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1

Self-Assembly Strategies for Integrating Light Harvesting and Charge Separation in Artificial Photosynthetic Systems  

SciTech Connect

In natural photosynthesis, organisms optimize solar energy conversion through organized assemblies of photofunctional chromophores and catalysts within proteins that provide specifically tailored environments for chemical reactions. As with their natural counterparts, artificial photosynthetic systems for practical solar fuels production must collect light energy, separate charge, and transport charge to catalytic sites where multielectron redox processes will occur. While encouraging progress has been made on each aspect of this complex problem, researchers have not yet developed self-ordering and self-assembling components and the tailored environments necessary to realize a fully-functional artificial system. Previously researchers have used complex, covalent molecular systems comprised of chromophores, electron donors, and electron acceptors to mimic both the light-harvesting and the charge separation functions of photosynthetic proteins. These systems allow for study of the dependencies of electron transfer rate constants on donor?acceptor distance and orientation, electronic interaction, and the free energy of the reaction. The most useful and informative systems are those in which structural constraints control both the distance and the orientation between the electron donors and acceptors. Self-assembly provides a facile means for organizing large numbers of molecules into supramolecular structures that can bridge length scales from nanometers to macroscopic dimensions. The resulting structures must provide pathways for migration of light excitation energy among antenna chromophores, and from antennas to reaction centers. They also must incorporate charge conduits, that is, molecular 'wires' that can efficiently move electrons and holes between reaction centers and catalytic sites. The central scientific challenge is to develop small, functional building blocks with a minimum number of covalent linkages, which also have the appropriate molecular recognition properties to facilitate self-assembly of complete, functional artificial photosynthetic systems. In this Account, we explore how self-assembly strategies involving ?-stacking can be used to integrate light harvesting with charge separation and transport.

Wasielewski, Michael R. (NWU)

2011-09-28

2

Zinc chlorins for artificial light-harvesting self-assemble into antiparallel stacks forming a microcrystalline solid-state material  

PubMed Central

We introduce a concept to solve the structure of a microcrystalline material in the solid-state at natural abundance without access to distance constraints, using magic angle spinning (MAS) NMR spectroscopy in conjunction with X-ray powder diffraction and DFT calculations. The method is applied to a novel class of materials that form (semi)conductive 1D wires for supramolecular electronics and artificial light-harvesting. The zinc chlorins 3-devinyl-31-hydroxymethyl-132-demethoxycarbonylpheophorbide a (3?,5?-bis-dodecyloxy)benzyl ester zinc complex 1 and 3-devinyl-31-methoxymethyl-132-demethoxycarbonylpheophorbide a (3?,5?-bis-dodecyloxy)benzyl ester zinc complex 2, self-assemble into extended excitonically coupled chromophore stacks. 1H-13C heteronuclear dipolar correlation MAS NMR experiments provided the 1H resonance assignment of the chlorin rings that allowed accurate probing of ring currents related to the stacking of macrocycles. DFT ring-current shift calculations revealed that both chlorins self-assemble in antiparallel ?-stacks in planar layers in the solid-state. Concomitantly, X-ray powder diffraction measurements for chlorin 2 at 80 °C revealed a 3D lattice for the mesoscale packing that matches molecular mechanics optimized aggregate models. For chlorin 2 the stacks alternate with a periodicity of 0.68 nm and a 3D unit cell with an approximate volume of 6.28 nm3 containing 4 molecules, which is consistent with space group P21221.

Ganapathy, Swapna; Sengupta, Sanchita; Wawrzyniak, Piotr K.; Huber, Valerie; Buda, Francesco; Baumeister, Ute; Wurthner, Frank; de Groot, Huub J. M.

2009-01-01

3

Self-assembled photosynthesis-inspired light harvesting material and solar cells containing the same  

DOEpatents

A solar cell is described that comprises: (a) a semiconductor charge separation material; (b) at least one electrode connected to the charge separation material; and (c) a light-harvesting film on the charge separation material, the light-harvesting film comprising non-covalently coupled, self-assembled units of porphyrinic macrocycles. The porphyrinic macrocycles preferably comprise: (i) an intramolecularly coordinated metal; (ii) a first coordinating substituent; and (iii) a second coordinating substituent opposite the first coordinating substituent. The porphyrinic macrocycles can be assembled by repeating intermolecular coordination complexes of the metal, the first coordinating substituent and the second coordinating substituent.

Lindsey, Jonathan S. (Raleigh, NC); Chinnasamy, Muthiah (Raleigh, NC); Fan, Dazhong (Raleigh, NC)

2009-12-15

4

A nanoscale bio-inspired light-harvesting system developed from self-assembled alkyl-functionalized metallochlorin nano-aggregates.  

PubMed

Self-assembled supramolecular organization of nano-structured biomimetic light-harvesting modules inside solid-state nano-templates can be exploited to develop excellent light-harvesting materials for artificial photosynthetic devices. We present here a hybrid light-harvesting system mimicking the chlorosomal structures of the natural photosynthetic system using synthetic zinc chlorin units (ZnChl-C6, ZnChl-C12 and ZnChl-C18) that are self-aggregated inside the anodic aluminum oxide (AAO) nano-channel membranes. AAO nano-templates were modified with a TiO2 matrix and functionalized with long hydrophobic chains to facilitate the formation of supramolecular Zn-chlorin aggregates. The transparent Zn-chlorin nano-aggregates inside the alkyl-TiO2 modified AAO nano-channels have a diameter of ?120 nm in a 60 ?m length channel. UV-Vis studies and fluorescence emission spectra further confirm the formation of the supramolecular ZnChl aggregates from monomer molecules inside the alkyl-functionalized nano-channels. Our results prove that the novel and unique method can be used to produce efficient and stable light-harvesting assemblies for effective solar energy capture through transparent and stable nano-channel ceramic materials modified with bio-mimetic molecular self-assembled nano-aggregates. PMID:24909123

Ocakoglu, Kasim; Joya, Khurram S; Harputlu, Ersan; Tarnowska, Anna; Gryko, Daniel T

2014-07-24

5

Self-assembled artificial cilia  

PubMed Central

Due to their small dimensions, microfluidic devices operate in the low Reynolds number regime. In this case, the hydrodynamics is governed by the viscosity rather than inertia and special elements have to be introduced into the system for mixing and pumping of fluids. Here we report on the realization of an effective pumping device that mimics a ciliated surface and imitates its motion to generate fluid flow. The artificial biomimetic cilia are constructed as long chains of spherical superparamagnetic particles, which self-assemble in an external magnetic field. Magnetic field is also used to actuate the cilia in a simple nonreciprocal manner, resulting in a fluid flow. We prove the concept by measuring the velocity of a cilia-pumped fluid as a function of height above the ciliated surface and investigate the influence of the beating asymmetry on the pumping performance. A numerical simulation was carried out that successfully reproduced the experimentally obtained data.

Vilfan, Mojca; Potocnik, Anton; Kavcic, Blaz; Osterman, Natan; Poberaj, Igor; Vilfan, Andrej; Babic, Dusan

2010-01-01

6

Artificial photosynthetic reaction centers coupled to light-harvesting antennas  

NASA Astrophysics Data System (ADS)

We analyze a theoretical model for energy and electron transfer in an artificial photosynthetic system. The photosystem consists of a molecular triad (i.e., with a donor, a photosensitive unit, and an acceptor) coupled to four accessory light-harvesting-antenna pigments. The resonant energy transfer from the antennas to the artificial reaction center (the molecular triad) is described here by the Förster mechanism. We consider two different kinds of arrangements of the accessory light-harvesting pigments around the reaction center. The first arrangement allows direct excitation transfer to the reaction center from all the surrounding pigments. The second configuration transmits energy via a cascade mechanism along a chain of light-harvesting chromophores, where only one chromophore is connected to the reaction center. We show that the artificial photosynthetic system using the cascade energy transfer absorbs photons in a broader wavelength range and converts their energy into electricity with a higher efficiency than the system based on direct couplings between all the antenna chromophores and the reaction center.

Ghosh, Pulak Kumar; Smirnov, Anatoly Yu.; Nori, Franco

2011-12-01

7

Artificial leaf structures as a UV detector formed by the self-assembly of ZnO nanoparticles.  

PubMed

Artificial leaf structures have been fabricated by the self-assembly of ZnO nanoparticles. A hydrothermal method was used to synthesize the nanoparticles. The self-assembly patterns showed asymmetric dendritic morphologies, larger surface-to-volume ratios, a broad absorption band and high resistance. A non-equilibrium two-stage-formation process included diffusion limited aggregation, and the phase-field model was introduced to explain the formation mechanism of the pattern. A high-performance ultraviolet detector was fabricated on the artificial leaf structures, which showed that the current under the irradiation of a UV lamp (1.21 mW cm(-2)) was about 10(4) times greater than in the dark. The various and functional properties of the pattern show us the vast prospects of potential applications for light harvesting systems and other optical-electric devices. PMID:23446434

Wang, Fei; Zhao, Dongxu; Guo, Zhen; Liu, Lei; Zhang, Zhenzhong; Shen, Dezhen

2013-04-01

8

Hybrid artificial photosynthetic systems comprising semiconductors as light harvesters and biomimetic complexes as molecular cocatalysts.  

PubMed

Solar fuel production through artificial photosynthesis may be a key to generating abundant and clean energy, thus addressing the high energy needs of the world's expanding population. As the crucial components of photosynthesis, the artificial photosynthetic system should be composed of a light harvester (e.g., semiconductor or molecular dye), a reduction cocatalyst (e.g., hydrogenase mimic, noble metal), and an oxidation cocatalyst (e.g., photosystem II mimic for oxygen evolution from water oxidation). Solar fuel production catalyzed by an artificial photosynthetic system starts from the absorption of sunlight by the light harvester, where charge separation takes place, followed by a charge transfer to the reduction and oxidation cocatalysts, where redox reaction processes occur. One of the most challenging problems is to develop an artificial photosynthetic solar fuel production system that is both highly efficient and stable. The assembly of cocatalysts on the semiconductor (light harvester) not only can facilitate the charge separation, but also can lower the activation energy or overpotential for the reactions. An efficient light harvester loaded with suitable reduction and oxidation cocatalysts is the key for high efficiency of artificial photosynthetic systems. In this Account, we describe our strategy of hybrid photocatalysts using semiconductors as light harvesters with biomimetic complexes as molecular cocatalysts to construct efficient and stable artificial photosynthetic systems. We chose semiconductor nanoparticles as light harvesters because of their broad spectral absorption and relatively robust properties compared with a natural photosynthesis system. Using biomimetic complexes as cocatalysts can significantly facilitate charge separation via fast charge transfer from the semiconductor to the molecular cocatalysts and also catalyze the chemical reactions of solar fuel production. The hybrid photocatalysts supply us with a platform to study the photocatalytic mechanisms of H2/O2 evolution and CO2 reduction at the molecular level and to bridge natural and artificial photosynthesis. We demonstrate the feasibility of the hybrid photocatalyst, biomimetic molecular cocatalysts, and semiconductor light harvester for artificial photosynthesis and therefore provide a promising approach for rational design and construction of highly efficient and stable artificial photosynthetic systems. PMID:23730891

Wen, Fuyu; Li, Can

2013-11-19

9

Out of the cleanroom, self-assembled magnetic artificial cilia.  

PubMed

Micro-sized hair-like structures, such as cilia, are abundant in nature and have various functionalities. Many efforts have been made to mimic the fluid pumping function of cilia, but most of the fabrication processes for these "artificial cilia" are tedious and expensive, hindering their practical application. In this paper a cost-effective in situ fabrication technique for artificial cilia is demonstrated. The cilia are constructed by self-assembly of micron sized magnetic beads and encapsulated with soft polymer coatings. Actuation of the cilia induces an effective fluid flow, and the cilia lengths and distribution can be adjusted by varying the magnetic bead concentration and fabrication parameters. PMID:23846423

Wang, Ye; Gao, Yang; Wyss, Hans; Anderson, Patrick; den Toonder, Jaap

2013-09-01

10

Guest-induced photophysical property switching of artificial light-harvesting dendrimers.  

PubMed

An artificial light-harvesting multiporphyrin dendrimer (8PZn PFB ) composed of a focal freebase porphyrin (PFB ) with eight zinc(II) porphyrin (PZn ) wings exhibited unique photophysical property switching in response to specific guest molecule binding. UV/Vis titration studies indicated stable 1:2 host-guest complex formation between 8PZn PFB and meso-tetrakis(4-pyridyl)-porphyrin (TPyP) for which the first and second association constants were estimated to be >10(8) ?M(-1) and 3.0×10(7) ?M(-1) , respectively. 8PZn PFB originally shows 94?% energy transfer efficiency from PZn to the focal PFB . By the formation of the host-guest complex (8PZn PFB ?2TPyP) the emission intensity of 8PZn PFB is significantly decreased, and an ultrafast charge separation state is generated. The energy transfer process from PZn wings to the PFB core in 8PZn PFB is almost entirely switched to an electron transfer process by the formation of 8PZn PFB ?2TPyP. PMID:24828751

Jeong, Young-Hwan; Son, Minjung; Yoon, Hongsik; Kim, Pyosang; Lee, Do-Hyung; Kim, Dongho; Jang, Woo-Dong

2014-07-01

11

Design and Assembly of Functional Light-Harvesting Complexes  

Microsoft Academic Search

Two complementary model systems are described, which are used to study the assembly of functional light-harvesting (LH) complexes.\\u000a One system is based on rational design of cofactor-binding motifs and their capacity to assembly model LH2 complexes via expression\\u000a in native-like membranes. The second takes advantage of the highly reversible self-assembly of the LH1 complex in artificial\\u000a membranes and provides a

Paula Braun; Leszek Fiedor

12

Self-assembled monolayers of porphyrin perylenetetracarboxylic diimide [60] fullerene on indium tin oxide electrodes: enhancement of light harvesting in the visible light region  

NASA Astrophysics Data System (ADS)

The porphyrin-perylenetetracarboxylic diimide-fullerene triad has been designed to act as an efficient light-to-current converter in molecular devices. Light absorption by the perylenetetracarboxylic diimide-porphyrin dyad occurs in complementary regions, giving extended absorption in the visible light region. This dyad of perylenetetracarboxylic diimide-porphyrin was covalently linked with C60, which can act as an electron acceptor, to construct porphyrin-perylenetetracarboxylic diimide-fullerene (FPP) self-assembled monolayers (SAMs) on the indium tin oxide (ITO) surface. The relative strong photocurrent generation of the ITO/FPP/ methyl viologen (MV2+)/Pt system in the continuous visible light region (from 400 to 650 nm) indicated that this system is highly promising as regards light-energy conversion.

Li, Yongjun; Li, Yuliang; Liu, Huibiao; Wang, Shu; Wang, Ning; Zhuang, Junpeng; Li, Xiaofang; He, Xiaorong; Zhu, Daoben

2005-09-01

13

Artificial light-harvesting arrays: electronic energy migration and trapping on a sphere and between spheres.  

PubMed

A sophisticated model of the natural light-harvesting antenna has been devised by decorating a C(60) hexa-adduct with ten yellow and two blue boron dipyrromethene (Bodipy) dyes in such a way that the dyes retain their individuality and assist solubility of the fullerene. Unusually, the fullerene core is a poor electron acceptor and does not enter into light-induced electron-transfer reactions with the appended dyes, but ineffective electronic energy transfer from the excited-state dye to the C(60) residue competes with fluorescence from the yellow dye. Intraparticle electronic energy transfer from yellow to blue dyes can be followed by steady-state and time-resolved fluorescence spectroscopy and by excitation spectra for isolated C(60) nanoparticles dissolved in dioxane at 293 K and at 77 K. The decorated particles can be loaded into polymer films by spin coating from solution. In the dried film, efficient energy transfer occurs such that photons absorbed by the yellow dye are emitted by the blue dye. Films can also be prepared to contain C(60) nanoparticles loaded with the yellow Bodipy dye but lacking the blue dye and, under these circumstances, electronic energy migration occurs between yellow dyes appended to the same nanoparticle and, at higher loading, to dye molecules on nearby particles. Doping these latter polymer films with the mixed-dye nanoparticle coalesces these multifarious processes in a single system. Thus, long-range energy migration occurs among yellow dyes attached to different particles before trapping at a blue dye. In this respect, the film resembles the natural photosynthetic light-harvesting complexes, albeit at much reduced efficacy. The decorated nanoparticles sensitize amorphous silicon photocells. PMID:22148681

Iehl, Julien; Nierengarten, Jean-François; Harriman, Anthony; Bura, Thomas; Ziessel, Raymond

2012-01-18

14

Quantum coherence controls the charge separation in a prototypical artificial light-harvesting system  

PubMed Central

The efficient conversion of light into electricity or chemical fuels is a fundamental challenge. In artificial photosynthetic and photovoltaic devices, this conversion is generally thought to happen on ultrafast, femto-to-picosecond timescales and to involve an incoherent electron transfer process. In some biological systems, however, there is growing evidence that the coherent motion of electronic wavepackets is an essential primary step, raising questions about the role of quantum coherence in artificial devices. Here we investigate the primary charge-transfer process in a supramolecular triad, a prototypical artificial reaction centre. Combining high time-resolution femtosecond spectroscopy and time-dependent density functional theory, we provide compelling evidence that the driving mechanism of the photoinduced current generation cycle is a correlated wavelike motion of electrons and nuclei on a timescale of few tens of femtoseconds. We highlight the fundamental role of the interface between chromophore and charge acceptor in triggering the coherent wavelike electron-hole splitting.

Andrea Rozzi, Carlo; Maria Falke, Sarah; Spallanzani, Nicola; Rubio, Angel; Molinari, Elisa; Brida, Daniele; Maiuri, Margherita; Cerullo, Giulio; Schramm, Heiko; Christoffers, Jens; Lienau, Christoph

2013-01-01

15

Light-harvesting nanorods based on pheophorbide-appending cellulose.  

PubMed

In contrast to the success in artificial DNA- and peptide-based nanostructures, the ability of polysaccharides to self-assemble into one-, two-, and three-dimensional nanostructures are limited. Here, we describe a strategy for designing and fabricating nanorods using a regioselectively functionalized cellulose derivative at the air-water interface in a stepwise manner. A semisynthetic chlorophyll derivative, pyro-pheophorbide a, was partially introduced into the C-6 position of the cellulose backbone for the design of materials with specific optical properties. Remarkably, controlled formation of cellulose nanorods can be achieved, producing light-harvesting nanorods that display a larger bathochromic shift than their solution counterparts. The results presented here demonstrate that the self-assembly of functionalized polysaccharides on surfaces could lead the nanostructures mimicking the naturally occurring chloroplasts. PMID:23865684

Sakakibara, Keita; Granström, Mari; Kilpeläinen, Ilkka; Helaja, Juho; Heinilehto, Santtu; Inoue, Rintaro; Kanaya, Toshiji; Hill, Jonathan P; Nakatsubo, Fumiaki; Tsujii, Yoshinobu; Ariga, Katsuhiko

2013-09-01

16

Genetic exchange leading to self-assembling RNA species upon encapsulation in artificial protocells.  

PubMed

The encapsulation of information-bearing macromolecules inside protocells is a critical step in scenarios for the origins of life on the Earth as well as for the construction of artificial living systems. For these protocells to emulate life, they must be able to transmit genetic information to other cells. We have used a water-in-oil emulsion system to simulate the compartmentalization of catalytic RNA molecules. By exploiting RNA-directed recombination reactions previously developed in our laboratory, including a ribozyme self-assembly pathway, we demonstrate that it is possible for information to be exchanged among protocells. This can happen either indirectly by the passage of divalent cations through the inter-protocellular medium (oil), or by the direct interaction of two or more protocells that allows RNA molecules to be exchanged. The degree of agitation affects the ability of such exchange. The consequences of these results include the implications that prototypical living systems can transmit information among compartments, and that the environment can regulate the extent of this crosstalk. PMID:17567246

Zenisek, Sergio-Francis M; Hayden, Eric J; Lehman, Niles

2007-01-01

17

Controlled disassembling of self-assembling systems: Toward artificial molecular-level devices and machines  

PubMed Central

Investigations on self-assembling/induced-disassembling systems have led to the design of molecular-level devices capable of performing a variety of functions. Some of the work carried out in this field is illustrated.

Balzani, Vincenzo; Credi, Alberto; Venturi, Margherita

2002-01-01

18

Nanorings and rods interconnected by self-assembly mimicking an artificial network of neurons  

NASA Astrophysics Data System (ADS)

Molecular electronics based on structures ordered as neural networks emerges as the next evolutionary milestone in the construction of nanodevices with unprecedented applications. However, the straightforward formation of geometrically defined and interconnected nanostructures is crucial for the production of electronic circuitry nanoequivalents. Here we report on the molecularly fine-tuned self-assembly of tetrakis-Schiff base compounds into nanosized rings interconnected by unusually large nanorods providing a set of connections that mimic a biological network of neurons. The networks are produced through self-assembly resulting from the molecular conformation and noncovalent intermolecular interactions. These features can be easily generated on flat surfaces and in a polymeric matrix by casting from solution under ambient conditions. The structures can be used to guide the position of electron-transporting agents such as carbon nanotubes on a surface or in a polymer matrix to create electrically conducting networks that can find direct use in constructing nanoelectronic circuits.

Escárcega-Bobadilla, Martha V.; Zelada-Guillén, Gustavo A.; Pyrlin, Sergey V.; Wegrzyn, Marcin; Ramos, Marta M. D.; Giménez, Enrique; Stewart, Andrew; Maier, Gerhard; Kleij, Arjan W.

2013-11-01

19

Protein refolding assisted by self-assembled nanogels as novel artificial molecular chaperone  

Microsoft Academic Search

Molecular chaperone-like activity for protein refolding was investigated using nanogels of self-assembly of cholesterol-bearing pullulan. Nanogels effectively prevented protein aggregation (i.e. carbonic anhydrase and citrate synthase) during protein refolding from GdmCl denaturation. Enzyme activity recovered in high yields upon dissociation of the gel structure in which the proteins were trapped, by the addition of cyclodextrins. The nanogels assisted protein refolding

Yuta Nomura; Masahiro Ikeda; Nozomi Yamaguchi; Yasuhiro Aoyama; Kazunari Akiyoshi

2003-01-01

20

Natural strategies for photosynthetic light harvesting.  

PubMed

Photosynthetic organisms are crucial for life on Earth as they provide food and oxygen and are at the basis of most energy resources. They have a large variety of light-harvesting strategies that allow them to live nearly everywhere where sunlight can penetrate. They have adapted their pigmentation to the spectral composition of light in their habitat, they acclimate to slowly varying light intensities and they rapidly respond to fast changes in light quality and quantity. This is particularly important for oxygen-producing organisms because an overdose of light in combination with oxygen can be lethal. Rapid progress is being made in understanding how different organisms maximize light harvesting and minimize deleterious effects. Here we summarize the latest findings and explain the main design principles used in nature. The available knowledge can be used for optimizing light harvesting in both natural and artificial photosynthesis to improve light-driven production processes. PMID:24937067

Croce, Roberta; van Amerongen, Herbert

2014-06-17

21

Self-Assembly Game  

NSDL National Science Digital Library

This is a quick game about self-assembly. Like the molecules of DNA, learners will self-assemble into a pattern by following a simple set of rules. The icebreaker game is part of a larger self-assembly lesson plan, and additional self-assembly game ideas and a video can be found in the related links.

Twin Cities Public Television, Inc.

2008-01-01

22

Self-Assembly  

NSDL National Science Digital Library

Self-assembly is the process of matter organizing autonomously and without human intervention (Whitesides, Mathias, and Seto 1991; Withesides and Boncheva 2002). The process of self-assembly can be introduced in a range of contexts in the natural and appl

Krajcik, Joseph S.; Sutherland, Leeann M.; Stevens, Shawn Y.

2009-10-14

23

Self-assembled monolayers of A? peptides on Au electrodes: an artificial platform for probing the reactivity of redox active metals and cofactors relevant to Alzheimer's disease.  

PubMed

The water-soluble hydrophilic part of human A? peptide has been extended to include a C-terminal cysteine residue. Utilizing the thiol functionality of this cysteine residue, self-assembled monolayers (SAM) of these peptides are formed on Au electrodes. Atomic force microscopy imaging confirms formation of small A? aggregates on the surface of the electrode. These aggregates bind redox active metals like Cu and cofactors like heme, both of which are proposed to generate toxic partially reduced oxygen species (PROS) and play a vital role in Alzheimer's disease. The spectroscopic and electrochemical properties of these Cu and heme bound A? SAM are similar to those reported for the soluble Cu and heme bound A? peptide. Experiments performed on these A?-SAM electrodes clearly demonstrate that (1) heme bound A? is kinetically more competent in reducing O(2) than Cu bound A?, (2) under physiological conditions the reduced Cu site produces twice as much PROS (measured in situ) than the reduced heme site, and (3) chelators like clioquinol remove Cu from these aggregates, while drugs like methylene blue inhibit O(2) reactivity of the heme cofactor. This artificial construct provides a very easy platform for investigating potential drugs affecting aggregation of human A? peptides and PROS generation by its complexes with redox active metals and cofactors. PMID:22709431

Pramanik, Debajyoti; Sengupta, Kushal; Mukherjee, Soumya; Dey, Somdatta Ghosh; Dey, Abhishek

2012-07-25

24

Quantum mechanical modeling of self-assembly and photoinduced electron transfer in PNA-based artificial living organisms.  

PubMed

In order to support the creation of both artificial living organisms in the USA LANL "Protocell Assembly" project and programmable nano-biorobots in the EU "Programmable Artificial Cell Evolution" project, we used quantum mechanical (QM), density functional theory (DFT), the semiempirical PM3 method, and molecular mechanics (MM) software to investigate various complex photosynthetic systems based on peptide nucleic acid (PNA) in a water environment. Quantum mechanical DFT PBEPBE simulations, including electron correlations, confirm that water molecules that surround all the photosynthetic complex of the LANL protoorganism are main constructing factors and stabilize this system consisting of: PNA fragment attached by covalent bond sensitizer 1,4-bis(N,N-dimethylamino)naphthalene molecule, lipid precursor molecule and fragment of lipid molecules mono layer. The absorption spectrum shift to the red wavelengths in the complex artificial protocell photosynthetic center might be used as the measure of the complexity of this system. The electron pi-pi* transitions in the first and third excited states are from HOMO and HOMO-1 located on the conjugated water molecules and sensitizer 1,4-bis(N,N-dimethylamino)naphthalene molecule to the LUMO of the lipid precursor molecule as calculated using the time dependent (TD) PBEPBE/6-31G model. Electron charge tunneling in the first and third excited states should induce metabolic photodissociation of the lipid precursor molecule because of localization of the transferred electron cloud on the head (waste) of the lipid precursor molecule. TD electron correlation PBEPBE/6-31G calculations show that in the different energies of excitation, the charge transfer tunneling is from sensitizer to lipid precursor and cytosine molecules. One should note that in a water solvent, the electron charge transfer pi-pi* transition in the fifth and sixth excited state is from the HOMO and HOMO-1 located on the sensitizer 1,4-bis(N,N-dimethylamino)naphthalene molecule to the LUMO+2 located on the cytosine-PNA fragment molecule. Investigation results indicate that strong back electron tunneling from the sensitizer 1,4-bis(N,N-dimethylamino)naphthalene molecule to the cytosine molecule in the LANL artificial photosynthetic system exists. PMID:16736752

Tamulis, A; Tamulis, V; Graja, A

2006-04-01

25

Toward a molecular programming language for algorithmic self-assembly  

Microsoft Academic Search

Self-assembly is the process whereby relatively simple components autonomously combine to form more complex objects. Nature exhibits self-assembly to form everything from microscopic crystals to living cells to galaxies. With a desire to both form increasingly sophisticated products and to understand the basic components of living systems, scientists have developed and studied artificial self-assembling systems. One such framework is the

Matthew John Patitz

2010-01-01

26

Self-assembling RNA square  

SciTech Connect

The three-dimensional structures of noncoding RNA molecules reveal recurring architectural motifs that have been exploited for the design of artificial RNA nanomaterials. Programmed assembly of RNA nanoobjects from autonomously folding tetraloop-receptor complexes as well as junction motifs has been achieved previously through sequence-directed hybridization of complex sets of long oligonucleotides. Due to size and complexity, structural characterization of artificial RNA nanoobjects has been limited to low-resolution microscopy studies. Here we present the design, construction, and crystal structure determination at 2.2 {angstrom} of the smallest yet square-shaped nanoobject made entirely of double-stranded RNA. The RNA square is comprised of 100 residues and self-assembles from four copies each of two oligonucleotides of 10 and 15 bases length. Despite the high symmetry on the level of secondary structure, the three-dimensional architecture of the square is asymmetric, with all four corners adopting distinct folding patterns. We demonstrate the programmed self-assembly of RNA squares from complex mixtures of corner units and establish a concept to exploit the RNA square as a combinatorial nanoscale platform.

Dibrov, Sergey M.; McLean, Jaime; Parsons, Jerod; Hermann, Thomas (UCSD)

2011-12-22

27

Photovoltaic self-assembly.  

SciTech Connect

This late-start LDRD was focused on the application of chemical principles of self-assembly on the ordering and placement of photovoltaic cells in a module. The drive for this chemical-based self-assembly stems from the escalating prices in the 'pick-and-place' technology currently used in the MEMS industries as the size of chips decreases. The chemical self-assembly principles are well-known on a molecular scale in other material science systems but to date had not been applied to the assembly of cells in a photovoltaic array or module. We explored several types of chemical-based self-assembly techniques, including gold-thiol interactions, liquid polymer binding, and hydrophobic-hydrophilic interactions designed to array both Si and GaAs PV chips onto a substrate. Additional research was focused on the modification of PV cells in an effort to gain control over the facial directionality of the cells in a solvent-based environment. Despite being a small footprint research project worked on for only a short time, the technical results and scientific accomplishments were significant and could prove to be enabling technology in the disruptive advancement of the microelectronic photovoltaics industry.

Lavin, Judith; Kemp, Richard Alan; Stewart, Constantine A.

2010-10-01

28

Modeling Protein Self Assembly  

ERIC Educational Resources Information Center

Understanding the structure and function of proteins is an important part of the standards-based science curriculum. Proteins serve vital roles within the cell and malfunctions in protein self assembly are implicated in degenerative diseases. Experience indicates that this topic is a difficult one for many students. We have found that the concept…

Baker, William P.; Jones, Carleton Buck; Hull, Elizabeth

2004-01-01

29

Self-assembled plasmonic nanostructures.  

PubMed

Self-assembly of plasmonic nanoparticles offers a labour- and cost-efficient strategy for the expansion of the library of plasmonic nanostructures with highly tunable, coupled optical properties. This review covers recent advances in solution-based self-assembly of plasmonic nanoparticles, modelling of the self-assembly process and of the optical properties of the resulting nanostructures, and potential applications of self-assembled plasmonic nanostructures. PMID:24599020

Klinkova, Anna; Choueiri, Rachelle M; Kumacheva, Eugenia

2014-06-01

30

Self Assembly of Colloids  

NASA Astrophysics Data System (ADS)

We are exploring the self assembly of colloidal matter using building blocks with complex shapes and functionalities. Our toolbox includes particles with tunable cavities and protrusions, particles with flexible ball-and-socket joints, colloidal cubes and particles with magnetic patches. Using these building blocks and a variety of interactions, including chemical, steric, magnetic and lock-and-key shape recognition, we aim to develop new assembly schemes to build structures with a reconfigurable structural arrangement.

Sacanna, Stefano

2012-02-01

31

Binary ionic porphyrin nanosheets: electronic and light-harvesting properties regulated by crystal structure  

NASA Astrophysics Data System (ADS)

Crystalline solids self-assembled from anionic and cationic porphyrins provide a new class of multifunctional optoelectronic micro- and nanomaterials. A 1 : 1 combination of zinc(ii) tetra(4-sulfonatophenyl)porphyrin (ZnTPPS) and tin(iv) tetra(N-methyl-4-pyridiniumyl)porphyrin (SnTNMePyP) gives porphyrin nanosheets with high aspect ratios and varying thickness. The room temperature preparation of the nanosheets has provided the first X-ray crystal structure of a cooperative binary ionic (CBI) solid. The unit cell contains one and one-half molecules of aquo-ZnTPPS4- (an electron donor) and three half molecules of dihydroxy-SnTNMePyP4+ (an electron acceptor). Charge balance in the solid is reached without any non-porphyrinic ions, as previously determined for other CBI nanomaterials by non-crystallographic means. The crystal structure reveals a complicated molecular arrangement with slipped ?-? stacking only occurring in isolated dimers of one of the symmetrically unique zinc porphyrins. Consistent with the crystal structure, UV-visible J-aggregate bands indicative of exciton delocalization and extended ?-? stacking are not observed. XRD measurements show that the structure of the Zn/Sn nanosheets is distinct from that of Zn/Sn four-leaf clover-like CBI solids reported previously. In contrast with the Zn/Sn clovers that do exhibit J-aggregate bands and are photoconductive, the nanosheets are not photoconductive. Even so, the nanosheets act as light-harvesting structures in an artificial photosynthesis system capable of reducing water to hydrogen but not as efficiently as the Zn/Sn clovers.Crystalline solids self-assembled from anionic and cationic porphyrins provide a new class of multifunctional optoelectronic micro- and nanomaterials. A 1 : 1 combination of zinc(ii) tetra(4-sulfonatophenyl)porphyrin (ZnTPPS) and tin(iv) tetra(N-methyl-4-pyridiniumyl)porphyrin (SnTNMePyP) gives porphyrin nanosheets with high aspect ratios and varying thickness. The room temperature preparation of the nanosheets has provided the first X-ray crystal structure of a cooperative binary ionic (CBI) solid. The unit cell contains one and one-half molecules of aquo-ZnTPPS4- (an electron donor) and three half molecules of dihydroxy-SnTNMePyP4+ (an electron acceptor). Charge balance in the solid is reached without any non-porphyrinic ions, as previously determined for other CBI nanomaterials by non-crystallographic means. The crystal structure reveals a complicated molecular arrangement with slipped ?-? stacking only occurring in isolated dimers of one of the symmetrically unique zinc porphyrins. Consistent with the crystal structure, UV-visible J-aggregate bands indicative of exciton delocalization and extended ?-? stacking are not observed. XRD measurements show that the structure of the Zn/Sn nanosheets is distinct from that of Zn/Sn four-leaf clover-like CBI solids reported previously. In contrast with the Zn/Sn clovers that do exhibit J-aggregate bands and are photoconductive, the nanosheets are not photoconductive. Even so, the nanosheets act as light-harvesting structures in an artificial photosynthesis system capable of reducing water to hydrogen but not as efficiently as the Zn/Sn clovers. Electronic supplementary information (ESI) available: Details of the crystallographic refinement, tables of refinement parameters and bond distances and NSD analysis, and figures showing SEM images of Zn/Sn nanosheets and clovers, the solid grown at different porphyrin concentrations, SEM images of nanosheets at high and low magnification, an ORTEP image showing the five crystallographically distinct porphyrin molecules and the water molecules, and a view of the crystal structure down the b axis are given in the ESI. CCDC reference number 833006. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2nr11826b

Tian, Yongming; M. Beavers, Christine; Busani, Tito; Martin, Kathleen E.; Jacobsen, John L.; Mercado, Brandon Q.; Swartzentruber, Brian S.; van Swol, Frank; Medforth, Craig J.; Shelnutt, John A.

2012-02-01

32

Toward a molecular programming language for algorithmic self-assembly  

NASA Astrophysics Data System (ADS)

Self-assembly is the process whereby relatively simple components autonomously combine to form more complex objects. Nature exhibits self-assembly to form everything from microscopic crystals to living cells to galaxies. With a desire to both form increasingly sophisticated products and to understand the basic components of living systems, scientists have developed and studied artificial self-assembling systems. One such framework is the Tile Assembly Model introduced by Erik Winfree in 1998. In this model, simple two-dimensional square 'tiles' are designed so that they self-assemble into desired shapes. The work in this thesis consists of a series of results which build toward the future goal of designing an abstracted, high-level programming language for designing the molecular components of self-assembling systems which can perform powerful computations and form into intricate structures. The first two sets of results demonstrate self-assembling systems which perform infinite series of computations that characterize computably enumerable and decidable languages, and exhibit tools for algorithmically generating the necessary sets of tiles. In the next chapter, methods for generating tile sets which self-assemble into complicated shapes, namely a class of discrete self-similar fractal structures, are presented. Next, a software package for graphically designing tile sets, simulating their self-assembly, and debugging designed systems is discussed. Finally, a high-level programming language which abstracts much of the complexity and tedium of designing such systems, while preventing many of the common errors, is presented. The summation of this body of work presents a broad coverage of the spectrum of desired outputs from artificial self-assembling systems and a progression in the sophistication of tools used to design them. By creating a broader and deeper set of modular tools for designing self-assembling systems, we hope to increase the complexity which is attainable. These tools provide a solid foundation for future work in both the Tile Assembly Model and explorations into more advanced models.

Patitz, Matthew John

33

Functionalized Nanoparticles and Surfaces for Controlled Chemical Catalysis and Effective Light Harvesting  

SciTech Connect

We have prepared a range of such arrays as key components for biotechnology and photonic applications. These involve self-assembled arrays of increasing complexity with three-dimensionally disposed multilayer interactions. These arrays also include dendrimers as the distinguishing structural building blocks. These photoactive integrated systems have a regular, highly-branched, three-dimensional architecture. Structural modifications of these units include variation of the core, bridging layers, and terminal groups. These modifications result in a large array of dendritic molecules with potential applications for light harvesting.

Marye Anne Fox, James K. Whitesell

2012-11-02

34

Molecular Self-Assembly  

SciTech Connect

This report is divided into two parts: a study of the glass transition in confined geometries, and formation mechanisms of block copolymer mesophases by solvent evaporation-induced self-assembly. The effect of geometrical confinement on the glass transition of polymers is a very important consideration for applications of polymers in nanotechnology applications. We hypothesize that the shift of the glass transition temperature of polymers in confined geometries can be attributed to the inhomogeneous density profile of the liquid. Accordingly, we assume that the glass temperature in the inhomogeneous state can be approximated by the Tg of a corresponding homogeneous, bulk polymer, but at a density equal to the average density of the inhomogeneous system. Simple models based on this hypothesis give results that are in remarkable agreement with experimental measurements of the glass transition of confined liquids. Evaporation-induced self-assembly (EISA) of block copolymers is a versatile process for producing novel, nanostructured materials and is the focus of much of the experimental work at Sandia in the Brinker group. In the EISA process, as the solvent preferentially evaporates from a cast film, two possible scenarios can occur: microphase separation or micellization of the block copolymers in solution. In the present investigation, we established the conditions that dictate which scenario takes place. Our approach makes use of scaling arguments to determine whether the overlap concentration c* occurs before or after the critical micelle concentration (CMC). These theoretical arguments are used to interpret recent experimental results of Yu and collaborators on EISA experiments on Silica/PS-PEO systems.

CURRO, JOHN G.; MCCOY, JOHN DWANE; FRISCHKNECHT, AMALIE L.; YU, KUI

2001-11-01

35

Photocurrent generation by helical peptide monolayers integrating light harvesting and charge-transport functions.  

PubMed

In this study, we construct photoenergy-conversion systems with chromophores located with molecular precision to facilitate efficient light harvesting and charge transport. 3(10) -Helical peptides carrying a disulfide group at the N-terminal, linearly arranged six naphthyl groups at the side chains, and an energy acceptor (anthryl, pyrenyl, or N-ethylcarbazolyl group) at the C-terminal were immobilized on a gold surface via a gold-sulfur linkage to form a well-defined self-assembled monolayer with vertical orientation. The monolayer composed of helical peptides terminated with a naphthyl group instead of an energy acceptor was used as control. Upon photoexcitation of the naphthyl groups of the monolayers in solutions containing an electron donor, all the monolayers generated an anodic photocurrent. The photocurrent generation by the monolayers with an acceptor is composed of the following three steps: (1) photon capture by the side-chain naphthyl groups and energy transfer to the terminal acceptor (light harvesting), (2) electron donation from the aqueous donor to the excited acceptor (electron generation), and (3) electron transport from the terminal to gold via the side-chain naphthyl groups (electron hopping). Unfortunately, it was found that introduction of an energy acceptor facilitates the light-harvesting step but suppresses the electron-generation and electron-hopping steps, resulting in slight reduction of the efficiency of photocurrent generation compared to the control system. Further detailed discussion on photoenergy and electron transport processes shows a prospect to realize efficient photocurrent generation systems taking advantages of both light harvesting and charge-transport functions in future. © 2012 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 100: 1-13, 2013. PMID:23335163

Moritoh, Ryosuke; Morita, Tomoyuki; Kimura, Shunsaku

2013-04-01

36

Self-Assembling Dessert Toppings  

NSDL National Science Digital Library

This is an activity (located on page 3 of the PDF) about self-assembly, the ability of molecules to assemble themselves according to certain rules. Learners will use food-grade components to create delicious dessert topping-filled gel capsules, macroscale relatives of the capsules nanoscientists make in a lab to carry medicine to targeted cells of the body. Relates to linked video, DragonflyTV Nano: Self-Assembly.

Twin Cities Public Television, Inc.

2008-01-01

37

Light-harvesting pigments in photosynthetic bacteria  

SciTech Connect

The major pigments of photosynthetic organisms occur in two functionally different roles in the photon-converting membranes. The major portion (typically up to 99% or more) serve as light-harvesting pigments to absorb the incident radiation and transfer the resulting electronic excitation to photosynthetic reaction centers. There, the second portion of the chlorophylls play an essential role in initiating the primary electron transfer. All of these pigments are thought to exist in specific complexes with proteins in the photosynthetic membranes. These pigments in the photosynthetic bacteria, Rhodopseudomonas sphaeroides, are briefly discussed in this paper. (JMT)

Bolt, J.D. (Columbia Univ., New York, NY); Hunter, C.N.; Niederman, R.A.; Sauer, K.

1981-07-01

38

Rod-like nano-light harvester.  

PubMed

Imitating the natural "energy cascade" architecture, we present a single-molecular rod-like nano-light harvester (NLH) based on a cylindrical polymer brush. Block copolymer side chains carrying (9,9-diethylfluoren-2-yl)methyl methacrylate units as light absorbing antennae (energy donors) are tethered to a linear polymer backbone containing 9-anthracenemethyl methacrylate units as emitting groups (energy acceptors). These NLHs exhibit very efficient energy absorption and transfer. Moreover, we manipulate the energy transfer by tuning the donor-acceptor distance. PMID:24327396

Ling, Jun; Zheng, Zhicheng; Köhler, Anna; Müller, Axel H E

2014-01-01

39

Quantum mechanical light harvesting mechanisms in photosynthesis  

NASA Astrophysics Data System (ADS)

More than 10 million billion photons of light strike a leaf each second. Incredibly, almost every red-coloured photon is captured by chlorophyll pigments and initiates steps to plant growth. Last year we reported that marine algae use quantum mechanics in order to optimize photosynthesis [1], a process essential to its survival. These and other insights from the natural world promise to revolutionize our ability to harness the power of the sun. In a recent review [2] we described the principles learned from studies of various natural antenna complexes and suggested how to utilize that knowledge to shape future technologies. We forecast the need to develop ways to direct and regulate excitation energy flow using molecular organizations that facilitate feedback and control--not easy given that the energy is only stored for a billionth of a second. In this presentation I will describe new results that explain the observation and meaning of quantum-coherent energy transfer. [4pt] [1] Elisabetta Collini, Cathy Y. Wong, Krystyna E. Wilk, Paul M. G. Curmi, Paul Brumer, and Gregory D. Scholes, ``Coherently wired light-harvesting in photosynthetic marine algae at ambient temperature'' Nature 463, 644-648 (2010).[0pt] [2] Gregory D. Scholes, Graham R. Fleming, Alexandra Olaya-Castro and Rienk van Grondelle, ``Lessons from nature about solar light harvesting'' Nature Chem. 3, 763-774 (2011).

Scholes, Gregory

2012-02-01

40

Bacteriochlorophyll aggregates self-assembled on functionalized gold nanorod cores as mimics of photosynthetic chlorosomal antennae: a single molecule study.  

PubMed

We prepare artificial aggregates that mimic the structure and function of natural chlorosomal light harvesting complexes of green photosynthetic bacteria. Gold nanorods functionalized with hydroxyl groups and immobilized on a substrate serve as cores for the growth of bacteriochlorophyll (BChl) aggregates from a buffer solution. The BChl pigments form large self-assembled aggregate particles with sizes more than twice that of natural chlorosomes. The size is controllable by the aggregation time. The aggregates are characterized on a single-particle level by atomic force microscopy, electron microscopy, and single-molecule spectroscopy. The absorption and fluorescence spectral properties which reflect the molecular level arrangement of the BChl aggregates closely resemble those of the natural chlorosomes of the photosynthetic bacterium Chlorobaculum tepidum. On the other hand, the results of linear dichroism and circular dichroism are different from those of the chlorosomes and indicate a different mesoscopic structure for the artificial aggregates. These results emphasize the structural role played by the baseplate pigment-protein complex in natural chlorosomes. PMID:24559170

Furumaki, Shu; Vacha, Frantisek; Hirata, Shuzo; Vacha, Martin

2014-03-25

41

Nanoparticle induced self-assembly  

NASA Astrophysics Data System (ADS)

Self-assembly has for the large part focused on the assembly of molecules without guidance or management from an outside source. However, self-assembly is in principle by no means limited to molecules or the nanoscale. A particularly interesting method to the self-assembly of micro- to millimetre sized components is the use of the 'magnetic hole' effect. In this method, nonmagnetic particles can be manipulated by external magnetic fields by immersing them in a dispersion of colloidal, magnetic nanoparticles, denoted ferrofluids. Nonmagnetic particles in magnetized ferrofluids are in many ways ideal model systems to test various forms of particle self-assembly and dynamics. When microspheres are confined to a monolayer between two parallel plates and subjected to static or oscillating magnetic fields they show a variety of dynamical behaviours and assemblages, depending on the frequency and direction of the external fields. A single pair of magnetic holes oscillating in a ferrofluid layer may be used to measure the viscosity of tiny volumes of the fluid. We have also observed ordering of dilute dispersions of macromolecules and nanoparticles in magnetized ferrofluids. The self-assembly at this length scale results from structural correlations between these nanostructures and ferrofluid particles rather than from the macroscopic magnetostatic effect for the magnetic holes.

Helgesen, G.; Svåsand, E.; Skjeltorp, A. T.

2008-05-01

42

Self-assembled three-dimensional nanocrown array.  

PubMed

Although an ordered nanoplasmonic probe array will have a huge impact on light harvesting, selective frequency response (i.e., nanoantenna), and quantitative molecular/cellular imaging, the realization of such an array is still limited by conventional techniques due to the serial processing or resolution limit by light diffraction. Here, we demonstrate a thermodynamically driven, self-assembled three-dimensional nanocrown array that consists of a core and six satellite gold nanoparticles (GNPs). Our ordered nanoprobe array is fabricated over a large area by thermal dewetting of thin gold film on hexagonally ordered porous anodic alumina (PAA). During thermal dewetting, the structural order of the PAA template dictates the periodic arrangement of gold nanoparticles, rendering the array of gold nanocrown. Because of its tunable size (i.e., 50 nm core and 20 nm satellite GNPs), arrangement, and periodicity, the nanocrown array shows multiple optical resonance frequencies at visible wavelengths as well as angle-dependent optical properties. PMID:22672061

Hong, Soongweon; Kang, Taewook; Choi, Dukhyun; Choi, Yeonho; Lee, Luke P

2012-07-24

43

Self-assembling amphiphilic peptides.  

PubMed

The self-assembly of several classes of amphiphilic peptides is reviewed, and selected applications are discussed. We discuss recent work on the self-assembly of lipopeptides, surfactant-like peptides and amyloid peptides derived from the amyloid-? peptide. The influence of environmental variables such as pH and temperature on aggregate nanostructure is discussed. Enzyme-induced remodelling due to peptide cleavage and nanostructure control through photocleavage or photo-cross-linking are also considered. Lastly, selected applications of amphiphilic peptides in biomedicine and materials science are outlined. © 2014 The Authors. Journal of Peptide Science published by European Peptide Society and John Wiley & Sons, Ltd. PMID:24729276

Dehsorkhi, Ashkan; Castelletto, Valeria; Hamley, Ian W

2014-07-01

44

Self-assembled neuromorphic networks  

NASA Astrophysics Data System (ADS)

This paper details our experimental progress towards the synthesis of self-assembled nanostructures that may exhibit collective computational activity. Self assembled two dimensional networks of heterostructured quantum dots, linked by resistive and capacitive connections, can function as Boolean logic circuits, associative memory, image processors, and combinatorial optimizers. Computational or signal processing activity is elicited from simple charge interactions between the dots which act as non-linear resistors. Such circuits could be massively parallel, fault-tolerant, ultrafast, ultradense and dissipate very little power.

Bandyopadhyay, Supriyo; Menon, Latika; Kouklin, Nikolai A.; Williams, Paul F.; Ianno, Natale J.

2001-11-01

45

Long range excitonic transport in a biomimetic system inspired by the bacterial light-harvesting apparatus  

NASA Astrophysics Data System (ADS)

Photosynthesis, the process by which energy from sunlight drives cellular metabolism, relies on a unique organization of light-harvesting and reaction center complexes. Recently, the organization of light-harvesting LH2 complexes and dimeric reaction center-light-harvesting I-PufX core complexes in membranes of purple non-sulfur bacteria was revealed by atomic force microscopy [S. Bahatyrova et al., Nature (London) 430, 1058 (2004)]. Here, we discuss optimal exciton transfer in a biomimetic system closely modeled on the structure of LH2 and its organization within the membrane using a Markovian quantum model with dissipation and trapping added phenomenologically. In a deliberate manner, we neglect the high level detail of the bacterial light-harvesting complex and its interaction with the phonon bath in order to elucidate a set of design principles that may be incorporated in artificial pigment-scaffold constructs in a supramolecular assembly. We show that our scheme reproduces many of the most salient features found in their natural counterpart and may be largely explained by simple electrostatic considerations. Most importantly, we show that quantum effects act primarily to enforce robustness with respect to spatial and spectral disorder between and within complexes. The implications of such an arrangement are discussed in the context of biomimetic photosynthetic analogs capable of transferring energy efficiently across tens to hundreds of nanometers.

Harel, Elad

2012-05-01

46

Three-Dimensional Self-Assembled Photonic Crystal Waveguide  

NASA Astrophysics Data System (ADS)

Photonic crystals (PCs), two- or three-dimensionally periodic, artificial, and dielectric structures, have a specific forbidden band for electromagnetic waves, referred to as photonic bandgap (PBG). The PBG is analogous to the electronic bandgap in natural crystal structures with periodic atomic arrangement. A well-defined and embedded planar, line, or point defect within the PCs causes a break in its structural periodicity, and introduces a state in the PBG for light localization. It offers various applications in integrated optics and photonics including optical filters, sharp bending light guides and very low threshold lasers. Using nanofabrication processes, PCs of the 2-D slab-type and 3-D layer-by-layer structures have been investigated widely. Alternatively, simple and low-cost self-assembled PCs with full 3-D PBG, inverse opals, have been suggested. A template with face centered cubic closed packed structure, opal, may initially be built by self-assembly of colloidal spheres, and is selectively removed after infiltrating high refractive index materials into the interstitials of spheres. In this dissertation, the optical waveguides utilizing the 3-D self-assembled PCs are discussed. The waveguides were fabricated by microfabrication technology. For high-quality colloidal silica spheres and PCs, reliable synthesis, self-assembly, and characterization techniques were developed. Its theoretical and experimental demonstrations are provided and correlated. They suggest that the self-assembled PCs with PBG are feasible for the applications in integrated optics and photonics.

Baek, Kang-Hyun

47

Ordering self-assembled nanostructures  

NASA Astrophysics Data System (ADS)

Many innovative applications of nanosciences, such as semiconductor lasers, quantum computing, information storage, quantum cryptography, and semiconductor transistors largely rely on the ability to fabricate long-range ordered nanostructures. However, conventional top-down techniques have mostly reached a bottleneck that thwarts the progress toward future miniaturization needed for the next generation of nanodevices. This constraint imposes the need to develop new manufacturing methods to engineering nanodevices on the single-digit-nanometer scale. Self-assembly, the spontaneous formation of regular arrays, is emerging as one of the most promising avenues for both miniaturization and fabrication. While self-assembly can bring us the direct large scale fabrication of nanostructures, the stochastic nature stemming from symmetry breaking bifurcation inhibits the full realization of ordered nano-arrays. Since the quality of electronic, optical, magnetic and photonic properties of nanodevices depends substantially on the uniformity of their arrangement, avoiding imperfections in self-assembly is important; thus forms the central subject of this dissertation. We propose a method for ordering self-assembled nanostructures by imposing control on the deposition using an opaque mask placed a finite distance above the substrate. This choice is motivated by studies of symmetry breaking, which suggest that boundary conditions provide a means to select among all possible broken symmetry states. We have conducted both linear and nonlinear stability analyses to derive optimal control parameters that support specific pattern formation. Numerical integrations of two morphological self-assembly models (2D biphasic surface islands in a monolayer and 3D epitaxial quantum dot growth in Stranski-Krastanow mode) show that the proposed method can indeed give large scale, well organized nanostructures.

Shi, Feng

48

Light harvesting in a fluctuating antenna.  

PubMed

One of the major players in oxygenic photosynthesis, photosystem II (PSII), exhibits complex multiexponential fluorescence decay kinetics that for decades has been ascribed to reversible charge separation taking place in the reaction center (RC). However, in this description the protein dynamics is not taken into consideration. The intrinsic dynamic disorder of the light-harvesting proteins along with their fluctuating dislocations within the antenna inevitably result in varying connectivity between pigment-protein complexes and therefore can also lead to nonexponential excitation decay kinetics. On the basis of this presumption, we propose a simple conceptual model describing excitation diffusion in a continuous medium and accounting for possible variations of the excitation transfer rates. Recently observed fluorescence kinetics of PSII of different sizes are perfectly reproduced with only two adjustable parameters instead of the many decay times and amplitudes required in standard analysis procedures; no charge recombination in the RC is required. The model is also able to provide valuable information about the structural and functional organization of the photosynthetic antenna and in a straightforward way solves various contradictions currently existing in the literature. PMID:24870124

Chmeliov, Jevgenij; Trinkunas, Gediminas; van Amerongen, Herbert; Valkunas, Leonas

2014-06-25

49

Self-assembled plasmonic metamaterials  

NASA Astrophysics Data System (ADS)

Nowadays for the sake of convenience most plasmonic nanostructures are fabricated by top-down nanofabrication technologies. This offers great degrees of freedom to tailor the geometry with unprecedented precision. However, it often causes disadvantages as well. The structures available are usually planar and periodically arranged. Therefore, bulk plasmonic structures are difficult to fabricate and the periodic arrangement causes undesired effects, e.g., strong spatial dispersion is observed in metamaterials. These limitations can be mitigated by relying on bottom-up nanofabrication technologies. There, self-assembly methods and techniques from the field of colloidal nanochemistry are used to build complex functional unit cells in solution from an ensemble of simple building blocks, i.e., in most cases plasmonic nanoparticles. Achievable structures are characterized by a high degree of nominal order only on a short-range scale. The precise spatial arrangement across larger dimensions is not possible in most cases; leading essentially to amorphous structures. Such self-assembled nanostructures require novel analytical means to describe their properties, innovative designs of functional elements that possess a desired near- and far-field response, and entail genuine nanofabrication and characterization techniques. Eventually, novel applications have to be perceived that are adapted to the specifics of the self-assembled nanostructures. This review shall document recent progress in this field of research. Emphasis is put on bottom-up amorphous metamaterials. We document the state-of-the-art but also critically assess the problems that have to be overcome.

Mühlig, Stefan; Cunningham, Alastair; Dintinger, José; Scharf, Toralf; Bürgi, Thomas; Lederer, Falk; Rockstuhl, Carsten

2013-07-01

50

Multifunctional self-assembled monolayers  

SciTech Connect

This is the final report of at three year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The specific goals of this research project were threefold: to develop multifunctional self-assembled monolayers, to understand the role of monolayer structure on the functioning of such systems, and to apply this knowledge to the development of electrochemical enzyme sensors. An array of molecules that can be used to attach electrochemically active biomolecules to gold surfaces has been synthesized. Several members of a class of electroactive compounds have been characterized and the factors controlling surface modification are beginning to be characterized. Enzymes have been attached to self-assembled molecules arranged on the gold surface, a critical step toward the ultimate goal of this project. Several alternative enzyme attachment strategies to achieve robust enzyme- modified surfaces have been explored. Several means of juxtaposing enzymes and mediators, electroactive compounds through which the enzyme can exchange electrons with the electrode surface, have also been investigated. Finally, the development of sensitive biosensors based on films loaded with nanoscale-supported gold particles that have surface modified with the self-assembled enzyme and mediator have been explored.

Zawodzinski, T.; Bar, G.; Rubin, S.; Uribe, F. [Los Alamos National Lab., NM (United States); Ferrais, J. [Texas Univ., Dallas, TX (United States)

1996-06-01

51

Stereochemistry in subcomponent self-assembly.  

PubMed

Conspectus As Pasteur noted more than 150 years ago, asymmetry exists in matter at all organization levels. Biopolymers such as proteins or DNA adopt one-handed conformations, as a result of the chirality of their constituent building blocks. Even at the level of elementary particles, asymmetry exists due to parity violation in the weak nuclear force. While the origin of homochirality in living systems remains obscure, as does the possibility of its connection with broken symmetries at larger or smaller length scales, its centrality to biomolecular structure is clear: the single-handed forms of bio(macro)molecules interlock in ways that depend upon their handednesses. Dynamic artificial systems, such as helical polymers and other supramolecular structures, have provided a means to study the mechanisms of transmission and amplification of stereochemical information, which are key processes to understand in the context of the origins and functions of biological homochirality. Control over stereochemical information transfer in self-assembled systems will also be crucial for the development of new applications in chiral recognition and separation, asymmetric catalysis, and molecular devices. In this Account, we explore different aspects of stereochemistry encountered during the use of subcomponent self-assembly, whereby complex structures are prepared through the simultaneous formation of dynamic coordinative (N ? metal) and covalent (N?C) bonds. This technique provides a useful method to study stereochemical information transfer processes within metal-organic assemblies, which may contain different combinations of fixed (carbon) and labile (metal) stereocenters. We start by discussing how simple subcomponents with fixed stereogenic centers can be incorporated in the organic ligands of mononuclear coordination complexes and communicate stereochemical information to the metal center, resulting in diastereomeric enrichment. Enantiopure subcomponents were then incorporated in self-assembly reactions to control the stereochemistry of increasingly complex architectures. This strategy has also allowed exploration of the degree to which stereochemical information is propagated through tetrahedral frameworks cooperatively, leading to the observation of stereochemical coupling across more than 2 nm between metal stereocenters and the enantioselective synthesis of a face-capped tetrahedron containing no carbon stereocenters via a stereochemical memory effect. Several studies on the communication of stereochemistry between the configurationally flexible metal centers in tetrahedral metal-organic cages have shed light on the factors governing this process, allowing the synthesis of an asymmetric cage, obtained in racemic form, in which all symmetry elements have been broken. Finally, we discuss how stereochemical diversity leads to structural complexity in the structures prepared through subcomponent self-assembly. Initial use of octahedral metal templates with facial stereochemistry in subcomponent self-assembly, which predictably gave rise to structures of tetrahedral symmetry, was extended to meridional metal centers. These lower-symmetry linkages have allowed the assembly of a series of increasingly intricate 3D architectures of varying functionality. The knowledge gained from investigating different aspects of the stereochemistry of metal-templated assemblies thus not only leads to new means of structural control but also opens pathways toward functions such as stereoselective guest binding and transformation. PMID:24793652

Castilla, Ana M; Ramsay, William J; Nitschke, Jonathan R

2014-07-15

52

Exciton coupling induces vibronic hyperchromism in light-harvesting complexes  

NASA Astrophysics Data System (ADS)

The recently suggested possibility that weak vibronic transitions can be excitonically enhanced in light-harvesting complexes is studied in detail. A vibronic exciton dimer model that includes ground-state vibrations is investigated using the multi-configuration time-dependent Hartree method with a parameter set typical to photosynthetic light-harvesting complexes. The absorption spectra are discussed based on the Coulomb coupling, the detuning of the site energies, and the number of vibrational modes. Fluorescence spectra calculations show that the spectral densities obtained from the low-temperature fluorescence line-narrowing measurements of light-harvesting systems need to be corrected for the effects of excitons. For the J-aggregate configuration, as in most light-harvesting complexes, the true spectral density has a larger amplitude than that obtained from the measurement.

Schulze, Jan; Torbjörnsson, Magne; Kühn, Oliver; Pullerits, Tõnu

2014-04-01

53

Synergistic Two-Photon Absorption Enhancement in Photosynthetic Light Harvesting  

NASA Astrophysics Data System (ADS)

The grand scale fixation of solar energies into chemical substances by photosynthetic reactions of light-harvesting organisms provides Earth's other life forms a thriving environment. Scientific explorations in the past decades have unraveled the fundamental photophysical and photochemical processes in photosynthesis. Higher plants, green algae, and light-harvesting bacteria utilize organized pigment-protein complexes to harvest solar power efficiently and the resultant electronic excitations are funneled into a reaction center, where the first charge separation process takes place. Here we show experimental evidences that green algae (Chlorella vulgaris) in vivo display a synergistic two-photon absorption enhancement in their photosynthetic light harvesting. Their absorption coefficients at various wavelengths display dramatic dependence on the photon flux. This newly found phenomenon is attributed to a coherence-electronic-energy-transfer-mediated (CEETRAM) photon absorption process of light-harvesting pigment-protein complexes of green algae. Under the ambient light level, algae and higher plants can utilize this quantum mechanical mechanism to create two entangled electronic excitations adjacently in their light-harvesting networks. Concerted multiple electron transfer reactions in the reaction centers and oxygen evolving complexes can be implemented efficiently by the coherent motion of two entangled excitons from antennae to the charge separation reaction sites. To fabricate nanostructured, synthetic light-harvesting apparatus, the paramount role of the CEETRAM photon absorption mechanism should be seriously considered in the strategic guidelines.

Chen, Kuo-Mei; Chen, Yu-Wei; Gao, Ting-Fong

2012-06-01

54

Self-assembling magnetic "snakes"  

SciTech Connect

Nickel particles float peacefully in a liquid medium until a giant snake seems to swim by and snatch several particles up, adding to its own mass. The self-assembled "snakes" act like biological systems, but they are not alive and are driven by a magnetic field. The research may someday offer some insight into the organization of life itself. Read more at Wired: http://www.wired.com/wiredscience/2009/03/snakes/ Research and video by Alex Snezhko and Igor Aronson, Argonne National Laboratory.

None

2010-01-01

55

Synthesis and photophysical studies of self-assembled multicomponent supramolecular coordination prisms bearing porphyrin faces.  

PubMed

Multicomponent self-assembly, wherein two unique donor precursors are combined with a single metal acceptor instead of the more common two-component assembly, can be achieved by selecting Lewis-basic sites and metal nodes that select for heteroligated coordination spheres. Platinum(II) ions show a thermodynamic preference for mixed pyridyl/carboxylate coordination environments and are thus suitable for such designs. The use of three or more unique building blocks increases the structural complexity of supramolecules. Herein, we describe the synthesis and characterization of rectangular prismatic supramolecular coordination complexes (SCCs) with two faces occupied by porphyrin molecules, motivated by the search for new multichromophore complexes with promising light-harvesting properties. These prisms are obtained from the self-assembly of a 90° Pt(II) acceptor with a meso-substituted tetrapyridylporphyrin (TPyP) and dicarboxylate ligands. The generality of this self-assembly reaction is demonstrated using five dicarboxylate ligands, two based on a rigid central phenyl ring and three alkyl-spaced variants, to form a total of five free-base and five Zn-metallated porphyrin prisms. All 10 SCCs are characterized by (31)P and (1)H multinuclear NMR spectroscopy and electrospray ionization mass spectrometry, confirming the structure of each self-assembly and the stoichiometry of formation. The photophysical properties of the resulting SCCs were investigated revealing that the absorption and emission properties of the free-base and metallated porphyrin prisms preserve the spectral features associated with free TPyP. PMID:24979805

Shi, Yanhui; Sánchez-Molina, Irene; Cao, Changsheng; Cook, Timothy R; Stang, Peter J

2014-07-01

56

Self-Assembly at All Scales  

Microsoft Academic Search

Self-assembly is the autonomous organization of components into patterns or structures without human intervention. Self-assembling processes are common throughout nature and technology. They involve components from the molecular (crystals) to the planetary (weather systems) scale and many different kinds of interactions. The concept of self-assembly is used increasingly in many disciplines, with a different flavor and emphasis in each.

George M. Whitesides; Bartosz Grzybowski

2002-01-01

57

Self-Assembled Peptide-Amphiphiles & Self-Assembled Peptide Nanofiber Networks Presenting Multiple Signals.  

National Technical Information Service (NTIS)

The present invention provides a mixture of self-assembling peptide-amphiphiles with complementary charges whose design and function is patterned after proteins having biological functions. The oppositely charged peptide amphiphiles may be self-assembled ...

J. D. Hartgerlink K. L. Niece S. I. Stupp

2003-01-01

58

Self-Assembled Organic Nanotubes: A Novel Platform for Drug Design and Discovery  

Microsoft Academic Search

Self-assembly and self-organization processes are the thread that connects the reductionism of chemical reactions to the complexity and emergence of a living dynamic system. Artificial self-assembly derives its principles from nature and its processes, and uses this understanding to design nanoscale devices with predefined function. However, complex forms of organized matter cannot be synthesized bond-by-bond. Rather, a new type of

Hicham Fenniri

2004-01-01

59

3D Programmable Micro Self Assembly.  

National Technical Information Service (NTIS)

This project has succeeded to: generate new techniques, improve understandings of the physical foundations, and create algorithms for self- assembling systems in 2D and 3D. We have developed a 'self assembly tool box' consisting of a range of methods for ...

K. F. Bohringer B. A. Parviz E. Klavins

2005-01-01

60

Self-Assembly: How Nature Builds  

ERIC Educational Resources Information Center

Self-assembly or spontaneous assembly is a process in which materials build themselves without assistance. This process plays a central role in the construction of biological structures and materials such as cells, viruses, and bone, and also in abiotic processes like phase transitions and crystal formation. The principles of self-assembly help…

Jones, M. Gail; Falvo, Michael R.; Broadwell, Bethany; Dotger, Sharon

2006-01-01

61

Limits of quantum speedup in photosynthetic light harvesting  

NASA Astrophysics Data System (ADS)

It has been suggested that excitation transport in photosynthetic light-harvesting complexes features speedups analogous to those found in quantum algorithms. Here we compare the dynamics in these light-harvesting systems to the dynamics of quantum walks, in order to elucidate the limits of such quantum speedups. For the Fenna-Matthews-Olson complex of green sulfur bacteria, we show that while there is indeed speedup at short times, this is short lived (70 fs) despite longer-lived (ps) quantum coherence. Remarkably, this timescale is independent of the details of the decoherence model. More generally, we show that the distinguishing features of light-harvesting complexes not only limit the extent of quantum speedup but also reduce the rates of diffusive transport. These results suggest that quantum coherent effects in biological systems are optimized for efficiency or robustness rather than the more elusive goal of quantum speedup.

Hoyer, Stephan; Sarovar, Mohan; Whaley, K. Birgitta

2010-06-01

62

Quantum entanglement in photosynthetic light-harvesting complexes  

NASA Astrophysics Data System (ADS)

Light-harvesting components of photosynthetic organisms are complex, coupled, many-body quantum systems, in which electronic coherence has recently been shown to survive for relatively long timescales, despite the decohering effects of their environments. Here, we analyse entanglement in multichromophoric light-harvesting complexes, and establish methods for quantification of entanglement by describing necessary and sufficient conditions for entanglement and by deriving a measure of global entanglement. These methods are then applied to the Fenna-Matthews-Olson protein to extract the initial state and temperature dependencies of entanglement. We show that, although the Fenna-Matthews-Olson protein in natural conditions largely contains bipartite entanglement between dimerized chromophores, a small amount of long-range and multipartite entanglement should exist even at physiological temperatures. This constitutes the first rigorous quantification of entanglement in a biological system. Finally, we discuss the practical use of entanglement in densely packed molecular aggregates such as light-harvesting complexes.

Sarovar, Mohan; Ishizaki, Akihito; Fleming, Graham R.; Whaley, K. Birgitta

2010-06-01

63

Building-block synthesis of porphyrin light-harvesting arrays  

SciTech Connect

Photosynthetic organisms employ light-harvesting complexes to capture dilute sunlight and funnel energy to the reaction centers. Light-harvesting complexes are remarkable in achieving efficient energy migration among hundreds of pigments with avoidance of non-energy transfer quenching processes. In this communication we report a convergent strategy for preparing rigid, soluble arrays of covalently-linked porphyrins in various metalation states. The strategy employs readily available tetraarylporphyrins as modular building blocks. The porphyrins bear peripheral iodo or ethynyl groups and are facially-encumbered to suppress aggregation. The free base or metalloporphyrins are then joined via homogeneous Pd-mediated coupling reactions under basic conditions to give a desired assembly. We believe that this building-block approach provides an ideal route to model light-harvesting compounds. 10 refs., 1 fig.

Prathapan, S.; Johnson, T.E.; Lindsey, J.S. (Carnegie Mellon Univ., Pittsburgh, PA (United States))

1993-08-11

64

Two-dimensional patterning of bacterial light-harvesting 2 complexes on lipid-modified gold surface  

NASA Astrophysics Data System (ADS)

In a photosynthetic membrane, nano-scale patterns of light-harvesting (LH) pigment-protein complexes play an essential role in capturing photons and ensuring efficient excitation energy transfer. LH complexes 1 and 2 have drawn attention as building blocks of a nano-scale photoelectric device. For obtaining a device with efficiency comparable to that of the natural photosynthesis, a method has to be established for forming a two-dimensional assembly of LH complexes around a metal electrode. In this study, LH2 complexes isolated from Rb. sphaeroides were immobilized on a patterned gold surface. Quenching of photo-excitation energy by gold was prevented through the placement of a self-assembled phospholipid monolayer between the LH2 complexes and the gold surface.

Yajima, Shunsuke; Furukawa, Rei A.; Nagata, Morio; Sakai, Shunsuke; Kondo, Masaharu; Iida, Kouji; Dewa, Takehisa; Nango, Mamoru

2012-06-01

65

Quantifying the quantum correlations in light-harvesting complexes  

Microsoft Academic Search

Biological systems have been of recent interest for the role that quantum correlations may play for functionality or in evolution. One such biological phenomenon under study is the photosynthesis of certain organisms, for instance low light adapted green sulfur bacteria. The Fenna-Matthews-Olson (FMO) protein complex is a biological light harvesting complex that is found in such systems. It has drawn

Sai Vinjanampathy; Kamil Bradler; Mark Wilde; Dmitry B. Uskov

2010-01-01

66

Incoherent energy transfer within light-harvesting complexes  

NASA Astrophysics Data System (ADS)

Rate equations are used to model spectroscopic observation of incoherent energy transfer in light-harvesting antenna systems based upon known structures. A two-parameter two-dimensional model is proposed. The transfer rates obtained, by matching the fluorescent decay, are self-consistent within our model.

Ting, Julian Juhi-Lian

1999-10-01

67

Light-harvesting photocatalysis for water oxidation using mesoporous organosilica.  

PubMed

An organic-based photocatalysis system for water oxidation, with visible-light harvesting antennae, was constructed using periodic mesoporous organosilica (PMO). PMO containing acridone groups in the framework (Acd-PMO), a visible-light harvesting antenna, was supported with [Ru(II) (bpy)3 (2+) ] complex (bpy=2,2'-bipyridyl) coupled with iridium oxide (IrOx ) particles in the mesochannels as photosensitizer and catalyst, respectively. Acd-PMO absorbed visible light and funneled the light energy into the Ru complex in the mesochannels through excitation energy transfer. The excited state of Ru complex is oxidatively quenched by a sacrificial oxidant (Na2 S2 O8 ) to form Ru(3+) species. The Ru(3+) species extracts an electron from IrOx to oxidize water for oxygen production. The reaction quantum yield was 0.34?%, which was improved to 0.68 or 1.2?% by the modifications of PMO. A unique sequence of reactions mimicking natural photosystem?II, 1)?light-harvesting, 2)?charge separation, and 3)?oxygen generation, were realized for the first time by using the light-harvesting PMO. PMID:24890840

Takeda, Hiroyuki; Ohashi, Masataka; Goto, Yasutomo; Ohsuna, Tetsu; Tani, Takao; Inagaki, Shinji

2014-07-14

68

Bottom-Up Nanomanufacturing: Self Assembly  

NSDL National Science Digital Library

This overview of nanotechnology is presented by the NaMCATE project. "The process of self assembly is defined as the spontaneous association of numerous individual units of material into well organized, well defined structures without external instruction." An understanding of self assembly requires background knowledge in physics, chemistry, and biology and this module focuses on these fields. This lesson introduces these concepts by providing two learning activities on self assembly as well as a pre-test and performance assessment. Additionally, a powerpoint presentation is included.Users must create a free login in order to access the materials.

2011-09-22

69

Self-assembled chitin nanofibers and applications.  

PubMed

Self-assembled natural biomaterials offer a variety of ready-made nanostructures available for basic science research and technological applications. Most natural structural materials are made of self-assembled nanofibers with diameters in the nanometer range. Among these materials, chitin is the second most abundant polysaccharide after cellulose and is part of the exoskeleton or arthropods and mollusk shells. Chitin has several desirable properties as a biomaterial including mechanical strength, chemical and thermal stability, and biocompatibility. However, chitin insolubility in most organic solvents has somewhat limited its use. In this research highlight, we describe recent developments in producing biogenic chitin nanofibers using self-assembly from a solution of squid pen ?-chitin in hexafluoroisopropanol. With this solution based assembly, we have demonstrated chitin-silk composite self-assembly, chitin nanofiber fabrication across length-scales, and manufacturing of chitin nanofiber substrates for tissue engineering. PMID:24556234

Rolandi, Marco; Rolandi, Ranieri

2014-05-01

70

Self-Assembly: How Nature Builds  

NSDL National Science Digital Library

Self-assembly or spontaneous assembly is a process in which materials build themselves without assistance (Goodsell 2000). Presented here is a simple in-class exercise that underlines the basic principles of self-assembly and helps students understand how the scale of molecules and atoms is different than the human-scale world (Campbell, Freidinger, and Querns 2001). Principally, the activity illustrates that nanoscale objects are always moving around (thermal motion) and that they tend to stick to each other (intermolecular bonds). The exercise is also a design project, in which students use their imagination in concert with the basic rules of self-assembly (multiple weak bonds and lock-and-key) to produce complex self-assembled models.

Broadwell, Bethany; Jones, M. G.; Falvo, Michael R.; Dotger, Sharon

2006-12-01

71

Directed Self-Assembly of Nanodispersions  

SciTech Connect

Directed self-assembly promises to be the technologically and economically optimal approach to industrial-scale nanotechnology, and will enable the realization of inexpensive, reproducible and active nanostructured materials with tailored photonic, transport and mechanical properties. These new nanomaterials will play a critical role in meeting the 21st century grand challenges of the US, including energy diversity and sustainability, national security and economic competitiveness. The goal of this work was to develop and fundamentally validate methods of directed selfassembly of nanomaterials and nanodispersion processing. The specific aims were: 1. Nanocolloid self-assembly and interactions in AC electric fields. In an effort to reduce the particle sizes used in AC electric field self-assembly to lengthscales, we propose detailed characterizations of field-driven structures and studies of the fundamental underlying particle interactions. We will utilize microscopy and light scattering to assess order-disorder transitions and self-assembled structures under a variety of field and physicochemical conditions. Optical trapping will be used to measure particle interactions. These experiments will be synergetic with calculations of the particle polarizability, enabling us to both validate interactions and predict the order-disorder transition for nanocolloids. 2. Assembly of anisotropic nanocolloids. Particle shape has profound effects on structure and flow behavior of dispersions, and greatly complicates their processing and self-assembly. The methods developed to study the self-assembled structures and underlying particle interactions for dispersions of isotropic nanocolloids will be extended to systems composed of anisotropic particles. This report reviews several key advances that have been made during this project, including, (1) advances in the measurement of particle polarization mechanisms underlying field-directed self-assembly, and (2) progress in the directed self-assembly of anisotropic nanoparticles and their unique physical properties.

Furst, Eric M [University of Delaware] [University of Delaware

2013-11-15

72

Self-assembled DNA Structures for Nanoconstruction  

Microsoft Academic Search

In recent years, a number of research groups have begun developing nanofabrication methods based on DNA self-assembly. Here we review our recent experimental progress to utilize novel DNA nanostructures for self-assembly as well as for templates in the fabrication of functional nano-patterned materials. We have prototyped a new DNA nanostructure known as a cross structure. This nanostructure has a 4-fold

Hao Yan; Peng Yin; Sung Ha Park; Hanying Li; Liping Feng; Xiaoju Guan; Dage Liu; John H. Reif; Thomas H. Labean

2004-01-01

73

Limits of quantum speedup in photosynthetic light harvesting  

NASA Astrophysics Data System (ADS)

It has been suggested that excitation transport in photosynthetic light harvesting complexes features speedups analogous to those found in quantum algorithms. Here we compare dynamics in these systems to quantum walks to elucidate the limits of such quantum speedups. For the Fenna-Matthews-Olson (FMO) complex of green sulfur bacteria, we show that while there is indeed speedup at short times, this is short lived (70 fs) despite longer lived (ps) quantum coherence. Remarkably, this time scale is independent of the details of the decoherence model. More generally, we show that the distinguishing features of light-harvesting complexes limit quantum speedup and cause even diffusive transport to be slowed. These results suggest that quantum coherent effects in biological systems are optimized for efficiency and robustness rather than for achieving the more elusive goal of quantum speedup.

Hoyer, Stephan; Sarovar, Mohan; Whaley, Birgitta

2010-03-01

74

Regulation and dynamics of the light-harvesting system.  

PubMed

Photosynthetic organisms are continuously subjected to changes in light quantity and quality, and must adjust their photosynthetic machinery so that it maintains optimal performance under limiting light and minimizes photodamage under excess light. To achieve this goal, these organisms use two main strategies in which light-harvesting complex II (LHCII), the light-harvesting system of photosystem II (PSII), plays a key role both for the collection of light energy and for photoprotection. The first is energy-dependent nonphotochemical quenching, whereby the high-light-induced proton gradient across the thylakoid membrane triggers a process in which excess excitation energy is harmlessly dissipated as heat. The second involves a redistribution of the mobile LHCII between the two photosystems in response to changes in the redox poise of the electron transport chain sensed through a signaling chain. These two processes strongly diminish the production of damaging reactive oxygen species, but photodamage of PSII is unavoidable, and it is repaired efficiently. PMID:24471838

Rochaix, Jean-David

2014-04-29

75

Self-assembly in nature: using the principles of nature to create complex nanobiomaterials.  

PubMed

Self-assembly is a ubiquitous process in biology where it plays numerous important roles and underlies the formation of a wide variety of complex biological structures. Over the past two decades, materials scientists have aspired to exploit nature's assembly principles to create artificial materials, with hierarchical structures and tailored properties, for the fabrication of functional devices. Toward this goal, both biological and synthetic building blocks have been subject of extensive research in self-assembly. In fact, molecular self-assembly is becoming increasingly important for the fabrication of biomaterials because it offers a great platform for constructing materials with high level of precision and complexity, integrating order and dynamics, to achieve functions such as stimuli-responsiveness, adaptation, recognition, transport, and catalysis. The importance of peptide self-assembling building blocks has been recognized in the last years, as demonstrated by the literature available on the topic. The simple structure of peptides, as well as their facile synthesis, makes peptides an excellent family of structural units for the bottom-up fabrication of complex nanobiomaterials. Additionally, peptides offer a great diversity of biochemical (specificity, intrinsic bioactivity, biodegradability) and physical (small size, conformation) properties to form self-assembled structures with different molecular configurations. The motivation of this review is to provide an overview on the design principles for peptide self-assembly and to illustrate how these principles have been applied to manipulate their self-assembly across the scales. Applications of self-assembling peptides as nanobiomaterials, including carriers for drug delivery, hydrogels for cell culture and tissue repair are also described. PMID:23929805

Mendes, Ana C; Baran, Erkan T; Reis, Rui L; Azevedo, Helena S

2013-01-01

76

A light-harvesting array of synthetic porphyrins  

NASA Astrophysics Data System (ADS)

An array of five porphyrin molecules has been synthesized and used as a simple model of the light-harvesting complex found in natural photosynthesis. Efficient Förster energy transfer occurs from antenna zinc porphyrins to a central free-base porphyrin molecule. This central porphyrin retains long-lived singlet and triplet excited states that can be quenched by diffusional processes, Both electron and energy transfer quenching reactions can be observed.

Davila, Jorge; Harriman, Anthony; Milgrom, Lionel R.

1987-05-01

77

Light Harvesting by Lamellar Chromatophores in Rhodospirillum photometricum.  

PubMed

Purple photosynthetic bacteria harvest light using pigment-protein complexes which are often arranged in pseudo-organelles called chromatophores. A model of a chromatophore from Rhodospirillum photometricum was constructed based on atomic force microscopy data. Molecular-dynamics simulations and quantum-dynamics calculations were performed to characterize the intercomplex excitation transfer network and explore the interplay between close-packing and light-harvesting efficiency. PMID:24896130

Chandler, Danielle E; Strümpfer, Johan; Sener, Melih; Scheuring, Simon; Schulten, Klaus

2014-06-01

78

Connecting photosynthetic light harvesting and charge separation at higher detail.  

PubMed

Beside the unique reaction center, efficient organismic photosynthesis requires additional arrays of chromophores to harvest photons and direct them by resonance energy transfer to the interspersed sites of charge separation. A crystal structure of the complex of a bacterial reaction center with light-harvesting complex I now reveals new details on how the storage ring interacts with and connects to the site of charge separation. PMID:24976042

Einsle, Oliver

2014-07-28

79

Self-Assembling Behavior and Inhibition Effect of Dodecanethiol Self-Assembled Monolayers on Copper Surface  

NASA Astrophysics Data System (ADS)

The self-assembling behavior and inhibition effect of dodecanethiol self-assembled monolayers (SAMs) on copper surface were investigated by atomic force microscopy (AFM) and electrochemical methods. The assembling process was monitored by AFM phase images. The assembling time influences the corrosion protection efficiency of dodecanethiol SAMs. Surface friction significantly decreases when the copper surface is covered by SAMs.

Zhang, Xiulan; Zhang, Heng; Yang, Yihong; Chen, Zhenyu

2013-08-01

80

Biomimetic Branched Hollow Fibers Templated by Self-assembled Fibrous Polyvinylpyrrolidone (PVP) Structures in Aqueous Solution  

PubMed Central

Branched hollow fibers are common in nature, but to form artificial fibers with a similar branched hollow structure is still a challenge. We discovered that polyvinylpyrrolidone (PVP) could self-assemble into branched hollow fibers in an aqueous solution after aging the PVP solution for about two weeks. Based on this finding, we demonstrated two approaches by which the self-assembly of PVP into branched hollow fibers could be exploited to template the formation of branched hollow inorganic fibers. First, inorganic material such as silica with high affinity against the PVP could be deposited on the surface of the branched hollow PVP fibers to form branched hollow silica fibers. To extend the application of PVP self-assembly in templating the formation of hollow branched fibers, we then adopted a second approach where the PVP molecules bound to inorganic nanoparticles (using gold nanoparticles as a model) co-self-assemble with the free PVP molecules in an aqueous solution, resulting in the formation of the branched hollow fibers with the nanoparticles embedded in the PVP matrix constituting the walls of the fibers. Heating the resultant fibers above the glass transition temperature of PVP led to the formation of branched hollow gold fibers. Our work suggests that the self-assembly of the PVP molecules in the solution can serve as a general method for directing the formation of branched hollow inorganic fibers. The branched hollow fibers may find potential applications in microfluidics, artificial blood vessel generation, and tissue engineering.

Qiu, Penghe; Mao, Chuanbin

2010-01-01

81

Molecular self-assembly on graphene.  

PubMed

The formation of ordered arrays of molecules via self-assembly is a rapid, scalable route towards the realization of nanoscale architectures with tailored properties. In recent years, graphene has emerged as an appealing substrate for molecular self-assembly in two dimensions. Here, the first five years of progress in supramolecular organization on graphene are reviewed. The self-assembly process can vary depending on the type of graphene employed: epitaxial graphene, grown in situ on a metal surface, and non-epitaxial graphene, transferred onto an arbitrary substrate, can have different effects on the final structure. On epitaxial graphene, the process is sensitive to the interaction between the graphene and the substrate on which it is grown. In the case of graphene that strongly interacts with its substrate, such as graphene/Ru(0001), the inhomogeneous adsorption landscape of the graphene moiré superlattice provides a unique opportunity for guiding molecular organization, since molecules experience spatially constrained diffusion and adsorption. On weaker-interacting epitaxial graphene films, and on non-epitaxial graphene transferred onto a host substrate, self-assembly leads to films similar to those obtained on graphite surfaces. The efficacy of a graphene layer for facilitating planar adsorption of aromatic molecules has been repeatedly demonstrated, indicating that it can be used to direct molecular adsorption, and therefore carrier transport, in a certain orientation, and suggesting that the use of transferred graphene may allow for predictible molecular self-assembly on a wide range of surfaces. PMID:24155272

MacLeod, J M; Rosei, F

2014-03-26

82

Self-assembly of compounds based on a glycerin skeleton as C-3 building block. Part II  

Microsoft Academic Search

Part I reviewed the properties of alkyl glyceryl ethers and their derivatives in forming self-assemblies such as liquid crystals.\\u000a Part II covers strategies for the synthesis of several types of artificial ether lipids with a glycerin backbone, such as\\u000a dicephalic surfactants, gemini surfactants, calamitic bola-amphiphiles, dendrimers, and membrane components of archaebacteria,\\u000a which have been reported to constitute unique self-assemblies useful

Kouichi Urata; Naotake Takaishi

2002-01-01

83

Self-assembly on "recordable CDs".  

PubMed

Gold substrates for self-assembly were constructed from recordable compact disks (CD-Rs) with simple and straight-forward wet-chemical treatment. In particular, they were made into desired sizes and shapes that satisfy different experimental needs. Self-assembled monolayers (SAMs) of long-chain alkanethiols (e.g., n-C18H37SH) adsorbed on gold substrates prepared from CD-Rs have been characterized by wetting measurements, electrochemistry, infrared (IR) spectroscopy, and scanning tunneling microscopy (STM). The results showed that there were no distinct differences in the quality and structure between these monolayers and SAMs formed on standard gold substrates (i.e., prepared from vacuum evaporation of pure gold onto glass slides). The present work demonstrates the applicability of recordable CDs as inexpensive, simple, and versatile gold substrates for self-assembly studies. PMID:11605856

Yu, H Z

2001-10-01

84

S-Layer Protein Self-Assembly  

PubMed Central

Crystalline S(urface)-layers are the most commonly observed cell surface structures in prokaryotic organisms (bacteria and archaea). S-layers are highly porous protein meshworks with unit cell sizes in the range of 3 to 30 nm, and thicknesses of ~10 nm. One of the key features of S-layer proteins is their intrinsic capability to form self-assembled mono- or double layers in solution, and at interfaces. Basic research on S-layer proteins laid foundation to make use of the unique self-assembly properties of native and, in particular, genetically functionalized S-layer protein lattices, in a broad range of applications in the life and non-life sciences. This contribution briefly summarizes the knowledge about structure, genetics, chemistry, morphogenesis, and function of S-layer proteins and pays particular attention to the self-assembly in solution, and at differently functionalized solid supports.

Pum, Dietmar; Toca-Herrera, Jose Luis; Sleytr, Uwe B.

2013-01-01

85

Self-assembly of peptides to nanostructures.  

PubMed

The formation of well-ordered nanostructures through self-assembly of diverse organic and inorganic building blocks has drawn much attention owing to their potential applications in biology and chemistry. Among all organic building blocks, peptides are one of the most promising platforms due to their biocompatibility, chemical diversity, and resemblance to proteins. Inspired by the protein assembly in biological systems, various self-assembled peptide structures have been constructed using several amino acids and sequences. This review focuses on this emerging area, the recent advances in peptide self-assembly, and formation of different nanostructures, such as tubular structures, fibers, vesicles, and spherical and rod-coil structures. While different peptide nanostructures have been discovered, potential applications are explored in drug delivery, tissue engineering, wound healing, and surfactants. PMID:24756480

Mandal, Dindyal; Nasrolahi Shirazi, Amir; Parang, Keykavous

2014-06-14

86

Self-Assembly Modularity and Physical Complexity  

NASA Astrophysics Data System (ADS)

Self-assembly is ubiquitous in physics, chemistry and biology, and has many applications in materials science and engineering. Here we present a general approach for finding the simplest set of building blocks that will assemble into a given physical structure. Our procedure can be adapted to any given geometry, and thus to any given type of physical system. The amount of information required to describe this simplest set of building blocks provides a quantitative measure of the structure's physical complexity, which is capable of detecting any symmetry or modularity in the underlying structure.We also introduce the notions of joint, mutual and conditional complexity for self-assembling structures. We illustrate our approach using self-assembling polyominoes, and demonstrate the breadth of its potential applications by using it to quantify the physical complexity of protein complexes.

Ahnert, S. E.

2012-12-01

87

Spatially controlled reversible colloidal self-assembly  

NASA Astrophysics Data System (ADS)

We studied the localized self-assembly of colloidal crystals on a topographically patterned substrate. A competition between particle and pattern interactions provided the ability to reversibly assemble quasi-two-dimensional colloidal crystals on a periodic landscape. The assembly process was visualized and controlled in real-space and real-time using video microscopy. Independent measurements and computer simulations were used to quantify all interactions controlling self-assembly. Steady-state studies characterized spatially inhomogeneous, coexisting fluid and crystal microstructures at various stages of assembly. Microstructures arise from a balance of local sedimentation equilibria within potential energy features and a tunable pairwise depletion attraction between colloids. Transient colloidal crystal self-assembly occurred via a quasiequilibrium process as characterized by continuously evolving spatial profiles of local density, bond orientational order, and self-diffusivities.

Fernandes, Gregory E.; Beltran-Villegas, Daniel J.; Bevan, Michael A.

2009-10-01

88

White-light-emitting self-assembled nanofibers and their evidence by microspectroscopy of individual objects.  

PubMed

The self-assembly of a blue-emitting light-harvesting organogelator and specifically designed highly fluorescent tetracenes yields nanofibers with tunable emissive properties. In particular, under near-UV excitation, white light emission is achieved in organogels and dry films of nanofibers. Confocal fluorescence microspectroscopy demonstrates that each individual nanofiber emits white light. A kinetic study shows that an energy transfer (ET) occurs between the blue-emitting anthracene derivative and the green- and red-emitting tetracenes, while inter-tetracene ETs also take place. Moreover, microscopy unravels that the nanofibers emit polarized emission in the blue spectral region, while at wavelengths higher than 500 nm the emission is not significantly polarized. PMID:21182256

Giansante, Carlo; Raffy, Guillaume; Schäfer, Christian; Rahma, Hakim; Kao, Min-Tzu; Olive, Alexandre G L; Del Guerzo, André

2011-01-19

89

Polystyrene Containing Self-Assembled Nanoribbons  

Microsoft Academic Search

Polystyrene Containing Self-Assembled Nanoribbons Leiming Li^a, John C. Stendahl^a, Eugene R. Zoubarev^a, Eli D. Sone^b, Martin U. Pralle^a, and Samuel I. Stupp^a,b,c ^aDepartment of Materials Science and Engineering, ^bDepartment of Chemistry, ^cMedical School, Northwestern University, Evanston, Illinois 60208 Small amounts, less than 1 weight synthesized in our laboratory and known as dendron rodcoils (DRCs) self-assemble into nanoribbons which in turn

Leiming Li; John Stendahl; Eugene Zoubarev; Eli Sone; Martin Pralle; Samuel Stupp

2001-01-01

90

Self-assembly of lithographically patterned nanoparticles  

PubMed Central

The construction of three dimensional (3D) objects, with any desired surface patterns, is both critical to and easily achieved in macroscale, science and engineering. However, on the nanoscale, 3D fabrication is limited to particles with only very limited surface patterning. Here, we demonstrate a self-assembly strategy that harnesses the strengths of well established 2D nanoscale patterning techniques and additionally enables the construction of stable 3D polyhedral nanoparticles. As a proof of the concept, we self-assembled cubic particles with sizes as small as 100 nm and with specific and lithographically defined surface patterns.

Cho, Jeong-Hyun; Gracias, David H.

2009-01-01

91

From Self-Assembled Vesicles to Protocells  

PubMed Central

Self-assembled vesicles are essential components of primitive cells. We review the importance of vesicles during the origins of life, fundamental thermodynamics and kinetics of self-assembly, and experimental models of simple vesicles, focusing on prebiotically plausible fatty acids and their derivatives. We review recent work on interactions of simple vesicles with RNA and other studies of the transition from vesicles to protocells. Finally we discuss current challenges in understanding the biophysics of protocells, as well as conceptual questions in information transmission and self-replication.

Chen, Irene A.; Walde, Peter

2010-01-01

92

From self-assembled vesicles to protocells.  

PubMed

Self-assembled vesicles are essential components of primitive cells. We review the importance of vesicles during the origins of life, fundamental thermodynamics and kinetics of self-assembly, and experimental models of simple vesicles, focusing on prebiotically plausible fatty acids and their derivatives. We review recent work on interactions of simple vesicles with RNA and other studies of the transition from vesicles to protocells. Finally we discuss current challenges in understanding the biophysics of protocells, as well as conceptual questions in information transmission and self-replication. PMID:20519344

Chen, Irene A; Walde, Peter

2010-07-01

93

Light harvesting complex II B850 excitation dynamics  

PubMed Central

The dynamics of excitation energy transfer within the B850 ring of light harvesting complex 2 from Rhodobacter sphaeroides and between neighboring B850 rings is investigated by means of dissipative quantum mechanics. The assumption of Boltzmann populated donor states for the calculation of intercomplex excitation transfer rates by generalized Förster theory is shown to give accurate results since intracomplex exciton relaxation to near-Boltzmann population exciton states occurs within a few picoseconds. The primary channels of exciton transfer between B850 rings are found to be the five lowest-lying exciton states, with non-850 nm exciton states making significant contributions to the total transfer rate.

Strumpfer, Johan; Schulten, Klaus

2009-01-01

94

Light harvesting complex II B850 excitation dynamics  

NASA Astrophysics Data System (ADS)

The dynamics of excitation energy transfer within the B850 ring of light harvesting complex 2 from Rhodobacter sphaeroides and between neighboring B850 rings is investigated by means of dissipative quantum mechanics. The assumption of Boltzmann populated donor states for the calculation of intercomplex excitation transfer rates by generalized Förster theory is shown to give accurate results since intracomplex exciton relaxation to near-Boltzmann population exciton states occurs within a few picoseconds. The primary channels of exciton transfer between B850 rings are found to be the five lowest-lying exciton states, with non-850 nm exciton states making significant contributions to the total transfer rate.

Strümpfer, Johan; Schulten, Klaus

2009-12-01

95

Self-assembled thin film chemical sensors  

SciTech Connect

This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Current chemical sensors suffer from poor molecular specificity, sensitivity, and stability and seldom have the recovery properties needed for real-time monitoring applications. We have employed self-assembly techniques to covalently bond species- selective reagents directly to the surface of the transducer so that analyte/reagent chemistry occurs at the interface between the transducer and the media to be monitored. The use of self-assembling monolayer and -multilayer (SAM) techniques results in stable sensing elements with optimal specificity built in through the use of reagents that have been designed for molecular recognition. Moreover, self-assembly chemistry applied to oxide surfaces allows flexible means of transduction spanning optical, electrochemical, mass-loading, and conduction methods. The work conducted on this project focused on demonstration of the methodology and the application to selected organic vapors (aromatic compounds and halogenated hydrocarbons). We have been able to develop a series of surface acoustic wave (SAW) sensors that are specific for aromatic compounds and halogenated hydrocarbons based on self-assembled thin films of cyclodextrins and calixarenes. Monolayers of seven different cyclodextrins and clixarenes have been attached to SAW transducers and their response to several organic molecules in the vapor phase have been measured. This preliminary data confirms the efficacy of this approach for real- time monitoring of hydrocarbons.

Swanson, B.; Li, DeQuan

1996-11-01

96

Colloidal self-assembly: Interlocked octapods  

NASA Astrophysics Data System (ADS)

Suspensions of octapod-shaped nanocrystals are seen to spontaneously interlock into chains, which in turn aggregate side-by-side to form three-dimensional crystals. The observed hierarchical self-assembly can be explained by the octapod's shape and the solvent-tunable van der Waals interactions.

Rupich, Sara M.; Talapin, Dmitri V.

2011-11-01

97

Polystyrene Containing Self-Assembled Nanoribbons  

NASA Astrophysics Data System (ADS)

Polystyrene Containing Self-Assembled Nanoribbons Leiming Li^a, John C. Stendahl^a, Eugene R. Zoubarev^a, Eli D. Sone^b, Martin U. Pralle^a, and Samuel I. Stupp^a,b,c ^aDepartment of Materials Science and Engineering, ^bDepartment of Chemistry, ^cMedical School, Northwestern University, Evanston, Illinois 60208 Small amounts, less than 1 weight synthesized in our laboratory and known as dendron rodcoils (DRCs) self-assemble into nanoribbons which in turn form gel-forming networks in organic solvents. The gels induced by self-assembly of DRCs are birefringent and the solvents include monomers such as styrene and 2-ethylhexyl methacrylate. The gels contain supramolecular ribbons that are approximately 10 nm wide, 2 nm thick, and 1 micron long. After polymerization of the gels, birefringent solids form which reveal enhanced chain orientation relative to pure polymer when samples are mechanically drawn under identical conditions. This difference was observed by both x-ray diffraction and optical measurements in samples containing polystyrene. Furthermore, small percentages of fluorescent dyes such as tetramethylrhodamine lead to drawn samples with enhanced photoluminescence anisotropy. The scaffolding of polystyrene or other polymers by the self-assembled nanoribbons and their networks could lead to enhancement of physical properties.

Li, Leiming; Stendahl, John; Zoubarev, Eugene; Sone, Eli; Pralle, Martin; Stupp, Samuel

2001-03-01

98

Self-assembly micro optical filter  

NASA Astrophysics Data System (ADS)

Optical communication and sensor industry face critical challenges in manufacturing for system integration. Due to the assembly complexity and integration platform variety, micro optical components require costly alignment and assembly procedures, in which many required manual efforts. Consequently, self-assembly device architectures have become a great interest and could provide major advantages over the conventional optical devices. In this paper, we discussed a self-assembly integration platform for micro optical components. To demonstrate the adaptability and flexibility of the proposed optical device architectures, we chose a commercially available MEMS fabrication foundry service - MUMPs (Multi-User MEMS Process). In this work, polysilicon layers of MUMPS are used as the 3-D structural material for construction of micro component framework and actuators. However, because the polysilicon has high absorption in the visible and near infrared wavelength ranges, it is not suitable for optical interaction. To demonstrate the required optical performance, hybrid integration of materials was proposed and implemented. Organic compound materials were applied on the silicon-based framework to form the required optical interfaces. Organic compounds provide good optical transparency, flexibility to form filters or lens and inexpensive manufacturing procedures. In this paper, we have demonstrated a micro optical filter integrated with self-assembly structures. We will discuss the self-assembly mechanism, optical filter designs, fabrication issues and results.

Zhang, Ping; Le, Kevin; Malalur-Nagaraja-Rao, Smitha; Hsu, Lun-Chen; Chiao, J.-C.

2006-01-01

99

The dynamics of nacre self-assembly  

Microsoft Academic Search

We show how nacre and pearl construction in bivalve and gastropod molluscs can be understood in terms of successive processes of controlled self-assembly from the molecular- to the macro-scale. This dynamics involves the physics of the formation of both solid and liquid crystals and of membranes and fluids to produce a nanostructured hierarchically constructed biological composite of polysaccharides, proteins and

Julyan H. E. Cartwright; Antonio G. Checa

2007-01-01

100

Molecular Self-assembly for Organic Electronics  

NASA Astrophysics Data System (ADS)

Self-assembled thin films of novel organic molecules hold the promise of emerging technologies and applications ranging from sensors for biological applications to organic electronics and more efficient organic photovoltaics. Self-assembled monolayers (SAMs) form as a result of a delicate balance between competing molecule-substrate and intermolecular interactions. To control such self-assembly processes, it is mandatory to understand how this balance reflects onto the SAM's final structure. Here we present an ultra-high vacuum scanning tunneling microscopy (STM) study of the self-assembly of novel pentacene derivatives and functionalized fullerenes (F-C60) on metal surfaces. Pentacene is known to exhibit large carrier mobility and has been studied extensively as a semiconductor in organic thin film devices. However, it is subject to facile photo-oxidation that limits device lifetime. We recently synthesized novel pentacene derivatives that show a dramatically increased resistance to photo-oxidation. We identified 6,13-dichloropentacene as a promising candidate for organic electronics. On the compact surface of gold, 6,13-dichloropentacene forms self-assembled domains with various high symmetry orientations. The quality of the SAM is seem to dramatically improve when the 6,13-dichloropentacene are deposited on the (788) vicinal surface of gold where the presence of parallel atomic steps will select only one of the possible SAM orientations due to the molecule-step interaction. Thus we observe the formation of very large self-assembled 6,13-dichloropentacene monolayers with perfect single domain orientation. We have also studied the self-assembly of C60 functionalized with alkyl chains of various lengths (F-C60) on Ag(111). We find that as a function of the alkyl chain length various structures are forming, ranging from zigzag like to linear arrays of C60 fullerene cages. The symmetry and unit cell size of the F-C60 SAMs is dictated by the alkyl-surface and the intermolecular interactions. These results show that C60 molecules can be assembled in 2D and non-compact molecular arrays with a surface density controllable via appropriate chemical functionalization. Those structures show promise as candidates for selfassembled molecular junctions.

Wang, Jun; Kaur, Irvinder; Diaconescu, Bogdan; Jazdzyk, Mikael; Miller, Glen P.; Pohl, Karsten

2009-10-01

101

Self-assembled nanolaminate coatings (SV)  

SciTech Connect

Sandia National Laboratories (Sandia) and Lockheed Martin Aeronautics (LM Aero) are collaborating to develop affordable, self-assembled, nanocomposite coatings and associated fabrication processes that will be tailored to Lockheed Martin product requirements. The purpose of this project is to develop a family of self-assembled coatings with properties tailored to specific performance requirements, such as antireflective (AR) optics, using Sandia-developed self-assembled techniques. The project met its objectives by development of a simple and economic self-assembly processes to fabricate multifunctional coatings. Specifically, materials, functionalization methods, and associated coating processes for single layer and multiple layers coatings have been developed to accomplish high reflective coatings, hydrophobic coatings, and anti-reflective coatings. Associated modeling and simulations have been developed to guide the coating designs for optimum optical performance. The accomplishments result in significant advantages of reduced costs, increased manufacturing freedom/producibility, improved logistics, and the incorporation of new technology solutions not possible with conventional technologies. These self-assembled coatings with tailored properties will significantly address LMC's needs and give LMC a significant competitive lead in new engineered materials. This work complements SNL's LDRD and BES programs aimed at developing multifunctional nanomaterials for microelectronics and optics as well as structure/property investigations of self-assembled nanomaterials. In addition, this project will provide SNL with new opportunities to develop and apply self-assembled nanocomposite optical coatings for use in the wavelength ranges of 3-5 and 8-12 micrometers, ranges of vital importance to military-based sensors and weapons. The SANC technologies will be applied to multiple programs within the LM Company including the F-35, F-22, ADP (Future Strike Bomber, UAV, UCAV, etc.). The SANC technologies will establish LMA and related US manufacturing capability for commercial and military applications therefore reducing reliance on off-shore development and production of related critical technologies. If these technologies are successfully licensed, production of these coatings in manufactory will create significant technical employment opportunities.

Fan, H.

2012-03-01

102

Solvation Effects in Self-Assembled Systems  

SciTech Connect

Many types of self-assembly can be found in nature. They include crystallization, the formation of micelles, and the folding of proteins. Recently there has been much interest in pursuing nano-to-microscopically engineered materials by way of self-assembly on imprinted or templated surfaces. In all of these diverse cases, wetting plays a critical role in the assembly process. Wetting involves the interactions of the substrate or amphiphilic molecule or macromolecule with a solvent. In many self-assembled systems we find that the critical feature of the system is a substrate! or macromolecule with a both hydrophilic and hydrophobic nature. In this paper we discuss the wetting properties of a striped surface where the stripes represent alternating chemical characteristics. We show how the chemical heterogeneity affects the wetting properties of the surface (e.g. the static contact angle), and discuss the length limitations on the soft lithography approach. In this paper, the wetting of a chemically heterogeneous surface is studied using a nonlocal Density Functional Theory (DFT). The results for the heterogeneous surface model we discuss have immediate implications for soft-lithography by self-assembly. It also lends fundamental insight into the mechanisms controlling self-assembly of macromolecules. We present the results of nonlocal 2D DFT calculations on the wetting properties of chemically heterogeneous surfaces. These calculations showed complex density distributions and phase behavior as a result of the heterogeneity. The location of the wetting transition are found to be strongly dependent on the extent and strength of the heterogeneity, and complete wetting was suppressed altogether if the hydrophobic parts of the surface were large enough. In these cases, the condensed nanophase may crystallize if the hydrophilic surface-fluid interactions are strong enough. By exploring the phase space including strength of hydrophilic interactions and extent of chemical heterogeneity, an operational phase diagram was established that could be used for designing nanoscopically tailored devices and materials.

Frink, L.J.D.

1998-11-10

103

Self assembling phenylene vinylene materials and devices  

NASA Astrophysics Data System (ADS)

A new class of self assembling rodcoil molecules was recently synthesized and their solid state structure was rigorously characterized. These molecules have a triblock architecture with a rigid rod molecular compound coupled to a diblock coil composed of an oligomeric flexible spacer and a bulky coil. The molecular structure has integrated photonic properties resulting from phenylene vinylene segments in the rigid backbone of the rod segment. It has been found that these molecules aggregate spontaneously when cast from solution into discrete objects with dimensions on the order of a few nanometers. The driving force for this aggregation is the crystallization of rod segments. To probe structure-property relationships in these materials, piezoelectric measurements were carried out in films and spontaneous piezoelectric activity was demonstrated without prior poling procedures. Upon poling the net polarization was enhanced and piezoelectric activities equal to that of quartz were observed. By applying both positive and negative fields a hysteresis was observed suggesting that these materials exhibit ferroelectric character. Through novel synthesis a structure was synthesized in the author's laboratory modeled after the triblock but targeting a diode-like aggregate upon self assembly. The molecules contained emissive phenylene vinylene segments in the rod block and hole transporting triphenylamine groups in the coil. Through subsequent characterization it was shown that the formation of nanoaggregates is indeed governed by the molecular architecture rather than the specific chemical functions of the three molecular segments. Inspired by these supramolecular diodes, self assembled organic light emitting diodes were fabricated based on a different self assembly approach. Prior to annealing, electron microscopy clearly showed kinetically trapped phase separated films. However after annealing a bilayer arrangement was observed with the hole conducting oligomer on the hole injecting electrode and the emissive phenylene vinylene dendron segregated to the electron injecting metal, the desired self assembled state. (Abstract shortened by UMI.)

Pralle, Martin Ulrich

104

Regulation of photosystem I light harvesting by zeaxanthin.  

PubMed

In oxygenic photosynthetic eukaryotes, the hydroxylated carotenoid zeaxanthin is produced from preexisting violaxanthin upon exposure to excess light conditions. Zeaxanthin binding to components of the photosystem II (PSII) antenna system has been investigated thoroughly and shown to help in the dissipation of excess chlorophyll-excited states and scavenging of oxygen radicals. However, the functional consequences of the accumulation of the light-harvesting complex I (LHCI) proteins in the photosystem I (PSI) antenna have remained unclarified so far. In this work we investigated the effect of zeaxanthin binding on photoprotection of PSI-LHCI by comparing preparations isolated from wild-type Arabidopsis thaliana (i.e., with violaxanthin) and those isolated from the A. thaliana nonphotochemical quenching 2 mutant, in which violaxanthin is replaced by zeaxanthin. Time-resolved fluorescence measurements showed that zeaxanthin binding leads to a previously unrecognized quenching effect on PSI-LHCI fluorescence. The efficiency of energy transfer from the LHCI moiety of the complex to the PSI reaction center was down-regulated, and an enhanced PSI resistance to photoinhibition was observed both in vitro and in vivo. Thus, zeaxanthin was shown to be effective in inducing dissipative states in PSI, similar to its well-known effect on PSII. We propose that, upon acclimation to high light, PSI-LHCI changes its light-harvesting efficiency by a zeaxanthin-dependent quenching of the absorbed excitation energy, whereas in PSII the stoichiometry of LHC antenna proteins per reaction center is reduced directly. PMID:24872450

Ballottari, Matteo; Alcocer, Marcelo J P; D'Andrea, Cosimo; Viola, Daniele; Ahn, Tae Kyu; Petrozza, Annamaria; Polli, Dario; Fleming, Graham R; Cerullo, Giulio; Bassi, Roberto

2014-06-10

105

Hierarchical molecular self-assemblies: construction and advantages.  

PubMed

Hierarchical molecular self-assembly offers many exotic and complicated nanostructures which are of interest in nanotechnology and material science. In the past decade, various strategies leading to hierarchical molecular self-assemblies have been developed. In this review we summarize the recent advances in the creation and application of solution-based self-assembled nanostructures that involve more than one level of arrangement of building blocks. The strategies for construction hierarchical self-assembled structures and the advantages brought up by these assemblies are focused on. The following contents are included: (1) general approaches to fabricate hierarchical self-assembly, including self-assemblies based on supramolecules and specially designed block copolymers; (2) the advantages brought about by the hierarchical self-assembly, including the fabrication of special self-assembled structures, rich responsiveness to external stimuli, and the materials' performance. PMID:24806718

Wang, Andong; Huang, Jianbin; Yan, Yun

2014-05-21

106

Self-assembling membranes and related methods thereof  

SciTech Connect

The present invention relates to self-assembling membranes. In particular, the present invention provides self-assembling membranes configured for securing and/or delivering bioactive agents. In some embodiments, the self-assembling membranes are used in the treatment of diseases, and related methods (e.g., diagnostic methods, research methods, drug screening).

Capito, Ramille M; Azevedo, Helena S; Stupp, Samuel L

2013-08-20

107

Modeling coherent excitation energy transfer in photosynthetic light harvesting systems  

NASA Astrophysics Data System (ADS)

Recent non-linear spectroscopy experiments suggest the excitation energy transfer in some biological light harvesting systems initially occurs coherently. Treating such processes brings significant challenge for conventional theoretical tools that usually involve different approximations. In this dissertation, the recently developed Iterative Linearized Density Matrix (ILDM) propagation scheme, which is non-perturbative and non-Markovian is extended to study coherent excitation energy transfer in various light harvesting complexes. It is demonstrated that the ILDM approach can successfully describe the coherent beating of the site populations on model systems and gives quantitative agreement with both experimental results and the results of other theoretical methods have been developed recently to going beyond the usual approximations, thus providing a new reliable theoretical tool to study this phenomenon. This approach is used to investigate the excited energy transfer dynamics in various experimentally studied bacteria light harvesting complexes, such as Fenna-Matthews-Olsen (FMO) complex, Phycocyanin 645 (PC645). In these model calculations, quantitative agreement is found between computed de-coherence times and quantum beating pattens observed in the non-linear spectroscopy. As a result of these studies, it is concluded that the stochastic resonance behavior is important in determining the optimal throughput. To begin addressing possible mechanics for observed long de-coherence time, various models which include correlation between site energy fluctuations as well as correlation between site energy and inter-site coupling are developed. The influence of both types of correlation on the coherence and transfer rate is explored using with a two state system-bath hamiltonian parametrized to model the reaction center of Rhodobacter sphaeroides bacteria. To overcome the disadvantages of a fully reduced approach or a full propagation method, a brownian dynamics method is developed that only treats those degrees of freedom which directly couple to quantum systems and hence maintain the non-Markovian nature of the dynamics in contrast to the fully reduced master equation. This brownian dynamics approach has a significant reduced computational cost compared with ILDM propagation. The algorithm is tested with a spin-boson-global bath model, and shows potential for capturing non-markovian features that will be lost with a fully reduced master equation description of the excitation energy transfer.

Huo, Pengfei

108

Self-assembled tunable photonic hyper-crystals  

PubMed Central

We demonstrate a novel artificial optical material, the “photonic hyper-crystal”, which combines the most interesting features of hyperbolic metamaterials and photonic crystals. Similar to hyperbolic metamaterials, photonic hyper-crystals exhibit broadband divergence in their photonic density of states due to the lack of usual diffraction limit on the photon wave vector. On the other hand, similar to photonic crystals, hyperbolic dispersion law of extraordinary photons is modulated by forbidden gaps near the boundaries of photonic Brillouin zones. Three dimensional self-assembly of photonic hyper-crystals has been achieved by application of external magnetic field to a cobalt nanoparticle-based ferrofluid. Unique spectral properties of photonic hyper-crystals lead to extreme sensitivity of the material to monolayer coatings of cobalt nanoparticles, which should find numerous applications in biological and chemical sensing.

Smolyaninova, Vera N.; Yost, Bradley; Lahneman, David; Narimanov, Evgenii E.; Smolyaninov, Igor I.

2014-01-01

109

Self-assembled tunable photonic hyper-crystals.  

PubMed

We demonstrate a novel artificial optical material, the "photonic hyper-crystal", which combines the most interesting features of hyperbolic metamaterials and photonic crystals. Similar to hyperbolic metamaterials, photonic hyper-crystals exhibit broadband divergence in their photonic density of states due to the lack of usual diffraction limit on the photon wave vector. On the other hand, similar to photonic crystals, hyperbolic dispersion law of extraordinary photons is modulated by forbidden gaps near the boundaries of photonic Brillouin zones. Three dimensional self-assembly of photonic hyper-crystals has been achieved by application of external magnetic field to a cobalt nanoparticle-based ferrofluid. Unique spectral properties of photonic hyper-crystals lead to extreme sensitivity of the material to monolayer coatings of cobalt nanoparticles, which should find numerous applications in biological and chemical sensing. PMID:25027947

Smolyaninova, Vera N; Yost, Bradley; Lahneman, David; Narimanov, Evgenii E; Smolyaninov, Igor I

2014-01-01

110

Directed Self-Assembly: Expectations and Achievements  

NASA Astrophysics Data System (ADS)

Nanotechnology has been a revolutionary thrust in recent years of development of science and technology for its broad appeal for employing a novel idea for relevant technological applications in particular and for mass-scale production and marketing as common man commodity in general. An interesting aspect of this emergent technology is that it involves scientific research community and relevant industries alike. Top-down and bottom-up approaches are two broad division of production of nanoscale materials in general. However, both the approaches have their own limits as far as large-scale production and cost involved are concerned. Therefore, novel new techniques are desired to be developed to optimize production and cost. Directed self-assembly seems to be a promising technique in this regard; which can work as a bridge between the top-down and bottom-up approaches. This article reviews how directed self-assembly as a technique has grown up and outlines its future prospects.

Kumar, Prashant

2010-09-01

111

Directed Self-Assembly: Expectations and Achievements  

PubMed Central

Nanotechnology has been a revolutionary thrust in recent years of development of science and technology for its broad appeal for employing a novel idea for relevant technological applications in particular and for mass-scale production and marketing as common man commodity in general. An interesting aspect of this emergent technology is that it involves scientific research community and relevant industries alike. Top–down and bottom–up approaches are two broad division of production of nanoscale materials in general. However, both the approaches have their own limits as far as large-scale production and cost involved are concerned. Therefore, novel new techniques are desired to be developed to optimize production and cost. Directed self-assembly seems to be a promising technique in this regard; which can work as a bridge between the top–down and bottom–up approaches. This article reviews how directed self-assembly as a technique has grown up and outlines its future prospects.

2010-01-01

112

Self-Assembled Colloidal Superparticles from Nanorods  

NASA Astrophysics Data System (ADS)

Colloidal superparticles are nanoparticle assemblies in the form of colloidal particles. The assembly of nanoscopic objects into mesoscopic or macroscopic complex architectures allows bottom-up fabrication of functional materials. We report that the self-assembly of cadmium selenide-cadmium sulfide (CdSe-CdS) core-shell semiconductor nanorods, mediated by shape and structural anisotropy, produces mesoscopic colloidal superparticles having multiple well-defined supercrystalline domains. Moreover, functionality-based anisotropic interactions between these CdSe-CdS nanorods can be kinetically introduced during the self-assembly and, in turn, yield single-domain, needle-like superparticles with parallel alignment of constituent nanorods. Unidirectional patterning of these mesoscopic needle-like superparticles gives rise to the lateral alignment of CdSe-CdS nanorods into macroscopic, uniform, freestanding polymer films that exhibit strong photoluminescence with a striking anisotropy, enabling their use as downconversion phosphors to create polarized light-emitting diodes.

Wang, Tie; Zhuang, Jiaqi; Lynch, Jared; Chen, Ou; Wang, Zhongliang; Wang, Xirui; LaMontagne, Derek; Wu, Huimeng; Wang, Zhongwu; Cao, Y. Charles

2012-10-01

113

Perspective: Detecting and measuring exciton delocalization in photosynthetic light harvesting.  

PubMed

Photosynthetic units perform energy transfer remarkably well under a diverse range of demanding conditions. However, the mechanism of energy transfer, from excitation to conversion, is still not fully understood. Of particular interest is the possible role that coherence plays in this process. In this perspective, we overview photosynthetic light harvesting and discuss consequences of excitons for energy transfer and how delocalization can be assessed. We focus on challenges such as decoherence and nuclear-coordinate dependent delocalization. These approaches complement conventional spectroscopy and delocalization measurement techniques. New broadband transient absorption data may help uncover the difference between electronic and vibrational coherences present in two-dimensional electronic spectroscopy data. We describe how multipartite entanglement from quantum information theory allows us to formulate measures that elucidate the delocalization length of excitation and the details of that delocalization even from highly averaged information such as the density matrix. PMID:24655162

Scholes, Gregory D; Smyth, Cathal

2014-03-21

114

Maximizing omnidirectional light harvesting in metal oxide hyperbranched array architectures.  

PubMed

The scrupulous design of nanoarchitectures and smart hybridization of specific active materials are closely related to the overall photovoltaic performance of an anode electrode. Here we present a solution-based strategy for the fabrication of well-aligned metal oxide-based nanowire-nanosheet-nanorod hyperbranched arrays on transparent conducting oxide substrates. For these hyperbranched arrays, we observe a twofold increment in dye adsorption and enhanced light trapping and scattering capability compared with the pristine titanium dioxide nanowires, and thus a power conversion efficiency of 9.09% is achieved. Our growth approach presents a strategy to broaden the photoresponse and maximize the light-harvesting efficiency of arrays architectures, and may lead to applications for energy conversion and storage, catalysis, water splitting and gas sensing. PMID:24874204

Wu, Wu-Qiang; Feng, Hao-Lin; Rao, Hua-Shang; Xu, Yang-Fan; Kuang, Dai-Bin; Su, Cheng-Yong

2014-01-01

115

Perspective: Detecting and measuring exciton delocalization in photosynthetic light harvesting  

NASA Astrophysics Data System (ADS)

Photosynthetic units perform energy transfer remarkably well under a diverse range of demanding conditions. However, the mechanism of energy transfer, from excitation to conversion, is still not fully understood. Of particular interest is the possible role that coherence plays in this process. In this perspective, we overview photosynthetic light harvesting and discuss consequences of excitons for energy transfer and how delocalization can be assessed. We focus on challenges such as decoherence and nuclear-coordinate dependent delocalization. These approaches complement conventional spectroscopy and delocalization measurement techniques. New broadband transient absorption data may help uncover the difference between electronic and vibrational coherences present in two-dimensional electronic spectroscopy data. We describe how multipartite entanglement from quantum information theory allows us to formulate measures that elucidate the delocalization length of excitation and the details of that delocalization even from highly averaged information such as the density matrix.

Scholes, Gregory D.; Smyth, Cathal

2014-03-01

116

Self-Assembly of Paired Nanoribbons  

Microsoft Academic Search

Self-assembly of surface phase domains is a promising route to fabricate stable nanometer-scale structures. This Letter reports a novel labyrinth structure of orthogonal nanoscale ribbons of Cu4Pb3 ordered-alloy on Cu(100) formed by electrochemical deposition. The labyrinth develops as loops of Cu4Pb3 ribbons elongate as closely spaced paired stripes. The structure is explained in terms of elastic interactions between anisotropic surface

R. V. Kukta; N. Vasiljevic; N. Dimitrov; K. Sieradzki

2005-01-01

117

Self-assembly of tubular fullerenes  

Microsoft Academic Search

Carbon nanotubes in the form of multiwalled fullerenes are shown here to self-assemble under homogeneous gas-phase conditions of carbon condensation in an inert atmosphere heated to 1200$DGR@C-conditions previously thought to be optimal only for the annealing and growth of Cââ and other spheroidal shells. Tubular fullerenes are known to be less stable than their spheroidal counterparts and have thus far

Ting Guo; P. Nikolaev; A. G. Rinzler; Daniel T. Colbert; Richard E. Smalley; D. Tomanek

1995-01-01

118

Single photon ionisation of self assembled monolayers  

NASA Astrophysics Data System (ADS)

Self assembled monolayers formed from benzenethiol, diphenylsulphide and diphenyldisulphide have been analysed using secondary ion mass spectrometry (SIMS), sputter neutral mass spectrometry (SNMS) and laser desorption photoionisation mass spectrometry (LDPI). The peak corresponding to the parent ion was much stronger in LDPI than with SIMS or SNMS analysis and fragmentation was lower. A useful yield of order 0.5% was obtained for LDPI from diphenyldisulphide.

King, B. V.; Savina, M. R.; Tripa, C. E.; Calaway, W. F.; Veryovkin, I. V.; Moore, J. F.; Pellin, M. J.

2002-05-01

119

Computability and Complexity in Self-assembly  

Microsoft Academic Search

This paper explores the impact of geometry on computability and complexity in Winfree’s model of nanoscale self-assembly.\\u000a We work in the two-dimensional tile assembly model, i.e., in the discrete Euclidean plane ?×?. Our first main theorem says\\u000a that there is a roughly quadratic function f such that a set A??+ is computably enumerable if and only if the set X

James I. Lathrop; Jack H. Lutz; Matthew J. Patitz; Scott M. Summers

2011-01-01

120

Computability and Complexity in Self-assembly  

Microsoft Academic Search

This paper explores the impact of geometry on computability and complexity in Winfree's model of nanoscale self-assembly. We work in the two-dimensional tile assembly model, i.e., in the discrete Euclidean plane Z×Z. Our first main theorem says that there is a roughly quadratic function f such that a set AZ+ is computably enumerable if and only if the set XA

James I. Lathrop; Jack H. Lutz; Matthew J. Patitz; Scott M. Summers

2008-01-01

121

Remembrances of self-assemblies past.  

PubMed

Research on four types of self-assemblies (micelles, coacervates, gels, and vesicles) is discussed via a particular investigative methodology (in order of appearance): kinetics, dynamic NMR, PGSE-NMR, double-(13)C labeling, molecular dynamics computations, phase diagrams, cryo-HRSEM, rheology, light/electron microscopy, electrophoretic mobility, electroformation, confocal microscopy, and calorimetry. The emphasis here is on how a given method, each in its own special way, illuminates a complex system. PMID:20945842

Menger, Fredric M

2011-05-01

122

Polymer Self-assembly on Carbon Nanotubes  

NASA Astrophysics Data System (ADS)

This chapter analyses the poly(3-hexylthiophene) self-assembly on carbon nanotubes and the interaction between the two materials forming a new hybrid nanostructure. The chapter starts with a review of the several studies investigating polymers and biomolecules self-assembled on nanotubes. Then conducting polymers and polythiophenes are briefly introduced. Accordingly, carbon nanotube structure and properties are reported in Sect. 3. The experimental section starts with the bulk characterisation of polymer thin films with the inclusion of uniformly distributed carbon nanotubes. By using volume film analysis techniques (AFM, TEM, UV-Vis and Raman), we show how the polymer's higher degree of order is a direct consequence of interaction with carbon nanotubes. Nevertheless, it is through the use of nanoscale analysis and molecular dynamic simulations that the self-assembly of the polymer on the nanotube surface can be clearly evidenced and characterised. In Sect. 6, the effect of the carbon templating structure on the P3HT organisation on the surface is investigated, showing the chirality-driven polymer assembly on the carbon nanotube surface. The interaction between P3HT and CNTs brings also to charge transfer, with the modification of physical properties for both species. In particular, the alteration of the polymer electronic properties and the modification of the nanotube mechanical structure are a direct consequence of the P3HT ?-? stacking on the nanotube surface. Finally, some considerations based on molecular dynamics studies are reported in order to confirm and support the experimental results discussed.

Giulianini, Michele; Motta, Nunzio

123

Approximate Self-assembly of the Sierpinski Triangle  

NASA Astrophysics Data System (ADS)

Winfree introduced the Tile Assembly Model in order to study the nanoscale self-assembly of DNA crystals. Lathrop, Lutz, and Summers proved that the Sierpinski triangle S cannot self-assemble in the "strict" sense in which tiles are not allowed to appear at positions outside the target structure. Here we investigate the strict self-assembly of sets that approximate S. We show that every set that does strictly self-assemble disagrees with S on a set with fractal dimension at least that of S (? 1.585), and that no subset of S with fractal dimension greater than 1 strictly self-assembles. We show that our bounds are tight by presenting a strict self-assembly that adds communication fibers to the fractal structure without disturbing it. To verify this strict self-assembly we develop a generalization of the local determinism method of Soloveichik and Winfree to tile assembly systems that use a blocking technique.

Lutz, Jack H.; Shutters, Brad

124

Self-assembly of azide containing dipeptides.  

PubMed

Functional structures and materials are formed spontaneously in nature through the process of self-assembly. Mimicking this process in vitro will lead to the formation of new substances that would impact many areas including energy production and storage, biomaterials and implants, and drug delivery. The considerable structural diversity of peptides makes them appealing building blocks for self-assembly in vitro. This paper describes the self-assembly of three aromatic dipeptides containing an azide moiety: H-Phe(4-azido)-Phe(4-azido)-OH, H-Phe(4-azido)-Phe-OH, and H-Phe-Phe(4-azido)-OH. The peptide H-Phe(4-azido)-Phe(4-azido)-OH self-assembled into porous spherical structures, whereas the peptides H-Phe(4-azido)-Phe-OH and H-Phe-Phe(4-azido)-OH did not form any ordered structures under the examined experimental conditions. The azido group of the peptide can serve as a photo cross-linking agent upon irradiation with UV light. To examine the effect of this group and its activity on the self-assembled structures, we irradiated the assemblies in solution for different time periods. Using electron microscopy, we determined that the porous spherical assemblies formed by the peptide H-Phe(4-azido)-Phe(4-azido)-OH underwent a structural change upon irradiation. In addition, using FT-IR, we detected the chemical change of the peptide azido group. Moreover, using indentation experiments with atomic force microscopy, we showed that the Young's modulus of the spherical assemblies increased after 20?min of irradiation with UV light. Overall, irradiating the solution of the peptide assemblies containing the azido group resulted in a change both in the morphology and mechanical properties of the peptide-based structures. These ordered assemblies or their peptide monomer building blocks can potentially be incorporated into other peptide assemblies to generate stiffer and more stable materials. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd. PMID:24889029

Yuran, Sivan; Razvag, Yair; Das, Priyadip; Reches, Meital

2014-07-01

125

Characterization of circular differential selective scattering in randomly and magnetically oriented chloroplasts and light harvesting chlorophyll a/b aggregates  

SciTech Connect

Comparative circular dichroism studies were carried out in chloroplasts and the aggregated chlorophyll a/b light harvesting pigment protein complex (LHC). Much of the intense circular dichroism (CD) signal of chloroplasts and that of aggregated, isolated LHC were found to originate in circular differential light scattering (CDS). The difference spectra obtained between the CD spectra of randomly and magnetically oriented thylakoids resembled the selective light scattering spectra of chloroplasts. Furthermore, orientation-dependent changes in the CDS signal outside the principal absorbance bands were correlated with changes in the non-selective forward light scattering. These results provide evidence of a significant contribution by CDS to the CD spectrum of chloroplasts. A comparison between the CD signals of chloroplasts and aggregated LHC revealed that both preparations exhibit ''anomalous'' CD bands. The spectral shape and amplitude of these bands are changed dramatically upon magnetic alignment of the particles. These similarities are suggestive of the existence of similar helical domains in chloroplasts and the isolated LHC aggregate; hence our experimental results support the hypothesis of Faludi-Daniel and Mustardy that the LHC in the thylakoid membrane is aggregated in a liquid crystal-like structure resembling that which self-assembles in vitro. 17 refs., 4 figs.

Garab, G.; Faludi-Daniel, A.; Sutherland, J.C.; Hind, G.

1986-01-01

126

Integrated Nanosystems Templated by Self-assembled Virus Capsids  

NASA Astrophysics Data System (ADS)

This dissertation presents the synthesis and modeling of multicomponent nanosystems templated by self-assembled virus capsids. The design principles, synthesis, analysis, and future directions for these capsid-based materials are presented. Chapter 1 gives an overview of the literature on the application of virus capsids in constructing nanomaterials. The uses of capsids in three main areas are considered: (1) as templates for inorganic materials or nanoparticles; (2) as vehicles for biological applications like medical imaging and treatment; and (3) as scaffolds for catalytic materials. In light of this introduction, an overview of the material in this dissertation is described. Chapters 2-4 all describe integrated nanosystems templated by bacteriophage MS2, a spherical icosahedral virus capsid. MS2 possesses an interior and exterior surface that can be modified orthogonally using bioconjugation chemistry to create multivalent, multicomponent constructs with precise localization of components attached to the capsid proteins. Chapter 2 describes the use of MS2 to synthesize a photocatalytic construct by modifying the internal surface with sensitizing chromophores and the external surface with a photocatalytic porphyrin. The chromophores absorbed energy that the porphyrin could not, and transferred it to the porphyrin via FRET through the protein shell. The porphyrin was then able to utilize the energy to carry out photocatalysis at new wavelengths. In Chapter 3, porphyrins were installed on the interior surface of MS2 and DNA aptamers specific for Jurkat leukemia T cells on the exterior surface. The dual-modified capsids were able to bind to Jurkat cells, and upon illumination the porphyrins generated singlet oxygen to kill them selectively over non-targeted cells. Chapter 4 explores integrating MS2 with DNA origami in order to arrange the capsids at larger length scales. Capsids modified with fluorescent dyes inside and single-stranded DNA outside were able to bind to origami tiles bearing complementary DNA probes. The tiles could then be used to arrange the capsids in a one-dimensional array with dimensions far exceeding those of individual MS2 particles. In Chapter 5, the use of a different capsid, that of the tobacco mosaic virus (TMV) is described. The defect tolerance of light harvesting systems built using TMV as a scaffold was investigated using a kinetic Monte Carlo model to simulate the energy transfer processes. The results of the simulation were used to understand and explain experimental results obtained from the system.

Stephanopoulos, Nicholas

127

Self-assembled nanostructure of Au nanoparticles on a self-assembled monolayer  

Microsoft Academic Search

We investigated self-assembled nanostructure of Au nanoparticles (AuNPs) on a dithiol-inserted self-assembled monolayer (SAM) using scanning tunneling microscopy (STM). Phosphine-stabilized AuNPs were immobilized on the SAM covering an Au(111) surface by the dithiol anchoring bridges. The phosphine-stabilized AuNPs were transformed to dithiol-stabilized AuNPs by a ligand exchange reaction. The additional phosphine-stabilized AuNPs were attached to the dithiol-stabilized AuNPs on the

Satoshi Wakamatsu; Jun-ichi Nakada; Shintaro Fujii; Uichi Akiba; Masamichi Fujihira

2005-01-01

128

Experimental studies and numerical simulations on light-harvesting devices  

NASA Astrophysics Data System (ADS)

Obtaining high solar energy conversion efficiencies with materials that require minimal processing or refining is critical to next generation light-harvesting systems. Organic dyes and inorganic nanostructured semiconductors are two material types that address this need and are studied herein. Two sets of organic chromophore systems were characterized. First, triarylamine multi-chromophore dendrimers with purposely designed biphenyl-based trap sites were investigated using fluorescence upconversion spectroscopy. A rise in the fluorescence from the biphenyl site after the excitation pulse demonstrated that excitons were trapped with 99% efficiency. These data show that excitons can be directed to a specific site in a molecular chromophore. Separately, thiophene macrocycles were investigated to determine if molecular systems could show high energetic degeneracy. The chromophore coupling constants of two thiophene rings were quantified using time-resolved fluorescence anisotropy measurements. The calculated chromophore coupling constants for the cyclic system were an order of magnitude higher than linear chains. In addition, the cyclic system had a two photon absorption cross section of 1470 GM, which is over a thousand times greater than the linear chain and useful for applications in imaging and lithography. Nanostructured inorganic semiconductors were also the subject of study. In one set of experiments, the first example of macroporous p-GaP(100) was reported and its ability to perform photosynthetic water splitting was demonstrated and assessed. Macroporous films were prepared using a two-electrode cell with a halogen acid electrolyte and pulsed anodic etching voltage waveform. Control over the macroporous film morphology was explored by varying halogen acid type, concentration, and etching voltage. Macroporous p-GaP has applications in photonic and light-harvesting systems. To this end, the relationship between optoelectronic properties and the obtainable solar energy conversion efficiency was determined in nanostructured semiconductors. The photocurrent-potential response of lightly and heavily doped silicon nanowires were quantified, with the heavily doped semiconductors demonstrating superior energy conversion. For low dopant density nanowires, the low energy conversion efficiencies were attributed to a lack of an internal electric field, which resulted in a high majority carrier recombination at the interface. These data provide design principles for efficient solar energy conversion systems based on nanostructured semiconductors.

Hagedorn, Kevin V.

129

A Clustering Algorithm Based on the Ants Self-Assembly Behavior  

Microsoft Academic Search

\\u000a We have presented in this paper an ants based clustering algorithm which is inspired from the self-assembling behavior observed\\u000a in real ants. These ants progressively become connected to an initial point called the support and then successively to other\\u000a connected ants. The artificial ants that we have defined similarly build a tree where each ant represents a node\\/data. Ants\\u000a use

Hanene Azzag; Nicolas Monmarché; Mohamed Slimane; Christiane Guinot; Gilles Venturini

2003-01-01

130

Self-Assembly of Paired Nanoribbons  

NASA Astrophysics Data System (ADS)

Self-assembly of surface phase domains is a promising route to fabricate stable nanometer-scale structures. This Letter reports a novel labyrinth structure of orthogonal nanoscale ribbons of Cu4Pb3 ordered-alloy on Cu(100) formed by electrochemical deposition. The labyrinth develops as loops of Cu4Pb3 ribbons elongate as closely spaced paired stripes. The structure is explained in terms of elastic interactions between anisotropic surface stress domains, wherein stripes of different phase variants form attractive dipoles. An energetic analysis determines the physical conditions necessary for the structure to form.

Kukta, R. V.; Vasiljevic, N.; Dimitrov, N.; Sieradzki, K.

2005-10-01

131

Self-assembled nanoparticle antiglare coatings.  

PubMed

Here we report a simple and scalable bottom-up technology for assembling close-packed nanoparticle monolayers on both sides of a glass substrate as high-quality antiglare coatings. Optical measurements show that monolayer coatings consisting of 110 nm silica nanoparticles can significantly reduce optical reflectance and enhance specular transmittance of the glass substrate for a broad range of visible wavelengths. Both experiments and numerical simulations reveal that the antiglare properties of the self-assembled colloidal monolayers are significantly affected by the size of the colloidal particles. PMID:23114302

Askar, Khalid; Phillips, Blayne M; Dou, Xuan; Lopez, Juan; Smith, Carl; Jiang, Bin; Jiang, Peng

2012-11-01

132

Wettability of azobenzene self-assembled monolayers.  

PubMed

The wettability properties of azobenzene self-assembled monolayers (SAMs), in the trans and cis forms, are investigated herein by classical Molecular Dynamics simulations of validated assembly structures described with a dedicated force field. The two different methodologies used for the calculation of the contact angle, one based on the Young's equation and the other on geometrical models, have provided a consistent description of the SAMs wettability in line with available experimental results. Furthermore, we provide an atomistic description of the first layers of water molecules at the solvent-SAM interface, which rationalizes the wettability difference between the cis- and trans-SAMs. PMID:24673397

Pipolo, Silvio; Corni, Stefano

2014-04-22

133

REVIEW ARTICLE: Self-assembly on silicon carbide nanomesh templates  

NASA Astrophysics Data System (ADS)

Well-ordered two-dimensional functional nanostructure arrays have a broad range of potential applications in molecular electronics, ultra-high density data storage, biosensors, single-electron, single-photon and quantum computation devices. Various surface nanotemplates that are naturally or artificially patterned at the nanometre scale have been used to guide the formation of highly periodic nanostructure arrays. In this paper, we review recent progress in the development of various surface nanotemplates as well as the self-assembly of nanostructures on them, with particular emphasis on the unique SiC nanomesh template. The formation mechanism of this nanomesh template is attributed to the self-assembly of accumulated carbon atoms into well-ordered honeycomb superstructures at the nanometre scale on the 6H-SiC(0 0 0 1) surface. The size and spacing of unit cells of the SiC nanomesh can be tailored in the 2-2.5 nm range by adjusting the annealing time. This nanomesh is demonstrated to be an effective template for the formation of well-ordered molecular arrays of copper(II) phthalocyanine (CuPc). The growth of C60 on the nanomesh follows a typical Stranski-Krastanov mode, and a complete C60 wetting monolayer can be epitaxially grown on this nanotemplate. It is effective in isolating metal nanoclusters, resulting in the formation of monodispersed Co nanoclusters with a narrow size distribution. The adsorption and desorption of Co nanoclusters and C60 do not change its atomic structure, making it a chemically and thermally stable nanotemplate for the formation of well-ordered nanostructures arrays as well as monodispersed metal nanoclusters.

Chen, Wei; Thye Shen Wee, Andrew

2007-10-01

134

Electron transport and light-harvesting switches in cyanobacteria.  

PubMed

Cyanobacteria possess multiple mechanisms for regulating the pathways of photosynthetic and respiratory electron transport. Electron transport may be regulated indirectly by controlling the transfer of excitation energy from the light-harvesting complexes, or it may be more directly regulated by controlling the stoichiometry, localization, and interactions of photosynthetic and respiratory electron transport complexes. Regulation of the extent of linear vs. cyclic electron transport is particularly important for controlling the redox balance of the cell. This review discusses what is known of the regulatory mechanisms and the timescales on which they occur, with particular regard to the structural reorganization needed and the constraints imposed by the limited mobility of membrane-integral proteins in the crowded thylakoid membrane. Switching mechanisms requiring substantial movement of integral thylakoid membrane proteins occur on slower timescales than those that require the movement only of cytoplasmic or extrinsic membrane proteins. This difference is probably due to the restricted diffusion of membrane-integral proteins. Multiple switching mechanisms may be needed to regulate electron transport on different timescales. PMID:24478787

Mullineaux, Conrad W

2014-01-01

135

Quantifying the quantum correlations in light-harvesting complexes  

NASA Astrophysics Data System (ADS)

Biological systems have been of recent interest for the role that quantum correlations may play for functionality or in evolution. One such biological phenomenon under study is the photosynthesis of certain organisms, for instance low light adapted green sulfur bacteria. The Fenna-Matthews-Olson (FMO) protein complex is a biological light harvesting complex that is found in such systems. It has drawn considerable attention as a template to understand the role of quantum correlations. Many measures exist that can be employed to characterize quantum correlations. One such measure, quantum discord, captures all non-classical correlations that are present in the system. Since discord may be robust against various models of decoherence, there is further interest in understanding whether there is quantum discord present in the FMO complex. The first picosecond is relevant for the transfer of excitation. We study many related measures of quantum correlations such as quantum discord, mutual information and relative entropy of entanglement to understand the nature of correlations and the timescales over which they persist in the FMO complex.

Vinjanampathy, Sai; Bradler, Kamil; Wilde, Mark; Uskov, Dimitri

2010-03-01

136

Energy transfer between two aggregates in light-harvesting complexes  

NASA Astrophysics Data System (ADS)

Energy transfer processes between two aggregates in a coupled chromophoric-pigment (protein) system are studied via the standard master equation approach. Each pigment of the two aggregates is modeled as a two-level system. The excitation energy is assumed to be transferred from the donor aggregate to the acceptor aggregate. The model can be used to theoretically simulate many aspects of light-harvesting complexes (LHCs). By applying the real bio-parameters of photosynthesis, we numerically investigate the efficiency of energy transfer (EET) between the two aggregates in terms of some factors, e.g., the initial coherence of the donor aggregate, the coupling strengthes between the two aggregates and between different pigments, and the effects of noise from the environment. Our results provide evidence for that the actual numbers of pigments in the chromophoric rings of LHCs should be the optimum parameters for a high EET. We also give a detailed analysis of the effects of noise on the EET.

Wang, Xiao-Lian; Li, Hong-Rong; Zhang, Pei; Li, Fu-Li

2013-11-01

137

Supramolecular concepts in self-assembly of complex polymer systems  

Microsoft Academic Search

We discuss the complexation, the self-assembly behaviour and nanostructures obtained in comb-like liquid crystalline polymers formed by ionic complexation of cationic dendronized polymers and anionic lipids. The resulting self-assembled materials exhibit thermotropic liquid crystalline behaviour and a rich state diagram. The topology of the LC phases resulting from the self-assembly process, their lattice parameter and the distribution of polymer and

Raffaele Mezzenga

2007-01-01

138

Transmetalation of self-assembled, supramolecular complexes.  

PubMed

Substituting one metal for another in inorganic and organometallic systems is a proven strategy for synthesizing complex molecules, and in some cases, provides the only route to a particular system. The multivalent nature of the coordination in metal-ligand assemblies lends itself more readily to some types of transmetalation. For instance, a binding site can open up for exchange without greatly effecting the many other interactions holding the structure together. In addition to exchanging the metal and altering the local binding environment, transmetalation in supramolecular systems can also lead to substantial changes in the nature of the secondary and tertiary structure of a larger assembly. In this tutorial review we will cover discrete supramolecular assemblies in which metals are exchanged. First we will address fully formed structures where direct substitution replaces one type of metal for another without changing the overall supramolecular assembly. We will then address systems where the disruptive exchange of one metal for another leads to a larger change in the supramolecular assembly. When possible we have tried to highlight systems that use supramolecular self-assembly in tandem with transmetalation to synthesize new structures not accessible through a more direct approach. At the end of this review, we highlight the use of transmetalation in self-assembled aqueous inorganic clusters and discuss the consequences for material science applications. PMID:24346298

Carnes, Matthew E; Collins, Mary S; Johnson, Darren W

2014-03-21

139

Self-Assembly of Gemini Surfactants  

NASA Astrophysics Data System (ADS)

The self-assembly behavior of Gemini (dimeric or twin-tail) dicarboxylate disodium surfactants is studied using molecular dynamics simulations. This gemini architecture, in which two single tailed surfactants are joined through a flexible hydrophobic linker, has been shown to exhibit concentration-dependent aqueous self-assembly into lyotropic phases including hexagonal, gyroid, and lamellar morphologies. Our simulations reproduce the experimentally observed phases at similar amphiphile concentrations in water, including the unusual ability of these surfactants to form gyroid phases over unprecedentedly large amphiphile concentration windows. We demonstrate quanitative agreement between the predicted and experimentally observed domain spacings of these nanostructured materials. Through careful conformation analyses of the surfactant molecules, we show that the gyroid phase is electrostatically stabilized related to the lamellar phase. By starting with a lamellar phase, we show that decreasing the charge on the surfactant headgroups by carboxylate protonation or use of a bulkier tetramethyl ammonium counterion in place of sodium drives the formation of a gyroid phase.

Yethiraj, Arun; Mondal, Jagannath; Mahanthappa, Mahesh

2013-03-01

140

Micropatterning of bioactive self-assembling gels†  

PubMed Central

Microscale topographical features have been known to affect cell behavior. An important target in this area is to integrate top down techniques with bottom up self-assembly to create three-dimensional (3D) patterned bioactive mimics of extracellular matrices. We report a novel approach toward this goal and demonstrate its use to study the behavior of human mesenchymal stem cells (hMSCs). By incorporating polymerizable acetylene groups in the hydrophobic segment of peptide amphiphiles (PAs), we were able to micro-pattern nanofiber gels of these bioactive materials. PAs containing the cell adhesive epitope arginine–glycine–aspartic acid–serine (RGDS) were allowed to self-assemble within microfabricated molds to create networks of either randomly oriented or aligned ~30 nm diameter nanofiber bundles that were shaped into topographical patterns containing holes, posts, or channels up to 8 ?m in height and down to 5 ?m in lateral dimensions. When topographical patterns contained nanofibers aligned through flow prior to gelation, the majority of hMSCs aligned in the direction of the nanofibers even in the presence of hole microtextures and more than a third of them maintained this alignment when encountering perpendicular channel microtextures. Interestingly, in topographical patterns with randomly oriented nanofibers, osteoblastic differentiation was enhanced on hole microtextures compared to all other surfaces.

Mata, Alvaro; Hsu, Lorraine; Capito, Ramille; Aparicio, Conrado; Henrikson, Karl

2009-01-01

141

Quantifying quality in DNA self-assembly  

NASA Astrophysics Data System (ADS)

Molecular self-assembly with DNA is an attractive route for building nanoscale devices. The development of sophisticated and precise objects with this technique requires detailed experimental feedback on the structure and composition of assembled objects. Here we report a sensitive assay for the quality of assembly. The method relies on measuring the content of unpaired DNA bases in self-assembled DNA objects using a fluorescent de-Bruijn probe for three-base ‘codons’, which enables a comparison with the designed content of unpaired DNA. We use the assay to measure the quality of assembly of several multilayer DNA origami objects and illustrate the use of the assay for the rational refinement of assembly protocols. Our data suggests that large and complex objects like multilayer DNA origami can be made with high strand integration quality up to 99%. Beyond DNA nanotechnology, we speculate that the ability to discriminate unpaired from paired nucleic acids in the same macromolecule may also be useful for analysing cellular nucleic acids.

Wagenbauer, Klaus F.; Wachauf, Christian H.; Dietz, Hendrik

2014-04-01

142

Quantifying quality in DNA self-assembly.  

PubMed

Molecular self-assembly with DNA is an attractive route for building nanoscale devices. The development of sophisticated and precise objects with this technique requires detailed experimental feedback on the structure and composition of assembled objects. Here we report a sensitive assay for the quality of assembly. The method relies on measuring the content of unpaired DNA bases in self-assembled DNA objects using a fluorescent de-Bruijn probe for three-base 'codons', which enables a comparison with the designed content of unpaired DNA. We use the assay to measure the quality of assembly of several multilayer DNA origami objects and illustrate the use of the assay for the rational refinement of assembly protocols. Our data suggests that large and complex objects like multilayer DNA origami can be made with high strand integration quality up to 99%. Beyond DNA nanotechnology, we speculate that the ability to discriminate unpaired from paired nucleic acids in the same macromolecule may also be useful for analysing cellular nucleic acids. PMID:24751596

Wagenbauer, Klaus F; Wachauf, Christian H; Dietz, Hendrik

2014-01-01

143

Quantifying quality in DNA self-assembly  

PubMed Central

Molecular self-assembly with DNA is an attractive route for building nanoscale devices. The development of sophisticated and precise objects with this technique requires detailed experimental feedback on the structure and composition of assembled objects. Here we report a sensitive assay for the quality of assembly. The method relies on measuring the content of unpaired DNA bases in self-assembled DNA objects using a fluorescent de-Bruijn probe for three-base ‘codons’, which enables a comparison with the designed content of unpaired DNA. We use the assay to measure the quality of assembly of several multilayer DNA origami objects and illustrate the use of the assay for the rational refinement of assembly protocols. Our data suggests that large and complex objects like multilayer DNA origami can be made with high strand integration quality up to 99%. Beyond DNA nanotechnology, we speculate that the ability to discriminate unpaired from paired nucleic acids in the same macromolecule may also be useful for analysing cellular nucleic acids.

Wagenbauer, Klaus F.; Wachauf, Christian H.; Dietz, Hendrik

2014-01-01

144

Self-assembled software and method of overriding software execution  

DOEpatents

A computer-implemented software self-assembled system and method for providing an external override and monitoring capability to dynamically self-assembling software containing machines that self-assemble execution sequences and data structures. The method provides an external override machine that can be introduced into a system of self-assembling machines while the machines are executing such that the functionality of the executing software can be changed or paused without stopping the code execution and modifying the existing code. Additionally, a monitoring machine can be introduced without stopping code execution that can monitor specified code execution functions by designated machines and communicate the status to an output device.

Bouchard, Ann M.; Osbourn, Gordon C.

2013-01-08

145

Bio-inspired supramolecular self-assembly towards soft nanomaterials  

PubMed Central

Supramolecular self-assembly has proven to be a reliable approach towards versatile nanomaterials based on multiple weak intermolecular forces. In this review, the development of bio-inspired supramolecular self-assembly into soft materials and their applications are summarized. Molecular systems used in bio-inspired “bottom-up self-assembly” involve small organic molecules, peptides or proteins, nucleic acids, and viruses. Self-assembled soft nanomaterials have been exploited in various applications such as inorganic nanomaterial synthesis, drug or gene delivery, tissue engineering, and so on.

LIN, Yiyang; MAO, Chuanbin

2011-01-01

146

Bio-inspired supramolecular self-assembly towards soft nanomaterials.  

PubMed

Supramolecular self-assembly has proven to be a reliable approach towards versatile nanomaterials based on multiple weak intermolecular forces. In this review, the development of bio-inspired supramolecular self-assembly into soft materials and their applications are summarized. Molecular systems used in bio-inspired "bottom-up self-assembly" involve small organic molecules, peptides or proteins, nucleic acids, and viruses. Self-assembled soft nanomaterials have been exploited in various applications such as inorganic nanomaterial synthesis, drug or gene delivery, tissue engineering, and so on. PMID:21980594

Lin, Yiyang; Mao, Chuanbin

2011-09-01

147

Beyond molecules: Self-assembly of mesoscopic and macroscopic components  

PubMed Central

Self-assembly is a process in which components, either separate or linked, spontaneously form ordered aggregates. Self-assembly can occur with components having sizes from the molecular to the macroscopic, provided that appropriate conditions are met. Although much of the work in self-assembly has focused on molecular components, many of the most interesting applications of self-assembling processes can be found at larger sizes (nanometers to micrometers). These larger systems also offer a level of control over the characteristics of the components and over the interactions among them that makes fundamental investigations especially tractable.

Whitesides, George M.; Boncheva, Mila

2002-01-01

148

Light harvesting proteins for solar fuel generation in bioengineered photoelectrochemical cells.  

PubMed

The sun is the primary energy source of our planet and potentially can supply all societies with more than just their basic energy needs. Demand of electric energy can be satisfied with photovoltaics, however the global demand for fuels is even higher. The direct way to produce the solar fuel hydrogen is by water splitting in photoelectrochemical (PEC) cells, an artificial mimic of photosynthesis. There is currently strong resurging interest for solar fuels produced by PEC cells, but some fundamental technological problems need to be solved to make PEC water splitting an economic, competitive alternative. One of the problems is to provide a low cost, high performing water oxidizing and oxygen evolving photoanode in an environmentally benign setting. Hematite, ?-Fe2O3, satisfies many requirements for a good PEC photoanode, but its efficiency is insufficient in its pristine form. A promising strategy for enhancing photocurrent density takes advantage of photosynthetic proteins. In this paper we give an overview of how electrode surfaces in general and hematite photoanodes in particular can be functionalized with light harvesting proteins. Specifically, we demonstrate how low-cost biomaterials such as cyanobacterial phycocyanin and enzymatically produced melanin increase the overall performance of virtually no-cost metal oxide photoanodes in a PEC system. The implementation of biomaterials changes the overall nature of the photoanode assembly in a way that aggressive alkaline electrolytes such as concentrated KOH are not required anymore. Rather, a more environmentally benign and pH neutral electrolyte can be used. PMID:24678669

Ihssen, Julian; Braun, Artur; Faccio, Greta; Gajda-Schrantz, Krisztina; Thöny-Meyer, Linda

2014-01-01

149

Light Harvesting Proteins for Solar Fuel Generation in Bioengineered Photoelectrochemical Cells  

PubMed Central

The sun is the primary energy source of our planet and potentially can supply all societies with more than just their basic energy needs. Demand of electric energy can be satisfied with photovoltaics, however the global demand for fuels is even higher. The direct way to produce the solar fuel hydrogen is by water splitting in photoelectrochemical (PEC) cells, an artificial mimic of photosynthesis. There is currently strong resurging interest for solar fuels produced by PEC cells, but some fundamental technological problems need to be solved to make PEC water splitting an economic, competitive alternative. One of the problems is to provide a low cost, high performing water oxidizing and oxygen evolving photoanode in an environmentally benign setting. Hematite, ?-Fe2O3, satisfies many requirements for a good PEC photoanode, but its efficiency is insufficient in its pristine form. A promising strategy for enhancing photocurrent density takes advantage of photosynthetic proteins. In this paper we give an overview of how electrode surfaces in general and hematite photoanodes in particular can be functionalized with light harvesting proteins. Specifically, we demonstrate how low-cost biomaterials such as cyanobacterial phycocyanin and enzymatically produced melanin increase the overall performance of virtually no-cost metal oxide photoanodes in a PEC system. The implementation of biomaterials changes the overall nature of the photoanode assembly in a way that aggressive alkaline electrolytes such as concentrated KOH are not required anymore. Rather, a more environmentally benign and pH neutral electrolyte can be used.

Ihssen, Julian; Braun, Artur; Faccio, Greta; Gajda-Schrantz, Krisztina; Thony-Meyer, Linda

2014-01-01

150

Fabrication of bioinspired nanostructured materials via colloidal self-assembly  

NASA Astrophysics Data System (ADS)

Through millions of years of evolution, nature creates unique structures and materials that exhibit remarkable performance on mechanicals, opticals, and physical properties. For instance, nacre (mother of pearl), bone and tooth show excellent combination of strong minerals and elastic proteins as reinforced materials. Structured butterfly's wing and moth's eye can selectively reflect light or absorb light without dyes. Lotus leaf and cicada's wing are superhydrophobic to prevent water accumulation. The principles of particular biological capabilities, attributed to the highly sophisticated structures with complex hierarchical designs, have been extensively studied. Recently, a large variety of novel materials have been enabled by natural-inspired designs and nanotechnologies. These advanced materials will have huge impact on practical applications. We have utilized bottom-up approaches to fabricate nacre-like nanocomposites with "brick and mortar" structures. First, we used self-assembly processes, including convective self-assembly, dip-coating, and electrophoretic deposition to form well oriented layer structure of synthesized gibbsite (aluminum hydroxide) nanoplatelets. Low viscous monomer was permeated into layered nanoplatelets and followed by photo-curing. Gibbsite-polymer composite displays 2 times higher tensile strength and 3 times higher modulus when compared with pure polymer. More improvement occurred when surface-modified gibbsite platelets were cross-linked with the polymer matrix. We observed ˜4 times higher strength and nearly 1 order of magnitude higher modulus than pure polymer. To further improve the mechanical strength and toughness of inorganicorganic nanocomposites, we exploited ultrastrong graphene oxide (GO), a single atom thick hexagonal carbon sheet with pendant oxidation groups. GO nanocomposite is made by co-filtrating GO/polyvinyl alcohol suspension on 0.2 im pore-sized membrane. It shows ˜2 times higher strength and ˜15 times higher ultimate strains than nacre and pure GO paper (also synthesized by filtration). Specifically, it exhibits ˜30 times higher fracture energy than filtrated graphene paper and nacre, ˜100 times tougher than filtrated GO paper. Besides reinforced nanocomposites, we further explored the self-assembly of spherical colloids and the templating nanofabrication of moth-eye-inspired broadband antireflection coatings. Binary crystalline structures can be easily accomplished by spin-coating double-layer nonclose-packed colloidal crystals as templates, followed by colloidal templating. The polymer matrix between self-assembled colloidal crystal has been used as a sacrificial template to define the resulting periodic binary nanostructures, including intercalated arrays of silica spheres and polymer posts, gold nanohole arrays with binary sizes, and dimple-nipple antireflection coatings. The binary-structured antireflection coatings exhibit better antireflective properties than unitary coatings. Natural optical structures and nanocomposites teach us a great deal on how to create high performance artificial materials. The bottom-up technologies developed in this thesis are scalable and compatible with standard industrial processes, promising for manufacturing high-performance materials for the benefits of human beings.

Huang, Wei-Han

151

Optically nonlinear energy transfer in light-harvesting dendrimers.  

PubMed

Dendrimeric polymers are the subject of intense research activity geared towards their implementation in nanodevice applications such as energy harvesting systems, organic light-emitting diodes, photosensitizers, low-threshold lasers, and quantum logic elements, etc. A recent development in this area has been the construction of dendrimers specifically designed to exhibit novel forms of optical nonlinearity, exploiting the unique properties of these materials at high levels of photon flux. Starting from a thorough treatment of the underlying theory based on the principles of molecular quantum electrodynamics, it is possible to identify and characterize several optically nonlinear mechanisms for directed energy transfer and energy pooling in multichromophore dendrimers. Such mechanisms fall into two classes: first, those where two-photon absorption by individual donors is followed by transfer of the net energy to an acceptor; second, those where the excitation of two electronically distinct but neighboring donor groups is followed by a collective migration of their energy to a suitable acceptor. Each transfer process is subject to minor dissipative losses. In this paper we describe in detail the balance of factors and the constraints that determines the favored mechanism, which include the excitation statistics, structure of the energy levels, laser coherence factors, chromophore selection rules and architecture, possibilities for the formation of delocalized excitons, spectral overlap, and the overall distribution of donors and acceptors. Furthermore, it transpires that quantum interference between different mechanisms can play an important role. Thus, as the relative importance of each mechanism determines the relevant nanophotonic characteristics, the results reported here afford the means for optimizing highly efficient light-harvesting dendrimer devices. PMID:15260800

Andrews, David L; Bradshaw, David S

2004-08-01

152

Strong antenna-enhanced fluorescence of a single light-harvesting complex shows photon antibunching.  

PubMed

The nature of the highly efficient energy transfer in photosynthetic light-harvesting complexes is a subject of intense research. Unfortunately, the low fluorescence efficiency and limited photostability hampers the study of individual light-harvesting complexes at ambient conditions. Here we demonstrate an over 500-fold fluorescence enhancement of light-harvesting complex 2 (LH2) at the single-molecule level by coupling to a gold nanoantenna. The resonant antenna produces an excitation enhancement of circa 100 times and a fluorescence lifetime shortening to ~\

Wientjes, Emilie; Renger, Jan; Curto, Alberto G; Cogdell, Richard; van Hulst, Niek F

2014-01-01

153

Strong antenna-enhanced fluorescence of a single light-harvesting complex shows photon antibunching  

PubMed Central

The nature of the highly efficient energy transfer in photosynthetic light-harvesting complexes is a subject of intense research. Unfortunately, the low fluorescence efficiency and limited photostability hampers the study of individual light-harvesting complexes at ambient conditions. Here we demonstrate an over 500-fold fluorescence enhancement of light-harvesting complex 2 (LH2) at the single-molecule level by coupling to a gold nanoantenna. The resonant antenna produces an excitation enhancement of circa 100 times and a fluorescence lifetime shortening to ~\

Wientjes, Emilie; Renger, Jan; Curto, Alberto G.; Cogdell, Richard; van Hulst, Niek F.

2014-01-01

154

Supramolecular self-assemblies as functional nanomaterials.  

PubMed

In this review, we survey the diversity of structures and functions which are encountered in advanced self-assembled nanomaterials. We highlight their flourishing implementations in three active domains of applications: biomedical sciences, information technologies, and environmental sciences. Our main objective is to provide the reader with a concise and straightforward entry to this broad field by selecting the most recent and important research articles, supported by some more comprehensive reviews to introduce each topic. Overall, this compilation illustrates how, based on the rules of supramolecular chemistry, the bottom-up approach to design functional objects at the nanoscale is currently producing highly sophisticated materials oriented towards a growing number of applications with high societal impact. PMID:23832165

Busseron, Eric; Ruff, Yves; Moulin, Emilie; Giuseppone, Nicolas

2013-08-21

155

Supramolecular self-assemblies as functional nanomaterials  

NASA Astrophysics Data System (ADS)

In this review, we survey the diversity of structures and functions which are encountered in advanced self-assembled nanomaterials. We highlight their flourishing implementations in three active domains of applications: biomedical sciences, information technologies, and environmental sciences. Our main objective is to provide the reader with a concise and straightforward entry to this broad field by selecting the most recent and important research articles, supported by some more comprehensive reviews to introduce each topic. Overall, this compilation illustrates how, based on the rules of supramolecular chemistry, the bottom-up approach to design functional objects at the nanoscale is currently producing highly sophisticated materials oriented towards a growing number of applications with high societal impact.

Busseron, Eric; Ruff, Yves; Moulin, Emilie; Giuseppone, Nicolas

2013-07-01

156

Magnetic Nanostructures by Templated Self Assembly  

NASA Astrophysics Data System (ADS)

Self assembly techniques provide a route to the rapid synthesis of nanostructures whose long range order and registration can be controlled by pre-patterning the substrate lithographically. This presentation will focus on two processes. First, masks made from templated block copolymer films are used for patterning of metallic magnetic films and multilayers into arrays of lines or dots with feature sizes of 10 nm and above. Second, codeposition of spinel and perovskite oxide phases leads to epitaxial thin film nanocomposites in which ferrimagnetic cobalt ferrite pillars are embedded in a ferroelectric bismuth orthoferrite matrix. The pillars form a regular array when templated by pits of pitch 60 nm and above, and have a strong magnetoelastic anisotropy. Magnetic properties of the resulting nanostructured materials are described.

Ross, Caroline

2013-03-01

157

Self-assembled magnetic surface swimmers.  

SciTech Connect

We report studies of novel self-assembled magnetic surface swimmers (magnetic snakes) formed from a dispersion of magnetic microparticles at a liquid-air interface and energized by an alternating magnetic field. We show that under certain conditions the snakes spontaneously break the symmetry of surface flows and turn into self-propelled objects. Parameters of the driving magnetic field tune the propulsion velocity of these snakelike swimmers. We find that the symmetry of the surface flows can also be broken in a controlled fashion by attaching a large bead to a magnetic snake (bead-snake hybrid), transforming it into a self-locomoting entity. The observed phenomena have been successfully described by a phenomenological model based on the amplitude equation for surface waves coupled to a large-scale hydrodynamic mean flow equation.

Snezhko, A.; Belkin, M.; Aranson, I. S.; Kwok, W.-K.; Materials Science Division; Illinois Inst. of Tech.

2009-03-20

158

Smart self-assembled hybrid hydrogel biomaterials.  

PubMed

Hybrid biomaterials are systems created from components of at least two distinct classes of molecules, for example, synthetic macromolecules and proteins or peptide domains. The synergistic combination of two types of structures may produce new materials that possess unprecedented levels of structural organization and novel properties. This Review focuses on biorecognition-driven self-assembly of hybrid macromolecules into functional hydrogel biomaterials. First, basic rules that govern the secondary structure of peptides are discussed, and then approaches to the specific design of hybrid systems with tailor-made properties are evaluated, followed by a discussion on the similarity of design principles of biomaterials and macromolecular therapeutics. Finally, the future of the field is briefly outlined. PMID:22806947

Kope?ek, Jind?ich; Yang, Jiyuan

2012-07-23

159

Self-assembling multimeric nucleic acid constructs  

DOEpatents

The invention is directed to constructs and compositions containing multimeric forms of nucleic acid. Multimeric nucleic acids comprise single-stranded nucleic acids attached via biotin to streptavidin and bound with a functional group. These constructs can be utilized in vivo to treat or identify diseased tissue or cells. Repeated administrations of multimeric nucleic acid compositions produce a rapid and specific amplification of nucleic acid constructs and their attached functional groups. For treatment purposes, functional groups may be toxins, radioisotopes, genes or enzymes. Diagnostically, labeled multimeric constructs may be used to identify specific targets in vivo or in vitro. Multimeric nucleic acids may also be used in nanotechnology and to create self-assembling polymeric aggregates such as membranes of defined porosity, microcircuits and many other products.

Cantor, Charles R. (Boston, MA); Niemeyer, Christof M. (Bremen, DE); Smith, Cassandra L. (Boston, MA); Sano, Takeshi (Boston, MA); Hnatowich, Donald J. (Brookline, MA); Rusckowski, Mary (Southborough, MA)

1996-01-01

160

Self-assembling multimeric nucleic acid constructs  

DOEpatents

The invention is directed to constructs and compositions containing multimeric forms of nucleic acid. Multimeric nucleic acids comprise single-stranded nucleic acids attached via biotin to streptavidin and bound with a functional group. These constructs can be utilized in vivo to treat or identify diseased tissue or cells. Repeated administrations of multimeric nucleic acid compositions produce a rapid and specific amplification of nucleic acid constructs and their attached functional groups. For treatment purposes, functional groups may be toxins, radioisotopes, genes or enzymes. Diagnostically, labeled multimeric constructs may be used to identify specific targets in vivo or in vitro. Multimeric nucleic acids may also be used in nanotechnology and to create self-assembling polymeric aggregates such as membranes of defined porosity, microcircuits and many other products. 5 figs.

Cantor, C.R.; Niemeyer, C.M.; Smith, C.L.; Sano, Takeshi; Hnatowich, D.J.; Rusckowski, M.

1996-10-01

161

Self-assembling multimeric nucleic acid constructs  

DOEpatents

The invention is directed to constructs and compositions containing multimeric forms of nucleic acid. Multimeric nucleic acids comprise single-stranded nucleic acids attached via biotin to streptavidin and bound with a functional group. These constructs can be utilized in vivo to treat or identify diseased tissue or cells. Repeated administrations of multimeric nucleic acid compositions produce a rapid and specific amplification of nucleic acid constructs and their attached functional groups. For treatment purposes, functional groups may be toxins, radioisotopes, genes or enzymes. Diagnostically, labeled multimeric constructs may be used to identify specific targets in vivo or in vitro. Multimeric nucleic acids may also be used in nanotechnology and to create self-assembling polymeric aggregates such as membranes of defined porosity, microcircuits and many other products.

Cantor, Charles R. (Boston, MA); Niemeyer, Christof M. (Bremen, DE); Smith, Cassandra L. (Boston, MA); Sano, Takeshi (Boston, MA); Hnatowich, Donald J. (Brookline, MA); Rusckowski, Mary (Southborough, MA)

1999-10-12

162

Self assembly properties of primitive organic compounds  

NASA Technical Reports Server (NTRS)

A central event in the origin of life was the self-assembly of amphiphilic, lipid-like compounds into closed microenvironments. If a primitive macromolecular replicating system could be encapsulated within a vesicular membrane, the components of the system would share the same microenvironment, and the result would be a step toward true cellular function. The goal of our research has been to determine what amphiphilic molecules might plausibly have been available on the early Earth to participate in the formation of such boundary structures. To this end, we have investigated primitive organic mixtures present in carbonaceous meteorites such as the Murchison meteorite, which contains 1-2 percent of its mass in the form of organic carbon compounds. It is likely that such compounds contributed to the inventory of organic carbon on the prebiotic earth, and were available to participate in chemical evolution leading to the emergence of the first cellular life forms. We found that Murchison components extracted into non-polar solvent systems are surface active, a clear indication of amphiphilic character. One acidic fraction self-assembles into vesicular membranes that provide permeability barriers to polar solutes. Other evidence indicates that the membranes are bimolecular layers similar to those formed by contemporary membrane lipids. We conclude that bilayer membrane formation by primitive amphiphiles on the early Earth is feasible. However, only a minor fraction of acidic amphiphiles assembles into bilayers, and the resulting membranes require narrowly defined conditions of pH and ionic composition to be stable. It seems unlikely, therefore, that meteoritic infall was a direct source of membrane amphiphiles. Instead, the hydrocarbon components and their derivatives more probably would provide an organic stock available for chemical evolution. Our current research is directed at possible reactions which would generate substantial quantities of membranogenic amphiphiles. One possibility is photochemical oxidation of hydrocarbons.

Deamer, D. W.

1991-01-01

163

Self assembled structures for 3D integration  

NASA Astrophysics Data System (ADS)

Three dimensional (3D) micro-scale structures attached to a silicon substrate have various applications in microelectronics. However, formation of 3D structures using conventional micro-fabrication techniques are not efficient and require precise control of processing parameters. Self assembly is a method for creating 3D structures that takes advantage of surface area minimization phenomena. Solder based self assembly (SBSA), the subject of this dissertation, uses solder as a facilitator in the formation of 3D structures from 2D patterns. Etching a sacrificial layer underneath a portion of the 2D pattern allows the solder reflow step to pull those areas out of the substrate plane resulting in a folded 3D structure. Initial studies using the SBSA method demonstrated low yields in the formation of five different polyhedra. The failures in folding were primarily attributed to nonuniform solder deposition on the underlying metal pads. The dip soldering method was analyzed and subsequently refined. A modified dip soldering process provided improved yield among the polyhedra. Solder bridging referred as joining of solder deposited on different metal patterns in an entity influenced the folding mechanism. In general, design parameters such as small gap-spacings and thick metal pads were found to favor solder bridging for all patterns studied. Two types of soldering: face and edge soldering were analyzed. Face soldering refers to the application of solder on the entire metal face. Edge soldering indicates application of solder only on the edges of the metal face. Mechanical grinding showed that face soldered SBSA structures were void free and robust in nature. In addition, the face soldered 3D structures provide a consistent heat resistant solder standoff height that serve as attachments in the integration of dissimilar electronic technologies. Face soldered 3D structures were developed on the underlying conducting channel to determine the thermo-electric reliability of face soldered structures.

Rao, Madhav

164

Meso-Scale Self-Assembly Pilot Study.  

National Technical Information Service (NTIS)

The project investigates the formation of micro-scale structures using capillary force-driven self-assembly. Two main activities were undertaken during the course of the project: determination of the proper self-assembly environment and scaling of the met...

B. A. Parviz

2007-01-01

165

Self-assembly of uniform nanoporous silica fibers  

Microsoft Academic Search

Self-assembly of nanoporous silica shapes is of great interest for modern nanotechnology because of uniform pore size, simplicity, and low cost of production. However, there are two major problems that prevent broad use of the self-assembly process. First, the process brings too broad a variety of the assembled shapes. Secondly, the yield of the desired shapes is far from 100%.

Yaroslav Kievsky; Igor Sokolov

2005-01-01

166

Capillary Forces in Micro-Fluidic Self-Assembly  

Microsoft Academic Search

Parallel self-assembly in the fluidic phase is a promising al- ternative technique to conventional pick-and-place assembly. In this work the hydrophobic-hydrophilic material system between binding sites for microparts is simulated with re- spect to alignment precision. The results are compared with experimental findings and allow predictions for the optimiza- tion of the fluidic self assembly technique.

Andreas Greiner; Jan Lienemann; Jan G. Korvink; Xiaorong Xiong; Yael Hanein; Karl F. Böhringer

2002-01-01

167

MD Simulations of DNA-Programmable Nanoparticle Self-Assembly  

NASA Astrophysics Data System (ADS)

Self-assembly through linker mediated hybridization is a powerful technique to control self-assembly at the nanoscale. Recent experiments with complementary ssDNA attached to Au nanoparticles have shown crystallization into BCC and FCC crystals. We give a brief overview of a coarse grained model and present molecular dynamics simulations of the model. We discuss its static and dynamical properties.

Knorowski, Christopher; Travesset, Alex

2011-03-01

168

Spectroscopic readout of polyoxometalates' molecular information via self-assembly.  

PubMed

Polyoxometalates [SiM12O40](4-) (M = Mo(VI), W(VI)) and hemicyanine-derived chiral amphiphiles self-assemble in organic media where intermolecular interactions between POMs and hemicyanine units differ depending on the constituent metal ion species: this information is amplified to distinct spectral and self-assembling characteristics. PMID:24281651

Noguchi, Takao; Kimizuka, Nobuo

2014-01-18

169

IRON-INDUCED CHANGES IN LIGHT HARVESTING AND PHOTOCHEMICAL ENERGY CONVERSION IN EUKARYOTIC MARINE ALGAE  

EPA Science Inventory

The role of iron in regulating light harvesting and photochemical energy conversion process was examined in the marine unicellular chlorophyte Dunaliella tertiolecta and the marine diatom Phaeodactylum tricornutum. In both species, iron limitation led to a reduction in cellular c...

170

Photoenergy Harvesting Organic PV Cells Using Modified Photosynthetic Light-Harvesting Complex for Energy Harvesting Materials.  

National Technical Information Service (NTIS)

The purpose of this research is to use modified photosynthetic light- harvesting (LH) complexes from modern biosynthetic manufacturing methods of purple photosynthetic bacteria in order to control the direction and orientation of the complex on electrodes...

M. Nango

2008-01-01

171

Primary Light-Harvesting System: Phycobilisomes and Associated Membranes. Progress Report, December 1979-January 1983.  

National Technical Information Service (NTIS)

The structure of phycobilisomes, which serve as primary light-harvesting complexes for photosynthesis, were investigated in red and blue-green algae (cyanobacteria). Structurally the phycobilisomes have the same fundamental arrangement in the various spec...

E. Gantt

1983-01-01

172

Multilayer self-assemblies as electronic and optical materials  

SciTech Connect

The layer-by-layer growth of film structures consisting of sequential depositions of oppositely charged polymers and macrocycles (ring-shaped molecules) have been constructed using molecular self-assembly techniques. These self-assembled thin films were characterized with X-ray reflectometry, which yielded (1) the average electron density, (2) the average thicknesses, and (3) the roughness of the growth surface of the self-assembled multilayer of macrocycles and polymers. These observations suggest that inorganic-organic interactions play an important role during the initial stages of thin-film growth, but less so as the thin film becomes thicker. Optical absorption techniques were also used to characterize the self-assembled multilayers. Phorphyrin and phthalocyanine derivatives were chosen as one of the building blocks of the self-assembled multilayers because of their interesting optical properties.

Li, D.; Luett, M.; Shi, X.; Fitzsimmons, M.R.

1997-12-31

173

Self-assembly: from amphiphiles to chromophores and beyond.  

PubMed

Self-assembly has been recognised as a ubiquitous aspect of modern chemistry. Our understanding and applications of self-assembly are substantially based on what has been learned from biochemical systems. In this review, we describe various aspects of self-assembly commencing with an account of the soft structures that are available by assembly of surfactant amphiphiles, which are important scientific and industrial materials. Variation of molecular design using rules defined by surfactant self-assembly permits synthesis of functional nanostructures in solution and at surfaces while increasing the strength of intermolecular interactions through ?-? stacking, metal cation coordination and/or hydrogen bonding leads to formation of highly complex bespoke nanostructured materials exemplified by DNA assemblies. We describe the origins of self-assembly involving aggregation of lipid amphiphiles and how this subject has been expanded to include other highly advanced chemical systems. PMID:24959684

Hill, Jonathan P; Shrestha, Lok Kumar; Ishihara, Shinsuke; Ji, Qingmin; Ariga, Katsuhiko

2014-01-01

174

Self-Assembly of Optical Molecules with Supramolecular Concepts  

PubMed Central

Fabrication of nano-sized objects is one of the most important issues in nanoscience and nanotechnology. Soft nanomaterials with flexible properties have been given much attention and can be obtained through bottom-up processing from functional molecules, where self-assembly based on supramolecular chemistry and designed assembly have become crucial processes and techniques. Among the various functional molecules, dyes have become important materials in certain areas of nanotechnology and their self-assembling behaviors have been actively researched. In this short review, we briefly introduce recent progress in self-assembly of optical molecules and dyes, based mainly on supramolecular concepts. The introduced examples are classified into four categories: self-assembly of (i) low-molecular-weight dyes and (ii) polymeric dyes and dye self-assembly (iii) in nanoscale architectures and (iv) at surfaces.

Okamoto, Ken; Chithra, Parayalil; Richards, Gary J.; Hill, Jonathan P.; Ariga, Katsuhiko

2009-01-01

175

Architecture of a Charge-Transfer State Regulating Light Harvesting in a Plant Antenna Protein  

Microsoft Academic Search

Energy-dependent quenching of excess absorbed light energy (qE) is a vital mechanism for regulating photosynthetic light harvesting in higher plants. All of the physiological characteristics of qE have been positively correlated with charge transfer between coupled chlorophyll and zeaxanthin molecules in the light-harvesting antenna of photosystem II (PSII). We found evidence for charge-transfer quenching in all three of the individual

Tae Kyu Ahn; Thomas J. Avenson; Matteo Ballottari; Yuan-Chung Cheng; Krishna K. Niyogi; Roberto Bassi; Graham R. Fleming

2008-01-01

176

Self-assembly of Janus particles confined in a channel  

NASA Astrophysics Data System (ADS)

Janus particles present an important class of building blocks for directional assembly. These are compartmentalized colloids with two different hemispheres. Here, we consider a two-dimensional model of Janus disks consisting of a hydrophobic semicircle and an electro-negatively charged one. Placed in a solution, the hydrophobic sides will attract each other while the charged sides will give rise to a repulsive force. Using molecular dynamics simulations, we study the morphology of these particles when confined in a channel-like environment using a one dimensional harmonic confinement potential. The interest to this system is first of all due to the fact that it could serve as a simple model for membrane formation. Indeed, the recently synthesized new class of artificial amphiphiles, known as Janus dendrimers, were shown to self-assemble in bilayer structures mimicking biological membranes. In turn, Janus particles that combine the amphiphilicity and colloidal rigidity serve as a good model for Janus dendrimers. A variety of ordered membrane-like morphologies are found consisting of single and multiple chain configurations with different orientations of the particles with respect to each other that we summarize in a phase diagram.

Sobrino Fernández, M.; Misko, V. R.; Peeters, F. M.

2014-02-01

177

Self-assembled ultra small ZnO nanocrystals for dye-sensitized solar cell application  

NASA Astrophysics Data System (ADS)

We demonstrate a facile chemical approach to produce self-assembled ultra-small mesoporous zinc oxide nanocrystals using sodium salicylate (SS) as a template under hydrothermal conditions. These ZnO nanomaterials have been successfully fabricated as a photoanode for the dye-sensitized solar cell (DSSC) in the presence of N719 dye and iodine-triiodide electrolyte. The structural features, crystallinity, purity, mesophase and morphology of the nanostructure ZnO are investigated by several characterization tools. N2 sorption analysis revealed high surface areas (203 m2 g-1) and narrow pore size distributions (5.1-5.4 nm) for different samples. The mesoporous structure and strong photoluminescence facilitates the high dye loading at the mesoscopic void spaces and light harvesting in DSSC. By utilizing this ultra-small ZnO photoelectrode with film thickness of about 7 ?m in the DSSC with an open-circuit voltage (VOC) of 0.74 V, short-circuit current density (JSC) of 3.83 mA cm-2 and an overall power conversion efficiency of 1.12% has been achieved.

Patra, Astam K.; Dutta, Arghya; Bhaumik, Asim

2014-07-01

178

Self-assembled nanostructures in oxide ceramics  

NASA Astrophysics Data System (ADS)

Self-assembled nanoislands in the gadolinia-doped ceria (GDC)/ yttria-stabilized zirconia (YSZ) system have recently been discovered. This dissertation is an attempt to study the mechanism by which these nanoislands form. Nanoislands in the GDC/YSZ system form via a strain based mechanism whereby the stress accumulated in the GDC-doped surface layer on the YSZ substrate is relieved by creation of self-assembled nanoislands by a mechanism similar to the ATG instability. Unlike what was previously believed, a modified surface layer is not required prior to annealing, that is, this modification can occur during annealing by surface diffusion of dopants from the GDC sources (distributed on the YSZ surface in either lithographically defined patch or powder form) with simultaneous breakup, which occurs at the hold temperature independent of the subsequent cooling. Additionally, we have developed a simple powder based process of producing nanoislands which bypasses lithography and thin film deposition setups. The versatility of the process is apparent in the fact that it allows us to study the effect of experimental parameters such as soak time, temperature, cooling rate and the effect of powder composition on nanoisland properties in a facile way. With the help of this process, we have shown that nanoislands are not peculiar to Gd containing oxide source materials on YSZ substrates and can also be produced with other source materials such as La2O3, Nd2O3, Sm 2O3, Eu2O3, Tb2O3 and even Y2O3, which is already present in the substrate and hence simplifies the system further. We have extended our work to include YSZ substrates of the (110) surface orientation and have found that instead of nanoisland arrays, we obtain an array of parallel nanobars which have their long axes oriented along the [1-10] direction on the YSZ-(110) surface. STEM EDS performed on both the bars and the nanoislands has revealed that they are solid YSZ-rich solid solutions with the dopant species and are heterogeneous in composition with dopant enrichment at the top of the islands (bars) while their bases are pure YSZ. Finally, we discuss some of the future work directions and possible applications of these nanostructures that are being explored in collaboration with our colleagues Kunal Parikh and Prof. Jessica O. Winter in the Dept. of Chemical and Biomolecular Engineering and Michael Susner and Prof. Michael Sumption in the Dept. of Materials Science and Engineering.

Ansari, Haris Masood

179

Self-assembly and interactions of biomimetic thin films  

NASA Astrophysics Data System (ADS)

Bilayer lipid membranes create the natural environment for the immobilization of functional proteins and have been used as a model for understanding structure and properties of cell membranes. The development of biomimetic surfaces requires in depth knowledge of surface science, self-assembly, immobilization techniques, nanofabrication, biomolecular interactions and analytical techniques. This research is focused on synthesizing and characterizing biomimetic artificial surfaces for fundamental studies in membrane structure and better understanding of specific and non-specific interactions. The other main focus is on surface engineering of self-assembled, nanostructured interfaces that mimic cell membranes. These structures provide a powerful bottom-up approach to the studies of the structure and functionality of cell membranes and their interactions with other molecules. One of the advantages of this approach is that the complexity of the system can be controlled and gradually increased to add functionalities. This dissertation provides a first single molecule force measurement of the specific interactions between Salmonella typhimurium and P22 bacteriophage. This dissertation also provides a novel model system for the confined crystallization of drug molecules such as aspirin using the concept of phospholipid bilayer assembly at surfaces. The results will impact the development of biosensors and drug delivery. The defense will focus on the preparation and bio-recognition interactions between a monolayer of bacteriophage P22, covalently bound to glass substrates through a bifunctional cross linker 3-aminopropyltrimethoxysilane, and the outer membrane of Salmonella, lipopolysaccharides (LPS). The LPS bilayer was deposited on poly (ethylenimine)-modified mica from their sonicated unilamellar vesicle solution. The specific binding of Salmonella typhimurium to the phage monolayer was studied by enzyme-linked immunosorbent assay (ELISA) and atomic force microscopy (AFM). Using AFM force measurements discrete unbinding forces between surface attached P22 and LPS were obtained. Both whole P22 and tailspike proteins separated from the P22 capsid were used. The unbinding force histograms point to discrete forces between substrate-supported P22 and LPS. The unit unbinding force was found to decrease with decreasing force loading rate and increasing temperature. By fitting the force data with the Bell model, an energy barrier of approximately 55 KJ/mol was obtained. The resilience of phage binding to pH variation and hydration/dehydration cycles argues for the robustness of potential phage-based devices.

Handa, Hitesh

180

Plasmon-Enhanced Light Harvesting of Chlorophylls on Near-Percolating Silver Films via One-Photon Anti-Stokes Upconversion  

NASA Astrophysics Data System (ADS)

There exists a wealth of means of efficient utilization of solar energy in nature, with photosynthesis of chlorophylls as a prime example. Separately, artificially structured plasmonic materials are versatile in light harvesting and energy conversion. Using a simple and scalable design of near-percolating silver nanostructures, we demonstrate that the light-harvesting efficiency of chlorophylls can be drastically enhanced by tuning the plasmon frequency of the constituent silver nanoparticles to coincide with the maximal photon flux of sunlight. In particular, we show that the photon upconversion efficiency can be readily enhanced by over 20 folds, with the room-temperature fluorescence quantum yield increased by a factor of 2.63. The underlying mechanism for the upconversion enhancement is attributed to a one-electron-per-photon anti-Stokes process, involving absorption of a characteristic phonon mode of the chlorophylls. These findings suggest that chlorophylls can serve as molecular building blocks for high-efficiency light harvesting and solar energy conversion.

Wang, Ya-Lan; Nan, Fan; Liu, Xiao-Li; Zhou, Li; Peng, Xiao-Niu; Zhou, Zhang-Kai; Yu, Ying; Hao, Zhong-Hua; Wu, Yan; Zhang, Wei; Wang, Qu-Quan; Zhang, Zhenyu

2013-05-01

181

Plasmon-enhanced light harvesting of chlorophylls on near-percolating silver films via one-photon anti-Stokes upconversion.  

PubMed

There exists a wealth of means of efficient utilization of solar energy in nature, with photosynthesis of chlorophylls as a prime example. Separately, artificially structured plasmonic materials are versatile in light harvesting and energy conversion. Using a simple and scalable design of near-percolating silver nanostructures, we demonstrate that the light-harvesting efficiency of chlorophylls can be drastically enhanced by tuning the plasmon frequency of the constituent silver nanoparticles to coincide with the maximal photon flux of sunlight. In particular, we show that the photon upconversion efficiency can be readily enhanced by over 20 folds, with the room-temperature fluorescence quantum yield increased by a factor of 2.63. The underlying mechanism for the upconversion enhancement is attributed to a one-electron-per-photon anti-Stokes process, involving absorption of a characteristic phonon mode of the chlorophylls. These findings suggest that chlorophylls can serve as molecular building blocks for high-efficiency light harvesting and solar energy conversion. PMID:23689426

Wang, Ya-Lan; Nan, Fan; Liu, Xiao-Li; Zhou, Li; Peng, Xiao-Niu; Zhou, Zhang-Kai; Yu, Ying; Hao, Zhong-Hua; Wu, Yan; Zhang, Wei; Wang, Qu-Quan; Zhang, Zhenyu

2013-01-01

182

Self-assembly models for lipid mixtures  

NASA Astrophysics Data System (ADS)

Solutions of mixed long and short (detergent-like) phospholipids referred to as ``bicelle'' mixtures in the literature, are known to form a variety of different morphologies based on their total lipid composition and temperature in a complex phase diagram. Some of these morphologies have been found to orient in a magnetic field, and consequently bicelle mixtures are widely used to study the structure of soluble as well as membrane embedded proteins using NMR. In this work, we report on the low temperature phase of the DMPC and DHPC bicelle mixture, where there is agreement on the discoid structures but where molecular packing models are still being contested. The most widely accepted packing arrangement, first proposed by Vold and Prosser had the lipids completely segregated in the disk: DHPC in the rim and DMPC in the disk. Using data from small angle neutron scattering (SANS) experiments, we show how radius of the planar domain of the disks is governed by the effective molar ratio qeff of lipids in aggregate and not the molar ratio q (q = [DMPC]/[DHPC] ) as has been understood previously. We propose a new quantitative (packing) model and show that in this self assembly scheme, qeff is the real determinant of disk sizes. Based on qeff , a master equation can then scale the radii of disks from mixtures with varying q and total lipid concentration.

Singh, Divya; Porcar, Lionel; Butler, Paul; Perez-Salas, Ursula

2006-03-01

183

Electronically Guided Self Assembly within Quantum Corrals  

NASA Astrophysics Data System (ADS)

A grand challenge of nanoscience is to master the control of structure and properties in order to go beyond present day functionality. The creation of nanostructures via atom manipulation by means of a scanning probe represents one of the great achievements of the nano era. Here we build on this achievement to self-assemble nanostructures within quantum corrals. We constructed circular and triangular Fe quantum corrals on Ag(111) substrate via STM manipulation and studied the quantum confinement of electronic states and the diffusion of Gd atoms inside the corrals. Statistical results reveal the motion of the Gd atoms forming several individual orbits that are closely related to the local density of states. We experimentally demonstrate that different self-organized Gd atomic structures are formed within 30-nm circular and triangular Fe quantum corrals with a step-by-step guiding process. The findings demonstrate that quantum confinement can be used to engineer atomic structures and atom diffusion. And 30-nm resolution can be reached by means of advanced lithography. Adding quantum engineering to augment it opens new possibilities for local functionality design down to the atomic scale.

Cao, Rongxing; Miao, Bingfeng; Zhong, Zhangfeng; Sun, Liang; You, Biao; Zhang, Wei; Wu, Di; Hu, An; Bader, Samuel; Ding, Haifeng

2013-03-01

184

Self Assembly of Tethered Nanoparticle Telechelics  

NASA Astrophysics Data System (ADS)

Simulations, theory, and experiement predict that aggregating nanoparticles functionalized with polymer tethers can self-assemble to form phases seen in block copolymer and surfactant systems, but with additional nanoparticle ordering and mesophase complexity. Here we consider a novel class of ``telechelic'' tethered nanoparticle building blocks, where two nanoparticles are connected together by a polymer tether. The architecture is similar to a triblock copolymer, but with additional geometric constraints imposed by the rigid particle end groups. Using Brownian dynamics simulations, we explore the phase diagrams of several examples of this class of nano-building-block, and present predictions of novel phases and their dependence on particle size, tether length, and thermodynamic parameters. We compare our results with recent simulations of di-tethered nanospheres [1, 2] and mono-tethered nanospheres [2, 3]. *Iacovella, C. R.; Glotzer, S. C.; Soft Matter 2009, 5, 4492-4498. *Iacovella, C. R.; Keys, A.S..; Glotzer, S. C. PNAS, in press. arXiv:1102.5589. *Phillips, C. L.; Iacovella, C. R.; Glotzer, S. C.; Soft Matter 2010, 6, 1693-1703.

Marson, Ryan; Phillips, Carolyn; Anderson, Joshua; Glotzer, Sharon

2012-02-01

185

Self-assembling holographic biosensors and biocomputers.  

SciTech Connect

We present concepts for self-assembly of diffractive optics with potential uses in biosensors and biocomputers. The simplest such optics, diffraction gratings, can potentially be made from chemically-stabilized microtubules migrating on nanopatterned tracks of the motor protein kinesin. We discuss the fabrication challenges involved in patterning sub-micron-scale structures with proteins that must be maintained in aqueous buffers to preserve their activity. A novel strategy is presented that employs dry contact printing onto glass-supported amino-silane monolayers of heterobifunctional crosslinkers, followed by solid-state reactions of these cross-linkers, to graft patterns of reactive groups onto the surface. Successive solution-phase addition of cysteine-mutant proteins and amine-reactive polyethylene glycol allows assembly of features onto the printed patterns. We present data from initial experiments showing successful micro- and nanopatterning of lines of single-cysteine mutants of kinesin interleaved with lines of polyethylene, indicating that this strategy can be employed to arrays of features with resolutions suitable for gratings.

Light, Yooli Kim; Bachand, George David (Sandia National Laboratories, Albuquerque, NM); Schoeniger, Joseph S.; Trent, Amanda M. (Sandia National Laboratories, Albuquerque, NM)

2006-05-01

186

Self-assembled biomimetic superhydrophobic hierarchical arrays.  

PubMed

Here, we report a simple and inexpensive bottom-up technology for fabricating superhydrophobic coatings with hierarchical micro-/nano-structures, which are inspired by the binary periodic structure found on the superhydrophobic compound eyes of some insects (e.g., mosquitoes and moths). Binary colloidal arrays consisting of exemplary large (4 and 30 ?m) and small (300 nm) silica spheres are first assembled by a scalable Langmuir-Blodgett (LB) technology in a layer-by-layer manner. After surface modification with fluorosilanes, the self-assembled hierarchical particle arrays become superhydrophobic with an apparent water contact angle (CA) larger than 150°. The throughput of the resulting superhydrophobic coatings with hierarchical structures can be significantly improved by templating the binary periodic structures of the LB-assembled colloidal arrays into UV-curable fluoropolymers by a soft lithography approach. Superhydrophobic perfluoroether acrylate hierarchical arrays with large CAs and small CA hysteresis can be faithfully replicated onto various substrates. Both experiments and theoretical calculations based on the Cassie's dewetting model demonstrate the importance of the hierarchical structure in achieving the final superhydrophobic surface states. PMID:23786830

Yang, Hongta; Dou, Xuan; Fang, Yin; Jiang, Peng

2013-09-01

187

Magnetic manipulation of self-assembled colloidal asters.  

SciTech Connect

Self-assembled materials must actively consume energy and remain out of equilibrium to support structural complexity and functional diversity. Here we show that a magnetic colloidal suspension confined at the interface between two immiscible liquids and energized by an alternating magnetic field dynamically self-assembles into localized asters and arrays of asters, which exhibit locomotion and shape change. By controlling a small external magnetic field applied parallel to the interface, we show that asters can capture, transport, and position target microparticles. The ability to manipulate colloidal structures is crucial for the further development of self-assembled microrobots

Snezhko, A.; Aranson, I. S. (Materials Science Division)

2011-09-01

188

Material self-assembly as a physicochemical process.  

PubMed

Material self-assembly as exemplified in protobiogeneses is shown to be result of molecular exchange interaction in reacting chemicals. Temporally and spatially correlated aggregates of reacting chemicals work as vertices of molecular exchange interaction. If the material accumulation rate at a locally correlated aggregate spontaneously happens to become positive at a certain time, the material accumulation due to self-assembly will increase with time afterward. A spontaneous formation of looped reaction at locally correlated aggregates of reacting chemicals can initiate a material self-assembly at succeeding times. PMID:7248486

Matsuno, K

1981-01-01

189

Structural and Chemical Control of Supramolecular Coordination Self-Assembly Confined on Metal Surfaces  

NASA Astrophysics Data System (ADS)

This thesis is concerned with the structural and chemical control of two-dimensional (2D) supramolecular self-assemblies through judiciously manipulating bonding motifs at various intrinsic and external conditions. The self-selection and the self-recognition of the noncovalent interactions among organic and/or metallic building blocks govern the structural and chemical properties of the resultant self-assembled two-dimensional nanostructures, accompanying with the thermodynamic and kinetic process as well. In this thesis, we have investigated the supramolecular self-assembly achieved via coordination bonds assisted by transition metals and functional ligands on metal surfaces. The self-assembled nanostructures were studied by ultra-high vacuum scanning tunneling microscopy working at room temperatures. The structural transition processes were also inspected via the low energy electron diffraction. Further, artificial "quantum dots" represented by the cavities of the self-assembled networks were investigated. The modulation of surface electrons by these "quantum dots" was characterized by the local density of states detected by low-temperature scanning tunneling spectroscopy. The major contributions of this thesis are outlined as below: (1) Through modifying the chemical states of organic ligands, a unique coordination Kagome network structure was obtained for the first time by two distinct methods. TPyP (5, 10, 15, 20-tetra(4-pyridyl)porphyrin) species on Au(111) surfaces form the TPyP-Au coordination Kagome network achieved by a novel treatment that was suggested to modify the chemical state of the TPyP. In a condition that the TPyP coexists with Cu on a Au(111), Cu adatoms play two roles in the self-assembly---the coordination with pyridyl end-groups and the reaction with TPyP macrocycles, which control the chemical and structural phase of the self-assembly. Following a high temperature annealing, the same Kagome structure emerged from a precursor rhombus network structure. We proposed a new mechanism which provides a consistent explanation to both assembly methods. ZnTPyP (zinc 5, 10, 15, 20-tetra(4- pyridyl)porphyrin) molecules show chemical stability at high annealing temperature, which allows for preparing chemically pure ZnTPyP-Cu bimetallic networks. Furthermore, a reversible structural transformation between a hydrogen-bonded network and a coordination network was realized by either adding Cu atoms or annealing samples at certain temperatures. (2) The influence of the thermodynamic and kinetic effects on the selection of binding modes was studied by a combined STM and LEED investigation which offered spatial as well as temporal insights. The molecules of TPyB (1,3,5-trispyridylbenzene) coordinate with Cu or Fe respectively, forming two distinct polymorphism network structures. Two coordination binding modes show different binding energies. By the kinetic and thermodynamic control, either of binding modes was selected. LEED patterns revealed the dynamic process of structural transition from that of low binding-energy mode to that of high binding-energy mode. In the latter section the structural phase transition induced by two-dimensional compression is introduced. Pyridyl-Cu coordination bond is of certain liability, allowing for the alternation of bonds under various environments. Through increasing the coverage of molecules, distinctive polygraphic networks presented via different pyridyl-Cu binding modes. (3) The self-assembly of multiple components represent a much more complicated assembly system, where the elaborate balance of interactions among all components and substrates comprises greater challenging. To study such a system, the third part deals with the multiple-ligand self-assembly. Achieved by TPyP and PBTP 4',4"-(1,4- phenylene)bis(2,2':6',2"-terpyridine)) molecules and Fe, two types of network structure formed on Au(111) surfaces. Both networks coexisted due to similar bonding configurations and free energies. However, the entropy is presumably suggested to promote the

Shi, Ziliang

190

Toward three-dimensional microelectronic systems: directed self-assembly of silicon microcubes via DNA surface functionalization.  

PubMed

The huge and intelligent processing power of three-dimensional (3D) biological "processors" like the human brain with clock speeds of only 0.1 kHz is an extremely fascinating property, which is based on a massively parallel interconnect strategy. Artificial silicon microprocessors are 7 orders of magnitude faster. Nevertheless, they do not show any indication of intelligent processing power, mostly due to their very limited interconnectivity. Massively parallel interconnectivity can only be realized in three dimensions. Three-dimensional artificial processors would therefore be at the root of fabricating artificially intelligent systems. A first step in this direction would be the self-assembly of silicon based building blocks into 3D structures. We report on the self-assembly of such building blocks by molecular recognition, and on the electrical characterization of the formed assemblies. First, planar silicon substrates were functionalized with self-assembling monolayers of 3-aminopropyltrimethoxysilane for coupling of oligonucleotides (single stranded DNA) with glutaric aldehyde. The oligonucleotide immobilization was confirmed and quantified by hybridization with fluorescence-labeled complementary oligonucleotides. After the individual processing steps, the samples were analyzed by contact angle measurements, ellipsometry, atomic force microscopy, and fluorescence microscopy. Patterned DNA-functionalized layers were fabricated by microcontact printing (?CP) and photolithography. Silicon microcubes of 3 ?m edge length as model objects for first 3D self-assembly experiments were fabricated out of silicon-on-insulator (SOI) wafers by a combination of reactive ion etching (RIE) and selective wet etching. The microcubes were then surface-functionalized using the same protocol as on planar substrates, and their self-assembly was demonstrated both on patterned silicon surfaces (88% correctly placed cubes), and to cube aggregates by complementary DNA functionalization and hybridization. The yield of formed aggregates was found to be about 44%, with a relative fraction of dimers of some 30%. Finally, the electrical properties of the formed dimers were characterized using probe tips inside a scanning electron microscope. PMID:23786592

Lämmerhardt, Nico; Merzsch, Stephan; Ledig, Johannes; Bora, Achyut; Waag, Andreas; Tornow, Marc; Mischnick, Petra

2013-07-01

191

Differential self-assembly and tunable emission of aromatic Peptide bola-amphiphiles containing perylene bisimide in polar solvents including water.  

PubMed

We demonstrate the self-assembly of bola-amphiphile-type conjugates of dipeptides and perylene bisimide (PBI) in water and other polar solvents. Depending on the nature of the peptide used (glycine-tyrosine, GY, or glycine-aspartic acid, GD), the balance between H-bonding and aromatic stacking can be tailored. In aqueous buffer, PBI-[GY]2 forms chiral nanofibers, resulting in the formation of a hydrogel, while for PBI-[GD]2 achiral spherical aggregates are formed, demonstrating that the peptide sequence has a profound effect on the structure formed. In water and a range of other polar solvents, self-assembly of these two PBI-peptides conjugates results in different nanostructures with highly tunable fluorescence performance depending on the peptide sequence employed, e.g., fluorescent emission and quantum yield. Organogels are formed for the PBI-[GD]2 derivative in DMF and DMSO while PBI-[GY]2 gels in DMF. To the best of our knowledge, this is the first successful strategy for using short peptides, specifically, their sequence/structure relationships, to manipulate the PBI nanostructure and consequent optical properties. The combination of controlled self-assembly, varied optical properties, and formation of aqueous and organic gel-phase materials may facilitate the design of devices for various applications related to light harvesting and sensing. PMID:24911955

Bai, Shuo; Debnath, Sisir; Javid, Nadeem; Frederix, Pim W J M; Fleming, Scott; Pappas, Charalampos; Ulijn, Rein V

2014-07-01

192

Insights into the Photoprotective Switch of the Major Light-harvesting Complex II (LHCII)  

PubMed Central

Light-harvesting antennae of the LHC family form transmembrane three-helix bundles of which two helices are interlocked by conserved arginine-glutamate (Arg-Glu) ion pairs that form ligation sites for chlorophylls. The antenna proteins of photosystem II have an intriguing dual function. In excess light, they can switch their conformation from a light-harvesting into a photoprotective state, in which the excess and harmful excitation energies are safely dissipated as heat. Here we applied magic angle spinning NMR and selective Arg isotope enrichment as a noninvasive method to analyze the Arg structures of the major light-harvesting complex II (LHCII). The conformations of the Arg residues that interlock helix A and B appear to be preserved in the light-harvesting and photoprotective state. Several Arg residues have very downfield-shifted proton NMR responses, indicating that they stabilize the complex by strong hydrogen bonds. For the Arg C? chemical shifts, differences are observed between LHCII in the active, light-harvesting and in the photoprotective, quenched state. These differences are attributed to a conformational change of the Arg residue in the stromal loop region. We conclude that the interlocked helices of LHCII form a rigid core. Consequently, the LHCII conformational switch does not involve changes in A/B helix tilting but likely involves rearrangements of the loops and helical segments close to the stromal and lumenal ends.

Sunku, Kiran; de Groot, Huub. J. M.; Pandit, Anjali

2013-01-01

193

Enzymatic Self-Assembly of Nanostructures for Theranostics  

PubMed Central

Self-assembly of small molecules or macromolecules through non-covalent or covalent bonds to build up supramolecular nanostructures is a prevalent and important process in nature. While most chemists use small molecules to assemble nanostructures with physical or chemical perturbations, nature adopts enzymes to catalyze the reaction to assemble biological, functional nanostructures with high efficiency and specificity. Although enzymatic self-assembly of nanostructures has been remained challenging for chemists, there are still a few examples of using important enzymes to initiate the self-assembly of nanostructures for diagnosis or therapy of certain diseases because down-regulation or overexpression of certain enzymes always associates with abnormalities of tissues/organs or diseases in living body. Herein, we introduce the concept of enzymatic self-assembly and illustrate the design and application of enzyme-catalyzed or -regulated formation of nanostructures for theranostics.

Chen, Yue; Liang, Gaolin

2012-01-01

194

Novel Materials and Devices From Self-Assembled Periodic Structures.  

National Technical Information Service (NTIS)

The research program developed novel mesoscopically periodic materials for use in novel optical devices such as optical limiters (OL) and switches. These materials are fabricated using the crystalline colloidal array (CCA) self assembly motif. We develope...

S. A. Asher

1996-01-01

195

Directed self-assembly of proteins into discrete radial patterns  

PubMed Central

Unlike physical patterning of materials at nanometer scale, manipulating soft matter such as biomolecules into patterns is still in its infancy. Self-assembled monolayer (SAM) with surface density gradient has the capability to drive biomolecules in specific directions to create hierarchical and discrete structures. Here, we report on a two-step process of self-assembly of the human serum albumin (HSA) protein into discrete ring structures based on density gradient of SAM. The methodology involves first creating a 2-dimensional (2D) polyethylene glycol (PEG) islands with responsive carboxyl functionalities. Incubation of proteins on such pre-patterned surfaces results in direct self-assembly of protein molecules around PEG islands. Immobilization and adsorption of protein on such structures over time evolve into the self-assembled patterns.

Thakur, Garima; Prashanthi, Kovur; Thundat, Thomas

2013-01-01

196

Self Assembly Properties of Primitive Organic Compounds (Abstract Only).  

National Technical Information Service (NTIS)

A central event in the origin of life was the self-assembly of amphiphilic, lipid-like compounds into closed microenvironments. If a primitive macromolecular replicating system could be encapsulated within a vesicular membrane, the components of the syste...

D. W. Deamer

1991-01-01

197

Differentially photo-crosslinked polymers enable self-assembling microfluidics  

PubMed Central

An important feature of naturally self-assembled systems such as leaves and tissues is that they are curved and have embedded fluidic channels that enable the transport of nutrients to, or removal of waste from, specific three-dimensional (3D) regions. Here, we report the self-assembly of photopatterned polymers, and consequently microfluidic devices, into curved geometries. We discovered that differentially photo-crosslinked SU-8 films spontaneously and reversibly curved upon film de-solvation and re-solvation. Photolithographic patterning of the SU-8 films enabled the self-assembly of cylinders, cubes, and bidirectionally folded sheets. We integrated polydimethylsiloxane (PDMS) microfluidic channels with these SU-8 films to self-assemble curved microfluidic networks.

Jamal, Mustapha; Zarafshar, Aasiyeh M.; Gracias, David H.

2012-01-01

198

Nano-Engineering by Optically Directed Self-Assembly.  

National Technical Information Service (NTIS)

Lack of robust manufacturing capabilities have limited our ability to make tailored materials with useful optical and thermal properties. For example, traditional methods such as spontaneous self-assembly of spheres cannot generate the complex structures ...

A. D. Gorby A. M. Grillet C. M. Brother M. D. Reichert N. S. Bell R. A. Molecke T. P. Koehler

2009-01-01

199

Self-assembled nanostructured optical fiber strain and pressure sensors  

Microsoft Academic Search

A simple optical fiber-based strain and pressure sensor has been fabricated using nanostructured self-assembled elastomeric free-standing thin film materials. The fabrication of the sensor material and a demonstration of the sensor performance are described.

Jennifer H. Lalli; Jeffrey B. Mecham; Bradley Davis; Francisco J. Arregui; Ignacio R. Matias; Richard O. Claus

2004-01-01

200

Self-Assembling Nano-Electronics Turn a Corner  

NSF Publications Database

... describe how carefully chosen mixtures of polymers can be made to assemble themselves into nanoscale ... two years ago, using a simpler mix of polymers that could self-assemble only into regular ...

201

Directed self-assembly of proteins into discrete radial patterns  

NASA Astrophysics Data System (ADS)

Unlike physical patterning of materials at nanometer scale, manipulating soft matter such as biomolecules into patterns is still in its infancy. Self-assembled monolayer (SAM) with surface density gradient has the capability to drive biomolecules in specific directions to create hierarchical and discrete structures. Here, we report on a two-step process of self-assembly of the human serum albumin (HSA) protein into discrete ring structures based on density gradient of SAM. The methodology involves first creating a 2-dimensional (2D) polyethylene glycol (PEG) islands with responsive carboxyl functionalities. Incubation of proteins on such pre-patterned surfaces results in direct self-assembly of protein molecules around PEG islands. Immobilization and adsorption of protein on such structures over time evolve into the self-assembled patterns.

Thakur, Garima; Prashanthi, Kovur; Thundat, Thomas

2013-05-01

202

Converting molecular information of redox coenzymes via self-assembly.  

PubMed

?-Nicotinamide adenine dinucleotide (NAD(+)) and its reduced form NADH specifically interact with a cyanine dye in aqueous media, giving distinct spectral and nanostructural characteristics to which molecular information of constituent coenzymes are converted via self-assembly. PMID:23042134

Morikawa, Masa-aki; Kimizuka, Nobuo

2012-11-21

203

Self-assembly in block polyelectrolytes.  

PubMed

The self-consistent field theory (SCFT) complemented with the Poisson-Boltzmann equation is employed to explore self-assembly of polyelectrolyte copolymers composed of charged blocks A and neutral blocks B. We have extended SCFT to dissociating triblock copolymers and demonstrated our approach on three characteristic examples: (1) diblock copolymer (AB) melt, (2) symmetric triblock copolymer (ABA) melt, (3) triblock copolymer (ABA) solution with added electrolyte. For copolymer melts, we varied the composition (that is, the total fraction of A-segments in the system) and the charge density on A blocks and calculated the phase diagram that contains ordered mesophases of lamellar, gyroid, hexagonal, and bcc symmetries, as well as the uniform disordered phase. The phase diagram of charged block copolymer melts in the charge density--system composition coordinates is similar to the classical phase diagram of neutral block copolymer melts, where the composition and the Flory mismatch interaction parameter ?(AB) are used as variables. We found that the transitions between the polyelectrolyte mesophases with the increase of charge density occur in the same sequence, from lamellar to gyroid to hexagonal to bcc to disordered morphologies, as the mesophase transitions for neutral diblocks with the decrease of ?(AB). In a certain range of compositions, the phase diagram for charged triblock copolymers exhibits unexpected features, allowing for transitions from hexagonal to gyroid to lamellar mesophases as the charge density increases. Triblock polyelectrolyte solutions were studied by varying the charge density and solvent concentration at a fixed copolymer composition. Transitions from lamellar to gyroid and gyroid to hexagonal morphologies were observed at lower polymer concentrations than the respective transitions in the similar neutral copolymer, indicating a substantial influence of the charge density on phase behavior. PMID:21303089

Yang, Shuang; Vishnyakov, Aleksey; Neimark, Alexander V

2011-02-01

204

Inspection of directed self-assembly defects  

NASA Astrophysics Data System (ADS)

Directed Self-Assembly (DSA) is considered as a potential patterning solution for future generation devices. One of the most critical challenges for translating DSA into high volume manufacturing is to achieve low defect density in the DSA patterning process. The defect inspection capability is fundamental to defect reduction in any process, particularly the DSA process, as it provides engineers with information on the numbers and types of defects. While the challenges of other candidates of new generation lithography are well known (for example, smaller size, noise level due to LER etc.), the DSA process causes certain defects that are unique. These defects are nearly planar and in a material which produces very little defect scattering signal. These defects, termed as "dislocation" and "disclination" have unique shapes and have very little material contrast. While large clusters of these unique defects are easy to detect, single dislocation and disclination defects offer considerable challenge during inspection. In this investigation, etching the DSA pattern into a silicon (Si) substrate structure to enhance defect signal and Signal-to-Noise Ratio (SNR) is studied. We used a Rigorous Coupled-Wave Analysis (RCWA) method for solving Maxwell's equations to simulate the DSA unique defects and calculate inspection parameters. Controllable inspection parameters include various illumination and collection apertures, wavelength band, polarization, noise filtering, focus, pixel size, and signal processing. From the RCWA simulation, we compared SNR between "Post-SiN etch" and "Post-SiN+Si-substrate etch" steps. The study is also extended to investigate wafer-level data at post etch inspection. Both the simulations and inspection tool results showed dramatic signal and SNR improvements when the pattern was etched into the SiN+Si substrate allowing capture of DSA unique defect types.

Ito, Chikashi; Durant, Stephane; Lange, Steve; Harukawa, Ryota; Miyagi, Takemasa; Nagaswami, Venkat; Rincon Delgadillo, Paulina; Gronheid, Roel; Nealey, Paul

2014-03-01

205

Self-assemblying systems in shear flow  

NASA Astrophysics Data System (ADS)

The Ginzburg-Landau free-energy approach [1] used to describe the equilibrium phase diagram of self-assemblying systems and ternary mixtures can be extended to take into account the presence of imposed flows [2,3]. Our results mainly concern the effects of a shear flow on transient and stationary properties of microemulsions. Equal time and two-time correlations have been calculated in the framework of a self-consistent approximation. The structure factor is anisotropic and at high shear rates is dominated by two peaks at kx = 0 corresponding to interfaces aligned with the flow. The stress as a function of the shear rate has been calculated: shear thinning is observed to occurr at two characteristic shear rates, the first corresponding to the inverse of the structural relaxation time. When the flow is applied starting from a quiescent condition, the transient behaviour shows a maximum of the stress followed by a relaxation to the stationary value. This can be interpreted as an accumulation of stress in the original microemulsion structure followed by a topology change with breakdowns in the interface connectivity. We have also done a similar study for micellar solutions comparing our results with the experimental data of [4]. [1] G. Gompper and M. Schick, Phys. Rev. Lett. 65, 1116 (1990). [2] G. Pätzold and K. Dawson, Phys. Rev. E 54, 1669 (1996); G. Pätzold and K. Dawson, J. Chem. Phys. 104, 5932 (1996). [3] F. Corberi, G. Gonnella, and D. Suppa, cond-mat/0004282, Phys. Rev. E - Rapid Comm. 63, 040501(R) (2001). [4] P. Boltenhagen, Yuntao Hu, E.F. Matthys and D.J. Pine, Europhys. Lett. 38, 389 (1997). R. Bandyopadhyay, G. Basappa and A. K. Sood, Phys. Rev. Lett.

Gonnella, Giuseppe; Ruggieri, Marco; Corberi, Federico

2002-03-01

206

Vortical superlattices in a gold nanorods' self-assembled monolayer  

NASA Astrophysics Data System (ADS)

This paper describes the novel vortical self-assembly of CTAB-capped gold nanorods. Representative left-hand, radial, and right-hand vortices are shown. Micelles formed by CTAB molecules enhance the organized self-assembly process. The drag force of solvent flow and dynamic vortex flow in the thin solvent layer are thought to be responsible for the final vortical superlattices. FDTD simulation suggests these structures have potential applications in nanofocusing and polarized light response.

Xie, Yong; Liang, Yujia; Chen, Dongxue; Wu, Xiaochun; Dai, Luru; Liu, Qian

2014-02-01

207

Vortical superlattices in a gold nanorods' self-assembled monolayer.  

PubMed

This paper describes the novel vortical self-assembly of CTAB-capped gold nanorods. Representative left-hand, radial, and right-hand vortices are shown. Micelles formed by CTAB molecules enhance the organized self-assembly process. The drag force of solvent flow and dynamic vortex flow in the thin solvent layer are thought to be responsible for the final vortical superlattices. FDTD simulation suggests these structures have potential applications in nanofocusing and polarized light response. PMID:24513644

Xie, Yong; Liang, Yujia; Chen, Dongxue; Wu, Xiaochun; Dai, Luru; Liu, Qian

2014-03-21

208

Physics and applications of self-assembled quantum dots  

Microsoft Academic Search

Linear and nonlinear spectroscopic invsetigations of self-assembled quantum dots open up the possibility to study model quantum mechanical systems with potential applications in solid-state based quantum information processing. In this article we review recent advances in our understanding of the physics of self-assembled quantum dots and novel devices based upon them. We focus our attention on four key areas: (i)

E. Beham; M. Betz; S. Trumm; M. Kroutvar; Y. Ducommun; H. J. Krenner; M. Bichler; A. Leitenstorfer; J. J. Finley; A. Zrenner; G. Abstreiter

2004-01-01

209

Self-Assembled Monolayers of Chromophores on Gold Surfaces  

Microsoft Academic Search

In the last two decades the field of self-assembled monolayers (SAMs) has received much attention\\u000a both in research and for applications because of the stability and the simple handling of SAMs. In\\u000a this account we present a short overview about the morphology and preparation of the different\\u000a gold surfaces used for SAMs and about self-assembled alkanethiol monolayers on Au(111). The synthetic

Volker Kriegisch; Christoph Lambert

210

Scratch Drive Actuator Driven Self-assembled Variable Optical Attenuator  

Microsoft Academic Search

This paper describes the new concept and design for a self-assembled variable optical attenuator (VOA) derived by using surface micromachining technology. A residual stress-induced flexure curved beam with corrugated trench anchors can lift up the reflective mirror shutter. This self-assembled reflective shutter can be driven by a set of scratch drive actuator (SDA), then slides into the spacing between input

Chengkuo Lee; Yen-Jyh Lai; Chia-Yu Wu; Yu-Shen Lin; Ming Hung Tasi; Ruey-Shing Huang; Min-Shyong Lin

2004-01-01

211

3-D self-assembling and actuation of electrostatic microstructures  

Microsoft Academic Search

An advanced three-dimensional (3-D) self-assembling technique of surface micro-machined polysilicon structures is presented here for the realization of dedicated actuators for optical applications such as micro-mirror arrays with large deflection angles. Three-dimensional polysilicon microparts are self-assembled by beam buckling induced by integrated scratch drive actuators (SDAs). With this technique, 380×250 ?m2 microplates were lifted 30 ?m above the substrate plane.

E. Quevy; L. Buchaillot; D. Collard

2001-01-01

212

Self-assembly of side chain liquid crystalline block copolymers  

Microsoft Academic Search

We present a new model based on self-consistent field theory (SCFT) approach to characterize the self assembly behavior in side-chain liquid crystalline block copolymers. Our model considers a micromechanical representation of flexible coil-coil diblock copolymers, with rod-like units grafted to one of the blocks. We present results which elucidate self-assembly arising from the interplay between block copolymer microphase separation and

Manas Shah; Victor Pryamitsyn; Venkat Ganesan

2008-01-01

213

Self-assembly of polymeric microspheres of complex internal structures  

Microsoft Academic Search

Self-assembly can easily produce intricate structures that would be difficult to make by conventional fabrication means. Here, self-assembly is used to prepare multicomponent polymeric microspheres of arbitrary internal symmetries. Droplets of liquid prepolymers are printed onto a water-soluble hydrogel, and are allowed to spread and coalesce into composite patches. These patches are then immersed in an isodense liquid, which both

Marcin Fialkowski; Agnieszka Bitner; Bartosz A. Grzybowski

2005-01-01

214

Application of DNA Self-assembly on Maximum Clique Problem  

Microsoft Academic Search

Computation by self-assembly of DNA is an efficient method of executing parallel DNA computing, in which information is encoded\\u000a in DNA tiles and a large number of tiles can be self-assembled via sticky end associations. Here, we investigate how basic\\u000a ideas on tiling can be applied to solve maximum clique problem (MCP). We suggest that these procedures can be realized

Guangzhao Cui; Cuiling Li; Haobin Li; Xuncai Zhang; Xiaoguang Li

215

Ordered Self-Assembling of Tetrahedral Oxide Nanocrystals  

Microsoft Academic Search

Self-assembling of size, shape, and phase controlled nanocrystals into superlattices with translational and even orientational ordering is a new approach for engineering nanocrystal materials and devices. High purity tetrahedral nanocrystals of CoO, with edge lengths of 4.4 6 0.2 nm, were synthesized and separated from Co nanocrystals, using a novel magnetic field phase-selection technique. Self- assembling of the faceted CoO

J. S. Yin; Z. L. Wang

1997-01-01

216

Various Aspects of the Interfacial Self-Assembly of Nanoparticles  

Microsoft Academic Search

\\u000a We describe the interfacial self-assembly of nanoparticles at liquid–liquid interfaces and in block copolymers. At the interface\\u000a of two immiscible liquids, the particles assemble into disordered but densely packed monolayers. This self-assembly process\\u000a was investigated ex situ with scanning force microscopy (SFM) and transmission electron microscopy (TEM), and laser scanning\\u000a confocal microscopy (LCSM) methods. Adsorbed particles can be crosslinked at

Nicole Popp; Sergej Kutuzov; Alexander Böker

2010-01-01

217

Dynamics of Self-Assembling Systems: Analogy with Chemical Kinetics  

Microsoft Academic Search

In this article, we propose a new analyzing method for self-assembling systems. Its initial purpose was to predict the yield—the final amount of desired product—of our original self-assembling mechanical model. Moreover, the method clarifies the dynamical evolution of the system. In this method, the quantity of each intermediate product is adopted as state variables, and the dynamics that dominates the

Kazuo Hosokawa; Isao Shimoyama; Hirofumi Miura

1994-01-01

218

Stability of surface tension self-assembled 3D MOEMS  

Microsoft Academic Search

The thermal and mechanical stability of self-assembled MOEMS components consisting of 3D mirrors have been evaluated. The thermal–mechanical constants of the hinge material (AZ4562 photoresist) used to power the surface tension self-assembly process have been measured and used to predict the stability of assemblies. The Young's moduli and thermal expansion coefficients showed constant values of average 6.78×109N\\/m2 and 4.08×10?6°C?1 under

Y. K. Hong; R. R. A. Syms

2006-01-01

219

Molecular Recognition Directed Self-Assembly of Supramolecular Liquid Crystals  

Microsoft Academic Search

The first part of this paper discusses the molecular design of selected examples of structural units containing taper shaped exo-receptors and various crown ether, oligooxyethylenic, and H-bonding based endo-receptors, which self-assemble into cylindrical channel-like architectures via principles resembling those of tobacco mosaic virus (TMV). The ability of these structural units to self-assemble via a delicate combination of exo- and endo-recognition

V. Percec; J. Heck; G. Johansson; D. Tomazos; M. Kawasumi; P. Chu; G. Ungar

1994-01-01

220

Molecular-Recognition-Directed Self-Assembly of Supramolecular Polymers  

Microsoft Academic Search

The first part of this paper discusses the molecular design of selected examples of structural units containing taper-shaped exo-receptors and various crown ether, oligooxyethylenic, and H-bonding-based endo-receptors, which self-assemble into cylindrical channel-like architectures via principles resembling those of tobacco mosaic virus. The ability of these structural units to self-assemble via a delicate combination of exo-and endo-recognition processes will be presented.

V. Percec; J. Heck; G. Johansson; D. Tomazos; M. Kawasumi; G. Ungar

1994-01-01

221

Electric Field Controlled Self-Assembly of Hierarchically Ordered Membranes  

PubMed Central

Self-assembly in the presence of external forces is an adaptive, directed organization of molecular components under nonequilibrium conditions. While forces may be generated as a result of spontaneous interactions among components of a system, intervention with external forces can significantly alter the final outcome of self-assembly. Superimposing these intrinsic and extrinsic forces provides greater degrees of freedom to control the structure and function of self-assembling materials. In this work we investigate the role of electric fields during the dynamic self-assembly of a negatively charged polyelectrolyte and a positively charged peptide amphiphile in water leading to the formation of an ordered membrane. In the absence of electric fields, contact between the two solutions of oppositely charged molecules triggers the growth of closed membranes with vertically oriented fibrils that encapsulate the polyelectrolyte solution. This process of self-assembly is intrinsically driven by excess osmotic pressure of counterions, and the electric field is found to modify the kinetics of membrane formation, and also its morphology and properties. Depending on the strength and orientation of the field we observe a significant increase or decrease of up to nearly 100% in membrane thickness, as well as the controlled rotation of nanofiber growth direction by 90 degrees, resulting in a significant increase in mechanical stiffness. These results suggest the possibility of using electric fields to control structure in self-assembly processes involving diffusion of oppositely charged molecules.

Velichko, Yuri S.; Mantei, Jason R.; Bitton, Ronit; Carvajal, Daniel; Shull, Kenneth R.; Stupp, Samuel I.

2012-01-01

222

Tuning the self-assembly of rectangular amphiphilic cruciforms.  

PubMed

The self-assembly of a series of nonionic amphiphilic cruciforms based on the 1,2,4,5-tetrakis(phenylethynyl)benzene (TPEB) skeleton, in which the peripheral substituents have been modified to modulate the morphology of the supramolecular structures, is reported. The presence of linear paraffinic and hydrophilic chains in TPEBs 1 and 2 gives rise to two-dimensional structures of high aspect ratio. In contrast, the incorporation of dendronized hydrophilic chains results in the formation of twisted ribbons in amphiphile 3 and impedes the organized self-assembly of TPEB 4. Theoretical calculations show that the self-assembly of these amphiphiles might be initiated with the formation of ?-stacked dimeric units. Compound 2, which self-assembles into different morphologies depending on the solvent, interacts by ?-stacking and also by the interdigitation of the peripheral decyl tails to generate bidimensional supramolecular structures. The steric demand exerted by the dendronized polar wedges in 3 and 4 strongly conditions their supramolecular organization. This steric demand together with the interdigitation of the decyl chains results in the self-assembly of cruciform 3 into helical aggregates. However, the lack of the paraffinic chains in 4 impedes this helical organization, and the formation of amorphous material is visualized. The joint experimental and theoretical study presented herein provides relevant guidelines for the modulated self-assembly of nonionic amphiphilic molecules. PMID:24802522

García, Fátima; Costa, Rubén D; Aragó, Juan; Bolink, Henk J; Ortí, Enrique; Sánchez, Luis

2014-05-27

223

Organization and Assembly of Light-Harvesting Complexes in the Purple Bacterial Membrane  

Microsoft Academic Search

Recent in situ surface images of the intracytoplasmic membrane (ICM) of purple photosynthetic bacteria obtained at submolecular\\u000a resolution by atomic force microscopy (AFM), have revealed multiple, species-dependent patterns of supramolecular organizations\\u000a for their light-harvesting (LH) antennas, suggested earlier from spectroscopic studies. These have varied from highly ordered\\u000a linear arrays of dimeric reaction center-light-harvesting 1-PufX (RC-LH1-PufX) core complexes in Rhodobacter (Rba.)

James N. Sturgis; Robert A. Niederman

224

Energy Transfer in the Major Intrinsic Light-Harvesting Complex from Amphidinium carterae †  

Microsoft Academic Search

Carbonyl carotenoids are important constituents of the antenna complexes of marine organisms. These carotenoids possess an excited state with a charge-transfer character (intramolecular charge transfer state, ICT), but many details of the carotenoid to chlorophyll energy transfer mechanisms are as yet poorly understood. Here, we employ femtosecond transient absorption spectroscopy to study energy transfer pathways in the intrinsic light-harvesting complex

Tomáš Polívka; Ivo H. M. van Stokkum; Donatas Zigmantas; Rienk van Grondelle; Villy Sundström; Roger G. Hiller

2006-01-01

225

Strigolactones are positive regulators of light-harvesting genes in tomato  

PubMed Central

Strigolactones are newly identified plant hormones, shown to participate in the regulation of lateral shoot branching and root development. However, little is known about their effects on biological processes, genes, and proteins. Transcription profiling of roots treated with GR24, a synthetic strigolactone with proven biological activity, and/or indole acetic acid (IAA) was combined with physiological and transcriptional analysis of a tomato mutant (Sl-ORT1) deficient in strigolactone production. GR24 treatment led to markedly induced expression of genes putatively involved in light harvesting. This was apparent in both the presence and absence of exogenously applied IAA, but not with IAA treatment alone. Following validation of the microarray results, transcriptional induction by light of the GR24-induced genes was demonstrated in leaves exposed to high or low light intensities. Sl-ORT1 contained less chlorophyll and showed reduced expression of light harvesting-associated genes than the wild type (WT). Moreover, perfusion of GR24 into WT and Sl-ORT1 leaves led to induction of most of the examined light harvesting-associated genes. Results suggest that GR24 treatment interferes with the root's response to IAA treatment and that strigolactones are potentially positive regulators of light harvesting in plants.

Mayzlish-Gati, Einav; LekKala, Sivarama P.; Resnick, Nathalie; Wininger, Smadar; Bhattacharya, Chaitali; Lemcoff, J. Hugo; Kapulnik, Yoram; Koltai, Hinanit

2010-01-01

226

Atomistic study of energy funneling in the light-harvesting complex of green sulfur bacteria.  

PubMed

Phototrophic organisms such as plants, photosynthetic bacteria, and algae use microscopic complexes of pigment molecules to absorb sunlight. Within the light-harvesting complexes, which frequently have several functional and structural subunits, the energy is transferred in the form of molecular excitations with very high efficiency. Green sulfur bacteria are considered to be among the most efficient light-harvesting organisms. Despite multiple experimental and theoretical studies of these bacteria, the physical origin of the efficient and robust energy transfer in their light-harvesting complexes is not well understood. To study excitation dynamics at the systems level, we introduce an atomistic model that mimics a complete light-harvesting apparatus of green sulfur bacteria. The model contains approximately 4000 pigment molecules and comprises a double wall roll for the chlorosome, a baseplate, and six Fenna-Matthews-Olson trimer complexes. We show that the fast relaxation within functional subunits combined with the transfer between collective excited states of pigments can result in robust energy funneling to the initial excitation conditions and temperature changes. Moreover, the same mechanism describes the coexistence of multiple time scales of excitation dynamics frequently observed in ultrafast optical experiments. While our findings support the hypothesis of supertransfer, the model reveals energy transport through multiple channels on different length scales. PMID:24405318

Huh, Joonsuk; Saikin, Semion K; Brookes, Jennifer C; Valleau, Stéphanie; Fujita, Takatoshi; Aspuru-Guzik, Alán

2014-02-01

227

Characterization of nanoporous gold disks for photothermal light harvesting and light-gated molecular release.  

PubMed

Nanoporous gold disks (NPGDs) with 400 nm diameter, 75 nm thickness, and 13 nm pores exhibit large specific surface area and effective photothermal light harvesting capability with a conversion efficiency of 56%. A potential application is demonstrated by light-gated, multi-step molecular release of the pre-adsorbed R6G fluorescent dye on arrayed NPGDs. PMID:24789410

Santos, Greggy M; Zhao, Fusheng; Zeng, Jianbo; Shih, Wei-Chuan

2014-06-01

228

Subunit Interactions and Protein Stability in the Cyanobacterial Light-Harvesting Proteins.  

National Technical Information Service (NTIS)

Strain 4R is a phycocyanin-minus mutant of the unicellular cyanobacterium Synediocysfis sp. strain 6803. Although it lacks the light-harvesting protein phycocyanin, 4R has normal levels of phycocyanin (cpc) transcripts. Sequence analysis of the cpcB gene ...

T. Plank C. Toole L. K. Anderson

1995-01-01

229

Self-assembled liposomal nanoparticles in photodynamic therapy  

PubMed Central

Photodynamic therapy (PDT) employs the combination of non-toxic photosensitizers (PS) together with harmless visible light of the appropriate wavelength to produce reactive oxygen species that kill unwanted cells. Because many PS are hydrophobic molecules prone to aggregation, numerous drug delivery vehicles have been tested to solubilize these molecules, render them biocompatible and enhance the ease of administration after intravenous injection. The recent rise in nanotechnology has markedly expanded the range of these nanoparticulate delivery vehicles beyond the well-established liposomes and micelles. Self-assembled nanoparticles are formed by judicious choice of monomer building blocks that spontaneously form a well-oriented 3-dimensional structure that incorporates the PS when subjected to the appropriate conditions. This self-assembly process is governed by a subtle interplay of forces on the molecular level. This review will cover the state of the art in the preparation and use of self-assembled liposomal nanoparticles within the context of PDT.

Sadasivam, Magesh; Avci, Pinar; Gupta, Gaurav K.; Lakshmanan, Shanmugamurthy; Chandran, Rakkiyappan; Huang, Ying-Ying; Kumar, Raj; Hamblin, Michael R.

2013-01-01

230

Nanostructures formed by cyclodextrin covered aminobenzophenones through supramolecular self assembly.  

PubMed

Cyclodextrin (? and ?) based nanostructures formed with 2-aminobenzophenone, 3-aminobenzophenone through the supramolecular self assembly are studied by absorption, fluorescence, time-resolved fluorescence, SEM, TEM, FT-IR, DSC, PXRD and (1)H NMR. The unequal layer by layer nanosheets and nanoribbons are formed through self assembly of 3ABP/CD inclusion complexes. 2ABP/?-CD complex nanostructures show the self assembly hierarchical thread structure and ?-CD complexes displays a nanobrick structure. The formation of nanostructures are prearranged to HO?H, NH2?O and H2N?H intermolecular hydrogen bond between individual complexes. The absorption and fluorescence spectral changes explicit formation of 1:1 inclusion complexes and solvent study demonstrate the ESIPT and TICT present in both molecules. The thermodynamic parameters (?H, ?G and ?S) of 2ABP and 3ABP molecule and the inclusion complexes were determined from semiempirical PM3 calculations. PMID:24632156

Rajendiran, N; Sankaranarayanan, R K; Saravanan, J

2014-06-01

231

Self-assembled tunable networks of sticky colloidal particles.  

PubMed

Surfaces decorated with dense arrays of microscopic fibres exhibit unique materials properties, including superhydrophobicity and low friction. Nature relies on 'hairy' surfaces to protect blood capillaries from wear and infection (endothelial glycocalyx). Here we report on the discovery of self-assembled tunable networks of microscopic polymer fibres ranging from wavy colloidal 'fur' to highly interconnected networks. The networks emerge via dynamic self-assembly in an alternating electric field from a non-aqueous suspension of 'sticky' polymeric colloidal particles with a controlled degree of polymerization. The resulting architectures are tuned by the frequency and amplitude of the electric field and surface properties of the particles. We demonstrate, using atomic layer deposition, that the networks can serve as a template for a transparent conductor. These self-assembled tunable materials are promising candidates for large surface area electrodes in batteries and organic photovoltaic cells, as well as for microfluidic sensors and filters. PMID:24445324

Demortière, Arnaud; Snezhko, Alexey; Sapozhnikov, Maksim V; Becker, Nicholas; Proslier, Thomas; Aranson, Igor S

2014-01-01

232

Self-assembled tunable networks of sticky colloidal particles  

NASA Astrophysics Data System (ADS)

Surfaces decorated with dense arrays of microscopic fibres exhibit unique materials properties, including superhydrophobicity and low friction. Nature relies on ‘hairy’ surfaces to protect blood capillaries from wear and infection (endothelial glycocalyx). Here we report on the discovery of self-assembled tunable networks of microscopic polymer fibres ranging from wavy colloidal ‘fur’ to highly interconnected networks. The networks emerge via dynamic self-assembly in an alternating electric field from a non-aqueous suspension of ‘sticky’ polymeric colloidal particles with a controlled degree of polymerization. The resulting architectures are tuned by the frequency and amplitude of the electric field and surface properties of the particles. We demonstrate, using atomic layer deposition, that the networks can serve as a template for a transparent conductor. These self-assembled tunable materials are promising candidates for large surface area electrodes in batteries and organic photovoltaic cells, as well as for microfluidic sensors and filters.

Demortière, Arnaud; Snezhko, Alexey; Sapozhnikov, Maksim V.; Becker, Nicholas; Proslier, Thomas; Aranson, Igor S.

2014-01-01

233

Random versus sequential pathway of molecular self-assembly  

NASA Astrophysics Data System (ADS)

Two important assumptions are often made in the analysis of molecular self-assembly at equilibrium, viz., that sequential is preferred to random aggregation and that the equilibrium constants at each stage of aggregation are equal, though both assumptions have not been justified strictly. In the present work we show that molecular self-assembly leading to formation of linear polymers and proceeding in a random manner appears to be less entropically favored than sequential aggregation, which provides a physical background for assuming sequential aggregation when studying molecular self-assembly in solution. Exact equations for analysis of experimental data for molecular assembly proceeding in a sequential manner were derived by taking strict account of the profile of the equilibrium constant, which provides a physically more correct approach than that using the conventional indefinite equilibrium constant (EK) model.

Evstigneev, Maxim P.; Buchelnikov, Anatoly S.; Evstigneev, Vladyslav P.

2012-06-01

234

Self-assembled Ag nanoparticles for surface enhanced Raman scattering  

NASA Astrophysics Data System (ADS)

Uniform and reproducible substrates for surface enhanced Raman scattering (SERS) are fabricated by self-assembly of Ag nanoparticles (NPs) on 3-aminopropyltrimethoxysilane (APTES) modified glass. Experimental results indicate that the Ag NPs with a narrow size distribution were assembled as a sub-monolayer which exhibits an excellent SERSactivity. The SERS enhancement factor is estimated to be 7.5 × 106 and the detection limit for crystal violet (CV) solution is about ˜10-11 M. The uniformity and reproducibility of the SERS signals are tested by point-to-point and batch-to-batch measurements. It is confirmed that the self-assembled Ag NPs substrates has a high SERS reproducibility and a low standard deviation with respect to the Ag NPs on non-functionalized glass substrates. The self-assembled Ag NPs substrates can be widely used for the application of chemical and biochemical sensing.

Zhu, Shuangmei; Fan, Chunzhen; Wang, Junqiao; He, Jinna; Liang, Erjun

2013-09-01

235

Nanostructures formed by cyclodextrin covered aminobenzophenones through supramolecular self assembly  

NASA Astrophysics Data System (ADS)

Cyclodextrin (? and ?) based nanostructures formed with 2-aminobenzophenone, 3-aminobenzophenone through the supramolecular self assembly are studied by absorption, fluorescence, time-resolved fluorescence, SEM, TEM, FT-IR, DSC, PXRD and 1H NMR. The unequal layer by layer nanosheets and nanoribbons are formed through self assembly of 3ABP/CD inclusion complexes. 2ABP/?-CD complex nanostructures show the self assembly hierarchical thread structure and ?-CD complexes displays a nanobrick structure. The formation of nanostructures are prearranged to Hsbnd O⋯H, NH2⋯O and H2N⋯H intermolecular hydrogen bond between individual complexes. The absorption and fluorescence spectral changes explicit formation of 1:1 inclusion complexes and solvent study demonstrate the ESIPT and TICT present in both molecules. The thermodynamic parameters (?H, ?G and ?S) of 2ABP and 3ABP molecule and the inclusion complexes were determined from semiempirical PM3 calculations.

Rajendiran, N.; Sankaranarayanan, R. K.; Saravanan, J.

2014-06-01

236

Scratch Drive Actuator Driven Self-assembled Variable Optical Attenuator  

NASA Astrophysics Data System (ADS)

This paper describes the new concept and design for a self-assembled variable optical attenuator (VOA) derived by using surface micromachining technology. A residual stress-induced flexure curved beam with corrugated trench anchors can lift up the reflective mirror shutter. This self-assembled reflective shutter can be driven by a set of scratch drive actuator (SDA), then slides into the spacing between input and output fiber ends. The attenuation range of proposed microelectromechanical systems (MEMS) VOA is determined by the vertical position of self-assembled pop-up polysilicon reflective shutter in which it is controlled by the value of applied dc voltage. This new VOA demonstrates continuous attenuation capability and wide attenuation range based on using an electrostatic actuator that is a new residual stress-induced flexure curved beam with corrugated-trench anchors. This device exhibits attenuation range of 70 dB and insertion loss less than 1 dB.

Lee, Chengkuo; Lai, Yen-Jyh; Wu, Chia-Yu; Lin, Yu-Shen; Tasi, Ming Hung; Huang, Ruey-Shing; Lin, Min-Shyong

2004-06-01

237

Design of protein struts for self-assembling nanoconstructs  

PubMed Central

Bacteriophage T4 tail fibers have a quaternary structure of bent rigid rods, 3 × 160 nm in size. The four proteins which make up these organelles are able to self-assemble in an essentially irreversible manner. To use the self-assembly domains of these proteins as elements in construction of mesoscale structures, we must be able to rearrange these domains without affecting the self-assembly properties and add internal binding sites for other functional elements. Here we present results on several alterations of the P37 component of the T4 tail fiber that change its length and add novel protein sequences into the protein. One of these sequences is an antibody binding site that is used to inactivate phage carrying the modified gene.

Hyman, Paul; Valluzzi, Regina; Goldberg, Edward

2002-01-01

238

Actinide Sequestration Using Self-Assembled Monolayers on Mesoporous Supports  

SciTech Connect

Surfactant templated synthesis of mesoporous ceramics provides a versatile foundation upon which to create high efficiency environmental sorbents. These nanoporous ceramic oxides condense a huge amount of surface area into a very small volume. The ceramic oxide interface is receptive to surface functionalization through molecular self-assembly. The marriage of mesoporous ceramics with self-assembled monolayer chemistry creates a powerful new class of environmental sorbent materials called self-assembled monolayers on mesoporous supports (SAMMS). These SAMMS materials are highly efficient sorbents, whose interfacial chemistry can be fine-tuned to selectively sequester a specific target species, such as heavy metals, tetrahedral oxometallate anions and radionuclides. Details addressing the design, synthesis and characterization of SAMMS materials specifically designed to sequester actinides, of central importance to the environmental clean-up necessary after 40 years of weapons grade plutonium production, as well as evaluation of their binding affinities and kinetics are presented.

Fryxell, Glen E.; Lin, Yuehe; Fiskum, Sandra K.; Birnbaum, Jerome C.; Wu, Hong; Kemner, K. M.; Kelly, Shelley

2005-03-01

239

Self-assembly and switching in ferroelectrics and multiferroics  

NASA Astrophysics Data System (ADS)

Molecules of low symmetry often self-assemble in Nature to produce mesoscopic structures of symmetry higher than their constituent building blocks, including “super-cubic” structures. Such self-assembled hexagonal domains have recently been observed in orthorhombic polymeric ferroelectrics, and resemble those known in surfactants and in magnetic bubble domains. Ferroelastic nanodomains in ferroelectric films also self-assemble into bundles of tens of nanometers diameter within each ferroelectric domain that locally average polarization \\langle P\\rangle and strain \\langle s\\rangle to small values. Under applied stress or electric or magnetic field these bundles exhibit higher mobility than expected and switch polarization via magnetostriction plus piezoelectricity. The phenomenon is analogous to Anderson's 1962 model of “vortex bundle” motion in Type-II superconductors.

Scott, J. F.

2013-08-01

240

Self-assembly of tunable protein suprastructures from recombinant oleosin  

PubMed Central

Using recombinant amphiphilic proteins to self-assemble suprastructures would allow precise control over surfactant chemistry and the facile incorporation of biological functionality. We used cryo-TEM to confirm self-assembled structures from recombinantly produced mutants of the naturally occurring sunflower protein, oleosin. We studied the phase behavior of protein self-assembly as a function of solution ionic strength and protein hydrophilic fraction, observing nanometric fibers, sheets, and vesicles. Vesicle membrane thickness correlated with increasing hydrophilic fraction for a fixed hydrophobic domain length. The existence of a bilayer membrane was corroborated in giant vesicles through the localized encapsulation of hydrophobic Nile red and hydrophilic calcein. Circular dichroism revealed that changes in nanostructural morphology in this family of mutants was unrelated to changes in secondary structure. Ultimately, we envision the use of recombinant techniques to introduce novel functionality into these materials for biological applications.

Vargo, Kevin B.; Parthasarathy, Ranganath; Hammer, Daniel A.

2012-01-01

241

Dynamic self-assembly of coordination polymers in aqueous solution.  

PubMed

The construction of supramolecular polymers has been intensively pursued because the nanostructures formed through weak non-covalent interactions can be triggered by external stimuli leading to smart materials and sensors. Self-assemblies of coordination polymers consisting of metal ions and organic ligands in aqueous solution also provide particular contributions in this area. The main motivation for developing those coordination polymers originates from the value-added combination between metal ions and ligands. This review highlights the recent progress of the dynamic self-assembly of coordination polymers that result from the sophisticated molecular design, towards fabricating stimuli-responsive systems and bio-related materials. Dynamic structural changes and switchable physical properties triggered by various stimuli are summarized. Finally, the outlook for aqueous nanostructures originated from the dynamic self-assembly of coordination polymers is also presented. PMID:24955807

Li, Wen; Kim, Yongju; Li, Jingfang; Lee, Myongsoo

2014-08-01

242

Interfacial and mechanical properties of self-assembling systems  

NASA Astrophysics Data System (ADS)

Self-assembly is a fascinating phenomena where interactions between small subunits allow them to aggregate and form complex structures that can span many length scales. These self-assembled structures are especially important in biology where they are necessary for life as we know it. This dissertation is a study of three very different self-assembling systems, all of which have important connections to biology and biological systems. Drop shape analysis was used to study the interfacial assembly of amphiphilic block copolymers at the oil/water interface. When biologically functionalyzed copolymers are used, this system can serve as a model for receptor-ligand interactions that are used by cells to perform many activities, such as interact with their surroundings. The physical properties of a self-assembling membrane system were quantified using membrane inflation and swelling experiments. These types of membranes may have important applications in medicine such as drug eluting (growth factor eluting) scaffolds to aid in wound healing. The factors affecting the properties of bis(leucine) oxalamide gels were also explored. We believe that this particular system will serve as an appropriate model for biological gels that are made up of fiber-like and/or rod-like structures. During the course of the research presented in this dissertation, many new techniques were developed specifically to allow/aid the study of these distinct self-assembling systems. For example, numerical methods were used to predict drop stability for drop shape analysis experiments and the methods used to create reproducibly create self-assembling membranes were developed specifically for this purpose. The development of these new techniques is an integral part of the thesis and should aid future students who work on these projects. A number ongoing projects and interesting research directions for each one of the projects is also presented.

Carvajal, Daniel

243

Modulating Adaptive Immune Responses to Peptide Self-Assemblies  

PubMed Central

Self-assembling peptides and peptide derivatives have received significant interest for several biomedical applications, including tissue engineering, wound healing, cell delivery, drug delivery, and vaccines. This class of materials has exhibited significant variability in immunogenicity, with many peptides eliciting no detectable antibody responses but others eliciting very strong responses without any supplemental adjuvants. Presently, strategies for either avoiding strong antibody responses or specifically inducing them are not well developed, even though they are critical for the use of these materials both within tissue engineering and within immunotherapies. Here, we investigated the molecular determinants and immunological mechanisms leading to the significant immunogenicity of the self-assembling peptide OVA-Q11, which has been shown previously to elicit strong antibody responses in mice. We show that these responses can last for at least a year. Using adoptive transfer experiments and T cell knockout models, we found that these strong antibody responses were T cell-dependent, suggesting a route for avoiding or ensuring immunogenicity. Indeed, by deleting amino acid regions in the peptide recognized by T cells, immunogenicity could be significantly diminished. Immunogenicity could also be attenuated by mutating key residues in the self-assembling domain, thus preventing fibrillization. A second self-assembling peptide, KFE8, was also non-immunogenic, but nanofibers of OVA-KFE8 elicited strong antibody responses similar to OVA-Q11, indicating that the adjuvant action was not dependent on the specific self-assembling peptide sequence. These findings will facilitate the design of self-assembled peptide biomaterials, both for applications where immunogenicity is undesirable and where it is advantageous.

Rudra, Jai S.; Sun, Tao; Bird, Katelyn C.; Daniels, Melvin D.; Gasiorowski, Joshua Z.; Chong, Anita S.; Collier, Joel H.

2012-01-01

244

Self-assembled autonomous runners and tumblers.  

PubMed

A class of artificial microswimmers with combined translational and rotational self-propulsion is studied experimentally. The chemically fueled microswimmers are made of doublets of Janus colloidal beads with catalytic patches that are positioned at a fixed angle relative to one another. The mean-square displacement and the mean-square angular displacement of the active doublets are analyzed in the context of a simple Langevin description, using which the physical characteristics of the microswimmers such as the spontaneous translational and rotational velocities are extracted. Our work suggests strategies for designing microswimmers that could follow prescribed cycloidal trajectories. PMID:20866681

Ebbens, Stephen; Jones, Richard A L; Ryan, Anthony J; Golestanian, Ramin; Howse, Jonathan R

2010-07-01

245

Self-assembly behavior of A( 4-miktoarm star terpolymers  

NASA Astrophysics Data System (ADS)

The self-assembly of miktoarm star terpolymers provides a powerful route to obtain complex microstructures. Here we use self-consistent field theory to investigate the melt morphologies self-assembled from A(   4-miktoarm star terpolymers composed of a homopolymer arm A and three copolymer arms BC. A variety of ordered microstructures are predicted by controlling the volume fractions of different components and the Flory-Huggins interaction parameters. At the same time a series of order-order and order-disorder transitions are observed. The results may be helpful for the design of novel microstructures.

Zhou, Ling; Fang, Jinghuai; Peng, Ju; Zhang, Jianguo

2013-11-01

246

Backfilled, self-assembled monolayers and methods of making same  

DOEpatents

Backfilled, self-assembled monolayers and methods of making the same are disclosed. The self-assembled monolayer comprises at least one functional organosilane species and a substantially random dispersion of at least one backfilling organosilane species among the functional organosilane species, wherein the functional and backfilling organosilane species have been sequentially deposited on a substrate. The method comprises depositing sequentially a first organosilane species followed by a backfilling organosilane species, and employing a relaxation agent before or during deposition of the backfilling organosilane species, wherein the first and backfilling organosilane species are substantially randomly dispersed on a substrate.

Fryxell, Glen E. (Kennewick, WA); Zemanian, Thomas S. (Richland, WA); Addleman, R. Shane (Benton City, WA); Aardahl, Christopher L. (Sequim, WA); Zheng, Feng (Richland, WA); Busche, Brad (Raleigh, NC); Egorov, Oleg B. (West Richland, WA)

2009-06-30

247

Nano-engineering by optically directed self-assembly.  

SciTech Connect

Lack of robust manufacturing capabilities have limited our ability to make tailored materials with useful optical and thermal properties. For example, traditional methods such as spontaneous self-assembly of spheres cannot generate the complex structures required to produce a full bandgap photonic crystals. The goal of this work was to develop and demonstrate novel methods of directed self-assembly of nanomaterials using optical and electric fields. To achieve this aim, our work employed laser tweezers, a technology that enables non-invasive optical manipulation of particles, from glass microspheres to gold nanoparticles. Laser tweezers were used to create ordered materials with either complex crystal structures or using aspherical building blocks.

Furst, Eric (University of Delaware, Newark, DE); Dunn, Elissa (Yale University, New Haven, CT); Park, Jin-Gyu (Yale University, New Haven, CT); Brinker, C. Jeffrey; Sainis, Sunil (Yale University, New Haven, CT); Merrill, Jason (Yale University, New Haven, CT); Dufresne, Eric (Yale University, New Haven, CT); Reichert, Matthew D.; Brotherton, Christopher M.; Bogart, Katherine Huderle Andersen; Molecke, Ryan A.; Koehler, Timothy P.; Bell, Nelson Simmons; Grillet, Anne Mary; Gorby, Allen D.; Singh, John (University of Delaware, Newark, DE); Lele, Pushkar (University of Delaware, Newark, DE); Mittal, Manish (University of Delaware, Newark, DE)

2009-09-01

248

Calixarene-encapsulated nanoparticles: self-assembly into functional nanomaterials†  

PubMed Central

Calixarenes are excellent surfactants for enhancing the dispersion and self-assembly of metal nanoparticles into well-defined structures, particularly those with unit length scales in the 10–100 nm size range. Particles within these ensembles are strongly coupled, giving rise to unique collective optical or magnetic properties. The self-assembled nanostructures described in this feature article include 2D arrays of colloidal Au nanoparticles with size-dependent plasmonic responses, and sub-100 nm Co nanoparticle rings with chiral magnetic states. These nanoparticle assemblies may be further developed for applications in chemical sensing based on surface-enhanced Raman scattering (SERS) and as binary elements for nonvolatile memory, respectively.

Wei, Alexander

2007-01-01

249

Self-Assembly at a Nonequilibrium Critical Point  

NASA Astrophysics Data System (ADS)

We use analytic theory and computer simulation to study patterns formed during the growth of two-component assemblies in two and three dimensions. We show that these patterns undergo a nonequilibrium phase transition, at a particular growth rate, between mixed and demixed arrangements of component types. This finding suggests that principles of nonequilibrium statistical mechanics can be used to predict the outcome of multicomponent self-assembly, and suggests an experimental route to the self-assembly of multicomponent structures of a qualitatively defined nature.

Whitelam, Stephen; Hedges, Lester O.; Schmit, Jeremy D.

2014-04-01

250

Self-assembly at a nonequilibrium critical point.  

PubMed

We use analytic theory and computer simulation to study patterns formed during the growth of two-component assemblies in two and three dimensions. We show that these patterns undergo a nonequilibrium phase transition, at a particular growth rate, between mixed and demixed arrangements of component types. This finding suggests that principles of nonequilibrium statistical mechanics can be used to predict the outcome of multicomponent self-assembly, and suggests an experimental route to the self-assembly of multicomponent structures of a qualitatively defined nature. PMID:24785052

Whitelam, Stephen; Hedges, Lester O; Schmit, Jeremy D

2014-04-18

251

Synthesizing Minimal Tile Sets for Patterned DNA Self-assembly  

NASA Astrophysics Data System (ADS)

The Pattern self-Assembly Tile set Synthesis (PATS) problem is to determine a set of coloured tiles that self-assemble to implement a given rectangular colour pattern. We give an exhaustive branch-and-bound algorithm to find tile sets of minimum cardinality for the PATS problem. Our algorithm makes use of a search tree in the lattice of partitions of the ambient rectangular grid, and an efficient bounding function to prune this search tree. Empirical data on the performance of the algorithm shows that it compares favourably to previously presented heuristic solutions to the problem.

Göös, Mika; Orponen, Pekka

252

A pathway for self-assembly of metallic nanostructures on quantum-modulated flat Pb(111)/Si(111) substrate  

NASA Astrophysics Data System (ADS)

A mechanism of self-assembly of metallic nanostructures on a quantum-modulated flat Pb(111) thin film with patterned Si(111) substrate is proposed based on recent experimental observations [S. M. Binz, M. Hupalo, and M. C. Tringides, Phys. Rev. B 78, 193407 (2008)] which indicates that because of quantum size effects (QSE), the buried steps act as real steps on surfaces. This intriguing feature offers a potential pathway for self-assembly of functional metallic nanostructures, e.g., nanowires on flat Pb(111) films with designed patterned Si(111) surface as substrate, where QSE can be controlled artificially. The growth conditions for nanowires on a designed Pb(111)/Si(111) substrate is explored by kinetic Monte Carlo simulations.

Zhang, Cuipeng; Li, Maozhi

2010-02-01

253

TectoRNP: self-assembling RNAs with peptide recognition motifs as templates for chemical peptide ligation.  

PubMed

TectoRNA, an artificial RNA with self-assembling ability, has been employed as a structural platform for RNA nanotechnology and RNA synthetic biology. In this study, tectoRNA was applied as a specific template for chemical peptide ligation. On the basis of a self-assembling tectoRNA, we designed and constructed a template RNA that facilitates peptide ligation depending on controlled dimer formation. Two RNA-binding peptides were recognized by two peptide-binding RNA motifs embedded in the template RNA, and chemical ligation was promoted because of the entropic effect of Mg(2+) -dependent dimerization. In a series of biochemical analyses, we determined the relationship between the structures of the tectoRNA-based templates and the extent of acceleration in peptide ligation. PMID:22927166

Yamashita, Kohei; Tanaka, Takahiro; Furuta, Hiroyuki; Ikawa, Yoshiya

2012-10-01

254

DNA biosensors based on self-assembled carbon nanotubes  

Microsoft Academic Search

DNA biosensors based on self-assembled multi-walled carbon nanotubes (MWNTs) were described in this paper, in which the probe DNA oligonucleotides were immobilized by forming covalent amide bonds between carboxyl groups at the nanotubes and amino groups at the ends of the DNA oligonucleotides. Hybridization between the probe and target DNA oligonucleotides was confirmed by the changes in the voltammetric peak

S. G. Wang; Ruili Wang; P. J. Sellin; Qing Zhang

2004-01-01

255

Self-assembled materials from thermosensitive and biohybrid block copolymers  

Microsoft Academic Search

In this research, several block copolymers were synthesized and characterized with regard to possible pharmaceutical applications. All block copolymers were thermosensitive and self-assembled at 37 °C into structures like micelles and hydrogels, which can be used for innovative drug delivery purposes. Some of the synthesized polymers were biohybrid, in the sense that they contained peptide segments which enabled their cleavage

A. J. de Graaf

2012-01-01

256

Self-assembling electroactive hydrogels for flexible display technology  

NASA Astrophysics Data System (ADS)

We have assessed the potential of self-assembling hydrogels for use in conformal displays. The self-assembling process can be used to alter the transparency of the material to all visible light due to scattering by fibres. The reversible transition is shown to be of low energy by differential scanning calorimetry. For use in technology it is imperative that this transition is controlled electrically. We have thus synthesized novel self-assembling hydrogelator molecules which contain an electroactive group. The well-known redox couple of anthraquinone/anthrahydroquinone has been used as the hydrophobic component for a series of small molecule gelators. They are further functionalized with peptide combinations of L-phenylalanine and glycine to provide the hydrophilic group to complete 'head-tail' models of self-assembling gels. The gelation and electroactive characteristics of the series were assessed. Cyclic voltammetry shows the reversible redox cycle to be only superficially altered by functionalization. Additionally, spectroelectrochemical measurements show a reversible transparency and colour change induced by the redox process.

Jones, Scott L.; Hou Wong, Kok; Thordarson, Pall; Ladouceur, François

2010-12-01

257

Optical fiber gas sensor based on self-assembled gratings  

Microsoft Academic Search

The electrostatic self-assembled monolayer synthesis process is used to fabricate gas sensors by building up grating sensor elements on the ends of multimode optical fibers. These novel sensors can be designed to operate in the transmission windows of standard optical fibers and implemented using specific reference wavelengths to normalize the output signals. Experimental results for such sensors designed to detect

Francisco J. Arregui; Richard O. Claus; Kristie L. Cooper; Carlos Fernández-Valdivielso; Ignacio R. Matías

2001-01-01

258

Self-Assembled Molecular Spin Arrays for Computation.  

National Technical Information Service (NTIS)

In the initial part of the project experiments were carried out to prepare a lattice of electron spins based on a self-assembled monolayer of an electron accepting molecules. In the first period we reported that a combination of quantitative infrared vibr...

D. L. Allara, B. Hasslacher

2005-01-01

259

Hierarchical self-assembly of complex polyhedral microcontainers  

PubMed Central

The concept of self-assembly of a two-dimensional (2D) template to a three-dimensional (3D) structure has been suggested as a strategy to enable highly parallel fabrication of complex, patterned microstructures. We have previously studied the surface tension based self-assembly of patterned, microscale polyhedral containers (cubes, square pyramids and tetrahedral frusta). In this paper, we describe the observed hierarchical self-assembly of more complex, patterned polyhedral containers in the form of regular dodecahedra and octahedra. The hierarchical design methodology, combined with the use of self-correction mechanisms, was found to greatly reduce the propagation of self-assembly error that occurs in these more complex systems. It is a highly effective way to mass-produce patterned, complex 3D structures on the microscale and could also facilitate encapsulation of cargo in a parallel and cost-effective manner. Furthermore, the behavior that we have observed may be useful in the assembly of complex systems with large numbers of components.

Filipiak, David J.; Azam, Anum; Leong, Timothy G.; Gracias, David H.

2009-01-01

260

Cooperative self-assembly of peptide gelators and proteins.  

PubMed

Molecular self-assembly provides a versatile route for the production of nanoscale materials for medical and technological applications. Herein, we demonstrate that the cooperative self-assembly of amphiphilic small molecules and proteins can have drastic effects on supramolecular nanostructuring of resulting materials. We report that mesoscale, fractal-like clusters of proteins form at concentrations that are orders of magnitude lower compared to those usually associated with molecular crowding at room temperature. These protein clusters have pronounced effects on the molecular self-assembly of aromatic peptide amphiphiles (fluorenylmethoxycarbonyl- dipeptides), resulting in a reversal of chiral organization and enhanced order through templating and binding. Moreover, the morphological and mechanical properties of the resultant nanostructured gels can be controlled by the cooperative self-assembly of peptides and protein fractal clusters, having implications for biomedical applications where proteins and peptides are both present. In addition, fundamental insights into cooperative interplay of molecular interactions and confinement by clusters of chiral macromolecules is relevant to gaining understanding of the molecular mechanisms of relevance to the origin of life and development of synthetic mimics of living systems. PMID:24256076

Javid, Nadeem; Roy, Sangita; Zelzer, Mischa; Yang, Zhimou; Sefcik, Jan; Ulijn, Rein V

2013-12-01

261

Synthesis of a Self-Assembling Supramolecular Lattice.  

National Technical Information Service (NTIS)

The goal of this project is to construct a self-assembling, closed, hollow, uniform, supramolecular lattice in which the lattice dimensions measure between 10 and 100 nm, and which exhibits two hierarchical levels of molecular order. Our approach is novel...

C. A. Hunt R. D. MacGregor

1991-01-01

262

Towards lysozyme nanotube and 3D hybrid self-assembly  

NASA Astrophysics Data System (ADS)

We report lysozyme self-assembly into nanotubes, under the effect of hydrolysis at pH 2 and 90 °C. We resolve the final steps of the fibrillation pathway, entailing the closure of multi-stranded helical ribbons into nanotubes, and we provide evidence of ?-sheet arrangement within the nanotubes, demonstrating amyloid-like aggregation. Addition of chloroauric acid to the self-assembled structures can lead to generation of either gold single crystal nanoplatelets or gold nanoparticles (when a reducing agent is added) decorating the nanotube and ribbon surfaces. The crystal-based organic-inorganic hybrids further assemble into 3D ``sandwiched'' structures.We report lysozyme self-assembly into nanotubes, under the effect of hydrolysis at pH 2 and 90 °C. We resolve the final steps of the fibrillation pathway, entailing the closure of multi-stranded helical ribbons into nanotubes, and we provide evidence of ?-sheet arrangement within the nanotubes, demonstrating amyloid-like aggregation. Addition of chloroauric acid to the self-assembled structures can lead to generation of either gold single crystal nanoplatelets or gold nanoparticles (when a reducing agent is added) decorating the nanotube and ribbon surfaces. The crystal-based organic-inorganic hybrids further assemble into 3D ``sandwiched'' structures. Electronic supplementary information (ESI) available: Materials and methods, further images and FTIR data. See DOI: 10.1039/c3nr02194g

Lara, Cecile; Handschin, Stephan; Mezzenga, Raffaele

2013-07-01

263

Self-assembled arginine-coated peptide nanosheets in water.  

PubMed

The surfactant-like peptide (Ala)(6)(Arg) is found to self-assemble into 3 nm-thick sheets in aqueous solution. Scanning transmission electron microscopy measurements of mass per unit area indicate a layer structure based on antiparallel dimers. At higher concentration the sheets wrap into unprecedented ultrathin helical ribbon and nanotube architectures. PMID:23360959

Hamley, Ian W; Dehsorkhi, Ashkan; Castelletto, Valeria

2013-03-01

264

Reversible insulin self-assembly under carbohydrate control.  

PubMed

Insulin with built-in pairs of boronates and polyols can produce soluble high molecular weight self-assemblies under control by carbohydrates. The illustrated principle has potential utility for general protein and peptide protraction and controlled drug release. PMID:15853306

Hoeg-Jensen, Thomas; Havelund, Svend; Nielsen, Peter K; Markussen, Jan

2005-05-01

265

Chemical mimicry of viral capsid self-assembly  

PubMed Central

Stable structures of icosahedral symmetry can serve numerous functional roles, including chemical microencapsulation and delivery of drugs and biomolecules, epitope presentation to allow for an efficient immunization process, synthesis of nanoparticles of uniform size, observation of encapsulated reactive intermediates, formation of structural elements for supramolecular constructs, and molecular computing. By examining physical models of spherical virus assembly we have arrived at a general synthetic strategy for producing chemical capsids at size scales between fullerenes and spherical viruses. Such capsids can be formed by self-assembly from a class of molecules developed from a symmetric pentagonal core. By designing chemical complementarity into the five interface edges of the molecule, we can produce self-assembling stable structures of icosahedral symmetry. We considered three different binding mechanisms: hydrogen bonding, metal binding, and formation of disulfide bonds. These structures can be designed to assemble and disassemble under controlled environmental conditions. We have conducted molecular dynamics simulation on a class of corannulene-based molecules to demonstrate the characteristics of self-assembly and to aid in the design of the molecular subunits. The edge complementarities can be of diverse structure, and they need not reflect the fivefold symmetry of the molecular core. Thus, self-assembling capsids formed from coded subunits can serve as addressable nanocontainers or custom-made structural elements.

Olson, Arthur J.; Hu, Yunfeng H. E.; Keinan, Ehud

2007-01-01

266

Developmental self-assembly of a DNA tetrahedron.  

PubMed

Kinetically controlled isothermal growth is fundamental to biological development, yet it remains challenging to rationally design molecular systems that self-assemble isothermally into complex geometries via prescribed assembly and disassembly pathways. By exploiting the programmable chemistry of base pairing, sophisticated spatial and temporal control have been demonstrated in DNA self-assembly, but largely as separate pursuits. By integrating temporal with spatial control, here we demonstrate the "developmental" self-assembly of a DNA tetrahedron, where a prescriptive molecular program orchestrates the kinetic pathways by which DNA molecules isothermally self-assemble into a well-defined three-dimensional wireframe geometry. In this reaction, nine DNA reactants initially coexist metastably, but upon catalysis by a DNA initiator molecule, navigate 24 individually characterizable intermediate states via prescribed assembly pathways, organized both in series and in parallel, to arrive at the tetrahedral final product. In contrast to previous work on dynamic DNA nanotechnology, this developmental program coordinates growth of ringed substructures into a three-dimensional wireframe superstructure, taking a step toward the goal of kinetically controlled isothermal growth of complex three-dimensional geometries. PMID:24720462

Sadowski, John P; Calvert, Colby R; Zhang, David Yu; Pierce, Niles A; Yin, Peng

2014-04-22

267

Computer Simulations of Block Copolymer Tethered Nanoparticle Self-Assembly  

NSDL National Science Digital Library

We perform molecular simulations to study the self-assembly of block copolymer tethered cubic nanoparticles. Minimal models of the tethered nanoscale building blocks (NBBs) are utilized to explore the structures arising from self-assembly. We demonstrate that attaching a rigid nanocube to a diblock copolymer affects the typical equilibrium morphologies exhibited by the pure copolymer. Lamellar and cylindrical phases are observed in both systems but not at the corresponding relative copolymer tether block fractions. The effect of nanoparticle geometry on phase behavior is investigated by comparing the self-assembled structures formed by the tethered NBBs with those of their linear ABC triblock copolymer counterparts. The tethered nanocubes exhibit the conventional triblock copolymer lamellar and cylindrical phases when the repulsive interactions between different blocks are symmetric. The rigid and bulky nature of the cube induces interfacial curvature in the tethered NBB phases compared to their linear ABC triblock copolymer counterparts. We compare our results with those structures obtained from diblock copolymer tethered nanospheres to further elucidate the role of cubic nanoparticle geometry on self-assembly.

Chan, Elaine; Ho, Lin C.; Glotzer, Sharon C.

2006-07-03

268

Fractal intermediates in the self-assembly of silicatein filaments  

Microsoft Academic Search

Silicateins are proteins with catalytic, structure-directing activity that are responsible for silica biosynthesis in certain sponges; they are the constituents of macroscopic protein filaments that are found occluded within the silica needles made by Tethya aurantia. Self-assembly of the silicatein monomers and oligomers is shown to form fibrous structures by a mechanism that is fundamentally different from any previously described

Meredith M. Murr; Daniel E. Morse

2005-01-01

269

Engineering building blocks for self-assembling protein nanoparticles  

Microsoft Academic Search

Like natural viruses, manmade protein cages for drug delivery are to be ideally formed by repetitive subunits with self-assembling properties, mimicking viral functions and molecular organization. Naturally formed nanostructures (such as viruses, flagella or simpler protein oligomers) can be engineered to acquire specific traits of interest in biomedicine, for instance through the addition of cell targeting agents for desired biodistribution

Esther Vázquez; Antonio Villaverde

2010-01-01

270

Self-assembly from milli- to nanoscales: methods and applications  

PubMed Central

The design and fabrication techniques for microelectromechanical systems (MEMS) and nanodevices are progressing rapidly. However, due to material and process flow incompatibilities in the fabrication of sensors, actuators and electronic circuitry, a final packaging step is often necessary to integrate all components of a heterogeneous microsystem on a common substrate. Robotic pick-and-place, although accurate and reliable at larger scales, is a serial process that downscales unfavorably due to stiction problems, fragility and sheer number of components. Self-assembly, on the other hand, is parallel and can be used for device sizes ranging from millimeters to nanometers. In this review, the state-of-the-art in methods and applications for self-assembly is reviewed. Methods for assembling three-dimensional (3D) MEMS structures out of two-dimensional (2D) ones are described. The use of capillary forces for folding 2D plates into 3D structures, as well as assembling parts onto a common substrate or aggregating parts to each other into 2D or 3D structures, is discussed. Shape matching and guided assembly by magnetic forces and electric fields are also reviewed. Finally, colloidal self-assembly and DNA-based self-assembly, mainly used at the nanoscale, are surveyed, and aspects of theoretical modeling of stochastic assembly processes are discussed.

Mastrangeli, M; Abbasi, S; Varel, C; Van Hoof, C; Celis, J-P; Bohringer, K F

2009-01-01

271

Electrostatic Self-assembly : A New Route Towards Nanostructures  

Microsoft Academic Search

During the last 3 years, our group has investigated extensively the complexation mechanism between neutral-polyelectrolyte block copolymers with oppositely charged species. These species are surfactant micelles, multivalent counterions and inorganic nanoparticles. In the three cases, we have established the thermodynamical phase diagram of these systems, and found broad regions where supramolecular aggregates spontaneously form via electrostatic self-assembly. From earlier works,

J.-F. Berret; P. Herve; M. Morvan; K. Yokota; M. Destarac; J. Oberdisse; I. Grillo; R. Schweins

2005-01-01

272

Scanning probe lithography of self-assembled monolayers  

Microsoft Academic Search

Systematic studies on scanning probe lithography (SPL) methodologies have been performed using self-assembled monolayers (SAMs) on Au as examples. The key to achieving high spatial precision is to keep the tip-surface interactions strong and local. Approaches include three atomic force microscopy (AFM) based methods, nanoshaving, nanografting, and nanopen reader and writer (NPRW), which rely on the local force, and two

Guohua Yang; Nabil A. Amro; Gang-yu Liu

2003-01-01

273

Sambot: A Self-Assembly Modular Robot System  

Microsoft Academic Search

The design and structure of a self-assembly modu- lar robot (Sambot) are presented in this paper. Each module has its own autonomous mobility and can connect with other modules to form robotic structures with different manipulation abilities. Sambot has a versatile, robust, and flexible structure. The com- puting platform provided for each module is distributed and con- sists of a

Hongxing Wei; Youdong Chen; Jindong Tan; Tianmiao Wang

2011-01-01

274

Dynamic self-assembly of hierarchical software structures/systems.  

SciTech Connect

We present initial results on achieving synthesis of complex software systems via a biophysics-emulating, dynamic self-assembly scheme. This approach offers novel constructs for constructing large hierarchical software systems and reusing parts of them. Sets of software building blocks actively participate in the construction and subsequent modification of the larger-scale programs of which they are a part. The building blocks interact through a software analog of selective protein-protein bonding. Self-assembly generates hierarchical modules (including both data and executables); creates software execution pathways; and concurrently executes code via the formation and release of activity triggering bonds. Hierarchical structuring is enabled through encapsulants that isolate populations of building block binding sites. The encapsulated populations act as larger-scale building blocks for the next hierarchy level. Encapsulant populations are dynamic, as their contents can move in and out. Such movement changes the populations of interacting sites and also modifies the software execution. ''External overrides'', analogous to protein phosphorylation, temporarily switch off undesired subsets of behaviors (code execution, data access/modification) of other structures. This provides a novel abstraction mechanism for code reuse. We present an implemented example of dynamic self-assembly and present several alternative strategies for specifying goals and guiding the self-assembly process.

Bouchard, Ann Marie; Osbourn, Gordon Cecil

2003-01-01

275

Casting Metal Nanowires Within Discrete Self-Assembled Peptide Nanotubes  

Microsoft Academic Search

Tubular nanostructures are suggested to have a wide range of applications in nanotechnology. We report our observation of the self-assembly of a very short peptide, the Alzheimer's beta-amyloid diphenylalanine structural motif, into discrete and stiff nanotubes. Reduction of ionic silver within the nanotubes, followed by enzymatic degradation of the peptide backbone, resulted in the production of discrete nanowires with a

Meital Reches; Ehud Gazit

2003-01-01

276

Limitations of Self-Assembly at Temperature 1  

Microsoft Academic Search

We prove that if a set X ? Z2 weakly self-assembles at temperature 1 in a deterministic (Winfree) tile assembly system satisfying a natural condition known as pumpability, then X is a semilinear set. This shows that only the most simple of infinite shapes and patterns can be constructed using pumpable temperature 1 tile assembly systems, and gives evidence for

David Doty; Matthew J. Patitz; Scott M. Summers

2009-01-01

277

Engineering silicon oxide surfaces using self-assembled monolayers  

Microsoft Academic Search

Although a molecular monolayer is only a few nanometers thick it can completely change the properties of a surface. Molecular monolayers can be readily prepared using the Langmuir-Blodgett methodology or by chemisorption on metal and oxide surfaces. This Review focuses on the use of chemisorbed self-assembled monolayers (SAMs) as a platform for the functionalization of silicon oxide surfaces. The controlled

Steffen Onclin; Bart Jan Ravoo; David N. Reinhoudt

2005-01-01

278

An exactly solvable model of hierarchical self-assembly  

NASA Astrophysics Data System (ADS)

Many living and nonliving structures in the natural world form by hierarchical organization, but physical theories that describe this type of organization are scarce. To address this problem, a model of equilibrium self-assembly is formulated in which dynamically associating species organize into hierarchical structures that preserve their shape at each stage of assembly. In particular, we consider symmetric m-gons that associate at their vertices into Sierpinski gasket structures involving the hierarchical association of triangles, squares, hexagons, etc., at their corner vertices, thereby leading to fractal structures after many generations of assembly. This rather idealized model of hierarchical assembly yields an infinite sequence of self-assembly transitions as the morphology progressively organizes to higher levels of the hierarchy, and these structures coexists at dynamic equilibrium, as found in real hierarchically self-assembling systems such as amyloid fiber forming proteins. Moreover, the transition sharpness progressively grows with increasing m, corresponding to larger and larger loops in the assembled structures. Calculations are provided for several basic thermodynamic properties (including the order parameters for assembly for each stage of the hierarchy, average mass of clusters, specific heat, transition sharpness, etc.) that are required for characterizing the interaction parameters governing this type of self-assembly and for elucidating other basic qualitative aspects of these systems. Our idealized model of hierarchical assembly gives many insights into this ubiquitous type of self-organization process.

Dudowicz, Jacek; Douglas, Jack F.; Freed, Karl F.

2009-06-01

279

Self-Assembly of Globular Protein-Polymer Diblock Copolymers  

NASA Astrophysics Data System (ADS)

The self-assembly of globular protein-polymer diblock copolymers into nanostructured phases is demonstrated as an elegant and simple method for structural control in biocatalysis or bioelectronics. In order to fundamentally investigate self-assembly in these complex block copolymer systems, a red fluorescent protein was expressed in E. coli and site-specifically conjugated to a low polydispersity poly(N-isopropyl acrylamide) (PNIPAM) block using thiol-maleimide coupling to form a well-defined model globular protein-polymer diblock. Functional protein materials are obtained by solvent evaporation and solvent annealing above and below the lower critical solution temperature of PNIPAM in order to access different pathways toward self-assembly. Small angle x-ray scattering and microscopy are used to show that the diblock forms lamellar nanostructures and to explore dependence of nanostructure formation on processing conditions. Circular dichroism and UV-vis show that a large fraction of the protein remains in its folded state after conjugation, and wide angle x-ray scattering demonstrates that diblock copolymer self-assembly changes the protein packing symmetry.

Thomas, C. S.; Olsen, B. D.

2011-03-01

280

Self-assembly in additive manufacturing: opportunities and obstacles  

Microsoft Academic Search

Purpose – Additive manufacturing (AM) offers substantial flexibility in shape, but much less flexibility in materials and functionality – particularly at small size scales. A system for automatically incorporating microscale components would enable the fabrication of objects with more functionality. The purpose of this paper is to consider the potential of self-assembly to serve as an automated programmable integration method.

N. B. Crane; J. Tuckerman; G. N. Nielson

2011-01-01

281

Molecular recognition directed self-assembly of supramolecular architectures  

Microsoft Academic Search

This paper reviews some of our research on three classes of supramolecular architectures which are generated via various combinations of molecular, macromolecular and supramolecular chemistry. The ability of these supramolecular architectures to form liquid crystalline phases is determined by the shape of the self-assembled architecture and will be used to visualize it via various characterization techniques. The molecular design of

C. Percec; J. Heck; G. Johansson; D. Tomazos; M. Kawasumi; P. Chu; G. Ungar

1994-01-01

282

Self-assembly of functionalized fullerenes on strained metallic interfaces.  

NASA Astrophysics Data System (ADS)

The process of growing ordered arrays of molecules or nanometer sized clusters with tailorable properties on the dislocation networks of strained metallic thin films requires a detailed understanding of the nucleation processes and film-molecule and intermolecular interactions. We compare two different self-assembly mechanisms of functionalized fullerenes on strained metallic films of Ag on Ru(0001). We found that by controlling the molecular coverage and/or the strain in the thin film, various interactions can dominate the self-assembly process, thus resulting in a richness of structures with controllable properties. At low molecular coverage on 1 monolayer Ag films on Ru(0001), ordered triangular arrays of clusters, 4.9 nm apart, with a tunable number of molecules can be grown. This process is driven by strain relaxation in the metal film, as confirmed by 2D Frenkel-Kontorova models, and was found to be a general one working for various functionalized molecules. At higher molecular coverage and different Ag film thickness, the intermolecular interaction becomes dominant and the symmetry and unit cell size of the self-assembled monolayer are a consequence of the molecular structure and functionality. Both these processes are generally applicable to many functionalized C60 molecules thus opening avenues towards complex self-assembled structures based on lock and key type approach.

Diaconescu, Bogdan; Jazdzyk, Mikael; Miller, Glen; Pohl, Karsten

2008-03-01

283

Molecular engineering and characterization of self-assembled biorecognition surfaces  

Microsoft Academic Search

The development of molecular engineering techniques for the fabrication of biomaterial surfaces is of importance in the field of biomaterials. It offers opportunities for better understanding of biological processes on material surfaces and rational design of contemporary biomaterials. Our work in this area aims to develop novel engineering strategies to design biorecognition surfaces via self-assembly and surface derivatization. Fundamental issues

Sheng Pan

1999-01-01

284

A Two-Piece Derivative of a Group I Intron RNA as a Platform for Designing Self-Assembling RNA Templates to Promote Peptide Ligation  

PubMed Central

Multicomponent RNA-peptide complexes are attractive from the viewpoint of artificial design of functional biomacromolecular systems. We have developed self-folding and self-assembling RNAs that serve as templates to assist chemical ligation between two reactive peptides with RNA-binding capabilities. The design principle of previous templates, however, can be applied only to limited classes of RNA-binding peptides. In this study, we employed a two-piece derivative of a group I intron RNA from the Tetrahymena large subunit ribosomal RNA (LSU rRNA) as a platform for new template RNAs. In this group I intron-based self-assembling platform, modules for the recognition of substrate peptides can be installed independently from modules holding the platform structure. The new self-assembling platform allows us to expand the repertoire of substrate peptides in template RNA design.

Tanaka, Takahiro; Furuta, Hiroyuki; Ikawa, Yoshiya

2012-01-01

285

Patterned organosilane monolayers as lyophobic-lyophilic guiding templates in surface self-assembly: monolayer self-assembly versus wetting-driven self-assembly.  

PubMed

Monolayer self-assembly (MSA) was discovered owing to the spectacular liquid repellency (lyophobicity) characteristic of typical self-assembling monolayers of long tail amphiphiles, which facilitates a straightforward visualization of the MSA process without the need of any sophisticated analytical equipment. It is this remarkable property that allows precise control of the self-assembly of discrete, well-defined monolayers, and it was the alternation of lyophobicity and lyophilicity (liquid affinity) in a system of monolayer-forming bifunctional organosilanes that allowed the extension of the principle of MSA to the layer-by-layer self-assembly of planed multilayers. On this basis, the possibility of generating at will patterned monolayer surfaces with lyophobic and lyophilic regions paves the way to the engineering of molecular templates for site-defined deposition of materials on a surface via either precise MSA or wetting-driven self-assembly (WDSA), namely, the selective retention of a liquid repelled by the lyophobic regions of the pattern on its lyophilic sites. Highly ordered organosilane monolayer and thicker layer-by-layer assembled structures are shown to be ideally suited for this purpose. Examples are given of novel WDSA and MSA processes, such as guided deposition by WDSA on lyophobic-lyophilic monolayer and bilayer template patterns at elevated temperatures, from melts and solutions that solidify upon cooling to the ambient temperature, and the possible extension of constructive nanolithography to thicker layer-by-layer assembled films, which paves the way to three-dimensional (3D) template patterns made of readily available monofunctional n-alkyl silanes only. It is further shown how WDSA may contribute to MSA on nanoscale template features as well as how combined MSA and WDSA modes of surface assembly may lead to composite surface architectures exhibiting rather surprising new properties. Finally, a critical evaluation is offered of the scope, advantages, and limitations of MSA and WDSA in the bottom-up fabrication of surface structures on variable length scales from nano to macro. PMID:19835384

Zeira, Assaf; Chowdhury, Devasish; Hoeppener, Stephanie; Liu, Shantang; Berson, Jonathan; Cohen, Sidney R; Maoz, Rivka; Sagiv, Jacob

2009-12-15

286

Light harvesting and energy transfer in laser-dye-labeled poly(aryl ether) dendrimers  

SciTech Connect

The photophysical properties of a series of laser-dye-labeled poly(aryl ether) dendrimers, generations 1--4, have been determined. The dendrimers act as extremely efficient light-harvesting antennae capable of transferring light energy through space from their periphery to their core. The light-harvesting ability of these molecules increases with generation due to an increase in the number of peripheral chromophores. The energy-transfer efficiency was found to be quantitative for generations 1--3, with only a slight decrease observed for the fourth generation ({approximately}93%). Due to high extinction coefficients and fluorescence quantum yields of the chromophores and the efficient intramolecular energy transfer of the dendritic assemblies, these macromolecules have the potential to become integral components of molecular photonic devices.

Adronov, A.; Gilat, S.L.; Frechet, J.M.J.; Ohta, K.; Neuwahl, F.V.R.; Fleming, G.R.

2000-02-16

287

Distribution of entanglement in light-harvesting complexes and their quantum efficiency  

NASA Astrophysics Data System (ADS)

Recent evidence of electronic coherence during energy transfer in photosynthetic antenna complexes has reinvigorated the discussion about whether coherence and/or entanglement have any practical functionality for these molecular systems. Here we investigate quantitative relationships between the quantum yield of a light-harvesting complex and the distribution of entanglement among its components. Our study focuses on the entanglement yield or average entanglement surviving a time scale comparable to the average excitation trapping time. We consider the Fenna-Matthews-Olson (FMO) protein of green sulfur bacteria as a prototype system and show that there is an inverse relationship between the quantum efficiency and the average entanglement between distant donor sites. Our results suggest that long-lasting electronic coherence among distant donors might help in the modulation of the light-harvesting function.

Fassioli, Francesca; Olaya-Castro, Alexandra

2010-08-01

288

Plasmon-controlled light-harvesting: design rules for biohybrid devices via multiscale modeling.  

PubMed

Photosynthesis is triggered by the absorption of light by light-harvesting (LH) pigment-protein complexes followed by excitation energy transfer to the reaction center(s). A promising strategy to achieve control on and to improve light harvesting is to complement the LH complexes with plasmonic particles. Here a recently developed QM/MM/continuum approach is used to investigate the LH process of the peridinin-chlorophyll-protein (PCP) complex on a silver island film. The simulations not only reproduce and interpret the experiments but they also suggest general rules to design novel biohybrid devices; hot-spot configurations in which the LH complex is sandwiched between couples of metal aggregates are found to produce the largest amplifications. Indications about the best distances and orientations are also reported together with illumination and emission geometries of the PCP-NP system necessary to achieve the maximum enhancement. PMID:23981059

Andreussi, Oliviero; Biancardi, Alessandro; Corni, Stefano; Mennucci, Benedetta

2013-09-11

289

Anti-Correlated Pigment Fluctuations of Allophycocyanin for Highly Efficient Photosynthetic Light Harvesting in Cyanobacteria  

NASA Astrophysics Data System (ADS)

The phycobiliprotein, allophycocyanin (APC), is an excellent model system for the study of light harvesting pigment interactions with a protein bath. This work investigates the relaxation of electronic excitations in APC with electric field-resolved transient grating and photon echo spectroscopies. Transient grating experiments observe a 35 fs internal conversion process between single exciton levels. Most importantly, our analysis shows that anti-correlated phycocyanobilin pigment energy level fluctuations cause the anti-diagonal orientation of the node in the measured dispersive photon echo spectrum. We believe this novel observation to reflect concerted protein bath fluctuations over the 2 nm length scale that separates the pigments. Consideration of the Forster energy transfer rate theory suggests that APC has evolved with this property to enhance its photosynthetic light harvesting efficiency.

Moran, Andrew; Nome, Rene; Scherer, Norbert

2008-03-01

290

ARCHITECTURE OF A CHARGE-TRANSFER STATE REGULATING LIGHT HARVESTING IN A PLANT ANTENNA PROTEIN  

SciTech Connect

Energy-dependent quenching of excess absorbed light energy (qE) is a vital mechanism for regulating photosynthetic light harvesting in higher plants. All of the physiological characteristics of qE have been positively correlated with charge-transfer between coupled chlorophyll and zeaxanthin molecules in the light-harvesting antenna of photosystem II (PSII). In this work, we present evidence for charge-transfer quenching in all three of the individual minor antenna complexes of PSII (CP29, CP26, and CP24), and we conclude that charge-transfer quenching in CP29 involves a de-localized state of an excitonically coupled chlorophyll dimer. We propose that reversible conformational changes in CP29 can `tune? the electronic coupling between the chlorophylls in this dimer, thereby modulating the energy of the chlorophylls-zeaxanthin charge-transfer state and switching on and off the charge-transfer quenching during qE.

Fleming, Graham; Ahn, Tae Kyu; Avenson, Thomas J.; Ballottari, Matteo; Cheng, Yuan-Chung; Niyogi, Krishna K.; Bassi, Roberto; Fleming, Graham R.

2008-04-02

291

Efficient energy transfer in light-harvesting systems, I: optimal temperature, reorganization energy and spatial-temporal correlations  

NASA Astrophysics Data System (ADS)

Understanding the mechanisms of efficient and robust energy transfer in light-harvesting systems provides new insights for the optimal design of artificial systems. In this paper, we use the Fenna-Matthews-Olson (FMO) protein complex and phycocyanin 645 (PC 645) to explore the general dependence on physical parameters that help maximize the efficiency and maintain its stability. With the Haken-Strobl model, the maximal energy transfer efficiency (ETE) is achieved under an intermediate optimal value of dephasing rate. To avoid the infinite temperature assumption in the Haken-Strobl model and the failure of the Redfield equation in predicting the Forster rate behavior, we use the generalized Bloch-Redfield (GBR) equation approach to correctly describe dissipative exciton dynamics, and we find that maximal ETE can be achieved under various physical conditions, including temperature, reorganization energy and spatial-temporal correlations in noise. We also identify regimes of reorganization energy where the ETE changes monotonically with temperature or spatial correlation and therefore cannot be optimized with respect to these two variables.

Wu, Jianlan; Liu, Fan; Shen, Young; Cao, Jianshu; Silbey, Robert J.

2010-10-01

292

Crystal Structure of a Light-Harvesting Protein C-Phycocyanin from Spirulina platensis  

Microsoft Academic Search

The crystal structure of C-phycocyanin, a light-harvesting phycobiliprotein from cyanobacteria (blue-green algae) Spirulina platensis has been solved by molecular replacement technique. The crystals belong to space group P21 with cell parameters a = 107.20, b = 115.40, c = 183.04 Å; ? = 90.2°. The structure has been refined to a crystallographic R factor of 19.2% (Rfree = 23.9%) using

Anil K. Padyana; Vadiraja B. Bhat; K. M. Madyastha; K. R. Rajashankar; S. Ramakumar

2001-01-01

293

Enhanced infrared light harvesting of inorganic nanocrystal photovoltaic and photodetector on graphene electrode  

Microsoft Academic Search

We demonstrate an enhancement of infrared light harvesting of inorganic PbS nanocrystal photovoltaic and photodetector devices based on the transparent graphene electrode. Due to high infrared transparency of the graphene electrode with respect to indium tin oxide (ITO), the infrared photoresponse of the graphene-based device is superior to the ITO-based counterpart, in spite of a higher sheet resistance of the

Chih-Cheng Lin; Di-Yan Wang; Kun-Hua Tu; You-Ting Jiang; Meng-Hsiang Hsieh; Chia-Chun Chen; Chun-Wei Chen

2011-01-01

294

Revealing Linear Aggregates of Light Harvesting Antenna Proteins in Photosynthetic Membranes  

PubMed Central

How light energy is harvested in a natural photosynthetic membrane through energy transfer is closely related to the stoichiometry and arrangement of light harvesting antenna proteins in the membrane. The specific photosynthetic architecture facilitates a rapid and efficient energy transfer among the light harvesting proteins (LH2 and LH1) and to the reaction center. Here we report the identification of linear aggregates of light harvesting proteins, LH2, in the photosynthetic membranes under ambient conditions by using atomic force microscopy (AFM) imaging and spectroscopic analysis. Our results suggest that the light harvesting protein, LH2, can exist as linear aggregates of 4±2 proteins in the photosynthetic membranes and that the protein distributions are highly heterogeneous. In the photosynthetic membranes examined in our measurements, the ratio of the aggregated to the non-aggregated LH2 proteins is about 3:1 to 5:1 depending on the intensity of the illumination used during sample incubation and on the bacterial species. AFM images further identify that the LH2 proteins in the linear aggregates are monotonically tilted at an angle 4°±2° from the plane of the photosynthetic membranes. The aggregates result in red-shifted absorption and emission spectra that are measured using various mutant membranes, including an LH2 knock-out, LH1 knock-out, and LH2 at different population densities. Measuring the fluorescence lifetimes of purified LH2 and LH2 in membranes, we have observed that the LH2 proteins in membranes exhibit biexponential lifetime decays whereas the purified LH2 proteins gave single exponential lifetime decays. We attribute that the two lifetime components originate from the existence of both aggregated and non-aggregated LH2 proteins in the photosynthetic membranes.

He, Yufan; Zeng, Xiaohua; Mukherjee, Saptarshi; Rajapaksha, Suneth; Kaplan, Samuel; Lu, H. Peter

2010-01-01

295

Atomic model of plant light-harvesting complex by electron crystallography  

Microsoft Academic Search

The structure of the light-harvesting chlorophyll a\\/b-protein complex, an integral membrane protein, has been determined at 3.4 Å resolution by electron crystallography of two-dimensional crystals. Two of the three membrane-spanning alpha-helices are held together by ion pairs formed by charged residues that also serve as chlorophyll ligands. In the centre of the complex, chlorophyll a is in close contact with

Werner Kühlbrandt; Da Neng Wang; Yoshinori Fujiyoshi

1994-01-01

296

Spectroscopic Studies of Individual Extramembranous Light-Harvesting Complexes of Green Photosynthetic Bacteria  

NASA Astrophysics Data System (ADS)

Green photosynthetic bacteria have extramembranous light-harvesting complexes chlorosomes as major antenna apparatus. In chlorosomes, bacteriochlorophyll(BChl)s c, d, and e self-aggregate to form photofunctional core complexes by only pigment-pigment interaction. Single supramolecule spectroscopy of chlorosomes has been performed to obtain their structural and functional information without heterogeneity among individual chlorosomes. This paper briefly summarizes our recent results of single supramolecule spectroscopy of chlorosomes.

Saga, Yoshitaka

2013-09-01

297

Solid-state NMR applied to photosynthetic light-harvesting complexes  

Microsoft Academic Search

This short review describes how solid-state NMR has provided a mechanistic and electronic picture of pigment–protein and pigment–pigment\\u000a interactions in photosynthetic antenna complexes. NMR results on purple bacterial antenna complexes show how the packing of\\u000a the protein and the pigments inside the light-harvesting oligomers induces mutual conformational stress. The protein scaffold\\u000a produces deformation and electrostatic polarization of the BChl macrocycles

Anjali Pandit; Huub J. M. de Groot

298

A thioredoxin-like/?-propeller protein maintains the efficiency of light harvesting in Arabidopsis  

PubMed Central

The light-harvesting complexes of plants have evolved the ability to switch between efficient light harvesting and quenching forms to optimize photosynthesis in response to the environment. Several distinct mechanisms, collectively termed “nonphotochemical quenching” (NPQ), provide flexibility in this response. Here we report the isolation and characterization of a mutant, suppressor of quenching 1 (soq1), that has high NPQ even in the absence of photosystem II subunit S (PsbS), a protein that is necessary for the rapidly reversible component of NPQ. The formation of NPQ in soq1 was light intensity-dependent, and it exhibited slow relaxation kinetics and other characteristics that distinguish it from known NPQ components. Treatment with chemical inhibitors or an uncoupler, as well as crosses to mutants known to affect other NPQ components, showed that the NPQ in soq1 does not require a transthylakoid pH gradient, zeaxanthin formation, or the phosphorylation of light-harvesting complexes, and it appears to be unrelated to the photosystem II damage-and-repair cycle. Measurements of pigments and chlorophyll fluorescence lifetimes indicated that the additional NPQ in soq1 is the result of a decrease in chlorophyll excited-state lifetime and not pigment bleaching. The SOQ1 gene was isolated by map-based cloning, and it encodes a previously uncharacterized thylakoid membrane protein with thioredoxin-like and ?-propeller domains located in the lumen and a haloacid-dehalogenase domain exposed to the chloroplast stroma. We propose that the role of SOQ1 is to prevent formation of a slowly reversible form of antenna quenching, thereby maintaining the efficiency of light harvesting.

Brooks, Matthew D.; Sylak-Glassman, Emily J.; Fleming, Graham R.; Niyogi, Krishna K.

2013-01-01

299

Nanometric self-assembling peptide layers maintain adult hepatocyte phenotype in sandwich cultures  

PubMed Central

Background Isolated hepatocytes removed from their microenvironment soon lose their hepatospecific functions when cultured. Normally hepatocytes are commonly maintained under limited culture medium supply as well as scaffold thickness. Thus, the cells are forced into metabolic stress that degenerate liver specific functions. This study aims to improve hepatospecific activity by creating a platform based on classical collagen sandwich cultures. Results The modified sandwich cultures replace collagen with self-assembling peptide, RAD16-I, combined with functional peptide motifs such as the integrin-binding sequence RGD and the laminin receptor binding sequence YIG to create a cell-instructive scaffold. In this work, we show that a plasma-deposited coating can be used to obtain a peptide layer thickness in the nanometric range, which in combination with the incorporation of functional peptide motifs have a positive effect on the expression of adult hepatocyte markers including albumin, CYP3A2 and HNF4-alpha. Conclusions This study demonstrates the capacity of sandwich cultures with modified instructive self-assembling peptides to promote cell-matrix interaction and the importance of thinner scaffold layers to overcome mass transfer problems. We believe that this bioengineered platform improves the existing hepatocyte culture methods to be used for predictive toxicology and eventually for hepatic assist technologies and future artificial organs.

2010-01-01

300

Quantum coherence spectroscopy reveals complex dynamics in bacterial light-harvesting complex 2 (LH2).  

PubMed

Light-harvesting antenna complexes transfer energy from sunlight to photosynthetic reaction centers where charge separation drives cellular metabolism. The process through which pigments transfer excitation energy involves a complex choreography of coherent and incoherent processes mediated by the surrounding protein and solvent environment. The recent discovery of coherent dynamics in photosynthetic light-harvesting antennae has motivated many theoretical models exploring effects of interference in energy transfer phenomena. In this work, we provide experimental evidence of long-lived quantum coherence between the spectrally separated B800 and B850 rings of the light-harvesting complex 2 (LH2) of purple bacteria. Spectrally resolved maps of the detuning, dephasing, and the amplitude of electronic coupling between excitons reveal that different relaxation pathways act in concert for optimal transfer efficiency. Furthermore, maps of the phase of the signal suggest that quantum mechanical interference between different energy transfer pathways may be important even at ambient temperature. Such interference at a product state has already been shown to enhance the quantum efficiency of transfer in theoretical models of closed loop systems such as LH2. PMID:22215585

Harel, Elad; Engel, Gregory S

2012-01-17

301

Antheraxanthin, a light harvesting carotenoid found in a chromophyte alga. [Chrysophaera magna Becher, Phaeodactylum tricornutum  

SciTech Connect

The pigments of the chromophyte freshwater alga, Chrysophaera magna Belcher were analyzed by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) to reveal the presence of chlorophylls a and c, ..beta..-carotene, fucoxanthin, and antheraxanthin. The presence of antheraxanthin was verified by comparison of TLC R/sub F/ values, HPLC retention times, and absorption features to those of authentic, synthetic antheraxanthin. Antheraxanthin accounted for about 15% of the total carotenoid content of C. magna. The molar ratio of the major carotenoids was antheraxanthin:fucoxanthin:..beta..-carotene, 1:2.3:3.3. The whole-cell absorption spectrum revealed a broad band between 470 and 520 nanometers which was attributed to fucoxanthin and antheraxanthin in vivo. Upon extraction in hydrocarbon, this broad absorption region was lost. The in vivo fluorescence excitation spectrum for 680 nm emission revealed the energy transfer activities and light harvesting roles of chlorophylls a and c, and fucoxanthin. In addition, an excitation band was resolved at 487 nanometers which could be attributed only to antheraxanthin. Comparison of whole-cell fluorescence excitation spectra of C. magna with the diatom Phaeodactylum tricornutum, which possesses fucoxanthin but not antheraxanthin, supports the assignment of the 487 nm band to antheraxanthin. This is the first report of a photosynthetic light harvesting function of the xanthophyll, antheraxanthin. This carotenoid broadens the absorption cross-section for photosynthesis in C. magna and extends light harvesting into the green portion of the spectrum.

Alberte, R.S.; Andersen, R.A.

1986-02-01

302

Functional quantum dot-protein nano bio-assembly for superior light harvesting applications  

NASA Astrophysics Data System (ADS)

The formation of functional bio-assemblies is crucial for the advanced biophotonic applications. In this work, we formed a nano bio-assembly, consisting of green fluorescent protein (GFP) and inorganic quantum dots (QDs), to employ as an excitonic biofunctional composite to use for light harvesting and biosensing applications. Using QDs as donor molecules with the acceptor GFP in the formed bio-assembly, we observed up-to 15-fold enhancement on the GFP emission, mediated by the strong nonradiative energy transfer. The lifetime modifications of the donor-acceptor pair were studied as a function of the number of proteins per quantum dot, and in good agreement with the proposed theoretical model based on the excitonic interaction among the species. Apart from the light harvesting system, a biosensing medium was also established, facilitated by the enzymatic activity destructing the light harvesting complex. The energy transferring QD-GFP complex was controllably modified by the addition of trypsin, by destroying the bond in between the QD-GFP complex, as verified by the observation of lifetime modifications. In summary, we developed functional excitonic nano-bio-assemblies, which we believe will open up new possibilities for advanced biophotonic applications.

Mutlugun, Evren; Ozgur Safak Seker, Urartu; Hernandez-Martinez, Pedro Ludwig; Sharma, Vijay Kumar; Lesnyak, Vladimir; Gaponik, Nikolai; Eychmuller, Alexander; Demir, Hilmi Volkan

2013-03-01

303

Directed assembly of hierarchical light-harvesting complexes using virus capsid scaffolds and DNA origami tiles  

NASA Astrophysics Data System (ADS)

Directed assembly of nanostructures with molecular precision is of great importance to develop an insightful understanding of assembly pathways and dynamics as well as to derive new functionalities. In this work, we explore the use of virus capsids and DNA origami tiles as 3D scaffolds and 2D templates for directed assembly of light-harvesting molecules and plasmonic gold nanoparticles to achieve tunable photoemission. Bacteriophage MS2 virus capsids with well-defined spherical macromolecular structures are genetically modified to provide predictable steric arrangements of light-harvesting molecules. DNA origami tiles act as programmable planar templates to provide higher-order organization of oligonucleotide-functionalized light-harvesting capsids and plasmonic gold nanoparticles. The direct observation of distance dependent photoluminescence emission is carried out by our correlative approach combining atomic force microscopy and confocal fluorescence microscopy, which is in good agreement with our numerical simulation and theoretical calculation. This work will facilitate the construction of multicomponent biological-metal hybrid plasmonic nanostructures for nanophotonics and biosensing applications.

Wang, Debin; Capehart, Stacy; Pal, Suchetan; Liu, Minghui; Lau, Jolene; Yan, Hao; Francis, Matthew; Deyoreo, Jim

2013-03-01

304

Quantum coherence spectroscopy reveals complex dynamics in bacterial light-harvesting complex 2 (LH2)  

PubMed Central

Light-harvesting antenna complexes transfer energy from sunlight to photosynthetic reaction centers where charge separation drives cellular metabolism. The process through which pigments transfer excitation energy involves a complex choreography of coherent and incoherent processes mediated by the surrounding protein and solvent environment. The recent discovery of coherent dynamics in photosynthetic light-harvesting antennae has motivated many theoretical models exploring effects of interference in energy transfer phenomena. In this work, we provide experimental evidence of long-lived quantum coherence between the spectrally separated B800 and B850 rings of the light-harvesting complex 2 (LH2) of purple bacteria. Spectrally resolved maps of the detuning, dephasing, and the amplitude of electronic coupling between excitons reveal that different relaxation pathways act in concert for optimal transfer efficiency. Furthermore, maps of the phase of the signal suggest that quantum mechanical interference between different energy transfer pathways may be important even at ambient temperature. Such interference at a product state has already been shown to enhance the quantum efficiency of transfer in theoretical models of closed loop systems such as LH2.

Harel, Elad; Engel, Gregory S.

2012-01-01

305

Design principles and fundamental trade-offs in biomimetic light harvesting  

NASA Astrophysics Data System (ADS)

Recent developments in synthetic and supramolecular chemistry have created opportunities to design organic systems with tailored nanoscale structure for various technological applications. A key application area is the capture of light energy and its conversion into electrochemical or chemical forms for photovoltaic or sensing applications. In this work we consider cylindrical assemblies of chromophores that model structures produced by several supramolecular techniques. Our study is especially guided by the versatile structures produced by virus-templated assembly. We use a multi-objective optimization framework to determine design principles and limitations in light harvesting performance for such assemblies, both in the presence and absence of disorder. We identify a fundamental trade-off in cylindrical assemblies that is encountered when attempting to maximize both efficiency of energy transfer and absorption bandwidth. We also rationalize the optimal design strategies and provide explanations for why various structures provide optimal performance. Most importantly, we find that the optimal design strategies depend on the amount of energetic and structural disorder in the system. The aim of these studies is to develop a program of quantum-informed rational design for construction of organic assemblies that have the same degree of tailored nanoscale structure as biological photosynthetic light harvesting complexes, and consequently have the potential to reproduce their remarkable light harvesting performance.

Sarovar, Mohan; Whaley, K. Birgitta

2013-01-01

306

Synthesis and characterization of self-assembling water-soluble polymers.  

National Technical Information Service (NTIS)

The synthesis is proposed of water-soluble vinyl and other polymers capable of self-assembly through hydrophobic bonding of pendent fluorocarbon and other hydrophobic groups. The self-assembly process will be studied by viscometry and dynamic viscoelastic...

T. E. Hogen-Esch E. J. Amis

1992-01-01

307

Self-Assembling Peptides Incorporating Modifications and Methods of use Thereof.  

National Technical Information Service (NTIS)

The invention provides a self-assembling peptide comprising (1) a first amino acid domain that mediates self-assembly, wherein the domain comprises alternating hydrophobic and hydrophilic amino acids that are complementary and structurally compatible and ...

E. Genove S. Zhang C. Semino

2004-01-01

308

Self-location of acceptors as "isolated" or "stacked" energy traps in a supramolecular donor self-assembly: a strategy to wavelength tunable FRET emission.  

PubMed

Control over supramolecular assemblies of donor and acceptor arrays in nanoscale dimension that facilitate efficient energy transfer resulting in tunable emission is an outstanding challenge. In pursuit of this goal, we have designed a supramolecular donor-acceptor organogel with tunable emission from green to red through controlled energy transfer by simply varying the acceptor concentration. Temperature-dependent UV/vis absorption, XRD, and AFM studies of the coassembly of 1 (donor) and 2 (acceptor) revealed the intercalation of 2 within the self-assembly of 1. Upon excitation of the decane gels of 1 with 0-2 mol % of 2, quenching of the emission of the former at 509 nm with the formation of the monomer emission of the latter at 555 nm is observed. Upon further addition of 2 (2-20 mol %), the emission was continuously red-shifted to 610 nm, which corresponds to the aggregate emission of 2. Consequently, a 98% quenching of the donor emission was observed at 509 nm. Fluorescence microscopic studies provided visual evidence for the color tuning of the FRET emission. Thus efficient trapping of excitons by "isolated" or "aggregated" acceptors through a subtle control of the self-assembly and the photophysical properties of the donor-acceptor building blocks allowed a continuous shifting of the emission color anywhere between green and red (lambdamax, 509-610 nm) in a supramolecular light harvesting system. PMID:16734466

Ajayaghosh, Ayyappanpillai; Vijayakumar, Chakkooth; Praveen, Vakayil K; Babu, S Santhosh; Varghese, Reji

2006-06-01

309

Self-assembled photosystem-I biophotovoltaics on nanostructured TiO2 and ZnO  

NASA Astrophysics Data System (ADS)

The abundant pigment-protein membrane complex photosystem-I (PS-I) is at the heart of the Earth's energy cycle. It is the central molecule in the ``Z-scheme'' of photosynthesis, converting sunlight into the chemical energy of life. Commandeering this intricately organized photosynthetic nanocircuitry and re-wiring it to produce electricity carries the promise of inexpensive and environmentally friendly solar power. We here report that dry PS-I stabilized by surfactant peptides functioned as both the light-harvester and charge separator in solar cells self-assembled on nanostructured semiconductors. Contrary to previous attempts at biophotovoltaics requiring elaborate surface chemistries, thin film deposition, and illumination concentrated into narrow wavelength ranges the devices described here are straightforward and inexpensive to fabricate and perform well under standard sunlight yielding open circuit photovoltage of 0.5 V, fill factor of 71%, electrical power density of 81 µW/cm2 and photocurrent density of 362 µA/cm2, over four orders of magnitude higher than any photosystem-based biophotovoltaic to date.

Mershin, Andreas; Matsumoto, Kazuya; Kaiser, Liselotte; Yu, Daoyong; Vaughn, Michael; Nazeeruddin, Md. K.; Bruce, Barry D.; Graetzel, Michael; Zhang, Shuguang

2012-02-01

310

Integrated self-assembling and holding technique applied to a 3-D MEMS variable optical attenuator  

Microsoft Academic Search

The application of polysilicon\\/gold bimorph stress-induced curved beams for three-dimensional self-assembly of MEMS devices is reported. The mechanical principle behind this self-assembling procedure is presented and comparison with current assembling methods are made. With this self-assembling technique, no postprocessing is required. A free-space optical MEMS device in the form of a variable optical attenuator (VOA) has been fabricated and self-assembled

Lijie Li; Justyna Zawadzka; Deepak Uttamchandani

2004-01-01

311

Solid state nanofibers based on self-assemblies: from cleaving from self-assemblies to multilevel hierarchical constructs.  

PubMed

Self-assemblies and their hierarchies are useful to construct soft materials with structures at different length scales and to tune the materials properties for various functions. Here we address routes for solid nanofibers based on different forms of self-assemblies. On the other hand, we discuss rational "bottom-up" routes for multi-level hierarchical self-assembled constructs, with the aim of learning more about design principles for competing interactions and packing frustrations. Here we use the triblock copolypeptide poly(L-lysine)-b-poly(gamma-benzyl-L-glutamate)-b-poly(L-lysine) complexed with 2'-deoxyguanosine 5'-monophosphate. Supramolecular disks (G-quartets) stabilized by metal cations are formed and their columnar assembly leads to a packing frustration with the cylindrical packing of helical poly(gamma-benzyl-L-glutamate), which we suggest is important in controlling the lateral dimensions of the nanofibers. We foresee routes for functionalities by selecting different metal cations within the G-quartets. On the other hand, we discuss nanofibers that are cleaved from bulk self-assemblies in a "top-down" manner. After a short introduction based on cleaving nanofibers from diblock copolymeric self-assemblies, we focus on native cellulose nanofibers, as cleaved from plant cell wall fibers, which are expected to have feasible mechanical properties and to be templates for functional nanomaterials. Long nanofibers with 5-20 nm lateral dimensions can be cleaved within an aqueous medium to allow hydrogels and water can be removed to allow highly porous, lightweight, and flexible aerogels. We further describe inorganic/ organic hybrids as prepared by chemical vapour deposition and atomic layer deposition of the different nanofibers. We foresee functional materials by selecting inorganic coatings. Finally we briefly discuss how the organic template can be removed e.g., by thermal treatments to allow completely inorganic hollow nanofibrillar structures. PMID:20334096

Ikkala, Olli; Ras, Robin H A; Houbenov, Nikolay; Ruokolainen, Janne; Pääkko, Marjo; Laine, Janne; Leskelä, Markku; Berglund, Lars A; Lindström, Tom; ten, Brinke Gerrit; Iatrou, Hermis; Hadjichristidis, Nikos; Faul, Charl F J

2009-01-01

312

Development of self-assembling nanowires containing electronically active oligothiophenes  

NASA Astrophysics Data System (ADS)

This dissertation discusses the development of conductive one-dimensional nanowires from self-assembling oligothiophene molecules. Self-assembly has been demonstrated to be a promising alternative approach towards high performance, solution processable, and low-cost organic electronics. One of the many challenges in this field is the control of supramolecular morphologies of ordered structures containing pi-conjugated moieties. This research demonstrated several successful strategies to achieve self assembly of conductive nanowires using synergistic interactions combining pi stacking and hydrogen bonding. The first approach used was to develop a hairpin-shaped sexithiophene molecule, which features two arms of the conjugated structure. The diamidocyclohexyl headgroup of this molecule successfully directs the self-assembly from hydrogen bonding among the amides, forming high-aspect-ratio one-dimensional nanowires with well-defined diameters of 3.0 +/- 0.3 nm. The molecular orientation in the nanostructures promotes formation of sexithiophene H and J aggregates that facilitate efficient charge transport. Organic field-effect transistors were fabricated to reveal improved intrinsic hole mobility from films of the nanostructures, 3.46 x 10-6 cm2V-1s-1, which is one order of magnitude higher than films cast from unassembled molecules. Bulk heterojunction solar cells were developed from this molecule and fullerenes utilizing solution-phase fabrication methods. Intimate mix of the molecule and phenyl-C61-butyric acid methyl ester creates structured interfaces for efficient exciton splitting. The charge carrier mobilities of each material are improved by self-assembly in solution and thermal-energy assisted phase separation.The photovoltaic devices achieved the highest open-circuit voltage of 0.62 V, short-circuit current of 1.79 mA/cm2, fill factor of 35%, and power conversion efficiency of 0.48%. Another strategy to one-dimensional nanowires studied here involved the modification of a class of peptide lipids. The tripeptide segments in the molecular structure promote beta-sheet formation in nonpolar organic solvents, which is the main driving force for their self-assembly into 1D nanowires. Left-handed helical nanowires were formed with diameters of 8.9 nm and pitches between 50--150 nm. Substitutions of oligothiophenes lead to unprecedented supercoiling phenomena manifested as the transformation from helical to coiled or curved nanowires. We proposed that the curving of the nanowires is the consequence of relaxation from torsionally strained nanohelices, a process similar to supercoiling of strained DNA double helix. This process is governed by the mismatch in intermolecular distances required for peptide beta-sheets vs. pi-pi interactions of the conjugated segments decorating the periphery of the nanowires. Circular dichroism revealed helical arrangements of the conjugated moieties in these peptide lipids manifesting supercoiling phenomena. Peptide lipids without helical arrangement of the conjugated segments only exhibit helical morphologies. The self-assembly process of peptide lipids also leads to hierarchical assemblies of energetically favored single, double, and triple-helical nanostructures with well-defined dimensions. Self-assembled nanowires from oligothiophene-substituted peptide lipids revealed increased conductivity of 1.39--1.41 x 10-5 S/cm, two orders of magnitude higher than unassembled films and one order of magnitude higher than unsubstituted peptide lipids. The role of the primary beta-helix in controlling supramolecular organization was investigated by varying the chirality of the tripeptide segments, GAA. Four diastereomers of a peptide lipid substituted with p-toluene carboxylates were compared using L or D-alanines. Molecules with all L residues self-assemble into left-handed helical nanofibers with a pitch of 160 +/- 30 nm. Substitution of one or two D-alanines leads to assemblies of cylindrical nanofibers without any twisting, left-handed helices with smaller pitches (40 +/- 6 nm), or aggregates with

Tsai, Wei-Wen

313

Integrated Miniaturized Materials - From Self-Assembly to Device Integration. Volume 1272.  

National Technical Information Service (NTIS)

Symposium OO intended to provide a forum for discussing what might be termed 'complex self-assembly', even though it features 'hierarchical self- assembly' in its title. The idea of the symposium is that the units of self assembly themselves should have c...

A. Goyal A. Saiani C. J. Martinez D. Gracias R. R. Naik

2011-01-01

314

Self-assembly of hybrid structures on nano templates  

NASA Astrophysics Data System (ADS)

This dissertation describes the investigation on the synthesis of hybrid structures on nano-templates. Fabrication of molecular nano-patterns of organic amphiphiles (e.g. fatty acids) by self-assembly has been discussed here, and their application as templates for two-dimensional in situ synthesis of metal soap molecular pattern has been demonstrated. The synthesis of nanoparticle---nanorod hybrid structure represents another effort to achieve hybrid materials. Therefore, methods to create complex inorganic---organic nano---hybrid are provided by this work. AFM disclosed the pattern structures of the self-assembled monolayers as designed nanoscaled patterns. It is observed two pattern periodicities reflecting the head-to-head and head-to-tail molecular assembly tendencies of the fatty acids and their dependence on the molecular structure and chain length, which exhibits a linear increase in the periodicity with an increasing molecular chain length. The investigation on molecular patterns of self-assembled monolayers of metal arachidates on graphite by AFM and FTIR is described. Metal arachidate self-assemblies show similar stripe pattern and periodicities as those of arachidic acid. The monolayer structure is mainly dictated by graphite, while the type of metal ions mainly affects the domain size, shape and regularity. The results of AFM and FTIR are correlated to the Irving-Williams Series, which predicts bond strength of the metal ions to ligands. The spin coated films from binary solutions of nanoparticles and fatty acids with different chain lengths (Even number of carbon, C18--C26), have been used to study the effect of nanoparticles on self-assemble pattern of fatty acids. C18--C22 acids formed uniform nanorods attached and induced by nanoparticles, while the self-assembled stripe patterns of C24 and C26 were unaffected by the presence of nanoparticles. The nanoparticles were aligned on C26 monolayer. The seeded nucleation mechanism has been studied by AFM, TEM, UV-Vis and in situ EDS and it is disclosed the confinement effect of nanoparticles and the competition between template effects from nanoparticle and from graphite. This strategy is proven to be universal, and nano-hybrids have been fabricated using different nanoparticle seeds, fatty acids, and solvents.

Wang, Ruomiao

315

Dynamic supramolecular complexes constructed by orthogonal self-assembly.  

PubMed

Conspectus Supramolecular complexes, including various low-molecular-mass structures and large molecular aggregates that are assembled by reversible and highly directional noncovalent interactions, have attracted more and more attention due to their fascinating and unconventional chemical and physical properties that are different from those of traditional architectures encountered by covalently linked backbones. Supramolecular complexes are by nature dynamic architectures considering the reversibility of noncovalent interactions by which small molecular monomers can assemble into specific architectures that are able to be repeatably reorganized through the assembly/disassembly processes under certain environmental factors such as temperature, concentration, and solvent conditions. The construction of supramolecular complexes by orthogonal self-assembly with different types of highly specific, noninterfering interactions is currently attracting considerable interest since they not only can dynamically self-assemble, but also can be tuned by various external stimuli through addressing each type of noncovalent interaction separately. Therefore, these dynamic supramolecular complexes, especially with external responsiveness, represent the most outstanding candidates for the future development of functional and smart materials, and even mimic the assembling process of natural systems. In this Account, we will summarize the recent advances of dynamic supramolecular complexes constructed by orthogonal self-assembly in soluiton in two sections: (1) Construction strategies for supramolecular complexes based on orthogonal self-assembly, whose dynamic behaviors with external responsiveness were not experimentally investigated but potentially existed due to the intrinsic reversibility of noncovalent bonds; (2) dynamic behaviors of multiresponsive supramolecular complexes, which were experimentally reported to exhibit reversible multi-responsiveness to external stimuli. Dynamic nature is one of intrinsic properties of supramolecular complexes constructed by self-assembly. Therefore, in the first section, we will describe the dynamic self-assembly in the construction of supramolecular complexes, but will focus on their external responsive dynamic behaviors in the second section. In addition, considering that an increasing number of supramolecular complexes constructed by biological building blocks through bio-orthogonal assembly as mimics of biological systems have been reported in recent years, in the second section we will also present some typical examples on such special dynamic biological supramolecular complexes. The final part of this Account is devoted to foreseeing the rapid development of dynamic supramolecular complexes toward applications in functional and smart materials and fundamental questions facing dynamic supramolecular complexes in the future. PMID:24873508

Hu, Xiao-Yu; Xiao, Tangxin; Lin, Chen; Huang, Feihe; Wang, Leyong

2014-07-15

316

Efficient light harvesting in a dark, hot, acidic environment: the structure and function of PSI-LHCI from Galdieria sulphuraria.  

PubMed

Photosystem I-light harvesting complex I (PSI-LHCI) was isolated from the thermoacidophilic red alga Galdieria sulphuraria, and its structure, composition, and light-harvesting function were characterized by electron microscopy, mass spectrometry, and ultrafast optical spectroscopy. The results show that Galdieria PSI is a monomer with core features similar to those of PSI from green algae, but with significant differences in shape and size. A comparison with the crystal structure of higher plant (pea) PSI-LHCI indicates that Galdieria PSI binds seven to nine light-harvesting proteins. Results from ultrafast optical spectroscopy show that the functional coupling of the LHCI proteins to the PSI core is tighter than in other eukaryotic PSI-LHCI systems reported thus far. This tight coupling helps Galdieria perform efficient light harvesting under the low-light conditions present in its natural endolithic habitat. PMID:21190665

Thangaraj, Balakumar; Jolley, Craig C; Sarrou, Iosifina; Bultema, Jelle B; Greyslak, Jason; Whitelegge, Julian P; Lin, Su; Kou?il, Roman; Subramanyam, Rajagopal; Boekema, Egbert J; Fromme, Petra

2011-01-01

317

Efficient Light Harvesting in a Dark, Hot, Acidic Environment: The Structure and Function of PSI-LHCI from Galdieria sulphuraria  

Microsoft Academic Search

Photosystem I-light harvesting complex I (PSI-LHCI) was isolated from the thermoacidophilic red alga Galdieria sulphuraria, and its structure, composition, and light-harvesting function were characterized by electron microscopy, mass spectrometry, and ultrafast optical spectroscopy. The results show that Galdieria PSI is a monomer with core features similar to those of PSI from green algae, but with significant differences in shape and

Balakumar Thangaraj; Craig C. Jolley; Iosifina Sarrou; Jelle B. Bultema; Jason Greyslak; Julian P. Whitelegge; Su Lin; Roman Kouril; Rajagopal Subramanyam; Egbert J. Boekema; Petra Fromme

2011-01-01

318

Chameleon-like self-assembling peptides for adaptable biorecognition nanohybrids.  

PubMed

We present here the development of adaptable hybrid materials in which self-assembling peptides can sense the diameter/curvature of carbon nanotubes and then adjust their overall structures from disordered states to ?-helices, and vice versa. The peptides within the hybrid materials show exceptionally high thermal-induced conformational stability and molecular recognition capability for target RNA. This study shows that the context-dependent protein-folding effects can be realized in artificial nanosystems and provides a proof of principle that nanohybrid materials decorated with structured and adjustable peptide units can be fabricated using our strategy, from which smart and responsive organic/inorganic hybrid materials capable of sensing and controlling diverse biological molecular recognition events can be developed. PMID:23844930

Jeong, Woo-jin; Choi, Sung-ju; Choi, Jun Shik; Lim, Yong-beom

2013-08-27

319

Self-assembled free-standing graphene oxide fibers.  

PubMed

It is a great challenge to directly assemble two-dimensional (2D) graphene oxide (GO) sheets into 1D fibers without any polymer or surfactant for their promising multifunctional applications. Herein, a facile self-assembly strategy is proposed to fabricate neat GO fibers from cost-efficient, aqueous GO suspension at a liquid/air interface based on the repulsive electrostatic forces, attractive van der Waals forces, and ?-? stacking. During the self-assembly process and ultrasonic cleaning, the morphology variated from the source graphite powder through GO sheets to GO fibers and finally to neat GO fiber films. It is interesting to note that the electrical property of the GO fiber films was improved dramatically after subsequent low-temperature thermal annealing. The morphological evolution process and formation mechanism were analyzed on the basis of optical microscopy, scanning electron microscopy, and transmission electron microscopy observation, and the electrical characteristics was also discussion. PMID:23369286

Tian, Zhengshan; Xu, Chunxiang; Li, Jitao; Zhu, Gangyi; Shi, Zengliang; Lin, Yi

2013-02-01

320

pH dependence of actin self-assembly.  

PubMed Central

Fluorescence enhancement and fluorescence photobleaching recovery have been utilized to examine actin self-assembly over the pH range 6.6-8.0. The kinetics of assembly are faster and the critical concentrations are lower at lower pH. Filament diffusion coefficients are not a function of pH, indicating that average filament lengths are not pH dependent. Although critical actin concentrations are a sensitive function of the concentrations of various cations in the medium, the relative pH dependences of critical concentrations are similar for all combinations of cations employed. The pH dependence of actin self-assembly is sufficiently great that it should be taken into account when comparing data from different reports and when relating in vitro measurements to cytoplasmic mechanisms.

Wang, F; Sampogna, R V; Ware, B R

1989-01-01

321

Multilayered self-assembled optical fiber sensors for biomedical applications  

NASA Astrophysics Data System (ADS)

We report recent developments in the design and fabrication of molecularly self-assembled thin film materials that may be incorporated with optical fiber waveguides to form humidity and other gas sensors of use in biomedical diagnositc systems. Optical fiber distal end sensors based on this concept may be fabricated by molecularly self-assembling selected polymers and functionalized inorganic nanoclustesr into multilayered optical thin films on the cleaved and polished flat ends of singlemode optical fibers. Prior work reported at this meeting has studied the synthesis process and sensor dynamics, including sensor 10-90% risetime on the order of microseconds. This paper briefly reviews that work but then reports new developments in the synthesis of the sensor films.

Mecham, Jeffrey B.; Kang, Y.; Davis, B.; Arregui, Francisco J.; Matias, Ignacio R.; Claus, Richard O.

2003-07-01

322

Self-Assembly of Graphene on Carbon Nanotube Surfaces  

NASA Astrophysics Data System (ADS)

The rolling up of a graphene sheet into a tube is a standard visualization tool for illustrating carbon nanotube (CNT) formation. However, the actual processes of rolling up graphene sheets into CNTs in laboratory syntheses have never been demonstrated. Here we report conformal growth of graphene by carbon self-assembly on single-wall and multi-wall CNTs using chemical vapor deposition (CVD) of methane without the presence of metal catalysts. The new graphene layers roll up into seamless coaxial cylinders encapsulating the existing CNTs, but their adhesion to the primary CNTs is weak due to the existence of lattice misorientation. Our study shows that graphene nucleation and growth by self-assembly of carbon on the inactive carbon basal plane of CNTs occurs by a new mechanism that is markedly different from epitaxial growth on metal surfaces, opening up the possibility of graphene growth on many other non-metal substrates by simple methane CVD.

Li, Kaiyuan; Eres, Gyula; Howe, Jane; Chuang, Yen-Jun; Li, Xufan; Gu, Zhanjun; Zhang, Litong; Xie, Sishen; Pan, Zhengwei

2013-08-01

323

Unimolecular photoconversion of multicolor luminescence on hierarchical self-assemblies.  

PubMed

Facile tuning of photophysical properties is highly desirable for boosting the performance and versatility of photoluminescent materials. In an attempt to overcome the challenge of achieving the photoswitching of multicolor luminescence on unimolecular platforms, we here report a novel hierarchical self-assembly of a cyanostilbene-naphthalimide dyad as the realization of phototunable luminescence at the unimolecular level. The work takes advantage of the photoisomerization of the cyanostilbene moiety from the Z form to its E form, which causes a morphological disorder in the molecular self-assembly and gives rise to a dual fluorescent characteristic accompanied by a progressive luminescent color conversion from yellow to green and finally to blue. Such systems with convertible multicolor luminescence might exhibit application potentials for unimolecular selective imaging and labeling, as exemplified by the cell imaging studies presented in this work. PMID:23488680

Zhu, Liangliang; Li, Xin; Zhang, Quan; Ma, Xing; Li, Menghuan; Zhang, Huacheng; Luo, Zhong; Ågren, Hans; Zhao, Yanli

2013-04-01

324

Amphipathicity and self-assembly behavior of amphiphilic alginate esters.  

PubMed

Amphiphilic alginate esters (Alg-C(n)) with different degree of substitution (DS) and hydrophobic alkyl length were synthesized by the reaction between partially protonated sodium alginate and aliphatic alcohols (octanol, dodecanol or hexadecanol) and characterized by conventional methods. The critical micelles concentration (CMC) of Alg-C(n) was determined by measuring the fluorescence intensity of pyrene as a fluorescent probe, conductance and surface tension (SFT). Formation and characteristics of the self-assembly micelles of Alg-C(n) were studied by transmission electron microscopy (TEM) and Zetasizer Nano Series method. The results indicate that CMC value and the self-assembled micelle size decreased with the increasing of the hydrophobic alkyl chain length, as the DS of Alg-C(n) is similar. PMID:23218287

Yang, Ji Sheng; Zhou, Qi Quan; He, Wen

2013-01-30

325

The collagen assisted self-assembly of silicon nanowires  

NASA Astrophysics Data System (ADS)

The paper reports on self-assembly of silicon nanowire junctions assisted by protocollagen, a low cost soluble long fiber protein and precursor of collagen fibrils. First, the collagen was combed on an octadecyl-terminated silicon surface with gold electrodes. Then the combed surface was exposed to an aqueous suspension of silicon nanowires. In order to increase electrostatic interactions between the positively charged collagen and the nanowires, the nanowires were chemically modified with negatively charged sulfonate groups. The interaction of collagen with the sulfonated nanowires, which mimics the native collagen/heparin sulfate interaction, induced self-assembly of the nanowires localized between gold electrodes. The proof of concept for the formation of spontaneous electrode-nanowire-electrode junctions using collagen as a template was supported by current-voltage measurements.

Salhi, Billel; Vaurette, François; Grandidier, Bruno; Stiévenard, Didier; Melnyk, Oleg; Coffinier, Yannick; Boukherroub, Rabah

2009-06-01

326

Self-assembly of amorphous calcium carbonate microlens arrays  

PubMed Central

Biological materials are often based on simple constituents and grown by the principle of self-assembly under ambient conditions. In particular, biomineralization approaches exploit efficient pathways of inorganic material synthesis. There is still a large gap between the complexity of natural systems and the practical utilization of bioinspired formation mechanisms. Here we describe a simple self-assembly route leading to a CaCO3 microlens array, somewhat reminiscent of the brittlestars' microlenses, with uniform size and focal length, by using a minimum number of components and equipment at ambient conditions. The formation mechanism of the amorphous CaCO3 microlens arrays was elucidated by confocal Raman spectroscopic imaging to be a two-step growth process mediated by the organic surfactant. CaCO3 microlens arrays are easy to fabricate, biocompatible and functional in amorphous or more stable crystalline forms. This shows that advanced optical materials can be generated by a simple mineral precipitation.

Lee, Kyubock; Wagermaier, Wolfgang; Masic, Admir; Kommareddy, Krishna P.; Bennet, Mathieu; Manjubala, Inderchand; Lee, Seung-Woo; Park, Seung B.; Colfen, Helmut; Fratzl, Peter

2012-01-01

327

Helix self-assembly through the coiling of cylindrical micelles.  

NASA Astrophysics Data System (ADS)

Both single and double helical superstructures with the length of several micrometers have been created through solution self-assembly of cylindrical micelles for the first time. Helical micelles which occur as a racemic mixture were formed from the co-assembly of poly(acrylic acid)-block-poly(methyl acrylate)-block-polystyrene triblock copolymers with triethylenetetramine or diethylenetriamine. Kinetic study reveals that the helix cylinders evolve from the stacking of intermediate micelle domains. The helix pitch could be efficiently adjusted by adjusting the amount and type of multiamine added. For example, the pitch distance would increase nearly 20% by increasing the relative molar amount of triethylenetetramine by 50% or substituting the tetraamine triethylenetetramine by the triamine diethylenetriamine. The helical structure exhibits unprecedented regularity for a nanostructure self-assembled from solution, which is proposed to be the result of long range electrostatic interactions coupled with uniaxial tension along the cylinder.

Zhong, Sheng; Cui, Honggang; Chen, Zhiyun; Wooley, Karen; Pochan, Darrin

2008-03-01

328

DNA Self-Assembly: From Chirality to Evolution  

PubMed Central

Transient or long-term DNA self-assembly participates in essential genetic functions. The present review focuses on tight DNA-DNA interactions that have recently been found to play important roles in both controlling DNA higher-order structures and their topology. Due to their chirality, double helices are tightly packed into stable right-handed crossovers. Simple packing rules that are imposed by DNA geometry and sequence dictate the overall architecture of higher order DNA structures. Close DNA-DNA interactions also provide the missing link between local interactions and DNA topology, thus explaining how type II DNA topoisomerases may sense locally the global topology. Finally this paper proposes that through its influence on DNA self-assembled structures, DNA chirality played a critical role during the early steps of evolution.

Timsit, Youri

2013-01-01

329

Self-assembled electrical circuits and their electronic properties.  

PubMed

A straightforward method for the self assembly of single walled carbon nanotubes (SWNTs) between gold electrodes was developed. The technique utilizes the hybridization between short complementary DNA sequences located on metal contacts and SWNTs. new technique enables simple production of hundreds of devices with high yields. The electrical characteristics are shown to depend strongly on the existence of the chemical binding groups at the contacts as well as along the tubes. This technique was used to drive the self assembly of SWNT-based field effect transistors (CNTFETs). In principle, the devices made by this method behave like those made using direct metal-carbon nanotube contacts. The inverse subthreshold slope of the CNTFETs depends on the source-drain voltage applied to the device, confirming that the conductance of CNTFETs is determined by the Schottky barriers at the interfaces between the CNTs and the gold electrodes. PMID:16512380

Hazani, Miron; Shvarts, Dmitry; Peled, Dana; Sidorov, Victor; Naaman, Ron

2006-01-01

330

Self Assembled Structures by Directional Solidification of Eutectics  

NASA Technical Reports Server (NTRS)

Interest in ordered porous structures has grown because of there unique properties such as photonic bandgaps, high backing packing density and high surface to volume ratio. Inspired by nature, biometric strategies using self assembled organic molecules dominate the development of hierarchical inorganic structures. Directional solidification of eutectics (DSE) also exhibit self assembly characteristics to form hierarchical metallic and inorganic structures. Crystallization of diphasic materials by DSE can produce two dimensional ordered structures consisting of rods or lamella. By selective removal of phases, DSE is capable to fabricate ordered pore arrays or ordered pin arrays. Criteria and limitations to fabricate hierarchical structures will be presented. Porous structures in silicon base alloys and ceramic systems will be reported.

Dynys, Frederick W.; Sayir, Ali

2004-01-01

331

Self-Assembly of Graphene on Carbon Nanotube Surfaces  

PubMed Central

The rolling up of a graphene sheet into a tube is a standard visualization tool for illustrating carbon nanotube (CNT) formation. However, the actual processes of rolling up graphene sheets into CNTs in laboratory syntheses have never been demonstrated. Here we report conformal growth of graphene by carbon self-assembly on single-wall and multi-wall CNTs using chemical vapor deposition (CVD) of methane without the presence of metal catalysts. The new graphene layers roll up into seamless coaxial cylinders encapsulating the existing CNTs, but their adhesion to the primary CNTs is weak due to the existence of lattice misorientation. Our study shows that graphene nucleation and growth by self-assembly of carbon on the inactive carbon basal plane of CNTs occurs by a new mechanism that is markedly different from epitaxial growth on metal surfaces, opening up the possibility of graphene growth on many other non-metal substrates by simple methane CVD.

Li, Kaiyuan; Eres, Gyula; Howe, Jane; Chuang, Yen-Jun; Li, Xufan; Gu, Zhanjun; Zhang, Litong; Xie, Sishen; Pan, Zhengwei

2013-01-01

332

Self-assembly of cinnamic acid-capped gold nanoparticles  

NASA Astrophysics Data System (ADS)

In this work, a new capping agent, cinnamic acid (CA) was used to synthesize Au nanoparticles (NPs) under ambient conditions. The size of the NPs can be controlled by adjusting the concentration of reductant (in our experiment sodium borohydride was used) or CA. The CA-stabilized Au NPs can self-assemble into 'nanowire-like' or 'pearl-necklace-like' nanostructures by adjusting the molar ratio of CA to HAuCl4 or by tuning the pH value of the Au colloidal solution. The process of Au NPs self-assembly was investigated by UV-vis spectroscopy and transmission electron microscopy. The results reveal that the induced dipole-dipole interaction is the driving force of Au NP linear assemblies.

Wang, Li; Wei, Gang; Sun, Lanlan; Liu, Zhiguo; Song, Yonghai; Yang, Tao; Sun, Yujing; Guo, Cunlan; Li, Zhuang

2006-06-01

333

A switch based on self-assembled thymine  

NASA Astrophysics Data System (ADS)

The DNA base thymine is deposited at 100 K on Cu(111) and investigated and manipulated by low-temperature scanning tunneling microscopy at 5 K. At submonolayer coverage paired rows are observed. At monolayer coverage a hexagonal commensurate self-assembled layer with the methyl group pointing away from the surface forms. A reversible local manipulation of molecules within the self-assembled layer is demonstrated. This manipulation is interpreted as an out-of-plane relaxation of molecules within the layer induced by the change of the adsorption geometry of individual molecules between two meta-stable orientations. A positive field of 2-4 V leads to this local change in the molecular arrangement, while a field larger than 4 V restores the original geometry.

Kalkan, Fatih; Mehlhorn, Michael; Morgenstern, Karina

2012-10-01

334

Chemical reaction mediated self-assembly of PTCDA into nanofibers  

NASA Astrophysics Data System (ADS)

Uniform and crystalline nanofibers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), an insoluble organic semiconducting molecule, have been achieved by self-assembling the molecules using chemical reaction mediated conversion of an appropriately designed soluble precursor, perylene tetracarboxylic acid (PTCA) using carbodiimide chemistry.Uniform and crystalline nanofibers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), an insoluble organic semiconducting molecule, have been achieved by self-assembling the molecules using chemical reaction mediated conversion of an appropriately designed soluble precursor, perylene tetracarboxylic acid (PTCA) using carbodiimide chemistry. Electronic supplementary information (ESI) available: Synthesis protocols and schemes, plausible mechanism of reaction, additional TEM images, TEM images for stability of fibers after extraction in DCM and aqueous potassium carbonate, detailed FTIR spectra, mass spectroscopy, and XRD of fibers of PTCDA. See DOI: 10.1039/c1nr10579e

Sayyad, Arshad S.; Balakrishnan, Kaushik; Ajayan, Pulickel M.

2011-09-01

335

Chiral plasmonics of self-assembled nanorod dimers  

PubMed Central

Chiral nanoscale photonic systems typically follow either tetrahedral or helical geometries that require four or more different constituent nanoparticles. Smaller number of particles and different chiral geometries taking advantage of the self-organization capabilities of nanomaterials will advance understanding of chiral plasmonic effects, facilitate development of their theory, and stimulate practical applications of chiroplasmonics. Here we show that gold nanorods self-assemble into side-by-side orientated pairs and “ladders” in which chiral properties originate from the small dihedral angle between them. Spontaneous twisting of one nanorod versus the other one breaks the centrosymmetric nature of the parallel assemblies. Two possible enantiomeric conformations with positive and negative dihedral angles were obtained with different assembly triggers. The chiral nature of the angled nanorod pairs was confirmed by 4? full space simulations and the first example of single-particle CD spectroscopy. Self-assembled nanorod pairs and “ladders” enable the development of chiral metamaterials, (bio)sensors, and new catalytic processes.

Ma, Wei; Kuang, Hua; Wang, Libing; Xu, Liguang; Chang, Wei-Shun; Zhang, Huanan; Sun, Maozhong; Zhu, Yinyue; Zhao, Yuan; Liu, Liqiang; Xu, Chuanlai; Link, Stephan; Kotov, Nicholas A.

2013-01-01

336

Intramolecular energy transfer with butadiyne-linked chlorophyll and porphyrin dimer-faced, self-assembled prisms.  

SciTech Connect

The synthesis and photophysical properties of butadiyne-linked chlorophyll and porphyrin dimers in toluene solution and in several self-assembled prismatic structures are described. The butadiyne linkage between the 20-positions of the macrocycles results in new electronic transitions polarized along the long axes of the dimers. These transitions greatly increase the ability of these dimers to absorb the solar spectrum over a broad wavelength range. Femtosecond transient absorption spectroscopy reveals the relative rate of rotation of the macrocycles around the butadiyne bond joining them. Following addition of 3-fold symmetric, metal-coordinating ligands, both macrocyclic dimers self-assemble into prismatic structures in which the dimers comprise the faces of the prisms. These structures were confirmed by small-angle X-ray scattering experiments in solution using a synchrotron source. Photoexcitation of the prismatic assemblies reveals that efficient, through-space energy transfer occurs between the macrocyclic dimers within the prisms. The distance dependence of energy transfer between the faces of the prisms was observed by varying the size of the prismatic assemblies through the use of 3-fold symmetric ligands having arms with different lengths. These results show that self-assembly of discrete macrocyclic prisms provides a useful new strategy for controlling singlet exciton flow in antenna systems for artificial photosynthesis and solar cell applications.

Kelley, R. F.; Lee, S. J.; Wilson, T. M.; Nakamura, Y.; Tiede, D. M.; Osuka, A.; Hupp, J. T.; Wasielewski, M. R.; SUF-USR; Chemical Sciences and Engineering Division; Northwestern Univ.; Kyoto Univ.

2008-01-01

337

Molecular Detection with Self-Assembled Gold Nanoparticle Wires  

Microsoft Academic Search

Recently, we have reported the creation of gold nanowires by evaporation-driven vertical colloidal deposition (VCD) of gold nanoparticles. Subsequently, we have noted systematic changes in conductivity associated with post-deposition annealing. Here we describe the change in room temperature conductivity of gold nanoparticle wires after exposure to thiol-derivatized molecules. A self-assembled gold nanoparticle wire is immersed into a solution of octadecanethiol

J. B. Hutchison; J. A. Hoffmann; J. W. Sun; M. E. Reeves

2006-01-01

338

Self-assembled monolayers formed on AZ31 Mg alloy  

NASA Astrophysics Data System (ADS)

Self-assembled monolayer (SAM) was successfully adsorbed on the AZ31 Mg alloy surface using oleic acid and stearic acid with various organic solvents, such as acetone, ethanol, and hexane. The surface monolayers were characterized using contact angle measurements, X-ray photoelectron spectroscopy (XPS) and anodic polarization test. It was shown that the higher contact angle and the best anti-corrosion property were obtained with treatment in oleic acid with ethanol solution.

Salman, S. A.; Okido, M.

2012-07-01

339

Development of self-assembled bacterial cellulose–starch nanocomposites  

Microsoft Academic Search

A bioinspired bottom-up process was developed to produce self-assembled nanocomposites of cellulose synthesized by Acetobacter bacteria and native starch. This process takes advantage of the way some bacteria extrude cellulose nanofibres and of the transport process that occurs during the gelatinization of starch.Potato and corn starch were added into the culture medium and partially gelatinized in order to allow the

Cristian J. Grande; Fernando G. Torres; Clara M. Gomez; Omar P. Troncoso; Josep Canet-Ferrer; Juan Martínez-Pastor

2009-01-01

340

Self-assembled Metal Rubber(TM) mechanical sensors  

Microsoft Academic Search

Molecular-level self-assembly processes allow the formation of novel materials with properties that are not achievable using conventional fabrication methods. For example, nanostructured metals and polymers may be combined to form inorganic\\/organic materials that exhibit properties typically associated with each of these species separately, namely high electrical conductivity and low Young's modulus. The combination of such properties is of interest for

Richard O. Claus; Richard M. Goff; Jennifer H. Lalli; Andrea B. Hill

2006-01-01

341

Folding and self-assembly of a small heterotetramer  

NASA Astrophysics Data System (ADS)

Designed miniproteins offer a possibility to study folding and association of protein complexes, both experimentally and in silico. Using replica exchange molecular dynamics and the coarse-grain UNRES force field, we have simulated the folding and self-assembly of the heterotetramer BBAThet1, comparing it with that of the homotetramer BBAT1 which has the same size and ???-fold. For both proteins, association of the tetramer precedes and facilitates folding of the individual chains.

Ya?ar, Fatih; Sieradzan, Adam K.; Hansmann, Ulrich H. E.

2014-03-01

342

The multiple faces of self-assembled lipidic systems  

Microsoft Academic Search

ABSTRACT: Lipids, the building blocks of cells, common to every living organisms, have the propensity to self-assemble into well-defined structures over short and long-range spatial scales. The driving forces have their roots mainly in the hydrophobic effect and electrostatic interactions. Membranes in lamellar phase are ubiquitous in cellular compartments and can phase-separate upon mixing lipids in different liquid-crystalline states. Hexagonal

Guillaume Tresset

2009-01-01

343

Self-assembled monolayer growth on chemically modified polymer surfaces  

Microsoft Academic Search

We report a study of the self-assembled monolayer (SAM) growth of bis[3(triethoxysilane)propyl]tetrasulfide (Tetrasulfide) on low dielectric constant (low-k) aromatic hydrocarbon SiLK whose surface chemistry was modified using sulfuric acid, He plasma treatment, and N2 plasma treatment. X-ray photoelectron spectroscopy (XPS) spectra show that there is no detectable growth of Tetrasulfide SAM on untreated SiLK surfaces. After the SiLK surfaces have

S. Pimanpang; Pei-I. Wang; G.-C. Wang; T.-M. Lu

2006-01-01

344

Orientation of surfactant self-assembled aggregates on graphite  

Microsoft Academic Search

Micellar aggregates on surfaces can provide a self-healing corrosion protection or lubrication layer. It has been observed experimentally that on a single crystal surface this layer often consists of oriented hemi-cylindrical micelles which are aligned with the underlying crystal lattice (``orientation effect''). A key feature of this self-assembly process is the interplay between detergent--detergent and detergent--surface interactions. Since the dimensions

Maria Sammalkorpi; Antti-Pekka Hynninen; Athanassios Z. Panagiotopoulos; Mikko Haataja

2007-01-01

345

Novel Piezoelectric DDVP Sensor Based on Self?Assembly Method  

Microsoft Academic Search

A novel piezoelectric sensor was fabricated by depositing the films of polyvinyl pyrrolindone (PVP) and PVP with butyl cholinesterase (BuChE) (BuChE?PVP), respectively, on the surface of quartz crystal microbalance (QCM) using self?assembly method. The sensitive films were characterized with online examination and XPS technique. The obtained sensors were applied to measure o,o?dimethyl?o?2,2?dichlorovinyl phosphate (DDVP) pesticide concentration. It shows that BuChE?PVP

Hongjuan Zeng; Yadong Jiang; Guangzhong Xie; Junsheng Yu

2007-01-01

346

Fibrin self-assembly inhibitor turnover in rats  

SciTech Connect

The aim of this investigation was to study changes in the concentration of the fibrin self-assembly inhibitor and the mechanism of the changes in diametrically opposite states of blood coagulation, namely, the acceleration and restriction of thrombin formation. Fibrin monomer was obtained from bovine plasma. The inhibitor, a polypeptide, was labelled with potassium iodide activated with iodine 131. The radioactive inhibitor was injected and its concentration determined by chromatography and tracer analysis.

Chiryat'ev, E.A.; Umutbaeva, M.K.; Byshevskii, A.Sh.

1987-10-01

347

Bicontinuous Surfaces in Self-assembling Amphiphilic Systems  

Microsoft Academic Search

Amphiphiles are molecules which have both hydrophilic and hydrophobic parts. In water- and\\/or oil-like solvent, they self-assemble\\u000a into extended sheet-like structures due to the hydrophobic effect. The free energy of an amphiphilic system can be written\\u000a as a functional of its interfacial geometry, and phase diagrams can be calculated by comparing the free energies following\\u000a from different geometries. Here we

Ulrich Schwarz; Gerhard Gompper

2002-01-01

348

Cold atoms and molecules in self-assembled dipolar lattices.  

PubMed

We study the realization of lattice models, where cold atoms and molecules move as extra particles in a dipolar crystal of trapped polar molecules. The crystal is a self-assembled floating mesoscopic lattice structure with quantum dynamics given by phonons. We show that within an experimentally accessible parameter regime extended Hubbard models with tunable long-range phonon-mediated interactions describe the effective dynamics of dressed particles. PMID:18352346

Pupillo, G; Griessner, A; Micheli, A; Ortner, M; Wang, D-W; Zoller, P

2008-02-01

349

Cold Atoms and Molecules in Self-Assembled Dipolar Lattices  

SciTech Connect

We study the realization of lattice models, where cold atoms and molecules move as extra particles in a dipolar crystal of trapped polar molecules. The crystal is a self-assembled floating mesoscopic lattice structure with quantum dynamics given by phonons. We show that within an experimentally accessible parameter regime extended Hubbard models with tunable long-range phonon-mediated interactions describe the effective dynamics of dressed particles.

Pupillo, G.; Griessner, A.; Micheli, A.; Ortner, M.; Zoller, P. [Institute for Theoretical Physics, University of Innsbruck, A-6020, Innsbruck (Austria); Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020, Innsbruck (Austria); Wang, D.-W. [Physics Department and NCTS, National Tsing-Hua University, Hinschu, Taiwan (China)

2008-02-08

350

Self-Assembled and Nanostructured siRNA Delivery Systems  

Microsoft Academic Search

A wide range of organic and inorganic materials have been used in the development of nano-scale self-assembling gene delivery\\u000a systems to improve the therapeutic efficacy of nucleic acid drugs. Small interfering RNA (siRNA) has recently been recognized\\u000a as a promising and potent nucleic acid medicine for the treatment of incurable genetic disorders including cancer; however,\\u000a siRNA-based therapeutics suffer from the

Ji Hoon Jeong; Tae Gwan Park; Sun Hwa Kim

351

Self-Assembled Hexa-peri-hexabenzocoronene Graphitic Nanotube  

Microsoft Academic Search

An amphiphilic hexa-peri-hexabenzocoronene self-assembles to form a pi-electronic, discrete nanotubular object. The object is characterized by an aspect ratio greater than 1000 and has a uniform, 14-nanometer-wide, open-ended hollow space, which is an order of magnitude larger than those of carbon nanotubes. The wall is 3 nanometers thick and consists of helical arrays of the pi-stacked graphene molecule, whose exterior

Jonathan P. Hill; Wusong Jin; Atsuko Kosaka; Takanori Fukushima; Hideki Ichihara; Takeshi Shimomura; Kohzo Ito; Tomihiro Hashizume; Noriyuki Ishii; Takuzo Aida

2004-01-01

352

Photobleaching-activated micropatterning on self-assembled monolayers  

Microsoft Academic Search

Functional chemical micropatterns were fabricated by exploiting the photobleaching of dye-coupled species near methacrylate self-assembled monolayers. Using this approach we have demonstrated that multiple chemistries can be coupled to the monolayer using a standard fluorescence microscope. The surface bound functional groups remain active and patterns with feature sizes down to 3 µm can be readily achieved with excellent signal-to-noise ratio.

Jan Scrimgeour; Vamsi K. Kodali; Daniel T. Kovari; Jennifer E. Curtis

2010-01-01

353

Toward self-assembly of phage-like nanorobot  

Microsoft Academic Search

The assembly of DNA nanostructures can allow for promising nanometer-sized machines. Synthetic DNA motifs are known to assemble into a wide range of nanoarchitectures by sequence programming. For the purpose of constructing strictly-controlled biological nanomachines, we design the self-assembly system consisting of DNA strands with the ability of producing a functional molecule. In this work we demonstrate that DNA motifs

M. Hirabayashi; K. Oiwa; A. Nishikawa; F. Tanaka; M. Hagiya

2009-01-01

354

The position of hydrophobic residues tunes peptide self-assembly.  

PubMed

The final structure and properties of synthetic peptides mainly depend on their sequence composition and experimental conditions. This work demonstrates that a variation in the positions of hydrophobic residues within a peptide sequence can tune the self-assembly. Techniques employed are atomic force microscopy, transmission electron microscopy and an innovative method based on surface acoustic waves. In addition, a systematic investigation on pH dependence was carried out by utilizing constant experimental parameters. PMID:24995505

Bortolini, Christian; Liu, Lei; Gronewold, Thomas M A; Wang, Chen; Besenbacher, Flemming; Dong, Mingdong

2014-08-21

355

Computation via dynamic self-assembly of idealized protein networks.  

SciTech Connect

We describe stochastic agent-based simulations of protein-emulating agents to perform computation via dynamic self-assembly. The binding and actuation properties of the types of agents required to construct a RAM machine (equivalent to a Turing machine) are described. We present an example computation and describe the molecular biology and non-equilibrium statistical mechanics, and information science properties of this system.

Bouchard, Ann Marie; Osbourn, Gordon Cecil

2003-08-01

356

Infrared photodetection with semiconductor self-assembled quantum dots  

Microsoft Academic Search

Semiconductor self-assembled quantum dots are potential candidates to develop a new class of midinfrared quantum photodetectors and focal plane arrays. In this article, we present the specific midinfrared properties of InAs\\/GaAs quantum dots associated with the intersublevel transitions. The electronic structure, which accounts for the strain field in the islands, is obtained within the framework of a three-dimensional 8 band

Philippe Boucaud; Sébastien Sauvage

2003-01-01

357

Self-assembly of semiconductor nanocrystals into ordered superstructures  

Microsoft Academic Search

Organization of uniform objects into periodic structures can be found in many natural systems, such as atomic and molecular\\u000a solids, opals, sponges and bacterial colonies — self-assembly is the fundamental phenomenon that generates structural organization\\u000a on all scales [1]. In this chapter we discuss the structures spontaneously formed by nanoparticles which attracted significant interest from\\u000a different branches of science and

Elena V. Shevchenko; Dmitri V. Talapin

358

Electrical communication between components of self-assembled mixed monolayers  

Microsoft Academic Search

The use of an alkanethiol-based self-assembled mixed monolayer as an electronic relay system effecting mediated electron transfer between immobilized glucose oxidase (GOx) and a gold electrode is reported. We compare the behavior of mixed monolayers of various compositions of 16-ferrocenylhexadecanethiol (16FAT) and aminoethanethiol, to which GOx is attached, as biosensors for glucose. The amperometric response of such electrodes in the

Shai Rubin; T. A. Jr. Zawodzinski; J. T. Chow; J. P. Ferraris

1996-01-01

359

Dynamic self-assembly and computation : from biological to information systems.  

SciTech Connect

We present two ways in which dynamic self-assembly can be used to perform computation, via stochastic protein networks and self-assembling software. We describe our protein-emulating agent-based simulation infrastructure, which is used for both types of computations, and the few agent properties sufficient for dynamic self-assembly. Examples of protein-network-based computation and self-assembling software are presented. We describe some novel capabilities that are enabled by the inherently dynamic nature of the self-assembling executable code.

Bouchard, Ann Marie; Osbourn, Gordon Cecil

2003-08-01

360

Phonon line emission revealed by self-assembly of colloidal nanoplatelets.  

PubMed

We show that colloidal nanoplatelets can self-assemble to form a 1D superlattice. When self-assembled, an additional emission line appears in the photoluminescence spectrum at low temperatures. This emission line is a collective effect, greatly enhanced when the NPLs are self-assembled. It is attributed to the longitudinal optical (LO) phonon replica of the band-edge exciton, and its presence in self-assembled nanoplatelets is explained using a model based on an efficient photons reabsorption between neighboring nanoplatelets. The presence of phonon replica at low temperatures in ensemble measurements suggests the possibility to design a laser, based on self-assembled nanoplatelets. PMID:23458277

Tessier, Mickaël D; Biadala, Louis; Bouet, Cécile; Ithurria, Sandrine; Abecassis, Benjamin; Dubertret, Benoit

2013-04-23

361

Hierarchically Organized Structures Engineered from Controlled Evaporative Self-Assembly  

NASA Astrophysics Data System (ADS)

By constraining an asymmetric comb block copolymer (CBCP) toluene solution to evaporate in a wedge-on-Si geometry composed of a wedge lens situated on a Si substrate, gradient concentric stripe-like surface patterns of CBCP at the microscopic scale were yielded as a direct consequence of controlled evaporative self-assembly of CBCP. The formation of either straight stripes or jagged stripes was dictated by the height of the wedge. Upon subsequent solvent vapor annealing, hierarchically organized structures of CBCP were produced, resulting from the interplay of solvent vapor-assisted, unfavorable interfacial interaction-driven destabilization of CBCP from the Si substrate at the microscopic scale and the solvent vapor-promoted reconstruction of CBCP nanodomains within the stripes at the nanometer scale. This facile approach of combining controlled evaporative self-assembly with subsequent solvent vapor annealing offers a new platform to rationally design and engineer self-assembling building blocks into functional materials and devices in a simple, cost-effective manner.

Lin, Zhiqun; Byun, Myunghwan; Han, Wei; Bowden, Ned

2011-03-01

362

Self-assembly of lipopolysaccharide layers on allantoin crystals.  

PubMed

Self-assembly of lipopolysaccharides (LPS) on solid surfaces is important for the study of bacterial membranes, but has not been possible due to technical difficulties and the lack of suitable solid supports. Recently we found that crystals of the natural compound allantoin selectively bind pure LPS with sub-nanomolar affinity. The physicochemical origins of this selectivity and the adsorption mode of LPS on allantoin crystals remain, however, unknown. In this study we present evidence that LPS adsorption on allantoin crystals is initiated through hydrogen-bond attachment of hydrophilic LPS regions. Hydrophobic interactions between alkyl chains of adjacently adsorbed LPS molecules subsequently promote self-assembly of LPS layers. The essential role of hydrogen-bond interactions is corroborated by our finding that allantoin crystals bind to practically any hydrophilic surface chemistry. Binding contributions of hydrophobic interactions between LPS alkyl chains are evidenced by the endothermic nature of the adsorption process and explain why the binding affinity for LPS is several orders of magnitude higher than for proteins (lysozyme, BSA and IgG) and polysaccharides. Self-assembly of LPS layers via hydrogen-bond attachment on allantoin crystals emerges as a novel binding mechanism and could be considered as a practical method for preparing biomimetic membranes on a solid support. PMID:24905674

Vagenende, Vincent; Ching, Tim-Jang; Chua, Rui-Jing; Jiang, Qiu Zhen; Gagnon, Pete

2014-08-01

363

Three dimensional self-assembly at the nanoscale  

NASA Astrophysics Data System (ADS)

At the nanoscale, three dimensional manipulation and assembly becomes extremely challenging and also cost prohibitive. Self-assembly provides an attractive and possibly the only highly parallel methodology to structure truly three dimensional patterned materials and devices at this size scale for applications in electronics, optics, robotics and medicine. This is a concise review along with a perspective of an important and exciting field in nanotechnology and is related to a Nanoengineering Pioneer Award that I received at this SPIE symposium for my contributions to the 3D selfassembly of nanostructures. I detail a historical account of 3D self-assembly and outline important developments in this area which is put into context with the larger research areas of 3D nanofabrication, assembly and nanomanufacturing. A focus in this review is on our work as it relates to the self-assembly with lithographically patterned units; this approach provides a means for heterogeneous integration of periodic, curved and angled nanostructures with precisely defined three dimensional patterns.

Gracias, D. H.

2013-05-01

364

Algorithmic Self-Assembly of DNA Sierpinski Triangles  

PubMed Central

Algorithms and information, fundamental to technological and biological organization, are also an essential aspect of many elementary physical phenomena, such as molecular self-assembly. Here we report the molecular realization, using two-dimensional self-assembly of DNA tiles, of a cellular automaton whose update rule computes the binary function XOR and thus fabricates a fractal pattern—a Sierpinski triangle—as it grows. To achieve this, abstract tiles were translated into DNA tiles based on double-crossover motifs. Serving as input for the computation, long single-stranded DNA molecules were used to nucleate growth of tiles into algorithmic crystals. For both of two independent molecular realizations, atomic force microscopy revealed recognizable Sierpinski triangles containing 100–200 correct tiles. Error rates during assembly appear to range from 1% to 10%. Although imperfect, the growth of Sierpinski triangles demonstrates all the necessary mechanisms for the molecular implementation of arbitrary cellular automata. This shows that engineered DNA self-assembly can be treated as a Turing-universal biomolecular system, capable of implementing any desired algorithm for computation or construction tasks.

2004-01-01

365

Molecular motions in functional self-assembled nanostructures.  

PubMed

The construction of "smart" materials able to perform specific functions at the molecular scale through the application of various stimuli is highly attractive but still challenging. The most recent applications indicate that the outstanding flexibility of self-assembled architectures can be employed as a powerful tool for the development of innovative molecular devices, functional surfaces and smart nanomaterials. Structural flexibility of these materials is known to be conferred by weak intermolecular forces involved in self-assembly strategies. However, some fundamental mechanisms responsible for conformational lability remain unexplored. Furthermore, the role played by stronger bonds, such as coordination, ionic and covalent bonding, is sometimes neglected while they can be employed readily to produce mechanically robust but also chemically reversible structures. In this review, recent applications of structural flexibility and molecular motions in self-assembled nanostructures are discussed. Special focus is given to advanced materials exhibiting significant performance changes after an external stimulus is applied, such as light exposure, pH variation, heat treatment or electromagnetic field. The crucial role played by strong intra- and weak intermolecular interactions on structural lability and responsiveness is highlighted. PMID:23348927

Dhotel, Alexandre; Chen, Ziguang; Delbreilh, Laurent; Youssef, Boulos; Saiter, Jean-Marc; Tan, Li

2013-01-01

366

Self-assembly in sugar-oil complex glasses.  

PubMed

In aqueous systems, the hydrophobic effect drives the self-assembly of amphiphiles into a broad range of micellar, rod-like, bicontinuous and liquid-crystalline complex fluids. Many of these are relevant to biological matter or technological applications. However, amphiphilic self-assembly is not limited to aqueous systems. Replacement of water with supercritical carbon dioxide, for example, results in complex fluids that combine the properties of gases and liquids. Along this vein, we explore the self-assembly of surfactants in anhydrous sugars. Our study reveals that anhydrous powders of sugars and surfactants suspended in oil spontaneously form molten glasses with nanometre-size domains of sugar and liquid oil without mixing. The low cost, water solubility, low toxicity and stabilizing properties of glassy sugars make them ideal water replacements for many pharmaceutical, food and materials synthesis applications. The optical clarity and solid appearance of these glasses at room temperature belie their inclusion of more than 50% (vol.) oil, which confers liquid-like diffusivity. The unique combination of solid- and liquid-like properties may lead to applications in sensors and optical devices. PMID:17384636

Dave, Hiteshkumar; Gao, Feng; Lee, Jing-Huei; Liberatore, Matthew; Ho, Chia-Chi; Co, Carlos C

2007-04-01

367

Intercalators as molecular chaperones in DNA self-assembly.  

PubMed

DNA intercalation has found many diagnostic and therapeutic applications. Here, we propose the use of simple DNA intercalators, such as ethidium bromide, as tools to facilitate the error-free self-assembly of DNA nanostructures. We show that ethidium bromide can influence DNA self-assembly, decrease the formation of oligomeric side products, and cause libraries of multiple equilibrating structures to converge into a single product. Using a variety of 2D- and 3D-DNA systems, we demonstrate that intercalators present a powerful alternative for the adjustment of strand-end alignment, favor the formation of fully duplexed "closed" structures, and create an environment where the smallest, most stable structure is formed. A new 3D-DNA motif, the ninja star, was self-assembled in quantitative yield with this method. Moreover, ethidium bromide can be readily removed using isoamyl alcohol extractions combined with intercalator-specific spin columns, thereby yielding the desired ready-to-use DNA structure. PMID:23829631

Greschner, Andrea A; Bujold, Katherine E; Sleiman, Hanadi F

2013-07-31

368

Polymer adsorption-driven self-assembly of nanostructures.  

PubMed

Driven by prospective applications, there is much interest in developing materials that can perform specific functions in response to external conditions. One way to design such materials is to create systems which, in response to external inputs, can self-assemble to form structures that are functionally useful. This review focuses on the principles that can be employed to design macromolecules that when presented with an appropriate two-dimensional surface, will self-assemble to form nanostructures that may be functionally useful. We discuss three specific examples: (a) biomimetic recognition between polymers and patterned surfaces. (b) control and manipulation of nanomechanical motion generated by biopolymer adsorption and binding, and (c) creation of patterned nanostructuctures by exposing molten diblock copolymers to patterned surfaces. The discussion serves to illustrate how polymer sequence can be manipulated to affect self-assembly characteristics near adsorbing surfaces. The focus of this review is on theoretical and computational work aimed toward elucidating the principles underlying the phenomena pertinent to the three topics noted above. However, synergistic experiments are also described in the appropriate context. PMID:11326074

Chakraborty, A K; Golumbfskie, A J

2001-01-01

369

Dynamic self-assembly and control of microfluidic particle crystals  

PubMed Central

Engineered two-phase microfluidic systems have recently shown promise for computation, encryption, and biological processing. For many of these systems, complex control of dispersed-phase frequency and switching is enabled by nonlinearities associated with interfacial stresses. Introducing nonlinearity associated with fluid inertia has recently been identified as an easy to implement strategy to control two-phase (solid-liquid) microscale flows. By taking advantage of inertial effects we demonstrate controllable self-assembling particle systems, uncover dynamics suggesting a unique mechanism of dynamic self-assembly, and establish a framework for engineering microfluidic structures with the possibility of spatial frequency filtering. Focusing on the dynamics of the particle–particle interactions reveals a mechanism for the dynamic self-assembly process; inertial lift forces and a parabolic flow field act together to stabilize interparticle spacings that otherwise would diverge to infinity due to viscous disturbance flows. The interplay of the repulsive viscous interaction and inertial lift also allow us to design and implement microfluidic structures that irreversibly change interparticle spacing, similar to a low-pass filter. Although often not considered at the microscale, nonlinearity due to inertia can provide a platform for high-throughput passive control of particle positions in all directions, which will be useful for applications in flow cytometry, tissue engineering, and metamaterial synthesis.

Lee, Wonhee; Amini, Hamed; Stone, Howard A.; Di Carlo, Dino

2010-01-01

370

Controlling RNA self-assembly to form filaments  

PubMed Central

Fundamental control over supra-molecular self-assembly for organization of matter on the nano-scale is a major objective of nanoscience and nanotechnology. ‘RNA tectonics’ is the design of modular RNA units, called tectoRNAs, that can be programmed to self-assemble into novel nano- and meso-scopic architectures of desired size and shape. We report the three-dimensional design of tectoRNAs incorporating modular 4-way junction (4WJ) motifs, hairpin loops and their cognate loop–receptors to create extended, programmable interaction interfaces. Specific and directional RNA–RNA interactions at these interfaces enable conformational, topological and orientational control of tectoRNA self-assembly. The interacting motifs are precisely positioned within the helical arms of the 4WJ to program assembly from only one helical stacking conformation of the 4WJ. TectoRNAs programmed to assemble with orientational compensation produce micrometer-scale RNA filaments through supra-molecular equilibrium polymerization. As visualized by transmission electron microscopy, these RNA filaments resemble actin filaments from the protein world. This work emphasizes the potential of RNA as a scaffold for designing and engineering new controllable biomaterials mimicking modern cytoskeletal proteins.

Nasalean, Lorena; Baudrey, Stephanie; Leontis, Neocles B.; Jaeger, Luc

2006-01-01

371

Lung Self-Assembly Is Modulated by Tissue Surface Tensions  

PubMed Central

To identify cell-intrinsic properties that facilitate interaction between epithelial endodermal and mesenchymal mesodermal cells during lung morphogenesis, we developed a model of lung self-assembly that mimics fetal lung formation in structure, polarity, vasculature, and extracellular matrix expression. Three-dimensional pulmonary bodies (PBs) spontaneously self-assemble from single-cell suspensions and exhibit liquid-like properties that allow measurements of compaction rate and cohesion, and that may help to specify cellular self-organization. We hypothesized that changes in one or more of these parameters could potentially explain the lung hypoplasia associated with abnormal lung development. We examined the impact of endothelial/monocyte–activating polypeptide (EMAP) II in PBs, because EMAPII is highly expressed in lung hypoplasia. EMAPII significantly increased compaction rate and decreased overall cohesion of PBs composed of both epithelial and mesenchymal cells. Moreover, the effects of EMAPII on compaction and cohesion act exclusively through the mesenchymal cell population by interfering with fibronectin matrix assembly. We also show that EMAPII alters epithelial cell polarity and surfactant protein C expression. Our findings demonstrate, for the first time, that PBs possess liquid-like properties that can help to guide the self-assembly of fetal lungs, and that EMAPII expression can influence both mesenchymal and epithelial cells but through different molecular mechanisms.

Schwarz, Margaret A.; Zheng, Haihua; Legan, Susan; Foty, Ramsey A.

2011-01-01

372

Spectroscopic critical dimension technology (SCD) for directed self assembly  

NASA Astrophysics Data System (ADS)

Directed self-assembly (DSA) is being actively investigated as a potential patterning solution for future generation devices. While SEM based CD measurement is currently used in research and development, scatterometry-based techniques like spectroscopic CD (SCD) are preferred for high volume manufacturing. SCD can offer information about sub-surface features that are not available from CD-SEM measurement. Besides, SCD is a non-destructive, high throughput technique already adopted in HVM in several advanced nodes. The directed self assembly CD measurement can be challenging because of small dimensions and extremely thin layers in the DSA stack. In this study, the SCD technology was investigated for a 14 nm resolution PS-b-PMMA chemical epitaxy UW process optimized by imec. The DSA stack involves new materials such as cross-linkable polysterene (XPS) of thickness approximately 5 nm, ArF immersion resist (subsequently removed), -OH terminated neutral brush layer, and BCP material (Polystyrene-blockmethyl methacrylate of thickness roughly 20 to 30 nm). The mask contains a large CD and pitch matrix, for studying the quality of self-assembly as a function of the guide pattern dimensions. We report on the ability of SCD to characterize the dimensional variation in these targets and hence provide a viable process control solution.

Nishibe, Senichi; Dziura, Thaddeus; Nagaswami, Venkat; Gronheid, Roel

2014-04-01

373

Electrostatic force microscopy of self-assembled peptide structures.  

PubMed

In this report electrostatic force microscopy (EFM) is used to study different peptide self-assembled structures such as tubes and particles. It is shown that not only geometrical information can be obtained using EFM, but also information about the composition of different structures. In particular we use EFM to investigate the structures of diphenylalanine peptide tubes, particles, and CSGAITIG peptide particles placed on pre-fabricated SiO(2) surfaces with a backgate. We show that the cavity in the peptide tubes could be due to the presence of water residues. Additionally we show that self-assembled amyloid peptides form spherical solid structures containing the same self-assembled peptide in its interior. In both cases transmission electron microscopy is used to verify these structures. Further, the limitations of the EFM technique are discussed, especially when the observed structures become small compared with the radius of the AFM tip used. Finally, an agreement between the detected signal and the structure of the hollow peptide tubes is demonstrated. PMID:21506135

Clausen, Casper Hyttel; Dimaki, Maria; Panagos, Spyros Pantoleon; Kasotakis, Emmanouil; Mitraki, Anna; Svendsen, Winnie Edith; Castillo-León, Jaime

2011-01-01

374

Electrostatic self-assembly of macroscopic crystals using contact electrification  

NASA Astrophysics Data System (ADS)

Self-assembly of components larger than molecules into ordered arrays is an efficient way of preparing microstructured materials with interesting mechanical and optical properties. Although crystallization of identical particles or particles of different sizes or shapes can be readily achieved, the repertoire of methods to assemble binary lattices of particles of the same sizes but with different properties is very limited. This paper describes electrostatic self-assembly of two types of macroscopic components of identical dimensions using interactions that are generated by contact electrification. The systems we have examined comprise two kinds of objects (usually spheres) made of different polymeric materials that charge with opposite electrical polarities when agitated on flat, metallic surfaces. The interplay of repulsive interactions between like-charged objects and attractive interactions between unlike-charged ones results in the self-assembly of these objects into highly ordered, closed arrays. Remarkably, some of the assemblies that form are not electroneutral-that is, they possess a net charge. We suggest that the stability of these unusual structures can be explained by accounting for the interactions between electric dipoles that the particles in the aggregates induce in their neighbours.

Grzybowski, Bartosz A.; Winkleman, Adam; Wiles, Jason A.; Brumer, Yisroel; Whitesides, George M.

2003-04-01

375

Materials self-assembly and fabrication in confined spaces  

SciTech Connect

Molecular assemblies have been mainly researched in open spaces for long time. However, recent researches have revealed that there are many interesting aspects remained in self-assemblies in confined spaces. Molecular association within nanospaces such as mesoporous materials provide unusual phenomena based on highly restricted molecular motions. Current research endeavors in materials science and technology are focused on developing either new class of materials or materials with novel/multiple functionalities which is often achived via molecular assembly in confined spaces. Template synthesis and guided assemblies are distinguishable examples for molecular assembly in confined spaces. So far, different aspects of molecular confinements are discussed separately. In this review, the focus is specifically to bring some potential developments in various aspects of confined spaces for molecular self-assembly under one roof. We arrange the sections in this review based on the nature of the confinements; accordingly the topological/geometrical confinements, chemical and biological confinements, and confinements within thin film, respectively. Following these sections, molecular confinements for practical applications are shortly described in order to show connections of these scientific aspects with possible practical uses. One of the most important facts is that the self-assembly in confined spaces stands at meeting points of top-down and bottom-up fabrications, which would be an ultimate key to push the limits of nanotechnology and nanoscience.

Ramanathan, Nathan Muruganathan [ORNL; Kilbey, II, S Michael [ORNL; Ji, Dr. Qingmin [National Institute for Materials Science, Tsukuba, Japan; Hill, Dr. Jonathan P [National Institute for Materials Science, Tsukuba, Japan; Ariga, Katsuhiko [National Institute for Materials Science, Tsukuba, Japan

2012-01-01

376

Iterative linearized density matrix propagation for modeling coherent excitation energy transfer in photosynthetic light harvesting.  

PubMed

Rather than incoherent hopping between chromophores, experimental evidence suggests that the excitation energy transfer in some biological light harvesting systems initially occurs coherently, and involves coherent superposition states in which excitation spreads over multiple chromophores separated by several nanometers. Treating such delocalized coherent superposition states in the presence of decoherence and dissipation arising from coupling to an environment is a significant challenge for conventional theoretical tools that either use a perturbative approach or make the Markovian approximation. In this paper, we extend the recently developed iterative linearized density matrix (ILDM) propagation scheme [E. R. Dunkel et al., J. Chem. Phys. 129, 114106 (2008)] to study coherent excitation energy transfer in a model of the Fenna-Matthews-Olsen light harvesting complex from green sulfur bacteria. This approach is nonperturbative and uses a discrete path integral description employing a short time approximation to the density matrix propagator that accounts for interference between forward and backward paths of the quantum excitonic system while linearizing the phase in the difference between the forward and backward paths of the environmental degrees of freedom resulting in a classical-like treatment of these variables. The approach avoids making the Markovian approximation and we demonstrate that it successfully describes the coherent beating of the site populations on different chromophores and gives good agreement with other methods that have been developed recently for going beyond the usual approximations, thus providing a new reliable theoretical tool to study coherent exciton transfer in light harvesting systems. We conclude with a discussion of decoherence in independent bilinearly coupled harmonic chromophore baths. The ILDM propagation approach in principle can be applied to more general descriptions of the environment. PMID:21073214

Huo, P; Coker, D F

2010-11-14

377

Formation of light-harvesting complexes of photosystem II in Scenedesmus  

Microsoft Academic Search

The patterns of accumulation of photosynthetic pigments, mRNAs transcribed from the genes encoding chlorophyll a\\/b-binding proteins (Lhc mRNAs), and light-harvesting complex (LHC) apoproteins have been compared in dark- and light-grown cells of wild-type (WT) Scenedesmus obliquus and the mutants WT-LHC1, C-6D, C-6E, C-2A', C-2A'-LHC1 and C-2A'-LHC2. In contrast to the WT, which developed the complete photosynthetic apparatus in darkness, mutant

Dieter Hermsmeier; Riidiger Schulz; Horst Senger

1994-01-01

378

Coherence dynamics in light-harvesting complexes with two-colour spectroscopy  

NASA Astrophysics Data System (ADS)

We investigate coherent dynamics in the cryptophyte light-harvesting complex Phycocyanin-645 (PC-645). A two-colour four-wave mixing experiment allows us to isolate a coherence pathway and observe its evolution in the absence of other signals. We measured a decoherence time of 540fs for the coherence [1]. Additionally oscillations in the signal pathway give evidence for the coherent excitation of states outside the bandwidth of the laser pulse. This suggests strong coupling between the excited states and phonon modes [1].

Richards, Gethin H.; Curmi, Paul M. G.; Wilk, Krystyna E.; Quiney, Harry M.; Davis, Jeffrey A.

2013-03-01

379

Self-assembly triggered by self-assembly: Optically active, paramagnetic micelles encapsulated in protein cage nanoparticles.  

PubMed

In this contribution, optically active and paramagnetic micelles of the ligand 1,4,7,10-tetraaza-1-(1-carboxymethylundecane)-4,7,10-triacetic acid cyclododecane (DOTAC10) have been incorporated inside capsids of the cowpea chlorotic mottle virus (CCMV) protein through a hierarchical process of self-assembly triggered by self-assembly. The DOTAC10 ligand was used to complex Gd(III), in order to form paramagnetic micelles, as well as to encapsulate an amphiphilic Zn(II) phthalocyanine (ZnPc) dye that optically confirmed the encapsulation of the micelles. The incorporation of ZnPc molecules in the paramagnetic micelles led to high capsid loading of both Gd(III) and ZnPc, as the micelles were stabilized by the amphiphilic dye encapsulation. The resulting protein cage nanoparticles (PCNs) show an improved r1 relaxivity, suggesting the possible use of these nanostructures as contrast agents (CAs) for magnetic resonance imaging (MRI). Since the encapsulated ZnPc dye also has a potential therapeutic value, the present results represent a first step towards the consecution of fully self-assembled PCNs for multimodal imaging and therapy. PMID:24513535

Millán, Jealemy Galindo; Brasch, Melanie; Anaya-Plaza, Eduardo; de la Escosura, Andrés; Velders, Aldrik H; Reinhoudt, David N; Torres, Tomás; Koay, Melissa S T; Cornelissen, Jeroen J L M

2014-07-01

380

Nanostructured artificial photosynthesis  

Microsoft Academic Search

We have proposed a novel strategy for artificial photosynthesis where porphyrins and fullerenes are assembled as building blocks into nanostructured artificial photosynthetic systems by the help of self-assembled monolayers. Photodynamical studies on porphyrin–fullerene-linked systems revealed that fullerenes accelerate photo-induced electron transfer and charge-shift and slow down charge recombination, which is in sharp contrast with the modalities of conventional two-dimensional aromatic

Hiroshi Imahori; Yukie Mori; Yoshihiro Matano

2003-01-01

381

Fluorescence intermittency from the main plant light-harvesting complex: sensitivity to the local environment.  

PubMed

The time-resolved fluorescence intensity fluctuations from single, immobilized complexes of the main light-harvesting complex (LHCII) of plants were investigated in different pH environments close to room temperature and under different light conditions. The efficiency of light harvesting, which was represented by complexes typically residing for long periods in strongly fluorescing states, was significantly reduced by decreasing the pH or increasing the incident photon flux. The same environmental changes significantly increased the switching frequency between strongly and weakly fluorescing states. The environmental dependence became more evident when the various accessed intensity levels were first resolved, a technique that significantly reduced the obscuring effect of shot noise. The strong environmental sensitivity suggests that the immediate environment of an LHCII complex can modulate the amount of energy dissipation. A simple model illustrates how this may be achieved: the dynamic equilibrium between the strongly and weakly fluorescing states can be shifted by environmentally controlling the conformational diffusion on the potential energy surface of LHCII. PMID:21452801

Krüger, Tjaart P J; Ilioaia, Cristian; Valkunas, Leonas; van Grondelle, Rienk

2011-05-12

382

Assembly of the Major Light-Harvesting Complex II in Lipid Nanodiscs  

PubMed Central

Self-aggregation of isolated plant light-harvesting complexes (LHCs) upon detergent extraction is associated with fluorescence quenching and is used as an in vitro model to study the photophysical processes of nonphotochemical quenching (NPQ). In the NPQ state, in vivo induced under excess solar light conditions, harmful excitation energy is safely dissipated as heat. To prevent self-aggregation and probe the conformations of LHCs in a lipid environment devoid from detergent interactions, we assembled LHCII trimer complexes into lipid nanodiscs consisting of a bilayer lipid matrix surrounded by a membrane scaffold protein (MSP). The LHCII nanodiscs were characterized by fluorescence spectroscopy and found to be in an unquenched, fluorescent state. Remarkably, the absorbance spectra of LHCII in lipid nanodiscs show fine structure in the carotenoid and Qy region that is different from unquenched, detergent-solubilized LHCII but similar to that of self-aggregated, quenched LHCII in low-detergent buffer without magnesium ions. The nanodisc data presented here suggest that 1), LHCII pigment-protein complexes undergo conformational changes upon assembly in nanodiscs that are not correlated with downregulation of its light-harvesting function; and 2), these effects can be separated from quenching and aggregation-related phenomena. This will expand our present view of the conformational flexibility of LHCII in different microenvironments.

Pandit, Anjali; Shirzad-Wasei, Nazhat; Wlodarczyk, Lucyna M.; van Roon, Henny; Boekema, Egbert J.; Dekker, Jan P.; de Grip, Willem J.

2011-01-01

383

Crystal structure of spinach major light-harvesting complex at 2.72 A resolution.  

PubMed

The major light-harvesting complex of photosystem II (LHC-II) serves as the principal solar energy collector in the photosynthesis of green plants and presumably also functions in photoprotection under high-light conditions. Here we report the first X-ray structure of LHC-II in icosahedral proteoliposome assembly at atomic detail. One asymmetric unit of a large R32 unit cell contains ten LHC-II monomers. The 14 chlorophylls (Chl) in each monomer can be unambiguously distinguished as eight Chla and six Chlb molecules. Assignment of the orientation of the transition dipole moment of each chlorophyll has been achieved. All Chlb are located around the interface between adjacent monomers, and together with Chla they are the basis for efficient light harvesting. Four carotenoid-binding sites per monomer have been observed. The xanthophyll-cycle carotenoid at the monomer-monomer interface may be involved in the non-radiative dissipation of excessive energy, one of the photoprotective strategies that have evolved in plants. PMID:15029188

Liu, Zhenfeng; Yan, Hanchi; Wang, Kebin; Kuang, Tingyun; Zhang, Jiping; Gui, Lulu; An, Xiaomin; Chang, Wenrui

2004-03-18

384

Synthesis, characterization and light harvesting properties of nickel(II) diimine dithiolate complexes  

NASA Astrophysics Data System (ADS)

Four Ni(II) diimine dithiolato complexes viz. [Ni{(S2C2Ph2)(1,10-Phenanthroline)}] (2), [Ni{(S2C2Ph2)(3,3'-dicarboxy-2,2'-bipyridyl)}] (3), [Ni{(S2C2Ph2)(4,4'-dicarboxy-2,2'-bipyridyl)}] (4) [Ni{(S2C2Ph2)(2,2'-bipyridyl)}] (5) have been prepared from [Ni(S2C2Ph2)2] (1) and characterized by microanalyses, UV-Vis, IR, 1H and 13C NMR. Attempts have been made to explain the nature of charge transfer in these molecules through quantum chemical calculations. The light harvesting properties of all the compounds have been studied using these compounds as photosensitizers in TiO2-based DSSC. The change in position of anchoring group on diimine derivative leads to different structural, electronic and light harvesting properties about the Ni(II) diimine dithiolate dyes.

Kumar, Abhinav; Auvinen, Sami; Trivedi, Manoj; Chauhan, Ratna; Alatalo, Matti

2013-11-01

385

Lutein epoxide cycle, light harvesting and photoprotection in species of the tropical tree genus Inga.  

PubMed

Dynamics and possible function of the lutein epoxide (Lx) cycle, that is, the reversible conversion of Lx to lutein (L) in the light-harvesting antennae, were investigated in leaves of tropical tree species. Photosynthetic pigments were quantified in nine Inga species and species from three other genera. In Inga, Lx levels were high in shade leaves (mostly above 20 mmol mol(-1) chlorophyll) and low in sun leaves. In Virola surinamensis, both sun and shade leaves exhibited very high Lx contents (about 60 mmol mol(-1) chlorophyll). In Inga marginata grown under high irradiance, Lx slowly accumulated within several days upon transfer to deep shade. When shade leaves of I. marginata were briefly exposed to the sunlight, both violaxanthin and Lx were quickly de-epoxidized. Subsequently, overnight recovery occurred only for violaxanthin, not for Lx. In such leaves, containing reduced levels of Lx and increased levels of L, chlorophyll fluorescence induction showed significantly slower reduction of the photosystem II electron acceptor, Q(A), and faster formation as well as a higher level of non-photochemical quenching. The results indicate that slow Lx accumulation in Inga leaves may improve light harvesting under limiting light, while quick de-epoxidation of Lx to L in response to excess light may enhance photoprotection. PMID:18208510

Matsubara, Shizue; Krause, G Heinrich; Seltmann, Martin; Virgo, Aurelio; Kursar, Thomas A; Jahns, Peter; Winter, Klaus

2008-04-01

386

Crystal structure of plant light-harvesting complex shows the active, energy-transmitting state  

PubMed Central

Plants dissipate excess excitation energy as heat by non-photochemical quenching (NPQ). NPQ has been thought to resemble in vitro aggregation quenching of the major antenna complex, light harvesting complex of photosystem II (LHC-II). Both processes are widely believed to involve a conformational change that creates a quenching centre of two neighbouring pigments within the complex. Using recombinant LHC-II lacking the pigments implicated in quenching, we show that they have no particular role. Single crystals of LHC-II emit strong, orientation-dependent fluorescence with an emission maximum at 680 nm. The average lifetime of the main 680 nm crystal emission at 100 K is 1.31 ns, but only 0.39 ns for LHC-II aggregates under identical conditions. The strong emission and comparatively long fluorescence lifetimes of single LHC-II crystals indicate that the complex is unquenched, and that therefore the crystal structure shows the active, energy-transmitting state of LHC-II. We conclude that quenching of excitation energy in the light-harvesting antenna is due to the molecular interaction with external pigments in vitro or other pigment–protein complexes such as PsbS in vivo, and does not require a conformational change within the complex.

Barros, Tiago; Royant, Antoine; Standfuss, Jorg; Dreuw, Andreas; Kuhlbrandt, Werner

2009-01-01

387

The phycobilisome, a light-harvesting complex responsive to environmental conditions.  

PubMed Central

Photosynthetic organisms can acclimate to their environment by changing many cellular processes, including the biosynthesis of the photosynthetic apparatus. In this article we discuss the phycobilisome, the light-harvesting apparatus of cyanobacteria and red algae. Unlike most light-harvesting antenna complexes, the phycobilisome is not an integral membrane complex but is attached to the surface of the photosynthetic membranes. It is composed of both the pigmented phycobiliproteins and the nonpigmented linker polypeptides; the former are important for absorbing light energy, while the latter are important for stability and assembly of the complex. The composition of the phycobilisome is very sensitive to a number of different environmental factors. Some of the filamentous cyanobacteria can alter the composition of the phycobilisome in response to the prevalent wavelengths of light in the environment. This process, called complementary chromatic adaptation, allows these organisms to efficiently utilize available light energy to drive photosynthetic electron transport and CO2 fixation. Under conditions of macronutrient limitation, many cyanobacteria degrade their phycobilisomes in a rapid and orderly fashion. Since the phycobilisome is an abundant component of the cell, its degradation may provide a substantial amount of nitrogen to nitrogen-limited cells. Furthermore, degradation of the phycobilisome during nutrient-limited growth may prevent photodamage that would occur if the cells were to absorb light under conditions of metabolic arrest. The interplay of various environmental parameters in determining the number of phycobilisomes and their structural characteristics and the ways in which these parameters control phycobilisome biosynthesis are fertile areas for investigation.

Grossman, A R; Schaefer, M R; Chiang, G G; Collier, J L

1993-01-01

388

Zeaxanthin Radical Cation Formation in Minor Light-Harvesting Complexes of Higher Plant Antenna  

SciTech Connect

Previous work on intact thylakoid membranes showed that transient formation of a zeaxanthin radical cation was correlated with regulation of photosynthetic light-harvesting via energy-dependent quenching. A molecular mechanism for such quenching was proposed to involve charge transfer within a chlorophyll-zeaxanthin heterodimer. Using near infrared (880-1100 nm) transient absorption spectroscopy, we demonstrate that carotenoid (mainly zeaxanthin) radical cation generation occurs solely in isolated minor light-harvesting complexes that bind zeaxanthin, consistent with the engagement of charge transfer quenching therein. We estimated that less than 0.5percent of the isolated minor complexes undergo charge transfer quenching in vitro, whereas the fraction of minor complexes estimated to be engaged in charge transfer quenching in isolated thylakoids was more than 80 times higher. We conclude that minor complexes which bind zeaxanthin are sites of charge transfer quenching in vivo and that they can assume Non-quenching and Quenching conformations, the equilibrium LHC(N)<--> LHC(Q) of which is modulated by the transthylakoid pH gradient, the PsbS protein, and protein-protein interactions.

Avenson, Thomas H.; Ahn, Tae Kyu; Zigmantas, Donatas; Niyogi, Krishna K.; Li, Zhirong; Ballottari, Matteo; Bassi, Roberto; Fleming, Graham R.

2008-01-31

389

Excited state dynamics in photosynthetic reaction center and light harvesting complex 1  

NASA Astrophysics Data System (ADS)

Key to efficient harvesting of sunlight in photosynthesis is the first energy conversion process in which electronic excitation establishes a trans-membrane charge gradient. This conversion is accomplished by the photosynthetic reaction center (RC) that is, in case of the purple photosynthetic bacterium Rhodobacter sphaeroides studied here, surrounded by light harvesting complex 1 (LH1). The RC employs six pigment molecules to initiate the conversion: four bacteriochlorophylls and two bacteriopheophytins. The excited states of these pigments interact very strongly and are simultaneously influenced by the surrounding thermal protein environment. Likewise, LH1 employs 32 bacteriochlorophylls influenced in their excited state dynamics by strong interaction between the pigments and by interaction with the protein environment. Modeling the excited state dynamics in the RC as well as in LH1 requires theoretical methods, which account for both pigment-pigment interaction and pigment-environment interaction. In the present study we describe the excitation dynamics within a RC and excitation transfer between light harvesting complex 1 (LH1) and RC, employing the hierarchical equation of motion method. For this purpose a set of model parameters that reproduce RC as well as LH1 spectra and observed oscillatory excitation dynamics in the RC is suggested. We find that the environment has a significant effect on LH1-RC excitation transfer and that excitation transfers incoherently between LH1 and RC.

Strümpfer, Johan; Schulten, Klaus

2012-08-01

390

Self-assembly of amphiphilic molecules in organic liquids  

NASA Astrophysics Data System (ADS)

Amphiphilic molecules are well-known for their ability to self-assemble in water to form structures such as micelles and vesicles. In comparison, much less is known about amphiphilic self-assembly in nonpolar organic liquids. Such "reverse" self assembly can produce many of the counterparts to structures found in water. In this dissertation, we focus on the formation and dynamics of such reverse structures. We seek to obtain fundamental insight into the driving forces for reverse self-assembly processes. Three specific types of reverse structures are studied: (a) reverse wormlike micelles, i.e., long, flexible micellar chains; (b) reverse vesicles, i.e., hollow containers enclosed by reverse bilayers; and (c) organogel networks. While our focus is on the fundamentals, we note that reverse structures can be useful in a variety of applications ranging from drug delivery, controlled release, hosts for enzymatic reactions, and templates for nanomaterials synthesis. In the first part of this study, we describe a new route for forming reverse wormlike micelles in nonpolar organic liquids. This route involves the addition of trace amounts of a bile salt to solutions of the phospholipid, lecithin. We show that bile salts, due to their unique "facially amphiphilic" structure, can promote the aggregation of lecithin molecules into these reverse micellar chains. The resulting samples are viscoelastic and show interesting rheological properties. Unusual trends are seen in the temperature dependence of their rheology, which indicates the importance of hydrogen-bonding interactions in the formation of these micelles. Another remarkable feature of their rheology is the presence of strain-stiffening, where the material becomes stiffer at high deformations. Strain-stiffening has been seen before for elastic gels of biopolymers; here, we demonstrate the same properties for viscoelastic micellar solutions. The second reverse aggregate we deal with is the reverse vesicle. We present a new route for forming stable unilamellar reverse vesicles, and this involves mixing short- and long-chain lipids (lecithins) with a trace of sodium chloride. The ratio of the short to long-chain lipid controls the type and size of self-assembled structure formed, and as this ratio is increased, a transition from reverse micelles to vesicles occurs. The structural changes can be explained in terms of molecular geometry, with the sodium chloride acting as a "glue" in binding lipid headgroups together through electrostatic interactions. The final part of this dissertation focuses on organogels. The two-tailed anionic surfactant, AOT, is well-known to form spherical reverse micelles in organic solvents. We have found that trace amounts (e.g., less than 1 mM) of the dihydroxy bile salt, sodium deoxycholate (SDC) can transform these dilute micellar solutions into self-supporting, transparent organogels. The structure and rheology of these organogels is reminiscent of the self-assembled networks formed by proteins such as actin in water. The organogels are based on networks of long, rigid, cylindrical filaments, with SDC molecules stacked together in the filament core.

Tung, Shih-Huang

391

Self-assembly of condensed actin rod phases  

NASA Astrophysics Data System (ADS)

This work is concerned with the phase behavior, structure, and governing interactions in a novel class of high-order biomolecular self-assemblies, where new condensed phases of cytoskeletal biopolymers are formed through their interactions with oppositely charged ions of varying complexity. Intuitively, two like-charged macromolecules in aqueous solution are expected to repel one another, which is essentially the prediction of prevailing mean-field theories. In the presence of multivalent ions, however, many biopolymers actually attract one another and condense into compact, ordered states. The origin of this attraction has been the recent subject of intense theoretical debate, but no consensus on the mechanism has emerged. Actin is a cytoskeletal protein that self-assembles into rigid helical polymeric rods with a diameter of ~8 nm and a persistence length of ~10 microns. It has been observed that these like-charged actin rods (charge density ~4e/nm) can condense into bundles at sufficiently high concentrations of divalent metal cations. Moreover, cationic membranes can induce actin to self-assemble into a new phase of corrugated mesoscopic tubules with no direct analog in simple amphiphilic systems. The actin rods within the tubules are ordered into a compact superlattice arrangement of corrugated quasi-2D sheets, implying the existence of an unexpected attractive interaction between these like-charged rods. Using high resolution small angle x-ray scattering, confocal microscopy and electron microscopies, we will present a systematic structural investigation of these condensed actin phases, and the resultant implications for the attraction between like-charged polyelectrolytes.

Wong, Gerard C. L.

2000-03-01

392

Self-Assembly of Cyclo-diphenylalanine Peptides in Vacuum.  

PubMed

The diphenylalanine (FF) peptide self-assembles into a variety of nanostructures, including hollow nanotubes that form in aqueous solution with an unusually high degree of hydrophilic surface area. In contrast, diphenylalanine can also be vapor-deposited in vacuum to produce rodlike assemblies that are extremely hydrophobic; in this process FF has been found to dehydrate and cyclize to cyclo-diphenylalanine (cyclo-FF). An earlier study used all-atom molecular dynamics (MD) simulations to understand the early stages of the self-assembly of linear-FF peptides in solution. Here, we examine the self-assembly of cyclo-FF peptides in vacuum and compare it to these previous results to understand the differences underlying the two cases. Using all-atom replica exchange MD simulations, we consider systems of 50 cyclo-FF peptides and examine free energies along various structural association coordinates. We find that cyclo-FF peptides form ladder-like structures connected by double hydrogen bonds, and that multiple such ladders linearly align in a cooperative manner to form larger-scale, elongated assemblies. Unlike linear-FFs which mainly assemble through the interplay between hydrophobic and hydrophilic interactions, the assembly of cyclo-FFs in vacuum is primarily driven by electrostatic interactions along the backbone that induce alignment at long-range, followed by van der Waals interactions between side chains that become important for close-range packing. While both solution and vacuum phase driving forces result in ladder-like structures, the clustering of ladders is opposite: linear-FF peptide ladders form assemblies with side-chains buried inward, while cyclo-FF ladders point outward. PMID:24877752

Jeon, Joohyun; Shell, M Scott

2014-06-19

393

Self-Assembly of Heterogeneously Charged Particles under Confinement  

PubMed Central

Self-assembly—the spontaneous organization of microscopic units into well-defined mesoscopic structures—is a fundamental mechanism for a broad variety of nanotechnology applications in material science. The central role played by the anisotropy resulting from asymmetric shapes of the units and/or well-defined bonding sites on the particle surface has been widely investigated, highlighting the importance of properly designing the constituent entities in order to control the resulting mesoscopic structures. Anisotropy driven self-assembly can also result from the multipolar interactions characterizing many naturally occurring systems, such as proteins and viral capsids, as well as experimentally synthesized colloidal particles. Heterogeneously charged particles represent a class of multipolar units that are characterized by a competitive interplay between anisotropic attractive and repulsive interactions, due to the repulsion/attraction between charged-like/oppositely charged regions on the particle surface. In the present work, axially symmetric quadrupolar colloids are considered in a confined planar geometry; the role of both the overall particle charge and the patch extension as well as the effect of the substrate charge are studied in thermodynamic conditions such that the formation of extended structures is favored. A general tendency to form quasi-two-dimensional aggregates where particles align their symmetry axes within the plane is observed; among these planar self-assembled scenarios, a clear distinction between the formation of microcrystalline gels—branched networks consisting of purely crystalline domains—as opposed to disordered aggregates can be observed based on the specific features of the particle–particle interaction. Additionally, the possible competition of interparticle and particle–substrate interactions affects the size and the internal structure of the aggregates and can possibly inhibit the aggregation process.

2013-01-01

394

Platelets self-assemble into porous nacre during freeze casting.  

PubMed

Nacre possesses a remarkable combination of mechanical properties. Its high stiffness, strength and toughness are attributed to a highly aligned structure of aragonite platelets "glued" together by a small fraction (?5vol%) of polymer; theoretically it can be described by a shear-lag model of staggered tensile elements between which loads are transferred via shear. Despite extensive research, it has not been possible yet to manufacture this aligned structure as a bulk material of considerable volume with a fast and easy production process. Particularly porous materials would benefit from enhanced wall material properties to compensate for performance loss due to their high porosity. An important application for such porous materials are tissue scaffolds for bone substitution. Bone, like nacre, exhibits excellent mechanical properties, particularly an exceptionally high toughness, because of its composite structure of hydroxyapatite platelets aligned in a ?35vol% polymer matrix. Through the freeze casting process, which results in a fast and straightforward self-assembly of platelet-shaped particles during directional solidification, highly porous bulk materials with nacre-like cell walls can now be created. This porous nacre outperforms by a factor of 1.5-4 in terms of stiffness, strength and toughness materials that have the same amount of porosity but do not exhibit the nacre-like microarchitecture. The self-assembly process presented in this study thus has tremendous potential for the creation of highly porous, yet mechanically strong tissue scaffolds for low or medium load bearing bone substitute materials. Due to the versatility of the freeze casting process, materials with a self-assembled cell wall structure can be created from high-aspect ratio particles of all material classes. This enables material optimization for a great variety of applications such as impact protection, filtration, catalysis, energy generation and storage, in addition to those with excellent mechanical properties at high porosity. PMID:23313642

Hunger, Philipp M; Donius, Amalie E; Wegst, Ulrike G K

2013-03-01

395

Self-assembly of heterogeneously charged particles under confinement.  

PubMed

Self-assembly--the spontaneous organization of microscopic units into well-defined mesoscopic structures--is a fundamental mechanism for a broad variety of nanotechnology applications in material science. The central role played by the anisotropy resulting from asymmetric shapes of the units and/or well-defined bonding sites on the particle surface has been widely investigated, highlighting the importance of properly designing the constituent entities in order to control the resulting mesoscopic structures. Anisotropy driven self-assembly can also result from the multipolar interactions characterizing many naturally occurring systems, such as proteins and viral capsids, as well as experimentally synthesized colloidal particles. Heterogeneously charged particles represent a class of multipolar units that are characterized by a competitive interplay between anisotropic attractive and repulsive interactions, due to the repulsion/attraction between charged-like/oppositely charged regions on the particle surface. In the present work, axially symmetric quadrupolar colloids are considered in a confined planar geometry; the role of both the overall particle charge and the patch extension as well as the effect of the substrate charge are studied in thermodynamic conditions such that the formation of extended structures is favored. A general tendency to form quasi-two-dimensional aggregates where particles align their symmetry axes within the plane is observed; among these planar self-assembled scenarios, a clear distinction between the formation of microcrystalline gels--branched networks consisting of purely crystalline domains--as opposed to disordered aggregates can be observed based on the specific features of the particle-particle interaction. Additionally, the possible competition of interparticle and particle-substrate interactions affects the size and the internal structure of the aggregates and can possibly inhibit the aggregation process. PMID:23627740

Bianchi, Emanuela; Likos, Christos N; Kahl, Gerhard

2013-05-28

396

Particle self-assembly at ionic liquid-based interfaces.  

PubMed

This review presents an overview of the nature of ionic liquid (IL)-based interfaces and self-assembled particle morphologies of IL-in-water, oil- and water-in-IL, and novel IL-in-IL Pickering emulsions with emphasis on their unique phenomena, by means of experimental and computational studies. In IL-in-water Pickering emulsions, particles formed monolayers at ionic liquid-water interfaces and were close-packed on fully covered emulsion droplets or aggregated on partially covered droplets. Interestingly, other than equilibrating at the ionic liquid-water interfaces, microparticles with certain surface chemistries were extracted into the ionic liquid phase with a high efficiency. These experimental findings were supported by potential of mean force calculations, which showed large energy drops as hydrophobic particles crossed the interface into the IL phase. In the oil- and water-in-IL Pickering emulsions, microparticles with acidic surface chemistries formed monolayer bridges between the internal phase droplets rather than residing at the oil/water-ionic liquid interfaces, a significant deviation from traditional Pickering emulsion morphology. Molecular dynamics simulations revealed aspects of the mechanism behind this bridging phenomenon, including the role of the droplet phase, surface chemistry, and inter-particle film. Novel IL-in-IL Pickering emulsions exhibited an array of self-assembled morphologies including the previously observed particle absorption and bridging phenomena. The appearance of these morphologies depended on the particle surface chemistry as well as the ILs used. The incorporation of particle self-assembly with ionic liquid science allows for new applications at the intersection of these two fields, and have the potential to be numerous due to the tunability of the ionic liquids and particles incorporated, as well as the particle morphology by combining certain groups of particle surface chemistry, IL type (protic or aprotic), and whether oil or water is incorporated. PMID:24230971

Frost, Denzil S; Nofen, Elizabeth M; Dai, Lenore L

2014-04-01

397

Decisive influence of substitution positions in molecular self-assembly.  

PubMed

Molecular self-assembly provides a versatile tool for creating functional molecular structures at surfaces. A rational design of molecular structure formation requires not only an in-depth understanding of the subtle balance between intermolecular and molecule-surface interactions, but might also involve considering chemical changes of the molecules, such as deprotonation. Here, we present a systematic investigation of a comparatively simple class of molecules, namely dihydroxybenzoic acid, which, nevertheless, enables creating a rich variety of structures when deposited onto calcite (10.4) held at room temperature. Based on non-contact atomic force microscopy measurements in ultra-high vacuum, our study demonstrates the decisive impact of the positions of the hydroxyl groups on the structure formation. Six isomers of dihydroxybenzoic acid exist which form six different molecular structures on the calcite surface. Surprisingly, only two isomers arrange into stable, ordered structures at sub-monolayer coverage: 2,5-dihydroxybenzoic acid forms a commensurate (1 × 5) structure, composed of deprotonated molecules. A double-row structure consisting of protonated molecules is observed for 3,5-dihydroxybenzoic acid. The positions of the functional groups steer the molecular self-assembly of dihydroxybenzoic acids in three distinct ways, namely by (a) affecting the deprotonation tendency of the acid group, (b) influencing the intermolecular interaction as already indicated by greatly different bulk structures and (c) altering the molecule-substrate matching. Our results, thus, shed light on the impact of rather small changes in the molecular structure on the structural variety in molecular self-assembly on surfaces. PMID:24947801

Neff, Julia L; Kittelmann, Markus; Bechstein, Ralf; Kühnle, Angelika

2014-08-01

398

Matrix Development in Self-Assembly of Articular Cartilage  

PubMed Central

Background Articular cartilage is a highly functional tissue which covers the ends of long bones and serves to ensure proper joint movement. A tissue engineering approach that recapitulates the developmental characteristics of articular cartilage can be used to examine the maturation and degeneration of cartilage and produce fully functional neotissue replacements for diseased tissue. Methodology/Principal Findings This study examined the development of articular cartilage neotissue within a self-assembling process in two phases. In the first phase, articular cartilage constructs were examined at 1, 4, 7, 10, 14, 28, 42, and 56 days immunohistochemically, histologically, and through biochemical analysis for total collagen and glycosaminoglycan (GAG) content. Based on statistical changes in GAG and collagen levels, four time points from the first phase (7, 14, 28, and 56 days) were chosen to carry into the second phase, where the constructs were studied in terms of their mechanical characteristics, relative amounts of collagen types II and VI, and specific GAG types (chondroitin 4-sulfate, chondroitin 6-sulfate, dermatan sulfate, and hyaluronan). Collagen type VI was present in initial abundance and then localized to a pericellular distribution at 4 wks. N-cadherin activity also spiked at early stages of neotissue development, suggesting that self-assembly is mediated through a minimization of free energy. The percentage of collagen type II to total collagen significantly increased over time, while the proportion of collagen type VI to total collagen decreased between 1 and 2 wks. The chondroitin 6- to 4- sulfate ratio decreased steadily during construct maturation. In addition, the compressive properties reached a plateau and tensile characteristics peaked at 4 wks. Conclusions/Significance The indices of cartilage formation examined in this study suggest that tissue maturation in self-assembled articular cartilage mirrors known developmental processes for native tissue. In terms of tissue engineering, it is suggested that exogenous stimulation may be necessary after 4 wks to further augment the functionality of developing constructs.

Ofek, Gidon; Revell, Christopher M.; Hu, Jerry C.; Allison, David D.; Grande-Allen, K. Jane; Athanasiou, Kyriacos A.

2008-01-01

399

Directed self-assembly defectivity assessment. Part II  

NASA Astrophysics Data System (ADS)

The main concern for the commercialization of directed self-assembly (DSA) for semiconductor manufacturing continues to be the uncertainty in capability and control of defect density. Our research investigates the defect densities of various DSA process applications in the context of a 300mm wafer fab cleanroom environment; this paper expands substantially on the previously published DSA defectivity study by reporting a defect density process window relative to chemical epitaxial pre-pattern registration lines; as well as investigated DSA based contact hole shrinking and report critical dimension statistics for the phase separated polymers before and after etch, along with positional accuracy measurements and missing via defect density.

Bencher, Chris; Yi, He; Zhou, Jessica; Cai, Manping; Smith, Jeffrey; Miao, Liyan; Montal, Ofir; Blitshtein, Shiran; Lavi, Alon; Dotan, Kfir; Dai, Huixiong; Cheng, Joy Y.; Sanders, Daniel P.; Tjio, Melia; Holmes, Steven

2012-03-01

400

Self-assembled GaN hexagonal micropyramid and microdisk  

SciTech Connect

The self-assembled GaN hexagonal micropyramid and microdisk were grown on LiAlO{sub 2} by plasma-assisted molecular-beam epitaxy. It was found that the (0001) disk was established with the capture of N atoms by most-outside Ga atoms as the (1x1) surface was constructing, while the pyramid was obtained due to the missing of most-outside N atoms. The intensity of cathode luminescence excited from the microdisk was one order of amplitude greater than that from M-plane GaN.

Lo Ikai; Hsieh, C.-H.; Hsu, Y.-C.; Pang, W.-Y.; Chou, M.-C. [Department of Physics, Department of Materials and Optoelectronic Science, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan (China)

2009-02-09

401

Self-assembly of nanohydroxyapatite in mesoporous silica  

Microsoft Academic Search

A novel material hexagonal mesoporous silica-hydroxyapatite (HMS-HA) has been developed based on self-assembly of nanohydroxyapatite\\u000a in mesoporous silica in situ. The structural and textural properties of the materials are, respectively, characterized via\\u000a X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption, thermogravimetic analysis, and high-resolution transmission electron spectroscopy (HRTEM). Variable crystallinity\\u000a of HA involved in the mesopores yields from different

Xuetao Shi; Yingjun Wang; Kun Wei; Li Ren; Chen Lai

2008-01-01

402

The art and science of self-assembling molecular machines  

NASA Astrophysics Data System (ADS)

In this review, we show how noncovalent bonding interactions between 0957-4484/7/3/004/img1-electron rich aromatic ring systems (e.g. hydroquinone) and the 0957-4484/7/3/004/img1-electron deficient tetracationic cyclophane, cyclobis(paraquat-p-phenylene) can be used to self-assemble novel molecular architectures which are not only interesting to us, because of their fascinating topologies, but also because they have the potential to be developed into molecular structures with switchable properties on the nanometre scale. The high efficiency observed in the self-assembly of a [2]catenane, and its dynamic properties in solution, represent the first step in the design and self-assembly of other molecular assemblies better suited for the study of molecular switching processes. Therefore, a series of [2]rotaxanes, mechanically-interlocked molecular compounds, consisting of a linear 0957-4484/7/3/004/img1-electron rich dumbbell-shaped component and the 0957-4484/7/3/004/img1-electron deficient tetracationic cyclophane as the cyclic component, have been self-assembled and evaluated. All of the so-called molecular shuttles show translational isomerism and one of them, comprising benzidine and biphenol recognition sites as the non-degenerate 0957-4484/7/3/004/img1-electron rich sites, shows molecular switching properties when it is perturbed by external stimuli, such as electrons and protons. The versatility of our approach to nanoscale molecular switches is proven by the description of a series of molecular assemblies and supramolecular arrays, consisting of 0957-4484/7/3/004/img1-electron rich and 0957-4484/7/3/004/img1-electron deficient components, which display molecular switching properties when they are influenced by external stimuli that are photochemical, electrochemical and/or chemical in nature. However, the molecular switching phenomena take place in the solution state. Therefore, finally we describe how simple molecular structures can be ordered on to a solid support at the macroscopic level using Langmuir - Blodgett techniques. This is a necessary condition which must be fulfilled if we wish to construct supramolecular structures with device-like properties at the macroscopic level.

Gómez-López, Marcos; Preece, Jon A.; Fraser Stoddart, J.

1996-09-01

403

Formation and Characterization of Silicon Self-assembled Nanodots  

NASA Astrophysics Data System (ADS)

Silicon self-assembled quantum dots have been successfully prepared on corning glass (7059) substrate. The samples were fabricated using the common technique RF magnetron sputtering system depend on plasma excitation at varying growth parameters and high temperature of more than 500° C. The measurements of average dots size estimated to be 36 nm is confirmed by using AFM. The PL peak located at 570 nm, informed band gap energy = 2.10 eV larger than bulk material band gap, that confirmed the miniaturized of the dots. To measure the Silicon atomic% deposit on corning glass (7059) substrate EDX has been used.

Idrees, Fatima Aldaw; Sakrani, Samsudi; Othaman, Zulkafli

2011-05-01

404

Intermediate structures in two-dimensional molecular self-assembly  

NASA Astrophysics Data System (ADS)

We discuss the occurrence of transition structures observed in molecular self-assembly at surfaces. The increasing surface coverage transitions from low coverage structures to high coverage structures are a common phenomenon. However, often observed and not perfectly understood is the formation of intermediate structures, sometimes with lower lateral density than the initial phase. We will present different examples from our recent work and discuss the possible mechanisms of intermediate phase formation. In addition, we present intermediate structures occurring due to temperature-controlled reversible phase transitions.

Ernst, Karl-Heinz

2010-12-01

405

Scanner effects on directed self-assembly patterning  

NASA Astrophysics Data System (ADS)

Directed self-assembly (DSA) of various polymers is a potential next-generation lithography component. Lithographers can use an ArF scanner to print guide structures with pitches accessible with current technology. The DSA materials, in a non-exposure step, perform pitch multiplication of 1-D and 2-D guide structures. While research has investigated defects inherent to the DSA material, ArF scanner effects have received little attention. This work uses DSA models and scanner models to assess requirements for ArF immersion scanners for DSA complimentary lithography.

Renwick, Stephen P.

2014-03-01

406

Simulations of calcite crystallization on self-assembled monolayers.  

PubMed

This paper presents simulations of calcium carbonate ordering in contact with self-assembled monolayers. The calculations use potential-based molecular dynamics to model the crystallization of calcium carbonate to calcite expressing both the (00.1) and (01.2) surfaces. The effect of monolayer properties: ionization; epitaxial matching; charge density; and headgroup orientation on the crystallization process are examined in detail. The results demonstrate that highly charged surfaces are vital to stimulate ordering and crystallization. Template directed crystallization requires charge epitaxy between both the crystal surface and the monolayer. The orientation of the headgroup appears to make no contribution to the selection of the crystal surface. PMID:18672912

Freeman, Colin L; Harding, John H; Duffy, Dorothy M

2008-09-01

407

Computational Design of a Self-Assembling ?-Peptide Oligomer  

PubMed Central

The first computationally designed self-assembling oligomer consisting of exclusively ?-amino acids (?AAs) is presented. The packing of a ?-314 helix into coiled-coils of varying stoichiometries as a function of amino acid sequence is examined. ?-Peptides with hVal repeating every third residue in the sequence appeared to have a strong propensity to pack into hexameric bundles. The designed sequence was synthesized and characterized with CD spectroscopy, NMR, and analytical ultracentrifugation, suggesting that the peptide adopts a well-folded hexameric structure.

Korendovych, Ivan V.; Kim, Yong Ho; Ryan, Andrew H.; Lear, James D.; DeGrado, William F.; Shandler, Scott J.

2013-01-01

408

Unifying Interfacial Self-Assembly and Surface Freezing  

SciTech Connect

X-ray investigations reveal that the monolayers formed at the bulk alkanol-sapphire interface are densely packed with the surface-normal molecules hydrogen bound to the sapphire. About 30-35 C above the bulk, these monolayers both melt reversibly and partially desorb. This system exhibits balanced intermolecular and molecule-substrate interactions which are intermediate between self-assembled and surface-frozen monolayers, each dominated by one interaction. The phase behavior is rationalized within a thermodynamic model comprising interfacial interactions, elasticity, and entropic effects. Separating the substrate from the melt leaves the monolayer structurally intact.

B Ocko; H Hlaing; P Jepsen; S Kewalramani; A Tkachenko; D Pontoni; H Reichert; M Deutsch

2011-12-31

409

Unifying Interfacial Self-Assembly and Surface Freezing  

SciTech Connect

X-ray investigations reveal that the monolayers formed at the bulk alkanol-sapphire interface are densely packed with the surface-normal molecules hydrogen bound to the sapphire. About 30-35 C above the bulk, these monolayers both melt reversibly and partially desorb. This system exhibits balanced intermolecular and molecule-substrate interactions which are intermediate between self-assembled and surface-frozen monolayers, each dominated by one interaction. The phase behavior is rationalized within a thermodynamic model comprising interfacial interactions, elasticity, and entropic effects. Separating the substrate from the melt leaves the monolayer structurally intact.

Ocko, B.M.; Hlaing, H.; Jepsen, P.N.; Kewalramani, S.; Tkachenko, A.; Pontoni, D.; Reichert, H.; Deutsch, M.

2011-03-30

410

Water in nanoconfinement between hydrophilic self-assembled monolayers.  

PubMed

Molecular dynamics (MD) simulations of water confined to subnanometer thicknesses between carboxyl-terminated alkanethiol self-assembled monolayers (SAMs) on gold were performed to address conflicts in the literature on the structure and response of water in confinement. The amount of water was varied to yield submonolayer to bilayer structures. The orientation of the water is affected by the confinement, especially in the submonolayer case. We find that the diffusion coefficient decreases as the film becomes thinner and at higher pressures. However, in all cases studied, liquid diffusion is always found. At maximal suppression, the diffusion constant is 2 orders of magnitude smaller than the bulk value. PMID:18412381

Lane, J Matthew D; Chandross, Michael; Stevens, Mark J; Grest, Gary S

2008-05-20

411

Chiral tubule self-assembly from an achiral diynoic lipid  

PubMed Central

Tubules possessing ?m-scale chiral substructure self-assemble from an achiral isomer of the tubule-forming diynoic phosphatidylcholine, 1,2-bis(10,12-tricosadiynoyl)sn-glycero-3-phosphocholine [DC(8,9)PC], showing that molecular chirality is not essential for tubule formation. CD spectroscopy shows that these structures' helical sense of handedness instead originates in a spontaneous cooperative chiral symmetry-breaking process. We conclude that the chiral symmetry-breaking must originate in the unusual feature common to the chiral and achiral tubule-forming molecules, the diynes centered in their hydrocarbon tails.

Pakhomov, Serhii; Hammer, Robert P.; Mishra, Bijaya K.; Thomas, Britt N.

2003-01-01

412

Magnetic properties of self-assembled interacting nanoparticles  

NASA Astrophysics Data System (ADS)

The temperature-dependent magnetization and the hysteresis properties (remanence and coercivity) of magnetic nanoparticle arrays are studied by Monte Carlo simulations. An oscillatory variation of the remanence with layer coverage and accompanying peaks in the coercive field are predicted at low temperatures, due to dipolar interparticle interactions. The blocking temperature of the arrays decreases with the inverse cube of the interparticle spacing (Tb~d-3) and it remains almost unchanged with film thickness above one monolayer. Our results are compared with recent experiments on self-assembled Co nanoparticle arrays.

Kechrakos, D.; Trohidou, K. N.

2002-12-01

413

Self-assembly of free-standing RNA membranes.  

PubMed

RNA has emerged as a promising material for nanostructure and microstructure engineering. Although rare, some macroscopic RNA structures have also been constructed using lipid or polymer materials. Here, we report the first example of an enzymatically generated RNA membrane. This robust and free-standing RNA membrane has a macroscopic structure and is generated without any polymer support or complexation. Our RNA membrane is fabricated following two sequential processes, complementary rolling circle transcription and evaporation-induced self-assembly, and its structural and functional properties are rationally controlled by adjusting RNA base pairing. In this study, three types of RNA membranes are fabricated and are used to demonstrate potential applications. PMID:24994070

Han, Daehoon; Park, Yongkuk; Kim, Hyejin; Lee, Jong Bum

2014-01-01

414

Self-assembling peptide amphiphile nanostructures for cancer therapy  

NASA Astrophysics Data System (ADS)

The application of nanotechnology to cancer therapy shows great promise for reducing the burden of the disease. By virtue of their size, nanoscale objects preferentially accumulate in tumor tissue through an enhanced permeability and retention (EPR) effect. However, to fully overcome the issues that limit current cancer treatments, viable nanostructures must also impart multifunctionality and be fully compatible with their biological surrounds. The self-assembling peptide amphiphile (PA) materials studied extensively in the Stupp Research Group form very biocompatible high aspect ratio nanostructures that meet these criteria. This thesis investigates the development of PA nanostructures designed to treat cancer. We first look to use the PA as a drug delivery vehicle by entrapping a small hydrophobic anti-cancer drug, camptothecin, in the core of the nanostructures. Using a solvent evaporation technique to load the drug into the PA nanofibers, we are able to improve the aqueous solubility of the molecule by nearly 30-fold. TEM and AFM studies show that entrapment of drug molecules does not disrupt the self-assembled morphology of the nanofiber. In vitro and in vivo studies are also conducted to demonstrate the bioactivity of the drug after its entrapment. As a potential platform for novel therapeutics, we next develop techniques for using light irradiation to trigger self-assembly inside the confined space of liposomes. We encapsulate PA monomers that assemble under acidic conditions along with a photoacid generator inside liposomes. Upon exposure to 254 nm light, the PA monomers self assemble inside the liposome to form nanostructures, which we observe through a quick freeze/deep etch technique that allows us to look inside the liposomes by SEM and TEM. Last of all, the development and discovery of epitopes for targeting PA nanostructures to tumors are explored. Using phage display technology we generate two groups of peptide sequences, one of which can potentially target tumor blood vessel formation, while the other is directed toward the ErbB2 receptor, which is over-expressed in certain aggressive breast cancers. Two peptide sequences from the literature that target breast cancer are also incorporated into PA molecules and we assess their biological affinity in vitro and in vivo.

Soukasene, Stephen

415

Microwave-assisted self-assembled ZnS nanoballs  

NASA Astrophysics Data System (ADS)

Self-assembled zinc sulfide nanoballs were prepared in saturated aqueous solutions via a microwave-assisted route. Zinc acetate and thioacetamide were selected as zinc source and sulfur source, respectively. Powder X-ray diffraction, transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectra, Fourier transform infrared and Thermogravimetric analysis were used to characterize the as-prepared products and the optical properties was studied by diffuse reflection spectra and photoluminescence spectra. Zinc sulfate and zinc nitrite can also used to prepare ZnS nanoparticles instead of nanoballs. The mechanism for the assembly of ZnS nanoballs was also discussed.

Zhao, Yu; Hong, J.-M.; Zhu, J.-J.

2004-10-01

416

Self-assembly and mineralization of peptide-amphiphile nanofibers.  

PubMed

We have used the pH-induced self-assembly of a peptide-amphiphile to make a nanostructured fibrous scaffold reminiscent of extracellular matrix. The design of this peptide-amphiphile allows the nanofibers to be reversibly cross-linked to enhance or decrease their structural integrity. After cross-linking, the fibers are able to direct mineralization of hydroxyapatite to form a composite material in which the crystallographic c axes of hydroxyapatite are aligned with the long axes of the fibers. This alignment is the same as that observed between collagen fibrils and hydroxyapatite crystals in bone. PMID:11721046

Hartgerink, J D; Beniash, E; Stupp, S I

2001-11-23

417

Customizing mesoscale self-assembly with three-dimensional printing  

NASA Astrophysics Data System (ADS)

Self-assembly due to capillary forces is a common method for generating two-dimensional mesoscale structures from identical floating particles at the liquid-air interface. Designing building blocks to obtain a desired mesoscopic structure is a scientific challenge. We show herein that it is possible to shape the particles with a low cost three-dimensional printer, for composing specific mesoscopic structures. Our method is based on the creation of capillary multipoles inducing either attractive or repulsive forces. Since capillary interactions can be downscaled, our method opens new paths toward low cost microfabrication.

Poty, M.; Lumay, G.; Vandewalle, N.

2014-02-01

418

Photoreactive self assembled monolayers for tuning the surface polarity  

NASA Astrophysics Data System (ADS)

In this contribution the modification of gold surfaces by self assembled monolayers (SAMs) of the photoreactive compound 11-mercaptoundecanoic acid, phenyl ester (MUAP) is presented. Upon irradiation with UV-light (? = 254 nm) the phenyl ester groups photoisomerize to give hydroxyketones (photo-Fries reaction). Due to the formation of polar hydroxy groups the surface tension of the SAMs changes. The photogenerated hydroxyl groups were selectively modified with perfluorobutyryl chloride. This postexposure modification led to a significant change in wetting behaviour and surface energy and XPS indicates that patterning is possible.

Griesser, Thomas; Track, Anna; Koller, Georg; Ramsey, Michael; Kern, Wolfgang; Trimmel, Gregor

419

Synthesis, properties and supramolecular self-assembly of novel n-type organic semiconductors  

NASA Astrophysics Data System (ADS)

In the quest to develop low cost energy production, utilization of solar energy to generate electrical energy has gained wide attention in recent years. Artificial photosynthetic systems, mimicking natural photosynthesis, are emerging as a promising approach for efficient photoinduced electron transfer and, consequently, a powerful technique to afford low cost electrical energy. Hydrogen-bonded supramolecular systems hold great promise in this application due to the involvement of H-bonds in electronic communication. Therefore, such a system possessing multi-point, hydrogen-bonded groups have the potential to enhance the photo conversion efficiency significantly. Among the small organic molecule n-type semiconductors, perylene tetracarboxylic diimides (PDIs) and perylene tetracarboxylic dianhydrides (PTCDs) possess great potential due to the combination of a variety of desirable characteristics such as excellent thermal and photostability, high molar absorptivities and good electron accepting properties. Because of these attractive properties, PDIs are being heavily researched as materials in the burgeoning field of organic electronics such as organic photovoltaic, n-channel materials, organic thin film transistors, etc. PDIs have great potential due to their ability to form self-assembled complex architectures via their high propensity for pi-pi stacking which can be coupled with other intermolecular interactions, such as hydrogen bonding, to form ordered functional systems. This dissertation focuses on the convenient synthesis and separation of 1,6- and 1,7-regioisomers of PDIs and PTCDs, the comparison of their anonymous properties, the effect of multi-point hydrogen bonding motifs on the self-assembly of PDIs, and the electron transport properties of novel derivatives of PTCDs.

Verma, Nisha

420

Cooperative Macromolecular Self-Assembly toward Polymeric Assemblies with Multiple and Bioactive Functions.  

PubMed

Conspectus In the past decades, polymer based nanoscale polymeric assemblies have attracted continuous interest due to their potential applications in many fields, such as nanomedicine. Many efforts have been dedicated to tailoring the three-dimensional architecture and the placement of functional groups at well-defined positions within the polymeric assemblies, aiming to augment their function. To achieve such goals, in one way, novel polymeric building blocks can be designed by controlled living polymerization methodology and advanced chemical modifications. In contrast, by focusing on the end function, others and we have been practicing strategies of cooperative self-assembly of multiple polymeric building blocks chosen from the vast library of conventional block polymers which are easily available. The advantages of such strategies lie in the simplicity of the preparation process and versatile choice of the constituent polymers in terms of their chemical structure and functionality as well as the fact that cooperative self-assembly based on supramolecular interactions offers elegant and energy-efficient bottom-up strategies. Combination of these principles has been exploited to optimize the architecture of polymeric assemblies with improved function, to impart new functionality into micelles and to realize polymeric nanocomplexes exhibiting functional integration, similar to some natural systems like artificial viruses, molecular chaperones, multiple enzyme systems, and so forth. In this Account, we shall first summarize several straightforward designing principles with which cooperative assembly of multiple polymeric building blocks can be implemented, aiming to construct polymeric nanoassemblies with hierarchal structure and enhanced functionalities. Next, examples will be discussed to demonstrate the possibility to create multifunctional nanoparticles by combination of the designing principles and judiciously choosing of the building blocks. We focus on multifunctional nanoparticles which can partially address challenges widely existing in nanomedicine such as long blood circulation, efficient cellular uptake, and controllable release of payloads. Finally, bioactive polymeric assemblies, which have certain functions closely mimicking those of some natural systems, will be used to conceive the concept of functional integration. PMID:24694280

Zhang, Zhenkun; Ma, Rujiang; Shi, Linqi

2014-04-15

421

Directed assembly of functional light harvesting antenna complexes onto chemically patterned surfaces  

NASA Astrophysics Data System (ADS)

We report the directed assembly of the photosynthetic membrane proteins LH1 and LH2 isolated from the purple bacterium Rhodobacter sphaeroides onto chemically patterned substrates. Nanoimprint lithography was used to pattern discrete regions of amino- and fluoro-terminated or poly(ethylene glycol) self-assembled monolayers onto a glass substrate. Densely packed layers of assembled protein complexes were observed with atomic force microscopy. The protein complexes attached selectively to the amino-terminated regions by electrostatic interactions. Spectral images generated with a hybrid scanning probe and fluorescence microscope confirmed that the patterned proteins retained their native optical signatures.

Escalante, Maryana; Maury, Pascale; Bruinink, Christiaan M.; van der Werf, Kees; Olsen, John D.; Timney, John A.; Huskens, Jurriaan; Hunter, C. Neil; Subramaniam, Vinod; Otto, Cees

2008-01-01

422

Real time monitoring of superparamagnetic nanoparticle self-assembly on surfaces of magnetic recording media  

NASA Astrophysics Data System (ADS)

Nanoparticle self-assembly dynamics are monitored in real-time by detecting optical diffraction from an all-nanoparticle grating as it self-assembles on a grating pattern recorded on a magnetic medium. The diffraction efficiency strongly depends on concentration, pH, and colloidal stability of nanoparticle suspensions, demonstrating the nanoparticle self-assembly process is highly tunable. This metrology could provide an alternative for detecting nanoparticle properties such as colloidal stability.

Ye, L.; Qi, B.; Pearson, T.; Cordeau, Y.; Mefford, O. T.; Crawford, T. M.

2014-05-01

423

Bottom-up surface self-assembly of polymer colloids to form patterned arrays  

Microsoft Academic Search

Self-assembled particle arrays have received a significant amount of attention recently because of their interesting optical properties. In contrast to top-down self-assembly approaches, in which a pattern is imposed upon the system by such processes as microcontact printing or photolithography, bottom-up self-assembly relies upon the system to both define the pattern and assemble the individual elements. In this latter approach,

Matthew Alan Ray

2006-01-01

424

Feasibility study of self-assembly mechanism for variable optical attenuator  

Microsoft Academic Search

This paper describes the feasibility study result for a variable optical attenuator (VOA) realized by a new concept of self-assembled polysilicon structures and a continuously position-controllable curved beam actuator based on surface micromachining technology. The self-assembly mechanism includes a residual stress induced curved beam which lifts up the reflective mirror shutter first. This self-assembled reflective pop-up shutter is locked and

Chengkuo Lee; Yen-Jyh Lai; Chia-Yu Wu; J. Andrew Yeh; Ruey-Shing Huang

2005-01-01

425

Self-assembly of polystyrene nanospheres and its applications as templates for plasmonic structures  

Microsoft Academic Search

Monodispersed colloidal polystyrene spheres have been self-assembled into various structures as templates for the fabrication of different nanostructures. Two unique self-assembly processes have been developed and systematically investigated. A method to make the multi-layer and mono-layer close-packed structure by means of capillary-convective force has been developed. By directly visualizing the self-assembling process using optical microscopy, a mechanism based on the

Shih-Hsin Chang

2010-01-01

426

Molecular simulation of self-assembly of hydrophilic functionalized aromatics in aqueous solutions  

Microsoft Academic Search

This study identifies mechanisms of self-assembly of hydrophilic functionalized aromatic molecules—a distinct class of lyotropic materials. Results from molecular dynamics studies used to understand the moieties of the lyotropic molecule that affect the structure are consistent with experimental observations of these self-assembled structures. Coulombic forces, dominated by ?–? interactions drives the self-assembly of this class of materials. Intra-molecular configurations of

S. Mohanty

2006-01-01

427

Molecular Self-Assembly at Metal-Electrolyte Interfaces  

PubMed Central

The self-assembly of molecular layers has become an important strategy in modern design of functional materials. However, in particular, large organic molecules may no longer be sufficiently volatile to be deposited by vapor deposition. In this