Structure of a thiol monolayer-protected gold nanoparticle at 1.1 A resolution

Structural information on nanometer-sized gold particles has been limited, due in part to the problem of preparing homogeneous material. Here we report the crystallization and x-ray structure determination of a p-mercaptobenzoic acid (p-MBA)-protected gold nanoparticle, which comprises 102 gold atoms and 44 p-MBAs. The central gold atoms are packed in a Marks decahedron, surrounded by additional layers of gold atoms in unanticipated geometries. The p-MBAs interact not only with the gold but also with one another, forming a rigid surface layer. The particles are chiral, with the two enantiomers alternating in the crystal lattice. The discrete nature of the particle may be explained by the closing of a 58-electron shell.     

Novel Colloidal Interactions in Anisotropic Fluids

Small water droplets dispersed in a nematic liquid crystal exhibit a novel class of colloidal interactions, arising from the orientational elastic energy of the anisotropic host fluid. These interactions include a short-range repulsion and a long-range dipolar attraction, and they lead to the formation of anisotropic chainlike structures by the colloidal particles. The repulsive interaction can lead to novel mechanisms for colloid stabilization.     

黄浦江上游近自然混交林和人工纯林水源涵养功能评价

以上海黄浦江上游水源涵养林为研究对象,选择近自然混交林、香樟(Cinnamomum camphora)人工纯林和无患子(Sapindus mukorossi)人工纯林,对比了地上部分、枯落物层、土壤层三个垂直层次的持水量,综合评价了其水源涵养功能。结果表明:地上部分持水量近自然混交林与香樟纯林持平,大于无患子纯林,分别为16.36t/hm2,16.85t/hm2,12.54t/hm2;枯落物层最大持水量依次为近自然混交林(0.37t/hm2)无患子纯林(0.004t/hm2)香樟纯林(0.003t/hm2);土壤层最大持水量近自然混交林(2 657.02t/hm2)无患子纯林(2 526.81t/hm2)香樟纯林(2 474.80t/hm2)。土壤层对森林涵养水源功能的贡献最大,但同时离不开地上部分及枯落物层三者间的相互依存和影响。综合评价得到不同类型林分的总持水量为近自然混交林(2 673.73t/hm2)无患子纯林(2 539.35t/hm2)香樟纯林(2 491.65t/hm2)。由此可见,林分复杂、树种多样、林下植被丰富的近自然混交林涵养水源的能力最强,优于单一的无患子纯林,而香樟纯林最差。     

溴虫腈与哒螨灵对朱砂叶螨的联合作用

为明确溴虫腈与哒螨灵的联合杀螨活性,采用玻片浸渍法测定了溴虫腈与哒螨灵不同配比混剂对朱砂叶螨雌成螨的杀螨活性,并以共毒因子法和共毒系数法评价混剂的增效作用。结果表明,溴虫腈和哒螨灵对朱砂叶螨雌成螨处理后24 h的致死中质量浓度(LC50)分别为8.80、17.69mg/L;溴虫腈与哒螨灵的质量比为49∶51、47∶53、45∶55时增效最明显,对朱砂叶螨处理后24 h的共毒系数分别为177.94、178.49、173.73,LC50分别为6.65、6.72、7.00 mg/L,其毒力分别是哒螨灵的2.66倍、2.63倍、2.53倍。因此,45%~49%溴虫腈与51%~55%哒螨灵混合具有显著的增效作用。