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Computational engineering of metallic nanostructures and nanomachines.

Small structures with dimensions in the nanometer regime play an important role within a lot of modern technological branches like, for example, genetics, chip fabrication, material science, medicine, or chemistry. While highly sophisticated characterization methods would be necessary to study such nanostructures, computational methods and models have made their entrance into the field of nanotechnology. The present work gives an overview of the problems connected with quantum mechanics, many-particle systems, and nanophysical models. Further, the application of molecular dynamics (MD)--a typical computational method suitable for modelling at the nanolevel--is introduced and outlined. The setup and use of specific MD models, advanced computation techniques, and efficient algorithms are discussed, while the focus is laid on the subjects nanodesign and nanoengineering which are demonstrated for the example of metallic nanostructures. Finally, the introduced techniques and methods are applied to stability studies of theoretical nanomachines.

Computer Simulation↗

Organic-inorganic nanostructured colloids.

The synthesis and applications of organic-inorganic nanostructured colloids and colloidal-based materials are reviewed here. Emphasis is placed on the strategies and synthetic methods developed to organize organic-inorganic architectures. The article begins with a description and a general hierarchical classification of different systems, from inorganic particle synthesis and surface modification to more elaborate nanostructured colloids obtained through in situ encapsulation and/or self-assembly techniques. Ordering of colloids into two- and three-dimensional arrays and their use as templates is also considered. For every system, typical examples are given that highlight the advantages and limitations of the techniques, as are more recent developments. Some properties and applicability of organic-inorganic colloids in catalysis, medicine, and coating technologies are also cited.

Colloids↗

Synthesis and characterization of nanostructural hydrogel and template for CdS nanofibers.

Hydrogels based on beta-D-glucopyranoside-substituent thiosemicarbazide derivatives were synthesized and used as template to fabricate netlike CdS nanofibers. The self-assembling properties of the hydrogels and their effect on the synthesis of CdS nanostructure were studied. Fourier transform infrared spectra, UV-visible absorption spectra and X-ray diffraction revealed that pi-pi stacking, hydrogen bonds and interdigitated interactions between hydrophobic chains had influence on the formation of self-assembled lamellar hydrogel. Transmission electron microscopic and electron diffraction observation showed the formation of hexagonal stacking nanofiber-based CdS semiconductor materials. The transmission electron microscopic pictures of the CdS nanostructure in difference growth stages revealed the growth mechanism of CdS nanofibers templated by hydrogel.

Cadmium Compounds↗

Nanostructured biofilms and biocrystals.

The design, the physical properties and the implementation of nanostructured protein biofilms and nanostructured biocrystals are here summarized from ab initio considerations. Particular emphasis is placed on those being developed in our Institute having unique properties useful in a wide range of applications.

Animals↗

Iridescent plumage in satin bowerbirds: structure, mechanisms and nanostructural predictors of individual variation in colour.

Iridescence is produced by coherent scattering of light waves from alternating layers of materials of different refractive indices. In birds, iridescent colours are produced by feather barbules when light is scattered from alternating layers of keratin, melanin and air. The structure and organization of these layers, and hence the appearance of bird species with different types of plumage iridescence, varies extensively. One principal distinction between different types of iridescent colours is whether they are produced by a single pair of layers or by multiple pairs of layers. Multi-layer iridescence, such as that displayed by hummingbirds, has been relatively well characterized, but single-layer iridescence has only recently been modeled successfully. Here we use electron microscopy, spectrometry and thin-film optical modeling to investigate the glossy, ultraviolet-blue iridescent plumage colouration of adult male satin bowerbirds Ptilonorhynchus violaceus minor. The flattened barbules of adult males are composed of a superficial keratin layer overlying a melanin layer that is several granules thick. A thin-film model based on the thickness of the keratin layer and its two associated interfaces (air/keratin and keratin/melanin) generates predicted reflectance spectra that closely match measured spectra. In addition, hues predicted from this model are positively correlated with measured hues. As predicted from our thin-film model, measured hues shifted to shorter wavelengths at increasing angles of incidence and reflectance. Moreover, we found that individual variation in barbule nanostructure can predict measured variation in both hue and UV-chroma. Thus, we have characterized the microstructure of satin bowerbird barbules, uncovered the mechanisms responsible for producing ultraviolet iridescence in these barbules, and provided the first evidence of a nanostructural basis for individual variation in iridescent plumage colour.

Animals↗

Towards the standard-module approach to disulfide-linked polypeptide nanostructures. I. Methodological prerequisites and mass spectrometric characterization of the test two-loop structure.

Potentially biologically-active nanostructures can be created from single chains of unmodified peptides by cross-linking different regions of the chain by disulfide bonds and cleaving the chain at specified sites to obtain the final configuration. The availability of techniques for assembly and characterization of such structures was tested on a two-loop structure created from a 21-residue linear peptide. Directed intra-molecular disulfide bond formation was performed by inserting partial sequences favoring intra-molecular SS bond formation ("loops") separated by partial sequences disfavoring such a process ("spacers") into the precursor sequence. Peptide bond cleavage by partial acid hydrolysis at specific sites (GG, NP/DP) inside the loops opened them; the same process in the spacer separated the loops. Synthesis, oxidation and bond cleavage were monitored by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI ToF MS). The hydrolysis fragments of the produced nanostructures were characterized by tandem electrospray ionization Fourier transform mass spectrometry (ESI FT-MS) with collisional and electron capture dissociations. The latter technique was especially useful as it cleaves SS bonds preferentially. The feasibility of the proposed synthesis approach and the adequacy of the analysis techniques for the test structure were demonstrated.

Amino Acid Sequence↗

Analysis of nanostructured porous films by measurement of adsorption isotherms with optical fiber and ellipsometry.

An optical method to determine the nanostructure and the morphology of porous thin films is presented. This procedure is based on the response of a side-polished optical fiber with the film under study, when an adsorption-desorption cycle is carried out. Spectroscopic ellipsometry provides additional information about the optical properties and adsorption behavior of the film. Pore size distribution, anisotropy, and inhomogeneity of films can be determined by use of these two complementary techniques. To check the performances and suitability of the optical method, we have characterized a typical porous material: a TiO2 film deposited by evaporation. Water vapor has been used for the adsorption cycles. The well-known columnar structure of the evaporated TiO2 has been evidenced, and the relation between the nanostructure and the optical properties of the film is showed.

Journal Article↗

Enhanced nonlinear optical conversion from a periodically nanostructured metal film.

We demonstrate an approximately10(4) increase in conversion efficiency for optical second-harmonic generation (SHG) from a periodically nanostructured metal structure consisting of a single subwavelength aperture in a thin silver film surrounded by a set of concentric surface grooves. The forward-transmitted second-harmonic radiation from this structure is measured relative to that from an identical aperture with no surrounding surface periodicity. We explain the observed SHG enhancement quantitatively in terms of a measured 120x increase in the strength of the fundamental radiation in the vicinity of the aperture resulting from the periodic nanostructuring.

Journal Article↗

Sub-100 nm photolithography using TE-polarized waves in transparent nanostructures.

The optical near field and its polarization anisotropy in transparent nanostructures were studied by polarization near-field optical microscopy. From experimental results and finite-difference time-domain calculations, we conclude that localized optical near fields exist at topographically higher regions of nanostructures under the TE-polarization condition. Optical near fields with a feature size smaller than 100 nm are applied for contact photomask lithography. We demonstrate photolithographic patterns with 80 nm width by using a 442 nm helium cadmium laser.

Journal Article↗

[DNA complexes, formed on aqueous phase surfaces: new planar polymeric and composite nanostructures].

The formation of DNA complexes with Langmuir monolayers of the cationic lipid octadecylamine (ODA) and the new amphiphilic polycation poly-4-vinylpyridine with 16% of cetylpyridinium groups (PVP-16) on the surface of an aqueous solution of native DNA of low ionic strength was studied. Topographic images of Langmuir-Blodgett films of DNA/ODA and DNA/PVP-16 complexes applied to micaceous substrates were investigated by the method of atomic force microscopy. It was found that films of the amphiphilic polycation have an ordered planar polycrystalline structure. The morphology of planar DNA complexes with the amphiphilic cation substantially depended on the incubation time and the phase state of the monolayer on the surface of the aqueous DNA solution. Complex structures and individual DNA molecules were observed on the surface of the amphiphilic monolayer. Along with quasi-linear individual bound DNA molecules, characteristic extended net-like structures and quasi-circular toroidal condensed conformations of planar DNA complexes were detected. Mono- and multilayer films of DNA/PVP-16 complexes were used as templates and nanoreactors for the synthesis of inorganic nanostructures via the binding of metal cations from the solution and subsequent generation of the inorganic phase. As a result, ultrathin polymeric composite films with integrated DNA building blocks and quasi-linear arrays of inorganic semiconductor (CdS) and iron oxide nanoparticles and nanowires were obtained. The nanostructures obtained were characterized by scanning probe microscopy and transmission electron microscopy techniques. The methods developed are promising for investigating the mechanisms of structural organization and transformation in DNA and polyelectrolyte complexes at the gas-liquid interface and for the design of new extremely thin highly ordered planar polymeric and composite materials, films, and coatings with controlled ultrastructure for applications in nanoelectronics and nanobiotechnology.

DNA↗

[Fluorescence spectra characters of nanostructured gold thin-film].

Gold colloid was prepared via electrochemical method. Nanostructured gold thin-films were deposited on glass by using self-assembled technique. UV-visible spectra and fluorescence emission spectra were measured at room temperature. The absorption spectrum features show two peaks and the longer wavelength one at 610 nm corresponds to linear aggregated gold nanochains. The fluorescence emission peaks at about 375 nm and 700 nm are due to the local field enhancement via coupling to the transverse and longitudinal surface plasmon resonance from gold nanochains. Both the intensity and number of the fluorescence emission peaks increase with increasing excited light and the layers number. It is indicated that the nanostructured gold thin-films formed a disordered particles system. Further more, multiple scattering takes place in these self-organized random micro-cavities.

English Abstract↗

[9-nitrocamptothecin nanostructured lipid carrier system: in vitro releasing characteristics, uptake by cells, and tissue distribution in vivo].

AIM: To study the release and cell uptake characteristics of 9-nitrocamptothecin (9-NC) nanostructured lipid carrier system (NLC) in vitro and its tissue distribution characteristics in vivo. METHODS: Mouse peritoneal macrophages were used to investigate the uptake of nanoparticles by cells in vitro. The tissue distribution of 9-nitrocamptothecin solution and stealth nanostructured lipid carrier system (S-NLC) was determined after intravenous administration to mice at a single dose of 1.5 mg kg(-1). The release and crystalloid characteristics were also investigated. RESULTS: X-ray diffraction spectrum showed that 9-NC probably was amorphous in S-NLC. The liquid lipid did not change the characteristics of the solid matrix in nanoparticles. The in vitro release and cell uptake characteristics of stealth and non-stealth 9-NC-NLC were investigated, separately. The results showed that the stealth 9-NC-NLC had sustained-release characteristics and could resist the absorption effect of the additional plasmas to a certain extent. In addition, the cell uptake percentage of stealth 9-NC-NLC was much lower than that of the non-stealth ones. The tissues distribution results showed that 9-NC in the S-NLC was mainly found in the lung, liver, pancreas and ovary/uterus, while the quantity of 9-NC was much lower in heart and kidney. The AUQ(0-t), of S-NLC in blood, ovary/uterus, pancreas, liver and lung were higher than that of 9-nitrocamptothecin solution. The weight-average drug targeting efficiency (Te*) of S-NLC in liver and lung were significantly higher than that of 9-nitrocamptothecin solution. The mean residence times (MRT) of S-NLC was 44 h, while that of 9-nitrocamptothecin solution was 8 h. Therefore, S-NLC showed obvious targeting effects on liver and lung. CONCLUSION: S-NLC with PEG flexible chains has sustained-release characteristics and can prolong its circulation in blood and have good targeting efficiency on liver and lung.

Animals↗

Flaw tolerant bulk and surface nanostructures of biological systems.

Bone-like biological materials have achieved superior mechanical properties through hierarchical composite structures of mineral and protein. Gecko and many insects have evolved hierarchical surface structures to achieve extraordinary adhesion capabilities. We show that the nanometer scale plays a key role in allowing these biological systems to achieve their superior properties. We suggest that the principle of flaw tolerance may have had an overarching influence on the evolution of the bulk nanostructure of bone-like materials and the surface nanostructure of gecko-like animal species. We demonstrate that the nanoscale sizes allow the mineral nanoparticles in bone to achieve optimum fracture strength and the spatula nanoprotrusions in Gecko to achieve optimum adhesion strength. In both systems, strength optimization is achieved by restricting the characteristic dimension of the basic structure components to nanometer scale so that crack-like flaws do not propagate to break the desired structural link. Continuum modeling and atomistic simulations have been conducted to verify the concept of flaw tolerance at nanoscale. A simple tension-shear chain model has been developed to model the stiffness and fracture energy of biocomposites. It is found that, while the problem of low toughness of mineral crystals is alleviated by restricting the crystal size to nanoscale, the problem of low modulus of protein has been solved by adopting a large aspect ratio for the mineral platelets. The fracture energy of biocomposites is found to be proportional to the effective shear strain and the effective shear stress in protein along its path of deformation to fracture. The bioengineered mineral-protein composites are ideally suited for fracture energy dissipation as the winding paths of protein domain unfolding and slipping along protein-mineral interfaces lead to very large effective strain before fracture. The usual entropic elasticity of biopolymers may involve relatively small effective stress and may not be able to ensure simultaneous domain unfolding and interface slipping. Cross-linking mechanisms such as Ca++ induced sacrificial bonds in bone can increase the shear stress in protein and along the protein-mineral interface, effectively converting the behavior of entropic elasticity to one that resembles metal plasticity. The sacrificial bond mechanism not only builds up a large effective stress in protein but also allows protein deformation and interface slipping to occur simultaneously under similar stress levels, making it possible to engineer a very long range of deformation under significant stress in order to maximize energy absorption. Optimization of mineral platelets near theoretical strength is found to be crucial for allowing a large effective stress to be built up in protein via cross-linking mechanisms such as Ca++ induced sacrificial bonds. Similarly, for gecko adhesion, the strength optimization of individual spatulas is found to play a critical role in enhancing adhesion energy at the higher hierarchical level.

Biocompatible Materials↗

Ionic liquids for the convenient synthesis of functional nanoparticles and other inorganic nanostructures.

Ionic liquids are a new class of organic solvents with high polarity and a preorganized solvent structure. Very polar reactions can be carried out in these liquid in the absence of or with a controlled amount of water, and crystalline nanoparticles can be synthesized conveniently at ambient temperatures. The pronounced self-organization of the solvent is used in the synthesis of self-assembled, highly organized hybrid nanostructures with unparalleled quality. The extraordinary potential of ionic liquids in materials synthesis is described in this minireview and a physicochemical explanation is given.

Metals, Heavy↗

A study of the influence of polysaccharides on collagen self-assembly: nanostructure and kinetics.

Collagen, a critical part of the extra-cellular matrix of tissues, is a popular native material for building scaffolding for tissue-engineering applications. To mimic the structural and functional profiles of materials found in the native extra-cellular matrix, numerous efforts have been made toward developing a novel scaffold combining collagen with other biomacromolecules. All of these works have been focused on improving the mechanical or biochemical properties of the collagen-based matrix. Unfortunately, most of these studies have failed to consider the nanostructure of collagen in the complex matrix. The aim of our study was to investigate the aggregation pattern of collagen after addition of polysaccharides with positive or negative charge, the dose-response relationship, and the effect on reconstitution kinetics. Generally, collagen self-assembles into fibrils with a diameter of around 95 nm but, in the presence of various polysaccharides in varying amounts, collagen self-assembles into different shapes with larger diameters compared with collagen alone. Although the morphology and diameter of the collagen fibrils varies with reconstitution conditions, the D-periods of the fibrils all remained the same regardless of the species or concentration of polysaccharides. The kinetics of fibril formation was determined from turbidity-time curves. All turbidity curves demonstrated that polysaccharides only alter the lag time and time frame of reconstitution, but have no significant effect on the mechanism of reconstitution. Together our data indicate that the presence of biomacromolecules can alter the kinetics and the 3D fibril ultrastructure of assembled collagen and that the consequent structural changes may affect cellular responses in medical applications.

Alginates↗

Shape-controlled synthesis of metal nanostructures: the case of silver.

The concept of shape-controlled synthesis is discussed by investigating the growth mechanisms for silver nanocubes, nanowires, and nanospheres produced through a polymer-mediated polyol process. Experimental parameters, such as the concentration of AgNO(3) (the precursor to silver), the molar ratio between poly(vinylpyrrolidone) (PVP, the capping agent) and AgNO(3), and the strength of chemical interaction between PVP and various crystallographic planes of silver, were found to determine the crystallinity of seeds (e.g., single crystal versus decahedral multiply twinned particles). In turn, the crystallinity of a seed and the extent of the PVP coverage on the seed were both instrumental in controlling the morphology of final product. The ability to generate silver nanostructures with well-defined morphologies provides a great opportunity to experimentally and systematically study the relationship between their properties and geometric shapes.

Citrates↗

The molecular basis of self-assembly of dendron-rod-coils into one-dimensional nanostructures.

We describe here a comprehensive study of solution and solid-state properties of self-assembling triblock molecules composed of a hydrophilic dendron covalently linked to an aromatic rigid rod segment, which is in turn connected to a hydrophobic flexible coil. These dendron-rod-coil (DRC) molecules form well-defined supramolecular structures that possess a ribbonlike morphology as revealed by transmission-electron and atomic-force microscopy. In a large variety of aprotic solvents, the DRC ribbons create stable networks that form gels at concentrations as low as 0.2% by weight DRC. The gels are thermally irreversible and do not melt at elevated temperatures, indicating high stability as a result of strong noncovalent interactions among DRC molecules. NMR experiments show that the strong interactions leading to aggregation involve mainly the dendron and rodlike blocks, whereas oligoisoprene coil segments remain solvated after gelation. Small-angle X-ray scattering (SAXS) profiles of different DRC molecules demonstrate an excellent correlation between the degree-of-order in the solid-state and the stability of gels. Studies on two series of analogous molecules suggest that self-assembly is very sensitive to subtle structural changes and requires the presence of at least four hydroxyl groups in the dendron, two biphenyl units in the rod, and a coil segment with a size comparable to that of the rodlike block. A detailed analysis of crystal structures of model compounds revealed the formation of stable one-dimensional structures that involve two types of noncovalent interactions, aromatic pi-pi stacking and hydrogen bonding. Most importantly, the crystal structure of the rod-dendron compound shows that hydrogen bonding not only drives the formation of head-to-head cyclic structures, but also generates multiple linkages between them along the stacking direction. The cyclic structures are tetrameric in nature and stack into ribbonlike objects. We believe that DRC molecules utilize the same arrangement of hydrogen bonds and stacking of aromatic blocks observed in the crystals, explaining the exceptional stability of the nanostructures in extremely dilute solutions as well the thermal stability of the gels they form. This study provides mechanistic insights on self-assembly of triblock molecules, and unveils general strategies to create well-defined one-dimensional supramolecular objects.

Anthracenes↗

Exceptional affinity of nanostructured organic-inorganic hybrid materials towards dioxygen: confinement effect of copper complexes.

We report the exceptional reactivity towards dioxygen of a nanostructured organic-inorganic hybrid material due to the confinement of copper cyclam within a silica matrix. The key step is the metalation reaction of the ligand, which can occur before or after xerogel formation through the sol-gel process. The incorporation of a Cu(II) center into the material after xerogel formation leads to a bridged Cu(I)/Cu(II) mixed-valence dinuclear species. This complex exhibits a very high affinity towards dioxygen, attributable to auto-organization of the active species in the solid. The remarkable properties of these copper complexes in the silica matrix demonstrate a high cooperative effect for O(2) adsorption; this is induced by close confinement of the two copper ions leading to end-on mu-eta(1):eta(1)-peroxodicopper(II) complexes. The anisotropic packing of the tetraazamacrocycle in a lamellar structure induces an exceptional reactivity of these copper complexes. We show for the first time that the organic-inorganic environment of copper complexes in a silica matrix fully model the protecting role of protein in metalloenzymes. For the first time an oxygenated dicopper(II) complex can be isolated in a stable form at room temperature, and the reduced Cu(2) (I,I) species can be regenerated after several adsorption-desorption cycles. These data also demonstrate that the coordination scheme and reactivity of the copper cyclams within the solid are quite different from that observed in solution.

Adsorption↗