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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

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

PubMed

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-3(1)-hydroxymethyl-13(2)-demethoxycarbonylpheophorbide a (3',5'-bis-dodecyloxy)benzyl ester zinc complex 1 and 3-devinyl-3(1)-methoxymethyl-13(2)-demethoxycarbonylpheophorbide a (3',5'-bis-dodecyloxy)benzyl ester zinc complex 2, self-assemble into extended excitonically coupled chromophore stacks. (1)H-(13)C heteronuclear dipolar correlation MAS NMR experiments provided the (1)H 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 pi-stacks in planar layers in the solid-state. Concomitantly, X-ray powder diffraction measurements for chlorin 2 at 80 degrees 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 nm(3) containing 4 molecules, which is consistent with space group P2(1)22(1). PMID:19587237

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

2009-07-08

4

Self-assembly and energy transfer in artificial light-harvesting complexes of bacteriochlorophyll  c with astaxanthin  

Microsoft Academic Search

Chlorosomes, the light-harvesting antennae of green photosynthetic bacteria, are based on large aggregates of bacteriochlorophyll\\u000a molecules. Aggregates with similar properties to those in chlorosomes can also be prepared in vitro. Several agents were shown\\u000a to induce aggregation of bacteriochlorophyll c in aqueous environments, including certain lipids, carotenes, and quinones. A key distinguishing feature of bacteriochlorophyll\\u000a c aggregates, both in vitro

J. Alster; T. Polívka; J. B. Arellano; P. H?íbek; F. Vácha; J. Hála; J. Pšen?ík

5

DNA-directed artificial light-harvesting antenna.  

PubMed

Designing and constructing multichromophoric, artificial light-harvesting antennas with controlled interchromophore distances, orientations, and defined donor-acceptor ratios to facilitate efficient unidirectional energy transfer is extremely challenging. Here, we demonstrate the assembly of a series of structurally well-defined artificial light-harvesting triads based on the principles of structural DNA nanotechnology. DNA nanotechnology offers addressable scaffolds for the organization of various functional molecules with nanometer scale spatial resolution. The triads are organized by a self-assembled seven-helix DNA bundle (7HB) into cyclic arrays of three distinct chromophores, reminiscent of natural photosynthetic systems. The scaffold accommodates a primary donor array (Py), secondary donor array (Cy3) and an acceptor (AF) with defined interchromophore distances. Steady-state fluorescence analyses of the triads revealed an efficient, stepwise funneling of the excitation energy from the primary donor array to the acceptor core through the intermediate donor. The efficiency of excitation energy transfer and the light-harvesting ability (antenna effect) of the triads was greatly affected by the relative ratio of the primary to the intermediate donors, as well as on the interchromophore distance. Time-resolved fluorescence analyses by time-correlated single-photon counting (TCSPC) and streak camera techniques further confirmed the cascading energy transfer processes on the picosecond time scale. Our results clearly show that DNA nanoscaffolds are promising templates for the design of artificial photonic antennas with structural characteristics that are ideal for the efficient harvesting and transport of energy. PMID:21714548

Dutta, Palash K; Varghese, Reji; Nangreave, Jeanette; Lin, Su; Yan, Hao; Liu, Yan

2011-07-15

6

Self-assembly of light-harvesting crystalline nanosheets in aqueous media.  

PubMed

A methodology leading to facile self-assembly of crystalline aromatic arrays in dilute aqueous solutions would enable efficient fabrication and processing of organic photonic and electronic materials in water. In particular, soluble 2D crystalline nanosheets may mimic the properties of photoactive thin films and self-assembled monolayers, covering large areas with ordered nanometer-thick material. We designed such solution-phase arrays using hierarchical self-assembly of amphiphilic perylene diimides in aqueous media. The assemblies were characterized by cryogenic transmission electron microscopy (cryo-TEM), revealing crystalline order and 2D morphology (confirmed by AFM studies). The order and morphology are preserved upon drying as evidenced by TEM and AFM. The 2D crystalline-like structures exhibit broadening and red-shifted absorption bands in UV-vis spectra, typical for PDI crystals and liquid crystals. Photophysical studies including femtosecond transient absorption spectroscopy reveal that two of the assemblies are superior light-harvesters due to excellent solar spectrum coverage and fast exciton transfer, in one case showing exciton diffusion comparable to solid-state crystalline systems based on perylene tetracarboxylic dianhidride (PTCDA). PMID:23521176

Shahar, Chen; Baram, Jonathan; Tidhar, Yaron; Weissman, Haim; Cohen, Sidney R; Pinkas, Iddo; Rybtchinski, Boris

2013-04-05

7

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

8

Powering the future of molecular artificial photosynthesis with light-harvesting metallosupramolecular dye assemblies.  

PubMed

Chemical ingenuity will play a significant role in solving the greatest challenge currently facing society: providing clean and carbon neutral energy for all of humanity. Molecular artificial photosynthesis is an emerging technology based on principles learned from Nature where individual components perform the essential light-harvesting, charge-separation, and water splitting functions to store solar energy in the form of chemical bonds. This tutorial review focuses specifically on the application of metallosupramolecular self-assembly strategies to interface solar fuel catalysts with photosensitizers and construct light-harvesting antennae capable of achieving panchromatic absorption and directional energy concentration. PMID:22850767

Frischmann, Peter D; Mahata, Kingsuk; Würthner, Frank

2012-07-31

9

Structure determination of a bio-inspired self-assembled light-harvesting antenna by solid-state NMR and molecular modeling.  

PubMed

The molecular stacking of an artificial light-harvesting antenna self-assembled from 3(1)-aminofunctionalized zinc-chlorins was determined by solid-state NMR in combination with quantum-chemical and molecular-mechanics modeling. A library of trial molecular stacking arrangements was generated based on available structural data for natural and semisynthetic homologues of the Zn-chlorins. NMR assignments obtained for the monomer in solution were validated for self-assembled aggregates and refined with (1)H-(13)C heteronuclear correlation spectroscopy data collected from samples with (13)C at natural abundance. Solid-state ring-current shifts for the (1)H provided spatial constraints to determine the molecular overlap. This procedure allows for a discrimination between different self-assembled structures and a classification of the stacking mode in terms of electric dipole alignment and ?-? interactions, parameters that determine the functional properties of light-harvesting assemblies and conducting nanowires. The combination with quantum-mechanical modeling then allowed building a low-resolution packing model in silico from molecular stacks. The method allows for moderate disorder and residual polymorphism at the stack or molecular level and is generally applicable to determine molecular packing structures of aromatic molecules with structural asymmetry, such as is commonly provided by functionalized side chains that serve to tune the self-assembly process. PMID:23566216

Pandit, Anjali; Ocakoglu, Kasim; Buda, Francesco; van Marle, Thomas; Holzwarth, Alfred R; de Groot, Huub J M

2013-05-03

10

Anisotropic organization and microscopic manipulation of self-assembling synthetic porphyrin microrods that mimic chlorosomes: bacterial light-harvesting systems.  

PubMed

Being able to control in time and space the positioning, orientation, movement, and sense of rotation of nano- to microscale objects is currently an active research area in nanoscience, having diverse nanotechnological applications. In this paper, we demonstrate unprecedented control and maneuvering of rod-shaped or tubular nanostructures with high aspect ratios which are formed by self-assembling synthetic porphyrins. The self-assembly algorithm, encoded by appended chemical-recognition groups on the periphery of these porphyrins, is the same as the one operating for chlorosomal bacteriochlorophylls (BChl's). Chlorosomes, rod-shaped organelles with relatively long-range molecular order, are the most efficient naturally occurring light-harvesting systems. They are used by green photosynthetic bacteria to trap visible and infrared light of minute intensities even at great depths, e.g., 100 m below water surface or in volcanic vents in the absence of solar radiation. In contrast to most other natural light-harvesting systems, the chlorosomal antennae are devoid of a protein scaffold to orient the BChl's; thus, they are an attractive goal for mimicry by synthetic chemists, who are able to engineer more robust chromophores to self-assemble. Functional devices with environmentally friendly chromophores-which should be able to act as photosensitizers within hybrid solar cells, leading to high photon-to-current conversion efficiencies even under low illumination conditions-have yet to be fabricated. The orderly manner in which the BChl's and their synthetic counterparts self-assemble imparts strong diamagnetic and optical anisotropies and flow/shear characteristics to their nanostructured assemblies, allowing them to be manipulated by electrical, magnetic, or tribomechanical forces. PMID:22148684

Chappaz-Gillot, Cyril; Marek, Peter L; Blaive, Bruno J; Canard, Gabriel; Bürck, Jochen; Garab, Gyozo; Hahn, Horst; Jávorfi, Tamás; Kelemen, Loránd; Krupke, Ralph; Mössinger, Dennis; Ormos, Pál; Reddy, Chilla Malla; Roussel, Christian; Steinbach, Gábor; Szabó, Milán; Ulrich, Anne S; Vanthuyne, Nicolas; Vijayaraghavan, Aravind; Zupcanova, Anita; Balaban, Teodor Silviu

2011-12-09

11

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

12

Influence of phospholipid composition on self-assembly and energy-transfer efficiency in networks of light-harvesting 2 complexes.  

PubMed

In the photosynthetic membrane of purple bacteria networks of light-harvesting 2 (LH2) complexes capture the sunlight and transfer the excitation energy. In order to investigate the mutual relationship between the supramolecular organization of the pigment-protein complexes and their biological function, the LH2 complexes were reconstituted into three types of phospholipid membranes, consisting of L-?-phosphatidylglycerol (PG), L-?-phosphatidylcholine (PC), and L-?-phosphatidylethanolamine (PE)/PG/cardiolipin (CL). Atomic force microscopy (AFM) revealed that the type of phospholipids had a crucial influence on the clustering tendency of the LH2 complexes increased from PG over PC to PE/PG/CL, where the LH2 complexes formed large, densely packed clusters. Time-resolved spectroscopy uncovered a strong quenching of the LH2 fluorescence that is ascribed to singlet-singlet and singlet-triplet annihilation by an efficient energy transfer between the LH2 complexes in the artificial membrane systems. Quantitative analysis reveals that the intercomplex energy transfer efficiency varies strongly as a function of the morphology of the nanostructure, namely in the order PE/PG/CL > PC > PG, which is in line with the clustering tendency of LH2 observed by AFM. These results suggest a strong influence of the phospholipids on the self-assembly of LH2 complexes into networks and concomitantly on the intercomplex energy transfer efficiency. PMID:23919556

Sumino, Ayumi; Dewa, Takehisa; Noji, Tomoyasu; Nakano, Yuki; Watanabe, Natsuko; Hildner, Richard; Bösch, Nils; Köhler, Jürgen; Nango, Mamoru

2013-08-28

13

Controlling the efficiency of an artificial light-harvesting complex  

PubMed Central

Adaptive femtosecond pulse shaping in an evolutionary learning loop is applied to a bioinspired dyad molecule that closely mimics the early-time photophysics of the light-harvesting complex 2 (LH2) photosynthetic antenna complex. Control over the branching ratio between the two competing pathways for energy flow, internal conversion (IC) and energy transfer (ET), is realized. We show that by pulse shaping it is possible to increase independently the relative yield of both channels, ET and IC. The optimization results are analyzed by using Fourier analysis, which gives direct insight to the mechanism featuring quantum interference of a low-frequency mode. The results from the closed-loop experiments are repeatable and robust and demonstrate the power of coherent control experiments as a spectroscopic tool (i.e., quantum-control spectroscopy) capable of revealing functionally relevant molecular properties that are hidden from conventional techniques.

Savolainen, Janne; Fanciulli, Riccardo; Dijkhuizen, Niels; Moore, Ana L.; Hauer, Jurgen; Buckup, Tiago; Motzkus, Marcus; Herek, Jennifer L.

2008-01-01

14

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

NASA Astrophysics Data System (ADS)

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 104 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.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 104 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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr33748k

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

2013-03-01

15

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

2013-06-01

16

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

NASA Astrophysics Data System (ADS)

Ultrafast spectroscopy and quantum-dynamics simulations of an artificial supramolecular light-harvesting system — a supramolecular triad - provide strong evidence that the quantum-correlated wavelike motion of electrons and nuclei on a timescale of few tens of femtoseconds governs the ultrafast electronic charge transfer.

Falke, S. M.; Rozzi, C. A.; Spallanzani, N.; Rubio, A.; Molinari, E.; Brida, D.; Maiuri, M.; Cerullo, G.; Schramm, H.; Christoffers, J.; Lienau, C.

2013-03-01

17

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

18

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

2011-12-28

19

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

20

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

PubMed

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. PMID:23511467

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

2013-01-01

21

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

2013-08-06

22

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

23

Investigation of macrocyclic polymers as artificial light harvesters: subpicosecond energy transfer in poly(9,9-dimethyl-2-vinylfluorene).  

PubMed

The spectroscopy and dynamics of a novel molecular architecture that mimics natural light harvesting have been characterized. The deployment of 9,9-dimethyl-2-fluorenyl (DMF) chromophores in atactic macrocyclic poly(9,9-dimethyl-2-vinylfluorene) is similar to that in the light harvesting antenna LH2 of the purple photosynthetic bacteria. A variety of spectroscopic probes are used to study the dynamics in these novel polymer systems. The number of chromophores is tuned from 12-142 identical chromophore units. Steady-state absorption and emission measurements, time-resolved fluorescence, and ultrafast transient absorption anisotropy techniques provide evidence for distinct differences in the photophysics of matching molecular weight linear and cyclic polymers and of the occurrence of energy transfer in these polymers. There is direct evidence of energy transfer in these macrocycles manifested in the depolarization decay components, which are characterized by two exponentials and are substantially faster than observed for reorientation of the free DMF chromophore. The time constants for the macrocycles are 700-900 fs and 7-8 ps and are size dependent; the biexponential decay arises from conformational and stereochemical disorder and can be well described by a master equation simulation assuming Förster incoherent hopping on model polymer structures. The results suggest energy hopping between adjacent chromophores on a 1 ps time scale. The pathway for energy migration is shown to be primarily between nearest neighbors along the cyclic backbone, but there is a considerable spread in the site-to-site hopping rates. Small cycles adopt a pseudoplanar ring type arrangement of the chromophore transition dipoles as observed in bacterial light harvesting antenna, and it is found that the linear polymers also show similar short-range planarity of transition dipoles. Overall, it is found that such small macrocyclic polymers possess excellent characteristics for light harvesting among identical chromophores and behave as a circular photonic wire. PMID:19367891

Johnson, Jerainne M; Chen, Rong; Chen, Xiyi; Moskun, Amy C; Zhang, Xi; Hogen-Esch, Thieo E; Bradforth, Stephen E

2008-12-25

24

Photosynthetic Light-Harvesting  

NASA Astrophysics Data System (ADS)

Photosynthetic organisms utilize (bacterio) chlorophylls and carotenoids as main light-harvesting pigments. In this chapter, we review bacteriochlorophyll light-harvesting in photosynthetic purple bacteria; we discuss intra- and intercomplex energy transfer processes as well as energy trapping by reaction centers. From the viewpoint of light-harvesting, in most organisms carotenoids are accessory pigments absorbing in the blue-green region of the solar spectrum, where chlorophylls and bacteriochlorophylls have weak absorption. Here, we discuss carotenoid light-harvesting in a pigment-protein complex having carotenoids as main lightharvesting pigment, the peridinin chlorophyll protein (PCP).

Pullerits, T.; Polivka, T.; Sundström, V.

25

Light harvesting arrays  

DOEpatents

A light harvesting array useful for the manufacture of devices such as solar cells comprises: (a) a first substrate comprising a first electrode; and (b) a layer of light harvesting rods electrically coupled to the first electrode, each of the light harvesting rods comprising a polymer of Formula I: X.sup.1.paren open-st.X.sup.m+1).sub.m (I) wherein m is at least 1, and may be from two, three or four to 20 or more; X.sup.1 is a charge separation group (and preferably a porphyrinic macrocycle, which may be one ligand of a double-decker sandwich compound) having an excited-state of energy equal to or lower than that of X.sup.2, and X.sup.2 through X.sup.m+1 are chromophores (and again are preferably porphyrinic macrocycles).

Lindsey, Jonathan S. (Raleigh, NC)

2002-01-01

26

Introduction of selective intersubunit disulfide bonds into self-assembly protein scaffold to enhance an artificial multienzyme complex's activity.  

PubMed

In nature, many enzymes participating in multienzyme reactions are often assembled to enhance efficiencies of multiple reactions. Therefore, much attention has been focused on self-assembly of multiple enzymes fused with a protein/peptide that interacts with a specific protein to enhance artificial multienzyme reactions. Sulfolobus solfataricus proliferating cell nuclear antigen (PCNA) is a ring-shaped symmetric heterotrimer consisting of PCNA1, PCNA2 and PCNA3. Multiple enzymes can be co-localized on the PCNA ring by fusing them to the C-termini of the three PCNA subunits. However, an advantage of the specific non-covalent complex formation is inextricably associated with the disadvantage of its concentration-dependent dissociation. In this study, disulfide bonds were introduced between the PCNA subunits by Cys substitution at the sites neighboring the interface for heterotrimerization. Selective intersubunit disulfide bond formation between PCNA1 and PCNA3 and between PCNA2 and PCNA3 by a natural oxidizing reagent successfully stabilized an artificial multienzyme complex, which is composed of a bacterial cytochrome P450 and its two redox partner proteins. The covalent stabilization of the multienzyme complex enhanced its cytochrome P450 activity because of the absence of inactive dissociated components. PMID:23404255

Hirakawa, Hidehiko; Kakitani, Ayano; Nagamune, Teruyuki

2013-02-22

27

Genetic Exchange Leading to Self-Assembling RNA Species upon Encapsulation in Artificial Protocells  

Microsoft Academic Search

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

Sergio-francis M. Zenisek; Eric J. Hayden; Niles Lehman

2007-01-01

28

Dynamic, self-assembled aggregates of magnetized, millimeter-sized objects rotating at the liquid-air interface: Macroscopic, two-dimensional classical artificial atoms and molecules  

SciTech Connect

This paper describes self-assembly of millimeter-sized, magnetized disks floating on a liquid-air interface, and rotating under the influence of a rotating external magnetic field. Spinning of the disks results in hydrodynamic repulsion between them, while the rotating magnetic field produces an average confining potential acting on all disks. The interplay between hydrodynamic and magnetic interactions leads to the formation of patterns. Theoretical analysis of hydrodynamic and magnetic forces indicates that the interactions in this system are similar to those acting in systems of finite numbers of particles behaving classically (''classical artificial atoms''). Macroscopic artificial atoms and molecules are described, and the rules governing their morphologies outlined.

Grzybowski, Bartosz A.; Jiang, Xingyu; Stone, Howard A.; Whitesides, George M.

2001-07-01

29

The chlorosome: a prototype for efficient light harvesting in photosynthesis  

PubMed Central

Three phyla of bacteria include phototrophs that contain unique antenna systems, chlorosomes, as the principal light-harvesting apparatus. Chlorosomes are the largest known supramolecular antenna systems and contain hundreds of thousands of BChl c/d/e molecules enclosed by a single membrane leaflet and a baseplate. The BChl pigments are organized via self-assembly and do not require proteins to provide a scaffold for efficient light harvesting. Their excitation energy flows via a small protein, CsmA embedded in the baseplate to the photosynthetic reaction centres. Chlorosomes allow for photosynthesis at very low light intensities by ultra-rapid transfer of excitations to reaction centres and enable organisms with chlorosomes to live at extraordinarily low light intensities under which no other phototrophic organisms can grow. This article reviews several aspects of chlorosomes: the supramolecular and molecular organizations and the light-harvesting and spectroscopic properties. In addition, it provides some novel information about the organization of the baseplate.

Oostergetel, Gert T.; van Amerongen, Herbert

2010-01-01

30

Efficient exciton transport in layers of self-assembled porphyrin derivatives.  

PubMed

The photosynthetic apparatus of green sulfur bacteria, the chlorosome, is generally considered as a highly efficient natural light-harvesting system. The efficient exciton transport through chlorosomes toward the reaction centers originates from self-assembly of the bacteriochlorophyll molecules. The aim of the present work is to realize a long exciton diffusion length in an artificial light-harvesting system using the concept of self-assembled natural chlorosomal chromophores. The ability to transport excitons is studied for porphyrin derivatives with different tendencies to form molecular stacks by self-assembly. A porphyrin derivative denoted as ZnOP, containing methoxymethyl substituents ({meso-tetrakis[3,5-bis(methoxymethyl)phenyl]porphyrinato}zinc(II)) is found to form self-assembled stacks, in contrast to a derivative with tert-butyl substituents, ZnBuP ({meso-tetrakis[3,5-bis(tert-butyl)phenyl]porphyrinato}zinc(II)). Exciton transport and dissociation in a bilayer of these porphyrin derivatives and TiO2 are studied using the time-resolved microwave conductivity (TRMC) method. For ZnOP layers it is found that excitons undergo diffusive motion between the self-assembled stacks, with the exciton diffusion length being as long as 15 +/- 1 nm, which is comparable to that in natural chlorosomes. For ZnBuP a considerably shorter exciton diffusion length of 3 +/- 1 nm is found. Combining these exciton diffusion lengths with exciton lifetimes of 160 ps for ZnOP and 74 ps for ZnBuP yields exciton diffusion coefficients equal to 1.4 x 10(-6) m2/s and 1 x 10(-7) m2/s, respectively. The larger exciton diffusion coefficient for ZnOP originates from a strong excitonic coupling for interstack energy transfer. The findings show that energy transfer is strongly affected by the molecular organization. The efficient interstack energy transfer shows promising prospects for application of such self-assembled porphyrins in optoelectronics. PMID:18247606

Huijser, Annemarie; Suijkerbuijk, Bart M J M; Klein Gebbink, Robertus J M; Savenije, Tom J; Siebbeles, Laurens D A

2008-02-05

31

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

2012-07-11

32

Light harvesting in photosystem II.  

PubMed

Water oxidation in photosynthesis takes place in photosystem II (PSII). This photosystem is built around a reaction center (RC) where sunlight-induced charge separation occurs. This RC consists of various polypeptides that bind only a few chromophores or pigments, next to several other cofactors. It can handle far more photons than the ones absorbed by its own pigments and therefore, additional excitations are provided by the surrounding light-harvesting complexes or antennae. The RC is located in the PSII core that also contains the inner light-harvesting complexes CP43 and CP47, harboring 13 and 16 chlorophyll pigments, respectively. The core is surrounded by outer light-harvesting complexes (Lhcs), together forming the so-called supercomplexes, at least in plants. These PSII supercomplexes are complemented by some "extra" Lhcs, but their exact location in the thylakoid membrane is unknown. The whole system consists of many subunits and appears to be modular, i.e., both its composition and organization depend on environmental conditions, especially on the quality and intensity of the light. In this review, we will provide a short overview of the relation between the structure and organization of pigment-protein complexes in PSII, ranging from individual complexes to entire membranes and experimental and theoretical results on excitation energy transfer and charge separation. It will become clear that time-resolved fluorescence data can provide invaluable information about the organization and functioning of thylakoid membranes. At the end, an overview will be given of unanswered questions that should be addressed in the near future. PMID:23595278

van Amerongen, Herbert; Croce, Roberta

2013-04-18

33

Biohybrid photosynthetic antenna complexes for enhanced light-harvesting.  

PubMed

Biohybrid antenna systems have been constructed that contain synthetic chromophores attached to 31mer analogues of the bacterial photosynthetic core light-harvesting (LH1) ?-polypeptide. The peptides are engineered with a Cys site for bioconjugation with maleimide-terminated chromophores, which include synthetic bacteriochlorins (BC1, BC2) with strong near-infrared absorption and commercial dyes Oregon green (OGR) and rhodamine red (RR) with strong absorption in the blue-green to yellow-orange regions. The peptides place the Cys 14 (or 6) residues before a native His site that binds bacteriochlorophyll a (BChl-a) and, like the native LH proteins, have high helical content as probed by single-reflection IR spectroscopy. The His residue associates with BChl-a as in the native LH1 ?-polypeptide to form dimeric ??-subunit complexes [31mer(-14Cys)X/BChl](2), where X is one of the synthetic chromophores. The native-like BChl-a dimer has Q(y) absorption at 820 nm and serves as the acceptor for energy from light absorbed by the appended synthetic chromophore. The energy-transfer characteristics of biohybrid complexes have been characterized by steady-state and time-resolved fluorescence and absorption measurements. The quantum yields of energy transfer from a synthetic chromophore located 14 residues from the BChl-coordinating His site are as follows: OGR (0.30) < RR (0.60) < BC2 (0.90). Oligomeric assemblies of the subunit complexes [31mer(-14Cys)X/BChl](n) are accompanied by a bathochromic shift of the Q(y) absorption of the BChl-a oligomer as far as the 850-nm position found in cyclic native photosynthetic LH2 complexes. Room-temperature stabilized oligomeric biohybrids have energy-transfer quantum yields comparable to those of the dimeric subunit complexes as follows: OGR (0.20) < RR (0.80) < BC1 (0.90). Thus, the new biohybrid antennas retain the energy-transfer and self-assembly characteristics of the native antenna complexes, offer enhanced coverage of the solar spectrum, and illustrate a versatile paradigm for the construction of artificial LH systems. PMID:22375881

Springer, Joseph W; Parkes-Loach, Pamela S; Reddy, Kanumuri Ramesh; Krayer, Michael; Jiao, Jieying; Lee, Gregory M; Niedzwiedzki, Dariusz M; Harris, Michelle A; Kirmaier, Christine; Bocian, David F; Lindsey, Jonathan S; Holten, Dewey; Loach, Paul A

2012-02-29

34

Bioinspired molecular design of light-harvesting multiporphyrin arrays.  

PubMed

Recent progress in fundamental studies on multiporphyrin arrays has provided structural parameters for the molecular design of artificial light-harvesting antennae which mimic the wheel-like antenna complexes of photosynthetic purple bacteria. Covalent and noncovalent approaches have been employed for the construction of artificial light-harvesting multiporphyrin arrays. Such arrays are categorized into ring-shaped, windmill-shaped, star-shaped, and dendritic architectures. In particular, dendritic multiporphyrin arrays have been proven to be promising candidates for both providing a large absorption cross-section and enabling the vectorial transfer of energy over a long distance to a designated point. Such molecular and supramolecular systems are also expected to be potent components for molecular electronics and photonic devices. PMID:14695602

Choi, Myung-Seok; Yamazaki, Tomoko; Yamazaki, Iwao; Aida, Takuzo

2004-01-01

35

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

36

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

37

Energy, Charge, and Spin Transport in Molecules and Self-Assembled Nanostructures Inspired by Photosynthesis  

SciTech Connect

Electron transfer in biological molecules provides both insight and inspiration for developing chemical systems having similar functionality. Photosynthesis is an example of an integrated system in which light harvesting, photoinduced charge separation, and catalysis combine to carry out two thermodynamically demanding processes, the oxidation of water and the reduction of carbon dioxide. The development of artificial photosynthetic systems for solar energy conversion requires a fundamental understanding of electron-transfer reactions between organic molecules. Since these reactions most often involve single-electron transfers, the spin dynamics of photogenerated radical ion pairs provide important information on how the rates and efficiencies of these reactions depend on molecular structure. Given this knowledge, the design and synthesis of large integrated structures to carry out artificial photosynthesis is moving forward. An important approach to achieving this goal is the development of small, functional building blocks, having a minimum number of covalent bonds, which also have the appropriate molecular recognition sites to facilitate self-assembly into a complete, functional artificial photosynthetic system.

Wasielewski, Michael R. (NWU)

2008-10-03

38

Microtubule Self- Assembly  

NASA Astrophysics Data System (ADS)

Microtubules are important structural elements for neurons. Microtubles are cylindrical pipes that are self-assembled from tubulin dimers, These structures are intimately related to the neuron transport system. Abnormal microtubule disintegration contributes to neuro-disease. For several decades, experimentalists investigated the structure of the microtubules using TEM and Cryo-EM. However, the detailed structure at a molecular level remain incompletely understood. . In this presentation, we report numerically studies of the self-assembly process using a toy model for tubulin dimers. We investigate the nature of the interactions which are essential to stabilize such the cylindrical assembly of protofilaments. We use Monte Carlo simulations to suggest the pathways for assembly and disassembly of the microtubules.

Jho, Yongseok; Choi, M. C.; Farago, O.; Kim, Mahnwon; Pincus, P. A.

2008-03-01

39

Microtubule Self Assembly  

Microsoft Academic Search

Microtubules are important structural elements for neurons. Microtubles are cylindrical pipes that are self-assembled from tubulin dimers, These structures are intimately related to the neuron transport system. Abnormal microtubule disintegration contributes to neuro-disease. For several decades, experimentalists investigated the structure of the microtubules using TEM and Cryo-EM. However, the detailed structure at a molecular level remain incompletely understood. . In

Yongseok Jho; M. C. Choi; O. Farago; Mahnwon Kim; P. A. Pincus

2008-01-01

40

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

PubMed

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-ZnTPPS(4-) (an electron donor) and three half molecules of dihydroxy-SnTNMePyP(4+) (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. PMID:22310932

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

2012-02-07

41

Algorithmic DNA Self-assembly  

Microsoft Academic Search

Self-assembly is the ubiquitous process by which objects autonomously assemble into complexes. This phenomenon is common in\\u000a nature and yet is poorly understood from mathematical and programming perspectives. It is believed that self-assembly technology\\u000a will ultimately permit the precise fabrication of complex nanostructures. Of particular interest is DNA self-assembly. Double\\u000a and triple crossover DNA molecules have been designed that can

Ming-yang Kao

2006-01-01

42

Alkane Self Assembling  

NASA Astrophysics Data System (ADS)

Self-assembling of organic molecules has awaken scientific and technological interest. In this work we study the self-assembling process of long chain hydrocarbons, mainly n-dotriacontane (n-C32H66). We dip-coated C32 monolayers onto silicon wafers covered by their native silicon oxide layer (Si(100)/SiO2). Our results show that withdrawing speed affects the coverage and morphology of the C32 films. For slow withdrawing speeds, alkanes formed islands with a dragon-fly shape, while for fast withdrawing alkanes assembled in stripes with widths in the order of microns. When we quantified coverage and morphology versus withdrawing speed, we found an inflection, which we associate with a transition between two film deposition kinetics. These transitions have been previously described by de Gennes [1]. For slow withdrawing, film deposition follows the Langmuir-Blodget process and above a threshold speed, solution on the solid enters a Landau-Levich regime. This work opens the possibility for growing microstructures with nanometric thickness using a very simple method. These organic microstructures could be used as templates or as grids for optical diffraction. [0pt] [1] P.G. de Gennes, Colloid & Polymer Sci. 264, 463-465 (1986).

Corrales, Tomas; Homm, Pia; Ferrari, Piero; Retamal, Maria Jose; Del Campo, Valeria; Volkmann, Ulrich G.

2011-03-01

43

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

44

Solar cells incorporating light harvesting arrays  

DOEpatents

A solar cell incorporates a light harvesting array that comprises: (a) a first substrate comprising a first electrode; and (b) a layer of light harvesting rods electrically coupled to the first electrode, each of the light harvesting rods comprising a polymer of Formula I: X.sup.1.paren open-st.X.sup.m+1).sub.m (I) wherein m is at least 1, and may be from two, three or four to 20 or more; X.sup.1 is a charge separation group (and preferably a porphyrinic macrocycle, which may be one ligand of a double-decker sandwich compound) having an excited-state of energy equal to or lower than that of X.sup.2 ; and X.sup.2 through X.sup.m+1 are chromophores (and again are preferably porphyrinic macrocycles).

Lindsey, Jonathan S. (Raleigh, NC); Meyer, Gerald J. (Baltimore, MD)

2002-01-01

45

Chiral Self-Assembly  

NASA Astrophysics Data System (ADS)

Chirality, the lack of reflection symmetry, at the molecular level has a profound influence on the ordering of molecular assemblages at the macroscopic scale. The example discussed here is the self-assembly of monolayers of rod-like fd virus particles, with the virus particles oriented on the average perpendicular to the plane of the layer, like a single layer of a smectic-A liquid crystal. Because these virus particles are chiral, they would prefer a twisted packing, which is incompatible with the layer structure. The twisted packing can only appear locally, at layer edges or in isolated defects in the interior of the layer. As chirality increases, the twisted regions achieve lower energy, until they can drive remarkable transformations to structures with longer edges and/or a greater number of defects.

Meyer, Robert

2012-02-01

46

Lessons from nature about solar light harvesting  

NASA Astrophysics Data System (ADS)

Solar fuel production often starts with the energy from light being absorbed by an assembly of molecules; this electronic excitation is subsequently transferred to a suitable acceptor. For example, in photosynthesis, antenna complexes capture sunlight and direct the energy to reaction centres that then carry out the associated chemistry. In this Review, we describe the principles learned from studies of various natural antenna complexes and suggest how to elucidate strategies for designing light-harvesting systems. We envisage that such systems will be used for solar fuel production, to direct and regulate excitation energy flow using molecular organizations that facilitate feedback and control, or to transfer excitons over long distances. Also described are the notable properties of light-harvesting chromophores, spatial-energetic landscapes, the roles of excitonic states and quantum coherence, as well as how antennas are regulated and photoprotected.

Scholes, Gregory D.; Fleming, Graham R.; Olaya-Castro, Alexandra; van Grondelle, Rienk

2011-10-01

47

Photon echo studies of photosynthetic light harvesting  

Microsoft Academic Search

The broad linewidths in absorption spectra of photosynthetic complexes obscure information related to their structure and\\u000a function. Photon echo techniques represent a powerful class of time-resolved electronic spectroscopy that allow researchers\\u000a to probe the interactions normally hidden under broad linewidths with sufficient time resolution to follow the fastest energy\\u000a transfer events in light harvesting. Here, we outline the technical approach

Elizabeth L. Read; Hohjai Lee; Graham R. Fleming

2009-01-01

48

Nanotechnology and Quasicrystals: From Self-Assembly to Photonic Applications  

NASA Astrophysics Data System (ADS)

After providing a concise overview on quasicrystals and their discovery more than a quarter of a century ago, I consider the unexpected interplay between nano-technology and quasiperiodic crystals. Of particular relevance are efforts to fabricate artificial functional micro- or nanostructures, as well as efforts to control the self-assembly of nanostructures, where current knowledge about the possibility of having long-range order without periodicity can provide significant advantages. I discuss examples of systems ranging from artificial metamaterials for photonic applications, through self-assembled soft matter, to surface waves and optically-induced nonlinear photonic quasicrystals.

Lifshitz, R.

49

Self-Assembled Circuit Patterns  

Microsoft Academic Search

Self-assembly is a process in which basic units aggregate un- der attractive forces to form larger compound structures. Recent theo- retical work has shown that pseudo-crystalline self-assembly can be al- gorithmic, in the sense that complex logic can be programmed into the growth process (26). This theoretical work builds on the theory of two- dimensional tilings (8), using rigid square

Matthew Cook; Paul W. K. Rothemund; Erik Winfree

2003-01-01

50

Gold nanoparticle functionalized artificial nacre: facile in situ growth of nanoparticles on montmorillonite nanosheets, self-assembly, and their multiple properties.  

PubMed

Artificial nacre based on clay nanosheets have been emerging as a new generation of bioinspired materials due to their super mechanical, fire-retardant, heat-shield, and gas barrier properties. Functional design in artificial nacre is highly demanded to further broaden the applications of these promising bioinspired materials. However, there is rarely a report on the functionalization of artificial nacre at present possibly due to the lack of a feasible strategy to introduce functional components in nacre-like materials without weakening other properties. In this study, we report a feasible method to fabricate artificial nacre-like functional hybrid films by using Au nanoparticle (NP) modified natural clay montmorillonite (MTM) nanosheets as efficient two-dimensional building blocks. First, Au NPs-chitosan-MTM hybrid nanosheets were prepared and homogeneously dispersed in deionized water by the facile in situ growth of Au NPs on chitosan-MTM nanosheets. Then, the obtained Au NPs-chitosan-MTM hybrid nanosheet suspension can be sprayed or vacuum filtrated to form nacre-like layered hybrid nanocoatings or free-standing hybrid films, respectively. Finally, as-fabricated artificial nacre nanocoatings or hybrid films have been demonstrated to behave with surface enhanced Raman scattering (SERS), catalytic, and photothermal conversion properties indicating the successful functionalization of artificial nacre by introducing Au NPs. PMID:22909252

Yao, Hong-Bin; Mao, Li-Bo; Yan, You-Xian; Cong, Huai-Ping; Lei, Xuan; Yu, Shu-Hong

2012-08-29

51

Accessing exciton transport in light-harvesting structures with plasmonic nanotip  

NASA Astrophysics Data System (ADS)

Natural light-harvesting complexes, such as that of plant cells or photosynthetic bacteria, are considered as possible prototypes for artificially designed solar cell materials. In these structures the energy of light absorbed by a peripheral antenna is transmitted very efficiently in a form of excitons to a reaction center. Usually, information about the exciton transport is obtained from time-resolved nonlinear optical experiments where the frequencies of a pump and a probe fields select particular electronic transitions in the light-harvesting complex. We explore a complimentary setup utilizing a plasmonic nanotip as a local sub-wavelength probe of excitation dynamics. As specific examples we consider an LHII complex involved in the light-harvesting process of purple bacteria and a Fenna-Matthews-Olson pigment-protein complex of green-sulphur bacteria.

Saikin, Semion K.; Feist, Johannes; Homer Reid, M. T.; Lukin, Mikhail D.; Aspuru-Guzik, Alan

2012-02-01

52

Light-harvesting in photosystem I.  

PubMed

This review focuses on the light-harvesting properties of photosystem I (PSI) and its LHCI outer antenna. LHCI consists of different chlorophyll a/b binding proteins called Lhca's, surrounding the core of PSI. In total, the PSI-LHCI complex of higher plants contains 173 chlorophyll molecules, most of which are there to harvest sunlight energy and to transfer the created excitation energy to the reaction center (RC) where it is used for charge separation. The efficiency of the complex is based on the capacity to deliver this energy to the RC as fast as possible, to minimize energy losses. The performance of PSI in this respect is remarkable: on average it takes around 50 ps for the excitation to reach the RC in plants, without being quenched in the meantime. This means that the internal quantum efficiency is close to 100 % which makes PSI the most efficient energy converter in nature. In this review, we describe the light-harvesting properties of the complex in relation to protein and pigment organization/composition, and we discuss the important parameters that assure its very high quantum efficiency. Excitation energy transfer and trapping in the core and/or Lhcas, as well as in the supercomplexes PSI-LHCI and PSI-LHCI-LHCII are described in detail with the aim of giving an overview of the functional behavior of these complexes. PMID:23645376

Croce, Roberta; van Amerongen, Herbert

2013-05-04

53

Protocols for self-assembly and imaging of DNA nanostructures.  

PubMed

Programed molecular structures allow us to research and make use of physical, chemical, and biological effects at the nanoscale. They are an example of the "bottom-up" approach to nanotechnology, with structures forming through self-assembly. DNA is a particularly useful molecule for this purpose, and some of its advantages include parallel (as opposed to serial) assembly, naturally occurring "tools," such as enzymes and proteins for making modifications and attachments, and structural dependence on base sequence. This allows us to develop one, two, and three dimensional structures that are interesting for their fundamental physical and chemical behavior, and for potential applications such as biosensors, medical diagnostics, molecular electronics, and efficient light-harvesting systems. We describe five techniques that allow one to assemble and image such structures: concentration measurement by ultraviolet absorption, titration gel electrophoresis, thermal annealing, fluorescence microscopy, and atomic force microscopy in fluids. PMID:21674362

Sobey, Thomas L; Simmel, Friedrich C

2011-01-01

54

Design principles of photosynthetic light-harvesting.  

PubMed

Photosynthetic organisms are capable of harvesting solar energy with near unity quantum efficiency. Even more impressively, this efficiency can be regulated in response to the demands of photosynthetic reactions and the fluctuating light-levels of natural environments. We discuss the distinctive design principles through which photosynthetic light-harvesting functions. These emergent properties of photosynthesis appear both within individual pigment-protein complexes and in how these complexes integrate to produce a functional, regulated apparatus that drives downstream photochemistry. One important property is how the strong interactions and resultant quantum coherence, produced by the dense packing of photosynthetic pigments, provide a tool to optimize for ultrafast, directed energy transfer. We also describe how excess energy is quenched to prevent photodamage under high-light conditions, which we investigate through theory and experiment. We conclude with comments on the potential of using these features to improve solar energy devices. PMID:22470965

Fleming, Graham R; Schlau-Cohen, Gabriela S; Amarnath, Kapil; Zaks, Julia

2012-01-01

55

Combinatorial optimization problems in self-assembly  

Microsoft Academic Search

Self-assembly is the ubiquitous process by which simple objects autonomously assemble into intricate complexes. It has been suggested that intricate self-assembly processes will ultimately be used in circuit fabrication, nano-robotics, DNA computation, and amorphous computing. In this paper, we study two combinatorial optimization problems related to efficient self-assembly of shapes in the Tile Assembly Model of self-assembly proposed by Rothemund

Leonard M. Adleman; Qi Cheng; Ashish Goel; Ming-Deh A. Huang; David Kempe; Pablo Moisset de Espanés; Paul Wilhelm Karl Rothemund

2002-01-01

56

Xanthophylls in light-harvesting complex II of higher plants: light harvesting and triplet quenching  

Microsoft Academic Search

A spectral and functional assignment of the xanthophylls in monomeric and trimeric light- harvesting complex II of green plants has been obtained using HPLC analysis of the pigment composition, laser-flash induced triplet-minus-singlet, fluorescence excitation, and absorption spectra. It is shown that violaxanthin is not present in monomeric preparations, that it has most likely a red-most absorption maximum at 510 nm

Erwin J. G. Peterman; Claudiu C. Gradinaru; Florentine Calkoen; Jeroen C. Borst; Rienk van Grondelle; Herbert van Amerongen

1997-01-01

57

Self-assembly of methyl zinc (3¹R)- and (3¹S)-bacteriopheophorbides d  

Microsoft Academic Search

The methyl zinc (3¹R)- and (3¹S)-[8Et, 12Me] bacteriopheophorbides d - analogs of the light-harvesting bacteriochlorophylls in photosynthetic bacteria - self-assemble in nonpolar solvents. While in dilute dichloromethane solution both epimers prevail in their monomeric form, complex equilibria of aggregates with gradually red-shifting Q{sub y} absorptions are formed at either higher concentration or lower temperature or upon dilution with hexane. Dynamic

T. S. Balaban; A. R. Holzwarth; K. Schaffner; Hitoshi Tamiaki

1997-01-01

58

Indicators of quantum coherence in light-harvesting dynamics  

Microsoft Academic Search

Characterizing quantum dynamics of electronic excitations in a variety of light-harvesting systems is currently of much interest [1]. In particular, it is important to identify measures that appropriately quantify the strength of coherent dynamics and its impact on different time scales of the light-harvesting process. In this talk I will discuss quantum transport performance measures that are defined based on

Alexandra Olaya-Castro

2011-01-01

59

A self-assembled ionophore  

Microsoft Academic Search

Ionophores are compounds that bind and transport ions. Ion binding and transport are fundamental to many biological and chemical processes. In this thesis we detail the structural characterization and cation binding properties of a self-assembled ionophore built from an isoguanosine (isoG) derivative, 5sp'-t-butyldimethylsilyl-2sp',3sp'-isopropylidene isoG 30. We begin with a summary of the themes that facilitate ionophore design and the definitions

Sampath K. Tirumala

1997-01-01

60

Self-assembled pyrazinacene nanotubes.  

PubMed

Nanotubes of a pentacene derivative, 6,13-bis(1-n-dodecyl)-[a,c,l,n]-tetrabenzo-5,6,7,12,13,14-hexaazapentacene, have been prepared by a hierarchical self-assembly mechanism. The oligoazaacenes 1-3, referred to as pyrazinacenes due to their structures of linearly fused pyrazine heterocycles, can also be considered as two azatriphenylenes fused through a reduced pyrazine ring. Dissolution of 6,13-bis(1-n-dodecyl)-[a,c,l,n]-tetrabenzo-5,6,7,12,13,14-hexaaza pentacene in nearly boiling toluene followed by standing of the solution at room temperature yields self-assembled (sa) pyrazinacene (Pa) nanotubes (NT's), or sa-PaNTs. Self-assembled-PaNTs are formed after initial aggregation of the pyrazinacene giving a 130-nm-wide 2-dimensional tape followed by helical twisting of this tape into a hollow cylindrical form of 150-200 nm diameter which can exceed 10 ?m in length. The morphologies of the tape and nanotube structures were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and electron absorption spectroscopy (UV/Vis). The latter indicates that the tubes may be formed by chromophore J-aggregation. Also, high resolution TEM of the tubes reveals that they can be composed of several tapes while powder X-ray diffraction revealed the lamellar structure of the tapes composing the tubes. PMID:21225075

Richards, Gary J; Hill, Jonathan P; Labuta, Jan; Wakayama, Yutaka; Akada, Misaho; Ariga, Katsuhiko

2011-01-12

61

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

62

Nanoparticles in a capillary trap: dynamic self-assembly at fluid interfaces.  

PubMed

Dynamic self-assembly is an emerging scientific concept aimed to construct artificial systems of adaptative behavior. Here, we present a first nanoscopic system that is able to dynamically self-assemble in two dimensions. This system is composed of charged gold nanoparticles, dispersed at the air-water interface, which self-assemble into a dense monolayer of area of several square centimeters in response to surface tension gradient. The surface tension gradient is imposed by localized addition or removal of organic solvent from the interface. After the surface tension is equalized over the whole fluid interface, the nanoparticles return to their initial dispersed state. The arrangement of nanoparticles before and after the self-assembly was characterized using SEM microscopy and SAXS spectroscopy. The constructed self-assembling system offers a "chemical" alternative for the Langmuir-Blodgett technique. Also, it was applied for creating self-erasing nanoparticle patterns on a fluid surface. PMID:24016224

Sashuk, Volodymyr; Winkler, Katarzyna; Zywoci?ski, Andrzej; Wojciechowski, Tomasz; Górecka, Ewa; Fia?kowski, Marcin

2013-09-09

63

Nanotechnology and Quasicrystals: From Self-Assembly to Photonic Applications  

Microsoft Academic Search

After providing a concise overview on quasicrystals and their discovery more than a quarter of a century ago, I consider the\\u000a unexpected interplay between nano-technology and quasiperiodic crystals. Of particular relevance are efforts to fabricate\\u000a artificial functional micro- or nanostructures, as well as efforts to control the self-assembly of nanostructures, where current\\u000a knowledge about the possibility of having long-range order

Ron Lifshitz; Beverly Sackler

2009-01-01

64

Self-assembling magnetic "snakes"  

ScienceCinema

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.

65

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

66

Biogeography of Photosynthetic Light-Harvesting Genes in Marine Phytoplankton  

PubMed Central

Background Photosynthetic light-harvesting proteins are the mechanism by which energy enters the marine ecosystem. The dominant prokaryotic photoautotrophs are the cyanobacterial genera Prochlorococcus and Synechococcus that are defined by two distinct light-harvesting systems, chlorophyll-bound protein complexes or phycobilin-bound protein complexes, respectively. Here, we use the Global Ocean Sampling (GOS) Project as a unique and powerful tool to analyze the environmental diversity of photosynthetic light-harvesting genes in relation to available metadata including geographical location and physical and chemical environmental parameters. Methods All light-harvesting gene fragments and their metadata were obtained from the GOS database, aligned using ClustalX and classified phylogenetically. Each sequence has a name indicative of its geographic location; subsequent biogeographical analysis was performed by correlating light-harvesting gene budgets for each GOS station with surface chlorophyll concentration. Conclusion/Significance Using the GOS data, we have mapped the biogeography of light-harvesting genes in marine cyanobacteria on ocean-basin scales and show that an environmental gradient exists in which chlorophyll concentration is correlated to diversity of light-harvesting systems. Three functionally distinct types of light-harvesting genes are defined: (1) the phycobilisome (PBS) genes of Synechococcus; (2) the pcb genes of Prochlorococcus; and (3) the iron-stress-induced (isiA) genes present in some marine Synechococcus. At low chlorophyll concentrations, where nutrients are limited, the Pcb-type light-harvesting system shows greater genetic diversity; whereas at high chlorophyll concentrations, where nutrients are abundant, the PBS-type light-harvesting system shows higher genetic diversity. We interpret this as an environmental selection of specific photosynthetic strategy. Importantly, the unique light-harvesting system isiA is found in the iron-limited, high-nutrient low-chlorophyll region of the equatorial Pacific. This observation demonstrates the ecological importance of isiA genes in enabling marine Synechococcus to acclimate to iron limitation and suggests that the presence of this gene can be a natural biomarker for iron limitation in oceanic environments.

Bibby, Thomas S.; Zhang, Yinan; Chen, Min

2009-01-01

67

Carotenoids and the Assembly of Light-harvesting Complexes  

Microsoft Academic Search

Carotenoids are constitutive components of all light-harvesting complexes in plants and many such complexes in bacteria. In the crystal structures of several light-harvesting complexes, carotenoids are seen to span the lipid bilayer and connect components of the complex on both membrane surfaces and\\/or to mediate the interaction of transmembrane protein helices. This important stabilizing function suggests that these pigments are

Harald Paulsen

68

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

69

Self-assembling chimeric polypeptide-doxorubicin conjugate nanoparticles that abolish tumours after a single injection  

Microsoft Academic Search

New strategies to self-assemble biocompatible materials into nanoscale, drug-loaded packages with improved therapeutic efficacy are needed for nanomedicine. To address this need, we developed artificial recombinant chimeric polypeptides (CPs) that spontaneously self-assemble into sub-100-nm-sized, near-monodisperse nanoparticles on conjugation of diverse hydrophobic molecules, including chemotherapeutics. These CPs consist of a biodegradable polypeptide that is attached to a short Cys-rich segment. Covalent

J. Andrew Mackay; Mingnan Chen; Jonathan R. McDaniel; Wenge Liu; Andrew J. Simnick; Ashutosh Chilkoti

2009-01-01

70

Optical properties, light-harvesting, and energy transfer in hybrid nanomaterials  

NASA Astrophysics Data System (ADS)

Modern nanotechnology involves both nanocrystals (metal and semiconductor) and biomaterials. Using biomolecules as linkers, solid-state nanocrystals with modified surfaces can be assembled into hybrid (i.e. assembled from different materials) superstructures with unique optical properties. In a superstructure, individual building blocks (nanocrystals and biomolecules) strongly interact and these interactions bring new properties. In particular, Coulomb and electromagnetic interactions in a hybrid nanostructure cause several interesting effects: Energy transfer between nanoparticles (NPs), plasmon enhancement, modified exciton diffusion in nanowires, Fano interference effect, non-linear phenomena, etc. In our studies, we also look at the properties of artificial light- harvesting complexes composed of chlorophylls, photosynthetic bacterial reaction centers, and NPs. Using superior optical properties of metal and semiconductor NPs, it is possible to strongly enhance an efficiency of light harvesting in such complexes. In conclusion, our theory explains current experimental results and also provides rationale for future experiments and applications. Potential applications of dynamic hybrid nanostructures include sensors, nonlinear optical media, and light-harvesting systems.

Govorov, Alexander

2011-10-01

71

Randomized Self-assembly for Approximate Shapes  

Microsoft Academic Search

In this paper we design tile self-assembly systems which assemble arbitrarily close approximations to target squares with arbitrarily high probability. This is in contrast to previous work which has only considered deterministic assemblies of a single shape. Our technique takes advantage of the ability to assign tile concentrations to each tile type of a self-assembly system. Such an assignment yields

Ming-yang Kao; Robert T. Schweller

2008-01-01

72

Self-assembly of membrane junctions.  

PubMed Central

We present a mechanism for the aggregation of mobile intermembrane junctions, such as the connexon dyad of gap junctions. The model demonstrates that intermembrane repulsion provides a powerful self-assembly pressure. If the membrane repulsion is strong enough to prevent membrane adhesion, then the self-assembly pressure is of effective infinite range. Images FIGURE 1

Bruinsma, R; Goulian, M; Pincus, P

1994-01-01

73

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

74

Peptide self-assembly in functional polymer science and engineering  

Microsoft Academic Search

Biological self-assembly systems lie at the interface between molecular biology, chemistry, polymer science and engineering. The key elements in molecular self-assembly are chemical complementarity and structural compatibility. Several types of self-assembling peptides have been engineered. Type I peptides undergo intermolecular self-assembly, type II peptides undergo self-assembly and disassembly, i.e. intermolecular and intramolecular self-assembly under the influence of various conditions. Type

Shuguang Zhang; Michael Altman

1999-01-01

75

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

76

Self-assembling materials for therapeutic delivery.  

PubMed

A growing number of medications must be administered through parenteral delivery, i.e., intravenous, intramuscular, or subcutaneous injection, to ensure effectiveness of the therapeutic. For some therapeutics, the use of delivery vehicles in conjunction with this delivery mechanism can improve drug efficacy and patient compliance. Macromolecular self-assembly has been exploited recently to engineer materials for the encapsulation and controlled delivery of therapeutics. Self-assembled materials offer the advantages of conventional crosslinked materials normally used for release, but also provide the ability to tailor specific bulk material properties, such as release profiles, at the molecular level via monomer design. As a result, the design of materials from the "bottom up" approach has generated a variety of supramolecular devices for biomedical applications. This review provides an overview of self-assembling molecules, their resultant structures, and their use in therapeutic delivery. It highlights the current progress in the design of polymer- and peptide-based self-assembled materials. PMID:19010748

Branco, Monica C; Schneider, Joel P

2008-10-10

77

Self-assembled Materials for Catalysis  

SciTech Connect

The purpose of this review is to highlight developments on self-assembled nanostructured materials (i.e. mesoporous and nanoparticle based materials) and their catalytic applications. Since there are some reviews available for metal-based nanoparticles as catalysts, this review will mainly focus on self-assembled oxide-based catalytic materials. The content includes: (1) Design and synthetic strategy toward self-assembled mesoporous catalysts; (2) Polyoxometalates (POMs) based nanocatalysts; (3) Dendrimers based nanocatalysts; (4) Shaped nanomaterials and catalytic applications. We show that self-assemblies of molecules, crystalline seeds, nano-building blocks into organized mesoscopic structures paved new roads for tailoring porosities of heterogeneous catalysts and catalytic active sites.

Zhu, Kake; Wang, Donghai; Liu, Jun

2009-01-01

78

Self-assembling materials for therapeutic delivery?  

PubMed Central

A growing number of medications must be administered through parenteral delivery, i.e., intravenous, intramuscular, or subcutaneous injection, to ensure effectiveness of the therapeutic. For some therapeutics, the use of delivery vehicles in conjunction with this delivery mechanism can improve drug efficacy and patient compliance. Macromolecular self-assembly has been exploited recently to engineer materials for the encapsulation and controlled delivery of therapeutics. Self-assembled materials offer the advantages of conventional crosslinked materials normally used for release, but also provide the ability to tailor specific bulk material properties, such as release profiles, at the molecular level via monomer design. As a result, the design of materials from the “bottom up” approach has generated a variety of supramolecular devices for biomedical applications. This review provides an overview of self-assembling molecules, their resultant structures, and their use in therapeutic delivery. It highlights the current progress in the design of polymer- and peptide-based self-assembled materials.

Branco, Monica C.; Schneider, Joel P.

2009-01-01

79

Distributed agreement in tile self-assembly  

Microsoft Academic Search

Laboratory investigations have shown that a formal theory of fault-tolerance will be essential to harness nanoscale self-assembly\\u000a as a medium of computation. Several researchers have voiced an intuition that self-assembly phenomena are related to the field\\u000a of distributed computing. This paper formalizes some of that intuition. We construct tile assembly systems that are able to\\u000a simulate the solution of the

Aaron Sterling

2011-01-01

80

Distributed Agreement in Tile Self-Assembly  

Microsoft Academic Search

Laboratory investigations have shown that a formal theory of fault-tolerance will be essen- tial to harness nanoscale self-assembly as a medium of computation. Several researchers have voiced an intuition that self-assembly phenomena are related to the field of distributed computing. This paper formalizes some of that intuition. We construct tile assembly systems that are able to simulate the so- lution

Aaron Sterling

2009-01-01

81

Identifying Shapes Using Self-assembly  

Microsoft Academic Search

In this paper, we introduce the following problem in the theory of algorithmic self-assembly: given an input shape as the\\u000a seed of a tile-based self-assembly system, design a finite tile set that can, in some sense, uniquely identify whether or\\u000a not the given input shape—drawn from a very general class of shapes—matches a particular target shape. We first study the

Matthew J. Patitz; Scott M. Summers

82

From Solvolysis to Self-Assembly*  

PubMed Central

My sojourn from classical physical-organic chemistry and solvolysis to self-assembly and supramolecular chemistry, over the last forty years, is described. My contributions to unsaturated reactive intermediates, namely vinyl cations and unsaturated carbenes, along with my decade long involvement with polyvalent iodine chemistry, especially alkynyliodonium salts, as well as my more recent research with metal-ligand, coordination driven and directed self-assembly of finite supramolecular ensembles are discussed.

Stang, Peter J.

2009-01-01

83

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

84

Designing artificial photosynthetic devices using hybrid organic-inorganic modules based on polyoxometalates.  

PubMed

Artificial photosynthesis aims at capturing solar energy and using it to produce storable fuels. However, while there is reason to be optimistic that such approaches can deliver higher energy conversion efficiencies than natural photosynthetic systems, many serious challenges remain to be addressed. Perhaps chief among these is the issue of device stability. Almost all approaches to artificial photosynthesis employ easily oxidized organic molecules as light harvesters or in catalytic centres, frequently in solution with highly oxidizing species. The 'elephant in the room' in this regard is that oxidation of these organic moieties is likely to occur at least as rapidly as oxidation of water, meaning that current device performance is severely curtailed. Herein, we discuss one possible solution to this problem: using self-assembling organic-polyoxometalate hybrid structures to produce compartments inside which the individual component reactions of photosynthesis can occur without such a high incidence of deleterious side reactions. PMID:23816903

Symes, Mark D; Cogdell, Richard J; Cronin, Leroy

2013-07-01

85

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. WIREs Nanomed Nanobiotechnol 2013, 5:582-612. doi: 10.1002/wnan.1227 Conflict of interest: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website. PMID:23929805

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

2013-08-08

86

Self-assembly induced protein crystallization  

NASA Astrophysics Data System (ADS)

The strongly anisotropic nature of inter-protein interactions naturally leads them to self-assemble into structures mirroring the symmetry of the inter-protein potential. Self-assembly is a thermodynamically distinct phenomenon from phase separation, and we consider whether it can play a direct role in nucleating protein crystallization. Previous simulations and measurements have established that protein clusters formed below the critical point for liquid-liquid phase separation (Tc) can facilitate crystal nucleation. However, recent experiments have indicated the existence of clustering-induced protein nucleation even for T > Tc, where phase separation does not exist. Here we simulate a minimal model of patchy particles and indeed find that transient clusters formed through self-assembly (even above Tc) can nucleate crystal growth. Importantly, the self-assembled clusters help to select the symmetry of the resulting crystal growth. In contrast, protein crystallization for T < Tc does not have this directing influence, and polycrystalline growth forms, such as spherulites, are then prevalent. Our simulations suggest that self-assembly directed crystallization might be common in protein solutions and that this process is relevant for understanding protein crystallization polymorphism.

Liu, Hongjun; Kumar, Sanat; Douglas, Jack

2009-03-01

87

Light harvesting in hybrid epitaxial/colloidal nanostructures  

NASA Astrophysics Data System (ADS)

The performance of light harvesting devices is improved by utilising resonance energy transfer. A hybrid structure of colloidal quantum dots (QDs) and a quantum well (QW) p-i-n heterostructure is investigated. After highly absorbing QDs absorb photons, the excitations are efficiently transferred to a QW p-i-n heterostructure via resonance energy transfer. The generated electron-hole pairs in the heterostructure are subsequently separated by the built-in electric field and collected by the corresponding electrodes. In order to increase the energy transfer rate, the donor-acceptor separation distance is minimised by fabricating channel structures on the heterostructure surface penetrating its active layers. Consequently, a six-fold enhancement of photocurrent conversion efficiency is demonstrated. The proposed hybrid structures offer efficient light harvesting devices where high absorption of the colloidal QDs is utilised and their low charge transfer is overcome.

Lagoudakis, Pavlos G.; Chanyawadee, Soontorn

2009-08-01

88

Ultraviolet-B photodestruction of a light-harvesting complex.  

PubMed Central

Cyanobacteria are important contributors to global photosynthesis in both marine and terrestrial environments. Quantitative data are presented on UV-B-induced damage to the major cyanobacterial photosynthetic light harvesting complex, the phycobilisome, and to each of its constituent phycobiliproteins. The photodestruction quantum yield, phi295 nm, for the phycobiliproteins is high (approximately 10(-3), as compared with approximately 10(-7) for visible light). Energy transfer on a picosecond time scale does not compete with photodestruction. Photodamage to phycobilisomes in vitro and in living cells is amplified by causing dissociation and loss of function of the complex. In photosynthetic organisms, UV-B damage to light-harvesting complexes may significantly exceed that to DNA. Images Fig. 1

Lao, K; Glazer, A N

1996-01-01

89

Light harvesting in hybrid epitaxial\\/colloidal nanostructures  

Microsoft Academic Search

The performance of light harvesting devices is improved by utilising resonance energy transfer. A hybrid structure of colloidal quantum dots (QDs) and a quantum well (QW) p-i-n heterostructure is investigated. After highly absorbing QDs absorb photons, the excitations are efficiently transferred to a QW p-i-n heterostructure via resonance energy transfer. The generated electron-hole pairs in the heterostructure are subsequently separated

Pavlos G. Lagoudakis; Soontorn Chanyawadee

2009-01-01

90

Optical Spectroscopy of Individual Light-Harvesting Complexes  

Microsoft Academic Search

In this contribution we present an overview of the results of detailed spectroscopic investigations of individual light-harvesting\\u000a complexes of photosynthetic purple bacteria at 1.2 K. By applying single-molecule detection techniques the properties of the\\u000a electronically excited states of the assemblies of bacteriochlorophyll a (BChl a) pigment molecules in the individual complexes are revealed, without ensemble averaging. The results show that

Thijs J. Aartsma; Jürgen Köhler

91

Chlorophyll Binding to Monomeric Light-harvesting Complex  

Microsoft Academic Search

The chromophore binding properties of the higher plant light-harvesting complex II have been studied by site-directed mutagenesis of pigment-binding residues. Mutant apoproteins were overexpressed in Escherichia coli and then refolded in vitro with purified chro- mophores to yield holoproteins selectively affected in chlorophyll-binding sites. Biochemical and spectro- scopic characterization showed a specific loss of pig- ments and absorption spectral forms

Rosaria Remelli; Claudio Varotto; Dorianna Sandona; Roberta Croce; Roberto Bassi

1999-01-01

92

Theory of Programmable Hierarchic Self-Assembly  

NASA Astrophysics Data System (ADS)

We present a theoretical analysis of the inverse problem in self-assembly. A particular scheme is proposed for building an arbitrary desired nanostructure out of self-assembled building blocks (“octopus” nanoparticles). The conditions for robust self-assembly of the target structure are identified. This includes the minimal number of “colors” needed to encode interparticle bonds, which are to be implemented as pairs of complementary DNA sequences. As a part of this analysis, it is demonstrated that a floppy network with thermal fluctuations, in a certain range of coordination numbers ?Z?, possesses entropic rigidity and can be described as a traditional elastic solid. The onset of the entropic rigidity, ?Z?=d+1, determines the minimal number of bond types per particle needed to encode the desired structure. Thermodynamic considerations give additional conditions for the implementation of this scheme.

Tkachenko, Alexei V.

2011-06-01

93

Thermodynamics of Phospholipid Self-Assembly  

PubMed Central

Negatively charged phospholipids are an important component of biological membranes. The thermodynamic parameters governing self-assembly of anionic phospholipids are deduced here from isothermal titration calorimetry. Heats of demicellization were determined for dioctanoyl phosphatidylglycerol (PG) and phosphatidylserine (PS) at different ionic strengths, and for dioctanoyl phosphatidic acid at different pH values. The large heat capacity (?CoP ? ?400 J.mol?1 K?1 for PG and PS), and zero enthalpy at a characteristic temperature near the physiological range (T? ? 300 K for PG and PS), demonstrate that the driving force for self-assembly is the hydrophobic effect. The pH and ionic-strength dependences indicate that the principal electrostatic contribution to self-assembly comes from the entropy associated with the electrostatic double layer, in agreement with theoretical predictions. These measurements help define the thermodynamic effects of anionic lipids on biomembrane stability.

Marsh, Derek

2012-01-01

94

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

95

S-layer protein self-assembly.  

PubMed

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. PMID:23354479

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

2013-01-25

96

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

97

Separating annihilation and excitation energy transfer dynamics in light harvesting systems.  

PubMed

The dependence of excitation energy transfer kinetics on the electronic state of the acceptor (ground vs excited) has been resolved with a novel multipulse prePump-Pump-Probe spectroscopy. The primary energy transfer and annihilation dynamics in two model light-harvesting systems were explored: an artificially synthesized carotenoid-zinc-phthalocyanine dyad and a naturally occurring light-harvesting peridinin-chlorophyll protein complex from Amphidinium carterae. Both systems use carotenoid as the primary excitation energy donor with porphyrin chromophores as the acceptor molecules. The prePump-Pump-Probe transient signals were analyzed with Monte Carlo modeling to explicitly address the underlying step-by-step kinetics involved in both excitation migration and annihilation processes. Both energy transfer and annihilation dynamics were demonstrated to occur with approximately the same rate in both systems, regardless of the excitation status of the acceptor pigments. The possible reasons for these observations are discussed in the framework of the Förster energy transfer model. PMID:23662680

Vengris, Mikas; Larsen, Delmar S; Valkunas, Leonas; Kodis, Gerdenis; Herrero, Christian; Gust, Devens; Moore, Thomas; Moore, Ana; van Grondelle, Rienk

2013-05-28

98

Noise-assisted energy transfer in quantum networks and light-harvesting complexes  

NASA Astrophysics Data System (ADS)

We provide physically intuitive mechanisms for the effect of noise on excitation energy transfer (EET) in networks. Using these mechanisms of dephasing-assisted transport (DAT) in a hybrid basis of both excitons and sites, we develop a detailed picture of how noise enables energy transfer with efficiencies well above 90% across the Fenna-Matthew-Olson (FMO) complex, a type of light-harvesting molecule. We demonstrate explicitly how noise alters the pathways of energy transfer across the complex, suppressing ineffective pathways and facilitating direct ones to the reaction centre. We explain that the fundamental mechanisms underpinning DAT are expected to be robust with respect to the considered noise model but show that the specific details of the exciton-phonon coupling, which remain largely unknown in these type of complexes, and in particular the impact of non-Markovian effects, result in variations of dynamical features that should be amenable to experimental verification with current or planned technology. A detailed understanding of DAT in natural compounds could open up a new paradigm of 'noise-engineering' by which EET can be optimized in artificial light-harvesting structures.

Chin, A. W.; Datta, A.; Caruso, F.; Huelga, S. F.; Plenio, M. B.

2010-06-01

99

Self-Assembly-Induced Protein Crystallization  

NASA Astrophysics Data System (ADS)

Previous work has established that protein clusters formed inside the liquid-liquid coexistence envelope can facilitate crystal nucleation. However, recent experiments have indicated the existence of clustering-induced protein nucleation even “outside” this phase boundary. Here we simulate a minimal model of patchy particles, which are more representative of anisotropic interprotein interactions, and find that transient clusters formed through self-assembly can nucleate crystal growth even under conditions where a dense protein liquid is thermodynamically unstable. The patchy nature of protein interactions thus greatly facilitates their self-assembly, which then “guides” the subsequent crystal morphology.

Liu, Hongjun; Kumar, Sanat K.; Douglas, Jack F.

2009-07-01

100

Electrostatically self-assembled nanocomposite reactive microspheres.  

PubMed

Nanocomposite reactive microspheres with diameters of approximately 1-5 mum were created via electrostatic self-assembly of aluminum and cupric oxide nanoparticles. The ability to utilize this novel approach of bottom-up assembly to create these reactive materials allows for the potential for a more intimate mixture between the two nanoreactants and, thus, an overall more energetic combustion process. Experiments with the self-assembled material demonstrate the ability to achieve ignition and sustain a combustion wave in rectangular microchannels, which does not occur with material having similar amounts of organics mixed via the traditional sonication method. PMID:20356109

Malchi, Jonathan Y; Foley, Timothy J; Yetter, Richard A

2009-11-01

101

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

102

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

103

Inverse Problem in Self-assembly  

NASA Astrophysics Data System (ADS)

By decorating colloids and nanoparticles with DNA, one can introduce highly selective key-lock interactions between them. This leads to a new class of systems and problems in soft condensed matter physics. In particular, this opens a possibility to solve inverse problem in self-assembly: how to build an arbitrary desired structure with the bottom-up approach? I will present a theoretical and computational analysis of the hierarchical strategy in attacking this problem. It involves self-assembly of particular building blocks (``octopus particles''), that in turn would assemble into the target structure. On a conceptual level, our approach combines elements of three different brands of programmable self assembly: DNA nanotechnology, nanoparticle-DNA assemblies and patchy colloids. I will discuss the general design principles, theoretical and practical limitations of this approach, and illustrate them with our simulation results. Our crucial result is that not only it is possible to design a system that has a given nanostructure as a ground state, but one can also program and optimize the kinetic pathway for its self-assembly.

Tkachenko, Alexei

2012-02-01

104

Self-assembled microdevices driven by muscle  

Microsoft Academic Search

Current procedures for manual extraction of mature muscle tissue in micromechanical structures are time consuming and can damage the living components. To overcome these limitations, we have devised a new system for assembling muscle-powered microdevices based on judicious manipulations of materials phases and interfaces. In this system, individual cells grow and self-assemble into muscle bundles that are integrated with micromechanical

Jianzhong Xi; Jacob J. Schmidt; Carlo D. Montemagno

2005-01-01

105

Directed Self-Assembly Using Graph Grammars  

Microsoft Academic Search

In this paper we describe the graph grammar approach to modeling self-assembly. The approach is used to describe how the topol- ogy of an assembling aggregate changes as it grows. The main purpose of the paper is to demonstrate the utility of the approach by giving detailed examples. We also describe the beginnings of our approach to physically embedding graph

Eric Klavins

2004-01-01

106

Incremental Self Assembly in the Fluid Limit  

Microsoft Academic Search

Self assembly (SA) processes are fundamental to a number of computational and fabrication technologies in nanoscience. Indeed, their e-ciency and robustness are crit- ical to the success of the underlying concepts. SA typically involves random phenomena at some level, yet the development of reference theories for the study of random SA pro- cesses is scarcely begun. This paper studies a

Yuliy Baryshnikov; Petar Momcilovic

107

Large branched self-assembled DNA complexes  

NASA Astrophysics Data System (ADS)

Many biological molecules have been demonstrated to self-assemble into complex structures and networks by using their very efficient and selective molecular recognition processes. The use of biological molecules as scaffolds for the construction of functional devices by self-assembling nanoscale complexes onto the scaffolds has recently attracted significant attention and many different applications in this field have emerged. In particular DNA, owing to its inherent sophisticated self-organization and molecular recognition properties, has served widely as a scaffold for various nanotechnological self-assembly applications, with metallic and semiconducting nanoparticles, proteins, macromolecular complexes, inter alia, being assembled onto designed DNA scaffolds. Such scaffolds may typically contain multiple branch-points and comprise a number of DNA molecules selfassembled into the desired configuration. Previously, several studies have used synthetic methods to produce the constituent DNA of the scaffolds, but this typically constrains the size of the complexes. For applications that require larger self-assembling DNA complexes, several tens of nanometers or more, other techniques need to be employed. In this article, we discuss a generic technique to generate large branched DNA macromolecular complexes.

Tosch, Paul; Wälti, Christoph; Middelberg, Anton P. J.; Davies, A. Giles

2007-04-01

108

Self-Assembly at the Macroscopic Scale  

Microsoft Academic Search

In this paper, we review half a century of research on the design of systems displaying (physical) self-assembly of macroscopic components. We report on the experience gained in the design of 21 such systems, exhibiting components ranging from passive mechanical parts to mobile robots. We present a taxonomy of the systems and discuss design principles and functions. Finally, we summarize

R. Gross; M. Dorigo

2008-01-01

109

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

110

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

111

Multifunctional Materials Based on Self Assembly of Molecular Nanostructures.  

National Technical Information Service (NTIS)

In this program we developed an important class of multifunctional and self assembling materials based on the use of triblock molecular structures that had both luminescent chromophores and dipole moments. The objective was to integrate self assembly, enc...

S. I. Stupp

2001-01-01

112

Enhanced photovoltaic efficiency via light-triggered self-assembly.  

PubMed

Light-initiated, radical and hydrogen-bond induced self-assembly of bis-acetamido-functionalized triarylamines is demonstrated to occur in strongly dipolar "push-pull" molecules. This self-assembly process results in the formation of self-assembled nanostructures which in turn increase the efficiency of organic photovoltaic devices. PMID:23770756

Kumar, Rohan J; Churches, Quentin I; Subbiah, Jegadesan; Gupta, Akhil; Ali, Abdelsalem; Evans, Richard A; Holmes, Andrew B

2013-06-14

113

Self-assembling membranes and related methods thereof  

DOEpatents

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

114

Self-assembly approaches to photonic structures  

NASA Astrophysics Data System (ADS)

Self-assembly of spherical colloids has been demonstrated as a simple and effective strategy for fabricating a variety of photonic structures that include photonic crystals, arrayed microlenses, and waveguides. Unlike the top-down fabrication techniques, self-assembly approaches can produce functional structures under ambient conditions of pressure and temperature without the need for costly instruments. A confined self-assembly approach was developed to organize spherical colloids into highly ordered three-dimensional photonic crystals. Such colloidal photonic crystals can block the propagation of photons for a range of wavelengths along specific directions. The capability of this method has been demonstrated with monodispersed spherical colloids of various materials and a range of dimensions. The orientation of the crystals can be controlled by assembling the colloids against two-dimensional arrays of templates patterned in the surfaces of substrates. The colloidal crystals were further explored to fabricate inverse opals with complementary structures. Photonic bandgap properties of these crystals have been characterized by measuring their transmission and reflectance spectra. Self-assembly of nonspherical building blocks may lead to the formation of photonic crystals that can prohibit a band of optical frequencies in all directions of propagation. As the first step along this direction, a general approach based on physical confinement and attractive capillary force has been developed to produce nonspherical building blocks with well-defined structures and dimensions. Complex aggregates such as polygonal and polyhedral clusters, zigzag or helical chains have been fabricated using monodispersed polymer or silica colloids. Arrayed microlenses were fabricated by self-assembling monodispersed polymer colloids in two-dimensional arrays of cylindrical holes patterned on substrates. The spherical colloids were subsequently transformed into mushroom-shaped and then hemispherical microlenses by annealing the samples at elevated temperatures. The optical parameters of these microlenses could be precisely controlled by changing the annealing time. The minimization of waveguiding structures would allow the fabrication of highly integrated lightwave circuits. A number of methods have been developed based on the self-assembly approaches, including coupled resonator optical waveguide constructed from arrays of plain colloids, plasmon waveguide built from arrays of gold@silica core-shell colloids, and photonic crystal waveguide generated by introducing line defects into a photonic crystal.

Yin, Yadong

115

Self-assembly between biomacromolecules and lipids  

NASA Astrophysics Data System (ADS)

Anionic DNA and cationic lipsomes can self-assemble into a multi-lamellar structure where two-dimensional (2-D) lipid sheets confine a periodic one-dimensional (1-D) lattice of parallel DNA chains, between which Cd2+ ions can condense, and be subsequently reacted with H 2S to template CdS nanorods with crystallographic control analogous to biomineralization. The strong electrostatic interactions align the templated CdS (002) polar planes parallel to the negatively charged sugar-phosphate DNA backbone, which indicates that molecular details of the DNA molecule are imprinted onto the inorganic crystal structure. The resultant nanorods have (002) planes tilted by ˜60° with respect to the rod axis, in contrast to all known II-VI semiconductor nanorods. Rational design of the biopolymer-membrane templates is possible, as demonstrated by the self-assembly between anionic M13 virus and cationic membrane. The filamentous virus has diameter ˜3x larger but similar surface charge density as DNA, the self-assembled complexes maintain the multi-lamellar structure, but pore sizes are ˜10x larger in area, which can be used to package and organize large functional molecules. Not only the counter-charged objects can self-assemble, the like-charged biopolymer and membrane can also self-assemble with the help of multivalent ions. We have investigated anionic lipid-DNA complexes induced by a range of divalent ions to show how different ion-mediated interactions are expressed in the self-assembled structures, which include two distinct lamellar phases and an inverted hexagonal phase. DNA can be selectively organized into or expelled out of the lamellar phases depending on membrane charge density and counterion concentration. For a subset of ion (Zn2+ etc.) at high enough concentration, 2-D inverted hexagonal phase can be formed where DNA strands are coated with anionic lipid tubes via interaction with Zn2+ ions. We suggest that the effect of ion binding on lipid's spontaneous curvature is sufficient to explain the lamellar to inverted hexagonal transition. Finally, we studied the interaction of anionic DNA with zwitterionic lipids at the presence of multivalent ions. Polymorphism of phases was found depending on lipid's intrinsic curvature. The anionic lipid-DNA and zwitterionic lipid-DNA complexes are currently emerged as new types of gene delivery systems with low cytotoxicity.

Liang, Hongjun

116

Architecture and function of plant light-harvesting complexes II.  

PubMed

The antenna system associated with plant photosystem II (PSII) comprises a series of light-harvesting complexes II (LHCIIs) which are supramolecular assemblies of chlorophylls, carotenoids, lipids and integral membrane proteins. These complexes not only function in capturing and transmitting light energy, but also have pivotal roles in photoprotection under high-light conditions through a mechanism known as non-photochemical quenching process. Among them, the most abundant major species (majLHCII) is located at the periphery of PSII and forms homo/hetero-trimers. Besides, three minor species, named CP29, CP26 and CP24, are adjacent to the PSII core, exist in monomeric form and bridge the majLHCII trimers with the core complex. Structural studies on majLHCII and CP29 have revealed the overall architecture of plant LHC family, the binding sites of pigment molecules and the distribution pattern of chromophores in three-dimensional space. The high-resolution structural data of LHCIIs serve as fundamental bases for an improved understanding on the mechanisms of light harvesting, energy transfer and photoprotection processes in plants. PMID:23623335

Pan, Xiaowei; Liu, Zhenfeng; Li, Mei; Chang, Wenrui

2013-04-26

117

Polyelectrolytes with Azobenzene for Self-Assembled Smart Materials  

NASA Astrophysics Data System (ADS)

Electrostatic self-assembly of polyelectrolytes containing photoswitchable azo chromophores into multilayers from aqueous solutions is a promising method for the fabrication of thin films containing desired ``smart'' functionalities and/or sensing material. Using various reflection methods (Ellipsometry, SPR, Neutron) and an atomic force microscope (AFM) for force measurements, we show here how the structural, mechanical, and optical properties can depend on the ionization fraction of the assembling polymers. By controlling such film properties as layer thickness, density, kinetics of assembly, adhesion, and elastic response, we are able to custom-design polymer films with a desired architecture and mechanical response. Applications demonstrated will include a light-induced mechanical response for actuation as artificial muscles, and mass transport of the polymers on a Si surface for nanopatterning and holographic information storage.

Barrett, Christopher; Yager, Kevin

2005-03-01

118

Toward minimum size self-assembled counters  

Microsoft Academic Search

DNA self-assembly is a promising paradigm for nanotechnology. In this paper we study the problem of finding tile systems of\\u000a minimum size that assemble a given shape in the Tile Assembly Model, defined by Rothemund and Winfree (Proceedings of the\\u000a thirty-second annual ACM symposium on theory of computing, 2000). We present a tile system that assembles an $$N\\\\times\\\\lceil\\\\log_2 N\\\\rceil$$ rectangle

Pablo Moisset De Espanés; Ashish Goel

2008-01-01

119

Triangular Tile Self-assembly Systems  

Microsoft Academic Search

\\u000a We discuss theoretical aspects of the self-assembly of triangular tiles; in particular, right triangular tiles and equilateral\\u000a triangular tiles. Contrary to intuition, we show that triangular tile assembly systems and square tile assembly systems are\\u000a not comparable in general. More precisely, there exists a square tile assembly system S such that no triangular tile assembly system that is a division

Lila Kari; Shinnosuke Seki; Zhi Xu

2010-01-01

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.\\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

121

Formal Verification of Self-Assembling Systems  

Microsoft Academic Search

This paper introduces the theory and practice of formal verification of\\u000aself-assembling systems. We interpret a well-studied abstraction of\\u000ananomolecular self assembly, the Abstract Tile Assembly Model (aTAM), into\\u000aComputation Tree Logic (CTL), a temporal logic often used in model checking. We\\u000athen consider the class of \\

Aaron Sterling

2010-01-01

122

Cage molecules for self-assembly  

Microsoft Academic Search

Self-assembled monolayers using functionalized cage molecules offer distinct advantages because of their symmetry, lack of conformational flexibility, and well-defined chemistries. While these systems have not yet been studied to the extent that linear alkanethiols on Au{111} have been, early explorations indicate great promise and important differences. For simple cage molecules that bind upright on the substrate, tilt domain boundaries found

J. Nathan Hohman; Shelley A. Claridge; Moonhee Kim; Paul S. Weiss

2010-01-01

123

Anisotropic Self-Assembly of Nanoparticle Amphiphiles  

NASA Astrophysics Data System (ADS)

It is easy to understand the self-assembly of particles having anisotropic shapes or interactions, such as Co nanoparticles or proteins, into highly extended structures. However, there is no experimentally established strategy for creating anisotropic structures from common spherical nanoparticles. We demonstrate that spherical nanoparticles, uniformly grafted with macromolecules, robustly self-assemble into a range of anisotropic superstructures when they are dispersed in the corresponding homopolymer matrix. This phenomenon is driven by the microphase separation between the inorganic nanoparticles and the (organic) polymeric chains grafted to their surfaces in a fashion similar to block copolymers. This microphase separation driven particle self-assembly provides a unique means of controlling the global nanoparticle dispersion state in polymer nanocomposites. The relationship between the state of particle dispersion and nanocomposite properties can thus be critically examined, and in particular we focus on the mechanical reinforcement afforded when particles are added to polymers. Grafted nanoparticles are thus versatile building blocks for creating tunable and functional particle superstructures with significant practical applications. With Pinar Akcora, Hongjun Liu, Yu Li, Brian Benicewicz, Linda Schadler, Thanos Panagiotopoulos, Jack Douglas, P. Thiyagarajan and Ralph Colby.

Kumar, Sanat

2009-03-01

124

Engineered Self-Assembly of Plasmonic Nanomaterials  

NASA Astrophysics Data System (ADS)

A critical need in nanotechnology is the development of new tools and methods to organize, connect, and integrate solid-state nanocomponents. Self-assembly -- where components spontaneously organize themselves -- can be carried out on a massively parallel scale to construct large-scale architectures using solid-state nanocrystal building blocks. I will present our recent work on the synthesis and self-assembly of nanocrystals for plasmonics, where light is propagated, manipulated, and confined by solid-state components that are smaller than the wavelength of light itself. We show the organization of polymer-grafted metal nanocrystals into hierarchical nanojunction arrays that possess intense ``hot spots'' due to electromagnetic field localization. We also show that doped semiconductor nanocrystals can serve as a new class of plasmonic building blocks, where shape and carrier density can be actively tuned to engineer plasmon resonances. These examples demonstrate that nanocrystals possess unique electromagnetic properties that rival top-down structures, and the potential of self-assembly for fabricating designer plasmonic materials.

Tao, Andrea

2013-03-01

125

Self-assembly of methyl zinc (3{sup 1}R)- and (3{sup 1}S)-bacteriopheophorbides d  

SciTech Connect

The methyl zinc (3{sup 1}R)- and (3{sup 1}S)-[8Et, 12Me] bacteriopheophorbides d - analogs of the light-harvesting bacteriochlorophylls in photosynthetic bacteria - self-assemble in nonpolar solvents. While in dilute dichloromethane solution both epimers prevail in their monomeric form, complex equilibria of aggregates with gradually red-shifting Q{sub y} absorptions are formed at either higher concentration or lower temperature or upon dilution with hexane. Dynamic {sup 1}H-NMR and FT-IR spectroscopies show that the 3{sup 1}-hydroxy group participates directly in the self-assembly through oxygen ligation to zinc and through hydrogen bridging to the 13{sup 1}-keto group of the ligated hydroxyls in intermediate unsymmetrical dimers. The basic unit, combining three molecules through >C=O...H-O...Zn bonding, and the existence of equilibria between monomers, dimers, and oligomers of varying size depending on the conditions parallel the scheme proposed previously for bacteriochlorophylls c and d. In some respects the CD, {sup 1}H-NMR, and IR spectral behavior of the two epimers indicates diastereoselective conformational and kinetic differences at the levels of dimers and larger oligomers. Inter alia, the self-assembly of a 1:1 mixture of the (3{sup 1}R) and (3{sup 1}S) epimers proceeds more rapidly than that of the separate epimers. 29 refs., 11 figs.

Balaban, T.S.; Holzwarth, A.R.; Schaffner, K. [Max-Planck-Institut fuer Strahlenchemie, Muelheim an der Ruhr (Germany); Tamiaki, Hitoshi [Ritsumeikan Univ., Shiga (Japan)

1997-04-24

126

Self-Assembly of Photosynthetic Membranes  

PubMed Central

Bacterial photosynthetic membranes, also known as chromatophores, are tightly packed with integral membrane proteins that work together to carry out photosynthesis. Chromatophores display a wide range of cellular morphologies; spherical, tubular, and lamellar chromatophores have all been observed in different bacterial species, or with different protein constituents. Through recent computational modeling and simulation, it has been demonstrated that the light-harvesting complexes abundant in chromatophores induce local membrane curvatures via multiple mechanisms. These protein complexes assemble to generate a global curvature and sculpt the chromatophores into various cellular-scale architectures.

Hsin, Jen; Chandler, Danielle E.; Gumbart, James; Harrison, Christopher B.; Sener, Melih; Strumpfer, Johan; Schulten, Klaus

2011-01-01

127

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

128

Self-assembly of ordered nanostructures  

NASA Astrophysics Data System (ADS)

Several different kinds of nanostructure materials were studied in this thesis: self-assembled monodispersive nanocrystals, photonic crystals, ordered mesoporous silica and hierarchically ordered nanostructured materials. Tetrahedral nanocrystals of CoO, with edge-lengths of 4.4 +/- 0.2 nm, were synthesized at high purity and monodispersity. The size, shape and phase selections of the nanocrystals were performed using a novel magnetic field separation technique. These nanocrystals behave like molecules, forming a face-centered cubic self-assembly of nanocrystal superlattices. In-situ behavior of self-assembled CoO nanocrystal arrays was also analyzed using transmission electron microscopy and associated techniques. The surface passivation layer started to evaporate/decompose at temperatures as low as ˜200°C, but the exposed cores of nanocrystals preserved the geometrical configuration of the assembly due to the strong adhesion of the carbon substrate. As the temperature is further increased from 300 to 600°C, the intrinsic crystal structure of the CoO nanoparticles experiences a replacement reaction, resulting in the formation of cobalt carbides. Two-dimensional self-assembling of cobalt nanocrystals with an average particle size of 9.2 nm and polydispersity of 9% is processed. Phtonic crystals were processed by a template-assisted method. Ordered self-assembly of pores of titania nanocrystals formed a face-centered cubic packing structure. The walls of the pores were made of anatase nanocrystals of ˜8 nm in diameter. Cobalt can be doped into the walls of the pores by solution infiltration of cobalt carbonyl. Cobalt titanium oxide may be formed on the internal surface of the ordered pore structure. This type of structure is likely to be an excellent supporting material for catalysis. The experimental results suggest that transition metal elements can be incorporated into porous titania without blocking the interconnected pores. Hierarchically ordered nanostructured materials with high porosity at dual length-scale were prepared by a single annealing procedure. The plasma energy of this porous materials shifts about 1.2 eV to lower energy, compared to the fully densed silica spheres. This type of material is expected to have not only large surface area for catalysis, but also low dielectric constant for low-loss dielectric applications.

Yin, Jinsong

2000-10-01

129

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

130

Designing dye-nanochannel antenna hybrid materials for light harvesting, transport and trapping.  

PubMed

We discuss artificial photonic antenna systems that are built by incorporating chromophores into one-dimensional nanochannel materials and by organizing the latter in specific ways. Zeolite L (ZL) is an excellent host for the supramolecular organization of different kinds of molecules and complexes. The range of possibilities for filling its one-dimensional channels with suitable guests has been shown to be much larger than one might expect. Geometrical constraints imposed by the host structure lead to supramolecular organization of the guests in the channels. The arrangement of dyes inside the ZL channels is what we call the first stage of organization. It allows light harvesting within the volume of a dye-loaded ZL crystal and also the radiationless transport of energy to either the channel ends or center. One-dimensional FRET transport can be realized in these guest-host materials. The second stage of organization is realized by coupling either an external acceptor or donor stopcock fluorophore at the ends of the ZL channels, which can then trap or inject electronic excitation energy. The third stage of organization is obtained by interfacing the material to an external device via a stopcock intermediate. A possibility to achieve higher levels of organization is by controlled assembly of the host into ordered structures and preparation of monodirectional materials. The usually strong light scattering of ZL can be suppressed by refractive-index matching and avoidance of microphase separation in hybrid polymer/dye-ZL materials. The concepts are illustrated and discussed in detail on a bidirectional dye antenna system. Experimental results of two materials with a donor-to-acceptor ratio of 33:1 and 52:1, respectively, and a three-dye system illustrate the validity and challenges of this approach for synthesizing dye-nanochannel hybrid materials for light harvesting, transport, and trapping. PMID:21337487

Calzaferri, Gion; Méallet-Renault, Rachel; Brühwiler, Dominik; Pansu, Robert; Dolamic, Igor; Dienel, Thomas; Adler, Pauline; Li, Huanrong; Kunzmann, Andreas

2011-02-17

131

Phycobilisome: architecture of a light-harvesting supercomplex.  

PubMed

The phycobilisome (PBS) is an extra-membrane supramolecular complex composed of many chromophore (bilin)-binding proteins (phycobiliproteins) and linker proteins, which generally are colorless. PBS collects light energy of a wide range of wavelengths, funnels it to the central core, and then transfers it to photosystems. Although phycobiliproteins are evolutionarily related to each other, the binding of different bilin pigments ensures the ability to collect energy over a wide range of wavelengths. Spatial arrangement and functional tuning of the different phycobiliproteins, which are mediated primarily by linker proteins, yield PBS that is efficient and versatile light-harvesting systems. In this review, we discuss the functional and spatial tuning of phycobiliproteins with a focus on linker proteins. PMID:24081814

Watanabe, Mai; Ikeuchi, Masahiko

2013-10-01

132

Broadband Light Harvesting Nanostructures Robust to Edge Bluntness  

NASA Astrophysics Data System (ADS)

Metallic structures with sharp corners harvest the energy of incident light through plasmonic resonances, concentrating it in the corners and greatly increasing the local energy density. Despite its wide array of applications, this effect is normally strongly dependent on how sharp the corners are, presenting problems for fabrication. In this Letter, an analytical approach is proposed, based on transformation optics, to investigate a general class of plasmonic nanostructures with blunt edges or corners. Comprehensive discussions are provided on how the geometry affects the local field enhancement as well as the frequency and energy of each plasmonic resonance. Remarkably, our results evidence the possibility of designing broadband light harvesting devices with an absorption property insensitive to the geometry bluntness.

Luo, Yu; Lei, Dang Yuan; Maier, Stefan A.; Pendry, J. B.

2012-01-01

133

Excitation-emission polarization spectroscopy of single light harvesting complexes.  

PubMed

Excitation and emission polarization dependence of fluorescence intensity of single LH2 complexes from Rhodopseudomonas acidophila 10050 and Rhodobacter sphaeroides is reported. The results are presented as two-dimensional polarization plots and interpreted in terms of tilted light harvesting complexes indicating that sample preparation leads to partially oriented LH2 cylinders. An alternative explanation of the observation can be structural deformation. Fluorescence intensity of the complexes has four qualitatively distinct excitation-emission polarization dependencies. The differences in excitation polarization dependence are interpreted as due to the tilt of the complexes, whereas the emission polarization behavior is mainly determined by spectral inhomogeneity of the emitting B850 ring. Some complexes show abrupt reversible variations of the total emission intensity together with changes of the polarization properties which cannot be described by the simplest model of tilted LH2s with spectral disorder. PMID:21486039

Tubasum, Sumera; Cogdell, Richard J; Scheblykin, Ivan G; Pullerits, Tõnu

2011-04-12

134

Dimerization-assisted energy transport in light-harvesting complexes  

NASA Astrophysics Data System (ADS)

We study the role of the dimer structure of light-harvesting complex II (LH2) in excitation transfer from the LH2 [without a reaction center (RC)] to the LH1 (surrounding the RC) or from the LH2 to another LH2. The excited and unexcited states of a bacteriochlorophyll (BChl) are modeled by a quasispin. In the framework of quantum open system theory, we represent the excitation transfer as the total leakage of the LH2 system and then calculate the transfer efficiency and average transfer time. For different initial states with various quantum superposition properties, we study how the dimerization of the B850 BChl ring can enhance the transfer efficiency and shorten the average transfer time.

Yang, S.; Xu, D. Z.; Song, Z.; Sun, C. P.

2010-06-01

135

Potential of light-harvesting proton pumps for bioenergy applications.  

PubMed

Concerns about the security and longevity of traditional energy sources have increased interest in alternative methods of energy production, particularly those which utilize abundantly available solar energy. Solar energy can be harvested either indirectly through the conversion of plant or algal byproducts into biofuels or directly using engineered microorganisms. Here we summarize the main features of light-harvesting proton pumps, which may provide a relatively simple way to boost the efficiency of energy-limited biological processes in fuel production. This family of proton pumps, which includes bacteriorhodopsin and proteorhodopsin, directly uses light energy to create a proton motive force (pmf) which can be used by other enzymes to facilitate active transport, regulate transmembrane proteins, or to generate ATP and NADH. PMID:20371172

Walter, Jessica M; Greenfield, Derek; Liphardt, Jan

2010-04-06

136

Self-assembled biomimetic antireflection coatings  

NASA Astrophysics Data System (ADS)

The authors report a simple self-assembly technique for fabricating antireflection coatings that mimic antireflective moth eyes. Wafer-scale, nonclose-packed colloidal crystals with remarkable large hexagonal domains are created by a spin-coating technology. The resulting polymer-embedded colloidal crystals exhibit highly ordered surface modulation and can be used directly as templates to cast poly(dimethylsiloxane) (PDMS) molds. Moth-eye antireflection coatings with adjustable reflectivity can then be molded against the PDMS master. The specular reflection of replicated nipple arrays matches the theoretical prediction using a thin-film multilayer model. These biomimetic films may find important technological application in optical coatings and solar cells.

Linn, Nicholas C.; Sun, Chih-Hung; Jiang, Peng; Jiang, Bin

2007-09-01

137

Rheology of Self-Assembling Colloidal Chains  

NASA Astrophysics Data System (ADS)

We probe the rheology of self-assembling chains of ``pacman'' particles using a Zimm viscometer, a modified Couette apparatus. Pacman particles are microscopic spherical particles specially designed to have a spherical indentation on their surface. In the presence of a depletant, overlap between the indentation and another particle's surface maximizes the excluded volume between the two interacting particles, resulting in a selective attraction between them. Careful tuning of the interaction strength in a suspension of particles induces the formation of long chains. Shearing this material can twist, stretch, and break the chains, causing the material to exhibit unique rheological properties.

Edmond, Kazem V.; Sacanna, Stefano; Forbes, Zachary D.; Hollingsworth, Andrew D.; Pine, David J.

2013-03-01

138

Self-assembly of colloidal surfactants  

NASA Astrophysics Data System (ADS)

We developed colloidal dumbbells with a rough and a smooth part, based on a method reported in Ref. [1]. Specific attraction between the smooth parts occurs upon addition of non-adsorbing polymers of appropriate size. We present the first results in terms of the assemblies that emerge in these systems. [4pt] [1] D.J. Kraft, W.S. Vlug, C.M. van Kats, A. van Blaaderen, A. Imhof and W.K. Kegel, Self-assembly of colloids with liquid protrusions, J. Am. Chem. Soc. 131, 1182, (2009)

Kegel, Willem

2012-02-01

139

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

140

Self-assembled BLMs: biomembrane models and biosensor applications  

Microsoft Academic Search

In the last few years, there have been a number of research papers on self-assemblies of molecules as ‘advanced’ or ‘smart’ materials. The inspiration for this exciting research, without question, comes from the biological world, where, for example, the lipid bilayer of the cell membrane is the most important self-assembling system. Although the first report on self-assembled bilayer lipid membranes

A. Ottova; V. Tvarozek; J. Racek; J. Sabo; W. Ziegler; T. Hianik; H. T. Tien

1997-01-01

141

Complexities for Generalized Models of Self-Assembly  

Microsoft Academic Search

In this paper, we study the complexity of self-assembly under models that are natural generalizations of the tile self-assembly model. In particular, we extend Rothemund and Winfree's study of the tile complexity of tile self-assembly (Proceedings of the 32nd Annual ACM Symposium on Theory of Computing, Portland, OR, 2000, pp. 459-468). They provided a lower bound of ?( log N

Gagan Aggarwal; Qi Cheng; Michael H. Goldwasser; Ming-yang Kao; Pablo Moisset De Espanés; Robert T. Schweller

2005-01-01

142

Programmable Control of Nucleation for Algorithmic Self-assembly  

Microsoft Academic Search

Abstract. Algorithmic self-assembly has been proposed as a mecha-nism for autonomous DNA computation and for bottom-up fabrication of complex nanodevices. Whereas much previous work has investigated self-assembly programs using an abstract model of irreversible, errorless assembly, experimental studies as well as more sophisticated reversible kinetic models indicate that algorithmic self-assembly is subject to sev-eral kinds of errors. Previously, it was

Rebecca Schulman; Erik Winfree

2004-01-01

143

A case of adaptive self-assembly.  

PubMed

We report in this paper direct observation of redox-induced uptake of a charged species in micelles with a complex coacervate core, using a system consisting of negatively charged iron-coordination polymers and positively charged-b-neutral block co-polyelectrolytes. Neutral, charge-balanced micelles are first prepared by stoichiometric mixing of the oppositely charged components. Upon a redox stimulus, the micelles develop excess charges, which (as proposed in our previous work) most likely lead to sequestration of oppositely charged species, as the charge balance has to be restored. In this work we verify this prediction by using a rigid, rod-like iron coordination polymer, namely, the positively charged MEPE, as the species to be taken up. After uptake of this rigid cargo, the morphology of the micelles was found to transform from spheres to banana-shaped bundles and fibers, which clearly indicate the uptake of MEPE in the micellar core. Our result proves that the redox stimulus indeed induces excess charges in the core, which forces the self-assembled particles to change both composition and shape. As an interesting example of "adaptive self-assembly", our findings also pave the way to novel redox-triggered uptake and release systems. PMID:22208815

Ding, Yi; Yang, Yang; Yang, Lu; Yan, Yun; Huang, Jianbin; Cohen Stuart, Martien A

2012-01-12

144

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.

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

Spontaneous propagation of self-assembly in a continuous medium  

NASA Astrophysics Data System (ADS)

We report a mechanism in which self-assembly propagates spontaneously in a continuous medium, enabling the delivery of local order information to distance. In a large stable system a locally self-assembled structure as a precursor destabilizes its surrounding areas through a dipole interaction. The newly formed structures inherit the same order information from the precursor and further activate the self-assembly of their neighbors. This process causes spatial extension of self-assembly and replication of the order, producing extremely long-range ordered superlattice without defects.

Zhao, Zhouzhou; Lu, Wei

2012-04-01

148

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

149

Light-harvesting processes in the dynamic photosynthetic antenna.  

PubMed

We present our perspective on the theoretical basis of light-harvesting within the photosynthetic membrane. Far from being a static structure, the photosynthetic membrane is a highly dynamic system, with protein mobility playing an important role in the damage/repair cycle of photosystem II (PSII), in balancing the input of energy between PSI and PSII, and in the photoprotection of PSII in response to a sudden excess of illumination. The concept of a photosynthetic antenna is illustrated and the state transition phenomenon is discussed as an example of purposeful antenna mobility. We discuss fluorescence recovery after photo-bleaching as a technique for visualising membrane mobility, before introducing light-induced grana membrane reorganisation as an integral part of the rapid photoprotective switch in plants. We then discuss current theoretical approaches to modelling the energy transfer dynamics of the PSII antenna: the atomistic models of intra-complex transfer and the coarse-grained approach to the inter-complex dynamics. Finally we discuss the future prospect of extending these methods, beyond the static picture of the membrane, to the dynamic PSII photosynthetic antenna. PMID:23868502

Duffy, C D P; Valkunas, L; Ruban, A V

2013-10-16

150

Understanding photosynthetic light-harvesting: a bottom up theoretical approach.  

PubMed

We discuss a bottom up approach for modeling photosynthetic light-harvesting. Methods are reviewed for a full structure-based parameterization of the Hamiltonian of pigment-protein complexes (PPCs). These parameters comprise (i) the local transition energies of the pigments in their binding sites in the protein, the site energies; (ii) the couplings between optical transitions of the pigments, the excitonic couplings; and (iii) the spectral density characterizing the dynamic modulation of pigment transition energies and excitonic couplings by protein vibrations. Starting with quantum mechanics perturbation theory, we provide a microscopic foundation for the standard PPC Hamiltonian and relate the expressions obtained for its matrix elements to quantities that can be calculated with classical molecular mechanics/electrostatics approaches including the whole PPC in atomic detail and using charge and transition densities obtained with quantum chemical calculations on the isolated building blocks of the PPC. In the second part of this perspective, the Hamiltonian is utilized to describe the quantum dynamics of excitons. Situations are discussed that differ in the relative strength of excitonic and exciton-vibrational coupling. The predictive power of the approaches is demonstrated in application to different PPCs, and challenges for future work are outlined. PMID:23361062

Renger, Thomas; Müh, Frank

2013-01-29

151

2-D Pigment Langmuir Monolayer Assemblies for Light Harvesting Applications.  

NASA Astrophysics Data System (ADS)

The use of Coulombic forces to isolate charged, water-soluble macrocycles at the air/water interface (through their interactions with the oppositely charged headgroups of a phospholipid Langmuir monolayer) is currently being exploited in this laboratory as a means to create two-dimensional arrays of pigments for light-harvesting purposes. Significant differences have been observed in the surface pressure-molecular area (?-A) isotherms of dihexadecyl phosphate on subphases containing either tetra-(N-methylaza)- phthalocyanine (i.e., tetra-(N-methyl)-2,3-pyridinoporphyrazine) or tetra- (N-methylpyridyl)-porphyrin, both of which are cationic. In situ x-ray specular reflectivity has been employed to determine interfacial organization in these systems and to elucidate the origin of their different phase behavior at the air/water interface. In addition, electronic absorption spectra and electronic linear dichroism have been utilized to determine average pigment orientation in transferred films. * Ames Laboratory is operated by Iowa State University for the U.S. Department of Energy under Cotract No. W-4705-Eng-82.

Gregory, Brian W.; Vaknin, David; Cotton, Therese M.; Struve, Walter S.

1996-03-01

152

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

153

Metal-Directed Protein Self Assembly  

PubMed Central

CONSPECTUS Proteins are Nature’s premier building blocks for constructing sophisticated nanoscale architectures that carry out complex tasks and chemical transformations. It is estimated that 70–80% of all proteins are permanently oligomeric, that is, they are composed of multiple proteins that are held together in precise spatial organization through non-covalent interactions. While it is of great fundamental interest to understand the physicochemical basis of protein self-assembly, the mastery of protein-protein interactions (PPIs) would also allow access to novel biomaterials using Nature’s favorite and most versatile building block. With this possibility in mind, we have developed a new approach, Metal Directed Protein Self-Assembly (MDPSA), which utilizes the strength, directionality and selectivity of metal-ligand interactions to control PPIs. At its core, MDPSA is inspired by supramolecular coordination chemistry which exploits metal coordination for the self-assembly of small molecules into discrete, more-or-less predictable higher-order structures. Proteins, however, are not exactly small molecules or simple metal ligands: they feature extensive, heterogeneous surfaces that can interact with each other and with metal ions in unpredictable ways. We will start this Account by first describing the challenges of using entire proteins as molecular building blocks. This will be followed by our work on a model protein (cytochrome cb562) to both highlight and overcome those challenges toward establishing some ground rules for MDPSA. Proteins are also Nature’s metal ligands of choice. In MDPSA, once metal ions guide proteins into forming large assemblies, they are by definition embedded within extensive interfaces formed between protein surfaces. These complex surfaces make an inorganic chemist’s life somewhat difficult, yet they also provide a wide platform to modulate the metal coordination environment through distant, non-covalent interactions – exactly as natural metalloproteins and enzymes do. We will describe our computational and experimental efforts on restructuring the non-covalent interaction network formed between proteins surrounding the interfacial metal centers. This approach of metal templating followed by the redesign of protein interfaces (Metal-Templated Interface Redesign, MeTIR) not only provides a route to engineer de novo PPIs and novel metal coordination environments, but also carries possible parallels to the evolution of metalloproteins.

SALGADO, ERIC N.; RADFORD, ROBERT J.

2010-01-01

154

Computer simulations of self-assembled membranes.  

PubMed

Molecular dynamics simulations in three dimensions of particles that self-assemble to form two-dimensional, membrane-like objects are presented. Anisotropic, multibody forces, chosen so as to mimic real interactions between amphiphilic molecules, generate a finite rigidity and compressibility of the assembled membranes, as well as a finite line tension at their free edges. This model and its generalizations can be used to study a large class of phenomena taking place in fluctuating membranes. For instance, both fluid and solid-like phases, separated by a phase transition, are obtained and some of the large-scale properties of these membranes studied. In particular, thermal undulations of quasi-spherical fluid vesicles are analyzed, in a manner similar to recent experiments in lipid systems. PMID:1962193

Drouffe, J M; Maggs, A C; Leibler, S

1991-11-29

155

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

156

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

157

Random Phenomena in Algorithmic Self Assembly: Computing Times at Nanoscale  

Microsoft Academic Search

Speed of computation and power consumption are two principal parameters of conventional computing devices implemented in microelectronic circuits. As performance of such devices approaches physical limits, new computing paradigms are emerging. This paper focuses on computing by molecular self assembly processes, where computing elements are fashioned from DNA. For purposes of analysis, DNA-based self assembly can be abstracted to growth

E. G. Cofiman

158

The Program-Size Complexity of Self-Assembled Squares  

Microsoft Academic Search

Molecular self-assembly gives rise to a great diversity of com- plex forms, from crystals and DNA helices to microtubules and holoenzymes. We study a formal model of pseudo- crystalline self-assembly, called the Tile Assembly Model, in which a tile may be added to the growing object when the total interaction strength with its neighbors exceeds a parameter 7-. This model

Paul W. K. Rothemund; Erik Winfree

2001-01-01

159

Small-angle neutron scattering studies of chemical reaction and reaction-induced self-assembly  

NASA Astrophysics Data System (ADS)

We have investigated a self-assembling process of cellulose artificially synthesized via enzymatic polymerization by means of in-situ and time-resolved small-angle neutron scattering (SANS). The results elucidated the following: (i) cellulose molecules were synthesized at a special reaction site of the enzyme (cellulase) located on or near the smooth surface of the self-assembled enzymes formed in the reaction medium; (ii) the synthesized molecules associated themselves via diffusion-limited aggregation (DLA) and crystallized into fibrils and (iii) the fibrils formed the aggregates, which had the surface fractal dimension Ds increasing from 2 to 2.3 with the reaction time, on the smooth surface of the enzyme aggregates.

Tanaka, H.; Koizumi, S.; Hashimoto, T.; Kurosaki, K.; Ohmae, M.; Kobayashi, S.

2006-11-01

160

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

161

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

162

Optically nonlinear energy transfer in light-harvesting dendrimers  

NASA Astrophysics Data System (ADS)

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.

Andrews, David L.; Bradshaw, David S.

2004-08-01

163

Water coordinated zinc dioxo-chlorin and porphyrin self-assemblies as chlorosomal mimics: variability of supramolecular interactions.  

PubMed

Semisynthetic zinc chlorins are shown for the first time to self-assemble in the absence of an intrinsic hydroxy group, which is always present in the chlorosomal bacteriochlorophylls (BChl's) c, d and e. Instead, the presently studied compounds have carbonyl groups. These cannot function as hydrogen bond donating groups. However due to interspacing water molecules bound to the zinc ion, double hydrogen bonding can occur to adjacent tetrapyrrolic macrocycles equipped with carbonyl recognition groups. Solution studies comprising UV-Vis absorption, electronic circular dichroism (ECD) and FT-IR show that different aggregates are formed in hydrated solvents in comparison to dry nonpolar solvents. Single crystal X-ray studies show variable supramolecular interactions either with interspacing water molecules coordinating the Zn ion within a porphyrin or with the 17(2) carbonyl group of a chlorin ligating the Zn ion. Our findings have implications for a minimalistic design of self-assembling chromophores, which can act as efficient light-harvesting units. PMID:22522667

Jesorka, Aldo; Holzwarth, Alfred R; Eichhöfer, Andreas; Reddy, Chilla Malla; Kinoshita, Yusuke; Tamiaki, Hitoshi; Katterle, Martin; Naubron, Jean-Valère; Balaban, Teodor Silviu

2012-04-20

164

Artificial and natural nucleic acid self-assembling systems  

NASA Astrophysics Data System (ADS)

Nucleic acids are good candidates for nanomachine construction. They participate in all the processes of life, and so can function as structural building blocks and dynamic catalysts. However, to use nucleic acids as nanomachines, a better understanding of their material properties, how to design structures using them, and their dynamics is needed. We have tried to address these issues, in a small way, with nucleic acid force field development, an attempt at nanostructural design and synthesis using DNA, and a study of the RNA/protein regulatory dynamics of the tryptophan regulatory attenuation protein.

Wood, Marcus

165

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

166

Primary Light Harvesting System: Phycobilisomes and Associated Membranes. Progress Report, January 1, 1978--December 31, 1978.  

National Technical Information Service (NTIS)

Phycobilisomes, attached to photosynthetic membranes of the red and blue-green algae, function as the major light harvesters for photosynthesis. They represent one of the most efficient energy transfer systems in photosynthetic organisms. Allophycocyanin ...

E. Gantt

1978-01-01

167

Primary Light Harvesting System: Phycobilisomes and Associated Membranes. Progress Report, January 1, 1976--December 31, 1976.  

National Technical Information Service (NTIS)

Phycobilisomes, which function as light harvesting antennae in red and blue-green algae, are structured for maximum energy transfer from the phycobiliproteins to chlorophyll in the photosynthetic lamellae. An immunoelectron microscopic procedure was devis...

E. Gantt

1976-01-01

168

Evolution and functional properties of photosystem II light harvesting complexes in eukaryotes.  

PubMed

Photoautotrophic organisms, the major agent of inorganic carbon fixation into biomass, convert light energy into chemical energy. The first step of photosynthesis consists of the absorption of solar energy by pigments binding protein complexes named photosystems. Within photosystems, a family of proteins called Light Harvesting Complexes (LHC), responsible for light harvesting and energy transfer to reaction centers, has evolved along with eukaryotic organisms. Besides light absorption, these proteins catalyze photoprotective reactions which allowed functioning of oxygenic photosynthetic machinery in the increasingly oxidant environment. In this work we review current knowledge of LHC proteins serving Photosystem II. Balance between light harvesting and photoprotection is critical in Photosystem II, due to the lower quantum efficiency as compared to Photosystem I. In particular, we focus on the role of each antenna complex in light harvesting, energy transfer, scavenging of reactive oxygen species, chlorophyll triplet quenching and thermal dissipation of excess energy. This article is part of a Special Issue entitled: Photosystem II. PMID:21704018

Ballottari, Matteo; Girardon, Julien; Dall'osto, Luca; Bassi, Roberto

2011-06-15

169

Light harvesting complexes of Chromera velia, photosynthetic relative of apicomplexan parasites.  

PubMed

The structure and composition of the light harvesting complexes from the unicellular alga Chromera velia were studied by means of optical spectroscopy, biochemical and electron microscopy methods. Two different types of antennae systems were identified. One exhibited a molecular weight (18-19kDa) similar to FCP (fucoxanthin chlorophyll protein) complexes from diatoms, however, single particle analysis and circular dichroism spectroscopy indicated similarity of this structure to the recently characterized XLH antenna of xanthophytes. In light of these data we denote this antenna complex CLH, for "Chromera Light Harvesting" complex. The other system was identified as the photosystem I with bound Light Harvesting Complexes (PSI-LHCr) related to the red algae LHCI antennae. The result of this study is the finding that C. velia, when grown in natural light conditions, possesses light harvesting antennae typically found in two different, evolutionary distant, groups of photosynthetic organisms. PMID:23428396

Tichy, Josef; Gardian, Zdenko; Bina, David; Konik, Peter; Litvin, Radek; Herbstova, Miroslava; Pain, Arnab; Vacha, Frantisek

2013-02-18

170

Solvent mediated self-assembly of solids  

SciTech Connect

Solvent-mediated crystallization represents a robust approach to self-assembly of nanostructures and microstructures. In organic systems, the relative ease with which the structure of hydrogen- bonded molecules can be manipulated allows for generation of a wide variety of nanoscale crystal structures. In living organisms, control over the micron-to-millimeter form of inorganic crystals is achieved through introduction of bio-organic molecules. The purpose of this proposal is to understand the interplay between solution chemistry, molecular structure, surface chemistry, and the processes of nucleation and crystal growth in solvent-mediated systems, with the goal of developing the atomic and molecular basis of a solvent-mediated self-assembly technology. We will achieve this purpose by: (1) utilizing an atomic force microscopy (AFM) approach that provides in situ, real time imaging during growth from solutions, (2) by modifying kinetic Monte Carlo (KMC) models to include solution-surface kinetics, (3) by introducing quantum chemistry (QC) calculations of the potentials of the relevant chemical species and the near-surface structure of the solution, and (4) by utilizing molecular dynamics (MD) simulations to identify the minimum energy pathways to the solid state. Our work will focus on two systems chosen to address both the manometer and micron-to-millimeter length scales of assembly, the family of 2,5- diketopiperazines (X-DKPs) and the system of CaCO{sub 3} with amino acids. Using AFM, we will record the evolution of surface morphology, critical lengths, step speeds, and step-step interactions as a function of supersaturation and temperature. In the case of the X-DKPs, these measurements will be repeated as the molecular structure of the growth unit is varied. In the case of CaCO{sub 3}, they will be performed as a function of solution chemistry including pH, ionic strength, and amino acid content. In addition, we will measure nucleation rates and orientations of CaCO{sub 3} on polyamino acid templates. From these measurements, we will extract fundamental growth parameters for input into KMC simulations whose predictions will in turn be compared to the experimental observations. The KMC simulations will incorporate atomic processes representing the minimum energy pathways as determined from the MD calculations. The interaction potentials of the relevant chemical species as well as the hydrated surface, including the electrochemical double layer, used in the MD simulations will be determined using coupled solutions to the Schrodinger and Poisson-Boltzmann equations which take account of electronic relaxation effects.

De Yoreo, J.; Wilson, W.D.; Palmore, T.

1997-12-12

171

The role of carotenoids in bacterial light harvesting  

NASA Astrophysics Data System (ADS)

The results of time-resolved and steady state spectroscopies are combined with ab initio calculations to elucidate the light harvesting role of carotenoids in purple photosynthetic bacteria. In these bacteria, carotenoids absorb light and transfer the electronic excitation energy to nearby bacteriochlorophyll with remarkable efficiency, despite the short lifetimes of their strongly allowed S2 (Bu) states and the dipole- forbidden nature of their S1 (Ag) states. In this work, the mechanisms underpinning efficient carotenoid to bacteriochlorophyll energy transfer are addressed, and the first definitive measurement of S1-Q y energy transfer is reported. Fluorescence upconversion data show rapid decay (54 +/- 8 fs) of carotenoid S2 population and rise ( ~ 110 fs) of bacteriochlorophyll Qy population following excitation of the carotenoid. These data are compared with energy transfer rates calculated using the new transition density cube method, which provides for accurate calculation of Coulombic couplings between electronic transitions, even at very small separations. Analysis of the experimental data and quantum chemical calculations suggest that each carotenoid effectively couples to several nearby bacteriochlorophyll yielding rapid carotenoid S2 to bacteriochlorophyll Qx energy transfer. S2 to Qy and S1 to Qy pathways may account for small, but significant, amounts of carotenoid to bacteriochlorophyll energy transfer in some species. Ab initio super-molecule calculations reveal extensive mixing (delocalization) of carotenoid and bacteriochlorophyll excited states. Calculations show the carotenoids significantly modify the B800-B850 Coulombic coupling, which may partially explain the discrepancy between energy transfer timescales of previous calculations ( ~ 2 ps) and experiments (650-700 fs). Two-photon fluorescence excitation provides the first definitive evidence of carotenoid S1 to bacteriochlorophyll Qy energy transfer by directly exciting the dipole-forbidden carotenoid S1 state and observing fluorescence from the bacteriochlorophyll Qy state following S1-Qy energy transfer. The resulting two-photon fluorescence excitation spectrum determines the in situ carotenoid S 1 energy as 14,000 +/- 100 cm- 1. Appendices describe units in energy transfer equations, the newly introduced transition density cube method for calculating Coulombic couplings between molecules of arbitrary size and symmetry, and the construction and alignment of the fluorescence upconversion spectrometer.

Krueger, Brent Phillip

1999-12-01

172

Enzyme-assisted self-assembly under thermodynamic control  

NASA Astrophysics Data System (ADS)

The production of functional molecular architectures through self-assembly is commonplace in biology, but despite advances, it is still a major challenge to achieve similar complexity in the laboratory. Self-assembled structures that are reproducible and virtually defect free are of interest for applications in three-dimensional cell culture, templating, biosensing and supramolecular electronics. Here, we report the use of reversible enzyme-catalysed reactions to drive self-assembly. In this approach, the self-assembly of aromatic short peptide derivatives provides a driving force that enables a protease enzyme to produce building blocks in a reversible and spatially confined manner. We demonstrate that this system combines three features: (i) self-correction-fully reversible self-assembly under thermodynamic control; (ii) component-selection-the ability to amplify the most stable molecular self-assembly structures in dynamic combinatorial libraries; and (iii) spatiotemporal confinement of nucleation and structure growth. Enzyme-assisted self-assembly therefore provides control in bottom-up fabrication of nanomaterials that could ultimately lead to functional nanostructures with enhanced complexities and fewer defects.

Williams, Richard J.; Smith, Andrew M.; Collins, Richard; Hodson, Nigel; Das, Apurba K.; Ulijn, Rein V.

2009-01-01

173

Enzyme-assisted self-assembly under thermodynamic control.  

PubMed

The production of functional molecular architectures through self-assembly is commonplace in biology, but despite advances, it is still a major challenge to achieve similar complexity in the laboratory. Self-assembled structures that are reproducible and virtually defect free are of interest for applications in three-dimensional cell culture, templating, biosensing and supramolecular electronics. Here, we report the use of reversible enzyme-catalysed reactions to drive self-assembly. In this approach, the self-assembly of aromatic short peptide derivatives provides a driving force that enables a protease enzyme to produce building blocks in a reversible and spatially confined manner. We demonstrate that this system combines three features: (i) self-correction--fully reversible self-assembly under thermodynamic control; (ii) component-selection--the ability to amplify the most stable molecular self-assembly structures in dynamic combinatorial libraries; and (iii) spatiotemporal confinement of nucleation and structure growth. Enzyme-assisted self-assembly therefore provides control in bottom-up fabrication of nanomaterials that could ultimately lead to functional nanostructures with enhanced complexities and fewer defects. PMID:19119277

Williams, Richard J; Smith, Andrew M; Collins, Richard; Hodson, Nigel; Das, Apurba K; Ulijn, Rein V

2008-12-21

174

Modeling Light Harvesting and Primary Charge Separation in Photosystem I and Photosystem II  

Microsoft Academic Search

We discuss how the light harvesting in photosystem I, photosystem II and in light-harvesting complex II can be modeled at\\u000a a quantitative level by taking into account the exciton structure of the chromophores in the pigment-protein complexes, static\\u000a (conformational) disorder, and coupling of electronic excitations and charge-transfer (CT) states to fast nuclear motion.\\u000a We show examples of simultaneous fitting of

Rienk van Grondelle; Vladimir I. Novoderezhkin; Jan P. Dekker

175

Phosphorylation Controls the Three-dimensional Structure of Plant Light Harvesting Complex II  

Microsoft Academic Search

The most abundant chlorophyll-binding complex in plants is the intrinsic membrane protein light-harvest- ing complex II (LHC II). LHC II acts as a light-harvesting antenna and has an important role in the distribution of absorbed energy between the two photosystems of pho- tosynthesis. We used spectroscopic techniques to study a synthetic peptide with identical sequence to the LHC IIb N

Anders Nilsson; Dalibor Stys; Torbjorn Drakenberg; Michael D. Spangfort; Sture Forsen; John F. Allen

1997-01-01

176

Tandem mass spectrometric identification of spinach Photosystem II light-harvesting components  

Microsoft Academic Search

Light-harvesting proteins harness light energy for photosynthesis. Sequences of the Photosystem II (PS II) light harvesting proteins, Lhcb1-6, have been deduced from many plants. However, limited information is available for spinach Lhcb sequences, although a spinach PS II preparation (BBY) is commonly used as a model for plant photosynthetic oxygen evolution (DA Berthold, GT Babcock and CF Yocum (1981) FEBS

Anthony J. A. Ouellette; Bridgette A. Barry

2002-01-01

177

Tandem mass spectrometric identification of spinach Photosystem II light-harvesting components  

Microsoft Academic Search

Light-harvesting proteins harness light energy for photosynthesis. Sequences of the Photosystem II (PS II) light harvesting\\u000a proteins, Lhcb1–6, have been deduced from many plants. However, limited information is available for spinach Lhcb sequences,\\u000a although a spinach PS II preparation (BBY) is commonly used as a model for plant photosynthetic oxygen evolution [DA Berthold,\\u000a GT Babcock and CF Yocum (1981) FEBS

Anthony J. A. Ouellette; Bridgette A. Barry

2002-01-01

178

A Protein Family Saga: From Photoprotection to Light-Harvesting (and Back?)  

Microsoft Academic Search

Photoprotection seems to be an intrinsic property of light-harvesting systems, and an interesting question to address is whether\\u000a the light-harvesting or the photoprotection function was the “original” function, and which function evolved subsequently.\\u000a It appears that the cyanobacterial one-helix proteins, the presumed ancestors to the LHC proteins, were not designed as antenna\\u000a proteins but were involved in photoprotection and \\/or

Stefan Jansson

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

Molecular Adaptation of Photoprotection: Triplet States in Light-Harvesting Proteins  

PubMed Central

The photosynthetic light-harvesting systems of purple bacteria and plants both utilize specific carotenoids as quenchers of the harmful (bacterio)chlorophyll triplet states via triplet-triplet energy transfer. Here, we explore how the binding of carotenoids to the different types of light-harvesting proteins found in plants and purple bacteria provides adaptation in this vital photoprotective function. We show that the creation of the carotenoid triplet states in the light-harvesting complexes may occur without detectable conformational changes, in contrast to that found for carotenoids in solution. However, in plant light-harvesting complexes, the triplet wavefunction is shared between the carotenoids and their adjacent chlorophylls. This is not observed for the antenna proteins of purple bacteria, where the triplet is virtually fully located on the carotenoid molecule. These results explain the faster triplet-triplet transfer times in plant light-harvesting complexes. We show that this molecular mechanism, which spreads the location of the triplet wavefunction through the pigments of plant light-harvesting complexes, results in the absence of any detectable chlorophyll triplet in these complexes upon excitation, and we propose that it emerged as a photoprotective adaptation during the evolution of oxygenic photosynthesis.

Gall, Andrew; Berera, Rudi; Alexandre, Maxime T.A.; Pascal, Andrew A.; Bordes, Luc; Mendes-Pinto, Maria M.; Andrianambinintsoa, Sandra; Stoitchkova, Katerina V.; Marin, Alessandro; Valkunas, Leonas; Horton, Peter; Kennis, John T.M.; van Grondelle, Rienk; Ruban, Alexander; Robert, Bruno

2011-01-01

181

Molecular adaptation of photoprotection: triplet states in light-harvesting proteins.  

PubMed

The photosynthetic light-harvesting systems of purple bacteria and plants both utilize specific carotenoids as quenchers of the harmful (bacterio)chlorophyll triplet states via triplet-triplet energy transfer. Here, we explore how the binding of carotenoids to the different types of light-harvesting proteins found in plants and purple bacteria provides adaptation in this vital photoprotective function. We show that the creation of the carotenoid triplet states in the light-harvesting complexes may occur without detectable conformational changes, in contrast to that found for carotenoids in solution. However, in plant light-harvesting complexes, the triplet wavefunction is shared between the carotenoids and their adjacent chlorophylls. This is not observed for the antenna proteins of purple bacteria, where the triplet is virtually fully located on the carotenoid molecule. These results explain the faster triplet-triplet transfer times in plant light-harvesting complexes. We show that this molecular mechanism, which spreads the location of the triplet wavefunction through the pigments of plant light-harvesting complexes, results in the absence of any detectable chlorophyll triplet in these complexes upon excitation, and we propose that it emerged as a photoprotective adaptation during the evolution of oxygenic photosynthesis. PMID:21843485

Gall, Andrew; Berera, Rudi; Alexandre, Maxime T A; Pascal, Andrew A; Bordes, Luc; Mendes-Pinto, Maria M; Andrianambinintsoa, Sandra; Stoitchkova, Katerina V; Marin, Alessandro; Valkunas, Leonas; Horton, Peter; Kennis, John T M; van Grondelle, Rienk; Ruban, Alexander; Robert, Bruno

2011-08-17

182

Self-Assembly of Helical Ribbons  

NASA Astrophysics Data System (ADS)

The self-assembly of helical ribbons is examined in a variety of multicomponent enantiomerically pure systems that contain a bile salt or a nonionic detergent, a phosphatidylcholine or a fatty acid, and a steroid analog of cholesterol. In almost all systems, two different pitch types of helical ribbons are observed: high pitch, with a pitch angle of 54± 2 degrees, and low pitch, with a pitch angle of 11± 2 degrees. Although the majority of these helices are right-handed, a small proportion of left-handed helices is observed. Additionally, a third type of helical ribbon, with a pitch angle in the range 30-47 degrees, is occasionally found. These experimental findings suggest that the helical ribbons are crystalline rather than liquid crystal in nature and also suggest that molecular chirality may not be the determining factor in helix formation. The large yields of helices produced will permit a systematic investigation of their individual kinetic evolution and their elastic moduli.

Zastavker, Yevgeniya V.; Asherie, Neer; Lomakin, Aleksey; Pande, Jayanti; Donovan, Joanne M.; Schnur, Joel M.; Benedek, George B.

1999-07-01

183

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

184

Self-Assembled CoAs Nanostructures  

SciTech Connect

At low coverages, the codeposition of Co and As on the GaAs(100)c(4×4) surface results in the formation of two different types of self-assembled nanostructures; one has a "mesa" configuration, and the other a large aspect ratio "nanostripe" configuration. Minimum-energy calculations have been performed on several possible surface reconstructions for the latter configuration. The favored structure has a rather small unit that repeats essentially endlessly along the [10] direction. This unit contains one Co atom substituted between adjacent c(4×4) As dimers that straddle a misfit dislocation in the two-dimensional c(4×4) lattice. The distorted octahedral bonding around these Co atoms is completed by the addition of three As atoms to the repeat unit. A dip or a valley is formed on each side of the nanostripe by removing As atoms from the substrate. This valley partially relieves the compressive strain along the [110] direction across the nanostripes, and it helps to insure that each Co atom is surrounded by the requisite 18 valence electrons. The detailed atomic structure of the mesas was not determined. However, it is suggested that they are CoAs crystallites with a specific orientation relative to the substrate.

Helen H. Farrell

2003-07-01

185

Self-Assembled Monolayers with Molecular Gradients  

NASA Astrophysics Data System (ADS)

In recent years, biosensors and sensor arrays have developed into very important analytical tools, which found applications in many fields such as pharmaceutical (high-throughput) screening, medical diagnosis, or industrial process control. One of the major challenges for material research is the preparation of appropriate sensor surfaces, providing an interface with a high sensitivity and selectivity toward a given analyte. This chapter discusses some straightforward and flexible approaches to study structure and/or composition-function relationships and response characteristics of polymeric and molecular sensor materials. The controlled continuous deposition of self-assembled monolayers (SAMs), e.g. of substituted thiols or silanes, paves the way for the generation of molecular gradients on solid surfaces. These are useful for the preparation of interfaces with spatially controlled chemical composition and/ or physical properties. These tools can help to improve the selectivity and specificity of surfaces for biosensors and biochips. They can also be utilized for the study of fundamental protein adsorption and exchange phenomena.

Schäferling, Michael; Riepl, Michael; Liedberg, Bo

186

Computer simulation studies of self-assembling macromolecules.  

PubMed

Coarse-grained (CG) molecular models are now widely used to understand the structure and functionality of macromolecular self-assembling systems. In the last few years, significant efforts have been devoted to construct quantitative CG models based on data from molecular dynamics (MD) simulations with more detailed all-atom (AA) intermolecular force fields as well as experimental thermodynamic data. We review some of the recent progress pertaining to the MD simulation of self-assembling macromolecular systems, using as illustrations the application of CG models to probe surfactant and lipid self-assembly including liposome and dendrimersome formation as well as the interaction of biomembranes with nanoparticles. PMID:22402497

Shinoda, Wataru; DeVane, Russell; Klein, Michael L

2012-03-06

187

The Lost Work in Dissipative Self-Assembly  

NASA Astrophysics Data System (ADS)

A general thermodynamic analysis is given of dissipative self-assembly (DSA). Subsequently, the analysis is used to quantify the lost work in a recently published chemical realization of DSA (Boekhoven et al., Angew Chem Int Ed 49:4825, 2010) where a formation reaction produces the monomers that subsequently self-assemble and are finally annihilated by means of a destruction reaction. For this example, the work lost in self-assembly itself is found to be negligibly small compared to the work lost in the reactions driving the non-spontaneous formation reaction and the kinetically hindered destruction reaction.

Koper, G. J. M.; Boekhoven, J.; Hendriksen, W. E.; van Esch, J. H.; Eelkema, R.; Pagonabarraga, I.; Rubí, J. M.; Bedeaux, D.

2013-07-01

188

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

2013-06-20

189

Organization of Inorganic Nanomaterials via Programmable DNA Self-Assembly and Peptide Molecular Recognition  

PubMed Central

An interesting alternative to top-down nanofabrication is to imitate biology, where nanoscale materials frequently integrate organic molecules for self-assembly and molecular recognition with ordered, inorganic minerals to achieve mechanical, sensory, or other advantageous functions. Using biological systems as inspiration, researchers have sought to mimic the nanoscale composite materials produced in nature. Here, we describe a combination of self-assembly, molecular recognition, and templating, relying on an oligonucleotide covalently conjugated to a high-affinity gold-binding peptide. After integration of the peptide-coupled DNA into a self-assembling superstructure, the templated peptides recognize and bind gold nanoparticles. In addition to providing new ways of building functional multi-nanoparticle systems, this work provides experimental proof that a single peptide molecule is sufficient for immobilization of a nanoparticle. This molecular construction strategy, combining DNA assembly and peptide recognition, can be thought of as programmable, granular, artificial biomineralization. We also describe the important observation that the addition of 1–2% Tween 20 surfactant to the solution during gold particle binding allows the gold nanoparticles to remain soluble within the magnesium containing DNA assembly buffer under conditions that usually lead to the aggregation and precipitation of the nanoparticles.

Carter, Joshua D.; LaBean, Thomas H.

2011-01-01

190

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

191

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

192

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

193

Origins of viscoelastic dissipation in self-assembled organic monolayers.  

National Technical Information Service (NTIS)

Although self-assembled monolayers (SAMs) are promising candidates for interfacial lubricants in micro-electromechanical systems, the relationship between the monolayer structure and its viscoelastic properties is not understood. Using Acoustic Wave Dampi...

N. D. Shinn T. A. Michalske

1998-01-01

194

Alkanethiols on Platinum: Multicomponent Self-Assembled Monolayers.  

National Technical Information Service (NTIS)

We have studied the formation of self-assembled monolayers (SAMs) of n-alkanethiols on platinum thin films using X-ray photoelectron spectroscopy (XPS), reflection-absorption infrared spectroscopy (RAIRS), spectroscopic ellipsometry (SE), and contact angl...

A. Opdahl D. Y. Petrovykh H. Kimura-Suda L. J. Richter M. J. Tarlov

2006-01-01

195

Self-assembled dextran sulphate nanoparticles for targeting rheumatoid arthritis.  

PubMed

The amphiphilic block copolymer, composed of hydrophilic dextran sulfate as the targeting ligand and hydrophobic polycaprolactone as the hydrophobic segment, was prepared via click chemistry to develop self-assembled nanoparticles for targeting rheumatoid arthritis. PMID:23942894

Kim, Seol-Hee; Kim, Jong-Ho; You, Dong Gil; Saravanakumar, Gurusamy; Yoon, Hong Yeol; Choi, Ki Young; Thambi, Thavasyappan; Deepagan, V G; Jo, Dong-Gyu; Park, Jae Hyung

2013-10-10

196

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

197

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

PubMed Central

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

2013-01-01

198

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

199

Self assembly: An approach to terascale integration  

SciTech Connect

Surely one of the most remarkable accomplishments of modern times has been the miniaturization of electronic components, starting with discrete transistors and leading to Very Large Scale Integrated (VLSI) Circuits which will soon contain almost 100 million components in a few square centimeters. It led to an information processing industry that fuels almost every aspect of industrial societies and that has brought manifold benefits to their citizens. Although continuation of the miniaturization process is likely to produce even greater benefits, many experts are concerned that extrapolation of traditional silicon VLSI techniques will meet with increasingly severe difficulties. Some of these are fundamental in nature, e. g., granularity and fluctuations in semiconductors and interconnects and proximity effects such as tunneling. The first major difficulty to be encountered will be a rising cost of products due to increased complexity and difficulty of manufacturing and assembly. Such difficulties are likely to be seen in about 10 years when minimum component sizes are expected to decrease below 0.15--0.2 {mu}m. If alternatives to present VLSI techniques are to be available when needed, work on them must start now. At Los Alamos, we are exploring the feasibility of ultrasmall wires and switches that self-assemble themselves into computing elements and circuits. Their operation is based on the quantum properties of nanometer scale molecular clusters. This paper will describe our efforts in the development of these components and will summarize our work in four areas: (1) the development of conducting molecular wires, (2) conducting nanoparticle wires and switches based on the Coulomb Blockade principle, (3) the development of advanced architectures that benefit from the use of such components and that significantly advance the art of high performance computing, and (4) the development of novel methods for attaining sub-Angstrom 3-D non-destructive imaging.

Singer, S.

1993-09-01

200

Self assembly: An approach to terascale integration  

NASA Astrophysics Data System (ADS)

Surely one of the most remarkable accomplishments of modern times has been the miniaturization of electronic components starting with discrete transistors and leading to Very Large Scale Integrated (VLSI) Circuits which will soon contain almost 100 million components in a few square centimeters. It led to an information processing industry that fuels almost every aspect of industrial societies and that has brought manifold benefits to their citizens. Although continuation of the miniaturization process is likely to produce even greater benefits, many experts are concerned that extrapolation of traditional silicon VLSI techniques will meet with increasingly severe difficulties. Some of these are fundamental in nature, e.g., granularity and fluctuations in semiconductors and interconnects and proximity effects such as tunneling. The first major difficulty to be encountered will be a rising cost of products due to increased complexity and difficulty of manufacturing and assembly. Such difficulties are likely to be seen in about 10 years when minimum component sizes are expected to decrease below 0.15 - 0.2 microns. If alternatives to present VLSI techniques are to be available when needed, work on them must start now. At Los Alamos, we are exploring the feasibility of ultrasmall wires and switches that self-assemble themselves into computing elements and circuits. Their operation is based on the quantum properties of nanometer scale molecular clusters. This paper will describe our efforts in the development of these components and will summarize our work in four areas: (1) the development of conducting molecular wires; (2) conducting nanoparticle wires and switches based on the Coulomb Blockade principle; (3) the development of advanced architectures that benefit from the use of such components and that significantly advance the art of high performance computing; and (4) the development of novel methods for attaining sub-Angstrom 3-D non-destructive imaging.

Singer, S.

201

Evolving tiles for automated self-assembly design  

Microsoft Academic Search

Self-assembly is a distributed, asynchronous mech- anism that is pervasive across natural systems where hierarchi- cal complex structures are built from the bottom-up. The lack of a centralised master plan, no external intervention, and pre- programmed interactions among entities are within its most relevant and technologically appealing properties. This paper tackles the self-assembly Wang tiles designability problem by means of

Germán Terrazas; Marian Gheorghe; Graham Kendall; Natalio Krasnogor

2007-01-01

202

Programming Methodology for Biologically-Inspired Self-Assembling Systems  

Microsoft Academic Search

We present a programming methodology for self-assembling complex structures from vast numbers of locally-interacting identically-programmed agents, using techniques inspired by developmental biology. We demonstrate this approach through two examples: shape formation on a reconfig- urable sheet, and self-assembling two dimensional structures through replication. In each case, the desired global shape is specified using an abstract geometry-based language, and the agent

Radhika Nagpal; Attila Kondacs; Catherine Chang

2003-01-01

203

DNA Origami as Self-assembling Circuit Boards  

Microsoft Academic Search

\\u000a DNA origami have the potential to serve as self-assembling circuit boards for nanoelectronic devices. This paper focuses on\\u000a understanding just one aspect of the hierarchical self-assembly of DNA origami—the oligomerization of individual origami to\\u000a form chains of aligned and oriented origami. The eventual goal is to place small numbers of nanomagnets in specific locations\\u000a on the DNA origami in such

Kyoung Nan Kim; Koshala Sarveswaran; Lesli Mark; Marya Lieberman

2010-01-01

204

Programmable Control of Nucleation for Algorithmic Self-Assembly  

Microsoft Academic Search

Algorithmic self-assembly, a generalization of crystal growth processes, has\\u000abeen proposed as a mechanism for autonomous DNA computation and for bottom-up\\u000afabrication of complex nanostructures. A `program' for growing a desired\\u000astructure consists of a set of molecular `tiles' designed to have specific\\u000abinding interactions. A key challenge to making algorithmic self-assembly\\u000apractical is designing tile set programs that make

Rebecca Schulman; Erik Winfree

2010-01-01

205

Algorithmic Self-Assembly of DNA Sierpinski Triangles  

Microsoft Academic Search

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,

Paul W. K Rothemund; Nick Papadakis; Erik Winfree

2004-01-01

206

Approximate Self-Assembly of the Sierpinski Triangle  

Microsoft Academic Search

The Tile Assembly Model is a Turing universal model that Winfree introduced in order to study the nanoscale self-assembly\\u000a of complex DNA crystals. Winfree exhibited a self-assembly that tiles the first quadrant of the Cartesian plane with specially\\u000a labeled tiles appearing at exactly the positions of points in the Sierpinski triangle. More recently, Lathrop, Lutz, and Summers\\u000a proved that the

Jack H. Lutz; Brad Shutters

207

DNA Self-Assembly For Constructing 3D Boxes  

Microsoft Academic Search

We propose a mathematical model of DNA self-assembly us- ing 2D tiles to form 3D nanostructures. This is the first work to combine studies in self-assembly and nanotechnology in 3D, just as Rothemund and Winfree did in the 2D case. Our model is a more precise super- set of their Tile Assembly Model that facilitates building scalable 3D molecules. Under

Ming-Yang Kao; Vijay Ramachandran

2001-01-01

208

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

209

Approximate Self-assembly of the Sierpinski Triangle  

Microsoft Academic Search

The Tile Assembly Model is a Turing universal model that Winfree introduced\\u000ain order to study the nanoscale self-assembly of complex (typically aperiodic)\\u000aDNA crystals. Winfree exhibited a self-assembly that tiles the first quadrant\\u000aof the Cartesian plane with specially labeled tiles appearing at exactly the\\u000apositions of points in the Sierpinski triangle. More recently, Lathrop, Lutz,\\u000aand Summers proved

Jack H. Lutz; Brad Shutters

2010-01-01

210

Identifying Shapes Using Self-Assembly (extended abstract)  

Microsoft Academic Search

In this paper, we introduce the following problem in the theory of algorithmic self-assembly: given an input shape as the seed of a tile-based self-assembly system, design a finite tile set that can, in some sense, uniquely identify whether or not the given input shape--drawn from a very general class of shapes--matches a particular target shape. We first study the

Matthew J. Patitz; Scott M. Summers

2010-01-01

211

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

212

Self-assembled aerogel-like low dielectric constant films  

Microsoft Academic Search

A series of new spin-on nanoporous silica films with controlled porosity and dielectric constants were prepared by evaporation induced self-assembly (EISA) during spin-coating. Starting with a homogeneous solution of soluble silica and surfactant\\/swelling agent prepared in an alcohol\\/water solvent, preferential evaporation of alcohol during spin-coating results in the hierarchical self-assembly of surfactants plus swelling agent and soluble silica into a

Hongyou Fan; Holly R Bentley; Kyle R Kathan; Paul Clem; Yunfeng Lu; C. Jeffrey Brinker

2001-01-01

213

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

214

Automated Self-Assembly Programming Paradigm: Initial Investigations  

Microsoft Academic Search

This paper presents a model that simulates a self-assembly process for software components. Initial investigations on the automated self-assembly programming paradigm (ASAP2) is presented whereby software components are treated as a gas' molecules and their interactions, within a confined area with specific temperature and pressure constraints, give rise to a variety of program architectures. We present experimental results that show

Lin Li; Natalio Krasnogor; Jon Garibaldi

2006-01-01

215

Self-Assembled Heterogeneous Integrated Fluorescence Detection System  

Microsoft Academic Search

We present the current progress towards a fully integrated fluorescence detection system constructed via self-assembly of independently microfabricated excitation sources and photosensors onto a common template. The system template contains specifically shaped binding sites for micron-scale components and electrical interconnects. The self-assembly process allows for using materials such as plastic or glass for constructing the template that are incompatible with

Samuel S. Kim; Ehsan Saeedi; Deirdre R. Meldrum; Babak A. Parviz

2007-01-01

216

Self-assembly and photoluminescence of molybdenum oxide nanoparticles  

Microsoft Academic Search

We report on the synthesis of self-assembled hillock shaped MoO3 nanoparticles on thin films exhibiting intense photoluminescence (PL) by RF magnetron sputtering and subsequent oxidation.\\u000a MoO3 nanocrystals of size ?29 nm are self-assembled into uniform nanoparticles with diameter ?174 nm. The mechanism of the intense\\u000a PL behaviour from MoO3 nanoparticles is investigated and systematically discussed. The films exhibit two bands;

I. Navas; R. Vinodkumar

2011-01-01

217

Exploiting amyloid fibril lamination for nanotube self-assembly  

Microsoft Academic Search

Fundamental questions about the relative arrangement of the β-sheet arrays within amyloid fibrils remain central to both its structure and the mechanism of self-assembly. Recent computational analyses suggested that sheet-to-sheet lamination was limited by the length of the strand. On the basis of this hypothesis, a short seven-residue segment of the Alzheimer's disease-related Aβ peptide, Aβ(16-22), was allowed to self-assemble

K. Lu; J. Jacob; P. Thiyagarajan; V. P. Conticello; D. G. Lynn

2010-01-01

218

Reducing tile complexity for self-assembly through temperature programming  

Microsoft Academic Search

We consider the tile self-assembly model and how tile complexity can be eliminated by permitting the tem- perature of the self-assembly system to be adjusted throughout the assembly process. To do this, we pro- pose novel techniques for designing tile sets that permit an arbitrary length m binary number to be encoded into a sequence of O(m) temperature changes such

Ming-Yang Kao; Robert T. Schweller

2006-01-01

219

Self-assembly of (sub-)micron particles into supermaterials  

NASA Astrophysics Data System (ADS)

We review aspects of static self-assembly with regard to the synthesizing of new types of three-dimensional materials made of specifically designed particles in the 100 nm to 10 µm range. Mechanical interconnection technologies based on static friction used in the assembly of macroscopic systems (such as screws and nails) are unsuitable for self-assembly. An analogy of self-assembly with first-order phase transitions is used to argue that self-assembly is a process requiring interfaces separating assembled and disordered regions. Available types of interaction are reviewed with emphasis on scaling. We discuss at some length how interaction and dynamic properties scale with respect to the particle size. Chains of particles seem to be of particular importance as they might form three-dimensional structures similar to proteins. These structures are constrained by the sequence of the particles and by their interactions between themselves and with the solvent. Using chains might provide a viable route to complex, inhomogeneous, supermaterials and systems. Kinetic processes, specifically nucleation and the relationship between self-assembly and thermodynamic phase transitions form a major part of this paper. Finally we review some applications of self-assembly, notably in MEMS, and put forward some ideas for the assembly of new types of (smart) supermaterials with interesting optical, mechanical, electrical and magnetic properties and describe some of the technological challenges we face when attempting to realize these materials and systems thereof.

Elwenspoek, Miko; Abelmann, Leon; Berenschot, Erwin; van Honschoten, Joost; Jansen, Henri; Tas, Niels

2010-06-01

220

Insight into the Structure of Light Harvesting Complex II and its Stabilization in Detergent Solution  

SciTech Connect

The structure of spinach light-harvesting complex II (LHC II), stabilized in a solution of the detergent n-octyl-{beta}-d-glucoside (BOG), was investigated by small-angle neutron scattering (SANS). Physicochemical characterization of the isolated complex indicated that it was pure (>95%) and also in its native trimeric state. SANS with contrast variation was used to investigate the properties of the protein-detergent complex at three different H{sub 2}O/D{sub 2}O contrast match points, enabling the scattering properties of the protein and detergent to be investigated independently. The topological shape of LHC II, determined using ab initio shape restoration methods from the SANS data at the contrast match point of BOG, was consistent with the X-ray crystallographic structure of LHC II (Liu et al. Nature 2004 428, 287-292). The interactions of the protein and detergent were investigated at the contrast match point for the protein and also in 100% D{sub 2}O. The data suggested that BOG micelle structure was altered by its interaction with LHC II, but large aggregate structures were not formed. Indirect Fourier transform analysis of the LHC II/BOG scattering curves showed that the increase in the maximum dimension of the protein-detergent complex was consistent with the presence of a monolayer of detergent surrounding the protein. A model of the LHC II/BOG complex was generated to interpret the measurements made in 100% D{sub 2}O. This model adequately reproduced the overall size of the LHC II/BOG complex, but demonstrated that the detergent does not have a highly regular shape that surrounds the hydrophobic periphery of LHC II. In addition to demonstrating that natively structured LHC II can be produced for functional characterization and for use in artificial solar energy applications, the analysis and modeling approaches described here can be used for characterizing detergent-associated {alpha}-helical transmembrane proteins.

Cardoso, Mateus B [ORNL; Smolensky, Dmitriy [ORNL; Heller, William T [ORNL; O'Neill, Hugh Michael [ORNL

2009-01-01

221

Insight into the structure of light-harvesting complex II and its stabilization in detergent solution.  

PubMed

The structure of spinach light-harvesting complex II (LHC II), stabilized in a solution of the detergent n-octyl-beta-D-glucoside (BOG), was investigated by small-angle neutron scattering (SANS). Physicochemical characterization of the isolated complex indicated that it was pure (>95%) and also in its native trimeric state. SANS with contrast variation was used to investigate the properties of the protein-detergent complex at three different H(2)O/D(2)O contrast match points, enabling the scattering properties of the protein and detergent to be investigated independently. The topological shape of LHC II, determined using ab initio shape restoration methods from the SANS data at the contrast match point of BOG, was consistent with the X-ray crystallographic structure of LHC II (Liu et al. Nature 2004 428, 287-292). The interactions of the protein and detergent were investigated at the contrast match point for the protein and also in 100% D(2)O. The data suggested that BOG micelle structure was altered by its interaction with LHC II, but large aggregate structures were not formed. Indirect Fourier transform analysis of the LHC II/BOG scattering curves showed that the increase in the maximum dimension of the protein-detergent complex was consistent with the presence of a monolayer of detergent surrounding the protein. A model of the LHC II/BOG complex was generated to interpret the measurements made in 100% D(2)O. This model adequately reproduced the overall size of the LHC II/BOG complex, but demonstrated that the detergent does not have a highly regular shape that surrounds the hydrophobic periphery of LHC II. In addition to demonstrating that natively structured LHC II can be produced for functional characterization and for use in artificial solar energy applications, the analysis and modeling approaches described here can be used for characterizing detergent-associated alpha-helical transmembrane proteins. PMID:19954150

Cardoso, Mateus B; Smolensky, Dmitriy; Heller, William T; O'Neill, Hugh

2009-12-24

222

Lipid-like self-assembling peptides.  

PubMed

One important question in prebiotic chemistry is the search for simple structures that might have enclosed biological molecules in a cell-like space. Phospholipids, the components of biological membranes, are highly complex. Instead, we looked for molecules that might have been available on prebiotic Earth. Simple peptides with hydrophobic tails and hydrophilic heads that are made up of merely a combination of these robust, abiotically synthesized amino acids and could self-assemble into nanotubes or nanovesicles fulfilled our initial requirements. These molecules could provide a primitive enclosure for the earliest enzymes based on either RNA or peptides and other molecular structures with a variety of functions. We discovered and designed a class of these simple lipid-like peptides, which we describe in this Account. These peptides consist of natural amino acids (glycine, alanine, valine, isoleucine, leucine, aspartic acid, glutamic acid, lysine, and arginine) and exhibit lipid-like dynamic behaviors. These structures further undergo spontaneous assembly to form ordered arrangements including micelles, nanovesicles, and nanotubes with visible openings. Because of their simplicity and stability in water, such assemblies could provide examples of prebiotic molecular evolution that may predate the RNA world. These short and simple peptides have the potential to self-organize to form simple enclosures that stabilize other fragile molecules, to bring low concentration molecules into a local environment, and to enhance higher local concentration. As a result, these structures plausibly could not only accelerate the dehydration process for new chemical bond formation but also facilitate further self-organization and prebiotic evolution in a dynamic manner. We also expect that this class of lipid-like peptides will likely find a wide range of uses in the real world. Because of their favorable interactions with lipids, these lipid-like peptides have been used to solubilize and stabilize membrane proteins, both for scientific studies and for the fabrication of nanobiotechological devices. They can also increase the solubility of other water-insoluble molecules and increase long-term stability of some water-soluble proteins. Likewise, because of their lipophilicity, these structures can deliver molecular cargo, such as small molecules, siRNA, and DNA, in vivo for potential therapeutic applications. PMID:22720818

Zhang, Shuguang

2012-06-21

223

Fractal Dimension Analysis in Self-Assembled Poly(dA)·poly(dT) DNA Network on Mica Surface  

Microsoft Academic Search

Characteristics of the self-assembled poly(dA)·poly(dT) DNA network adhered on the mica substrate are experimentally investigated based on the AFM observations and the fractal dimension analysis. Artificial B-type double stranded DNA, which consists of 50 base pairs of adenine and thymine, is specially prepared for the experiment. The manufacturing process of DNA network is done in the aqueous solution of poly(dA)·poly(dT)

Satoyuki Kawano

2005-01-01

224

Assembly of the precursor and processed light-harvesting chlorophyll a\\/b protein of Lemna into the light-harvesting complex II of barley etiochloroplasts  

Microsoft Academic Search

When the in vitro synthesized precursor of a light-harvesting chlorophyll a\\/b binding protein (LHCP) from Lemna gibba is imported into barley etiochloroplasts, it is processed to a single form. Both the processed form and the precursor are found in the thylakoid membranes, assembled into the light-har- vesting complex of photosystem II. Neither form can be detected in the stromal fraction.

Parag R. Chitnis; Eitan Harel; Bruce D. Kohorn; Elaine M. Tobin; J. Philip Thornber

1986-01-01

225

Electronic coherence lineshapes reveal hidden excitonic correlations in photosynthetic light harvesting  

NASA Astrophysics Data System (ADS)

The effective absorption cross-section of a molecule (acceptor) can be greatly increased by associating it with a cluster of molecules that absorb light and transfer the excitation energy to the acceptor molecule. The basic mechanism of such light harvesting by Förster resonance energy transfer (FRET) is well established, but recent experiments have revealed a new feature whereby excitation is coherently shared among donor and acceptor molecules during FRET. In the present study, two-dimensional electronic spectroscopy was used to examine energy transfer at ambient temperature in a naturally occurring light-harvesting protein (PE545 of the marine cryptophyte alga Rhodomonas sp. strain CS24). Quantum beating was observed across a range of excitation frequencies. The shapes of those features in the two-dimensional spectra were examined. Through simulations, we show that two-dimensional electronic spectroscopy provides a probe of the adiabaticity of the free energy landscape underlying light harvesting.

Wong, Cathy Y.; Alvey, Richard M.; Turner, Daniel B.; Wilk, Krystyna E.; Bryant, Donald A.; Curmi, Paul M. G.; Silbey, Robert J.; Scholes, Gregory D.

2012-05-01

226

Nomenclature for membrane-bound light-harvesting complexes of cyanobacteria.  

PubMed

Accessory chlorophyll-binding proteins (CBP) in cyanobacteria have six transmembrane helices and about 11 conserved His residues that might participate in chlorophyll binding. In various species of cyanobacteria, the CBP proteins bind different types of chlorophylls, including chlorophylls a, b, d and divinyl-chlorophyll a, b. The CBP proteins do not belong to the light-harvesting complexes (LHC) superfamily of plant and algae. The proposed new name of CBP for this class of proteins, which is a unique accessory light-harvesting superfamily in cyanobacteria, clarifies the confusion of names of prochlorophytes chlorophyll binding protein (Pcb), PSII-like light-harvesting proteins and iron-stress-induced protein A (IsiA). The CBP complexes are a member of a larger family that includes the chlorophyll a-binding proteins CP43 and CP47 that function as core antennas of photosystem II. PMID:17912604

Chen, Min; Zhang, Yinan; Blankenship, Robert E

2007-10-03

227

Independent evolution of the prochlorophyte and green plant chlorophyll a/b light-harvesting proteins.  

PubMed

The prochlorophytes are oxygenic prokaryotes differing from other cyanobacteria by the presence of a light-harvesting system containing both chlorophylls (Chls) a and b and by the absence of phycobilins. We demonstrate here that the Chl a/b binding proteins from all three known prochlorophyte genera are closely related to IsiA, a cyanobacterial Chl a-binding protein induced by iron starvation, and to CP43, a constitutively expressed Chl a antenna protein of photosystem II. The prochlorophyte Chl a/b protein (pcb) genes do not belong to the extended gene family encoding eukaryotic Chl a/b and Chl a/c light-harvesting proteins. Although higher plants and prochlorophytes share common pigment complements, their light-harvesting systems have evolved independently. PMID:8986795

La Roche, J; van der Staay, G W; Partensky, F; Ducret, A; Aebersold, R; Li, R; Golden, S S; Hiller, R G; Wrench, P M; Larkum, A W; Green, B R

1996-12-24

228

Light Harvesting as a Simple and Versatile Way to Enhance Brightness of Luminescent Sensors  

PubMed Central

The emissive output of indicator dyes in luminescent sensors can be amplified by the addition of antenna dyes with a higher brightness. The highly concentrated antenna dye molecules absorb the excitation light and transfer the energy to an indicator dye. This harvesting of light makes thin sensor layers (thickness <500 nm) and nanometer sized sensor particles with exceptionally high brightness and compatible with the most powerful LEDs available. The performance of sensor layers of ?250 nm thickness employing light harvesting was investigated and compared with established sensors. The principle is demonstrated for oxygen and ammonia sensors. An overview of possible application of light harvesting to various reagent mediated optical sensing schemes is given.

2009-01-01

229

Perfluoroalkyl chains direct novel self-assembly of insulin.  

PubMed

The self-assembly of biopharmaceutical peptides into multimeric, nanoscale objects, as well as their disassembly to monomers, is central for their mode of action. Here, we describe a bioorthogonal strategy, using a non-native recognition principle, for control of protein self-assembly based on intermolecular fluorous interactions and demonstrate it for the small protein insulin. Perfluorinated alkyl chains of varying length were attached to desB30 human insulin by acylation of the ?-amine of the side-chain of LysB29. The insulin analogues were formulated with Zn(II) and phenol to form hexamers. The self-segregation of fluorous groups directed the insulin hexamers to self-assemble. The structures of the systems were investigated by circular dichroism (CD) spectroscopy and synchrotron small-angle X-ray scattering. Also, the binding affinity to the insulin receptor was measured. Interestingly, varying the length of the perfluoroalkyl chain provided three different scenarios for self-assembly; the short chains hardly affected the native hexameric structure, the medium-length chains induced fractal-like structures with the insulin hexamer as the fundamental building block, while the longest chains lead to the formation of structures with local cylindrical geometry. This hierarchical self-assembly system, which combines Zn(II) mediated hexamer formation with fluorous interactions, is a promising tool to control the formation of high molecular weight complexes of insulin and potentially other proteins. PMID:22129241

Malik, Leila; Nygaard, Jesper; Hoiberg-Nielsen, Rasmus; Arleth, Lise; Hoeg-Jensen, Thomas; Jensen, Knud J

2011-12-22

230

Self assembled materials: design strategies and drug delivery perspectives.  

PubMed

Self assembly of small molecules in complex supramolecular structures provides a new avenue in the development of materials for drug delivery applications. Owing to the low aqueous solubility of various drugs, an effective delivery system is often required to reach sufficient drug bioavailability and/or to facilitate clinical use. Micelles, amphiphilic gels, vesicles (liposomes), nanodisks, cubosomes, colloidosomes, tubules, microemulsions, lipid particles, polyelectrolyte capsules etc. are some of the intriguing structures formed via self assembly. As well as enabling improved solubilization, such materials can be tuned to offer a range of other advantages, including controlled or stimuli sensitive drug release, protection from drug hydrolysis and chemical or enzymatic degradation, a reduction in toxicity, improvement of drug availability, prevention of RES uptake or selective targeting to organelles etc. Such multiple functionalities can be brought together by self assembly of different functional molecules. This route offers a cost effective means of developing drug delivery carriers tailored to specific needs. Our current understanding of the microstructure evolution of self assembled materials will go a long way towards designing/selecting molecules to create well defined structures. We believe that most of the potential resources mentioned above are untapped and that there is a need to further strengthen research in this area to fully exploit their potential. Selective cross linking of core or shell, stimuli sensitive amphiphiles, prodrug amphiphiles, antibody coupled amphiphiles etc. are only some of the new approaches for the development of effective drug delivery systems via self assembly. PMID:23907560

Verma, Gunjan; Hassan, P A

2013-09-25

231

Rapid self-assembly of DNA on a microfluidic chip.  

PubMed

BACKGROUND: DNA self-assembly methods have played a major role in enabling methods for acquiring genetic information without having to resort to sequencing, a relatively slow and costly procedure. However, even self-assembly processes tend to be very slow when they rely upon diffusion on a large scale. Miniaturisation and integration therefore hold the promise of greatly increasing this speed of operation. RESULTS: We have developed a rapid method for implementing the self-assembly of DNA within a microfluidic system by electrically extracting the DNA from an environment containing an uncharged denaturant. By controlling the parameters of the electrophoretic extraction and subsequent analysis of the DNA we are able to control when the hybridisation occurs as well as the degree of hybridisation. By avoiding off-chip processing or long thermal treatments we are able to perform this hybridisation rapidly and can perform hybridisation, sizing, heteroduplex analysis and single-stranded conformation analysis within a matter of minutes. The rapidity of this analysis allows the sampling of transient effects that may improve the sensitivity of mutation detection. CONCLUSIONS: We believe that this method will aid the integration of self-assembly methods upon microfluidic chips. The speed of this analysis also appears to provide information upon the dynamics of the self-assembly process. PMID:15717935

Zheng, Yao; Footz, Tim; Manage, Dammika P; Backhouse, Christopher James

2005-02-18

232

Evolving reaction-diffusion ecosystems with self-assembling structures in thin films.  

PubMed

Recently, new types of coupled isothermal polynucleotide amplification reactions for the investigation of in vitro evolution have been established that are based on the multi-enzyme 3SR reaction. Microstructured thin-film open bioreactors have been constructed in our laboratory to run these reactions spatially resolved in flow experiments. Artificial DNA/RNA chemistries close to the in vitro biochemistry of these systems have been developed, which we have studied in computer simulations in configurable hardware (NGEN). These artificial chemistries are described on the level of individual polynucleotide molecules, each with a defined sequence, and their complexes. The key feature of spatial pattern formation provides a weak stabilization of cooperative catalytic properties of the evolving molecules. Of great interest is the step to include extended self-assembly processes of flexible structures-allowing the additional stabilization of cooperation through semipermeable, flexible, self-organizing membrane boundaries. We show how programmable matter simulations of experimentally relevant molecular in vitro evolution can be extended to include the influence of self-assembling flexible membranes. PMID:9798273

Breyer, J; Ackermann, J; McCaskill, J

1998-01-01

233

Directed Self-Assembly of Gradient Concentric Carbon Nanotube Rings  

NASA Astrophysics Data System (ADS)

Hundreds of gradient concentric rings of linear conjugated polymer, (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4- phenylenevinylene], i.e., MEH-PPV) with remarkable regularity over large areas were produced by controlled, repetitive ``stick- slip'' motions of the contact line in a confined geometry consisting of a sphere on a flat substrate (i.e., sphere-on-flat geometry). Subsequently, MEH-PPV rings exploited as template to direct the formation of gradient concentric rings of multiwalled carbon nanotubes (MWNTs) with controlled density. This method is simple, cost effective, and robust, combining two consecutive self-assembly processes, namely, evaporation-induced self- assembly of polymers in a sphere-on-flat geometry, followed by subsequent directed self-assembly of MWNTs on the polymer- templated surfaces.

Hong, Suck Won; Jeong, Wonje; Ko, Hyunhyub; Tsukruk, Vladimir; Kessler, Michael; Lin, Zhiqun

2008-03-01

234

Cooperative self-assembly of a macrocyclic Schiff base complex.  

PubMed

A metal template approach affords in high yield a tetra-Zn(salphen) macrocycle (3) which shows strong and cooperative self-assembly mediated by the formation of Zn(salphen) dimer units held together via ?(2)-phenoxo interactions. A cooperative binding mode for the tetranuclear Zn(4) macrocycle 3 is supported by comparison of UV-vis and fluorescence titration data recorded for 3 when compared with respective mononuclear and dinuclear Zn(salphen) model compounds. UV-vis dilution experiments carried out for Zn(4) macrocycle 3 and its Pd(4) analogue 4, as well as comparative TEM studies involving the same tetranuclear macrocycles further support the strong assembly behavior of 3. This self-assembly seems to be primarily dictated by its ability to form multiple, self-assembled dimeric [Zn(salphen)](2) units. PMID:21455521

Salassa, Giovanni; Castilla, Ana M; Kleij, Arjan W

2011-04-01

235

Production of self-assembling biomaterials for tissue engineering.  

PubMed

Self-assembling peptide-based biomaterials are being developed for use as 3D tissue engineering scaffolds and for therapeutic drug-release applications. Chemical synthesis provides custom-made peptides in small quantities, but production approaches based upon transgenic organisms might be more cost-effective for large-scale peptide production. Long lead times for developing appropriate animal clones or plant lines and potential negative public opinion are obstacles to these routes. Microbes, particularly safe organisms used in the food industry, offer a more rapid route to the large-scale production of recombinant self-assembling biomaterials. In this review, recent advances and challenges in the recombinant production of collagen, elastin and de novo designed self-assembling peptides are discussed. PMID:19497631

Kyle, Stuart; Aggeli, Amalia; Ingham, Eileen; McPherson, Michael J

2009-06-06

236

Efficient Algorithms for Self Assembling Triangular and Other Nano Structures  

Microsoft Academic Search

Nano fabrication with biomolecular\\/DNA self assembly is a promising area of research. Building nano structures with self assembly\\u000a is both efficient and inexpensive. Winfree [1] formalized a two dimensional (2D) tile assembly model based on Wang’s tiling\\u000a technique. Algorithms with an optimal tile complexity of (\\u000a\\u000a\\u000a\\u000a\\u000a\\u000aQ<\\/font\\u000a>(\\\\fraclog(N)log(log(N)))\\\\Theta(\\\\frac{\\\\log(N)}{\\\\log(\\\\log(N))})) were proposed earlier to uniquely self assemble an N×N square (with a

Vamsi Kundeti; Sanguthevar Rajasekaran

2009-01-01

237

Directing the self-assembly of nanocrystals beyond colloidal crystallization.  

PubMed

This article gives an overview of recent progress in the self-assembly of nanocrystals. Classic self-assembly of nanocrystals, so-called colloidal crystallization driven by van der Waals interactions, is highlighted first with an emphasis on the recent realization of binary colloidal crystals. Next, new developments in the integration of nanocrystals into clusters based on electrostatic interactions, hydrogen bonding and dipole-dipole interactions are summarized, shedding light on the defined control of the interactions between the nanocrystals. Finally, the fabrication of heterogenous nanocrystals, obtained via either phase selective modification at the water/oil interface or facet-selective crystal growth on non-spherical nanocrystals is discussed. These last materials may provide significant building blocks for mimicking molecular self-assembly. PMID:16835676

Zhang, Hao; Edwards, Erik W; Wang, Dayang; Möhwald, Helmuth

2006-06-01

238

Production of self-assembling biomaterials for tissue engineering  

PubMed Central

Self-assembling peptide-based biomaterials are being developed for use as 3D tissue engineering scaffolds and for therapeutic drug-release applications. Chemical synthesis provides custom-made peptides in small quantities, but production approaches based upon transgenic organisms might be more cost-effective for large-scale peptide production. Long lead times for developing appropriate animal clones or plant lines and potential negative public opinion are obstacles to these routes. Microbes, particularly safe organisms used in the food industry, offer a more rapid route to the large-scale production of recombinant self-assembling biomaterials. In this review, recent advances and challenges in the recombinant production of collagen, elastin and de novo designed self-assembling peptides are discussed.

Kyle, Stuart; Aggeli, Amalia; Ingham, Eileen; McPherson, Michael J.

2009-01-01

239

Self-assembled ordered polymer nanocomposites directed by attractive particles  

SciTech Connect

We theoretically investigate general conditions under which an inorganic phase can direct the self-assembly of an ordered polymer nanocomposite. For this purpose, we consider a solution of triblock copolymers forming a hexagonal phase of micelles and investigate the effect of adding attractive particles. We show that if the triblock is functionalized at its ends by attaching groups with specific affinity for the particles, thus effectively becoming a pentablock, the particles direct the self-assembly of the system into phases where both the polymers and the particles exhibit mesoscopic order. Different lamellar and gyroid phases (both with Iad and I4132 space symmetries) are presented in detail. Our results show that functionalization is a very powerful route for directing self-assembly of polymer nanocomposites. We briefly discuss the connections with recent theoretical and experimental results in diblock melts with nanoparticles as well as for problems where polymers are used to template the growth of an inorganic phase in solution.

Knorowski, C.; Anderson, J.; Travesset, A.

2008-04-24

240

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

241

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

242

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

243

Recombinant self-assembling peptides as biomaterials for tissue engineering  

PubMed Central

Synthetic nanostructures based on self-assembling systems that aim to mimic natural extracellular matrix are now being used as substrates in tissue engineering applications. Peptides are excellent starting materials for the self-assembly process as they can be readily synthesised both chemically and biologically. P11-4 is an 11 amino acid peptide that undergoes triggered self-assembly to form a self-supporting hydrogel. It exists as unimers of random coil conformations in water above pH 7.5 but at low pH adopts an antiparallel ?-sheet conformation. It also self-assembles under physiological conditions in a concentration-dependent manner. Here we describe an unimer P11-4 production system and the use of a simple site-directed mutagenesis approach to generate a series of other P11-family peptide expression vectors. We have developed an efficient purification strategy for these peptide biomaterials using a simple procedure involving chemical cleavage with cyanogen bromide then repeated filtration, lyophilisation and wash steps. We report peptide-fusion protein yields of ca. 4.64 g/L and we believe the highest reported recovery of a recombinant self-assembling peptide at 203 mg/L of pure recombinant P11-4. This peptide forms a self-supporting hydrogel under physiological conditions with essentially identical physico-chemical properties to the chemically synthesised peptide. Critically it also displays excellent cytocompatibility when tested with primary human dermal fibroblasts. This study demonstrates that high levels of a series of recombinant self-assembling peptides can be purified using a simple process for applications as scaffolds in tissue engineering.

Kyle, Stuart; Aggeli, Amalia; Ingham, Eileen; McPherson, Michael J.

2010-01-01

244

Large Femtosecond Two-Photon Absorption Cross-Sections of Fullerosome Vesicle Nanostructures Derived from Highly Photoresponsive Amphiphilic C60-Light-Harvesting Fluorene Dyad  

PubMed Central

We demonstrated ultrafast femtosecond nonlinear optical (NLO) absorption characteristics of bilayered fullerosome vesicle nanostructures derived from molecular self-assembly of amphiphilic oligo(ethylene glycolated) C60-(light-harvesting diphenylaminofluorene antenna). Fullerene conjugates were designed to enhance photoresponse in a femtosecond time scale by applying an isomerizable periconjugation linker between the C60 cage and diphenylaminofluorene antenna subunit in an intramolecular contact distance of only < 3.0 Å. Morphology of C60(>DPAF-EG12C1)-based fullerosome nanovesicles in H2O was characterized to consist of a bilayered shell with a sphere diameter of 20–70 nm and a chromophore shell-width of 9.0–10 nm, fitting well with a head-to-head packing configuration of the molecular length. At the estimated effective nanovesicle concentration as low as 5.5 × 10?8 MV (molecular molar concentration of 5.0 × 10?4 M) in H2O, two-photon absorption (2PA) phenomena were found to be the dominating photophysical events showing a large molar concentration-insensitive 2PA cross-section value equivalent to 8500 GM in a form of nanovesicles, on average. The observed NLO characteristics led to a sharp trend of efficient light-transmittance intensity reduction at the input laser intensity above 100 GW/cm2.

Wang, Min; Nalla, Venkatram; Jeon, Seaho; Mamidala, Venkatesh; Ji, Wei; Tan, Loon-Seng; Cooper, Thomas; Chiang, Long Y.

2011-01-01

245

FRET sensitization of tungsten-alkylidyne complexes by zinc porphyrins in self-assembled dyads.  

PubMed

The photophysical properties of self-assembled zinc-porphyrin/tungsten-alkylidyne dyads have been investigated with the aim of determining whether the porphyrin S excited state sensitizes the tungsten-alkylidyne (3)[d?*] state. The luminescent metalloligand W(?CC(6)H(4)CCpy)(dppe)(2)Cl (1; dppe = 1,2-bis(diphenylphosphino)ethane) has been synthesized and shown by electronic and NMR spectroscopy to coordinate axially to ZnTPP and ZnTP(Cl)P (TP(Cl)P = tetra(p-chlorophenyl)porphyrin) via the terminal pyridyl group. Coordination of 1 to ZnPor results in partial quenching of porphyrin S(1) fluorescence and a decrease in the (3)[d?*] excited-state lifetime of 1. Transient-absorption spectroscopy shows that fluorescence quenching occurs via intramolecular Förster resonance energy transfer from the porphyrin S(1) state to the (1)[d?*] excited state of 1, which then undergoes rapid singlet-triplet intersystem crossing to produce the (3)[d?*] excited state. Sensitization of the (3)[d?*] state occurs with high overall efficiency (?(EnT) ? 80%), thus strongly enhancing light harvesting for the tungsten-alkylidyne compound. The mechanism and rates of the net S(1)?(3)[d?*] energy transfer are found to differ significantly from those for previously reported zinc-porphyrin/tungsten-alkylidyne dyads that are constructed from similar components but connected instead with covalent bonds at the porphyrin edge. Density functional theory calculations indicate that these differences are due in part to the degree of orbital mixing between the porphyrin and metal-alkylidyne subunits. PMID:23374026

Moravec, Davis B; Hopkins, Michael D

2013-02-15

246

Designing Isotropic Interactions for Self-Assembly of Complex Lattices  

NASA Astrophysics Data System (ADS)

We present a direct method for solving the inverse problem of designing isotropic potentials that cause self-assembly into target lattices. Each potential is constructed by matching its energy spectrum to the reciprocal representation of the lattice to guarantee that the desired structure is a ground state. We use the method to self-assemble complex lattices not previously achieved with isotropic potentials, such as a snub square tiling and the kagome lattice. The latter is especially interesting because it provides the crucial geometric frustration in several proposed spin liquids.

Edlund, E.; Lindgren, O.; Jacobi, M. Nilsson

2011-08-01

247

Ultrafine luminescent structures through nanoparticle self-assembly  

NASA Astrophysics Data System (ADS)

We report the fabrication of ultrafine structures consisting of regular arrays of nanoemitters through the self-assembly of luminescent nanoparticles on a silicon wafer. Nanoparticles of yttrium aluminium garnet (YAG) doped with Eu3+ ions were synthesized by a sonochemical technique. These particles, suspended in ethanol, are introduced onto a pre-patterned silicon wafer, covered with a thin oxide layer. On annealing the sample in an ultrahigh-vacuum chamber, the nanoparticles self-assemble along the pattern. We demonstrate this 'chemical lithography' by assembling the nanoparticles along a variety of patterns. We believe that such self-organized nanopatterning of functional structures is important for the realization of nanodevices.

Prabhakaran, K.; Götzinger, S.; Shafi, K. V. P. M.; Mazzei, A.; Schietinger, S.; Benson, O.

2006-08-01

248

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

249

Origin of enhanced light harvesting in colloidal-crystal-based dye-sensitised solar cells  

Microsoft Academic Search

The light harvesting enhancement observed when photonic colloidal crystals are integrated in dye sensitized titanium oxide solar cells is investigated herein. Such absorptance increment is explained in terms of slow photon propagation at certain ranges of wavelengths lying within the photonic pseudogap and partial localization in an absorbing layer placed onto the colloidal lattice. Based on those findings, not only

A. Mihi; F. J. López-Alcaraz; H. Míguez

2006-01-01

250

Studying the Effect of Light Quality on the Size of the Photosystem II Light Harvesting Complex  

ERIC Educational Resources Information Center

|In this article the effect of light quality on the size of the photosystem II (PSII) light harvesting complex (LHCII) is studied by measuring the chlorophyll fluorescence emitted by leaf sections of oat ("Avena sativa," var. Prevision) plants previously treated with either white light or with light filtered through blue, green, red or farred…

Muhoz, Romualdo; Quiles, Maria J.

2003-01-01

251

Molecular Biology of the Photoregulation of Photosynthetic Light-Harvesting Complexes in Marine Dinoflagellates.  

National Technical Information Service (NTIS)

Our goal is to continue to use biotechnological techniques to study the genetic bases of light- and nutrient-regulation of photosynthetic light-harvesting complexes in marine dinoflagellates. We chose the peridinin-chlorophyll a-protein (PCP) complexes of...

B. B. Prezelin E. L. Triplett

1991-01-01

252

Single-Molecule Electron Tunneling Spectroscopy of the Higher Plant Light-Harvesting Complex LHC II  

Microsoft Academic Search

Electronic spectroscopy of a single biological molecule is demonstrated with ?4 Å spatial resolution. The light-harvesting complex II (LHC II), in the ground and photo-excited states, was studied using scanning tunneling microscopy and spectroscopy of intact Photosystem II complexes. Analysis of the spectra indicates that the main mechanisms of tunneling between the STM tip and the surface involve delocalized electronic

Philip B. Lukins

1999-01-01

253

Taxonomic distribution and origins of the extended LHC (light-harvesting complex) antenna protein superfamily  

Microsoft Academic Search

BACKGROUND: The extended light-harvesting complex (LHC) protein superfamily is a centerpiece of eukaryotic photosynthesis, comprising the LHC family and several families involved in photoprotection, like the LHC-like and the photosystem II subunit S (PSBS). The evolution of this complex superfamily has long remained elusive, partially due to previously missing families. RESULTS: In this study we present a meticulous search for

Johannes Engelken; Henner Brinkmann; Iwona Adamska

2010-01-01

254

Optimization of light harvesting and photoprotection: molecular mechanisms and physiological consequences.  

PubMed

The distinctive lateral organization of the protein complexes in the thylakoid membrane investigated by Jan Anderson and co-workers is dependent on the balance of various attractive and repulsive forces. Modulation of these forces allows critical physiological regulation of photosynthesis that provides efficient light-harvesting in limiting light but dissipation of excess potentially damaging radiation in saturating light. The light-harvesting complexes (LHCII) are central to this regulation, which is achieved by phosphorylation of stromal residues, protonation on the lumen surface and de-epoxidation of bound violaxanthin. The functional flexibility of LHCII derives from a remarkable pigment composition and configuration that not only allow efficient absorption of light and efficient energy transfer either to photosystem II or photosystem I core complexes, but through subtle configurational changes can also exhibit highly efficient dissipative reactions involving chlorophyll-xanthophyll and/or chlorophyll-chlorophyll interactions. These changes in function are determined at a macroscopic level by alterations in protein-protein interactions in the thylakoid membrane. The capacity and dynamics of this regulation are tuned to different physiological scenarios by the exact protein and pigment content of the light-harvesting system. Here, the molecular mechanisms involved will be reviewed, and the optimization of the light-harvesting system in different environmental conditions described. PMID:23148272

Horton, Peter

2012-12-19

255

Light-harvesting antenna composition controls the macrostructure and dynamics of thylakoid membranes in Arabidopsis.  

PubMed

We characterized a set of Arabidopsis mutants deficient in specific light-harvesting proteins, using freeze-fracture electron microscopy to probe the organization of complexes in the membrane and confocal fluorescence recovery after photobleaching to probe the dynamics of thylakoid membranes within intact chloroplasts. The same methods were used to characterize mutants lacking or over-expressing PsbS, a protein related to light-harvesting complexes that appears to play a role in regulation of photosynthetic light harvesting. We found that changes in the complement of light-harvesting complexes and PsbS have striking effects on the photosystem II macrostructure, and that these effects correlate with changes in the mobility of chlorophyll proteins within the thylakoid membrane. The mobility of chlorophyll proteins was found to correlate with the extent of photoprotective non-photochemical quenching, consistent with the idea that non-photochemical quenching involves extensive re-organization of complexes in the membrane. We suggest that a key feature of the physiological function of PsbS is to decrease the formation of ordered semi-crystalline arrays of photosystem II in the low-light state. Thus the presence of PsbS leads to an increase in the fluidity of the membrane, accelerating the re-organization of the photosystem II macrostructure that is necessary for induction of non-photochemical quenching. PMID:21919982

Goral, Tomasz K; Johnson, Matthew P; Duffy, Christopher D P; Brain, Anthony P R; Ruban, Alexander V; Mullineaux, Conrad W

2011-10-21

256

Structural and functional heterogeneity in the major light-harvesting complexes of higher plants  

Microsoft Academic Search

The major light-harvesting complex (LHC IIb) of higher plants plays a crucial role in capturing light energy for photosynthesis and in regulating the flow of energy within the photosynthetic apparatus. Multiple isoforms of the protein bind chlorophyll and xanthophyll chromophores, but it is commonly believed that the pigment-binding properties of different LHC IIb complexes are conserved within and between species.

Robin G. Walters; Peter Horton

1999-01-01

257

The importance of PS I chlorophyll red forms in light-harvesting by leaves  

Microsoft Academic Search

We have investigated the importance of the long wavelength absorbing spectral forms (red forms) of Photosystem I in photosynthetic light harvesting by leaves. To this end leaf spectra were simulated by using a linear combination of absorption (OD) spectra of purified Photosystem I, Photosystem II and LHC II, multiplied by an empirical multiple scattering chloroplast\\/leaf conversion function. In this way

Andrea Rivadossi; Giuseppe Zucchelli; Flavio M. Garlaschi; Robert C. Jennings

1999-01-01

258

Structural and functional organization of the peripheral light-harvesting system in Photosystem I  

Microsoft Academic Search

This review centers on the structural and functional organization of the light-harvesting system in the peripheral antenna of Photosystem I (LHC I) and its energy coupling to the Photosystem I (PS I) core antenna network in view of recently available structural models of the eukaryotic Photosystem I–LHC I complex, eukaryotic LHC II complexes and the cyanobacterial Photosystem I core. A

Alexander N. Melkozernov; Robert E. Blankenship

2005-01-01

259

A Major Light-Harvesting Polypeptide of Photosystem II Functions in Thermal Dissipation  

Microsoft Academic Search

Under high-light conditions, photoprotective mechanisms minimize the damaging effects of excess light. A primary photoprotective mechanism is thermal dissipation of excess excitation energy within the light-harvesting complex of photosystem II (LHCII). Although roles for both carotenoids and specific polypeptides in thermal dissipation have been reported, neither the site nor the mechanism of this process has been defined precisely. Here, we

Dafna Elrad; Krishna K. Niyogi; Arthur R. Grossman

2002-01-01

260

Lamellar Organization of Pigments in Chlorosomes, the Light Harvesting Complexes of Green Photosynthetic Bacteria  

Microsoft Academic Search

Chlorosomes of green photosynthetic bacteria constitute the most efficient light harvesting complexes found in nature. In addition, the chlorosome is the only known photosynthetic system where the majority of pigments (BChl) is not organized in pigment-protein complexes but instead is assembled into aggregates. Because of the unusual organization, the chlorosome structure has not been resolved and only models, in which

J. Psencik; T. P. Ikonen; P. Laurinmäki; M. C. Merckel; S. J. Butcher; R. E. Serimaa; R. Tuma

2004-01-01

261

Multiscale simulation on a light-harvesting molecular triad.  

PubMed

We have investigated the effect of solvation and confinement on an artificial photosynthetic material, carotenoid-porphyrin-C(60) molecular triad, by a multiscale approach and an enhanced sampling technique. We have developed a combined approach of quantum chemistry, statistical physics, and all-atomistic molecular dynamics simulation to determine the partial atomic charges of the ground-state triad. To fully explore the free energy landscape of triad, the replica exchange method was applied to enhance the sampling efficiency of the simulations. The confinement effects on the triad were modeled by imposing three sizes of spherocylindrical nanocapsules. The triad is structurally flexible under ambient conditions, and its conformation distribution is manipulated by the choice of water models and confinement. Two types of water models (SPC/E and TIP3P) are used for solvation. When solvated by SPC/E water, whose HOH angle follows an ideal tetrahedron, the structural characteristics of triad is compact in the bulk systems. However, under a certain nanosized confinement that drastically disrupts hydrogen bond networks in solvent, the triad favors an extended configuration. By contrast, the triad solvated by TIP3P water shows a set of U-shaped conformations in the confinement. We have shown that a slight structural difference in the two water models with the same dipole moment can have great distinction in water density, water orientation, and the number of hydrogen bonds in the proximity of a large flexible compound such as the triad. Subsequently, it has direct impact on the position of the triad in a confinement as well as the distribution of conformations at the interface of liquid and solid in a finite-size system. PMID:22352456

Su, Guoxiong; Czader, Arkadiusz; Homouz, Dirar; Bernardes, Gabriela; Mateen, Sana; Cheung, Margaret S

2012-03-06

262

Supramolecular energy transfer from photoexcited chlorosomal zinc porphyrin self-aggregates to a chlorin or bacteriochlorin monomer as models of main light-harvesting antenna systems in green photosynthetic bacteria.  

PubMed

Self-aggregates of a synthetic zinc porphyrin worked as a light absorber and photoexcited energy donor, transferred the collected energy to a small amount of 3-acetyl-(bacterio)chlorin monomer, and induced near-infrared fluorescence from the acceptors in aqueous micellar solution. These artificial supramolecular systems are novel models of the main light-harvesting antennas of green photosynthetic bacteria, chlorosomes. PMID:22801645

Kataoka, Yumiko; Shibata, Yutaka; Tamiaki, Hitoshi

2012-06-28

263

Ultrafast Energy Transfer in an Artificial Photosynthetic Antenna  

NASA Astrophysics Data System (ADS)

We temporally resolved energy transfer kinetics in an artificial light-harvesting dyad composed of a phthalocyanine covalently linked to a carotenoid. Upon carotenoid photo-excitation, energy transfers within ?100fs (?52% efficiency) to the phthalocyanine.

Maiuri, M.; Snellenburg, J. J.; van Stokkum, I. H. M.; Pillai, S.; Gust, D.; Moore, T. A.; Moore, A. L.; van Grondelle, R.; Cerullo, G.; Polli, D.

2013-03-01

264

Visible-light harvesting iridium complexes as singlet oxygen sensitizers for photooxidation of 1,5-dihydroxynaphthalene.  

PubMed

Visible-light harvesting cyclometalated Ir(III) complexes were used as (1)O(2) sensitizers for the photooxidation of 1,5-dihydroxynaphthalene (DHN) and substantially improved photooxidation capability was observed compared to the conventional Ir(III) complex sensitizers that show no visible light-harvesting capabilities. PMID:22301532

Sun, Jifu; Zhao, Jianzhang; Guo, Huimin; Wu, Wanhua

2012-02-02

265

Higher plants light harvesting proteins. Structure and function as revealed by mutation analysis of either protein or chromophore moieties  

Microsoft Academic Search

Mutation analysis of higher plants light harvesting proteins has been prevented for a long time by the lack of a suitable expression system providing chromophores essential for the folding of these membrane-intrinsic pigment-protein complexes. Early work on in vitro reconstitution of the major light harvesting complex of photosystem II (LHCII) indicated an alternative way to mutation analysis of these proteins.

Dorianna Sandonà; Roberta Croce; Aldo Pagano; Massimo Crimi; Roberto Bassi

1998-01-01

266

Structure and Order of Phosphonic Acid-Based Self-Assembled Based Self-Assembled  

SciTech Connect

Organophosphonic acid self-assembled monolayers (SAMs) on oxide surfaces have recently seen increased use in electrical and biological sensor applications. The reliability and reproducibility of these sensors require good molecular organization in these SAMs. In this regard, packing, order, and alignment in the SAMs is important, as it influences the electron transport measurements. In this study, we examine the order of hydroxyl- and methyl-terminated phosphonate films deposited onto silicon oxide surfaces by the tethering by aggregation and growth method using complementary, state-of-art surface characterization tools. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and in situ sum frequency generation (SFG) spectroscopy are used to study the order of the phosphonate SAMs in vacuum and under aqueous conditions, respectively. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry results show that these samples form chemically intact monolayer phosphonate films. NEXAFS and SFG spectroscopy showed that molecular order exists in the octadecylphosphonic acid and 11-hydroxyundecylphosphonic acid SAMs. The chain tilt angles in these SAMs were approximately 37{sup o} and 45{sup o}, respectively.

Dubey, M.; Weidner, T; Gamble, L; Castner, D

2010-01-01

267

Chemical reaction mediated self-assembly of PTCDA into nanofibers.  

PubMed

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. PMID:21814688

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

2011-08-03

268

Rational molecular design of complementary self-assembling peptide hydrogels.  

PubMed

Rational molecular design of self- assembling peptide-based materials that spontaneously form self-supporting hydrogels shows potential in many healthcare applications. Binary peptides based on complementary charged sequences are developed, and the use of biophysical analysis and cell-based studies highlights that the charged interactions can influence the properties of peptide materials and ultimately affect biomaterial applications. PMID:23184800

Kyle, Stuart; Felton, Susan H; McPherson, Michael J; Aggeli, Amalia; Ingham, Eileen

2012-07-12

269

Analysis of capillary forces in electrowetting and precision self assembly  

Microsoft Academic Search

Developments in micro and nano technology have great potential in many applications. Two applications that will be addressed in this work are self assembly of microdevices and Electrowetting in microfluidics. Capillary forces are the most critical factor in both of these techniques and need proper characterization. This thesis describes a detailed study of these forces and explains how they were

Vivek Ramadoss

2008-01-01

270

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

271

Self-assembly of Nanoparticles into Planar Modulated Superstructures  

Microsoft Academic Search

The advance in the synthesis of nanoparticles and colloids opens up the possibility to use them as building blocks for self-assembling novel materials. Ordered structures are especially interesting because they have unique photonic and electronic properties. Among the most complex ordered phases are commensurately and incommensurately modulated crystals. Although frequently found on the atomic scale in the bulk and as

Michael Engel

2011-01-01

272

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

273

Complexities for generalized models of self-assembly  

Microsoft Academic Search

In this paper, we extend Rothemund and Winfree's examination of the tile complexity of tile self-assembly [6]. They provided a lower bound of ?(log N\\/log log N) on the tile complexity of assembling an N × N square for almost all N. Adleman et al. [1] gave a construction which achieves this bound. We consider whether the tile complexity for

Gagan Aggarwal; Michael H. Goldwasser; Ming-Yang Kao; Robert T. Schweller

2004-01-01

274

From Local to Global Behavior in Intelligent Self-Assembly  

Microsoft Academic Search

In this paper we present a method by which to orga- nize the interactions of autonomous assembly agents in Intelligent Self-Assembly (ISA). Each assembly agent has limited and local sensing and local rule-based control. A Transition Rule Set (TRS) Compiler is presented which takes a desired goal structure as input and gives as output a set of rules. When each

Chris Jones; Maja J. Mataric

2002-01-01

275

Assemble time for self-assembling square tiles  

Microsoft Academic Search

As technology drives components smaller, tradi- tional methods of assembling these components become ever more impractical. Self-assembly is a viable solution in which the individual components autonomously organize themselves without the external guidance of a supervising agent. In this paper we look at the assembly times for various one and two dimensional objects that are assembled with square tiles in

James Solberg

276

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

277

Electrochemically assisted self-assembly of mesoporous silica thin films  

Microsoft Academic Search

Supported mesostructured thin films are of major importance for applications in optical, electrochemical and sensing devices. However, good performance is restricted to mesostructured phases ensuring good accessibility from the film surface, which would be straightforward with cylindrical pores oriented normal to the underlying support, but this remains challenging. Here, we demonstrate that electrochemistry is likely to induce self-assembly of surfactant-templated

E. Sibottier; M. Etienne; J. Ghanbaja; A. Walcarius

2007-01-01

278

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

279

Directed intermixing in multi-component self-assembling biomaterials  

PubMed Central

The non-covalent co-assembly of multiple different peptides can be a useful route for producing multifunctional biomaterials. However, to date such materials have almost exclusively been investigated as homogeneous self-assemblies, having functional components uniformly distributed throughout their supramolecular structures. Here we illustrate control over the intermixing of multiple different self-assembling peptides, in turn providing a simple but powerful means for modulating these materials’ mechanical and biological properties. In beta-sheet fibrillizing hydrogels, significant increases in stiffening could be achieved using heterobifunctional cross-linkers by sequestering peptides bearing different reactive groups into distinct populations of fibrils, thus favoring inter-fibril cross-linking. Further, by specifying the intermixing of RGD-bearing peptides in 2-D and 3-D self-assemblies, the growth of HUVECs and NIH 3T3 cells could be significantly modulated. This approach may be immediately applicable towards a wide variety of self-assembling systems that form stable supramolecular structures.

Gasiorowski, Joshua Z.; Collier, Joel H.

2011-01-01

280

Transparent self-assembled films of reduced graphene oxide platelets  

Microsoft Academic Search

Transparent conducting films have been fabricated in one step, combining self-assembly and chemical reduction of graphene oxide platelets dispersed in water. The films are of centimeter scale and their thickness can be controlled by the concentration of the graphene oxide suspension. The optical transmittance values at a wavelength of 550 nm were 87% and 96% for the films made from

Yanwu Zhu; Weiwei Cai; Richard D. Piner; Aruna Velamakanni; Rodney S. Ruoff

2009-01-01

281

Subcomponent self-assembly: a quick way to new metallogels.  

PubMed

1-2-3 gel! Subcomponent self-assembly is introduced as a new design route towards multistimuli-responsive metallogels. It offers a rapid and facile access to supramolecular gels and allows to design smart materials with diverse functional and structural properties by simply exchanging one (or more) of the components. Herein, the exchange of the metal ions is emphasized. PMID:24038302

Bunzen, Hana; Nonappa; Kalenius, Elina; Hietala, Sami; Kolehmainen, Erkki

2013-08-28

282

Covalently stabilized self-assembled chlorophyll nanorods by olefin metathesis.  

PubMed

A new chlorophyll derivative with peripheral olefinic chains has been synthesised and its self-assembly properties have been studied, revealing formation of well-defined nanorods. These nanorods were stabilized and rigidified by olefin metathesis reaction as confirmed by spectroscopic and microscopic methods. PMID:22555512

Sengupta, Sanchita; Würthner, Frank

2012-05-03

283

Halogen bonding driven self-assembly of fluorocarbons and hydrocarbons  

Microsoft Academic Search

Halogen bonding, the interaction between halogen atoms and lone pair possessing atoms, overcomes the low affinity existing between perfluorocarbon and hydrocarbon derivatives. This interaction effectively drives the self-assembly of materials wherein perfluorocarbon and hydrocarbon layers alternate thanks to a remarkable module segregation. The approach has been exploited in supramolecular polymer coating.

Pierangelo Metrangolo; Tullio Pilati; Giuseppe Resnati; Andrea Stevenazzi

2003-01-01

284

Targeted delivery with peptidomimetic conjugated self-assembled nanoparticles.  

PubMed

Peptides produce specific nanostructures, making them useful for targeting in biological systems but they have low bioavailability, potential immunogenicity and poor metabolic stability. Peptidomimetic self-assembled NPs can possess biological recognition motifs as well as providing desired engineering properties. Inorganic NPs, coated with self-assembled macromers for stability and anti-fouling, and conjugated with target-specific ligands, are advancing imaging from the anatomy-based level to the molecular level. Ligand conjugated NPs are attractive for cell-selective tumor drug delivery, since this process has high transport capacity as well as ligand dependent cell specificity. Peptidomimetic NPs can provide stronger interaction with surface receptors on tumor cells, resulting in higher uptake and reduced drug resistance. Self-assembled NPs conjugated with peptidomimetic antigens are ideal for sustained presentation of vaccine antigens to dendritic cells and subsequent activation of T cell mediated adaptive immune response. Self-assembled NPs are a viable alternative to encapsulation for sustained delivery of proteins in tissue engineering. Cell penetrating peptides conjugated to NPs are used as intracellular delivery vectors for gene expression and as transfection agents for plasmid delivery. In this work, synthesis, characterization, properties, immunogenicity, and medical applications of peptidomimetic NPs in imaging, tumor delivery, vaccination, tissue engineering, and intracellular delivery are reviewed. PMID:19085091

Jabbari, Esmaiel

2008-12-17

285

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

PubMed

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. PMID:20209016

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

2009-07-01

286

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

287

Structural control in model microtubule self-assembly  

NASA Astrophysics Data System (ADS)

Being able to control the structure formed in self-assembly is the goal of many nanoscience studies. Here we explore various ways to control the structure of self-assembled tubules. We have previously developed a model wedge-shaped monomer that can self-assemble into tubule structures. We now add chirality and a lock-and-key mechanism to the model to enhance structural control of the self-assembly. Previously, we found that helical tubes are frequently formed despite the fact that chiral symmetry is not present in the monomer. We now identify the physical origin of helicity as the large overlap in the energy distributions between nonhelical and helical tubes. The helical tubes typically undergo a twist deformation that lowers the energy substantially. We find that a modification of the location of binding sites on the bottom and top surfaces of the wedge into a lock-and-key configuration leads to a better control of the helicity and twist deformation of the assembled tubes. Better control occurs when the interaction strength between the vertical binding sites is stronger than that between the lateral ones. We can also control the pitch of the helicity by adjusting the location of binding sites on the lateral surfaces of the monomer. Our results shed new light on the structure of in vitro microtubules formed with various numbers of protofilaments of tubulins, which also exhibit twisted structures when the number is different from 13.

Cheng, Shengfeng; Stevens, Mark

2013-03-01

288

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

289

Artificial increase of the light-harvesting ability of photosynthetic units in isolated chloroplasts  

Microsoft Academic Search

A synthetic fluorochromous lipid, rhodaminyl triglyceride (rhodaminyl TG), was intercalated into isolated thylakoid membranes of chloroplasts up to 30 molecules per 100 molecules of chlorophyll. As a result of fluorochrome presence, an absorption band appeared in a yellow-green spectrum region, its intensity being comparable with the red and blue chlorophyll bands. The energy absorbed by rhodaminyl TG was transferred through

E. M. Sorokin; G. S. Bobylyev; Y. G. Molotkovsky

1990-01-01

290

Staging the Self-Assembly Process: Inspiration from Biological Development.  

PubMed

Abstract One of the practical challenges facing the creation of self-assembling systems is being able to exploit a limited set of fixed components and their bonding mechanisms. The method of staging divides the self-assembly process into time intervals, during which components can be added to, or removed from, an environment at each interval. Staging addresses the challenge of using components that lack plasticity by encoding the construction of a target structure in the staging algorithm itself and not exclusively in the design of the components. Previous staging strategies do not consider the interplay between component physical features (morphological information). In this work we use morphological information to stage the self-assembly process, during which components can only be added to their environment at each time interval, to demonstrate our concept. Four experiments are presented, which use heterogeneous, passive, mechanical components that are fabricated using 3D printing. Two orbital shaking environments are used to provide energy to the components and to investigate the role of morphological information with component movement in either two or three spatial dimensions. The benefit of our staging strategy is shown by reducing assembly errors and exploiting bonding mechanisms with rotational properties. As well, a doglike target structure is used to demonstrate in theory how component information used at an earlier time interval can be reused at a later time interval, inspired by the use of a body plan in biological development. We propose that a staged body plan is one method towards scaling self-assembling systems with many interacting components. The experiments and body plan example demonstrate, as proof of concept, that staging enables the self-assembly of more complex morphologies not otherwise possible. PMID:23373983

Bhalla, Navneet; Bentley, Peter J; Vize, Peter D; Jacob, Christian

2013-02-01

291

The Self-Made Puzzle: Integrating Self-Assembly and Pattern Formation Under Non-Random Genetic Regulation  

NASA Astrophysics Data System (ADS)

On the one hand, research in self-assembling systems, whether natural or artificial, has traditionally focused on pre-existing components endowed with fixed shapes. Biological development, by contrast, dynamically creates new cells that acquire selective adhesion properties through differentiation induced by their neighborhood. On the other hand, pattern formation phenomena are generally construed as orderly states of activity on top of a continuous 2-D or 3-D substrate. Yet, again, the spontaneous patterning of an organism into domains of gene expression arises within a multicellular medium in perpetual expansion and reshaping. Finally, both phenomena are often thought in terms of stochastic events, whether mixed components that randomly collide in self-assembly, or spots and stripes that occur unpredictably from instabilities in pattern formation. Here too, these notions need significant revision if they are to be extended and applied to embryogenesis. Cells are not randomly mixed but pre-positioned where cell division occurs. Genetic identity domains are not randomly distributed but highly regulated in number and position. In this work, I present a computational model of program-mable and reproducible artificial morphogenesis that integrates self-assembly and pattern formation under the control of a nonrandom gene regulatory network. The specialized properties of cells (division, adhesion, migration) are determined by the gene expression domains to which they belong, while at the same time these domains further expand and segment into subdomains due to the self-assembly of specialized cells. Through this model, I also promote a new discipline, embryomorphic engineering to solve the paradox of "meta-designing" decentralized, autonomous systems.

Doursat, René

292

Design of Nanostructured Biological Materials Through Self-Assembly of Peptides and Proteins.  

National Technical Information Service (NTIS)

Introduction Self-assembly can be defined as the spontaneous organization of individual components into an ordered structure without human intervention. The key elements of molecular self-assembly are complementarity in shape among the individual componen...

S. Zhang D. M. Marini W. Hwang S. Santoso

2002-01-01

293

Tissue engineering by self-assembly and bio-printing of living cells.  

PubMed

Biofabrication of living structures with desired topology and functionality requires the interdisciplinary effort of practitioners of the physical, life and engineering sciences. Such efforts are being undertaken in many laboratories around the world. Numerous approaches are pursued, such as those based on the use of natural or artificial scaffolds, decellularized cadaveric extracellular matrices and, most lately, bioprinting. To be successful in this endeavor, it is crucial to provide in vitro micro-environmental clues for the cells resembling those in the organism. Therefore, scaffolds, populated with differentiated cells or stem cells, of increasing complexity and sophistication are being fabricated. However, no matter how sophisticated scaffolds are, they can cause problems stemming from their degradation, eliciting immunogenic reactions and other a priori unforeseen complications. It is also being realized that ultimately the best approach might be to rely on the self-assembly and self-organizing properties of cells and tissues and the innate regenerative capability of the organism itself, not just simply prepare tissue and organ structures in vitro followed by their implantation. Here we briefly review the different strategies for the fabrication of three-dimensional biological structures, in particular bioprinting. We detail a fully biological, scaffoldless, print-based engineering approach that uses self-assembling multicellular units as bio-ink particles and employs early developmental morphogenetic principles, such as cell sorting and tissue fusion. PMID:20811127

Jakab, Karoly; Norotte, Cyrille; Marga, Francoise; Murphy, Keith; Vunjak-Novakovic, Gordana; Forgacs, Gabor

2010-06-02

294

Self-assembling viral mimetics: one long journey with short steps.  

PubMed

Recently, the Foresight Institute has pronounced six economic challenges that can be addressed through the progress of nanotechnology. One of these is the health and longevity of human life. Amongst applications anticipated to provide a solution to this challenge, gene therapy appears to be particularly promising. In theory, many diseases that result from genetic disorders can be cured by correcting defective genes. In practice, finding efficient and safe delivery vectors remains the stumbling point on the path of genetic therapies to the clinic. Viruses, otherwise the most efficient transfectors, pose safety concerns over immune reactions, whereas synthetic gene packages greatly lack the structural integrity of viruses. An ideal vector is therefore seen as a compromise between the two: a nanoscale device, which would mimic a virus and act as a virus, but would do this at the designer's whim. A strategy to achieve this is offered by the virus architecture itself, the principles of which are translated into the function via exquisitely reproducible self-assembly mechanisms. Thus, to mimic a virus is to mimic the way it is built, i.e., self-assembly. With just a few attempts made so far, the journey to an artificial virus has had a short lifetime, but the promise it holds is not expected to reduce any time soon. PMID:21165940

Lamarre, Baptiste; Ryadnov, Maxim G

2010-12-16

295

The mechanical stimulation of cells in 3D culture within a self-assembling peptide hydrogel.  

PubMed

The aim of this present study was to provide a scaffold as a tool for the investigation of the effect of mechanical stimulation on three-dimensionally cultured cells. For this purpose, we developed an artificial self-assembling peptide (SPG-178) hydrogel scaffold. The structural properties of the SPG-178 peptide were confirmed by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and transmission electron microscopy (TEM). The mechanical properties of the SPG-178 hydrogel were studied using rheology measurements. The SPG-178 peptide was able to form a stable, transparent hydrogel in a neutral pH environment. In the SPG-178 hydrogel, mouse skeletal muscle cells proliferated successfully (increased by 12.4 ± 1.5 times during 8 days of incubation; mean ± SEM). When the scaffold was statically stretched, a rapid phosphorylation of ERK was observed (increased by 2.8 ± 0.2 times; mean ± SEM). These results demonstrated that the developed self-assembling peptide gel is non-cytotoxic and is a suitable tool for the investigation of the effect of mechanical stimulation on three-dimensional cell culture. PMID:22056753

Nagai, Yusuke; Yokoi, Hidenori; Kaihara, Keiko; Naruse, Keiji

2011-11-05

296

Self-assembly and mineralization of genetically modifiable biological nanofibers driven by beta-structure formation  

PubMed Central

Bio-inspired mineralization is an innovative approach to the fabrication of bone biomaterials mimicking the natural bone. Bone mineral hydroxylapatite (HAP) is preferentially oriented with c-axis parallel to collagen fibers in natural bone. However, such orientation control is not easy to achieve in artificial bone biomaterials. To overcome the lack of such orientation control, we fabricated a phage-HAP composite by genetically engineering M13 phage, a non-toxic bio-nanofiber, with two HAP-nucleating peptides derived from one of the non-collagenous proteins, Dentin Matrix Protein-1 (DMP1). The phage is a biological nanofiber that can be mass produced by infecting bacteria and is non-toxic to human beings. The resultant HAP-nucleating phages are able to self-assemble into bundles by forming ?-structure between the peptides displayed on their side walls. The ?-structure further promotes the oriented nucleation and growth of HAP crystals within the nanofibrous phage bundles with their c-axis preferentially parallel to the bundles. We proposed that the preferred orientation resulted from the stereochemical matching between the negatively charged amino acid residues within the ?-structure and the positively charged calcium ions on the (001) plane of HAP crystals. The self-assembly and mineralization driven by the ?-structure formation represent a new route for fabricating mineralized fibers that can serve as building blocks in forming bone repair biomaterials and mimic the basic structure of natural bones.

Xu, Hong; Cao, Binrui; George, Anne; Mao, Chuanbin

2011-01-01

297

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

298

Light-harvesting chlorophyll a/b-binding protein inserted into isolated thylakoids binds pigments and is assembled into trimeric light-harvesting complex.  

PubMed Central

The light-harvesting chlorophyll a/b-binding protein (LHCP) is largely protected against protease (except for about 1 kD on the N terminus) in the thylakoid membrane; this protease resistance is often used to assay successful insertion of LHCP into isolated thylakoids in vitro. In this paper we show that this protease resistance is exhibited by trimeric light-harvesting complex of photosystem II (LHCII) but not by monomeric LHCII in which about 5 kD on the N terminus of LHCP are cleaved off by protease. When a mutant version of LHCP that is unable to trimerize in an in vitro reconstitution assay is inserted into isolated thylakoids, it gives rise to only the shorter protease digestion product indicative of monomeric LHCII. We conclude that more of the N-terminal domain of LHCP is shielded in trimeric than in monomeric LHCII and that this difference in protease sensitivity can be used to distinguish between LHCP assembled in LHCII monomers or trimers. The data presented prove that upon insertion of LHCP into isolated thylakoids at least part of the protein spontaneously binds pigments to form LHCII, which then is assembled in trimers. The dependence of the protease sensitivity of thylakoid-inserted LHCP on the oligomerization state of the newly formed LHCII justifies caution when using a protease assay to verify successful insertion of LHCP into the membrane.

Kuttkat, A; Grimm, R; Paulsen, H

1995-01-01

299

Algorithm for elliptic curve Diffie-Hellman key exchange based on DNA tile self-assembly  

Microsoft Academic Search

DNA tile self-assembly is a promising paradigm for nanotechnology. Recently, many researches show that computation by DNA tile self-assembly maybe scalable. In this paper, we propose the algorithm for elliptic curve Diffie-Hellman key exchange based on DNA tile self-assembly. First we give the DNA tile self-assembly model to compute the scalar multiplication, then we can successfully implement the Diffie-Hellman key

Zhen Cheng; Yufang Huang; Jin Xu

2008-01-01

300

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

301

Exciton annihilation and energy transfer in self-assembled peptide-porphyrin complexes depends on peptide secondary structure.  

PubMed

We used picosecond transient absorption and fluorescence lifetime spectroscopy to study singlet exciton annihilation and depolarization in self-assembled aggregates of meso-tetra(4-sulfonatophenyl)porphine (TPPS(4)) and a synthetic 22-residue polypeptide. The polypeptide was designed and previously shown to bind three TPPS(4) monomers via electrostatic interactions between the sulfonate groups and cationic lysine residues. Additionally, the peptide induces formation of TPPS(4) J-aggregates in acidic solutions when the peptide secondary structure is disordered. In neutral solutions, the peptide adopts an ?-helical secondary structure that can bind TPPS(4) with high affinity but J-aggregate formation is inhibited. Detailed analysis of excitation-power dependent transient absorption kinetics was used to obtain rate constants describing the energy transfer between TPPS(4) molecules in an aggregate under acidic and neutral conditions. Independently, such analysis was confirmed by picosecond fluorescence emission depolarization measurements. We find that energy transfer between TPPS(4) monomers in a peptide-TPPS(4) complex is more than 30 times faster in acidic aqueous solution than in neutral solutions (9 vs 279 ps). This result was attributed to a conformational change of the peptide backbone from disordered at low pH to ?-helical at neutral pH and suggests a new approach to control intermolecular energy transfer with possible applications in fluorescent sensors or biomimetic light harvesting antennas. PMID:21069973

Kuciauskas, Darius; Kiskis, Juris; Caputo, Gregory A; Gulbinas, Vidmantas

2010-11-11

302

Self-assembled photosystem-I biophotovoltaics on nanostructured TiO(2 )and ZnO.  

PubMed

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/cm(2) and photocurrent density of 362?µA/cm(2), over four orders of magnitude higher than any photosystem-based biophotovoltaic to date. PMID:22355747

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

2012-02-02

303

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

PubMed Central

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

2012-01-01

304

Using artificial physics to control agents  

Microsoft Academic Search

We introduce a novel framework called “artificial physics”, which provides distributed control of large collections of agents. The agents react to artificial forces that are motivated by natural physical laws. This framework provides an effective mechanism for achieving self-assembly, fault-tolerance, and self-repair. Examples are shown for various regular geometric configurations of agents. A further example demonstrates that self-assembly via distributed

William M. Spears; Diana F. Gordon

1999-01-01

305

Modeling of Fluorescence Quenching by Lutein in the Plant Light-Harvesting Complex LHCII.  

PubMed

Photoprotective non-photochemical quenching (NPQ) in higher plants is the result of the formation of energy quenching traps in the light-harvesting antenna of photosystem II (PSII). It has been proposed that this quenching trap is a lutein molecule closely associated with the chlorophyll terminal emitter of the major light-harvesting complex LHCII. We have used a combination of time-dependent density functional theory (TD-DFT) and the semiempirical MNDO-CAS-CI method to model the chlorophyll-lutein energy transfer dynamics of the highly quenched crystal structure of LHCII. Our calculations reveal that the incoherent "hopping" of energy from Chla612 to the short-lived, dipole forbidden 2(1)Ag(-) state of lutein620 accounts for the strong fluorescence quenching observed in these crystals. This adds weight to the argument that the same dissipative pathway is responsible for in vivo NPQ. PMID:23234311

Duffy, C D P; Chmeliov, J; Macernis, M; Sulskus, J; Valkunas, L; Ruban, A V

2012-12-27

306

Phylogenetic viewpoints on regulation of light harvesting and electron transport in eukaryotic photosynthetic organisms.  

PubMed

The comparative study of photosynthetic regulation in the thylakoid membrane of different phylogenetic groups can yield valuable insights into mechanisms, genetic requirements and redundancy of regulatory processes. This review offers a brief summary on the current understanding of light harvesting and photosynthetic electron transport regulation in different photosynthetic eukaryotes, with a special focus on the comparison between higher plants and unicellular algae of secondary endosymbiotic origin. The foundations of thylakoid structure, light harvesting, reversible protein phosphorylation and PSI-mediated cyclic electron transport are traced not only from green algae to vascular plants but also at the branching point between the "green" and the "red" lineage of photosynthetic organisms. This approach was particularly valuable in revealing processes that (1) are highly conserved between phylogenetic groups, (2) serve a common physiological role but nevertheless originate in divergent genetic backgrounds or (3) are missing in one phylogenetic branch despite their unequivocal importance in another, necessitating a search for alternative regulatory mechanisms and interactions. PMID:22971817

Grouneva, Irina; Gollan, Peter J; Kangasjärvi, Saijaliisa; Suorsa, Marjaana; Tikkanen, Mikko; Aro, Eva-Mari

2012-09-13

307

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

308

Nature-inspired light-harvesting liquid crystalline porphyrins for organic photovoltaics  

SciTech Connect

A new class of nanoscale light-harvesting discotic liquid crystalline porphyrins, with the same basic structure of the best photoreceptor in nature (chlorophyll), was synthesized. These materials can be exceptionally aligned into a highly ordered architecture in which the columns formed by intermolecular {pi}-{pi} stacking are spontaneously perpendicular to the substrate. The homeotropic alignment, well confirmed by synchrotron X-ray diffraction, could not only provide the most efficient pathway for hole conduction along the columnar axis crossing the device thickness, but also offer the largest area to the incident light for optimized light harvesting. Their preliminary photocurrent generation and photovoltaic performances were also demonstrated. The results provide new and efficient pathways to the development of organic photovoltaics by using homeotropically aligned liquid crystal thin films.

Li, Lanfang; Kang, Shin-Woong; Harden, John; Sun, Qingjiang; Zhou, Xiaoli; Dai, Liming; Jakli, Antal; Kumar, Satyendra; Li, Quan (NSF); (Kent); (Dayton)

2008-12-22

309

Quantitative investigations of quantum coherence for a light-harvesting protein at conditions simulating photosynthesis.  

PubMed

Recent measurements using two-dimensional electronic spectroscopy (2D ES) have shown that the initial dynamic response of photosynthetic proteins can involve quantum coherence. We show how electronic coherence can be differentiated from vibrational coherence in 2D ES. On that basis we conclude that both electronic and vibrational coherences are observed in the phycobiliprotein light-harvesting complex PC645 from Chroomonas sp. CCMP270 at ambient temperature. These light-harvesting antenna proteins of the cryptophyte algae are suspended in the lumen, where the pH drops significantly under sustained illumination by sunlight. Here we measured 2D ES of PC645 at increasing levels of acidity to determine if the change in pH affects the quantum coherence; quantitative analysis reveals that the dynamics are insensitive to the pH change. PMID:22374579

Turner, Daniel B; Dinshaw, Rayomond; Lee, Kyung-Koo; Belsley, Michael S; Wilk, Krystyna E; Curmi, Paul M G; Scholes, Gregory D

2012-02-29

310

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

311

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

2013-08-30

312

Self-Organization in Coordination-Driven Self-Assembly  

PubMed Central

Conspectus Self-assembly allows for the preparation of highly complex molecular and supramolecular systems from relatively simple starting materials. Typically, self-assembled supramolecules are constructed by combining complementary pairs of two highly symmetric molecular components, thus limiting the chances of forming unwanted side products. Combining asymmetric molecular components or multiple complementary sets of molecules in one complex mixture can produce myriad different ordered and disordered supramolecular assemblies. Alternatively, spontaneous self-organization phenomena can promote the formation of specific product(s) out of a collection of multiple possibilities. Self-organization processes are common throughout much of nature and are especially common in biological systems. Recently, researchers have studied self-organized self-assembly in purely synthetic systems. This Account describes our investigations of self-organization in the coordination-driven self-assembly of platinum(II)-based metallosupramolecules. The modularity of the coordination-driven approach to self-assembly has allowed us to systematically study a wide variety of different factors that can control the extent of supramolecular self-organization. In particular, we have evaluated the effects of the symmetry and polarity of ambidentate donor subunits, differences in geometrical parameters (e.g. the size, angularity, and dimensionality) of Pt(II)-based acceptors and organic donors, the influence of temperature and solvent, and the effects of intermolecular steric interactions and hydrophobic interactions on self-organization. Our studies have shown that the extent of self-organization in the coordination-driven self-assembly of both 2D polygons and 3D polyhedra ranges from no organization (a statistical mixture of multiple products), to amplified organization (wherein a particular product or products are favored over others), and all the way to the absolute self-organization of discrete supramolecular assemblies. In many cases, inputs such as dipolar interactions, steric interactions, and differences in the geometric parameters of subunits—used either alone or as multiple factors simultaneously—can achieve absolute self-organization of discrete supramolecules. We have also observed instances where self-organization is not absolute and varies in its deviation from statistical results. Steric interactions are particularly useful control factors for driving such amplified self-organization because they can be subtly tuned through small structural variations. Having the ability to fully understand and control the self-organization of complex mixtures into specific synthetic supramolecules can provide a better understanding of analogous processes in biological systems. Furthermore, self-organization may allow for the facile synthesis of complex multifunctional, multicomponent systems from simply mixing a collection of much simpler, judiciously designed individual molecular components.

Northrop, Brian H.; Zheng, Yao-Rong; Chi, Ki-Whan; Stang, Peter J.

2009-01-01

313

Primary light-harvesting system: phycobilisomes and associated membranes. Progress report, December 1979January 1983  

Microsoft Academic Search

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 species, with allophycocyanin being in the core from which peripheral rods composed of phycocyanin or phycocyanin-phycoerythyrin radiate. Such studies were extended to show that energetically functional phycobilisomes could be

Gantt

1983-01-01

314

Evolution of light-harvesting complex proteins from Chl c -containing algae  

Microsoft Academic Search

Background  Light harvesting complex (LHC) proteins function in photosynthesis by binding chlorophyll (Chl) and carotenoid molecules that\\u000a absorb light and transfer the energy to the reaction center Chl of the photosystem. Most research has focused on LHCs of plants\\u000a and chlorophytes that bind Chl a and b and extensive work on these proteins has uncovered a diversity of biochemical functions, expression

Gabriel E Hoffman; M Virginia Sanchez Puerta; Charles F Delwiche

2011-01-01

315

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

Microsoft Academic Search

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

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

2004-01-01

316

Noise-assisted energy transfer in quantum networks and light-harvesting complexes  

Microsoft Academic Search

We provide physically intuitive mechanisms for the effect of noise on excitation energy transfer (EET) in networks. Using these mechanisms of dephasing-assisted transport (DAT) in a hybrid basis of both excitons and sites, we develop a detailed picture of how noise enables energy transfer with efficiencies well above 90% across the Fenna–Matthew–Olson (FMO) complex, a type of light-harvesting molecule. We

Alex W. Chin; Animesh Datta; Filippo Caruso; Susana F. Huelga; Martin B. Plenio

2010-01-01

317

Assemblies of semiconductor quantum dots and light-harvesting-complex II  

Microsoft Academic Search

A novel hybrid system composed of fluorescent core\\/shell semiconductor quantum dots and the light harvesting complex II (LHCIIb), a membrane protein of higher plants, has been assembled. Experiments with different mutants show that hybrid formation can be mediated by a C-terminal His6 tag attached to the protein as well as by positive charges of the first N-terminal amino acids of

Wolfgang Erker; Stephanie Boggasch; Renguo Xie; Götz Grundmann; Harald Paulsen; Thomas Basché

2010-01-01

318

Noise-assisted energy transfer in quantum networks and light-harvesting complexes  

Microsoft Academic Search

We provide physically intuitive mechanisms for the effect of noise on excitation energy transfer (EET) in networks. Using these mechanisms of dephasing-assisted transport (DAT) in a hybrid basis of both excitons and sites, we develop a detailed picture of how noise enables energy transfer with efficiencies well above 90% across the Fenna-Matthew-Olson (FMO) complex, a type of light-harvesting molecule. We

A. W. Chin; A. Datta; F. Caruso; S. F. Huelga; M. B. Plenio

2010-01-01

319

A Bloch equation approach to intensity dependent optical spectra of light harvesting complex II  

Microsoft Academic Search

On the basis of the recent progress in the resolution of the structure of the antenna light harvesting complex II (LHC II)\\u000a of the photosystem II, we propose a microscopically motivated theory to predict excitation intensity-dependent spectra. We\\u000a show that optical Bloch equations provide the means to include all 2\\u000a N\\u000a excited states of an oligomer complex of N coupled

Marten Richter; Thomas Renger; Andreas Knorr

2008-01-01

320

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

PubMed

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. PMID:23818601

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

2013-07-01

321

Investigations of photosynthetic light harvesting by two-dimensional electronic spectroscopy  

Microsoft Academic Search

Photosynthesis begins with the harvesting of sunlight by antenna pigments, organized in a network of pigment-protein complexes that rapidly funnel energy to photochemical reaction centers. The intricate design of these systems---the widely varying structural motifs of pigment organization within proteins and protein organization within a larger, cooperative network---underlies the remarkable speed and efficiency of light harvesting. Advances in femtosecond laser

Elizabeth Louise Read

2008-01-01

322

Purification and Characterization of the Polypeptides of Core Light-Harvesting Complexes from Purple Sulfur Bacteria  

Microsoft Academic Search

Although the polypeptides of core light-harvesting complexes (LH1) from many purple nonsulfur bacteria have been well characterized,\\u000a little information is available on the polypeptides of LH1 from purple sulfur photosynthetic organisms. We present here the\\u000a results of isolation and characterization of LH1 polypeptides from two purple sulfur bacteria, Thermochromatium (Tch.) tepidum and Allochromatium (Ach.) vinosum. Native LH1 complexes were extracted

Zheng-Yu Wang; Masahiro Shimonaga; Hiroaki Suzuki; Masayuki Kobayashi; Tsunenori Nozawa

2003-01-01

323

Structural and functional diversification of the light-harvesting complexes in photosynthetic eukaryotes  

Microsoft Academic Search

Eukaryotes acquired photosynthetic metabolism over a billion years ago, and during that time the light-harvesting antennae\\u000a have undergone significant structural and functional divergence. The antenna systems are generally used to harvest and transfer\\u000a excitation energy into the reaction centers to drive photosynthesis, but also have the dual role of energy dissipation. Phycobilisomes\\u000a formed the first antenna system in oxygenic photoautotrophs,

Jonathan A. D. Neilson; Dion G. Durnford

2010-01-01

324

Involvement of the light-harvesting complex in cation regulation of excitation energy distribution in chloroplasts  

Microsoft Academic Search

A highly purified light-harvesting pigment--protein complex (LHC) was obtained by fractionation of cation-depleted chloroplast membranes using the nonionic detergent, Triton X-100. The isolated LHC had a chlorophyll a\\/b ratio of 1.2 and exhibited no photochemical activity. SDS-polyacrylamide gel electrophoresis of the LHC revealed three polypeptides in the molecular weight classes of 23, 25, and 30 x 10³. Antibodies were prepared

J. J. Burke; C. L. Ditto; C. J. Arntzen

1978-01-01

325

Evolution of the Inner Light-Harvesting Antenna Protein Family of Cyanobacteria, Algae, and Plants  

Microsoft Academic Search

Two hypotheses account for the evolution of the inner antenna light-harvesting proteins of oxygenic photosynthesis in cyanobacteria,\\u000a algae, and plants: one in which the CP43 protein of photosytem II gave rise to the extrinsic CP43-like antennas of cyanobacteria\\u000a (i.e. IsiA and Pcb proteins), as a late development, and the other in which CP43 and CP43-like proteins derive from an ancestral

Yinan Zhang; Min Chen; Bing Bing Zhou; Lars S. Jermiin; Anthony W. D. Larkum

2007-01-01

326

Nomenclature for membrane-bound light-harvesting complexes of cyanobacteria  

Microsoft Academic Search

Accessory chlorophyll-binding proteins (CBP) in cyanobacteria have six transmembrane helices and about 11 conserved His residues\\u000a that might participate in chlorophyll binding. In various species of cyanobacteria, the CBP proteins bind different types\\u000a of chlorophylls, including chlorophylls a, b, d and divinyl-chlorophyll a, b. The CBP proteins do not belong to the light-harvesting complexes (LHC) superfamily of plant and algae.

Min Chen; Yinan Zhang; Robert E. Blankenship

2008-01-01

327

Light-induced fluorescence quenching in the light-harvesting chlorophyll a\\/b protein complex  

Microsoft Academic Search

Irradiation of the principal photosystem II light-harvesting chlorophyll-protein antenna complex, LHC II, with high light intensities brings about a pronounced quenching of the chlorophyll fluorescence. Illumination of isolated thylakoids with high light intensities generates the formation of quenching centres within LHC II in vivo, as demonstrated by fluorescence excitation spectroscopy. In the isolated complex it is demonstrated that the light-induced

Robert C. Jennings; Flavio M. Garlaschi; Giuseppe Zucchelli

1991-01-01

328

Photon upconversion in hetero-nanostructured photoanodes for enhanced near-infrared light harvesting.  

PubMed

A hetero-nanostructured photoanode with enhanced near-infrared light harvesting is developed for photo-electrochemical cells. By spatially coating upconversion nanoparticles and quantum dot photosensitizers onto TiO2 inverse opal, this architecture allows direct irradiation of upconversion nanoparticles to emit visible light that excites quantum dots for charge separation. Electrons are injected into TiO2 with minimal carrier losses due to continuous electron conducting interface. PMID:23288630

Su, Liap Tat; Karuturi, Siva Krishna; Luo, Jingshan; Liu, Lijun; Liu, Xinfeng; Guo, Jun; Sum, Tze Chien; Deng, Renren; Fan, Hong Jin; Liu, Xiaogang; Tok, Alfred Iing Yoong

2013-01-03

329

Chlorophylls, ligands and assembly of light-harvesting complexes in chloroplasts  

Microsoft Academic Search

Chlorophyll (Chl) b serves an essential function in accumulation of light-harvesting complexes (LHCs) in plants. In this article, this role of\\u000a Chl b is explored by considering the properties of Chls and the ligands with which they interact in the complexes. The overall\\u000a properties of the Chls, not only their spectral features, are altered as consequences of chemical modifications on

J. Kenneth Hoober; Laura L. Eggink; Min Chen

2007-01-01

330

A Phylogenetic Assessment of the Eukaryotic Light-Harvesting Antenna Proteins, with Implications for Plastid Evolution  

Microsoft Academic Search

.   The light-harvesting complexes (LHCs) are a superfamily of chlorophyll-binding proteins present in all photosynthetic eukaryotes.\\u000a The Lhc genes are nuclear-encoded, yet the pigment–protein complexes are localized to the thylakoid membrane and provide a marker\\u000a to follow the evolutionary paths of plastids with different pigmentation. The LHCs are divided into the chlorophyll a\\/b-binding proteins of the green algae, euglenoids, and

D. G. Durnford; J. A. Deane; S. Tan; G. I. McFadden; E. Gantt; B. R. Green

1999-01-01

331

Extended red light harvesting in a poly(3-hexylthiophene)\\/iron disulfide nanocrystal hybrid solar cell  

Microsoft Academic Search

A polymer solar cell based on poly(3-hexylthiophene) (P3HT)\\/iron disulfide (FeS2) nanocrystal (NC) hybrid is presented. The FeS2 NCs of 10 nm in diameter were homogeneously blended with P3HT to form an active layer of a solar cell. An extended red light harvesting up to 900 nm resulting from the NCs in the device has been demonstrated, compared to a typical

Yun-Yue Lin; Di-Yan Wang; Hung-Chi Yen; Hsuen-Li Chen; Chia-Chun Chen; Chun-Ming Chen; Chih-Yuan Tang; Chun-Wei Chen

2009-01-01

332

Rapid energy transfer in a dendrimer having pi-conjugated light-harvesting antennas  

Microsoft Academic Search

We investigate rapid energy transfer (ET) and its temperature dependence in a star-shaped stilbenoid phthalocyanine (SSS1Pc) dendrimer having pi-conjugated light-harvesting (LH) antennas, and develop an appropriate model. In SSS1Pc, an intense core photoluminescence (PL) band appears under the selective excitation of the absorption bands of the LH antenna due to highly efficient ET at room temperature (RT). The transient response

I. Akai; K. Miyanari; T. Shimamoto; A. Fujii; H. Nakao; A. Okada; K. Kanemoto; T. Karasawa; H. Hashimoto; A. Ishida; A. Yamada; I. Katayama; J. Takeda; M. Kimura

2008-01-01

333

Bacteriochlorophyll-protein complexes from the light-harvesting antenna of photosynthetic bacteria  

Microsoft Academic Search

Detergent-solubilized bacteriochlorophyll--protein complexes corresponding to the light-harvesting antenna are isolated from Rhodopseudomonas sphaeroides, strain 2.4.1 (wild-type) and R-2 (carotenoidless) mutant, and from Rhodospirillum rubrum, wild-type. Detailed studies of the complex derived from the R-26 mutant indicate that it contains two bacteriochlorophyll (BChl) molecules and two copies of a peptide of 8.5 kdaltons, together with about 20 percent phospholipid in a

Kenneth Sauer; Lynn A. Austin

1978-01-01

334

Pharmaceutical Nanotechnology Self-assembled drug delivery systems 1. Properties and in vitro\\/in vivo behavior of acyclovir self-assembled nanoparticles (SAN)  

Microsoft Academic Search

Self-assembled drug delivery systems (SADDS) were designed in the paper. They can be prepared from the amphiphilic conjugates of hydrophilic drugs and lipids through self-assembling into small-scale aggregates in aqueous media. The outstanding characteristic of SADDS is that they are nearly wholly composed of amphiphilic prodrugs. The self-assembled nanoparticles (SAN) as one of SADDS had been prepared from the lipid

Yiguang Jin; Miao Li; Xinpu Hou

335

Metal-enhanced fluorescence of chlorophylls in light-harvesting complexes coupled to silver nanowires.  

PubMed

We investigate metal-enhanced fluorescence of peridinin-chlorophyll protein coupled to silver nanowires using optical microscopy combined with spectrally and time-resolved fluorescence techniques. In particular we study two different sample geometries: first, in which the light-harvesting complexes are deposited onto silver nanowires, and second, where solution of both nanostructures are mixed prior deposition on a substrate. The results indicate that for the peridinin-chlorophyll complexes placed in the vicinity of the silver nanowires we observe higher intensities of fluorescence emission as compared to the reference sample, where no nanowires are present. Enhancement factors estimated for the sample where the light-harvesting complexes are mixed together with the silver nanowires prior deposition on a substrate are generally larger in comparison to the other geometry of a hybrid nanostructure. While fluorescence spectra are identical both in terms of overall shape and maximum wavelength for peridinin-chlorophyll-protein complexes both isolated and coupled to metallic nanostructures, we conclude that interaction with plasmon excitations in the latter remains neutral to the functionality of the biological system. Fluorescence transients measured for the PCP complexes coupled to the silver nanowires indicate shortening of the fluorescence lifetime pointing towards modifications of radiative rate due to plasmonic interactions. Our results can be applied for developing ways to plasmonically control the light-harvesting capability of photosynthetic complexes. PMID:23533354

Kowalska, Dorota; Krajnik, Bartosz; Olejnik, Maria; Twardowska, Magdalena; Czechowski, Nikodem; Hofmann, Eckhard; Mackowski, Sebastian

2013-03-04

336

Discrete Redox Signaling Pathways Regulate Photosynthetic Light-Harvesting and Chloroplast Gene Transcription  

PubMed Central

In photosynthesis in chloroplasts, two related regulatory processes balance the actions of photosystems I and II. These processes are short-term, post-translational redistribution of light-harvesting capacity, and long-term adjustment of photosystem stoichiometry initiated by control of chloroplast DNA transcription. Both responses are initiated by changes in the redox state of the electron carrier, plastoquinone, which connects the two photosystems. Chloroplast Sensor Kinase (CSK) is a regulator of transcription of chloroplast genes for reaction centres of the two photosystems, and a sensor of plastoquinone redox state. We asked whether CSK is also involved in regulation of absorbed light energy distribution by phosphorylation of light-harvesting complex II (LHC II). Chloroplast thylakoid membranes isolated from a CSK T-DNA insertion mutant and from wild-type Arabidopsis thaliana exhibit similar light- and redox-induced 32P-labelling of LHC II and changes in 77 K chlorophyll fluorescence emission spectra, while room-temperature chlorophyll fluorescence emission transients from Arabidopsis leaves are perturbed by inactivation of CSK. The results indicate indirect, pleiotropic effects of reaction centre gene transcription on regulation of photosynthetic light-harvesting in vivo. A single, direct redox signal is transmitted separately to discrete transcriptional and post-translational branches of an integrated cytoplasmic regulatory system.

Allen, John F.; Santabarbara, Stefano; Allen, Carol A.; Puthiyaveetil, Sujith

2011-01-01

337

Structural and functional diversification of the light-harvesting complexes in photosynthetic eukaryotes.  

PubMed

Eukaryotes acquired photosynthetic metabolism over a billion years ago, and during that time the light-harvesting antennae have undergone significant structural and functional divergence. The antenna systems are generally used to harvest and transfer excitation energy into the reaction centers to drive photosynthesis, but also have the dual role of energy dissipation. Phycobilisomes formed the first antenna system in oxygenic photoautotrophs, and this soluble protein complex continues to be the dominant antenna in extant cyanobacteria, glaucophytes, and red algae. However, phycobilisomes were lost multiple times during eukaryotic evolution in favor of a thylakoid membrane-integral light-harvesting complex (LHC) antenna system found in the majority of eukaryotic taxa. While photosynthesis spread across different eukaryotic kingdoms via endosymbiosis, the antenna systems underwent extensive modification as photosynthetic groups optimized their light-harvesting capacity and ability to acclimate to changing environmental conditions. This review discusses the different classes of LHCs within photosynthetic eukaryotes and examines LHC diversification in different groups in a structural and functional context. PMID:20596891

Neilson, Jonathan A D; Durnford, Dion G

2010-07-02

338

A major light-harvesting polypeptide of photosystem II functions in thermal dissipation.  

PubMed

Under high-light conditions, photoprotective mechanisms minimize the damaging effects of excess light. A primary photoprotective mechanism is thermal dissipation of excess excitation energy within the light-harvesting complex of photosystem II (LHCII). Although roles for both carotenoids and specific polypeptides in thermal dissipation have been reported, neither the site nor the mechanism of this process has been defined precisely. Here, we describe the physiological and molecular characteristics of the Chlamydomonas reinhardtii npq5 mutant, a strain that exhibits little thermal dissipation. This strain is normal for state transition, high light-induced violaxanthin deepoxidation, and low light growth, but it is more sensitive to photoinhibition than the wild type. Furthermore, both pigment data and measurements of photosynthesis suggest that the photosystem II antenna in the npq5 mutant has one-third fewer light-harvesting trimers than do wild-type cells. The npq5 mutant is null for a gene designated Lhcbm1, which encodes a light-harvesting polypeptide present in the trimers of the photosystem II antennae. Based on sequence data, the Lhcbm1 gene is 1 of 10 genes that encode the major LHCII polypeptides in Chlamydomonas. Amino acid alignments demonstrate that these predicted polypeptides display a high degree of sequence identity but maintain specific differences in their N-terminal regions. Both physiological and molecular characterization of the npq5 mutant suggest that most thermal dissipation within LHCII of Chlamydomonas is dependent on the peripherally associated trimeric LHC polypeptides. PMID:12172023

Elrad, Dafna; Niyogi, Krishna K; Grossman, Arthur R

2002-08-01

339

Direct evidence of quantum transport in photosynthetic light-harvesting complexes  

PubMed Central

The photosynthetic light-harvesting apparatus moves energy from absorbed photons to the reaction center with remarkable quantum efficiency. Recently, long-lived quantum coherence has been proposed to influence efficiency and robustness of photosynthetic energy transfer in light-harvesting antennae. The quantum aspect of these dynamics has generated great interest both because of the possibility for efficient long-range energy transfer and because biology is typically considered to operate entirely in the classical regime. Yet, experiments to date show only that coherence persists long enough that it can influence dynamics, but they have not directly shown that coherence does influence energy transfer. Here, we provide experimental evidence that interaction between the bacteriochlorophyll chromophores and the protein environment surrounding them not only prolongs quantum coherence, but also spawns reversible, oscillatory energy transfer among excited states. Using two-dimensional electronic spectroscopy, we observe oscillatory excited-state populations demonstrating that quantum transport of energy occurs in biological systems. The observed population oscillation suggests that these light-harvesting antennae trade energy reversibly between the protein and the chromophores. Resolving design principles evident in this biological antenna could provide inspiration for new solar energy applications.

Panitchayangkoon, Gitt; Voronine, Dmitri V.; Abramavicius, Darius; Caram, Justin R.; Lewis, Nicholas H. C.; Mukamel, Shaul; Engel, Gregory S.

2011-01-01

340

Direct evidence of quantum transport in photosynthetic light-harvesting complexes.  

PubMed

The photosynthetic light-harvesting apparatus moves energy from absorbed photons to the reaction center with remarkable quantum efficiency. Recently, long-lived quantum coherence has been proposed to influence efficiency and robustness of photosynthetic energy transfer in light-harvesting antennae. The quantum aspect of these dynamics has generated great interest both because of the possibility for efficient long-range energy transfer and because biology is typically considered to operate entirely in the classical regime. Yet, experiments to date show only that coherence persists long enough that it can influence dynamics, but they have not directly shown that coherence does influence energy transfer. Here, we provide experimental evidence that interaction between the bacteriochlorophyll chromophores and the protein environment surrounding them not only prolongs quantum coherence, but also spawns reversible, oscillatory energy transfer among excited states. Using two-dimensional electronic spectroscopy, we observe oscillatory excited-state populations demonstrating that quantum transport of energy occurs in biological systems. The observed population oscillation suggests that these light-harvesting antennae trade energy reversibly between the protein and the chromophores. Resolving design principles evident in this biological antenna could provide inspiration for new solar energy applications. PMID:22167798

Panitchayangkoon, Gitt; Voronine, Dmitri V; Abramavicius, Darius; Caram, Justin R; Lewis, Nicholas H C; Mukamel, Shaul; Engel, Gregory S

2011-12-13

341

Investigations of photosynthetic light harvesting by two-dimensional electronic spectroscopy  

NASA Astrophysics Data System (ADS)

Photosynthesis begins with the harvesting of sunlight by antenna pigments, organized in a network of pigment-protein complexes that rapidly funnel energy to photochemical reaction centers. The intricate design of these systems---the widely varying structural motifs of pigment organization within proteins and protein organization within a larger, cooperative network---underlies the remarkable speed and efficiency of light harvesting. Advances in femtosecond laser spectroscopy have enabled researchers to follow light energy on its course through the energetic levels of photosynthetic systems. Now, newly-developed femtosecond two-dimensional electronic spectroscopy reveals deeper insight into the fundamental molecular interactions and dynamics that emerge in these structures. The following chapters present investigations of a number of natural light-harvesting complexes using two-dimensional electronic spectroscopy. These studies demonstrate the various types of information contained in experimental two-dimensional spectra, and they show that the technique makes it possible to probe pigment-protein complexes on the length- and time-scales relevant to their functioning. New methods are described that further extend the capabilities of two-dimensional electronic spectroscopy, for example, by independently controlling the excitation laser pulse polarizations. The experiments, coupled with theoretical simulation, elucidate spatial pathways of energy flow, unravel molecular and electronic structures, and point to potential new quantum mechanical mechanisms of light harvesting.

Read, Elizabeth Louise

342

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

343

Metal-Enhanced Fluorescence of Chlorophylls in Light-Harvesting Complexes Coupled to Silver Nanowires  

PubMed Central

We investigate metal-enhanced fluorescence of peridinin-chlorophyll protein coupled to silver nanowires using optical microscopy combined with spectrally and time-resolved fluorescence techniques. In particular we study two different sample geometries: first, in which the light-harvesting complexes are deposited onto silver nanowires, and second, where solution of both nanostructures are mixed prior deposition on a substrate. The results indicate that for the peridinin-chlorophyll complexes placed in the vicinity of the silver nanowires we observe higher intensities of fluorescence emission as compared to the reference sample, where no nanowires are present. Enhancement factors estimated for the sample where the light-harvesting complexes are mixed together with the silver nanowires prior deposition on a substrate are generally larger in comparison to the other geometry of a hybrid nanostructure. While fluorescence spectra are identical both in terms of overall shape and maximum wavelength for peridinin-chlorophyll-protein complexes both isolated and coupled to metallic nanostructures, we conclude that interaction with plasmon excitations in the latter remains neutral to the functionality of the biological system. Fluorescence transients measured for the PCP complexes coupled to the silver nanowires indicate shortening of the fluorescence lifetime pointing towards modifications of radiative rate due to plasmonic interactions. Our results can be applied for developing ways to plasmonically control the light-harvesting capability of photosynthetic complexes.

Kowalska, Dorota; Krajnik, Bartosz; Olejnik, Maria; Czechowski, Nikodem; Mackowski, Sebastian

2013-01-01

344

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

345

Self-assembling fluorinated porphyrin derivatives on metal surfaces  

NASA Astrophysics Data System (ADS)

The production of two-dimensional molecular networks on the nanometer scale is one of the most promising routes to create electronic devices. An elegant method towards such a goal is provided by self-assembly of functional organic molecules, thus exploiting the principles of supramolecular chemistry. By means of scanning tunnelling microscopy operated in ultra-high vacuum conditions and at room temperature, the self-assembly of two different porphyrins derivatives, below a full monolayer, is studied on coinage metal surfaces. We show that the deposition rate plays a central role in the formation of different molecular patterns. Of special interest is a very stable porous network stabilized by an intriguing arrangement of the molecules having pentafluoro-groups quite close to each other. Furthermore, we show that the pores of the network can host a guest molecule.

Iacovita, Cristian; Wiss, Jerome; Enache, Mihaela; Samuely, Tomas; Voigt, Tobias; Hornung, Jens; Diederich, François; Jung, Thomas; Stohr, Meike

2010-03-01

346

Self-assembly of double helical nanostructures inside carbon nanotubes.  

PubMed

We use molecular dynamics (MD) simulations to show that a DNA-like double helix of two poly(acetylene) (PA) chains can form inside single-walled carbon nanotubes (SWNTs). The computational results indicate that SWNTs can activate and guide the self-assembly of polymer chains, allowing them to adopt a helical configuration in a SWNT through the combined action of the van der Waals potential well and the ?-? stacking interaction between the polymer and the inner surface of SWNTs. Meanwhile both the SWNT size and polymer chain stiffness determine the outcome of the nanostructure. Furthermore, we also found that water clusters encourage the self-assembly of PA helical structures in the tube. This molecular model may lead to a better understanding of the formation of a double helix biological molecule inside SWNTs. Alternatively, it could form the basis of a novel nanoscale material by utilizing the 'empty' spaces of SWNTs. PMID:23334090

Lv, Cheng; Xue, Qingzhong; Shan, Meixia; Jing, Nuannuan; Ling, Cuicui; Zhou, Xiaoyan; Jiao, Zhiyong; Xing, Wei; Yan, Zifeng

2013-05-21

347

Self-assembly of a bipolar model of biomacromolecules.  

PubMed

Extending recent work on a generic bipolar model proposed to study the nanochain formation of amelogenin molecules, we conduct a systematic investigation in this paper on the self-assembly of such a model via sweeping the relative parameter space. The bipolar model consists of a short-range attraction and an off-center Coulomb repulsion for the supermolecule. Through the Brownian dynamics simulation of both translational and rotational motions, we study the kinetics of the self-assembly and the structure of clusters formed within the system for various interaction settings. From the results of structure factor and cluster analysis, we find that the range of the repulsive interaction has a sensitive impact in controlling the cluster size, while the strength of the attractive interaction dominates the cluster morphology such that the greater the attraction among particles, the more elongated the cluster formed. PMID:23484544

Li, Wei; Chakrabarti, Amitabha; Gunton, James D

2013-03-27

348

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

2013-02-11

349

Self-assembly and semiconductivity of an oligothiophene supergelator.  

PubMed

A bis(trialkoxybenzamide)-functionalized quaterthiophene derivative was synthesized and its self-assembly properties in solution were studied. In non-polar solvents such as cyclohexane, this quaterthiophene ?-system formed fibril aggregates with an H-type molecular arrangement due to synergistic effect of hydrogen bonding and ?-stacking. The self-assembled fibres were found to gelate numerous organic solvents of diverse polarity. The charge transport ability of such elongated fibres of quaterthiophene ?-system was explored by the pulse radiolysis time resolved microwave conductivity (PR-TRMC) technique and moderate mobility values were obtained. Furthermore, initial AFM and UV-vis spectroscopic studies of a mixture of our electron-rich quaterthiophene derivative with the electron acceptor [6,6]-phenyl-C??-butyric acid methyl ester (PCBM) revealed a nanoscale segregated assembly of the individual building blocks in the blend. PMID:21160557

Pratihar, Pampa; Ghosh, Suhrit; Stepanenko, Vladimir; Patwardhan, Sameer; Grozema, Ferdinand C; Siebbeles, Laurens D A; Würthner, Frank

2010-11-16

350

Biomolecular decision-making process for self assembly.  

SciTech Connect

The brain is often identified with decision-making processes in the biological world. In fact, single cells, single macromolecules (proteins) and populations of molecules also make simple decisions. These decision processes are essential to survival and to the biological self-assembly and self-repair processes that we seek to emulate. How do these tiny systems make effective decisions? How do they make decisions in concert with a cooperative network of other molecules or cells? How can we emulate the decision-making behaviors of small-scale biological systems to program and self-assemble microsystems? This LDRD supported research to answer these questions. Our work included modeling and simulation of protein populations to help us understand, mimic, and categorize molecular decision-making mechanisms that nonequilibrium systems can exhibit. This work is an early step towards mimicking such nanoscale and microscale biomolecular decision-making processes in inorganic systems.

Osbourn, Gordon Cecil

2005-01-01

351

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

352

Self-Assembly for Integration of Microscale Thermoelectric Coolers  

NASA Astrophysics Data System (ADS)

Optimum thermoelectric cooling (TEC) solutions often require the integration of component sizes inaccessible by common manufacturing techniques such as thin-film processing and robotic assembly. This work considers an application case in which small elements (100 ?m to 300 ?m thick) are optimal. A capillary self-assembly process is presented as a potential route to manufacturing TECs in these size ranges. A millimeter-scale demonstration of the assembly concept is presented and Monte Carlo simulation is used to study the scaling of the self-assembly approach to assemblies with more components. While assembly rate and system yield can be a challenge, several approaches are presented for increasing both rate and yield.

Crane, Nathan B.; Mishra, Pradeep; Murray, Jeffrey L.; Nolas, G. S.

2009-07-01

353

Self-assembly and semiconductivity of an oligothiophene supergelator  

PubMed Central

Summary A bis(trialkoxybenzamide)-functionalized quaterthiophene derivative was synthesized and its self-assembly properties in solution were studied. In non-polar solvents such as cyclohexane, this quaterthiophene ?-system formed fibril aggregates with an H-type molecular arrangement due to synergistic effect of hydrogen bonding and ?-stacking. The self-assembled fibres were found to gelate numerous organic solvents of diverse polarity. The charge transport ability of such elongated fibres of quaterthiophene ?-system was explored by the pulse radiolysis time resolved microwave conductivity (PR-TRMC) technique and moderate mobility values were obtained. Furthermore, initial AFM and UV-vis spectroscopic studies of a mixture of our electron-rich quaterthiophene derivative with the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) revealed a nanoscale segregated assembly of the individual building blocks in the blend.

Pratihar, Pampa; Ghosh, Suhrit; Stepanenko, Vladimir; Patwardhan, Sameer; Grozema, Ferdinand C; Siebbeles, Laurens D A

2010-01-01

354

Catalysts from Self-Assembled Organometallic Block Copolymers  

NASA Astrophysics Data System (ADS)

Heterogeneous catalysts were prepared by crosslinking the polyisoprene block of a microphase separated poly(vinyl ferrocenium triflate-block-isoprene) copolymer. The poly(vinyl ferrocenium triflate) moieties are responsible for catalytic activity while the polyisoprene block provides the support structure. The efficacy of the catalyst was analyzed by studying the Michael addition of ethyl-2-oxycyclopentane carboxylate and methyl vinyl ketone. The materials were studied via Transmission Electron Microscopy and the reaction rates were monitored by NMR spectroscopy. The activities obtained with our self-assembled heterogeneous catalyst were within experimental error of the rate of monomeric ferrocenium triflate as well as other homogeneous catalyst analogues. Our method for synthesizing catalysts is unique because the structures of both the support and active sites are controlled by molecular self-assembly.

Durkee, David; Ellsworth, Mark; Balsara, Nitash

2005-03-01

355

Highly tunable self-assembled plasmonic lattices through nanosphere lithography.  

PubMed

This Letter reports a method to produce two-dimensional self-assembled plasmonic nanopillar (NP) arrays with independent control of the diameter (d), spacing (s), and height (h) of the NPs. A plasmonic lattice was designed and optimized for maximum plasmonic activity at 980 nm using three-dimensional finite-difference time-domain simulations. The optimized lattice with d=365??nm, s=410??nm, and h=70??nm was fabricated utilizing a self-assembled nanosphere lithography approach. Outstanding agreement between the observed and predicted results confirms the validity of the design process and the controllability and repeatability of the fabrication process. The excellent short-range order in the lattice structure suggests that this method can replace the electron-beam lithography approach in a scalable and cost-effective manner. PMID:23939007

Farrokh Baroughi, M; Dachhepati, D; Gautam, U; Bayat, K; May, S

2013-06-15

356

Self-Assembly: Nature's Way to Do It  

NSDL National Science Digital Library

Biology operates at two levels: the large scale which we can see and the underlying microscopic one. This video lecture describes how intermolecular forces cause protein arrays to self-assemble, enabling nature to fabricate the large scale components of living systems. The lecturer explains how scale, forces and information cooperate to form complex structures. There are demonstrations of gravity, surface tension and capillary forces assembling materials, as well as experiments producing thin films from a ferritin solution. The presenter introduces his Protein Array Project, which attempts to fabricate thin hexagonal lattice films by imitating the beauty and utility of nature. Links to resources on self-assembly and nanotechnology are provided. The lecture is 58 minutes in length.

2007-04-17

357

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

358

Self-assembled carboxylate complexes of zinc, nickel and copper  

NASA Astrophysics Data System (ADS)

A metallo-organic hybrid acid namely tetra-aquo bis-4-carboxy-N-phthaloylglycinato zinc(II) dihydrate is prepared and characterised. In this complex the hydrogen bonding by free carboxylic acid group and ? ? interactions between the rings in crystal lattice contributes to the formation of self-assembled structure. A monomeric nickel complex from 2-carbomethoxy benzoic acid (L2H) and pyridine [Ni(L2)(py)3(H2O)2]L2 is prepared (where py = pyridine). This complex has ionic as well as monodentate carboxylates. It forms self-assembly by C H?? as well as hydrogen-bonding interactions. The 2-carbomethoxy benzoic acid (L2H) forms dimeric copper complex [Cu2(L2)4(H2O)2]2H2O which has an extended chain structure through hydrogen-bond interactions.

Deka, Kaustavmoni; Barooah, Nilotpal; Sarma, Rupam Jyoti; Baruah, Jubaraj B.

2007-02-01

359

Self-assembly of amorphous calcium carbonate microlens arrays  

NASA Astrophysics Data System (ADS)

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.; Cölfen, Helmut; Fratzl, Peter

2012-03-01

360

Self-assembly of amorphous calcium carbonate microlens arrays.  

PubMed

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 CaCO(3) 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 CaCO(3) microlens arrays was elucidated by confocal Raman spectroscopic imaging to be a two-step growth process mediated by the organic surfactant. CaCO(3) 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. PMID:22395616

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

2012-03-06

361

Self-assembled carbon nanotube honeycomb networks using a butterfly wing template as a multifunctional nanobiohybrid.  

PubMed

Insect wings have many unique and complex nano/microstructures that are presently beyond the capabilities of any current technology to reproduce them artificially. In particular, Morpho butterflies are an attractive type of insect because their multifunctional wings are composed of nano/microstructures. In this paper, we show that carbon nanotube-containing composite adopts honeycomb-shaped networks when simply self-assembled on Morpho butterfly wings used as a template. The unique nano/microstructure of the composites exhibits multifunctionalities such as laser-triggered remote-heating, high electrical conductivity, and repetitive DNA amplification. Our present study highlights the important progress that has been made toward the development of smart nanobiomaterials for various applications such as digital diagnosis, soft wearable electronic devices, photosensors, and photovoltaic cells. PMID:23952240

Miyako, Eijiro; Sugino, Takushi; Okazaki, Toshiya; Bianco, Alberto; Yudasaka, Masako; Iijima, Sumio

2013-08-22

362

Nanoparticle self-assembly by a highly stable recombinant spider wrapping silk protein subunit.  

PubMed

Artificial spider silk proteins may form fibers with exceptional strength and elasticity. Wrapping silk, or aciniform silk, is the toughest of the spider silks, and has a very different protein composition than other spider silks. Here, we present the characterization of an aciniform protein (AcSp1) subunit named W1, consisting of one AcSp1 199 residue repeat unit from Argiope trifasciata. The structural integrity of recombinant W1 is demonstrated in a variety of buffer conditions and time points. Furthermore, we show that W1 has a high thermal stability with reversible denaturation at ?71°C and forms self-assembled nanoparticle in near-physiological conditions. W1 therefore represents a highly stable and structurally robust module for protein-based nanoparticle formation. PMID:23994530

Xu, Lingling; Tremblay, Marie-Laurence; Orrell, Kathleen E; Leclerc, Jérémie; Meng, Qing; Liu, Xiang-Qin; Rainey, Jan K

2013-08-28

363

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

2013-07-15

364

MALDI-TOF MS sample preparation by using alkanethiolate self-assembled monolayers  

NASA Astrophysics Data System (ADS)

Samples originating from body fluids often contain a complex mixture of inorganic salts, buffers, chaotropic agents, surfactant/detergents, preservatives, and other solubilizing agents. The presence of those contaminants often precludes direct analysis by matrix-assisted laser-desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Self-assembled monolayers (SAMs) on coinage metal can provide versatile modeling systems for studies of interfacial electron transfer, biological interactions, molecular recognition and other interfacial phenomena. In this study, SAMs surface was used for MALDI-TOF MS sample cleanup application. Experimental results from MALDI-TOF MS have revealed the better S/N ratio and resolution of using functionalized SAMs surface for the demonstration of bovine serum albumin (BSA) in artificial human urine sample. This paper reports a surface modification and cleanup method that greatly simplifies this sample preparation process.

Tyan, Yu-Chang; Yang, Ming-Hui; Liao, Pao-Chi; Liao, Jiunn-Der; Jong, Shiang-Bin; Liu, Chia-Yuan; Wang, Ming-Chen; Grunze, Michael

2007-04-01

365

Synthesis of self-assembled photosensitive molecules in mesoporous silicates  

NASA Astrophysics Data System (ADS)

Self-assembled functional molecules in mesoporous materials are synthesized directly either by co-assembly of dye-bound surfactant of ferrocenyl TMA with silicate or Pc (phthalocyanine) molecules doped in the C16TMA micelles with oxides framework such as V2O5, MoO3, WO3 and SiO2. The process provides well-organized molecular doped mesoporous structure by direct and simple procedure.

Honma, Itaru; Zhou, H.-S.

1997-02-01

366

Self-assembly of Epitaxial Monolayers for Vacuum Wafer Bonding  

Microsoft Academic Search

Self-assembled epitaxial metal monolayers can be used for hetero-integration of mismatched semiconductors, leading to simultaneously low interfacial resistance and high optical transparency. Lattice-mismatched wafers of Si(100) and Si(111) were bonded at room temperature in situ after vacuum deposition of a single atomic layer of Ag on them. The interfacial resistance was measured to be 3.9x 10-4 ohm. cm^ 2 and

Igor Altfeder; Biqin Huang; Ian Appelbaum; Barry Walker

2007-01-01

367

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

368

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

369

Casting Metal Nanowires Within Discrete Self-Assembled Peptide Nanotubes  

NASA Astrophysics Data System (ADS)

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 ?-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 long persistence length. The same dipeptide building block, made of D-phenylalanine, resulted in the production of enzymatically stable nanotubes.

Reches, Meital; Gazit, Ehud

2003-04-01

370

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

371

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

372

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

373

Self-assembly and magnetic properties of cobalt nanoparticles  

NASA Astrophysics Data System (ADS)

Two- and three-dimensional superlattices of passivated cobalt nanoparticles were formed by a self-assembly technique. The size and stabilization of the cobalt nanoparticles are controlled by using the combination of oleic acid and triphenylphosphine. The cobalt nanoparticles are stable for at least 90 days without oxidation at room temperature under ambient conditions. The magnetic properties of the cobalt nanoparticles in different forms are compared, which provides helpful information on the magnetostatic interaction of the nanoparticles.

Yang, H. T.; Shen, C. M.; Su, Y. K.; Yang, T. Z.; Gao, H. J.; Wang, Y. G.

2003-06-01

374

Transformations and Preservation of Self-assembly Dynamics through Homotheties  

Microsoft Academic Search

We introduce a new notion in self-assembly, that of transforming the dynamics of assembly. This notion allows us to have transformation\\u000a of the plane computed within the assembly process. Then we apply this notion to zooming. The possibility of zooming depends\\u000a on the order condition. This shows that this condition, which arose from engineering concerns (how to design understandable tile

Florent Becker

2008-01-01

375

Running time and program size for self-assembled squares  

Microsoft Academic Search

Recently Rothemund and Winfree [6] have considered the program size complexity of constructing squares by self-assembly. Here, we consider the time complexity of such constructions using a natural generalization of the Tile Assembly Model defined in [6]. In the generalized model, the Rothemund-Winfree construction of n \\\\times n squares requires time &THgr;(n log n) and program size &THgr;(log n). We

Leonard M. Adleman; Qi Cheng; Ashish Goel; Ming-Deh A. Huang

2001-01-01

376

Transducers with Programmable Input by DNA Self-assembly  

Microsoft Academic Search

\\u000a Notions of Wang tiles, finite state machines and recursive functions are tied together. We show that there is a natural way\\u000a to simulate finite state machines with output (transducers) with Wang tiles and we show that recursive (computable) functions\\u000a can be obtained as composition of transducers through employing Wang tiles. We also show how a programmable transducer can\\u000a be self-assembled

Natasa Jonoska; Shiping Liao; Nadrian C. Seeman

2004-01-01

377

Identifying Shapes Using Self-Assembly (extended abstract)  

Microsoft Academic Search

In this paper, we introduce the following problem in the theory of\\u000aalgorithmic self-assembly: given an input shape as the seed of a tile-based\\u000aself-assembly system, design a finite tile set that can, in some sense,\\u000auniquely identify whether or not the given input shape--drawn from a very\\u000ageneral class of shapes--matches a particular target shape. We first study the

Matthew J. Patitz; Scott M. Summers

2010-01-01

378

Self-assembled containers based on extended tetrathiafulvalene.  

PubMed

Two original self-assembled containers constituted each by six electroactive subunits are described. They are synthesized from a concave tetratopic ?-extended tetrathiafulvalene ligand bearing four pyridyl units and cis-M(dppf)(OTf)2 (M = Pd or Pt; dppf = 1,1'-bis(diphenylphosphino)ferrocene; OTf = trifluoromethane-sulfonate) complexes. Both fully characterized assemblies present an oblate spheroidal cavity that can incorporate one perylene molecule. PMID:23795694

Bivaud, Sébastien; Goeb, Sébastien; Croué, Vincent; Dron, Paul I; Allain, Magali; Sallé, Marc

2013-06-27

379

Self-assembled organic microfibers for nonlinear optics.  

PubMed

While highly desired in integrated optical circuits, multiresponsive and tunable nonlinear optical (NLO) active 1D (sub)wavelength scale superstructures from organic materials are rarely reported due to the strong tendency of organic molecules to self-assembly in centrosymmetric modes. Here a solution-processed assembly approach is reported to generate non-centrosymmetric single-crystalline organic microfibers with a cumulative dipole moment for anisotropic combined second- and third-order NLO. PMID:23427048

Xu, Jialiang; Semin, Sergey; Niedzialek, Dorota; Kouwer, Paul H J; Fron, Eduard; Coutino, Eduardo; Savoini, Matteo; Li, Yuliang; Hofkens, Johan; Uji-I, Hiroshi; Beljonne, David; Rasing, Theo; Rowan, Alan E

2013-02-21

380

Modelling self-assembling of colloid particles in multilayered structures  

Microsoft Academic Search

Simulations of particle multilayer build-up in the layer by layer (LbL) self-assembling processes have been performed according to the generalized random sequential adsorption (RSA) scheme. The first (precursor) layer having an arbitrary coverage of adsorption centers was generated using the standard RSA scheme pertinent to homogeneous surface. Formation of the consecutive layers (up to 20) was simulated by assuming short-range

Zbigniew Adamczyk; Pawe? Wero?ski; Jakub Barbasz; Marta Kolasinska

2007-01-01

381

Room temperature photoluminescence of individual self-assembled quantum dots  

Microsoft Academic Search

We investigate the emission spectra of individual lens-shaped self-assembled quantum dots (QDs) in the high-temperature regime in order to contribute to the fine structural analysis and to the appreciation of the QDs’ optical response. Our theoretical analysis results in an expression for the photoluminescence (PL) intensity of QDs in the linear regime, which reproduces satisfactorily the experimentally observed PL signal

A. Zora; C. Simserides; G. P. Triberis

2008-01-01

382

Controlling guest-host interactions in self-assembled materials  

NASA Astrophysics Data System (ADS)

Aqueous solutions of self-assembling macromolecules can be found in many industrial formulations, as well as in many living organisms. Regardless of the specific system, the self-assembling macromolecules are rarely found in the absence of other solutes or guest species. Such components may include fragrance molecules incorporated into block-copolymer micelles for use in detergents, dyes included in micellar precursor solutions for the synthesis of mesostructured silica-block copolymer composites, or specifically designed additives for controlling protein folding and activity. A detailed understanding of the structures and dynamic molecular interactions among the various species in solution and their influences on macromolecule aggregation and phase behaviors is of paramount importance for designing systems with improved properties and performance. Unambiguous measurements of the loci of interaction and solubilization of small molecule species (e.g., dyes or surfactants) within self-assembling block-copolymer species or proteins in aqueous solutions have been established. This has been achieved by exploiting powerful correlative multidimensional nuclear magnetic resonance (NMR) spectroscopy techniques, including pulsed-field-gradient diffusion measurements, which provide detailed molecular insights into a variety of heterogeneous self-assembled systems. Furthermore, these insights and measurements enable the solution conditions to be established that permit the control and release of such guest molecules from association with macromolecular carrier species into the surrounding solution. Specifically, the use of temperature to control the distribution of porphyrin guest-species in a block-copolymer host and the light-dependent folding and unfolding of bovine serum albumin through varying interactions with an azo-benzene functionalized surfactant are demonstrated. In the absence of long-range order in these complex systems, advanced NMR spectroscopy methods provide crucial and highly selective means for characterizing component structures, dynamics and interactions at a molecular level. The analytical approach and the resulting insights developed here are general and anticipated to be of broad applicability to systems of interest in medicine, biology, and industry.

Steinbeck, Christian Alexander

383

Self-assembly of double helical nanostructures inside carbon nanotubes  

NASA Astrophysics Data System (ADS)

We use molecular dynamics (MD) simulations to show that a DNA-like double helix of two poly(acetylene) (PA) chains can form inside single-walled carbon nanotubes (SWNTs). The computational results indicate that SWNTs can activate and guide the self-assembly of polymer chains, allowing them to adopt a helical configuration in a SWNT through the combined action of the van der Waals potential well and the ?-? stacking interaction between the polymer and the inner surface of SWNTs. Meanwhile both the SWNT size and polymer chain stiffness determine the outcome of the nanostructure. Furthermore, we also found that water clusters encourage the self-assembly of PA helical structures in the tube. This molecular model may lead to a better understanding of the formation of a double helix biological molecule inside SWNTs. Alternatively, it could form the basis of a novel nanoscale material by utilizing the `empty' spaces of SWNTs.We use molecular dynamics (MD) simulations to show that a DNA-like double helix of two poly(acetylene) (PA) chains can form inside single-walled carbon nanotubes (SWNTs). The computational results indicate that SWNTs can activate and guide the self-assembly of polymer chains, allowing them to adopt a helical configuration in a SWNT through the combined action of the van der Waals potential well and the ?-? stacking interaction between the polymer and the inner surface of SWNTs. Meanwhile both the SWNT size and polymer chain stiffness determine the outcome of the nanostructure. Furthermore, we also found that water clusters encourage the self-assembly of PA helical structures in the tube. This molecular model may lead to a better understanding of the formation of a double helix biological molecule inside SWNTs. Alternatively, it could form the basis of a novel nanoscale material by utilizing the `empty' spaces of SWNTs. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr33157h

Lv, Cheng; Xue, Qingzhong; Shan, Meixia; Jing, Nuannuan; Ling, Cuicui; Zhou, Xiaoyan; Jiao, Zhiyong; Xing, Wei; Yan, Zifeng

2013-05-01

384

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

385

Self-assembling sweep-and-sleep sensor systems  

Microsoft Academic Search

This paper describes a self-assembling sleep-wake sensor system that is scalable, easily implemented, and energy conserving. Sensors actively detecting events form wave fronts that sweep the sensor field. An application of concepts from cellular automata theory accounts for much of its novelty. The system has additional, highly desirable properties such as a self-healing capability, fault tolerance, asynchronous operation, seamless accommodation

Kyung Joon Kwak; Yuliy M. Baryshnikov; Edward G. Coffman Jr.

2008-01-01

386

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

387

Demonstration of three-dimensional microstructure self-assembly  

Microsoft Academic Search

Self-assembly of three-dimensional microstructures using the surface tension force of molten solder to produce out-of-plane rotation is demonstrated. The generic nature of the technique is illustrated by reconfiguring structures formed in both Ni metal and single crystal Si. The structures do not have a hinge to constrain the rotation. This considerably simplifies fabrication and eliminates problems associated with the compatibility

P. W. Green; R. R. A. Syms; E. M. Yeatman

1995-01-01

388

Self-Assembling in Polymerization Processes of N-Isopropylacrylamide  

Microsoft Academic Search

The self-assembling process during the polymerization of N-Isopropylacrylamide (NIPA) was investigated with time-resolved small angle X-ray scattering (SAXS). During the polymerization process at 35.0 °C which is above the cloud point curve of poly-N-Isopropylacrylamide (PNIPA)\\/water solution, the phase separation via spinodal decomposition occurs simultaneously. The SAXS profile can be well expressed by the sum of Porod law and Ornstein-Zernike form.

Mikihito Takenaka; Naoki Iwase; Shotaro Nishitsuji; Kazuki Ito

2007-01-01

389

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

390

Surface plasmons and vibrations of self-assembled silver nanocolumns.  

PubMed

Optical and vibrational properties of novel self-assembled silver nanocolumns are studied experimentally and theoretically. The split of the surface plasmon resonance into transverse and longitudinal modes verifies the one-dimensional character of the nanocolumns. In this work, we have identified the acoustic vibration modes of the nanocolumns using Raman scattering, as spheroid-like modes (l = 2, m = +/-2) involving vibrations of the nanocolumns along their minor axes and the existence of surface plasmon-vibration coupling mechanisms. PMID:16968022

Margueritat, Jeremie; Gonzalo, Jose; Afonso, Carmen N; Mlayah, Adnen; Murray, Daniel B; Saviot, Lucien

2006-09-01

391

Microcolumns with self-assembled particle frits for proteomics  

Microsoft Academic Search

LC–MS–MS experiments in proteomics are usually performed with packed microcolumns employing frits or outlets smaller than the particle diameter to retain the packing material. We have developed packed microcolumns using self-assembled particles (SAPs) as frits that are smaller than the size of the outlet. A five to one ratio of outlet size to particle diameter appears to be the upper

Yasushi Ishihama; Juri Rappsilber; Jens S Andersen; Matthias Mann

2002-01-01

392

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

393

Model-driven optimization of multicomponent self-assembly processes.  

PubMed

Here, we report an engineering approach toward multicomponent self-assembly processes by developing a methodology to circumvent spurious, metastable assemblies. The formation of metastable aggregates often hampers self-assembly of molecular building blocks into the desired nanostructures. Strategies are explored to master the pathway complexity and avoid off-pathway aggregates by optimizing the rate of assembly along the correct pathway. We study as a model system the coassembly of two monomers, the R- and S-chiral enantiomers of a ?-conjugated oligo(p-phenylene vinylene) derivative. Coassembly kinetics are analyzed by developing a kinetic model, which reveals the initial assembly of metastable structures buffering free monomers and thereby slows the formation of thermodynamically stable assemblies. These metastable assemblies exert greater influence on the thermodynamically favored self-assembly pathway if the ratio between both monomers approaches 1:1, in agreement with experimental results. Moreover, competition by metastable assemblies is highly temperature dependent and hampers the assembly of equilibrium nanostructures most effectively at intermediate temperatures. We demonstrate that the rate of the assembly process may be optimized by tuning the cooling rate. Finally, it is shown by simulation that increasing the driving force for assembly stepwise by changing the solvent composition may circumvent metastable pathways and thereby force the assembly process directly into the correct pathway. PMID:24101463

Korevaar, Peter A; Grenier, Christophe; Markvoort, Albert J; Schenning, Albertus P H J; de Greef, Tom F A; Meijer, E W

2013-10-07

394

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

395

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

2013-01-24

396

Modeling the self-assembly of nanoparticle and nanorod superlattices  

NASA Astrophysics Data System (ADS)

Coloidal semiconductor PbSe/CdSE nanoparticles (NP) of the sizes of 3-10 nm can self-assemble in fcc, hcp and single-hexagonal (sh) superlattices [1]. We model the Coulombic, van der Waals and steric interactions between these NPs to understand the exact conditions under which they can self-assemble in these lattice structures. Our simulations show that non-local dipoles of the NPs and their screening by the conducting substrate are both crucial for the sh lattice formation. We model analogously the self-assembly of semiconducting CdSe nanorods (NRs), realized also in the presence of electric fields [2], and the binary semiconducting-metallic nanoparticle superlattices [3]. [1] D. Talapin, E. Shevchenko, C. B. Murray, A. Titov and P. Kr'al, Nano Letters 7, 1213 (2007). [2] A. Titov and P. Kr'al, submitted. [3] E. V. Shevchenko, D. V. Talapin, N. A. Kotov, S. O'Brien, C. B. Murray, Nature 439, 55-59 (2006).

Titov, Alexey; Kral, Petr

2008-03-01

397

Various Aspects of the Interfacial Self-Assembly of Nanoparticles  

NASA Astrophysics Data System (ADS)

We describe the interfacial self-assembly of nanoparticles at liquid-liquid interfaces and in block copolymers. At the interface of two immiscible liquids, the particles assemble into disordered but densely packed monolayers. This self-assembly process was investigated ex situ with scanning force microscopy (SFM) and transmission electron microscopy (TEM), and laser scanning confocal microscopy (LCSM) methods. Adsorbed particles can be crosslinked at the interface to fabricate mechanically stable capsules and membranes. In addition, it was shown by pendant drop tensiometry that Janus particles consisting of gold and iron oxide show a significantly higher interfacial activity than homogeneous gold or iron oxide nanoparticles of comparable size and chemical nature. For the self-assembly of nanoparticles in block copolymer mixtures, it was shown theoretically and experimentally that these composite materials form hierarchically ordered structures. Therefore, thin films from mixtures of a cylindrical polystyrene-block-poly(2-vinylpyridine), with tri-n-octylphosphine oxide-covered CdSe nanoparticles were prepared and investigated with SFM, TEM, and grazing-incidence small angle x-ray scattering (GISAXS) after thermal annealing.

Popp, Nicole; Kutuzov, Sergej; Böker, Alexander

398

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

399

Nanoscale rings fabricated using self-assembled triblock terpolymer templates.  

PubMed

Although there has been extensive work on the use of self-assembled diblock copolymers for nanolithography, there are few reports of the use of multiblock copolymers, which can form a more diverse range of nanoscale pattern geometries. Pattern transfer from a self-assembled poly(butadiene-b-styrene-b-methyl methacrylate) (PB-b-PS-b-PMMA) triblock terpolymer thin film has been investigated. Polymers of different total molecular weight were synthesized with a predicted morphology consisting of PMMA-core/PS-shell cylinders in a PB matrix. By adjusting the solvent-annealing conditions and the film thickness, thin films with vertically oriented cylinders were formed. The PMMA cylinder cores and the PB matrix were then removed using selective etching to leave an array of PS rings, and the ring pattern was transferred into a silica film by reactive ion etching to form 19 nm high silica rings. This result illustrates the design and use of triblock terpolymers for self-assembled lithography. PMID:19206445

Chuang, Vivian P; Ross, Caroline A; Bilalis, Panayiotis; Hadjichristidis, Nikos

2008-10-28

400

Diverse self-assembly in soluble oligoazaacenes: a microscopy study.  

PubMed

The synthesis and morphologies of self-assembled aggregates of novel oligoazapentacene 2 and oligoazaheptacene 3 derivatives are reported. Double nucleophilic substitution on 2,3-dicyano-[h,j]-dibenzo-1,4,5,10-tetrazaanthracene 4 gives the corresponding dihydro-oligoacene derivatives, which were then N-alkylated using n-dodecyl bromide to yield self-assembling acene molecules. 2 and 3 self-assemble in solution, leading to a variety of aggregated structures including rolled-up sheets, foams, and fibrous structures reminiscent of organogels. These structures are of substantial interest because of their potential electronic properties and because individual fibers can be "exfoliated". Structures of the aggregates are discussed. Additionally, the crystal structure of precursor 4 is reported because it gives information regarding the intermolecular interactions (hydrogen bonding and intermolecular stacking) in similar compounds. Crystal data for 4: space group P2(1)/n, a = 9.3164(17) angstroms, b = 7.0649(13) angstroms, c = 23.684(4) angstroms, alpha = 90.00 degrees, beta = 99.945(3) degrees, gamma = 90.00 degrees, and V = 1535.4(5) angstroms3. PMID:19281267

Richards, Gary J; Hill, Jonathan P; Okamoto, Ken; Shundo, Atsuomi; Akada, Misaho; Elsegood, Mark R J; Mori, Toshiyuki; Ariga, Katsuhiko

2009-08-01

401

Sunlight-initiated self-assembly of cyclodextrin networks  

NASA Astrophysics Data System (ADS)

We demonstrate sunlight initiated self-assembly of three-dimensional networks of ?-cyclodextrin using simulated AM1.5 sunlight conditions. These all-organic networks display a highly porous hierarchical structure of interconnected fibers similar to the TiO2-Cyclodextrin hybrid networks prepared previously. These results clearly identify cyclodextrin as the structure-directing agent providing important new insights into the network formation mechanism. Vibrational and thermal analysis suggest that the cyclodextrin molecules are dehydrated and their cone structure is broken to form a more stable molecular unit. From this data we introduce a formation model based on titania photocatalyzed reaction of cyclodextrin molecules. Subsequently, hydrophobic and surface tension forces drive the self-assembly into large networks of interconnected fibers resembling marine sponges. These results are significant because they demonstrate that cyclodextrin can be used to template the self-assembly of hierarchical networks of both organic and inorganic materials. More broadly, this technique represents a simple and eco-effective route to grow biomimetic structures directly using sunlight.

Han, Sungmin; Yoon, Sungkwon; Nichols, William T.

2012-11-01

402

Exploiting amyloid fibril lamination for nanotube self-assembly.  

PubMed

Fundamental questions about the relative arrangement of the beta-sheet arrays within amyloid fibrils remain central to both its structure and the mechanism of self-assembly. Recent computational analyses suggested that sheet-to-sheet lamination was limited by the length of the strand. On the basis of this hypothesis, a short seven-residue segment of the Alzheimer's disease-related Abeta peptide, Abeta(16-22), was allowed to self-assemble under conditions that maintained the basic amphiphilic character of Abeta. Indeed, the number increased over 20-fold to 130 laminates, giving homogeneous bilayer structures that supercoil into long robust nanotubes. Small-angle neutron scattering and X-ray scattering defined the outer and inner radii of the nanotubes in solution to contain a 44-nm inner cavity with 4-nm-thick walls. Atomic force microscopy and transmission electron microscopy images further confirmed these homogeneous arrays of solvent-filled nanotubes arising from a flat rectangular bilayer, 130 nm wide x 4 nm thick, with each bilayer leaflet composed of laminated beta-sheets. The corresponding backbone H-bonds are along the long axis, and beta-sheet lamination defines the 130-nm bilayer width. This bilayer coils to give the final nanotube. Such robust and persistent self-assembling nanotubes with positively charged surfaces of very different inner and outer curvature now offer a unique, robust, and easily accessible scaffold for nanotechnology. PMID:12785778

Lu, Kun; Jacob, Jaby; Thiyagarajan, Pappannan; Conticello, Vincent P; Lynn, David G

2003-05-28

403

Nanoparticle Assemblies via Self-Assembling Peptide Molecules  

NASA Astrophysics Data System (ADS)

The bottom up approach towards nano-scale patterning presents the possibility of creating hierarchical architectures through simple self-assembly strategies. Herein, we elucidate the self-assembly of different types of peptide molecules into unique nano-scale morphologies and demonstrate their application in the construction of linear arrays of inorganic nanoparticles. A 20 amino acid peptide, consisting of alternating hydrophilic (lysine) and hydrophobic (valine) residues flanking a central diproline turn sequence (VKVKVKVKVPPTKVKVKVKV-NH2) was employed as a nano-scale template for the organization of 2nm gold particles. This peptide self assembles into a laminated morphology in solution and has a periodic nanostructure consisting of alternating hydrophobic and hydrophilic layers with a lateral periodicity of 2.5 nm. Negatively charged gold nanoparticles are templated into the positively charged lysine layer through electrostatic interaction and are aligned within the template to form laterally spaced (2D) linear arrays. Also, a long chain alanine-rich polypeptide was used to create 1D nanoparticle assemblies. This peptide assembles into fibrils with monodisperse widths and presents its charged functional groups periodically along the length of the fibril. These functional groups bind nanoparticles that results in their spatially modulated linear arrangement.

Sharma, Nikhil; Lamm, Matthew; Schneider, Joel; Kiick, Kristi; Pochan, Darrin

2009-03-01

404

Sequence, Conformation and Hierarchical Self-Assembly in Model Collagens  

NASA Astrophysics Data System (ADS)

The conformation, crystal structure and self-assembly behavior of four peptides with collagen-like hexapeptide repetitive sequences GAPGPP, GVPGPP, GAPGPA, and GSPGPP. The peptides were characterized using a variety of spectoscopic, morphological characterization, and diffraction techniques. Correlations were sought between the molecular geometry and conformation dictated by each sequence and the details of self-assembled long-range ordered structures. All four peptides were examined as bulk soids, dried at 3 C. Samples of three of the peptides, at ambient temperature and at 5 C, were examined as films dried from aqueous solution, air-water interfacial films, and chloroform-water interfacial films. The bulk solids had a sinusoidally varying surface structure, observed in AFM tapping mode phase images, due to the architecture of the peptides (solubilizing acid blocks at both ends) and changing molecular orientation. Similar sinusoidal textures were observed for the interfacial samples. Differences in the periodicity of the banded structure for different sequences were observed, and correlate with crystallographically determined interhelical packing angles (from crystallites coexisting with the banded morphology. These differences in packing angle are an empirical measure of the effective asymmetry and shape of the molecular cross section. A weak correlation between morphology and the ride per residue of the triple helical conformation is also observed. In addition to higher-order self-assembly effects, environment-dependent conformational polymorphism of the triple helix is observed.

Valluzzi, Regina; Kaplan, David

2000-03-01

405

Self-Assembled Magnetic Filter for Highly Efficient Immunomagnetic Separation  

PubMed Central

We have developed a compact and inexpensive microfluidic chip, the Self Assembled Magnetic filter, to efficiently remove magnetically tagged cells from suspension. The self-assembled magnetic filter consists of a microfluidic channel built directly above a self-assembled NdFeB magnet. Micrometer-sized grains of NdFeB assemble to form alternating magnetic dipoles, creating a magnetic field with a very strong magnitude B (from the material) and field gradient ?B (from the configuration) in the microfluidic channel. The magnetic force imparted on magnetic beads is measured to be comparable to state-of-the-art microfabricated magnets, allowing for efficient separations to be performed in a compact, simple device. The efficiency of the magnetic filter is characterized by sorting non-magnetic (polystyrene) beads from magnetic beads (iron oxide). The filter enriches the population of non-magnetic beads to magnetic beads by a factor of >105 with a recovery rate of 90% at 1 mL/hr. The utility of the magnetic filter is demonstrated with a microfluidic device that sorts tumor cells from leukocytes using negative immunomagnetic selection, and concentrates the tumor cells on an integrated membrane filter for optical detection.

Issadore, David; Shao, Huilin; Chung, Jaehoon; Newton, Andita; Pittet, Mikael; Weissleder, Ralph; Lee, Hakho

2010-01-01

406

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

407

Functionalized self-assembling peptide nanofiber hydrogels mimic stem cell niche to control human adipose stem cell behavior in vitro.  

PubMed

A class of designer functionalized self-assembling peptide nanofiber scaffolds developed from self-assembling peptide RADA16-I (AcN-RADARADARADARADA-CONH2) has become increasingly attractive not only for studying spatial behaviors of cells, but also for developing approaches for a wide range of medical applications including regenerative medicine, rapid hemostasis and cell therapy. In this study, we report three functionalized self-assembling peptide hydrogels that serve as a three-dimensional (3-D) artificial microenvironment to control human adipose stem cell (hASC) behavior in vitro. Short peptide motifs SKPPGTSS (bone marrow homing motif), FHRRIKA (heparin-binding motif) and PRGDSGYRGDS (two-unit RGD cell adhesion motif) were used to extend the C-terminus of RADA16-I to obtain functionalized peptides. Atomic force microscopy confirmed the formation of self-assembling nanofibers in the mixture of RADA16-I peptide and functionalized peptides. The behaviors of hASCs cultured in 3-D peptide hydrogels, including migration, proliferation and growth factor-secretion ability, were studied. Our results showed that the functionalized peptide hydrogels were suitable 3-D scaffolds for hASC growth with higher cell proliferation, migration and the secretion of angiogenic growth factors compared with tissue culture plates and pure RADA16-I scaffolds. The present study suggests that these functionalized designer peptide hydrogels not only have promising applications for diverse tissue engineering and regenerative medicine applications as stem cell delivery vehicles, but also could be a biomimetic 3-D system to study nanobiomaterial-stem cell interactions and to direct stem cell behaviors. PMID:23380207

Liu, Xi; Wang, Xiumei; Wang, Xiujuan; Ren, Hui; He, Jin; Qiao, Lin; Cui, Fu-Zhai

2013-02-04

408

Linear and nonlinear optics of light harvesting complexes: TCL- and Bloch Equations for linear spectra and saturation dynamics  

Microsoft Academic Search

Bloch equations for the optical and electronic processes in light-harvesting-complexes, important nanostructures in photo-processes, are presented. The theory includes Förster excitation transfer, electron-phonon coupling and arbitrary strong light fields leading to saturation phenomena.

Marten Richter; Thomas Renger; Andreas Knorr

2007-01-01

409

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

PubMed Central

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.

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

2011-01-01

410

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

411

Characterization of Circular Differential Selective Scattering in Randomly and Magnetically Oriented Chloroplasts and Light Harvesting Chlorophyll a/B Aggregates.  

National Technical Information Service (NTIS)

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 ...

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

1986-01-01

412

Probing the Bacteriochlorophyll Binding Site Requirements of the Core Light-Harvesting Complex of Photosynthetic Bacteria Using BChl Analogs.  

National Technical Information Service (NTIS)

The methodology developed for reconstitution of the light-harvesting (LH) complex of Rhodospirillum rubrum, B873, and its structural subunit (B820) has made it possible to begin probing structural requirements of the bacteriochlorophyll (BChl) binding sit...

P. A. Loach T. Michalski P. S. Parkes-Loach

1989-01-01

413

Construction of supramolecular self-assembled microfibers with fluorescent properties through a modified ionic self-assembly (ISA) strategy.  

PubMed

Highly ordered supramolecular microfibers were constructed through a simple ionic self-assembly strategy from complexes of the N-tetradecyl-N-methylpyrrolidinium bromide (C(14)MPB) surface-active ionic liquid and the small methyl orange (MO) dye molecule, with the aid of patent blue VF sodium salt. By using scanning electron microscopy and polarized optical microscopy, the width of these self-assembled microfibers is observed to be about 1 to 5??m and their length is from tens of micrometers to almost a millimeter. The (1)H?NMR spectra of the microfibers indicates that the supramolecular complexes are composed of C(14)MPB and MO in equal molar ratio. The electrostatic, hydrophobic, and ?-? stacking interactions are regarded as the main driving forces for the formation of microfibers. Furthermore, through characterization by using confocal fluorescence microscopy, the microfibers were observed to show strong fluorescent properties and may find potential applications in many fields. PMID:23197332

Zhao, Mingwei; Zhao, Yurong; Zheng, Liqiang; Dai, Caili

2012-11-29

414

Dimension Controlled Self-Assembly of Perylene Based Molecules  

NASA Astrophysics Data System (ADS)

Recent advances in the self-assembly of highly organized structures of organic semiconducting molecules by controlled non-covalent interactions has opened avenues for creating materials with unique optical and electrical properties. The main focus of this thesis lies in the synthesis and self-assembly of n-type perylene based organic semiconducting molecules into highly organized materials. Perylene based molecules used in this study are perylene diimide (PTCDI, two side-chains), perylene mono imide (m-PTCI, one side-chain), perylene tetracarboxylic acid (PTCA, no side-chain) and tetra-alkali metal salts of PTCA (M4-PTCA, no side-chain), which are synthesized from the parent perylene tetracarboxylic dianhydride (PTCDA). The self-assembly of these molecules have been performed using solution processing methods (dispersion, phase-transfer, and phase-transfer at high temperature) by taking advantage of the changes in solubility of the molecules, wherein the molecular interactions are maximized to favorably allow for the formation of highly organized structures. Dimension control (1D, 2D and 3D structures) of self-assembly has been obtained for different perylene based molecules by appropriate design of the molecule followed by controlling the conditions of assembly. In case of PTCDI, a new solution processing method phase-transfer at high temperature (2L-HT) allowed for the controlled formation of extremely long and fluorescent 1D structure. For the m-PTCI molecules the organization by the 2L-HT method was found to result in highly organized, single-crystalline, fluorescent 2D sheets. In the case of perylene based molecules with no side-chains two different methods have been developed for the realization of organized 1D nanostructures. The first method utilizes the chemical conversion of a highly soluble PTCA into 1D nanofibers of the parent insoluble perylene tetracarboxylic anhydride. The second method utilizes the assembly of tetra potassium salt of PTCA (K 4-PTCA) into 1D nanostructures. Furthermore, it has been demonstrated that these 1D nanostructures can be chemically converted to two different chemical species, both of which still retain the 1D morphological characteristic, though with changes in the size. Various functional self-assembled structures developed in this thesis opens up new avenues to explore structure-property-function relationships and their use in applications such as sensors, electronics and opto-electronic devices.

Sayyad, Arshad S.

415

The family of light-harvesting-related proteins (LHCs, ELIPs, HLIPs): was the harvesting of light their primary function?  

Microsoft Academic Search

Light-harvesting complex proteins (LHCs) and early light-induced proteins (ELIPs) are essential pigment-binding components of the thylakoid membrane and are encoded by one of the largest and most complex higher plant gene families. The functional diversification of these proteins corresponded to the transition from extrinsic (phycobilisome-based) to intrinsic (LHC-based) light-harvesting antenna systems during the evolution of chloroplasts from cyanobacteria, yet the

Marie-Hélène Montané; Klaus Kloppstech

2000-01-01

416

AplA, a Member of a New Class of Phycobiliproteins Lacking a Traditional Role in Photosynthetic Light Harvesting  

Microsoft Academic Search

All known phycobiliproteins have light-harvesting roles during photosynthesis and are found in water- soluble phycobilisomes, the light-harvesting complexes of cyanobacteria, cyanelles, and red algae. Phycobil- iproteins are chromophore-bearing proteins that exist as heterodimers of and subunits, possess a number of highly conserved amino acid residues important for dimerization and chromophore binding, and are invariably 160 to 180 amino acids long.

Beronda L. Montgomery; Elena Silva Casey; Arthur R. Grossman; David M. Kehoe

2004-01-01

417

Photosynthetic light-harvesting: Reconciling dynamics and structure of purple bacterial LH2 reveals function of photosynthetic unit  

Microsoft Academic Search

Great progress in the study of structure and dynamics of photosynthetic light-harvesting pigment-protein complexes has recently resulted in detailed understanding of the light-harvesting and light-conversion processes of photosynthesis. The authors review and discuss recent results on the elementary excitation transfer dynamics of the purple bacterial LH2 peripheral complex. When combining the information from the two LH2 structures that are now

Villy Sundström; Tõnu Pullerits; Rienk van Grondelle

1999-01-01

418

A Theoretical and Experimental Study of DNA Self-assembly  

NASA Astrophysics Data System (ADS)

The control of matter and phenomena at the nanoscale is fast becoming one of the most important challenges of the 21st century with wide-ranging applications from energy and health care to computing and material science. Conventional top-down approaches to nanotechnology, having served us well for long, are reaching their inherent limitations. Meanwhile, bottom-up methods such as self-assembly are emerging as viable alternatives for nanoscale fabrication and manipulation. A particularly successful bottom up technique is DNA self-assembly where a set of carefully designed DNA strands form a nanoscale object as a consequence of specific, local interactions among the different components, without external direction. The final product of the self-assembly process might be a static nanostructure or a dynamic nanodevice that performs a specific function. Over the past two decades, DNA self-assembly has produced stunning nanoscale objects such as 2D and 3D lattices, polyhedra and addressable arbitrary shaped substrates, and a myriad of nanoscale devices such as molecular tweezers, computational circuits, biosensors and molecular assembly lines. In this dissertation we study multiple problems in the theory, simulations and experiments of DNA self-assembly. We extend the Turing-universal mathematical framework of self-assembly known as the Tile Assembly Model by incorporating randomization during the assembly process. This allows us to reduce the tile complexity of linear assemblies. We develop multiple techniques to build linear assemblies of expected length N using far fewer tile types than previously possible. We abstract the fundamental properties of DNA and develop a biochemical system, which we call meta-DNA, based entirely on strands of DNA as the only component molecule. We further develop various enzyme-free protocols to manipulate meta-DNA systems and provide strand level details along with abstract notations for these mechanisms. We simulate DNA circuits by providing detailed designs for local molecular computations that involve spatially contiguous molecules arranged on addressable substrates via enzyme-free DNA hybridization reaction cascades. We use the Visual DSD simulation software in conjunction with localized reaction rates obtained from biophysical modeling to create chemical reaction networks of localized hybridization circuits that are then model checked using the PRISM model checking software. We develop a DNA detection system employing the triggered self-assembly of a novel DNA dendritic nanostructure. Detection begins when a specific, single-stranded target DNA strand triggers a hybridization chain reaction between two distinct DNA hairpins. Each hairpin opens and hybridizes up to two copies of the other, and hence each layer of the growing dendritic nanostructure can in principle accommodate an exponentially increasing number of cognate molecules, generating a nanostructure with high molecular weight. We build linear activatable assemblies employing a novel protection/deprotection strategy to strictly enforce the direction of tiling assembly growth to ensure the robustness of the assembly process. Our system consists of two tiles that can form a linear co-polymer. These tiles, which are initially protected such that they do not react with each other, can be activated to form linear co-polymers via the use of a strand displacing enzyme.

Chandran, Harish

419

Fractal Dimension Analysis in Self-Assembled Poly(dA)·poly(dT) DNA Network on Mica Surface  

NASA Astrophysics Data System (ADS)

Characteristics of the self-assembled poly(dA)·poly(dT) DNA network adhered on the mica substrate are experimentally investigated based on the AFM observations and the fractal dimension analysis. Artificial B-type double stranded DNA, which consists of 50 base pairs of adenine and thymine, is specially prepared for the experiment. The manufacturing process of DNA network is done in the aqueous solution of poly(dA)·poly(dT) DNA, and the systematical experimental runs are made for various concentration of the solution. It is found that the 2D fractal dimension strongly depends on the fabrication process of the DNA network.

Kawano, Satoyuki

420

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

421

Measures and implications of electronic coherence in photosynthetic light-harvesting.  

PubMed

We review various methods for measuring delocalization in light-harvesting complexes. Direct relations between inverse participation ratios (IPRs) and entanglement measures are derived. The B850 ring from the LH2 complex in Rhodopseudomonas acidophila is studied. By analysing electronic energy transfer dynamics in the B850 ring using different metrics for quantifying excitonic delocalization, we conclude that measures of entanglement are far more robust (in terms of time scale, temperature and level of decoherence) than IPRs, and are therefore more appropriate for the purpose of studying the time evolution of coherence in a system. PMID:22753823

Smyth, Cathal; Fassioli, Francesca; Scholes, Gregory D

2012-08-13

422

Energy transfer from conjugated polymer to bacterial light-harvesting complex  

NASA Astrophysics Data System (ADS)

Energy transfer from a conjugated polymer blend (poly(9,9-dioctylfluorenyl-2,7-diyl):poly (2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene) to a light-harvesting complex 2 from purple bacteria has been demonstrated using time-resolved fluorescence spectroscopy. For our hybrid nanostructure, we observe a 30% reduction of the fluorescence lifetime of the polymer emission as compared to the pure polymer layer. This result is an important step towards integrating naturally evolved biomolecules with synthetic materials into biohybrid organic electronic systems.

Buczynska, D.; Bujak, ?.; Loi, M. A.; Brotosudarmo, T. H. P.; Cogdell, R.; Mackowski, S.

2012-10-01

423

Large organized surface domains self-assembled from nonpolar amphiphiles.  

PubMed

For years, researchers had presumed that Langmuir monolayers of small C(n)F(2n+1)C(m)H(2m+1) (FnHm) diblock molecules (such as F8H16) consisted of continuous, featureless films. Recently we have discovered that they instead form ordered arrays of unusually large (~30-60 nm), discrete self-assembled surface domains or hemimicelles both at the surface of water and on solid substrates. These surface micelles differ in several essential ways from all previously reported or predicted molecular surface aggregates. They self-assemble spontaneously, even at zero surface pressure, depending solely on a critical surface concentration. They are very large (~100 times the length of the diblock) and involve thousands of molecules (orders of magnitude more than classical micelles). At the same time, the surface micelles are highly monodisperse and self-organize in close-packed hexagonal patterns (two-dimensional crystals). Their size is essentially independent from pressure, and they do not coalesce and are unexpectedly sturdy for soft matter (persisting even beyond surface film collapse). We and other researchers have observed large surface micelles for numerous diblocks, using Langmuir-Blodgett (LB) transfer, spin-coating and dip-coating techniques, or expulsion from mixed monolayers, and on diverse supports, establishing that hemimicelle formation and ordering are intrinsic properties of (perfluoroalkyl)alkanes. Notably, they involve "incomplete" surfactants with limited amphiphilic character, which further illustrates the outstanding capacity for perfluoroalkyl chains to promote self-assembly and interfacial film structuring. Using X-ray reflectivity, we determined a perfluoroalkyl-chain-up orientation. Theoretical investigations assigned self-assembly and hemimicelle stability to electrostatic dipole-dipole interactions at the interface between Fn- and Hm-sublayers. Grazing-incidence small-angle X-ray scattering (GISAXS) data collected directly on the surface of water unambiguously demonstrated the presence of surface micelles in monolayers of diblocks prior to LB transfer for atomic force microscopy imaging. We characterized an almost perfect two-dimensional crystal, with 12 assignable diffraction peaks, which established that self-assembly and regular nanopatterning were not caused by transfer or induced by the solid support. These experiments also provide the first direct identification of surface micelles on water, and the first identification of such large-size domains using GISAXS. Revisiting Langmuir film compression behavior after we realized that it actually was a compression of nanometric objects led to further unanticipated observations. These films could be compressed far beyond the documented film "collapse", eventually leading to the buildup of two superimposed, less-organized bilayers of diblocks on top of the initially formed monolayer of hemimicelles. Remarkably, the latter withstood the final, irreversible collapse of the composite films. "Gemini" tetrablocks, di(FnHm), with two Fn-chains and two Hm-chains, provided two superposed layers of discrete micelles, apparently the first example of thin films made of stacked discrete self-assembled nanoobjects. Decoration of solid surfaces with domains of predetermined size of these small "nonpolar" molecules is straightforward. Initial examples of applications include deposition of metal dots and catalytic oxidation of CO, and nanopatterning of SiO(2) films. PMID:22185721

Krafft, Marie Pierre

2011-12-21

424

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

425

A Programmable Transducer Self-Assembled from DNA  

PubMed Central

A transducer consists of an input/output alphabet, a finite set of states, and a transition function. From an input symbol applied to a given state, the transition function determines the next state, and an output symbol. Using DNA, we have constructed a transducer that divides a number by 3. The input consists of a series of individually addressable 2-state DNA nanomechanical devices that control the orientations of a group of flat 6-helix DNA motifs; these motifs have edge domains tailed in sticky ends corresponding to the numbers 0 and 1. Three-domain DNA molecules (TX tiles) act as computational tiles that correspond to the transitions that the transducer can undergo. The output domain of these TX tiles contains sticky ends that also correspond to 0 or 1. Two different DNA tiles can chelate these output domains: A 5 nm gold nanoparticle is attached to the chelating tile that binds to 0-domains and a 10 nm gold nanoparticle is attached to the chelating tile that binds to 1-domains. The answer to the division is represented by the series of gold nanoparticles, which can be interpreted as a binary number. The answers of the computation are read out by examination of the transducer complexes under a transmission electron microscope. The start or end points of the output sequence can be indicated by the presence of a 15 nm gold nanoparticle. This work demonstrates two previously unreported features integrated in a single framework: [1] a system that combines DNA algorithmic self-assembly with DNA nanomechanical devices that control that input, and [2] the arrangement of non-DNA species, here metallic nanoparticles, through DNA algorithmic self-assembly. The nanomechanical devices are controlled by single-stranded DNA strands, allowing multiple input sequences to be applied to the rest of the system, thus guiding the algorithmic self-assembly to a variety of outputs.

Chakraborty, Banani; Jonoska, Natasha; Seeman, Nadrian C.

2012-01-01

426

Effect of wettability and surface functional groups on protein adsorption and cell adhesion using well-defined mixed self-assembled monolayers  

Microsoft Academic Search

Self-assembled monolayers (SAMs) of alkanethiols, which can provide flat and chemically well-defined surfaces, were employed as model surfaces to understand cellular interaction with artificial materials. SAMs presenting a wide range of wettabilities were prepared by mixing two kinds of alkanethiols carrying terminal methyl (CH3), hydroxyl (OH), carboxylic acid (COOH), or amino (NH2) groups. Adhesion behavior of human umbilical vein endothelial

Yusuke Arima; Hiroo Iwata

2007-01-01

427

Energy levels in self-assembled quantum arbitrarily shaped dots.  

PubMed

A model to determine the electronic structure of self-assembled quantum arbitrarily shaped dots is applied. This model is based principally on constant effective mass and constant potentials of the barrier and quantum dot material. An analysis of the different parameters of this model is done and compared with those which take into account the variation of confining potentials, bands, and effective masses due to strain. The results are compared with several spectra reported in literature. By considering the symmetry, the computational cost is reduced with respect to other methods in literature. In addition, this model is not limited by the geometry of the quantum dot. PMID:15740390

Tablero, C

2005-02-01

428

Molecular dynamics simulations of friction in self-assembled monolayers  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations were performed to study friction in self-assembled monolayers of alkanethiols on gold. The simulations yield a frictional force that is proportional to the applied load, consistent with Amontons' second law for macroscopic systems. It is further demonstrated that the chain length of the alkanethiols and the load under which the surfaces interact has an effect on the structure of the monolayer film during compression. The simulations suggest, however, that these changes in structure have little effect on the friction properties of the monolayer film. Also, the mode of energy dissipation in both this system and a system in which two monolayer films interact is examined.

Tupper, Kenneth J.; Brenner, Donald W.

1994-12-01

429

Coherent plasmonic engineering in self-assembled reduced symmetry nanostructures  

NASA Astrophysics Data System (ADS)

Multiple coherent effects including Fano resonances are observed in self-assembled reduced symmetry gold nanorod systems, in particular Dolmen configurations. The bottom-up chemical method provides high quality units and assemblies (single crystal with low surface roughness and sub 5 nm gaps) that reduce radiative losses from the plasmonic structures. Multiple dark and bright plasmonic resonances are observed in optical dark-field scattering measurements and electron energy loss spectroscopy. These high fidelity structures and narrow resonances are promising for future design of high figure of merit sensors, ultrafast switches and slow light devices for optical information processing.

Biswas, Sushmita; Duan, Jinsong; Mahalingam, Krishnamurthy; Nepal, Dhriti; Pachter, Ruth; Drummy, Larry; Brown, Dean; Vaia, Richard A.

2013-09-01

430

Multiexciton Spectroscopy of a Single Self-Assembled Quantum Dot  

NASA Astrophysics Data System (ADS)

We apply low temperature confocal optical microscopy to spatially resolve, and spectroscopically study, a single self-assembled quantum dot. By comparing the emission spectra obtained at various excitation levels to a theoretical many body model, we show that (a) single exciton radiative recombination is very weak, and (b) sharp spectral lines are due to optical transitions between confined multiexcitonic states among which excitons thermalize within their lifetimes. Once these few states are fully occupied, broadbands appear due to transitions between states which contain electrons in the continuum.

Dekel, E.; Gershoni, D.; Ehrenfreund, E.; Spektor, D.; Garcia, J. M.; Petroff, P. M.

1998-06-01

431

Nitrogen Substituted Phenothiazine Derivatives: Modelling of Molecular Self-Assembling  

PubMed Central

The study aims to present a detailed theoretical investigation of noncovalent intermolecular interactions between different ?–? stacking nitrogen substituted phenothiazine derivatives by applying second-order Møller-Plesset perturbation (MP2), density functional (DFT) and semiempirical theories. The conformational stability of these molecular systems is mainly given by the dispersion-type electron correlation effects. The density functional tight-binding (DFTB) method applied for dimer structures are compared with the results obtained by the higher level theoretical methods. Additionally, the optimal configuration of the investigated supramolecular systems and their self-assembling properties are discussed.

Bende, Attila; Turcu, Ioan

2011-01-01

432

Surfactant Two-Dimensional Self-Assembly under Confinement  

SciTech Connect

Confinement-induced structural rearrangements in supported self-assembled surfactant layers in aqueous salt solutions are investigated using classical Density Functional Theory. The systematic study of the influence of the nature of electrolyte revealed that 2:1 electrolyte stabilizes the hemicylindrical configuration of ionic surfactant layers, while a confinement-induced transition to a tilted monolayer configuration was found in symmetric 1:1 and 2:2 electrolytes. On the basis of this study we formulate a general model for the energetics of structural rearrangements in supported surfactant layers.

Sushko, Maria L.; Liu, Jun

2011-03-28

433

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

434

Tunable resonant optical microcavities by self-assembled templating.  

PubMed

Micrometer-scale optical cavities are produced by a combination of template sphere self-assembly and electrochemical growth. Transmission measurements of the tunable microcavities show sharp resonant modes with Q factors of >300 and 25-fold local enhancement of light intensity. The presence of transverse optical modes confirms the lateral confinement of photons. Calculations show that submicrometer mode volumes are feasible. The small mode volumes of these microcavities promise to lead to a wide range of applications. in microlasers, atom optics, quantum information, biophotonics, and single-molecule detection. PMID:15259726

Vijaya Prakash, G; Besombes, L; Kelf, T; Baumberg, Jeremy J; Bartlett, P N; Abdelsalam, M E

2004-07-01

435

Biomimetic self-assembly of a functional asymmetrical electronic device  

PubMed Central

This paper introduces a biomimetic strategy for the fabrication of asymmetrical, three-dimensional electronic devices modeled on the folding of a chain of polypeptide structural motifs into a globular protein. Millimeter-size polyhedra—patterned with logic devices, wires, and solder dots—were connected in a linear string by using flexible wire. On self-assembly, the string folded spontaneously into two domains: one functioned as a ring oscillator, and the other one as a shift register. This example demonstrates that biomimetic principles of design and self-organization can be applied to generate multifunctional electronic systems of complex, three-dimensional architecture.

Boncheva, Mila; Gracias, David H.; Jacobs, Heiko O.; Whitesides, George M.

2002-01-01

436

Self-assembly of ordered epitaxial nanostructures on polygonal nanowires.  

PubMed

We study the self-assembly of ordered nanostructures, that is, nanorings (NRs) and quantum dots (QDs), epitaxially grown on a polygonal cross-section nanowire (PCS-NW) using both theoretical and phase-field modeling. Our studies show that, by increasing the PCS-NW size, transitions from ordered NRs to ordered QDs on facets and further to ordered QDs on ridges occur. The predicted morphologies and their transitions are in excellent agreement with existing experiments. Our study suggests a novel approach to fabricate ordered nanostructures on nanowires. PMID:23323519

Lu, Liang-Xing; Bharathi, M S; Zhang, Yong-Wei

2013-01-22

437

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

NASA Astrophysics Data System (ADS)

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 ca