Copper complexation by fulvic acid affects copper toxicity to the larvae of the polychaete Hydroides elegans

Copper toxicity is influenced by a variety of environmental factors including dissolved organic matter (DOM). We examined the complexation of copper by fulvic acid (FA), one of the major components of DOM, by measuring the decline in labile copper by anodic stripping voltammetrically (ASV). The data were described using a one-site ligand binding model, with a ligand concentration of 0.19 mu mol site mg(-1) C, and a logK' of 6.2. The model was used to predict labile copper concentration in a bioassay designed to quantify the extent to which Cu-FA complexation affected copper toxicity to the larvae of marine polychaete Hydroides elegans. The toxicity data, when expressed as labile copper concentration causing abnormal development, were independent of FA concentration and could be modeled as a logistic function, with a 48-h EC50 of 58.9 mu g 1(-1). However, when the data were expressed as a function of total copper concentration, the toxicity was dependent on FA concentration, with a 48-h EC50 ranging from 55.6 mu g 1(-1) in the no-FA control to 137.4 mu g 1(-1) in the 20 mg 1(-1) FA treatment. Thus, FA was protective against copper toxicity to the larvae, and such an effect was caused by the reduction in labile copper due to Cu-FA complexation. Our results demonstrate the potential of ASV as a useful tool for predicting metal toxicity to the larvae in coastal environment where DOM plays an important role in complexing metal ions. (c) 2007 Elsevier Ltd. All rights reserved.

天然溶解有机质和环境污染物的相互作用--以铜、汞离子和卡马西平为例

天然溶解有机质（natural dissolved organic matter，DOM）是由动植物残体经过复杂的物理、化学和生物过程形成的高分子有机混合物，它广泛分布于水体、土壤和沉积物中。DOM的结构十分复杂，分子量从几百到几十万不等，元素组成和化学结构随时空和来源不同而变化。腐殖物质是DOM的主要组成部分，以溶解有机碳计约占DOM总量的50%~80%。腐殖物质可以分为：富里酸（fulvic acid， FA任何pH值条件下都溶于水），腐殖酸（humic acid，HA在pH 1时不溶于水）和胡敏素（humin，任何pH条件下都不溶于水）。 DOM能影响许多生物地球化学过程。例如DOM是一个重要的碳汇，它能影响微生物的食物链和全球碳循环；DOM和营养元素含量、食物链结构等一起决定水生生态系统的属性和发展动态；它还能吸收自然光，从而影响紫外线在水中的穿透能力和浮游植物的光合作用；DOM含有多种弱酸和弱碱官能团，是天然水体pH的调节剂和控制因素；DOM和痕量金属离子或有机污染物发生作用，从而影响它们的形态、毒性、迁移转化和生物有效性；在饮用水消毒过程中，DOM能生成致癌物三卤甲烷和其它消毒副产物。 天然水体中的痕量金属离子（如Cu2+和Hg2+）主要以DOM络合态存在。在海水中DOM控制铜的主要存在形态；在淡水中 90%以上的铜离子与DOM发生配位。通过配位作用DOM能抑制浮游生物对Hg的吸收，增加鱼类对Hg的蓄积。目前，人们对金属离子在环境中的迁移转化机理的理解还不够深入，尤其是对有机质参与下的有毒重金属循环还缺乏必要地认识。条件稳定常数是描述重金属离子与DOM配位能力的基本参数。前人运用多种手段对DOM与金属离子的结合能力进行了研究，主要包括：离子选择性电极法、溶出伏安法、超滤及荧光淬灭滴定法等。紫外吸收滴定法可用于研究单一有机化合物和金属离子的相互作用，在这一领域的应用尚未报道。本文首次将紫外吸收滴定法应用于测定DOM与Cu2+和Hg2+的条件稳定常数。实验表明紫外吸收滴定法迅速、简便、可望成为研究DOM和痕量金属离子相互作用的有力工具。 药品和个人护理品（pharmaceuticals and personal care products，PPCPs）在环境中普遍存在。有证据表明，环境中的有些PPCPs能对生物体产生影响，如改变生物体的性别比例，影响植物生长，动物幼虫的孵化，甚至具有明显的致畸效应。卡马西平（Carbamazepine，CBZ）是一种常用的抗癫痫、止痛药物和抗抑郁药。毒理学实验表明，环境中的CBZ能严重影响鱼、蚌等水生生物的免疫和循环系统。CBZ使用量大，在环境中含量高，在地下水渗透过程和常规污水处理中保持稳定，因此CBZ成为衡量人类活动和污水处理工艺效率的标志物。但是目前人们对CBZ的环境地球化学循环知之甚少。DOM能与许多有机污染物发生相互作用，从而影响它们的生物环境地球化学行为，但DOM对CBZ的影响尚未见报道。本论文利用三维荧光光谱技术和同步荧光光谱技术，研究了DOM与CBZ的结合强度、结合类型、影响因素，并且初步总结了DOM对CBZ环境地球化学循环的影响。为理解其它PPCPs的生物地球化学循环，预测它们的迁移转化、归宿和环境毒性提供参考。 本文运用紫外吸收滴定法和荧光淬灭滴定法研究了不同来源的DOM和金属离子（Cu2+和Hg2+）的相互作用，运用三维荧光光谱法和同步扫描荧光光谱法研究了DOM和卡马西平的相互作用。主要成果简述如下： 1、本文首次将紫外吸收滴定法应用于测定金属离子和DOM的条件稳定常数，结果表明紫外吸收滴定法操作更简便、测定迅速、仪器普及率高，可在DOM含量很低（约10-5 ~ 10-7 mol/L）的情况下也可以直接进行测定，不必进行复杂的预富集。可望成为DOM和痕量有毒重金属离子相互作用的有力工具。 2、重金属离子（Hg2+和Cu2+）与DOM的羧基和酚羟基等基团配位。配位后电子的离域性增加，导致紫外吸收增加。与此同时配位后分子极性的改变和铜离子顺磁性作用，引起DOM荧光淬灭。在Cu2+和Hg2+的滴定过程中，紫外吸光度和荧光强度之间呈极显著线性负相关关系（R2=0.99，P<0.001）。这说明荧光和紫外从不同侧面揭示了DOM和金属离子的配位作用。 3、紫外吸收滴定法和荧光淬灭滴定法测定其条件稳定常数（log K）一致，介于3.5 ~ 5.5之间。强配位作用是DOM影响有毒重金属离子环境地球化学行为的根源。研究还表明配位作用的强弱受DOM来源和体系pH的影响。 4、 CBZ和DOM能发生强烈的相互作用，结合常数（log K）介于3.41 ~ 5.04之间。DOM能明显减少游离态CBZ的浓度，提高CBZ溶解度和迁移转化能力。这对认识CBZ和其它PPCPs的环境地球化学循环及其影响因素具有指导意义。 5、荧光光谱研究表明CBZ对DOM发射的荧光具有明显的猝灭作用，其猝灭机理为静态猝灭。疏水作用是CBZ和DOM之间的主要作用力。DOM-CBZ受pH值的影响不大， Cu2+对CBZ和DOM的结合有一定的影响。

An Amino Acid Substitution Matrix for Protein Conformation Identification

Amino acid substitution matrices play an essential role in protein sequence alignment, a fundamental task in bioinformatics. Most widely used matrices, such as PAM matrices derived from homologous sequences and BLOSUM matrices derived from aligned segments of PROSITE, did not integrate conformation information in their construction. There are a few structure-based matrices, which are derived from limited data of structure alignment. Using databases PDB_SELECT and DSSP, we create a database of sequence-conformation blocks which explicitly represent sequence-structure relationship. Members in a block are identical in conformation and are highly similar in sequence. From this block database, we derive a conformation-specific amino acid substitution matrix CBSM60. The matrix shows an improved performance in conformational segment search and homolog detection.

Preparation And Tribology Studies of Alkyl Carboxylic Acid Monolayer Films on Pei-Coated Glass Substrate

首次在涂敷PEI的玻璃表面上制备了癸酸及全氟癸酸的单分子层膜。研究了成膜机理及摩擦特性。结果表明。脱水剂DCCD促进了癸酸或全氟癸酸与PEI酞胺化的反应。导致两种羧酸在PEI表面产生了靠化学键（酞胺键）连接的稳定的单分子层膜,摩擦、磨损实验表明。单分子层有机膜的摩擦特性受膜的组成、表面能及有序性和堆积密度的重要影响。表面能越低,有序性和堆积密度越高。摩擦系数越低。与碳氢化合物相比。碳氟化合物形成的有序膜具有更高的强度和抗磨性能。

Preparation and Tribological Studies of Stearic Acid Self-Assembled Monolayers on Polymer-Coated Silicon Surface

We present a good alternative method to improve the tribological properties of polymer films by chemisorbing a long-chain monolayer on the functional polymer surface. Thus, a novel self-assembled monolayer is successfully prepared on a silicon substrate coated with amino-group-containing polyethyleneimine (PEI) by the chemical adsorption of stearic acid (STA) molecules. The formation and structure of the STA-PEI film are characterized by means of contact-angle measurement and ellipsometric thickness measurement, and of Fourier transformation infrared spectrometric and atomic force microscopic analyses. The micro- and macro-tribological properties of the STA-PEI film are investigated on an atomic force microscope (AFM) and a unidirectional tribometer, respectively. It has been found that the STA monolayer about 2.1-nm thick is produced on the PEI coating by the chemical reaction between the amino groups in the PEI and the carboxyl group in the STA molecules to form a covalent amide bond in the presence of N,N'-dicyclohexylcarbodiimide (DCCD) as a dehydrating regent. By introducing the STA monolayer, the hydrophilic PEI polymer surface becomes hydrophobic with a water contact angle to be about 105degrees. Study of the time dependence of the film formation shows that the adsorption of PEI is fast, whereas at least 24 h is needed to generate the saturated STA monolayer. Whereas the PEI coating has relatively high adhesion, friction, and poor anti-wear ability, the STA-PEI film possesses good adhesive resistance and high load-carrying capacity and anti-wear ability, which could be attributed to the chemical structure of the STA-PEI thin film. It is assumed that the hydrogen bonds between the molecules of the STA-PEI film act to stabilize the film and can be restored after breaking during sliding. Thus, the self-assembled STA-PEI thin film might find promising application in the lubrication of micro-electromechanical systems (MEMS).

Effects of Molecular Length, Ortientation and Amino Acid Mutation on Kinetics of Selectin/Ligand interactions

Receptor/ligand interactions are basic issues to cell adhesion, which are important to many physiological and pathological processes such as lymphocyte-mediated cytotoxicity, tumor metastasis and inflammatory reactionl. Selectin/carbohydrate ligand bindings have been found to mediate the fast rolling of leukocytes on activated endothelial monolayer. Kinetic rate and binding affinity constants are essential determinants of cell adhesion...