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1

Self-assembly strategies for integrating light harvesting and charge separation in artificial photosynthetic systems.  

PubMed

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 pi-stacking can be used to integrate light harvesting with charge separation and transport. Our current strategy uses covalent building blocks based on chemically robust arylene imide and diimide dyes, biomimetic porphyrins, and chlorophylls. We take advantage of the shapes, sizes, and intermolecular interactions--such as pi-pi and/or metal-ligand interactions--of these molecules to direct the formation of supramolecular structures having enhanced energy capture and charge-transport properties. We use small- and wide-angle X-ray scattering (SAXS/WAXS) from a synchrotron source to elucidate the solution phase structures of these monodisperse noncovalent aggregates. We expect that a greater understanding of self-assembly using pi-stacking and molecular designs that combine those features with hydrogen bonding and metal-ligand bonding could simplify the structure of the building blocks for artificial photosynthetic complexes, while retaining their ability to assemble complex, photofunctional structures. PMID:19803479

Wasielewski, Michael R

2009-12-21

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. PMID:19587237

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

2009-01-01

3

Quantum-dot-induced self-assembly of cricoid protein for light harvesting.  

PubMed

Stable protein one (SP1) has been demonstrated as an appealing building block to design highly ordered architectures, despite the hybrid assembly with other nano-objects still being a challenge. Herein, we developed a strategy to construct high-ordered protein nanostructures by electrostatic self-assembly of cricoid protein nanorings and globular quantum dots (QDs). Using multielectrostatic interactions between 12mer protein nanoring SP1 and oppositely charged CdTe QDs, highly ordered nanowires with sandwich structure were achieved by hybridized self-assembly. QDs with different sizes (QD1, 3-4 nm; QD2, 5-6 nm; QD3, ?10 nm) would induce the self-assembly protein rings into various nanowires, subsequent bundles, and irregular networks in aqueous solution. Atomic force microscopy, transmission electron microscopy, and dynamic light scattering characterizations confirmed that the size of QDs and the structural topology of the nanoring play critical functions in the formation of the superstructures. Furthermore, an ordered arrangement of QDs provides an ideal scaffold for designing the light-harvesting antenna. Most importantly, when different sized QDs (e.g., QD1 and QD3) self-assembled with SP1, an extremely efficient Förster resonance energy transfer was observed on these protein nanowires. The self-assembled protein nanostructures were demonstrated as a promising scaffold for the development of an artificial light-harvesting system. PMID:24601558

Miao, Lu; Han, Jishu; Zhang, Hao; Zhao, Linlu; Si, Chengye; Zhang, Xiyu; Hou, Chunxi; Luo, Quan; Xu, Jiayun; Liu, Junqiu

2014-04-22

4

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

DOEpatents

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

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

2009-12-15

5

Self-assembled artificial cilia  

PubMed Central

Due to their small dimensions, microfluidic devices operate in the low Reynolds number regime. In this case, the hydrodynamics is governed by the viscosity rather than inertia and special elements have to be introduced into the system for mixing and pumping of fluids. Here we report on the realization of an effective pumping device that mimics a ciliated surface and imitates its motion to generate fluid flow. The artificial biomimetic cilia are constructed as long chains of spherical superparamagnetic particles, which self-assemble in an external magnetic field. Magnetic field is also used to actuate the cilia in a simple nonreciprocal manner, resulting in a fluid flow. We prove the concept by measuring the velocity of a cilia-pumped fluid as a function of height above the ciliated surface and investigate the influence of the beating asymmetry on the pumping performance. A numerical simulation was carried out that successfully reproduced the experimentally obtained data. PMID:19934055

Vilfan, Mojca; Poto?nik, Anton; Kav?i?, Blaž; Osterman, Natan; Poberaj, Igor; Vilfan, Andrej; Babi?, Dušan

2010-01-01

6

Efficient energy transfer from peripheral chromophores to the self-assembled zinc chlorin rod antenna: a bioinspired light-harvesting system to bridge the "green gap".  

PubMed

An artificial light-harvesting rod aggregate based on zinc chlorin and covalently linked naphthalene bisimide chromophore has been realized by self-assembly. Efficient energy transfer (phiET >/= 0.99) takes place upon excitation at 620 nm from peripheral naphthalene bisimides to the zinc chlorin rod aggregate backbone. The appended naphthalene bisimide dyes improve the total LH efficiency of the rod aggregate by 26%. Thus, the present bioinspired antenna system is promising for application in nanodevices for the effective utilization of solar energy by bridging the "green gap". PMID:16704238

Röger, Cornelia; Müller, Marc G; Lysetska, Marina; Miloslavina, Yulia; Holzwarth, Alfred R; Würthner, Frank

2006-05-24

7

Wide-range light-harvesting donor-acceptor assemblies through specific intergelator interactions via self-assembly.  

PubMed

We have synthesized two new low-molecular-mass organogelators based on tri-p-phenylene vinylene derivatives, one of which could be designated as the donor whereas the other one is an acceptor. These were prepared specifically to show the intergelator interactions at the molecular level by using donor-acceptor self-assembly to achieve appropriate control over their macroscopic properties. Intermolecular hydrogen-bonding, ?-stacking, and van der Waals interactions operate for both the individual components and the mixtures, leading to the formation of gels in the chosen organic solvents. Evidence for intergelator interactions was acquired from various spectroscopic, microscopic, thermal, and mechanical investigations. Due to the photochromic nature of these molecules, interesting photophysical properties, such as solvatochromism and J-type aggregation, were clearly observed. An efficient energy transfer was exhibited by the mixture of donor-acceptor assemblies. An array of four chromophores was built up by inclusion of two known dyes (anthracene and rhodamine 6G) for the energy-transfer studies. Interestingly, an energy-transfer cascade was observed in the assembly of four chromophores in a particular order (anthracene-donor-acceptor-rhodamine 6G), and if one of the components was removed from the assembly the energy transfer process was discontinued. This allowed the build up of a light-harvesting process with a wide range. Excitation at one end produces an emission at the other end of the assembly. PMID:23074067

Samanta, Suman K; Bhattacharya, Santanu

2012-12-01

8

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. PMID:18509052

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

2008-01-01

9

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

PubMed

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

Wen, Fuyu; Li, Can

2013-11-19

10

G-Quartet-Based Nanostructure for Mimicking Light-Harvesting Antenna.  

PubMed

Artificial light-harvesting systems have received great attention for use in photosynthetic and optoelectronic devices. Herein, a system involving G-quartet-based hierarchical nanofibers generated from the self-assembly of guanosine 5'-monophosphate (GMP) and a two-step Förster resonance energy transfer (FRET) is presented that mimics natural light-harvesting antenna. This solid-state property offers advantages for future device fabrication. The generation of photocurrent under visible light shows it has potential for use as a nanoscale photoelectric device. The work will be beneficial for the development of light-harvesting systems by the self-assembly of supramolecular nanostructures. PMID:25423890

Pu, Fang; Wu, Li; Ran, Xiang; Ren, Jinsong; Qu, Xiaogang

2014-11-25

11

Verification of the vibronic origin of long-lived coherence in an artificial molecular light harvester  

E-print Network

Is quantum coherence responsible for the surprisingly high efficiency of natural light harvesters? If so, how do such systems avoid the loss of coherence due to interaction with their warm, wet and noisy environments? The answer to these important questions rests in the beneficial interplay between electronic and vibrational degrees of freedom. Here we report experimental and theoretical verification of coherent exciton-vibrational (vibronic) coupling as the origin of long-lasting coherence in an artificial light harvester, a molecular J-aggregate. In this macroscopically aligned tubular system, polarization controlled 2D spectroscopy delivers an uncongested and specific optical response. This clarity of signal provided the opportunity to unambiguously assign the origin of the observed long-lived coherences to vibronic coupling and rule out other explanations based upon correlated fluctuations. The discussed vibronic coupling is functionally relevant, as it describes interaction between vibrations and electro...

Lim, James; Caycedo-Soler, Felipe; Lincoln, Craig N; Prior, Javier; von Berlepsch, Hans; Huelga, Susana F; Plenio, Martin B; Zigmantas, Donatas; Hauer, Jürgen

2015-01-01

12

Artificial light-harvesting antennae: electronic energy transfer by way of molecular funnels.  

PubMed

Electronic energy transfer (EET) plays a critical role in many biological processes and is used by nature to direct energy to a site where chemical reactions need to be initiated. Such EET can occur over large distances and can involve many individual molecules of identical, similar or disparate chemical identity. Advances in spectroscopy and data processing have allowed the rates of EET to be measured on extremely fast timescales such that improved mechanistic insight becomes feasible. At the same time, highly sophisticated synthetic operations have been devised that facilitate the isolation and purification of elaborate multi-component molecular arrays. A key feature of these arrays concerns the logical positioning of individual units in a way that favours directed EET along the molecular axis or along some other preferred pathway. The availability of these novel molecular materials allows close examination of popular theoretical models and paves the way for the development of advanced molecular sensors, artificial light harvesters, fluorescent labels and sensitizers. Of particular interest is the spectacular growth in the application of boron dipyrromethene dyes as basic reagents in such artificial photon collectors and these compounds have dominated the market in recent years because of their synthetic versatility and valuable photophysical properties. In this article, recent developments in the field are highlighted in terms of synthesis and subsequent spectroscopic exploration. PMID:20957235

Ziessel, Raymond; Harriman, Anthony

2011-01-14

13

Design and Assembly of Functional Light-Harvesting Complexes  

Microsoft Academic Search

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

Paula Braun; Leszek Fiedor

14

Design and self-assembly of simple coat proteins for artificial viruses.  

PubMed

Viruses are among the simplest biological systems and are highly effective vehicles for the delivery of genetic material into susceptible host cells. Artificial viruses can be used as model systems for providing insights into natural viruses and can be considered a testing ground for developing artificial life. Moreover, they are used in biomedical and biotechnological applications, such as targeted delivery of nucleic acids for gene therapy and as scaffolds in material science. In a natural setting, survival of viruses requires that a significant fraction of the replicated genomes be completely protected by coat proteins. Complete protection of the genome is ensured by a highly cooperative supramolecular process between the coat proteins and the nucleic acids, which is based on reversible, weak and allosteric interactions only. However, incorporating this type of supramolecular cooperativity into artificial viruses remains challenging. Here, we report a rational design for a self-assembling minimal viral coat protein based on simple polypeptide domains. Our coat protein features precise control over the cooperativity of its self-assembly with single DNA molecules to finally form rod-shaped virus-like particles. We confirm the validity of our design principles by showing that the kinetics of self-assembly of our virus-like particles follows a previous model developed for tobacco mosaic virus. We show that our virus-like particles protect DNA against enzymatic degradation and transfect cells with considerable efficiency, making them promising delivery vehicles. PMID:25150720

Hernandez-Garcia, Armando; Kraft, Daniela J; Janssen, Anne F J; Bomans, Paul H H; Sommerdijk, Nico A J M; Thies-Weesie, Dominique M E; Favretto, Marco E; Brock, Roland; de Wolf, Frits A; Werten, Marc W T; van der Schoot, Paul; Stuart, Martien Cohen; de Vries, Renko

2014-09-01

15

Design and self-assembly of simple coat proteins for artificial viruses  

NASA Astrophysics Data System (ADS)

Viruses are among the simplest biological systems and are highly effective vehicles for the delivery of genetic material into susceptible host cells. Artificial viruses can be used as model systems for providing insights into natural viruses and can be considered a testing ground for developing artificial life. Moreover, they are used in biomedical and biotechnological applications, such as targeted delivery of nucleic acids for gene therapy and as scaffolds in material science. In a natural setting, survival of viruses requires that a significant fraction of the replicated genomes be completely protected by coat proteins. Complete protection of the genome is ensured by a highly cooperative supramolecular process between the coat proteins and the nucleic acids, which is based on reversible, weak and allosteric interactions only. However, incorporating this type of supramolecular cooperativity into artificial viruses remains challenging. Here, we report a rational design for a self-assembling minimal viral coat protein based on simple polypeptide domains. Our coat protein features precise control over the cooperativity of its self-assembly with single DNA molecules to finally form rod-shaped virus-like particles. We confirm the validity of our design principles by showing that the kinetics of self-assembly of our virus-like particles follows a previous model developed for tobacco mosaic virus. We show that our virus-like particles protect DNA against enzymatic degradation and transfect cells with considerable efficiency, making them promising delivery vehicles.

Hernandez-Garcia, Armando; Kraft, Daniela J.; Janssen, Anne F. J.; Bomans, Paul H. H.; Sommerdijk, Nico A. J. M.; Thies-Weesie, Dominique M. E.; Favretto, Marco E.; Brock, Roland; de Wolf, Frits A.; Werten, Marc W. T.; van der Schoot, Paul; Stuart, Martien Cohen; de Vries, Renko

2014-09-01

16

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. PMID:23511467

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

17

Selective internalization of self-assembled artificial oil bodies by HER2/neu-positive cells  

NASA Astrophysics Data System (ADS)

A novel delivery carrier was developed using artificial oil bodies (AOBs). Plant seed oil bodies (OBs) consist of a triacylglycerol matrix surrounded by a monolayer of phospholipids embedded with the storage protein oleosin (Ole). Ole consists of a central hydrophobic domain with two amphiphatic arms that extrude from the surface of OBs. In this study, a bivalent anti-HER2/neu affibody domain (ZH2) was fused with Ole at the C terminus. After overproduction in Escherichia coli, the fusion protein (Ole-ZH2) was recovered to assemble AOBs. The size of self-assembled AOBs was tailored by varying the oil/Ole-ZH2 ratio and pH to reach a nanoscale. Upon co-incubation with tumor cells, the nanoscale AOBs encapsulated with a hydrophobic fluorescence dye were selectively internalized by HER2/neu-overexpressing cells and displayed biocompatibility with the cells. In addition, the ZH2-mediated endosomal entry of AOBs occurred in a time- and AOB dose-dependent manner. The internalization efficiency was as high as 90%. The internalized AOBs disintegrated at the non-permissive pH (e.g. in acidic endosomes) and the cargo dye was released. Results of in vitro study revealed a sustained and prolonged release profile. Taken together, our findings indicate the potential of AOBs as a delivery carrier.

Chiang, Chung-Jen; Lin, Li-Jen; Lin, Che-Chin; Chang, Chih-Hsiang; Chao, Yun-Peng

2011-01-01

18

Impact of Assembly State on the Defect Tolerance of TMV-Based Light Harvesting Arrays  

E-print Network

-mail: francis@cchem.berkeley.edu Abstract: Self-assembling, light harvesting arrays of organic chromophores canImpact of Assembly State on the Defect Tolerance of TMV-Based Light Harvesting Arrays Rebekah A in the photosynthetic process is the collection of sunlight by an array of pigments within the light harvesting (LH

Geissler, Phillip

19

Self-assembled chromophores within mesoporous nanocrystalline TiO2: towards biomimetic solar cells.  

PubMed

Artificial light-harvesting antennas consisting of self-assembled chromophores that mimic the natural pigments of photosynthetic bacteria have been inserted into voids induced in porous titania (TiO2, anatase) in order to investigate their suitability for hybrid solar cells. Mesoporous nanocrystalline TiO2 with additional uniform macropores was treated with precursor solutions of the pigment which was then induced to self-assemble within the voids. The chromophores were tailored to combine the self-assembly characteristics of the natural bacteriochlorophylls with the robustness of artificial Zn-porphyrins being stable for prolonged periods even upon heating to over 200 degrees C. They assemble on the TiO2 surface to form nano- to micro-crystalline structures with lengths from tens of nm up to several microm and show a photosensitization effect which is supposed to be dependent on the assembly size. The natural examples of these antennas are found in green sulfur bacteria which are able to use photosynthesis in deep water regions with minute light intensities. The implementation of biomimetic antennas for light harvesting and a better photon management may lead to a rise in efficiency of dye-sensitized solar cells also under low light illumination conditions. PMID:19504907

Marek, Peter L; Sieger, Hermann; Scherer, Torsten; Hahn, Horst; Balaban, Teodor Silviu

2009-06-01

20

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

21

Natural strategies for photosynthetic light harvesting.  

PubMed

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

Croce, Roberta; van Amerongen, Herbert

2014-07-01

22

Self assembling magnetic tiles  

E-print Network

Self assembly is an emerging technology in the field of manufacturing. Inspired by nature's ability to self assembly proteins from amino acids, this thesis attempts to demonstrate self assembly on the macro-scale. The ...

Rabl, Jessica A. (Jessica Ann)

2006-01-01

23

Self-Assembly Game  

NSDL National Science Digital Library

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

2012-06-26

24

Self-Assembly  

NSDL National Science Digital Library

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

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

2009-10-14

25

Error Free Self-assembly Using Error Prone Tiles  

Microsoft Academic Search

DNA self-assembly is emerging as a key paradigm for nano-technology, nano-computation, and several related disciplines. In nature, DNA self-assembly is often equipped with explicit mechanisms for both error prevention and error correction. For artificial self-assembly, these problems are even more important since we are interested in assembling large systems with great precision. We present an error-correction scheme, called snaked proof-reading,

Ho-lin Chen; Ashish Goel

2004-01-01

26

OligArch: A software tool to allow artificially expanded genetic information systems (AEGIS) to guide the autonomous self-assembly of long DNA constructs from multiple DNA single strands  

PubMed Central

Summary Synthetic biologists wishing to self-assemble large DNA (L-DNA) constructs from small DNA fragments made by automated synthesis need fragments that hybridize predictably. Such predictability is difficult to obtain with nucleotides built from just the four standard nucleotides. Natural DNA's peculiar combination of strong and weak G:C and A:T pairs, the context-dependence of the strengths of those pairs, unimolecular strand folding that competes with desired interstrand hybridization, and non-Watson–Crick interactions available to standard DNA, all contribute to this unpredictability. In principle, adding extra nucleotides to the genetic alphabet can improve the predictability and reliability of autonomous DNA self-assembly, simply by increasing the information density of oligonucleotide sequences. These extra nucleotides are now available as parts of artificially expanded genetic information systems (AEGIS), and tools are now available to generate entirely standard DNA from AEGIS DNA during PCR amplification. Here, we describe the OligArch (for "oligonucleotide architecting") software, an application that permits synthetic biologists to engineer optimally self-assembling DNA constructs from both six- and eight-letter AEGIS alphabets. This software has been used to design oligonucleotides that self-assemble to form complete genes from 20 or more single-stranded synthetic oligonucleotides. OligArch is therefore a key element of a scalable and integrated infrastructure for the rapid and designed engineering of biology. PMID:25161743

Bradley, Kevin M

2014-01-01

27

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

PubMed

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

Tamulis, A; Tamulis, V; Graja, A

2006-04-01

28

Molecular Self-Assembly  

NSDL National Science Digital Library

In this activity, students interact with 12 models to observe emergent phenomena as molecules assemble themselves. Investigate the factors that are important to self-assembly, including shape and polarity. Try to assemble a monolayer by "pushing" the molecules to the substrate (it's not easy!). Rotate complex molecules to view their structure. Finally, create your own nanostructures by selecting molecules, adding charges to them, and observing the results of self-assembly.

2012-07-19

29

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

2013-10-01

30

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

31

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

32

Natural Light Harvesting Systems: Unraveling the quantum puzzles  

E-print Network

In natural light harvesting systems, the sequential quantum events of photon absorption by specialized biological antenna complexes, charge separation, exciton formation and energy transfer to localized reaction centers culminates in the conversion of solar to chemical energy. A notable feature in these processes is the exceptionally high efficiencies ($>$ 95\\%) at which excitation is transferred from the illuminated protein complex site to the reaction centers. The high speeds of excitation propagation within a system of interwoven biomolecular network structures, is yet to be replicated in artificial light harvesting complexes. A clue to unraveling the quantum puzzles of nature may lie in the observations of long lived coherences lasting several picoseconds in the electronic spectra of photosynthetic complexes which occurs even in noisy environmental baths. The exact nature of the association between the high energy propagation rates and strength of quantum coherences remains largely unsolved. This review presents recent developments in quantum theories, and links information-theoretic aspects with photosynthetic light-harvesting processes in biomolecular systems. There is examination of various attempts to pinpoint the processes that underpin coherence features arising from the light harvesting activities of biomolecular systems, with particular emphasis on the effects that factors such non-Markovianity, zeno mechanisms, teleportation, quantum predictability and the role of multipartite states have on the quantum dynamics of biomolecular systems. A discussion of how quantum thermodynamical principles and agent-based modeling and simulation approaches can improve our understanding of natural photosynthetic systems is included.

A. Thilagam

2014-11-23

33

Energy, charge, and spin transport in molecules and self-assembled nanostructures inspired by photosynthesis.  

PubMed

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. PMID:16808492

Wasielewski, Michael R

2006-07-01

34

Self-assembling cytotoxins.  

PubMed

Decanal and N-amino-N'-1-octylguanidine (AOG), combined at 28 microM each, mediated erythrocyte lysis within 80 minutes under physiological conditions. By contrast, no lysis was observed after 20 hours with either decanal (56 microM) or AOG (100 microM) alone. The pronounced synergism observed for these chemicals and similar reactive pairs of chemicals is due to the self-assembly of more cytotoxic hydrazones in situ. Decanal and AOG also exhibit synergistic activity against cultured human cells (HeLa) and bacteria (Escherichia coli J96). This synergism may be useful in the design of cytotoxins that would self-assemble selectively from nontoxic precursors within tumors, while sparing normal tissue. PMID:3523757

Rideout, D

1986-08-01

35

Self Assembly of Colloids  

NASA Astrophysics Data System (ADS)

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

Sacanna, Stefano

2012-02-01

36

A DNA-Directed Light-Harvesting/Reaction Center System.  

PubMed

A structurally and compositionally well-defined and spectrally tunable artificial light-harvesting system has been constructed in which multiple organic dyes attached to a three-arm-DNA nanostructure serve as an antenna conjugated to a photosynthetic reaction center isolated from Rhodobacter sphaeroides 2.4.1. The light energy absorbed by the dye molecules is transferred to the reaction center, where charge separation takes place. The average number of DNA three-arm junctions per reaction center was tuned from 0.75 to 2.35. This DNA-templated multichromophore system serves as a modular light-harvesting antenna that is capable of being optimized for its spectral properties, energy transfer efficiency, and photostability, allowing one to adjust both the size and spectrum of the resulting structures. This may serve as a useful test bed for developing nanostructured photonic systems. PMID:25340853

Dutta, Palash K; Levenberg, Symon; Loskutov, Andrey; Jun, Daniel; Saer, Rafael; Beatty, J Thomas; Lin, Su; Liu, Yan; Woodbury, Neal W; Yan, Hao

2014-11-26

37

A novel artificial nerve graft for repairing long-distance sciatic nerve defects: a self-assembling peptide nanofiber scaffold-containing poly(lactic-co-glycolic acid) conduit  

PubMed Central

In this study, we developed a novel artificial nerve graft termed self-assembling peptide nanofiber scaffold (SAPNS)-containing poly(lactic-co-glycolic acid) (PLGA) conduit (SPC) and used it to bridge a 10-mm-long sciatic nerve defect in the rat. Retrograde tracing, behavioral testing and histomorphometric analyses showed that compared with the empty PLGA conduit implantation group, the SPC implantation group had a larger number of growing and extending axons, a markedly increased diameter of regenerated axons and a greater thickness of the myelin sheath in the conduit. Furthermore, there was an increase in the size of the neuromuscular junction and myofiber diameter in the target muscle. These findings suggest that the novel artificial SPC nerve graft can promote axonal regeneration and remyelination in the transected peripheral nerve and can be used for repairing peripheral nerve injury.

Wang, Xianghai; Pan, Mengjie; Wen, Jinkun; Tang, Yinjuan; Hamilton, Audra D.; Li, Yuanyuan; Qian, Changhui; Liu, Zhongying; Wu, Wutian; Guo, Jiasong

2014-01-01

38

Nanopropulsion by biocatalytic self-assembly.  

PubMed

A number of organisms and organelles are capable of self-propulsion at the micro- and nanoscales. Production of simple man-made mimics of biological transportation systems may prove relevant to achieving movement in artificial cells and nano/micronscale robotics that may be of biological and nanotechnological importance. We demonstrate the propulsion of particles based on catalytically controlled molecular self-assembly and fiber formation at the particle surface. Specifically, phosphatase enzymes (acting as the engine) are conjugated to a quantum dot (the vehicle), and are subsequently exposed to micellar aggregates (fuel) that upon biocatalytic dephosphorylation undergo fibrillar self-assembly, which in turn causes propulsion. The motion of individual enzyme/quantum dot conjugates is followed directly using fluorescence microscopy. While overall movement remains random, the enzyme-conjugates exhibit significantly faster transport in the presence of the fiber forming system, compared to controls without fuel, a non-self-assembling substrate, or a substrate which assembles into spherical, rather than fibrous structures upon enzymatic dephosphorylation. When increasing the concentration of the fiber-forming fuel, the speed of the conjugates increases compared to non-self-assembling substrate, although directionality remains random. PMID:25162764

Leckie, Joy; Hope, Alexander; Hughes, Meghan; Debnath, Sisir; Fleming, Scott; Wark, Alastair W; Ulijn, Rein V; Haw, Mark D

2014-09-23

39

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

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

2012-03-01

41

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

42

Microfluidic self assembly  

E-print Network

Recent progress in colloidal science has led to elaborate self-assembled structures whose complexity raises hopes for elaborating new materials. However, the throughputs are extremely low and consequently, the chance to produce materials of industrial interest, for instance, groundbreaking optical devices, harnessing complete three-dimensional band gaps, is markedly low. We discovered a novel hydrodynamic effect that may unlock this bottleneck. It is based on the dipolar flow interactions that build up when droplets are slowed down by the microchannel walls along which they are transported. Coupled with depletion forces, we succeeded to form, via a continuous flow process, at unprecedented speeds and under exquisite control, a rich ensemble of monodisperse planar and tridimensional clusters, such as chains, triangles, diamonds, tetahedrons, heterotrimers, possessing geometrical, chemical, and/or magnetic anisotropies enabling directional bonding. Continuous productions of millions of building blocks per second for elaborating new functional materials can be envisioned.

Bingqing Shen; Joshua Ricouvier; Mathilde Reyssat; Florent Malloggi; Patrick Tabeling

2014-09-14

43

?-Carotene to bacteriochlorophyll c energy transfer in self-assembled aggregates mimicking chlorosomes  

Microsoft Academic Search

Carotenoids are together with bacteriochlorophylls important constituents of chlorosomes, the light-harvesting antennae of green photosynthetic bacteria. Majority of bacteriochlorophyll molecules form self-assembling aggregates inside the chlorosomes. Aggregates of bacteriochlorophylls with optical properties similar to those of chlorosomes can also be prepared in non-polar organic solvents or in aqueous environments when a suitable non-polar molecule is added. In this work, the

J. Alster; T. Polívka; J. B. Arellano; P. Chábera; F. Vácha; J. Pšen?ík

2010-01-01

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

Phycobilisomes: light-harvesting pigment complexes  

Microsoft Academic Search

Phycobilisomes, as a light-harvesting sytem, appear to be organized for maximum energy transfer, with chlorophyll of the lamellae the final acceptor. Phycobilisomes were first observed by electron microscopy, and the suggestion was made that they are sites of phycobiliproteins. The shape of the phycobilisomes may be determined by the predominant phycobiliproteins present, and their size is quite constant with a

Elisabeth Gantt

1975-01-01

46

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

47

Self-Assembling Dessert Toppings  

NSDL National Science Digital Library

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

Twin Cities Public Television, Inc.

2008-01-01

48

Self-Assembly with Nanomanufacturing  

NSDL National Science Digital Library

In this activity, by the Concord Consortium's Molecular Literacy project, students learn the "necessary conditions for self-assembly (random motion and molecular stickiness), play with some example models of self-assembling biological structures (quartenary structures such as hemoglobin, fibers, and microtubules), and then design their own self-assembly structures." Upon completion of this activity students should be able to identify and manipulate two key characteristics of molecules that allow them to self assemble; describe the effect of temperature on self-assembly; and give examples of the effect of molecular shape on the larger structures built by self-assembly. The activity itself is a java-based interactive resource built upon the free, open source Molecular Workbench software. In the activity, students are allowed to explore at their own pace in a digital environment full of demonstrations, illustrations, and models they can manipulate. In addition to the activity, visitors will find an overview of the activity, a test and rubric, central concepts, and their correlation to AAAS standards.

2008-10-23

49

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

2012-09-25

50

Evolution and function of light harvesting proteins.  

PubMed

Photosynthetic eukaryotes exhibit very different light-harvesting proteins, but all contain membrane-intrinsic light-harvesting complexes (Lhcs), either as additional or sole antennae. Lhcs non-covalently bind chlorophyll a and in most cases another Chl, as well as very different carotenoids, depending on the taxon. The proteins fall into two major groups: The well-defined Lhca/b group of proteins binds typically Chl b and lutein, and the group is present in the 'green lineage'. The other group consists of Lhcr/Lhcf, Lhcz and Lhcx/LhcSR proteins. The former are found in the so-called Chromalveolates, where they mostly bind Chl c and carotenoids very efficient in excitation energy transfer, and in their red algae ancestors. Lhcx/LhcSR are present in most Chromalveolates and in some members of the green lineage as well. Lhcs function in light harvesting, but also in photoprotection, and they influence the organisation of the thylakoid membrane. The different functions of the Lhc subfamilies are discussed in the light of their evolution. PMID:25240794

Büchel, Claudia

2015-01-01

51

Self-assembling amphiphilic peptides†  

PubMed Central

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

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

2014-01-01

52

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

53

Patterning self-assembled monolayers using microcontact  

E-print Network

228 reviews Patterning self-assembled monolayers using microcontact printing: a new technology for biosensors? Milan Mrksich and George M. Whitesides Self-assembled monolayers (SAMs), formed upon. The system of self-assembled monolayers (SAMs) of alkanethiolates on gold is probably the best that is cur

Mrksich, Milan

54

Quantum mechanical light harvesting mechanisms in photosynthesis  

NASA Astrophysics Data System (ADS)

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

Scholes, Gregory

2012-02-01

55

Two-dimensional crystallization of the light-harvesting complex from Rhodospirillum rubrum.  

PubMed

Homogeneous detergent-solubilized B873 light-harvesting complexes from a carotenoid-less mutant of the purple non-sulfur bacterium, Rhodospirillum rubrum G9, were reassembled spontaneously into two-dimensional (2D) hexagonal arrays during extensive and controlled dialysis. As the complexes contain only 1 to 2 mol phospholipid per mol alpha beta dimer, the arrays formed by a self assembly process are primary due to protein-protein interactions. The hexagonal lattices were analyzed by negative stain electron microscopy and digital image processing. They exhibited a unit cell size of 12.3 nm, in close agreement with the particle diameter of the active photo-unit in native chromatophore membranes. The unit cell contains a central 5 nm stain-filled depression, embraced by a ring with an outer diameter of 10 nm. PMID:8510160

Ghosh, R; Hoenger, A; Hardmeyer, A; Mihailescu, D; Bachofen, R; Engel, A; Rosenbusch, J P

1993-05-20

56

Dynamic formation of hybrid peptidic capsules by chiral self-sorting and self-assembly.  

PubMed

Owing to their versatility and biocompatibility, peptide-based self-assembled structures constitute valuable targets for complex functional designs. It is now shown that artificial capsules based on ?-barrel binding motifs can be obtained by means of dynamic covalent chemistry (DCC) and self-assembly. Short peptides (up to tetrapeptides) are reversibly attached to resorcinarene scaffolds. Peptidic capsules are thus selectively formed in either a heterochiral or a homochiral way by simultaneous and spontaneous processes, involving chiral sorting, tautomerization, diastereoselective induction of inherent chirality, and chiral self-assembly. Self-assembly is shown to direct the regioselectivity of reversible chemical reactions. It is also responsible for shifting the tautomeric equilibrium for one of the homochiral capsules. Two different tautomers (keto-enamine hemisphere and enol-imine hemisphere) are observed in this capsule, allowing the structure to adapt for self-assembly. PMID:25298130

J?drzejewska, Hanna; Wierzbicki, Micha?; Cmoch, Piotr; Rissanen, Kari; Szumna, Agnieszka

2014-12-01

57

Patchy particles by self assembly  

NASA Astrophysics Data System (ADS)

Patchy particles offer novel means for colloidal assembly or clustering of functional groups but are generally made by batch processes rather than self-assembly. Selective binding of multivalent ligands within a mixture of polyvalent amphiphiles provides, in principle, a mechanism for driving domain formation in self-assemblies. Divalent cations are shown here to crossbridge polyanionic amphiphiles, which thereby demix from neutral amphiphiles and form spots or rafts within vesicles as well as stripes within cylindrical micelles. Calcium- and copper-crossbridged domains of synthetic block copolymers or natural lipid (phosphatidylinositol-4,5-bisphosphate) possess tunable sizes, shapes and/or spacings that can last for years. Lateral segregation in these `responsive Janus assemblies' couples weakly to curvature and proves to be restricted within phase diagrams to narrow regimes of pH and cation concentration that are centred near the characteristic binding constants for polyacid interactions. Remixing at high pH is surprising, but a theory for strong lateral segregation shows that counterion entropy dominates electrostatic crossbridges, thus illustrating the insights gained into ligand-induced pattern formation within self-assemblies. REFERENCES - [1] D.A. Christian, A. Tian, W.G. Ellenbroek, I. Levental, P.A. Janmey, A.J. Liu, T. Baumgart, D.E. Discher. Spotted vesicles, striped micelles, and Janus assemblies induced by ligand binding. Nature Materials 8: 843--849 (2009).

Discher, Dennis; Christian, David

2010-03-01

58

Structure-based model for light-harvesting properties of nucleic acid nanostructures  

PubMed Central

Programmed self-assembly of DNA enables the rational design of megadalton-scale macromolecular assemblies with sub-nanometer scale precision. These assemblies can be programmed to serve as structural scaffolds for secondary chromophore molecules with light-harvesting properties. Like in natural systems, the local and global spatial organization of these synthetic scaffolded chromophore systems plays a crucial role in their emergent excitonic and optical properties. Previously, we introduced a computational model to predict the large-scale 3D solution structure and flexibility of nucleic acid nanostructures programmed using the principle of scaffolded DNA origami. Here, we use Förster resonance energy transfer theory to simulate the temporal dynamics of dye excitation and energy transfer accounting both for overall DNA nanostructure architecture as well as atomic-level DNA and dye chemical structure and composition. Results are used to calculate emergent optical properties including effective absorption cross-section, absorption and emission spectra and total power transferred to a biomimetic reaction center in an existing seven-helix double stranded DNA-based antenna. This structure-based computational framework enables the efficient in silico evaluation of nucleic acid nanostructures for diverse light-harvesting and photonic applications. PMID:24311563

Pan, Keyao; Boulais, Etienne; Yang, Lun; Bathe, Mark

2014-01-01

59

Development of Scaffolds for Light Harvesting and Photocatalysis from the Coat Protein of Tobacco Mosaic Virus  

NASA Astrophysics Data System (ADS)

The utility of a previously developed TMV-based light harvesting system has been dramatically expanded through the introduction of reactive handles for the site-specific modification of the interior and exterior surfaces. Further experiments to reengineer the coat protein have produced structures with unique, unexpected, and useful assembly properties that complement the newly available surface modifications. Energy transfer from chromophores in the RNA channel of self-assembled TMV structures to the exterior was made possible by conjugation of acceptor dyes and porphyrins to the N-terminus. By repositioning the N-terminus to the pore through circular permutation, this process was repeated to create structures that mimic the light harvesting 1 complex of photosynthetic bacteria. To study and improve upon natural photosynthesis, closely packed chromophore arrays and gold nanoparticles were tethered to the pore of stabilized TMV disks through introduction of a uniquely reactive lysine. Finally, a dimeric TMV coat protein was produced to control the distribution and arrangement of synthetic groups with synergistic activity.

Dedeo, Michel Toussaint

60

Stereochemistry in subcomponent self-assembly.  

PubMed

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

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

2014-07-15

61

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

SciTech Connect

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

Harel, Elad [Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208 (United States)

2012-05-07

62

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

PubMed

Photosynthesis, the process by which energy from sunlight drives cellular metabolism, relies on a unique organization of light-harvesting and reaction center complexes. Recently, the organization of light-harvesting LH2 complexes and dimeric reaction center-light-harvesting I-PufX core complexes in membranes of purple non-sulfur bacteria was revealed by atomic force microscopy [S. Bahatyrova et al., Nature (London) 430, 1058 (2004)]. Here, we discuss optimal exciton transfer in a biomimetic system closely modeled on the structure of LH2 and its organization within the membrane using a Markovian quantum model with dissipation and trapping added phenomenologically. In a deliberate manner, we neglect the high level detail of the bacterial light-harvesting complex and its interaction with the phonon bath in order to elucidate a set of design principles that may be incorporated in artificial pigment-scaffold constructs in a supramolecular assembly. We show that our scheme reproduces many of the most salient features found in their natural counterpart and may be largely explained by simple electrostatic considerations. Most importantly, we show that quantum effects act primarily to enforce robustness with respect to spatial and spectral disorder between and within complexes. The implications of such an arrangement are discussed in the context of biomimetic photosynthetic analogs capable of transferring energy efficiently across tens to hundreds of nanometers. PMID:22583207

Harel, Elad

2012-05-01

63

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

NASA Astrophysics Data System (ADS)

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

Harel, Elad

2012-05-01

64

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

65

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

PubMed

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

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

2014-07-01

66

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

PubMed Central

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

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

2014-01-01

67

Self-assembling magnetic "snakes"  

SciTech Connect

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

None

2010-01-01

68

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

69

SELF-ASSEMBLING AUTOMATA: A MODEL OF CONFORMATIONAL SELF-ASSEMBLY  

E-print Network

SELF-ASSEMBLING AUTOMATA: A MODEL OF CONFORMATIONAL SELF-ASSEMBLY KAZUHIRO SAITOU Department An abstract model of self-assembling systems is presented where assembly instruc- tions are written as conformational switches ­ local rules that specify conforma- tional changes of a component. The model, the self

Saitou, Kazuhiro "Kazu"

70

How Nature Builds Itself: Self-Assembly  

NSDL National Science Digital Library

By designing and building models with Legos and placing them in a reaction chamber, students will simulate the process of molecular self-assembly. This activity provides a basis for understanding that thermal energy at the nanometer scale is a determining factor for whether or not self-assembly occurs.

Taylor, Amy R.; Broadwell, Bethany P.; Jones, M. G.; Falvo, Michael R.

2007-01-01

71

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

72

Self-assembled granular walkers  

E-print Network

Mechanisms of locomotion in microscopic systems are of great interest not only for technological applications, but also for the sake of understanding, and potentially harnessing, processes far from thermal equilibrium. Down-scaling is a particular challenge, and has led to a number of interesting concepts including thermal ratchet systems and asymmetric swimmers. Here we present a system which is particularly intriguing, as it is self-assembling and uses a robust mechanism which can be implemented in various settings. It consists of small spheres of different size which adhere to each other, and are subject to an oscillating (zero average) external force eld. An inherent nonlinearity in the mutual force network leads to force rectication and hence to locomotion. We present a model that accounts for the observed behaviour and demonstrates the wide applicability and potential scalability of the concept.

Z. S. Khan; A. Steinberger; R. Seemann; and S. Herminghaus

2010-03-08

73

Self-Assembly of Supramolecular Nanofibers  

NASA Astrophysics Data System (ADS)

The development of functional nanofibers via self-assembly is an area of growing interest. Whereas self-assembly has been successful in creating nanostructures, the fabrication of hierarchical architectures from multiple functional components and the development of synergistic functions are emerging as challenging issues. In this chapter, various self-assembly approaches that are used to construct nanofibers are summarized. Self-assembly of amphiphilic supermolecules provides a key strategy to hierarchically fabricate multicomponent architectures. Amphiphilic pairs of nanofiber-forming molecules can be screened from a wide range of functional molecules, including biomolecules. As examples of nanofibers whose functions are dynamically controlled based on self-assembly, lipophilic one-dimensional metal complexes and their unique characteristics are introduced.

Kimizuka, Nobuo

74

Bottom-Up Nanomanufacturing: Self Assembly  

NSDL National Science Digital Library

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

2011-09-22

75

Self-Assembly of Biomolecular Soft Matter  

PubMed Central

Self-assembly programmed by molecular structure and guided dynamically by energy dissipation is a ubiquitous phenomenon in biological systems that build functional structures from the nanoscale to macroscopic dimensions. This paper describes examples of one-dimensional self-assembly of peptide amphiphiles and the consequent biological functions that emerge in these systems. We also discuss here hierarchical self-assembly of supramolecular peptide nanostructures and polysaccharides, and some new results are reported on supramolecular crystals formed by highly charged peptide amphiphiles. Reflecting on presentations at this Faraday Discussion, the paper ends with a discussion of some of the future opportunities and challenges of the field. PMID:24611266

Zha, R. Helen; Palmer, Liam C.; Cui, Honggang; Bitton, Ronit

2014-01-01

76

One-dimensional staged self-assembly  

E-print Network

We introduce the problem of staged self-assembly of one-dimensional nanostructures, which becomes interesting when the elements are labeled (e.g., representing functional units that must be placed at specific locations). ...

Demaine, Erik D.

77

Self-Assembly: How Nature Builds  

NSDL National Science Digital Library

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

Bethany Broadwell

2006-12-01

78

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

79

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. PMID:19111062

Stang, Peter J.

2009-01-01

80

Simulations of Computing by Self-Assembly  

Microsoft Academic Search

Winfree (1996) proposed a Turing-universal model of DNA self-assembly.In this abstract model, DNA double-crossover molecules self-assemble to form analgorithmically-patterned two-dimensional lattice. Here, we develop a more realisticmodel based on the thermodynamics and kinetics of oligonucleotide hydridization.Using a computer simulation, we investigate what physical factors influence the errorrates, i.e., when the more realistic model deviates from the ideal of the abstract

Erik Winfree

1998-01-01

81

Lamellar Self-Assembly Nanostructured Magnetic Materials  

Microsoft Academic Search

Synthesis of lamellar self-assemblies symmetric polystyrene–polybutylmethacrylate (PS–PBMA) copolymers, doped by magnetic nanoparticles was described. Self-assembly is a spontaneous process by which molecules and nanophase entities may materialize into organized aggregates or networks. As soon as particles are coated by a grafted PS layer, they can be confined in the PS layer of the polymeric smectic. The lamellar order was maintained

B. Hamdoun

2004-01-01

82

Self-Assembly DOI: 10.1002/anie.200602914  

E-print Network

Self-Assembly DOI: 10.1002/anie.200602914 Electrostatic Self-Assembly of Polystyrene Microspheres--that directs the self- assembly of chemically modified polystyrene microspheres to form three materials for electrostatic self-assembly. We control the contact electrifi- cation of these microspheres

Prentiss, Mara

83

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

2013-08-13

84

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

PubMed Central

Branched hollow fibers are common in nature, but to form artificial fibers with a similar branched hollow structure is still a challenge. We discovered that polyvinylpyrrolidone (PVP) could self-assemble into branched hollow fibers in an aqueous solution after aging the PVP solution for about two weeks. Based on this finding, we demonstrated two approaches by which the self-assembly of PVP into branched hollow fibers could be exploited to template the formation of branched hollow inorganic fibers. First, inorganic material such as silica with high affinity against the PVP could be deposited on the surface of the branched hollow PVP fibers to form branched hollow silica fibers. To extend the application of PVP self-assembly in templating the formation of hollow branched fibers, we then adopted a second approach where the PVP molecules bound to inorganic nanoparticles (using gold nanoparticles as a model) co-self-assemble with the free PVP molecules in an aqueous solution, resulting in the formation of the branched hollow fibers with the nanoparticles embedded in the PVP matrix constituting the walls of the fibers. Heating the resultant fibers above the glass transition temperature of PVP led to the formation of branched hollow gold fibers. Our work suggests that the self-assembly of the PVP molecules in the solution can serve as a general method for directing the formation of branched hollow inorganic fibers. The branched hollow fibers may find potential applications in microfluidics, artificial blood vessel generation, and tissue engineering. PMID:20158250

Qiu, Penghe; Mao, Chuanbin

2010-01-01

85

Waveguide arrays for light harvesting in microfluidic chips  

NASA Astrophysics Data System (ADS)

We demonstrate a way of light harvesting in integrated microfluidic chips fabricated by femtosecond laser micromachining. The architecture consists of waveguide arrays fabricated in the vicinity of the microchannel filled with a fluorescent organic solution (e.g., polyfluorene solution). Amplified spontaneous emission from the microchannel is efficiently coupled by the waveguides to the outside of the chip.

Guduru, Surya S. K.; Paiè, Petra; Bolis, Serena; Osellame, Roberto; Ramponi, Roberta; Virgili, Tersilla; Vishnubhatla, Krishna Chaitanya

2014-07-01

86

Light-harvesting materials: Soft support for energy conversion  

NASA Astrophysics Data System (ADS)

To convert solar energy into viable fuels, coupling light-harvesting materials to catalysts is a crucial challenge. Now, the combination of an organic supramolecular hydrogel and a non-precious metal catalyst has been demonstrated to be effective for photocatalytic H2 production.

Stolley, Ryan M.; Helm, Monte L.

2014-11-01

87

Self-assembly, modularity, and physical complexity  

NASA Astrophysics Data System (ADS)

We present a quantitative measure of physical complexity, based on the amount of information required to build a given physical structure through self-assembly. Our procedure can be adapted to any given geometry, and thus, to any given type of physical structure that can be divided into building blocks. We illustrate our approach using self-assembling polyominoes, and demonstrate the breadth of its potential applications by quantifying the physical complexity of molecules and protein complexes. This measure is particularly well suited for the detection of symmetry and modularity in the underlying structure, and allows for a quantitative definition of structural modularity. Furthermore we use our approach to show that symmetric and modular structures are favored in biological self-assembly, for example in protein complexes. Lastly, we also introduce the notions of joint, mutual and conditional complexity, which provide a useful quantitative measure of the difference between physical structures.

Ahnert, S. E.; Johnston, I. G.; Fink, T. M. A.; Doye, J. P. K.; Louis, A. A.

2010-08-01

88

Templated self-assembly of patchy particles  

E-print Network

We explore the use of templated self-assembly to facilitate the formation of complex target structures made from patchy particles. First, we consider the templating of high-symmetry shell structures around a spherical core particle. We find that nucleation around the core particle can inhibit aggregate formation, a process which often hinders self-assembly. In particular, this new assembly pathway allows dodecahedral shells to form readily, whereas these structures never form in the absence of the template. Secondly, we consider the self-assembly of multi-shell structures, where the central icosahedral core is known to form readily on its own, and which could then template the growth of further layers. We are able to find conditions under which two- and three-shell structures successfully assemble, illustrating the power of the templating approach.

Alexander J. Williamson; Alex W. Wilber; Jonathan P. K. Doye; Ard A. Louis

2010-11-24

89

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

90

?-Carotene to bacteriochlorophyll c energy transfer in self-assembled aggregates mimicking chlorosomes  

NASA Astrophysics Data System (ADS)

Carotenoids are together with bacteriochlorophylls important constituents of chlorosomes, the light-harvesting antennae of green photosynthetic bacteria. Majority of bacteriochlorophyll molecules form self-assembling aggregates inside the chlorosomes. Aggregates of bacteriochlorophylls with optical properties similar to those of chlorosomes can also be prepared in non-polar organic solvents or in aqueous environments when a suitable non-polar molecule is added. In this work, the ability of ?-carotene to induce aggregation of bacteriochlorophyll c in aqueous buffer was studied. Excitation relaxation and energy transfer in the carotenoid-bacteriochlorophyll assemblies were measured using femtosecond and nanosecond transient absorption spectroscopy. A fast, ˜100-fs energy transfer from the S 2 state of ?-carotene to bacteriochlorophyll c was revealed, while no evidence for significant energy transfer from the S 1 state was found. Picosecond formation of the carotenoid triplet state (T 1) was observed, which was likely generated by singlet homo-fission from the S 1 state of ?-carotene.

Alster, J.; Polívka, T.; Arellano, J. B.; Chábera, P.; Vácha, F.; Pšen?ík, J.

2010-07-01

91

Communications Self-assembly of Tiled Perovskite  

E-print Network

with specific electronic, magnetic, optical, catalytic, and other properties. Toward this goal, perovskiteCommunications Self-assembly of Tiled Perovskite Monolayer and Multilayer Thin Films Raymond E adsorption is a convenient way to make thin films of materials with specific stacking sequences.1

92

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

93

Self-assembled Monolayer Films: Microcontact Printing  

E-print Network

Self-assembled Monolayer Films: Microcontact Printing , Microcontact printing (PCP), one of the non to generate two-dimensional patterns by print- * ing the molecules of an "ink" onto the surface of a solid(dimethylsiloxane) (PDMS), the "ink" is an alkanethiol, and the substrate on which the printing occurs is a thin

Prentiss, Mara

94

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

95

Diblock copolymer based self-assembled nanomagnetoelectric  

E-print Network

O4 (CFO)] nano cylinders within a matrix of ferroelectric lead zirconium titanate [Pb1.1(Zr(0.53)Ti(0.47))O3(PZT)] when thin films were prepared by spin coating. The initial magnetic permeability of the self-assembled CFO/PZT nanocomposite changes...

Ren, Shenqiang; Briber, Robert M.; Wuttig, Manfred

2008-10-31

96

Molecular self-assembly: Searching sequence space  

NASA Astrophysics Data System (ADS)

Short peptides are among the most intriguing building blocks in nanotechnology, but it would be very challenging to experimentally study the properties of large numbers of different sequences. Now, a computational analysis of all 8,000 possible tripeptides has been used to identify those with interesting self-assembly behaviour.

Gazit, Ehud

2015-01-01

97

Self-assembly with degenerate prototropy.  

PubMed

This work describes a rational approach for addressing the prototropy-related problems in heterocycle-based self-assembling systems by the use of degenerate prototropy. As a proof of principle, the utility of degenerate prototropy is demonstrated herein by developing heterocycle-based AADD-type self-assembling modules that exist as "single set of protameric pair (duplex)" in both solution and solid states. These self-assembling modules are quickly accessible in good yield by reacting 2-amino-5,5-disubstituted-1H-pyrimidine-4,6-diones, available in one step by the condensation of alpha,alpha-dialkyl malonates and free guanidine, with isocyanates. Evidence from NMR spectroscopy, ESI mass spectrometry, and single-crystal X-ray diffraction studies confirmed the formation of molecular duplexes. The effect of electronic repulsion in duplex formation is also investigated. Their ready synthetic accessibility, remarkably high propensity to crystal formation, and the novel property of degenerate prototropy would make these novel self-assembling molecules promising candidates for many proposed applications. PMID:16050710

Baruah, Pranjal K; Gonnade, Rajesh; Phalgune, Usha D; Sanjayan, Gangadhar J

2005-08-01

98

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

99

Toward a molecular programming language for algorithmic self-assembly.  

E-print Network

??Self-assembly is the process whereby relatively simple components autonomously combine to form more complex objects. Nature exhibits self-assembly to form everything from microscopic crystals to… (more)

Patitz, Matthew John

2010-01-01

100

Toward a molecular programming language for algorithmic self-assembly.  

E-print Network

?? Self-assembly is the process whereby relatively simple components autonomously combine to form more complex objects. Nature exhibits self-assembly to form everything from microscopic crystals… (more)

Patitz, Matthew John

2010-01-01

101

A design for self-assembling robots in a system  

E-print Network

This thesis presents the design, construction, control, and application for a novel concept of self-assembling robots in a system. The system is composed of multiple cooperative robots that are designed to self-assemble ...

Kim, Myunghee, Ph. D. Massachusetts Institute of Technology

2006-01-01

102

Early events in the biosynthesis and assembly of the cyanobacterial light-harvesting system  

NASA Astrophysics Data System (ADS)

The cyanobacteria are photosynthetic procaryotes that employ a mechanism of photosynthesis which is essentially identical to the systems found in plant chloroplasts and the eukaryotic green algae. Cyanobacteria can drive photosynthesis with light energy from a broad region of the visible spectrum (500 - 650 nm wavelength) that is not available to plants and green algae, which are limited to the narrow band of light energy that is absorbed by chlorophyll (660-680 nm). The light-harvesting capacity of the cyanobacteria is a function of a complex protein structure that resides on the surface of the photosynthetic membrane in contact with the PSII chlorophyll reaction centers. This light-harvesting complex is called a phycobilisome and functions as a protein scaffold for a rigid array of chromophores that absorbs light energy and transfers it to chlorophyll. The chromophores are linear tetrapyrroles (the bilins) that are covalently attached to the biliproteins, which comprise 80 - 85% of the total phycobilisome mass. There are three major classes of spectrally distinct biliproteins [phycoerythrin (PE), (lambda) max equals 565 nm; phycocyanin (PC), (lambda) max equals 617 nm; and allophycocyanin (AP), (lambda) max equals 650 nm] and their spatial organization within the phycobilisome creates an array of donor and acceptor chromophores that is optimized for resonance energy transfer to chlorophyll on a picosecond timescale and at close to 100% efficiency. The cyanobacteria can exert control over the biliprotein composition of the phycobilisomes in response to both light quality and light quantity, and they do so primarily by light-responsive transcription control mechanisms. The biosynthesis and assembly of a phycobilisome is an interesting example of self-assembly in a complex protein system. A phycobilisome from Synechocystis sp. strain 6701 can contain 400 proteins derived from a repertoire of 16 different polypeptides that includes the (alpha) and (beta) subunits for each major biliprotein and the achromic linker proteins that mediate assembly throughout the structure. The biliprotein subunit structures all show an identical motif that is reflected by significant amino acid sequence similarities across the different classes. Since phycobilisomes can comprise up to 40% of the cyanobacterial dry mass, assembly of these complexes must occur in the presence of high localized concentrations of components that are very similar in structure. That phycobilisome assembly is an efficient process with no evidence of significant misassembly suggests that effective molecular recognition during phycobilisome biosynthesis is based upon the subtle differences between subunits of different class biliproteins. We are using a protein engineering approach to examine structural features that mediate molecular recognition in two of the earliest steps of phycobilisome assembly, the docking of (alpha) and (beta) subunits and the selective attachment of chromophores.

Anderson, Lamont

1996-02-01

103

Direct evidence of quantum transport in photosynthetic light-harvesting complexes  

E-print Network

Photosynthetic organisms employ light-harvesting antennae to capture and transport solar energy to the reactionDirect evidence of quantum transport in photosynthetic light-harvesting complexes Gitt, CA, and approved October 17, 2011 (received for review April 04, 2011) The photosynthetic light-harvesting

Mukamel, Shaul

104

Structure and growth of self-assembling monolayers  

Microsoft Academic Search

The structural phases and the growth of self-assembled monolayers (SAMs) are reviewed from a surface science perspective, with emphasis on simple model systems. The concept of self-assembly is explained, and different self-assembling materials are briefly discussed. A summary of the techniques used for the study of SAMs is given. Different general scenarios for structures obtained by self-assembly are described. Thiols

Frank Schreiber

2000-01-01

105

Photosynthetic light-harvesting is tuned by the heterogeneous polarizable environment of the protein.  

PubMed

In photosynthesis, special antenna proteins that contain multiple light-absorbing molecules (chromophores) are able to capture sunlight and transfer the excitation energy to reaction centers with almost 100% quantum efficiencies. The critical role of the protein scaffold in holding the appropriate arrangement of the chromophores is well established and can be intuitively understood given the need to keep optimal dipole-dipole interactions between the energy-transferring chromophores, as described by Fo?rster theory more than 60 years ago. However, the question whether the protein structure can also play an active role by tuning such dipole-dipole interactions has not been answered so far, its effect being rather crudely described by simple screening factors related to the refractive index properties of the system. Here, we present a combined quantum chemical/molecular mechanical approach to compute electronic couplings that accounts for the heterogeneous dielectric nature of the protein-solvent environment in atomic detail. We apply the method to study the effect of dielectric heterogeneity in the energy migration properties of the PE545 principal light-harvesting antenna of the cryptomonad Rhodomonas CS24. We find that dielectric heterogeneity can profoundly tune by a factor up to ?4 the energy migration rates between chromophore sites compared to the average continuum dielectric view that has historically been assumed. Our results indicate that engineering of the local dielectric environment can potentially be used to optimize artificial light-harvesting antenna systems. PMID:21322565

Curutchet, Carles; Kongsted, Jacob; Muñoz-Losa, Aurora; Hossein-Nejad, Hoda; Scholes, Gregory D; Mennucci, Benedetta

2011-03-01

106

Light-harvesting materials: Soft support for energy conversion  

SciTech Connect

To convert solar energy into viable fuel sources, coupling light-harvesting materials to catalysts is a critical challenge. Now, coupling between an organic supramolecular hydrogel and a non precious metal catalyst has been demonstrated to be effective for photocatalytic H2 production. Ryan M. Stolley and Monte L. Helm are at Pacific Northwest National Laboratory (PNNL), Richland, WA, USA 99352. PNNL is operated by Battelle for the US Department of Energy. e-mail: Monte.Helm@pnnl.gov

Stolley, Ryan M.; Helm, Monte L.

2014-11-10

107

Autonomous Programmable Biomolecular Devices Using Self-Assembled DNA Nanostructures  

E-print Network

Autonomous Programmable Biomolecular Devices Using Self-Assembled DNA Nanostructures John H. Reif · Programmable: the tasks executed can be modified without entirely redesigning the nanostructure. Self-Assembled DNA Nanostructures: · use synthetic DNA to self-assemble into DNA nanostructure devices. Goals

Reif, John H.

108

Random Number Selection in Self-Assembly , Jack H. Lutz  

E-print Network

Random Number Selection in Self-Assembly David Doty , Jack H. Lutz , Matthew J. Patitz , Scott M unbounded space. 1 Introduction The development of DNA tile self-assembly has moved nanotechnology closer self-assembly that enables us to explore the potentialities and limitations of this kind of molecular

Doty, David

109

DNA Computing by Self-Assembly ERIK WINFREE  

E-print Network

DNA Computing by Self-Assembly ERIK WINFREE Departments of Computer Science and Computation algorithm, based on molecular self- assembly of heterogeneous crystals, that illustrates some aspects synthetic DNA molecules; how well these techniques will scale remains to be seen. ALGORITHMIC SELF-ASSEMBLY

Batzoglou, Serafim

110

Self-Assembly of Dendron Rodcoil Molecules into Nanoribbons  

E-print Network

Self-Assembly of Dendron Rodcoil Molecules into Nanoribbons Eugene R. Zubarev, Martin U. Pralle on designed molecules that self-order or fold. The focus on self-assembly throughout the 90s has generated to control the dimensionality and shape of self- assembled structures through molecular design remains a chal

Zubarev, Eugene

111

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

112

Self-assembled tunable photonic hyper-crystals  

PubMed Central

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

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

2014-01-01

113

Self-assembly of Fmoc-diphenylalanine inside liquid marbles.  

PubMed

Liquid marbles made from Lycopodium clavatum spores are used to encapsulate aqueous solutions of 9-fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF). Acidification of the Fmoc-FF solution at the liquid/air interface of the liquid marble triggers the self-assembly of ribbon-like peptide fibrils into an ultrathin peptide membrane (50-500 nm). The membrane incorporates the lycopodium microparticles and as a result stabilizes the liquid marble against collapse, that could otherwise occur through particle disintegration at the floating interphase. Ultrathin nanostructured peptide membrane formation at the liquid/air interface is also observed within artificial microstructured floating objects. Thus, peptide membranes formed were inspected by SEM and TEM. Electron diffraction data reveal information about the molecular organization inside the oligopeptide membranes. PMID:22584262

Braun, Hans-Georg; Cardoso, André Zamith

2012-09-01

114

Self Assembly of Complex Building Blocks  

NASA Astrophysics Data System (ADS)

A genetic search algorithm for optimizing the packing density of self-assembled multicomponent crystals of nanoparticles applied to complex colloidal building blocks will be presented. The algorithm searches the complex multi-dimensional space to find preferred crystal structures where standard methods fail. Mixtures of colloidal molecules and the structures found to be preferred to phase separation for different species of coloidal molecule mixtures will be shown.

Stucke, David; Crespi, Vincent

2004-03-01

115

Templated Self Assemble of Nano-Structures  

SciTech Connect

This project will identify and model mechanisms that template the self-assembly of nanostructures. We focus on a class of systems involving a two-phase monolayer of molecules adsorbed on a solid surface. At a suitably elevated temperature, the molecules diffuse on the surface to reduce the combined free energy of mixing, phase boundary, elastic field, and electrostatic field. With no template, the phases may form a pattern of stripes or disks. The feature size is on the order of 1-100 nm, selected to compromise the phase boundary energy and the long-range elastic or electrostatic interaction. Both experimental observations and our theoretical simulations have shown that the pattern resembles a periodic lattice, but has abundant imperfections. To form a perfect periodic pattern, or a designed aperiodic pattern, one must introduce a template to guide the assembly. For example, a coarse-scale pattern, lithographically defined on the substrate, will guide the assembly of the nanoscale pattern. As another example, if the molecules on the substrate surface carry strong electric dipoles, a charged object, placed in the space above the monolayer, will guide the assembly of the molecular dipoles. In particular, the charged object can be a mask with a designed nanoscale topographic pattern. A serial process (e.g., e-beam lithography) is necessary to make the mask, but the pattern transfer to the molecules on the substrate is a parallel process. The technique is potentially a high throughput, low cost process to pattern a monolayer. The monolayer pattern itself may serve as a template to fabricate a functional structure. This project will model fundamental aspects of these processes, including thermodynamics and kinetics of self-assembly, templated self-assembly, and self-assembly on unconventional substrates. It is envisioned that the theory will not only explain the available experimental observations, but also motivate new experiments.

Suo, Zhigang [Harvard University

2013-04-29

116

The dynamics of nacre self-assembly  

PubMed Central

We show how nacre and pearl construction in bivalve and gastropod molluscs can be understood in terms of successive processes of controlled self-assembly from the molecular- to the macro-scale. This dynamics involves the physics of the formation of both solid and liquid crystals and of membranes and fluids to produce a nanostructured hierarchically constructed biological composite of polysaccharides, proteins and mineral, whose mechanical properties far surpass those of its component parts. PMID:17251136

Cartwright, Julyan H.E; Checa, Antonio G

2006-01-01

117

Metal-enhanced fluorescence of chlorophylls in single light-harvesting complexes.  

PubMed

Ensemble and single-molecule spectroscopy demonstrates that both emission and absorption of peridinin-chlorophyll-protein photosynthetic antennae can be largely enhanced through plasmonic interactions. We find up to 18-fold increase of the chlorophyll fluorescence for complexes placed near a silver metal layer. This enhancement, which leaves no measurable effects on the protein structure, is observed when exciting either chlorophyll or carotenoid and is attributed predominantly to an increase of the excitation rate in the antenna. The enhancement mechanism comes from plasmon-induced amplification of electromagnetic fields inside the complex. This result is an important step toward applying plasmonic nanostructures for controlling the optical response of complex biomolecules and improving the design and functioning of artificial light-harvesting systems. PMID:18154316

Mackowski, Sebastian; Wörmke, Stephan; Maier, Andreas J; Brotosudarmo, Tatas H P; Harutyunyan, Hayk; Hartschuh, Achim; Govorov, Alexander O; Scheer, Hugo; Bräuchle, Christoph

2008-02-01

118

Molecular Factors Controlling Photosynthetic Light-Harvesting by Carotenoids  

PubMed Central

Carotenoids are naturally-occurring pigments that absorb light in the spectral region in which the sun irradiates maximally. These molecules transfer this energy to chlorophylls, initiating the primary photochemical events of photosynthesis. Carotenoids also regulate the flow of energy within the photosynthetic apparatus and protect it from photo-induced damage caused by excess light absorption. To carry out these functions in nature, carotenoids are bound in discrete pigment-protein complexes in close proximity to chlorophylls. A few 3D structures of these carotenoid complexes have been determined by X-ray crystallography. Thus, the stage is set for attempting to correlate the structural information with the spectroscopic properties of carotenoids to understand the molecular mechanism(s) of their function in photosynthetic systems. In this Account, we summarize current spectroscopic data describing the excited state energies and ultrafast dynamics of purified carotenoids in solution and bound in light-harvesting complexes from purple bacteria, marine algae, and green plants. Many of these complexes can be modified using mutagenesis or pigment exchange which facilitates making the correlations between structure and function. We describe the structural and electronic factors controlling the function of carotenoids as energy donors. We also discuss unresolved issues related to the nature of spectroscopically dark excited states, which could play a role in light-harvesting. To illustrate the interplay between structural determinations and spectroscopic investigations that exemplifies work in the field, we describe the spectroscopic properties of four light-harvesting complexes whose structures have been determined to atomic resolution. The first, the LH2 complex from the purple bacterium Rhodopseudomonas acidophila, contains the carotenoid, rhodopin glucoside. The second is the LHCII trimeric complex from higher plants which uses the carotenoids, lutein, neoxanthin and violaxanthin to transfer energy to chlorophyll. The third, the peridinin-chlorophyll-protein (PCP) from the dinoflagellate, Amphidinium carterae, is the only known complex where the bound carotenoid (peridinin) pigments outnumber the chlorophylls. The last is xanthorhodopsin from the eubacterium, Salinibacter ruber. This complex contains the carotenoid, salinixanthin, which transfers energy to a retinal chromophore. The carotenoids in these pigment-protein complexes transfer energy with high efficiency by optimizing both the distance and orientation of the carotenoid donor and chlorophyll acceptor molecules. Importantly, the versatility and robustness of carotenoids in these light-harvesting pigment-protein complexes have led to their incorporation in the design and synthesis of nanoscale antenna systems. In these bio-inspired systems, researchers are seeking to improve the light capture and use of energy from the solar emission spectrum. PMID:20446691

Polívka, Tomáš; Frank, Harry A.

2010-01-01

119

Molecular factors controlling photosynthetic light harvesting by carotenoids.  

PubMed

Carotenoids are naturally occurring pigments that absorb light in the spectral region in which the sun irradiates maximally. These molecules transfer this energy to chlorophylls, initiating the primary photochemical events of photosynthesis. Carotenoids also regulate the flow of energy within the photosynthetic apparatus and protect it from photoinduced damage caused by excess light absorption. To carry out these functions in nature, carotenoids are bound in discrete pigment-protein complexes in the proximity of chlorophylls. A few three-dimensional structures of these carotenoid complexes have been determined by X-ray crystallography. Thus, the stage is set for attempting to correlate the structural information with the spectroscopic properties of carotenoids to understand the molecular mechanism(s) of their function in photosynthetic systems. In this Account, we summarize current spectroscopic data describing the excited state energies and ultrafast dynamics of purified carotenoids in solution and bound in light-harvesting complexes from purple bacteria, marine algae, and green plants. Many of these complexes can be modified using mutagenesis or pigment exchange which facilitates the elucidation of correlations between structure and function. We describe the structural and electronic factors controlling the function of carotenoids as energy donors. We also discuss unresolved issues related to the nature of spectroscopically dark excited states, which could play a role in light harvesting. To illustrate the interplay between structural determinations and spectroscopic investigations that exemplifies work in the field, we describe the spectroscopic properties of four light-harvesting complexes whose structures have been determined to atomic resolution. The first, the LH2 complex from the purple bacterium Rhodopseudomonas acidophila, contains the carotenoid rhodopin glucoside. The second is the LHCII trimeric complex from higher plants which uses the carotenoids lutein, neoxanthin, and violaxanthin to transfer energy to chlorophyll. The third, the peridinin-chlorophyll-protein (PCP) from the dinoflagellate Amphidinium carterae, is the only known complex in which the bound carotenoid (peridinin) pigments outnumber the chlorophylls. The last is xanthorhodopsin from the eubacterium Salinibacter ruber. This complex contains the carotenoid salinixanthin, which transfers energy to a retinal chromophore. The carotenoids in these pigment-protein complexes transfer energy with high efficiency by optimizing both the distance and orientation of the carotenoid donor and chlorophyll acceptor molecules. Importantly, the versatility and robustness of carotenoids in these light-harvesting pigment-protein complexes have led to their incorporation in the design and synthesis of nanoscale antenna systems. In these bioinspired systems, researchers are seeking to improve the light capture and use of energy from the solar emission spectrum. PMID:20446691

Polívka, Tomás; Frank, Harry A

2010-08-17

120

Electron properties in directed self-assembly Ge/SiC/Si quantum dots  

NASA Astrophysics Data System (ADS)

Artificially ordered semiconductor quantum dot (QD) patterns may be used to implement functionalities such as spintronic bandgap systems, quantum simulation and quantum computing, by manipulating the interaction between confined carriers via direct exchange coupling. In this dissertation, magnetotransport measurements have been conducted to investigate the electronic orbital and spin states of directed self-assembly single- and few-Ge/SiC/Si QD devices, fabricated by a directed self-assembly QD growth technique developed by our group. Diamagnetic and Zeeman energy shifts of electrons confined around the QD have been observed from the magnetotransport experiments. A triple-barrier resonant tunneling model has been proposed to describe the electron and spin transport. The strength of the Coulomb interaction between electrons confined at neighboring QDs has been observed dependent on the dot separation, and represents an important parameter for fabricating QD-based molecules and artificial arrays, which may be implemented as building blocks for future quantum simulation and quantum computing architectures.

Yang, Dongyue

121

Formation of OTS self-assembled monolayers at chemically treated titanium surfaces  

Microsoft Academic Search

Enhanced biocompatibility of titanium implants highly depends on the possibility of achieving high degrees of surface functionalization\\u000a for a low immune response and\\/or enhanced mineralization of bioactive minerals, such as hydroxyapatite. In this respect, surface\\u000a modification with Self Assembled Monolayers (SAMs) has a great potential in delivering artificial surfaces of improved biocompatibility.\\u000a Herein, the effectiveness of common chemical pre-treatments, i.e.

Elnaz Ajami; Kondo-Francois Aguey-Zinsou

2011-01-01

122

Regulation of photosystem I light harvesting by zeaxanthin  

PubMed Central

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

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

2014-01-01

123

Green grasses as light harvesters in dye sensitized solar cells.  

PubMed

Chlorophylls, the major pigments presented in plants are responsible for the process of photosynthesis. The working principle of dye sensitized solar cell (DSSC) is analogous to natural photosynthesis in light-harvesting and charge separation. In a similar way, natural dyes extracted from three types of grasses viz. Hierochloe Odorata (HO), Torulinium Odoratum (TO) and Dactyloctenium Aegyptium (DA) were used as light harvesters in dye sensitized solar cells (DSSCs). The UV-Vis absorption spectroscopy, Fourier transform infrared (FT-IR), and liquid chromatography-mass spectrometry (LC-MS) were used to characterize the dyes. The electron transport mechanism and internal resistance of the DSSCs were investigated by the electrochemical impedance spectroscopy (EIS). The performance of the cells fabricated with the grass extract shows comparable efficiencies with the reported natural dyes. Among the three types of grasses, the DSSC fabricated with the dye extracted from Hierochloe Odorata (HO) exhibited the maximum efficiency. LC-MS investigations indicated that the dominant pigment present in HO dye was pheophytin a (Pheo a). PMID:25168231

Shanmugam, Vinoth; Manoharan, Subbaiah; Sharafali, A; Anandan, Sambandam; Murugan, Ramaswamy

2015-01-25

124

Proteomics of Chlamydomonas reinhardtii Light-Harvesting Proteins  

PubMed Central

With the recent development of techniques for analyzing transmembrane thylakoid proteins by two-dimensional gel electrophoresis, systematic approaches for proteomic analyses of membrane proteins became feasible. In this study, we established detailed two-dimensional protein maps of Chlamydomonas reinhardtii light-harvesting proteins (Lhca and Lhcb) by extensive tandem mass spectrometric analysis. We predicted eight distinct Lhcb proteins. Although the major Lhcb proteins were highly similar, we identified peptides which were unique for specific lhcbm gene products. Interestingly, lhcbm6 gene products were resolved as multiple spots with different masses and isoelectric points. Gene tagging experiments confirmed the presence of differentially N-terminally processed Lhcbm6 proteins. The mass spectrometric data also revealed differentially N-terminally processed forms of Lhcbm3 and phosphorylation of a threonine residue in the N terminus. The N-terminal processing of Lhcbm3 leads to the removal of the phosphorylation site, indicating a potential novel regulatory mechanism. At least nine different lhca-related gene products were predicted by comparison of the mass spectrometric data against Chlamydomonas expressed sequence tag and genomic databases, demonstrating the extensive variability of the C. reinhardtii Lhca antenna system. Out of these nine, three were identified for the first time at the protein level. This proteomic study demonstrates the complexity of the light-harvesting proteins at the protein level in C. reinhardtii and will be an important basis of future functional studies addressing this diversity. PMID:14555480

Stauber, Einar J.; Fink, Andreas; Markert, Christine; Kruse, Olaf; Johanningmeier, Udo; Hippler, Michael

2003-01-01

125

Triplet Energy Transport in Platinum-Acetylide Light Harvesting Arrays.  

PubMed

Light harvesting and triplet energy transport is investigated in chromophore-functionalized polystyrene polymers featuring light harvesting and energy acceptor chromophores (traps) at varying loading. The series of precision polymers was constructed via reversible addition-fragmentation transfer polymerization and functionalized with platinum acetylide triplet chromophores by using an azide-alkyne "click" reaction. The polymers have narrow polydispersity and degree of polymerization ?60. The chromophores have the general structure, trans-[-R-C6H4-C?C-Pt(PBu3)2-C?C-Ar], where R is the attachment point to the polystyrene backbone and Ar is either -C6H4-C?C-Ph or -pyrenyl (PE2-Pt and Py-Pt, respectively, with triplet energies of 2.35 and 1.88 eV). The polychromophores contain mainly the high-energy PE2-Pt units (light absorber and energy donor), with randomly distributed Py-Pt units (3-20% loading, energy acceptor). Photophysical methods are used to study the dynamics and efficiency of energy transport from the PE2-Pt to Py-Pt units in the polychromophores. The energy transfer efficiency is >90% for copolymers that contain 5% of the Py-Pt acceptor units. Time-resolved phosphorescence measurements combined with Monte Carlo exciton dynamics simulations suggest that the mechanism of exciton transport is exchange energy transfer hopping between PE2-Pt units. PMID:25337631

Chen, Zhuo; Hsu, Hsien-Yi; Arca, Mert; Schanze, Kirk S

2014-11-13

126

Green grasses as light harvesters in dye sensitized solar cells  

NASA Astrophysics Data System (ADS)

Chlorophylls, the major pigments presented in plants are responsible for the process of photosynthesis. The working principle of dye sensitized solar cell (DSSC) is analogous to natural photosynthesis in light-harvesting and charge separation. In a similar way, natural dyes extracted from three types of grasses viz. Hierochloe Odorata (HO), Torulinium Odoratum (TO) and Dactyloctenium Aegyptium (DA) were used as light harvesters in dye sensitized solar cells (DSSCs). The UV-Vis absorption spectroscopy, Fourier transform infrared (FT-IR), and liquid chromatography-mass spectrometry (LC-MS) were used to characterize the dyes. The electron transport mechanism and internal resistance of the DSSCs were investigated by the electrochemical impedance spectroscopy (EIS). The performance of the cells fabricated with the grass extract shows comparable efficiencies with the reported natural dyes. Among the three types of grasses, the DSSC fabricated with the dye extracted from Hierochloe Odorata (HO) exhibited the maximum efficiency. LC-MS investigations indicated that the dominant pigment present in HO dye was pheophytin a (Pheo a).

Shanmugam, Vinoth; Manoharan, Subbaiah; Sharafali, A.; Anandan, Sambandam; Murugan, Ramaswamy

2015-01-01

127

Wettability of azobenzene self-assembled monolayers.  

PubMed

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

Pipolo, Silvio; Corni, Stefano

2014-04-22

128

Microstructure to substrate self-assembly using capillary forces  

Microsoft Academic Search

We have demonstrated the fluidic self-assembly of micromachined silicon parts onto silicon and quartz substrates in a preconfigured pattern with submicrometer positioning precision. Self-assembly is accomplished using photolithographically defined part and substrate binding sites that are complementary shapes of hydrophobic self-assembled monolayers. The patterned substrate is passed through a film of hydrophobic adhesive on water, causing the adhesive to selectively

Uthara Srinivasan; Dorian Liepmann; Roger T. Howe

2001-01-01

129

Organization of the Bacterial Light-Harvesting Apparatus Rationalized by Exciton Transport Optimization  

Microsoft Academic Search

Photosynthesis, the process by which energy from sunlight drives cellular metabolism, relies on a unique organization of light-harvesting and reaction center complexes. Recently, the organization of light-harvesting LH2 complexes and dimeric reaction center-light harvesting I-PufX (RC-LH1-PufX) core complexes in membranes of purple non-sulfur bacteria was revealed by atomic force microscopy (AFM)1. Here, we report that the structure of LH2 and

Elad Harel

2011-01-01

130

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. PMID:21980594

LIN, Yiyang; MAO, Chuanbin

2011-01-01

131

Self-assembled virus-membrane complexes  

SciTech Connect

Anionic polyelectrolytes and cationic lipid membranes can self-assemble into lamellar structures ranging from alternating layers of membranes and polyelectrolytes to 'missing layer' superlattice structures. We show that these structural differences can be understood in terms of the surface-charge-density mismatch between the polyelectrolyte and membrane components by examining complexes between cationic membranes and highly charged M13 viruses, a system that allowed us to vary the polyelectrolyte diameter independently of the charge density. Such virus-membrane complexes have pore sizes that are about ten times larger in area than DNA-membrane complexes, and can be used to package and organize large functional molecules; correlated arrays of Ru(bpy){sub 3}{sup 2+} macroionic dyes have been directly observed within the virus-membrane complexes using an electron-density reconstruction. These observations elucidate fundamental design rules for rational control of self-assembled polyelectrolyte-membrane structures, which have applications ranging from non-viral gene therapy to biomolecular templates for nanofabrication.

Yang, Lihua; Liang, Hongjun; Angelini, Thomas; Butler, John; Coridan, Robert; Tang, Jay; Wong, Gerard (UIUC); (Brown)

2010-11-16

132

Micropatterning of bioactive self-assembling gels†  

PubMed Central

Microscale topographical features have been known to affect cell behavior. An important target in this area is to integrate top down techniques with bottom up self-assembly to create three-dimensional (3D) patterned bioactive mimics of extracellular matrices. We report a novel approach toward this goal and demonstrate its use to study the behavior of human mesenchymal stem cells (hMSCs). By incorporating polymerizable acetylene groups in the hydrophobic segment of peptide amphiphiles (PAs), we were able to micro-pattern nanofiber gels of these bioactive materials. PAs containing the cell adhesive epitope arginine–glycine–aspartic acid–serine (RGDS) were allowed to self-assemble within microfabricated molds to create networks of either randomly oriented or aligned ~30 nm diameter nanofiber bundles that were shaped into topographical patterns containing holes, posts, or channels up to 8 ?m in height and down to 5 ?m in lateral dimensions. When topographical patterns contained nanofibers aligned through flow prior to gelation, the majority of hMSCs aligned in the direction of the nanofibers even in the presence of hole microtextures and more than a third of them maintained this alignment when encountering perpendicular channel microtextures. Interestingly, in topographical patterns with randomly oriented nanofibers, osteoblastic differentiation was enhanced on hole microtextures compared to all other surfaces. PMID:20047022

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

2009-01-01

133

Quantifying quality in DNA self-assembly  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

134

Self-assembled Nanofibrils for Immunomodulation  

NASA Astrophysics Data System (ADS)

This thesis has been mainly focused on applying self-assembled nanofibrils as unique depots for controlled release to modulate immune system, with two major chapters on modulation of innate immunity in chapter 2 and adaptive immunity in chapter 3, respectively. There are 5 chapters in the thesis. Chapter 1 gives a detailed review on the discovery, synthesis and application of self-assembled nanofibrils of therapeutic agents (termed as "self-delivery drugs"), including bioactive molecules; Chapter 2 demonstrates the supramolecular hydrogel of chemotactic peptides as a prolonged inflammation model through proper molecular engineering; Chapter 3 reports a suppressive antibody response achieved by encapsulation of antigens by supramolecular hydrogel of glycopeptide; Chapter 4 illustrates an example of supramolecular hydrogel formation of molecules with extremely low solubility, based on the fact that many small organic drugs have poor solubility. Chapter 5 used beta-galatosidase as a model to study glycosidase-instructed supramolecular hydrogel formation, with potential to target cancer cells due to their distinct metabolic profile.

Zhao, Fan

135

Quantifying quality in DNA self-assembly  

PubMed Central

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

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

2014-01-01

136

Self-Assembly of Gemini Surfactants  

NASA Astrophysics Data System (ADS)

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

Yethiraj, Arun; Mondal, Jagannath; Mahanthappa, Mahesh

2013-03-01

137

Self-assembly of DNA-oligo(p-phenylene-ethynylene) hybrid amphiphiles into surface-engineered vesicles with enhanced emission.  

PubMed

Surface-addressable nanostructures of linearly ?-conjugated molecules play a crucial role in the emerging field of nanoelectronics. Herein, by using DNA as the hydrophilic segment, we demonstrate a solid-phase "click" chemistry approach for the synthesis of a series of DNA-chromophore hybrid amphiphiles and report their reversible self-assembly into surface-engineered vesicles with enhanced emission. DNA-directed surface addressability of the vesicles was demonstrated through the integration of gold nanoparticles onto the surface of the vesicles by sequence-specific DNA hybridization. This system could be converted to a supramolecular light-harvesting antenna by integrating suitable FRET acceptors onto the surface of the nanostructures. The general nature of the synthesis, surface addressability, and biocompatibility of the resulting nanostructures offer great promises for nanoelectronics, energy, and biomedical applications. PMID:24962762

Albert, Shine K; Thelu, Hari Veera Prasad; Golla, Murali; Krishnan, Nithiyanandan; Chaudhary, Soma; Varghese, Reji

2014-08-01

138

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

139

Perspective: Detecting and measuring exciton delocalization in photosynthetic light harvesting  

SciTech Connect

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

Scholes, Gregory D., E-mail: greg.scholes@utoronto.ca; Smyth, Cathal [Department of Chemistry, University of Toronto, 80 St. George St., Toronto, Ontario M5S 3H6 (Canada)] [Department of Chemistry, University of Toronto, 80 St. George St., Toronto, Ontario M5S 3H6 (Canada)

2014-03-21

140

Maximizing omnidirectional light harvesting in metal oxide hyperbranched array architectures  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

141

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

2011-05-01

142

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

E-print Network

Calixarene-encapsulated nanoparticles: self-assembly into functional nanomaterials{ Alexander Wei Article on the web 25th January 2006 DOI: 10.1039/b515806k Calixarenes are excellent surfactants calixarenes for enhancing the dispersion and self-assembly of metal nanoparticles, as well as fundamental

Wei, Alexander

143

Controlling Self-Assembled Perovskite-Spinel Nanostructures  

E-print Network

Controlling Self-Assembled Perovskite-Spinel Nanostructures Haimei Zheng,*, Qian Zhan, Florin We report a discovery that self-assembled perovskite-spinel nanostructures can be controlled simply of single-crystalline spinel nanopillars heteroepitaxially embedded in a perovskite matrix.11

Chen, Long-Qing

144

Self-Assembly-Driven Nematization Khanh Thuy Nguyen,  

E-print Network

Self-Assembly-Driven Nematization Khanh Thuy Nguyen, Francesco Sciortino,, and Cristiano De Michele: The anisotropy of attractive interactions between particles can favor, through a self-assembly process benchmark for recent theoretical approaches and to assess their ability to capture the coupling between self

Sciortino, Francesco

145

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

146

Robotics. Programmable self-assembly in a thousand-robot swarm.  

PubMed

Self-assembly enables nature to build complex forms, from multicellular organisms to complex animal structures such as flocks of birds, through the interaction of vast numbers of limited and unreliable individuals. Creating this ability in engineered systems poses challenges in the design of both algorithms and physical systems that can operate at such scales. We report a system that demonstrates programmable self-assembly of complex two-dimensional shapes with a thousand-robot swarm. This was enabled by creating autonomous robots designed to operate in large groups and to cooperate through local interactions and by developing a collective algorithm for shape formation that is highly robust to the variability and error characteristic of large-scale decentralized systems. This work advances the aim of creating artificial swarms with the capabilities of natural ones. PMID:25124435

Rubenstein, Michael; Cornejo, Alejandro; Nagpal, Radhika

2014-08-15

147

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

NASA Astrophysics Data System (ADS)

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 modification of the Cys residues with a structurally diverse set of hydrophobic small molecules, including chemotherapeutics, leads to spontaneous formation of nanoparticles over a range of CP compositions and molecular weights. When used to deliver chemotherapeutics to a murine cancer model, CP nanoparticles have a fourfold higher maximum tolerated dose than free drug, and induce nearly complete tumour regression after a single dose. This simple strategy can promote co-assembly of drugs, imaging agents and targeting moieties into multifunctional nanomedicines.

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

2009-12-01

148

Supramolecular self-assemblies as functional nanomaterials  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

149

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

150

Self assembly properties of primitive organic compounds  

NASA Technical Reports Server (NTRS)

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

Deamer, D. W.

1991-01-01

151

Aquatic Botany 75 (2003) 261274 Light harvesting and the package effect in the  

E-print Network

Aquatic Botany 75 (2003) 261­274 Light harvesting and the package effect in the seagrasses is likely to result in a severe package effect, i.e. the loss of linearity between light harvesting Science B.V. All rights reserved. Keywords: Seagrass; Photoacclimation; Package effect; Chlorophyll; Light

Cummings, Molly E.

152

Increased light harvesting in dye-sensitized solar cells with energy relay dyes  

E-print Network

Increased light harvesting in dye-sensitized solar cells with energy relay dyes Brian E. Hardin1 efficiency when using an energy relay dye (PTCDI) with an organic sensitizing dye (TT1). We estimate on the basis of light harvesting using a sensitizing dye (SD) attached to a wide- bandgap semiconductor1

McGehee, Michael

153

Accelerated Publications Time-Resolved Dissociation of the Light-Harvesting 1 Complex of Rhodospirillum  

E-print Network

Accelerated Publications Time-Resolved Dissociation of the Light-Harvesting 1 Complex: For the first time, data are presented on the time-resolved disassembly reaction of a highly organized membrane protein complex in vitro. The photosynthetic core light-harvesting complex of the bacterial strain

van Stokkum, Ivo

154

Stark spectroscopy of the light-harvesting complex II in different oligomerisation states  

E-print Network

Stark spectroscopy of the light-harvesting complex II in different oligomerisation states Miguel A 2003 Abstract The electric field-induced absorption changes (Stark effect) of light-harvesting complex is absorbed by plants and bacteria and used to synthesize organic compounds. In order to perform the reactions

van Stokkum, Ivo

155

Light harvesting with non covalent carbon nanotube / porphyrin compounds. C. Roqueleta  

E-print Network

Light harvesting with non covalent carbon nanotube / porphyrin compounds. C. Roqueleta , B- ized nanotubes, where the general philosophy is to put together organic molecules and carbon nanotubes for long term applications such as light harvesting and bio labeling. In the latte

Paris-Sud XI, Université de

156

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

E-print Network

Energy Transfer in the Major Intrinsic Light-Harvesting Complex from Amphidinium carterae Toma organisms. These carotenoids possess an excited state with a charge-transfer character (intramolecular transfer pathways in the intrinsic light-harvesting complex (LHC) of dinoflagellates, which contains

van Stokkum, Ivo

157

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. PMID:19564931

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

2009-01-01

158

Calixarene-stabilised cobalt nanoparticle rings: Self-assembly and collective magnetic properties Alexander Weia  

E-print Network

Calixarene-stabilised cobalt nanoparticle rings: Self-assembly and collective magnetic properties 10 October 2008) Calixarenes can be used to promote the self-assembly of thermoremanent cobalt phenomenon. Keywords: calixarenes; encapsulation; magnetism; nanoparticles; self-assembly; transmission

Dunin-Borkowski, Rafal E.

159

Simulations and theory of model microtubule self-assembly  

NASA Astrophysics Data System (ADS)

We used molecular dynamics simulations to study the self-assembly of artificial microtubules. The model monomer has a wedge-shape to promote formation of rings that stack to form tubules. Attractive interaction sites are on the sides for ring formation and top/bottom for filament growth. We have studied the assembly kinetics and dynamics as a function of these lateral and vertical interaction strengths. A full structure diagram was calculated. The range of interaction strengths that best form tubules has been determined. We found that tubules form better when the lateral strength is stronger than the filamental stength, which contrast the picture for microtubules. The interaction strengths must be weak enough to allow for reformation of the clusters that initially form. Besides tubules, a variety of structures form depending on the interaction parameters. Interestingly, helical tubes and other helical structures are frequently observed despite the fact that the minimum energy substructure is a nonhelical ring. We have used a simple Flory-Huggins type theory to characterize the structure diagram.

Stevens, Mark; Cheng, Shengfeng; Aggarwal, Ankush

2012-02-01

160

Silica Biomineralization via the Self-Assembly of Helical Biomolecules.  

PubMed

The biomimetic synthesis of relevant silica materials using biological macromolecules as templates via silica biomineralization processes attract rapidly rising attention toward natural and artificial materials. Biomimetic synthesis studies are useful for improving the understanding of the formation mechanism of the hierarchical structures found in living organisms (such as diatoms and sponges) and for promoting significant developments in the biotechnology, nanotechnology and materials chemistry fields. Chirality is a ubiquitous phenomenon in nature and is an inherent feature of biomolecular components in organisms. Helical biomolecules, one of the most important types of chiral macromolecules, can self-assemble into multiple liquid-crystal structures and be used as biotemplates for silica biomineralization, which renders them particularly useful for fabricating complex silica materials under ambient conditions. Over the past two decades, many new silica materials with hierarchical structures and complex morphologies have been created using helical biomolecules. In this review, the developments in this field are described and the recent progress in silica biomineralization templating using several classes of helical biomolecules, including DNA, polypeptides, cellulose and rod-like viruses is summarized. Particular focus is placed on the formation mechanism of biomolecule-silica materials (BSMs) with hierarchical structures. Finally, current research challenges and future developments are discussed in the conclusion. PMID:25339438

Liu, Ben; Cao, Yuanyuan; Huang, Zhehao; Duan, Yingying; Che, Shunai

2014-10-22

161

Versatility of cyclodextrins in self-assembly systems of amphiphiles Lingxiang Jiang, Yun Yan, Jianbin Huang  

E-print Network

Versatility of cyclodextrins in self-assembly systems of amphiphiles Lingxiang Jiang, Yun Yan Keywords: Surfactants Cyclodextrins Self-assembly H-bonds Unamphiphilic Recently, cyclodextrins (CDs) were

Huang, Jianbin

162

Strongly Coupled Plasmonic Modes on Macroscopic Areas via Template-Assisted Colloidal Self-Assembly.  

PubMed

We present ensembles of surface-ordered nanoparticle arrangements, which are formed by template-assisted self-assembly of monodisperse, protein-coated gold nanoparticles in wrinkle templates. Centimeter-squared areas of highly regular, linear assemblies with tunable line width are fabricated and their extinction cross sections can be characterized by conventional UV/vis/NIR spectroscopy. Modeling based on electrodynamic simulations shows a clear signature of strong plasmonic coupling with an interparticle spacing of 1-2 nm. We find evidence for well-defined plasmonic modes of quasi-infinite chains, such as resonance splitting and multiple radiant modes. Beyond elementary simulations on the individual chain level, we introduce an advanced model, which considers the chain length distribution as well as disorder. The step toward macroscopic sample areas not only opens perspectives for a range of applications in sensing, plasmonic light harvesting, surface enhanced spectroscopy, and information technology but also eases the investigation of hybridization and metamaterial effects fundamentally. PMID:25347293

Hanske, Christoph; Tebbe, Moritz; Kuttner, Christian; Bieber, Vera; Tsukruk, Vladimir V; Chanana, Munish; König, Tobias A F; Fery, Andreas

2014-12-10

163

Supramolecular chemical biology; bioactive synthetic self-assemblies.  

PubMed

The regulation of recognition events in nature via dynamic and reversible self-assembly of building blocks has inspired the emergence of supramolecular architectures with similar biological activity. Synthetic molecules of diverse geometries self-assemble in water to target biological systems for applications ranging from imaging and diagnostics, through to drug delivery and tissue engineering. Many of these applications require the ability of the supramolecular system to actively recognize specific cell surface receptors. This molecular recognition is typically achieved with ligands, such as small molecules, peptides, and proteins, which are introduced either prior to or post self-assembly. Advantages of the non-covalent organization of ligands include the responsive nature of the self-assembled structures, the ease of supramolecular synthesis and the possibility to incorporate a multiple array of different ligands through pre-mixing of the building blocks. This review aims to highlight the diversity of self-assembled nanostructures constructed from mono-disperse synthetic building blocks; with a particular focus on their design, self-assembly, functionalization with bioactive ligands and effects thereof on the self-assembly, and possible applications. PMID:23160566

Petkau-Milroy, Katja; Brunsveld, Luc

2013-01-14

164

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

165

Ultrafast light harvesting dynamics in the cryptophyte phycocyanin 645.  

PubMed

Steady-state and femtosecond time-resolved optical methods have been used to study spectroscopic features and energy transfer dynamics in the soluble antenna protein phycocyanin 645 (PC645), isolated from a unicellular cryptophyte Chroomonas CCMP270. Absorption, emission and polarization measurements as well as one-colour pump-probe traces are reported in combination with complementary quantum chemical calculations of electronic transitions of the bilins. Estimation of bilin spectral positions and energy transfer rates aids in the development of a model for light harvesting by PC645. At higher photon energies light is absorbed by the centrally located dimer (DBV, beta50/beta61) and the excitation is subsequently funneled through a complex interference of pathways to four peripheral pigments (MBV alpha19, PCB beta158). Those chromophores transfer the excitation energy to the red-most bilins (PCB beta82). We suggest that the final resonance energy transfer step occurs between the PCB 82 bilins on a timescale estimated to be approximately 15 ps. Such a rapid final energy transfer step cannot be rationalized by calculations that combine experimental parameters and quantum chemical calculations, which predict the energy transfer time to be 40 ps. PMID:17721595

Mirkovic, Tihana; Doust, Alexander B; Kim, Jeongho; Wilk, Krystyna E; Curutchet, Carles; Mennucci, Benedetta; Cammi, Roberto; Curmi, Paul M G; Scholes, Gregory D

2007-09-01

166

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

167

Hierarchical Self-Assembly of Asymmetric Amphiphatic Spherical Colloidal Particles  

E-print Network

From dumbbells to FCC crystals, we study the self-assembly pathway of amphiphatic, spherical colloidal particles as a function of the size of the hydrophobic region using molecular dynamics simulations. Specifically, we analyze how local inter-particle interactions correlate to the final self-assembled aggregate and how they affect the dynamical pathway of structure formation. We present a detailed diagram separating the many phases that we find for different sizes of the hydrophobic area, and uncover a narrow region where particles self-assemble into hollow, faceted cages that could potentially find interesting engineering applications.

William L. Miller; Angelo Cacciuto

2009-08-21

168

Bacteria Repellent Properties of Trichlorosilane Self-Assembled Graphene  

NASA Astrophysics Data System (ADS)

The bacteria repellent property and thermal stability of pristine graphene and graphene chemically modified with a trichlorosilane (HDF-S) self-assembled monolayer (SAM) were investigated. The contact angles of HDF-S self-assembled graphene (105.8±0.5°) improved by ?30% compared with those of pristine graphene (79.4±0.9°). In a bacterial atmosphere, while the bacteria were able to migrate to the pristine graphene surface, they were not able to migrate to the surface of the HDF-S self-assembled graphene. Moreover, the HDF-S SAM on graphene showed stable hydrophobic properties from -40 to 500 °C.

Bong, Jihye; Kim, Dae Hwan; Kim, Hyunsook; Lee, Sang-Seob; Ju, Sanghyun

2013-12-01

169

Self-assembly: an option to nanoporous metal nanocrystals.  

PubMed

Nanoporous metal nanocrystals involving both nanoscale effects and nanopore properties hold enormous promising potential for various important applications due to their unique structures such as large surface area per unit volume and interconnected open framework. Self-assembly, as an excellent option, has been developed to control the desired structure and rational performance of nanoporous metal nanocrystals. After identifying features of their methodologies and structures, the control of synthesis based on the self-assembly technique is thoroughly discussed. The development of the self-assembly synthesis methodology is then presented in detail. The emerging application, mainly in catalysis, and corresponding design are finally summarized. PMID:25135425

Ying, Jie; Yang, Xiao-Yu; Tian, Ge; Janiak, Christoph; Su, Bao-Lian

2014-11-21

170

Self-assembly: an option to nanoporous metal nanocrystals  

NASA Astrophysics Data System (ADS)

Nanoporous metal nanocrystals involving both nanoscale effects and nanopore properties hold enormous promising potential for various important applications due to their unique structures such as large surface area per unit volume and interconnected open framework. Self-assembly, as an excellent option, has been developed to control the desired structure and rational performance of nanoporous metal nanocrystals. After identifying features of their methodologies and structures, the control of synthesis based on the self-assembly technique is thoroughly discussed. The development of the self-assembly synthesis methodology is then presented in detail. The emerging application, mainly in catalysis, and corresponding design are finally summarized.

Ying, Jie; Yang, Xiao-Yu; Tian, Ge; Janiak, Christoph; Su, Bao-Lian

2014-10-01

171

Peptide-directed self-assembly of hydrogels  

PubMed Central

This review focuses on the self-assembly of macromolecules mediated by the biorecognition of peptide/protein domains. Structures forming ?-helices and ?-sheets have been used to mediate self-assembly into hydrogels of peptides, reactive copolymers and peptide motifs, block copolymers, and graft copolymers. Structural factors governing the self-assembly of these molecules into precisely defined three-dimensional structures (hydrogels) are reviewed. The incorporation of peptide motifs into hybrid systems, composed of synthetic and natural macromolecules, enhances design opportunities for new biomaterials when compared to individual components. PMID:18952513

Kope?ek, Jind?ich; Yang, Jiyuan

2009-01-01

172

Molecularly Engineered Self-Assembling Membranes for Cell-Mediated Degradation.  

PubMed

The use of peptide engineering to develop self-assembling membranes that are responsive to cellular enzyme activities is reported. The membranes are obtained by combining hyaluronan (HA) and a rationally designed peptide amphiphile (PA) containing a proteolytic domain (GPQGIWGQ octapeptide) sensitive to matrix metalloproteinase-1 (MMP-1). Insertion of an octapeptide in a typical PA structure does not disturb its self-assembly into fibrillar nanostructures neither the ability to form membranes with HA. In vitro enzymatic degradation with hyaluronidase and MMP-1 shows that membranes containing the MMP-1 substrate exhibit enhanced enzymatic degradation, compared with control membranes (absence of MMP-1 cleavable peptide or containing a MMP-1 insensitive sequence), being completely degraded after 7 days. Cell viability and proliferation is minimally affected by the enzymatically cleavable functionality of the membrane, but the presence of MMP-1 cleavable sequence does stimulate the secretion of MMP-1 by fibroblasts and interfere with matrix deposition, particularly the deposition of collagen. By showing cell-responsiveness to biochemical signals presented on self-assembling membranes, this study highlights the ability of modulating certain cellular activities through matrix engineering. This concept can be further explored to understand the cellular remodeling process and as a strategy to develop artificial matrices with more biomimetic degradation for tissue engineering applications. PMID:25413155

Ferreira, Daniela S; Lin, Yi-An; Cui, Honggang; Hubbell, Jeffrey A; Reis, Rui L; Azevedo, Helena S

2014-11-21

173

Picosecond Kinetics of Light Harvesting and Photoprotective Quenching in Wild-Type and Mutant Phycobilisomes Isolated from the  

E-print Network

of Synechocystis PCC 6803 (hereafter called Synechocystis) are well-organized light-harvesting com- plexes composedPicosecond Kinetics of Light Harvesting and Photoprotective Quenching in Wild-Type and Mutant In high light conditions, cyanobacteria dissipate excess absorbed energy as heat in the light-harvesting

van Stokkum, Ivo

174

The light-harvesting function of carotenoids in the cyanobacterial stress-inducible IsiA complex  

E-print Network

. In photosynthetic organisms, carote- noids are active in light harvesting, photoprotection and structureThe light-harvesting function of carotenoids in the cyanobacterial stress-inducible IsiA complex Available online xxxx Keywords: Carotenoids Light harvesting Ultrafast spectroscopy Cyanobacteria a b s t r

van Stokkum, Ivo

175

Functional Self-Assembled Nanofibers by Electrospinning  

NASA Astrophysics Data System (ADS)

Electrospinning constitutes a unique technique for the production of nanofibers with diameters down to the range of a few nanometers. In strong contrast to conventional fiber producing techniques, it relies on self-assembly processes driven by the Coulomb interactions between charged elements of the fluids to be spun to nanofibers. The transition from a macroscopic fluid object such as a droplet emerging from a die to solid nanofibers is controlled by a set of complex physical instability processes. They give rise to extremely high extensional deformations and strain rates during fiber formation causing among others a high orientational order in the nanofibers as well as enhanced mechanical properties. Electrospinning is predominantly applied to polymer based materials including natural and synthetic polymers, but, more recently, its use has been extended towards the production of metal, ceramic and glass nanofibers exploiting precursor routes. The nanofibers can be functionalized during electrospinning by introducing pores, fractal surfaces, by incorporating functional elements such as catalysts, quantum dots, drugs, enzymes or even bacteria. The production of individual fibers, random nonwovens, or orientationally highly ordered nonwovens is achieved by an appropriate selection of electrode configurations. Broad areas of application exist in Material and Life Sciences for such nanofibers, including not only optoelectronics, sensorics, catalysis, textiles, high efficiency filters, fiber reinforcement but also tissue engineering, drug delivery, and wound healing. The basic electrospinning process has more recently been extended towards compound co-electrospinning and precision deposition electrospinning to further broaden accessible fiber architectures and potential areas of application.

Greiner, A.; Wendorff, J. H.

176

Self-assembled biomimetic superhydrophobic hierarchical arrays.  

PubMed

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

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

2013-09-01

177

Macroscopic self-assembly through molecular recognition  

NASA Astrophysics Data System (ADS)

Molecular recognition plays an important role in nature, with perhaps the best known example being the complementarity exhibited by pairs of nucleobases in DNA. Studies of self-assembling and self-organizing systems based on molecular recognition are often performed at the molecular level, however, and any macroscopic implications of these processes are usually far removed from the specific molecular interactions. Here, we demonstrate that well-defined molecular-recognition events can be used to direct the assembly of macroscopic objects into larger aggregated structures. Acrylamide-based gels functionalized with either host (cyclodextrin) rings or small hydrocarbon-group guest moieties were synthesized. Pieces of host and guest gels are shown to adhere to one another through the mutual molecular recognition of the cyclodextrins and hydrocarbon groups on their surfaces. By changing the size and shape of the host and guest units, different gels can be selectively assembled and sorted into distinct macroscopic structures that are on the order of millimetres to centimetres in size.

Harada, Akira; Kobayashi, Ryosuke; Takashima, Yoshinori; Hashidzume, Akihito; Yamaguchi, Hiroyasu

2011-01-01

178

Self-assembling holographic biosensors and biocomputers.  

SciTech Connect

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

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

2006-05-01

179

Amphiphilic self-assemblies decorated by nucleobases.  

PubMed

Phosphatidyl-nucleosides are a class of functional amphiphiles, where a nucleic acid monomer is conjugated to a lipid skeleton. These derivatives self-organize in aqueous solution as assemblies of various size, shape, and interfacial curvature. This paper presents a comparison of the aggregation behavior of different 1-R,2-R-sn-glycero-3-phosphatidyl-nucleosides, where R = 8 (DiC8PN) or R = 12 (DLPN) and N is either adenosine (a purine) or uridine (a pyrimidine), a complementary pair in RNA. Surface tension, small angle neutron scattering, cryo-TEM, and circular dichroism are used to highlight and distinguish the impact of the hydrophobic assembler and of the base substitution on the solution phase behavior. Our main conclusion is that the nucleic functionalization provides an additional parameter to control self-assembly through specific interactions among the polar heads. Further nonideal effects are induced by mixing nucleolipids with complementary base substitution. We show that these contributions alter the aggregation thresholds and modulate properties of the aggregates on the mesoscale. PMID:17880129

Berti, Debora; Bombelli, Francesca Baldelli; Fortini, Martina; Baglioni, Piero

2007-10-11

180

Computational Analysis of ?-Peptide Self-Assembly  

NASA Astrophysics Data System (ADS)

?-peptides are a class of synthetic oligomers that are capable of folding in precise patterns. The wide variety of side chains that are available for insertion into ?-peptide sequences along with the stability of these folded secondary structures allow precise control over the nanoscale presentation of various chemical functional groups in three dimensional space. Some ?-peptides have been shown to spontaneously fold into complex supramolecular structures, and others have been shown to be effective antimicrobial agents that are believed to act by aggregating in certain types of cell membranes. However, more work is needed to understand what drives this assembly in order to design ?-peptides that assemble in particular ways. Using molecular simulations, the process of ?-peptide aggregation is examined in a variety of environments that allow for direct comparison to experiment. Using new simulation techniques, the structure of the aggregates formed by several ?-peptides are predicted in both bulk solutions, and at interfaces. Free energy surfaces are generated using multiple geometric parameters to directly compare the favorability of different modes of aggregation. By analyzing these results, we gain an understanding of the factors that drive self-assembly and aggregation.

McGovern, Michael

2011-03-01

181

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

PubMed

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

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

2014-07-01

182

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

PubMed

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

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

2014-01-01

183

Light Harvesting Proteins for Solar Fuel Generation in Bioengineered Photoelectrochemical Cells  

PubMed Central

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

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

2014-01-01

184

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

PubMed Central

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

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

2014-01-01

185

Self-assembly of colloidal lattices at pickering emulsion interfaces.  

E-print Network

??Self-assembly of colloidal lattices has been of tremendous interest due to their potential applications in advanced materials, sensors, and electro-optical devices. However, most research has… (more)

Guttula, Shashidhar M.

2007-01-01

186

Self-assembly and hydrogelation of Fmoc-phenylalanine derivatives.  

E-print Network

??The ability of peptides and small molecules to spontaneously self-assemble into amyloid-like fibrils has been exploited in the development of noncovalent hydrogels. Noncovalent hydrogels have… (more)

Ryan, Derek M. (1985 - )

2012-01-01

187

Proofreading Tile Sets: Error Correction for Algorithmic Self-Assembly  

Microsoft Academic Search

For robust molecular implementation of tile-based algorith- mic self-assembly, methods for reducing errors must be developed. Pre- vious studies suggested that by control of physical conditions, such as temperature and the concentration of tiles, errors (\\

Erik Winfree; Renat Bekbolatov

2003-01-01

188

Aqueous self-assembly of chromophore-conjugated amphiphiles.  

PubMed

The self-assembly of ?-conjugated building blocks has been a topic of interest in last few years owing to their close relevance to optoelectronic device applications. If such building blocks are made amphiphilic by appropriate derivatization, then the self-assembly can be realized in water by the strong hydrophobic repulsive forces between the polar medium and the rigid ?-surface. On the other hand, as ?-? interactions are directional, such self-assembly can produce structurally precise nano-structures, compared to classical surfactants. With these objectives, the self-assembly of several amphiphilic ?-systems has been studied in the recent past and is described in this article. Examples include electron-deficient, electron-rich and also mixed assemblies of donor and acceptor type chromophores which produce many elegant soft structures such as micelles, vesicle, nanotubes and fibres etc. PMID:25375094

Molla, Mijanur Rahaman; Ghosh, Suhrit

2014-12-28

189

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. PMID:22068594

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

2012-01-01

190

Mechanical behavior and microstructure of self-assembling oligopeptide gels  

E-print Network

Hydrogels have become widely used in the fields of tissue engineering and drug delivery. One class of hydrogel is formed from synthetic oligopeptides that self-assemble into a solution of beta-sheet filaments. These filaments ...

Hammond, Nathan Allen

2010-01-01

191

Enabling complex nanoscale pattern customization using directed self-assembly  

NASA Astrophysics Data System (ADS)

Block copolymer directed self-assembly is an attractive method to fabricate highly uniform nanoscale features for various technological applications, but the dense periodicity of block copolymer features limits the complexity of the resulting patterns and their potential utility. Therefore, customizability of nanoscale patterns has been a long-standing goal for using directed self-assembly in device fabrication. Here we show that a hybrid organic/inorganic chemical pattern serves as a guiding pattern for self-assembly as well as a self-aligned mask for pattern customization through cotransfer of aligned block copolymer features and an inorganic prepattern. As informed by a phenomenological model, deliberate process engineering is implemented to maintain global alignment of block copolymer features over arbitrarily shaped, ‘masking’ features incorporated into the chemical patterns. These hybrid chemical patterns with embedded customization information enable deterministic, complex two-dimensional nanoscale pattern customization through directed self-assembly.

Doerk, Gregory S.; Cheng, Joy Y.; Singh, Gurpreet; Rettner, Charles T.; Pitera, Jed W.; Balakrishnan, Srinivasan; Arellano, Noel; Sanders, Daniel P.

2014-12-01

192

The Statistical Mechanics of Dynamic Pathways to Self-Assembly.  

PubMed

This review describes some important physical characteristics of the pathways (i.e., dynamical processes) by which molecular, nanoscale, and micrometer-scale self-assembly occurs. We highlight the existence of features of self-assembly pathways that are common to a wide range of physical systems, even though those systems may differ with respect to their microscopic details. We summarize some existing theoretical descriptions of self-assembly pathways and highlight areas-notably, the description of self-assembly pathways that occur far from equilibrium-that are likely to become increasingly important. Expected final online publication date for the Annual Review of Physical Chemistry Volume 66 is March 31, 2015. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates. PMID:25493714

Whitelam, Stephen; Jack, Robert L

2014-12-01

193

Host-Guest Self-assembly in Block Copolymer Blends  

E-print Network

Ultrafine, uniform nanostructures with excellent functionalities can be formed by self-assembly of block copolymer (BCP) thin films. However, extension of their geometric variability is not straightforward due to their ...

Park, Woon Ik

194

Self-assembly of globular protein-polymer diblock copolymers  

E-print Network

Self-assembly of protein-polymer block copolymers provides a simple bottom-up approach towards protein nanopatteming for the fabrication of more effective and efficient bioelectronic and biocatalytic devices. Changes in ...

Thomas, Carla S. (Carla Stephanie)

2014-01-01

195

Directed self-assembly of proteins into discrete radial patterns  

PubMed Central

Unlike physical patterning of materials at nanometer scale, manipulating soft matter such as biomolecules into patterns is still in its infancy. Self-assembled monolayer (SAM) with surface density gradient has the capability to drive biomolecules in specific directions to create hierarchical and discrete structures. Here, we report on a two-step process of self-assembly of the human serum albumin (HSA) protein into discrete ring structures based on density gradient of SAM. The methodology involves first creating a 2-dimensional (2D) polyethylene glycol (PEG) islands with responsive carboxyl functionalities. Incubation of proteins on such pre-patterned surfaces results in direct self-assembly of protein molecules around PEG islands. Immobilization and adsorption of protein on such structures over time evolve into the self-assembled patterns. PMID:23719678

Thakur, Garima; Prashanthi, Kovur; Thundat, Thomas

2013-01-01

196

Hierarchical self-assembly of metallo-dendrimers.  

PubMed

2,3-Dihydroxybenzylic esters with Frechet-type dendritic branches as the alcohol component form, in a hierarchical self-assembly process, disk shaped dendrimers when titanium(IV) and lithium ions are added. PMID:20596558

Albrecht, Markus; Baumert, Miriam; Winkler, Henrick D F; Schalley, Christoph A; Fröhlich, Roland

2010-08-21

197

Self-assembly of amphiphilic peanut-shaped nanoparticles  

NASA Astrophysics Data System (ADS)

We use computer simulation to investigate the self-assembly of Janus-like amphiphilic peanut-shaped nanoparticles, finding phases of clusters, bilayers, and micelles in accord with ideas of packing familiar from the study of molecular surfactants. However, packing arguments do not explain the hierarchical self-assembly dynamics that we observe, nor the coexistence of bilayers and faceted polyhedra. This coexistence suggests that experimental realizations of our model can achieve multipotent assembly of either of two competing ordered structures.

Whitelam, Stephen; Bon, Stefan A. F.

2010-02-01

198

Using lateral capillary forces to compute by self-assembly  

Microsoft Academic Search

Investigations of DNA computing have highlighted a fundamental connection between self-assembly (SA) and computation: in prin-ciple, any computation can be performed by a suitable self-assembling system. In practice, exploration of this connection is limited by our ability to control the geometry and specificity of binding interactions. Recently, a system has been developed that uses surface tension to assemble plastic tiles

Paul W. K. Rothemund

2000-01-01

199

Vortical superlattices in a gold nanorods' self-assembled monolayer  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

200

Templated self-assembly of functional oxide nanocomposites.  

PubMed

In perovskite/spinel self-assembled oxide nanocomposites, the substrate surface plays a dominant role in determining the final morphology. Topgraphic features, such as pits and trenches, are written in the substrate using either Focused Ion Beam or wet etching through a block co-polymer mask. These features are effective at templating the self-assembly, resulting in a wide range of attainable nano-assemblies. PMID:24677515

Aimon, Nicolas M; Choi, Hong Kyoon; Sun, Xue Yin; Kim, Dong Hun; Ross, Caroline A

2014-05-21

201

Design of nanostructured materials from block copolymer self-assembly  

Microsoft Academic Search

We present two classes of nanostructured materials by combining the self assembly of block copolymer (BCP) with suitable small molecule chemistry, which are applicable to organic electro-optics (EO) and as etch-resistant masks for nanofabrication. The underlying principles of designing the specific interactions between BCP host and guest molecules, driving the self-assembly in bulk and thin film, and dictating domain orientation

Melvina Leolukman

2010-01-01

202

Self-assembly of diblock copolymers confined in cylindrical nanopores  

Microsoft Academic Search

Self-assembly of AB diblock copolymers confined in cylindrical nanopores is studied using a simulated annealing technique. The pore diameter and surface preference are systematically varied to examine their effects on the self-assembled morphologies and the chain conformations. For bulk lamella-forming and cylinder-forming diblock copolymers, novel structures such as helices and concentric (perforated) lamellae spontaneously form when the copolymers are confined

Bin Yu; Pingchuan Sun; Tiehong Chen; Qinghua Jin; Datong Ding; Baohui Li; An-Chang Shi

2007-01-01

203

Self-assembly of amphiphilic peanut-shaped nanoparticles  

E-print Network

We use computer simulation to investigate the self-assembly of Janus-like amphiphilic peanut-shaped nanoparticles, finding phases of clusters, bilayers and micelles in accord with ideas of packing familiar from the study of molecular surfactants. However, packing arguments do not explain the hierarchical self-assembly dynamics that we observe, nor the coexistence of bilayers and faceted polyhedra. This coexistence suggests that experimental realizations of our model can achieve multipotent assembly of either of two competing ordered structures.

Stephen Whitelam; Stefan A. F. Bon

2009-07-18

204

Self-assembly of DNA-polymer complexes using template polymerization.  

PubMed Central

The self-assembly of supramolecular complexes of nucleic acids and polymers is of relevance to several biological processes including viral and chromatin formation as well as gene therapy vector design. We now show that template polymerization facilitates condensation of DNA into particles that are <150 nm in diameter. Inclusion of a poly(ethylene glycol)-containing monomer prevents aggregation of these particles. The DNA within the particles remains biologically active and can express foreign genes in cells. The formation or breakage of covalent bonds has until now not been employed to compact DNA into artificial particles. PMID:9722638

Trubetskoy, V S; Budker, V G; Hanson, L J; Slattum, P M; Wolff, J A; Hagstrom, J E

1998-01-01

205

Effect of polymerization on hierarchical self-assembly into nanosheets.  

PubMed

The oligomers consisting of phenyl-capped bithiophene and tetra(ethylene glycol)s linked by azide-alkyne Huisgen cycloaddition were synthesized. The relationship between the degree of polymerization and self-assembling ability was investigated in o-dichlorobenzene and dimethyl sulfoxide. From the absorption spectrum, it was confirmed that the critical degree of polymerization (CDP) for thiophene unit aggregation was 4. The morphology of the aggregated product was observed by atomic force microscopy. The oligomers 4mer and 5mer could not self-assemble into well-defined structures due to the weak driving force for the self-assembly. In the cases of 6mer and 7mer, aggregates with nonwell-defined and nanosheet structures coexisted. In the cases of 8mer and 9mer, the nanosheet was the main product. The critical point between 7mer and 8mer could be confirmed by different aggregation behaviors in the cooling process of the solution (nonsigmoidal and sigmoidal). In the cases of 8mer and 9mer, polymer folding prior to intermolecular self-assembly, which was supported by sigmoidal aggregation behavior, leads to the nanosheet formation. On the contrary, shorter oligomers than 8mer experience intermolecular aggregation prior to intramolecular polymer folding, which was supported by the nonsigmoidal aggregation behavior. This is the first report to prove the existence of CDP for folded polymer nanosheet formation which requires hierarchical self-assembly, i.e., polymer folding followed by intermolecular self-assembly. PMID:25526560

Ikeda, Taichi

2015-01-20

206

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

E-print Network

Phototrophic organisms such as plants, photosynthetic bacteria and algae use microscopic complexes of pigment molecules to absorb sunlight. Within the light-harvesting complexes, which frequently have multiple functional and structural subunits, the energy is transferred in the form of molecular excitations with very high efficiency. Green sulfur bacteria are considered to be amongst the most efficient light-harvesting organisms. Despite multiple experimental and theoretical studies of these bacteria the physical origin of the efficient and robust energy transfer in their light-harvesting complexes is not well understood. To study excitation dynamics at the systems level we introduce an atomistic model that mimic a complete light-harvesting apparatus of green sulfur bacteria. The model contains about 4000 pigment molecules and comprises a double wall roll for the chlorosome, a baseplate and six Fenna-Matthews-Olson trimer complexes. We show that the fast relaxation within functional subunits combined with the...

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

2013-01-01

207

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

Microsoft Academic Search

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

Alex Adronov; Sylvain L. Gilat; J. M. J. Frechet; Kaoru Ohta; Frederik V. R. Neuwahl; Graham R. Fleming

2000-01-01

208

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. PMID:23689426

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

2013-01-01

209

Producibility in hierarchical self-assembly Three results are shown on producibility in the hierarchical model of tile self-assembly.  

E-print Network

Producibility in hierarchical self-assembly David Doty Abstract Three results are shown on producibility in the hierarchical model of tile self-assembly. It is shown that a simple greedy polynomial, an assembly is considered terminal if nothing can attach to it; viewing self-assembly as a computation

Doty, David

210

Self-Assembled Surfactant Cyclic Peptide Nanostructures as Stabilizing Agents  

PubMed Central

A number of cyclic peptides including [FR]4, [FK]4, [WR]4, [CR]4, [AK]4, and [WK]n (n = 3-5) containing L-amino acids were produced using solid-phase peptide synthesis. We hypothesized that an optimal balance of hydrophobicity and charge could generate self-assembled nanostructures in aqueous solution by intramolecular and/or intermolecular interactions. Among all the designed peptides, [WR]n (n = 3-5) generated self-assembled vesicle-like nanostructures at room temperature as shown by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and/or dynamic light scattering (DLS). This class of peptides represents the first report of surfactant-like cyclic peptides that self-assemble into nanostructures. A plausible mechanistic insight into the self-assembly of [WR]5 was obtained by molecular modeling studies. Modified [WR]5 analogues, such as [WMeR]5, [WR(Me)2]5, [WMeR(Me)2]5, and [WdR]5, exhibited different morphologies to [WR]5 as shown by TEM observations. [WR]5 exhibited a significant stabilizing effect for generated silver nanoparticles and glyceraldehyde-3-phosphate dehydrogenase activity. These studies established a new class of surfactant-like cyclic peptides that self-assembled into nanostructures and could have potential applications for the stabilization of silver nanoparticles and protein biomolecules. PMID:24187575

Mandal, Dindyal; Oh, Donghoon; Ye, Guofeng; Banerjee, Antara; Yadav, Arpita; Parang, Keykavous

2013-01-01

211

Self-Assembly for the Synthesis of Functional Biomaterials  

PubMed Central

The use of self-assembly for the construction of functional biomaterials is a highly promising and exciting area of research, with great potential for the treatment of injury or disease. By using multiple noncovalent interactions, coded into the molecular design of the constituent components, self-assembly allows for the construction of complex, adaptable, and highly tunable materials with potent biological effects. This review describes some of the seminal advances in the use of self-assembly to make novel systems for regenerative medicine and biology. Materials based on peptides, proteins, DNA, or hybrids thereof have found application in the treatment of a wide range of injuries and diseases, and this review outlines the design principles and practical applications of these systems. Most of the examples covered focus on the synthesis of hydrogels for the scaffolding or transplantation of cells, with an emphasis on the biological, mechanical, and structural properties of the resulting materials. In addition, we will discuss the distinct advantages conferred by self-assembly (compared with traditional covalent materials), and present some of the challenges and opportunities for the next generation of self-assembled biomaterials. PMID:23457423

Stephanopoulos, Nicholas; Ortony, Julia H.; Stupp, Samuel I.

2012-01-01

212

Actinide Sequestration Using Self-Assembled Monolayers on Mesoporous Supports  

SciTech Connect

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

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

2005-03-01

213

Exploiting classical nucleation theory for reverse self-assembly  

E-print Network

In this paper we introduce a new method to design interparticle interactions to target arbitrary crystal structures via the process of self-assembly. We show that it is possible to exploit the curvature of the crystal nucleation free-energy barrier to sample and select optimal interparticle interactions for self-assembly into a desired structure. We apply this method to find interactions to target two simple crystal structures: a crystal with simple cubic symmetry and a two-dimensional plane with square symmetry embedded in a three-dimensional space. Finally, we discuss the potential and limits of our method and propose a general model by which a functionally infinite number of different interaction geometries may be constructed and to which our reverse self-assembly method could in principle be applied.

William L. Miller; Angelo Cacciuto

2010-12-17

214

Self-assembly properties of a model RING domain  

PubMed Central

RING domains act in a variety of essential cellular processes but have no general function ascribed to them. Here, we observe that purified arenaviral protein Z, constituted almost entirely by its RING domain, self-assembles in vitro into spherical structures that resemble functional bodies formed by Z in infected cells. By using a variety of biophysical methods we provide a thermodynamic and kinetic framework for the RING-dependent self-assembly of Z. Assembly appears coupled to substantial conformational reorganization and changes in zinc coordination of site II of the RING. Thus, the rate-limiting nature of conformational reorganization observed in the folding of monomeric proteins can also apply to the assembly of macromolecular scaffolds. These studies describe a unique mechanism of nonfibrillar homogeneous self-assembly and suggest a general function of RINGs in the formation of macromolecular scaffolds that are positioned to integrate biochemical processes in cells. PMID:11792829

Kentsis, Alex; Gordon, Ronald E.; Borden, Katherine L. B.

2002-01-01

215

Guided and magnetic self-assembly of tunable magnetoceptive gels  

NASA Astrophysics Data System (ADS)

Self-assembly of components into complex functional patterns at microscale is common in nature, and used increasingly in numerous disciplines such as optoelectronics, microfabrication, sensors, tissue engineering and computation. Here, we describe the use of stable radicals to guide the self-assembly of magnetically tunable gels, which we call ‘magnetoceptive’ materials at the scale of hundreds of microns to a millimeter, each can be programmed by shape and composition, into heterogeneous complex structures. Using paramagnetism of free radicals as a driving mechanism, complex heterogeneous structures are built in the magnetic field generated by permanent magnets. The overall magnetic signature of final structure is erased via an antioxidant vitamin E, subsequent to guided self-assembly. We demonstrate unique capabilities of radicals and antioxidants in fabrication of soft systems with heterogeneity in material properties, such as porosity, elastic modulus and mass density; then in bottom-up tissue engineering and finally, levitational and selective assembly of microcomponents.

Tasoglu, S.; Yu, C. H.; Gungordu, H. I.; Guven, S.; Vural, T.; Demirci, U.

2014-09-01

216

Self-assembled intrinsic nanoscale phase separation in polymers  

NASA Astrophysics Data System (ADS)

It was thought that stable nanostructures did not exist in the phase separation behaviors of polymers. Now it is demonstrated that strongly correlated chains induced by hydrogen bonding can lead to a new self-assembly: intrinsic nanoscale phase separation. High-density nanorings, nanodiscs and nanospheres exist over large areas in the self-assembly of polymethylmethacrylate and poly(vinylidene fluoride-trifluoroethylene) blend films. Their typical size changes from 100 nm to 20 nm, depending on substrate effect and film thickness. The phenomenon that controllable nanoscale self-assembly exists in miscible polymer blends is beyond the conventional understanding of the phase separation behavior. This may open a new way in the design of nanostructured polymers and multifunctional polymers.

Zhang, Lei

2011-03-01

217

Self-assembly of silicotungstate anions on silver surfaces  

SciTech Connect

We report here the self assembly of {alpha}-dodecatungstosilicate anions, {alpha}-SiW{sub 12}O{sub 40}{sup 4-}, on Ag(111) surfaces from acidic aqueous solution. The ability of {alpha}-SiW{sub 12}O{sub 40}{sup 4-} to form self-assembled monolayers on Ag(111) offers great opportunity for generalization to other functionalized inorganic molecules on other surfaces. We find that the silicotungstate anions will also adhere to Cu surfaces, and we anticipate that they will bind to other oxophilic surfaces (e.g., Al, W, Ni) once the oxide layer is removed. Polyoxometalates function as superacids, ion exchangers, corrosion inhibitors, electron transfer reagents, catalysts, and photochemical oxidants. Since they can accommodate a wide range of organic, organometallic, and inorganic functional groups, we anticipate widespread exploration of these and other classes of inorganic molecules as self-assembled monolayers. 22 refs., 2 figs.

Ge, M.; Zhong, B.; Klemperer, W.G.; Gewirth, A.A. [Univ. of Illinois, Urbana, IL (United States)] [Univ. of Illinois, Urbana, IL (United States)

1996-06-19

218

Guided and magnetic self-assembly of tunable magnetoceptive gels  

PubMed Central

Self-assembly of components into complex functional patterns at microscale is common in nature, and used increasingly in numerous disciplines such as optoelectronics, microfabrication, sensors, tissue engineering and computation. Here, we describe the use of stable radicals to guide the self-assembly of magnetically tunable gels, which we call ‘magnetoceptive’ materials at the scale of hundreds of microns to a millimeter, each can be programmed by shape and composition, into heterogeneous complex structures. Using paramagnetism of free radicals as a driving mechanism, complex heterogeneous structures are built in the magnetic field generated by permanent magnets. The overall magnetic signature of final structure is erased via an antioxidant vitamin E, subsequent to guided self-assembly. We demonstrate unique capabilities of radicals and antioxidants in fabrication of soft systems with heterogeneity in material properties, such as porosity, elastic modulus and mass density; then in bottom-up tissue engineering and finally, levitational and selective assembly of microcomponents. PMID:25175148

Tasoglu, S.; Yu, C.H.; Gungordu, H.I.; Guven, S.; Vural, T.; Demirci, U.

2014-01-01

219

Comparing open and closed molecular self-assembly  

E-print Network

We study theoretically in the present work the self-assembly of molecules in an open system, which is fed by monomers and depleted in partial or complete clusters. Such a scenario is likely to occur for example in the context of viral self-assembly. We provide a general formula for the mean-field size distribution which is valid both at equilibrium in a closed system, and in the stationary state in an open system. This allows us to explore in a simple way out-of-equilibrium features for self-assembly and compare them to equilibrium properties. In particular, we identify a region of parameter space for which the out-of-equilibrium size distribution in the presence of external fluxes is equal to the equilibrium size distribution in the absence of external fluxes, up to a constant renormalization factor. The range of validity of this result and its consequences are discussed.

Martin Castelnovo; Timothée Verdier; Lionel Foret

2014-02-17

220

Self-assembled liposomal nanoparticles in photodynamic therapy  

PubMed Central

Photodynamic therapy (PDT) employs the combination of non-toxic photosensitizers (PS) together with harmless visible light of the appropriate wavelength to produce reactive oxygen species that kill unwanted cells. Because many PS are hydrophobic molecules prone to aggregation, numerous drug delivery vehicles have been tested to solubilize these molecules, render them biocompatible and enhance the ease of administration after intravenous injection. The recent rise in nanotechnology has markedly expanded the range of these nanoparticulate delivery vehicles beyond the well-established liposomes and micelles. Self-assembled nanoparticles are formed by judicious choice of monomer building blocks that spontaneously form a well-oriented 3-dimensional structure that incorporates the PS when subjected to the appropriate conditions. This self-assembly process is governed by a subtle interplay of forces on the molecular level. This review will cover the state of the art in the preparation and use of self-assembled liposomal nanoparticles within the context of PDT. PMID:24348377

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

2013-01-01

221

Structure-based model for light-harvesting properties of nucleic acid nanostructures  

E-print Network

Programmed self-assembly of DNA enables the rational design of megadalton-scale macromolecular assemblies with sub-nanometer scale precision. These assemblies can be programmed to serve as structural scaffolds for secondary ...

Pan, Keyao

222

Interfacial and mechanical properties of self-assembling systems  

NASA Astrophysics Data System (ADS)

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

Carvajal, Daniel

223

Probing Peptide amphiphile self-assembly in blood serum.  

PubMed

There has been recent interest in designing smart diagnostic or therapeutic self-assembling peptide or polymeric materials that can selectively undergo morphological transitions to accumulate at a disease site in response to specific stimuli. Developing approaches to probe these self-assembly transitions in environments that accurately amalgamate the diverse plethora of proteins, biomolecules, and salts of blood is essential for creating systems that function in vivo. Here, we have developed a fluorescence anisotropy approach to probe the pH-dependent self-assembly transition of peptide amphiphile (PA) molecules that transform from spherical micelles at pH 7.4 to nanofibers under more acidic pH's in blood serum. By mixing small concentrations of a Ru(bipy)3(2+)-tagged PA with a Gd(DO3A)-tagged PA having the same lipid-peptide sequence, we showed that the pH dependence of self-assembly is minimally affected and can be monitored in mouse blood serum. These PA vehicles can be designed to transition from spherical micelles to nanofibers in the pH range 7.0-7.4 in pure serum. In contrast to the typical notion of serum albumin absorbing isolated surfactant molecules and disrupting self-assembly, our experiments showed that albumin does not bind these anionic PAs and instead promotes nanofibers due to a molecular crowding effect. Finally, we created a medium that replicates the transition pH in serum to within 0.08 pH units and allows probing self-assembly behavior using conventional spectroscopic techniques without conflicting protein signals, thus simplifying the development pathway from test tube to in vivo experimentation for stimuli-responsive materials. PMID:25347387

Ghosh, Arijit; Buettner, Christian J; Manos, Aaron A; Wallace, Ashley J; Tweedle, Michael F; Goldberger, Joshua E

2014-12-01

224

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

PubMed Central

Light-harvesting antennae of the LHC family form transmembrane three-helix bundles of which two helices are interlocked by conserved arginine-glutamate (Arg-Glu) ion pairs that form ligation sites for chlorophylls. The antenna proteins of photosystem II have an intriguing dual function. In excess light, they can switch their conformation from a light-harvesting into a photoprotective state, in which the excess and harmful excitation energies are safely dissipated as heat. Here we applied magic angle spinning NMR and selective Arg isotope enrichment as a noninvasive method to analyze the Arg structures of the major light-harvesting complex II (LHCII). The conformations of the Arg residues that interlock helix A and B appear to be preserved in the light-harvesting and photoprotective state. Several Arg residues have very downfield-shifted proton NMR responses, indicating that they stabilize the complex by strong hydrogen bonds. For the Arg C? chemical shifts, differences are observed between LHCII in the active, light-harvesting and in the photoprotective, quenched state. These differences are attributed to a conformational change of the Arg residue in the stromal loop region. We conclude that the interlocked helices of LHCII form a rigid core. Consequently, the LHCII conformational switch does not involve changes in A/B helix tilting but likely involves rearrangements of the loops and helical segments close to the stromal and lumenal ends. PMID:23629658

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

2013-01-01

225

Self-assembly of DNA-coded nanoclusters  

E-print Network

We present a theoretical discussion of a self-assembly scheme which makes it possible to use DNA to uniquely encode the composition and structure of micro- and nanoparticle clusters. These anisotropic DNA-decorated clusters can be further used as building blocks for hierarchical self-assembly of larger structures. We address several important aspects of possible experimental implementation of the proposed scheme: the competition between different types of clusters in a solution, possible jamming in an unwanted configuration, and the degeneracy due to symmetry with respect to particle permutations.

Nicholas A. Licata; Alexei V. Tkachenko

2007-02-27

226

Towards lysozyme nanotube and 3D hybrid self-assembly.  

PubMed

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. PMID:23824259

Lara, Cecile; Handschin, Stephan; Mezzenga, Raffaele

2013-08-21

227

Thermally triggered self-assembly of folded proteins into vesicles.  

PubMed

We report thermally triggered self-assembly of folded proteins into vesicles that incorporates globular proteins as building blocks. Leucine zipper coiled coils were combined with either globular proteins or elastin-like polypeptides as recombinant fusion proteins, which form "rod-coil" and "globule-rod-coil" protein complex amphiphiles. In aqueous solution, they self-assembled into hollow vesicles via temperature-responsive inverse phase transition. The characteristic of the protein vesicle membranes enables preferential encapsulation of simultaneously formed protein coacervate. Furthermore, the type of encapsulated cargo extends to small molecules and nanoparticles. Our approach offers a versatile strategy to create protein vesicles as vehicles with biological functionality. PMID:25495148

Park, Won Min; Champion, Julie A

2014-12-31

228

Self-Assembly at a Nonequilibrium Critical Point  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

229

Thermally Reversible Self-Assembly of Nanoparticles via Polymer Crystallization.  

PubMed

The directed self-assembly of gold nanoparticles through the crystallization of surface-grafted polyethylene oxide (PEO) in ethanol-water mixtures is described. This process is fully reversible and tunable through either the size of the core or the polymeric coating. Characterization by X-ray scattering and electron microscopy of the self-assembled structures reveals order at the nanoscale, typically not the case for thermoresponsive gold nanoparticles coated with lower or upper critical solution temperature polymers. A further novelty is the result of selective binding of calcium ions to the PEO in the fluid state: a reversible thermoresponsive transition become irreversible. PMID:25315899

Kinnear, Calum; Balog, Sandor; Rothen-Rutishauser, Barbara; Petri-Fink, Alke

2014-12-01

230

Structural simulations of nanomaterials self-assembled from ionic macrocycles.  

SciTech Connect

Recent research at Sandia has discovered a new class of organic binary ionic solids with tunable optical, electronic, and photochemical properties. These nanomaterials, consisting of a novel class of organic binary ionic solids, are currently being developed at Sandia for applications in batteries, supercapacitors, and solar energy technologies. They are composed of self-assembled oligomeric arrays of very large anions and large cations, but their crucial internal arrangement is thus far unknown. This report describes (a) the development of a relevant model of nonconvex particles decorated with ions interacting through short-ranged Yukawa potentials, and (b) the results of initial Monte Carlo simulations of the self-assembly binary ionic solids.

van Swol, Frank B.; Medforth, Craig John (University of New Mexico, Albuquerque, NM)

2010-10-01

231

Nano-engineering by optically directed self-assembly.  

SciTech Connect

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

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

2009-09-01

232

Analyzing mechanisms and microscopic reversibility of self-assembly.  

PubMed

We use computer simulations to investigate self-assembly in a system of model chaperonin proteins, and in an Ising lattice gas. We discuss the mechanisms responsible for rapid and efficient assembly in these systems, and we use measurements of dynamical activity and assembly progress to compare their propensities for kinetic trapping. We use the analytic solution of a simple minimal model to illustrate the key features associated with such trapping, paying particular attention to the number of ways that particles can misbind. We discuss the relevance of our results for the design and control of self-assembly in general. PMID:22149800

Grant, James; Jack, Robert L; Whitelam, Stephen

2011-12-01

233

Self-assembly of amphiphilic peanut-shaped nanoparticles.  

PubMed

We use computer simulation to investigate the self-assembly of Janus-like amphiphilic peanut-shaped nanoparticles, finding phases of clusters, bilayers, and micelles in accord with ideas of packing familiar from the study of molecular surfactants. However, packing arguments do not explain the hierarchical self-assembly dynamics that we observe, nor the coexistence of bilayers and faceted polyhedra. This coexistence suggests that experimental realizations of our model can achieve multipotent assembly of either of two competing ordered structures. PMID:20170245

Whitelam, Stephen; Bon, Stefan A F

2010-02-21

234

Self-assembly at a nonequilibrium critical point.  

PubMed

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

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

2014-04-18

235

Advanced molecular self-assemblies facilitated by simple molecules.  

PubMed

Advanced materials are often based on smart molecular self-assemblies that either respond to external stimuli or have hierarchical structures. Approaches to this goal usually stem from complicated molecular design and difficult organic synthesis. In this invited feature article, we demonstrate that desired molecular self-assemblies can be made conveniently by introducing simple functional molecules into amphiphilic systems. We show that upon introducing specific small molecules which serve as responders, modulators, or even building blocks, smart supramolecular architectures can be achieved which avoid complicated organic synthesis. We expect that this could be a general and economical way to produce advanced materials in the near future. PMID:24870151

Wu, Zheng; Yan, Yun; Huang, Jianbin

2014-12-01

236

Backfilled, self-assembled monolayers and methods of making same  

DOEpatents

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

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

2009-06-30

237

CCMR: Interfacial Study of Self-Assembled Monolayers and Water  

NSDL National Science Digital Library

This project is a study of the ultrafast dynamics of water at hydrophobic and hydrophilic surfaces using sum-frequency generation and surface-specific 2D spectroscopy that is being developed in Dr. Poul Petersenâs lab. By determining the dynamics of water, many theories and models of water and interfacial processes can be corrected. This summer, the methods of making hydrophobic self-assembled monolayers was determined. These self-assembled monolayers will be the hydrophobic and hydrophilic interfaces used in the study to look at water.

Cagle, Courtney

2010-08-15

238

Self-assembly of flagellin on Au(111) surfaces.  

PubMed

The adsorption of flagellin monomers from Pseudomonas fluorescens on Au(111) has been studied by Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS), Surface Plasmon Resonance (SPR), and electrochemical techniques. Results show that flagellin monomers spontaneously self-assemble forming a monolayer thick protein film bounded to the Au surface by the more hydrophobic subunit and exposed to the environment the hydrophilic subunit. The films are conductive and allow allocation of electrochemically active cytochrome C. The self-assembled films could be used as biological platforms to build 3D complex molecular structures on planar metal surfaces and to functionalize metal nanoparticles. PMID:25112916

González Orive, Alejandro; Pissinis, Diego E; Diaz, Carolina; Miñán, Alejandro; Benítez, Guillermo A; Rubert, Aldo; Daza Millone, Antonieta; Rumbo, Martin; Hernández Creus, Alberto; Salvarezza, Roberto C; Schilardi, Patricia L

2014-11-01

239

Molecular dynamics simulations and electronic excited state properties of a self-assembled peptide amphiphile nanofiber with metalloporphyrin arrays.  

PubMed

We have employed molecular dynamics simulations and quantum chemistry methods to study the structures and electronic absorption properties of a novel type of photonic nanowire gel constructed by the self-assembly of peptide amphiphiles (PAs) and the chromophore-(PPIX)Zn molecules. Using molecular dynamics simulations, structures of the self-assembled fiber were determined with atomistic detail, including the distribution of chromophores along the nanofiber and the relative distances and orientations of pairs of chromophores. In addition, quantum chemistry calculations were used to determine the electronic structure and absorption properties of the chromophores in the fiber, so as to assess the capabilities of the nanofiber for photonics applications. The calculations show that the PA nanofiber provides an effective scaffold for the chromophores in which the chromophores form several clusters in which nearest neighbor chromophores are separated by less than 20 Å. The calculations also indicate that the chromophores can be in both the hydrophilic shell and hydrophobic core portions of the fiber. There are only small spectral shifts to the B-band of the porphyrins arising from the inhomogeneous microelectronic environment provided by the fiber. However, there are much stronger electronic interactions between nearby pairs of chromophores, leading to a more significant red shift of the B-band that is similar to what is found in the experiments and to significant excitonic coupling that is seen in circular dichroism spectra. This electronic interaction between chromophores associated with the PA nanofiber structure is crucial to future applications of these fibers for light-harvesting applications. PMID:24735017

Yu, Tao; Lee, One-Sun; Schatz, George C

2014-09-18

240

Enhancing light-harvesting power with coherent vibrational interactions: a quantum heat engine picture  

E-print Network

Recent evidence suggests that quantum effects may have functional importance in biological light-harvesting systems. Along with delocalized electronic excitations, it is now suspected that quantum coherent interactions with certain near-resonant vibrations contribute to light-harvesting performance. However, the actual quantum advantage offered by such coherent vibrational interactions has not yet been established. We investigate a quantum design principle, whereby coherent exchange of single energy quanta between electronic and vibrational degrees of freedom can enhance a light-harvesting system's power above what is possible by thermal mechanisms alone. We present a prototype quantum heat engine which cleanly illustrates this quantum design principle, and quantify its quantum advantage using thermodynamic measures of performance. We also demonstrate the principle's applicability for realistic biological structures.

Killoran, Nathan; Plenio, Martin B

2014-01-01

241

Enhancing light-harvesting power with coherent vibrational interactions: a quantum heat engine picture  

E-print Network

Recent evidence suggests that quantum effects may have functional importance in biological light-harvesting systems. Along with delocalized electronic excitations, it is now suspected that quantum coherent interactions with certain near-resonant vibrations contribute to light-harvesting performance. However, the actual quantum advantage offered by such coherent vibrational interactions has not yet been established. We investigate a quantum design principle, whereby coherent exchange of single energy quanta between electronic and vibrational degrees of freedom can enhance a light-harvesting system's power above what is possible by thermal mechanisms alone. We present a prototype quantum heat engine which cleanly illustrates this quantum design principle, and quantify its quantum advantage using thermodynamic measures of performance. We also demonstrate the principle's applicability for realistic biological structures.

Nathan Killoran; Susana F. Huelga; Martin B. Plenio

2014-12-12

242

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

243

Differential Self-Assembly of Novel Redox Crown Ethers  

NASA Astrophysics Data System (ADS)

Retinal prosthesis relies on the stimulation of living nerve tissue behind the rods and cones of the eye. The current state of the art relies on electrodes controlled by cameras which directly stimulate the nerve tissue to elicit a response to an image. These types of retinal implants have allowed for short-term crude vision in patients but have had limited long term success due to external battery packs and electroplating of the implanted electrodes. Ionic stimulation is one of the principle mechanisms that sensory neurons utilize in the generation of an action potential. In a complex transduction pathway, ionic gradients are constantly altered inside the neuron by voltage sensors or mechanically controlled gates embedded in the neuronal cell membrane; responsible for the open and close state of these ion channels. It has been demonstrated that local concentration increases of K + by direct injection proximal to the nerve can elicit nerve firing at a concentration of 15-20 mM (3-4X normal concentration) increase in K + concentration. As part of a larger concept of integrating biotechnology with nanofabrication, the materials for the development of potassium selective sequestration/storage and delivery were developed in the form of a redox-gated K+ selective crown ether. The structure of the anthraquinone-based crown was deduced by computational simulation and stoichiometry of the complex confirmed by mass spec. along with 2D diffusion NMR techniques. In this instance, the stoichiometry could be controlled by the addition of different salts to give a 1:1 complex with large, aromatic anions and a 2:1 complex with smaller anions such as triflate. The synthesis of the molecule was optimized by computational modeling and simulations of transport through an artificial membrane. The selectivity of the architecture developed was specific for K+ over Na+, the other major ionic species present in the blood. The mechanism influencing the self-assembly of this class of compounds has much to do with the breakage of intramolecular pi-stacking interactions and the formation of stronger intermolecular pi-stacking interactions. Finally, the transport of K+ through nanoporous membranes and single nanopores with novel PEG-type polymeric dispersions is demonstrated. This thesis concludes with future work toward developing more advanced transporters and proposes novel uses for anthraquinone-appended polymers as proton exchange membranes and DNA-base pair interchelators.

Merithew, Andrew William

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. PMID:22022620

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

2011-01-01

245

Plasmonic Mode Engineering with Templated Self-Assembled Nanoclusters  

E-print Network

Plasmonic Mode Engineering with Templated Self-Assembled Nanoclusters Jonathan A. Fan, Kui Bao, Li nanoclusters can be assembled onto a lithographically defined elastomeric substrate with relatively high yields 30%. The assembly of plasmonic nanoclusters on an elastomer paves the way for new classes

Capasso, Federico

246

Molecular engineering and characterization of self-assembled biorecognition surfaces  

Microsoft Academic Search

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

Sheng Pan

1999-01-01

247

Effect of several sterilisation techniques on homogeneous self assembled monolayers  

Microsoft Academic Search

Understanding how cells sense their environment and are able to regulate their metabolism is of great importance for the success of biomaterials implantation. Self assembled monolayers (SAMs) are in use nowadays to model the surface of such materials. They permit the control of different surface parameters (like chemistry, surface energy and topography) enabling to get a greater insight in cells

S. Fleith; A. Ponche; R. Bareille; J. Amédée; M. Nardin

2005-01-01

248

Photoresponsive self-assemblies based on fatty acids.  

PubMed

Photoresponsive surfactant system based on fatty acids has been developed by the introduction in aqueous solution of a photoacid generator (PAG). Self-assembly transitions are triggered by UV irradiation due to a pH change induced by the presence of PAG. PMID:25582497

Fameau, A-L; Arnould, A; Lehmann, M; von Klitzing, R

2015-02-01

249

Solder self-assembly for three-dimensional microelectromechanical systems  

Microsoft Academic Search

A solder technology has been developed that utilizes molten solder surface tension forces to self-assemble MEMS 3-D structures. Using solder, a single batch reflow process can be used to accomplish hundreds or thousands of precision assemblies, and the cost per assembly can be reduced considerably. A model, based on surface energy minimization of molten liquids, has been developed for predicting

Kevin F. Harsh; Victor M. Bright; Y. C. Lee

1999-01-01

250

Developmental self-assembly of a DNA tetrahedron.  

PubMed

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

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

2014-04-22

251

BULK TITANIUM MICROFLUIDIC NETWORKS FOR PROTEIN SELF-ASSEMBLY STUDIES  

E-print Network

BULK TITANIUM MICROFLUIDIC NETWORKS FOR PROTEIN SELF-ASSEMBLY STUDIES E.R. Parker1 , L.S. Hirst2 developed micromachining technique to fabricate microfluidic networks in thin titanium foils. These devices been integrated into the fabrication process in order to minimize protein adsorption to the titanium

MacDonald, Noel C.

252

Theoretical Modelling of Self-Assembly of Molecular Networks  

NASA Astrophysics Data System (ADS)

The phenomenon of self-assembly of atomic and molecular superstructures on crystal surfaces has attracted an increasing interest in nanotechnology. Self-organised nano-templates where the self-assembled monolayer traps other molecules with selected functional properties, can be used as building blocks for larger nanoscale structures. These superstructures can form chiral domains ranging from 1D chains to 2D monolayers. In particular, there have been many scanning tunneling microscopy (STM)studies of self-assembly of melamine, perylene tetra-carboxylic di-imide(PTCDI) or perylene tetra-carboxylic di-anhydride (PTCDA) molecules on the Au(111). STM images of these networks do not reveal the exact details of the intermolecular bonding and process of network growth. It is therefore the task of theory to determine the exact atomic structure of these networks. We present a theoretical study of self-assembly of molecular networks based on different molecules by using a systematic approach to build molecular superstructures. The energies of these structures are calculated using the density-functional theory SIESTA code. The theoretically predicted monolayer structures are in very good agreement with the results of STM measurements.

Mura, Manuela; Martsinovich, Natalia; Kantorovich, Lev

2008-03-01

253

Multistep hierarchical self-assembly of chiral nanopore arrays.  

PubMed

A series of simple hierarchical self-assembly steps achieve self-organization from the centimeter to the subnanometer-length scales in the form of square-centimeter arrays of linear nanopores, each one having a single chiral helical nanofilament of large internal surface area and interfacial interactions based on chiral crystalline molecular arrangements. PMID:25246585

Kim, Hanim; Lee, Sunhee; Shin, Tae Joo; Korblova, Eva; Walba, David M; Clark, Noel A; Lee, Sang Bok; Yoon, Dong Ki

2014-10-01

254

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

255

Chemical mimicry of viral capsid self-assembly  

PubMed Central

Stable structures of icosahedral symmetry can serve numerous functional roles, including chemical microencapsulation and delivery of drugs and biomolecules, epitope presentation to allow for an efficient immunization process, synthesis of nanoparticles of uniform size, observation of encapsulated reactive intermediates, formation of structural elements for supramolecular constructs, and molecular computing. By examining physical models of spherical virus assembly we have arrived at a general synthetic strategy for producing chemical capsids at size scales between fullerenes and spherical viruses. Such capsids can be formed by self-assembly from a class of molecules developed from a symmetric pentagonal core. By designing chemical complementarity into the five interface edges of the molecule, we can produce self-assembling stable structures of icosahedral symmetry. We considered three different binding mechanisms: hydrogen bonding, metal binding, and formation of disulfide bonds. These structures can be designed to assemble and disassemble under controlled environmental conditions. We have conducted molecular dynamics simulation on a class of corannulene-based molecules to demonstrate the characteristics of self-assembly and to aid in the design of the molecular subunits. The edge complementarities can be of diverse structure, and they need not reflect the fivefold symmetry of the molecular core. Thus, self-assembling capsids formed from coded subunits can serve as addressable nanocontainers or custom-made structural elements. PMID:18093950

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

2007-01-01

256

Self-assembling electroactive hydrogels for flexible display technology.  

PubMed

We have assessed the potential of self-assembling hydrogels for use in conformal displays. The self-assembling process can be used to alter the transparency of the material to all visible light due to scattering by fibres. The reversible transition is shown to be of low energy by differential scanning calorimetry. For use in technology it is imperative that this transition is controlled electrically. We have thus synthesized novel self-assembling hydrogelator molecules which contain an electroactive group. The well-known redox couple of anthraquinone/anthrahydroquinone has been used as the hydrophobic component for a series of small molecule gelators. They are further functionalized with peptide combinations of L-phenylalanine and glycine to provide the hydrophilic group to complete 'head-tail' models of self-assembling gels. The gelation and electroactive characteristics of the series were assessed. Cyclic voltammetry shows the reversible redox cycle to be only superficially altered by functionalization. Additionally, spectroelectrochemical measurements show a reversible transparency and colour change induced by the redox process. PMID:21406771

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

2010-12-15

257

Self-assembling electroactive hydrogels for flexible display technology  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

258

Self-assembly of Superparamagnetic Nanoparticles with Permanent Magnetization  

NASA Astrophysics Data System (ADS)

Magnetic nanoparticles (MNPs) exhibit superparamagnetism when thermal fluctuations overcome the potential barrier for spin reversal set by magnetocrystalline anisotropy. The magnetic moment in such a material oscillates between the easy axes leading to zero net magnetization. Stable colloidal dispersions of MNPs exploit this state to prevent agglomeration. Self-assembly of MNPs presents an excellent bottom up nanofabrication technique due to the wide range of structures that can be formed. A stable dispersion of MNPs is an essential starting point for good control of the process. In this study we explore the theoretical basis for a self-assembled MNP structure with permanent magnetization starting from a dispersion of superparamangetic MNPs. Magnetostatic coupling of dipole moments enhance the potential barrier for magnetization reversals. We use X-Ray microCT and TEM to visualize the self-assembled structures. We use a stochastic form of the Landau-Lifshitz-Gilbert equation to simulate the magnetization dynamics in each MNP. Permanent magnetization in self-assembled structures generated in situ promise several significant applications such as targeted drug delivery, tissue engineering and novel soft composites.

Ghosh, Suvojit; Puri, Ishwar

2012-02-01

259

Templated self-assembly for complex pattern fabrication  

E-print Network

The long-term goal of my Ph.D. study has been controlling the self-assembly of various materials using state-of-the-art nanofabrication techniques. Electron-beam lithography has been used for decades to generate nanoscale ...

Chang, Jae-Byum

2014-01-01

260

Title of dissertation: THE SELF-ASSEMBLY OF PARTICLES WITH  

E-print Network

ABSTRACT Title of dissertation: THE SELF-ASSEMBLY OF PARTICLES WITH MULTIPOLAR INTERACTIONS Justin Department of Physics In this thesis, we describe results from investigations of the self multipolar interactions on the patterns of self-organization. Using an experimental model system

Anlage, Steven

261

Self-Organization and the Self-Assembling Process in  

E-print Network

Self-Organization and the Self-Assembling Process in Tissue Engineering Kyriacos A. Athanasiou. Keywords tissue engineering, regenerative medicine, scaffoldless, self-organization, self to include a new and growing subfield of scaffoldless techniques that generate self-organizing and self

Athanasiou, Kyriacos

262

Towards lysozyme nanotube and 3D hybrid self-assembly  

NASA Astrophysics Data System (ADS)

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

Lara, Cecile; Handschin, Stephan; Mezzenga, Raffaele

2013-07-01

263

Conformational flexibility facilitates self-assembly of complex DNA nanostructures  

E-print Network

, out of DNA three-point star motifs. In the current study, we have integrated tensegrity principle, but others do not. Ac- cording to tensegrity principle, triangular faces will lead to rigid structures (11, 12, 17­20). This fact prompts us to integrate the tensegrity principle into DNA self-assembly when

Jiang, Wen

264

Entangled spin states in self-assembled monolayer systems  

Microsoft Academic Search

We discuss the opportunity for creation of an entangled spin state in a self-assembled monolayer molecular system. A group of spin radicals can be transferred to the entangled state using resonant electromagnetic pulses. The magnetic dipole-dipole interaction within a group is taken into account while the same interaction between the groups is neglected. A high external magnetic field at low

Gennady P. Berman; Vladimir I. Tsifrinovich; David L. Allara

2002-01-01

265

Self-assembly in additive manufacturing: opportunities and obstacles  

Microsoft Academic Search

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

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

2011-01-01

266

Amphiphilic self-assembly of alkanols in protic ionic liquids.  

PubMed

Strong cohesive forces in protic ionic liquids (PILs) can induce a liquid nanostructure consisting of segregated polar and apolar domains. Small-angle X-ray scattering has shown that these forces can also induce medium chain length n-alkanols to self-assemble into micelle- and microemulsion-like structures in ethylammonium (EA(+)) and propylammonium (PA(+)) PILs, in contrast to their immiscibility with both water and ethanolammonium (EtA(+)) PILs. These binary mixtures are structured on two distinct length scales: one associated with the self-assembled n-alkanol aggregates and the other with the underlying liquid nanostructure. This suggests that EA(+) and PA(+) enable n-alkanol aggregation by acting as cosurfactants, which EtA(+) cannot do because its terminating hydroxyl renders the cation nonamphiphilic. The primary determining factor for miscibility and self-assembly is the ratio of alkyl chain lengths of the alkanol and PIL cation, modulated by the anion type. These results show how ILs can support the self-assembly of nontraditional amphiphiles and enable the creation of new forms of soft matter. PMID:25068766

Jiang, Haihui Joy; FitzGerald, Paul A; Dolan, Andrew; Atkin, Rob; Warr, Gregory G

2014-08-21

267

Bicontinuous Surfaces in Self-assembling Amphiphilic Systems  

E-print Network

Bicontinuous Surfaces in Self-assembling Amphiphilic Systems Ulrich Schwarz1 and Gerhard Gompper2 1¨orperforschung, Forschungszentrum J¨ulich, D-52425 J¨ulich Abstract. Amphiphiles are molecules which have both hydrophilic due to the hydrophobic effect. The free energy of an amphiphilic system can be written as a functional

Schwarz, Ulrich

268

Excitons and Disorder in Molecular Nanotubes: A 2D Electronic Spectroscopy Study and First Comparison to a Microscopic Model  

E-print Network

the idea to use self-assembled tubules for building artificial light-harvesting complexes or to combine The efficiency of natural light-harvesting complexes relies on delocalization and directed transfer of excitation light harvesters is the transfer of the self-organization tendency of organic surfactants to molecular

Mukamel, Shaul

269

Hierarchical growth of curved organic nanowires upon evaporation induced self-assembly.  

PubMed

Self-assembly of a TTF derivative capable of forming self-assembled monolayers at the surface of graphite displays hierarchical growth of multilayers and concentric nanorings upon evaporation of the solvent as observed by AFM. PMID:25027031

Li, Bing; Puigmartí-Luis, Jiosep; Jonas, Alain M; Amabilino, David B; De Feyter, Steven

2014-11-11

270

Controlled evaporative self-assembly of hierarchically structured bottlebrush block copolymer with nanochannels  

E-print Network

Controlled evaporative self-assembly of hierarchically structured bottlebrush block copolymer as toluene evaporated, thereby yielding gradient stripes at the microscopic scale. Subsequent selective. This facile approach of combining the controlled evaporative self-assembly with subsequent solvent vapor

Lin, Zhiqun

271

Luminescent Silicon Nanoparticles Capped by Conductive Polyaniline through the Self-Assembly Method  

E-print Network

Luminescent Silicon Nanoparticles Capped by Conductive Polyaniline through the Self-Assembly Method polymer coating on free-standing luminescent silicon nanoparticles. The silicon nanoparticles maintained electron microscopy. The silane self-assembled monolayer effectively protected the silicon particles

Swihart, Mark T.

272

Dynamics, self-assembly, and function of multicomponent coordination supramolecular systems.  

E-print Network

??Self-assembly allows for the preparation of highly complex molecular and supramolecular systems from relatively simple starting materials. Self-assembled supramolecules are typically constructed by combining complementary… (more)

Zheng, Yaorong

2011-01-01

273

Role of hydrophobicity, aromaticity, and turn nucleation in peptide self-assembly.  

E-print Network

??Peptide self-assembly into cross-? amyloid is the hallmark of several amyloid pathologies and the inspiration for biomaterials. Peptide self-assembly is governed by noncovalent interactions such… (more)

Doran, Todd M. (1983 - )

2012-01-01

274

Noncanonical Self-Assembly of Multifunctional DNA Nanoflowers for Biomedical Applications  

E-print Network

Noncanonical Self-Assembly of Multifunctional DNA Nanoflowers for Biomedical Applications Guizhi the noncanonical self-assembly of multifunctional DNA nanostructures, termed as nanoflowers (NFs Information ABSTRACT: DNA nanotechnology has been extensively explored to assemble various functional

Tan, Weihong

275

Nanostructured gene and drug delivery systems based on molecular self-assembly  

E-print Network

Molecular self-assembly describes the assembly of molecular components into complex, supramolecular structures governed by weak, non-covalent interactions. In recent years, molecular self-assembly has been used extensively ...

Wood, Kris Cameron

2007-01-01

276

Three-dimensional nanofabrication by electron-beam lithography and directed self-assembly  

E-print Network

In this thesis, we investigated three-dimensional (3D) nanofabrication using electron-beam lithography (EBL), block copolymer (BCP) self-assembly, and capillary force-induced self-assembly. We first developed new processes ...

Do, Hyung Wan

2014-01-01

277

Clustering and self-assembly in colloidal systems  

NASA Astrophysics Data System (ADS)

A colloidal dispersion consists of small particles called colloids, typically tens of nanometers to a few micrometers in size, suspended in a solvent. Due to collisions with the much smaller particles in the solvent, colloids perform Brownian motion: randomly directed movements that cause the particles to diffuse through the system. In principle, this motion allow the system of particles to explore all configurations available to them, sampling all of phase space according to the Boltzmann distribution. Analogous to molecular and atomic systems, colloidal systems can form disordered gas and liquid phases, as well as more ordered phases such as crystals, liquid crystals, or finite-sized aggregates. Since the particles form these phases based purely on their interactions and the Brownian motion that results from thermal fluctuations in their solvent, the process of forming these ordered structures is called self-assembly. In this thesis, we study the self-assembly of a variety of colloidal systems. We attempt to determine what structures can be expected to form, investigate the order and stability of these phases, and examine the nucleation of self-assembled crystals. To do this, we make use of computers to simulate the behavior of colloidal particles in suspension. Depending on the system under consideration, we perform either Monte Carlo simulations or event-driven molecular dynamics. In particular, we study the self-assembly of particles of several shapes in external electric or magnetic fields, the phase behavior of hard colloidal cubes, and the phase diagrams of charged colloidal spheres with a constant surface potential. Furthermore, we investigate the nucleation of binary hard sphere mixtures, the self-assembly of colloidal particles in evaporating emulsion droplets, and the formation of colloidal micelles. Where possible, we compare our results with experimental findings in similar systems.

Smallenburg, F.

2012-01-01

278

Development of stochastic models for dynamics of self-assembled surfactant systems  

NASA Astrophysics Data System (ADS)

Understanding dynamic processes in surfactant self-assembled systems is crucial in various technological applications. The goal of this study is to develop stochastic models for dynamic processes in surfactant systems using coarse-grained molecular dynamics simulations. Two types of processes are considered. The first of the investigated processes is molecular transport across oil-water interfaces covered by nonionic surfactants. Resistance of the surfactant monolayer to the solute transport is shown to be controlled by dense regions in the monolayer. Resistance to the transport of a hydrophobic (hydrophilic) solute increases as the length of the surfactant head (tail) group increases. Barriers for solute transport through surfactant monolayers are also influenced by the solute size. The non-adiabatic coupling of the monolayer with the solute position and configuration causes deviations of the system dynamics from the minimum energy path, which effectively leads to an increase of the barrier for the solute transport. The second type of the considered processes is micellar self-assembly and disaggregation. We present a detailed model for two of the elementary steps involved in self-assembly of surfactants, namely addition/removal of a single surfactant molecule to/from a spherical micelle. Multi-dimensional free energy landscapes parametrized by monomer and micellar degrees of freedom are obtained using a series of constrained simulations. We observe that the system trajectory on the free energy landscape is multi-dimensional and cannot be reduced to motion along a one-dimensional path on this surface. In order to elucidate the collective dynamics of the multiple degrees of freedom, the most likely path is identified on the free energy landscapes. Since the majority of natural and artificial surfactants are ionic, we also study the effects of electrostatic interactions on self-assembly of ionic surfactants. By solving the Poisson equation, it is shown that electrostatic potentials effectively increase (decrease) energy barriers of the addition (removal) of a surfactant molecule to (from) a micelle. It is anticipated that the approaches discussed in this study can be extended to investigation of more complex dynamic processes in amphiphilic systems.

Ahn, Yong Nam

279

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

PubMed Central

Biofabrication of living structures with desired topology and functionality requires the interdisciplinary effort of practitioners of the physical, life, medical and engineering sciences. Such efforts are being undertaken in many laboratories around the world. Numerous approaches are being pursued, such as those based on the use of natural or artificial scaffolds, decellularized cadaveric extracellular matrices and 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, scaffolds, no matter how sophisticated they are, 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 is 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 bioink particles and employs early developmental morphogenetic principles, such as cell sorting and tissue fusion. PMID:20811127

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

2013-01-01

280

Heirarchical Self Assembly: Self Organized nano-structures in a nematically ordered matrix of self assembled polymeric chains  

E-print Network

We report many different nano-structures which are formed when model nano-particles of different sizes (diameter {\\sigma} n ) are allowed to aggregate in a background matrix of semi-flexible self assembled polymeric worm like micellar chains. The different nano-structures are formed by the dynamical arrest of phase-separating mixtures of micellar monomers and nano-particles. The different mor- phologies obtained are the result of an interplay of the available free volume, the elastic energy of deformation of polymers, the density (chemical potential) of the nano-particles in the polymer ma- trix and, of course, the ratio of the size of self assembling nano-particles and self avoidance diameter of polymeric chains. We have used a hybrid semi-grand canonical Monte Carlo simulation scheme to obtain the (non-equilibrium) phase diagram of the self-assembled nano-structures. We observe rod-like structures of nano-particles which get self assembled in the gaps between the nematically ordered chains as well as percolating gel-like network of conjoined nanotubes. We also find a totally unexpected interlocked crystalline phase of nano-particles and monomers, in which each crytal plane of nanoparticles is separated by planes of perfectly organized polymer chains. We identified the con- dition which leads to such interlocked crystal structure. We suggest experimental possibilities of how the results presented in this paper could be used to obtain different nano-structures in the lab.

Shaikh Mubeena; Apratim Chatterji

2014-12-04

281

Structural Transformations in self-assembled Semiconductor Quantum Dots as inferred by Transmission Electron Microscopy  

E-print Network

Structural Transformations in self-assembled Semiconductor Quantum Dots as inferred by Transmission of self-assembled semiconductor quantum dots are reported. III-V and II-VI quantum dots as grown and controlling structural transformations in self-assembled semiconductor quantum dots may also offer

Moeck, Peter

282

Self-Assembly of Filamentous Amelogenin Requires Calcium and Phosphate: From Dimers via Nanoribbons to Fibrils  

E-print Network

Self-Assembly of Filamentous Amelogenin Requires Calcium and Phosphate: From Dimers via Nanoribbons, San Francisco, California 94143, United States *S Supporting Information ABSTRACT: Enamel matrix self-assembly tested if amelogenin, the main enamel matrix protein, can self-assemble into ribbon-like structures

Sali, Andrej

283

A Hierarchical Self-Assembly Route to Three-Dimensional Polymer-Quantum Dot Photonic Arrays  

E-print Network

A Hierarchical Self-Assembly Route to Three-Dimensional Polymer-Quantum Dot Photonic Arrays HudaVed February 1, 2007. In Final Form: March 19, 2007 We demonstrate a new hierarchical self-assembly strategy for the formation of photonic arrays containing quantum dots (QDs), in which sequential self-assembly steps

Brolo, Alexandre G.

284

Post-Self-Assembly Cross-Linking to Integrate Molecular Nanofibers with Copolymers in Oscillatory Hydrogels  

E-print Network

Post-Self-Assembly Cross-Linking to Integrate Molecular Nanofibers with Copolymers in Oscillatory Information ABSTRACT: We study the use of post-self-assembly cross- linking to combine molecular nanofibers. The combination of supramolecular self-assembly with copolymerization offers a versatile and facile approach

Epstein, Irving R.

285

Molecular-level Thermodynamic and Kinetic Parameters for the Self-assembly of Apoferritin  

E-print Network

Molecular-level Thermodynamic and Kinetic Parameters for the Self-assembly of Apoferritin Molecules Association, Marshal Space Flight Center, Huntsville AL 35875, USA The self-assembly of apoferritin molecules biological and biomedical phenomena, as well as for pro- tein and virus self-assembly. We use the atomic

Vekilov, Peter

286

Modeling self-assembling of proteins: Assembled structures, relaxation dynamics, and phase coexistence  

E-print Network

Modeling self-assembling of proteins: Assembled structures, relaxation dynamics, and phase of a self-assembling system, which also produces a -barrel. In molecular dynamics MD simulations, both and understanding the self-assembly of free, complex molecules into organized structures such as monolayers

Berry, R. Stephen

287

Error Free Self-Assembly using Error Prone Tiles Ho-Lin Chen  

E-print Network

Error Free Self-Assembly using Error Prone Tiles Ho-Lin Chen Stanford University Ashish Goel Stanford University Abstract. DNA self-assembly is emerging as a key paradigm for nano-technology, nano-computation, and several related disciplines. In nature, DNA self-assembly is often equipped with explicit mechanisms

Batzoglou, Serafim

288

Self-assembled monolayers from a designed combinatorial library of de novo  

E-print Network

Self-assembled monolayers from a designed combinatorial library of de novo -sheet proteins Guofeng-dimensional protein layers, we studied the self-assembly properties of de novo proteins from a designed combinatorial. Proteins play key roles in controlling the self-assembly of biological materials (1­5). In recent years

Hecht, Michael H.

289

Self-assembled multivalent vancomycin on cell surfaces against vancomycin-resistant enterococci (VRE)  

E-print Network

Self-assembled multivalent vancomycin on cell surfaces against vancomycin-resistant enterococci 2003 A vancomycin (Van) derivative self-assembles in a phos- phate buffer as a divalent Van and on cell (Van) derivative (2) that self-assembles to form a multivalent inhibitor on the cell surface. It offers

Xing, Bengang

290

Using self-assembled monolayers to model the extracellular matrix q Milan Mrksich *  

E-print Network

Review Using self-assembled monolayers to model the extracellular matrix q Milan Mrksich, orientations and environments. Among these approaches, self-assembled monolayers of alkanethiolates on gold Ltd. All rights reserved. Keywords: Cell­matrix interactions; Self-assembled monolayers; Modelling

Mrksich, Milan

291

Self-Assembly and Disassembly of Regioregular, Water Soluble Polythiophenes: Chemoselective  

E-print Network

Self-Assembly and Disassembly of Regioregular, Water Soluble Polythiophenes: Chemoselective% head-to-tail (HT) couplings1,2 has led to the discovery of materials that self-assemble both aggregation is precursive to a microcrystalline, self-assembled structure which has been characterized by X

McCullough, Richard D.

292

Programming biomolecular self-assembly pathways Peng Yin1,2  

E-print Network

LETTERS Programming biomolecular self-assembly pathways Peng Yin1,2 , Harry M. T. Choi1 , Colby R. Calvert1 & Niles A. Pierce1,3 In nature, self-assembling and disassembling complexes of pro- teins have largely focused on engineering molecules that self-assemble into prescribed target structures

Pierce, Niles A.

293

Collagen I Self-Assembly: Revealing the Developing Structures that Generate Turbidity  

E-print Network

Collagen I Self-Assembly: Revealing the Developing Structures that Generate Turbidity Jieling Zhu the structures responsible for the turbidity that develops during collagen self-assembly. Information from CRM self-assemble into fibrillar structures that may cross-link and/or entangle to form viscoelastic gels

Kaufman, Laura

294

Self-Assembling Cyclic Peptides: Molecular Dynamics Studies of Dimers in Polar and Nonpolar Solvents  

E-print Network

Self-Assembling Cyclic Peptides: Molecular Dynamics Studies of Dimers in Polar and Nonpolar-6323 ReceiVed: December 22, 2005; In Final Form: March 17, 2006 The self-assembly of cyclic D. Introduction Ghadiri and co-workers have designed remarkable synthetic nanotubes, which are formed by the self-assembly

Nielsen, Steven O.

295

Supplementary Information for: Integrating DNA Strand Displacement Circuitry with DNA Tile Self-assembly  

E-print Network

Supplementary Information for: Integrating DNA Strand Displacement Circuitry with DNA Tile Self-assembly of Contents: · Supplementary Figures 1. Native polyacrylamide gel electrophoresis of DNA tile self-assembly 2. UV absorbance annealing and melting curves of DNA tile self-assembly 3. Characterization

Zhang, David Yu

296

Negative Interactions in Irreversible Self-Assembly Beno^it Masson  

E-print Network

Negative Interactions in Irreversible Self-Assembly David Doty Lila Kari Beno^it Masson§ Abstract Tile-based self-assembly is a model of "algorithmic crystal growth" in which square "tiles" represent plausible mechanism for growth through time. Winfree defined a model of tile-based self-assembly known

Doty, David

297

Limitations of Self-Assembly at Temperature 1 , Matthew J. Patitz, and Scott M. Summers  

E-print Network

Limitations of Self-Assembly at Temperature 1 David Doty , Matthew J. Patitz, and Scott M. Summers,mpatitz,summers}@cs.iastate.edu Abstract We prove that if a set X Z2 weakly self-assembles at temperature 1 in a deterministic (Winfree. We employ this result to show that, unlike the case of temperature 2 self-assembly, no discrete self

Doty, David

298

Negative Interactions in Irreversible Self-Assembly Beno^it Masson  

E-print Network

Negative Interactions in Irreversible Self-Assembly David Doty Lila Kari Beno^it Masson§ Abstract Introduction Tile-based self-assembly is a model of "algorithmic crystal growth" in which square "tiles plausible mechanism for growth through time. Winfree defined a model of tile-based self-assembly known

Doty, David

299

Peptide self-assembly as a model of proteins in the pre-genomic world  

E-print Network

Peptide self-assembly as a model of proteins in the pre-genomic world Indraneel Ghosh1 and Jean-based biopolymers have been designed to self assemble. Addresses 1 Department of Chemistry, University of Arizona a range of catalytic activities [3,4]. However, there has also been great interest in exploring other self-assembling

Ghosh, Indraneel

300

DOI: 10.1002/chem.200802337 Cyclic PeptidePolymer Complexes and Their Self-Assembly  

E-print Network

DOI: 10.1002/chem.200802337 Cyclic Peptide­Polymer Complexes and Their Self-Assembly Dominique Rationally designed cyclic peptides with flat conformations can self-assemble into tubular nanostructures. In a recent study,[5] our groups found that the medium in which the self-assembly of cyclic peptides takes

Zhao, Yue

301

Randomized Self-Assembly for Exact Shapes Department of Computer Science  

E-print Network

Randomized Self-Assembly for Exact Shapes David Doty Department of Computer Science Iowa State question of Kao and Schweller (Randomized Self-Assembly for Approximate Shapes, ICALP 2008), who showed how the approximation could be made exact with high probability. 1. INTRODUCTION Self-assembly is a term used

Doty, David

302

Equilibrium self-assembly of colloids with distinct interaction sites: Thermodynamics, percolation, and cluster distribution functions  

E-print Network

of self-assembly, which can be quantified by the maxima of the specific heat at constant volumeEquilibrium self-assembly of colloids with distinct interaction sites: Thermodynamics, percolation for functional materials and devices. A promising approach is self-assembly, which is the spontaneous

Sciortino, Francesco

303

Self-Assembly in Mixtures of Polymers and Small Associating Molecules Haim Diamant and David Andelman*  

E-print Network

Self-Assembly in Mixtures of Polymers and Small Associating Molecules Haim Diamant and David of the interaction, compete with intrachain repulsion and eventually drive a joint self-assembly of the two species with experiments on the onset of self-assembly in diverse polymer- surfactant systems. The threshold concentration

Andelman, David

304

Self-Assembly of Flat Micro Components by Capillary Forces and Shape Recognition  

E-print Network

Self-Assembly of Flat Micro Components by Capillary Forces and Shape Recognition J. Fang, S. Liang, K. Wang, X. Xiong, K. F. Böhringer* This paper summarizes our recent reports on self-assembly of flat micro components based on two major mechanisms: capillary-driven self-assembly and feature

305

Self-assembly, modularity and physical complexity S. E. Ahnert,1  

E-print Network

Self-assembly, modularity and physical complexity S. E. Ahnert,1 I. Johnston,2 T. M. A. Fink,3, 4 structure through self-assembly. Our procedure can be adapted to any given geometry, and thus to any given type of physical system. We illustrate our approach using self-assembling polyominoes, and demonstrate

Halligan, Daniel

306

Novel trimethyl lock based enzyme switch for the self-assembly and disassembly of gold nanoparticlesw  

E-print Network

Novel trimethyl lock based enzyme switch for the self-assembly and disassembly of gold-responsive gold nanoparticles (AuNPs) conjugate was developed to control the self-assembly and disassembly of Au and surface enhanced Raman scatter- ing (SERS) measurements. The programmed self-assembly of gold

Xing, Bengang

307

Self-assembly of long chain alkanes and their derivatives on graphite Teng Yang,1  

E-print Network

Self-assembly of long chain alkanes and their derivatives on graphite Teng Yang,1 Savas Berber,1 initio calculations to study the self-assembly of long chain alkanes and related alcohol and carboxylic the ordering of long chain alkanes in self-assembled monolayers and ways to modify it using alcohol and acid

308

Localized and Delocalized Electronic Excitations in Biological and Artificial Antenna Complexes Sergei Tretiak1  

E-print Network

in these biological and artificial light-harvesting antenna complexes. Introduction Advances in organic synthesis , and organic superlattices5 . In addition, molecular aggregates are common in biological processes such as light-harvesting complexes in photosynthesis6 . X-ray and NMR techniques provide the geometry

Tretiak, Sergei

309

Artificial Inorganic Leafs for Efficient Photochemical Hydrogen Production Inspired by Natural  

E-print Network

for photosynthesis in which light harvesting, photoinduced charge separation, and catalysis modules combine-shaped hierarchical structures, named artificial inorganic leaf (AIL), for efficient harvesting of light energy the structural effect. Actually, the whole structure of natural leaves strongly favors light harvesting:[12

Osterloh, Frank

310

Energy Transfer from Quantum Dots to Metal-Organic Frameworks for Enhanced Light Harvesting  

E-print Network

-harvesting applications. We report here the function- alization of porphyrin-based MOFs with CdSe/ZnS core/ shell quantum to natural porphyrin-type light-harvesting and photosynthesis pigments,12 porphyrin-based MOFs might that in a zinc porphyrin-based MOF the photogenerated exciton can migrate over 10-30 porphyrin struts within its

311

A pigment-binding protein essential for regulation of photosynthetic light harvesting  

Microsoft Academic Search

Photosynthetic light harvesting in plants is regulated in response to changes in incident light intensity. Absorption of light that exceeds a plant's capacity for fixation of CO2 results in thermal dissipation of excitation energy in the pigment antenna of photosystem II by a poorly understood mechanism. This regulatory process, termed nonphotochemical quenching, maintains the balance between dissipation and utilization of

Xiao-Ping Li; Olle Bjorkman; Connie Shih; Arthur R. Grossman; Magnus Rosenquist; Stefan Jansson; Krishna K. Niyogi

2000-01-01

312

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

313

Enhancing the light harvesting capability of a photosynthetic reaction center by a tailored molecular fluorophore.  

PubMed

Light machine: The simplest photosynthetic protein able to convert sunlight into other energy forms is covalently functionalized with a tailored organic dye to obtain a fully functional hybrid complex that outperforms the natural system in light harvesting and conversion ability. PMID:23011764

Milano, Francesco; Tangorra, Rocco Roberto; Hassan Omar, Omar; Ragni, Roberta; Operamolla, Alessandra; Agostiano, Angela; Farinola, Gianluca M; Trotta, Massimo

2012-10-29

314

Plasmon Enhanced Light Harvesting: Multiscale Modeling of the FMO Protein Coupled with Gold Nanoparticles.  

PubMed

Plasmonic systems, such as metal nanoparticles, are becoming increasingly important in spectroscopies and devices because of their ability to enhance, even by several orders of magnitude, the photophysical properties of neighboring systems. In particular, it has been shown both theoretically and experimentally that combining nanoplasmonic devices with natural light-harvesting proteins substantially increases the fluorescence and absorption properties of the system. This kind of biohybrid device can have important applications in the characterization and design of efficient light-harvesting systems. In the present work, the FMO light-harvesting protein was combined with gold nanoparticles of different sizes, and its photophysical properties were characterized using a multiscale quantum-mechanical classical-polarizable and continuum model (QM/MMPol/PCM). By optimal tuning of the plasmon resonance of the metal nanoparticles, fluorescence enhancements of up to 2 orders of magnitude were observed. Orientation effects were found to be crucial: amplifications by factors of up to 300 were observed for the absorption process, while the radiative decay of the emitting state increased at most by a factor of 10, mostly as a result of poor alignment of the emitting state with the considered metal aggregates. Despite being a limiting factor for high-fluorescence-enhancement devices, the strong orientation dependence may represent an important feature of the natural light-harvesting system that could allow selective enhancement of a specific excited state of the complex. PMID:25419640

Andreussi, Oliviero; Caprasecca, Stefano; Cupellini, Lorenzo; Guarnetti-Prandi, Ingrid; Guido, Ciro A; Jurinovich, Sandro; Viani, Lucas; Mennucci, Benedetta

2014-12-01

315

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

316

Structure, Dynamics, and Function in the Major Light-Harvesting Complex of Photosystem II  

E-print Network

Structure, Dynamics, and Function in the Major Light-Harvesting Complex of Photosystem II Gabriela of Photosystem II (LHCII), the most abundant PPC in green plants. Studies using two-dimensional electronic to photochemical energy con- version in green plants, the Photosystem II supercomplex, is shown in Fig. 1a

Fleming, Graham R.

317

Crystal structure of an integral membrane light-harvesting complex from photosynthetic bacteria  

Microsoft Academic Search

The crystal structure of the light-harvesting antenna complex (LH2) from Rhodopseudomonas acidophila strain 10050 shows that the active assembly consists of two concentric cylinders of helical protein subunits which enclose the pigment molecules. Eighteen bacteriochlorophyll a molecules sandwiched between the helices form a continuous overlapping ring, and a further nine are positioned between the outer helices with the bacteriochlorin rings

G. McDermott; S. M. Prince; A. A. Freer; A. M. Hawthornthwaite-Lawless; M. Z. Papiz; R. J. Cogdell; N. W. Isaacs

1995-01-01

318

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

PubMed

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

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

2014-02-01

319

Organization of the Bacterial Light-Harvesting Apparatus Rationalized by Exciton Transport Optimization  

E-print Network

Photosynthesis, the process by which energy from sunlight drives cellular metabolism, relies on a unique organization of light-harvesting and reaction center complexes. Recently, the organization of light-harvesting LH2 complexes and dimeric reaction center-light harvesting I-PufX (RC-LH1-PufX) core complexes in membranes of purple non-sulfur bacteria was revealed by atomic force microscopy (AFM)1. Here, we report that the structure of LH2 and its organization within the membrane can be largely rationalized by a simple physical model that relies primarily on exciton transfer optimization. The process through which the light-harvesting complexes transfer excitation energy has been recognized to incorporate both coherent and incoherent processes mediated by the surrounding protein environment. Using the Haken-Strobl model, we show that the organization of the complexes in the membrane can be almost entirely explained by simple electrostatic considerations and that quantum effects act primarily to enforce robust...

Harel, Elad

2011-01-01

320

Organization of the Bacterial Light-Harvesting Apparatus Rationalized by Exciton Transport Optimization  

E-print Network

Photosynthesis, the process by which energy from sunlight drives cellular metabolism, relies on a unique organization of light-harvesting and reaction center complexes. Recently, the organization of light-harvesting LH2 complexes and dimeric reaction center-light harvesting I-PufX (RC-LH1-PufX) core complexes in membranes of purple non-sulfur bacteria was revealed by atomic force microscopy (AFM)1. Here, we report that the structure of LH2 and its organization within the membrane can be largely rationalized by a simple physical model that relies primarily on exciton transfer optimization. The process through which the light-harvesting complexes transfer excitation energy has been recognized to incorporate both coherent and incoherent processes mediated by the surrounding protein environment. Using the Haken-Strobl model, we show that the organization of the complexes in the membrane can be almost entirely explained by simple electrostatic considerations and that quantum effects act primarily to enforce robustness with respect to spatial disorder between complexes. The implications of such an arrangement are discussed in the context of biomimetic photosynthetic analogs capable of transferring energy efficiently across tens to hundreds of nanometers

Elad Harel

2011-10-31

321

Resonant cavity enhanced light harvesting in flexible thin-film organic solar cells  

E-print Network

Resonant cavity enhanced light harvesting in flexible thin-film organic solar cells Nicholas P and photocurrent in flexible organic solar cells. We demonstrate that this enhancement is attributed to a broadband://dx.doi.org/10.1364/OL.38.001431 Organic solar cells (OSCs) are promising candidates for large-scale deployment

Fan, Shanhui

322

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

E-print Network

stages in the conversion of solar energy into chemical and other useful forms of energy for humanEfficient energy transfer in light-harvesting systems, I: optimal temperature, reorganization energy, and spatial- temporal correlations Jianlan Wu, Fan Liu, Young Shen, Jianshu Cao1 and Robert J

Cao, Jianshu

323

Light harvesting by planar photonic crystal in solar cells: The case of amorphous silicon  

E-print Network

Light harvesting by planar photonic crystal in solar cells: The case of amorphous silicon Guillaume particularly focus on photovoltaic devices including amorphous silicon absorbers patterned as 2D PhCs. Physical solar cell, Hydrogenated amorphous silicon, Holographic lithography 1. Introduction During the past

Boyer, Edmond

324

Light Harvesting and Blue-Green Light Induced Non-Photochemical Quenching in Two Different CPhycocyanin Mutants of Synechocystis  

E-print Network

: Cyanobacteria are oxygen-evolving photosynthetic organisms that harvest sunlight and convert excitation energyLight Harvesting and Blue-Green Light Induced Non-Photochemical Quenching in Two Different into chemical energy. Most of the light is absorbed by large light harvesting complexes called phycobilisomes

van Stokkum, Ivo

325

Tracing the Evolution of the Light-Harvesting Antennae in Chlorophyll a/b-Containing Organisms1[OA  

E-print Network

Tracing the Evolution of the Light-Harvesting Antennae in Chlorophyll a/b-Containing Organisms1[OA of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 (P.K.) The light-harvesting and 9 genes. In organisms containing secondary plastids, we found no evidence for orthologs to the plant

Durnford, Dion G.

326

Excitation Energy Transfer in Dimeric Light Harvesting Complex I: A Combined Streak-Camera/Fluorescence Upconversion Study  

E-print Network

Excitation Energy Transfer in Dimeric Light Harvesting Complex I: A Combined Streak harvesting complex I, the peripheral light harvesting complex associated with photosystem I in green plants, was studied by time-resolved fluorescence spectroscopy. A unique combination of two techniques, fluorescence

van Stokkum, Ivo

327

Interplay of slow bath fluctuations and energy transfer in 2D spectroscopy of the FMO light-harvesting complex: benchmarking  

E-print Network

Interplay of slow bath fluctuations and energy transfer in 2D spectroscopy of the FMO light-harvesting-Matthews-Olson light-harvesting complex. Fast fluctuations induce population redistribution between exciton energy in chromophore aggregates.2­8 Spectra are usually simulated using the nonlinear response formalism combined

Mukamel, Shaul

328

Mediation of Ultrafast Light-Harvesting by a Central Dimer in Phycoerythrin 545 Studied by Transient Absorption and Global Analysis  

E-print Network

Mediation of Ultrafast Light-Harvesting by a Central Dimer in Phycoerythrin 545 Studied at 77 K. An evolution-associated difference spectra (EADS) analysis is combined with estimations is extremely fast. Introduction In photosynthesis, light-harvesting antenna proteins bind chromophores

van Stokkum, Ivo

329

Excitons in a photosynthetic light-harvesting system: A combined molecular dynamics, quantum chemistry, and polaron model study  

E-print Network

Excitons in a photosynthetic light-harvesting system: A combined molecular dynamics, quantum of pigment-pigment and pigment-protein interactions in light-harvesting complexes is studied with an approach that combines molecular dynamics simulations with quantum chemistry calculations and a polaron model analysis

Kosztin, Ioan

330

Self-assembly of hybrid structures on nano templates  

NASA Astrophysics Data System (ADS)

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

Wang, Ruomiao

331

Dynamic supramolecular complexes constructed by orthogonal self-assembly.  

PubMed

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

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

2014-07-15

332

Highly efficient nonradiative energy transfer mediated light harvesting in water using aqueous CdTe quantum dot antennas.  

PubMed

We present light harvesting of aqueous colloidal quantum dots to nonradiatively transfer their excitonic excitation energy efficiently to dye molecules in water, without requiring ligand exchange. These as-synthesized CdTe quantum dots that are used as donors to serve as light-harvesting antennas are carefully optimized to match the electronic structure of Rhodamine B molecules used as acceptors for light harvesting in aqueous medium. By varying the acceptor to donor concentration ratio, we measure the light harvesting factor, along with substantial lifetime modifications of these water-soluble quantum dots, from 25.3 ns to 7.2 ns as a result of their energy transfer with efficiency levels up to 86%. Such nonradiative energy transfer mediated light harvesting in aqueous medium holds great promise for future quantum dot multiplexed dye biodetection systems. PMID:20588924

Mutlugun, Evren; Samarskaya, Olga; Ozel, Tuncay; Cicek, Neslihan; Gaponik, Nikolai; Eychmüller, Alexander; Demir, Hilmi Volkan

2010-05-10

333

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

334

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

PubMed

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. PMID:18327918

Kelley, Richard F; Lee, Suk Joong; Wilson, Thea M; Nakamura, Yasuyuki; Tiede, David M; Osuka, Atsuhiro; Hupp, Joseph T; Wasielewski, Michael R

2008-04-01

335

Functional analysis of light-harvesting-like protein 3 (LIL3) and its light-harvesting chlorophyll-binding motif in Arabidopsis.  

PubMed

The light-harvesting complex (LHC) constitutes the major light-harvesting antenna of photosynthetic eukaryotes. LHC contains a characteristic sequence motif, termed LHC motif, consisting of 25-30 mostly hydrophobic amino acids. This motif is shared by a number of transmembrane proteins from oxygenic photoautotrophs that are termed light-harvesting-like (LIL) proteins. To gain insights into the functions of LIL proteins and their LHC motifs, we functionally characterized a plant LIL protein, LIL3. This protein has been shown previously to stabilize geranylgeranyl reductase (GGR), a key enzyme in phytol biosynthesis. It is hypothesized that LIL3 functions to anchor GGR to membranes. First, we conjugated the transmembrane domain of LIL3 or that of ascorbate peroxidase to GGR and expressed these chimeric proteins in an Arabidopsis mutant lacking LIL3 protein. As a result, the transgenic plants restored phytol-synthesizing activity. These results indicate that GGR is active as long as it is anchored to membranes, even in the absence of LIL3. Subsequently, we addressed the question why the LHC motif is conserved in the LIL3 sequences. We modified the transmembrane domain of LIL3, which contains the LHC motif, by substituting its conserved amino acids (Glu-171, Asn-174, and Asp-189) with alanine. As a result, the Arabidopsis transgenic plants partly recovered the phytol-biosynthesizing activity. However, in these transgenic plants, the LIL3-GGR complexes were partially dissociated. Collectively, these results indicate that the LHC motif of LIL3 is involved in the complex formation of LIL3 and GGR, which might contribute to the GGR reaction. PMID:24275650

Takahashi, Kaori; Takabayashi, Atsushi; Tanaka, Ayumi; Tanaka, Ryouichi

2014-01-10

336

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

2013-10-01

337

Control of gene expression by modulated self-assembly  

E-print Network

Numerous transcription factors self-assemble into different order oligomeric species in a way that is actively regulated by the cell. Until now, no general functional role has been identified for this widespread process. Here we capture the effects of modulated self-assembly in gene expression with a novel quantitative framework. We show that this mechanism provides precision and flexibility, two seemingly antagonistic properties, to the sensing of diverse cellular signals by systems that share common elements present in transcription factors like p53, NF-kappaB, STATs, Oct, and RXR. Applied to the nuclear hormone receptor RXR, this framework accurately reproduces a broad range of classical, previously unexplained, sets of gene expression data and corroborates the existence of a precise functional regime with flexible properties that can be controlled both at a genome-wide scale and at the individual promoter level.

Vilar, Jose M G

2011-01-01

338

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

339

Self-assembled liquid-crystal microlasers, microresonators, and microfibres  

NASA Astrophysics Data System (ADS)

When liquid crystals are dispersed in an immiscible fluid, microdroplets of liquid crystal are spontaneously formed in a fraction of a second. They have optically anisotropic internal structure, which is determined by the ordering of liquid crystal molecules at the interface. Spherical droplets of a nematic liquid crystal can function as whispering-gallery-mode microresonators with an unprecedented width of wavelength tunability by an electric field. WGM pulsed lasing in dyedoped nematic microdroplets is sensitive to strain, temperature and presence of molecules that change molecular orientation at the interface. Omnidirectional 3D lasing was demonstrated in droplets of chiral nematic liquid crystals that form 3D Bragg-onion resonators. We present recent progress in this field, including electric tuning of 3D lasing from chiral nematic droplets and self-assembly of ferroelectric smectic-C* microdroplets with the onion-Bragg structure. We show that anisotropic fibres could be self-assembled from smectic liquid crystals.

Muševi?, I.; Peng, Huang; Nikkhou, M.; Humar, M.

2014-03-01

340

Control of gene expression by modulated self-assembly  

E-print Network

Numerous transcription factors self-assemble into different order oligomeric species in a way that is actively regulated by the cell. Until now, no general functional role has been identified for this widespread process. Here we capture the effects of modulated self-assembly in gene expression with a novel quantitative framework. We show that this mechanism provides precision and flexibility, two seemingly antagonistic properties, to the sensing of diverse cellular signals by systems that share common elements present in transcription factors like p53, NF-kappaB, STATs, Oct, and RXR. Applied to the nuclear hormone receptor RXR, this framework accurately reproduces a broad range of classical, previously unexplained, sets of gene expression data and corroborates the existence of a precise functional regime with flexible properties that can be controlled both at a genome-wide scale and at the individual promoter level.

Jose M. G. Vilar; Leonor Saiz

2011-05-25

341

Self-assembling enzymes and the origins of the cytoskeleton  

PubMed Central

The bacterial cytoskeleton is composed of a complex and diverse group of proteins that self-assemble into linear filaments. These filaments support and organize cellular architecture and provide a dynamic network controlling transport and localization within the cell. Here, we review recent discoveries related to a newly appreciated class of self-assembling proteins that expand our view of the bacterial cytoskeleton and provide potential explanations for its evolutionary origins. Specifically, several types of metabolic enzymes can form structures similar to established cytoskeletal filaments and, in some cases, these structures have been repurposed for structural uses independent of their normal role. The behaviors of these enzymes suggest that some modern cytoskeletal proteins may have evolved from dual-role proteins with catalytic and structural functions. PMID:22014508

Barry, Rachael; Gitai, Zemer

2011-01-01

342

Self Assembled Structures by Directional Solidification of Eutectics  

NASA Technical Reports Server (NTRS)

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

Dynys, Frederick W.; Sayir, Ali

2004-01-01

343

Self-Reproduction of Nanoparticles through Synergistic Self-Assembly.  

PubMed

We describe a self-reproduction mechanism of nanometer-sized particles (i.e., nanodiscs) through chemical ligation of the precursors and self-assembly of the building blocks. The ligation reaction was accelerated on lipid bilayer surfaces, and the products spontaneously assembled into nanodiscs with lipid molecules. With the increase in the number of nanodiscs, a rapid proliferation of the nanodiscs occurred through the spatial rearrangements of the molecules between the pre-existing nanodiscs and the unreacted materials, rather than template- or complex-enhanced ligation of the precursors. The subsequent process of surface-enhanced ligation of integrated precursors matured the nanoparticles into identical copies of the pre-existing assembly. Our study showed that the synergistic self-assembly mechanism probably underlie the self-replication principles for heterogeneous multimolecular systems. PMID:25541673

Ikeda, Keisuke; Nakano, Minoru

2015-01-13

344

DNA Self-Assembly: From Chirality to Evolution  

PubMed Central

Transient or long-term DNA self-assembly participates in essential genetic functions. The present review focuses on tight DNA-DNA interactions that have recently been found to play important roles in both controlling DNA higher-order structures and their topology. Due to their chirality, double helices are tightly packed into stable right-handed crossovers. Simple packing rules that are imposed by DNA geometry and sequence dictate the overall architecture of higher order DNA structures. Close DNA-DNA interactions also provide the missing link between local interactions and DNA topology, thus explaining how type II DNA topoisomerases may sense locally the global topology. Finally this paper proposes that through its influence on DNA self-assembled structures, DNA chirality played a critical role during the early steps of evolution. PMID:23591841

Timsit, Youri

2013-01-01

345

Stable doping of carbon nanotubes via molecular self assembly  

SciTech Connect

We report a novel method for stable doping of carbon nanotubes (CNT) based on methods of molecular self assembly. A conformal growth of a self-assembled monolayer of fluoroalkyl trichloro-silane (FTS) at CNT surfaces results in a strong increase of the sheet conductivity of CNT electrodes by 60–300%, depending on the CNT chirality and composition. The charge carrier mobility of undoped partially aligned CNT films was independently estimated in a field-effect transistor geometry (?100?cm{sup 2}V{sup ?1}s{sup ?1}). The hole density induced by the FTS monolayer in CNT sheets is estimated to be ?1.8?×?10{sup 14?}cm{sup ?2}. We also show that FTS doping of CNT anodes greatly improves the performance of organic solar cells. This large and stable doping effect, easily achieved in large-area samples, makes this approach very attractive for applications of CNTs in transparent and flexible electronics.

Lee, B.; Chen, Y.; Podzorov, V., E-mail: podzorov@physics.rutgers.edu [Department of Physics and Institute for Advanced Materials and Devices for Nanotechnology, Rutgers University, New Jersey 08854 (United States); Cook, A.; Zakhidov, A. [Department of Physics and NanoTech Institute, University of Texas at Dallas, Richardson, Texas 75083 (United States)

2014-10-14

346

Self-Assembly of Graphene on Carbon Nanotube Surfaces  

PubMed Central

The rolling up of a graphene sheet into a tube is a standard visualization tool for illustrating carbon nanotube (CNT) formation. However, the actual processes of rolling up graphene sheets into CNTs in laboratory syntheses have never been demonstrated. Here we report conformal growth of graphene by carbon self-assembly on single-wall and multi-wall CNTs using chemical vapor deposition (CVD) of methane without the presence of metal catalysts. The new graphene layers roll up into seamless coaxial cylinders encapsulating the existing CNTs, but their adhesion to the primary CNTs is weak due to the existence of lattice misorientation. Our study shows that graphene nucleation and growth by self-assembly of carbon on the inactive carbon basal plane of CNTs occurs by a new mechanism that is markedly different from epitaxial growth on metal surfaces, opening up the possibility of graphene growth on many other non-metal substrates by simple methane CVD. PMID:23912638

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

2013-01-01

347

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

348

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. PMID:21160557

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

2010-01-01

349

Reinforcement of Shear Thinning Protein Hydrogels by Responsive Block Copolymer Self-Assembly  

PubMed Central

Shear thinning hydrogels are promising materials that exhibit rapid self-healing following the cessation of shear, making them attractive for a variety of applications including injectable biomaterials. In this work, self-assembly is demonstrated as a strategy to introduce a reinforcing network within shear thinning artificially engineered protein gels, enabling a responsive transition from an injectable state at low temperatures with a low yield stress to a stiffened state at physiological temperatures with resistance to shear thinning, higher toughness, and reduced erosion rates and creep compliance. Protein-polymer triblock copolymers capable of the responsive self-assembly of two orthogonal networks have been synthesized by conjugating poly(N-isopropylacrylamide) to the N- and C- termini of a protein midblock decorated with coiled-coil self-associating domains. Midblock association forms a shear-thinning network, while endblock aggregation at elevated temperatures introduces a second, independent physical network into the protein hydrogel. These new, reversible crosslinks introduce extremely long relaxation times and lead to a five-fold increase in the elastic modulus, significantly larger than is expected from transient network theory. Thermoresponsive reinforcement reduces the high temperature creep compliance by over four orders of magnitude, decreases the erosion rate by at least a factor of five, and increases the yield stress by up to a factor of seven. The reinforced hydrogels also exhibit enhanced resistance to plastic deformation and failure in uniaxial compression. Combined with the demonstrated potential of shear thinning artificial protein hydrogels for various uses, including the minimally-invasive implantation of bioactive scaffolds, this reinforcement mechanism broadens the range of applications that can be addressed with shear-thinning physical gels.

Glassman, Matthew J.; Chan, Jacqueline

2014-01-01

350

Self-Assembled Semiconductor Quantum Dots with Nearly Uniform Sizes  

Microsoft Academic Search

Self-assembled PbSe quantum dots on PbTe quasisubstrates, where the quasisubstrate layer is grown on Si(111), show a size distribution as low as 2%, below any other reported size distribution. The result is explained by nonoverlapping diffusion radii for most of the dots and their nucleation occurring mainly at defects (glide steps of the quasisubstrate), conditions which are not met by

K. Alchalabi; D. Zimin; G. Kostorz; H. Zogg

2003-01-01

351

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

352

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

353

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

2013-07-10

354

Dispersion of nanoparticulate suspensions using self-assembled surfactant aggregates  

NASA Astrophysics Data System (ADS)

The dispersion of particles is critical for several industrial applications such as paints, inks, coatings, and cosmetics. Several emerging applications such as abrasives for precision polishing, and drug delivery systems are increasingly relying on nanoparticulates to achieve the desired performance. In the case of nanoparticles, the dispersion becomes more challenging because of the lack of fundamental understanding of dispersant adsorption and interparticle force prediction. Additionally, many of these processes use severe processing environments such as high normal forces (>100 mN/m), high shear forces (>10,000 s -1), and high ionic strengths (>0.1 M). Under such processing conditions, traditionally used dispersants based on electrostatics, and steric force repulsion mechanism may not be adequate. Hence, the development of optimally performing dispersants requires a fundamental understanding of the dispersion mechanism at the atomic/molecular scale. This study explores the use of self-assembled surfactant aggregates at the solid-liquid interface for dispersing nanoparticles in severe processing environments. Surfactant molecules can provide a feasible alternative to polymeric or inorganic dispersants for stabilizing ultrafine particles. The barrier to aggregation in the presence of surfactant molecules was measured using atomic force microscopy. The barrier heights correlated to suspension stability. To understand the mechanism for nanoparticulate suspension stability in the presence of surfactant films, the interface was characterized using zeta potential, contact angle, adsorption, and FT-IR (adsorbed surfactant film structure measurements). The effect of solution conditions such as pH and ionic strength on the suspension stability, and the self-assembled surfactant films was also investigated. It was determined that a transition from a random to an ordered orientation of the surfactant molecules at the interface was responsible for stability of nanoparticulates. Additionally, the role of the surface in surfactant self-assembly was investigated. Mechanical and thermodynamic properties of the self-assembled layer at the solid-liquid interface were calculated based on experimental results, and compared to the corresponding properties in the bulk solution.

Singh, Pankaj Kumar

355

Electronic transport in self-assembled quantum dots  

Microsoft Academic Search

This dissertation discusses electron transport measurements in InAs self-assembled quantum dots. Strain induced clustering of InAs grown on GaAs results in coherent, defect free islands approximately 300A diameter. The dots are grown in close proximity (100A) to a two dimensional electron gas (2DEG) at a GaAs\\/AlGaAs heterojunction. The 2DEG is laterally patterned with fine metal gates and shallow trenches fabricated

Steven Louis Konsek

2001-01-01

356

Propagating waves of self-assembly in organosilane monolayers  

PubMed Central

Wavefronts associated with reaction–diffusion and self-assembly processes are ubiquitous in the natural world. For example, propagating fronts arise in crystallization and diverse other thermodynamic ordering processes, in polymerization fronts involved in cell movement and division, as well as in the competitive social interactions and population dynamics of animals at much larger scales. Although it is often claimed that self-sustaining or autocatalytic front propagation is well described by mean-field “reaction–diffusion” or “phase field” ordering models, it has recently become appreciated from simulations and theoretical arguments that fluctuation effects in lower spatial dimensions can lead to appreciable deviations from the classical mean-field theory (MFT) of this type of front propagation. The present work explores these fluctuation effects in a real physical system. In particular, we consider a high-resolution near-edge x-ray absorption fine structure spectroscopy (NEXAFS) study of the spontaneous frontal self-assembly of organosilane (OS) molecules into self-assembled monolayer (SAM) surface-energy gradients on oxidized silicon wafers. We find that these layers organize from the wafer edge as propagating wavefronts having well defined velocities. In accordance with two-dimensional simulations of this type of front propagation that take fluctuation effects into account, we find that the interfacial widths w(t) of these SAM self-assembly fronts exhibit a power-law broadening in time, w(t) ? t?, rather than the constant width predicted by MFT. Moreover, the observed exponent values accord rather well with previous simulation and theoretical estimates. These observations have significant implications for diverse types of ordering fronts that occur under confinement conditions in biological or materials-processing contexts. PMID:17566108

Douglas, Jack F.; Efimenko, Kirill; Fischer, Daniel A.; Phelan, Fredrick R.; Genzer, Jan

2007-01-01

357

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

358

Self-Assembled Three-Dimensional Non-Volatile Memories  

Microsoft Academic Search

The continuous increase in capacity of non-volatile data storage systems will lead to bit densities of one bit per atom in 2020. Beyond this point, capacity can be increased by moving into the third dimension. We propose to use self-assembly of nanosized elements, either as a loosely organised associative network or into a cross-point architecture. When using principles requiring electrical

Leon Abelmann; Niels Tas; Erwin Berenschot; Miko Elwenspoek

2010-01-01

359

Self-Assembly of Phenylalanine-Based Molecules.  

PubMed

Using molecular dynamics, we study the self-assembly of phenylalanine with charged end-groups at various temperatures and concentrations. As in the case of diphenylalanine, we observe the formation of nanotubes; however, phenylalanine aggregates in layers of four, not six, molecules. The observed aggregates are consistent with recent experimental measurements of fibrils obtained from mice with phenylketonuria. We investigate the stability and the mechanism by which these tubular structures form and discuss potential toxicity mechanisms. PMID:25347763

German, Helen W; Uyaver, Sahin; Hansmann, And Ulrich H E

2014-11-01

360

Self-Assembled Hexa-peri-hexabenzocoronene Graphitic Nanotube  

Microsoft Academic Search

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

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

2004-01-01

361

Self assembled monolayers of rigid thiols on Gold  

Microsoft Academic Search

Self assembled monolayers (SAM) of phi-functionalized mercaptobiphenyls (phi-MBP) are stable, molecularly engineered ultrathin organic films, which can be used for the design of model surfaces with well-defined chemical and physical properties. For example, the number and distribution of terminal hydroxyl groups can be tailored to study water-surface interactions or the chemisorption of organic molecules from solution. We have prepared and

Svetlana Stoycheva; Joerg Fick; Alexander Kornviakov; Avi Ulman; Michael Himmelhaus; Michael Grunze

2005-01-01

362

Corner Cube Reflectors by Surface Tension Self-Assembly  

Microsoft Academic Search

A method of fabricating micromachined Corner Cube Reflectors (CCRs) with high surface flatness and accurate control of mirror angle is demonstrated. A parallel, automated three-dimensional self-assembly process is presented, using bonded silicon-on-insulator material and out-of-plane rotation powered by the surface tension of thick photoresist pads. Precise alignment is achieved by minimising the number of movable parts and controlling the assembly

Y. K. Hong; R. R. A. Syms; K. S. J. Pister; L. X. Zhou

363

Lighting up cells with lanthanide self-assembled helicates  

PubMed Central

Lanthanide bioprobes and bioconjugates are ideal luminescent stains in view of their low propensity to photobleaching, sharp emission lines and long excited state lifetimes permitting time-resolved detection for enhanced sensitivity. We show here how the interplay between physical, chemical and biochemical properties allied to microfluidics engineering leads to self-assembled dinuclear lanthanide luminescent probes illuminating live cells and selectively detecting biomarkers expressed by cancerous human breast cells. PMID:24511387

Bünzli, Jean-Claude G.

2013-01-01

364

Logical computation using algorithmic self-assembly of DNA triple-crossover molecules.  

PubMed

Recent work has demonstrated the self-assembly of designed periodic two-dimensional arrays composed of DNA tiles, in which the intermolecular contacts are directed by 'sticky' ends. In a mathematical context, aperiodic mosaics may be formed by the self-assembly of 'Wang' tiles, a process that emulates the operation of a Turing machine. Macroscopic self-assembly has been used to perform computations; there is also a logical equivalence between DNA sticky ends and Wang tile edges. This suggests that the self-assembly of DNA-based tiles could be used to perform DNA-based computation. Algorithmic aperiodic self-assembly requires greater fidelity than periodic self-assembly, because correct tiles must compete with partially correct tiles. Here we report a one-dimensional algorithmic self-assembly of DNA triple-crossover molecules that can be used to execute four steps of a logical (cumulative XOR) operation on a string of binary bits. PMID:11028996

Mao, C; LaBean, T H; Relf, J H; Seeman, N C

2000-09-28

365

Logical computation using algorithmic self-assembly of DNA triple-crossover molecules  

NASA Astrophysics Data System (ADS)

Recent work has demonstrated the self-assembly of designed periodic two-dimensional arrays composed of DNA tiles, in which the intermolecular contacts are directed by `sticky' ends. In a mathematical context, aperiodic mosaics may be formed by the self-assembly of `Wang' tiles, a process that emulates the operation of a Turing machine. Macroscopic self-assembly has been used to perform computations; there is also a logical equivalence between DNA sticky ends and Wang tile edges. This suggests that the self-assembly of DNA-based tiles could be used to perform DNA-based computation. Algorithmic aperiodic self-assembly requires greater fidelity than periodic self-assembly, because correct tiles must compete with partially correct tiles. Here we report a one-dimensional algorithmic self-assembly of DNA triple-crossover molecules that can be used to execute four steps of a logical (cumulative XOR) operation on a string of binary bits.

Mao, Chengde; LaBean, Thomas H.; Reif, John H.; Seeman, Nadrian C.

2000-09-01

366

Size-controlled self-assembly of superparamagnetic polymersomes.  

PubMed

We report the size-controlled self-assembly of polymersomes through the cooperative self-assembly of nanoparticles and amphiphilic polymers. Polymersomes densely packed with magnetic nanoparticles in the polymersome membrane (magneto-polymersome) were fabricated with a series of different sized iron oxide nanoparticles. The distribution of nanoparticles in a polymersome membrane was size-dependent; while small nanoparticles were dispersed in a polymer bilayer, large particles formed a well-ordered superstructure at the interface between the inner and outer layer of a bilayer membrane. The yield of magneto-polymersomes increased with increasing the diameter of incorporated nanoparticles. Moreover, the size of the polymersomes was effectively controlled by varying the size of incorporated nanoparticles. This size-dependent self-assembly was attributed to the polymer chain entropy effect and the size-dependent localization of nanoparticles in polymersome bilayers. The transverse relaxation rates (r2) of magneto-polymersomes increased with increasing the nanoparticle diameter and decreasing the size of polymersomes, reaching 555 ± 24 s(-1) mM(-1) for 241 ± 16 nm polymersomes, which is the highest value reported to date for superparamagnetic iron oxide nanoparticles. PMID:24369711

Hickey, Robert J; Koski, Jason; Meng, Xin; Riggleman, Robert A; Zhang, Peijun; Park, So-Jung

2014-01-28

367

DNA assisted self-assembly of PAMAM dendrimers.  

PubMed

We report DNA assisted self-assembly of polyamidoamine (PAMAM) dendrimers using all atom Molecular Dynamics (MD) simulations and present a molecular level picture of a DNA-linked PAMAM dendrimer nanocluster, which was first experimentally reported by Choi et al. (Nano Lett., 2004, 4, 391-397). We have used single stranded DNA (ssDNA) to direct the self-assembly process. To explore the effect of pH on this mechanism, we have used both the protonated (low pH) and nonprotonated (high pH) dendrimers. In all cases studied here, we observe that the DNA strand on one dendrimer unit drives self-assembly as it binds to the complementary DNA strand present on the other dendrimer unit, leading to the formation of a DNA-linked dendrimer dimeric complex. However, this binding process strongly depends on the charge of the dendrimer and length of the ssDNA. We observe that the complex with a nonprotonated dendrimer can maintain a DNA length dependent inter-dendrimer distance. In contrast, for complexes with a protonated dendrimer, the inter-dendrimer distance is independent of the DNA length. We attribute this observation to the electrostatic complexation of a negatively charged DNA strand with the positively charged protonated dendrimer. PMID:25205346

Mandal, Taraknath; Kumar, Mattaparthi Venkata Satish; Maiti, Prabal K

2014-10-01

368

Self-assembly of lipopolysaccharide layers on allantoin crystals.  

PubMed

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

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

2014-08-01

369

Cyclic peptide-polymer complexes and their self-assembly.  

PubMed

The efficient synthesis of novel chiral cyclic peptides cyclo[NHCHX-CH=CHCH(2)CO(NHCH(2)CH=CHCH(2)CO)(2)] designed to develop hydrogen-bonding interactions with suitable polymers is described. Complexation of a carboxylic acid derivatized cyclic peptide 2 (X = CH(2)OCOCH(2)CH(2)CO(2)H) capable of self-assembling as "endless" tubes, with poly(vinyl alcohol) (PVA) led to a vast weak-interaction network, in which the cyclopeptide developed extensive hydrogen-bonding interactions with the hydroxyl groups of PVA through not only the carboxylic acid, but also its ester carbonyl and amide groups. In aqueous solution, the peptide/PVA complexes self-assemble into long-grain ricelike aggregates compatible with the stacking of cyclic peptides through intercycle hydrogen bonds. Upon casting on silicon wafer, the anisotropic aggregates can coalesce to form filaments tens of micrometers long. The study demonstrates that complexing functionalized cyclic peptides with polymers through hydrogen bonding is a useful approach for using polymers to mediate the self-assembly and self-organization of cyclic peptides. PMID:19263443

Bélanger, Dominique; Tong, Xia; Soumaré, Sadia; Dory, Yves L; Zhao, Yue

2009-01-01

370

Molecular recognition directed self-assembly of supramolecular architectures  

NASA Astrophysics Data System (ADS)

This paper reviews some of our research on three classes of supramolecular architectures which are generated via various combinations of molecular, macromolecular and supramolecular chemistry. The ability of these supramolecular architectures to form liquid crystalline phases is determined by the shape of the self-assembled architecture and will be used to visualize it via various characterization techniques. The molecular design of selected examples of structural units containing taper shaped exo-receptors and crown-ether, oligooxyethylenic, and H-bonding based endo-receptors which self-assemble into cylindrical channel-like architectures via principles resembling those of tobacco mosaic virus (TMV), of macrocyclics which self-assemble into a willow-like architecture will be discussed. In the case of TMV-like supramolecular architectures a comparison between various supramolecular (generated via H-bonding, ionic and electrostatic interactions) and molecular 'polymer backbones' will be made. The present state of the art of the engineering of these supramolecular architectures and some possible novel material functions derived from them will be briefly mentioned.

Percec, C.; Heck, J.; Johansson, G.; Tomazos, D.; Kawasumi, M.

1994-06-01

371

Polymer adsorption-driven self-assembly of nanostructures.  

PubMed

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

Chakraborty, A K; Golumbfskie, A J

2001-01-01

372

Synthesis and self-assembly of a DNA molecular brush.  

PubMed

We report herein on the polymer-crystallization-assisted thiol-ene photosynthesis of an amphiphilic comb/graft DNA copolymer, or molecular brush, composed of a hydrophobic poly(2-oxazoline) backbone and hydrophilic short single-stranded nucleic acid grafts. Coupling efficiencies are above 60% and thus higher as compared with the straight solid-phase-supported synthesis of amphiphilic DNA block copolymers. The DNA molecular brushes self-assemble into sub-micron-sized spherical structures in water as evidenced by light scattering as well as atomic force and electron microscopy imaging. The nucleotide sequences remain functional, as assessed by UV and fluorescence spectroscopy subsequent to isoindol synthesis at the surface of the structures. The determination of a vesicular morphology is supported by encapsulation and subsequent spectroscopy monitoring of the release of a water-soluble dye and spectroscopic quantification of the hybridization efficiency (30% in average) of the functional nucleic acid strands engaged in structure formation: about one-half of the nucleotide sequences are available for hybridization, whereas the other half are hindered within the self-assembled structure. Because speciation between complementary and non complementary sequences in the medium could be ascertained by confocal laser scanning microscopy, the stable self-assembled molecular brushes demonstrate the potential for sensing applications. PMID:25105945

Kedracki, Dawid; Chekini, Mahshid; Maroni, Plinio; Schlaad, Helmut; Nardin, Corinne

2014-09-01

373

Capillary-based static self-assembly in higher organisms  

PubMed Central

Organized structures produced by dynamic self-assembly are often observed in animal groups. Static self-assembly, however, has to date only been observed at the cellular and sub-cellular levels. The aim of this study was to analyse organized structures in immobile whirligig beetle groups on the water surface. We used theoretical and computational approaches to model the meniscus around whirligig beetles and to calculate the surface energy for configurations involving two beetles. Theoretical predictions were then tested using live insects and resin casts. Observations were also made for three and more casts. The meniscus of whirligig beetles had a bipolar shape with two concave parts. For two beetles, predicted configurations based on energy minima corresponded to beetles in contact by their extremities, forming lines and arrows, and agreed well with observations. Experimental results for three and more beetle casts revealed new geometrical arrangements similar to those obtained with colloids at interfaces. This study provides the first example of static self-assembly at the inter-organism level and shows the importance of capillary interactions in such formations. We identify the ecological context in which our findings are of relevance. PMID:21367777

Voise, Jonathan; Schindler, Michael; Casas, Jérôme; Raphaël, Elie

2011-01-01

374

Surface effects mediate self-assembly of amyloid-? peptides.  

PubMed

Here we present a label-free method for studying the mechanism of surface effects on amyloid aggregation. In this method, spin-coating is used to rapidly dry samples, in a homogeneous manner, after various incubation times. This technique allows the control of important parameters for self-assembly, such as the surface concentration. Atomic force microscopy is then used to obtain high-resolution images of the morphology. While imaging under dry conditions, we show that the morphologies of self-assembled aggregates of a model amyloid-? peptide, A?(12-28), are strongly influenced by the local surface concentration. On mica surfaces, where the peptides can freely diffuse, homogeneous, self-assembled protofibrils formed spontaneously and grew longer with longer subsequent incubation. The surface fibrillization rate was much faster than the rates of fibril formation observed in solution, with initiation occurring at much lower concentrations. These data suggest an alternative pathway for amyloid formation on surfaces where the nucleation stage is either bypassed entirely or too fast to measure. This simple preparation procedure for high-resolution atomic force microscopy imaging of amyloid oligomers and protofibrils should be applicable to any amyloidogenic protein species. PMID:25229233

Lin, Yi-Chih; Petersson, E James; Fakhraai, Zahra

2014-10-28

375

Versatile Bisethynyl[60]fulleropyrrolidine Scaffolds for Mimicking Artificial Light-Harvesting Photoreaction Centers.  

PubMed

Fullerene-based tetrads, triads, and dyads are presented in which [60]fulleropyrrolidine synthons are linked to an oligo(p-phenyleneethynylene) antenna at the nitrogen atom and to electron-donor phenothiazine (PTZ) and/or ferrocene (Fc) moieties at the ? carbon of the pyrrolidine cycle through an acetylene spacer. Cyclic voltammetry and UV/ Vis absorption spectra evidence negligible ground-state electronic interactions among the subunits. By contrast, strong excited-state interactions are detected upon selective light irradiation of the antenna (UV) or of the fullerene scaffold (Vis). When only PTZ is present as electron donor, photoinduced electron transfer to the fullerene unit is unambiguously detected in benzonitrile, but this is not the case when Fc is part of the multicomponent system. These results suggest that Fc is a formidable energy transfer quencher and caution should be used in choosing it as electron donor to promote efficient charge separation in multicomponent arrays. PMID:25418041

Kremer, Adrian; Bietlot, Emerance; Zanelli, Alberto; Malicka, Joanna M; Armaroli, Nicola; Bonifazi, Davide

2014-11-21

376

An Investigation of Computational Models for Surfactant Self-Assembly  

NASA Astrophysics Data System (ADS)

Surfactants are used in a wide variety of industrial and biological applications due to their self-assembling ability. Computational models can be used to understand the self-assembly process on an atomistic level. Creating a model that can quantitatively reproduce system properties has proven elusive. Since atomistic models can have difficulty reaching the necessary time and length scales for self-assembly, models have been investigated that are of different resolutions and predictive power. Molecular dynamics and Monte Carlo simulations were performed to determine the ability of these models to reproduce thermodynamic properties of surfactant self-assembly. A recent set of explicit solvent coarse grained (CG) chemistry-specific models are able to reproduce the equilibrium properties of critical micelle concentration (CMC) and aggregate size distribution. Non-ionic and zwitterionic surfactants were modeled using molecular dynamics. The CG models are able to achieve equilibrium in reduced computational time. Replica exchange can also provide a modest improvement in equilibration time. However, further model refinement is needed in order to match experimental values quantitatively and the models are unable to capture the temperature dependence of these properties due to the lack of solvent orientation. Two additional studies with two different types of models were performed. Using Grand Canonical Monte Carlo and histogram reweighting, an implicit solvent model was developed with the ability to capture the temperature dependence of the CMC of ionic surfactants. The model can approximate the temperature dependence for two cationic surfactants without direct parameterization. The phase space of an atomistic model used to model sodium alkyl sulfates was also explored. The model is able to qualitatively account for the decrease in CMC with increasing salt concentration. The method of assessing the CMC of a model was improved by using an empirical equation which accounts for total surfactant concentration and counterion association. This method provided agreement in the CMC across multiple total surfactant concentrations. Also, the model is shown to qualitatively reproduce the effect of alkyl tail length and the minimum in the CMC with respect to temperature. Other atomistic models were tested and shown to provide higher CMC values, but all models underpredict the CMC. This indicates that there is a need for further development of atomistic models which are frequently used to parameterize coarser grained models. All of these studies can provide insight for developing a quantitative model for surfactant self-assembly.

Sanders, Samantha A.

377

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.

378

Molecular Self-Assembly into One-Dimensional Nanostructures  

PubMed Central

CONSPECTUS Self-assembly of small molecules into one-dimensional nanostructures offers many potential applications in electronically and biologically active materials. The recent advances discussed in this Account demonstrate how researchers can use the fundamental principles of supramolecular chemistry to craft the size, shape, and internal structure of nanoscale objects. In each system described here, we used atomic force microscopy (AFM) and transmission electron microscopy (TEM) to study the assembly morphology. Circular dichroism, nuclear magnetic resonance, infrared, and optical spectroscopy provided additional information about the self-assembly behavior in solution at the molecular level. Dendron rod–coil molecules self-assemble into flat or helical ribbons. They can incorporate electronically conductive groups and can be mineralized with inorganic semiconductors. To understand the relative importance of each segment in forming the supramolecular structure, we synthetically modified the dendron, rod, and coil portions. The self-assembly depended on the generation number of the dendron, the number of hydrogen-bonding functions, and the length of the rod and coil segments. We formed chiral helices using a dendron–rod–coil molecule prepared from an enantiomerically enriched coil. Because helical nanostructures are important targets for use in biomaterials, nonlinear optics, and stereoselective catalysis, researchers would like to precisely control their shape and size. Tripeptide-containing peptide lipid molecules assemble into straight or twisted nanofibers in organic solvents. As seen by AFM, the sterics of bulky end groups can tune the helical pitch of these peptide lipid nanofibers in organic solvents. Furthermore, we demonstrated the potential for pitch control using trans-to-cis photoisomerization of a terminal azobenzene group. Other molecules called peptide amphiphiles (PAs) are known to assemble in water into cylindrical nanostructures that appear as nanofiber bundles. Surprisingly, TEM of a PA substituted by a nitrobenzyl group revealed assembly into quadruple helical fibers with a braided morphology. Upon photocleavage of this the nitrobenzyl group, the helices transform into single cylindrical nanofibers. Finally, inspired by the tobacco mosaic virus, we used a dumbbell-shaped, oligo(phenylene ethynylene) template to control the length of a PA nanofiber self-assembly (<10 nm). AFM showed complete disappearance of long nanofibers in the presence of this rigid-rod template. Results from quick-freeze/deep-etch TEM and dynamic light scattering demonstrated the templating behavior in aqueous solution. This strategy could provide a general method to control size the length of non-spherical supramolecular nanostructures. PMID:18754628

PALMER, LIAM C.; STUPP, SAMUEL I.

2008-01-01

379

Energy transfer in an LH4-like light harvesting complex from the aerobic purple photosynthetic bacterium Roseobacter denitrificans  

SciTech Connect

A peripheral light-harvesting complex from the aerobic purple bacterium Roseobacter (R.) denitrificans was purified and its photophysical properties characterized. The complex contains two types of pigments, bacteriochlorophyll (BChl) a and the carotenoid (Car) spheroidenone and possesses unique spectroscopic properties. It appears to lack the B850 bacteriochlorophyll a Q{sub y} band that is typical for similar light-harvesting complex 2 antennas. Circular dichroism and low temperature steady-state absorption spectroscopy revealed that the B850 band is present but is shifted significantly to shorter wavelengths and overlaps with the B800 band at room temperature. Such a spectral signature classifies this protein as a member of the light-harvesting complex 4 class of peripheral light-harvesting complexes, along with the previously known light-harvesting complex 4 from Rhodopseudomonas palustris. The influence of the spectral change on the light-harvesting ability was studied using steady-state absorption, fluorescence, circular dichroism, femtosecond and microsecond time-resolved absorption and time-resolved fluorescence spectroscopies. The results were compared to the properties of the similar (in pigment composition) light-harvesting complex 2 from aerobically grown Rhodobacter sphaeroides and are understood within the context of shared similarities and differences and the putative influence of the pigments on the protein structure and its properties.

Niedzwiedzki, Dariusz; Fuciman, Marcel; Frank, Harry A.; Blankenship, R. E.

2011-01-01

380

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

381

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

2013-02-01

382

Hyperdiversity of Genes Encoding Integral Light-Harvesting Proteins in the Dinoflagellate Symbiodinium sp  

PubMed Central

The superfamily of light-harvesting complex (LHC) proteins is comprised of proteins with diverse functions in light-harvesting and photoprotection. LHC proteins bind chlorophyll (Chl) and carotenoids and include a family of LHCs that bind Chl a and c. Dinophytes (dinoflagellates) are predominantly Chl c binding algal taxa, bind peridinin or fucoxanthin as the primary carotenoid, and can possess a number of LHC subfamilies. Here we report 11 LHC sequences for the chlorophyll a-chlorophyll c2-peridinin protein complex (acpPC) subfamily isolated from Symbiodinium sp. C3, an ecologically important peridinin binding dinoflagellate taxa. Phylogenetic analysis of these proteins suggests the acpPC subfamily forms at least three clades within the Chl a/c binding LHC family; Clade 1 clusters with rhodophyte, cryptophyte and peridinin binding dinoflagellate sequences, Clade 2 with peridinin binding dinoflagellate sequences only and Clades 3 with heterokontophytes, fucoxanthin and peridinin binding dinoflagellate sequences. PMID:23112815

Boldt, Lynda; Yellowlees, David; Leggat, William

2012-01-01

383

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

384

Silica Entrapment for Significantly Stabilized, Energy-Conducting Light-Harvesting Complex (LHCII).  

PubMed

The major light-harvesting chlorophyll a/b complex (LHCII) of the photosynthetic apparatus in green plants consists of a membrane protein and numerous noncovalently bound pigments that make up about one-third of the molecular mass of the pigment-protein complex. Due to this high pigment density, LHCII is potentially interesting as a light-harvesting component in synthetic constructs. However, for such applications its stability needs to be significantly improved. In this work, LHCII was dramatically stabilized by enclosing it within polymerizing colloidal silica. The entrapped LHCII stayed functional at 50 °C for up to 24 h instead of a few minutes in detergent solution and clearly showed energy transfer between complexes. Entrapment yield was enhanced by a polycationic peptide attached to the N terminus. Both the extent of stabilization and the yield of entrapment strongly increased with decreasing diameters of the silica particles. PMID:25365647

Roeder, Sebastian; Hobe, Stephan; Paulsen, Harald

2014-12-01

385

Energy transfer from quantum dots to metal-organic frameworks for enhanced light harvesting.  

PubMed

Because of their efficient energy-transport properties, porphyrin-based metal-organic frameworks (MOFs) are attractive compounds for solar photochemistry applications. However, their absorption bands provide limited coverage in the visible spectral range for light-harvesting applications. We report here the functionalization of porphyrin-based MOFs with CdSe/ZnS core/shell quantum dots (QDs) for the enhancement of light harvesting via energy transfer from the QDs to the MOFs. The broad absorption band of the QDs in the visible region offers greater coverage of the solar spectrum by QD-MOF hybrid structures. We show through time-resolved emission studies that photoexcitation of the QDs is followed by energy transfer to the MOFs with efficiencies of more than 80%. This sensitization approach can result in a >50% increase in the number of photons harvested by a single monolayer MOF structure with a monolayer of QDs on the surface of the MOF. PMID:23293894

Jin, Shengye; Son, Ho-Jin; Farha, Omar K; Wiederrecht, Gary P; Hupp, Joseph T

2013-01-23

386

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

387

Atomic model of plant light-harvesting complex by electron crystallography  

Microsoft Academic Search

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

Werner Kühlbrandt; Da Neng Wang; Yoshinori Fujiyoshi

1994-01-01

388

Evidence for a common origin of chloroplasts with light-harvesting complexes of different pigmentation  

Microsoft Academic Search

THE red algae (Rhodophyta), which like cyanobacteria have only chlorophyll a and use phycobilisomes for light-harvesting1,2, are often considered to have originated independently of other photosynthetic eukaryotes, namely the chlorophyll a\\/b-containing Chlorophyta and the chlorophyll a\\/c-containing Chromophyta3. Here we report that the red alga Porphyridium cruentum has a chlorophyll a-containing antenna complex functionally associated with photosystem I, and that polypeptides

G. R. Wolfe; F. X. Cunningham; D. Durnfordt; B. R. Green; E. Gantt

1994-01-01

389

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

390

Excitation energy transfer and carotenoid radical cation formation in light harvesting complexes — A theoretical perspective  

Microsoft Academic Search

Light harvesting complexes have been identified in all chlorophyll-based photosynthetic organisms. Their major function is the absorption of light and its transport to the reaction centers, however, they are also involved in excess energy quenching, the so-called non-photochemical quenching (NPQ). In particular, electron transfer and the resulting formation of carotenoid radical cations have recently been discovered to play an important

Michael Wormit; Philipp H. P. Harbach; Jan M. Mewes; Sergiu Amarie; Josef Wachtveitl; Andreas Dreuw

2009-01-01

391

Photoexcitation of a Light-Harvesting Supramolecular Triad: A Time-Dependent DFT Study  

Microsoft Academic Search

We present the first time-dependent density functional theory (TDDFT) calculation on a light-harvesting triad carotenoid-diaryl-porphyrin-C60. Besides the numerical challenge that the ab initio study of the electronic structure of such a large system presents, we show that TDDFT is able to provide an accurate description of the excited-state properties of the system. In particular, we calculate the photoabsorption spectrum of

N. Spallanzani; C. A. Rozzi; D. Varsano; T. Baruah; M. R. Pederson; F. Manghi; A. Rubio

2009-01-01

392

Improvement of photosynthesis in dense microalgal suspension by reduction of light harvesting pigments  

Microsoft Academic Search

The effects of light-harvesting pigments (LHP) inmicroalgal cells on photosynthetic activity in adense cell suspension were\\u000a examined. The results suggest that a lower LHP content should result in higher photosynthetic productivity under high light\\u000a intensity. The idea was first proposed by Lien and San Pietro in 1975 that photosynthesis could be improved by reducing the\\u000a LHP content in microalgal cells,

Yuji Nakajima; Ryohei Ueda

1997-01-01

393

Effect of denaturants on the stability of light-harvesting complex  

Microsoft Academic Search

The effect of denaturants such as urea and normal alcohols on the formation of light-harvesting (LH) polypeptides\\/bacteriochlorophyll\\u000a a (BChla) complex (LH1 complex) in n-octyl-?-D-glucopyranoside (OG) micelle was examined to provide an insight into stability of the complex. The stabilities\\u000a of the LH1 complex in OG micelle and of the complex in the chromatophore of photosynthetic bacteria were compared by addition

K. Iida; M. Nango; H. Yasue; K. Okuda; M. Okita; A. Kashiwada; N. Takada; M. Maekawa; Y. Kurono

1998-01-01

394

N-terminal methylation of the core light-harvesting complex in purple photosynthetic bacteria  

Microsoft Academic Search

Several core light-harvesting complexes from both sulfur and non-sulfur purple photosynthetic bacteria have been identified to be methylated at the N-terminal ?-amino group of ?-polypeptides by using matrix-assisted laser desorption\\/ionization time-of-flight mass spectrometry and nuclear magnetic resonance. Monomethylation has been confirmed for the N-terminal alanine residues of the ?-polypeptides from Rhodospirillum rubrum, Thermochromatium tepidum and Chromatium vinosum, but not for

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

2002-01-01

395

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

PubMed Central

The light-harvesting complexes of plants have evolved the ability to switch between efficient light harvesting and quenching forms to optimize photosynthesis in response to the environment. Several distinct mechanisms, collectively termed “nonphotochemical quenching” (NPQ), provide flexibility in this response. Here we report the isolation and characterization of a mutant, suppressor of quenching 1 (soq1), that has high NPQ even in the absence of photosystem II subunit S (PsbS), a protein that is necessary for the rapidly reversible component of NPQ. The formation of NPQ in soq1 was light intensity-dependent, and it exhibited slow relaxation kinetics and other characteristics that distinguish it from known NPQ components. Treatment with chemical inhibitors or an uncoupler, as well as crosses to mutants known to affect other NPQ components, showed that the NPQ in soq1 does not require a transthylakoid pH gradient, zeaxanthin formation, or the phosphorylation of light-harvesting complexes, and it appears to be unrelated to the photosystem II damage-and-repair cycle. Measurements of pigments and chlorophyll fluorescence lifetimes indicated that the additional NPQ in soq1 is the result of a decrease in chlorophyll excited-state lifetime and not pigment bleaching. The SOQ1 gene was isolated by map-based cloning, and it encodes a previously uncharacterized thylakoid membrane protein with thioredoxin-like and ?-propeller domains located in the lumen and a haloacid-dehalogenase domain exposed to the chloroplast stroma. We propose that the role of SOQ1 is to prevent formation of a slowly reversible form of antenna quenching, thereby maintaining the efficiency of light harvesting. PMID:23818601

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

2013-01-01

396

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

397

Towards experimental verifications of the transport mechanisms in light-harvesting dynamics  

NASA Astrophysics Data System (ADS)

Recently, we identified the key mechanisms explaining the very- high efficiency and robustness of excitation energy transfer in bacterial photosynthesis, finding that dephasing noise may remarkably enhance the capability of transmitting energy (classical/quantum information) in light-harvesting systems (in communication complex networks [Caruso et al., PRL 2010]), by opening up additional transport pathways and suppressing the ineffective ones. To verify the relevance of such mechanisms in the actual bio-molecular systems, we propose how to gain control over the light-harvesting dynamics by using quantum optimal control tools. In this way, by means of optimally shaped and `robust' laser pulses, we can: i) faithfully prepare the photosystem in some specific initial state (local site or coherent superposition, e.g. quasi-dark and -bright states), and ii) probe efficiently the dynamics, under realistic experimental conditions, i.e. sample of randomly oriented light-harvesting complexes and extra laser constraints related to an experiment in progress. These results could allow us to more easily discriminate the different transport pathways, to characterize the environmental properties, and so enhance our comprehension of coherent processes in biological complexes.

Caruso, F.; Montangero, S.; Calarco, T.; Huelga, S. F.; Plenio, M. B.

2011-03-01

398

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

PubMed Central

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

Harel, Elad; Engel, Gregory S.

2012-01-01

399

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

400

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. PMID:23533354

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

2013-01-01

401

Efficient light harvesting by photosystem II requires an optimized protein packing density in Grana thylakoids.  

PubMed

A recently developed technique for dilution of the naturally high protein packing density in isolated grana membranes was applied to study the dependence of the light harvesting efficiency of photosystem (PS) II on macromolecular crowding. Slight dilution of the protein packing from 80% area fraction to the value found in intact grana thylakoids (70%) leads to an improved functionality of PSII (increased antenna size, enhanced connectivity between reaction centers). Further dilution induces a functional disconnection of light-harvesting complex (LHC) II from PSII. It is concluded that efficient light harvesting by PSII requires an optimal protein packing density in grana membranes that is close to 70%. We hypothesize that the decreased efficiency in overcrowded isolated grana thylakoids is caused by excited state quenching in LHCII, which has previously been correlated with neoxanthin distortion. Resonance Raman spectroscopy confirms this increase in neoxanthin distortion in overcrowded grana as compared with intact thylakoids. Furthermore, analysis of the changes in the antenna size in highly diluted membranes indicates a lipid-induced dissociation of up to two trimeric LHCII from PSII, leaving one trimer connected. This observation supports a hierarchy of LHCII-binding sites on PSII. PMID:20360011

Haferkamp, Silvia; Haase, Winfried; Pascal, Andrew A; van Amerongen, Herbert; Kirchhoff, Helmut

2010-05-28

402

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. PMID:22167798

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

2011-01-01

403

Live visualizations of single isolated tubulin protein self-assembly via tunneling current: effect of electromagnetic pumping during spontaneous growth of microtubule  

NASA Astrophysics Data System (ADS)

As we bring tubulin protein molecules one by one into the vicinity, they self-assemble and entire event we capture live via quantum tunneling. We observe how these molecules form a linear chain and then chains self-assemble into 2D sheet, an essential for microtubule, --fundamental nano-tube in a cellular life form. Even without using GTP, or any chemical reaction, but applying particular ac signal using specially designed antenna around atomic sharp tip we could carry out the self-assembly, however, if there is no electromagnetic pumping, no self-assembly is observed. In order to verify this atomic scale observation, we have built an artificial cell-like environment with nano-scale engineering and repeated spontaneous growth of tubulin protein to its complex with and without electromagnetic signal. We used 64 combinations of plant, animal and fungi tubulins and several doping molecules used as drug, and repeatedly observed that the long reported common frequency region where protein folds mechanically and its structures vibrate electromagnetically. Under pumping, the growth process exhibits a unique organized behavior unprecedented otherwise. Thus, ``common frequency point'' is proposed as a tool to regulate protein complex related diseases in the future.

Sahu, Satyajit; Ghosh, Subrata; Fujita, Daisuke; Bandyopadhyay, Anirban

2014-12-01

404

Live visualizations of single isolated tubulin protein self-assembly via tunneling current: effect of electromagnetic pumping during spontaneous growth of microtubule.  

PubMed

As we bring tubulin protein molecules one by one into the vicinity, they self-assemble and entire event we capture live via quantum tunneling. We observe how these molecules form a linear chain and then chains self-assemble into 2D sheet, an essential for microtubule, --fundamental nano-tube in a cellular life form. Even without using GTP, or any chemical reaction, but applying particular ac signal using specially designed antenna around atomic sharp tip we could carry out the self-assembly, however, if there is no electromagnetic pumping, no self-assembly is observed. In order to verify this atomic scale observation, we have built an artificial cell-like environment with nano-scale engineering and repeated spontaneous growth of tubulin protein to its complex with and without electromagnetic signal. We used 64 combinations of plant, animal and fungi tubulins and several doping molecules used as drug, and repeatedly observed that the long reported common frequency region where protein folds mechanically and its structures vibrate electromagnetically. Under pumping, the growth process exhibits a unique organized behavior unprecedented otherwise. Thus, "common frequency point" is proposed as a tool to regulate protein complex related diseases in the future. PMID:25466883

Sahu, Satyajit; Ghosh, Subrata; Fujita, Daisuke; Bandyopadhyay, Anirban

2014-01-01

405

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

2007-12-01

406

Redox control of GPx catalytic activity through mediating self-assembly of Fmoc-phenylalanine selenide into switchable supramolecular architectures.  

PubMed

Artificial enzymes capable of achieving tunable catalytic activity through stimuli control of enzymatic structure transition are of significance in biosensor and biomedicine research. Herein we report a novel smart glutathione peroxidise (GPx) mimic with modulatory catalytic activity based on redox-induced supramolecular self-assembly. First, an amphiphilic Fmoc-phenylalanine-based selenide was designed and synthesized, which can self-assemble into nanospheres (NSs) in aqueous solution. The NSs demonstrate extremely low GPx activity. Upon the oxidation of hydroperoxides (ROOH), the selenide can be quickly transformed into the selenoxide form. The change of the molecular structure induces complete morphology transition of the self-assemblies from NSs to nanotubes (NTs), resulting in great enhancement in the GPx catalytic activity. Under the reduction of GSH, the selenoxide can be further reversibly reduced back into the selenide; therefore the reversible switch between the NSs and NTs can be successfully accomplished. The relationship between the catalytic activity and enzymatic structure was also investigated. The dual response nature makes this mimic play roles of both a sensor and a GPx enzyme at the same time, which can auto-detect the signal of ROOH and then auto-change its activity to achieve quick or slow/no scavenging of ROOH. The dynamic balance of ROOH is vital in organisms, in which an appropriate amount of ROOH does benefit to the metabolism, whereas surplus ROOH can cause oxidative damage of the cell instead and this smart mimic is of remarkable significance. We expect that such a mimic can be developed into an effective antioxidant drug and provide a new platform for the construction of intelligent artificial enzymes with multiple desirable properties. PMID:25366375

Huang, Zupeng; Luo, Quan; Guan, Shuwen; Gao, Jianxiong; Wang, Yongguo; Zhang, Bo; Wang, Liang; Xu, Jiayun; Dong, Zeyuan; Liu, Junqiu

2014-12-28

407

Bacterial expression of self-assembling peptide hydrogelators  

NASA Astrophysics Data System (ADS)

For tissue regeneration and drug delivery applications, various architectures are explored to serve as biomaterial tools. Via de novo design, functional peptide hydrogel materials have been developed as scaffolds for biomedical applications. The objective of this study is to investigate bacterial expression as an alternative method to chemical synthesis for the recombinant production of self-assembling peptides that can form rigid hydrogels under physiological conditions. The Schneider and Pochan Labs have designed and characterized a 20 amino acid beta-hairpin forming amphiphilic peptide containing a D-residue in its turn region (MAX1). As a result, this peptide must be prepared chemically. Peptide engineering, using the sequence of MAX1 as a template, afforded a small family of peptides for expression (EX peptides) that have different turn sequences consisting of natural amino acids and amenable to bacterial expression. Each sequence was initially chemically synthesized to quickly assess the material properties of its corresponding gel. One model peptide EX1, was chosen to start the bacterial expression studies. DNA constructs facilitating the expression of EX1 were designed in such that the peptide could be expressed with different fusion partners and subsequently cleaved by enzymatic or chemical means to afford the free peptide. Optimization studies were performed to increase the yield of pure peptide that ultimately allowed 50 mg of pure peptide to be harvested from one liter of culture, providing an alternate means to produce this hydrogel-forming peptide. Recombinant production of other self-assembling hairpins with different turn sequences was also successful using this optimized protocol. The studies demonstrate that new beta-hairpin self-assembling peptides that are amenable to bacterial production and form rigid hydrogels at physiological conditions can be designed and produced by fermentation in good yield at significantly reduced cost when compared to chemical synthesis.

Sonmez, Cem

408

Particle self-assembly at ionic liquid-based interfaces.  

PubMed

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

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

2014-04-01

409

A Programmable Transducer Self-Assembled from DNA.  

PubMed

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. PMID:23139854

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

2012-01-01

410

Platelets self-assemble into porous nacre during freeze casting.  

PubMed

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

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

2013-03-01

411

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

NASA Astrophysics Data System (ADS)

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

Verma, Nisha

412

Passivation effects in B doped self-assembled Si nanocrystals  

NASA Astrophysics Data System (ADS)

Doping of semiconductor nanocrystals has enabled their widespread technological application in optoelectronics and micro/nano-electronics. In this work, boron-doped self-assembled silicon nanocrystal samples have been grown and characterised using Electron Spin Resonance and photoluminescence spectroscopy. The passivation effects of boron on the interface dangling bonds have been investigated. Addition of boron dopants is found to compensate the active dangling bonds at the interface, and this is confirmed by an increase in photoluminescence intensity. Further addition of dopants is found to reduce the photoluminescence intensity by decreasing the minority carrier lifetime as a result of the increased number of non-radiative processes.

Puthen Veettil, B.; Wu, Lingfeng; Jia, Xuguang; Lin, Ziyun; Zhang, Tian; Yang, Terry; Johnson, Craig; McCamey, Dane; Conibeer, Gavin; Perez-Würfl, Ivan

2014-12-01

413

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. PMID:21686172

Bende, Attila; Turcu, Ioan

2011-01-01

414

Selective electroless copper deposition on self-assembled dithiol monolayers.  

PubMed

The paper reports the use of self-assembled monolayers (SAMs) of dithiols to induce electroless copper deposition on a gold substrate. The metallization catalyst, palladium nanoparticles, is bound on the dithiol SAM. The assembly process is followed by IR and X-ray photoelectron spectroscopies to confirm the formation of a monolayer with bound catalyst. Electroless metallization is then carried out with a steady deposition rate of 130 nm/min. Additionally, microcontact printing of the catalyst on the SAM by poly(dimethylsiloxane) stamps is used to localize copper deposits. Resulting metallization is selective and allows for a high resolution. PMID:20355979

Aldakov, Dmitry; Bonnassieux, Yvan; Geffroy, Bernard; Palacin, Serge

2009-03-01

415

Self-assembling peptide amphiphile nanostructures for cancer therapy  

NASA Astrophysics Data System (ADS)

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

Soukasene, Stephen

416

Customizing mesoscale self-assembly with 3D printing  

E-print Network

Self-assembly due to capillary forces is a common method for generating 2D mesoscale structures from identical floating particles at the liquid-air interface. Designing building blocks to obtain a desired mesoscopic structure is a scientific challenge. We show herein that it is possible to shape the particles with a low cost 3D printer, for composing specific mesoscopic structures. Our method is based on the creation of capillary multipoles inducing either attractive or repulsive forces. Since capillary interactions can be downscaled, our method opens new ways to low cost microfabrication.

M. Poty; G. Lumay; N. Vandewalle

2013-10-17

417

The art and science of self-assembling molecular machines  

NASA Astrophysics Data System (ADS)

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

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

1996-09-01

418

Self-Assembly and Mineralization of Peptide-Amphiphile Nanofibers  

NASA Astrophysics Data System (ADS)

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

Hartgerink, Jeffrey D.; Beniash, Elia; Stupp, Samuel I.

2001-11-01

419

Buckling instability of self-assembled colloidal columns.  

PubMed

Suspended, slender self-assembled domains of magnetically responsive colloids are observed to buckle in microgravity. Upon cessation of the magnetic field that drives their assembly, these columns expand axially and buckle laterally. This phenomenon resembles the buckling of long beams due to thermal expansion; however, linear stability analysis predicts that the colloidal columns are inherently susceptible to buckling because they are freely suspended in a Newtonian fluid. The dominant buckling wavelength increases linearly with column thickness and is quantitatively described using an elastohydrodynamic model and the suspension thermodynamic equation of state. PMID:25302919

Swan, James W; Vasquez, Paula A; Furst, Eric M

2014-09-26

420

Buckling Instability of Self-Assembled Colloidal Columns  

NASA Astrophysics Data System (ADS)

Suspended, slender self-assembled domains of magnetically responsive colloids are observed to buckle in microgravity. Upon cessation of the magnetic field that drives their assembly, these columns expand axially and buckle laterally. This phenomenon resembles the buckling of long beams due to thermal expansion; however, linear stability analysis predicts that the colloidal columns are inherently susceptible to buckling because they are freely suspended in a Newtonian fluid. The dominant buckling wavelength increases linearly with column thickness and is quantitatively described using an elastohydrodynamic model and the suspension thermodynamic equation of state.

Swan, James W.; Vasquez, Paula A.; Furst, Eric M.

2014-09-01

421

Dynamics of water on self-assembled monolayers  

NASA Astrophysics Data System (ADS)

Nanoscale surface interactions of water at polymeric interfaces are important for a number of applications including biophysics, nanofluidics and MEMS devices. Using molecular dynamics simulations we investigate the fundamental properties of water at interfaces for a variety of water models and surfaces. We report results for the contact angle and wetting dynamics of TIP3P and SPC/E water on self-assembled monolayers (SAMs) of alkylsilanes on amorphous silica and alkanethiols on gold with various hydrophilic and hydrophobic head groups. For comparison we also investigate water interactions on bare amorphous silica substrates. Simulations of the dynamics of water confined between two surfaces coated with SAMs will also be presented.

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

2007-03-01

422

Purification of ethanol for highly sensitive self-assembly experiments  

PubMed Central

Summary Ethanol is the preferred solvent for the formation of self-assembled monolayers (SAMs) of thiolates on gold. By applying a thin film sensor system, we could demonstrate that even the best commercial qualities of ethanol contain surface-active contaminants, which can compete with the desired thiolates for surface sites. Here we present that gold nanoparticles deposited onto zeolite X can be used to remove these contaminants by chemisorption. This nanoparticle-impregnated zeolite does not only show high capacities for surface-active contaminants, such as thiols, but can be fully regenerated via a simple pyrolysis protocol. PMID:25161861

Barbe, Kathrin; Kind, Martin; Pfeiffer, Christian

2014-01-01

423

Growth of a self-assembled monolayer by fractal aggregation  

SciTech Connect

Atomic force microscope images show that self-assembled monolayers of octadecyltrichlorosilane form on mica by nucleating isolated, self-similar domains. With increasing coverage, the fractal dimension of the growing domains evolves from 1.6 to 1.8. At higher coverage, continued growth is limited by adsorption from solution. Monte Carlo simulations that include, for the first time, adsorption as well as surface diffusion qualitatively reproduce both the growth kinetics and evolution of fractal structure, much better than a two-dimensional diffusion-limited-aggregation model.

Schwartz, D.K.; Steinberg, S.; Israelachvili, J.; Zasadzinski, J.A.N. (Department of Chemical and Nuclear Engineering, University of California Santa Barbara, Santa Barbara, California 93106 (United States))

1992-12-07

424

Transparent thin-film transistor with self-assembled nanocrystals  

NASA Astrophysics Data System (ADS)

The paper presents the fabrication of transparent devices using nanofabrication and nanomaterials. Clear and functional structures can be constructed over a large area with highly transparent nanocrystals via layer-by-layer self-assembly. The 12 nm SnO2 and SiO2 nanocrystals can form ultra-thin and uniform multilayers, serving as the active and insulating layers, respectively. Transistors fabricated by this method have a high optical transparency and reliable electrical performance. The averaged optical transmittance is higher than 85%. The usage of nanofabrication and nanomaterials solves some of the current fabricating problems for transparent devices. This technique is applicable to other transistor devices and circuits.

Zhang, Qiaohui; Saraf, L. V.; Hua, Feng

2007-05-01

425

Rapid self-assembly of uranyl polyhedra into crown clusters.  

PubMed

Clusters built from 32 uranyl peroxide polyhedra self-assemble and crystallize within 15 min after combining uranyl nitrate, ammonium hydroxide, and hydrogen peroxide in aqueous solution under ambient conditions. These novel crown-shaped clusters are remarkable in that they form so quickly, have extraordinarily low aqueous solubility, form with at least two distinct peroxide to hydroxyl ratios, and form in very high yield. The clusters, which have outer diameters of 23 Å, topologically consist of eight pentagons and four hexagons. Their rapid formation and low solubility in aqueous systems may be useful properties at various stages in an advanced nuclear energy system. PMID:21608972

Sigmon, Ginger E; Burns, Peter C

2011-06-22

426

Chiral tubule self-assembly from an achiral diynoic lipid.  

PubMed

Tubules possessing microm-scale chiral substructure self-assemble from an achiral isomer of the tubule-forming diynoic phosphatidylcholine, 1,2-bis(10,12-tricosadiynoyl)sn-glycero-3-phosphocholine [DC(8,9)PC], showing that molecular chirality is not essential for tubule formation. CD spectroscopy shows that these structures' helical sense of handedness instead originates in a spontaneous cooperative chiral symmetry-breaking process. We conclude that the chiral symmetry-breaking must originate in the unusual feature common to the chiral and achiral tubule-forming molecules, the diynes centered in their hydrocarbon tails. PMID:12626752

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

2003-03-18

427

Self-assembled GaN hexagonal micropyramid and microdisk  

SciTech Connect

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

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

2009-02-09

428

Model for dynamic self-assembled magnetic surface structures.  

SciTech Connect

We propose a first-principles model for the dynamic self-assembly of magnetic structures at a water-air interface reported in earlier experiments. The model is based on the Navier-Stokes equation for liquids in shallow water approximation coupled to Newton equations for interacting magnetic particles suspended at a water-air interface. The model reproduces most of the observed phenomenology, including spontaneous formation of magnetic snakelike structures, generation of large-scale vortex flows, complex ferromagnetic-antiferromagnetic ordering of the snake, and self-propulsion of bead-snake hybrids.

Belkin, M.; Glatz, A.; Snezhko, A.; Aranson, I. S.; Materials Science Division; Northwestern Univ.

2010-07-07

429

Self-Assembly of Channel Type ?-CD Dimers Induced by Dodecane  

PubMed Central

Cyclodextrins (CDs) can hardly self-assemble into well-defined structures. Here we report if they preassemble into channel type dimers assisted by dodecane, well-defined vesicles and bricks can be formed. Unlike the traditional self-assembly of amphiphilic molecules driven by hydrophobic effect, the self-assembly of the channel type dodecane@2?-CD supramolecular building block is predoninantly driven by hydrogen-bonds. More water molecules are found in the lyophilized vesicles than in the bricks, suggesting water molecules play an important role in the self-assembly of the channel-type dimers of ?-CD. The amount of structural water in the self-assembly is closely related to the curvature of the final self-assembled structures. Our work reveals that the channel-type dimer of ?-CD may represent a new sort of building block for advanced structures. PMID:25532046

Zhou, Chengcheng; Cheng, Xinhao; Zhao, Qiang; Yan, Yun; Wang, Jide; Huang, Jianbin

2014-01-01

430

Self-Assembly of Channel Type ?-CD Dimers Induced by Dodecane  

NASA Astrophysics Data System (ADS)

Cyclodextrins (CDs) can hardly self-assemble into well-defined structures. Here we report if they preassemble into channel type dimers assisted by dodecane, well-defined vesicles and bricks can be formed. Unlike the traditional self-assembly of amphiphilic molecules driven by hydrophobic effect, the self-assembly of the channel type dodecane@2?-CD supramolecular building block is predoninantly driven by hydrogen-bonds. More water molecules are found in the lyophilized vesicles than in the bricks, suggesting water molecules play an important role in the self-assembly of the channel-type dimers of ?-CD. The amount of structural water in the self-assembly is closely related to the curvature of the final self-assembled structures. Our work reveals that the channel-type dimer of ?-CD may represent a new sort of building block for advanced structures.

Zhou, Chengcheng; Cheng, Xinhao; Zhao, Qiang; Yan, Yun; Wang, Jide; Huang, Jianbin

2014-12-01

431

Self-Assembly of Channel Type ?-CD Dimers Induced by Dodecane.  

PubMed

Cyclodextrins (CDs) can hardly self-assemble into well-defined structures. Here we report if they preassemble into channel type dimers assisted by dodecane, well-defined vesicles and bricks can be formed. Unlike the traditional self-assembly of amphiphilic molecules driven by hydrophobic effect, the self-assembly of the channel type dodecane@2?-CD supramolecular building block is predoninantly driven by hydrogen-bonds. More water molecules are found in the lyophilized vesicles than in the bricks, suggesting water molecules play an important role in the self-assembly of the channel-type dimers of ?-CD. The amount of structural water in the self-assembly is closely related to the curvature of the final self-assembled structures. Our work reveals that the channel-type dimer of ?-CD may represent a new sort of building block for advanced structures. PMID:25532046

Zhou, Chengcheng; Cheng, Xinhao; Zhao, Qiang; Yan, Yun; Wang, Jide; Huang, Jianbin

2014-01-01

432

Molecular self-assembly routes to optically functional thin films: Electroluminescent multilayer structures  

SciTech Connect

This contribution describes the use of layer-by-layer self-limiting siloxane chemisorption processes to self-assemble structurally regular multilayer organic LED (OLED) devices. Topics discussed include: (1) the synthesis of silyl-functionalized precursor molecules for hole transport layer (HTL), emissive layer (EML), and electron transport layer (ETL) self-assembly, (2) the use of layer-by-layer self-assembly for ITO electrode modification/passivation/hole-electron balancing in a vapor-deposited device, (3) the microstructure/chemical characterization of HTL self-assembly using a prototype triarylamine precursor, (4) fabrication and properties of a hybrid self-assembled + vapor deposited two-layer LED, and (5) fabrication and properties of a fully self-assembled two-layer OLED.

Li, W.; Malinsky, J.E.; Chou, H. [and others

1998-07-01

433

The Ring Structure and Organization of Light Harvesting 2 Complexes in a Reconstituted Lipid Bilayer, Resolved by Atomic Force Microscopy  

Microsoft Academic Search

The main function of the transmembrane light-harvesting complexes in photosynthetic organisms is the absorption of a light quantum and its subsequent rapid transfer to a reaction center where a charge separation occurs. A combination of freeze-thaw and dialysis methods were used to reconstitute the detergent-solubilized Light Harvesting 2 complex (LH2) of the purple bacterium Rhodopseudomonas acidophila strain 10050 into preformed

Amalia Stamouli; Sidig Kafi; Dionne C. G. Klein; Tjerk H. Oosterkamp; Joost W. M. Frenken; Richard J. Cogdell; Thijs J. Aartsma

2003-01-01

434

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

SciTech Connect

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

Ye, L.; Pearson, T.; Crawford, T. M., E-mail: crawftm@mailbox.sc.edu [Department of Physics and Astronomy, University of South Carolina, 712 Main Street, Columbia, South Carolina 29208 (United States); Qi, B.; Cordeau, Y.; Mefford, O. T. [Department of Materials Science and Engineering, Clemson University, 161 Sirrine Hall, Clemson, South Carolina 29634 (United States); Center for Optical Materials Science and Engineering Technologies (COMSET), 91 Technology Dr., Anderson, South Carolina 29625 (United States)

2014-05-07

435

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

436

Computational Study of DNA-Directed Self-Assembly of Colloids.  

E-print Network

??Immense insight into fundamental processes necessity for the fabrication of nanostructures is gathered from studying the self-assembly of colloidal suspensions. These fundamental processes include crystal… (more)

Scarlett, Raynaldo Theodore

2010-01-01

437

Polymer Nanocomposites through Controlled Self-Assembly of Cubic Silsesquioxane Scaffolds  

E-print Network

Polymer Nanocomposites through Controlled Self-Assembly of Cubic Silsesquioxane Scaffolds Lei Zheng nanocomposites using cubic silsesquioxanes (POSS) nanoparticles as building blocks is reported. The design

438

Self Assembly of Nano Metric Metallic Particles for Realization of Photonic and Electronic Nano Transistors  

PubMed Central

In this paper, we present the self assembly procedure as well as experimental results of a novel method for constructing well defined arrangements of self assembly metallic nano particles into sophisticated nano structures. The self assembly concept is based on focused ion beam (FIB) technology, where metallic nano particles are self assembled due to implantation of positive gallium ions into the insulating material (e.g., silica as in silicon on insulator wafers) that acts as intermediary layer between the substrate and the negatively charge metallic nanoparticles. PMID:20559513

Shahmoon, Asaf; Limon, Ofer; Girshevitz, Olga; Zalevsky, Zeev

2010-01-01

439

Developing novel polymer architectures for applications In magnetic resonance imaging and self-assembly  

E-print Network

Macromolecular scaffolds for drug delivery, self-assembly, and imaging applications have attracted significant attention over the last several decades. As polymerization techniques become more sophisticated, it becomes ...

McCombs, Jessica R. (Jessica Rose)

2013-01-01

440

Self-assembling microsphere-based dextran hydrogels for pharmaceutical applications.  

E-print Network

??In this thesis novel self-assembling hydrogels, based on physical interactions between dextran microgels, potentially suitable for controlled drug delivery and tissue engineering, are presented. Two… (more)

Van Tomme, S.R.

2007-01-01

441

Precise hierarchical self-assembly of multicompartment micelles  

PubMed Central

Hierarchical self-assembly offers elegant and energy-efficient bottom-up strategies for the structuring of complex materials. For block copolymers, the last decade witnessed great progress in diversifying the structural complexity of solution-based assemblies into multicompartment micelles. However, a general understanding of what governs multicompartment micelle morphologies and polydispersity, and how to manipulate their hierarchical superstructures using straightforward concepts and readily accessible polymers remains unreached. Here we demonstrate how to create homogeneous multicompartment micelles with unprecedented structural control via the intermediate pre-assembly of subunits. This directed self-assembly leads to a step-wise reduction of the degree of conformational freedom and dynamics and avoids undesirable kinetic obstacles during the structure build-up. It yields a general concept for homogeneous populations of well-defined multicompartment micelles with precisely tunable patchiness, while using simple linear ABC triblock terpolymers. We further demonstrate control over the hierarchical step-growth polymerization of multicompartment micelles into micron-scale segmented supracolloidal polymers as an example of programmable mesoscale colloidal hierarchies via well-defined patchy nanoobjects. PMID:22426231

Gröschel, André H.; Schacher, Felix H.; Schmalz, Holger; Borisov, Oleg V.; Zhulina, Ekaterina B.; Walther, Andreas; Müller, Axel H.E.

2012-01-01

442

Precise hierarchical self-assembly of multicompartment micelles.  

PubMed

Hierarchical self-assembly offers elegant and energy-efficient bottom-up strategies for the structuring of complex materials. For block copolymers, the last decade witnessed great progress in diversifying the structural complexity of solution-based assemblies into multicompartment micelles. However, a general understanding of what governs multicompartment micelle morphologies and polydispersity, and how to manipulate their hierarchical superstructures using straightforward concepts and readily accessible polymers remains unreached. Here we demonstrate how to create homogeneous multicompartment micelles with unprecedented structural control via the intermediate pre-assembly of subunits. This directed self-assembly leads to a step-wise reduction of the degree of conformational freedom and dynamics and avoids undesirable kinetic obstacles during the structure build-up. It yields a general concept for homogeneous populations of well-defined multicompartment micelles with precisely tunable patchiness, while using simple linear ABC triblock terpolymers. We further demonstrate control over the hierarchical step-growth polymerization of multicompartment micelles into micron-scale segmented supracolloidal polymers as an example of programmable mesoscale colloidal hierarchies via well-defined patchy nanoobjects. PMID:22426231

Gröschel, André H; Schacher, Felix H; Schmalz, Holger; Borisov, Oleg V; Zhulina, Ekaterina B; Walther, Andreas; Müller, Axel H E

2012-01-01

443

Self-assembled single-phase perovskite nanocomposite thin films.  

PubMed

Thin films of perovskite-structured oxides with general formula ABO(3) have great potential in electronic devices because of their unique properties, which include the high dielectric constant of titanates, (1) high-T(C) superconductivity in cuprates, (2) and colossal magnetoresistance in manganites. (3) These properties are intimately dependent on, and can therefore be tailored by, the microstructure, orientation, and strain state of the film. Here, we demonstrate the growth of cubic Sr(Ti,Fe)O(3) (STF) films with an unusual self-assembled nanocomposite microstructure consisting of (100) and (110)-oriented crystals, both of which grow epitaxially with respect to the Si substrate and which are therefore homoepitaxial with each other. These structures differ from previously reported self-assembled oxide nanocomposites, which consist either of two different materials (4-7) or of single-phase distorted-cubic materials that exhibit two or more variants. (8-12) Moreover, an epitaxial nanocomposite SrTiO(3) overlayer can be grown on the STF, extending the range of compositions over which this microstructure can be formed. This offers the potential for the implementation of self-organized optical/ferromagnetic or ferromagnetic/ferroelectric hybrid nanostructures integrated on technologically important Si substrates with applications in magnetooptical or spintronic devices. PMID:20039695

Kim, Hyun-Suk; Bi, Lei; Paik, Hanjong; Yang, Dae-Jin; Park, Yun Chang; Dionne, Gerald F; Ross, Caroline A

2010-02-10

444

Self assembled monolayers on silicon for molecular electronics.  

PubMed

We present an overview of various aspects of the self-assembly of organic monolayers on silicon substrates for molecular electronics applications. Different chemical strategies employed for grafting the self-assembled monolayers (SAMs) of alkanes having different chain lengths on native oxide of Si or on bare Si have been reviewed. The utility of different characterization techniques in determination of the thickness, molecular ordering and orientation, surface coverage, growth kinetics and chemical composition of the SAMs has been discussed by choosing appropriate examples. The metal counterelectrodes are an integral part of SAMs for measuring their electrical properties as well as using them for molecular electronic devices. A brief discussion on the variety of options available for the deposition of metal counterelectrodes, that is, soft metal contacts, vapor deposition and soft lithography, has been presented. Various theoretical models, namely, tunneling (direct and Fowler-Nordheim), thermionic emission, Poole-Frenkel emission and hopping conduction, used for explaining the electronic transport in dielectric SAMs have been outlined and, some experimental data on alkane SAMs have been analyzed using these models. It has been found that short alkyl chains show excellent agreement with tunneling models; while more experimental data on long alkyl chains are required to understand their transport mechanism(s). Finally, the concepts and realization of various molecular electronic components, that is, diodes, resonant tunnel diodes, memories and transistors, based on appropriate architecture of SAMs comprising of alkyl chains (sigma- molecule) and conjugated molecules (pi-molecule) have been presented. PMID:17761249

Aswal, D K; Lenfant, S; Guerin, D; Yakhmi, J V; Vuillaume, D

2006-05-24

445

Self-assembly scenarios of patchy colloidal particles  

E-print Network

The rapid progress in precisely designing the surface decoration of patchy colloidal particles offers a new, yet unexperienced freedom to create building entities for larger, more complex structures in soft matter systems. However, it is extremely difficult to predict the large variety of ordered equilibrium structures that these particles are able to undergo under the variation of external parameters, such as temperature or pressure. Here we show that, by a novel combination of two theoretical tools, it is indeed possible to predict the self-assembly scenario of patchy colloidal particles: on one hand, a reliable and efficient optimization tool based on ideas of evolutionary algorithms helps to identify the ordered equilibrium structures to be expected at T = 0; on the other hand, suitable simulation techniques allow to estimate via free energy calculations the phase diagram at finite temperature. With these powerful approaches we are able to identify the broad variety of emerging self-assembly scenarios for spherical colloids decorated by four patches and we investigate and discuss the stability of the crystal structures on modifying in a controlled way the tetrahedral arrangement of the patches.

G. Doppelbauer; E. G. Noya; E. Bianchi; G. Kahl

2012-06-13

446

Self-assembly mechanism in colloids: perspectives from Statistical Physics  

E-print Network

Motivated by recent experimental findings in chemical synthesis of colloidal particles, we draw an analogy between self-assembly processes occurring in biological systems (e.g. protein folding) and a new exciting possibility in the field of material science. We consider a self-assembly process whose elementary building blocks are decorated patchy colloids of various types, that spontaneously drive the system toward a unique and predetermined targeted macroscopic structure. To this aim, we discuss a simple theoretical model -- the Kern-Frenkel model -- describing a fluid of colloidal spherical particles with a pre-defined number and distribution of solvophobic and solvophilic regions on their surface. The solvophobic and solvophilic regions are described via a short-range square-well and a hard-sphere potentials, respectively. Integral equation and perturbation theories are presented to discuss structural and thermodynamical properties, with particular emphasis on the computation of the fluid-fluid (or gas-liquid) transition in the temperature-density plane. The model allows the description of both one and two attractive caps, as a function of the fraction of covered attractive surface, thus interpolating between a square-well and a hard-sphere fluid, upon changing the coverage. By comparison with Monte Carlo simulations, we assess the pros and the cons of both integral equation and perturbation theories in the present context of patchy colloids, where the computational effort for numerical simulations is rather demanding.

Achille Giacometti

2012-07-24

447

Facile self-assembly and stabilization of metal oxide nanoparticles.  

PubMed

This paper describes a facile method of self-assembling different metal oxide nanoparticles into nanostructured materials via di-carboxylate linkers (oxalic acid) using TiO2 as an example. In this method, the di-carboxylate linkers react with surface hydroxyls on metal oxide nanoparticles forming covalent, ester-like bonds, which enable the binding of two metal oxide particles, one at either end of the linker and facilitates efficient self-assembly of one group of metal oxide nanoparticles homogeneously distributed onto the surface of another group. The oxalate linkers can then be removed by thermal decomposition. This approach is shown to be effective using differently-sized TiO2 nanoparticles, namely in-house synthesized 3-5nm anatase nanocrystals and Degussa P25 titania particles (mean 21nm particle size). Our data show that the application of a high temperature heat treatment (450°C for 30min), conventionally applied to achieve a stable porous structure by thermal decomposition of the linker molecules and by inducing inter-particle necking, damages the surface area of the nanostructured material. However, here we show that sintering at 300°C for 30min or by flash near infrared radiation sintering for 12s efficiently decomposes the oxalate linkers and stabilizes the nanostructure of the material whilst maintaining its high surface area. PMID:25525978

Charbonneau, Cecile; Holliman, Peter J; Davies, Matthew L; Watson, Trystan M; Worsley, David A

2015-03-15

448

Self-assembly processes in the prebiotic environment  

PubMed Central

An important question guiding research on the origin of life concerns the environmental conditions where molecular systems with the properties of life first appeared on the early Earth. An appropriate site would require liquid water, a source of organic compounds, a source of energy to drive polymerization reactions and a process by which the compounds were sufficiently concentrated to undergo physical and chemical interactions. One such site is a geothermal setting, in which organic compounds interact with mineral surfaces to promote self-assembly and polymerization reactions. Here, we report an initial study of two geothermal sites where mixtures of representative organic solutes (amino acids, nucleobases, a fatty acid and glycerol) and phosphate were mixed with high-temperature water in clay-lined pools. Most of the added organics and phosphate were removed from solution with half-times measured in minutes to a few hours. Analysis of the clay, primarily smectite and kaolin, showed that the organics were adsorbed to the mineral surfaces at the acidic pH of the pools, but could subsequently be released in basic solutions. These results help to constrain the range of possible environments for the origin of life. A site conducive to self-assembly of organic solutes would be an aqueous environment relatively low in ionic solutes, at an intermediate temperature range and neutral pH ranges, in which cyclic concentration of the solutes can occur by transient dry intervals. PMID:17008220

Deamer, David; Singaram, Sara; Rajamani, Sudha; Kompanichenko, Vladimir; Guggenheim, Stephen

2006-01-01

449

Structure and optical properties of self-assembled distyrylbenzene electrolytes  

NASA Astrophysics Data System (ADS)

Conjugated Oligoelectrolytes (COEs) are of interest as optical components in solution based biosensors and as electron transport layers in organic light-emitting diodes (OLEDs). These applications require solution processing of the COEs where the packing of oligoelectrolyte aggregates (directed by intermolecular interactions) governs their optical and electronic properties. The structural organization of distyrylbenzene derivatives dissolved in water is systematically studied as a function of the oligoelectrolyte concentration. Small angle neutron scattering (SANS) shows that above a critical micelle concentration these oligoelectrolytes self-assemble into cylindrical micelles with diameter ˜ 3.5 nm. The inter micelle distance decreases with increasing concentration and finally these organization arrange themselves into a cluster with a characteristic length scale ˜ 50 nm as derived from Guinier analysis of the SANS. Complementary structural studies have also been performed using liquid atomic force microscopy and cryogenic transmission electron microscopy techniques. The optical properties of this self-assembled oligoelectrolyte system will also be presented. We acknowledge NCNR NIST for facilitating the SANS experiments.

Chatterjee, Tirtha; Ortony, Julia H.; Chworos, Arkadiusz; Kramer, Edward J.

2010-03-01

450

Chiral plasmonics of self-assembled nanorod dimers  

PubMed Central

Chiral nanoscale photonic systems typically follow either tetrahedral or helical geometries that require four or more different constituent nanoparticles. Smaller number of particles and different chiral geometries taking advantage of the self-organization capabilities of nanomaterials will advance understanding of chiral plasmonic effects, facilitate development of their theory, and stimulate practical applications of chiroplasmonics. Here we show that gold nanorods self-assemble into side-by-side orientated pairs and “ladders” in which chiral properties originate from the small dihedral angle between them. Spontaneous twisting of one nanorod versus the other one breaks the centrosymmetric nature of the parallel assemblies. Two possible enantiomeric conformations with positive and negative dihedral angles were obtained with different assembly triggers. The chiral nature of the angled nanorod pairs was confirmed by 4? full space simulations and the first example of single-particle CD spectroscopy. Self-assembled nanorod pairs and “ladders” enable the development of chiral metamaterials, (bio)sensors, and new catalytic processes. PMID:23752317

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

2013-01-01

451

Self-assembly processes in the prebiotic environment.  

PubMed

An important question guiding research on the origin of life concerns the environmental conditions where molecular systems with the properties of life first appeared on the early Earth. An appropriate site would require liquid water, a source of organic compounds, a source of energy to drive polymerization reactions and a process by which the compounds were sufficiently concentrated to undergo physical and chemical interactions. One such site is a geothermal setting, in which organic compounds interact with mineral surfaces to promote self-assembly and polymerization reactions. Here, we report an initial study of two geothermal sites where mixtures of representative organic solutes (amino acids, nucleobases, a fatty acid and glycerol) and phosphate were mixed with high-temperature water in clay-lined pools. Most of the added organics and phosphate were removed from solution with half-times measured in minutes to a few hours. Analysis of the clay, primarily smectite and kaolin, showed that the organics were adsorbed to the mineral surfaces at the acidic pH of the pools, but could subsequently be released in basic solutions. These results help to constrain the range of possible environments for the origin of life. A site conducive to self-assembly of organic solutes would be an aqueous environment relatively low in ionic solutes, at an intermediate temperature range and neutral pH ranges, in which cyclic concentration of the solutes can occur by transient dry intervals. PMID:17008220

Deamer, David; Singaram, Sara; Rajamani, Sudha; Kompanichenko, Vladimir; Guggenheim, Stephen

2006-10-29

452

New materials and processes for directed self-assembly  

NASA Astrophysics Data System (ADS)

Directed self-assembly (DSA) of block copolymers (BCPs) is a promising technology for advanced patterning at future technology nodes, but significant hurdles remain for commercial implementation. The most widely studied material for DSA is poly(styrene-block-methyl methacrylate) (PS-PMMA), but the relatively weak segregation strength of PSPMMA results in some limitations. This paper reports on these limitations for PS-PMMA and highlights a path to success through use of more strongly segregated "high-?" block copolymers. In general, stronger segregation is predicted to lower defectivity at equilibrium, but unfortunately, kinetics of self assembly also becomes much slower as segregation strength increases. Recognizing diffusion is much faster for cylinder morphologies than lamellar ones, we have investigated new cylinder-forming BCPs that enable defect elimination with thermal annealing processes. In addition, a formulation strategy is presented that further improves the kinetics of the assembly process, enabling tremendous improvements in defectivity over simple BCP systems. Excitingly, successful chemoepitaxy DSA with a high-? lamellar BCP is also demonstrated using a thermal annealing process and no top coat. These technologies hold promise to enable DSA with thermal annealing processing across pitches from 40 - 16 nm.

Chang, Shih-wei; Evans, Jessica P.; Ge, Shouren; Ginzburg, Valeriy V.; Kramer, John W.; Landes, Brian; Lee, Christopher; Meyers, Greg F.; Murray, Daniel J.; Park, Jong; Sharma, Rahul; Trefonas, Peter; Weinhold, Jeffrey D.; Zhang, Jieqian; Hustad, Phillip D.

2013-03-01

453

Self-assembled biomimetic monolayers using phospholipid-containing disulfides.  

PubMed

Several phospholipid-based disulfide molecules were synthesized and attached onto the gold-coated silicon wafer using the self-assembling method. The syntheses of these surface-modifying agents were conducted by introducing bromoethylphosphorate (PBr), phosphorylcholine (PC) or phosphorylethanolamine (PE) groups on the terminals of a dialkyl disulfide. After disulfides adsorption onto gold substrate surfaces, the composition, the film thickness, and the conformational order of self-assembled monolayer surfaces were explored and discussed in detail based on reflection-absorption infrared spectroscopy, contact angle measurement, Auger electron spectroscopy, X-ray photoelectron spectroscopy, and so on. The monolayer having the PBr end group could also be converted to a PC surface by treating with trimethylamine. The model functional surfaces of Au-SC11-PC, -PE, -PBr, -OH or corresponding mixed layers were used to mimic biomembrane surfaces. The monolayer having PC groups was found to reduce fibrinogen adsorption as evaluated from protein adsorption experiments using quartz crystal microbalance. It also showed relatively low platelet adherence compare to the glass, PBr and PE surfaces. The cell viability test also revealed that the PC surface displayed lower cytotoxicity than other surfaces. PMID:15585234

Chung, Yi Chang; Chiu, Yi Hong; Wu, Yin Wei; Tao, Yu Tai

2005-05-01

454

The multiple faces of self-assembled lipidic systems  

PubMed Central

Lipids, the building blocks of cells, common to every living organisms, have the propensity to self-assemble into well-defined structures over short and long-range spatial scales. The driving forces have their roots mainly in the hydrophobic effect and electrostatic interactions. Membranes in lamellar phase are ubiquitous in cellular compartments and can phase-separate upon mixing lipids in different liquid-crystalline states. Hexagonal phases and especially cubic phases can be synthesized and observed in vivo as well. Membrane often closes up into a vesicle whose shape is determined by the interplay of curvature, area difference elasticity and line tension energies, and can adopt the form of a sphere, a tube, a prolate, a starfish and many more. Complexes made of lipids and polyelectrolytes or inorganic materials exhibit a rich diversity of structural morphologies due to additional interactions which become increasingly hard to track without the aid of suitable computer models. From the plasma membrane of archaebacteria to gene delivery, self-assembled lipidic systems have left their mark in cell biology and nanobiotechnology; however, the underlying physics is yet to be fully unraveled. PACS Codes: 87.14.Cc, 82.70.Uv PMID:19374753

Tresset, Guillaume

2009-01-01

455

Cyclization and catenation directed by molecular self-assembly.  

PubMed

We report here that molecular self-assembly can effectively direct and enhance specific reaction pathways. Using perylene pi-pi stacking weak attractive forces, we succeeded in synthesizing perylene bisimide macrocyclic dimer and a concatenated dimer-dimer ring from dynamic self-assembly of monomeric bis-N,N'-(2-(2-(2-(2-thioacetylethoxy)ethoxy)ethoxy)ethyl)perylenetetracarboxylic diimide. The monocyclic ring closure and the dimer-dimer ring concatenation were accomplished through formation of disulfide bonds, which was readily triggered by air oxidization under basic deacetylation conditions. The perylene cyclic dimer and its concatenated tetramer were characterized using both structural methods (NMR, mass spectroscopy) and photophysical measurements (UV-vis spectroscopy). Kinetic analyses offer informative insights about reaction pathways and possible mechanisms, which lead to the formation of complex concatenated rings. Molecular dynamic behaviors of both the monocyclic dimer and the concatenated dimer-dimer ring were modeled with the NWChem molecular dynamics software module, which shows distinct stacking activities for the monocyclic dimer and the concatenated tetramer. PMID:16925433

Wang, Wei; Wang, LiQiong; Palmer, Bruce J; Exarhos, Gregory J; Li, Alexander D Q

2006-08-30

456

Liposomes self-assembled from electrosprayed composite microparticles  

NASA Astrophysics Data System (ADS)

Composite microparticles, consisting of polyvinylpyrrolidone (PVP), naproxen (NAP) and lecithin (PC), have been successfully prepared using an electrospraying process and exploited as templates to manipulate molecular self-assembly for the synthesis of liposomes in situ. Field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) observations demonstrate that the microparticles have an average diameter of 960 ± 140 nm and a homogeneous structure. X-ray diffraction (XRD) patterns, differential scanning calorimetry (DSC) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) results verify that the building blocks NAP and PC are scattered in the polymer matrix in a molecular way owing to the very fast drying of the electrospraying process and the favorable secondary interactions among the components. FESEM, scanning probe microscope (SPM) and TEM observations demonstrate that the liposomes can be achieved through molecular self-assembly in situ when the microparticles contact water thanks to ‘like prefers like’ and by means of the confinement effect of the microparticles. The liposomes have an encapsulation rate of 91.3%, and 80.7% of the drug in the liposomes can be freed into the dissolution medium in a sustained way and by a diffusion mechanism over a period of 24 h. The developed strategy not only provides a new, facile, and effective method to assemble and organize molecules of multiple components into liposomes with electrosprayed microparticles as templates, but also opens a new avenue for nanofabrication in a step-by-step and controllable way.

Yu, Deng-Guang; Yang, Jun-He; Wang, Xia; Tian, Feng

2012-03-01

457

Conformational flexibility facilitates self-assembly of complex DNA nanostructures.  

PubMed

Molecular self-assembly is a promising approach to the preparation of nanostructures. DNA, in particular, shows great potential to be a superb molecular system. Synthetic DNA molecules have been programmed to assemble into a wide range of nanostructures. It is generally believed that rigidities of DNA nanomotifs (tiles) are essential for programmable self-assembly of well defined nanostructures. Recently, we have shown that adequate conformational flexibility could be exploited for assembling 3D objects, including tetrahedra, dodecahedra, and buckyballs, out of DNA three-point star motifs. In the current study, we have integrated tensegrity principle into this concept to assemble well defined, complex nanostructures in both 2D and 3D. A symmetric five-point-star motif (tile) has been designed to assemble into icosahedra or large nanocages depending on the concentration and flexibility of the DNA tiles. In both cases, the DNA tiles exhibit significant flexibilities and undergo substantial conformational changes, either symmetrically bending out of the plane or asymmetrically bending in the plane. In contrast to the complicated natures of the assembled structures, the approach presented here is simple and only requires three different component DNA strands. These results demonstrate that conformational flexibility could be explored to generate complex DNA nanostructures. The basic concept might be further extended to other biomacromolecular systems, such as RNA and proteins. PMID:18667705

Zhang, Chuan; Su, Min; He, Yu; Zhao, Xin; Fang, Ping-an; Ribbe, Alexander E; Jiang, Wen; Mao, Chengde

2008-08-01

458

Molecular Self-Assembly at Metal-Electrolyte Interfaces  

PubMed Central

The self-assembly of molecular layers has become an important strategy in modern design of functional materials. However, in particular, large organic molecules may no longer be sufficiently volatile to be deposited by vapor deposition. In this case, deposition from solution may be a promising route; in ionic form, these molecules may even be soluble in water. In this contribution, we present and discuss results on the electrochemical deposition of viologen- and porphyrin molecules as well as their co-adsorption on chloride modified Cu(100) and Cu(111) single crystal electrode surfaces from aqueous acidic solutions. Using in situ techniques like cyclic voltametry and high resolution scanning tunneling microscopy, as well as ex-situ photoelectron spectroscopy data the highly ordered self-assembled organic layers are characterized with respect to their electrochemical behavior, lateral order and inner conformation as well as phase transitions thereof as a function of their redox-state and the symmetry of the substrate. As a result, detailed structure models are derived and are discussed in terms of the prevailing interactions. PMID:23439555

Phan, Thanh Hai; Wandelt, Klaus

2013-01-01

459

Glycosylated Self-Assembled Monolayers for Arrays and Surface Analysis  

PubMed Central

Over the past few decades, carbohydrates (glycans) have received growing attention for their many roles in biological systems, including pathogenesis, receptor-ligand interactions, and cell signaling. To unravel the biology of this important category of biomolecules, a host of new tools have been developed for glycomics investigation. At the forefront is the carbohydrate microarray, developed to immobilize functional glycans on a solid substrate to rapidly screen a variety of potential binding partners (carbohydrates, proteins, nucleic acids, cells, and viruses). The essential role played by surface modification on glycan microarray performance requires new methods to rigorously characterize glycan surface chemistries. Due to their highly reproducible nature and well-studied properties, self-assembled monolayers (SAMs) on gold are powerful models for presenting glycans on a solid substrate, engineering biomimetic microenvironments and exploring the bioactivity of immobilized carbohydrates via surface plasmon resonance (SPR). However, it can be challenging to prepare high quality glycosylated SAMs (glyco-SAMs) that retain their biological function following surface immobilization. Herein, a selection of versatile methods for the preparation of glyco-SAMs using natural and chemically modified glycans is described. This chapter will highlight the following three immobilization techniques: (1) direct self assembly using thiolated glycosides onto gold, (2) tethering aminated glycosides onto amine-reactive SAMs, and (3) conjugating natural glycan onto divinyl sulfone-activated SAMs. PMID:22057519

Cheng, Fang; Ratner, Daniel M.

2013-01-01

460

Ionic self-assembly for functional hierarchical nanostructured materials.  

PubMed

CONSPECTUS: The challenge of constructing soft functional materials over multiple length scales can be addressed by a number of different routes based on the principles of self-assembly, with the judicious use of various noncovalent interactions providing the tools to control such self-assembly processes. It is within the context of this challenge that we have extensively explored the use of an important approach for materials construction over the past decade: exploiting electrostatic interactions in our ionic self-assembly (ISA) method. In this approach, cooperative assembly of carefully chosen charged surfactants and oppositely char