Electronic structure and electron g factors of HgTe quantum dots

The electronic structure and electron g factors of HgTe quantum dots are investigated, in the framework of the eight-band effective-mass approximation. It is found that the electron states of quantum spheres have aspheric properties due to the interaction between the conduction band and valence band. The highest hole states are S (l = 0) states, when the radius is smaller than 9.4 nm. the same as the lowest electron states. Thus strong luminescence from H-Te quantum dots with radius smaller than 9.4 nm has been observed (Rogach et al 2001 Phys. Statits Solidi b 224 153). The bandgap of H-Te quantum spheres is calculated and compared with earlier experimental results (Harrison et al 2000 Pure Appl. Chem. 72 295). Due to the quantum confinement effect, the bandgap of the small HgTe quantum spheres is positive. The electron g factors of HgTe quantum spheres decrease with increasing radius and are nearly 2 when the radius is very small. The electron g factors of HgTe quantum ellipsoids are also investigated. We found that as some of the three dimensions increase, the electron g factors decrease. The more the dimensions increase, the more the g factors decrease. The dimensions perpendicular to the direction of the magnetic field affect the g factors more than the other dimension.

Hg胁迫对两种基因型小麦生长及其过氧化物酶活性的影响

用不同浓度Hg处理两种基因型小麦种子,较低浓度的Hg对小麦种子萌发影响比较小,对抗旱品种的小麦种子(陕合)的萌发有略微的刺激作用。小剂量、短时间的重金属处理可以提高POD的活性,发芽后受到Hg胁迫的陕合对Hg的耐受性低于发芽前就受到Hg胁迫的陕合,也低于同样胁迫处理的小麦品种(郑引)。发芽后进行Hg胁迫处理情况下,陕合对于Hg胁迫比较敏感,POD活性随着Hg浓度的升高而下降;而郑引,低浓度Hg对其POD活性有促进作用。在小麦发芽前就受到Hg胁迫的情况下,陕合和郑引的POD活性都随着Hg浓度增加表现为先上升而后下降趋势。

土壤复合污染条件下对二氯苯和重金属吸附行为与生态毒性

环境污染问题实际上是多种污染物共存引起的复合污染。多元体系复合污染条件下的交互作用，特别是有机与无机污染物复合污染，使得污染物在土壤中的环境行为、联合生态毒性效应及其发生机制变得更加复杂、更加不可预测。由于疏水性有机污染物（HOCs）和重金属在理化性质上存在极大差异，致使开展HOCs-重金属复合体系下，污染物的土壤环境行为和毒性效应机制的研究还存在一定的难度，这方面的研究也还不多。 本研究选择了典型的HOCs对二氯苯（1,4-DCB）和土壤中典型有毒重金属元素Cd、Cu为研究对象，着重分析共存污染物的存在对其各自环境吸附行为的影响及其作用规律；并开展了二者复合污染对土壤酶系统、土壤-植物复合生态系统的联合生态毒性效应的研究。 Cd、Cu的存在对1,4-DCB在棕壤和黑土上的吸附产生了竞争抑制作用，增加了其向土壤环境中的释放。其中，Cu的抑制程度高于Cd，老化Cd的抑制程度要高于未老化Cd。而1,4-DCB对Cd、Cu在两种土壤的吸附能力基本没有产生影响，但降低了Cd的解吸滞后性系数，对Cu的解吸影响较小。 1,4-DCB和Cd在土壤中的存在具有一定的生态风险，多数情况下抑制土壤脱氢酶和脲酶活性。 二者联合毒性类型表现复杂：低浓度1,4-DCB（50 mg kg-1）和Cd复合污染主要产生协同效应，而高浓度（100 mg kg-1）则产生协同、拮抗以及加和作用，与其浓度组合、土壤持留时间及酶种类有关。因此，用土壤酶活性变化作为指标来定量表征二者复合污染所引起的土壤环境质量变化还存在一定难度。 在土壤-植物复合系统中，不同植物叶片和根系具有不同的对抗污染物氧化胁迫的生理生化机制，各抗氧化剂会协同对抗，表现出不同的氧化损伤效应。1,4-DCB与Cd对植物膜脂质过氧化和抗氧化酶系统的联合毒性效应不仅与其浓度组合有关，还与植物种类以及受试部位有关。二者单一与复合处理均导致大豆叶片和小麦根部MDA含量升高，表明氧化胁迫作用的存在。因此，大豆叶片和小麦根部中MDA含量增加似乎更能反映其受污染物胁迫的程度。 采用多隔层根际箱方法，研究了1,4-DCB与Cd对不同植物根际各毫米级微域土壤酶活性的联合毒性效应。在相同浓度水平下，二者对大豆和小麦根际各级微域土壤酶活性的影响不一致，随根际距离增加，酶活性没有呈现一致的变化趋势。总的来说，二者联合胁迫下，大豆近根际区域（特别是1mm）土壤脲酶活性受到诱导，而小麦中央区域和1、2mm近根际区域土壤脱氢酶活性则被抑制。

运用含有偶氮苯的自组装单层膜在光化学条件下可逆地控制细胞黏附

细胞生物学研究的一个重要方向是动态地控制细胞在基底上的黏附。最近，随着表面化学的研究深入，尤其是对烷基硫醇在金基底上形成自组装单层膜（self-assembled monolayers, SAMs）这一体系的研究，使得人们能在分子水平的表面上控制细胞黏附。精氨酸-甘氨酸-天冬氨酸（arginine-glycine-aspartate, RGD）序列首先是从细胞外基质蛋白中分离出来的，能够识别并非共价结合细胞膜表面的整合素受体，从而促进细胞黏附。以前的一些工作已经证实，将含有RGD的肽链连接到SAMs表面之后，能够生物特异性地黏附动物细胞。已有的手段比如光照、电压、加热、微电极、微流控以及表面纳米形貌的梯度变化，都不能真正实现可逆地控制细胞黏附，原因是这些方法所用的化学有限；这些方法也不能得到完全抗拒细胞黏附的表面，原因是这些方法产生的表面缺陷等不完整。用两种不同波长的光（紫外光和可见光）照射偶氮苯，偶氮苯会发生可逆的光致异构变化，因此，偶氮苯的光致异构性质可以用来可逆地控制细胞在表面黏附。运用含有偶氮苯的混合SAMs，偶氮苯的末端连接GRGDS肽，混合SAMs中是以末端为六聚乙二醇的硫醇为背景，该SAMs修饰而成的表面能够黏附或者抗拒细胞黏附，其表面黏附性质取决于SAMs中偶氮苯的构象。该方法提供了一种在分子水平的表面上我们所了解到的唯一能可逆控制细胞黏附的方法，该方法需要用到的光源来自于标准荧光显微镜所配置的汞灯。 为了实现在金基底表面可逆的控制细胞黏附，我们合成了如下三个化合物： 由于化合物1的溶解性很差，几乎在所有溶剂里都不溶，所以不能直接用化合物1制备SAMs；化合物2能高效地抗拒细胞的黏附；化合物3的偶氮苯末端是活化酯，能够连接GRGDS肽，从而控制细胞黏附。 将化合物2和化合物3以一定的比例均匀混合在金基底表面形成SAMs，然后将GRGDS肽连接到偶氮苯(反式)的末端（通过GRGDS肽的甘氨酸上的伯胺基与偶氮苯末端的活化酯反应），从而得到细胞黏附的表面。用紫外光照射该细胞黏附表面5-10小时，随着偶氮苯的构象由反式变为顺式，偶氮苯末端的GRGDS肽淹没在化合物2的六聚乙二醇中，得到抗拒细胞黏附的惰性表面。再用可见光照射该惰性表面1个小时，随着偶氮苯的构象由顺式变为反式，原先埋没在六聚乙二醇中的GRGDS肽伸展至单层膜的末端，又得到了细胞黏附的表面。因此，该表面能完全可逆地控制细胞在金表面黏附。 An important area in cell biology is the dynamic control of cell adhesion on substrates. Recent advancements in surface chemistry, in particular, self-assembled monolayers (SAMs) of alkanethiols on gold substrates, have permitted unprecedented control of cell adhesion via molecularly defined surfaces. The tri-peptide sequence arginine-glycine-aspartate (RGD), initially isolated from the extracellular matrix (ECM) proteins, can recognize and non-covalently bind with integrin receptors on cell membranes to promote cell adhesion. Some previous work has demonstrated that RGD peptide grafted on SAMs can allow bio-specific adhesion of mammalian cells that mimic natural adhesion. Existing technologies such as light, voltage, heat, microelectrodes, microfluidic systems and surface gradient of nanotopography, either cannot realize fully reversible control of cell adhesion, due to the limitation in the chemistry used, or cannot yield a surface completely resistant against cell adhesion, due to the imperfection of surfaces. Azobenzenes undergo reversible photo-induced isomerization rapidly at two different wavelengths of light (UV and visible light), it therefore potentially allows the reversible control of cell adhesion on a surface. By using a mixed SAMs presenting azobenzene groups terminated in GRGDS peptides in a background of hexa(ethylene glycol) groups, the surface can either accommodate or resist cell adhesion depending on the conformation of the azobenzene embedded in SAMs. This method provides the only means we know to control cell adhesion reversibly on a molecularly well-defined surface by using light generated by a mercury lamp equipped on standard fluorescence microscopes. To realize the reversible control of cell adhesion on gold surface, we synthesized three kinds of compounds as following, We found that it was difficult to obtain SAMs directly from compound 1 because of its poor solubility in almost all kinds of solvents; compound 2 can resist cell adhesion efficiently; compound 3 presents an azobenzene terminated with NHS-activated ester, which can couple with a GRGDS peptide to control cell adhesion. After coating a gold surface with compound 2 and 3 in appropriate ratios to form a SAM followed by coupling the GRGDS peptides with NHS-activated esters at the end of azobenzene (E configuration) resulted in a cell-adhesive SAM. Irradiating this cell-adhesive SAM with UV light for 5-10 h converted the E configuration of azobenzene into the Z form, the GRGDS peptides becoming masked in the PEG, resulting in a cell-resistant surface. These SAM could again support cell adhesion as a result of the conformational switch of azobenzene from Z to E with the irradiation of visible light for 1 h. This surface, therefore, allows completely reversible control of cell adhesion on a gold surface.