Hierarchical self-assembly of amphiphilic metallohosts to give discrete nanostructures

The synthesis and aggregation behavior of a new class of rigid metallohosts is described. The molecules consist of a ruthenium-bipyridine complex functionalized with a glycoluril-based receptor cavity. By specific molecular recognition processes in water, the metallohosts self-assemble to form large arrays of molecules. Depending on the size of the cavity side walls of the host, these arrays can grow in a hierarchical process into discrete rectangular and cigar-like aggregates of nanometer size, which can be visualized by electron microscopy.     

Engineering of ferrimagnetic Cu12-cluster arrays through supramolecular interactions

Ferrimagnetic oxo-bridged Cu12 aggregates can be organised into a variety of arrays by utilising structure-directing effects of counter ions, solvent molecules and linker units.     

Electronic coupling and exciton energy transfer in CdTe quantum-dot molecules

Stable dispersions of molecularlike aggregates of CdTe quantum dots are prepared by chemical cross-linking. Cryo-TEM images confirm the presence of cross-linked quantum dots and show that the size of the small aggregates can be controlled by the amount of cross-linker added. Optical measurements reveal two types of interdot interactions within these quantum-dot molecules: exciton energy transfer and electronic coupling. Quantitative information on the energy transfer rates in quantum-dot molecules is obtained by photoluminescence lifetime measurements. The degree of electronic coupling is dependent on the size of the quantum dots, which is supported by quantum mechanical calculations.     

Two-dimensionally self-arranged protein nanoarrays on diblock copolymer templates

Novel methods for creating protein arrays with two-dimensional control can significantly enhance basic biological research as well as various bioarray applications. We demonstrate that the structural variety and chemical heterogeneity of self-assembled, hexagonal polystyrene-b-poly(vinylpyridine) micelles can be successfully exploited as templates for easy and rapid fabrication of functional protein arrays over a large scale. Spontaneous formation of such polymeric template-guided protein molecules yields high-density protein arrays that exhibit repeat spacings in a nanoscopic dimension. The ensuing self-assembled protein molecules in the array maintain their natural conformation and activity over a very long time period. By tuning the size of the underlying block copolymer templates, our amphiphilic diblock copolymer-based approach to create high-density protein patterns also permits spatial control over two-dimensional repeat spacings of protein nanoarrays. These unique advantages of polystyrene-b-poly(vinylpyridine) templates make the spontaneously constructed protein nanoarrays highly suitable as functional protein sensor substrates. Therefore, our novel two-dimensional protein assembly method can be greatly beneficial for high-throughput proteomic assays and multiplexed high-density protein sensing applications.     

应用纳米球刻蚀法在自组装膜修饰的硅表面生成中尺度的网状蛋白层

The patterning and immobilization of protein molecules onto functionalized silicon substrate through surface silane chemistry is of interest because protein patterning is an important prerequisite for the development of protein-based diagnostics in biological and medicinal fields. As a model system, mesoscale netty lysozyme arrays were assembled on oxidized undecyltrichlorosilane (UTSox) monolayer coated silicon surface through nanosphere lithography. The size of the arrays ranged from nanometer to micrometer can be easily adjusted by changing the size of nanospheres applied on the surface. By using nanosphere lithography, we are capable of fabricating a regular array of protein islands over centimeter sample regions. The created lysozyme protein patterns were characterized by atomic force microscopy (AFM) and fluorescence microscope, respectively. The analysis has demonstrated that this newly established approach offers a faster and more reliable process to fabricate netty protein arrays over large areas compared to conventional scanning-probe based fabrication methods. Furthermore, the carboxylic acid-terminated layer on surfaces is particularly effective for immobilizing protein molecules through either electrostatic interactions or covalent attachment via imine bonds. Therefore, the negative-toned protein structure on the surface with carboxylic acid groups coated on the bare areas makes it possible to fabricate two types of protein molecules on one surface.     

Structural phase transformations induced by the addition of decanol to the hexagonal phase of the binary sodium decyl sulphate/water system

The hexagonal phase of the sodium decyl sulphate/water system transforms into a lamellar phase on the introduction of decanol. This transformation occurs in several steps. We present here a study of the sequence of the corresponding phase transformations. The various phases are identified according to their textures by optical microscopy. It can be seen that, as the decanol/soap ratio increases the two dimensional hexagonal phase is followed by two dimensional rectangular phases before the one dimensional lamellar phase is reached. The symmetries of the structures of the phases and the shapes of their aggregates of amphiphilic molecules were determined by small angle X-ray and neutron scattering studies (SAXS and SANS). Two rectangular phases with cmm and pgg symmetries show up successively between the hexagonal and lamellar phases. The shape of the aggregates evolves along the sequence in an unexpected manner. In the two dimensional hexagonal phase, the aggregates are cylinders with an isotropic circular section at low decanol/soap ratio, which become anisotropic as this ratio increases, i.e. the aggregates become ribbon-like aggregates. The aggregates keep this shape in the rectangular phases, with changes of size, and also, most probably, in the lamellar phase near the two dimensional rectangular phases where it can be seen that the lamellae are fragmented. The local organization of decanol and sodium decyl sulphate molecules within the ribbon-like aggregates was also investigated by SANS and deuteron magnetic resonance (DMR). The SANS studies show that the two molecules are not distributed uniformly within the aggregates, while the DMR measurements show that both amphiphilic molecules stay anchored at the amphiphile/water interface by their polar heads. It can then be inferred that the decanol molecules are preferably in the regions of lowest interfacial curvature and the sodium decyl sulphate molecules are in the regions of highest interfacial curvature. This study shows that addition of decanol in the hexagonal phase induces deformation of the cylinders into ribbons by a local flattening of the interface. This deformation, which starts already deep within the hexagonal phase, is not associated with a change of symmetry of the structure. It also appears that a further deformation of the ribbons into lamellae is not needed for the rectangular phase to change into the lamellar phase when the decanol content increases. Thus, in this sequence of phases, the symmetry of the aggregates and those of their organization are not necessarily related.     

Influence of intermolecular orientation on the photoinduced charge transfer kinetics in self-assembled aggregates of donor-acceptor arrays

The kinetics of photoinduced charge transfer reactions in covalently linked donor-acceptor molecules often undergoes dramatic changes when these molecules self-assemble from a molecular dissolved state into a nanoaggregate. Frequently, the origin of these changes is only partially understood. In this paper, we describe the intermolecular spatial organization of three homologous arrays, consisting of a central perylene bisimide (PERY) acceptor moiety and two oligo(p-phenylene vinylene) (OPV) donor units, in nanoaggregates and identify both face-to-face (H-type) and slipped (J-type) stacking of the OPV and PERY chromophores. For the J-type aggregates, short intermolecular OPV-PERY distances are created that give rise to a charge-transfer absorption band. The proximity of the donor and acceptor groups in the J-type aggregates enables a highly efficient photoinduced charge separation with a rate (k(cs) > 10(12) s(-1)) that significantly exceeds the rate of the intramolecular charge transfer of the same compounds when molecularly dissolved, even in the most polar media. In the H-type aggregates, on the other hand, the intermolecular OPV-PERY distance is not reduced compared to the intramolecular separation, and hence, the rates of the electron transfer reactions are not significantly affected compared to the molecular dissolved state. Similar to the forward electron transfer, the kinetics of the charge recombination in the aggregated state can be understood by considering the different interchromophoric distances that occur in the H- and J-type aggregates. These results provide the first consistent rationalization of the remarkable differences that are observed for photoinduced charge-transfer reactions of donor-acceptor compounds in molecularly dissolved versus aggregated states.     

Amphiphilicity-driven organization of nanoparticles into discrete assemblies

We present a method for organizing metallic nanoparticles in solution that is based on the hydrophobic effect and does not require either hydrogen bonding or molecular recognition. When amphiphilic V-shaped molecules are attached to a gold cluster, an aggregation process ensues in aqueous solution and leads to the formation of well-defined cylindrical and vesicular nanoarrays of particles. The metallic clusters densely pack at the boundary separating the hydrophobic core from the hydrophilic corona of the hybrid micelle-like aggregates. This design allows one to assemble and disassemble the nanoparticles in a reversible manner and control the size and the morphology of the arrays by changing the conditions of the solution preparation. The versatility of this method is demonstrated by its applicability to different metals with covalently attached amphiphilic arms with various chemical compositions (PS-PEO and PB-PEO) and molecular weights.     

光调控分子有序聚集体及其功能化研究进展

双亲分子在溶液中可以缔合形成胶束、囊泡、液晶、乳液等有序分子聚集体。在分子中引入功能性的基团,通过改变分子的结构、浓度或引入外部刺激,可以对有序分子聚集体的类型和性能进行调控。光作为一种绿色可控的清洁能源,是一种理想的外部刺激信号。在双亲分子中引入感光基团,可以通过光照调节有序聚集体的组装,并进一步实现功能性的调控。本文综述了近年来在光调控分子有序聚集体方面的研究及其在生物、传导、纳米材料制备中的应用。同时,对光调控的功能性有序分子聚集体未来的发展前景进行了展望。     

Light‐Induced Self‐Assembly and Decay of J Aggregates of Thiamonomethinecyanine Dyes

Formation of J aggregates, that is, one‐dimensional supramolecular self‐organizations in which the transition moments of individual molecules are aligned parallel to the line joining their centers through a “head‐to‐tail” arrangement, normally proceed via electrostatic interactions between oppositely charged molecular groups; this is facilitated by an electrolyte medium. Here, we show that J aggregates of thiamonomethinecyanine dyes in a solution can be assembled from dye dimers by illuminating the solution with light of the appropriate wavelength to induce excitation of the dye dimers. The reverse process is also demonstrated by application of light of the correct wavelength to induce excitation of the J aggregates. Our results indicate that spontaneous J aggregation in the dark and formation of J aggregates through illumination proceed through different mechanisms; the former resulting in an increase in the number of the aggregates and the latter in an increase in the size of the aggregates.     

Additional peaks in the cluster size distribution of amphiphile + water systems: a clue for shape/phase transition or statistical uncertainty

In some works on the lattice Monte Carlo simulation of amphiphilic systems additional peaks in the cluster size distribution has been interpreted as a clue for the phase or shape transition of micellar aggregates. On the other hand, some other works showed that the additional peaks are a result of finite size of the lattice box. In this paper using calculating energy-auto-correlation function and statistical error in correlated data, it is shown that how these apparently contradictory results are the same. To do this, we have simulated a pure system containing amphiphile and water molecules. A simple model of potential containing the main feature for these systems (the hydrophobicity of surfactant molecules) that cause the aggregates to be formed is considered to avoid any synthetic results due to additional non-real parameters. To relax the initial configuration faster, configurational bias Monte Carlo move is used in addition to reptation move. Periodic boundary condition and self-avoiding walks are used as former published works in this field. It is shown that the additional peaks is a result of the statistical errors for averaged cluster size distribution and can not be interpreted as a clue for shape or phase transition.     

Specific binding of large aggregates of amphiphilic molecules to the respective antibodies

The Binding of nonylphenol to respective antibodies immobilized on solid substrates was studied with the methods of total internal reflection ellipsometry (TIRE) and QCM (quartz crystal microbalance) impedance spectroscopy. The binding reaction was proved to be highly specific having an association constant of KA=1.6x10(6) mol(-1) L and resulted in an increase in both the adsorbed layer thickness of 23 nm and the added mass of 18.3 microg/cm2 at saturation. The obtained responses of both TIRE and QCM methods are substantially higher than anticipated for the immune binding of single molecules of nonylphenol. The mechanism of binding of large aggregates of nonylphenol was suggested instead. Modeling of the micelle of amphiphilic nonylphenol molecules in aqueous solutions yielded a micelle size of about 38 nm. The mechanism of binding of large molecular aggregates to respective antibodies can be extended to other hydrophobic low-molecular-weight toxins such as T-2 mycotoxin. The formation of large molecular aggregates of nonylphenol and T-2 mycotoxin molecules on the surface was proved by the AFM study.     

Stoichiometry and physical chemistry of promiscuous aggregate-based inhibitors

Many false positives in early drug discovery owe to nonspecific inhibition by colloid-like aggregates of organic molecules. Despite their prevalence, little is known about aggregate concentration, structure, or dynamic equilibrium; the binding mechanism, stoichiometry with, and affinity for enzymes remain uncertain. To investigate the elementary question of concentration, we counted aggregate particles using flow cytometry. For seven aggregate-forming molecules, aggregates were not observed until the concentration of monomer crossed a threshold, indicating a "critical aggregation concentration" (CAC). Above the CAC, aggregate count increased linearly with added organic material, while the particles dispersed when diluted below the CAC. The concentration of monomeric organic molecule is constant above the CAC, as is the size of the aggregate particles. For two compounds that form large aggregates, nicardipine and miconazole, we measured particle numbers directly by flow cytometry, determining that the aggregate concentration just above the CAC ranged from 5 to 30 fM. By correlating inhibition of an enzyme with aggregate count for these two drugs, we determined that the stoichiometry of binding is about 10,000 enzyme molecules per aggregate particle. Using measured volumes for nicardipine and miconazole aggregate particles (2.1 x 10(11) and 4.7 x 10(10) A(3), respectively), computed monomer volumes, and the observation that past the CAC all additional monomer forms aggregate particles, we find that aggregates are densely packed particles. Finally, given their size and enzyme stoichiometry, all sequestered enzyme can be comfortably accommodated on the surface of the aggregate.     

Controllable size, shape and morphology of molybdic acid self-aggregated with rhodamine B to construct functional material

Controllable size, shape and morphology of rhodamine B/molybdic acid (RBMA) aggregates were prepared from a self-aggregation reaction in a molybdic acid and rhodamine B (RhB) coexisting solution. Nanodisks, as well as microcrystal rods and polyhexagonal microcrystal rods, have been obtained in conventional bulk solutions at different temperatures. Large-sized network microcrystal rods and branched fractal aggregates constructed with nanosubunits after the nucleation duration of an ice-water-cooled process have also been achieved under the evaporation-enhanced conditions on glass substrates. The factors affecting the size, shape and morphology of RBMA aggregates including temperature, nucleation and growth, and processing conditions are discussed. The results show that photofunctional molecules (RhB) modified the surface of the molybdic acid particles and influenced their self-aggregation. The temperature and nucleation play key roles in the formation of RBMA aggregates. The structures of RBMA aggregates were characterized by X-ray diffraction, infrared spectra and elemental dispersive spectroscopy. The results indicate that the aggregates show the characteristics of RhB-mediated hydrated ammonium molybdenum bronze with the metastable hexagonal phase. Visible-light-induced electrons transfer reactions in the RBMA aggregates from rhodamine B molecules to MoO3 matrixes were measured by UV-vis spectra and X-ray photoelectron spectra, and the fluorescent image was observed by laser scanning confocal microscopy.     

Photoisomerization of azobenzene derivatives in nanostructured silica

A series of derivatized azobenzene molecules are synthesized such that one of the phenyl groups can be chemically bonded to mesostructured silica and the other, derivatized with dendrons, is free to undergo large-amplitude light-driven motion. The silica frameworks on which the motion takes place are either 150 nm thick films containing ordered hexagonal arrays of tubes (inner diameter about 2 nm) containing the bonded azobenzenes, or particles (about 500 nm in diameter) containing the same ordered arrays of functionalized tubes. The photoisomerization yields and the rate constants for the thermal cis to trans back-reaction of the azobenzenes in the tubes are measured and compared to those of the molecules in solution. The rate constants decrease with increasing size of the dendrons. Fluorescence spectra of the cis and trans isomers in the pores show that the photoisomerization in the nanostructured materials is selectively driven by specific wavelengths of light and is reversible.     

Applications of self-assembled monolayers in materials chemistry

Self-assembly provides a simple route to organise suitable organic molecules on noble metal and selected nanocluster surfaces by using monolayers of long chain organic molecules with various functionalities like -SH,-COOH,-NH₂, silanes etc. These surfaces can be effectively used to build-up interesting nano level architectures. Flexibility with respect to the terminal functionalities of the organic molecules allows the control of the hydrophobicity or hydrophilicity of metal surface, while the selection of length scale can be used to tune the distant-dependent electron transfer behaviour. Organo-inorganic materials tailored in this fashion are extremely important in nanotechnology to construct nanoelctronic devices, sensor arrays, supercapacitors, catalysts, rechargeable power sources etc. by virtue of their size and shape-dependent electrical, optical or magnetic properties. The interesting applications of monolayers and monolayer-protected clusters in materials chemistry are discussed using recent examples of size and shape control of the properties of several metallic and semiconducting nanoparticles. The potential benefits of using these nanostructured systems for molecular electronic components are illustrated using Au and Ag nanoclusters with suitable bifunctional SAMs.     

Evaluation of molecule-microbe interactions with capillary electrophoresis: procedures, utility and restrictions

Understanding the interactions between molecules and living organisms is of paramount importance for the evaluation of pharmaceutical activity, chemical toxicity and all manner of microbiological studies. The capability of capillary electrophoresis (CE) in the evaluation of molecule-microbe interactions is examined in the present paper. The fundamental chemical concept of the binding or association constant for molecular systems measured in free solution is discussed for biological systems where microorganisms uptake or associate with molecules from their environment. The heterogeneity of the living organisms must be understood and accounted for including differences related to semantics such as concentration units and the nature of the associations between two entities and large differences in the size and number of microorganisms as compared to molecules. Finally, the added complexity and even inhomogeneity of a cell compared to most molecular systems must be considered and possibly controlled. The binding of specific molecules to viruses is discussed. CE can be utilized to quickly determine if a molecule binds very strongly or not at all to a cell (i.e., a binary yes/no answer). This could be useful for initial high-throughput screening purposes when using capillary arrays, for example. CE can be useful for determining unusual (large) molecule/microbe stoichiometries. Finally, CE can sometimes be used to determine the size of binding constants (K(RL)) within certain limits provided experimental conditions can be formulated that minimize problems of biological heterogeneity.     

金纳米粒子组装结构中的表面重组现象

以纳米粒子为基本结构单元构筑的各种二维或三维超晶格结构受到了广泛的重视［１］．人们的兴趣一方面来源于在纳米尺度上控制材料结构 ,另一方面则因为组织化的纳米材料或结构具有独特的性质 ,以期在非线性光学、纳米电子学等前沿领域得到应用［２］．当前研究最多的结构形式是固体表面上的纳米粒子阵列或单层薄膜 ,通常是胶体粒子靠某种特殊相互作用吸附或沉积在固体表面上（亦称为“纳米粒子在表面上的组装［３］”） ,因此对纳米粒子及固体表面进行功能化的修饰 ,从而控制纳米粒子在表面上的排列和聚集状态 ,是制备这类复合结构的核心问…     

Formation of Neutral Peptide Aggregates as Studied by Mass‐Selective IR Action Spectroscopy

The spontaneous aggregation of proteins and peptides is widely studied owing to its relation to neurodegenerative diseases. To understand the underlying principles of peptide aggregation, elucidation of structure and structural changes upon their formation is key. This level of detail can be obtained by studying the peptide self‐assembly in the gas phase. Structural characterization of aggregates is mainly done on charged species, as adding charges is an intrinsic part of the technique to bring molecules into the gas phase. Studying neutral peptide aggregates will complement the existing picture. These studies are restricted to dimers due to experimental limitations. Herein, we present advances in laser desorption molecular beam spectroscopy to form neutral peptide aggregates consisting of up to 14 monomeric peptides in the gas phase. The combination of this technique with IR–UV spectroscopy allowed us to select each aggregate by size and subsequently characterize its structure.     

Drying dissipative structures of cationic gel spheres of lightly cross-linked poly(2-vinylpyridine) in deionized aqueous suspension

Drying dissipative patterns of cationic gel crystals of lightly cross-linked poly(2-vinylpyridine) spheres (CAIBA-P2VP(0.1), CAIBA-P2VP(0.5), and CAIBA-P2VP(1), 107?~?113 nm in diameter and 0.1, 0.5, and 1 in degrees of cross-linking) were observed on a cover glass, a watch glass, and a Petri glass dish. Convectional spoke line and cluster patterns were recognized with the naked eyes, which supports that these poly(2-vinylpyridine) gel spheres aggregate temporarily and reversibly during the course of drying. Two kinds of broad rings were observed at the outside edge and inner region in the macroscopic drying pattern. The size of the inner rings decreased with gel concentration. Formation of similar-sized aggregates (or agglomerates) and their ordered arrays ((a) ordered ring, (b) spoke lines, (c) net structures, and (d) lattice structures) were observed, though the arrays were not so complete compared with those of large-sized analogous gel spheres. One of the main causes of the incomplete ordering of the aggregates is the rather high polydispersities in the sphere size. The ordering of similar-sized aggregates is common among the gel spheres including anionic poly(N-isopropylacrylamide) and cationic poly(2-vinylpyridine). Size effect of cationic gel spheres on the ordering of the agglomerates was clarified definitely in this work. The role of the convectional flow and the electrical double layers around the agglomerates and their interaction with the substrates during drying was also clarified to be very important for the drying pattern formation.