有较强的损伤作用。研究发现，NRR、MN和TNA三种指标对于衡量重金属污染对四角蛤蜊血细胞的毒性效应有很好的协同检测作用，可望作为有效的生物标志物在环境监测技术中得以应用。

DSP等赤潮藻毒素对哺乳类细胞的毒性效应及机制研究

本文研究了腹泻性贝毒的主要组分大田软海绵酸以及几株重要赤潮藻的提取物对四株哺乳类细胞的毒性效应，并探讨了应用细胞毒性检测方法作为赤潮藻毒素毒性检测常规方法的可能性。 结果发现：OA和利玛原甲藻提取物显著地抑制四株细胞的增殖并诱导四株细胞发生凋亡；四株细胞对毒素的敏感性存在一定的差异，人肝癌细胞和小鼠神经瘤细胞较敏感，其次分别为人肝细胞和小鼠皮肤细胞。 小鼠神经瘤细胞对OA反应敏感，细胞毒性检测指标及检测方法灵敏、快速，应用小鼠神经瘤细胞Neuro-2a进行的DSP毒素细胞毒性测试方法具有发展为该类毒素毒性监测常规方法的潜能。 米氏凯伦藻内存在抑制细胞增殖的毒性物质，且该物质是一种具有一定极性的脂溶性物质；该物质能够导致细胞肿胀、破裂，并诱导细胞发生脂质过氧化，导致脂质过氧化产物丙二醛(MDA)的积累。 相关亚历山大藻的去藻过滤液内存在抑制细胞增殖和诱导细胞凋亡的毒性物质，该毒性物质的分子量＞5K，这与本实验室以往的研究结果一致。 　　总之，通过我们的研究发现：DSP等赤潮藻毒素或毒性物质对哺乳类细胞存在毒性影响，且不同毒素的危害机制存在差异，赤潮藻毒素或赤潮藻产生的一些毒性物质威胁人类的健康，应引起我们的高度关注。

Effects of the dinoflagellate Alexandrium tamarense on early development of the scallop Argopecten irradians concentricus

The effects of Alexandrium tamarense (strain ATHK) on early development of the bay scallop Argopecten irradians concentricus were studied under laboratory conditions. The algal culture was verified by HPLC to produce paralytic shellfish poisoning (PSP) at a level of 37.48 fmol/cell. Survival of the scallop larvae was not affected when they were grown with A. tamarense at concentrations of 500-10,000 cells/ml for 48 h. However, the activity of D-shape larvae was inhibited after 48-h exposure to A. tamarense at the algal cell density of 10,000 cells/ml. Scallop growth was inhibited significantly by A. tantarense during a 14-day exposure starting at the eye-spot larval stage. The size of juvenile scallops in the group of 10,000 cells/ml was only about 32% of that of the controls, although no obvious effect of A. tamarense was found on the rate of larval metamorphosis. All juvenile scallops survived in algal concentrations of 600-2400 cells/ml, however, attachment rates were significantly lower than control values after a 5-h exposure to A. tamarense at concentrations >600 cells/ml, while they were not obviously reduced after only 1 h of exposure. At concentrations >600 cells/ml, the climbing ability of juveniles was clearly reduced by exposure to A. tamarense after only 1 h. The climbing rate and height were only 55% and 45%, respectively, of those of the controls, when exposed to A. tantarense at a concentration of 600 cells/ml. The results indicated that A. tamarense blooms may have detrimental impacts on shellfish at early life stages, therefore, special attention should be paid to the toxic algal blooms in shellfish breeding area. (C) 2003 Elsevier Science B.V. All rights reserved.

A modified HPLC method for analysis of PSP toxins in algae and shellfish from China

Improvements to an established HPLC method are introduced. The modified method is more efficient for separation and detection of the toxins responsible for paralytic shellfish poisoning (PSP). The PSP toxin content of two strains of Alexandrium tamarense and approximately forty shellfish samples collected from different locations in China have been analyzed with this HPLC method. Only one shellfish sample, collected from Lianyungang, China, contained PSP toxins.

Transfer of paralytic shellfish toxins via marine food chains: A simulated experiment

Objective To study the transfer of paralytic shellfish toxins (PST) using four simulated marine food chains: dinoflagellate Alexandrium tamarense -> Arterriia Artemia salina -> Mysid shrimp Neomysis awatschensis; A. tamarense-N. awatschensis: A. taniarense A. salina -> Perch Lateolabrax japonicus; and A. tamarense -> L. japonicus. Methods The ingestion of A. tamarense, a producer of PST, by L. japonicus, N. awatschensis, and A. salina was first confirmed by microscopic observation of A. tamarense cells in the intestine samples of the three different organisms, and by the analysis of Chl.a levels iii the samples. Toxin accumulation in L. japonicus and N. awatschensis directly from the feeding on A. tamarense or indirectly ibrough the vector of A. salina was then studied. The toxicity of samples was measured using the AOAC mouse bioassay method, and the toxin content and profile of A. tamarense were analyzed by the HPLC method. Results Both A. salina and N. awatschensis could ingest A. tamarense cells. However, the ingestion capability of A. salina exceeded that of N. awatschensis. After the exposure to the culture of A. tamarense (2 000 cells(.)mL(-1)) for 70 minutes, the content of ChLa in A. salina and N. awatschensis reached 0.87 and 0.024 mu g-mg(-1), respectively. Besides, A. tamarense cells existed in the intestines of L. japonicus, N. awatschensis and A. salina by microscopic observation. Therefore, the three organisms could ingest A. tamarense cells directly. A. salina could accumulate high content of PST, and the toxicity of A. salina in samples collected on days 1, 4, and 5 of the experiment was 2.18, 2.6, and 2.1 MU(.)g(-1), respectively. All extracts from the samples could lead to death of tested mice within 7 minutes, and the toxin content in arternia sample collected on the 1st day was estimated to be 1.65x10(-5) pg STX equa Vindividual. Toxin accumulation in L. japonicus and N. awatschensis directly from the feeding on A. tamarense or indirectly froin the vector of A. salina was also studied. The mice injected with extracts from L. japonicus and N. awatschensis samples that accumulated PST either directly or indirectly showed PST intoxication symptoms, indicating that low levels of PST existed in these samples. Conclusion Paralytic shellfish toxins can be transferred to L. japonicus, N. awatschensis, and A. salina from A. taniarense directly or indirectly via the food chains.

Synthesis and evaluation of a thiourea-modified chitosan derivative applied for adsorption of Hg(II) from synthetic wastewater

In this work, a thiourea-modified chitosan derivative (TMCD) was synthesized through two steps, O-carboxymethylated first and then modified by a polymeric Schiff's base of thiourea/glutaraldehyde. The adsorption behavior of mercury (II) ions onto TMCD was investigated through batch method. The maximum adsorption capacity for Hg(II) was found to be 6.29 mmol/g at pH 5.0 and both kinetic and thermodynamic parameters of the adsorption process were obtained. The results indicated that adsorption process was spontaneous exothermic reaction and kinetically followed pseudo-second-order model. The adsorption experiments also demonstrated TMCD had high adsorption selectivity towards Hg(II) ions when coexisted with Cu(II), Zn(II), Cd(II) and Ca(II) in solution and it could be easily regenerated and efficiently reused. (C) 2010 Elsevier B.V. All rights reserved.

Selective and specific detection of sulfate-reducing bacteria using potentiometric stripping analysis

A fast, sensitive and reliable potentiometric stripping analysis (PSA) is described for the selective detection of the marine pathogenic sulfate-reducing bacterium (SRB). Desulforibrio caledoiensis. The chemical and electrochemical parameters that exert influence on the deposition and stripping of lead ion, such as deposition potential, deposition time and pH value were carefully studied. The concentration of SRB was determined in acetate buffer solution (pH 5.2) under the optimized condition (deposition potential of -1.3 V. deposition time of 250 s, ionic strength of 0.2 mol L-1 and oxidant mercury (II) concentration of 40 mg L-1). A linear relationship between the stripping response and the logarithm of the bacterial concentration was observed in the range of 2.3 x 10 to 2.3 x 10(7) cfu mL(-1). In addition, the potentiometric stripping technique gave a distinct response to the SRB, but had no obvious response to Escherichia coli. The measurement system has a potential for further applications and provides a facile and sample method for detection of pathogenic bacteria. (C) 2010 Elsevier B.V. All rights reserved.

Livestock grazing, plateau pikas and the conservation of avian biodiversity on the Tibetan plateau

On the Qinghai-Tibet plateau increased livestock numbers have resulted in degradation of the grasslands with potential impacts on native biodiversity. Concurrently, perceived increases in populations of native small mammals such as plateau pikas (Ochotona curzoniae) have led to poisoning programs, with uncertain impacts on species such as ground-nesting birds. We explored the relationships between the local seasonal abundance of small birds and (1) the density of pika burrows; (2) livestock grazing practices; and (3) local poisoning of pikas. Around Naqu prefecture, central Tibet, we used a nested experimental design to collect data from areas rested from grazing over summer, nearby areas with year-round grazing and areas subjected to pika poisoning. Additional data were collected from a site where grazing had not occurred for at least 4 years prior to the study. Poisoning pikas in spring had no detectable effect on the local abundance of birds the following autumn. However, two ground-nesting species, white-rumped and rufous-necked snowfinches, showed positive associations with the density of pika burrows, indicating that long-term 'pika poisoning could reduce the density of these species by reducing the density of pika burrows. Rufous-necked snowfinches and non ground-nesting species including horned larks and common hoopoes showed positive responses to reduced grazing pressure from livestock, particularly in the long-rested site, indicating current grazing levels could be having a negative impact on these species. Conservation of small passerine biodiversity in this system will require changed management practices for livestock and pikas that consider the complex three-way interaction between livestock grazing, pikas and small birds. (C) 2008 Elsevier Ltd. All rights reserved.