Polymer-supported membranes as models of the cell surface

Lipid-bilayer membranes supported on solid substrates are widely used as cell-surface models that connect biological and artificial materials. They can be placed either directly on solids or on ultrathin polymer supports that mimic the generic role of the extracellular matrix. The tools of modern genetic engineering and bioorganic chemistry make it possible to couple many types of biomolecule to supported membranes. This results in sophisticated interfaces that can be used to control, organize and study the properties and function of membranes and membrane-associated proteins. Particularly exciting opportunities arise when these systems are coupled with advanced semiconductor technology.     

Successive action of DnaK, DnaJ and GroEL along the pathway of chaperone-mediated protein folding.

The main stress proteins of Escherichia coli function in an ordered protein-folding reaction. DnaK (heat-shock protein 70) recognizes the folding polypeptide as an extended chain and cooperates with DnaJ in stabilizing an intermediate conformational state lacking ordered tertiary structure. Dependent on GrpE and ATP hydrolysis, the protein is then transferred to GroEL (heat-shock protein 60) which acts catalytically in the production of the native state. This sequential mechanism of chaperone action may represent an important pathway for the folding of newly synthesized polypeptides.     

半导体量子线制备方法及研究动态

一维半导体材料由于其在空间二维的量子限域作用，而显示出非线性光学性能、光致发光、独特的光电性能以及单电子效应等，这些特性在电子和光电子元件方面具有潜在的巨大应用价值。一维半导体材料的制备技术已得到广泛研究，文献中报道了许多制备方法。对目前国内外制备半导体量子线的最新研究成果和方法进行了讨论，并对半导体量子线制备研究的发展趋势进行了预测。     

纳米材料毒性机制及其影响因素

纳米材料以其独特的物理化学性质被广泛应用到工农业和人们生活的各个领域,随着纳米材料的生产加工和使用,纳米材料可以经过大气循环、水循环、生物循环进入生态环境,进而侵染生物体,影响人类健康.因此,纳米材料的毒性问题日益受到人们的关注,而纳米材料毒性机制和影响因素是纳米材料毒性研究的热点问题之一.目前,氧化应激和炎症反应是解释纳米材料毒性的两种主要机制,此外,越来越多的研究表明自噬也是纳米材料毒性的一种潜在机制,并且自噬可能与氧化应激和炎症反应相互关联.另一方面,纳米材料的物理化学性质如尺寸、形状、表面修饰等对其毒性产生重要影响.本文首先概括了纳米颗粒进入环境及侵染生物体的方式,分析纳米材料引起生物和环境毒性的机制,最后对影响纳米材料毒性的因素进行深入探讨,以期为纳米毒理学研究提供帮助.     

Different conformations for the same polypeptide bound to chaperones DnaK and GroEL.

The proteins DnaK (hsp70) and GroEL (cpn60) from Escherichia coli are prototypes of two classes of molecular chaperones conserved throughout evolution. The analysis of transferred nuclear Overhauser effects in two-dimensional NMR spectra is ideally suited to determine chaperone-bound conformations of peptides. The peptide vsv-C (amino-acid sequence KLIGVLSSLFRPK) stimulates the ATPase of BiP and Hsc70 (ref. 3) and the intrinsic ATPase of DnaK. The affinity of the vsv-C peptide for DnaK is greatly reduced in the presence of ATP. Here we analyse transferred nuclear Overhauser effects and show that the peptide is in an extended conformation while bound to DnaK but is helical when bound to GroEL. NMR also indicates that the mobility of the peptide backbone is reduced more by binding to DnaK than by binding to GroEL, whereas the side chains are less mobile when bound to GroEL.     

Multifunctional artificial nacre via biomimetic matrix-directed mineralization

Natural nacre, one of the most studied biological structural materials with delicate hierarchical structures and extraordinary performance, has inspired the design and fabrication of artificial structural ceramics with high fracture toughness. However, to meet the diverse requirements of different applications, future structural materials must be multifunctional with superior mechanical properties, such as strength, hardness, and toughness. Herein, based on the matrix-directed mineralization method for producing biomimetic structural materials, we introduce nanoparticles with different inherent functions into the platelets of artificial nacre via the co-mineralization of aragonite and the nanoparticles. Besides their enhanced mechanical properties, the obtained artificial nacre materials also exhibit different functions depending on the type of the nanoparticles. To extend the versatility of this strategy, the effects of nanoparticles of different sizes and zeta potentials on mineralization are also analyzed. This universal strategy can be applied to the fabrication of other types of functionalized biomimetic structural ceramics that have potential applications in various fields, such as biomedical science.     

Global unfolding of a substrate protein by the Hsp100 chaperone ClpA.

The bacterial protein CIpA, a member of the Hsp100 chaperone family, forms hexameric rings that bind to the free ends of the double-ring serine protease ClpP. ClpA directs the ATP-dependent degradation of substrate proteins bearing specific sequences, much as the 19S ATPase 'cap' of eukaryotic proteasomes functions in the degradation of ubiquitinated proteins. In isolation, ClpA and its relative ClpX can mediate the disassembly of oligomeric proteins; another similar eukaryotic protein, Hsp104, can dissociate low-order aggregates. ClpA has been proposed to destabilize protein structure, allowing passage of proteolysis substrates through a central channel into the ClpP proteolytic cylinder. Here we test the action of ClpA on a stable monomeric protein, the green fluorescent protein GFP, onto which has been added an 11-amino-acid carboxy-terminal recognition peptide, which is responsible for recruiting truncated proteins to ClpAP for degradation. Fluorescence studies both with and without a 'trap' version of the chaperonin GroEL, which binds non-native forms of GFP, and hydrogen-exchange experiments directly demonstrate that ClpA can unfold stable, native proteins in the presence of ATP.     

电网设备中载银纳米材料的抗菌性能研究

研究电网设备的载银纳米材料抗菌性能。给出原子团簇形成过程,制备研究的载银纳米材料。采用透射电子显微镜观察纳米粒子微观结构,显示纳米粒子外形。通过微量注射泵获取去离子水,令水滴和纳米薄膜接触,利用接触角测量仪测量二者间的接触角。测试纳米材料亲水/疏水性;并对纳米薄膜进行力学性能测试。通过计算抑菌圈大小对纳米材料抗菌性进行测试。对不同光照条件和不同沉积时间下的纳米材料抗菌性能进行测试,研究沉积量、沉积形态对载银纳米材料抗菌性能的影响,获取一组最优性能的工艺参数。进行细胞膜完整性实验,通过温度对纳米颗粒的速度分布进行有效控制,提高抗菌镀层的耐磨性能。结果表明,制备纳米材料疏水性和力学性能均较高;在沉积时间为30 min、Ag沉积量为7%、沉积形态为柱状时,纳米材料的抗菌性能最佳;通过细胞膜完整性实验可知,优化后的纳米材料能够提高细胞死亡率,有效实现杀菌。     

Three-dimensional optical metamaterial with a negative refractive index

Metamaterials are artificially engineered structures that have properties, such as a negative refractive index, not attainable with naturally occurring materials. Negative-index metamaterials (NIMs) were first demonstrated for microwave frequencies, but it has been challenging to design NIMs for optical frequencies and they have so far been limited to optically thin samples because of significant fabrication challenges and strong energy dissipation in metals. Such thin structures are analogous to a monolayer of atoms, making it difficult to assign bulk properties such as the index of refraction. Negative refraction of surface plasmons was recently demonstrated but was confined to a two-dimensional waveguide. Three-dimensional (3D) optical metamaterials have come into focus recently, including the realization of negative refraction by using layered semiconductor metamaterials and a 3D magnetic metamaterial in the infrared frequencies; however, neither of these had a negative index of refraction. Here we report a 3D optical metamaterial having negative refractive index with a very high figure of merit of 3.5 (that is, low loss). This metamaterial is made of cascaded 'fishnet' structures, with a negative index existing over a broad spectral range. Moreover, it can readily be probed from free space, making it functional for optical devices. We construct a prism made of this optical NIM to demonstrate negative refractive index at optical frequencies, resulting unambiguously from the negative phase evolution of the wave propagating inside the metamaterial. Bulk optical metamaterials open up prospects for studies of 3D optical effects and applications associated with NIMs and zero-index materials such as reversed Doppler effect, superlenses, optical tunnelling devices, compact resonators and highly directional sources.     

Selection of peptides with semiconductor binding specificity for directed nanocrystal assembly

In biological systems, organic molecules exert a remarkable level of control over the nucleation and mineral phase of inorganic materials such as calcium carbonate and silica, and over the assembly of crystallites and other nanoscale building blocks into complex structures required for biological function. This ability to direct the assembly of nanoscale components into controlled and sophisticated structures has motivated intense efforts to develop assembly methods that mimic or exploit the recognition capabilities and interactions found in biological systems. Of particular value would be methods that could be applied to materials with interesting electronic or optical properties, but natural evolution has not selected for interactions between biomolecules and such materials. However, peptides with limited selectivity for binding to metal surfaces and metal oxide surfaces have been successfully selected. Here we extend this approach and show that combinatorial phage-display libraries can be used to evolve peptides that bind to a range of semiconductor surfaces with high specificity, depending on the crystallographic orientation and composition of the structurally similar materials we have used. As electronic devices contain structurally related materials in close proximity, such peptides may find use for the controlled placement and assembly of a variety of practically important materials, thus broadening the scope for 'bottom-up' fabrication approaches.     

用于染料敏化太阳能电池的铌、氟双掺杂二氧化钛微球

为了提高染料敏化太阳能电池的性能,对其光阳极半导体材料进行了改性.用一步水热法制备了铌、氟双掺杂二氧化钛(NFT)微球,它是由多层纳米管和纳米颗粒组合在一起形成的微米级球状颗粒.这种特殊的结构使得用NFT材料制作的光阳极具有较大的表面积,有利于染料吸附.NFT的结晶性比未掺杂的二氧化钛显著增强,且结晶度随掺杂量的增加而增强,有利于提高其中的电子迁移速率并降低表面极化,因此有助于提高染料敏化电池的短路电流密度和开路电压.入射单色光子-电子转换效率(IPCE)的测试结果表明,NFT制备的电池在可见光范围内的转换效率有显著提高,在紫外波段的本征转化效率也有一定提高,电池的整体转换效率比未掺杂时提高了38%.     

Three-dimensional binary superlattices of magnetic nanocrystals and semiconductor quantum dots

Recent advances in strategies for synthesizing nanoparticles--such as semiconductor quantum dots, magnets and noble-metal clusters--have enabled the precise control of composition, size, shape, crystal structure, and surface chemistry. The distinct properties of the resulting nanometre-scale building blocks can be harnessed in assemblies with new collective properties, which can be further engineered by controlling interparticle spacing and by material processing. Our study is motivated by the emerging concept of metamaterials-materials with properties arising from the controlled interaction of the different nanocrystals in an assembly. Previous multi-component nanocrystal assemblies have usually resulted in amorphous or short-range-ordered materials because of non-directional forces or insufficient mobility during assembly. Here we report the self-assembly of PbSe semiconductor quantum dots and Fe2O3 magnetic nanocrystals into precisely ordered three-dimensional superlattices. The use of specific size ratios directs the assembly of the magnetic and semiconducting nanoparticles into AB13 or AB2 superlattices with potentially tunable optical and magnetic properties. This synthesis concept could ultimately enable the fine-tuning of material responses to magnetic, electrical, optical and mechanical stimuli.     

阿维菌素缓释纳米粒子的制备及其性能研究

以β-环糊精为载体,用共沉淀法制备了阿维菌素缓释纳米粒子,并对其制备工艺、缓释性能和防紫外光降解作用进行了研究。结果表明,所制备的纳米粒子外观呈球状,平均粒径在50～120nm之间,β-环糊精对阿维菌素具有良好的包合作用,包合率最高可达65.82%;阿维菌素缓释纳米粒子与其原药相比缓释效果明显,并具有良好的防紫外光降解的作用,在300min内与原药相比降解缓慢。纳米粒子在96h后才释放出94.20%的阿维菌素,其累积释放动力学方程为Ra=-88.4348e^-0.1031t+86.0599,符合一级动力学释放模型。     

辐射腔体的空腔效应

由辐射性能一致的漫射表面组成的腔体,在温度一致的条件下,其辐射行为可以归结到由腔体开口的表现来描述,这就是所谓空腔效应。本文从辐射表面之间的换热规律出发,推导出反映空腔效应的定量概念－空腔因子,建立了空腔因子与腔体形状和腔体材料的关系。     

CdSe量子点修饰物DSPE-PAA对其荧光增强效应的研究

采用有机热溶剂法制备出荧光量子效率高、单分散性良好的油溶性CdSe半导体量子点,将其用水溶性低分子量两性聚合物DSPE-PAA[poly（acylicacid）-1,2-distearoyl-sn-glycero-3-phosphoethanolamine,聚丙烯酸-1,2-二硬脂酰-sn-丙三醇-3-磷脂酰乙醇胺]进行修饰,得到水溶性和生物相容性良好的量子点。用透射电子显微镜（TEM）和荧光光谱等方法对CdSe纳米微粒的结构、形貌和光学特性分别进行了表征。并探讨和研究了在修饰过程中发生的DSPE-PAA对量子点由于荧光共振能量转移（FRET）作用产生的量子点荧光增强的现象。     

TiO2纳米刺球制备和表征

采用溶胶-凝胶法制备出球形TiO2纳米粒子,通过离心的方法将TiO2纳米粒子从乙醇中转移到水中.在60℃下,将分散剂聚乙烯吡咯烷酮(PVP)和刻蚀剂NaBH4加入到TiO2纳米粒子水分散体系中,经61h的恒温刻蚀反应,制备出TiO2纳米刺球.此外,该刻蚀方法同样被应用于Au@SiO2@TiO2纳米刺球的制备.用扫描电子显微镜(SEM)、动态光散射(DLS)、透射电镜(TEM)及X射线衍射实验(XRD)等方法对TiO2纳米粒子和Au@SiO2@TiO2纳米粒子及其纳米刺球进行表征,进而探索NaBH4刻蚀TiO2的机理.该刻蚀方法所需的设备和实验步骤相对简单,反应条件温和可控,较易实现大批量的TiO2纳米刺球的合成并且也适用于外壳层为TiO2的复合核壳结构纳米刺球的制备.     

A family of related ATP-binding subunits coupled to many distinct biological processes in bacteria

Many biological processes are coupled to ATP hydrolysis. We describe here a class of closely related ATP-binding proteins, from several bacterial species, which are associated with a variety of cellular functions including membrane transport, cell division, nodulation in Rhizobium and haemolysin export. These proteins comprise a family of structurally and functionally related subunits which share a common evolutionary origin, bind ATP and probably serve to couple ATP hydrolysis to each of these biological processes. This finding suggests a specific role for ATP in cell division, nodulation during nitrogen fixation and protein export, and allows us to assign a probable function to one of the protein components from each of these systems.     

碳掺杂二氧化钛的稀磁特性

作为新型材料的稀磁半导体(DMS)在大规模集成电路、高频率器件和光电子器件等方面得到广泛的运用.这主要源于稀磁半导体(DMS)同时具备半导体的电学性质和磁性材料的磁学性质.采用放电等离子烧结(SPS)制备了碳纳米管掺杂的锐钛矿相二氧化钛和未掺杂锐钛矿相二氧化钛样品,样品的结构、形貌、成分、氧空位和磁性等物理性质分别通过XRD,TEM,Raman,XPS,PL,VSM等表征手段进行了分析.综合实验结果,发现氧空位的存在和室温铁磁性正相关.     

富勒烯C_(60)的物理、化学性质及其应用研究进展

介绍了富勒烯C60的结构,富勒烯C60的溶解性、磁性、非线性光学性质、超导、光电导性等物理性质以及富勒烯C60与金属反应、加成反应、聚合反应等化学性质.综述了富勒烯C60在催化剂、光学材料、半导体、太阳能电池、润滑剂、化妆品、生物医药等方面应用研究,并展望了富勒烯C60的发展前景和趋势.